Water Quality in the

Trinity River Basin

Texas, 1992–95

U.S. Department of the Interior

U.S. Geological Survey Circular 1171

science for a changing world
Trinity River Basin Study Unit, contact:

District Chief

U.S. Geological Survey

Water Resources Division

8011 Cameron Rd.

Austin, TX 78754

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Division

12201 Sunrise Valley Drive, M.S. 413

Reston, VA 20192

Coordination among agencies and organizations is an integral part of the NAWQA Program. We thank 

the following agencies and organizations who contributed through their participation in the Study Unit Liaison 

Committee.

Federal Agencies:

• U.S. Army Corps of Engineers

• U.S. Department of Agriculture, Natural Resources 

Conservation Service

• U.S. Department of the Interior, Bureau of 

Reclamation

• U.S. Environmental Protection Agency

• U.S. Fish and Wildlife Service

State Agencies:

• Railroad Commission of Texas

• Texas Department of Agriculture

• Texas Natural Resource Conservation Commission

• Texas Parks and Wildlife Department

• Texas State Soil and Water Conservation Board

• Texas Water Development Board

Local Organizations:

• City of Arlington

• City of Fort Worth

• City of Irving

• Dallas Water Utilities Department

• Tarrant County Water Control and Improvement 

District No. 1

• Trinity River Authority

Universities and other organizations:

• Galveston Bay National Estuary Program

• North Central Texas Council of Governments

• Texas Water Resources Institute

• University of North Texas

• University of Texas at Austin

Summary of compound detections and concentrations tables (p. 30–35) were provided by Sarah J. Ryker, Jonathon

C. Scott, and Alan L. Haggland.

Editing, graphics, and report-processing support were provided by Gloria J. Smith, Stanley H. Crenwelge, Peter W.

Bush, Gail J. Sladek, and Judy A. Voigt.

Information on the NAWQA Program is also available on the Internet via the World Wide Web. You may 

connect to the NAWQA Home Page using the Universal Resources Locator (URL):

http://wwwrvares.er.usgs.gov/nawqa/nawqa_home.html

The Trinity River Basin Study Unit’s Home Page is at URL:

http://txwww.cr.usgs.gov/trin/index.html

Front cover: Dallas skyline at dusk. The channelized Trinity River is in foreground. (Photograph courtesy of TEXAS 

HIGHWAYS Magazine. © by Richard Stockton. Used with permission.)

Back cover: Longhorns grazing north of Denton. (Photograph by Larry F. Land, U.S. Geological Survey.)

A COORDINATED EFFORT

FOR ADDITIONAL INFORMATION ON THE

NATIONAL WATER-QUALITY ASSESSMENT (NAWQA) PROGRAM:
U.S. GEOLOGICAL SURVEY CIRCULAR

Water Quality in the Trinity River Basin, 

Texas, 1992–95

1171

By Larry F. Land, J. Bruce Moring, Peter C. Van Metre, 

David C. Reutter, Barbara J. Mahler, Allison A. Shipp, 

and Randy L. Ulery

CONTENTS

National Water-Quality Assessment Program ................................................................................................................... 1

Summary of Major Issues and Findings in the Trinity River Basin .................................................................................. 2

Environmental Setting and Hydrologic Conditions in the Trinity River Basin ................................................................ 4

Major Issues and Findings ................................................................................................................................................. 6

Nutrients in Streams ..................................................................................................................................................... 6

Pesticides in Streams .................................................................................................................................................... 8

Determining Water-Quality Trends Using Sediment Cores, White Rock Lake, Dallas ............................................... 10

Organochlorines in Streambed Sediments and Aquatic Biota ..................................................................................... 12

Stream-Habitat Characteristics and Fish-Community Degradation ............................................................................. 14

Stream-Habitat Characteristics ................................................................................................................................ 15

Fish-Community Degradation ................................................................................................................................. 16

Use of a New Method, Semipermeable Membrane Device (SPMD), to Assess the Occurrence of 

Water-Borne Polycyclic Aromatic Hydrocarbons (PAHs) in Streams ....................................................................... 17

Fish-Community Changes Reflect Water-Quality Improvements in the Trinity River Downstream 

From Dallas ................................................................................................................................................................ 19

How Has the Water Quality Improved? .................................................................................................................. 19

How Has the Fish Community Changed as a Result? ............................................................................................. 20

Quality of Ground Water in Aquifer Outcrops ............................................................................................................. 22

Trinity Aquifer ......................................................................................................................................................... 22

Woodbine Aquifer ................................................................................................................................................... 22

Carrizo-Wilcox Aquifer ........................................................................................................................................... 23

Gulf Coast Aquifer .................................................................................................................................................. 23

Water-Quality Conditions in a National Context .............................................................................................................. 24

Comparison of Trinity River Basin Study Unit Surface-Water Results with Nationwide NAWQA 

Findings ...................................................................................................................................................................... 24

Comparison of Trinity River Basin Study Unit Ground-Water Results With Nationwide NAWQA 

Findings ...................................................................................................................................................................... 26

Study Design and Data Collection in the Trinity River Basin .......................................................................................... 28

Summary of Compound Detections and Concentrations .................................................................................................. 30

References ......................................................................................................................................................................... 36

Glossary ............................................................................................................................................................................. 37
Library of Congress Cataloging in Publications Data

The use of firm, trade, and brand names in this report is for identification purposes only and

does not constitute endorsement by the U.S. Government.

Free on application to the

U.S. Geological Survey

Information Services

Box 25286 Federal Center

Denver, CO 80225

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Thomas J. Casadevall, Acting Director

Water quality in the Trinity River Basin, Texas, 1992–95 / by Larry F. Land ... [et al.].

p. cm.— (U.S. Geological Survey circular ; 1171)

ISBN 0–607–89233–1 (pbk.)

1. Water quality—Texas—Trinity River watershed. I. Land, Larry F. 

II. Series.

TD224.T4W378 1998

363.739'42'0976414—dc21 98–4639

CIP

1998
U.S. Geological Survey Circular 1171 1

“The USGS Trinity NAWQA 

Program has been an 

invaluable resource for the 

Texas Natural Resource 

Conservation Commission 

and the Texas Clean Rivers 

Program. Since 1993, 

NAWQA hydrologists and 

biologists have provided the 

TNRCC staff and Texas 

Clean Rivers Program 

partners with their technical 

expertise on data analysis 

procedures and monitoring 

and assessment protocols. 

As the challenges in data 

assessment and monitoring 

continue for the Texas Clean 

Rivers Program, the TNRCC 

will look to the USGS and 

the lessons learned from the 

Trinity NAWQA Program.” 

Sally C. Gutierrez, 

Director, 

Water Quality Division

Texas Natural Resource 

Conservation Commission

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

Began in 1991

Began in 1994

Began in 1997

Not scheduled yet

EXPLANATION

Knowledge of the quality of the Nation's streams and aquifers is important because

of the implications to human and aquatic health and because of the significant costs

associated with decisions involving land and water management, conservation, and

regulation. In 1991, the U.S. Congress appropriated funds for the U.S. Geological

Survey (USGS) to begin the National Water-Quality Assessment (NAWQA) Program

to help meet the continuing need for sound, scientific information on the areal extent

of the water-quality problems, how these problems are changing with time, and an

understanding of the effects of human actions and natural factors on water-quality

conditions. 

The NAWQA Program is assessing the water-quality conditions of more than 50 of

the Nation's largest river basins and aquifers, known as Study Units. Collectively,

these Study Units cover about one-half of the United States and include sources of

drinking water used by about 70 percent of the U.S. population. Comprehensive

assessments of about one-third of the Study Units are ongoing at a given time. Each

Study Unit is scheduled to be revisited every decade to evaluate changes in waterquality conditions. NAWQA studies rely heavily on existing information collected by

the USGS and many other agencies as well as the use of nationally consistent study

designs and methods of sampling and analysis. Such consistency simultaneously provides information about the status and trends in water-quality conditions in a particular stream or aquifer and, more importantly, provides the basis to make comparisons

among watersheds and improve our understanding of the factors that affect waterquality conditions regionally and nationally. 

