U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2011–5097

Prepared in cooperation with the San Antonio River Authority and the San Antonio Metropolitan 

Health District Public Center for Environmental Health

Assessment of Selected Contaminants in Streambed- and 

Suspended-Sediment Samples Collected in Bexar County, 

Texas, 2007–09
Front cover: U.S. Geological Survey hydrologic technician collecting streambed-sediment sample from 

Martinez Creek at Farm Road 1518 near St. Hedwig, Texas, February 2008. 

Back cover: U.S. Geological Survey hydrologic technician collecting streambed-sediment sample from 

Rosillo Creek at New Sulphur Springs Road, San Antonio, Texas, August 2009. 
Assessment of Selected Contaminants 

in Streambed- and Suspended-Sediment 

Samples Collected in Bexar County, Texas, 

2007–09

By Jennifer T. Wilson

Prepared in cooperation with the San Antonio River Authority and the San 

Antonio Metropolitan Health District Public Center for Environmental Health

Scientific Investigations Report 2011–5097

U.S. Department of the Interior

U.S. Geological Survey
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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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Wilson, J.T., 2011, Assessment of selected contaminants in streambed- and suspended-sediment samples collected 

in Bexar County, Texas, 2007–09: U.S. Geological Survey Scientific Investigations Report 2011–5097, 57 p. 

(Appendixes available online at http://pubs.usgs.gov/sir/2011/5097/.)
iii

Acknowledgments

Lackland Air Force Base personnel assisted with base access. The Base Closure and 

Realignment Commission assisted with historical sample results. San Antonio Missions 

National Historical Park, National Park Service, provided access to the sampling site on the 

San Antonio River near Interstate Highway 410. Christopher Ellison, U.S. Geological Survey, 

provided assistance with statistical analyses.

v

Contents

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

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

Purpose and Scope .............................................................................................................................4

Description of Study Area ..................................................................................................................7

Previous Studies ..................................................................................................................................8

Methods ........................................................................................................................................................12

Sample Collection ..............................................................................................................................13

Streambed-Sediment Samples ...............................................................................................14

Large-Volume Suspended-Sediment Samples ....................................................................14

Analytical Methods ............................................................................................................................17

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

Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples ........19

Occurrence and Distribution of Sediment-Associated Constituents ........................................20

Comparison of Findings to Sediment-Quality Guidelines ............................................................29

Comparison of Findings to Data from Previous Studies ..............................................................33

Statistical Analyses ...........................................................................................................................36

Similarity or Difference of Contaminant Concentration by Watershed ...........................37

Relations Between Land Use and Streambed-Sediment Contaminant 

Concentrations ............................................................................................................39

Indicators of Selected Organic Contaminant Sources ................................................................45

Summary .......................................................................................................................................................49

References Cited .........................................................................................................................................52

Appendixes (available online at http://pubs.usgs.gov/sir/2011/5097/)

1.1. Concentrations of major and trace elements in streambed-sediment and largevolume suspended-sediment (LVSS) samples collected from sites in Bexar County, 

Texas, 2007–09

1.2. Concentrations of halogenated organic compounds in streambed-sediment and 

large-volume suspended-sediment (LVSS) samples collected from sites in Bexar 

County, Texas, 2007–09

1.3. Concentrations of semivolatile organic compounds and polycyclic aromatic 

hydrocarbons in streambed-sediment and large-volume suspended-sediment 

(LVSS) samples collected from sites in Bexar County, Texas, 2007–09

1.4. Suspended-sediment concentration (SSC) and grain size in large-volume 

suspended-sediment (LVSS) samples collected from selected sites in Bexar 

County, Texas, 2008–09

2.1. Quality-control samples for major and trace element analyses of streambed- and 

suspended-sediment samples collected from selected sites in Bexar County, 

Texas, 2007–09

2.2. Quality-control samples for halogenated organic compound analyses of 

streambed- and suspended-sediment samples collected from selected sites in 

Bexar County, Texas, 2007–09. 

2.3. Quality-control samples for semivolatile organic compound and polycyclic 

aromatic hydrocarbon analyses of streambed- and suspended-sediment samples 

collected from selected sites in Bexar County, Texas, 2007–09

3.1. Concentrations of trace elements and halogenated organic compounds in 

biological samples collected by the U.S. Geological Survey from sites in 

selected watersheds of Bexar County, Texas, 1995–97
vi

3.2. Concentrations of trace elements, organic carbon, halogenated organic 

compounds, and polycyclic aromatic hydrocarbons in streambed-sediment 

samples collected by the U.S. Geological Survey from sites in selected 

watersheds of Bexar County, Texas, 1995–2001

4.0. Concentrations of selected trace elements, halogenated organic compounds, and 

polycyclic aromatic hydrocarbons in streambed-sediment samples collected by 

the U.S. Air Force Center for Engineering and the Environment from sites on Leon 

Creek in Bexar County, Texas, 1994–2008

Figures

1–2. Maps showing: 

1. Locations of streambed-sediment and suspended-sediment sampling sites 

in Bexar County, Texas, 2007–09 ......................................................................................3

2. Land use in associated contributing area of each site where streambedsediment and suspended-sediment samples were collected in Bexar County, 

Texas, 2007–09 .....................................................................................................................5

3. Graph showing top 10 potential sources of contamination in contributing areas 

of sites where streambed-sediment and suspended-sediment samples were 

collected in Bexar County, Texas, 2007–09 ..............................................................................9

4. Map showing location of U.S. Air Force Center for Engineering and the 

Environment (AFCEE) and U.S. Geological Survey (USGS) streambed-sediment 

sampling sites on Leon Creek, Bexar County, Texas ...........................................................10

5. Hyetograph showing rainfall at San Antonio International Airport and hydrographs 

showing stream discharge and streambed-sediment and suspended-sediment 

sampling at selected sites in Bexar County, Texas, 2007–09 ..............................................15

6. Schematic (A) and photographs (B and C) of passive samplers used to collect 

large-volume suspended-sediment samples at selected sites in Bexar County, 

Texas, 2007–09 ............................................................................................................................16

7–13. Graphs showing: 

7. Detection frequencies of halogenated organic compounds in streambedsediment and suspended-sediment samples, by watershed, in Bexar County, 

Texas, 2007–09 ...................................................................................................................24

8. Concentrations of the four most frequently detected brominated flame 

retardants in streambed-sediment and suspended-sediment samples 

collected from sites in Bexar County, Texas, 2007–09 ................................................26

9. Comparison of concentrations of selected contaminants in streambedsediment samples to concentrations in suspended-sediment samples 

collected from selected sites in Bexar County, Texas, 2007–09 ...............................28

10. Comparison of consensus-based sediment-quality guidelines with 

concentrations of selected trace elements in streambed-sediment and 

suspended-sediment samples collected from sites in Bexar County, Texas, 

2007–09 ...............................................................................................................................30

11. Comparison of consensus-based sediment-quality guidelines with 

concentrations of selected halogenated organic compounds in streambedsediment and suspended-sediment samples collected from sites in Bexar 

County, Texas, 2007–09 ....................................................................................................32

12. Graphs showing comparison of consensus-based sediment-quality guidelines 

with concentrations of selected polycyclic aromatic hydrocarbons (PAHs) 

and total PAHs in streambed-sediment and suspended-sediment samples 

collected from sites in Bexar County, Texas, 2007–09 ................................................34
vii

13. Mean probable effect concentration quotient of streambed-sediment and 

suspended-sediment samples collected from sites in Bexar County, Texas, 

2007–09 ...............................................................................................................................35

14. Map showing locations of U.S. Environmental Protection Agency (USEPA) 

Superfund sites and Toxics Release Inventory (TRI) Program facilities and 

industries in contributing areas of streambed-sediment sampling sites in Bexar 

County, Texas, 2007–09 .............................................................................................................40

15–16. Graphs showing:

15. Concentrations of detected polychlorinated biphenyl (PCB) congeners 

normalized to concentrations of total PCBs in streambed-sediment samples 

collected from selected sites in Bexar County, Texas, 2007–09 ...............................46

16. Comparison of polycyclic aromatic hydrocarbon (PAH) profiles for various 

PAH sources summarized in Van Metre and Mahler to PAH profile for 

average Bexar County sediment computed from samples from selected 

sites in Bexar County, Texas, 2007–09 ...........................................................................48

Tables

1. Constituents analyzed in streambed-sediment and suspended-sediment 

samples collected in Bexar County, Texas, 2007–09, and constituent rank on 2007 

“Comprehensive Environmental Response, Compensation, and Liability Act Priority 

List of Hazardous Substances” .................................................................................................4

2. Characteristics of associated contributing area of each site where streambedsediment and suspended-sediment samples were collected in Bexar County, 

Texas, 2007–09 ..............................................................................................................................6

3. Streambed-sediment and suspended-sediment samples collected in contributing 

areas of sites in Bexar County, Texas, 2007–09 ....................................................................13

4. Suspended-sediment concentration and mass of contaminant per unit volume of 

stormwater for large-volume suspended-sediment samples collected by passive 

samplers at selected sites in Bexar County, Texas, 2008–09 .............................................21

5. Consensus-based sediment-quality guidelines used for comparison to 

contaminant concentrations in streambed-sediment and suspended-sediment 

samples collected from sites in Bexar County, Texas, 2007–09 .........................................31

6. Percent detections, ranges, means, and standard deviations of sedimentassociated constituents in sediment samples collected by the U.S. Air Force 

Center for Engineering and the Environment (AFCEE) during 1994–2008 and by the 

U.S. Geological Survey (USGS) during 2007–09 from Leon Creek in Bexar County, 

Texas ............................................................................................................................................37

7. Percent detections, ranges, means, and standard deviations of selected 

constituents in suspended-sediment samples collected from streams in the 

Austin, Texas, area during 1999–2004, from streams in the Fort Worth, Texas, area 

during 2000–2002, and from streams in Bexar County, Texas, during 2007–09 ................38

8. Results of Kruskal-Wallis nonparametric tests for differences among trace 

element, halogenated organic compound, and polycyclic aromatic hydrocarbon 

concentrations in streambed-sediment samples from sample-collection sites in 

Bexar County, Texas, 2007–09 ..................................................................................................41

9. Military installations, U.S. Environmental Protection Agency Superfund sites, 

and U.S. Environmental Protection Agency Toxics Release Inventory Program 

facilities and industries in the contributing areas of the streambed-sediment 

sampling sites in Bexar County, Texas, 2007–09 ...................................................................42
viii

10. Results of Mann-Whitney U test used to assess differences in contaminant 

concentrations measured in streambed-sediment samples on the basis of the 

presence or absence of suspected contaminant sources in selected watersheds 

of Bexar County, Texas, 2007–09 .............................................................................................43

11. Kendall’s tau nonparametric correlation coefficients between population density, 

land use, or potential sources of contamination (PSOCs) and median streambedsediment contaminant concentrations in all 20 contributing areas of the sampling 

sites in Bexar County, Texas, 2007–09 ....................................................................................44

12. Chemical mass balance model results and average fractional loading of total 

polycyclic aromatic hydrocarbons by source category for sampling sites in Bexar 

County, Texas, 2007–09 .............................................................................................................49

Conversion Factors, Datum, Water-Quality Units, and 

Selected Abbreviations

Inch/Pound to SI

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2

) 0.3861 square mile (mi2)

Volume

liter (L) 0.2642 gallon (gal)

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

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

Pressure

kilopascal (kPa) 0.009869 atmosphere, standard (atm)

kilopascal (kPa) 0.01 bar

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

°F=(1.8×°C)+32

Datum

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

Water-Quality Units 

g/kg, grams per kilogram

μg/g, micrograms per gram

μg/kg, micrograms per kilogram

μg/L, micrograms per liter

μm, micrometers

mg/L, milligrams per liter

ng/L, nanograms per liter

Selected Abbreviations

ATSDR Agency for Toxic Substances and Disease Registry

AFB Air Force Base

AFCEE Air Force Center for Engineering and the Environment

CMB Chemical mass balance

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

DSHS Department of State Health Services

DDD Common name for dichlorodiphenyldichloroethane

DDE Common name for dichlorodiphenyldichloroethylene

DDT Common name for dichlorodiphenyltrichloroethane

HAC Health-based assessment comparison

IRL Interim reporting level

LVSS Large-volume suspended-sediment 

LRL Laboratory reporting level

NAWQA National Water-Quality Assessment

NWQL National Water Quality Laboratory

PCB Polychlorinated biphenyl

PAH Polycyclic aromatic hydrocarbon

PBDE Polybrominated diphenyl ether

PSOC Potential sources of contamination

PEC Probable effect concentration

RCRA Resource Conservation and Recovery Act

SQG Sediment quality guideline

SVOC Semivolatile organic compound

SSC Suspended sediment concentration

TCEQ Texas Commission on Environmental Quality

TEC Threshold effect concentration

USEPA U.S. Environmental Protection Agency
 
Abstract

Elevated concentrations of sediment-associated 

contaminants are typically associated with urban areas such 

as San Antonio, Texas, in Bexar County, the seventh most 

populous city in the United States. This report describes an 

assessment of selected sediment-associated contaminants in 

samples collected in Bexar County from sites on the following 

streams: Medio Creek, Medina River, Elm Creek, Martinez 

Creek, Chupaderas Creek, Leon Creek, Salado Creek, and San 

Antonio River. During 2007–09, the U.S. Geological Survey 

periodically collected surficial streambed-sediment samples 

during base flow and suspended-sediment (large-volume 

suspended-sediment) samples from selected streams during 

stormwater runoff. All sediment samples were analyzed for 

major and trace elements and for organic compounds including halogenated organic compounds and polycyclic aromatic 

hydrocarbons (PAHs). Selected contaminants in streambed 

and suspended sediments in watersheds of the eight major 

streams in Bexar County were assessed by using a variety of 

methods—observations of occurrence and distribution, comparison to sediment-quality guidelines and data from previous 

studies, statistical analyses, and source indicators. 

Trace elements concentrations were low compared to the 

consensus-based sediment-quality guidelines threshold effect 

concentration (TEC) and probable effect concentration (PEC). 

Trace element concentrations were greater than the TEC in 

28 percent of the samples and greater than the PEC in 1.5 percent of the samples. Chromium concentrations exceeded 

sediment-quality guidelines more frequently than concentrations of any other constituents analyzed in this study (greater 

than the TEC in 69 percent of samples and greater than the 

PEC in 8 percent of samples). Mean trace element concentrations generally are lower in Bexar County samples compared 

to concentrations in samples collected during previous studies 

in the Austin and Fort Worth, Texas, areas, but considering 

the relatively large ranges and standard deviations associated 

with the concentrations measured in all three areas, the trace 

element concentrations are similar. On the basis of MannWhitney U test results, the presence of a military installation 

in a watershed was associated with statistically significant 

higher chromium, mercury, and zinc concentrations in streambed sediments compared to concentrations of the same elements in a watershed without a military installation.

Halogenated organic compounds analyzed in sediment 

samples included pesticides (chlordane, dieldrin, DDT, DDD, 

and DDE), polychlorinated biphenyls (PCBs), and brominated 

flame retardants. Three or more halogenated organic compounds were detected in each sediment sample, and 66 percent 

of all concentrations were less than the respective interim 

reporting levels. Halogenated organic compound concentrations were mostly low compared to consensus-based 

sediment quality guidelines—TECs were exceeded in 11 percent of the analyses and PECs were exceeded in 1 percent of 

the analyses. Chlordane compounds were the most frequently 

detected halogenated organic compounds with one or more 

detections of chlordane compounds in every watershed; 

concentrations were greater than the TEC in 6 percent of the 

samples. Dieldrin was detected in 50 percent of all samples, 

however all concentrations were much less than the TEC. The 

DDT compounds (p,p'-DDT, p,p'-DDD, and p,p'-DDE) were 

detected less frequently than some other halogenated organic 

compounds, however most detections exceeded the TECs. 

p,p'-DDT was detected in 13 percent of the samples (TEC 

exceeded in 67 percent); p,p'-DDD was detected in 19 percent 

of the samples (TEC exceeded in 78 percent); and p,p'-DDE 

was detected in 35 percent of the samples (TEC exceeded in 

53 percent). p,p'-DDE concentrations in streambed-sediment 

samples correlate positively with population density and residential, commercial, and transportation land use. One or more 

PCB congeners were detected in 90 percent of the samples. 

Additionally, total PCB concentrations in streambed-sediment 

samples correlated positively with residential, industrial, and 

mining land uses. The PCB mixtures in the samples from Leon 

Creek, Salado Creek, and the San Antonio River were dominated by PCB congeners 138, 180, and 187. The similar PCB 

congener patterns suggest similar PCB sources in the three 

watersheds. The results of the Mann-Whitney U test indicate 

that the presence of a military installation in a watershed was 

associated with statistically significant higher total chlordane, p,p'-DDE, and total PCB concentrations. Brominated 

flame retardant compounds were detected most frequently in 

Assessment of Selected Contaminants in Streambedand Suspended-Sediment Samples Collected in 

Bexar County, Texas, 2007–09

By Jennifer T. Wilson 
2 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

samples from the Medio Creek, Leon Creek, and San Antonio 

River watersheds. No sediment-quality guidelines exist for 

brominated flame retardant compounds. Mean halogenated 

organic compound concentrations generally are lower in Bexar 

County samples compared to concentrations in samples collected during previous studies in the Austin and Fort Worth 

areas. 

The PAHs were detected most frequently in samples from 

the Leon Creek and San Antonio River watersheds. Total PAH 

concentrations exceeded the TEC in 14 percent of the samples 

and none of the concentrations exceeded the PEC. Total PAH 

concentrations in streambed-sediment samples correlate 

positively with population density; residential, commercial, 

transportation, and mining land-use categories; and industrial 

wastewater outfall, wastewater liftstation, and petroleum storage tank potential source of contamination categories. Mean 

total PAH concentrations generally are lower in Bexar County 

samples compared to concentrations in samples collected during previous studies in the Austin and Fort Worth areas, but 

considering the large ranges and standard deviations associated with the concentrations measured in all three areas, total 

PAH concentrations are similar. PAH sources were investigated by comparing the ratios of individual PAH compounds 

to total PAH of several common PAH sources, such as coal 

combustion (power plants), automobile-related sources, and 

coal-tar parking lot sealcoat, and the Bexar County streambedand suspended-sediment samples. The contribution from each 

PAH source was estimated by using a chemical mass balance 

model, which indicated that parking lot coal-tar sealcoat dust 

is the largest PAH source to the average Bexar County sediment, accounting for 70.2 to 78.9 percent of the PAHs in the 

mixture. 

The overall degree of sediment contamination of the 

Bexar County sediment samples was assessed by using 

the mean PEC quotient. The incidence of sediment toxicity is highly correlated to the mean PEC quotient. Samples 

from Leon Creek at Lackland Air Force Base, Leon Creek 

at Quintana Road, Leon Creek at Interstate Highway 35, 

Leon Creek at Southwest Military Drive (Loop 13), and San 

Antonio River at Loop 410 (in order of decreasing values) had 

the highest mean PEC quotients. 

Introduction

Elevated concentrations of sediment-associated contaminants are often measured in urban areas (for example, Rice, 

1999; Wong and others, 2000; Chalmers and others, 2007). 

San Antonio, Tex. (fig. 1) currently (2010) is the seventh 

most populous city in the United States (U.S. Census Bureau, 

2009), and as in other large cities, sediment-associated contaminants have been detected in the greater metropolitan area 

and documented in previous studies. For example, bottomsediment core samples collected in August 1996 from Lorence 

Creek Lake in the Salado Creek watershed in Bexar County 

showed upward trends in zinc, chlordane, and polycyclic 

aromatic hydrocarbon (PAH) concentrations over time 

(Ging and others, 1999). Legacy pollutants—lead, DDT 

(common name for dichlorodiphenyltrichloroethane), and 

polychlorinated biphenyls (PCBs)—also were detected 

in the bottom-sediment samples collected from Lorence 

Creek Lake. Many sediment-associated contaminants pose 

a threat to aquatic organisms and human health because 

they are persistent, bioaccumulative, and (or) toxic (U.S. 

Environmental Protection Agency, 1997). The Comprehensive 

Environmental Response, Compensation, and Liability Act 

(CERCLA) requires the Agency for Toxic Substances and 

Disease Registry (ATSDR) and U.S. Environmental Protection 

Agency (USEPA) to prepare a list, in order of priority, of 

substances that are found most commonly at facilities on the 

National Priorities List and that are determined to pose the 

most substantial potential threat to human health because of 

their known or suspected toxicity and potential for human 

exposure at these National Priorities List sites (Agency for 

Toxic Substances and Disease Registry, 2007a). The 2007 

“CERCLA Priority List of Hazardous Substances” identified 

275 substances, including 43 constituents that were analyzed in samples collected in Bexar County during 2007–09 

(table 1).

Most trace elements and many human-made organic 

contaminants bind to sediments, and sediments accumulate 

on the streambed during low flows (Williamson and others, 

1998). Constituents that bind preferentially to sediments and 

do not remain in the water column in appreciable amounts are 

classified as hydrophobic (Stumm and Morgan, 1981). Many 

researchers recognize that water-quality investigations of 

hydrophobic constituents are incomplete if studies of sediment 

chemistry are not included. Bradford and Horowitz (1988, 

p. 1) note, “the strong association of numerous toxic chemicals—both organic (such as PCBs, DDT, mirex, and kepone) 

and inorganic (such as arsenic, mercury, cadmium, and lead)—

with sediment means that much of the downstream transport of 

these materials cannot be detected or evaluated solely through 

the sampling and analysis of water.” Furthermore, nonpointsource contributions of many of these contaminants might 

be intermittent or storm-related, thus single or periodic water 

sampling might not detect the contaminants (Shelton and 

Capel, 1994). Streambed-sediment samples from depositional 

environments provide a time-integrated sample of particulate 

matter transported by a stream. Suspended-sediment samples 

are useful for determining the concentration of hydrophobic 

contaminants in suspended sediments, which are ultimately 

deposited as bed sediment in a receiving water body, are in 

direct contact with aquatic biota of all trophic levels, and are 

more uniform in size and composition than streambed sediments and therefore have less spatial and temporal variability 

(Mahler and Van Metre, 2003). Passive samplers provide a 

cost effective means for collecting large-volume suspendedsediment samples that can be used to determine if a particular 

constituent is present in a stream during the rising limb of the 

hydrograph as a result of stormwater runoff (Van Metre and 

others, 2003).
Figure 1. Locations of streambed-sediment and suspended-sediment sampling sites in Bexar County, Texas, 2007–09.

ATASCOSA COUNTY

COMAL 

COUNTY

BANDERA COUNTY

KERR COUNTY

KENDALL 

COUNTY

MEDINA COUNTY

MEDINA COUNTY

BEXAR COUNTY

15'

99°30'

99°00'

45'

30'

29°30'

29°45'

Leon

Creek

Salado

Medio

Elm

Creek

Creek

San

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Lorence

Rosillo San Pedro Creek

Alazan

Lorence

Creek

Lake

MedinaLake

Mitchell

Lake

Medina

River

Cibolo

Creek

Creek

Geronimo San

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Anto

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alaveras

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Antonio River

Base modified from U.S. Geological Surveydigital data, 1:24,000 quadranglesMilitary bases from City of San Antonio digital dataTexas State Plane Coordinate System, FIPS 4204 North American Datum of 1983

Floodwater-

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0 5 1 10 5 20 MILES

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EXPLANATION

Cummulative drainage area formost downstream site of streamMedio CreekMedina RiverElm CreekMartinez CreekChupaderas CreekLeon CreekSalado CreekSan Antonio RiverStudy area boundaryMunicipal boundaryFloodwater-retention structure National Weather Service cooperative station 417945

1 ! Sediment sampling site and map identifier



Map

identifier

Site identifier

(table 2)

 1 Medio 90 2 Medio Pearsall  3 Medina 4 Elm 5 Martinez St. Hedwig 6 Martinez 1518 7 Chupaderas 8 Leon Rodriguez 9 Leon 9010 Leon Morey

11 Leon Lackland12 Leon Military13 Leon Quintana14 Leon 3515 Salado 1316 Rosillo17 Salado Southton18 SAR Theo19 SAR 41020 SAR Elmendorf

Map

identifier

Site identifier

(table 2)

Study a
4 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

The U.S. Geological Survey (USGS), in cooperation 

with the San Antonio River Authority and the San Antonio 

Metropolitan Health District Public Center for Environmental 

Health, completed a reconnaissance-level investigation of 

the contaminants in sediment samples collected from selected 

streams in Bexar County during 2007–09. The investigation 

was designed to enable decision-makers to determine which 

watershed areas have contaminants in streambed sediments 

at concentrations of concern, to assess which contaminants need further study, and to provide information on the 

sources and transport of sediment-associated contaminants 

in streams in Bexar County that drain to the San Antonio 

River. Investigations of the relations of sediment-contaminant 

concentrations to sediment-quality guidelines, possible sources 

of contamination, and land use, such as the investigation documented by this report, also can provide insight into the types 

of sediment-bound contaminants that are or might become of 

concern to aquatic life and human health (Mahler and others, 

2006). The land use of the runoff-contributing areas (hereinafter, contributing areas) for each site in Bexar County where 

sediment samples were collected during 2007–09 varies considerably (detailed land-use data were only available in Bexar 

County [Steve Gonzales, San Antonio River Authority, written 

commun., 2005]), so only land use in Bexar County was considered. The municipal boundary of San Antonio is entirely in 

Bexar County (fig. 1). Some of the contributing areas in Bexar 

County are largely urbanized (Leon Creek, Salado Creek, and 

San Antonio River) and others less so (Medio Creek, Medina 

River, Elm Creek, Martinez Creek, and Chupaderas Creek) 

(fig. 2; table 2). The less developed contributing areas provide 

information on regional background concentrations. 

Purpose and Scope

This report describes an assessment of the concentrations 

of selected hydrophobic contaminants (trace elements, halogenated organic compounds, and PAHs) in streambed-sediment 

and suspended-sediment samples collected from sites on eight 

streams (Medio Creek, Medina River, Elm Creek, Martinez 

Creek, Chupaderas Creek, Leon Creek, Salado Creek, 

and San Antonio River) in Bexar County during 2007–09. 

Observations are made about the occurrence and distribution 

of trace elements and organic compounds measured in Bexar 

County during 2007–09, including comparisons of trace element and organic contaminant concentrations among watersheds or site contributing areas and between streambed- and 

suspended-sediment samples. The frequencies with which the 

halogenated organic compounds were detected in streambedand suspended-sediment samples are assessed. 

Trace element and organic compound concentrations 

measured in Bexar County during 2007–09 (appendixes 1.1, 

1.2, and 1.3) are compared to sediment-quality guidelines; 

they are also compared to the results of previous studies by 

the USGS in Bexar County (1995–2001), to the results from 

streambed-sediment samples collected from eight U.S. Air 

Force Center for Engineering and the Environment (AFCEE) 

sampling sites during 1994–2008, and to sediment-associated 

constituents measured in sediment samples collected during 

Table 1. Constituents analyzed in streambed-sediment and suspended-sediment samples collected in Bexar County, Texas, 2007–09, 

and constituent rank on 2007 “Comprehensive Environmental Response, Compensation, and Liability Act Priority List of Hazardous 

Substances” (Agency for Toxic Substances and Disease Registry, 2007a).

