Groundwater Quality of Springs and Wells of the Sinkhole Plain in Southwestern Illinois: Determination of the Dominant Sources of Nitrate

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Groundwater Quality of Springs and Wells of the Sinkhole Plain in Southwestern Illinois: Determination of the Dominant Sources of Nitrate

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Groundwater Quality of Springs and Wells of the Sinkhole Plain in Southwestern Illinois: Determination of the Dominant Sources of Nitrate
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Circular 570 2007
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K.C. Hackley, S.V. Panno, H.-H. Hwang, and W.R. Kelly Circular 570 2007 Illinois Department of Natural Resources ILLINOIS STATE GEOLOGICAL SURVEY William W. Shilts, Chief 615 E. Peabody Drive Champaign, Illinois 61820-6964 217-333-4747 www.isgs.uiuc.edu Abstract About half the residents living in the area of southwestern Illinois known as the sinkhole plain obtain their potable water from the region's shallow karst aquifer. Previous work has shown that the groundwater from approximately 18% of the wells in the sinkhole plain has nitrate concentrations in excess of the U.S. Environmental Protection Agency's drinking water standard of 10 mg of N/L of water. The nitrate concentrations in water samples collected from approximately 50% of the wells and from all of the springs in the sinkhole plain area are greater than background concentrations, suggesting that sources other than naturally occurring organic matter in soil have contributed additional nitrate to groundwater in the shallow karst aquifer. This investigation characterized the geochemistry of the groundwater to determine which source of nitrogen in the sinkhole plain is the major contributor to the anomalous concentration of nitrate observed in the shallow karst aquifer. Considering the dominance of agriculture and the expansion of urban development in the study area, sources of excessive nitrate and groundwater contamination include agrichemical, livestock, and sewage waste. Water samples from 10 karst springs and 17 wells were collected during different seasons and analyzed for chemical, isotopic, and bacterial characteristics. The samples from each spring were a representative composite of the shallow water recharging the associated watershed. Samples from the wells reflect individual points within the watersheds and were more susceptible to influ- ence from local environments, including anthropogenic activities. Chemical characteristics and the isotopic composition of some of the dissolved constituents varied seasonally in the samples of spring water, attesting to the rapid infiltration of surface and soil water into the karst aquifer. Bacteria concentrations in the springs and most of the wells were greater than those allowed by county and state regulations for drinking water. Nitrate concentrations in the springs covered a fairly narrow range, from 1.7 to 7.5 mg of N/L. In the wells, nitrate concentrations varied greatly, ranging from less than the detection limit (0.2 mg of N/L) to 81 mg of N/L. The isotopic data for the dissolved nitrate (NO 3 -) from the springs and wells were useful in distinguishing NO 3​ -sources. The nitrogen and oxygen isotope composition of the NO 3​ -ranged from 2.2 to 25.9 per mil (%) and 5.1 and 21.9% respectively. These isotopic results suggest that the nitrate sources in spring water were dominated by fertilizer nitrogen and soil organic nitrogen that mixed with nitrate having en enriched 18O signature. The isotopic results for the wells indicate that the largest NO 3 -concentrations (between 13 and 80 mg of N/L) originated primarily from septic and livestock wastes. The isotopic results for most of the wells with NO 3 -concentrations between 2 and 12 mg of N/L indicate that nitrogen fertilizer was the dominant NO 3 -source. The combined chemical, bacterial, and isotopic analyses of springs and individual wells provided independent evidence concerning the major susceptibility of the karst aquifer to surface contamination and helped to differentiate the sources of NO 3 -in the groundwater. Although many livestock facilities and septic systems were present in individual watersheds, the typical isotopic character- istics of NO - originating from such point sources were overwhelmed by the constant input of nonpoint source nitrogen for the composite samples of spring water. However, results from groundwater samples from several residential wells did show the impact of point sources in NO 3 -contamination on a local scale.
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Groundwater Quality of Springs and Wells of the Sinkhole Plain in Southwestern Illinois: Determination of the Dominant Sources of Nitrate K.C. Hackley, S.V. Panno, H.-H. Hwang, and W.R. Kelly Circular 570 2007 State of Illinois Rod R. Blagojevich, Governor Illinois Department of Natural Resources Illinois State Geological Survey Soil Org Septic/manure Mineraliz ed fe r tiliz erNW -17 Septic HW -3 HW -3 HW -1 AM-6 AM-5 Solution-28-NO3Solution-28-NH4 and Urea Synthetic fe r tiliz er NO3 NW -5 NW -13 NW -21 NW -28 03.0 3.16.0 6.19.0 9.112.0 12.115.0 15.118.0 18.121.0 >21 septic and liv estock w aste To ta l N (m g/ L) 0 5 10 15 20 25 30 35 15N ()0 5 10 15 20 25 18O ()

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Equal opportunity to participate in programs of the Illinois Department of Natural Resources (IDNR) and those funded by the U.S. Fish and Wildlife Service and other agencies is available to all individuals regardless of race, sex, national origin, disability, age, religion, or other non-merit factors. If you believe you have been discriminated against, contact the funding sources civil rights office and/or the Equal Employment Opportunity Officer, IDNR, One Natural Resources Way, Springfield, Illinois 62701-1271; 217-785-0067; TTY 217-782-9175. This information may be provided in an alternative format if required. Contact the IDNR Clearinghouse at 217-782-7498 for assistance. Front Cover: Keith Hackley is shown here collecting a water sample from Falling Springs near Dupo, Illinois. The sam pling location is on a ledge several meters below the mouth of Falling Springs cave and about 20 m above the base of the bluff. ( Photograph by S.V. Panno.) The inset gure is of the nitrogen and oxygen isostope composition of NO 3 of well water and end-member samples. Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Gov ernment. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed or represents that its use would not infringe privately owned rights. Reference herein to a specic commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reect those of the United States Government, any agency thereof, or those of Kinder-Morgan, Inc. or Peoples Energy Corporation. Released by the authority of the State of Illinois 11/07

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Circular 570 2007 Illinois Department of Natural Resources ILLINOIS STATE GEOLOGICAL SURVEY William W. Shilts, Chief 615 E. Peabody Drive Champaign, Illinois 61820-6964 217-333-4747 www.isgs.uiuc.edu Groundwater Quality of Springs and Wells of the Sinkhole Plain in Southwestern Illinois: Determination of the Dominant Sources of Nitrate K.C. Hackley, S.V. Panno, H.-H. Hwang, and W.R. Kelly

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Contents Abstract 1 Introduction 1 Study Area Description 3 Geology and Basin Hydrology 3 Land Use 3 Background 4 Potential Nitrogen Sources 4 Stable Isotopes 5 15 N and 18 O of NO 3 5 D and 18 O of Water 6 13 C in Groundwater 6 34 S in Groundwater 7 Methodology 7 Water Sampling 7 Analytical Techniques 8 Results and Discussion 9 End-Member Samples: Chemical Composition 9 End-Member Samples: Isotopic Composition 10 Spring Samples: Chemical Composition 10 Spring Samples: Bacterial Composition 13 Spring Samples: Isotopic Composition 19 15 N and 18 O of NO 3 19 13 C of DIC 23 D and 18 O of Water 23 34 S of Sulfate 23 Well Samples: Chemical Composition 23 Well Samples: Bacterial Composition 30 Well Samples: Isotopic Composition 30 15 N and 18 O of NO 3 30 13 C of DIC and 3 H of water 31 D and 18 O of Water 32 34 S of Sulfate 32 Summary and Conclusions 34 Acknowledgments 35 References 35

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Tables 1 Spring locations, descriptions of their groundwater basins, and land use within the groundwater basins in the study area 4 2 Isotopic natural abundance of nitrogen, oxygen, carbon, hydrogen, and sulfur in the study area 5 3 Field parameters and total alkalinity of samples analyzed for end-member sources of NO 3 9 4 Chemical composition of samples analyzed for end-member sources of NO 3 10 5 Isotopic data of samples that were analyzed for end-member sources of NO 3 11 6 Field parameters and total alkalinity for water samples collected from springs in the study area 12 7 Chemical results for water samples collected from springs in the study area 14 8 Bacterial analyses for water samples collected from springs in the study area 17 9 Bacteria present in springs in the study area, percentage of time the bacteria were detected in samples, and ranking based on their dominance in the groundwater samples 18 10 Isotopic results by season for water samples collected from springs in the study area 20 11 Field parameters and total alkalinity for water samples from wells in the study area 25 12 Chemical data for water samples from wells in the study area 26 13 Descriptive statistics of NO 3 concentrations for a limited number of water samples from wells from karst and covered karst regions and water samples from caves and springs of the sinkhole plain 28 14 Bacterial analyses for water samples collected from wells in the study area 30 15 Bacteria present in water samples from wells and their ranking relative to their dominance in the groundwater samples 31 16 Isotopic data for water samples from wells in the study area 33 Figures 1 Map of the study area showing karst terrane (sinkhole areas) and the location of springs and wells sampled during this investigation 2 2 Saturation indices for each spring sampled from fall 1998 through winter 2000 15 3 Temperature of each spring sampled for six consecutive seasons 15 4 Chloride and sodium concentrations of all spring samples showing trends and distinct differences among the individual springs 16 5 Seasonal variation of uoride concentrations in spring samples 16 6 Calcium and sulfate concentrations for spring samples and runoff 16

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7 Nitrate concentrations of the spring samples over six consecutive seasons 16 8 Isotopic composition of NO 3 from springs and end-member samples including fertilizers, septic systems, and livestock waste 21 9 Nitrate concentrations versus 15 N values for the springs 22 10 18 O and 15 N of NO 3 from springs showing isotopic values of samples from precipitation collected in the study area 22 11 18 O of NO 3 and 18 O of water samples collected from springs during four seasons in the study area 22 12 13 C of dissolved inorganic carbon in spring water samples from six sampling dates in the study area 22 13 Isotopic composition ( D and 18 O) of the springs in relation to the global meteoric water line and along a trajectory typical of evaporation 24 14 34 S versus SO 4 2 concentration of runoff and spring samples 24 15 Calcite saturation indices for wells sampled in the study area 27 16 Specic conductance of the well water sampled in the study area 27 17 Sodium and chloride concentrations for the well-water samples, including the end-member samples of eld runoff, septic systems, and hog waste 27 18 Nitrate concentrations and well depth 27 19 North-south cross section through many of the wells sampled, showing water table, topography of the bedrock surface, and NO 3 concentrations for the wells of various depths 28 20 Chloride and total inorganic nitrogen concentrations for the well and end-member samples including eld runoff, septic systems, and livestock waste 29 21 Trilinear diagram comparing the distribution of major cations and anions in the springs, wells, and end-member samples 29 22 Bacterial analyses results for total coliforms by depth of wells sampled 31 23 Bacterial analyses results for fecal enterococci by depth of wells sampled 31 24 15 N and 18 O of NO 3 for the wells and end-member samples including fertilizers and septic and livestock waste 32 25 15 N vs. ln[NO 3 N] of groundwater samples showing effects of denitrification and groundwater mixing 33 26 Correlation between 13 C of dissolved inorganic carbon and 3 H for the wells 33 27 Nitrate concentration and 3 H values for wells sampled 34 28 Isotopic composition ( D and 18 O) of groundwater sampled from wells 34

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Illinois State Geological Survey Circular 570 1 Introduction Nitrate (NO 3 ) is among the leading pollutants of rivers, lakes, estuaries, and groundwater (Parry 1998). In drinking water, NO 3 in excess of 10 mg of N/L may be toxic to infants and may be responsible for an increased occurrence of stomach cancer in adults (ORiordan and Bentham 1993). Nearly half of the residents living in the karst regions of St. Clair, Monroe, and Randolph Counties in southwest ern Illinois use the shallow karst aqui fer of Illinois sinkhole plain (Figure 1) as their potable water source. Nitrate concentrations in excess of the U.S. Environmental Protection Agencys (USEPA) 1992 drinking water stan dard of 10 mg of N/L have been found in more than 18% of the wells in the sinkhole plain, even though these are bedrock wells ranging in depth from 20 to over 100 m (Panno et al. 1996). In addition, groundwater samples from 52% of the drilled wells in this area exceed a preliminary threshold concentration of 1.4 mg of N/L (Panno et al. 1996). Subsequent work by these authors yielded a revised threshold concentration of 2.5 mg of N/L for spring water and 2.1 mg of N/L for well water (Panno et al. 2006). Nitrate and other nutrients enter surface streams in the Midwest via drainage tiles, groundwater dis charge, springs, and surface runoff to ultimately discharge into the Mis sissippi River. Recent studies in the vicinity of the Mississippi Delta have suggested that nutrient-rich water from the Mississippi River may con tribute to a 15,500-km 2 hypoxia zone in the Gulf of Mexico, resulting in the death of marine life (Rabalais et al. 1996). The determination of the NO 3 sources in groundwater, then, is an important rst step in the process of improving the groundwater quality within the karst aquifers of Illinois sinkhole plain and perhaps reducing the amount of NO 3 discharging to water bodies downstream. In the southwestern sinkhole plain of Illinois, agriculture is the dominant land use, and the number of private septic systems is increasing because of urban development. The numerous sinkholes and associated macropores in the relatively thin soil overlying the karstied limestone are conducive to Abstract About half the residents living in the area of southwestern Illinois known as the sinkhole plain obtain their potable water from the regions shal low karst aquifer. Previous work has shown that the groundwater from approximately 18% of the wells in the sinkhole plain has nitrate concentra tions in excess of the U.S. Environ mental Protection Agencys drinking water standard of 10 mg of N/L of water. The nitrate concentrations in water samples collected from approxi mately 50% of the wells and from all of the springs in the sinkhole plain area are greater than background concen trations, suggesting that sources other than naturally occurring organic matter in soil have contributed addi tional nitrate to groundwater in the shallow karst aquifer. This investiga tion characterized the geochemistry of the groundwater to determine which source of nitrogen in the sink hole plain is the major contributor to the anomalous concentration of nitrate observed in the shallow karst aquifer. Considering the dominance of agriculture and the expansion of urban development in the study area, sources of excessive nitrate and groundwater contamination include agrichemical, livestock, and sewage waste. Water samples from 10 karst springs and 17 wells were col lected during different seasons and analyzed for chemical, isotopic, and bacterial characteristics. The samples from each spring were a representa tive composite of the shallow water recharging the associated watershed. Samples from the wells reect indi vidual points within the watersheds and were more susceptible to inu ence from local environments, includ ing anthropogenic activities. Chemical characteristics and the isotopic composition of some of the dissolved constituents varied season ally in the samples of spring water, attesting to the rapid inltration of surface and soil water into the karst aquifer. Bacteria concentrations in the springs and most of the wells were greater than those allowed by county and state regulations for drinking water. Nitrate concentrations in the springs covered a fairly narrow range, from 1.7 to 7.5 mg of N/L. In the wells, nitrate concentrations varied greatly, ranging from less than the detection limit (<0.2 mg of N/L) to 81 mg of N/L. The isotopic data for the dissolved nitrate (NO 3 ) from the springs and wells were useful in distinguish ing NO 3 sources. The nitrogen and oxygen isotope composition ( 15 N and 18 O) of the NO 3 ranged from 2.2 to 25.9 per mil () and 5.1 to 21.9, respectively. These isotopic results suggest that the NO 3 sources in spring water were dominated by fertilizer nitrogen and soil organic nitrogen that mixed with NO 3 having an enriched 18 O signature. The isotopic results for the wells indi cate that the largest NO 3 concentra tions (between 13 and 80 mg of N/L) originated primarily from septic and livestock wastes. The isotopic results for most of the wells with NO 3 con centrations between 2 and 12 mg of N/L indicate that nitrogen fertilizer was the dominant NO 3 source. The combined chemical, bacterial, and isotopic analyses of springs and individual wells provided indepen dent evidence concerning the major susceptibility of the karst aquifer to surface contamination and helped to differentiate the sources of NO 3 in the groundwater. Although many livestock facilities and septic systems were present in individual water sheds, the typical isotopic character istics of NO 3 originating from such point sources were overwhelmed by the constant input of nonpoint source nitrogen for the composite samples of spring water. However, results from groundwater samples from several residential wells did show the impact of point sources in NO 3 contamina tion on a local scale.

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2 Circular 570 Illinois State Geological Survey Spr ings W ells Sinkhole areas 0 08 Km 5 Mi NMi ssissi p pi Ri v er Lo w landsMississippiRiverMONR OE CO RANDOLPH CO ST CLAIR CO F alling Sparro w Creek Camp V ande v enter A uctioneer F rog IL Ca ve rn s K elly Collier Sensel 1 16 3 14 11 10 4 5,6,17 7 18 13 12 2 8Indian Hole 9 Figure 1 Map of the study area showing karst terrane (sinkhole areas) and the location of springs and wells sampled during this investigation (modified from Panno et al. 2001).

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Illinois State Geological Survey Circular 570 3 rapid inux of surface and soil water that potentially carries agrichemicals (fertilizers and pesticides), livestock waste, and septic efuent directly into the shallow karst aquifer. This inux has resulted in contamination of the karst aquifer in southwestern Illinois, which feeds springs, streams, and residential wells in the region (Panno et al. 1996). The dominance of agri cultural land use and the strong cor relation of NO 3 and atrazine in spring water following springtime planting (Panno et al. 1996) suggest that agri cultural sources of NO 3 are probably considerable. Land use in the sink hole plain is predominantly row crops and, to a lesser extent, livestock; 86% of the land surface in Monroe County is used for agricultural purposes (Southwestern Illinois Metropolitan and Regulatory Planning Commis sion, unpublished report 1977). The objectives of this investiga tion were (1) to characterize the quality and general geochemistry of the groundwater in the karst aquifer of the sinkhole plain region in southwestern Illinois and (2) to determine the dominant source of anomalously large concentrations of NO 3 in groundwater. The overall quality and geochemical character istics of the karst groundwater were examined using chemical, isotopic, and bacterial analyses. Analyses of nitrogen and oxygen isotopes were used to determine the major sources of NO 3 in groundwater. Analyses of the stable isotopes of the NO 3 ion have been shown to be effective for identifying the dominant sources of NO 3 in groundwater and to deter mine whether denitrication has occurred (Heaton 1986, Mariotti et al. 1988, Bttcher et al. 1990, Wassenaar 1995, Aravena and Robertson 1998, Mengis et al. 1999). Most applications using nitrogen and oxygen isotopes of NO 3 in surface water and associ ated groundwater have been limited to relatively small geographic areas, such as small single watersheds, con tamination plumes, or the edges of a cultivated eld. This present study seasonally sampled springs that were discharge points from 10to 100-km 2 watersheds to obtain samples that represented composite compositions of the groundwater basins. These results were compared with specic well sites distributed throughout the watersheds. This research extends the work by Panno et al. (2001). Study Area Description Geology and Basin Hydrology The study area was located on the western margin of the Illinois Basin known as the Illinois sinkhole plain (Figure 1). Area bedrock consists of Mississippian limestone, sandstone, and shale that lie at or near the sur face and dip gently to the east, toward the center of the Illinois Basin. Much of the area is characterized by karst topography and has approximately 10,000 sinkholes (Panno 1996). Numerous large springs and the lon gest caves in the state are found in this region. The majority of caves and sinkholes occur in the calcite-rich Mississippian age Ste. Genevieve and St. Louis Limestones (Panno et al. 1997a). The upland area (about twothirds of Monroe County) is, for the most part, covered with Illinoian gla cial till and/or residuum overlain by a relatively thick layer of windblown Wisconsin age loess (Piskin and Berg strom 1975). The loess is typically less than 15 m thick but can be 20 m or more thick. The unconsolidated loess is easily eroded, forming steep-sided sinkholes and associated gullies. Data from drillers logs indicate that the water table is closest to the sur face (approximately within 3 to 6 m) beneath the covered karst region and becomes much deeper (approximately 25 to 38 m) in karst topography. The term covered karst refers to areas of the sinkhole plain that are underlain with karstied limestone but contain no sinkholes in the overlying negrained terrane. Where the water table is above the soil-bedrock inter face, as much as 40% of the weight of the sediment may be supported by the buoyant force of water (Crawford et al. 1989). When the water table is lowered, buoyant support is lost, intergranular pressure increases, and water drains from the loess, increas ing stress on the unconsolidated sedi ments (Freeze and Cherry 1979). As a result, sediment spalls and caves into crevices in bedrock, and sinkholes develop (Crawford et al. 1989). Con sequently, water is quickly drained from the surface through sinkholes, solution-enlarged ssures, and cave systems. The springs selected for groundwater sampling are the discharge points of groundwater basins and represent a composite of the groundwater ow ing within each basin (Quinlan 1990). Thus, the inputs from surface sources via sinkholes, macropores, and soil water are averaged across the whole watershed. Wells, however, receive water from small areas of a groundwater basin and are more apt to be inuenced by the local surface envi ronment. Many residents depend on well water as their major potable water source, and the wells in this region have a wide range of NO 3 con centrations. The wells chosen for sampling varied in depth, allow ing comparison of the water quality of shallow and deep groundwater samples. Land Use Agriculture is the dominant land use throughout the study area (Panno et al. 1996). The 10 springs sampled are discharge points for 10 individual groundwater basins within the sinkhole plain (Figure 1; Table 1). Livestock commonly graze in the groundwater basins drained by Kelly and Frog Springs, and row crops dominate land use in the other groundwater basins. Livestock are also present, but to a lesser extent, in the drainage basins of Collier, Indian Hole, and Sensel Springs. Increased urban development of land in the groundwater basins of Falling, Spar row Creek, Camp Vandeventer, and Auctioneer Springs during the past several years has probably resulted in additional input of septic efuent to these basins. Nine of the springs are discharge points of branchwork-type caves in the limestone bedrock and drain the karst terrane. Sensel Spring dis charges from the same host rock but drains an area of mantled karstied

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4 Circular 570 Illinois State Geological Survey bedrock (Figure 1; Table 1). Kelly Spring is also unique in that its catch ment includes both a surface stream and a cave system. The upper half of Kelly Springs watershed is drained by a surface stream, Dry Run Creek, that intersects Kruegers Dry Run Cave upon entering the karst terrane and ows underground for the other half of its catchment area prior to exiting at Kelly Spring. Background Potential Nitrogen Sources Nitrate is very mobile in the natural environment (Hem 1985). The major mechanism for mobilizing NO 3 from eld soils in humid climates, such as Illinois, is through leaching during rain events (Tisdale et al. 1993). The background concentrations of NO 3 in the shallow karst aquifer of the sink hole plain ranges from 0.4 to 2.5 mg of N/L for springs and 0.1 to 2.1 mg N/L for wells (Panno et al. 2006); 2.5 mg N/L should be used as an upper bound for background concentrations in the sinkhole plain. However, as stated earlier, most of the springs and wells sampled in the sinkhole plain area contain NO 3 concentrations that are considerably larger than the background concentrations. Probable NO 3 sources in the sinkhole plain include soil organic matter, nitrogen fertilizers, livestock wastes, and septic systems. Although the nitrogen of most fertilizers and septic efuent is in the reduced form, as ammonium or organic nitrogen, aerobic microbes in the upper soil zone are capable of quickly oxidizing this nitrogen to NO 3 through nitrication. The annual application of nitrogen fertilizers (primarily anhydrous ammonia and urea) ranges from about 120 to 150 lbs/acre (135 to 168 kg/ha) for corn and about 80 to 100 lbs/acre (90 to 112 kg/ha) for wheat and other grains (P. Kremmell, per sonal communication 1998). Anhy drous ammonia and urea are usually applied in the early spring for corn, and ammonium nitrate and urea are used in the late winter (February and March) for wheat. The water samples from springs were analyzed for atrazine because atrazine is considered representative of herbicides used in the study area (Panno et al. 1996) and is applied during the spring at approximately 1.0 to 1.5 lbs/acre (1.12 to 1.68 kg/ha) (P. Kremmell, personal communications 1997). Panno et al. (1996) concluded that the largest concentrations of agrichemicals entered groundwater via runoff into sinkholes during and immediately following spring plant ing. Thus, atrazine could be con sidered an indirect indicator for the source of some of the NO 3 present in the shallow karst aquifer. The efuent of septic systems may contribute substantially to local sources of NO 3 in groundwater. Ear lier work by Panno et al. (2007) found that total dissolved N, as NO 3 and/or ammonia (NH 4 + ), in efuent discharg ing from 22 septic systems ranged from 2.85 to 67 mg of N/L (mean and median, 24 mg of N/L). Livestock businesses in the area are generally small, and contamination from those operations is probably limited to indi vidual wells or localized portions of groundwater basins. Table 1 Spring locations, descriptions of their groundwater basins, and land use within the groundwater basins in the study area. 1 Spring Location 2 Groundwater basin description Land use Falling 15/01N/10W Resurgence of a small cave and waterfall Row crops, housing development Sparrow Creek 36/01N/10W Resurgence for Stemler/Sparrow Creek Cave Row crops, housing development Collier 16/04S/09W Resurgence for a large, suspected cave Row crops, livestock Indian Hole 16/04S/09W Resurgence for Fogelpole Cave Row crops, livestock Sensel 29/04S/09W Karst spring draining a covered karst area Row crops, livestock Illinois Caverns 31/03S/09W Cave stream at cave entrance Row crops, village Kelly 29/03S/09W Resurgence of Kruegers Dry Run Cave Row crops, livestock, forest Camp Vandeventer 21/02S/10W Resurgence of a small cave Row crops, housing development Auctioneer 36/02S/11W Resurgence of a small cave/waterfall Row crops, housing development Frog 31/02S/10W Resurgence of Frog Cave Row crops, livestock 1 The boundaries of the groundwater basins were estimated from work by Panno and Weibel (1999) and Aley and Aley (1998, unpublished report). Springs are described by Webb et al. (1994) and Panno et al. (1996, 1998a, 1998b, 1999). Caves described as small refer to those thought to be dominated by passages less than 1 m in height. 2 Location is reported as section, township, and range.

