U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2011–5146

U.S. Geological Survey National Water-Quality Assessment Program

Hydrogeology, Chemical Characteristics, and Water Sources 

and Pathways in the Zone of Contribution of a Public-Supply 

Well in San Antonio, Texas

NW

Spring

FAULT

EdwardsTrinity aquifer

Trinity 

aquifer

Edwards

aquifer

EDWARDS PLATEAU

Saline

Fresh

Not to scale

Recharge

zone 

Confined zone

BALCONES

FAULT ZONE

Contributing zone

(Catchment area)

NE

SE

Recharge

Discharge

Urban area

Spring Generalized

groundwater

 flow

Generalized conduit system

Upper

confining units

Supply

well
 
Hydrogeology, Chemical Characteristics, 

and Water Sources and Pathways in the 

Zone of Contribution of a Public-Supply 

Well in San Antonio, Texas

By MaryLynn Musgrove, Lynne Fahlquist, Gregory P. Stanton, Natalie A. Houston, 

and Richard J. Lindgren

U.S. Geological Survey National Water-Quality Assessment Program

Scientific Investigations Report 2011–5146

U.S. Department of the Interior

U.S. Geological Survey
Suggested citation:

Musgrove, M., Fahlquist, L., Stanton, G.P., Houston, N.A., and Lindgren, R.J., 2011, Hydrogeology, chemical characteristics, and water sources and pathways in the zone of contribution of a public-supply well in San Antonio, Texas: U.S. 

Geological Survey Scientific Investigations Report 2011–5146, 194 p.

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Foreword

The U.S. Geological Survey (USGS) is committed to providing the Nation with reliable 

scientific information that helps to enhance and protect the overall quality of life and 

that facilitates effective management of water, biological, energy, and mineral resources 

(http://www.usgs.gov/). Information on the Nation’s water resources is critical to ensuring longterm availability of water that is safe for drinking and recreation and is suitable for industry, 

irrigation, and fish and wildlife. Population growth and increasing demands for water make the 

availability of that water, measured in terms of quantity and quality, even more essential to the 

long-term sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 

1991 to support national, regional, State, and local information needs and decisions related to 

water-quality management and policy (http://water.usgs.gov/nawqa). The NAWQA Program 

is designed to answer: What is the quality of our Nation’s streams and groundwater? How 

are conditions changing over time? How do natural features and human activities affect the 

quality of streams and groundwater, and where are those effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and aquatic life, 

the NAWQA Program aims to provide science-based insights for current and emerging water 

issues and priorities. From 1991 to 2001, the NAWQA Program completed interdisciplinary 

assessments and established a baseline understanding of water-quality conditions in 51 of the 

Nation’s river basins and aquifers, referred to as Study Units (http://water.usgs.gov/nawqa/

studies/study_units.html).

National and regional assessments are ongoing in the second decade (2001–12) of the 

NAWQA Program as 42 of the 51 Study Units are selectively reassessed. These assessments 

extend the findings in the Study Units by determining water-quality status and trends at sites 

that have been consistently monitored for more than a decade, and filling critical gaps in 

characterizing the quality of surface water and groundwater. For example, increased emphasis 

has been placed on assessing the quality of source water and finished water associated with 

many of the Nation’s largest community water systems. During the second decade, NAWQA is 

addressing five national priority topics that build an understanding of how natural features and 

human activities affect water quality, and establish links between sources of contaminants, the 

transport of those contaminants through the hydrologic system, and the potential effects of contaminants on humans and aquatic ecosystems. Included are studies on the fate of agricultural 

chemicals, effects of urbanization on stream ecosystems, bioaccumulation of mercury in stream 

ecosystems, effects of nutrient enrichment on aquatic ecosystems, and transport of contaminants to public-supply wells. In addition, national syntheses of information on pesticides, volatile organic compounds (VOCs), nutrients, trace elements, and aquatic ecology are continuing. 

The USGS aims to disseminate credible, timely, and relevant science information to 

address practical and effective water-resource management and strategies that protect and 

restore water quality. We hope this NAWQA publication will provide you with insights and 

information to meet your needs and will foster increased citizen awareness and involvement in 

the protection and restoration of our Nation’s waters. 

The USGS recognizes that a national assessment by a single program cannot address all 

water-resource issues of interest. External coordination at all levels is critical for cost-effective 

management, regulation, and conservation of our Nation’s water resources. The NAWQA 

Program, therefore, depends on advice and information from other agencies—Federal, State, 

regional, interstate, Tribal, and local—as well as nongovernmental organizations, industry, academia, and other stakeholder groups. Your assistance and suggestions are greatly appreciated.

 William H. Werkheiser

USGS Associate Director for Water
 
v

Contents

Abstract ..........................................................................................................................................................1

Introduction ....................................................................................................................................................2

Purpose and Scope .............................................................................................................................3

Description of the Study Area ...........................................................................................................3

Overview of Karst Aquifers ................................................................................................................9

Summary of Previous Studies ............................................................................................................9

Acknowledgments .............................................................................................................................10

Methods ........................................................................................................................................................10

Design of Well Network ....................................................................................................................10

Drilling, Well Installation, Coring, and Core Analysis ..................................................................11

Geophysical and Depth-Dependent Flow Measurements ..........................................................12

Collection of Water Samples ...........................................................................................................13

Depth-Dependent Samples ..............................................................................................................14

Temporal Water Samples .................................................................................................................14

Laboratory Analytical Methods .......................................................................................................14

Groundwater Age-Dating Methods ................................................................................................16

Quality Control ....................................................................................................................................17

Statistical Methods and Geochemical Modeling .........................................................................20

Hydrogeologic Setting ................................................................................................................................20

Aquifer Framework and Lithology ...................................................................................................20

Estimation of Aquifer Properties .....................................................................................................22

Groundwater Occurrence and Movement ....................................................................................23

Potential Sources of Contamination ...............................................................................................27

Groundwater Chemistry .............................................................................................................................29

Field Parameters ................................................................................................................................29

Chemical Composition and Mineral Saturation Indexes .............................................................31

Major Elements and Trace Metals ..................................................................................................32

Oxidation-Reduction Conditions ......................................................................................................36

Dissolved Gases .................................................................................................................................39

Nutrients and Stable Isotopes of Nitrogen ....................................................................................39

Strontium Isotopes .............................................................................................................................42

Stable Isotopes of Hydrogen and Oxygen .....................................................................................42

Organic Constituents .........................................................................................................................43

Groundwater Age Tracers and Age Distributions ........................................................................47

Depth-Dependent Water Chemistry ...............................................................................................56

Temporal Variability in Water Chemistry ........................................................................................61

Processes Affecting Transport of Natural and Anthropogenic Contaminants to the PublicSupply Well .....................................................................................................................................72

Sources of Water and Solutes and Movement to Supply Wells ................................................72

Supply-Well Vulnerability to Natural and Anthropogenic Contaminants .................................73

Summary .......................................................................................................................................................77

References ...................................................................................................................................................79
vi

Figures

1. Map showing hydrogeologic setting and location of regional aquifer publicsupply wells (ranked by pumping quartile) sampled for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells in the San 

Antonio segment of the Edwards aquifer and the local-scale study area, near San 

Antonio, south-central Texas, 2004−9 ......................................................................................4

2. Map showing diagrammatic north-northwest-to-south-southeast section showing 

hydrogeologic framework and generalized groundwater flow directions, Edwards 

Plateau to Gulf Coastal Plain, San Antonio region, Texas ....................................................5

3. Map showing local-scale study area for the study of the transport of anthropogenic 

and natural contaminants (TANC) to public-supply wells showing the selected 

public-supply well and well field, monitoring wells, and regional aquifer publicsupply wells (ranked and shown by pumping quartile) near San Antonio, southcentral Texas, 2004−9 ..................................................................................................................6

4. Schematic east-west (strike) cross section showing location of study area 

hydrogeologic units (HGUs) as modeled by Lindgren and others (2011b) and relation 

of HGUs at well-field, monitoring well, and depth-dependent (W4) sample sites, 

near San Antonio, south-central Texas ...................................................................................8

5. Graphs showing time series (April 1 to December 31, 2009) climatic and hydrologic 

data for the south-central Texas study area .........................................................................15

6. Graphs showing time series (2004−9) climatic and hydrologic data for the southcentral Texas study area ..........................................................................................................21

7. Borehole geophysical data for the public-supply well (W4) near San Antonio, 

south-central Texas, including, from left to right, natural gamma and caliper logs, 

fluid conductivity, temperature, flowmeter (under ambient and pumping conditions), 

stratigraphic unit, and hydrogeologic unit (HGU) .................................................................24

8. Borehole geophysical data for the deep Zarzamora monitoring well (Z–DED) near 

San Antonio, south-central Texas, including, from left to right, natural gamma and 

caliper logs, fluid conductivity and temperature, flowmeter, borehole image, 

stratigraphic unit, and hydrogeologic unit (HGU) .................................................................25

9. Borehole geophysical data for the deep Timberhill monitoring well (T–DED) near 

San Antonio, south-central Texas, including, from left to right, natural gamma 

and caliper logs, fluid conductivity and temperature, flowmeter (no appreciable 

measured flow), borehole image, stratigraphic unit, and hydrogeologic unit (HGU) .....26

10. Map showing land use in the local-scale study area for the study of the transport 

of anthropogenic and natural contaminants (TANC) to public-supply wells, and 

location of selected public-supply well and well field, near San Antonio, southcentral Texas ..............................................................................................................................28

11. Map showing location of potential sources of contamination (PSOCs) in the localscale study area for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public-supply wells, and location of selected publicsupply well and well field, near San Antonio, south-central Texas ..................................29

12. Map showing location of potential sources of atrazine contamination in the localscale study area for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public-supply wells, and location of selected publicsupply well and well field, near San Antonio, south-central Texas ..................................30

13. Map showing location of potential sources of chloroform contamination in the 

local-scale study area for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public-supply wells, and location of selected publicsupply well and well field, near San Antonio, south-central Texas ..................................31
vii

14. Map showing location of potential sources of tetrachloroethene (PCE) 

contamination in the local-scale study area for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, and 

location of selected public-supply well and well field, near San Antonio, southcentral Texas ..............................................................................................................................32

15. Graphs showing relation between well depth and selected physicochemical and 

geochemical constituents for groundwater samples collected from regional 

aquifer public-supply wells in the confined part of the San Antonio segment of the 

Edwards aquifer, south-central Texas, 2004–5 .....................................................................33

16. Piper or trilinear diagram showing relations between major cations and anions for 

groundwater samples collected for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9 ......34

17. Graphs showing relation between well depth and selected mineral saturation 

indexes for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, southcentral Texas, 2004–9 ................................................................................................................35

18. Graph showing relation between magnesium to calcium molar ratio and dolomite 

mineral saturation index for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (TANC) to public-supply 

wells, south-central Texas, 2004–9 .........................................................................................36

19. Graphs showing relation between well depth and selected geochemical 

constituents or between calcium and selected geochemical constituents for 

groundwater samples collected for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9 ......37

20. Graphs showing relation between well depth and selected geochemical 

constituents for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, southcentral Texas, 2004–9 ................................................................................................................38

21. Graph showing relation between well depth and nitrate concentration for 

groundwater samples collected for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9 ......40

22. Graph showing isotopic composition of nitrate for groundwater samples collected 

for the study of the transport of anthropogenic and natural contaminants (TANC) 

to public-supply wells, south-central Texas, 2004–9 ...........................................................41

23. Graph showing relation between well depth and strontium isotope composition 

for groundwater samples collected for the study of the transport of anthropogenic 

and natural contaminants (TANC) to public-supply wells, south-central Texas, 

2004–9 ..........................................................................................................................................43

24. Graph showing relation between deuterium and oxygen isotopes for groundwater 

samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public-supply wells, south-central Texas, 2004–9 ....................44

25. Graph showing detection frequency for the most frequently detected anthropogenic 

contaminants for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, southcentral Texas, 2004–9 ................................................................................................................45

26. Graphs showing median concentration of the most frequently detected 

anthropogenic contaminants for groundwater samples collected for the study of the 

transport of anthropogenic and natural contaminants (TANC) to public-supply wells, 

south-central Texas, 2004–9. Two scales are shown for selected contaminants for 

comparison .................................................................................................................................46
viii

27. Graphs showing relation between well depth and concentration for selected 

organic contaminants for groundwater samples collected for the study of the 

transport of anthropogenic and natural contaminants (TANC) to public-supply 

wells, south-central Texas, 2004–9 .........................................................................................48

28. Graph showing relation between apparent age and excess delta helium-4 

(terrigenic) for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, southcentral Texas, 2004–9 ................................................................................................................50

29. Graph showing relation between tritium (3H) concentration and 3H to initial tritium 

(

3

H0) ratio (3H/3H0) for groundwater samples collected for the study of the transport 

of anthropogenic and natural contaminants (TANC) to public-supply wells, southcentral Texas, 2004–9, and lumped-parameter modeled curves for various 

groundwater age distributions ................................................................................................52

30. Graph showing relation between apparent age and the tritium (3H) to initial tritium 

(

3

H0) ratio for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, southcentral Texas, 2004–9 ................................................................................................................53

31. Graphs showing relation between tritium concentration (3H) and chlorofluorocarbon 

(CFC) age tracers for groundwater sample collected from the well-field well, W5, 

for the study of the transport of anthropogenic and natural contaminants (TANC) to 

public-supply wells, south-central Texas, 2004–9, and lumped-parameter modeled 

curves for various groundwater age distributions ...............................................................54

32. Graphs showing relation between chlorofluorocarbon (CFC) age tracers (CFC-11, 

CFC-12, and CFC-113) for groundwater sample collected from the well-field well, 

W5, for the study of the transport of anthropogenic and natural contaminants

(TANC) to public-supply wells, south-central Texas, 2004–9, and lumped-parameter 

modeled curves for various groundwater age distributions ..............................................55

33. Graph showing particle-track age distribution to selected public-supply well for 

the study of the transport of anthropogenic and natural contaminants (TANC) to 

public-supply wells, based on local-scale study model results described by 

Lindgren and others (2011b) in the San Antonio segment of the Edwards aquifer, 

south-central Texas ...................................................................................................................56

34. Graphs showing relation between sample collection date and tritium for 

groundwater samples collected for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9 ......57

35. Schematic east-west (strike) cross section showing location of study area 

hydrogeologic units (HGUs) as modeled by Lindgren and others (2011b), relation of 

HGUs at selected sample sites, and summary of groundwater apparent-age results 

based on tritium/helium-3 tracer measurements (piston-flow model ages) near San 

Antonio, south-central Texas ...................................................................................................58

36. Graphs showing relation between tritium to initial tritium ratio (3H/3H0) and selected 

geochemical constituents for groundwater samples collected for the study of the 

transport of anthropogenic and natural contaminants (TANC) to public-supply 

wells, south-central Texas, 2004–9 .........................................................................................59

37. Graphs showing relation between tritium to initial tritium ratio (3H/3H0) and 

selected geochemical constituents for groundwater samples collected for the 

study of the transport of anthropogenic and natural contaminants (TANC) to publicsupply wells, south-central Texas, 2004–9 ............................................................................60

38. Graphs showing geochemical results for selected constituents for groundwater 

samples collected from different depths and under different flow conditions for 

the study of the transport of anthropogenic and natural contaminants (TANC) to 

public-supply wells, south-central Texas, 2004–9 ................................................................62
ix

39. Graphs showing historical magnesium to calcium molar ratio data for well-field 

public-supply wells sampled for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public-supply wells, south-central Texas .....................69

40. Graphs showing geochemical results for selected constituents in groundwater 

samples collected in response to a rain event (October through November, 2009) 

for the study of the transport of anthropogenic and natural contaminants (TANC) to 

public-supply wells, south-central Texas ..............................................................................70

41. Map showing hydrogeologic setting, location of, and ranges of tetrachloroethene 

(PCE) concentration (highest value shown where multiple measurements were 

made during the study period) for regional aquifer public-supply wells sampled for 

the study of the transport of anthropogenic and natural contaminants (TANC) to 

public-supply wells in the San Antonio segment of the Edwards aquifer, southcentral Texas, 2004–9 ................................................................................................................74

42. Map showing hydrogeologic setting, location of, and ranges of nitrate 

concentration (highest value shown where multiple measurements were made 

during the study period) for regional aquifer public-supply wells sampled for the 

study of the transport of anthropogenic and natural contaminants (TANC) to 

public-supply wells in the San Antonio segment of the Edwards aquifer, southcentral Texas, 2004–9 ................................................................................................................75

43. Graph showing results of forecasting exercise of time-series of hypothetical 

contaminant concentrations at the selected public-supply well for the study of 

the transport of anthropogenic and natural contaminants (TANC) to publicsupply wells; results are based on 30 years of contaminant input (at a relative 

concentration of 1) in the modeled contributing area .........................................................76

Tables

1. Site information for wells sampled for the study of the transport of anthropogenic 

and natural contaminants (TANC) to public supply wells in the San Antonio segment 

of the Edwards aquifer near San Antonio, south-central Texas, 2004−9 .........................91

2. Summary of constituents by group for wells sampled for the study of the transport 

of anthropogenic and natural contaminants (TANC) to public supply wells in the San 

Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9 ..........................................................................................................................................95

3. Summary of depth-dependent sampling for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public supply wells in the San 

Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9 ..........................................................................................................................................99

4. Sample collection for temporal sampling for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public supply wells in the San 

Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2009 ............................................................................................................................................100

5. Summary of organic content and elemental composition from acid extractions for 

core materials collected for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public supply wells in the San Antonio segment of 

the Edwards aquifer near San Antonio, south-central Texas, 2004−9 ............................101

6. Summary of X-ray diffraction results for core materials collected for the study of 

the transport of anthropogenic and natural contaminants (TANC) to public supply 

wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9 ..............................................................................................................103
x

7. Physicochemical measurements for groundwater samples collected for the study 

of the transport of anthropogenic and natural contaminants (TANC) to public supply 

wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9 ..............................................................................................................105

8. Dissolved solids and major ion measurements for groundwater samples collected 

for the study of the transport of anthropogenic and natural contaminants (TANC) to 

public supply wells in the San Antonio segment of the Edwards aquifer near San 

Antonio, south-central Texas, 2004−9 ..................................................................................108

9. Trace element measurements for groundwater samples collected for the study of 

the transport of anthropogenic and natural contaminants (TANC) to public supply 

wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9 ..............................................................................................................114

10. Dissolved gas and associated data for groundwater samples collected for the 

study of the transport of anthropogenic and natural contaminants (TANC) to public 

supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, 

south-central Texas, 2004−9 ...................................................................................................120

11. Nutrient measurements for groundwater samples collected for the study of the 

transport of anthropogenic and natural contaminants (TANC) to public supply 

wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9 ..............................................................................................................121

12. Isotope and radionuclide measurements for groundwater samples collected for 

the study of the transport of anthropogenic and natural contaminants (TANC) to 

public supply wells in the San Antonio segment of the Edwards aquifer near San 

Antonio, south-central Texas, 2004−9 ..................................................................................124

13. Wastewater indicator compounds for groundwater samples collected for the study 

of the transport of anthropogenic and natural contaminants (TANC) to public supply 

wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9 ..............................................................................................................126

14. Volatile organic and fuel oxygenate compounds for groundwater samples collected 

for the study of the transport of anthropogenic and natural contaminants (TANC) to 

public supply wells in the San Antonio segment of the Edwards aquifer near San 

Antonio, south-central Texas, 2004−9 ..................................................................................134

15. Soluble pesticide compounds for groundwater samples collected for the study of 

the transport of anthropogenic and natural contaminants (TANC) to public supply 

wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9 ..............................................................................................................158

16. Polar pesticide compounds for groundwater samples collected for the study of 

the transport of anthropogenic and natural contaminants (TANC) to public supply 

wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9 ..............................................................................................................178

17. Acetamide pesticide compounds for groundwater samples collected for the study 

of the transport of anthropogenic and natural contaminants (TANC) to public supply 

wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9 ..............................................................................................................186

18. Summary of sulfur hexafluoride and chlorofluorocarbon age-tracer data and 

piston-flow model results for groundwater samples collected for the study of the 

transport of anthropogenic and natural contaminants (TANC) to public supply 

wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9 ..............................................................................................................190
xi

19. Summary of tritium/helium-3 age-tracer data and piston-flow model results for 

groundwater samples collected for the study of the transport of anthropogenic 

and natural contaminants (TANC) to public supply wells in the San Antonio 

segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9 .......192

20. Results of forecasting analysis for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public supply wells in the San Antonio segment of 

the Edwards aquifer near San Antonio, south-central Texas, 2004−9 ............................194

Conversion Factors and Abbreviations

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

millimeter (mm) 0.03937 inch (in.)

micrometer (μm) 1,000 millimeter (mm)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

million gallons (Mgal) 3,785 cubic meter (m3

)

cubic centimeter (cm3

) 0.06102 cubic inch (in3)

milliliter (mL) 0.03381 fluid ounce (oz)

liter (L) 0.2642 gallon (gal)

cubic meter (m3

) 264.2 gallon (gal) 

Flow rate

gallon per minute (gal/min) 0.06309 liter per second (L/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

Mass/weight

gram (g) 0.3527 ounce avoirdupois (oz avdp)

kilogram (kg) 2.205 pound (lb)

Transmissivity*

foot squared per day (ft2

/d) 0.09290 meter squared per day (m2/d) 

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88) and to the National Geodetic Vertical Datum of 1929 (NGVD 29) for Bexar County 

index well (J–17).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.
xii

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or in micrograms per liter (μg/L).

Explanation of Isotope Units

The δ values for stable-isotope ratios discussed in this report are referenced to the following 

standard materials: 

Element R Standard identity and reference

Hydrogen Hydrogen-2/hydrogen-1 Vienna Standard Mean Ocean Water (VSMOW) (Casciotti and 

others, 2002)

Oxygen Oxygen-18/oxygen-16 Vienna Standard Mean Ocean Water (VSMOW) (Casciotti and 

others, 2002)

Nitrogen Nitrogen-15/nitrogen-14 Nitrogen in air
Abstract

In 2001, the National Water-Quality Assessment 

(NAWQA) Program of the U.S. Geological Survey initiated a 

series of studies on the transport of anthropogenic and natural 

contaminants (TANC) to public-supply wells (PSWs). The 

main goal of the TANC project was to better understand the 

source, transport, and receptor factors that control contaminant 

movement to PSWs in representative aquifers of the United 

States. Regional- and local-scale study areas were selected 

from within existing NAWQA study units, including the southcentral Texas Edwards aquifer. The local-scale TANC study 

area, nested within the regional-scale NAWQA study area, 

is representative of the regional Edwards aquifer. The PSW 

selected for study is within a well field of six production wells. 

Although a single PSW was initially selected, because of constraints of well-field operation, samples were collected from 

different wells within the well field for different components 

of the study. Data collected from all of the well-field wells 

were considered comparable because of similar well construction, hydrogeology, and geochemistry. An additional 38 PSWs 

(mostly completed in the confined part of the aquifer) were 

sampled throughout the regional aquifer to characterize water 

quality. Two monitoring well clusters, with wells completed at 

different depths, were installed to the east and west of the well 

field (the Zarzamora and Timberhill monitoring well clusters, 

respectively). One of the monitoring wells was completed in 

the overburden to evaluate potential hydrologic connectivity 

with the Edwards aquifer. Geophysical and flowmeter logs 

were collected from one of the well-field PSWs to determine 

zones of contribution to the wellbore. These contributing 

zones, associated with different hydrogeologic units, were 

used to select monitoring well completion depths and groundwater sample collection depths for depth-dependent sampling. 

Depth-dependent samples were collected from the PSW from 

three different depths and under three different pumping 

conditions. Additionally, selected monitoring wells and one of 

the well-field PSWs were sampled several times in response to 

a rainfall and recharge event to assess short-term (event-scale) 

temporal variations in water quality. For comparison purposes, 

groundwater samples were categorized as being from regional 

aquifer PSWs, from the well field (wellhead samples), from 

the monitoring wells (excluding the overburden well), from 

the overburden well, from the PSW depth-dependent sampling, and from temporal sampling. Groundwater samples 

were analyzed for inorganic, organic, isotopic, and age-dating 

tracers to characterize geochemical conditions in the aquifer 

and provide understanding of the mechanisms of mobilization and movement of selected constituents from source 

areas to a PSW. Sources, tracers, and conditions used to 

assess water quality and processes affecting the PSW and the 

aquifer system included (1) carbonate host rock composition; 

(2) physicochemical constituents; (3) major and trace element 

concentrations; (4) saturation indices with respect to minerals in aquifer rocks; (5) elemental ratios, such as magnesium 

to calcium ratios, that are indicative of water-rock interaction 

processes; (6) oxidation-reduction conditions; (7) nutrient 

concentrations, in particular nitrate concentrations; (8) the isotopic composition of nitrate, which can point to specific nitrate 

sources; (9) strontium isotopes; (10) stable isotopes of hydrogen and oxygen; (11) organic contaminant concentrations, 

including pesticides and volatile organic compounds; (12) age 

tracers, apparent-age distribution, and dissolved gas data used 

in age interpretations; (13) depth-dependent water chemistry 

collected from the PSW under different pumping conditions to 

assess zones of contribution; and (14) temporal variability in 

groundwater composition from the PSW and selected monitoring wells in response to an aquifer recharge event. 

Geochemical results indicate that the well-field and 

monitoring well samples were largely representative of 

groundwater in the regional confined aquifer. Constituents of 

concern in the Edwards aquifer for the long-term sustainability 

of the groundwater resource include the nutrient nitrate and 

anthropogenic organic contaminants. Nitrate concentrations 

(as nitrogen) for regional aquifer PSWs had a median value of 

1.9 milligrams per liter, which is similar to previously reported 

values for the regional aquifer. Nitrate-isotope compositions for groundwater samples collected from the well-field 

PSWs and monitoring wells had a narrow range, with values 

Hydrogeology, Chemical Characteristics, and Water 

Sources and Pathways in the Zone of Contribution of a 

Public-Supply Well in San Antonio, Texas

By MaryLynn Musgrove, Lynne Fahlquist, Gregory P. Stanton, Natalie A. Houston, and Richard J. Lindgren
2 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

indicative of natural soil organic values. A comparison with 

historical nitrate-isotope values, however, suggests that a 

component of nitrate in groundwater from biogenic sources 

might have increased over the last 30 years. Several organic 

contaminants (the pesticide atrazine, its degradate deethylatrazine, trichloromethane (chloroform; a drinking-water disinfection byproduct), and the solvent tetrachloroethene (PCE)) were 

widely distributed throughout the regional aquifer and in the 

local-scale TANC study area at low concentrations (less than 

1 microgram per liter). Higher concentrations of PCE were 

detected in samples from the well-field PSWs and Zarzamora 

monitoring wells relative to the regional aquifer PSWs. The 

urban environment is a likely source of contaminants to the 

aquifer, and these results indicate that one or more local urban 

sources might be supplying PCE to the Zarzamora monitoring wells and the well-field wells. Samples from the well 

field also had high concentrations of chloroform relative to 

the monitoring wells and regional aquifer PSWs. For samples 

from the regional aquifer PSWs, the most frequently detected 

organic contaminants generally decreased in concentration 

with increasing well depth. Deeper wells might intercept 

longer regional flow paths with higher fractions of older water 

or water recharged in rural recharge areas in the western part 

of the aquifer that have been less affected by anthropogenic 

contaminants. A scenario of hypothetical contaminant loading 

was evaluated by using results from groundwater-flow-model 

particle tracking to assess the response of the aquifer to potential contamination. Results indicate that the aquifer responds 

quickly (less than 1 year to several years) to contaminant 

loading; however, it takes a relatively long time (decades) for 

concentrations to reach peak values. The aquifer also responds 

quickly (less than 1 year to several years) to the removal of 

contaminant loading; however, it also takes a relatively long 

time (decades) to reach near background concentrations.

Interpretation of geochemical age tracers in this wellmixed karst system was complicated by contamination of a 

majority of measured tracers and complexities of extensive 

mixing. Age-tracer results generally indicated that groundwater samples were composed of young, recently recharged 

water with piston-flow model ages ranging from less than 1 

to 41 years, with a median of 17 years. Although a pistonflow model is typically not valid for karst aquifers, the model 

ages provide a basis for comparing relative ages of different 

samples and a reference point for more complex hydrogeologic models for apparent-age interpretations. Young groundwater ages are consistent with particle-tracking results from 

hydrogeologic modeling for the local-scale TANC study area. 

Age-tracer results compared poorly with other geochemical 

indicators of groundwater residence time and anthropogenic 

effects on water quality, indicating that hydrogeologic conceptual models used in groundwater age interpretations might not 

adequately account for mixing in this karst system. Groundwater samples collected from the well field under a variety 

of pumping conditions were relatively homogeneous and 

well mixed for numerous geochemical constituents (with the 

notable exception of age tracers). Groundwater contributions 

to the PSW were dominated by well-mixed, relatively homogeneous groundwater, typical of the regional confined aquifer. 

Zones of preferential flow were determined for the PSW, but 

groundwater samples from different stratigraphic units were 

not geochemically distinct. Variations in chemical constituents 

in response to a rainfall and aquifer recharge event occurred 

but were relatively minor in the PSW and monitoring wells. 

This observation is consistent with the hypothesis that the 

response to individual recharge events in the confined aquifer, 

unless intersecting conduit flow paths, might be attenuated by 

mixing processes along regional flow paths. Results of this 

study are consistent with the existing conceptual understanding of aquifer processes in this karst system and are useful for 

water-resource development and management practices. 

Introduction

About a third of the population of the United States 

receives drinking water from public groundwater systems 

(Toccalino and Hopple, 2010). The vulnerability of drinkingwater public-supply wells (PSWs) to contamination has raised 

numerous health concerns. Anthropogenic contaminants—

such as solvents, drinking-water disinfection byproducts, 

other volatile organic compounds, and pesticides—have been 

detected in low concentrations in water from PSWs across 

the United States (Gilliom and others, 2006; Ivahnenko and 

Zogorski, 2006; Schaap and Zogorski, 2006; Zogorski and 

others, 2006; Carter and others, 2007; Hopple and others, 

2009). Groundwater contamination from nutrients such as 

nitrate (NO3) is widespread (Nolan and others, 1998). Naturally occurring contaminants such as radon, uranium (U), 

and arsenic (As) also are present in groundwater from many 

drinking-water wells (Focazio and others, 1999; Sowerby and 

others, 2000; Welch and others, 2000; Jurgens and others, 

2008; Landon and others, 2008). In response to these concerns, the U.S. Geological Survey (USGS) National WaterQuality Assessment (NAWQA) Program began a series of 

studies in 2001 to assess the vulnerability of PSWs to contamination from compounds commonly found in the environment, 

specifically with regard to the transport of anthropogenic and 

naturally occurring contaminants (TANC) to PSWs at regional 

and local scales at several sites across the United States 

(Eberts and others, 2005). The TANC project was built on previous NAWQA studies that found low levels of contaminants 

and mixtures of contaminants in groundwater beneath urban 

areas (Hamilton and others, 2004). TANC study sites have 

included a range of hydrogeologic settings and management 

practices that were selected to be representative of drinkingwater resources used by a majority of the U.S. population.

The goal of the TANC project is to understand the source, 

transport, and receptor factors that control the movement of 

contaminants to PSWs in representative aquifers of the United 

States (Eberts and others, 2005). Specific objectives are to 

(1) identify the dominant contaminants and their sources in 

PSWs; (2) assess the effects of natural processes and human 
Introduction 3

activities on the occurrence of contaminants in PSWs; (3) 

identify the factors that are most important for PSW vulnerability assessments in different settings and at different scales; 

(4) develop simple methods and models for evaluating PSWs 

for vulnerability to contamination in unstudied areas and 

from emerging contaminants; and (5) increase understanding 

of the potential effects of water-resources development and 

management decisions on the quality of water from PSWs 

(Eberts and others, 2005). Because subsurface processes and 

management practices differ among aquifers and public-water 

systems, PSWs in different parts of the United States are not 

equally susceptible or vulnerable to contamination (Focazio 

and others, 2002), even where similar contaminant sources 

might exist. Concentrations of anthropogenic or natural 

contaminants can change along groundwater flow paths from 

recharge or source areas to PSWs as a result of many factors. 

These factors can be broadly grouped into those concerning 

sources, including contaminant loading or mobilization; transport, including migration and reaction; and receptors (wells), 

including PSW operations (Franke and others, 1998; Focazio 

and others, 2002). 

TANC studies were conducted at regional scales of up 

to thousands of square miles (mi2

) at 11 locations and at local 

scales of less than 1,100 mi2 at six additional locations; these 

were delineated from within six NAWQA study units of differing hydrogeology (Connecticut, glacial deposits; Nebraska, 

unconsolidated sediment; California, unconsolidated sediment; 

Florida, conduit-dominated karstic carbonate; New Mexico, 

unconsolidated sediment; and Texas, mixed carbonate). 

Local-scale study areas were selected that met the following 

criteria: location in an aquifer previously studied under the 

NAWQA Program; availability of existing source (raw water) 

water-quality data from PSWs; previous detection of natural or 

anthropogenic contaminants in source waters; and previously 

developed regional groundwater model(s). One of the selected 

local-scale study areas was the San Antonio segment of the 

Edwards aquifer, within the South-Central Texas (SCTX) 

regional study unit of the NAWQA Program (Bush and others, 

2000). This report describes the hydrogeology and geochemistry of the 1,098-mi2

 SCTX local-scale study area, which contains the zone of contribution to a selected PSW, and discusses 

factors controlling the transport of selected anthropogenic and 

natural contaminants to PSWs.

Purpose and Scope

The purposes of this report are to document the hydrogeologic setting, the occurrence and distribution of selected 

chemical characteristics, and factors controlling transport of 

selected anthropogenic and natural contaminants to PSWs 

in the local-scale TANC study area at San Antonio, Texas. 

A description of the design of the local-scale monitoring 

well network and methods of data collection and analysis 

are included. The hydrogeologic setting of the local-scale 

study area is described, as are general water geochemistry 

characteristics such as field parameters, oxidation-reduction 

(redox) conditions, the occurrence and distribution of selected 

inorganic and organic constituents, and the distribution of 

interpreted groundwater ages. The occurrence and distribution of contaminants and contaminant point sources are 

described to help assess factors influencing transport of these 

anthropogenic and natural contaminants to PSWs in the localscale TANC study area. This report is intended to serve as a 

foundation for analyses comparing results from this local-scale 

TANC study area with other TANC study areas.

Description of the Study Area

The regional-scale NAWQA and local-scale TANC 

study areas considered in this report (hereinafter, regionalscale study area and local-scale study area, respectively) are in 

south-central Texas within the Edwards aquifer (fig. 1). 

The regional-scale study area includes the extent of the San 

Antonio segment of the Edwards aquifer, which is within a 

narrow band along the Balcones fault zone from the western 

groundwater divide in Kinney County to the groundwater 

divide north of San Marcos Springs in Hays County (fig. 1). 

The Balcones escarpment is the surface manifestation of 

the Balcones fault zone (fig. 1). Late Cenozoic faulting of 

the predominantly flat-lying region along the Balcones fault 

zone formed a series of high-angle normal en echelon downtoward-the-coast faults. The faulting resulted in a series of 

blocks of Edwards aquifer rocks that are partially to completely offset and divide the confined and unconfined parts of 

the aquifer (Maclay and Small, 1983) (fig. 2). The local-scale 

study area is nested within the larger regional-scale study area 

(Lindgren and others, 2011a). Although this report focuses 

on the results of the local-scale study, an understanding of the 

characteristics of the regional-scale aquifer provides insight 

into movement of water and solutes along groundwater 

flow paths to PSWs at the local scale. Characteristics of the 

regional-scale study area around San Antonio are described by 

Lindgren and others (2011a). Characteristics of the Edwards 

aquifer that influence water quality have been previously 

described by numerous studies, including Bush and others 

(2000), Fahlquist and Ardis (2004), and Musgrove and others 

(2010). A hydrogeologic model constructed and calibrated 

to simulate groundwater flow and age distribution in the 

local-scale study area is described in a companion report by 

Lindgren and others (2011b). 

The local-scale study area is predominantly in Bexar and 

Medina Counties and includes the northwestern part of San 

Antonio (fig. 1). The local-scale study area and model boundary were determined by using the regional-scale hydrogeologic model (Lindgren and others, 2011b) to identify the area 

contributing recharge (ACR) to the PSW and by bounding 

the likely ACR with the local-scale model area. The localscale study area includes the active area of the local-scale 

model (recharge and confined zones) and a small part of the 

catchment area (contributing zone) north of the Edwards 

aquifer recharge zone (fig. 3). The local-scale study area is 

bounded on the west and east by the western and eastern 
Figure 1. Hydrogeologic setting and location of regional aquifer public-supply wells (ranked by pumping quartile) sampled for the study of the transpnatural contaminants (TANC) to public-supply wells in the San Antonio segment of the Edwards aquifer and the local-scale study area, near San Anto2004−9. 

1,000 mg/L 1,000 mg/L

Contributing zone

Recharge zone

Confined zone

CALDWE

ATASCOSA

BEXAR

GUADALUPE

COMAL

KENDALL

HAYS

GILLESPIE BLANCO

TRAVIS

ZAVALA FRIO

KINNEY UVALDE MEDINA

BANDERA

REAL

EDWARDS KERR

Hondo

Uvalde

Brackettville

Castroville

San

Antonio

New

Braunfels

San

Marcos

Austin

!

!

!

!

!

!!

!

!

!

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!

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!

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!

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!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

! San 

Antonioairport

Creek

Nueces River

Nueces River

River

Onion

Barton Creek

Blanco Creek

Sabinal River

Hondo

Creek

Medina River

Cibolo Creek

Salado Creek

Guadalupe River San Marcos River

Blanco River

VerdeCreek

Nueces River

Lake

Travis

Canyon Lake

MedinaLake

West

Frio

Colorado River

Lo

st

Edwa

0 15 30 15 30 45 

98°

99°

100°

30°

29° Base from Aquifers: Texas Water Development Board (2007); 

Ashworth and Hopkins (1995), 1:250,000 Counties: Texas General Land Office (1999), 1:24,000Cities: Texas Natural Resources Information System digital data (1995)Projection: Texas Centric Mapping System-Albers equal area Datum: North American Datum of 1983

Groundwater divide—San Antonio segment of the Edwards aquifer is bound on the easternmost and westernmost ends by groundwater dividesRegional aquifer public-supply wells  (confined and unconfined aquifer), by pumping quartile—Black dot indicates well depth is greater than 1,000 feet 1st quartile 2d quartile 3d quartile 4th quartile

Edwards aquifer Recharge zone (unconfined) Confined zone

Barton Springs segment

Balcones escarpment (modified from Abbott and Woodruff, 1986, fig. 1)Urban area boundaryLocal-scale study area boundaryFreshwater/saline-water transition (1,000 milligrams per liter (mg/L)  dissolved solids concentration) (Schultz, 1994)

!!!!

EXPLANATION

Selected public-supply well  and well fieldJ–17 (Bexar County index well)Spring

!
Figure 2. Diagrammatic north-northwest-to-south-southeast section showing hydrogeologic framework and generalized groundwater flow directionCoastal Plain, San Antonio region, Texas (modified from Barker and Ardis, 1996, plates 1 and 3). 

EDWARDS PLATEAU

HILL COUNTRY

GU

Edwards

Trinity Group

Edwards Group Trinity

Group Del Rio Clay

Eagle Ford Group, Austin 

and overly

Trinity Group

Edwards Group

Hammett Shale

Group

Balcones

escarpment

NOT TO SCALE

Trinity Grou

Edwards aquifer recharge zone

Balcones fault zone

Contributing zone

Unconfined

aquifer Confined aquifer

EXPLANATION

Upper confining unitEdwards aquifer Unconfined aquifer Confined aquiferEdwards-Trinity aquiferTrinity aquifer

LimestoneSandUnderlying rock unitsApproximate freshwater/saline- water interfaceGeneralized conduit systemGeneralized direction of groundwater flowFault—Arrows indicate direction of movement
6 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

extents of the ACR to the selected PSW; these boundaries 

are near Hondo Creek in Medina County and near Salado 

Creek in Bexar Country, respectively (fig. 1). It is bounded 

on the south approximately by the 1,000-milligrams-per-liter 

(mg/L) dissolved-solids concentration line (updip boundary 

of the freshwater/saline-water transition zone). The northern 

boundary is north of the updip limit of contiguous, outcropping rocks of the Edwards Group, Georgetown Formation, and 

their westward stratigraphic equivalents (Edwards rocks). The 

local-scale model area is oriented with the regional direction 

of groundwater flow and the major faults in the Balcones fault 

zone (Lindgren and others, 2011b). 

The construction and operational practices of the 

selected PSW are representative of many PSWs that use the 

Edwards aquifer for supplying the population of the San 

Antonio metropolitan area. The selected PSW is a primary 

Figure 3. Local-scale study area for the study of the transport of anthropogenic and natural contaminants (TANC) to public-supply 

wells showing the selected public-supply well and well field, monitoring wells, and regional aquifer public-supply wells (ranked and 

shown by pumping quartile) near San Antonio, south-central Texas, 2004−9. 

Hondo

Castroville San

Antonio

E

E

San Pedro

 Springs

San Antonio 

 Springs

Hondo Creek

Medina

River

Verde

Medina

Lake

Creek

Salado

Creek

Culebra

Creek

Leon Creek

Medio Creek

Quihi Creek

Black Creek

San Francisco Perez Creek

San Geronim o Creek

Helotes Creek

San Antonio

River

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BEXAR COUNTY

MEDINA COUNTY

BANDERA COUNTY

0 2.5 5 7.5 MILES 10

0 2.5 5 7.5 KILOMETERS 10

Contributing zone

Recharge zone

Confined zone

98°30'

98°45' 99°00'

99°15'

29°30'

29°15'

Base from

Aquifers: Texas Water Development Board (2007); Ashworth

and Hopkins (1995), 1:250,000

Counties: Texas General Land Office (1999), 1:24,000

Cities: Texas Natural Resources Information System digital data (1995)

Projection: Texas Centric Mapping System-Albers equal area

Datum: North American Datum of 1983 

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E

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!

Selected public-supply well and well field

Zarzamora monitoring well cluster

Timberhill monitoring well cluster

Unconfined monitoring well 

 (AY–68–27–610) (event sampling)

Spring

Regional aquifer public-supply wells 

 (confined and unconfined aquifer), 

 by pumping quartile

 1st quartile

 2d quartile

 3d quartile

 4th quartile

Unconfined aquifer

Confined aquifer

Urban area boundary

Local-scale study area boundary

Freshwater/saline-water 

 interface (1,000 milligrams 

 per liter dissolved solids 

 concentration) (Schultz,

 1994)

EXPLANATION
Introduction 7

community-water-system PSW, which a public-water purveyor made available for the study. NAWQA-study analyses 

of groundwater samples from the PSW have detected multiple contaminants at low concentrations (substantially below 

drinking-water standards). The combination of low concentrations of detected contaminants, typical well construction 

and operational practices, and cooperation of the water utility 

prompted the selection of this PSW for the local-scale study. 

The selected PSW is within a well field of six wells in northwest San Antonio.

Probabilistic assessments of zones of contribution to the 

selected PSW, based on forward and backward particle tracks 

that were generated by using two regional groundwater flow 

models (Lindgren and others, 2004; Lindgren, 2006), were 

considered in delineating the local-scale study area (fig. 3). 

Although such determinations are likely unrealistic at a local 

scale in a fractured karst system, the study area was sufficiently large (1,098 mi2

) to reasonably approximately probable 

zones of flow to the selected PSW. The probable zones of contribution selected from models is similar to those represented 

by previous conceptualizations (Maclay and Land, 1988; Clark 

and Journey, 2006). 

In the local-scale study area, the layered fractured karstic 

carbonate rocks are approximately 450–500 feet (ft) thick 

(Rose, 1972) and consist of eight hydrogeologic units (HGUs) 

previously defined for the Edwards aquifer on the basis of 

hydrogeologic properties (Maclay, 1995; Stein and Ozuna, 

1995). The regional paleogeographic and structural features 

associated with the Edwards aquifer, and the previously 

defined stratigraphic units associated with these features, 

are detailed by Lindgren and others (2011b). A conceptual 

cross-sectional schematic of the hydrogeology of the localscale study area and well-field and monitoring well sites in the 

context of HGUs is shown in figure 4. The local-scale model 

includes four additional HGUs, including one confining HGU 

in the overburden overlying the aquifer and one confining 

HGU in the Trinity aquifer underlying the Edwards aquifer 

(Lindgren and others, 2011b) (fig. 4). Among the eight previously identified units (Stein and Ozuna, 1995), the Kirschberg 

evaporite member and the leached and collapsed members 

(composed of the leached and collapsed members, undivided, 

hereinafter, leached and collapsed) generally are the most 

porous and permeable units (fig. 4). Two highly conductive 

HGUs (5 and 9) were added to the base of these two members 

to represent highly transmissive zones within these two members in the local-scale hydrologic model (Lindgren and others, 

2011b) (fig. 4). The cyclic and marine HGU (composed of the 

cyclic and marine members, undivided; hereinafter cyclic and 

marine (HGU 3)) within the Person Formation is also considered moderately permeable (Stein and Ozuna, 1995) but was 

not divided into multiple HGUs. 

Land surface elevation in the local-scale study area 

ranges from 1,745 ft in the northwestern part of the study 

area in Medina County to 551 ft along the Medina River in 

southern Bexar County (National Hydrography Dataset Plus, 

2010). Mean annual precipitation decreases across the region 

from east to west, ranging from 32.5 inches (in.) in the eastern 

part to 27.5 in. in the western part of the local-scale study 

area (Daly and Taylor, 2000). The region is prone to climatic 

and hydrologic extremes (Griffiths and Strauss, 1985; Jones, 

1991); mean annual rainfall at San Antonio International Airport is 29 in., but annual rainfall has ranged from 10 to 52 in. 

(1893–2009) (National Oceanic and Atmospheric Administration, 2010). Some of the most extreme 1-day-duration storms 

in the world have occurred along the Balcones escarpment 

(Slade, 1986). Storms often produce rapid runoff that provides recharge to the aquifer. Droughts lasting from many 

months to years have been documented in the region since the 

earliest settlers began keeping records (Texas State Historical 

Association, 2009). The mean annual maximum temperature 

(1970–2000), measured in July, is 36.1 degrees Celsius (°C), 

and the average annual minimum temperature, measured in 

January, is 1.7°C (U.S. Department of Agriculture, 2010). 

Land use that overlies the (recharge and confined zones of the) 

Edwards aquifer in the local-scale study area is 35.6 percent 

rangeland, 27.8 percent forest, 23.1 percent urban/built-up, 

11.8 percent agricultural, and 1.7 percent water, wetland, or 

barren land (Homer and others, 2001). Most of the rangeland, 

forest, and agricultural land is to the west of San Antonio in 

Medina County. Most of the outcrop (unconfined zone) is 

rangeland and forest, and most of the agricultural area overlies 

the confined part of the aquifer. Nearly all urban/built-up land 

overlies unconfined and confined parts of the aquifer in the 

San Antonio area in Bexar County. 

The city of San Antonio, the principal urban area in the 

local-scale study area, includes much of Bexar County in the 

east-central part of the aquifer region. San Antonio is the seventh largest city in the United States, with a 2007 population 

of about 1.3 million (U.S. Census Bureau, 2009). Although 

pumping in the San Antonio area has increased about fivefold 

since the 1930s, aquifer water-level altitudes have not shown 

long-term declines because the aquifer readily recharges during periods of rainfall (Bush and others, 2000). 

Potential sources of contamination and the fractured 

karstic hydrogeologic conditions of the Edwards aquifer in the 

San Antonio area are characteristic of many communities that 

withdraw water from carbonates and fractured rocks. Potential 

contamination sources include chlorinated organic solvents 

from historical chemical use at small commercial facilities 

typically found in urban areas, NO3 and pesticides from irrigated cultivated and urban land, and As and U from carbonate or marine sediments. Movement of these contaminants 

through the aquifer system might be enhanced by increased 

groundwater flow velocities caused by temporal response to 

rainfall, increased pumping during summer or drought, and 

increased recharge from precipitation. Moreover, the common 

practice of constructing supply wells across large (greater than 

100 ft) open intervals of the aquifer to improve well yields 

can contribute to rapid movement of contaminants (Zinn and 

Konikow, 2007). 
Figure 4. Schematic east-west (strike) cross section showing location of study area hydrogeologic units (HGUs) as modeled by Lindgren and others HGUs at well-field, monitoring well, and depth-dependent (W4) sample sites, near San Antonio, south-central Texas. HGUs 5 and 9 are highly conductHGUs 4 and 8, respectively. Relatively small (less than 80 percent) displacement modeled faults are not shown.

L

WEST EAST Public-supply well field (W2–W6)

Simulated hydraulic head

HGU 11 Basal nodular member

HGU 10 Dolomitic member

HGU 7 Grainstone member

HGU 4 Leached and collapsed members, undividedHGU 3 Cyclic and marine members, undivided

HGU 1 Overburden (including various formations)

HGU 12 Trinity Group

HGU 6 Regional dense member

HGU 8 Kirschberg evaporite member

HGU 2 Georgetown Formation

HGU 5 High-conductivity zone

HGU 9 High-conductivity zone

OveShaDeeInte

Intermediate

Deep

Zarzamora 

Timberhill monitoring well c

monitoring well cluster

Aquifer

2 6 35 4

Open interval for well field wellsApproximate sampling interval for well-field (W4) depth-dependent  samples and monitoring well samples

EXPLANATION
Introduction 9

Overview of Karst Aquifers

Karst aquifers, such as the Edwards aquifer, are composed of soluble host rocks, usually carbonates, that have dissolved preferentially to form large voids and conduits (White, 

1988). Karst aquifers tend to be extremely heterogeneous, 

with orders of magnitude ranges of porosity and permeability. 

Groundwater transport can be rapid through high-porosity 

voids and conduits, with little opportunity for subsurface 

filtration, sorption, or degradation of dissolved or particulate 

constituents (White, 1988). As a result, karst aquifer systems 

are particularly susceptible to contamination.

Karst aquifer permeability ranges from matrix permeability, characterized by high storage and low transmissivity, 

to conduit permeability, characterized by low storage and high 

transmissivity (Schuster and White, 1971; Atkinson, 1977). 

Karst aquifers commonly are conceptualized as dual-flow 

systems that comprise a continuum-flow system with Darcian flow comparable to porous media and a discrete conduit 

network frequently with turbulent flow conditions (Birk and 

others, 2003). Most groundwater storage occurs within the 

aquifer matrix, but most transport occurs within conduits, 

which often dominate groundwater flow where present (White, 

2002). Fluid flow in karst aquifers can be highly variable and 

difficult to measure or predict.

Recharge to karst aquifers occurs as direct infiltration 

into karst features such as sinkholes and fractures (focused 

recharge) and as distributed infiltration into the rock matrix 

(diffuse recharge); the proportion of focused and diffuse 

recharge can vary greatly in time and space depending on a 

number of variables (Worthington, 2003; Mahler and others, 

2006). In wells and springs that are dominantly affected by 

conduit flow, physicochemical properties, concentrations of 

geochemical constituents, and discharge (from springs) or 

water-level altitudes (in wells) can change rapidly (minutes 

to hours to days) following rainfall and aquifer recharge. In 

contrast, water-level altitudes in wells and springs that are 

dominantly affected by matrix flow might show little response 

to recharge events and less variability in physicochemical properties and geochemistry. Natural discharge in karst 

aquifers often occurs through large springs, which represent a 

composite (integrator) of all water moving through the aquifer; 

as a result, variations in spring discharge, physicochemical 

constituents, and geochemistry provide insight into karst aquifer hydrogeology (White, 2002).

Summary of Previous Studies

PSW contamination is a potential health threat and has 

had negative economic effects on communities that need to 

treat contaminated water or find alternative water supplies. 

Investigations at multiple spatial scales across the United 

States have indicated that shallow groundwater quality is 

affected by land-use activities in many locations but that water 

quality is less frequently affected at the greater depths where 

PSWs typically are screened (Nolan and Stoner, 2000; 

Gilliom and others, 2006; Zogorski and others, 2006). In 1991, 

the USGS implemented the NAWQA Program to characterize, in a nationally consistent manner, water quality of major 

surface-water and groundwater resources of the Nation, to 

determine natural and human factors that affect water quality, and to define trends in water quality (Gilliom and others, 

1995). Between 1996 and 2009, the NAWQA Program collected and analyzed groundwater samples from numerous sites 

throughout the San Antonio segment of the Edwards aquifer 

in the SCTX study unit; specific NAWQA studies include an 

analysis of samples collected between 1996 and 2006 (Musgrove and others, 2010) and samples collected as part of the 

local-scale study, which is the focus of this report. NAWQA 

analyses of water samples for anthropogenic contaminants in 

the San Antonio segment of the Edwards aquifer have detected 

numerous anthropogenic contaminants, mostly at low concentrations, less than 1 microgram per liter (μg/L) (Bush and 

others, 2000; Fahlquist and Ardis, 2004). Two regional-scale 

groundwater flow models were previously developed for the 

regional aquifer by using MODFLOW2000 (Harbaugh and 

others, 2000): (1) a model that includes simulated, continuously connected conduits and barrier faults that influence flow 

(Lindgren and others, 2004) and (2) a model without simulated 

conduits in which flow occurs through small fractures and 

openings (Lindgren, 2006). Both models were calibrated for 

steady-state and transient conditions. A hydrogeologic model 

has been constructed for the local-scale study area, which 

is described in a companion report by Lindgren and others 

(2011b). 

Previous studies of the Edwards aquifer provide insight 

into its hydrology and geochemistry. Geochemical processes 

that affect groundwater geochemistry and water quality 

include interaction with overlying soils, mineral-solution 

reactions, and mixing with saline waters from downdip and 

underlying hydrostratigraphic units (Clement and Sharp, 

1988; Oetting and others, 1996; Groschen and Buszka, 1997; 

Musgrove and Banner, 2004; Musgrove and others, 2010). 

Geochemical tracers of mineral-solution reactions (such as the 

molar ratios of magnesium to calcium (Mg/Ca) concentrations 

and strontium to calcium (Sr/Ca) concentrations and dolomite 

mineral saturation indices) can be indicative of groundwater 

residence time, which is a function of both flow path and 

water flux (Musgrove and Banner, 2004; Wong, 2008; Musgrove and others, 2010). Previous studies in the San Antonio 

and Barton Springs segments of the Edwards aquifer have 

documented extensive surface-water–groundwater interaction, 

relations between variable hydrologic conditions and water 

quality, and movement of anthropogenic contaminants and dissolved constituents through the aquifer (Hauwert, Johns, and 

others, 2004; Hauwert, Samson, and others 2004; Mahler and 

others, 2006; Garner and Mahler, 2007; Mahler and Massei, 

2007; Mahler and Garner, 2009; Musgrove and others, 2010).
10 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Acknowledgments

The authors gratefully acknowledge many individuals 

and organizations that contributed to this study. The City of 

San Antonio, regulatory authorities, and others (public-water 

purveyors, Edwards Aquifer Authority, Texas Department 

of Licensing and Regulation) helped address challenges of 

obtaining permissions, designing, drilling, and installing 

monitoring wells in this complex hydrogeologic setting. We 

are particularly thankful to the public water purveyor that 

participated in this study. Peer reviews by B.G. Katz and M.K. 

Landon greatly improved the report.

Methods

Methods used for this study are described in the sections 

below, including the design of the well network; drilling, monitoring well installation, coring, and core analysis; collection 

and analysis of water samples; collection of depth-dependent 

flow and chemistry data; quality assurance of water-quality 

data; and a description of statistical and geochemical modeling 

methods.

Design of Well Network

The well network was designed so that an existing 

PSW would be the focus of the study. Monitoring wells were 

installed to allow monitoring of groundwater at different 

depths along likely flow paths from potential source areas 

contributing to the PSW. An additional 38 PSWs that tap the 

regional aquifer were sampled to characterize water quality throughout the aquifer and over a wide range of pumping 

conditions (fig. 1; table 1 at end of report).

In the selected well field, at least one of the six wells is 

pumping in the well field at any time. Two wells are routinely 

pumping during summer months when demand increases, and 

more than two wells might be pumping during peak demand 

periods. Annual pumpage from the well field was about 7,840 

million gallons (Mgal) in 2008 (TANC study water purveyor, 

written commun., 2008), and the well field produced about 

11 percent of total pumpage provided by the purveyor (one 

of several purveyors in the greater San Antonio area). The 

first well in the well field was installed in 1963 (one of four 

installed in the 1960s), and the sixth well was installed in 

1984 (one of two installed in the 1980s). The PSWs are cased 

with steel in the overlying confining units and are open hole 

through most or all of the Edwards aquifer. The open interval of the wells were acidified at the time of construction to 

increase production. Depths to the top of the open interval 

in the wellbores (at or near the top of the aquifer) at the well 

field range from 321 to 360 ft. Open-interval lengths range 

from 454 to 495 ft. Open-hole diameters range from approximately 30 to 36 in. Open-hole diameters are variable because 

of vuggy porosity and collapsed limestone. Rated pump 

capacities for the well-field wells range from 11.2 to 20.7 million gallons per day (Mgal/d) (TANC study water purveyor, 

written commun., 2008).

One or more wells in the well field were not operational 

at any given time during the study period. Well 3 (W3) was 

initially selected for study. However, well 4 (W4) was sampled 

for depth-dependent sampling because there was no pump in 

the well, which permitted access for depth-dependent sampling equipment, and well 6 (W6) was sampled for temporal 

characterization because W3 was not operational at the time 

of the hydrologic event during which temporal changes were 

evaluated. As a result, although a single PSW was initially 

selected, different components of the study collected samples 

from different PSWs within the well field. Well construction, 

hydrogeology, and geochemistry among all the PSWs in the 

well field are similar, and data collected from each of the wells 

are presumed to be comparable for the purposes of this study.

It was not possible to characterize karstic flow paths to 

the selected PSW because of the large capture zone for the 

well and because of the karstic nature of the system. Therefore, two vertically nested monitoring well clusters were 

installed in proximity to the PSW to evaluate processes close 

to the PSW. The locations of the two clusters were selected 

on the basis of the two potential flow zones to the PSW from 

groundwater modeling results (Lindgren and others, 2011b). 

The monitoring well clusters were drilled as close to the PSW 

as possible. The Zarzamora well cluster was about 0.5 mile 

(mi) to the east-northeast of the PSW, and the Timberhill well 

cluster was about 1.5 mi to the west (fig. 4). 

The Zarzamora monitoring well cluster, consisting of 

four wells, was installed in August–September 2007 (fig. 4). 

The first monitoring well (Z–DED) was drilled with the goal 

of being completed near the top of the karstic Kirschberg 

evaporite member (HGU 8) in the lower part (Kainer Formation) of the Edwards aquifer. This unit is known to be a prolific water-bearing zone (Maclay, 1995). Information learned 

from drilling and logging this first deep Edwards monitoring 

well (Z–DED) was used to determine the target depths of 

the other two Edwards monitoring wells completed at this 

location. An intermediate-depth well (Z–IED) was drilled 

to target the bottom of the leached and collapsed members 

of the Edwards aquifer (HGUs 4 and 5), also known to be a 

prolific water-bearing zone (Maclay, 1995). The shallowest 

well (Z–SED) was completed at the top of the Edwards Group 

in the cyclic and marine members of the Edwards aquifer 

(HGU 3). A fourth monitoring well (Z–OVB) was completed 

in an overburden unit (HGU 1), the overlying water-bearing 

Buda Limestone (fig. 4). This well (Z–OVB) was constructed 

to evaluate the possibility of a hydrologic connection between 

the Edwards aquifer and overlying formations at this location. 

The Timberhill monitoring well cluster, consisting of 

two wells, was installed in April 2008 (fig. 4). Similar to the 

deep- and intermediate-depth wells at the Zarzamora site, the 

Timberhill wells were completed near the top of the Kirschberg evaporite member (T–DED) (HGU 8) and near the top of 

the leached and collapsed members (T–IED) (HGU 4). 
Methods 11

PSWs throughout the regional aquifer were identified, 

and a subset was selected for sampling to characterize water 

quality in PSWs throughout the aquifer. A total of 299 PSWs 

were identified throughout the regional extent of the San Antonio segment of the Edwards aquifer and were separated into 

four quartiles based on pumpage. Thirty-nine wells (including 

the selected PSW) were randomly selected for sampling by 

quartile, spaced at least 0.62 mi apart within a quartile (fig. 1). 

Fifteen wells from the largest quartile of pumping were 

selected, and eight were selected from each of the lower three 

quartiles of pumping. From the largest pumping quartile, 13 of 

the wells were in Bexar County, 1 in Uvalde County, and 1 in 

Comal County. Wells from the lower three pumping quartiles 

were in Uvalde, Medina, Bexar, and Comal Counties. Water 

samples were collected from the top quartile wells (in 2004) 

and the lower three quartile wells (in 2005) and were analyzed 

for major ions, nutrients, trace elements, dissolved organic 

carbon (DOC), ultraviolet (UV) absorbance, pesticide compounds (including breakdown products), and volatile organic 

compounds (VOCs). A subset (8 of 15) of the top quartile 

wells were resampled for a subset of organic compounds in 

2005. Results from the top quartile wells are described in 

Carter and others (2007) and Hopple and others (2009), and 

results from all of the 39 PSWs are described in Musgrove and 

others (2010).

Drilling, Well Installation, Coring, and Core 

Analysis

Monitoring well design was reviewed and approved by 

Edwards Aquifer Authority and San Antonio Water System 

permitting authorities and met requirements of the Texas 

Department of Licensing and Regulation. Monitoring wells 

were installed by USGS by using an air rotary drill rig and 

generally followed procedures modified from Lapham and 

others (1995) for drilling in karstic limestone. Equipment was 

decontaminated by steamcleaning between drill sites. 

The design was similar for all Edwards aquifer monitoring wells. A 14-in.-diameter hole was drilled to a depth 

of approximately 20 ft, where a 12.75-in.-diameter surface 

protector casing was installed and cemented. This protector 

casing was used to prevent excavated materials from entering 

the borehole during drilling. An 11-in.-diameter borehole was 

then drilled through overlying confining units (Austin Chalk, 

Eagle Ford Group, Buda Limestone, and Del Rio Clay) to a 

10-ft depth into the Georgetown Formation at the top of the 

Edwards aquifer. Thickness of confining units was approximately 320 ft at the Zarzamora location and 385 ft at the Timberhill location. A 6.63-in.-diameter steel casing was installed 

to this depth to isolate the overlying units from the Edwards 

aquifer. Cement was subsequently installed in stages by tremie 

technique to prevent loss of cement to voids. After waiting 

24 hours for cement surrounding the steel casing to cure, a 

6-in. borehole was drilled to the desired depth in the Edwards 

aquifer. A schedule 80, 2.5-in.-diameter polyvinyl chloride 

(PVC) casing was installed in the borehole to a depth of about 

10 ft above the targeted zone. The PVC casing was reduced to 

2 in. diameter at this depth. About 3 ft of 2-in.-diameter PVC 

casing was added below the reducer. Two bell-shaped rubber 

formation packers (shale traps) were clamped around this casing to make a seal between the PVC pipe and formation above 

the screen. A screen of desired length was installed below the 

formation packers. Screen slot size was 0.04 in. (0.040 slot). 

Screen lengths ranged from 10 to 30 ft depending on the presence and sizes of voids identified from geophysical logs and 

whether the well could be completed in the desired zone. Steel 

casing was not required for the overburden well (Z–OVB). 

Bentonite pellets were poured from land surface to seal the 

zone between the depth of shale traps to a depth inside steel 

casing. Bentonite and Portland cement were used to seal the 

well from about 20 ft below to about 3 ft above land surface. 

Wells were completed with a surface cement wellpad, locking metal shroud, and locking cap for PVC pipe. Wells were 

developed by jetting after drilling was completed. Completed 

wells were subsequently pumped until stabilization of field 

properties (water temperature, specific conductance, pH, dissolved oxygen, and turbidity).

Cores were collected by using a 4-in.-diameter, 10-ft-long 

core barrel at eight selected intervals: three in the overburden 

units and five in the Edwards aquifer. The intervals in the 

overburden units included Austin Chalk/Eagle Ford Group 

contact, Eagle Ford Group/Buda Limestone contact, and the 

Buda Limestone/Del Rio Clay contact (fig. 2). Intervals in the 

Edwards aquifer included Del Rio Clay/Georgetown Formation contact, leached and collapsed members, regional dense 

member/grainstone member contact, grainstone member, and 

Kirschberg evaporite member HGUs (fig. 4).

Core samples were collected aerobically, and then 

subsets of material were collected from each core and placed 

in airtight jars under a nitrogen (N) atmosphere to minimize 

oxidation reactions. Samples were stored chilled to about 4°C 

until treatment. Solid materials to be analyzed for inorganic 

(selected major ion and trace element) chemical analysis were 

removed from the airtight containers and were crushed to less 

than 2 millimeters (mm) diameter at the University of Texas 

at San Antonio Geoscience Laboratory. Crushed samples were 

returned to a N atmosphere and sent to the USGS National 

Research Program Inorganic Chemistry Laboratory in Reston, 

Va., for chemical analysis of selected ions. Crushed samples 

under a N atmosphere also were sent to the USGS National 

Water Quality Laboratory in Denver, Colo., for analysis of 

percent total carbon and percent inorganic carbon. Bulk samples were sent to the USGS National Research Program Clay 

Mineralogy X-ray Diffraction Laboratory in Reston, Va., for 

X-ray diffraction (XRD) analysis. Selected major, minor, and 

trace element concentrations of core samples were determined 

from two acid extractions (leaches): 6 normal (N) hydrochloric 

acid (HCl) (Cornwell and Morse, 1987; Brugam and others, 

1988), and 10 percent nitric acid (HNO3

)(Rabinowitz and 

Bellinger, 1988). Identical extraction procedures for each acid 

were used; 5.0 ± 0.5 grams (g) of crushed core sample was 
12 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

weighed into a 50-milliliter (mL) polycarbonate centrifuge 

tube. One 15-mL aliquot of acid was added. The tube was left 

open to the atmosphere for 30 minutes to permit the evolution 

of carbon dioxide (CO2) gas from sediments with high carbonate content and then was tightly capped. Extractions were 

performed on an “as received” basis; that is, wet. Analytical 

concentrations were corrected to dry weight after calculating 

for moisture content. Sample tubes were placed on a shaker 

table at room temperature for 6 hours to ensure complete mixing. Samples were centrifuged, and the supernatant (leachate) 

was withdrawn with 20-mL polycarbonate disposable syringes 

and filtered through 0.45-micrometer (μm) disposable polycarbonate filters into 10-mL centrifuge tubes. The leachate was 

analyzed for selected major ions and trace elements by using 

inductively coupled plasma-emission spectrophotometry (ICPES). Leachates derived from the 6 N HCl extractions were 

diluted to 1.2 N HCl, and leachates from the 10 percent HNO3

extractions were diluted to 2 percent HNO3 prior to analysis 

with the ICP-ES. Further dilution (5–20 times) was required 

for analysis of As, lead, selenium, and U with inductively 

coupled plasma-mass spectroscopy (ICP-MS). Concentrations for As are not reported for the HCl extractions because 

of mass interference of As with chloride (Cl). Concentrations derived from the leachate analyses are semiquantitative 

because a small amount of residual solids remained after 

extractions. The methods for XRD scans, carbonate digestions, and calculations of semiquantitative weight percents 

are described in detail in Webster and Jones (1994). XRD was 

performed on bulk samples and on samples that were digested 

to remove carbonate so that residual particulates of less than 1 

mm size could be analyzed. In some cases, a second digestion 

was performed. The qualitative carbonate digestion technique 

was designed to release clay minerals bound within grains 

of carbonate. Excess carbonate was abundant after chemical 

treatments, but enough clay was separated to make reasonable 

phase identifications. Any mineral with quantifiable principal 

or secondary peaks resolved significantly above background 

was identified. Some trace identifications could not be quantitatively discriminated from background and were identified 

as trace. Although qualitative weight percent abundance is 

provided in the data (table 6 at end of report), identifications 

are listed in the order of the relative intensity of principal 

peaks where not quantified. Peak intensity is proportional to 

weight percent in an indirect and sometimes unreliable way. 

XRD weight percent calculations have large errors because 

peak intensities routinely vary by 10 percent or more from one 

scan to the next, even when the same slide is analyzed. 

Geophysical and Depth-Dependent Flow 

Measurements

Borehole geophysical logs such as caliper, normal resistivity, induction conductivity, and natural gamma, as well as 

fluid resistivity and temperature, and vertical flow rates were 

collected in PSW W4 and in the deepest monitoring wells 

in the two monitoring well nests (Z–DED and T–DED). W4 

was logged through 30-in.-diameter steel casing from land 

surface datum (LSD) to 320 ft below LSD and through open 

hole from 321 ft to the depth of 753 ft (total depth of hole is 

816 ft) below LSD with the production pump removed. For 

flow measurements in PSW W4, a temporary turbine pump 

was lowered below the existing water-level depth such that 

the intake was a few feet above the bottom of the steel casing, allowing for drawdown and a pumping rate of 650–850 

gallons per minute (gal/min). This pump was used to stress 

the well to simulate production conditions during the pumped 

flowmeter logging and depth-dependent water sample collection. This pumping rate, however, is considerably lower (by 

one to two orders of magnitude) than typical well production 

rates and rated pump capacities (TANC study water purveyor, 

written commun., 2008). The monitoring wells were logged in 

open hole prior to completion under ambient conditions. 

Fluid resistivity logs provide a record of the capacity of 

the borehole fluid to conduct electrical current (Keys, 1997). 

Changes of fluid resistivity are measured by ring electrodes 

inside a housing that allows borehole fluid to flow through it. 

The best fluid resistivity logging results are achieved when 

logging downward into boreholes containing ambient water 

that has had sufficient time to stabilize. Ideally, fluid resistivity logs are collected as the first logging run to record ambient 

conditions before other probes have passed through the borehole and vertically mixed the borehole fluid. Curve deflections 

on the fluid resistivity log might indicate horizontal or vertical 

flow movement, stratification of borehole fluid, or screen 

openings in cased wells. The fluid resistivity values can also 

be used in conjunction with other geophysical measurements 

and logs. Fluid conductivity, the reciprocal of fluid resistivity, 

was compared with measured specific conductance values. 