This report is intended to summarize major findings that emerged between 1992

and 1995 from the water-quality assessment of the Trinity River Basin Study Unit 

and to relate these findings to water-quality issues of regional and national concern.

The information is primarily intended for those who are involved in water-resource

management. Indeed, this report addresses many of the concerns raised by regulators,

water-utility managers, industry representatives, and other scientists, engineers, 

public officials, and members of stakeholder groups who provided advice and input to

the USGS during this NAWQA Study Unit investigation. Yet, the information contained here might also interest those who simply wish to know more about the quality

of water in the rivers and aquifers in the area where they live. 

 Robert M. Hirsch, Chief Hydrologist
2 Water Quality in the Trinity River Basin, Texas, 1992–95

Nutrients in streams (p. 6–7)

Nutrients in tributary streams rarely are at concentrations unacceptable for drinking water. 

• Total nitrogen concentrations are similar in urban and agricultural streams and are larger in urban and agricultural 

streams than in streams in rangeland and forest areas. 

• The only samples with nitrate concentrations greater than the U.S. Environmental Protection Agency (EPA) drinkingwater standard are from Calloway Branch (an urban stream) and the Trinity River downstream from Dallas (affected by 

point sources).

• Total phosphorus concentrations are similar in all tributaries, regardless of land use. 

• Nutrient concentrations in streams vary seasonally and are as much as 100 percent greater during the spring than during 

the winter.

Pesticides in streams (p. 8–9)

Pesticides are in most streams. Much of the streamflow is captured by reservoirs, which are sources of 

drinking water. 

• Four to six herbicides commonly were detected in streams draining urban and agricultural areas. Atrazine was detected in 

samples from all streams draining urban and agricultural areas. Atrazine concentrations in agricultural streams often 

exceed the drinking-water standard during the spring when atrazine is applied to fields and rains producing runoff are 

most common.

• Two to four insecticides commonly were detected in streams draining urban areas, and usually no more than one 

insecticide was detected in streams draining agricultural areas. Diazinon is in all samples from streams draining urban 

areas. Diazinon concentrations in urban streams exceed the EPA health advisory level for drinking water in 15 percent of 

samples.

Determining water-quality trends using sediment cores (p. 10–11)

Lead, DDT, and polychlorinated biphenyl (PCB) concentrations have decreased, but chlordane, polycyclic 

aromatic hydrocarbon (PAH), and zinc concentrations have increased in sediments from urban streams 

since the mid-1960s.

• Environmental trends in contaminants tend to follow historical use. For example, lead concentrations in a White Rock 

Lake sediment core peaked in the 1970s at about 5 times background concentrations and decreased since the introduction 

of unleaded gasoline to about 2 times background concentrations by the early 1990s. 

• DDT and PCB concentrations have decreased about 90 percent in the White Rock Lake core since their use was banned 

in the 1970s.

• Chlordane concentrations increased in response to urban growth and increasing use of chlordane during the 1970s and 

1980s and peaked soon after use was banned in the late 1980s.

• PAH concentrations in the White Rock Lake sediment core are 20 times greater in recent sediments than in preurbanization sediments, and zinc concentrations have increased about 60 percent. Both probably result largely from 

automobile use in the watershed. 

Organochlorines in streambed sediments and aquatic biota (p. 12–13)

Concentrations of some toxic compounds in sediments commonly exceed Texas Natural Resource 

Conservation Commission screening concentrations.

• Concentrations of chlordane, dieldrin, and the DDT environmental degradation products, DDD and DDE, in bed 

sediment are larger in streams draining urban areas than in streams draining agricultural areas and exceed Texas Natural 

Resource Conservation Commission screening concentrations for these compounds in sediment.

• Chlordane, DDT, and PCBs are more commonly detected in fish in streams draining urban areas than agricultural areas. 

SUMMARY OF MAJOR ISSUES AND FINDINGS IN THE TRINITY RIVER BASIN
U.S. Geological Survey Circular 1171 3

Stream-habitat characteristics and fish-community degradation (p. 14–16)

Fish communities are affected by characteristics of streamflow and the structure of physical habitats in 

the stream channel, in addition to water chemistry. In streams where historical patterns of streamflow have 

been altered by channelization, degradation in the fish community has occurred. 

• Streams in developed urban and agricultural settings generally have more variable streamflow, more degraded and less 

diverse physical habitats, and more degraded fish communities than comparable streams in less-developed settings.

• The urban stream West Fork Trinity River in Fort Worth has highly variable streamflow, is channelized with little or no 

meandering, has few woody snags in the stream, and has low woody-species diversity in the riparian zone. As a result, 

more nonnative and generally more pollutant-tolerant species of fish are in this stream than in comparable natural 

streams.

• The Blackland Prairie stream Chambers Creek is channelized and leveed in its lower reach, which has reduced the 

structural complexity of physical habitat. A high percentage of tolerant fish species are present in this reach of Chambers 

Creek.

Use of a new method, semipermeable membrane device (SPMD), to assess the occurrence of water-borne 

PAHs in streams (p. 17–18)

The SPMD is an effective tool to detect trace organic compounds in water. The small concentrations of 

many compounds in streams might not be detected by more traditional water-sampling techniques.

• Twenty-five PAHs were detected in SPMDs deployed in urban streams in the Dallas-Fort Worth metropolitan area.

• Nine of the PAHs detected by the SPMDs are on the Public Health Service Agency for Toxic Substances and Disease 

Registry priority list of 275 hazardous substances, and two, benzo(a)pyrene and benzo(b)fluoranthene, are ranked in the 

top 10.

Fish-community changes reflect water-quality improvements (p. 19–21)

Improvements in the treatment of wastewater in the Dallas-Fort Worth area from the early 1970s through 

the mid-1990s have been beneficial to the water quality of the Trinity River. 

• Ammonia plus organic nitrogen concentrations in the Trinity River downstream from Dallas have decreased about 95 

percent from more than 10 milligrams per liter in the 1970s to near trace concentrations in the mid-1990s.

• Dissolved oxygen conditions in the Trinity River downstream from Dallas have improved vastly from the 1970s, when 

occurrences of nearly no dissolved oxygen were common, to the mid-1990s, when concentrations were almost never less 

than 5 milligrams per liter.

• The fish community has improved markedly since the mid-1980s when several fishkills occurred. Now (1998), many 

native species of fish that were absent in the 1970s have returned to the Trinity River downstream from Dallas.

Quality of ground water in aquifer outcrops (p. 22–23)

Pesticide, volatile organic compound (VOC), and elevated nutrient concentrations were present in some 

shallow (outcrop) water wells in urban and agricultural areas; however, most samples did not exceed 

drinking-water standards.

• About 10 to 30 percent of samples from the shallow zone (outcrop) of each of four aquifers contained herbicides, and 

about 5 to 50 percent contained insecticides. None of the pesticide concentrations in samples of shallow ground water 

exceeded drinking-water standards or health advisory levels. Thirteen percent of nitrate concentrations in the shallow 

zone of the Woodbine aquifer exceeded the EPA standard for drinking water. 

• VOCs were detected in one or more samples from each of the four aquifers sampled. The most commonly detected VOC 

was MTBE, a gasoline additive, in the urban part of the Woodbine aquifer.

• None of the samples from the Trinity aquifer exceeded EPA maximum contaminant levels for drinking water; however, 

the insecticide diazinon was detected in nearly one-half the samples.

SUMMARY OF MAJOR ISSUES AND FINDINGS IN THE TRINITY RIVER BASIN
4 Water Quality in the Trinity River Basin, Texas, 1992–95

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Grand Prairie: The terrain is 

characterized by nearly level plains 

and rolling hills and is naturally 

devoid of trees except along streams. 

