Proceedings of the 2005 U.S. Geological Survey Karst Interest Group, Rapid City, South Dakota, September 12-15, 2005

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Proceedings of the 2005 U.S. Geological Survey Karst Interest Group, Rapid City, South Dakota, September 12-15, 2005

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Proceedings of the 2005 U.S. Geological Survey Karst Interest Group, Rapid City, South Dakota, September 12-15, 2005
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USGS - Scientific Investigations
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USGS Karst Interest Group
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USGS Scientific Investigations Report 05-5160
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Kuniansky, Eve L.
U.S. Geological Survey Karst Interest Group
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University of South Florida Library
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K26-03291 ( USFLDC DOI )
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Introduction and Acknowledgments -- Agenda ( .pdf )

Application of Seismic Refraction Tomography to Karst Cavities / Jacob R. Sheehan, and William E. Doll, David B. Watson, and Wayne A. Mandell ( .pdf )

Structural Controls on Karst Development in Fractured Carbonate Rock, Edwards and Trinity Aquifers, South-Central Texas / Jason R. Faith, Charles D. Blome, Allan K. Clark, George B. Ozuna, and Bruce D. Smith ( .pdf )

The Case of the Underground Passage: Putting the Clues Together to Understand Karst Processes / B. Mahler, B. Garnier, and N. Massei ( .pdf )

Comparison of Water Chemistry in Spring and Well Samples from Selected Carbonate Aquifers in the United States / Marian P. Berndt, Brian G. Katz, Bruce D. Lindsey, Ann F. Ardis, and Kenneth A. Skach ( .pdf )

An Appalachian Regional Karst Map and Progress Towards a New National Karst Map / D.J. Weary ( .pdf )

Hydrogeologic Framework Mapping of Shallow, Conduit-Dominated Karst-Components of a Regional GIS-Based Approach / Charles J. Taylor, Hugh L. Nelson Jr., Gregg Hileman, and William P. Kaiser ( .pdf )

Application of Multiple Tracers to Characterize Sediment and Pathogen Transport in Karst / Tiong Ee Ting, Ralph K. Davis, J.V. Brahana, P.D. Hays, and Greg Thoma ( .pdf )

National Evaporite Karst-Some Western Examples / Jack B. Epstein ( .pdf )

Gypsum and Carbonate Karst Along the I-90 Development Corridor, Black Hills, South Dakota / Larry D. Stetler and Arden D. Davis ( .pdf )

Vulnerability (Risk) Mapping of the Madison Aquifer near Rapid City, South Dakota / Scott L. Miller, Arden D. Davis, and Alvis L. Lisenbee ( .pdf )

Adaptation of the Residence Time Distribution (RTD)-Biodegradation Model to Quantify Peroxide-Enhanced Fuel Biodegradation in a Single Karst Well / Lashun K. King, Roger D. Painter, and T.D. Byl ( .pdf )

Free-Living Bacteria or Attached Bacteria: Which Contributes More to Bioremediation? / Roger D. Painter, Shawkat Kochary, and T.D. Byl ( .pdf )

Desorption Isotherms for Toluene and Karstic Materials and Implications for Transport in Karst Aquifers / Mario Beddingfield, Khalid Ahmed, Roger Painter, and T.D. Byl ( .pdf )

Introduction to Three Field Trip Guides: Karst Features in the Black Hills, Wyoming and South Dakota, Prepared for the Karst Interest Group Workshop, September 2005 / Jack B. Epstein and Larry D. Putnam ( .pdf )

Field Trip Guide 2 Karst Features of the Northern Black Hills, South Dakota and Wyoming, Karst Interest Group workshop, September 15, 2005 / Jack B. Epstein, Arden D. Davis, Andrew J. Long, Larry D. Putnam, and J.Foster Sawyer ( .pdf )

Field Trip Guide 3 for a Self-Guided Trip to Karst Features of the Western Black Hills, Wyoming and South Dakota, Karst Interest Group Workshop, September 12-15, 2005 / Jack B. Epstein ( .pdf )

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180 Free-Living Bacteria or Attached Ba cteria: Which Contributes More to Bioremediation? Roger D. Painter 1 Shawkat Kochary 1 and Tom D. Byl 2,1 1 Civil and Environmental Engine ering, Tennessee State Univ ersity, Nashville, TN 37209 2 U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, TN 37211 ABSTRACT Researchers have implied that natural bioremediation in karst or fractured rock is unlikely to occur because of the lack of bacteria biofilm in karst aquifers Hydrologic and geologic characteristics of fractured rock aquifers have been described as not being suite d for natural bioremediation because of small microbial populations. If bioremediation in bedr ock aquifers is dependent upon c ontact between surface-attached bac teria and contaminants, then bior emediation would be limited by the low surface area to volume ratio (SA/V) of karst aquifers. A quantitative basis, howe ver, for accepting or rej ecting the assumption that attached bacteria dominate the biod egradation process in karst conduits has not been shown. The objective of this research was to de termine if free-living karst bacteria cont ributed as much to toluene biodegradation as attached bacteria. Two flow-through reactor systems were established to test the different biodegradation rates. Each reactor system consiste d of four 1.24-liter cylinders connec ted together with glass tubing for a total open volume of appr oximately 5 liters. The second reactor syst em was similar to the open system except the cylinders were filled with acid-washed, circular glass spheres th at increased surface area to vol ume ratio approximately fivefold co mpared to the open system. Rhodam ine dye was used to calculate the different residence-time distributions in each system. A sterile control study established that less than 3 per cent of the toluene was lost to abiotic processes. Next raw water from a karst aqui fer containing live, indig enous bacteria was pumped through each system for 5 days to establis h a biofilm on the glass surfaces. Colonization of the surface was confir med by microscope visualization before toluene was added to the sys tems. The resulting first-order rate co nstants were computed to be 0.014 per hour fo r the open system and 0.0155 per hour for the packed reacto r system. If surface-attached bacteria were the main contributors to the biodegradation process and the SA/V ra tio was increased fivefold, a signif icantly higher biodegradation rate should have occurred in the packed r eactor. The results of this study in dicate that the free-living bacteria indigenous to a karst aquifer contribute as much to the toluene biodegradation process as attached bacteria. INTRODUCTION The lack of studies examining biodegradation in karst aquifers may be due to the widespread per ception that contaminants are rapidly flushed out of karst aquifers. In highly developed and wellconnected conduit systems, the rate of contaminant migration is expected to be much faster than the rate of biodegradation. Field (1993) states that remedia tion techniques such as ground-water extraction or bioremediation are impractical in karst aquifers dominated by conduit flow; however, he also states that the belief that contam inants are rapidly flushed out of karst aquifers is a popular misconception. Large volumes of water may be trapped in fractures along bedding planes and other features isolated from active ground-water flow paths in karst aqui fers (Wolfe and others, 1997 ). In areas isolated from the major conduit flow path s, contaminant migration may be slow enough that biodegradation could reduce contaminant mass if favorable microorgan isms, food sources, and ge ochemical conditions are present. Researchers have implie d that natural biore mediation in karst or fract ured rock is unlikely to occur because of the microb iological characteristics of karst aquifers; small microbial populations and low surface area to volu me (SA/V) ratio (Vogel, 1994). Typical microbial numbers for material from

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181 unconsolidated aquifers have been reported to range from 1 x 10 4 to 1 x 10 7 cells per milliliter (cells/mL) (Ghiorse and Wilson, 1988). Studies have shown that water from bedrock (gra nite and karst) aquifers also may contain microbial populations within this range. For example, total microbial populations of 9.7 x 10 5 to 8.5 x 10 6 cells/mL and heterotrophic bacteria populations of 3.5 x 10 3 to 5.0 x 10 5 cells/mL were detected in ground-water samples collected from a gasoline-contaminated karst aqui fer in Missouri (O'Connor and Brazos, 1991). The fact that greater than 70 percent of bacteria in con solidated aquifers are attached to solid surfaces (Harvey and others, 1984; Harvey and Barber, 1992) may have led to the assumption that natural biore mediation in karst conduits is negligible because contact between attached b acteria and contaminants would be limited by the SA/V ratio. Research currently underway at Tennessee State University in cooper ation with the U.S. Geo logical Survey focuses on modeling biodegradation of contaminants in karst systems. The research pre sented in this paper comp ares the biodegradation of toluene by attached and free-living bacteria in two laboratory karst systems. Conservative tracer stud ies, sterile controls and quantified toluene biodegra dation were used to ma thematically determine biodegradation rates for tw o laboratory karst sys tems representing a different SA/V ratio. The toluene-biodegradation resu lts from the laboratory karst systems were analyzed in terms of chemical reaction kinetics and mass transfer principles. The math used to calculate whether the degradation was predominantly a function of volume through freeliving microbes or a function of surface area through attached bacteria is described in the Methods and Materials section of this paper. METHODS AND MATERIALS Flow-through microcosms were constructed using a 20-liter glass rese rvoir, a multi-channel peri staltic pump, 10-milliliters (mL) stirred injection cells, four 1-liter volumetric flasks (actual volume when full = 1,240 mL), and 3-millimeter (mm) inner-diameter glass tubi ng connecting the pieces (fig. 1). One system was packed with a sufficient number of flat, glass spheres to increase the surface to volume area fivefold in the packed system as compared to the unpack ed system. Water was pumped into both systems by using a high-perfor mance peristaltic pump. A stirred injection cell (10 mL volume) was placed at the entrance of each replicate system for the inj ection of dye or toluene. The water traveled from the stirred injection cell Flow-through tubes of nonuniform dimensions Sampling Ports Stirred Injection Cell In j ection Port Reservoir with water (not to scale) pump Figure 1. A schematic of the experimental karst s y stems.

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182 through a thin glass tube to the bottom of graduated cylinders arranged in series. The water and injected constituents traveled through a series of nonuni form-size cylindrical glass tubes ranging from 3to 56-mm in diameter. The non-uniform dimensions in the systems contributed to non-ideal flow conditions such as eddies and currents. During the conservative dye tracer study, a con stant flow rate of approximately 3 milliliters per minute (mL/min) was established for both systems. The pump was stopped at the beginning of the tracer study, 476 micrograms ( g) of Rhodamine dye was injected into each stirred in jection cell, and the pump was restarted. The Rhodam ine concentration at the discharge port was monitored through time by col lecting samples at 1to 2hour time intervals over a 4-day period. A Turner 700 fluorometer was used to quantify the Rhodamine in the water samples. The lower detection limit on the fluorometer was estab lished at 100 parts per trillion. Before the toluene biodegradation study was initiated, the experimental systems were sterilized with bleach. The bleach was neutralized with sterile sodium thiosulfate. Filter-sterilized toluene (87 g) dissolved in 100 microliters ( L) of methanol was delivered into the injectio n cell and pushed through the system with sterile water that had a pH of 10. Previous work indicated that elevating the pH to 10 to maintain an abiotic system. Toluene concentration was monitored at the discharge port over the next 5 days. Water samples were collected in clean 40-mL volatile organic com pound (VOC) vials every 1 to 4 hours. The water samples were immediately analyzed on a Syntex gas chromatograph (GC) equipped with a purgeand-trap system, 30 meter (m) X 0.32 mm, 1.8-micrometer ( m) silica-film capillary column, argon-carrying gas, and micro-argon ionization detector. The lower detectio n limit for toluene on the GC was 0.5 microgram per liter ( g/L). Every fourth sample was either a duplic ate sample or a standard of known toluene quantity and a complete calibra tion curve was run every 6-12 hours. The biodegradation experiments used water containing live bacteria collected from a 120-footdeep well completed in a karst aquifer in south-cen tral Kentucky. An 87g aliquot of toluene was dis solved in 100 L of methanol and placed in the stirred injection chamber at time zero. The flow rate used in all experiments was kept constant at approx imately 3.0 mL/min. Data results from the tracer tests and the biodegradation studies were entered into a computer spreadsheet and all calculations regarding residence-time distribution (RTD) and biodegradation rates were documented in the spreadsheets. Experimental runs consisted of running the packed system and an unpa cked system in parallel under similar conditions. In order to document the presence of attached bacteria, glass slides were sus pended in both the packed and unpacked systems. The suspended slides were removed prior to and at the end of the experiments and viewed using an epi fluorescent microscope and the direct-count method (Eaton and others, 1995). Toluene was selected as the experimental con taminant because it is a component in most fuels and because previous work indicated Pseudomonad bac teria, which are heterotrophic aerobic bacteria (HAB), from the Kentucky site could grow using toluene as a food source (Byl and others, 2001; Byl and others, 2002). The concentration of HAB in the water was determined by using the most probable number (MPN) method (Eaton and others, 1995). The MPN bacteria concentra tions in the abiotic sys tems were less than on e colony-forming unit per 100 millimeter. The bacteria concentration in ground water from the karst aquifer ranged from 600,000 to 700,000 HAB/mL at the beginning and end of the experiment. DESCRIPTION OF THE MATHEMATICS USED TO CALCULATE BIODEGRADATION RATES The fate of biodegradable contaminants in a karst aquifer system is dependant upon the rate of their biodegradation and th e amount of time they spend in the system with th e bacteria (referred to as residence-time distribution or RTD). As a result, the difference in amount of toluene that is biodegraded in each of the systems is not sufficient to numeri cally predict the fate of contaminants in a karst

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183 aquifer. The biodegradation-rate equation must be coupled to the RTD formula since the removal of the contaminant is a function of RTD and biodegrada tion reaction rate. Once the eq uation is established, it can be re-arranged to so lve for the biodegradation rate using the experiment al data. Following is a description of how the biodegradation rate and RTD equation were coupled. For a sparingly soluble contaminant (A) reacting with a rate-limiting constituent (B), which may be the microbes themselves or different elec tron acceptors, the reaction may be second order (symbols are defined in Appendix): dCAdt --------kCACB= In a situation where the microbes are acclimated and at steady state and el ectron acceptors are not limiting the concentratio n, the reaction, C B may not change appreciably while C A changes. Treating C B like a constant, the equation can be rewritten as a first-order equation: dCAdt --------kCACBk CA = where k' = kC B is the pseudo first-order rate con stant. Oxygen and microbes were assumed to be not limiting in this laboratory system because the initial water was saturated, allowing use of the pseudo first-order equation. In this context, the rela tive contributions of sur face and volumetric biodegradation to the observed biodegradation rate can be determined by experi ments with varying SA/V. If free-living bacteria dominate, the biodegradatio n reaction is volumetric and the observed pseudo first-order rate constants for the packed and unpacked reactors will be of sim ilar magnitude. If, on the other hand, attached bacte ria dominate, then the reac tion is surface controlled and the observed pseudo first-order rate constants will not be of similar magnitude. If attached bacteria dominate the biodegradation reaction, the rate con stant will be directly proportional to SA/V ratio. The non-ideal hydraulic and mass transfer char acteristics for systems with different SA/V ratios would lead to different lengths of residence time in each system. The dissimilar residence times in the packed and unpacked system s used in this study can be offset by using the RTD formula (Bischoff, and Levenspiel, 1962). The RTD of solutes in each sys tem was determined using a conservative dye study to compensate for the shorter residence time in the system with less volume (that is, packed with glass spheres). The residence time ( ) is related to the mean residence time ob tained from the RTD as: tm1 2 Pe----+ = The Peclet number (Pe) is obtained from the vari ance of the RTD according to: 2Pe 2-----2 Pe----8 Pe 2-----+ = The Peclet numbers and the amount of toluene biodegraded ( X m ) obtained from the biotic experi ments in the packed and unpacked systems were used to obtain the rate of biodegradation by rearranging the following: Xm1 4 qePe2 1 q + 2ePeq 2 1 q 2 ePeq 2 ------------------------------------------------------------------------------ = where: q 14 DAPe + = The Damkohler number (D A ) incorporates the bio degradation reaction rate (k') and time. The equa tion can be rearranged and solved for k'. RESULTS AND DISCUSSION The RTD for each system was calculated from the conservative dye study. The data were numeri cally integrated to determine the mean residence time (t m ) and the variance ( 2 ) for the packed and unpacked laboratory karst systems. These parame ters where then used to cal culate the Peclet numbers, which are an indicator of the dispersion as the solute moves through the system. The results of the conser vative dye study are shown in figure 2. After the dye study, the reactor systems were sterilized and tolu ene was injected to measur e the amount of removal by abiotic processes. A mass balance was done on the toluene injected and recovered from the sterile

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184 Dye Study Results0 100 200 300 400 500 600 700 800 900 01020304050607080 Time, in hoursRhodamine, in parts per million Figure 2. Rhodamine concentration at the end sampling port as a function of time for the high-surface area (packed) system and low-surface area (unpacked) system and the mean residence time (tm), variability ( 2) and Peclet value (Pe) for each system. systems. Approximately 3 percent of the injected toluene was lost to abiotic processes in each of the experimental systems during the sterile run. In the third phase of the study, water containing live bacteria was pumped through the laboratory systems for 4 days to establish a biofilm on the glass surfaces. Bacteria counts using MPN and micro scopic methods were used to confirm that bacteria covered the glass surfaces and were suspended in the water at the beginning and end of the experiments (photos 1 and 2). A solution containing 87.0 g of toluene was injected into each system. Numerical integration of the resulting effluent toluene concen tration and time (fig. 3) indicated recovery of 61 g toluene from the unpacked reactor and 69 g toluene from the packed reactor. The resulting observed tol uene biodegradation value ( X m ) for the packed and unpacked systems was 0.21 and 0.31, respectively. These X m values where used in the equation listed above to calculate th e observed reaction rate constants ( k' observed ). The values of k' observed were 0.014 per hour and 0.0155 per hour for the packed and unpacked systems, respectively. The above results for conversion and rate constants for the packed and unpacked sy stems seem counter-intui tive at first glance; that is, the packed system has lower conversion and higher reaction rate of the two systems. This occurs be cause of the complex rela tion between hydraulic and chemical reaction kinet ics in a non-ideal flow system. When the residence time is taken into consid eration in each system, however, the rate of bi odegradation for the free-liv ing bacteria alone, or volumetric rate, k' volumetric = 0.0135 per hour for both systems. Unpacked tm = 27.4 hr2 = 142.3 Pe = 15.8 Packed tm = 15.3 hr2 = 36.6 Pe = 13.7

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185 SUMMARY AND CONCLUSION Biodegradation of toluene in flow-through lab oratory karst systems of varying SA/V indicated that the observed biodegradation of toluene was a func tion of free-living and attached bacteria. This was evidenced by the fact that the system with fivefold greater surface area had only a 10-percent increase (B) (A) Photograph 2. Free-living bacteria (dark objects) collected from the water column after 3 days. Flagella can be observed attached to the rod-shaped bacteria (1,000x magnification, bright field). Photograph 1. (A) Bacteria (white objects) attached to the surface of the glass after 3 days of pumpin g water through the system (400x magnification, epifluorescent), and (B) close up of a bacteria cluster on the surface of the glass (800 x magnification, epifluorescent). Figure 3. The concentration of toluene as a function of time in the packed system and unpacked systems. The Xobserved refers to the amount biodegraded, and the Kobserved refers to the first-order exponential rate of biodegradation calc ulated from the experimental data. T o lu en e Deg r ad atio n R esu lts 0 5 10 15 20 25 30 0 1 02 0 3 04 0 5 06 0 7 0 T i m e in ho u r s T o lu e n e in p a r t s p e r millio n Packed X obser ved = 0.210 K obser ved = 0.014 hr -1 Unpacked X obser ved = 0.310 K obser ved = 0.0155 hr -1

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186 in biodegradation. If attach ed bacteria were prima rily responsible for biodegradation, a proportional increase in biodegradation with an increase in sur face area would be expected; however, the free-liv ing bacteria appear to contribute as much to biodegradation processes as attached bacteria. The volumetric reaction rate constant ( k' volumetric ) of 0.135 per hour corresponds to a half-life for toluene of approximately 51 hours without consideration of surface bacteria. Thus, di ssolved toluene that resided for several days in a karst conduit with char acteristics similar to those in this study could expe rience substantial biodegradation regardless of interaction with the surface area. REFERENCES Bischoff, K.B., and Levenspiel, O., 1962, Fluid disper sion-generalization and comp arison of mathematical models—I. generalization of models: Chemical Engi neering Science 17 p. 245-255. Byl, T.D., Hileman, G.E., Williams, S.D., and Farmer, J.J., 2001, Geochemical and microbial evidence of fuel biodegradation in a contam inated karst aquifer in southern Kentucky, June 1999, in Kuniansky, E.L. (ed.), U.S. Geological Survey Karst Interest Group Proceedings, St. Petersburg, Florida, February 13-16, 200:.U.S. Geological Survey Water-Resources Investi gations Report 2001-4011, p. 151-156, accessed Janu ary 27, 2005, at http://water.usgs.gov/ogw/karst/kig conference/proceedings.htm Byl, T.D., Hileman, G.E., Williams, S.D., Metge, D.W., and Harvey, R.W., 2002. Microbial strategies for deg radation of organic contaminants in karst, in Aiken, G.R., and Kuniansky, E.L. (eds.), U.S. Geological Survey Artificial Recharge Workshop Proceedings, Sacramento, California, April 2-4, 2002: U.S. Geolog ical Survey Open-File Report 2002-89, p. 61-62, accessed January 27, 2005 at http://water.usgs.gov/ogw/pubs/ofr0289/ Eaton, A.D., Clesceri, L.S., Greenberg, A.E., and Bran son, M.A.H., eds., 1995, Standard methods for the examination of water and wa stewater (19th ed.): Wash ington, D.C., American Public Health Association, 1268 p. Field, M.S., 1993, Karst hydrology and chemical con tamination: Journal of Environmental Systems, v. 22, no. 1, p. 1-26. Ghiorse, W.C., and Wilson, J.T., 1988, Microbial ecology of the terrestrial subsurf ace: Advances in Applied Microbiology, v. 33, p. 107-172. Harvey, R.W., and Barber, L.B ., II, 1992, Associations of free-living bacteria and dissolved organic compounds in a plume of contaminated groundwater: Journal of Contaminant Hydrology, v. 9, p. 91-103 Harvey, R.W., Smith, R.L., and George, Leah, 1984, Effect of organic contamination upon microbial distri butions and heterotrophic uptake in a Cape Cod, Mass., aquifer: Applied and Environmental Microbiology, v. 48, no. 1, p. 1197–1202. O'Connor, J.T., and Brazos, B.J., 1991, The Response of Natural Ground Water Bacteria to Ground Water Con tamination by Gasoline in a Karst Region, in Erickson, L.E. (ed.), Proceedings of the Conference on Hazard ous Waste Research: Kansas State University, Manhat tan, Kansas, p. 81-293, 1991. Vogel, T.M., 1994. Natural bioremediation of chlorinated solvents, in Norris, R.D., and Matthew, J.E., eds., Handbook of bioremediation: Boca Raton, Fla., Lewis Publishers, p. 201-224. Wolfe, W.J., Haugh, C.J., Webbers, Ank, and Diehl, T.H., 1997, Preliminary conceptual models of the occurrence, fate, and transport of chlorinated solvents in karst regions of Tennessee: U.S. Geological Survey Water-Resources Investigat ions Report 97-4097, 80 p.

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187 Appendix. Symbol notation and unit of measure C solute concentration, moles per liter [M/L] CAinitial contaminant concentration [M/L] CBbacteria-electron-acceptor concentration [M/L] C(t) concentration of tracer as a function of time [M/L] DA Damkohler Number k' pseudo first-order rate constant [T-1] Pe Peclet Number [VL/D] space time [T] t time [T] tm mean residence time [T] X(m) observed or calculated value of chemical biodegraded [M/L] 2 variance [T2]



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74 Comparison of Water Chemistry in Spring and Well Samples from Selected Carbonate Aquife rs in the United States By Marian P. Berndt 1 Brian G. Katz 1 Bruce D. Lindsey 2 Ann F. Ardis 3 and Kenneth A. Skach4 1 U.S. Geological Survey, 2010 Le vy Avenue, Tallahassee, FL 32310 2 U.S. Geological Survey, 215 Lime kiln Road, New Cu mberland, PA 17070 3 U.S. Geological Survey, 8027 Exch ange Drive, Austin, TX 78754 4 U.S. Geological Survey, 10615 SE Cherry Blossom Drive, Portland, OR 97216 ABSTRACT Water chemistry in samples from 226 wells and 176 springs were assessed to determine if samples from springs and wells have similar concentrations of select ed properties such as dissolved solids, dissolved oxy gen, nitrate, and calcite and dolom ite saturation indices. Samples were collected in seven carbonate aqui fersEdwards-Trinity, Flor idan, Mississippian, Basin and Range, Valley and Ridge, Springfield Plateau, and Ozark. Comparisons were made between concentrations of inorga nic constituents in water samples from springs and from wells within the same aquifer. Results were variable but showed that concentrations were not significantly different betw een samples from springs and wells fo r most properties. Nitrate and dis solved solids concentrations were on ly significantly different between sp ring and well samples in one or two of the seven aquifers; however, dissolved oxygen conc entrations were significan tly different between well and spring samples in four of the seven aquifers. Medi an calcite and dolomite sa turation index values were significantly different between well an d spring samples in three of the seven aquifers. Spring samples prob ably represent water from shallower pa rts of the aquifer flow systems and thus represent parts of the flow system that are most susceptible to contamination from land-use practices These results indicate that the collection of water from springs should be considered critical to adequately char acterize water quality in carbonate aquifers. INTRODUCTION About 20 percent of the ground water with drawn for drinking water in the United States is from carbonate aquifer systems (M.A. Maupin, U.S. Geo logical Survey, written commun., 2004). Under standing the factors that control water quality in these systems requires information on water chemis try from the aquifer matrix fractures, and from sec ondary porosity features (e.g., solution conduits). Comprehensive monitoring strategies that include the sampling of both spri ngs and wells (Quinlan, 1989) have been used to interpret geochemical vari ability that arises from gr ound-water flow through different parts of a carbonate aquifer system (Scan lon, 1990; Adamski, 2000). Water samples were collected from 226 wells and 176 springs in seven carbonate aquifers from 1993 through 2003 as part of the U.S. Geological Surveys National Wate r-Quality Assessment Pro gram. This number of samples from carbonate aqui fers around the United States represents an opportunity to explore th e differences in major-ion chemistry between samples collected from wells and from springs. Limestone and dolomite units were sampled within the follo wing aquifers : EdwardsTrinity, Floridan, Mississippian, Basin and Range, Valley and Ridge, Springfield Plateau, and Ozark (fig. 1). These limestone an d dolomite units range in age from Cambrian to Quat ernary (Adamski, 2000; Miller, 1990; Maclay, 1995) and some are interlay ered with sandstone or ch ert layers (Dettinger and others, 1995; Johnson, 2002; Kingsbury and Shel ton, 2002). COMPARISON OF SAMPLES FROM SPRINGS AND WELLS WITHIN SELECTED AQUIFERS Spring and well water samples were collected from seven aquifersEdwards-Trinity, Floridan, Mississippian, Valley and Ridge, Basin and Range,

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75 Springfield Plateau, and Ozark. Within each aquifer, the number of water samples collected from springs ranged from 6 to 58 samples and the number of sam ples from wells ranged from 18 to 57 (fig. 2). In the Floridan aquifer system, samples were collected exclusively from the Upper Floridan aquifer, thus Upper Floridan will be used for the remainder of this discussion. Comparisons were made only between the water samples from spri ngs and wells within a given hydrogeologic setting in each aquifer. For example, in the Upper Floridan aquifer, samples were collected fro m throughout the extent of the aquifer, but spring water samples were col lected only in southwestern Georgia; thus, these spring water samples were compared only to well samples collected in the same hydrogeologic setting in southwestern Georgia. The nonparametric Wil coxon rank-sum test (Helsel and Hirsch, 1992) was used to determine if con centrations of constituents were significantly different (level of significance 0.05) between water sampl es collected from wells and springs. Major Dissolved Species Calcium-bicarbonate is the dominant water type for all of the aquife rs and aquifer systems; however, the chemical composition of water sam ples from the springs and wells in the Basin and Range aquifer system was highly variable. In most aquifers, fewer than half of the 14 inorganic constit uents examined showed significant differences in Figure 1. Location of spring and well sites sampled from 1993-2003. Figure 2. Number of spring and well samples collected from selected aquifers.

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76 concentrations between springs and well samples (table 1). The greatest number of inorganic constitu ents with significant diff erences in concentration was seven in the Springfield Plateau aquifer. In three aquifersEdwards-Trinity, Mississippian and Basin and Rangesignificant differences in con centrations were noted for only one or two proper ties, indicating that samples collected from springs and wells were collected from ground water from similar locations within the aquifer flow systems. The range in dissolved solids concentrations among the seven aquifers provides some informa tion about the relative residence times and flow path lengths in the aquifers. Aquifers with greatest median dissolved solids concentrations in spring and well samples, the Edwards-Trinity aquifer (322 and 294 milligrams per liter (mg/L), respectively) and the Basin and Range aquifer (410 and 364 mg/L, respectively), also had th e greatest median well depths,270 feet (Edwards-Trinity) and 940 feet (Basin and Range). The median well depths for wells in the other aquifers ranged from 87 to 227 feet. Water from the deep er wells with greater dissolved solids concentra tions may indicate that longer flow paths and older ground water are being sampled in these aquifers. Dissolved solids concen trations were only significantly different between spring and well samples in the Valley and Ridge and Ozark aquifers (fig. 3). Median dissolved oxygen concentrations ranged from 2.5 mg/L in water samples from the Basin and Range aquifer wells to about 8 mg/L for springs in several of the aquifers (fig. 4). In four of the seven aquifers, dissolved oxygen concentrations were significantly different between samples from springs and wells (fig. 4). In each aquifer where sig nificant differences in di ssolved oxygen were noted, the spring samples have the greater dissolved oxy gen concentrations, indicating generally younger waters and more dynamic flow systems. The median dissolved oxygen concentr ation in water samples from wells was greater than that for springs in the Edwards-Trinity a quifer. Deeper, more regional circulation of ground water may account for lower dissolved oxygen concentrations in some springs in the Edwards-Trinity aquifer. Table 1. Summary of p-values from Wilcoxon rank-sum test comparing concentrations between samples from springs and wells.[P-values lower than the level of significan ce, 0.05, are shaded gray; <, less than]Aquifer Calcium Magne -sium Sodium Potassium Iron Manganese Bicabonate Sulfate Chloride NitrateSilicapH Dissolved oxygen Dissolved solids EdwardsTrinity0.200.780.460.361.000.51 0.010.630.520.980.750.980.630.38 Upper Floridan0.680.690.580.59 0.01 0.010.450.371.000.160.80 <0.010.120.52 Mississippian0.700.610.050.720.140. 440.740.380.080.360.180.11 <0.010.40 Valley and Ridge0.360.180.170.06 <0.01 <0.010.16 0.010.290.090.100.08 <0.01 0.05 Basin and Range0.080.850.250.44 <0.01 <0.010.250.240.920.981.000.090.660.25 Springfield Plateau0.340.080.54 <0.010.330.10 <0.010.16 <0.01 <0.01 <0.01 <0.01 <0.010.05 Ozark <0.01 <0.01 0.040.510.450.09 0.050.120.230.950.940.05 <0.01 <0.01

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77 Saturation Indices with Respect to Calcite and Dolomite Saturation indices were calculated for calcite and dolomite using the program PHREEQC (Parkhurst and Appelo, 1999 ). In most aquifers, the calcite saturation index values for the spring and well samples were at or near equilibrium (values of 0 +/0.2 are considered to represent equilibrium) (fig 5a). Most water samp les were undersaturated with respect to calcite (val ues less than -0.2) for the Mississippian aquifer. Minerals in these aquifer materials may be less soluble than the aquifer mate rials in most of the other carbonate aquifers sampled. Calcite saturation index values were signifi cantly different between water samples from springs and wells in three of th e seven aquifersUpper Floridan, Springfield Plat eau Ozark aquifers (fig. 5a). In each aquifer where the calcite saturation index values were significantly different (and in three of the other aquifers where significant differ ences were not noted), the significantly lower values were in the spring sampl es, indicating waters from Figure 3. Distribution of dissolved solids concentrations in samples from springs and wells. Figure 4. Distribution of dissolved oxygen concentrations in samples from springs and wells.

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78 Figure 5. Distribution values for (a) calcite saturation index, (b) dolomite saturation index, and (c) calcium to magnesium molar ratio in samples from springs and wells.

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79 springs were more undersaturated with respect to calcite than water from wells. The lower calcite sat uration index values also indicate that spring waters may originate from shallower parts of the flow sys tems than the water withdrawn from wells. Spring and well water samples for most of the aquifers were undersaturated with respect to dolo mite (fig 5b). Only spring and well samples from the Basin and Range aquifer and well samples from the Ozark aquifer were at or near equilibrium with respect to dolomite (values mostly between -0.2 to 0.2) (fig 5b). Dolomite saturation index values for the spring and well samples were significantly dif ferent in three of the sev en aquifersUpper Flori dan, Springfield Plateau, and Ozark (fig. 5b)the same three aquifers where significant differences were noted for calcite sa turation index values. In each of the three aquifers where dolomite saturation index values were significan tly different (and in the four aquifers where significant differences were not noted), the significantly lo wer values were in the spring samples indicating that the spring samples were more undersaturated w ith respect to dolomite than the samples from wells. The molar ratio of calcium to magnesium was calculated for each sample to determine if this ratio correlates with the relative amount of dolomite in the carbonate aquifers. Results show that in five of the aquifers, calcium-magne sium molar ratios were less than about 5, and are consistent with the reported mineralogy for the Edwards-Trinity, Mis sissippian, Valley and Ridge, Basin and Range, and Ozark aquifers (fig. 5c) (Maclay, 1995, Kingsbury and Shelton, 2002, John son, 2002, Dettinger and others, 1995, and Adamski, 2000). The three aqui fers where the most dolomite is indicated (where the calcium-magnesium ratios were lowest), EdwardsTrinity, Basin and Range and Ozark aquifers, were also the aquifers where dolomite saturation index values were highest (great er than -1.0) (figs. 5b and 5c). Nitrate Median nitrate concentra tions in the seven aqui fers ranged from 0.32 to 2.5 mg/L (fig. 6). Median concentrations were lowest (less than 1.0 mg/L) in the spring and well wate r samples from the Basin and Range and the Ozark aquifers. Although median nitrate concentrations did not exceed the maximum contaminant level of 10 mg/L, several median nitrate concentrations ra nged from 1 to 4 mg/L, which may indicate anthro pogenic inputs. Nitrate concentrations were only significantly different between spring and wells samples in the Springfield Plateau aquifer. The significantly higher concentra tions in nitrate in water samples from springs rela tive to wells in the Springfield Plateau was noted by Adamski (2000) who attributed the higher nitrate concentrations to the greater susceptibility of Figure 6. Distribution of nitrate concentrations in samples from springs and wells.

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80 springs to surface sources of contamination. The land use in the area overly ing the Springfield Plateau aquifer is predominantly agriculture (Adamski, 1996). IMPLICATIONS FOR USE OF SPRINGS IN THE CHARACTERIZATION OF WATER QUALITY IN CARBONATE AQUIFERS Differences in chemistry between spring waters and well water reflect ground-water movement in distinct parts of the flow system. Higher dissolved oxygen concentrations, lower saturation indices with respect to calcite an d dolomite, and lower dis solved solids concentrations relative to water from wells, indicate that spring s discharge ground water mainly from shallow parts of most of the studied aquifer systems. Exceptions are the Basin and Range and the Edwards-Trinity aq uifers, where deeper cir culation of ground water may occur prior to dis charge from springs. Chem ical differences between water from springs or wells also are related to the hydrologic conditions at the time of sampling. Rain fall patterns should be evaluated along with spring discharge at the time of sampling to characterize the contribution of recent recharge to the aquifer and its impact on ground-water chemistry. There were no consistent patterns when com paring nitrate concentratio ns in spring waters and well water. Nitrate concentr ations were significantly higher in spring water than in ground water in the Springfield Plateau aquifer, but not in the adjacent Ozark aquifer. Nitrate conc entrations were higher in spring waters than in we ll waters from the Valley and Ridge aquifer, but n itrate concentrations in spring waters were similar or lower than nitrate con centrations in well waters from the Edwards-Trinity, Upper Floridan, Mississipian, and Ozark aquifers. These differences likely reflect the complex relation between nitrate concentratio ns in ground water and various nitrogen sources, and include past and present land-use and waste-management practices, and hydrologic and climatic variability. Spring samples most likely represent water from shallower parts of the aquifer flow systems, and flow through large solution openings in carbon ate aquifer systems. These parts of the flow system are also the parts of the aquifer systems most suscep tible to contamination from land-use practices. For these reasons, obtaining wa ter samples from springs, in addition to wells, may be necessary for adequate characterization of water quality in carbonate aqui fers and for addressing th eir susceptibility to con tamination. REFERENCES Adamski, J.C., 1996, Nitrate and pesticides in ground water of the Ozark Plateaus region in Arkansas, Kan sas, Missouri, and Oklahoma: U.S. Geological Survey Fact Sheet FS-182-96, 4 p. Adamski, J.C., 2000, Geochemistry of the Springfield Plateau aquifer of the O zark Plateau Province in Arkansas, Kansas, Missouri, and Oklahoma, USA: Hydrological Processes, vol. 14, p. 849-866. Dettinger, M.D., Harrill, J.R., Schmidt, D.L., and Hess, J.W., 1995, Distribution of carbonate-rock aquifers and the potential for their development, southern Nevada and adjacent parts of Arizon a, California, and Utah: U.S. Geological Survey Water-Resources Investiga tions Report 91-4146, 100 p. Helsel, D.R., and Hirsch, R.M ., 1992, Statistical methods in water resources: New York, Elsevier, 522 p. Johnson, G.C., 2002, Water quality of springs in the Valley and Ridge Physiographic Province in the Upper Tennessee River Basin, 1997 : U.S. Geological Survey Water-Resources Investigat ions Report 02-4180, 24 p. Kingsbury, J.A., and Shelton, J.M., 2002, Water quality of the Mississippian carbonate aquifer in parts of middle Tennessee and northern Alabama, 1999: U.S. Geological Survey Water-R esources Investigations Report 02-4083, 36 p. Maclay, R.W., 1995, Geology and hydrology of the Edwards aquifer in the San Antonio Area, Texas: U.S. Geological Survey Water-R esources Investigations Report 95-4186, 64 p. Miller, J.A., 1990, Ground water atlas of the United States, Segment 6, Alabama, Florida, Georgia, and South Carolina: U.S. Geological Survey Hydrologic Investigations Atlas 730-G, 28 p. Parkhurst, D.L., and Appelo, C.A.J., 1999, User's Guide to PHREEQC (Version 2)-A Computer Program for Speciation, Batch-React ion, One-Dimensional

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81 Transport, and Inverse Ge o-chemical Calculations. U.S. Geological Survey Water-Resources Investiga tions Report 99-4259, accessed at http://www brr.cr.usgs.gov/projects/ GWC_coupled/phreeqc/html/ final.html on June 2, 2005. Quinlan, J.F., 1989, Ground-water monitoring in karst terranes: Recommended pr otocols and implicit assumptions: U.S. Environmental Protection Agency Report EPA/600/X-89/050, 79 p. Scanlon, B.R., 1990, Relationships between groundwater contamination and major-ion chemistry in a karst aqui fer. Journal of Hydrology, 119, p. 271-291.


Description
Contents:
Introduction and Acknowledgments --
Agenda.
--
National Programs
Establishing the National Cave and Karst Research Institute
as a Robust Research and Education Center/ Louise D.
Hose.
--
Geophysical Methods for Karst Studies:
The State of the Art of Geophysics and Karst: A General
Literature Review/ D.V. Smith --
Review of Airborne Electromagnetic Geophysical Surveys over
Karst Terrains/ Bruce D. Smith, Jeffrey T. Gamey, and
Greg Hodges --
Overview of Karst Effects and Karst Detection in Seismic Data
from the Oak Ridge Reservation, Tennessee/ W.E. Doll,
B.J. Carr, and J.R. Sheehan, and W.A. Mandell --
Application of Seismic Refraction Tomography to Karst
Cavities/ Jacob R. Sheehan, and William E. Doll, David B.
Watson, and Wayne A. Mandell --
Borehole Geophysical Techniques to Determine Groundwater Flow
in the Freshwater/Saline-Water Transition of the Edwards
Aquifer, South Central Texas/ R.B. Lambert, A.G. Hunt,
and G.P. Stanton, and John Waugh --
An Evaluation of Methods Used to Measure Horizontal Borehole
Flow/ Wayne A. Mandell, James R. Ursic, William H.
Pedler, Jeffrey J. Jantos, E. Randall Bayless, and Kirk G.
Thideaux.
--
The Edwards Aquifer, Texas:
Characterization of Hydrostratigraphic Units of the Capture,
Recharge, and Confining Zones of the Edwards Aquifer using
Electrical and Natural Gamma Signatures, Medina, Uvalde, And
Bexar Counties, Texas/ Bruce D. Smith, Allan K. Clark,
Jason R. Faith, and Gregory P. Stanton --
Use of Helium Isotopes to Discriminate Between Flow Paths
Associated with the Freshwater/Saline Water Transition Zone
of the Edwards Aquifer, South Central Texas/ Andrew G.
Hunt, Rebecca B. Lambert, Gary P. Landis, and John Waugh --
Airborne and Ground Electrical Surveys of the Edwards and
Trinity aquifers, Medina, Uvalde, and Bexar Counties,
Texas/ Bruce D. Smith, David V. Smith, Jeffrey G. Paine,
and Jared D. Abraham --
Magnetic Geophysical Applications Reveal Igneous Rocks and
Geologic Structures in the Edwards Aquifer, Texas/ D.V.
Smith, C. Foss, and B.D. Smith --
Structural Controls on Karst Development in Fractured
Carbonate Rock, Edwards and Trinity Aquifers, South-Central
Texas/ Jason R. Faith, Charles D. Blome, Allan K. Clark,
George B. Ozuna, and Bruce D. Smith.
--
Numerical Modeling of Karst Systems
Simulating Ground-Water Flow in the Karstic Madison Aquifer
using a Porous Media Model/ L.D. Putnam and A.J. Long --
Dual Conductivity Module (DCM), A MODFLOW Package for
Modeling Flow in Karst Aquifers/ Scott L. Painter, Ronald
T. Green, and Alexander Y. Sun --
Conceptualization and Simulation of the Edwards Aquifer, San
Antonio Region, Texas/ R.J. Lindgren, A.R. Dutton, S.D.
Hovorka, S.R.H. Worthington, and Scott Painter --
The role of MODFLOW in numerical modeling of karst flow
systems/ J. J. Quinn, David Tomasko, and J.A. Kuiper.
--
Springs and the Use of Geochemistry in Karst
Studies:
The Case of the Underground Passage: Putting the Clues
Together to Understand Karst Processes/ B. Mahler, B.
Garnier, and N. Massei --
Spatial and Temporal Variations in Epikarst Storage and Flow
in South Central Kentucky's Pennyroyal Plateau Sinkhole
Plain/ Chris Groves, Carl Bolster, and Joe Meiman --
Comparison of Water Chemistry in Spring and Well Samples from
Selected Carbonate Aquifers in the United States/ Marian
P. Berndt, Brian G. Katz, Bruce D. Lindsey, Ann F. Ardis, and
Kenneth A. Skach --
Interpretation of Water Chemistry and Stable Isotope Data
from a Karst Aquifer According to Flow Regimes Identified
through Hydrograph Recession Analysis/ D.H. Doctor and
E.C. Alexander, Jr.
--
Hydrogeologic Mapping and Tracer Techniques in Karst
Areas:
An Appalachian Regional Karst Map and Progress Towards a New
National Karst Map/ D.J. Weary --
Hydrogeologic Framework Mapping of Shallow, Conduit-Dominated
Karst-Components of a Regional GIS-Based Approach/
Charles J. Taylor, Hugh L. Nelson Jr., Gregg Hileman, and
William P. Kaiser --
Application of Multiple Tracers to Characterize Sediment and
Pathogen Transport in Karst/ Tiong Ee Ting, Ralph K.
Davis, J.V. Brahana, P.D. Hays, and Greg Thoma --
Estimating Ground-Water Age Distributions from CFC and
Tritium Data in the Madison Aquifer, Black Hills, South
Dakota/ Andrew J. Long and Larry D. Putnam --
A Multi-Tracer Approach for Evaluating the Transport of
Whirling Disease to Mammoth Creek Fish Hatchery Springs,
Southwestern Utah/ Larry E. Spangler, Meiping Tong, and
William Johnson.
--
Black Hills and Evaporite Karst:
National Evaporite Karst-Some Western Examples/ Jack B.
Epstein --
Gypsum and Carbonate Karst Along the I-90 Development
Corridor, Black Hills, South Dakota/ Larry D. Stetler and
Arden D. Davis --
Karst Features as Animal Traps: Approximately 500,000 Years
Of Pleistocene And Holocene Fauna and Paleoenvironmental Data
in the Northern High Plains/ Larry D. Agenbroad and
Kristine M. Thompson --
Developing a Cave Potential Map of Wind Cave to Guide
Exploration Efforts/ Rodney D. Horrocks --
The Potential Extent of the Jewel Cave System/ Michael E.
Wiles.
--
Karst Studies in Arkansas and the Ozarks:
Geologic Controls on a Transition Between Karst Aquifers at
Buffalo National River, Northern Arkansas/ Mark R.
Hudson, David N. Mott, and Kenzie J. Turner, and Kyle E.
Murray --
Quantification of Hydrologic Budget Parameters for the Vadose
Zone and Epikarst in Mantled Karst/ J.V. Brahana, Tiong
Ee Ting, Mohammed Al-Qinna, John F. Murdoch, Ralph K. Davis,
Jozef Laincz, Jonathan J. Killingbeck, Eva Szilvagyi,
Margaret Doheny-Skubic, Indrajeet Chaubey, P.D. Hays, and
Gregg Thoma --
Characterization of Nutrient Processing at the Field and
Basin Scale in the Mantled Karst of the Savoy Experimental
Watershed, Arkansas/ Jozef Laincz, .P.D. Hays, Sue
Ziegler, Byron Winston, J.V. Brahana, Ken Steele, Indrajeet
Chaubey, and Ralph K. Davis.
--
Water Supply and Land Use Issues in Karst
Areas:
Transport Potential of Cryptosporidium parvum Oocysts in a
Drinking-Water, Karstic-Limestone Aquifer: What We Have
Learned Using Oocyst-Sized Microspheres in a 100-m Convergent
Tracer Test at Miami's Northwest Well Field/ Ronald W.
Harvey, Allen M. Shapiro, Robert A. Renken, David W. Metge,
Joseph N. Ryan, Christina L. Osborn, and Kevin J. Cunningham
--
Ground-Water Quality Near a Swine Waste Lagoon in a Mantled
Karst Terrane in Northwestern Arkansas/ Christopher M.
Hobza, David C. Moffit, Danny P. Goodwin, Timothy Kresse,
John Fazio, John V. Brahana, and Phillip D. Hays --
Vulnerability (Risk) Mapping of the Madison Aquifer near
Rapid City, South Dakota/ Scott L. Miller, Arden D.
Davis, and Alvis L. Lisenbee --
Hydrogeologic Characteristics of Four Public Drinking-Water
Supply Springs in the Ozark Plateaus of Northern
Arkansas/ Joel M. Galloway --
Adaptation of the Residence Time Distribution
(RTD)-Biodegradation Model to Quantify Peroxide-Enhanced Fuel
Biodegradation in a Single Karst Well/ Lashun K. King,
Roger D. Painter, and T.D. Byl --
Free-Living Bacteria or Attached Bacteria: Which Contributes
More to Bioremediation?/ Roger D. Painter, Shawkat
Kochary, and T.D. Byl --
Desorption Isotherms for Toluene and Karstic Materials and
Implications for Transport in Karst Aquifers/ Mario
Beddingfield, Khalid Ahmed, Roger Painter, and T.D. Byl --
Computer Program that Uses Residence-Time Distribution and
First-Order Biodegradation to Predict BTEX Fate in Karst
Aquifers/ Ryan Fitzwater, Roger Painter, Valetta Watson,
and T.D. Byl --
Lactate Induction of Ammonia-Oxidizing Bacteria and PCE
Cometabolism / LyTreese Hampton, Roneisha Graham, and T.D.
Byl (Note: File FileStorage/USGS_KIG/2005/Part3_2.pdf is not
available) --
Biodegradation of Toluene as It Continuously Enters a
5-Liter Laboratory Karst System / Fuzail Faridi, Roger
Painter, and T.D. Byl. (Note: File
FileStorage/USGS_KIG/2005/Part3_2.pdf is not available) --
Bacteria Induced Dissolution of Limestone in
Fuel-Contaminated Karst Wells/ Serge Mondesir and T. D.
Byl.
--
Field Trip Guides:
Introduction to Three Field Trip Guides: Karst Features in
the Black Hills, Wyoming and South Dakota, Prepared for the
Karst Interest Group Workshop, September 2005/ Jack B.
Epstein and Larry D. Putnam --
Field Trip Guide 1 Karst Features of the Southern Black
Hills, South Dakota, Karst Interest Group Workshop, September
12, 2005/ Jack B. Epstein, Larry Agenbroad, Mark
Fahrenbach, Rodney D. Horrocks, Andrew J. Long, Larry D.
Putnam, J. Foster Sawyer, and Kristine M. Thompson --
Field Trip Guide 2 Karst Features of the Northern Black
Hills, South Dakota and Wyoming, Karst Interest Group
workshop, September 15, 2005/ Jack B. Epstein, Arden D.
Davis, Andrew J. Long, Larry D. Putnam, and J.Foster Sawyer
--
Field Trip Guide 3 for a Self-Guided Trip to Karst Features
of the Western Black Hills, Wyoming and South Dakota, Karst
Interest Group Workshop, September 12-15, 2005/ Jack B.
Epstein.
--



PAGE 1

199 Field Trip Guide 1 Karst Features of the Southern Black Hills, South Dakota, Karst Inter est Group Workshop, September 12, 2005 By Jack B. Epstein 1 editor, Larry Agenbroad 2 Mark Fahrenbach 3 Rodney D. Horrocks 4 Andrew J.Long 5 Larry D. Putnam 5 J. Foster Sawyer 6 and Kristine M. Thompson 7 1 Geologist Emeritus, U.S. Geological Survey National Center, MS 926A, Reston, VA 20192 2 Director, Mammoth Site of Hot Springs, South Dakota Inc., P.O. Box 692, Hot Springs, SD 57747-0692. 3 Senior Geologist, South Dakota Geological Survey, Rapid City, SD 57702. 4 Physical Science Specialist, Wind Cave National Park, RR 1 Box 190, Hot Springs, SD 57747-9430. 5 Hydrologist, U.S. Geological Survey, 1608 Mountain View Road, Rapid City, SD 57702. 6 Hydrology Specialist, South Dakota Geol ogical Survey, Rapid City, SD 57702. 7 In-Situ Bonebed Curator/Educator/Geologist, Mammoth Si te of Hot Springs, South Dakota, Inc., P.O. Box 692, Hot Springs, SD 57747-0692. Figure 1. Route map to karst stops in the southern Black Hills.

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200 The field trip originates from the headquarters at the Holiday Inn-Rushmore Plaza, 505 North Fifth Street, Rapid City, South Dakota. The first number is total miles from start and the second number is the miles from the last stop. 0.00.0 Leave Holiday Inn parking lot. Turn right on 6th Street. 0.20.2 Cross Omaha Street. 0.40.2 Cross Main Street. 0.50.1 Turn left on St. Joseph Street. 1.30.8 South Dakota School of Mines and Technology on right. Museum of Geology contains excellent mineral and paleonto logic exhibits (free admission). 1.50.2 Geology building to right. 1.70.2 OHarra stadium on right. Hills underlain by black shales of the Belle Fourche Shale of Late Cretaceous age. 2.60.9 Bear right and merge onto Route 79 South. 3.7 1.1 East Minnesota Street. Hills in distance to right underlain by rocks in the "Dakota hog back", defining the physiographic boundary of the Blac k Hills. The Dakota Sand stone was a earlier name for rocks now termed the In yan Kara Group. The structural bounda ry of the Black Hills, however, extends farther out into the surrou nding Upper Cretaceous sediments in the Great Plains. 5.82.1 Climbing to top of terrace, underlain by Quaternary gravels disconformably overlying the Belle Fourche Shale. 10.34.5 Cross Spring Creek. Streamflow in Spring Creek near Highway 79 at USGS gaging sta tion 06408500 for 56 years of record (US. Geological Survey, 1949-75; U.S. Geological Survey, 19762004) was less than 1 cubic feet per second about 54 pe rcent of the time. Most of the base flow in Spring Creek, which originates in the higher elevations of the Black Hills, is lo st to swallow holes as the stream crosses outcrops of the Pahasapa Li mestone and Minnelusa Formation that are located about 6 miles upstream. 11.31.0 Road ascends Belle Fourche Shale unconformabl y overlain by tuffaceous deposits of the White River Group of Oligocene-Miocene age. Martin and others (1996) describe these rocks along this route. 13.21.9 Harney Peak comprising Precamb rian granite in distance to right, highest point in the Black Hills (7,242 feet). 14.51.3 Pine-covered hills to right he ld up by sandstones of the In yan Kara Group (Early Creta ceous) dipping moderately to the east on the east limb of the Black Hills uplift. 16.82.3 Custer County. 18.21.4 US 40 to Keystone on right, continue on 79 south.

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201 18.90.7 US 36 towards Custer State Park on right, continue straight on 79. 26.98.0 Road to Fairburn on left. 29.72.8 Road to Fairburn on left. 30.20.5 Cross French Creek. Gold was first discover ed along this creek near Custer, SD, which heralded the gold rush to the Black Hills. 34.94.7 Greenhorn Limestone (Late Cretaceous) holds up hill on left. It is an argillaceous lime stone with no known karstic features. Moderately di pping beds of the Fall Rive r Formation of the Inyan Kara Group at 1 oclock. 39.04.1 Inyan Kara hogback to right dipping eastward towards us; smaller hill of Greenhorn Lime stone on left dipping less steep ly in the Greenhorn "piggyback". 40.01.0 The valley narrows here between the Inyan Ka ra and Greenhorn because the dips of the beds have steepened. See Martin and others (1996) for a description of the Greenhorn here. Abundant oys ters are found in the limestone, possibly edible with the proper cocktail sauce. 42.42.4 Beaver Creek. 42.90.5 Road to Buffalo Gap on left. The small canyon to the left is Calico Canyon in which dec orative variegated sandstone ha s been quarried from the Unkp apa Sandstone of Jurassic age. 44.21.3 Road to Buffalo Gap on left. 45.00.8 Fall River County line. 46.21.2 Elm Creek. 47.41.2 Pine trees favor the siliceous Mowry Shale of Late Cretaceous age in this area. 48.81.4 Greenhorn piggyback on left. 51.02.2 Junction with US 18/US 385; turn right towards Hot Springs. 51.60.6 Fall River Falls historic marker on left. Sp ringflow accounted for about 97 percent of the streamflow in Fall River during 1987 to 1996 (Carter and others, 2001). FALL RIVER FALLS HISTORIC MARKER The eight mile long Fall River, winding through Fall River Canyon after the joining of Cold and Hot Brook streams above the city of Hot Springs, tumbles below over an outcropping of sandstone falling about 50 feet to form Fall River Falls, as viewed from the gazebo. In 1907 the city of Hot Spring s built a low dam above the falls directing th e 89F water through a flume of native wood staves banded with iron rods and wire wrapped. Older residents remember as children walking the 4,700 foot flume to a point below the falls. Upon leaving the flume the water dropped 115 feet to a small hydroelectric plant which supplied part of Hot Springs' electric power until the late 1960's. The white powe r house and part of the staircase are still visible in the canyon.

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202 There exists, however, a dark undercurrent to the picturesque scene lying below. Multiple drown ings have occured in the waters bene ath the falls, and in August of 19 95 a tragic triple drowning took place over a two day period. Later, a temporary di version of the falls revealed a small cave beneath which creates a whirlpool effect in the wa ter that can trap even strong swimmers. 51.70.1 Passing through the Dakota hogback. Contact between the Fall River Sandstone and Skull Creek Shale on right, dipping 8 o to east. 51.80.1 Cross Fall River, type locality of Fa ll River Sandstone seen on right. 52.60.8 Fall River sandstones to right. 53.9 1.3 Lakota Formation 54.70.8 Entering Hot Spring. Hi storic marker on right. HOT SPRINGS, SOUTH DAKOTA HISTORIC MARKER Tribal tradition states that as long ago as the 16 th century the Fall River Valley and canyon area were seldom without groups of tip is belonging to the North American Plains Tribes. They knew the curative value of the warm springs located there and used them for bathing their sick and lame. Exploration of the area by white men in 1874-75 led to settlement and discovery of 75 geothermal springs. The crystal clear water issues from clefts in rocks or bubbles out of the ground. Bathhouses, swimming plunges, hotels hospitals and sanitariums were built tu rning the City of Hot Springs into an early national health resort. So me of these structures still exis t, including a sanitarium now used as the VA Center, and the Sout h Dakota Soldiers Home. Cowboys and others crippled by rheumatism and othe r afflictions would arrive in wagons or trains and leave on horseback after three weeks in the springs. From this point the rushing Fa ll River can be seen and heard. 55.10.4 Truck Route US 18 to left, continue straight. 55.80.7 Traffic light, continue straight. 56.00.2 Bear left on US 385. 56.10.1 Bear right on US 385. 56.30.2 Coarse terrace gravels to left are about 50 f eet thick,consisting of massive and crossbed ded gravels with angular to well rounded clasts of limestone, sandstone and some chert as much as one foot long from the Minnekahta Limestone and Minnelusa Formation in a tan to reddish calcareous sand matrix. The gravels dip 13 o to the south. So far, no one has given an explanation for the dip. The brown stone buildings in this area date back to the late 19 th century when that area de veloped into a major health spa because of the many hot spring s. The sandstones were derived from the surrounding Fall River Sand stone. The gazebo across the creek to left was built in 1920, protecting Kidney Springs, one of 179 springs within the Hot Springs Valley. A metal plaque proclaims "Useful in the treatment of chronic diseases of the gastro-intestinal tract, diseases of the liver and biliary passages disorder s of the genito-urinary tract and sluggish conditions of the alimentry tract. The following chemical anal ysis (in part per million) is also

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203 given: Sodium Chloride, 242.60; Potassium Chlori de, 68.44; Magnesium Chloride, 118.00; Lithium Sul phate, 15.21; Calcium Sulphate, 703.99; Calcium Phosphate, 2.76; Silica, 23.64;Tota l solids, 1174.64. 56.50.2 Nice exposure of coarse terrace gravels along sidewalk to right. 56.70.2 Stop sign. Continue straight across US 385. White gypsum in Spea rfish redbeds to right. 56.80.1 Evans Plunge on right built in 1890. The building houses a recreation pool deriving water from several springs in the creek bed with a total flow of 5,000 gallons per minute. The history of Evans Plunge and an analysis of the wate r is shown on the sign to left: Long before the white man discovered the valley of healing waters, the Sioux and Cheyenne Indian tribes fought for possession of the natural wa rm water springs. Legend te lls us that the battle raged on the high peak above the spri ngs and the Sioux em erged victorious. The Mammoth spring at the north end in the interior of the plunge is known as the Original Indian Spring. Here the Indians drank and bathed in its warm healing water. The Evans Plunge was built in 1890 over numerous small sparkling springs and one mammoth spring of mineral water with a temperature of 87 degrees and of medicinal qualities proclaimed, on good authority, to be superior to that of the famous Warm Springs, Georgia. From the inflow of 5,000 gallons of water per minute from the springs arising out of the pebble bottom, there is a complete change of water 16 times daily, thus insuring clean, fresh, living water at all times. The pool, 50 x 200 feet, ranges in depth from 4 feet to 6 feet with two shallow enclosures for children. CHEMICAL ANALYSIS Water temperature....87 degrees Total residue.............87.9995 Inorganic & non-volatile4.9160 Organic & volatile......8.050 Sulphate of sodium...8.824 Sulphate of potassium3.331 Sulphate of calcium...16.290 Nitrate of magnesium0.150 Iron susqui-oxide.......0.260 Alumia ......................0.021 Silica ........................1.830 56.90.1 Y in road. Continue straight on Fall Rive r Co 18B. Terrace gravels cap Spearfish For mation to left. 57.00.1 Minnekahta Limestone on left. 57.10.1 Small cave high up in Minnekahta on left. The Minnekahta here is about 50 feet thick. 57.30.2 Minnekahta Limestone rises ab ove purplish shales at the top of the underlying Opeche Shale. One belief is that the purple shales were pr oduced during weathering and is an ancient soil, but another explanation is that it is due to bleaching from water percolating downward from the overlying Minnekahta (see Stop 10 of Northern Trip).

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204 57.50.2 Note undulations in the Minnekahta on left, du e to differential collaps e in the underlying Minnelusa. 57.70.2 Brecciated uppermost Minnelusa (see figure 2A). 58.00.3 Brecciated Minnelusa with distorted bedding overlain by Opeche Shale and Minnekahta Limestone straight ahead (see figure 2B). 58.90.9 Buses pull off to the side of the road at curve. STOP 1: HOT BROOK CANYON: MINNELUSA EVAPORITE KARST Leaders: Mark Fahrenbach and Jack Epstein The Minnelusa Formation comprises interbedded sandstone, limestone, dolomite, shale, and anhydrite, and ranges from more than 1,000 feet thick in the southern Black Hills to about 400 feet thick in the northern Hills (Jarrell, 2000). As much as 235 feet of anhydrite has been obser ved from well logs describing the sub surface near Jewel Cave, occurring mainly in the midd le of the formation (Bra ddock, 1963; Brobst and Epstein, 1963). In Hot Brook Canyon about 300 feet of the Minnelusa is exposed, the lower part of the for mation and the contact with the Pahasapa Limestone are covered. The red shale, siltstone, and sandstone of the overlying Opeche Formatio n, and the succeeding Minnekahta Limest one, are visible at the very top of the cliff. Minnelusa and Opeche are the Lakota nam es for Rapid Creek and Battle Creek respectively, and Minnekahta is the Lakota word for hot springs. The Minnelusa Formation is an important stratigrap hic unit in a geologic mapping project of five quad rangles located between Jewel and Wi nd Caves in the southe rn Black Hills (Wind Cave, Pringle, Argyle, Fourmile, and Jewel Cave quadrangles) The Minnelusa can be subdivided into six stratigraphic units. The initial mapping, which began as a co operative venture between the Natio nal Park Service, the U.S Geolog ical Survey and the South Dakota Geological Survey, covered units 1-4 of the Minnelusa Formation to see if there was any correlation with th e Minnelusa units and cave develo pment in the underlying Pahasapa Limestone. This is one of several methods to determ ine the location of undiscovered cave passages in the Jewel Cave-Wind Cave area that will be discussed at th is KIG Conference. Fracture orientations were also measured to see if these trends were visible or cont rolled passage orientation in Jewel Cave. Subsequently, it was decided to map units 5 and 6 of the Minnelusa Formation, with the long term goal of mapping the entire quadrangles. No evaporites are present at the outcrop of Stop 1. They have been removed by solution at depth, result ing in foundering of the overlying beds. Characteristic evaporate dissolution features that are produced are collapse breccias, breccia pipes, distorted bedding, an d cavities (fig. 2C). Elsewhere, such as in Redbird Canyon, 12 miles southeast of Newcastle, WY, collap se sinkholes are present in the cliff faces (Epstein, Field Trip Guide 3, Western Black Hills, this volume, fig. 8). In Hot Brook Canyon, the position of the anhydrite th at has been removed and is clearly deciphered on the canyon wall by the disrupted bedding, with approximately 200 feet of the upper Minnelusa being brec ciated. Below the steep covered slope in the middle of the exposure at this locality the beds are undisturbed (fig. 2B). The anhydrite, therefore, was positioned at the level of the covered slope above the undisturbed beds.

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205 Figure 2. Evaporite karst features in the Minnelusa Formation, Hot Brook Canyon, Hot Springs, Fall River Co., SD. A Angular clasts of all sizes form a characterist ic breccia in the upper part of the formation. B The position of many tens of feet of anhydrite that were remo ved from the Minnelusa is indicated by brecciated rocks above and non-brecciated rocks below the covered slope. The uppermost Minnelusa beds are wavy due to subsidence, as are the beds in the Minnekahta Limestone above. C Breccia pipe extending to the top of the Minnelusa. D Near-vertical breccia pipes (short dash) in moderately dipping (15 o ) beds (long dash) of the Minnelusa Fomation, at mileage 59.3, sugges ting that the beds were tilted prior to pipe formation. Brecciation, caused by removal of anhydrite at depth, was undoubted ly initiated after the Black Hills were uplifted and the Minnelusa breached after the La te Cretaceous. Dissolution probably occurred within a zone about 1,000 feet below the ground surface based on breccia pipes extending as high as the Lakota Formation and the tota l thickness of these overlying formations. A short distance west of Stop 1, to be seen as the bu ses continue up the canyon to turn around, there are near-vertical breccia pip es cutting beds that dip 15 o westward (fig. 2D). If the brecciation occurred prior to tilting, the pipes, which would have formed vertically, would have been rotated by the tilting. Clearly, because the pipes are vertical, they formed after the be ds were tilted. Similar rela tionships can be seen else where in the Black Hills (Epstein, 2005b, figure 8). Close-up examination of the Minn elusa shows extensive fracturing and brecciation producing angular blocks of many sizes (fig. 2A). Effects of brecciatio n appear to decrease upwards in the formation, and the effects of collapse in the overlying formations are not dramatically appa rent. The resistant, thin, Minne kahta Limestone, overlying the red beds of the Opeche Shale above the Minnelusa, contains only scattered collapse features such as sinkholes (Stop 3) and brecia pipes that may be ascribed to foundering in the

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206 underlying Minnelusa (Stop 4). The most significant effect on the Minnekahta is the undulation of beds visible in outcrop throughout the Black H ills. The limestone may have a local relief of several tens of feet, and basins and saddles are common. The soft sediments of the Opeche may have acted as a buffer between the Minnekahta and Minnelusa, absorb ing some of the differential settleme nt. Bedding in the Opeche is not generally visible because of poor exposure. Resume driving west on Hot Brook Canyon Road. 59.30.4 Vertical breccia pipe in brecciated Minnelusa beds that dip 15 o to the west indicate that brecciation occurred after the defo rmation that formed the Black Hills uplift (fig. 2D; Epstein, this volume figure 8). Turn around and retrace ro ute back to Hot Springs. 60.71.4 Closer view of Minnelusa breccia to left. 62.11.4 Stop sign. Continue straight along US 385 South into Hot Springs. 62.70.6 Bear left on US 385 South towards Mammoth Site. 62.80.1 Bear right on US 385 South. 62.90.1 Stop light, continue straight. 63.70.8 Turn right (west) on Truck US 16 towards route 71. 64.50.8 Intersection with Route 71 on left, continue straight ahead. Mammoth Site, historic sign: MAMMOTH SITE OF HOT SPRINGS, SOUTH DAKOTA HISTORIC MARKER Gigantic Mammoths, ancestors of the elephants of today once roamed freely across the High Plains of North America. A repository of their remains, along with other prehistoric animals, lay undisturbed until their discovery over 26,000 years later, in June of 1974. Limestone deposits beneath the Earth's surface dissolved in water from underground springs. The land then collapsed and the resulting sinkhole fille d with 95 degree water that lured mammoths to drink or feed on vegetation. Once in the water they could not go up the slippery, steep incline. Death by starvation or drowning was the fate of most an imals that came to the si nkhole. Along with the mammoth, remains of the giant short faced bear, wh ite-tailed prairie dog, fish and other associated fauna have also been found at this site. As centuries passed the sinkhole gradually filled. Rain, snow and wind deposited soil leaving a hil1 of buried skeletons. This hill remained undisturbed until1 974 when excavation for a housing project by Phil and Elenora Anderson revealed bones and tusks of these huge animals. In 1975, Mammoth Site of Hot Springs, South Da kota, Inc. was formed as a non-profit corporation dedicated to the preservation of the fossils, protecting and developing th e site as an insitu (bones left as found) exhibit. The Mammoth site is quite different from most museums. It is not merely a display of collected items; most of the excavated bones remain exactly we re they were found. Visitors also witness the complete process of paleontology from start to finish. Along with the scientists, they will see for the first time bones of animals that lived before any person walked the land. In 1980 the Mammoth Site was designated as a Registered National Landmark by the Department of the Interior. The Mammoth Site of Hot Springs is truly a gift from Natureour inheritance held in trust for over 26000 years. We would diminish ourselves if we failed to perceive the historical and scientific value of this discovery. Turn into parking area and park.

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207 STOP 2: THE MAMMOTH SITE: A PLEISTOCENE FAUNA SINKHOLE TRAP Leaders: Kris Thompson and Larry Agenbroad The Mammoth Site is located within the southern city limits of Hot Springs, South Dakota. The site represents a hydrologic-geologic natural trap of late Pleistocene fauna. Located within the Spearfish For mation, which is exposed at the margin s of the interior Black Hills, the su rface expression is that of a low hill. This topographic feature is th e result of inverse topography, in that the former topographic sink became a topographic high due to differentia l erosion. The sedimentary fill of the sinkhole containing Pleistocene fossils was more resistant than the surrounding Spearfish Formation. The sinkhole formation is interpre ted as a consequence of extensive dissolution and removal of up to 76 m of anhydrite in the Minnelusa Formation by grou nd water. The Minnelusa Formation is stratigraphi cally located approximately 60 m below the Spearfish Formation. Post-solution collapse within the Min nelusa initiated subsidence an d the upward development of vertical br eccia pipes, as much as 76 meters in diameter. Down hole collapse within these breccia pipes has produced numerous steep-walled sinkholes in the Black Hills since early Tertiary. The Mammoth Site at Hot Springs resides in one of these sinks. In addition to the physical formatio n of the breccia pipe and resulting sinkhole, a critical factor in pro ducing an animal trap in what wo uld otherwise be just another sinkhole was the presence of an artesian spring. Groundwater in the Minnelusa flowed up th e conduit formed by the breccia pipe, producing the spring and contributed to the standing body of water. The water was warm, estimated at 35 o C (95 o F) based on biological and sedimentary evidence. The sinkhole deposit is located on the fourth terrace above the modern bed of Fall River (fig. 3). The Mammoth Site sinkhole is roughly an elliptical featur e measuring 150 by 120 feet (~46 m by ~37 m). The Spearfish Formation walls are very steep, measuring greater than 60 o slopes. A large spring conduit was identified in the northeast section of the deposit, with minor conduits in the south-southwest and northnorthwest areas of the sinkhole. In 1978, the South Dakota Geological Survey drilled th ree test holes in the sinkh ole fill (fig. 4). The deepest hole (test hole no. 3) was stopped at 65 feet (~20 m) below the drill surface. At that depth, bones and fill sediment were still being retrieved. We do not currently know the total depth of the fossiliferous fill deposits. Three recognized episod es of fill are classified in the deposit; phases I, II, and III. Phase I is the initial collapse incl uding marginal gravels derived from river terraces incorporated as the walls fell in. Phase II sediments reflect a pond en vironment with fine-grained, lamina ted depositional units. Phase III reflects a declining water table-probab ly due to lateral migration to the entrenched Fall River. The sinkhole sedimentation was reduced, and the depression became essentially a bioturbated mud hole (fig. 5). Late Pleistocene fauna are included in all phases of sedimentation (fig. 6). The trap was a burial place for late Pleistocene mammoths, plus 47 associated fauna (7 extinct, 40 ex tant). Worldwide there is no com parable deposit known as a repository for mammoths. To date, we have identifie d 50 Columbian mammoths (Mammuthus columbi) and 3 woolly mammoths ( Mammuthus primigenius ) in the excavations that represent approximately 40% of the known sinkhole fill area (fig. 7). There is a paucity of reported Plei stocene sites in the Black Hills. As a result, paleoenvironmental inter pretations for the Black Hills are limited. In summary, the Black Hills are an im portant but inadequately understood region, and thus an ideal place to study the invertebrate and vertebrate faunas of the present as

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208 well as the recent glacial past. The approximately 26 ,000 yr B.P. faunal rema ins recovered from the Mam moth Site provide a rare glimpse into the middle Wisconsinan environmental c onditions in the northern Great Plains/Black Hills southw est of the Laurentide ice sheet. Figure 3. Simplified geologic and physiographic setting of the Ma mmoth Site sinkhole. Terrace 0 is the present flood plain of Fall River. The city of Hot Springs is built on all six terraces. Horizontal distance not drawn to scale. From Laury (1980). Figure 4. Map of the Mammoth Site sinkhole located in t he Spearfish Formation, showing dip of pond sediments, slope of sinkhole wall, and drillhole sites. (From Laury, 1980).

