Drinking water distribution line break impacts on Barton Springs Salamander

Citation
Drinking water distribution line break impacts on Barton Springs Salamander

Material Information

Title:
Drinking water distribution line break impacts on Barton Springs Salamander
Creator:
Herrington, Chris
Turner, Martha
Publisher:
City of Austin
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Barton Springs (Austin, Texas, United States) ( 30.263819, -97.771395 )
Genre:
Technical Report
serial ( sobekcm )
Location:
United States
Coordinates:
30.263819 x -97.771395

Notes

General Note:
"Chlorine from broken water lines has the potential to be toxic to the endangered Barton Springs salamander. Spills which enter Barton Springs Pool from Barton Creek overtopping the upper dam, overland directly into the pool, or through the aquifer were considered. Only a break in the 48" main near Barton Skyway poses a threat to overtop the dam and enter the pool at a concentration that would be lethal to the salamander. Plume modeling is needed for overland flows entering the pool. However, preliminary estimates of pool concentrations assuming complete mixing indicate that 1 inch diameter pipes are not a problem. As the pipes get larger, the amount of time available to fix the pipe or divert the flow before the pool concentration reaches toxic levels decreases. Flow diversion techniques should be considered. There are water mains in Barton, Williamson, and Slaughter Creeks which have the potential via the aquifer to result in spring concentrations exceeding toxic levels. No critical water lines were identified in Bear or Onion Creek. Two different methods, both estimating decay within the aquifer, are discussed. Both are likely to be conservative indicating the need to position staff at the pool measuring chlorine in the spring discharge if predicted concentrations exceed toxic levels. Then if observed levels at the pool do start to approach toxic levels, immediate action to remove salamanders can be taken." -- Authors
Restriction:
Open Access - Permission by Publisher
General Note:
See Extended description for more information.

Record Information

Source Institution:
University of South Florida Library
Holding Location:
University of South Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
K26-01320 ( USFLDC DOI )
k26.1320 ( USFLDC Handle )
11561 ( karstportal - original NodeID )

USFLDC Membership

Aggregations:
Added automatically
Karst Information Portal

Postcard Information

Format:
serial

Downloads

This item has the following downloads:


Full Text
Description
"Chlorine from broken water lines has the potential to be
toxic to the endangered Barton Springs salamander. Spills
which enter Barton Springs Pool from Barton Creek overtopping
the upper dam, overland directly into the pool, or through
the aquifer were considered. Only a break in the 48" main
near Barton Skyway poses a threat to overtop the dam and
enter the pool at a concentration that would be lethal to the
salamander. Plume modeling is needed for overland flows
entering the pool. However, preliminary estimates of pool
concentrations assuming complete mixing indicate that 1 inch
diameter pipes are not a problem. As the pipes get larger,
the amount of time available to fix the pipe or divert the
flow before the pool concentration reaches toxic levels
decreases. Flow diversion techniques should be considered.
There are water mains in Barton, Williamson, and Slaughter
Creeks which have the potential via the aquifer to result in
spring concentrations exceeding toxic levels. No critical
water lines were identified in Bear or Onion Creek. Two
different methods, both estimating decay within the aquifer,
are discussed. Both are likely to be conservative indicating
the need to position staff at the pool measuring chlorine in
the spring discharge if predicted concentrations exceed toxic
levels. Then if observed levels at the pool do start to
approach toxic levels, immediate action to remove salamanders
can be taken." --
Authors