Much of Fort Worth is located on the 

Grand Prairie.

Surface water, almost entirely from reservoirs, supplies more than 90 percent of the water used in the basin. With the large 

population and concentration of businesses and industries in the Dallas-Fort Worth area, many reservoirs have been built for 

water supply and flood protection. Relatively little water is used for irrigating crops. Aquifers outcrop in all or parts of the 

Western and Eastern Cross Timbers, Eastern Timberlands, Texas Claypan, and Coastal Prairie and Marsh. Ground water is 

used for municipal and domestic supply in some of the smaller towns and in rural areas. 

The environmental setting is an integration of many physical and hydrologic features and human activities. Physical and 

hydrologic features include location, topography, physiography, geology, soils, climate, natural vegetation, streams, and aquifers. A classification of Integrated Land Resource Units characterizes the physical and hydrologic features (Ulery and others, 

1993). Past and current human activities, including construction of reservoirs, urbanization, farming, ranching, and oil and gas 

production, have greatly altered the natural environment in the Trinity River Basin.

North Central Prairie: 

The terrain is nearly level to 

hilly and covered with 

natural vegetation, which 

mostly is prairie grass. 

However, brush has 

encroached into much of 

the area. Substantial 

amounts of oil and gas are 

produced in the area. The 

principal agricultural 

product is cattle.

Western and Eastern Cross Timbers: 

The terrain is hilly and oak trees are a 

prominent feature, especially when 

contrasted with prairies immediately to the 

east and west of each of these areas. The 

area is suitable for raising cattle. The 

Eastern Cross Timbers between Fort Worth 

and Dallas has been urbanized. 

Blackland Prairie: The terrain varies 

from nearly level to rolling hills, has very 

fertile soils, and, in its natural state, is 

largely a grassy plain except along the 

streams. Much of the area has been 

cultivated in the past; however, a large 

part of the cultivated acreage has been 

converted back to pasture for cattle 

grazing. Much of the Dallas metropolitan 

area is on the Blackland Prairie. 

Texas Claypan: The terrain is mostly rolling 

hills. The natural vegetation is mostly prairie 

grasses and oaks. Agriculture is dominated by 

cattle ranching. Lignite coal is mined locally and 

is used to fuel nearby electric power plants.

Eastern Timberlands: 

The terrain varies from a 

rolling plain to gently rolling 

hills. The area is noted for 

piney woods and produces 

nearly all the commercial 

timber in Texas. The area 

also is a major producer of 

oil and gas. Perennial 

streams are prevalent. 

Coastal Prairie and Marsh: The area is very flat. 

Natural vegetation is prairie grasses with stands of 

hardwoods and pines. The area is extensively cultivated 

for growing rice. However, much of the cultivated 

acreage is being converted to pasture for cattle grazing. 

Oil and gas also are produced in the area. 

Bottomlands: The Bottomlands lie along the 

Trinity River and the lower reaches of major 

tributaries. Many reservoirs in the Trinity River 

Basin have greatly reduced the historical 

magnitude and frequency of floods in the 

Bottomlands.

ENVIRONMENTAL SETTING AND HYDROLOGIC CONDITIONS IN THE TRINITY RIVER BASIN

Dallas-Fort Worth

metropolitan area
U.S. Geological Survey Circular 1171 5

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Hydrologic conditions in the Trinity River Basin are best characterized by precipitation and streamflow. Precipitation varies 

considerably across the Study Unit, with average annual rainfall ranging from about 27 inches in the northwestern part to 

about 52 inches in the southeastern part. Streamflow generally is proportional to precipitation and the size of the watershed, 

except downstream from reservoirs and point sources such as wastewater-treatment plants. To characterize the hydrologic conditions in the Trinity River Basin during the March 1993–September 1995 intensive sampling phase, monthly precipitation and 

daily streamflow from October 1992 to September 1995 at selected stations are graphed and interpreted.

Precipitation: Essentially all the precipitation in the Trinity River Basin is rain. At the three selected precipitation sites 

across the basin, rainfall was about normal in 1993 and 1994 and about one-third greater than normal in 1995. The greatest 

flooding occurred in October 1994 in the southern part of the study area where 18.5 inches was recorded in 1 day and more 

than 26 inches in 3 days. The rainfall data suggest that water-quality data collected during and shortly after the October 1994

flood would reflect unusual hydrologic conditions.

Streamflow: Two stream configurations are in the Trinity River Basin; one is tributary streams and the other is the main 

stem of the Trinity River. Much of the water in tributary streams is captured by reservoirs and becomes a water supply. Water 

in the main stem provides water to Lake Livingston, also used for water supply, and to coastal bays and estuaries. The 

hydrographs for two tributaries, Big Sandy Creek and Chambers Creek, show streamflow decreases to relatively low levels 

each year during the summer. Flow in the Trinity River at Romayor, about 70 miles upstream from the mouth, is controlled by 

releases from Lake Livingston. The hydrographs indicate that data collected during the sampling period are representative of 

normal conditions, except during 1995 in the lower reach of the Trinity River when flows were well above average. 

Reservoirs: There are 22 reservoirs in the Trinity River Basin with more than 

10,000 acre-feet of storage and hundreds of smaller reservoirs, mostly floodcontrol structures built by the Natural Resources Conservation Service (Ulery and 

others, 1993). These reservoirs have an appreciable effect on streamflow and water 

quality in the basin. They tend to increase base flow in streams by releasing stored 

water during dry periods. They tend to reduce flood peaks by storing floodwaters. 

They affect water quality by trapping sediment and associated nutrients and 

contaminants and by altering the stream habitat both in the flooded lake area and 

downstream. 

1993 1994 1995 1

100,000

10

100

1,000

10,000

EXPLANATION

Daily mean streamflow

Average streamflow for period of record

Average discharge for October–September

1993 1994 1995 1

100,000

10

100

1,000

10,000

1993 1994 1995 1

100,000

10

100

1,000

10,000

08064100

08044000

08066500

STREAMFLOW, IN CUBIC FEET PER SECOND PER DAY

1993 1994 1995 0

15

5

10

EXPLANATION

Monthly precipitation

Average precipitation for 1961–90 

Average precipitation for October–September 

1993 1994 1995 0

15

5

10

1993 1994 1995

15

5

10

Jacksboro

Corsicana

Liberty 29.59

PRECIPITATION, IN INCHES

Trinity River at Romayor

Big Sandy Creek near Bridgeport 

Chambers Creek near Rice

Jacksboro Fort Worth

Corsicana

Dallas

Liberty

08066500

08064100

08044000

LAKE

LIVINGSTON

Streamflow-gaging station

ENVIRONMENTAL SETTING AND HYDROLOGIC CONDITIONS IN THE TRINITY RIVER BASIN
6 Water Quality in the Trinity River Basin, Texas, 1992–95

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Nutrients (nitrogen and phosphorus

compounds) in surface water are

essential for aquatic plant and animal

life; but large concentrations of nutrients can have adverse ecological

effects. Fertilizer, manure, plant decay,

and atmospheric fallout are major

nonpoint sources of nitrogen and phosphorus. Wastewater-treatment plant

effluent is a major point source.

The EPA (1996) maximum contaminant level (MCL) for nitrate (as

nitrogen) is 10 milligrams per liter.

Excessive nitrate can restrict oxygen

transport in the bloodstream. Ammonia in surface water is naturally converted to nitrate. This conversion, in

addition to increasing nitrate concentration, removes oxygen from the

water, which also can adversely affect

fish and invertebrates.

The EPA recommends that total

phosphorus concentration (as

phosphorus) not exceed 0.10 milligram

per liter in streams not discharging

directly into reservoirs and not exceed

0.05 milligram per liter in streams

discharging directly into reservoirs.