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209 Figure 5. Schematic showing the physical character of the Mammo th Site sinkhole hydraulics, sedimentary fills, and host breccia pipe. From Agenbroad (1994). Figure 6. Sequence of events in history of the Mammoth Site si nkhole. Cross sections are simplified northward views. A, Sinkhole as it may have appeared i mmediately after breccia-pipe collapse. B, End of Phase I sedimentation, a period of rapid wall erosion and pond sedimentation. C, N ear end of Phase II sedimentation, a longer period of sedi mentation than Phase I in which more mammoths were trapped. D, Late Phase III sedimentation. The water table had dropped during renewed Fall River entrenchment, spring disch arge virtually ceased, and the pond was reduced to a mud puddle. (From Laury, 1994).

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210 Figure 7. Distribution of bone in the Mammoth Site sinkhole. 65.00.5 Resume driving. Leave Parking lot, turn left on truck Route US 16. 65.40.4 Route 71 towards Cascade Springs, turn righ t. Red beds of the Spearfish Formation over lain by Sundance Formation, including pinkish beds, on the higher slope, capped by sandstones of the Inyan Kara Group on left. 67.82.4 Pull off to side of road. STOP 3: MINNEKAHTA SINKHOLES; WHAT IS KARST? Leaders: Jack Epstein and Rod Horrocks The Minnekahta Limestone is 40 feet thick in this area, comprising laminate d gray limestone with a purplish tinge (light gray, N7 to light reddish gray, 10R 7/1). Three sin kholes are present at this locality, the most prominent one is 60 feet in diameter (fig 8, 9). The depth of the hole is 40 feet and it probably encompasses the entire thickness of the Minnekahta. Two other sinkholes within 100 feet to the west are about 20 feet in diameter with about 4 feet of Minnek ahta exposed, and another is 50 feet in diameter with no limestone exposed. It is doubtfu l that the sinkhole is due to solu tion within the limestone because the hole extends below the Minnekahta. Th e shape of the hole is partly cont rolled by intersecting joint trends, mainly N. 78 o E., N. 10 o E., and N. 62 o E. A sinkhole about 400 feet to the south across the road is about 300 feet in diameter and about 35 feet deep. The sinkhole was probably formed by cover collapse due to anhydrite removal in the Minnelusa Fo rmation, more than 200 feet below. Sinkholes in the Minnekahta are not common in the Black Hills, except loca lly (Epstein, Davis, and others, 2005, this volume fig. 22). Other sinkholes in this formation have been reported by Darton (1909), see fig. 10) and Gries (1963). The sparce soil cover associated with these sinkholes is quite di fferent from that in much of the humid eastern United States (fig. 11) where sinkhole formation is generally the result of piping and su bsidence of soil or uncon solidation overburden (the plug that fills or covers the void.

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211 Figure 8. Map and profile of sinkholes in the Minnek ahta Limestone at Stop 3. The base of the Minnekahta is probably immediatel y below the bottom of the pit. Figure 10. Sinkhole near Four Corners, Wyoming, northwestern Black Hills (Darton, 1909), similar to the one at Stop 3. The hole extends down through the entire Minnekahta. Figure 9. Steep sided sinkhole in Minnekahta Limestone. The hole is 40 feet deep and encompasses the entire thickness of the formation.

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212 Karst is defined as A type of topography that is formed over limestone, dolomite, or gypsum by dis solving or solution, and that is ch aracterized by closed depressions or sinkholes, caves, and underground drainage (Gary and others, 1972). At this stop, and especially at Stop 4, we will discuss whether the sink hole in the Minnekahta as well as ot her collapse features are truly karst , according to the above definition. Resume driving. Continue south on Route 71. 67.90.1 Large sinkhole to left. 69.21.3 Skeletal remains of cow on slope to right (2004). 72.83.6 Disembark from bus; buses proceed and park at Cascade Springs at 73.1. STOP 4: CASCADE SPRINGS: HYDROLOGY, GYPSUM SHENANIGANS, PULL APARTS, BIOLOGY. LUNCH LEADERS: Andy Long, Jack Epstein, and Larry Putnam 73.10.3 Buses park at Cascade Springs. This stop is located along the west limb of the Cascade anticline at th e south end of the Black Hills uplift (fig. 12). First we will examine structures in gyps um in the Spearfish forma tion along SD Highway 71 (fig. 13 A ), followed by a 100-foot vertical hike to see large fractures in the Minnekahta Limestone (fig.13 B ), and contemplating whether this is related to karst. Then we will discuss the hydrology, origin, and biology of Cascade Springs (fig. 13 C ). Figure 11. Typical sinkhole in the humid eastern United States. This one developed by collapse of the residual soil cover in the Beekmantown Formation of Ordovician age in eastern Pennsylvania near a quarry whose pumping has significantly lowered the water table.

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213 A Gypsum Shenanigans In the cascade springs area the Spea rfish Formation is 330 feet thick, comprising interbedded red beds and gypsum, the gypsum totaling about 70 feet (Post, 1 967). The beds dip moderately to the west on the west limb of the Cascade anticline, ranging between 15 and 50 degrees (fig. 14), the steepest dips are 2,000 feet to the northwest along the highway. The bottom of the roadside exposure at locality A is about 75 feet stratigraphically above the base of the Spearfish Formation; the top of th e Minnekahta Limestone lies in a ravi ne just north of the road. About 50 feet of interbedded gypsum and red siltstone and shale ar e exposed. About 30 feet above the road there is a 2-foot bed of non-calcareous gr eenish-gray-weathering (5GY6/1) siltsto ne to fine-grained sandstone. The gypsum is contorted and many vein lets, generally less than one inch thick, extend from the parent beds (fig. 15 A ). The shale at the base of the exposure is highly fractured and bedding is not readily discernable. These features combine to create a secondary po rosity in the Spearfish at this locality. Post (1967) and Hayes (1 999) noted two breccia pipes in this exposure; the easternmost one is shown in figure 15 A Hayes believed that breccia pipes extendin g up from the Minnelusa Formation are the con duits for the artesian springs at Cascade Springs. The gypsum bed in figure 15 A is thickened and down warped and is immediately underlain by about five feet of breccia containing blocks more than 1 foot long, some of which appear to have risen from below (fig. 15 B ) To the side of this st ructure the red siltstone is highly fractured and contains a con tinuous 4-inch-thick bed of light-oliv e gray (5Y6/1) siltstone that is incorporated as clasts in the red shal e of the breccia and is at a higher position than to the side. The beds immediately above the structure are flat, lying athwart the structure, and do not appear to have subsided. Beds below consist of minutely fractured and brecciat ed siltstone which is trav ersed by gypsum veinlets.

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214 Figure 12. Location map showing Cascade Springs, other nearby springs, and miscellaneous rock and ground-water sampling sites (from Hayes (1999).

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215 It is interesting to compare this p ipe with those seen in the Minnel usa at Hot Brook Canyon, Stop 1. The exposure that Po st (1967) saw (fig. 15 C ) was different from the one seen now because of subsequent road widening, suggesting that we now see only the edge of the pipe. Post describes the feature thus: High radioactivity, as much as 35 times background, was note d at a bleached and struct urally disturbed zone in the Spearfish Formation on the south side of State High way 87 in the SW1/4 SE1/4 sec. 20, T. 8 S., R. 5 E. (See fig. 87-Posts figure ). This disturbed zone is approximately 15 feet wide and extends vertically up the face of the roadcut. Bedding in the zone is obliterated. The rock consists of a mass of disoriented fragments of siltstone, gypsum, and black muds tone. The siltstone, whic h is the major constituen t, has been bleached to a moderate greenish gray from its normal, reddish-br own color. The character of this disturbed zone, its proximity to the hot springs at Cascad e Springs, and the presence of cavern s in the gypsum at the top of the roadcut just to the east of this zone suggest that the structural distur bance and bleaching were caused by a hot spring similar to those presently active at Cascade Springs. The disturbe d zone may, in fact, be the upper part of a breccia pipe similar to those described by Bowles and Braddock (1963). Figure 13. Stop locations at Cascade Springs showing general geology, location of springs and breccia pipes (from Hayes, 1999).



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216 Figure 14. Cross section through the area of the gazebo at Ca scade Springs showing localities to be examined, and breccia pipes, believed to be former conduits for the springs, extending up from dissolution cavities in the Minnelusa Formation at depth. Fractured Minnekah ta shown in figure 16 lies about 100 fe et above the gazebo at locality B. Green shale of the Stockade Beaver Me mber of the Sundance Formation caps t he Spearfish west of S.D. highway 71. The other pipe, about 150 feet to the west as no ted by Hayes (1999), is characterized by a gypsum bed that is downwarped a few feet, and beds above and below are not affected The many veinlets represent a zone where much gyps um has been removed by solution and/or have been intruded into the su rrounding rock from the parent bed by pr ocesses not fully understood. Broken beds of gypsum several feet thick merge laterally into gypsum-red bed breccia (fig. 15 C) and veinlets. The impression is that the original bedd ed gypsum at this locality has been modified by solution removal, injec tion into veins, contortion by expansio n, and brecciation. It is possible that much of the original mass of gypsum has been removed. Also, anhydrite, which may have been the original fo rm of calcium sulfate, when converted to gypsum, may have expanded consider ably to create the force for vein injection and bed crumpling. However, several beds at the northernmost end of the exposure along SD 71 were X-rayed and no anhydrite was found in veins or beds, only gypsum (John Johnson, USGS, pers. comm.). B Fractures (pull apart) in the Minnekahta Limestone Walk several hundred feet to the we st along the highway and pass through an open gate before the park ing lot at Cascade Springs and climb up the slope. Bedding in the Minn ekahta wobbles a bit, but the dip averages about 20 o to the southwest. Many large fractures (fig. 16 are found in a zone between 70 and 100 feet vertically above the base of the slope in an area about 150 feet long. The fractures are more than 10 feet deep in places, and probably extend the entire 40-foot thickness of the Minnekahta. They are as much as 10 feet wide and have various orientations, including N. 35 o E., E.-W., N. 5 o E., and N. 70 o E., following prominent joint directions. There are three possible or igins that might be consid ered for these structures: (1) subsidence due to solution of gypsum below, (2) gravity sliding on the soft sediments of the Opeche Shale, and (3) a combination of slid ing and weakening of material below by solution. An initial impression is that these fractures are caused by tension due to downhill sliding. An interest ing comparison with similar fractures in the Moenkopi Formation related to dissolutio n of salt at depth in the Holbrook basin (Epstein and Johnson, 2003) will be made. Th ere are many small-scale structures, folds and faults, such as those described at mileage 4.5, that have been attributed to gravity sliding, believed to have occurred after erosion had exposed the surface of the Minnekahta (Epstein, 1958; Brobst and Epstein, 1963).

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217 Figure 15. Structures in gypsum in the Spearfish Formation at locality A. A Downwarped gypsum bed interpreted to be part of a breccia pipe by Post (1967) and Hayes (1999). Note abundant thin veins extending into surrounding red beds. Shale and siltstone at base of outcrop is minutely fractured. B Brecca just below the "pipe". C Breccia pipe figured by Post (1967, fig. 87) at same spot as structure in fig. 15 A Note lack of bedding in the bleached pipe as compared to stringers subparallel to bedding in the surrounding rock. D Brecciated gypsum believed not to be sediment ary because of limited horizontal extent.

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218 Figure 16. Fractures in Minnekahta Limestone, a pparently extending down through the entire thickness of the formation, locality B, Cascade Springs, Stop 4. C 1 Hydrology of Cascade Springs Cascade Springs is a group of warm (~20 o C) artesian springs (fig. 13) with collective flow of about 19.6 ft 3 /s and a surface drainage area of 0.47 square miles. The drainage area is not large enough to supply this large flow rate to the spring indicating that its source water is not local. The large springflow rate sug gests that a large contribution of flow probably is su pplied by the highly permeable Madison aquifer, more than 800 feet below. Hydraulic head in the Madison a quifer is higher than that of the overlying Minnelusa aquifer in the vicinity of the spri ngs, which would result in upward fl ow from the Madison to the Minnelusa aquifer if adequate vertical permeab ility exists. Back and others (198 3) examined geochemical and hydro logic data of the springs and conclu ded that Madison aquifer water, which is recharged in the western and southwestern Black Hills, sweeps eastwa rd around the southern end of th e Black Hills and supplies most of Cascade Springs, but they are also partially supplied from the Minnelusa aquifer. Stable isotopes of oxygen confirm the interpretation that the sour ce of spring water is from recharge in the Black Hills many miles to the northwest of Cascade Springs (Naus and ot hers, 2001). A spring-water sample had a 18 O value of 15.4 parts per thousand, which is co nsiderably lighter than the local recharge but is similar to water recharged on outcrops of Paleozoic rocks near the Pennington-Custer County line. Naus and others (2001) concluded that the low tritium concentr ations in spring water indicate that a large proportion of greater than 40 year old ground water discharges from the springs. This long residence time is consistent with the con clusion that the recharge area is many miles from the springs. Moreover, the combination of geochemical information generally excludes substa ntial contribution from regional flow outside of the Black Hills (Naus and others, 2001). A long-term response in flow from Cascade Spring s may reveal some interesting aspects about karst aquifer storage. Although dry cond itions and declining ground-water le vels have prevailed in the Black

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219 Hills during recent years, an anomalous increase in springflow of from 1.5 to 2.0 ft 3 /s over the normally steady flow rates occurred during the spring of 2005. This could be explained by a long-term lag time in the low-frequency response comp onent of springflow (or hy draulic head), which can occur in karst aquifers because of the unique storage properties of karst. If this is the case, the recent increase in springflow would be in response to wet conditions dur ing the mid 1990s. An alternate ex planation might be that declining water levels caused flowpaths to shift, po ssibly focusing more flow to Cascade Springs. C 2 The Origin of Cascade Spring (Summarized from Hayes, 1996 and 1999) Beginning on February 28, 1992, a large discharge of red suspended sediment was observed from two of the six known discharge points. Similar events during 1906-07 and 1969 were documented by local res idents and newspaper accounts, and a resident reported a similar reddening of the water during 2003, although not as prolific as in previous years.. This pe riodic sediment discharge at Cascade Springs probably results from episodic collapse that is caused by subsurface dissolution of anhydrite beds and cement in the middle and upper Minnelusa Formation, accompanied by replacement of dolomite by calcite. Mineralogic and grain size analyses support a hypothesis that many breccia pipes now exposed in outcrops of the Black Hills were, at one time, throats of artesian springs. Some of these sp rings have been abandoned as water levels have declined over geologic time due to the lowe ring of the Black Hills by erosion. The flow paths for Cascade Springs is believed to be along breccia pipes that also will someday be abando ned. Hence, the locations of artesian spring discharge points probably have been shifting outward from the center of the Black Hills uplift, essentially keepin g pace with regional erosion over geologic time (Epstein, 2001, 2003). Furthermore, artesian springflow probably is a fact or in controlling water leve ls in the Madison and Min nelusa aquifers, with hydraulic head declining over geologic time in response to development of new dis charge points. A suitable hydrologic and geochemical model for Cascade Springs involves dissolution of anhydrite accompanied by dedolomitization in the upper Minnelusa Formation, wh ich is caused by upward leakage of relatively fresh water from the Ma dison aquifer (fig. 17). The anhydrite dissolution and dedolomitization account for the net remo val of minerals, creating cavities that woul d lead to breccia pipe formation by grav itational collapse. Networks of interconnected brecci a layers and breccia dikes are also common in the upper Minnelusa. These breccia structures, along with vertical fractures and faults, are likely pathways for transmitting upward flow from the Ma dison to the Mi nnelusa aquifer.

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220 C 3 Biology of Cascade Spring (Summarized from various materials provided by The Nature Conservancy, Black Hills Ecoregion 8100 Sheridan Lake Road, Rapid City, SD 57702, Phone: (605) 342-4040, Fax: (605) 348-6060 http://www.nature.org/w herewework/northameric a/states/southdakota/pr eserves/art9147.html) The springs support a unique warm ri verine system that includes four rare plant species tulip gentian, beaked spikerush, southern maidenh ead fern, and stream orchid found no where else in the Black Hills or the surrounding Great Plains. Their presence in the Blac k Hills is due in large pa rt to the warm water of Cascade Springs, which allows for their surviv al during severe winters. Tulip gentian ( eustoma grandiflo rum ) requires a fairly high water table in moist open fields and meadows underlain by sandy alluvial soils. Its habitat has been reduced to the po int that it is now rare over much of its former range. Beaked spikerush ( eleocharis rostellata ) is an obligate wetland species that occurs in many types of al kaline wetlands, includ ing hot spring edges. It typically o ccurs on sand bars and along stream ed ges in saturated so il. Also, beaked spikerush can occur in marl beds, which are formed from calcium-carbonate precipitates. Southern maiden hair fern ( adiantum capillus-veneris ) owes its localized occurrence along Cascade Creek to the warm, limey waters of Cascade Springs. Stream orchid ( epipactis gigantean ) grows on calcareous, porous substrates or thin, partially decomposed, wet orga nic substrates and is more common in the open than in forests. Figure 17. Geologic features t hat could enhance vertical hydraulic conductivity including (a) breccia pipe that formed along a fracture and (b) breccia pipe initiated by collapse of Minnelusa Formation into Pahasapa Limestone cave.

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221 This area contains prime mountain lion habitat, with a nearby active den, and it includes an unusual Townsend's big-eared bat nursery roost. Because Casca de Creek remains ice-free throughout the year, it's a valuable winter fishery and provides an important wate r source for wildlife especi ally birds. This unique riverine system has received The Nature Conservancy's second-highest biodiversity ranking, making it an outstanding example of an extr emely rare natu ral community. Resume driving. Leave parking lot, turn left on Route 71 back towards Hot Springs. 81.07.9 Intersection with Truck Rout e US 18 East, turn right. 81.70.7 Turn left on US 385 North into Hot Springs. 82.60.9 Stop light, intersection with US 16, continue straight following US 385. 83.40.8 Three-way stop sign. Turn right, continuing on US 385 North. 83.50.1 Gypsum in Spearfish Formation to left. 83.60.1 Fire tower atop Battle Mountain to right. HISTORIC MARKER The historic sign states: Accordi ng to tradition, American Indians were stricken with an epidemic known as "fell disease" about the midd le of the 16th century that thre atened to obliterate the tribes. A Messenger arrived from the Great West with news of a wonderful water which, he said, had been touched by the finger of the Great Spirit and woul d cure all manner of diseases. Indians came to these springs by the thousands. After a lapse of more than 200 years, the Chey enne took possession of the springs and built an immense tipi city covering hundreds of acres. In the following years, the Sioux migrated west and disputed the ownership of the springs. This culminated in a fierce conflict in about 1869, the memory of which is preserv ed in the name of the eminence to the east, Battle Mounta in, where the besieged Cheyenne establishe d fortifications. The Sioux won the battle and po ssession of the springs which they ca lled wi-wi-la-kah-to (Springs hot). They called the area Minnekahta (Water hot) an d termed the Black Hills a great "Medicine Home". After the Battle Mountain fight, tradition says the Sioux and Cheyenne agreed to allow the springs to be a health sanctuary to give their sick and la me the benefit of the hea ling waters. Around 1880, pioneers began to settle the area. 84.10.5 Quarry located in the Minnekahta Limestone to left. The Minnekahta is the most impor tant source for aggregate in the Black Hills. We are riding in the Red Valley comprising weak beds of the Spearfish Formation, straddled betw een the Dakota hogback on the right and hills of the Minnelusa on the left. 86.22.1 Entering Custer County. 88.82.6 Minnelusa Formation in gulley to right. 89.50.7 Entering Wind Cave National Park. Keep an eye out for bison, coyotes, and prairie dogs.

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222 89.60.1 Undulating Minnekahta Limestone at entran ce to park. Poorly exposed, progressively older rocks are encountered traveling north throug h the park, including th e Minnelusa Formation, Pahasapa Limestone, and Deadwood Formation, and Precambrian rocks. 92.52.9 Turn left to Park Visitor Center. 93.20.7 Park at Visitor Center. STOP 5. WIND CAVE NATIONAL PARK: CAVE AND KARST VULNERABILITY LEADERS: Rod Horrocks and Marc Ohms Significance of Wind Cave: Most boxwork of any known cave The most complex rectilinear ma ze cave known in the world 4th longest surveyed cave in world (over 117 miles currently surveyed) One of best paleokarst exposures known anywhere One of the strongest blowing barometric wind caves Diverse mineralogical assemblage Diverse and unusual speleothem types Intersects the water table Cave/Karst Vulnerability: The National Park Service built the infrastructure to fa cilitate visitors viewing Wind Cave within an erosional window through the Minnel usa Formation and on top of the Pahasapa Limestone and adjacent to the natural entrance of the cave. This is, arguably the worst place such struct ures could have been built. Since the Park can not remove these historic Civilia n Conservation Corps (CCC)-e ra structures, it is now attempting to mitigate the impact from thes e structures on sensitive cave resources. Sewage systems, roads, parking lots, fire suppressi on, and buildings change the quality, direction, and amount of water entering Wind Cave. To better protect Wind Cave, the old leaking sewer lines above the cave were replaced with dual-contained HDPE sewer li nes in 2001. The inner, primary line was surrounded by an outer, secondary line, whic h captures and contains any leaks th at may arise from the primary line. Visual inspection ports were built into the system, allowing the park to quickly and easily monitor the line for leaks and fix them before any spillage occurs. To stop contaminated runoff from the parking lot from entering Wind Cave, the park replaced the asphalt lot with concrete in 2004. Th e concrete has mitigated the effect of dripping gasoline and antifreeze melting the asphalt and releasing hy drocarbons which were washed into the cave in as little as 6 hours. It is also no longer necessary to conduc t annual chip sealing of cracks in the asphalt, a major hydrocarbon source. In addition, the new concrete lot captures all runoff and funnels it through an oil and grease separator before releasing it into Wind Cave Canyon. Due to decades of fire suppression and planting of trees by the CCC during the 30s, the area above Wind Cave contains many more trees than it histori cally did. This second overgrowth has reduced the amount of water entering th e cave. The park has initia ted an active prescribed fi re program to reintroduce fire back into the ecosystem. Artificial entrances to Wind Cave ha ve impacted the cave's climate by allowing increased or unnatural airflow. When warm summer air enters the cave, it cools and water condenses on the walls of the cave.

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223 When cool, dry winter air enters the cave it warms up and evaporates water. When the cave is expelling air due to barometric pressure changes, as much as 16.1 gallo ns of water is lost per ho ur out the natural entrance (Nepstad, 1986). The most dramatic effect of climate change on the cave were th ree collapses that occurred near the walk-in entrance that were caused by frost we dging. To help control thes e changes, a revolving door was added to the Walk-In En trance and airlocks were added to the two elevator landings. We are currently monitoring and studying the cave climatology to help us better understand the whole system and to deter mine if further actions are necessary to restore natural climatological conditions. The developed tour route portion of Wind Cave is impacted from construction-generated dust, dust from tours traveling over unpaved trails, dust tracked into caves on shoes or brought in on clothes, lint accu mulations, and other materials shed from humans. Human visitors shed a plethora of materials into caves including lint, hair, dandruff, mites, microbes, shoe rubber, and pet animal fu r (Jablonsky 1994). Lint and dust removal projects are conducted in Wind Cave to restore natural conditions, prevent unnatural spele othem dissolution, remove artificial fo od sources, eliminate unnatural odors, and to restore visual scenes. Many of these concerns, although seemingly unrelated, are part of a bigger picture. The relationships between animals, plants, fire, water, the cave and people are all interconne cted. No one part of the ecosystem is separate from another. We try to understand, conser ve, and interpret all aspects of Wind Cave National Park as this is the mission of the National Park Service. Barometric Breathing Cave: The strong barometric wind coming from or blowing in to the natural entrance of Wind Cave is one of its defining characteristics and the reason for the name of the cave. This wind is a reaction to changing atmo spheric pressure conditions. When there is a high pressure outside, air ru shes inside towards the lower pres sure. This exchange happens because the cave is fair ly well sealed by the overla ying Minnelusa Formation and because of the small number of entrances (2) and blowholes (6). Wind speeds up to 25 miles an hour have been reported through the na tural entrance. Airflow has been do cumented flowing in the same direc tion (out or in) for up to 32 hours, thus indicating a very large volume for the cave (Pflitsch, 2002). The barometric airflow through th e natural entrance provides an op portunity to determine the approx imate volume of Wind Cave. In the mid 1960s, Herb Conn built an instrument to measure the wind flow through the Natural Entrance. He calculated th at Wind Cave had a volume of 56,000,000 m 3 (Conn, 1966). The current surveyed portion of the cave has a volume of 1,400,000 m 3 a little over 2% of his estimate (However, it should be pointed out th at a significant percent of this vol ume may be in cracks too tight for humans to enter or in-between breakdown blocks). Conn s research was repeated by Daniels in 2001, this time taking into account the Snak e Pit entrance and more accurate and precise instrumentation. There are numerous potential sources of error in any measurements of cave airflow. There are at least six documented blowholes near Wind Ca ve that are likely to be connected to the cave. The revolving door at the Natural Entrance leaks air, as does the elevator shaft and Snakep it Entrance cover. Cavers have observed airflow in high dead-end domes near the su rface, possibly indicating diffuse airflow through the bedrock and overburden. All of these were not accounted for in Daniels study, and will lead to an underes timate of the airflow. However, Daniel s estimated the total volume of Wi nd Cave to be between 6,000,000 m 3 10,000,000 m 3 significantly lower than Conns estimate. However, it is reasonab le to conclude from both Conns 1966 research and Daniels 2001 research that airflow indicates that there is a significant amount of cave that has not yet been discovered in Wind Cave.

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224 Cave Potential: A very active exploration and mapp ing program, which began in the 1950s, is still on-going within Wind Cave. Currently, 3-4 miles are ad ded to the surveyed length of the cave each year. It is not uncommon to hear cavers participating in the current survey effo rt remark about the endless potential of the cave. A famous diary quote from 1891 by an early Wind Cave explorer, Alvin McDonald, said, Have given up the idea of finding the end of Wind Cave (McDonald 1891). This is as true today as it was then. Many people have speculated on the potential exte nt of Wind Cave, even to the possible connection with the worlds second longest cave, Jewel Cave, locat ed 18 miles to the NW. A lthough, theoretically pos sible, this seems highly unlikely b ased on how both caves react to surface changes in barometric pressure, how network maze caves form, and upon their geologic setting. By ca lculating passage density within the current boundaries of Wind Cave, a minimum potential length of humanly accessible passages in the cave was determined (Horrocks and Szukalski, 2002). Based on the total density in each of five distinct regions of the cave, a minimum length of 250 miles for Wind Cave was estimated. The current 117 miles of survey represents no more than 47% of that minimum predicte d length. By examining the geologic factors, a likely potential areal extent was also identified. It was dete rmined that the current cave boundaries cover 1/8 of the likely extent of the cave. Based on the known passage density, the length of the Wind Cave survey could be as much as 1,100 miles. The current mapped 117 miles represents about 10% of that maximum potential length. The final mapped length of the cave will de pend on human caving capab ilities. Whether 10% or 46% of the cave has been surveyed, it is obvious that a tremendous amou nt of surveyable passage remains within the cave system. Based on cu rrent mapping rates, it seems probable that Wind Cave will soon become the third longest known cave in the wo rld. It is doubtful that it will ever attain the first or second position. Boxwork: Wind Cave is known for its world-class displays of boxwork. Boxwork consists of thin interconnecting veins of calcite that protrude from all surfaces within Wind Cave, especially in th e Middle Level and within layers of dolomite. The formation of these calcite veins pre-date the cave. Therefore, boxwork is a speleo gen, a dissolution feature that formed when the surrounding bedrock was dissolved or weathered away. These veins are truncated by paleokarst features and t hus predate that event and the formation of the cave. The current theory states that these veins resulted from fractures that formed when anhydrite hydrated to gypsum and expanded, fracturing the surrounding limestone soon after the rocks were deposited. These gyp sum veins were later replaced by calcite when fresh wa ter circulated through the limestone late in the Mis sissippian Period. Subsequent removal of the surrounding limestone left th e calcite vein fillings standing in relief. The bedrock was more easily removed because it c onsists of calcite crystals which are pseudomorphs after gypsum that are held together by a sparse secondary quartz cement and which became a friable sand upon partial dissolution along the grain boundaries (Palmer and Palmer, 2000). Paleokarst: Wind Cave is one of the best spots in the Unite d States to view paleokarst. Between 310-320 million years ago, a karst surface was developed on the Pahasa pa Limestone. Sinkholes, vertical pipes, and short horizontal caves developed within th is landscape. The caves appear to ha ve been developed under phreatic conditions in zones of freshwater-saltwater mixing. About 310 million years ago, a marine transgression filled in these karst features with layers of red sand, silt an d clay, along with fragments of limestone, chert, and sandstone derived from previously overlying sedimen ts that were entirely eroded away. These filled-in features became an important structur al control during the development of Wind Cave 40-60 million years ago. Many of these features were partially or who lly excavated when the ma in passages in Wind Cave formed. These paleofills are readily seen on the Garden of Eden and Fairgrounds Tour Routes in Wind Cave. These features are concentrated in the upper half of the Pahasapa Limestone.

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225 Development of Wind Cave: (Note: The stages referred to belo w are only for convenience in this outline and include only the major events. They are not formal divisions. Art an d Peg Palmer (personal communication, 1999). Stage 1 : Deposition of the Pahasapa Limestone (Madison ) on a shallow sea floor 340-320 million years ago (Mississippian Period). Low areas of the continen t were covered by shallow sea water. Some of the major cave-forming limes tones and dolomitesof North Am erica were deposited at th is time. Several distinct lithologic layers formed, from bottom to top: massive dolomite (route to Lakes); bedded dolomite and lime stone (major boxwork zones); chert (ceiling of Ice Pa lace); and massive limestone (Fairgrounds, Garden of Eden). Gypsum (hydrated calc ium sulfate) and anhy drite (calcium sulfate) were also deposited within some of the lower and middle layers. Stage 2 : Gypsum and anhydrite are physically and chem ically unstable. Soon after the rocks were deposited (about 320 million years ago) they were uplifted slightly above sea level, allowing the following to happen: Anhydrite hydrated to gypsum, causing expansion th at formed many small cr acks in the surrounding rocks, especially the dolom ite beds in the middle Pahasapa Limeston e. Dissolution of dolomite followed by crystallization of calcite, as well as plastic deformation of the sulfates, probably contributed to the fractur ing. Subsequent calcite was deposited in the fractures. The pressure of the overlying rock s forced the gypsum and anhydrite to migrate into fractures in the surrounding rock. Reduction of gypsum and anhydrite in the deeper layers produced hydrogen sulfide, which migrated upward to oxygen-rich areas, where it was oxidized to sulfuric acid. The reaction of this acid with the sur rounding limestone formed the earliest cave openings --generally small pockets and fissures--and the adja cent limestone and dolomite were altere d to a weak, crumbly, bleached zone The basic layout of the cave passages was determined at this time. Some of the hydrogen sulfide comb ined with dissolved iron to prod uce iron sulfide (pyrite, etc.). Stage 3 : The climate became wetter, an d considerable amounts of fresh water entered from the surface. Gypsum and anhydrite were replaced by calcite. Oxidat ion of the iron sulfide around the old hydrogen sul fide zones produced red and yellow zones of iron oxide in and around the cave, and the calcite deposited at this time is orange-brown as a result. This includes the veins that now protrude as boxwork fins. In the upper strata, gypsum was simply dissolved away, leaving a fra ctured jumbled breccia in the limestone (as in the Garden of Eden). Stage 4 : Eventually the climate became so wet that sinkholes and solutional fissures formed at the sur face, and new caves were formed or enlarged forming part of the upper level of the cave, most of which were subsequently filled by sediment during stage 5. Some of the fissures extended below the chert level intersecting the cave network established in Stage 2. Mu ch of the cave enlargemen t simply followed earlier openings, fractures, and altered rock zones. Stage 5 : About 300 million years ago, during the Pennsylvanian Period a rise in sea level caused the lower part of the Minnelusa Formation (mainly sandstone) to be deposited, filling in the sinkholes, fissures, and most early caves. Much of the sandstone was deposited by rivers along the paleo-shoreline. The red sand and clay deposits in the Beauty Parl or and Garden of Eden are derived fro m the lowest layers of this formation.

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226 Stage 6 : Continued deposition of sediments buried the Pahasapa Limestone to a depth of at least one mile during the Pennsylvanian thro ugh Cretaceous Periods (300-70 millio n years ago). A layer of white cal cite (dogtooth spar) was deposited on the walls of earlier cave openings. Stage 7 : The Black Hills and Rocky Moun tains began to rise about 70 mi llion years ago. Mobilization of deep fluids early in this stage caused deposition of hydrothermal minerals in some of the early caves and pockets, including quartz crys tals (Crown Jewels, etc.). Stage 8 : As the Black Hills continued to rise, the sedimentary rocks we re stripped off by erosion, exposing very old (Precambrian) igneous and metamorp hic rock at the center of the uplift (Harney Peak, Mt. Rushmore, etc.). The eroded edges of the sediment ary rocks, including the Pa hasapa Limestone, were exposed around the perimeter of the Black Hills. Ground water moved throug h the rocks in co nsiderable vol ume, and most cave enlargement took place during this time. Again, the enlargement was concentrated along the zones of older cave development and alterati on. Except in a few places the cave does not extend to the top or bottom of the Pahasapa Limestone, nor does it extend far below the water table. Evidently the cave is not the product of simple artesian groundwater flow, infiltration from the surface, or hydrothermal water rising from depth. If it were, the cave would be la rgest where the water first entered the limestone. It is clearly the result of mixing between two or more of these water sources, which produced a zone of solu tionally aggressive water. It s main solutional phase was about 60-40 million years ago. Stage 9 : As the water table dropped, weathering of the limestone walls took place and continues today. Most important, the crumbly, altered dolomite of St age 2 has decomposed into a powdery sand that formed files of sediment on the cave floors and allowed the thin calcite veins (mainly the orange-brown veins of Stage 2) to protrude as boxwork. Bedrock walls have developed a thin weathering rind of fluffy powder, stained red, yellow, and black from the oxidation of mi nerals in the rock (such as the pyrite from Stage 2). Moist air rising from the lower levels produces condensation on the walls of the cooler upper levels and con densation erosion. This dissolutio n produces domes and chutes in the ce ilings of upper level passages. The condensation moisture become s saturated with dissolved calcite and seeps through the bedrock to the water table, although some of it evaporat es in the lower levels to produce aragonite frostwork and popcorn. Other deposits are also formed by water seeping from the surface. Active drips fed by infiltration from surface water deposit flowstone, stalactites, etc. In zones of po nding, such as the lakes, a wall crust of calcite has formed, and calcite rafts form at th e surface. This water is supersaturated with calcite and cannot dissolve limestone. Older crusts higher in the cave, including dogtooth spar in larg er openings (Stage 6), have been shaved off by condensation corrosion and weathering. Major time indicators: Orange-brown calcite (boxwork fins ); older than 320 million years. It is cut by the red paleofill and never occurs in the paleofill, except as eroded fragments. Red sediment fill (sand and clay paleofill); about 300 million years old. This marks the well-known unconformity that separates the Mi ssissippian and Pennsylvanian rocks throughout the western states. Be careful--many of the dolomite beds weat her to red colors too, as in the Post Office. Much of the paleofill in the cave has subsided into lower levels as the cave enlarg ed, but this can be easily recognized by the lack of (or disruption of) the white calcite coatings and vein fillings (described below). White calcite veins and in cluding dogtooth spar ; between 300 and 70 million years ago, probably toward the younger end. This fills cracks and coats pockets in the red pa leofill, so it is definitely younger. It is cut by the present fills and over lain by deposits such as wall crusts.

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227 Quartz crystals ; about 100-70 m illion years old. In places they coat the dogtooth spar, especially along faults. The cave itself has an origin that spans the entire pe riod from about 320 million years ago to the present. The major solutional phase was abou t 60-40 million years ago, during which time th e present topography developed. However, the present cav e follows the patterns of the earl y gypsum and anhydrite zones, as shown by the fact that the orange calcite (originally gy psum) is concentrated only around the present caves. In large breakdown or blasted areas the density of calc ite veins can be seen to diminish away from the cave. Therefore, the cave pattern predates the uplift of th e Black Hills. The pattern seems well adjusted to the Black Hills uplift, with fractures radiating away from the center of the hills. Howe ver, the Black Hills dome has long been an area of uplift and weakness in th e earth's crust, and fractures tend to maintain the same patterns and are repeatedly reactivated. Resume driving. Leave Visitor Center returning to US 385. 93.90.7 Turn left on US 385 towards Custer. 94.70.8 Sewage lagoon on right. Minn elusa exposed on cliff face. 95.00.3 Poorly exposed Minnelusa littered with co bbles from the overlyingWhite River Forma tion. 96.11.1 Prairie dog mounds on right. Coyotes may be seen occasionally ex amining these morsels. 96.40.3 Junction with Route 87 north. Continue straight on US 385. 96.70.3 Sandstone outcrops of the Deadwood Formation in creek to right. For the next 50 miles we will be riding on a variety of Precambrian metamo rphic and igneous rocks making up the core of the Black Hills. Lovely scenery, no karst, enjoy the views! 102.9 6.2 Junction with Route 89, bear right on US 385 and US 89 north towards Custer. 106.2 3.3 Mine tailings to right from feld spar workings in pegmatite. 114.2 8.0 Traffic light. Intersection with US 16. Turn right on US 16/US 385/Rte 89 into Custer. 114.6 0.4 Traffic light in Custer. Make left turn on to US 16 towards Chie f Crazy Horse Mountain and Mount Rushmore. 116.8 2.2 The hills to the right are held up by the Harney Peak granite intruded into mica schist. Chief Crazy Horse Mountain carving at 2 oclock. 117.2 0.4 Chief Crazy Horse at 1 o'clock. 119.0 1.8 Entrance to Chief Crazy Horse Mountain (figure 18). Chief Crazy Horse and Chief Sitting Bull were responsible for the defeat of Custer at th e Little Big Horn, following conflicts with the White Man after gold was discovered in th e Black Hills in 1874. The monument, carved in pegmatitic granite of Thunderhead Mountain, is the largest in the world, as tall as the Wash ington Monument and taller than the pyramids at Giza. Sculptor Korczak Ziolkowski was invited by Lakota Indian Chiefs to carve Crazy Horse in the Black Hills in 1939 and he began blasting in 1948. When comp leted the mountain carving will be 641 feet long by 563 feet high. The head of Crazy Horse is 87 feet tall or 22 stor ies high, and equals in vol ume all the heads at Mt Rushmore. His outstretched arm is nearly as long as a football field and points to

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228 my lands are where my dead lie buried, a quote repo rtedly given in response to a taunting question asked of a white man after the defeat of the Indians. 121.6 2.6 Cross Pennington County line. 124.9 3.3 Route 89/87 to right, the Ne edles Highway to Sylvan Lake continue straight ahead. 125.0 0.1 Turn right on Route 244 East. 132.1 7.1 Harney Peak Granite country. 132.3 0.2 Enter Mt. Rushmore Nation al Memorial (figure 19). The birth of our nation was guided by the vision and courage of George Washington. Thomas Jef ferson always had dreams of a grea ter, more perfect nation, first in the words of the Declaration of Independence and later in the expansion of our nation through the Louisiana Purchase. Preservation of the union was paramount to Abraham Lincoln, a nation where all men were free and equal. At the turn of the Twentieth Century Theo dore Roosevelt envisioned a grea t nation, a leader on the world stage, our nation was changing from a rural republic to a world power. The ideals of these presidents laid a foundation for the United States of America as solid as the rock from which their figures were carved. (Mt. Rushmore Natio nal Park service Web Site). Figure 18. Chief Crazy Horse Memorial and model. Figure 19. Mt. Rushmore National Memorial.

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229 133.8 1.5 Traffic light; main entrance to Mt. Rushmo re national Memorial, continue straight. Mount Rushmore National Memorial is carved into the Harney Peak Granite that intruded older Pre cambrian schist about 1.7 billion years ago. Sixty-foot -high heads of four preside nts, representing the first 150 years of the Nations history, are carved in bold relief: George Washingt on, Thomas Jefferson, Abra ham Lincoln and Theodore Roosevelt. The sculptor, Gutzon Borglum, selected Mt. Rushmore because of the consistency of the granite, dominating height, and th e southern exposure. Work began in 1927, funded by the Federal government, and completed 14 years later. 134.2 0.4 Nice view of Mt. Rushmore in your rearview mirror. 135.3 1.1 Junction with US 16A. Continue straight on US 16A towards Keystone. 135.7 0.4 Keystone. 138.7 3.0 Bear right on US 16 towards Rapid City. 143.7 5.0 Rockerville, a town straddle d by the four-lane highway. 145.7 2.0 Entering Touristville. 147.1 3.4 Minnelusa on left. 148.2 1.1 Minnekahta Limestone atop Opeche red shales. 148.4 0.2 Undulating Minnekahta Limestone. 148.9 0.5 Crossing the Red Valley in the Spearfi sh Formation. Note gypsum ledges. 150.2 1.3 Sandstones in the Sundance formation cap hill on left. 150.8 0.6 Flat uplands on top of the Dakota hogback underlain by sandstones of the Inyan Kara Group. Great Plains in distance to the right and mountains with Preca mbrian rocks to left. 153.8 3.0 Entering Rapid City while descending thr ough the sandstones of the Inyan Kara Group. 155.6 1.8 Omaha Street, turn right. 156.9 1.3 Fifth Street, turn left. 157.1 0.2 Turn left on New York Street and immediat e right into Holiday Inn Parking lot. End of trip References Agenbroad, L.D., 1994, Geol ogy, Hydrology, and Exca vation of the Site, in Agenbroad, L.D. and Mead, J.I., eds, The Hot Springs mammoth Site: A Decade of Field and Laboratory Research in Paleontology, Geol ogy, and Paleoecology, Fenske Printing, Rapid City, S.D., p. 15-27. Back, W., Hanshaw, B. B., Plummer, L. N., Rahn, P. H., Rightmire, C. T., and Rubin, M., 1983, Process and rate of dedolomitization: Mass transfer and 14C dating in a regional carbonate aquifer: Geological Society of America Bulletin, v. 94, p. 1415-1429. Bowles, C.G., and Braddock, W.A., 1963, Solution brec cia of the Minnelusa Format ion in the Black Hills, South Dakota and Wyoming, in Short papers in geol ogy and hydrology: U.S. Geological Survey Profes sional Paper 475-C, p. C91-C95.

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230 Braddock, W.A., 1963, Geology of the Jewel Cave SW Quadrangle, Custer County, South Dakota: U.S. Geo logical Survey Bulletin 1063-G, p. 217-268 Brobst, D.A., and Epstein, J.B., 1963, Geology of the Fanny Peak quadrangle, Wyoming-South Dakota: U.S. Geological Survey Bulletin 1063-I, p. 323-377. Carter, J.M., Drisco ll, D.G., Hamade, G.R., and Jarrell, G. J., 2001, Hydrologic budgets for the Madison and Minnelusa aquifers, Black Hills of South Dakota and Wyoming, water years 1987-96: US. Geological Survey Water-Resources Investigations Report 01-4119, 53 p. Conn, Herb, 1966, Barometric Wind in Wind and Jewel Caves, South Dakota: The National Speleological Society Bulletin, v. 28, p. 55-69. Daniels, Noah, 2000, Using Barometric Winds to Deter mine the Volume of Wind Cave, South Dakota: Inside Earth, a Newsletter of the NPS Cave & Karst Pro grams, v. 4, p. 9-11. Darton, N. H., 1909, Geology and water resources of the northern portion of the Black Hills and adjoining regions in South Dakota and Wyoming: U.S. Geol. Survey Prof. Paper 65, p. 105. Epstein, J.B., 1958, Geology of part of the Fanny peak quadrangle, Wyoming-South Dakota: M.A. thesis, University of Wyoming and U.S. Geological Survey Open-File Report 454, 90 p. Epstein, J.B., 2001: Hydrology, Hazards, and Geomor phic Development of Gypsum Karst in the Northern Black Hills, South Dakota and Wyoming: in Kunian sky, E.L., editor, U.S. Geological Survey Karst Interest Group Proceedings, St. Peters burg, Florida, February 13-16, 2001: U.S. Geological Survey Water-Resources Investigations Report 01-4011, p. 30-37. Epstein, J.B., 2003, Gypsum karst in the Black Hills, South Dakota-Wyoming: in Evaporite karst and engi neering/environmental proble ms in the United States, Johnson, K.S., and Neal, J.T., eds, Oklahoma Geologi cal Survey, Report: 109, p.241-254. Epstein, J.B., a, 2005, Field Trip 3, Karst Field Trip to the Western Black Hills: in Kuniansky, E.L., editor, U.S. Geological Survey, Karst In terest Group Proceedings, Rapid City, South Dakota, September 12-15, 2005: U.S. Geological Survey Scientifc Investigations Report 2005-5160, this volume. Epstein, J.B., b, 2005, National Evaporite Karstsome western examples: in Kuniansky, E.L., editor, U.S. Geological Survey, Karst In terest Group Proceedings, Rapid City, South Dakota, September 12-15, 2005: U.S. Geological Survey Scientifc Investigations Report 2005-5160, this volume. Epstein, J.B., Davis, A.D., Long, A.J., Putnam, L.D., and Sawyer, J.F., 2005, Field Trip Guide 2, Karst features of the Northern Black Hills, South Dakota, Karst Inter est Group workshop, September 15, 2005, in Kunian sky, E.L., editor, U.S. Geol ogical Survey, Karst Inter est Group Proceedings, Ra pid City, South Dakota, September 12-15, 2005: U.S. Geological Survey Sci entifc Investigations Report 2005-5160, this volume. Epstein, J.B. and Johnson, K.S., 2003, The need for a national evaporite-karst map, in Johnson, K.S., and Neal, J.T., eds., Evaporite karst engineering/environ mental problems in the Un ited States: Oklahoma Geo logical Survey Circular 109, p. 21-30. Gries, J.P., 1963, Sinkholes in the Minnekahta Formation, Black Hills: Proceedings of the South Dakota Acad emy of Science, v. 42, p. 76-78. Gary, Margaret, McCafee, Robert, Jr., and Wolf, C.L, 1972, Glossary of Geology: American Geological Institute, with a forward by Ian Campbell, 858 p. Hayes, Timothy S., 1996, Suspended-sediment 'redden ing;' in Cascade Springs, southern Black Hills, South Dakota: Geological Society of America, Abstract with Programs, Rocky Mountain Section, 48th Annual Meeting, v. 2, no. 4, p. 11, April 18-19, 1996, Rapid City, South Dakota. Hayes, T.S., 1999, Episodic sediment-discharge events in Cascade Springs, southern Black Hills, South Dakota: U.S. Geological Survey Water Resources Investiga tions Report 99-4168, 34 p. Horrocks, R.D., and Szukalski, B.W., 2002, Developing a Cave Potential Map for Wind Cave, Wind Cave National Park: National Spel eological Society Journal of Cave and Karst Studies, volume 64, p. 63-70. Jablonsky, Pat, 1994, Final Report, Develop Preventive Measures for Future Accumulations of Cave Lint: Denver Museum of Natural History, Unpublished Report, Physical Science f iles, Wind Cave National Park, 74 p. Jarrell, G.J., 2000, Digital map of generalized thickness of the Minnelusa Formation, Black Hills, South

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231 Dakota: U.S. Geological Su rvey data available on the World Wide Web, accessed July 2, 2001, at URL http:/ /water.usgs.gov/lookup !getspatial?sdJIUlls_thk Laury, R.L., 1980, Paleoenvir onment of a late Quaternary mammoth-bearing sinkhole deposit, Hot Springs, South Dakota: Geological So ciety of America Bulletin, v. 91, p. 465-475. Laury, R.L., 1994, Paleoenvironment of the Hot Springs Mammoth Site, in Agenbroad, L.D. a nd Mead, J.I., eds, The Hot Springs mammoth Site: A Decade of Field and Laboratory Research in Paleontology, Geology, and Paleoecology, Fenske Printing, Rapid City, SD, p. 28-67. Martin, J.E., Bell, G.L., Jr., Schumacher, B.A., and Fos ter, J.F., 1996, Geology and Paleontology of Late Cre taceous Deposits of the Southern Black Hills region: Road Log, Field trip 8, in Paterson, C.J. and Kirchner, J.G., eds., Guidebook to the Geology of the Black Hills, South Dakota: South Dakota School of Mines and technology, Bulletin No. 19, p. 51-77. McDonald, Alvin, 1891. Personal Diary, 1891-1893. Unpublished diary, Wind Cave National Park files. p. 133 Naus, C.A., Driscoll, D.G., and Carter, J.M., 2001, Geochemistry of the Madison and Minnelusa aquifers in the Black Hills area, South Dakota: U.S. Geological Survey Water-Resources Investigations Report 01-4129, 118 p. Nepstad, J.A. 1986: Wind Cave Climate Study: Unpub lished Report, Physical Sc ience files, Wind Cave National Park, 5 p. Palmer, Art, and Palmer, Peggy, 2000, Speleogenesis of the Black Hills Maze Caves, South Dakota, U.S.A.: Speleogenesis, Evolution of Karst Aquifers, National Speleological Society, p. 274-181. Pflitsch, Andreas, 2002, Cave Climatology Investigation in the Wind Cave of South Dakota: Unpublished Report, Physical Science files, Wind Cave National Park. 19 p. Post, E.V., 1967, Geology of the Cascade Springs Quad rangle, Fall River County, South Dakota: U.S. Geolog ical Survey Bulletin 1063-L, p. 443-504. U.S. Geological Survey, 1949 -75, Water resources data for South Dakota, 1949-74part 1. Surface-water records (published annually). U.S. Geological Survey, 1976-2005, Water resources data for South Dakota, water years 1975-2004: US. Geological Survey Water-D ata Reports SD-75-1 to SD-04-1 (published annually).



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U.S. Geological Survey Karst Interest Group Proceedings, Rapid City, South Dakota September 12-15, 2005 Scientific Investigations Report 2005-5160 U.S. Department of the Interior U.S. Geological Survey U.S. Army Environmental Center

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U.S. Geological Survey Karst Interest Group Proceedings, Rapid City, South Dakota September 12-15, 2005 Edited by Eve L. Kuniansky Prepared in cooperati on with U.S. Army Environmental CenterScientific Investigations Report 2005-5160 U.S. Department of the Interior U.S. Geological Survey

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U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey Charles G. Groat, directorU.S. Geological Survey, Reston, Virginia: 2005 For sale by U.S. Geological Survey, Information Services Box 25286, Denver Federal Center Denver, CO 80225 For more information about the USGS and its products: Telephone: 1-888-ASK-USGS World Wide Web: http://www.usgs.gov/ Any use of trade, product, or firm names in this public ation is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained with this report. Suggested citation: Kuniansky, E.L., 2005, U.S. Geological Survey Karst In terest Group proceedings, Rapid City, South Dakota, September 12-15, 2005: U.S. Geological Survey Scientific Investigations Report 2005-5160, 296 p.

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iii Contents Introduction and Acknowledgments............................................................................................... ............................1 Agenda, U.S. Geological Survey Karst Interest Group Work shop............ .............. .............. .............. ............. ..........3 National Programs Establishing the National Cave and Karst Research In stitute as a Robust Resear ch and Education Center, by Louise D. Hose.............................................................................................................. ...................................9 Geophysical Methods for Karst Studies The State of the Art of Geophysics and Karst: A General Li terature Review, by D.V. Sm ith................. ...............10 Review of Airborne Electromagnetic Geophysical Surveys over Karst Terrai ns, by Bruce D. Smith, Jeffrey T. Gamey, and Greg Hodges.............................................................................................. .....................17 Overview of Karst Effects and Karst Detection in Seismic Data from the Oak Ridge Reservation, Tennessee, by W.E. Doll, B.J. Carr, and J.R. Sheehan, and W.A. Mandell ................................................................... ......20 Application of Seismic Refraction Tomography to Karst Cavities, by Jacob R. Sheehan, and William E. Doll, David B. Watson, and Wayne A. Mande ll .............. .............. .............. .............. ............ ...29 Borehole Geophysical Techniques to Determine Groundwat er Flow in the Freshwater/Saline-Water Transition of the Edwards Aquifer, South Central Texas, by R.B. Lambert, A.G. Hunt, and G.P. Stanton, and John Waugh................................................................................................................. .................................39 An Evaluation of Methods Used to Measure Horizontal Borehole Flow, by Wayne A. Mandell, James R. Ursic, William H. Pedler, Jeffrey J. Jantos, E. Randall Bayless, and Kirk G. Thideaux....................40 The Edwards Aquifer, Texas Characterization of Hydrostr atigraphic Units of the Capture, Rechar ge, and Confining Zones of the Edwards Aquifer using Electrical and Natural Gamma Signatures, Medina, Uvalde, And Bexar Counties, Texas, by Bruce D. Smith, Allan K. Clark, Jason R. Faith, and Gregory P. Stanton............... ......................................4 1 Use of Helium Isotopes to Discriminate Between Flow Path s Associated with the Freshw ater/Saline Water Transition Zone of the Edwards Aquifer, South Central Te xas, by Andrew G. Hunt, Rebecca B. Lambert, Gary P. Landis, and John Waugh ................................................................................................ .......................42 Airborne and Ground Electrical Surveys of the Edwards and Trinity aquifers, Medina, Uvalde, and Bexar Counties, Texas, by Bruce D. Smith, David V. Smith, Jeffrey G. Paine, and Jared D. Abraham.....43 Magnetic Geophysical Applications Reveal Igneous Rocks and Geologic Structures in the Edwards Aquifer, Texas, by D.V. Smith, C. Foss and B.D. Smith.......................................................... 44 Structural Controls on Karst Development in Fractured Carbonate Rock, Edwards and Trinity Aquifers, South-Central Texas, by Jason R. Faith, Charles D. Blome, Allan K. Clar k, George B. Ozuna, and Bruce D. Smith............................................................................................................. ................................45

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iv Numerical Modeling of Karst Systems Simulating Ground-Water Flow in the Karstic Madison Aquifer using a Porous Media Model, by L.D. Putnam and A.J. Long................................................................................................... .........................46 Dual Conductivity Module (DCM), A MODFLOW Package for Modeling Flow in Karst Aquifers, by Scott L. Painter, Ronald T. Green, and Alexander Y. Sun..................................................................... ........47 Conceptualization and Simulation of the Edwards Aquifer, San Antonio Region, Texas, by R.J. Lindgren, A.R. Dutton, S.D. Hovorka, S.R.H. Wort hington, and Scott Painter.....................................48 The role of MODFLOW in numerical modeling of kars t flow systems, by J. J. Quinn, David Tomasko, and J.A. Kuiper................................................................................................................ ....................................58 Springs and the Use of Geochemistry in Karst Studies The Case of the Underground Passage: Putting the Clues Together to Understand Karst Processes, by B. Mahler, B. Garnier, and N. Massei........................................................................................ ....................63 Spatial and Temporal Variations in Epikarst Storage and Flow in South Central Kentuckys Pennyroyal Plateau Sinkhole Plain, by Chris Groves, Carl Bolster, and Joe Meiman.... .............. .............. .......64 Comparison of Water Chemistry in Spring and Well Samples fr om Selected Carbonate Aquifers in the United States, by Marian P. Berndt, Brian G. Katz, Bruce D. Lindsey, A nn F. Ardis, and Kenneth A. Skach.........................74 Interpretation of Water Chemistry and Stable Isotope Da ta from a Karst Aquifer According to Flow Regimes Identified through Hy drograph Recession Analysis, by D.H. Doctor and E.C. Alexander, Jr ............... ............82 Hydrogeologic Mapping and Tracer Techniques in Karst Areas An Appalachian Regional Karst Map an d Progress Towards a New National Kars t Map, by D.J. Weary....... .......93 Hydrogeologic Framework Mapping of Shallow, Co nduit-Dominated KarstComponents of a Regional GIS-Based Approach, by Charles J. Tayl or, Hugh L. Nelson Jr., Gregg Hile man, and William P. Kaiser.....103 Application of Multiple Tracer s to Characterize Sediment and Pathogen Transport in Karst, by Tiong Ee Ting, Ralph K. Davis, J.V. Brahana, P.D. Hays, and Greg Thoma........................................................................ ....114 Estimating Ground-Water Age Distributions from CFC and Tritium Data in the Madison Aquifer, Black Hills, South Dakota, by Andrew J. Long and Larry D. Putnam.............. .............. .............. ............ .......11 5 A Multi-Tracer Approach for Evaluatin g the Transport of Whirling Disease to Mammoth Creek Fish Hatchery Springs, Southwestern Utah, by Larry E. Spangler, Meiping Tong, and Willia m Johnson..............................116 Black Hills and Evaporite Karst National Evaporite KarstSome Western Examples, by Jack B. Epstein............................................................. 122 Gypsum and Carbonate Karst Along the I-90 Development Corridor, Black Hills, South Dakota, by Larry D. Stetler and Arden D. Davis......................................................................................... ...................134 Karst Features as Animal Traps: Approximately 500,000 Years Of Pleistocene And Holocene Fauna and Paleoenvironmental Data in the Northern High Plains, by Larry D. Agenbroad and Kristine M. Thompson....................................................................................................... .........................135 Developing a Cave Potential Map of Wind Cave to Guide Exploration Efforts, by Rodney D. Horrocks............141 The Potential Extent of the Jewel Cave System, by Mich ael E. Wiles............................................................. ......142

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v Karst Studies in Arkansas and the Ozarks Geologic Controls on a Transition Between Karst Aquife rs at Buffalo National River, Northern Arkansas, by Mark R. Hudson, David N. Mott, and Kenzie J. Turner and Kyle E. Murray............................................143 Quantification of Hydrologic Budget Parameters for the Vadose Zone and Epikarst in Mantled Karst, by J.V. Brahana, Tiong Ee Ting, Mohammed Al-Qinna, John F. Murdoch, Ralph K. Davis, Jozef Laincz, Jonathan J. Killingbeck, Eva Szilvagy i, Margaret Doheny-Skubi c, Indrajeet Chaubey, P.D. Hays, and Gregg Thoma..................................................................................................... .......................144 Characterization of Nutrient Processing at the Field and Basin Scale in the Mantled Karst of the Savoy Experimental Watershed, Arkansas, by Jozef Lain cz, .P.D. Hays, Sue Ziegler, Byron Winston, J.V. Brahana, Ken Steele, Indrajeet Chaubey, and Ralph K. Davis............................................................... ..153 Water Supply and Land Use Issues in Karst Areas Transport Potential of Cryptosporidium parvum Oocysts in a Drinking-Water Karstic-Limestone Aquifer: What We Have Learned Using Oocyst -Sized Microspheres in a 100-m Convergent Tracer Test at Miami's Northwest Well Field, by Ronald W. Harvey, Allen M. Shapiro, Robert A. Renken, David W. Metge, Joseph N. Ryan, Christina L. Osborn, and Kevin J. Cunn ingham................................................................... .154 Ground-Water Quality Near a Swine Waste Lagoon in a Mantled Karst Terrane in Northwestern Arkansas, by Christopher M. Hobza, David C. Moffit, Dan ny P. Goodwin, Timothy Kresse, John Fazio, John V. Brahana, and Phillip D. Ha ys................ .............. .............. ............... ........... ........... .......... ....................155 Vulnerability (Risk) Mapping of the Madison Aquifer near Rapid City, South Dakota, by Scott L. Miller, Arden D. Davis, and Alvis L. Lisenbee.......................................................................................... ..................163 Hydrogeologic Characteristi cs of Four Public Drinking-Water S upply Springs in the Ozark Plateaus of Northern Arkansas, by Joel M. Galloway...................................................................................... ...............164 Adaptation of the Residence Time Distribution (RTD)-Biodegradation Model to Quantify Peroxide-Enhanced Fuel Biodegradation in a Single Karst Well, by Lashun K. King, Roger D. Painter, and T.D. Byl.................174 Free-Living Bacteria or Attached Bacteria: Which Co ntributes More to Bioremediation? by Roger D. Painter, Shawkat Kochary, and T.D. Byl.................................................................................................. ......................180 Desorption Isotherms for Toluene and Karstic Materials and Implications for Transport in Karst Aquifers, by Mario Beddingfield, Khalid Ahmed, Roger Painter, and T.D. Byl..............................................................1 88 A Computer Program that Uses Re sidence-Time Distribution and First-Order Biodegradation to Predict BTEX Fate in Karst Aquifers, by Ryan Fitzwater, Roger Painter, Valetta Watson, and T.D. Byl...................189 Lactate Induction of Ammonia-Ox idizing Bacteria and PCE Cometabolism, by LyTreese Hampton, Roneisha Graham, and T.D. Byl.................................................................................................. .....................190 Biodegradation of Toluene as It Continuously Enters a 5-Liter Laboratory Karst System, by Fuzail Faridi, Roger Painter, and T.D. Byl.................................................................................................... ..........................191 Bacteria Induced Dissolution of Limestone in Fuel-Contaminated Karst Wells, by Serge Mondesir and T. D. Byl.................................................................................................................. ...................................192

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vi Field Trip Guides Introduction to Three Field Trip Guides: Karst Features in the Black Hills, Wyoming and South DakotaPrepared for the Karst Interest Group Work shop, September 2005, by Jack B. Epstein and Larry D. Putnam............................................................................................................ .............................193 Field Trip Guide 1 Karst Features of the Southern Black Hills, South Dakota, Karst Interest Group Workshop, September 12 2005, by Jack B. Epstein, Larry Agenbroad, Mark Fahrenbach, Rodney D. Horrocks, Andrew J. Long, Larry D. Putnam, J. Foster Sawyer, and Kristine M. Thompson.........................199 Field Trip Guide 2 Karst Features of the Northern Black Hills, South Dakota and Wyoming, Karst Interest Group workshop, September 15, 2005, by Jack B. Epstein, Arden D. Davis, Andrew J. Long, Larry D. Putnam, and J.Foster Sawyer.................. ......................................................................... ...................232 Field Trip Guide 3 for a Self-Guided Tr ip to Karst Features of the Western Black Hills, Wyoming and South Dakota, Karst Interest Group Workshop, September 12-15, 2005, by Jack B. Epstein.................................................283

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1 INTRODUCTION AND ACKNOWLEDGMENTS Karst aquifer systems are present throughout parts of the United States and some of its territories. The complex depositional environments th at form carbonate rocks combined with post-depositional tectonic events and the diverse climatic regimes under which these rocks were formed, re sult in unique systems. The dissolution of calcium carbonate and the subsequent development of distinct and beautiful landscapes, caverns, and springs have resulted in some karst areas of the United States being designated as national or state parks and commercial caverns. Karst aquifers and landscapes that fo rm in tropical areas, such as the north coast of Puerto Rico differ greatly from karst ar eas in more arid climates, such as central Texas or South Dakota. Many of these public and private lands contain unique flora and fauna associated with the karstic hydrologic systems. Thus, multiple Federal, state, and local agencies have an interest in the study of karst areas. Carbonate sediments and rocks are composed of greater than 50 percent carbonate (CO 3 ) and the predominant carbonate mineral is calcium carbonate or limestone (CaCO 3 ).Unlike terrigenous clastic sedimentation, the depositional pr ocesses that produce carbonate rock s are complex, involving both biological and physical processe s. These depositional processes impa ct greatly the development of permeability of the sediments. Ca rbonate minerals readily dissolve and precipitate depending on the chemistry of the water flowing throug h the rock, thus the study of both marine and meteoric diagenesis of carbonate sediments is multidisciplinary. Even with a better understanding of the depositional environment and the subseque nt diagenesis, the dual porosity nature of karst aquifers presents challenges to scientists attempting to study ground-water flow an d contaminant transport. Many of the major springs and aquifers in the Unite d States develop in carbonate rocks and karst areas. These aquifers and spring s serve as major water-supply sources and as unique biological habitats. Commonly, there is competition for th e water resources of karst aquifers and urban development in karst areas can impact the ecosystem and water quality of these aquifers. The concept for developing a Karst Interest Group evolved from the November 1999, National Ground-Water Meeting of the U.S. Geological Survey Water Resources Division. As a result, the Karst Interest Group was formed in 2000 The Karst Interest Group is a lo ose-knit grass-roots organization of U.S. Geological Survey employees devoted to fost ering better communication among scientis ts working on, or interested in, karst hydrology studies. The mission of the Karst Interest Group is to enc ourage and support interdisciplinary collaboration and technology transfer among U.S. Geological Survey scientists working in kars t areas. Additionally, the Karst Interest Group encourages cooperative studie s between the different disciplines of the U.S. Geological Survey and other Department of Interior agencies, and university researchers or research institutes. The first Karst Interest Group Worksh op was held in St. Petersburg, Florida, February, 13-16, 2001, in the vicinity of karst features of the Floridan aquifer. The proceeding of that first meeting, WaterResources Investigations Report 01-4011 is available online at: http://water.usgs.gov/ogw/karst/index.htm The U.S. Geological Survey, Office of Ground Water, provides support for the Karst Interest Group website. The second Karst Interest Group workshop was held August 20-22, 2002 in Shepherdstown, West Virginia, in close proximity to the carbonate aquifers of the northern Shenandoah Valley. The proceedings

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2 of the second workshop were published in Water-Res ources Investigations Report 02-4174, which is available online at the prev iously mentioned website. The third workshop of the Karst In terest Group was held September 12-15, 2005 in Rapid City, South Dakota, which is in close proximity to karst features in the semi-arid Black Hills of South Dakota and Wyoming, Wind Cave National Park and Jewell Ca ve National Monument, and the Madison Limestone aquifer. Financial support of the third workshop was obtained from Wayne A. Mandell, U.S. Army Environmental Center; Louise Hose, National Cave and Karst Research Institute; Thomas J. Casadevall, Regional Director, Central Region, U.S. Geological Survey; and Kevin F. Dennehy, Ground-Water Resources Program Coordinator, U.S. Geological Survey. Numerous individuals contributed to the workshop and proceedings, and especially to the development of the field trips to karst features of the Black Hills in South Dakota and Wyomin g. Three field trips were offered at this workshop, none of which were duplicativ e, as evidenced in the thre e field trip guides. Trips to the southern and northern karst features of the Bl ack Hills were scheduled fo r Monday and Thursday and the third field trip to the western part of the Blac k Hills was designed to be accomplished on your own using the field trip guide. These field trips allow atte ndees of all the previous workshops to compare karst in the more humid eastern United States to karst in the semi-arid central United States. Geologist Emeritus, USGS, Jack Epstein agreed to help lead the planning and development of the field trips and field trip guides. The members of the Field Trip Comm ittee are: David Weary, Andrew Long, and Larry Putnam, USGS; Rod Horrocks and Mike Wiles, Nationa l Park Service; Arden Davis and Scott Miller, South Dakota SMT; Larry Agenbroad and Kristine Thom as, Mammoth Site; Mark Fahrenbach and Foster Sawyer, South Dakota Department of Environmental and Natural Resources; and Bob Paulson, The Nature Conservancy. Larry Putnam also helped with logistical support fo r the field trips and the meeting. Additionally, Linda Stool and Todd Suess, Superintendents of Wind and Jewel Cave National Parks, respectively, have given permission for two guided evening trips for 25 people at their Parks. Rod Horrocks and Mike Wiles, Cave Specia lists at Wind and Jewel Cave Natio nal Parks, respectively, will lead each evening trip. The session planning committee for this third wo rkshop included: Louise Hose, National Cave and Karst Research Institute; and Alan Bu rns, Kevin Dennehy, Perry Jones, Brian Katz, Eve Kuniansky, Randy Orndorff, Bruce Smith, Larry Spangler, Greg Stanton, and Chuck Taylor, U.S. Geological Survey, and Jack Epstein, Geologist Emeritus, U.S. Geological Survey. We sincerely hope that this workshop promotes future collaboration among scientists of va ried backgrounds and improves of our understanding of karst systems in the Unite d States and its territories. The extended abstracts of U.S. Ge ological Survey authors were revi ewed and approved for publication by the U.S. Geological Survey. Articles submitted by university researchers and other Department of Interior agencies did not go through the U.S. Geolog ical Survey review process, and therefore may not adhere to our editorial standards or stratigraphic nomenclature. All ar ticles were edited for consistency of appearance in the publishe d proceedings. The use of trade nam es in any article does not constitute endorsement by the U.S. Government. The cover illustration was designed by Ann Tiha nsky, U.S. Geological Survey, St. Petersburg, Florida, for the first Karst Interest Group Workshop. Eve L. Kuniansky Karst Interest Group Coordinator

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3 AGENDA U.S. GEOLOGICAL SURVEY KARTS INTEREST GROUP WORKSHOP September 12-15, 2005 Rapid City South Dakota Rushmore Plaza Civic Center 444 Mt. Rushmore Road Rapid City, South Dakota 57701 Monday, September 12 TimeTitle 8:00 5:00Field Trip 1 Karst Features of the Southern Black Hills NOTE: BUS LEAVES FROM THE HOLIDAY INN PARKING LOT ADJACENT TO THE RUSHMORE PLAZA CIVIC CENTER -505 North Fifth Street, Rapid City, SD. Tuesday, September 13 Registration All day pick up name tags and proceedings Welcome 8:30 8: 40Welcome-Eve Kuniansky, U.S. Geological Survey, Karst Interest Group Coordinator Geophysical Methods for Karst Studies 8:40 9:00The State of the Art of Geophysics and Karst: A General Literature ReviewDavid V. Smith, U.S. Geological Survey 9:00 9:20Review of Airborne Electromagnetic Geophysical Surveys over Karst Terrains Bruce D. Smith, U.S. Geological Survey, Je ffrey T. Gamey, Batelle, and Greg Hodges, Fugro Airborne 9:20 9:40Overview of Karst Effects and Karst Detection in Seismic Data from the Oak Ridge Reservation, TennesseeWilliam E. Doll, Batte lle, Bradley J. Carr, Geophex, and Jacob R. Sheehan, Battelle, and Wayne A. Mandell, U.S. Army Environmental Center 9:40 10:00Application of Seismic Refraction Tomography to Karst CavitiesJacob R. Sheehan and William E. Doll, Battelle, David B. Wa tson, Environmental Sciences Division, Oak Ridge National Laboratory, and Wayne A. Mandell, U.S. Army Environmental Center 10:00 10:40BREAK 10:40 11:00Borehole Geophysical Techniques to Determine Groundwater Flow in the Freshwater/Saline-Water Rransition of the Edwards Aquifer, South Central Texas Rebecca B. Lambert, Andrew G Hunt, and Gregory P. Stanton, U.S. Geological Survey, and John Waugh, San Antonio Water System The Edwards Aquifer, Texas 11:00 11:20Characterization of Hydrostratigraphic Units of the Capture, Recharge, and Confining Zones of the Edwards Aquifer using Electrical and Natural Gamma Signatures, Medina, Uvalde, and Bexar Counties, TexasBruce D. Smith, Allan K. Clark, Jason R. Faith, and Greg Stanton, U.S. Geological Survey

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4 11:20 11:40Use of Helium Isotopes to Discriminate Between Flow Paths Associated with the Freshwater/Saline Water Transition Zone of the Edwards Aquifer, South Central Texas Andrew G. Hunt, Rebecca B. Lambert, and Gary P. Landis, U.S. Geological Survey, and John Waugh, San Antonio Water System 11:40 1:20 LUNCH At the Civic Center, Luncheon Speakers, Tom Casadevall, Central Regional Director, U.S. Geological Survey, plus update from Louise Hose, Director of the National Cave and Karst Research Institute, Establishing the National Cave and Karst Research Institute as a Robust Research and Education Center Numerical Modeling of Karst Systems 1:20 1:40Simulating Ground-Water Flow in the Ka rstic Madison Aquifer using a Porous Media ModelLarry Putnam and Andy Long, U.S. Geological Survey 1:40 2:00Dual Conductivity Module ( DCM), A MODFLOW Package for Modeling Flow in Karst AquifersScott L. Painter, Ronald T. Green, and Alexander Y. Sun, Southwest Research Institute 2:00 2:40Conceptualization and Simulation of the Edwards Aquifer, San Antonio Region, Texas Richard J. Lindgren, U.S. Geological Survey, Alan R. Dutton, University of Texas, Susan D. Hovorka, Bureau of Economic Ge ology, S.R.H. Worthington, Worthington Groundwater, and Scott L. Painter, Southwest Research Institute 2:40 3:20BREAK Springs and the Use of Geochemistry in Karst Studies 3:20 3:40The Case of the Underground Passage: Putting the Clues Together to Understand Karst ProcessesBarbara Mahler, U.S. Geological Survey, B. Garner, and N. Massei, Dpartement de Gologie, Universit de Rouen, 3:40 4:00Spatial and Temporal Variations in Epikarst Storage and Flow in South Central Kentuckys Pennyroyal Plateau Sinkhole PlainChris Groves, Western Kentucky University, Carl Bolster, U. S. Department of Agriculture, and Joe Meiman, National Park Service 4:00 4:20Comparison of Water Chemistry in Spring and Well Samples from Selected Carbonate Aquifers in the United StatesMarian P. Berndt, Brian G. Katz, Bruce D. Lindsey, Ann F. Ardis, and Kenneth A. Skach, U.S. Geological Survey 4:20 4:40Interpretation of Water Chemistry a nd Stable Isotope Data from a Karst Aquifer According to Flow Regimes Identified through Hydrograph Recession Analysis Daniel H. Doctor, U.S. Geological Survey and E. Calvin Alexander, Jr., University of Minnesota 4:40 6:40 POSTER SESSION

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5 Wednesday, September 14 TimeTitle Hydrogeologic Mapping and Tracer Techniques in Karst Areas 8:00 8:20An Appalachian Regional Karst Map and Progress Towards a New National Karst MapDavid J. Weary, U.S. Geological Survey 8:20 8:40Hydrogeologic Framework Mapping of Shallow, Conduit-Dominated Karst Components of a Regional GIS-Based Approach Charles J. Taylor, Hugh L. Nelson Jr., Gregg Hileman, and William P. Kaiser, U.S. Geological Survey 8:40 9:00Application of Multiple Tracers to Characterize Sediment and Pathogen Transport in KarstTiong Ee Ting, Ralph Davis, Van Br ahana, P.D. Hays, and Greg Thoma, University of Arkansas 9:00 9:20Estimating Ground-Water Age Distributions from CFC and Tritium Data in the Madison Aquifer, Black Hills, South DakotaAndrew Long and Larry Putnam, U.S. Geological Survey Black Hills and Evaporite Karst 9:20 9:40National Evaporite KarstSome Western ExamplesJack Epstein, U.S. Geological Survey, Geologist Emeritus 9:40 10:00Black Hills Evaporite Karst: A MultiTiered Dissolution FrontJack Epstein, U.S. Geological Survey, Geologist Emeritus 10:00 10:40BREAK 10:40 11:00Gypsum and Carbonate Karst Along the I-90 Development Corridor, Black Hills, South DakotaLarry D. Stetler and Arden D. Davis, Department of Geology and Geological Engineering, South Dakota School of Mines and Technology 11:00 11:20Karst Features as Animal Traps: Approximately 500,000 Years Of Pleistocene And Holocene Fauna and Paleoenvironmental Data in the Northern High PlainsLarry D. Agenbroad and Kristine M. Thompson, Mammoth Site of Hot Springs, South Dakota, Incorporated 11:20 11:40Developing a Cave Potential Map of Wind Cave to Guide Exploration EffortsRod Horrocks, National Park Service 11:40 12:00The Potential Extent of the Jewel Cave SystemMike Wiles, National Park Service 12:00 1:40LUNCH At the Civic Center, Luncheon Speaker, Larry AgenbroadMammoth Site Karst Studies in Ar kansas and the Ozarks 1:40 2:00Geologic Controls on a Transition Between Karst Aquifers at Buffalo National River, Northern ArkansasMark R. Hudson, U.S. Geological Survey, David N. Mott, National Park Service, and Kenzie J. Turner and Kyle E. Murray, University of Texas, San Antonio 2:00 2:20Quantification of Hydrologic Budget Parameters for the Vadose Zone and Epikarst in Mantled KarstVan Brahana, Tiong Ee Ting, Mohammed Al-Qinna, John Murdoch, Ralph Davis, Jozef Laincz, Jonathan J. Killi ngbeck, Eva Szilvagyi, Margaret Doheny-Skubic, and Indrajeet Chaubey, University of Arkans as, and P.D. Hays, U.S. Geological Survey

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6 2:20 2:40Characterization of Nutrient Processing at the Field and Basin Scale in the Mantled Karst of the Savoy Experimental Watershed, ArkansasJozef Laincz, Sue Ziegler, Byron Winston, Van Brahana, Ken Steele, Indrajeet Chaubey, and Ralph Davis, University of Arkansas, and Phil Hays, U.S. Geological Survey 2:40 3:00BREAK Water Supply and Land Use Issues in Karst Areas 3:00 3:20Transport Potential of Cryptosporidium parvum Oocysts in a Drinking-Water, KarsticLimestone Aquifer: What We Have Learned Using Oocyst-Sized Microspheres in a 100-m Convergent Tracer Test at Miami's Northwest Well FieldRonald W. Harvey, Allen M. Shapiro, Robert A. Renken, Davi d W. Metge, Joseph N. Ryan, Christina L. Osborn, and Kevin J. Cunningham, U.S. Geological Survey 3:20 3:40Ground-Water Quality Near a Swine Waste Lagoon in a Mantled Karst Terrane in Northwestern ArkansasChristopher Hobza and Phillip D. Hays, U.S. Geological Survey, David C. Moffit and Danny Goodwin, Natural Resources Conservation Service, and Van Brahana, University of Arkansas 3:40 4:00Vulnerability (Risk) Mapping of the Madison Aquifer near Rapid City, South Dakota Scott Miller, Arden D. Davis, and Alvis L. Lisenbee, South Dakota School of Mines and Technology, Department of Geology and Geological Engineering 4:00 4:20Hydrogeologic Assessment of Four Pub lic Drinking-Water Supply Springs in the Ozark Plateaus of Northern ArkansasJoel M. Galloway, U.S. Geological Survey 4:20 6:20 POSTER SESSION Thursday, September 15 8:00 5:00Field Trip 2 Karst Features of the Northern Black Hills NOTE: BUS LEAVES FROM THE HOLLIDAY INN PARKING LOT ADJACENT TO THE RUSHMORE PLAZA CIVIC CENTER 505 North Fifth Street, Rapid City, SD.