PAGE 1

Chris Herrington, P.E. and Martha Turner, P.E. Environmental Resources Management Division Watershed Protection Department City of Austin SR-09-03 September 2009 Drinking water distribution line break impacts on Barton Springs Salamander Abstract Ch lo rin e from b r oken wa ter li n e s ha s th e po t e n tia l to b e to xic to th e enda ng ered Ba rton Sp ring s sa l a man d e r. S p ills wh ich enter Ba rt o n Sp ri n g s Po o l from Ba rton Creek o vertopp ing the up p e r d a m, overla nd d i rectly in to t h e po ol or t h r o u g h t h e a q u i f e r w e re co nsi d e r ed Onl y a bre a k i n t h e 4 8 m a i n nea r B a rt o n Skyw ay p o ses a t h reat to o v ertop th e d a m an d en ter th e poo l a t a co n c en tra tio n tha t wou ld b e leth a l t o th e sa lamand er. Plume modeling is ne eded for overl a nd flows e n tering the pool. However, preliminar y estimates of pool c onc entrations ass u mi ng co m p l e t e mi xi n g i n di cat e t h at 1 i n ch di a m et er pi pes are n o t a p r obl e m As t h e pi pe s get l a r g er, t h e amount of time av ailable t o fi x the pipe or di vert th e flow before the pool conce n tr ation reac hes toxic l evels d ecrea ses. Flow d iversion tech n i q u e s sh ou ld b e con s id ered Th ere a r e w a t e r ma in s in Barto n Willia mso n a n d Slaughter Cree ks which have t h e pote n tial vi a the aquifer to result in s p ri ng c once n tr ations excee ding t o xic levels. No critical water li nes were identified in Be ar or Oni o n Creek. Tw o different methods, bot h estimating d eca y with in t h e aq u ifer, a r e d iscu s sed. Bo t h a r e likely to b e co nserva tive in d ica ting the n e ed to po sitio n sta ff a t the pool me as uring chl o rine i n the s p ring discharge if pre d icted conce n tr ations excee d t o xic levels. Then if obs erved levels at the pool do start to approach toxic levels, imme diate act i on t o re move s a lamanders c a n be taken. Introduction Chlorine in tr eated drinkin g water m a y be toxic to t h e endangered Barton Sprin g s salamander. A t y pical chlorine concentration in d istribution lin es is 1.5 m g /L. Total chlo rine toxicit y t ests on Eurycea nana y ield a 48-h o u r no-effects concentration (NOEC) of 0.062 5 m g /L and a 48hour LC50 concentration of 0.08 8 m g /L. A substantial am ount of chl o rinated water is spilled when a water main is broken. The potent ial discharge from broken water mains pressurized at 90 lb/in2 is shown in Tabl e 1. Chlorine decay m a y be described as a fir s t-order r eacti on (decay ) over ti m e How e ver, overland travel times for chlorinated water from distribution line breaks are difficult to predict, so decay with distance was e s ti m a t e d for local spills. Overland distan ce traveled is easy to predict using GIS. Three scenari o s that could i m pact Barto n Springs sala m anders are evaluated: Scenario 1 : A break in a water line that will flow int o Barton Creek and overtop the upper dam of Barton Spr i ngs Pool Scenario 2 : A break in a water line that will flow ov erland directly into Barton Springs Pool (downstream of the bypass channel diverting Ba rton C r eek flow around Barton Springs Pool). Scenario 3 : A break in the recharge or contributi ng z one that will r echarge the aquifer and discharge from Barton Springs. SR-09-03 Page 1 of 13 Septem ber 2009

PAGE 2

Table 1. Potential Discharge* from Broken Water Mains pressurized at 90 lb/in2. pipe diameter (in) gal/min ft3/s gal/hour 1 198 0.4 11,880 2 792 1.8 47,520 3 1,783 4.0 106,980 6 7,131 15.9 427,860 4 3,169 7.1 190,140 8 12,677 28.2 760,620 12 28,524 63.6 1,711,440 16 50,708 113.0 3,042,480 24 114,094 254.2 6,845,640 30 203,818 397.2 10,696,320 36 178,272 572.0 15,402,660 48 456,376 1017.0 27,382,560 60 713,087 1589.0 42,785,220 72 1,026,846 2288.2 61,610,760 *Greeley equation for roughly circular holes: Q(gpm)=30.394*area(in2)* [pressure(lbs/in2)]. Decay with distance Chlorine decay was estimated based on distance traveled using total chlorine samples at measured points downstream of water line breaks (Figure 1). Total chlo rine measurements were made in the field using a HACH spectrophotometer with a colori metric indicator (HACH method 2231). Six individual water line break events were monitored by City of Aus tin Spill and Complaint Response (SCRP) staff. 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 010002000300040005000600070008000 Distance (ft)Cl (mg/L) 1 8" fast 2 6" mod 4 6" fast 5 2" slow 6 ? mod 7 ? mod Figure 1. Loss of total chlorine versus distance traveled measured by SCRP staff. Average chlorine loss with distan ce rates were calculated for several surface types (Table 2) by linear regression. The overall average (all surfaces) was used to estimate decay for predicting impacts to Barton Springs from chlorinated water line breaks. Decay is greatest for flows over natural (non-pavement) surfaces most likely due to increased organic material and decreased linear velocity due to friction. The SR-09-03 Page 2 of 13 September 2009