The fluid conductivity values for this study were recorded at 

the ambient borehole temperature and were not corrected to a 

standard temperature. A Century model 8044 multiparameter 

E-log probe (Century Geophysical Corporation, Tulsa, Okla.) 

was used to log fluid resistivity and temperature. Calibration 

of the fluid resistivity logging probes was completed with 

solutions of known conductivity/resistivity in a two-point calibration. Fluid resistivity and temperature logs were completed 

in W4 during ambient conditions (well field off) and with the 

well field pumping (well field on). 

Natural gamma logs provide a record of gamma radiation 

detected at depth in a borehole and are useful in determining lithologies and contact depths of the strata penetrated by 

the borehole. Fine-grained sediments that contain abundant 

clay tend to be more radioactive than quartz-rich sandstones 

or carbonates (Keys, 1997). The natural gamma log was run 

simultaneously with the fluid resistivity log and was recorded 

in natural gamma counts per second by using a natural gamma 

sensor with a sodium iodide detector built into a Century 

8144c multiparameter probe. The natural gamma sensor, factory calibrated, requires no field calibration. Natural gamma 

count rates, which typically increase in the proximity of clay 

and shale, might also increase slightly when adjacent to any 
Methods 13

bentonite seals in the wells. The caliper log was measured 

by using a three-arm caliper, which measures the diameter of 

the borehole by using a three-arm configuration that can be 

opened downhole. 

The electromagnetic (EM) flowmeter probe measures the 

vertical flow rate and direction of vertical flow in a borehole 

by using the principle of Faraday’s Law of Induction. The 

EM flowmeter probe consists of an electromagnet and two 

electrodes oriented 180 degrees apart and 90 degrees to the 

magnetic field inside a hollow cylinder or tube. The voltage 

induced by a conductor moving at right angles through the 

magnetic field is directly proportional to the velocity of the 

conductor (water) through the field (Century Geophysical 

Corporation, 2010). The direction of vertical water flow is 

determined by the polarity of the response, with upward flow 

being positive and downward flow being negative. Downward 

and upward flow were calibrated at a rate of 1 gal/min through 

the tool in a controlled environment with a bypass factor calculated for high flow within the wellbore. Flowmeter and fluid 

properties data for W4 were collected for four different pumping conditions: (1) no pumping in the PSW or well field (an 

operationally rare condition) (“ambient 1”); (2) no pumping 

in the PSW, but with pumping nearby well(s) in the well field 

(greater than 7,000 gal/min) (“ambient 2”); (3) PSW pumping 

(850 gal/min), no other pumping in the well field (“moderate”); (4) PSW pumping (850 gal/min) and with pumping of 

nearby well(s) in the well field (greater than 7,000 gal/min) 

(“normal”). 

Collection of Water Samples

Groundwater samples were collected from PSWs in the 

regional aquifer, monitoring wells (Timberhill and Zarzamora 

wells and an overburden well), and well-field PSWs during 

2004–9 (table 1). Well-field samples included wellhead samples (W2, W3, W4, W5, and W6) and depth-dependent (W4) 

and temporal (time series in response to a rainfall/recharge 

event) samples (W6). Temporal samples also were collected 

from the Zarzamora Edwards aquifer monitoring wells and an 

upgradient unconfined monitoring well (AY–68–27–610). For 

the purposes of comparing water chemistry, groundwater samples were categorized as being from regional aquifer PSWs, 

from the well field (wellhead samples), from the monitoring 

wells (Zarzamora and Timberhill monitoring well clusters, 

excluding the overburden well), from the overburden monitoring well, from the PSW depth-dependent sampling, and from 

temporal sampling (from the PSW and selected monitoring 

wells (including an upgradient unconfined monitoring well)). 

Constituents analyzed for are summarized in table 2 at end 

of report. It was not possible to collect a surface discharge 

(wellhead) sample during the depth-dependent sample collection from W4; alternatively, this sample was approximated by 

placing the sample pump intake just below the bottom of the 

turbine pump intake (near the bottom of the casing at 320 ft of 

depth). The water sample collected from this intake point was 

assumed to represent discharge at the surface and is considered 

hereinafter as the wellhead sample from W4. Depth-dependent 

and temporal samples are described in more detail in the two 

following sections. 

Sampling protocols used for this study are described in 

detail in Koterba and others (1995), Koterba (1998), Lapham 

and others (1995), and U.S. Geological Survey (variously 

dated). Groundwater samples were collected and processed 

in a mobile water-quality laboratory. Existing pumps, permanently installed in each PSW (except W4), were used to 

deliver water to the land surface. In most cases, a permanent 

spigot near the wellhead was used as the sampling point. In 

a few instances, plumbing connections near the wellhead 

were modified temporarily for sampling purposes. Water was 

transferred from the wellhead spigot to the mobile laboratory by using Teflon® (DuPontTM) tubing with stainless steel 

fittings. To minimize risk of contamination, sample collection 

and preservation took place in chambers consisting of clear 

polyethylene bags supported by plastic frames, much like 

laboratory glove boxes. Equipment that came in contact with 

the water sample was cleaned between each well sampling 

by using a progression of (1) dilute phosphate-free detergent 

to remove both organic and inorganic residues, (2) deionized 

water rinse to remove detergent, (3) methanol wash to remove 

organic residue, and (4) deionized water rinse to remove any 

remaining methanol residue. Monitoring wells were sampled 

by using a portable positive displacement groundwater sample 

pump. 

Wells were purged before sampling. During the initial 

pumping period, measurements of field parameters (specific conductance, pH, temperature, dissolved oxygen) were 

routinely monitored in a sealed flowthrough cell. Turbidity 

was monitored by collecting periodic water samples from a 

discharge tube and analyzing with a portable field turbidimeter. Water samples were collected after stable measurements 

of these properties were achieved (Koterba and others, 1995; 

U.S. Geological Survey, variously dated). Water was redirected by way of a manifold to the sample chamber inside the 

mobile laboratory for sample collection. 

Additional parameters measured at the time of sample 

collection were carbonate alkalinity, ferrous and total iron, and 

sulfide. Alkalinity was measured by using an inflection point 

titration method (Rounds, 2003). Iron species and sulfide were 

analyzed by field spectrophotometric methods, and results 

are considered qualitative. Additional samples were collected 

for analysis of major ions (mineral analysis), nutrients (N 

and phosphorus compounds), DOC, UV absorbance (organic 

carbon), trace elements (mostly metals), pesticide compounds 

(pesticides and their degradates), VOCs, and wastewater indicator compounds. Samples for analysis of selected isotopes, 

radon gas, radium-226 and radium-228, and age-dating compounds and isotopes (chlorofluorocarbons (CFCs, specifically 

CFC-11, -12, and -113), sulfur hexafluoride (SF6

), tritium (3H), 

helium-3 (3He), and associated dissolved gases) were collected 

at a subset of wells. Most analyses were performed at the 

USGS National Water Quality Laboratory. Dissolved gases, 
14 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

CFCs, and SF6 were analyzed at the USGS Reston Chlorofluorocarbon Laboratory in Virginia. Helium-3 was analyzed 

at the Gas Extraction Laboratory of Lamont-Doherty Earth 

Observatory in Palisades, N.Y. Tritium was analyzed at the 

Gas Extraction Laboratory of Lamont-Doherty Earth Observatory or at the USGS Isotope Tracers of Biogeochemical 

and Hydrologic Processes Laboratory in Menlo Park, Calif. 

(Thatcher and others, 1977). Age-dating analyses and methods 

are further described below in the section “Groundwater AgeDating Methods.”

Depth-Dependent Samples

Geophysical and flowmeter logs were collected from 

W4 to determine zones of contribution to the wellbore prior 

to sampling; the W4 borehole was selected because it did not 

contain a production pump. Prior to logging and sampling, a 

“test” turbine pump, capable of pumping up to 850 gal/min, 

was installed in the borehole of W4 to approximate PSW 

pumping conditions. Although the test pump did not pump at 

the capacity of production pumps, it was deemed sufficient 

to stress the well for the purpose of this study. As described 

earlier in the section “Geophysical and Depth-Dependent Flow 

Measurements,” four pumping conditions were logged with 

the flowmeter: ambient 1, ambient 2, moderate, and normal. 

The normal pumping condition (for example, with one or two 

wells in the well field pumping at total discharge rates from 

approximately 7,778 to 28,270 gal/min) was likely to be most 

representative of pumping conditions associated with the 

production of supply water. Each of the pumping conditions 

produced different results for stratigraphic zones that contributed water to the well. This information was used to select 

three depth intervals for depth-dependent sampling under three 

of the four pumping conditions: ambient 1 (hereinafter, ambient), moderate, and normal. 

Selected depths for sampling based on zones of flow 

within the well were (1) shallow (380 ft), which was just 

above the high-conductivity zone, (2) intermediate (430 ft), 

and (3) deep (540 ft), which are associated with three different HGUs, specifically, (1) the cyclic and marine members 

(HGU 3), (2) the leached and collapsed members (HGUs 

4 and 5), and (3) above the Kirschberg evaporite member 

(HGUs 8 and 9) in the grainstone member of the Edwards 

Group (HGU 7), respectively (fig. 4). Depth-dependent 

samples were collected by suspending 2.5-in.-diameter PVC 

casing (tubing) to the three selected depths. A positive displacement sample pump (1.8-in. outside diameter) was placed 

inside the PVC casing and used to collect water samples from 

the three selected depths. This approach is similar to that used 

by Izbicki (2004) to collect samples from discrete depths in 

production wells under pumping conditions. The PVC tubing 

was purged of three casing volumes prior to sampling. Water 

samples were collected at the selected depth intervals for each 

of the three pumping conditions as defined above (ambient, 

moderate, and normal). An additional sample was collected 

under the moderate condition from below the existing casing of the wellbore to approximate the wellhead sample for 

W4. Depth-dependent sampling details for the PSW, as well 

as sampling of the monitoring wells completed at different 

depths, are shown in table 3 at end of report.

Temporal Water Samples

Selected monitoring wells and one of the well-field PSWs 

(W6) were sampled several times in response to a rainfall and 

recharge event that occurred in October 2009 to assess shortterm (event-scale) temporal variations in water quality for 

the TANC study area. Sampled monitoring wells were three 

Zarzamora wells (Z–SED, Z–IED, and Z–DED) and an upgradient unconfined monitoring well (AY–68–27–610) (table 1). 

Well AY–68–27–610 is one of the shallow/urban unconfined 

monitoring wells described by Musgrove and others (2010). It 

is approximately 4.5 mi to the north of the well field (fig. 3). 

A baseline sample was collected from these five wells 

on April 8 through 14, 2009. At that time, it was believed that 

heavy spring rains were likely. However, an extended drought 

continued in the region throughout the summer of 2009, as 

evidenced by declining water levels in the Bexar County index 

well (J–17) (fig. 1), indicative of very dry regional conditions 

(fig. 5). From June through August 2009, a total of approximately 1.4 in. of rain was recorded at the San Antonio airport. 

The sampled storm event was preceded by 6.35 in. of rain in 

September, which resulted in an increase in water level close 

to that observed when the baseline sample was collected in 

April (fig. 5). Between October 3 and 4, 2009, 6.06 in. of rain 

was recorded at the San Antonio airport, and no additional rain 

was recorded until October 9, 2009. The first event samples 

were collected from October 4 through October 6, 2009. A 

total of six samples, including the baseline sample, were collected from each designated well through November 19, 2009 

(table 4 at end of report). An additional 6.73 in. of rain was 

recorded at the San Antonio airport between October 9 and 

November 19, 2009. As a result, the response in the study area 

to the designated rain and recharge event cannot be distinguished from subsequent rain and recharge during the event 

sampling interval.

Laboratory Analytical Methods

Depending on sampling event, samples were analyzed 

for a variety of constituents, including major ions, nutrients, 

UV absorbance, DOC, pesticides and pesticide degradates, 

VOCs and wastewater indicator compounds, fuel oxygenates, stable and radiogenic isotopes (N, oxygen, hydrogen, 

strontium), trace elements, radon-222 gas, or radium-226 and 

-228 (table 2). The above constituents were not collected in 

every sample; rather, they were collected for particular study 

objectives. Selected groundwater samples were analyzed for 

dissolved gases and geochemical age-dating compounds and 

isotopes: CFCs, SF6

, 3H, and 3He.
Methods 15

Samples for major ions, trace elements, and nutrients 

were filtered through a 0.45-μm capsule filter and analyzed by 

using ICP-ES, ICP-MS, ion-exchange chromatography, and 

colorimetry procedures described in Fishman and Friedman 

(1989), Faires (1993), Fishman (1993), McClain (1993), 

Garbarino (1999), Garbarino and others (2006), and Patton 

and Kryskalla (2003). Hydrogen sulfide was measured in the 

field by using colorimetric methods (Hach Company, 2002). 

Water samples for radon-222 were collected in a syringe prior 

to contact with the atmosphere and injected into a mineraloil-based scintillation solution in a 30-mL glass scintillation 

vial. The sample was shipped overnight to the laboratory and 

analyzed by liquid-scintillation counting methods (Prichard 

and Gesell, 1977; American Society for Testing and Materials, 

1996). Samples for stable isotopes of hydrogen (δD), oxygen 

(δ18O), and NO3 (δ15N and δ18O of NO3) were analyzed by the 

USGS Stable Isotope Laboratory in Reston, Va. Isotope data 

are presented in delta (δ) notation as the ratio of the heavy to 

the light isotope, normalized to a standard (eq. 1). 

δsample = 1,000 [(Rsample/Rstandard) −1] (1) 

where 

Rsample is the ratio of the heavy to the light isotope in the 

sample and 

Rstandard is the ratio of the heavy to the light isotope in the 

standard. 

δD and δ18O were analyzed by using an isotope ratiomass spectrometer by hydrogen gas-water equilibration and 

CO2

-water equilibration techniques, respectively, and are 

Figure 5. Time series (April 1 to December 31, 2009) climatic and hydrologic data for the south-central Texas study area. A, Bexar 

County index well (J–17) water-level altitude (Edwards Aquifer Authority, 2009), and dates of sample collection for event sampling (well 

field W6). B, San Antonio rainfall (recorded at the San Antonio International Airport) (National Oceanic and Atmospheric Administration, 

2010). 

2009

April May June July August September October November December

0

1

2

3

4

5

6

Daily rainfall, in inches 

635

640

645

650

655

660

665

670

675

Water-level altitude, in feet above 

National Geodetic Vertical Datum of 19291

A

B

Bexar County index well

 (J–17) water-level altitude1

Event sample collection

EXPLANATION

1

 Source agency reports water-level altitude referenced to sea level

 (Edwards Aquifer Authority, 2009)
16 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

reported relative to Vienna Standard Mean Ocean Water 

(Epstein and Mayeda, 1953; Coplen and others, 1991; Coplen, 

1994; Révész and Coplen, 2008a, 2008b). Nitrate isotopes 

(δ15N and δ18O of NO3) were analyzed by bacterial conversion 

of NO3 to nitrous oxide and reported relative to N2 gas in 

air and Vienna Standard Mean Ocean Water, respectively 

(Sigman and others, 2001; Casciotti and others, 2002; Révész 

and Casciotti, 2007).

VOCs, pesticides, pesticide degradates, DOC, major 

ions, trace elements, nutrients, and radon-222 were analyzed 

by the USGS National Water Quality Laboratory. Samples for 

VOCs and fuel oxygenates were unfiltered and determined by 

gas chromatography and mass spectrometry by using methods 

described in Connor and others (1998) and Rose and Sandstrom (2003). Pesticides samples were filtered by using a 0.7-

μm glass-fiber filter and analyzed by carbon-18 solid-phase 

extraction and capillary column gas chromatography and mass 

spectrometry (Zaugg and others, 1995; Lindley and others, 

1996; Furlong and others, 2001; Sandstrom and others, 2001; 

Lee and Strahan, 2003; Madsen and others, 2003). Wastewater indicator compounds were collected similarly to pesticide 

samples and were analyzed as described in Zaugg and others 

(2002).

DOC samples were collected by forcing raw water samples through a 0.45-μm glass-fiber filter by using high-purity 

N2

 gas. DOC samples were analyzed by methods described 

by Brenton and Arnett (1993). Nitrogen species concentrations are reported as N (for example, NO3

 as N; hereinafter, 

NO3), and phosphorus species concentrations are reported as 

phosphorus (P).

Groundwater Age-Dating Methods

To facilitate comparison of results between groundwater age tracers, multiple tracers were measured in selected 

groundwater samples, including concentrations of CFCs, 

SF6, 3H, and the ratio of the parent/daughter isotopes 3H/3He. 

Because the solubility of atmospheric tracers varies as a function of temperature, dissolved gas concentrations (argon, CO2

, 

methane, N2

, and oxygen) were also measured to estimate the 

temperature of groundwater at the time of recharge, as well 

as to calculate the amount of excess air and excess N. Excess 

air is that which is trapped in pores (for example, after a rapid 

water table rise) and subsequently dissolved in groundwater 

to concentrations above ambient conditions. Excess N reflects 

reactions with N species, such as denitrification. Helium-4 

(4He) was also measured to determine whether the 3H/3He agetracer method was suitable.

Anthropogenic activities have released SF6, CFCs, and 3

H into the atmosphere in low concentrations since the 1940s 

and 1950s (Schlosser and others, 1988, 1989; Busenberg and 

Plummer, 1992, 2000; Solomon and others, 1992). Precipitation incorporates these constituents from the atmosphere, 

and as a result, groundwater recharge carries a chemical or 

isotopic signature that can be related to atmospheric conditions at the time of recharge. The 3

H/3He method is based on 

the radioactive decay of 3H to 3He. Each age-tracer technique 

has associated uncertainties and might be affected differently 

by aquifer processes. Because all physical and chemical processes that might affect age-tracer results cannot be accounted 

for, results using these techniques are reported as apparent 

ages. CFC and SF6 dating techniques are described in Busenberg and Plummer (1992, 2000, respectively). Techniques for

3

H/3He dating are described by Schlosser and others (1988, 

1989) and Solomon and Cook (1999). 

Dissolved helium (He) in groundwater is derived from 

both atmospheric and terrigenic (from earth) sources. The 

atmospheric component includes air-soluble He and excess-air 

He (He derived from excess air) that results from dissolution 

of air bubbles trapped just below the water table. Another 

atmospheric source of He (as 3He) is from decay of 3H in 

recently (less than 60 years old) recharged water; 3H concentrations in rainfall, some of which became recharge, during the 

mid-20th century were increased substantially by atmospheric 

testing of nuclear weapons (Michel, 1989). The He derived 

from 3H decay is the He component of interest for the 3H/3He 

age-tracer method. Helium is also produced by the radioactive decay of U and thorium in crustal rocks and aquifer solids 

(crustal He) and from upward diffusion or advection of He 

from the mantle (mantle He). Together, crustal and mantle He 

are termed terrigenic He (Solomon, 2000). Potential sources 

of terrigenic He in the Edwards aquifer include igneous rock 

intrusions, oil and gas hydrocarbons that are widely present 

in Edwards Group rocks downdip from the freshwater zone 

of the Edwards aquifer, rocks composing the underlying and 

adjacent Trinity aquifer, and rocks underlying the Trinity 

aquifer. Corrections for atmospherically derived excess He are 

included in estimating ages. If excess He concentrations are 

higher than those which result from atmospheric sources, then 

it is generally not possible to estimate an age with the 3H/3He 

age-tracer method. 

Samples for age-dating and dissolved gas analyses were 

collected according to protocols described by the U.S. Geological Survey Reston Chlorofluorocarbon Laboratory (2010). 

Dissolved gas samples, including samples to be screened 

for 4

He, were collected in preweighed, previously evacuated 

150-mL glass septum bottles. Upon removal of the rubber 

stopper, a sample discharge tube was placed at the bottom of 

the sample bottle. After the sample bottle was initially filled, 

it was placed in a 1-liter (L) beaker filled with sample water 

such that the top of the sample bottle was under water. The 

sample discharge tube flowed continuously during this process 

until three or more sample-bottle volumes had flowed from 

the sample discharge tube into the septum bottle. The sample 

discharge tube was removed, and a rubber stopper containing 

a needle was inserted into the top of the septum bottle while 

still submerged. The needle was removed after the stopper 

was securely placed. Septum bottles were stored inverted and 

chilled until analysis. CFC samples were collected in 125-

mL glass bottles that were sealed with screw caps lined with 

aluminum foil. Sample bottles were filled by using a similar 

method as the dissolved gas samples. Bottle caps were kept 
Methods 17

under water until after they were applied to the top of the 

sample bottle. Bottle caps were taped to prevent loosening, 

and samples were stored inverted at room temperature until 

analysis. SF6 samples were collected in 1-L glass bottles and 

sealed with polyseal screw caps. The sample discharge tube 

was placed at the bottom of the sample bottles, and sample 

water flowed into the bottles for three or more sample-bottle 

volumes. The sample tube was removed, and samples were 

capped such that no headspace was allowed to form prior 

to sealing the sample bottle. Sample caps were taped, and 

samples were stored at room temperature until analysis. 3H 

samples were collected in 1-L polyethylene bottles. The 

sample discharge tube was placed at the bottom of the sample 

bottle until the bottle was filled such that a small headspace 

remained. Sample bottles were sealed with polyseal screw 

caps, and the caps were taped. Samples were stored at room 

temperature until analysis. 3He samples were collected in 

copper tubes mounted on trays that contained clamps at each 

end. The sample discharge tube was attached to the inlet side 

of the copper tube, and a plastic tube (Tygon®, Saint-Gobain 

Performance Plastics) containing a valve was attached at the 

outlet side of the copper tube. Sample water flowed through 

the copper tube with some back pressure applied by way of the 

attached valve. The copper tube was gently tapped to remove 

any bubbles that might have formed during the sampling 

procedure. After the copper tube was purged with three sample 

volumes, the clamps on the copper trays were tightly closed 

to seal the copper tubes, and the external tubing was removed. 

Samples were stored at room temperature until analysis. 

Groundwater samples were analyzed for dissolved gases, 

SF6, and CFCs at the USGS Reston Chlorofluorocarbon Laboratory in Virginia. Dissolved gases were extracted from headspaces of glass samplers and analyzed by gas chromatography 

(Busenberg and others, 1998). Analytical methods for SF6

followed those described by Busenberg and Plummer (2000). 

CFCs were analyzed by using purge and trap gas chromatography with electron-capture detector (GC-ECD) (Bullister, 

1984; Bullister and Weiss, 1988; Busenberg and Plummer, 

1992). Groundwater samples for 3H and 3He were analyzed 

by the Gas Extraction Laboratory of Lahmont-Doherty Earth 

Observatory in Palisades, New York, by using quantitative 

gas extraction followed by mass spectrometric techniques; 

methods are described by Clark and others (1976), Ludin and 

others (1998), and Schlosser and others (1989). The 3

H/3He 

methods included analysis of concentrations of 4He and neon 

(Ne), which are used in 3H/3He age-tracer calculations.

In spite of the analytical precision available for measurement of many geochemical age tracers, there are numerous 

uncertainties associated with groundwater age interpretations 

(Phillips and Castro, 2003; Bethke and Johnson, 2008). Age 

interpretation for a sample that consists of water of a single 

age might be relatively simple but becomes increasingly complex for a sample that consists of a mixture of water; that is, a 

mixture of water “parcels,” each of which has a discrete age 

(Böhlke, 2006). Age-interpretation complexities associated 

with mixing might be especially important in karst aquifers, 

where each component of a complex network of conduits, 

fractures, and matrix porosity might have a different groundwater age and a well or spring might discharge water from 

any combination of porosity types (Plummer and Busenberg, 

2005; Long and Putnam, 2006). Models for the hypothetical 

concentrations of age tracers in water samples with different age distributions that consider the effects of hydrologic 

processes such as dispersion, exponential mixing, and binary 

mixing of shallow and deep groundwater have been developed 

to facilitate interpretation of geochemical age tracers (Böhlke, 

2006; Long and Putnam, 2006). Age-tracer concentrations 

were compared with results expected from different lumpedparameter models by using atmospheric input data for tracers 

and using age-date tracer modeling software developed by 

Böhlke (2006). Lumped-parameter models assume a steadystate flow system and also assume that selected tracers behave 

like a water molecule.

Quality Control 

Quality-control (QC) samples are collected and analyzed 

to evaluate bias and variability of environmental samples. Bias 

is systematic error inherent in a method or caused by some 

artifact of the measurement system. Variability is the degree 

of variation in independent measurements that results from 

repeated application of the process under specified conditions (T.L. Schertz, U.S. Geological Survey, written commun., 

1997). QC data are particularly useful for analyzing and interpreting water quality data analyzed for small concentrations, 

including those measured at μg/L levels for many constituents 

in this study. QC samples collected and analyzed for this study 

consisted of three types of samples collected onsite: blanks, 

replicate environmental samples, and environmental matrixspike samples. In addition to QC samples submitted from the 

field, the USGS National Water Quality Laboratory analyzes 

laboratory blanks, replicates, and spikes. QC data stored in 

USGS databases are available upon request. 

Blank samples test for bias from introduction of contaminants to environmental samples. Three types of blank 

samples were analyzed in this study: source-solution, equipment, and field. Source-solution blanks consist of high-purity 

organics-free or inorganics-free water, prepared and tested by 

the USGS National Water Quality Laboratory for the NAWQA 

Program. Source-solution blanks were collected with associated equipment or field blanks and were occasionally analyzed 

for VOCs, DOC, trace elements, or nutrients. Source-solution 

blanks document the purity of the high-purity waters used 

to collect field and equipment blanks. A total of 22 blanks 

(combination of inorganic, organic, field, and equipment) were 

collected during this study in comparison with 97 environmental samples.

Equipment and field blanks were analyzed for concentrations of a combination of major ions, nutrients, DOC, trace 

elements, pesticide compounds, or VOCs. Two equipment 

blanks were collected during the study period prior to collection of the first environmental samples to indicate whether 
18 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

the equipment or sample collection process would bias the 

data. Both equipment blanks contained several inorganic 

constituents, primarily trace metals. Trace metals detected 

at low concentrations (less than 1 μg/L) included aluminum, 

cadmium, chromium, manganese, nickel, and vanadium. Zinc 

was detected in both equipment blanks at concentrations of 

about 2 and 3 μg/L, and lead was detected in one equipment 

blank at a concentration of about 2 μg/L. The source of these 

metals, though at low concentrations, is unknown. Stainless 

steel fittings were replaced as a result of these detections, 

and these metals were not evaluated for this study. Calcium 

(Ca), sodium (Na), silica (Si), sulfate (SO4), and iodide (I) 

also were detected at low concentrations (less than 1 mg/L) 

in one equipment blank, well below concentrations observed 

in environmental samples. DOC and phenol were detected at 

low concentrations (less than 1 mg/L and less than 1 μg/L, 

respectively) in one equipment blank. Occurrences of DOC 

and phenol are discussed below.

Field blanks were collected at periodic intervals onsite 

to indicate whether analytical bias occurred from sample collection, cleaning protocols, or contamination of the mobile 

laboratory. Eleven (organic and inorganic) field blank suites 

were collected following environmental sample collection and 

subsequent equipment cleaning. Field blanks were processed 

the same as environmental samples—by pumping high-purity 

water through cleaned sample collection equipment, including filter apparatuses, where applicable. DOC was detected 

in two field blanks. DOC was detected at very high concentrations (greater than 100 mg/L) in one of the field blanks 

collected in 2005 and was attributed to insufficient removal of 

methanol during cleaning. Several environmental samples had 

DOC concentrations that were higher (greater than 10 mg/L) 

than expected, and it is presumed that the cleaning procedure 

during 2004–5 affected the concentrations of these samples. 

Environmental DOC concentrations measured in 2004–5 are 

considered suspect and are marked with a “V” in data tables, 

indicating possible contamination. The cleaning process was 

corrected during the sampling period with additional deionized 

water rinsing to remove methanol from sampling equipment. 

Among samples collected in 2004–5 and analyzed for the 

wastewater schedule, phenol, benzophenone, and 4-nonylphenol were sometimes detected, mostly below method reporting 

levels, in field blanks and environmental samples. Concentrations in three field blank samples were higher than those in 

environmental samples. Results for these organic compounds 

and for caffeine and camphor, on USGS National Water Quality Laboratory Schedule 1433, were not considered to reflect 

environmental concentrations because of analytical limitations during the study period (Zaugg and Leiker, 2006). The 

VOCs toluene and styrene were detected at low concentrations 

(less than 0.09 μg/L) in two field blanks and one sourcesolution blank. The high-purity blank water might have been 

the source for toluene and styrene, which were not evaluated 

in this study. Benzene was detected at a low concentration 

(0.018 μg/L) in one field blank; that blank also contained 

toluene, indicating a possible contamination with fuel used to 

power field generators. One field blank contained chloroform 

(trichloromethane) at a concentration of 0.017 μg/L, which is 

below the long-term method reporting level (0.03 μg/L) and 

in the range of environmental data evaluated in this study.

Chloroform is rarely found in blanks when examining all 

groundwater QC blanks collected during 1996–2009 by the 

NAWQA Program in this study area; therefore, the presence 

of chloroform at such a low concentration, in one field blank, 

although unexplained, is not considered problematic for interpretation in this study. No pesticide compounds were detected 

in blanks.

Some trace elements were detected at low concentrations (less than 1 μg/L) in field blanks: chromium, cobalt, 

manganese, nickel, silver, strontium, and zinc. Aluminum was 

detected in two field blanks; one sample contained aluminum 

(3.8 μg/L) above the method reporting level. Aluminum and 

vanadium were each detected in a source-solution blank. The 

high-purity blank water might have been a source for low concentrations of these constituents in some blank samples. The 

more likely source for some trace elements in blank samples 

is corrosion of stainless steel fittings. One field blank sample 

contained a low concentration (less than 1 mg/L) of Ca, 

and two field blanks contained low concentrations of silica. 

Concentrations of these constituents are orders of magnitude 

below those of environmental samples. Three field blank 

samples contained total N, and two of the sample concentrations were above the method reporting level. The detections in 

field blanks were well below those measured in environmental 

samples.

Replicate samples are used to evaluate variability in 

measurements associated with analytical processes, sample 

collection protocols, or natural variation. Eleven replicate 

samples were collected sequentially after environmental samples and analyzed for a combination of major ions, nutrients, 

DOC, trace elements, radon, pesticide compounds, VOCs, 

or wastewater indicator compounds. Precision can be evaluated by comparing concentrations between environmental and 

replicate samples. Precision is expressed as relative percent 

difference (RPD) and is computed as

RPD = {|C1−C2| ÷ [(C1+C2) ÷ 2]} × 100, (2)

where

C1 is the concentration of an analyte measured in the 

environmental sample, in concentration units; and

C2 is the concentration of the analyte measured in the 

replicate sample, in the same concentration units. 

Consideration of the magnitude of concentrations 

being evaluated should be given when evaluating RPDs. For 

example, the RPD computed from environmental and replicate 

concentrations of 100 and 101 mg/L is 1.0, the RPD computed 

from environmental and replicate concentrations of 10 and 11 

mg/L is 9.5, and the RPD computed from environmental and 

replicate concentrations of 1 and 2 mg/L is 67. Although the 
Methods 19

difference between environmental and replicate concentrations 

is the same in each of the examples, the difference evaluated 

relative to the mean of the measured concentrations increases 

as the concentrations being evaluated decrease. Constituents 

measured at small concentrations might yield a large RPD. 

RPDs were computed only from pairs of analytes that were 

detected. If one or both analyses in a constituent pair were 

reported as less than the applicable detection limit, then that 

constituent pair was not evaluated.

Most mean RPDs computed for the analytes were less 

than 5, indicating excellent reproducibility. In general, mean 

RPDs computed for this study indicate that the amount of variability in measurements between environmental and replicate 

samples is acceptable. Relatively large RPDs (greater than 20 

percent) resulted for a number of constituents that occurred at 

low concentrations: aluminum (two replicates), boron, chromium, copper, fluoride (F), iron, lead, manganese (two replicates), selenium, thallium, zinc (three replicates), radium-226, 

atrazine, deethylatrazine, and metsulfuron-methyl. Although 

the RPDs were relatively high, concentrations for these replicate pairs were low. Concentrations of copper, lead, nickel, 

zinc, and DOC in one replicate-sample pair resulted in large 

RPDs (greater than 30 percent) for those constituents. Even 

though concentrations were relatively low, the cause of the 

large sample variability in these constituents might be indicative of the natural variability of aquifer chemistry at this location or might be a result from sample collection procedures 

at this site or analytical variability at low concentrations close 

to the Mimimum Reporting Level (MRL). These constituents 

are not described in this report.

Field spikes are used to assess bias and variability from 

groundwater matrix interference or degradation of organic 

constituent concentrations during sample processing, storage, and analysis. Field spikes are environmental samples 

to which a known volume and concentration of analytes is 

added. Analytical recoveries of the spiked constituents are 

expressed as percentages of expected (theoretical) concentrations. Computed field-spike recoveries are compared to 

theoretical and lab recoveries to evaluate matrix interferences or degradation of organic compounds (pesticides and 

VOCs). 

Recovery (percentage) is computed as

Recovery = [(Cspiked – Cunspiked) ÷ Cexpected] × 100, (3) 

where 

Cspiked is the measured concentration of analyte in the spiked 

environmental sample, in micrograms per liter; 

and 

Cunspiked is the measured concentration of analyte in the 

unspiked environmental sample, in micrograms 

per liter. 

Cexpected is the theoretical concentration of analyte in the 

spiked environmental sample, in micrograms per 

liter, and is computed as

Cexpected = Csolution x Vspike ÷ Vsample, (4) 

where

Csolution is the concentration of analyte in spiked 

environmental solution, in micrograms per 

milliliter;

Vspike is the volume of spike added to environmental 

sample, in milliliters; and

Vsample is the volume of environmental sample, in liters. 

Organic compound spikes and spike replicates were 

added to environmental samples and their replicates, resulting 

in 11 spiked samples for a combination of VOCs or pesticide 

compounds. Mean percent recoveries were computed for the 

most frequently detected compounds: atrazine, 98.7 percent; 

deethylatrazine, 44.0 percent; tetrachloroethene (PCE), 97.9 

percent; chloroform, 113 percent. The mean percent recoveries for spikes of atrazine and PCE were similar to laboratory 

surrogate recoveries; therefore, concentrations measured in 

environmental samples probably represent actual concentrations. A high (greater than 100 percent) mean percent recovery for chloroform indicates a high bias for this compound. 

Therefore, actual concentrations of chloroform probably were 

less than reported concentrations. Results for deethylatrazine 

were qualified as estimated (“E”) by the USGS National Water 

Quality Laboratory under laboratory reporting conventions 

used during the study period. A remark code of “E” was used 

when compounds were identified, but concentrations could not 

be accurately quantified. Analytical recoveries typically were 

lower than expected for deethylatrazine; therefore, concentrations were qualified (Sandstrom and others, 2001). Actual 

concentrations of deethylatrazine probably were higher than 

reported concentrations. 

In addition to field spikes, surrogate compounds are 

added to environmental samples in the laboratory at the time 

of analysis. Surrogates are compounds that have a range of 

expected (observed in the laboratory in 2004–9) recoveries, 

usually near 100 percent, and are used to verify that analyses 

are acceptable. Surrogate compounds, which generally do not 

occur in nature, are similar in physical and chemical properties to analytes of interest. At the laboratory, they are added to 

samples to provide information on matrix effects and potential 

gross sample-processing problems. Surrogate compound concentrations were evaluated for analytical schedules containing 

the most frequently detected organic compounds (atrazine, 

deethylatrazine, PCE, and chloroform). Organic compound 

analyses for the most part were within laboratory QC limits, 

indicating that analytical instrument performance was satisfactory. Three surrogates (1,2-dichloroethane-d4

; 1,4-bromofluorobenzene; and toluene-d8

) were added to the VOC analytical 

schedule, and two surrogates (alpha-HCH-d6 and diazinon-d10) 

were added to the selected pesticide schedule. The VOC surrogates were within the acceptable laboratory QC limits for 

all VOC samples. Recoveries for environmental surrogates of 

alpha-HCH-d6 ranged from 53.3 to 129 percent. The highest and lowest environmental surrogate alpha-HCH-d6

 values 
20 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

were outside the acceptable limit range of 64–121 percent. 

Eleven environmental surrogate samples for diazinon-d10 were 

below acceptable QC limits, indicating that recoveries for 

diazinon (and similar compounds) might be suspect. Diazinon 

was not frequently detected; therefore, it was not evaluated in 

this report.

For samples with complete ion analyses, the percent 

difference in the charge balance between cations (positively 

charged) and anions (negatively charged) is used as a QC 

check on the quality of the major ion analyses; the percent difference was less than 2 percent in all but three samples. In two 

of these samples the percent difference was about 4.5 percent, 

still within acceptable limits of about 5 percent difference. The 

percent difference for one sample was considered unacceptable at 12 percent. The alkalinity measurement for that sample 

was low when compared to the dataset and was considered as 

estimated rather than quantified. 

Statistical Methods and Geochemical Modeling

Nonparametric statistical tests were used for all data 

interpretation. A nonnormal distribution is a common characteristic of water-resource data (Helsel and Hirsch, 2002), 

and as a result, nonparametric methods are generally better 

suited than are traditional parametric methods to evaluate 

water-resource data. The Kendall’s tau coefficient is a nonparametric, rank-based test used to measure the strength of the 

monotonic relation between x and y (linear and nonlinear) and 

is resistant to the effects of outliers (Helsel and Hirsch, 2002). 

The tau coefficient ranges from -1 to 1; a value of 0 indicates 

no correlation, and values approaching -1 or 1 indicate an 

increasing strength of correlation. The tau coefficient values 

generally will be lower than values of traditional correlation 

coefficients for linear associations of the same strength; for 

example, a strong linear correlation of greater than or equal to 

(≥) 0.9 corresponds to a tau value of about ≥0.7 (Helsel and 

Hirsch, 2002). Independent groups of data were compared for 

differences by using the Mann-Whitney U test. For this report, 

statistical results with p-values less than 0.05 were considered 

statistically significant and are reported. Estimated values (less 

than the laboratory method reporting level) were considered at 

the estimated concentration.

The geochemical modeling program PHREEQC 

(Parkhurst, 1995) was used to calculate ion speciation and 

mineral saturation states. The precipitation or dissolution of 

mineral phases can be an important control on fluid composition. In a carbonate aquifer, such as the Edwards aquifer, 

the dissolution or precipitation of minerals such as calcite 

and dolomite, which compose the aquifer rocks, will add 

or remove carbonate constituents. Water-rock interaction 

with gypsum, a trace mineral present in the Edwards Group 

(Maclay and Small, 1983), might affect groundwater SO4

/Cl 

ratios and SO4 concentrations; downdip saline-zone groundwater, for example, shows evidence of incongruent gypsum 

dissolution (Oetting and others, 1996). A saturation index (SI) 

of 0 indicates equilibrium conditions, a value greater than 0 

indicates saturation with respect to a mineral phase and the 

potential for precipitation, and a value less than 0 indicates 

undersaturation with respect to a mineral phase and the potential for dissolution. 

Hydrogeologic Setting

The south-central Texas Edwards aquifer developed in 

Early Cretaceous-age limestone and dolomite rocks that are 

extensively faulted, fractured, and karstified. Like many karst 

aquifers, the Edwards aquifer is characterized by hydrologic 

variability. Water-level altitudes in the aquifer can rise rapidly 

in response to rainfall and corresponding recharge and can be 

accompanied by increases in springflow; conversely, waterlevel altitudes and springflow decrease during periods of 

low rainfall and recharge. Records of San Antonio rainfall 

(recorded at the San Antonio International Airport) (National 

Oceanic and Atmospheric Administration, 2010), discharge 

at Comal Springs, and water-level altitudes at well J−17 

(Edwards Aquifer Authority, 2009) illustrate the hydrologic 

variability of the Edwards aquifer (fig. 6). 

Aquifer Framework and Lithology

The Cretaceous strata of south-central Texas regionally 

include three aquifers: the Edwards aquifer in the Balcones 

fault zone and the Trinity and Edwards-Trinity aquifers in the 

Edwards Plateau (fig. 2). The aquifer is composed of carbonate rocks of the Georgetown Formation (not shown in fig. 2) 

and Edwards Group (or their stratigraphic equivalents), which 

range in thickness from approximately 450 to 550 ft (Burchett 

and others, 1986) (fig. 2). The Georgetown Formation overlies 

the Edwards Group and is part of the Edwards aquifer. The 

less permeable upper member of the Glen Rose Limestone, 

which is the uppermost part of the Trinity aquifer, underlies 

the Edwards aquifer and acts as a lower confining unit across 

much of the region. Where confined, the aquifer is overlain by 

the Del Rio Clay and other units with relatively low permeability. Depositional stratigraphy of the carbonate facies are 

discussed in more detail in Lindgren and others (2011b). 

The San Antonio segment of the Edwards aquifer is about 

180 mi long from west to east, ranges from 5 to 40 mi wide 

from north to south (Maclay, 1995), and is characterized by 

relatively high transmissivities (summarized by Lindgren, 

2006; Lindgren and others, 2011a, 2011b). The northern limit 

of the recharge zone (outcrop) defines the northern aquifer 

boundary. The aquifer is bounded to the south by the downdip 

limit of potable water in the aquifer, below which groundwater 

salinity rises rapidly downgradient (Abbott, 1975; Sharp and 

Banner, 1997). The freshwater/saline-water interface (Schultz, 

1994) represents the transition (1,000 mg/L dissolved-solids 

concentration) from a zone of more active flow with fresh 

groundwater to a downdip zone of less active flow with saline 

groundwater. The downdip saline zone is characterized by 
Hydrogeologic Setting 21

numerous complex saline hydrochemical facies (Clement and 

Sharp, 1988; Oetting and others, 1996) which might locally 

influence groundwater geochemistry in the freshwater zone 

(Musgrove and others, 2010). A small number of volcanic and 

intrusive igneous rocks locally cross-cut the aquifer, which 

might also affect groundwater geochemistry on a local scale. 

Three core samples were collected from the overburden 

(Austin Chalk/Eagle Ford Group contact, Buda Limestone/

Del Rio Clay contact), one sample from the contact of the 

overburden units with the top of the Edwards aquifer (Del Rio 

Clay/Georgetown Formation contact); and four samples were 

collected from selected HGUs of the Edwards Group (leached 

and collapsed members, regional dense member/grainstone 

member contact, grainstone member, Kirschberg evaporite 

member) (fig. 4; tables 5 and 6 at end of report). For the most 

part, bulk samples were largely dominated by the carbonate 

mineral calcite (42.2–96.5 percent, based on relative peak 

intensity), with lesser amounts of quartz (trace–44.3 percent 

where present), clays (3.2–26.3 percent), and dolomite (trace 

to 31.5 percent) (table 6). These minerals were present in varying proportions in each of the core samples. Original deposits 

in the region of aragonite, calcite, dolomite, and gypsum 

Figure 6. Time series (2004−9) climatic and hydrologic data for the south-central Texas study area. A, Bexar County index well (J–17) 

water-level altitude and Comal Springs discharge (Edwards Aquifer Authority, 2009). B, San Antonio daily rainfall (recorded at the San 

Antonio International Airport) (National Oceanic and Atmospheric Administration, 2010).

Date

1/1/2004

1/1/2005

1/1/2006

1/1/2007

1/1/2008

1/1/2009

1/1/2010

0

100

200

300

400

500

600

Discharge,

in cubic feet per second

630

640

650

660

670

680

690

700

710

0

1

2

3

4

5

6

 Daily rainfall, in inches Water-level altitude, in feet above National Geodetic Vertical Datum of 19291

A

B

Comal 

Springs

Bexar County

index well (J–17)

1

 Source agency reports water-level altitude referenced to sea level

 (Edwards Aquifer Authority, 2009)
22 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

have been extensively replaced by calcite within the aquifer 

and form a highly porous and heterogeneous limestone rock. 

Dolomite and dolomitic limestone abundance varies spatially 

as well as stratigraphically (Maclay and Small, 1983, 1984). 

Mixing-zone dissolution near the downdip freshwater/salinewater interface, driven by gypsum dissolution, has created 

high porosity and high permeability where dolomite has been 

dissolved (Maclay and Small, 1984; Hovorka and others, 

1998).

One or two digestions (dissolution) were performed 

on bulk core samples to remove most of the calcite so that 

mineral phases of less than 1 mm could be identified. Residual 

clays were present in all samples and, where identified, 

included kaolinite, illite, smectite, and chlorite. Kaolinite was 

generally the most abundant clay. Other minerals present in 

small amounts in some digested samples included goethite 

(Del Rio Clay/Georgetown Formation contact, possibly 

Kirschberg evaporite member), pyrite (Buda Limestone/Del 

Rio Clay contact, regional dense member/grainstone member 

contact), possibly hornblende (Del Rio Clay/Georgetown 

Formation contact, regional dense member/grainstone member 

contact), feldspar (Austin Chalk/Eagle Ford Group contact), 

and possibly anhydrite or oriented feldspar (Buda Limestone/

Del Rio Clay contact).

Total carbon and inorganic carbon were analyzed in 

core samples (table 5). Solid phase particles (less than 2 mm) 

contained concentrations of total carbon that ranged from 59 

to 129 grams per kilogram (g/kg) (median 113) and inorganic 

carbon that ranged from 54 to 118 g/kg (median 110). Almost 

no organic carbon was present in several of the samples.

Estimation of Aquifer Properties

Extensive data have been collected on the hydraulic 

properties of the Edwards aquifer in the San Antonio region, in 

particular, permeability, hydraulic conductivity, transmissivity, 

anisotropy, and storativity. An interpretation of the distribution of relative permeability by HGU of the Edwards aquifer 

and its confining units is based on field observations, stratigraphic studies by Rose (1972), and data from test-drilling 

and geophysical-logging programs (Maclay and Small, 1983). 

These distributions apply to the confined zone and might not 

be strictly applicable to the unconfined zone. Permeability in 

the Edwards aquifer—which includes matrix, fracture, and 

conduit permeability—varies over eight orders of magnitude 

(Hovorka and others, 1998). The carbonate matrix of the 

aquifer is very permeable; however, in many intervals, the 

very high permeabilities resulting from conduits and fractures 

dwarf the matrix contribution. The highest matrix permeability 

occurs in downdip parts of the aquifer, where the mixing of 

freshwater and saline water has maximized dolomite dissolution (Hovorka and others, 1998). 

Transmissivity and hydraulic conductivity of the Edwards 

aquifer each vary over several orders of magnitude (detailed in 

Lindgren and others, 2011b). Local-scale variability in specific 

capacity, transmissivity, and hydraulic conductivity is likely 

quite large; even closely spaced measurements might differ by 

a factor of 1,000 (Hovorka and others, 1998). The difference 

likely reflects the variable contributions of matrix, fracture, 

and conduit permeability to the measured average values 

obtained in aquifer tests. Vertical variations in permeability in 

the Edwards aquifer indicate that the entire aquifer is highly 

permeable and highly variable. Anisotropy of an aquifer is 

indicated when the permeability shows variations with the 

direction of measurement at any given point in a geologic 

formation. An anisotropic aquifer will have a dominant permeability in one or more directions depending upon geologic and 

hydrologic conditions. The quantitative magnitude of anisotropy of the Edwards aquifer is largely unknown but might be 

influenced by the presence of barrier faults with large vertical 

displacements and the development of conduits. The amount 

and distribution of water in the Edwards aquifer are related to 

the development of porosity and the storage characteristics of 

the aquifer. Hovorka and others (1996) estimated that Edwards 

aquifer porosity varies vertically from lows of 4–12 percent to 

highs of 20–42 percent, with an average for the entire aquifer 

of 18 percent. Kuniansky and others (2001) found that an 

effective porosity of 1–3 percent was needed to match estimated traveltimes derived from geochemical mixing models. 

Flowmeter and geophysical data provide insight into 

hydraulic properties of the Edwards aquifer, specifically with 

respect to head differences and vertical gradients within the 

aquifer, as well as with respect to well-field dynamics. An 

understanding of the effect of pumping conditions on flow in 

a PSW might contribute to knowledge of how contaminants 

migrate to the PSW and how contaminant concentrations 

might vary in time and space. Vertical flow was measured at 

several discrete depths throughout the portion of the W4 borehole that is open to the Edwards aquifer. Paillet (2000) showed 

that two quasi-steady flow profiles measured in a borehole can 

be combined with a measurement of the water-level difference 

between pumping and nonpumping conditions (drawdown) to 

calculate estimates of zone transmissivity and far-field hydraulic head conditions. The flowmeter measurements in W4 were 

calculated by using the drawdown during pumping, the measured flow through the flowmeter tool, and a flow bypass factor by using the diameter of the tool and the borehole diameter 

at the depth of the measurement. The corrected measurements 

were entered into an analytical model which utilizes the Thiem 

equation (Thiem, 1906) and plotted with lines of model fit 

representing the four dynamic conditions of flow (ambient 1, 

ambient 2, moderate, normal). With these lines of model-fitted 

flow and observed and calculated drawdown, transmissivity was calculated to approximate aquifer conditions at four 

selected zones in the well. The estimated transmissivity values 

with increasing depths were

Zone 1: 340–415 ft below LSD, estimated to be 33,901 square 

feet per day (ft2/d),

Zone 2: 415–600 ft below LSD, estimated to be 2,396 ft2/d,

Zone 3: 600–675 ft below LSD, estimated to be 17,693 ft2/d, 

and

Zone 4: 675–755 ft below LSD, estimated to be 8,339 ft2

/d. 
Hydrogeologic Setting 23

The total transmissivity for the well, estimated as the sum 

of these four zones, was 62,329 ft2/d. This estimate is consistent with transmissivities estimated by other methods (Lindgren and others, 2004; Lindgren, 2006) for this general area.

The movement of water in the PSW borehole was variable under different pumping conditions. Flowmeter data and 

resulting estimated hydraulic properties for W4 are shown 

in figure 7. The large casing diameter (30 in.) and variable 

borehole diameter (15–36 in.) are shown on the caliper log and 

represent the enlarged borehole after acidification. The large 

diameter has an effect on other logs such as the natural gamma 

and flowmeter logs. The natural gamma counts per second 

were somewhat lower than expected in the strata penetrated 

because of the large spherical zone of detection of the natural gamma tool. Flowmeter values also were affected by the 

variable borehole diameter; therefore, a correction factor was 

generated for flowmeter values on the basis of the borehole 

diameter. The correction factor is a calculated flow bypass, 

which calculates the surface area of the borehole by using 

caliper data and the surface area of the skirt/tool; the ratio of 

these is the percentage of flow that the tool measures. Because 

the borehole diameter varied throughout the borehole, an individual correction factor was calculated for each measurement/

depth. Fluid conductivity and temperature probes are generally used only to measure the fluid flowing through the tool 

and, thus, do not represent any horizontal variation of the fluid 

qualities across a large diameter borehole.

Four lines of model fit of the flowmeter data, representing the four dynamic conditions of flow (ambient 1, ambient 

2, moderate, normal) are also shown (fig. 7). Arrows indicate 

the direction of flow under each of the pumping conditions 

toward the borehole (toward the model line) or away from 

the borehole (away from the model line) and up or down the 

borehole. During condition 1 (“ambient 1”), there were small 

amounts of mostly downward vertical flow in the wellbore 

(fig. 7). Water entered the borehole from the cyclic and 

marine members (HGU 3) (between zones 1 and 2), flowed 

downward, and exited the borehole in the dolomitic member 

(HGU 10). During condition 2 (“ambient 2”) flow in the 

wellbore was mostly upward. Water was pulled into the 

borehole from the Kirschberg evaporite member (HGU 8) 

(zone 3). Flow was upward and exited the borehole in a highly 

transmissive zone (zone 2) at the top of the leached and collapsed members (HGU 4). During condition 3 (“moderate”), 

nearly all water entered the borehole from the cyclic and 

marine members (HGU 3) in the upper part of the well. That 

flow was subdivided into two zones, coming from zone 1 

and above zone 2. During condition 4 (“normal”), flow in the 

wellbore was complex, with water both entering and exiting. 

The borehole gained water from the dolomitic member (HGU 

10) (zone 4) and Kirschberg evaporite member (HGU 8) 

(zone 3) in the lower part of the borehole. Some water exited 

the borehole at the top of the leached and collapsed members (HGU 4) (zone 2). The borehole gained a large amount 

of water again at the top of the cyclic and marine members 

(HGU 3) (zone 1).

Fluid conductivity and temperature were logged in the 

vertical extent of the W4 borehole in ambient conditions, both 

with the well field off (“ambient 1”) and with the well field on 

(“ambient 2”); differences in fluid conductivity and temperature were minor (less than 1 percent) and close to analytical 

uncertainties. These results are consistent with other geochemical data that indicate that water from W4 and other wells in 

the well field is relatively well mixed and homogeneous under 

a range of pumping conditions. The two deepest monitoring 

wells in each of the monitoring well clusters (Z–DED and 

T–DED) were logged in open hole under ambient conditions 

prior to completion; results are summarized in figures 8 and 

9, respectively. Although logs were collected during ambient 

conditions, some downward flow (8.6 gal/min) was detected 

in the Z–DED borehole. This flow might have been caused 

by nearby pumping stress from the PSW well field (approximately 0.5 mi to the west). As discussed above, most of the 

flow in the PSW entered the wellbore from the leached and 

collapsed members. Ambient flow in Z–DED also entered the 

borehole in the leached and collapsed members and exited 

into the Kirschberg evaporite member. If the two wells were 

hydraulically connected, then a linkage of outflow to the 

Kirschberg evaporite member at the Z–DED borehole and 

inflow to W4 is plausible. Throughout the zone of highest flow 

in Z–DED, fluid conductance consistently measured about 300 

microsiemens per centimeter (μS/cm), and temperature was 

about 21.0°C. These results are considerably different from 

measured values for the monitoring wells (table 7 at end of 

report) and might reflect differences in measurement tools and 

calibrations. In the deep Timberhill monitoring well (T–DED), 

approximately 1.5 mi west of the PSW well field, there was 

little or no measureable flow throughout the entire section of 

the well open to the Edwards aquifer. The fluid conductance 

consistently measured about 500 μS/cm, and temperature was 

about 21.4°C. This well appeared to have little or no connection to outside pumping stresses, including those from the 

PSW well field. 

Groundwater Occurrence and Movement

The groundwater flow system of the Edwards aquifer in 

the San Antonio region includes the Edwards Plateau catchment or contributing zone, the recharge (outcrop) zone, and 

the confined zone (fig. 1). Streams flowing south and east 

toward the Gulf of Mexico drain the Edwards Plateau contributing zone and recharge the aquifer by streamflow losses 

across the Balcones fault zone, where the porous and permeable limestone of the Edwards Group outcrops. The recharge 

zone consists of approximately 1,250 mi2

 of Edwards Group 

limestone exposed at the surface (Hamilton and others, 2008) 

(fig. 1). Most stream base flow and much of the stormflow 

recharges the aquifer through open solution channels (Maclay 

and Land, 1988). The majority of recharge to the regional 

aquifer occurs as losing streams flow across the recharge zone, 

with estimates of recharge from streams ranging from 60 to 

80 percent (Klemt and others, 1979; Maclay and Land, 1988; 
Figure 7. Borehole geophysical data for the public-supply well (W4) near San Antonio, south-central Texas, including, from left to right, natural gammconductivity, temperature, flowmeter (under ambient and pumping conditions), stratigraphic unit, and hydrogeologic unit (HGU). 

Transmissivity = 33,901 ft2/d

Transmissivity = 2,396 ft2/d

Transmissivity = 17,693 ft2/d

Transmissivity = 8,339 ft2/d

Zone 1Zone 2Zone 3Zone 4 172 gal/min

540 gal/min

150 gal/min

460 gal/min

850 gal/min

850 gal/min

340 gal/min

476 gal/min

185 gal/min

185 gal/min

12–30 gal/min14–21 gal/min

IN

IN

OUT

OUT

OUT

IN

IN IN

IN

IN

300100200400500600700

Aust

(comb

existing 

 by p

Eagle 

Buda L

Del 

Georgetow

Cycli

m

(u

Le

c

m

(u

den

GK

eD

Person Formation Kainer Formation

Depth

below

land

surface

feet

Gamma (natural)

counts per second

Temperature

degrees Celsius

Fluid conductivity 

Caliper

inches

AMBIENT - Well field OFF

gal/min

PUMPING at 850 gal/min - Well field ON

gal/min

PUMPING at 850 gal/min - Well field OFF

gal/min

AMBIENT - Well field ON at low

gal/min

Stratigrap

Fluid conductivity Temperature Gamma (natural)

degrees Celsius

microsiemens 

per centimeter

microsiemens 

per centimeter

2323

2121

100

36

016

600600

350350

1,0001,000

-1,000

-1,000

1,0001,000

-1,000-1,000

Flow measurement, by pumping condition

All depths are reported in feet below land surface

Direction of flow—In and out represents into and out

of borehole. Measured amount of flow shown

Numerical model fit

gal/min = gallons per minute

ft2/d = square feet per day

Zones 1–4 represent selected depth zones for transmissivity estimate

during well field ON

PUMPING - Well field OFFPUMPING - Well field ON

AMBIENT - Well field OFFAMBIENT - Well field ON at low

PUMPING - Well field OFFPUMPING - Well field ON

AMBIENT - Well field OFFAMBIENT - Well field ON at low

EXPLANATION

Well field 

OFF

ON

EXPLANATION

Well field 

OFF

ON

EXPLANATION

Bottom of casing = 321 feet
Figure 8. Borehole geophysical data for the deep Zarzamora monitoring well (Z–DED) near San Antonio, south-central Texas, including, from left to rcaliper logs, fluid conductivity and temperature, flowmeter, borehole image, stratigraphic unit, and hydrogeologic unit (HGU). 

Austin Cha

Eagle Ford Sh

Buda Limest

Del Rio Cla

Georgetown Lim

Cyclic and marin

 (undivid

Leached and c

members (un

Regional dens

Grainstone m

Kirschberg evapo

Person Formation Kainer Formation

100200300

400

500

600

20 230 1,000

Gamma (natural)

0 100 counts per second

 Caliper

5 15 inches

Fluid conductivity

Temperature

degrees Celsius

Ambient flow

-10 gallons per minute 10 Borehole image Stratigraphic 

0° 90° 180° 270° 0°

microsiemens

per centimeter

Depth

below

land

surface

feet

Bottom of steel casingand log run one
Figure 9. Borehole geophysical data for the deep Timberhill monitoring well (T–DED) near San Antonio, south-central Texas, including, from left to ricaliper logs, fluid conductivity and temperature, flowmeter (no appreciable measured flow), borehole image, stratigraphic unit, and hydrogeologic un

Austin C

Eagle Ford 

Buda Lime

Del Rio 

Georget

Limest

Cyclic and 

memb

(undivi

Leache

collapsed m

(undivi

Regional 

memb

Grainstone 

Kirsch

evaporite 

Person Formation Kainer Formation

Gamma (natural)

counts per second

Caliper Stratigrap

unit

0 100

Temperature

degrees Celsius 5 15 21 23 inch

Borehole image

0° 90° 180° 270° 0°

Fluid conductivity

0 1,000 microsiemens per centimeter Heat pulse ambient flow

-1 gallons per minute 1 

100200300400500600

Depth

below

land

surface

feet
Hydrogeologic Setting 27

Thorkildsen and McElhaney, 1992; Ockerman, 2005). Most 

of the remaining recharge occurs as direct infiltration on the 

recharge zone, with some recharge occurring by leakage from 

the underlying Trinity aquifer (Sharp and Banner, 1997; Mace 

and Hovorka, 2000; Lindgren and others, 2004). Estimates 

of the combined recharge to the San Antonio segment of 

the Edwards aquifer from stream seepage and infiltration 

of rainfall range from a low of 53.9 million cubic meters 

(m3) during 1956 to a high of 3,066 million m3 during 1992 

(Hamilton and others, 2003). The long-term (1934–2002) 

mean annual recharge to the Edwards aquifer is 862.2 million 

m3 (median 688.1 million m3) and for 1993–2002 is 979.6 

million m3 (median 710.9 million m3) (Hamilton and others, 

2003). In the local-scale study area, major streams crossing 

the recharge zone are the Medina River and Hondo and Salado 

Creeks (fig. 3). Much of the annual flow of the Medina River 

is impounded in Medina Lake (U.S. Army Corps of Engineers, 

1965). Of the volume impounded, about one-half seeps into 

the Edwards aquifer from the lake and its irrigation facilities 

(U.S. Army Corps of Engineers, 1965).

Karst features and faults provide pathways for water to 

move from stream channels to the water table of the unconfined aquifer in the recharge zone. Water that recharges in the 

recharge zone moves from the unconfined to confined parts 

of the aquifer through generally southeasterly flow paths. 

Regional groundwater flow in the confined zone is to the east 

and northeast with natural discharge occurring at large springs, 

predominantly Comal and San Marcos Springs (fig. 1). 

Conduits are likely major contributors to flow (Hovorka and 

others, 1998, 2004; Worthington, 2004). Faults can either 

increase or decrease total transmissivity (Hovorka and others, 

1998) and might serve as either conduits or barriers to flow 

(George, 1952; Holt, 1959; Maclay and Small, 1983, 1984; 

Maclay and Land, 1988; Maclay, 1995; Groschen, 1996; 

Clark and Journey, 2006). The potentiometric surface varies considerably depending on hydrologic conditions (fig. 6). 

Domestic, livestock, municipal, agricultural, and industrial 

withdrawals, by way of wells, also contribute to groundwater 

discharge throughout the region (Hamilton and others, 2008). 

Recharge and discharge are not evenly distributed across the 

aquifer; most recharge occurs in the westernmost catchments, 

whereas most discharge occurs in the eastern area. The proportion of discharge by wells relative to springs varies from year 

to year; springflow typically exceeds well discharge in wet 

years, and well discharge typically exceeds springflow in dry 

years (Hamilton and others, 2008). Comal Springs (fig. 1), 

one of the major aquifer discharge points, is hydrologically 

isolated from large sources of local recharge (Ogden and others, 1986). As such, Comal Springs represents the integration 

of the regional flow system of the San Antonio segment of the 

aquifer, and its flow rate and geochemistry provide an indicator of regional hydrologic conditions. Several wells in the 

aquifer, such as the Bexar County index well (J−17), intersect 

major flow paths and respond quickly to changes in recharge 

and pumping; water-level altitude variations in well J−17 are 

assumed to reflect Edwards aquifer water-level changes on a 

regional scale and are also indicative of regional hydrologic 

conditions. Previous studies indicate that groundwater flow is 

focused in highly permeable units and is affected by faulting 

throughout the aquifer (Abbott, 1975; Woodruff and Abbott, 

1979; Maclay and Small, 1986; Maclay and Land, 1988; 

Sharp, 1990).

Potential Sources of Contamination

Natural contaminants such as As, U, or radon generally 

are not problematic with respect to public drinking-water 

quality for the Edwards aquifer. Although these contaminants 

are commonly detected, they rarely occur at concentrations of 

concern for drinking-water quality. Nitrate can result from natural and anthropogenic sources, and concentrations might be 

increasing with the increase in human activities in the region 

(Musgrove and others, 2010); however, concentrations are not 

high with respect to drinking-water quality. A small number 

of organic contaminants are routinely detected in the Edwards 

aquifer at low concentrations (Musgrove and others, 2010).

Land use often is considered when evaluating potential 

sources of contaminants to groundwater (Brawley and others, 2000; Hiscock and others, 2007; McMahon and others, 

2008). Land use in the recharge zone for the PSW (Lindgren 

and others, 2011b) is 91.6 percent rangeland and forest, 7.6 

percent urban/built-up, and 0.8 percent water, wetland, barren, 

and agricultural (fig. 10). Agricultural land use in the recharge 

zone for the PSW is insignificant at 0.04 percent. In the localscale study area, urban/built-up land use is the most likely 

nonpoint source of potential contaminants. 

A database containing locations of points of potential 

sources of contaminants (PSOCs) was previously compiled 

by the Texas Commission on Environmental Quality (TCEQ) 

(written commun., 2006) and examined for the local-scale 

study area; more than 10,000 PSOCs were identified (fig. 11). 

Potential sources of contaminants include, but are not limited 

to, locations that manufacture or store chemicals, cemeteries, retail centers that store and sell chemicals, oilfield-related 

activities, water and wastewater treatment facilities, landfills, 

and pipelines. Most of the PSOCs were in the San Antonio 

metropolitan area, with an additional large number of oilfieldrelated PSOCs in the southern part of the study area overlying 

the downdip limit of the freshwater zone of the aquifer. 

The TCEQ PSOC database (written commun., 2006) was 

examined specifically for the most frequently detected anthropogenic compounds: atrazine, chloroform, and PCE (figs. 12, 

13, and 14, respectively), results of which indicate that the 

urban environment dominates potential sources for these 

compounds. There were 688 potential point sources of atrazine 

identified, and most were in the urban San Antonio area. Most 

of the potential locations were sites of manufacture, sales, or 

application of pesticides; municipal solid waste facilities; and 

industrial wastewater outfalls, among others. There were 831 

potential point sources of chloroform identified (fig. 13), and 

most sources were in the San Antonio urban area. Sources of 

chloroform included municipal solid waste facilities; metal 
28 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

plating businesses; industrial wastewater outfalls; pesticide 

manufacturing, sales, or application locations; pipelines; plastic manufacturing; and wastewater treatment, among others. 

There were 1,991 potential sources of PCE identified (fig. 14). 

Like the other compounds, most potential sources of PCE 

were in the urban area, and a few were in the San Antonio area 

recharge zone. Potential sources of PCE included air transportation facilities, auto parts and repair businesses, dry cleaners, 

industrial wastewater outfalls, municipal solid waste facilities, 

new and used oil sites, paint shops, sites of manufacture or 

sales of pesticides, and sites of plastic manufacturing, among 

others. The TCEQ PSOC database provides insight into potential sources of contaminants but is not necessarily comprehensive of all potential sources; additional contaminant sources, 

for example, include application of pesticides on urban lawns, 

return flows from treated wastewater applied on the landscape, 

septic systems, and swimming pools.

An additional potential source of PCE, a U.S. Environmental Protection Agency (USEPA) Superfund site about 2.6 

mi northwest of the PWS well field with PCE- and TCEcontaminated groundwater in overburden units, was identified 

during the time period of the TANC project (U.S. Environmental Protection Agency, 2011; hereinafter, Bandera Road 

Groundwater Plume). Some groundwater wells, three of which 

were completed at the top of the Edwards aquifer, contained 

PCE at concentrations above the USEPA public drinkingwater standard (U.S. Environmental Protection Agency, 2011) 

(5 μg/L). Model particle tracks indicate that groundwater flow 

paths in this area are from the contamination site to the southsoutheast toward the well field; however, water-level and dyetracer data in the vicinity of the Bandera Road Groundwater 

Plume indicate that water might be moving more westward 

in the area immediately upgradient of the well field and that 

barrier faults in the vicinity may inhibit flow (C. Villarreal, 

Figure 10. Land use in the local-scale study area for the study of the transport of anthropogenic and natural contaminants (TANC) to 

public-supply wells, and location of selected public-supply well and well field, near San Antonio, south-central Texas. 

Hondo

Castroville San

Antonio

!

EXPLANATION

Land-use category

 Urban/built-up

 Agricultural

 Rangeland

 Forest

 Water !

 Wetland

 Barren

Local-scale study area boundary

Edwards aquifer zone boundary

Selected public-supply well

 and well field

Contributing zone

Recharge zone

Confined zone

Contributing zone

Recharge zone

0 2.5 5 7.5 MILES 10

0 2.5 5 7.5 KILOMETERS 10

98°30'

98°45' 99°00'

99°15'

29°30'

29°15'

Base from

Aquifers: Texas Water Development Board (2007); Ashworth

and Hopkins (1995), 1:250,000

Counties: Texas General Land Office (1999), 1:24,000

Cities: Texas Natural Resources Information System digital data (1995)

Projection: Texas Centric Mapping System-Albers equal area

Datum: North American Datum of 1983 

Medina

Lake

Land use from Homer and others (2001)

BEXAR COUNTY

MEDINA COUNTY

BANDERA COUNTY
Hydrogeologic Setting 29

U.S. Environmental Protection Agency, written commun.). 

The Bandera Road Groundwater Plume is currently (2011) the 

only identified USEPA superfund site with PCE contamination 

that is upgradient of the well field. No hydrologic connection 

between the Bandera Road Groundwater Plume and the well 

field has been documented, however, and other sources are 

possible.

Groundwater Chemistry

This section describes the chemical characteristics 

of groundwater samples with respect to water types, field 

parameters, SIs for selected minerals, reduction-oxidation 

(redox) conditions, dissolved gases, major and trace element 

and nutrient concentrations, isotopic compositions, organic 

constituents, and age tracers. Special emphasis is placed on 

understanding groundwater chemistry in the context of waterrock interaction processes, groundwater flow patterns and flow 

paths, residence time, and mixing, and temporal variations in 

groundwater chemistry.

Field Parameters

Field parameter (physicochemical) data indicated that 

well-field and monitoring well samples are representative of 

groundwater in the regional confined aquifer. The well-field 

and monitoring well samples had relatively narrow ranges in 

field parameters (table 7) with median values for specific conductance, pH, temperature, dissolved oxygen concentration, 

Figure 11. Location of potential sources of contamination (PSOCs) in the local-scale study area for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, and location of selected public-supply well and well field, near 

San Antonio, south-central Texas; based on Texas Commission of Environmental Quality potential sources of contamination (PSOC) 

database (written commun., 2006). 

Hondo

Castroville San

Antonio

Hondo Creek

Medina

River

Verde

Medina

Lake

Creek

Salado

Creek

Culebra

Creek

Leon Creek

Medio Creek

San Antonio Ri ver

Quihi Creek

Black Creek

San Francisco Perez Creek

San Geronim o Creek

Helotes Creek

BEXAR COUNTY

MEDINA COUNTY

BANDERA COUNTY

!