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Illinois State Geological Survey Circular 570 5 Stable Isotopes The stable isotopes of an element have the same number of protons and the same electron conguration but a different number of neutrons in the nuclei of their atoms. Thus, the isotopes of a particular element have similar chemical behavior but slightly different atomic masses. The differences in atomic mass cause the isotopes to react at slightly different rates during physiochemical and bio chemical processes. Such processes could involve changes in phase (e.g., evaporation), chemical reactions (e.g., precipitation of minerals), or biologi cal activity (e.g., biologically mediated reactions such as denitrication). Thus, the concentration of isotopes that naturally occur in coexisting chemical phases or in reacting chemi cal compounds can be different. In general, lighter isotopes have slightly faster reaction rates and tend to con centrate in main reaction products relative to the heavier isotopes. The overall natural abundance of the iso topes of elements used in this study are listed in Table 2. Because differences in isotopic abundance of an element from one substance to another are small, con centrations are expressed in delta ( ) notation. The -value of an isotope in a sample is the per mil ( parts per thousand) difference in the ratio of the less abundant isotope to the most abundant isotope relative to the same ratio in a known standard. This rela tionship is represented by the follow ing equation: [1] where X stands for the isotope of interest (e.g., 18 O or 15 N), and R is the ratio of the less abundant iso tope relative to the most abundant isotope (e.g., 18 O/ 16 O or 15 N/ 14 N). The isotopic results of this study are reported against reference standards. The reference standards used for 15 N is nitrogen in air; for isotopic oxygen and deuterium ( 18 O and D), Vienna-Standard Mean Ocean Water (V-SMOW); for isotopic carbon ( 13 C), Vienna PeeDee Belemnite (VPDB); and for isotopic sulfur ( 34 S), Canyon Diablo Troilite (CDT). 15 N and 18 O of NO 3 Generally, dif ferent sources of NO 3 have different 15 N values. The 15 N value for fertil izers is about 0 4 (Heaton 1986, Gormly and Spalding 1979). The 15 N values for NO 3 from animal waste and septic systems commonly range from 8 to 22 (Heaton 1986). The 15 N of NO 3 from soil organic matter varies considerably but is gener ally between 2 and 10 for most soils (Feigin et al. 1974, Heaton 1986, Mariotti et al. 1988, Shearer and Kohl 1988, Fogg et al. 1998, Kendall 1998). Although the 15 N of the individual sources of NO 3 (the end members) may initially be different, certain geochemical processes, such as deni trication (the reduction of NO 3 to nitrogen gas, N 2 ), cause isotope frac tionation to alter the isotopic compo sition of the NO 3 During microbial denitrication, the lighter isotope ( 14 N) is preferentially partitioned to the reduced N 2 gas. The heavier iso tope ( 15 N) becomes enriched in the remaining NO 3 Thus, as denitrica tion occurs, the isotopic composition of the remaining NO 3 changes, and it becomes difcult to distinguish its source using only 15 N values. To help resolve this problem, 18 O value of the NO 3 was also analyzed. The 18 O of NO 3 varies depending on the source of oxygen in the NO 3 and geochemical processes such as denitrication. In some cases, such as with synthetic nitrate fertilizer, the source of oxygen is completely atmospheric; in other cases, such as with nitrication of ammonium in groundwater, the source of oxygen is a combination of groundwater oxygen and atmospheric oxygen. During nitrication, it is generally thought that approximately two-thirds of the oxygen in NO 3 is from groundwater ( 18 O values of groundwater are usu ally negative and vary depending on geographic location), and onethird is from the atmosphere ( 18 O is approximately 23.5) (Amberger and Schmidt 1987, Bttcher et al. 1990, Kendall 1998). However, recent studies (Mayer et al. 2001, Burns and Kendall 2002) indicate this suggested distribution may be an oversimpli cation for predicting the 18 O of NO 3 during nitrication. Based on incuba tion experiments and measurements of NO 3 from forest soils, those studies found that the 18 O was greater than expected, suggesting that perhaps the contribution of atmospheric oxygen might sometimes be greater than one-third. Mayer et al. (2001) sug gested that in some environments, such as those with low pH, which they observed in forest soils, a different bacterial process dominates the nitri cation reaction and utilizes a greater amount of atmospheric oxygen. There is also the possibility that the 18 O of the soil water at some locations might be enriched in 18 O from respiratory isotope fractionation and/or evapo rative effects within the soil zone (Kendall 1998, Burns and Kendall 2002). Thus, the isotopically heavier soil water would contribute oxygen to NO 3 with greater 18 O values than Table 2 Isotopic natural abundance of nitrogen, oxygen, carbon, hydrogen, and sulfur in the study area. 1 Isotope Abundance (%) 14 N 99.64 15 N 0.36 16 O 99.76 17 O 0.04 18 O 0.2 12 C 98.89 13 C 1.11 14 C 10 0 (t 1/2 = 5,730 years) 2 1 H 99.984 D or 2 H 0.015 3 H 10 14 to 10 (t 1/2 = 12.33 years) 3 32 S 95.02 33 S 0.75 34 S 4.21 35 S <10 11 (t 1/2 = 87.2 days) 36 S 0.02 1 Hoefs (1980), Fritz and Fontes (1980), and Coplen (1993). 2 t 1/2 radioactive half-life. 3 Lucas and Unterweger (2000). X = [ ]103 Rsample RstandardRstandard

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6 Circular 570 Illinois State Geological Survey expected from local groundwater iso tope values. The 18 O values are usually fairly low for NO 3 in shallow groundwater in agricultural settings, and many of the larger values in these areas are attributed to denitrication or fast throughput of NO 3 fertilizers (Ara vena et al. 1993, Mengis et al. 2001, Beaumont 2003). The lower 18 O values of the NO 3 in those studies are consistent with the nitrication pro cess that purports two-thirds oxygen from groundwater and one-third from atmospheric oxygen. However, there is always a range of values that prob ably reect the variable 18 O of the soil water and inuences from some of the processes just discussed. It appears that the environmental setting and climatic conditions affect the initial 18 O value of NO 3 during nitrication of reduced N sources. Our study sam ples are primarily from agricultural settings. In order to estimate initial 18 O values of NO 3 for nitrication of reduced nitrogen sources, we have assumed that the nitrication pro cess that dominates in the study area uses two-thirds water and one-third atmospheric contribution. The range of 18 O of NO 3 from the nitrication reaction will, of course, vary depend ing on the 18 O of the shallow ground water that comes in contact with the nitrifying bacteria. The other process that strongly affects the 18 O value of NO 3 is denitrica tion. Denitrication fractionates the oxygen isotopes, causing the residual NO 3 to become more enriched in 18 O. Although the fractionation factor for both 15 N and 18 O exhibits a range of values depending on local conditions and rates of reactions, when com pared with each other, the 15 N and 18 O isotopes fractionate at a relatively constant ratio during denitrica tion (Kendall 1998). Thus, using both 15 N and 18 O measurements helps to determine the major sources of NO 3 and indicates whether denitrication has occurred in the groundwater system. A 1:2.1 relationship between 18 O and 15 N of NO 3 has been observed (Bttcher et al. 1990, Ara vena and Robertson 1998) in detailed groundwater studies involving NO 3 attenuation at sites in Germany and in Ontario, Canada. A strong correlation between decreasing NO 3 concentra tion and increasing 15 N and 18 O values was observed in both stud ies. In a recent study by Mengis et al. (1999), a similar linear relationship was observed between the 18 O and the 15 N of the NO 3 ; however, correla tion was poor between decreasing NO 3 concentrations and increas ing isotopic composition of NO 3 This poor correlation was explained by variable inputs of NO 3 into the groundwater caused by crop rotation of the cultivated eld, riparian buffer zone, and mixing with local, deeper groundwater. Thus, denitrication may be identied in a groundwater system by using 15 N and 18 O of the dissolved NO 3 even though decreases in NO 3 concentration may not be strongly correlated with increasing isotopic values. D and 18 O of Water The D and 18 O isotopes in precipitation from around the world follow a consistent relationship that is characteristic of latitude and climatic conditions (Craig 1961, Dansgaard 1964). This relationship results in a straight line referred to as the global meteoric water line (GMWL): D = 8( 18 O) 10. [2] The 18 O and D values are generally not altered in meteoric water after it enters the soil zone and inltrates to the shallow groundwater (Fontes 1980). However, under certain condi tions, noticeable deviations from the GMWL are caused by physical and chemical processes that affect the isotopic composition of the water subsequent to precipitation; examples are evaporation and geothermal water-rock interactions (Coplen 1993, Fontes 1980). The conservative nature of 18 O and D in low-temperature environments allows these isotopes to be used in leakage or mixing studies between reservoirs of water that are isotopically distinct. Furthermore, in nitrate studies, the 18 O of ground water should be determined in order to estimate the 18 O of NO 3 produced from nitrication of reduced nitro gen in the soil zone. This process for estimating 18 O of the NO 3 produced from nitrication was described in the previous section. 13 C in Groundwater The carbon isotope ( 13 C) of dissolved inorganic carbon (DIC) in groundwater is useful in determining the geochemical evo lution of the groundwater because of the differences in isotopic composi tion of the major sources of carbon and the fractionation of its isotopes caused by certain geochemical reac tions. The 13 C of DIC in shallow groundwater is initially dependent on several factors, including the isotopic composition of the soil CO 2 the input of carbon from dissolution of carbon ate minerals as groundwater perco lates into the subsurface, and whether the dissolution of carbonate minerals has occurred in isolation relative to soil CO 2 The partial pressure of CO 2 in soil is usually 10 to 100 times that of atmo spheric CO 2 and comes primarily from root respiration and decompo sition of organic debris (Mora et al. 1993, Clark and Fritz 1997). Thus, the 13 C of soil CO 2 and, hence, DIC of the recharging groundwater depend on the vegetation growing in the region. The 13 C of plant carbon depends on the photosynthetic pathway of the plants. The majority of plants, includ ing agricultural crops such as wheat and soybeans, utilize the Calvin cycle (C 3 ), a photosynthetic pathway that results in low 13 C values averaging 27. Some grasses, including corn, utilize the Hatch-Slack pathway (C 4 ), which results in 13 C values averaging 12. Normally, there is a combina tion of C 3 and C 4 plants, resulting in soil CO 2 13 C values between 12 and 27 (Clark and Fritz 1997). Another possible source of organic carbon in soils of agricultural areas is organic fertilizers, such as urea, which has very low 13 C composition, near 50 (Zlotnick 1992). The actual isotopic composition of soil CO 2 is usually more enriched in 13 C than the over all composition of the vegetation rate because of a 4.4 fractionation caused by diffusion of CO 2 through the soil to the atmosphere (Cerling et

PAGE 15

Illinois State Geological Survey Circular 570 7 al. 1991). Measured 13 C values of soil CO 2 in east-central and south-central Illinois ranged from 16.7 to 22.4 (Hackley and Liu, unpublished data). The 13 C of DIC for shallow groundwater in recharge areas is initially quite negative (isotopically light) because most of the DIC is from soil CO 2 which has been dissolved into the soil water and carried down into the subsurface with groundwater ow. As the water percolates into the ground, rocks containing inor ganic carbon, such as limestone and dolomite, dissolve and add to the DIC pool. Carbonate minerals usu ally have isotopically heavier 13 C values than do plants. The 13 C of most marine carbonates is close to 0 (Anderson and Arthur 1983). The nal 13 C of the DIC depends on the type of system in which carbon ate dissolution occurs (Mook 1980, Clark and Fritz 1997). If dissolution is completely open to exchange between soil CO 2 and DIC, then the isotopic composition of the DIC is controlled by the reservoir of soil CO 2 However, if the dissolution of carbonate occurs under conditions closed to exchange between DIC and soil CO 2 (i.e., in the saturated zone), then the 13 C of the DIC becomes an intermediate value between the two end members: soil CO 2 and carbonate carbon. Typically, the DIC of groundwater for temper ate areas with C 3 plants dominating has a 13 C value between 10 to 13 (i.e., between the average soil CO 2 and average carbonate mineral composi tions). 34 S in Groundwater Sulfate in groundwater is generally derived from the dissolution of sulfate minerals, such as gypsum, and/or the oxida tion of reduced sulde minerals, such as pyrite. In some cases, sulde oxidation may be associated with denitrication (Kelly 1997, Klle et al. 1985). The 34 S of sulfate from gypsum evaporite deposits is usually consid erably different from that of sulfate from the oxidization of sedimentary sulde minerals. 34 S values from evaporite deposits are generally about 20 but vary with age (Holser and Kaplan 1966, Nielsen 1976, Claypool et al. 1980). The 34 S values of reduced suldes in sediments and sedimen tary rocks vary widely, mostly in the general range of 50 to +10 (Kaplan 1983, Caneld and Teske 1996). Typi cally, however, sedimentary suldes usually have values ranging from 10 to 30 (Hoefs 1980). The isotopic composition of sulfur in dissolved sulfate helps to delineate the source of sulfate in the groundwater and to indicate whether the concentration changes within an aquifer are the result of microbial sulfate reduction reactions or the mixing of waters with different amounts of sulfate. Methodology Water Sampling Groundwater samples were collected from 10 springs and 17 wells in the Illinois sinkhole plain during dif ferent seasons of the year. Several samples of individual NO 3 sources (end-member samples) were also collected including Solution-28 (a nitrogen fertilizer in solution form, containing 30% urea and 40% ammo nium nitrate), urea (a nitrogen fertil izer in solid pellet form), livestock waste (hog waste), monitoring wells contaminated by hog waste, septic efuent, water from eld runoff, and atmospheric NO 3 from precipita tion. Water samples from the springs were collected during six consecutive seasons: fall (November) 1998, winter (February/March) 1999, spring (May) 1999, summer (August) 1999, fall (November) 1999, and winter (March) 2000. During the 1999 winter sam pling event, two separate collection trips were made to the springs. Sam ples collected during the initial trip, the third week of February, included only nine springs and were used for chemical analyses, for 18 O and D of the water and 13 C of the DIC. The samples for nitrogen and oxygen iso topes of the dissolved NO 3 and 34 S of sulfate were collected 2 weeks later, in March. The second trip was needed because of a complication with the preservative used for the NO 3 isotope samples from the initial sampling. During this resampling trip, samples for chemical and isotopic analyses were collected from Frog Spring. No precipitation fell during the interval between the two sampling trips. Field conditions at the springs, such as discharge and NO 3 concentrations, were essentially the same. Thus, the chemical and isotopic data for the water samples collected from springs during winter 1999 are presented together as one sampling event. Sam ples collected from Falling Springs were generally taken from the top and bottom of the falls. Falling Springs discharges from the middle of a cliff and spills over and through a large tufa deposit, forming a stream at the base of the cliff. Water samples from the wells were collected during spring (May) 1999 and fall (November) 1999. Well water was sampled from residential homes through outside spigots to avoid the effects of water softeners, as outside spigots are not normally connected to residential water softener systems. Samples of aeration-type septic system efuent were collected at the discharge end of the overow pipe or directly from the nal septic cham ber. Samples were collected in large 2.3-L glass containers and ltered in the laboratory using a high-capacity lter and peristaltic pump. The hog waste samples were taken directly from waste pits at active hog opera tions. Two hog waste samples and hog waste-contaminated monitoring wells were collected in south-central Illinois and included here as examples of the chemical and isotope composi tions from large hog waste facilities. All water, septic, and waste samples were analyzed in the eld for temper ature, pH, redox potential (Eh), and specic conductance. Field measure ments for pH and specic conduc tance were made using meters that allowed temperature compensation. All instruments were calibrated using appropriate standards. Groundwater samples were collected in accordance with eld techniques described by Wood (1981) and Panno et al. (1996). Groundwater samples were collected from the springs and wells for cation, anion, dissolved organic carbon (DOC), atrazine, bacteria, and the stable isotope analyses, including nitrogen, oxygen, hydrogen, carbon, and sulfur isotopes. Samples col

PAGE 16

8 Circular 570 Illinois State Geological Survey lected for cations, anions, DOC, and stable isotopes were ltered through 0.45-m membranes and stored in polyethylene bottles. Samples ana lyzed for cations were acidied in the eld with ultrapure nitric acid to pH <2.0. Separate samples were col lected for ammonium analyses from the septic systems and hog waste pit. Most groundwater samples were not analyzed for ammonium because of its very low concentration in the springs (Panno et al. 1998a, 2005). Groundwater samples for nitrogen and oxygen isotopic analyses of dis solved NO 3 were collected in 2-L bottles and were preserved with hydrochloric acid to a pH <2 or with the addition of several drops of mer curic chloride solution. Samples for tritium ( 3 H) analysis were collected in 500-ml polyethylene bottles. Atrazine samples were unltered and were collected in precleaned, 1-L glass bottles. Bacterial samples also were unltered and were collected in two sterilized 120-ml bottles. All samples were transported in ice-lled coolers to the appropriate laboratories and kept refrigerated at approximately 4 C until analyses were completed. Analytical Techniques Cation concentrations in the water samples were determined as described by Panno et al. (1996) using a Model 1100 Thermo-Jarrell Ash Inductively Coupled Argon Plasma Spectrometer (ICAP). Instrument control, automatic background cor rection, and spectral interference cor rections were performed using a DEC Micro PDP 11/23 computer. Solution concentrations of anions were deter mined using a Dionex 211i ion chro matograph, following USEPA Method 300 (ODell et al. 1984). All water chemistry data were evaluated with the Geochemists Workbench (Bethke 1994) reaction model to determine saturation states. Dissolved organic carbon was deter mined by difference (total carbon minus inorganic carbon) (Greenburg et al. 1987). In summary, total carbon was determined by completely com busting an aliquot of ltered water sample on a heated coil (950 C) and measuring the amount of CO 2 driven off by a CO 2 coulometer. The DIC was determined by using a weak solution of nitric acid on an aliquot of ltered water and measuring the amount of the CO 2 released with a coulometer (ASTM 1994). Atrazine and bacteria were ana lyzed by the Illinois Department of Agricultures Animal Disease Labora tory in Centralia, Illinois. Atrazine samples were analyzed using gas chromatography and mass spectrom etry techniques (U.S. Environmental Protection Agency 1982). Bacterial samples were analyzed within 24 hr of collection for total coliforms, fecal coliforms, and total bacteria using standard methods to isolate and identify bacterial colonies present (Clesceri et al. 1989). Concentrations of bacteria are reported as colonyforming units (cfu) per 100 ml of water. Bacterial species were identi ed and listed from most dominant to least. The dominance of each bacte rial species was summarized using ranking (arithmetic mean) and preva lence (percentage) of each species in water samples (Panno et al. 1997b). Bacteria were ranked from 1 (most dominant) to 15 (least dominant) for all water samples collected during each sampling period. The ranks for each bacterium were added, and mean ranking was determined (e.g., the lowest mean ranking is the most abundant); non-detections were given the highest rank for this calculation. Tritium ( 3 H) was analyzed using electrolytic enrichment (Ostlund and Dorsey 1977) and liquid scintillation counting. The electrolytic enrichment process basically consisted of distil lation, electrolysis, and purication of enriched samples. The results are reported in tritium units (TU). One TU is dened as one 3 H atom per 10 18 hydrogen atoms. The precision for the analyses in this study is 0.25 TU. Nitrogen and oxygen isotopic analy ses of NO 3 in water samples were conducted using methods similar to those described by Silva et al. (1994, 2000) and Wassenaar (1995) with the modications of Hwang et al. (1999). The samples were rst boiled under acidication to remove bicarbonate (HCO 3 ) and dissolved CO 2 The DOC and sulfate (SO 4 2 ) ions also were removed to minimize contamination of the 18 O by oxygen in the SO 4 2 ions and the dissolved organic matter and to help eliminate anionic interference during the ion-exchange step for NO 3 extraction. The dissolved organic matter was removed using a silicalite molecular sieve, and SO 4 2 ions were removed by precipitation as barium sulfate (BaSO 4 ). After removal of HCO 3 SO 4 2 and DOC, the NO 3 was extracted using an anion-exchange column packed with BioRad AG 1-X8 resin (Silva et al. 2000). Nitrate col lected on the anion-exchange column was eluted with hydrogen bromide (HBr) solution (Hwang et al. 1999) and converted to silver nitrate (AgNO 3 ) by adding silver oxide (AgO 2 ). The AgNO 3 was precipitated by freeze-drying the sample in a vacuum system. The dried AgNO 3 was converted to CO 2 and N 2 for 18 O and 15 N analysis, respectively, by sealed quartz-tube combustion techniques with and without graphite as described by Silva et al. (2000) and Hwang et al. (1999). The standard deviation for 15 N was less than or equal to 0.4: the mean value was 0.1. We discovered a problem part way through the study involving the use of quartz wool with the combus tion procedure for determining 18 O of NO 3 Many of the samples for which extra AgNO 3 remained were reana lyzed, changing the 18 O values an average of 1.4. For those samples that could not be rerun, a correction factor was applied. The standard deviation of 18 O NO3 for the reanalyzed samples was less than or equal to 0.9; the mean was 0.3. For those mathematically corrected sam ples, the standard deviation for 18 O was 1.7. Recently, Rvsz and Bohlke (2002) published a new method for deter mining the 18 O of NO 3 that does not employ any quartz tubing but instead uses a graphite tube and high temperature conversion elemental analysis (TCEA) technique. In order to compare the 18 O NO 3 values reported here using quartz-tube combustions to 18 O NO 3 values determined by the newly developed (TCEA) method, the following equation can be used:

PAGE 17

Illinois State Geological Survey Circular 570 9 Y = 1.284X 3.3. The equation is based on a comparison of our analyses of the National Institute of Standards and Technology (NIST) nitrate stan dards (IAEA-N3 and USGS-34 and -35) with 18 O values reported by Bohlke et al., (2003). However, most of the data for 18 O of nitrate in the published literature have been prepared using sealed quartz-tube combustion tech niques, so, for this publication, we have reported the quartz-tube com bustion 18 O values. The 18 O of the water samples was determined using the CO 2 H 2 O equilibration method as originally described by Epstein and Mayeda (1953) with modications of Hack ley et al. (1999). The D of water was determined using the zinc-reduc tion method (Coleman et al. 1982, Vennemann and ONeil 1993) with modications described by Hackley et al. (1999). The 13 C of DIC was deter mined by the gas evolution technique in a manner similar to that described by Atekwana and Krishnamurthy (1998). Instead of 85% phosphoric acid, we used 2 g of crystalline orthophosphoric acid (99%) that was placed into vials that were then sealed with a septum and evacuated. Approxi mately 10 ml of the water sample was injected into the vials, and the CO 2 released at room temperature was extracted from the vial and puried cryogenically as described by Ate kwana and Krishnamurthy (1998). The puried gases (N 2 CO 2 H 2 and SO 2 ) were analyzed on an isotope ratio mass spectrometer. Analytical reproducibility for D, 18 O, 13 C, and 34 S is equal to or less than 1.0, 0.1, 0.15, and 0.3, respec tively. Results and Discussion End-Member Samples: Chemical Composition As expected, the results of some eld parameters and chemical analyses (Tables 3 and 4) for the different endmember sources of NO 3 were anoma lous compared with values for natural groundwater composition. For exam ple, values for specic conductance, chloride, sodium, nitrogen, and bicar bonate for most of the septic samples and the livestock (hog) waste samples were considerably greater than typi cal values for shallow groundwater chemistry. Specic conductance is a relative measure of the dissolved ions in solu tion and gives a quick indication in the eld of whether the chemical com position of the water has an anoma lously large concentration of dis solved ions. The specic conductance of the septic system efuents and the livestock waste was high compared with that of the spring-water samples, which were typically between 400 and 800 micro-Siemens ( S)/cm. The spe cic conductivities for the septic sys tems ranged between 819 and 1,983 S/cm. The specic conductivity for the hog waste samples ranged from 11,400 to 38,200 S/cm (Table 3). Compared with the samples of spring Table 3 Field parameters and total alkalinity of samples analyzed for end-member sources of NO 3 Date Sample Temp. Eh 2 Sp. Cond. Tot. Alk. sampled Sample 1 description (C) pH (mV) (S/cm) (mg of CO 3 /L) Septic efuence 09/18/96 96-42 Septic 25.6 6.9 253 1,031 327 09/18/96 96-44 Septic 20.0 7.3 324 1,225 346 09/18/96 96-47 Septic 24.6 6.9 349 819 117 09/18/96 96-49 Septic 23.7 6.6 602 1,148 118 09/18/96 96-56 Septic 28.0 6.5 11 1,983 368 11/18/99 NW-17-septic Septic 12.0 8.6 365 1,723 385 03/21/01 SS-1 Septic 10.0 7.5 321 1,840 402 03/21/01 SS-2 Septic 12.8 7.5 355 1,246 513 03/21/01 SS-3 Septic 9.2 7.5 51 1,699 501 Animal waste 03/21/01 HW1 Hog waste -6.8 -29,130 8,210 03/21/01 HW2 Hog waste -8.0 -11,400 4,300 03/21/01 HW3 Hog waste -7.8 -38,200 14,370 03/21/01 Am5 Hog waste 3 10.1 6.6 242 2,240 574 03/21/01 Am6 Hog waste 3 11.1 7.1 228 1,616 697 Fertilizers 03/21/01 Soln-28 Soln-28 NH 3 -----03/21/01 Soln-28 Soln-28 NO 3 -----03/21/01 Urea Urea Field runoff 05/14/99 Runoff Field water 19.4 9.2 -231 97 1 HW2 (HW E458-01), HW3 (HW E254-01), Am5 (HW A 467-02), and Am6 (HW A 469-02) from south-central Illinois. 2 Temp., temperature; Eh, redox potential, calibrated with Zobell solution; Sp. Cond., specic conductivity; Tot. Alk., total alkalin ity; Soln, solution; --, not determined. 3 Contaminated groundwater.