PAGE 3

differences in estimated decay between flow in enclo sed pipes and over pavement are most likely due to sunlight. Table 2. Chlorine decay with flow path distance slopes from linear regression. Surface Type Chlorine decay (mg/Lft) Enclosed Pipe 0.00019 Pavement 0.00023 Natural Surface 0.00041 Overall Average 0.00021 Predicted decay rates based on field data (equation 1) are only representative of initial conditions. As the time of the water line break flow increases, decay rates will most likely decrease. Linear decay rates measured in Gilleland Creek by COA staff where re sidual chlorine from treated wastewater discharge provides a constant source of chlorine to the creek were more than an order of magnitude lower (0.0000085 mg/Lft). [chlorine, mg/L] = ([chlorine, mg/L] in pipe) (0.00021 mg/Lft)distance(ft) (equation 1) Decay with Time Once in the aquifer, chlorine decay was estimated ba sed on time of travel using a first-order decay model as modified by Abdel-Gawad and Bewtra (1988) with a decay rate of 0.133 d-1 (neglecting evaporation and photolysis and assuming turbulent flow conditions at 20C) as ( t in days): [chlorine] = 1.5e-0.133t (equation 2) In an alternate method, decay within the aquife r was estimated from the Worthington equation which relates the mass of dye injected into a karst aquifer to spring discharge concentrations (Worthington and Smart, 2003). m = 0.73 (tQc)0.97 (equation 3) where: m is the mass of dye injected in grams, t is the time elapsed between injec tion and peak recovery in seconds, Q is the output discharge in m3/s, and c is the peak recovery dye concentration in g/m3 Solving for concentration in equations 3: c = 1.38 m1.03093 / tQ (equation 4) Scenario 1: Water line breaks in surface flow in Barton Creek that overtops the dam and flows into Barton Springs Pool Flows in Barton Creek above Barton Springs Pool in excess of 500 ft3/s will overtop the upper dam of Barton Springs Pool and enter salamander habitat. Using a total chlorine decay rate of -0.00021 mg/Lft and a starting (in-pipe) chlorine concentration of 1.5 mg/L, any water line break within 6,858 feet could yield total chlorine concentrations greater than the NOEC at the point of entry into the pool (equation 1). SR-09-03 Page 3 of 13 September 2009