0 2.5 5 7.5 MILES 10

0 2.5 5 7.5 KILOMETERS 10

Contributing zone

Recharge zone

Confined zone

98°30'

98°45' 99°00'

99°15'

29°30'

29°15'

Base from

Aquifers: Texas Water Development Board (2007); Ashworth

and Hopkins (1995), 1:250,000

Counties: Texas General Land Office (1999), 1:24,000

Cities: Texas Natural Resources Information System digital data (1995)

Projection: Texas Centric Mapping System-Albers equal area

Datum: North American Datum of 1983 

Local-scale study area boundary

Edwards aquifer zone boundary

Potential source of contamination

! Selected public-supply well and well field

EXPLANATION
30 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

and alkalinity (CaCO3) of 586 μS/cm, 7.1, 24.0°C, 4.3 mg/L, 

and 258 mg/L, respectively. The sample collected from the 

overburden well (Z–OVB) was chemically distinct from the 

well-field and monitoring well samples, with higher specific 

conductance (971 μS/cm) and temperature (28.3°C) values. 

These results indicate that the overburden unit is likely not 

a dominant source of water to the PSW or the aquifer in the 

study area. Measured values for field parameters for the wellfield and monitoring well samples were otherwise similar to 

those measured for regional aquifer PSWs (table 7), as well 

as those described by Musgrove and others (2010) for the 

regional aquifer. 

Results for several field parameters for samples from 

regional (confined) aquifer PSWs were correlated with well 

depth; both pH and temperature increase with well depth 

(Kendall’s tau = 0.26 and 0.39, respectively), whereas specific 

conductance and alkalinity decrease with well depth (Kendall’s tau = -0.35 and -0.33, respectively) (fig. 15). The relation between dissolved oxygen concentration and well depth 

was not statistically significant. These relations between field 

parameters and well depth were not evident for the monitoring wells, although the monitoring wells cover a more limited 

depth range than do the regional aquifer PSWs. The observed 

relation of decreasing specific conductance with depth for 

samples from the regional (confined) aquifer PSWs is somewhat counterintuitive. In the absence of other sources of salinity, specific conductance values would be expected to generally increase along aquifer flow paths as a result of progressive 

mineral-solution reactions. Additionally, deeper groundwater 

in the Edwards aquifer can be affected by mixing with more 

Figure 12. Location of potential sources of atrazine contamination in the local-scale study area for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, and location of selected public-supply well and well field, near 

San Antonio, south-central Texas; based on Texas Commission of Environmental Quality potential sources of contamination (PSOC) 

database (written commun., 2006). 

Hondo

Castroville San

Antonio

Hondo Creek

Medina

River

Verde

Medina

Lake

Creek

Salado

Creek

Culebra

Creek

Leon Creek

Medio Creek

Quihi Creek

Black Creek

San Francisco Perez Creek

San Geronim o Creek

Helotes Creek

San Antonio

River

BEXAR COUNTY

MEDINA COUNTY

BANDERA COUNTY

!

0 2.5 5 7.5 MILES 10

0 2.5 5 7.5 KILOMETERS 10

Contributing zone

Recharge zone

Confined zone

98°30'

98°45' 99°00'

99°15'

29°30'

29°15'

Base from

Aquifers: Texas Water Development Board (2007); Ashworth

and Hopkins (1995), 1:250,000

Counties: Texas General Land Office (1999), 1:24,000

Cities: Texas Natural Resources Information System digital data (1995)

Projection: Texas Centric Mapping System-Albers equal area

Datum: North American Datum of 1983 

EXPLANATION

Local-scale study area boundary

Edwards aquifer zone boundary

Potential source of atrazine contamination

! Selected public-supply well and well field
Hydrogeologic Setting 31

saline downdip water. However, at the regional aquifer scale, 

specific conductance values in shallow/urban unconfined 

Edwards aquifer groundwater samples are higher relative to 

deeper unconfined and confined groundwater samples, which 

indicates that urban land use affects water quality and might 

be a potential source of dissolved constituents to groundwater 

(Musgrove and others, 2010).

Chemical Composition and Mineral Saturation 

Indexes

Groundwater samples from the well-field and monitoring 

wells and regional aquifer PSWs exhibited a relatively narrow 

range in major ion compositions. A trilinear (“Piper”) diagram 

(Piper, 1953) is a useful tool for evaluating the relative 

abundance of major cations and anions and classifying major 

water types. Groundwater samples are mostly a dilute calcium 

bicarbonate facies, with similar compositions in all sample 

types and locations (well-field wells, monitoring wells, and 

regional aquifer PSWs) except the overburden monitoring well 

(Z–OVB) (fig. 16). Regional aquifer PSW samples show the 

most variability, with cation concentrations ranging between 

about 20–40 percent Mg and between about 60–80 percent Ca 

(fig. 16). With respect to anions, groundwater composition is 

less variable. Cl concentration exceeds 20 percent in only the 

overburden monitoring well.

Saturation indices (SIs) with respect to calcite, dolomite, 

and gypsum reflect the carbonate mineralogy of the aquifer 

host rocks (fig. 17; table 8 at end of report). All groundwater 

Figure 13. Location of potential sources of chloroform contamination in the local-scale study area for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, and location of selected public-supply well and well field, near 

San Antonio, south-central Texas; based on Texas Commission of Environmental Quality potential sources of contamination (PSOC) 

database (written commun., 2006).

Hondo

Castroville San

Antonio

Hondo Creek

Medina

River

Verde

Medina

Lake

Creek

Salado

Creek

Culebra

Creek

Leon Creek

Medio Creek

Quihi Creek

Black Creek

San Francisco Perez Creek

San Geronim o Creek

Helotes Creek

San Antonio

River

BEXAR COUNTY

MEDINA COUNTY

BANDERA COUNTY

!

0 2.5 5 7.5 MILES 10

0 2.5 5 7.5 KILOMETERS 10

Contributing zone

Recharge zone

Confined zone

98°30'

98°45' 99°00'

99°15'

29°30'

29°15'

Base from

Aquifers: Texas Water Development Board (2007); Ashworth

and Hopkins (1995), 1:250,000

Counties: Texas General Land Office (1999), 1:24,000

Cities: Texas Natural Resources Information System digital data (1995)

Projection: Texas Centric Mapping System-Albers equal area

Datum: North American Datum of 1983 

Local-scale study area boundary

Edwards aquifer zone boundary

Potential source of chloroform contamination

! Selected public-supply well and well field

EXPLANATION
32 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

samples were near saturation with respect to calcite (-0.5 to 

0.5) and very undersaturated with respect to gypsum (less 

than -1.7). Dolomite SIs range from undersaturated to near 

saturation. Dolomite SIs for samples from the well-field and 

monitoring wells were mostly near saturation to undersaturated (-0.48 to -0.11, median = -0.28), whereas results for 

the regional aquifer PSW samples have a larger range (-1.36 

to 0.26, median = -0.34) and are correlated with well depth 

(fig. 17; Kendall’s tau = 0.25). Musgrove and others (2010) 

reported that water from the confined part of the aquifer is 

generally closer to equilibrium than is water from the unconfined part of the aquifer with respect to calcite and dolomite, 

reflecting greater extents of water-rock interaction. Increasing dolomite SIs in the regional Edwards aquifer have been 

previously proposed to be an indicator of increasing extents 

of progressive water-rock interaction processes and relative 

groundwater residence time (Musgrove and others, 2010). This 

hypothesis is further supported by the correlation between 

dolomite SIs and Mg/Ca molar ratios for regional groundwater 

as discussed in Musgrove and others (2010) and the correlation shown for regional aquifer PSWs (a subset of the regional 

groundwater wells detailed in Musgrove and others, 2010) in 

fig. 18 (Kendall’s tau = 0.35). This relation is not evident in 

the well-field and monitoring wells (fig. 18), which cover a 

more limited depth range than do the regional aquifer PSWs. 

Major Elements and Trace Metals

Major element concentrations and groundwater facies 

(fig. 16) associated with samples collected from regional 

Figure 14. Location of potential sources of tetrachloroethene (PCE) contamination in the local-scale study area for the study of the 

transport of anthropogenic and natural contaminants (TANC) to public-supply wells, and location of selected public-supply well and well 

field, near San Antonio, south-central Texas; based on Texas Commission of Environmental Quality potential sources of contamination 

(PSOC) database (written commun., 2006). 

Hondo

Castroville San

Antonio

Hondo Creek

Medina

River

Verde

Medina

Lake

Creek

Salado

Creek

Culebra

Creek

Leon Creek

Medio Creek

Quihi Creek

Black Creek

San Francisco Perez Creek

San Geronim o Creek

Helotes Creek

San Antonio

River

BEXAR COUNTY

MEDINA COUNTY

BANDERA COUNTY

!

0 2.5 5 7.5 MILES 10

0 2.5 5 7.5 KILOMETERS 10

Contributing zone

Recharge zone

Confined zone

98°30'

98°45' 99°00'

99°15'

29°30'

29°15'

Base from

Aquifers: Texas Water Development Board (2007); Ashworth

and Hopkins (1995), 1:250,000

Counties: Texas General Land Office (1999), 1:24,000

Cities: Texas Natural Resources Information System digital data (1995)

Projection: Texas Centric Mapping System-Albers equal area

Datum: North American Datum of 1983 

Local-scale study area boundary

Edwards aquifer zone boundary

Potential source of tetrachloroethene (PCE) contamination

! Selected public-supply well and well field

EXPLANATION
Figure 15. Relation between well depth and selected physicochemical and geochemical constituents for groundwater samples collected from regiowells in the confined part of the San Antonio segment of the Edwards aquifer, south-central Texas, 2004–5. A, pH. B, Specific conductance. C, Temper

400 450 500 550 600 6

Specific conductance, in microsiemens per centim

6.5 6.6 6.7 6.8 6.9 7 7.1 7.2 7.3 7.4 7.5

pH

100 150 200 250 300 

Alkalinity, in milligrams per liter as calcium carbon

15 17 19 21 23 25 27 29 30

Temperature, in degrees Celsius

500

1,0001,5002,0002,500

Well depth, in

feet below land surface

0

500

1,0001,5002,0002,500

Well depth, in

feet below land surface

0

C D A B 

Kendall’s tau = 0.39 Kendall’s tau = -0.33Kendall’s tau = 0.26 Kendall’s tau = -0.35

EXPLANATION

Regional public-supply well  (confined aquifer)
34 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

aquifer PSWs, well-field wells, and monitoring wells reflect 

the carbonate composition of the aquifer host rock and carbonate geochemical reactions. As noted earlier, major element 

concentrations (table 8) and groundwater facies for TANC 

study samples, with the exception of the overburden monitoring well, showed little variation (fig. 16). Geochemical 

processes of water-rock interaction and progressive groundwater evolution in carbonate groundwater (for example, by 

processes of calcite recrystallization, incongruent dolomite 

dissolution, and prior precipitation of calcite along flow paths) 

can result in increases in Mg/Ca and Sr/Ca molar ratios with 

increasing groundwater residence time over multiple time 

scales (Plummer, 1977; Trudgill and others, 1980; Lohmann, 

1988; Fairchild and others, 2000; Musgrove and Banner, 

2004). Given this evolution pathway, Mg/Ca and Sr/Ca ratios 

typically increase along flow paths with increasing extents 

of water-rock interaction. Fluid evolution and water-rock 

interaction processes noted from the results of this study 

are consistent with results for the regional Edwards aquifer as discussed in Musgrove and others (2010). Calcium 

Figure 16. Piper or trilinear diagram showing relations between major cations and anions for groundwater samples collected for the 

study of the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9.

Well-field (W4) depth-dependent sampling

Timberhill monitoring wells

Zarzamora monitoring wells (includes event sampling)

Overburden monitoring well

Regional public-supply wells (confined aquifer)

Regional public-supply wells (unconfined aquifer)

Shallow unconfined upgradient well (event sampling)

Well-field (W6) event sampling

Well-field (wellhead) sampling 

EXPLANATION

Chloride

Calcium + magnesium

Sulfate + chloride

Sodium + potassium

Sulfate

Calcium

Bicarbonate

Magnesium

PERCENT

20

40

60

80

100

0

20

40

60

80

100

0

100

80

60

40

20

0

20

40

60

80

100

0

20

0

40

60

80

100

20

0

40

60

80

100

80

100

60

40

20

0

80

60

40

20

100

0

80

60

40

20

100

0

20

40

60

80

0

100
Hydrogeologic Setting 35

Figure 17. Relation between well depth and selected mineral saturation indexes for groundwater samples collected for the study 

of the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. A, Calcite. B, 

Dolomite. C, Gypsum.

-3.0 -2.5 -2.0 -1.5 -1.0

Gypsum, mineral saturation index

-1.5 -1.0 -0.5 0 0.5

Dolomite, mineral saturation index

-1.0 -0.5 0 0.5 1.0

Calcite, mineral saturation index

Well depth, in feet

below land surface

0

500

1,000

1,500

2,000

2,500

Well depth, in feet

below land surface

0

500

1,000

1,500

2,000

2,500

Well depth, in feet

below land surface

500

1,000

1,500

2,000

2,500

0

Kendall’s tau = 0.25 (regional public-supply wells only)

B

A

C

 

Timberhill monitoring well 

 sample 

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well 

 sample 

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Overburden monitoring well

 (Z–OVB) sample

Regional public-supply well 

 sample 

 Confined

 Unconfined

Well-field (wellhead) well 

 sample 

 W2

 W3

 W4

 W5

 W6

EXPLANATION
36 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

concentrations in regional aquifer PSW samples decreased 

with depth and were negatively correlated with Mg/Ca and 

Sr/Ca ratios (fig. 19). Mineral-solution reactions, including the 

precipitation of calcite along flow paths, can result in increasing Mg/Ca and Sr/Ca ratios with respect to Ca concentrations 

(fig. 19). Mg/Ca and Sr/Ca ratios for regional groundwater 

samples increased with depth (fig. 20), which is indicative 

of greater extents of water-rock interaction associated with 

longer flow paths. Mg/Ca and Sr/Ca ratios for TANC groundwater samples were well correlated (Kendall’s tau = 0.78). 

Other than for carbonate-associated elements (Ca, Mg, Sr), 

major element and trace metal concentrations and elemental 

ratios (such as Cl to bromide (Cl/Br)) are not strongly correlated with depth. Sr concentrations were well correlated with 

lithium and F concentrations (Kendall’s tau = 0.55 and 0.50, 

respectively) in regional aquifer PSW samples. These relations might be an indication of small amounts of mixing with 

downdip saline-zone groundwater, which has relatively high 

concentrations of these constituents.

Natural contaminants such as U and As are a waterquality concern in some aquifer systems, but in the Edwards 

aquifer these constituents generally have low and relatively 

uniform concentrations (table 9 at end of report). The USEPA 

maximum contaminant level (MCL) is 30 μg/L for U and is 

10 μg/L for As. Uranium and As concentrations in well-field 

well, monitoring well, and regional aquifer PSW samples are 

well below these MCLs. Uranium concentrations range from 

0.56 to 1.17 μg/L, with a median value of 0.84 μg/L. Arsenic 

concentrations range from 0.31 to 0.75 μg/L, with a median 

value of 0.44 μg/L. 

Both U and As concentrations in aquifer host rock 

core samples were generally low (less than 3 milligrams per 

kilogram (mg/kg)), with one higher As value of 9.9 mg/kg 

measured in the leached and collapsed members) (table 5). 

The oxidation of pyrite in limestone is a potential source of 

As (Appelo and Postma, 2005). Pyrite is a recognized trace 

mineral in the Edwards Group downgradient of the freshwater/

saline-water transition zone but is generally not present in the 

Edwards Group in the freshwater part of the aquifer (Maclay 

and Small, 1983). U and As concentrations do not vary significantly with depth in regional aquifer PSWs or in the monitoring wells.

Oxidation-Reduction Conditions

Oxidation-reduction (redox) conditions are an important 

control on geochemical processes in groundwater that affect 

a variety of contaminants, including the speciation of elements such as As, iron (Fe), and sulfur and the transformation/

biodegradation of NO3

 and some organic compounds. Redox 

Figure 18. Relation between magnesium to calcium molar ratio and dolomite mineral saturation index for groundwater samples 

collected for the study of the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 

2004–9.

0 0.1 0.2 0.3 0.4 0.5

Magnesium to calcium, molar ratio

-1.5

-1.0

-0.5

0

0.5

Dolomite, mineral saturation index

Timberhill monitoring well 

 sample 

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well 

 sample 

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Overburden monitoring well

 (Z–OVB) sample

Regional public-supply well 

 sample 

 Confined

 Unconfined

Well-field (wellhead) well 

 sample 

 W2

 W3

 W4

 W5

 W6

EXPLANATION

Kendall’s tau = 0.35 (regional public-supply wells only)
Hydrogeologic Setting 37

Figure 19. Relation between well depth and selected geochemical constituents or between calcium and selected geochemical 

constituents for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (TANC) to 

public-supply wells, south-central Texas, 2004–9. A, Relation between well depth and calcium concentration. B, Relation between 

magnesium to calcium molar ratio and calcium concentration. C, Relation between strontium to calcium molar ratio (×103

) and calcium 

concentration. 

40 60 80 100 120 140 160

Calcium, in milligrams per liter

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Magnesium to calcium, molar ratio

0 2.00 4.00 6.00 8.00 10.00 12.00

Strontium to calcium, molar ratio (×103)

0

500

1,000

1,500

2,000

2,500

40

60

80

100

120

140

160

Calcium, in milligrams per liter 

40

60

80

100

120

140

160

Calcium, in milligrams per liter 

Well depth, in feet

below land surface

A

B

C

Kendall’s tau = -0.75 (regional public-supply wells only)

Kendall’s tau = -0.69 (regional public-supply wells only)

Timberhill monitoring well 

 sample 

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well 

 sample 

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Overburden monitoring well 

 (Z–OVB) sample

Regional public-supply well 

 sample 

 Confined

 Unconfined

Well-field (wellhead) well 

 sample 

 W2

 W3

 W4

 W5

 W6

EXPLANATION

Kendall’s tau = -0.48 (regional public-supply wells only)
38 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

conditions in groundwater were evaluated with the classification of McMahon and Chapelle (2008) by using the software 

of Jurgens and others (2009), which is based on concentrations of dissolved oxygen, NO3

, manganese (Mn), Fe, SO4, 

and sulfide (H2S). On the basis of this redox classification, it 

was found that the freshwater part of the San Antonio segment 

of the Edwards aquifer is generally oxic (oxygen reducing), which is defined by concentrations of dissolved oxygen 

greater than 0.5 mg/L, Mn less than 0.05 mg/L, and Fe less 

than 0.1 mg/L (NO3 and SO4

 concentrations are not considered when dissolved oxygen concentration is greater than 

0.5 mg/L). Dissolved oxygen concentrations in the regional 

aquifer PSW samples ranged from 1.53 to 9.39 mg/L, with 

a median value of 5.1 mg/L (table 7). Conditions are oxic in 

the local-scale study area, with a median dissolved oxygen 

value similar to that for the regional aquifer PSW samples, 

Figure 20. Relation between well depth and selected geochemical constituents for groundwater samples collected for the study of 

the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. A, Magnesium to 

calcium molar ratio. B, Strontium to calcium molar ratio (×103

). 

0 2.00 4.00 6.00 8.00 10.00 12.00

Strontium to calcium, molar ratio (×103)

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Magnesium to calcium, molar ratio

0

500

1,000

1,500

2,000

2,500

0

500

1,000

1,500

2,000

2,500

Well depth, in

feet below land surface

Well depth, in

feet below land surface

A

B

Kendall’s tau = 0.50 (regional public-supply wells only)

Kendall’s tau = 0.54 (regional public-supply wells only)

EXPLANATION

Timberhill monitoring well

 sample

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well

 sample

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Overburden monitoring well

 (Z–OVB) sample

Regional public-supply

 well sample

 Confined

 Unconfined

Well-field (wellhead) well

 sample

 W2

 W3

 W4

 W5

 W6
Hydrogeologic Setting 39

but with a narrower range; dissolved oxygen concentrations 

for well-field and monitoring well samples ranged from 3.65 

to 5.26 mg/L, with a median value of 4.6 mg/L (table 7). The 

dissolved oxygen concentration in the overburden monitoring well (Z–OVB) was similar, with a value of 4.98 mg/L 

(table 7).

In the vicinity of the freshwater/saline-water interface 

(fig. 1), dissolved oxygen concentrations decrease, and 

NO3-reducing/Mn-reducing conditions are widely present 

(described by concentrations of less than 0.5 mg/L dissolved 

oxygen, less than 0.5 mg/L NO3, greater than 0.1 mg/L Mn, 

greater than 0.5 mg/L SO4, and an Fe to H2S ratio between 

0.3 and 10). It is possible that mixed redox or anoxic conditions could occur locally in the freshwater part of the aquifer 

as a result of point source occurrences of contamination from 

spills, leaking septic areas, or wastewater lines, or from mixing with less oxic water from the Trinity Group or overlying 

units (for example, the Buda Limestone or Austin Chalk). 

Dissolved Gases

Dissolved gas concentrations (argon, methane, CO2, N2, 

oxygen, and He) were measured to estimate properties used in 

age-tracer calculations, including the temperature of groundwater at the time of recharge and the amounts of excess air. 

Measured and calculated results, excluding He, are shown in 

table 10 at end of report; He results are described in the section “Groundwater Age Tracers and Age Distributions” later 

in the report. Concentrations of N2 and argon are consistent 

with atmospheric equilibration during groundwater recharge 

with excess air added during recharge. Calculated excess air 

concentrations range from 1.9 to 11.0 cubic centimeters per 

kilogram at standard temperature and pressure (cm3 STP/

kg), with a median value of 5.8 cm3 STP/kg. Most groundwater contains excess air, which is generally attributed to air 

entrainment during recharge (Heaton and Vogel, 1981). Excess 

air concentrations are typically from near 0 to 3 cm3 STP/kg, 

although higher values have been measured (Busenberg and 

Plummer, 2000) and might be associated with some flow conditions in fractured rocks or in aquifers with rapid variations in 

water table elevation such as karst (Busenberg and Plummer, 

1992; L.N. Plummer, U.S. Geological Survey, oral commun., 

2009). No excess N2

, such as would occur from denitrification 

of NO3, was detected in any dissolved gas samples (table 10). 

These results are consistent with an absence of denitrification 

in the sampled groundwater based on oxic conditions. 

Nutrients and Stable Isotopes of Nitrogen

Nutrients are defined as those elements important to plant 

growth and survival and include the primary mineral nutrients 

N, phosphorus, and potassium. Anthropogenic activity has 

transformed the global N cycle, and elevated nutrient concentrations in water resources are an issue of worldwide concern 

(Schlesinger and others, 2006; Galloway and others, 2008). 

Nitrogen is the most soluble of these nutrients, which generally occurs as nitrate (NO3

), nitrite (NO2), and ammonium 

(NH4) in groundwater (Hem, 1992). Ammonium strongly 

adsorbs on mineral surfaces, whereas NO3 and NO2 are readily 

transported in water (Hem, 1992). Reduction of NO3 to NO2

(denitrification) occurs in anoxic conditions. Anthropogenic 

N sources include agricultural fertilizer, animal wastes, septic 

systems, municipal sewage-treatment systems, leaking sewerlines, and N oxide emissions. Atmospheric deposition and 

precipitation, decaying organic matter, and soil mineralization 

processes are also potential N sources. Natural N sources are 

not common in limestone and dolomitic aquifer rocks; thus, N 

concentrations greater than the prevailing background concentration likely represent anthropogenic sources. National 

background concentrations of NO3 have been estimated to be 

1.0 mg/L for groundwater (Dubrovsky and others, 2010).

Concentrations of NO2 were negligible where detected 

and below laboratory method reporting levels for most 

samples (table 11 at end of report), which is consistent with 

generally oxic conditions in the aquifer. As a result, measured 

concentrations of NO3+NO2 primarily represent concentrations 

of NO3; where NO2 was detected, NO3 concentrations were 

calculated as the difference between NO3+NO2 and NO2. 

All measured NO3 concentrations were below the MCL 

of 10 mg/L for drinking water (U.S. Environmental Protection 

Agency, 1993). The overburden monitoring well (Z–OVB) 

sample had the highest NO3 concentration, with a value of 

3.82 mg/L. Groundwater samples from regional aquifer 

PSWs had NO3 concentrations ranging from 0.73 to 3.12, 

with a median of 1.86 mg/L. The median for samples from 

regional (confined) aquifer PSWs was 1.87 mg/L, which is 

similar to the previously reported median values for regional 

groundwater in the aquifer (1.67 mg/L) (Musgrove and others, 

2010). Well-field and monitoring well samples had a slightly 

narrower range of NO3 concentrations (1.65–2.74 mg/L) 

(table 11) with a similar median value of 2.04 mg/L. 

Concentrations of NO3 for regional aquifer PSW samples 

showed a decrease in concentration with depth (Kendall’s tau 

= -0.25) (fig. 21). This relation is not evident for well-field 

and monitoring well samples, which cover a more limited 

depth range than do the regional aquifer PSWs (fig. 21). 

Land use might affect NO3

 concentrations in Edwards aquifer 

groundwater; higher NO3 concentrations have been measured 

in groundwater from shallow unconfined monitoring wells in 

the urban San Antonio area. These patterns are consistent with 

either greater amounts of anthropogenically derived NO3 in 

the urban environment and (or) dilution of ambient NO3 by 

surface-water recharge (Musgrove and others, 2010).

Nitrate isotopes (δ15N and δ18O of NO3) have been widely 

applied to trace the cycling and sources of NO3 in hydrologic 

systems (Kendall, 1998). Different sources or reservoirs of 

NO3 have characteristic isotopic “signatures” that reflect the 

source of the NO3 (Kendall, 1998; Mengis and others, 2001). 

Values shown on figure 22 reflect typical ranges of major NO3 

reservoirs, although the boundaries are not absolute (Kendall, 

1998), and local endmember values of these sources have not 
40 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

been determined. Additionally, the isotopic composition of the 

NO3 in a water sample might reflect a single source or a mix 

of sources with different isotopic compositions. The isotopic 

signature can also be modified by biogeochemical processes, 

such as denitrification (fig. 22). Nitrate-isotope samples were 

collected from well-field and monitoring wells, including 

depth-dependent sampling in W4, and from the overburden 

well (Z–OVB) (table 12). Results for δ15N range from 6.84 per 

mil to 8.16 per mil with a median of 7.91 per mil; results for 

δ18O range from 4.59 per mil to 5.52 per mil, with a median 

of 5.23 per mil. Nitrate-isotope results for all TANC study 

samples, excluding the overburden well, are within a very narrow range that is within analytical uncertainty (±0.5 per mil) 

(fig. 22). The overburden well, in the Buda Limestone, has a 

slightly lower δ15N value (6.84 per mil) (fig. 22). Based on the 

ranges of different NO3 sources shown in figure 22 (Kendall, 1998; Mengis and others, 2001), δ15N values for TANC 

groundwater samples are mostly within the range of natural 

soil organic values, near the higher values that transition to 

NO3 sourced from human and (or) animal waste (fig. 22). 

Samples collected from Barton Springs (the main discharge 

point for the Barton Springs segment of the aquifer) during 

2008–10 under a range of flow conditions have similar median 

NO3-isotope values (7.57 per mil for δ15N and 5.58 per mil for 

δ18O) (Mahler and others, 2011).

Nitrate-isotope results confirm that denitrification is not 

an important process affecting NO3 in the Edwards aquifer. 

This finding is consistent with oxic conditions throughout 

the aquifer and the absence of excess N2

 gas, an indicator of 

denitrification, in all samples collected for this study. Denitrification has been identified as an important process in other 

shallow (Panno and others, 2001) and deep karst aquifers 

(Katz and others, 2007). 

The median δ15N composition of Edwards aquifer 

groundwater collected for this study (7.91 per mil) is higher 

than historical values. A previous study of regional unconfined (n=33) and confined (n=34) groundwater in the Edwards 

aquifer measured median δ15N values of 6.60 and 6.00 per 

mil, respectively (Kreitler and Browning, 1983). Higher 

δ15N values are likely indicative of NO3 from human and 

(or) animal waste, including septic systems and wastewater 

sources (fig. 22). Historical regional Edwards aquifer δ15N 

values from Kreitler and Browning (1983) (n=67) are statistically different (based on Mann-Whitney U testing) from recent 

results for samples collected during the TANC study (n=20). 

This comparison suggests that NO3 sources to groundwater in 

the Edwards aquifer, although primarily in the soil organic N 

range, might include a potential component of manure and (or) 

septic/sewage sources. Kreitler and Browning (1983) did not 

measure δ18O compositions; thus, only historical δ15N results 

were compared. This comparison with historical measurements of δ15N should be interpreted with caution, however, 

because interlaboratory and intermethod comparisons could 

not be made. Nonetheless, other data are consistent with the 

possibility that δ15N values for TANC study samples are higher 

than historical values as a result of changes in potential NO3 

sources and loadings to the aquifer. The median NO3 concentration for regional confined groundwater samples collected by 

Figure 21. Relation between well depth and nitrate concentration for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. 

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Nitrate, in milligrams per liter as nitrogen

500

1,000

1,500

2,000

2,500

Well depth, in feet below land surface

0

Kendall’s tau = -0.25 (regional public-supply wells only)

EXPLANATION

Timberhill monitoring well

 sample

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well

 sample

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Overburden monitoring well

 (Z–OVB) sample

Regional public-supply

 well sample

 Confined

 Unconfined

Well-field (wellhead) well

 sample

 W2

 W3

 W4

 W5

 W6
Figure 22. Isotopic composition of nitrate for groundwater samples collected for the study of the transport of anthropogenic and natural contaminanwells, south-central Texas, 2004–9. Historical data for delta nitrogen-15 (δ15N) of nitrate shown for comparison are based on results from Kreitler and B

oxygen-18 of nitrate (δ18O) was not measured for historical samples). Common fields of δ15N and δ18O are modified from Kendall (1998), Mengis and oth

others (2002). -5 0 5 10 15 20 25 Delta nitrogen-15 of nitrate, in per mil -10

0

102030405060

Delta oxygen-18 of nitrate, in per mil

Soil nitrate

Nitrate from ammonium fertilizers Nitrate from human and (or) animal waste

Synthetic nitrate fertilizer

Nitrate in precipitation

Denitrification
42 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Kreitler and Browning (1983) was 1.40 mg/L, which is significantly lower than that for regional aquifer PSW samples. An 

upward trend for NO3 concentrations (1938–2006) in the San 

Antonio segment of the aquifer was previously proposed by 

Musgrove and others (2010). Mahler and others (2011) found 

that nitrate concentrations for recent (2008–10) samples from 

the Barton Springs segment of the aquifer are elevated relative 

to historical (1990–2008) samples. Additionally, Mahler and 

others (2011) found that recent (2008–10) δ15N values for 

samples from Barton Springs were significantly higher than 

historical values (1990–94). 

Strontium Isotopes

Strontium isotopes (87Sr/86Sr) are a useful tracer in the 

hydrologic cycle, in particular for sources of dissolved constituents to a fluid (Banner, 2004). Strontium (Sr) isotopes in 

hydrology have been used to trace flow paths, mineral-solution reactions, and variations in recharge and flow routes in a 

number of different groundwater settings (McNutt and others, 

1990; Banner and others, 1994). In the Edwards aquifer, 

87Sr/86Sr values have been applied previously in conjunction 

with element ratios (Mg/Ca, Sr/Ca) as a tracer of water-rock 

interaction, groundwater residence time, recharge, unsaturated zone flow-routes, and the influence of soil composition 

on groundwater geochemistry (Oetting and others, 1996; 

Musgrove and Banner, 2004; Garner, 2005; Wong and others, 2011). Sr isotope ratios in the Edwards aquifer generally 

decrease with increasing water-rock interaction, approaching 

values similar to those of the host limestone aquifer rocks 

(Oetting and others, 1996; Sharp and Banner, 1997; Musgrove 

and Banner, 2004; Musgrove and others, 2010). Cretaceousage carbonate host rocks that compose the Edwards aquifer 

have 87Sr/86Sr values ranging from 0.7074 to 0.7077 (Koepnick 

and others, 1985; Oetting, 1995). Higher 87Sr/86Sr values for 

groundwater relative to the aquifer host rocks are indicative 

of a source of more radiogenic Sr (enriched in 87Sr) to the 

groundwater, which has been proposed to be a result of chemical interaction of groundwater with overlying soils and proportionally less interaction with aquifer host rocks (Musgrove 

and Banner, 2004). The Sr isotope composition of regional 

Edwards aquifer groundwater demonstrates a progression 

toward lower 87Sr/86Sr values with increased mineral-solution 

reactions as allowed by increased residence time and longer 

flow paths; Sr isotope results are consistent with a characterization of confined groundwater samples from the well-field 

and monitoring wells as more geochemically evolved relative 

to shallow and unconfined groundwater (Musgrove and others, 

2010). 

Sr isotopes were not measured for regional aquifer 

PSWs; thus, only values for the well-field and monitoring 

wells are evaluated. The strontium isotope composition of 

well-field and monitoring well samples had a relatively narrow range (0.70767–0.70784). The median value of 0.70772 is 

very close to the range of the carbonate host rocks, indicative 

of relatively geochemically evolved groundwater (that is, 

groundwater that has undergone extensive mineral-solution 

reaction with the carbonate host rocks). Values for the wellfield samples and samples from the Zarzamora monitoring 

wells are mostly within analytical uncertainty of each other; 

values for the samples from the Timberhill monitoring wells 

are slightly elevated in comparison (median of 0.70783). The 

87Sr/86Sr value for the sample from the overburden monitoring 

well (Z–OVB) (0.70785) was also slightly elevated in comparison, similar to values for the Timberhill monitoring wells. 

Slightly higher 87Sr/86Sr values for the Timberhill monitoring 

wells might reflect differences in flow paths supplying these 

wells or might indicate that groundwater from these wells 

are less geochemically evolved than is groundwater from the 

well-field and Zarzamora monitoring wells. 87Sr/86Sr values 

for the Buda Limestone have not been characterized. Both the 

Zarzamora and Timberhill monitoring well values decrease 

slightly with depth, although since results for most of the 

monitoring wells are within analytical uncertainty of each 

other, any 87Sr/86Sr trend with depth in the monitoring wells 

is poorly constrained (fig. 23). A trend of decreasing 87Sr/86Sr 

with depth, however, would be consistent with more geochemically evolved groundwater associated with deeper flow paths 

in the aquifer. 

Stable Isotopes of Hydrogen and Oxygen

Stable isotope ratios of hydrogen and oxygen (δD and 

δ18O) are commonly used to study hydrologic processes and 

have been applied to assess groundwater origin, mixing, 

and evaporation, as well as hydrograph separation and the 

response of karst systems to storms, aquifer recharge, subsurface flow routing (diffuse relative to conduit), and antecedent 

conditions (Craig, 1961; Gat, 1981; Lakey and Krothe, 1996; 

Jones and others, 2000; Desmarais and Rojstaczer, 2002; 

Maloszewski and others, 2002). Well-field and monitoring 

well samples were analyzed for δD and δ18O; results showed 

little variability, with median values of -22.7 per mil and -4.1 

per mil, respectively (table 12 at end of report). A comparison of these data with both the global meteoric water line 

(GMWL), which represents a regression line for the isotopic 

composition of rainfall around the globe (Craig, 1961), and 

the local meteoric water line (LMWL) (Pape and others, 2010) 

indicates that groundwater samples were meteoric in origin 

(fig. 24). On the basis of stable isotope and other geochemical results, a small number of regional groundwater samples 

have been previously interpreted to be affected by mixing 

with (a) downdip saline water, (b) recent recharge associated 

with tropical cyclonic storms, or (c) recharge water that has 

undergone evaporation (Musgrove and others, 2010). Regional 

aquifer PSW samples were not analyzed for δD and δ18O, but 

previous results for Edwards aquifer groundwater indicate that 

confined groundwater is less variable relative to shallow/urban 

unconfined and unconfined groundwater (Musgrove and others, 2010). The absence of variability in δD and δ18O results 
Hydrogeologic Setting 43

for samples from TANC well-field and monitoring wells is 

consistent with the study characterization of the PSW samples 

as well-mixed, homogeneous, confined groundwater that is 

typical of the regional aquifer. 

Organic Constituents

The presence of organic constituents that do not occur 

naturally in hydrologic systems, such as pesticides and VOCs, 

is a direct result of anthropogenic activities. Anthropogenic 

organic contaminants are of concern in groundwater and 

drinking-water supplies because of their potential detrimental effects on the environment and to human health. Many 

of these compounds are relatively soluble and thus can be 

present in groundwater if anthropogenic sources are present. Pesticides and pesticide degradation products generally 

include toxic compounds used to kill or control plants (herbicides), insects (insecticides), fungi (fungicides), and rodents 

(rodenticides). VOCs are carbon-based compounds that 

readily volatilize and are commonly found in paints, solvents, 

gasoline-related compounds, refrigerants, fumigants, and 

other industrial compounds. VOCs include trihalomethanes 

(THMs), which are a byproduct created by the disinfection 

of drinking water by chlorination. The frequency of detection 

and spatial distribution of anthropogenic contaminants provide 

insight into their potential sources, as well as into effects of 

anthropogenic activities on water quality.

Samples for organic constituents on the analytical schedule for wastewater indicator compounds were collected from 

regional aquifer PSWs (table 13 at end of report). Results from 

these analyses were almost entirely nondetections, so these 

constituents are not discussed further. 

Pesticides and VOCs were analyzed in samples collected 

from the well-field and monitoring wells and the regional 

aquifer PSWs. A subset of the regional aquifer PSWs (n=39) 

that were sampled in 2004 were resampled in 2005 for only 

pesticides (n=8) and VOCs (n=7). TANC results for organic 

contaminants were consistent with previous studies that have 

documented the occurrence of anthropogenic organic contaminants in the Edwards aquifer at low concentrations (Bush and 

others, 2000; Fahlquist and Ardis, 2004; Musgrove and others, 

2010). Pesticides and VOCs were detected in all analyzed well 

categories, including well-field wells, monitoring wells, and 

regional aquifer PSWs. Detected concentrations of organic 

constituents were mostly less than 1 μg/L and were typically 

orders of magnitude below USEPA MCLs for those constituents for which MCLs currently exist. The detection of at least 

one pesticide compound and (or) VOC in samples from most 

of the regional aquifer PSWs collected in 2004 through 2005 

Figure 23. Relation between well depth and strontium isotope composition for groundwater samples collected for the study of the 

transport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. Range for Cretaceousage carbonate rocks that compose the Edwards aquifer (0.7074 to 0.7077) from Koepnick and others (1985) and Oetting (1995). 

Range in 87Sr/86Sr

for Edwards aquifer rocks

0.7075 0.7076 0.7077 0.7078 0.7079 0.7080

Strontium-87/strontium-86 isotopic ratio (87Sr/86Sr)

200

300

400

500

600

700

800

900

1,000

Well depth, in feet below land surface

Timberhill monitoring well

 sample

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well

 sample

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Overburden monitoring well

 (Z–OVB) sample

Well-field (wellhead) well

 sample

 W2

 W3

 W4

 W5

 W6

Error bar—Represents 2-sigma

 analytical uncertainty

EXPLANATION
44 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

(tables 14–17 at end of report) indicates that some fraction of 

groundwater in the regional Edwards aquifer is affected by 

anthropogenic activities. 

One or more pesticide compounds were detected in 79 

percent of the regional aquifer PSW samples, and one or more 

VOCs were detected in 87 percent of these samples. The number of organic compounds detected in any single groundwater 

sample ranged from 0 to 10, with a median of 5. A total of 17 

pesticide compounds and 11 VOCs were detected; most were 

detected infrequently. A small number of compounds were 

consistently and frequently detected (≥50 percent of samples) 

in regional aquifer PSW samples, indicating that there are 

likely widespread, low-level inputs of these constituents 

from multiple sources. The most frequently detected organic 

constituents were (1) the pesticide atrazine, (2) the atrazine 

degradate 2-chloro-4-isopropylamino-6-amino-s-triazine 

(CIAT, also known as deethylatrazine or, hereinafter, DEA), 

(3) the THM chloroform, and (4) the solvent PCE, which 

were detected in 60, 74, 72, and 50 percent of samples from 

regional aquifer PSWs, respectively (fig. 25). In samples from 

the regional aquifer PSWs, median concentrations of atrazine, 

DEA, chloroform, and PCE were 0.005 μg/L, 0.006 μg/L, 

0.020 μg/L and 0.008 μg/L, respectively (fig. 26). These concentrations are orders of magnitude below the USEPA MCLs 

for these compounds, which are 3 μg/L for atrazine, 80 μg/L 

for total THMs, including chloroform, and 5 μg/L for PCE. 

Other pesticides that were frequently detected were simazine 

and prometon, which were detected in 38 and 30 percent of 

the regional aquifer PSW samples, respectively (fig. 25). The 

atrazine degradates deisopropylatrazine (or 2-chloro-6-ethylamino-4-amino-s-triazine (hereinafter, CEAT)) and hydroxyatrazine (or 2-hydroxy-4-isopropylamino-6-ethylamino-s-triazine (hereinafter, OIET)) were analyzed for in only a subset 

of the regional aquifer PSW samples (n=15) and were detected 

in 25 and 15 percent of those samples, respectively. In the 

regional aquifer PSW samples, median concentrations of 

CEAT, OIET, simazine, and prometon were below laboratory 

method reporting levels of 0.08 μg/L, 0.032 μg/L, 0.005 μg/L, 

and 0.010 μg/L, respectively. The THMs bromoform, dibromochloromethane, and bromodichloromethane were detected 

in 26, 17, and 17 percent of the regional aquifer PSW samples, 

respectively. In regional aquifer PSW samples, total THM 

concentrations ranged from below laboratory method reporting 

levels to 3.178 μg/L, with a median value of 0.023 μg/L. 

The frequent detection of atrazine, DEA, chloroform, 

and PCE, as well as the common detection of simazine and 

prometon at low concentrations, is consistent with constituent 

occurrence patterns in the Edwards aquifer previously noted 

by Mahler and others (2006) and Musgrove and others (2010). 

Lindsey and others (2009) report similar findings for other carbonate aquifers in similar land use settings. Where detected, 

organic constituents tend to co-occur; that is, concentrations 

of the most frequently detected organic compounds are correlated. For example, for the regional aquifer PSW samples, 

Figure 24. Relation between deuterium and oxygen isotopes for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. Local and global meteoric water 

lines are shown for comparison, based on Pape and others (2010) and Craig (1961), respectively. 

-7 -6 -5 -4 -3 -2 -1 0

Delta oxygen-18, in per mil

-40

-35

-30

-25

-20

-15

-10

-5

0

Delta deuterium, in per mil

GLOBAL METEORIC WATER LINE

LOCAL METEORIC WATER LINE

EXPLANATION

Timberhill monitoring well

 sample

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well

 sample

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Overburden monitoring well

 (Z–OVB) sample

Well-field (wellhead) well

 sample

 W2

 W3

 W4

 W5

 W6
Hydrogeologic Setting 45

concentrations of atrazine were correlated with concentrations 

of DEA, simazine, PCE, and chloroform (Kendall’s tau = 0.69, 

0.55, 0.56, 0.46, respectively). 

Atrazine, DEA, simazine, chloroform, and PCE were 

frequently detected in the well-field (n=5) and monitoring well 

(n=5) samples, though at different frequencies (fig. 25) and 

median concentrations (fig. 26) than in the regional aquifer 

PSW samples. DEA and PCE were detected in 100 percent of 

the well-field and monitoring well samples. Atrazine and chloroform were detected in 100 percent of the well-field samples; 

simazine was detected in 60 percent of these samples, and 

prometon was not detected. Bromoform and dibromochloromethane were detected in 80 and 60 percent of the well-field 

samples, respectively. Detection frequencies for the two sets of 

monitoring wells were different for some organic constituents 

(fig. 25); atrazine and simazine were detected in 100 percent 

of the Timberhill monitoring well samples (n=2) but had 

lower detection frequencies in the Zarzamora monitoring well 

samples (n=3). For the Timberhill monitoring wells, chloroform was detected in only the deeper well sample.

A comparison of median concentrations for the most 

frequently detected organic constituents in the different well 

categories provides insight into potential sources and transport of anthropogenic constituents to the well field. Median 

concentrations of atrazine, DEA, and PCE in the regional 

aquifer PSW samples (0.005, 0.006, and 0.008 μg/L, respectively) are representative of regional confined groundwater on 

the basis of their similarity with this groundwater category as 

detailed by Musgrove and others (2010). Median concentrations of these contaminants, however, are significantly higher 

(on the basis of Mann-Whitney U testing) in the well-field 

and monitoring well samples compared to the regional aquifer 

PSW samples (fig. 26); this result may indicate that the well 

field is affected by some additional, and likely local, source(s) 

Figure 25. Detection frequency for the most frequently detected anthropogenic contaminants for groundwater samples collected for 

the study of the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. 

Contaminant

Atrazine

Deethylatrazine (DEA)

2-chloro-6-ethylamino-4-

amino-s-triazine (CEAT)

2-hydroxy-4-isopropylamino-6-

ethylamino-s-triazine (OIET)

Prometon

Simazine

Tetrachloroethene (PCE)

Dibromochloromethane

Bromodichloromethane

Tribromomethane 

(bromoform)

Trichloromethane (chloroform)

0

20

40

60

80

100

Detection frequency, in percent

Regional public-supply wells (n ranges

 from 19 to 47)

Well-field (wellhead) wells (n=5)

Zarzamora monitoring wells (n=3)

Timberhill monitoring wells (n=2)

n, Number of samples

EXPLANATION
46 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Figure 26. Median concentration of the most frequently detected anthropogenic contaminants for groundwater samples collected for 

the study of the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. Two 

scales are shown for selected contaminants for comparison. A, Full scale. B, Reduced scale.

Contaminant

Contaminant

Atrazine

Deethylatrazine (DEA)

2-chloro-6-ethylamino-4-

amino-s-triazine (CEAT)

2-hydroxy-4-isopropylamino-6-

ethylamino-s-triazine (OIET)

Prometon

Simazine

Atrazine

Deethylatrazine (DEA)

2-chloro-6-ethylamino-4-

amino-s-triazine (CEAT)

2-hydroxy-4-isopropylamino-6-

ethylamino-s-triazine (OIET)

Prometon

Simazine

Tetrachloroethene (PCE)

Dibromochloromethane

Bromodichloromethane

Tribromomethane 

(bromoform)

Trichloromethane (chloroform)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Median concentration, in 

micrograms per liter

0

0.005

0.01

0.015

0.02

Median concentration, in 

micrograms per liter

Regional public-supply wells (n ranges

 from 19 to 47)

Well-field (wellhead) wells (n=5)

Zarzamora monitoring wells (n=3)

Timberhill monitoring wells (n=2)

Overburden monitoring well (n=1)

n, Number of samples

EXPLANATION

A

B
Hydrogeologic Setting 47

of these contaminants. A previous evaluation of organic constituents in the Edwards aquifer found that the urban environment is a potential source of anthropogenic contaminants to 

the aquifer; shallow/urban unconfined groundwater had higher 

median concentrations of atrazine, DEA, and PCE (0.008, 

0.009, and 0.027 μg/L, respectively) and a higher frequency of 

detection than did regional confined groundwater (Musgrove 

and others, 2010). Median concentrations of PCE are significantly higher (on the basis of Mann-Whitney U testing), in 

particular, in the well-field samples (0.176 μg/L) and the Zarzamora monitoring well samples (0.365 μg/L) in comparison 

with both regional aquifer PSW samples (fig. 26) and shallow/

urban unconfined groundwater described by Musgrove and 

others (2010). 

The most frequently detected organic contaminants generally showed a trend of decreasing concentration with depth 

for the regional aquifer PSW samples; atrazine, simazine, 

PCE, and chloroform concentrations were correlated with well 

depth (Kendall’s tau = -0.36, -0.37, -0.28, -0.25, respectively). 

More specifically, the relation with well depth for most of the 

frequently detected organic contaminants tends to be bimodal 

(fig. 27). Median concentrations and the frequency of detection for atrazine, DEA, simazine, PCE, and chloroform in the 

regional aquifer PSW samples are consistently higher for wells 

that are less than 1,000 ft in depth. For wells that are greater 

than 1,000 ft deep, median concentrations for these organic 

contaminants are all less than the laboratory method reporting 

levels. The concentration difference between the two groups 

(that is, wells less than 1,000 and greater than 1,000 ft deep) 

for all of these organic contaminants is statistically significant 

on the basis of Mann-Whitney U testing. About half of the 

deep (greater than 1,000 ft deep) regional (confined) aquifer 

PSWs are near or along the southern boundary of the confined 

segment of the aquifer (fig. 1). These deeper confined PSWs 

might intersect downgradient regional flow paths that have 

been less affected by anthropogenic contaminants. Samples 

from these deep wells (greater than 1,000 ft deep) show 

other evidence for a large component of more geochemically 

evolved and potentially older waters, such as higher Mg/Ca 

ratios and dolomite SIs, both of which have been shown to 

be qualitative indicators of residence time in this aquifer 

(Musgrove and others, 2010). Both Mg/Ca ratios and dolomite 

SIs were significantly different between samples collected 

from shallower wells (less than 1,000 ft deep) and those collected from deeper wells (greater than 1,000 ft deep) on the 

basis of Mann-Whitney U testing. It is possible that groundwater from these deep wells might be affected by mixing with a 

component of downdip saline-zone water, which might dilute 

concentrations of anthropogenic contaminants. However, there 

is no clear indication that such mixing has likely occurred; 

for example, concentrations of ions associated with the saline 

zone (for example, Cl, SO4

, Sr, and F) were not statistically 

different for samples from the regional (confined) aquifer 

PSWs with well depths greater than 1,000 ft, with the exception of Sr. These results are consistent with a previous study 

of low-level VOC concentrations in the San Antonio area that 

found fewer VOC detections in deeper wells and proposed 

that these deep wells might intercept regional flow paths that 

contain higher fractions of water recharged in rural areas in the 

western portion of the aquifer (Plummer and others, 2008).

The frequent detection of chloroform at low concentrations in samples from the well-field wells, monitoring wells, 

and regional aquifer PSWs is consistent with widespread 

detection of chloroform in other studies in the Edwards aquifer 

(Mahler and others, 2006; Musgrove and others, 2010), in 

other carbonate aquifers (Lindsey and others, 2009), and in 

many aquifers across the United States (Zogorski and others, 

2006). This frequent detection in a variety of well types and 

land-use settings has been partly attributed to the recycling 

of chlorinated waters (Moran and others, 2002; Zogorski and 

others, 2006). Anthropogenic sources of chloroform include 

drinking-water treatment processes, leaking water and wastewater lines, septic systems, and recharge from irrigation 

with treated water. Public-water-supply sources also include 

the possible use of treated water as a downhole well-pump 

lubricant. Natural sources of chloroform include volcanic 

gases, biomass burning, marine algae, and soil microorganisms (Ivahnenko and Barbash, 2004). 

In addition to chloroform, other THMs that are also a 

byproduct of drinking-water treatment processes—bromoform, dibromochloromethane, and bromodichloromethane—

were frequently detected (80, 60, and 60 percent, respectively) 

in the well-field samples (fig. 25). The median bromoform 

concentration for the well-field samples (0.756 μg/L) was 

higher than the median concentration of any other organic 

constituent in any other sample category (fig. 26). Higher 

concentrations of brominated THMs relative to chloroform is 

unusual, as chloroform is the THM produced in the highest 

concentrations during chlorination (Ivahnenko and Barbash, 

2004). Ivahnenko and Barbash (2004) indicate that the formation of brominated THMs might occur in the presence of 

unusually high bromide concentrations, which is not the case 

for the Edwards aquifer. The source of bromoform to the wellfield samples is likely local to the well field but is currently 

unknown. 

Groundwater Age Tracers and Age Distributions

Groundwater age estimates have been used to determine 

recharge rates, estimate rates of geochemical and microbiological processes, calibrate groundwater flow models, evaluate 

aquifer susceptibility to contamination, and improve waterresource management (Plummer, 2005). Groundwater age estimates are based on the measurement of a dissolved solute, gas, 

or isotope in groundwater that has been transported through 

the aquifer to the point of sampling. As such, groundwater 

age estimates are model dependent, based on an interpretation 

of recharge and flow mechanisms, and might be affected by 

a variety of physical and geochemical processes (Cook and 

Böhlke, 2000; Plummer, 2005).

Age tracers—concentrations of CFCs (CFC-11, CFC-12, 

and CFC-113), SF6

, 3H and the ratio of the parent/daughter 
Figure 27. Relation between well depth and concentration for selected organic contaminants for groundwater samples collected for the study of the and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. A, Atrazine. B, Tetrachloroethene (PCE). C, Simazine. D, Trichlor

Median concentration; detection frequency<1,000 feet = 0.023 μg/L; 88% (n=32)

>1,000 feet = <0.024 μg/L; 36% (n=14)

Median concentration; detection frequency<1,000 feet = 0.005 μg/L; 52% (n=31)

>1,000 feet = <0.005 μg/L; 7% (n=14)

Median concentration; detection frequency<1,000 feet = 0.006 μg/L; 81% (n=32)

>1,000 feet = <0.007 μg/L; 13% (n=15)

Median concentration; detection frequency<1,000 feet = 0.046 μg/L; 69% (n=32)

>1,000 feet = <0.03 μg/L; 7% (n=14)

0 0.005 0.01 0.015 0.02

Concentration, in micrograms per liter (μg/L)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Concentration, in micrograms per liter (μg/L)

Concentration, in micrograms per liter (μg/L) Concentration, in micrograms per liter (μg/L)

0 0.002 0.004 0.006 0.008 0.010 0.012 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

0

500

1,0001,5002,0002,500

0

500

1,0001,5002,0002,500

0

500

1,0001,5002,0002,500

0

500

1,0001,5002,0002,500

Well depth, in feet

below land surface

Well depth, in feet

below land surface

X

XXXXX

X

XXX

X

X

X

XXXXXX

X

X

X

X

X

X

XXXX

X

XX

X

X

XXXXXXX

X

XXXXXX

XXXXXXXXX

X

X

X

X

X X

XX

XX

X

X

X

XX

X

XX

X

XX

X

X

A. AtrazineC. Simazine

B. Tetrachloroethene (PCE)D. Trichloromethane (chloroform)
Hydrogeologic Setting 49

isotopes 3H/3He, and dissolved gases (methane, CO2, He, 

N2, oxygen, argon, and Ne)—were measured for most of the 

well-field and monitoring well samples, as well as for the W4 

depth-dependent samples. Groundwater age tracers were not 

measured on samples from the regional aquifer PSWs, but 

previous NAWQA studies have measured a variety of age tracers in shallow/urban unconfined groundwater and unconfined 

groundwater samples, as well as 3H in confined groundwater 

from the regional aquifer (Musgrove and others, 2010). Those 

results, with a median apparent groundwater age of 20 years 

(based on a piston-flow model interpretation), indicate that the 

Edwards aquifer is dominated by “young” or “modern” water, 

with extensive mixing of groundwater, likely of different ages. 

“Young” groundwater is defined as water recharged within 

approximately the past 50 years, the time scale of which 

is largely defined by the dating range of applicable tracers 

(Plummer and Friedman, 1999; Plummer and Busenberg, 

2005). “Modern” groundwater has been similarly defined; that 

is, as water that has recharged within the past few decades 

in a system with an active hydrologic cycle (Clark and Fritz, 

1997). Similar to Musgrove and others (2010), this report considers modern groundwater to represent samples with apparent 

ages that belong to the present day; that is, within 10 years of 

the time of sampling. This report considers “old” groundwater 

as that recharged prior to 50 years ago. Previous studies of 

age tracers and dye-tracing tests in the Edwards aquifer have 

documented a range of possible groundwater traveltimes and 

groundwater mixing, largely dominated by young and modern 

water (Pearson and others, 1975; Campana and Mahin, 1985; 

Ogden and others, 1986; Johnson and Schindel, 2008; Johnson 

and others, 2010). Apparent groundwater age in the Edwards 

aquifer has been demonstrated to vary temporally as a result of 

changes in hydrologic conditions; that is, variability in hydrologic conditions results in different mixtures of groundwater of 

different apparent ages (Musgrove and others, 2010). Temporal variability in apparent age results for karst groundwater in 

response to changes in hydrologic conditions has also been 

demonstrated in the Floridan aquifer (Katz, 2004; Happell and 

others, 2006). These results indicate that a one-time sampling 

of groundwater age tracers in karst might not be representative 

over a range of hydrologic conditions. 

Because of contamination effects and age interpretation 

complexities (which are described in more detail below), age 

interpretations were based largely on 3

H/3He results, even 

though other age tracers were measured. Thus, a comparison 

of independent apparent ages determined by different dating 

tracers was not possible. Interpretation of age-tracer results 

were complicated by some natural background or low-level 

anthropogenic contamination of groundwater samples by 

non-atmospheric sources of some tracers; that is, the measured 

tracer concentration in the groundwater sample was greater 

than that theoretically possible, on the basis of equilibrium 

of the groundwater sample with the maximum atmospheric 

concentration. As a result, most of the age-dating tracer results 

did not yield resolvable apparent groundwater ages. These 

results are consistent with previous efforts to interpret results 

of groundwater age tracers in the Edwards aquifer, which 

indicated that low-level contamination issues in the aquifer 

are common, in particular with respect to CFC and SF6 tracers 

(Thompson and Hayes, 1979; Musgrove and others, 2010). 

Contamination from CFCs might be particularly associated 

with urban areas (Musgrove and others, 2010). Possible urban 

CFC sources include septic tanks, leaking sewerlines and 

storage tanks, sewage treatment plant effluent, and industrial 

wastes (Plummer and Busenberg, 2005). An early study of 

CFCs identified a plume of CFC-11 in the Edwards aquifer 

from a proposed point source in the urban San Antonio area to 

the northeast along a regional flow gradient (Thompson and 

Hayes, 1979). Age-tracer results for all samples analyzed for 

SF6 and all but one location analyzed for CFCs indicated that 

samples were contaminated with excess tracer and that age 

interpretations were not resolvable (table 18 at end of report) 

from these compounds. CFC results for one of the well-field 

samples (W5) yielded independent age interpretations based 

on CFC-11, CFC-12, and CFC-113 tracers (table 18). However, these resolvable ages might still be affected by excess 

CFC from widespread low-level aquifer contamination and, as 

a result, might still be questionable.

Interpreting groundwater ages with 3H is qualitative, 

but 3H concentrations can provide insight into distinguishing 

between prebomb and postbomb water based on the history 

of 3H input to the atmosphere from nuclear weapons testing. 

Based on its relatively short half-life (12.3 years), the presence of 3

H in groundwater is indicative of recent groundwater 

recharge (Clark and Fritz, 1997; Plummer, 2005). The input of 

3

H to the atmosphere as a result of nuclear testing dominated 

the concentrations of 3H in rainfall for about 50 years, with 

concentrations increasing above natural levels beginning in 

the early 1950s and peaking in the 1960s. Concentrations of 

3

H in recent rainfall (since 2006) have globally decreased to 

approximately prebomb background levels (Clark and Fritz, 

1997; Phillips and Castro, 2003; R.L. Michel, U.S. Geological Survey, written commun., 2009). Concentrations of 3

H 

in the well-field and monitoring well samples (excluding the 

overburden well) (2007–8; n=19) ranged from less than 1 to 

2.23 3

H units (TU), with a median of 1.97 TU (table 19 at 

end of report). An additional sample collected from the shallow Zarzamora monitoring well (Z–SED) in 2009 had a 3

H 

concentration of 1.74 TU. The overburden monitoring well 

sample (Z–OVB) had a 3H concentration of 1.30 TU. Tritium 

concentrations showed no relation with well depth or sampling depth. Groundwater 3

H concentrations were compared 

to a local 3H input function derived from a combination of 3H 

concentrations measured in rainfall at Waco, Tex. (1961–87) 

and 3H concentrations measured in rainfall at Vienna, Austria 

(1961–2006) (International Atomic Energy Agency/World 

Meteorological Organization, 2008). Results for 3H concentration from this study and from Musgrove and others (2010) 

are indicative of dominantly young and modern groundwater 

throughout the Edwards aquifer. 

The decay of 3H produces the stable isotope 3He; the ratio 

of parent to daughter isotopes is used to estimate the time 
50 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

since recharge (Plummer and others, 1993). Tritium decay, 

however, is not the only possible source of 3He, and determining the amount of 3

He from the decay of 3H (tritiogenic 3He, 

or 3Htrit) requires an assessment of other possible 3He sources. 

Excess air, introduced to groundwater when entrapped air 

bubbles dissolve, is common in groundwater and is usually 

the source of most additional 3He (Busenberg and Plummer, 

2000). Ne concentrations are used in excess-air correction calculations. Helium can also be introduced to groundwater from 

terrigenic sources (Heterr) because it is produced by the decay 

of uranium-series (U-series) radionuclides. Age calculations 

are sensitive to the amount of terrigenic helium-4 (4Heterr). 4

Heterr (relative to the total 4He) for samples which yielded 

resolvable apparent ages ranged from near 0 to 20.3 percent, 

with an average value of around 7 percent (table 19). Two 

samples had negative values for 4Heterr, which might indicate a 

loss of 3He and yield an older estimated age. 4Heterr values for 

both of these samples, however, were close to 0, and the negative values might also reflect analytical uncertainties for very 

young samples with low 4Heterr values. For these two samples, 

age calculations were not corrected for 4Heterr, and calculated 

apparent ages were relatively young (0.8 and 3.4 years). A 

large fraction of 4Heterr (greater than 10 percent) is an additional source of uncertainty in age calculations, which are 

dependent on the 3He/4He ratio of the Heterr (Plummer, 2005). 

The highest Δ4Heterr values (4Heterr as a percentage of measured 

He) for samples with resolvable ages were associated with the 

Timberhill monitoring wells (17.5 and 20.3 percent). There 

was no significant relation between Δ4Heterr and U concentration in the water samples, and U concentrations in well-field 

well and monitoring well samples had a narrow range (0.80–

1.17 μg/L). Terrigenic 4He likely accumulates from U-series 

decay in aquifer host carbonates where U is present in low 

concentrations (up to 1.7 mg/kg) (table 5) or from migration 

from other sources such as deep crustal rocks (Hunt and others, 2010). Values of Δ4

Heterr (percent) increased with interpreted age (Kendall’s tau = 0.89) (fig. 28), which suggests that 

Δ4Heterr values might provide an indicator of relative residence 

time in this aquifer (Hunt and others, 2010). 

Results for 3H/3He measurements were used to estimate 

groundwater ages in 15 samples, including those from the 

monitoring wells (n=5), well-field (n=4) and depth-dependent 

sampling from W4 (n=6). Apparent ages (summarized in 

table 19) were not resolvable for several samples, including 

the well field sample (W5) that had CFC results. Measured 3H 

concentrations in the overburden well (1.30 TU) and in one 

of the W4 depth-dependent samples (less than 1 TU) were too 

low to obtain a corresponding 3H/3He interpreted age. Results 

for several additional samples did not yield resolvable age 

interpretations because of effects of probable degassing during 

sample collection (negative Δ4Heterr or ΔNe values) (table 19). 

An evaluation of geochemical age-dating tracers in a 

complex karst system such as the Edwards aquifer requires 

consideration of flow-system dynamics. Lumped-parameter 

models were used to represent different conceptual flowsystem characteristics, specifically, a piston-flow model, 

Figure 28. Relation between apparent age and excess delta helium-4 (terrigenic) for groundwater samples collected for the study of 

the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9.

-5 0 5 10 15 20 25

Excess delta helium-4 (terrigenic), in percent

0

10

20

30

40

Apparent age (piston-flow model), in years

Kendall’s tau = 0.89

EXPLANATION

Timberhill monitoring well

 sample

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well

 sample

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Well-field (wellhead) well

 sample

 W2

 W3

 W4

 W5

 W6

Well-field (W4)

 depth-dependent 

 sample, by pumping

 condition-depth

 Ambient-intermediate

 Ambient-deep

 Moderate-shallow

 Moderate-intermediate

 Moderate-deep

 Normal-shallow
Hydrogeologic Setting 51

an exponential mixing model, and several combinations of 

binary mixing models of older water with younger water. A 

piston-flow model, which is the simplest and most commonly 

assumed transport model, assumes that the tracer concentrations were not altered by transport processes (Plummer and 

Busenberg, 2005). This simplified approach assumes that no 

mixing or dispersion affects the tracer concentration and that 

all groundwater flow lines have similar velocity. A piston-flow 

model likely does not adequately represent a mixed groundwater sample with a range of ages, which is especially valid 

for karst aquifers (Long and Putnam, 2006). In spite of these 

uncertainties in age interpretation, piston-flow model ages 

provide an initial reference point for comparison of different 

age tracers and time scales of flow processes in the aquifer. 

An exponential mixing model describes a hydrologic transport model in which the mean residence time of groundwater 

is exponentially distributed; that is, groundwater is a mixture 

of recharge from past years. Groundwater contributions to 

well or spring discharge would be dominated by the most 

recent recharge and decrease exponentially in proportion to 

older recharge. An exponential mixing model might represent 

a reasonable approximation of a homogeneous unconsolidated aquifer but, like the piston-flow model, is likely not an 

adequate representation of a karst aquifer, where traveltimes 

can vary widely between matrix-flow-dominated and conduitflow-dominated endmembers. The mean age of the exponential mixture was varied in evaluating exponential models. 

Binary mixing models assume that groundwater is composed 

of a mixture of two endmembers of different ages, for example 

relatively young (modern) water (recharged within the past 

10 years) mixed with relatively older water (recharged several 

or more decades ago with little to no detectable tracer concentrations). Lumped-parameter models of binary mixtures were 

evaluated for a variety of young and old age combinations; for 

example, piston-flow models for both endmembers, a pistonflow model for the old endmember and an exponential flow 

model for the young endmember, and an exponential flow 

model for the old endmember and a piston-flow model for the 

young endmember. For modeling purposes, both endmembers 

of a binary mixture can be any age, but for purposes of this 

effort it was assumed that one endmember was modern (that 

is, recharged within the past zero to 5 years) and the other 

was young to old (that is, recharged 30–70 years ago, which 

includes that time period for which there would be little to 

no detectable tracer concentrations). For binary mixtures of 

modern and old water, the 3

H/3He method is particularly useful 

for determining the age of the younger fraction; the isotopic 

ratio is nearly independent of dilution with old 3H-free water 

(Plummer and others, 1998). Plots of age-frequency distributions based on tracer-tracer concentrations for collected 

samples relative to theoretical curves for different lumpedparameter models can provide insight into the distribution 

of apparent ages in an aquifer, age mixtures at wells, and the 

representativeness of different hydrogeologic concepts of the 

flow system. 

Lumped-parameter-model results for different hydrogeologic conceptual models and different mixtures of age 

combinations did not clearly indicate that any one conceptual 

hydrogeologic model can account for the range of measured 

age-tracer concentrations. For the tracer-tracer plot showing 

the relation between 3

H and 3H/3H0, most of the samples plot 

above the piston-flow-model curve and slightly above the 

exponential model curve (fig. 29). The sample with the lowest 

3

H/3H0 ratio and oldest interpreted age (T–IED) plots well 

below the piston-flow-model curve but close to the exponential model curve. The 3

H0 value is the sum of the measured 

concentrations of 3H and 3Hetrit (tritiogenic 3H, derived from 

the decay of 3H) and represents the initial 3H concentration 

at the time of recharge. The ratio of tritium to initial tritium 

(3H/3H0)is a proxy for the relative age of water; values near 

zero represent older water, whereas a value approaching 1 represents younger water (Böhlke, 2002). 3

H/3H0 values are correlated with piston-flow groundwater ages (Kendall’s tau = -1.0) 

(fig. 30). The W4 depth-dependent ambient-deep sample deviated from the trend of this relation relative to the rest of the 

samples; the cause of this deviation is unclear. Other lumpedparameter models shown on tracer-tracer plots (figs. 29, 31, 

and 32) are for an exponential model with a mean groundwater 

model age of 3 years, a combined piston-flow/exponentialflow model, and binary mixture models with modern and 

young endmember ages of 0.5 and 30 years (binary mix 1 with 

piston-flow models for both endmembers; binary mix 2 with 

an exponential-flow model for the modern endmember and a 

piston-flow model for the young endmember; and binary mix 

3 with a piston-flow model for the modern endmember and 

an exponential-flow model for the young endmember). These 

potential mixture ages are consistent with particle-track results 

from a calibrated groundwater-flow model for the local-scale 

study area, described by Lindgren and others (2011b). These 

modeling results indicate that approximately 48 percent of particle tracks to the study PSW are within a 0- to less than 2-year 

range of traveltimes, an additional 40 percent are within the 2- 

to less than 5-year range of traveltimes, an additional 8 percent 

are within the 5- to less than 10-year range of traveltimes, 

and 4 percent have a greater than 10 year traveltime (fig. 33). 

While different lumped-parameter models might account 

for different samples on the basis of tracer-tracer plots (fig. 

29), no prevailing model accounts for the range of age-tracer 

results and consistently seems to describe the flow system. 

An exponential-flow mixing model can be used to 

estimate the mean age of groundwater in a sample; the W4 

well-field sample and the depth-dependent samples for normal 

pumping conditions fall close to the exponential-flow model 

(fig. 29). A comparison of model estimates with 3

H0 values 

suggests that samples from the monitoring wells and well 

field compose a large range of mean ages, from close to 0 

to approaching 50 years (fig. 34A). A similar comparison of 3

H concentrations with model-estimated mean ages does not 

allow for distinguishing different mean ages between samples 

as a result of the narrow range of 3H concentrations and the 

convergence of model curves for the narrow range of sample 
Figure 29. Relation between tritium (3H) concentration and 3H to initial tritium (3H0) ratio (3H/3H0) for groundwater samples collected for the study of th

anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9, and lumped-parameter modeled curves for variodistributions.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Tritium to initial tritium ratio

0123456

Tritium, in tritium units 
Hydrogeologic Setting 53

collection dates (fig. 34B). Based on wellbore flow characteristics, flow to W4 under normal pumping conditions (with 

multiple wells in the well field pumping) is sourced from 

multiple stratigraphic units in the Edwards section (fig. 7). The 

mean exponential model age for the W4 well-field sample, 

which is assumed to represent conditions of water quality for 

water produced from the PSW, was younger than the other 

wellhead samples and most of the depth-dependent samples, 

with a model (apparent) age of approximately 3 years. 