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10 Circular 570 Illinois State Geological Survey water, the septic systems and hog wastes had anomalous concentra tions of several chemical constituents including chloride, sodium, potas sium, and total nitrogen (as NO 3 or ammonium). The hog wastes also had high concentrations of bicarbonate (Table 4). Of these ions, chloride is an important constituent to monitor because it is one of the most conser vative ions in groundwater; that is, it does not tend to react or exchange with other minerals or ions as groundwater ows through the sub surface environment. Many other ions have the tendency to react with the surrounding environment and are not as dependable as tracers. Decreases in chloride concentrations from point sources such as septic systems or feedlots are primarily the result of dilution when the contaminated waste water mixes with groundwater. End-Member Samples: Isotopic Composition The end-member samples were measured primarily for their 15 N composition; however, a few of the samples were measured for some other common stable isotopes (Table 5). The 15 N values for the ammonium and NO 3 of the septic system and hog waste samples ranged from +4.7 to +35. Three values were lower than the range typically observed in the literature for septic and manure waste (+8 to +22). The rst ve septic samples listed in Table 5 were col lected prior to this study, and, thus, no 18 O values were available for the dissolved NO 3 However, because those septic systems were collected from the sinkhole plain area, we have included the 15 N results here. The eld runoff sample had enough sulfate for 34 S analysis and could be used as an end member for cultivated eld sulfate. Spring Samples: Chemical Composition Overall, the general chemical com position of the spring-water samples (Tables 6 and 7) was typical of shallow groundwater in contact with carbon ate bedrock. Some of the parameters measured for these samples showed seasonal variations; other parameters were typical of soil-water or surfacewater chemistry. Groundwater samples from the springs were Ca 2+ HCO 3 -type water and were supersaturated to slightly undersaturated with respect to cal cite, aragonite, and dolomite. All of the samples from springs were super saturated with respect to quartz. Saturation indices with respect to a particular mineral are a reection of rock-water interactions as the ground water passes through the soil zone, epikarst, and bedrock formations. The saturation indices for calcite indi cate that the water discharging from the springs ranged from very super saturated to slightly undersaturated conditions (Figure 2). Falling Springs and Auctioneer Spring had the great est degree of calcite saturation and also had large tufa deposits associated with them. The waters discharging from these two springs have vertical drops 4 to 20 m, causing considerable agitation, which contributes to the degassing of CO 2 and the concomitant precipitation of calcite at the springs (e.g., Hubbard and Herman 1991). Sensel Spring had the most undersat urated water with respect to calcite. Most of Sensel Springs discharge is from soil water that enters the lime stone bedrock just before discharging to a spring house. The undersaturated conditions at this spring suggest there was minimal time for the water to become saturated with respect to calcite. The pH values for the springs ranged from 6.7 to 8.2. Most of the spring samples had values greater than pH 7.5 (Table 6). The greater pH values reect the buffering effects of the car bonate bedrock. Groundwater from Table 4 Chemical composition (mg/L) of samples analyzed for end-member sources of NO 3 1 Sample Ca 2+ Mg 2+ Na + K + NH 4 -N HCO 3 Cl SO 4 2 NO 3 -N SiO 2 Al B Ba Br F Fe Mn Sr 2+ Zn Septic efuent 96-42 66.8 25.6 88.9 17 34.6 399 69.1 95.1 1.66 12.9 <0.02 1.15 0.06 0.1 -1 <0.05 <0.01 0.28 0.10 96-44 69.1 24.5 115 17 36.5 422 84.3 130 0.53 16.6 <0.02 0.70 0.02 0.08 -<0.05 <0.01 0.21 0.04 96-47 68.1 26 70.1 16 0.14 143 63.2 76.9 25.9 14.8 <0.02 0.18 0.05 0.06 -<0.05 <0.01 0.25 0.09 96-49 118 24.3 77.4 28 0.09 144 147 84.1 25.4 9.6 <0.02 1.73 0.05 --<0.05 <0.01 0.28 0.06 96-56 65.6 23.6 225 33 21.2 449 312 91.7 0.83 7.9 0.12 0.33 0.10 0.07 -1.12 0.1 0.29 0.46 NW17-septic 59.5 6.48 80.2 345 -1 470 91.7 59.0 70.1 29.5 0.03 0.13 0.04 0.47 0.2 0.01 <0.01 0.14 0.02 SS-1 84.0 18.6 416 11 16.9 490 504 51.6 <0.1 20.4 <0.3 0.97 0.10 0.09 0.4 0.11 0.03 0.22 0.02 SS-2 33.0 10.1 224 12 34.8 626 91.0 38.5 <0.02 23.5 <0.3 0.05 0.03 0.09 0.3 0.17 0.04 0.07 0.01 S-3 64.5 23.2 262 22 45.6 611 253 73.4 0.26 13.2 <0.3 0.77 0.03 <0.05 1 0.45 0.53 0.14 0.01 Animal waste HW1 343 70.2 493 2,760 3,670 10,010 900 797 <0.25 68.5 <0.3 3.90 0.04 <0.6 <1.2 5.7 1.10 0.82 0.06 HW2 34.0 3.1 348 2,010 323 5,243 794 1.9 <0.1 33.4 -2.43 0.023 0.823 <0.5 0.30 0.036 0.087 -HW3 26.0 0.9 1,190 4,950 1,806 17,520 1,980 47 <0.2 50.1 -5.11 0.031 1.413 <1 2.06 0.011 0.073 -Am5 275 117 70 2 <0.01 700 280 52 12.7 11.1 -0.03 0.199 0.360 0.1 0.01 0.537 0.349 -Am6 116 84 113 23 13.4 850 171 23 0.05 21.2 -0.15 0.417 0.216 0.2 0.06 0.062 0.471 Runoff 36.5 2.28 0.70 14 -118 15.0 14.0 0.52 0.4 0.145 0.02 0.03 <0.18 0.52 0.03 0.01 0.06 <0.01 1 --, not determined.

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Illinois State Geological Survey Circular 570 11 Sensel Spring usually had the lowest pH. This lower pH probably reects a major inuence of soil water (more dissolved CO 2 ) and minimal contact with the limestone bedrock prior to discharging at the surface. The temperature of the water dis charging from springs can be indica tive of the seasons and the openness of the ow system. For example, the largest variability in water tempera ture was measured at Kelly Spring, followed by Indian Hole Spring (Figure 3). Such results reect a more open conduit system for these springs relative to the others. As mentioned previously, the water discharging at Kelly Spring ows on the surface for half of its watershed before plunging into a sinkhole and entering Krue gers Dry Run Cave. The difference in temperature between top and bottom samples from Falling Springs illus trates how quickly exposure to surface conditions (openness) can affect the measured water temperature. Sensel Spring had the most consistent water temperature (13.9 to 14.2 C) measured during the different seasons. The con stant temperatures at Sensel Spring suggest that this ow system, through the sediments covering the limestone bedrock, was more consistent and less open to rapid surface inux than were those of the other springs sampled. Specic conductance ranged from 386 to 823 S/cm for the springs. The most consistent values were observed at Sensel Spring, followed by Frog Spring. In general, the data collected during this investigation agreed with previous data from the sinkhole plain area, which indicated that specic conductance is a rough measure of the total alkalinity of Ca 2+ HCO 3 -type groundwater (Panno et al. 1996). Specic conductance and alka linity were also directly proportional to the Na + Ca 2+ Mg 2+ SO 4 2 and Cl concentrations, which are usually a function of inputs from limestone and accessory minerals within the rock formation through which groundwa ter ows. The oxidation/reduction potential of the water ranged from +336 to +513 mV. These Eh values indicate that the spring water was exposed to atmo spheric oxygen along its ow path (generally through air-lled caves or conduits). The lowest Eh values, indi cating the most reducing conditions for each spring, were usually mea sured during the summer sampling event, possibly reecting the greater biological activity during the warmer season. The largest Eh values, indicat ing the most oxidizing conditions, were primarily measured during spring and could reect the inux of more oxygenated water as recharge is usually greatest for this area during spring (Panno et al. 1998b). Chloride (Cl ) concentrations for the spring water ranged from 6.5 to 24.7 mg/L. The greatest concentrations were consistently observed in Spar row Creek, Illinois Caverns, and Kelly and Frog Springs. Potential sources for Cl include agrichemicals (potash or potassium chloride), road salt, Table 5 Isotopic data of samples that were analyzed for end-member sources of NO 3 15 N NH4 15 N NO3 18 O NO3 18 O D 13 C 34 S Sample () () () () () () () Septic efuent 96-42 4.7 -1 -----96-44 7.7 ------96-47 -9.1 -----96-49 -10.5 -----96-56 12.1 ------NW-17-septic 12.7 4.1 ----SS-1 11.6 --4.64 33.3 13.7 -SS-2 8.9 --4.22 31.3 10.8 -SS-3 12.2 --7.38 54.2 8.6 -Animal waste HW1 7.1 --2.90 -7.9 3.1 HW2 35.0 --1.10 5.30 25.8 -HW3 18.8 --0.07 2.20 37.1 -Am5 -35.1 10.3 4.96 36.2 6.96 -Am6 23.0 --5.78 38.5 11.4 -Fertilizer Solution-28 0.6 -----Solution-28 -0.3 22.4 ----Urea 0.4 2 ---47.8 -Runoff 16.4 15.2 5.69 40.1 10.8 2.7 Rainwater RWA-99 -4.8 32.5 ----RWAU-99 --2.5 23.1 ----RWJN-00 --0.8 23.8 ----RWJY2k --3.3 42.9 ----1 --, not determined. 2 Organic nitrogen. Table 4 Chemical composition (mg/L) of samples analyzed for end-member sources of NO 3 1 Sample Ca 2+ Mg 2+ Na + K + NH 4 -N HCO 3 Cl SO 4 2 NO 3 -N SiO 2 Al B Ba Br F Fe Mn Sr 2+ Zn Septic efuent 96-42 66.8 25.6 88.9 17 34.6 399 69.1 95.1 1.66 12.9 <0.02 1.15 0.06 0.1 -1 <0.05 <0.01 0.28 0.10 96-44 69.1 24.5 115 17 36.5 422 84.3 130 0.53 16.6 <0.02 0.70 0.02 0.08 -<0.05 <0.01 0.21 0.04 96-47 68.1 26 70.1 16 0.14 143 63.2 76.9 25.9 14.8 <0.02 0.18 0.05 0.06 -<0.05 <0.01 0.25 0.09 96-49 118 24.3 77.4 28 0.09 144 147 84.1 25.4 9.6 <0.02 1.73 0.05 --<0.05 <0.01 0.28 0.06 96-56 65.6 23.6 225 33 21.2 449 312 91.7 0.83 7.9 0.12 0.33 0.10 0.07 -1.12 0.1 0.29 0.46 NW17-septic 59.5 6.48 80.2 345 -1 470 91.7 59.0 70.1 29.5 0.03 0.13 0.04 0.47 0.2 0.01 <0.01 0.14 0.02 SS-1 84.0 18.6 416 11 16.9 490 504 51.6 <0.1 20.4 <0.3 0.97 0.10 0.09 0.4 0.11 0.03 0.22 0.02 SS-2 33.0 10.1 224 12 34.8 626 91.0 38.5 <0.02 23.5 <0.3 0.05 0.03 0.09 0.3 0.17 0.04 0.07 0.01 S-3 64.5 23.2 262 22 45.6 611 253 73.4 0.26 13.2 <0.3 0.77 0.03 <0.05 1 0.45 0.53 0.14 0.01 Animal waste HW1 343 70.2 493 2,760 3,670 10,010 900 797 <0.25 68.5 <0.3 3.90 0.04 <0.6 <1.2 5.7 1.10 0.82 0.06 HW2 34.0 3.1 348 2,010 323 5,243 794 1.9 <0.1 33.4 -2.43 0.023 0.823 <0.5 0.30 0.036 0.087 -HW3 26.0 0.9 1,190 4,950 1,806 17,520 1,980 47 <0.2 50.1 -5.11 0.031 1.413 <1 2.06 0.011 0.073 -Am5 275 117 70 2 <0.01 700 280 52 12.7 11.1 -0.03 0.199 0.360 0.1 0.01 0.537 0.349 -Am6 116 84 113 23 13.4 850 171 23 0.05 21.2 -0.15 0.417 0.216 0.2 0.06 0.062 0.471 Runoff 36.5 2.28 0.70 14 -118 15.0 14.0 0.52 0.4 0.145 0.02 0.03 <0.18 0.52 0.03 0.01 0.06 <0.01 1 --, not determined.

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12 Circular 570 Illinois State Geological Survey animal waste, septic efuent, and natural sources (minerals and upwell ing saline groundwater). The spring time sampling event had the highest Cl concentrations (Table 7). Spring time recharge could have brought in a greater amount of anthropogenic sources of Cl possibly related to agrichemicals, livestock, septic efu ent, and road salt. The fall and winter sampling events generally had the lowest Cl concentrations. The Na + and Cl concentrations were positively correlated, but plotted below (toward greater Na + concentra tions) the stoichiometric line showing a 1:1 relationship (Figure 4). This shift toward higher Na + concentrations suggested that cation exchange (Na + with Ca 2+ and Mg 2+ ) probably played a role in the chemical makeup of the spring waters. The samples from Kelly Spring showed even greater Na + enrichment than the other springs. The reason for the distinctly different plot of the Kelly Spring samples for these ions was unclear. The uoride (F ) concentration for the springs ranged from approximately 0.1 to 0.35 mg/L and followed a sea sonal trend; concentrations were greatest during spring and summer (Figure 5). Because phosphatic fertilizers are used throughout Illi nois (Hamamo et al. 1995) and are derived from carbonate-uorapatite, this F enrichment possibly was a consequence of cropland drainage after spring fertilizer application (Aswathanarayana et al. 1985). Sulfate (SO 4 2 ) concentrations ranged from 17.5 to 93.5 mg/L. When the SO 4 2 concentrations were plotted against Ca 2+ the data for several of the springs clustered. A few of the springs showed a somewhat linear relation ship, and data for one spring, Kelly, were clustered differently from the others (Figure 6). Such results prob ably reect a variety of inputs to the groundwater system in the sinkhole plain. Sources for SO 4 2 include the dissolution of gypsum (CaSO 4 2H 2 O) and anhydrite (CaSO 4 ) and the oxida tion of pyrite (FeS 2 ) from the St. Louis Limestone; agricultural sulfate min erals such as (NH 4 )2SO 4 MgSO 4 and CaSO 4 ; and CuSO 4 added to sinkhole ponds (farm ponds) to control algal growth. Gypsum and anhydrite have been found in cores that intersected the northern half of the St. Louis Limestone formation in southern Illinois (Saxby and Lamar 1957). Although only small occurrences of these evaporites have been identi ed in cores from boreholes located in St. Clair County (Saxby and Lamar 1957), their presence could explain the elevated concentrations of SO 4 2 in samples from Falling and Sparrow Creek Springs and their slightly differ ent trend in Figure 6. Pyrite nodules and pyrite crystal clusters are also present near the top of the St. Louis Limestone along discrete bedding planes (Z. Lasemi, ISGS, personal communications 1999); once oxi dized, pyrite could contribute SO 4 2 to inltrating water. The DOC in water samples from the springs in the sinkhole plain ranged from 1.7 to 13.8 mg/L. These concen trations are generally higher than those typical for groundwater, which Table 6 Field parameters and total alkalinity for water samples collected from springs in the study area. Tot. Alk. Date Temp. Eh 1 Sp. Cond. (mg Sample sampled Spring (C) pH (mV) (S/cm) CaCO 3 /L) Fall 1998 IG-1T 11/19 Falling, top 12.6 8.1 496 766 321 IG-1B 11/19 Falling, bottom 12.8 8.1 475 770 323 IG-2 11/19 Sparrow Creek 13.5 7.3 506 624 243 IG-3 11/19 Collier 13.7 7.3 448 471 200 IG-4 11/19 Indian Hole 13.9 7.2 455 481 182 IG-5 11/19 Sensel 14.0 6.9 460 611 272 IG-6 11/19 Illinois Caverns 13.3 8.2 485 554 229 IG-7 11/19 Kelly 12.8 8.0 472 663 245 IG-8 11/19 Camp Vandeventer 13.6 8.0 483 543 238 IG-9 11/19 Auctioneer 12.7 8.1 460 591 279 Winter 1999 IG-1AT 03/04 Falling, top -2 ---323 IG-1AB 03/04 Falling, bottom 11.6 7.8 451 688 304 IG-2A 02/19 Sparrow Creek 12.0 7.3 462 572 219 IG-3A 02/19 Collier 12.4 7.4 436 521 228 IG-4A 02/19 Indian Hole 11.2 7.7 450 467 186 IG-5A 02/19 Sensel 14.0 6.8 476 605 273 IG-6A 02/19 Illinois Caverns 12.3 7.9 456 535 209 IG-7A 02/19 Kelly 9.1 7.8 481 616 213 IG-8A 02/19 Camp Vandeventer 11.8 7.8 461 476 200 IG-9A 02/19 Auctioneer 11.9 7.8 438 547 254 IG-10A 03/04 Frog 12.3 7.7 -620 253 Spring 1999 IG-1BT 05/18 Falling, top 13.0 7.9 -814 364 IG-1BB 05/18 Falling, bottom 13.2 8.0 476 806 351 IG-2B 05/18 Sparrow Creek 13.3 7.0 456 734 287 IG-3B 05/18 Collier 13.6 7.2 513 523 237 IG-4B 05/18 Indian Hole 13.9 7.6 508 527 233 IG-5B 05/18 Sensel 14.0 7.8 508 604 290 IG-6B 05/18 Illinois Caverns 13.5 7.7 492 573 240 IG-7B 05/18 Kelly 14.4 7.6 492 694 246 IG-8B 05/18 Camp Vandeventer 13.5 7.5 430 588 267 IG-9B 05/18 Auctioneer 13.2 7.7 467 626 314 IG-10B 05/18 Frog 13.3 7.2 485 650 288 (continued)

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Illinois State Geological Survey Circular 570 13 Table 6 (continued) Field parameters and total alkalinity for water samples col lected from springs in the study area. Tot. Alk. Date Temp. 1 Eh Sp. Cond. (mg Sample sampled Spring (C) pH (mV) (S/cm) CaCO 3 /L) Summer 1999 IG-1CT 08/23 Falling, top 14.2 7.9 383 823 367 IG-1CB 08/23 Falling, bottom 15.0 8.1 336 802 365 IG-2C 08/24 Sparrow Creek 13.5 7.0 414 733 295 IG-3C 08/24 Collier 14.8 7.1 418 506 229 IG-4C 08/24 Indian Hole 16.1 7.2 438 438 190 IG-5C 08/24 Sensel 13.9 7.0 452 610 280 IG-6C 08/24 Illinois Caverns 13.4 7.5 421 577 239 IG-7C 08/24 Kelly 15.2 7.6 425 694 262 IG-8C 08/24 Camp Vandeventer 14.2 7.6 420 622 282 IG-9C 08/24 Auctioneer 13.9 8.0 379 628 295 IG-10C 08/24 Frog 13.9 7.2 432 647 283 Fall 1999 IG-1DT 11/17 Falling, top 12.1 8.1 421 770 357 IG-1DB 11/17 Falling, bottom 11.4 8.2 392 745 318 IG-2D 11/17 Sparrow Creek 12.4 7.3 425 754 320 IG-3D 11/17 Collier 13.4 7.4 405 620 301 IG-4D 11/17 Indian Hole 13.4 7.2 463 629 271 IG-5D 11/17 Sensel 14.2 6.9 485 587 279 IG-6D 11/17 Illinois Caverns 13.2 8.2 442 525 221 IG-7D 11/17 Kelly 13.3 8.1 451 730 289 IG-8D 11/17 Camp Vandeventer 13.4 7.9 443 452 198 IG-9D 11/17 Auctioneer 12.7 8.0 410 575 272 IG-10D 11/17 Frog 13.2 7.5 442 638 288 Winter 2000 IG-1ET 03/07 Falling, top 12.8 8.0 459 710 326 IG-1EB 03/07 Falling, bottom 12.6 8.1 450 700 332 IG-2E 03/07 Sparrow Creek 13.1 7.3 455 555 201 IG-3E 03/07 Collier 12.9 7.1 444 386 156 IG-4E 03/07 Indian Hole 12.4 7.2 464 478 191 IG-5E 03/07 Sensel 14.1 6.7 486 597 282 IG-6E 03/07 Illinois Caverns 13.1 7.9 472 555 237 IG-7E 03/07 Kelly 11.8 7.8 468 777 221 IG-8E 03/07 Camp Vandeventer 13.2 8.0 452 555 248 IG-9E 03/07 Auctioneer 12.9 7.9 449 563 269 IG-10E 03/07 Frog 13.1 7.6 508 635 285 1 Temp., temperature; Eh, redox potential; Sp. Cond., specic conductivity; Tot. Alk., total alkalinity. 2 --, not determined. Nitrate-N concentrations for the springs ranged from 1.74 to 7.48 mg of N/L. These concentrations are less than 10 mg of N/L, the USEPAs (1992) regulatory standard for drink ing water, but typically greater than 2 mg of N/L, the threshold for back ground NO 3 concentrations (Panno et al. 2003). Thus, one or more of the sources discussed previously have contributed NO 3 to the ow system. The NO 3 concentrations for the dif ferent springs tended to cluster and are without a consistent seasonal trend (Figure 7). Atrazine typically was detected during the springtime and summer sampling events. During the fall and winter sampling events, atrazine was usually less than detection limits (Table 7). Because atrazine is applied only during the spring, it follows that a portion of it was mobilized and rapidly incorporated into the shallow karst aquifer during rainfall events, as has been observed by Panno et al. (1996). These results attest to the rapid inux of surface water into the shallow groundwater of a karst system. Spring Samples: Bacterial Composition Bacterial colonies present in water samples from the springs included coliforms, fecal coliforms, fecal enterococci, and bacteria common to soil and aqueous environments. The bacterial counts were usually greater than 3 10 6 cfu for total aerobic bacte ria, from 1 to more than 4,800 cfu for total coliforms, from 0 to more than 2,400 cfu for fecal coliforms (FC), and from 0 to more than 4,800 for fecal enterococci (Table 8). Many of the species are opportunistic patho gens and are typical of those found in springs throughout the sinkhole plain (Panno et al. 1996). For com parison, Illinois water quality regula tions require that waters suitable for primary contact (intimate contact with water such as swimming) must not exceed 200 cfu FC for a geometric mean of a minimum of ve samples collected during a period of 30 days or less between May and October. Ten percent of the samples cannot exceed usually contains less than 2 mg/L of DOC (Drever 1997). Falling, Spar row Creek, Collier, Indian Hole, and Kelly Springs contained consistently greater DOC for each sampling event than did the remaining springs (Table 7). The DOC concentrations for all springs were more consistent with the DOC concentrations detected in surface water samples (2 to 15 mg/L) (Degens 1982) than those in groundwater samples. The DOC in groundwater is usually derived from the organic-rich layer in soils (Drever 1997) and plays an important role in NO 3 reduction as an electron donor (Appelo and Postma 1994). High DOC concentrations could be associated with agricultural activities (Cane and Clark 1999), septic systems (Clark and Fritz 1997), or both. Many of the springs sampled for this study are resurgent cave streams that receive surface runoff through sinkholes and associated macropores of the karst terrane, and the chemical composi tion of the springs would be expected to have some characteristics similar to those of surface streams.