Phosphorus commonly is associated

with eutrophication—the enrichment

of a body of water with nutrients

resulting in accelerated algal or plant

production. Eutrophication can result

in fishkills, unpleasant odors, loss of

recreational value, and other waterquality-related problems.

Water samples of tributary streams

draining rangeland and forest land,

agricultural land, and urban land,

and of the Trinity River downstream

from Dallas were collected from

March 1993 to September 1995. For

nitrate, only two samples exceeded the

MCL; one was from Calloway Branch,

a small urban stream northeast of

Fort Worth, and the other was from the

Trinity River downstream from Dallas.

Only 2 of 480 samples from

44 stream sites had nitrate

concentrations that exceeded

1996 EPA maximum contaminant

levels.

Most nitrate (as nitrogen) concentrations were less than 2.5 milligrams per

liter. The distribution patterns of total

nitrogen and three nitrogen species in

the tributary streams draining agricultural and urban areas were very

similar. Tributary streams draining

rangeland and forest land had fewer

samples with concentrations greater

than 2.5 milligrams per liter, a result

that is attributed to lesser amounts of

fertilizer applied in rangeland and forest land than in agricultural and urban

lands. Samples from the Trinity River

downstream from Dallas, where the

streamflow is dominated by effluent

from regional wastewater-treatment

plants, had appreciably greater concentrations of nitrate and total nitrogen

than streams affected only by nonpoint

sources (Shipp, 1995a).

About 30 percent of the total phosphorus samples from tributary streams

draining the three land-use areas had

concentrations greater than the EPA

guideline, and all the samples from

the Trinity River downstream from

Dallas had concentrations greater than

the EPA guideline. For the 10 sampling sites on tributaries that flow

directly into reservoirs, concentrations

in about 50 percent of the samples

exceeded the EPA guideline. The

distributions of total and dissolved

phosphorus and orthophosphate concentrations were similar for tributary

streams draining urban, rangeland, and

forest land. In agricultural areas, fewer

sample concentrations were greater

than 0.10 milligram per liter. Within

the agricultural area, concentrations of

total phosphorus (and total nitrogen)

tend to increase as the percentage of

cropland increases.

Nutrient sampling sites on streams of the Trinity River Basin during

1993–95. The greatest density of sites is in agricultural and urban areas.

MAJOR ISSUES AND FINDINGS

Nutrients in Streams

Urban land

Agricultural land

Rangeland

Forest land

Water

Wetland

Urban land

Agricultural land

Rangeland and forest land

Trinity River downstream from Dallas

Sampling sites

Land use/land cover

EXPLANATION

Calloway Branch near Fort Worth
U.S. Geological Survey Circular 1171 7

MAJOR ISSUES AND FINDINGS

Nutrients In Streams

The largest nutrient concentrations were downstream from

wastewater point sources, and

the smallest nutrient concentrations were immediately downstream from reservoirs.

Total nitrogen and total phosphorus

concentrations show noticeable seasonal patterns (Land and Shipp, 1996).

Median total nitrogen concentrations

increase from midwinter to midspring,

decline in the summer, and increase

again in the fall; median total phosphorus concentrations follow a generally

similar pattern. Because much greater

amounts of fertilizer are applied in the

spring than in other seasons, the timing

Dissolved Ammonia

Total Ammonia Organic Nitrogen

Nitrate

Total Nitrogen

Dissolved Ammonia

Total Ammonia Organic Nitrogen

Nitrate

Total Nitrogen

Dissolved Ammonia

Total Ammonia Organic Nitrogen

Nitrate

Total Nitrogen

Dissolved

Total ammonia +

Nitrate nitrogen

Total nitrogen

NITROGEN

Rangeland Urban land Trinity River down- Agricultural land

ammonia nitrogen

organic nitrogen

0 50 100

Dissolved Orthophosphate

Dissolved Phosphorus

Total Phosphorus

Dissolved Orthophosphate

Dissolved Phosphorus

Total Phosphorus

Dissolved Orthophosphate

Dissolved Phosphorus

Total Phosphorus

0 50 100

Dissolved

Dissolved

Total

PHOSPHORUS

PERCENTAGE OF SAMPLES

0 50 100 100 0 50

orthophosphate

phosphorus

phosphorus

Concentration, in

Less than 0.25

0.25 to 2.5

Greater than 2.5

EXPLANATION

milligrams per liter

Less than 0.01

0.01 to 0.1

Greater than 0.1

Distributions of nitrogen and phosphorus concentrations in streams of the Trinity River Basin during 1993–95

reflect agricultural and urban land-use practices.

and forest land stream from Dallas

An algal bloom in Richland Creek

is indicative of excess nutrients.

Seasonality of nitrogen and phosphorus concentrations in streams of the

Trinity River Basin during 1993–95. Each bar shows the range between the

10th and 90th percentiles. The black line in each bar shows the monthly

median concentration as a percentage of the annual median.

Total phosphorus Total nitrogen

J FMAMJ J ASOND

MONTH

10

10,000

20

50

100

200

500

1,000

2,000

5,000

PERCENTAGE OF ANNUAL

J FMAMJ J ASOND

MONTH

Total nitrogen Total phosphorus

MEDIAN CONCENTRATION

of the applications would seem to be

the major reason for increases in concentrations in the spring. However,

total nitrogen and (especially) total

phosphorus concentrations were

found to relate more closely to streamflow than to fertilizer applications.

Monthly mean streamflow usually

peaks in the spring, declines in the

summer, and rises to a lesser peak in

the fall.

Nutrient concentrations at most

sampling sites did not change

appreciably from 1974 to 1991.

Nutrient concentrations at most

sampling sites did not change appreciably from 1974 to 1991 (Van Metre

and Reutter, 1995). The exceptions

are five sites downstream from major

wastewater-treatment plants in the

Dallas area. As a result of upgrades

to the treatment plants, ammonia plus

organic nitrogen at the sampling

sites decreased about 95 percent;

concurrently, nitrate increased by a

similar magnitude. The decrease in

ammonia has led to an increase in dissolved oxygen, which reduces the

threat of fishkills downstream from the

wastewater-treatment plants.
8 Water Quality in the Trinity River Basin, Texas, 1992–95

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o

o

30

0 20 40 60 MILES

0 20 40 60 KILOMETERS

Pesticides (herbicides, insecticides,

and fungicides) are present in streams

throughout the basin (Shipp, 1995b;

Ulery and Brown, 1995). Herbicides

are used to control nuisance plants. In

agricultural areas, they commonly are

applied to the soil in late winter or

early spring and during the growing

season to improve crop yields and

quality. In urban areas, they are used to

control weeds in lawns and unwanted

vegetation along streets and highways

to improve safety and reduce maintenance. Insecticides are used to control

insects that might damage crops, landscaping, and buildings or cause disease

in humans and animals. Modern insecticides are designed to decompose into

less harmful products faster than many

older insecticides. Fungicides are used

to control plants such as molds and

mildews. Even though pesticides are

very useful, they can be harmful to

humans, domestic animals and wildlife, desirable plants and insects, and

whole ecosystems.

In most streams of the Trinity Basin,

herbicides are more prevalent than

insecticides—the number of herbicide

detections was greater than the number

of insecticide detections. The most

commonly detected herbicide in 284

samples collected from March 1993 to

September 1995 is atrazine. Atrazine

typically is used on fields of corn, hay,

and sorghum and on lawns. Atrazine

was detected in about one-half the 38

samples from 17 rangeland and forest

stream sites, in more than 95 percent of

the 148 samples from 15 agricultural

stream sites, in all 75 samples from

About 6 percent of 277 samples

from 44 stream sites had concentrations of atrazine, the most

commonly detected herbicide,

that exceeded the 1996 EPA MCL.

