Data Series 836

Version 1.1, January 2015

Prepared in cooperation with the San Antonio River Authority and 

the Guadalupe-Blanco River Authority

Concentrations of Selected Constituents in Surface-Water 

and Streambed-Sediment Samples Collected From Streams 

In and Near an Area of Oil and Natural-Gas Development, 

South-Central Texas, 2011–13

U.S. Department of the Interior

U.S. Geological Survey

TEXAS

Guadalupe River

Basin

San Antonio

River Basin

Study area

Eagle Ford 

Shale

GULF OF 

MEXICO
Front cover:

Background, A drill rig on a drill pad in Karnes County, Texas (photograph taken on January 26, 2012, by 

Stephen Opsahl). 

Back cover:

Top, U.S. Geological Survey hydrographer collecting a streambed-sediment sample from the San

Antonio River near Elmendorf, Texas (photograph taken on November 3, 2011, by Stephen Opsahl). 

Middle, U.S. Geological Survey hydrographer collecting a water sample from the San Antonio River

near Elmendorf, Texas (photograph taken on November 7, 2011, by Stephen Opsahl). 

Bottom, U.S. Geological Survey hydrographer using a 2-millimeter sieve to process a streambedsediment sample collected from Cibolo Creek near Falls City, Texas (photograph taken on November 7, 

2011, by Stephen Opsahl). 
Concentrations of Selected Constituents in 

Surface-Water and Streambed-Sediment 

Samples Collected From Streams In and 

Near an Area of Oil and Natural-Gas 

Development, South-Central Texas, 2011–13

By Stephen P. Opsahl and Cassi L. Crow

Prepared in cooperation with the San Antonio River Authority and 

the Guadalupe-Blanco River Authority

Data Series 836

Version 1.1, January 2015

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia 

First release: 2014, online and in print

Revised: January 2015 (ver. 1.1), online 

Suggested citation:

Opsahl, S.P., and Crow, C.L., 2015, Concentrations of selected constituents in surface-water and streambed-sediment 

samples collected from streams in and near an area of oil and natural-gas development, south-central Texas, 2011–13 

(ver. 1.1, January 2015): U.S. Geological Survey Data Series 836, 25 p., http://dx.doi.org/10.3133/ds836. 

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

ISSN 2327-0271 (print)

ISSN 2327-638X (online)

ISBN 978-1-4113-3780-0
iii

Contents

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

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

Purpose and Scope .............................................................................................................................2

Description of Study Area ..................................................................................................................2

Methods ..........................................................................................................................................................4

Collection of Streamflow Data ...........................................................................................................4

Collection and Processing of Surface-Water and Streambed-Sediment Samples ..................6

Sample Analyses ...............................................................................................................................10

Quality Assurance ..............................................................................................................................10

Quality Assurance for Surface-Water Samples ..................................................................12

Quality Assurance for Streambed-Sediment Samples .......................................................12

Concentrations of Selected Constituents ...............................................................................................13

Constituents in Surface-Water Samples .......................................................................................13

Constituents in Streambed-Sediment Samples ............................................................................20

Summary .......................................................................................................................................................21

References ...................................................................................................................................................23

Appendixes (available at http://pubs.usgs.gov/ds/836/)

1. Physicochemical properties and concentrations of inorganic constituents and 

methylene blue active substances in unfiltered surface-water samples 

collected in the San Antonio River Basin, Texas, 2011–13.

2. Concentrations of semivolatile organic compounds in unfiltered surface-water 

samples collected in the San Antonio River Basin, Texas, 2011–13.

3. Concentrations of volatile organic compounds in unfiltered surface-water 

samples collected in the San Antonio River Basin, Texas, 2011–13.

4. Concentrations of glycols in unfiltered surface-water samples collected in the 

San Antonio River Basin, Texas, 2011–13.

5. Concentrations of total organic carbon in unfiltered surface-water samples 

collected in the San Antonio River Basin, Texas, 2011–13.

6. Concentrations of inorganic constituents in streambed-sediment samples 

collected in the San Antonio River Basin, Texas, 2011–12.

7. Concentrations of n-alkanes in streambed-sediment samples collected in the 

San Antonio River Basin, Texas, 2011–13.

8. Concentrations of total organic carbon in streambed-sediment samples 

collected in the San Antonio River Basin, Texas, 2011–12.

9. Concentrations of polycyclic aromatic hydrocarbons in streambed-sediment 

samples collected in the San Antonio River Basin, Texas, 2011–12.

10. Quality-assurance data for physicochemical properties and concentrations of 

inorganic constituents and methylene blue active substances in unfiltered 

surface-water samples collected from the San Antonio River Basin, Texas, 

2011–12.

11. Quality-assurance data for semivolatile organic compounds in unfiltered 

surface-water samples collected from the San Antonio River Basin, Texas, 

2011–12.

12. Quality-assurance data for volatile organic compounds in unfiltered surfacewater samples collected from the San Antonio River Basin, Texas, 2011–12.
iv

13. Quality-assurance data for glycols in unfiltered surface-water samples 

collected from the San Antonio River Basin, Texas, 2011–12.

14. Quality-assurance data for total organic carbon in unfiltered surface-water 

samples collected from the San Antonio River Basin, Texas, 2011–12.

15. Quality-assurance data for inorganic constituents in streambed-sediment 

samples collected from the San Antonio River Basin, Texas, 2011–12.

16. Quality-assurance data for n-alkanes in streambed-sediment samples collected 

from the San Antonio River Basin, Texas, 2011–12.

17. Quality-assurance data for total organic carbon in streambed-sediment samples 

collected from the San Antonio River Basin, Texas, 2011–12.

18. Quality-assurance data for polycyclic aromatic hydrocarbons in streambedsediment samples collected from the San Antonio River Basin, Texas, 2011–12.

Figures

1. Map showing locations of surface-water sampling sites in the San Antonio 

River Basin, Texas, 2011–13 .......................................................................................................3

2. Photographs showing samplers used in the collection of surface-water 

samples, San Antonio River Basin, Texas, 2011–13 ...............................................................7

3. Photographs showing equipment and samplers used in the collection of 

streambed-sediment samples, San Antonio River Basin, Texas, 2011–13 .........................8

4. Graphs showing concentrations of selected anions in unfiltered surface-water 

samples collected from the San Antonio River Basin, Texas, 2011–13. A, Bromide. 

B, Chloride. C, Sulfate. D, Fluoride ..........................................................................................15

5. Graphs showing concentrations of selected cations in unfiltered surface-water 

samples collected from the San Antonio River Basin, Texas, 2011–13. A, Calcium. 

B, Magnesium. C, Potassium. D, Sodium ...............................................................................16

6. Graphs showing concentrations of selected inorganic constituents in unfiltered 

surface-water samples collected from the San Antonio River Basin, Texas, 

2011–13 ........................................................................................................................................18

7. Graph showing concentrations of methylene blue active substances in unfiltered 

surface-water samples collected from the San Antonio River Basin, Texas, 

2011–13 ........................................................................................................................................20

8. Graph showing concentrations of total saturated hydrocarbons in streambedsediment samples collected from the San Antonio River Basin, Texas, 2011–13 ...........20

9. Graph showing concentrations of total polycyclic aromatic hydrocarbons in 

streambed-sediment samples collected from the San Antonio River Basin, 

Texas, 2011–12 ............................................................................................................................21

Tables

1. Data-collection sites in the San Antonio River Basin, Texas, 2011–13 ...............................4

2. Summary of stream discharge and physicochemical properties in surfacewater samples collected at data-collection sites from selected streams in the 

San Antonio River Basin, Texas, 2011–13 ................................................................................5
v

3. Comparison of total polycyclic aromatic hydrocarbon and total saturated 

hydrocarbon concentrations and results of particle-size distribution analyses 

in less than 63 micrometer and less than 2 millimeter size fractions of selected 

streambed-sediment samples collected in June, 2012 .........................................................9

4. Analytical methods used in the chemical analyses of surface-water and 

streambed-sediment samples collected from selected streams in the San 

Antonio River Basin, Texas, 2011–13 ......................................................................................11

5. Summary of semivolatile and volatile organic compounds detected in 

unfiltered surface-water samples collected in the San Antonio River Basin, 

Texas, 2011–13 ............................................................................................................................14

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 0.00254 micrometer (μm)

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

liter (L) 0.2642 gallon (gal)

milliliter (mL) 0.03382 ounce, fluid (fl. oz.)

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

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

(NAVD 88).

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.

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 in either milligrams per liter (mg/L) 

or micrograms per liter (μg/L). Concentrations of chemical constituents in streambed sediment 

are given in milligrams per kilogram (mg/kg), micrograms per kilogram (μg/kg), or grams per 

kilogram (g/kg).

Concentrations of Selected Constituents in SurfaceWater and Streambed-Sediment Samples Collected From 

Streams In and Near an Area of Oil and Natural-Gas 

Development, South-Central Texas, 2011–13

By Stephen P. Opsahl and Cassi L. Crow

Abstract

During 2011–13, the U.S. Geological Survey, in 

cooperation with the San Antonio River Authority and the 

Guadalupe-Blanco River Authority, analyzed surface-water 

and streambed-sediment samples collected from 10 sites 

in the San Antonio River Basin to provide data for a broad 

range of constituents that might be associated with hydraulic 

fracturing and the produced waters that are a consequence 

of hydraulic fracturing. Among surface-water samples, all 

sulfide concentrations were less than the method detection 

limit of 0.79 milligrams per liter. Four glycols—diethylene 

glycol, ethylene glycol, propylene glycol, and triethylene 

glycol—were analyzed for in surface-water samples collected 

for this study, and none were detected. Of the 91 semivolatile 

organic compounds analyzed for this study, there were six 

detections, all but one of which were in storm-runoff samples. 

The base-flow sample collected at the San Antonio River at 

Goliad, Tex. (SAR Goliad), site contained bis(2-ethylhexyl) 

phthalate, a plasticizer in polyvinyl chloride and a constituent 

in hydraulic fracturing fluids. The storm-runoff samples 

collected at the San Antonio River near Elmendorf, Tex. 

(SAR Elmendorf), and Ecleto Creek at County Road 326 near 

Runge, Tex. (Ecleto 2), sites also contained bis(2-ethylhexyl) 

phthalate. The storm-runoff sample collected at the SAR 

Elmendorf site contained the plasticizer diethyl phthalate. 