PAGE 22

14 Circular 570 Illinois State Geological Survey Table 7 Chemical results (mg/L) for water samples collected from springs in the study area. Atrazine Sample Ca 2+ Mg 2+ Na + K + HCO 3 Cl SO 4 2 NO 3 -N SiO 2 Al B Ba F Fe Mn Sr 2+ Zn DOC 1 (g/L) Fall 1998 IG-1T 119 28.7 20.9 <1 392 12.3 77.2 3.47 30.6 0.04 0.03 0.10 0.17 <0.01 0.01 0.22 <0.01 12.3 -2 IG-1B 118 28.6 20.9 <1 394 12.4 73.8 3.50 30.4 0.03 0.05 0.09 0.17 <0.01 0.01 0.22 <0.01 13.8 <0.10 IG-2 93.3 17.1 21.9 5 296 17.0 52.5 3.64 22.7 0.05 0.03 0.09 0.13 0.03 0.05 0.21 <0.01 11.0 <0.10 IG-3 75.1 10.5 15.0 4 244 9.9 21.8 3.98 19.1 0.04 <0.01 0.10 0.11 0.02 <0.01 0.19 <0.01 11.1 <0.10 IG-4 68.9 12.4 21.0 4 222 11.9 38.2 4.25 16.0 0.04 <0.01 0.09 0.12 0.03 0.05 0.19 <0.01 11.2 <0.10 IG-5 105 11.0 26.6 <1 332 8.9 28.1 5.16 32.9 <0.02 <0.01 0.07 0.09 <0.01 <0.01 0.16 <0.01 8.8 <0.10 IG-6 91.7 11.1 22.3 <1 279 15.2 25.4 6.65 21.4 0.03 <0.01 0.08 0.08 <0.01 <0.01 0.18 <0.01 7.7 <0.10 IG-7 80.9 20.4 45.4 5 299 20.5 69.4 4.68 14.8 0.03 0.03 0.09 0.13 0.01 0.01 0.20 <0.01 12.0 <0.10 IG-8 83.4 14.4 21.5 2 290 12.2 31.7 2.86 19.5 0.05 <0.01 0.08 0.1 <0.01 0.02 0.19 <0.01 10.8 <0.10 IG-9 105 13.9 16.4 <1 340 8.2 22.0 5.12 33.8 <0.02 0.02 0.08 0.13 <0.01 0.02 0.18 <0.01 9.3 <0.10 Winter 1999 IG-1AT 113 26.5 20.2 3 394 11.3 60.8 2.89 30.0 0.02 0.02 0.09 0.22 <0.01 0.04 0.22 <0.01 11.2 -IG-1AB 111 26.1 19.9 3 371 11.3 57.6 2.86 29.5 0.04 0.03 0.09 0.22 <0.01 0.04 0.22 <0.01 11.1 <0.10 IG-2A 98.7 16.6 22.3 <1 267 15.4 54.9 3.56 23.7 <0.01 <0.02 0.09 0.18 <0.01 0.05 0.20 <0.01 11.1 <0.10 IG-3A 99.7 10.6 17.3 <1 278 8.4 26.6 3.50 24.4 <0.01 <0.02 0.10 0.13 <0.01 0.02 0.20 <0.01 10.9 <0.10 IG-4A 79.3 12.3 21.6 <1 227 9.7 38.5 2.76 17.7 <0.01 <0.02 0.09 <0.10 <0.01 0.04 0.19 <0.01 9.9 <0.10 IG-5A 123 12.6 26.9 <1 333 9.0 27.9 4.88 36.6 <0.01 <0.02 0.08 <0.10 <0.01 <0.01 0.17 <0.01 11.9 <0.10 IG-6A 96.3 11.4 23.0 <1 255 16.1 27.5 7.08 22.7 <0.01 <0.02 0.09 0.11 <0.01 0.02 0.18 <0.01 7.0 <0.10 IG-7A 88.7 20.9 42.6 <1 260 19.6 76.2 3.60 16.0 <0.01 <0.02 0.09 <0.10 <0.01 0.01 0.21 <0.01 13.1 <0.10 IG-8A 83.3 13.2 19.3 <1 244 10.7 28.7 2.97 19.3 <0.01 <0.02 0.09 0.11 <0.01 0.01 0.18 <0.01 10.3 <0.10 IG-9A 106 13.2 14.0 <1 310 7.8 22.2 4.36 32.1 <0.01 <0.02 0.09 0.18 <0.01 0.14 0.19 <0.01 11.1 <0.10 IG-10A 94.7 13.6 25.4 2.5 309 16.5 50.7 7.48 21.8 <0.01 <0.01 0.08 0.17 <0.01 0.01 0.19 0.02 9.6 -Spring 1999 IG-1BT 130 32.6 23.6 <1 444 17.5 73.4 3.07 27.0 <0.02 <0.02 0.10 0.35 <0.01 0.02 0.23 <0.01 --IG-1BB 128 32.6 23.6 <1 428 17.5 73.2 3.00 27.0 <0.02 0.05 0.10 0.35 <0.01 0.01 0.23 <0.01 7.4 0.16 IG-2B 113 20.9 29.4 3 351 24.7 67.6 4.83 21.6 <0.02 0.04 0.08 0.31 <0.01 0.03 0.22 <0.01 6.7 12.1 IG-3B 91.4 10.2 16.4 <1 289 13.6 27.8 3.91 19.1 <0.02 0.04 0.10 0.26 <0.01 0.02 0.19 <0.01 6.5 5.21 IG-4B 83.0 13.0 21.9 2.5 285 14.2 37.4 2.84 14.8 <0.02 0.025 0.09 0.28 <0.01 0.07 0.20 <0.01 6.9 1.09 IG-5B 106 10.9 25.2 <1 354 12.9 28.5 4.61 27.6 <0.02 <0.02 0.07 0.23 <0.01 <0.01 0.15 <0.01 4.2 0.11 IG-6B 95.4 11.1 24.0 <1 293 19.3 28.0 6.46 18.3 <0.02 <0.02 0.09 0.23 <0.01 0.01 0.18 <0.01 3.3 0.19 IG-7B 87.6 24.7 40.6 3 300 20.2 93.5 4.00 12.5 <0.02 <0.02 0.09 0.28 <0.01 0.01 0.22 <0.01 5.6 3.2 IG-8B 93.5 15.8 23.5 <1 326 16.4 35.0 2.89 17.4 <0.02 <0.02 0.09 0.26 <0.01 0.02 0.19 <0.01 4.9 0.21 IG-9B 113 14.1 16.7 <1 384 13.1 26.9 4.92 29.3 <0.02 <0.02 0.08 0.33 <0.01 0.02 0.18 <0.01 3.5 <0.10 IG-10B 106 14.3 24.9 <1 351 19.5 33.5 5.51 21.6 <0.02 <0.02 0.08 0.31 <0.01 0.02 0.10 <0.03 5.0 0.1 Summer 1999 IG-1CT 125 32.9 22.0 <1 447 13.9 68.0 3.29 26.7 <0.02 0.02 0.11 0.32 <0.01 0.01 0.22 <0.01 9.5 0.23 IG-1CB 121 32.3 21.7 <1 445 13.8 67.9 3.20 26.5 <0.02 <0.02 0.10 0.34 <0.01 0.01 0.22 <0.01 7.2 -IG-2C 114 21.8 25.6 <1 360 18.7 58.8 -22.7 0.04 <0.02 0.10 0.27 <0.01 0.05 0.23 <0.01 9.1 0.14 IG-3C 85.4 10.3 13.3 <1 280 13.4 19.8 3.44 17.8 <0.02 0.02 0.12 0.23 <0.01 0.03 0.21 <0.01 7.8 1.4 IG-4C 65.4 11.2 16.0 <1 232 10.1 25.7 2.28 10.9 <0.02 <0.02 0.10 0.26 <0.01 0.14 0.18 <0.01 7.6 1.76 IG-5C 103 10.8 25.1 <1 341 11.2 26.1 4.67 27.8 <0.02 <0.02 0.07 0.21 <0.01 <0.01 0.15 <0.01 6.5 0.12 IG-6C 91.6 11.0 22.4 <1 292 17.5 23.9 6.23 17.8 <0.02 <0.02 0.09 0.22 <0.01 <0.01 0.18 <0.01 4.5 0.11 IG-7C 86.1 21.9 41.9 <1 320 20.3 65.2 4.66 13.5 <0.02 <0.02 0.11 0.31 <0.01 0.03 0.22 <0.01 7.1 <0.10 IG-8C 96.8 16.7 23.7 <1 344 14.6 31.6 2.87 18.8 <0.02 <0.02 0.10 0.26 <0.01 0.02 0.22 <0.01 6.1 0.1 IG-9C 111 14.2 17.1 <1 360 11.6 22.6 5.48 29.7 <0.02 <0.02 0.09 0.31 <0.01 0.01 0.19 <0.01 6.0 <0.10 IG-10C 109 14.1 22.7 <1 345 16.0 26.8 6.03 23.1 <0.02 <0.02 0.09 0.31 <0.01 0.01 0.2 <0.01 5.2 0.19 Fall 1999 IG-1DT 113 31.2 17.4 2 436 10.1 67.1 3.07 24.4 0.04 <0.02 0.08 0.25 <0.01 0.01 0.19 <0.01 5.0 <0.10 IG-1DB 111 31.5 18.5 3 388 10.2 66.7 3.06 24.6 0.03 <0.02 0.08 0.24 <0.01 <0.01 0.20 <0.01 5.9 <0.10 IG-2D 110 21.7 22.0 3 390 17.6 60.8 4.12 20.7 0.04 0.02 0.07 0.22 <0.01 0.02 0.20 <0.01 5.0 <0.10 IG-3D 97.6 13.5 16.8 3 367 9.3 20.7 3.60 18.1 <0.02 <0.02 0.09 0.19 <0.01 0.02 0.21 <0.01 4.4 <0.10 IG-4D 81.7 18.3 24.4 2 331 12.3 46.6 2.80 14.3 <0.02 <0.02 0.09 0.23 <0.01 0.03 0.23 <0.01 3.5 0.14 IG-5D 95.2 9.68 18.9 <1 340 7.3 20.8 4.20 25.0 <0.02 <0.02 0.05 0.11 <0.01 <0.01 0.13 <0.01 3.4 <0.10 IG-6D 79.1 10.1 17.3 3 270 14.7 19.1 6.00 16.3 <0.02 <0.02 0.06 0.12 <0.01 <0.01 0.14 <0.01 2.1 <0.10 IG-7D 84.3 22.8 36.4 4 353 19.3 73.4 3.30 12.2 0.03 <0.02 0.07 0.18 <0.01 0.01 0.18 <0.01 4.3 0.11 IG-8D 64.1 11.8 13.1 4 242 8.6 25.1 1.74 12.6 0.03 0.02 0.06 0.19 <0.01 0.03 0.14 <0.01 7.0 <0.10 IG-9D 92.6 13.3 14.4 2 332 7.9 18.2 5.55 27.2 <0.02 <0.02 0.06 0.22 <0.01 <0.01 0.14 <0.01 2.1 <0.10 IG-10D 99.5 13.0 18.9 3 351 12.7 23.3 5.57 20.5 <0.02 <0.02 0.06 0.22 <0.01 0.01 0.16 <0.01 1.7 <0.10 Winter 2000 IG-1ET 112 29.5 19.9 <2 398 11.9 53.4 2.95 24.2 0.02 0.04 0.09 0.26 0.02 0.014 0.223 <0.001 8.1 <0.10 IG-1EB 111 29.5 20.1 <2 405 11.9 53.3 2.83 24.2 0.04 0.04 0.09 0.29 <0.01 0.014 0.223 <0.001 9.8 <0.10 IG-2E 74.5 16.2 21.6 7 245 17.6 39.1 3.27 15.9 0.02 0.03 0.08 0.24 0.02 0.005 0.179 <0.001 12.0 <0.10 IG-3E 60.1 10.0 12.8 4 190 6.5 20.3 4.39 14.8 0.06 0.01 0.08 0.17 0.05 0.006 0.169 0.003 11.2 <0.10 IG-4E 67.6 13.9 22.9 <2 233 9.4 32.2 3.86 12.3 0.02 <0.01 0.08 0.21 0.02 0.019 0.197 <0.001 11.4 <0.10 IG-5E 103 10.9 26.2 <2 344 7.6 20.5 4.27 28.2 0.02 <0.01 0.07 0.12 <0.01 <0.001 0.154 0.003 6.9 <0.10 IG-6E 91.7 12.0 23.4 <2 289 14.2 18.7 6.21 18.4 0.03 <0.01 0.08 0.12 <0.01 <0.001 0.190 <0.001 5.9 <0.10 IG-7E 76.0 21.6 48.7 3 270 22.6 76.9 5.07 8.9 0.03 <0.01 0.08 0.19 0.03 0.003 0.196 <0.001 10.9 <0.10 IG-8E 86.8 16.8 23.3 <2 303 12.5 28.3 2.41 16.5 0.02 <0.01 0.08 0.17 <0.01 0.007 0.207 <0.001 8.8 <0.10 IG-9E 99.8 15.8 17.9 <2 328 8.3 17.5 5.07 29.7 0.02 <0.01 0.08 0.23 <0.01 0.004 0.180 <0.001 6.7 <0.10 IG-10E 108 15.8 24.8 <2 348 15.0 22.8 4.78 22.0 0.02 <0.01 0.08 0.24 <0.01 0.005 0.198 0.005 6.6 <0.10 1 DOC, dissolved organic carbon. 2 --, not determined.

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Illinois State Geological Survey Circular 570 15 groundwater basin populated only by wildlife near Mammoth Cave in Kentucky, the mean was 67 cfu FC/L, and the maximum was about 300 cfu FC/L (Meiman 1993). Given that 1 g of feces contains tens of millions to tens of billions of FC bacteria (Feachem et al. 1983), their presence in spring water, as noted by Meiman (1993), was expected. As a comparison, weekly water samples from two springs Table 7 Chemical results (mg/L) for water samples collected from springs in the study area. Atrazine Sample Ca 2+ Mg 2+ Na + K + HCO 3 Cl SO 4 2 NO 3 -N SiO 2 Al B Ba F Fe Mn Sr 2+ Zn DOC 1 (g/L) Fall 1998 IG-1T 119 28.7 20.9 <1 392 12.3 77.2 3.47 30.6 0.04 0.03 0.10 0.17 <0.01 0.01 0.22 <0.01 12.3 -2 IG-1B 118 28.6 20.9 <1 394 12.4 73.8 3.50 30.4 0.03 0.05 0.09 0.17 <0.01 0.01 0.22 <0.01 13.8 <0.10 IG-2 93.3 17.1 21.9 5 296 17.0 52.5 3.64 22.7 0.05 0.03 0.09 0.13 0.03 0.05 0.21 <0.01 11.0 <0.10 IG-3 75.1 10.5 15.0 4 244 9.9 21.8 3.98 19.1 0.04 <0.01 0.10 0.11 0.02 <0.01 0.19 <0.01 11.1 <0.10 IG-4 68.9 12.4 21.0 4 222 11.9 38.2 4.25 16.0 0.04 <0.01 0.09 0.12 0.03 0.05 0.19 <0.01 11.2 <0.10 IG-5 105 11.0 26.6 <1 332 8.9 28.1 5.16 32.9 <0.02 <0.01 0.07 0.09 <0.01 <0.01 0.16 <0.01 8.8 <0.10 IG-6 91.7 11.1 22.3 <1 279 15.2 25.4 6.65 21.4 0.03 <0.01 0.08 0.08 <0.01 <0.01 0.18 <0.01 7.7 <0.10 IG-7 80.9 20.4 45.4 5 299 20.5 69.4 4.68 14.8 0.03 0.03 0.09 0.13 0.01 0.01 0.20 <0.01 12.0 <0.10 IG-8 83.4 14.4 21.5 2 290 12.2 31.7 2.86 19.5 0.05 <0.01 0.08 0.1 <0.01 0.02 0.19 <0.01 10.8 <0.10 IG-9 105 13.9 16.4 <1 340 8.2 22.0 5.12 33.8 <0.02 0.02 0.08 0.13 <0.01 0.02 0.18 <0.01 9.3 <0.10 Winter 1999 IG-1AT 113 26.5 20.2 3 394 11.3 60.8 2.89 30.0 0.02 0.02 0.09 0.22 <0.01 0.04 0.22 <0.01 11.2 -IG-1AB 111 26.1 19.9 3 371 11.3 57.6 2.86 29.5 0.04 0.03 0.09 0.22 <0.01 0.04 0.22 <0.01 11.1 <0.10 IG-2A 98.7 16.6 22.3 <1 267 15.4 54.9 3.56 23.7 <0.01 <0.02 0.09 0.18 <0.01 0.05 0.20 <0.01 11.1 <0.10 IG-3A 99.7 10.6 17.3 <1 278 8.4 26.6 3.50 24.4 <0.01 <0.02 0.10 0.13 <0.01 0.02 0.20 <0.01 10.9 <0.10 IG-4A 79.3 12.3 21.6 <1 227 9.7 38.5 2.76 17.7 <0.01 <0.02 0.09 <0.10 <0.01 0.04 0.19 <0.01 9.9 <0.10 IG-5A 123 12.6 26.9 <1 333 9.0 27.9 4.88 36.6 <0.01 <0.02 0.08 <0.10 <0.01 <0.01 0.17 <0.01 11.9 <0.10 IG-6A 96.3 11.4 23.0 <1 255 16.1 27.5 7.08 22.7 <0.01 <0.02 0.09 0.11 <0.01 0.02 0.18 <0.01 7.0 <0.10 IG-7A 88.7 20.9 42.6 <1 260 19.6 76.2 3.60 16.0 <0.01 <0.02 0.09 <0.10 <0.01 0.01 0.21 <0.01 13.1 <0.10 IG-8A 83.3 13.2 19.3 <1 244 10.7 28.7 2.97 19.3 <0.01 <0.02 0.09 0.11 <0.01 0.01 0.18 <0.01 10.3 <0.10 IG-9A 106 13.2 14.0 <1 310 7.8 22.2 4.36 32.1 <0.01 <0.02 0.09 0.18 <0.01 0.14 0.19 <0.01 11.1 <0.10 IG-10A 94.7 13.6 25.4 2.5 309 16.5 50.7 7.48 21.8 <0.01 <0.01 0.08 0.17 <0.01 0.01 0.19 0.02 9.6 -Spring 1999 IG-1BT 130 32.6 23.6 <1 444 17.5 73.4 3.07 27.0 <0.02 <0.02 0.10 0.35 <0.01 0.02 0.23 <0.01 --IG-1BB 128 32.6 23.6 <1 428 17.5 73.2 3.00 27.0 <0.02 0.05 0.10 0.35 <0.01 0.01 0.23 <0.01 7.4 0.16 IG-2B 113 20.9 29.4 3 351 24.7 67.6 4.83 21.6 <0.02 0.04 0.08 0.31 <0.01 0.03 0.22 <0.01 6.7 12.1 IG-3B 91.4 10.2 16.4 <1 289 13.6 27.8 3.91 19.1 <0.02 0.04 0.10 0.26 <0.01 0.02 0.19 <0.01 6.5 5.21 IG-4B 83.0 13.0 21.9 2.5 285 14.2 37.4 2.84 14.8 <0.02 0.025 0.09 0.28 <0.01 0.07 0.20 <0.01 6.9 1.09 IG-5B 106 10.9 25.2 <1 354 12.9 28.5 4.61 27.6 <0.02 <0.02 0.07 0.23 <0.01 <0.01 0.15 <0.01 4.2 0.11 IG-6B 95.4 11.1 24.0 <1 293 19.3 28.0 6.46 18.3 <0.02 <0.02 0.09 0.23 <0.01 0.01 0.18 <0.01 3.3 0.19 IG-7B 87.6 24.7 40.6 3 300 20.2 93.5 4.00 12.5 <0.02 <0.02 0.09 0.28 <0.01 0.01 0.22 <0.01 5.6 3.2 IG-8B 93.5 15.8 23.5 <1 326 16.4 35.0 2.89 17.4 <0.02 <0.02 0.09 0.26 <0.01 0.02 0.19 <0.01 4.9 0.21 IG-9B 113 14.1 16.7 <1 384 13.1 26.9 4.92 29.3 <0.02 <0.02 0.08 0.33 <0.01 0.02 0.18 <0.01 3.5 <0.10 IG-10B 106 14.3 24.9 <1 351 19.5 33.5 5.51 21.6 <0.02 <0.02 0.08 0.31 <0.01 0.02 0.10 <0.03 5.0 0.1 Summer 1999 IG-1CT 125 32.9 22.0 <1 447 13.9 68.0 3.29 26.7 <0.02 0.02 0.11 0.32 <0.01 0.01 0.22 <0.01 9.5 0.23 IG-1CB 121 32.3 21.7 <1 445 13.8 67.9 3.20 26.5 <0.02 <0.02 0.10 0.34 <0.01 0.01 0.22 <0.01 7.2 -IG-2C 114 21.8 25.6 <1 360 18.7 58.8 -22.7 0.04 <0.02 0.10 0.27 <0.01 0.05 0.23 <0.01 9.1 0.14 IG-3C 85.4 10.3 13.3 <1 280 13.4 19.8 3.44 17.8 <0.02 0.02 0.12 0.23 <0.01 0.03 0.21 <0.01 7.8 1.4 IG-4C 65.4 11.2 16.0 <1 232 10.1 25.7 2.28 10.9 <0.02 <0.02 0.10 0.26 <0.01 0.14 0.18 <0.01 7.6 1.76 IG-5C 103 10.8 25.1 <1 341 11.2 26.1 4.67 27.8 <0.02 <0.02 0.07 0.21 <0.01 <0.01 0.15 <0.01 6.5 0.12 IG-6C 91.6 11.0 22.4 <1 292 17.5 23.9 6.23 17.8 <0.02 <0.02 0.09 0.22 <0.01 <0.01 0.18 <0.01 4.5 0.11 IG-7C 86.1 21.9 41.9 <1 320 20.3 65.2 4.66 13.5 <0.02 <0.02 0.11 0.31 <0.01 0.03 0.22 <0.01 7.1 <0.10 IG-8C 96.8 16.7 23.7 <1 344 14.6 31.6 2.87 18.8 <0.02 <0.02 0.10 0.26 <0.01 0.02 0.22 <0.01 6.1 0.1 IG-9C 111 14.2 17.1 <1 360 11.6 22.6 5.48 29.7 <0.02 <0.02 0.09 0.31 <0.01 0.01 0.19 <0.01 6.0 <0.10 IG-10C 109 14.1 22.7 <1 345 16.0 26.8 6.03 23.1 <0.02 <0.02 0.09 0.31 <0.01 0.01 0.2 <0.01 5.2 0.19 Fall 1999 IG-1DT 113 31.2 17.4 2 436 10.1 67.1 3.07 24.4 0.04 <0.02 0.08 0.25 <0.01 0.01 0.19 <0.01 5.0 <0.10 IG-1DB 111 31.5 18.5 3 388 10.2 66.7 3.06 24.6 0.03 <0.02 0.08 0.24 <0.01 <0.01 0.20 <0.01 5.9 <0.10 IG-2D 110 21.7 22.0 3 390 17.6 60.8 4.12 20.7 0.04 0.02 0.07 0.22 <0.01 0.02 0.20 <0.01 5.0 <0.10 IG-3D 97.6 13.5 16.8 3 367 9.3 20.7 3.60 18.1 <0.02 <0.02 0.09 0.19 <0.01 0.02 0.21 <0.01 4.4 <0.10 IG-4D 81.7 18.3 24.4 2 331 12.3 46.6 2.80 14.3 <0.02 <0.02 0.09 0.23 <0.01 0.03 0.23 <0.01 3.5 0.14 IG-5D 95.2 9.68 18.9 <1 340 7.3 20.8 4.20 25.0 <0.02 <0.02 0.05 0.11 <0.01 <0.01 0.13 <0.01 3.4 <0.10 IG-6D 79.1 10.1 17.3 3 270 14.7 19.1 6.00 16.3 <0.02 <0.02 0.06 0.12 <0.01 <0.01 0.14 <0.01 2.1 <0.10 IG-7D 84.3 22.8 36.4 4 353 19.3 73.4 3.30 12.2 0.03 <0.02 0.07 0.18 <0.01 0.01 0.18 <0.01 4.3 0.11 IG-8D 64.1 11.8 13.1 4 242 8.6 25.1 1.74 12.6 0.03 0.02 0.06 0.19 <0.01 0.03 0.14 <0.01 7.0 <0.10 IG-9D 92.6 13.3 14.4 2 332 7.9 18.2 5.55 27.2 <0.02 <0.02 0.06 0.22 <0.01 <0.01 0.14 <0.01 2.1 <0.10 IG-10D 99.5 13.0 18.9 3 351 12.7 23.3 5.57 20.5 <0.02 <0.02 0.06 0.22 <0.01 0.01 0.16 <0.01 1.7 <0.10 Winter 2000 IG-1ET 112 29.5 19.9 <2 398 11.9 53.4 2.95 24.2 0.02 0.04 0.09 0.26 0.02 0.014 0.223 <0.001 8.1 <0.10 IG-1EB 111 29.5 20.1 <2 405 11.9 53.3 2.83 24.2 0.04 0.04 0.09 0.29 <0.01 0.014 0.223 <0.001 9.8 <0.10 IG-2E 74.5 16.2 21.6 7 245 17.6 39.1 3.27 15.9 0.02 0.03 0.08 0.24 0.02 0.005 0.179 <0.001 12.0 <0.10 IG-3E 60.1 10.0 12.8 4 190 6.5 20.3 4.39 14.8 0.06 0.01 0.08 0.17 0.05 0.006 0.169 0.003 11.2 <0.10 IG-4E 67.6 13.9 22.9 <2 233 9.4 32.2 3.86 12.3 0.02 <0.01 0.08 0.21 0.02 0.019 0.197 <0.001 11.4 <0.10 IG-5E 103 10.9 26.2 <2 344 7.6 20.5 4.27 28.2 0.02 <0.01 0.07 0.12 <0.01 <0.001 0.154 0.003 6.9 <0.10 IG-6E 91.7 12.0 23.4 <2 289 14.2 18.7 6.21 18.4 0.03 <0.01 0.08 0.12 <0.01 <0.001 0.190 <0.001 5.9 <0.10 IG-7E 76.0 21.6 48.7 3 270 22.6 76.9 5.07 8.9 0.03 <0.01 0.08 0.19 0.03 0.003 0.196 <0.001 10.9 <0.10 IG-8E 86.8 16.8 23.3 <2 303 12.5 28.3 2.41 16.5 0.02 <0.01 0.08 0.17 <0.01 0.007 0.207 <0.001 8.8 <0.10 IG-9E 99.8 15.8 17.9 <2 328 8.3 17.5 5.07 29.7 0.02 <0.01 0.08 0.23 <0.01 0.004 0.180 <0.001 6.7 <0.10 IG-10E 108 15.8 24.8 <2 348 15.0 22.8 4.78 22.0 0.02 <0.01 0.08 0.24 <0.01 0.005 0.198 0.005 6.6 <0.10 1 DOC, dissolved organic carbon. 2 --, not determined. 400 cfu FC/100 mL (Illinois Environ mental Protection Agency, Illinois Pollution Control Board 1999). The quality of the water owing through the karst aquifers of south western Illinois is similar to that of springs and caves in other karst environments. For 19 samples col lected in 1990 and 1991 from Buffalo Creek Spring, which drains a pristine Fr og Illinois Ca ve rn s Sparro w Creek Collier Indian Hole Ke lly Camp V ande v enter Fa lling Spri ngs Sensel .0 0.0 .5 0.5 1.0 1.5 Sl Calcite 11/19/98 2/19/99 5/18/99 8/23/99 1/17/99 3/7/900Au ctioneerUndersaturated Supersaturated Figure 2 Saturation indices for each spring sampled from fall 1998 through winter 2000. The zero line marks the boundary between undersaturation and supersaturation (modified from Panno et al., 2001). 9 11 13 15 17 Temperature ( C)Sparro w C ree k Collier Indian Hole Sensel Illinois Ca v er ns Ke ll y Camp Va ndev e nter Au ctioneer Fr og Fa l ling (top ) Fa lling (bot.) Fa ll 98 Winter 99 Spr ing 99 Summer 99 Fa ll 99 Winter 00 Figure 3 Temperature of each spring sampled for six con secutive seasons.