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7 Poster Session Titles A Multi-Tracer Approach for Evaluating the Transport of Whirling Disease to Mammoth Creek Fish Hatchery Springs, Southwestern Utah, by Larry Spangler, U.S. Geological Surv ey, Meiping Tong and William Johnson, University of Utah The role of MODFLOW in numerical modeling of karst flow systems, by John J. Quinn, David Tomasko, and James A. Kuiper, Argonne National Laboratory Structural Controls on Karst Development in Fractured Ca rbonate Rock, Edwards and Trinity Aquifers, South-Central Texas, by Jason R. Faith, Charles D. Blome, Allan K. Clark, and Bruce D. Smith, U.S. Geological Survey Structural and Stratigraphic 3-D Modeling of the Edwards Aqui fer, Medina County, Texas, Using helicopter EM Survey Data to Evaluate and Extrapolate Geologic Mapping and Drillhole Data, by Michael P. Pantea, James C. Cole, Bruce D. Smith, and Maria Deszcz-Pan, U.S. Geological Survey Airborne and Ground Electrical Surveys of the Edwards and Trinity aquifers, Medina, Uvalde, and Bexar Counties, Texas, by Bruce D. Smith, David V. Smith, Jeffrey G. Paine, and Jared D. Abraham, U.S. Geological Survey An Evaluation of Methods Used to Measure Horizontal Borehole Flow, by Wayne A. Mandell, U.S. Army Environmental Center, James R. Ursic, U.S. Environmenta l Protection Agency, William H. Pedler a nd Jeffrey J. Jantos (RAS, Inc., Golden, Colorado), and E. Randall Bayless and Kirk G. Thideaux, U.S. Geological Survey Magnetic Geophysical Applications Reveal Igneous Rocks and Geologic Structures in the Edwards Aquifer, Texas, by David V. Smith, U.S. Geological Survey, Clive Foss, Enco m Technology, Sydney, Australia and Bruce D. Smith, U.S. Geological Survey Desorption Isotherms for Toluene and Karstic Materials and Implications for Transport in Karst Aquifers, by Mario Beddingfield, Khalid Ahmed, and Roger Painter, Tennessee St ate University, and T.D. Byl, U.S. Geological Survey A Computer Program that Uses Residence-Time Distribution a nd First-Order Biodegradation to Predict BTEX Fate in Karst Aquifers, by Ryan Fitzwater, Roger Pa inter, and Valetta Watson, Tennessee St ate University, and T.D. Byl, U.S. Geological Survey Lactate Induction of Ammonia-Oxidizing Bacteria and PCE Cometabolism, by LyTreese Hampton and Roneisha Graham, Tennessee State University, and T. D. Byl, U.S. Geological Survey Biodegradation of Toluene as It Continuously Enters a 5-Lite r Laboratory Karst System, by Fuzail Faridi and Roger Painter, Tennessee State University, and T. D. Byl, U.S. Geological Survey Bacteria Induced Dissolution of Limestone in Fuel-Conta minated Karst Wells, by Serge Mondesir, Tennessee State University, and T. D. Byl, U.S. Geological Survey Adaptation of the Residence Time Distribution (RTD)-Biodegradation Model to Quantify Peroxide-Enhanced Fuel Biodegradation in a Single Karst Well, by Lashun K. King and R oger D. Painter, Tennessee State University, and T.D. Byl, U.S. Geological Survey Free-Living Bacteria or Attached Bacteria: Which Contributes More to Bioremediation?, by Roger D. Painter and Shawkat Kochary, Tennessee State University, a nd T.D. Byl, U.S. Geological Survey

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9 Establishing the National Cave an d Karst Research Institute as a Robust Research and Education Center By Louise D. Hose NCKRI-National Park Service, 1400 Commerce Dr., Carlsbad, NM 88220 LHose@nckri.org ABSTRACT The U.S. Congress directed the National Park Servic e (NPS) to establish the National Cave and Karst Research Institute (NCKRI) through legislation in 1998. Th e mandated purposes are to: (1) further the sci ence of speleology; (2) centralize and standardize spel eological information; (3) foster interdisciplinary cooperation in cave and karst research programs; (4) promote public education; (5) promote national and international cooperation in protectin g the environment for the benefit of cave and karst landforms; and (6) promote and develop environmentally sound and sustai nable resource management practices. To achieve this mission, an academic entity (now identified as New Mexico Instit ute of Mining and Technology) will administer NCKRI on a day-to-day basis while the NPS will retain ultimate responsibility and indirect control. An interim board of directors that incl udes representatives from a diverse collection of cave and karst programs nationwide is preparing Articles of Incorporation and Bylaws in conjunction with NPS and New Mexico Tech representatives to establish the National Cave and Ka rst Research Institute, Inc. The board and New Mexico Tech expect to formalize the 501.c.3 corporation and begin day-to-day operation of NCKRI by October 1, 2005. The City of Carlsbad has designed and will soon bu ild a 24,000 ft 2 headquarters building through a combination of state, federal, and local funding. They anticipate gr oundbreaking this fall and completion within two years. Another major effort for NCKRI in volves a Karst Digital Portal initiative in partnership with the University of New Mexico an d the University of South Florida. The conceived network portal will enhance information access and improved communication within the national and international karst com munity. The partnership will develop an on-line digita l portal housed at the thr ee institutions and provide free access to a variety of informatio n including journal articles, images, maps, datasets, bibliographies, and gray literature. The portal should en hance international awareness and accessibility to National Karst Map products, as well.

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10 The State of the Art of Geophysics an d Karst: A General Literature Review By D.V. Smith1 1 U.S. Geological Survey, Box 2504 6 MS964, Denver, CO 80225-0046 ABSTRACT To assess the state of the art of geophysi cs as applied to karst investigations, a general review of the literature over the period 2001-2005 was undertaken. Th is time frame witnessed rapid advances in instrumentation and data process ing for interpretation and visualizatio n of subsurface geology. Essentially, it has become possible to rapidly acquire, process and view high quality data in the field. GPS technology has been ad apted to most commercial geophysical instruments, allowing for high geolocation accuracy with unprecedented ease. To answer the question: What methods work best for karst investigations and under what conditions?, this review re lied mainly on the GeoRef database for abstracts. GeoRef is an on-line indexing service maintained by th e American Geological Ins titute. It is the most com prehensive database in the geosciences, with references to journal articles, society proceedings, books, theses, and gov ernment reports. Keyword searches were completed for a comprehensive list of geophysical methods, ranging from conventional to exotic. As a general review of a wide variety of methods, no attempt is made to explain the theory of operation beyond fundamental principles. INTRODUCTION Geophysical surveys have been performed for decades to characterize karst, sometimes with success, but often with mixed results. Thei r applicability to karst was summarized in past reviews (Greenfield, 1979, Dobecki, 1990). Now, due to advances in computerization, minia turization, and data processing, combined with global position system (GPS) geol ocation technology, it has become possible to conduct investigations with unprece dented speed and accuracy. Wi th the recognition that no one technique can solve the problem at hand, whether geotechnical, geohydrological, or environmental, more emphasis is being placed on in tegrated surveys, in which two or more complementary methods are combined to constrain an interpretation. Ex amples abound, particularly seismic refraction combined with earth resistivity imag ing (Sumanovac and Weisser, 2001), and different electri cal methods (Tarhule and others, 2003). The success of the recent advances in geophysical methods is reflected not only in a growing geot echnical consulting industry, but also in the many studies and case histories presented by researchers, as the new hardware and software tools become available. For simplicity, the methods are separated into sur face, borehole, and airborne categories, since these strongly distinguish the vari ous tools that are available. SURFACE METHODS Surface methods predominate in karst investigations, both because of available, the logistical ease of deploy ment, and the relatively low co st compared to airborne and borehole methods. Some attempts have been made to standardize the selection of di fferent methods for specific problems (ASTM, 1999), but by and large the ones selected for use on any given assignment are based on time and cost. Surface methods fall into three broad cate gories: 1) electromagnetic, involving time-varying mag netic and electric fields across the spectrum, from DC (the static limit) to high frequenci es, 2) seismic, based on the propagation of acoustic waves in earth media, and 3) potential field, including gr avity and magnetics, for which the physics of potential field theory apply. Electromagnetic This category embraces the greatest variety of tech niques, which cover the elec tromagnetic spectrum from DC (0 Hz) to UHF (100 MHz). Sources and detectors operate in electric and/or magnetic field mode in various

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11 combinations and geometrical arrangements. The theory underpinning their operation, based upon Maxwells equations, is ma ture and highly devel oped. Recent years have seen significant advances in instrumentation and data processing capabilities. Multielectrode resistivity (referred to variously as electrical resistivity imaging (ERI) and electrical resistivity tomography (ERT)) is increasingly used because modern, automated multi-electrode control units simplify the acquisition of high quality data. Case histories are numerous, and excellent examples are readily available (Roth and others, 2002; Van Schoor, 2002). The topic of which array configura tion is optimal for given s ite conditions has received attention (Zhou and others, 2002). Robust algo rithms for generating ps eudo-sections and inver sions (resistivity profiles) are commercially available. While these instruments can acquire 3D data over a 2D spatial arrangement of electrodes, no true 3D inversions capab ility exists yet. Standard practice is to arrange 2D profiles in fence diagrams in order to visualize the 3D distribution of apparent resistivities. As a result, ambiguities are still intro duced by lateral inhomogeneities. Ground penetrating radar (GPR) finds wide application in karst inves tigations, particularly in settings like Florida wher e the limestones are hori zontally stratified and the soils and overburden do not severely attenuate the signals. Interpretation is subjective and prone to error because of complex scattering phenomena and reflections from off-line (transverse) inhomogeneities, often referred to as 3D effects. Commercial GPR units are continually improved, and GPR research and applications are practiced worldwide (Baradello and Yabar, 2002). Case histories and developments are regularly reported in annual intern ational conferences devoted to this method. Frequency-domain electromagnetic (EM) sur veys Time-domain electromagnetic (TEM) surveys for voids have been found to be more effective and cheaper than seismic in places (Xue and others, 2004). Software packages for interpreting both EM and TEM data. The very-low frequency (VLF) method has been used for decades for locating ground water aquifers. A recent paper (Bosch and Mueller, 2001) describes a possible new approach for mapping karst. Self potential (SP), also known as natural potential and streaming pote ntial, continues to be used to distinguish active sinkholes from filled depressions (Adams and others, 2002; Vichabian and Morgan, 2002). Anomal ous voltages are present over an air-filled cavity when ground water is inflowing from the surface. Seismic Small scale shallow seismic surveys are regu larly performed in karst te rrain, primarily to answer geotechnical questions relating to thickness of over burden and bedrock compet ency. By measuring the seismic velocities of compressional (P), shear (S), and/or surface (Rayleigh) waves, as they are either refracted or reflected off acoustic boundaries, a velocity-versus-depth profile can be derived along the seismic line. Steady im provements in instrumen tation, seismic sources and inversion software make the seismic method attractive. The multichannel analys is of surface waves (MASW) method is used to evaluate the elastic modulus of the shallow surface, and has been used to detect subsurface voids (Bonila and others, 2004). A similar method, spectral analysis of surface waves (SASW), employs an electromechanical harmonic shaker as a frequency-controlled active source (Kayen, 2005). Its use in ka rst investigations has not yet been reported. The basal plane of epikarst has been determined from seismic refraction plus electrical resistivity and gravity, thus limiting the epikarst zone from geo physical point of view (Bosak and Benes, 2003). Seismic refraction tomograp hy (P and S wave) was used with ERT and GPR to identify loosened rock around a cave at an archaeological site (Leucci, 2003). While the theory and practice of seismology are well developed, on-going theoretical work on under standing effects of karst on acoustic wave scattering and attenuation (Hackert and Parra, 2003), may improved the practice.

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12 Gravity Gravity methods have long been used in karst investigations, mainly in search of voids and cav erns. Tedious field work, involving careful survey ing and tie points, has limited its use. A new generation of automated digital-output gravity meters attain 5 microGal accuracy, which is suffi cient to detect shallow voids. Absolute gravity meters with 10 microGal accuracy are now available which eliminate the need to tie into an established benchmark. While global positioning systems (GPS) have generally replaced surveying with total sta tions, GPS elevation measurements are insuffi ciently accurate for void detection. Th e theoretical gravity vertical gradient is 3.086 microGal/cm. Therefore, to realize the precision of modern gravimeters, local elevation control has to be kept to about 1 cm. This can be do ne by combining GPS, to establish an accurate local benchmark, and an opti cal surveying instrument to measure relative eleva tions. Data analysis and modeling is made easier through automated corrections and advanced gravity inversion software, some of which uses 3D voxel models instead of 2D slab approximations. Micro gravity has been used in conjunction with GPR to map shallow caves (Beres and others, 2001). Magnetics High-resolution ground magnetic surveys rarely take place in kars t investigations. Carbonate rocks do not, as a rule, contain sufficient magnetic minerals to cause magnetic anomalies. In cases where high susceptibility sed iments overlie karstic limestone, it is possible to map areas where the soils are depleted or concentrated, as with an active sink hole. Magnetometers with 0.01 nT sensitivity can directly detect such voids and caves (Rybakov and others, 2005). Research into the origin of magnetic soils in karst regions (Rivers and others, 2004) can lead to the further appli cation of magnetic surveys. BOREHOLE METHODS By placing geophysical instruments directly in the earth, borehole methods can offer superior results over surface meth ods but at a cost: bore holes are not cheap, especially in karst. Many tools require open holes, while other tools can operate through plastic casing. Furthermore, investigations involving tomographic techniques require multiple boreholes. Unlike surface methods, borehole meth ods are largely immune to above ground cultural noise. Because of the wealth of information obtained, every borehole should be logged as stan dard practice. Integrated approaches to borehole data have been followed to identify hi gh transmissivity zones (Brandon and others, 2001) and to investigate con tamination in fractured sedimentary bedrock (Will iams, 2002). Electromagnetic Much work has been do ne by the mining indus try to detect voids and obstacles. There is a strong reliance on borehole radar to image the conditions around a single borehole (bi-static mode) and between pairs of boreholes (tomographic mode). Because the tools are expens ive and difficult to use, they have found limited use in karst studies. Logging Borehole logging tools are now available with miniaturized versions of virtually all surface electro magnetic techniques, plus nuclear (gamma, neutron) measurement capabilities. Bo rehole logging should be considered indispensable during installation of a well, as it provides detailed lithologic and porosity information. Many case st udies are reported annu ally (e.g., Brandon and others, 2001). Televiewer Visual and acoustic televiewers are extremely valuable in classifying porosity, fractures, and voids, as well as lithologic changes, as determined from fabric, grain, color. Combined with ArcGIS and Spatial Analyst software digital images can be used to derive the spatial distribution of macropore density. Seismic The oil and gas industry relies heavily on bore hole seismic techniques. Sp in-offs of this technol ogy have benefited near-surface geophysics, particularly in ground wate r investigations. Vertical seismic profiling (VSP) in which geophone receivers are lowered in a well to measure acoustic

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13 waves generated by a source on the surface, and cross-well tomography (CWT), in which both receivers and sources are positioned in adjacent boreholes, have the capab ility of directly detecting cavities and conduits. Because of the high cost fac tor, these methods are still in the research stage as applied to karst studies, and are not widely used. AIRBORNE METHODS When it is impossible to gain access to land for laying out seismic lines or resistivity arrays, air borne methods offer one means of acquiring high resolution data. Though costly, they can be cost effective for large area reconnaissance mapping of large-scale structures under cover, such as faults and lithology. In kart terrain surface conductivity varia tions can sometimes be related to surface subsidence over sinkholes. Electromagnetic Early work in a karst setting (Doll and others, 1993) and subsequent papers based on the helicopter data showed effectiveness in mapping geology in the Appalachian fold-and-t hrust belt, and anomalies correlating with known kars t features were noted (Doll and others, 2000). These anomalies were fol lowed up using surface geophysical techniques. A program of airborne and surface geophysics was undertaken to delineate in potential pathways for contamination transport in karst (Gamey and others, 2001). More recent work (Smith and others, 2003; Hodges, 2004; Smith and others, 2005) demon strated ability to map structure and lithology in a karst aquifer. However, the ability to map large voids and conduits has yet to be shown definitively. Future investigations us ing improved sensors and improved GPS will help answer this question. Aeromagnetic Although magnetic surveys cannot, as a rule, directly map karst features, they can provide valu able information on geologic structure. A highresolution aeromagnetic survey was flown in 2001 over the western extent of the Edwards aquifer in Medina and Uvalde Counties, Texas. The objective of the survey was to im prove the geohydrologic framework of this import ant world-class karst aqui fer. This data set (Sm ith and others, 2002) has helped to develop a 3D geologic model of the aqui fer, which will be used to refine ground water mod els for aquifer management. In addition to analyzing how newly detected igneous bodies may influence regional ground water flow. Aeromagnetic data from a helicopter survey over a small study area cen tered on a sinkhole reve aled a magnetic lineation aligned with a major fau lt juxtaposing the Edwards and Glen Rose limestones (S mith and Pratt, 2003). LIDAR Subtle changes in topographic features can be indicative of karst features, such as dolines and active sinkholes. Current light detection and ranging (LIDAR) systems can achieve accuracies of 15 cm vertically and less than 1 m horizontally at flying altitudes of 300 2,000 m. Measurements can be degraded by ground cover, however. One paper (Montane and Whitman, 20 00) examined the rela tionship of LIDAR topography to subsurface karst structures, but no reports have since been published on the topic. Remote Sensing The airborne visible/infrared imaging spec trometer (AVIRIS) and satellite (LANDSAT) plat forms obtain spectral and hyperspectral images of the earths surface. Emissions in various bands can be related to vegetation and mineralization. Over karst terrain, variations of vegetation, in particular, can be used as indicators of active drainage and recharge sites. Other studies used photographic images and digital eleva tion models (Jemcov and others, 2002), and true geological remote sensing (Hung and Batelaan, 2003; Rouse and others, 2004). Aerial thermography, by which slight temperature variations (0.1 deg C) are mapped, has b een used to characterize karst hydrology (Campbell and Keith, 2001). FRONTIER METHODS In very recent years commercial equipment has become available based on the surface nuclear mag netic resonance (SNMR) geophysical technique pioneered in Russia. The method of magnetic

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14 resonance sounding (MRS) is based upon the pre cession of protons of hydrogen of water when acted on by a strong magnetic field. Its possible applica tions are beginning to be explored (Valla and Legchenko, 2003). The meth od has the capability of measuring the quantity and depth of free (not surface bound) water. Thus, it may be possible to detect perched water and water filled cavities in karst (Vouillamoz and Le gchenko, 2003). Advances in this field are presented at an annual European Sym posium on NMR Spectroscopy in Soil, Geo and Environmental Sciences. Gravity and magnetic tensor gradiometry are evolving rapidly as commercial versions of military systems become available. As gradiometric devices, they measure field variations caused by near sources more than from distance sources. Thus, tensor microgravimetry might prove effective in mapping density variations in the near surface. REFERENCES Adams, A.L., Zhou, W., Wang, J., and Beck, B.F., 2002, A differentiation of karst hazards based on ground pen etrating radar and natural potential measurements, in Abstracts with Programs, Geological Society of Amer ica, 34; 2, p. 89. ASTM International 1999, D6429: Standard Guide for Selecting Surface Geophysical Methods Baradello, L., and Yabar, D.N., 2002, Singlefold and multifold GPR techniques to detect karst caves, Alti del Museo Civico di Storia Naturale di Trieste, 49, Suppl.; p. 23-28. Beres, M., Luetscher, M., Oliver, R., 2001, Integration of ground penetrating radar and microgravimetric meth ods to map shallow caves, Journal of Applied Geo physics, Vol. 46, No. 4. Bonila, C., Rehwoldt, E.B, and Dunscomb, M.H., 2004, Geophysical testing for voids caused by non-com pacted backfill, in Proceedings of the Symposium on Engineering Geology and Geotechnical Engineering, 39, p. 197-205. Bosak, P., and Benes, V., 2003, Geophysical characteris tics of epikarst; case studies from Zagros Mts. (Iran) and the Koneprusy region (Czech Republic), Acta Car sologica, 32;2, p. 255-267. Bosch, F.P., and Mueller, I., 2001, Continuous gradient VLF measurements; a new possibility for high resolu tion mapping of karst structur es, First Break 19; 6, p. 343-349. Brandon, W.C., Behr, R.E., Bl ackey, M.E., and Zay, A., 2001, Identification of discrete high transmissivity zones in sparsely fractured limestone; an integrated approach using fracture tr ace analysis and surface and borehole geophysical methods, Loring, Maine, in Abstracts with Programs, Geological Society of Amer ica, 33; 6, p. 413. Campbell, C. W., and Keith, A.G., 2001, Karst groundwater hydrologic analyses based on aerial thermogra phy, Hydrological Science and Technology, 17;1-4, p. 59-68. Dobecki, T.L., 1990, Review of geophysical methods for karst detection and mapping; Bulletin of the Houston Geological Society. 32; 5, p. 21-24. Doll, W.E., Nyquist, J.E., Holladay, J.S., Labson, V.F., and Pellerin, L., 1993, Pre liminary Results of a Heli copter Electromagnetic and Magnetic Survey of the Oak Ridge Reservation, Tennessee for Environmental and Geologic Site Characteri zation, in Proceedings of the Symposium on the Application of Geophysics to Engineering and environmental Problems, p. 15. Doll, W.E., Nyquist, J.E., Beard, L.P., and Gamey, T.J., 2000, Case History: Airborne geophysical surveying for hazardous waste site characterization on the Oak Ridge Reservation, Tennessee, Geophysics, Vol. 65, No. 5, p. 1372-1387. Gamey, T.J., Thompson, M., Ma ndell, W., and Frano, G., 2001, Karst pathway delineation using combined spa tial and geophysical analysis at Camp Crowder, Mis souri, in Abstracts with Programs, Geological Society of America, 33; 6, p. 132. Greenfield, R.J., 1979, Review of geophysical approaches to the detection of karst; Bulletin of the Association of Engineering Geologists, 16; 3, p. 393408. Hackert, C.L., and Parra, J.O., 2003, Estimating scatter ing attenuation from vugs or karsts, Geophysics, 68;4, p. 1182-1188.

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15 Hodges, G., 2004, Practical Inversions for Helicopter Electromagnetic Data: Airborne Geophysical Methods Workshop, Symposium on the Application of Geo physics to Environmental and Engineering Problems, p. 45-58. Hung, L.Q., and Batelaan, O., 2003, Environmental geo logical remote sensing and GIS analysis of tropical karst areas in Vietnam, In ternational Geoscience and Remote Sensing Symposium (IGARSS), Vol. 4, p. 2964-2966. Jemcov, I., Pavlovic, R., and Stevanovic, Z., 2002, Mor photectonic analysis in hydr ogeological research of karst terrains; a case study of SW Kucaj Massif, eastern Serbia, Theoretical and Applied Karstology, 15, p. 5159. Kayen, R., 2005, The Spectral Analysis of Surface Waves Measured at William Street Park, San Jose, California, Using Swept-Sine Harmonic Waves, in Asten, M.W. and Boore, D.M., eds., Blind comparisons of shear wave velocities at closely spaced sites in San Jose, Cal ifornia: U.S. Geological Survey Open-File Report 2005-1169, p. 7 Leucci, G., 2003, Evaluation of karst cave stability using integrated geophysical methods, GeoActa, 2, p. 75-88. Montane, J.M, and Whitman, D., 2000, Relationships between micro-topography and subsurface karst struc tures from airborne LIDAR and GPR data, in Abstracts with Programs, Geological So ciety of America, 32; 7, p. 515. Rivers, J.M., Nyquist, J.E., Roh, Y., Terry, D.O., Doll, W.E., 2004, Investigation into the origin of magnetic soils on the Oak Ridge Reservation, Tennessee, Soil Science Society of America Journal, 68;5, p. 17721779. Roth, M.J.S., Mackey, J.R., Mackey, C., and Nyquist, J.E., 2002, A case study of the reliability of multielec trode earth resistivity testing for geotechnical investi gations in karst terrains, Engineering Geology, 65;2-3, p. 225-232. Rouse, K.J, Palmer, J.R., and Young, G., 2004, Multi spectral image analysis as a guide to identifying poten tial soil-bedrock karst coll apse hazards in urban set tings, Farmington, Missouri, in Abstracts with Programs, Geological Society of America, 36; 3, p. 6. Rybakov, M., Rotsetin, Y., Shirman, B., and Al-Zoubi, A., 2005, Cave detection n ear the Dead Sea a micro magnetic feasibility study, The Leading Edge, p 585590. Smith, B.D., Smith, D.V., Hill, P.L., and Labson, V.F., 2003, Helicopter Electromagnetic and Magnetic Survey Data and Maps, Seco Creek Area, Medina and Uvalde Counties, Texas: U.S. Geological Survey Open-File Report 03-0226, p. 12. Smith, B.D., Cain, M.J., Clark, A.K.,. Moore, D.W., Faith, J.R., and Hill, P.L., 2005, Helicopter Electro magnetic and Magnetic Survey Data and Maps, North ern Bexar County, Texas: U.S. Geological Survey Open-File Report 05-1158, p. 83. Smith, D.V., Smith, B.D., Hill, P.L., 2002, Aeromagnetic Survey of Medina and Uvalde Counties, Texas: A Web Site for Distribution of Data: U.S. Geological Survey Open-File Report 02-0049. Smith, D.V., and Pratt, D. 2003, Advanced Processing and Interpretation of the High-resolution aeromagnetic Survey data over the Central Edwards Aquifer, Texas, in Proceedings of the Soci ety for the Application of Geophysics to Engineering and Environmental Prob lems, p. 11. Sumanovac, F., and Weisser, M., 2001, Evaluation of resistivity and seismic methods for hydrogeological mapping in karst terrains, Journal of Applied Geophys ics, Vol. 47, No. 1. Tarhule, A., Dewers, T., Young, R., Witten, A., and Hali han, T., 2003, Integrated subsurface imaging tech niques for detecting cavities in the gypsum karst of Oklahoma, Oklahoma Geological Survey Circular, p. 77-84. Valla, P., and Legchenko, A., 2002, Surface nuclear mag netic resonance; what is possible?, Journal of Applied Geophysics, Vol. 50, No2. 1-2. Van Schoor, M., 2002, Detection of sinkholes using 2D electrical resistivity imaging, Journal of Applied Geo physics, V. 50, No. 4. Vichabian, Y., and Morgan, F. D., 2002, Self potentials in cave detection, The Leading Edge, 21:9, p. 866. Vouillamoz, J.M., Legchenko, A., et al., 2003, Localiza tion of saturated karst aquifer with magnetic resonance sounding and resistivity imagery, Ground Water, 41:5, p. 578-586.

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16 Williams, J.H., 2002, Borehole geophysics for contami nation investigations in fractured sedimentary bedrock, in Abstracts with Programs Geological Society of America, 34: 6, p. 228. Xue, G., Song, J., and Xian, Y., 2004, Detecting shallow caverns in China using TEM, The Leading Edge, 23;7, p. 694-695. Zhou, W., Beck, B.F., and Adams, A.L., 2002, Selection of an effective electrode arra y to map sinkholes in karst terranes using electrical re sistivity tomography, in Abstracts with Programs, Geological society of Amer ica, 34:2, p. 16.

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17 Review of Airborne Electromagneti c Geophysical Surveys over Karst Terrains By Bruce D. Smith1, Jeffery T. Gamey2, Greg Hodges3 1 U.S. Geological Survey, MS 964, Box 25046, Denver Federa l Center, Denver, CO 80225, 2 Battelle, 105 Mitchell Rd, Suit e 103, Oak Ridge, TN 37830 3 Fugro Airborne, 2270 Argentia Road Mississauga (Toronto), Ontario ABSTRACT This paper describes airborne electromagnetic geophysi cal surveys that have be en applied to geologic or hydrologic studies of karst terrain in the United States. These surveys have a ll used helicopter frequency domain electromagnetic (HEM) system s to map subsurface electrical condu ctivity (or equivalently its recip rocal, resistivity). The first pub lished survey was at the Oak Ridge Reservation including the Oak Ridge National Laboratory (Tennessee) in 1993-1994 (Doll and others, 2000; Nyquist and Beard, 1999). The sur vey used a 6-frequency HEM system with three frequencies each for horizontal and vertical coplanar coil configurations. The frequency range was from approximat ely 850 to 36,000 Hz. This survey showed excel lent examples of geophysical mapping of Permian lim estone and dolomite lithologies, structure, and map ping of anomalous electrical conductivity highs associated with karst features. The karst features consisting of dolines, depressions, and disappearin g streams, were postulated to be important controls for ground water flow paths and potential flow of contaminants. The second survey was conducted in 1999 at Camp Crowder in Southeastern Missouri (Gamey and oth ers, 2000). This HEM survey used five frequencies from approximately 400 to 102,000 Hz. This was an integrated study using photo-interpretation, ground and airborne electromagnetic (EM) surveys, seismic profiling, ground resistivity depth im aging surveys, and natural potentia l methods. Depth imaging methods for HEM data had progressed and at the time this survey was done, ther e was greater flexibility and resolu tion. The karstic bedrock produced similar types of electrical signatures as the survey at Oak Ridge. The interpreted resistivity depth sections from the HEM survey agreed well with other geophysical data and with the borehole data and provided signi ficantly greater aerial coverage. An important characteristic of the geo logic setting of Camp Crowder is th e 5 to 50 meter thick McDowell Resi duum that provides an important ground water storage and pathway to the karstic bedrock. The high frequency HEM apparent resistivity data maps the colluvium and residuum. Th e residuum thickness can be interp reted in detail from the HEM resis tivity depth sections and shows subsurface bedrock topo graphic karstic features that are important in migra tion of shallow ground water. These near surface pa thways interpreted from th e HEM data help explain some of the complex results of tracer studies. Based in part on the success of these surveys, a HEM survey was flown (200 2) over the Seco Creek area in the Cretaceous Edwards Aquifer in Central Texas (Smith and others, 2003a,b). The HEM system used here was similar to that used at Camp Crowde r with a frequency range fro m 400 to 115,000 Hz for horizontal co-planer coils. This survey successfully mapped structure, stratigraphy, and karst features within the recharge zone of exposed Edwards limestone, the artesian zo ne where the Edwards is buried by younger sediments, and the capture z one of older Glen Rose limestone. In this geol ogic setting the highest frequency is a direct reflection of bedrock geology be cause there is little development of a residuum or Qua ternary alluvial deposits. The HEM data has mapped mu ch more structure than the previously mapped geol ogy confirming the importance of structural features in this karst setting. Co mputation of electrical

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18 resistivity depth sections had progressed even from th e time of the Camp Crowder survey. In addition the calibration and noise levels of the HEM system had improved. Different invers ion schemes for the HEM data were evaluated to compute resistivity depth sec tions along flight lines (Sm ith and others, 2003a). Due to the improvements in the airborne geophysical system, the HEM data co uld be used in three-dimensional imaging of geology (Pantea and others, 2005) and karst features (Smith and others 2004). A more recent survey in N. Bexar County of Texas (Smith and othe rs 2005) has demonstrated applications to mapping karst features in the Glen Rose Li mestones of the Trinity Aquifer. The final example of mapping karst features is from a survey in the Canada over Silurian limestones (Hodges, 2004). The objective of this survey was to map the thickness of glacial overburden in the area of a known sinkhole in order to determine if other signif icant sinkholes existed in the area. These survey data were used to develop and refine automatic inversion of the HEM data to interpret overburden depth maps. In particular, seismic lines and drill ho le data was used to constrain star ting models. Seismic data was used to map the depth of overburden in the sinkhole beca use the 150-meter thickness of the conductive overbur den was too great to be resolved by the HEM data. Ho wever, elsewhere, the constrained inversion provided realistic depth estimates for the overburden. A paleochannel was mapped in one corner of the survey area but no other major sinkholes where found. Helicopter electromagnetic surveys have proven to be cost effective and efficient in mapping large areas of karstic terrain that often are inaccessible. Th ough the surveys have not identified specific cave sys tems or other voids, they have iden tified structure, stratigraphy, and othe r features such as dolines that can be important in the control of groundwater flow paths. SELECTED REFERENCES Doll, W.E, Nyquist, J.E., B eard, L.P., and Gamey, T.J., 2000, Airborne Geophysical Surveying for Hazardous Waste Site Characterization on the Oak Ridge Reservation, Tennessee: Geophysics, vol. 65, no. 5., p 1372-1387. Nyquist J.E. and Beard, L.P., 1999, Clean Enough for Industry? An Airborne Geophysical Case Study: Symposium on the Application of Geophysics to Environmental and Engineering Problems. Gamey, T.J., Thompson, M., Mandell, W., Frano, G., Miller, S., 2000, Karst Pathway Delineation using Combined Spatial and Geophysical Analysis at Camp Crowder, Mi ssouri,: Symposium on the Application of Geophysics to Environmental and Engineering Problems 12 p. Hodges, G., 2004, Practical Inversions for Helicopter Electromagnetic Data: Airborne Geophysical Methods Work shop, Symposium on the Application of Geophysics to Environmental and Engineering Problems, p. 45 58. Pantea, M.P., Cole, J.C., Smith, B.D., and Deszcz-Pan, M. 2005, Structural and stratigraphic 3-D modeling of the Edwards Aquifer, Medina County, Texas, using helicopter EM survey data to evaluate and extrapolate geologic mapping and drillhole da ta, these proceedings. Smith, B.D., Irvine, R., Blome, C.D., Clark, A.K., and Smith, D.V., 2003a, Pre liminary Results, Helicopter Electro magnetic and Magnetic Survey of the Seco Creek Area, Medina and Uval de Counties, Texas: Proceedings for the Symposium on the Application of Geophysics to Environmental and Engineering Problems, San Antonio, Texas, 15 p. Smith, B.D., Smith, D.V., Hill, P.L., and Labson, V.F., 2003 b, Helicopter electromagnetic and magnetic survey data and maps, Seco Creek Area, Medina and Uvalde counties, Texas: U.S. Geolog ical Survey Open-F ile Report 03-226, 43 p.

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19 Smith, B.D. Cain, M.J., Clark, A.K.,. Moore, D.W., Faith, J. R., and Hill, P. L., 2005, Helicopter Electromagnetic and Magnetic Survey Data and Maps, Northern Bexar County, Texas: U.S. Geological Survey Open-File Report 051158, 83 p.

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20 Overview of Karst Effects and Karst De tection in Seismic Data from the Oak Ridge Reservation, Tennessee W. E. Doll 1 B. J. Carr 2 J. R. Sheehan 1 and W. A. Mandell 3 1 Battelle, 105 Mitchell Rd., Suite 103, Oak Ridge, TN 37830 2 Geophex, 605 Mercury Street, Raleigh, NC 27603 3 U.S. Army Environmental Center, 5179 Hoadley Rd, Aberdeen, MD 21010 ABSTRACT The Oak Ridge Reservation (ORR), Tennessee has an abun dance of karst features, including sinkholes, voids, and epikarstal features. In addition to nonseismic investigations, seve ral seismic surveys, primarily seismic reflection and refraction, were conducted on the ORR between 1992 and 2 005. In some cases, karst was the target of the seismic investigations, but in others, karst had de trimental effects on data ac quired for other applications. In this paper, we sum marize the results of these surveys as well as the modeling th at we conducted to understand these results, and present our observations on the strength s and limitations of seismic me thods for karst investigations. OAK RIDGE RESERVATION KARST The Oak Ridge Reservation (ORR), Tennessee has an abundance of karst features, including sinkholes, voids, and epikarstal features (Figure 1). These features are of concern in that they can cr itically impact the offsite migration of contaminants. As an example, groundwater monitoring well GW-734, drilled near the Y-12 Plant on the ORR intercepted a mud-f illed void in 1992, and a number of geophysical surveys were subsequently con ducted to assess the karst feature at this site (Doll et al., 1999; Carpenter et al.,1998). In addition to several nonseismic investigations, many seismic surveys, primarily Figure 1. Karst features on the ORR

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21 seismic reflection and refraction, were conducted on the ORR between 1991 and 2005 (Figure 2). Seis mic refraction surveys were conducted for depth to bedrock measurements (e.g. at the proposed Advanced Neutron Source ANS site, Nyquist et al., 1996), and sinkhole imaging. Seismic reflection surveys were conducted primarily for mapping structures that control co ntaminant transport in the vicinity of high-level waste sites (e.g. Doll et al., 1998; Doll, 1998; Carr et al., 1997; Liu and Doll, 1997). The results were used for selection of groundwater monitoring well locations. In some cases (e.g. Doll et al., 1999; Carpenter et al., 1998; Sheehan et al., 2005), karst was the target of the seis mic investigations, but in the seismic reflection stud ies and many of the refraction studies, karst had detrimental effects on data acquired for other appli cations. Figure 3. Karst effects in seismic reflection stacked section, Line M, ETTP data group, ORR. Figure 2 Locations of seismic reflection and refraction lines on the ORR. T h ru s t F a u lt

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22 KARST IN SEISMIC REFLECTION DATA Seismic reflection data can yield indicators of karst, but infrequently pr ovides a satisfactory degree of imaging. Figure 3 shows a portion of ETTP seis mic reflection line M, a north-south line which is oriented perpendicular to strike from the northern portion of the ORR. The da ta were acquired with an IVI Minivib source, sweeping 20-200 Hz with 96 recording channels for a 0.55s section, as described in Liu et al., 1997. A known sinkhole causes disrup tion of shallow reflections, as shown. Other disrup tions of shallow reflections may be associated with sinkholes that are presently unknown. At other sites, shallow karst completely obliterates deeper reflec tions. At the Bear Creek Burial Grounds (Figure 4; Doll, 1998), data were acquired along two southdipping strike-parallel lines using the KGS Auger gun 8-guage source and 48 receiving channels. The data in the northern line (BCV Line 1) were acquired in the Nolichucky Formatio n, an interbedded shale and limestone unit that is no t prone to karstification. The southern line (BCV Line 3) occurs in the May nardville Formation, a limestone unit that is fre quently karst-bearing on the ORR. The stacked section for Line 1 (figure 5) is a very nice image of the underlying structure of the site. On Line 3a (Fig ure 6), only a few reflections can be recognized in a largely diffuse image. Seismic Lines 3b and 3c do not display any reflections. Thus the shallow karst on Line 3 prevents acquisition of useable reflection data. In none of the stacked sections described above is it possible to determine the size or shape of the karst features or to even state conclusively that karst is responsible for the absence of reflections. Other authors have reported downward deflection of reflections, weak amplitude s or lack of laterally coherent reflections as indicators of karst (e.g. Branham and Steeples, 1988 ; Steeples and Miller, 1987). Figure 4. Map view of the lines that comprise the Bear Creek Valley data group

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23 Figure 6. Stacked section from BCV seismic reflection Line 3A, collected over highly karstified limestone unit. Few coherent reflections appear. Figure 5. Coherent reflections from stacked seismic reflection section collected over thick shale unit.Time (s)

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24 Karst Effects on Shot Gathers in Seismic Reflection Data Many of the effects of karst are likely to be eliminated through the stacking of CDP gathers in seismic reflection processing. It is therefore appro priate to inspect data at a more fundamental level to assess karst effects. Primary indicators are diffrac tions; attenuated, absent or discontinuous reflec tions; or variations in s hot gathers that prevent stacking of reflections. We have observed ampli tude reductions as well as diffraction hyperbolae in shot gathers where karst is known to occur. Figure 7 shows these effects for thre e shot gathers acquired with the IVI Minivib on ETTP Line C. Each of these shot gathers had first arrivals picked and refraction static corrections applied to eliminate effects due to surface elevation changes. In addition to the receive r effects shown in Fig ure 7, we also note that frequency attenuation occurs when the source is placed directly over the karst fea ture. Figure 8 shows this effect, using data from ETTP Line M. Shot 88 is fired 3m south of the exposed collapse structure (F ig. 8a). The dominant frequency of the direct arrivals is 120 Hz, and the amplitudes do not exhibit severe phase rotations across the shot. In the s ubsequent shot, Shot 89 (Fig. 8b), acquired 3m from Shot 88 and less than 1m north of the exposed si nkhole, the amplitude and phase characteristics are disturbed, and the domi nant frequency falls to 80 Hz. Models of Karst in Reflection Data We have developed a series of finite difference models to obtain a bette r understanding of karst effects in shallow seismic reflection data. These results are incorporated into a paper (Carr et al., in preparation) that provides greater detail. In general, the results validat e the observations that we have presented above from field measurements. In gen eral, air-filled karst attenuates the most energy, pro duces the largest diffractio ns, and interferes most with first arrivals and subsequent reflections. Waterand soil-filled voids produce these effects to a lesser degree, but also produce large amplitude multiples. Fi gure 7 K arst e ff ects i n s h ot gat h ers f rom ETTP Li ne C Summary of Reflection Me thods for Karst Imaging These results demonstrate the difficulty of imaging karst with seismic reflection methods. The assumptions that are inhere nt in seismic reflection analysis are in conflict with attributes of karst struc tures, such as steeply dipping boundaries, rough interfaces, and laterally discontinuous interfaces. In addition, the dimensions of typical karst features can be near to, or less than th e wavelength of the seismic waves that are often used in an attempt to image them. This makes it more likely that the seismic energy will be scattered than reflected. In addition, surface waves, refracted waves, and other forms of source-generated interference make it very difficult to enhance reflections shallower than about 50 ms, and this is often the portion of the record that is crit ical for karst sites.

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25 SEISMIC REFRACTION AT KARST SITES Seismic refraction methods have been used on the ORR and elsewhere to determine depth to bed rock, and other structures rela ted to karst terrains. It is appropriate for mapping soil-filled sinkholes, where these occur as a shallow low velocity soil or soil/rock unit subtended by a higher velocity consol idated layer (presumably carbonates). As carbonates tend to have high velocitie s, these contacts are good refraction candidates, even when moderately weath ered. Deeper karst, however, is more problematic for conventional delay-time or generalized reciprocal methods for refraction anal ysis. Air-, mudor water-filled voids are manifested as low-velocity zones, and these methods assume constant velocity, or constant gradient layers. These assumptions are incompatible with the th ree-dimensional heteroge neity that is dominant at karst sites. As a result, con ventional seismic refrac tion methods often yield indicators of karst such as an apparent thickening of layers above karst voids. Seismic refraction analysis methods that allow baseme nt velocity to vary beneath a constant velocity upper layer (such as the refraction statics routines in seismic reflection soft ware packages) can also yield artificially low base ment velocities beneath the void. These results show that seismic refrac tion data can respond to voids, but conventional meth ods or data sets have inherent weaknesses that preclude proper imaging. To demonstrate this effect, we show results from data acquired above a known karst feature at the Y-12 site, at well GW-7 34. The mud-filled void at this site was encountere d during installation of a monitoring well with the to p of the void at 18m and at least 12m of vertical extent. More details on the site are available in Carpenter et al., 1998 and Doll et al., 1999. Conventional delay-time analysis of a seismic refraction line at the site yields the result shown in Figure 9. This result provides no indication that a karst feature might occur at this site. Figure 8. Frequency attenuation in shot gathers where the source is above a karst feature

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26 A more suitable approach is provided within seismic reflection software in a module that corrects for near-surface time delays that influence underly ing reflection travel times. This near surface time correction is known as a static correction. Tomo graphic seismic refraction statics routines in the FOCUS software package allow bedrock velocity to vary while assuming that the surface layer velocity remains constant. In practice, of course, the soil layer velocity will not be constant, but the allowance for a varying bedrock velocity is an improvement over constant velocity assumptions. When applied to the data from GW-734, we observe two effects (Figures 10 and 11). A profile of the depth to bed rock (Fig.10) shows a depressed bedrock surface at the location of the void. The calculated bedrock velocity (Fig. 11) is lower in the area of the void than in adjacent areas. The FOCUS refraction statics results require more shots across the geophone spread than does the conventional delay-time resu lt. On the other hand, they provide strong indicators of the presence of karst that cannot be derived from the delay-time analysis. Both methods rely only on the travel times of first-arrivals, whereas the seismic reflection results are concerned with more of the waveform. Most importantly, the FOCUS results demonstrate that analysis of seismic firs t arrivals is sensitive to the presence of karst, even though the restrictions of both techniques described here are inappropriate for karst terrains. Figure 9. Delay-time result for first arrival analysis at well GW-734.

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27 More recently, we have directed our effort toward application of to mographic refraction analy sis methods, which have fewer restrictions, and appear to be more effective than the methods described in this paper. Results from this effort are described in a subsequent paper in this volume (Sheehan et al., this volume) and will not be dupli cated here. CONCLUSIONS Based on analysis of extensive seismic data acquired on the ORR over a period of more than a decade, we can reach some general conclusions about karst effects in seismic data at this location. Karst can significantly in fluence the quality of stacked seismic reflection profiles, and can create artifacts in the stacked profiles as well as shot gath ers that indicate the presence of karst. These effects are neither consistent nor unique to karst, so seismic reflection profiling is a poor choice for imaging or unambiguously locating kars t-related structures. The conventional delay-time or similar proce dures for analyzing seismi c refraction data have inherent assumptions about the nature of the seismic velocity structure that conf lict with the typical struc tures at karst sites. As a result, they produce artifacts that are caused by the kars t but do not accurately represent the structure of the karst features. Tomo graphic static routines in seismic reflection software packages provide stronger indications of the karst features, but are still too restrictive for proper struc tural representation of karst. Based on these results, we believe that seismic refraction tomography with fewer constraints on the seismic velocity structure are more effective in imaging karst than conven tional seismic reflectio n and refraction. Figure 10. Bedrock surface, as determined with FOCUS refraction statics Figure 11. Bedrock velocity as produced by the FOCUS tomographic refraction statics module.

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27 More recently, we have directed our effort toward application of to mographic refraction analy sis methods, which have fewer restrictions, and appear to be more effective than the methods described in this paper. Results from this effort are described in a subsequent paper in this volume (Sheehan et al., this volume) and will not be dupli cated here. CONCLUSIONS Based on analysis of extensive seismic data acquired on the ORR over a period of more than a decade, we can reach some general conclusions about karst effects in seismic data at this location. Karst can significantly in fluence the quality of stacked seismic reflection profiles, and can create artifacts in the stacked profiles as well as shot gath ers that indicate the presence of karst. These effects are neither consistent nor unique to karst, so seismic reflection profiling is a poor choice for imaging or unambiguously locating kars t-related structures. The conventional delay-time or similar proce dures for analyzing seismi c refraction data have inherent assumptions about the nature of the seismic velocity structure that conf lict with the typical struc tures at karst sites. As a result, they produce artifacts that are caused by the kars t but do not accurately represent the structure of the karst features. Tomo graphic static routines in seismic reflection software packages provide stronger indications of the karst features, but are still too restrictive for proper struc tural representation of karst. Based on these results, we believe that seismic refraction tomography with fewer constraints on the seismic velocity structure are more effective in imaging karst than conven tional seismic reflectio n and refraction. Figure 10. Bedrock surface, as determined with FOCUS refraction statics Figure 11. Bedrock velocity as produced by the FOCUS tomographic refraction statics module.

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28 Here, we have dealt ex clusively with methods that involve primary body waves (P-waves) in this analysis. We have not discussed shear wave meth ods, or surface wave ap proaches s such as multi channel analysis of surface waves (Park et al., 1999), that may also be suitable to karst sites. We have had mixed success with these methods on the ORR, and believe that they merit further study. ACKNOWLEDGEMENTS We thank Rick Miller an d the Kansas Geologi cal Survey for acquiring the seismic reflection data that we subsequently processed and discuss in this paper. We thank David Watson (ORNL) for provid ing the karst map in Figure 1. REFERENCES Branham, K. L., and D. W. Steeples, 1998, Cavity detec tion using high-resolution seismic reflection methods. Mining Engineering 115-119. Carpenter, P. J., W. E. Doll, and R. D. Kaufmann, 1998, Geophysical character of buried sinkholes on the Oak Ridge Reservation, Tennessee, Jour. Environmental and Engineering Geophysics, v. 3, p. 133-146. Carr, B. J., W. E. Doll, and R. D. Miller, 1997, Near-sur face seismic imaging and re flectivity studies of the Melton Valley waste areas, Oak Ridge Reservation, Expanded Abstracts, 1997 Soc. Expl. Geophy. Annual Meeting, p. 772-775. Carr, B. J., W. E. Doll, and R. Bainer, in preparation, Seismic detection of shallow karst on the Oak Ridge Reservation. Doll, W. E., R. D. Miller, and J. Xia, 1998, A non-inva sive shallow seismic sour ce comparison on the Oak Ridge Reservation, Tennessee Geophysics v. 63, n. 4, p. 1318-1331. Doll, W. E., Reprocessing of shallow seismic reflection data to image faults near a hazardous waste site on the Oak Ridge Reservation, Tennessee, Proceedings of the 1998 Symposium on the Application of Geophysics to Engineering and Environmental Problems March 2226, 1998, Chicago, IL, p. 705-714. Doll, W. E., J. E. Nyquist, P. J. Carpenter, R. D. Kauf mann, and B. J. Carr, 1999, Geophysical surveys of a known karst feature: Oak Ridge Y-12 Plant, Oak Ridge, Tennessee, in Geo-engineering for under ground facilities ASCE Geotechnical Special Publica tion No. 90, G. Fernandez and R. Bauer, ed., p. 684694. Liu, Z. and W. E. Doll, 1997, Seismic reflection process ing for characterization of a hazardous waste site, Pro ceedings of the 1997 Symposiu m on the Application of Geophysics to Engineering and Environmental Prob lems p. 291-299. Nyquist, J.E., W.E. Doll, R.K. Davis, and R.A. Hopkins, 1996, Cokriging surface topography and seismic refraction data for bedrock topography, Jour. Environ mental and Engineering Geophysics, v. 1, n. 1, p. 6774. Park, C.B., R.D. Miller, and J. Xia, 1999 Multichannel analysis of surface waves, Geophysics, 64, 800-808 Sheehan, J. R., W. E. Doll, D. B. Watson, and W. A. Man dell, this volume Detecting cavities with seismic refraction tomography, 12pp. Sheehan, J. R., W. E. Doll, D. B. Watson, and W. A. Man dell, 2005, Detecting cavities wit seismic refraction tomography: Can it be done?, Proceedings of the 2005 Symposium on the Application of Geophysics to Engi neering and Environmental Problems, p. 989-1003. Steeples, D. W., and R. D. Miller, 1987, Direct detection of shallow subsurface void s using high-resolution seis mic-reflection techniques; in Beck, B. F. Wilson, W. L., and Balkema, A. A., Eds., Karst Hydrogeology; Engineering and Environmental Applications, 179183.

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28 Here, we have dealt ex clusively with methods that involve primary body waves (P-waves) in this analysis. We have not discussed shear wave meth ods, or surface wave ap proaches s such as multi channel analysis of surface waves (Park et al., 1999), that may also be suitable to karst sites. We have had mixed success with these methods on the ORR, and believe that they merit further study. ACKNOWLEDGEMENTS We thank Rick Miller an d the Kansas Geologi cal Survey for acquiring the seismic reflection data that we subsequently processed and discuss in this paper. We thank David Watson (ORNL) for provid ing the karst map in Figure 1. REFERENCES Branham, K. L., and D. W. Steeples, 1998, Cavity detec tion using high-resolution seismic reflection methods. Mining Engineering 115-119. Carpenter, P. J., W. E. Doll, and R. D. Kaufmann, 1998, Geophysical character of buried sinkholes on the Oak Ridge Reservation, Tennessee, Jour. Environmental and Engineering Geophysics, v. 3, p. 133-146. Carr, B. J., W. E. Doll, and R. D. Miller, 1997, Near-sur face seismic imaging and re flectivity studies of the Melton Valley waste areas, Oak Ridge Reservation, Expanded Abstracts, 1997 Soc. Expl. Geophy. Annual Meeting, p. 772-775. Carr, B. J., W. E. Doll, and R. Bainer, in preparation, Seismic detection of shallow karst on the Oak Ridge Reservation. Doll, W. E., R. D. Miller, and J. Xia, 1998, A non-inva sive shallow seismic sour ce comparison on the Oak Ridge Reservation, Tennessee Geophysics v. 63, n. 4, p. 1318-1331. Doll, W. E., Reprocessing of shallow seismic reflection data to image faults near a hazardous waste site on the Oak Ridge Reservation, Tennessee, Proceedings of the 1998 Symposium on the Application of Geophysics to Engineering and Environmental Problems March 2226, 1998, Chicago, IL, p. 705-714. Doll, W. E., J. E. Nyquist, P. J. Carpenter, R. D. Kauf mann, and B. J. Carr, 1999, Geophysical surveys of a known karst feature: Oak Ridge Y-12 Plant, Oak Ridge, Tennessee, in Geo-engineering for under ground facilities ASCE Geotechnical Special Publica tion No. 90, G. Fernandez and R. Bauer, ed., p. 684694. Liu, Z. and W. E. Doll, 1997, Seismic reflection process ing for characterization of a hazardous waste site, Pro ceedings of the 1997 Symposiu m on the Application of Geophysics to Engineering and Environmental Prob lems p. 291-299. Nyquist, J.E., W.E. Doll, R.K. Davis, and R.A. Hopkins, 1996, Cokriging surface topography and seismic refraction data for bedrock topography, Jour. Environ mental and Engineering Geophysics, v. 1, n. 1, p. 6774. Park, C.B., R.D. Miller, and J. Xia, 1999 Multichannel analysis of surface waves, Geophysics, 64, 800-808 Sheehan, J. R., W. E. Doll, D. B. Watson, and W. A. Man dell, this volume Detecting cavities with seismic refraction tomography, 12pp. Sheehan, J. R., W. E. Doll, D. B. Watson, and W. A. Man dell, 2005, Detecting cavities wit seismic refraction tomography: Can it be done?, Proceedings of the 2005 Symposium on the Application of Geophysics to Engi neering and Environmental Problems, p. 989-1003. Steeples, D. W., and R. D. Miller, 1987, Direct detection of shallow subsurface void s using high-resolution seis mic-reflection techniques; in Beck, B. F. Wilson, W. L., and Balkema, A. A., Eds., Karst Hydrogeology; Engineering and Environmental Applications, 179183.



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29 Application of Seismi c Refraction Tomography to Karst Cavities Jacob R. Sheehan1, William E. Doll1, David B. Watson2, Wayne A. Mandell3 1 Battelle, 105 Mitchell Rd, Suit e 103, Oak Ridge, TN 37830 2 Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, TN 37831 3 U.S. Army Environmental Center, 5179 Hoadley Rd, Aberdeen, MD 21010 ABSTRACT For three years we have used synthetic and field da ta to investigate the effectiveness of commercial refraction tomography codes on both simple and comple x subsurface velocity structures, with the ultimate goal of determining the suitability of the method for karst problems. The results of these studies indicate that refraction tomography is able to resolve karst feat ures under some conditions. Th e analysis of field data acquired on the Oak Ridge Reservation, TN shows low velo city zones on three paralle l seismic lines. These zones are located at similar depths and fall on a line that is parallel to geologic st rike, leading to an interpre tation of a possible karst conduit. Th is feature has velocities of about 1500-2000 m/s in a matrix of 30004000 m/s, reasonable velocities for a mud filled void in saprolite at these depths. Drilling of this feature is anticipated in the near future. Anal ysis of a seismic line taken over the known mud-fille d cavity shows a low velocity feature with a location co nsistent with drilling resu lts. The velocity of th e feature is about 1000 m/s, a value that is a little lower than that found fo r the features discussed abov e. Synthetic modeling some times generates results similar to the field results, but often fails to image cavities as well, or at all. Ongoing investigations are aimed at refining our understanding of the circumst ances where these methods can be suc cessful, and investigating the relevance of model results to actual field conditions. INTRODUCTION Oak Ridge National Labo ratory and Battelle have been working with the United States Army Environmental Center to assess the performance of seismic refraction tomograp hy (SRT) for karst ter rains (Sheehan et al, 2005a, Sheehan et al, 2004, Sheehan et al, 2003). Th ese terrains frequently con tain sinkholes, irregular and gradational bedrock interfaces, remnants of high velocity bedrock above these interfaces, deeply weathered fractures, and voids that may be air-, water-, or mud-filled. The seismic velocity of unconsolidated sedi ments and voids associated with karst features usu ally differs significantly from carbonate parent rock, making seismic methods a po ssible tool for mapping such features. In this paper, we are concerned with detection of karst voids, and will not be concerned with depressions, pinnacles, grikes, or other karst morphologic features (Carpenter et al, 1998). Many seismic methods have been applied to karst problems, but few have been successful. Some success has been attained in detecting sink holes, or other structural features that lie above voids, but it has proven di fficult to image or detect cavities with seismic meth ods. Conventional seis mic refraction methods (e.g delay-time or general ized reciprocal) in particular fall short because airwateror mud-filled voids occur as velocity lows, and these are largely incomp atible with the constant velocity layered models th at these methods require (Doll et. al, 1999). Our first step in evaluating the effectiveness of SRT for karst detection was to use synthetic travel times generated from 2-D models using the refrac tion tomography code GeoCT-II (version 2.3) (GeoTomo, LLC). The synthe tic models allow us to have a reference model with which to compare the results generated by SRT using another refraction tomography code, Rayfract (version 2.51, Intelli gent Resources Inc.). No synthetic model will ever be a completely accurate depiction of the real subsurface. Models are comprised of discrete units, which are further

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30 broken down into small cons tant velocity grid cells. This means that however carefully constructed and applied, numerical analysis is based upon simplified and digitized representations of physical laws and models. In addition, most commercially available numerical modeling packages are based on two dimensional models. Three dimensional numerical analysis is in development, but is currently too com putationally-intensive to be practical for most appli cations. Field testing complements the models by pro viding realistic parameters and a basis for determin ing model validity. For this we used five refraction tomography profiles collected in support of the Nat ural and Accelerated Bioremediation Research (NABIR) Field Research Center (FRC). NABIR is a DOE sponsored research program to develop and evaluate bioremediation tools for contaminated sites. Liquid wastes containing nitrate, uranium, technetium, tetrachlor oethylene, and other contami nants were disposed of in sludge ponds until the mid-1980s, at which time the ponds were remedi ated and capped with a pa rking lot. A large contam ination plume within the underlying unconsolidated saprolite and inter-bedded shale and carbonate bed rock is now spreading away from the site of the old ponds. CONVENTIONAL AND TOMOGRAPHIC REFRACTION TOMOGRAPHY Conventional refraction inversion methods use a layer cake approach. Th e subsurface is divided into a number of continuous constant velocity layers with velocities and thic knesses that are varied through interactive forward modeling in an effort to match the traveltimes that are determined from the field data. These methods require that sections of the traveltime curves be mapped to refractors, a task that can be difficult at best in karst situations. The pres ence of karst features mean s that there can be large and sudden changes in th e shape of the bedrock. There can also be locali zed features such as voids that contradict the assumption of continuous con stant velocity layers. Unlike conventional refra ction methods, SRT does not require that the model be broken into constant velocity contin uous layers. Instead the model is made up of a high number of small constant velocity grid cells or nod es. Inversion is performed by an automated procedure which involves raytrac ing through an initial mode l and comparing the mod eled traveltimes to the field data, and adjusting the model grid-by grid in order to match the modeled traveltimes to the field da ta. This process is itera tively repeated until a preset number of iterations as been reached. Because ther e is no assumption of continuous constant veloc ity layers, SRT can model localized velocity anomalies. RESULTS Synthetic Synthetic models were used to test various properties, limitations and capabilities of SRT for cavity detection. A sample of the models that have been studied and the inversion results are shown in Figure 1. The most basic requirement for detecting a cavity is to have adequate ray coverage in the area surrounding it. Both survey geometry and the veloc ity structure affect the ray coverage. As the effect of geometry is well-understo od, we will focus on the effect of the velocity structure. In order to be able to image a cavity success fully, there must be rays that penetrate deeper than the cavity and can be refracted back to the surface. One factor that can limit the depth of penetration is the presence of sharp hi gh-contrast velocity bound aries. These boundaries cause most of the seismic energy to be reflected back to the surface. The energy that passes through the transition is refracted to shallow angles, limiting the depth of penetration within the area below the transition. Even if energy does penetrate to adequate depths to image a cavity, it must have a path back to the surface in order to be detected. Seismic rays can return to the surface if there is a change in velocity under the cavity. This can be in the form of a verti cal velocity gradient. No rmally, velocities will increase slightly with depth in sedimentary rocks, so in a karst investigation this requisite can be easily met.

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31 Ray coverage alone is not enough to insure that the cavity can be detected. Models that are otherwise identical can be created w ith and without voids to evaluate travel time changes due to the void. We have found cases where the ray coverage around the cavity is extensive, but th e first arrival traveltimes generated from the model do not reflect the presence of the cavity, making it impossible for the inversion algorithm to detect the cav ity. Even when a cavity has a significant effect on the travel times, the inver sion may result in a feature with velocities only slightly lower than that of the surrounding volume. This muted response is unlik ely to give the user con fidence that a cavity has actually been detected. In some cases applying matrix smoothing to the synthetic model before performing raytracing increases the effect of the cavity on the traveltimes, and allows the inverted result to better match the true model. An example of this is shown in Figure 2. In other cases smoothing has no effect at all. SRT can create false positives as well as false negatives such as in the top result shown in Figure 1. These artifacts have been observed when inverting synthetic data, which does not include the inevitable noise and picking errors and inaccuracies. The inclu sion of such factors is li kely to increase the occur rence of both false negatives and positives. One way artifacts can sometimes be distinguished from real features is by examining the ray coverage. In the case of a real low-velocity feature, the ray coverage should be nearly zero with in the feature. Artifacts are usually caused by an area of low ray coverage, but not as low as is usually the case with a true fea ture. A good example of this is shown in Figure 3. Figure 3a shows an artifact where indicated. Figure 3b shows the ray coverage for this model. The ray coverage in the vicinity of the cavity is low com pared to the high coverage area above it that is caused by the increase in velocity. Figure 3c shows a feature that is real. Note that the ray coverage (Fig ure 3d) is drastically lower in the area of the cavity. Field Results Four new refraction tomography profiles (des ignated by Line A, C, D and E, Figure 4) were acquired in support of research at the NABIR FRC site (Sheehan et. al, 2005b). Lines A and C are ori ented parallel to an earlier line (Doll et al., 2002), designated Line B for this paper. Lines A, D, and E used one-meter receiver spacing and two-meter shot spacing. Line B con sisted of three collinear lines and combined for anal ysis. Line C was collected using 2 meter receiver spacing and 4 meter shot spacing. All data were col lected using a 48 channel Geometrics Strataview seismograph. Ten Hz geophones were used for Lines A, C, D and E and 40 Hz receivers were used for line B. Lines A, B and C each show a very well-defined (~ 10m wide) low velocity feature (Figure 5). These low velocity features are a ll similar in size, at the same approximate depth, and fall on a line that is parallel to geologic strike at the field site (Figure 4). There is no such feature in lines D or E, which run roughly parallel to strike and perpendicular to the other three lines. The ray coverage for Lines A and C are shown in Figure 6. In both cases the area of the low veloc ity feature has very low ray coverage, just as in the example discussed ab ove and shown in Figure 3. Because of this and the correlation to geologic strike it is reasonable to assume th at these low velocity fea tures are not artifacts, but rather indicate a long con duit in the carbonate bedrock. This feature yields seismic velocities of ap proximately 1500-2000 m/s in a matrix of 3000-4000 m/s. The apparent cavity is below the water table so it cannot be air-filled, but its velocity is so low that we must surmise that it is wateror mud-filled. Mud-filled Cavity We examined a refraction tomography line taken over a know n mud-filled cavity centered on a well designated GW-734 inves tigated by Doll et al., 1999 and described in Doll et al., this volume. In the previous work at this s ite various geophysical meth ods were utilized in an effo rt to characterize a known mud-filled cavity. One of th e methods used was con ventional delay-time refraction analysis. The seis mic analysis provided a bedrock profile that

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32 matched the drilling logs, bu t was unable to image the cavity. During installation of well GW-734, drillers encountered the cavity starting at a depth of 18 meters, and extending to at least 30 meters. Conven tional refraction analysis at this site failed to show the cavity (Figure 7). The SRT result for the line shows a low velocity feat ure with a location consis tent with the drilling results (Figure 8). The velocity of the feature is about 1000 m/s. The velo city of the surrounding area is about 2750 m/s, which is consis tent with measured velo cities for fractured and weathered carbonate at this locale. CONCLUSIONS Our assessment of synthetic models for deter mining the capabilities an d limitations of seismic refraction for cavity detection has had mixed results. Usually the cavity will be represented in the inver sion result, but the velocity will not be as low as it should be. At other times the cavity is not detected at all. In one case applying matrix smoothing to the model before generating th e synthetic data allowed the cavity to be detected when it was previously undetectable. However, smoothing other models did not have such a positive effect, demonstrating the complexity of synthetic modeling and analysis. Analysis of field data suggests that SRT is capa ble of imaging cavities. Four seismic lines from two separate sites on the Oak Ridge Reservation show possible and known cavities. At the FRC a low velocity feature occurs at a consistent depth and fall ing along a line parallel to geologic strike. Another seismic line was collected over a cavity that had been found by drilling. The drilling found that the top of the cavity is at a depth of about 18 meters and the bottom was at 30 meters or deeper. The SRT result shows a low velocity feature at a depth that is consistent with the drilling results. SRT has the potential to be an effective tool for studies where the presence of cavities needs to be detected. It is not a fail-proof method, however. False positives and negatives are possible. Future Work We hope to build a ph ysical scaled model in order to further evaluate the effectiveness of refrac tion tomography and to im prove synthetic modeling procedures. This will a llow controlled acquisition of data from a known three-dimensional model while avoiding many of the limitations of computer models. To the extent that a model is an accurate representation of the problem of interest, data collected using a physical model will more reliably replicate the physical resp onse without errors asso ciated with discretizing the pr operties of a model. In addition, a physical model, as long as it is large enough, will include 3-D effects. Comparison of the traveltimes generated from digital and physical versions of the same model should greatly improve our understanding of the behavior of digital computer models. This would in turn allow more effective use of computer models for all types of geologic settings. REFERENCES Carpenter, P. J., W. E. Doll, and R. D. Kaufmann, 1998 Geophysical character of buried sinkholes on the Oak Ridge Reservation, Tennessee, Jour. Environmental and Engineering Geophysics, v. 3, p. 133-146. Doll, W.E., J. E. Nyquist, P. J. Carpenter, R. D. Kauf mann and B. J. Carr, 1998 Geophysical Surveys of a Known Karst Feature, Oak Ridge Y-12 Plant, Oak Ridge, Tennessee, Jour. Environmental and Engineer ing Geophysics, v. 3, p. 133-146, 1998 Doll, W.E., J.E. Nyquist, P.J. Carpenter, R.D. Kaufmann, and B.J. Carr, 1999, Geophysical surveys of a known karst feature: Oak Ridge Y-12 Plant, Oak Ridge, Ten nessee, in Geo-engineering for underground facilities ASCE Geotechnical Special Publication No. 90, G. Fernandez and R. Bauer, ed., p. 684-694. Doll, W.E., T.J. Gamey, D.B. Watson, and P.M. Jardine, 2002. Geophysical profiling in support of a nitrate and uranium groundwater remediation study 2002 Annual Meeting of the Symposium on the Application of Geo physics to Engineering and Environmental Problems, Las Vegas, NV, February 10-14 2002.