Both storm-runoff samples collected at the Ecleto Creek near 

Runge, Tex. (Ecleto 1), and Ecleto 2 sites contained benzyl 

alcohol, a solvent commonly used in paints. Of the 67 volatile 

organic compounds analyzed in this study, there were a total 

of six detections, all of which were in base-flow samples. The 

surface-water sample collected at the SAR Elmendorf site 

contained bromodichloromethane, dibromochloromethane, 

and trichloromethane, all of which are disinfection byproducts 

associated with the chlorination of municipal water supplies 

and of treated municipal wastewater. The sample collected 

at the Cibolo Creek near Saint Hedwig, Tex. (Cibolo St. 

Hedwig), site contained toluene, a fuel additive, solvent, and 

industrial feedstock used to produce benzene and a constituent 

associated with produced waters. The Cibolo St. Hedwig 

site is upstream from current (2014) oil and natural-gas 

production areas. Dichloromethane, an industrial solvent with 

multiple uses, was detected in surface-water samples at both 

the San Antonio River at State Highway 72 near Runge, Tex. 

(SAR 72), and SAR Goliad sites. 

In streambed-sediment samples, concentrations of total 

saturated hydrocarbons (TSH) ranged from an estimated 

260 micrograms per kilogram (μg/kg) in the less than (<) 

2-millimeter (mm) size-fraction sample collected at the SAR 

Goliad site to 11,000 μg/kg in the <2-mm size-fraction sample 

collected at the Ecleto 1 site. TSH concentrations were greater 

in the <63-micrometer (μm) size-fraction samples than in 

the <2-mm size-fraction samples in streambed-sediment 

samples collected from 5 of the 9 sites. Total polycyclic 

aromatic hydrocarbons (PAHs) were calculated as the sum 

of the individual PAHs and alkylated PAHs. Total PAH 

concentrations ranged from less than the method detection 

limit in the <2-mm size-fraction samples collected from 

multiple sites to 1,600 μg/kg in the <2-mm size-fraction 

sample collected from the San Antonio River near McFaddin, 

Tex. (SAR McFaddin), site. Total PAH concentrations were 

greater in the <63-μm size-fraction samples than in the <2-mm 

size-fraction samples at 7 of the 9 sites.

During collection of streambed-sediment samples, 

additional samples from a subset of three sites (the SAR 

Elmendorf, SAR 72, and SAR McFaddin sites) were processed 

by using a 63-μm sieve on one aliquot and a 2-mm sieve on a 

second aliquot for PAH and n-alkane analyses. The purpose of 

analyzing PAHs and n-alkanes on a sample containing sand, 

silt, and clay versus a sample containing only silt and clay 

was to provide data that could be used to determine if these 

organic constituents had a greater affinity for silt- and claysized particles relative to sand-sized particles. The greater 

concentrations of PAHs in the <63-μm size-fraction samples at 

all three of these sites are consistent with a greater percentage 

of binding sites associated with fine-grained (<63 μm) 

sediment versus coarse-grained (<2 mm) sediment. The larger 

difference in total PAHs between the <2-mm and <63-μm 
2 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas

size-fraction samples at the SAR Elmendorf site might be 

related to the large percentage of sand in the <2-mm sizefraction sample which was absent in the <63-μm size-fraction 

sample. In contrast, the <2-mm size-fraction sample collected 

from the SAR McFaddin site contained very little sand and 

was similar in particle-size composition to the <63-μm sizefraction sample.

Introduction

Concerns about possible environmental effects associated 

with the use of hydraulic fracturing processes for extracting 

oil and natural gas have been growing as these processes 

have increasingly been implemented throughout the United 

States in the past 10 years (U.S. Environmental Protection 

Agency, 2013a). Hydraulic fracturing has become a highly 

contentious public policy issue because of concerns about 

the environmental and health effects of its use (Geologic 

Society of America, 2013). Some of the concerns expressed 

by the public, staff members of State and local water resource 

agencies, and State and Federal regulatory agencies include 

the possible release of organic and inorganic constituents 

found in hydraulic fracturing fluids and produced waters 

(Mahler and Van Metre, 2001; Kresse and others, 2012; U.S. 

Environmental Protection Agency, 2013a). “Produced water” 

is the term used by the oil and gas industry to describe the 

mix of surface water, groundwater (or both), and hydraulic 

fracturing fluids injected into a well with the water naturally 

occurring in formation that flows to the surface throughout 

the development and operation lifespan of an oil or gas 

well (Schramm, 2011). For this report, the water-based 

solution that flows back to the surface after the completion of 

hydraulic fracturing (referred to by the oil and gas industry as 

“flowback”) (Schramm, 2011) is included among produced 

waters. Constituents of concern include those frequently used 

in hydraulic fracturing fluids such as glycols and surfactants 

and those found in produced waters such as n-alkanes and 

polycyclic aromatic hydrocarbons (PAHs) (U.S. Geological 

Survey, 2011; FracFocus Chemical Disclosure Registry, 

2013). Individual constituents from these sources differ in 

their chemical, physical, and toxicological properties (U.S. 

Environmental Protection Agency, 2012a). 

In Texas, the production rate of natural gas and oil from 

the Eagle Ford Shale (fig. 1) has greatly increased in recent 

years, from about 2 million cubic feet per day in 2008 to 

3,204 million cubic feet per day in October 2013 (Railroad 

Commission of Texas, 2013a). Oil production also increased, 

from about 352 barrels per day in 2008 to 649,129 barrels 

per day in October 2013 (Railroad Commission of Texas, 

2013b). Part of the San Antonio River Basin intersects a 

large area of natural-gas and oil production from the Eagle 

Ford Shale (fig. 1). The network of well pads, roadways, and 

pipelines associated with expansion of oil and natural-gas 

production represents potential pathways for inorganic and 

organic constituents to enter surface-water systems (Kappel 

and others, 2013). Scant data are available pertaining to the 

concentrations of constituents that might be related to oil and 

natural-gas development in the water and sediment of streams 

in and near this area of oil and gas development. Therefore, 

there is a need to analyze different types of constituents in 

both water and streambed-sediment samples to effectively 

identify constituents that might be associated with oil and 

natural-gas production in Texas. The U.S. Geological Survey 

(USGS), in cooperation with the San Antonio River Authority 

and the Guadalupe-Blanco River Authority, analyzed surfacewater and streambed-sediment samples collected from 10 sites 

in the San Antonio River Basin to provide data for a broad 

range of constituents that might be associated with hydraulic 

fracturing and the produced waters that are a consequence of 

hydraulic fracturing.

Description of Study Area

The study area encompasses parts of Bexar, Comal, 

Guadalupe, Wilson, Karnes, DeWitt, Goliad, Victoria, and 

Refugio Counties in south-central Texas and consists of 

2,150 square miles (mi2

) in the San Antonio River Basin 

and 2 mi2 in the Guadalupe River Basin (fig. 1). Since 2008, 

rapid expansion of oil and natural-gas production with the 

use of hydraulic fracturing in the Eagle Ford Shale has 

taken place in south Texas (Railroad Commission of Texas, 

2013c). A large part of three counties—Wilson, DeWitt, 

and Karnes Counties—is the location where most of the 

hydraulic fracturing for oil and natural-gas development is 

taking place in the study area (Railroad Commission of Texas, 

2013c). Sampling site locations were chosen to provide data 

for a broad range of constituents that might be associated 

with hydraulic fracturing and the produced waters that are a 

consequence of hydraulic fracturing. The short names listed 

in table 1 for the sampling sites are used for referring to the 

sites throughout the text of this report. Map identifiers listed in 

table 1 are used in figure 1.

Purpose and Scope

This report summarizes the detections and concentrations 

of inorganic and organic constituents measured in surfacewater and streambed-sediment samples collected from selected 

streams in the San Antonio River Basin in south-central Texas 

during 2011–13. Surface-water samples were collected during 

base flow and storm runoff. Streambed-sediment samples 

were collected twice during base flow. Several large storm 

events occurred between the first and second collections 

of streambed-sediment samples. The results from three 

streambed-sediment samples collected for the comparison 

of different sediment particle-size fractions provide data that 

could be used to assess whether PAHs and n-alkanes had a 

greater affinity for silt- and clay-sized particles relative to 

sand-sized particles.
COASTAL LOWLANDS

AQUIFER SYSTEM

TEXAS COASTAL UPLANDS

AQUIFER SYSTEM

EDWARDS-TRINITY

AQUIFER SYSTEM EXPLANATION Eagle Ford Shale—Extent of the Eagle F

 oil and gas development has been do Energy Information Administration, 20Study areaAquifer system boundary (modified from  Kasmarek and Robinson, 2004) U.S. Geological Survey streamflow-gag

HF01 map identifier—See table 1

97°00

98°00'

29°30'

29°00'

28°30'

BEE COUNTY

LIVE OAK

COUNTY

BEXAR COUNTY

ATASCOSA COUNTY

VICTORIA COUN

DEWITT

COUNTY

WILSON COUNTY

WILSON COUNTY

KARNES COUNTY

GONZALES

COUNTY

GUADALUPE COUNTY

KARNES COUNTY

REFUGIO

COUNTY

GOLIAD

COUNTY

GOLIAD

COUNTY

COMAL

COUNTY

87

183

281

87

281

77

90

59

77

281

181

77

181

37

35

35

10

35

410

35

37

10

410

Poth

Falls 

City

Floresville

Stockdale

Nixon

Cibolo

San

Antonio

Goliad

Mc

Kenedy

Runge

Karnes

City

Yorktown

St. Hedwig

Elmendorf

Selma

Sutherland

Springs

HF01

HF03

HF02

HF04

HF05

HF06

HF07

HF08

HF09 

TEXAS

Guadalupe River

Basin

San Antonio

River Basin

Study area

Eagle Ford 

Shale

GULF OF 

MEXICO

Base modified from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator, zone 14North American Datum of 1983

Modified from Lizarraga and Ockerman 

0 5 10 15 20 MILES

0 10 15 20 KILOMETERS 5

Medin

 River

a

Manahuilla Creek

Ecleto Creek

San Antonio River

San Antonio River

Martinez

Calaveras Lake

San Antonio

CiboloCreek

 River

Cibolo Creek

San Antonio River

Cabeza Creek

Creek

H

HF01HF02HF03HF04HF05HF06HF07HF08HF09HF10

SAR ElmendorfSAR Falls CityCibolo St. HedwCibolo Falls CityEcleto 1Ecleto 2SAR 72SAR GoliadSAR McFaddinGR Tivoli

Map 

identifier

Short name 

(table 1)

Figure 1. Locations of surface-water sampling sites in the San Antonio River Basin, Texas, 2011–13.
4 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas

The northern part of the study area overlies the EdwardsTrinity aquifer system (fig. 1). The remainder of the study area 

overlies the Texas Coastal Uplands and Coastal Lowlands 

aquifer systems (Ryder, 1996). The Cretaceous-age rocks 

of the Edwards-Trinity aquifer system primarily consist of 

limestone and sandstone (Ashworth and Hopkins, 1995). 