11 urban stream sites, and in all 16

samples from a site on the Trinity

River downstream from Dallas. The

EPA 1996 MCL for atrazine is 3.0

micrograms per liter. Generally, the

agricultural stream samples had larger

atrazine concentrations than samples

from rangeland and forest streams,

urban streams, or the Trinity River

downstream from Dallas. About 12

percent of the agricultural stream samples had atrazine concentrations

greater than the MCL; none of the

samples from rangeland and forest

streams, urban streams, and the Trinity

River downstream from Dallas had

atrazine concentrations greater than

the MCL.

Atrazine concentrations show a seasonal pattern. Concentrations tend to

rise to seasonal highs in the spring and

then decline to seasonal lows that last

from late summer through midwinter

(Land and Brown, 1996). The median

atrazine concentration among all samples was 0.26 microgram per liter. The

highest monthly median concentration,

in April, was about 70 percent of the

MCL for atrazine; monthly median

concentrations from late summer to

midwinter were less than one-tenth of

the April median concentration.

The most commonly detected insecticide in the 277 samples was diazinon.

Diazinon generally is applied to lawns,

gardens, and landscaped areas. Diazinon was detected in about one-half of

the rangeland and forest samples and

agricultural samples, in all the urban

samples, and in about 90 percent of the

Trinity River downstream from Dallas

samples. The EPA 1996 lifetime health

advisory (HA) (the concentration in

drinking water that is not expected to

cause any adverse noncarcinogenic

effects over a lifetime of exposure) for

diazinon is 0.6 microgram per liter.

About 4 percent of 277 samples

from 44 stream sites had concentrations of diazinon, the most

commonly detected insecticide,

that exceeded the 1996 EPA HA.

Urban land

Agricultural land

Rangeland

Forest land

Water

Wetland

Urban land

Agricultural land

Rangeland and forest land

Trinity River downstream from Dallas

Sampling sites

Land use/land cover

EXPLANATION

Pesticide sampling sites on streams of the Trinity River Basin during

1993–95. The greatest density of sites is in agricultural and urban areas.

MAJOR ISSUES AND FINDINGS

Pesticides in Streams

Richland-Chambers Reservoir
U.S. Geological Survey Circular 1171 9

Seasonality of atrazine and diazinon concentrations in streams of the

Trinity River Basin during 1993–95 reflects the timing of applications and

runoff. Each bar shows the range between the 10th and 90th percentiles.

The black line in each bar shows the monthly median concentration as a

percentage of the annual median.

Generally, diazinon concentrations are

larger in urban stream samples than in

stream samples from other settings.

About 15 percent of the diazinon concentrations in the urban streams

exceeded the HA.

Diazinon concentrations do not

show a distinct seasonal pattern. The

median diazinon concentration among

all samples was 0.008 microgram per

liter. None of the monthly median

concentrations exceeded the HA for

diazinon.

Pesticides other than atrazine and

diazinon also are commonly detected

in basin streams. Twenty-three

different herbicides were detected in

rangeland and forest streams, 19 in

agricultural streams, and 24 in urban

streams. Among herbicides other than

atrazine, prometon was detected in

almost 40 percent of the agricultural

stream samples and in more than 90

percent of the urban stream samples

at concentrations well below its

1996 EPA HA of 100 micrograms

per liter. Metolachlor and simazine

were detected in more than one-half

the samples from agricultural and

urban streams and from the Trinity

River downstream from Dallas, each

at concentrations below its respective

1996 EPA HA (for metolachlor) and

MCL (for simazine).

Five different insecticides were

detected in rangeland and forest

streams, 10 in agricultural streams, and

10 in urban streams. Among insecticides other than diazinon, carbaryl and

chlorpyrifos were detected in slightly

more than 60 percent of the urban tributary stream samples, each of those

compounds at concentrations below its

respective 1996 EPA HA.

Although the concentrations of individual pesticides in most samples were

less than EPA MCLs and HAs, some

concerns remain. One involves pesticide concentrations in reservoirs: In

the Trinity River Basin, nearly all

streamflow is captured by reservoirs,

many of which provide drinking water

to urban areas. Pesticide concentrations in reservoirs could be greater

than average concentrations in inflowing streams because much of the

annual inflow to reservoirs occurs in

the spring when runoff and pesticide

use are greatest. For example, five

samples from Richland-Chambers

Reservoir collected in 1995 contained

from six to eight pesticides each, and

the three samples collected in June,

after spring runoff, had atrazine concentrations of about 3 micrograms per

liter (Land, 1997). Another concern

involving pesticides in drinking water

is that there is a lack of understanding

of the toxicity of combinations of pesticides. Current EPA MCLs and HAs

are only for individual compounds.

Distributions of selected herbicides and pesticides in streams of the Trinity River Basin during 1993–95 are related

to land-use practices.

2,4-D

Alachlor

Atrazine

Fluometuron

Metolachlor

Metribuzin

Molinate

Pendimethalin

Prometon

Propanil

Simazine

Tebuthiuron

Thiobencarb

Trifluralin

Rangeland Agricultural land Urban land Trinity River downHERBICIDES

0 50 100 0 50 100 0 50 100 0 50 100

Carbaryl

Carbofuran

Chlorpyrifos

p,p'-DDE

Diazinon

Dieldrin

Malathion

INSECTICIDES

PERCENTAGE OF SAMPLES

EXPLANATION

Detected and less than 0.1

0.1 to 1.0

Greater than 1.0

Detected and less than 0.1

0.1 to 1.0

Greater than 1.0

Concentration, in

 micrograms per liter

More than 10 percent of

samples exceed 1996

EPA MCL or HA

J F M A M J J A S O N S

MONTH

1

10,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

PERCENTAGE OF ANNUAL

Atrazine

Insufficient data

J F M A M J J A S O N D

MONTH

10

10,000

20

50

100

200

500

1,000

2,000

5,000 Diazinon

Insufficient data

MCL

HA

MAJOR ISSUES AND FINDINGS

Pesticides in Streams

MEDIAN CONCENTRATION

and forest land stream from Dallas
10 Water Quality in the Trinity River Basin, Texas, 1992–95

WHITE ROCK LAKE

Coring

 location

0 0.5 1 MILE

0 0.5 1 KILOMETER

White Roc k Cr.

0 4 8 MILES

0 4 8 KILOMETERS

Urban land, 1990

White Rock Creek Basin

White Rock Lake was built in 1912 

at a time when agriculture dominated 

land use. Since that time, the watershed has been incorporated into the 

growing Dallas metropolitan area. In 

1935, urban land use in the watershed 

was 6 percent; by 1990, urban land 

use was 72 percent. The watershed is 

100 square miles, and the surface area 

of the reservoir is 1.7 square miles. 

Sedimentation in the reservoir since its 

construction has reduced its storage 

capacity by one-half.

Sediment cores were collected near 

the dam from a pontoon boat. The 

reservoir sediment has a large water 

content relative to the pre-reservoir 

sediment, which was dry and crumbly. 

The cores, measured in centimeters 

(2.54 centimeters = 1 inch), were 

sliced into 2- to 5-centimeter sections 

that were analyzed for a number of 

constituents, including trace elements, 

organochlorine compounds, and polycyclic aromatic hydrocarbons (PAHs).

Age-dating of core sediments was 

done by analysis of their cesium-137 

content. Cesium-137 is a by-product 

of nuclear weapons testing. It first 

occurred in the atmosphere in about 

1952 and peaked during 1963–64. It 

adsorbs strongly to fine-grained 

sediments and therefore can be used to 

determine the time of deposition of 

sediments that have been exposed to 

atmospheric fallout. Cesium-137 first 

was detected in White Rock Lake core 

sediments at a depth of 60 to 63 centimeters (1952) and peaked at a depth of 

48 to 51 centimeters (1963). The depth 

of the interface between pre-reservoir 

and reservoir sediment, 136 centimeters, corresponds to the reservoir construction date (1912), and the top of 

the core corresponds to the sampling 

date (July 1994).