Trace elements

1. Arsenic 49. Cobalt 101. Thorium 214. Silver

2. Lead 53. Nickel 109. Barium 219. Antimony

3. Mercury 74. Zinc 117. Manganese

7. Cadmium 77. Chromium 128. Copper

42. Beryllium 98. Uranium 198. Vanadium

Halogenated organic compounds

5. Polychlorinated biphenyls 21. p,p'-DDE 64. trans-Chlordane 171. Oxychlordane

12. p,p'-DDT 25. p,p'-DDD 93. Hexachlorobenzene

17. Dieldrin 57. Endosulfan I 127. Chlorpyrifos

20. Chlordane 59. cis-Chlordane 150. Trifluralin

Polycyclic aromatic hydrocarbons

8. Polycyclic aromatic hydrocarbons 39. Benzo(a)anthracene 137. Chrysene 253. Pyrene

9. Benoz(a)pyrene 62. Benzo(k)fluoranthene 161. Acenaphthene

10. Benzo(b)fluoranthene 78. Naphthalene 174. Indenopyrene

15. Dibenzo(a,h)anthracene 110. Fluoranthene 246. Pheananthrene
Introduction 5

Figure 2. Land use in associated contributing area of each site where streambed-sediment and suspended-sediment samples were 

collected in Bexar County, Texas, 2007–09. 

Camp Stanley Camp Bullis

Ft. Sam

Houston

Martindale Army

Air Field

Brooks

Air Force 

Base

Lackland Air

Force Base

Former Kelly Air

Force Base

Randolph Air 

Force Base

!

!

!

!

!

!

!

!

!

!

! !

!

!

!

!

!

!

!

!

Calaveras Cree k

Parita Creek

Calaveras

Lake

River

San Antonio

Braunig

Lake

Elm

Creek

Leon

Creek

Salado

Medio

Creek

San

Apache 

Rosillo

Alazan

Cibolo

Creek

Creek

Geronimo

San

Creek

Creek

Creek

Creek

Saltrillo

Creek

Antonio

Medina

River

Zarzamora 

Creek

Indian

Creek

Martinez

Salado

Creek

Creek

Culebra

Creek

San Pedro

Creek

MartinezCreek Mitchell

Lake

Chupaderas Creek

98°10'

20'

30' 98°40'

29°40'

30'

20'

29°10'

WILSON COUNTY

BEXAR COUNTY

ATASCOSA COUNTY

COMAL 

KENDALL 

COUNTY

MEDINA COUNTY

COUNTY

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Base modified from U.S. Geological Survey

digital data, 1:24,000 quadrangles

Military bases from City of San Antonio digital data

Texas State Plane Coordinate System, FIPS 4204 

North American Datum of 1983

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Land use

Undeveloped

Open space

Residential

Commercial

Industrial

Transportation

Mining

Utilities

Water

Site contributing area boundary

Study area boundary

Military base boundary

! Sediment sampling site and map identifier 20

Map

identifier

Site identifier

(table 2)

 1 Medio 90

 2 Medio Pearsall 

 3 Medina

 4 Elm

 5 Martinez St. Hedwig

 6 Martinez 1518

 7 Chupaderas

 8 Leon Rodriguez

 9 Leon 90

10 Leon Morey

11 Leon Lackland

12 Leon Military

13 Leon Quintana

14 Leon 35

15 Salado 13

16 Rosillo

17 Salado Southton

18 SAR Theo

19 SAR 410

20 SAR Elmendorf

Map

identifier

Site identifier

(table 2)

BEXAR COUNTY

Study area Area enlarged

Land use from Steve Gonzales, San Antonio River

Authority (written commun., 2005)
Table 2. Characteristics of associated contributing area of each site where streambed-sediment and suspended-sediment samples were collected 2007–09. [km2, square kilometers; --, not applicable] U.S. Geological Survey station number and name Map identi- fier (figs. 1, 2, 4, 14) Site identifier Site contri- buting area1 (km2) Popu- lation2 (per km2) Land-use category3 (percent) 

Un- devel- oped Open space Resi- dential Com- mer- cial Indus- trial Trans- por- tation Min

ing 

08180740 Medio Creek at U.S. Highway 90, San Antonio, Tex. 1 Medio 90 100 453 66.0 4.7 17.8 2.8 0.59 7.7 0 

08180750 Medio Creek at Pearsall Road, San Antonio, Tex. 2 Medio Pearsall 123 425 58.1 11.9 18.1 2.5 1.5 7.5 0 

08181500 Medina River at San Antonio, Tex. 3 Medina 3,368 112 65.7 7.3 14.4 2.2 2.6 6.7 .25 

08180840 Elm Creek at State Highway 16, San Antonio, Tex. 4 Elm 195 54 79.2 8.7 4.9 .79 .39 4.9 0 

08185100 Martinez Creek near St. Hedwig, Tex. 5 Martinez St. Hedwig 210 329 58.1 16.8 12.0 2.7 .64 8.1 0 

08185095 Martinez Creek at Farm Road 1518 near St. Hedwig, Tex. 6 Martinez 1518 152 415 54.9 17.6 11.0 3.5 .81 10.2 0 

08182410 Chupaderas Creek at State Road 106 near San Antonio, Tex. 7 Chupaderas 19 61 83.6 5.0 5.0 .46 .46 3.0 0 

292443098364600 Leon Creek at Rodriguez Park, San Antonio, Tex. 8 Leon Rodriguez 488 422 58.4 5.6 21.3 3.7 1.6 8.4 .64 

08181445 Leon Creek at State Highway 90, San Antonio, Tex. 9 Leon 90 491 424 58.3 5.5 21.4 3.7 1.6 8.5 .64 

292338098360501 Leon Creek at Morey Road, San Antonio, Tex. 10 Leon Morey 500 422 58.0 5.6 21.2 3.6 1.9 8.6 .63 

292240098353600 Leon Creek at Lackland Air Force Base golf course, San Antonio, Tex. 11 Leon Lackland 513 434 56.7 6.0 22.1 3.6 2.1 8.5 .61 

292156098350900 Leon Creek at Southwest Military Drive, San Antonio, Tex. 12 Leon Military 517 440 56.3 6.2 22.2 3.6 2.3 8.5 .61 

292029098351400 Leon Creek at Quintana Road, San Antonio, Tex. 13 Leon Quintana 532 433 55.3 6.0 21.7 3.5 4.2 8.4 .59 

08181480 Leon Creek at Interstate Highway 35, San Antonio, Tex. 14 Leon 35 536 429 55.3 6.0 21.6 3.5 4.3 8.5 .58 

08178800 Salado Creek at Loop 13, San Antonio, Tex. 15 Salado 13 479 616 28.2 4.8 43.3 4.8 6.0 12.0 .44 

08178825 Rosillo Creek at New Sulphur Springs Road, San Antonio, Tex. 16 Rosillo 70 657 41.0 3.8 24.6 4.6 11.9 13.5 0 

08178830 Salado Creek at Southton Road, San Antonio, Tex. 17 Salado Southton 571 602 31.6 4.7 39.6 4.7 6.6 12.1 .37 

08178505 San Antonio River at Theo Avenue, San Antonio, Tex. 18 SAR Theo 229 1768 6.1 3.1 50.9 7.3 5.3 25.7 1.18 

08178565 San Antonio River at Loop 410, San Antonio, Tex. 19 SAR 410 297 1765 7.0 2.5 51.1 6.1 6.3 25.7 .91 

08181800 San Antonio River near Elmendorf, Tex. 20 SAR Elmendorf 4,508 290 49.9 5.9 25.1 3.2 4.1 10.5 .33 

Median 483 427 56.5 5.7 21.5 3.5 2.2 8.5 .40 

1 Sum of all contributing areas for sites on a given stream is considered the watershed for that stream. 2 U.S. Census Bureau, 2001. 3 Land use digital data from Steve Gonzales, San Antonio River Authority, written commun., 2005.
Introduction 7

previous studies in the Austin and Fort Worth, Tex., areas. 

Inferences concerning potential sources of the contaminants 

measured in the eight watersheds where samples were collected are made by analyzing potential sources of contamination and land use in the contributing area for each samplecollection site in Bexar County by evaluating trace element 

and organic compound concentrations with statistical analyses, 

including:

•	 Similarity of or difference between contaminant concentration by watershed;

•	 Relations between land use and potential sources of 

contaminants measured in streambed- and suspendedsediment samples; and

•	 A preliminary evaluation of possible sources of the 

PCBs and PAHs measured in streambed-sediment 

samples. 

Description of Study Area

The study area consists of the cumulative drainage 

areas (watersheds) for eight streams where streambed- and 

suspended-sediment sites were sampled in Bexar County 

during 2007–09 (fig. 1). The sampling sites are located in 

the contributing areas of the following eight streams: Medio 

Creek, Medina River, Elm Creek, Martinez Creek, Chupaderas 

Creek, Leon Creek, Salado Creek, and San Antonio River. The 

sum of all contributing areas for sites on a given stream is considered the watershed for that stream. The watersheds for the 

sampling sites compose most of Bexar County, as well as parts 

of adjacent counties to the west and north (fig. 1). Most of the 

urban development in the study area has occurred in Bexar 

County where San Antonio is located. For each sampling site, 

the part of the contributing area located in Bexar County is 

delineated in figure 2. Characteristics of the contributing area 

for each sampling site such as size, population density, land 

use (table 2), and potential sources of contamination vary 

widely. Most contributing areas in the study area drain to the 

downstream-most sampling site on the San Antonio River 

(USGS station 08181800 San Antonio River near Elmendorf, 

Tex.) (hereinafter, SAR Elmendorf site [fig. 2, map identifier 20]). Martinez Creek is the easternmost stream of the eight 

major streams in the study area sampled for this study and 

the only stream that does not contribute flow directly to the 

San Antonio River. Martinez Creek in eastern Bexar County 

drains toward the east into Cibolo Creek, which flows into 

the San Antonio River north of Karnes City, Tex. (approximately 90 kilometers [km] southeast of San Antonio). The 

population density and percentages of residential, commercial, and industrial land use are lowest in the Elm Creek and 

Chupaderas Creek contributing areas and highest in the Salado 

Creek and San Antonio River contributing areas (table 2). 

Population density and percentages of residential, commercial, 

and industrial land use in the Leon Creek contributing area are 

typical (near the median) for the study area in Bexar County. 

There are several military installations in Bexar County, and 

the land use for each military installation includes a mixture 

of undeveloped, residential, commercial, industrial, and open 

space (fig. 2). The Camp Bullis Military Training Reservation 

in northern Bexar County is in the contributing area of USGS 

station 08178800 Salado Creek at Loop 13, San Antonio, Tex. 

(hereinafter, Salado 13 site [fig. 2, map identifier 15]). When 

Loop 13 was built, much of the road incorporated parts of the 

older Southwest Military Drive, and official station names 

in the USGS National Water Information System (NWIS) 

(U.S. Geological Survey, 2011) refer to Loop 13 or Southwest 

Military Drive depending on when the station was installed 

(A.M. Miller, U.S. Geological Survey, oral commun., 2011). 

The former Kelly Air Force Base (AFB), which was decommissioned in 2001, is mostly in the contributing areas of 

USGS stations 292240098353600 Leon Creek at Lackland 

AFB golf course, San Antonio, Tex. (hereinafter, Leon 

Lackland site [fig. 2, map identifier 11]); 292156098350900 

Leon Creek at Southwest Military Drive, San Antonio, Tex. 

(hereinafter, Leon Military site [fig. 2, map identifier 12]); 

and 292029098351400 Leon Creek at Quintana Road, San 

Antonio, Tex. (hereinafter, Leon Quintana site [fig. 2, map 

identifier 13]). Most of Lackland AFB is in the contributing 

area of USGS station 08180750 Medio Creek at Pearsall Road, 

San Antonio, Tex. (hereinafter, Medio Pearsall site [fig. 2, 

map identifier 2]). Randolph AFB is partly in the contributing 

area of USGS station 08185095 Martinez Creek at Farm Road 

1518 near St. Hedwig, Tex. (hereinafter, Martinez 1518 site 

[fig. 2, map identifier 6]) and partly in the contributing area 

of USGS station 08185100 Martinez Creek near St. Hedwig, 

Tex. (hereinafter, Martinez St. Hedwig site [fig. 2, map identifier 5]). Fort Sam Houston is in the contributing area of the 

Salado 13 site. Brooks AFB is in part of the contributing areas 

of USGS station 08178565 San Antonio River at Loop 410, 

San Antonio, Tex. (hereinafter, SAR 410 site [fig. 2, map identifier 19]) and the SAR Elmendorf site.

The locations of floodwater-retention structures in 

the study area were compiled by the San Antonio River 

Authority (John Refolo, written commun., 2010). A total of 

44 floodwater-retention structures (small dams) on streams are 

depicted in figure 1. Not all streams and floodwater-retention 

structures in the study area are depicted; according to the San 

Antonio River Authority, there are 89 floodwater-retention 

structures in the study area, many of which are on first-order 

streams not shown on figure 1. The floodwater-retention structures trap sediment during stormwater runoff, preventing some 

of the sediment from being transported downstream. 

The Texas Commission on Environmental Quality 

(TCEQ) is required by the 1996 Safe Drinking Water Act 

Amendments to assess every public drinking water source 

for susceptibility to certain chemicals (Texas Commission 

on Environmental Quality, 2009a). The TCEQ Source Water 

Assessment Program (SWAP) fulfills that requirement and 

includes a detailed listing of potential sources of contamination (PSOC) that might affect source waters. Although 

San Antonio drinking water is not obtained from any of the 
8 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

streams in the study area (San Antonio Water System, 2009), 

the SWAP PSOC list is useful for understanding what chemicals are known to be present in the contributing areas of sites 

where streambed- and suspended-sediment samples were collected during 2007–09 (fig. 3). The top 10 PSOC categories in 

the contributing area of each site in Bexar County were identified and ranked on the basis of the standard area of impact 

(Texas Commission on Environmental Quality, 2009a) designated for each type of PSOC (fig. 3). Abandoned municipal 

solid-waste landfills and industrial wastewater outfalls are the 

most common PSOC in all contributing areas in Bexar County. 

TCEQ determined that the third most prominent PSOC at each 

site in the Leon Creek contributing areas are active or abandoned mined lands (fig. 3). Plastic manufacturing and sales 

and septic systems are not shown in figure 3 because of their 

low occurrence (0 to 4 percent for both PSOC categories) in 

all contributing areas except in the contributing areas of the 

Medio sites, where plastic manufacturing and sales and septic 

systems represent 11 to 16 percent of the PSOC categories. 

Previous Studies

The USGS and other Federal agencies and State agencies have assessed the concentrations of various contaminants 

in Bexar County streams in previous studies. This section 

provides a brief review of those sampling efforts, the results of 

which are useful for comparison to the results obtained from 

samples collected during 2007–09. Samples collected during 

previous studies were obtained at the same sampling sites used 

during 2007–09 (or at nearby locations) and were analyzed for 

the same constituents as the 2007–09 samples. 

The USGS collected streambed-sediment samples at the 

Medio Pearsall site, at USGS station 08181480 Leon Creek at 

Interstate Highway 35, San Antonio, Tex., (hereinafter, Leon 

35 site; [fig. 2, map identifier 14]), and at the Salado 13, SAR 

410, and SAR Elmendorf sites between 1995 and 2001. The 

samples were analyzed for trace elements, halogenated organic 

compounds, and PAHs. During 1995–97, the USGS collected 

biological samples (organisms) at the Leon 35, Salado 13, and 

SAR Elmendorf sites. The organisms were analyzed for trace 

elements or halogenated organic compounds, or both. Detailed 

comparisons between previous USGS sampling results and 

the 2007–09 results are provided in the section of this report 

entitled “Comparison of Findings to Data from Previous 

Studies.” 

In 1982, an Installation Restoration Program (IRP) at 

Kelly AFB initiated the investigation and cleanup of contaminated sites on the base. The AFCEE oversees compliance 

sampling of groundwater, Leon Creek surface water, and 

sediment near the former Kelly AFB, done semiannually as 

required by TCEQ hazardous waste and permit compliance 

(Paul Carroll, Department of Defense, Defense Base Closure 

and Realignment Commission, Environmental Coordinator, 

personal commun., January 2011). AFCEE sampled 31 sites 

on Leon Creek during 1994–2008 for streambed sediment; 8 

of those 31 sites were selected for comparison to the 2007–09 

results on the basis of their proximity to the 7 USGS Leon 

Creek streambed-sediment sampling sites (fig. 4) and the 

availability of similar analytical results at the sites. Among 

the constituents of interest for this report, p,p'-DDT and 

PCBs were analyzed in samples from the eight AFCEE sites. 

Detailed comparisons between the results of semiannual compliance sampling and the present USGS study are provided in 

the “Comparison of Findings to Data from Previous Studies” 

section of this report. 

The industrial processes associated with military operations at the former Kelly AFB involved many hazardous 

substances. Industrial wastes entered the environment through 

leaks, spills, and previously approved disposal practices (U.S. 

Air Force, 2007). A tier 2 screening level ecological risk 

assessment (CH2M Hill, 2001) provided descriptions of the 

historical operations at sites affected by industrial wastes near 

Leon Creek at the former Kelly AFB. For the assessment, 

CH2M Hill divided the former Kelly AFB into five areas or 

zones; Leon Creek flows through or adjacent to zones 1 and 2. 

Eleven sites in zone 1 and 16 sites in zone 2 were evaluated. 

Zone 1 included sites used for the disposal of scrap metal, 

munitions, electroplating sludge, pesticides, and waste petroleum, oil, and lubricants. A waste oil burn pit or chemical disposal pit was also at one of the disposal sites. One site was a 

sludge spreading area for waste sludge containing high heavy 

metal concentrations. Zone 2 included a disposal pit for chromium plating sludge and waste; a chemical evaporation pit for 

disposal of solvents, insecticides, and sludges; two industrial 

waste treatment plants (IWTPs) that received plating, painting, 

and degreasing effluents; a liquid incineration site that handled 

pesticides; an industrial waste lagoon; and a sludge spreading 

area for wastes from a former IWTP. Many of these sites were 

regraded (leveled) and filled, capped, or remediated. However, 

the ecological risk assessment identified the presence of contaminants in surface soils at the affected sites, including trace 

elements, pesticides, PCBs, and PAHs (CH2M Hill, 2001, 

appendix B, table 5–3), and migration pathways from the 

affected sites to Leon Creek, primarily through overland flow 

associated with storms.

Although the former Kelly AFB receives considerable 

attention from Federal and State regulatory agencies, in part 

because fish consumption advisories were issued in 2003 and 

2010 (Texas Department of Health, 2003; Texas Department 

of State Health Services, 2010) for the reach of Leon Creek 

between State Highway 90 and Loop 13, environmental 

investigations also have been done at all other military installations in Bexar County. For example, the ATSDR performed a 

public health assessment in 1998 at Brooks AFB to investigate 

volatile organic compound (VOC) contamination of groundwater attributed to a fire protection training area. The ATSDR 

concluded that the groundwater contamination did not present 

a public health hazard (Agency for Toxic Substances and 

Disease Registry, 1998). A USEPA facility report on Brooks 

AFB lists the installation in the Air Facility, (hazardous waste) 

Biennial Reporters, CERCLA, National Compliance, Resource 

Conservation and Recovery Act (RCRA), and Safe Drinking 
Figure 3. Top 10 potential sources of contamination (Texas Commission on Environmental Quality, 2009a) in contributing areas of sites where streamsuspended-sediment samples were collected in Bexar County, Texas, 2007–09. 

0

102030405060708090

100

Medio 90

Medio Pearsall

Medina

Elm

Martinez St. Hedwig

Martinez 1518

Chupaderas

Leon Rodriguez

Leon 90

Leon Morey

Leon Lackland

Leon Military

Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR 410

SAR Theo

SAR Elmendorf

Potential sources of contamination

in drainage area of site, in percent

Site identifier (table 2)

Top 10 potcontaminAbandoneIndustrial WastewatWastewatActive or WastewatPetroleum Active muChemical Auto repa
10 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 4. Location of U.S. Air Force Center for Engineering and the Environment (AFCEE) and U.S. Geological Survey (USGS) 

streambed-sediment sampling sites on Leon Creek, Bexar County, Texas. 

!(

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!(

!(

!(

!(

!(

!(

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!(

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!(

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Former

Kelly Air

Force Base

£¤151

£¤90

§ ̈¦35

Morey Rd. Southwest Military Drive (Loop 13)

Quintana Rd.

Growdon Rd.

Indian

Medio Creek

Leon

14

13

12

11

10

9

8

Lackland

Air Force

Base

LC065

LC066

LC040

LC063

LC024

LC015

LC067

LC068

RODRIGUEZ 

PARK

Loop 410

Zone 1

Zone 2

Creek

Creek

36' 98°34'

29°25'

24'

23'

22'

21'

29°20'

98°38'

Map

identifier

Site identifier

(table 2)

 8 Leon Rodriguez

 9 Leon 90

10 Leon Morey

11 Leon Lackland

12 Leon Military

13 Leon Quintana

14 Leon 35

BEXAR COUNTY

Area enlarged

Base modified from U.S. Geological Survey digital data, 1:24,000 quadrangles

Military bases and highways from Texas Natural Resources

Information System (http://www.tnris.state.tx.us/)

Texas State Plane Coordinate System, FIPS 4204

North American Datum of 1983

0 1 0.5 KILOMETER

0 1 0.5 MILE

!(

!(

Military base boundary

USGS streambed-sediment sampling

site and map identifier

AFCEE streambed-sediment sampling

site and identifier (appendix 4)

EXPLANATION

11

LC068

Medio Creek watershed 

Medina River watershed 

Leon Creek watershed 

San Antonio River watershed 

CH2M Hill zone 1 and 2 boundaries

Former Kelly Air Force Base 

golf course
Introduction 11

Water information systems (U.S. Environmental Protection 

Agency, 2011). It is classified as a small-quantity generator of 

hazardous wastes, producing less than 1,000 kilograms (kg) 

but more than 100 kg of hazardous wastes per month. Mostly 

laboratory wastes and chemicals are products of laboratory test 

procedures (Brooks Air Force Base, 2000). In 2008, the U.S. 

Army Environmental Command (2009) evaluated the environmental restoration sites at Camp Bullis and Fort Sam Houston. 

Camp Bullis environmental restoration activities are being 

done under the RCRA; Fort Sam Houston environmental 

restoration activities are being done under the CERCLA and 

the Clean Water Act (U.S. Army Environmental Command, 

2009). The TCEQ is the lead agency for environmental 

restoration activities at Camp Bullis and Fort Sam Houston. 

One landfill at Camp Bullis and 11 landfills at Fort Sam 

Houston are open sites under the IRP. Camp Bullis and Fort 

Sam Houston each have two munitions sites that are open sites 

under the Military Munitions Response Program. Additionally, 

there are three Compliance Cleanup open sites—an open burn/

open detonation site at Camp Bullis, a former dry cleaning facility at Fort Sam Houston, and a newly discovered 

landfill suspected to contain construction debris at Fort Sam 

Houston (U.S. Army Environmental Command, 2009). A 

USEPA facility report on Lackland AFB lists the installation in the Air Facility, CERCLA, Integrated Compliance, 

National Compliance, National Emissions, RCRA, Safe 

Drinking Water, and Toxics Release Inventory systems (U.S. 

Environmental Protection Agency, 2010b). Randolph AFB is 

listed in the Air Facility, Integrated Compliance, RCRA, Safe 

Drinking Water, and Toxic Release Inventory information 

systems (U.S. Environmental Protection Agency, 2010a). 

The Texas Department of State Health Services (DSHS) 

Seafood and Aquatic Life Group (formerly Texas Department 

of Health Seafood Safety Division) tests for certain contaminants in tissue samples to inform recreational fishermen of 

possible disease or contamination in fish and other aquatic 

species. Fish from the San Antonio River were tested in 1998 

for trace elements, pesticides, PCBs, semivolatile organic 

compounds (SVOCs), and VOCs and were determined to 

pose no apparent public health hazard (Texas Department 

of State Health Services, 2008). A fish consumption advisory 

for the lower Leon Creek reach was issued for PCBs in all 

species of fish on the basis of analytical results from 22 

fish skin-off fillet samples obtained from fish collected in 

2002 from three sites near sites in this study—USGS station 

08181445 Leon Creek at State Highway 90, San Antonio, 

Tex. (hereinafter, Leon 90 site [fig. 2, map identifier 9]); Leon 

Lackland (referred to as KAFB by the DSHS); and Leon 

Military (Texas Department of Health, 2003). The tissues 

were analyzed for trace elements (no chromium), pesticides, 

PCBs, SVOCs, and VOCs. At least one contaminant was 

detected in every sample. Although the concentrations of 

most constituents were not much larger than the respective 

laboratory reporting limit (LRL) established by the analytical laboratory for each constituent, concentrations of PCBs 

in some samples were much greater than the respective LRL. 

Mercury, selenium, and zinc were detected (concentrations 

greater than the respective LRL) in all samples; in contrast, 

arsenic and lead were not detected (concentrations less than 

the respective LRL) in any samples. Chlordane and p,p'-DDE 

were commonly detected in fish from all three sites. The compound p,p'-DDT was detected at low concentrations in some 

samples from a site near the former Kelly AFB golf course. 

PCBs were detected in fish tissues from all three Leon Creek 

sites (Leon 90, Leon Lackland, and Leon Military); the most 

frequent detections and highest PCB concentrations, particularly Aroclor 1260, were detected in samples collected from 

the Leon Lackland site near the former Kelly AFB golf course 

(fig. 4). The Texas Department of Health (2003) concluded 

that all trace element and pesticide concentrations were low, 

did not exceed the health-based assessment comparison (HAC) 

values, and were therefore of no toxicological significance, 

but that consumption of any fish species from Leon Creek 

at or near the former Kelly AFB golf course poses a public 

health hazard because the fish might contain unsafe amounts 

of PCBs. 

The DSHS resampled fish in Leon Creek in November 

2007 and analyzed skin-off fillet samples from 50 edible 

fish to assess potential adverse human health effects from 

consumption of fish from the stream (Texas Department of 

State Health Services, 2010). The fish were collected during 

2007 by the DSHS from five sites where sediment samples 

were collected by the USGS during 2007–09—USGS station 292443098364600 Leon Creek at Rodriguez Park, San 

Antonio, Tex. (hereinafter, Leon Rodriguez site [fig. 2, map 

identifier 8]); Leon 90; Leon Lackland (called KAFB by the 

DSHS); Leon Quintana (called Ruiz Ranch by the DSHS 

); and Leon 35. Analyses included trace elements (no chromium), pesticides, PCB congeners, VOCs, SVOCs, and congeners of polychlorinated dibenzofurans (PCDFs) or dibenzop-dioxins (PCDDs), or both. VOC and SVOC concentrations 

did not exceed levels of concern (Texas Department of State 

Health Services, 2010). Copper, lead, mercury, selenium, and 

zinc were detected (concentrations greater than the respective 

LRL) in all samples. Arsenic was detected in 31 of 50 fish 

samples and cadmium was less than the LRL in all samples. 