The Texas Coastal Uplands aquifer system is composed 

of formations of Paleocene and Oligocene age, with the 

sediments (in order of dominance) consisting mostly of sand, 

silt, and clay, distributed as relatively uniform sequences of 

predominantly fine- or coarse-grained material (Ryder, 1996). 

The Coastal Lowlands aquifer system is composed of younger 

formations from Oligocene through Holocene age that dip 

and thicken towards the Gulf of Mexico, with sediments that 

exist in complex, overlapping mixtures of sand, silt, and clay 

as a result of numerous oscillations of ancient shorelines 

(Lizárraga and Ockerman, 2010).

In the study area (fig. 1), the San Antonio River extends 

about 190 miles (mi) from near Elmendorf, Tex., to the 

confluence of the San Antonio and Guadalupe Rivers. The 

length of Cibolo Creek from Selma, Tex., to the confluence of 

Cibolo Creek and the San Antonio River is about 75 mi. The 

length of Ecleto Creek is about 55 mi from northern Wilson 

County to the confluence of Ecleto Creek and the San Antonio 

River in Karnes County. The San Antonio River ends at the 

confluence of the San Antonio and Guadalupe Rivers. From 

its confluence with the San Antonio River, the Guadalupe 

River continues southeast about 9 mi before emptying into 

the Guadalupe Bay in the Gulf of Mexico. The study area 

is composed of gently sloping, rolling terrain; the coastal 

uplands are somewhat more dissected and rolling compared 

to the coastal lowlands (Ryder, 1996). The land cover 

consists mostly of brush and grassland (Multi-Resolution 

Land Characteristics Consortium, 2013), and average annual 

precipitation ranges from about 30 inches in the northern 

sections of the San Antonio River Basin to about 40 inches 

in the southern sections of the basin near the coast (National 

Oceanic and Atmospheric Administration, 2013).

Methods

Collection of Streamflow Data

Continuous streamflow was measured at USGS 

streamflow-gaging stations by using methods described by 

Rantz and others (1982a, b) and Turnipseed and Sauer (2010). 

A stage-discharge relation (rating curve) was developed on 

the basis of the discrete discharge and stage measurements 

made at each site (Kennedy, 1984; Turnipseed and Sauer, 

2010). Adjustments were made to site stage-discharge ratings 

when discrete discharge measurements indicated changing 

channel conditions. From the stage-discharge ratings, stage 

data were used to compute continuous discharge (Kennedy, 

1983). Discrete discharge measurements were made preceding 

surface-water sample collection in accordance with USGS 

methods (Rantz and others, 1982a, b; Turnipseed and 

Sauer, 2010). Streams were waded, and stream velocity 

measurements were made by using rod-mounted acoustic 

velocity meters (Xylem Analytics, 2012). Discharge 

measurements at the time of sample collection (table 2) were 

obtained from stage-discharge relations. Two sampling sites, 

San Antonio River at Highway 181 at Falls City, Tex. (SAR 

Falls City), and Ecleto Creek at County Road 326 near Runge, 

Tex. (Ecleto 2), were not equipped with continuous streamflow 

gages, and no discrete discharge measurements were made at 

the time of sample collection at these two sites.

Table 1. Data-collection sites in the San Antonio River Basin, Texas, 2011–13.

[USGS, U.S. Geological Survey; NAD 83, horizontal coordinate information referenced to North American Datum of 1983; dd, degrees; mm, minutes; 

ss, seconds; SAR, San Antonio River; St., Saint; GR, Guadalupe River]

Map 

identifier 

(as shown 

in fig. 1)

Short name

USGS 

station 

number

USGS station name

Latitude

(NAD 83)

(dd mm ss)

Longitude

(NAD 83)

(dd mm ss)

HF01 SAR Elmendorf 08181800 San Antonio River near Elmendorf, Tex. 29° 13ʹ 20ʺ 98° 21ʹ 21ʺ

HF02 SAR Falls City 08183550 San Antonio River at Highway 181 near Falls City, Tex. 28° 58ʹ 38ʺ 98° 00ʹ 37ʺ

HF03 Cibolo St. Hedwig 08185065 Cibolo Creek near Saint Hedwig, Tex. 29° 30ʹ 05ʺ 98° 11ʹ 10ʺ

HF04 Cibolo Falls City 08186000 Cibolo Creek near Falls City, Tex. 29° 00ʹ 51ʺ 97° 55ʹ 49ʺ

HF05 Ecleto 1 08186500 Ecleto Creek near Runge, Tex. 28° 55ʹ 13ʺ 97° 46ʹ 20ʺ

HF06 Ecleto 2 08186550 Ecleto Creek at County Road 326 near Runge, Tex. 28° 53ʹ 28ʺ 97° 45ʹ 03ʺ

HF07 SAR 72 08188060 San Antonio River at State Highway 72 near Runge, Tex. 28° 50ʹ 55ʺ 97° 44ʹ 13ʺ

HF08 SAR Goliad 08188500 San Antonio River at Goliad, Tex. 28° 38ʹ 57ʺ 97° 23ʹ 05ʺ

HF09 SAR McFaddin 08188570 San Antonio River near McFaddin, Tex. 28° 31ʹ 52ʺ 97° 02ʹ 33ʺ

HF10 GR Tivoli 08188800 Guadalupe River near Tivoli, Tex. 28° 30ʹ 20ʺ 96° 53ʹ 04ʺ
Table 2. Summary of stream discharge and physicochemical properties in surface-water samples collected at data-collection sites from selected stRiver Basin, Texas, 2011–13.[USGS, U.S. Geological Survey; mm/dd/yyyy, month/day/year; ft3/s, cubic feet per second; mg/L, milligrams per liter; μS/cm at 25 °C, microsiemens per centimeter at 25 degre

FNU, formazin nephelometric units; SAR, San Antonio River; B, base flow; S, storm runoff; St., Saint; GR, Guadalupe River; E, estimated; --, not recorded]

Map 

identifier 

(as 

shown in 

fig. 1)

Short name

USGS 

station 

number

USGS station name Date (mm/dd/yyyy)

Streamflow 

condition

Discharge 

(ft3/s)

Dissolved 

oxygen 

(mg/L)

pH

Specific 

conductance 

(μS/cm 

at 25 °C)

Temperature 

(°C)

HF01 SAR Elmendorf 08181800 San Antonio River near Elmendorf, Tex. 11/03/2011 B 160 7.4 8.1 1,090 22.6 

HF01 SAR Elmendorf 08181800 San Antonio River near Elmendorf, Tex. 08/19/2012 S 11,600 4.5 8.0 250 24.9 

HF02 SAR Falls City 08183550 San Antonio River at Highway 

181 at Falls City, Tex.

11/07/2011 B -- 10.1 8.2 1,130 19.4 

HF02 SAR Falls City 08183550 San Antonio River at Highway 

181 at Falls City, Tex.

04/28/2013 S -- -- -- -- -- 

HF03 Cibolo St. Hedwig 08185065 Cibolo Creek near Saint 

Hedwig, Tex.

11/02/2011 B 6.2 6.2 8.0 929 18.0 

HF03 Cibolo St. Hedwig 08185065 Cibolo Creek near Saint 

Hedwig, Tex.

09/17/2012 S 195 5.0 7.5 846 23.4 

HF04 Cibolo Falls City 08186000 Cibolo Creek near Falls City, Tex. 11/07/2011 B 25 10.5 8.2 1,120 19.7 

HF04 Cibolo Falls City 08186000 Cibolo Creek near Falls City, Tex. 09/29/2012 S 47 8.4 8.1 719 26.9 

HF05 Ecleto 1 08186500 Ecleto Creek near Runge, Tex. 01/09/2013 S 1.1 6.8 7.5 1,180 14.2 

HF06 Ecleto 2 08186550 Ecleto Creek at County Road 326 

near Runge, Tex.

03/20/2012 S -- 6.8 7.8 738 19.3 

HF07 SAR 72 08188060 San Antonio River at State Highway 72 near Runge, Tex. 11/09/2011 B 110 12.4 8.7 1,250 19.2 

HF07 SAR 72 08188060 San Antonio River at State Highway 72 near Runge, Tex. 09/30/2012 S 409 7.2 8.0 895 26.1 

HF08 SAR Goliad 08188500 San Antonio River at Goliad, Tex. 11/09/2011 B 155 8.7 8.3 1,260 19.0 

HF08 SAR Goliad 08188500 San Antonio River at Goliad, Tex. 01/09/2013 S 327 9.8 8.0 1,020 13.8 

HF09 SAR McFaddin 08188570 San Antonio River near McFaddin, Tex. 11/08/2011 B 218 9.1 8.2 1,240 21.2 

HF09 SAR McFaddin 08188570 San Antonio River near McFaddin, Tex. 01/10/2013 S 406 9.8 8.2 1,130 13.8 

HF10 GR Tivoli 08188800 Guadalupe River near Tivoli, Tex. 11/08/2011 B 485 7.5 -- 857 19.9 

HF10 GR Tivoli 08188800 Guadalupe River near Tivoli, Tex. 01/10/2013 S 1,020 9.4 8.1 783 13.3 
6 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas

Collection and Processing of Surface-Water and 

Streambed-Sediment Samples

During 2011–13, 18 surface-water and 22 streambedsediment samples were collected at 10 sites including the San 

Antonio River near Elmendorf, Tex. (SAR Elmendorf); SAR 

Falls City; Cibolo Creek near St. Hedwig, Tex. (Cibolo St. 