Tracer-tracer plots for CFC concentrations show mean 

results for only the single well-field PSW (W5) for which CFC 

concentrations were not contaminated for age-tracer purposes. 

CFC concentrations for CFC-11 relative to CFC-12 and for 

CFC-11 relative to CFC-113 indicate that tracer concentrations 

might have been affected by tracer contamination or degradation because sample concentrations plot far outside the area 

of different flow models (fig. 32). CFC degradation, which 

can occur in anoxic environments, is unlikely because of the 

generally oxic condition of the aquifer (Plummer, 2005). The 

widespread CFC contamination throughout the aquifer (this 

study; Musgrove and others, 2010) indicates that potential 

CFC contamination of the W5 well is also plausible. On the 

tracer-tracer plot for CFC-12 relative to CFC-113, the W5 

sample plots in between an exponential-flow model curve and 

a combined piston-exponential model curve (fig. 32). Results 

for the W5 sample on tracer-tracer plots for CFC-12 and CFC113 concentrations relative to the measured 3

H concentration 

(fig. 31) are generally consistent with either the piston-flow 

or exponential-flow lumped-parameter models. It is difficult, 

however, to evaluate any particular flow model based on 

a single sample, and results for sample W5 are not consistent with any single lumped-parameter model. These results 

indicate that apparent ages on the basis of CFC concentrations 

for the sample from W5 should be interpreted with caution. 

Piston-flow-model interpreted ages for W5 (mean) were 38.7, 

30.9, and 26.4 years based on CFC-11, CFC-12, and CFC-113 

tracers, respectively. An exponential model yields a mean age 

of approximately 17 years for this sample based on the 3

H0

concentration (fig. 34), although this approach is not ideal 

because a 3H/3He age was not resolvable for this sample.

A comparison of model ages provides insight into flowsystem dynamics supplying water to the well field. Pistonflow-model groundwater ages based on 3

H/3He results for 

all samples, including depth-dependent samples (which are 

discussed in more detail in the subsequent section), range 

from 0.8 to 41.3 years, with a median of 16.6 years. Pistonflow-model groundwater ages (fig. 35) are inversely stratified for both sets of monitoring wells, with younger ages for 

the deeper monitoring wells. The oldest apparent ages are 

for the Timberhill monitoring wells (41.3 and 31.6 years, 

Figure 30. Relation between apparent age and the tritium (3H) to initial tritium (3H0) ratio for groundwater samples collected for the 

study of the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9.

0 0.2 0.4 0.6 0.8 1.0 1.2

Tritium to initial tritium ratio

0

10

20

30

40

45

Apparent age (piston-flow model), in years

Kendall’s tau = -1.0

EXPLANATION

Timberhill monitoring well

 sample

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well

 sample

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Well-field (wellhead) well

 sample

 W2

 W3

 W4

 W6

Well-field (W4)

 depth-dependent 

 sample, by pumping

 condition-depth

 Ambient-intermediate

 Ambient-deep

 Moderate-shallow

 Moderate-intermediate

 Moderate-deep

 Normal-shallow
54 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Figure 31. Relation between tritium concentration (3H) and chlorofluorocarbon (CFC) age tracers for groundwater sample collected 

from the well-field well, W5, for the study of the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, 

south-central Texas, 2004–9, and lumped-parameter modeled curves for various groundwater age distributions. A, Relation between 

tritium and CFC-11. B, Relation between tritium and CFC-12. C, Relation between tritium and CFC-113.

0 20 40 60 80 100

Chlorofluorocarbon (CFC)-113, in parts per trillion by volume

0 100 200 300 400 500 600

Chlorofluorocarbon (CFC)-12, in parts per trillion by volume

0 50 100 150 200 250 300

Chlorofluorocarbon (CFC)-11, in parts per trillion by volume

0

1

2

3

4

5

6

Tritium, in tritium units 

0

1

2

3

4

5

6

Tritium, in tritium units 

0

1

2

3

4

5

6

Tritium, in tritium units 

A

B

C

EXPLANATION

Lumped-parameter

 flow model

 Piston

 Exponential

 Piston-exponential

 Binary mix 1

 Binary mix 2

 Binary mix 3

Well-field (wellhead) well

 W5 sample

 
Hydrogeologic Setting 55

Figure 32. Relation between chlorofluorocarbon (CFC) age tracers (CFC-11, CFC-12, and CFC-113) for groundwater sample collected 

from the well-field well, W5, for the study of the transport of anthropogenic and natural contaminants (TANC) to public-supply wells, 

south-central Texas, 2004–9, and lumped-parameter modeled curves for various groundwater age distributions. A, Relation between 

CFC-12 and CFC-113. B, Relation between CFC-12 and CFC-11. C, Relation between CFC-11 and CFC-113.

Chlorofluorocarbon (CFC)-11, in parts per trillion by volume

0 100 200 300 400 500 600

Chlorofluorocarbon (CFC)-12, in parts per trillion by volume

Chlorofluorocarbon (CFC)-12, in parts per trillion by volume

0 100 200 300 400 500 600

0 50 100 150 200 250 300

0

10

20

30

40

50

60

70

80

90

100

Chlorofluorocarbon (CFC)-113, 

in parts per trillion by volume

0

50

100

150

200

250

300

Chlorofluorocarbon (CFC)-11, 

in parts per trillion by volume

0

10

20

30

50

60

70

80

90

100

40

Chlorofluorocarbon (CFC)-113, 

in parts per trillion by volume

A

B

C EXPLANATION

Lumped-parameter

 flow model

 Piston

 Exponential

 Piston-exponential

 Binary mix 1

 Binary mix 2

 Binary mix 3

Well-field (wellhead) well

 W5 sample

 
56 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

respectively, for the intermediate and deep monitoring wells). 

Apparent ages for the Zarzamora monitoring wells (excluding 

the overburden well) are quite young in the deepest well (1.3 

years); the apparent age for the shallow Zarzamora monitoring 

well (27.5) approaches the deeper Timberhill monitoring well 

age. Apparent ages based on 3H/3He results for the well-field 

samples are similar (16.6–18.4 years), with the exception of 

W4, which yielded a much younger age (3.4 years). Depthdependent samples had apparent ages ranging from 0.8 to 21.7 

years, but the ages were not consistently related to depth or to 

pumping condition (fig. 35; table 19). These results are consistent with extensive mixing in this complex karst hydrogeologic system. The range of piston-flow-model ages for TANC 

study samples is similar to the range reported for Edwards 

aquifer unconfined groundwater samples by Musgrove and 

others (2010) of 1 to 52 years and with a median of 20 years. 

Selected geochemical constituents were compared with 

the ratio of 3

H/3H0, which, as noted earlier, is a proxy for the 

relative age of water (with relative ages becoming younger as 

3

H/3H0 values approach 1) (Böhlke, 2002). Inorganic geochemical parameters compared to 3

H/3H0 included specific conductance, Mg/Ca molar ratios, 87Sr/86Sr values, and dolomite 

SI. Specific conductance generally increases with increased 

groundwater residence time. Dolomite SIs, Mg/Ca ratios, and 

Sr isotopes have been demonstrated to be qualitative indicators of residence time in the Edwards aquifer (Musgrove and 

others, 2010). With longer residence time and greater extents 

of water-rock interaction, dolomite SIs approach equilibrium, 

Mg/Ca ratios increase, and 87Sr/86Sr values decrease toward 

values similar to the host aquifer rocks. A comparison of 

these constituents with 3H/3H0 ratios, however, does not indicate a consistent relation with interpreted groundwater age 

(fig. 36). The relation of 3H/3H0 with specific conductance and 

Mg/Ca ratios was not statistically significant. The relation of 

3

H/3H0 with dolomite SIs and 87Sr/86Sr values was significant 

(Kendall’s tau = 0.36 and -0.34, respectively). The relation 

was inverse, however, to that expected for these constituents 

with groundwater age: dolomite SIs approach equilibrium in 

younger apparent-age samples, and 87Sr/86Sr values approach 

values similar to the aquifer rocks in younger apparent-age 

samples. The relation of 3H/3H0 with dolomite SIs and 87Sr/86Sr 

values was strongly influenced by values for the Timberhill 

monitoring wells; if these data were not considered, the relations were no longer statistically significant. 

Similar to inorganic constituents, anthropogenic organic 

constituents were not clearly related to apparent age. Concentrations and detections of anthropogenic contaminants 

are generally expected to be higher in younger groundwater. 

However, the relation of 3H/3H0 with the number of detections 

of organic contaminants and with atrazine, DEA, and PCE 

concentrations was not significant (fig. 37). The relation with 

other frequently detected organic contaminants, such as simazine and chloroform, also was not significant. 

The absence of significant relations of inorganic geochemical indicators and anthropogenic constituents to apparent 

age indicates that mixing processes in this aquifer are complex 

and that hydrogeologic conceptual models used in groundwater age interpretations might not adequately account for 

mixing in this karst system. Age tracers in this aquifer provide 

insight into the young nature of the groundwater but might 

not readily allow for distinguishing the mixed water history 

or be well suited to distinguish relatively small differences in 

groundwater age as a result of mixing processes. This hypothesis is consistent with the relatively homogeneous geochemistry for many constituents in groundwater samples collected 

from the regional aquifer PSWs and from the well-field and 

monitoring wells. 

Depth-Dependent Water Chemistry

Variations in depth-dependent geochemical results can 

provide insight into water quality of different parts of the 

aquifer that might contribute water to the PSW, as well as 

differences in water quality in the Edwards aquifer relative 

to overburden units. Variations in geochemical results from 

different pumping conditions can provide insight into the 

distribution of groundwater flow paths contributing water to 

the PSW. Previous studies indicate that groundwater flow in 

the Edwards aquifer is focused in highly permeable units and 

is affected by faulting (Abbott, 1975; Woodruff and Abbott, 

1979; Maclay and Small, 1986; Maclay and Land, 1988; 

Sharp, 1990; Lindgren and others, 2011b). 

As described earlier in the sections “Geophysical and Depth-Dependent Flow Measurements” and 

Figure 33. Particle-track age distribution to selected publicsupply well for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public-supply wells, based on 

local-scale study model results described by Lindgren and others 

(2011b) in the San Antonio segment of the Edwards aquifer, southcentral Texas. 

<0.5 0.5 to <2 2–4.9 5–9.9 10–19.9 20–50 51–100 >100

Simulated particle-track traveltime, in years

0

10

20

30

40

50

Proportion of flow to public-supply well, in percent
Hydrogeologic Setting 57

“Depth-Dependent Samples,” flow measurements and groundwater samples were collected from W4 from three different 

depths (fig. 4) and under three different pumping conditions 

(ambient, moderate, and normal) to characterize the water 

quality of different parts of the aquifer that might contribute 

water to the PSW. The normal pumping condition is likely to 

be most representative of pumping conditions associated with 

the production of supply water and should have chemistry 

similar to surface discharge samples (wellhead samples) collected from the well field under normal production operations. 

As noted earlier, it was not possible to collect a surface 

discharge (wellhead) sample from W4; a sample was instead 

collected with the sample pump directly near the bottom of the 

casing (at a depth of approximately 320 ft).

Flow measurement results indicated that the distribution of the flow of water entering W4 during normal pumping 

conditions was complex but likely largely originated from the 

Kirschberg evaporite member (HGUs 8 and 9) and the combined leached and collapsed and cyclic and marine members 

(HGUs 3-5), with some contribution from the lower dolomitic 

Figure 34. Relation between sample collection date and tritium for groundwater samples collected for the study of the transport 

of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. A, Relation between sample 

collection date and initial tritium concentration (3

H0). B, Relation between sample collection date and tritium concentration (3H). 

Both A and B are shown with exponential mixing model based trendlines for expected 3

H0 and 3H concentrations for selected mean 

groundwater ages.

1950 1960 1970 1980 1990 2000 2010

Sample collection date

2

0

4

6

8

10

12

14

16

18

20

Initial tritium concentration,

 in tritium units 

0

1

2

3

4

5

6

 Tritium concentration,

in tritium units 

X

A

B

X

Exponential mixing model 

 mean groundwater age,

 in years

 0.5

 2

 3

 5

 8

 10

 12

 15

 17

 20

 50

Timberhill monitoring well

 sample

 Intermediate (T–IED)

 Deep (T–DED)

Zarzamora monitoring well

 sample

 Shallow (Z–SED)

 Intermediate (Z–IED)

 Deep (Z–DED)

Well-field (wellhead) well

 sample

 W2

 W3

 W4

 W5

 W6

Well-field (W4)

 depth-dependent 

 sample, all pumping

 conditions-depths

Nondetection, shown at

 the laboratory method

 reporting level

EXPLANATION
Figure 35. Schematic east-west (strike) cross section showing location of study area hydrogeologic units (HGUs) as modeled by Lindgren and otherat selected sample sites, and summary of groundwater apparent-age results based on tritium/helium-3 tracer measurements (piston-flow model agescentral Texas. 

Open interval for well-field wellsApproximate sampling interval for well-field (W4) depth-dependent  samples and monitoring well samplesPiston-flow-model groundwater apparent age, in years

EXPLANATION

WEST EAST

Public-supply

well field (W2–W6)

Simulated hydraulic head

HGU 11 Basal nodular member

HGU 10 Dolomitic member

HGU 7 Grainstone member

HGU 4 Leached and collapsed members, undividedHGU 3 Cyclic and marine members, undivided

HGU 1 Overburden (including various formations)

HGU 12 Trinity Group

HGU 6 Regional dense member

HGU 8 Kirschberg evaporite member

HGU 2 Georgetown Formation

HGU 5 High-conductivity zone

HGU 9 High-conductivity zone

Zarzamora 

Timberhill monitoring well c

monitoring well cluster

Aquifer

2 18.2±0.6

3 18.4±0.6

4 3.4±1.0

5 --

6 16.6±0.8

Ov --Sh27.DeInt11.

Intermediate

41.3 ± 2.1

Deep

31.6 ± 1.9

18.4±0.6

Depth-dependent (W4) pumping condition

Ambient Moderate Normal

Shallow -- 11.1 ± 1.0 0.8 ± 1.0

Intermediate 12.9 ± 0.8 21.7 ± 1.1 --Deep 13.5 ± 2.6 19.9 ± 0.9 --

 -- Age not resolvable
Figure 36. Relation between tritium to initial tritium ratio (3H/3H0) and selected geochemical constituents for groundwater samples collected for the s

anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. A, Specific conductance. B, Magnesium to calciisotope composition. D, Dolomite mineral saturation index.

550 560 570 580 590 600 610 620 630 640 650

Specific conductance, in

microsiemens per centimeter

0.100 0.150 0.200 0.250 0.300 0.350 0.400

Magnesium to calcium, molar ratio

0.7076 0.7077 0.7078 0.7079 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2

Strontium-87/strontium-86 isotopic ratio Dolomite, mineral saturation index

0.600.20.40.81.01.2

00.20.40.60.81.01.2

Tritium to initial tritium ratio Tritium to initial tritium ratio C D

A B

Kendall’s tau = -0.34 Kendall’s tau = 0.36

Old Young Old Young
Figure 37. Relation between tritium to initial tritium ratio (3H/3H0) and selected geochemical constituents for groundwater samples collected for the s

anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. A, Number of organic constituents detected. B, Dconcentration. C, Atrazine concentration. D, Tetrachloroethene (PCE) concentration.

0 1 2 3 4 5 6 7 8 9

Number of organic constituents detected

0.005 0.01 0.015 0.02

Deethylatrazine (DEA), 

in micrograms per liter

0 0.005 0.01 0.015 0.02 0.025 0.03

Atrazine, in micrograms per liter

0 0.1

0

0.2 0.3 0.4 0.5 0.6

Tetrachloroethene (PCE), in micrograms per liter

0.025

0.600.20.40.81.01.2

00.20.40.60.81.01.2

Tritium to initial tritium ratio Tritium to initial tritium ratio C D

A B

X

Old Young Old Young
Hydrogeologic Setting 61

member (HGU 10) (fig. 7). Under one pumping condition 

(described below), some loss of flow in the leached and collapsed members (HGUs 4 and 5) was observed. Intermediate 

depth-dependent samples were collected within the leached 

and collapsed members (HGUs 4 and 5), and the shallow 

depth-dependent samples were collected within the cyclic and 

marine members (HGU 3). The deep depth-dependent samples 

were collected from within the grainstone member (HGU 7) 

but are considered representative of water flowing upward in 

the wellbore from the Kirschberg evaporite member (HGUs 8 

and 9) and dolomitic member (HGU 10). 

Depth-dependent samples collected from W4 during 

normal pumping conditions indicated that, although much of 

the groundwater was coming from high-conductivity zones, 

the water quality throughout different HGUs was relatively 

homogeneous, indicative of substantial mixing in the aquifer. 

Geochemical results were compared for different sampling 

depths and flow conditions, as well as with samples from 

the monitoring wells. For comparison purposes between the 

depth-dependent samples and monitoring well samples, results 

were compared by HGU (fig. 38). A comparison by sample 

depth for the depth-dependent samples and well depth for the 

monitoring well samples is complicated by inferred faulting 

between the well-field and monitoring well locations. Faulting is inferred because of widespread occurrence in the study 

area and because of observed differences in depths to HGUs 

between the well-field PSWs and monitoring wells in the 

Zarzamora monitoring well cluster. 

There were generally minor differences in physicochemical properties and chemical and isotopic constituents in depthdependent samples (fig. 38); this observation is consistent 

with the hypothesis that water from the PSW is relatively well 

mixed and homogeneous regardless of pumping conditions. 

However, several constituents show some differences in depth 

profiles under different pumping conditions. The sample collected from the intermediate sampling interval (HGUs 4 and 5) 

under normal pumping conditions had a higher 87Sr/86Sr value 

(0.70789) than under ambient or moderate pumping conditions (fig. 38K). This value is higher than those for well-field 

samples, which had a narrow 87Sr/86Sr range of 0.70768 to 

0.70772. The sample collected from the intermediate and deep 

sampling intervals also had a higher boron (B) concentration 

under normal pumping conditions than under ambient and 

moderate pumping conditions (fig. 38N). Sr isotope compositions in the regional aquifer generally decrease to lower values 

with increased residence time, whereas B concentrations tend 

to be higher in the confined part of the aquifer (Musgrove 

and others, 2010). Although the 87Sr/86Sr and B concentration 

results for these depth-dependent samples were different from 

the remainder of the W4 and monitoring well samples, they 

were within the range of variability for the regional aquifer 

(Musgrove and others, 2010). Samples from the Timberhill monitoring wells had similar elevated 87Sr/86Sr values 

(fig. 38K). Samples collected from the Timberhill monitoring 

wells also had lower dolomite SIs, and the sample collected 

from the deep Timberhill monitoring well (T–DED) had a 

slightly lower Mg/Ca ratio. These results are consistent with 

the Timberhill monitoring well samples representing less 

geochemically evolved groundwater, although this hypothesis 

contrasts with apparent-age results for these samples (which 

had the oldest interpreted ages of 41.3 and 31.6 years for the 

intermediate and deep Timberhill monitoring well samples, 

respectively). When compared with the depth-dependent 

samples, results for the monitoring well samples show some 

minor differences in major ion concentrations, with slightly 

higher alkalinity and Ca concentrations and slightly lower 

SO4 concentrations and dolomite SIs, although the values are 

within the range of variability for the regional aquifer (Musgrove and others, 2010). 

PCE concentrations in samples from the shallow and 

intermediate Zarzamora monitoring wells (Z–SED and Z–

IED) were elevated with respect to the W4 depth-dependent 

samples, as well as with respect to regional aquifer PSW 

samples (fig. 38W; fig. 26; table 14). As discussed earlier (in 

the section “Organic Constituents”), PCE concentrations in 

samples from W4 were higher than the median for those from 

regional (confined) aquifer PSWs. These results suggest that 

the shallower Zarzamora monitoring wells and W4 have some 

hydraulic connection with urban contaminant sources. The 

most notable geochemical variability for the depth-dependent 

and monitoring well samples is for results of age-tracer 

data and corresponding model (apparent) ages (fig. 38). As 

discussed earlier (in the section “Groundwater Age Tracers 

and Age Distribution”), the variability in apparent-age results 

and their relation with other geochemical constituents indicates that age interpretations might not adequately account for 

extensive mixing processes in this complex karst system.

The water sample collected from the overburden monitoring well (Z–OVB) was markedly different in geochemistry 

from W4 depth-dependent samples, well-field samples, and 

monitoring well samples, with higher specific conductance, 

higher alkalinity, and higher concentrations of major ions and 

trace elements, NO3

, chloroform, and PCE and a different 

composition with respect to stable isotopes (fig. 38). These 

results indicate that there is likely not a substantial hydrologic 

connection between the overburden units and the Edwards 

aquifer at this location although, as noted earlier, higher concentrations of PCE in samples from the shallow and intermediate Zarzamora monitoring wells (Z–SED and Z–IED) are 

similar to the value measured in the sample from the overburden well. 

Temporal Variability in Water Chemistry

Karst aquifers are characterized by extreme variability 

and rapid response to changes in environmental, climatic, and 

hydrologic conditions, which exert a fundamental control on 

groundwater geochemistry and water quality (for example, 

Hess and White, 1993; Desmarais and Rojstaczer, 2002; 

Vesper and White, 2004; Winston and Criss, 2004). Temporal 

variability in hydrologic conditions for the Edwards aquifer 

is apparent in data for rainfall, aquifer recharge, water-level 
Figure 38. Geochemical results for selected constituents for groundwater samples collected from different depths and under different flow conditiotransport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas, 2004–9. Results are presented on the basis ounit (HGU) for monitoring-well samples and public-supply well depth-dependent samples; results for well-field samples and the overburden monitorincomparison. A, Specific conductance. B, Temperature. C, pH. D, Dissolved oxygen concentration. 

550 600 650

Specific conductance, in 

microsiemens per centimeter (μS/cm)

at 25 degrees Celsius

6.0 6.5 7.0 7.5 8.0

pH

20 22 24 26 28 30

Temperature, in 

degrees Celsius

2 3 

Dissolve

milligra

341

2–10*

5689

10

Hydrogeologic unit (HGU) 7

Z–OVB off scale

(971 μS/cm)

A B C D

Monitoring well Overburden (Z–OVB)  Zarzamora  Timberhill

EXPLANATION

Well-field (wellhead) well * W4 W2, W3, W5, W6

Well-field (W4) depth-dependent  sample, by pumping condition Ambient Moderate Normal * Open intervals to HGUs 2–10
Figure 38. E, Alkalinity concentration. F, Chloride concentration. G, Sulfate concentration. H, Calcium concentration.—Continued

Alkalinity, as calcium carbonate,

in milligrams per liter

Chloride, in

milligrams per liter (mg/L)

Sulfate, in 

milligrams per liter

Ca

milligra

220 240 260 280 30012 14 16 18 2020 25 30 3570 80 

341

2–10*

5689

10

Hydrogeologic unit (HGU) 7

Z–OVB off scale

(60.6 mg/L)

Z–OVB off scale

(97.6 mg/L)

E F G H

Monitoring well Overburden (Z–OVB)  Zarzamora  Timberhill

EXPLANATION

Well-field (wellhead) well * W4 W2, W3, W5, W6

Well-field (W4) depth-dependent  sample, by pumping condition Ambient Moderate Normal * Open intervals to HGUs 2–10
Figure 38. I, Magnesium to calcium molar ratio. J, Strontium to calcium molar ratio (×103). K, Strontium isotope composition. L, Dolomite mineral satu

0.1000 0.2000 0.3000 0.4000 0.7076 0.7077 0.7078 0.7079 0.7080 1.00 2.00 3.00 4.00 5.00 -0.8 -0.6 -0.4 

Strontium-87/strontium-86

isotopic ratio

Magnesium to calcium,

molar ratio

Strontium to calcium,

molar ratio (x103)

Dolomi

satura

341

2–10*

5689

10

Hydrogeologic unit (HGU) 7

I J K L

Monitoring well Overburden (Z–OVB)  Zarzamora  TimberhillError bar—Represents 2-sigma analytical uncertainty

EXPLANATION

Well-field (wellhead) well * W4 W2, W3, W5, W6

Well-field (W4) depth-dependent  sample, by pumping condition Ambient Moderate Normal * Open intervals to HGUs 2–10
Figure 38. M, Fluoride concentration. N, Boron concentration. O, Strontium concentration. P, Uranium concentration.—Continued

Fluoride, in

milligrams per liter

0.1 0.3 0.5 0.7 0.9 0.6 0.8 

Ura

microgr

400 450 500 550 600

Strontium, in

micrograms per liter (μg/L)

Boron, in

micrograms per liter (μg/L)

20 0 40 60 80 100

341

2–10*

5689

10

Hydrogeologic unit (HGU) 7

X

Z–OVB off scale

(270 μg/L)

Z–OVB off scale

(1,040 μg/L)

M N O P

Monitoring well Overburden (Z–OVB)  Zarzamora  Timberhill

EXPLANATION

Well-field (wellhead) well * W4 W2, W3, W5, W6

Well-field (W4) depth-dependent  sample, by pumping condition Ambient Moderate Normal * Open intervals to HGUs 2–10

Nondetection, shown at the laboratory method reporting level

X
Figure 38. Q, Nitrate concentration. R, Delta nitrogen-15 of nitrate composition. S, Delta oxygen-18 composition. T, Groundwater apparent age (base

age tracers).—Continued

1 2 3 4

Nitrate, in milligrams per liter,

as nitrogen

-4.6 -4.4 -4.2 -4.0 -3.8 -3.6 6.5 7.0 7.5 8.0 8.5

Delta nitrogen-15 of 

nitrate, in per mil

Delta oxygen-18,

 in per mil

10 0 20 

Appar

in years (pist

341

2–10*

5689

10

Hydrogeologic unit (HGU) 7

Q R S T

Monitoring well Overburden (Z–OVB)  Zarzamora  Timberhill

EXPLANATION

Well-field (wellhead) well * W4 W2, W3, W5, W6

Well-field (W4) depth-dependent  sample, by pumping condition Ambient Moderate Normal * Open intervals to HGUs 2–10
Figure 38. U, Atrazine concentration. V, Deethylatrazine (DEA) concentration. W, Tetrachloroethene (PCE) concentration. X, Trichloromethane (chlor

Continued

0 0.01 0.02 0.03 0.04

Atrazine, in

micrograms per liter

0.1 

Trichloro

(chloro

microgram

0.1 0.2 0.3 0.4 0.5

Tetrachloroethene (PCE), 

in micrograms per liter

0.01 0 0.02 0.03

Deethylatrazine (DEA), in

micrograms per liter

0 0

341

2–10*

5689

10

Hydrogeologic unit (HGU) 7 X

X

U V W X

Monitoring well X Overburden (Z–OVB)  Zarzamora  Timberhill

EXPLANATION

Well-field (wellhead) well * W4 W2, W3, W5, W6

Well-field (W4) depth-dependent  sample, by pumping condition Ambient Moderate Normal * Open intervals to HGUs 2–10

Nondetection, shown at the laboratory method reporting level
68 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

altitudes in wells, and springflow (for example, fig. 6). Temporal changes in hydrologic conditions such as water-level 

altitudes, recharge, groundwater traveltimes, and flow routing 

affect hydrogeologic processes, including water-rock interaction processes, and dilution and mixing of recharge, which 

affect water quality. Rapidly changing hydrologic conditions 

and a continuum of flow pathways from matrix flow to conduit flow imply that hydrogeologic processes might operate 

on different temporal and spatial scales in different parts of 

the aquifer. For example, groundwater dominated by matrix/

diffuse flow or less affected by focused recharge might exhibit 

less temporal variability than would groundwater affected by 

focused recharge and conduit flow. 

Previous work in the Edwards aquifer has demonstrated 

temporal variability in geochemistry and water quality over 

multiple time scales in response to changes in hydrologic 

conditions (Musgrove and Banner, 2004; Mahler and others, 

2006; Mahler and Massei, 2007; Mahler, 2008; Musgrove 

and others, 2010; Wong and others, 2011). In conjunction 

with samples collected for this study, historical data for 

samples collected from two wells in the well field extend over 

an 11-year period, from 1998 through 2009. Historical data 

collected from these two PSWs (W3 and W6) indicate that 

geochemistry of the confined groundwater produced by the 

well field has varied in response to changes in hydrologic 

conditions over this time period. For example, variability in 

Mg/Ca molar ratios, indicative of geochemical evolution 

processes, is consistent with regional-scale changes in hydrologic conditions. Higher Mg/Ca ratios in PSW groundwater 

samples, indicative of longer groundwater residence times, 

are correlated with lower water levels in the Bexar County 

index well (J–17); lower water levels reflect drier regional 

hydrologic conditions (figs. 6 and 39). The small range of 

variability for historical samples from the well field relative to 

regional aquifer variability (Musgrove and others, 2010), 

as well as similar Mg/Ca ratios relative to the median value 

for the regional aquifer PSW samples (0.32), is consistent 

with the hypothesis that the well-field PSWs produce water 

typical of the confined regional aquifer. In comparison with 

groundwater from shallow unconfined wells, groundwater 

from most confined aquifer wells, unless intersecting a fastflow conduit, is likely dominated by longer residence time 

matrix flow, which would be accompanied by attenuation of 

inputs from storm and recharge events. The geochemistry 

of matrix groundwater is likely less variable and changes 

more slowly in response to longer term regional hydrologic 

conditions. Relatively rapid changes in geochemistry have 

been documented for unconfined wells in the vicinity of the 

local-scale study area (Musgrove and others, 2010), but the 

time scales of geochemical variability for the confined aquifer 

in response to recharge events has, to date, been largely 

undocumented.

One of the well-field PSWs (W6) and four selected monitoring wells (Zarzamora monitoring wells Z–SED, Z–IED, 

and Z–DED and an upgradient unconfined monitoring well, 

AY–68–27–610) were sampled several times in response to a 

storm event that supplied recharge to the aquifer in October 

2009 (fig. 5; table 4). Event sampling is described earlier in 

the section “Collection of Water Samples.”

Time-series results for water-level altitudes and (or) geochemical constituents from W6 and sampled monitoring wells 

during the period of event sampling were compared with the 

regional water-level altitude in the Bexar County index well 

(J–17) (fig. 40). Water-table altitudes rose in the Bexar County 

index well (J–17), reflecting regional hydrologic conditions, 

as well as in the sampled monitoring wells, in response to 

the recharge event (fig. 40) (water-level altitudes were not 

measured in W6). The geochemistry in the upgradient monitoring well is notably distinct from that of W6 and the Zarzamora monitoring wells. The upgradient well is characterized 

by higher specific conductance, Sr isotope composition, and 

concentrations of NO3

 and chloroform and by lower 

Mg/Ca molar ratios, dolomite SIs, and PCE concentrations 

(fig. 40). The lower Mg/Ca ratios and dolomite SIs and higher 

Sr isotope compositions measured in samples from the upgradient monitoring well are consistent with the hypothesis that 

groundwater from the upgradient unconfined recharge zone 

has undergone less water-rock interaction than has groundwater sampled from confined PSWs and Zarzamora monitoring 

wells. This is consistent with results for shallow unconfined 

monitoring wells presented in Musgrove and others (2010), 

which indicated that groundwater from the shallow unconfined 

aquifer is less geochemically evolved relative to the deeper 

unconfined and confined part of the aquifer. Higher concentrations of NO3

 (2.62–2.99 mg/L) and chloroform (0.066–0.192 

μg/L) in samples from the upgradient unconfined monitoring 

well might be indicative of local sources of these constituents 

to this well; these concentrations are higher than the median 

values for shallow/urban unconfined groundwater (1.85 mg/L 

and 0.032 μg/L, respectively) as described by Musgrove and 

others (2010). Lower PCE concentrations in samples from 

the upgradient unconfined monitoring well indicate that this 

well is not affected by local PCE sources, unlike the well-field 

wells and the Zarzamora monitoring wells.

Geochemical variability in response to the sampled 

recharge event is generally small in the well-field PSW and 

the monitoring wells in comparison to the range of geochemical variability observed in the regional aquifer. These 

results are consistent with the hypothesis that the response 

to individual recharge events in the confined aquifer, unless 

intersecting conduit flow paths, might be attenuated by mixing 

processes along regional flow paths. Nonetheless, numerous 

geochemical constituents in W6 and the monitoring wells 

changed in response to the sampled recharge event. Recharging water associated with a rain event would likely be more 

dilute than groundwater with longer residence time; although 

specific conductance showed minor variability in response to 

the recharge event, Cl concentrations showed a dilution curve 

(an initial decrease, then subsequent increase) in W6 and the 

monitoring wells as regional water levels rise, consistent with 
Hydrogeologic Setting 69

Figure 39. Historical magnesium to calcium molar ratio data for well-field public-supply wells sampled for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas. A, Time-series (1997–2009) of Bexar County 

index well (J–17) water-level altitude (Edwards Aquifer Authority, 2009) and historical magnesium to calcium molar ratios for TANC 

study well-field wells (W3 and W6). B, Relation between Bexar County index well (J–17) water level altitude and historical magnesium to 

calcium molar ratios for TANC study well-field wells (W3 and W6).

0.240 0.260 0.280 0.300 0.320 0.340 0.360

Magnesium to calcium, molar ratio

June 1997

June 1999

June 2001

June 2003

June 2005

June 2007

June 2009

Date

600

610

620

630

640

640

650

660

670

680

690

700

710

650

660

670

680

690

700

710

720

730

Magnesium to calcium, molar ratio

0.240

0.260

0.280

0.300

0.320

0.340

0.360

Bexar County index well (J–17) water-level altitude, 

in feet above National Geodetic Vertical Datum of 19291

Bexar County index well (J–17) water-level altitude, 

in feet above National Geodetic Vertical Datum of 19291

Bexar County

index well (J–17)

A

B

Kendall’s tau = -0.65 (all data)

W3 W6

Well-field public-supply well

EXPLANATION

W3 W6

Well-field public-supply well

1 EXPLANATION

 Source agency reports water-level

 altitude referenced to sea level

 (Edwards Aquifer Authority, 2009)
Figure 40. Geochemical results for selected constituents in groundwater samples collected in response to a rain event (October through Novembertransport of anthropogenic and natural contaminants (TANC) to public-supply wells, south-central Texas. Water-level altitude in Bexar Country index comparison. 

A, Water-level altitude. 

B, Specific conductance. 

C, Temperature. 

D, Delta oxygen-18 composition. 

E, Chloride concentration. 

F, Strontium 

4/1 5/1 6/1 7/1 8/1 9/1 

Date (2009)

4/1 5/1 6/1 7/1 8/1 9/1 10/1 11/1 12/1 

Date (2009)

650660670

680680 

640650660670

650640 680 640 660670

Bexar County index well (J–17) water-level altitude, 

in feet above National Geodetic Vertical Datum of 19291

1 Source agency reports water-level

 altitude referenced to sea level (Edwards Aquifer Authority, 2009)

232425262728

Temperature, 

In degrees Celsius

170165175180185190195200205

Water-level altitude, in

feet below land surface

212022

15.5

16.015.0

16.5

17.0

17.5

18.019.0

18.5

Chloride, in

milligrams per liter

-4.4-4.3-4.2-4.1-4.0-3.9-3.8-3.7-3.6-3.5-4.5

Delta oxygen-18, in per mil

560540580600

Specific conductance, in 

microsiemens per centimeter 

at 25 degrees Celsius 620 640

660680

0.70810.7082

0.7080

0.70770.70780.7079

Strontium-87/strontium-86

isotopic ratio

A

C

E

B

D

F

Well-field well (W6)Monitoring well Z–SED Z–IED Z–DED AY–68–27–610Bexar County index well (J–17)  water-level altitude1

EXPLANATION

Analytical uncertainty—Represents 2-sigma analytical uncertainty and, as shown, is representative of each data point
Figure 40.

G, Nitrate concentration. 

H, Magnesium to calcium molar ratio. I, Dolomite mineral saturation index. 

J, Tetrachloroethene (PCE) concentra

(chloroform) concentration. L, Bromoform concentration.—Continued 

4/1 5/1 6/1 7/1 8/1 9/1 

Date (2009)

4/1 5/1 6/1 7/1 8/1 9/1 10/1 11/1 12/1 

Date (2009)

650660670

680

680

640650660670

650640680

640

660670

0

0

0.05

0.10

0.15

0.20

0.25

0.10.30.50.70.9

0

0.20.40.60.81.0

1.2

0.2000.1800.2200.2400.2600.2800.3000.320

1.51.71.92.12.32.52.72.92.95

-0.9-0.7-0.5-0.3-0.1

Magnesium to calcium,

Nitrate, in 

molar ratio

milligrams per liter as nitrogen

Dolomite,

mineral saturation index

Trichloromethane (chloroform), 

in micrograms per liter

Tetrachloroethene (PCE), in 

micrograms per liter

Bromoform, in

micrograms per liter

0

XXX 

X X

G

H

I J

K L

Well-field well (W6)Monitoring well Z–SED Z–IED Z–DED AY–68–27–610Bexar County index well (J–17)  water-level altitude1

EXPLANATION

Nondetection, shown at the laboratory method reporting level

X

Bexar County index well (J–17) water-level altitude, 

in feet above National Geodetic Vertical Datum of 19291

1 Source agency reports water-level

 altitude referenced to sea level (Edwards Aquifer Authority, 2009)
72 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

temporary dilution during the event following by a return to 

ambient conditions (fig. 40E). The decrease in Cl concentration was accompanied by decreases in NO3

 concentration and 

Mg/Ca ratios (fig. 40). Mg/Ca ratios at W6 and the Zarzamora 

monitoring wells showed a dilution curve, as did dolomite 

SIs. These results are consistent with previous studies that 

have proposed that aquifer NO3 concentrations are diluted by 

incoming recharge; lower Mg/Ca ratios and dolomite SIs are 

consistent with shorter residence times that would be associated with recent, less geochemically evolved recharge (Musgrove and others, 2010). The increase in regional water levels 

associated with the recharge event is also accompanied by an 

increase and subsequent decrease in PCE concentrations in 

W6 and the two shallowest Zarzamora monitoring wells 

(Z–SED and Z–IED), characteristic of a breakthrough curve. 

This response is consistent with other PSW results, which 

indicate that the well field and in particular the Zarzamora 

monitoring wells are affected by a local PCE source and 

receive recharge with higher PCE concentrations. 

Chloroform concentrations were low at W6 and the Zarzamora monitoring wells relative to the upgradient monitoring 

well, where chloroform concentration increased during the 

event sampling period (fig. 40K). Bromoform was not detected 

at any of the monitoring wells during event sampling, but 

concentrations show a breakthrough curve at W6. This result 

is consistent with relatively high bromoform concentrations 

measured in the well field in comparison with regional aquifer 

PSW and monitoring well samples (fig. 26) and indicates that 

W6 is affected by a local bromoform source. Chloroform and 

bromoform are drinking-water chlorination byproducts that 

are commonly detected nationwide, which is in part attributed 

to the recycling of chlorinated waters (Zogorski and others, 

2006). Backflow to supply wells or the possible use of treated 

water as a downhole lubricant of well pumps are potential 

sources of chloroform and bromoform to supply wells.

Processes Affecting Transport 

of Natural and Anthropogenic 

Contaminants to the Public-Supply 

Well

Sources of Water and Solutes and Movement to 

Supply Wells

Surface water from losing streams is the primary source 

of recharge in the regional aquifer and the local-scale study 

area. Stable isotopes of δD and δ18O indicate that this water 

is meteoric in origin. Some evaporation might affect recharge 

and associated groundwater near specific recharge locations 

(Musgrove and others, 2010). Groundwater compositions 

and dissolved-ion sources reflect processes of water-rock 

interaction with the host limestone aquifer rocks. Previous 

studies indicate that groundwater in the unconfined part of the 

aquifer geochemically evolves to the composition of groundwater in the confined part of the aquifer (Musgrove and others, 

2010). Groundwater flow in the San Antonio segment of the 

aquifer is generally west to east, although model-derived and 

tracer-inferred flow characteristics can vary markedly in this 

karst aquifer (Lindgren and others, 2009). The major components of model-derived groundwater flow in the TANC 

local-scale model area are (1) from the recharge zone southward into the confined zone and (2) from west to east in the 

confined zone (Lindgren and others, 2011b). 

Anthropogenic sources that might influence groundwater 

quality include septic systems, leakage from municipal water 

and wastewater systems, and general industrial, commercial, 

or residential use of fertilizers, pesticides, and VOCs. There 

are only minor agricultural areas in the region (fig. 10), and 

these are primarily downgradient of the local-scale study 

area. There are point sources in the study area and vicinity of 

the well field for some of these contaminants (figs. 11–14), 

although nonpoint sources are also likely given the widespread 

detections of these contaminants in samples from the regional 

aquifer PSWs. Previous work has indicated that the urban 

environment is a potential source of organic contaminants to 

the aquifer (Musgrove and others, 2010).

Results for TANC study groundwater samples had no 

anthropogenic contaminants at levels of regulation, but they 

did contain several organic contaminants at low concentrations (mostly less than 1 μg/L). Frequent low-level detection 

of several pesticides and VOCs in samples from the regional 

aquifer PSWs indicates that sources of pesticides and VOCs 

are widely distributed in the regional Edwards aquifer. The 

primary pesticides detected were atrazine, its degradate DEA, 

and, at less frequent detections, simazine and prometon. The 

primary VOCs detected were PCE and chloroform, and there 

were less frequent detections of other THMs (bromoform, 

dibromochloromethane, and bromodichloromethane). PCE 

detections and concentrations in samples from the well-field 

wells and Zarzamora monitoring wells were higher than those 

for samples from the regional aquifer PSWs. There are point 

sources in the vicinity of the well field for PCE, including 

a known plume (Bandera Road Groundwater Plume) to the 

northwest of the well field. Groundwater flow directions are 

consistent with the possibility that this might be a possible 

source of PCE to the well-field wells and Zarzamora monitoring wells, although other sources are also possible. Spatial 

variations in PCE in the study area indicate that higher PCE 

concentrations are associated with the urban San Antonio area, 

with a cluster of higher concentrations in the direct vicinity 

and north of the well field (fig. 41).

Nitrate concentrations in the aquifer were below levels of 

regulation for drinking water. Well-field samples had a median 

NO3

 concentration of 2.2 mg/L. Nitrate concentrations in the 

regional groundwater wells suggest that NO3 in the aquifer 

likely results from nonpoint sources, although a few wells 

with NO3

 concentrations greater than 3 mg/L might be affected 
Processes Affecting Transport of Natural and Anthropogenic Contaminants to the Public-Supply Well 73

by local NO3 sources (fig. 42). Previous studies have proposed 

that surface-water recharge dilutes background groundwater 

NO3 concentrations, and lower NO3 concentrations are generally associated with groundwater collected from unconfined 

recharge-zone wells (Mahler and others, 2006; Musgrove and 

others, 2010). Nitrate concentrations are also generally higher 

in samples from the urban San Antonio area than outside 

(Musgrove and others, 2010; fig. 42). Oxic conditions indicate 

that denitrification is not an important process in this aquifer, 

and thus, no natural NO3 attenuation is likely to occur. Near 

the downgradient saline-zone boundary, however, deeper 

Edwards aquifer groundwater can be locally affected by mixing with more saline and less oxic downdip water. A small 

number of groundwater samples from regional wells show 

evidence for mixing with more saline and less oxic downdip 

groundwater, which might also be associated with downdip 

water moving up along faults (Oetting and others, 1996; Musgrove and others, 2010). Groundwater in the local-scale and 

regional-scale study areas contains no natural contaminants 

(such as U and As) at levels of concern, and aquifer conditions are not conducive to increases in concentrations of these 

contaminants. 

Results for age tracers indicate that groundwater reaching 

the well field had a median apparent age of 17 years. The largest fraction of water reaching W4, however, might be younger, 

with a piston-flow-model age of 3 years. These results are 

consistent with particle-tracking results from hydrologic 

modeling for the study area (Lindgren and others, 2011b) 

indicating that greater than 85 percent of particle tracks to W4 

have traveltimes of less than 5 years and that greater than 95 

percent have traveltimes less than 10 years (fig. 33). Apparent 

ages are not well correlated with other geochemical tracers of 

residence time (for example, Mg/Ca ratios, dolomite SIs, and 

Sr isotopes) (fig. 36). Aquifer units were found to have zones 

of preferential flow, although samples dominated by groundwater from different stratigraphic units were not geochemically distinct. Aquifer units are composed of Cretaceous-age 

limestone with minor variations in geochemistry (tables 5 and 

6). Groundwater collected from W4 was relatively homogeneous and well mixed under a variety of pumping conditions 

for numerous geochemical constituents, with a notable exception of age tracers. These results suggest that mixing processes 

in the aquifer are complex and that hydrogeologic conceptual 

models used for age interpretations might not adequately 

account for mixing processes in this aquifer. 

Supply-Well Vulnerability to Natural and 

Anthropogenic Contaminants

Like many karst aquifers, high porosity and permeability 

and rapid flow of recharging surface water through conduits, 

with little to no filtration, render the Edwards aquifer highly 

susceptible to contamination. Constituents of concern in 

the Edwards aquifer for the long-term sustainability of the 

groundwater resource include NO3

 and organic contaminants. 

Measured concentrations of NO3 and organic contaminants 

are currently low relative to levels of regulation. Nonetheless, 

the dominance of very young groundwater in the TANC study 

area and, specifically, groundwater that reaches the well field 

indicates that the aquifer and water supply are vulnerable to 

contamination.

Other TANC studies have determined that changes 

in pumping conditions can affect water quality (Katz and 

others, 2007; Landon and others, 2008; Jurgens and others, 

2008; Brown and others, 2009; Bexfield and others, 2011). In 

contrast, for the Edwards aquifer TANC study area, although 

changes in pumping conditions might change the distribution 

of groundwater flow paths contributing water to the well field, 

under all pumping conditions the majority of the groundwater was young and, as such, is susceptible to anthropogenic 

contaminants. Borehole imaging of W4 revealed large solution 

features, consistent with high connectivity throughout the 

aquifer. Although zones of preferential flow were determined 

for W4, groundwater samples from different stratigraphic units 

could not be distinguished geochemically, and no water-quality effects were discernable on the basis of sample stratigraphy. The location of the PSW within an urban area increases 

the vulnerability of the water supply and its potential susceptibility to contamination.

Groundwater geochemistry and water quality in the 

Edwards aquifer is affected by changes in hydrologic conditions. Temporal changes in hydrologic conditions such as 

water-level altitudes, recharge, groundwater traveltimes, and 

flow routing affect hydrogeologic processes, including the 

extent of variability in water-rock interaction processes, dilution of recharge, and associated geochemistry. Specifically 

for the Edwards aquifer, drier hydrologic conditions are likely 

associated with lower concentrations of atrazine and higher 

concentrations of nitrate (Musgrove and others, 2010), but 

this relation for individual wells is likely affected by specific 

flow paths. For example, groundwater dominated by matrix/

diffuse flow or less affected by focused recharge might be less 

variable in water quality than groundwater affected by focused 

recharge and conduit flow. 

Water-quality data from the regional aquifer PSWs and 

well-field monitoring wells, collected over a range of depths 

in the Edwards aquifer, show little variability. Regional (confined) aquifer PSW samples from the same stratigraphic units 

where the aquifer is deeper in the subsurface (samples from 

wells greater than 1,000 ft in depth), however, show notable 

chemical differences from the rest of the regional aquifer, with 

lower concentrations of organic contaminants and geochemical evidence for more evolved groundwater compositions.

Understanding how land use affects water quality of 

PSWs is important because of the strong influence of land 

use on water quality and the rapid pace at which changes in 

land use are occurring in the urban part of the study area. 

This understanding has practical implications with respect 

to human health (McMahon and others, 2008) but might be 

complicated by spatial and temporal variations in land use 

(Brawley and others, 2000; Hiscock and others, 2007) and by 
Figure 41. Hydrogeologic setting, location of, and ranges of tetrachloroethene (PCE) concentration (highest value shown where multiple measuremestudy period) for regional aquifer public-supply wells sampled for the study of the transport of anthropogenic and natural contaminants (TANC) to pubAntonio segment of the Edwards aquifer, south-central Texas, 2004–9.

Contributing zone

Recharge zone

Confined zone

CALDWE

ATASCOSA

BEXAR

GUADALUPE

COMAL

KENDALL

HAYS

GILLESPIE BLANCO

TRAVIS

ZAVALA FRIO

KINNEY UVALDE MEDINA

BANDERA

REAL

EDWARDS KERR

Hondo

Uvalde

Brackettville

Castroville

San

Antonio

New

Braunfels

San

Marcos

Austin

Creek

Nueces River

Nueces River

River

Onion

Barton Creek

Blanco Creek

Sabinal River

Hondo

Creek

Medina River

Cibolo Creek

Salado Creek

Guadalupe River San Marcos River

Blanco River

VerdeCreek

Nueces River

Lake

Travis

Canyon Lake

MedinaLake

West

Frio

Colorado River

!

!

!

!!

!!

!

!!

!

!

!!

!

!

!

!

!

!!

!

!

!!

!

!

!

!

!

!

!

!

!

!

!

!

!

!!

!

!!

Lo

st

Edwa

0 15 30 15 30 45 

98°

99°

100°

30°

29° Base from Aquifers: Texas Water Development Board (2007); 

Ashworth and Hopkins (1995), 1:250,000 Counties: Texas General Land Office (1999), 1:24,000Cities: Texas Natural Resources Information System digital data (1995)Projection: Texas Centric Mapping System-Albers equal area Datum: North American Datum of 1983

Tetrachloroethene (PCE) concentration, in micrograms per liter, for regional aquifer public-supply wells, well-field wells, and monitoring wells

 Not detected Greater than or equal to 0.01 and less than or equal to 0.10 Greater than 0.10 and less than or equal to 0.40 Greater than 0.40 and less than or equal to 0.80 Greater than 0.80

Edwards aquifer—San Antonio segment bound on the easternmost and westernmost ends by groundwater divides Recharge zone (unconfined) Confined zoneUrban area boundaryLocal-scale study area boundaryGroundwater divide

EXPLANATION

!!!!!
Figure 42. Hydrogeologic setting, location of, and ranges of nitrate concentration (highest value shown where multiple measurements were made dregional aquifer public-supply wells sampled for the study of the transport of anthropogenic and natural contaminants (TANC) to public-supply wells iof the Edwards aquifer, south-central Texas, 2004–9.

Contributing zone

Recharge zone

Confined zone

CALDWE

ATASCOSA

BEXAR

GUADALUPE

COMAL

KENDALL

HAYS

GILLESPIE BLANCO

TRAVIS

ZAVALA FRIO

KINNEY UVALDE MEDINA

BANDERA

REAL

EDWARDS KERR

Hondo

Uvalde

Brackettville

Castroville

San

Antonio

New

Braunfels

San

Marcos

Austin

Creek

Nueces River

Nueces River

River

Onion

Barton Creek

Blanco Creek

Sabinal River

Hondo

Creek

Medina River

Cibolo Creek

Salado Creek

Guadalupe River San Marcos River

Blanco River

VerdeCreek

Nueces River

Lake

Travis

Canyon Lake

MedinaLake

West

Frio

Colorado River

!

!

!!

!!

!

!!

!

!

!!

!

!

!

!

!

!!

!

!

!!

!

!

!

!

!

!

!

!

!

!

!

!

!

!!

!

!!

Lo

st

Edwa

0 15 30 15 30 45 

98°

99°

100°

30°

29° Base from Aquifers: Texas Water Development Board (2007); 

Ashworth and Hopkins (1995), 1:250,000 Counties: Texas General Land Office (1999), 1:24,000Cities: Texas Natural Resources Information System digital data (1995)Projection: Texas Centric Mapping System-Albers equal area Datum: North American Datum of 1983

Nitrate concentration, in milligrams per liter, for regional aquifer public-supply wells, well-field wells, and monitoring wells

 Not detected Less than or equal to 1.0 Greater than 1.0 and less than or equal to 2.0 Greater than 2.0 and less than or equal to 3.0 Greater than 3.0

Edwards aquifer—San Antonio segment bound on the easternmost and westernmost ends by groundwater divides Recharge zone (unconfined) Confined zoneUrban area boundaryLocal-scale study area boundaryGroundwater divide

EXPLANATION

!!!!!
76 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

mixing waters of different age and source in long well screens 

that are typical in PSWs (Kauffman and others, 2001; Böhlke, 

2002; Weissmann and others, 2002; Osenbrück and others, 

2006; Eberts and others, 2006). Age distributions of water captured by individual long-screen wells in some aquifer settings 

might span years to millennia or more (Kauffman and others, 

2001; Weissmann and others, 2002; McMahon and others, 

2004; Plummer and others, 2004; Sturchio and others, 2004; 

Clark and others, 2007; Starn and Brown, 2007; Crandall and 

others, 2008; Jurgens and others, 2008). These age distributions in captured water could have positive and negative 

consequences for the quality of water from a PSW, such as 

dilution of contaminant concentrations and long lag times in 

responding to land use change or best management practices. 

An important implication of long lag times is that, in spite of 

corrective management actions, contaminant concentrations in 

water from PSWs could increase in the future (before eventually decreasing) as the fraction of already contaminated young 

recharge captured by wells increases (Fogg and others, 1999; 

Böhlke, 2002; Fogg and LaBolle, 2006). 

Although TANC study results for the local-scale study 

area indicate that long lag times are not a likely feature of 

the Edwards aquifer, understanding the potential response of 

water quality in the PSW to land-use changes, and the resulting time scales of response in the PSW, is useful for water 

resource management. A post-MODPATH spreadsheet model 

(L.J. Kauffman, U.S. Geological Survey, written commun., 

2011) that incorporates MODPATH particle-tracking results 

(Pollock, 1994) and contaminant reaction (degradation) processes was used to analyze the response of water quality in the 

selected PSW to land-use change. The water-quality response 

to land-use change was dependent on age distributions of 

water captured by the PSW. Groundwater flow and particletracking simulations are described by Lindgren and others 

(2011b). Flow and traveltimes associated with the particle 

tracking to the PSW were used to estimate relative contaminant concentrations in the PSW; a hypothetical conservative 

(nonreactive) contaminant was modeled. A relative contaminant concentration was assigned to each particle on the basis 

of the traveltime and by assuming an input concentration 

history of the contaminant in the contributing area (recharge 

zone), as described below. Flux-weighted average contaminant 

concentrations for the PSW were determined by summing the 

product of concentrations assigned to each particle by the total 

flow associated with that particle and dividing by the total 

flow. 

Simulated age distribution for contributing-area particles of the PSW ranged from less than 1 to 342 years, with 

a median of 2.0 years (fig. 33). Particle-track results indicate 

that 99 percent of the PSW water was less than 50 years old 

and that 88 percent of the water was less than 5 years old. 

Younger water (less than 50 years old) is more likely to be 

affected by human activities, and if present, most anthropogenic contaminants would be associated with younger water. 

As previously described, these model results concur with the 

conceptual understanding that a large fraction of water in the 

Edwards aquifer, and particularly in the PSW, is young (less 

than 50 years old). Water samples from the PSW, other wells 

in the well field, and other PSWs completed in the regional 

aquifer contained detectable concentrations of a small number 

of some pesticides and VOCs (fig. 25; tables 14–17). Natural 

attenuation processes are also likely to be limited in flow systems with young groundwater, in particular for conditions or 

contaminants where degradation processes are slow (Chapelle 

and Bradley, 1999; McMahon and others, 2008), such as is the 

case in this oxic aquifer. In flow systems with a higher fraction 

of older water (that is, greater than 50 years old), that fraction 

could dilute anthropogenic contaminant concentrations when 

waters of different ages mix within the aquifer and the open 

borehole of a PSW (Osenbrück and others, 2006). 

In a model-forecasting exercise, slug inputs were used 

to examine the range in lag times, dilution, and degradation 

that might be expected at the PSW. Results of this exercise 

might be representative of a rapid land-use change overlying 

the contributing area (recharge area) of a PSW in this aquifer and might represent how quickly the aquifer responds to 

mitigation. A hypothetical contaminant was introduced over 

the PSW-model-contributing area continuously for 30 years. 

Contaminant input concentrations were equal to 1, and all 

simulated concentrations for the well were relative to this unit 

value. After 30 years, the contaminant input returned to zero. 

The hypothetical responses at the PSW for (1) a simulation 

with no contaminant degradation and (2) a simulation with 

degradation at a first-order reaction kinetics degradation rate 

Figure 43. Results of forecasting exercise of time-series of 

hypothetical contaminant concentrations at the selected publicsupply well for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public-supply wells; results 

are based on 30 years of contaminant input (at a relative 

concentration of 1) in the modeled contributing area (based on 

model and particle-track results described in Lindgren and others, 

2011b).

0 10 20 30 40 50 60 70 80

Elapsed time, in years

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Relative contaminant concentration

Input

period

No degradation

With degradation (0.1)

EXPLANATION
Summary 77

of 0.1/year (10 percent per year) are illustrated in figure 43. 

For both responses (curves in fig. 43), concentrations at the 

PSW began to rise within 1 year after loading began and rose 

quickly to reach 50 percent of peak concentration in 3 and 

4 years, respectively. The nondegradation curve continued 

to rise rapidly until about 5 years, when 77 percent of peak 

concentration was reached. Concentrations continued to rise 

for both curves until peak concentrations were reached at the 

end of the input period of 30 years. Maximum concentrations 

were 98 percent of input for the nondegradation curve and 73 

percent of input for the with-degradation curve. Once the input 

was stopped after 30 years, both simulations responded with a 

rapid drop in concentration. Concentration decreased to about 

50 percent of input in 3 years in the nondegradation simulation 

and in a little more than 2 years for the degradation simulation. Concentration decreased to 25 percent of input in about 

5 years and in less than 4 years, respectively. Although peak 

concentrations dropped quickly after input ceased, 32 and 12 

years were required, respectively, to flush 99 percent of the 

hypothetical contaminant and achieve near-background conditions (table 20 at end of report). 

Lag times would be expected to be shorter for wells with 

large fractions of young water (McMahon and others, 2008), 

such as observed for this study, than for wells with smaller 

fractions of young water. The effect of short-circuit pathways, 

for example karst conduits, in the flow system on the movement of young water to the PSW could greatly alter contaminant arrival times compared to what might be expected from 

advection in a system without short circuiting. This observation is particularly valid for karst such as the Edwards aquifer: 

numerous voids are present in wells completed in this aquifer, 

including the PSW. The simulated concentrations show rapid 

initial response at the beginning and end of chemical input, 

followed by more gradual response as older water moves 

through the system. The nature of karst groundwater flow, 

where flow dominantly occurs via conduit flow paths, could 

lead to relatively rapid water-quality responses to land-use 

changes.

This analysis did not consider chemical storage and 

traveltimes in the unsaturated zone, dispersion/diffusion, or 

transient flow conditions in the aquifer, which might yield 

substantially different results. Storage of large amounts of 

chemical mass in, and long transit times through, unsaturated 

zones could result in longer flushing times, as well as longer arrival and lag times, in the aquifer. The impact of not 

considering dispersion is likely minimized because the focus 

herein is for large pumping wells and nonpoint sources of 

contamination. Transient conditions in the flow system could 

result in more complex areas contributing recharge and more 

complex groundwater age distributions than were assessed 

here and should be considered in future studies (Franke and 

others, 1998; Rock and Kupfersberger, 2002). Spatial variability in input, which would likely have considerable effect 

on concentrations and movement of contaminants, also was 

not considered. Short-circuit pathways, such as karst conduits, 

in some PSW contributing areas can affect age distributions 

by allowing relatively rapid movement of young water to the 

open interval of the PSW. The spatial component of landuse change is important because the complex distribution of 

particle traveltimes within the contributing areas strongly 

influences contaminant arrival times and degradation reaction progress. Results from this and other similar exercises 

(McMahon and others, 2008) indicate that time scales for 

change in the quality of water from the PSW could be on the 

order of a few years to decades for land-use changes that occur 

over days to decades, which has implications for source-water 

protection strategies that rely on land-use change to achieve 

water-quality objectives. 

Summary

In 2001, the National Water-Quality Assessment 

(NAWQA) Program of the U.S. Geological Survey initiated a 

series of studies on the transport of anthropogenic and natural 

contaminants (TANC) to public-supply wells (PSWs). The 

main goal of the TANC project was to better understand the 

source, transport, and receptor factors that control contaminant 

movement to PSWs in representative aquifers of the United 

States. Regional- and local-scale study areas were selected 

from within existing NAWQA study units, including southcentral Texas. This report describes the hydrogeology and 

geochemistry of the local-scale TANC study near San Antonio, Tex., and discusses factors that might control transport of 

selected anthropogenic and natural contaminants to a publicsupply well within a productive well field. The study area is 

within the San Antonio segment of the Edwards aquifer, a 

highly productive karst aquifer developed in Cretaceous-age 

carbonates. Like many karst aquifers, the Edwards aquifer is 

subject to rapid changes in flow and discharge rates, waterlevel altitudes, and water quality and as a result is susceptible 

to contamination. An understanding of the source, transport, 

and receptor factors that control contaminant movement to 

PSWs in the Edwards aquifer is important for water-management practices and the long-term sustainability of the groundwater resource. Results for a variety of geochemical constituents and tracers were compared for groundwater samples from 

regional aquifer PSWs (mostly from the confined part of the 

aquifer), from the well field (wellhead samples), from the 

monitoring wells (Zarzamora and Timberhill monitoring well 

clusters), from a monitoring well in the overburden, from the 

PSW depth-dependent sampling, and from temporal sampling 

in response to a rainfall and recharge event (from the PSW and 

selected monitoring wells).

Constituents of concern in the Edwards aquifer for the 

long-term sustainability of the groundwater resource include 

anthropogenic organic contaminants and the nutrient nitrate. 

Natural contaminants, such as arsenic or uranium, are not of 

concern for the Edwards aquifer, and oxic aquifer conditions 

are not conducive to increases in concentrations of these contaminants. Geochemical and isotopic data are useful tracers 

of recharge, groundwater flow, fluid mixing, and water-rock 
78 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

interaction processes that affect water quality. Sources of 

dissolved constituents to the Edwards aquifer and to the 

PSW include dissolution of and geochemical interaction with 

overlying soils and calcite and dolomite minerals that compose the aquifer. The well-field and monitoring well samples 

had relatively narrow ranges in field parameters and most 

geochemical constituents were, for the most part, similar in 

composition to samples from regional aquifer PSWs. Groundwater samples were mostly a dilute calcium bicarbonate or 

calcium magnesium bicarbonate facies. Mineral saturation 

indices with respect to calcite, dolomite, and gypsum reflect 

the carbonate mineralogy of the aquifer host rocks. TANC 

study results for molar ratios of magnesium to calcium and 

strontium to calcium, and for strontium isotopes, were used 

to assess relative extents of water-rock interaction associated 

with shorter and longer flow paths. Molar ratios of magnesium 

to calcium and strontium to calcium in carbonate groundwater typically increase along flow paths; strontium isotopes in 

Edwards aquifer groundwater typically decrease along flow 

paths, toward values similar to the limestone aquifer rocks. 

Oxidation-reduction conditions were oxic, which is typical 

of the regional aquifer, except very close to the downgradient 

transition, which had more saline, less oxic water. 

Nitrate concentrations for samples collected during this 

study from regional aquifer PSWs (specifically, PSWs in 

the confined part of the aquifer) were below drinking-water 

standards and had a similar median value (1.9 milligrams per 

liter) to regional aquifer samples from the confined part of the 

aquifer collected in previous studies. Nitrate-isotope results 

for the well-field and monitoring well samples indicate that 

soil organic nitrogen is the dominant source of nitrate in the 

regional aquifer. A comparison with historical nitrate-isotope 

values, however, suggests that a possible component of nitrate 

in groundwater from biogenic sources might have increased 

over the last 30 years. Results for stable isotopes of hydrogen and oxygen for groundwater samples from the well-field 

wells and monitoring wells indicated that the groundwater is 

meteoric in origin. A small number of organic contaminants 

were routinely or frequently detected in groundwater samples 

collected for this study. These were the pesticides atrazine; 

its degradate deethylatrazine; the drinking-water disinfection 

byproduct, trichloromethane (chloroform); and the solvent 

tetrachloroethene (PCE). Detected concentrations of all 

organic constituents were low (mostly less than 1 microgram 

per liter), which is consistent with previous NAWQA findings. The common detection of these anthropogenic contaminants indicates that the aquifer is vulnerable to contamination 

and effects on water-quality that result from anthropogenic 

activities. The geochemistry of groundwater from the PSW 

was similar to that of samples collected from PSWs throughout the extent of the regional confined aquifer. These results 

indicate that water from the PSW is generally representative 

of the regional confined aquifer. All samples collected from 

the well field and specifically those collected from different 

depths in the PSW under a variety of pumping conditions 

were relatively homogeneous and well mixed for numerous 

geochemical constituents, with the notable exception of age 

tracers. Although multiple age tracers were sampled, because 

of contamination effects and age-interpretation complexities, 

all age interpretations were based on tritium/helium-3 results. 

Apparent ages based on a piston-flow model for samples 

from the well field and monitoring wells ranged from less 

than 1 to 41 years, with a median of 17 years. Apparent ages 

were inversely stratified for both sets of monitoring wells, 

with older ages for the deeper monitoring wells. Results for 

depth-depending samples from the PSW yielded a range of 

apparent ages (less than 1 to 22 years) but with no consistency 

with respect to depth or stratigraphic unit contributing to the 

PSW. Selected geochemical constituents that might provide 

independent information about groundwater residence time 

(for example, magnesium to calcium molar ratios, dolomite 

mineral saturation indices, and strontium isotope ratios) or the 

extent of impact from anthropogenic activities (for example, 

the number of organic contaminants detected, concentration of 

selected organic contaminants) were compared to age-tracer 

results for groundwater samples. Results of this comparison 

were not consistent with the range of interpreted apparent ages 

or age-tracer results, indicating that hydrogeologic conceptual 

models used in groundwater age interpretations might not 

adequately account for mixing in this karst system. Mixing 

processes in this aquifer are complex, and although age tracers 

provide insight into the young nature of the groundwater, they 

might not readily allow for distinguishing the mixed water 

history of water at a PSW or be well suited to distinguish 

relatively small differences in groundwater age as a result of 

mixing processes. Nonetheless, age interpretations, indicating that water supplied to the PSW is young, were consistent 

with particle-tracking results from a companion hydrogeologic 

modeling study. 

One of the well-field PSWs and four selected monitoring 

wells were sampled several times in response to a storm event 

that recharged the regional aquifer. Geochemical variability in 

response to the sampled recharge event was generally small 

in the well-field PSW and monitoring wells in comparison to 

the range of geochemical variability observed in the regional 

aquifer. Several geochemical constituents, however, showed 

consistent variability in the PSW and monitoring wells that 

corresponded with associated changes in hydrologic conditions in response to the sampled recharge event. The observed 

temporal variations in water chemistry were consistent with 

the hypothesis that the response to individual recharge events 

in the confined aquifer, unless intersecting conduit flow paths, 

might be attenuated by mixing processes along regional flow 

paths.

Anthropogenic sources that might influence groundwater 

water quality at the PSW include septic systems, leakage 

from municipal water and wastewater systems, and general 

industrial, commercial, or residential use of pesticides and 

volatile organic compounds. Although the urban San Antonio 

environment is a likely source of anthropogenic contaminants 

to the PSW, sampling of regional aquifer PSWs indicates that 

a few specific organic contaminants are widely distributed 
References 79

throughout the aquifer at low concentrations. There are point 

sources in the vicinity of the well field for PCE. Higher 

concentrations of PCE were detected in samples from the well 

field and Zarzamora monitoring wells relative to the regional 

aquifer PSWs, which is consistent with the possibility that 

a local urban source (or sources) might be supplying PCE 

to these wells. Under all pumping conditions, the majority 

of water from the PSW was young and, as such, susceptible 

to contamination. Although zones of preferential flow were 

determined for the PSW, groundwater samples from different 

stratigraphic units were not geochemically distinct. Results 

from groundwater-flow-model particle tracking were used to 

evaluate a hypothetical contaminant-loading scenario to assess 

the potential response of the aquifer to contamination. Results 

indicate that the aquifer responds rapidly (less than 1 year 

to several years) to contaminant loading; however, it takes a 

relatively long time (decades) for concentrations to reach the 

highest values. The aquifer also responds quickly (less than 

1 year to several years) to the removal of contaminant loading; again however, it takes a relatively long time (decades) to 

reach near background concentrations. These results corroborate the existing conceptual understanding of aquifer behavior 

to contaminant loading.

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Table 1. Site information for wells sampled for the study of the transport of anthropogenic and natural contaminants (TANC) to public supply wells in of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category and by aquifer category (unconfined, confined). USGS, U.S. Geological Survey; NAD 83, North American Datum of 1983; Y, yes; N, no; --, not measuredsampled 6 times for temporal response to rainfall; psw, public-supply well; **, sampled 9 times for vertically discrete samples; ft, feet; NAVD 1988, North American Vertical Dper minute; in., inches; PVC, polyvinyl chloride; †, borehole diameter (diam.), screen is 2.5-in. diam.; ‡, borehole diam., screen is 4.5-in. diam.]