In 10 of 50 samples analyzed for pesticides, p,p'-DDE and 

chlordane concentrations were greater than the applicable 

LRL. PCB concentrations greater than the LRL for each 

congener were detected in all fish tissue samples. PCBs were 

the only contaminant that equaled or exceeded the HAC values 

for evaluating systemic (noncancerous) adverse human health 

effects (HACnoncan) from consumption of fish from Leon Creek. 

PCB concentrations in fish samples from Leon 90, Leon 

Lackland (KAFB), Leon Quintana (Ruiz Ranch), and Leon 35 

exceeded DSHS guidelines for protection of human health. No 

trace elements or other organic compounds were detected at 

concentrations of public health concern (Texas Department of 

State Health Services, 2010).

Every 2 years, the TCEQ determines if surface-water 

bodies in Texas are meeting State water-quality standards on 

the basis of available data and recently reported its findings 
12 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

in the “Draft 2010 Texas Integrated Report for Clean Water 

Act Sections 305(b) and 303(d)” (Texas Commission on 

Environmental Quality, 2010b), formerly called the “Texas 

Water Quality Inventory and 303(d) List.” Water bodies 

that are not meeting the water-quality standards established 

for their intended use (such as aquatic life, recreation, fish 

consumption, or general use) are included in the report. Once 

water bodies are added to the impaired or 303(d) list, the State 

develops and implements strategies to meet those standards 

(Texas Commission on Environmental Quality, 2010b). The 

draft 2010 list of impaired water bodies includes Cibolo 

Creek from its confluence with the San Antonio River north 

of Karnes City to a point 100 meters (m) downstream from 

Interstate Highway 10 in Bexar County. This reach of Cibolo 

Creek is included because of high levels of bacteria and an 

impaired fish community; it receives runoff from the contributing areas of the Martinez 1518 and Martinez St. Hedwig 

sites. Segments of Leon Creek from its confluence with the 

Medina River to its confluence with Indian Creek are listed 

as impaired, including the segment extending 3 km upstream 

from Highway 353, which is listed as impaired because of 

low dissolved oxygen concentrations, as are the segment 

from 3 km upstream from Highway 353 to U.S. Highway 90 

and the segment from 5 km upstream from the confluence 

with Medina River to the confluence with Indian Creek. The 

segment of Leon Creek from 3 km upstream from Highway 

353 to U.S. Highway 90 also is listed as impaired because of 

PCB detections in edible fish tissue. Salado Creek is listed 

because of impaired fish and macrobenthic communities, and 

the San Antonio River upstream from San Pedro Creek is 

listed because of an impaired fish community. Apache Creek 

from its confluence with San Pedro Creek to just upstream 

from its confluence with Zarzamora Creek is listed because 

of high bacteria levels; Alazan Creek from its confluence 

with Apache Creek upstream to its confluence with a small 

tributary named Martinez Creek (different from the Martinez 

Creek in eastern Bexar County from which samples were collected) and San Pedro Creek from its confluence with the San 

Antonio River to its confluence with Apache Creek also are 

listed because of high bacteria levels. These three streams are 

new additions to the draft 2010 list of impaired water bodies 

since the last list was prepared in 2008 (Texas Commission 

on Environmental Quality, 2010b). Apache, Alazan, and 

San Pedro Creeks are tributaries to the San Antonio River 

upstream from USGS station 08178505 San Antonio River at 

Theo Avenue, San Antonio, Tex. (hereinafter, SAR Theo site 

[fig. 2, map identifier 18]). These impairments were attributed 

to non-point, unknown point, or unknown sources; loss of 

riparian habitat; dams or impoundments; or habitat modification (Texas Commission on Environmental Quality, 2010b). 

Medio Creek, Medina River, and Rosillo Creek (fig. 1) were 

evaluated but not listed. Concerns noted but not on the 303(d) 

list are measurable cadmium and silver concentrations in Leon 

Creek sediment from its confluence with the Medina River 

to its confluence with Indian Creek (Texas Commission on 

Environmental Quality, 2010b). 

Methods

The USGS periodically collected surficial streambedsediment samples during base flow and suspended-sediment 

samples during periods of stormwater runoff from selected 

streams. The collection of streambed-sediment samples 

was based on methods of the USGS National Water-Quality 

Assessment (NAWQA) program (Shelton and Capel, 1994). 

The NAWQA streambed-sediment collection guidelines 

recommend collecting fine-grained particulates from 5 to 10 

depositional zones along a stream reach about 100 m in length, 

however 2 to 5 depositional zones along stream reaches ranging from 60 to 500 m in length were sampled in Bexar County 

during 2007–09 (table 3) because many suitable depositional 

zones were too deeply inundated with water to wade, too 

widely spaced along the stream reach, inaccessible because of 

thick vegetation or steep banks, or in access-restricted parts of 

military installations.

When possible, sites where the USGS collected samples 

during 2007–09 were at or near previous sediment or biological sampling locations and at existing USGS streamflowgaging stations. The streambed-sediment sampling sites were 

located along stream reaches with several depositional zones 

that could be readily sampled by wading the stream. All sites 

were required to be underwater during sampling because 

comparability of wet to dry sediment chemistry is unreliable, 

especially for organic compounds (Shelton and Capel, 1994). 

Furthermore, the site locations were selected on the basis of 

their physical accessibility by field personnel.

The amount of urban development differs among contributing areas in Bexar County for each of the eight streams. 

Urban development is greater in the contributing areas for 

Leon Creek, Salado Creek, and San Antonio River compared to the contributing areas for Medio Creek, Medina 

River, Elm Creek, Martinez Creek, and Chupaderas Creek. 

Streambed- and suspended-sediment samples were collected 

more frequently from sites in the more developed contributing areas compared to sites in the less developed contributing 

areas. Two or more streambed-sediment sampling sites were 

selected in the contributing areas of each of the eight streams 

in Bexar County and their major tributaries, with the following 

exceptions: One site on Elm Creek (USGS station 08180840 

Elm Creek at State Highway 16, San Antonio, Tex. [hereinafter, Elm site; fig. 2, map identifier 4]); one site on the Medina 

River downstream from Elm Creek (USGS station 08181500 

Medina River at San Antonio, Tex. (hereinafter, Medina site; 

fig. 2, map identifier 3]); and one site on Chupaderas Creek 

(USGS station 808182410 Chupaderas Creek at State Road 

106 near San Antonio, Tex. [hereinafter, Chupaderas site; 

fig. 2, map identifier 7]). Calaveras Creek was considered 

for sampling but was dry during field reconnaissance. Five 

biological-monitoring sites and numerous existing streambedsediment sampling sites on Leon Creek were sampled semiannually for AFCEE compliance (for example, CH2M 

Hill, 1999) for regulatory (compliance-monitoring) purposes (fig. 4); locations of existing sampling sites on Leon 
Methods 13

Creek were used to help determine the locations of sites on 

Leon Creek that were sampled during 2007–09. The Leon 

Rodriguez site was the most upstream site sampled for 

streambed sediments during 2007–09; Leon Creek upstream 

from the Leon Rodriguez site is usually dry except immediately after a storm. The SAR Theo site was sampled only one 

time because construction of bank-retention walls and other 

channel improvements began at the site after the first sample 

was collected, disturbing the soils and sediments in the stream 

channel (Brian Petri, U.S. Geological Survey, written commun., 2007). 

In addition to collecting streambed-sediment samples, 

large-volume suspended-sediment (LVSS) samples were collected at selected sites. LVSS samples were collected from 

the downstream-most sites on Martinez Creek (Martinez St. 

Hedwig site), Leon Creek (Leon 35 site), and Salado Creek 

(USGS station 08178830 Salado Creek at Southton Road, San 

Antonio, Tex. [hereinafter, Salado Southton site; fig. 2, map 

identifier 17), from the SAR 410 and SAR Elmendorf sites 

on the San Antonio River, and from the Medina site on the 

Medina River (fig. 1; table 3). The LVSS sampler was installed 

at the SAR 410 site upstream from where the Medina River 

and Salado Creek flow into the San Antonio River (fig. 1).

Sample Collection

The location of each sampling site was documented by 

using a global positioning system (GPS), digital photographs, 

and field notes to describe the site relative to surrounding 

landmarks, as well as plotting the site on USGS quadrangle 

maps or smaller scale site maps when necessary. Streambedsediment and LVSS samples were collected more frequently 

at sites with more developed contributing areas (sites on Leon 

Creek, Salado Creek, and San Antonio River) compared with 

sites with less development in their contributing areas (sites on 

Medio Creek, Medina River, Elm Creek, Martinez Creek, and 

Table 3. Streambed-sediment and suspended-sediment samples collected in contributing areas of sites in Bexar County, Texas, 

2007–09.

[Shading indicates streambed-sediment sample; X indicates large-volume suspended-sediment sample]

Map identifier

(figs. 1, 2, 4, 14)

Site identifier

(table 2)

Length of reach 

(meters)

Number of 

depositional 

zones1

Collection of samples

2007 2008 2009

1 Medio 90 170 3

2 Medio Pearsall 160 3

3 Medina 130 4 X

4 Elm 60 3

5 Martinez St. Hedwig 90 5 X X

6 Martinez 1518 100 3

7 Chupaderas 90 4

8 Leon Rodriguez 190 3

9 Leon 90 180 3

10 Leon Morey 230 5

11 Leon Lackland 500 4

12 Leon Military 100 3

13 Leon Quintana 180 4

14 Leon 35 160 4 X X

15 Salado 13 90 3

16 Rosillo 190 5

17 Salado Southton 130 4 X X

18 SAR Theo 100 3

19 SAR 410 260 4 X

20 SAR Elmendorf 190 2 X X

1

 Streambed-sediment sample for each site composited from multiple depositional zones within a single stream reach.
14 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Chupaderas Creek) (fig. 2). The LVSS samples were collected 

at some sites that were active USGS streamflow-gaging stations (Medina, Martinez St. Hedwig, Leon 35, SAR 410, and 

SAR Elmendorf sites). The number of depositional zones, type 

of sample, and year of sample collection at each site are shown 

in table 3. 

Sampling began in November 2007 and was completed 

in August 2009. Streambed-sediment samples were collected 

during November and December 2007; February, March, 

April, and August 2008; and August 2009. LVSS samples 

were retrieved after rainfall caused sufficient runoff for sampling, which varied depending on the site. LVSS samples were 

collected in July and August 2008, and March and May 2009 

(fig. 5). Fewer LVSS samples were collected than originally 

planned because relatively few storms resulted in sufficient 

runoff for sampling during the study period. Figure 5 shows 

rainfall for National Weather Service cooperative station 

417945 San Antonio International Airport during November 

2007–August 2009. 

Streambed-Sediment Samples

Streambed-sediment samples were composited from 

multiple depositional zones within a single stream reach at 

each site (table 3). The smallest number of depositional zones 

sampled was two zones at the SAR Elmendorf site, where field 

personnel were only able to access areas of thick deposits of 

fine-grained sediment near the banks. Five zones each were 

sampled at the Martinez St. Hedwig site, one site on Leon 

Creek (USGS station 292338098360501 Leon Creek at Morey 

Road, San Antonio, Tex., [hereinafter, Leon Morey site; fig. 2, 

map identifier 10]), and one site in the Salado Creek watershed (USGS station 08178825 Rosillo Creek at New Sulphur 

Springs Road, San Antonio, Tex. [hereinafter, Rosillo site; 

fig. 2, map identifier 16]), where the depositional zones were 

small and had small amounts of fine-grained surficial sediments. All sediment samples were collected by wading the 

stream; each depositional zone was approached by one or two 

field personnel at a time from the downstream direction so as 

not to disturb the streambed sediment. The GPS coordinates 

of each depositional zone sampled were recorded. After rinsing the sampling equipment with native water, two scoops of 

the surficial streambed sediment were collected from smaller 

depositional zones and three scoops were collected from larger 

depositional zones and composited in a glass bowl. The total 

volume of streambed sediment collected at each stream reach 

was about 1 liter (L) (wet). 

Streambed-sediment samples were processed either in the 

field or in the laboratory of the USGS Texas Water Science 

Center, San Antonio office. Samples not processed in the field 

were stored on ice immediately after collection until processed 

later in the laboratory. Samples were mixed and then sieved to 

reduce grain-size variability thus allowing for more informative comparisons among samples. 

Trace element concentrations measured in streambedsediment samples were not normalized by grain size; these 

samples were sieved to a uniform grain size. About one-half 

of the sample was sieved with a 63-micrometer (μm) nyloncloth sieve for analysis of major and trace elements. Sediment 

greater than 63 μm (the diameter differentiating larger sand 

size particles from smaller clay and silt size particles) was 

discarded. The fine material (less than 63 μm) was transferred 

into 125-milliliter (mL) polypropylene jars that were placed 

on ice and transported to the local USGS laboratory in San 

Antonio. The samples were then transported on ice to the 

USGS Texas Water Science Center, Austin office; freeze-dried 

and pulverized; and shipped to the USGS Mineral Resources 

Program Analytical Laboratories in Lakewood, Colo., for analysis. The remaining part of the sample that was not analyzed 

for major and trace elements was sieved with a 2.0-millimeter 

(mm) stainless-steel mesh sieve on the opening of a 500-mL 

pre-cleaned glass jar and analyzed for organic compounds. 

Coarse sediment (greater than 2.0 mm) was discarded. The 

samples for organic compound analyses were stored chilled 

in the same manner as samples for major and trace element 

analysis and similarly shipped on ice to the USGS National 

Water Quality Laboratory (NWQL) in Lakewood, Colo., for 

analysis.

Large-Volume Suspended-Sediment Samples

LVSS samples were collected to investigate the occurrence and distribution of sediment contaminants in stormwater; sample collection followed the methods of Mahler 

and Van Metre (2003) and Van Metre and others (2003). 

As stormwater runoff enters streams, the stage, discharge, 

suspended-sediment concentration (SSC), and turbidity all 

increase (Curriero and others, 2001; Mahler and others, 2006). 

Analysis of constituents sorbed to particulates in the streamflow containing stormwater runoff provides information on 

transport of sediment-associated constituents (Larson and 

others, 2010). LVSS samples were collected with passive 

samplers (fig. 6) that filled once the stage of the stream 

increased to a predetermined threshold as a result of stormwater runoff . Once the carboy was full, no more water 

entered the carboy, resulting in a sample from the rising limb 

of the hydrograph (also referred to as a first-flush sample). 

The LVSS passive samplers consisted of a 25-L polyethylene sample bottle inside a cylindrical steel housing installed 

near the stream channel (fig. 6). Each sampler had two water 

intake nozzles pointed upstream and an air vent line designed 

to passively collect first-flush grab samples at the sampling 

sites when the stream depth increased and inundated the intake 

nozzles. Intake nozzles were about 0.6 m above the bottom of 

the cylinder. The amount of flow required to collect a sample 

varied by site. The air vent line allowed air in the bottle to 

leave as water flowed in and blocked outflow when the bottle 

was full so that water did not continue to cycle through the 

bottle. After the storm passed and streamflow receded, the 

LVSS sample was removed from the sampler and transported 

to the laboratory at the USGS Austin or San Antonio office for 

processing. 
Methods 15

Figure 5. Hyetograph showing rainfall at San Antonio International Airport and hydrographs showing stream discharge and 

streambed-sediment and suspended-sediment sampling at selected sites in Bexar County, Texas, 2007–09. 

11/1/2007

12/1/2007

1/1/2008

2/1/2008

3/1/2008

4/1/2008

5/1/2008

6/1/2008

7/1/2008

8/1/2008

9/1/2008

10/1/2008

11/1/2008

12/1/2008

1/1/2009

2/1/2009

3/1/2009

4/1/2009

5/1/2009

6/1/2009

7/1/2009

8/1/2009

9/1/2009

Date

0

1

2

3

4

0

10

20

30

40

0

2

4

6

8

0

2

4

6

8

14

0

0.1

0.2

0.3

0

10

20

30

50

0

20

40

60

80

100

Daily average discharge, in cubic meters per second

Daily rainfall, 

in centimeters

5

10

12

40

08181800 San Antonio River near Elmendorf, Tex.

(SAR Elmendorf site)

08178800 Salado Creek at Loop 13, San Antonio, Tex.

(Salado 13 site)

08185100 Martinez Creek near St. Hedwig, Tex.

(Martinez St. Hedwig site)

08181500 Medina River at San Antonio, Tex.

(Medina site)

08181480 Leon Creek at Interstate Highway 35, San Antonio, Tex.

(Leon 35 site)

08178565 San Antonio River at Loop 410, San Antonio, Tex.

(SAR 410 site)

National Weather Service cooperative station 417945

San Antonio International Airport, San Antonio, Tex.

(National Oceanic and Atmospheric Administration, 2010)

EXPLANATION

Streambedsediment sample 

collected

Large-volume

suspended-sediment 

sample collected
16 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 6. Schematic (A) and photographs (B and C) of passive samplers used to collect large-volume suspended-sediment samples at 

selected sites in Bexar County, Texas, 2007–09. 

Approximately 0.6 meter

25-liter

sample

bottle

Air

vent

line

Water intake

lines (2) Intake nozzles (2)

Flow direction

direction

Debris deflector Vent holes

Siphon brake

(trapped air space)

Intake/vent

pressure

difference

Venting

system

Mounting

tabs

Steel

housing

Intake

nozzles

Debris

deflector

Leon Creek at Interstate Highway 35

A

B C
Methods 17

An LVSS sample was transferred from the 25-L sample 

bottle into a custom 50-L churn so the sample could be stirred 

constantly during subsampling and filtration. The LVSS samples were filtered with a 0.45-μm Teflon membrane to separate 

the sediment from the water. To enable water to readily pass 

through the filters, the Teflon membranes were sprayed with 

methanol before placing them on the filter holders. About 

two-thirds of the sample was filtered for organic compound 

analyses with a stainless-steel filter holder. The remaining onethird of the sample was filtered for analysis of major and trace 

elements with an acrylic filter holder. Duplicate samples of 

unfiltered water were pumped from the churned sample during 

filtration for SSC analysis. After filtration, the sediment was 

gently scraped from the Teflon membranes and transferred 

into sample jars. Samples for organic analyses were placed 

into pre-cleaned glass jars and shipped on ice to the NWQL 

for analysis. Samples for inorganic analyses were placed into 

polypropylene jars, freeze-dried, and pulverized before sending to the analytical laboratory. Both jars of the streambedsediment sample collected from the Martinez 1518 site on 

August 11, 2009, for the analysis of organic compounds broke 

during shipment to the laboratory. SSC samples inadvertently 

were not obtained from the LVSS samples collected from the 

Leon 35 site on May 16, 2009, and from the SAR Elmendorf 

site on March 12, 2009. 

The LVSS samples were not sieved. For 18 of the 21 

LVSS samples analyzed for grain size, more than 90 percent of 

particles were finer than 63 μm (appendix 1.4). 

Analytical Methods

Streambed-sediment samples were analyzed for major 

and trace elements and organic compounds. Organic compounds included halogenated organic compounds (chlordane, 

dieldrin, DDT, DDD [common name for dichlorodiphenyldichloroethane], and DDE [common name for dichlorodiphenyldichloroethylene], PCBs, and brominated flame retardants), 

SVOCs, and PAHs. 

LVSS samples were analyzed for the same constituents 

as streambed-sediment samples; SSC also was determined for 

most LVSS samples. The USGS Sediment Laboratory at the 

Louisiana Water Science Center, Baton Rouge office, analyzed 

the LVSS samples for SSC by using the filtration method 

described by Guy (1969).

Freeze-dried sediment samples were analyzed for major 

and trace elements by the USGS Mineral Resources Program 

Analytical Laboratories in Lakewood, Colo. Total and inorganic carbon were determined by using methods described 

by Taggart (2002). Total carbon was analyzed by combustion 

with an automated carbon analyzer; inorganic carbon was 

determined as carbon dioxide by coulometric titration. Organic 

carbon was computed as the difference between the concentrations of total and inorganic carbon. Samples for major and 

trace element analyses were digested completely by using a 

mixture of hydrochloric, nitric, perchloric, and hydrofluoric 

acids and analyzed by inductively coupled plasma-mass 

spectrometry (ICP–MS) (Briggs and Meier, 2002). Concentrations of mercury were determined by continuous flow-cold 

vapor-atomic fluorescence spectrometry (CVAFS) (Hageman, 

2007). 

The sediment samples were analyzed for SVOCs and 

PAHs by gas chromatography/mass spectrometry (GC/MS) 

(Zaugg and others, 2006) at the NWQL. Surrogate compounds 

were added to the sample prior to extraction to monitor laboratory preparation, matrix effects, and method performance. The 

samples were extracted twice by using the ASE 200 accelerated solvent extraction system (Dionex, Sunnyvale, Calif.) at a 

pressure of 13,800 kilopascals with a water/isopropyl alcohol mixture (50:50, volume-to-volume ratio) at 120 degrees 

Celsius (°C) and then a water/isopropyl alcohol mixture 

(20:80, volume-to-volume ratio) at 200 °C for 40 minutes. The 

constituents of interest were isolated from the extract by using 

disposable solid-phase extraction (SPE) cartridges containing 

divinylbenzene-vinylpyrrolidone copolymer resin. The SPE 

cartridge was dried partially with nitrogen gas, and sorbed 

compounds were eluted with a dichloromethane/diethyl ether 

mixture (80:20, volume-to-volume ratio) and passed through a 

second SPE cartridge, either a sodium sulfate or Florisil SPE 

cartridge, to dry and further “clean up” the extract by removing unwanted impurities. The concentrated extract was solvent 

exchanged into ethyl acetate, the solvent volume reduced, 

internal standard compounds added, and then analyzed by 

capillary-column GC/MS on an Agilent Technologies Model 

5973, with the MS operated in the electron impact, full scan 

mode (Zaugg and others, 2006). 

The samples were analyzed for halogenated organic compounds at the NWQL by using a custom analytical method. 

Custom methods have not been completely evaluated with 

USGS guidelines for developing official laboratory methods 

(U.S. Geological Survey, 2004), thus the official method 

prove-out has not been completed at the time of sample 

analyses. The samples were extracted by using the ASE 200 

accelerated solvent extraction system as described previously 

for the PAHs. The extracts were analyzed by capillary-column 

GC/MS on an Agilent Technologies Model 5975, with the MS 

operated in the electron capture negative ion (ECNI) mode 

using ammonia as the reactant gas. The halogenated organic 

compounds were identified by selected ion monitoring (SIM) 

using the ions of interest (Mark Burkhardt and Steven Zaugg, 

U.S. Geological Survey, written commun., 2007). 

Quality Control

Quality control for major and trace elements consisted 

of analyzing one or more laboratory blank samples, standard 

reference materials (SRMs), and duplicate or replicate samples 

submitted with each set of environmental samples (appendix 

2.1). The samples collected during 2007–09 were analyzed for 

major and trace elements in 11 different sets. A lower reporting limit described by Taggart (2002, p. viii) as greater than 

or equal to “five times the standard deviation determined from 

the method blank” was used for major and trace elements. 
18 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Major and trace element concentrations less than the respective lower reporting limits are hereinafter referred to as nondetections or nondetected concentrations, and concentrations 

equal to or greater than the respective lower reporting limits 

are hereinafter referred to as detections or detected concentrations. One or more major or trace elements were detected 

in 3.5 percent of the blank samples; beryllium, lithium, and 

scandium were the most frequently detected. The laboratory 

analyzed SRMs, compared the values to published or standard 

results, and computed the percent recovery. The SRM results 

are used to assess bias for each analysis. It is difficult to assess 

the results of the SRMs because the acceptable uncertainty 

of concentrations varies between elements and SRMs. For 

example, the National Institute of Standards and Technology 

(NIST) SRMs 8704 and 2709 were analyzed with the samples 

collected in Bexar County during 2007–09 (appendix 2.1). The 

true concentration of lead in SRM 8704 is 150 micrograms per 

gram (μg/g) plus or minus 11 percent (1 standard deviation), 

whereas the true concentration of cadmium in SRM 2709 is 

18.9 μg/g plus or minus 2.6 percent (1 standard deviation) 

(National Institute of Standards and Technology, 2008 and 

2003, respectively). The certificates of analysis could not 

be obtained for all SRMs analyzed with the Bexar County 

samples collected during 2007–09; therefore, no conclusions 

are made about the overall acceptability of the results of the 

SRMs. 

Quality control for organic analyses consisted of analyzing a laboratory blank sample, a spike sample, and a duplicate sample, as well as monitoring recovery of surrogate 

compounds with each set of environmental samples (Mark 

Burkhardt and Steven Zaugg, U.S. Geological Survey, written 

commun., 2007). The samples collected during 2007–09 were 

analyzed for halogenated organic compounds in 12 different 

sets (appendix 2.2). Halogenated organic compound concentrations less than the respective interim reporting levels (IRLs) 

are hereinafter referred to as nondetections or nondetected 

concentrations, and concentrations equal to or greater than 

the respective IRLs are referred to as detections or detected 

concentrations. The IRL is a temporary reporting level used 

for new or custom schedules when long-term method detection level data are unavailable and an LRL has not yet been 

established (William Foreman, U.S. Geological Survey, written commun., 2011). In 7 percent of the blank samples, one or 

more halogenated organic compounds were detected; triclosan 

and polybrominated diphenyl ethers (PBDEs) 47, 99, and 100 

were the most frequently detected compounds. Detections in 

the triclosan, PBDE 47, PBDE 99, and PBDE 100 blanks were 

at concentrations greater than the respective IRLs 85 percent 

of the time. Detections of halogenated organic compounds 

in blank samples, particularly at concentrations equal to or 

greater than the IRLs, indicate the possibility of false positives during environmental sample analyses. Whenever a 

halogenated organic compound was detected and identified 

in the blank, the quantification of that same compound in the 

environmental sample was qualified as estimated with the “E” 

remark code. 

Spike results provide information about method performance and are used to assess potential bias of environmental 

sample results (Pirkey and Glodt, 1998). The average halogenated organic compound spike recoveries, by compound, 

ranged from 54.2 percent for PCB 52 to 145.2 percent for 

PBDE 47 (appendix 2.2). The overall average spike recovery 

for the halogenated organic compounds was 80.7 percent. The 

NWQL established acceptable spike recovery ranges after the 

analysis of some of the samples collected during 2007–09; 

those acceptable ranges were reported with the last three sets 

of samples and applied to all spike results. Spike recoveries were within acceptable ranges for 98 percent of the spike 

results. Spike recoveries were low in set one for PCB 206 and 

pentabromotoluene; in set two for fipronil sulfide; in set four 

for pendimethalin; in set 200926406 for triclosan and pentabromotoluene; and in set 201002204 for triclosan, desulfinyl 

fipronil, fipronil, fipronil sulfide, and pentabromotoluene 

(appendix 2.2). Spike recoveries were high in set one for 

cyhalothrin, p,p ́-DDD, and PBDE 47; in set two for PBDE 

47; in set ten for PCB 49; and in sets 200926405 and 

200926406 for fipronil (appendix 2.2). Concentrations of the 

halogenated organic compounds in those sets with low or high 

spike recoveries were considered unreliable and the environmental sample results were qualified as estimated with an 

“E” remark code when detected concentrations were reported 

(appendix 1.2). 