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16 Circular 570 Illinois State Geological Survey IG-1 IG-2 IG-3 IG-4 IG-5 IG-6 IG-7 IG-8 IG-9 IG-10 1:1 Cl:Na 20 30 40 50 60 Cl (mg/L)0 10 10 20 30 40 50 Na+ (mg/L) Figure 4 Chloride and sodium concentrations of all spring samples showing trends and distinct differences among the individual springs. Kelly Spring (IG-7) is well separated from the other springs. 0.05 0.1 0.15 0.2 0.25 0.3 0.35 F (mg/L) 11/19/98 2/19/99 3/4/99 5/18/99 8/23/99 11/17/99 3/7/00Sampling date 1 1B 3 4 5 6 8 1B 10 1T 1B 3 5, 6 8 91 T 1B 2 3 5 6 1T 1B 2 3, 8 4 5 6 1T 1B 2 4 9 2 ,7, 9 2, 10 4, 7 7, 9, 10 4, 8 7, 9, 10 7, 10 5, 6 3, 8 1T 2, 9 6, 8 3 Figure 5 Seasonal variation of fluoride in spring samples. Note increase in fluoride for spring and summer sampling events. Springs are identified according to numbers in Table 7 (1 and 1.5 refer to Falling Springs, top and bottom). 1 1.5 2 2.5 3 3.5 Ca2+ (mmol/L)0.5 0 0.2 0.4 0.6 0.8 1 SO4 2 (mmol/L) Fa lling Sparro w Creek Collier Indian Hole Sensel IL Ca ve rn s Ke lly Camp V and. A uctioneer F rog Runoff Figure 6 Calcium and sulfate concentrations for spring samples and runoff. Kelly Spring, Sparrow Creek, and Falling Springs show larger sulfate concentrations than do the rest of the springs. 0 1 2 3 4 5 6 7 8 NO3 (mg/L) 1 2 3 4 5 6 7 8 9 10 Spr ing IG number F rog Illinois Ca ve rn s Fa lling To p, Bottom Sparro w Creek Collier Indian Hole Ke lly Camp Va ndev enter A uctioneer Sensel F all 98 Winter 99 Spr ing 99 Summer 99 Fa ll 99 Winter 00 Figure 7 Nitrate concentrations of the spring samples over six consecutive seasons. The upper boundary for back ground concentration of NO 3 about 2.0 mg of N/L (Panno et al. 2003), is shown by the horizontal line.

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Illinois State Geological Survey Circular 570 17 that drain groundwater basins used for animal grazing in West Virginia yielded 0 to 1,434 cfu FC/L; mean concentrations were 101 and 139 cfu FC/L (Pasquarell and Boyer 1995). In a similar setting in Kentucky, ood pulses in springs have been shown to contain a short-term increase in FC and associated turbidity (Ryan and Meiman 1996). The effects of ooding on the water quality of springs in the present study are apparent in the ele vation of FC, fecal streptococci (FS), and fecal enterococci concentrations during the spring and early fall when abundant rainfall and surface runoff (into sinkholes) are most prevalent. Except for Sensel Spring, the bacte rial species isolated from the spring samples in the study area were almost identical and included between 10 and 15 genera and species (Table 9). The four most dominant bacteria, Bacillus spp., Pseudomonas spp., Klebsiella pneumoniae and Serratia spp., were typically present in over 90% of the spring samples. These bacteria are ubiquitous in the natu ral environment. Bacillus spp. and Pseudomonas spp. are especially associated with the soil zone and are classied as opportunistic pathogens by Geldreich (1996). Also present in about 90% of the spring samples, but ranking lower, were Enterococ cus faecium, Enterococcus faecalis, and Escherichia coli These three enteric species (associated with fecal materials) suggest the inuence of livestock (animal) waste and possibly private septic systems. Ranked lower but present in some of the springs were Aeromonas hydrophila, Cit robacter spp., and, to a lesser extent, Providencia stuartii and Proteus spp. Aeromonas hydrophila is commonly associated with cold-blooded verte brates (e.g., amphibians) (Freeman 1985). Panno et al. (1999) frequently found Aeromonas hydrophila in cave water and suggested that the species is an indicator of conduit systems of the sinkhole plain. These systems are typically greater than 1 cm in width and even larger in height, contain an air-water interface, are connected to the surface at some point, and are large enough to provide amphibian habitats. Table 8 Bacterial analyses for water samples collected from springs in the study area. 1 Total aerobic Total Fecal Fecal colonies coliforms coliforms enterococci Sample Spring (cfu /L) 1 (cfu/L) (cfu/L) (cfu/L) Fall 1998 IG-1T Falling, top -2 ---IG-1B Falling, bottom >3 10 6 >2,419 49 60 IG-2 Sparrow Creek >3 10 6 >2,419 108 104 IG-3 Collier >3 10 6 >2,419 68 136 IG-4 Indian Hole >3 10 6 >2,419 73 126 IG-5 Sensel 600 1 0 0 IG-6 Illinois Caverns 9 10 5 >2,419 59 108 IG-7 Kelly >3 10 6 >2,419 86 290 IG-8 Camp Vandeventer >3 10 6 >2,419 223 143 IG-9 Auctioneer >3 10 6 >2,419 68 116 Winter 1999 IG-1AB Falling, bottom >3 10 6 3,466 40 36 IG-2A Sparrow Creek >3 10 6 >4,800 108 1,540 IG-3A Collier >3 10 6 3,106 192 722 IG-4A Indian Hole >3 10 6 2,600 86 278 IG-5A Sensel 34 4 0 0 IG-6A Illinois Caverns >3 10 6 3,106 156 114 IG-7A Kelly >3 10 6 3,106 96 1,374 IG-8A Camp Vandeventer >3 10 6 3,972 172 222 IG-9A Auctioneer >3 10 6 1,842 220 104 IG-10A Frog ----Spring 1999 IG-1BT Falling, top IG-1BB Falling, bottom >3 10 6 2,600 86 72 IG-2B Sparrow Creek >3 10 6 >4,800 570 208 IG-3B Collier >3 10 6 >4,800 182 1,096 IG-4B Indian Hole >3 10 6 >4,800 110 552 IG-5B Sensel 1,200 86 2 10 IG-6B Illinois Caverns >29 10 3 1,960 130 210 IG-7B Kelly >3 10 6 >4,800 230 922 IG-8B Camp Vandeventer >3 10 6 2,240 186 160 IG-9B Auctioneer >3 10 6 1,454 17 334 IG-10B Frog >3 10 6 >4,800 192 216 Summer 1999 IG-1CT Falling, top 27,000 3,466 12 62 IG-1CB Falling, bottom 22,000 1,226 8 14 IG-2C Sparrow Creek 49,000 1,226 32 94 IG-3C Collier 78,000 4,838 50 368 IG-4C Indian Hole 79,000 4,800 56 146 IG-5C Sensel 900 40 0 4 IG-6C Illinois Caverns 63,000 4,838 110 400 IG-7C Kelly 71,000 >4,800 94 922 IG-8C Camp Vandeventer 97,000 >4,800 304 536 IG-9C Auctioneer 95,000 >4,800 100 518 IG-10C Frog 89,000 4,800 168 280 Fall 1999 IG-1DT Falling, top 17,000 870 14 42 IG-1DB Falling, bottom 1,430 390 8 30 IG-2D Sparrow Creek 4,700 976 62 278 IG-3D Collier 27,000 1,842 626 644 IG-4D Indian Hole 1,600 476 2 62 IG-5D Sensel 340 6 0 4 IG-6D Illinois Caverns 7,600 582 66 88 IG-7D Kelly 14,000 616 100 324 IG-8D Camp Vandeventer >3 10 6 >4,838 394 >4,838 IG-9D Auctioneer 45,000 2,600 1,632 >4,838 IG-10D Frog 120,000 3,106 2,406 >4,838 Winter 2000 IG-1ET Falling, top 5,300 976 20 118 IG-1EB Falling, bottom 4,100 1,034 8 145 IG-2E Sparrow Creek 4,900 282 20 48 IG-3E Collier 1,300 220 40 540 IG-4E Indian Hole 2,300 570 12 66 IG-5E Sensel 400 14 0 16 IG-6E Illinois Caverns 1,100 154 2 80 IG-7E Kelly 6,500 870 18 22 IG-8E Camp Vandeventer 14,000 1,034 40 128 IG-9E Auctioneer 5,700 1,226 10 140 IG-10E Frog 6,300 2,240 10 140 1 cfu, colony-forming units. 2 --, not detected.

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18 Circular 570 Illinois State Geological Survey Table 9 Bacteria (genera and species) present in springs in the study area, percentage of time the bacteria were detected in samples, and ranking based on their dominance in the groundwater samples. 1 November February May August November March Rank 1998 1999 1999 1999 1999 2000 1 Bacillus Bacillus Pseudomonas Pseudomonas Pseudomonas Bacillus 100 100 91 100 100 100 2 Pseudomonas Pseudomonas Bacillus Bacillus K. pneumoniae Pseudomonas 100 100 91 91 100 100 3 Klebsiella K. pneumoniae K. pneumoniae K. pneumoniae Serratia E. aerogenes pneumoniae 89 82 100 91 82 100 4 Serratia Serratia Serratia Serratia Enterobacter E. faecium 89 89 82 91 91 100 5 Escherichia coli A. hydrophila A. hydrophila Citrobacter E. faecium K. pneumoniae 89 89 82 82 91 63 6 Aeromonas E. coli E. faecium E. faecium E. faecalis E. coli hydrophila 89 91 91 91 91 78 7 Enterococcus E. faecium C. freundii E. faecalis Citrobacter Citrobacter faecium 89 54 91 64 54 89 8 E nterococcus P. mirabilis E. coli Staphylococcus Bacillus E. faecalis faecalis 56 82 100 91 27 89 9 Staphylococcus Citrobacter Enterobacter E. coli A. hydrophila Serratia 67 freundii cloacae 73 45 18 33 27 10 Providencia E. faecalis E. faecalis Micrococcus E. coli P. mirabilis stuartii 56 45 9 36 9 22 11 Proteus mirabilis Staphylococcus P. mirabilis Enterococcus P. mirabilis 11 aureus 45 9 18 56 12 Enterobacter P. mirabilis aerogenes 9 18 13 Enterococcus avium 18 14 S. aureus 54 15 P. stuartii 9 1 Rank was based on the bacteria that were most dominant in the water samples. Dominance was based on the largest concentration to small est concentration of bacteria genera and species present in the water samples. The number below each genera is the percent of time they were detected in the samples.

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Illinois State Geological Survey Circular 570 19 Spring Samples: Isotopic Composition As with several of the chemical con stituents, some isotopic character istics showed seasonal variations for the water samples from springs. The isotopic results (Table 10) help to improve our understanding of the geochemical evolution of the ground water in the sinkhole plain and to delineate the origin of the NO 3 in the spring water samples. 15 N and 18 O of NO 3 The 15 N and 18 O of the NO 3 from the springs ranged from +3.2 to +12.5 and from +5.1 to +21.9, respectively. Many of the 15 N and 18 O data appeared to be positively correlated (Figure 8). Figure 8 illustrates the typical areas for different NO 3 sources (Kendall et al. 1995, Clark and Fritz 1997, Mengis et al. 2001). The range of 18 O values for the NO 3 domains originating from the reduced N sources (reduced fertil izer, soil organic matter, and manure and sewage) were estimated based on the assumption that the nitrica tion process for these soils derives one-third of the oxygen from the atmosphere and two-thirds from the surrounding water. The lowest isoto pic values for the NO 3 from the spring samples clustered near the area typi cally observed for NO 3 originating primarily from mineralized fertilizer nitrogen. Values for most of the spring 1999 and winter 2000 samples plotted very close to the mineralized fertilizer domain. The isotopic values for most of the summer, fall, and winter 1999 samples are more positive. Many of the samples had isotopic values that generally followed the denitrica tion trend (arrows, Figure 8). When comparing 15 N and NO 3 concentra tions, the trend for most of the data follows a negative slope, which would be expected with denitrication pro cesses (Figure 9). However, there also appears to be a major mixing com ponent involved, as indicated by the spread of data points shown in Figure 8 and the small correlation coefcient in Figure 9; however, the correlation is also weak when 15 N is plotted versus the 1/[NO 3 ] and versus ln([NO 3 ]). Both of those relationships have been used in the literature (Mariotti et al. 1988) to help determine whether NO 3 con concentrations in the water samples from springs were certainly high enough to support the denitrication process. Several of the water samples from springs had considerably greater 18 O values of NO 3 than would be expected from denitrication alone, and these values plot well above the denitrication trajectories shown in Figure 8. The greater 18 O values suggest that (1) these samples con tained a source of NO 3 that had more of the heavy oxygen isotope ( 18 O), such as atmospheric NO 3 ; (2) during the nitrication process, a greater amount of atmospheric oxygen con tributed to the NO 3 oxygen; or (3) the 18 O of the soil zone water was greater due to evapotranspiration effects (Mayer et al. 2001, Burns and Kendall 2002). The most positive 18 O values for NO 3 were observed for the winter and summer samples. These samples also had relatively small amounts of NO 3 making them more susceptible to inuences of isotopically heavier NO 3 The source of the more positive 18 O values may have been the NO 3 of ammonium nitrate fertilizer or pos sibly atmospheric NO 3 which has very positive 18 O values. Atmospheric NO 3 can have 18 O values ranging from +20 to +75 in precipitation (Kendall et al. 1995) and can affect the NO 3 leaching through soils (Durka et al. 1994, Campbell et al. 2002). The average NO 3 -N concentration in precipitation for this area is about 0.3 0.15 mg/L (National Atmospheric Deposition Program 1998). Four precipitation samples, collected at Illinois Caverns in Monroe County, contained enough NO 3 to allow 15 N and 18 O analyses. The 18 O of the NO 3 ranged from 23.1 to 42.9 (precipitation included in Figure 10), which agrees with 18 O values of atmospheric NO 3 reported in the lit erature. As demonstrated by Mengis et al. (2001), however, the impact of larger 18 O values from nitrate fertil izer, and probably atmospheric NO 3 is typically not observed. Rapid con sumption and/or transformation of NO 3 to organic nitrogen within the soil zone and reoxidation back to NO 3 resets the 18 O value. Additionally, we would expect that the greater 18 O centration and 15 N variability was due to mixing or denitrication pro cesses, respectively. Typically, a plot of 15 N vs. 1/[NO 3 ] should yield a straight line for mix tures of two sources, whereas a plot of 15 N versus ln([NO 3 ]) will yield a linear correlation for denitrication. Thus, these types of plots did not help dif ferentiate between denitrication and mixing. We did not have 18 O and 15 N values for mineralized nitrogen fertilizer in the soil zone for the study area. However, we measured the 15 N for three fertilizers commonly used in the sinkhole plain. The mean 15 N value for these fertilizers was 0.44 (Table 5), which is within the range of lit erature values described for fertilizer nitrogen (Kendall 1998). The 18 O of NO 3 produced from reduced nitrogen, such as ammonium, can be estimated using the two-thirds groundwater one-third atmospheric O 2 assumption of Bttcher et al. (1990). The average 18 O of the groundwater sampled from the springs is 5.5, and the average 18 O for atmospheric oxygen is about +23.5 (Amberger and Schmidt 1987, Clark and Fritz 1997). Thus, the 18 O of NO 3 from NH 4 would have a value of approximately +4.2 for the sink hole plain area. This value is in very good agreement with the NO 3 mea sured from a septic system, which had enough NO 3 for us to analyze 18 O (Table 5). However, when fertilizer application for the area is considered, approximately 85% of nitrogen is applied as reduced nitrogen and 15% as ammonium nitrate (Paul Krem mell, personal communication 1999). Because half of the nitrogen of ammo nium nitrate is synthetic NO 3 which typically has a 18 O value of about +22, we added a 7.5% contribution of this isotopically heavy NO 3 to esti mate the range of 18 O composition (+4 to +5.7) for the fertilizer-derived end member (Figure 8). Assuming the diamond symbols within the mineral ized fertilizer domain of Figure 8 rep resent the average isotopic values for NO 3 in the upper soil zone, the data suggest that a considerable degree of denitrication occurred within the soil zone, epikarst, and shallow karst aquifer of the study area. The DOC

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20 Circular 570 Illinois State Geological Survey Table 10 Isotopic results by season for water samples collected from springs in the study area. 15 N NO3 18 O NO3 18 O D 13 C 34 S Tritium Sample Spring () () () () () () (TU) 1 Fall 1998 IG-1T Falling, top 6.8 8.2 6.30 39.2 12.0 0.2 -2 IG-1B Falling, bottom --6.42 41.2 11.8 0.1 -IG-2 Sparrow Creek 6.5 8.1 5.68 38.3 12.1 1.6 -IG-3 Collier 5.4 13.2 5.38 33.7 11.9 0.7 -IG-4 Indian Hole 5.8 10.5 5.32 34.0 12.0 2.1 -IG-5 Sensel 6.0 11.5 6.74 45.3 13.9 1.9 -IG-6 Illinois Caverns 5.6 5.6 6.24 44.1 10.0 2.0 -IG-7 Kelly 7.7 7.4 5.80 37.9 10.7 4.9 -IG-8 Camp Vandeventer 7.6 14.8 5.10 36.2 11.1 1.4 -IG-9 Auctioneer 5.7 8.1 6.05 39.2 10.9 2.1 -Winter 1999 IG-1AT Falling, top 3.2 7.7 3 ---0.5 -IG-1AB Falling, bottom 6.0 13.4 3 6.41 39.4 12.4 0.9 6.5 IG-2A Sparrow Creek 6.2 9.3 3 6.00 39.3 11.9 1.2 7.9 IG-3A Collier 6.4 10.1 3 6.06 40.2 11.5 0.4 4.7 IG-4A Indian Hole 9.0 21.9 3 5.91 38.0 11.1 2.0 5.6 IG-5A Sensel 7.6 8.2 3 6.33 39.7 13.9 2.0 6.8 IG-6A Illinois Caverns 10.5 10.1 3 6.33 40.4 10.6 2.2 5.7 IG-7A Kelly 12.5 13.2 3 6.06 37.7 11.0 4.2 5.4 IG-8A Camp Vendeventer 7.5 7.8 3 5.47 36.5 11.1 0.9 5.5 IG-9A Auctioneer 8.4 11.9 3 6.20 41.7 11.1 2.3 5.8 IG-10A Frog 4.6 10.7 3 ---0.5 6.8 Spring 1999 IG-1BT Falling, top --5.97 39.6 12.9 0.5 -IG-1BB Falling, bottom 5.7 7.2 3 6.15 40.2 12.6 0.8 6.2 IG-2B Sparrow Creek 3.7 7.5 3 5.81 39.6 12.3 2.4 5.9 IG-3B Collier 4.5 6.9 3 5.87 38.7 12.0 0.6 5.8 IG-4B Indian Hole 6.2 8.6 3 5.24 33.8 13.0 1.6 5.8 IG-5B Sensel 4.2 5.6 6.08 40.1 13.6 2.1 6.3 IG-6B Illinois Caverns 3.4 6.5 3 6.05 37.1 11.6 2.1 5.4 IG-7B Kelly 5.5 11.8 3 5.29 34.5 12.3 7.0 5.9 IG-8B Camp Vendeventer 5.4 8.7 3 4.78 35.6 12.1 1.8 5.6 IG-9B Auctioneer 3.5 5.5 6.06 40.8 11.8 2.2 5.6 IG-10B Frog 4.8 6.7 3 5.98 39.2 12.1 0.9 5.5 Summer 1999 IG-1CT Falling, top --6.18 40.2 13.1 0.4 -IG-1CB Falling, bottom 5.7 8.2 6.06 41.1 12.5 0.4 7.1 IG-2C Sparrow Creek 7.0 7.9 3 5.50 -13.2 2.9 5.2 IG-3C Collier 7.5 17.6 4.21 30.9 13.7 0.2 5.8 IG-4C Indian Hole 9.0 20.1 3 2.57 24.3 13.1 3.2 5.7 IG-5C Sensel 4.8 -5.56 40.0 13.6 2.0 6.5 IG-6C Illinois Caverns 3.9 7.1 3 5.25 39.2 12.5 1.9 4.9 IG-7C Kelly 7.3 8.0 3 3.60 32.1 12.0 6.5 5.6 IG-8C Camp Vandeventer 7.0 -4.34 32.2 13.5 2.9 5.3 IG-9C Auctioneer 4.3 -6.03 40.2 11.8 1.8 5.1 IG-10C Frog 5.6 8.8 3 5.07 37.7 13.1 0.8 5.5 Fall 1999 IG-1DT Falling, top 6.9 9.5 5.93 40.2 11.7 -5.9 IG-1DB Falling, bottom 7.5 7.6 3 5.96 39.9 11.4 -5.7 IG-2D Sparrow Creek 6.7 10.1 5.28 37.9 12.0 -7.8 IG-3D Collier 7.2 6.8 3 4.81 35.4 12.2 -4.8 IG-4D Indian Hole 9.7 9.9 3 4.76 36.6 10.9 -5.8 IG-5D Sensel 5.2 8.3 5.69 39.6 13.4 -6.6 IG-6D Illinois Caverns 4.6 7.2 5.99 36.8 9.3 2.1 4.9 IG-7D Kelly 8.4 10.2 4.62 34.5 10.7 6.4 4.6 IG-8D Camp Vandeventer 7.4 12.0 0.54 16.4 11.5 1.4 -(continued)