Hedwig); Cibolo Creek near Falls City, Tex. (Cibolo Falls 

City); Ecleto Creek near Runge, Tex. (Ecleto 1); Ecleto 2; 

San Antonio River at State Highway 72 near Runge, Tex. 

(SAR 72); San Antonio River at Goliad, Tex. (SAR Goliad); 

San Antonio River near McFaddin, Tex. (SAR McFaddin); 

and Guadalupe River near Tivoli, Tex. (GR Tivoli), sites 

(map identifiers HF01–HF10, respectively; fig. 1, table 1) for 

analysis of concentrations of selected inorganic and organic 

constituents (apps. 1–9). Values of physicochemical properties 

of surface water (dissolved oxygen concentration, pH, specific 

conductance, water temperature, and turbidity) were measured 

and recorded from the centroid of each stream site by using 

a YSI 6920 multiparameter water-quality monitor prior to 

collection of samples (table 2). Surface-water samples were 

collected over a variety of hydrologic conditions ranging from 

a minimum streamflow of 1.1 cubic feet per second (ft3

/s) at 

the Ecleto 1 site on January 9, 2013, to a maximum streamflow 

of 11,600 ft3/s at the SAR Elmendorf site on August 19, 2012 

(table 2). Ecleto Creek was an ephemeral stream. Although the 

sample collected at a discharge of 1.1 ft3/s does not represent 

a large discharge for this creek, the sample was categorized 

as a storm-runoff sample because it was collected while 

streamflow was receding after a small rain event sufficient to 

create flow at this site. One of the storm-runoff samples could 

not be safely collected from the Ecleto 1 site at the time of 

sampling and was instead collected from the Ecleto 2 site, 

which is approximately 3.25 mi downstream from the Ecleto 1 

site. Although there were two sampling sites located on Ecleto 

Creek, these sites were in proximity and were considered to 

represent the same area in figures used within this report.

Surface-water samples were collected and processed 

by following the methods and guidelines described in U.S. 

Geological Survey (variously dated) and Shelton (1997). At 

each sampling site, surface-water samples were collected at 

a minimum of 10 locations spaced at equal width increments 

across the stream by using samplers designed to allow water 

to enter the sampler with no change in speed or direction 

(isokinetic). When stream depths were shallow enough to 

be waded, surface-water samples were collected by using a 

US DH-81 1-liter bottle sampler (Davis, 2005) attached to 

a wading rod (fig. 2A). When the stream was too deep to be 

waded, surface-water samples were collected by using a US 

DH-2 1-liter collapsible bag sampler (Davis, 2005) attached 

to a reel and crane system (fig. 2B). Surface-water samples 

collected by using the US DH-81 sampler at streamflow 

velocities less than (<) 1.5 feet per second (ft/s) and samples 

collected by using the US DH-2 sampler at velocities <2.0 

ft/s were labeled as grab samples because the samplers are 

unable to collect isokinetic samples at those velocities. 

Surface-water samples were composited into a 14-liter Teflon 

(polytetrafluoroethylene) churn, and aliquots of representative 

whole-water (unfiltered) samples were dispensed from the 

churn into the appropriate sample bottles. 

Two sets of streambed-sediment samples were collected 

during base flow. Several large storm events occurred between 

the first and second sets of streambed-sediment samples. 

Streambed-sediment samples were collected either manually 

with a scoop while wading (fig. 3A) or by using a ponar 

sampler (fig. 3B) from a watercraft or bridge by following 

standard USGS methods as described by Shelton and Capel 

(1994) and Edwards and Glysson (1999). At each site, a 

depositional area was identified, and a minimum of three 

separate samples were collected and composited into a single 

volume. Each sample was collected from an area at least 

20 centimeters (cm) by 20 cm, and only the top 2–3 cm of 

streambed sediment was collected. For the first set of samples, 

streambed sediment was composited and put through either 

a stainless steel 2-millimeter (mm) sieve in preparation for 

the analyses of organic constituents or a 63-micrometer (μm) 

sieve in preparation for the analyses of inorganic constituents. 

Streambed-sediment samples that pass through a 2-mm 

sieve contain sand-, silt-, and clay-sized particles, whereas 

streambed-sediment samples that pass through a 63-μm sieve 

contain only the smaller silt- and clay-sized particles (Guy, 

1969). For the second set of samples, streambed sediment was 

composited and put through only a 63-μm sieve in preparation 

for the analyses of both organic and inorganic constituents. An 

additional stream-bed sediment sample was collected from the 

Ecleto 1 site because the n-alkane analysis was not completed 

on the first stream-bed sediment sample following a sample 

processing error and a recollection was required (app. 7). 

During collection of the second sample set, additional samples 

from a subset of three sites (the SAR Elmendorf, SAR 72, and 

SAR McFaddin sites; fig. 1) were processed by using a 63-μm 

sieve on one aliquot and a 2-mm sieve on a second aliquot for 

PAH and n-alkane analyses. The purpose of analyzing PAHs 

and n-alkanes on a sample containing sand, silt, and clay 

versus a sample containing only silt and clay was to provide 

data that could be used determine if these organic constituents 

had a greater affinity for silt- and clay-sized particles relative 

to sand-sized particles. An unsieved portion of each of the 

three samples collected for the comparison of different size 

fractions also was analyzed for particle-size distribution 

(table 3).
Methods 7

A. US DH-81

B. US DH-2

Figure 2. Samplers used in the collection of surface-water samples, San Antonio River Basin, Texas, 2011–13. A, US DH-81 1-liter 

bottle sampler. B, US DH-2 1-liter collapsible bag sampler.
8 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas

B. Ponar

A. Scoop

Figure 3. Equipment and samplers used in the collection of streambed-sediment samples, San Antonio River Basin, Texas, 2011–13. A, 

Manual collection with a scoop while wading. B, Collection with a ponar sampler from a watercraft.
Table 3. Comparison of total polycyclic aromatic hydrocarbon and total saturated hydrocarbon concentrations and results of particle-size distributiomicrometer and less than 2 millimeter size fractions of selected streambed-sediment samples collected in June, 2012.[USGS, U.S. Geological Survey; mm/dd/yyyy, month/day/year; PAH, polycyclic aromatic hydrocarbon; μg/kg, micrograms per kilogram; TSH, total saturated hydrocarbon; <, lμm, micrometer; SAR, San Antonio River; E, estimated; --, no data]

Map 

identifier 

(as shown 

in fig. 1)

Short name

USGS 

station 

number

USGS station name

Sample 

date

(mm/dd/yyyy)

Total PAHs 

(μg/kg)

<2 mm <63 μm 

HF01 SAR Elmendorf 08181800 San Antonio River near Elmendorf, Tex. 06/25/2012 120 460 

HF07 SAR 72 08188060 San Antonio River at State Highway 72 near Runge, Tex. 06/20/2012 48 160 

HF09 SAR McFaddin 08188570 San Antonio River near McFaddin, Tex. 06/26/2012 250 340 

Map 

identifier 

(as shown 

in fig. 1)

Short name

Suspended-sediment fall diameter 

(percentage)

Smaller 

than 

0.002 mm

Smaller 

than 

0.004 mm

Smaller 

than

 0.008 mm

Smaller 

than 

0.016 mm

Smaller 

than 

0.031 mm

Smaller 

than 

0.0625 mm

Smaller 

than 

0.125 mm

Smaller 

than 

0.25 mm

Smaller 

than 

0.5 mm

Small

than 

1 mm

HF01 SAR Elmendorf 7 8 8 9 11 16 23 37 69 92 

HF07 SAR 72 10 12 12 13 17 23 37 59 93 100 

HF09 SAR McFaddin 43 57 65 75 81 86 91 99 99 100 

Well pad site in Karnes County, Texas. Drilling rig in Karnes County, Texas. 
10 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas

Sample Analyses 

Surface-water samples were analyzed for concentrations 

of total dissolved solids (TDS) (app. 1), total suspended 

solids (TSS) (app. 1), inorganic constituents (app. 1), sulfides 

(app. 1), methylene blue active substances (MBAS) (app. 1), 

semivolatile organic compounds (SVOCs) (app. 2), volatile 

organic compounds (VOCs) (app. 3), glycols (app. 4), 

and total organic carbon (TOC) (app. 5) by TestAmerica 

Laboratory (TAL) in Denver, Colorado. Streambed-sediment 

samples were analyzed for moisture content (app. 6) and 

concentrations of inorganic constituents (app. 6), n-alkanes 

(app. 7), and TOC (app. 8) by TAL. Streambed-sediment 

samples also were analyzed for concentrations of PAHs and 

alkylated PAHs (app. 9) by the USGS National Water Quality 

Laboratory (NWQL) in Denver. A complete list of the methods 

used by TAL and the NWQL to analyze the surface-water 

and streambed-sediment samples for chemical constituents is 

provided in table 4. The three streambed-sediment samples 

were submitted to the USGS Kentucky Water Science Center 

Sediment Laboratory in Louisville for particle-size analysis in 

accordance with methods described in Guy (1969). 

For constituents analyzed by TAL in accordance with 

U.S. Environmental Protection Agency (EPA) methods (in 

which the method detection limit [MDL] is the minimum 

concentration of a substance that can be measured and 

reported with 99-percent confidence that the concentration 

is greater than zero [U.S. Environmental Protection Agency, 

1997]), reported values less than the MDL were considered 

to be nondetections as described by Glaser and others (1981). 

The MDL was calculated by using a minimum of seven 

replicate spike samples processed over a short time period 

(usually 2 days). TAL sets their reporting limits (RLs) 

as 2–10 times the MDL, depending on the constituent. 

Concentrations less than the MDL were considered to be 

nondetections and were reported as less than the MDL. 

Concentrations greater than the RL were reported as 

detections. Concentrations greater than the MDL but less than 

the RL were reported by TAL as estimated concentrations. 

Additionally, if there was a concentration of a constituent in 

a TAL lab blank and the concentration equated to less than 

20 percent of the corresponding sample detection, the result 

was reported by the USGS as an estimated concentration. 

For streambed-sediment samples analyzed for PAH and 

alkylated PAH concentrations by the NWQL, the method for 

censoring data was based on the long-term method detection 

limits (LT-MDL) and laboratory reporting limits (LRL). 