Surrogates are used to monitor the recovery efficiency of 

the analytical processes. Surrogate recoveries are not used to 

correct concentrations because the surrogates do not chemically mimic all compounds in the laboratory method (Noriega 

and others, 2003). The average surrogate recoveries of all 

environmental and quality control samples analyzed for halogenated organic compounds were 61.1, 67.4, and 79.4 percent 

for dibromoocta-fluorobiphenyl, PCB 202-13C12, and DDT-d8

, 

respectively. Surrogate recovery control limits are established 

similarly to spike recoveries. Surrogate recoveries were within 

control limits of 20 to 104 percent for dibromooctafluorobiphenyl, 38 to 110 percent for PCB 202-13C12, and 39 to 129 

percent for DDT-d8 for 88 percent of the sample analyses. The 

NWQL checks and adjusts the method when surrogate recoveries are outside control limits (Mark Burkhardt and Steven 

Zaugg, U.S. Geological Survey, written commun., 2007).

The samples were analyzed for SVOCs and PAHs in 11 

sets (appendix 2.3). Compound concentrations less than the 

respective IRLs are hereinafter referred to as nondetections 

or nondetected concentrations, and concentrations equal to or 

greater than the respective IRLs are referred to as detections 

or detected concentrations. Detections were reported in 28 

percent of the blank results, with most detections for 2-ethylhexyl phthalate, diethyl phthalate, fluoranthene, naphthalene, 

phenanthrene, and pyrene. Most of the blank detections (97 

percent) were less than the IRLs for the respective compounds 

except for 2-ethylhexyl phthalate, which was detected in the 

blanks at concentrations greater than the IRLs in 64 percent of 

the sample sets. Diethyl phthalate was detected in 27 percent 

of the set blanks at concentrations greater than the IRLs. 
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 19

Concentrations of fluoranthene, pyrene, and benzo(g,h,i)

perylene were greater than the IRLs in the blank sample for 

set 200901505. Whenever an SVOC or PAH was detected and 

identified in the blank, the quantification of that same compound in the environmental sample was qualified as estimated

with an “E” remark code. 

The average spike recoveries by compound ranged from 

54.9 percent for pentachloronitrobenzene to 95.8 percent for 

benzo(b)fluoranthene. The overall average spike recovery for 

the SVOCs and PAHs was 81.2 percent. The NWQL establishes annually acceptable spike recovery ranges on the basis 

of historical spike analyses. Spike recoveries were within 

acceptable ranges for 98 percent of the spike results. Spike 

recoveries of hexachlorobenzene and pentachloroanisol in set 

200926502 were slightly less than the acceptable recovery 

ranges, and naphthalene in set 200826801 and benzo(e)pyrene 

and benzo(k)fluoranthene in set 200915405 were slightly 

greater than the acceptable recovery ranges (appendix 2.3). 

Spike recoveries of 1,2,4-trichlorobenzene in sets 200915405 

and 200826801 were much greater than the acceptable range 

of 19 to 89 percent and the concentrations of the compound 

in the two sets are considered unreliable (positive bias). 

Concentrations of SVOCs or PAHs in those sets with low or 

high spike recoveries were considered unreliable and the environmental sample results were qualified as estimated with an 

“E” remark code when detected concentrations were reported 

(appendix 1.3).

The average surrogate recoveries of all environmental 

and quality control samples analyzed for SVOCs and PAHs 

were 63.6, 37.3, and 73.3 percent for 2-fluorobiphenyl, 

nitrobenzene-d5, and p-terphenyl-d14, respectively. Surrogate 

recoveries were within control limits of 0 to 151 percent for 

2-fluorobiphenyl, 4 to 157 percent for nitrobenzene-d5, and 37 

to 120 percent for p-terphenyl-d14, for 93 percent of the sample 

analyses. The NWQL checks and adjusts the method when 

surrogate recoveries are outside the control limits (Zaugg and 

others, 2006).

Two types of duplicate or replicate samples were used—

laboratory replicates in which the laboratory runs the analysis 

two or more times, and environmental duplicates in which 

two or more separate jars of sediment collected concurrently 

or sequentially are submitted to the laboratory for separate 

analyses. Replicates provide information about variability 

in the analytical process, but their results can be affected by 

sample heterogeneity, particularly when sediments are the 

sample media (Pirkey and Glodt, 1998). The relative percent 

difference (RPD) was computed between each pair of duplicate analyses to provide a measure of precision by using the 

equation 

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

where 

C1 is the constituent concentration, in micrograms per gram 

or micrograms per kilogram, from the environmental 

sample; and 

C2 is the constituent concentration, in micrograms per gram 

or micrograms per kilogram, from the duplicate 

sample.

Eleven environmental samples were analyzed in duplicate or replicate for major and trace elements (appendix 

2.1). The overall average RPD for the major and trace element duplicates was 5.1 percent. Nine laboratory duplicate 

and two environmental duplicate samples were analyzed for 

halogenated organic compounds (appendix 2.2). The overall 

average RPD for the halogenated organic compound duplicates was 45.4 percent. Two environmental duplicate samples 

were analyzed for SVOCs and PAHs (appendix 2.3) with an 

overall average RPD of 40.6 percent. The RPDs of duplicate 

organic analyses are larger than in previous USGS sediment 

studies using the NWQL and similar analyses (for example, 

Van Metre and others, 2003; Van Metre and others, 2004).

Numerous factors affect the analytical results of organic 

compounds reported by the NWQL. The IRLs for organic 

compounds increase as the sediment mass available for 

analysis decreases. This results in higher IRLs for small-mass 

samples such as the LVSS samples. The NWQL uses an “E” 

remark code to signify that the concentration is an estimated 

value for one or more possible reasons. For most samples, at 

least one constituent was qualified as estimated with an “E” 

remark code. When an organic compound is detected in the 

blank sample, an “E” remark code is assigned to the results of 

that same compound in the environmental sample. All alkylated PAH results are assigned an “E” remark code because 

no calibration standards exist for these compounds. Some 

organic compounds are assigned an “E” remark code either 

because of matrix interference or because the compounds are 

highly variable and the precision or accuracy of the analytical 

method is questionable. Concentrations that are extrapolated 

because they are less than the lowest calibration standard, 

method range, or instrument range are also assigned an “E” 

remark code (Childress and others, 1999). All major and trace 

element, SVOC, and PAH data from discrete environmental 

samples collected by the USGS, including results for qualitycontrol samples, were published in the USGS National Water 

Information System (NWIS) (U.S. Geological Survey, 2011).

Assessment of Selected Contaminants 

in Streambed- and SuspendedSediment Samples 

Selected constituents in streambed-sediment samples 

and suspended-sediment (LVSS) samples collected at sites 

in the watersheds of eight major streams in Bexar County 

during 2007–09 were assessed by using a variety of methods. 

The concentrations of trace elements and organic compounds 

measured in the streambed-sediment and LVSS samples are 

described and concentrations in streambed-sediment samples 

and LVSS samples are compared. Contaminant concentrations 
20 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

also are compared to sediment-quality guidelines (SQGs) and 

to concentrations in samples collected previously at the same 

locations.

Statistical analyses are used to describe similarities or 

differences in the sediment concentrations between watersheds 

and to describe the relation between concentrations and land 

use. Detailed land-use data were only available for Bexar 

County, resulting in less than 100-percent land-use coverage in the study area for the Medio Creek, Medina River, and 

Elm Creek contributing areas (figs. 1–2; table 2). Lastly, the 

sources of PCBs and PAHs are investigated by using source 

indicator ratios, profiles, and a chemical mass balance model 

(PAHs only). 

Total concentrations of chlordane, DDT, PCBs, and PAHs 

were estimated by by using the Kaplan-Meier method to determine the mean concentration of a group of compounds while 

accounting for censored data points and then multiplying the 

mean by the number of compounds in the group to produce an 

estimate of the total (Helsel, 2009). Estimated concentrations 

(assigned an “E” remark code) were used at their concentration values and no values were substituted for the nondetected 

concentrations in the computation of means. In groups with a 

single detection, an estimate of the total concentration was not 

possible with the Kaplan-Meier method and the total concentration was listed as “not detected.”

Occurrence and Distribution of SedimentAssociated Constituents

Comparisons of sediment-associated constituents 

between sites can be affected by variability in sediment properties such as grain size and organic carbon content. Trace 

element concentrations correlate positively with the less-than125-μm (very fine sand and finer) and less-than-63-mm (silt 

and finer) sediment fractions (Horowitz and Elrick, 1987). The 

streambed-sediment samples were sieved and the fraction finer 

than 63 μm was analyzed for major and trace elements. The 

consistent grain size of LVSS samples also precluded the need 

to normalize trace-element concentrations for these samples. 

Hydrophobic organic compounds are known to sorb 

to the organic matter in sediments (for example, Chiou and 

others, 1979; Karickhoff and others, 1979). A Kruskal-Wallis 

analysis of variance test (Iman and Conover, 1983) was used 

to determine that the amounts of organic carbon in each watershed have equivalent distributions; the attained significance 

level (p-value) was .062. Because the percent organic carbon 

did not vary significantly (p-value less than .05 statistically 

significant) among analyses obtained from sites in the eight 

watersheds, the concentrations of organic compounds were not 

normalized for organic carbon. 

The average SSC was computed for each LVSS sample 

by using the SSC measured in the duplicate samples collected 

during churning and filtration (table 4). Because SSC samples 

were inadvertently not obtained from the LVSS sample at the 

Leon 35 site on May 16, 2009, and the SAR Elmendorf site 

on March 12, 2009, those SSCs are estimates computed as 

the average of the SSCs measured in other samples collected 

from the same sites. SSC for all sites ranged from relatively 

low values in samples from the Martinez St. Hedwig and Leon 

35 sites (360 and 362 milligrams per liter [mg/L], respectively) to relatively high values in samples from the Medina 

and SAR 410 sites (2,296 and 2,744 mg/L, respectively). The 

SSC in the samples from the Salado Southton site was about 

1 order of magnitude less in 2009 (311 mg/L) compared to 

2008 (1,988 mg/L).

The mass of contaminant per unit volume of stormwater 

was compared among sites. The mass of contaminant per unit 

volume of stormwater (micrograms or nanograms per liter) 

was calculated by dividing the concentration of contaminant 

by the average SSC of each suspended-sediment sample. 

Compared to concentrations measured at others sites in the 

study area, relatively high contaminant concentrations and 

SSCs were measured in LVSS samples from the SAR 410 

site. Some of the highest contaminant concentrations (except 

for cadmium, p,p'-DDE, and a brominated flame retardant, 

dechlorane plus) and some of the highest SSCs in the study 

area were measured in samples collected from the SAR 410 

site (table 4); these high LVSS concentrations are consistent 

with the streambed-sediment contaminant concentrations at 

the site. Conversely, despite high contaminant concentrations 

in the streambed-sediment and LVSS samples collected from 

the Leon 35 site, the mass of contaminant per liter of stormwater at this site is not particularly large because of the moderate SSCs in the stormwater samples. Samples collected from 

the Martinez St. Hedwig site typically had the lowest values of 

mass of contaminant per liter of stormwater, which is a result 

of both low LVSS contaminant concentrations and low SSCs. 

Trace elements may be derived from geologic materials and anthropogenic sources (Garbarino and others, 1995). 

Arsenic, lead, mercury, and cadmium are among the top 

10 (table 1) of the “CERCLA Priority List of Hazardous 

Substances” (Agency for Toxic Substances and Disease 

Registry, 2007a), all four priority trace elements were detected 

in all samples collected at all sites. 

Arsenic was used as an agricultural insecticide until the 

1950s and as a wood preservative until 2003. Arsenic also 

occurs naturally in groundwater in small amounts (generally 

3 micrograms per liter [μg/L] or less) in central Texas (Ryker, 

2001) and groundwater contributes to streamflow in the study 

area (Ockerman and McNamara, 2003). The greatest concentrations of arsenic were in streambed-sediment samples 

collected from the following sites: Chupaderas (22.2 μg/g), 

Leon 90 (12.8 μg/g), and Leon Morey (12.2 μg/g) (appendix 1.1). The Chupaderas Creek watershed is the smallest of 

the watersheds for the eight major streams in Bexar County. 

The contributing area of the Chupaderas site has one of the 

lowest population densities (61 people per square kilometer) 

among all contributing areas composing the eight major watersheds in Bexar County and is 83.6 percent undeveloped land 

(table 2). Abandoned municipal solid waste landfill sites are 

the most common PSOC in the Chupaderas Creek watershed 
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 21

Table 4. Suspended-sediment concentration and mass of contaminant per unit volume of stormwater for large-volume suspendedsediment samples collected by passive samplers at selected sites in Bexar County, Texas, 2008–09.

[SSC, suspended-sediment concentration; mg/L, milligrams per liter; μg/L, micrograms per liter; E, estimated (SSC sample inadvertently not obtained from 

large-volume suspended-sediment sample; therefore, SSC estimated from average of SSCs measured in other samples collected at site); ng/L, nanograms per 

liter; PCBs, polychlorinated biphenyls; PAHs, polycyclic aromatic hydrocarbons; PBDE, polybrominated diphenyl ether; ND, not detected]

Site identifier

(table 2)

Sample 

collection 

date

Average SSC 

(mg/L)

Arsenic 

(μg/L)

Cadmium 

(μg/L)

Chromium 

(μg/L)

Copper 

(μg/L)

Mercury 

(μg/L)

Nickel 

(μg/L)

Lead 

(μg/L)

Zinc 

(μg/L)

Medina 08/20/2008 2,296 17 0.73 109 36 0.05 46 38 181

Martinez St. Hedwig 08/19/2008 360 2.3 .10 26 7.5 .01 8.5 8.2 47

Martinez St. Hedwig 05/25/2009 583 2.6 .24 27 11 .02 10 12 69

Leon 35 07/24/2008 574 5.2 2.5 69 17 .04 14 29 77

Leon 35 05/16/2009 E470 3.0 1.5 36 9.9 .03 9.7 17 39

Leon 35 05/23/2009 362 3.0 1.1 27 9.8 .03 8.5 18 56

Salado Southton 08/20/2008 1,988 16 .78 112 42 .10 43 69 262

Salado Southton 05/25/2009 311 2.2 .11 16 6.8 .01 6.9 11 39

SAR 410 07/07/2008 2,744 18 1.3 151 113 .16 57 187 453

SAR 410 07/24/2008 1,321 10 .66 87 47 .08 37 77 231

SAR Elmendorf 07/25/2008 515 2.6 .12 22 6.9 .02 8.0 10 37

SAR Elmendorf 08/18/2008 459 3.4 .23 30 13 .03 11 24 76

SAR Elmendorf 03/12/2009 E490 2.0 .11 20 6.6 .01 6.6 7.6 36

Site identifier

(table 2)

Sample 

collection 

date

Average 

SSC 

(mg/L)

Dieldrin 

(ng/L)

Total 

chlordane1

(ng/L)

p,p ́-

DDD 

(ng/L)

p,p ́-

DDE 

(ng/L)

Total 

PCBs2

(ng/L)

Total 

PAHs3

(ng/L)

PBDE 

153 

(ng/L)

PBDE 

154 

(ng/L)

Dechlorane plus 

(ng/L)

1,2-bis

(2,4,6-tribromophenoxy)-

ethane4

(ng/L)

Medina 08/20/2008 2,296 0.11 0.56 ND ND 2.8 ND 0.73 0.52 0.21 0.09

Martinez St. Hedwig 08/19/2008 360 ND ND ND ND ND ND ND ND .09 .04

Martinez St. Hedwig 05/25/2009 583 ND ND ND ND ND ND ND ND ND ND

Leon 35 07/24/2008 574 .18 2.2 4.0 ND 15 92 .24 .20 2.2 .18

Leon 35 05/16/2009 E470 ND ND ND ND 3.9 ND ND ND .33 ND

Leon 35 05/23/2009 362 ND .94 ND ND 4.7 724 .12 .09 .40 .16

Salado Southton 08/20/2008 1,988 .66 7.4 ND 8.2 9.9 477 1.2 .79 2.0 .48

Salado Southton 05/25/2009 311 ND .48 ND ND ND 528 .12 .08 .96 ND

SAR 410 07/07/2008 2,744 1.3 13 44 ND 49 5,762 1.2 .96 .53 .94

SAR 410 07/24/2008 1,321 1.1 8.9 8.2 ND 13.2 4,756 1.0 .98 1.7 .41

SAR Elmendorf 07/25/2008 515 .04 .46 .72 ND 1.6 ND .21 .17 .25 .10

SAR Elmendorf 08/18/2008 459 .15 2.0 ND 2.8 5.5 ND .50 .35 .55 .25

SAR Elmendorf 03/12/2009 E490 ND .45 ND ND 1.3 ND ND ND .24 ND

1

 Total chlordane is sum of cis-chlordane, trans-chlordane, cis-nonachlor, trans-nonachlor, and oxychlordane.

2

 Total PCBs is sum of PCB congeners 49, 52, 70, 101, 110, 118, 138, 146, 149, 151, 170, 174, 177, 180, 183, 187, 194, and 206.

3

 Total PAHs is sum of acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, chrysene, dibenzo(a,h)anthracene, fluoranthene, 

fluorene, naphthalene, phenanthrene, and pyrene.

4

 Firemaster 680.
22 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

(Texas Commission on Environmental Quality, 2009a; fig. 3). 

According to the Alamo Area Council of Governments (2002), 

two unauthorized landfills of unknown size and unknown 

dates of use were found near Chupaderas Creek; contaminants leaching from these landfills might be contributing to 

elevated arsenic concentrations in streambed sediment at the 

Chupaderas site.

Much of the lead in the environment comes from the 

burning of fossil fuels, mining, and manufacturing (Agency 

for Toxic Substances and Disease Registry, 2007b). The greatest lead concentrations, 69.3 and 65.0 μg/g, were measured 

in streambed-sediment samples collected from the Leon 35 

and Leon Quintana sites, respectively. A lead concentration 

of 68.2 μg/g was measured in an LVSS sample collected from 

the SAR 410 site (appendix 1.1). The percentages of industrial 

and mining land use in the contributing areas for these three 

sites are larger than the median values for all contributing 

areas in the study area (table 2). 

Mercury historically was used in thermometers and other 

scientific meters and in dental amalgams. Mercury is emitted to the atmosphere by oceans, volcanoes, coal-fired power 

plants, waste incineration, gold mining, and caustic soda, 

cement, and metal production (Pacyna and others, 2006). 

Mercury concentrations were greatest in streambed-sediment 

samples collected from the Leon Quintana site (0.09 and 0.08 

μg/g), an LVSS sample collected from the SAR Elmendorf 

site (0.07 μg/g), and two LVSS samples collected from the 

Leon 35 site (both 0.07 μg/g) (appendix 1.1). The percentages 

of industrial and mining land use in the contributing areas for 

these three sites are relatively large compared to the median 

values for all contributing areas in the study area (table 2).

Cadmium is used predominantly in nickel-cadmium 

batteries but also has minor uses for coating and electroplating, in pigments, as a polyvinylchloride (PVC) stabilizer, and 

as an alloy in a variety of other metals; until the 1980s, cadmium was commonly used for coating metals to prevent corrosion and as a pigment (Llewellyn, 1994). The greatest concentrations of cadmium were in streambed-sediment samples 

collected from the Leon Quintana site (6.5 and 5.4 μg/g), an 

LVSS sample collected from the Leon 35 site (4.4 μg/g), and 

a streambed-sediment sample collected from the Leon 35 site 

(4.1 μg/g) (appendix 1.1). As previously stated, the percentages of industrial and mining land use in the contributing 

areas for these two sites are larger than the median values for 

all contributing areas in the study area (table 2). In addition, 

activities that used or involved cadmium such as electroplating 

and disposal of scrap metals were known to occur in zones 1 

and 2 at the former Kelly AFB (fig. 4), upstream from the two 

sampling sites (CH2M Hill, 2001). 

Halogenated organic compounds that were measured in 

sediment samples include pesticides, PCBs, and brominated 

flame retardants. At least three or more halogenated organic 

compounds were detected in each sediment sample collected 

from the Bexar County sites during 2007–09 (appendix 1.2) 

and 66 percent of the halogenated organic compound concentrations measured were less than the respective IRLs 

(nondetections). Detection frequencies of halogenated organic 

compounds in all streambed-sediment and LVSS samples 

are shown in figure 7 by watershed. Chlordane was widely 

used as an insecticide in agriculture and residential applications and for termite control until being banned in the United 

States in the 1980s (Agency for Toxic Substances and Disease 

Registry, 1994). Chlordane is a mixture of numerous related 

compounds; samples collected during 2007–09 were analyzed 

for two isomers (cis-chlordane and trans-chlordane), two 

other components (cis-nonachlor and trans-nonachlor), and a 

metabolite (oxychlordane). For this report, total chlordane is 

defined as the sum of these five chlordane-related compounds. 

The chlordane compounds were the most frequently detected 

of the halogenated organic compounds (detected in 94 percent 

of samples) with one or more detections of chlordane compounds in every watershed (fig. 7). The highest concentrations of total chlordane were in a streambed-sediment sample 

collected from the Leon Lackland site (11 micrograms per 

kilogram [μg/kg]) and in an LVSS sample collected from the 

SAR 410 site (6.7 μg/kg) (appendix 1.2). Chlordane was commonly used as a termite pesticide, especially in the southern 

U.S. Because of its widespread historical use and extreme 

environmental persistence, chlordane is commonly found in 

the environment throughout most of the United States (Agency 

for Toxic Substances and Disease Registry, 1994). 

DDT is a pesticide that was used widely in the United 

States in agriculture applications and for the control of 

disease-carrying insects (such as mosquitoes and malaria) 

until being banned in 1972 because of its persistence in the 

environment and toxicity to wildlife. The parent product, 

DDT, and its breakdown products, DDD and DDE, all have 

similar chemical and physical properties (Agency for Toxic 

Substances and Disease Registry, 2002). Each compound has 

three forms (for example, the three forms of DDT are p,p ́-

DDT, o,p ́-DDT, and o,o ́-DDT), but only the primary form 

(p,p ́) was analyzed in the samples collected during 2007–09. 

The most frequently detected compound of the group was the 

breakdown product p,p ́-DDE. Concentrations of p,p ́-DDT, 

p,p ́-DDD, or p,p ́-DDE were not detected in samples from 

sites in the Medina River, Elm Creek, or Chupaderas Creek 

watersheds (fig. 7). The DDT compounds were detected most 

frequently in the Leon Creek and San Antonio River watersheds. The highest concentrations were in streambed-sediment 

samples collected from the Leon Lackland and Leon Military 

sites (appendix 1.2), adjacent to zones 1 and 2 of the former 

Kelly AFB (fig. 4), where CH2M Hill (2001) documented the 

presence of pesticide disposal sites. Sediments with relatively 

higher concentrations of DDT than DDE are likely the result 

of a recent introduction of parent DDT into the environment 

(Hitch and Day, 1992). A DDE/DDT ratio greater than 1 is 

indicative of long-term degradation of DDT (Lindsey and 

others, 1998). Four samples had detections of DDE and 

DDT—three from the Leon Lackland site (DDE/DDT ratios 

0.37, 1.3, and 0.19) and one from the Leon Military site (DDE/

DDT ratio 4.3). The ratios less than 1 at the Leon Lackland 

site imply recent introduction of parent DDT at or upstream 
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 23

from the sampling site, possibly by disturbance of buried 

waste or by recent use. 

Dieldrin, an agricultural pesticide and termiticide widely 

used from the 1950s to 1970s, was detected occasionally in all 

eight major watersheds except the Chupaderas Creek watershed (fig. 7). Dieldrin was detected in 50 percent of all samples collected during 2007–09 but not detected in any samples 

from the Martinez 1518, Chupaderas, and Leon Morey sites. 

Dieldrin concentrations were highest in a streambed-sediment 

sample from the Leon Rodriguez site (1.1 μg/kg) and an LVSS 

sample from the SAR 410 site (0.84 μg/kg) (appendix 1.2). 

Dieldrin is commonly found in the environment because of its 

persistence and widespread use as a termiticide. 

Fipronil is currently (2010) a widely used broad spectrum 

insecticide. The compound or its metabolites, desulfinyl fipronil and fipronil sulfide, were detected frequently in samples 

from all sites except from the Elm Creek and Chupaderas 

Creek watersheds (fig. 7).

PCBs were first synthesized in the early 1930s and have 

had widespread industrial uses, primarily as plasticizers, 

hydraulic lubricants, and dielectric fluids in electrical capacitors (Smith and others, 1988). Adverse human health effects 

and cancer in animals have been associated with exposure 

to PCBs. PCBs were no longer manufactured in the United 

States beginning in 1977 and were banned in 1979 (Agency 

for Toxic Substances and Disease Registry, 2000). PCBs 

include as many as 209 theoretically possible chlorinated compounds, called congeners, with various numbers and positions 

of chlorine atoms attached to the biphenyl structure. Each 

congener has been assigned a congener number that generally 

increases with increasing chlorination of the biphenyl structure (Ballschmiter and Zell, 1980). The NWQL quantified 18 

common PCB congeners for the sediment samples collected 

during 2007–09. Total PCBs, representing the sum of the 18 

reported congeners (appendix 1.2), were computed by using 

the Kaplan-Meier method (Helsel, 2009). 

PCBs sorb to organic matter and particulates and are 

commonly detected in sediments from urban water bodies 

(Van Metre and others, 1997; Wong and others, 2000). The 

larger congeners tend to sorb strongly to solids such as sediments, whereas the smaller congeners are more likely to volatilize (Eisenreich, Capel, and Looney, 1983; Eisenreich and 

others, 1992; Pearson and others, 1996). One or more PCB 

congeners were detected in 90 percent of streambed-sediment 

and LVSS samples collected from all sites (appendix 1.2). 

Samples with the fewest detections of PCBs were collected 

from the Martinez St. Hedwig and Chupaderas sites, whereas 

samples with the most detections were collected from the 

Leon Lackland, Leon 35, and SAR 410 sites. 

In most watersheds, larger congeners (PCBs 118 to 206) 

were detected more frequently than the smaller congeners 

(PCBs 49 to 110). The highest total PCB concentrations were 

in a streambed-sediment sample collected from the Leon 

Lackland site (77 μg/kg) and an LVSS sample collected from 

the Leon 35 site (26 μg/kg). The percentage of industrial land 

use in the contributing area for the Leon Lackland site is near 

the median value for all contributing areas in the study area; in 

addition CH2M Hill (2001) documented the disposal of waste 

lubricants in zone 1 of the former Kelly AFB (fig. 4). The 

percentage of industrial land use in the contributing area for 

the Leon 35 site is larger than the median value for all contributing areas in the study area, which might explain the higher 

PCB concentrations in samples collected from these sites. 

Brominated flame retardants are added to plastics 

and textiles polymers to increase the fire resistance of 

products such as electronics, clothing, and furniture (U.S. 