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Illinois State Geological Survey Circular 570 21 value from nitrate fertilizer would have been incorporated into the over all background value for mineralized nitrate fertilizer. However, this type of fertilizer is only applied during winter months for the winter wheat crops. Thus, plant uptake during winter would be low, and rapid throughput of the 18 O-enriched NO 3 may occur during large precipitation events or snow melts as observed by Mengis et al. (2001) on experimental plots. This scenario, plus the possibility of atmo spheric NO 3 contribution, may help explain some of the isotopically heavy 18 O values for NO 3 during some of the winter sampling events. How ever, isotopically heavy 18 O values also were observed during summer and fall sampling events, which were several months after nitrate fertilizer application, and during extensive bio logical activity. Perhaps some of the elevated 18 O values, especially those from the summer and fall sampling events, reect the inuence of 18 O enrichment of soil water by evaporation or evapo transpiration during nitrication (e.g., Burns and Kendall 2002, Mayer et al. 2001). Two of the summer sam ples from springs that had relatively large 18 O values for NO 3 also had more positive 18 O values for water (Figure 11). However, this relationship obviously needs to be investigated Table 10 (continued) Isotopic results by season for water samples collected from springs in the study area. 15 N NO3 18 O NO3 18 O D 13 C 34 S Tritium Sample Spring () () () () () () (TU) 1 IG-9D Auctioneer 5.0 11.3 5.76 40.4 10.5 1.6 5.0 IG-10D Frog 6.1 7.1 5.89 38.5 11.9 0.3 5.5 Winter 2000 IG-1ET Falling, top 7.4 7.2 3 5.86 38.9 11.4 3.1 -IG-1EB Falling, bottom 8.0 7.5 3 5.84 37.7 11.4 1.3 5.5 IG-2E Sparrow Creek 7.1 8.3 5.84 37.5 9.9 3.3 4.7 IG-3E Collier 3.5 7.8 5.70 37.6 6.6 1.8 -IG-4E Indian Hole 4.6 6.9 5.52 37.8 10.5 2.4 4.0 IG-5E Sensel 4.8 5.1 5.92 37.6 13.5 -4.7 IG-6E Illinois Caverns 4.2 5.2 6.14 38.7 9.4 -3.9 IG-7E Kelly 6.9 7.6 3 5.85 38.8 10.6 2.5 -IG-8E Camp Vandeventer 7.1 7.1 3 4.47 33.1 9.5 0.5 -IG-9E Auctioneer 4.1 6.7 3 5.88 39.2 10.0 -4.8 IG-10E Frog 5.8 5.2 5.48 37.6 10.8 -4.5 1 TU, tritium units. 2 --, not determined. 3 Standard deviation, 1.7. Figure 8 Isotopic composition of NO 3 from springs and end-member samples including fertilizers (fert.), septic systems, and livestock waste. The 18 O val ues were calculated (calc.) for the NO 3 that would be produced from reduced nitrogen sources, such as most fertilizers (urea and NH 3 ), hog waste (HW), and most septic effluent (see text for details). The arrows represent the typical trend expected for denitrification and bracket the main cluster of samples that appear to follow the denitrification trend. Isotopic ranges characteristic of different sources are also shown (general domains taken from Kendall et al. 1995, Clark and Fritz 1997, Mengis et al. 2001). S28, Solution-28. Stippled area indicates most typical 15 N values for soil organic nitrogen. Synthetic fe rt NO3 S28 & Urea S28 & Urea NW -17 septicS28-NO3 Septic/manure Soil Org Mineraliz ed fe r tiliz er F all 98 Winter 99 Spr ing 99 Summer 99 F all 99 Winter 00 End Members Red-N-f er t. (calc. 18O) NO3 -f er t. Septic (calc. 18O) HW (calc. 18O) Contaminated HW Contaminated HW (calc. 18O) Field r unoff 0 5 10 15 20 25 18O () 0 5 10 15 20 25 30 35 15N ()

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22 Circular 570 Illinois State Geological Survey 2 3 4 5 6 8 7 NO3 (mg/L)1 2 4 6 8 10 12 14 Fa lling Sparro w Creek Collier Indian Hole Sensel IL Ca ve rn s Ke lly Camp V and. A uctioneer Fr og 15N () Figure 9 Nitrate concentrations versus 15 N values for the springs. Slope for most of the samples is generally negative(r 2 = 0.4, excluding three outliers). Atmospher ic NO3RW RW RW RWSynthetic Fe rt NO3S-28-NO3S28 & Urea S28 & Urea NW -17 septic-10 -5 0 5 10 15 20 25 30 35 15N () 0 10 20 30 40 50 18O ()Septic/manureSoil Org.Mineraliz ed Fe r tiliz er F all 98 Winter 99 Spr ing 99 Summer 99 F all 99 Winter 00 End Members Precip NO3 Red-N-f er t. (calc. 18O) NO3 -f er t. Septic (calc. 18O) HW (calc. 18O) Contaminated / HW Contaminated / HW (calc. 18O) Field r unoff Figure 10 18 O and 15 N of NO 3 from springs showing iso topic values of samples from precipitation collected in the study area. The dashed domain for isotopic range character istic of precipitation NO 3 extends to larger 18 O values than shown here (Kendall et al. 1995). Precip., precipitation; fert., fertilizers; calc., calculated; HW, hog waste. 4 6 8 10 12 14 16 18 20 22 0 18O (NO3 )18O (H2O) Fa ll 98 Spr ing 99 Summer 99 Winter 99 Figure 11 18 O of NO 3 and 18 O of water samples collected from springs during four seasons in the study area. .5 .5 .5 .5 .5 13C 1B 2 3 4,1T 5 6 7 8 9 1B 2 3 4,8 5 6 7 9 1T 1B 3 4 5 6 7,2 9 10,8 1T ,10 1B ,6 2 3 4 5 7 8 9 1T 1B 2 3 456 7 8 9 10 1T ,1B 234,7 5 6 8 9 1011/19/98 3/4/99 5/18/99 8/23/99 11/17/99 3/7/00DIC Figure 12 13 C of dissolved inorganic carbon (DIC) in spring water samples from six sampling dates in the study area.

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Illinois State Geological Survey Circular 570 23 in more detail because two other samples from different springs did not have such large 18 O for the NO 3 although they did have relatively enriched 18 O water values. There is also the possibility that atmospheric oxygen contributes more than onethird of the oxygen for the nitrica tion process (Mayer et al. 2001) within some of the watersheds in this study area. The more negative 18 O values observed in the winter 2000 samples from Frog and Sensel Springs and Illinois Caverns suggested some NO 3 contribution from livestock and/or septic waste. This source is supported by the range of 15 N values obtained for septic and hog waste samples and the measured 18 O value for one of the septic efuent samples contain ing enough NO 3 to allow analysis of oxygen isotopes. Furthermore, some of the land near Frog and Sensel Springs is used for raising livestock, and a small village is located just upgradient of Illinois Caverns. The more negative 18 O values for these specic samples may indicate a greater soil organic nitrogen contribution at the time of sampling. In general, live stock and septic efuents likely play a minor role as a source of NO 3 in most of the spring water of the sinkhole plain (Figures 8 and 10). This conclu sion is supported by the mass loading calculations of Panno et al. (2003). 13 C of DIC The 13 C values of the DIC for the spring water ranged from 6.6 to 13.9, which probably reects the amount of water-rock interaction that occurred in the sub surface after inltration of ground water from the soil zone. Springtime water samples with the most negative 13 C values suggest a greater contribu tion of soil zone water; those samples with more positive 13 C values suggest more water-rock interaction, espe cially the dissolution of limestone. A plot of 13 C values and sampling dates (Figure 12) shows that 13 C values tended to be more negative during the spring and summer (May and August) than during the fall and winter (November and March). This seasonal trend coincides with greater biological activity in the soil during the growth periods of the spring and summer than during dormant peri ods of fall and winter. Greater bio logical activity in the soil zone would increase the concentration of soil CO 2 and amount of soil CO 2 dissolved in the inltrating groundwater. The seasonal uctuations of 13 C values observed in the waters from springs supports earlier suggestions that inl tration of surcial water into much of the shallow karst aquifer was typi cally quite rapid. The 13 C values for one of the springs, Sensel Spring, did not follow the same seasonal trend observed for the other springs. The consistently more negative 13 C values for Sensel Spring suggest that its dis charge water comes primarily from the soil zone. These isotope results support the chemical results showing lower pH and undersaturation with respect to calcite. The more negative 13 C values indicate that the water discharging from Sensel Spring was relatively more open to exchange with soil CO 2 than was water from the rest of the springs sampled in this study. D and 18 O of Water Data for D and 18 O cluster near the GMWL (Figure 13). The isotopic composition of water from summer and fall sam pling events plot along a trajectory representative of evaporation, indi cating that considerable evaporation occurred at the land surface prior to water inltration into the subsurface in some of the watersheds. Most of the samples collected during spring plotted on or very close to the GMWL. Seasonal detection of evaporational effects in the groundwater discharging from the springs was another indica tion of rapid inux of surface water to the karst aquifer of the sinkhole plain. 34 S of Sulfate The 34 S values for the springs ranged from 6 to +2.5. Because no strong correlation between the sulfur isotope data and NO 3 concentrations was observed, pyrite oxidation probably did not play a major role in NO 3 reduction in the sinkhole plain karst environment The correlation between sulfate concen trations and 34 S values was negative (r 2 = 0.65 ) for most of the springs sampled. The sulfur isotope data from Falling Springs were unique. For most of the springs, the samples with greater sulfate concentrations gener ally had more negative 34 S values, suggesting that pyrite oxidation contributed sulfate to these samples. However, many of the springs had 34 S values ranging between 1 to +2.2, which were similar to the +2.7 for the 34 S measured from the water runoff end member sampled from a corneld in the study area (Table 5). The origin of the sulfate in the runoff sample was assumed to be from fertil izer application and the oxidation of organic matter in the upper horizons of the soil zone. Freney and Williams (1983) indicated that sulfur in the upper horizons of well-drained aer ated soils occurs primarily as organic sulfur from plant debris, and much of the inorganic sulfate in the lower horizons of these soils is a result of mineralization of the organic sulfur. The typical range of 34 S for terrestrial primary plant sulfur is about 0 to +12, as measured from low-sulfur coals and freshwater peat deposits throughout the world (summarized by Hackley and Anderson 1986). The lower end of this range is also similar to that observed for most of the spring waters. The 34 S values for several of the springs suggested that much of the sulfate was the result of fertilizer sulfate and the oxidation of organic sulfur from the soil zone. The distri bution of 34 S values observed in the springs can be explained by sulfate from the upper soil zone that had more positive 34 S values mixing with sulfate that had more negative 34 S values caused by pyrite oxidation as the groundwater percolated deeper into the sediments and bedrock units (Figure 14). Well Samples: Chemical Composition The variation in chemical composi tion observed for the well samples (Tables 11 and 12) reected the impact of local conditions (e.g., back ground, point and non-point source contamination) on groundwater chemistry. The chemical character istics of some of the well samples were similar to the spring samples, but samples from other wells showed the inuence of local, anthropogenic inputs.

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24 Circular 570 Illinois State Geological Survey Groundwater samples from the wells were mostly undersaturated or near equilibrium with respect to calcite (Figure 15). The saturation indices for the well samples were noticeably different from those for the water samples from springs; spring water samples were predominantly super saturated with respect to calcite. The pH for the samples from 16 wells ranged from 6.7 to 7.2 (Table 11). The variation was small when compared with that for the spring samples, and no major trends were observed for depth or season. The pH of the well samples was similar to that of Sensel Spring, which primarily drained the soil zone above the limestone bed rock. The lower pH values and under saturated calcite conditions for many of the well samples indicate that the water owing into these wells had not been buffered by the limestone bedrock to the same degree as most of the spring water had. The water owing into most of the wells prob ably travels quickly from the soil zone through fractures and ssures in the bedrock to the well screen because most of the wells are cased only from 1 to 4 m below the top of limestone bedrock (Panno et al. 1996). Pumping the wells would decrease water level and draw water in through the most permeable zone near the top of the bedrock where the limestone is most weathered and contains dissolutionenlarged ssures and fractures in the top 10 to 15 m (Panno et al. 1996). The temperature for most of the well samples was consistent and ranged from 14.1 to 15.8 C. Two wells had temperatures that fell outside this range. Sample NW-16 from well 15 ran through the residential water softener and was slightly warmer. Sample NW-42 from well 17 reected the cold season (winter) because of a long dis tribution pipe buried just below the land surface from the well head to the outside spigot. The range of the Eh measurements for most of the well samples fell between +334 and +529 mV, which was similar to the range for the samples of spring water, indicating a similar exposure to atmospheric oxygen along its ow path. The specic conductance for the wells ranged from 539 to 1,718 S/cm. The values were generally greatest for the shallower wells (Figure 16) and for wells located on property with livestock facilities. The high specic conductance observed for site NW-16 was because the water had passed through a residential water softener, as reected by the anomalously large Na + and Cl concentrations (Table 12). The range of Cl concentrations for the wells was much greater than that for the springs. The Cl ranged from 3.1 to 127 mg/L for the wells; concentrations were greatest for the shallower wells and for those sites in close proximity to livestock areas. Like the spring water samples, the Na + and Cl concentrations for the water samples from wells are correlated roughly along the 1:1 stoichiometric line, although Na + concentrations tend to be greater (Figure 17). This positive shift of Na + concentrations was also observed in the data for water samples from springs and sug gests that ion exchange (with Ca 2+ ) probably plays a role in the chemical makeup of the karst aquifer system. Greater Na + concentrations could also come from weathering of sodium silicate minerals and anthropogenic sources such as septic systems, live stock waste, and fertilizers such as NaNO 3 Many residential homes have water softeners, which would increase GMWL Ev aporation F all 98 Spr ing 99 Summer 99 F all 99 Winter 99 Winter 00 0 10 D () 0 18O () Figure 13 Isotopic composition ( D and 18 O) of the springs in relation to the global meteoric water line (GMWL) and along a trajectory typical of evaporation. 8 Spr ings and r unoff Mixing cur ve 1 1.5 2 3 4 5 6 7 8 9 10 Runoff 6 4 2 0 2 4 20 40 60 80 100 120 140 SO4 2 (mg/L) 0 34S () Figure 14 34 S versus SO 4 2 concentration of runoff and spring samples. Spring samples are identified by number. A mixing curve is included to show the trend for mixing sulfate containing more positive 34 S values with sulfate containing more negative 34 S values. The mixing curve was generated using end-member sulfate concentrations of 20 and 120 mg/L and 34 S values of +4 and 8, respectively.

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Illinois State Geological Survey Circular 570 25 the Na + concentration in septic dis charge. Although sample NW-16 was not septic discharge, its increased Na + concentration shows the effect of water softeners (Figure 17). The DOC concentrations for the samples from wells were somewhat less than for the water samples from springs, but usually larger relative to typical groundwater, which contains less than 2 mg of DOC /L (Drever 1997). The DOC in water samples from the wells, excluding NW-16, ranged from less than the detection limit to 5.8 mg/L. Sample NW-16 had 9.9 mg of DOC/L but was contaminated with a high concentration of Cl which could have interfered with DOC analyses. As with the springs, the elevated con centrations of DOC may have been associated with agricultural activities and/or septic systems. There are two types of wells in south western Illinois, bored wells and drilled wells. Bored wells are dug completely within and open to the soil zone to depths of 6 to 10 m. Drilled wells are typically cased only through the soil zone and about a meter into bedrock, allowing soil water and very shallow groundwater to seep into the open borehole and contaminate the well, regardless of whether deep or shallow (Panno et al. 1996). Nitrate concentrations for well sam ples ranged from less than the detec tion limit (<0.02 mg of N/L) to 80.9 mg of N/L. Five of 17 wells contained concentrations greater than the USEPA (1992) regulatory standard for drinking water. The shallower wells consistently had the highest NO 3 con centrations (Figure 18). The shallow wells were all located in the covered karst region where the water table was higher (above the soil-bedrock inter face) than in the karst topography (below the soil-bedrock interface). A cross section connecting many of the sampled wells shows the effects of the karst terrain on the local hydrology and the distribution and stratica tion of NO 3 in the karst aquifer of the region (Figure 19). Generally, most wells drilled into the covered karst region of the sinkhole plain contained signicant NO 3 concentrations, regardless of depth (Table 13; Figure 19). In contrast to the samples from the covered karst region, groundwater Table 11 Field parameters and total alkalinity for water samples from wells in the study area. Well Specic Total Date depth Temp. 1 Eh conductivity alkalinity Sample Well sampled (m) (C) pH (mV) (S/cm) (mg CaCO 3 /L) NW-1 1 05/14/99 93 14.6 6.9 795 866 314 NW-2 2 05/14/99 170 15.3 7.2 529 616 251 NW-3 3 05/14/99 61 14.4 7.0 469 602 325 NW-4 4 05/14/99 17 14.1 6.9 494 810 334 NW-5 5 05/14/99 6 15.8 6.7 504 1,595 386 NW-7 7 05/19/99 95 15.5 7.0 453 588 311 NW-8 8 05/19/99 -2 15.3 7.1 432 578 291 NW-9 9 05/19/99 73 15.1 6.7 485 1,122 385 NW-10 10 05/19/99 105 14.8 6.9 423 753 320 NW-11 11 05/19/99 33 14.8 6.8 448 586 226 NW-12 12 05/19/99 13 15.4 7.0 467 844 290 NW-13 13 05/19/99 89 15.4 7.1 420 702 346 NW-14 14 05/19/99 10 15.1 7.0 494 1,064 352 NW-15 14 07/06/99 -. -----NW-16 15 07/06/99 154 16.6 7.0 415 1,378 468 NW-17 1 11/18/99 93 14.7 6.8 409 804 315 NW-18 2 11/18/99 170 15.2 7.1 430 618 277 NW-19 3 11/18/99 61 15.0 7.0 465 594 323 NW-20 4 11/18/99 17 14.8 6.9 463 796 336 NW-21 5 11/18/99 6 15.8 6.9 432 1,718 410 NW-21D 6 11/18/99 37 15.2 6.9 144 776 413 NW-22 8 11/18/99 -14.9 6.9 450 591 315 NW-23 9 11/17/99 73 14.5 6.8 -929 412 NW-24 10 11/17/99 105 14.4 7.1 334 730 313 NW-25 11 11/18/99 33 14.5 6.9 429 539 219 NW-26 12 11/18/99 13 15.2 6.8 417 894 304 NW-27 14 11/18/99 10 15.6 6.9 396 1,232 410 NW-28 13 11/18/99 89 14.7 7.0 407 676 347 NW-40 16 03/21/01 69 14.7 7.0 281 748 361 NW-42 17 03/21/01 108 8.3 7.1 422 831 372 1 Temp., temperature; Eh, redox potential. 2 --, not determined.

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26 Circular 570 Illinois State Geological Survey Table 12 Chemical data for water samples from wells in the study area. Atrazine Sample Ca 2+ Mg 2+ Na + K + NH 4 -N HCO 3 Cl SO 4 2 NO 3 -N SiO 2 Al Ba Br F Fe Mn Sr 2+ Zn DOC (g/L) NW-1 127 15.6 52.6 <1 -1 383 47.5 54.8 7.43 20.7 <0.02 0.09 <0.18 0.25 <0.01 <0.01 0.19 <0.01 -<0.10 NW-2 71.7 15.4 52.2 <1 -306 14.5 42.4 7.61 15.7 <0.02 0.05 <0.18 0.34 <0.01 <0.01 0.18 <0.01 -<0.10 NW-3 83.2 36.7 7.7 <1 -397 9.0 20.2 1.99 13.5 <0.02 0.15 <0.18 0.65 <0.01 <0.01 0.35 <0.01 -<0.10 NW-4 99.2 23.6 60.8 <1 -407 26.6 36.7 12.5 16.2 <0.02 0.09 <0.18 0.31 <0.01 <0.01 0.19 <0.01 -<0.10 NW-5 203 66.8 67.2 <1 -470 120 53.9 57.8 23.3 <0.02 0.31 0.60 0.32 <0.01 <0.01 0.56 0.05 -<0.10 NW-7 77.1 33.5 11.4 <1 -380 8.7 20.7 1.63 13.8 <0.02 0.17 <0.18 0.58 <0.01 <0.01 0.25 0.02 5.2 <0.10 NW-8 104 13.4 13.2 <1 -355 8.4 26.0 2.24 26.5 <0.02 0.05 <0.18 0.30 <0.01 <0.01 0.14 <0.01 5.8 <0.10 NW-9 145 39.7 52.9 <1 -469 50.4 31.7 30.1 18.3 <0.02 0.12 0.30 0.29 <0.01 <0.01 0.23 0.05 3.1 0.14 NW-10 86.1 27.9 54.5 <1 -391 10.5 73.6 4.88 12.3 <0.02 0.07 <0.18 0.31 <0.01 0.03 0.23 0.01 4.8 0.18 NW-11 105 7.35 19.4 <1 -276 22.7 36.9 5.99 22.9 0.02 0.06 <0.18 0.19 <0.01 <0.01 0.19 0.01 2.8 <0.10 NW-12 100 19.4 68.2 <1 -354 35.4 50.0 16.2 17.1 <0.02 0.11 0.24 0.29 <0.01 <0.01 0.19 0.03 1.9 <0.10 NW-13 69.3 43.3 39.1 <1 -422 11.9 37.6 1.54 9.5 <0.02 0.15 <0.18 1.85 <0.01 <0.01 0.85 0.02 0.8 <0.10 NW-14 95 43.7 83.8 <1 -430 41.7 64.0 24.6 18.7 <0.02 0.09 0.26 0.40 <0.01 0.01 0.24 <0.01 -0.65 NW-15 ------------------1.2 -NW-16 0.63 0.075 344 2 -571 115 53.3 5.17 27.1 <0.02 <0.01 0.54 0.34 <0.01 <0.01 <0.01 <0.01 9.9 0.1 NW-17 128 15.5 43.9 2 -384 38.5 46.1 5.78 21.0 0.03 0.09 <0.02 0.17 <0.01 <0.01 0.20 0.02 2.3 <0.1 NW-18 72.6 15.2 49.5 3 -338 8.4 36.0 6.66 15.1 0.03 0.05 <0.02 0.23 <0.01 <0.01 0.16 <0.01 4.4 <0.1 NW-19 83.1 33.7 7.5 3 -394 3.4 13.0 1.91 13.5 <0.02 0.13 <0.02 0.50 <0.01 <0.01 0.31 <0.01 5.3 <0.1 NW-20 95.9 21.5 58.4 3 -410 21.5 29.8 12.0 15.6 <0.02 0.09 0.07 0.20 <0.01 <0.01 0.17 0.01 0.3 <0.1 NW-21 205 63.6 66.5 2 -500 127 59.1 80.9 22.5 0.03 0.30 0.39 0.19 <0.01 0.01 0.53 0.13 1.3 <0.1 NW-21D 92.2 31.2 27.9 2 -504 11.2 21.9 <0.02 12.6 <0.02 0.15 0.09 0.32 1.32 0.11 0.33 0.01 2.0 <0.1 NW-22 103 18.0 11.6 3 -384 3.1 13.9 2.12 22.2 0.03 0.05 <0.02 0.24 <0.01 <0.01 0.16 <0.01 <0.2 <0.1 NW-23 127 31.7 44.7 2 -503 32.6 13.7 15.4 18.1 0.04 0.09 0.14 0.20 <0.01 <0.01 0.20 0.05 5.7 <0.1 NW-24 80.7 24.4 48.1 2 -382 3.7 64.0 3.39 11.7 <0.02 0.06 <0.02 0.20 <0.01 0.12 0.21 <0.01 0.7 <0.1 NW-25 98.8 5.73 17.3 2 -267 14.7 23.2 5.27 22.7 <0.02 0.04 <0.02 0.09 <0.01 <0.01 0.17 <0.01 2.4 0.18 NW-26 107 19.8 64.6 2 -371 38.4 44.6 21.4 16.6 <0.02 0.11 0.08 0.18 <0.01 <0.01 0.19 0.05 2.9 <0.1 NW-27 113 43.8 102 2 -500 51.3 81.8 36.0 17.9 0.02 0.10 0.11 0.31 <0.01 <0.01 0.26 <0.01 2.9 <0.1 NW-28 63.5 38.1 33.3 2 -423 5.7 31.3 0.72 8.7 <0.02 0.12 <0.02 1.82 <0.01 <0.01 0.80 0.02 0.9 <0.1 NW-40 102 28.0 51.7 <1 <0.01 440 31.8 24.4 0.71 16.9 <0.3 0.15 <0.05 0.50 0.27 0.05 0.26 0.06 --NW-42 92.6 32.3 77.0 <1 <0.01 454 23.0 51.1 7.71 15.5 <0.3 0.14 0.09 0.30 1.15 0.09 0.24 0.08 --1 --, not determined.