PAGE 4

Critical water lines were identified in GIS using a 6,858 ft buffer around the Pool. The flow length function was used to generate a grid of real flow path distances accounting for topology based on the flow direction grid (using a 10 m cell size). All water lin es within a minimum overland flow path distance of 6,858 ft of Barton Springs Pool were identified and ev aluated to not only verify that the water would flow to the pool, but also whether the water would flow to Barton Creek upstream of the dam or to the pool itself (Figure 2). Breaks in mains were modeled as a completely sever ed line yielding the maximum possible flow rate assuming the line was pressurized to 90 lb/in2. For this scenario, the pool is treated as a steady-state, completely mixed batch reactor. Chlorine impacts were assessed under varying Barton Creek flow above Barton Sp rings Pool (USGS gage 08155400) and Barton Springs dischar ge (USGS gage 0815550 0) conditions to account for both dilution and whether the addition of chlorinated water to Bart on Creek would result in sufficient total creek flow to potentially overtop the dam. At least 220 indivi dually mapped water lines were identified that could break and drain to Barton Creek upstream of the pool with a chlorine concentration above the NOEC at the upper dam. When Barton Creek above Barton Springs is dry (approximately 25% of the time), only a break from a 48 main (flow = 1017 ft3/s) would yield sufficient flow to overtop the dam. A 48 line crosses Barton Creek near the eastern end of Barton Skyway. At any Barton Springs discharge a 48 line break would yield chlorine concentrations in the pool above the LC50 if Barton Creek is not flowing. Even at Barton Creek flow approaching the 99th percentile of existing gauge data (94 ft3/s), some segments of the 48 main still have the potential to deliver chlorine to Ba rton Springs pool above the NOEC at any historically measured Barton Springs flow. When Barton Creek is dry (chlorine concentrations from the break are at a maximum), the maximum total chlorine concentration in the break flow is estimated to be 0.20 mg/L from the 48 main at the upper dam (prior to mixing with Barton Springs water). Flow from any other break would not be sufficient to overtop the dam except in combination with Barton Creek water during extreme high flow conditions (approaching the 98th percentile of flow in Barton Creek), likely to occur only during storm events. Just as the dam is overtopped (when combined break and Barton Creek flow equals 501 ft3/s), any historically measured Barton Springs discharge would be sufficient to dilute chlorine concentrations in the pool to less than the NOEC assuming complete mixing. Any Barton Creek natural flows above the 97th percentile would sufficiently dilute break flows to levels that any historically measured Barton Springs discharge values would further dilute to less than the NOEC. Scenario 1 Conclusion: Based on scenario 1 analyses, only a break in the 48 main near Barton Skyway poses a threat to overtop the dam and enter the pool at a concentration that would be lethal to the salamander. SR-09-03 Page 4 of 13 September 2009

PAGE 5

Figure 2. Water lines within critical distance of Barton Springs Pool. Scenario 2: Water line breaks that flow overland into Barton Springs Pool Water line breaks that flow directly into the pool ap pear more problematic. Any of the identified lines 2 in diameter or larger have the ability to produce chlo rine concentrations in Barton Springs pool above the NOEC. The specific interactions of flows from each of these breaks must be modeled indi vidually to determine if the chlorine plume would reach salamander habitat. At least 78 water lines were identified that if broken could flow directly into Barton Springs pool based on the flow direction grid (Figure 2). The point of entry for all lines south of the pool is (at the westernmost edge) approximately 30 feet east of the diving board, downstream of the salamander habitat near the spring discharge fissures. The maximum diameter of any of the lines south of the pool is 16, yielding a maximum possible 113 ft3/s of discharge. The two 16 lines are located near Barton Hills Road and Rabb Road. Evaluation of flow patterns within Barton Sp rings pool is necessary to estimate the impacts of these breaks. SR-09-03 Page 5 of 13 September 2009

PAGE 6

Figure 3. Water Lines with Diameter in In ches in the Vicinity of Barton Springs Pool Identified water lines north of the pool have the poten tial to flow into the pool upstream of salamander habitat near the spring discharge fissures. The maximum line diameter north of the pool within the critical area is 6, yielding a maximum possible flow of 15.9 ft3/s. Based on dilution with existing spring discharge, no measured historical spring discharge woul d be sufficient to dilute chlorine concentrations from these lines to the NOEC. Temporary flow divers ion of this line should be instituted in case of breakage. Individual drinking water spill effects based on flow patterns within the pool must be evaluated. For example, on 28 September 1992, when Barton Springs discharge was 121 ft3/s, improper application of chlorine used to clean the pool resulted in a fish k ill. Following this fish kill, salamanders were only found in a 50 ft2 area immediately around the largest of the main springs outflow points, instead of throughout the more extensive habitat area of approximately 4,300 ft2 where they had previously been located (Chippindale et al 1993). Plume modeling is planned, but is dependent on accurate depth measurements and some estimates of flow velo city at multiple points within the pool. Preliminary Estimate Prior to Plume Modeling A preliminary estimate of pool chlorine concentrati ons can be made by assuming complete instantaneous mixing in the pool with chlorine decay from 1.5 to 1.0 mg/L prior to the chlorinated drinking water entering the pool. Table 3 shows the time it would take for the pool to reach the NOEC and the 48-hour lethal concentration (LC50) of 0.088 mg/L following a water line break for the specified spring discharge levels. SR-09-03 Page 6 of 13 September 2009