Environmental Protection Agency, 2010c). Global annual 

production of brominated flame retardants is in the hundreds 

of thousands tons per year (Alaee and others, 2003). Some 

brominated flame retardants have been in use since the 1960s, 

and the global demand for the compounds grew substantially 

during the 1990s and 2000s. One group of brominated flame 

retardants, PBDEs, includes 209 possible compounds; these 

compounds are structurally similar to PCBs and are also 

referred to as congeners (Agency for Toxic Substances and 

Disease Registry, 2004). PBDEs are ubiquitous in the environment and have been detected in house dust, sediments, 

human blood serum, and biota (Zegers and others, 2000; 

Sjödin, Patterson, and Bergman, 2001; Norstrom and others, 2002; Sjödin and others, 2008). There is some evidence 

that the compounds may have toxic effects on humans and 

animals (U.S. Environmental Protection Agency, 2010c). The 

European Union (European Parliament and European Council, 

2003) and the U.S. Environmental Protection Agency (2006) 

have banned the manufacture and use of some PBDEs.

The sediment samples collected during 2007–09 were 

analyzed for PBDEs and three other brominated flame retardants: dechlorane plus, pentabromotoluene, and 1,2-bis(2,4,6-

tribromophenoxy)ethane (Firemaster 680). Brominated flame 

retardants were not detected in the samples collected from 

the Elm Creek or Chupaderas Creek watersheds (fig. 7). The 

most frequent detections occurred in samples collected from 

the Medio Creek, Leon Creek, and San Antonio River watersheds. The highest concentrations of the four most frequently 

detected brominated flame retardants, PBDEs 100, 153, 154, 

and dechlorane plus, were in samples collected from the 

Medio 90, Leon 35, Salado Southton, SAR 410, and SAR 

Elmendorf sites (fig. 8). This is one of the few instances when 

some of the highest concentrations of a constituent were measured in a sediment sample collected from the Medio 90 site 

and could be related to the high percentage of plastic manufacturing and sales in the contributing areas of Medio Creek 

watershed (see last paragraph in “Description of Study Area” 

section). Few reports describing the deposition of individual 

PBDEs to sediments in the United States have been published; the majority of reports describe total PBDEs or relative 

concentrations (not concentrations of individual congeners), 

PBDEs in animals, PBDEs sampled with semipermeable 

devices, or PBDEs in other media such as air or dust. Dodder 

and others (2002) reported PBDE congener concentrations 

in bottom sediments from Hadley Lake in northwest Indiana, 

south of the Great Lakes region, where PBDEs are of concern. 
24 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 7. Detection frequencies of halogenated organic compounds in streambed-sediment and suspended-sediment samples, by 

watershed, in Bexar County, Texas, 2007–09. 

Benfluralin (Benefin)

Chlorpyrifos

Cyfluthrin

Cyhalothrin

DCPA (Dacthal)

Endosulfan I

Octachlorostyrene

Oxyfluorfen

Pendimethalin

Tefluthrin

Tetradifon (Tedion)

cis-Chlordane

trans-Chlordane

cis-Nonachlor

trans-Nonachlor

Oxychlordane

p,p’-DDT

p,p’-DDD

p,p’-DDE

PCB 49

PCB 52

PCB 70

PCB 101

PCB 110

PCB 118

PCB 138

PCB 146

PCB 149

PCB 151

PCB 170

PCB 174

PCB 177

PCB 180

PCB 183

PCB 187

PCB 194

PCB 206

PBDE 47

PBDE 66

PBDE 71

PBDE 85

PBDE 99

PBDE 100

PBDE 138

PBDE 153

PBDE 154

PBDE 183

Dechlorane plus

Pentabromotoluene

1,2-bis(2,4,6-Tribromophenoxy)ethane

(Firemaster 680)

Triclosan

Methoxytriclosan

Desulfnyl fipronil

Dieldrin

Fipronil

Fipronil sulfide

Trifluralin

Antibacterial/

antifungal Other pesticides Chlordanes DDTs Polychlorinated biphenyls (PCBs) Brominated flame retardants

Halogenated organic compounds

Pesticides

0

20406080

100

0

20406080

100

0

20406080

100

0

20406080

100

Detections, in percent

[n, number of samples; DCPA, dimethyltetrachloro terephthalate; DDT, dichlorodiphenyltrichloroethane; DDD, dichlorodiphenyldichloroethane;

DDE, dichlorodiphenyldichloroethylene; PCB, polychlorinated biphenyl; PBDE, polybrominated diphenyl ether]

Medio

Creek

(n=3)

Martinez

Creek

(n=4)

Elm

Creek

(n=2)

Medina

River

(n=2)
Benfluralin (Benefin)

Chlorpyrifos

Cyfluthrin

Cyhalothrin

DCPA (Dacthal)

Endosulfan I

Octachlorostyrene

Oxyfluorfen

Pendimethalin

Tefluthrin

Tetradifon (Tedion)

cis-Chlordane

trans-Chlordane

cis-Nonachlor

trans-Nonachlor

Oxychlordane

p,p’-DDT

p,p’-DDD

p,p’-DDE

PCB 49

PCB 52

PCB 70

PCB 101

PCB 110

PCB 118

PCB 138

PCB 146

PCB 149

PCB 151

PCB 170

PCB 174

PCB 177

PCB 180

PCB 183

PCB 187

PCB 194

PCB 206

PBDE 47

PBDE 66

PBDE 71

PBDE 85

PBDE 99

PBDE 100

PBDE 138

PBDE 153

PBDE 154

PBDE 183

Dechlorane plus

Pentabromotoluene

1,2-bis(2,4,6-Tribromophenoxy)ethane

(Firemaster 680)

Triclosan

Methoxytriclosan

Desulfnyl fipronil

Dieldrin

Fipronil

Fipronil sulfide

Trifluralin

Antibacterial/

antifungal Other pesticides Chlordanes DDTs Polychlorinated biphenyls (PCBs) Brominated flame retardants

Halogenated organic compounds

Pesticides

0

20406080

100

0

20406080

100

0

20406080

100

0

20406080

100

Detections, in percent

[n, number of samples; DCPA, dimethyltetrachloro terephthalate; DDT, dichlorodiphenyltrichloroethane; DDD, dichlorodiphenyldichloroethane;

DDE, dichlorodiphenyldichloroethylene; PCB, polychlorinated biphenyl; PBDE, polybrominated diphenyl ether]

Chupaderas

Creek

(n=1)

Leon

Creek

(n=19)

Salado

Creek

(n=7)

San

Antonio

River

(n=10)

Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 25

Figure 7.—Continued. 
26 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 8. Concentrations of the four most frequently detected brominated flame retardants in streambed-sediment and suspendedsediment samples collected from sites in Bexar County, Texas, 2007–09. 

0

0.2

0.4

0.6

0.8

1.0

1.2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Concentration of brominated flame retardant, in micrograms per kilogram

Medio Pearsall

Medina

Martinez St. Hedwig

Martinez 1518

Chupaderas

Leon Rodriguez

Leon 90

Leon Morey

Leon Lackland

Leon Military

Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR 410

SAR Elmendorf

Medio 90

SAR Theo

Elm

Site identifier (table 2)

Dechlorane

plus

Polybrominated 

diphenyl ether 154

Polybrominated 

diphenyl ether 153

Polybrominated 

diphenyl ether 100 EXPLANATION

Streambed-sediment sample, detection

Suspended-sediment sample, detection

Streambed-sediment sample, 

nondetection at interim reporting level

Suspended-sediment sample, 

nondetection at interim reporting level
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 27

Five PBDE congeners (47, 99, 100, 153, and 154) were common between the Hadley Lake study and the samples collected 

during 2007–09 in Bexar County. Dodder and others (2002, 

table 2) reported PBDE congener concentrations ranging from 

less than 0.02 μg/kg (PBDE 190) to 22 μg/kg (PBDE 99), 

with a median concentration of 1.35 μg/kg and an 83-percent 

detection frequency. Concentrations of these same PBDE 

congeners in the samples collected during 2007–09 in Bexar 

County ranged from less than 0.1 μg/kg (PBDEs 47, 99, 100, 

153, and 154) to 5.2 μg/kg (PBDE 47), with a median concentration of 0.34 μg/kg and a 45-percent detection frequency. 

PAHs are ubiquitous in the urban environment and are 

derived from numerous sources. Common sources in urban 

settings include automobile exhaust, used motor oil, automobile tire particles, parking lot sealcoat, and burning wood, oil, 

coal, or other combustibles for cooking, heating, or energy 

production; the relative contribution of PAHs to sediments 

from each of these sources varies (Van Metre and Mahler, 

2010). PAHs rarely occur in the environment as individual 

compounds but are present as complex mixtures. PAHs are 

potential human health hazards; several PAH compounds, 

known as B2 PAHs, have been identified as probable carcinogens (U.S. Environmental Protection Agency, 1993). In this 

report, total PAH is the sum of 12 compounds: acenaphthene, 

acenaphthylene, anthracene, benz(a)anthracene, benzo(a)

pyrene, chrysene, dibenzo(a,h)anthracene, fluoranthene, 

fluorene, naphthalene, phenanthrene, and pyrene (Ingersoll 

and others, 2001; 2-methylnaphthalene not included because 

not measured by the NWQL). PAHs were most frequently 

detected in the Leon Creek and San Antonio River watersheds 

(appendix 1.3). The greatest total PAH concentrations were 

measured in a streambed-sediment sample collected in 2007 

from the Leon Rodriguez site (4,000 μg/kg) and in an LVSS 

sample collected in 2008 from the SAR 410 site (3,600 μg/kg). 

Land use in the contributing area of the Leon Rodriguez site 

is typical of the study area (table 2) and therefore provides no 

insight to the relatively high PAH concentrations measured in 

the streambed-sediment sample collected from the site. Total 

PAH concentrations in streambed-sediment samples collected 

at the Leon Rodriguez site in 2008 (170 μg/kg) and 2009 (260 

μg/kg) were not similarly high. Relatively high total PAH concentrations in sediment samples collected from the SAR 410 

site are expected because of the relatively high percentages of 

residential, commercial, industrial, and transportation land use 

in the contributing area of the SAR 410 site compared to these 

land uses in contributing areas of other sites in the study area. 

The land use in the contributing area of the SAR Theo site is 

similar to that of the SAR 410 site, and total PAH concentrations in streambed-sediment samples collected from the SAR 

Theo site (1,500 μg/kg) and SAR 410 site (2,000, 760, and 460 

μg/kg) were similarly high. PAHs were not detected often and 

only at relatively low concentrations in the samples collected 

at sites on Medio Creek, Medina River, Elm Creek, Martinez 

Creek, and Chupaderas Creek (appendix 1.3); contributing 

areas for these sites are among the most undeveloped in the 

study area.

Kendall’s tau nonparametric correlation coefficients 

(Helsel, 2005) were computed to measure the strength of 

association between SSC and LVSS contaminant concentrations. The 13 LVSS samples were collected as follows: 1 at 

the Medina site, 2 at the Martinez St. Hedwig site, 3 at the 

Leon 35 site, 2 at the Salado Southton site, 2 at the SAR 410 

site, and 3 at the SAR Elmendorf site. Correlation coefficients 

were computed three different ways: for the entire dataset of 

13 samples, for the 3 samples collected from the Leon 35 site, 

and for the 3 samples collected from the SAR Elmendorf site. 

When considering the entire dataset, Kendall tau correlation 

coefficients were only statistically significant (p-value less 

than .05) for dieldrin (tau = .416; p-value .048; 8 nondetections) and p,p'-DDD (tau = .414; p-value .049; 10 nondetections). Tau correlation coefficient values closer to +1.0 

indicate a stronger, positive association between the variables; 

tau values closer to -1.0 indicate a stronger, negative association; and tau values near 0 indicate the variables are unrelated 

(Helsel and Hirsch, 2002). There were no statistically significant correlations between the SSC and LVSS contaminant 

concentrations for the datasets from the Leon 35 or SAR 

Elmendorf sites, which both had small sample sizes. 

Loads were not computed using the LVSS samples collected in Bexar County during 2007–09; in some studies, an 

estimate of load (total mass of contaminant per storm) can be 

computed by using the contaminant concentration, SSC, and 

volume of stormwater (Mahler and others, 2006). Mahler and 

others (2006) measured sediment chemistry and mass in discreet samples over the storm hydrograph; contaminant concentrations were typically greatest in the first-flush samples, but 

the SSC was typically greatest in the samples collected at peak 

flow. When temporal loads were computed over a hydrograph, 

the variations in loads generally followed the same form as 

the hydrograph because the contaminant load was a function 

of sediment load. The first-flush samples collected during 

2007–09 do not provide adequate information to compute 

contaminant loads. Additional measurements of SSC and contaminant concentrations over the hydrograph, stream discharge 

measurements, and stormwater samples from the center of the 

stream channel using an isokinetic sampler (intake does not 

change velocity of stream water) would be needed to provide 

meaningful estimates of loads. The addition of automatic 

water samplers at existing streamflow-gaging locations could 

provide the measurements and stormwater samples needed to 

compute loads. 

Selected trace element and organic contaminant concentrations were compared between streambed-sediment and 

LVSS samples. A previous investigation of sediments in Fort 

Worth watersheds determined that the concentrations of most 

trace elements in streambed and suspended sediments were 

similar, whereas concentrations of organic contaminants in 

suspended sediments were often higher compared to concentrations in streambed sediments (Van Metre and others, 2003). 

The contaminant concentrations in the Bexar County streambed-sediment and LVSS samples varied similarly (fig. 9). The 

median ratio of median LVSS contaminant concentrations to 
28 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 9. Comparison of concentrations of selected contaminants in streambed-sediment samples to concentrations in suspendedsediment samples collected from selected sites in Bexar County, Texas, 2007–09. 

Site identifier (table 2)

Site identifier (table 2)

Medina

Martinez

St. Hedwig

Leon 35

Salado

Southton

SAR 410

SAR

Elmendorf

Medina

Martinez

St. Hedwig

Leon 35

Salado

Southton

SAR 410

SAR

Elmendorf

Concentration, in micrograms per kilogram

Concentration, in micrograms per gram

0

0.2

0.4

0.6

0.8

1.0

0

0.4

0.8

1.2

1.6

0

10

20

30

0

1,000

2,000

3,000

4,000

0

1

2

3

4

5

0

40

80

120

160

0

20

40

60

80

Dieldrin

trans-Nonachlor

Total 

polychlorinated

biphenyls

Total

polycyclic

aromatic

hydrocarbons

Cadmium

Chromium

Lead

EXPLANATION

Streambed-sediment sample, detection

Suspended-sediment sample, detection

Streambed-sediment sample, 

nondetection at interim reporting level

Suspended-sediment sample, 

nondetection at interim reporting level

Note: Nondetections not shown for total

polychlorinated biphenyls and total

polycyclic aromatic hydrocarbons
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 29

median streambed-sediment contaminant concentrations was 

1.18 for trace elements and 3.16 for organic contaminants. 

Van Metre and others (2003) proposed two hypotheses to 

explain the difference in streambed- and suspended-sediment 

contaminant concentrations: (1) LVSS contaminant concentrations are highly variable and typical concentrations are not 

well represented by a small sample size; and (2) contaminants 

are removed during transport and deposition through desorption as organic carbon breaks down, or by microbial degradation or bioaccumulation of the contaminants. Another possible 

explanation is that streambed sediments are typically coarser, 

even after sieving, than suspended sediments resulting in less 

surface area per given mass of sediment for adsorption of contaminants. This could also be related to differences in organic 

carbon values in streambed-sediment samples compared to 

values in LVSS samples. However, the median organic carbon 

values in streambed-sediment and LVSS samples collected 

during 2007–09 were 1.92 and 2.05 percent, respectively; 

for 36 streambed-sediment and 13 LVSS samples, the distributions in the two groups did not differ significantly at the 

95-percent confidence level (p-value < .05) according to the 

Mann-Whitney test results (two-sided p-value = .41). The 

Mann-Whitney test is described in detail in Helsel and Hirsch 

(2002). 

Comparison of Findings to Sediment-Quality 

Guidelines

Sediment contaminant concentrations can be compared 

to SQGs to determine the degree of contamination. The SQGs 

used in this report are not regulatory limits but benchmarks to 

evaluate the potential toxicity of bed sediment to biota. SQGs 

have been published by research scientists and government 

agencies to evaluate the potential toxicity of sediment-associated contaminants to benthic biota (for example, Ingersoll and 

others, 2000; MacDonald, Ingersoll, and Berger, 2000; Texas 

Commission on Environmental Quality, 2010a). SQGs were 

developed for streambed sediment but not for suspended sediment; however, the LVSS sample concentrations were evaluated relative to SQGs for comparisons between sites. 

There are typically two SQG concentration levels—a 

lower level, below which adverse effects to aquatic biota are 

not expected, and a higher level, above which adverse effects 

are expected to occur. MacDonald, Ingersoll, and Berger 

(2000) developed consensus-based SQGs from numerous sets 

of published guidelines (table 5). The threshold effect concentration (TEC), or lower level, and probable effect concentration (PEC), or higher level, of MacDonald, Ingersoll, and 

Berger (2000) were used to evaluate the concentrations of 

trace elements, halogenated organic compounds, and PAHs in 

the streambed-sediment and LVSS samples collected during 

2007–09. Sediment-contaminant concentrations less than the 

TEC should not have a harmful effect on sediment-dwelling 

organisms, whereas concentrations greater than the PEC are 

likely to have a harmful effect (MacDonald, Ingersoll, and 

Berger, 2000). TCEQ, the environmental enforcement agency 

for the State, publishes screening levels for sediment similar to SQGs (Texas Commission on Environmental Quality, 

2010a); many of these screening levels are based on the SQGs 

published by other researchers. All TCEQ sediment screening 

levels for the trace elements, halogenated organic compounds, 

and PAHs discussed in this section are identical to the higherlevel PECs of MacDonald, Ingersoll, and Berger (2000). 

There are consensus-based SQGs for eight trace elements: arsenic, cadmium, chromium, copper, lead, mercury, 

nickel, and zinc. Generally, concentrations of trace elements 

in the samples collected during 2007–09 were low compared 

to SQGs (fig. 10). Trace element concentrations were greater 

than the PEC in 1.5 percent of the samples and greater than the 

TEC in 28 percent of the samples. Chromium concentrations 

exceeded SQGs more frequently than concentrations of any 

other constituents (greater than the TEC and PEC in 69 and 8 

percent of samples, respectively). The PECs for both cadmium 

and chromium were exceeded in the two samples collected 

from the Leon Quintana site. The PEC for chromium also 

was exceeded in two samples collected from the Leon 35 site. 

The trace elements most frequently detected at concentrations greater than the TEC were chromium and lead (69 and 

33 percent of all analyses, respectively), then zinc (35 percent), nickel (20 percent), cadmium (16 percent), arsenic 

(12 percent), and copper (10 percent). No concentrations of 

mercury were greater than the TEC (fig. 10). On the basis of 

the percentages of concentrations greater than the TEC for all 

eight trace elements, the greatest amounts of trace elements in 

the sediments were at the Leon Quintana (63 percent), Leon 

35 (54 percent), and SAR 410 (48 percent) sites; the least 

amounts of trace elements in the sediments were at the Leon 

Rodriguez (8 percent), Medina (6 percent), Elm (0), and SAR 

Theo (0) sites. The SAR Theo site is about 9.7 km upstream 

from the SAR 410 site; trace element concentrations at these 

sites were expected to be similar. However, construction 

activities observed on the stream channel during the collection 

of samples at the SAR Theo site are believed to have increased 

sediment contributions at this site and diluted the trace element concentrations. There is no consensus-based SQG 

for silver, however the National Oceanic and Atmospheric 

Administration (Buchman, 2008) provides screening guidelines for silver in marine sediments at a lower level (effects 

range low—ERL) of 1.0 μg/g and a higher level (effects range 

median—ERM) of 3.7 μg/g. Silver concentrations were less 

than the method detection level of 1 μg/g at all sites except the 

Leon Quintana and Leon 35 sites. In two streambed-sediment 

samples collected from the Leon Quintana site, silver concentrations were 3.8 μg/g, which exceeded the ERM. Silver 

concentrations ranged from 1.5 to 2.5 μg/g in samples from 

the Leon 35 site. High trace element concentrations occurred 

most frequently in the Leon Creek watershed downstream 

from the former Kelly AFB where activities that involved 

the use and disposal of trace elements, such as electroplating 

and chrome plating sludge and paint disposal, were known to 

occur (CH2M Hill, 2001).
30 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 10. Comparison of consensus-based sediment-quality guidelines (MacDonald, Ingersoll, and Berger, 2000) with concentrations 

of selected trace elements in streambed-sediment and suspended-sediment samples collected from sites in Bexar County, Texas, 

2007–09. 

Medio Pearsall

Medina

Martinez St. Hedwig

Martinez 1518

Chupaderas

Leon Rodriguez

Leon 90

Leon Morey

Leon Lackland

Leon Military

Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR 410

SAR Elmendorf

Medio 90

SAR Theo

Elm

Site identifier (table 2)

Medio Pearsall

Medina

Martinez St. Hedwig

Martinez 1518

Chupaderas

Leon Rodriguez

Leon 90

Leon Morey

Leon Lackland

Leon Military

Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR 410

SAR Elmendorf

Medio 90

SAR Theo

Elm

Site identifier (table 2)

0 

5 

10 

15 

20 

25 

0 

40 

80 

120 

160 

0 

0.02

0.04

0.06

0.08

0.10

0 

20 

40 

60 

80 

Concentration, in micrograms per gram

0 

1 

2 

3 

4 

5 

6 

7 

0 

5 

10 

15 

20 

25 

30 

35 

40 

45 

0 

5 

10

15

20

25

30

35

0 

50

100 

150 

200 

Lead Zinc

Nickel

Copper

Cadmium Arsenic

Chromium

Mercury

EXPLANATION

Streambed-sediment sample concentration

Greater than probable effect concentration

Greater than threshold effect concentration

Less than threshold effect concentration

Suspended-sediment sample concentration

Greater than probable effect concentration

Greater than threshold effect concentration

Less than threshold effect concentration
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 31

MacDonald, Ingersoll, and Berger (2000) developed 

consensus-based SQGs for six of the halogenated organic 

compounds included in the analyses of sediment samples 

collected during 2007–09 in Bexar County: chlordane, dieldrin, DDD, DDE, DDT, and PCBs. The halogenated organic 

compounds for which SQGs are recommended are not the 

exact same compounds that were analyzed for this study. 

DDD, DDE, and DDT are primarily mixtures of different 

isomers, and the toxicity of each isomer is different (Ginsburg, 

1947). For example, technical grade DDT that was generally 

used as an insecticide is primarily a mixture of the isomers 

p,p'-DDT (active ingredient, comprising 65 to 80 percent 

of the mixture), o,p'-DDT (15 to 21 percent), and p,p'-DDD 

(up to 4 percent) (Metcalf, 1995). MacDonald, Ingersoll, 

and Berger (2000) recommended SQGs for the sum of the 

three isomers of the DDD, DDE, and DDT compounds. 

However, for this report only the p,p'-form of each compound was determined by the NWQL so there might be 

more SQG exceedances than reported here because the 

concentrations of the o,p'- and o,o'-forms of DDT, DDD, 

and DDE were not measured in the samples. MacDonald, 

Ingersoll, and Berger (2000) defined total chlordane as the 

sum of the two isomers cis-chlordane and trans-chlordane, 

and the sum of the two isomers was computed for the sediment samples collected in 2007–09 for comparison to the 

SQGs. MacDonald, Dipinto, and others (2000) did not designate total PCBs as a sum of specific congeners or Aroclors, 

but instead derived SQGs for an intentionally undefined 

mixture of PCBs, referred to as total PCBs because PCBs 

occur as complex mixtures in field-collected sediments. In this 

report, total PCBs was computed as the sum of the 18 reported 

congeners. 

Concentrations of halogenated organic compounds in the 

2007–09 samples generally were low in comparison to SQGs 

(fig. 11). The TECs of the six halogenated organic compounds 

with SQGs were exceeded in 32 of 288 analyses (11 percent) 

and PECs were exceeded in 3 of 288 analyses (1 percent). The 

PECs of DDT, DDD, and DDE were exceeded in one streambed-sediment sample collected from the Leon Lackland site 

on December 3, 2007 (110 μg/kg of p,p'-DDT, 55 μg/kg of 

p,p'-DDD, and 41 μg/kg of p,p'-DDE). DDD and DDE, in 

addition to composing part of the technical grade of DDT, 

are the most common metabolites of DDT; under aerobic 

conditions DDT degrades to DDE and under anaerobic conditions degrades to DDD (Spencer and Cliath, 1972). Although 

DDD and DDE were detected less frequently than other 

halogenated organic compounds, most detected concentrations exceeded the TECs. DDT was detected in 13 percent 

of the samples with 67 percent of those detections exceeding 

the TEC. DDD and DDE were detected in 19 and 35 percent 

of the samples with 78 and 53 percent of those detections 

exceeding the TECs, respectively. Chlordane compounds were 

detected in 94 percent of the samples and 6 percent of the 

analyses of cis-chlordane plus trans-chlordane were greater 

than the TEC. All dieldrin concentrations were less than the 

TEC of 1.90 μg/kg. Only one sample exceeded the TEC for 

Table 5. Consensus-based sediment-quality guidelines used 

for comparison to contaminant concentrations in streambedsediment and suspended-sediment samples collected from sites 

in Bexar County, Texas, 2007–09.

[μg/g, micrograms per gram; μg/kg, micrograms per kilogram; PCBs, 

polychlorinated biphenyls; PAHs, polycyclic aromatic hydrocarbons]

Constituent Threshold effect 

concentration1

Probable effect 

concentration1

Trace elements (μg/g)

Arsenic 9.79 33.0

Cadmium .99 4.98

Chromium 43.4 111

Copper 31.6 149

Lead 35.8 128

Mercury .18 1.06

Nickel 22.7 48.6

Zinc 121 459

Halogenated organic compounds (μg/kg)

Chlordane 3.24 17.6

Dieldrin 1.90 61.8

DDD 4.88 28.0

DDE 3.16 31.3

DDT 4.16 62.9

Total PCBs 59.8 676

Polycyclic aromatic hydrocarbons (μg/kg)

Anthracene 57.2 845

Benzo(a)pyrene 150 1,450

Benz(a)anthracene 108 1,050

Chrysene 166 1,290

Dibenzo(a,h)anthracene 33.0 none

Fluoranthene 423 2,230

Fluorene 77.4 536

Naphthalene 176 561

Phenanthrene 204 1,170

Pyrene 195 1,520

Total PAHs 1,610 22,800

1

 From MacDonald, Ingersoll, and Berger (2000).
32 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 11. Comparison of consensus-based sediment-quality guidelines (MacDonald, Ingersoll, and Berger, 2000) with concentrations 

of selected halogenated organic compounds in streambed-sediment and suspended-sediment samples collected from sites in Bexar 

County, Texas, 2007–09. Medio Pearsall

Medina

Martinez St. Hedwig

Martinez 1518

Chupaderas

Leon Rodriguez

Leon 90

Leon Morey

Leon Lackland

Leon Military

Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR 410

SAR Elmendorf

Medio 90

SAR Theo

Elm

Site identifier (table 2)

Medio Pearsall

Medina

Martinez St. Hedwig

Martinez 1518

Chupaderas

Leon Rodriguez

Leon 90

Leon Morey

Leon Lackland

Leon Military

Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR 410

SAR Elmendorf

Medio 90

SAR Theo

Elm

Site identifier (table 2)

Concentration, in micrograms per kilogram

0

0.2

0.4

0.6

0.8

1.0

1.2

0

10

20

30

0

5

10

15

20

0

5

10

15

20

0

2

4

6

0

2

4

6

8

ND ND

(77) (55)

(41) (110)

(52)

p,p’-DDE

Total polychlorinated biphenyls

Dieldrin cis-Chlordane plus

trans-chlordane

p,p’-DDD

p,p’-DDT

EXPLANATION

Streambed-sediment sample concentration

Greater than probable effect concentration

Greater than threshold effect concentration

Less than threshold effect concentration

Nondetection at interim reporting level

Indicates concentration value off scale

Suspended-sediment sample concentration

Greater than threshold effect concentration

Less than threshold effect concentration

Nondetection at interim reporting level

(77)

Note: Nondetections not shown for cis-chlordane plus

trans-chlordane and for total polychlorinated biphenyls
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 33

total PCBs—the streambed-sediment sample collected from 

the Leon Lackland site on December 3, 2007.