Trends in DDT and PCBs in the 

White Rock Lake core coincide with 

historical use of these compounds. Use 

of the insecticide DDT peaked in the 

early 1960s before being banned by 

the EPA in 1972. Annual sales of 

PCBs, which have a variety of industrial uses, peaked in 1970. The EPA 

placed a voluntary ban on their use in 

1973 and a complete ban in 1979. 

PCBs, DDT, and the DDT environmental degradation products DDE and 

DDD adsorb strongly to sediments and 

0 2 1

CESIUM-137, IN

PICOCURIES PER GRAM

0

140

20

40

60

80

100

120

DEPTH IN CORE, IN CENTIMETERS

Nondetections

1912

Reservoir built

1952

Cesium first detected

1963

Cesium peaks

1994

Core collected

Cores are collected by lowering 

the coring tool from the 15-foot 

aluminum A-frame on a custombuilt pontoon boat.

Removal of a 5-centimeter 

subsample of the sediment core 

for laboratory analysis.

Undeveloped land

MAJOR ISSUES AND FINDINGS

Determining Water-Quality Trends Using Sediment Cores, White Rock Lake, Dallas

Cesium-137, a by-product of 

nuclear testing, was used to date 

sections of reservoir sediment from 

the core.
U.S. Geological Survey Circular 1171 11

(Agency for Toxic Substances and Disease Registry, 1994). PAH and 

benzo(a)pyrene concentrations in sediments increased more than 20 times 

from pre-1950s to the early 1990s. 

Lead concentrations in sediments 

deposited from 1952 to 1976 correspond to an increase in urbanization of 

the drainage basin and increased use of 

leaded gasoline. The marked decrease 

in lead concentrations in sediments 

deposited after 1976 coincides with the 

change from leaded to unleaded gasoline. Median lead concentrations have 

remained constant since the mid-1980s 

at double the pre-1952 concentrations, 

reflecting urban and industrial sources 

other than gasoline. The trend in lead 

concentrations thus reflects the effects 

of the change to unleaded gasoline and 

increased urbanization on water quality in White Rock Creek.

Zinc is used in tires and in a number 

of industrial processes and is present in 

concentrations 66 percent larger in 

recently deposited sediments than in 

those deposited before 1952. 

are resistant to further chemical breakdown (Van Metre and Callender, 

1997).

Sediment cores from White Rock 

Lake record the effects of DDT, 

PCB, and chlordane use, and 

their subsequent bans, on water 

quality in White Rock Creek.

Unlike DDT and PCBs, chlordane 

was permitted for selected uses until 

the late 1980s. The primary uses in 

urban areas were the control of fire 

ants and termites. Chlordane concentrations in the White Rock Lake 

sediment core peaked about 1990 

(Van Metre and Callender, 1997). 

Temporal trends in chlordane indicate 

relatively recent urban use of chlordane.

Concentrations of benzo(a)pyrene, 

lead, and zinc were relatively small 

and constant in sediments deposited 

before 1952 but began to increase in 

sediments deposited after that date. 

Benzo(a)pyrene is a PAH and is in 

a class of carcinogenic compounds 

produced by the combustion of oil and 

gasoline. Elevated concentrations 

commonly are detected in urban areas. 

Benzo(a)pyrene is ranked eighth on 

the priority list of hazardous substances prepared by the Public Health 

Service in cooperation with EPA 

TOTAL DDT, IN

MICROGRAMS

PCBs, IN

MAJOR ISSUES AND FINDINGS

Determining Water-Quality Trends Using Sediment Cores, White Rock Lake, Dallas

DDT, PCB, and chlordane concentrations in sediments reflect historical 

use. Concentrations decreased after their use was banned. 

Increases in PAHs and heavy trace elements reflect the urbanization of the 

watershed. 

DDT PRODUCTION

AND USE, IN

METRIC TONS

PCB SALES, IN

METRIC TONS

0 10 5

CHLORDANE, IN 

MICROGRAMS

0 1,000

CHLORDANE USE,

IN METRIC TONS

0 30 10 20

1905

1995

1935

1965

0 100,000 0

0 30 10 20

0 40,000

Agricultural

use

Urban

use

DDT

use

DDT

production

PCB sales

NONDETECTIONS

YEAR

0 200 100

BENZO(A)PYRENE, IN

MICROGRAMS PER KILOGRAM

1905

1995

1935

1965

YEAR

0 100 50

URBAN LAND USE,

IN PERCENT

0 100 50

LEAD, IN

MICROGRAMS PER GRAM

50 150 100

ZINC, IN 

MICROGRAMS

Lead Zinc

Urban land use

Benzo(a)pyrene

PER KILOGRAM PER KILOGRAM

MICROGRAMS

PER KILOGRAM

PER GRAM
12 Water Quality in the Trinity River Basin, Texas, 1992–95

30o

31o

95o

32o

33 o

96

98

o

o

97 o

Dallas

Fort

 Worth

Corsicana

Denton

McKinney

Waxahachie

LAKE

 LIVINGSTON

TRINITY BAY 0 20 40 60 MILES

0 20 40 60 KILOMETERS

Urban land

Agricultural land

Rangeland

Forest land

Water

Wetland

EXPLANATION

Land use/land cover

Data-collection sites

Use of organochlorine pesticides

and PCBs was widespread beginning

in the 1940s until bans and use restrictions were placed on these compounds

in the 1970s and 1980s. Organochlorine compounds tend to be persistent in

the environment. Compounds such as

chlordane, DDT and its environmental

degradation products (DDD and

DDE), and PCBs are water insoluble,

are strongly associated with organic

carbon and fine sediment, and have

long half-lives. Organochlorine compounds were selected by NAWQA for

assessment because these compounds

are not metabolized rapidly and

because they have high bioaccumulation and bioconcentration factors

(Crawford and Luoma, 1993).

The distribution of organochlorine

compounds in streambed sediments

and biota is, in part, a reflection of the

historical applications of pesticides.

In the Trinity River Basin, pesticide

uses were concentrated in agricultural

areas, particularly the Blackland

Prairie (Ulery and Brown, 1995), and

in urban settings such as the DallasFort Worth metropolitan area.

Surficial streambed-sediment and

aquatic-biota samples were collected

at 16 sites in the Trinity River Basin

during late winter 1992 and early

spring 1993 (Moring, 1997). Sites on

Trinity River tributaries were chosen

to reflect general urban, agricultural,

rangeland, and forest land-use areas.

Aquatic-biota samples from tributary

sites were corbicula (asiatic clams).

Four Trinity River main-stem sites also

were selected. Because corbicula were

scarce at the main-stem sites, aquaticbiota samples at these sites were common carp and blue catfish.

Overall, more organochlorine

compounds were detected in

sediment than in biological

tissues; however, certain

organochlorines like chlordane

and PCBs were detected more

frequently in aquatic biota than

sediment.

Organic compounds contained

in chlordane (the sum of all chlordane

and nonachlor compounds and oxychlordane), an insecticide typically

used for the extermination of termites

and fire ants, were more commonly

detected in urban streams both in

tissues and in sediment. The DDT degradation products, DDD and DDE,

were more commonly detected in tissues at agricultural sites and more

commonly detected in sediment at

urban sites.

 At least one concentration of each

of nine organochlorine pesticides

exceeded the TNRCC screening levels

for these pesticides in streambed

sediments (Texas Natural Resource

Conservation Commission, 1996).

These screening levels are based on

the 85th-percentile concentration from

statewide historical data and are not

health or toxicity based. Each exceedance represents 1 of the 16 sites

sampled. Concentrations of the insecticide dieldrin more frequently exceeded

the TNRCC screening level than did

concentrations of any other organochlorines. Urban sites, more than agricultural or Trinity River main-stem

sites, had concentrations that exceeded

the screening levels for chlordane,

dieldrin, DDD, DDE, and DDT. Since

their use in agriculture was restricted

Land-use and streambed-sediment and aquatic-biota collection sites in the

Trinity River Basin, Texas.