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33 Doll, W.E., B.J. Carr, J.R. Sheehan, and W.A. Mandell, this volume Application of Seismic Refraction Tomography to Karst Cavities Sheehan, J.R., W. E. Doll, and W. Mandell, 2003. Evalu ation of refraction tomography codes for near-surface applications. Extended abstract, presented at the 2003 Annual Meeting of the So ciety of Exploration Geo physicists, Dallas TX, October 26-31, 2003, 4. Sheehan, J.R., W. E. Doll and W. Mandell, 2004. Com parison of MASW and Refraction Tomography. Extended abstract, presented at the 2004 Annual Meeting of the Symposium on the Application of Geo physics to Engineering and Environmental Problems, Colorado Springs, CO, February 22-26 2004. Sheehan, J.R., W. E. Doll and W.A. Mandell, 2005a. An Evaluation of Methods and Available Software for Seismic Refraction Tomography Analysis, Jour. Envi ronmental and Engineering Geophysics, v. 10, p. 2134, 2005 Sheehan, J.R., W. E. Doll an d W.A. Mandell, and D.B. Watson, 2005b. Detecting Cavities with Seismic Refraction Tomography: Can it be done? Extended abstract, presented at the 2005 Annual Meeting of the Symposium on the Application of Geophysics to Engi neering and Environmental Problems, Atlanta, GA, April 3-7, 2005.

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34 Figure 2: Smoothed velocity (m/s) Model 4(top), inversion results for smoothed version (bottom). 0102030405060708090 80 100Elevation (m) 050100150200250 25 50 75 100Elevation (m) 050100150200250 50 75 100Elevation (m) 050100150200250 50 75 100Elevation (m) 2501250225032504500 12502250325042505250 5001500250035004500 500125020002750 0102030405060708090 Position (m) 80 90 100Elevation (m) 050100150200250300 Position (m) 50 100Elevation (m) 050100150200250300 Position (m) 50 100Elevation (m) 050100150200250300 Position (m) 50 100Elevation (m) 2501250225032504250 12502250325042505250 5001500250035004500 500125020002750 0 25 50 75 0100200300 0 25 50 0100200300 0 25 020406080100 0 25 50 75 0100200300 0 25 50 75 0100200300 0 25 50 0100200300 0 25 020406080100 0 25 50 75 0100200300Figure 1: Synthetic velocity(m/s) models (left), ray coverage (middle) and inversion results (right). Note the muted or missing low-velocity zones in the inversion results. Also note the false low velocity zone in the top inversion result, from positions 65 to 80 meters. 050100150200250 Position ( m ) 50 100Elevation (m) 050100150200250300 Position (m) 50 100Elevation (m) 250 500 750 100 0 125 0 150 0 175 0 200 0 225 0 250 0 275 0 300 0

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35 050100150200250 Position (m) 50 100 050100150200250 Position (m) 50 100 0 100 200 300 400 0102030405060708090 Position (m) 80 100Elevation (m) 0102030405060708090 Position (m) 80 100Elevation (m) 0 100 200 300 400 500 500150025003500 500150025003500Artifact Real Velocity Velocity Ray Density Ray Density 050100150200250 Position (m) 50 100 050100150200250 Position (m) 50 100 0 100 200 300 400 0102030405060708090 Position (m) 80 100Elevation (m) 0102030405060708090 Position (m) 80 100Elevation (m) 0 100 200 300 400 500 500150025003500 500150025003500Artifact Real Velocity Velocity Ray Density Ray Densityc b a d Fi3Dttifthdiffiftiftdlit 9175 9200 9225 9250 9275 9300 9325 1570015750158001585015900159501600016050 Admin. Coord. (m) S t r i k e 9175 9200 9225 9250 9275 9300 9325 1570015750158001585015900159501600016050 Admin. Coord. (m) S t r i k e Figure 3: Demonstration of the difference in ray coverage of an artifact and a real cavity. Figure 4: Relative locations of 5 seismic refraction tomography lines collected in support of FRC. The sections of lines A, B, and C that are marked white represent the areas where the low velocity feature appears. Note that no such feature appears on Lines D and E. Although Line E does cross the line containing the three low-velocity features, it does not overlap it enough to see to the depth of the feature.

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36 051015202530354045 Position (m) 75 80 85 90 95 100Elevation (m) 0102030405060708090 Position (m) 60 70 80 90 100Elevation (m) 5001500250035004500 3040506070809010011012013 0 Position (m) 70 80 90 100Elevation (m) Figure 5: Velocity results (m/s) from three parallel seismic lines all showing a similar low-velocity zone. The top line is A, the middle line is B, and the bottom line is C.

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37 051015202530354045 Position (m) 75 80 85 90 95 100Elevation (m) 0102030405060708090 Position ( m ) 270 280 290 300Elevation (m) 0 50 10 0 15 0 20 0 25 0 30 0 35 0 Figure 6: Ray coverage for FRC lines A (top) and C (bottom). Note the low coverage areas that correspond to the low velocity zones. This is in contrast to the case for the artifact shown in figure 3.

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38 Figure 7: Conventional refraction analysis over known mud-filled cavity. 0102030405060708090 Position (m) 70 80 90 100Elevation (m) 200700120017002200 18 meters depth Well GW-734 N S 0102030405060708090 Position (m) 70 80 90 100Elevation (m) 200700120017002200 18 meters depth Well GW-734 N S 0102030405060708090 Position (m) 70 80 90 100Elevation (m) 200700120017002200 18 meters depth Well GW-734 N S Figure 8: SRT result from a seismic line collected over a known mud-filled cavity. The well indicated encountered weathered bedrock at 11 meters, fresh bedrock at 13 meters and the cavity at 18 meters (interpreted cavity shown by dotted white line).

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39 Borehole geophysical techniques to determine groundwater flow in the freshwater/saline-water transiti on zone of the Edwards aquifer, south-central Texas By R.B. Lambert1, A.G. Hunt2, G.P. Stanton3, and J. Waugh4 1 U.S. Geological Survey, 5563 De Zavala Rd., Suite 290, San Antonio, TX 78249 2 U.S. Geological Survey, Bldg 21, M.S. 963, Denver Federal Center, Denver, CO 80225 3 U.S. Geological Survey, 8027 Exch ange Drive, Austin, TX 78754 4 San Antonio Water System, 1001 E. Market St., San Antonio, TX 78298 ABSTRACT The Edwards aquifer is the primary water supply fo r nearly 2 million people in the San Antonio area of south-central Texas. The freshwa ter/saline-water transition zone in th is carbonate aquifer is fresh to moderately saline with dissolved-so lids concentrations ranging from 1,00 0 to 10,000 milligrams per liter. Recent work by the U.S. Geological Survey in coop eration with the San Antoni o Water System has shown that the transition zone is physica lly and chemically more dynamic than previously thought, and that there is vertical and horizontal stratification within the transition zone. Borehole geophysical techniques includ ing fluid profiling of conductance an d temperature, acoustic televiewer surveys, and flowmeter surveys are being used in monitor well transects to indicate whic h fractures and hydrostratig raphic subdivisions in the Edwards aquifer are more transmissive. When combined with other geologic, geochemical, and hydrologic information, these data can provide a two-dimensiona l subsurface representation of the freshwater/salinewater transition zone. This information is needed to improve the und erstanding of how water moves in and near the transition zone.

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40 An Evaluation of Methods Used to Measure Horizontal Borehole Flow By Wayne A. Mandell1, James R. Ursic2, William H. Pedler3, Jeffrey J. Jantos3, E. Randall Bayless4, and Kirk G. Thibodeaux5 1 U.S. Army Environmental Center, Aberdeen Proving Ground, Maryland 2 U.S. Environmental Protection Agency, Chicago, Illinois 3 RAS, Inc., Golden, Colorado 4 U.S. Geological Survey Indianapolis, Indiana 5 U.S. Geological Survey, Sten nis Space Center, Mississippi ABSTRACT Identifying and quantifying ground -water-flow rates and di rections are importan t components of most hydrologic investigations. High fl ow rates through preferential-flow zones commonly observed in karstic bedrock and the potential for rapid transport of dissolve d solutes accentuate the value of flow-rate and direc tion information. Typically, field ch aracterization of preferential-flow zones in fractured-rock aquifers relies on tracer studies and vertical-flowmeter measurem ents. In unconsolidated aq uifers, identification of flow rate and direction relies on multiple well installa tions and geometric triangula tion. Horizontal borehole flowmeters and hydrophysical logging may provide qu ick, direct, and cost-effective alternatives for char acterizing flow through discrete borehole intervals. A collaborative investigation by the U.S. Army En vironmental Center, the U.S. Environmental Protec tion Agency, the U.S. Geological Survey, and RAS, Inc ., has been evaluating three borehole flowmeters and hydrophysical logging in an aquifer-simulation cham ber at the USGS Hydraulic Instrumentation FacilityHydraulic Laboratory. The evalua tion assesses the capabilities of the methods to measure horizontal ground-water flow and their applicabili ty to field situations. The chamber is 4x4x6 feet and contains approx imately 8,000 pounds of granular media. Hydraulic gradient, ground-water flow and direction are controlled by fluid levels in reservoirs on opposite ends of the chamber. Hydraulic heads are monitored with nine pie zometers along the axis of the chamber and tank discha rge is measured with inli ne paddle flowmeters and volumetric measurements. During 2003 and 2005, flow rates and directions were measured in 2and 6-inch slotted-PVC well screens and 4and 6-inch wire-wound well screens. Th e well screens were installe d during 2003 in a sim ulated aquifer of uniformly sized medium sand and during 2005 in a simulated aquifer of uniformly sized fine (granule) gravel. Flow rates through the aquifer-simulation chamber ranged from approximately 4 to 155 feet/day and hydraulic gradients ranged from 0.0017 to 0.167 feet/foot. Hydrophysical logging (NxHpL) and the horizontal heat-pulse flowmeter (KVA Model 200) were capable of measuring flow and flow direction through a 6-inch slotted-PV C well screen installed in the sim ulated medium-sand aquifer. The ac oustic flowmeter (prototype ADV) and optical flowmeter (prototype SCBFM) were hampered by the relatively low transport of colloidal matter through the well screen. All four methods measured flow thr ough the simulated gravel aquifer, however the 3.5-inch diameter of the ADV prohibited measurements in the 2-inch well. Results of this study indicate that the NxHpL, KVA, and SCBFM accurately measured ground-waterflow rate, and the KVA an d SCBFM accurately measur ed ground-water-flow di rection. The NxHpL does not measure ground-water-flow direction. The ADV wa s inaccurate at measuring ground-water-flow rate and direction. Detailed information about the strengths and limitations of each method and a complete pre sentation of the data and analysis will be presen ted at the USGS Karst Interest Group Workshop.

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41 Characterization of Hydrostratigraphic Units of the Capture, Recharge, and Confining Zones of the Edward s Aquifer Using Electrical and Natural Gamma Signatures By Bruce D. Smith1, Allan K. Clark2, Jason R. Faith2,and Gregory P. Stanton3 1 U.S. Geological Survey, MS 964, Box 25046, Denver Federa l Center, Denver, CO 80225, 2 U.S. Geological Survey, 5563 DeZavala Rd, San Antonio, TX 78249, 3 U.S. Geological Survey, 8027 Exch ange Drive, Austin, TX 78754 ABSTRACT Two high resolution multi-frequency airborne resistivity surveys have been completed over the Edwards aquifer capture (lower conf ining units), recharge, and upper confining areas in different geologic and structural settings. Borehole geophysical logs have been acquired to assist in characterization and map ping of hydrostratigraphic units. These surveys shed additional light on the comp lex hydrostratigraphy and structure of one of the most productive and permeable car bonate aquifers in the United States. Detailed map ping of near surface units and structure is essential in understanding possible su bsurface groundwater flow paths, aquifer resources, and vulnerability to near su rface contamination. The ge ophysical surv eys map the near surface variations in electrical conductivity that can be correlated wi th variations in hydrostratigraphic units. Alluvial deposits and Quaternary formations are thin so the very high frequency resistivity data (around 100 kHz) provide a surrogate map of the bedrock geology and structure. Detailed comparison of the geology and geophysics suggests that hydrostratigra phic subdivision of the stratigraphic sequence cor relates better with the lithologic comp lexity mapped by the airborne geoph ysics. Particular levels of resis tivity of the bedrock hydrostratigraphy can be interprete d from the airborne surveys just as particular levels of resistivity are interpre ted from borehole geophysical logs. In particular the Del Rio and Eagle Ford for mations consisting mostly of clays are the lowest resis tivity hydrostratigraphic un its in the upper confining zone. These units are excellent marker beds for interp retation of stratigraphy for the airborne survey in Medina County. Another low resistivity unit is associat ed with the upper-most unit of the lower member of the Glen Rose Limestone. This unit serves as an excelle nt marker unit for the bottom of hydrostratigraphic interval E of the Trinity aquifer in Bexar County. All of the units of the Edwards group have high resistiv ities but in Medina County the upper and lower Devils River can be separa ted on the basis of a lower overall resistivity of the upper unit in Me dina County. The Trinity aquifer (Gle n Rose Limestone) has a lower over all resistivity than the Edwards is consistent with its role as the lowe r confining unit. However, there are thin high resistivity limestone units in the upper zone that can be mapped in detail by the airborne geophys ics. Hydrostratigraphic unit D in the upper Trinity aquifer is characterized by a very high resistivity and can be used as a marker unit in stratigra phic interpretation. Current work is focusing on utilizing the detailed airborne resistivity surveys to refine bedrock geologic maps and construct 3D geologic models. This infor mation will be critical to future generations of groundwater mo dels of the Edwards Aquifer.

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42 Use of Helium Isotopes to Disc riminate Between Flow Paths Associated with the Freshwater/Sa line Water Transition Zone of the Edwards Aquifer, South-Central Texas. By Andrew G. Hunt1,Rebecca B. Lambert2, Gary P. Landis1, and John R. Waugh3 1 U.S. Geological Survey, MS 963, Bld. 21, Denver Federa l Center, Denver, CO 80225 2 U.S. Geological Survey, Texas Wa ter Science Center,5563 De Zavala Rd, San Antonio, TX 78249 3 San Antonio Water Systems, 1101 E. Market St., San Antonio, TX 78298 ABSTRACT The Edwards Aquifer currently is the primary source of water in south central Texas for agriculture, municipal, industrial, and ecological needs, supplyin g over 1.5 million people and supporting unique habi tats for endangered species. The aq uifer consists of limestone with so me dolostone members of the Edwards Group (lower Cretaceous) that dip in a southeasterly direction. Structura lly the aquifer is faulted by the Bal cones fault zone, a system of Miocene age normal faults that run parallel to the strike of the aquifer. The updip freshwater zone of the aquifer is recharged with su rface water along the northern area of the outcropping Edwards Group. Adjacent to the fre shwater zone is the sa line-water zone that forms an interface at the down-dip limit of the fresh water. Though the freshwater/saline-water in terface is spatially defined within the aquifer, little is known about the nature of groundwater flow between and along its surface. Concerns are that structural, lithologic and hydrologic feat ures and freshwater extraction may influence the possible up-dip migration of the sa line water into the freshwate r zone and may adversely affect current freshwater supplies. Discrete samples were taken from an existing monitoring well network representing a variety of differ ent flow regimes spanning the transition zone. The re sults show that the saline waters are overwhelmingly enriched in helium (up to 4000 times that of atmospheric sol ubility). Sources of helium in a ground water sample include atmospheric helium at solubility, helium associated with excess air incorporated during recharge, and excess helium derived from external sources such as release from the rocks that comprise the aquifer or a basal helium flux into the aquifer. In the fresh water zone, atmospheric solubility (R/R A ~ 0.989) and excess air sources (R/R A =1.0) characterize the compos ition of the helium isotopes in the samples. In the salin e waters, the externally so urced helium dominates the sample composition, with two distinctive end member compositions of 0.13 and 0.22 R/R A apparent from the data set. The unique isotopic ratio of the excess helium indi cates that the excess helium is mainly associated with a basal flux to the aquifer that appears to be geog raphically controlled by the Balcones fault system. This dichotomy in helium isotopic compositio ns allows us to use the helium data to deduce flow co mpartmentalization observed in the monitoring well transect s and estimate the influence of grou nd water flow and mixing within the freshwater/ saline water transition zone.

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43 Airborne and Ground Electrical Su rveys of the Edwards and Trinity Aquifers, Medina, Uvalde, and Bexar Counties, Texas By Bruce D Smith1, David V. Smith1, Jeffrey G. Paine2, and Jared D. Abraham1 1 U.S. Geological Survey, MS 964, Box 25046, Denver Federa l Center, Denver, CO 80225, 2 Bureau of Economic Geology, Jackson School of Geol ogical Sciences, The Univer sity of Texas at Austin, Univ. Station, Box X, Austin, TX 78713 ABSTRACT Helicopter electromagnetic (HEM) and magnetic surveys were flown in the Seco Creek area, (Medina and Uvalde Counties, TX, 2002) and in Northern Bexar County (TX, 2003). The purpose of these surveys was to map structure and lithology of the Edwards and Trinity aquifers consistin g of the catchment zone (Glen Rose, Trinity Group), recharge zone (Devils Ri ver, Edwards Group), and confined zone. The latter survey concentrated on Camps Stanley and Bullis, whic h are located mostly on the Glenn Rose. The south ern part of Camp Bullis includes the faulted contac t between the Edwards Grou p (recharge zone) and the catchment (Glenn Rose). Ground geophysical surveys at Seco Creek, conducted by the USGS in April 20 02, consisted of total field magnetics, dc resistivity and shallow terrain co nductivity measurements. In May 2003, BEG (Bureau of Economic Geology) acquired ground electrical co nductivity measurements at 379 locations. Re-mapping of the geology along the nine geophysical lines was done at the same time. The sh allow ground conductivity interpretations were supplemented by time domain EM (TDEM) soundi ngs by the USGS. Ground-based measurements demonstrate that (a) mapped geologic units consisting of Cretaceous age limestones and dolomitized limestones, marls, mudsto nes, shales, and Quaternary allu vial deposits have differences in apparent conductivity, (b) geologic st ructures such as faults and karst ca n have detectable apparent conduc tivity signatures, and (c) conductivity measurements can be combined with geologic maps and outcrop stud ies to identify hidden contacts, covered strata, and unmapped structural features. Limited comparisons of measurements confirm that the ground and airborne geoph ysical systems produce similar apparent electrical conductivities at comparable fre quencies and coil orientation. The ground based geophysical surveys refine the airb orne geophysical data, reve aling greater structural complexity than depicted in the original geologic mapping. Ramp structures are well defined by the geo physical surveys including a large complexly breached ramp along Seco Creek. The airborne geophysical data indicate a distinct difference in electrical resis tivity between the upper and lower Devils River forma tions in the recharge area. In additio n the electrical data have been used to map the subsurface configuration of upper confining clay units (Del Rio and Eagle Fo rd). The Glenn Rose formatio n has a lower resistivity than the Edwards group formations. A previously un known collapse feature in the study area is inferred from a high resistivity area along Seco Creek in the Trinity Aquifer. Geologic maps of four 7.5-minute quad rangles of the Seco Creek area have been digitized and revised based on the geophysical surveys. The geo physical data has been critical in the construction of a 3D geologic model of the study area because of deficient well data for subsu rface information and the extent of colluvi um hiding near surface structures and bedrock. Ground geophysical surveys can capture sma ll-scale lateral electrical conductivity changes, com plementing smoothed but spatially de nse airborne electrical conductivit y measurements. Airborne surveys cover large areas that are inaccessible or impractical to survey using ground-based instruments. They also provide aerial detail of the subsu rface not available from photo-geologic and other near-surface mapping methods.

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44 Magnetic Geophysical Applicatio ns Reveal Igneous Rocks and Geologic Structures in th e Edwards Aquifer, Texas By D.V. Smith1, C. Foss2, and B.D. Smith1 (Authors) 1 U.S. Geological Survey, Box 2504 6 MS964, Denver, CO 80225-0046 2 Encom Technology Pty Ltd, Level 2, 118 Alfr ed Street, Milsons Point NSW 2061, Australia ABSTRACT High-resolution aeromagnetic surveys were completed over the Edwards aquifer in Uvalde and Medina Counties west of San Antonio, Texas. These surveys have provided new information on the geology and structure of one of the most productive and permeable carbonate aquifers in the United States. A regional scale fixed-wing survey, flown in 2001, revealed the widespread occurance of sh allow igneous rocks. Geo physical interpretations show many of the magnetic anomalies to be vertical or subverti cal volcanic pipes. Other shallow anomalies are interpreted as sills, lava lakes and pyro clastic flows. The absence of dikes and dike-like structures leads to the hypothesis that the emplaced volcanic rocks affect ground water flow locally, but not significantly on a re gional scale. The interpreted intrus ive boundaries and geometry can be used in regional hydrologic models to evaluate th eir influence on ground water flow. Deeper seated anom alies are interpreted as magmatic reservoirs that perh aps served as sources for the late-Cretaceous volcan ism. A small scale very high resolution magnetic data set was acquired in 2003 as part of a helicopter elec tromagnetic survey of the North Seco Creek study area, which is outside th e main Uvalde volcanic field. In addition to a single small vo lcanic pipe, this data set reveals the tr ace of the Woodard Cave fault, a major normal fault juxtaposing the rocks of the Trinity Group, comp rising the upper Trinity aquifer to the north, with the Devils River Formation, cons tituting the Edwards aquife r to the south. This important finding, that a fault between adjoining limestone un its is associated with a linear ma gnetic low, led to a re-examination of the fixed-wing aeromagnetic da ta. Through careful microleveling, filtering and image enhancement tech niques, we see that major faults of the Balcones fault zone are associate d with vestigial magnetic lineaments on a regional scale.



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45 Structural Controls on Karst De velopment in Fractured Carbonate Rock, Edwards and Trinity Aquifers, South-Central Texas By Jason R. Faith1, Charles D. Blome2, Allan K. Clark1, George B. Ozuna1, and Bruce D. Smith2 1 U.S. Geological Survey, San Antonio, TX 2 U.S. Geological Survey, Denver, CO ABSTRACT The Edwards aquifer of south-central Texas lies within and adjacent to, the Ba lcones fault zone and is one of the most productive carbonate aquifers in the Un ited States. The Trinity aq uifer outcrops to the north of the Balcones fault zone and suppli es baseflow to streams flowing south over the Edwards recharge zone. The geology of Edwards and Trinity aquifers consists of approximately 400 meters of Lower Cretaceous carbonates with interbedded marl and dolostone. Miocene age faults w ithin the Balcones fault zone are en echelon exhibiting primarily normal displacement, trending northeast and downthrown to the southeast. Numerous cross-faults oriented perpendicular to the pr imary faults trend to the southeast. In the Edwards aquifer, cross-faults breach relay ramps between overlap ping faults, providing both a mechanical and hydro logic link between the primary faults. The fracturing within relay ramps an d adjacent to the primary faults in the Edwards aquifer is quite vari able, resulting in the development of circuitous and prolific ground-water flow paths. Because of the crys talline nature of the host rock an d the susceptibility of the carbonate strata to karst formation, the enhancement of secondary porosity and permeability in fracture zones an d fault planes is highly likely in both the Edwards and Trinity aquifers. Vertical displacement of the terrain from north to south by Balcones faults allows for steep hydraulic gradients to develop, maintaining high flow ve locities of meteoric ground water in the shallow sub-surface duri ng recharge events. Th is process of karst fo rmation resulting from the dissolution of fractures and enhancem ent of fracture zone permeability oc curs primarily parallel to the down-dip direction, along high-angle cross-faults and fracture zones that trend n early perpendicular to the regional ground-water flow direction. In both the Edwards and Trinity aquifers, a relation between fractures and faults and their susceptibility to dissolution by groundwater can often be observed in outcrop as recrys tallized calcite or cavities f illed with oxidized clays. Mapping in the Edwards and Trinity aquifer region in south-central Texas reveals a bimodal distribu tion of fracture zones and faults and corresponding cave passages oriented both parallel and nearly perpen dicular to the northeast-trending, primary faults. The most well-deve loped caves and solution zones are not aligned with the major fau lts, but are oriented along the northwest to southeast trend of cross-faults and shorter fracture zones, that parallel the down-dip dir ection of the Balcones fault zone, and are nearly per pendicular to regional ground-water flow direction. The location and extent of mo st sensitive karst features in the region are unmapped and those that are have no t been released to the pub lic. However, the fracture zones and faults that influence the location and di rection of secondary porosity development have been mapped; thus providing a representati ve surface expression of potential zones of karst enhanced fractures and highly developed cavern systems. Understanding the relation between these fracture zones/faults and the subsequent karst development can assist in the identification and qu antification of high volume, high velocity ground-water flow paths in the Edwards and Trinity aquifers.

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46 Simulating Ground-Water Flow in the Karstic Madison Aquifer using a Porous Media Model By L.D. Putnam and A.J. Long U.S. Geological Survey, 1608 Mountain Vi ew Road, Rapid City, South Dakota, 57702 Ground-water flow in karstic aquife rs is characterized by the prefer ential solution enlargement of frac tures and openings creating an integr ated network of conduits with rapi d flow. Although these conduits can be a predominant feature in characterizing ground-wat er flow, ground-water storage may occur primarily in the surrounding diffuse network of fractures and sm aller openings. A porous media model can provide a reasonable approximation of ground-water flow in th e diffuse network; however, simulation of conduit flow in conjunction with the diffuse flow is more problematic. Co mbinations of heterogeneity, anisotropy, flow barriers, and multiple model layers were used to simulate diffuse an d conduit ground-water flow in the karstic Madison Limestone near Rapid City, Sout h Dakota. The finite-di fference MODFLOW model included 140 rows, 110 columns, and 5 layers. Cells were 492 feet on a side in the Rapid City area and increased to 6,562 feet near the perimeter of the mode l. Transient calibration included a 10-year period with 20 stress periods of 6 months. Layers 3 and 4 represented the Madison Limestone with layer 3 representing the upper part of the formation that generally contains more karst features than th e less permeable lower part of the formation. Layers1 and 2 represented the overlying Minnelusa Formation, and layer 5 represented the underlying Deadwood Formation. High velocity flow paths in the Madison Limest one were simulated with conduit zones in layer 3 that were about 1,500 feet wide. Hydraulic conductiviti es within these zones ranged from about 65 to 1,150 feet/day comp ared to an average for the surroundin g area of about 35 feet per day. The average hydraulic conductivity of layer 4 was 0.32 feet/day. Anisotropy rati os aligned with the high velocity flowpaths ranged from 5:1 to 20:1. The Modflow horizontal flow barrier package was used to sim ulate the hydrologic effect of a fault. Ground-water tr acer studies, transient hydraulic heads, and springflow measurements were used to calibrate the model. Simulated ground-water velocities for high velocity flow paths were about 500 to 1,000 feet/d ay compared to observed dye tracer velocities that ranged from about 1,000 to 5,000 feet/day. For the tran sient simulation, the average differe nce between observed and simulated hydraulic heads for 269 measurements was 7 feet and the average absolute differ ence was 31 feet. Linear regression of the observed and simulated hydraulic heads had an R 2 of 0.92. Observed average springflow for the transient period was 21.6 cubic feet per secon d compared to simulated av erage springflow of 20.4 cubic feet per second.

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47 Dual Conductivity Module (DCM), A MODFLOW Package for Modeling Flow in Karst Aquifers By Scott L. Painter, Ronald T. Green, an d Alexander Y. Sun Geosciences and Engineering Division, Southwest Rese arch Institute, 6220 Culebra Road, San Antonio, Texas, 78238 ABSTRACT A MODFLOW module, DCM, has been developed to better represent the dynamic, multiple time-scale hydraulic response of karst aquifers. DCM adopts a dual -conductivity approach in which the aquifer is con ceptualized as being composed of two interacting flow systems a hi ghly transmissive conduit system embedded in a relatively low permeab ility diffuse flow system. This co upled-system conceptualization allows not only water levels, but also aquifer dynamics related to rapid conduit flows to be represented. The conduit system may be modeled as a pervasive (continuu m) system or as a sparse ne twork of individual con duits, depending on the scale of investigation and the natu re of the karst system being investigated. Conduits may be partially or fully filled with water, and transitions between the pa rtially filled and fully filled states are accommodated, which makes it possible to model high ly complex hydraulic responses. Flow in the con duit system may be turbulent, laminar, or transitional. Our preliminar y results show improved match to both water level measurements and spring discharges records.

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48 Conceptualization and Simulation of the Edwards Aquifer, San Antonio Region, Texas By R.J. Lindgren1, A.R. Dutton2, S.D. Hovorka3, S.R.H. Worthington4, and Scott Painter5 1 U.S. Geological Survey, 5563 De Zavala Road, Suite 290, San Antonio, TX 78249 2 The University of Texas at San An tonio, Department of Earth and En vironmental Sciences, 6900 N. Loop 1604 W., San Antonio, TX 78249 3 The University of Texas at Aust in, Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University Station, Box X, Austin, TX 78713 4 Worthington Groundwater, 55 Mayfair Avenue, Dundas, Ontario, Canada, L9H 3K9 5 Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 ABSTRACT A new numerical ground-water-flow model (Edwards aquifer model) that inco rporates important com ponents of the latest info rmation and a conduit-flow dominated co nceptualization of the Edwards aquifer was developed. The conceptualiza tion emphasizes conduit development and conduit flow, as opposed to predominately diffuse, porous-media flow. The model incorporates conduits simulated as generally contin uously connected, one-cell-wide (1,320 feet) zones w ith very large hydraulic-con ductivity values (as much as 300,000 feet per day). The locations of the conduits are based on a number of factors, including major potentiometric-surface troughs in the aquifer, the pr esence of sinking streams, geochemical information, and geologic structures (for example, faults and grabens). The model includes both the San An tonio and Barton Springs segments of the Edwards aquifer in the San Antonio region, Texas, and was calibrated for st eady-state (193946) and transient (1947000) con ditions. Transient simulations were conducted using monthly recharge and pumpage (withdrawals) data. The root mean square errors for hydraulic heads repres ent about 4 to 8 percent of the total head differences across the model area. The root mean square errors for Comal, San Ma rcos, San Antonio, and San Pedro Springs, as a percentage of the range of discharge fluctuat ions measured at each of the springs, are less than 10 percent. The simulated directions of flow in the Edwards aqui fer model are most strongly influenced by the pres ence of simulated conduits and barrier faults. The simu lated conduits tend to faci litate flow. The simulated subregional flow directions generally are toward the nearest conduit and subsequently through and parallel to the conduits from the recharge zone into the confined zone and toward the major springs. Structures sim ulated in the Edwards aquifer model th at tend to restrict ground-water fl ow are barrier faults. The influence of simulated barrier faults on flow directions is most evident in no rthern Medina County. INTRODUCTION The Edwards aquifer in the Balcones fault zone of south-central Texas (fig. 1) is one of the most per meable and most productive aquifers in the world. The sole source of drinking water supply in the San Antonio and Austin areas, the aquifer is critical to farming and ranching economies west of San Anto nio and recreational economies northeast of the city. There is also concern that drought or the increasing demand for ground water, or both, might result in the deterioration of habitats for several endangered spe cies. To evaluate the hydrologic response to various alternative proposals for managing the Edwards aquifer in the San Antonio region, the Edwards Aquifer Authority (EAA), to gether with other San Antonio water-resource managers and planners, expressed the need for an improved numerical ground-water-flow model. As a result of this need, a study was conducted from 2000 to 2003 by the U.S. Geological Survey (USGS) and The University of Texas at Austin, Bureau of Economic Geology

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49 (BEG), in cooperation with the U.S. Department of Defense (DOD) and the EAA; and a numerical ground-water-flow model w as developed (Lindgren and others, 2004). CONCEPTUALIZATION OF THE EDWARDS AQUIFER The conceptualization of the Edwards aquifer presented in Lindgren and others (2004) emphasizes conduit development and conduit flow. The degree to which conduits pervad e the Edwards aquifer and influence ground-water flow remains controversial, however. An alternate conc eptualization, which can be called the diffuse-flow conceptualization, reflects the hypothesis that, alth ough conduits likely are present, flow in the aquifer predominately is through a network of small fractures and openings suffi ciently numerous that the aquifer can be considered a porous-media continuum at the regional scale. Whether conduit flow or diffuse flow predominates at the regional scale is an open question. The Edwards aquifer is pa rt of an aquifer sys tem developed in thick an d regionally extensive Lower Cretaceous carbonates that underlie large areas of Texas. The gentle southeastward dip of Cre taceous strata in the Edwards Plateau and Hill Figure 1. Location of hydrogeologic zones, ground-water-flow model area, and physiographic regions, San Antonio region, Texas.

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50 Country is interrupted ac ross the Balcones fault zone by a system of en ec helon faults that generally strike northeastward (Mac lay, 1995). The Edwards aquifer is unconfined adjace nt to and in the outcrop (recharge zone) and confined in downdip parts of the Balcones fault zone by overlying hydrogeologic units of small to very small permeability. The con fined zone of the aquifer is defined on its downdip (gulfward) margin by a freshwater/saline-water transition zone of brackish water. The aquifer thick ness in the confined zone ranges from about 450 feet (ft) near the recharge zone in Bexar, Comal, and Hays Counties to about 1,100 ft in Kinney County. Permeability in the Edwards aquifer includes matrix, fracture, and co nduit permeability, varies more than eight orders of magnitude, and is multi modal with distinct but overlapping data populations (Hovorka and others, 1998). Mean hydraulic con ductivity of the confined zone (34 feet per day [ft/d]) is more than 120 times grea ter than mean hydraulic conductivity in the unconfined, or recharge, zone (0.28 ft/d) (Hovorka and others, 1998). Vertical variations in permeability in the Edwards aquifer indicate that the entire aqui fer is highly permeable, as well as highly variable. Painter and others (2002) estimated hydraulic conduc tivity for the Edwards aquifer in the San Antonio region using a combina tion of spatial statistical methods and advanced tech niques for automatic model calibration. The estimated hydraulic cond uctivity ranges from less than or equal to 20 to 7,347 ft/d. Hovorka and others (1998) reported that tran smissivity ranges from 10 -1 to 10 7 feet squared per day (ft 2 /d), and hydraulic conductivity ranges from 10 -3 to 10 5 ft/d, on the basis of specific-capacity and other aquifer tests. Evidence of the karstic nature of the Edwards aquifer includes outcrop ev idence, subsurface data, hydrologic evidence, and tracer tests. More than 400 caves have been inventoried in the Edwards outcrop (Veni, 1988; Elliott and Ve ni, 1994). Hovorka and others (1998) reported that in two-dimensional cross section, karst features make up 1 to 5 percent of the area of the outcrop. The existence of karst in the deep-subsurface saturated zone is known from bore hole televiewer images of caves and solutionenlarged fractures, cave textures and sediments recovered in cores, bit drops during well construc tion, and oversize caliper logs and off-scale porosity logs. Evidence of karst flow in the Edwards aquifer is the heterogeneous and rapidly responsive nature of water-level variation. Water levels in the aquifer and discharge at springs rise rapidly after rainfall and then decline at a variable rate, showing drainage from rocks characterized by both conduits and matrix permeability (Atkin son, 1977). Wells close together can have differe nt responses to a single recharge pulse (Johnson and others, 2002). Tomasko and others (2001) and Worthington (2004) docu mented rapid spring respon se to rainfall. Tracer test ing that began in the San Antonio segment of the Edwards aquifer has shown rapid flow from wells to the nearby high-flow springs (Ogden and others, 1986; Schindel and others, 2002). A regionally extensive system of high-perme ability zones (conduits) is defined by broad troughs in the potentiometric surface in the confined zone of the Edwards aquifer (Hov orka and others, 2004; Worthington, 2004). Particularly favorable locations for development of conduits are in grabens and syn clines (Worthington, 2004). In addition, high poros ity and permeability in th e deepest parts of the aquifer near the freshwater/saline-water transition zone, anomalously high well yields, and sharp chemical gradients all indi cate that conduit develop ment and flow might be focused in this area. The primary source of recharge to the Edwards aquifer is provided by seepage from streams cross ing the outcrop area (recharge zone). Estimates of the combined recharge to the San Antonio segment of the Edwards aquifer from stream seepage and infiltration of rainfall range from a low of 43,700 acre-feet (acre-ft) during 1956 to a high of 2,486,000 acre-ft during 1992 (Hamilton and others, 2003). The Edwards aquifer in ma ny areas in the Balcones fault zone is juxtaposed ag ainst the Trinity aquifer, both at the surface and at depth; therefore, the Trin ity aquifer likely discharges directly into the Edwards aquifer. Estimates of this flow range from 2 percent (LBG-Guyton Associates, 1995) to 9 per cent (Mace and others, 2000) of the average esti mated annual recharge to the Edwards aquifer.

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51 Most discharge from the Edwards aquifer occurs as: (1) springflow and (2) withdrawals by industrial, irrigation, and public-supply wells. Springflow totaled 69,800 acre-ft during the 1950s drought and reached a record high of 802,800 acreft in 1992 (Hamilton and others, 2003). Comal and San Marcos Springs are th e largest springs, with total discharges of 274,800 and 195,900 acre-ft, respectively, in 2002 (Ham ilton and others, 2003). Total ground-water withdrawals by wells increased steadily at an average annual rate of about 4,500 acre-feet per year (acre-f t/yr), more than tripling between 1939 and 2000. Water levels in the Edwards aquifer do not show a long-term decline as a result of ground-water withdrawals. The aquifer is dynamic, with water lev els generally responding to temporal variations in recharge and spatial distributions of ground-water withdrawals. During periods of drought, water lev els decline, but recover rapidly in response to recharge. The drought of the early 1950s is docu mented in well hydrographs by the downward trends of water levels at these we lls. The highest water lev els occurred in the early 1990s. Karstic conduits are majo r contributors of flow in the Edwards aquifer (Hovorka and others, 2004; Worthington, 2004). The contribution of matrix per meability to regional-scal e hydraulic conductivity likely is minor, and most Edwards aquifer water flows through fractures and conduits (Hovorka and others, 1998). Water enteri ng the Edwards aquifer in the recharge zone moves downdip from unconfined to confined parts of the aquifer through generally southeasterly flow paths. In the confined zone of the San Antonio segment of the aquifer, the water moves under low hydraulic gradients through frac tured, highly transmissive, cavernous strata toward the east and northeast, where it is discharged through springs (primarily Comal and San Marcos Springs) and high-capacity wells. In the Barton Springs seg ment of the aquifer, the ground-water-flow direction is generally to the east and northeast toward Barton Springs. Faults can either increase or decrease total transmissivity in the Edwards aquifer (Hovorka and others, 1998) and thereby tend to convey or to restrict flow. Some of the abundant, interconnected fractures in intensely fractured and brecciated zones adjacent to faults have been enlarged, and they might focus flow parallel to faults. Where calcite cement fills breccia, cross-fault flow might be decreased. Stratigraphic offset of permeable zones along faults might also decrease the cross-fault flow (Maclay and Small, 1986). Maclay (1995) and Groschen (1996) characteri zed flow in the Edwards aquifer as being controlled la terally by barrier faults that locally compartmenta lize, or restrict, flow within, to, and from parts of the aquifer, especially toward the eastern part of the San Antonio segment. SIMULATION OF GROUND-WATER FLOW A numerical model of ground-water flow was constructed on the basis of a conduit-flow domi nated conceptual model of the Edwards aquifer. The FORTRAN computer-model code MODFLOW (McDonald and Harbaugh, 1988; Harbaugh and McDonald, 1996; Harbaugh and others, 2000), a modular finite-difference ground-water-flow code developed by the USGS, was used to simulate ground-water flow in the Edwards aquifer. As a way to represent conduits, other than by use of a coupledcontinuum pipe flow or dualor triple-porosity model, conduits are simu lated in the Edwards aqui fer model by narrow (one-c ell wide), continuously connected zones with larg e hydraulic-conductivity values (fig. 2). Calibration and evaluatio n of the Edwards aqui fer model were conducted for steady-state (1939 46) and for transient (1 947) conditions. Once it was demonstrated that the model could approxi mate observed historical conditions (1947), the model then was used to simulate the effects of stresses for a time period not used initially for model calibration (model testing period, 1991000). Model Description The Edwards aquifer model area includes the San Antonio and Barton Springs segments of the Edwards aquifer. The model area was subdivided into rectangular finite-di fference grid cells within which the properties of the aquifer material repre sented are assumed to be uniform. The uniformly

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52 spaced finite-difference grid used to spatially dis cretize the model area has 370 rows and 700 col umns. The dimensions of the grid cells are uniformly 0.25 mile (mi) (1,320 ft ) along rows and columns, with about 33 percent of th e cells in the grid being active. The grid was rotated 35 degrees counter clockwise from horizontal to achieve the best align ment with the direction of ground-water flow and orientation of major faults near Comal and San Mar cos Springs. A single mode l layer was used to repre sent the multiple hydrogeolo gic units that comprise the Edwards aquifer. The Edwards aquifer was not discretized vertically becau se of a lack of sufficient hydrogeologic data needed to spatially define indi vidual hydrogeologic units within the geologic sec tion. Where possible, natural hydrologic boundaries were used to establish the ex tent of the active area of the Edwards aquifer model. The northern boundary of the model corresponds to the northern limit of the Edwards aquifer recharge zone. A head-dependent flux boundary (MODFLOW general-head boundary package) was used for the northern model boundary to account for the inflow of water from the adjacent Trinity aquifer. During transient simulation, the MODFLOW well package was used to simulate a constant flux, equal to the model-computed generalhead boundary flux of the steady-state simulation, through the northern mode l boundary for all stress periods. The northern part of the eastern model bound ary is defined by the location of the Colorado River, which is a regional sink for the Edwards aquifer. Stream-aquifer leakage is simulated in the model as head-dependent flux nodes using the MODFLOW river package (McDonald and Harbaugh, 1988). The southern part of the eastern model boundary (south of the Colorado River) was assigned a no-flow Figure 2. Simulated locations of conduits in the Edwa rds aquifer model, San Antonio region, Texas.

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53 boundary condition. The western model boundary coincides with the locatio n of a poorly defined ground-water divide near Brackettville in Kinney County (LBG-Guyton Associates, 1995). Minimal flow across this boundary was assumed and a noflow boundary condition was initially assigned. During model calibration, however, a specified-flux boundary, with inflow into the Edwards aquifer, was imposed for the northern pa rt of the boundary. The southern part of the boundary was maintained as a no-flow boundary. The southern Edwards aquifer boundary typi cally has been defined by the 1,000-milligrams per liter (mg/L) line of equal dissolved solids concentra tion, which coincides with the updip boundary of the transition zone (Schultz, 1993, 1994). The 10,000-mg/L concentrati on line (A.L. Schultz, con sultant, written commun., 2000) was used in the Edwards aquifer model as a more conservative boundary, constituting th e limit of ground-water flow in the freshwater zone of the aquifer. A no-flow boundary condition was imposed. The anisotropic effects of faults were incorpo rated in the Edwards aquifer model using the MOD FLOW horizontal-flow barrier package. The hydraulic characteristic of the barrier (fault) is an inverse measure of the degree to which it acts as a barrier to flow. The greater the assigned value for the hydraulic characteristic of the fault, the less it acts as a barrier to flow. For the model, the assump tion was made that the degree to which a fault acts as a barrier to ground-water flow is proportional to the fault displacement, with the hydraulic character istic of the barrier being in versely proportional to the fault displacement. The final calibrated hydraulic characteristic values assigned to simulated faults range from 1.0 x 10 -9 to 2.0 x 10 -2 days -1 The initial locations of conduit zones in the Edwards aquifer model were assigned on the basis of the conduit locations inferred by Worthington (2004, fig. 21). The confined-zone conduit segments are based on potentiometric-surface troughs, geo logic structure, and preferential development of con duits near the freshwate r/saline water transition zone. In addition, the ma jor sinking streams were interpreted to be connected to the major springs by conduits. During model calibration, revisions were made to the simulated co nduit segments, including the deletion of a northwest-southeast trending seg ment in southeastern Uvalde and northwestern Frio Counties (fig. 2). The hydraulic-conductivit y distribution for the Edwards aquifer model includes two components. The first component is th e hydraulic-conductivity distribution developed by Painter and others (2002). An approach based on nonparametric geostatistics, stochastic simulation, and numerical flow simula tion was used to upscale and interpolate hydraulicconductivity estimates to th e model grid. The second component, superimposed on the base distribution of Painter and others (2002), is the network of con duits, initially as inferred by Worthington (2004, fig. 21). For the Barton Spri ngs segment of the aqui fer, the hydraulic-condu ctivity distribution from Scanlon and others (2002), ra ther than that of Painter and others (2002), was used. Horizontal hydraulic conductivities were varied during model calibration to better match measured hydraulic heads and springflows. Hydraulic conductivities were decreased by varying amounts, as compared to the initial simulated values from Painter and others (2002), in Kinney County and south of the 1,000-mg/L dissolved so lids concentration line. Liedl and others (2003) and Worthington (2004) indicate that conduits increase in size or number, or both, in the di rection of downgradient springs. Therefore, the final calibrated hydraulic conductivities assigned to the conduits were: (1) 1,000 to 10,000 ft/d for the conduit segments originating in the rechar ge zone, farthest from Comal and San Marcos Springs and areas of lesser conduit development (Hovorka and others, 1998; Worthington, 2004), (2) 100,000 ft/d for the seg ments in the confined zone of the aquifer, but still distant from the major springs, and (3) 200,000 ft/d for the segments in the conf ined zone of the aquifer near the major springs. Storativity values, incl uding specific storage and specific yield, were assigned to each active cell for the transient simulations. Initially, uniform val ues for specific storage and specific yield were assigned, on the basis of reported values from

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54 previous numerical ground -water-flow models of the aquifer (Maclay and Land, 1988; Scanlon and others, 2002). Storativity values subsequently were varied during model calib ration, resulting in a zona tion of values. The final ca librated storativity zones include five zones for specific yield, ranging from 0.005 to 0.15, and five zones for specific storage, ranging from 5.0 x 10 -7 to 5.0 x 10 -6 ft -1 The storat ivity values of the simulated conduit cells are the same as the values for the non-conduit cells in the storativity zone in whic h the conduit cells occur. A specified-flux bounda ry, simulated using the MODFLOW recharge package, was used to repre sent recharge to the Edward s aquifer in the recharge zone (McDonald and Harbaugh, 1988). Simulated recharge to the aquifer by seepage from streams and infiltration of rainfall was assigned to cells in the recharge zone for eight major recharging streams and their interstream are as (recharge subzones), on the basis of annual recharge rates to the Edwards aquifer calculated by the USGS for 1934000. Average annual recharge rates during 1939 were applied for the steady-state simulation. Monthly recharge rates were applied for the transient simula tion (1947-2000). The simulated annual and monthly recharge rates for six recharge basins in the Barton Springs segment of the aquifer were derived from published rates in Slade and others (1986) and unpublished rates compile d by B.R. Scanlon (Uni versity of Texas, Bureau of Economic Geology, written commun., 2001). Fo r both the San Antonio and Barton Springs segment s, 85 percent of the recharge was applied to streambed cells and the remaining 15 percent app lied to the interstream cells. As a result of model calibration, the simulated recharge rates for periods of greatly above-normal rainfall and recharge were reduced, as compared to reported rates. The USGS reported monthly recharge rates for the years 1958, 1973, 1981, 1987, 1991, and 1992 were multip lied by factors ranging from 0.60 to 0.85. The reported annual recharge for each of these years was greater than 1,400,000 acreft. The USGS reported recharge rates for the Cibolo Creek and Dry Comal Creek recharge subzone were reduced by 50 percent for all stress periods. The primary simulated discharges of water from the Edwards aquifer are withdrawals by wells and springflows. The MODFLOW well package was used to simulate the withdrawals by wells. As with recharge, average withdrawal rates during 19396 were used for steady-state simulations, and monthly rates were assigned for each stress period of the transient simulation. Co mal, San Marcos, Leona, San Antonio, and San Pedro Springs were simulated in the Edwards aquifer mo del and used for model calibration. The springs we re simulated in the model using the MODFLOW drain package. Model Calibration The steady-state calibration targets for the Edwards aquifer model in clude: (1) average mea sured water levels during 193946 in 144 wells and (2) median springflows during 1939 for Comal, San Marcos, Leona, San Antonio, and San Pedro Springs. The mean absolute difference between sim ulated and measured hydraulic heads is 19.4 ft, and the mean algebraic difference is 4.5 ft, indicating the positive differences were approximately balanced by the negative differences. The root mean square (RMS) error for the 144 targ et wells is 26.5 ft, rep resenting about 4 percent of the total head difference across the model area. The closest-match simulated springflows were within 3 and 13 percent of the measured median springflows for Comal and San Marcos Springs, respectively. The transient calibration targets include: (1) synoptic sets of water levels in multiple wells during periods of below-normal and above-normal rainfall (potentiometric surface maps), (2) a series of mea surements of water level within single wells over time (hydrographs), and (3) springflows for 1947 2000 for Comal, San Marcos, Leona, San Antonio, and San Pedro Springs. Th e closest-match simulated hydraulic heads for the transient simulation for a period of below-normal rainfall (MayNovember 1956, during the 1950s drought, when the lowest water levels on record were recorded) were within 30 ft of measured water levels at 123 of the 172 wells for which water-level data were available. The RMS error is 58.7 ft, representing about 8 percent of the total head difference across the model area. The closest-match simulated hydraulic heads for a period of above-normal rainfa ll (November 1974July 1975, a period of near record-high water levels in

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55 wells) were within 30 ft of measured water levels at 129 of the 169 wells for wh ich water-level data were available. The RMS error is 33.5 ft, representing about 5 percent of the total head difference across the model area. The transient simulation for 1947000 accept ably reproduces measured fluctuations in hydraulic heads in the Edwards aquifer. The match between simulated and measured hydraulic heads is generally closer for wells completed in the confined zone of the aquifer than for those in and near the recharge zone. The RMS error ranged from 4.1 to 23.2 ft in 11 wells with water-level measurements for varying periods during 1947000; these errors represent 7.8 to 30.8 percent of the range in water-level fluc tuations of each well. Generally acceptable agreement also was obtained between simulated and measured spring flow at the simulated spri ngs. The RMS errors for Comal, San Marcos, Leona, San Antonio, and San Pedro Springs ranged from 230,700 cubic feet per day (ft 3 /d) for San Pedro Springs to 3,967,000 ft 3 /d for Comal Springs. The RM S errors for the five springs, as a percentage of the range of springflow fluctuations measured at th e springs, varied from 7.0 percent for San Marcos Spri ngs to 36.6 percent for Leona Springs and were less than 10 percent for all but Leona Springs. The mean algebraic differences between simulated and measured spring discharges are 6.7 and 15.0 ft 3 /s for Comal and San Marcos Springs, respectively, indicating a small bias in the residuals toward high flows. Model Results A ground-water divide in the Edwards aquifer occurs near Kyle in south-central Hays County, from which ground-water flow is to the east toward Barton Springs or to the west toward San Marcos Springs. Model simulation results indicate that the position of this ground-water divide varies, depend ing on the water-level co nditions. For steady-state and above-normal rainfall and recharge conditions, the simulated position of th e ground-water divide is coincident with its common ly defined position near Kyle. In contrast, during drought conditions the position of the simulated gr ound-water divide shifts westward to near San Marcos Springs. Simulation results indicate that the simulated flow in the Edwards aquife r model is strongly influ enced by the locations of the simulated conduits, which tend to convey flow. The simulated subre gional flow directions are generally toward the near est conduit and subsequen tly along the conduits from the recharge zone into the confined zone and toward the major springs. The influence of simu lated barrier faults on flow directions is most evident in northern Medina County. In this area, the direc tion of ground-water flow is affected primarily by parallel northeastward-strik ing faults and conduit segments that divert the flow toward the southwest. For the steady-state simulation, recharge accounts for 93.5 percent of the sources of water to the Edwards aquifer, and inflow through the north ern and northwestern model boundaries contributes 6.5 percent. The largest discharges are spring dis charge (73.7 percent) and ground-water withdrawals by wells (25.7 percent). The principal source of water to the aquifer for th e transient simulation is recharge. The principal discharges from the aquifer for the transient simulation are springflows and withdrawals by wells. During 1956, representing drought conditions, the change in storage (net water released from storage) is much greater than recharge, comprising 75.9 percent of the total flow compared to 14.5 percent for recharge. Conversely, during 1975, representing above-normal rainfall and recharge conditions, recharge constitutes 79.9 per cent of the total flow comp ared to 7.1 percent for the change in storage (net water added to storage). A series of sensitivity tests were made to ascer tain how the model results were affected by varia tions greater than and less than the calibrated values of input data. Simulated h ydraulic heads and spring discharge in the Edwards aquifer model were most sensitive to recharge, withdrawals, hydraulic con ductivity of the conduit segm ents, and specific yield; and comparatively insensitiv e to spring-orifice con ductance, northern boundary inflow, and specific storage. Larger values of hydraulic conductivity, coupled with reduced recharge because model cells went dry, resulted in smal ler simulated springflows.

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56 If the reduced recharge is accounted for, however, larger values of hydraulic conductivity result in increased springflows. The effect of lowering the simulated spring-orifice altitudes of Comal and San Marcos Springs was to ap preciably lower simulated hydraulic heads in the aq uifer, because the springorifice altitudes serve as a controlling base level for hydraulic heads in the aqui fer. The effect on simu lated springflow was to minimally increase spring flow for Comal Springs and appreciably decrease springflow for Leona Springs. REFERENCES Atkinson, T.C., 1977, Diffuse flow and conduit flow in limestone terrain in the Mendip Hills, Somerset (Great Britain): Journal of Hydrology, v. 35, no. 1, p. 93-110. Elliott, W.R., and Veni, George, eds., 1994, The caves and karst of TexasGuidebook for the 1994 conven tion of the National Spel eological Society with emphasis on the southweste rn Edwards Plateau: Hunts ville, Ala., National Spel eological Society, 342 p. Groschen, G.E., 1996, Hydrogeol ogic factors that affect the flowpath of water in se lected zones of the Edwards aquifer, San Antonio region, Texas: U.S. Geological Survey, Water-Resources Investigations Report 96 4046, 73 p. Hamilton, J.M., Johnson, S. Esquilin, R., Thompson, E.L., Luevano, G., Wiatrek, A., Mireles, J., Gloyd, T., Sterzenback, J., Hoyt, J.R., and Schindel, G., 2003, Edwards Aquifer Authority hydrogeological data report for 2002: San Antonio, Tex., Edwards Aquifer Authority, 134 p. [Available online at www.edward saquifer.org.] Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, M.G., 2000, MODFLOW2000, the U.S. Geological Survey modular ground-water modelUser guide to modularization concepts an d the ground-water flow process: U.S. Geological Survey Open-File Report 00-92, 121 p. Harbaugh, A.W., and McDona ld, M.G., 1996, Users documentation for MODFLO W, an update to the U.S. Geological Survey modular finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 96485, 56 p. Hovorka, S.D, Mace, R.E., an d Collins. E.W., 1998, Per meability structure of the Edwards aquifer, south TexasImplications for aquifer management: Austin, University of Texas, Bureau of Economic Geology Report of Investigations 250, 55 p. Hovorka, S.D., Phu, T, Nicot, J.P., and Lindley, A., 2004, Refining the conceptual mode l for flow in the Edwards aquiferCharacterizing the ro le of fractures and con duits in the Balcones fault zone segment: Contract report to Edwards Aquifer Authority, 53 p. Johnson, S.B., Schindel, G. M., and Hoyt, J.R., 2002, Ground-water chemistry ch anges during a recharge event in the karstic Edwards aquifer, San Antonio, Texas: Geological Societ y of America, Online Abstract 186. LBG-Guyton Associates, 1995, Edwards aquifer groundwater divides assessment, San Antonio region, Texas: San Antonio, Edwards Underground Water District Report 9501, 35 p. Liedl, R., Sauter, M., Hckin ghaus, D., Clemens, T., and Teutsch, G., 2003, Simulation of the development of karst aquifers using a coupled continuum pipe flow model: Water Resources Research, v. 39, no. 3, p. 1,057,067. Lindgren, R.J., Dutton, A.R., Hovorka, S.D., Worthing ton, S.R.H., and Painter, Scott, 2004, Conceptualiza tion and simulation of the Edwards aquifer, San Anto nio region, Texas: U.S. Geological Survey Scientific Investigations Report 20045277, 143 p. Mace, R.E., Chowdhury, A.H. Anaya, Roberto, Way, S.C, 2000, Groundwater availability of the Trinity aquifer, Hill Country ar ea, TexasNumerical simula tions through 2050, Texas Water Development Board Report 353, 169 p. Maclay, R.W., 1995, Geology and hydrology of the Edwards aquifer in the San Antonio area, Texas: U.S. Geological Survey Water-R esources Investigations Report 95 4186, 64 p. Maclay, R.W., and Land, L.F., 1988, Simulation of flow in the Edwards aquifer, San Antonio Region, Texas, and refinements of storage and flow concepts: U.S. Geological Survey Water-Supply Paper 2336A, 48 p. Maclay, R.W., and Small, T.A., 1986, Carbonate geology and hydrology of the Edwards aquifer in the San Antonio area, Texas: Texas Water Development Board Report 296, 90 p.

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57 McDonald, M.G., and Harbaugh, A.W., 1988, A modular three-dimensional finite-difference ground-water flow model: U.S. Geological Surv ey, Techniques of WaterResources Investigations, book 6, chap. A1 [variously paged]. Ogden, A.E., Quick, R.A., Rothermel, S.R., and Lunds ford, D.L., 1986, Hydrological and hydrochemical investigation of the Edwards aquifer in the San Marcos area, Hays County, Texas: San Marcos, Tex., Edwards Aquifer Research and Data Center, 364 p. Painter, Scott, Jiang, Yefang, and Woodbury, Allan, 2002, Edwards aquifer parameter estimation project final report: Southwest Research Institute [variously paged]. Puente, Celso, 1978, Method of estimating natural recharge to the Edwards aq uifer in the San Antonio area, Texas: U.S. Geological Survey Water-Resources Investigations Report 7810, 34 p. Scanlon, B.R., Mace, R.E., Smit h, Brian, Hovorka, S. D., Dutton, A.R., and Reedy, R.C., 2002, Groundwater availability of the Barton Springs segment of the Edwards aquifer, TexasNumerical simulations through 2050: Austin, Universi ty of Texas, Bureau of Economic Geology, final report prepared for Lower Colorado River Authority under contract no. UTA99 0, 36 p. Schindel, G.M., Johnson, S.B., Worthington, S.R.H., Alexander, E.C., Jr., Alexander, Scott, and Schnitz, Lewis, 2002, Groundwater flow velocities for the deep artesian portion of the Ed wards aquifer, near Comal Springs, Texas, in Annual Meeting of the Geological Society of America, Denv er, Colo., October 2730, 2002: Geological Society of America Abstracts with Programs, v. 34, no. 6, p. 347. Schultz, A.L., 1993, Defining the Edwards aquifer fresh water/saline-water interface wi th geophysical logs and measured data (San Antonio to Kyle, Texas): San Antonio, Edwards Underground Water District Report 936, Texas, 81 p. Schultz, A.L., 1994, 1994 review and update of the posi tion of the Edwards aquifer freshwater/ saline-water interface from Uvalde to Kyle, Texas: San Antonio, Edwards Underground Water District Report 945, 31 p. Slade, R.M., Jr., Dorsey, M.E. and Stewart, S.L., 1986, Hydrology and water quality of the Edwards aquifer associated with Barton Sp rings in the Austin area, Texas: U.S. Geological Survey, Water-Resources Investigations Report 8636, 96 p. Tomasko, David, Fisher, AnnMarie, Williams, G.P, and Pentecost, E.D, 2001, A statistical study of the hydro logic characteristics of the Edwards aquifer: Chicago, Argonne National Labs, 38 p. Veni, George, 1988, The caves of Bexar County (2d ed.): Austin, University of Texas, Texas Memorial Museum Speleological Monograph 2, 300 p. Worthington, S.R.H., 2004, Conduits and turbulent flow in the Edwards aquifer: Worthington Groundwater, contract report to Edwards Aquifer Authority, San Antonio, Tex., 41 p.

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58 The Role of MODFLOW in Numerical Modeling of Karst Flow Systems By J.J. Quinn, D. To masko, and J.A. Kuiper Environmental Assessment Division, Argonne Na tional Laboratory, Argonne, IL 60439 ABSTRACT Mixed-flow karst systems convey groundwater thro ugh a combination of conduit and diffuse flow. Building a conceptual model of the fl ow system is possible, but advancin g to the next stage, a numerical model, poses difficulties because of th e complexities inherent to karst fl ow. Yet a numerical model may be desired to test the conceptual model, qu antify fluxes, and identify data gaps. Approaches to modeling karst flow have included the equivalent porous medium approach, black box reproductions of input and spring discharge, very hi gh hydraulic conductivity fl owpaths, fracture network simulations, and open channel equiva lents. These are discussed in gr eater detail in Quinn and Tomasko (2000). All of these methods have advantages and disadvantages relevant to a given modeling purpose. Numerical models of karst flow systems have traditionally relied on high-permeability zones to handle the karstified portion of a carbonate system, and spring s have been represented by a single model feature, such as a drain cell, at the spring location. This ap proach, however, ignores the bulk of the flow from the conduit system. The question remains whether numeri cal models, such as the U.S. Geological Surveys MODFLOW, are suitable for creating models of karst flow systems. This study illustrates a method of numerical modeling that has perform ed well in two case studies, one in Missouri and one in Germany. In each case, the conduit system is in ferred by a variety of indirect evi dence and modeled using MODFLOW as a network of connected drains feeding each outflow spring. INTRODUCTION The modeling of groundwater flow in karst aquifer systems is di fficult because of the complexities of conduit geometries and arrange ment and the relationship between diffuse and con duit flow within the aquifer. From local to regional scale, models constructed in karst settings require assumptions regarding the flow regime, as well as supporting data, some of which may be unavailable. Numerical modeling of karst flow has nonethe less been attempted with a variety of approaches in twoor three-dimensional models of local to regional scale. Finite element examples include Laroque et al. (1999, 2000), who modeled springs as constant head locations, and Gonzalez-Herrara et al. (2002), who modeled karst features in a regional study area using equivalent porous media and large element dimensions. Examples of MODFLOW used in porous media are al so in the literature (e.g. Witkowski et al. 2003, Guvanasen et al. 2000, Scanlon et al. 2003, Zhang and Keeler 1998, Lan gevin 2003, and Sepulveda 2002). Several of these papers are cases in which each spring was simulated as a single model cell with a MODFLOW drain (Scanlon et al. 2003, Sepu lveda 2003) or with a MODFLOW general head boundary (Zhang and Keeler 1998). The approach of equivalent porous media with a single model feature representing each spring is limiting and generally restricted to regional water resources st udies, and is not useful for local issues such as flow directions, flow rates, protection zone delineation, or point source con tamination modeling (Scanlon et al. 2003, Langevin 2003). APPROACH In several examples di scussed above, conduit flow was modeled by installing a drain or general head feature at a spring location. Calibration was achieved by adjusting hy draulic conductivity in a zone upgradient from the spring. However, this

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59 technique ignores the rapid discharge to a conduit system laced throughout la rge portions of the aqui fer. Our approach relies on a conceptually more complete modeling of the inferred or estimated con duits. They are modeled as continuous, branching networks of MODFLOW drain cells. In this man ner, diffuse discha rge throughout the aquifer has the potential to reach tributar ies of the conduit system, to be essentially removed from the flow system, and to be accounted for as discharge at the outlet spring in combination with all contributing conduit branches. The MODFLOW drain package was originally developed to simulate drain tiles; however, it is a reasonable analogue for conduits in karst. Two types of information are needed as drain input. Drain elevations must be specified along a modeled conduit. At the downgradie nt end, these are set to the elevation of discharge spring, while at the upgra dient locations, the elevations are specified based on drilling data. The second type of input is drain con ductance. Setting this term to a high value promotes removal of water from flow system, and the model is insensitive to chan ges in its value. This approach is geared toward solving a mixed-flow karst system, w ith equipotentials within the diffuse portion of the aquifer matrix bending at conduits (e.g., Field 1993, Quinlan and Ewers 1985). The Groundwater Modeling System (GMS) is used as a preand post-processor. GMS assigns ele vations along the drain segments by performing lin ear interpolation between the nodes of a branching system of drains. Model calibration is made by manually adjust ing elevations of drains, hydraulic conductivity, and recharge to match target heads and fluxes (spring outflow), or by parameter estimation of aquifer and recharge parameters. SOURCES OF INPUT Critical to implementing this approach is esti mating or inferring the loca tions of conduits within the karst terrain. Drain networks were assigned in each study area by relying on available data, which could include dye tracing results, geophysical anom alies (lineaments), surficial features (dry valleys, fractures, sinkholes), spring locations, and spring flow measurements. For assigning initial drain elevations, drilling data is used to estimate the depth of the weathered/ unweathered contact within the carbonate. Initial values of hydraulic cond uctivity are assigned to zones on the basis of aquifer testing data. MISSOURI CASE STUDY This site, located on the Burlington-Keokuk limestone of Missouri, has in put data in the form of numerous dye traces conducted by the Missouri DNR (Figure 1), a main spring with a long outflow monitoring record, abundant aquifer test data (Fig ure 2), widespread drilling data to determine the depth of the weathered zone many monitoring wells for calibrating heads (Figure 3), and infiltration field studies to address specific site features. On the basis of drilling data and aq uifer testing, the model ing included two layers: a deeper unweathered unit and a shallower weathered unit. Figure 1. Site setting and results of Missouri DNR tests. Calibration to the target head surface and to average flux at the main spring to the north was made by adjusting drain elevations. The resulting calibrated model (Figure 4) provided a strong match

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60 to target heads and to spring outflow. Details of this study are provided in Quinn and Tomasko (2000). The flow model was used in an application to deter mine the effect a disposal cell would have on the local flow system. GERMANY CASE STUDY This site is the Hohe nfels Combat Maneuver Training Center (CMTC), located on the Malm For mation of Bavaria (Figure 5). Portions of the study area have been intensivel y investigated by geophys icists of Argonne National Laboratorys Energy Systems Division. Their re sults identified numerous anomalies attributed to the presence of karst con duits (Figure 6). The site is primarily comprised of carbonates of the Malm Formation. The site characterization also includes several dye tracing experiments (Figure 7), limited coverage of monitoring wells and target head data, several measurements of spring flow, and detailed physical feature mapping (sinkholes, dry valleys) only on the training center property. The MODFLOW model of 610 600 600 590 590 580 580 570 560 560 560 550 540 530 520 510 500 Surface WaterContour interval = 10 feetMonitoring Well Location Surface WaterOne inch equals approx. 135 feet. Monitoring Well Location Disposal Cell 30 ft/d 3 ft/d 1.6 ft/d (most of modeling domain) Figure 2. Hydraulic conductivity distribution of upper model layer, based on aquifer testing. Figure 3. Target heads and monitoring well locations. Figure 4. Missouri site calibrated heads. Figure 5. CMTC, Lautertal, and regional features.

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61 this site included the en tire CMTC site and extended to several external areas to make use of regional groundwater divides as boundary conditions. Drains were included in the finite-difference model on the basis of the dye traces, geophysical linea ments, and valley orientations. Figure 6. Drain cells and geophysical lineaments. Figure 7. Hydraulic connections established through dye tracing. The focus of the field and modeling efforts was a portion of the CMTC calle d the Lautertal. Here, model results clearly show the influence of the inter connected drain cells laced through the aquifer (Fig ure 8). Because of the sparse amount of target head data at the site, detailed calibration was not possible. However, the resulting heads of the calibrated model provide an adequate match to the available data in the area most intensively characterized with physi cal features mapping, geophysics, and tracer tests. Drain output matched reasonably well with spot measurements of outflow at several springs. Details of this study are provid ed in Quinn and Tomasko (2000) and Quinn et al. (in review). CONCLUSIONS Results from applying the technique of inter connected MODFLOW drain cells have shown promise in two case studies in mixed-flow karst ter rain. Calibration to both target heads and target spring fluxes is achievable, though the calibration of transient models to varying spring discharge has not yet been attempted. This approach is more realistic compared to other numerical approaches and has served well to test conceptual models and identify data gaps at two sites. It is also easy to implement with currently available software. The accuracy of the method depends on the coverage of quality field data, espe cially dye tracing, geophysics, hydraulic conductiv ity estimates, and target heads and fluxes (spring outflow). An advantage of this method is that the modeling is performed with out detailed information on the geometry of the conduits, which is difficult or impossible to obtain. Geophysical Lineament Ephemeral Stream Beds Drain Cell 0 km 5 L a u t e r a c hF o r e l l e n b a c h C r e e k Lautertal study area R i v e rR i v e r Allersburg Hohenburg AdertshausenL a u t e r a c hR i v e r Lautertal 0 km 1 Geophysical Lineament Ephemeral Stream Beds Drain CellFigure 8. Zoom view of flow vectors near Lautertal, illustrating the relationship between the drain locations and the flow field.

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62 REFERENCES Field, M.S., 1993. Karst hydrology and chemical contam ination. Journal of Environmental Systems, 22 (1), 126. Gonzalez-Herrara, R., Sanchezy-Pinto, I., and GamboaVargas, J., 2002, Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico: Hydrogeology Jour nal, vol. 10, p. 539-552. Guvanasen, V., Wade, S.C., and Barcelo, M.D., 2000, Simulation of Regional Ground Water Flow and Salt Water Intrusion in Hernando County, Florida: Ground Water, vol. 38, no. 5, p. 772-783. Langevin, C.D., 2003, Simulation of submarine ground water discharge to a marine estuary: Biscayne Bay, Florida: Ground Water, vol. 41, no. 6, p. 758-771. Larocque, M., Banton, O., and Razack, M., 2000, Tran sient-State History Matching of a Karst Aquifer Ground Water Flow Model: Ground Water, vol. 38, no. 6, p. 939-946. Larocque, M., Banton, O., Ackerer P., and Razack, M., 1999, Determining karst tranmissivities with inverse modeling and an equivalent porous media: Ground Water, vol. 37, no. 6, p. 897-903. Quinlan, J.F. and Ewers, R.O., 1985. Ground water flow in limestone terraces: strate gy, rationale and procedure for reliable, efficient monitoring of ground water qual ity in karst areas. In: Pro ceedings, Fifth National Sym posium on Aquifer Restoration and Ground Water Monitoring. National Water Well Association, Dublin, Ohio, pp. 197-234. Quinn, J. and Tomasko, D., 2000, A Numerical Approach to Simulating Mixed Flow in Karst Aquifers, in I. Sasowsky and C. Wicks, ed s., Groundwater Flow and Contaminant Transport in Carbonate Aquifers: Rotter dam, Holland, A.A. Balkema, p. 147-156. Quinn, J.J., Tomasko, D., an d Kuiper, J.A., in review, Modeling Complex Flow in a Karst Aquifer: submitted to Sedimentary Geology. Scanlon, B.R., Mace, R.E., Ba rrett, M.E., and Smith, B., 2003, Can we simulate regional groundwater flow in a karst system using equivalent porous media models: Case study, Barton Springs Edwards aquifer, USA: Journal of Hydrology, vol. 276, p. 137-158. Sepulveda, N., 2002, Simulation of ground-water flow in the Intermediate and Floridan Aquifer Systems in Pen insular Florida: U.S. Geological Survey, WaterResources Investigations Report 02-4009. Witkowski, A.J., Rubin, K., Kowalczyk, A., Rozkowski, A., and Wrobel, J., 2003, Groundwater vulnerability map of the Chrzanow karst-fissured Triassic aquifer (Poland): Environmental Geology, vol. 44, p. 59-67. Zhang, Y.-K., and Keeler, R., 1998, Modeling of ground water flow with MODFLOW in a fractured-karst aqui fer in the Big Spring Basi n, Iowa: Proceedings of MODFLOW `98: Golden, CO, International Ground Water Modeling Center, p. 149-156.