Consensus-based SQGs were developed for several 

individual PAH compounds (anthracene, benz(a)anthracene, 

benzo(a)pyrene, chrysene, dibenzo(a,h)anthracene, fluorene, 

fluoranthene, naphthalene, phenanthrene, and pyrene) and 

total PAHs (MacDonald, Ingersoll, and Berger, 2000). The 

five PAHs with the highest average concentrations (benzo(a)

pyrene, chrysene, fluoranthene, phenanthrene, and pyrene) and 

total PAH were selected for comparison to the SQGs (fig. 12). 

The TECs of the six selected PAHs were exceeded in 40 of 

288 analyses (14 percent). None of the PAH concentrations 

exceeded the PECs. The PAH concentrations were typically 

highest in samples collected from the following sites: Leon 

Rodriguez, Leon Lackland, Leon 35, Salado Southton, and 

SAR 410. PAHs were not detected in the samples collected 

from the Medina and Chupaderas sites, except for perylene 

and 2,6-dimethylnaphthalene, which are not necessarily 

indicative of human-related contamination. Perylene is thought 

to be produced by in situ diagenesis under anoxic conditions 

and typically occurs in aquatic sediments a few centimeters 

below the sediment-water interface (Gschwend and others, 

1983; Silliman and others, 1998). A study of water quality 

in the upper Snake River watershed in Idaho and Wyoming 

attributed frequent detections of 2,6-dimethylnaphthalene to 

industrial and recreational activities (Clark and others, 1998, 

p. 16). During sampling for the USGS NAWQA Contaminant 

Trends in Lake Sediments Program (Van Metre and others, 

2004), 2,6-dimethylnaphthalene was frequently detected in 

streambed, suspended, and lake bottom sediments regardless 

of land use in the watersheds, possibly because of a problem 

with the analytical method that was used (Barbara Mahler, 

U.S. Geological Survey, written commun., 2006).

The overall degree of sediment contamination of the 

Bexar County sampling sites was assessed with the mean PEC 

quotient (MacDonald, Ingersoll, and Berger, 2000). The mean 

PEC quotient is derived by using the three groups of constituents for which consensus-based SQGs exist—trace elements, 

halogenated organic compounds, and PAHs. To compute the 

mean PEC quotient, the concentration of each constituent is 

divided by its respective PEC to get the individual PEC quotient, and then the individual PEC quotients are summed for 

each sample and divided by the number of PEC quotients to 

get the mean PEC quotient. Nondetected concentrations were 

included in the mean PEC quotient computations by following 

the procedures that Helsel (2009) used for toxic equivalence 

factors and by using the Kaplan-Meier procedure. The mean 

PEC quotient for the streambed-sediment sample collected 

from the Martinez 1518 site on August 11, 2009, included 

only the trace element concentrations because no halogenated 

organic compound or PAH concentrations were available 

(sample jar broke during shipment to analytical laboratory). 

Mean PEC quotients provide a basis for predicting sediment 

toxicity. MacDonald, Ingersoll, and Berger (2000) determined 

that a mean PEC quotient greater than 0.5 is a reasonable 

indicator of whether the sediment is toxic to benthic biota and 

were able to correctly predict toxicity in 85 percent of samples tested; and the higher the mean PEC quotient, the higher 

the incidence of toxicity in sediments. The SQGs were not 

developed for suspended sediments, and using the mean 

PEC quotient for predicting sediment toxicity has not been 

shown to apply to suspended sediments, however the guidelines still provide useful benchmarks for comparing constituent concentrations measured in samples collected from the 

different sites. The mean PEC quotient is less than 0.5 for all 

but one of the samples collected in this study. The highest 

mean PEC quotient (0.51) was measured in the streambedsediment sample collected from the Leon Lackland site on 

December 3, 2007. The next highest mean PEC quotients were 

measured in samples collected from the Leon Quintana, Leon 

35, Leon Military, and SAR 410 (in order of increasing values; 

fig. 13). 

Comparison of Findings to Data from Previous 

Studies

Several studies have demonstrated that benthic organisms bioaccumulate many sediment-associated contaminants 

and that concentrations of sediment contaminants, particularly 

organic compounds, correlate positively with the concentrations of these contaminants in benthic organisms (for example, 

Brown and others, 1998; Chalmers, 2002). The USGS collected biological samples at the Leon 35, Salado 13, and SAR 

Elmendorf sites during 1995–97. Asian clam, common carp, 

channel catfish, gray redhorse minnow, and spotted bass were 

collected and analyzed for trace elements and halogenated 

organic compounds (appendix 3.1). All eight trace elements 

with SQGs were detected in at least one organism from each 

site except for mercury, which was not detected in the sample 

collected from the SAR Elmendorf site. The highest concentrations of trace elements were measured in the Asian clam 

sample from the Leon 35 site, except for copper and zinc, 

which were highest in a common carp sample from the SAR 

Elmendorf site in 1996. The high concentrations of trace 

elements measured in biological samples from the Leon 35 

and SAR Elmendorf sites are consistent with trace element 

concentrations in the streambed-ediment and LVSS samples in 

this study, which were elevated frequently in samples collected 

from sites on Leon Creek and the San Antonio River (fig. 10). 

Silver was detected in both the Asian clam and common 

carp samples from the Leon 35 site and in one common carp 

sample from the SAR Elmendorf site, but not in any biological samples from the Salado 13 site. Similarly, silver was 

detected in all 2007–09 sediment samples from the from Leon 

35 site but not in any of the sediment samples from the SAR 

Elmendorf or Salado Creek sites (appendix 1.1). The organic 

analyses of biological samples included total PCBs, dieldrin, 

and various forms of chlordane and DDT. Total PCB concentrations typically were highest in biological samples from the 

SAR Elmendorf site (appendix 3.1). In contrast, total PCB 

concentrations in the 2007–09 sediment samples generally 
34 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 12. Comparison of consensus-based sediment-quality guidelines (MacDonald, Ingersoll, and Berger, 2000) with concentrations 

of selected polycyclic aromatic hydrocarbons (PAHs) and total PAHs in streambed-sediment and suspended-sediment samples 

collected from sites in Bexar County, Texas, 2007–09. Medio Pearsall Medina Martinez St. Hedwig Martinez 1518 Chupaderas Leon Rodriguez Leon 90 Leon Morey Leon Lackland Leon Military Leon Quintana Leon 35 Salado 13

Rosillo

Salado Southton

SAR 410

SAR Elmendorf

Medio 90

SAR Theo

Elm

Site identifier (table 2)

Medio Pearsall

Medina

Martinez St. Hedwig

Martinez 1518

Chupaderas

Leon Rodriguez

Leon 90

Leon Morey

Leon Lackland

Leon Military

Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR 410

SAR Elmendorf

Medio 90

SAR Theo

Elm

Site identifier (table 2)

Concentration, in micrograms per kilogram

0

100

200

300

400

500

0

100

200

300

400

500

600

700

800

0

200

400

600

800

1,000

0

200

400

600

800

1,000

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

0

100

200

300

400

500

(<1,200) (<760; <1,500) (<900; <2,500)

(<1,200) (<1,500) (<1,200) (<1,500) (<900; <2,500) (<2,500)

(<1,200) (<1,500) (<2,500)

(<1,200) (<760; <1,500) (<900; <2,500)

Pyrene

Fluoranthene

Benzo(a)pyrene

Total PAHs

Phenanthrene

Chrysene

EXPLANATION

Streambed-sediment sample concentration

Greater than threshold effect concentration

Less than threshold effect concentration

Nondetection at interim reporting level

Indicates concentration value off scale,

but less than indicated value

Suspended-sediment sample concentration

Greater than threshold effect concentration

Less than threshold effect concentration

Nondetection at interim reporting level

(<1,200) Note: Nondetections not shown for total PAHs
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 35

were higher at the Leon 35 site than at the SAR Elmendorf site 

(appendix 1.2). 

The USGS collected streambed-sediment samples at 

the Medio Pearsall site in 1999, the Leon 35, Salado 13, and 

SAR Elmendorf sites in 1995 and 2001, and the SAR 410 in 

2001 (appendix 3.2). These samples were analyzed for one or 

more of the following groups of constituents: trace elements, 

halogenated organic compounds, and PAHs. The 1995–2001 

samples were sieved for grain size homogeneity (62 μm and 2 

μm for trace elements and organic constituents, respectively) 

before being submitted to the laboratory for analysis (sample 

processing was similar during the Bexar County 2007–09 

study). Most trace element concentrations were highest in the 

streambed-sediment sample collected in 1995 from the Leon 

35 site, with six of eight concentrations exceeding the TECs. 

Among all trace elements, chromium concentrations were 

highest, exceeding the TEC of 43.4 μg/g in the streambedsediment samples from the Medio Pearsall, Leon 35, Salado 

13, and SAR Elmendorf sites. The chromium concentrations 

in the 1995–99 streambed-sediment samples are similar to the 

chromium concentrations measured in the 2007–09 streambed-sediment and LVSS samples, where the most frequent 

exceedances of the TEC were for chromium (69 percent) and 

some of the highest concentrations were at the Leon 35 site 

(fig. 10). During 1995–99, silver was detected in samples from 

the Medio Pearsall, Leon 35, Salado 13, and SAR Elmendorf 

sites; the highest silver concentration was in a streambedsediment sample from the Leon 35 site (appendix 3.2). During 

2007–09, silver was detected only in samples from the Leon 

35 and Leon Quintana sites (appendix 1.1). Selected 1995 

samples from the Leon 35, Salado 13, and SAR Elmendorf 

sites were analyzed for some halogenated organic compounds—various forms of chlordane and DDT, dieldrin, and 

total PCBs; dieldrin and total PCBs were not detected in any 

of these samples (appendix 3.2). In contrast, dieldrin and total 

PCBs were detected in some of the 2007–09 samples from 

the Leon 35, Salado 13, and SAR Elmendorf sites (appendix 

1.2), but concentrations were less than the minimum reporting levels used to analyze samples collected in 1995. None of 

the halogenated organic compounds were detected in the 1995 

sample collected the SAR Elmendorf site, but several halogenated organic compounds were detected in the 2007–09 samples; concentrations ranged from less than historical minimum 

reporting levels to more than historical minimum reporting 

levels. The more frequent detections of halogenated organic 

compounds in recent samples may be a result of the lower 

IRLs in the current study, sample variability, or new sources—

the reason there were more detections is not possible to 

determine with the available data. Various forms of chlordane 

and DDT were detected in the 1995 samples from the Leon 35 

and Salado 13 sites and in the 2007–09 samples from the same 

sites; the 1995 chlordane and DDT concentrations generally 

were higher than the 2007–09 concentrations. Ten streambedsediment samples collected in either 1995 or 2001 were 

analyzed for the 16 PAH compounds on the USEPA Priority 

Pollutants list (Code of Federal Regulations, 1998). The 

highest PAH concentrations were measured in the September 

2001 sample from the Leon 35 site, in which all 16 PAHs were 

Figure 13. Mean probable effect concentration quotient of streambed-sediment and suspended-sediment samples collected from 

sites in Bexar County, Texas, 2007–09. 

EXPLANATION

Streambed-sediment sample

Suspended-sediment sample

Mean probable effect concentration quotient

0

0.1

0.2

0.3

0.4

0.5

0.6

Medio Pearsall

Medina

Martinez St. Hedwig

Martinez 1518

Chupaderas

Leon Rodriguez

Leon 90

Leon Morey

Leon Lackland

Leon Military

Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR 410

SAR Elmendorf

Medio 90

SAR Theo

Elm

Site identifier (table 2)
36 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

detected and total PAH was 7,000 μg/kg (appendix 3.2). The 

second highest PAH concentrations were at the SAR 410 site. 

PAH concentrations were less than the IRL in more than 50 

percent of the samples from the SAR Elmendorf site. PAH 

concentrations in samples collected in either 1995 or 2001 at 

the Leon 35, Salado 13, and SAR Elmendorf sites are typically 

higher than the PAH concentrations in the 2007–09 samples 

from these sites. PAH concentrations exceeded TECs in an 

average of 28 percent of the 1995 and 2001 samples compared 

to an average of 14 percent of the 2007–09 samples. The data 

are not sufficient to determine if lower concentrations of chlordane, DDT, and PAHs in the current study relative to historical data indicate downward trends in these contaminants over 

time, or are a result of either sample variability or differences 

in analytical techniques.

The AFCEE oversees the semiannual compliance sampling near the former Kelly AFB of groundwater and Leon 

Creek surface water and streambed sediment. The results from 

streambed-sediment samples collected from eight selected 

AFCEE sampling sites (fig. 4) during 1994–2008 (appendix 4.0) and the results from streambed-sediment and LVSS 

samples collected from the Leon Creek sites during 2007–09 

are compared in table 6. The means and standard deviations 

were computed by using the Kaplan-Meier method when there 

were censored data (Helsel, 2005). Differences between the 

AFCEE and USGS analytical techniques make comparisons 

of the results somewhat uncertain. The mean concentrations of 

trace elements in the USGS samples are typically higher than 

those in the AFCEE samples. However, most of the AFCEE 

samples were extracted by using EPA method SW3050B (U.S. 

Environmental Protection Agency, 1996), which is a strong 

acid but not a total digestion, whereas the USGS method is 

a total digestion. The range of organic compound concentrations is much larger in the AFCEE samples compared to the 

range in the USGS samples, with numerous large outliers 

among the results for the AFCEE samples. Total chlordane 

was computed similarly for both sets of data, by using the 

sum of alpha- and gamma- chlordane isomers for the AFCEE 

samples and cis- and trans-chlordane isomers for the USGS 

samples. PCB Aroclors 1016, 1221, 1232, 1242, 1248, 1254, 

and 1260 were analyzed in the AFCEE samples. Aroclor is the 

industrial trade name for commercial PCB mixtures produced 

in the United States (Agency for Toxic Substances and Disease 

Registry, 2000). Total PCBs in the AFCEE samples was computed as the sum of the reported PCB Aroclors. Total PCBs 

in the USGS samples is the sum of 18 congeners (appendix 

1.2). Total PAHs was computed as the sum of the same 12 

PAH compounds in both sets of samples (acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, 

chrysene, dibenzo(a,h)anthracene, fluoranthene, fluorene, 

naphthalene, phenanthrene, and pyrene). All summations with 

censored data were computed by using the Kaplan-Meier 

method (Helsel, 2005). Despite differences in analytical methods, the USGS results are within concentration ranges of the 

AFCEE samples for all trace elements except zinc, all halogenated organic compounds except p,p'-DDD and p,p'-DDE, 

and for total PAHs (table 6). The mean concentrations of lead, 

mercury, dieldrin, p,p'-DDE, total PCBs, and total PAHs are 

higher in the AFCEE samples compared to concentrations 

in the USGS samples. Inconsistencies in analytical methods 

used by the AFCEE and USGS preclude identifying changes 

in streambed-sediment chemistry over time, but could indicate 

that more frequent semiannual compliance sampling captures 

a wider range of contaminant concentrations than observed in 

the samples collected during 2007–09.

To evaluate sediment quality in Bexar County in a 

broader context, concentrations of sediment-associated 

constituents for LVSS samples collected from Bexar County 

streams during 2007–09 were compared with sediment-associated constituents measured in LVSS samples collected during 

previous studies in the Austin and Fort Worth areas (Mahler 

and others, 2006; Van Metre and others, 2003, respectively). 

The Austin and Fort Worth area studies included watersheds 

with land uses and background or reference conditions similar 

to those of the contributing areas in Bexar County, except that 

the Austin and Fort Worth watersheds did not have military 

installations. All three studies used similar LVSS sample 

collection and filtration methods and the same methods to 

analyze samples for trace elements. Mean trace element 

concentrations in the Bexar County LVSS samples generally were lower compared to the mean concentrations in the 

Austin and Fort Worth LVSS samples, but considering the 

relatively large ranges and standard deviations associated with 

the concentrations measured in all three areas, the trace element concentrations from the three areas are similar (table 7). 

LVSS samples for the analysis of halogenated organic compounds and PAHs from the Austin and Fort Worth areas were 

analyzed at the NWQL by using an older analytical method 

with Soxhlet extraction (Noriega and others, 2003; Olson and 

others, 2004) compared to the ASE method used for the Bexar 

County samples collected. The Soxhlet extraction method 

reported technical chlordane concentrations for the Austin and 

Fort Worth samples. The mean concentrations of the halogenated organic compounds and total PAH generally are lower in 

the Bexar County samples than in the Austin and Fort Worth 

samples but are similar overall when considering the large 

ranges and standard deviations.

Statistical Analyses

To compare the results obtained in the different watersheds and explore possible explanatory variables, concentrations of sediment-associated contaminants measured during 

2007–09 in streambed-sediment samples collected from the 

sampling sites in Bexar County were evaluated by using 

statistical tests. LVSS samples were not included in the 

statistical analyses because they were not collected from all 

watersheds and the concentrations of organic compounds 

were markedly different (higher) in LVSS samples compared 

to concentrations in streambed-sediment samples. The 

Bexar County sediment contaminant concentration data set 

is small (less than 100 samples) and non-normally distributed 
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 37

(Helsel, 2005). Concentrations are positively skewed (bulk 

of values below the mean) with a few high outliers (figs. 

10–12), particularly for the halogenated organic compounds. 

Some constituents such as the halogenated organic compounds were frequently not detected. Nonparametric statistical 

tests were used that accounted for non-normal distributions 

of data, outliers, and numerous nondetected concentrations 

for some constituents. Statistica 9.0 was used for all statistical analyses (StatSoft, Inc., 2009) except the multiple 

comparison tests (Tukey’s method), which were done with 

S-PLUS statistical analysis software (TIBCO Software Inc., 

2008).

Similarity or Difference of Contaminant 

Concentration by Watershed

The Kruskal-Wallis test is a nonparametric test that can 

be used to determine the general equivalence of groups of 

Table 6. Percent detections, ranges, means, and standard deviations of sediment-associated constituents in sediment samples 

collected by the U.S. Air Force Center for Engineering and the Environment (AFCEE) during 1994–2008 and by the U.S. Geological Survey 

(USGS) during 2007–09 from Leon Creek in Bexar County, Texas. 

[μg/g, micrograms per gram; μg/kg, micrograms per kilogram; <, nondetection (less than interim reporting level for USGS samples); PCBs, polychlorinated 

biphenyls; PAHs, polycyclic aromatic hydrocarbons]

Constituent

AFCEE USGS

Number 

of 

samples

Percent 

detectionsRange Mean Standard 

deviation

Number 

of 

samples

Percent 

detectionsRange Mean Standard 

deviation

Arsenic (μg/g) 136 85 <0.6–46.1 6.6 5.4 19 100 5.7–12.8 8.5 2.1

Cadmium (μg/g) 136 78 <.05–26 1.9 3.8 19 100 .3–6.5 2.0 2.0

Chromium (μg/g) 136 99 <.5–1,120 55.5 123 19 100 36.9–145 74.6 37.4

Copper (μg/g) 136 98 <1.0–73.8 11.5 10.0 19 100 12.8–42.7 21.0 9.0

Lead (μg/g) 136 100 5.8–1,760 44.4 151 19 100 15.2–69.3 37.9 17.2

Mercury (μg/g) 136 45 <.004–9.5 .35 1.5 19 100 .02–.09 .04 .02

Nickel (μg/g) 136 100 .9–61.0 11.0 6.2 19 100 13.6–24.5 20.0 2.8

Zinc (μg/g) 133 95 <.2–124 49.1 26.1 19 100 62.8–156 102 28.4

Dieldrin (μg/kg) 129 8 <.19–14 1.5 10.3 19 37 <.1–1.1 .12 .26

Total chlordane1

 (μg/kg) 128 23 <.16–9.0 .71 1.8 19 95 <.2–7.8 1.1 1.8

p,p ́-DDD (μg/kg) 120 39 <.78–51 5.5 12.8 19 32 <1.0–55.0 5.5 13.2

p,p ́-DDE (μg/kg) 120 67 <.39–37 6.7 12.5 19 47 <1.0–41.0 4.5 10.0

p,p ́-DDT (μg/kg) 118 42 <1.2–130 6.6 15.5 19 21 <.1–110 9.0 27.2

Total PCBs2

 (μg/kg) 132 40 <2.0–2,100 56.9 215 19 95 <.1–77.0 9.6 17.6

Total PAHs3

 (μg/kg) 143 70 <29–29,400 848 2,720 19 89 <12–4,000 627 977

1

 Total chlordane is the sum of alpha and gamma-chlordane for AFCEE samples and the sum of cis-chlordane and trans-chlordane for USGS samples; USGS 

samples are censored at the highest interim reporting level of the individual compounds in the summation.

2

 Total PCBs is the sum of PCB Aroclors 1016, 1221, 1232, 1242, 1248, 1254, and 1260 for AFCEE samples and the sum of PCB congeners 49, 52, 70, 101, 

110, 118, 138, 146, 149, 151, 170, 174, 177, 180, 183, 187, 194, and 206 for USGS samples; USGS samples are censored at the highest interim reporting level 

of the individual compounds in the summation.

3

 Total PAHs is the sum of acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, chrysene, dibenzo(a,h)anthracene, fluoranthene, 

fluorene, naphthalene, phenanthrene, and pyrene (Ingersoll and others, 2001) for both sets of samples; USGS samples are censored at the highest interim reporting level of the individual compounds in the summation.
Table 7. Percent detections, ranges, means, and standard deviations of selected constituents in suspended-sediment samples collected from streamduring 1999–2004 (Mahler and others, 2006), from streams in the Fort Worth, Texas, area during 2000–2002 (Van Metre and others, 2003), and from streduring 2007–09. [n, number of samples; μg/g, micrograms per gram; μg/kg, micrograms per kilogram; <, nondetection less than interim reporting level; PCBs, polychlorinated biphenyls; PAHs, 

bon] Constituent Austin (n=61) Fort Worth (n=45) Bexa

Percent detec- tions Range Mean Standard deviation Percent detec- tions Range Mean Standard deviation Percent detec- tions Range 

Arsenic (μg/g) 100 5.5–22.8 12.4 4.2 100 7.0–18.4 11.6 2.4 100 4.2–9.0 

Cadmium (μg/g) 100 .21–3.5 .70 .68 100 .15–2.7 1.1 .7 100 .23–4.4 

Chromium (μg/g) 100 28.4–94.3 59.1 15.6 100 39.4–110 66.3 15.3 100 40.3–12

Copper (μg/g) 100 10.3–72.9 26.1 12.2 100 13.0–281 50.0 47.5 100 13.4–41

Lead (μg/g) 100 12.6–196 41.4 32.6 100 13.0–237 94.6 55.2 100 15.7–68

Mercury (μg/g) 100 .03–.20 .06 .03 100 .03–.3 .09 .06 100 .02–.07 

Nickel (μg/g) 100 10.7–52.3 28.4 7.5 100 9.0–42.9 28.5 6.6 100 13.5–28

Zinc (μg/g) 100 50.4–607 168 110 100 67.3–1,600 324 259 100 71.6–17

Dieldrin (μg/kg) 21 <.5–5.9 1.3 2.2 65 <1.5–94 13.8 19.3 54 <.1–.84 

Technical chlordane1 (μg/kg) 38 <5.5–250 28 39 76 <15–750 160 180 77 <1.0–6.

p,p'-DDT (μg/kg) 38 <.5–71 8.0 14 41 <1.5–13,000 300 1,900 0 <.1–<4.

p,p'-DDD (μg/kg) 20 <.5–51 2.6 7.8 9 <1.5–460 13 77 31 <.1–16 

p,p'-DDE (μg/kg) 61 <.5–70 8.4 14 91 <1.5–620 23 90 15 <1.0–6.

Total PCBs2 (μg/kg) 16 <16–170 30 43 57 <45–1,220 130 220 77 <1.0–2

Total PAHs3 (μg/kg) 100 30.2–98,200 12,800 22,100 100 64.3–75,200 12,500 16,300 38 <90–3,6

1 Technical chlordane is reported by the laboratory for Austin and Fort Worth samples; for Bexar County samples computed as sum of cis-chlordane, trans-chlordane, cis-non

oxychlordane and censored at highest interim reporting level of the individual compounds in the summation. 2 Total PCBs is the sum of PCB Aroclors 1242, 1254, and 1260 for Austin and Fort Worth samples and the sum of PCB congeners 49, 52, 70, 101, 110, 118, 138, 146, 149, 15

194, and 206 for Bexar County samples; Bexar County samples censored at highest interim reporting level of the individual compounds in the summation. 3 Total PAHs is the sum of acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, chrysene, dibenzo(a,h)anthracene, fluoranthene, fluorene, naphthalBexar County samples censored at highest interim reporting level of the individual compounds in the summation.
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 39

data (Helsel and Hirsch, 2002). Data from sampling sites were 

grouped by watershed, and the Kruskal-Wallis test was used in 

an attempt to answer the question: “Are contaminant concentrations the same or different among all the watersheds?” A 

minimum of five samples is required to perform the test, which 

restricted the assessment to the Leon Creek, Salado Creek, and 

San Antonio River watersheds. Different IRLs were frequently 

used for the same organic compounds depending on the mass 

of sample available for analysis. If some concentrations for a 

given constituent were nondetected concentrations, all values 

less than the highest IRL, including detections, were censored 

at the highest IRL so that they were ranked equally (Helsel, 

2005). The null hypothesis that all groups had identical distributions and that the data were one group was rejected 

when the p-value was less than .05, providing a 95-percent 

confidence level. The alternate hypothesis is that at least one 

of the distributions is different than one of the other distributions. The Kruskal-Wallis test results did not indicate a 

statistically significant difference among the concentrations 

of chromium, copper, mercury, nickel, lead, zinc, or silver in 

streambed-sediment samples collected from the Leon Creek, 

Salado Creek, and San Antonio River watersheds (table 8). 

Test results did indicate a statistically significant difference 

among arsenic and cadmium concentrations from the three 

watersheds. The test results also did not indicate a statistically significant difference among concentrations of dieldrin, 

total chlordane, p,p'-DDT, p,p'-DDD, p,p'-DDE, or total 

PAH from the three watersheds; however, the test results did 

indicate a statistically significant difference among total PCB 

concentrations.