The LT-MDL was modified from the MDL analysis used 

by the EPA (Childress and others, 1999). Like the MDL, 

the LT-MDL also establishes the minimum concentration 

of a constituent that can be measured and reported with a 

99-percent confidence level when the analyte concentration 

in the sample is greater than zero. The LT-MDL was designed 

to capture greater method variability than does the MDL 

because the LT-MDL requires a larger dataset collected over 

an extended period of time that incorporates more of the 

measurement variability that is typical for routine analyses 

in a laboratory, such as multiple instruments, operators, 

calibrations, and sample preparation events. The LT-MDL 

limits the risk of false positive values in a sample but does 

not address the possibility of false negatives in a sample 

when the constituent might be present in the sample but is 

not detected. The LRL is a laboratory quantification limit 

that generally is two times the LT-MDL and is designed to 

minimize the number of false negatives in a dataset. Because 

information-rich mass spectrometry methods were used to 

augment identification of selected PAHs and alkylated PAHs 

described in this report, estimated concentrations less than 

the LT-MDL were considered detections of the constituent. 

Detections were reported when the concentration of the 

constituent equaled or exceeded the LT-MDL, when qualified 

concentrations were less than the LT-MDL, and when the 

presence of the constituent was verified but not quantified. 

In this report, PAH and alkylated PAH concentrations were 

qualified as estimated values if the quantification of the 

analyte was considered by the NWQL to be highly variable; 

if the constituent concentration was extrapolated below the 

calibration curve; or if, at the discretion of the analyst, the 

constituent concentration was less than the LT-MDL (U.S. 

Geological Survey, 2010). Constituents that were verified but 

not quantified were qualified with an “M” remark code. Total 

saturated hydrocarbons (TSH) and total PAHs were calculated 

by summing the concentrations of individual n-alkanes and 

individual PAHs, respectively. For both TSH and total PAHs, 

values below the detection limit were not included in the 

calculation.

Quality Assurance

For quality-assurance purposes, quality-control samples 

were collected to qualify the precision and accuracy of the 

environmental samples collected. Field blank samples were 

collected to determine the extent of contamination that might 

have been introduced during sample collection, sample 

processing, and laboratory analysis. Split replicate samples 

were collected with environmental samples to determine the 

amount, or degree, of variability that might have resulted 

from the procedures used to collect, process, and analyze the 

samples. All quality-assurance samples were analyzed for the 

same analytical schedules that were used for analysis of the 

environmental samples.
Table 4. Analytical methods used in the chemical analyses of surface-water and streambed-sediment samples collected from selected streams in tTexas, 2011–13.[W, water sample; TAL, Test America Laboratory; EPA, U.S. Environmental Protection Agency; °C, degrees Celsius; S, streambed-sediment sample; NWQL, U.S. Geological SLaboratory]

Constituents Sample medium Laboratory Analysis method Method description Re

Total dissolved solids W TAL EPA 2540C Dried at 180 °C Clesceri and others (19

Total suspended solids W TAL EPA 2540D Dried at 103–105 °C Clesceri and others (19Methylene blue active substances W TAL EPA 425.1 Color intensity U.S. Environmental PrCations W, S TAL EPA 6010B Inductively coupled plasmaatomic emission spectrometry U.S. Environmental Pr

Trace elements W, S TAL EPA 6020A Inductively coupled plasma-mass 

spectrometry 

U.S. Environmental Pr

Total organic carbon W, S TAL EPA 9060 Carbonaceous analyzer U.S. Environmental Pr

Anions W TAL EPA 300.0A Ion chromatography U.S. Environmental PrSulfide W TAL EPA 9030B Distillation U.S. Environmental Pr

TAL EPA 9034 Distillation U.S. Environmental Pr

Volatile organic compounds W TAL EPA 8260B Gas chromatography/mass spectrometry U.S. Environmental PrSemivolatile organic compounds W TAL EPA 8270C Gas chromatography/mass spectrometry U.S. Environmental PrGlycols W TAL EPA 8015B Gas chromatography/flame 

ionization detector 

U.S. Environmental Pr

Percent moisture S TAL D2216 Weighing the sample before and 

after drying 

American Society for T

n-alkanes S TAL EPA 8015C Gas chromatography U.S. Environmental Pr

Polycyclic aromatic hydrocarbons and alkylated polycyclic aromatic hydrocarbons S NWQL Schedule 5507 Gas chromatography/mass spec- trometry Zaugg and others (200
12 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas

Quality Assurance for Surface-Water Samples

To provide information on the bias and variability 

associated with constituents analyzed in surface-water 

samples, two field blanks were analyzed as quality-assurance 

samples. Field blank samples were collected and processed by 

using organic-free or inorganic-free deionized water obtained 

from the NWQL and certified to contain no detectable 

concentrations of the constituents that were analyzed. Field 

blank samples were collected on November 3, 2011, at the 

SAR Elmendorf site and on September 30, 2012, at the SAR 

72 site (apps. 10–14). TDS concentrations were less than the 

MDL in both field blank samples; however, an estimated TSS 

concentration of 1.2 milligrams per liter (mg/L) was reported 

in the field blank sample collected at the SAR 72 site (app. 

10). Multiple inorganic constituents were detected in both 

field blanks at relatively small concentrations compared to 

those measured in surface-water samples (app. 10). Sulfide, 

MBAS, and SVOCs were not detected in either field blank 

sample (apps. 10–11). No VOCs were detected in the field 

blank sample collected on November 3, 2013, but there were 

two detections of VOCs in the field blank sample collected 

on September 30, 2012, including acetone (estimated value 

of 2.1 micrograms per liter [μg/L]) and trichloromethane 

(estimated value of 0.17 μg/L) (app. 12). No glycols were 

detected in either field blank sample (app. 13). A relatively 

small concentration of TOC (estimated value of 0.22 mg/L) in 

comparison to environmental samples was measured in both 

blank samples (app. 14). 

For those constituents with concentrations greater than 

or equal to the MDL in the field blank samples, the data were 

evaluated to determine if concentrations of those constituents 

should be rejected from the environmental-sample dataset. 

If the detected concentration in the field blank sample was 

greater than 20 percent of the detected concentration in the 

environmental sample, the detection in the environmental 

sample was rejected and not included in the calculations 

of summary statistics. If the detection in the blank sample 

was less than or equal to 20 percent of the detection in the 

environmental sample, the detection in the environmental 

sample was retained. The same criteria were applied to 

laboratory blank samples that TAL analyzed with the 

environmental samples. For those cases in which a constituent 

was detected in a field blank sample but was not rejected, 

the reported concentrations in environmental samples should 

be considered potentially biased high because the sampling 

equipment may have introduced small amounts of the given 

constituent to the environmental samples. 

For quality assurance of surface-water samples, two 

split replicate samples were collected along with paired 

environmental samples from the SAR Elmendorf site on 

November 3, 2011, and from the SAR 72 site on September 

30, 2012. The split replicate sample results were compared to 

the environmental sample results by calculating the relative 

percent difference (RPD) for each detected concentration pair 

by using the following equation:

RPD = |C1 – C2|/((C1 + C2)/2) x 100, (1)

where

C1 is the detected concentration in the 

environmental sample, and

C2 is the detected concentration in the split 

replicate sample.

RPDs were calculated for only those constituent pairs 

with detectable concentrations greater than or equal to the 

RL or LRL in both the environmental and the split replicate 

samples. RPDs were not computed for constituent pair 

concentrations that had one or more nondetected values. 

RPDs of less than or equal to 15 percent were considered 

to indicate similar environmental and split replicate sample 

results when concentrations were sufficiently greater than the 

RL or LRL. The RPDs calculated for inorganic constituents 

ranged from 0.0 percent for multiple constituents to 33 percent 

for cadmium, with a median of 1.7 percent (app. 10). RPDs 

for SVOCs could not be calculated because these constituents 

were not detected in the quality-control samples (app. 11). 

RPDs calculated for three paired VOC concentrations from the 

sample collected at the SAR Elmendorf site on November 3, 

2011, ranged from 9.5 percent to 12 percent (app. 12). RPDs 

for glycols could not be calculated because these constituents 

were not detected in the split replicate samples (app. 13). 

RPDs calculated for TOC concentrations were 6.8 percent for 

the sample collected at the SAR Elmendorf site on November 

3, 2011, and 2.5 percent for the sample collected at the SAR 

72 site on September 30, 2012 (app. 14). 

Quality Assurance for Streambed-Sediment 

Samples

For quality assurance of streambed-sediment samples, 

one split replicate sample was collected at the SAR 

Elmendorf site on November 3, 2013. The split replicate 

sample results were compared to the environmental sample 

results by calculating the RPD for each detected constituent 

pair by using equation 1. RPDs were calculated for all 

inorganic constituents except antimony because the antimony 

concentration in the environmental sample was less than the 

RL and the antimony concentration in the replicate sample 

was verified but not quantified (app. 15). RPDs among the 

remaining inorganic constituents ranged from 0.0 percent for 

multiple constituents to 39 percent for silver, with a median 

RPD of 12 percent (app. 15). RPDs for n-alkanes ranged 

from 0.0 percent for multiple constituents to 120 percent 

for hentriacontane, with a median of 52 percent (app. 16). 

A median of 52 percent indicates a relatively high degree of 

methodological variability for n-alkanes. The RPD for TOC 

was 46 percent (app. 17); however, one value was estimated 

and could not be reanalyzed for verification. RPDs for PAHs 

could not be calculated because there were no detections in 

either the environmental or replicate samples used for quality 

assurance of the streambed-sediment samples (app. 18).
Concentrations of Selected Constituents 13

Concentrations of Selected 

Constituents 

For this report, the three-county area consisting of 

Wilson, Karnes, and DeWitt Counties is considered the area 

of active oil and natural-gas production in the study area. The 

SAR Elmendorf and Cibolo St. Hedwig sites were upstream 

from most active oil and natural-gas production. The SAR 

Falls City, Cibolo Falls City, Ecleto 1, Ecleto 2, and SAR 72 

sites were in the area of active oil and natural-gas production. 

The SAR Goliad, SAR McFaddin, and GR Tivoli sites were 

downstream from the area of active oil and natural-gas 

production.

Constituents in Surface-Water Samples

Surface-water samples were analyzed for concentrations 

of inorganic and organic constituents in this study because of 

the potential usefulness of those constituents as indicators of 

the presence of hydraulic fracturing fluids or produced waters. 