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63 The Case of the Underground Passage: Putting the Clues Together to Understand Karst Processes By B. Mahler1, B. Garner1, and N. Massei2 1 U.S. Geological Survey, 8027 Exch ange Drive, Austin, TX 78754 2 UMR 6143 M2C, Dpartement de Gologie, Universit de Rouen, 76821 Mont Saint-Aignan cedex, France ABSTRACT Contaminants in surface water entering karst aquifers in focused recharge can be transported rapidly through the system to discharge at springs. Such c ontaminants act as anthropogenic tracers of ground-water transport; analysis of their breakthrough curves as they discharge from springs allows identification and ap portionment of contaminant sources, and can provide insigh t into aquifer structure and fu nction. At Barton Springs, th e principal outlet for the Bar ton Springs segment of the Edwards aqui fer, near Austin, Texas, breakthrou gh curves for several anthropogenic and natural tracers have been analyzed. The proportion of dischar ge composed of recent recharge is determined with a mix ing model for oxygen-18: following rainfall an initial increase in discharge related to pressure transfer is clearly seen, followed by a further increase consisting of an increasing proportion of recently recharged water, which reaches a max imum about 48 hours after rainfall. First appearance of contaminants varies from less than 20 to more than 40 hours after rainfall, depending on the contam inant, aquifer conditions, and location of contaminant so urce. Decomposition of breakthrough curves of sediment, nutrients, pesticides, and volatile organic compounds at the different spring ori fices indicates the existence and approxim ate location of multiple conduit flow ro utes, contaminant times of travel, and probable contaminant sources. Differences in breakthroug h curve shape and magnitude indicate urban runoff, contam inant spills, and infiltration through th e soil zone as sources of different co ntaminants. Comparison of contaminant loads in recharging surface water to those estimated for th e decomposed breakthrough cu rves allows apportionment of contaminants to the five watersheds contributing recharge to the aquifer.

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64 Spatial and Temporal Variations in Epikarst Storage and Flow in South Central Kentuckys Pennyroyal Plateau Sinkhole Plain By Chris Groves 1 Carl Bolster 2 and Joe Meiman 3 1 Hoffman Environmental Research Institute, Western Kentucky University, Bowling Green KY 42101 2 USDA ARS Animal Waste Management Research Unit, Bowling Green KY 42104 3 Division of Science and Resource Management, Mammoth Cave National Park, Mammoth Cave, KY 42259 ABSTRACT The well-developed karst aquifers of south centra l Kentuckys Pennyroyal Plateau are impacted by contamination from animal waste and other agricultural inputs. Understand ing fate and transport of these and other contaminants first requires knowledge of flow and storage behaviors within the impacted aquifers, complicated by signif icant heterogeneity, anisotropy, and rapid temporal variations. Here we report on spatial and temporal variations in vadose zone flow and water chemistry (or quality ) within Cave Spring Caverns, Kentucky beneath agricultural lands on a we ll-developed sinkhole plai n. Weekly sampling of three underground waterfalls show statistically significant differences in water quality, though the sites are laterally within 160 m and are all located about 25 m underground, in a groundwater basin of about 315 km 2 These reflect a combination of differences in epikar st flow and land use abov e the cave. High-resolution (minutes) monitoring of precipitation recharge along with flow and specific conductance in one of the waterfalls reveals a significant storage and mixing reservoir within the soil /epikarst zone. Varying precipitation rates and antece dent moisture conditions result in a ra nge of storm responses observed at the waterfall, depending in part on whether this reservoi r is filled or depleted. Slow and rapid flow paths through this storage zone were observ ed, the latter triggered by high rech arge rates. These observations are generally consistent with the interpretations of Perrin and others (2003) from a Swiss limestone aquifer in a somewhat different hydrogeologic se tting, strengthening the idea that ep ikarst and, more generally, vadose zone storage play a key role influencing flow and transport within karst aquifer systems. INTRODUCTION Well-developed karst aquifers are extremely vulnerable to contamination due to the ease and rapidity with which fluids can enter and move through these systems. Fo r example, within south central Kentuckys Pennyroyal Plateau, contamina tion of groundwater by ag ricultural contaminants associated with animal wast e such as fecal bacteria and nitrate is widespread (Currens, 2002; Conrad and others, 1999). Understanding agricultural impacts on karst aquifers is particularly challenging due to significant heteroge neity and anisotropy typ ically found in these system s, which can lead to large spatial and temporal varia tions in flow and water chemistry conditions. The epikarstic, or subcutaneous zone (Will iams, 1983; Perrin and others, 2003; Jones and oth ers, 2003) forms an impo rtant component of many karst flow systems. The ty pically perched epikarst aquifer forms in the vici nity of the soil/bedrock interface where fractures have been widened from dissolution by acidic soil water. As the infiltrating water quickly approaches equilibrium with respect to the limestone bedrock, dissolution rates drop, as does solutionally-enhanced permeability. As a result the epikarst constitutes a relatively high permeabil ity zone in comparison w ith less permeable rocks below. Evaluating the impacts of epikarst flow and storage is critical for understanding the fate and transport of agricultural co ntaminants within karst aquifers.

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65 Recently progress has been made in under standing the details of karst flow and geochemical processes by high-resolution monitoring with elec tronic probes and digital da ta loggers (e.g. Baker and Brunsdon, 2003; Charleton, 2003; Groves and Meiman, 2005; Liu and others, 2004). The impor tance for understanding karst dynamics comes not as much for the ability to auto matically collect data in relatively remote locations, as for the ability to col lect high temporal resolution data. Flow and chemi cal data with a resolution of minutes capture all significant structures of hydrologic variation, even for karst systems. This can be useful for interpreting information about aquifer structure by comparing the detailed timing and magnitudes of related phe nomena. In a recent example, Liu and others (2004) interpreted controls on aq uifer behavior in south west Chinas tower karst by comparing rates, direc tions, and magnitudes of ch anges in water levels, specific conductance (spC), saturation indices, and PCO 2 in storm responses from a large karst spring and nearby well. While the long-term goal of the research we describe here is to quan titatively understand funda mental controls on relationships between agricul tural land use and karst gr oundwater quality, here we evaluate epikarst flow and storage within south cen tral Kentuckys Pennyroyal Plateau sinkhole plain based on vadose water sampling from three water falls located beneath activ e farming land. Evaluating the hydrologic behavior of th e epikarst at the site is a critical step to quantita tively evaluating the fate and transport of agricultur al contaminants. FIELD SITE Three subsurface waterfalls are being moni tored, as well as rainfall and other atmospheric parameters, within and above Cave Spring Caverns (Figures 1-4) near Smiths Grove, Kentucky. The cave is located beneath a sm all portion of the exten sive sinkhole plain of the Pennyroyal Plateau within the Mississippian Plateaus Section of the Interior Low Plateaus Physiographic Province. Just over 2 km of large horizontal cave passages pass beneath several farm fields, with the cave floor typically about 25 m below the ground su rface. Water enters at numerous locations as perennial or intermittent streams or waterfalls. The recharge area lies within the Graham Springs Groundwater Basin (Ray and Currens, 1998) which discharges at Wilkins Blue hole on the Barren River, 18 km to the southwest. Wilkins Bluehole is the se cond largest spring in Kentucky, with a minimum discharge of 0.56 m 3 /s (Ray and Blair, in press). The cave is formed within the upper part of the Mississippian St. Louis Limestone (Richards, 1964). The Lost River Chert, a discontinuous unit of silicareplaced limestone typically 2-3 m thick near the site, lies between the ground surface and the cave. Locally, beds dip gently to the west at about 1-2. South central Kentucky has a humid-subtropi cal climate. Using climatic data from the Mammoth Cave and Bowling Green areas, Hess (1974) esti mated that the area has a mean precipitation of 1,264 mm/yr, and the mean-annual temperature is 13 o C. Late summer and early fall are drier than other months. Hess (1974) estimated that mean-annual potential evaporation is 800 mm, varying from near zero to over 100 mm/mo. The three percolation waterfalls--1, 2, and 3 in order moving into the cave--fall between about 5 and 8 m from the ceiling along the east side of the main passage starting about 40 m north of the caves entrance, within a 160 m section of the passage (Figure 1). METHODS There are three related sampling programs: sur face weather conditions, weekly sampling and labo ratory analysis of water at the three waterfalls, and 2-minute monitoring of flow, specific conductance (spC), pH, and temperature at waterfall 1. Details of these sampling programs are provided as follows: Surface Rainfall On the surface 110 m south of the cave entrance is an automated HOBO TM weather station that col lects rainfall, temperature, wind speed and direction,

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66 relative humidity, and solar radiation (Figure 2). Rainfall is resolved to the nearest 0.25 mm, and summed every five minutes. Due to interference by birds over part of the reported period, we utilized five-minute rainfall after 25 March 2005 (including storms 2, 3, and 4 discussed below) from the National Park Service Atmo spheric Monitoring Sta tion near the town of Pig, 9.5 km to the northeast. Field Collection and Laboratory Analysi s Water was collected from each waterfall weekly in sterile, acid-washed HDPE bottles and stored on ice. In most cases water was analyzed within three hours of collection. Water samples were analyzed for a suite of parameters indicative of limestone weathering (e.g. Ca, Mg, alkalinity, and specific conductance (spC)) and agricultural impact (e.g., NO 3 PO 4 and NH 4 ). Alkalinity was measured using the inflection point titration method (Rounds and Wilde, 2001) and reported as mg/L CaCO 3 mg/L. Ca and Mg were anal yzed in triplicate using inductively coupled plasma optical emission spectroscopy (ICP-OES). NO 3 PO 4 and NH 4 were measured in triplicate using a Lachat QuickChem method. Preliminary analysis indicated that particulate-associated Ca, Mg, and nutrients were minimal; subsequently wa ter samples were not filtered prior to analysis. Dissolved oxygen (DO), pH and spC were measured in the field with a YSI 556 multi probe system (YSI Environmental). Data were collected from February 23, 2005 to May 25, 2005 for Ca, Mg, spC, and DO (n=13), March 3, 2005 to May 25, 2005 for alkalinity (n=12), and March 23, 2005 to May 25, 2005 for NO 3 PO 4 and NH 4 (n=10). Data Logging at Waterfall One The site is equipped with an array of electronic sensors and loggers and tied to a common tipping bucket rain gauge (Cam pbell Scientific (CSI) TE525) resolving tips of 0.1 mm. Discharge from the rain gauge is directed into 10-mm Tygon tubing which feeds a PVC flow-through chamber (20 mm ID) mounted with a serie s of three Cole-Parmer double-junction industrial in-line ATC pH sensors. Each pH sensor is connected to a three-meter shielded coaxial cable and terminates in the instru ment box (Pelican 1400) at a Cole-Parmer preampli fier to increase signal stability. This pH system can resolve pH to +/0.01 SU. The pH flow-through chamber discharges into a section of 10-mm Tygon tubing where it is split into three paths, each passing through a CSI CS547A-L specific conductance/tem perature sensor. This sensor can resolve temperature to +/0.1 o C and specific conduc tivity to +/0.001 mS. The three paths are then rejoined into a single section of tubing and pos itioned at an elevation approximately 40 cm higher than the sensors to assure pipe-full conditions. Th e signal from the rain gauge is split into three cables, each connected to a CSI CR10X digital micrologger (Figure 3). Each micrologger is connected to its corresponding set of pH, conductivity (spC) and temperature sensors. This redundancy in spC, temperature, pH, and data loggers not only ensures ba ckup in the case of mal function, but when fully operational we calculate means, standard deviations, and coefficients of vari ation (CV) for each observation. The 14,359 spC observations (each made in triplicate) reported in this paper had an average CV of 2.7%. This value is similar to the CV of Waterworks Spring (2%) which has been considered the only perennial "diffuse flow" spring in the region. Waterworks Spring is located near conduit domi nated Wilkins Bluehole, which has a greater CV at 14% (Quinlan and others, 1983; p. 57). Every 30 seconds the micrologger program is executed. The program is set to output tip totals from the rain gauge every five minutes, and to average the 30-second pH, spC, and temperature values every two minutes. To reduce redundant data the program compares the current two-minute average values of each sensor to that of the previous two-minute aver age. If the absolute value of change exceeds a preset value--the current two-minute average values for all sensors is committed to final storage. In any event, the current two-minute values are always stored once per hour. In this way we achieve two-minute resolution even during hourly recording, because we know under those static co nditions the observations have not varied beyond the threshold value.

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67 The waterfall flow data are given in tips per minute for the tipping bucket gage, but these do not yield discharge directly because some of the water, especially at higher flows, falls outside of the bucket orifice. These data thus only give a relative flow indication, but the signals (Figure 5) give a clear indication of dry and wet conditions and their correlation with rainfall events. We are in the process of developing a ra ting curve relating tips per minute to actual discharge, which we measure periodically by catching the flow in a large tarp and measuring the volumetric flow rate with a 10 liter bucket. Statistical Analysis of Water Quality Data Single-factor analysis of variance (ANOVA) was used to determine if statistically significant differences exist in important water quality parameters between the th ree waterfalls. Differences between waterfall locations may reflect different residence times and land use activities at the surface. Prior to analysis, Ca, NO 3 PO 4 and spC were logtransformed whereas Mg was inverse-transformed to obtain approximatel y normal distributions. Alkalinity, on the othe r hand, was normally distributed so no transformation was needed. Fishers t-test was used to compare means between different waterfalls (Helsel and Hirsch, 1993). All statistical analyses were performed using SAS version 9.1 (SAS Institute Inc., 2003). RESULTS Temporal Variations at Waterfall One Between 21 March and 10 April 2005, precipi tation, waterfall flow, and sp C data reflect four suc ceeding rain events that occurred over progressively wetter antecedent moisture conditions. Although we currently lack data for a rating curve, discharge directly measured under ve ry dry conditions at the waterfall (31 May 2005) was 0.04 L s -1 Using an empirical value of 1.98 L s -1 km -2 for unit base flow (Quinlan and Ray, 1995), derived from preliminary data for the autogenic recharge area of the Graham Springs Basin (Joe Ray, Kentucky Division of Water, personal communi cation, 2005), this dis charge corresponds to an estimated recharge area for the waterfall of about 2 ha Estimates of three epikarst spring recharge areas at other sites in Ken tucky range from 4-8 ha (Ray and Idstein, 2004). Although the rainfall data after 25 March (storms 2-4) are from 9.5 km away, they show close correla tion to the cave signals when there was a response. Responses of the cave parameters show a vary ing behavior following the different storm events and thus provide information on flow and storage within the aquifer system. Flow in the waterfall, ini tially under relatively dr y conditions, began to increase within 2.3 hours of the onset of significant rainfall measured abov e the cave system, and showed a clear flow increase of about 120% that returned to the original condition within about 1.5 days. However, there was no systematic change in the spC signal following this rainfall, as explained later. About three days later a more intense storm occurred with obvious di fferences in the cave response. While the timing of the flow increase was similar to the first storm (t hough rain data for this storm are from the NPS stat ion), flow rates stayed more than twice as high as the initial condition for more than four days without significant rainfall, rather than returning quickly to pre-storm levels. The spC signal from relative ly dilute rainfall quickly moving through the system was also clear and corre sponded to rainfall intensity, reaching a low of about 160 S cm -1 or about 70% of pre-storm levels, after an intense thunderstorm ce ll in which rainfall inten sity exceeded 5 cm hr -1 We lost data on peak water fall flow rate because the fl ow exceeded the limits of the tipping bucket mechanis m, but later modified the equipment to accommodate higher flows. The next storm, about four days later, was dif ferent from the first two with respect to both signals. Flow rates continued at a similarly high level with out an appreciable increase, while spC dropped again in very clear relation to rainfall. In contrast to the second storm, however, spC took more than seven days to rise to the same level that had taken

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68 only two days after the previous rainfall, even though starting at a higher minimum level. Finally, a small storm about five days later, which began with waterfall flow rates at a similarly high rate and spC still unif ormly rising through time to pre-storm three levels, had little or no impact on waterfall behavior. Spatial Water Quality Variations Significant variations in water quality were observed between the three waterfalls (Figure 6). Both Ca and Mg were significantly higher in water fall 2 and this is consistent with higher alkalinity and spC values at this locati on. The average Ca concen tration for waterfall 2 was 50.7 mg L -1 compared to 32.1 mg L -1 and 33.4 mg L -1 for waterfalls 1 and 3, respectively (Figure 6A). Similarly, the average concentration of Mg in waterfall 2 was 8.57 mg L -1 compared to 5.93 mg L -1 for waterfall 1 and 5.02 mg L -1 for waterfall 3 (Figure 6B). Alkalinity and spC were also highest in wate rfall 2. Mean alkalinity for waterfall 2 was 106 mg CaCO 3 L -1 and for water falls 1 and 3 the mean con centrations were 73.3 mg CaCO 3 L -1 and 60.0 mg CaCO 3 L -1 respectively (Figure 6C). Mean spC was 328 s cm -1 for water fall 2, 236 s cm -1 for waterfall 1, and 238 s cm -1 for waterfall 3. Differenc es between waterfall 2 and waterfalls 1 and 3 were stat istically significant at the 99% confidence le vel (Figure 6D). As was the case with Ca, Mg, spC, and alkalin ity, PO 4 was significantly higher in waterfall 2 (p < 0.001) compared to waterfalls 1 and 3 (Figure 6E). PO 4 concentrations averaged 0.204 mg L -1 in water fall 2 whereas mean concentrations were only 0.063 mg L -1 and 0.047 mg L -1 for waterfalls 1 and 3, respectively. NO 3 on the other hand, was highest in waterfall 3 and lowest in waterfall 1 (Figure 6F). The average concentrations of NO 3 -N were 10.4 mg L -1 8.19 mg L -1 and 5.60 mg L -1 for waterfalls 1, 2, and 3, respectively. (For reference, the EPA NO 3 -N Maximum Contaminant Level for drinking water is 10 mg L -1 ) Statistical analysis on log-transformed NO 3 -N data indicated that concentrations between the three waterfalls were significantly different (p < 0.001). NH 4 concentrations were at or below detection limit (0.02 mg L -1 ) for all sampling times at each location. DISCUSSION Although the three wate rfalls are separated lat erally by a total of only about 160 m and at about the same depth underground, within a groundwater basin of over 315 km 2 (Ray and Currens, 1998), sta tistically significant differences occur in water chemistry between the three sites. These appear to result from a combination of different land use types and subsurface flow path conditions. Differences between parameters expect ed to result from dissolu tion of limestone, including Ca, Mg, alkalinity (closely related to bicarbon ate concentrations), and spC, appear to indicate a difference in residence times for the flow paths le ading to these waterfalls. Increased residence times may be due to greater flow path lengths and/or slower rates of movement through the epikarst and sections of the vadose zone below. Waterfall 2, for example (Figures 6A-6D), shows significantly higher concentrations than waterfalls 1 and 3 with respect to each of these four parameters. The elevated concentrations of NO 3 and PO 4 measured in the waterfalls, pa rticularly in waterfalls 2 and 3, suggest impact from agricultural land use in the caves recharge zone. Although we currently lack data to discriminate the individual waterfall recharge zones (tracer testing is in progress to eval uate these), there are thre e different patterns in the concentrations of these co mpounds (Figures 6E and 6F) and indeed three general types of land use above the cave (Figure 1). Above and south of the first 90 m of the cave entrance (Figure 1, parcel A) is resi dential, the area to the north over the next 200 m (parcel B) had row crops (wheat) during the sam pling period, and the area across the road to the east (parcel C) had cattle production. The row crops had both animal waste and ch emical fertilizers applied before and during the study, while no chemicals were applied to either parcel A or C during or before sampling. While somewhat speculative until more data become available, a hypothesis consistent with the results so far might indi cate that waterfalls 1, 2,

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69 Figure 1. Map of the entrance area to Cave Spring Caverns showing sampling locations in relation to surface. Figure 4. Water sampling at Waterfall Three using remote device to avoid a shower while sampling. Figure 2. Weather station for recharge measurements, showing typical surface landscape above the cave system. Figure 3. Triplicate Data logger system at Waterfall One.

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70 and 3 have at least partial recharge zones in parcels A, B, and C, respectively. This is indicated by water relatively low in both NO 3 and PO 4 from A (residen tial), higher in both fro m B (animal and chemical fertilizers), and from C where NO 3 is high from cattle waste but PO 4 is low because no fertilizer was applied. As the rocks w ithin which the cave has formed are dipping to the west, it is feasible that some parts of the waterfall recharge zones could be located to the east in parcel C. Comparison between rainfall and flow and spC at waterfall 1 (Figure 6) reveals significant storage within the soil/epikarst above the cave, as well as slow and rapid flow paths through the epikarst whose functions depend on recharge rates and ante cedent moisture. The spC sign al at the onset of the record (~220 mS cm -1 ) represents water that has reached an approximate ch emical equilibrium with the soil/epikarst system. Th is signal is at times diluted by rainfall that has a typical spC of 10-15 mS cm -1 as measured at the N PS Atmospheric Monitor ing Station (Bob Carson, National Park Service, per sonal communication). While the flow conditions clearly responded to the input from the fi rst rainfall (~day 81) the fact that spC did not change suggests that no dilute rainwater reached the probes, and that the storm input altered the hydraulic gradients with in the epikarst in a way that pushed through a sl ug of previously-stored water, which drained through in about 1.5 days. While another possibility is that rainwater did indeed come through quickly but had within a short period developed the chemical characteristics of the epikarst storage, consideration of later storms, dis cussed below, makes this unlikely. The intense rainfall begi nning on day 86 was sufficient to impact the waterfalls spC indicating a relatively rapid transport of rainwater through the system within about one-half day, although it is impossible to measure th is timing more accurately as these rainfall data came from 9.5 km away. Once this flow had been established, water from a large, very intense thunderstorm cell (occurring over the cave at about the same time as the more distant rain gauge, based on observations at the cave) caused a precipitous drop in spC w ithin hours. While the spC returned to within 5% of its pre-storm values with less than eight hours after the spC minimum, the fact that flow remained high instead points to a signifi cant epikarst storage reservoir. We interpret the dif ferences in these two storms to suggest that this reservoir was relatively depleted during the dry ante cedent conditions prior to the first storm, but was replenished during the large recharge event of storm 2. Differences in the three-dimensional head distributions within the ep ikarst water between the filled and depleted reservoi r conditions account for differences in the responses. The more gradual return to prestorm spC co nditions over the next sev eral days reflects both mixing of storage and rainfall waters, as well as chemical reactions (limestone dis solution, for example) that increase the ionic strength of recharge water. The storm 2 response also suggests a recharge intensity threshold above which a rapid flow path is established, in addition to the more diffuse flow pa ths continually present. These interpretations ar e consistent with the response from the third storm (day 92), which was intense but occurred unde r antecedent conditions with relatively full epikarst storage. The return to pre-storm chemical conditions is more gradual than in the previous storm, however, reflecting the greater proportion of storm to chemically equili brated water within the reservoir. These two responses also indicate that the timescale for chemi cal mixing/ equilibration for these waters is on the order of several or more days, confirming that the slug of water pushed through during the first storm was already in the aquifer prior to that storms onset. Using flow and isotope measurements of rain fall and spring water, as well as underground streams leading to the spring, Perrin and others (2003) concluded that the soil/epikarst system forms an important mixing reservoir and were able to dis criminate waters contributed by diffuse and rapid flow through the epikarst reservoir, the latter operat ing when a threshold recharge rate has been exceeded. These findings are similar to those obtained in the present stud y, and taken together, the

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71 Figure 5. Plots of flow rate and mean specific conductance for waterfall 1 in Cave Spring Caverns, along with rainfall above the cave.

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72 Figure 6. Boxplots of (A) calcium (mg L-1), (B) magnesium (mg L-1), (C) alkalinity as CaCO3 (mg L-1), (D) specific conductance ( S cm-1), (E) phosphate (mg L-1), and (F) nitrate-N (mg L-1). Boxes with same letter are not significantly different based on F ishers ttest on means of transformed (ca, Mg, Spc, NO3, and PO4) and untransformed data (alkalinity).

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73 two studies provide quantitative evidence to strengthen the hypothesis that vadose zone storage plays a key role influencing flow and transport within a variety of karst aquifer systems. ACKNOWLEDGMENTS Funding for this work was provided by the US Department of Agriculture Agricultural Research Service. We appreciate very much the kind cooper ation of Bill, Linda, and Ni ck Marohnic for access to their land and cave, as well as the assistance of Stacy Antle, Ben Estes, Deana Groves, Pat Kambesis, Tinesha Mack, Alanna Storey, Ben Tobin, Heather Veerkamp, and Carol Wicks who provided support to the project. We also thank Joe Ray and Chuck Taylor for thoughtful reviews of this manuscript. REFERENCES Baker, A. and C. Brunsdon, 2003, Non-linearities in drip water hydrology; an example from stump Cross Cav erns, Yorkshire. Journal of Hydrology, v. 277, pp.151163. Charleton, R.A., 2003, Towards defining a scallop domi nant discharge for vadose conduits; some preliminary results. Cave and Karst Science v. 30, p. 3-7. Conrad, P.G., D.I. Carey, J. S. Webb, J.S. Dinger, and M.J. McCourt, 1999, Ground Water Quality in Ken tucky: Nitrate-Nitrogen. Kentucky Geological Survey Information Circular 60, Series IX, 5 p. Currens, J.C, 2002, Changes in groundwater quality in a conduit-flow-dominated karst aquifer, following BMP implementation. Environmental Geology v. 42, p. 525-531. Groves, C. and J. Meiman, 2005, Weathering, geomor phic work, and karst landscape evolution in the Cave City groundwater basin, Mammoth Cave, Kentucky Geomorphology v. 67, p. 115-126. Helsel, D.R., and R.M. Hirsch 1993, Statistical methods in water resources. Elsevier, Amsterdam, p. 529. Hess, J., 1974, Hydrochemical Investigations of the cen tral Kentucky Karst Aquifer System Ph.D. thesis, Department of Geosciences The Pennsylvania State University. Jones, W.K., D.C. Culver, and J.S. Herman (eds.), 2004, Epikarst Charles Town, WV: Karst Waters Institute, 160 p. Liu, Z., C. Groves, D. Yuan, and J. Meiman, 2004, South China Karst Aquifer Storm-Scale Hydrochemistry, Ground Water v. 42, p. 491-499. Quinlan, J.F. and Ray, J.A., 1995, Normalized base-flow discharge of ground water basins: A useful parameter for estimating recharge area of springs and for recognizing drainage anom alies in karst terranes, in Beck, B.F. and Stephenson, B.F., ed., The Engineering Geology and Hydrogeology of Karst Terranes : Rotterdam, A.A. Balkema, p. 149-164. Perrin, J., P-Y. Jeannin, and F. Zwahlen, 2003, Epikarst storage in a karst aquifer: a conceptual model based on isotopic data, Milandre test site, Switzerland. Journal of Hydrology vol. 279, p. 106124. Ray, J.A., and Idstein, P.J, 2004, Unpredictable surface exposure of epikarst springs in Kentucky, USA: in Epikarst, Jones, W.K., D.C. Culver, and J.S. Herman (eds.), Karst Waters Institute Special Publication 9, p. 140-141. Ray, J.A. and Currens, J. C., 1998, Mapped karst groundwater basins in the Beaver Dam 30 x 60 Minute Quad rangle, Kentucky Geological Survey. Richards, P.W., 1964, Geologic map of the Smiths Grove quadrangle, Kentucky. US Geological Survey Geo logic Quadrangle Map GQ 357. Rounds, S.A., and Wilde, F. D., eds., September 2001, Alkalinity and acid neutralizing capacity (2d ed.): U.S. Geological Survey Techni ques of Water-Resources Investigations, book 9, chap. A6., section 6.6. SAS System for Windows, version 9.1, SAS Institute Inc., Cary, NC, 2002. Williams, P.W., 1983, The role of the subcutaneous zone in karst hydrology. Journal of Hydrology v. 61, p. 45-67.

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74 Comparison of Water Chemistry in Spring and Well Samples from Selected Carbonate Aquife rs in the United States By Marian P. Berndt 1 Brian G. Katz 1 Bruce D. Lindsey 2 Ann F. Ardis 3 and Kenneth A. Skach4 1 U.S. Geological Survey, 2010 Le vy Avenue, Tallahassee, FL 32310 2 U.S. Geological Survey, 215 Lime kiln Road, New Cu mberland, PA 17070 3 U.S. Geological Survey, 8027 Exch ange Drive, Austin, TX 78754 4 U.S. Geological Survey, 10615 SE Cherry Blossom Drive, Portland, OR 97216 ABSTRACT Water chemistry in samples from 226 wells and 176 springs were assessed to determine if samples from springs and wells have similar concentrations of select ed properties such as dissolved solids, dissolved oxy gen, nitrate, and calcite and dolom ite saturation indices. Samples were collected in seven carbonate aqui fersEdwards-Trinity, Flor idan, Mississippian, Basin and Range, Valley and Ridge, Springfield Plateau, and Ozark. Comparisons were made between concentrations of inorga nic constituents in water samples from springs and from wells within the same aquifer. Results were variable but showed that concentrations were not significantly different betw een samples from springs and wells fo r most properties. Nitrate and dis solved solids concentrations were on ly significantly different between sp ring and well samples in one or two of the seven aquifers; however, dissolved oxygen conc entrations were significan tly different between well and spring samples in four of the seven aquifers. Medi an calcite and dolomite sa turation index values were significantly different between well an d spring samples in three of the seven aquifers. Spring samples prob ably represent water from shallower pa rts of the aquifer flow systems and thus represent parts of the flow system that are most susceptible to contamination from land-use practices These results indicate that the collection of water from springs should be considered critical to adequately char acterize water quality in carbonate aquifers. INTRODUCTION About 20 percent of the ground water with drawn for drinking water in the United States is from carbonate aquifer systems (M.A. Maupin, U.S. Geo logical Survey, written commun., 2004). Under standing the factors that control water quality in these systems requires information on water chemis try from the aquifer matrix fractures, and from sec ondary porosity features (e.g., solution conduits). Comprehensive monitoring strategies that include the sampling of both spri ngs and wells (Quinlan, 1989) have been used to interpret geochemical vari ability that arises from gr ound-water flow through different parts of a carbonate aquifer system (Scan lon, 1990; Adamski, 2000). Water samples were collected from 226 wells and 176 springs in seven carbonate aquifers from 1993 through 2003 as part of the U.S. Geological Surveys National Wate r-Quality Assessment Pro gram. This number of samples from carbonate aqui fers around the United States represents an opportunity to explore th e differences in major-ion chemistry between samples collected from wells and from springs. Limestone and dolomite units were sampled within the follo wing aquifers : EdwardsTrinity, Floridan, Mississippian, Basin and Range, Valley and Ridge, Springfield Plateau, and Ozark (fig. 1). These limestone an d dolomite units range in age from Cambrian to Quat ernary (Adamski, 2000; Miller, 1990; Maclay, 1995) and some are interlay ered with sandstone or ch ert layers (Dettinger and others, 1995; Johnson, 2002; Kingsbury and Shel ton, 2002). COMPARISON OF SAMPLES FROM SPRINGS AND WELLS WITHIN SELECTED AQUIFERS Spring and well water samples were collected from seven aquifersEdwards-Trinity, Floridan, Mississippian, Valley and Ridge, Basin and Range,

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75 Springfield Plateau, and Ozark. Within each aquifer, the number of water samples collected from springs ranged from 6 to 58 samples and the number of sam ples from wells ranged from 18 to 57 (fig. 2). In the Floridan aquifer system, samples were collected exclusively from the Upper Floridan aquifer, thus Upper Floridan will be used for the remainder of this discussion. Comparisons were made only between the water samples from spri ngs and wells within a given hydrogeologic setting in each aquifer. For example, in the Upper Floridan aquifer, samples were collected fro m throughout the extent of the aquifer, but spring water samples were col lected only in southwestern Georgia; thus, these spring water samples were compared only to well samples collected in the same hydrogeologic setting in southwestern Georgia. The nonparametric Wil coxon rank-sum test (Helsel and Hirsch, 1992) was used to determine if con centrations of constituents were significantly different (level of significance 0.05) between water sampl es collected from wells and springs. Major Dissolved Species Calcium-bicarbonate is the dominant water type for all of the aquife rs and aquifer systems; however, the chemical composition of water sam ples from the springs and wells in the Basin and Range aquifer system was highly variable. In most aquifers, fewer than half of the 14 inorganic constit uents examined showed significant differences in Figure 1. Location of spring and well sites sampled from 1993-2003. Figure 2. Number of spring and well samples collected from selected aquifers.

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76 concentrations between springs and well samples (table 1). The greatest number of inorganic constitu ents with significant diff erences in concentration was seven in the Springfield Plateau aquifer. In three aquifersEdwards-Trinity, Mississippian and Basin and Rangesignificant differences in con centrations were noted for only one or two proper ties, indicating that samples collected from springs and wells were collected from ground water from similar locations within the aquifer flow systems. The range in dissolved solids concentrations among the seven aquifers provides some informa tion about the relative residence times and flow path lengths in the aquifers. Aquifers with greatest median dissolved solids concentrations in spring and well samples, the Edwards-Trinity aquifer (322 and 294 milligrams per liter (mg/L), respectively) and the Basin and Range aquifer (410 and 364 mg/L, respectively), also had th e greatest median well depths,270 feet (Edwards-Trinity) and 940 feet (Basin and Range). The median well depths for wells in the other aquifers ranged from 87 to 227 feet. Water from the deep er wells with greater dissolved solids concentra tions may indicate that longer flow paths and older ground water are being sampled in these aquifers. Dissolved solids concen trations were only significantly different between spring and well samples in the Valley and Ridge and Ozark aquifers (fig. 3). Median dissolved oxygen concentrations ranged from 2.5 mg/L in water samples from the Basin and Range aquifer wells to about 8 mg/L for springs in several of the aquifers (fig. 4). In four of the seven aquifers, dissolved oxygen concentrations were significantly different between samples from springs and wells (fig. 4). In each aquifer where sig nificant differences in di ssolved oxygen were noted, the spring samples have the greater dissolved oxy gen concentrations, indicating generally younger waters and more dynamic flow systems. The median dissolved oxygen concentr ation in water samples from wells was greater than that for springs in the Edwards-Trinity a quifer. Deeper, more regional circulation of ground water may account for lower dissolved oxygen concentrations in some springs in the Edwards-Trinity aquifer. Table 1. Summary of p-values from Wilcoxon rank-sum test comparing concentrations between samples from springs and wells.[P-values lower than the level of significan ce, 0.05, are shaded gray; <, less than]Aquifer Calcium Magne -sium Sodium Potassium Iron Manganese Bicabonate Sulfate Chloride NitrateSilicapH Dissolved oxygen Dissolved solids EdwardsTrinity0.200.780.460.361.000.51 0.010.630.520.980.750.980.630.38 Upper Floridan0.680.690.580.59 0.01 0.010.450.371.000.160.80 <0.010.120.52 Mississippian0.700.610.050.720.140. 440.740.380.080.360.180.11 <0.010.40 Valley and Ridge0.360.180.170.06 <0.01 <0.010.16 0.010.290.090.100.08 <0.01 0.05 Basin and Range0.080.850.250.44 <0.01 <0.010.250.240.920.981.000.090.660.25 Springfield Plateau0.340.080.54 <0.010.330.10 <0.010.16 <0.01 <0.01 <0.01 <0.01 <0.010.05 Ozark <0.01 <0.01 0.040.510.450.09 0.050.120.230.950.940.05 <0.01 <0.01

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77 Saturation Indices with Respect to Calcite and Dolomite Saturation indices were calculated for calcite and dolomite using the program PHREEQC (Parkhurst and Appelo, 1999 ). In most aquifers, the calcite saturation index values for the spring and well samples were at or near equilibrium (values of 0 +/0.2 are considered to represent equilibrium) (fig 5a). Most water samp les were undersaturated with respect to calcite (val ues less than -0.2) for the Mississippian aquifer. Minerals in these aquifer materials may be less soluble than the aquifer mate rials in most of the other carbonate aquifers sampled. Calcite saturation index values were signifi cantly different between water samples from springs and wells in three of th e seven aquifersUpper Floridan, Springfield Plat eau Ozark aquifers (fig. 5a). In each aquifer where the calcite saturation index values were significantly different (and in three of the other aquifers where significant differ ences were not noted), the significantly lower values were in the spring sampl es, indicating waters from Figure 3. Distribution of dissolved solids concentrations in samples from springs and wells. Figure 4. Distribution of dissolved oxygen concentrations in samples from springs and wells.

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78 Figure 5. Distribution values for (a) calcite saturation index, (b) dolomite saturation index, and (c) calcium to magnesium molar ratio in samples from springs and wells.

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79 springs were more undersaturated with respect to calcite than water from wells. The lower calcite sat uration index values also indicate that spring waters may originate from shallower parts of the flow sys tems than the water withdrawn from wells. Spring and well water samples for most of the aquifers were undersaturated with respect to dolo mite (fig 5b). Only spring and well samples from the Basin and Range aquifer and well samples from the Ozark aquifer were at or near equilibrium with respect to dolomite (values mostly between -0.2 to 0.2) (fig 5b). Dolomite saturation index values for the spring and well samples were significantly dif ferent in three of the sev en aquifersUpper Flori dan, Springfield Plateau, and Ozark (fig. 5b)the same three aquifers where significant differences were noted for calcite sa turation index values. In each of the three aquifers where dolomite saturation index values were significan tly different (and in the four aquifers where significant differences were not noted), the significantly lo wer values were in the spring samples indicating that the spring samples were more undersaturated w ith respect to dolomite than the samples from wells. The molar ratio of calcium to magnesium was calculated for each sample to determine if this ratio correlates with the relative amount of dolomite in the carbonate aquifers. Results show that in five of the aquifers, calcium-magne sium molar ratios were less than about 5, and are consistent with the reported mineralogy for the Edwards-Trinity, Mis sissippian, Valley and Ridge, Basin and Range, and Ozark aquifers (fig. 5c) (Maclay, 1995, Kingsbury and Shelton, 2002, John son, 2002, Dettinger and others, 1995, and Adamski, 2000). The three aqui fers where the most dolomite is indicated (where the calcium-magnesium ratios were lowest), EdwardsTrinity, Basin and Range and Ozark aquifers, were also the aquifers where dolomite saturation index values were highest (great er than -1.0) (figs. 5b and 5c). Nitrate Median nitrate concentra tions in the seven aqui fers ranged from 0.32 to 2.5 mg/L (fig. 6). Median concentrations were lowest (less than 1.0 mg/L) in the spring and well wate r samples from the Basin and Range and the Ozark aquifers. Although median nitrate concentrations did not exceed the maximum contaminant level of 10 mg/L, several median nitrate concentrations ra nged from 1 to 4 mg/L, which may indicate anthro pogenic inputs. Nitrate concentrations were only significantly different between spring and wells samples in the Springfield Plateau aquifer. The significantly higher concentra tions in nitrate in water samples from springs rela tive to wells in the Springfield Plateau was noted by Adamski (2000) who attributed the higher nitrate concentrations to the greater susceptibility of Figure 6. Distribution of nitrate concentrations in samples from springs and wells.

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80 springs to surface sources of contamination. The land use in the area overly ing the Springfield Plateau aquifer is predominantly agriculture (Adamski, 1996). IMPLICATIONS FOR USE OF SPRINGS IN THE CHARACTERIZATION OF WATER QUALITY IN CARBONATE AQUIFERS Differences in chemistry between spring waters and well water reflect ground-water movement in distinct parts of the flow system. Higher dissolved oxygen concentrations, lower saturation indices with respect to calcite an d dolomite, and lower dis solved solids concentrations relative to water from wells, indicate that spring s discharge ground water mainly from shallow parts of most of the studied aquifer systems. Exceptions are the Basin and Range and the Edwards-Trinity aq uifers, where deeper cir culation of ground water may occur prior to dis charge from springs. Chem ical differences between water from springs or wells also are related to the hydrologic conditions at the time of sampling. Rain fall patterns should be evaluated along with spring discharge at the time of sampling to characterize the contribution of recent recharge to the aquifer and its impact on ground-water chemistry. There were no consistent patterns when com paring nitrate concentratio ns in spring waters and well water. Nitrate concentr ations were significantly higher in spring water than in ground water in the Springfield Plateau aquifer, but not in the adjacent Ozark aquifer. Nitrate conc entrations were higher in spring waters than in we ll waters from the Valley and Ridge aquifer, but n itrate concentrations in spring waters were similar or lower than nitrate con centrations in well waters from the Edwards-Trinity, Upper Floridan, Mississipian, and Ozark aquifers. These differences likely reflect the complex relation between nitrate concentratio ns in ground water and various nitrogen sources, and include past and present land-use and waste-management practices, and hydrologic and climatic variability. Spring samples most likely represent water from shallower parts of the aquifer flow systems, and flow through large solution openings in carbon ate aquifer systems. These parts of the flow system are also the parts of the aquifer systems most suscep tible to contamination from land-use practices. For these reasons, obtaining wa ter samples from springs, in addition to wells, may be necessary for adequate characterization of water quality in carbonate aqui fers and for addressing th eir susceptibility to con tamination. REFERENCES Adamski, J.C., 1996, Nitrate and pesticides in ground water of the Ozark Plateaus region in Arkansas, Kan sas, Missouri, and Oklahoma: U.S. Geological Survey Fact Sheet FS-182-96, 4 p. Adamski, J.C., 2000, Geochemistry of the Springfield Plateau aquifer of the O zark Plateau Province in Arkansas, Kansas, Missouri, and Oklahoma, USA: Hydrological Processes, vol. 14, p. 849-866. Dettinger, M.D., Harrill, J.R., Schmidt, D.L., and Hess, J.W., 1995, Distribution of carbonate-rock aquifers and the potential for their development, southern Nevada and adjacent parts of Arizon a, California, and Utah: U.S. Geological Survey Water-Resources Investiga tions Report 91-4146, 100 p. Helsel, D.R., and Hirsch, R.M ., 1992, Statistical methods in water resources: New York, Elsevier, 522 p. Johnson, G.C., 2002, Water quality of springs in the Valley and Ridge Physiographic Province in the Upper Tennessee River Basin, 1997 : U.S. Geological Survey Water-Resources Investigat ions Report 02-4180, 24 p. Kingsbury, J.A., and Shelton, J.M., 2002, Water quality of the Mississippian carbonate aquifer in parts of middle Tennessee and northern Alabama, 1999: U.S. Geological Survey Water-R esources Investigations Report 02-4083, 36 p. Maclay, R.W., 1995, Geology and hydrology of the Edwards aquifer in the San Antonio Area, Texas: U.S. Geological Survey Water-R esources Investigations Report 95-4186, 64 p. Miller, J.A., 1990, Ground water atlas of the United States, Segment 6, Alabama, Florida, Georgia, and South Carolina: U.S. Geological Survey Hydrologic Investigations Atlas 730-G, 28 p. Parkhurst, D.L., and Appelo, C.A.J., 1999, User's Guide to PHREEQC (Version 2)-A Computer Program for Speciation, Batch-React ion, One-Dimensional

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81 Transport, and Inverse Ge o-chemical Calculations. U.S. Geological Survey Water-Resources Investiga tions Report 99-4259, accessed at http://www brr.cr.usgs.gov/projects/ GWC_coupled/phreeqc/html/ final.html on June 2, 2005. Quinlan, J.F., 1989, Ground-water monitoring in karst terranes: Recommended pr otocols and implicit assumptions: U.S. Environmental Protection Agency Report EPA/600/X-89/050, 79 p. Scanlon, B.R., 1990, Relationships between groundwater contamination and major-ion chemistry in a karst aqui fer. Journal of Hydrology, 119, p. 271-291.



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82 Interpretation of Water Chemistry an d Stable Isotope Data from a Karst Aquifer According to Flow Regime s Identified through Hydrograph Recession Analysis By D. H. Doctor 1 and E. C. Alexander, Jr. 2 1 U.S. Geological Survey, 345 Middlefiel d Rd., MS 434, Menlo Park, CA, 94025 2 Univ. of Minnesota, Dept. of Geology and Geop hysics, 310 Pillsbury Dr. SE, Minneapolis, MN, 55414 ABSTRACT In this study the relation between flow regime and chemistry of a major karst groundwater resurgence zone in southwestern Slovenia was examined using spring hydrograph recession an alysis. Long-term (>2 weeks) recession periods were isolated from 6 years of flow data. Breaks in slope on a plot of the natural log of the discharge versus time a llowed for the identification of four separate flow regimes of the aquifer outflow. Major ion chemistry and stable isotopic composition ( 18 O of water and 13 C of DIC) of samples collected twice monthly for two years were then groupe d according to where they had been collected within each identified flow regime. Patterns in the chemical and isotopic data emerged which indicated shifting sources of water contributing to the outflow of the spring under differe nt hydrologic conditions This type of analysis may be a valuable water resource management tool in other karst regions. INTRODUCTION A primary challenge for the management of karst water resources is to characterize water quality changes with discharge variability. In order to accomplish this goal, managers must be able to effi ciently assess two aspects of the karst aquifer system that interact and determin e overall water quality: the hydrologic and the hydrochemical variability. Often, however, resources for char acterizing water quality across the full range of hydrologic variability are limited, resulting in a frequ ency of water sampling that is far lower than the actual time scale of chemi cal changes taking place at the point of measure ment. Therefore, a need exists for a method through which relatively infrequent wa ter quality data can be used to accurately unders tand and possibly predict major changes in water qu ality as the hydrologic conditions change. In this paper, we descr ibe a technique in which long-term records of discharge and relatively infre quent water quality samplin g can be combined for the purpose of studying wa ter quality changes with flow. The steps are not mathematically complex, allowing for straightforward and rapid culling of information from data whic h already exists for many springs. The analysis begins with examination of the recession limbs of a long-term (several years) record of discharge. Fi rst suggested by Maillet (1905), sev eral authors have since pr oposed that the recession limb of a karst spring hydrograph can be approxi mated by a function that is the sum of several expo nential segments of the total recession (Forkasiewicz and Paloc, 1967; Hall, 1968, Mil anovic 1981; Bonacci, 1993; Tallaksen, 1995). Thus, the entire discharge-time relationship of the recession is expressed as: Qt q i 0 ei t i 1 = N = .(eq, 1) Where Q is the discharge at time t N is the num ber of exponential segments of the recession, q o i is the discharge at the beginning of each recession seg ment, and i is the recession coefficient for each seg ment. In this model, each exponential segment is interpreted to represent th e depletion of an aquifer reservoir, with the rate of depletion of that reservoir being represented by the recession coefficient ( i ). Accordingly, the segment wi th the greatest recession coefficient would represent the most rapid drainage of the karst network (pr esumably surface runoff or displacement of water into the largest conduits) and the recession segment with the smallest coefficient would represent the baseflow (i.e., the slow drainage of that portion of the aquifer with the lowest trans missivity). The latter is often termed the diffuse flow

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83 portion of the aquifer, wh ile the most transmissive conduits are referred to as the quickflow portion of the aquifer. Intermediate segments of the total hydrograph recession are thought to represent the emptying of aquifer volumes having intermediate values of hydraulic conductivity. In reality, it is not cl ear whether the above con ceptual interpretation has any definitive physical validity. It is extremely di fficult to quantify the pro portions of various transmissive elements of a karst aquifer given the high degree of heterogeneity in karst. Moreover, the con ceptual model of a karst aquifer having separate diffuse flow and quick flow components may be misleading, as the physi cal connectivity between fractures and solutionally enlarged conduits exists more as a continuum of transmissivities within the aquifer. Nonetheless, the full recession of the hydrograph contains much use ful information, particular ly concerning (1) the vol ume of water drained from the system over time after peak flows, regardless of where the flow origi nates in the body of the aq uifer, and (2) changes in the rate of discharge that occur at discrete values of discharge, thus placing quan tifiable limits on aquifer flow regimes. Constructing a Master Recession Curve Assuming individual recession segments can be identified, the mean values of q o and for each seg ment can be used to cons truct a Master Recession Curve (MRC) of the spring or well (in the absence of identifiable linear segments on a semi-log plot of discharge vs. time, other models may be applied to estimate the segments of the MRC; see Sujono and others, 2004 for examples ). Each segment of the MRC is only a portion of an individual exponential recession curve, the constants of which are defined by the values of the recession constant ( and the initial discharge defining the upper limit of the recession segment ( q o ). Taken individually, each of these curves represents aquifer drainage under a par ticular flow regime, defined by the discharge mea sured over a specified time interval after the onset of the recession. Except for the tail end of the baseflow recession curve, the time intervals of all of the reces sion segments overlap. Thus, the volumes of water contributed by the underlying curves must be accounted for as part of the volume of water drained solely by an individual segment. For example, let us assume an arbitrary master recession curve of a karst spring, represented in semi-log space in Figure 1 Three exponential recession curves ( Q f (t) =fast flow, Q i (t) =intermedi ate flow and Q b (t) =baseflow) combine to give the overall recession, which is represented by the upper most surface of the intersecting lines shown in Fig ure 1. The total volume of water drained across the fast flow portion of the recession is equivalent to the integration of recession curve Q f (t) on the interval t o to t i In this way, the calcul ation sums together the volumes V f f V i f and V b f Lacking any a priori knowledge of the physical significance of these vol umes for the functioning of the aquifer, their estima tion may not seem consequent ial. However, for the purposes of water quality interpretation it may be desirable to separate the fastest flow portion from the other volumes drained across the MRC. Thus, we may calculate the fast flow volume ( V F ) deter mined solely by the largest recession constant ( f ) and separated from the ba seflow and intermediate flow volumes as: VFV f f Q0ft exp tq0i it exp t dtiti dt0ti == (eq. 2) By integrating the MRC only on the interval from the time of peak flow un til the break in slope and intersection with the next recession curve, the expression in eq. 2 quantifies the volume drained solely under the fastest drai ning portion of the MRC; it is only the volume of the fast flow regime that we seek to define. The fast flow volume is not equiv alent to the total theoretic al volume drained by the uppermost recession curverather, it is a flow regime we are defining independent of (but domi nated by) that recession curve. The fast flow regime thus includes theoretical contributions from all 3 recession segments.

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84 Figure 1. Schematic representation of a Master Recession Curve (MRC) and the theoretical drainage volumes obtained by integration beneath individual linear segments (see text for details). portion of the MRC; it is on ly the volume of the fast flow regime that we seek to define. The fast flow volume is not equivalent to the total theoretical vol ume drained by the uppermost recession curverather, it is a flow regime we are defining independent of (but dominated by) that recession curve. The fast flow regime thus includes theoretical contributions from all 3 recession segments. Similarly, the intermediate flow ( V I ) and base flow ( V B ) volumes (represented in Figure 1 by the stippled region and cross-hatched region, respec tively) can be calculated by the following equations: VIq i0it expt0tb dtq b0 t0tb = bt dt exp (eq. 4) VBq b0bt exp t dt0t = (eq. 5) Thus, the total volume of water, V T drained across the entire recession, from t =0 to t = is: VTVFVIVB ++ = (eq. 6) Using these expressions to quantify theoretical volumes of outflow for a particular spring, one may now look to characterize th e quality of water drained from those volumes based upon chemical and/or iso topic data. This was the approach taken for the case study described herein. STUDY SITE AND BACKGROUND This study was conducted within the Classical Karst, located along the border between southwest ern Slovenia and northeastern Italy. The Slovene name for this region is Kras and this term will be used hereafter in order to signify the geographic location. The Kras region is an uplifted, overturned anticlinal block of Cretaceous limestone forming a plateau at approximately 400 m above sea level. The Kras region is 40 km long, up to 13 km wide, and covers approximately 440 km 2 with mean annual precipitation between 14 00 and 1600 mm (Kranjc, 1997). Rainfall easily infiltrates into the limestone bedrock, due to thin soil thickness (0 to 0.5 m) and the abundance of bare karst bedrock surfaces. No surface streams exist on the Kras plateau. Given the abundant annual precipitation, highly permeable land surface, and lack of surface water runoff, auto genic recharge on the Kras surface is a major com ponent of recharge to the underlying aquifer. In the past, hydrogeological research on the Kras focused mainly on the source of water of the Timavo springs. The Timavo springs are the largest natural source of groundwater in the region, and have been an object of cu riosity for centuries (Galli, 1999). The largest of these springs has been dived to a depth greater than 80 m below sea level, where phreatic conduits of diameters in the tens of meters have been mapped (Guglia, 1994). Collectively, the long-term average discharge of the springs is approximately 30.2 m 3 /sec (variable within the years studied between 18 m 3 /sec and 39.4 m 3 /sec), with low flows averaging around 9 m 3 /sec, and max imum flows over 130 m 3 /sec (Gemiti, 1984). The Timavo springs represent the major com ponent of outflow (85%) of the regional karst groundwater system (Civita and others, 1995). Sev eral other springs in proximity to the Timavo springs form the remainder of th e groundwater resurgence zone. Of these, Sardos spring and Moschenizze North spring are also reclaimed for water supply.

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85 These springs, as well th e water from a supply well (B-4) and a monitoring we ll (B-3) were sampled in this study ( Figure 2 ). The water supply well B-4 provides the sole water sour ce for the inhabitants of the Kras region in Slovenia, serving a population of approximately 25,000 people. The monitoring well B-3 is completed within a zone of fluctuating water level, and was observed to be dry after a drought period. Samples collected from the well before and after the drought exhibited nearly identical water chemistry; thus, this well contains water that is dis placed from storage within the local vadose zone. A large river, the Soca River, drains the high Julian Alps along the western border between Italy and Slovenia. This river loses a large amount of flow into the karst aquifer (20 m 3 /sec), and is believed to account for much of the flow from the springs in Figure 2. The groundwater resurgence zone of the Kras re gion (after Krivic, 1981). the summer (Mosetti & DAmbrosi, 1963; Urbanc & Kristan, 1998). The primary goal of this study was to determine how the contribution from the Soca River affects the outflow of the springs with changing flow conditions. Daily discharge measur ements exist at the Timavo springs as a consequence of their reclama tion for water use. In orde r to quantitatively define the flow regimes considered here, a hydrograph analysis of the Timavo springs discharge was per formed. Six years of discharge records were avail able, from 1995-2000. Out of the six-year record, six of the longest recession periods were chosen for detailed analysis. The recessi on flows at the Timavo springs were fit by a series of linear segments of the hydrograph recession in semi-log space. The simple exponential decay relation ( eq. 1 ) appears to provide an adequate model for the analysis of all discharge regimes at the springs. METHODS From our hydrograph recession analysis, a Mas ter Recession Curve (MRC) ( Figure 3 ) was con structed. Individual storm event recessions from the long-term discharge record s of the Timavo springs were compiled to form th e MRC. Four distinct seg ments to the Timavo MRC we re identified, each cor responding to a characteristic flow regime. The breaks in slope define the approximate discharge limits of each flow regime. The MRC construction was performed manu ally by visual inspection of the individual event hydrographs. Individual event recession periods were isolated from the en tire discharge record and were plotted as the natural log of the flow (ln Q ) vs. time ( t ). Figure 4 shows one of these recession hydrographs of the Timavo springs. Linear ordinary least-squares regression lines were then fit to each segment of each event hydrograph in semi-log space. The slopes of the regression lines are equal to the values of the recession coefficient ( ) for each flow regime of the MRC in units of day -1 and the yintercept of the regression lines are the value of dis charge at the start of the recession (q o at t =0). The values of and q o that were obtained from the linear regressions of the six event hydrographs were tabu lated for each segment of each event, an d averaged. These results are presented in Table 1

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86 Figure 3. Master Recession Curve for the Timavo springs. Lines indicate ordinary least-squares regression through recession segments. Average daily discharge data are shown as dots. Figure 4. Representative recession hydrograph of the Timavo springs. Since it was a common occurrence that reces sion segments would be cut off by increases in dis charge resulting from ne w recharge events, the values of and q o were weighted according the time duration of each segment pr ior to an increase in dis charge. Thus, values of and q o obtained from indi vidual recessions that persisted for longer time periods were more heavily weighted in the calcula tion of the mean values for that portion of the MRC. This practice lends a deliberate bias towards the larger events; the largest events recharge a greater portion of the vadose zone as the water table of the aquifer rises, thus they produce longer, more infor mative, recessions. A limitation to the analysis in this case is that the Timavo springs, having been engineered for water reclamation, are fitted with a sluice gate that controls the discharge at low flow. The consequence of the control structures is that the baseflow never drops below 9 m 3 /sec. Thus, the true baseflow reces sion slope may be absent. Nonetheless, significantly long periods of recession that were not influenced by the control structures were observed such that repro ducible recession segments could be fit to the dis charge record. RESULTS AND DISCUSSION Four flow regimes of the Kras aquifer were defined through the hydrograph analysis: (1) flood flow, (2) high flow (3) mo derate flow, and (4) base flow. The flood flow regi me is for flows of the Timavo springs above approximately 50 m 3 /sec, high flow is between 30 and 50 m 3 /sec, moderate flow is between 15 and 30 m 3 /sec, and baseflow dis charge is below 15 m 3 /sec. The individual segments of the MRC were inte grated to provide an area below the curve that repre sents the total theoretical storage volume of the aquifer that supplies the discharge of the Timavo springs. These results are shown in Table 1 Comparison between flow regimes, isotopes, and chemistry The isotopic and chemical data collected in this study were grouped into the four flow regimes according to the discharge measured at the Timavo springs on the date the water sample was collected. Oxygen ( 18 O of water) and carbon ( 13 C of dis solved inorganic carbon, or 13 C DIC ) stable isotope data of the Timavo sp rings collected between November 1998 and November 2000 were grouped together by flow regime, and box plots were con structed.

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87 TABLE 1. Results of Timavo springs hydrograph recession analysis Recession segment Flow regime Discharge range (m 3 /sec) (day -1 ) q o (m 3 /s) Recession Period (days) Storage volume (m 3 ) % of total storage 1 Flood flow > 50 1.64 x 10 -1 101.49 0 (peak Q) 4 0.06 x 10 8 1.0% 2 High flow 30 to 50 4.10 x 10 -2 61.56 4 17 0.13 x 10 8 2.2% 3 Moderate flow 15 to 30 1.70 x 10 -2 40.98 17 58 0.48 x 10 8 8.2% 4 Baseflow <15 3.00 x 10 -3 18.00 58 or more 5.18 x 10 8 88.5% Total: 5.85 x 10 8 100 % The relation between 18 O and flow regime is opposite to the relation between 13 C DIC and flow regime ( Figure 5a & 5b ). The 18 O values become more negative with higher flow while 13 C DIC val ues become more pos itive. The increase in 18 O and corresponding decrease in 13 C DIC with increasing flow is consistent througho ut the sampling period. In addition, similar seasonal tr ends are apparent among the isotopic variation of all of the groundwaters ( Figure 6 ). Note that all the groundwaters can be approximated as a mixture between the water of well B-3 (autogenic recharge) and the Soca River. The high-altitude (>2000 m) alpine source of the Soca River lends it 18 O values that are more negative than the water de rived from local rainfall on the Kras. The 18 O of weighted mean annual pre cipitation is -6.5, essen tially equal to the compo sition of well B-3. Thus, the difference in 18 O between these sources of water allows for discrimi nation between them in the mixtures of the ground waters. Similarly, the difference in 13 C DIC values between the Soca River and autogenic recharge (rep resented by the composition of well B-3) adds a sec ond parameter by which to discriminate between these sources in the outflow. Lower 13 C DIC values in the autogenic recharge water reflect a greater pro portion of DIC derived from soil CO 2 which tends to be low in 13 C DIC as a result of the oxidation of organic matter (Deines, 1980; Deines and others, 1974). The partial pressure of CO 2 in the unsatur ated zone is 10-100 tim es that of the atmosphere with 13 C values between -20 and -25 (Doctor, 2002), thus lower 13 C DIC values indicate water that has been stored within the vadose zone of the karst. Figure 5. Changes in stable isotopic composition with flow regimes at the Timavo springs. Outlier values corre spond to samples collected immediately after or during storm events.

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88 Figure 6. Time series of oxygen isotope values of the Kras groundwaters, with the average daily discharge of the Timavo springs shown for reference. Note that all the groundwaters are a mixture between the water of well B-3 (autogenic recharge) and the Soca River. Together, these isotopic data present a concep tual model of two compone nt mixing between allo genic Soca River water and autogenic recharge from local precipitation to account for the obse rved isoto pic compositions of the Kr as groundwaters. The pro portion of Soca River wate r issuing from the springs is apparently greatest un der lower flow conditions, while increasing amounts of autogenic recharge water are released from storage in the vadose zone during higher flows. The chemistry data from the present study was combined with the chemistry data of Gemiti & Lic ciardello (1977) and of Cancian (1987), assuming similarity between the flow regimes determined by those authors and the flow regimes determined by the recession analysis of the present study. For the combined chemistry data it was possible to charac terize only three flow regimes, since Cancian (1987) reports only three in his data summary. Therefore, the mean values of the flood flow and high flow regime from the recession analysis were combined into high flow, and the baseflow values are defined as low flow. The results of the water chemistries grouped according to flow regime are shown in Figures 7 to 9. Figure 7 shows the Ca/Mg ratios of all the groundwaters tend to approach that of the Soca River as the flow decreases with the exception of well B-4, which shows a relatively constant Ca/Mg ratio regardless of flow regime. Of the other springs, Timavo has the highest Ca/Mg values, followed by Sardos and then by Moschenizze North. Well B-3 has a much higher and constant Ca/Mg than the other waters, thus the progressive shift toward higher Ca/Mg values with increasing flow regime implies a shift toward a greater proportion of autoge nic recharge water supplying the springs. For Cl all of the groundwaters show similar concentrations except for well B-4, which has the highest Cl concentrations of all of the groundwaters ( Figure 8 ). Cl levels in the other groundwaters are relatively constant at 5-10 ppm across the flow

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89 regimes, while fo r well B-4 the Cl is highest at high flow (>50 ppm on average) and decreases to approx imately 20 ppm on average at low flow. Well B-3 has a low and constant Cl concentration of 3.0 ppm. Figure 7. Ca/Mg ratio of Kras groundwaters with flow regime. Figure 8. Cl of Kras groundwaters with flow regime. Figure 9. SO 4 2of Kras groundwaters with flow regime. Well B-4 also shows anomalous chemistry with respect to SO 4 2; it has the highest SO 4 2concentra tions of all the groundwaters at high flow and the lowest SO 4 2at low flow ( Figure 9 ). SO 4 2concen trations at Timavo and Sardos stay relatively con stant regardless of flow regime, at between 12-14 ppm on average. SO 4 2at well B-4 and Moschenizze North decreases with decreasing flow regime, and at low flow they exhibit the lowest SO 4 2concentra tions of all the groundwaters. High chloride (>100 ppm) and sulfate (>30 ppm) concentrations have been observed from two shafts intersecting the water table nearby the Timavo springs (Gemiti, 1994). The water in these shafts is derived from local storage of autogenic recharge within the epikarst, and may be influenced by anthropogenic activities. Th is water stored within the unsaturated zone impacts well B-4 and Moschenizze North spring under elevated hydraulic head conditions, and to a le sser extent at low flow. Because these two sites exhibit higher Cl and SO 4 2when the water table rises, it is likely that an over flow connection permits the higher salinity water to affect both well B-4 and, to a lesser degree, Moschenizze North spring under high flow conditions.

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90 CONCLUSIONS Hydrochemical and isotopic data collected at a frequency of approximately twice monthly over a two-year period was interpreted through identifica tion of discrete flow regi mes of the karst aquifer by means of hydrograph recession analysis. Grouping the chemistry data together within the defined flow regimes illuminated broad patterns of water quality variability according to ch anging discharge condi tions. The simple exponential decay model used for fitting multiple linear recession segments to the out flow of the Timavo spring s was adequate for deter mining the flow regimes of the groundwater resurgence of the Slovene Kras region. As a result of the recession analysis, four distinct flow regimes of the Timavo springs have been defined: flood flow (>50 m 3 /s), high flow (3050 m 3 /s), moderate flow (1530 m 3 /s), and baseflow (<15 m 3 /s). The esti mated storage volume of the baseflow regime repre sents the greatest proportion (88.5%) of the total theoretical storage volume, with the flood and high flow regimes together representing 3.2%. These per centages highlight the impo rtance of the baseflow regime for providing the majority of flow at the Timavo springs. Although high flows do not drain those portions of the aquife r with a large capacity for water storage, floods are responsible for recharging other parts of the aquifer system, thus flood waters may remain in storage for longer periods of time than otherwise may be indicated by the rapid drain age under higher flow regimes. The flow at the Timavo springs serves as an adequate proxy for the flow of the other local springs that drain the aquifer. Similar trends in the stable isotopic composition ( 18 O and 13 C DIC ) of the water exist among the Timavo springs, Sardos spring, and well B-4 when compared to the dis charge of the Timavo sp rings. For each of these groundwaters, the 18 O values are lowest during lowest flow periods and highest during the highest flow periods, while the 13 C DIC values are lowest during high flow and highest during low flow. These results indicate mixing between similar sources at each of these outflow points, as well as a change in the proportions of each source under changing hydrologic conditions. The more negative 18 O and more positive 13 C DIC values of the waters are con sistent with a predominant Soca River source during low flow periods, while the more positive 18 O and more negative 13 C DIC values are consistent with a predominant source of storage within the vadose zone. The relations among the flow regimes and water chemistry are similar to the results previously reported by Gemiti and Licc iardello (1977) and Can cian (1987). There is a general trend of decreasing Ca/Mg ratio with decreasing flow regime in all of the groundwaters sampled except for well B-4. Since the Soca River show s the lowest Ca/Mg ratio of all the waters, and autogenic recharge water (well B-3) shows the highest Ca/Mg ratio, the decreasing trend supports the conclusi on of variable mixing between the Soca River and autogenic recharge such that under lower flow co nditions Soca River water has a greater influence on the groundwater of the aquifer. The anomalous Cl and SO 4 2chemistry observed at the Klarici su pply well (well B-4) indi cates a high salinity component that affects this well when phreatic head levels are elevated during high flows. Water chemistries of local vadose shafts indi cate that the source of this high salinity water is likely a shallow perched zone of water in storage within the epikarst. This water may be anthropogen ically impacted. The trends observed in both isotopic and chem ical composition of the groundwaters as flow regimes change indicate that pronounced shifts in the water sources feeding the groundwaters of the Kras aquifer resurgence zone occur as hydrologic conditions vary. These data show that under low flow conditions the outflow contains a greater pro portion of Soca River water, while under high flow conditions more water discharged from the springs is derived from the vadose zone. In addition, a third source of water with high levels of Cl and SO 4 2exists in vadose storage and influences some of the groundwaters under elevat ed flow conditions. The techniques developed in this study may be applied to other karst aquifers wher e water quality and flow monitoring is taking place.

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91 ACKNOWLEDGMENTS Funding for this work was provided by the United States Fulbright and David L. Boren interna tional fellowship programs We gratefully acknowl edge A.C.E.G.A. Trieste, Italy and Kraki Vodovod, Slovenia for access to sa mpling sites. Additional samples were provided by Geokarst Engineering s.r.l., Trieste. The first au thor was kindly hosted by the Dept. of Environmental Sciences at the Joef Stefan Research Institute, Ljubljana, Slovenia and the GSF Institute for Hydrology, Neuherberg, Ger many during this study. Thoughtful reviews by Paul Hsieh and John Tinsley of the U.S. Geological Sur vey significantly improv ed this manuscript. REFERENCES Bonacci, O. (1993) Karst sp rings hydrographs as indica tors of karst aquifers. Hydrological SciencesJournal des Sciences Hydro logiques 38 (1,2), 51-62. Cancian, G. (1987) Lidrologia del Carso goriziano-tries tino tra lIsonzo e le risorgive del Timavo. Studi Tren tini di Scienze Naturali vol. 64, p. 77-98. Civita, M., Cucchi, F., Euse bio, A., Garavoglia, S., Maranzana, F. & Vigna, B. (1995) The Timavo hydro geologic system: an import ant reservoir of supplemen tary water resources to be reclaimed and protected. Proc. Int. Symp. Man on Karst, Postojna 1993, Acta Carsologica 24: 169-186. Deines, P. (1980) The isotopic composition of reduced organic carbon. In: Handbook of Environmental Iso tope Geochemistry, Vol. 1 (P. Fritz and J.Ch. Fontes, eds.). Amsterdam: Elsevier, pp. 329-406. Deines, P., Langmuir, D., and Harmon, R. (1974) Stable carbon isotope ratios and the existence of a gas phase in the evolution of carbonate ground waters. Geochim ica et Cosmochimica Acta vol. 38, p.1147-1164. Doctor, D.H. (2002) The Hydrogeology of the Classical Karst (Kras) Aquifer of Southwestern Slovenia. Ph.D. dissertation, University of Minnesota, 252 pp. Forkasiewicz, J. and Paloc, H., (1967) Le rgime de tarissement de la Foux de la Vis. Etude prliminaire. AIHS Coll. Hydrol. des roches fissures, Dubrovnik (Yugoslavia), vol. 1, pp. 213-228. Galli, Mario (1999) Timavo: Esplorazione e studi. Sup plemento no. 23 di Atti e Memorie della Commissione Grotte Eugenio Boegan Trieste, 195 pp. Gemiti, F. (1984) La portata del Timavo alle risorgive di S. Giovanni di Duino. Annali Gruppo Grotte Ass. 30Ott., Trieste 7:23-41. Gemiti, F. (1994) Indagini idrochemiche alle risorgive del Timavo. Atti e Memorie della Commissione Grotte E. Boegan vol. 30, pp 73-83. Gemiti, F., and Licciardello, M. (1977) Indagini sui rap porti di alimentazione delle acque del Carso triestino e goriziano mediante lutilizzo di alcuni traccianti natu rali. Annali Gruppo Grotte Ass. XXX Ott. sez. C.A.I. Trieste, 6, 43-61. Guglia, P. (1994) Risultati esplorativi del Progetto Timavo (1990-1993). Atti e Memorie della Commis sione Grotta E. Boegan, 31/1992-93: 25-48. Hall, F.R. (1968) Base-flow recessionsa review. Water Resources Research vol. 4 (5): 973-983. Kranjc, A.,ed., (1997) Slovene Classical Karst-Kras. Postojna: Institut za razi skovanja krasa ZRC SAZU, 254 pp. Krivic, P. (1981) Etude hydrodynamique dun aquifre karstique ctiere: le Kras de Slovenie, Yougoslavie. Accadmie Montpellier, Univ Sc. Techn. Languedoc, Thse de Docteur-In gnieur Universit Montpellier II: 108 pp. Maillet, E. (1905) Essai dHydraulique Souterraine et Fluviale Librarie Scientifique A. Hermann: Paris. Milanovic P. T. (1981) Karst Hydrogeology. Littleton, Colorado: Water Resources Publications, 434 pp. Mosetti, F. & DAmbrosi, C. (1963) Alcune ricerche pre liminari in merito a supposti legami di alimentazione fra il Timavo e lIsonzo. Boll. Geograf. Teor. ed Appl ., n. 17. Sujono, J., Shikasho, S., Hiramatsu, K. (2004) A compar ison of techniques for hydrograph recession analysis. Hydrological Processes 18, 403-413.