Tukey’s multiple comparison test was used to determine 

which watersheds are different following the rejection of the 

null hypothesis for arsenic, cadmium, and total PCB concentrations by using the Kruskal-Wallis test. The Tukey’s test 

computes a least significant range, or the distance between 

any two means that must be exceeded for the two groups to be 

considered significantly different, and is a powerful multiple 

comparison test for unequal sample sizes. The streambedsediment concentrations were rank transformed and Tukey’s 

test was performed on the ranks for a nonparametric multiple 

comparison test (Helsel and Hirsch, 2002). Arsenic concentrations in the streambed-sediment samples from the Leon Creek 

watershed were significantly higher compared to concentrations from the San Antonio River watershed (p-value less 

than .05). The cadmium concentrations from the Leon Creek 

watershed were significantly higher compared to concentrations from the Salado Creek and San Antonio River watersheds (p-value less than .05). Total PCB concentrations from 

the San Antonio River watershed were significantly higher 

compared to concentrations from the Salado Creek watershed 

(p-value less than .05). No statistical differences were determined between total PCB concentrations from the Leon Creek 

watershed compared to concentrations from the Salado Creek 

watershed or San Antonio River watershed. The large range of 

total PCB concentrations in the Leon Creek samples (multiple 

nondetected concentrations and some concentrations as high 

as 77 and 16 μg/kg) is such that differences among watersheds could not be determined statistically even though mean 

total PCB concentrations in the streambed-sediment samples 

from each watershed are substantially different (Leon Creek, 

9.2 μg/kg; Salado Creek, no detected concentrations; and San 

Antonio River, 6.6 μg/kg). 

Relations Between Land Use and StreambedSediment Contaminant Concentrations

The nonparametric Mann-Whitney U (rank-sum) test 

was used to assess whether contaminant concentrations in 

streambed-sediment samples measured in the various watersheds in the study area differed depending on the presence 

or absence of suspected contaminant sources—military installations, USEPA Superfund sites, and USEPA Toxics Release 

Inventory (TRI) Program facilities and industries—in the 

watersheds. For example, the relations among six military 

installations and contaminant concentrations measured at 

sampling sites associated with each installation were assessed 

(fig. 14; table 9). Sixteen USEPA Superfund sites in the contributing areas of sediment-sampling sites reported releases 

of trace elements and PAHs (U.S. Environmental Protection 

Agency, 2010d) that were among the constituents analyzed 

in this study. Twenty-five USEPA TRI Program facilities and 

industries in the contributing areas of sediment-sampling 

sites also reported releases of trace elements and PAHs 

common to the constituents analyzed in this study (U.S. 

Environmental Protection Agency, 2010e). If some reported 

concentrations for a given constituent in a streambed-sediment 

sample were nondetected concentrations, all reported values 

less than the highest IRL, including detections, were censored to a common value so they were ranked equally (Helsel, 

2005). For computed totals, such as total chlordane and total 

PCBs, data were censored at the highest IRL of the individual compounds summed. The results of the Mann-Whitney 

U test indicate that the presence of military installations is 

associated with statistically significant (p-value less than .05) 

higher concentrations of chromium, mercury, zinc, total 

chlordane, p,p'-DDE, and total PCBs in the watersheds where 

those military installations are located. The test results also 

indicate that the presence of USEPA Superfund sites and TRI 

Program facilities and industries had no statistically significant 

relation to sediment contaminant concentrations in the watersheds where those sites, facilities, or industries are present 

(table 10).

Kendall’s tau nonparametric correlation coefficients 

were computed to measure the strength of the relation among 

population, land uses (fig. 2; table 2), or PSOCs (fig. 3) in all 

20 contributing areas of each sampling site and the median 

streambed-sediment constituent concentrations measured at 

each sampling site (table 11). Data were censored at the highest IRL when computing the medians and the Kendall’s tau 

statistic. Tau correlation coefficient values closer to +1.0 indicate a stronger, positive association between the variables; tau 

values closer to -1.0 indicate a stronger, negative association; 
40 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 14. Locations of U.S. Environmental Protection Agency (USEPA) Superfund sites and Toxics Release Inventory (TRI) Program 

facilities and industries in contributing areas of streambed-sediment sampling sites in Bexar County, Texas, 2007–09 (Superfund and TRI 

sites from U.S. Environmental Protection Agency, 2010d, e). 

"

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" BEXAR COUNTY

WILSON COUNTY

GUADALUPE

COUNTY

ATASCOSA COUNTY

COMAL

COUNTY

MEDINA COUNTY

BANDERA

COUNTY

KENDALL

COUNTY 

io

1

2

3

4

6 5

7

8

9

10 11

12

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14

15

16

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Culebra

Leon

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Salado

Medio

Elm

Creek

San

Apache 

Lorence

Rosillo

Alazan

Mitchell

Lake

Cibolo

Creek

Creek

Geronimo

San

Creek

Creek

Antonio

Creek

River

Creek

Creek

Creek

Martinez

Creek

Creek

Braunig

Lake

Calaveras

Lake River

Zarzamora

Creek

Indian

Creek

Saltrillo

Creek

Calaveras

Creek

Chupaderas Creek

Parita Cree

Medina

k

BEXAR COUNTY

Study area Area enlarged

0 5 2.5 7.5 10 MILES

0 5 2.5 7.5 10 KILOMETERS

EXPLANATION

"A

"Z

Cummulative drainage area for

most downstream site of stream

Medio Creek

Medina River

Elm Creek

Martinez Creek

Chupaderas Creek

Leon Creek

Salado Creek

San Antonio River

Study area boundary

USEPA Superfund site with map

identifier (table 9)

1 !

Map

identifier

Site identifier

(table 2)

 1 Medio 90

 2 Medio Pearsall 

 3 Medina

 4 Elm

 5 Martinez St. Hedwig

 6 Martinez 1518

 7 Chupaderas

 8 Leon Rodriguez

 9 Leon 90

10 Leon Morey

11 Leon Lackland

12 Leon Military

13 Leon Quintana

14 Leon 35

15 Salado 13

16 Rosillo

17 Salado Southton

18 SAR Theo

19 SAR 410

20 SAR Elmendorf

Map

identifier

Site identifier

(table 2)

USEPA TRI Program facility or

industry with map identifier (table 9)

Sediment sampling site and map identifier

29°40'

30'

98°40' 30'

98°20'

20'

29°10'

Base modified from U.S. Geological Survey

digital data, 1:24,000 quadrangles

Texas State Plane Coordinate System, FIPS 4204

North American Datum of 1983

U.S. Environmental Protection Agency

Superfund and TRI sites from Texas

Natural Resources Information System
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 41

Table 8. Results of Kruskal-Wallis nonparametric tests for differences among trace element, halogenated organic compound, and 

polycyclic aromatic hydrocarbon concentrations in streambed-sediment samples from sample-collection sites in Bexar County, Texas, 

2007–09. 

[μg/g, micrograms per gram; <, nondetection less than lower reporting limit (silver) or less than interim reporting level (organic compounds); μg/kg, micrograms 

per kilogram; PCBs, polychlorinated biphenyls; PAHs, polycyclic aromatic hydrocarbons; shaded cells indicate statistically significant tests (p-values less than 

.05)]

Constituent Watershed Number of samples Median concentration Average rank p-value

Arsenic (μg/g) Leon Creek 16 7.8 16.2 .015

Salado Creek 5 7.1 13.4

San Antonio River 5 6.0 4.9

Cadmium (μg/g) Leon Creek 16 .60 17.8 .001

Salado Creek 5 .28 4.9

San Antonio River 5 .33 8.3

Chromium (μg/g) Leon Creek 16 52.4 14.9 .341

Salado Creek 5 47.2 9.2

San Antonio River 5 43.8 13.2

Copper (μg/g) Leon Creek 16 15.5 12.8 .578

Salado Creek 5 16.9 12.4

San Antonio River 5 19.3 16.7

Mercury (μg/g) Leon Creek 16 .03 13.6 .276

Salado Creek 5 .03 9.6

San Antonio River 5 .04 17.2

Nickel (μg/g) Leon Creek 16 19.3 14.6 .575

Salado Creek 5 18.3 10.6

San Antonio River 5 17.5 12.8

Lead (μg/g) Leon Creek 16 29.8 14.5 .429

Salado Creek 5 26.2 9.5

San Antonio River 5 38.8 14.4

Zinc (μg/g) Leon Creek 16 89.6 12.5 .293

Salado Creek 5 97.5 12.0

San Antonio River 5 132 18.3

Silver (μg/g) Leon Creek 16 <1 15.1 .160

Salado Creek 5 <1 11.0

San Antonio River 5 <1 11.0

Dieldrin (μg/kg) Leon Creek 16 <.1 13.1 .642

Salado Creek 5 <.1 12.2

San Antonio River 5 .10 16.0

Total chlordane1

 (μg/kg) Leon Creek 16 <1.0 12.6 .143

Salado Creek 5 <1.0 10.9

San Antonio River 5 2.5 18.9

p,p'-DDT (μg/kg) Leon Creek 16 <4.0 14.8 .245

Salado Creek 5 <4.0 11.5

San Antonio River 5 <4.0 11.5

p,p'-DDD (μg/kg) Leon Creek 16 <2.0 14.8 .244

Salado Creek 5 <2.0 11.5

San Antonio River 5 <2.0 11.5

p,p'-DDE (μg/kg) Leon Creek 16 1.0 14.3 .289

Salado Creek 5 <1.0 9.1

San Antonio River 5 1.7 15.2

Total PCBs2

 (μg/kg) Leon Creek 16 3.0 13.9 .012

Salado Creek 5 <2.0 6.0

San Antonio River 5 7.7 19.8

Total PAHs3

 (μg/kg) Leon Creek 16 270 12.9 .088

Salado Creek 5 180 9.2

San Antonio River 5 760 19.6

1

 Total chlordane is the sum of cis-chlordane, trans-chlordane, cis-nonachlor, trans-nonachlor, and oxychlordane; censored at the highest interim reporting 

level of the individual compounds in the summation.

2

 Total PCBs is the sum of PCB congeners 49, 52, 70, 101, 110, 118, 138, 146, 149, 151, 170, 174, 177, 180, 183, 187, 194, and 206; censored at the highest 

interim reporting level of the individual compounds in the summation.

3

 Total PAHs is the sum of acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, chrysene, dibenzo(a,h)anthracene, fluoranthene, 

fluorene, naphthalene, phenanthrene, and pyrene. 
42 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Table 9. Military installations, U.S. Environmental Protection Agency Superfund sites, and U.S. Environmental Protection Agency 

Toxics Release Inventory Program facilities and industries in the contributing areas of the streambed-sediment sampling sites in Bexar 

County, Texas, 2007–09. 

[- -, not applicable]

Map 

identifier

(fig. 14)

Site identifier

(table 2) Facility name Chemical released

Military installations

2 Medio Pearsall Lackland Air Force Base - -

5, 6 Martinez St. Hedwig, Martinez 1518 Randolph Air Force Base - -

11, 12, 13 Leon Lackland, Leon Military, Leon 

Quintana

Kelly Air Force Base - -

15 Salado 13 Camp Bullis - -

15 Salado 13 Fort Sam Houston - -

19, 20 SAR 410, SAR Elmendorf Brooks Air Force Base - -

U.S. Environmental Protection Agency (2010d) Superfund sites

A Medio 90 River City Metal Finishing Metals

B Medio Pearsall Lackland Air Force Base Not specified 

C Elm Shepherd Lead Lead

D Leon Rodriguez Camp Stanley Storage Not specified 

E Leon Lackland, Leon Military, Leon 

Quintana

Kelly Air Force Base Not specified 

F Salado 13 Camp Bullis Not specified 

G Salado 13 El Dorado Chemical Co. Industrial organic and inorganic chemicals; 

pesticides and agricultural chemicals

H Salado 13 Fort Sam Houston Not specified 

I SAR Theo Eldridge Avenue lead site Lead

J SAR Theo First Quality Cylinder Chromium

K SAR Theo San Antonio Gas and Electric Co. Gas Plant Not specified

L SAR 410 Age Refining Petroleum

M SAR 410 *R and H Oil Naphthalene, arsenic, barium, and zinc

M SAR 410 *Tropicana Energy Co. Petroleum

N SAR 410, SAR Elmendorf Brooks Air Force Base Not specified 

O SAR Elmendorf J.C. Pennco Waste Oil Service Metals, polycyclic aromatic hydrocarbons

U.S. Environmental Protection Agency (2010e) Toxics Release Inventory Program facilities and industries

B Medio Pearsall Lackland Air Force Base Naphthalene, lead

P Medina Avanzar Interior Technologies Chromium

P Medina Toyota Motor Manufacturing Naphthalene, nickel, zinc

Q Medina Martin Marietta Materials Polycyclic aromatic hydrocarbons

R Chupaderas York International Manganese, copper

S Leon Rodriguez CMC Steel Fabricators Nickel

T Leon Rodriguez Pratt and Whitney Chromium, cobalt, nickel

U Leon Rodriguez TK Holdings Inc. Chromium, nickel, zinc

V Leon Rodriguez XYtronics Ltd. Lead

W Leon Quintana Standard Aero Inc. Lead

F Salado 13 Camp Bullis Copper, lead

X Salado 13 Capitol Cement Polycyclic aromatic hydrocarbons, chromium, lead, mercury, nickel

Y Salado 13 Exxon Mobil Corporation Polycyclic aromatic hydrocarbons, lead

Z Salado 13 Green Light Co. Arsenic

a Salado 13 Hanson Pipe and Products Inc. Lead

b Salado 13 Johnson Controls Battery Group Inc. Lead

c Salado 13 Trinity Industries Inc. Chromium, manganese, nickel, zinc

d Rosillo Berridge Manufacturing Naphthalene, chromium, lead

e Rosillo Flint Hill Resources Polycyclic aromatic hydrocarbons, lead

f Rosillo Safety-Kleen Systems Polycyclic aromatic hydrocarbons, lead

g Rosillo Southwest Galvanizing Inc. Lead, zinc

h SAR Theo Allied Aviation Fueling Co. Naphthalene

i SAR Theo, SAR 410 Industrial Chrome Plate Inc. Chromium, lead

L SAR 410 Age Refining Naphthalene

k SAR 410 Warren Industrial Lubricants Co. Zinc

*

 On National Priorities List (Agency for Toxic Substances and Disease Registry, 2007a).
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 43

Table 10. Results of Mann-Whitney U test used to assess differences in contaminant concentrations measured in streambed-sediment 

samples on the basis of the presence or absence of suspected contaminant sources in selected watersheds of Bexar County, Texas, 

2007–09. 

[μg/g, micrograms per gram; <, nondetection less than lower reporting limit (silver) or less than interim reporting level (organic compounds); 

μg/kg, micrograms per kilogram; PCBs, polychlorinated biphenyls; PAHs, polycyclic aromatic hydrocarbons; shaded cells indicate statistically 

significant tests (p-value less than .05)]

Constituent

Presence of suspected contaminant sources Absence of suspected contaminant sources

Number of U p-value

samples

Median 

concentration

Number of 

samples

Median 

concentration

Military installations1

Arsenic (μg/g) 16 7.0 20 6.9 140.5 .55

Cadmium (μg/g) 16 .34 20 .30 137.0 .47

Chromium (μg/g) 16 55.3 20 42.8 69.0 .004

Copper (μg/g) 16 17.8 20 15.2 101.0 .063

Mercury (μg/g) 16 .04 20 .03 92.5 .033

Nickel (μg/g) 16 18.8 20 18.5 129.0 .33

Lead (μg/g) 16 29.8 20 21.8 100.0 .058

Zinc (μg/g) 16 113 20 90.3 97.0 .046

Silver (μg/g) 16 <1 20 <1 159.0 .99

Dieldrin (μg/kg) 15 <.1 20 <.1 128.5 .48

Total chlordane2

 (μg/kg) 15 2.4 20 <1.0 69.0 .007

p,p'-DDT (μg/kg) 15 <4.0 20 <4.0 110.0 .19

p,p'-DDD (μg/kg) 15 <2.0 20 <2.0 110.0 .19

p,p'-DDE (μg/kg) 15 1.1 20 <1.0 87.5 .039

Total PCBs3

 (μg/kg) 15 4.5 20 <2.0 71.5 .009

Total PAHs4

 (μg/kg) 15 260 20 165 105.0 .14

U.S. Environmental Protection Agency (2010d) Superfund sites5

Arsenic (μg/g) 18 6.3 18 7.3 125.5 .25

Cadmium (μg/g) 18 .33 18 .32 154.0 .81

Chromium (μg/g) 18 53.0 18 44.4 116.0 .15

Copper (μg/g) 18 17.2 18 15.4 113.5 .13

Mercury (μg/g) 18 .04 18 .03 110.5 .11

Nickel (μg/g) 18 18.5 18 18.9 162.0 .99

Lead (μg/g) 18 27.5 18 23.7 125.0 .25

Zinc (μg/g) 18 108 18 91.3 119.0 .18

Silver (μg/g) 18 <1 18 <1 156.0 .86

Total PAHs4

 (μg/kg) 18 300 17 160 106.0 .12

U.S. Environmental Protection Agency (2010e) Toxics Release Inventory Program facilities and industries6

Arsenic (μg/g) 14 7.1 22 6.6 147.5 .85

Cadmium (μg/g) 14 .30 22 .36 98.0 .072

Chromium (μg/g) 14 44.0 22 52.3 108.0 .14

Copper (μg/g) 14 16.8 22 16.0 147.0 .83

Mercury (μg/g) 14 .03 22 .03 152.0 .96

Nickel (μg/g) 14 18.8 22 18.5 135.5 .56

Lead (μg/g) 14 25.7 22 25.8 148.0 .86

Zinc (μg/g) 14 98.2 22 97.8 153.5 1.00

Silver (μg/g) 14 <1 22 <1 119.0 .26

Total PAHs4

 (μg/kg) 14 280 21 200 110.0 .22

1

 Located in Medio Pearsall, Martinez St. Hedwig, Martinez 1518, Leon Lackland, Leon Military, Leon Quintana, Salado 13, SAR 410, and SAR Elmendorf 

contributing areas (fig. 14; table 9).

2

 Total chlordane is the sum of cis-chlordane, trans-chlordane, cis-nonachlor, trans-nonachlor, and oxychlordane; censored at the highest interim reporting 

level of the individual compounds in the summation.

3

 Total PCBs is the sum of PCB congeners 49, 52, 70, 101, 110, 118, 138, 146, 149, 151, 170, 174, 177, 180, 183, 187, 194, and 206; censored at the highest 

interim reporting level of the individual compounds in the summation.

4

 Total PAHs is the sum of acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, chrysene, dibenzo(a,h)anthracene, fluoranthene, 

fluorene, naphthalene, phenanthrene, and pyrene; censored at the highest interim reporting level of the individual compounds in the summation.

5

 Located in Medio 90, Medio Pearsall, Elm, Leon Rodriguez, Leon Lackland, Leon Military, Leon Quintana, Salado 13, SAR Theo, SAR 410, and SAR 

Elmendorf contributing areas (fig. 14; table 9).

6

 Located in Medio Pearsall, Medina, Chupaderas, Leon Rodriguez, Leon Quintana, Salado 13, Rosillo, SAR Theo, and SAR 410 contributing areas (fig. 14; 

table 9).
44 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Table 11. Kendall’s tau nonparametric correlation coefficients between population density, land use, or potential sources of 

contamination (PSOCs) and median streambed-sediment contaminant concentrations in all 20 contributing areas of the sampling sites in 

Bexar County, Texas, 2007–09. 

[PCBs, polychlorinated biphenyls; PAHs, polycyclic aromatic hydrocarbons; shaded cells indicate statistically significant (p-value less than .05) tau correlation 

coefficients]

Variable Arsenic Cadmium Chromium Copper Mercury Nickel Lead Zinc Silver

Population density -.090 .153 .179 .295 .342 .085 .216 .332 .060

Land-use categories

Residential -.026 .195 .053 .168 .275 .085 .142 .164 .060

Commercial .090 .142 -.021 .137 .129 .106 .121 .111 -.060

Industrial .047 .237 .026 .042 .185 .127 .100 .079 .179

Transportation -.069 .069 .022 .084 .140 .032 .026 .079 -.131

Mining .235 .358 .062 .061 .173 .208 .162 .112 .114

Utilities -.269 -.385 -.147 -.084 -.253 -.317 -.227 -.185 -.274

PSOCs

Abandoned municipal solid waste landfill .575 .406 .053 -.147 -.118 .286 .185 -.026 .370

Industrial wastewater outfall -.042 .016 -.189 .032 .039 -.085 -.026 -.079 -.179

Wastewater holding pond -.005 -.227 -.053 .063 .095 -.011 .037 .047 -.227

Wastewater holding tank -.174 -.111 .021 .095 .107 -.106 -.047 .058 -.227

Active or abandoned mined land .269 .438 .042 -.200 -.129 .053 -.069 -.100 .155

Wastewater liftstation .026 .164 0 .053 .062 .138 .069 .005 .012

Petroleum storage tank -.190 .011 .047 .227 .225 -.027 .042 .201 -.036

Active municipal solid waste landfill -.143 -.048 -.095 -.085 -.141 -.170 -.122 -.143 .108

Chemical pipeline -.413 -.011 .058 .280 .236 -.058 .011 .265 .060

Auto repair, sales, salvage, and towing -.185 -.280 -.232 .116 .039 -.233 -.090 .016 -.346

Variable Dieldrin Total 

chlordane1 p,p’-DDT p,p’-DDD p,p’-DDE Total PCBs2

Total 

PAHs3

Population density .507 .391 .131 .155 .411 .300 .457

Land-use categories

Residential .466 .287 .131 .155 .452 .443 .446

Commercial .452 .274 .060 .036 .356 .222 .511

Industrial .425 .208 -.012 .012 .247 .326 .272

Transportation .384 .287 .060 .036 .260 .222 .402

Mining .363 .117 .215 .190 .509 .484 .530

Utilities -.425 -.182 -.155 -.179 -.507 -.534 -.294

PSOCs

Abandoned municipal solid waste landfill -.027 -.248 .155 .179 -.014 .065 -.185

Industrial wastewater outfall .302 .117 .036 .012 .219 .104 .370

Wastewater holding pond .178 .182 -.012 -.036 .137 .065 .109

Wastewater holding tank .082 .130 .012 -.012 .192 .078 .141

Active or abandoned mined land -.151 -.274 .370 .346 .123 .143 .065

Wastewater liftstation .411 .300 -.012 .012 .260 .339 .359

Petroleum storage tank .316 .189 -.060 -.036 .162 .235 .376

Active municipal solid waste landfill -.069 -.020 -.252 -.228 -.289 -.262 -.350

Chemical pipeline .041 .111 -.203 -.179 .041 .235 .224

Auto repair, sales, salvage, and towing .055 -.039 -.179 -.203 -.069 -.091 .120

1

 Total chlordane is the sum of cis-chlordane, trans-chlordane, cis-nonachlor, trans-nonachlor, and oxychlordane.

2

 Total PCBs is the sum of PCB congeners 49, 52, 70, 101, 110, 118, 138, 146, 149, 151, 170, 174, 177, 180, 183, 187, 194, and 206.

3

 Total PAHs is the sum of acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, chrysene, dibenzo(a,h)anthracene, fluoranthene, 

fluorene, naphthalene, phenanthrene, and pyrene.
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 45

and tau values near 0 indicate the variables are unrelated 

(Helsel and Hirsch, 2002). The concentrations of mercury, 

zinc, dieldrin, total chlordane, p,p'-DDE, and total PAHs in 

streambed-sediment samples were positively correlated with 

population density. Positive correlations also exist between 

dieldrin, p,p'-DDE, and total PAHs and land-use categories 

(residential and commercial) typical of densely populated 

areas. Total PAHs also have a statistically significant positive correlation with the transportation land-use category and 

the industrial wastewater outfall, wastewater liftstation, and 

petroleum storage tank PSOC categories; and a negative correlation with the active municipal solid waste land-use category. 

Arsenic concentrations and abandoned municipal solid waste 

sites had the strongest, positive statistically significant correlation (tau = .575); cadmium and silver also were positively correlated with abandoned municipal solid waste sites. 

Statistically significant positive correlations exist between 

cadmium, dieldrin, p,p'-DDE, total PCBs, and total PAHs 

and the mining land-use category and between cadmium, 

p,p'-DDT, and p,p'-DDD concentrations and the PSOC category of active or abandoned mined land. Total PCB concentrations also correlate positively with residential and industrial land-use categories. The strongest, negative correlation 

(tau = -.534) is between total PCB concentrations and the 

utilities land-use category; cadmium, dieldrin, and p,p'-DDE 

also were negatively correlated with the utilities land-use 

category. The negative correlation between the utilities landuse category and PCBs is surprising considering that PCBs 

were used until the mid-1970s as insulating fluids and coolants 

in electrical equipment (transformers and capacitors). The 

contributing areas of the Martinez St. Hedwig and Martinez 

1518 sites have the highest percentages of utilities land use, 

0.42 and 0.56 percent, respectively, and very low concentrations or nondetected concentrations of PCB congeners in the 

samples. One possible explanation for the negative correlation of PCBs and utilities in the Martinez Creek watershed is 

that the utilities might have been constructed in the watershed 

after the use of PCBs was halted. Chromium, which exceeded 

the SQGs more than any other constituent, copper, nickel, 

and lead do not correlate with any of the available land-use or 

PSOC categories.

Indicators of Selected Organic Contaminant 

Sources

PCB sources were explored by comparing the relative 

distributions of PCB congeners in the streambed-sediment 

samples. Patterns of PCB concentrations can be indicative 

of different PCB sources (Colman, 2000; Johnson and others, 

2000; Cacela and others, 2002). PCB congener distribution 

patterns were determined by normalizing individual congener concentrations; normalization was done by dividing individual PCB congener concentrations by the sum of PCB 

congener concentrations for the 13 different PCB congeners with sufficient data (fig. 15). Because of limited use 

for comparison, samples in which fewer than 50 percent 

of the analyzed congeners were detected were excluded. 

Furthermore, PCB congeners not detected more than 50 percent of the time in the selected samples were excluded. This 

censoring excluded 15 of the 35 streambed-sediment samples 

and 5 of the 18 PCB congeners. Nondetected concentrations 

were not included in plots of the PCB congener distribution 

patterns to avoid creating false or misleading patterns by 

substituting zeroes or estimated values in place of the nondetected concentrations. Removing the nondetected concentrations resulted in discontinuous profiles for several of the 

samples.

The normalized PCB congeners were grouped by 

watershed and plotted for visual comparison of the congener 

patterns (fig. 15). The dominant congeners in the samples 

collected from sites in the Leon Creek, Salado Creek, and San 

Antonio River watersheds are PCB congeners 138, 180, and 

187. With a few exceptions, the PCB congener patterns for 

the samples collected from these three watersheds are similar 

to one another. The similar PCB congener pattern suggests 

similar PCB sources in the three watersheds. One possible 

exception is the sample collected from the Leon Lackland 

site on December 3, 2007, with a total PCB concentration 

(77 μg/kg) higher than in all other samples in this study. The 

ratios of the individual PCB congener concentrations to the 

total PCB concentration for this sample is markedly different relative to other samples (lower, less variable ratios for 

PCB congeners 151 through 206); this difference in congener patterns might indicate a different source of PCBs at the 

Leon Lackland site compared to the other samples collected 

from Leon Creek, Salado Creek, or the San Antonio River. 