PAGE 7

Table 3. Time for the Average Chlorine Concentr ation in Barton Springs Pool to Exceed the NOEC and LC50 following a Water Main Break. Pipe size (inches) @ 90 psi / pipe discharge (cfs) Time for the average pool chlorine concentration to exceed the NOEC of 0.0625 mg/L at 0-120 cfs from spring and 1mg/L chlorine from spill inflow Time for the average pool chlorine concentration to exceed the LC50 of 0.088 mg/L at 0-120 cfs from spring and 1mg/L chlorine from spill inflow 1 inch / 0.4 cfs 26.5 hours at 0 cfs 37.6 hours at 0 cfs 56 hours at 5 cfs will not exceed at >5 cfs will not exceed at >10 cfs 2 inch / 1.8 cfs 5.8 hours at 0 cfs 8.3 hours at 0 cfs 7.3 hours at 10 cfs 9.7 hours at 5 cfs 16.25 hours at 25 cf s 11.9 hours at 10 cfs will not exceed at >30 cfs 16.75 hours at 15 cfs will not exceed at >20 cfs 4 inch / 7.1 cfs 1.5 hours at 0 cfs 2.1 hours at 0 cfs 1.65 hours at 20 cfs 2.5 hours at 20 cfs 2 hours at 50 cfs 3.5 hours at 50 cfs 6.3 hours at 105 cfs 6.6 hours at 70 cfs Will not exceed at 110 cfs will not exceed at >75 cfs 6 inch / 15.9 cfs 40 to 55 minutes 57 minutes at 0 cfs 62 minutes at 25 cfs 76 minutes at 75 cfs 100 minutes at 120 cfs 8 inch / 28.2 cfs 23 to 27 minutes 32 to 41 minutes 16 inch / 113 cfs 6 minutes 8-9 minutes A 1 pipe break is not projected to be a threat to the salamander problem except an extreme drought. A 2 pipe break is not projected to be threat to the salamander unless spring flow is less than 30 ft3/s, and because a 2 pipe break would have to run uncontai ned for many hours to reach problematic chlorine levels there should be enough time to contain, divert, or fix the break. For 4 pipes, however, there would be only 2 to 6 h ours to control the situation. As pipe sizes increase, the time is too short for effective intervention unless the chlorinated water enters the pool downstream of the salamander habitat so that the gates in the downs tream dam can be opened to divert the flow. If the flow is below 54 ft3/s then the gates cannot be opened (no pool drawdown can occur under the 10a permit conditions) and all effort should be directed towards protecting the salamanders in Eliza Spring rather than in the main pool. In the pool it is likely onl y those salamanders closest to the spring outlet would survive. Scenario 3: Water Li ne Break in recharge or contributing zone All water lines in the recharge zone and in the contri buting zone within the critical distance (6,858 feet) of the upper recharge zone boundary were assessed. Following the assumptions detailed for scenario 1, wa ter line breaks in the contributing zone were assumed to flow overland to the upper recharge zone boundary with a decay in total chlorine concentration of -0.00021 mg/Lft (equation 1). Rech arge was assumed to occur immediately and up to the maximum predicted recharge rates (Barrett and Charbeneau 1996) at the upper recharge zone boundary (Table 4) at the point where the creek crossed the boundary. Additional discharge above maximum predicted recharge rates was assumed to continue downstream across the recharge zone. For SR-09-03 Page 7 of 13 September 2009