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92 Tallaksen, L.M. (1995) A review of baseflow recession analysis. Journal of Hydrology, 165 : 349-370. Urbanc, J., and Kristan, S. (1 998) Isotope investigation of the Brestovica water source during an intensive pump ing test. RMZ Materials and Geoenvironment vol. 45, no. 1-2, p. 187-191.

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93 An Appalachian Regional Karst Map and Progress Towards a New National Karst Map By D.J. Weary U.S. Geological Survey, MS926A National Center, Reston, VA 20192 ABSTRACT A new 1:1 million scale, lithology-based, digital kars t map has been construc ted for the Appalachian region. This map is serving as the nucleus for a new na tional karst map and as a test for methodologies used in developing the national karst ma p and data base. The map comprises data compiled from various state and regional sources. Issues encountered in the compilation process include un evenness between the vari ous data sets in resolution, lithologic description, and classification. Regional geologic and karst data sets providing information on gl acial deposits and cave and sinkhole lo cations are valuable components of the compilation and may also be used as tools for testing the validity of portions of the map and for creating derived products such as karst dens ity maps. Compilation of the national karst map will become more dif ficult as it progresses to include semi-arid western stat es that contain evaporate karst, karst aquifers, karstic features propagated from buried evaporites into surface ro cks of non-karstic lithology, and various features analogous to karst. INTRODUCTION In 2001 the U.S. Geological Survey Karst Applied Research Studies Through geologic map ping (KARST) Project began the task of construct ing a new national karst map, which would improve on the Davies and others (1984) 1:7.5 million scale National Atlas karst map. The new map will be digitally-based and constructed, edited and updated in a GIS environment. The working resolution of the new map is 1:1 million scale with paper versions planned at scales of 1:7.5 and 1:2.5 million. As a first step, we are publishing a digital map of karst in the Appalachian states as a U.S. Geological Survey Open-File Report. Production of this map has revealed some of the prob lems and issues regarding compilation of diverse and inconsistent data sets supplied from various sources. The Appalachian Region The Appalachian region, as defined by the Appalachian Regional Commission (ARC) was used as an arbitrary geog raphic area for our initial compilation effort (fig. 1). This area, based on socioeconomic and political factors, makes a compact swath covering the central and southern Appala chian Mountains, the Piedmont and parts of the east ern Midcontinent, Atlantic Coastal Plain, and the Gulf Coastal Plain. This area includes the states of New York, Pennsylvania, Oh io, Maryland, Virginia, West Virginia, Kentucky, North Carolina, Tennes see, South Carolina, Georgia, Alabama, and Missis sippi. Included on our map, so that it will be complete to the Atlantic coast, are the states of New Jersey and Delaware. Figure 1. The Appalachian region as defined by the ARC, in gray. States of New Jersey and Delaware are included in this study for completeness to the Atlantic coast.

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94 COMPILATION Karst and Geologic data Representatives of all of the state geological surveys in the region were contacted and invited to participate in a workshop on Appalachian karst sponsored by the U.S. Ge ological Survey and the Kentucky Geological Survey in September, 2002. States that could not attend were asked for sources of karst or geologic data or publicly available geologic data were located on the in ternet. Karst or geologic data at a scale of 1:1 millio n or larger were acquired for each state and loaded into ArcMap-ArcInfo for manipulation. Some states, such as Kentucky and Ohio, already had a state-scale karst map completed (Appendix 1). Those karst areas were simply incor porated into the map and assigned the appropriate attributes. For other areas it is assumed that, in the eastern U.S., where there is sufficient rainfall, car bonate areas, extracted from bedrock maps would suffice as proxies for areas of karst. Geologic units with no carbonates in th eir unit description were deleted. Lithologic unit descriptions from the origi nal data sets were cross-checked against descrip tions in the U.S. Geological Survey National Geologic Map Database (http://ngmdb.usgs.gov/ Geolex/geolex_home.html) References to data sources for each state are listed in Appendix 1. Since the resolution of the individual data sources varied from scales of 1:1 million to 1:24,000 the distance between vertices in the polygon bound aries was generalized in ArcInfo to a spacing of 150 meters for uniformity and to eliminate some of the very small polygons and curves that would not be visible at the working scale of 1:1 million. Also, all polygons with an area of less than 40,000 m 2 were deleted, as they are too sm all to portray visibly on the map. Each polygon was then assigned the following attributes: 1). K_TYPE = an abbreviation for the karst type; state = state name; REF_CODE = refer ence code, an alphanumeric code to the data source(s). Structural data After the areal distributio n of potentially karstic rocks was mapped, a scanned and georegistered image of a Tectonic lithofacies map of the Appala chian orogen (Williams, 1978) was used as a visual template for segregating fo lded and faulted rocks east of the Allegheny structural front from flat-lying to gently dipping rocks to the west. The rationale for this division is the strong influence that the struc tural nature of the host bedrock has on cave passage patterns and, presumably, other karst features (Palmer, 2000). Glacial data Because glacial beveling and cover by glacial sediments has a profound effect on karst distribution in the northern portion of the United States, data on thickness of glacial sedimen ts were integrated into the karst map. Fortunately, a digital dataset of gla cial sediment cover for the United States east of the Rocky Mountains already exists (Soller and Pack ard, 1998). Areas with glacial cover exceeding 50 ft thick (fig. 2) were extracted from this dataset and intersected with the karst areas to define areas of potential karst buried un der glacially derived sedi ments. Figure 2. Distribution of glacial sediments greater than 50 ft thick (in gray) in part of the Appalachian region. Derived from data from Soller and Packard (1998). RESULTS A draft, first version of the Appalachian karst map is shown in figure 3. A portion of the Davies

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95 and others map (1984) is shown in figure 4 for com parison. The most substantial apparent difference between the two maps is th e better resolution of the new map, 1:1 million vs 1: 7.5 million. The new map also includes more Atlantic Coastal Plain units as potentially karstic than did Davies and others (1984). This is the first iteration in a process of compi lation and refinement of the map. Publication as a digital product will facilita te release of revised ver sions as corrections and adjustments are made in the future. Figure 3. Draft map of Appalachia n karst. CPL = Coasta l Plain limestones; CPU = Coastal Plain unconsolidated calcareous sediments; FFC = folded and faul ted carbonate rocks; FFCG = folded and faulted carbonate rocks with glacial cover greater than 50 ft thick; GC = flat -lying to gently folded carbonate rocks; GCG = flat-lying to gently folded carbonate rocks wit h glacial cover greater than 50 ft thick; M =marble; MG = marble with glacial cover greater than 50 ft thick; TJB = Triassic and Jurassic basin-fill carbonates.

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96 Description of karst units Karst-type map units in the new map incorporate lithology, regional structural style, and glacial sedimentary cover greater than 50 ft thick. Further subdivisions and refinements will be made as the project progresses. Full descriptions of the karsttype map units currently assigned follows: CPUCoastal Plain unconsolidated: Coastal Plain deposits of unconsolidat ed, calcareous sediments. Includes chalks, marls, and units with shelly buildups. Dissolution may r esult in subtle, shallow subsidence sinkholes. CPLCoastal Plain limestones: indurated, flatlying, carbonate rocks. Dissolution may result in solution, collapse, and cover-collapse sinkholes. FFCFolded, faulted carbonate rocks: Limestone and dolomite in structura lly deformed zones zones. May be intensely folded and faulted, commonly well jointed, possibly wi th cleavage. Dissolution may produce solution, colla pse, and cover-collapse sinkholes. Caves range from small and simple to long and complex systems. Geometry of cave passage patterns tend to show at least some structural control. FFCGFolded, faulted carbonate rocks with glacial cover: Limestone and do lomite in structurally deformed zones covered by 50 ft (15 m) or more of unconsolidated, glacially derived sediment. May be intensely folded and faulted, commonly well jointed, possibly with cleavage. Karst features usually not apparent at surface but solution features probably present at depth. GCGently-folded and flat-l ying carbonates rocks: indurated limestone and dolomite that has not been strongly deformed. Predominantly found in interior plateaus and lowlands. Dissolution may produce solution, collapse, and cover-collapse sinkholes. Where carbonates are thic k and extensive cave systems may be long and complex. Where thin and interbedded with non-carbonates, caves are small and short. Geometry of ca ve passage patterns often shows lithologic and bedding-plane control. GCGGently-folded and flat-lying carbonates rocks with glacial cover: indurated limestone and dolomite that has not b een strongly deformed covered by 50 ft (15 m) or more of unconsolidated glacially derived sediment. Predominantly found in interior plateaus and lo wlands. Karst features usually not apparent at surface but solution features probably present at depth. MMarbles and metalimest ones: highly deformed carbonate rocks, usually f ound in long, thin, linear belts or pods. Dissolution may result in solution, collapse, and cover-collapse sinkholes and small, short caves. MGMarbles with glacial cover: highly deformed carbonate rocks, usually f ound in long, thin, linear belts or pods, covered by 50 ft (15 m) or more of unconsolidated glacially derived sediment. Karst features usually not apparent at surface but solution features probably present at the sediment-rock interface. Figure 4. A portion of the digital version of Davies and others (1984) map showing karst areas, in gray tones, in the Appa lachian region (Tobin and Weary, 2004).

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97 TJBTriassic and Jurassic basin fill calcareous sediments. Includes calcareous conglomerates and minor lacustrine limestone s. Dissolution may result in solution and subsiden ce sinkholes and small caves. DISCUSSION Problems Most of the major problems in the new map are differences in delineation of karst areas across state boundaries on state geologic maps. Karst areas for the state of Pennsylvania and the edges of the adjoin ing states are shown on figure 5 to illustrate some of these differences. Notice that areas delineated as karstic in western Pennsylvania are not currently identified in Ohio and West Virginia. These areas were, however, shown in a gross manner in the Davies and others (1984) (fig. 4) map. Figure 5. The Pennsylvania portion of the new Appalachian karst map showing discontinuities across boundaries of neighboring states. Explanation of map units as in figure 3. These areas represent the extent of the Pennsyl vanian Allegheny Formation and the Mississippian Mauch Chunk Formation (Miles and others, 2001). The Allegheny Formation comprises chiefly clastic rocks, but also contains the Vanport Limestone which contains caves and other karst features. Like wise, the Mauch Chunk Formation includes the Loy alhanna, Greenbrier, Wymps Gap, and Deer Valley Limestones. The Loyalhanna and Greenbrier Lime stones, in particular, contain caves and other karst features. The Vanport was pr obably not included in the state karst map of Ohio (Pavey and others, 2002) because it thins to less than 10 ft thick west of the Ohio River. Some belts of carbonate units equivalent-inpart to the Mississippian Mauch Chunk Formationcontinue on into Maryland and West Virginia but are thinner and discontinuous having been subdivided from the thicker clastic units in those states (Peper and others, 2001; West Virg inia Bureau of Public Health, 1998). Ongoing work to compile and refine karst maps of Pennsylvania by Bill Kochanov at the Pennsylva nia Geological Survey (o ral commun., 2005) will be incorporated in the Appalach ian map in the future to revise the extent of karst within that state and will probably resolve most of the boundary mismatches with Maryland and West Virginia. In addition the extent of the Vanport Li mestone will probably be extended to the west, feathering-out in eastern Ohio. A section of the Appalachian karst map cen tered on the Atlantic Coastal Plain areas of North and South Carolina is shown on Fig. 6. The medium and dark gray areas delin eate potentially karstic units derived from individual state data sources. There is not good matchi ng between the mapped Coastal Plain units across the state borders. Differ ences in lithologic descriptions and each states clas sification and grouping scheme affect the aerial extent of the units. Some areas of potential karst, especially in the unconso lidated units, are undoubt edly overstated. Areas of lig ht gray on figure 6 show the extent of potentially karstic units derived from a database for the entire Atlantic Coastal Plain (New ell and others, unpublished data) and areas of very dark gray indicates the overlap of that data set with kart areas delineated by the individual state data. Use of the regional data set eliminates most of the discontinuities between the state boundaries, but, because it is focused on surficial units it does not include some important bedrock limestone units such as the Eocene Castle Hayne Limestone in east ern North Carolina. Resolution of these prob lems in the Coastal Plain will require combin ing the information from the various data sets and a search for more detailed

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98 information on the distribution of calcareous sedi ments and whether there are, in fact, karst features in some of these units. Figure 6. The North and South Carolina part of the new Ap plachian karst map showing discontinuities in data sets. Reported cave locations in the U.S., east of the Mississippi River, plotted on the Appalachian karst map are shown on figure 7. Because they cross state lines and are, presumably, evenly sampled, regional data sets such as this are valuable for checking the accuracy of the karst delineation. Data sets for other karst features, such as sinkhole and spring locations also exist, although most are limited to a particular state or smaller area. If some of these data can be acquired and joined together they will enable further geostatistical analyses of karst across large areas. The density of caves within a part of the Appala chian karst map is shown in figure 8 as an example. This particular plot was generated purely for demon stration purposes, with little thought to rigorous sta tistical meaning, and should not be taken seriously at this point. It does, howe ver, show interesting pat terns in the variation of cave density, with concen trations of caves in central Kentucky, the northeastern corner of Alabama and the southwest ern tip of Virginia. Future studies of regional karst feature distribution should lead to new ideas about the effect of tectonism, lithologic facies, hydrologic regime, glaciation, and othe r factors on the intensity of karstification. Figure 7. Cave locations (black dots, n=1395) plotted on karst areas in the Appalachians. Cave location data from David Culver, American University, 2004, written communication. Figure 8. Cave density mapped within the Appalachian karst polygons.

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99 As the nucleus formed by the Appalachian karst map is solidified, state by state coverages, forming the new National Karst map, will be accreted to it. Classifying karst areas in the western part of the country will be a challenge. West of the 32.5-in. mean precipitation line, th e nature of wearthering and expression of karst features in the United States changes (fig. 9; Epstein an d Johnson, 2003). Issues include mapping buried karst, deeply buried evapo rates that propagate karst features to non-karstic rocks at the surface, and wh ere to cut the continuum from surface karstic rocks into karst aquifers. A U.S. Geological Survey sponsored workshop involving the state geological surveys of Kansas, Arkansas, Illinois, Iowa, Nebraska, and Wisconsin focusing on these issues will be held Au gust 17 and 18, 2005 at the Kansas Geological Su rvey. Hopefully we can make some real progress towards generating rules of thumb for mapping these phenomena. Figure 9. Map showing distribution of outcropping and sub surface evaporate rocks in the United States and areas of reported evaporate karst. The 32.5-in. mean-annual-precipi tation line approximates the boundary between eastern and western karst (from Epstein and Johnson, 2003, fig. 5) REFERENCES Daly, C., and Taylor, G., 200 0, United States average annual precipitation, 1961-1990: Spatial Climate Analysis Service, Oregon State University; USDANRCS National Cartography and Geospatial Center, Fort Worth, Texas; online linkage: http:// www.ftw.nrcs.usda.gov/prismdata.html. Davies, W.E., Simpson, J. H., Ohlmacher, G.C., Kirk, W.S., and Newton, E.G., 1984, Engineering aspects of karst: U.S. Geological Su rvey, National Atlas, scale 1:7,5000. Dunrud, C.R., and Nevins, B.B., 1981, Solution mining and subsidence in evaporate ro cks in the United States: U.S. Geological Survey Mi scellaneous Investigation Series Map I-1298, 2 sheets. Epstein, J.B., and Johnson, K.S., 2003, The need for a national evaporate karst map, in Johnson, K.S. and Neal, J.T., eds., Evaporite karst and engineering/envi ronmental problems in the United States: Norman, Oklahoma Geological Survey, Circular 109, p. 21-30. Johnson, K.S., 1997, Evaporite karst in the United States: Carbonates and Evaporites, v. 12, p. 2-14. Miles, C.E., Whitfield, G.T. and other staff and interns of the Pennsylvania Geological Survey, 2001, Bedrock geologic units of Pennsylvania, based on: Berg, T.M., Edmunds, W.E., Geyer, A.R., Glover, A.D., Hoskins, D.M., MacLachlan, D.B., Root S.I., Sevon, W.D., and Socolow, A.A., 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey, Map 1, scale 1:250000. http://www.dcnr.state.pa.us/topogeo/map1/ bedmap.aspx Palmer, A.N., 2000, Hydrogeologic control of cave pat terns, in Klimchouk, A.B. and others, eds., Spelogene sis evolution of karst aquifers: Huntsville, National Speleological Society, p. 77-90. Pavey, R.R., Hull, D. N., Brockman, C. S., Schumacher, G. A., Stith, D. A., Swinford, E. M., Sole, T.L., Vor bau, K. E., Kallini, K. D., Evans, E. E., Slucher, E. R., and R. G. Van Horn, 2002, Known and probably karst in Ohio, 2002: Ohio Geological Survey, EG-1, version, GIS data on CD provided by the Ohio Geological Sur vey, scale 1:24,000. Peper, J.D., McCartan, L.B., Horton, J.W., Jr., and Reddy, J.E., 2001, Preliminary lithogeochemical map showing near-surface rock types in the Chesapeake Bay watershed, Virginia and Maryland: U.S. Geologi cal Survey Open-File Re port 01-187, resolution 1:500,000.Maryland part based on the Cleaves, 1968, Geologic map of Maryland. http://pubs.usgs.gov/open file/of01-187/ Soller, D.R. & Packard, P.H. (1998). Digital representa tion of a map showing the thickness and character of Quaternary sediment in the glaciated United States east of the Rocky Mountains: U.S. Geological Survey

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100 Digital Data Series DDS-38, scale 1:1,000,000. http:// pubs.usgs.gov/dds/dds38/shape.html Tobin B.D. and Weary, D.J., 2004, Digital Engineering Aspects of Karst Map: A GIS Version of Davies, W.E., Simpson, J.H., Ohlm acher, G.C., Kirk, W.S., and Newton, E.G., 1984, Engineering Aspects of Karst: U.S. Geological Survey, National Atlas of the United States of Ameri ca, Scale 1:7,500,000. http:// pubs.usgs.gov/of/2004/1352/ West Virginia Bureau of Public Health, 1998, Karst regions derived from 1968 geological map of West Virginia: West Virginia GIS Technical Center, online data http://wvgis.wvu.edu/data/dataset.php?action= search&ID=133, resolution 1:250,000. Williams, Harold, compiler,1978, Tectonic lithofacies map of the Appalachian orogen: St John's : Memorial University of Newfoundland, scale 1:1 000,000.

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101 APPENDIX 1 State by state annotated sources for karst a nd geologic data (in alphabetical order) Alabama Szabo, M.W., Osborne, W.E., Copeland, C.W., Jr ., and Neathery, T.L., 1988, Geologic Map of Alabama: Geological Survey of Alabama, Special Map 200; digital version: Digital geologic map of Alabama, Beta Version 1, 2002: Geologic Survey of Alabama, scale 1:250,000. [Used for entire state] Delaware Nenad Spoljaric, Jordan, R.R., Generalized geologic map of Delaware, revised 1976 by Pick ett, T.E.: Delaware Geological Su rvey, 1 sheet, scale ca. 1:600,000. [Map scanned and digitized at U.S. Geological Survey; Used for entire state] Georgia Alhadeff, J.S., Musser, J. W., Sandercock, A. C., and Dyar, T.R., 2001, Digital environmental atlas of Georgia: Georgia Geologic Survey Publica tion CD-1, ver. 2., scale 1: 250,000. [Used for entire state] Kentucky Paylor, R.L., and Currens, J.C., 2002, Karst Occurrence in Kentucky: Kentucky Geological Survey, KGS Map and Chart 33, scale 1:500,000. http://www.uky.edu/KGS/wa ter/general/karst/karst gis.htm [Used for entire state]. Maryland Peper, J.D., McCartan, L.B. Horton, J.W., Jr., and Reddy, J.E., 2001, Preliminary litho geochemical map showing near-surfa ce rock types in the Chesapeake Bay watershed, Virginia and Mary land: U.S. Geological Survey Open-File Report 01-187, resolution 1:500,000.Maryland part based on the Cleaves, 1968, Geologic map of Mary land. http://pubs.us gs.gov/openfile/of01-187/ [Used for entire state, except Coastal Plain] Newell, W. L, Prowell, D., Kranz, D., Powars, D., Mixon, R., Weem s, R., Stone, B., and Willard, D., Surficial geology and geomorphology of the Atlantic Co astal Plain: U.S. Geolog ical Survey, unpublished data.; [Used in Coastal Plain only] Mississippi Online data from Mississipp i Automated Resource Informatio n System (MARIS) at: http:/ /www.maris.state.ms.us/HTM/Data%2 0Warehouse/Statewide_alpha.htm No metadata available (4/ 2004) scale 1:500,000. [Map units compared with desc riptions on published paper maps: 1. Bicker, A.R. Jr., (compiler) 1985, Geologic Map of Mississippi: Mi ssissippi Geological Survey, scale 1:500,000. 2. Booth, D.C. and Schmitz, D.W. (compilers), 1983, Ec onomic minerals map of Mississippi: Mississippi Bureau of Geology, Mississippi Minera l Resources Insititute scale 1:500,000.] New Jersey Vector graphic files of karst units of New Jersey were supplied by Donald Monteverde, New Jersey Geological Survey and were converted to GI S at the U.S. Geological Survey. These units were extracted from: 1.) Dalton, R.F., 1996, Bedrock geol ogic map of northern New Jersey: U.S. Geological Survey, Miscellaneous Investigations Series, I-2540-A, scale 1:100,000. 2.) Owens, J.P., Sugarman, P.J., Sohl, N.F., Parker, R.A., Houghton, H.F., Volkert, R. A., Drake, A.A., and Orndo rff, R.C., 1995, Geologic map of New Jersey: central sheet: New Jersey Geol ogical Survey, scale 1:100,000. 3.) Owens, J.P., Sug arman, P.J., Sohl, N.F., Parker, R. A., Houghton, H.F., Volkert, R.A., Drake, A.A., and Orndorff, R.C., 1995, Geologic map of New Jersey: southern sheet: New Jersey Geological Survey, scale 1:100,000. [Used for entire state.] New York Fickies, R.H. and Fallis, E., 1996, Rock Type Map of New York State: New York State Geo logical Survey, Open file Report 1g1222, scale 1:1,000,000. [GIS data provided by the New York Geo logical Survey; Used for entire state.]

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102 North Carolina North Carolina Geological Survey, 1999, Geology North Carolina: North Carolina Department of Environment and Natural Resources -D ivision of Land Resourc es, North Carolina Corpo rate Geographic Database online data, http://www.geology.enr.state. nc.us/gis/geol250d.htm. resolution 1:250,000. [Calcareous rocks extracted based on description of map units. Used for entire state.] Ohio Pavey, R.R., Hull, D. N., Broc kman, C. S., Schu macher, G. A., Stith, D. A ., Swinford, E. M., Sole, T.L., Vorbau, K. E., Kallini, K. D., Evans, E. E., Slucher, E. R., and R. G. Van Horn, 2002, Known and probable karst in Ohio, 2002: Ohio Geological Survey, EG-1, version, GIS data on CD provided by the Ohio Geological Survey, scale 1:24,000. [Polygons gene ralized and reclassified. Used for entire state.] Pennsylvania Miles, C.E., Whitfield, G.T. and other sta ff and interns of the Pe nnsylvania Geological Survey, 2001, Bedrock geologic units of Pennsylvania, based on: Berg, T.M., Edmunds, W.E., Geyer, A.R., Glover, A.D., Hoskins, D.M., MacLachlan, D. B., Root, S.I., Sevon, W. D., and Socolow, A.A., 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey, Map 1, scale 1:250000. http:// www.dcnr.state.pa.us/topogeo/map1/bedmap.aspx [Car bonate units extracted based on map descriptions. Used for Entire state.] South Carolina Horton, J.W. Jr., 2001, Preliminary digita l geologic map of the Appalachian Piedmont and Blue Ridge, South Carolina Segment: U.S. Geol ogical Survey, Open-file Report 01-298, http:// pubs.usgs.gov/openfile/of01-298/, scale 1:500,000. [Car bonate units extracted ba sed on unit labels and descriptions of units found in the U.S. Geological Survey Geologic names lexicon: http:// ngmsvr.wr.usgs.gov/Geolex/geolex_home.html; Used for Blue Ridge and Piedmont Provinces only.] Newell, W. L, Prowell, D., Kranz, D., Powars, D., Mixon, R., Weem s, R., Stone, B., and Willard, D., Surficial geology and geomorphology of the Atlantic Co astal Plain: U.S. Geolog ical Survey, unpublished data: [Carbonate units extracted based on unit labels and descriptions of units found in the U.S. Geolog ical Survey Geologic names lexi con: http://ngmsvr.wr .usgs.gov/Geolex/geolex_home.html; Used for Coastal Plain province only.] Tennessee Greene, D.C., and Wolfe, W. J., 2000, Superfund GIS 1:25 0,000 geology of Tennessee: U.S. Geological Survey, digital version of Tennessee Division of Geology, 1966, Geologic map of Ten nessee: Tennessee Division of Geology, Willia m D. Hardeman, State Ge ologist, 4 sheets, scale 1:250,000. http://water.usgs.gov/GIS/metadata/usgsw rd/geo250k.html [Calcareous rocks extracted based on description of map units Used for entire state.] Virginia Virginia Division of Mineral Resources, 2003 Digital representation of the 1993 geologic map of Virginia: Virginia Division of Mineral Resources Publication 174 [CD-ROM; 2003, December 31]. Adapted from Virginia Division of Mineral Resources 1993, Geologic map of Virginia and Expanded Explanation: Virginia Division of Mineral Resources, scale 1:500,000. [Calcareous rocks extracted based on description of map units Used for entire state.] West Virginia West Virginia Bureau of Public Health, 1998, Karst regions derived from 1968 geological map of West Virginia: West Virginia GIS Techni cal Center, online data http://wvgis.wvu.edu/data/ dataset.php?action=search&ID=133, resolu tion 1:250,000. [Used for entire state.]



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103 Hydrogeologic-Framework Mapping of Shallow, Conduit-Dominated KarstComponents of a Regional GIS-Based Approach By Charles J. Taylor 1 Hugh L. Nelson Jr. 1 Gregg Hileman 2 and William P. Kaiser 3 1 USGS Kentucky Water Science Center, Louisville, KY 2 USGS Tennessee Water Scie nce Center, Nashville, TN 3 USGS HQ Geographic Informat ion Office, Sacramento, CA INTRODUCTION Recent advancements in geographic informa tion system (GIS) techno logy, coupled with the increased availability of Internet-accessible geospa tial datasets such as Digital Elevation Models (DEMs), Digital Orthophoto Quadrangles (DOQs), and Digital Raster Graphic Maps (DRGs), have greatly improved the comp ilation, interpretation, and visualization of inform ation needed to address water-resources management and protection issues. As applied to karst hydrogeo logic studies, GIS is an exceptionally useful way to assemble and process the complex datasets needed to map karst hydrogeo logic features (Florea and others, 2002; Gao, 2002) and also provides an effect ive means of identifying important but sometimes ob scure relations between surface and subsurface components of karst aquifer systems (Veni, 1999, 2003). This Abstract briefly describes the GIS-based approach being applied to synthesize available hydrogeologic mapping data as part of a regional karst study being conducted by the U.S. Geological Survey (USGS) Ground-Water Resources Program. The focus of the regional study is the shallow, conduit-dominated karst aqui fers of the Interior Low Plateaus physiographic region of the United States (fig. 1). These aquifers are located in seven geo graphically distinctive kars t terranes (fig. 1) that exhibit similar hydrogeologic characteristics. The framework for the karst aquife rs in each of the seven terranes consists of cont iguous karst drainage basins. Each karst drainage basin is defined by a spe cific geographic area where surface and ground water are highly interconnected and contribute to the flow within a dentritic conduit drainage network (fig. 2). Typically, each karst drainage basin dis charges to a large perennia l karst spring that func tions as the primary drainage element of a high-flow distributary (Quinlan and Ewers, 1989). The hydro logic behavior of the karst drainage basins and the springs is greatly affected, and often dominated, by concentrated recharge that originates as stormwater runoff drained rapidly to the subsurface by way of sinkholes and sinking streams. However, the bulk of the annual recharge to the karst drainage basins occurs by dispersed inf iltration of precipitation through the soil and by water stored and released from a leaky epikarst zone (Ray, 2001). COMPONENTS OF THE GIS-BASED APPROACH Much of the first year of the study has been devoted to gathering availa ble data and to develop ing GIS methods and datasets needed to map major karst hydrogeologic features at local to regional scale. Components of the GIS-based mapping approach include (1) sinkhole locations and catch ment areas defined by processing of DEMs, (2) springs identified in the USGS National Water Information System (NWI S) database, (3) topo graphic drainage divides derived from DEMs, (4) identified sinking or losing streams and relic stream valleys (karst paleovalleys ), (5) other hydrographic features such as perennial blue line streams and ponds or lakes, (6) 8and 10-digit hydrologic unit (HU) boundaries, (7) vectors representing subsur face flow paths inferred from reported dye-tracer test results, and (8) boundaries of karst drainage basins inferred by dyetracer tests and other hydrogeologic-mapping techniques.

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104 Figure 1. Interior Low Plateaus regional study area and its seven major karst terranes: (1) Mitchell Plain; (2) Central Ken tucky; (3) Inner Bluegrass; (4) West Highland Rim; (5) Nashville Basin; (6) Cumberland Plateau; and (7) East Highland Rim.

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105 Figure 2. Dendritic conduit flow paths, inferred by dye-tracer te st results (curvilinear arrows), are typical of karst drainag e basins in the regional study area. This example illustrates the flow paths and basin boundaries (dashed lines) delineated for Boiling Spring and Head-of-Doe Run Spring in the Central Kentucky karst terrane. (Modified from Joe Ray, Kentucky Divi sion of Water, unpub. data, 2005).

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106 Of the eight componen ts listed above, dyetracer test data are the most crucial and difficult to obtain. A considerable effo rt has been made to iden tify sources of, and obtain, all available (i.e., pub licly accessible) dye-tracer test data in the region. However, with the exception of Kentucky, where a systematic effort is being made by State agencies to map karst flow paths and dr ainage basin boundaries (Currens and Ray, 1999), th e availability and quality of dye-tracer test data vary greatly. In general, dyetracer test data are cluste red in certain geographic areas within each of the seven karst terranes delin eated in figure 1. Where dye-tracer test data are too sparse or lacking, GIS mapping of subsurface flow paths and karst drainage basin boundaries is not pos sible. Nevertheless, in these areas, as elsewhere in the region, the surficial karst features are being mapped, analyzed, and compared. One goal of this work is to obtain a regional karst features databasecomposed of the eight hydrogeologic mapping components listed aboveassembled as print-publishable map files (PMFs) that can be viewed and manipulated using ArcMap 1 or ArcReader GIS software. To emphasize the direct interconnection between ground and sur face water in karst terranes, a watershed cataloguing scheme is being used to index the PMFs: first, by 8digit HU codes; second, by 10-digit HU codes. An example of the watershed cataloguing scheme is shown in figure 3, which presents DEM data pro cessed with GIS to delinea te the 10-digit HUs, or topographic subbasins, included in the 8-digit Upper Green River HU (watershed) in the Central Ken tucky karst terrane. This cataloguing scheme will facilitate evaluation and comparison of karst fea tures within and among regional surface watersheds and will aid the transfer of karst hydrologic data to the USGS National Hydrography Dataset (NHD) ( http://nhd.usgs.gov/ ) and The National Map project ( http://nationalmap.gov/ ). The synthesis of data by watersheds also pro vides a useful means to easily correct or refine HU boundaries, which are used as basic water-account ing units by the NHD and are needed for a variety of Federal and State environmental and water-use reg ulatory programs. If HU boundaries, which are mapped using topographic drainage divides, are not corrected in karst areas to account for subsurface conduit routing of flow into or out of surface water sheds, appreciable errors may be introduced to the delineation of the contributing areas of surface streams, karst aquifer boundaries, and hydrologic calculations or models (Currens and Ray, 1999). Examples of this potential problem are shown in fig ure 3, where the inserts (figs. 3A and 3B) illustrate two locations in the Upper Green River watershed that the boundaries mapped for constituent 10-digit HUs do not coincide with the boundaries of the actual contributing area as determined by dye-trac ing tests. The errors po tentially introduced by assigning and using HU boundaries without correct ing for karst drainage can be appreciable. In this case, approximately 75 percent of the Upper Green Rivers drainage area is misattributed to the Barren Riveran adjacent 10-digit HU (Ray, 2001). In a preliminary assessment, using available dye-tracer test data, Ray and others (2000) estimated that approximately 15 to 20 percent of the Central Ken tucky karst terrane may exhibit such misbehaved drainage. The extent of this potential problem in the other karst terranes in the regional study area has not been determined. 1 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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107 Figure 3. Processed DEM of the Upper Green River watershed (8-digit HUC 05110001), Kentucky, showing 10-digit HUs (sub watersheds) and overlaid dye-tracer flow paths. Dye-tracer flow paths in (A) identify sinkhole drainage areas in a 10-digit HU (0511000113) mapped within the boundaries of the Upper Green River watershed that actually contribute to an adjacent 10-digit HU (not shown) located outside of the Upper Green River watershed. In contrast, dye-tracer flow paths in (B) identify a large area (approximately 85 square miles.) of sinkhole drainage mapped outside the boundaries of the Upper Green River watershed that, in fact, contribute to the watershed.

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108 DEM PROCESSING TO MAP SINKHOLE CATCHMENTS Sinkhole location maps have been, or are being, prepared by various State agencies in the regional study area; however, different sinkhole identifica tion and mapping criteria are being used and the catchment areas of the sinkholes are usually not delineated. In karst terrane s, delineation of sinkhole catchment areas is equally if not more important to hydrologic or water-quality studies and assessments as delineation of surface-str eam watersheds. For this regional study, individual sinkhole catchment areas define useful subbasin s within the 10-digit HUs. Therefore, a method of GIS processing of DEM data sets was developed to standardize and partly auto mate the mapping of sinkhole catchment areas. Topographic depressions in the DEMs are identified and artificially filled using GIS-processing tools, and a grid of the difference between the filled and unfilled depressions is developed. Throats, or locations within the depressi ons that are internally drained, are identified using a GIS SINK tool. Grid cells associated with these throats are grouped together by assigning them unique numeric values that lump throats together into clusters and tie the clusters to an associated topographic depression. Grouped topographic depressions and throats are then used as input data to define sinkhole catchment areas using a GIS WATERSHED delineation tool (fig. 4A). The grouping process helps eliminate over-tessellation (subdivision) of catchment areas for depressions identified in the raster grid (fig. 4B) and helps to produce more physically realistic delin eations of sinkhole catchments, complex sinkholes, and the watersheds of sinking streams that terminate in a sinkhole depressio n. Additional processing techniques, such as setting filters on depression size (area) and buffers near surface streams and perform ing cross-checks with sinkholes identified on avail able State maps, are needed to eliminate depressions in the raster grid that are not likely to be actual dis solution-generated sinkhole features. RELIC STREAM VALLEYS One unique component of the GIS processing being done for the regional study is the delineation of relic stream valleys, wh ich are also called paleov alleys (Thrailkill, 1985). Relic stream valleys are karst geomorphic features identifiable as alignments or trains of sinkholes so metimes co-located within shallow topographic valleys and often appear to be the downstream extensions of sinking or losing stream reaches. Relic stream valleys represent former surface-stream channels in which flow was abandoned as a result of subsurface conduit piracy. In this study, relic stream valleys are being delin eated using a GIS approach similar to that described by Glennon and Groves (2002) in which the DEMs are processed so that traces of the former surfaceflow routes develop as sinkhole depressions are arti ficially filled to their sp illover points (figs. 5A and 5B). The identification and mapping of relic stream valleys using GIS is a pot entially important outcome of this regional study because these features are often associated with the locations of major karst conduits and karst drainage basins (Thrailkill, 1985). The trends and geomorphic characteristics of the relic stream valleys also provide clues that are helpful in conceptualizing the pre-karst drainage history and in understanding the development of conduit networks and the directions of subsurface flow revealed by dye-tracer te sts (fig. 6). In addition, identification and mapping of relic stream valleys may help to identify poten tial flood hazard areas in the regions karst terranes. Flooding of relic stream valleysas with sinking or losing streamsoccurs when the drainage capacity of sinkholes, swallets, or karst conduits cannot ac commodate the volume of stormwater runoff generated within the surface catchment area (Ray, 2001). This mechanism has been identified in at least one location in the regional study area where flooding of a relic stream valley has resulted in substantial property damage (Bayless and others, 1994), and it may be an important, but poorly recognized, potential karst hazard elsewhere.

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109 Figure 4A. Delineation of sinkhole catchments (shaded or colored polygons) near Ver sailles, Kentucky, (Inner Bluegrass karst terrane) using GIS-processed DEM data. The im age shows the more realistic delineation of sinkhole catchments achieved by grouping throats (grid cells with internal drainage) within topographic depressions prior to apply ing the WATERSHED delineation tool. Figure 4B. Delineation of sinkhole catchments in the same area as that shown in figure 4A, illustrating the over-tessellation obtained by applying the WATERSHED delineation tool without grouping throats.

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110 Figure 5A. Example of DEM processing used to delineate relic stream valleys in part of the Central Kentucky karst ter rane. The image shows the geomorphologic patterns obtained by artificially filling identified sinkhole depressions to three different depths (indicated by shading).

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111 Figure 5B. Example of DEM processing used to delineate relic stream valleys in part of the Central Kentucky karst ter rane. The image shows the surface-flow routes generated by artificially filling all sinkhole depressions depicted in figure 5A to their spillover points. In GIS, these flow routeswhich delineate potential relic stream valleysare overlaid and compared with the blue-line streams data coverage to discriminate them from present-day valleys having actively flowing surface streams.

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112 Figure 6. GIS-processed image showing the apparent relation between relic stream valleys shown in figure 5B and subsur face-flow routes inferred from results of previously published dye-tracer tests (Taylor and McCombs, 1998). The curvilinear arrows that represent the dye-tracer flow paths were drawn to follow the configuration of the potentiometric surface mapped in 1997-98 and were not altered to follow the GIS-generated trends for the relic stream valleys.

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113 REFERENCES Bayless, E.R., Taylor, C.J. and Hopkins, M.S., 1994, Directions of ground-water flow and locations of ground-water divides in the Lost River watershed near Orleans, Indiana: U.S. Geological Survey WaterResources Investigations Re port 94-4195, 25 p., 2 pls. Currens, J.C., and Ray, J.A. 1999, Karst atlas for Ken tucky, in Beck, B.F., Pettit, A.J., and Herring, J.G., eds., Hydrogeology and engineering geology of sink holes and karstProceedings of the Seventh Multidis ciplinary Conference on Sink holes and the Engineering and Environmental Impacts of Karst, April 10-14, 1999: Harrisburg-Hershey, Penn., A.A. Balkema, Rot terdam, Holland the Netherlands, p. 85-90. Florea, L.J., Paylor, R.L., Si mpson, L., and Gulley, J., 2002, Karst GIS advances in Kentucky: Journal of Cave and Karst Studies, v. 64, no. 1, p. 58-62. Gao, Y., 2002, Karst feature distribution in southeastern MinnesotaExtending GIS-based database for spatial analysis and resource management: Minneapolis, Uni versity of Minnesota, Ph.D. dissertation, 210 p. Glennon, A., and Groves, C., 2002, An examination of perennial stream drainage patterns within the Mam moth Cave watershed, Kent ucky: Journal of Cave and Karst Studies, v. 64, no. 1, p. 82-91. Quinlan, J.F., and Ewers, R.O., 1989, Subsurface drain age in the Mammoth Cave area, in White, W.B., and White, E.L., eds., Karst hydrology concepts from the Mammoth Cave area: Van Nostrand Reinhold, New York, p. 65-104. Ray, J.A., 2001, Spatial interpretation of karst drainage basins, in Beck, B.F., ed., Geotechnical and environ mental applications of karst geology and hydrol ogyProceedings of the Ei ghth Multidisciplinary Conference on Sinkholes and the Environmental and Engineering Impacts of Karst, April 1-4, 2001: Louis ville, Ky., Swets & Seitlinge r, Lisse, Holland the Neth erlands, p. 235-244. Ray, J.A., Goodmann, P.T., and Meiman, J., 2000, Hydrologically valid delineation of watershed bound aries in Kentuckys karst terrane, in Proceedings of the Eighth Mammoth Cave Science Conference: Mam moth Cave National Park, p. 75-76. Taylor, C.J., and McCombs, G.K., 1998, Recharge-area delineation and hydrology, McCraken Springs, Fort Knox Military Reservation, Meade County, Kentucky: U.S. Geological Survey Water-Resources Investiga tions Report 98-4196, 12 p., 1 pl. Thrailkill, J., 1985, The Inner Bluegrass karst region, in Dougherty, P.H., ed., Caves and Karst of Kentucky: Kentucky Geological Survey Special Publication 12, Series IX, p. 28-62. Veni, G., 1999, A geomorphological strategy for conduct ing environmental impact a ssessments in karst areas: Geomorphology, v. 31, p. 151-180. Veni, G., 2003, GIS applications in managing karst groundwater and biological resources, in Beck, B.F., ed., Sinkholes and the engi neering and environmental impacts of karstProceedings of the Ninth Multidisci plinary Conference, September 6-10, 2003: Huntsville, Ala., American Society of Civil Engineers Geotechni cal Special Publication No. 122, p. 466-474.



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114 Application of Multiple Tracers to Characterize Comp lex Sediment and Pathogen Transport in Karst Tiong Ee Ting 1 Ralph K. Davis 2 J. V. Brahana 2 P.D. Hays 2,3 and Greg Thoma 1 1 Department of Chemical Enginee ring, 3202 Bell, University of Arkansas, Fayetteville, AR 72701 2 Department of Geosciences, 113 Ozark, University of Ar kansas, Fayetteville, AR 72701 3 US Department of Agriculture, Na tional Water Managemen t Center, 44 Ozark, Fayetteville, AR 72701 ABSTRACT Injections of multiple tracers were conduced to characterize ground-wat er flow, sediment transport, and E. coli transport in a mantled-karst aqui fer under variable flow conditions at the Savoy Experimental Water shed. Rhodamine WT and fluorescein, used as conserva tive tracers in this study, were injected two hours after the injection of lanthanum-la beled clay and europium-labeled E.coli into a losing-stream reach under a natural hydraulic gradient. The injection occurred on th e recessional limb of a major storm pulse, and fate and transport of the tracers were observed for multiple tests under varying hydrol ogic conditions using mul tiple tracers for two springs of an underflow/overflow spring complex. The underflow spring, Langle, is located approximately 490 meters in a straight-line direction from the inje ction point, in a different surfacewater catchment than the losing stream The major overflow spring, Copperh ead, is 453 meters in a straightline from the injection point, and it lie s in the same surface-water catchmen t as the losing stream. The alti tude of the resurgence of Langle Spring is about 3 centimeters less than the resurgence of Copperhead Spring, based on multiple surv eys using a total station. Results from the tracer breakthrough for near steady-state conditions showed the arrival of suspended sediment and E. coli at 10.7and 5.9 hours respectively before th e conservative dye tracers at Langle Spring. The early arrival of sediment and E. coli is hypothesized to result from gravitational settling velocity cou pled with the effect of pore-size exclusion. The cons ervative dye tracers arrived fi rst at Copperhead Spring, followed by E. coli and sediment, essentially a reversal of the sequence at Langle Spring. During later storm-induced tracer tests, all tracers were observed to arrive simultaneously at each spring, with Copper head Spring, along the shorter flow path, receiving the tracer pulses about an hour before Langle Spring. This and other tracer tests in this overflow /underflow system suggest that sediment and E. coli are stored in pools in the subsurface. These pools provide continuous full-conduit flow to Langle, the underflow spring, and only partially-full conduit flow to Copperhead, the overflow spring. However, during high flows asso ciated with transient storm events, the tracers are fl ushed from ephemeral storage in the pools and move as a pulse associated with the rising limb of the hydrograp h. The application of mu ltiple tracers proved to be an invaluable tool in provid ing mechanisms to fully char acterize the subsurface flow.

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115 Estimating Ground-Water Age Distri bution from CFC and Tritium Data in the Madison Aquifer, Black Hills, South Dakota By Andrew J. Long and Larry D. Putnam U.S. Geological Survey, 1608 Mountain Vi ew Rd, Rapid City, South Dakota 57702 Abstract Ground-water age distribution was estimated for wa ter collected from a well in the karstic Madison aquifer in the Black Hills of Sout h Dakota using a ground-water mi xing model for chlorofluorocarbon (CFC) and tritium data. Input functi ons for the model included precipita tion concentrations for four trac ersCFC12, CFC11, CFC113 (6-month data), and tritiu m (yearly data). Madison aquifer water often is a complex mixture of waters of various ages; however, existing ground-water age-dating methods generally are not well suited for estimating the unique age distri butions of ground water that can occur in karst aqui fers. CFC data alone often can provide estimates of piston-flow ages or binary mixtures of young and old water, but generally are inadequate for estimating age distributions at a finer time discretization. However, if a time series of tritium data is incorporated into an age-dating model along w ith CFC data, an age distri bution discretized to a 6-month time step can be estima ted with statistical significance by assuming that ground-water age fits a probability de nsity function (PDF). This method estimates one age distribution that satisfies all of the combined tracer data and thus has two advantages. The first of which is that the number of measured values applied to a single problem is ma ximized, which helps to constrain the solution, and second is that confidence in the solution is increased if a single solutio n satisfies more than one type of data. The PDF indicates the estimated fraction of water at a site for each 6-month age category. Because results from multiple age-dating tracers shoul d agree, and because to gether they may provid e complimentary infor mation, combining all of the data in to one model can be a powerful me thod for describing the history of recharge to a well or spring. The best fit of CFC and tritium data for samples from a municipal water supp ly well open to the Mad ison aquifer was a bimodal age distri bution, which was a composite of a uniform and a lognormal PDF. Data used in the model incl uded the concentrations for eac h of the 3 CFCs (1 sample) and a time series of tritium concentrations (4 samples ov er 10 years). These samples provided a total of 7 tracer concentrations, which were compared to the corresponding modeled values. Parameter optimization meth ods, which minimize the residuals of measured and modeled values, were used to estimate the 4 parameters that describe the bimodal age distribution. Because there were 7 measured trace r concentrations and only 4 parameters to be esti mated, the solution was adeq uately constrained, and the parameters could be estimated with reasonable con fidence. Results indicated that ab out 33 percent of the mixture was less than 2 years old (uniform PDF component), 5 percent was 10 to 30 years old (lognormal PDF componen t), and the remaining 62 percent was more than 50 years old. Because CFC and tritium co ncentrations in precipitatio n were very low before 1950, the age distribution of water more than about 50 years old could not be estimated. The bimodal age distribution was the only distribution tested that could explain the combin ed CFC and the tritium data with acceptable 95-percent confidence limits on the estimated parameter values.

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116 A Multi-Tracer Approach for Evalua ting the Transport of Whirling Disease to Mammoth Creek Fish Ha tchery Springs, Southwestern Utah By Lawrence E. Spangler 1 Meiping Tong 2 and William Johnson 2 1 U.S. Geological Survey, 2329 Orton Circle, Salt Lake City, Utah 84119 2 Department of Geology and Geophysics, Univer sity of Utah, Salt Lake City, Utah 84112 ABSTRACT The Utah Division of Wildlife Resources has been con cerned about the vulnerabi lity of selected springfed fish hatcheries to whirling disease caused by the microscopic parasite Myxobolus cerebralis Whirling disease is typically transmitted from one water body to another by bird s or fishermen but can potentially migrate along underground flow path s in areas where aquifer permeability is high and ground-water move ment is rapid enough to allow passage and survival of the parasite. Mammoth Creek Fish Hatchery in south western Utah tested positive for whirling disease in 2002. Because ad jacent Mammoth Creek also tested positive, a study was begun to evaluate potential hydrologic co nnections between the creek, an irrigation canal off the creek, and the hatchery springs. Dye-tracer studies indicate that water lost through the channel of Mammoth Creek discharges from the west and east hatchery springs. Ground-water time of tr avel to the springs was ab out 7.5 hours, well within the 2-week timeframe of viability of the parasite. Resu lts of studies using soil bacteria and club moss spores as surrogate particle tracers indicate that the potential for transport of the parasite through the fractured basalt may be low. Bacteria concentrations in spring water generally were belo w reporting limits, and club moss spores were recovered from only a few samples. However, peak concentratio ns for the bacteria and club moss spores in water from the east hatchery spring coincided with peak dye recovery. No particle trac ers were recovered from the west hatchery spring. INTRODUCTION The Utah Division of Wildlife Resources oper ates 10 fish hatcheries in Utah that use water from large springs and has been concerned about the vul nerability of these hatc heries to whirling disease caused by the microscopic parasite Myxobolus cere bralis. Whirling disease is typically transmitted from one water body to another by birds or fisher men. However, the triac tinomyxon spores (TAMs) produced by the parasite can potentially migrate along underground flow paths in areas where aquifer permeability is high, such as in karst and volcanic terrains, and the movement of ground water is suffi ciently rapid to allow viable passage of the spores. In 2000, whirling disease was detected in the Midway Fish Hatchery, about 30 miles (mi) south east of Salt Lake City. Resu lts of investigations by Carreon-Diazconti and others (2003) showed that the likely source of the parasite in the spring water supplying the hatchery was the Provo River. Water diverted from the river, which also tested positive for the disease, was used to irrigate farmland upgra dient from the hatchery and subsequently moved downward into the karst (t ravertine) aquifer supply ing the springs. Use of cultured soil bacteria as a sur rogate tracer for the parasite showed that transport of the spore to the springs th rough open conduits and fractures in the limestone was possible (Stephen Nelson and Alan Mayo, Brigham Young University, written commun., 2000). In 2002, Mammoth Creek Fish Hatchery in southwestern Utah became the second Stateoper ated facility to become infected by whirling disease. Because adjacent Mammoth Creek also tested posi tive, the U.S. Geological Survey, in cooperation with the Utah Division of Wildlife Resources, began a study to evaluate potential hydrologic connections and determine ground-water travel times between the creek, an irrigation canal off the creek, and the

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117 hatchery springs, and to assess the potential for transport of the parasite along underground flow paths to the springs. This paper summarizes the results of tracer studies. DESCRIPTION OF STUDY AREA Mammoth Creek State Fish Hatchery is located about 2 mi southwest of Hatch, Utah, at the mouth of Mammoth Creek Valley, at an altitude of 7,000 feet (ft) (fig. 1). The hatchery is situated at the base of a 40-ft-high basalt cliff, fro m which two major (west and east) springs discharge. Total discharge of the springs averages about 3 cubic feet per second (ft 3 /sec), with a variability of less than 1 ft 3 /sec. Flow from the springs is diverted through the hatch ery for fish-rearing operations and is then discharged into Mammoth Creek, which flows past the hatch ery. McCormick spring also discharges from near the base of the basalt cliff about 750 ft northeast of the hatchery springs, on private land (fig. 1). Dis charge of this spring was about 50 gallons per minute (gpm) during the st udy and appeared to be fairly constant. Bonanza spring emerges from talus alongside the channel of Mammoth Creek about 1,200 ft upstream from the hatchery (fig. 1) and dis charged about 40 gpm. Discharge of this spring was observed to vary with ch anges in streamflow in Mammoth Creek. During the summer, wa ter is diverted from Mammoth Creek into a canal about 2 mi west of the hatchery (fig. 1) for irrigatio n in the lower part of the valley. During the study, all water from the creek was diverted into the canal and only a small amount of inflow from springs was observed downstream in the channel, which subseq uently was lost through the streambed (fig. 2). Figure 1. Location of injection sites and springs and general directions of ground-water movement in the Mammoth Creek study area, southwestern Utah.

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118 Quaternary-age basaltic lava partly fills Mam moth Creek Valley and caps adjacent ridges. In the vicinity of the hatche ry, the basalt has been entrenched by Mammoth Creek to a depth of as much as 40 ft (fig. 2). Vertical and horizontal frac turing is pervasive th roughout the basalt. Lime stones, marls, and calcareous shales of the Tertiaryage Claron Formation underlie the basalt and adja cent hillsides and are locally cavernous. METHODOLOGY Major-ion chemistry, tritium age-dating, streamflow measurements, spring discharge vari ability, and tracer studies were used to determine hydrologic relations in the Mammoth Creek hatch ery area. Fluorescent dyes (sodium fluorescein and rhodamine WT) and sodium bromide were used to establish ground-water connections between Mam moth Creek, an irrigation can al off the creek, and the springs at, and in the vicini ty of, the fish hatchery. Automatic samplers collect ed water directly from the springs for analysis. Dye samples were analyzed by filter fluorometry (W ilson and others, 1986). Sodium bromide samples were analyzed by ion chromatography (Fishman and Friedman, 1989). Non-pathogenic cultured soil bacteria (Acidovorax) and club moss (Lycopodium) spores were used as surrogate particle tracers to simulate the size (10 to 100 microns) and transpor t characteristics of the whirling disease parasite through the fractured basalt aquifer. Bacteria samples were collected man ually in centrifuge vials, magnetically tagged, and analyzed by ferrographic techniques (Johnson and McIntosh, 2003). Club moss spores were collected in plankton nets (fig. 3), isolated by filtration, and analyzed by standard micr oscopic techniques (Gard ner and Gray, 1976). RESULTS AND DISCUSSION On the basis of dye-tracer tests completed in October 2002 and October 2 003 (table 1), water lost through the channel of Mammoth Creek about 3,000 ft southwest of the hatchery (at Sartini) discharges from the west and east hatchery springs and from McCormick spring (fig. 1) However, water lost through the channel fart her downstream appears Figure 2. Mammoth Creek channel at the Sartini tracerinjection site, looking downstream. Surface water seeps into the streambed and appears to move along fractures within the basalt to the springs. Figure 3. Plankton nets were used to collect club moss spores from the west and east hatchery springs. Spores were used as surrogate tracers (33 microns) for the whirl ing disease parasite.

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Table 1. Summary of tracer injections in the Ma mmoth Creek study area, southwestern Utah. [g, grams; kg, kilograms; , no data] Tracer-injection site Date-time of tracer injection Type of tracer Amount of tracer Tracer-recovery site Date-time of tracer recovery (first arrival) Travel time to first arrival (hours) Linear distance (feet) Mammoth Creek 10/02/02 1300 Rhodamine WT dye 1 liter Bonanza spring 10/02/02 2015 17.25 750 Mammoth Creek at Sartini 10/12/02 1300 Fluorescein dye 454 g Hatchery springs (combined) McCormick spring 10/12/02 10/13/02 2300 1100 10 222 2,800 3,300 Mammoth Creek at Sartini 10/09/03 10/09/03 10/09/03 1630 1615 1645 Rhodamine WT dye Bacteria (OY-107 strain) Club moss spores 1 liter 1014 cells 1 kg West hatchery spring East hatchery spring McCormick spring East hatchery spring East hatchery spring 10/10/03 10/10/03 10/10/03 10/10/03 10/10/03 0000 0100 1045 0700 1205 7.5 8.5 318.25 414.75 519.25 2,800 3,000 3,300 3,000 3,000 Mammoth Creek canal 10/10/02 10/11/02 1340 1720 Sodium bromide Sodium bromide 25 kg 25 kg No recovery No recovery Mammoth Creek canal 07/31/03 2200 Fluorescein dye 1.36 kg McCormick spring 08/19/03 1700 6451 (7) 1Samples collected downstream of spring; maximum travel time. 2Samples collected daily; maximum travel time. 3Samples collected twice daily; maximum travel time. 4Recovered near peak dye concen tration; maximum travel time. 5Represents composite sample over previous 13.5 hours. 6Dye recovered on activated charcoal; maximum travel time. 7Exact location of loss zone along canal unknown.

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120 to discharge only from Bonanza spring. Groundwater travel time (first arrival) from Mammoth Creek (at Sartini) to the west hatchery spring was about 7.5 hours with a lag of about 1 hour between the west and east springs (fig. 4). Time to peak dye concentration (about 7 pa rts per billion) occurred about 8 hours after first arrival. Total dye-mass recovery for both springs was about 22 percent of that injected. Ground-water movement from Mammoth Creek to the hatchery springs appears to be along flow path(s) that are separate from those to Bonanza spring and are probably related to fracturing within the basalt. However, because water from the hatchery springs and McCo rmick spring discharges from multiple outlets along the same horizon, flow appears to be, at least in part, along lateral zones of high permeability within the basalt. These zones could include horizontal fractures, interflow horizons between successive lava flows, or possibly the contact between the b ase of the basalt and the original valley floor. Although pathways of rapid ground-water flow exist between the losing reach along Mammoth Creek and the hatchery sp rings, low variability in spring flow indicates that this is probably a small component of total discharge and that average ground-water travel time with in the aquifer is likely to be considerably longer. The concentration of tritium (15.4 picocuries per liter) in water from the west hatchery spring indicates, however, a substantial component of modern (post-1960s) water. Results of dye-tracer studies indicate that ground-water time of travel between Mammoth Creek and the west and east hatchery springs is well within the 2-week timeframe of viability of the whirling disease parasite. However, results of studies using bacteria and club moss spores as surrogate tracers to simulate the size and movement of the parasite underground indicate that the potential for transport of the parasite through the fractured basalt aquifer from the creek may be low. Bacteria concentrations in water samples from the springs generally were be low reporting limits (less than 10 cells per milliliter), and club moss spores were recovered from only a few samples. Substantial losses of the particle tracers probably occurred during infiltration through the streambed sediments and during transp ort within the aquifer. Figure 4. Rhodamine WT dye-recovery curves, and bacteria and club moss spore peak recoveries for the east hatchery spring. No particle tracers were recovered from the west hatchery spring. 0 1 2 3 4 5 6 7 8 10/8/0310/9/0310/10/03 10/ 11/0 310/12/0310/13/03 10/14/03 10/15/0310/16/03 10/17/0310/18/0 3 Tracer injectio n (4:30 pm) Peak dye recovery (9:00 am) Club moss spore recovery (12:05 pm) Bacteria recovery (7:00 am) East spring W est sprin gDye concentration (parts per billion)

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121 Although the vast majority of particle tracers were not recovered, peak concen trations for the bacteria (about 10 cells per milliliter) and club moss spores (about 60 spores per milliliter) in water from the east hatchery spring coincided with peak dye recovery (fig. 4). No particle tracers were recovered from the west hatchery spring. Streamflow measurements along the irrigation canal off Mammoth Creek showed substantial losses along selected reaches, particularly in the upper part of the canal (fig. 1). Measured streamflow losses along a 2-mi reach below the diversion were as much as 2 ft 3 /sec, or about 22 percent of the flow. Bromide and dye tracers inje cted in the canal just below the diversion in Octo ber 2002 and July 2003, respectively, were not detected at the hatchery springs, but dye was detected at McCormick spring (table 1). Non-detection of the tracers at the hatchery springs probably resulted from dispersion and dilu tion within the matrix of the basalt aquifer, resulting in ground-water travel times greater than the 6-week monitoring period and (or) tracer concentrations below the detection limits Although water lost along the upper reaches of the canal probably dis charges at the hatchery springs, ground-water travel times likely exceed the tim eframe of viability for transport of the parasite through the basalt. SUMMARY Dye-tracer studies at the Mammoth Creek Fish Hatchery indicate that wate r lost through the channel of Mammoth Creek discharges from the west and east hatchery springs. Ground -water time of travel to the springs was about 7.5 hours, well within the 2week timeframe of viability of the whirling disease parasite. However, results of studies using soil bac teria ( Acidovorax ) and club moss ( Lycopodium ) spores as surrogate particle tracers for the parasite indicate that the potential for transport through the fractured basalt from the creek may be low. Substan tial losses of the particle tracers occurred during streambed infiltration and aq uifer transport. Bacteria concentrations generally were below reporting lim its and club moss spores were recovered from only a few samples. However, peak concentrations for the bacteria and club moss spores in water from the east hatchery spring coincided with peak dye recovery. No particle tracers were recovered from the west hatchery spring. In additio n, bromide and dye tracers injected in an irrigation canal were not detected at the hatchery springs. REFERENCES Carreon-Diazconti, C., Nelson S.T., Mayo, A.L., Tingey, D.G., and Smith, M., 2003, A mixed groundwater system at Midway, Utah: Di scriminating superimposed local and regional discharge: Journal of Hydrology, v. 273, p. 119-138. Fishman, M.J., and Friedman, L.C., 1989, Methods for determination of inorganic s ubstances in water and flu vial sediments: U.S. Geologi cal Survey Techniques of Water-Resources Investigat ions, Book 5, Chap. A1, 545 p. Gardner, G.D., and Gray, R.E., 1976, Tracing subsurface flow in karst regions using artificially colored spores: Bulletin of the Association of Engineering Geologists, v. 13, no. 3, p. 177-197. Johnson, W.P., and McIntosh, W.O., 2003, Tracking of injected and resident (pre viously injected) bacterial cells in groundwater using ferrographic capture: Jour nal of Microbiological Methods, v. 54, p. 153-164. Wilson, J.F., Jr., Cobb, E.D., and Kilpatrick, F.A., 1986, Fluorometric procedures for dye tracing: U.S. Geolog ical Survey Techniques of Water-Resour ces Investiga tions, Book 3, Chap. A12, 34 p.



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122 National Evaporite Kars t--Some Western Examples By Jack B. Epstein U.S. Geological Survey, National Center, MS 926A, Reston, VA 20192 ABSTRACT Evaporite deposits, such as gypsum, anhydrite, and rock salt, underlie about one-third of the United States, but are not necessarily exposed at the surface. In the humid eastern United States, evaporites exposed at the surface are rapidly removed by solution. However, in the semi-arid and arid western part of the United States, karstic features, including sinkholes, springs, joint enlargement, intrastratal collapse breccia, breccia pipes, and caves, locally ar e abundant in evaporites. Gypsum an d anhydrite are much more soluble than carbonate rocks, especially where they are associated w ith dolomite undergoing de dolomitization, a process which results in ground water that is continuously undersaturated with respect to gypsum. Dissolution of the host evaporites cause collapse in overlying non-soluble rocks, includ ing intrastratal collapse breccia, breccia pipes, and sinkholes. The di fferences between karst in carbonate and evapor ite rocks in the humid eastern United States and the semi-arid to arid wester n United States are delimited approximately by a zone of mean annual precipitation of 32 inches. Each of these two rock gr oups behaves differently in the humid eastern United States and the semi-arid to arid west. Low ground-water tables and decreased ground water circulation in the west retards carb onate dissolution and development of karst. In contrast, dissolution of sulphate rocks is more ac tive under semi-arid to arid conditions. The generally thicker soils in humid cli mates provide the carbonic acid necessary for carbonate dissolution. Gypsum and anhydrite, in contrast, are soluble in pure water lacking organic acids. Exampl es of western karst include the Black Hills of South Dakota and the Holbrook Basin in Ar izona. A draft national map of ev aporite karst is presented here. INTRODUCTION The present, the map indicating engineering aspects of karst (Davies and others, 1984, scale 1:7,500,000) adequately shows the distribution of carbonate karst in the Un ited States, but the wide spread distribution of evapor ite karst is inadequately portrayed. The map depicts areas of karstic rocks (limestone, dolomite, and evaporites), and pseudokarst, classified as to their engineering and geologic characteristics (size and depth of voids, depth of overburden, rock/s oil interface conditions, and geologic structure). In the eastern United States, where average annual precipitation commonly is greater than 30 inches, gypsum deposits generally are eroded or dis solved to depths of at leas t several meters or tens of meters below the land surfa ce. So, although gypsum in the east may locally be karstic, the lack of expo sures makes it difficult to prove this without subsurface study of the gypsum and its dissolution features. In the semi-arid western part of the United States, however, in areas where the average annual precipitation commonly is le ss than about 32 inches, gypsum tends to resist erosion and typically caps ridges, mesas, and buttes. In spite of its resistance to erosion in the west, gypsum commonly contains vis ible karst features, such as cavities, caves, and sink holes, attesting to the importance of ground-water movement, even in low-rainfall areas. Salt karst is less common at the earths surface than gypsum karst because it is so solubl e that it survives at the surface only in very arid areas. While the distribution of carbonate karst on the Davies map is generally adequate, the map only depicts gypsum karst in a few areas (fig. 1). In an extensive text on the back of the map, caves and fis sures in gypsum in western Oklahoma and the east ern part of the Texas Panhandle is mentioned. The

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123 map does not show the distribution of salt or salt karst even though the text mentions natural subsid ence and man-induced subs idence due to solution mining in salt beds in south-central and southwest ern Kansas. Several national maps of evaporite deposits were summarized by Epstein and Johnson (2003) who prepared a map showing the present perception of evaporite distribution an d evaporite karst in the United States (fig. 2). The map includes gypsum/ anhydrite and halite basins, and incorporates the limited areas of evaporite karst depicted by Davies and others (1984) compared to the larger areas of the same shown by Johnson (1 997). Collapse due to human activities, such as solution mining, are also shown, as well as a line of mean annual precipitation (32.5 in.) that approximates the boundary between distinctively different kars t characteristics, between the humid eastern United States and the semi-arid west. Also shown are the Holbrook Basin in Ari zona and the Black Hills of South Dakota and Wyoming, whose variety of surface and subsurface evaporite-karst features are described here. HOLBROOK BASIN, ARIZONA Many workers have reported a variety of evaporiteand carbonate-kar st features in Arizona (fig. 3A) that are not found on Davies (1984) map (fig. 3B). Subsurface ha lite deposits were mapped by Eaton and others (1972), Johnson and Gonzales (1978), Ege (1985), and Neal and others (1998); more detailed mapping of salt deposits in the Hol brook Basin was done by Peirce and Gerrard (1966) and Rauzi (2000). An area of breccia pipes was delimited in northwest Arizona by Harris (2002); they were probably the result of collapse over car bonate rocks, but evapor ite collapse could not be ruled out. Scattered gypsum and anhydrite localities were shown by Withington (1962). Comparing this composite map with the Davies map (fig. 3 B ) shows that many types of karstic features could be shown in both evaporite and carbonate rocks in Arizona. Figure 1. Map showing areas of evaporite karst in the United States, as depicted by Davies and others (1984).

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124 Figure 2. Distribution of outcropping and subsurface evaporite rocks in the United States and areas of reported evaporite karst (from Epstein and Johnson, 2003). The 32.5" meanannual-precipitation line approximates a diffuse boundary between eastern and western karst. The Holbrook Basin in east-central Arizona demonstrates that dissolution of deeply buried evaporites can cause subsidence of overlying nonsoluble rocks. The basin is more than 100 miles wide and contains an aggregate of about 1,000 feet of salt, anhydrite, and sy lvite interbedded with clas tic red beds in the Permian Sedona Group (formerly the Supai Group) (Peirce and Gerrard, 1966; Neal and others, 1998; Rauzi, 2000 ). The top of the salt is between 600 and 2,500 ft below the surface (Mytton, 1973). These workers describe the removal of evaporites at depth along a northwest-migrating dis solution front, causing the development of presently active collapse structures in the overlying Coconino Sandstone and Moenkopi Formation. For example, in the area about 10 mi northwest of Snowflake, AZ, the Coco nino and other rocks dip monoclinally southward along the Holbrook anti cline towards a large depression enclosing a dry lake. The depression is the result of subsidence due to evaporite removal. Collapse extends upwards from the salt, forming a network of spectacular sink holes in the overlying Coconino Sandstone (fig. 4, 5 A ) (Neal and others, 1998; Harris, 2002). Draping of the Coconino has caused opening of extensive tension fissures, some of which are many tens of feet deep (Neal and others, 19 98; Harris, 2002) (Fig. 5 B ). If the definition of karst is allowed to include sub sidence structures due to the dissolution and removal of soluble rock s below and extending upwards into non-soluble rocks, then a separate map category may be needed to delineate these rocks. Thus, any karst map must show non-soluble rocks whose collapse structures are the result of dissolu tion of evaporite rocks below. A somewhat similar situation prevails in the Black Hills of South Dakota and Wyoming and was alluded to at Stops 3 and 4 of the Southern Field Trip (Epstein, Agenbroad, and others, this volume, 2005).

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125 BLACK HILLS, WYOMING AND SOUTH DAKOTA In the semi-arid Black Hills of Wyoming and South Dakota, significant deposits of gypsum and lesser anhydrite are exposed at the surface in several stratigraphic units (Table 1, Epstein and Putnam, this volume ), including the Minnelusa, Spearfish, and Gypsum Spring Formations. The field guides that accompany this volu me document many of the karst features found in these rocks. The outcrop pat tern of sedimentary units in the Black Hills is con trolled by erosion on an ir regular domal uplift about 130 mi long and 60 mi wide. The central core of Precambrian rock is surrounded by four zones of sedimentary rock with c ontrasting lithologies and differing karst features. These are, from the center (oldest) outwards: (1) The limestone plateau, made up of Cambrian to Penn sylvanian limestone, dolo mite, and silici-clastic rocks, and containing worldclass caves such as Wind and Jewel Caves in the Pahasapa Limestone. Overlying these limestones is the Minnelusa Formation, which contains as much as 235 ft of anhydrite in its upper half in the subsur face. This anhydrite has been dissolved at depth, producing a variety of disso lution structures (Stop 1, Epstein, Agenbroad, and others, this volume; and Stop 4, Epstein, this volume ) (2) The Red Valley, predominantly underlain by red beds of the Spearfish Formation of Triassic and Permian age and containing several gypsum beds totaling more than 75 ft thick in places. Dissolution of these evaporites, and those in underlying rocks, has pro duced shallow depressions and sinkholes, some of which are more than 50 ft deep (Stops 8 and 9, of Epstein, Davis, and others, 2005, this volume). The Gypsum Spring Formation, which overlies the Spearfish, contains a gypsum unit, as much as Figure 3. Maps comparing types and distribution of ka rst features in Arizona: A) distribution of evaporite and carbonate karst as presented by various authors; B) distribution of carbonate karst (no evaporite karst was shown) as presented by Davies and others (1984).

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126 15 feet thick, that has developed abundant sinkholes in places. (3) The "Dakot a" hogback, held up by resistant Sandstone of the Inyan Kara Group of Cre taceous age, and underlain by shales and sandstones of the Sundance and Morris on Formations. Collapse structures, such as breccia pipes and sinkholes, extend up through some of these rocks from under lying soluble rocks, probab ly in the Minnelusa For mation. (4) Impure limestone and shale extending outward beyond the hogback, some of which are shown as karstic units on the map of Davies and oth ers (1984), but such features are unknown in those rocks. Figure 6 compares the map of limestone out crops shown by Davies and others (1984) for the Black Hills of South Dakota with the more detailed categories that are proposed here, including carbon ate and evaporite karst, intrastratal karst, and nonsoluble rocks with collapse features due to dissolu tion of other rock units at depth. This characteriza tion may also be suitable for other areas of the western United States. Anhydrite in the Minnelusa is generally not seen in surface outcrops. It has been, and continues to be, dissolved at depth, forming collapse breccias, breccia pipes, and sinkho les that extend upwards more than 1,000 ft into overlying units. Mapping this intrastratal karst is fairly easy, because the out crop distribution of the Minnelusa is well known. At depth, brecciation of the upper part of the Minnelusa has developed significant porosity, resulting in an important aquifer. Ground water migrates along breccia pipes that extend upwards through overlying formations. A migrating dissolution front (Epstein, 2001; 2003) similar to the situation reported for the Holbrook Basin in Arizon a, is summarized below. Dissolution Front in the Minnelusa Formation The upper half of the Minnelusa Formation con tains abundant anhydrite in the subsurface, and except for a few areas near Beulah and Sundance, Wyoming (Brady, 1931), an d in Hell Canyon in the southwestern Black Hills (Braddock, 1963), no anhydrite or gypsum crops out. A log of the upper part of the Minnelusa from Hell Canyon contains 235 ft (72 m) of anhydrite and gypsum (Braddock, 1963; Brobst and Epstein, 1963). Where anhydrite is present in the Minnelusa, its rocks are not brecci ated or only slightly so. Where the rocks are brecci ated in outcrop, anhydrite is absent. Clearly, the brecciation is the result of collapse following sub surface dissolution of anhydrite. The Madison and Minnelusa are the major aqui fers in the Black Hills. They are recharged by rain fall on and by streams fl owing across their up-dip outcrop area. In the Minnelusa, removal of anhy drite progresses downdip w ith continued dissolution of the anhydrite (fig. 7), collapse breccia is formed, breccia pipes extend upward s, and resurgent springs develop at the sites of sinkholes. Cox Lake, Mud Lake, Mirror Lake, and McNenny Springs (Stop 8, Epstein, Davis, and others, this volume ), are near the position of the dissolution front. As the Black Hills is slowly lowered by erosion, the anhydrite dissolu tion front in the subsurface Minnelusa moves down dip and radially away from the center of the uplift. The resurgent springs will dry up and new ones will form down dip as the geomorphology of the Black Hills evolves. Abandone d sinkholes on canyon walls (see figure 8, Epstein, Davis, and others, this volume ) attest to the former position of the dissolu tion front. Because ground water has dissolved the anhy drite in the Minnelusa in most areas of exposure, and because anhydrite is present in the subsurface, a transition zone should be present where dissolution of anhydrite is currently taking place. A model of this zone has been presented by Brobst and Epstein (1963, p. 335) and Gott and others (1974, p. 45) and is shown here in figure 7. Consequences of this model include (1) the up-dip part of the Minnelusa is thinner than the downdip pa rt because of removal of significant thickness of an hydrite, (2) the upper part of the Minnelusa should be continually collapsing, even today, and (3) the proper ties of the water in this transition zone may be different than elsewhere.