Sulfide was selected because of its common occurrence in 

produced waters (Tibbetts and others, 1992). All sulfide 

concentrations were less than the MDL of 0.79 mg/L (app. 1) 

provided by the TestAmerica analytical laboratory. Glycols 

are commonly used in hydraulic fracturing fluids as scale 

inhibitors (FracFocus Chemical Disclosure Registry, 2013). 

Four glycols—diethylene glycol, ethylene glycol, propylene 

glycol, and triethylene glycol—were analyzed for in surfacewater samples collected for this study, and none were detected 

at MDLs of 7.73 mg/L, 8.63 mg/L, 18.7 mg/L, and 8.45 mg/L, 

respectively (app. 4). The MDL for glycols for the stormrunoff sample collected at the SAR Falls City site was less 

than the MDLs of the other samples because it was analyzed 

later in the study, but there were no detections of glycols in 

that sample even at the lower MDLs.

Concentrations of SVOCs and VOCs also were analyzed 

for in this study because of their common occurrence as 

hydrocarbons in produced waters (Tibbetts and others, 1992). 

Of the 91 SVOCs analyzed for this study (app. 2), there were 

six detections, all but one of which were in storm-runoff 

samples (table 5). The base-flow sample collected at the SAR 

Goliad site contained bis(2-ethylhexyl) phthalate, a plasticizer 

in polyvinyl chloride and a constituent in hydraulic fracturing 

fluids (New York State Department of Environmental 

Conservation, 2013). The storm-runoff samples collected at 

the SAR Elmendorf and Ecleto 2 sites also contained bis(2-

ethylhexyl) phthalate. The storm-runoff sample collected 

at the SAR Elmendorf site contained the plasticizer diethyl 

phthalate. Both storm-runoff samples collected at the Ecleto 

1 and Ecleto 2 sites contained benzyl alcohol, a solvent 

commonly used in paints (U.S. National Library of Medicine, 

2001). Of the 67 VOCs analyzed in this study, there were a 

total of six detections, all of which were in base-flow samples. 

The surface-water sample collected at the SAR Elmendorf site 

contained bromodichloromethane, dibromochloromethane, 

and trichloromethane, all of which are disinfection byproducts 

associated with the chlorination of municipal water supplies 

and of treated municipal wastewater (Munson and others, 

1982; U.S. Environmental Protection Agency, 2013b; Larson 

and Weber, 1994). The sample collected at the Cibolo St. 

Hedwig site contained toluene, a fuel additive, solvent, 

and industrial feedstock used to produce benzene (U.S. 

Environmental Protection Agency, 2012b) and a constituent 

associated with produced waters (Tibbetts and others, 1992). 

The Cibolo St. Hedwig site is upstream from current (2014) 

oil and natural-gas production areas (fig. 1). Dichloromethane 

was detected in surface-water samples at both the SAR 72 and 

SAR Goliad sites. Dichloromethane is an industrial solvent 

with multiple uses (U.S. Environmental Protection Agency, 

2013c). 

Concentrations of selected anions (the negatively charged 

ions bromide, chloride, sulfate, and fluoride) were measured 

in surface-water samples collected at all sites during base 

flow and storm runoff (fig. 4). Bromide concentrations ranged 

from <0.11 mg/L at the SAR 72 site during storm runoff to 

0.66 mg/L at the Ecleto 1 site during storm runoff. Chloride 

concentrations ranged from 16 mg/L at the SAR Elmendorf 

site during storm runoff to 200 mg/L at the Ecleto 1 site during 

storm runoff. Sulfate concentrations ranged from 19 mg/L at 

the SAR Elmendorf site during storm runoff to 160 mg/L at 

the SAR Falls City site during storm runoff and the Cibolo 

Falls City site during base flow. Fluoride concentrations 

ranged from an estimated 0.13 mg/L at the SAR Elmendorf 

site during storm runoff to 0.64 mg/L at the SAR Elmendorf 

site during base flow. Greater anion concentrations were 

measured in samples collected during base flow than in 

samples collected during storm runoff at most of the sites.

Concentrations of selected cations (the positively charged 

ions calcium, magnesium, potassium, and sodium) in surfacewater samples varied substantially among sampling sites and 

streamflow conditions (fig. 5). Calcium concentrations ranged 

from 63 mg/L at the Cibolo St. Hedwig site during storm 

runoff to 230 mg/L at the SAR Elmendorf site during storm 

runoff. Magnesium concentrations ranged from 9.5 mg/L at 

the Ecleto 2 site during storm runoff to 20 mg/L at multiple 

sites during base flow. Potassium concentrations ranged from 

6.7 mg/L at the GR Tivoli site during storm runoff to 15 mg/L 

at the SAR Falls City site during storm runoff. Concentrations 

of sodium were greater than potassium concentrations and 

ranged from 12 mg/L at the SAR Elmendorf site during storm 

runoff to 150 mg/L at the Ecleto 1 site during storm runoff. 

All major cations usually occurred at greater concentrations 

during base flow than during storm runoff. 
Table 5. Summary of semivolatile and volatile organic compounds detected in unfiltered surface-water samples collected in the San Antonio River B[USGS, U.S. Geological Survey; μg/L, micrograms per liter; SAR, San Antonio River; St., Saint; GR, Guadalupe River; --, not detected; E, estimated; M, presence verified but n

Map identifier (as shown in fig. 1) Short name USGS station number USGS station name Semivolatile organic compounds Vol

organic c

Benzyl alcohol (μg/L) Bis(2- ethyl- hexyl) phthalate (μg/L) Diethyl phthalate (μg/L) Bromo- dichloro- methane (μg/L) Dibromo- chloro- methane (μg/L) Dic

me

(μ

Base flow HF01 SAR Elmendorf 08181800 San Antonio River near Elmendorf, Tex. -- -- -- 2.6 1.1 

HF02 SAR Falls City 08183550 San Antonio River at Highway 181 at Falls City, Tex. -- -- -- -- -- 

HF03 Cibolo St. Hedwig 08185065 Cibolo Creek near Saint Hedwig, Tex. -- -- -- -- -- HF07 SAR 72 08188060 San Antonio River at State Highway 72 near Runge, Tex. -- -- -- -- -- E

HF08 SAR Goliad 08188500 San Antonio River at Goliad, Tex. -- M -- -- -- E

HF09 SAR McFaddin 08188570 San Antonio River near McFaddin, Tex. -- -- -- -- -- 

HF10 GR Tivoli 08188800 Guadalupe River near Tivoli, Tex. -- -- -- -- -- 

Storm runoff HF01 SAR Elmendorf 08181800 San Antonio River near Elmendorf, Tex. -- E3.0 E2.2 -- -- 

HF02 SAR Falls City 08183550 San Antonio River at Highway 181 at Falls City, Tex. -- -- -- -- -- 

HF03 Cibolo St. Hedwig 08185065 Cibolo Creek near Saint Hedwig, Tex. -- -- -- -- -- 

HF04 Cibolo Falls City 08186000 Cibolo Creek near Falls City, Tex. -- -- -- -- -- 

HF05 Ecleto 1 08186500 Ecleto Creek near Runge, Tex. M M -- -- -- 

HF06 Ecleto 2 08186550 Ecleto Creek at County Road 326 near Runge, Tex. M -- -- -- -- 

HF07 SAR 72 08188060 San Antonio River at State Highway 72 near Runge, Tex. -- -- -- -- -- 

HF08 SAR Goliad 08188500 San Antonio River at Goliad, Tex. -- -- -- -- -- 

HF09 SAR McFaddin 08188570 San Antonio River near McFaddin, Tex. -- -- -- -- -- 

HF10 GR Tivoli 08188800 Guadalupe River near Tivoli, Tex. -- -- -- -- -- 
Concentrations of Selected Constituents 15

Short name (table 1) for sampling site

SAR Elmendorf

Cibolo St. Hedwig

SAR Falls City

Cibolo Falls City

Ecleto

SAR 72

SAR Goliad

SAR McFaddin

GR Tivoli

SAR Elmendorf

Cibolo St. Hedwig

SAR Falls City

Cibolo Falls City

Ecleto

SAR 72

SAR Goliad

SAR McFaddin

GR Tivoli

Short name (table 1) for sampling site

Concentration, in milligrams per liter

1.0

0.8

0.6

0.4

0.2

0

180

160

140

120

100

80

60

40

20

0

180

200

220

160

140

120

100

80

60

40

20

0

0.8

0.6

0.4

0.2

0

A. Bromide B. Chloride

C. Sulfate D. Fluoride

Base flow

Storm runoff

Nondetection—Base flow

EXPLANATION

Figure 4. Concentrations of selected anions in unfiltered surface-water samples collected from the San Antonio River Basin, Texas, 

2011–13. A, Bromide. B, Chloride. C, Sulfate. D, Fluoride.
16 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas SAR Elmendorf Cibolo St. Hedwig SAR Falls City Cibolo Falls City Ecleto SAR 72 SAR Goliad SAR McFaddin GR Tivoli SAR Elmendorf Cibolo St. Hedwig SAR Falls City Cibolo Falls City Ecleto SAR 72 SAR Goliad SAR McFaddin GR Tivoli

Short name (table 1) for sampling site Short name (table 1) for sampling site

250

200

150

100

50

25

20

15

10

5

16

14

12

10

8

6

4

2

0

160

140

120

100

80

60

40

20

0

Concentration, in milligrams per liter

A. Calcium B. Magnesium

C. Potassium D. Sodium

Base flow

Storm runoff

EXPLANATION

Figure 5. Concentrations of selected cations in unfiltered surface-water samples collected from the San Antonio River Basin, Texas, 

2011–13. A, Calcium. B, Magnesium. C, Potassium. D, Sodium.
Concentrations of Selected Constituents 17

Concentrations of selected inorganic constituents varied 

widely among sampling sites and streamflow conditions 

(fig. 6A–L). Aluminum concentrations ranged from 110 μg/L 

at the Cibolo Falls City site during base flow to 39,000 μg/L 

at the SAR Elmendorf site during storm runoff. Barium 

concentrations ranged from 29 μg/L during base flow at 

the SAR Elmendorf site to 280 μg/L during storm runoff 

at the Ecleto 2 site. Chromium concentrations ranged from 

<0.50 μg/L at multiple sites to 47 μg/L during storm runoff 

at the SAR Elmendorf site. Copper concentrations ranged 

from <0.56 μg/L at the Cibolo Falls City site during base 

flow to 25.0 μg/L at the SAR Elmendorf site during storm 

runoff. Iron concentrations varied widely among sites ranging 

from 110 μg/L at the Cibolo Falls City site during base flow 

to 38,000 μg/L at the SAR Elmendorf site during storm 

runoff. Lead concentrations ranged from <0.18 μg/L at the 

Cibolo Falls City site during base flow to 42 μg/L at the SAR 

Elmendorf site during storm runoff. Lithium concentrations 

ranged from 13 μg/L at the Cibolo St. Hedwig site during 

storm runoff to 54 μg/L at the Cibolo Falls City site during 

base flow. Manganese concentrations ranged from 8.7 μg/L 

at the Cibolo St. Hedwig site during base flow to 690 μg/L 

at the SAR Elmendorf site during storm runoff. Strontium 

concentrations ranged from 400 μg/L at the Ecleto 2 site 

during storm runoff to 900 μg/L at the SAR Goliad site during 

base flow. Zinc concentrations ranged from an estimated 

2.3 μg/L at the Cibolo Falls City site during base flow to 

130 μg/L at the SAR Elmendorf site during storm runoff. Both 

the smallest and greatest arsenic concentrations were measured 

at the SAR Elmendorf site, and they ranged from an estimated 

0.96 μg/L during base flow to 9.5 μg/L during storm runoff. 