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Illinois State Geological Survey Circular 570 27 0 2 4 6 8 10 12 14 16 18 We ll number .5 0 0.5 1 1.5 Saturation inde x f or calcite NW -1 NW -2 NW -3 NW -5 NW -7 NW -8 NW -10 NW -11 NW -12 NW -13 NW -14 NW -19 NW -20 NW -21 NW -22 NW -23 NW -24 NW -25 NW -26 NW -28 NW -40 NW -42Supersaturated UndersaturatedNW -18 NW -17 NW -4 NW -9 NW -27 NW -21 deep Figure 15 Calcite saturation indices for wells sampled in the study area. 400 600 800 1,000 1,200 1,400 1,600 1,800 Specific conductance (S/cm)0 25 50 75 100 125 150 175 Depth (m) NW -1 NW -3 NW -4 NW -5 NW -7 NW -9 NW -10 NW -11 NW -12 NW -13 NW -14 NW -16 NW -17 NW -2 NW -19 NW -20 NW -21 NW -23 NW -24 NW -25 NW -26 NW -27 NW -28 NW -21d NW -40 NW -42 NW -18 Figure 16 Specific conductance of the well water sampled in the study area. Note the generally larger values for the shallower wells. Figure 17 Sodium and chloride concentrations for the wellwater samples, including the end-member samples of field runoff, septic systems, and hog waste (HW1). 0 20 40 60 80 100 NO3 (mg of N/L) 0 50 100 150 200 We ll depth (m) USEP A limit NW -1 NW -2 NW -3 NW -4 NW -5 NW -7 NW -9 NW -10 NW -11 NW -12 NW -14 NW -16 NW -18 NW -20 NW -21 NW -23 NW -25 NW -26 NW -27 NW -40 NW -42 NW -28 NW -13 NW -24 NW -17 NW -19 Figure 18 Nitrate concentration and well depth. Concentrations were largest for the most shallow wells. The USEPA (1992) regulatory limit (10 mg of N/L) is identified by the horizontal line. 0 Na+ (mg/L)0 500 1,000 1,500 2,000 1:1 line We lls Septic Runoff Hog w aste Contaminated with hog w asteNW -16200 400 600 800 1,000 1,200 1,400 Cl (mg/L)

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28 Circular 570 Illinois State Geological Survey sampled from wells drilled in karst regions had smaller NO 3 concen trations that were similar to those from springs and caves. The largest NO 3 concentration for the karst area was from sample NW-9 (30.1 mg of N/L). The reason for this anomalous concentration is probably that the well was drilled into a buried bedrock depression (Figure 19) where water seeping through the soil zone would be channeled into the depression. Because the bedrock surface is frac tured, the NO 3 -enriched soil water could easily be funneled into the well. Three wells drilled on one property (wells 5, 6, and 17) demonstrated how crevice-controlled groundwater ow can result in a broad range of NO 3 concentrations because of vari able amounts of input from surcial water sources. Nitrate concentrations in these three wells ranged from less than 0.02 to 80.9 mg of N/L. The shal lowest well, well 5 (samples NW-5 and -21), was hand dug only 6 m into sediment. Well 6 (sample NW-21D) and well 17 (sample NW-42) were drilled into bedrock at a depth of 37 and 108 m, respectively (Figure 19). Wells 5 and 6 were close to hograising facilities. Well 17 was away from the hog facilities in the midst of row crops. Shallow well 5 had the greatest NO 3 concentration, indicat ing the inltration of animal waste. Medium-depth well 6 had the lowest NO 3 concentration (<0.2 mg of N/L) and was apparently drilled into the bedrock where the crevices are more isolated from surface water inltra tion. In fact, well 6 (NW-21D) was under reducing conditions and had a strong hydrogen sulde (H 2 S) odor (note low Eh, 144 mV). The residents using well 6 had problems with iron deposits at the well screen and in the house. The deepest well, well 17, had a NO 3 concentration of 7.7 mg of N/L, which was much less than the shallow well but greater than the background concentrations for this region. Of all wells sampled during this study, only 3 had NO 3 concentrations that were less than the 2.1 mg of N/L threshold for background concentra tions. Thus, most of the wells had been contaminated with NO 3 Wells with large NO 3 concentrations also had large Cl concentrations, suggest ing the source of these two ions was the same, probably livestock or septic waste. In order to show this relation ship and include the end member sources, Cl concentrations were plot ted against total inorganic nitrogen (NO 3 plus NH 4 + ) in Figure 20. An overall evaluation of the major cations and anions in the well samples indicated that these were Ca 2+ -HCO 3 -type to mixed cationHCO 3 type waters (Figure 21). For a more direct comparison, spring water and samples of animal waste and septic systems have been included on the trilinear diagram (Figure 21). The septic and animal waste samples were included because their greater con centration of contaminants might be affecting the chemical composition of some of the wells. Most wastewater samples fell in the Na + -Cl to Na + HCO 3 -type water regions of the tri linear diagram. It should be empha sized that ammoniaoften a major component of the septic and animal waste sampleswas not included in these trilinear plots. To compensate, total N was included by enlarging the 225 200 150 175 125 100 75 50 25 225 200 150 175 125 100 75 50 25Depth (abo ve MSL) Depth (abo ve MSL)wa ter tab le bedroc k surf ace NO3 concentration (mg/L) well identification Co v ered karst Karst NW -21D NW -2 NW -43 NW -42 NW -5 NW -4 NW -7 NW -3 NW -9 NW -8 NW -12 NW -14 NW -14 Nor th South 01 2 km 2 8 16 0.0 16 25 8 12 58 2 2 30 2ve r tical e xaggeration 2x Figure 19 North-south cross section through many of the wells sampled, show ing water table, topography of the bedrock surface, and NO 3 concentrations for the wells of various depths. Table 13 Descriptive statistics of NO 3 concentrations for a limited number of water samples from wells from karst and covered karst regions and water sam ples from caves and springs of the sinkhole plain. Wells in Wells in covered karst Caves and springs Parameter karst terrane terrane in karst terrane Samples, no. 9 7 62 Range, mg of N/L 1.63 to 30.5 <0.02 to 80.1 1.74 to 7.48 Median, mg of N/L 5.22 14.3 3.97 Mean, mg of N/L 6.75 22.6 4.19 Standard deviation, mg of N/L 7.44 24.7 1.27

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Illinois State Geological Survey Circular 570 29 diameter of the dots on the plot; the smallest and largest dots indicate the lowest and highest N concentrations, respectively. The samples with greater N concentrations typically fell to the right of the total group of samples on the cation, anion, and composite gures. The septic efuent and the hog waste samples showed distinct departures from the eld dened by groundwater samples and springs in the composite diagram. However, the two water samples known to be contaminated with hog waste did plot with some of the wells in the sinkhole plain that showed elevated NO 3 con centrations (Figure 21). Compared with the water samples from springs, many of the well samples tended to have greater Mg 2+ Na + Cl and NO 3 concentrations. The higher Mg 2+ concentrations were probably the result of greater dissolu tion of dolomite within the soil zone and/or within bedrock in the vicin ity of some of the wells. Dolomite is known to occur as thin beds within the St. Louis Limestone (Willman et al. 1975, Panno et al. 1997a). Most of the well samples that had relatively large NO 3 concentrations tended to plot toward the septic efuent and hog waste samples on the anion tri linear and composite diagram (Figure 21). The exceptions were samples NW-5 and NW-21, which had an unusually high Ca 2+ content (Table 12). In addition to the anomalously high Ca 2+ concentrations, NW-5 and NW-21 also had the greatest NO 3 and Mg 2+ concentrations. The large amounts of Ca 2+ and Mg 2+ were probably a result of carbonate mineral dissolution caused by the acidic conditions asso ciated with nitrication of ammo nium as efuent from animal waste migrated into the soil zone: Nitrication: NH 4 + + 2O 2 NO 3 + H 2 O + 2H + Calcite dissolution: 2CaCO 3 + 2H + 2Ca 2+ + 2HCO 3 Dolomite dissolution: CaMg(CO 3 ) 2 + 2H + Ca 2+ + Mg 2+ + 2HCO 3 1 2 3 4 5 r unoff 8 9 11 12 13 14 16 17 18 19 21 22 24 25 28 40 42 20 23 27 7 10 26 W ells Septic Systems Hog w aste Contaminated with/hog w aste 1E0 1E1 1E2 1E3 1E4Cl (mg/L)1E-1 1E0 1E1 1E2 1E3 1E4NO3 plus NH4 + (mg/L) Figure 20 Chloride and total inorganic nitrogen (NO 3 plus NH 4 ) concentrations for the wells and end-member samples including field runoff, septic systems, and livestock waste. Numbers represent NW sample identification numbers in Table 12. 80 80 20 20Ca2+ spr ingMg2+SO4 2 + CL + NO3 Cl + NO3 SO4 2 Ca2+ + Mg2+20202020 80 80 2080 80 208080(%meq/L)CO3 2 + HCO3 Na+ + K+03.0 3.16.0 6.19.0 9.112.0 12.115.0 15.118.0 18.121.0 >21 Septic and liv estoc k wa ste Contaminated with hog w aste (12.115.0) T otal N (mg/L) Figure 21 Trilinear diagram comparing the distribution of major cations and anions in the springs, wells, and end-member samples.

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30 Circular 570 Illinois State Geological Survey Samples NW-5 and NW-21 were col lected from well 5 next to a hog waste facility. As shown in Table 4, hog waste samples had very high ammo nium contents, even compared with the septic samples. Well Samples: Bacterial Composition Groundwater in wells in the sinkhole plain can be contaminated by a vari ety of bacterial genera and species similar to those found in the springs (Panno et al. 1996). County and state regulations for drinking water require fewer than 80 cfu/L for total coliforms and no fecal coliforms in private wells. Only 5 of the 15 wells consis tently met these criteria (Table 14). The two most dominant bacteria pres ent in the well-water samples were Pseudomonas and Bacillus spp. (Table 15). Pseudomonas spp. were present in all but 1 of the 15 wells (92%). Bacil lus spp. were present in all but 2 wells (86%). As with the spring water, these bacteria are associated with the natu ral ora present in the soil zone and aqueous environments. Escherichia coli was present only in well 14 (NW-14), which also contained the greatest amount of aerobic bac teria counted. This result suggested rapid recharge to the well because the half-life of E. coli is about 15 hours after leaving the host animal (Burks and Minnis 1994). NW-14 was a dug well immediately adjacent to livestock grazing in a barnyard. The presence of more than 3 10 6 cfu of aerobic bacteria/L, 870 cfu of coliforms/L, 46 cfu of FC/L, and 192 cfu of fecal enterococci/L (Table 14) indicated that animal waste was reaching this well. Wells 5 and 12, which were also dug wells located near livestock facili ties, contained the next highest con centrations of aerobic and coliform bacteria, suggesting that the ground water sampled by these wells was probably affected by animal waste efuent. As with NO 3 the distribution of coliforms and fecal enterococci con centrations was stratied by depth (Figures 22 and 23). The shallowest wells had the greatest bacterial con tamination. The most contaminated wells (wells 5, 12, and 14) were shallow wells where land use was dominated by livestock. Land use near well 4 was row crop agriculture; this well was drilled only a few meters into bedrock and was the shallowest of the bedrock wells. Groundwater from the deeper wells contained fewer FC and fecal enterococci, probably because these bacteria tend to die off rapidly after leaving the host animal. In general, the bacterial content of the well samples reected the suscepti bility of the wells in a karst aquifer to surface activities and land use. This same well susceptibility was seen for NO 3 and pesticides. Well Samples: Isotopic Composition 15 N and 18 O of NO 3 The 15 N and 18 O of the NO 3 in well samples ranged from +2.2 to +25.9 and from +5.5 to +15.5, respectively (Table 16). When plotted, isotope data for most of the well samples containing 15 mg/L NO 3 N tend to follow the denitrication trajectory (Figure 24). The lowest 15 N and 18 O values from the well samples plotted within the area typical of mineralized fertilizer nitrogen. None of the well samples showed the anomalously high 18 O values for NO 3 that were found in the spring samples. However, the isoto pic composition of NO 3 from several wells plotted below what would be expected for denitrication for this region, indicating that the NO 3 from these samples was predominantly from septic and/or livestock waste. We were able to analyze one sample of Table 14 Bacterial analyses for water samples collected from wells in the study area. Total aerobic Total Fecal Fecal colonies coliforms coliforms enterococci Sample Well (cfu/L) (cfu/L) (cfu/L) (cfu/L) NW-1 1 230 0 0 0 NW-2 2 140 44 0 0 NW-3 3 260 12 0 0 NW-4 4 8,000 450 0 44 NW-5 5 14,000 3,466 0 198 NW-7 7 220 2 0 6 NW-8 8 32 0 0 0 NW-9 9 67 0 0 0 NW-10 10 190 4 0 0 NW-11 11 38 4 0 2 NW-12 12 2,700 1,840 2 110 NW-13 13 20 0 0 0 NW-14 14 3 10 6 870 46 192 NW-15 14 -1 ---NW-16 15 570 650 8 2 NW-17 1 490 0 0 0 NW-18 2 410 0 0 0 NW-19 3 106 0 0 0 NW-20 4 350 0 0 0 NW-21 5 2,200 1,732 0 120 NW-21D 6 120 4 0 10 NW-22 8 50 0 0 8 NW-23 9 88 0 0 0 NW-24 10 130 6 0 38 NW-25 11 204 0 0 0 NW-26 12 1,400 106 10 46 NW-27 14 430 112 0 28 NW-28 13 22 2 0 0 NW-40 16 ----NW-42 17 ----1 --, not determined.

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Illinois State Geological Survey Circular 570 31 NO 3 directly from the discharge point of a septic system (NW-17-septic) and two samples just down-gradient from a hog facility (NW-5, NW-21). Those samples gave a good indication of where NO 3 inuenced by septic and livestock waste would plot (Figure 24). Other samples that plotted in the same area as NW-17-septic, NW-5, and NW-21 were undoubtedly inuenced by septic and/or livestock waste. The septic and livestock waste sam ples contained very high concentra tions of NO 3 or ammonium compared with those of most well and spring samples. However, those well samples that showed isotopic evidence of septic and livestock contamination also contained greater concentra tions of NO 3 (Figure 24). Many of the septic and livestock waste samples contained only ammonium, so a com posite nitrogen concentration (NO 3 plus NH 4 ) was used for this diagram. For those samples that contained ammonium only, the 18 O value was calculated (applying the assumptions discussed earlier) and used to plot the data. Two samples from well 13 (NW-13 and NW-28) had the highest 15 N and 18 O values for NO 3 and low NO 3 con centrations (0.7 and 1.5 mg/L). These results indicated that considerable denitrication had occurred in the groundwater at this site. When plotted on a 15 N vs. ln[NO 3 N] (Figure 25), many of the well samples (particularly those affected by N fer tilizers) follow a linear correlation (r 2 = 0.89) in which the isotopic com position increases with decreasing NO 3 N concentration. As noted ear lier, a linear correlation on this type of diagram indicates that NO 3 in the groundwater has undergone denitri cation (Mariotti et al. 1988). Samples containing relatively large NO 3 N con centrations (>15 mg/L) derived from animal waste and septic efuent plot along mixing lines to the right of the linear correlation. The small group of samples that plot to the left of the linear correlation have relatively low NO 3 N concentrations and probably represent groundwater samples in which the NO 3 concentration have decreased due to mixing with water containing little NO 3 N. 13 C of DIC and 3 H of Water The 13 C values of the DIC for the wells ranged from 7.7 to 14.3 (Table 16), which was similar to the range for the springs. As with the spring water, the more negative 13 C values for the well samples suggested that a considerable proportion of the water inltrated rapidly from the soil zone. The less negative 13 C values suggested that the groundwater had reacted with the rock to a greater degree after passing through the soil zone and, therefore, was probably older and had traveled a longer pathway before reaching the well. This interpretation is supported Table 15 Bacteria (genera and species) present in water samples from wells and their ranking relative to their domi nance in the groundwater samples. Relative Percent Final Genera and species rank present rank Pseudomonas spp. 2.0 92 1 Bacillus spp. 3.0 86 2 Klebsiella pneumoniae 4.9 57 3 Enterobacter aerogenes 6.3 36 4 Enterococcus faecium 6.8 36 5 Serratia spp. 6.9 21 6 Enterococcus faecalis 7.6 14 7 Escherichia coli 7.9 7.1 8 0 50 100 150 200 W ell depth (m)0 500 1,000 1,500 2,000 2,500 3,000 3,500 Total colif or ms (cfu/ml) NW -4 NW -5 NW -11 NW -12 NW -14 NW -16 NW -19 NW -21 NW -23 NW -26 NW -20 NW -27 NW -25 NW -21D NW -3 NW -9 NW -13, 28 NW -17,1,7 NW -10, 24 NW -2 NW -18 Rnoff 0 50 100 150 200 Fecal enterococci (cfu/ml)0 50 100 150 200 W ell depth (m) NW -13, 28 NW -1, 17 NW -5 NW -10 NW -11 NW -12 NW -16 NW -20 NW -21 NW -21D NW -24 NW -26 NW -27 NW -26 NW -25 NW -3, 19 NW -9, 23 NW -7 NW -2, 18 NW -4 NW -14 Rnoff Figure 22 Bacterial analyses results for total coliforms by depth of wells sampled. Figure 23 Bacterial analyses results for fecal enterococci by depth of wells sampled.

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32 Circular 570 Illinois State Geological Survey by the correlation between 13 C and 3 H observed for most of the wells (Figure 26). The samples with greater 3 H con centrations (5 to 6 TU) are indicative of younger water that very recently percolated into the subsurface sedi ments. Most samples that had larger 3 H con centrations also had greater NO 3 con centrations (Figure 27), which again suggested that the groundwater con taining high NO 3 concentrations was young water. However, the shallow well, well 5 (NW-21), did not follow this trend. Sample NW-21 had a small amount of 3 H, a large NO 3 concentra tion, and a relatively low 13 C value. These results suggested mixing of young inltrating water from the soil zone with older groundwater from the bedrock limestone. Panno et al. (1996) noted springs discharging through the loess deposits on this property. The spring water appears to originate from the bedrock limestone. D and 18 O of Water The values for D and 18 O of the water from the wells were very similar to those values for the water samples from springs; most samples plotted near the GMWL (Figure 28). The isotopic composi tion of water from at least seven of the wells plotted along the same trajec tory below the GMWL as several of the water samples from springs. The trajectory of these samples follows the evaporation line, which indicates that considerable evaporation took place prior to inltration into the sub surface in some of the watersheds of the sinkhole plain. The wells that fol lowed the evaporation trajectory were located in the same watersheds as spring samples that plotted along the evaporation line. These results sug gested a strong connection between the groundwater sampled by the wells and the crevice and conduit karst system supporting the springs. 34 S of Sulfate The range of 34 S values was much larger for water from the wells than for water from the springs. The 34 S of the well samples ranged from 13.6 to +3.8 (Table 16). Most of the groundwater sampled from the wells had 34 S values greater than 1, which were similar to values for the spring water, suggesting that the source of the sulfate in many of the wells was the same as in the spring water. However, samples from 3 wells had signicantly lower 34 S values, indicating a different sulfate source than that for the spring water. The more negative 34 S values for the sulfate in these 3 wells indicated oxi dation of reduced sulfur. The source of the reduced sulfur may have been from pyrite in the bedrock or dis solved H 2 S in the deeper groundwater. The sinkhole plain is known to have groundwater seeps containing H 2 S (Panno et al. 2005). Some of the wells possibly were screened in an area where deeper groundwater contain ing H 2 S mixed with younger recharge water containing dissolved oxygen that oxidized the sulde sulfur to sulfate. Two of the 3 wells containing considerably negative 34 S values also had relatively low 3 H concentrations, indicating an older groundwater com ponent. Well 13 (NW-13 and NW-28) had a quite negative 34 S rating, the most positive 15 N and 18 O values for NO 3 and very low NO 3 concen trations, suggesting that perhaps reduced sulfates ( pyrite) played a role in the denitrication process at this site. Soil Org Septic/manure Mineraliz ed fe r tiliz erNW -17 Septic HW -3 HW -3 HW -1 AM-6 AM-5 Solution-28-NO3Solution-28-NH4 and Urea Synthetic fe r tiliz er NO3 NW -5 NW -13 NW -21 NW -28 03.0 3.16.0 6.19.0 9.112.0 12.115.0 15.118.0 18.121.0 >21 septic and liv estock w aste To ta l N (m g/ L) 0 5 10 15 20 25 30 35 15N ()0 5 10 15 20 25 18O () Figure 24 15 N and 18 O of NO 3 for the wells and end-member samples includ ing fertilizers and septic and livestock waste. The relative nitrogen concentra tion (NO 3 plus NH 4 ) is depicted by the size of the circles (mg of N/L). The 18 O values for the fertilizer, the livestock waste, and most of the septic samples were calculated (except NW-17 and AM-5), as described in the text. Typical trends for denitrification are shown by the dashed arrows. Isotopic ranges characteristic of different sources are also shown (general domains taken from Kendall et al. 1995, Clark and Fritz 1997, Mengis et al. 2001). Stippled area indicates most typi cal 15 N values for soil organic nitrogen.