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127 Figure 4. Topographic map of "The Sinks", a se ries of depressions in the Coconino Sandstone, about 10 miles northwest of Snowflake, Arizona, in the Holbrook Basin. Wide depressions are highlighted with a dashed line; the one in the southwest corner of the map is about one mile long. Other depressions are as much as 100 feet deep.

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128 If this process is correct, then present resurgent springs should be eventu ally abandoned and new springs should develop down the regional hydraulic gradient of the Black Hills. One example might be along Crow Creek where a cloud of sediment from an upwelling spring lies 1,00 0 ft (300 m) north of McNenny Springs (See figure 15, Stop 8, Northern Field trip Guide). This circular area, about 200 ft across, might eventually replace McNenny Springs. Age of Brecciation Solution of anhydrite in the Minnelusa probably began soon after the Black Hills was uplifted in the early Tertiary and contin ues today. Recent subsid ence is evidenced by sink holes opening up within the last 20 years (See figure 26, Epstein, Davis and others, this volume), collap se in water wells and nat ural springs resulting in sediment disruption and contamination, fresh circular scarps surrounding shallow depressions, and calcium sulphate and sodium chloride issuing from spring water through out the Black Hills. The brecciation of the upper part of the Min nelusa formation occurred af ter the up-dip portion of the Minnelusa was breached following uplift. Ground water was then able to penetrate the imper meable layers overlying the Minnelusa and the anhydrite was dissolved. Darton and Paige (1925) found "older terrace deposits" with Oligocene fos sils on the Minnelusa, indicating that the breaching of the Minnelusa occurred before the Oligocene and after the Late Cretaceous uplift. An earlier alternative ex planation for the cause and timing of brecciation was given by Bates (1955) who believed the brecciation occurred almost con currently with the deposition of the Minnelusa when ground water converted the anhydrite to gypsum and the resulting expans ion heaved and shattered the sur rounding strata leaving ju mbled blocks that were reworked by the sea. Howe ver, field evidence sup ports the conclusion that brecciation occurred after, not during, the deposition of the Minnelusa. Dis ruption of bedding in the Minnelusa and in higher stratigraphic units beco mes less intense upwards from the zone of anhydrite removal in the Minnelusa (Stop 1, Epstein, Agenbroad, and others, 2005, this volume ). Subsidence effects in the overlying forma tions also become less dramatic. The resistant, thin, Minnekahta Limestone, lying between the red beds of the Opeche Shale and Sp earfish Formation, con tains few collapse features; some sinkholes pene trate the entire thickness of the Minnekahta and are therefore result of collapse from below (Stop 3, Epstein, Davis, and others, this volume ). The most significant effect on the Minnekahta is the undula tions seen in outcrop everyw here in the Black Hills. Breccia pipes and sinkholes are known as high as the Lakota Formation, about 1,000 feet above the Minnelusa. Figure 5. Collapse structures in clastic rocks overlying the salt-bearing Sedona Group in the Holbrook Basin, 810 mi northwest of Snowflake, AZ. A) Steep-sided sink hole in a hole-pocked area called "The Sinks," located in the Coconino Sandstone. Note the variable amount of subsidence along major joints. B) Open tension fractures in the Moekopi Formation caused by flexure of the Holb rook "anticline" (actually a monocline) due to dissolution of salt at depth. Also see figures in Harris (2002).

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129 Figure 6. Maps comparing depiction of karst areas in the Black Hills of South Dakota: A) carbonate-karst units, as presented by Davies and others (1984); B) carbonateand evaporite-karst units, as herein proposed for a new national karst map. There are several places in the Black hills where bedding in the Minnelusa is moderately or steeply dipping and intruded by breccia pipes. If the pipes formed soon after deposition of Minnelusa sedi ments, they should be nearly right angles to bedding. Such is not the case, as seen at mileage 59.3 in the Southern Field trip Guide, where the dip of bedding is moderate and shown in figure 8 where the dip is steeper. HUMID VERSUS SEMI-ARID KARST Comparing the known locations of surface evaporite karst with a map showing annual average rainfall shows a striking relationship between pre cipitation and the occurrence of evaporite karst (fig. 2). Most occurrences of surficial karst in gypsum shown in figure 2 lies west of a zone with annual precipitation of about 32 inches (represented by the 32.5-inch isobar). Many of the karst areas shown in figure 2 are due to dissolution at depth. In Michigan, earlier studies suggest that the karstic collapse fea tures there were formed soon after deposition of the Devonian evaporites (Landes, 1945), but Black (1997) showed that sinkhole development occurred after the most recent glaciation. The degree to which soluble rocks are dissolved depends, in part, on the amount of rainfall and the solubility of the rock. Sulphate-bearing rocks--gyp sum and anhydrite--are perhaps 10-30 times more soluble in water than car bonate rocks (Klimchouk, 1996). Both carbonates and sulphates behave differ ently in the humid eastern United States and the semi-arid to arid west. Low ground-water tables and decreased ground-water circulation in the west does not favor rapid carbonate dissolution and develop ment of karst. In contrast, sulphate rocks are dis solved much more read ily and actively than carbonate rocks, even unde r semi-arid to arid condi tions. The presence of extensive karst in carbonates in the west probably dates to a more humid history. Additionally, the generally thicker soils in humid climates provide the carbonic acid that enhances car bonate dissolution. Gypsum and anhydrite, in con trast, are more readily soluble in water that lacks organic acids. This relationship suggests an inter esting area for future study.

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130 In the eastern United States karstification occurs by acid-charg ed water percolating down ward altering soluble rocks below. While this is partly true in the west, much of the karst, such as in the Black Hills, is produ ced by artesian water migrating upward affecting overlying rocks in a dif ferent manner than in the humid east. Thus, as shown above, non-soluble rocks bear the imprint of karst. HUMAN-INDUCED KARST It is well known that su bsidence in karstic rocks can be exacerbated by human activities. Lowering of the water table by well-pumping or by draining of quarries can reduce support of soils overlying sink holes, thus causing their collapse. Subsurface min ing of salt and other evaporites may eventually cause collapse of overlying rocks, such as at the Retsof mine in Livingston County, NY (Nieto and Young, 1998; Gowan and Trader, 20 03). Localities of sub sidence due to solution mining were mapped by Dunrud and Nevins (1981) and are shown in figure 2. The bibliographic list of ground subsidence due to evaporite dissolution of Ege (1979) contains many instances where such subsidence was due to human activities. Knowing the location of shallow and deep mines is importan t to local officials, in order to understand the potential for such subsid ence. For example, aban doned gypsum mines in western New York are abundant, and recent settle ment of many houses near Buffalo, New York, partly may be the result of subsidence over these mines. Figure 7. Dissolution of anhydrite in the Minnelusa Formation and down-dip migration of the dissolution front.

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131 REFERENCES Bates, R. L., 1955, Permo-Pennsylvanian formations between Laramie Mountains, Wyoming, and Black Hills, South Dakota: Am. Assoc. Petroleum Geologists Bull., v. 39, p. 1979-2002. Black, T.J., 1997, Evaporite karst of northern lower Michigan: Carbonates and Evaporites, v. 12, p. 81-83. Braddock, W.A., 1963, Geology of the Jewel Cave SW Quadrangle, Custer County, South Dakota: U.S. Geo logical Survey Bulletin 1063-G, p. 217-268. Brady, F. H., 1931, Minnelusa formation of Beulah dis trict, northwestern Black Hills, Wyoming: Am. Assoc. Petroleum Geologists Bull., v. 15, p. 183-188 Brobst, D.A., and Epstein, J.B., 1963, Geology of the Fanny Peak quadrangle, Wyoming-South Dakota: U.S. Geological Survey Bulletin 1063-I, p. 323-377. Daly, Chris, and Taylor, George, 2000, United States Average Annual Precipitation, 1961-1990: Spatial Cli mate Analysis Service, Oregon State University; USDA -NRCS National Water and Climate Center, Portland, Oregon; USDA -NRCS National Cartogra phy and Geospatial Center, Fort Worth, Texas; Online linkage: Darton, N.H., and Paige, Sidney, 1925, Description of the central Black Hills, South Dakota: U.S. Geological Survey Geologic Atlas, folio 219, 34 p. Davies, W.E., Simpson, J. H., Ohlmacher, G.C., Kirk, W.S., and Newton, E.G., 1984, Map showing engineer ing aspects of karst in the United States: Reston, Va., U.S. Geological Survey National Atlas of the United States of America, scale 1:7,500,000. Dunrud, C.R., and Nevins, B.B., 1981, Solution mining and subsidence in evaporite rocks in the United States: U.S. Geological Survey Miscellaneous Investigation Series Map I-1298, 2 sheets. Eaton, G.P., Peterson, D.L., and Schumann, H.H., 1972, Geophysical, geohydrological, and geochemical recon naissance of the Luke salt bod y, central Arizona: U.S. Geological Survey Professional Paper 753, 28 p. Ege, J.R., 1979, Selected bibliography on ground subsid ence caused by dissolution and removal of salt and other soluble evaporites: U.S. Geological Survey Open-file Report 79-1133, 28 p. Ege, J.R., 1985, Maps showing distribution, thickness, and depth to salt deposits of the United States: U.S. Geological Survey Open-File Report 85-28, 11 p. Figure 8. Near-vertical breccia pipe (short dash) in steeply dipping beds (long dash) of the Minnelusa Formation, Fr annie Peak Canyon, Fanny Peak 7.5minute Quadrangle, six miles southeast of Newcastle, Wyoming, NW1/4 SE1/4, T. 44 N., R. 60 W.

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132 Epstein, J.B., 2001, Hydrol ogy, hazards, and geomorphic development of gypsum karst in the northern Black Hills, South Dakota and Wyoming: U.S. Geological Survey, report WRI 01-4011, p. 30-37. Epstein, J.B., 2003, Gypsum karst in the Black Hills, South Dakota-Wyoming; Geomorphic development, hazards, and hydrology: Oklahoma Geological Sur vey, report 109, p. 241-254. Epstein, J.B., 2005, Field Trip Guide 3, Karst Field Trip to the Western Black Hills: in Kuniansky, E.L., editor, U.S. Geological Survey, Karst Interest Group Proceed ings, Rapid City, South Dakota, September 12-15, 2005, this volume: U.S. Geological Survey Scientific Investigations Report Series 2005-5160, this volume. Epstein, J.B., Agenbroad, Larry, Fahrenbach, Mark, Hor rocks, R.D., Long, A.J., Putnam, L.D., Sawyer, J.F., and Thompson, K.M., 2005, Field Trip Guide 1, Karst Field Trip to the Southern Black Hills: in Kuniansky, E.L., editor, U.S. Geological Survey, Karst Interest Group Proceedings, Rapid City, South Dakota, Sep tember 12-15, 2005, this volume: U.S. Geological Survey Scientific Investigations Report Series 20055160, this volume. Epstein, J.B., Davis, A.D., Long, A.J., Putnam, L.D., and Sawyer, J.F., 2005, Field Trip Guide 2, Karst Field Trip to the Northern Black Hills: in Kuniansky, E.L., edi tor, U.S. Geological Survey, Karst Interest Group Pro ceedings, Rapid City, South Dakota, September 12-15, 2005, this volume: : U.S. Geological Survey Scientific Investigations Report Series 2005-5160, this volume. Epstein, J.B., and Putnam, L.D., 2005, Introduction to three field trip guides: karst features in the Black Hills, Wyoming and South DakotaPrepared for the Karst Interest Group Workshop, September 2005: in Kuniansky, E.L., editor, U.S. Geological Survey, Karst Interest Group Proceedings, Rapid City, South Dakota, September 12-15, 2005, this volume: U.S. Geological Survey Scientific Investigations Report Series 20055160, this volume. Epstein, J.B., and Johnson, K.S., 2003, The need for a national evaporite-karst map, in Johnson, K.S., and Neal, J.T., eds, Evaporite karst and engineering/envi ronmental problems in th e United States: Oklahoma Geological Survey Circular 109, p. 21-30. Gott, G.B., Wolcott, D.E., and Bowles, C.G., 1974, Stratigraphy of the Inyan Kara Group and localization of uranium deposits, southern Black Hills, South Dakota and Wyoming: U.S. Geological Survey Profes sional Paper 763, 57 p. Gowan, S. W., and Trader, S. M., 2003, Mechanism of Sinkhole Formation in Glacial Sediments above the Retsof Salt Mine, Western New York in Johnson, K.S., and Neal, J.T., eds, Evaporite karst and engineer ing/environmental problems in the United States: Oklahoma Geological Survey Circular 109, p. 21-30. Harris, R.C., 2002, A review and bibliography of karst features of the Colorado Plateau, Arizona: Arizona Geological Survey, Open-File Report 02-07, 43p. Johnson, K.S., 1997, Evaporite karst in the United States: Carbonates and Evaporites, v. 12, p. 2-14. Johnson, K.S., and Gonzales, S., 1978, Salt deposits in the United States and regiona l geologic characteristics important for storage of radi oactive waste; Prepared for Union Carbide Corporation, Nuclear Division, Office of Water Isolation, Y/OWI/SUB-7414/1, 188 p. Johnson, K. S., Gonzales, S., and Dean, W. E, 1989, Dis tribution and geologic characteristics of anhydrite deposits in the United States, in Dean, W.E.; and Johnson, K.S. (eds.), Anhydri te deposits of the United States and characteristics of anhydrite important for storage of radioactive wastes : U.S. Geological Survey Professional Paper 1794, p. 90. Klimchouk, Alexander, 1996, The dissolution and conversion of gypsum and anhydrite, in Klimchouk, Alexander; Lowe, David; Cooper, Anthony; and Sauro, Ugo (eds.), Gypsum karst of the World: Interna tional Journal of Speleology, v. 25, nos. 3-4, p. 21-36. Landes, K.K., 1945, The M ackinac Breccia: Michigan Geological Survey Publication 44, p.121-154. Laury, R.L., 1980, Paleoenvironment of a late Quaternary mammoth-bearing sinkhole deposit, Hot Springs, South Dakota: Geological Society of America Bulletin, v. 91, p. 465-475 Mytton, J. W., 1973, Two salt structures in Arizona--the Supai salt basin and the Luke salt body: U.S. Geologi cal Survey Open-file report, 40 p. Nieto, A.S., and Young, R. A., 1998, Retsof salt mine col lapse and aquifer dewatering, Genesee Valley, Living ston County, New York, in Borchers, J. W. (ed.), Land subsidence case studies and current research; Proceed ings of the Dr. Joseph F. Poland Symposium on Land

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133 Subsidence: Association of Engineering Geologists Special Publication 8, p. 309-325. Neal, J.T., Colpitts, R., and Johnson, K.S., 1998, Evapor ite karst in the Holbrook Basin, Arizona: in Borchers, J.W., ed., Land subsidence case studies and current research: Proceedings of the Dr. Joseph F. Poland Symposium on Land Subsidence: Association of Engi neering Geologists Special Publication No. 8, p. 373-384. Peirce, H. W., and Gerrard, T. A., 1966, Evaporite depos its of the Permian Holbrook basin, Arizona, in Rau, J. L., ed., Second symposium on salt, 1973: Cleveland, Ohio, Northern Ohio Geological Society, v. 1, p. 1-10. Rauzi, S. L., 2000, Permian salt in the Holbrook Basin, Arizona: Arizona Geolog ical Survey Open-File Report 00-03, 20 p. Withington, C. F., 1962, Gypsum and anhydrite in the United States, exclusive of Alaska and Hawaii: U.S. Geological Survey Mineral Investigations Resource Map MR-33.



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134 Gypsum and Carbonate Karst Along the I-90 Development Corridor, Black Hills, South Dakota By Larry D. Stetler and Arden D. Davis Department of Geology and Geological Engineering, So uth Dakota School of Mines and Technology, Rapid City, South Dakota 57701 ABSTRACT The Interstate 90 development co rridor extends from Rapid City to Spearfish, South Dakota, and over lies several formations that exhibit gypsum and carb onate karst features. Karst development commonly occurs within sections of three formations in the Black Hills region The oldest karst features occur in the Mississippian Madison Limestone, a limestone-dolomite system that exhibits a karsted surface as well as extensive cave formation. The Pe nnsylvanian-Permian Minnelusa Format ion contains anhydrite and thin limestone beds that have undergone localized and varied karstification. Hydration and swelling of primary anhydrite has resulted in multiple collapse structures w ithin the formation. The Triassic Spearfish Forma tion contains gypsum deposits throughout; however, ma ssively bedded gypsum up to 10 m thick is con tained at the top in the Gypsum Spring Member. All of these formations can exhib it karst topography and features where exposed, but their properties also influence ground-water flow in the subsurface. Dye tracer tests and geochemical analyses have pro vided evidence that flow paths thro ugh these formations are controlled la rgely by karst features and associ ated fracture systems. Ground water in the Madison aquifer in the Rapid City area converges from flows through karst from different surface wate rsheds to the south and the north. Springs at or near the contact of the Permian Minnekahta Limestone an d the overlying Spearfish Formation have been chemically tied to Madison water, indicating upward fl ow through collapse breccia in bo th the Minnelusa and Spearfish for mations. In addition, sinkholes are common occurre nces in the Spearfish Forma tion throughout the Inter state 90 development corridor in the Black Hills. Ground water supplies much of the municipal and private water needs in the Black Hills. As develop ment continues throughout the region, ground-water pr otection should receive fo cused attention, particu larly along the I-90 development corridor. Current re search is aimed toward geologic mapping, hazard identification, and assessment as tools to inform the general public and as planning guides for local govern ments.

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135 Karst Features as Animal Traps: Approximately 500,000 Years of Pleistocene and Holocene Fauna an d Paleoenvironmental Data from the Northern High Plains By Larry D. Agenbroad and Kristine M. Thompson Mammoth Site of Hot Springs, South Dakota, Inc., P. O. Box 692, Hot Springs, SD 57747 ABSTRACT Karst sinkhole features have served as natural animal traps for at least 500,00 0 years in the uplifted regions of the northern High Plains. We examine report ed karst traps that have faunas ranging from greater than 451,000 years ago, upward through Holocene time. Chronologies are based on tephra, biostratigraphy, and absolute dating. Full glacial and interglacial faunas from the late Irvingt onian Land Mammal Age through the Rancholabrean Land Mamm al Age into the Holocene, are repr esented. As such, sinkhole traps serve as time capsules preserving extinct fauna and clues to past environments. INTRODUCTION Fossil vertebrates dating to the mid-Pleistocene (Irvingtonian Land Mammal Age) to Holocene are known from filled and partially filled karst features. Located in the uplifted areas of the northern High Plains (Figure 1), at least seven of these features have served as natural traps yielding faunal and paleoenvironmental data covering the last 500,000 years. These repositories are often bell shaped solu tion caverns with narrow openings, allowing ingress, but preventing egress for trapped fauna. Some of the features have f illed with talus, roof col lapse and both eolian and alluvial sediments. Others have been sealed off naturally and have only recently been reopened. One natural trap (the Mam moth Site of Hot Springs, South Dakota) is a former karst feature preserved by differential erosion, creat ing a topographic high from a former topographic low (sink). All these karst traps have one thing in commonthey are the result of dissolution of limestone or dolomite, and possibly even gypsum. Often the opening to the cave is ve ry small, sometimes only a slot due to dissolution along fractures in the crystal line rocks. Others are the result of roof collapse cre ating small, somewhat circular openings. Still others represent massive cavern roof collapse creating breccia pipes extending to the surface. At least one karst trap (the Vore Buffalo Jump) is postulated to be the result of solution of gypsum beds within the Spearfish Formation (Epstein 2005). Figure 1. Locality of karst and natural animal traps. Many of these traps are located on, or near, the tops of ridges (Natural Trap, Salamander Cave, Graveyard Cave, Shield Cave) which were animal trails, especially during periods of heavy snow accu mulation. As such, with small entrance openings, they may have been masked by drifting snow, con cealing the entrance to the trap. Some features, such as Natural Trap, Wyoming, maintained a snow cone on top of the talus and de bris, allowing for lateral dispersal of large, heavy bodied fauna.

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136 DESCRIPTIONS Middle to late Pleistocene Natural Trap, Wyoming This trap is a large, somewhat bell-shaped cav ern formed in the Madison Formation of Mississip pian age (Figures 1, 2a, and 3; Table 1). The entrance is small with a free fall of up to 85 ft (27 m) as illustrated in Fig. 2. The entrance is located on a ridge which serves as a major animal trail from the summit of the Bighorn Mountains to the valley floor of the Bighorn River. The entrance is small enough to be hidden almost until at the edge, and it served as a trap for pursued herbivores and their pursuing car nivores. Excavation has only proceeded to a depth of about 25 ft (8 m), ceasing at a volcanic ash dating to 110,000 years ago. There are still bones beneath this marker horizon, but they have yet to be investigated. Several extinct, late Pleist ocene megafauna (animals over 100 pounds live weight) are represented, including mammoth, horses, musk oxen, American lions, short-faced bears, and other mammals. The first record of the cheetah in North America comes from this cave. Most of the studied fauna occur in the 12,000 to 20,000 year old horizons (Martin and Gilbert, 1978; Gilber t and Martin, 1984). Botanical information records a C-3 grassland being replaced by a C-4 grassland at around 12,000 years ago. A paleoenviron mental interpretation is that of an arctic steppe in a cooler, wetter environ ment, becoming warmer and drier as it approached the modern conditions. As su ch, the deposits reflect the last interglacial (San gomon), the last glacial (Wisconsinan) and Holo cene interglacial. Porcupine Cave, Colorado Originally formed in an Ordovician age Mani tou Dolomite, Porcupine Ca ve was sealed naturally, in the middle Pleistocene and reopened by miners (Figures 1, 2b, and 3; Table 1). Based on biostratig raphy, (Table 1) the deposits range from approxi mately 487,000 to 365,000 years ago (Anderson 1996; Barnowski et aI., 19 96). The fauna represents a glacial (Illinoian) to interglacial (Sangamonian) environmental change. Si gnificant information on the paleoenviroment of this period had been deter mined by the rich floral and faunal record. Salamander Cave, South Dakota A solution cavern in the Mississippian age Madison Limestone, Salamander Cave has a narrow, slot opening from dissolution along a fracture zone (Figures 1, 2c, and 3; Table 1). The cave has two major chambers and the ho rse room is a naturally sealed cave with a narrow connection to the modern entrance room. A flowstone seals the bone bearing stratum revealed in a crystal hunters prospect pit. Uranium-Thorium (U/Th) da tes on the flowstone are 252,000 years ago (Mead et al. 1996). It is estimated that initial bone deposition could have been as early as 451,000 years ago, based on biostratigraphy and a statistical estimate based on the U/Th dating (Mead et al. 1996). These data suggest a glacial (Illi noian) followed by an in terglacial, (Sangamonian) followed by the Wisconsin an glacial, and the Holocene interglacial. Late Pleistocene to Holocene Mammoth Site, South Dakota The Mammoth site is a filled karst feature which served as a condu it for thermal artesian springs, creating a pond within the sinkhole confines (Figures 1, 2d, and 3; Table 1). It became a natural trap, selective for young, male mammoths and their behavior patterns. In add ition, 47 species of other fauna were also preserved in this deposit. An aver age radiocarbon age from on e stratigraphic horizon provides a date of 26,000 years ago (Agenbroad 1994). It may have been an active trap for 300 to 750 years, ceasing to trap an imals after th e downcutting Fall River caused lateral migration of the artesian springs. The deposit is elliptical in form roughly 150 ft (46 m) by 125 ft (38 m). Drill cores by the South Dakota Geological Survey indicate a depth of greater than 65 ft (22m). Animals attracted to vege tation along the rim of a warm water pond were attracted into the sink, to find they could not climb out due to the wet, slippe ry, Spearfish Shale, and died of starvation or fatigue. Carnivores were attracted to the deposit by the smell of decaying ani mals. Some smaller fauna may have been

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137 Table 1. Generalized faunal assembl ages from High Plains Karst traps [V=Vore site, WY; G=Graveyard Cave, SD; Sa =Salamander Cave, SD; M=Mammoth Site, SD; NT=Natural Trap, WY; Sh=Shield Cave, MT; P=Porcupine Cave, CO] Non-mammals V G Sa M NT Sh P Mollusca X X X Pisces X X Amphibia X X X X Reptilia X X Aves X X X X Mammals Insectivora X X Chiroptera X X X Xenarthra X Lagomorpha X X X X X X Rodentia Sciuridae X X X X X X Geomyidae X X X Heteromyidae X X X Cricetidae X X X X X Eretezontidae X X X X Carnivora Mustelidae X X X X X X Canidae X X X X X X Felidae X(?) X X Ursidae X X X X Perissodactyla Equidae X X X X Artiodactyla Tayassuidae X Camelidae X X X X Cervidae X X Antilocapridae X X X X Bovidae X X X X X Proboscidea Elephantidae X X Figure 2.Plan and profile of karst animal traps in High Plains

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138 Figure 3.Chronology and paleoclimate of karst natural animal traps.

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139 incorporated by being wash ed into the sinkhole from surrounding uplands. The reworked, cemented sedi ment filling the sinkhole were more resistant to dif ferential erosion, and the former low topographic expression became a modem topographic high. Shield Cave, Montana Shield Cave is a 46 ft (14 m) deep bell-shaped cave in the Mississippian age Madison Limestone (Figures 1, 2e, and 3; Table 1). The trap is located near the top of a southwest ridge at an altitude of 6549 ft (2606 m), in the Pryor Mountains in Carbon County, Montana. The floor of the chamber is about 15 ft (5m) wide in an e lliptical configuration. The trap collected animals from 9,230 years ago to 1,250 years ago. At least 13 species of fauna have been identified from the site. The prominent fauna repre sented is bison. Other fauna from the deposits include prairie dogs and grizzly bears (Oliver, 1989). Graveyard Cave, South Dakota Graveyard Cave is located in Wind Cave National Park and is a small, bell-shaped pit. There is a small, circular opening along the north wall which allowed entrance fo r Holocene animals (Fig ures 1, 2f, and 3; Table 1). The floor of the cave is literally carpeted with bo nes. Manganaro (1994) investigated a 3 ft by 3 ft square test pit in the south east floor of the cave. A radiocarbon date of 2290 BP indicates a late Holocene accumulation. Thousands of bones were sorted from the fill and one bone awl was identified. The site was described as an archae ological site on the basis of this one anomalous arti fact. We suggest it is a pa leontological s ite with one probable artifact. Vore Buffalo Jump, Wyoming The Vore Buffalo Jump is an open sinkhole located between the westbound and eastbound lanes of the interstate (1-90), just west of the South Dakota state line near Beulah, Wyoming (Figures 1, 2g, and 3; Table 1). Testing by th e University of Wyoming, prior to highway construction, indicates the sinkhole was used, repeatedly, as a buffalo jump for at least 300 years. Plains Indians trapped and slaughtered thousands of bison by stam peding the animals over the steep rim. At least 22 stratified layers of bison bone beds have been recorded in the sinkhole fill. Radiocarbon dates and artifact typology place the period of use for this trap at the middle to late pre historic interval, about 450 years ago (Frison 1991). Epstein (2001) suggests the sinkhole may have formed by solution of gy psum beds in the lower Spearfish Formation. CONCLUSIONS The information provided by the seven karst animal traps in the northern High Plains is presented here. Nearly 500,000 years of faunal and environ mental data are represented in the interval repre sented in these deposits. At least the last two glacial and interglacial intervals are represented by both faunal and more limited botanical interpretations. The presence of highly fractured and tilted carbon ates in the uplifted areas of this physiographic region provide the possibility of many more solution fea tures than have currently been investigated, or reported. This in formation indicates the high poten tial of additional time cap sules recording both extinct and extra local faunal assemblages, and the prospect of additional pa leoenvironmental data. REFERENCES CITED Anderson, E. 1996, A preliminary report on the Carnivora of Porcupine Cave, Park County, Colorado in K. M. Stewart and K. L. Seymour, eds., Palaeoecology and Palaeoenvironment of late Cenozoic mammals, Uni versity of Toronto Press, Toronto. p. 259-282. Barnowsky, A. D., Rouse, T.I., Hadly, E.A., Wood, D.L., Keesing, F.L., and Schmidt, V.A., 1996, Comparison of mammalian response to glacial-interglacial transi tions in the middle and late Pleistocene, in K. M. Stew art and K. L.Seymour, eds. Palaeoecology and palaeo evnironment of late Cenozoic mammals. University of Toronto Press, Toronto. p. 16-33. Epstein, J. B. 2001. Hydrol ogy, hazards and geomorphic development of gypsum karst in the northern Black Hills, South Dakota and Wyoming, in Kuniansky, E.L., ed.,U.S. Geological Survey Karst Interest Group Pro ceedings, St. Petersburg, Florida February 13-16, 2001, Water-Resources Invest igations Report 01-4011, p. 30.37.

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140 Frison, G. C. 1991, Prehis toric hunters of the High Plains: San Diego, CA, Acad emic Press, p. 226-229. Gilbert, B. M. and Martin, L.D.,1984, Late Pleistocene fossils of Natural Trap Cave, Wyoming, and the cli matic model of extinction, in P. S. Martin and R. G. Klein eds. Quaternary Extinctions: the search for a cause. University of Arizona Press, Tucson. p. 138147. Manganaro, C. A., 1994, Graveyard Cave: a Holocene faunal record from the Black Hillsof South Dakota. Unpublished Master of Science thesis. Northern Ari zona University. 119p. Martin. L. D. and Gilbert, B. M, 1978, Excavations at Nat ural Trap Cave. Transactions of the Nebraska Acad emy of Sciences 6:107-116. Mead, J. 1., Manganaro, C.A., Reppening, C.A. and Agenbroad, L.D., 1996, Early Rancholabrean mam mals fromSalamander Cave, Black Hills, South Dakota. in K. M. Stewart and K. L. Seymour eds. Palaeoecology and palaeoenvi roment of late Cenozoic mammals. University of Toronto Press, Toronto. p. 458-482. Oliver, J. S., 1989, Analogues and site context: bone dam ages from Shield trap Cave (24CB91),Carbon County, Montana, USA. in R. Bonnichsen and M. H. Sorg eds. Bone Modification: Dexter MT. Thompson-Shore, Inc. p. 73-98.

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141 Developing a Cave Potential Map of Wind Cave to Guide Exploration Efforts By Rodney D. Horrocks Wind Cave National Park, RR 1 Box 190, Hot Springs, SD, 57747 ABSTRACT Although the known boundaries of Wind Cave are expanding only gradually, the length of the overall survey is increasing at a rate of about four miles pe r year. This expansion reflects the on-going exploration and survey work by cavers. As an ai de to these exploration efforts, a ca ve potential concept was developed. However, the cave potential map ac tually serves many purposes, incl uding, determining the likely maxi mum likely potential of the cave, calculating the potentia l length of the cave survey identifying likely areas where significant cave may be discovered, determining the relationship, if any, with nearby Jewel Cave, determining the cave watershed boundaries, identifying potential land management partners, and guiding future land management decisions. This paper will fo cus on the first four purposes related to cave explora tion. To develop the cave potential map, several data sets were gathered, includin g: structural geological factors, a contour map, plan and profile views of the cave survey, radio location data, geology map, blow hole location map, water table contour map, geogra phic information system (GIS) generated triangular irregular networks (TIN), orthophotoquads, and a park boundary map. By combin ing these data sets, this exercise demonstrated that is it un likely that Wind and Jewel Caves are connected, while at the same time it identified the maximum likely potential of Wind Cave By calculating passage density within the current boundaries of Wind Cave and then for the maximum likely boundaries, a minimum and maximum potential length of the cave was calculated. It was determined that the current ca ve boundaries cover 1/8 of the total maximum likely potential of the cave Interestingly, the maximum potential boundaries are roughly 97 per cent inside of the current boundaries of Wind Cave Na tional Park. Based on pas sage density, the length of the Wind Cave survey could range fro m 400 kilometers (250 miles) to 1, 760 kilometers (1,100 miles). The final length depends on whether the boundaries remain as they currently are or if they were expanded to their maximum likely potentia l. Since the current 185.6 kilometers (116 miles) of survey represents no more than 46 percent of the minimum predicted length of the cave or as little as 10 percent of the maximum predicted length of the cave, it is obvious that a tr emendous amount of survey able passage remains in the system.

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142 The Potential Extent of the Jewel Cave System By Michael E. Wiles Jewel Cave National Monument, 11149 US Highway 16, Bldg.12, Custer, SD 57730 ABSTRACT Currently, over 50 miles (40 percent) of the know n cave system is outside park boundaries, and baro metric airflow studies indicate that as much as 95 pe rcent remains to be discover ed. A first approximation of the maximum extent of humanly passable cave pa ssages based on volume estimates from barometric air flow, constraints presented by geologic contacts, the water table, and known structural features have been modeled. These relationships were quantified and analyzed using stru ctural and potentiometric contours from the U.S. Geological Survey Black Hills Hydrolog ic Study, surface and su bsurface mapping by the National Park Service, and other sour ces. The model serves as an impo rtant management tool for an enor mous resource requiring proactive measur es to ensure its continued protection.

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143 Geologic Controls on a Transition Between Karst Aquifers at Buffalo National River, Northern Arkansas By Mark R. Hudson 1 David N. Mott 2 Kenzie J. Turner 1 and Kyle E. Murray 3 1 U.S. Geological Survey, Box 2504 6, MS 980, Denver, CO 80225 2 National Park Service, Buffalo Na tional River, Harrison, AR 72601 3 University of Texas at San Antonio, San Antonio, TX 78249 ABSTRACT Most major springs, in the central part of the 190-km-long Buffalo River watershed of northern Arkan sas, discharge from limestone of the Mississippian Bo one Formation (the Springfield Plateau aquifer). However, the largest spring, Mitch Hill Spring, discharges fro m dolostone of the lowe r part of the underly ing Ordovician Everton Formation (part of the Ozark Plateau aquifer). New dye tracer studies and geologic mapping in and adjacent to the Davi s Creek subbasin of the Buffalo Rive r watershed have revealed the geo logic framework of this transition betwee n the upper and lower karst aquifers. Seventeen new dye injection traces conducted by Natio nal Park Service in 2001-2003 indicate that the recharge area for Mitch Hill Spring is twice that prev iously known. Springs in th e upper part of the Davis Creek subbasin locally draw interbasin recharge from th e adjacent Crooked Creek watershed to the north. Importantly, a losing section in the middle reach of Davis Creek has been documented by a dye trace to con tribute to Mitch Hill Spring, connectin g it to stream flow from the upper pa rt of the Davis Creek subbasin. Integration of geologic mapping w ith the dye tracer results highlights the stratigraphic and structural features that influence ground-water flow. In general, within the erosional relief of the Buffalo River water shed, structural lows localize the la rgest springs in the perched upper lim estone aquifer of the Mississippian Boone Formation whereas structural highs allow rechar ge and discharge of the lower karst aquifer repre sented by the lower part of the Ordovician Everton Formation. Most springs in the upper aquifer discharge near the base of the Mississippi an Boone Formation, par ticularly its basal St. Joe Limestone Member. Local shal ey facies in the St. Joe Limestone Member in this area help concentrate the springs at this stratigraphic horizon. As found in a previous study farther west, structural lows formed by faults an d folds in the Boone Formation localize the largest springs, including the discharge with known interbasin recharge. Development of the karst aquifer in the lower part of the Ordovician Everton Formation was facilitated by a change to carbonate-rich faci es from sand-rich facies of the forma tion farther west. The losing reach of Davis Creek coincides with outcrop of lower Evert on Formation brought to the surface by uplift along an anticline and monocline. Likewise, Mitc h Hill Spring is localized in a dolo stone interval near the base of the Everton Formation just above its contact with argillaceous dolos tone of the Ordovician Powell Dolo mite, a unit of lower karstic permeability. Both forma tions are exposed where the Buffalo River has eroded into the uplifted side of the northwest-trending Cane Branch monocline. Collaps e breccia is widely pre served in sandstone layers just above the dolostone horizon of Mitc h Hill Spring, providing further evidence of a major karst network. The west -trending Mill Creek graben interven es between outcrops of lower Ever ton Formation at the losing reach of Davis Creek and at Mitch Hill Spring A ground-water path across this graben probably utilizes do wn-dropped limes tone of the Boone Formation to link flanking zones of lower Everton Formation.

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144 Quantification of Hydrologic Budg et Parameters for the Vadose Zone and Epikarst in Mantled Karst J. V. Brahana 1 Tiong Ee Ting 2 Mohammed Al-Qinna 3 John F. Murdoch 4 Ralph K. Davis 1 Jozef Laincz 1 Jonathan J. Killingbeck 5 Eva Szilvagyi 6 Margaret DohenySkubic 7 Indrajeet Chaubey 4 P.D. Hays 1,8 and Greg Thoma 2 1 Department of Geosciences, 113 Ozark, University of Ar kansas, Fayetteville, AR 72701 2 Department of Chemical Enginee ring, 3202 Bell, University of Arkansas, Fayetteville, AR 72701 3 Faculty of Natural Resources and Environment, The Hashemite University, Zarqa 13115, Jordan 4 Department of Biological and Agricu ltural Engineering, University of Arkansas, Fayetteville, AR 72701 5 Department of Geology, Central Washingt on University, Ellensburg, Washington 6 Department of Geology, Beloit College 700 College St., Beloit, WI 53511 7 Department of Geology, Carleton College, 300 N. College St., No rthfield, MN 55057 8 US Department of Agriculture, Na tional Water Managemen t Center, 44 Ozark, Fayetteville, AR 72701 ABSTRACT Hydrologic studies at the Savoy Experimental Wate rshed initially focused on conduit-flow and trans port in the karst aquifers that unde rlie the site. Recently, in the last two years, a new research focus has shifted to the shallower, mo re diffuse-flow pathways that contribute water to the fast-flow conduits. The extended residence time and exponentia lly-increased particle su rface areas in the soil, regolith, and epikarst have been suspected to be active ge ochemical sites for microbe-soil-wate r-rock interaction. Preliminary chemical analyses indicate that the interface and in terflow zones are indeed optimum locations for bio geochemical processing. To more fully document and provide needed data on fluxes, hydraulic parameters, and calibration quantities for numerica l testing of hypotheses, an accurate characterization of hydrologic budget components within all aspect s of the flow system was undertaken This study briefly summarizes new infrastructure and presents preliminary results that ha ve helped refine a coherent, integrated conceptual model. INTRODUCTION The Savoy Experimental Watershed (SEW) is a University of Arkansas pr operty that encompasses about 1250 hectares typical of the karst terrane of the Ozark Plateaus of the mid-continent (Brahana et al., 1998). It is a long-term hy drologic research site that provides an opportunity to investigate processes of flow and contaminant fate and transport in situ at a well-characterized and we ll-instrumented site. The surface-water/ground-water interface and the interflow zones in the vadose region in the south ern part of Basin 1 (fig. 1) of SEW currently is an area of intensive hydrologic instrumentation and infrastructure buildup. A multidisciplinary research team of hydrogeologists, biologists, soil scientists, Figure 1. Basin 1 (ellipse), in Savoy Experimen tal Watershed.

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145 Figure 2. Vadose zone and epikarst research area showing geometry of infrastructure in Basin 1. Circles are weirs at springs, parallel lines identify the trench, and rectangles represent field plots. Details of the infrastructure are shown in figure 3. chemical engineers, biolog ical and agricultural engi neers, stable-isotope ge ochemists, ecologists, hydrologists, animal scie ntists, karst tracers, and crop scientists have insta lled a suite of instrumenta tion that includes: 4 tipping -bucket rain gages; a full weather station; 6 suction ly simeters in the soil zone (fig. 2); 5 epikarst wells; one deep well; one 2-meter deep sampling trench (figs. 2, 3, and 4); 36 v-notch weirs measuring surface ru noff and sheet flow from test plots (figs. 3 and 5); 3 H-flumes which capture and collect surface runoff from storms; 5 v-notch weirs and 1 H-flume on perched springs which drain the study site, 3 of which that are monitored contin uously for discharge and temperature (fig. 2); 2 vnotch weirs on an overflow/underflow spring system that underdrains the sha llow flow system through conduits in the shallowest phreatic carbonate aqui fer; and periodic continuous autosamplers at selected sites during selected transient flow condi tions. H-Flume TB Rain Gauge Surface/Subsurface Sensors Legend L L L L Ground-Water Sampling Trench We i r 1 2 3 T W M D R Springs/Seep Designations R -Red Dog D -Dribblin M -Memory W -Woodpecker T -Tree Suction LysemeterFigure 3. Numbered field plots of the vadose and epikars t research site. Note that the orientation of this figure has been rotated 120o clockwise from figure 2. Springs/Seeps

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146 OBJECTIVES, METHODOLOGY, AND BACKGROUND This report has two main objectives: 1) to pro vide a brief description of the type of infrastructure currently in place, includ ing methodology, rationale, and expected accuracy; and 2) to synthesize data and make hydrologic interpretations based on those data. Inasmuch as space limitations preclude a detailed summary of results, info rmation provided is not complete; the interested reader is directed to http:// www.uark.edu/depts/savoyres/index.html Discharge at springs is determined by measur ing the head in the pool behind 22.5 o v-notch weirs. The stage-discharge data are represented theoreti cally by the equation: Q = 274.4 H 2.5 (1) where Q is discharge in l iters per second, and H is head in meters above th e bottom of the v-notch (Grant and Dawson, 1997). Below 0.06 meters, the stage discharge relation was determined empirically. Spring stage is monitored by transducers on a 5minute interval, with an accuracy of 0.001 meter. Precipitation is monito red by tipping-bucket rain gages, which are set to record increments (0.01 feet) of rainfall instantaneously. These are recorded with a time stamp, totalized every 5 minutes by the weather station, and recorded on digital data loggers powered by solar cells. Lo ggers also record other relevant digital data, and are periodically down loaded on approximately bi-weekly intervals. Sensors attached to weirs measure the presence or absence of surface runoff during specific storms, and subsurface saturation sensors measure depth to soil saturation. There are 36 of each of these sen sors; accuracy is 0.002 meters (m) for the surface runoff sensors, and about 0.050 m for the subsurface saturation sensors. Water level in wells is measured with pressure transducers, which have an accuracy of 0.001 meters. Total flow from each of the plots is measured by pressure tr ansducers attached to still ing wells on H-flumes. The karst hydrogeology in SEW includes aqui fers covered by a thin, rocky soil, and a variable thickness of regolith which mantles the bedrock (figs. 4 and 5). Below the regolith lies the Boone Formation, a layer of im pure, cherty limestone of approximately 55 m thickness (Al-Rashidy, 1999). The Boone is widespread and is considered to be a karst-forming formation, but owing to its high con centration of insoluble cher t and clay (as much as 70%) insoluble debris remaining from weathering mantles the surface of the carbonate rock and plugs voids in the developing conduits and bedding planes. The resultin g overall karst nature of this for mation typically is masked Underneath the Boone Limestone is a relativelypure, crystalline, chertfree St. Joe Limestone, about 6 m thick (Al-Rashidy, 1999). The St. Joe Form ation is the predominant Figure 4. Redoximorphic and macropore features in the trench identify and provide access to preferred flow zones in the vadose zone above the epikarst.

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147 karst-forming unit in the area, and has most of the dominant zones in which the larger continuous springs, seeps, and caves occur. The ground-water flow in SEW and this part of the Ozarks is lithologically-controlled, with modification by structure (Brahana, 1997; Unger, 2004). The Chat tanooga Shale (a black, relatively impermeable but highly fractured shale) forms the underlying imper meable boundary of the shallow carbonate aquifer at the SEW. The ground water flows westward and dis charges directly into the ne arby Illinois River, which flows on top of the Chattanooga Shale from the south to the north. To explain the controlling influences of the aspects of the regolith and soil matrix, macropores, burrows, tubes, hardpans and other permeability contrasts in the nonindurated vadose zone (fig. 4) and epikarst of Basin 1 in SEW, we described a sim ple geometric conceptual model of the subsurface conduit network systems comprising three impor tant flow zones: 1) interface (soil zone); 2) interflow (lateral flow zone); an d 3) focused-flow (conduitflow zone) (fig. 5). Sampling infrastructure for each of the zones includes th e following: 1) inter face weirs and flumes (occasional; runoff rare); lysimeters (soil-water samplers; common for intense storms); 2) interflow interceptor trench (occasional; intense storms); seeps and springs at the intersection of the perching layer and the land sur face weirs and flumes (continuous flow); and 3) focused flow weirs (continuous springs issuing from limestone at the termin us of the ground-water basin). The interface is well-established as a zone where biogeochemical processing occurs, and the zone of focused flow is known for minimal process ing, whereas the interflow zone is poorly under stood. It is thought to be important for geochemical processing, especially for constituents such as nitrates and dissolved organic carbon (Laincz, 2005). The instrumentation to assess flow and stor age through these zones is therefore critical to understanding the hydrologic budget at this and sim ilar sites, owing to a longer residence time for water, and increased opportunity for enhanced biological activity. Figure 5. Schematic representation of environments in the shallow flow zone at the Savoy Experimental Watershed (figure modified from Laincz, 2005).

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148 DISCUSSION The measurement of interflow through the weirs at the seeps and springs (Tree, Woodpecker, and Red Dog) provides insi ght into a component of the hydrologic budget that is seldom quantified. For the period 15 July through 20 July 2005, measure ments of discharge were made in early morning and midafternoon using a graduated cylinder and a stopwatch. Ten measurements were averaged for each data point shown on th e graphs (fig. 6). All plots show a diurnal reduction in flow during the period of maximum solar radi ation, reflected also in the transducer measurements at each weir. This loss of water from the shallow ground-water system is interpreted to be to evapot ranspiration, and is on the order of 5 to 25 milliliters per second over the course of a diurnal cycle for each spring. The period of record is not long, owing to the recent installation of the weirs this past spring, but preliminary results reflect consistent and reproducible records using multiple tools, and provide confidence that the quan tities are accurate and reflect actual conditions in the subsurface. Another suite of data from the epikarst site shows transient variations in stage of the H-flume at Tree Spring, and water levels in 3 epikarst wells (fig. 7) within the field plots. Three transient storm pulses are reflected in the water-level records start ing on Julian date 112 (21 April 2004), with an obvi ous lag in the first record from plot 3 (fig. 3), reflecting the furthest downgradient well. This lag in water-level increase is interpreted to be caused by dryer conditions in a downgradient direction. Water level in the downgradient well does not rise until deficient soil moisture in the plot has been accom modated, after which time the water-level responses are rapid and coincident with the wells in plots 1 and 2. The delayed response of the H-flume at Tree Spring is explained by un saturated conditions along the flow path initially re quiring saturation. Once achieved, subsequent spring stage rises are almost instantaneous with precipitation occurrence and with ground water increases in wells (fig. 7). Physical and chemical water-quality parameters are valuable tools that also hold clues for under standing the complexities of flow in karst terranes (fig. 8 ). Continuous monitoring of two springs at the distal end of the groundwater flow path in Basin 1 provides an illust rative example. Langle Spring, the underflow part of the focused flow sys tem, is about 3 centimeter s lower than Copperhead, the overflow spring. During a 33-day period starting in December 1997, five major storms perturbed the stability of the temperature of these springs (fig. 8). These produced a general ov erall cooling in the dis charge waters of Langle, although the trend was by no means linear or gradual. Water from Copper head, on the other hand, showed both warming and cooling trends, numerous abrupt reversals in heating Figure 6. Diurnal variations in discharge (Q) in Tree, Woodpecker, and Red Dog Springs, interpreted to reflect increased transpiration during periods of maximum solar radiation. All springs are shallow and perched on chert in epikarst of lower 5 meters of the Boone Formation. 0 time is midnight, 15 July 2005.

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149 and cooling, as well as many more fluctuations of about 1 o C in the interval fro m December 13 through December 20. These diurnal variations were ultimately traced to a leak y, ephemeral surface pond that commonly stored wate r after periods of intense rainfall. The pond was e xposed to solar heating dur ing clear weather following storms, and the heated water leaked into the ka rst aquifer and as it mixed with water from other sources, it imparted the diur nal thermal signature to Copperhead Spring. The signature was not obvious at Langle, owing to its much longer distance from the leaky pond. The wider ranges of temp erature in Copperhead Spring suggest that this pa rt of the system is more open to surface water, and less thermally isolated than Langle. Cold water from the storm of 25 December obviously had an impact on the thermal regime of both springs, bu t the slope of the decrease at Langle supports the hypothesis that much of the water from the northern part of the spring system is more insulated from surface effects. Near identical temperatures from the two springs on 8 December 1997 is interpreted to be caused by point-source input to each spring from fractures nearby the orifices. This effect is repeated on 25 December, and is thought to be a strong indi cation of the temperature of the precipitation at the time of coincident temperatures. Based on a prelim inary assessment of all available data, the following Figure 7. Transient variations in water levels in shallow wells in the epikarst research area and from continuously monitored stage in the H-flume at Tree Spring. Three storms are reflected in rapid water level rises in all records. Wells were constructed by augering to refusal in epikarst. Julian date 112 starts midnight, 21 April 2004; increasing dates are successive days of 24 hours. Figure 8. Temperature of two springs, Langle and Copperhead, that resurge from the St. Joe Limestone (focused flow, figure 4) at the distal end of the ground-water flow path in Basin 1. Comparing and contrasting the temperature variations in response to precipitation allows a detailed assessment of contributions to point sources of discharge in this indurated carbonate aquifer.

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150 conceptual model is though t to describe the control ling influences of surfaceand ground-water interaction within the SEW (fig. 9). Ground-water recharge (from precipitation) within SEW is distrib uted areally across the mantled aquifer, yet prelimi nary data suggest that ru noff and recharge occur at discrete points. Lateral fl ow in the vadose zone, and temporal changes in directions of flow are a function of many factors which are highly variable, and can only be observed over long periods of observation that reflect the full range of hydrologic variability experienced at the site. Surface-water basins and ground-water basin boundaries do not coincide at SEW. This means that if a contaminant were spilled on the ground in one watershed, it may not necessar ily show up in wells or springs in the same water shed; it may be pirated along unseen underground flow routes to discharge at another resurgence point. Permeability contrasts with in the soil, at the soilrock interface, and within the solid-rock aquifer con centrate flow and distribute it down gradient along the flow paths of least resistance. These preferred pathways are a reflection of many factors, and are a dominant control on the hydrology. Springs in Basin 1 represent the interception of flowpaths with the land surface, and these range across a continuum of intermittent, infrequent fl owing seeps that barely trickle to continuous spring s that flow year-round. The epikarst developed on the Boone Formation, and the relatively-pure limestone of the St. Joe For mation represent the two most common zones in which continuous springs and seeps occur. Hydrau lic gradients of the ground-water, which generally appear to follow the tilt (str uctural dip) of the rock formations, act independently (are decoupled) from surface-water bodies wher e confinement by chert layers in the Boone Forma tion is effective. This decoupling is also lithologically controlled, but in areas of faults and major joints, exhibits strong structural control. Stream piracy is one manifesta tion of combined lithologic and structural control that is obvious in Basin 1. CONCLUSIONS The wealth of karst understanding at SEW has benefited from long-term integrated research of a truly multidisciplinary flavor. Research projects have grown from basic descriptive studies of resource assessments to sophisticated Figure 9. Conceptual model showing the relation between t he karst flow components of Basin 1 in SEW (Ting, 2005).

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151 process-oriented studies th at cut across the bound aries of disciplines and draw from the community of many sciences. The conceptual models of flow have evolved from simple two-component mixing models to sophisticated three-dime nsional models (fig. 10) that consider conservative and non-conservative constituents (Ting, 2005; Laincz, 2005; Al-Qinna, 2004). Numerical models of the site have been applied, and though not yet perfected, they provide insight and improving tools with which to test our hypotheses (Unger, 2004). Hydrologic budget parameters are but one com ponent of our recent emphasis, but such studies rep resent an essential part in gaining a thorough understanding of such co mplex systems. With our expanding infrastructure, burgeoning data bases, and our lengthening period of study, we feel that we are following the right path to finally get to solutions that will allow us to prov ide meaningful answers to pressing land-use questions. REFERENCES Al-Qinna, Mohammed, Measuring and modeling soil water and solute transport with emphasis on physical mechanisms in karst topography: unpublished Ph.D. dissertation, University of Arkansas, Fayetteville, 279 p. Al-Rashidy, S.M., 1999 Hydrogeologic Controls of Groundwater in the Shallow Mantled Karst Aquifer, Copperhead Spring, Savoy Experimental Watershed, Northwest Arkansas: unpublished M.S. thesis, Univer sity of Arkansas, Fayetteville, 124 p. Brahana, J.V., 1997, Rationale and methodology for approximating spring-basin boundaries in the mantled karst terrane of the Springf ield Plateau, northwestern Arkansas: in Beck, B.F. and Stephenson, J. Brad, eds., Figure 10. Proportional geometric model of the subsurface conduit network systems of Basin 1 in SEW. The storage unit is represented with a larger pipe in the conceptual conduit model, and is based on continuous flow data, tracing data, and long-term chemographs. (Ting, 2005)

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152 Sixth Multidisciplinary Conference on Engineering Geology and Hydrogeology of Karst Terranes, A.A. Balkema, Rotterdam, p. 77-82. Brahana, J.V., Sauer, T.J., Kr esse, Tim, Al-Rashidy, Said, Shirley, Tracy, and McKee, Paul, 1998, Tipping the scale in long-term karst researchHydrogeologic characterization of the Savoy Experimental Water shed: Proceedings Volume, Water Quality of Surface and Ground Water and Best Management Practice, Arkansas Water Resources Center, p. 9-17. Fanning, B.J., 1994, Geospeleologic analysis of cave and karst development within the Boone and St. Joe Forma tions of Benton and Madison counties, Northwest Arkansas: unpublished M.S. thesis, University of Arkansas, Fayetteville, 144 p. Grant, D.M and Dawson, B.D., 1997, Isco Open channel flow measurement handbook: Isco, Inc., Lincoln, Nebraska, 5 th ed. Laincz, Jozef, 2005, A biog eochemical /hydrological approach to characterize tran sport and cycling of nitro gen in mantled karst watershed: Arkansas Water Research Conference, Fayetteville, Conference Pro ceedings [compact disk]. National Research Council, 2001, Conceptual models of flow and transport in the fractured vadose zone: National Academy Press, Washington, 374 p. Palmer, A.N., 1990, Groundwater processes in karst ter ranes, in Higgins, C.G., and Coates, D.R. (eds.), Groundwater geomorphology: The role of subsurface water in Earth-surface processes and landforms, Boul der, Colorado: Geological Society of America Special Paper 252. Ting, Tiong Ee, 2005, Assessing bacterial transport, stor age and viability in mantled karst of Northwest Arkan sas using clay and Escheria coli labeled with lan thanide-series metals: unpublished Ph.D. dissertation, University of Arkansas, Fayetteville. Unger, Tim, 2004, Structural controls influencing groundwater flow within the mantled karst of the Savoy Experimental Watersh ed, Northwest Arkansas: unpublished M.S. thesis, University of Arkansas, Fayetteville, 124 p.

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153 Characterization of Nutrient Process ing at the Field and Basin Scale in the Mantled Karst of the Savoy Experimental Watershed, Arkansas By Jozef Laincz 1 P.D. Hays 2,3 Sue Ziegler 4 Byron Winston 4 J.F. Murdoch 5 J.V. Brahana 2 K.F. Steele 2 Indrajeet Chaubey 5 and Ralph K. Davis 2 1 Program of Environmental Dynami cs, 113 Ozark, University of Arkansas, Fayetteville, AR 72701 2 Department of Geosciences, 113 Ozark, University of Ar kansas, Fayetteville, AR 72701 3 US Department of Agriculture, Na tional Water Managemen t Center, 44 Ozark, Fayetteville, AR 72701 4 Department of Biological Sciences, 528 Science and En gineering, University of Arkansas, Fayetteville, AR 72701 5 Department of Biological and Agricultural Engineer ing, 203 Engineering, University of Arkansas, Fay etteville, AR 72701 ABSTRACT Animal production and associated pasture applicatio n of animal manures in vulnerable karst regions poses a significant threat to water quality. Balanced nutrient applicat ion presupposes an understanding of biogeochemical processes and controls on nitrogen tr ansport, transformation, and sequestrationan under standing that is not well evolved for karst. Concentration and bioavailability of dissolved or ganic carbon, and karst hydrogeological compart ments were investigated as importan t factors controlling nutrient cycli ng and transport. Additionally, con centration and isotopic composition of NO 3 was used to determine the ex tent of denitrification and immobilization of nitrate. The study incorporated sampling events during two hydrologic regimes, storm and base flow, to char acterize three components of a sha llow system of a karst watershed: (1) surface-water/ground-water inter face (soil/regolith) zone, (2) interflo w over permeability contrasts zone, an d (3) focused flow zone. The first two are presumably the zones with in creased biogeochemical processing of nutrients due to longer retention time and greater matrix/water ratios. The importance of the soil zone in nutri ent utilization and immobili zation is well established. Conversely, the minimal degree of nutrient processing that occurs in the focused flow zone in karst is also well docum ented; however, the amount of nutr ient processing that may occur in the interflow zone in karst setting has not been studied. The potential for nutrient processing that may occur in the interflow zone is important b ecause of the lack of processing in thin soils and the focused flow zones that typify karst. Study results indicate that dilutio n of dissolved nutrient species and flow bypassing the soil zone through macropores are two important controls on nitrogen behavior. A key finding of the study is that the decrease of nitrate concentrations observed within the in terflow zone is greater than can be ascribed to dilu tion, indicating that microbial processing of nitrate is an important occurrence. Hydrologic conditions dic tate flow-paths and affect biogeo chemical processing of nitrate. Once the biogeochemical mechanisms proposed are completely el ucidated, the impact of agricultural practices on the integrity of these zones, and the wa y the processes occurring within these zones can be cap italized upon for nutrient management can be tested.

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154 Transport Potential of Cryptosporidium parvum Oocysts in a DrinkingWater, Karstic-Limestone Aquifer: What We Have Learned Using Oocyst-Sized Microspheres in a 10 0-m Convergent Tracer Test at Miami's Northwest Well Field Ronald W. Harvey 1 Allen M. Shapiro 2 Robert A. Renken 3 David W. Metge 1 Joseph N. Ryan 4 Christina L. Osborn 4 and Kevin J. Cunningham 3 1 U.S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303 2 U.S. Geological Survey, 12201 Sunrise Valley Drive, Rest on, Virginia 20192 3 U.S. Geological Survey, 9100 NW 36th St., Miami, FL 33178 4 Dept. Civil, Environ., and Arch Eng., University of Colorado, Boulder, Colorado 80309 ABSTRACT Aquifers characterized by karstic limestone are highly vulnerable to contamin ation by pathogens, in part because their solution-enlarged conduits and fracture systems can result in rapid and significant pref erential flow. Contamination by Cryptosporidium parvum a waterborne pathogenic pr otist, is of particular concern in areas where shallo w karstic systems also serve as the drin king water supply. The vulnerability of Miamis Northwest Well Field (NWWF) to contamination by C. parvum oocysts was assessed in a largescale, forced-gradient (convergent) in jection and recovery test. The fiel d study involved simultaneous pulse introduction to the Biscayne Aquifer of a conservative tracer (SF 6 an inert gas) and a polydispersed suspen sion of oocyst-sized (2-5 m, diameter) carboxylated polystyren e microspheres. Estimated fractional recoveries for the microspheres at a municipal supply well 100-m downgra dient from the injection borehole were inversely related to microsphere diameter and rang ed from 2.8% for th e largest to 5.6% for the smallest size classes or from 4.7% 9.3%, resp ectively, if corrected for the inco mplete (~60%) cumulative recovery observed for SF 6 in the same field test. Results from flow -through column studies with NWWF limestone cores housed in a modified triaxial cell indicated that microsphere surrogates may underestimate the trans port potential of oocysts in Biscayne Aquifer by 4-6 fold, in part because of the microspheres more-reactive surface (more negative zeta potential) under the calcium, ionic strength, and very slightly alkaline condi tions of the Biscayne Aquifer. Our study suggests th at, although the karstic lim estone within the Biscayne Aquifer appears to have a substantiv e sorptive capacity for oocysts, it may take more than two hundred meters of transport to ensure even a 1-log unit remova l of oocysts in the vicinity of the NWWF, depending upon the local-scale heterogeneity and factoring in a r easonable margin of safety. Flow-through column studies involving intact limest one cores housed within a modified tria xial cell suggest that considerable spa tial variation in the transport behavior of microspher es relative to a conservative tracer may be expected because of the spatial variations in limestone structure beneath the NWWF.

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155 Ground-Water Quality Near a Swine Waste Lagoon in a Mantled Karst Terrane in Nort hwestern Arkansas Christopher M. Hobza 1 David C. Moffit 2 Danny P. Goodwin 3 Timothy Kresse 4 John Fazio 4 John V. Brahana 5 and Phillip D. Hays 1 1 U.S. Geological Survey Arkansas Water Science Center, Fayetteville, AR 2 Natural Resources Conservation Service National Water Management Center, Ft. Worth, TX 3 Natural Resources Conservation Service National Water Management Center, Little Rock, AR 4 Arkansas Department of Environm ental Quality, Little Rock, AR 5 University of Arkansas Department of Geosci ences, Fayetteville, AR ABSTRACT Livestock production is generally the predominan t agricultural practice in mantled karst terranes because the thin, rocky soils associat ed with carbonate bedrock are not conducive to crop production. Unfor tunately, livestock production in karst areas can creat e environmental problems because of rapid, focused flow through soil and regolith. A study was conducted by the U.S. Geological Surv ey in cooperation with the Natural Resources Conservation Service National Wa ter Management Center, th e University of Arkan sas, and the Arkansas Department of Environmental Qua lity to examine a swine w aste storage lagoon in a mantled karst terrane at the University of Arkansas' Savoy Experimental Watershed to evaluate the effects of a swine waste lagoon on groundwater quality. The Savoy Experimental Watershed is a long-term, multidisciplinary research site, which is approximately 1, 250 hectares and encompasses parts of six drainage basins. An anaerobic swine waste lagoon was construc ted at the Savoy Swine Faci lity in compliance with U.S. Department of Agriculture Natural Resources Conservation Service Conservation Waste Storage Prac tice Standard no. 313 in one of the drainage basins. An inventory of springs, seeps, sinkholes, and losing streams was conducted in the basin where the waste la goon was constructed. Based on the inventory, nine shallow monitoring wells we re augered to refusal in the regolith. Sh allow ground-water from wells, springs, and an interceptor trench was sampl ed and analyzed for nutrients, ma jor cations, and major anions during high-flow and low-flow conditions. Results from ground-wa ter sampling indicate conc entrations of chloride and nitrate were higher than concentrations from nonagricultural land-use areas in the Ozarks, but were comparable to concentrations near th e site prior to the construction of the swine facility. A sample collected from an interceptor trench indicated th at nutrients are able to pass throug h the clay liner. The results of an electromagnetic geophysical survey in dicated that there were no prefe rred flow paths from the swine waste storage lagoon. Based on these r esults, it appears that the swine wa ste lagoon built using the Natural Resources Conservation Service Conservation Practice no 313 is minimally affecting the ground-water quality of the area.

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156 INTRODUCTION Animal production in nor thwestern Arkansas is the predominant agricultu ral practice because the thin, rocky soils are unsuita ble for sustainable crop production. Nationally, Arkansas ranks 2nd in broiler production, 16th in cattle, and 17th in swine production (U.S. Department of Agriculture, 2003). Animal waste generated from these agricultural operations typically is ap plied to local pastures, often in excess of nutrient requirements. These excess nutrients have little opportunity for natural attenuation in a mantled karst setting because of thin soils and underlying karst geology that allow rapid, focused flow resulting in contaminated ground and surface waters. Adamski (1987) compared nutrient concentrations in springs in an intensely farmed area with a minimally affected fo rested area and reported that the areas of intense livestock production had elevated concentrations of nitrate and chloride. One potential source of ground-water contami nation is from animal waste stored in anaerobic lagoons generated from confined animal feeding operations. These lagoon stru ctures are designed to store animal waste for a sp ecified time period until the waste is ready to be ap plied as liquid fertilizer to adjacent pastures or cropland. If not properly located, designed, construc ted, and maintained, ani mal waste lagoons can advers ely affect water quality through the introduction of excess nutrients and bac teria (Ham and DeSutter, 2000). The Natural Resources Conservation Service (NRCS) has developed several Best Management Practices (BMPs) to reduce this risk of ground-water contamination. Waste Stor age Practice no. 313 was created to allow producers to safely and effectively store animal waste while protecting ground-water resources in envi ronmentally sensitiv e areas across a variety of hydrogeological environments (Natural Resources Conservation Service, 2003). Ideally, these structures are located in areas with thick soils, over deep or confined aquifers, and away from domestic water supplies. Wh en this is not possible, the NRCS provides options that allow an additional measure of safety such as an impermeable geosyn thetic membrane liner or a compacted liner con structed from native soil with a specific permeability. This BMP has been successful in protecting ground-water resources in other hydrogeologic set tings, (David Moffit, Natural Resources Conserva tion Service, oral commun., 2004) but its effectiveness has not been evaluated in areas with thin soils such as a mantled karst setting. To address this need, the U.S. Geologic al Survey in cooperation with the Natural Resources Conservation Service National Water Management Center, the University of Arkansas, and the Arkansas Department of Envi ronmental Quality designed a study to determine the effectiveness of Waste Storage Practice no. 313 for storing swine waste in a ma ntled karst setting. The purpose of this report is to describe ground-water quality near the swine waste lagoon. STUDY AREA The Savoy Swine Facility is located within the Savoy Experimental Watershed (SEW) in northern Washington County in northwestern Arkansas (fig. 1). The SEW serves as a long-term, multi-disci plinary research site to examine water-quality prob lems associated with livestock production in a mantled karst setting. Th e SEW offers a unique opportunity to test and ev aluate the en vironmental effects of different animal agricultural practices. In 2002 the University of Arkansas constructed the Savoy Swine Facility to improve planned largescale swine production. The Savoy Swine Facility is managed as a demonstration farm to provide a longterm model for environmentally friendly manage ment of animal nutrition, animal waste and odors (Maxwell and others, 2003). The Savoy Swine Facility is located within the Springfield Plateau (Fenneman, 1938), which is underlain by nearly flat lying Mississippian-age cherty limestones and limestones. These sedimentary sequences have been incised by streams to form dendr itic drainages and rolling hills. Karst features such as springs, sinkholes, losing streams, caves, an d conduits are present in the study area (Little, 1999).

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157 0 0 1 1 2 Miles 2 KilometersBase map modified from U.S. Geological Survey digital data, 199636 0730o36 10o94 2230o94 20o94 1730oFigure 1. Location of the Savoy Swine Farm and diagram of waste storage infrastructure within the Savoy Experimental Watershed. The major geologic units present in the study area are the Chattanooga Shale, the St. Joe Lime stone Member of the Boone Formation, and the Boone Formation. The Chattanooga Shale is a black, Devonian-age shale that is approximately 45 feet thick within the SEW (L ittle, 1999) that unconform ably underlies the St. Joe Limestone Member. The Chattanooga Shale acts as a regional confining unit where it is present in the Ozarks separating groundwater flow between the Mississippian-age lime stones which compose the Springfield Plateau aqui fer and the underlying Ordovician-age dolomites and sandstones which comp ose the Ozark aquifer (Imes and Emmett, 1994). The St. Joe Limestone Member, which is part of the Boone Formation is a relatively pure limestone, is conformably overlain by cherty limestone. The Boone Formation consists of Mississippian-age cherty limestones and is thick est beneath the uplands throughout the study area. The bedrock in the study area is overlain by regolith that is the weathering product of the cherty lime stone of the Boone Formation that creates the man tled karst topography. The soils formed from the regolith are composed of silt loams and the associ ated subsoils are silty clay loam or cherty silt loam (Harper and others, 1969). The waste storage infrastructure at the Savoy Swine Facility was construc ted in compliance with Waste Storage Practice no. 313 (Natural Resources Conservation Service, 2003). Because the swine facility was constructed ov er an unconfined lime stone aquifer, more string ent design options were considered for the waste lagoon. The most econom ical solution was to constr uct a compacted clay liner from sieved native soil with a target coefficient of permeability of 1.0 x 10 -7 centimeters per second (Stan Rose, Natural Resources Conservation Ser vice, oral commun., 2004). Because of budget con straints during the cons truction, the Savoy Swine Facility is only able to house half the animals it was initially designed for. As a result the waste storage

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158 infrastructure is substantially oversized with respect to the number of animals served (Karl VanDev ender, University of Arkansas, oral commun., 2004). The Savoy Swine Farm has a unique projectspecific design constructed with four holding ponds each designed to store animal waste for a set of ani mals with a specific diet (fig. 1). METHODS A karst inventory was conducted in the area of the swine farm to gain a better understanding of the ground-water system prior to sampling point selec tion and well drilling. An inventory of springs, seeps, sinkholes, and losing and gaining reaches of streams was compiled. Ni ne shallow monitoring wells were augered to the de pth of drilling refusal in the regolith. All wells were constructed with 2-inch polyvinyl chloride (PVC) casing and slotted PVC screen sections. A sand filter pack was installed sur rounding the screened section with 2 feet of bento nite overlying the filter pack to prevent surface contamination. An intercep tor trench was installed west of the anaerobic lagoon on the swine farm and was excavated with a backhoe to the bedrock surface to allow collection of lago on leachate moving downgradient from the anaerobic lagoon after a storm event (fig. 1). Sampling points consisted of monitoring wells, springs, seeps, and the interceptor trench. Waterquality samples were collected (fig. 2) during highflow conditions in April 2004 and low-flow condi tions in October 2004. Th e interceptor trench was sampled after one storm event on July 27, 2004. All samples were analyzed for nutrients including nitrate plus nitrite, ammonium, total Kjeldahl nitro gen, total phosphorus, and orthophosphate, major cations and major anions by the Arkansas Depart ment of Environmental Quality (ADEQ) Water Quality Laboratory in Littl e Rock, Arkansas. Nitrate plus nitrite concentrations are reported as nitrate for this report because nitrate is the dominant form of nitrogen for this analyte. Fewer monitoring wells 36 070o36 08o36 080o94 200o94 20o94 190o94 19o Base map modified from U.S. Geological Survey digital data, 1996 0 0 0.25 0.250.5 Kilometer 0.5 Mile ANAEROBIC LAGOON INTERCEPTOR TRENCH Figure 2. Location of water-quality sampling points within study area.