Boron concentrations ranged from 190 μg/L at the Cibolo St. 

Hedwig and GR Tivoli sites during storm runoff to 390 μg/L 

at the Ecleto 1 site during storm runoff. Inorganic constituents 

for which a majority of the concentrations were greater during 

storm runoff included aluminum, barium, chromium, copper, 

iron, lead, manganese, zinc, and arsenic. Inorganic constituents 

for which a majority of the concentrations were greater during 

base flow included strontium and boron. Lithium showed an 

equal number of concentrations that were greater during storm 

runoff and greater during base flow.

MBAS is a measurement of surfactants, organic 

substances that are used as wastewater indicators (Thomas 

and others, 1999) and as flowback additives during hydraulic 

fracturing (FracFocus Chemical Disclosure Registry, 2013). 

Eight of the samples analyzed for MBAS were analyzed 

after the recommended holding time of 48 hours had been 

exceeded. Analyzing samples after holding times have been 

exceeded could affect measured concentration. The data for 

these samples were included in the report for completeness. 

A total of five detections of MBAS were measured at the 

Cibolo St. Hedwig, Ecleto 1, SAR Goliad, SAR McFaddin, 

and GR Tivoli sites during storm runoff (fig. 7). Overall, 

MBAS concentrations ranged from <0.12 mg/L at multiple 

sites to an estimated 0.14 mg/L at the Ecleto 1 and SAR 

Goliad sites.

Central gathering facility in DeWitt County, Texas. 
18 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas

Short name (table 1) for sampling site

SAR Elmendorf

Cibolo St. Hedwig

SAR Falls City

Cibolo Falls City

Ecleto

SAR 72

SAR Goliad

SAR McFaddin

GR Tivoli

SAR Elmendorf

Cibolo St. Hedwig

SAR Falls City

Cibolo Falls City

Ecleto

SAR 72

SAR Goliad

SAR McFaddin

GR Tivoli

Short name (table 1) for sampling site

50

40

30

20

10

0

Concentration, in micrograms per liter

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0

10,000

20,000

30,000

40,000

0

50

100

150

200

250

300

0

4,000

8,000

12,000

16,000

20,000

24,000

28,000

32,000

36,000

40,000

0

5

10

15

20

25

30

35

40

45

50

C. Chromium D. Copper

A. Aluminum B. Barium

E. Iron F. Lead

Base flow

Storm runoff

Nondetection—Base flow

Nondetection—Storm runoff

EXPLANATION

Figure 6. Concentrations of selected inorganic constituents in unfiltered surface-water samples collected from the San Antonio River 

Basin, Texas, 2011–13. A, Aluminum. B, Barium. C, Chromium. D, Copper. E, Iron. F, Lead. G, Lithium. H, Manganese. I, Strontium. J, Zinc. 

K, Arsenic. L, Boron.
Concentrations of Selected Constituents 19

Short name (table 1) for sampling site

SAR Elmendorf

Cibolo St. Hedwig

SAR Falls City

Cibolo Falls City

Ecleto

SAR 72

SAR Goliad

SAR McFaddin

GR Tivoli

SAR Elmendorf

Cibolo St. Hedwig

SAR Falls City

Cibolo Falls City

Ecleto

SAR 72

SAR Goliad

SAR McFaddin

GR Tivoli

Short name (table 1) for sampling site

Concentration, in micrograms per liter

0

100

200

300

400

500

600

700

800

900

1,000

0

2

4

6

8

10

0

10

20

30

40

50

60

70

140

210

280

350

420

490

560

630

700

0

15

30

45

60

75

90

105

120

135

150

0

100

200

300

400

500

0

I. Strontium J. Zinc

G. Lithium H. Manganese

K. Arsenic L. Boron

Base flow

Storm runoff

EXPLANATION

Figure 6. Concentrations of selected inorganic constituents in unfiltered surface-water samples collected from the San Antonio River 

Basin, Texas, 2011–13. A, Aluminum. B, Barium. C, Chromium. D, Copper. E, Iron. F, Lead. G, Lithium. H, Manganese. I, Strontium. J, Zinc. 

K, Arsenic. L, Boron.—Continued
20 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas

Constituents in Streambed-Sediment Samples

Scant historical data are available describing inorganic 

constituent concentrations in streambed-sediment samples 

collected from the San Antonio River Basin. Inorganic 

constituents were measured in streambed-sediment samples 

to provide baseline information about the occurrence of these 

constituents (app. 6). Of the 28 inorganic constituents analyzed 

in streambed-sediment samples, all were measured in at least 

one sample except antimony. Antimony was not detected 

in any samples at MDLs that ranged from 0.01 milligrams 

per kilogram (mg/kg) to 0.05 mg/kg. Concentrations of 

the remaining inorganic constituents varied substantially. 

Attempting to differentiate between natural concentrations 

of inorganic constituents and elevated concentrations from 

introduced sources is not possible with such few data; 

however, these data provide some preliminary information 

about the constituents in streambed-sediment samples 

collected from sites upstream from, in, and downstream from 

the active oil and natural-gas production areas in the basin. 

Selected organic constituents including n-alkanes and 

PAHs were analyzed for in streambed-sediment samples for 

this study because of their potential usefulness as indicators 

of hydrocarbons associated with produced waters (Hostettler 

and others, 2013). Concentrations of individual n-alkanes are 

provided in appendix 7. Of the 38 n-alkanes analyzed for this 

study, only undecane was not detected in any of the samples 

(app. 7). Concentrations of TSH, which are calculated as 

the sum of the individual n-alkanes, are shown in figure 8. 

The <2-mm size-fraction samples include larger sand-sized 

particles, whereas the <63-μm size-fraction samples exclude 

larger sand-sized particles. Concentrations of TSHs ranged 

from an estimated 260 micrograms per kilogram (μg/kg) in the 

<2-mm size-fraction sample collected at the SAR Goliad site 

to 11,000 μg/kg in the <2-mm size-fraction sample collected 

at the Ecleto 1 site (fig. 8). TSH concentrations were greater 

in the <63-μm size-fraction sample than in the <2-mm sizefraction sample in streambed-sediment samples collected 

from 5 of the 9 sites. Concentrations of total PAHs, calculated 

as the sum of the individual PAHs and alkylated PAHs, are 

shown in figure 9. Total PAH concentrations ranged from less 

than the MDL in the <2-mm size-fraction samples collected 

from multiple sites to 1,600 μg/kg in the <2-mm size-fraction 

sample collected from the SAR McFaddin site. Total PAH 

concentrations were greater in the <63-μm size-fraction 

samples than in the <2-mm size-fraction samples at 7 of the 9 

sites.

Short name (table 1) for sampling site

SAR Elmendorf

Cibolo St. Hedwig

SAR Falls City

Cibolo Falls City

Ecleto

SAR 72

SAR Goliad

SAR McFaddin

GR Tivoli

Concentration, in milligrams per liter

0

0.12

0.24

0.36

0.48

0.60

0.72

0.84

0.96

1.08

1.20

1.32

Methylene blue active substances

Storm runoff

Nondetection—Base flow

Nondetection—Storm runoff

EXPLANATION

Figure 7. Concentrations of methylene blue active substances 

(MBAS) in unfiltered surface-water samples collected from the 

San Antonio River Basin, Texas, 2011–13.

Figure 8. Concentrations of total saturated hydrocarbons in 

streambed-sediment samples collected from the San Antonio 

River Basin, Texas, 2011–13.

Short name (table 1) for sampling site

SAR Elmendorf

Cibolo St. Hedwig

SAR Falls City

Cibolo Falls City

Ecleto

SAR 72

SAR Goliad

SAR McFaddin

GR Tivoli

Concentration, in micrograms per kilogram

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

12,000 Total saturated hydrocarbons

<2 millimeters

<63 micrometers

EXPLANATION

<, Less than
Summary 21

A subset of three streambed-sediment samples was 

analyzed for n-alkanes and PAHs by using both <63-μm and 

<2-mm size fractions from the same sample to determine 

whether or not there were greater concentrations of organic 

constituents in the <63-μm size fraction in comparison to 

the <2-mm size fraction (table 3). At all three sites, total 

PAH concentrations were greater in the <63-μm size-fraction 

samples than in the <2-mm size-fraction samples. In contrast, 

TSH concentrations were greater in the <63-μm size-fraction 

samples than in the <2-mm size-fraction samples at 1 of 

3 sites. Particle-size analysis shows a progressively greater 

percentage of fine-grained sediment in the downstream 

direction in the San Antonio River Basin. The sample collected 

at the SAR Elmendorf site, the farthest upstream sampling 

site on the San Antonio River, contained only 16 percent of 

the particles smaller than the sand/fine break (0.063 mm). The 

sample collected at the SAR 72 site contained 23 percent of 

the particles smaller than the sand/fine break, and the sample 

collected at the SAR McFaddin site, the farthest downstream 

sampling site on the San Antonio River, contained 86 percent 

of the particles smaller than the sand/fine break. The greater 

concentrations of PAHs in the <63-μm size-fraction samples at 

all three of these sites are consistent with a greater percentage 

of binding sites associated with fine-grained (<63 μm) 

sediment versus coarse-grained (<2 mm) sediment (Horowitz, 

1991). The larger difference in total PAHs between the <2-mm 

and <63-μm size-fraction samples at the SAR Elmendorf site 

might be related to the large percentage of sand in the <2-mm 

size-fraction sample which is absent in the <63-μm sizefraction sample. In contrast, the <2-mm size-fraction sample 

collected from the SAR McFaddin site contained very little 

sand and was similar in particle-size composition to the <63-

μm size-fraction sample. 