MAJOR ISSUES AND FINDINGS

Organochlorines in Streambed Sediments and Aquatic Biota
U.S. Geological Survey Circular 1171 13

Aldrin Chlordane Dieldrin DDD DDE DDT Endrin Hepta- Heptachlor

ORGANOCHLORINE PESTICIDE

0

40

10

20

30

PERCENTAGE OF SITES

Main-stem sites

Urban sites

Agricultural sites

chlor epoxide

Percentage of sites with organochlorine concentrations in sediments that

exceed TNRCC screening levels reflects major land uses and location on

the main-stem Trinity River.

0 20 40 60 80 100

PERCENTAGE OF SITES WITH DETECTIONS

cis-Chlordane

trans-Chlordane

DCPA (Dacthal)

o,p'-DDD

p,p'-DDD

o,p'-DDE

p,p'-DDE

o,p'-DDT

p,p'-DDT

Dieldrin

Endrin

alpha-HCH

beta-HCH

delta-HCH

gamma-HCH (lindane)

Heptachlor

Heptachlor epoxide

Hexachlorobenzene

o,p'-Methoxychlor

p,p'-Methoxychlor

Mirex

cis-Nonachlor

trans-Nonachlor

Oxychlordane

PCBs, total

Pentachloroanisole

Toxaphene

ORGANOCHLORINE COMPOUND

P

P

P

P

P

P

P

P

P

P

P

O

O

O

P

P

P

P

P

P

P

P

P

P

PCB

P

P

0 20 40 60 80 100

PERCENTAGE OF SITES WITH DETECTIONS

Toxaphene

trans-Permethrin

cis-Permethrin

Pentachloroanisole

PCBs, total

Oxychlordane

trans-Nonachlor

cis-Nonachlor

Mirex

p,p'-Methoxychlor

o,p'-Methoxychlor

Isodrin

Hexachlorobenzene

Heptachlor epoxide

Heptachlor

gamma-HCH (lindane)

delta-HCH

beta-HCH

alpha-HCH

Endrin ketone

Endrin aldehyde

Endrin

Endosulfan sulfate

Endosulfan II

Endosulfan I

Dieldrin

p,p'-DDT

o,p'-DDT

p,p'-DDE

o,p'-DDE

p,p'-DDD

o,p'-DDD

DCPA (Dacthal)

trans-Chlordane

cis-Chlordane

Aldrin

ORGANOCHLORINE COMPOUND

P

P

P

P

P

P

P

P

P

P

P

P

P

P

O

O

P

P

P

P

P

P

O

O

O

O

P

P

P

P

P

P

P

P

P

PCB

IN BIOLOGICAL TISSUE IN STREAMBED SEDIMENT

AGRICULTURAL SITES

URBAN SITES

P

PCB

O

ORGANOCHLORINE

POLYCHLORINATED

OTHER ORGANOCHLORINE COMPOUND

PESTICIDE

BIPHENYL

AGRICULTURAL SITES

URBAN SITES

P

PCB

O

ORGANOCHLORINE

POLYCHLORINATED

OTHER ORGANOCHLORINE COMPOUND

PESTICIDE

BIPHENYL

in the 1970s, chlordane and dieldrin

were more extensively used in urban

settings. However, DDT commonly

was used for pest control in agricultural crops before its ban in 1972.

The larger concentrations of DDD,

DDE, and DDT in urban stream sediments of the Trinity River Basin could

be a result of extensive applications

of DDT in the 1950s and 1960s for

mosquito control. Aldrin, endrin,

heptachlor, and its environmental degradation product, heptachlor epoxide,

exceeded their respective TNRCC

screening levels only at agricultural

sites in the Trinity River Basin. Aldrin,

endrin, and heptachlor were used principally on crops such as corn, wheat,

and cotton.

Percentage of sites with detections of organochlorine compounds during 1992–93 differs according to land-use

practices.

MAJOR ISSUES AND FINDINGS

Organochlorines in Streambed Sediments and Aquatic Biota
14 Water Quality in the Trinity River Basin, Texas, 1992–95

o

o

30

31

95

33

96

98

97

o

o

32

o

o

o

o

0 20 40 60 MILES

0 20 40 60 KILOMETERS

Urban land

Agricultural land

Rangeland

Forest land

Water

Wetland

Land use/land cover

EXPLANATION

The USGS NAWQA Program 

includes an assessment of fish communities as one of the measures of water 

quality. Because fish communities are 

strongly influenced by their habitat, 

instream habitat conditions also are 

assessed. Combining the habitat data, 

the biological-community data, and the 

water-chemistry data provides opportunities for developing a comprehensive understanding of the aquatic life 

in a stream. Additionally, habitat analyses can assist in the identification of 

limiting physical or chemical factors 

critical to establishing or maintaining 

healthy biological communities in the 

streams.

Stream-habitat characteristics 

were related to fish-community 

degradation at three very different 

stream reaches in the Trinity River 

Basin. The reaches were chosen to 

reflect major differences in environmental settings, flow conditions, land 

uses, and stream biota. West Fork 

Trinity River is a relatively large 

stream in an urban area; Chambers 

Creek is a relatively large stream 

draining an intensively farmed area; 

and Menard Creek is considered a 

reference site (minimally affected by 

human activities) in the forested lands 

of southeast Texas.

West Fork Trinity River: The West Fork Trinity River reach is 

a few miles east of downtown Fort Worth and in the Central 

Oklahoma/Texas Plains Ecoregion (Omernik, 1987). This reach 

of the West Fork Trinity River has been channelized and leveed 

for flood control. The channel substrate is coarse, dominated by 

cobble and gravel from outcrops of limestone. Flows in the reach 

respond quickly to precipitation. However, upstream reservoirs 

tend to moderate low and high flows. 

Chambers Creek: The Chambers Creek reach 

is in the Blackland Prairie Ecoregion, which is 

the most intensively cultivated ecoregion in the 

basin. The major crops are cotton, sorghum, 

corn, and wheat. This region is characterized by 

heavy clay soils, little relief, and stream channels in the lower part of the basin that have been 

straightened and leveed for flood control. 

Streams in this ecoregion respond to heavy precipitation with rapid rises and falls in stage and 

large sediment loads. 

Menard Creek: The Menard Creek 

reach is in the Western Gulf Coastal 

Plain Ecoregion and in the National 

Park Service’s Big Thicket Preserve. 

Adjacent land use is dominated by 

silviculture; however, the riparian zone 

and, to some extent, the flood plain 

contain secondary vegetative growth 

that has not been disturbed for many 

years. The watershed is characterized 

by acidic sandy soils, little relief, and 

meandering channels. Floods are attenuated by flood-plain and riparian vegetation, and stream stages change 

gradually. 

Land use and land cover and location of selected survey reaches.

MAJOR ISSUES AND FINDINGS

Stream-Habitat Characteristics and Fish-Community Degradation
U.S. Geological Survey Circular 1171 15

West Fork Trinity River.

Chambers Creek.

Menard Creek.

Stream-habitat characteristics

Stream

Sinuosity

(meandering)

(dimensionless)

Channel

gradient

(feet/mile)

Bank height/

channel

width ratio

(dimensionless)

Density of

woody

vegetation

(dimensionless)

Variation

of monthly

flow index

(dimensionless)

West Fork Trinity River 2.2 6.7 0.75 3.4 39

Chambers Creek 1.1 1.1 .60 7.1 82

Menard Creek 1.9 10.6 .24 20.4 26

Stream-Habitat Characteristics

The physical and chemical characteristics of water combined with the

physical features of the stream channel

influence the presence or absence of

particular aquatic organisms in a

stream. Habitat affects species distributions at different spatial scales. For

example, fish-species distribution in a

stream reach is affected by climate on

a regional scale, channel gradient on a

local scale, and particle size of substrate at a very detailed scale. Other

important factors such as stream meandering, steepness of banks, riparian

vegetation, and variability of streamflow affect the habitat for fish in the

stream. Not only does stream habitat

have to be suitable for a particular species, it also has to support other biota

that are prey for the species.