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159 were sampled during low-flow conditions because some of the wells were dry or did not yield water for sampling. An electromagnetic geophysical survey was conducted near the waste storage infrastructure to determine any areas of preferential seepage from the lagoon and to assess the selection and placement of the sampling points. An EM-31 is a frequency domain electromagnetic instrument that is capable of determining subsurface conductivity (Geonics, 1984). Electromagnetic su rveys have been success ful in the past locating areas of preferred seepage from animal waste lagoons. Areas of lagoon seepage result in anomalously high subsurface conductivities compared to una ffected areas (Bru ne and Doolittle, 1990). Conductivity data were collected with a hor izontal dipole instrument orientation providing an average depth of investigation of 6 meters. Global Positioning System (GPS) data and subsurface con ductivity data were collect ed simultaneously. These data were plotted and contoured using the computer program Surfer (2002) for vi sual interpretation of results. GROUND-WATER QUALITY Concentrations of nitrate and chloride for both high-flow and low-flow sampling events were above background concentrations but were low compared to other areas in the Ozarks affected by livestock production (table 1). Background concentrations for nitrate plus nitrite in forested, relatively pristine areas of the Ozarks are typically less than 0.5 milli grams per liter (mg/L) as nitrogen (N) and 5.0 mg/L for chloride (Steel e, 1983). Data co llected in this study indicate that local livestock production proba bly is affecting the ground-water quality of the area. Concentrations of nitrate ranged from 0.27 to 2.39 mg/L as N during high-flow conditions and 0.84 to 3.41 mg/L as N during low-flow conditions. Chlo ride concentrations ranged from 3.95 to 14.8 mg/L during high-flow conditions and 14.1 to 30.2 mg/L during low-flow conditions. Concentrations of both nitrate and chloride were higher during the low-flow sampling event probably because of mixing and dilution that occurs during high-flow conditions. Table 1. Concentrations of nitrate and chloride for low-flow and high-flow sampling events [Background concentrations of nitrate and chloride are from rela tively pristine, forested areas of the Ozarks. Source sample co llected from anaero bic lagoon] Sampling point High-flow sampling (concentrations in mg/L) Low-flow sampling (concentrations in mg/L) Date Nitrate as N Chloride Date Nitrate as N Chloride Ammonium as N Well 1 4-12-04 1.08 14.8 Well 2 4-12-04 2.10 6.96 10-5-04 1.37 18.4 Well 3 4-12-04 1.23 9.97 10-5-04 1.07 18.9 Well 4 4-12-04 0.32 5.87 10-5-04 0.98 14.4 Well 5 4-12-04 0.46 3.95 Well 6 4-12-04 0.75 5.87 10-6-04 0.84 15.2 Well 7 4-12-04 0.27 3.95 10-6-04 0.99 14.1 Well 8 4-12-04 0.62 14.3 10-5-04 2.22 29.1 Well 9 4-12-04 1.99 12.9 Hidden Spring 4-12-04 2.39 11.5 10-5-04 3.41 30.2 Dead Cow Spring 10-5-04 2.59 19.8 Seep 4-12-04 1.32 8.90 10-5-04 1.15 16.0 Interceptor Trench 7-27-04 23.5 10.5 1.19 Anaerobic lagoon 6-13-05 6-13-05 0.44 462 40.0 Background 1 0.5 5.0 1 From Steele (1983)

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160 These results were comparable to a previous study conducted prior to the construction of the Savoy Swine Facility. Little (1999) collected waterquality samples from springs, seeps, and wells prox imal to the study area under high-flow and low-flow sampling conditions. Nitrate concentrations ranged from 0.06 to 4.64 mg/L as N and chloride concentra tions ranged from 2.89 to 27.0 mg/L as N. The ele vated concentrations suggest that the basin probably was affected by local livestock production prior to the construction of the Sa voy Swine Facility. The highest concentrations of nitrate and chloride were detected near the University of Arkansas Beef Head quarters towards the eastern portion of the study area (fig. 2). The results from the interceptor trench sample indicate that nitrogen is seeping throug h the anaero bic lagoon liner as ammonium with nitrification converting the ammonium in to nitrate. The intercep tor trench sample had concentrations of nitrate at 23.5 mg/L as N and ammoni um concentrations at 1.19 mg/L as N. A water-quality sample was col lected from the anaerobic la goon on June 13, 2005. The form of nitrogen within the anaerobic lagoon is predominantly ammonium, with concentrations at 40.0 mg/L as N. Nitrate concentrations were 0.44 mg/L as N and chloride concentrations were 462 mg/L in the lagoon sample (table 1). The lagoon leachate is probably mixi ng with other waters result ing in lower concentrations of nitrate and chloride in downgradient sampled wells and springs. Based on these ground-water quality data, the swine waste lagoon built using the Na tural Resources Conserva tion Practice no. 313 is minimally affecting the ground-water quality of the area. ELECTROMAGNETIC GEOPHYSICAL SURVEY The results of the EM-31 survey did not identify any areas of preferential seepage from the holding ponds, settling basin, or anaerobic lagoon. Subsur face conductivities ranged from 0.6 to 21.0 millim hos per meter. It appears th at most of the leakage is from the anaerobic lagoon and the leachate is migrating from the source in a fairly uniform pattern (fig. 3). There is very little leakage from the waste holding ponds and settling ba sin. This is probably because the animal waste stored in both the holding ponds and settling basin cont ains a much higher pro portion of solid animal waste compared to the anaer obic lagoon. The solid waste is able to create a seal that decreases liner permea bility (Natural Resources Conservation Service, 2003). Based on the results of the EM-31 survey it appears that the oversizing of the waste storage infrastructure is having a negative impact on the effectiveness of the anaerobic lagoon.

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161 31 21 261 81 266963 0 0 50 Meters 50 Feet 36 0832o36 0835o36 0837o97 1937o97 1935o97 1932oFigure 3. Results of EM-31 electromagnetic survey. SUMMARY A study was conducted to evaluate the effects of a swine waste lagoon on gr ound-water quality in a mantled karst terrane at th e University of Arkansas' Savoy Experimental Watershed. An anaerobic swine waste lagoon was constructed at the Savoy Swine Facility in complianc e with U.S. Department of Agriculture NRCS Conservation Waste Storage Practice Standard no. 313. An inventory of springs, seeps, and losing streams was conducted in the basin where the waste lagoon was constructed. Based on the inventory, sampling sites were selected and nine shallow monitoring wells we re augered to the depth of drilling refusal in th e regolith. Shallow groundwater from wells, springs an d an interceptor trench was sampled for nutrients, major cations, and major anions during high-flow and low-flow conditions. Data collected in this study indicate that the ground-water quality of the area is probably being affected by local livestock production. The concen trations of nitrate and chloride for both high-flow and low-flow sampling events were above back ground concentrations, but were low compared to other agriculturally affected areas in the Ozarks. Concentrations of nitrate plus nitrite ranged from 0.27 to 2.39 mg/L as N during high-flow conditions and 0.84 to 3.41 mg/L as N during low-flow condi tions. Chloride concentratio ns ranged from 3.95 to 14.8 mg/L during high-flow conditions and 14.1 to 30.2 mg/L during low-flow conditions. Concentra tions of both nitrate and chloride were higher during the low-flow sampling even t probably because of mixing and dilution that occurs during high-flow conditions.

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162 These results were comparable to a previous study conducted prior to the construction of the Savoy Swine Facility. Water-quality samples were collected from springs, seeps, and wells within near the study area under high-flow and low-flow sam pling conditions. Nitrate co ncentrations ranged from 0.06 to 4.64 mg/L as N an d chloride concentrations ranged from 2.89 to 27.0 mg/L. The elevated con centrations suggest that gr ound water in the basin has been affected by loca l livestock production prior to the construction of the Savoy Swine Facility. A water-quality sample collected from an inter ceptor trench after a storm event on July 27, 2004 had concentrations of nitrat e at 23.5 mg/L as N and dissolved ammonium concentrations at 1.19 mg/L as N. The results from the interceptor trench sample indicate that nitrogen is seeping throug h the anaero bic lagoon liner as ammonium with nitrification converting the ammonium in to nitrate. The lagoon leachate probably is mixing with other waters result ing in lower concentrations of nitrate and chloride in downgradient sampled wells and springs. The results of an elect romagnetic geophysical survey identified no areas of preferred seepage from the holding ponds, settlin g basin, and anaerobic lagoon. Most of the leakage appears to be from the anaerobic lagoon and the le achate is migrating from the source in a fairly uniform pattern. Very little leakage from the waste ho lding ponds and settling basin occurs. This is probably because the animal waste stored in both th e holding ponds and settling basin contains a much higher proportion of solid ani mal waste compared to the anaerobic lagoon. Based on these results, the swine waste lagoon built using the Natural Resources Conservation Service Con servation Practice no. 313 is minimally affecting the ground-water quality of the area. SELECTED REFERENCES Adamski, J.C., 1987, The ef fect of agri culture on the quality of ground water in a karstified carbonate ter rain, northwest Arkansas: Unpublished M.S. Thesis, 124 p. Brune, D.E., and Doolittle, J., 1990, Locating lagoon seepage with radar and el ectromagnetic survey: Envi ronmental Geology Water Science, v. 16, no. 3, p. 195207. Fenneman, N.M., 1938. Physiography of eastern United States: New York, McGraw-H ill Book Co. Inc., 714 p. Geonics Limited, 1984, Operating manual for EM-31D non-contacting terrain conductivity meter: 60 p. Ham, J.M., and DeSutter T. M., 2000, Toward site-spe cific design standards for animal-waste lagoons: Pro tecting ground water quality: Journal of Environmental Quality, v. 29, p.1721-1732. Harper, M.D., Phillips, W.W., and Haley, G.J., 1969, Soil survey of Washington County, Arkansas: U.S. Depart ment of Agriculture, 94 p. Imes, J.L., and Emmett, L.F., 1994, Geohydrology of the Ozark Plateau aquifer system in parts of Missouri, Arkansas, Oklahoma, and Ka nsas: U.S. Geological Survey Professional Paper 1414-D, 127 p. Little, P.R., 1999, Dominant processes affecting ground water quality and flow in Basin 2, Savoy Experimental Watershed (SEW): Unpublished M. S. Thesis, 93 p. Maxwell, C.V., Van Devender K., Coffey, K.P., Moore, P.A., Chaubey, I., and Smith, D.R., 2003, Swine waste demonstration and training project: University of Arkansas, Division of Ag riculture, Final Project Report, 6 p. Natural Resources Conservatio n Service, 2003, Agricul tural waste management field handbook, Appendix 10D: 31 p. Steele, K. F., 1983, Chemistry of the springs of the Ozark Mountains, northwest Arkansas: Water Resources Completion Report A-055-Ark. 47 p. Surfer version 8.02, 2002, Surface mapping system: Golden Software. United States Department of Agriculture, 2003, United States Department of Ag riculture National Agricul tural Statistics Service, acce ssed June 10, 2005 at http:/ /www.usda.gov/nass/pubs/estindx.htm.



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163 Vulnerability (Risk) Mapping of th e Madison Aquifer near Rapid City, South Dakota By Scott L. Miller, Dr. Arden D. Davis, and Dr. Alvis L. Lisenbee South Dakota School of Mines and Technology, Depart ment of Geology and Geological Engineering, 501 East St. Joseph Street, Rapid City, SD 57701 ABSTRACT Water supplies for Rapid C ity, South Dakota, and surrounding subu rban and rural areas are extremely vulnerable to contamination. The impact of ground -water contamination could occur quickly and linger for many years. The City of Rapid C ity is located within the Rapid Cree k watershed in the east-central Black Hills and relies heavily on the Miss issippian Madison karst aquifer for drinking-water supplies, utilizing several wells and springs. The aquifer consists of limes tone and dolomite and contains paleokarst and recent karst that probably formed along a well-developed fracture system. Prev ious work indicates stream-related aquifer recharge from the watersheds of Spring Creek (to the south), Boxelder Creek (to the north), and Rapid Creek as well as direct recharge by precipitation on the entire outcrop area west of Rapid City. Spring Creek and Boxelder Creek lose all their flow to karst sinkholes in the aquifer except during periods of high discharge (greater than approximately 28 ft 3 /sec for Spring Creek and 50 ft 3 /sec for Boxelder Creek. Ground water from these watersheds converges on wells and springs in the Rapi d City area several miles away. Dye-tracer tests for this area indicate ground-wat er velocities on the order of 1,000 feet per day and residence times range from a few days to several years. A database of 329 wells, geologic maps, fractures, faults, geologic structures, water-quality data, and dye-tracer test results were analyzed to develop a geol ogic model to better define local ground-water flow paths and characterize sus ceptibility zones. Structure contour and depth-to-aquifer maps have been com pleted for the Madison aquifer. Inherent aquifer su sceptibility, combined with human influences, was used to develop a vulnerability (risk) ma p (1:24,000 scale) for the Madison aquifer for the Rapid City area.

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164 Hydrogeologic Characteristics of Fo ur Public Drinking-Water Supply Springs in the Ozark Plat eaus of Northern Arkansas By Joel M. Galloway U.S. Geological Survey, 401 Hard in Road, Little Rock, AR 72211 ABSTRACT In October 2000, a study was undertaken by the U.S. Geological Survey in cooperation with the Arkan sas Department of Health to dete rmine the hydrogeologic characteris tics, including th e extent of the recharge areas, for four springs in northern Arkans as used for public drinking -water supply. Information pertaining to each spring can be used to enable deve lopment of effective manageme nt plans to protect these water resources and public health. Analyses of discharge, temperature, and water quality were completed to describe ground-water flow characteristics, sourcewater characteristics, and c onnectivity of the groundwater system with surface runoff. Water-level contou r maps were constructed to determine ground-water flow directions, and ground-water tracer tests were cond ucted to determine the extent of the recharge areas and ground-water flow velocities. Two of the springs (Hughes and Stark Springs) we re characterized as being influenced by local recharge areas and two springs (Evening Shade and Roar ing Springs) reflected regi onal aquifer recharge. The discharge and water-quality data for Hughes and Stark Springs sh ow the ground-water systems are dominated by rapid recharge from surface runoff and main ly consist of conduit-type flow systems with little diffuse-type flow. The local recharge area for Hughes Spring was estimat ed as 15.8 square miles, and the local recharge area for Stark spring was estimated as 0.79 square mile Recharge to Evening Shade and Roaring Springs originates from water ente ring geologic formations in the Oz ark aquifer. As a result, a local recharge area was not delineated, as the area could include relatively remote lo cations where geologic for mations composing the Ozark aquifer are exposed and have sufficient po rosity and hydrau lic conductivity to convey water that falls as precipitation to the subsurface. INTRODUCTION Hughes Spring, Stark Spring, Evening Shade Spring, and Roaring Spring supply the public drink ing water to the communities of Marshall, Cushman, Evening Shade, and Cher okee Village, Arkansas (fig. 1). Anticipated nearby land-use changes may increase threats to the qua lity of the shallow ground water in part because of the karst terrain, and the extent and location of the recharge areas that con tribute water to these four public drinking-water supply springs were unknown. Shallow groundwater systems dominated by fracture or conduit flow may be subject to rapid input of surface contami nants and rapid transport of these contaminants to wells and springs with little opportunity for natural attenuation processes to occur. Many communities and towns in Arkansas have discontinued the use of springs that discharge shallow ground water because of surface-derived contamination. In October 2000, the U.S. Geological Survey (USGS) began a cooperative study with the Arkan sas Department of Health to characterize the hydro geology and extent of the recharge area for the springs. The purpose of this report is to describe the hydrogeologic characteristi cs, including the extent of the recharge areas, of Hughes, Stark, Evening Shade, and Roaring Spri ngs. A more detailed description of the results is discussed in Galloway (2004). This information w ill help water managers to develop plans to protect the recharge area from contamination related to land use and potential spills.

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165 METHODS OF INVESTIGATION Several methods were u sed to determine the hydrogeologic characteristics of each study area. Geomorphic and topographic data from existing maps were gathered and assessed to determine surf icial controls on infiltration, ground-water flow pathways, and boundaries to ground-water flow. A field inventory of karst features (caves, sinkholes, sinking streams, and enlarg ed vertical fractures and bedding planes), wells, an d springs also was con ducted in each study area to provide information on the connection of the grou nd-water system to the land surface and to develop water-level contour maps of the study areas. Several wells were used for borehole geophysical surveys within the study areas to provide information about the lithology, distribu tion of permeability, and nature of vertical flow within the ground-water system. To determine flow characteristics and aid in the estimate of the recharge area, the four springs were instrumented to measure discharge, water temperature, and precipitation for October 2001 to October 2002. Water-quality sam ples were collected at each spring to determine the geochemistry of the contributing geologic units and the susceptibility of the sp ring to contamination. Samples were collected during base-flow and highflow conditions and were analyzed for major ions, selected trace constituents, nutrients, fecal indicator bacteria, wastewater constituents, stable isotopes, Figure 1. Location of springs and study areas. Hughes Spring Stark Spring Evening Shade Spring Roaring SpringMarshall Evening Shade Cushman Batesville Ash Flat Cherokee Village HardyOzark Aquifer Springfield Plateau Aquifer Western Interior Plains Confining SystemIzard Stone Sharp Searcy Fulton Marion Baxter Van Buren Cleburne Independence ArkansasBase from U.S. Geological Survey digital data, 1:100,000 Missouri Arkansas020 Miles 10 020 Kilometers 10 3530' 3630' 9230' 9130' EXPLANATIONSpring Study Area

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166 and radiogenic isotopes. Qualitative tracer tests were conducted from January to June 2002 to iden tify possible ground-water flowpaths and velocities and confirm the locations of inferred ground-waterbasin boundaries. A more detailed discussion of the methods used in the study is presented in Galloway (2004). LOCALLY RECHARGED SPRINGS The study area for Hughes Spring includes the Western Interior Plains confining system and the Springfield Plateau and Ozark aquifers. Exposures of geologic units of the Springfield Plateau aquifer dominate the area, smaller parts of the Ozark aquifer are exposed in the northern part of the study area, and parts of the Western Interior Plains confining system are exposed in the so uthern part of the study area. Units generally dip south-southeast by 3 to 12 degrees and the only large structural feature is a fault, located in the southern part of the study area (Galloway, 2004). The Western Interior Plains con fining system contains Pennsylvanian-age shale, sandstone, and limestone (Pitkin Limestone, Fay etteville Shale, and Batesvil le Sandstone) (fig. 2). The geologic units of the Springfield Plateau aquifer consist of Mississippian-age limestone (Boone For mation) and are typically separated from the under lying Ozark aquifer by the Ozark confining unit composed of Devonian-age shale in areas of north ern Arkansas (fig. 2). Borehole geophysical surveys in several wells show the Ozark confining unit was thin or absent in the H ughes Spring study area; therefore, the unit is not shown in figure 2. The Ozark aquifer is exposed at low altitudes in stream valleys in the northern portion of the Hughes Spring study area. Geologic formations that compose the Ozark aquifer and are exposed in the study area include Devonianand Silurian-age limestone (Cason Shale, Fernvale Limestone, and Plattin Limestone), and Ordovician-age shale and lime stones, dolomites, and sandstones (St. Peter Sand stone and Everton Formation). Water-level data indicate a hydrologic connection exists between the Springfield Plateau aquifer and the Ozark aquifer because of the discontinuous presence of the Ozark confining unit (fig. 2). Karstic features were found in the Hughes Spring stud y area, mainly in the Mis sissippian-age Boone Form ation. These features develop as ground water percolates through the limestone resulting in the enlargement of fractures through the dissolution of the carbonate rock form ing solution channels (fig. 2). Karst features present in the study area include si nkholes, springs, sinking streams, and caves. No surface streams were observed to have flow throughout the year. Brush Creek was observed to have flow along its entire length in the study area only during periods of intense rainfall events. Hughes Spring discharges from fractures in units of the Ozark aquifer, although most of the water probably originates from the over lying Springfield Plateau aquifer as indicated by the geophysical data, ground-w ater tracer tests, and geochemical data discussed later in this report. The Boone Formation is exposed throughout most of the Stark Spring study area at higher alti tudes. Silurianand Devonian-age units are present in the northern and western parts of the study area, but are absent near Stark Spring, resulting in an unconformable contact of the Boone Formation and the Ordovician-age shales and dolomites (fig. 2). Field observations in the area indicate that where the Boone Formation is expo sed, surface runoff only occurs during periods of intense rainfall. Stark Spring is located near th e contact of the Boone For mation and the underlying less permeable and less karstic Cason Shale. The discharge for Hughes Spring and Stark Spring varied seasonally and temporally (fig. 3). The mean annual discharg es for Hughes Spring for water years 2001 and 2002 were 2.9 and 5.2 cubic feet per second (ft 3 /s), respectively (Brossett and Evans, 2003). Mean daily discharge ranged from approximately 0.5 to 14 ft 3 /s for water years 2001 and 2002. The mean annual discharge for Stark Spring for water years 2001 and 2002 was 0.5 and 1.5 ft 3 /s, respectively (Brossett and Evans, 2003). Mean daily discharge ranged from approximately 0.1 to 23 ft 3 /s for water year 2001 and from 0.1 to 49 ft 3 /s for water year 2002. The ratios of annual peak flow to base flow for Hughes Spring (28) and Stark Spring (491) indicated fast-response springs (White, 1988). Water temperature for H ughes Spring reflected seasonal variations throughout the monitoring

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167 period and demonstrated considerable changes dur ing summer high-flow events (fig. 3). The highest temperatures were recorded in the summer and fall with average temperatures of approximately 17 C for both seasons. The winter and spring had lower average temperatures of approximately 12 C and 13 C, respectively. Large water temperature varia tions corresponded to high-fl ow events. Large water temperature fluctuations were not noticeable for Stark Spring, although slight variations did occur during high-flow events (fig. 3). Recorded water temperature ranged from 13.5 C to 14.7 C with a mean of 14.5 C. Figure 2. Conceptual model of ground-water flow to Hughes Spring and Stark Spring. EVERTON FORMATION ST. PETER SANDSTONE FERNVALE LIMESTONE/PLATTIN LIMESTONE BOONE FORMATION RUDDELL SHALE MEMBER OF THE MOOREFIELD FORMATION FAYETTEVILLE SHALE/ BATESVILLE SANDSTONE PITKIN LIMESTONEHughes SpringNORTH SOUTHNOTTO SCALEB r u s h C r e e k CASON SHALE SINKHOLE SOLUTION CHANNELS EXPLANATIONGeneralized flow direction of Brush Creek Generalized ground-water flow direction Ozark Aquifer Springfield Plateau AquiferSpringfield Plateau Aquifer Ozark AquiferWestern Interior Plains Confining System Stark Spring Poke BayouLARGE CONDUITS BOONE FORMATION JOACHIM DOLOMITE ST. PETER SANDSTONE EVERTON FORMATION WEST EAST NOTTO SCALE CASON SHALE SINKHOLE ENLARGED FRACTURES EXPLANATIONGeneralized ground-water flow direction

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168 The major ion analyses for samples collected between September 2001 to October 2002 for Hughes Spring and Stark Spring show a chemistry that is a calcium bicarbonate type (Hem, 1989) and are indicative of waters fro m the Springfield Plateau aquifer. The calcium to magnesium ratio ranged from 26 to 38 for Hughes Sp ring and from 9 to 10 for Stark Spring, indicating co ntribution from limestone mineralogy (White, 1988). Ratios of calcium to magnesium calculated for other samples collected from wells and springs repr esenting the Springfield Plateau aquifer indicate ratios ranging from 3 to 70, with a median ratio value of 18, also indicating lime stone mineralogy. Wells and springs representing units in the Ozark aquifer had values for calcium to magnesium ratios ranging from 1 to 3 with a median value of 1, indicating a dolomitic mineralogy. The geochemistry of Hughes Spring and Stark Spring is characteristic of conduit-dominated ground-water flow systems. Samples collected dur ing base-flow conditions ha d calcite saturation index (SI calcite ) (Adamski, 2000) values near or greater than 0.4 (supersaturated w ith respect to calcite) for Hughes Spring and ranged from -0.12 to 0.16 for Stark Spring. High-flow samples had SI calcite values of 0.3 and -0.15 (supersaturated to undersaturated with respect to calcite ) for Hughes Spring and ranged from -1.05 to 0.34 for Stark Spring. Total dissolved solids (TDS) concentrations and hardness also changed with flow conditions. Both values decreased as discharge increased, reflecting the effects of reduced residence time of the water with the source rock at higher discharge, allowing for less dissolution at both springs. Stable isotopes of carbon ( 13C) indicated dif ferent characteristics of the recharge water as it enters the ground-water system at Hughes Spring compared to Stark Spring. The 13C data for Hughes Spring indicate that although the groundwater system is dominated by conduit flow, a sub stantial component of the so urce water interacts with surface material, such as soils and regolith, before entering the ground-water system during high-flow events. An enrichment of organically derived carbon occurs in the Hughes Spring discharge during highflow events from water infi ltrating into soils in the recharge area before entering the aquifer system. A connection of Hughes Spring with Brush Creek, shown by ground-water tracer tests, would provide pathways for water enriched in organically derived carbon to reach the spring discharge. During baseflow conditions, water in the ground-water system that feeds the Hughes Spring discharge has a longer residence time in the syst em that allows it to approach equilibri um and maintain an even distribu tion of inorganically and organically derived carbon, caused by buffering (low ering the acidity) from car bonate dissolution. The 13C data show that the recharge water for Stark Sp ring has less interaction with the soil and regolith be fore entering the groundwater system than observed at Hughes Spring. Stark Spring displayed a decrease in the calculated per centage of organically derived carbon during highflow conditions. These da ta indicate that runoff enters the ground-water system at a more rapid rate near Stark Spring than near Hughes Spring, and does not allow sufficient interaction with surface material in the recharge area for the transport of organically derived carbon into the ground-water system. Based on the ground-water tracer test data and the spring discharge, it appears that the recharge area for Hughes Spring generall y coincides with the sur face drainage area, which is approximately 15.8 square miles (mi 2 ). Tracers injected outside the surface drainage area (sites 5-7) were not detected STARK SPRING Oct Dec Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct 0.01 0.1 1 10 100 WATER-QUALITY SAMPLE HUGHES SPRING Oct Dec Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct DISCHARGE, IN CUBIC FEET PER SECOND 0.01 0.1 1 10 100 TOTAL MEAN DAILY TOTAL ESTIMATED MEAN DAILY BASEFLOW DATE Oct Dec Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct TEMPERATURE, IN DEGREES CELSIUS 8 10 12 14 16 18 20 22 24 STARK SPRING HUGHES SPRING WATER YEAR 2001 WATER YEAR 2002TOTAL MEAN DAILY BASEFLOW ee ee eeWATER-QUALITY SAMPLE Figure 3. Daily discharge and water temperature recorded at Hughes Spring and Stark Spring.

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169 within the surface-drainage area (fig. 4). Tracers injected at two sites inside the surface drainage area (sites 2 and 3) were detected at Hughes Spring and at springs along Brush Creek and in Brush Creek itself, indicating a connection between the surface flow in the stream and Hughes Spring. The tracertest data and spring-discharge data show that Hughes Spring may act as a distributary from Brush Creek during high-flow events, discharging a por tion of runoff waters r esulting from precipitation that occurs in the surface-drainage area. The recharge area computed from the recorded discharge indicated that the area approximated by the surface drainage was not large enough to pro duce the discharge observed at Stark Spring. The surface-drainage area is approximately 0.34 mi 2 An average computed recharge area of 0.79 mi 2 from five storms, assuming a 10 percent reduction in recharge volume from ev apotranspiration, soil absorption, and vegetation interception, was used with ground-water tracer t est data to delineate the recharge area for Stark Spring. The configuration of the recharge area for Stark Spring was found to be considerably different than the surface drainage from tracer-test data and geo logic characteristics of the area. The recharge area is controlled predominantly by the occurrence of the Boone Formation outcrop. No major structural fea tures were observed from geologic mapping or field observations near the spring, and tracer-test results show that the recharge area extends outside the surface-drainage area to the west of the spring surface-drainage area (fig. 4). Tracer tests demonstrated rapid ground-water flow velocities in both study areas, which are char acteristic of conduit-type flow often found in karst systems (White, 1988). Using distances measured along implied flowpaths from injection sites to recovery sites, estimated minimum velocities ranged from 0.04 to 1.30 miles per day for Hughes Spring and 0.06 miles per day for Stark Spring. REGIONALLY RECHARGED SPRINGS The Evening Shade Spring and Roaring Spring study areas lie on the outcrop of the Ozark aquifer (fig. 1) and include Ordovician-age limestone, dolo mite, and sandstone formatio ns. The units generally have a slight dip to the so uth-southeast with an angle of less than 1 degree es timated from geophysical logs. No major structural features were evident in the study areas from field observations and geophys ical logs. Few vertical fractures were observed in acoustic televiewer geophy sical logs, but horizontal bedding planes were observed and likely provide the preferred pathways for dissolution (Galloway, 2004). Evening Shade Sp ring discharges through two main discharge points in the Everton Formation outcrop (fig. 5). One has be en enclosed by a spring house for utilization as a pu blic-water supply and the other resurgent point is in the stream channel of Mill Creek near the springhouse. Roaring Spring dis charges near the contact between the Cotter Dolo mite and the Jefferson City Dolomite (fig. 5). The location of Evening Shad e Spring and Roaring Spring may be caused by a set of enlarged vertical fractures or conduits not readily visible at the sur face that may concentrate and convey flow to the surface from fractures and conduits in multiple for mations composing the Ozark aquifer (fig. 5). Water-level contours, cons tructed from static water levels measured in wells an d springs in both study areas, followed a similar pattern to the regional flow of the Ozark aquifer constructed by Pugh (1998) and Schrader (2001).

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170Figure 4. Locations of tracer injection and recovery sites with implied flowpaths of tracers and delineated recharge areas for Hughes and Stark Springs. g n i r p Sk e e r Ce k o Pu o y a Be v a CCreekStark Spring Cave Spring Mill Spring3 2 4 100.51 Mile 00.51 Kilometer 9142' 9139' 3551' 3549' 69EXPLANATION Site types (with site identifier) Injection sites Recovery sites1Stark Spring Implied flowpath Surface drainage area Estimated recharge areaBase from U.S. Geological Survey digital data, 1:100,000 h s u r Bk e e r CCreekBuffaloRiverRockyCreekr a e BSinkhole 7 6 5 3 2 1 4 S1 S9 S8 S6 S5 S4 S3 S2 S15 S16 S14 S13 S11 S10 W28 65 27 65 74 27 74 0 1 2Miles 0 12KilometersMarshall EXPLANATIONSite types (number is site identifier) Recovery sites S1 Injection sites 1 9236' 9242' 36 3554' Base from U.S. Geological Survey digital data, 1:100,000Hughes Spring Surface drainage and estimated recharge area for Hughes Spring Implied flowpaths

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171Figure 5. Conceptual model of ground-water flow to Evening Shade and Roaring Springs. Strawberry River Piney Fork Mill Creek Evening Shade Spring NORTH SOUTH NOTTO SCALE ST. PETER SANDSTONE EVERTON FORMATION POWELL DOLOMITE COTTER DOLOMITE JEFFERSON CITY DOLOMITEOZARK AQUIFERROUBIDOUX FORMATIONZONE OF LOW PERMEABILITY ENLARGED BEDDING PLANE EXPLANATIONGeneralized flow direction OZARK AQUIFER r e v i R g n i r p S k r o F h t u o S g n i r p S g n i r a o RCOTTER DOLOMITE DOLOMITE JEFFERSON CITY ROUBIDOUX FORMATION R E B M E M E N O T S D N A S R E T N U G ) n o i t a m r o F e d a n o c s a G (GASCONADE FORMATIONNORTH SOUTH NOTTO SCALEr e v i R g n i r p S k r o F h t u o S EXPLANATIONGeneralized flow direction

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172 The discharge for Even ing Shade Spring and Roaring Spring remained fa irly constant with time. The mean daily discharge for Evening Shade Spring, computed from the spring house discharge point, ranged from 0.88 to 2.29 ft 3 /s for water year 2001 and from 0.76 to 2.25 ft 3 /s for water year 2002 (fig. 6). The mean annual di scharge for water years 2001 and 2002 was 1.44 and 1.24 ft 3 /s, respectively (Brossett and Evans, 2003). The spring discharge periodically measured in the channel of Mill Creek ranged from 3.6 to 9.0 ft 3 /s during water years 2001 and 2002 (fig. 6). The mean daily discharge for Roaring Spring ranged from 4.8 to 7.2 ft 3 /s, and the mean discharge was 5.7 ft 3 /s for July 2001 to Octo ber 2002 (Brossett and Evan s, 2003) The ratio of base flow to peak flow for Evening Shade Spring ranged from 2.6 to 3.0 and the ratio for Roaring Spring was 1.5, indicating slow-response springs (White, 1988). The dischar ge for both springs con trasts with the fast response, storm input type of dis charge that was observed at Hughes and Stark Springs. The recorded water temperature for Evening Shade Spring ranged from 16.7 to 16.8 C from Feb ruary 2001 to July 2002, and the water temperature for Roaring Spring rang ed from 17.1 to 17.2 C (fig. 6). The relatively stable discharge and temper ature suggest that the Evening Shade Spring and Roaring Spring discharge is representative of a regional ground-water system. The major ion analyses from Evening Shade Spring and Roaring Spring demonstrated a calcium bicarbonate type water typical of the Ozark aquifer. All samples collected fro m Evening Shade Spring and Roaring Spring had cal cium to magnesium ratio values of 1.3 and 1.1, respectively, indicating contri bution from a dolomitic mineralogy (White, 1988) that also is representative of formations of the Ozark aquifer. SI calcite values from samples collected at Evening Shade Spring and Roaring Spring showed the waters are supersaturat ed with calcite. Values for SI calcite appeared to have an inverse relation with the quantity of discharge at the time the sample was col lected. At higher discharges, the SI calcite decreased and at lower discharges the value increased. Although it has been shown that there is not a large variation in spring discha rge during precipitation events, flow velocities in the ground-water system during periods of high precipitation (late winter, early spring) may increase enough to decrease the contact time of the water with the rock because of a steepening of the ground-water gradient. The 13C data show the water discharging from Evening Shade Spring and Roaring Spring reflected nearequilibrium conditions be tween the ground water and the aquifer material. The discharge, geochemical, and hydrogeologic data indicate that the discharges for Evening Shade Spring and Roaring Spring are representative of a regional ground-water flow system (Ozark aquifer) and do not allow for a dis tinct boundary to be delin eated for the recharge area contributing to the spring. Ground-water tracer tests conducted in the study area to identify a conn ection between Evening Shade Spring and local ground-water flow systems resulted in the negative reco very of the three tracers injected into two wells an d a sinkhole. Although the tracer tests did not establish that a local recharge area does not exist conclusi vely, they lend support that the Evening Shade Spri ng is mainly recharged from the Ozark aquifer. Tracer tests were not attempted in the Roaring Spring study area. The recharge areas for the two springs could include rel atively remote locations where hydrogeologic units EVENING SHADE SPRING Oct Dec Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct DISCHARGE, IN CUBIC FEET PER SECOND 0.01 0.1 1 10 100 TOTAL MEAN DAILY BASEFLOW ROARING SPRING Oct Dec Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct 0.01 0.1 1 10 100 DATE Oct Dec Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct TEMPERATURE, IN DEGREES CELSIUS 16.4 16.6 16.8 17.0 17.2 17.4 17.6 EVENING SHADE SPRING ROARING SPRING WATER YEAR 2001 WATER YEAR 2002TOTAL MEAN DAILY WATER-QUALITY SAMPLE BASEFLOW WATER-QUALITY SAMPLE ee ee e eFigure 6. Daily discharge and water temperature recorded at Evening Shade Spring and Roaring Spring.

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173 composing the Ozark aquife r are exposed and have sufficient porosity and hyd raulic conductivity to convey water that falls as precipitation to the subsur face. CONCLUSIONS Recharge to Hughes Spring and Stark Spring occurs mainly from the B oone Formation that com poses the Springfield Plateau aquifer. Ground-water tracer tests indicate that the recharge area for Hughes Spring generally coincides with the surface drainage area (15.8 mi 2 ) and that Hughes Spring is directly connected to th e surface flow in Brush Creek. Analyses of discharge data show that Stark Spring has a fast response to surface runoff and the estimated recharge area (0.79 mi 2 ) is larger than the surface-drainage area (0.34 mi 2 ). Ground-water tracer tests and the outcrop of the Boone Formation indicate that most of the recharge area extends out side the surface-drainage area. The geochemistry of Hughes Spring and Stark Spring demonstrated varia tions with flow conditions and the influence of surface-runoff in the recharge area. Calcite saturation in dices, total dissolved sol ids concentrations, and hardness demonstrate noticeable differences with flow conditions reflect ing the reduced residence time and interaction of water with the source rock at high-flow conditions for Hughes Spring. Large water temperature varia tions also corresponded to high-flow events at Hughes Spring although variations were not as noticeable for Stark Spring during high-flow events. Evening Shade and Roaring Springs originate from geologic formations composing the Ozark aquifer. Little variation in discharge and tempera ture was evident during high-flow events and throughout the monitoring period indicating that spring discharge is dominated by regional groundwater flow with small portions of local recharge. As a result, local recharge areas were not delineated, and the area could include relatively remote loca tions where geologic fo rmations composing the Ozark aquifer are exposed and have sufficient poros ity and hydraulic conductivity to convey water that falls as precipitation to the subsurface. REFERENCES Adamski, J.C., 2000, Geochemistry of the Springfield Plateau aquifer of the Ozark Plateaus Province in Arkansas, Kansas, Missouri and Oklahoma, USA: Hydrological Processes, v. 14, p. 849-866. Brossett, T. H. and Evans, D.A., 2003, Wat er resources data, Arkansas, water year 2002: U.S. Geological Survey Water-Data Report AR-02-1, 461 p. Galloway, J.M., 2004, Hydrog eologic characteristics of four public drinking-water supply springs in northern Arkansas: U.S. Geological Survey Water-Resources Investigations Report 03-4307, 68 p. Hem, J.D., 1989, Study and interpretation of the chemical characteristics of natural water: U.S. Geological Survey Water Supply Paper 2254, 264 p. Pugh, A.L., 1998, Potentiome tric surface of the Ozark aquifer in northern Arkansas, 1995: U.S. Geological Survey Water-Resour ces Investigations Report 984000, 7 p. Schrader, T.P., 2001, Potentio metric surface of the Ozark aquifer in northern Arkansas, 2001: U.S. Geological Survey Water-Resour ces Investigations Report 014233, 11 p. White, W.B., 1988, Geomorphology and hydrology of karst terrains: New York, New York, Oxford Univer sity Press, Inc., 464 p.

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174 Adaptation of the Residence Time Distribution (RTD)-Biodegradation Model to Quantify Peroxi de-Enhanced Fuel Biodegradation in a Single Karst Well Lashun K. King 1 Roger D. Painter 1 and Tom D. Byl 1,2 1 Dept. of Civil & Environmental Engineering, Tenne ssee State University Nashville, TN 37209 2 U.S. Geological Survey, 640 Grassmer e, Suite 100, Nashville, TN 37211 ABSTRACT This field study was conducted to determine if a numerical model incorpora ting residence time distri bution (RTD) coupled to a first-order rate of biodegrad ation (k') could be used to quantify toluene and ben zene removal in a single karst-well in jection system. This study involved injecting sodium chloride (NaCl) as a conservative tracer, as well as hydrogen peroxide (H 2 O 2 ), to enhance aerobic biodegradation of toluene and benzene. A 100-gallon volume of fuel-contaminate d karst aquifer water was pumped into a container. NaCl (1.25 kilograms) and 33 percent H 2 O 2 (4 liters) were mixed into the wa ter and injected back into the bedrock aquifer. The NaCl, dissolved oxygen, benzene and toluene concentrations were monitored for sev eral weeks. Results show that benzene and toluene co ncentrations declined appr oximately 10 times faster than the NaCl concentrations, indi cating enhanced biodegradation. The RTD was calculated by using the declining NaCl-concentration curve through time. The biodegradation rate was derived from the benzene and toluene data. The RTDbiodegradation formula (described in this paper) was used to predict and quan tify the enhanced biodegradation of benzene and toluen e in the karst aquifer. The RTD-biodegradation for mula predicted benzene and toluene co ncentrations in the well through tim e to within 1 microgram per liter ( g/L) of the actual concentration. This close agreement between the RTD-biodegradation model predic tion and the measured concentration c onfirms that this method can be used to quantify enhanced biodegra dation in a single karst injection well. INTRODUCTION Karst aquifers have been recognized as one of the most challeng ing geologic media in terms of ground-water modeling (Wolfe and others, 1997; White, 2002). Ground-water flow in karst aquifers is complex because of va riability in conduit size, shape, and direction (Field, 1993). Numerical mod els based on Darcys Law often are unable to accu rately characterize contaminant flow through the heterogeneous fractures and dissolution features. To successfully model ground-water flow in karst, a numerical model must provide an accurate mathe matical representation of th e physical karst aquifer system. The non-ideal, co mplex flow in karst aqui fers presents greater challenges for modeling bio degradation processes w ith partial differential equations for flow and transport. Chemical engi neers commonly use a resi dence-time distribution (RTD) formula to describe non-ideal flow through a reactor. This study adapted and used RTD to describe migration of a conservative tracer through a section of a karst aquifer in south-central Ken tucky. The RTD formula was modified to incorpo rate a biodegradation rate for predicting the removal of benzene and toluene. The objective of this study was to develop and adap t the RTD-biodegradation formula for predicting and quantifying biodegrada tion in a single well inject ed with hydrogen perox ide. This numerical approach was tested in a field study where hydrogen peroxide (H 2 O 2 ) was injected into a bedrock well to enhance aerobic biodegrada tion of jet fuel in the karst aquifer.

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175 DERIVATION OF THE RTD-BIODEGRADATION FORMULA Obtaining RTD for a Karst, Single-Well, Injection System The degree of mixing within a non-ideal flow karst system can be characterized by the residence time distribution function, E(t) Experimentally, the RTD function can be calculated using a quantitative tracer study. At an initial time of zero, t = 0, a known mass of conservative tracer ( M 0 ) dissolved in a known volume is injected into the karst system. The concentration of the conservative tracer, C is then measured in the well as a function of time ( t ). When the change in time, t is so small, the C(t) is essentially constant. Therefore, the amount of the tracer ( M) flowing between t and t+ t can be expressed as: MCt u t = (1) where the term C(t) represents the concentration of the tracer at some time (t) and the term u represents the flow rate of the system, which is constant. The fraction of the tracer in the non-ideal flow system between t and t + t can be mathematically described by as: dM M0------uCt M0------------t = (2) Based on this mass bala nce for the continuousinput tracer study, the RTD function, (E(t)) can be described as: Et d dt ---Ct C0---------= (3) The ratio of Ct C0---------is the water discharging from the system that has spent le ss than the mean theoret ical time in the flow. The first two moments of E(t) can be defined as the mean residence time and vari ance of the distribution. The mean residence time ( t m ) for the non-ideal flow system can be calculated using the equation: tmt d dt ---Ct C0 ---------t = (4) The variance ( 2 ) is defined as: 2t2* d dt ---Ct C0 ---------ttm 2 = (5) The E(t) t m and 2 for a single-well injection sys tem can be obtained by nume rical differentiation of the conservative tracer data. Obtaining Peclet Number for a Non-Ideal Flow System In describing a non-ideal flow system, the con vective and dispersive nature of the flow is often considered. The Peclet number ( P e ) characterizes the degree of flow diffusi vity compared to the advective transport. This dimensionless parameter quantitatively characterizes the transport diffusion and is inversely related to the dispersion value, d for a non-ideal flow system. Pe1/d = (6) It can be shown that the moments from the E(t) mean residence time and variance obtained from equations 7 and 8 below are related to the Peclet number ( P e ) as follows: tm1 2 Pe----+ = (7) and 22----2 Pe----8 Pe 2------+ = (8) The connection between Peclet number, E(t) mean residence time and variance is accomplished by treating (space-time) in the above equations as an unknown and first calculating P e based on the experimental RTD and then calculating for ( = V/u) (Bischoff and Levenspiel, 1962).

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176 Adaptation of the RTD-Biodegradation Model for a Single-Well Injection The fate of organic contaminants in a karst aquifer system also depe nds on their susceptibility to biodegradation. As a resu lt, the application of the RTD alone is not sufficient to numerically predict the fate of contaminants in a karst aquifer. The karstcontaminant model developed here uses RTD cou pled to a biodegradation rate reaction. The chemical kinetics of biodegradation are assumed to be represented by a rate equation such as: dCAdt --------kCACB= (9) Equation 9 describes a changing concentration of contaminant A ( dC A ) through time ( dt ) as a func tion of the biodegradation rate ( k ), the concentration of contaminant A in solution ( C A ), and bacteria and electron-acceptors, ( C B ). Since the rate is dependant upon two variables, the rate equation can be expressed as a second-order reaction. If the bacteria and electron acceptors, howe ver, are assumed to be present at a relatively steady state, then ( C B ) can be considered constant whil e the contaminant concen tration ( C A ) continually changes. In such conditions, C B is treated as a constant and the second-order equation is re-written as a pseudo first-order equa tion: dCAdt --------kCACBk CA = (10) where k = kC B becomes a pseudo first-order rate constant, which can be obtained by fitting the experimental and field data. The RTD function and biodegradation function can be coupled to develop the RTD-biodegradation function capable of quantifying biodegradable con taminants at a given time, C(t) This function can be mathematically expressed as: Ct C04*a* e1/2*1/Pe 1 a + 2*ea /2*1/ Pe 1 a a 2*1/ Pe ------------------------------------------------------------------------------------------------------------= (11) where a 1 k t 1/ Pe + = and C 0 = initial con taminant concentration. This RTD-biodegradation equation was used to pre dict and quantify benzene and toluene removal in a single karst well. This a pproach accounts for the non-ideal flow, axial dispersion, and biodegradation in the karst aquifer direc tly surrounding the injec tion well. The following section describes the results of applying this formula in a field study. METHODS AND MATERIALS A jet-fuel-contaminated karst site in south-cen tral Kentucky was selected because of the availabil ity of site history and previous research (Byl and others, 2002). An unknown quantity of fuel released over a 60-year period has slowly migrated down from the regolith into the bedrock aquifer. The geol ogy at this site consists of approximately 25 meters of regolith composed of chert (fused silica), clay, silt, sand, and gravel. Underl ying the regolith is 3 to 10 meters of epikarst (weathered bedrock embedded with clay). Below the epik arst is limestone bedrock that has water-filled conduit openings ranging from millimeters to 2 meters thick. A contaminated well was screened in the inter val from 38.4 to 41.5 me ters below ground surface; the top of bedrock is at 38.7 meters below ground surface. A jet pump equipped with a clean Teflon hose was lowered to a known conduit based on geo physical information (Gregg Hileman, U.S. Geolog ical Survey, oral commun., 2005). A no-purge method (Puls and Paul, 1995) was used to pump water at a low, constant rate of 2.6 liters per minute. Periodic water-level meas urements verified no decline in head while pu mping occurred, indicating that the water was coming from the aquifer. The water temperature was a steady 14.1 C with a spe cific conductance of 685 microsiemens per centime ter ( S/cm), and a pH of 10.5. A total of 378-liters (100 gallons) of contaminated aquifer water was pumped into containers and titrated to a pH of 6.5 with 0.1 molar HCl; then the treated water was returned to the aquifer system. A week following the pH adjustment, a 378-liter volume of aquifer water was pumped again and treated with 4 liters of 33 per cent H 2 O 2 Sodium chloride (1.25 kg) was also

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177 added for the quantitative tracer analysis. Benzene and toluene concentrations were stable at 6 micrograms per liter ( g/L) and 20 g/L, respec tively, prior to adding the HCl, and the H 2 O 2 and NaCl. Volatile organic compound (VOC) samples were collected from the test well and surrounding wells every few days using passive-diffusion bag (PDB) samplers. The PDB-sampling technique pro vided a 12-hour integrated sample of the well and did not show the temporal variability of grab sam ples. The dissolved oxygen and specific conduc tance were measured using a YSI-600 XLM datasonde that was placed in the well at the level of the conduit opening. Two additional karst wells within 100 yards of the in jection well also were equipped with monitoring devices and were sampled for VOCs. The first-order degradation rates (k') developed from the field data were 0.01357 per hour for tolu ene and 0.072 per hour for benzene biodegradation. The biodegradation rates we re then coupled to the RTD equation that had been modified for a singlewell system. RESULTS AND DISCUSSION A known amount of NaCl was dissolved in 100 gallons of water and injected as a single pulse, displacing an equal vol ume of water surrounding the injection well. A correlation between the NaCl concentration and the specific conductance was established. Thus specific con ductance data provided a mea sure of conservative tracer concentration with respect to time. Specific conductance was measured in the injection well and two nearby monitoring wells (fig. 1). The benzene concentra tion in the injection well is shown in figure 1 to illustrate the rapid decline in benzene as compared to NaCl. Dissolved oxygen levels went from less than 0.1 milligrams per liter (mg/L) to a supersaturated concentration of 55 mg/L as a result of the H 2 O 2 injection (data not shown). The dissolved oxygen declined slowly over a 6-week period. A comparison of the RTD-biodegradation model predictions and measured field concentra tions for toluene and ben zene indicated close agree ment between the two approaches (figs. 2 and 3). The graphs show the percentage of contaminants remaining in the water as calculated by the model and measured in the PDB samplers. The predictions of the RTD-biodegradation model and the measured amount of toluene and benzene removed through biodegradation were within 0.5 g/L at each sam pling point. CONCLUSION The concept that a karst aquifer is analogous to a non-ideal flow reactor was tested, as well as H 2 O 2 enhanced fuel biodegradation. The results indicate that biodegradation was enhanced and the RTD-bio degradation model could be used to describe the pro cess in a single well. This is the first known field application of the RTDbiodegradation model in conjunction with enhanced -fuel bioremediation in a karst aquifer. The numerical approach Post peroxide injection: specific conductance & benzene concentration y = -3.2141Ln(x) + 17.751 R2 = 0.9566 y = -0.2626Ln(x) + 3.2555 R2 = 0.9108 0 0.5 1 1.5 2 2.5 3 3.5 4 0100200300400500Time, in hoursSpecific conductance, in microsiemens per centimeter0 2 4 6 8 10 12 14 16 18 20Benzene concentration, in microgram ( g) per liter MCI-1 test well MCI-4 reference well MCI-3 reference well MCI-1 g/L benzene Log. (MCI-1 g/L benzene) Log. (MCI-1 test well) Figure 1. Specific conductance measured as a function of time in three karst bedrock wells. The benzene concentration is shown also with concentrations indicated on the second y-axis.

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178 13.68% 8.89% 28.57% Calculated Measured % Percent error Toluene Percentage 0 0.2 0.4 0.6 0.8 1.0 1.2 0 50 100 150 200 250 Time, in hours Toluene, in percent Benzene Percentage 0 0.2 0.4 0.6 0.8 1.0 1.2 0 50 100 150 200 250 Time, in hours Benzene, in percent 7.767 % 0.00 % % Percent error Calculated Measured 0.560 % Figure 2. The RTD-biodegradation model prediction compared to the measured field toluene concentrations. The graph shows close agreement between the model calculation and measured concentration. Figure 3. The RTD-biodegradation model prediction compared to the measured field benzene con-centrations. Close agreement is indicated between the two approaches. mathematically accounts for advection, dispersion, and biodegradation of a contaminant in a non-ideal flow system. These findings are important because they extend the potential for enhanced bioremediation to karst sites. This approach provides a method to predict and quantify biodegradation in a karst aquifer possibly providing new remediation strate-gies for gies for karst aquifers.

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179 REFERENCES Bischoff, K.B., and Levenspiel, Octave, 1962, Fluid dis persion-generalization and comparison of mathemati cal modelsI. generalization of models: Chemical Engineering Science 17 p. 245-255. Byl, T.D., Hileman, G.E., Williams, S.D., Metge, D.W., and Harvey, R.W., 2002, Microbial strategies for deg radation of organic contaminants in karst, in Aiken, G.R., and Kuniansky, E.L. (eds.), U.S. Geological Survey Artificial Recharge Workshop Proceedings, Sacramento, California, April 2-4, 2002: U.S. Geolog ical Survey Open-File Report 2002-89, p. 61-62, accessed January 27, 2005 at http://water.usgs.gov/ ogw/pubs/ofr0289/ Field, M.S., 1993, Karst hydrology and chemical contam ination. Journal of Environm ental Systems v. 22, no. 1, p. 126. Puls, R.W., and Paul, C.J., 1995, Low-flow purging and sampling of ground water monitoring well with dedi cated systems: Ground Water Monitoring & Remedia tion v. 1, no. 15, p. 116-123. White, W.B., 2002, Karst hydrology: recent develop ments and open questions. Engineering Geology v. 65, p. 855. Wolfe, W.J., Haugh, C.J., Webbers, A., and Deihl, T.H., 1997, Preliminary conceptu al models of the occur rence, fate, and transport of chlorinated solvents in karst aquifers of Tennessee: U.S. Geological Survey Water-Resources Investigat ions Report 97-4097, 80 p.



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188 Desorption Isotherms for Tolu ene and Karstic Materials and Implications for Transp ort in Karst Aquifers Mario Beddingfield 1 Khalid Ahmed 1 Roger Painter 1 and Tom D. Byl 2, 1 1 Dept. of Civil and Environmental Engineering, Tennessee State University, Nashville, TN 2 U.S. Geological Survey, Nashville, TN ABSTRACT Karst aquifers dominated by conduit flow are extrem ely vulnerable to fuel contamination such as from leaky underground storage tanks or spills. Direct flow paths through fractures and sinkholes often allow contaminants to move rapidly into the conduit system. Not much is know n about how the fuel will interact with the carbonate rock in the condu it system. The objective of this resea rch was to bridge this information gap by measuring sorption and desorption of fuels to kars t materials. The first phase of this study involved the dissolution and desorptio n processes. Initial experiments (n=5) us ed karst bedrock fra gments of known size soaked in toluene for 24 hours. Then the sterile toluene-soaked ro cks were placed in sterile distilled water. The concentration of toluene dissolved in the water was measured over increasing time periods. These data were used to derive a first-order expone ntial rate of desorption [C w (t)=C i e kt ]. The empirical value for k was 0.8958. The toluene concentration in the water reached a maximum carrying capacity in approximately 3 weeks. The second phase of this pr oject involved sorption st udies using limestone frag ments of known size and water contai ning a known concentration of dissolved toluene. The empirical value for the sorption k was 1.006. These resu lts show that sorption is faster th an desorption and ha ve implications for designing a model that predicts the fate and transport of fuel s in karst aquifers. This work was supported in part by the U.S. Ar my Corps of Engineers DACW62-00-H-0001 contract.

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189 A Computer Program that Uses Resi dence-Time Distribution and FirstOrder Biodegradation to Predic t BTEX Fate in Karst Aquifers Ryan Fitzwater 1 Roger Painter 1 Valetta Watson 1 and Tom D. Byl 2, 1 1 Dept of Civil and Environmen tal Engineering, Tennessee St ate University Nashville, TN; 2 U. S. Geological Surv ey, Nashville, TN 37211 ABSTRACT Approximately 40 percent of the United States east of the Mississippi River is underlain by karst aqui fers. Karst ground-water systems are extremely vulnerable to contaminatio n; however, the fate and transport of contaminants in karst areas are poorly understood because of the complex hydraulic characteristics of karst aquifers. Ground-water models developed using Darcys Law coupled to rates of biodegradation are useful for predicting the fate of fuel s in unconsolidated aquifers, but have little utility in karst conduits. Con ceptual models developed for karst aquifers have a co nsistent theme of non-ideal flow, storage, and active flow components. This research used a residence-tim e distribution (RTD) model approach that integrated residence times of contaminants isolated in storage ar eas with the residence time of contaminants moving through conduits coupled to a pseudo-first order rate of biodegradation. The microcosms consisted of four 1-liter chambers connected with small glass tubing. A pe ristaltic pump provided a consistent flow of karst water from a 10-gallon reservoir. Firs t, a quantitative dye study was do ne to establish the residence-time distribution of the three systems. This was followed by a sterile toluene run to measure sorption of toluene to the microcosm systems. The third microcosm run in corporated karst bacteria and toluene. The removal of toluene predicted by the RTD-bi odegradation model and the experiment were within 2 percent agreement (n=3). The RTD-biodegradation model was transforme d into a user-friendly program that utilizes MS Excel with Visual Basic interfaces. The input sheet of this prototype program requires site information, a biodegradation rate, and the results of a quantitative tracer study. The resu lts, or output pages, provide res idence-time distribution graphs and various statistical calculations. The output pa ges also report the calcu lated amount of BTEX removed during transport through the ka rst aquifer based on RTD and biodegradation. Additional wo rk is needed to incorpor ate dilution into the model. This work was supported in part by the U.S. Ar my Corps of Engineers DACW62-00-H-0001 contract.

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190 Lactate Induction of AmmoniaOxidizing Bacteria and PCE Cometabolism LyTreese Hampton P.D. Hays 1 Roneisha Graham 1 and Tom D. Byl 2, 1 1 Dept. of Civil and Environment al Engineering, Tennessee St ate University, Nashville, TN 2 U.S. Geological Survey, Nashville, TN ABSTRACT Water containing bacteria was collected from a PCEcontaminated karst aquifer in north-central Ten nessee to establish liquid, 1liter microcosms. The microcosms were sp iked with known co ncentrations of perchloroethylene (PCE) and 11 differe nt formulations of lactic acid The ammonia-lactate formulation caused a rapid removal of PCE and oxygen (O 2 ). Similar results that were achieved by using a second set of microcosms spiked with ammonia-lactate to re-test the remova l rate of PCE and O 2 indicated a possible cometabolic PCE-removal pr ocess. Although only one report of PCE-cometabolism was found in the liter ature, ammonia-oxidizing bacteria in digenous to the karst aquifer were hypothesized to be capable of come tabolizing PCE with the ammonia mono -oxygenase (AMO) pathway. To test this hypothesis, microcosms were established using different fo rms of ammonia (ammonia-lactate, ammonia-chloride, ammonium plus sodium lactate), reference controls (sterile, live withou t food, sodium lactate, ster ile + ammonia lactate), and ammonia mono-oxygenase inhibitors [2-chloro-6-(tri chloromethyl) pyridine, azide, and allylthiourea]. Microcosms treated with ammonia-lactate ha d the most rapid reduction of PCE and O 2 followed by the ammonium + sodium-lactate treatment. The other live microcosms treated with ammonia also experienced significant drops in PCE and O 2 after 24 hours. The control (sterile and live without food) microcosms did not experience a significant drop in PCE in the same time period. After 24 hours, the rapid PCE removal in all the ammonia-treated microcosms decreased due to the consumption of the ox ygen. Tests with the AMO inhibitor in the presence of ammonia-lact ate did not prevent the PCE removal or O 2 consumption. Lactate may stimulate AMO or protect the enzyme from inhibitio n. Additional tests need to be conducted to prove that AMO is responsible for the removal of PCE. Th ese preliminary results provide strong evidence that karst bacteria indigenous to th is aquifer can cometabolize PCE.

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191 Biodegradation of Toluene as It Continuously Enters a 5-Liter Laboratory Karst System Fuzail Faridi 1 Roger Painter 1 and Tom Byl 2,1 1 Dept. of Civil and Environmental Engineering, Tennessee State University, Nashville, TN 2 U.S. Geological Survey, Nashville, TN ABSTRACT Contamination releases can occur as slow, long-term spills rather than as instantaneous spills. These continuous releases can result in a stea dy state of contaminants that can l ast months to years. Predicting the fate and transport of these contamin ants in a karst aquifer is especially challenging because of the complex hydrogeology and uncertainties in residence time. The objective of this research was to adapt the residencetime distribution (RTD) biodegradation model, which w as developed to predict th e biotransformation of a single spill in a karst aquifer, for a continuous input of contaminants. Theoretically, the RTD for a karst system calculated from either a pulseor a continuous-input tracer study would be identical, but mathemat ical manipulation of the data for the two approaches is quite different. Determination of the RTD from a continuous input requires numerical differentiation of tracer response data as oppo sed to numerical integra tion for the pulse approach. Three experimental runs were conducted involving th e application of a contin uous input: (1) rhodamine dye alone to establish RTDs for the systems, (2) sterile toluene (25 micrograms per liter) to quantify abiotic sorption, and (3) toluene with karst bacteria to quantify biodegradation. The three replicate karst systems were each 5 liters and had a continuous flow rate of 3.3 milliliters per minute. The difference between the RTD-base d model prediction and the experimental toluene conversions was 17 percent. The continuous-input approach (numeri cal differentiation) had the tendency to magnify experi mental and random errors in the tracer response data as compared to the pulse-in put method (numerical inte gration). This work was supported in part by the U.S. Ar my Corps of Engineers DACW62-00-H-0001 contract.

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192 Bacteria Induced Dissolution of Li mestone in Fuel-Contaminated Karst Wells Serge Mondesir 1 and Tom D. Byl 2,1 1 Dept. of Civil & Environmental Engineering, Tenne ssee State University Nashville, TN 37209 2 U.S. Geological Survey, Nashville, TN 37211 ABSTRACT Karst landscapes are formed in water-soluble geolog ic formations, such as limestone, in which disso lution processes have enlarged wate r-transmitting openings. Approximately 20 percent of the United States is underlain by carbonate rocks and is classified as kars t, and 40 percent of the United States east of the Mis sissippi River is underlain by karst aquifers. Karst ground-water systems are extremely vulnerable to con tamination. Many organic contaminants such as fu els can stimulate bacteria biodegradation and the production of carbon dioxide (CO 2 ). The increased respiration by bacter ia in contaminated karsts aquifers can lead to a significant increase in CO 2 production and formation of carbonic acid. A quantitative study was conduc ted to determine the effe ct of elevated concentr ations of carbonic acid due to bacteria action on limestone dissolution. Sealed flasks were set up that contained 250 milliliters of distilled water, limestone fragmen ts of known size and weight, a nd varying concentrations of CO 2 The flasks with elevated CO 2 concentration had a 3-fold increase in the rate of calc ium carbonate dissolution. Water with elevated CO 2 concentrations had a slightly lowe r pH than water with the lower CO 2 concentra tions, but the difference in pH was not statistically significant at the 0.05 confidence level. Further tests were done to determine if these la b results applied to field conditions. Water samples were collected from wells completed in karst aquifers. The CO 2 concentrations in water samp les collected from fuel-contami nated wells were higher than in samples collected from wells with no fuel contam ination. Also, the dis solved calcium was usually two or three times greate r in the fuel-contaminated wells. The results have implications for redesigning geochemi cal models that predict conduit en largement when fuel contaminants are present in karst aquifers. This work was supported in part by the U.S. Ar my Corps of Engineers DACW62-00-H-0001 contract.

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193 INTRODUCTION TO THREE FIELD TRIP GUIDES: Karst Features in the Black Hills, Wyoming and South DakotaPrepared for the Karst Interest Group Workshop, September 2005 By Jack B. Epstein 1 and Larry D. Putnam 2 1 U.S. Geological Survey, National Center, MS 926A, Reston, VA 20192 2 Hydrologist, U.S. Geological Survey, 1608 Mountain View Road, Rapid City, SD 57702. This years Karst Interest Group (KIG) field trips will de monstrate the varieties of karst to be seen in the semi-arid Black Hills of South Dakota and Wyoming, and will offer comparisons to karst seen in the two previous KIG trips in Florida (Tihansky and Knoche nmus, 2001) and Virginia (Orndorff and Harlow, 2002) in the more humid eastern United States. The Black Hills comprise an irregul arly shaped uplift, elongated in a northwest direction, and about 130 miles long and 60 miles wide (figure 1). Erosion, following tectonic uplift in the late Cretaceous, has exposed a core of Precambrian metamo rphic and igneous rocks which are in turn rimmed by a series of sed iments of Paleozoic and Me sozoic age which generally dip away from the center of the uplift. The homocli nal dips are locally interrupt ed by monoclines, structural terraces, low-amplitude folds, faults, and igneous intrusions. These rocks are overlapped by Tertiary and Quaternary sediments and have been intruded by scattered Tertiary igneous rocks. The depositional environments of the Paleozoic an d Mesozoic sedimen tary rocks ranged from shallow marine to near shore-terrestrial. Study of the various sandstones, shales, siltstones, dolomites and limestones indicate that these rocks were deposited in shallow marine environ ments, tidal flats, sand dunes, carbo nate platforms, and by rivers. More than 300 ft (91 m) of gypsum and anhydrite were deposited at vari ous times in evaporite basins. Erosion of these uplifted rocks produced the landscape we see today. Rocks of the Pahasapa Limestone (Madison of some reports), Minnel usa Formation and older sediments fo rm a limestone plateau that rims the central Precambrian metamorphic co re. Erosion of weak red siltstone s and shales of the Spearfish For mation has formed the "Red Valley, the main area of present and proposed future housing and industrial development. White gypsum caps many of the hills in the Spearfish and is a co nspicuous landform in the overlying Gypsum Spring Formation. Resistant sands tones that are interbedded with other rocks lie out board from the Red Valley and form the hogback that en circles the Black Hills and defines its outer physi ographic perimeter. Relatively soluble rocks, includin g dolomite, limestone, gypsum and anhydrite, comprise about 35 per cent of the total stratigraphic sectio n within the topographic Black Hills, that is, the ar ea including and within the Dakota sandstone hogback (fig. 1), comprising rocks of the Inyan Kara Group (fig. 2). Karst is significant in many formations in the limestone plateau and Red Valley (fig. 2). World-class caves, sink ing streams, and other features are found in the Pahasap a Limestone. Lesser karst features are found in the other carbonate units. Evaporite karst has developed ex tensively in the anhydrite and gypsum in the Min nelusa, Spearfish, and Gypsum Spring Formations. So lution of soluble evaporate and carbonate rocks at depth has produced collapse in non-soluble bedrock an d surficial deposits at the surface, which in several places extends many hundreds of feet above the soluble rocks.

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194 Figure 1. Generalized diagram showing the geology and geomo rphology of the Black Hills and route of three 2005 Karst Interest Group field trips (southern trip, regular numbers ; Northern trip, italics; western trip, numbers underlined). Most of the urban development and karst features are in t he Red Valley, underlain by Triassic red beds and in the lime

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195Figure 2. Generalized stratigraphic section showing known karst features in sedimentary rocks in the Black Hills, South Dakota-Wyoming. Numbers indicate formations visited during the formal conference. Underlined num bers indicate stops in the supplementary western field trip.

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196 stone plateau, underlain by a variety of Pennsylvanian and Permian rocks. Modified from Strahler and Strahler (1987) with perm ission. Figure 2. Generalized stratigraph ic section showing known karst features in sedime ntary rocks in the Black H ills, South Dakota-Wyoming. Numbers indicate formations visited during the formal conference. Underlined numbers indicate stops in the supplementary western field trip -co ntinued.

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197 Two major aquifers are located in formations that include karstic rocks water in the Black Hills-c-rbonate karst in the Pahasapa Limestone, and evapor ite karst in the Minnelusa formation. The Madison and Minnelusa aquifers are two of th e most important aquifers in the Black Hills area and are used exten sively for water supplies. Headwater springs originating in the limestone plateau, streamflow losses to the Madison and Minnelusa outcrops, and large artesian sp rings in the Red Valley are important hydrologic fea tures that are associated with kars t processes in these aquifers. Locally secondary porosity has developed in the lower Spearfish formation due to gypsum dissolution. Sinkhole collapse in gypsum-b earing rocks is common. Sinkholes, of the types common in the eastern United States ar e rare. Solution in carbonate rocks has produced the third and sixth largest known recreation caves in the world, Jewel Cave and Wind Cave. A sinkhole in Hot Springs is one of the worlds great est vertebrate paleontologi c occurrences. Finally, car bonate rocks are the major aggregate resource in the Black Hills. Three field trips are offered this year. They are no t duplicative; each stop has something different to offer, demonstrating th e wide variety of evaporite and carbonate ka rst in the Black Hills The trip in the Southern Black Hills will examine evaporite karst in th e Minnelusa Formation, arte sian springs due to both carbonate and evaporite dissolution at depth, sinkhole s and fracturing in the Minnekahta raising the question of the definition of karst, a large si nkhole that trapped Pleistocene anim als, and a visit to Wind Cave. The northern trip will discuss dye tracing in carbonate rocks, hydrology in Spearfish Canyon that made the famous Black Hills gold mining possible, a variety of collapse features and gypsum intrusion in the lower Spearfish Formation creating a strong secondary porosity, effects of leaching in the Minnekahta, and a pro posed sewage lagoon in a precarious area of evaporite ka rst. A third trip to the western Black Hills is offered for those wishing to do it on their own. Highlights are an overlook of the steeply dipping rocks in flatirons in a major monocline, a sinkhole in non-so luble rocks extending more than 800 feet down to the source of collapse, the most spectacul ar cliff exposure of caves, sinkho les, brecciation, and disrupted bed ding in the Minnelusa formation, an d a trip to Jewel Cave. Two guided evening trips are also planned to Jewel and Wind Caves. Each field trip guide not only h as detailed information for driving in structions and text for each stop, but also, provides comments about sites to see from the ve hicle window and the text of historic markers and plaques along the way. The total m iles and miles between driving direc tions, comments, markers, and stops have been noted on each field trip guide. Parts of the field guide itineraries were borrowed freely from many excellent published guides to the Black Hills (Fahrenbach and Fox, 19 96; Gries, 1996; Lisenbee and othe rs, 1996; Martin and others, 1996; Rahn and others, 1977; Rahn and Davi s, 1996; Redden and Fahrenbach, 1 996). Additional sources of infor mation about the Black Hills or engineering geology are found in Darton (1909) and Rahn (1986). References Darton, N.H., 1909, Geology and water resources of the northern portion of the Black Hills and adjoining regions in South Dakota and Wyoming: U.S. Geologi cal Survey Professional Paper 65, 105 p. Fahrenbach, M.D., and Fox, J.F., 1996, Paleozoic Stratig raphy of the Northern Black Hills, South Dakota: Road Log, Field Trip 10, in Paterson, C.J. and Kirchner, J.G., eds., Guidebook to the Geology of the Black Hills, South Dakota: South Dakota School of Mines and technology, Bulletin No. 19, p. 90-107. Gries, J.P., 1996, Roadside Geology of South Dakota: Mountain Press Publishing Co., Missoula, Montana, 358 p. Lisenbee, A.L., Kirchner, J.G., and Paterson, C.J., 1996, Tertiary Igneous Intrusions and Related Gold Mineral ization, Northern Black Hills, South Dakota: Road Log, Field Trip 11, in Paterson, C.J. and Kirchner, J.G., eds., Guidebook to the Geology of the Black

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198 Hills, South Dakota: South Dakota School of Mines and technology, Bulletin No. 19, p. 108-128. Martin, J.E., Bell, G.L., Jr., Schumacher, B.A., and Fos ter, J.F., 1996, Geology and Paleontology of Late Cre taceous Deposits of the Southern Black Hills region: Road Log, Field trip 8: in Paterson, C.J. and Kirchner, J.G., eds., Guidebook to the Geology of the Black Hills, South Dakota: South Dakota School of Mines and technology, Bulletin No. 19, p. 51-77. Orndorff, R. C. and Harlow, G.E., 2002, Field Trip Guide, Hydrogeologic fram ework of the northern Shendoah Valley Carbonate aquifer system, in, Kuniansky, E.L. editor, U.S. Geological Survey Karst Interest Group Proceedings, Shepherdstown, West Vir ginia, August 20-22, 2002: U.S. Geological Survey Water-Resources Investig ations Report 02-4174, p. 81-89. Rahn., P.H., l986, Engineering Geology, an Environmen tal Approach: Prentice-Hall Upper Saddle River, NJ, 586 p. Rahn, P.H., Bump, V.L., an d Steece, F.W., 1977, Engi neering Geology of Central and Northern Black Hills, South Dakota: South Dakota School of Mines and Technology, Rapid City, S.D., 34 p. Rahn, P.H., and Davis, A.D. 1996, Engineering Geology of the Central and Northern Black Hills: Road Log, Field Trip 10, in Paterson, C.J. a nd Kirchner, J.G., eds., Guidebook to the Geology of the Black Hills, South Dakota: South Dakota School of Mines and tech nology, Bulletin No. 19, p. 38-50. Redden, J.A. and Fahrenbach, M.D., 1996, Major uncon formities of the Black Hills: Road Log, Field Trip 4, in Paterson, C.J. and Kirchner, J.G., eds., Guidebook to the Geology of the Black Hills, South Dakota: South Dakota School of Mines and technology, Bulletin No. 19, p. 30-35. Strahler, A.N., and Strahler, A.H., 1987, Modern Physical Geography: New York, John Wiley & Sons, 544 p. Tihansky, A.B. and Knochenmus, L.A., 2001, Karst fea tures and hydrogeology in west-central Florida-AField perspective, in, Kuniansky, E.L. editor, U.S. Geologi cal Survey Karst Interest Group Proceedings, St. Petersburg, Florida, Februa ry 13-16, 2001: U.S. Geo logical Survey Water-Resour ces Investigations Report 01-4011, pp 198-211.


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