Summary

Concerns about possible environmental effects associated 

with the use of hydraulic fracturing processes for extracting 

oil and natural gas have been growing as these processes 

have increasingly been implemented throughout the United 

States in the past 10 years. Some of the concerns expressed 

by the public, staff members of State and local water resource 

agencies, and State and Federal regulatory agencies include 

the possible release of organic and inorganic constituents 

found in hydraulic fracturing fluids and produced waters. 

Constituents of concern include those frequently used in 

hydraulic fracturing fluids such as glycols and surfactants 

and those found in produced waters such as n-alkanes and 

polycyclic aromatic hydrocarbons (PAHs). Therefore, there 

is a need to analyze different types of constituents in both 

water and streambed-sediment samples to effectively identify 

constituents that might be associated with oil and naturalgas production in Texas. The U.S. Geological Survey, in 

cooperation with the San Antonio River Authority and the 

Guadalupe-Blanco River Authority, analyzed surface-water 

and streambed-sediment samples collected from 10 sites in the 

San Antonio River Basin to provide data for a broad range of 

constituents that might be associated with hydraulic fracturing 

and the produced waters that are a consequence of hydraulic 

fracturing. 

During 2011–13, 18 surface-water and 22 streambedsediment samples were collected at 10 sites including the San 

Antonio River near Elmendorf, Tex. (SAR Elmendorf); San 

Antonio River at Highway 181 at Falls City, Tex.; Cibolo 

Creek near St. Hedwig, Tex. (Cibolo St. Hedwig); Cibolo 

Creek near Falls City, Tex.; Ecleto Creek near Runge, Tex. 

(Ecleto 1); Ecleto Creek at County Road 326 near Runge, 

Tex. (Ecleto 2); San Antonio River at State Highway 72 near 

Runge, Tex. (SAR 72); San Antonio River at Goliad, Tex. 

(SAR Goliad); San Antonio River near McFaddin, Tex. (SAR 

McFaddin); and Guadalupe River near Tivoli, Tex. (GR Tivoli) 

sites for analysis of concentrations of selected inorganic and 

organic constituents. Surface-water samples were analyzed 

for concentrations of total dissolved solids, total suspended 

solids, inorganic constituents, sulfides, methylene blue 

active substances (MBAS), semivolatile organic compounds 

Figure 9. Concentrations of total polycyclic aromatic 

hydrocarbons in streambed-sediment samples collected from the 

San Antonio River Basin, Texas, 2011–12.

Short name (table 1) for sampling site

SAR Elmendorf

Cibolo St. Hedwig

SAR Falls City

Cibolo Falls City

Ecleto

SAR 72

SAR Goliad

SAR McFaddin

GR Tivoli

Concentration, in micrograms per kilogram

2,000

1,500

1,000

500

0

Total polycyclic aromatic hydrocarbons

<2 millimeters

<63 micrometers

EXPLANATION

<, Less than
22 Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas

(SVOCs), volatile organic compounds (VOCs), glycols, and 

total organic carbon (TOC). Streambed-sediment samples 

were analyzed for moisture content, inorganic constituents, 

n-alkanes, TOC, PAHs, and alkylated PAHs. 

Surface-water samples were analyzed for concentrations 

of inorganic and organic constituents in this study because 

of the potential usefulness of those constituents as indicators 

of the presence of hydraulic fracturing fluids or produced 

waters. All sulfide concentrations were less than the method 

detection limit (MDL) of 0.79 milligrams per liter (mg/L). 

Four glycols—diethylene glycol, ethylene glycol, propylene 

glycol, and triethylene glycol—were analyzed for in surfacewater samples collected for this study, and none were detected 

at MDLs of 7.73 mg/L, 8.63 mg/L, 18.7 mg/L, and 8.45 

mg/L, respectively. Concentrations of SVOCs and VOCs 

also were analyzed for in this study because of their common 

occurrence as hydrocarbons in produced waters. Of the 91 

SVOCs analyzed for this study, there were six detections, 

all but one of which were in storm-runoff samples. The 

base-flow sample collected at the SAR Goliad site contained 

bis(2-ethylhexyl) phthalate, a plasticizer in polyvinyl 

chloride and a constituent in hydraulic fracturing fluids. The 

storm-runoff samples collected at the SAR Elmendorf and 

Ecleto 2 sites also contained bis(2-ethylhexyl) phthalate. 

The storm-runoff sample collected at the SAR Elmendorf 

site contained the plasticizer diethyl phthalate. Both stormrunoff samples collected at the Ecleto 1 and Ecleto 2 sites 

contained benzyl alcohol, a solvent commonly used in paints. 

Of the 67 VOCs analyzed in this study, there were a total of 

six detections, all of which were in base-flow samples. The 

surface-water sample collected at the SAR Elmendorf site 

contained bromodichloromethane, dibromochloromethane, 

and trichloromethane, all of which are disinfection byproducts 

most commonly associated with the chlorination of surface 

waters to produce finished municipal water supplies. The 

sample collected at the Cibolo St. Hedwig site contained 

toluene, a fuel additive, solvent, and industrial feedstock used 

to produce benzene. The Cibolo St. Hedwig site is upstream 

from current (2014) oil and natural-gas production areas. 

Dichloromethane, an industrial solvent with multiple uses, 

was detected in surface-water samples at both the SAR 72 and 

SAR Goliad sites. 

Concentrations of selected anions (the negatively 

charged ions bromide, chloride, sulfate, and fluoride) 

were measured in surface-water samples collected at all 

sites during base flow and storm runoff. Greater anion 

concentrations were measured in samples collected during 

base flow than in samples collected during storm runoff at 

most of the sites. Concentrations of selected cations (the 

positively charged ions calcium, magnesium, potassium, 

and sodium) in surface-water samples varied substantially 

among sampling sites and streamflow conditions. All major 

cations usually occurred at greater concentrations during base 

flow than during storm runoff. Concentrations of selected 

inorganic constituents varied widely among sampling sites 

and streamflow conditions. Inorganic constituents for which 

a majority of the concentrations were greater during storm 

runoff included aluminum, barium, chromium, copper, iron, 

lead, manganese, zinc, and arsenic. Inorganic constituents for 

which a majority of the concentrations were greater during 

base flow included strontium and boron. Lithium showed an 

equal number of concentrations that were greater during storm 

runoff and greater during base flow. MBAS is a measurement 

of surfactants, organic substances that are used as wastewater 

indicators and as flowback additives during hydraulic 

fracturing. A total of five detections of MBAS were measured 

at the Cibolo St. Hedwig, Ecleto 1, SAR Goliad, SAR 

McFaddin, and GR Tivoli sites during storm runoff. Overall, 

MBAS concentrations ranged from less than (<) 0.12 mg/L at 

multiple sites to an estimated 0.14 mg/L at the Ecleto 1 and 

SAR Goliad sites.

Inorganic constituents were measured in streambedsediment samples to provide baseline information about the 

occurrence of these constituents. Attempting to differentiate 

between natural concentrations of inorganic constituents 

and elevated concentrations from introduced sources is not 

possible with such few data. Selected organic constituents 

including n-alkanes and PAHs were analyzed for in 

streambed-sediment samples for this study because of their 

potential usefulness as indicators of hydrocarbons associated 

with produced waters. In streambed-sediment samples, 

concentrations of total saturated hydrocarbons (TSH) ranged 

from an estimated 260 micrograms per kilogram (μg/kg) in the 

<2-millimeter (mm) size-fraction sample collected at the SAR 

Goliad site to 11,000 μg/kg in the <2-mm size-fraction sample 

collected at the Ecleto 1 site. TSH concentrations were greater 

in the <63-micrometer (μm) size-fraction sample than in the 

<2-mm size-fraction sample in streambed-sediment samples 

collected from 5 of the 9 sites. Concentrations of total PAHs, 

calculated as the sum of the individual PAHs and alkylated 

PAHs, ranged from less than the MDL in the <2-mm sizefraction samples collected from multiple sites to 1,600 μg/kg 

in the <2-mm size-fraction sample collected from the SAR 

McFaddin site. Total PAH concentrations were greater in the 

<63-μm size-fraction samples than in the <2-mm size-fraction 

samples at 7 of the 9 sites.

During collection of the second sample set, additional 

samples from a subset of three sites (the SAR Elmendorf, 

SAR 72, and SAR McFaddin sites) were processed by using 

a 63-μm sieve on one aliquot and a 2-mm sieve on a second 

aliquot for PAH and n-alkane analyses. The purpose of 

analyzing PAHs and n-alkanes on a sample containing sand, 

silt, and clay versus a sample containing only silt and clay 

was to provide data that could be used determine if these 

organic constituents had a greater affinity for silt- and claysized particles relative to sand-sized particles. The greater 

concentrations of PAHs in the <63-μm size-fraction samples at 

all three of these sites are consistent with a greater percentage 

of binding sites associated with fine-grained (<63 μm) 

sediment versus coarse-grained (<2 mm) sediment. The larger 

difference in total PAHs between the <2-mm and <63-μm sizefraction samples at the SAR Elmendorf site might be related 
References 23

to the large percentage of sand in the <2-mm size-fraction 

sample which is absent in the <63-μm size-fraction sample. In 

contrast, the <2-mm size-fraction sample collected from the 

SAR McFaddin site contained very little sand and was similar 

in particle-size composition to the <63-μm size-fraction 

sample.

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Opsahl and Crow—Concentrations of Selected Constituents in Surface-Water and Streambed-Sediment Samples, South-Central Texas, 2011–13—DS 836, ver. 1.1

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