However, this is just one sample and the relatively anomalous 

PCB congener pattern was not corroborated by subsequent 

sampling along the same reach of Leon Creek. Additional 

information, such as PCB congener analyses of sediment or 

soil samples from contaminated areas in zones 1 and 2 at the 

former Kelly AFB plus the collection of a larger number of 

samples from the Leon Lackland site and other sites near the 

former Kelly AFB would be needed to make more definitive 

conclusions about the sources of PCBs measured in samples 

collected from the Leon Lackland site. The data are insufficient to make any conclusions about PCB sources to the sites 

in the Medio Creek watershed.

The PAH results were compared to common PAH sources 

documented in the literature (Van Metre and Mahler, 2010). 

Common PAH sources such as coal combustion (power 

plants), automobile-related sources, and coal-tar parking lot 

sealcoat were compared to PAH ratios measured in Bexar 

County streambed- and suspended-sediment samples with 

a chemical mass balance (CBM) source-receptor model. 

Source-receptor modeling uses an iterative process to attempt 

to quantify contributions of different sources to a receptor. 

The CMB source-receptor model is supported by the U.S. 

Environmental Protection Agency (2008) and requires source 

profiles (proportional concentrations of PAHs) and receptor 

data (PAH concentrations for streambed and suspended sediment). Van Metre and Mahler (2010, p. 336) summarized the 
46 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 15. Concentrations of detected polychlorinated biphenyl (PCB) congeners normalized to concentrations of total PCBs in 

streambed-sediment samples collected from selected sites in Bexar County, Texas, 2007–09. 

PCB

118

PCB

138

PCB

146

PCB

149

PCB

151

PCB

170

PCB

174

PCB

177

PCB

180

PCB

183

PCB

187

PCB

194

PCB

206

Normalized PCB congener

0

0.05

0.10

0.15

0.20

0

0.05

0.10

0.15

0.20

0

0.05

0.10

0.15

0.20

0

0.05

0.10

0.15

0.20

0

0.05

0.10

0.15

0.20

0

0.05

0.10

0.15

0.20

Ratio of individual PCB congener to total PCBs

Medio Pearsall; February 27, 2008

Medio 90; February 27, 2008

Site identifiers listed in table 2

EXPLANATION

Salado 13; December 18, 2007

EXPLANATION

EXPLANATION

Leon 90; November 29, 2007

Leon Rodriguez; November 29, 2007

Leon Rodriguez; August 5, 2008

Leon 90; August 12, 2009

EXPLANATION

Leon Military; December 3, 2007

Leon Lackland; December 3, 2007

Leon Lackland; August 5, 2008

Leon Lackland; August 12, 2009

EXPLANATION

Leon 35; December 11, 2007

Leon Quintana; November 29, 2007

Leon Quintana; August 13, 2009

Leon 35; August 6, 2008

EXPLANATION

SAR Theo; February 25, 2008

SAR 410; December 18, 2007

SAR Elmendorf; December 11, 2007

SAR 410; August 6, 2008

SAR 410; August 13, 2009
Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples 47

assumptions of the model: (1) the composition of each source 

emission is consistent over the period represented by receptor 

data, (2) chemical species do not react with each other or with 

the environment, (3) all sources that contribute significantly to 

the receptor have been identified and their chemical profile is 

known, (4) the composition of each source is linearly independent of other sources, and (5) measurement uncertainties are 

random, uncorrelated, and normally distributed (Li and others, 

2003). 

Van Metre and Mahler (2010, p. 337, table 1) compiled PAH source profiles documented in the literature to 

compare to bottom sediments deposited post-1990 in lakes 

across the United States. They normalized the concentrations 

of 12 selected PAH compounds (phenanthrene, anthracene, 

fluoranthene, pyrene, benz(a)anthracene, chrysene, benzo(b)

fluoranthene, benzo(k)fluoranthene, benzo(e)pyrene, benzo(a)

pyrene, indenopyrene, and benzo(g,h,i)perylene) to the sum 

of the 12 compounds to describe the variability of the PAH 

mixtures. The same 12 PAHs described by Van Metre and 

Mahler (2010) were normalized by their sum for the nine 

streambed-sediment and LVSS samples collected from the 

Leon Rodriguez, Leon Lackland, Leon Quintana, SAR 

Theo, and SAR 410 sites with detected concentrations of 

all 12 selected PAH compounds (appendix 1.3) to compute an 

average PAH profile for Bexar County sediment (hereinafter, 

average Bexar County sediment) which was compared graphically to the common PAH sources documented in the literature to determine which sources should be used in the CMB 

receptor model (fig. 16). Using PAH data from the nine 

samples collected during 2007–09 in Bexar County, PAH 

concentrations were normalized by dividing the individual 

PAH concentration by the sum of PAH concentration for 

each of the 12 PAHs with sufficient data. An overall average 

ratio profile for Bexar County sediment samples was computed by using samples with detected concentrations of all 

12 PAH compounds; this prevented nondetected concentrations from distorting the ratio profiles. Seven streambedsediment samples and two LVSS samples had detected concentrations for all 12 PAH compounds. Streambed-sediment 

samples used in the PAH analysis were collected from the 

Leon Rodriguez site on November 29, 2007; Leon Lackland 

site on December 3, 2007, and August 5, 2008; Leon Quintana 

site on November 29, 2007; SAR Theo site on February 25, 

2008; and SAR 410 site on December 18, 2007, and August 

6, 2008. The LVSS samples used in the PAH analysis were 

collected from the SAR 410 site on July 7, 2008, and July 24, 

2008. The PAH profile of the average Bexar County sediment sample indicates low concentrations of anthracene, 

benz(a)anthracene, benzo(k)fluoranthene, indenopyrene, and 

benzo(g,h,i)perylene and high concentrations of fluoranthene, 

pyrene, and benzo(b)fluoranthene relative to the overall PAH 

mixture. 

A graphical comparison of the PAH source profiles and 

average Bexar County sediment PAH profiles and the consideration of possible PAH sources in Bexar County guided the 

choice of model inputs. Evaluation of the model results was 

based on model performance measures of chi-squared (c2

) and 

R-square (R2). The similarity between source and sediment 

profiles was evaluated quantitatively with the c2 value—the 

lower the c2, the more similar the two profiles. The R2 was 

determined by a linear regression of measured to modelcalculated PAH values—an R2 close to 1.0 was desirable. An 

uncertainty of 40 percent was used for all source profiles (Li 

and others, 2003) and of 20 percent for all receptor profiles 

estimated using the average relative percent difference for 

a large group of duplicate samples analyzed with the same 

laboratory methods (Van Metre and Mahler, 2010). The CMB 

model was run 15 times using multiple combinations of source 

profiles with all 12 PAHs.

Results of the CMB model indicate that parking lot coaltar sealcoat dust is the largest PAH source to the average Bexar 

County sediment (70.2 to 78.9 percent; table 12). The source 

profile of parking lot coal-tar sealcoat dust used in the model 

is the average of dust swept from coal-tar sealcoated parking 

lots from six cities in the United States: Minneapolis, Minn., 

Chicago, Ill., Detroit, Mich., Washington, D.C., New Haven, 

Conn., and Austin, Tex. (Mahler and others, 2005; Van Metre 

and others, 2009). The next largest contributors of PAHs, in 

order of average fractional loading, are automobile emissions 

measured in tunnels, emissions from diesel-powered automobiles, emissions from gasoline-powered automobiles, emissions from coal-fired power plants, and used automobile motor 

oil. Automobile tire particles do not appreciably contribute 

to PAHs in the average Bexar County sediment on the basis 

of CMB model results. Overlap exists between the automobile emissions measured in tunnels, emissions from dieselpowered automobiles, and emissions from gasoline-powered 

automobiles. Measurements of air pollutants in tunnels can 

be used to quantify on-road traffic emissions (El-Fadel and 

Hashisho, 2001). Automobile emissions measured in tunnels 

are a combination of emissions from all types of automobiles 

passing through the tunnel, whereas emissions from diesel- or 

gasoline-powered automobiles are specific to automobiles 

using one type of fuel. Coal combustion activities are present 

in southern Bexar County, for example the power generating 

complex on Calaveras Lake (fig. 1) includes the J.K. Spruce, 

J.T. Deely, and O.W. Sommers power plants. Atmospheric 

deposition of PAHs from the emissions from these plants is 

possible—annual wind rose diagrams indicate the wind direction is predominately from the south (Texas Commission on 

Environmental Quality, 2009b). The results of the CMB model 

appear reasonable considering the presence of these sources in 

the Bexar County area and considering that these findings are 

consistent with the findings of Van Metre and Mahler (2010).
48 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

Figure 16. Comparison of polycyclic aromatic hydrocarbon (PAH) profiles for various PAH sources summarized in Van Metre and 

Mahler (2010, table 1, p. 337) to PAH profile for average Bexar County sediment computed from samples from selected sites in Bexar 

County, Texas, 2007–09. 

Individual PAH 

Individual PAH 

Phenanthrene

Anthracene

Fluoranthene

Pyrene

Benz(a)anthracene

Chrysene

Benzo(b)fluoranthene

Benzo(k)fluoranthene

Benzo(e)pyreneBenzo(a)pyrene

Indenopyrene

Benzo(g,h,i)perylene

Phenanthrene

Anthracene

Fluoranthene

Pyrene

Benz(a)anthracene

Chrysene

Benzo(b)fluoranthene

Benzo(k)fluoranthene

Benzo(e)pyreneBenzo(a)pyrene

Indenopyrene

Benzo(g,h,i)perylene

Ratio of individual PAH to total PAHs

0

0.05

0.10

0.15

0.20

0.25

0

0.05

0.10

0.15

0.20

0.25

0

0.10

0.20

0.30

0

0.10

0.20

0.30

0.40

0.50

0

0.05

0.10

0.15

0.20

0.25

0

0.10

0.20

0.30

0

0.10

0.20

0.30

LOW Molecular weight HIGH LOW Molecular weight HIGH

Parking lot coal-tar

sealcoat dust

Emissions from

coal-fired

power plants

Automobile emissions

measured in tunnels

Emissions from

gasoline-powered

automobiles

Emissions from

diesel-powered

automobiles

Used automobile

motor oil

Automobile

tire particles

EXPLANATION

PAH source

Average Bexar County sediment; 

1 standard deviation error bar 
Summary 49

Summary

The U.S. Geological Survey (USGS), in cooperation 

with the San Antonio River Authority and the San Antonio 

Metropolitan Health District Public Center for Environmental 

Health, completed a reconnaissance-level assessment of the 

contaminants detected in sediment samples collected from 

selected streams during 2007–09 in Bexar County, Texas. The 

USGS periodically collected surficial streambed-sediment 

samples during base flow and suspended-sediment (largevolume suspended-sediment) samples from selected streams 

during periods of stormwater runoff. All samples were analyzed for major and trace elements. All samples also were 

analyzed for organic compounds, including halogenated 

organic compounds (pesticides [for example, chlordane, 

dieldrin, DDT, DDD, and DDE]; polychlorinated biphenyls 

[PCBs]; and brominated flame retardants), semivolatile 

organic compounds (SVOCs), and polycyclic aromatic hydrocarbons (PAHs). 

Elevated concentrations of sediment-associated contaminants are typically associated with urban areas; San Antonio 

in Bexar County is a large urban area and currently (2010) 

the seventh most populous city in the United States. Previous 

sediment sampling in Bexar County water bodies documented 

high concentrations of several trace elements and organic 

contaminants that are of concern to aquatic life and human 

health. This report describes an assessment of selected 

sediment-associated contaminants in the cumulative drainage 

areas (watersheds) of sampling sites on eight streams in the 

Bexar County area: Medio Creek, Medina River, Elm Creek, 

Martinez Creek, Chupaderas Creek, Leon Creek, Salado 

Creek, and San Antonio River. Selected contaminants were 

assessed by using a variety of methods—observations of 

occurrence and distribution, comparison to sediment-quality 

guidelines and data from previous studies, statistical analyses, 

and source indicators.

The amount of urban development differs in the Bexar 

County part of the watersheds for each of these eight streams. 

Urban development is greater in the Leon Creek, Salado 

Creek, and San Antonio River watersheds compared to that 

in the Medio Creek, Medina River, Elm Creek, Martinez 

Creek, and Chupaderas Creek watersheds. Streambed- and 

suspended-sediment samples were collected more frequently 

from sites in the more developed watersheds than from sites in 

the less developed watersheds. 

Generally, concentrations of trace elements in the 

samples from this study were low compared to two consensus-based sediment-quality guidelines—the threshold effect 

concentration (TEC), or lower level, and the probable effect 

concentration (PEC), or higher level. Trace element concentrations were greater than the PEC in 1.5 percent of the samples 

and greater than the TEC in 28 percent of the samples. The 

highest arsenic concentrations were in streambed-sediment 

samples collected from USGS station 08182410 Chupaderas 

Creek at State Road 106 near San Antonio, Tex. (hereinafter, 

Chupaderas site) (22.2 micrograms per gram [μ/g]), USGS station 08181445 Leon Creek at State Highway 90, San Antonio, 

Tex. (12.8 μg/g), and USGS station 292338098360501 Leon 

Creek at Morey Road, San Antonio, Tex. (hereinafter, Leon 

Morey site) (12.2 μg/g). Arsenic concentrations exceeded the 

TEC in 12 percent of the samples. Kruskal-Wallis and Tukey’s 

multiple comparison test results indicate streambed-sediment 

Table 12. Chemical mass balance model results and average fractional loading of total polycyclic aromatic hydrocarbons by source 

category for sampling sites in Bexar County, Texas, 2007–09.

[--, source not included in model] 

Chemical mass balance model 

performance categories Polycyclic aromatic hydrocarbon source categories

Model c2 R2 Percent 

mass

Parking 

lot coal-tar 

sealcoat 

dust

Emissions 

from 

coal-fired 

power 

plants

Automobile 

emissions 

measured 

in tunnels

Emissions 

from 

gasolinepowered 

automobiles

Emissions 

from dieselpowered 

automobiles

Used 

automobile 

motor oil

Automobile 

tire 

particles

1 0.47 0.95 101.9 71.3 3.5 -- 10.0 15.2 -- --

2 .50 .94 99.5 70.2 14.5 14.4 -- -- -- --

5 .45 .95 102.1 73.2 -- -- 10.0 16.8 -- 0

6 .49 .94 99.5 70.9 14.5 14.6 -- -- -- --

7 .47 .95 101.9 71.3 3.5 -- 10.0 15.2 -- --

9 .33 .97 99.1 76.3 4.1 -- 9.8 4.4 5.3 --

11 .30 .96 98.5 78.2 6.1 10.2 -- -- 5.5 --

12 .31 .96 98.6 77.4 6.1 9.4 -- -- 5.6 --

14 .32 .96 99.2 78.9 -- -- 9.8 5.9 5.4 0
50 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

samples from Leon Creek had significantly higher arsenic 

concentrations compared to the San Antonio River streambedsediment samples. Arsenic concentrations in streambed-sediment samples and abandoned municipal solid waste sites had a 

statistically significant correlation (tau = .575). 

Cadmium concentrations were highest in samples from 

USGS station 292029098351400 Leon Creek at Quintana 

Road, San Antonio, Tex. (hereinafter, Leon Quintana site) 

(streambed sediments 6.5 and 5.4 μg/g) and USGS station 

08181480 Leon Creek at Interstate Highway 35, San Antonio, 

Tex. (hereinafter, Leon 35 site) (suspended sediment 4.4 μg/g 

and streambed sediment 4.1 μg/g). Concentrations exceeded 

the PEC in the two streambed-sediment samples from the 

Leon Quintana site and exceeded the TEC in 16 percent of 

samples from all sites. On the basis of results of KruskalWallis and Tukey’s multiple comparison tests, cadmium concentrations were significantly higher in streambed-sediment 

samples from Leon Creek compared to streambed-sediment 

samples from Salado Creek and San Antonio River. A statistically significant, positive correlation exists between cadmium 

concentrations in streambed-sediment samples and mining 

land-use and between cadmium concentrations and the potential source of contamination categories of active or abandoned 

mined land and abandoned municipal solid waste landfill 

listed by the Texas Commission on Environmental Quality for 

the Source Water Assessment Program. 

The PEC for chromium concentrations was exceeded 

in four samples, the two streambed-sediment samples from 

the Leon Quintana site and one streambed-sediment sample 

and one suspended-sediment sample from the Leon 35 site. 

Chromium concentrations exceeded the TEC in 69 percent of 

the samples and exceeded the sediment-quality guideline more 

frequently than concentrations of any other constituent analyzed in this study. Chromium concentrations in streambedsediment samples do not correlate with any of the available 

land-use or potential source of contamination categories.

Lead concentrations were highest in the samples from the 

Leon 35 site (streambed sediment 69.3 μg/g), USGS station 

08178565 San Antonio River at Loop 410, San Antonio, Tex. 

(hereinafter, SAR 410 site) (suspended sediment 68.2 μg/g), 

and Leon Quintana site (streambed sediment 65.0 μg/g). Lead 

concentrations exceeded the TEC in 33 percent of the samples; 

only chromium concentrations exceeded the sediment-quality 

guideline more frequently. 

Mercury concentrations were highest in two streambedsediments samples from the Leon Quintana site (0.09 and 0.08 

μg/g), one suspended-sediment sample from USGS station 

08181800 San Antonio River near Elmendorf, Tex. (hereinafter, SAR Elmendorf site) (0.07 μg/g), and two suspended-sediment samples from the Leon 35 site (0.07 μg/g). No mercury 

concentrations were greater than the TEC. 

Mean trace element concentrations in suspendedsediment samples collected in Bexar County during 2007–09 

generally were lower compared to mean concentrations in 

samples collected from the Austin and Fort Worth, Tex., areas 

during previous studies. However, considering the relatively 

large ranges and standard deviations associated with the 

concentrations measured in all three areas, the trace element 

concentrations are similar. 

On the basis of Mann-Whitney U test results, the presence of a military installation in a watershed was associated 

with statistically significant higher concentrations of chromium, mercury, and zinc in streambed sediments compared 

to the concentrations of the same elements in a watershed 

without a military installation. 

At least three or more halogenated organic compounds 

were detected in each sediment sample collected during 

2007–09 and 66 percent of the concentrations were less 

than the respective interim reporting levels (nondetections). 

Halogenated organic compound concentrations generally were 

low compared to consensus-based sediment-quality guidelines—TECs were exceeded in 11 percent of the analyses and 

PECs were exceeded by DDT, DDD, and DDE concentrations 

in one sample. 

Chlordane compounds were the most frequently detected 

halogenated organic compounds with one or more detections (concentrations equal to or greater than interim reporting levels) of chlordane compounds in every watershed. 

In this report, total chlordane is defined as the sum of cischlordane, trans-chlordane, cis-nonachlor, trans-nonachlor, 

and oxychlordane. The highest total chlordane concentrations were in a streambed-sediment sample from USGS 

station 292240098353600 Leon Creek at Lackland Air Force 

Base Golf Course, San Antonio, Tex. (hereinafter, Leon 

Lackland site) (11 micrograms per kilogram [μg/kg]) and in 

a suspended-sediment sample from the SAR 410 site (6.7 μg/

kg). Chlordane compounds were detected in 94 percent of 

the samples; 6 percent of the analyses had concentrations of 

cis-chlordane plus trans-chlordane greater than the TEC. The 

results of the Mann-Whitney U test indicate that the presence 

of a military installation in a watershed was associated with 

statistically significant higher total chlordane concentrations. 

Dieldrin was detected in 50 percent of all samples but 

not detected in any samples from USGS station 08185095 

Martinez Creek at Farm Road 1518 near St. Hedwig, Tex. 

(hereinafter, Martinez 1518 site), Chupaderas, or Leon Morey 

sites. Dieldrin concentrations were highest in a streambedsediment sample from USGS station 292443098364600 Leon 

Creek at Rodriguez Park, San Antonio, Tex. (hereinafter, Leon 

Rodriguez site) (1.1 μg/kg) and a suspended-sediment sample 

from the SAR 410 (0.84 μg/kg). All dieldrin concentrations 

were less than the TEC of 1.90 μg/kg. Dieldrin concentrations in streambed-sediment samples correlate positively with 

population density and land-use categories (residential and 

commercial) typical of densely populated areas. 

The DDT compounds (p,p'-DDT, p,p'-DDD, and p,p'-

DDE) were detected most frequently at sites in the Leon Creek 

and San Antonio River watersheds. The highest concentrations 

of all three DDT compounds were in a streambed-sediment 

sample from Leon Lackland (110 μg/kg of p,p'-DDT, 55 

μg/kg of p,p'-DDD, and 41 μg/kg of p,p'-DDE). The DDT 

compounds were detected less frequently than some other 
Summary 51

halogenated organic compounds, however most detections 

exceeded the TECs. The compound p,p'-DDT was detected in 

13 percent of the samples with 67 percent of those detections 

exceeding the TEC. The compounds p,p'-DDD and p,p'-DDE 

were detected in 19 and 35 percent of the samples with 78 and 

53 percent of those detections exceeding the TECs, respectively. The results of the Mann-Whitney U test indicate that 

the presence of a military installation in a watershed was associated with statistically significant higher p,p'-DDE concentrations. p,p'-DDE concentrations in streambed-sediment samples 

correlate positively with population density and and land-use 

categories (residential and commercial) typical of densely 

populated areas.

One or more PCB congeners were detected in 90 percent 

of the sediment samples collected from all sites. The fewest 

detections were in samples from the Martinez St. Hedwig and 

Chupaderas sites, whereas the most detections were in samples 

from the Leon Lackland, Leon 35, and SAR 410 sites. In most 

watersheds, the larger congeners (PCBs 118 to 206) were 

detected more frequently compared to the smaller congeners 

(PCBs 49 to 110). The highest concentrations of total PCBs 

(sum of the 18 reported congeners) were in a streambedsediment sample from Leon Lackland (77 μg/kg) and a 

suspended-sediment sample from Leon 35 (suspended sediment 26 μg/kg). Total PCB concentrations were significantly 

higher in the streambed-sediment samples from the San 

Antonio River compared to the streambed-sediment samples 

from Salado Creek, on the basis of the results of KruskalWallis and Tukey’s multiple comparison tests. The results of 

the Mann-Whitney U test indicate that the presence of a military installation in a watershed was associated with statistically significant higher total PCB concentrations. Additionally, 

the total PCB concentrations in streambed-sediment samples 

correlated positively with residential, industrial, and mining 

land uses. The PCB mixtures in samples from Leon Creek, 

Salado Creek, and the San Antonio River are dominated 

by PCB congeners 138, 180, and 187 on the basis of visual 

examination of the patterns of the ratios of individual PCB 

congeners to total PCBs. The similar PCB congener patterns 

suggest similar PCB sources in the three watersheds. 

Brominated flame retardant compounds were not 

detected in samples from the Chupaderas site or USGS station 08180840 Elm Creek at State Highway 16, San Antonio, 

Tex. The most frequent detections occurred in the samples 

from sites in the Medio Creek, Leon Creek, and San Antonio 

River watersheds. The highest concentrations of the four most 

frequently detected brominated flame retardants, polybrominated diphenyl ethers (PBDEs) 100, 153, 154, and dechlorane 

plus, were in samples from the Medio 90, Leon 35, Salado 

Southton, SAR 410, and SAR Elmendorf sites. No sedimentquality guidelines exist for the brominated flame retardant 

compounds for comparison. 

Mean halogenated organic compound concentrations in 

suspended-sediment samples collected from sites in Bexar 

County during 2007–09 generally were lower compared to 

mean concentrations in samples from the Austin and Fort 

Worth areas. However, considering the relatively large ranges 

and standard deviations associated with the concentrations 

measured in all three areas, the halogenated organic compound 

concentrations are similar. 

PAHs were detected most frequently in samples from 

sites in the Leon Creek and San Antonio River watersheds. 

PAHs were not detected often and only at relatively low concentrations in samples from the Medio Creek, Medina River, 

Elm Creek, Martinez Creek, and Chupaderas Creek watersheds. In this report, total PAH is the sum of 12 compounds: 

acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, 

benzo(a)-pyrene, chrysene, dibenz(a,h)anthracene, fluoranthene, fluorene, naphthalene, phenanthrene, and pyrene. 

The greatest total PAH concentrations were in a streambedsediment sample from Leon Rodriguez (4,000 μg/kg) and in 

a suspended-sediment sample from SAR 410 (3,600 μg/kg). 

Total PAH concentrations exceeded the TEC in 14 percent 

of the samples, and none of the total PAH concentrations 

exceeded the PEC. Total PAH concentrations in streambedsediment samples correlate positively with population density; 

residential, commercial, transportation, and mining land-use 

categories; and industrial wastewater outfall, wastewater 

liftstation, and petroleum storage tank potential source of 

contamination categories. Mean total PAH concentrations in 

suspended-sediment samples collected in Bexar County during 

2007–09 were generally lower, but similar overall when considering the large ranges and standard deviations, compared 

to mean total PAH concentrations measured during similar, 

previous studies in the Austin and Fort Worth areas. 

The overall degree of sediment contamination of the 

Bexar County sampling sites was assessed by using the mean 

PEC quotient. The mean PEC quotient is derived by using the 

three groups of constituents for which consensus-based SQGs 

exist—trace elements, halogenated organic compounds, and 

PAHs. To compute the mean PEC quotient, the concentration 

of each constituent is divided by its respective PEC to get the 

individual PEC quotient, and then the individual PEC quotients are summed for each sample and divided by the number 

of PEC quotients to get the mean PEC quotient. Mean PEC 

quotients provide a basis for predicting sediment toxicity—a 

mean PEC quotient greater than 0.5 is a reasonable indicator 

of whether the sediment is toxic to benthic biota and correctly 

predicts toxicity in 85 percent of samples tested. Moreover, 

the incidence of toxicity is highly correlated to the mean PEC 

quotient. The mean PEC quotient is less than 0.5 for all but 

one of the sediment samples collected from sites in Bexar 

County during 2007–09. A streambed-sediment sample collected from the Leon Lackland site had a mean PEC quotient 

of 0.51. The next highest mean PEC quotients were measured 

in samples from the Leon Quintana, Leon 35, Leon Military, 

and SAR 410 sites (in order of decreasing values). 

PAH sources were investigated by comparing the ratios of 

individual PAH compounds to total PAH of several common 

PAH sources such as coal combustion (power plants), automobile-related sources, and coal-tar parking lot sealcoat and the 

Bexar County streambed- and suspended-sediment samples. 
52 Assessment of Selected Contaminants in Streambed- and Suspended-Sediment Samples Collected in Bexar County, Texas

The contribution from each PAH source was estimated by 

using a chemical mass balance model, which indicated that 

parking lot coal-tar sealcoat dust is the largest PAH source to 

the average Bexar County sediment, accounting for 70.2 to 

78.9 percent of the PAHs in the mixture. 

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