PAGE 8

Barton Creek, this additional flow was assessed to de termine if it would overtop the dam and enter Barton Springs pool. Groundwater divides separating recharge of Cold Spring from Barton Spring as determined by dye tracing (Turner and ODonnell 2005) were us ed to divert water from portions of Barton and Williamson Creeks to Cold Springs. For prediction, at times when th ere was no existing natural flow in creek channels, 15 ft3/s of recharge was diverted to Cold Springs with the remainder of flow proceeding downstream. When natural flow was present, up to 30 ft3/s of discharge was diverted to Cold Springs with the remainder continuing downstream (Nico Hauwert pe rsonal communication 14 May 14 2007). Table 4. Maximum recharge rates by watershed (Barrett and Charbeneau 1996). Watershed Maximum recharge lost to Cold Springs (ft3/s) Maximum recharge rate to Barton Springs (ft3/s) Onion 0 120 Bear and Little Bear 0 66 Slaughter 0 52 Williamson 1 13* Barton 15-30** 250* *after recharge to Cold Springs **15 ft3/s when Barton Creek is dry, 30 ft3/s when Barton Creek is flowing Once in the creek channel, chlorinated water was dilu ted with varying natural creek discharge generated from USGS gages based on the available period of record (table 5). Water lines in the recharge zone were assumed to flow directly into the aquifer. Table 5. Summary of USGS gages to represent natural creek and spring flow. Watershed USGS Gage Barton Barton Creek @ Loop 360 (08155300) Slaughter Slaughter Creek @ FM1826 (08158840) Williamson Williamson Creek @ Oak Hill (08158920) Barton Springs Barton Springs @ Austin, TX (08155500) In the aquifer, chlorinated water was dilute d with varying Barton Springs discharge. Following dilution, chlorine decay in the aquifer was calculated using equation 2. [chlorine] = 1.5e-0.133t (equation 2) Time within the aquifer in equation 2 was estimated from dye studies done in the Barton Springs Zone (Table 6, Figure 4) (COA 2005). Table 6. Travel times in aquifer based on dye studies. Travel Time Zone Travel Time in hours Travel Time (hours) Used in Calculation from midpoint of range A 0-12 6 B 12-24 18 C 24-48 36 D 48-72 60 E >72 84 SR-09-03 Page 8 of 13 September 2009

PAGE 9

Figure 4. Time of Travel Zones for the Ba rton Springs Segment of the Edwards Aquifer (Zones: A <12 hrs, B<24 hrs, C< 48 hrs, D <72 hrs, E>72 hrs) In the contributing zone, at least 1,428 water line segme nts were identified within the critical distance of the recharge zone boundaries. No critical water lines were identified in Bear Creek or Onion Creek. The spatial extent of the water line coverage should be re-evaluated to confirm that there are no lines within the critical distance in these watersheds. When natural discharge in any given creek is absent, there are 358 water line segments in the contributing zone with pipe diameters varying from 6 to 48 a nd located within the Barton, Slaughter and Williamson creek watersheds that could not be diluted to NOEC at any historically measured Barton Springs discharge. An additional 267 water line segments are potentially problematic but could be diluted with Barton Springs discharge to NOEC in a reasonable range of Barton Springs discharge values (18 to 122 ft3/s). SR-09-03 Page 9 of 13 September 2009