USGS 

identification 

number

State well 

number

Local 

identifier 

Latitude 

(decimal 

degrees), 

NAD 83 

datum

Longitude

(decimal 

degrees), 

NAD 83 

datum

County Aquifer category

Within 

supplywell scale 

model area

Pumpage 

quartile 

(2004)

Network

Monitoring wells

292943098354401 AY–68–36–135 Z–OVB 29.49531 -98.59564 Bexar -- Y -- discrete interval, overburden 

292943098354402 AY–68–36–133 Z–SED 29.49540 -98.59559 Bexar confined Y -- discrete interval, temporal 

292943098354403 AY–68–36–134 Z–IED 29.49519 -98.59558 Bexar confined Y -- discrete interval, temporal 

292943098354404 AY–68–36–132 Z–DED 29.49545 -98.59566 Bexar confined Y -- discrete interval, temporal 

292851098374401 AY–68–35–315 T–IED 29.48074 -98.62901 Bexar confined Y -- discrete interval 

292851098374402 AY–68–35–314 T–DED 29.48073 -98.62916 Bexar confined Y -- discrete interval 

293252098380801 AY–68–27–610 Parkwood 29.54778 -98.63556 Bexar unconfined Y -- temporal 

Well-field wells

292919098360501 AY–68–36–103 W2 -- -- Bexar confined Y 1st wellfield 

292925098360201 AY–68–36–104 W3 -- -- Bexar confined Y 1st wellfield, psw survey 

292916098360701 AY–68–36–105 W4 -- -- Bexar confined Y 1st wellfield, depth dependent 

292920098360601 AY–68–36–130 W5 -- -- Bexar confined Y 1st wellfield 

292923098360301 AY–68–36–131 W6 -- -- Bexar confined Y 1st wellfield, temporal 

Regional aquifer public-supply wells

293359098290301 AY−68−29−414 -- -- -- Bexar confined Y 1st psw survey 

293358098231101 AY−68−29−610 -- -- -- Bexar confined N 1st psw survey 

293120098285801 AY−68−29−714 -- -- -- Bexar confined N 1st psw survey 

293145098224201 AY−68−29−929 -- -- -- Bexar confined N 1st psw survey 

293119098211201 AY−68−30−718 -- -- -- Bexar confined N 1st psw survey 

292843098425101 AY−68−35−106 -- -- -- Bexar confined Y 1st psw survey 

292459098382101 AY−68−35–913 -- -- -- Bexar confined Y 1st psw survey 

292822098325401 AY−68−36−206 -- -- -- Bexar confined Y 1st psw survey 

292944098292301 AY−68−37−105 -- -- -- Bexar confined Y 1st psw survey 

292522098291901 AY−68−37−426 -- -- -- Bexar confined Y 1st psw survey 

292643098241801 AY−68−37−601 -- -- -- Bexar confined N 1st psw survey 

292328098294601 AY−68−37−705 -- -- -- Bexar confined N 1st psw survey 

294225098080301 DX−68−23−601 -- -- -- Comal confined N 1st psw survey 

291210099475601 YP−69−50−506 -- -- -- Uvalde confined N 1st psw survey 
Table 1. Site information for wells sampled for the study of the transport of anthropogenic and natural contaminants (TANC) to public supply wells in of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category and by aquifer category (unconfined, confined). USGS, U.S. Geological Survey; NAD 83, North American Datum of 1983; Y, yes; N, no; --, not measuredsampled 6 times for temporal response to rainfall; psw, public-supply well; **, sampled 9 times for vertically discrete samples; ft, feet; NAVD 1988, North American Vertical Dper minute; in., inches; PVC, polyvinyl chloride; †, borehole diameter (diam.), screen is 2.5-in. diam.; ‡, borehole diam., screen is 4.5-in. diam.] USGS identification number State well number Local identifier Latitude (decimal degrees), NAD 83 datum Longitude (decimal degrees), NAD 83 datum County Aquifer category Within supply- well scale model area Pumpage quartile (2004) Network 

293111098340901 AY−68−28−807 -- -- -- Bexar confined Y 2d psw survey 

293512098291701 AY−68−29−109 -- -- -- Bexar unconfined Y 2d psw survey 292424098421501 AY−68−35−810 -- -- -- Bexar confined Y 2d psw survey 

292053098365501 AY−68−44−110 -- -- -- Bexar confined Y 2d psw survey 

293807098155301 DX−68−22−901 -- -- -- Comal confined N 2d psw survey 

292604098563201 TD−68−33−501 -- -- -- Medina confined Y 2d psw survey 

292116099095501 TD−69−47−305 -- -- -- Medina confined N 2d psw survey 

291232099470301 YP−69−50−339 -- -- -- Uvalde confined N 2d psw survey 

293128098473101 AY−68−26−814 -- -- -- Bexar unconfined Y 3d psw survey 

293451098313201 AY−68−28−601 -- -- -- Bexar unconfined Y 3d psw survey 

294604098060801 DX−68−16−708 -- -- -- Comal unconfined N 3d psw survey 

294019098114701 DX−68−23−504 -- -- -- Comal confined N 3d psw survey 

292215098580201 TD−68−41−103 -- -- -- Medina confined Y 3d psw survey 

292119098524901 TD−68−41−308 -- -- -- Medina confined Y 3d psw survey 

291943099163301 TD−69−46−601 -- -- -- Medina confined N 3d psw survey 

291840099382601 YP−69−43−606 -- -- -- Uvalde confined N 3d psw survey 

293518098332601 AY−68−28−203 -- -- -- Bexar unconfined Y 4th psw survey 

293023098355401 AY−68−28−702 -- -- -- Bexar confined Y 4th psw survey 

293042098305201 AY−68−28−913 -- -- -- Bexar confined Y 4th psw survey 

292442098474501 AY−68−34−803 -- -- -- Bexar confined Y 4th psw survey 

292405098371201 AY−68−36−704 -- -- -- Bexar confined Y 4th psw survey 

292931098274601 AY−68−37−124 -- -- -- Bexar confined Y 4th psw survey 

293729098173101 DX−68−30−215 -- -- -- Comal confined N 4th psw survey 

291219099095601 TD−69−55−604 -- -- -- Medina confined N 4th psw survey 
Table 1. Site information for wells sampled for the study of the transport of anthropogenic and natural contaminants (TANC) to public supply wells in of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category and by aquifer category (unconfined, confined). USGS, U.S. Geological Survey; NAD 83, North American Datum of 1983; Y, yes; N, no; --, not measuredsampled 6 times for temporal response to rainfall; psw, public-supply well; **, sampled 9 times for vertically discrete samples; ft, feet; NAVD 1988, North American Vertical Dper minute; in., inches; PVC, polyvinyl chloride; †, borehole diameter (diam.), screen is 2.5-in. diam.; ‡, borehole diam., screen is 4.5-in. diam.]

USGS 

identification 

number

Well 

type

Water 

use

Casing 

material

Landsurface 

altitude

(ft above 

NAVD 

1988)

Rated 

pump 

capacity

(gal/min)

Well 

depth 

(ft below 

land 

surface)

Depth to top 

of open or 

screened 

interval

(ft from land 

surface)

Depth to bottom of open 

or screened 

interval 

(ft from land 

surface)

Length 

of open 

interval

(ft)

Diameter of 

open 

interval 

(in.)

For

op

Monitoring wells

292943098354401 Observation Unused Steel, PVC 848 -- 280 203 243 40 11† Buda Limestone

292943098354402 Observation Unused Steel, PVC 848 -- 345 335 345 10 5.9† Cyclic and marine m

292943098354403 Observation Unused Steel, PVC 848 -- 480 397 417.5 20.5 5.9† Leached and collaps

292943098354404 Observation Unused Steel, PVC 848 -- 616 586 596.5 10.5 5.9† Kirschberg evaporit

292851098374401 Observation Unused Steel, PVC 795 -- 520 480 510 30 5.9† Leached and collaps

292851098374402 Observation Unused Steel, PVC 795 -- 660 645 655 10 5.9† Kirschberg evaporit

293252098380801 Observation Unused Steel, PVC 896 -- 229 149 229 80 6.5‡ Leached and collaps

grainstone memb

Well-field wells

292919098360501 Withdrawal Public Steel 910 8,750 824 342 824 482 30 All of Edwards

292925098360201 Withdrawal Public Steel 890 7,778 808 322 808 486 30 All of Edwards

292916098360701 Withdrawal Public Steel 890 7,778 816 321 816 495 30 All of Edwards

292920098360601 Withdrawal Public Steel 903 13,958 795 341 795 454 36 All of Edwards

292923098360301 Withdrawal Public Steel 906 14,375 820 360 820 460 36 All of Edwards

Regional aquifer public-supply wells

293359098290301 Withdrawal Public Steel 840 3,200 710 380 710 330 16 Most of Edwards

293358098231101 Withdrawal Public Steel 828 7,500 811 359 811 452 30 All of Edwards

293120098285801 Withdrawal Public Steel 758 8,701 848 408 848 440 30 All of Edwards

293145098224201 Withdrawal Public Steel 813 9,722 870 409 870 461 30 All of Edwards

293119098211201 Withdrawal Public Steel 895 3,100 877 530 877 347 -- Most of Edwards

292843098425101 Withdrawal Public Steel 955 8,264 760 460 750 290 36 Most of Edwards

292459098382101 Withdrawal Public Steel 754 8,472 1,040 594 1,040 446 30 All of Edwards

292822098325401 Withdrawal Public Steel 756 3,194 748 537 748 211 18 Top of Edwards

292944098292301 Withdrawal Public Steel 710 9,722 1,050 574 1,044 470 30 All of Edwards

292522098291901 Withdrawal Public Steel 640 8,958 1,114 774 1,114 340 24 Most of Edwards

292643098241801 Withdrawal Public Steel 686 3,472 1,150 1,012 1,150 138 20 Top of Edwards

292328098294601 Withdrawal Public Steel 601 8,472 1,800 1,333 1,800 467 30 Most of Edwards (fr

bers, undivided, t

294225098080301 Withdrawal Public Steel 680 2,100 365 92 365 273 -- One-half of Edward

291210099475601 Withdrawal Public Steel 900 500 525 191 525 334 12 Most of Edwards
Table 1. Site information for wells sampled for the study of the transport of anthropogenic and natural contaminants (TANC) to public supply wells in of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category and by aquifer category (unconfined, confined). USGS, U.S. Geological Survey; NAD 83, North American Datum of 1983; Y, yes; N, no; --, not measuredsampled 6 times for temporal response to rainfall; psw, public-supply well; **, sampled 9 times for vertically discrete samples; ft, feet; NAVD 1988, North American Vertical Dper minute; in., inches; PVC, polyvinyl chloride; †, borehole diameter (diam.), screen is 2.5-in. diam.; ‡, borehole diam., screen is 4.5-in. diam.] USGS identification number Well type Water use Casing material Land- surface altitude (ft above NAVD 1988) Rated pump capacity (gal/min) Well depth (ft below land surface) Depth to top of open or screened interval (ft from land surface) Depth to bot- tom of open or screened interval (ft from land surface) Length of open interval (ft) Diam- eter of open interval (in.) For

op

293111098340901 Withdrawal Public Steel 1,000 3,333 685 420 685 265 20 Half of Edwards 293512098291701 Withdrawal Public Steel 975 250 460 230 460 230 -- One-half of Edward

292424098421501 Withdrawal Public Steel 835 1,710 735 548 735 187 -- Less than one-half o

292053098365501 Withdrawal Public Steel 668 3,472 1,916 1,380 1,916 536 30 All of Edwards 293807098155301 Withdrawal Public Steel 760 1,850 255 148 255 107 -- Top of Edwards 292604098563201 Withdrawal Public Steel 1,035 650 1,462 1,190 1,462 272 -- One-half of Edward

292116099095501 Withdrawal Public Steel 910 1,200 1,418 1,206 1,418 212 -- One-half of Edward

291232099470301 Withdrawal Public Steel 904 1,200 400 260 400 140 -- Top of Edwards 293128098473101 Withdrawal Public Steel 1,040 153 1,400 900 1,400 500 8 All of Edwards 293451098313201 Withdrawal Public Steel 963 160 500 40 500 460 -- All of Edwards 294604098060801 Withdrawal Public Steel 802 150 400 200 400 200 6.5 Top of Edwards 294019098114701 Withdrawal Public Steel 750 750 215 119 215 96 -- Top of Edwards 292215098580201 Withdrawal Public Steel 1,012 750 1,431 1,280 1,431 151 10 Very top of Edward

292119098524901 Withdrawal Public Steel 758 320 715 700 715 15 -- Top of Edwards 291943099163301 Withdrawal Public Steel 884 265 1,289 920 1,289 369 -- Most of Edwards

291840099382601 Withdrawal Public Steel 1,000 700 698 206 698 492 -- All of Edwards

293518098332601 Withdrawal Public Steel 985 250 435 162 435 273 8 One-half of Edward

293023098355401 Withdrawal Public Steel 840 1,320 450 397 450 53 -- Top of Edwards

293042098305201 Withdrawal Public Steel 815 1,500 787 448 787 339 20 Most of Edwards

292442098474501 Withdrawal Public Steel 900 2,450 680 392 680 288 15 One-half of Edward

292405098371201 Withdrawal Public Steel 720 1,850 1,500 1,108 1,500 392 -- Most of Edwards

292931098274601 Withdrawal Public Steel 813 1,000 557 390 557 167 -- Top of Edwards

293729098173101 Withdrawal Public Steel 870 2,000 660 185 660 475 -- All of Edwards

291219099095601 Withdrawal Public Steel 900 500 2,350 2,100 2,350 250 8 One-half of Edward
Table 2 95

Table 2. Summary of constituents by group for wells sampled for the study of the transport of anthropogenic and natural contaminants 

(TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.

—Continued

[By sample category. USGS, U.S. Geological Survey; *, did not analyze in first temporal sample; --, not sampled; **,did not analyze in first three temporal 

samples; psw, public-supply well; 87Sr/86Sr, strontium-87/strontium-86; δD, delta deuterium; δ18O, delta oxygen-18; δ15N, delta nitrogen-15; NO3, nitrate]

USGS 

identification 

number

State well 

number County Purpose Local identifier 

Year 

sampled

Physicochemical 

constituents

Major 

ions

Trace 

elements

Nutrients

Monitoring wells

292943098354401 AY–68–36–135 Bexar discrete interval Z–OVB 2007 X X X X

292943098354402 AY–68–36–133 Bexar discrete interval Z–SED 2007 X X X X

temporal 2009 X X X X

292943098354403 AY–68–36–134 Bexar discrete interval Z–IED 2007 X X X X

temporal 2009 X X X X

292943098354404 AY–68–36–132 Bexar discrete interval Z–DED 2007 X X X X

temporal 2009 X X X X

292851098374401 AY–68–35–315 Bexar discrete interval T–IED 2008 X X X X

292851098374402 AY–68–35–314 Bexar discrete interval T–DED 2008 X X X X

293252098380801 AY–68–27–610 Bexar temporal Parkwood 2009 X X X X

Well-field wells 

292919098360501 AY–68–36–103 Bexar wellfield W2 2007 X X X X

292925098360201 AY–68–36–104 Bexar psw survey W3 2004 X X X X

selected resample 2005 X X -- --

wellfield 2007 X X X X

292916098360701 AY–68–36–105 Bexar wellfield, depth dependent W4 2007 X X X X

292920098360601 AY–68–36–130 Bexar wellfield W5 2007 X X X X

292923098360301 AY–68–36–131 Bexar wellfield W6 2007 X X X X

temporal 2009 X X X X

Regional aquifer public-supply wells

293359098290301 AY−68−29−414 Bexar psw survey -- 2004 X X X X

selected resample -- 2005 X -- -- --

293358098231101 AY−68−29−610 Bexar psw survey -- 2004 X X X X

selected resample -- 2005 X -- -- --

293120098285801 AY−68−29−714 Bexar psw survey -- 2004 X X X X

selected resample -- 2005 X -- -- --

293145098224201 AY−68−29−929 Bexar psw survey -- 2004 X X X X

293119098211201 AY−68−30−718 Bexar psw survey -- 2004 X X X X

292843098425101 AY−68−35−106 Bexar psw survey -- 2004 X X X X

292459098382101 AY−68−35–913 Bexar psw survey -- 2004 X X X X

292822098325401 AY−68−36−206 Bexar psw survey -- 2004 X X X X

selected resample -- 2005 X -- -- --

292944098292301 AY−68−37−105 Bexar psw survey -- 2004 X X X X

selected resample -- 2005 X -- -- --

Table 2
96 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 2. Summary of constituents by group for wells sampled for the study of the transport of anthropogenic and natural contaminants 

(TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.

—Continued

[By sample category. USGS, U.S. Geological Survey; *, did not analyze in first temporal sample; --, not sampled; **,did not analyze in first three temporal 

samples; psw, public-supply well; 87Sr/86Sr, strontium-87/strontium-86; δD, delta deuterium; δ18O, delta oxygen-18; δ15N, delta nitrogen-15; NO3, nitrate]

USGS 

identification 

number

State well 

number County Purpose Local identifier 

Year 

sampled

Physicochemical 

constituents

Major 

ions

Trace 

elements

Nutrients

292522098291901 AY−68−37−426 Bexar psw survey -- 2004 X X X X

292643098241801 AY−68−37−601 Bexar psw survey -- 2004 X X X X

selected resample -- 2005 X -- -- --

292328098294601 AY−68−37−705 Bexar psw survey -- 2004 X X X X

294225098080301 DX−68−23−601 Comal psw survey -- 2004 X X X X

selected resample -- 2005 X -- -- --

291210099475601 YP−69−50−506 Uvalde psw survey -- 2004 X X X X

293111098340901 AY−68−28−807 Bexar psw survey -- 2005 X X X X

293512098291701 AY−68−29−109 Bexar psw survey -- 2005 X X X X

292424098421501 AY−68−35−810 Bexar psw survey -- 2005 X X X X

292053098365501 AY−68−44−110 Bexar psw survey -- 2005 X X X X

293807098155301 DX−68−22−901 Comal psw survey -- 2005 X X X X

292604098563201 TD−68−33−501 Medina psw survey -- 2005 X X X X

292116099095501 TD−69−47−305 Medina psw survey -- 2005 X X X X

291232099470301 YP−69−50−339 Uvalde psw survey -- 2005 X X X X

293128098473101 AY−68−26−814 Bexar psw survey -- 2005 X X X X

293451098313201 AY−68−28−601 Bexar psw survey -- 2005 X X X X

294604098060801 DX−68−16−708 Comal psw survey -- 2005 X X X X

294019098114701 DX−68−23−504 Comal psw survey -- 2005 X X X X

292215098580201 TD−68−41−103 Medina psw survey -- 2005 X X X X

292119098524901 TD−68−41−308 Medina psw survey -- 2005 X X X X

291943099163301 TD−69−46−601 Medina psw survey -- 2005 X X X X

291840099382601 YP−69−43−606 Uvalde psw survey -- 2005 X X X X

293518098332601 AY−68−28−203 Bexar psw survey -- 2005 X X X X

293023098355401 AY−68−28−702 Bexar psw survey -- 2005 X X X X

293042098305201 AY−68−28−913 Bexar psw survey -- 2005 X X X X

292442098474501 AY−68−34−803 Bexar psw survey -- 2005 X X X X

292405098371201 AY−68−36−704 Bexar psw survey -- 2005 X X X X

292931098274601 AY−68−37−124 Bexar psw survey -- 2005 X X X X

293729098173101 DX−68−30−215 Comal psw survey -- 2005 X X X X

291219099095601 TD−69−55−604 Medina psw survey -- 2005 X X X X
Table 2 97

Table 2. Summary of constituents by group for wells sampled for the study of the transport of anthropogenic and natural contaminants 

(TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.

—Continued

[By sample category. USGS, U.S. Geological Survey; *, did not analyze in first temporal sample; --, not sampled; **,did not analyze in first three temporal 

samples; psw, public-supply well; 87Sr/86Sr, strontium-87/strontium-86; δD, delta deuterium; δ18O, delta oxygen-18; δ15N, delta nitrogen-15; NO3, nitrate]

USGS 

identification 

number

Dissolved 

organic 

carbon

Volatile organic 

compounds

Fuel 

oxygenates

Soluble 

pesticide 

compounds

Polar 

pesticide 

compounds

Acetamide 

pesticide 

compounds

Wastewater 

indicator 

compounds

Age 

tracers

Dissolved 

gases

87Sr/

86Sr

δD, 

δ18O

δ15N in 

NO3

, 

δ18O in 

NO3

RadonRadium

Monitoring wells

292943098354401 X X -- X -- -- -- X X X X X X X

292943098354402 X X -- X -- -- -- X X X X X X X

 -- X -- X** -- -- -- -- -- X* X -- -- --

292943098354403 X X -- X -- -- -- X X X X X X X

 -- X -- X** -- -- -- -- -- X* X -- -- --

292943098354404 X X -- X -- -- -- X X X X X X X

 -- X -- X** -- -- -- -- -- X* X -- -- --

292851098374401 X X -- X -- -- -- X X X X X X X

292851098374402 X X -- X -- -- -- X X X X X X X

293252098380801 -- X -- X** -- -- -- -- -- X* X -- -- --

Well-field wells 

292919098360501 X X -- X -- -- -- X X X X X -- X

292925098360201 X X X X X -- X -- -- -- -- -- -- --

 -- X -- X X -- -- -- -- -- -- -- -- --

X X -- X -- -- X X X X X X -- X

292916098360701 X X -- X -- -- -- X X X X X X X

292920098360601 X X -- X -- -- -- X X X X X -- X

292923098360301 X X -- X -- -- -- X X X X X -- X

 -- X -- X** -- -- -- -- -- X X* -- -- --

Regional aquifer public-supply wells

293359098290301 X X X X X -- X -- -- -- -- -- -- --

 -- X -- X X -- X -- -- -- -- -- -- --

293358098231101 X X X X X -- X -- -- -- -- -- -- --

 -- X -- X X -- X -- -- -- -- -- -- --

293120098285801 X X X X X -- X -- -- -- -- -- -- --

 -- X -- -- X -- -- -- -- -- -- -- -- --

293145098224201 X X X X X -- X -- -- -- -- -- -- --

293119098211201 X X X X X -- X -- -- -- -- -- -- --

292843098425101 X X X X X -- X -- -- -- -- -- -- --

292459098382101 X X X X X -- X -- -- -- -- -- -- --

292822098325401 X X X X X -- X -- -- -- -- -- -- --

 -- X -- X -- -- -- -- -- -- -- -- -- --

292944098292301 X X X X X -- X -- -- -- -- -- -- --

 -- -- -- X -- -- X -- -- -- -- -- -- --
98 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 2. Summary of constituents by group for wells sampled for the study of the transport of anthropogenic and natural contaminants 

(TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.

—Continued

[By sample category. USGS, U.S. Geological Survey; *, did not analyze in first temporal sample; --, not sampled; **,did not analyze in first three temporal 

samples; psw, public-supply well; 87Sr/86Sr, strontium-87/strontium-86; δD, delta deuterium; δ18O, delta oxygen-18; δ15N, delta nitrogen-15; NO3, nitrate]

USGS 

identification 

number

Dissolved 

organic 

carbon

Volatile organic 

compounds

Fuel 

oxygenates

Soluble 

pesticide 

compounds

Polar 

pesticide 

compounds

Acetamide 

pesticide 

compounds

Wastewater 

indicator 

compounds

Age 

tracers

Dissolved 

gases

87Sr/

86Sr

δD, 

δ18O

δ15N in 

NO3

, 

δ18O in 

NO3

RadonRadium

292522098291901 X X X X X -- X -- -- -- -- -- -- --

292643098241801 X X X X X -- X -- -- -- -- -- -- --

 -- X -- -- X -- -- -- -- -- -- -- -- --

292328098294601 X X X X X -- X -- -- -- -- -- -- --

294225098080301 X X X X X -- X -- -- -- -- -- -- --

 -- X -- X -- -- -- -- -- -- -- -- -- --

291210099475601 X X X X X -- X -- -- -- -- -- -- --

293111098340901 X X X X -- X -- -- -- -- -- -- -- --

293512098291701 X X X X -- X X -- -- -- -- -- -- --

292424098421501 X X X X -- X X -- -- -- -- -- -- --

292053098365501 X X X X -- X -- -- -- -- -- -- -- --

293807098155301 X X X X -- X X -- -- -- -- -- -- --

292604098563201 X X X X -- X X -- -- -- -- -- -- --

292116099095501 X X X X -- X X -- -- -- -- -- -- --

291232099470301 X X X X -- X X -- -- -- -- -- -- --

293128098473101 X X X X -- X X -- -- -- -- -- -- --

293451098313201 X X X X -- X X -- -- -- -- -- -- --

294604098060801 X X X X -- X X -- -- -- -- -- -- --

294019098114701 X X X X -- X X -- -- -- -- -- -- --

292215098580201 X X X X -- X X -- -- -- -- -- -- --

292119098524901 X X X X -- X X -- -- -- -- -- -- --

291943099163301 X X X X -- X X -- -- -- -- -- -- --

291840099382601 X X X X -- X X -- -- -- -- -- -- --

293518098332601 X X X X -- X X -- -- -- -- -- -- --

293023098355401 X X X X -- X X -- -- -- -- -- -- --

293042098305201 X X X X -- X X -- -- -- -- -- -- --

292442098474501 X X X X -- X X -- -- -- -- -- -- --

292405098371201 X X X X -- X X -- -- -- -- -- -- --

292931098274601 X X X X -- X X -- -- -- -- -- -- --

293729098173101 X X X X -- X -- -- -- -- -- -- -- --

291219099095601 X X X X -- X X -- -- -- -- -- -- --
Table 3. Summary of depth-dependent sampling for the study of the transport of anthropogenic and natural contaminants (TANC) to public supply wsegment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.[By sample category. USGS, U.S. Geological Survey; ft, feet; --, not applicable; DDS, depth-dependent sampling]

USGS 

identification 

number

State well 

number

Local 

identifier

Sample 

pump 

intake 

depth

(ft below 

land 

surface)

Well 

depth

(ft 

below 

land 

surface)

Depth 

to top 

of open 

interval

(ft below 

land 

surface)

Depth to 

bottom 

of open 

interval

(ft below 

land 

surface)

Length 

of open 

interval

(ft below 

land 

surface)

Formation 

at pump 

intake 

depth

Contributing 

formation(s) or 

flow zone(s)

Hydrogeologic 

unit 

(HGU)

Zarzamora monitoring wells

292943098354402 AY–68–36–133 Z–SED -- 345 335 345 10 -- Georgetown Formation 

and cyclic and marine members, undivided

2 and 3 

292943098354403 AY–68–36–134 Z–IED -- 480 397 417.5 20.5 -- Bottom of cyclic and 

marine members, undivided

3 

292943098354404 AY–68–36–132 Z–DED -- 616 586 596.5 10.5 -- Top of Kirschberg evaporite member 8 Unable 

interv

Timberhill monitoring wells

292851098374401 AY–68–35–315 T– IED -- 520 480 510 30 -- Mostly top of leached and 

collapsed members, undivided, and possibly some from bottom of cyclic and marine members, undivided

mostly 

4 (possibly 

some 3)

Unable 

becau

292851098374402 AY–68–35–314 T–DED -- 660 645 655 10 -- Kirschberg evaporite 

member

8 

Well-field public-supply well (W4)

292916098360701 AY–68–36–105 W4 (DDS 

“wellhead”)

320 816 320 320 496 Georgetown 

Formation

All contributing flow 

zones

2–10 Represe

all (4

W4 (DDS 

shallow)

380 816 380 380 -- Near middle 

of cyclic and marine members

Cyclic and marine members, undivided 3 Targete

memgainedifferbelow top oundiv

W4 (DDS 

intermediate)

430 816 430 430 -- Middle/top 

of leached and collapsed members

Leached and collapsed 

members, undivided

4 and 5 Targete

lapsehigh transcolla

W4 (DDS 

deep)

540 816 580 580 -- Grainstone 

member

Kirschberg evaporite 

member

8 (also 

possibly 

from 9 

and 10)

Targete

berg abovKirscone i
100 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 4. Sample collection for temporal sampling for the study of 

the transport of anthropogenic and natural contaminants (TANC) 

to public supply wells in the San Antonio segment of the Edwards 

aquifer near San Antonio, south-central Texas, 2009.

Sample number Sample collection dates

Pre-storm 4/9/2009−4/14/2009

Storm 1 10/4/2009−10/6/2009

Storm 2 10/7/2009−10/9/2009

Storm 3 10/17/2009−0/19/2009

Storm 4 10/28/2009−10/30/2009

Storm 5 11/17/2009−11/19/2009

Table 4
Table 5. Summary of organic content and elemental composition from acid extractions for core materials collected for the study of the transport of acontaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.[USGS, U.S. Geological Survey; ft, feet; LSD, land surface datum; <2 mm, less than 2 millimeters (size of particulates analyzed); g/kg, grams per kilogram; mg/kg, milligrams na, not available; N, normal; HCl, hydrochloric acid; %, percent; HNO3, nitric acid]

USGS 

identification 

number

State well 

number

Local 

identifier Sample identifier Date collected Geologic or hydrogeologic unit

Depth to top 

of sample 

interval

(ft from LSD)

Depth to bo

tom of samp

interval

(ft from LSD

292943098354403 AY–68–36–134 Z–IED TX 175A 8/17/2007 Austin Chalk-Eagle Ford Group contact 175.0 176.5 

TX 175B 175.0 176.5 

TX 175C 175.0 176.5 TX 209 8/18/2007 Eagle Ford Group-Buda Limestone contact 209.0 210.5 

TX 260 8/18/2007 Buda Limestone-Del Rio Clay contact 260.0 261.5 TX 314A 8/18/2007 Del Rio Clay-Georgetown Formation contact 314.0 315.5 

TX 314B 314.0 315.5 

TX 314C 314.0 315.5 TX 444 8/24/2007 Leached and collapsed members, undivided 444.0 446.0 

292943098354404 AY–68–36–132 Z–DED TX 526 8/13/2007 Regional dense member-grainstone member contact 525.0 527.0 

TX 550A 8/14/2007 Grainstone member 550.0 551.0 TX 550B 550.0 551.0 

TX 550C 550.0 551.0 TX 589 8/14/2007 Kirschberg evaporite member (fragments) 589.0 591.0 
Table 5. Summary of organic content and elemental composition from acid extractions for core materials collected for the study of the transport of acontaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Cont[USGS, U.S. Geological Survey; ft, feet; LSD, land surface datum; <2 mm, less than 2 millimeters (size of particulates analyzed); g/kg, grams per kilogram; mg/kg, milligrams pna, not available; N, normal; HCl, hydrochloric acid; %, percent; HNO3, nitric acid] Sample identifier Alumi- num (mg/kg) Barium (mg/kg) Iron (mg/kg) Potas- sium (mg/kg Manga- nese (mg/kg) Sodium (mg/kg) Silica (mg/kg) Magne- sium (mg/kg) Lead (mg/kg) Uranium (mg/kg) Arsenic (mg/kg) Sele- nium (mg/kg) Cal- cium (g/kg) Calcium carbon- ate (g/kg) Mag- nesium carbon- ate (g /kg) 

*Elemental analysis after hydrochloric acid (6N HCl, cold) leach TX 175A 390 9.2 540 400 462 230 200 3,800 0.19 1.3 -- <0.5 290 724 13.2 

TX 175B 330 8.6 490 340 430 190 180 3,300 .15 1.2 -- <.5 303 757 11.5 TX 175C 290 7.9 450 300 390 180 160 2,800 .17 1.4 -- <.5 308 769 9.72 

TX 209 1,100 17 4,700 880 120 160 450 1,000 .48 2.2 -- <.5 112 280 3.47 

TX 260 200 4.2 470 210 660 110 170 1,900 <.05 .7 -- <.5 350 874 6.59 TX 314A 1,400 56 8,300 690 410 130 360 1,200 7.31 .9 -- <.5 158 395 4.16 

TX 314B 1,600 48 9,300 830 400 140 410 1,200 7.74 .9 -- <.5 156 390 4.16 

TX 314C 1,300 46 7,500 710 360 110 410 1,300 7.46 .9 -- <.5 162 405 4.51 TX 444 34 1.3 <20 41 17 270 33 40,000 <.05 .3 -- <.5 109 272 139 

TX 526 300 4.4 600 330 21 150 200 5,200 .47 1.3 -- <.5 260 649 18.0 

TX 550A 35 1.4 110 16 15 47 140 1,100 .13 1.7 -- <.5 345 861 3.82 TX 550B 64 1.5 110 13 27 50 130 1,100 .11 1.3 -- <.5 275 687 3.82 TX 550C 35 1.5 120 16 15 48 100 1,100 .12 1.6 -- <.5 335 836 3.82 TX 589 36 2.4 130 14 13 41 84 15,000 <.05 .8 -- <.5 333 832 52.1 

*Elemental analysis after nitric acid (10% HNO3) leach TX 175A 54 5.2 140 94 240 120 130 2,200 .05 .2 1.1 .10 150 375 7.63 

TX 175B 59 4.3 170 79 200 90 120 2,100 .04 .2 1.0 .13 164 410 7.29 

TX 175C 43 4.3 180 75 190 100 75 2,100 .06 .3 .9 .13 163 407 7.29 

TX 209 360 12 670 390 100 140 150 820 2.80 1.3 7.9 .75 96 240 2.85 

TX 260 31 2.4 140 52 340 44 44 1,700 .09 1.5 22 <.1 166 415 5.90 

TX 314A 380 27 740 330 290 110 160 1,000 1.70 .4 2.4 <.1 157 392 3.47 

TX 314B 420 33 740 370 330 120 200 1,000 1.60 .4 1.6 .25 153 382 3.47 

TX 314C 420 34 680 360 330 120 180 1,100 1.60 .4 1.4 <.1 155 387 3.82 

TX 444 <20 .3 <20 <5 <5 35 < 20 5,900 .01 .1 9.9 <.1 15 37 20.5 

TX 526 65 2.8 200 98 10 68 180 2,900 .18 .4 2.4 <.1 150 375 10.1 

TX 550A <20 1.0 <20 12 7 12 30 540 .06 .3 1.7 <.1 173 432 1.87 

TX 550B <20 1.0 <20 12 8 13 40 540 <.01 .2 1.3 <.1 161 402 1.87 

TX 550C <20 1.1 <20 11 8 13 30 560 <.01 .6 1.2 <.1 168 419 1.94 

TX 589 <20 2.1 <20 13 8 21 29 7,400 .01 <.1 .1 <.1 139 347 25.7 

* Elemental analyses are based on leaches, not complete dissolution of samples (residue remaining after leach for most samples).
Table 6. Summary of X-ray diffraction results for core materials collected for the study of the transport of anthropogenic and natural contaminants (Tin the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[USGS, U.S. Geological Survey; <, less than; mm, millimeter; %, percent]

USGS 

identification 

number

State well 

number

Sample 

identifier

Date 

collected

Geologic or 

hydrogeologic 

unit

Local 

identifier

Sample 

top—depth 

from land 

surface 

(feet)

Sample 

bottom—

depth 

from land 

surface 

(feet)

Bulk X-ray diffraction X-R

292943098354403 AY–68–36–134 TX 175A 8/17/2007 Austin ChalkEagle Ford 

Group contact

Z–IED 175.0 176.5 Calcite 85.0%, dolomite 2.2%, 

quartz 3.8%, total clay 9.0%

Kaolinite 38

trace, and bonate: ca

TX 175B Dark gray pa

dolomite 07.8%, feld

292943098354403 AY–68–36–134 TX 209 8/18/2007 Eagle Ford 

Group-Buda Limestone contact

Z–IED 209.0 210.5 Calcite 52.7%, dolomite 2.0%, 

quartz 14.0%, total clay 21.8%, pyrite 9.5% 

Kaolinite 58

11.3%, chlate: calcite 

292943098354403 AY–68–36–134 TX 260A 8/18/2007 Buda LimestoneDel Rio Clay 

contact

Z–IED 260.0 261.5 Light chunks content: calcite 

84.0%, dolomite trace, quartz 3.5%, total clay 12.7%

Composite li

illite 34.3%

spar at traccalcite 19.

260B Dark chunks content: calcite 

71.2%, dolomite 2.5%, total clay 26.3%, quartz trace

292943098354403 AY–68–36–134 TX 314A 8/18/2007 Del Rio ClayGeorgetown 

Formation contact

Z–IED 314.0 315.5 Bulk yellow: calcite 42.2%, 

dolomite trace, quartz 44.3%, total clay 13.5%

Kaolinite 81

trace, chlohornblendcalcite 4.5

TX 314B Dark parting parallel to bedding: calcite 76.0%, possibly dolomite trace, quartz 

9.8%, total clay 14.2%

TX 314C Gray waxy nodules: calcite 

44.8%, quartz 36.9%, total clay 18.3%, possibly trace goethite and dolomite

TX 314D Bean-like red oxidized nodule 

with hard goethitic-looking inner core: calcite 3.9%, quartz 8.5%, total clay 

4.2%, goethite 83.4%

TX 314E Glassy semi-transparent shelllike nodule: calcite 87.3%, 

quartz 8.4%, total clay 2.8% (dominantly kaolinite)
Table 6. Summary of X-ray diffraction results for core materials collected for the study of the transport of anthropogenic and natural contaminants (Tin the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [USGS, U.S. Geological Survey; <, less than; mm, millimeter; %, percent] USGS identification number State well number Sample identifier Date collected Geologic or hydrogeologic unit Local identi- fier Sample top— depth from land surface (feet) Sample bottom— depth from land surface (feet) Bulk X-ray diffraction X-R

292943098354403 AY–68–36–134 TX 444A 8/24/2007 Leached and collapsed members, undivided Z–IED 444.0 446.0 Calcite 52.4%, dolomite 31.5%, total clay 11.2%, and quartz 4.5% Re-digestion

52.4%, dokaolinite 9and chlori

TX 444B Residual carb

olinite 19.and chlori

292943098354404 AY–68–36–132 TX 526 8/13/2007 Regional dense member- grainstone member contact Z–DED 525.0 526.0 Calcite 73.8%, dolomite 2.1%, quartz 6.5%, total clay 8.3%, pyrite 9.4% Kaolinite 50

(poorly extrace, and carbonate: 

292943098354404 AY–68–36–132 TX 550A 8/14/2007 Grainstone member Z–DED 550.0 551.0 Calcite 96.5%, dolomite trace, total clay 3.2% Calcite dilute

digestion: Residual cdolomite 0

TX 550B Kaolinite 35

trace. Calcual carbon0.9% 292943098354404 AY–68–36–132 TX 589A 8/14/2007 Kirschberg evaporite member 

(fragments)

Z–DED 589.0 591.0 Calcite 94.3%, dolomite 2.5%, 

total clay 3.2% 

Re-digestion 

kaolinite 4

tite. Residdolomite 7

Re-digestion

smectite trcalcite 2.9

TX 589B Dense yellow 

traces of qgoethite. Nbecause of 

pal peaks fbackgroun

TX 589C Clear crystal

dolomite 2

TX 589D Red crystals 

87.9%, doclay 11.3% sample TX 
Table 7 105

Table 7. Physicochemical measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; PSW, public-supply well; ft, feet; NTRU, nephelometric turbidity ratiometric unit; mmHg, millimeters of 

mercury; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; CaCO3, calcium carbonate; --, not measured; E, estimated; MW, 

monitoring well; OVB, overburden]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Depth to 

water

(ft below 

land 

surface)

Turbidity 

(NTRU)

Air 

pressure

(mmHg)

Dissolved 

oxygen

(mg/L)

pH

(standard 

units)

Specific 

conductance

(μS/cm 

at 25°C)

Water 

temperature

(°C)

Alkalinity

(mg/L 

as 

CaCO3

)

Regional aquifer public-supply wells

293359098290301 AY–68–29–414 1st (highest) quartile 2004/12/06 -- -- -- 2.76 7.0 642 23.0 292

293359098290301 AY–68–29–414 1st quartile 2005/09/01 -- 0.26 743 6.63 6.6 661 23.0 289

293358098231101 AY–68–29–610 1st quartile 2004/12/15 -- -- 761 3.74 7.0 618 22.0 285

293358098231101 AY–68–29–610 1st quartile 2005/08/29 -- .21 737 3.74 6.9 611 22.5 279

293120098285801 AY–68–29–714 1st quartile 2004/12/14 -- -- 765 5.04 7.0 620 21.9 304

293120098285801 AY–68–29–714 1st quartile 2005/08/30 -- .17 740 4.73 6.9 599 22.0 264

293145098224201 AY–68–29–929 1st quartile 2004/12/15 -- -- 761 5.52 7.2 519 24.0 260

293119098211201 AY–68–30–718 1st quartile 2004/12/16 -- -- 750 5.58 7.2 511 25.3 226

292843098425101 AY–68–35–106 1st quartile 2004/12/13 -- -- 756 3.89 7.2 560 22.2 226

292459098382101 AY–68–35–913 1st quartile 2004/12/13 -- -- 745 5.84 7.3 498 24.2 201

292925098360201 AY–68–36–104 1st quartile 2004/12/13 -- -- 756 4.50 7.1 596 22.3 250

292925098360201 AY–68–36–104 1st quartile 2005/08/31 -- .23 733 4.19 6.9 594 22.5 275

292822098325401 AY–68–36–206 1st quartile 2004/12/13 -- -- 756 3.92 7.2 556 23.5 223

292822098325401 AY–68–36–206 1st quartile 2005/08/31 -- .25 742 4.65 6.9 557 23.5 208

292944098292301 AY–68–37–105 1st quartile 2004/12/14 -- -- 765 5.07 7.1 552 23.0 250

292944098292301 AY–68–37–105 1st quartile 2005/08/31 -- .15 742 4.96 6.8 673 23.5 226

292522098291901 AY–68–37–426 1st quartile 2004/12/14 -- -- 768 6.65 7.2 502 24.8 220

292643098241801 AY–68–37–601 1st quartile 2004/12/15 -- -- 760 5.17 7.2 520 26.5 193

292643098241801 AY–68–37–601 1st quartile 2005/08/30 -- .28 742 4.92 7.0 509 26.5 196

292328098294601 AY–68–37–705 1st quartile 2004/12/14 -- -- 765 4.57 7.2 531 26.7 207

294225098080301 DX–68–23–601 1st quartile 2004/12/08 -- -- 750 2.15 7.1 565 23.4 243

294225098080301 DX–68–23–601 1st quartile 2005/09/01 -- .19 742 5.13 6.8 556 23.5 241

291210099475601 YP–69–50–506 1st quartile 2004/11/30 22.5 -- 742 4.68 6.9 557 23.3 **E155

293111098340901 AY–68–28–807 2d quartile 2005/05/26 -- .97 740 1.65 7.0 573 22.5 266

293512098291701 AY–68–29–109 2d quartile 2005/04/20 -- .60 734 7.90 7.3 663 23.0 300

292424098421501 AY–68–35–810 2d quartile 2005/04/21 -- E.32 732 6.95 7.2 494 24.0 214

292053098365501 AY–68–44–110 2d quartile 2005/05/26 -- .78 740 1.53 7.2 492 26.0 209

293807098155301 DX–68–22–901 2d quartile 2005/05/18 -- .52 736 3.69 7.2 518 22.0 232

292604098563201 TD–68–33–501 2d quartile 2005/05/16 -- .27 742 2.51 7.4 494 23.5 189

292116099095501 TD–69–47–305 2d quartile 2005/04/27 -- .34 733 6.74 6.9 479 24.5 211

291232099470301 YP–69–50–339 2d quartile 2005/05/11 -- .39 731 5.72 7.1 548 23.5 211

293128098473101 AY–68–26–814 3d quartile 2005/04/18 -- .32 742 3.59 7.4 544 24.5 213

293451098313201 AY–68–28–601 3d quartile 2005/05/17 -- .52 731 6.28 7.1 593 22.5 268

294604098060801 DX–68–16–708 3d quartile 2005/04/25 -- .36 738 6.04 7.2 613 22.0 286

294019098114701 DX–68–23–504 3d quartile 2005/05/18 -- .36 738 5.09 7.2 586 23.0 258

292215098580201 TD–68–41–103 3d quartile 2005/05/09 -- .49 742 6.38 7.3 501 24.0 207

292119098524901 TD–68–41–308 3d quartile 2005/04/27 -- .44 736 7.46 6.9 502 24.0 209

291943099163301 TD–69–46–601 3d quartile 2005/05/09 -- .46 733 6.85 7.2 480 24.0 205

291840099382601 YP–69–43–606 3d quartile 2005/05/11 -- .31 729 6.69 7.2 508 23.5 199

Table 7
106 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 7. Physicochemical measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; PSW, public-supply well; ft, feet; NTRU, nephelometric turbidity ratiometric unit; mmHg, millimeters of 

mercury; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; CaCO3, calcium carbonate; --, not measured; E, estimated; MW, 

monitoring well; OVB, overburden]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Depth to 

water

(ft below 

land 

surface)

Turbidity 

(NTRU)

Air 

pressure

(mmHg)

Dissolved 

oxygen

(mg/L)

pH

(standard 

units)

Specific 

conductance

(μS/cm 

at 25°C)

Water 

temperature

(°C)

Alkalinity

(mg/L 

as 

CaCO3

)

293518098332601 AY–68–28–203 4th quartile 2005/04/19 -- 2.60 735 9.39 7.0 740 22.5 286

293023098355401 AY–68–28–702 4th quartile 2005/04/26 -- .38 730 4.78 6.6 593 22.0 264

293042098305201 AY–68–28–913 4th quartile 2005/06/30 -- .79 744 5.34 6.9 617 22.5 258

292442098474501 AY–68–34–803 4th quartile 2005/04/20 -- .67 728 6.28 7.2 481 24.5 211

292405098371201 AY–68–36–704 4th quartile 2005/05/23 -- .37 736 6.52 7.2 495 25.0 207

292931098274601 AY–68–37–124 4th quartile 2005/05/25 -- .29 733 2.79 7.1 517 24.5 223

293729098173101 DX–68–30–215 4th quartile 2005/04/25 -- .42 726 7.14 7.1 633 22.0 281

291219099095601 TD–69–55–604 4th quartile 2005/05/16 -- .55 742 6.75 7.3 531 23.5 207

Monitoring wells

292943098354401 AY–68–36–135 TANC MW OVB 2007/10/30 127.4 .77 753 4.98 7.0 971 28.3 284

292943098354402 AY–68–36–133 TANC MW 2007/10/31 138.2 .39 749 3.65 7.1 599 27.1 255

292943098354403 AY–68–36–134 TANC MW 2007/10/30 138.2 .39 753 4.60 7.1 592 25.1 264

292943098354404 AY–68–36–132 TANC MW 2007/11/01 138.6 .46 751 4.27 7.1 588 26.8 263

292851098374401 AY–68–35–315 TANC MW 2008/05/06 105.7 .43 758 4.59 7.0 587 24.7 256

292851098374402 AY–68–35–314 TANC MW 2008/05/07 104.1 .34 750 4.71 7.0 611 26.8 267

Well-field depth-dependent sampling (W4)

292916098360701 AY–68–36–105 W4-shallow (380), 

normal

2007/11/16 182.6 .32 750 4.29 7.3 586 25.1 246

292916098360701 AY–68–36–105 W4-intermediate 

(430), normal

2007/11/15 183.1 .29 756 4.55 7.2 580 23.6 253

292916098360701 AY–68–36–105 W4-deep (540), 

normal

2007/11/15 182.8 .28 756 4.42 7.2 586 23.9 247

292916098360701 AY–68–36–105 W4-shallow (380), 

ambient

2007/11/16 182.6 .28 750 4.30 7.3 587 24.3 246

292916098360701 AY–68–36–105 W4-intermediate 

(430), ambient

2007/11/14 181.7 .35 756 4.00 7.3 585 25.6 248

292916098360701 AY–68–36–105 W4-deep (540), 

ambient

2007/11/15 182.8 .24 756 4.40 7.2 586 23.9 246

292916098360701 AY–68–36–105 W4-shallow (380), 

moderate

2007/11/16 182.7 .32 750 4.17 7.3 592 24.7 248

292916098360701 AY–68–36–105 W4-intermediate 

(430), moderate

2007/11/14 181.7 .29 753 4.31 7.2 582 24.4 242

292916098360701 AY–68–36–105 W4-deep (540), 

moderate

2007/11/15 182.8 .24 756 4.52 7.2 581 24.1 249

Well-field wells (wellhead sampling)

292919098360501 AY–68–36–103 wellhead 2007/11/29 -- .29 752 4.30 7.3 589 22.0 252

292925098360201 AY–68–36–104 wellhead 2007/11/28 -- .66 750 5.26 7.2 587 20.8 256

292916098360701 AY–68–36–105 *wellhead 2007/11/16 182.7 .35 750 4.29 7.2 592 24.1 251

292920098360601 AY–68–36–130 wellhead 2007/11/29 -- .35 752 4.59 7.3 592 21.9 255

292923098360301 AY–68–36–131 wellhead 2007/11/28 -- .29 750 4.32 7.1 589 21.9 258

Temporal sampling

292923098360301 AY–68–36–131 TANC PSW prestorm2009/04/09 -- .12 732 4.18 7.0 575 22.5 250

292923098360301 AY–68–36–131 TANC PSW storm 1 2009/10/06 -- .17 735 4.40 7.0 578 22.2 248
Table 7 107

Table 7. Physicochemical measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; PSW, public-supply well; ft, feet; NTRU, nephelometric turbidity ratiometric unit; mmHg, millimeters of 

mercury; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; CaCO3, calcium carbonate; --, not measured; E, estimated; MW, 

monitoring well; OVB, overburden]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Depth to 

water

(ft below 

land 

surface)

Turbidity 

(NTRU)

Air 

pressure

(mmHg)

Dissolved 

oxygen

(mg/L)

pH

(standard 

units)

Specific 

conductance

(μS/cm 

at 25°C)

Water 

temperature

(°C)

Alkalinity

(mg/L 

as 

CaCO3

)

292923098360301 AY–68–36–131 TANC PSW storm 2 2009/10/09 -- 0.17 738 4.28 7.0 572 21.9 254

292923098360301 AY–68–36–131 TANC PSW storm 3 2009/10/19 -- .13 744 4.58 7.0 583 21.9 259

292923098360301 AY–68–36–131 TANC PSW storm 4 2009/10/30 -- .14 737 4.64 7.0 581 21.9 252

292923098360301 AY–68–36–131 TANC PSW storm 5 2009/11/19 -- .14 743 4.30 7.1 579 21.9 253

292943098354402 AY–68–36–133 TANC MW prestorm2009/04/08 177.7 .39 737 3.90 7.0 552 27.6 254

292943098354402 AY–68–36–133 TANC MW storm 1 2009/10/05 180.4 .21 752 4.15 7.0 592 23.8 274

292943098354402 AY–68–36–133 TANC MW storm 2 2009/10/07 177.9 .23 738 4.40 7.0 586 24.6 262

292943098354402 AY–68–36–133 TANC MW storm 3 2009/10/17 179.1 .24 749 4.07 7.1 592 24.6 269

292943098354402 AY–68–36–133 TANC MW storm 4 2009/10/28 170.0 .23 732 4.18 7.1 589 23.7 258

292943098354402 AY–68–36–133 TANC MW storm 5 2009/11/18 173.6 .15 743 4.29 7.1 586 23.0 275

292943098354403 AY–68–36–134 TANC MW prestorm2009/04/09 178.0 .23 732 4.15 6.9 572 26.1 265

292943098354403 AY–68–36–134 TANC MW storm 1 2009/10/05 179.4 .24 752 4.63 7.0 592 24.3 264

292943098354403 AY–68–36–134 TANC MW storm 2 2009/10/08 177.9 .13 737 4.59 7.0 587 24.1 262

292943098354403 AY–68–36–134 TANC MW storm 3 2009/10/18 175.3 .13 750 4.33 7.0 590 23.7 267

292943098354403 AY–68–36–134 TANC MW storm 4 2009/10/29 170.2 .12 733 4.50 7.0 590 24.0 261

292943098354403 AY–68–36–134 TANC MW storm 5 2009/11/18 173.3 .18 743 4.45 7.1 583 23.3 262

292943098354404 AY–68–36–132 TANC MW prestorm

2009/04/09 178.0 1.67 732 4.12 7.0 582 25.2 262

292943098354404 AY–68–36–132 TANC MW storm 1 2009/10/05 180.5 .30 752 4.44 7.0 586 24.4 263

292943098354404 AY–68–36–132 TANC MW storm 2 2009/10/08 177.9 .18 737 4.81 7.0 583 24.6 266

292943098354404 AY–68–36–132 TANC MW storm 3 2009/10/18 177.5 .14 750 4.34 7.1 586 23.8 260

292943098354404 AY–68–36–132 TANC MW storm 4 2009/10/29 170.2 .15 733 4.55 7.0 586 23.5 259

292943098354404 AY–68–36–132 TANC MW storm 5 2009/11/18 174.2 .18 743 4.27 7.1 584 24.1 261

293252098380801 AY–68–27–610 TANC MW prestorm2009/04/14 189.7 .40 753 6.60 6.8 636 25.4 288

293252098380801 AY–68–27–610 TANC MW storm 1 2009/10/04 194.1*** 2.63 738 6.35 6.8 663 24.3 308

293252098380801 AY–68–27–610 TANC MW storm 2 2009/10/07 198.5*** 1.79 738 6.39 6.7 668 25.2 313

293252098380801 AY–68–27–610 TANC MW storm 3 2009/10/17 200.6*** .27 749 6.45 6.8 661 24.7 307

293252098380801 AY–68–27–610 TANC MW storm 4 2009/10/28 195.1*** .29 732 6.12 6.9 666 24.2 314

293252098380801 AY–68–27–610 TANC MW storm 5 2009/11/17 193.0*** .69 748 6.17 6.9 665 24.0 314

* Sample collected from top of open interval during depth-dependent sampling. 

** Alkalinity is low and considered suspect.

*** Data from Edwards Aquifer Authority. 
108 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 8. Dissolved solids and major ion measurements for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San 

Antonio, south-central Texas, 2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, milligrams per liter; °C, 

degrees Celsius; --, not measured; E, estimated; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Dissolved solids 

(residue on evaporation, dried at 180°C)

(mg/L)

Calcium

(mg/L)

Magnesium 

(mg/L)

Potassium

(mg/L)

Regional aquifer public-supply wells

293359098290301 AY–68–29–414 1st (highest) quartile 2004/12/06 362 110 12.5 1.25

293359098290301 AY–68–29–414 1st quartile 2005/09/01 -- -- -- --

293358098231101 AY–68–29–610 1st quartile 2004/12/15 360 106 13.3 2.59

293358098231101 AY–68–29–610 1st quartile 2005/08/29 -- -- -- --

293120098285801 AY–68–29–714 1st quartile 2004/12/14 352 105 13.9 1.41

293120098285801 AY–68–29–714 1st quartile 2005/08/30 -- -- -- --

293145098224201 AY–68–29–929 1st quartile 2004/12/15 296 76.6 16.4 1.44

293119098211201 AY–68–30–718 1st quartile 2004/12/16 284 68.8 16.6 1.26

292843098425101 AY–68–35–106 1st quartile 2004/12/13 313 82.0 17.3 1.32

292459098382101 AY–68–35–913 1st quartile 2004/12/13 272 70.1 15.5 1.22

292925098360201 AY–68–36–104 1st quartile 2004/12/13 336 93.0 16.1 1.62

292925098360201 AY–68–36–104 1st quartile 2005/08/31 -- -- -- --

292822098325401 AY–68–36–206 1st quartile 2004/12/13 315 79.9 16.8 1.47

292822098325401 AY–68–36–206 1st quartile 2005/08/31 -- -- -- --

292944098292301 AY–68–37–105 1st quartile 2004/12/14 315 80.8 16.8 1.49

292944098292301 AY–68–37–105 1st quartile 2005/08/31 -- -- -- --

292522098291901 AY–68–37–426 1st quartile 2004/12/14 273 69.5 16.1 1.29

292643098241801 AY–68–37–601 1st quartile 2004/12/15 291 68.1 17.1 1.31

292643098241801 AY–68–37–601 1st quartile 2005/08/30 -- -- -- --

292328098294601 AY–68–37–705 1st quartile 2004/12/14 292 69.6 17.7 1.40

294225098080301 DX–68–23–601 1st quartile 2004/12/08 318 85.1 16.2 1.47

294225098080301 DX–68–23–601 1st quartile 2005/09/01 -- -- -- --

291210099475601 YP–69–50–506 1st quartile 2004/11/30 294 87.5 8.15 1.14

293111098340901 AY–68–28–807 2d quartile 2005/05/26 343 94.2 13.2 1.23

293512098291701 AY–68–29–109 2d quartile 2005/04/20 361 123 9.93 .79

292424098421501 AY–68–35–810 2d quartile 2005/04/21 279 73.4 14.3 1.19

292053098365501 AY–68–44–110 2d quartile 2005/05/26 278 66.4 18.2 1.19

293807098155301 DX–68–22–901 2d quartile 2005/05/18 299 83.6 11.1 .89

292604098563201 TD–68–33–501 2d quartile 2005/05/16 285 69.1 17.3 1.34

292116099095501 TD–69–47–305 2d quartile 2005/04/27 270 70.3 15.2 1.17

291232099470301 YP–69–50–339 2d quartile 2005/05/11 309 89.0 10.1 1.05

293128098473101 AY–68–26–814 3d quartile 2005/04/18 327 80.0 22.4 1.50

293451098313201 AY–68–28–601 3d quartile 2005/05/17 344 107 8.12 1.18

294604098060801 DX–68–16–708 3d quartile 2005/04/25 344 109 16.1 1.18

294019098114701 DX–68–23–504 3d quartile 2005/05/18 332 88.0 15.9 1.40

Table 8
Table 8 109

Table 8. Dissolved solids and major ion measurements for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San 

Antonio, south-central Texas, 2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, milligrams per liter; °C, 

degrees Celsius; --, not measured; E, estimated; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Dissolved solids 

(residue on evaporation, dried at 180°C)

(mg/L)

Calcium

(mg/L)

Magnesium 

(mg/L)

Potassium

(mg/L)

292215098580201 TD–68–41–103 3d quartile 2005/05/09 293 71.6 16.0 1.12

292119098524901 TD–68–41–308 3d quartile 2005/04/27 293 71.8 15.6 1.20

291943099163301 TD–69–46–601 3d quartile 2005/05/09 265 72.5 15.3 1.04

291840099382601 YP–69–43–606 3d quartile 2005/05/11 290 80.5 11.2 1.01

293518098332601 AY–68–28–203 4th quartile 2005/04/19 435 141 7.8 1.20

293023098355401 AY–68–28–702 4th quartile 2005/04/26 346 101 15.5 1.58

293042098305201 AY–68–28–913 4th quartile 2005/06/30 339 100 16.5 1.31

292442098474501 AY–68–34–803 4th quartile 2005/04/20 265 74.5 13.7 1.19

292405098371201 AY–68–36–704 4th quartile 2005/05/23 275 69.3 17.0 1.11

292931098274601 AY–68–37–124 4th quartile 2005/05/25 300 73.4 16.9 1.34

293729098173101 DX–68–30–215 4th quartile 2005/04/25 360 112 11.6 1.38

291219099095601 TD–69–55–604 4th quartile 2005/05/16 292 71.8 15.1 1.10

Monitoring wells

292943098354401 AY–68–36–135 TANC MW OVB 2007/10/30 600 105 13.0 3.10

292943098354402 AY–68–36–133 TANC MW 2007/10/31 349 84.7 14.8 1.79

292943098354403 AY–68–36–134 TANC MW 2007/10/30 341 89.4 15.9 1.54

292943098354404 AY–68–36–132 TANC MW 2007/11/01 351 89.7 16.4 1.48

292851098374401 AY–68–35–315 TANC MW 2008/05/06 350 93.1 15.8 1.52

292851098374402 AY–68–35–314 TANC MW 2008/05/07 349 98.2 14.8 1.79

Well-field depth-dependent sampling (W4)

292916098360701 AY–68–36–105 W4-shallow (380), 

normal

2007/11/16 339 88.6 15.9 1.59

292916098360701 AY–68–36–105 W4-intermediate 

(430), normal

2007/11/15 343 88.4 16.0 1.56

292916098360701 AY–68–36–105 W4-deep (540), 

normal

2007/11/15 343 87.5 15.2 1.59

292916098360701 AY–68–36–105 W4-shallow (380), 

ambient

2007/11/16 343 88.2 15.9 1.56

292916098360701 AY–68–36–105 W4-intermediate 

(430), ambient

2007/11/14 233 86.4 15.7 1.54

292916098360701 AY–68–36–105 W4-deep (540), ambient2007/11/15 342 88.7 15.5 1.59

292916098360701 AY–68–36–105 W4-shallow (380), 

moderate

2007/11/16 341 93.1 15.5 1.66

292916098360701 AY–68–36–105 W4-intermediate 

(430), moderate

2007/11/14 255 86.9 15.8 1.54

292916098360701 AY–68–36–105 W4-deep (540), moderate2007/11/15 339 86.2 15.4 1.48
110 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 8. Dissolved solids and major ion measurements for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San 

Antonio, south-central Texas, 2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, milligrams per liter; °C, 

degrees Celsius; --, not measured; E, estimated; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Dissolved solids 

(residue on evaporation, dried at 180°C)

(mg/L)

Calcium

(mg/L)

Magnesium 

(mg/L)

Potassium

(mg/L)

Well-field wells (wellhead sampling)

292919098360501 AY–68–36–103 wellhead 2007/11/29 346 95.8 15.5 1.72

292925098360201 AY–68–36–104 wellhead 2007/11/28 349 92.9 16.6 1.59

292916098360701 AY–68–36–105 *wellhead 2007/11/16 343 89.9 15.1 1.57

292920098360601 AY–68–36–130 wellhead 2007/11/29 350 95.0 14.9 1.57

292923098360301 AY–68–36–131 wellhead 2007/11/28 357 94.0 15.4 1.59

Temporal sampling

292923098360301 AY–68–36–131 TANC PSW pre-storm 2009/04/09 342 87.7 15.0 1.47

292923098360301 AY–68–36–131 TANC PSW storm 1 2009/10/06 316 87.6 15.6 1.54

292923098360301 AY–68–36–131 TANC PSW storm 2 2009/10/09 336 87.1 16.0 1.54

292923098360301 AY–68–36–131 TANC PSW storm 3 2009/10/19 371 92.6 15.7 1.42

292923098360301 AY–68–36–131 TANC PSW storm 4 2009/10/30 340 90.9 16.3 1.47

292923098360301 AY–68–36–131 TANC PSW storm 5 2009/11/19 350 90.9 16.1 1.51

292943098354402 AY–68–36–133 TANC MW pre-storm 2009/04/08 348 93.6 16.0 1.61

292943098354402 AY–68–36–133 TANC MW storm 1 2009/10/05 342 91.5 15.8 1.50

292943098354402 AY–68–36–133 TANC MW storm 2 2009/10/07 338 90.0 15.5 1.45

292943098354402 AY–68–36–133 TANC MW storm 3 2009/10/17 364 93.8 15.7 1.47

292943098354402 AY–68–36–133 TANC MW storm 4 2009/10/28 344 94.7 16.3 1.51

292943098354402 AY–68–36–133 TANC MW storm 5 2009/11/18 351 93.4 15.7 1.47

292943098354403 AY–68–36–134 TANC MW pre-storm 2009/04/09 345 92.9 14.8 1.43

292943098354403 AY–68–36–134 TANC MW storm 1 2009/10/05 338 89.4 15.5 1.43

292943098354403 AY–68–36–134 TANC MW storm 2 2009/10/08 353 88.8 15.6 1.48

292943098354403 AY–68–36–134 TANC MW storm 3 2009/10/18 367 94.0 15.6 1.47

292943098354403 AY–68–36–134 TANC MW storm 4 2009/10/29 344 96.5 16.6 1.47

292943098354403 AY–68–36–134 TANC MW storm 5 2009/11/18 353 92.8 15.8 1.40

292943098354404 AY–68–36–132 TANC MW pre-storm 2009/04/09 342 96.1 17.7 1.60

292943098354404 AY–68–36–132 TANC MW storm 1 2009/10/05 341 87.9 16.2 1.41

292943098354404 AY–68–36–132 TANC MW storm 2 2009/10/08 334 86.5 16.4 1.43

292943098354404 AY–68–36–132 TANC MW storm 3 2009/10/18 412 92.7 16.7 1.41

292943098354404 AY–68–36–132 TANC MW storm 4 2009/10/29 348 93.2 17.2 1.47

292943098354404 AY–68–36–132 TANC MW storm 5 2009/11/18 344 91.2 16.5 1.47

293252098380801 AY–68–27–610 TANC MW pre-storm 2009/04/14 370 104 13.3 .98

293252098380801 AY–68–27–610 TANC MW storm 1 2009/10/04 386 115 13.8 .95

293252098380801 AY–68–27–610 TANC MW storm 2 2009/10/07 379 115 13.6 .91

293252098380801 AY–68–27–610 TANC MW storm 3 2009/10/17 408 115 13.5 .95

293252098380801 AY–68–27–610 TANC MW storm 4 2009/10/28 388 118 13.8 .96

293252098380801 AY–68–27–610 TANC MW storm 5 2009/11/17 386 111 13.4 .92
Table 8 111

Table 8. Dissolved solids and major ion measurements for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San 

Antonio, south-central Texas, 2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, milligrams per liter; °C, 

degrees Celsius; --, not measured; E, estimated; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

Sodium

(mg/L)

Bromide

(mg/L)

Chloride

(mg/L)

Fluoride

(mg/L)

Iodide

(mg/L)

Sulfate

(mg/L)

Silica

(mg/L)

Calcite, 

mineral 

saturation 

index

Dolomite, 

mineral 

saturation 

index

Gypsum, 

mineral 

saturation 

index

Regional aquifer public-supply wells

293359098290301 11.7 E0.20 18.3 0.21 0.003 16.2 14.4 0.11 -0.13 -2.38

293359098290301 -- -- -- -- -- -- -- -- -- --

293358098231101 10.3 .16 14.3 .23 .004 25.5 13.7 -.01 -.61 -2.05

293358098231101 -- -- -- -- -- -- -- -- -- --

293120098285801 9.85 .15 15.0 .22 .002 3.9 12.6 .02 -.53 -1.97

293120098285801 -- -- -- -- -- -- -- -- -- --

293145098224201 10.4 .15 16.6 .24 .002 22.1 14.0 .07 -.19 -2.22

293119098211201 11.0 .14 20.7 .28 .002 19.2 13.1 .02 -.22 -2.31

292843098425101 8.10 .14 12.1 .23 .002 39.1 13.2 .01 -.34 -1.95

292459098382101 9.44 .11 17.9 .20 .002 16.1 13.3 .02 -.28 -2.37

292925098360201 10.4 .15 15.6 .27 E.001 28.1 13.5 .01 -.43 -2.05

292925098360201 -- -- -- -- -- -- -- -- -- --

292822098325401 10.6 .13 16.3 .25 .002 32.3 13.9 .01 -.34 -2.04

292822098325401 -- -- -- -- -- -- -- -- -- --

292944098292301 10.9 .15 16.3 .23 .002 29.2 14.1 -.00 -.36 -2.08

292944098292301 -- -- -- -- -- -- -- -- -- --

292522098291901 10.7 .14 21.0 .23 .002 16.6 13.4 .02 -.28 -2.37

292643098241801 11.3 .15 23.6 .33 .002 24.2 13.5 -.00 -.24 -2.22

292643098241801 -- -- -- -- -- -- -- -- -- --

292328098294601 11.4 .15 24.0 .33 .002 27.7 13.6 -.02 -.26 -2.16

294225098080301 10.4 .14 16.8 .26 .002 22.5 13.6 .03 -.34 -2.17

294225098080301 -- -- -- -- -- -- -- -- -- --

291210099475601 15.2 .15 26.2 .16 .002 2.7 13.6 -.33 -1.36 -2.17

293111098340901 11.6 .12 15.4 .22 E.002 16.6 14.2 -.04 -.62 -2.27

293512098291701 12.4 .10 26.5 .15 <.002 1.7 14.7 .04 -.31 -2.31

292424098421501 9.46 .081 16.8 .22 <.002 16.6 13.4 .04 -.29 -2.34

292053098365501 10.1 .090 20.9 .28 <.002 15.5 13.3 -.07 -.33 -2.42

293807098155301 6.21 .090 10.5 .15 E.002 13.6 11.3 .01 -.54 -2.37

292604098563201 7.10 .085 10.8 .21 <.002 4.8 12.6 .12 -.03 -1.98

292116099095501 8.13 .071 12.7 .24 <.002 16.9 13.6 -.28 -.88 -2.35

291232099470301 13.9 .11 26.9 .12 <.002 14.4 13.6 -.00 -.62 -2.33

293128098473101 7.86 .075 14.0 .37 E.001 56.0 13.1 .24 .26 -1.82

293451098313201 8.42 .10 14.6 .16 E.001 15.2 13.7 .11 -.59 -2.25

294604098060801 7.91 .069 13.3 .20 <.002 15.2 13.3 .25 -.01 -2.27

294019098114701 7.91 .10 15.1 .21 E.001 22.6 13.4 .08 -.26 -2.16
112 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 8. Dissolved solids and major ion measurements for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San 

Antonio, south-central Texas, 2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, milligrams per liter; °C, 

degrees Celsius; --, not measured; E, estimated; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

Sodium

(mg/L)

Bromide

(mg/L)

Chloride

(mg/L)

Fluoride

(mg/L)

Iodide

(mg/L)

Sulfate

(mg/L)

Silica

(mg/L)

Calcite, 

mineral 

saturation 

index

Dolomite, 

mineral 

saturation 

index

Gypsum, 

mineral 

saturation 

index

292215098580201 9.56 0.086 18.6 0.21 <0.002 16.2 13.2 0.10 -0.11 -2.36

292119098524901 10.7 .10 20.8 .26 .002 16.5 13.2 -.31 -.94 -2.35

291943099163301 7.45 .070 12.0 .19 <.002 17.3 13.4 -.05 -.44 -2.33

291840099382601 10.9 .10 21.9 .13 <.002 13.1 13.2 .04 -.44 -2.40

293518098332601 20.2 .14 51.8 .12 E.002 15.8 14.2 .17 -.60 -2.17

293023098355401 10.0 .088 15.7 .26 E.001 24.2 13.0 -.40 -1.30 -2.09

293042098305201 10.5 .10 16.1 .22 E.001 37.4 12.4 -.11 -.69 -1.91

292442098474501 8.03 .037 11.9 .21 <.002 17.6 13.5 .04 -.31 -2.31

292405098371201 10.3 .10 20.0 .19 <.002 15.9 13.2 -.02 -.31 -2.39

292931098274601 10.6 .086 16.1 .21 <.002 22.3 13.8 -.05 -.40 -2.22

293729098173101 11.0 .083 20.4 .18 E.001 12.6 14.0 .19 -.29 -2.33

291219099095601 11.6 .12 25.4 .17 <.002 15.7 13.1 .12 -.03 -1.98

Monitoring wells

292943098354401 78.4 .33 97.6 .86 .006 60.6 26.7 .07 -.37 -1.73

292943098354402 13.2 .10 16.5 .26 .004 27.7 11.3 .06 -.26 -2.09

292943098354403 10.7 .094 15.9 .23 E.001 25.4 11.7 .04 -.31 -2.11

292943098354404 9.89 .10 15.5 .26 E.001 25.0 10.9 .07 -.24 -2.12

292851098374401 10.6 .10 15.3 .22 E.001 28.4 11.8 -.03 -.48 -2.05

292851098374402 10.5 .11 15.0 .22 E.002 26.9 12.5 -.00 -.46 -2.06

Well-field depth-dependent sampling (W4)