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Illinois State Geological Survey Circular 570 33 Table 16 Isotopic data for water samples from wells in the study area. 15 N 18 O NO3 18 O D 13 C 34 S Tritium Sample Well () () () () () () (TU) 1 NW-1 1 6.8 9.2 2 5.53 37.3 13.2 0.6 -3 NW-2 2 2.2 8.3 2 5.93 41.7 13.2 1.2 -NW-3 3 4.5 6.6 2 5.99 41.5 8.3 7.7 2.6 NW-4 4 4.3 10.4 2 5.25 35.4 14.1 1.3 -NW-5 5 11.7 7.1 6.26 42.3 13.0 --NW-7 7 4.1 9.4 2 6.21 41.2 8.9 11.2 1.8 NW-8 8 4.1 7.8 2 5.87 42.1 11.8 3.8 6.1 NW-9 9 12.0 7.8 3.85 29.8 12.1 1.6 6.1 NW-10 10 9.2 10.6 2 2.37 25.4 12.3 4.7 5.4 NW-11 11 4.8 5.8 6.10 45.9 11.9 1.9 5.6 NW-12 12 8.3 5.5 5.87 39 13.8 1.4 6.9 NW-13 13 22.9 14.9 2 6.91 38.9 7.8 13.4 2.2 NW-14 14 7.4 NW-15 14 12.9 6.7 6.38 45 14.3 0.5 9.2 NW-16 15 9.0 -6.42 43.9 14.1 2.7 7.2 NW-17 1 8.2 9.4 6.25 41.8 13.1 10.0 5.9 NW-18 2 2.5 7.3 2 6.3 42.6 12.8 -6.0 NW-19 3 4.3 7.1 6.4 42.0 8.6 -1.3 NW-20 4 3.1 6.4 5.94 40.8 13.2 -5.5 NW-21 5 10.3 8.3 6.495 42.4 13.2 2.5 2.5 NW-21D 6 --6.24 42.1 11.6 2.7 0.8 NW-22 8 2.9 8.6 6.43 40.4 10.9 -4.4 NW-23 9 10.9 9.5 2.87 25.6 12.3 2.3 4.9 NW-24 10 11.6 14.4 2.21 23.0 11.6 5.4 5.0 NW-25 11 5.2 9.7 2 5.71 38.5 11.1 1.3 6.1 NW-26 12 11.2 7.3 5.99 42.7 13.5 1.1 6.6 NW-27 14 12.3 7.2 6.32 40.2 13.2 -6.3 NW-28 13 25.9 15.5 2 6.74 46.2 7.7 13.6 2.0 NW-40 16 9.4 15.1 4.15 31.1 12.3 -5.6 NW-42 17 6.3 8.2 6.39 41.2 14.3 -5.6 1 TU, tritium units. 2 Standard deviation, 1.7. 3 --, not determined. 0 5 10 15 20 25 30 15N () -1 0 1 2 3 4 5 In [NO3 N]NW -1 NW -2 NW -3 NW -4 NW -5 NW -7 NW -8 NW -9 NW -10 NW -11 NW -12NW -13NW -16 NW17-septc NW -17 NW -18 NW-19NW -20 NW -21 NW -22 NW -23 NW -24 NW -25 NW -26 NW -27 NW-28NW -4 0 NW -42 Mixing trends MixingDenitr ificatio n tren d We ll s Mixing en d member s Figure 25 15 N versus ln[NO 3 N] of groundwater samples showing effects of denitrification and groundwater mixing. Samples affected by denitrification follow the diagonal trend, whereas groundwater samples for which nitrate is affected by mixing follow an arcuate or horizontal trend away from the denitrification line. NW -3 NW -7NW -8 NW -9NW -10 NW -11 NW -12 NW -13 NW -16 NW -15 NW -17 NW -18 NW -19 NW -20 NW -21 NW -21D NW -22 NW -23 NW -24NW -25NW -26 NW -27 NW -28 NW -40 NW -42 13C () 0 2 4 6 8 103H ( TU) Figure 26 Correlation between 13 C of dissolved inorganic carbon and 3 H for the wells, showing more negative 13 C val ues with greater tritium concentration. TU, tritium units.

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34 Circular 570 Illinois State Geological Survey Summary and Conclusions Seasonal variations in eld and chem ical measurements as well as isotopic results for the 10 springs sampled in the sinkhole plain of southwestern Illinois indicated that water from the surface and soil zone inltrates quite rapidly into the shallow karst aquifer. Temperature, uorite concentrations, and 13 C, 18 O, and D results varied by season for most of the springs. Both 3 H and 13 C of the DIC indicated that the karst aquifer was rapidly recharged with water from the soil zone that carried with it elevated amounts of NO 3 and chloride derived from anthropogenic sources. The bac terial results also attested to the rapid inltration of contaminants from the surface environment. The NO 3 concentrations in the springs, representative of the overall shallow karst groundwater system, were approximately 1.5 to nearly 4 times greater than the threshold background level of 2.5 mg of N/L. The isotopic data suggested that the sources of NO 3 in the spring water were dominated by nitrogen fertil izers and soil organic matter and that livestock and septic efuent played a very minor role. During the spring time, the isotopic values of NO 3 in the water samples plotted close to values typically expected for NO 3 originat ing from soil organic matter and nitrogen fertilizers, which are applied primarily in the early spring (late March and April). The 18 O of the NO 3 in several of the samples from the springs that contained relatively small NO 3 concentrations appeared to have been inuenced by NO 3 sources con taining isotopically heavy 18 O values. Such sources may include NO 3 fer tilizers, atmospheric NO 3 or NO 3 formed in the soil zone with greater than expected 18 O values because of soil water enrichment from evapo transpiration or nitrication (Mayer et al. 2001, Burns and Kendall 2002). More detailed investigations are nec essary to help determine which of these possible sources of 18 O-enriched NO 3 is more responsible for the rela tively large 18 O values observed for some of the NO 3 in shallow ground water and streams in the study area. Chemical, isotopic, and bacterial results indicated that many of the wells received a large portion of their water directly from the soil zone or from water originating close to the surface environment. Because most of the wells in this region are usu ally cased only down to the top few feet of the bedrock, contaminated surface and soil water may easily ow through the crevices and conduits of the weathered zone near the top of the limestone bedrock and into the wells. Five of the 17 wells sampled in this study had NO 3 concentrations that were greater than the USEPA (1992) drinking water standard of 10 mg of N/L. Twelve of the well samples had NO 3 concentrations that were greater than background concentrations. The greatest NO 3 concentrations were detected in the shallow wells located in covered karst areas. However, one of the deeper wells (>70 m) contained relatively large NO 3 concentrations, indicating that water from the surface may easily enter the deeper, uncased wells. The 15 N and 18 O data of the dissolved NO 3 indicate that the source of NO 3 in the wells containing the greatest NO 3 concentrations (>15 mg of N/L) was predominantly from livestock and/or septic waste. These same wells also had large concentra tions of chloride and considerable amounts of coliform bacteria, both of which are typical of animal waste. The isotopic composition of the NO 3 in the wells with smaller NO 3 con 0 20 40 60 80 100 NO3 (mg/L) 0 3H ( TU) 6 5 4 3 2 1 7 8NW -17 NW -11,42 NW -10 NW -3 NW -7 NW -9 NW -12 NW -13 NW -18 NW -16 NW -19 NW -21D NW -20 NW -21 NW -22 NW -23 NW -24 NW -26 NW -14 NW -27 NW -25 NW -8 NW -28 NW -40 Figure 27 Nitrate concentration and 3 H values for wells sampled. TU, tritium units. GMWL Ev aporation Spr ings W ells 0 18O () 10 0D () Figure 28 Isotopic composition ( D and 18 O) of ground water sampled from wells. Water samples from springs are shown for comparison.

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Illinois State Geological Survey Circular 570 35 centrations (1.7 to 12 mg of N/L) indi cated that the predominant source of NO 3 was from nitrogen fertilizers, soil organic matter, or both. The overall positive trend between 15 N and 18 O values, in both the spring and well samples, suggested the occurrence of denitrication within the soil zone, epikarst, and/or shallow karst hydrogeologic system. Microbial denitrication probably occurs primarily by oxidation of dis solved organic matter, considering concentrations of DOC in the samples were relatively large from both springs and wells. However, the very nega tive 34 S values and positive 15 N and 18 O for one well suggest that sulde (pyrite) oxidation could have also played a role in some cases for the denitrication process in this region. This study demonstrated the useful ness of measuring the 15 N and 18 O of dissolved NO 3 in water discharged from springs in a karst terrain to help determine the dominant sources of NO 3 in shallow groundwater basins and the occurrence of denitrication. Measurements of 15 N and 18 O of NO 3 in wells are useful for evaluating the impact of local land use practices on groundwater. The combination of chemical, isotopic, and bacterial anal yses demonstrated the openness of the karst aquifer. Seasonal variations in the chemical and isotopic analyses illustrated how surface contaminants can quickly affect the quality of both shallow and deep wells in a karst environment. Acknowledgments The authors acknowledge the Con servation 2000 Ecosystem Projects program supported by the Illinois Department of Natural Resources and administered through the MonroeRandolph Bi-County Health Depart ments, which funded most of this work. The authors thank W.R. Roy and R. Davis for their helpful sugges tions and insightful comments on earlier drafts of this manuscript. We also acknowledge S.E. Greenberg for her eld assistance and analysis of the oxygen, carbon, and tritium isotopes for this project. We thank Pamella Carrillo for gure drafting and docu ment layout and Mark Zulauf and Cheryl Nimz for editing assistance. References Anderson, T.F., and M.A. Arthur, 1983, Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenviron mental problems, in Stable isotopes in sedimentary geology: SEPM Short Course No. 10, p.1-11-151. ASTM, 1994, Standard test method for total and organic carbon in water by high temperature oxidation and by coulometric detection, Annual Book of ASTM Standards, Section 11.02, Water and Environ mental Technology: West Con shocken, Pennsylvania, p. 2328. Amberger, A., and H.-L. 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Illinois State Geological Survey Circular 570 37 sphere and atmosphere: A review: Chemical Geology, v. 59, no. 1, p. 87102. Hem, J.D., 1985, Study and interpreta tion of the chemical characteristics of natural water: Reston, Virginia, U.S. Geological Survey, WaterSupply Paper 2254, 3rd ed., 263 p. Hoefs, J., 1980, Stable isotope geo chemistry, 2nd ed., Minerals and Rocks Series, v. 9: New York, Springer-Verlag. Holser, W.T., and I. R. Kaplan, 1966, Isotope geochemistry of sedimen tary sulfates: Chemical Geology, v. 1, p. 93135. Hubbard, Jr., D.A., and J.S. Herman, 1991, Travertine-marlThe doughnut-hole of karst, in E.H. Kastning and K.M. Kastning, eds., Proceedings of the Appalachian Karst Symposium: Radford, Vir ginia, March 2326, p. 5964. Hwang, H.-H., C.-L. J. Liu, and K. C. Hackley, 1999, Method improve ment for oxygen isotope analysis in nitrates (abs.): Champaign, Illinois, Geological Society of America, Abstracts with Programs, NorthCentral Section, v. 31, no. 5, April 2223, p. A-23. Illinois Environmental Protection Agency-Illinois Pollution Control Board, 1999, Title 35Environ mental Protection, Subtitle C Water Pollution, Chapter I: Pollu tion Control Board, State of Illinois Rules and Regulations: 302.209. Kaplan, I.R., 1983, Stable isotopes of sulfur, nitrogen and deuterium in recent marine environments, in M.A. Arthur, T.F. Anderson, I.R. Kaplan, J. Veizer, and L.S. Land, eds., Stable isotopes in sedimen tary geology: Society of Economic Paleontologists and Mineralogists, SEPM Short Course No. 10, p. 2-12108. Kelly, W.R., 1997, Heterogeneities in groundwater geochemistry in a sand aquifer beneath an irrigated eld: Journal of Hydrology, v. 198, p. 154176. Kendall C., M.G. Sklash, and T.D. Bullen, 1995, Isotope tracers of water and solute sources in catch ments, in S.T. Trudgill, ed., Solute modelling in catchment systems: New York, John Wiley and Sons, p. 261303. Kendall, C., 1998, Tracing nitrogen sources and cycling in catchments, in C. 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Meiman, J., 1993, The effects of recharge basin land-use practices on water quality at Mammoth Cave National Park, Kentucky: Proceed ings of the National Cave Manage ment Symposium, Bowling Green, Kentucky, October 2326, 1991, p. 105115. Mengis, M., S.L. Schiff, M. Harris, M.C. England, R. Aravena, R.J. Elgood, and A. MacLean, 1999, Multiple geochemical and isotopic approaches for assessing ground water NO 3 elimination in a ripar ian zone: Ground Water, v. 37, no. 3, p. 448457. Mengis, M., U. Walther, S.M. Ber nasconi, and B. Wehrli, 2001, Limi tations of using 18 O for the source identication of nitrate in agricul tural soils: Environmental Science and Technology, v. 35, p. 18401844. Mook, W.G., 1980, Carbon-14 in hydro geologic studies, in J.C. Fontes, ed., Handbook of isotope geochemistry I: New York, Elsevier, p. 4974. Mora, C.I., D.E. Fastovsky, and S.G. Driese, 1993, Geochemistry and stable isotopes of paleosols: Uni versity of Tennessee, Department of Geological Science, Studies in Geology 23, Short Course Manual: Geological Society of America, Annual Meeting, October 2428, Boston, Massachusetts. National Atmospheric Deposition Program (NADP), (NRSP-3)/ National Trends Network, 1998, NADP Program Ofce: Champaign, Illinois, Illinois State Water Survey. Nielsen, H., 1976, SulfurIsotope in nature, in K.H. Wedepohl, ex. ed., Handbook of Geochemistry, v. II-2, sect. 16-B, p. 16-B-116-B-40. ODell, J.W., J.D. Psass, M.E. Gales, and G.D. McKee, 1984, Test method The determination of inorganic anions in water by ion chromatog raphyMethod 300.0 (EPA-600/484-017): U.S. Environmental Pro tection Agency. ORiordan, T., and G. Bentham, 1993, The politics of nitrate in the UK, in T.P. Burt, A.L. Heathwaite, and S.T. Trudgill, eds., NitrateProcesses, Patterns and Management: New York, John Wiley and Sons, p. 403416. Ostlund, H.G., and H.G. Dorsey, 1977, Rapid electrolytic enrichment and hydrogen gas proportional count ing of tritium, in Low-radioactivity measurements and applications: Proceedings of the International Conference on Low-Radioactivity Measurements and Applications, October 610, 1975, the High Tatras, Czechoslovakia, Slovenske Peda gogike Nakladatelstvo, Bratislava. Panno, S.V., 1996, Water quality in karst terrane: The Karst Window, v. 2, no. 2, p. 24.

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38 Circular 570 Illinois State Geological Survey Panno, S.V., K.C. Hackley, H.-H. Hwang, S. Greenberg, I. G. Krapac, S. Landsberger, and D.J. OKelly, 2005, Database for characterization and identication of the sources of sodium and chloride in natural waters of Illinois: Illinois State Geological Survey, Open File Series 2005-1. Panno, S.V., K.C. Hackley, H.-H. Hwang, and W.R. Kelly, 2001, Deter mination of the sources of nitrate contamination in karst springs using isotopic and chemical indica tors: Chemical Geology, v. 179, p. 113128. Panno, S.V., W.R. Kelly, A.T. Martinsek, and K.C. Hackley, 2006, Estimating background and threshold nitrate concentrations using probability graphs: Ground Water, v. 44, no. 5, p. 697709. Panno, S.V., W.R. Kelly, K.C. Hackley, and C.P. Weibel, 2007, Chemical and bacterial quality of aerationtype wastewater treatment system discharge: Ground Water Monitor ing and Remediation, v. 27, no. 2, p. 7176. Panno, S.V., W.R. Kelly, C.P. Weibel, I.G. Krapac, and S.L. Sargent, 1998a, The effects of land use on water quality and agrichemical loading in the Fogelpole Cave groundwa ter basin, southwestern Illinois: Proceedings of the Illinois Ground water Consortium Eighth Annual Conference, Research on Agricul tural Chemicals in Illinois Ground water, April 12, p. 215233. Panno, S.V., W.R. Kelly, C.P. Weibel, I.G. Krapac, and S.L. Sargent, 1998b, Water quality and agrichem ical loading in the Fogelpole Cave groundwater basin, southwestern Illinois: Illinois State Geological Survey, Final Report to the Illinois Groundwater Consortium, 40 p. Panno, S.V., W.R. Kelly, C.P. Weibel, I.G. Krapac, and S.L. Sargent, 2003, Water quality and agrichemical loading in two groundwater basins of Illinois sinkhole plain: Illinois State Geological Survey, Environ mental Geology 156, 36 p. Piskin, K., and R.E. Bergstrom, 1975, Glacial drift in IllinoisThickness and character: Illinois State Geo logical Survey, Circular 490, 35 p. Quinlan, J.F., 1990, Special problems of groundwater monitoring in karst terranes, in D.M. Nielsen and A.I. Johnson, eds., Groundwater and vadose zone monitoring, ASTM STP 1053: Philadelphia, Pennsylvania, ASTM, p. 275304. Rabalais, N.N., R.E. Turner, D. Justic., Q. Dortch, W.J. Wiseman Jr., and B.K. Sen Gupta, 1996, Nutrient changes in the Mississippi River and system responses on the adja cent continental shelf: Estuaries, v. 19, no. 2B, p. 386407. Rvsz, K., and J.-K. Bohlke, 2002, Comparison of 18 O measurements in nitrate by different combustion techniques: Analytical Chemistry, v. 74, p. 54105413. Ryan, M., and J. Meiman, 1996, An examination of short-term varia tions in water quality at a karst spring in Kentucky: Groundwater, v. 34, no. 1, p. 2330. Saxby, D.B., and J.E. Lamar, 1957, Gypsum and anhydrite in Illinois: Illinois State Geological Survey, Circular 226, 26 p. Shearer, G., and D.H. Kohl, 1988, Estimates of N 2 xation in ecosys temsThe need for and basis of the 15 N natural abundance method, in P.W. Rundel, J.R., Ehleringer, and K.A. Nagy, eds., Stable isotopes in ecological research: New York, Springer-Verlag, p. 342374. Silva, S.R., C. Kendall, C.C. Chang, J.C. Radyk, and D.H. Wilkison, 1994, A new method of preparing dissolved nitrate for nitrogen and oxygen iso topic analysis: American Geophysi cal Union, EOS Transactions, v. 75, no. 44, p. 280. Silva, S.R., C. Kendall, D.H. Wilkison, A.C. Ziegler, C.C.Y. Chang, R.J. Avanzino, 2000, A new method for collection of nitrate from fresh water and the analysis of nitro gen and oxygen ratios: Journal of Hydrology, v. 228, no. 1/2, p. 2236. Panno, S.V., I.G. Krapac, C.P. Weibel, and J.D. Bade, 1996, Groundwater contamination in karst terrain of southwestern Illinois: Illinois State Geological Survey, Environmental Geology 151, 43 p. Panno, S.V., E.C. Storment, C.P. Weibel, and I.G. Krapac, 1997b, Bacterial species isolated from groundwater from springs, caves and wells in southwestern Illinois sinkhole plain and their potential sources: Proceedings of the Annual Environmental Laboratories Semi nar, October 23. Springeld, Illi nois, p. 14. Panno, S.V., and C.P. Weibel, 1999, The use of sinkhole morphology and distribution as a means of delineat ing the groundwater basins of four large cave systems in southwest ern Illinois sinkhole plain (abs.): Abstracts with Programs, Geologi cal Society of America, North Cen tral Section, Champaign, Illinois, v. 31, no. 5, p. A 63. Panno, S.V., C.P. Weibel, and W. Li, 1997a, Karst regions of Illinois: Illi nois State Geological Survey, Open File Series 1997-2, 42 p. Panno, S.V., C.P. Weibel, C.M. Wicks, and J.E. Vandike, 1999, Geology, hydrology and water quality of the karst regions of southwestern Illi nois and southeastern Missouri: Field Trip Guidebook No. 2 for the 33rd Meeting of the North-Central Geological Society of America, Champaign-Urbana, Illinois, April 2223, 1999, Illinois State Geologi cal Survey, Guidebook 27, 38 p. Pasquarell, G.C., and D.B. Boyer, 1995, Water quality impacts of agri culture on karst conduit waters, Greenbrier, WV: Proceedings of the National Cave Management Sym posium, Bowling Green, Kentucky, October 2326, 1991, p. 7278. Parry, R., 1998, Agricultural phos phorous and water qualityA U.S. Environmental Protection Agency perspective: Journal of Environ mental Quality, v. 27, no. 2, p. 258261.

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Illinois State Geological Survey Circular 570 39 Tisdale, S.L., W.L. Nelson, J.D. Beaton, and J.L. Havlin, 1993, Soil fertility and fertilizers, 5th ed.: New York, Macmillan Publishing Company, 634 p. U.S. Environmental Protection Agency, 1982, Methods for chemical analysis for water and waste water: Washington, DC, U.S. Environmen tal Protection Agency, EPA-600/479/020, 608-1, 625-1. U.S. Environmental Protection Agency, 1992, SOCs and IOCs, Final Rule (Federal Regulation 56:20:3526): Washington, DC, U.S. Environmental Protection Agency. Vennemann, T.W., and J.R. ONeil, 1993, A simple and inexpensive method of hydrogen isotope and water analyses of minerals and rocks based on zinc reagent: Chem ical Geology, v. 103, p. 227234. Wassenaar, L.I., 1995, Evaluation of the origin and fate of nitrate in the Abbotsford Aquifer using the isotopes of 15 N and 18 O in NO 3 : Applied Geochemistry, v. 10, no. 4, p. 391405. Webb, D.W., S.J. Taylor, and J.K. Krejca, 1994, The biological resources of Illinois caves and other subter ranean environments: Illinois Natural History Survey, Technical Report 1993-8. Willman, H.B., E. Atherton, T.C. Buschbach, C. Collinson, J.C. Frye, M.E. Hopkins, J.A. Lineback, and J. A. Simon, 1975, Handbook of Illi nois stratigraphy: Illinois State Geo logical Survey, Bulletin 95, 261 p. Wood, W.W., 1981, Guidelines for collection and eld analysis of groundwater samples for selected unstable constituents: U.S. Geo logical Survey, Techniques of water resources investigations, bk 1, ch. D2, 24 p. Zlotnick, A.R., 1992, The geochem istry of carbon isotope composi tion of soil gases at the Sycamore Farm Experimental Agricultural Research Station, Madison Town ship, Montgomery County, Ohio: Dayton, Ohio, Wright State Univer sity, M.S. thesis, 113 p.


Description
K.C. Hackley, S.V. Panno, H.-H. Hwang, and
W.R. Kelly
Circular 570 2007
Illinois Department of Natural
Resources
ILLINOIS STATE GEOLOGICAL
SURVEY
William W. Shilts, Chief
615 E. Peabody Drive
Champaign, Illinois 61820-6964
217-333-4747 www.isgs.uiuc.edu
Abstract
About half the residents living in the area of
southwestern Illinois known as the sinkhole plain
obtain their potable water from the region's shallow
karst aquifer. Previous work has shown that the
groundwater from approximately 18% of the wells in the
sinkhole plain has nitrate concentrations in excess of
the U.S. Environmental Protection Agency's drinking
water standard of 10 mg of N/L of water. The nitrate
concentrations in water samples collected from
approximately 50% of the wells and from all of the
springs in the sinkhole plain area are greater than
background concentrations, suggesting that sources
other than naturally occurring organic matter in soil
have contributed additional nitrate to groundwater in
the shallow karst aquifer. This investigation
characterized the geochemistry of the groundwater to
determine which source of nitrogen in the sinkhole
plain is the major contributor to the anomalous
concentration of nitrate observed in the shallow karst
aquifer.
Considering the dominance of agriculture and the
expansion of urban development in the study area,
sources of excessive nitrate and groundwater
contamination include agrichemical, livestock, and
sewage waste. Water samples from 10 karst springs and
17 wells were collected during different seasons and
analyzed for chemical, isotopic, and bacterial
characteristics. The samples from each spring were a
representative composite of the shallow water
recharging the associated watershed. Samples from the
wells reflect individual points within the watersheds
and were more susceptible to influ- ence from local
environments, including anthropogenic activities.
Chemical characteristics and the isotopic
composition of some of the dissolved constituents
varied seasonally in the samples of spring water,
attesting to the rapid infiltration of surface
and soil water into the karst aquifer. Bacteria
concentrations in the springs and most of the
wells were greater than those allowed by county
and state regulations for drinking water. Nitrate
concentrations in the springs covered a fairly
narrow range, from 1.7 to 7.5 mg of N/L. In the
wells, nitrate concentrations varied greatly,
ranging from less than the detection limit
(<0.2 mg of N/L) to 81 mg of N/L.
The isotopic data for the dissolved nitrate
(NO
3
-) from the springs and wells were
useful in distinguishing NO
3
-sources. The nitrogen and oxygen
isotope composition of the NO
3
-ranged from 2.2 to 25.9 per mil (%)
and 5.1 and 21.9% respectively. These isotopic
results suggest that the nitrate sources in
spring water were dominated by fertilizer
nitrogen and soil organic nitrogen that mixed
with nitrate having en enriched
18O signature.
The isotopic results for the wells
indicate that the largest NO
3
-concentrations (between 13 and
80 mg of N/L) originated primarily from
septic and livestock wastes. The isotopic
results for most of the wells with NO
3
-concentrations between 2 and 12
mg of N/L indicate that nitrogen fertilizer
was the dominant NO
3
-source.
The combined chemical, bacterial,
and isotopic analyses of springs and
individual wells provided independent
evidence concerning the major
susceptibility of the karst aquifer
to surface contamination and helped
to differentiate the sources of NO
3
-in the groundwater.
Although many livestock facilities
and septic systems were present in
individual watersheds, the typical
isotopic character- istics of NO -
originating from such point sources
were overwhelmed by the constant
input of nonpoint source nitrogen for
the composite samples of spring
water. However, results from
groundwater samples from several
residential wells did show the impact
of point sources in NO
3
-contamination on a local
scale.


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