PAGE 10

Additional pre-existing natural creek flow would further dilute chlorine from water line breaks, although the contributing creeks typically maintain low to no flow during normal conditions suggesting that under nominal conditions dilution effects would not be substan tial. An improvement to this method could be to account for loss of chlorine with overland flow befo re chlorinated water recharges the aquifer at known karst features within the recharge zone. Preliminary Estimate Prior to the development of Maps Identifying Pipes Until maps of water main segments that could resu lt in pool concentrations over the NOEC or the LC50 are completed, a method to identify when the salama nder biologists should be concerned is needed. Two options are identified. Option 1 is based on the method discussed above and depends on decay of chlorine while traveling overland, dilution in the creek and in the aquifer and decay while traveling through the aquifer. Option 2 is based on predicte d dye concentrations at Barton Springs from a mass of dye injected directly into the aquifer (Worthington Equation, equation 4) (COA 2005). Since the interaction of dye with organic matter is hypothesized to be similar to that of chlorine, the decay determined by the Abdel-Gawad and Bewtra (equation 2) was not added onto the decay predicted by the Worthington Equation (equations 3,4). Option 1 predicts higher concentrations at the Ba rton Springs than Option 2, although Option 2 over estimates dye concentrations in some cases. Since both methods are likely to overestimate the chlorine concentrations at Barton Springs, a suggested proce dure would be to start monitoring total chlorine concentrations in the field hourly at Barton Springs if Option 1 indicates the potential for chlorine concentrations to exceed the LC50, and to start removing salamanders as soon as measured concentrations reach a critical value to be determined by salamander biologists. If Option 2 also indicates concentrations approaching the LC50, then increase the frequency of field chlorine monitoring and initiate salamander rescue operations. Option 1: This requires calculations! 1. Figure out the distance in feet from the water lin e break to the aquifer combining overland and creek distances. 2. Find the decrease in chlorine concentrations by apply a decay rate of -0.00021 mg/Lft (equation 1), assume a starting chlorine concentration in the pipe of 1.5 mg/L. (example: for 1,000 ft, the decrease is 1000 times -0.00021 mg/L = 0.21 mg/L and the chlorine level is now 1.5 0.21 = 1.29 mg/L) 3. If the creek is flowing, get the flow from the US GS website (see Table 5) and dilute the spill concentration with the creek flow. (example: cr eek flow = 8 cfs and pipe flow = 2 cfs and spill concentration after traveling 1000 ft is 1.29 mg/L: Concentration entering the aquifer is pipe flow divided by (creek flow + pipe flow) times the spill concentration or 2 cfs/(2 cfs+8 cfs) times 1.29 mg/L = 0.2*1.29 = 0.258 mg/L. 4. Estimate the travel time (see Figure 4 and Table 6); use 6 hours for Zone A, 18 hours for Zone B, etc. 5. Find the decrease in chlorine concentrations in the aquifer by using equation 2 ( t in days). [Chlorine] = chlorine at recharge e-0.133t (example: for Zone 2 or 18 hours, t=18/24 = .75 days chlorine =0.258 mg/L e-0.133 0.75 = 0.258 mg/L 0.905 = 0.234 mg/L) 6. Get Barton Springs discharge from the USGS web site and dilute the concentration in the combined creek and pipe flow with the aquifer discharge. (for example if the flow at Barton Springs is 20 cfs and the creek+pipe flow is 10 cfs, then the chlorine level is (10cfs/(10cfs+20cfs)).234 mg/L = 0.078 SR-09-03 Page 10 of 13 September 2009

PAGE 11

7. If the calculated concentration is above the NOEC of 0.0625 mg/L, immediately notify the salamander biologists and begin monitoring tota l chlorine in Barton Springs pool. If the predicted concentration is above the LC50 of 0.088 mg/L, initiate monitoring and consider salamander removal from the springs. Option 2 (Use Table 7): Use the regression equation (4) relating mass of dye (c hlorine) injected into the aquifer, spring flow, travel time and concentration at the spring (COA 2005, Worthington and Smart 2003) to determine what size water line breaks in which travel time zone are of concern. The water is assumed to enter the aquifer with a concentration of 1 mg/L. The mass of chlorine used in the equation is the mass spilled in one hour. A longer spill is assumed to maintain the same mass per hour and thus the same concentration at Barton Springs, but for a longer period of time. This process will typically overestimate the concentrations at the spring, since some overland flow prior to enteri ng the aquifer is usual, and the regression equation normally overestimates the dye concentrations at Barton Springs (COA, 2005). Equation 4 was used to determine what size water main, at what Barton Springs discharge, in what travel time zone (Figure 4), could result in a peak concentration at Barton Springs over the LC50 of 0.088 mg/L of chlorine. The results from the analysis are shown in Table 7. To use the table, first figure out what Zone you are in, then determine the discharge at Ba rton Springs. The associated pipe size tells you what the smallest pipe or spill size in gallons per minute is that would cause the concentrations at Barton Springs to exceed the LC50. If, for example, the break is in Zone A and your pipe is 1 then there is probably not a problem for the salamanders. If, however the discharge at Barton Springs is 35 cfs, and your pipe is 6 then the salamander biologists need to be notified. If discharge is 70 cfs and the pipe is 6 then notification is not needed. If the break can not be fixed for a long time then notification should occur. SR-09-03 Page 11 of 13 September 2009