292916098360701 10.7 .095 15.6 .23 <.002 29.7 12.0 .23 .07 -2.05

292916098360701 10.8 .10 15.6 .23 <.002 29.7 11.7 .11 -.20 -2.04

292916098360701 10.9 .10 15.9 .24 E.001 29.3 11.7 .11 -.21 -2.05

292916098360701 10.6 .10 15.6 .23 <.002 29.7 11.9 .23 .06 -2.05

292916098360701 10.7 .10 15.5 .22 <.002 29.7 12.4 .19 -.01 -2.05

292916098360701 11.0 .10 15.9 .21 <.002 29.2 11.9 .11 -.20 -2.05

292916098360701 11.4 .11 16.1 .23 E.001 29.0 12.7 .24 .05 -2.04

292916098360701 10.8 .10 15.4 .23 <.002 29.5 12.4 .15 -.09 -2.05

292916098360701 10.4 .095 15.7 .21 <.002 29.8 11.8 .11 -.19 -2.05
Table 8 113

Table 8. Dissolved solids and major ion measurements for groundwater samples collected for the study of the transport of 

anthropogenic and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San 

Antonio, south-central Texas, 2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, milligrams per liter; °C, 

degrees Celsius; --, not measured; E, estimated; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

Sodium

(mg/L)

Bromide

(mg/L)

Chloride

(mg/L)

Fluoride

(mg/L)

Iodide

(mg/L)

Sulfate

(mg/L)

Silica

(mg/L)

Calcite, 

mineral 

saturation 

index

Dolomite, 

mineral 

saturation 

index

Gypsum, 

mineral 

saturation 

index

Well-field wells (wellhead sampling)

292919098360501 11.5 0.10 16.2 0.23 <0.002 28.8 12.4 0.18 -0.11 -2.03

292925098360201 10.8 .083 15.6 .24 <.002 28.1 11.8 .07 -.31 -2.05

292916098360701 11.0 .10 16.2 .22 E.001 29.0 12.3 .13 -.18 -2.05

292920098360601 11.4 .089 16.2 .22 <.002 28.1 12.3 .19 -.11 -2.04

292923098360301 11.2 .091 16.2 .24 <.002 27.1 12.2 .07 -.34 -2.06

Temporal sampling

292923098360301 10.3 .090 16.4 .23 -- 29.2 12.1 -.11 -.67 -2.05

292923098360301 10.4 .094 16.6 .24 -- 28.4 12.7 -.09 -.62 -2.06

292923098360301 10.9 .10 16.1 .24 -- 28.6 12.0 -.10 -.62 -2.06

292923098360301 10.6 .090 16.2 .26 -- 27.3 12.0 -.04 -.53 -2.06

292923098360301 11.0 .091 16.2 .25 -- 28.2 12.1 -.10 -.63 -2.05

292923098360301 10.8 .086 16.3 .27 -- 29.1 12.0 .02 -.41 -2.04

292943098354402 11.4 .16 16.2 .19 -- 25.9 12.4 -.04 -.47 -2.09

292943098354402 10.5 .11 16.6 .23 -- 25.9 12.2 .01 -.41 -2.09

292943098354402 10.5 .11 16.6 .22 -- 26.2 11.7 -.04 -.51 -2.09

292943098354402 10.4 .11 16.3 .24 -- 25.9 11.8 .04 -.35 -2.09

292943098354402 10.9 .11 16.4 .22 -- 25.6 11.8 .05 -.34 -2.09

292943098354402 10.6 .11 16.9 .20 -- 26.9 11.8 .09 -.28 -2.07

292943098354403 9.86 .10 16.3 .23 -- 25.9 11.6 -.07 -.57 -2.09

292943098354403 10.1 .10 16.6 .23 -- 25.7 12.1 -.04 -.49 -2.10

292943098354403 10.4 .11 16.1 .23 -- 25.7 11.4 -.07 -.55 -2.11

292943098354403 10.2 .11 16.2 .24 -- 25.6 11.8 .01 -.43 -2.09

292943098354403 10.9 .10 16.4 .26 -- 25.4 11.9 -.02 -.46 -2.09

292943098354403 10.3 .10 16.4 .25 -- 25.9 11.6 .07 -.30 -2.09

292943098354404 10.9 .14 15.7 .20 -- 27.2 12.5 -.03 -.45 -2.06

292943098354404 9.39 .10 16.2 .24 -- 25.8 11.9 -.00 -.40 -2.11

292943098354404 9.90 .10 15.8 .25 -- 25.9 11.2 -.05 -.48 -2.11

292943098354404 9.83 .10 15.7 .25 -- 25.5 11.5 .02 -.36 -2.10

292943098354404 10.5 .10 16.0 .24 -- 25.4 11.5 -.02 -.44 -2.10

292943098354404 9.89 .10 16.0 .26 -- 26.2 11.4 .09 -.22 -2.09

293252098380801 8.83 .12 -- -- -- -- 13.4 -.08 -.70 --

293252098380801 9.45 .13 17.2 .17 -- 13.2 13.5 -.09 -.77 -2.31

293252098380801 9.54 .13 16.4 .16 -- 14.7 13.0 -.13 -.84 -2.27

293252098380801 9.33 .13 16.9 .16 -- 14.2 12.8 -.05 -.68 -2.29

293252098380801 10.2 .12 16.7 .15 -- 14.6 13.0 -.01 -.61 -2.27

293252098380801 9.89 .15 18.5 .13 -- 17.9 13.0 .01 -.57 -2.19

* Sample collected from top of open interval during depth-dependent sampling.
114 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 9. Trace element measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, micrograms per liter; --, not measured; E, estimated; 

<, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Aluminum

(μg/L)

Antimony

(μg/L)

Arsenic

(μg/L)

Barium

(μg/L)

Beryllium

(μg/L)

Boron

(μg/L)

Cadmium

(μg/L)

Chromium

(μg/L)

Cobalt

(μg/L)

Regional aquifer public-supply wells

293359098290301 AY–68–29–414 1st (highest) quartile 2004/12/06 E1.13 <0.2 0.46 43.0 <0.06 50.0 <0.04 <0.8 0.48

293359098290301 AY–68–29–414 1st quartile 2005/09/01 -- -- -- -- -- -- -- -- --

293358098231101 AY–68–29–610 1st quartile 2004/12/15 <1.6 <.2 .40 42.5 <.06 57.0 <.04 <.8 .25

293358098231101 AY–68–29–610 1st quartile 2005/08/29 -- -- -- -- -- -- -- -- --

293120098285801 AY–68–29–714 1st quartile 2004/12/14 <1.6 <.2 .39 34.8 <.06 41.8 <.04 <.8 .30

293120098285801 AY–68–29–714 1st quartile 2005/08/30 -- -- -- -- -- -- -- -- --

293145098224201 AY–68–29–929 1st quartile 2004/12/15 E1.26 <.2 .46 49.8 <.06 57.0 <.04 E.49 .18

293119098211201 AY–68–30–718 1st quartile 2004/12/16 <1.6 <.2 .54 103 <.06 50.7 <.04 <.8 .13

292843098425101 AY–68–35–106 1st quartile 2004/12/13 <1.6 <.2 .37 31.0 <.06 59.1 <.04 <.8 .22

292459098382101 AY–68–35–913 1st quartile 2004/12/13 E.80 <.2 .56 47.2 <.06 57.1 <.04 <.8 .18

292925098360201 AY–68–36–104 1st quartile 2004/12/13 <1.6 <.2 .45 37.0 <.06 62.5 <.04 <.8 .35

292925098360201 AY–68–36–104 1st quartile 2005/08/31 -- -- -- -- -- -- -- -- --

292822098325401 AY–68–36–206 1st quartile 2004/12/13 <1.6 <.2 .44 38.4 <.06 55.7 <.04 <.8 .22

292822098325401 AY–68–36–206 1st quartile 2005/08/31 -- -- -- -- -- -- -- -- --

292944098292301 AY–68–37–105 1st quartile 2004/12/14 <1.6 <.2 .36 40.8 <.06 69.0 <.04 <.8 .15

292944098292301 AY–68–37–105 1st quartile 2005/08/31 -- -- -- -- -- -- -- -- --

292522098291901 AY–68–37–426 1st quartile 2004/12/14 E.82 <.2 .57 58.5 <.06 43.2 <.04 <.8 .18

292643098241801 AY–68–37–601 1st quartile 2004/12/15 <1.6 <.2 .48 126 <.06 46.3 <.04 <.8 .14

292643098241801 AY–68–37–601 1st quartile 2005/08/30 -- -- -- -- -- -- -- -- --

292328098294601 AY–68–37–705 1st quartile 2004/12/14 <1.6 <.2 .57 121 <.06 67.0 E.02 <.8 .13

294225098080301 DX–68–23–601 1st quartile 2004/12/08 <1.6 <.2 .51 49.7 <.06 58.3 <.04 3.58 .17

291210099475601 YP–69–50–506 1st quartile 2004/11/30 <1.6 <.2 .68 60.8 <.06 89.5 <.04 <.8 .25

293111098340901 AY–68–28–807 2d quartile 2005/05/26 E1.34 <.2 .45 27.4 <.06 74.5 <.04 <.8 .19

293512098291701 AY–68–29–109 2d quartile 2005/04/20 <1.6 <.2 .75 52.7 <.06 42.6 <.04 <.8 .53

292424098421501 AY–68–35–810 2d quartile 2005/04/21 <1.6 <.2 .38 46.5 <.06 49.8 <.04 <.8 .23

292053098365501 AY–68–44–110 2d quartile 2005/05/26 E1.25 <.2 .53 60.1 <.06 70.8 <.04 <.8 .13

293807098155301 DX–68–22–901 2d quartile 2005/05/18 <1.6 <.2 .41 30.7 <.06 41.6 <.04 <.8 .27

292604098563201 TD–68–33–501 2d quartile 2005/05/16 E.80 <.2 .53 33.1 <.06 59.5 <.04 <.8 .19

292116099095501 TD–69–47–305 2d quartile 2005/04/27 <1.6 <.2 .48 38.6 <.06 52.2 <.04 <.8 .10

291232099470301 YP–69–50–339 2d quartile 2005/05/11 2.04 <.2 .62 53.0 <.06 64.6 <.04 <.8 .14

293128098473101 AY–68–26–814 3d quartile 2005/04/18 E.85 <.2 .36 30.7 <.06 78.7 <.04 <.8 .18

293451098313201 AY–68–28–601 3d quartile 2005/05/17 <1.6 <.2 .48 42.6 <.06 51.1 <.04 <.8 .29

294604098060801 DX–68–16–708 3d quartile 2005/04/25 <1.6 <.2 .38 34.6 <.06 46.3 <.04 <.8 .15

294019098114701 DX–68–23–504 3d quartile 2005/05/18 1.81 <.2 .42 46.9 <.06 65.1 <.04 E.65 .26

292215098580201 TD–68–41–103 3d quartile 2005/05/09 E1.03 <.2 .47 48.3 <.06 69.0 <.04 <.8 .13

292119098524901 TD–68–41–308 3d quartile 2005/04/27 E.84 <.2 .50 44.3 <.06 67.6 <.04 <.8 .11

291943099163301 TD–69–46–601 3d quartile 2005/05/09 <1.6 <.2 .38 37.1 E.03 50.8 <.04 <.8 .13

291840099382601 YP–69–43–606 3d quartile 2005/05/11 <1.6 <.2 .51 51.4 E.04 53.5 <.04 <.8 .13

Table 9
Table 9 115

Table 9. Trace element measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, micrograms per liter; --, not measured; E, estimated; 

<, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Aluminum

(μg/L)

Antimony

(μg/L)

Arsenic

(μg/L)

Barium

(μg/L)

Beryllium

(μg/L)

Boron

(μg/L)

Cadmium

(μg/L)

Chromium

(μg/L)

Cobalt

(μg/L)

293518098332601 AY–68–28–203 4th quartile 2005/04/19 E.84 <0.2 0.50 54.4 <0.06 58.5 <0.04 <0.8 0.33

293023098355401 AY–68–28–702 4th quartile 2005/04/26 <1.6 <.2 .34 33.0 <.06 60.0 <.04 <.8 .16

293042098305201 AY–68–28–913 4th quartile 2005/06/30 <1.6 <.2 .36 35.1 <.06 54.8 <.04 <.8 .24

292442098474501 AY–68–34–803 4th quartile 2005/04/20 <1.6 <.2 .74 42.5 <.06 52.0 <.04 <.8 .30

292405098371201 AY–68–36–704 4th quartile 2005/05/23 E.81 <.2 .44 51.2 <.06 59.7 <.04 <.8 .21

292931098274601 AY–68–37–124 4th quartile 2005/05/25 E.88 <.2 .47 33.9 <.06 76.5 <.04 <.8 .15

293729098173101 DX–68–30–215 4th quartile 2005/04/25 <1.6 <.2 .44 36.1 <.06 48.2 <.04 <.8 .18

291219099095601 TD–69–55–604 4th quartile 2005/05/16 <1.6 <.2 .57 58.9 <.06 64.6 <.04 <.8 .22

Monitoring wells

292943098354401 AY–68–36–135 TANC MW OVB 2007/10/30 <1.6 <.14 .49 64.7 <.01 270 <.04 .39 .10

292943098354402 AY–68–36–133 TANC MW 2007/10/31 2.36 <.14 .34 40.9 <.01 60.0 <.04 .32 .14

292943098354403 AY–68–36–134 TANC MW 2007/10/30 <1.6 <.14 .31 36.1 <.01 56.2 <.04 .20 .06

292943098354404 AY–68–36–132 TANC MW 2007/11/01 2.22 .22 .32 35.9 <.01 49.8 E.02 .44 .05

292851098374401 AY–68–35–315 TANC MW 2008/05/06 <1.6 <.14 .35 35.9 <.01 56.8 <.04 .49 .05

292851098374402 AY–68–35–314 TANC MW 2008/05/07 <1.6 <.14 .34 39.5 <.01 62.0 <.04 1.08 .10

Well-field depth-dependent sampling (W4)

292916098360701 AY–68–36–105 W4-shallow (380), 

normal

2007/11/16 26.5 <.42 .27 38.0 <.04 <30 <.12 <.36 <.10

292916098360701 AY–68–36–105 W4-intermediate 

(430), normal

2007/11/15 <1.6 <.14 .37 37.5 <.01 84.3 <.04 E.11 .05

292916098360701 AY–68–36–105 W4-deep (540), 

normal

2007/11/15 <1.6 <.14 .40 38.9 <.01 93.1 <.04 E.11 .05

292916098360701 AY–68–36–105 W4-shallow (380), 

ambient

2007/11/16 <1.6 <.14 .36 37.9 <.01 57.7 <.04 E.11 .07

292916098360701 AY–68–36–105 W4-intermediate 

(430), ambient

2007/11/14 <1.6 <.14 .35 36.9 <.01 57.6 <.04 .12 .05

292916098360701 AY–68–36–105 W4-deep (540), 

ambient

2007/11/15 <1.6 <.14 .37 38.6 <.01 58.0 <.04 .14 .06

292916098360701 AY–68–36–105 W4-shallow (380), 

moderate

2007/11/16 <1.6 <.14 .36 40.0 <.01 67.7 <.04 E.10 .05

292916098360701 AY–68–36–105 W4-intermediate 

(430), moderate

2007/11/14 <1.6 <.14 .34 37.1 <.01 56.9 <.04 .13 .04

292916098360701 AY–68–36–105 W4-deep (540), 

moderate

2007/11/15 <1.6 <.14 .36 37.2 <.01 59.5 <.04 E.10 .05

Well-field wells (wellhead sampling)

292919098360501 AY–68–36–103 wellhead 2007/11/29 <1.6 <.14 .37 40.4 <.01 53.2 <.04 .14 .04

292925098360201 AY–68–36–104 wellhead 2007/11/28 <1.6 <.14 .35 36.6 <.01 63.3 <.04 E.10 .04

292916098360701 AY–68–36–105 *wellhead 2007/11/16 1.77 <.14 .38 40.3 <.01 60.6 <.04 E.12 .07

292920098360601 AY–68–36–130 wellhead 2007/11/29 <1.6 <.14 .35 39.7 <.01 63.8 <.04 E.09 .05

292923098360301 AY–68–36–131 wellhead 2007/11/28 E.92 <.14 .37 38.1 <.01 59.2 <.04 .15 .04
116 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 9. Trace element measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, micrograms per liter; --, not measured; E, estimated; 

<, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Aluminum

(μg/L)

Antimony

(μg/L)

Arsenic

(μg/L)

Barium

(μg/L)

Beryllium

(μg/L)

Boron

(μg/L)

Cadmium

(μg/L)

Chromium

(μg/L)

Cobalt

(μg/L)

Temporal sampling

292923098360301 AY–68–36–131 TANC PSW prestorm2009/04/09 <4 E0.03 0.38 38.6 <0.02 55.6 <0.02 0.22 0.12

292923098360301 AY–68–36–131 TANC PSW storm 1 2009/10/06 11.8 E.03 .48 38.1 <.01 61.4 <.02 .19 .17

292923098360301 AY–68–36–131 TANC PSW storm 2 2009/10/09 <3.4 E.03 .41 36.4 <.01 58.8 <.02 .26 .15

292923098360301 AY–68–36–131 TANC PSW storm 3 2009/10/19 <3.4 E.03 .36 37.5 <.01 66.1 <.02 .16 .18

292923098360301 AY–68–36–131 TANC PSW storm 4 2009/10/30 <3.4 E.03 .39 36.8 <.01 56.6 <.02 E.11 .15

292923098360301 AY–68–36–131 TANC PSW storm 5 2009/11/19 <3.4 E.03 .43 39.2 <.01 62.6 <.02 E.12 .15

292943098354402 AY–68–36–133 TANC MW prestorm2009/04/08 <4 E.03 .34 40.2 <.02 57.5 <.02 .24 .14

292943098354402 AY–68–36–133 TANC MW storm 1 2009/10/05 7.35 E.03 .38 39.2 <.01 58.7 <.02 .31 .19

292943098354402 AY–68–36–133 TANC MW storm 2 2009/10/07 <3.4 E.03 .38 38.8 E.01 58.0 <.02 .22 .20

292943098354402 AY–68–36–133 TANC MW storm 3 2009/10/17 <3.4 E.03 .36 39.0 <.01 60.3 <.02 .29 .21

292943098354402 AY–68–36–133 TANC MW storm 4 2009/10/28 <3.4 E.03 .36 38.2 <.01 56.5 <.02 .14 .17

292943098354402 AY–68–36–133 TANC MW storm 5 2009/11/18 E2.22 E.03 .64 38.3 <.01 60.8 <.02 .16 .21

292943098354403 AY–68–36–134 TANC MW prestorm2009/04/09 <4 -- .34 36.1 <.02 52.8 <.02 .27 .13

292943098354403 AY–68–36–134 TANC MW storm 1 2009/10/05 <3.4 -- .39 36.7 <.01 57.0 <.02 .24 .24

292943098354403 AY–68–36–134 TANC MW storm 2 2009/10/08 <3.4 -- .37 35.7 <.01 61.2 <.02 .21 .19

292943098354403 AY–68–36–134 TANC MW storm 3 2009/10/18 <3.4 -- .36 36.0 <.01 61.1 <.02 .29 .20

292943098354403 AY–68–36–134 TANC MW storm 4 2009/10/29 <3.4 -- .38 36.3 <.01 58.5 <.02 E.11 .22

292943098354403 AY–68–36–134 TANC MW storm 5 2009/11/18 <3.4 -- .34 36.4 <.01 60.4 <.02 E.10 .16

292943098354404 AY–68–36–132 TANC MW prestorm2009/04/09 <4 -- .32 36.0 <.02 54.2 <.02 .26 .14

292943098354404 AY–68–36–132 TANC MW storm 1 2009/10/05 <3.4 -- .38 35.2 <.01 56.2 <.02 .23 .19

292943098354404 AY–68–36–132 TANC MW storm 2 2009/10/08 <3.4 -- .34 33.9 <.01 54.1 <.02 .24 .16

292943098354404 AY–68–36–132 TANC MW storm 3 2009/10/18 E2.26 -- .33 35.0 <.01 60.7 <.02 .21 .20

292943098354404 AY–68–36–132 TANC MW storm 4 2009/10/29 <3.4 -- .32 34.9 <.01 52.4 <.02 E.11 .16

292943098354404 AY–68–36–132 TANC MW storm 5 2009/11/18 3.68 -- .32 35.5 <.01 58.8 <.02 E.12 .21

293252098380801 AY–68–27–610 TANC MW prestorm2009/04/14 <4 <.04 .30 37.2 <.02 41.0 <.02 .20 .50

293252098380801 AY–68–27–610 TANC MW storm 1 2009/10/04 <3.4 <.054 .34 38.9 <.01 44.7 <.02 .57 .23

293252098380801 AY–68–27–610 TANC MW storm 2 2009/10/07 <3.4 <.054 .37 39.5 <.01 45.0 <.02 .42 .25

293252098380801 AY–68–27–610 TANC MW storm 3 2009/10/17 <3.4 E.03 .33 38.9 <.01 48.1 <.02 .33 .22

293252098380801 AY–68–27–610 TANC MW storm 4 2009/10/28 <3.4 <.054 .37 39.7 E.01 51.0 <.02 .18 .26

293252098380801 AY–68–27–610 TANC MW storm 5 2009/11/17 <3.4 <.054 .35 39.5 <.01 47.9 <.02 .17 .28
Table 9 117

Table 9. Trace element measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, micrograms per liter; --, not measured; E, estimated; 

<, nondetection less than laboratory method reporting level]

USGS 

identification 

number

Copper

(μg/L)

Iron

(μg/L)

Ferrous 

(II) iron

(μg/L)

Total 

iron

(μg/L)

Lead

(μg/L)

Lithium

(μg/L)

Manganese

(μg/L)

Molybdenum

(μg/L)

Nickel

(μg/L)

Selenium

(μg/L)

Silver

(μg/L)

Strontium

(μg/L)

Thallium

(μg/L

Uranium

(μg/L)

Vanadium

(μg/L)

Zinc

(μg/L)

Regional aquifer public-supply wells

293359098290301 3.04 <6 -- -- 0.30 3.07 <0.2 E0.36 2.78 E0.36 <0.20 232 <0.04 0.97 3.62 2.17

293359098290301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

293358098231101 3.52 <6 -- -- 2.16 7.92 <.2 .66 3.60 .52 <.20 353 .04 .95 2.73 5.59

293358098231101 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

293120098285801 1.97 <6 -- -- 1.03 3.67 <.2 .65 5.61 .70 <.20 421 <.04 .93 2.47 5.29

293120098285801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

293145098224201 3.13 <6 -- -- 1.29 4.44 <.2 1.28 5.12 .56 <.20 556 .08 .91 3.18 10.6

293119098211201 3.11 <6 -- -- .35 7.66 <.2 .90 .83 .69 <.20 1,100 .05 .77 3.30 2.34

292843098425101 2.06 <6 -- -- .26 4.31 <.2 .85 2.50 .63 <.20 598 <.04 .84 2.15 6.13

292459098382101 9.41 <6 -- -- 4.45 4.00 <.2 .78 1.59 .68 <.20 609 E.02 .83 3.60 2.30

292925098360201 3.14 <6 -- -- 1.28 4.65 <.2 .80 4.52 .69 <.20 538 <.04 .97 2.49 5.84

292925098360201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

292822098325401 4.59 <6 -- -- .92 4.91 <.2 .77 3.26 .66 <.20 555 <.04 .94 2.87 8.86

292822098325401 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

292944098292301 5.43 <6 -- -- 2.21 5.10 <.2 .73 1.41 .50 <.20 509 E.03 .90 2.81 23.6

292944098292301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

292522098291901 1.58 <6 -- -- 5.03 5.31 <.2 .87 2.48 .82 <.20 955 .04 .85 3.91 9.95

292643098241801 6.84 <6 -- -- 1.80 10.6 <.2 2.52 1.49 .76 <.20 1,540 .07 .94 3.49 4.92

292643098241801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

292328098294601 1.14 <6 -- -- 3.47 12.5 <.2 7.79 8.74 .88 <.20 1,710 .14 1.16 4.41 2.00

294225098080301 2.88 <6 -- -- 1.28 6.24 <.2 .67 .77 .79 <.20 598 E.03 .84 2.85 1.42

291210099475601 4.33 <6 -- -- .83 3.08 .23 .93 1.16 .80 <.20 324 .07 .88 6.08 5.08

293111098340901 6.32 <6 -- 0.02 .98 4.52 <.2 .59 4.09 1.03 <.20 436 <.04 .78 2.96 8.16

293512098291701 3.90 <6 -- .04 .32 2.19 <.2 E.21 14.2 1.00 <.20 214 <.04 .91 5.31 2.77

292424098421501 2.00 <6 -- .03 .85 2.78 E.12 .64 4.47 E.34 <.20 477 E.03 .83 3.91 .95

292053098365501 1.45 <6 -- .05 .13 3.90 <.2 1.16 3.08 .91 <.20 1,470 <.04 .82 3.88 1.19

293807098155301 2.77 <6 -- .00 .16 2.82 <.2 E.40 3.95 .51 <.20 154 <.04 .56 2.53 4.19

292604098563201 2.01 <6 -- .00 .68 4.85 <.2 .77 2.77 .65 <.20 542 <.04 .72 2.51 .71

292116099095501 4.26 <6 -- .01 .83 2.68 <.2 .70 .28 .73 <.20 350 E.03 .77 2.88 5.43

291232099470301 2.68 <6 -- .01 .20 2.42 <.2 .62 1.13 .59 <.20 261 E.04 .79 5.81 1.89

293128098473101 1.63 6.78 -- <.01 .14 5.66 .34 1.11 3.40 .67 <.20 945 E.02 .92 3.60 4.18

293451098313201 2.56 <6 -- .01 .09 3.45 E.16 E.35 4.38 .61 <.20 235 <.04 .72 3.01 29.2

294604098060801 3.46 <6 -- .05 .55 3.19 <.2 .42 .37 .74 <.20 426 <.04 .86 2.64 2.69

294019098114701 2.48 <6 -- .02 .42 6.64 <.2 .63 4.40 .77 <.20 524 <.08 .74 2.73 2.73

292215098580201 5.54 <6 -- .03 .74 3.84 E.11 .65 1.51 .82 <.20 659 E.03 .72 4.69 11.3

292119098524901 0.41 <6 -- .01 .12 3.82 <.2 .60 .37 .68 <.20 549 E.03 .73 3.17 4.88

291943099163301 3.14 <6 -- .01 .26 2.57 <.2 .61 1.03 .54 <.20 343 <.04 .73 3.40 6.28

291840099382601 2.13 <6 -- .01 .20 2.14 <.2 .54 1.02 .66 <.20 402 E.02 .71 4.15 2.50
118 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 9. Trace element measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, micrograms per liter; --, not measured; E, estimated; 

<, nondetection less than laboratory method reporting level]

USGS 

identification 

number

Copper

(μg/L)

Iron

(μg/L)

Ferrous 

(II) iron

(μg/L)

Total 

iron

(μg/L)

Lead

(μg/L)

Lithium

(μg/L)

Manganese

(μg/L)

Molybdenum

(μg/L)

Nickel

(μg/L)

Selenium

(μg/L)

Silver

(μg/L)

Strontium

(μg/L)

Thallium

(μg/L

Uranium

(μg/L)

Vanadium

(μg/L)

Zinc

(μg/L)

293518098332601 3.88 E3.61 -- 0.10 0.30 2.75 0.58 E0.25 5.90 0.74 <0.20 228 <0.04 0.77 4.06 3.52

293023098355401 2.88 <6 -- .06 .26 3.55 <.2 .76 .75 .63 <.20 499 <.04 .89 2.95 5.96

293042098305201 0.74 24.0 -- .03 .21 3.68 1.17 .67 3.24 .77 <.20 470 E.02 .84 2.41 1.06

292442098474501 4.09 <6 -- .05 .87 2.90 <.2 .62 8.36 .87 <.20 366 <.04 .77 4.05 5.61

292405098371201 4.73 <6 -- .10 .88 4.32 <.2 .65 1.65 .71 <.20 677 .04 .76 3.48 10.2

292931098274601 1.68 <6 -- .05 .26 3.81 <.2 .68 3.38 .94 <.20 475 E.02 .79 3.12 1.25

293729098173101 3.35 E5.20 -- .11 .35 3.32 .95 E.34 .60 .76 <.20 236 E.03 .81 3.35 2.91

291219099095601 1.87 <6 -- .02 1.45 3.85 <.2 .75 3.02 .91 <.20 890 E.04 .65 4.05 .64

Monitoring wells

292943098354401 <1 <8 -- -- <.08 35.1 1.03 .89 .89 3.89 <.1 1,040 <.04 1.17 1.52 E1.25

292943098354402 <1 <8 -- -- <.08 4.86 34.9 1.06 2.89 .60 <.1 470 0.06 1.03 2.19 3.30

292943098354403 E.54 <8 -- -- <.08 3.82 E.19 .85 .66 .52 <.1 482 <.04 .91 2.17 1.99

292943098354404 <1 <8 -- -- <.08 3.50 .46 .93 1.03 .50 <.1 495 <.04 .94 2.12 2.60

292851098374401 <1 <8 -- -- <.08 4.32 .38 .81 1.57 .50 <.1 487 <.04 .80 2.12 <1.8

292851098374402 E.60 <8 -- -- <.08 4.89 1.83 1.01 2.30 .55 <.1 461 <.04 .82 2.12 E1.14

Well-field depth-dependent sampling (W4)

292916098360701 <3 <8 -- -- <.24 <5 <.6 .67 <1.0 .54 <.3 492 <.12 .83 2.29 <5.4

292916098360701 <1 <8 -- -- <.08 5.05 <.2 .74 .77 .57 <.1 499 <.04 .86 2.45 <1.8

292916098360701 <1 <8 -- -- <.08 5.34 E.16 .77 .67 .58 <.1 486 <.04 .88 2.47 <1.8

292916098360701 <1 <8 -- -- <.08 3.90 E.14 .72 .83 .58 <.1 530 <.04 .83 2.41 <1.8

292916098360701 <1 <8 -- -- <.08 4.01 .85 .73 .61 .53 <.1 489 <.04 .82 2.32 <1.8

292916098360701 <1 <8 -- -- <.08 3.91 <.2 .76 .76 .58 <.1 480 <.04 .86 2.51 <1.8

292916098360701 <1 <8 -- -- <.08 3.86 <.2 .69 .49 .58 <.1 528 E.02 .89 2.47 <1.8

292916098360701 <1 <8 -- -- <.08 3.93 .99 .72 .59 .50 <.1 497 <.04 .83 2.36 <1.8

292916098360701 <1 <8 -- -- <.08 4.16 <.2 .73 .69 .57 <.1 488 <.04 .86 2.44 <1.8

Well-field wells (wellhead sampling)

292919098360501 1.39 <8 -- -- .16 3.75 <.2 .68 .71 .57 <.1 504 <.04 .90 2.23 3.84

292925098360201 4.26 <8 -- -- 1.53 4.48 <.2 .75 .69 .57 <.1 496 <.04 .87 2.31 2.93

292916098360701 <1 <8 -- -- <.08 3.98 E.10 .73 .83 .61 <.1 517 <.04 .88 2.54 E.92

292920098360601 4.38 <8 -- -- .90 4.26 <.2 .74 .81 .59 <.1 503 <.04 .91 2.44 2.03

292923098360301 3.71 <8 -- -- .39 3.99 .25 .72 .59 .59 <.1 518 <.04 .90 2.34 E1.52
Table 9 119

Table 9. Trace element measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, micrograms per liter; --, not measured; E, estimated; 

<, nondetection less than laboratory method reporting level]

USGS 

identification 

number

Copper

(μg/L)

Iron

(μg/L)

Ferrous 

(II) iron

(μg/L)

Total 

iron

(μg/L)

Lead

(μg/L)

Lithium

(μg/L)

Manganese

(μg/L)

Molybdenum

(μg/L)

Nickel

(μg/L)

Selenium

(μg/L)

Silver

(μg/L)

Strontium

(μg/L)

Thallium

(μg/L

Uranium

(μg/L)

Vanadium

(μg/L)

Zinc

(μg/L)

Temporal sampling

292923098360301 3.36 <4 -- -- 0.42 3.64 E0.11 0.73 0.67 0.60 <0.01 487 <.04 0.89 2.46 <2

292923098360301 4.85 <6 -- -- .56 4.20 <.26 .74 1.16 .67 .01 467 E.02 .89 2.57 E2.40

292923098360301 3.67 <6 -- -- .44 3.83 <.26 .66 1.14 .64 <.01 456 E.02 .82 2.29 E2.00

292923098360301 4.07 <6 -- -- .47 4.45 <.26 .70 1.07 .63 <.01 495 E.02 .88 2.39 E1.88

292923098360301 3.33 <6 -- -- .34 4.17 <.26 .71 1.02 .59 <.01 457 E.02 .87 2.36 E2.69

292923098360301 3.99 <6 -- -- .50 3.76 <.26 .72 1.12 .61 <.01 498 E.02 .88 2.39 E2.29

292943098354402 <1 E3.03 -- -- <.06 3.87 1.01 .85 1.30 .57 <.01 496 E.03 .96 2.22 <2

292943098354402 <1 <6 -- -- <.03 4.06 .51 .80 1.67 .64 E.01 463 .04 .93 2.16 <2.8

292943098354402 1.03 <6 -- -- <.03 3.93 .36 .79 1.84 .66 <.01 471 .04 .90 2.22 <2.8

292943098354402 <1 <6 -- -- <.03 4.11 .40 .78 1.68 .57 <.01 477 .04 .89 2.27 E1.89

292943098354402 <1 <6 -- -- <.03 4.15 .31 .76 1.46 .61 <.01 452 .03 .93 2.21 E1.43

292943098354402 <1 <6 -- -- <.03 3.88 .36 .79 1.57 .65 <.01 480 .03 .95 2.55 <2.8

292943098354403 <1 <4 -- -- <.06 3.32 E.14 .75 .81 .58 <.01 467 <.04 .90 2.25 <2

292943098354403 <1 <6 -- -- <.03 3.84 <.26 .79 1.55 .70 <.01 461 E.02 .90 2.20 <2.8

292943098354403 <1 <6 -- -- <.03 4.05 <.26 .78 1.38 .65 <.01 465 E.02 .88 2.23 <2.8

292943098354403 <1 <6 -- -- <.03 4.02 <.26 .72 1.15 .59 <.01 470 E.02 .87 2.30 <2.8

292943098354403 <1 <6 -- -- <.03 4.12 <.26 .79 1.25 .61 <.01 470 E.02 .92 2.34 <2.8

292943098354403 <1 <6 -- -- E.02 3.82 <.26 .79 1.18 .56 <.01 478 E.02 .92 2.17 <2.8

292943098354404 <1 <4 -- -- <.06 3.61 E.19 .83 1.30 .54 <.01 511 <.04 .93 2.16 <2

292943098354404 <1 <6 -- -- <.03 3.73 <.26 .77 1.32 .63 <.01 473 E.02 .89 2.21 <2.8

292943098354404 <1 <6 -- -- <.03 3.47 <.26 .76 1.27 .60 <.01 467 E.01 .86 2.08 <2.8

292943098354404 <1 <6 -- -- <.03 4.00 <.26 .78 1.17 .56 <.01 488 E.02 .87 2.25 <2.8

292943098354404 <1 <6 -- -- <.03 3.76 <.26 .76 1.10 .57 <.01 461 E.02 .90 2.17 <2.8

292943098354404 <1 <6 -- -- <.03 3.69 <.26 .82 1.21 .55 E.01 494 E.02 .91 2.12 <2.8

293252098380801 <1 <4 -- -- <.06 2.96 E.12 .51 .90 .44 <.01 318 <.04 .83 2.41 <2

293252098380801 <1 E4.28 -- -- <.03 3.21 E.16 .56 1.92 .55 <.01 310 .02 .87 2.36 <2.8

293252098380801 <1 <6 -- -- <.03 3.11 <.26 .48 1.97 .53 <.01 329 .02 .83 2.49 <2.8

293252098380801 <1 <6 -- -- <.03 3.36 <.26 .41 1.34 .44 <.01 323 .02 .85 2.46 <2.8

293252098380801 <1 <6 -- -- <.03 3.72 <.26 .42 1.49 .48 <.01 325 .02 .89 2.52 <2.8

293252098380801 <1 E3.17 -- -- <.03 3.16 <.26 .43 1.67 .47 <.01 323 .02 .91 2.36 <2.8

* Sample collected from top of open interval during depth-dependent sampling.
120 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 10. Dissolved gas and associated data for groundwater samples collected for the study of the transport of anthropogenic and 

natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central 

Texas, 2004−9.

[By sample category. mg/L, milligrams per liter; cm3 STP/kg, cubic centimeters per kilogram at standard temperature (20°C) and pressure (1 atmosphere); --, not 

measured or calculated]

USGS 

identification 

number

State well 

number

Local identifier 

and description

Sample 

date

Methane 

(mg/L)

Carbon 

dioxide 

(mg/L)

Nitrogen 

(mg/L)

*Oxygen 

(mg/L)

Argon 

(mg/L)

Calculated 

excess 

nitrogen 

(mg/L)

Calculated 

excess 

air 

(cm3 STP/

kg)

Monitoring wells

292943098354401 AY–68–36–135 Z–OVB 10/30/2007 <0.0005 51.3 23.4 3.40 0.76 0 6.2

292943098354402 AY–68–36–133 Z–SED 10/31/2007 <.0005 37.9 22.8 1.60 .71 0 7.3

292943098354403 AY–68–36–134 Z–IED 10/30/2007 <.0005 43.7 22.6 .21 .70 0 7.3

292943098354404 AY–68–36–132 Z–DED 11/1/2007 <.0005 37.6 21.3 2.16 .68 0 5.9

292851098374401 AY–68–35–315 T–IED 5/6/2008 <.0005 41.5 26.8 1.25 .79 0 11.0

292851098374402 AY–68–35–314 T–DED 5/7/2008 <.0005 37.7 21.2 1.40 .68 0 5.4

Well-field wells (wellhead sampling)

292919098360501 AY–68–36–103 W2 11/29/2007 <.0005 27.6 16.6 6.05 .58 0 1.9

292925098360201 AY–68–36–104 W3 11/28/2007 <.0005 34.6 19.8 5.00 .65 0 4.8

292916098360701 AY–68–36–105 **W4 11/16/2007 <.0005 39.1 20.9 2.00 .67 0 5.8

292920098360601 AY–68–36–130 W5 11/29/2007 <.0005 37.7 20.5 4.91 .67 0 5.1

292923098360301 AY–68–36–131 W6 11/28/2007 <.0005 37.3 20.3 4.82 .66 0 5.0

Well-field depth-dependent sampling (W4)

292916098360701 AY–68–36–105 W4-shallow 

(380), ambient

11/16/2007 <.0005 36.3 21.2 3.17 .68 0 5.9

292916098360701 AY–68–36–105 W4-intermediate 

(430), ambient

11/14/2007 -- -- -- -- -- -- --

292916098360701 AY–68–36–105 W4-deep (540), 

ambient

11/15/2007 <.0005 36.2 20.8 2.78 .67 0 5.3

292916098360701 AY–68–36–105 W4-shallow 

(380), moderate

11/16/2007 <.0005 38.5 20.9 2.42 .67 0 5.7

292916098360701 AY–68–36–105 W4 intermediate 

(430), moderate

11/14/2007 <.0005 34.6 21.3 3.97 .68 0 5.9

292916098360701 AY–68–36–105 W4-deep (540), 

moderate

11/15/2007 <.0005 34.6 20.8 3.66 .67 0 5.9

292916098360701 AY–68–36–105 W4-shallow 

(380), normal

11/16/2007 <.0005 36.2 21.1 3.01 .68 0 5.6

292916098360701 AY–68–36–105 W4-intermediate 

(430), normal

11/15/2007 <.0005 35.4 21.4 3.95 .68 0 6.0

292916098360701 AY–68–36–105 W4-deep (540), 

normal

11/15/2007 <.0005 36.5 20.5 2.71 .67 0 5.3

* Similar to dissolved oxygen in table 9; however, determined by laboratory rather than field method.

** Sample collected from top of open interval during depth-dependent sampling. 

Table 10
Table 11 121

Table 11. Nutrient measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, milligrams per liter; N, nitrogen; P, phosphorus; --, not measured; E, estimated; V, contamination; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Nitrate 

plus nitrite

(mg/L as N)

Ammonia

(mg/L 

as N)

Nitrite

(mg/L 

as N)

Orthophosphate

(mg/L as P)

Organic 

carbon

(mg/L)

Regional aquifer public-supply wells

293359098290301 AY–68–29–414 1st (highest) quartile 2004/12/06 2.16 <0.04 <0.008 0.011 V1.13

293359098290301 AY–68–29–414 1st quartile 2005/09/01 -- -- -- -- --

293358098231101 AY–68–29–610 1st quartile 2004/12/15 1.73 E.02 <.008 .007 V.43

293358098231101 AY–68–29–610 1st quartile 2005/08/29 -- -- -- -- --

293120098285801 AY–68–29–714 1st quartile 2004/12/14 1.59 <.04 <.008 .006 V.47

293120098285801 AY–68–29–714 1st quartile 2005/08/30 -- -- -- -- --

293145098224201 AY–68–29–929 1st quartile 2004/12/15 1.86 <.04 <.008 E.004 V.28

293119098211201 AY–68–30–718 1st quartile 2004/12/16 1.85 <.04 <.008 <.006 V.23

292843098425101 AY–68–35–106 1st quartile 2004/12/13 1.17 <.04 <.008 E.005 V.46

292459098382101 AY–68–35–913 1st quartile 2004/12/13 1.98 <.04 <.008 .006 V9.90

292925098360201 AY–68–36–104 1st quartile 2004/12/13 2.08 <.04 <.008 .006 V.48

292925098360201 AY–68–36–104 1st quartile 2005/08/31 -- -- -- -- --

292822098325401 AY–68–36–206 1st quartile 2004/12/13 1.69 <.04 <.008 E.005 V3.27

292822098325401 AY–68–36–206 1st quartile 2005/08/31 -- -- -- -- --

292944098292301 AY–68–37–105 1st quartile 2004/12/14 1.75 <.04 <.008 E.004 V.35

292944098292301 AY–68–37–105 1st quartile 2005/08/31 -- -- -- -- --

292522098291901 AY–68–37–426 1st quartile 2004/12/14 1.98 <.04 <.008 E.003 V.30

292643098241801 AY–68–37–601 1st quartile 2004/12/15 1.72 <.04 <.008 <.006 V.25

292643098241801 AY–68–37–601 1st quartile 2005/08/30 -- -- -- -- --

292328098294601 AY–68–37–705 1st quartile 2004/12/14 1.50 <.04 <.008 E.003 V.27

294225098080301 DX–68–23–601 1st quartile 2004/12/08 1.88 <.04 <.008 .006 V.47

294225098080301 DX–68–23–601 1st quartile 2005/09/01 -- -- -- -- --

291210099475601 YP–69–50–506 1st quartile 2004/11/30 3.12 <.04 <.008 .007 V12.8

293111098340901 AY–68–28–807 2d quartile 2005/05/26 2.34 <.04 <.008 E.003 V.47

293512098291701 AY–68–29–109 2d quartile 2005/04/20 2.32 <.04 <.008 .008 V.48

292424098421501 AY–68–35–810 2d quartile 2005/04/21 1.97 <.04 <.008 E.004 V.34

292053098365501 AY–68–44–110 2d quartile 2005/05/26 1.91 <.04 <.008 <.006 V.45

293807098155301 DX–68–22–901 2d quartile 2005/05/18 2.46 <.04 <.008 .012 V24.3

292604098563201 TD–68–33–501 2d quartile 2005/05/16 .73 <.04 <.008 <.006 V84.0

292116099095501 TD–69–47–305 2d quartile 2005/04/27 1.64 <.04 <.008 <.006 V.30

291232099470301 YP–69–50–339 2d quartile 2005/05/11 2.82 <.04 <.008 E.003 V.31

293128098473101 AY–68–26–814 3d quartile 2005/04/18 .95 <.04 <.008 <.006 V248

293451098313201 AY–68–28–601 3d quartile 2005/05/17 1.39 <.04 <.008 E.004 V58.7

294604098060801 DX–68–16–708 3d quartile 2005/04/25 1.85 <.04 <.008 <.006 V.46

294019098114701 DX–68–23–504 3d quartile 2005/05/18 1.80 <.04 <.008 E.004 V18.3

292215098580201 TD–68–41–103 3d quartile 2005/05/09 2.01 <.04 <.008 <.006 V.26

Table 11
122 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 11. Nutrient measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, milligrams per liter; N, nitrogen; P, phosphorus; --, not measured; E, estimated; V, contamination; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Nitrate 

plus nitrite

(mg/L as N)

Ammonia

(mg/L 

as N)

Nitrite

(mg/L 

as N)

Orthophosphate

(mg/L as P)

Organic 

carbon

(mg/L)

292119098524901 TD–68–41–308 3d quartile 2005/04/27 2.02 <0.04 <0.008 <0.006 V0.34

291943099163301 TD–69–46–601 3d quartile 2005/05/09 1.44 <.04 <.008 E.005 V.28

291840099382601 YP–69–43–606 3d quartile 2005/05/11 2.77 <.04 <.008 <.006 V.32

293518098332601 AY–68–28–203 4th quartile 2005/04/19 2.36 <.04 <.008 .006 V2.43

293023098355401 AY–68–28–702 4th quartile 2005/04/26 1.85 <.04 <.008 <.006 V.57

293042098305201 AY–68–28–913 4th quartile 2005/06/30 1.82 <.04 <.008 E.003 V15.6

292442098474501 AY–68–34–803 4th quartile 2005/04/20 1.81 <.04 <.008 <.006 V.37

292405098371201 AY–68–36–704 4th quartile 2005/05/23 1.98 <.04 <.008 <.006 V2.02

292931098274601 AY–68–37–124 4th quartile 2005/05/25 1.79 <.04 <.008 <.006 V.49

293729098173101 DX–68–30–215 4th quartile 2005/04/25 2.50 <.04 <.008 E.003 V.44

291219099095601 TD–69–55–604 4th quartile 2005/05/16 2.58 <.04 <.008 E.003 V92.5

Monitoring wells

292943098354401 AY–68–36–135 TANC MW OVB 2007/10/30 3.83 <.02 E.001 .010 7.23

292943098354402 AY–68–36–133 TANC MW 2007/10/31 1.86 <.02 .013 .006 .53

292943098354403 AY–68–36–134 TANC MW 2007/10/30 1.87 <.02 <.002 .008 1.03

292943098354404 AY–68–36–132 TANC MW 2007/11/01 1.69 <.02 .005 .007 .44

292851098374401 AY–68–35–315 TANC MW 2008/05/06 1.97 E.01 <.002 .011 .41

292851098374402 AY–68–35–314 TANC MW 2008/05/07 2.74 <.02 <.002 .010 .60

Well-field depth-dependent sampling (W4)

292916098360701 AY–68–36–105 W4-shallow (380), 

normal

2007/11/16 1.99 <.02 <.002 .008 E.36

292916098360701 AY–68–36–105 W4-intermediate 

(430), normal

2007/11/15 1.97 <.02 <.002 .008 E.36

292916098360701 AY–68–36–105 W4-deep (540), 

normal

2007/11/15 2.12 <.02 <.002 .009 E.38

292916098360701 AY–68–36–105 W4-shallow (380), 

ambient

2007/11/16 1.99 <.02 <.002 .008 E.35

292916098360701 AY–68–36–105 W4-intermediate 

(430), ambient

2007/11/14 1.97 <.02 <.002 E.006 .44

292916098360701 AY–68–36–105 W4-deep (540), 

ambient

2007/11/15 2.12 <.02 <.002 .009 .45

292916098360701 AY–68–36–105 W4-shallow (380), 

moderate

2007/11/16 2.18 <.02 <.002 .009 .43

292916098360701 AY–68–36–105 W4-intermediate 

(430), moderate

2007/11/14 1.97 <.02 <.002 .008 .56

292916098360701 AY–68–36–105 W4-deep (540), 

moderate

2007/11/15 1.97 <.02 <.002 .008 E.39

Well-field wells (wellhead sampling)

292919098360501 AY–68–36–103 wellhead 2007/11/29 2.24 <.02 <.002 .008 E.40

292925098360201 AY–68–36–104 wellhead 2007/11/28 1.97 <.02 <.002 .008 .42
Table 11 123

Table 11. Nutrient measurements for groundwater samples collected for the study of the transport of anthropogenic and natural 

contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 

2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; mg/L, milligrams per liter; N, nitrogen; P, phosphorus; --, not measured; E, estimated; V, contamination; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

Nitrate 

plus nitrite

(mg/L as N)

Ammonia

(mg/L 

as N)

Nitrite

(mg/L 

as N)

Orthophosphate

(mg/L as P)

Organic 

carbon

(mg/L)

292916098360701 AY–68–36–105 *wellhead 2007/11/16 2.21 <0.02 <0.002 0.009 0.43

292920098360601 AY–68–36–130 wellhead 2007/11/29 2.33 <.02 <.002 .008 E.35

292923098360301 AY–68–36–131 wellhead 2007/11/28 2.11 <.02 <.002 .009 E.39

Temporal sampling

292923098360301 AY–68–36–131 TANC PSW prestorm2009/04/09 1.95 <.02 <.002 .013 --

292923098360301 AY–68–36–131 TANC PSW storm 1 2009/10/06 1.97 <.02 <.002 .010 --

292923098360301 AY–68–36–131 TANC PSW storm 2 2009/10/09 1.95 <.02 <.002 .011 --

292923098360301 AY–68–36–131 TANC PSW storm 3 2009/10/19 1.92 <.02 <.002 .009 --

292923098360301 AY–68–36–131 TANC PSW storm 4 2009/10/30 1.94 <.02 <.002 .009 --

292923098360301 AY–68–36–131 TANC PSW storm 5 2009/11/19 1.95 <.02 <.002 <.008 --

292943098354402 AY–68–36–133 TANC MW prestorm2009/04/08 2.00 <.02 <.002 .011 --

292943098354402 AY–68–36–133 TANC MW storm 1 2009/10/05 1.92 <.02 <.002 .010 --

292943098354402 AY–68–36–133 TANC MW storm 2 2009/10/07 1.89 <.02 <.002 .010 --

292943098354402 AY–68–36–133 TANC MW storm 3 2009/10/17 1.89 <.02 <.002 .009 --

292943098354402 AY–68–36–133 TANC MW storm 4 2009/10/28 1.89 <.02 <.002 .010 --

292943098354402 AY–68–36–133 TANC MW storm 5 2009/11/18 1.91 <.02 <.002 <.008 --

292943098354403 AY–68–36–134 TANC MW prestorm2009/04/09 1.93 <.02 <.002 .012 --

292943098354403 AY–68–36–134 TANC MW storm 1 2009/10/05 1.92 <.02 <.002 .011 --

292943098354403 AY–68–36–134 TANC MW storm 2 2009/10/08 1.91 <.02 <.002 .010 --

292943098354403 AY–68–36–134 TANC MW storm 3 2009/10/18 1.89 <.02 <.002 .012 --

292943098354403 AY–68–36–134 TANC MW storm 4 2009/10/29 1.88 <.02 <.002 .009 --

292943098354403 AY–68–36–134 TANC MW storm 5 2009/11/18 1.89 <.02 <.002 .009 --

292943098354404 AY–68–36–132 TANC MW prestorm2009/04/09 1.82 <.02 <.002 .011 --

292943098354404 AY–68–36–132 TANC MW storm 1 2009/10/05 1.81 <.02 <.002 .010 --

292943098354404 AY–68–36–132 TANC MW storm 2 2009/10/08 1.80 <.02 <.002 .010 --

292943098354404 AY–68–36–132 TANC MW storm 3 2009/10/18 1.76 <.02 <.002 .009 --

292943098354404 AY–68–36–132 TANC MW storm 4 2009/10/29 1.79 <.02 <.002 .010 --

292943098354404 AY–68–36–132 TANC MW storm 5 2009/11/18 1.79 <.02 <.002 .008 --

293252098380801 AY–68–27–610 TANC MW prestorm2009/04/14 2.74 E.01 <.002 .012 --

293252098380801 AY–68–27–610 TANC MW storm 1 2009/10/04 2.94 <.02 <.002 .010 --

293252098380801 AY–68–27–610 TANC MW storm 2 2009/10/07 2.62 <.02 E.002 .084 --

293252098380801 AY–68–27–610 TANC MW storm 3 2009/10/17 2.85 <.02 <.002 .010 --

293252098380801 AY–68–27–610 TANC MW storm 4 2009/10/28 2.67 <.02 <.002 .011 --

293252098380801 AY–68–27–610 TANC MW storm 5 2009/11/17 2.99 <.02 <.002 .010 --

*

 Sample collected from top of open interval during depth-dependent sampling. 
124 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 12. Isotope and radionuclide measurements for groundwater samples collected for the study of the transport of anthropogenic 

and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; pCi/L, picoCuries per liter; δ18O, delta 

oxygen-18; δD, delta deuterium; 87Sr/86Sr, strontium-87/strontium-86; δ15N, delta nitrogen-15; NO3, nitrate; --, not measured; R, result less than sample-specific 

critical level]

USGS identification numberState well 

number

Group and 

description

Sample 

date

δ18O

(per 

mil)

δD

(per 

mil)

87Sr/86Sr

Radon222 

(pCi/L)

Radium226

(pCi/L)

Radium228

(pCi/L)

δ15N in 

NO3

(per 

mil)

δ18O in 

NO3

(per 

mil)

Monitoring wells

292943098354401 AY–68–36–135 TANC MW OVB 2007/10/30 -3.79 -22.7 0.70785 173 0.46 R.18 6.84 5.32

292943098354402 AY–68–36–133 TANC MW 2007/10/31 -4.11 -23.5 .70773 95 .24 .36 8.15 5.12

292943098354403 AY–68–36–134 TANC MW 2007/10/30 -4.10 -21.8 .70772 73 .11 R-.14 8.06 5.27

292943098354404 AY–68–36–132 TANC MW 2007/11/01 -4.10 -22.4 .70767 40 .19 R-.27 7.97 5.17

292851098374401 AY–68–35–315 TANC MW 2008/05/06 -4.11 -23.4 .70784 18 .18 R-.01 7.69 4.59

292851098374402 AY–68–35–314 TANC MW 2008/05/07 -4.03 -23.6 .70781 53 .17 R.02 8.04 4.82

Well-field depth-dependent sampling (W4)

292916098360701 AY–68–36–105 W4-shallow (380), 

normal

2007/11/16 -4.01 -22.7 .70769 35 .16 R.02 7.67 4.98

292916098360701 AY–68–36–105 W4-intermediate 

(430), normal

2007/11/15 -4.07 -22.8 .70789 30 .23 R.03 7.69 5.08

292916098360701 AY–68–36–105 W4-deep (540), 

normal

2007/11/15 -4.01 -22.7 .70769 46 .20 R.12 7.80 5.35

292916098360701 AY–68–36–105 W4-shallow (380), 

ambient

2007/11/16 -3.98 -22.0 .70782 34 .15 R.05 7.88 5.16

292916098360701 AY–68–36–105 W4-intermediate 

(430), ambient

2007/11/14 -3.99 -22.5 .70775 35 .16 R-.15 7.95 5.24

292916098360701 AY–68–36–105 W4-deep (540), 

ambient

2007/11/15 -3.98 -23.2 .70771 40 .18 R-.12 7.85 5.28

292916098360701 AY–68–36–105 W4-shallow (380), 

moderate

2007/11/16 -4.08 -22.6 .70774 67 .16 R.01 7.87 5.30

292916098360701 AY–68–36–105 W4-intermediate 

(430), moderate

2007/11/14 -3.96 -23.5 .70771 36 .18 R-.19 7.84 5.51

292916098360701 AY–68–36–105 W4-deep (540), 

moderate

2007/11/15 -3.99 -23.2 .70772 40 .07 R.03 7.82 5.22

Well-field wells (wellhead sampling)

292919098360501 AY–68–36–103 wellhead 2007/11/29 -4.06 -22.9 .70772 -- .20 R.08 8.16 5.45

292925098360201 AY–68–36–104 wellhead 2007/11/28 -4.01 -22.4 .70768 -- .16 R.02 7.93 5.15

292916098360701 AY–68–36–105 *wellhead 2007/11/16 -4.01 -21.6 .70768 57 .12 R-.04 7.94 5.06

292920098360601 AY–68–36–130 wellhead 2007/11/29 -4.11 -22.5 .70772 -- .20 R.05 8.09 5.35

292923098360301 AY–68–36–131 wellhead 2007/11/28 -4.02 -23.4 .70771 -- .18 R.20 8.12 5.52

Temporal sampling

292923098360301 AY–68–36–131 TANC PSW prestorm2009/04/09 -3.96 -22.7 -- -- -- -- -- --

292923098360301 AY–68–36–131 TANC PSW storm 1 2009/10/06 -4.00 -21.8 .70781 -- -- -- -- --

292923098360301 AY–68–36–131 TANC PSW storm 2 2009/10/09 -4.04 -21.3 .70779 -- -- -- -- --

292923098360301 AY–68–36–131 TANC PSW storm 3 2009/10/19 -4.08 -21.8 .70779 -- -- -- -- --

292923098360301 AY–68–36–131 TANC PSW storm 4 2009/10/30 -4.11 -22.8 .70778 -- -- -- -- --

292923098360301 AY–68–36–131 TANC PSW storm 5 2009/11/19 -4.03 -21.7 .70780 -- -- -- -- --

Table 12
Table 12 125

Table 12. Isotope and radionuclide measurements for groundwater samples collected for the study of the transport of anthropogenic 

and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, southcentral Texas, 2004−9.—Continued

[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; PSW, public-supply well; pCi/L, picoCuries per liter; δ18O, delta 

oxygen-18; δD, delta deuterium; 87Sr/86Sr, strontium-87/strontium-86; δ15N, delta nitrogen-15; NO3, nitrate; --, not measured; R, result less than sample-specific 

critical level]

USGS identification numberState well 

number

Group and 

description

Sample 

date

δ18O

(per 

mil)

δD

(per 

mil)

87Sr/86Sr

Radon222 

(pCi/L)

Radium226

(pCi/L)

Radium228

(pCi/L)

δ15N in 

NO3

(per 

mil)

δ18O in 

NO3

(per 

mil)

292943098354402 AY–68–36–133 TANC MW prestorm2009/04/08 -4.10 -22.1 -- -- -- -- -- --

292943098354402 AY–68–36–133 TANC MW storm 1 2009/10/05 -4.09 -22.9 0.70779 -- -- -- -- --

292943098354402 AY–68–36–133 TANC MW storm 2 2009/10/07 -4.11 -21.4 .70780 -- -- -- -- --

292943098354402 AY–68–36–133 TANC MW storm 3 2009/10/17 -4.19 -22.5 .70780 -- -- -- -- --

292943098354402 AY–68–36–133 TANC MW storm 4 2009/10/28 -4.14 -21.8 .70779 -- -- -- -- --

292943098354402 AY–68–36–133 TANC MW storm 5 2009/11/18 -4.15 -22.7 .70780 -- -- -- -- --

292943098354403 AY–68–36–134 TANC MW prestorm2009/04/09 -4.18 -21.8 -- -- -- -- -- --

292943098354403 AY–68–36–134 TANC MW storm 1 2009/10/05 -4.11 -23.2 .70778 -- -- -- -- --

292943098354403 AY–68–36–134 TANC MW storm 2 2009/10/08 -4.05 -23.6 .70782 -- -- -- -- --

292943098354403 AY–68–36–134 TANC MW storm 3 2009/10/18 -4.12 -23.8 .70779 -- -- -- -- --

292943098354403 AY–68–36–134 TANC MW storm 4 2009/10/29 -4.09 -23.8 .70776 -- -- -- -- --

292943098354403 AY–68–36–134 TANC MW storm 5 2009/11/18 -4.14 -22.6 .70776 -- -- -- -- --

292943098354404 AY–68–36–132 TANC MW prestorm2009/04/09 -4.08 -22.8 -- -- -- -- -- --

292943098354404 AY–68–36–132 TANC MW storm 1 2009/10/05 -4.10 -23.8 .70779 -- -- -- -- --

292943098354404 AY–68–36–132 TANC MW storm 2 2009/10/08 -4.10 -24.2 .70778 -- -- -- -- --

292943098354404 AY–68–36–132 TANC MW storm 3 2009/10/18 -4.13 -21.7 .70778 -- -- -- -- --

292943098354404 AY–68–36–132 TANC MW storm 4 2009/10/29 -4.14 -23.7 .70780 -- -- -- -- --

292943098354404 AY–68–36–132 TANC MW storm 5 2009/11/18 -4.15 -23.5 .70781 -- -- -- -- --

293252098380801 AY–68–27–610 TANC MW prestorm200904/14 -4.35 -23.8 -- -- -- -- -- --

293252098380801 AY–68–27–610 TANC MW storm 1 2009/10/04 -4.18 -23.3 .70807 -- -- -- -- --

293252098380801 AY–68–27–610 TANC MW storm 2 2009/10/07 -4.32 -23.7 .70809 -- -- -- -- --

293252098380801 AY–68–27–610 TANC MW storm 3 2009/10/17 -4.19 -24.0 .70809 -- -- -- -- --

293252098380801 AY–68–27–610 TANC MW storm 4 2009/10/28 -4.24 -23.1 .70809 -- -- -- -- --

293252098380801 AY–68–27–610 TANC MW storm 5 2009/11/17 -4.21 -23.6 .70811 -- -- -- -- --

* Sample collected from top of open interval during depth-dependent sampling. 
Table 13. Wastewater indicator compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminsupply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; <, nondetection less than laboratory method reporting level; --, not measured; V, contaminate

USGS identification number State well number Group and description Sample date 1,4-Di- chloro- benzene (μg/L) 1-Methyl- naphth- alene (μg/L) 2,6-Di- methyl- naphth- alene (μg/L) 2-Methyl- naphth- alene (μg/L) 3-beta- Copro- stanol (μg/L) 3-Methyl- 1H-indole (μg/L) 3-tert- Butyl- 4-hydroxy- anisole (μg/L) 4-

p

(

Regional aquifer public-supply wells 293359098290301 AY–68–29–414 1st (highest) quartile 2004/12/06 <0.5 <0.5 <0.5 <0.5 <2.0 <1.0 <5.0 

293359098290301 AY–68–29–414 1st quartile 2005/09/01 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293358098231101 AY–68–29–610 1st quartile 2004/12/15 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293358098231101 AY–68–29–610 1st quartile 2005/08/29 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293120098285801 AY–68–29–714 1st quartile 2004/12/14 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293120098285801 AY–68–29–714 1st quartile 2005/08/30 -- -- -- -- -- -- -- 

293145098224201 AY–68–29–929 1st quartile 2004/12/15 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293119098211201 AY–68–30–718 1st quartile 2004/12/16 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292843098425101 AY–68–35–106 1st quartile 2004/12/13 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292459098382101 AY–68–35–913 1st quartile 2004/12/13 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292925098360201 AY–68–36–104 1st quartile 2004/12/13 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292925098360201 AY–68–36–104 1st quartile 2005/08/31 -- -- -- -- -- -- -- 

292822098325401 AY–68–36–206 1st quartile 2004/12/13 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292822098325401 AY–68–36–206 1st quartile 2005/08/31 -- -- -- -- -- -- -- 

292944098292301 AY–68–37–105 1st quartile 2004/12/14 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292944098292301 AY–68–37–105 1st quartile 2005/08/31 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292522098291901 AY–68–37–426 1st quartile 2004/12/14 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292643098241801 AY–68–37–601 1st quartile 2004/12/15 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292643098241801 AY–68–37–601 1st quartile 2005/08/30 -- -- -- -- -- -- -- 

292328098294601 AY–68–37–705 1st quartile 2004/12/14 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

294225098080301 DX–68–23–601 1st quartile 2004/12/08 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

294225098080301 DX–68–23–601 1st quartile 2005/09/01 -- -- -- -- -- -- -- 

291210099475601 YP–69–50–506 1st quartile 2004/11/30 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 
Table 13. Wastewater indicator compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminsupply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; <, nondetection less than laboratory method reporting level; --, not measured; V, contaminate

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

1,4-Dichlorobenzene 

(μg/L)

1-Methylnaphthalene 

(μg/L)

2,6-Dimethylnaphthalene

(μg/L)

2-Methylnaphthalene

(μg/L)

3-betaCoprostanol

(μg/L)

3-Methyl1H-indole

(μg/L)

3-tertButyl4-hydroxyanisole

(μg/L)

4-

p

(

293111098340901 AY–68–28–807 2d quartile 2005/05/26 -- -- -- -- -- -- -- 

293512098291701 AY–68–29–109 2d quartile 2005/04/20 <0.5 <0.5 <0.5 <0.5 <2.0 <1.0 <5.0 

292424098421501 AY–68–35–810 2d quartile 2005/04/21 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292053098365501 AY–68–44–110 2d quartile 2005/05/26 -- -- -- -- -- -- -- 

293807098155301 DX–68–22–901 2d quartile 2005/05/18 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292604098563201 TD–68–33–501 2d quartile 2005/05/16 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292116099095501 TD–69–47–305 2d quartile 2005/04/27 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

291232099470301 YP–69–50–339 2d quartile 2005/05/11 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293128098473101 AY–68–26–814 3d quartile 2005/04/18 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293451098313201 AY–68–28–601 3d quartile 2005/05/17 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

294604098060801 DX–68–16–708 3d quartile 2005/04/25 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

294019098114701 DX–68–23–504 3d quartile 2005/05/18 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292215098580201 TD–68–41–103 3d quartile 2005/05/09 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292119098524901 TD–68–41–308 3d quartile 2005/04/27 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

291943099163301 TD–69–46–601 3d quartile 2005/05/09 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

291840099382601 YP–69–43–606 3d quartile 2005/05/11 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293518098332601 AY–68–28–203 4th quartile 2005/04/19 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293023098355401 AY–68–28–702 4th quartile 2005/04/26 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293042098305201 AY–68–28–913 4th quartile 2005/06/30 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292442098474501 AY–68–34–803 4th quartile 2005/04/20 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292405098371201 AY–68–36–704 4th quartile 2005/05/23 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

292931098274601 AY–68–37–124 4th quartile 2005/05/25 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

293729098173101 DX–68–30–215 4th quartile 2005/04/25 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 

291219099095601 TD–69–55–604 4th quartile 2005/05/16 <.5 <.5 <.5 <.5 <2.0 <1.0 <5.0 
Table 13. Wastewater indicator compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminsupply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; <, nondetection less than laboratory method reporting level; --, not measured; V, contaminate

USGS identification number 4-Nonyl- phenol dieth- oxylate (sum of isomers) (μg/L) 4-tert- Octyl- phenol dieth- oxylate (μg/L) 4-tert- Octyl- phenol mono- ethoxylate (μg/L) 4-tert- Octyl- phenol (μg/L) 5-Methyl- 1H- benzo- triazole (μg/L) 9,10- Anthra- quinone (μg/L) Aceto- phe- none (μg/L) Acetyl hexa- methyl tetrahydro naph- thalene (AHTN) (μg/L) Anth- racene (μg/L) Benzo- [a]- pyrene (μg/L) Benzo- phe- none (μg/L) beta- Sito- sterol (μg/L) beta- Stigma- stanol (μg/L) Brom- acil (μg/L) 

Regional aquifer public-supply wells 293359098290301 <5.0 <1.0 <1.0 <1.0 <2.0 <0.5 <0.5 <0.5 <0.5 <0.5 V0.068 <2.0 <2.0 <0.01

293359098290301 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

293358098231101 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

293358098231101 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

293120098285801 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

293120098285801 -- -- -- -- -- -- -- -- -- -- -- -- -- <.01

293145098224201 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

293119098211201 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

292843098425101 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

292459098382101 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

292925098360201 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

292925098360201 -- -- -- -- -- -- -- -- -- -- -- -- -- <.01292822098325401 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

292822098325401 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292944098292301 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

292944098292301 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

292522098291901 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

292643098241801 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01292643098241801 -- -- -- -- -- -- -- -- -- -- -- -- -- <.01292328098294601 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01

294225098080301 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01294225098080301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

291210099475601 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.01
Table 13. Wastewater indicator compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminsupply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; <, nondetection less than laboratory method reporting level; --, not measured; V, contaminated

USGS 

identification 

number

4-Nonylphenol 

diethoxylate 

(sum of 

isomers) 

(μg/L)

4-tertOctylphenol 

diethoxylate

(μg/L)

4-tertOctylphenol 

monoethoxylate

(μg/L)

4-tertOctylphenol

(μg/L)

5-Methyl1Hbenzotriazole

(μg/L)

9,10-

Anthraquinone

(μg/L)

Acetophenone

(μg/L)

Acetyl 

hexamethyl 

tetrahydro 

naphthalene 

(AHTN)

(μg/L)

Anthracene

(μg/L)

Benzo-

[a]-

pyrene

(μg/L)

Benzophenone

(μg/L)

betaSitosterol

(μg/L)

betaStigmastanol

(μg/L)

Bromacil

(μg/L)

293111098340901 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293512098291701 <5.0 <1.0 <1.0 <1.0 <2.0 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <2.0 <2.0 <0.5 

292424098421501 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.048 <2.0 <2.0 <.5 

292053098365501 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293807098155301 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.066 <2.0 <2.0 <.5 

292604098563201 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

292116099095501 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

291232099470301 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.030 <2.0 <2.0 <.5 

293128098473101 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

293451098313201 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.067 <2.0 <2.0 <.5 

294604098060801 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.220 <2.0 <2.0 <.5 

294019098114701 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

292215098580201 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.027 <2.0 <2.0 <.5 

292119098524901 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

291943099163301 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.013 <2.0 <2.0 <.5 

291840099382601 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.016 <2.0 <2.0 <.5 

293518098332601 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

293023098355401 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.027 <2.0 <2.0 <.5 

293042098305201 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.023 <2.0 <2.0 <.5 

292442098474501 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

292405098371201 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

292931098274601 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293729098173101 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 <.5 <2.0 <2.0 <.5 

291219099095601 <5.0 <1.0 <1.0 <1.0 <2.0 <.5 <.5 <.5 <.5 <.5 V.017 <2.0 <2.0 <.5 
Table 13. Wastewater indicator compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminsupply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; <, nondetection less than laboratory method reporting level; --, not measured; V, contaminated

USGS identification number Chol- esterol (μg/L) Cotinine (μg/L) N,N- diethyl- meta- tolua- mide (μg/L) D-Limo- nene (μg/L) Fluor- anthene (μg/L) Hexahydro- hexamethyl cyclopenta- benzopyran (HHCB) (μg/L) Indole (μg/L) Iso- borneol (μg/L) Iso- phorone (μg/L) Iso- propyl- benzene (μg/L) Iso- quino- line (μg/L) Men

tho

(μg/

Regional aquifer public-supply wells 293359098290301 <2.0 <1.0 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.

293359098290301 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 V.003 <.5 <.

293358098231101 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

293358098231101 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

293120098285801 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

293120098285801 -- -- -- -- -- -- -- -- -- -- -- -- 

293145098224201 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

293119098211201 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

292843098425101 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

292459098382101 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292925098360201 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292925098360201 -- -- -- -- -- -- -- -- -- -- -- -292822098325401 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292822098325401 -- -- -- -- -- -- -- -- -- -- -- -292944098292301 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292944098292301 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292522098291901 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292643098241801 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

292643098241801 -- -- -- -- -- -- -- -- -- -- -- -

292328098294601 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.294225098080301 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

294225098080301 -- -- -- -- -- -- -- -- -- -- -- -

291210099475601 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.
Table 13. Wastewater indicator compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminsupply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; <, nondetection less than laboratory method reporting level; --, not measured; V, contaminated

USGS 

identification 

number

Cholesterol

(μg/L)

Cotinine

(μg/L)

N,Ndiethylmetatoluamide

(μg/L)

D-Limonene

(μg/L)

Fluoranthene

(μg/L)

Hexahydrohexamethyl 

cyclopentabenzopyran 

(HHCB)

(μg/L)

Indole

(μg/L)

Isoborneol

(μg/L)

Isophorone

(μg/L)

Isopropylbenzene

(μg/L)

Isoquinoline

(μg/L)

Men

tho

(μg/

293111098340901 -- -- -- -- -- -- -- -- -- -- -- -- 

293512098291701 <2.0 <1.0 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.292424098421501 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292053098365501 -- -- -- -- -- -- -- -- -- -- -- -- 

293807098155301 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292604098563201 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292116099095501 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.291232099470301 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 V.023 <.5 <.

293128098473101 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

293451098313201 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

294604098060801 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

294019098114701 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

292215098580201 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

292119098524901 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

291943099163301 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

291840099382601 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

293518098332601 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

293023098355401 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.

293042098305201 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292442098474501 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292405098371201 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.292931098274601 -- -- -- -- -- -- -- -- -- -- -- -- 

293729098173101 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.291219099095601 <2.0 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.5 <.
Table 13. Wastewater indicator compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminsupply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; <, nondetection less than laboratory method reporting level; --, not measured; V, contaminate

USGS identification number Naphth- alene (μg/L) p-Cresol (μg/L) Phen- anthrene (μg/L) Phenol (μg/L) Pyrene (μg/L) Tetra- chloro- ethene (PCE) (μg/L) Tribromo- methane (bromo- form) (μg/L) Tributyl phos- phate (μg/L) Tri- closan (μg/L) Tri- ethyl citrate (μg/L) Tri- phenyl phos- phate (μg/L) Tris (2-but- oxyethy

phos- phate (μg/L) 

Regional aquifer public-supply wells 293359098290301 <0.5 <1.0 <0.5 V0.820 <.5 V0.280 <0.5 <0.5 <1.0 <0.5 <0.5 <0.5 

293359098290301 <.5 <1.0 <.5 <.5 <.5 V.250 <.5 <.5 <1.0 <.5 <.5 <.5 

293358098231101 <.5 <1.0 <.5 V.320 <.5 V.130 V.023 <.5 <1.0 <.5 <.5 <.5 293358098231101 <.5 <1.0 <.5 <.5 <.5 V.093 <.5 <.5 <1.0 <.5 <.5 <.5 

293120098285801 <.5 <1.0 <.5 V.890 <.5 V.086 V1.90 <.5 <1.0 <.5 <.5 <.5 293120098285801 -- -- -- -- -- -- -- -- -- -- -- -- 

293145098224201 <.5 <1.0 <.5 V1.50 <.5 V.037 <.5 <.5 <1.0 <.5 <.5 <.5 

293119098211201 <.5 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 

292843098425101 <.5 <1.0 <.5 V.210 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 

292459098382101 <.5 <1.0 <.5 V.480 <.5 <.5 V.054 <.5 <1.0 <.5 <.5 <.5 292925098360201 <.5 <1.0 <.5 <.5 <.5 V.055 V1.10 <.5 <1.0 <.5 <.5 <.5 

292925098360201 -- -- -- -- -- -- -- -- -- -- -- -- 

292822098325401 <.5 <1.0 <.5 V.210 <.5 V.022 <.5 <.5 <1.0 <.5 <.5 <.5 

292822098325401 -- -- -- -- -- -- -- -- -- -- -- -- 

292944098292301 <.5 <1.0 <.5 V1.10 <.5 V.032 <.5 <.5 <1.0 <.5 <.5 <.5 

292944098292301 <.5 <1.0 <.5 <.5 <.5 V.015 <.5 <.5 <1.0 <.5 <.5 <.5 

292522098291901 <.5 <1.0 <.5 V.460 <.5 <.5 V.024 <.5 <1.0 <.5 <.5 <.5 292643098241801 <.5 <1.0 <.5 V.690 <.5 <.5 V.660 <.5 <1.0 <.5 <.5 <.5 

292643098241801 -- -- -- -- -- -- -- -- -- -- -- -- 

292328098294601 <.5 <1.0 <.5 V.140 <.5 V.020 <.5 <.5 <1.0 <.5 <.5 <.5 

294225098080301 <.5 <1.0 <.5 V.400 <.5 V.072 <.5 <.5 <1.0 <.5 <.5 <.5 

294225098080301 -- -- -- -- -- -- -- -- -- -- -- -- 

291210099475601 <.5 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 
Table 13. Wastewater indicator compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminsupply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; <, nondetection less than laboratory method reporting level; --, not measured; V, contaminate

USGS 

identification 

number

Naphthalene

(μg/L)

p-Cresol

(μg/L)

Phenanthrene

(μg/L)

Phenol

(μg/L)

Pyrene

(μg/L)

Tetrachloroethene 

(PCE)

(μg/L)

Tribromomethane 

(bromoform)

(μg/L)

Tributyl 

phosphate

(μg/L)

Triclosan

(μg/L)

Triethyl 

citrate

(μg/L)

Triphenyl 

phosphate

(μg/L)

Tris 

(2-butoxyethy

phosphate

(μg/L)

293111098340901 -- -- -- -- -- -- -- -- -- -- -- -- 

293512098291701 <0.5 <1.0 <0.5 V1.90 <0.5 <0.5 <0.5 <0.5 <1.0 <0.5 <0.5 <0.5 292424098421501 <.5 <1.0 <.5 V1.70 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 292053098365501 -- -- -- -- -- -- -- -- -- -- -- -- 

293807098155301 <.5 <1.0 <.5 V1.50 <.5 <.5 V.500 <.5 <1.0 <.5 <.5 <.5 292604098563201 <.5 <1.0 <.5 V2.20 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 292116099095501 <.5 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 

291232099470301 <.5 <1.0 <.5 V.500 <.5 V.040 <.5 <.5 <1.0 <.5 <.5 <.5 

293128098473101 <.5 <1.0 <.5 V1.30 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 

293451098313201 <.5 <1.0 <.5 V1.00 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 294604098060801 <.5 <1.0 <.5 V.850 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 294019098114701 <.5 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 

292215098580201 <.5 V.024 <.5 V4.0 <.5 <.5 V.078 <.5 <1.0 <.5 <.5 <.5 

292119098524901 <.5 <1.0 <.5 <.5 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 

291943099163301 <.5 <1.0 <.5 V2.40 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 291840099382601 <.5 <1.0 <.5 V.280 <.5 <.5 V.026 <.5 <1.0 <.5 <.5 <.5 293518098332601 <.5 <1.0 <.5 V1.40 <.5 V.042 <.5 <.5 <1.0 <.5 <.5 <.5 

293023098355401 <.5 <1.0 <.5 V1.40 <.5 V.140 <.5 <.5 <1.0 <.5 <.5 <.5 

293042098305201 <.5 <1.0 <.5 V.180 <.5 V.130 <.5 <.5 <1.0 <.5 <.5 <.5 

292442098474501 <.5 <1.0 <.5 <.5 <.5 <.5 V1.80 <.5 <1.0 <.5 <.5 <.5 

292405098371201 <.5 <1.0 <.5 V.110 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 292931098274601 -- -- -- -- -- -- -- -- -- -- -- -- 

293729098173101 <.5 <1.0 <.5 V.850 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 <.5 

291219099095601 <.5 <1.0 <.5 V1.90 <.5 <.5 <.5 <.5 <1.0 <.5 <.5 V.098 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number State well number Group and description Sample date 1,1,1,2- Tetra- chloro- ethane (μg/L) 1,1,1-Tri- chloro- ethane (μg/L) 1,1,2,2- Tetra- chloro- ethane (μg/L) 1,1,2-Tri- chloro- 1,2,2-tri- fluoro- ethane (CFC-113) (μg/L) 1,1,2-Tri- chloro- ethane (μg/L) 1,1-Di- chloro- ethane (μg/L) 1,1-Di- chloro- ethene (μg/L) 1,1

ch

pro

(μ

Regional aquifer public-supply wells 293359098290301 AY–68–29–414 1st (highest) quartile 2004/12/06 <0.03 <0.032 <0.08 E0.038 <0.04 <0.035 <0.024 <0

293359098290301 AY–68–29–414 1st quartile 2005/09/01 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293358098231101 AY–68–29–610 1st quartile 2004/12/15 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293358098231101 AY–68–29–610 1st quartile 2005/08/29 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <

293120098285801 AY–68–29–714 1st quartile 2004/12/14 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293120098285801 AY–68–29–714 1st quartile 2005/08/30 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293145098224201 AY–68–29–929 1st quartile 2004/12/15 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293119098211201 AY–68–30–718 1st quartile 2004/12/16 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292843098425101 AY–68–35–106 1st quartile 2004/12/13 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292459098382101 AY–68–35–913 1st quartile 2004/12/13 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292925098360201 AY–68–36–104 1st quartile 2004/12/13 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292925098360201 AY–68–36–104 1st quartile 2005/08/31 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292822098325401 AY–68–36–206 1st quartile 2004/12/13 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <

292822098325401 AY–68–36–206 1st quartile 2005/08/31 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292944098292301 AY–68–37–105 1st quartile 2004/12/14 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292944098292301 AY–68–37–105 1st quartile 2005/08/31 -- -- -- -- -- -- -- 

292522098291901 AY–68–37–426 1st quartile 2004/12/14 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292643098241801 AY–68–37–601 1st quartile 2004/12/15 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292643098241801 AY–68–37–601 1st quartile 2005/08/30 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292328098294601 AY–68–37–705 1st quartile 2004/12/14 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <294225098080301 DX–68–23–601 1st quartile 2004/12/08 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <294225098080301 DX–68–23–601 1st quartile 2005/09/01 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <291210099475601 YP–69–50–506 1st quartile 2004/11/30 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <

293111098340901 AY–68–28–807 2d quartile 2005/05/26 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293512098291701 AY–68–29–109 2d quartile 2005/04/20 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292424098421501 AY–68–35–810 2d quartile 2005/04/21 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

1,1,1,2-

Tetrachloroethane

(μg/L)

1,1,1-Trichloroethane

(μg/L)

1,1,2,2-

Tetrachloroethane

(μg/L)

1,1,2-Trichloro1,2,2-trifluoroethane 

(CFC-113)

(μg/L)

1,1,2-Trichloroethane

(μg/L)

1,1-Dichloroethane

(μg/L)

1,1-Dichloroethene

(μg/L)

1,1

ch

pro

(μ

292053098365501 AY–68–44–110 2d quartile 2005/05/26 <0.03 <0.032 <0.08 <0.038 <0.04 <0.035 <0.024 <0293807098155301 DX–68–22–901 2d quartile 2005/05/18 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292604098563201 TD–68–33–501 2d quartile 2005/05/16 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292116099095501 TD–69–47–305 2d quartile 2005/04/27 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <

291232099470301 YP–69–50–339 2d quartile 2005/05/11 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293128098473101 AY–68–26–814 3d quartile 2005/04/18 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293451098313201 AY–68–28–601 3d quartile 2005/05/17 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <294604098060801 DX–68–16–708 3d quartile 2005/04/25 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <294019098114701 DX–68–23–504 3d quartile 2005/05/18 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292215098580201 TD–68–41–103 3d quartile 2005/05/09 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292119098524901 TD–68–41–308 3d quartile 2005/04/27 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <291943099163301 TD–69–46–601 3d quartile 2005/05/09 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <291840099382601 YP–69–43–606 3d quartile 2005/05/11 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <

293518098332601 AY–68–28–203 4th quartile 2005/04/19 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293023098355401 AY–68–28–702 4th quartile 2005/04/26 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293042098305201 AY–68–28–913 4th quartile 2005/06/30 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292442098474501 AY–68–34–803 4th quartile 2005/04/20 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292405098371201 AY–68–36–704 4th quartile 2005/05/23 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <292931098274601 AY–68–37–124 4th quartile 2005/05/25 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <293729098173101 DX–68–30–215 4th quartile 2005/04/25 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <291219099095601 TD–69–55–604 4th quartile 2005/05/16 <.03 <.032 <.08 <.038 <.04 <.035 <.024 <

Monitoring wells

292943098354401 AY–68–36–135 TANC MW OVB 2007/10/30 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292943098354402 AY–68–36–133 TANC MW 2007/10/31 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

292943098354403 AY–68–36–134 TANC MW 2007/10/30 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292943098354404 AY–68–36–132 TANC MW 2007/11/01 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number State well number Group and description Sample date 1,1,1,2- Tetra- chloro- ethane (μg/L) 1,1,1-Tri- chloro- ethane (μg/L) 1,1,2,2- Tetra- chloro- ethane (μg/L) 1,1,2-Tri- chloro- 1,2,2-tri- fluoro- ethane (CFC-113) (μg/L) 1,1,2-Tri- chloro- ethane (μg/L) 1,1-Di- chloro- ethane (μg/L) 1,1-Di- chloro- ethene (μg/L) 1,1

ch

pro

(μ

292851098374401 AY–68–35–315 TANC MW 2008/05/06 <0.04 <0.02 <0.1 <0.04 <0.06 <0.04 <0.02 <0292851098374402 AY–68–35–314 TANC MW 2008/05/07 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

Well-field depth-dependent sampling (W4) 292916098360701 AY–68–36–105 W4-shallow (380), normal 2007/11/16 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

292916098360701 AY–68–36–105 W4-intermediate (430), normal 2007/11/15 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

292916098360701 AY–68–36–105 W4-deep (540), normal 2007/11/15 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292916098360701 AY–68–36–105 W4-shallow (380), ambient 2007/11/16 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292916098360701 AY–68–36–105 W4-intermediate (430), ambient 2007/11/14 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292916098360701 AY–68–36–105 W4-deep (540), ambient 2007/11/15 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292916098360701 AY–68–36–105 W4-shallow (380), 

moderate

2007/11/16 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

292916098360701 AY–68–36–105 W4-intermediate 

(430), moderate

2007/11/14 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

292916098360701 AY–68–36–105 W4-deep (540), 

moderate

2007/11/15 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

Well-field wells (wellhead sampling)

292919098360501 AY–68–36–103 wellhead 2007/11/29 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

292925098360201 AY–68–36–104 wellhead 2007/11/28 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

292916098360701 AY–68–36–105 *wellhead 2007/11/16 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292920098360601 AY–68–36–130 wellhead 2007/11/29 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292923098360301 AY–68–36–131 wellhead 2007/11/28 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

Temporal sampling

292923098360301 AY–68–36–131 TANC PSW prestorm 2009/04/09 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292923098360301 AY–68–36–131 TANC PSW storm 1 2009/10/06 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

1,1,1,2-

Tetrachloroethane

(μg/L)

1,1,1-Trichloroethane

(μg/L)

1,1,2,2-

Tetrachloroethane

(μg/L)

1,1,2-Trichloro1,2,2-trifluoroethane 

(CFC-113)

(μg/L)

1,1,2-Trichloroethane

(μg/L)

1,1-Dichloroethane

(μg/L)

1,1-Dichloroethene

(μg/L)

1,1

ch

pro

(μ

292923098360301 AY–68–36–131 TANC PSW storm 2 2009/10/09 <0.04 <0.03 <0.14 <0.034 <0.046 <0.044 <0.022 <0292923098360301 AY–68–36–131 TANC PSW storm 3 2009/10/19 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292923098360301 AY–68–36–131 TANC PSW storm 4 2009/10/30 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292923098360301 AY–68–36–131 TANC PSW storm 5 2009/11/19 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <

292943098354402 AY–68–36–133 TANC MW prestorm 2009/04/08 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292943098354402 AY–68–36–133 TANC MW storm 1 2009/10/05 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354402 AY–68–36–133 TANC MW storm 2 2009/10/07 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354402 AY–68–36–133 TANC MW storm 3 2009/10/17 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354402 AY–68–36–133 TANC MW storm 4 2009/10/28 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354402 AY–68–36–133 TANC MW storm 5 2009/11/18 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354403 AY–68–36–134 TANC MW prestorm 2009/04/09 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292943098354403 AY–68–36–134 TANC MW storm 1 2009/10/05 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354403 AY–68–36–134 TANC MW storm 2 2009/10/08 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <

292943098354403 AY–68–36–134 TANC MW storm 3 2009/10/18 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354403 AY–68–36–134 TANC MW storm 4 2009/10/29 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354403 AY–68–36–134 TANC MW storm 5 2009/11/18 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354404 AY–68–36–132 TANC MW prestorm 2009/04/09 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <292943098354404 AY–68–36–132 TANC MW storm 1 2009/10/05 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354404 AY–68–36–132 TANC MW storm 2 2009/10/08 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354404 AY–68–36–132 TANC MW storm 3 2009/10/18 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354404 AY–68–36–132 TANC MW storm 4 2009/10/29 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <292943098354404 AY–68–36–132 TANC MW storm 5 2009/11/18 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <293252098380801 AY–68–27–610 TANC MW prestorm 2009/04/14 <.04 <.02 <.1 <.04 <.06 <.04 <.02 <

293252098380801 AY–68–27–610 TANC MW storm 1 2009/10/04 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <293252098380801 AY–68–27–610 TANC MW storm 2 2009/10/07 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <293252098380801 AY–68–27–610 TANC MW storm 3 2009/10/17 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <293252098380801 AY–68–27–610 TANC MW storm 4 2009/10/28 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <293252098380801 AY–68–27–610 TANC MW storm 5 2009/11/17 <.04 <.03 <.14 <.034 <.046 <.044 <.022 <
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number 1,2,3-Tri- chloro- benzene (μg/L) 1,2,3-Tri- chloro- propane (μg/L) 1,2,3-Tri- methyl- benzene (μg/L) 1,2,4-Tri- chloro- benzene (μg/L) 1,2,4-Tri- methyl- benzene (μg/L) 1,2-Di- bromo- 3-chloro- propane (μg/L) 1,2-Di- bromo- ethane (μg/L) 1,2-Di- chloro- benzene (μg/L) 1,2-Di- chloro- ethane (μg/L) 1,2-Di- chloro- propane (μg/L) 1,3,5-Tri- methyl- benzene (μg/L) 1,3-

chlo

benz

(μg

Regional aquifer public-supply wells 293359098290301 <0.18 <0.18 <0.06 <0.12 <0.056 <0.51 <0.036 <0.048 <0.13 <0.029 <0.044 <0.0

293359098290301 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293358098231101 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293358098231101 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293120098285801 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293120098285801 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293145098224201 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293119098211201 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292843098425101 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292459098382101 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292925098360201 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292925098360201 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292822098325401 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292822098325401 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292944098292301 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292944098292301 -- -- -- -- -- -- -- -- -- -- -- -

292522098291901 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292643098241801 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292643098241801 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292328098294601 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

294225098080301 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

294225098080301 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

291210099475601 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293111098340901 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293512098291701 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292424098421501 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

1,2,3-Trichlorobenzene

(μg/L)

1,2,3-Trichloropropane

(μg/L)

1,2,3-Trimethylbenzene

(μg/L)

1,2,4-Trichlorobenzene

(μg/L)

1,2,4-Trimethylbenzene

(μg/L)

1,2-Dibromo3-chloropropane

(μg/L)

1,2-Dibromoethane

(μg/L)

1,2-Dichlorobenzene

(μg/L)

1,2-Dichloroethane

(μg/L)

1,2-Dichloropropane

(μg/L)

1,3,5-Trimethylbenzene

(μg/L)

1,3-

chlo

benz

(μg

292053098365501 <0.18 <0.18 <0.06 <0.12 <0.056 <0.51 <0.036 <0.048 <0.13 <0.029 <0.044 <0.0

293807098155301 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292604098563201 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292116099095501 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

291232099470301 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293128098473101 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293451098313201 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

294604098060801 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

294019098114701 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292215098580201 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292119098524901 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

291943099163301 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

291840099382601 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293518098332601 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293023098355401 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293042098305201 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292442098474501 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292405098371201 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

292931098274601 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

293729098173101 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

291219099095601 <.18 <.18 <.06 <.12 <.056 <.51 <.036 <.048 <.13 <.029 <.044 <.0

Monitoring wells

292943098354401 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292943098354402 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292943098354403 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292943098354404 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number 1,2,3-Tri- chloro- benzene (μg/L) 1,2,3-Tri- chloro- propane (μg/L) 1,2,3-Tri- methyl- benzene (μg/L) 1,2,4-Tri- chloro- benzene (μg/L) 1,2,4-Tri- methyl- benzene (μg/L) 1,2-Di- bromo- 3-chloro- propane (μg/L) 1,2-Di- bromo- ethane (μg/L) 1,2-Di- chloro- benzene (μg/L) 1,2-Di- chloro- ethane (μg/L) 1,2-Di- chloro- propane (μg/L) 1,3,5-Tri- methyl- benzene (μg/L) 1,3-

chlo

benz

(μg

292851098374401 <0.08 <0.12 <0.08 <0.08 <0.04 <0.5 <0.04 <0.02 <0.06 <0.02 <0.04 <0.0

292851098374402 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

Well-field depth-dependent sampling (W4) 292916098360701 <.08 <.12 <.08 <.08 E.040 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292916098360701 <.08 <.12 <.08 <.08 E.046 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292916098360701 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292916098360701 <.08 <.12 <.08 <.08 E.026 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292916098360701 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292916098360701 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292916098360701 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292916098360701 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292916098360701 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

Well-field wells (wellhead sampling)

292919098360501 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292925098360201 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292916098360701 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292920098360601 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

292923098360301 <.08 <.12 <.08 <.08 <.04 <.5 <.04 <.02 <.06 <.02 <.04 <.0

Temporal sampling

292923098360301 <.06 <.12 <.08 <.04 <.04 <1 <.04 <.02 <.06 <.02 <.04 <.0

292923098360301 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

1,2,3-Trichlorobenzene

(μg/L)

1,2,3-Trichloropropane

(μg/L)

1,2,3-Trimethylbenzene

(μg/L)

1,2,4-Trichlorobenzene

(μg/L)

1,2,4-Trimethylbenzene

(μg/L)

1,2-Dibromo3-chloropropane

(μg/L)

1,2-Dibromoethane

(μg/L)

1,2-Dichlorobenzene

(μg/L)

1,2-Dichloroethane

(μg/L)

1,2-Dichloropropane

(μg/L)

1,3,5-Trimethylbenzene

(μg/L)

1,3-

chlo

benz

(μg

292923098360301 <0.06 <0.12 <0.06 <0.08 <0.032 <0.34 <0.05 <0.028 <0.08 <0.026 <0.032 <0.0

292923098360301 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292923098360301 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292923098360301 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354402 <.06 <.12 <.08 <.04 <.04 <1 <.04 <.02 <.06 <.02 <.04 <.0

292943098354402 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354402 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354402 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354402 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354402 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354403 <.06 <.12 <.08 <.04 <.04 <1 <.04 <.02 <.06 <.02 <.04 <.0

292943098354403 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354403 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354403 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354403 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354403 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354404 <.06 <.12 <.08 <.04 <.04 <1 <.04 <.02 <.06 <.02 <.04 <.0

292943098354404 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354404 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354404 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354404 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

292943098354404 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

293252098380801 <.06 <.12 <.08 <.04 <.04 <1 <.04 <.02 <.06 <.02 <.04 <.0

293252098380801 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

293252098380801 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

293252098380801 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

293252098380801 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0

293252098380801 <.06 <.12 <.06 <.08 <.032 <.34 <.05 <.028 <.08 <.026 <.032 <.0
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number 2,2-Di- chloro- propane (μg/L) 2- Chloro- toluene (μg/L) 2-Ethyl- toluene (μg/L) 3-Chloro- propene (μg/L) 4-Chloro- toluene (μg/L) 4-Iso- propyl- toluene (μg/L) Acetone (μg/L) Acrylo- nitrile (μg/L) Benzene (μg/L) Bromo- benzene (μg/L) Bromo- chloro- methane (μg/L) Bromo- dichloro- methane (μg/L) 

Regional aquifer public-supply wells 293359098290301 <0.05 <0.04 <0.06 <0.5 <0.05 <0.08 <6 <0.8 <0.021 <0.028 <0.12 <0.028 

293359098290301 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293358098231101 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293358098231101 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293120098285801 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 .163 

293120098285801 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 E.035 

293145098224201 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293119098211201 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292843098425101 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292459098382101 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292925098360201 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292925098360201 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292822098325401 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292822098325401 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292944098292301 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292944098292301 -- -- -- -- -- -- -- -- -- -- -- -- 

292522098291901 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292643098241801 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 .788 

292643098241801 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292328098294601 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

294225098080301 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

294225098080301 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

291210099475601 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293111098340901 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293512098291701 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 E.027 

292424098421501 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

2,2-Dichloropropane

(μg/L)

2-

Chlorotoluene

(μg/L)

2-Ethyltoluene

(μg/L)

3-Chloropropene

(μg/L)

4-Chlorotoluene

(μg/L)

4-Isopropyltoluene

(μg/L)

Acetone

(μg/L)

Acrylonitrile

(μg/L)

Benzene

(μg/L)

Bromobenzene

(μg/L)

Bromochloromethane

(μg/L)

Bromodichloromethane

(μg/L)

292053098365501 <0.05 <0.04 <0.06 <0.5 <0.05 <0.08 <6 <0.8 <0.021 <0.028 <0.12 E0.046 

293807098155301 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 E.056 

292604098563201 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292116099095501 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

291232099470301 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293128098473101 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293451098313201 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 E.029 

294604098060801 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

294019098114701 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292215098580201 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292119098524901 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

291943099163301 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

291840099382601 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293518098332601 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293023098355401 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293042098305201 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292442098474501 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 .123 

292405098371201 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

292931098274601 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

293729098173101 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

291219099095601 <.05 <.04 <.06 <.5 <.05 <.08 <6 <.8 <.021 <.028 <.12 <.028 

Monitoring wells

292943098354401 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292943098354402 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292943098354403 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292943098354404 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number 2,2-Di- chloro- propane (μg/L) 2- Chloro- toluene (μg/L) 2-Ethyl- toluene (μg/L) 3-Chloro- propene (μg/L) 4-Chloro- toluene (μg/L) 4-Iso- propyl- toluene (μg/L) Acetone (μg/L) Acrylo- nitrile (μg/L) Benzene (μg/L) Bromo- benzene (μg/L) Bromo- chloro- methane (μg/L) Bromo- dichloro- methane (μg/L) 

292851098374401 <0.06 <0.04 <0.04 <0.08 <0.04 <0.08 <4 <0.4 <0.02 <0.02 <0.06 <0.04 

292851098374402 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

Well-field depth-dependent sampling (W4) 292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

Well-field wells (wellhead sampling)

292919098360501 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292925098360201 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 E.071 

292916098360701 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 <.04 

292920098360601 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 E.032 

292923098360301 <.06 <.04 <.04 <.08 <.04 <.08 <4 <.4 <.02 <.02 <.06 E.037 

Temporal sampling

292923098360301 <.06 <.02 <.02 <.08 <.02 <.06 <4 <.4 <.016 <.02 <.06 <.04 

292923098360301 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 E.032 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

2,2-Dichloropropane

(μg/L)

2-

Chlorotoluene

(μg/L)

2-Ethyltoluene

(μg/L)

3-Chloropropene

(μg/L)

4-Chlorotoluene

(μg/L)

4-Isopropyltoluene

(μg/L)

Acetone

(μg/L)

Acrylonitrile

(μg/L)

Benzene

(μg/L)

Bromobenzene

(μg/L)

Bromochloromethane

(μg/L)

Bromodichloromethane

(μg/L)

292923098360301 <0.06 <0.028 <0.032 <0.08 <0.042 <0.06 <3.4 <0.8 <0.026 <0.022 <0.06 <0.034 

292923098360301 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 E.096 

292923098360301 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 E.066 

292923098360301 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354402 <.06 <.02 <.02 <.08 <.02 <.06 <4 <.4 <.016 <.02 <.06 <.04 

292943098354402 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354402 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354402 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354402 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354402 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354403 <.06 <.02 <.02 <.08 <.02 <.06 <4 <.4 <.016 <.02 <.06 <.04 

292943098354403 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354403 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354403 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354403 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354403 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354404 <.06 <.02 <.02 <.08 <.02 <.06 <4 <.4 <.016 <.02 <.06 <.04 

292943098354404 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354404 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354404 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354404 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

292943098354404 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

293252098380801 <.06 <.02 <.02 <.08 <.02 <.06 <4 <.4 <.016 <.02 <.06 <.04 

293252098380801 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 E.053 

293252098380801 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 <.034 

293252098380801 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 E.077 

293252098380801 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 E.071 

293252098380801 <.06 <.028 <.032 <.08 <.042 <.06 <3.4 <.8 <.026 <.022 <.06 .155 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and napublic supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number Chloro- benzene (μg/L) Chloro- ethane (μg/L) Chloro- methane (μg/L) cis-1,2- Di- chloro- ethene (μg/L) cis-1,3- Di- chloro- propene (μg/L) Di- bromo- chloro- methane (μg/L) Di- bromo- methane (μg/L) Dichloro- difluoro- methane (CFC-12) (μg/L) Di- chloro- meth- ane (μg/L) Di- ethyl ether (μg/L) Di- iso- propyl ether (μg/L) Ethyl meth- acrylate (μg/L) Ethyl methyl ketone (μg/L) 

Regional aquifer public-supply wells 293359098290301 <0.028 <0.12 <0.17 <0.024 <0.05 <0.1 <0.05 <0.18 <0.06 <0.08 <0.1 <0.18 <2 

293359098290301 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293358098231101 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293358098231101 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293120098285801 <.028 <.12 <.17 <.024 <.05 .519 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293120098285801 <.028 <.12 <.17 <.024 <.05 E.099 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293145098224201 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293119098211201 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292843098425101 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292459098382101 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292925098360201 <.028 <.12 <.17 <.024 <.05 .154 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292925098360201 <.028 <.12 <.17 <.024 <.05 E.057 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292822098325401 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292822098325401 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292944098292301 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292944098292301 -- -- -- -- -- -- -- -- -- -- -- -- -- 

292522098291901 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292643098241801 <.028 <.12 <.17 <.024 <.05 1.01 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292643098241801 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292328098294601 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

294225098080301 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

294225098080301 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

291210099475601 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293111098340901 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293512098291701 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292424098421501 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and napublic supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

Chlorobenzene

(μg/L)

Chloroethane

(μg/L)

Chloromethane

(μg/L)

cis-1,2-

Dichloroethene

(μg/L)

cis-1,3-

Dichloropropene

(μg/L)

Dibromochloromethane

(μg/L)

Dibromomethane

(μg/L)

Dichlorodifluoromethane 

(CFC-12)

(μg/L)

Dichloromethane

(μg/L)

Diethyl 

ether

(μg/L)

Diisopropyl 

ether

(μg/L)

Ethyl 

methacrylate

(μg/L)

Ethyl 

methyl 

ketone

(μg/L)

292053098365501 <0.028 <0.12 <0.17 <0.024 <0.05 E0.081 <0.05 <0.18 <0.06 <0.08 <0.1 <0.18 <2 

293807098155301 <.028 <.12 <.17 <.024 <.05 .166 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292604098563201 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292116099095501 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

291232099470301 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293128098473101 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293451098313201 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

294604098060801 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

294019098114701 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292215098580201 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292119098524901 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

291943099163301 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

291840099382601 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293518098332601 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293023098355401 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293042098305201 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292442098474501 <.028 <.12 <.17 <.024 <.05 .263 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292405098371201 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

292931098274601 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

293729098173101 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

291219099095601 <.028 <.12 <.17 <.024 <.05 <.1 <.05 <.18 <.06 <.08 <.1 <.18 <2 

Monitoring wells

292943098354401 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292943098354402 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292943098354403 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292943098354404 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and napublic supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number Chloro- benzene (μg/L) Chloro- ethane (μg/L) Chloro- methane (μg/L) cis-1,2- Di- chloro- ethene (μg/L) cis-1,3- Di- chloro- propene (μg/L) Di- bromo- chloro- methane (μg/L) Di- bromo- methane (μg/L) Dichloro- difluoro- methane (CFC-12) (μg/L) Di- chloro- meth- ane (μg/L) Di- ethyl ether (μg/L) Di- iso- propyl ether (μg/L) Ethyl meth- acrylate (μg/L) Ethyl methyl ketone (μg/L) 

292851098374401 <0.02 <0.1 <0.1 <0.02 <0.1 <0.12 <0.004 <0.14 <0.04 <0.12 <0.06 <0.14 <1.6 

292851098374402 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

Well-field depth-dependent sampling (W4) 292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

Well-field wells (wellhead sampling)

292919098360501 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292925098360201 <.02 <.1 <.1 <.02 <.1 .299 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292916098360701 <.02 <.1 <.1 <.02 <.1 <.12 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292920098360601 <.02 <.1 <.1 <.02 <.1 .123 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

292923098360301 <.02 <.1 <.1 <.02 <.1 .203 <.04 <.14 <.04 <.12 <.06 <.14 <1.6 

Temporal sampling

292923098360301 <.02 <.1 <.14 <.02 <.1 <.12 <.04 <.1 <.04 <.12 <.06 <.14 <1.6 

292923098360301 <.016 <.06 <.14 <.022 <.1 E.114 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and napublic supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

Chlorobenzene

(μg/L)

Chloroethane

(μg/L)

Chloromethane

(μg/L)

cis-1,2-

Dichloroethene

(μg/L)

cis-1,3-

Dichloropropene

(μg/L)

Dibromochloromethane

(μg/L)

Dibromomethane

(μg/L)

Dichlorodifluoromethane 

(CFC-12)

(μg/L)

Dichloromethane

(μg/L)

Diethyl 

ether

(μg/L)

Diisopropyl 

ether

(μg/L)

Ethyl 

methacrylate

(μg/L)

Ethyl 

methyl 

ketone

(μg/L)

292923098360301 <0.016 <0.06 <0.14 <0.022 <0.1 <0.12 <0.05 <0.1 <0.038 <0.08 <0.06 <0.14 <1.6 

292923098360301 <.016 <.06 <.14 <.022 <.1 .310 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292923098360301 <.016 <.06 <.14 <.022 <.1 .225 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292923098360301 <.016 <.06 <.14 <.022 <.1 E.115 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354402 <.02 <.1 <.14 <.02 <.1 <.12 <.04 <.1 <.04 <.12 <.06 <.14 <1.6 

292943098354402 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354402 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354402 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354402 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354402 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354403 <.02 <.1 <.14 <.02 <.1 <.12 <.04 <.1 <.04 <.12 <.06 <.14 <1.6 

292943098354403 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354403 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354403 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354403 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354403 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354404 <.02 <.1 <.14 <.02 <.1 <.12 <.04 <.1 <.04 <.12 <.06 <.14 <1.6 

292943098354404 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354404 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354404 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354404 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

292943098354404 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

293252098380801 <.02 <.1 <.14 <.02 <.1 <.12 <.04 <.1 <.04 <.12 <.06 <.14 <1.6 

293252098380801 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

293252098380801 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

293252098380801 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

293252098380801 <.016 <.06 <.14 <.022 <.1 <.12 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 

293252098380801 <.016 <.06 <.14 <.022 <.1 E.048 <.05 <.1 <.038 <.08 <.06 <.14 <1.6 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number Iodo- methane (μg/L) Iso- butyl methyl ketone (μg/L) Iso- propyl- ben- zene (μg/L) Methyl arylo- nitrile (μg/L) Methyl acrylate (μg/L) Methyl meth- acrylate (μg/L) Methyl tert- pentyl ether (μg/L) m- plus p- Xylene (μg/L) Naphth- alene (μg/L) n-Butyl methyl ketone (μg/L) n-Butyl- ben- zene (μg/L) n- Propyl- benzene (μg/L) o- Xylene (μg/L) 

Regional aquifer public-supply wells 293359098290301 <0.5 <0.37 <0.038 <0.4 <1 <0.2 <0.04 <0.06 <0.52 <0.4 <0.12 <0.042 <0.038 

293359098290301 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 293358098231101 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

293358098231101 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

293120098285801 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 293120098285801 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

293145098224201 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 293119098211201 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292843098425101 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292459098382101 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292925098360201 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

292925098360201 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

292822098325401 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292822098325401 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

292944098292301 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292944098292301 -- -- -- -- -- -- -- -- -- -- -- -- -- 

292522098291901 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292643098241801 <.5 <.37 <.038 <.4 <1 <.2 <.04 E.021 <.52 <.4 <.12 <.042 <.038 

292643098241801 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

292328098294601 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

294225098080301 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

294225098080301 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 291210099475601 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

293111098340901 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

293512098291701 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

292424098421501 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

Iodomethane

(μg/L)

Isobutyl 

methyl 

ketone

(μg/L)

Isopropylbenzene

(μg/L)

Methyl 

arylonitrile

(μg/L)

Methyl 

acrylate

(μg/L)

Methyl 

methacrylate

(μg/L)

Methyl 

tertpentyl 

ether

(μg/L)

mplus 

pXylene

(μg/L)

Naphthalene

(μg/L)

n-Butyl 

methyl 

ketone

(μg/L)

n-Butylbenzene

(μg/L)

nPropylbenzene

(μg/L)

oXylene

(μg/L)

292053098365501 <0.5 <0.37 <0.038 <0.4 <1 <0.2 <0.04 <0.06 <0.52 <0.4 <0.12 <0.042 <0.038 293807098155301 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292604098563201 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

292116099095501 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 291232099470301 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 293128098473101 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 293451098313201 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 294604098060801 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 294019098114701 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292215098580201 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292119098524901 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

291943099163301 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 291840099382601 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 293518098332601 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 293023098355401 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 293042098305201 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292442098474501 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292405098371201 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 292931098274601 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

293729098173101 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

291219099095601 <.5 <.37 <.038 <.4 <1 <.2 <.04 <.06 <.52 <.4 <.12 <.042 <.038 

Monitoring wells

292943098354401 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 292943098354402 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 292943098354403 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 292943098354404 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number Iodo- methane (μg/L) Iso- butyl methyl ketone (μg/L) Iso- propyl- ben- zene (μg/L) Methyl arylo- nitrile (μg/L) Methyl acrylate (μg/L) Methyl meth- acrylate (μg/L) Methyl tert- pentyl ether (μg/L) m- plus p- Xylene (μg/L) Naphth- alene (μg/L) n-Butyl methyl ketone (μg/L) n-Butyl- ben- zene (μg/L) n- Propyl- benzene (μg/L) o- Xylene (μg/L) 

292851098374401 <0.4 <0.4 <0.04 <0.2 <0.6 <0.2 <0.06 <0.08 <0.2 <0.6 <0.14 <0.04 <0.04 292851098374402 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

Well-field depth-dependent sampling (W4) 292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

Well-field wells (wellhead sampling)

292919098360501 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

292925098360201 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 292916098360701 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 292920098360601 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 292923098360301 <.4 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.14 <.04 <.04 

Temporal sampling

292923098360301 <.8 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.08 <.04 <.04 

292923098360301 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and nato public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

Iodomethane

(μg/L)

Isobutyl 

methyl 

ketone

(μg/L)

Isopropylbenzene

(μg/L)

Methyl 

arylonitrile

(μg/L)

Methyl 

acrylate

(μg/L)

Methyl 

methacrylate

(μg/L)

Methyl 

tertpentyl 

ether

(μg/L)

mplus 

pXylene

(μg/L)

Naphthalene

(μg/L)

n-Butyl 

methyl 

ketone

(μg/L)

n-Butylbenzene

(μg/L)

nPropylbenzene

(μg/L)

oXylene

(μg/L)

292923098360301 <0.26 <0.32 <0.042 <0.26 <0.56 <0.22 <0.06 <0.08 <0.18 <0.46 <0.08 <0.036 <0.032 292923098360301 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 292923098360301 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 

292923098360301 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 292943098354402 <.8 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.08 <.04 <.04 292943098354402 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 292943098354402 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 292943098354402 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 292943098354402 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 292943098354402 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 292943098354403 <.8 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.08 <.04 <.04 

292943098354403 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 

292943098354403 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 

292943098354403 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 

292943098354403 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 

292943098354403 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 

292943098354404 <.8 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.08 <.04 <.04 

292943098354404 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 

292943098354404 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 

292943098354404 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 292943098354404 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 292943098354404 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 293252098380801 <.8 <.4 <.04 <.2 <.6 <.2 <.06 <.08 <.2 <.6 <.08 <.04 <.04 293252098380801 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 293252098380801 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 293252098380801 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 293252098380801 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 

293252098380801 <.26 <.32 <.042 <.26 <.56 <.22 <.06 <.08 <.18 <.46 <.08 <.036 <.032 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and napublic supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number tert- Butyl alcohol (μg/L) tert- Butyl ethyl ether (μg/L) Methyl tert-butyl ether (MTBE) (μg/L) tert- Butyl- benzene (μg/L) Tetra- chloro- ethene (PCE) (μg/L) Tetra- chloro- methane (μg/L) Tetra- hydro- furan (μg/L) Toluene (μg/L) trans- 1,2-Di- chloro- ethene (μg/L) trans- 1,3-Di- chloro- propene (μg/L) trans- 1,4-Di- chloro- 2-butene (μg/L) Tri- bromo- meth- ane (bromo- form) (μg/L) Tri- chloro- ethene (TCE) (μg/L) 

Regional aquifer public-supply wells 293359098290301 <2 <0.03 <0.1 <0.06 0.549 <0.06 <1 <0.02 <0.032 <0.09 <0.7 0.1 0.038 

293359098290301 -- <.03 <.1 <.06 .830 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293358098231101 <2 <.03 <.1 <.06 .158 <.06 <1 <.02 <.032 <.09 <.7 <.1 E.016 

293358098231101 -- <.03 <.1 <.06 .183 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293120098285801 <2 <.03 <.1 <.06 .130 <.06 <1 <.02 <.032 <.09 <.7 1.90 E.023 

293120098285801 -- <.03 <.1 <.06 .244 <.06 <1 <.02 <.032 <.09 <.7 .386 E.021 

293145098224201 <2 <.03 <.1 <.06 E.046 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293119098211201 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292843098425101 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292459098382101 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292925098360201 <2 <.03 <.1 <.06 .107 <.06 <1 <.02 <.032 <.09 <.7 .477 <.038 

292925098360201 -- <.03 <.1 <.06 .140 <.06 <1 <.02 <.032 <.09 <.7 .352 <.038 

292822098325401 <2 <.03 <.1 <.06 E.017 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292822098325401 -- <.03 <.1 <.06 E.019 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292944098292301 <2 <.03 <.1 <.06 E.030 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292944098292301 -- -- -- -- -- -- -- -- -- -- -- -- -- 

292522098291901 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292643098241801 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 1.02 <.038 

292643098241801 -- <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292328098294601 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

294225098080301 <2 <.03 <.1 <.06 .110 <.06 <1 E.011 <.032 <.09 <.7 <.1 <.038 

294225098080301 -- <.03 <.1 <.06 E.087 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

291210099475601 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293111098340901 <2 <.03 <.1 <.06 E.046 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293512098291701 <2 <.03 <.1 <.06 E.037 <.06 <1 E.009 <.032 <.09 <.7 E.057 <.038 

292424098421501 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and napublic supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

tertButyl 

alcohol

(μg/L)

tertButyl 

ethyl 

ether

(μg/L)

Methyl 

tert-butyl 

ether 

(MTBE)

(μg/L)

tertButylbenzene

(μg/L)

Tetrachloroethene 

(PCE)

(μg/L)

Tetrachloromethane

(μg/L)

Tetrahydrofuran

(μg/L)

Toluene

(μg/L)

trans1,2-Dichloroethene

(μg/L)

trans1,3-Dichloropropene

(μg/L)

trans1,4-Dichloro2-butene

(μg/L)

Tribromomethane 

(bromoform)

(μg/L)

Trichloroethene 

(TCE)

(μg/L)

292053098365501 <2 <0.03 <0.1 <0.06 <0.03 <0.06 <1 <0.02 <0.032 <0.09 <0.7 0.347 <0.038 

293807098155301 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 .494 <.038 

292604098563201 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292116099095501 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

291232099470301 <2 <.03 <.1 <.06 E.069 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293128098473101 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293451098313201 <2 <.03 <.1 <.06 E.026 <.06 <1 <.02 <.032 <.09 <.7 <.1 E.01502 

294604098060801 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

294019098114701 <2 <.03 <.1 <.06 .120 <.06 <1 <.02 <.032 <.09 <.7 E.099 <.038 

292215098580201 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 .101 <.038 

292119098524901 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

291943099163301 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

291840099382601 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293518098332601 <2 <.03 <.1 <.06 E.059 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293023098355401 <2 <.03 <.1 <.06 .223 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293042098305201 <2 <.03 <.1 <.06 .197 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292442098474501 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 .345 <.038 

292405098371201 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

292931098274601 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 .172 <.038 

291219099095601 <2 <.03 <.1 <.06 <.03 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

293729098173101 <2 <.03 <.1 <.06 E.016 <.06 <1 <.02 <.032 <.09 <.7 <.1 <.038 

Monitoring wells

292943098354401 -- <.04 <.1 <.06 .372 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292943098354402 -- <.04 <.1 <.06 .365 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292943098354403 -- <.04 <.1 <.06 .479 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292943098354404 -- <.04 <.1 <.06 .174 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and napublic supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level] USGS identification number tert- Butyl alcohol (μg/L) tert- Butyl ethyl ether (μg/L) Methyl tert-butyl ether (MTBE) (μg/L) tert- Butyl- benzene (μg/L) Tetra- chloro- ethene (PCE) (μg/L) Tetra- chloro- methane (μg/L) Tetra- hydro- furan (μg/L) Toluene (μg/L) trans- 1,2-Di- chloro- ethene (μg/L) trans- 1,3-Di- chloro- propene (μg/L) trans- 1,4-Di- chloro- 2-butene (μg/L) Tri- bromo- meth- ane (bromo- form) (μg/L) Tri- chloro- ethene (TCE) (μg/L) 

292851098374401 -- <0.04 <0.1 <0.06 E0.060 <0.08 <1.4 <0.02 <0.02 <0.1 <0.6 <0.08 <0.02 

292851098374402 -- <.04 <.1 <.06 .164 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 E.066 

Well-field depth-dependent sampling (W4) 292916098360701 -- <.04 <.1 <.06 E.055 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292916098360701 -- <.04 <.1 <.06 E.055 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292916098360701 -- <.04 <.1 <.06 .127 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292916098360701 -- <.04 <.1 <.06 E.057 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292916098360701 -- <.04 <.1 <.06 E.078 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292916098360701 -- <.04 <.1 <.06 .102 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292916098360701 -- <.04 <.1 <.06 .137 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292916098360701 -- <.04 <.1 <.06 E.086 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292916098360701 -- <.04 <.1 <.06 E.049 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

Well-field wells (wellhead sampling)

292919098360501 -- <.04 <.1 <.06 .176 <.08 <1.4 <.02 <.02 <.1 <.6 .327 <.02 

292925098360201 -- <.04 <.1 <.06 .115 <.08 <1.4 <.02 <.02 <.1 <.6 2.01 <.02 

292916098360701 -- <.04 <.1 <.06 .126 <.08 <1.4 <.02 <.02 <.1 <.6 <.08 <.02 

292920098360601 -- <.04 <.1 <.06 .223 <.08 <1.4 <.02 <.02 <.1 <.6 .756 <.02 

292923098360301 -- <.04 <.1 <.06 .210 <.08 <1.4 <.02 <.02 <.1 <.6 1.15 <.02 

Temporal sampling

292923098360301 -- <.04 <.1 <.06 .208 <.06 <1.4 <.018 <.018 <.1 <.4 .260 <.02 

292923098360301 -- <.032 <.1 <.06 .292 <.052 <1.4 <.018 <.018 <.14 <.36 .561 <.022 
Table 14. Volatile organic and fuel oxygenate compounds for groundwater samples collected for the study of the transport of anthropogenic and napublic supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured or not applicable; E, estimated; <, nmethod reporting level]

USGS 

identification 

number

tertButyl 

alcohol

(μg/L)

tertButyl 

ethyl 

ether

(μg/L)

Methyl 

tert-butyl 

ether 

(MTBE)

(μg/L)

tertButylbenzene

(μg/L)

Tetrachloroethene 

(PCE)

(μg/L)

Tetrachloromethane

(μg/L)

Tetrahydrofuran

(μg/L)

Toluene

(μg/L)

trans1,2-Dichloroethene

(μg/L)

trans1,3-Dichloropropene

(μg/L)

trans1,4-Dichloro2-butene

(μg/L)

Tribromomethane 

(bromoform)

(μg/L)

Trichloroethene 

(TCE)

(μg/L)

292923098360301 -- <0.032 <0.1 <0.06 0.290 <0.052 <1.4 <0.018 <0.018 <0.14 <0.36 0.475 <0.022 

292923098360301 -- <.032 <.1 <.06 .408 <.052 <1.4 <.018 <.018 <.14 <.36 1.00 <.022 

292923098360301 -- <.032 <.1 <.06 .295 <.052 <1.4 <.018 <.018 <.14 <.36 .943 <.022 

292923098360301 -- <.032 <.1 <.06 .247 <.052 <1.4 <.018 <.018 <.14 <.36 .644 <.022 

292943098354402 -- <.04 <.1 <.06 .383 <.06 <1.4 <.018 <.018 <.1 <.4 <.1 <.02 

292943098354402 -- <.032 <.1 <.06 .634 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354402 -- <.032 <.1 <.06 .680 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354402 -- <.032 <.1 <.06 .681 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354402 -- <.032 <.1 <.06 .706 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354402 -- <.032 <.1 <.06 .574 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354403 -- <.04 <.1 <.06 .587 <.06 <1.4 <.018 <.018 <.1 <.4 <.1 <.02 

292943098354403 -- <.032 <.1 <.06 .727 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354403 -- <.032 <.1 <.06 .810 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354403 -- <.032 <.1 <.06 .814 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354403 -- <.032 <.1 <.06 .733 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354403 -- <.032 <.1 <.06 .733 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354404 -- <.04 <.1 <.06 .257 <.06 <1.4 <.018 <.018 <.1 <.4 <.1 <.02 

292943098354404 -- <.032 <.1 <.06 .277 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354404 -- <.032 <.1 <.06 .306 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354404 -- <.032 <.1 <.06 .288 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354404 -- <.032 <.1 <.06 .307 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

292943098354404 -- <.032 <.1 <.06 .265 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

293252098380801 -- <.04 <.1 <.06 E.037 <.06 <1.4 <.018 <.018 <.1 <.4 <.1 <.02 

293252098380801 -- <.032 <.1 <.06 E.025 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

293252098380801 -- <.032 <.1 <.06 E.024 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

293252098380801 -- <.032 <.1 <.06 <.026 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

293252098380801 -- <.032 <.1 <.06 E.018 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

293252098380801 -- <.032 <.1 <.06 E.020 <.052 <1.4 <.018 <.018 <.14 <.36 <.1 <.022 

*Sample collected from top of open interval during depth-dependent sampling.
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

1-Naphthol

(μg/L)

2,6-Diethylaniline

(μg/L)

2-Chloro4-isopropylamino-6-

amino-striazine 

(CIAT)

(μg/L)

2-ChloroN-(2,6-diethylphenyl)-

acetamide 

(alachlor 

2nd amide)

(μg/L)

2-Ethyl6-methylaniline

(μg/L)

3,4-Dichloroaniline

(μg/L)

3,5-Dichloro

aniline

(μg/L)

Regional aquifer public-supply wells

293359098290301 AY–68–29–414 1st (highest) quartile 2004/12/06 <0.088 <0.006 E0.011 <0.005 <0.005 <0.005 -- 

293359098290301 AY–68–29–414 1st quartile 2005/09/01 <.088 <.006 E.010 <.005 <.005 <.005 <0.004 

293358098231101 AY–68–29–610 1st quartile 2004/12/15 <.088 <.006 E.012 <.005 <.005 <.005 -- 

293358098231101 AY–68–29–610 1st quartile 2005/08/29 <.088 <.006 E.013 <.005 <.005 <.005 <.004 

293120098285801 AY–68–29–714 1st quartile 2004/12/14 <.088 <.006 E.011 <.005 <.005 <.005 -- 

293120098285801 AY–68–29–714 1st quartile 2005/08/30 -- -- E.012 -- -- -- -- 

293145098224201 AY–68–29–929 1st quartile 2004/12/15 <.088 <.006 <.01 <.005 <.005 <.005 -- 

293119098211201 AY–68–30–718 1st quartile 2004/12/16 <.088 <.006 <.006 <.005 <.005 <.005 -- 

292843098425101 AY–68–35–106 1st quartile 2004/12/13 <.088 <.006 <.006 <.005 <.005 <.005 -- 

292459098382101 AY–68–35–913 1st quartile 2004/12/13 <.088 <.006 <.006 <.005 <.005 <.005 -- 

292925098360201 AY–68–36–104 1st quartile 2004/12/13 <.088 <.006 E.009 <.005 <.005 <.005 -- 

292925098360201 AY–68–36–104 1st quartile 2005/08/31 <.088 <.006 E.008 <.005 <.005 <.005 <.004 

292822098325401 AY–68–36–206 1st quartile 2004/12/13 <.088 <.006 E.009 <.005 <.005 <.005 -- 

292822098325401 AY–68–36–206 1st quartile 2005/08/31 <.088 <.006 E.012 <.005 <.005 <.005 <.004 

292944098292301 AY–68–37–105 1st quartile 2004/12/14 <.088 <.006 E.010 <.005 <.005 <.005 -- 

292944098292301 AY–68–37–105 1st quartile 2005/08/31 <.088 <.006 E.011 <.005 <.005 <.005 <.004 

292522098291901 AY–68–37–426 1st quartile 2004/12/14 <.088 <.006 <.006 <.005 <.005 <.005 -- 

292643098241801 AY–68–37–601 1st quartile 2004/12/15 <.088 <.006 <.006 <.005 <.005 <.005 -- 

292643098241801 AY–68–37–601 1st quartile 2005/08/30 -- -- <.028 -- -- -- -- 

292328098294601 AY–68–37–705 1st quartile 2004/12/14 <.088 <.006 <.006 <.005 <.005 <.005 -- 

294225098080301 DX–68–23–601 1st quartile 2004/12/08 <.088 <.006 E.010 <.005 <.005 <.005 -- 

294225098080301 DX–68–23–601 1st quartile 2005/09/01 <.088 <.006 E.008 <.005 <.005 <.005 <.004 

291210099475601 YP–69–50–506 1st quartile 2004/11/30 <.088 <.006 E.006 <.005 <.005 <.005 -- 

293111098340901 AY–68–28–807 2d quartile 2005/05/26 <.088 <.006 E.007 <.005 <.005 <.005 -- 

293512098291701 AY–68–29–109 2d quartile 2005/04/20 <.088 <.006 E.010 <.005 <.005 <.005 -- 

292424098421501 AY–68–35–810 2d quartile 2005/04/21 <.088 <.006 E.008 <.005 <.005 <.005 -- 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

1-Naphthol

(μg/L)

2,6-Diethylaniline

(μg/L)

2-Chloro4-isopropylamino-6-

amino-striazine 

(CIAT)

(μg/L)

2-ChloroN-(2,6-diethylphenyl)-

acetamide 

(alachlor 

2nd amide)

(μg/L)

2-Ethyl6-methylaniline

(μg/L)

3,4-Dichloroaniline

(μg/L)

3,5-Dichloro

aniline

(μg/L)

292053098365501 AY–68–44–110 2d quartile 2005/05/26 <0.088 <0.006 E0.004 <0.005 <0.005 <0.005 -- 

293807098155301 DX–68–22–901 2d quartile 2005/05/18 <.088 <.006 E.005 <.005 <.005 <.005 -- 

292604098563201 TD–68–33–501 2d quartile 2005/05/16 <.088 <.006 <.006 <.005 <.005 <.005 -- 

292116099095501 TD–69–47–305 2d quartile 2005/04/27 <.088 <.006 E.006 <.005 <.005 <.005 -- 

291232099470301 YP–69–50–339 2d quartile 2005/05/11 <.088 <.006 E.005 <.005 <.005 -- -- 

--

293128098473101 AY–68–26–814 3d quartile 2005/04/18 <.088 <.006 <.006 <.005 <.005 <.005 -- 

293451098313201 AY–68–28–601 3d quartile 2005/05/17 <.088 <.006 E.015 <.005 <.005 E.003 -- 294604098060801 DX–68–16–708 3d quartile 2005/04/25 <.088 <.006 <.006 <.005 <.005 <.005 -- 

294019098114701 DX–68–23–504 3d quartile 2005/05/18 <.088 <.006 E.007 <.005 <.005 <.005 -- 

292215098580201 TD–68–41–103 3d quartile 2005/05/09 <.088 <.006 E.006 <.005 <.005 -- -- 292119098524901 TD–68–41–308 3d quartile 2005/04/27 <.088 <.006 E.005 <.005 <.005 <.005 -- 

291943099163301 TD–69–46–601 3d quartile 2005/05/09 <.088 <.006 <.006 <.005 <.005 -- -- 291840099382601 YP–69–43–606 3d quartile 2005/05/11 <.088 <.006 E.006 <.005 <.005 -- -- 

293518098332601 AY–68–28–203 4th quartile 2005/04/19 <.088 <.006 E.005 <.005 <.005 <.005 -- 

293023098355401 AY–68–28–702 4th quartile 2005/04/26 <.088 <.006 E.011 <.005 <.005 <.005 -- 

293042098305201 AY–68–28–913 4th quartile 2005/06/30 <.088 <.006 E.010 <.005 <.005 <.005 <.004 

292442098474501 AY–68–34–803 4th quartile 2005/04/20 <.088 <.006 E.013 <.005 <.005 <.005 -- 

292405098371201 AY–68–36–704 4th quartile 2005/05/23 <.088 <.006 E.006 <.005 <.005 <.005 -- 

292931098274601 AY–68–37–124 4th quartile 2005/05/25 <.088 <.006 E.009 <.005 <.005 <.005 -- 

293729098173101 DX–68–30–215 4th quartile 2005/04/25 <.088 <.006 E.006 <.005 <.005 <.005 -- 

291219099095601 TD–69–55–604 4th quartile 2005/05/16 <.088 <.006 E.006 <.005 <.005 <.005 -- 

Monitoring wells

292943098354401 AY–68–36–135 MW OVB 2007/10/30 <.04 <.006 E.010 <.01 <.010 <.006 <.008 

292943098354402 AY–68–36–133 TANC MW 2007/10/31 <.04 <.006 E.011 <.01 <.010 <.006 <.008 

292943098354403 AY–68–36–134 TANC MW 2007/10/30 <.04 <.006 E.013 <.01 <.010 <.006 <.008 

292943098354404 AY–68–36–132 TANC MW 2007/11/01 <.04 <.006 E.012 <.01 <.010 <.006 <.008 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel] USGS identification number State well number Group and description Sample date 1-Naph- thol (μg/L) 2,6-Di- ethyl- aniline (μg/L) 2-Chloro- 4-isopropyl- amino-6- amino-s- triazine (CIAT) (μg/L) 2-Chloro- N-(2,6-di- ethylphenyl)- acetamide (alachlor 2nd amide) (μg/L) 2-Ethyl- 6-methyl- aniline (μg/L) 3,4-Di- chloro- aniline (μg/L) 3,5-Di- chloro

aniline (μg/L) 

292851098374401 AY–68–35–315 TANC MW 2008/05/06 <0.04 <0.006 E0.013 <0.01 <0.010 <0.006 <0.008 

292851098374402 AY–68–35–314 TANC MW 2008/05/07 <.04 <.006 E.021 <.01 <.010 <.006 <.008 

Well-field depth-dependent sampling (W4) 292916098360701 AY–68–36–105 W4-shallow (380), normal 2007/11/16 <.04 <.006 E.011 <.01 <.010 <.006 <.008 

292916098360701 AY–68–36–105 W4-intermediate (430), normal 2007/11/15 <.04 <.006 E.011 <.01 <.010 <.006 <.008 

292916098360701 AY–68–36–105 W4-deep (540), normal 2007/11/15 <.04 <.006 E.013 <.01 <.010 <.006 <.008 

292916098360701 AY–68–36–105 W4-shallow (380), ambi- ent 2007/11/16 <.04 <.006 E.011 <.01 <.010 <.006 <.008 

292916098360701 AY–68–36–105 W4-intermediate (430), ambient 2007/11/14 <.04 <.006 E.012 <.01 <.010 <.006 <.008 

292916098360701 AY–68–36–105 W4-deep (540), ambient 2007/11/15 <.04 <.006 E.013 <.01 <.010 <.006 <.008 

292916098360701 AY–68–36–105 W4-shallow (380), moderate 2007/11/16 <.04 <.006 E.014 <.01 <.010 <.006 <.008 

292916098360701 AY–68–36–105 W4-intermediate (430), 

moderate

2007/11/14 <.04 <.006 E.013 <.01 <.010 <.006 <.008 

292916098360701 AY–68–36–105 W4-deep (540), moderate 2007/11/15 <.04 <.006 E.011 <.01 <.010 <.006 <.008 

Well-field wells (wellhead sampling)

292919098360501 AY–68–36–103 wellhead 2007/11/29 <.04 <.006 E.015 <.01 <.010 <.006 <.008 

292925098360201 AY–68–36–104 wellhead 2007/11/28 <.04 <.006 E.010 <.01 <.010 <.006 <.008 

292916098360701 AY–68–36–105 *wellhead 2007/11/16 <.04 <.006 E.015 <.01 <.010 <.006 <.008 

292920098360601 AY–68–36–130 wellhead 2007/11/29 <.04 <.006 E.015 <.01 <.010 <.006 <.008 

292923098360301 AY–68–36–131 wellhead 2007/11/28 <.04 <.006 E.012 <.01 <.010 <.006 <.008 

Temporal sampling

292923098360301 AY–68–36–131 TANC PSW pre-storm 2009/04/09 -- -- -- -- -- -- -- 

292923098360301 AY–68–36–131 TANC PSW storm 1 2009/10/06 -- -- -- -- -- -- -- 

292923098360301 AY–68–36–131 TANC PSW storm 2 2009/10/09 -- -- -- -- -- -- -- 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel]

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

1-Naphthol

(μg/L)

2,6-Diethylaniline

(μg/L)

2-Chloro4-isopropylamino-6-

amino-striazine 

(CIAT)

(μg/L)

2-ChloroN-(2,6-diethylphenyl)-

acetamide 

(alachlor 

2nd amide)

(μg/L)

2-Ethyl6-methylaniline

(μg/L)

3,4-Dichloroaniline

(μg/L)

3,5-Dichloro

aniline

(μg/L)

292923098360301 AY–68–36–131 TANC PSW storm 3 2009/10/19 <0.036 <0.006 E0.015 <0.010 <0.010 <0.004 <0.003 

292923098360301 AY–68–36–131 TANC PSW storm 4 2009/10/30 <.036 <.006 E.016 <.010 <.010 <.004 <.003 

292923098360301 AY–68–36–131 TANC PSW storm 5 2009/11/19 <.036 <.006 E.015 <.010 <.010 <.004 <.003 

292943098354402 AY–68–36–133 TANC MW pre-storm 2009/04/08 -- -- -- -- -- -- -- 

292943098354402 AY–68–36–133 TANC MW storm 1 2009/10/05 -- -- -- -- -- -- -- 

292943098354402 AY–68–36–133 TANC MW storm 2 2009/10/07 -- -- -- -- -- -- -- 

292943098354402 AY–68–36–133 TANC MW storm 3 2009/10/17 <.036 <.006 E.015 <.010 <.010 <.004 <.003 

292943098354402 AY–68–36–133 TANC MW storm 4 2009/10/28 <.036 <.006 E.015 <.010 <.010 <.004 <.003 

292943098354402 AY–68–36–133 TANC MW storm 5 2009/11/18 <.036 <.006 E.015 <.010 <.010 <.004 <.003 

292943098354403 AY–68–36–134 TANC MW pre-storm 2009/04/09 -- -- -- -- -- -- -- 

292943098354403 AY–68–36–134 TANC MW storm 1 2009/10/05 -- -- -- -- -- -- -- 

292943098354403 AY–68–36–134 TANC MW storm 2 2009/10/08 -- -- -- -- -- -- -- 

292943098354403 AY–68–36–134 TANC MW storm 3 2009/10/18 <.036 <.006 E.016 <.010 <.010 <.004 <.003 

292943098354403 AY–68–36–134 TANC MW storm 4 2009/10/29 <.036 <.006 E.019 <.010 <.010 <.004 <.003 

292943098354403 AY–68–36–134 TANC MW storm 5 2009/11/18 <.036 <.006 E.016 <.010 <.010 <.004 <.003 

292943098354404 AY–68–36–132 TANC MW pre-storm 2009/04/09 -- -- -- -- -- -- -- 

292943098354404 AY–68–36–132 TANC MW storm 1 2009/10/05 -- -- -- -- -- -- -- 

292943098354404 AY–68–36–132 TANC MW storm 2 2009/10/08 -- -- -- -- -- -- -- 

292943098354404 AY–68–36–132 TANC MW storm 3 2009/10/18 <.036 <.006 E.017 <.010 <.010 <.004 <.003 

292943098354404 AY–68–36–132 TANC MW storm 4 2009/10/29 <.036 <.006 E.018 <.010 <.010 <.004 <.003 

292943098354404 AY–68–36–132 TANC MW storm 5 2009/11/18 <.036 <.006 E.020 <.010 <.010 <.004 <.003 

293252098380801 AY–68–27–610 TANC MW pre-storm 2009/04/14 -- -- -- -- -- -- -- 

293252098380801 AY–68–27–610 TANC MW storm 1 2009/10/04 -- -- -- -- -- -- -- 

293252098380801 AY–68–27–610 TANC MW storm 2 2009/10/07 -- -- -- -- -- -- -- 

293252098380801 AY–68–27–610 TANC MW storm 3 2009/10/17 <.036 <.006 E.028 <.010 <.010 <.004 <.003 

293252098380801 AY–68–27–610 TANC MW storm 4 2009/10/28 <.036 <.006 E.032 <.010 <.010 <.004 <.003 

293252098380801 AY–68–27–610 TANC MW storm 5 2009/11/17 <.036 <.006 E.036 <.010 <.010 <.004 <.003 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel] USGS identification number alpha- Endo- sulfan (μg/L) Atra- zine (μg/L) Azin- phos- methyl oxygen analog (μg/L) Azin- phos- methyl (μg/L) Ben- fluralin (μg/L) Carb- aryl (μg/L) Carbo- furan (μg/L) Chlor- pyrifos (μg/L) cis- Perm- ethrin (μg/L) cis- Pro- picon- azole (μg/L) Cyana- zine (μg/L) Cyflu- thrin (μg/L) lambda- Cyhalo- thrin (μg/L) Cy- perm- ethrin (μg/L) 

Regional aquifer public-supply wells 293359098290301 -- 0.01 <0.070 <0.05 <0.010 <0.041 -- <0.005 <0.006 -- -- <0.008 -- <0.009 

293359098290301 <0.005 .008 <.070 <.05 <.01 <.041 <0.02 <.005 <.006 <0.008 <0.018 <.027 <0.009 <.009 

293358098231101 -- .014 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

293358098231101 <.005 .011 <.070 <.05 <.01 <.041 <.02 <.005 <.006 <.008 <.018 <.027 <.009 <.009 

293120098285801 -- <.01 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

293120098285801 -- E.005 -- -- -- -- -- -- -- -- -- -- -- -- 

293145098224201 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

293119098211201 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

292843098425101 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

292459098382101 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

292925098360201 -- .008 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

292925098360201 <.005 E.007 <.070 <.05 <.01 <.041 <.02 <.005 <.006 <.008 <.018 <.027 <.009 <.009 292822098325401 -- .007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

292822098325401 <.005 E.007 <.070 <.05 <.01 <.041 <.02 <.005 <.006 <.008 <.018 <.027 <.009 <.009 292944098292301 -- .008 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