PAGE 12

Table 7. Discharge Levels/ Spill size / Water Main Diameter/ Travel Time Zone resulting in Chlorine Levels exceeding the LC50 0f 0.088 mg/L at Barton Springs Travel Time Zone Travel Time in hours Discharge at Barton Springs (cfs) Water Main Diameter spill gallons per minute status chlorine > 0.088 mg/L = LC50 A 6 (0-12) 2 Inch No A 6 10 3 Inch 1783 Yes A 6 20 50 6 Inch 7133 Yes A 6 60 90 8 Inch 12683 Yes A 6 100 12 Inch 28517 Yes B 18 (12-24) 3 Inch No B 18 10 6 Inch 7133 Yes B 18 20 30 8 Inch 12683 Yes B 18 40 70 12 Inch 28517 Yes B 18 80 100 16 Inch 50700 Yes C 36 (24-48) 6 Inch No C 36 10 8 Inch 12683 Yes C 36 20 30 12 Inch 28517 Yes C 36 40 60 16 Inch 50700 Yes C 36 70 100 24 Inch 114100 Yes D 60 (48-72) 8 Inch No D 60 10 20 12 Inch 28517 Yes D 60 30 16 Inch 50700 Yes D 60 40 90 24 Inch 114100 Yes D 60 100 36 Inch 256717 Yes E 84 (>72) 8 Inch No E 84 10 12 Inch 28517 Yes E 84 20 16 Inch 50700 Yes E 84 30 60 24 Inch 114100 Yes E 84 70 100 36 Inch 256717 Yes SR-09-03 Page 12 of 13 September 2009

PAGE 13

SR-09-03 Page 13 of 13 September 2009 References Abdel-Gawad, S. T., and J. K. Bewtra. 1988. Decay of chlorine in diluted municipal effluents. Canadian Journal of Civil Engineering 15(6): 948-954. Barrett, M. E., and R. J. Charbeneau. 1996. A pa rsimonious model for simulation of flow and transport in a karst aquifer. Center for Research in Wa ter Resources, University of Texas at Austin. CRWR Technical Report 269. COA 2005. Turner, M., and L. ODonnell. Response Tier Development Document: Barton Springs Salamander Catastrophic Spill Plan. City of Austin, Watershed Prot ection and Development Review Department, Environmental Res ource Management Division. SR-05-01. Worthington, Stephen,R.H., and C. Smart, 2003. Empirical Determination of Tracer Mass for Sink to Spring Tests in Karst, in Sinkholes and the Engineering and Environmental Impacts of Karst, Geotechnical Special Publication No. 122, Proceedings of the Ninth Multidisciplinary Conference, September 6-10, Huntsville, Alabama, American Society of Civil engineers pp. 287295.


printinsert_linkshareget_appmore_horiz

Download Options

close
Choose Size
Choose file type
Cite this item close

APA

Cras ut cursus ante, a fringilla nunc. Mauris lorem nunc, cursus sit amet enim ac, vehicula vestibulum mi. Mauris viverra nisl vel enim faucibus porta. Praesent sit amet ornare diam, non finibus nulla.

MLA

Cras efficitur magna et sapien varius, luctus ullamcorper dolor convallis. Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Fusce sit amet justo ut erat laoreet congue sed a ante.

CHICAGO

Phasellus ornare in augue eu imperdiet. Donec malesuada sapien ante, at vehicula orci tempor molestie. Proin vitae urna elit. Pellentesque vitae nisi et diam euismod malesuada aliquet non erat.

WIKIPEDIA

Nunc fringilla dolor ut dictum placerat. Proin ac neque rutrum, consectetur ligula id, laoreet ligula. Nulla lorem massa, consectetur vitae consequat in, lobortis at dolor. Nunc sed leo odio.