292944098292301 <.005 E.007 <.070 <.05 <.01 <.041 <.02 <.005 <.006 <.008 <.018 <.027 <.009 <.009 

292522098291901 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

292643098241801 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

292643098241801 -- <.008 -- -- -- -- -- -- -- -- -- -- -- -- 

292328098294601 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

294225098080301 -- .008 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

294225098080301 <.005 E.006 <.070 <.05 <.01 <.041 <.02 <.005 <.006 <.008 <.018 <.027 <.009 <.009 

291210099475601 -- E.004 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.008 -- <.009 

293111098340901 -- .007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

293512098291701 -- .009 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

292424098421501 -- .007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel]

USGS 

identification 

number

alphaEndosulfan

(μg/L)

Atrazine

(μg/L)

Azinphosmethyl 

oxygen 

analog

(μg/L)

Azinphosmethyl

(μg/L)

Benfluralin

(μg/L)

Carbaryl

(μg/L)

Carbofuran

(μg/L)

Chlorpyrifos

(μg/L)

cisPermethrin

(μg/L)

cisPropiconazole

(μg/L)

Cyanazine

(μg/L)

Cyfluthrin

(μg/L)

lambdaCyhalothrin

(μg/L)

Cypermethrin

(μg/L)

292053098365501 -- <0.007 <0.070 <0.05 <0.010 <0.041 -- <0.005 <0.006 -- -- <0.027 -- <0.009 

293807098155301 -- E.004 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

292604098563201 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

292116099095501 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

291232099470301 -- E.004 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

-- --

293128098473101 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

293451098313201 -- .018 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

294604098060801 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

294019098114701 -- E.005 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

292215098580201 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

292119098524901 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

291943099163301 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

291840099382601 -- E.004 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

293518098332601 -- E.006 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

293023098355401 -- .012 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

293042098305201 <0.005 E.007 <.070 <.05 <.01 <.041 <0.02 <.005 <.006 <0.008 <0.018 <.027 <0.009 <.009 

292442098474501 -- E.005 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

292405098371201 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

292931098274601 -- .007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

293729098173101 -- E.005 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

291219099095601 -- <.007 <.070 <.05 <.010 <.041 -- <.005 <.006 -- -- <.027 -- <.009 

Monitoring wells

292943098354401 <.006 .009 <.042 <.12 <.0059 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 292943098354402 <.006 .009 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292943098354403 <.006 .012 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292943098354404 <.006 <.008 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292851098374401 <0.006 0.008 <0.06 <0.12 <0.01 <0.06 <0.02 <0.005 <0.01 <0.006 <0.02 <0.016 <0.004 <0.014 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel] USGS identification number alpha- Endo- sulfan (μg/L) Atra- zine (μg/L) Azin- phos- methyl oxygen analog (μg/L) Azin- phos- methyl (μg/L) Ben- fluralin (μg/L) Carb- aryl (μg/L) Carbo- furan (μg/L) Chlor- pyrifos (μg/L) cis- Perm- ethrin (μg/L) cis- Pro- picon- azole (μg/L) Cyana- zine (μg/L) Cyflu- thrin (μg/L) lambda- Cyhalo- thrin (μg/L) Cy- perm- ethrin (μg/L) 

292851098374402 <.006 E.014 <.042 <.12 <.01 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

Well-field depth-dependent sampling (W4) 292916098360701 <.006 E.008 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292916098360701 <.006 .011 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292916098360701 <.006 u <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292916098360701 <.006 .009 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292916098360701 <.006 E.011 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292916098360701 <.006 .015 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292916098360701 <.006 .016 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292916098360701 <.006 .012 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292916098360701 <.006 .011 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

Well-field wells (wellhead sampling)

292919098360501 <.006 .017 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292925098360201 <.006 .009 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292916098360701 <.006 .017 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292920098360601 <.006 .015 <.042 <.12 <.004 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

292923098360301 <.006 .015 <.042 <.12 <.0058 <.06 <.02 <.005 <.01 <.006 <.02 <.016 <.004 <.014 

Temporal sampling

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 <0.006 0.008 <0.042 <0.12 <0.014 <0.06 <0.060 <0.010 <0.014 <0.006 <0.022 <0.016 <0.010 <0.020 

292923098360301 <.006 E.006 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel]

USGS 

identification 

number

alphaEndosulfan

(μg/L)

Atrazine

(μg/L)

Azinphosmethyl 

oxygen 

analog

(μg/L)

Azinphosmethyl

(μg/L)

Benfluralin

(μg/L)

Carbaryl

(μg/L)

Carbofuran

(μg/L)

Chlorpyrifos

(μg/L)

cisPermethrin

(μg/L)

cisPropiconazole

(μg/L)

Cyanazine

(μg/L)

Cyfluthrin

(μg/L)

lambdaCyhalothrin

(μg/L)

Cypermethrin

(μg/L)

292923098360301 <.006 E.008 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 <.006 .009 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 

292943098354402 <.006 .009 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 

292943098354402 <.006 .008 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 

292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354403 <.006 .009 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 292943098354403 <.006 .009 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 292943098354403 <.006 .008 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 

292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354404 <.006 .009 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 292943098354404 <.006 .009 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 

292943098354404 <.006 .009 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 <.006 .017 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 

293252098380801 <.006 .015 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 

293252098380801 <.006 .017 <.042 <.12 <.014 <.06 <.060 <.010 <.014 <.006 <.022 <.016 <.010 <.020 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel] USGS identification number Diaz- inon (μg/L) Diaz- oxon (μg/L) Di- chlor- vos (μg/L) Di- croto- phos (μg/L) Diel- drin (μg/L) Di- meth- oate (μg/L) Di- sulf- oton sulfone (μg/L) Di- sulf- oton (μg/L) Endo- sulfan sulfate (μg/L) EPTC (μg/L) Ethion mon- oxon (μg/L) Ethion (μg/L) Etho- prop (μg/L) Fen- amiphos sulfone (μg/L) 

Regional aquifer public-supply wells 293359098290301 <0.005 <0.006 <0.012 <0.084 <0.009 <0.006 -- -- -- -- <0.002 <0.004 -- <0.049 

293359098290301 <.005 <.006 <.012 <.084 <.009 <.006 <0.006 <0.021 <0.014 <0.004 <.002 <.004 <0.005 <.049 

293358098231101 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293358098231101 <.005 <.006 <.012 <.084 <.009 <.006 <.006 <.021 <.014 <.004 <.002 <.004 <.005 <.049 

293120098285801 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293120098285801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293145098224201 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293119098211201 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292843098425101 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292459098382101 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292925098360201 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292925098360201 <.005 <.006 <.012 <.084 <.009 <.006 <.006 <.021 <.014 <.004 <.002 <.004 <.005 <.049 

292822098325401 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292822098325401 <.005 <.006 <.012 <.084 <.009 <.006 <.006 <.021 <.014 <.004 <.002 <.004 <.005 <.049 

292944098292301 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292944098292301 <.005 <.006 <.012 <.084 <.009 <.006 <.006 <.021 <.014 <.004 <.002 <.004 <.005 <.049 

292522098291901 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292643098241801 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292643098241801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292328098294601 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

294225098080301 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

294225098080301 <.005 <.006 <.012 <.084 <.009 <.006 <.006 <.021 <.014 <.004 <.002 <.004 <.005 <.049 

291210099475601 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293111098340901 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293512098291701 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292424098421501 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel]

USGS 

identification 

number

Diazinon

(μg/L) 

Diazoxon

(μg/L) 

Dichlorvos

(μg/L) 

Dicrotophos

(μg/L) 

Dieldrin

(μg/L) 

Dimethoate

(μg/L) 

Disulfoton 

sulfone

(μg/L) 

Disulfoton

(μg/L) 

Endosulfan 

sulfate

(μg/L) 

EPTC

(μg/L) 

Ethion 

monoxon

(μg/L) 

Ethion

(μg/L) 

Ethoprop

(μg/L) 

Fenamiphos 

sulfone

(μg/L) 

292053098365501 <0.005 <0.006 <0.012 <0.084 <0.009 <0.006 -- -- -- -- <0.002 <0.004 -- <0.049 

293807098155301 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292604098563201 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292116099095501 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

291232099470301 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293128098473101 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293451098313201 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

294604098060801 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

294019098114701 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292215098580201 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292119098524901 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

291943099163301 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

291840099382601 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293518098332601 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293023098355401 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293042098305201 <.005 <.006 <.012 <.084 <.009 <.006 <0.006 <0.021 <0.014 <0.004 <.002 <.004 <0.005 <.049 

292442098474501 <.005 <.006 <.012 <.084 E.003 <.006 -- -- -- -- <.002 <.004 -- <.049 

292405098371201 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

292931098274601 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

293729098173101 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

291219099095601 <.005 <.006 <.012 <.084 <.009 <.006 -- -- -- -- <.002 <.004 -- <.049 

Monitoring wells

292943098354401 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292943098354402 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.060 <.022 <.002 <.021 <.006 <.012 <.053 

292943098354403 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292943098354404 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292851098374401 <0.005 <0.006 <0.013 <0.084 <0.009 <0.006 <0.014 <0.04 <0.022 <0.002 <0.021 <0.006 <0.012 <0.053 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel] USGS identification number Diaz- inon (μg/L) Diaz- oxon (μg/L) Di- chlor- vos (μg/L) Di- croto- phos (μg/L) Diel- drin (μg/L) Di- meth- oate (μg/L) Di- sulf- oton sulfone (μg/L) Di- sulf- oton (μg/L) Endo- sulfan sulfate (μg/L) EPTC (μg/L) Ethion mon- oxon (μg/L) Ethion (μg/L) Etho- prop (μg/L) Fen- amiphos sulfone (μg/L) 

292851098374402 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

Well-field depth-dependent sampling (W4) 292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

Well-field wells (wellhead sampling)

292919098360501 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292925098360201 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292916098360701 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292920098360601 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

292923098360301 <.005 <.006 <.013 <.084 <.009 <.006 <.014 <.04 <.022 <.002 <.021 <.006 <.012 <.053 

Temporal sampling

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 <0.005 -- <0.02 <0.08 <0.009 <0.006 <0.014 <0.04 <0.014 <0.002 <0.021 <0.008 <0.016 <0.053 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel]

USGS 

identification 

number

Diazinon

(μg/L) 

Diazoxon

(μg/L) 

Dichlorvos

(μg/L) 

Dicrotophos

(μg/L) 

Dieldrin

(μg/L) 

Dimethoate

(μg/L) 

Disulfoton 

sulfone

(μg/L) 

Disulfoton

(μg/L) 

Endosulfan 

sulfate

(μg/L) 

EPTC

(μg/L) 

Ethion 

monoxon

(μg/L) 

Ethion

(μg/L) 

Ethoprop

(μg/L) 

Fenamiphos 

sulfone

(μg/L) 

292923098360301 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292923098360301 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292943098354402 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292943098354402 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354403 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292943098354403 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292943098354403 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354404 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292943098354404 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

292943098354404 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

293252098380801 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 

293252098380801 <.005 -- <.02 <.08 <.009 <.006 <.014 <.04 <.014 <.002 <.021 <.008 <.016 <.053 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel] USGS identification number Fip- ronil sulfide (μg/L) Fip- ronil sulfone (μg/L) Fip- ronil (μg/L) Fonofos oxygen analog (μg/L) Fon- ofos (μg/L) Hexa- zinone (μg/L) Ipro- dione (μg/L) Isofen- phos (μg/L) Mala- oxon (μg/L) Mala- thion (μg/L) Meta- laxyl (μg/L) Meth- ida- thion (μg/L) Methyl para- oxon (μg/L) Methyl para- thion (μg/L) Met

la

chl

(μg/

Regional aquifer public-supply wells 293359098290301 <0.013 <0.024 <0.016 <0.003 <0.003 <0.013 <0.387 <0.003 <0.030 <0.027 <0.005 <0.006 <0.030 <0.015 <0.0

293359098290301 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

293358098231101 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

293358098231101 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

293120098285801 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

293120098285801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293145098224201 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

293119098211201 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292843098425101 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292459098382101 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292925098360201 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292925098360201 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292822098325401 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292822098325401 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292944098292301 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292944098292301 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292522098291901 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292643098241801 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292643098241801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292328098294601 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

294225098080301 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

294225098080301 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

291210099475601 <.013 <.024 <.016 <.003 <.003 <.013 <.387 <.003 <.030 <.027 <.005 <.006 <.030 <.015 E.0

293111098340901 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0293512098291701 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0292424098421501 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel]

USGS 

identification 

number

Fipronil 

sulfide

(μg/L)

Fipronil 

sulfone

(μg/L) 

Fipronil

(μg/L)

Fonofos 

oxygen 

analog

(μg/L)

Fonofos

(μg/L)

Hexazinone

(μg/L)

Iprodione

(μg/L)

Isofenphos

(μg/L)

Malaoxon

(μg/L)

Malathion

(μg/L)

Metalaxyl

(μg/L)

Methidathion

(μg/L)

Methyl 

paraoxon

(μg/L)

Methyl 

parathion

(μg/L)

Met

la

chl

(μg/

292053098365501 <0.013 <0.024 <0.016 -- <0.003 <0.013 <0.538 <0.003 <0.030 <0.027 <0.005 <0.006 <0.030 <0.015 <0.0

293807098155301 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0292604098563201 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0292116099095501 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0291232099470301 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0293128098473101 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0293451098313201 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0294604098060801 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

294019098114701 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292215098580201 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292119098524901 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

291943099163301 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

291840099382601 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

293518098332601 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

293023098355401 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

293042098305201 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292442098474501 E.008 E.009 E.008 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

292405098371201 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0292931098274601 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0293729098173101 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0291219099095601 <.013 <.024 <.016 -- <.003 <.013 <.538 <.003 <.030 <.027 <.005 <.006 <.030 <.015 <.0

Monitoring wells

292943098354401 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292943098354402 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292943098354403 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292943098354404 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel] USGS identification number Fip- ronil sulfide (μg/L) Fip- ronil sulfone (μg/L) Fip- ronil (μg/L) Fonofos oxygen analog (μg/L) Fon- ofos (μg/L) Hexa- zinone (μg/L) Ipro- dione (μg/L) Isofen- phos (μg/L) Mala- oxon (μg/L) Mala- thion (μg/L) Meta- laxyl (μg/L) Meth- ida- thion (μg/L) Methyl para- oxon (μg/L) Methyl para- thion (μg/L) Met

la

chl

(μg/

292851098374401 <0.013 <0.024 <0.02 -- <0.01 <0.008 <0.01 <0.006 <0.02 <0.016 <0.007 <0.004 <0.01 <0.008 <0.0

292851098374402 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

Well-field depth-dependent sampling (W4) 292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

Well-field wells (wellhead sampling)

292919098360501 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292925098360201 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292916098360701 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292920098360601 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

292923098360301 <.013 <.024 <.02 -- <.01 <.008 <.01 <.006 <.02 <.016 <.007 <.004 <.01 <.008 <.0

Temporal sampling

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminantwells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection lelevel]

USGS 

identification 

number

Fipronil 

sulfide

(μg/L)

Fipronil 

sulfone

(μg/L) 

Fipronil

(μg/L)

Fonofos 

oxygen 

analog

(μg/L)

Fonofos

(μg/L)

Hexazinone

(μg/L)

Iprodione

(μg/L)

Isofenphos

(μg/L)

Malaoxon

(μg/L)

Malathion

(μg/L)

Metalaxyl

(μg/L)

Methidathion

(μg/L)

Methyl 

paraoxon

(μg/L)

Methyl 

parathion

(μg/L)

Met

la

chl

(μg/

292923098360301 <0.013 <0.024 <0.018 -- <0.004 <0.008 <0.014 <0.006 <0.08 <0.016 <0.007 <0.006 <0.010 <0.008 <0.0

292923098360301 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0292923098360301 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0292943098354402 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0

292943098354402 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292943098354403 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0292943098354403 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0292943098354403 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292943098354404 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0292943098354404 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0292943098354404 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 293252098380801 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0293252098380801 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0293252098380801 <.013 <.024 <.018 -- <.004 <.008 <.014 <.006 <.08 <.016 <.007 <.006 <.010 <.008 <.0
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (TAthe San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection less th

USGS identification number Oxy- fluor- fen (μg/L) Pendi- meth- alin (μg/L) Phor- ate oxy- gen analog (μg/L) Phor- ate (μg/L) Phos- met oxy- gen analog (μg/L) Phos- met (μg/L) Pro- meton (μg/L) Pro- metryn (μg/L) Pro- pyz- amide (μg/L) Prop- anil (μg/L) Prop- argite (μg/L) Sim- azine (μg/L) Tebu- con- azole (μg/L) Tebu- thi- uron (μg/L) Teflu- thrin (μg/L) Terb- ufos oxy- gen analog sul- fone (μg/L) Terb- ufos (μg/L) Ter- buthyl- azine (μg/L) 

Regional aquifer public-supply wells 293359098290301 -- <0.022 <0.105 <0.011 <0.051 <0.008 0.013 <0.005 <0.004 -- -- 0.008 -- <0.016 -- <0.068 <0.017 <0.010 

293359098290301 <0.007 <.022 <.105 <.011 <.051 <.008 .011 <.005 <.004 <0.011 <0.023 .009 <0.014 <.016 <0.008 <.068 <.017 <.010 

293358098231101 -- <.022 <.105 <.011 <.051 <.008 E.009 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 293358098231101 <.007 <.022 <.105 <.011 <.051 <.008 E.008 <.005 <.004 <.011 <.023 E.007 <.014 <.016 <.008 <.068 <.017 <.010 

293120098285801 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

293120098285801 -- -- -- -- -- -- -- -- -- -- -- -- -- <.026 -- -- -- -- 

293145098224201 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

293119098211201 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292843098425101 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292459098382101 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292925098360201 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292925098360201 <.007 <.022 <.105 <.011 u u E.004 <.005 <.004 <.011 <.023 E.006 <.014 <.016 <.008 <.068 <.017 <.010 

292822098325401 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292822098325401 <.016 <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 <.011 <.023 0.008 <.014 <.016 <.010 <.068 <.017 <.010 

292944098292301 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292944098292301 <.007 <.022 <.105 <.011 u u E.004 <.005 <.004 <.011 <.023 E.007 <.014 <.016 <.008 <.068 <.017 <.010 

292522098291901 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292643098241801 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292643098241801 -- -- -- -- -- -- -- -- -- -- -- -- -- <.026 -- -- -- -- 

292328098294601 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

294225098080301 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- .008 -- <.016 -- <.068 <.017 <.010 

294225098080301 <.007 <.022 <.105 <.011 <.051 <.008 E.007 <.005 <.004 <.011 <.023 .008 <.014 <.016 <.008 <.068 <.017 <.010 

291210099475601 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 293111098340901 -- <.022 <.105 <.011 -- u E.008 <.005 <.004 -- -- .007 -- <.016 -- <.068 <.017 <.0102 

293512098291701 -- <.022 <.105 <.011 <.051 <.008 0.010 <.005 <.004 -- -- .010 -- <.016 -- <.068 <.017 <.010 

292424098421501 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (TAthe San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection less tha

USGS 

identification 

number

Oxyfluorfen

(μg/L)

Pendimethalin

(μg/L)

Phorate 

oxygen 

analog

(μg/L) 

Phorate

(μg/L)

Phosmet 

oxygen 

analog

(μg/L)

Phosmet

(μg/L)

Prometon

(μg/L)

Prometryn

(μg/L)

Propyzamide

(μg/L)

Propanil

(μg/L)

Propargite

(μg/L)

Simazine

(μg/L)

Tebuconazole

(μg/L)

Tebuthiuron

(μg/L)

Tefluthrin

(μg/L)

Terbufos 

oxygen 

analog 

sulfone

(μg/L)

Terbufos

(μg/L)

Terbuthylazine

(μg/L)

292053098365501 -- <0.022 <0.105 <0.011 u u <0.010 <0.005 <0.004 -- -- <0.005 -- <0.016 -- <0.068 <0.017 <0.010 293807098155301 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- .006 -- <.016 -- <.068 <.017 <.010 

292604098563201 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292116099095501 -- <.022 <.105 <.011 u <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

291232099470301 -- <.022 <.105 <.011 <.051 <.008 E.005 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

293128098473101 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

293451098313201 -- <.022 <.105 <.011 <.051 <.008 E.007 <.005 <.004 -- -- .010 -- <.016 -- <.068 <.017 <.010 

294604098060801 -- <.022 <.105 <.011 u <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

294019098114701 -- <.022 <.105 <.011 <.051 <.008 E.005 <.005 <.004 -- -- .006 -- <.016 -- <.068 <.017 <.010 

292215098580201 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292119098524901 -- <.022 <.105 <.011 u <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

291943099163301 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

291840099382601 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

293518098332601 -- <.022 <.105 <.011 <.051 <.008 E.005 <.005 <.004 -- -- E.005 -- <.016 -- <.068 <.017 <.010 

293023098355401 -- <.022 <.105 <.011 u <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

293042098305201 <.007 <.022 <.105 <.011 <.051 <.008 E.005 <.005 <.004 <0.011 <0.023 E.007 <.014 <.016 <0.008 <.068 <.017 <.010 

292442098474501 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292405098371201 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

292931098274601 -- <.022 <.105 <.011 u u <.010 <.005 <.004 -- -- .006 -- <.016 -- <.068 <.017 <.010 

293729098173101 -- <.022 <.105 <.011 u <.008 E.008 <.005 <.004 -- -- .007 -- <.016 -- <.068 <.017 <.010 

291219099095601 -- <.022 <.105 <.011 <.051 <.008 <.010 <.005 <.004 -- -- <.005 -- <.016 -- <.068 <.017 <.010 

Monitoring wells

292943098354401 <.006 <.012 <.027 <.04 u <.008 <.01 <.006 <.004 <.006 <.04 E.006 <.018 <.016 <.003 <.045 <.018 <.008 

292943098354402 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 E.005 <.018 <.016 <.003 <.045 <.018 <.008 

292943098354403 <.006 <.012 <.027 <.04 u <.008 <.01 <.006 <.004 <.006 <.04 <.006 <.018 <.016 <.003 <.045 <.018 <.008 

292943098354404 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 <.006 <.018 <.016 <.003 <.045 <.018 <.008 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (TAthe San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection less th

USGS identification number Oxy- fluor- fen (μg/L) Pendi- meth- alin (μg/L) Phor- ate oxy- gen analog (μg/L) Phor- ate (μg/L) Phos- met oxy- gen analog (μg/L) Phos- met (μg/L) Pro- meton (μg/L) Pro- metryn (μg/L) Pro- pyz- amide (μg/L) Prop- anil (μg/L) Prop- argite (μg/L) Sim- azine (μg/L) Tebu- con- azole (μg/L) Tebu- thi- uron (μg/L) Teflu- thrin (μg/L) Terb- ufos oxy- gen analog sul- fone (μg/L) Terb- ufos (μg/L) Ter- buthyl- azine (μg/L) 

292851098374401 <0.006 <0.012 <0.027 <0.04 <0.051 <0.008 <0.01 <0.006 <0.004 <0.006 <0.04 E0.006 <0.018 <0.016 <0.003 <0.045 <0.018 <0.008 

292851098374402 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 E.006 <.018 <.016 <.003 <.045 <.018 <.008 

Well-field depth-dependent sampling (W4) 292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 <.006 <.018 <.016 <.003 <.045 <.018 <.008 

292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 .008 <.018 <.016 <.003 <.045 <.018 <.008 

292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 u <.006 <.04 <.006 <.018 <.016 <.003 <.045 <.018 u 

292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 E.005 <.018 <.016 <.003 <.045 <.018 <.008 

292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 <.006 <.018 <.016 <.003 <.045 <.018 u 

292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 .009 <.018 <.016 <.003 <.045 <.018 E.007 

292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 E.006 <.018 <.016 <.003 <.045 <.018 <.008 

292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 .009 <.018 <.016 <.003 <.045 <.018 <.008 

292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 .008 <.018 <.016 <.003 <.045 <.018 <.008 

Well-field wells (wellhead sampling)

292919098360501 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 E.005 <.018 <.016 <.003 <.045 <.018 <.008 

292925098360201 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 <.006 <.018 <.016 <.003 <.045 <.018 <.008 

292916098360701 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 E.005 <.018 <.016 <.003 <.045 <.018 <.008 

292920098360601 <.006 <.012 <.027 <.04 <.051 <.008 <.01 <.006 <.004 <.006 <.04 E.005 <.018 <.016 <.003 <.045 <.018 <.008 

292923098360301 <.006 <.012 <.027 <.04 u <.008 <.01 <.006 <.004 <.006 <.04 <.006 <.018 <.016 <.003 <.045 <.018 <.008 

Temporal sampling

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292923098360301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
Table 15. Soluble pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (TAthe San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; MW, monitoring well; OVB, overburden; μg/L, micrograms per liter; --, not measured; E, estimated; u, unable to determine; <, nondetection less th

USGS 

identification 

number

Oxyfluorfen

(μg/L)

Pendimethalin

(μg/L)

Phorate 

oxygen 

analog

(μg/L) 

Phorate

(μg/L)

Phosmet 

oxygen 

analog

(μg/L)

Phosmet

(μg/L)

Prometon

(μg/L)

Prometryn

(μg/L)

Propyzamide

(μg/L)

Propanil

(μg/L)

Propargite

(μg/L)

Simazine

(μg/L)

Tebuconazole

(μg/L)

Tebuthiuron

(μg/L)

Tefluthrin

(μg/L)

Terbufos 

oxygen 

analog 

sulfone

(μg/L)

Terbufos

(μg/L)

Terbuthylazine

(μg/L)

292923098360301 <0.010 <0.012 <0.027 <0.02 <0.051 <0.034 E0.008 <0.006 <0.004 <0.010 <0.020 <0.006 -- <0.028 <0.010 <0.045 <0.018 <0.006 

292923098360301 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 <.004 <.010 <.020 <.006 -- <.028 <.010 <.045 <.018 <.006 

292923098360301 <.010 <.012 <.027 <.02 u <.034 <.012 <.006 <.004 <.010 <.020 E.006 -- <.028 <.010 <.040 <.018 <.006 292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354402 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 <.007 <.010 <.020 .008 -- <.028 <.010 <.045 <.018 <.006 

292943098354402 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 u <.010 <.020 <.006 -- <.028 <.010 <.045 <.018 <.011 

292943098354402 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 <.004 <.010 <.020 E.007 -- <.028 <.010 <.045 <.018 <.007 

292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354403 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354403 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 u <.010 <.020 <.008 -- <.028 <.010 <.045 <.018 <.006 

292943098354403 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 <.004 <.010 <.020 E.003 -- <.028 <.010 <.045 <.018 <.006 

292943098354403 <.010 <.012 <.027 <.02 u <.034 <.012 <.006 u <.010 <.020 E.003 -- <.028 <.010 <.045 <.018 <.006 

292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354404 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292943098354404 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 <.009 <.010 <.020 <.008 -- <.028 <.010 <.045 <.018 <.006 

292943098354404 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 <.004 <.010 <.020 <.007 -- <.028 <.010 <.045 <.018 <.006 

292943098354404 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 <.004 <.010 <.020 <.007 -- <.028 <.010 <.045 <.018 <.006 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293252098380801 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 u <.010 <.020 .008 -- <.028 <.010 <.045 <.018 <.006 

293252098380801 <.010 <.012 <.027 <.02 <.051 <.034 E.004 <.006 <.004 <.010 <.020 E.007 -- <.028 <.010 <.045 <.018 <.006 

293252098380801 <.010 <.012 <.027 <.02 <.051 <.034 <.012 <.006 <.004 <.010 <.020 E.007 -- <.028 <.010 <.045 <.018 <.006 

* Sample collected from top of open interval during depth-dependent sampling.
Table 16. Polar pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; E, estimated; u, unable to determine; <, nondetection less than laboratory method reporting lev

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

2,4-D 

methyl 

ester

(μg/L)

2,4-D

(μg/L)

2,4-DB

(μg/L)

2-Chloro6-ethylamino4-aminos-triazine 

(CEAT)

(μg/L)

2-Hydroxy4-isopropylamino6-ethylamino-striazine 

(OIET)

(μg/L)

3-Ketocarbofuran

(μg/L)

3-Hydroxy 

carbofuran

(μg/L)

Acifluorfen

(μg/L)

Ald

carsul

on

(μg/

Regional aquifer public-supply wells

293359098290301 AY–68–29–414 1st (highest) quartile 2004/12/06 <0.016 <0.038 <0.02 E0.006 <0.032 <0.02 <0.008 <0.028 <0.0

293359098290301 AY–68–29–414 1st quartile 2005/09/01 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0

293358098231101 AY–68–29–610 1st quartile 2004/12/15 <.016 <.038 <.02 E.005 E.007 <.02 <.008 <.028 <.0

293358098231101 AY–68–29–610 1st quartile 2005/08/29 <.016 <.038 <.020 E.009 <.032 <.02 <.008 <.028 <.0

293120098285801 AY–68–29–714 1st quartile 2004/12/14 <.016 <.038 <.02 E.005 E.004 <.02 <.008 <.028 <.0

293120098285801 AY–68–29–714 1st quartile 2005/08/30 <.016 <.038 <.020 <.08 <.032 <.02 <.008 <.028 <.0

293145098224201 AY–68–29–929 1st quartile 2004/12/15 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0

293119098211201 AY–68–30–718 1st quartile 2004/12/16 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0

292843098425101 AY–68–35–106 1st quartile 2004/12/13 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0

292459098382101 AY–68–35–913 1st quartile 2004/12/13 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0

292925098360201 AY–68–36–104 1st quartile 2004/12/13 <.016 <.038 <.02 E.005 E.003 <.02 <.008 <.028 <.0

292925098360201 AY–68–36–104 1st quartile 2005/08/31 <.016 <.038 <.020 <.08 <.032 <.02 <.008 <.028 <.0

292822098325401 AY–68–36–206 1st quartile 2004/12/13 <.016 <.038 <.02 E.003 <.032 <.02 <.008 <.028 <.0

292822098325401 AY–68–36–206 1st quartile 2005/08/31 -- -- -- -- -- -- -- -- -- 

292944098292301 AY–68–37–105 1st quartile 2004/12/14 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0

292944098292301 AY–68–37–105 1st quartile 2005/08/31 -- -- -- -- -- -- -- -- -- 

292522098291901 AY–68–37–426 1st quartile 2004/12/14 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0

292643098241801 AY–68–37–601 1st quartile 2004/12/15 <.016 E.009 <.02 <.08 <.032 <.02 <.008 <.028 <.0

292643098241801 AY–68–37–601 1st quartile 2005/08/30 <.016 <.038 <.020 <.08 <.032 <.02 <.008 <.028 <.0

292328098294601 AY–68–37–705 1st quartile 2004/12/14 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0

294225098080301 DX–68–23–601 1st quartile 2004/12/08 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0

294225098080301 DX–68–23–601 1st quartile 2005/09/01 -- -- -- -- -- -- -- -- -- 

291210099475601 YP–69–50–506 1st quartile 2004/11/30 <.016 <.038 <.02 <.08 <.032 <.02 <.008 <.028 <.0
Table 16. Polar pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; E, estimated; u, unable to determine; <, nondetection less than laboratory method reporting lev

USGS 

identification 

number

State well 

number

Group and 

description

Sample 

date

2,4-D 

methyl 

ester

(μg/L)

2,4-D

(μg/L)

2,4-DB

(μg/L)

2-Chloro6-ethylamino4-aminos-triazine 

(CEAT)

(μg/L)

2-Hydroxy4-isopropylamino6-ethylamino-striazine 

(OIET)

(μg/L)

3-Ketocarbofuran

(μg/L)

3-Hydroxy 

carbofuran

(μg/L)

Acifluorfen

(μg/L)

Ald

carsul

on

(μg/

293111098340901 AY–68–28–807 2d quartile 2005/05/26 -- -- -- -- -- -- -- -- -- 

293512098291701 AY–68–29–109 2d quartile 2005/04/20 -- -- -- -- -- -- -- -- -- 

292424098421501 AY–68–35–810 2d quartile 2005/04/21 -- -- -- -- -- -- -- -- -- 

292053098365501 AY–68–44–110 2d quartile 2005/05/26 -- -- -- -- -- -- -- -- -- 

293807098155301 DX–68–22–901 2d quartile 2005/05/18 -- -- -- -- -- -- -- -- -- 

292604098563201 TD–68–33–501 2d quartile 2005/05/16 -- -- -- -- -- -- -- -- -- 

292116099095501 TD–69–47–305 2d quartile 2005/04/27 -- -- -- -- -- -- -- -- -- 

291232099470301 YP–69–50–339 2d quartile 2005/05/11 -- -- -- -- -- -- -- -- -- 

293128098473101 AY–68–26–814 3d quartile 2005/04/18 -- -- -- -- -- -- -- -- -- 

293451098313201 AY–68–28–601 3d quartile 2005/05/17 -- -- -- -- -- -- -- -- -- 

294604098060801 DX–68–16–708 3d quartile 2005/04/25 -- -- -- -- -- -- -- -- -- 

294019098114701 DX–68–23–504 3d quartile 2005/05/18 -- -- -- -- -- -- -- -- -- 

292215098580201 TD–68–41–103 3d quartile 2005/05/09 -- -- -- -- -- -- -- -- -- 

292119098524901 TD–68–41–308 3d quartile 2005/04/27 -- -- -- -- -- -- -- -- -- 

291943099163301 TD–69–46–601 3d quartile 2005/05/09 -- -- -- -- -- -- -- -- -- 

291840099382601 YP–69–43–606 3d quartile 2005/05/11 -- -- -- -- -- -- -- -- -- 

293518098332601 AY–68–28–203 4th quartile 2005/04/19 -- -- -- -- -- -- -- -- -- 

293023098355401 AY–68–28–702 4th quartile 2005/04/26 -- -- -- -- -- -- -- -- -- 

293042098305201 AY–68–28–913 4th quartile 2005/06/30 -- -- -- -- -- -- -- -- -- 

292442098474501 AY–68–34–803 4th quartile 2005/04/20 -- -- -- -- -- -- -- -- -- 

292405098371201 AY–68–36–704 4th quartile 2005/05/23 -- -- -- -- -- -- -- -- -- 

292931098274601 AY–68–37–124 4th quartile 2005/05/25 -- -- -- -- -- -- -- -- -- 

293729098173101 DX–68–30–215 4th quartile 2005/04/25 -- -- -- -- -- -- -- -- -- 

291219099095601 TD–69–55–604 4th quartile 2005/05/16 -- -- -- -- -- -- -- -- -- 
Table 16. Polar pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (Tin the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; E, estimated; u, unable to determine; <, nondetection less than laboratory method reporting lev

USGS identification number Ben- omyl (μg/L) Bensulf- uron- methyl (μg/L) Bentazon (μg/L) Brom- oxynil (μg/L) Carb- aryl (μg/L) Carbo- furan (μg/L) Chlor- amben methyl ester (μg/L) Chlor- im- uron- ethyl (μg/L) Chloro- diamino- s-triazine (CAAT) (μg/L) Chloro- thal- onil (μg/L) Clopyr- alid (μg/L) Cyclo- ate (μg/L) Dacthal- mono- acid (μg/L) Di- camba (μg/L) 

Regional aquifer public-supply wells 293359098290301 <0.022 <0.018 <0.012 <0.028 <0.018 <0.016 <0.024 <0.032 <0.04 <0.035 <0.024 <0.014 <0.028 <0.036 

293359098290301 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

293358098231101 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

293358098231101 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

293120098285801 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

293120098285801 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

293145098224201 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

293119098211201 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292843098425101 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292459098382101 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292925098360201 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292925098360201 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292822098325401 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292822098325401 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292944098292301 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292944098292301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292522098291901 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292643098241801 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292643098241801 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

292328098294601 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

294225098080301 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 

294225098080301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

291210099475601 <.022 <.018 <.012 <.028 <.018 <.016 <.024 <.032 <.04 <.035 <.024 <.014 <.028 <.036 
Table 16. Polar pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (Tin the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; E, estimated; u, unable to determine; <, nondetection less than laboratory method reporting lev

USGS 

identification 

number

Benomyl

(μg/L)

Bensulfuronmethyl

(μg/L)

Bentazon

(μg/L)

Bromoxynil

(μg/L)

Carbaryl

(μg/L)

Carbofuran

(μg/L)

Chloramben 

methyl 

ester

(μg/L)

Chlorimuronethyl

(μg/L)

Chlorodiaminos-triazine 

(CAAT)

(μg/L)

Chlorothalonil

(μg/L)

Clopyralid

(μg/L)

Cycloate

(μg/L)

Dacthalmonoacid

(μg/L)

Dicamba

(μg/L)

293111098340901 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293512098291701 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292424098421501 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292053098365501 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293807098155301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292604098563201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292116099095501 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

291232099470301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293128098473101 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293451098313201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

294604098060801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

294019098114701 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292215098580201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292119098524901 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

291943099163301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

291840099382601 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293518098332601 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293023098355401 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293042098305201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292442098474501 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292405098371201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292931098274601 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293729098173101 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

291219099095601 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
Table 16. Polar pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; E, estimated; u, unable to determine; <, nondetection less than laboratory method reporting lev

USGS identification number Diuron (μg/L) Fenuron (μg/L) Flumet- sulam (μg/L) Fluo- meturon (μg/L) Imaz- aquin (μg/L) Imaz- etha- pyr (μg/L) Imida- cloprid (μg/L) Linuron (μg/L) MCPA (μg/L) MCPB (μg/L) Methio- carb (μg/L) Meth- omyl (μg/L) 

Regional aquifer public-supply wells 293359098290301 <0.015 <0.019 <0.04 <0.016 <0.036 <0.038 <0.02 <0.014 <0.03 <0.01 <0.02 <0.025 

293359098290301 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 <.03 <.01 <.01 <.02 

293358098231101 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 u <.01 <.01 <.02 

293358098231101 <.015 <.019 <.040 <.016 <.036 <.038 <.020 <.014 <.030 <.010 <.010 <.020 

293120098285801 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 u <.01 <.01 <.02 

293120098285801 <.015 <.019 <.040 <.016 <.036 <.038 <.020 <.014 <.030 <.010 <.010 <.020 

293145098224201 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 u <.01 <.01 <.02 

293119098211201 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 u <.01 <.01 <.02 

292843098425101 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 <.03 <.01 <.01 <.02 

292459098382101 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 <.03 <.01 <.01 <.02 

292925098360201 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 <.03 <.01 <.01 <.02 

292925098360201 <.015 <.019 <.040 <.016 <.036 <.038 <.020 <.014 <.030 <.010 <.010 <.020 

292822098325401 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 <.03 <.01 <.01 <.02 

292822098325401 -- -- -- -- -- -- -- -- -- -- -- -- 

292944098292301 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 u <.01 <.01 <.02 

292944098292301 -- -- -- -- -- -- -- -- -- -- -- -- 

292522098291901 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 u <.01 <.01 <.02 

292643098241801 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 u <.01 <.01 <.02 

292643098241801 <.015 <.019 <.040 <.016 <.036 <.038 <.020 <.014 <.030 <.010 <.010 <.020 

292328098294601 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 u <.01 <.01 <.02 

294225098080301 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 <.03 <.01 <.01 <.02 

294225098080301 -- -- -- -- -- -- -- -- -- -- -- -- 

291210099475601 <.015 <.019 <.04 <.016 <.036 <.038 <.02 <.014 <.03 <.01 <.01 <.02 
Table 16. Polar pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; E, estimated; u, unable to determine; <, nondetection less than laboratory method reporting lev

USGS 

identification 

number

Diuron

(μg/L)

Fenuron

(μg/L)

Flumetsulam

(μg/L)

Fluometuron

(μg/L)

Imazaquin

(μg/L)

Imazethapyr

(μg/L)

Imidacloprid

(μg/L)

Linuron

(μg/L)

MCPA

(μg/L)

MCPB

(μg/L)

Methiocarb

(μg/L)

Methomyl

(μg/L)

293111098340901 -- -- -- -- -- -- -- -- -- -- -- -- 

293512098291701 -- -- -- -- -- -- -- -- -- -- -- -- 

292424098421501 -- -- -- -- -- -- -- -- -- -- -- -- 

292053098365501 -- -- -- -- -- -- -- -- -- -- -- -- 

293807098155301 -- -- -- -- -- -- -- -- -- -- -- -- 

292604098563201 -- -- -- -- -- -- -- -- -- -- -- -- 

292116099095501 -- -- -- -- -- -- -- -- -- -- -- -- 

291232099470301 -- -- -- -- -- -- -- -- -- -- -- -- 

293128098473101 -- -- -- -- -- -- -- -- -- -- -- -- 

293451098313201 -- -- -- -- -- -- -- -- -- -- -- -- 

294604098060801 -- -- -- -- -- -- -- -- -- -- -- -- 

294019098114701 -- -- -- -- -- -- -- -- -- -- -- -- 

292215098580201 -- -- -- -- -- -- -- -- -- -- -- -- 

292119098524901 -- -- -- -- -- -- -- -- -- -- -- -- 

291943099163301 -- -- -- -- -- -- -- -- -- -- -- -- 

291840099382601 -- -- -- -- -- -- -- -- -- -- -- -- 

293518098332601 -- -- -- -- -- -- -- -- -- -- -- -- 

293023098355401 -- -- -- -- -- -- -- -- -- -- -- -- 

293042098305201 -- -- -- -- -- -- -- -- -- -- -- -- 

292442098474501 -- -- -- -- -- -- -- -- -- -- -- -- 

292405098371201 -- -- -- -- -- -- -- -- -- -- -- -- 

292931098274601 -- -- -- -- -- -- -- -- -- -- -- -- 

293729098173101 -- -- -- -- -- -- -- -- -- -- -- -- 

291219099095601 -- -- -- -- -- -- -- -- -- -- -- -- 
Table 16. Polar pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; E, estimated; u, unable to determine; <, nondetection less than laboratory method reporting lev

USGS identification number Neburon (μg/L) Nico- sulfuron (μg/L) Nor- flurazon (μg/L) Oryz- alin (μg/L) Oxa- myl (μg/L) Pic- loram (μg/L) Prop- ham (μg/L) Propi- con- azole (μg/L) Prop- oxur (μg/L) Siduron (μg/L) Sulfo- meturon (μg/L) Terb

(μg

Regional aquifer public-supply wells 293359098290301 <0.04 <0.02 <0.012 <0.03 <0.032 <0.03 <0.01 <0.008 <0.02 <0.038 <0.016 u 

293359098290301 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <0.

293358098231101 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.

293358098231101 <.012 <.04 <.020 <.012 <.030 <.032 <.030 <.010 <.008 <.020 <.038 <.

293120098285801 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.

293120098285801 <.012 <.04 <.020 <.012 <.030 <.032 <.030 <.010 <.008 <.020 <.038 <.0

293145098224201 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.0

293119098211201 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.0

292843098425101 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.0

292459098382101 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.

292925098360201 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.

292925098360201 <.012 <.04 <.020 <.012 <.030 <.032 <.030 <.010 <.008 <.020 <.038 <.

292822098325401 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.

292822098325401 -- -- -- -- -- -- -- -- -- -- -- -

292944098292301 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.0

292944098292301 -- -- -- -- -- -- -- -- -- -- -- -

292522098291901 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.0

292643098241801 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.

292643098241801 <.012 <.04 <.020 <.012 <.030 <.032 <.030 <.010 <.008 <.020 <.038 <.

292328098294601 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.

294225098080301 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.

294225098080301 -- -- -- -- -- -- -- -- -- -- -- -

291210099475601 <.012 <.04 <.02 <.012 <.03 <.032 <.03 <.01 <.008 <.02 <.038 <.
Table 16. Polar pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminants (wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; E, estimated; u, unable to determine; <, nondetection less than laboratory method reporting lev

USGS 

identification 

number

Neburon

(μg/L)

Nicosulfuron(μg/L)

Norflurazon

(μg/L)

Oryzalin

(μg/L)

Oxamyl

(μg/L)

Picloram

(μg/L)

Propham

(μg/L)

Propiconazole

(μg/L)

Propoxur

(μg/L)

Siduron

(μg/L)

Sulfometuron

(μg/L)

Terb

(μg

293111098340901 -- -- -- -- -- -- -- -- -- -- -- -

293512098291701 -- -- -- -- -- -- -- -- -- -- -- -

292424098421501 -- -- -- -- -- -- -- -- -- -- -- -

292053098365501 -- -- -- -- -- -- -- -- -- -- -- -

293807098155301 -- -- -- -- -- -- -- -- -- -- -- -

292604098563201 -- -- -- -- -- -- -- -- -- -- -- -

292116099095501 -- -- -- -- -- -- -- -- -- -- -- -

291232099470301 -- -- -- -- -- -- -- -- -- -- -- -

293128098473101 -- -- -- -- -- -- -- -- -- -- -- -

293451098313201 -- -- -- -- -- -- -- -- -- -- -- -

294604098060801 -- -- -- -- -- -- -- -- -- -- -- -

294019098114701 -- -- -- -- -- -- -- -- -- -- -- -

292215098580201 -- -- -- -- -- -- -- -- -- -- -- -

292119098524901 -- -- -- -- -- -- -- -- -- -- -- -

291943099163301 -- -- -- -- -- -- -- -- -- -- -- -

291840099382601 -- -- -- -- -- -- -- -- -- -- -- -

293518098332601 -- -- -- -- -- -- -- -- -- -- -- -

293023098355401 -- -- -- -- -- -- -- -- -- -- -- -

293042098305201 -- -- -- -- -- -- -- -- -- -- -- -

292442098474501 -- -- -- -- -- -- -- -- -- -- -- -

292405098371201 -- -- -- -- -- -- -- -- -- -- -- -

292931098274601 -- -- -- -- -- -- -- -- -- -- -- -

293729098173101 -- -- -- -- -- -- -- -- -- -- -- -

291219099095601 -- -- -- -- -- -- -- -- -- -- -- -
Table 17. Acetamide pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminawells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9. [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; --, not measured; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Sample 

date

Group and 

description

2-[(2-Ethyl6-methylphenyl) 

amino]-

2-oxoethanesulfonic 

acid (N-(ethmethphen) 

ox ESA)

(μg/L)

Alachlor 

2nd 

amide,

(μg/L)

2-ChloroN-(2-ethyl6-methylphenyl)-acetamid 

(acetochlor 2nd 

amide)

(μg/L)

Acetochlor 

ethanesulfonic 

acid 

(acetochlor 

ESA)

(μg/L)

Acetochlor 

oxanilic 

acid 

(acetochlor 

OA)

(μg/L)

Acetochlor 

sulfynilacetic 

acid 

(acetochlor 

SAA)

(μg/L)

Alachlor 

ethanesulfonic 

acid 

secondary 

amide 

(alachlor 

ESA SA)

(μg/L)

Alachlor 

ethanesulfonic 

acid 

(alachlor 

ESA)

(μg/L)

Regional aquifer public-supply wells

293359098290301 AY–68–29–414 2004/12/06 1st (highest) 

quartile

-- -- -- -- -- -- -- -- 

293359098290301 AY–68–29–414 2005/09/01 1st quartile -- -- -- -- -- -- -- -- 

293358098231101 AY–68–29–610 2004/12/15 1st quartile -- -- -- -- -- -- -- -- 

293358098231101 AY–68–29–610 2005/08/29 1st quartile -- -- -- -- -- -- -- -- 

293120098285801 AY–68–29–714 2004/12/14 1st quartile -- -- -- -- -- -- -- -- 

293120098285801 AY–68–29–714 2005/08/30 1st quartile -- -- -- -- -- -- -- -- 

293145098224201 AY–68–29–929 2004/12/15 1st quartile -- -- -- -- -- -- -- -- 

293119098211201 AY–68–30–718 2004/12/16 1st quartile -- -- -- -- -- -- -- -- 

292843098425101 AY–68–35–106 2004/12/13 1st quartile -- -- -- -- -- -- -- -- 

292459098382101 AY–68–35–913 2004/12/13 1st quartile -- -- -- -- -- -- -- -- 

292925098360201 AY–68–36–104 2004/12/13 1st quartile -- -- -- -- -- -- -- -- 

292925098360201 AY–68–36–104 2005/08/31 1st quartile -- -- -- -- -- -- -- -- 

292822098325401 AY–68–36–206 2004/12/13 1st quartile -- -- -- -- -- -- -- -- 

292822098325401 AY–68–36–206 2005/08/31 1st quartile -- -- -- -- -- -- -- -- 

292944098292301 AY–68–37–105 2004/12/14 1st quartile -- -- -- -- -- -- -- -- 

292944098292301 AY–68–37–105 2005/08/31 1st quartile -- -- -- -- -- -- -- -- 

292522098291901 AY–68–37–426 2004/12/14 1st quartile -- -- -- -- -- -- -- -- 

292643098241801 AY–68–37–601 2004/12/15 1st quartile -- -- -- -- -- -- -- -- 

292643098241801 AY–68–37–601 2005/08/30 1st quartile -- -- -- -- -- -- -- -- 

292328098294601 AY–68–37–705 2004/12/14 1st quartile -- -- -- -- -- -- -- -- 

294225098080301 DX–68–23–601 2004/12/08 1st quartile -- -- -- -- -- -- -- -- 

294225098080301 DX–68–23–601 2005/09/01 1st quartile -- -- -- -- -- -- -- -- 

291210099475601 YP–69–50–506 2004/11/30 1st quartile -- -- -- -- -- -- -- -- 
Table 17. Acetamide pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminawells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; --, not measured; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

State well 

number

Sample 

date

Group and 

description

2-[(2-Ethyl6-methylphenyl) 

amino]-

2-oxoethanesulfonic 

acid (N-(ethmethphen) 

ox ESA)

(μg/L)

Alachlor 

2nd 

amide,

(μg/L)

2-ChloroN-(2-ethyl6-methylphenyl)-acetamid 

(acetochlor 2nd 

amide)

(μg/L)

Acetochlor 

ethanesulfonic 

acid 

(acetochlor 

ESA)

(μg/L)

Acetochlor 

oxanilic 

acid 

(acetochlor 

OA)

(μg/L)

Acetochlor 

sulfynilacetic 

acid 

(acetochlor 

SAA)

(μg/L)

Alachlor 

ethanesulfonic 

acid 

secondary 

amide 

(alachlor 

ESA SA)

(μg/L)

Alachlor 

ethanesulfonic 

acid 

(alachlor 

ESA)

(μg/L)

293111098340901 AY–68–28–807 2005/05/26 2d quartile <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 0.02 

293512098291701 AY–68–29–109 2005/04/20 2d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292424098421501 AY–68–35–810 2005/04/21 2d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292053098365501 AY–68–44–110 2005/05/26 2d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293807098155301 DX–68–22–901 2005/05/18 2d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292604098563201 TD–68–33–501 2005/05/16 2d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292116099095501 TD–69–47–305 2005/04/27 2d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

291232099470301 YP–69–50–339 2005/05/11 2d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293128098473101 AY–68–26–814 2005/04/18 3d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293451098313201 AY–68–28–601 2005/05/17 3d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

294604098060801 DX–68–16–708 2005/04/25 3d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

294019098114701 DX–68–23–504 2005/05/18 3d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292215098580201 TD–68–41–103 2005/05/09 3d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292119098524901 TD–68–41–308 2005/04/27 3d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

291943099163301 TD–69–46–601 2005/05/09 3d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

291840099382601 YP–69–43–606 2005/05/11 3d quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293518098332601 AY–68–28–203 2005/04/19 4th quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293023098355401 AY–68–28–702 2005/04/26 4th quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293042098305201 AY–68–28–913 2005/06/30 4th quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292442098474501 AY–68–34–803 2005/04/20 4th quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292405098371201 AY–68–36–704 2005/05/23 4th quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292931098274601 AY–68–37–124 2005/05/25 4th quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 0.02 

293729098173101 DX–68–30–215 2005/04/25 4th quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

291219099095601 TD–69–55–604 2005/05/16 4th quartile <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 
Table 17. Acetamide pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminawells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued [By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; --, not measured; <, nondetection less than laboratory method reporting level] USGS identification number De- chloro- ala- chlor (μg/L) De- chloro- di- methen- amid (μg/L) De- chloro- metola- chlor (μg/L) Di- methen- amid ethane- sulfonic acid (μg/L) Di- methen- amid oxa- nilic acid (μg/L) Di- methen- amid (μg/L) Flufen- acet ethane- sulfonic acid (μg/L) Flufen- acet oxa- nilic acid (μg/L) Flufen- acet (μg/L) Hy- droxy- aceto- chlor (μg/L) Hy- droxy- ala- chlor (μg/L) Hy- droxy- di- methen- amid (μg/L) Hy- droxy- metola- chlor (μg/L) Metola- chlor ethane- sulf- onic acid (μg/L) 

Regional aquifer public-supply wells 293359098290301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293359098290301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293358098231101 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293358098231101 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293120098285801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293120098285801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

293145098224201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 293119098211201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292843098425101 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292459098382101 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292925098360201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292925098360201 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292822098325401 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292822098325401 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

292944098292301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292944098292301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292522098291901 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292643098241801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292643098241801 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 292328098294601 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 294225098080301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

294225098080301 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 

291210099475601 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
Table 17. Acetamide pesticide compounds for groundwater samples collected for the study of the transport of anthropogenic and natural contaminawells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.—Continued[By sample category. USGS, U.S. Geological Survey; μg/L, micrograms per liter; --, not measured; <, nondetection less than laboratory method reporting level]

USGS 

identification 

number

Dechloroalachlor

(μg/L)

Dechlorodimethenamid

(μg/L)

Dechlorometolachlor

(μg/L)

Dimethenamid 

ethanesulfonic 

acid

(μg/L)

Dimethenamid 

oxanilic 

acid

(μg/L)

Dimethenamid

(μg/L)

Flufenacet 

ethanesulfonic 

acid

(μg/L)

Flufenacet 

oxanilic 

acid

(μg/L)

Flufenacet

(μg/L)

Hydroxyacetochlor

(μg/L)

Hydroxyalachlor

(μg/L)

Hydroxydimethenamid

(μg/L)

Hydroxymetolachlor

(μg/L)

Metolachlor 

ethanesulfonic 

acid

(μg/L)

293111098340901 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 

293512098291701 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292424098421501 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292053098365501 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293807098155301 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292604098563201 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292116099095501 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

291232099470301 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293128098473101 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293451098313201 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

294604098060801 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

294019098114701 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292215098580201 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292119098524901 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

291943099163301 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

291840099382601 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293518098332601 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293023098355401 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293042098305201 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292442098474501 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292405098371201 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

292931098274601 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

293729098173101 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 

291219099095601 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 
Table 18. Summary of sulfur hexafluoride and chlorofluorocarbon age-tracer data and piston-flow model results for groundwater samples collected transport of anthropogenic and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Anto2004−9.—Continued [By sample category. SF6, sulfur hexafluoride; CFC, chlorofluorocarbon; °C, degrees Celsius; m, meter; pptv, parts per trillion by volume; C, contaminated]

USGS 

identification 

number

State well 

number

Local 

identifier 

and 

description

Sample 

date

Recharge 

temperature 

(°C) 

Recharge 

elevation 

(m)

SF6, atmospheric 

mixing 

ratio 

(pptv)*

SF6, 

apparent age, 

(years)**

CFC-11, atmospheric 

mixing 

ratio 

(pptv)*

CFC-12, atmospheric 

mixing 

ratio 

(pptv)*

CFC-113, 

atmospheric mixing 

ratio 

(pptv)*

CF

pis

fl

app

a

(yea

Monitoring wells

292943098354401 AY–68–36–135 Z–OVB 10/30/2007 28.3 258.5 56.13, 

57.32

C 4515.5, 

4607.1

1972.9, 

1930.3

4040.7, 

3852.0

292943098354402 AY–68–36–133 Z–SED 10/31/2007 27.1 258.5 20.92, 

39.23

C 4541.5, 

4402.1

1487.8, 

1449.3

295.4, 

285.8

292943098354403 AY–68–36–134 Z–IED 10/30/2007 25.1 258.5 17.89, 

18.78

C 1615.9, 

4949.0, 

4488.3

1519.1, 1628.3, 

1403.0

244.2, 281.7, 

281.3

292943098354404 AY–68–36–132 Z–DED 11/1/2007 26.8 258.5 12.77, 

8.58

C 3563.5, 

3021.7

1375.4, 

1332.1

238.9, 

242.1

292851098374401 AY–68–35–315 T–IED 5/6/2008 16.7 242.3 7.37, 7.11 C 5588.6, 

5511.1

24893.7, 

23877.0

493.4, 

493.4

292851098374402 AY–68–35–314 T–DED 5/7/2008 15.8 242.3 11.84, 

11.59

C 2385.8, 

2482.6, 

2524.1

1279.6, 1366.7, 

1385.5

456.9, 485.9, 

493.5

Well-field wells (wellhead sampling)

292919098360501 AY–68–36–103 W2 11/29/2007 22.0 276.5 15.76, 

15.70

C 4548.4, 

4676.9

2566.0, 

2758.6

345.0, 

361.5

292925098360201 AY–68–36–104 W3 11/28/2007 20.8 269.8 11.44, 

16.94

C 4952.2, 

4967.3, 

4479.9

2033.1, 2074.9, 

2210.3

563.8, 485.7, 

526.7

292916098360701 AY–68–36–105 W4 11/16/2007 24.1 270.4 27.33, 

18.54

C 4952.2, 

4967.3, 

4479.9

4497.9, 3999.8, 

3337.9

258.6, 449.6, 

449.6

292920098360601 AY–68–36–130 W5 11/29/2007 21.9 275.2 17.54, 

24.67

C 5229.2, 

5592.4

3141.1, 

3072.6

441.0, 

404.9

292920098360601 AY–68–36–130 W5 replicate 58.4, 

47.8

248.8, 

229.7

28.0, 

24.0

38

3

292920098360601 AY–68–36–130 W5 replicate 53.3, 

49.1, 

63.1

223.7, 204.6, 

406.1

47.3, 21.7, 

26.1

3839

3

292923098360301 AY–68–36–131 W6 11/28/2007 21.9 276.2 16.11, 

21.46

C 4160.1, 

3616.1, 

4925.8

13871.5, 16355.0, 

5380.3

455.5, 373.5, 

404.6

292923098360301 AY–68–36–131 W6 replicate 4166.9, 

1400.9, 

5039.2

4762.2, 5377.8, 

2641.0

383.4, 332.8, 

371.7
Table 18. Summary of sulfur hexafluoride and chlorofluorocarbon age-tracer data and piston-flow model results for groundwater samples collected transport of anthropogenic and natural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Anto2004−9.—Continued[By sample category. SF6, sulfur hexafluoride; CFC, chlorofluorocarbon; °C, degrees Celsius; m, meter; pptv, parts per trillion by volume; C, contaminated]

USGS 

identification 

number

State well 

number

Local 

identifier 

and 

description

Sample 

date

Recharge 

temperature 

(°C) 

Recharge 

elevation 

(m)

SF6, atmospheric 

mixing 

ratio 

(pptv)*

SF6, 

apparent age, 

(years)**

CFC-11, atmospheric 

mixing 

ratio 

(pptv)*

CFC-12, atmospheric 

mixing 

ratio 

(pptv)*

CFC-113, 

atmospheric mixing 

ratio 

(pptv)*

CF

pis

fl

app

a

(yea

Well-field depth-dependent sampling (W4)

292916098360701 AY–68–36–105 W4-shallow 

(380), 

ambient

11/16/2007 24.3 270.4 39.62, 

40.24

C 3778.9, 

3757.7

3596.5, 

6780.4

549.3, 

542.1

292916098360701 AY–68–36–105 W4-intermediate (430), 

ambient

11/14/2007 25.6 270.4 12.86, 

9.52

C 3047.8, 

2311.2, 

1879.9, 

3080.8

3508.5, 2477.3, 2076.0, 

2626.5

527.0, 517.6, 444.0, 

585.0

292916098360701 AY–68–36–105 W4-deep 

(540), 

ambient

11/15/2007 23.9 270.4 24.60, 

32.54

C 4272.3, 

2249.2, 

3794.6

3045.7, 2169.3, 

3277.3

464.7, 342.5, 

497.4

292916098360701 AY–68–36–105 W4-shallow 

(380), 

moderate

11/16/2007 24.7 270.4 13.60, 

12.38

C 4497.8, 

4170.3, 

4498.5

3687.3, 

3110.6, 

4210.5

420.3, 457.8, 

420.2

292916098360701 AY–68–36–105 W4-intermediate (430), 

moderate

11/14/2007 24.4 270.4 41.21, 

30.57

C 3049.0, 

2437.7, 

1257.2

2656.7, 2647.3, 

2445.3

569.8, 263.6, 

437.8

292916098360701 AY–68–36–105 W4-deep 

(540), 

moderate

11/15/2007 24.1 270.4 15.73, 

11.08

C 3205.6, 

3399.0, 

3236.0

2480.6, 2558.7, 

4272.7

595.1, 554.2, 

537.4

292916098360701 AY–68–36–105 W4-shallow 

(380), 

normal

11/16/2007 25.1 270.4 23.62, 

15.13

C 3394.5, 

3032.0, 

2284.9

3919.6, 3640.5, 

3251.3

566.4, 553.3, 

506.2

292916098360701 AY–68–36–105 W4-intermediate (430), 

normal

11/15/2007 23.6 270.4 14.81, 

46.17

C 3031.0, 

3176.5, 

2919.2

3043.9, 2766.6, 

2319.1

541.8, 551.4, 

577.6

292916098360701 AY–68–36–105 W4-deep 

(540),

 normal

11/15/2007 23.9 270.4 25.91, 

47.14

C 4341.1, 

4033.8

3512.0, 

3430.5

260.6, 

261.8

* Corrected for excess air and recharge temperature.** C, contaminated, age not resolvable (tracer concentration greater than would result from atmospheric sources, indicating contamination for the purposes of apparent-age d
Table 19. Summary of tritium/helium-3 age-tracer data and piston-flow model results for groundwater samples collected for the study of the transponatural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9[By sample category. °C, degrees Celsius; m, meter; 3H, tritium; 3H0, tritium naught; 3He, helium-3; 3Hetrit, helium derived from tritium decay; 4He, helium-4; 4Heterr, helium deriv

cm3 STP/g H2O, cubic centimeters per gram at standard temperature (20°C) and pressure (1 atmosphere); --, not determined]

USGS 

identification 

number

State well 

number

Local identifier 

and description

Sample 

date

Recharge 

temperature 

(°C) 

Recharge 

elevation 

(m)

3H 

(tritium 

units)

3H error 

(tritium 

units)

Delta 3He 

(Δ3He), 

measured 

(uncorrected)

(percent)

Δ3He 

error 

(1 sigma)

(percent)

Helium

(4He)

measu

(cm3 ST

H2O)

Monitoring wells

292943098354401 AY–68–36–135 Z-OVB 10/30/2007 28.3 258.5 1.30 0.048 -8.94 0.23 8.34937

292943098354402 AY–68–36–133 Z-SED 10/31/2007 27.1 258.5 2.17 .061 -.44 .18 1.06614292943098354403 AY–68–36–134 Z-IED 10/30/2007 25.1 258.5 2.08 .056 -.21 .23 8.78542

292943098354404 AY–68–36–132 Z-DED 11/1/2007 26.8 258.5 2.13 .065 -1.88 .30 8.18674

292851098374401 AY–68–35–315 T-IED 5/6/2008 16.7 242.3 1.77 .185 .66 .17 1.39E292851098374402 AY–68–35–314 T-DED 5/7/2008 15.8 242.3 1.72 .185 -1.85 .23 9.49E

Well-field wells (wellhead samples)

292919098360501 AY–68–36–103 W2 11/29/2007 22 276.5 2.08 .060 -.04 .23 8.01809

292925098360201 AY–68–36–104 W3 11/28/2007 20.8 269.8 2.05 .057 -3.02 .23 8.19502292916098360701 AY–68–36–105 W4 11/16/2007 24.1 270.4 1.88 .075 .09 .29 7.8893292920098360601 AY–68–36–130 W5 11/29/2007 21.9 275.2 2.18 .070 3.87 .25 4.37746292923098360301 AY–68–36–131 W6 11/28/2007 21.9 276.2 1.91 .058 -1.03 .19 8.25234

Well-field depth-dependent sampling (W4)

292916098360701 AY–68–36–105 W4-shallow (380), ambient 11/16/2007 24.3 270.4 <1 -- -.40 .30 7.99629292916098360701 AY–68–36–105 W4-intermediate (430), ambient 11/14/2007 25.6 270.4 2.20 .074 -1.30 .19 7.96141292916098360701 AY–68–36–105 W4-deep (540), ambient 11/15/2007 23.9 270.4 1.97 .046 -.17 .30 8.04951292916098360701 AY–68–36–105 W4-shallow (380), moderate 11/16/2007 24.7 270.4 1.82 .066 -.93 .19 7.81165292916098360701 AY–68–36–105 W4-intermediate (430), moderate 11/14/2007 24.4 270.4 1.98 .161 -.06 .19 8.28429292916098360701 AY–68–36–105 W4-deep (540), moderate 11/15/2007 24.1 270.4 1.63 .073 -.77 .19 8.34208292916098360701 AY–68–36–105 W4-shallow (380), normal 11/16/2007 25.1 270.4 2.23 .071 -.54 .29 8.14245292916098360701 AY–68–36–105 W4-intermediate (430), normal 11/15/2007 23.6 270.4 1.78 .053 67.81 1.49 5.61E

292916098360701 AY–68–36–105 W4-deep (540), normal 11/15/2007 23.9 270.4 1.90 .058 3.58 .21 4.58499
Table 19. Summary of tritium/helium-3 age-tracer data and piston-flow model results for groundwater samples collected for the study of the transponatural contaminants (TANC) to public supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9[By sample category. °C, degrees Celsius; m, meter; 3H, tritium; 3H0, tritium naught; 3He, helium-3; 3Hetrit, helium derived from tritium decay; 4He, helium-4; 4Heterr, helium deriv

cm3 STP/g H2O, cubic centimeters per gram at standard temperature (20°C) and pressure (1 atmosphere); --, not determined]

USGS 

identification 

number

Excess 

Neon 

(ΔNe)

(percent)

Tritiogenic 

3He 

(3Hetrit) 

(tritium 

units)

3Hetrit, 

error 

(tritium 

units)

Terrigenic 

helium-4 

(4Heterr) 

(cm3 STP/g 

H2O)

4Heterr

(Δ4Heterr), 

percent of 

measured 

helium

“Tritium 

naught” 

(3H0) 

(3H+3Hetrit)

(tritium 

units)

3H/3H0

3H/3He 

apparent 

age, years 

(pistonflow 

model)

3H/3He 

apparentage 

error

(years)

Commen

Monitoring wells

292943098354401 79.0 -2.38** 0.16 2.5942E-09 3.11 -- -- -- -- Age not resolvable because of low 3H

292943098354402 101 8.03 .24 1.4519E-08 13.6 10.2 0.21 27.5 0.6

292943098354403 84.5 1.90 .18 3.009E-09 3.43 3.97 .52 11.5 .8

292943098354404 77.4 0.16 .64 1.222E-09 1.49 2.28 .93 1.3 5.0292851098374401 126 16.3 1.22 2.822E-08 20.3 18.1 .10 41.3 2.1292851098374402 63.9 8.43 .61 1.656E-08 17.5 10.1 .17 31.6 1.9

Well-field wells (wellhead samples)

292919098360501 61.1 3.71 .16 6.1193E-09 7.63 5.79 .36 18.2 .6292925098360201 58.6 3.73 .16 8.6435E-09 10.5 5.79 .35 18.4 .6292916098360701 73.1 .12 .64 -5.1124E-10 -.65** 2.00 .94 3.4* 1.0* Age calculation uncorrected for Δ4H

Δ4Heterr value

292920098360601 -26.3 9.04 .10 1.4099E-08 32.2 11.2 .19 -- -- Age not resolvable because of negati

292923098360301 66.7 2.95 .18 5.5689E-09 6.75 4.86 .39 16.6 .8

Well-field depth-dependent sampling (W4)

292916098360701 70.6 1.23 .63 1.8748E-09 2.34 -- -- -- -- Age not resolvable because of low 3H

292916098360701 65.2 2.33 .18 4.6682E-09 5.86 4.53 .48 12.9 .8

292916098360701 68.1 2.24 .62 3.5324E-09 4.39 4.21 .47 13.5 2.6

292916098360701 65.0 1.58 .17 2.9632E-09 3.79 3.40 .53 11.1 1.0292916098360701 64.1 4.73 .19 8.0402E-09 9.71 6.72 .30 21.7 1.1292916098360701 68.9 3.36 .19 6.1269E-09 7.34 4.99 .33 19.9 .9292916098360701 80.5 -.61** .67 -1.3155E-09 -1.62** 2.23 1.00 .8* 1.0* Age calculation uncorrected for 4Het

value

292916098360701 -- 4.44 .03 7.4103E-09 13,212 6.23 .29 -- -- Age not resolvable because of negati

ΔNe value

292916098360701 -21.1 8.70 .12 1.3561E-08 29.6 10.6 .18 -- -- Age not resolvable because of negati

low ΔNe value

* Age calculation not corrected for 4Heterr because of negative 4Heterr value.** Negative values result from errors associated with measurements values near 0.
194 Hydrogeology, Chemical Characteristics, and Water Sources and Pathways

Table 20

Table 20. Results of forecasting analysis for the study of the transport of anthropogenic and natural contaminants (TANC) to public 

supply wells in the San Antonio segment of the Edwards aquifer near San Antonio, south-central Texas, 2004−9.

Forecast model scenario

Peak 

concentration 

(or lag time, in 

years) relative 

to time zero 

(start of input)

Dilution at peak 

concentration 

(concentration 

at peak/concentration 

of input at time zero (1)) 

Arrival of 

1 percent 

of total 

mass 

(years)

Flush of 99 

percent 

of total 

mass (years) 

relative to 

year of 

end of input

Uniform input across area contributing recharge to well, no degradation30 0.98 1 32

Uniform input across area contributing recharge to well, firstorder reaction kinetics degradation rate constant = 0.1/year30 .73 1 12

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Musgrove, Fahlquist, Stanton, Houston, and Lindgren—Hydrogeology, Chemical Characteristics, and Water Sources and Pathways—SIR 2011–5146

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I SBN 978- 1- 4113-3270- 6

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