The measured habitat characteristics

at the three stream reaches strongly

reflect the differences in habitat

among the reaches. The low bank

height/channel width ratio and high

density of woody vegetation in the

Menard Creek reach create a setting

where woody snags and logjams provide habitat for fish and an excellent

environment for biota that supply food

for fish. The low bank height/channel

width ratio indicates bank stability and

a lack of channel incision or cutting.

The high density of woody vegetation

moderates temperature, corresponds

to stable banks with little erosion, and

provides a source of organic material

to the stream.

In contrast, the low sinuosity

(meandering) and low channel gradient in the Chambers Creek reach could

limit the number and size of pools and

ripples that create a variety of habitats.

Variety of habitat provides more

opportunity for large numbers and

varieties of species to thrive. The high

MAJOR ISSUES AND FINDINGS

Stream-Habitat Characteristics and Fish-Community Degradation

variation in flow at Chambers Creek is

associated with more frequent floods,

in which organisms can be physically

harmed or swept away, and more frequent very low flows, in which the volume of water is limited and species are

subject to large and rapid changes in

the pH, dissolved oxygen, and temperature of the water.

The high bank height/channel width

ratio and low density of woody vegetation at the West Fork Trinity River site

can be attributed to stream channelization associated with urban flood control. Channelization has resulted in a

stream reach with little or no woody

riparian vegetation to contribute structure and habitat to the channel. Channelization also causes deeper channel

incision, which reduces the amount of

stream-margin habitat for aquatic

organisms.
16 Water Quality in the Trinity River Basin, Texas, 1992–95

Fish-Community Degradation

The evaluation of fish-community

degradation involved measures of

the percentage of fish species in a

reach that (1) are known to be tolerant

of severe environmental stresses,

(2) are known to be omnivorous,

(3) are not native to the stream, and

(4) have physical anomalies that

can be visually detected. The fishcommunity degradation index is computed from the frequency of nonnative,

tolerant, and omnivorous individuals

at a site and from the frequency of

external anomalies observed for each

species of fish.

The table shows that Menard

Creek, with an index of 6, is the

least degraded of the three reaches

discussed here. Menard Creek percentages are lowest in all the measured categories. The Menard Creek habitat and

quality of water support a robust fish

community. The two other reaches,

West Fork Trinity River and Chambers

Creek, each have an index of 12. These

two reaches are examples of highly

altered streams characterized by

incised and leveed channels, low density of vegetation in the riparian zones,

and unstable streamflow characteristics. These and other factors, possibly

including water-chemistry conditions,

have contributed to degraded fish

communities.

Robust fish communities with

many native species are most

likely to be present in streams

with a complex habitat and

natural, unaltered flow regimes.

In the West Fork reach, the percentage of fish with external anomalies is

the greatest among the three reaches.

The relatively large incidence of external anomalies could be related to the

quality of water and sediment originating in the urban area. In a separate

study of organic contamination in bed

sediment and tissue of aquatic biota,

Moring (1997) reports the occurrence

and degree of contamination in streambed sediments and tissues of aquatic

biota in the Trinity River Basin to be

much greater in urban streams than in

non-urban streams.

MAJOR ISSUES AND FINDINGS

Stream-Habitat Characteristics and Fish-Community Degradation

Fish-community degradation

Stream

Tolerant

species

(percent)

Omnivorous

species

(percent)

Nonnative

species

(percent)

External

anomalies

(percent)

Fishcommunity

degradation

index

West Fork Trinity River 50 30 3 2.8 12

Chambers Creek 53 26 0 2.2 12

Menard Creek 37 8 0 .9 6
U.S. Geological Survey Circular 1171 17

Fossil

Little

C

Bear

a l loway

Creek

Br.

Creek Creek

Cr.

Johnson

Combs

Rush Cr.

Creek

Creek

Bear Creek

Sycamore

Big On ion

T RINITY

Chambers

RIVER

Creek

Creek

Mill Creek

White Rock

97 96o o

33o

32 30’ o

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

Trinity River

FORT WORTH

DALLAS

downstream

from Dallas

West Fork 

White Rock Creek

Trinity River

PAHs are a group of organic compounds that are abundant in the 

environment and are toxic and often 

carcinogenic to organisms. Major 

sources of PAHs are oil spills and 

the incomplete combustion of fossil 

fuels.

PAHs are metabolized and 

excreted by most higher vertebrates, particularly fishes, 

which can make assessment 

of concentrations in tissues 

impossible. 

SPMD technology (Huckins and 

others, 1990) is new. An SPMD simulates the exposure to and passive 

uptake of highly lipid-soluble organic 

compounds by biological membranes. 

An SPMD typically consists of a long 

strip of low-density, polyethylene tubing filled with a thin film of a purified 

lipid such as triolein. The long strip of 

tubing and lipid film provide a large 

surface area/volume ratio that simulates a biological membrane such as a 

fish gill. The SPMDs used in this study 

concentrate PAHs above ambient concentrations in water and simulate biological exposure over a controlled 

period of deployment.

One site on each of three streams 

was selected for monitoring the occurrence of PAHs. The sites were chosen 

to reflect varied urban land uses and 

the influences of point and nonpoint 

sources of contaminants or PAHs. The 

monitoring was done using SPMDs 

during a 30-day period in late May and 

June 1994. 

Twenty-five different PAHs were 

detected in the SPMDs. Twenty-three 

were detected at the Trinity River 

downstream from Dallas and White 

Rock Creek sites, and 21 were detected 

at the West Fork Trinity River site. 

Seventy-three percent of the PAHs 

from the White Rock Creek and Trinity River downstream from Dallas sites 

and 67 percent from the West Fork 

Trinity River site were substituted 

PAHs—that is, PAHs with one or more 

substituted alkyl groups attached. 

The largest concentrations were of 

unsubstituted (parent) PAHs, such as 

fluoranthene, chrysene, pyrene, and 

phenanthrene; concentrations of these 

PAHs consistently were largest at the 

White Rock Creek site and smallest at 

the West Fork Trinity River site. 

The Public Health Service Agency 

for Toxic Substances and Disease 

Registry (ATSDR), in cooperation 

with the EPA, has developed a comprehensive ranking of 275 hazardous 

substances on the basis of their 

frequency of occurrence at hazardous 

waste sites, toxicity, and potential for 

human exposure (Agency for Toxic 

Substances and Disease Registry, 

1994). 

Nine of the PAHs detected by 

the SPMDs have been ranked 

as hazardous substances by the 

Public Health Service. Benzo(a)

pyrene and benzo(b)fluoranthene are ranked in the top 10.

The results of application of SPMDs 

indicate that aquatic organisms at three 

sites near Dallas are exposed to toxic 

PAH compounds. The SPMD is an 

effective tool to detect hydrophobic 

organics in water. The small concentrations of the compounds in the 

streams might not be detected by more 

traditional water-sampling techniques.

Location of SPMD deployment sites in the Dallas-Fort Worth metropolitan 

area.

MAJOR ISSUES AND FINDINGS

Use of a New Method, Semipermeable Membrane Device (SPMD), to Assess the Occurrence of

Water-Borne Polycyclic Aromatic Hydrocarbons (PAHs) in Streams
18 Water Quality in the Trinity River Basin, Texas, 1992–95

MAJOR ISSUES AND FINDINGS

Use of a New Method, Semipermeable Membrane Device (SPMD), to Assess the Occurrence of 

Water-Borne Polycyclic Aromatic Hydrocarbons (PAHs) in Streams

10 10,000 100 1,000

2-Ethylnaphthalene

2,6-Dimethylnaphthalene

1,6-Dimethylnaphthalene

Acenaphthylene

1,2-Dimethylnaphthalene

Acenaphthene

2,3,6-Trimethylnaphthalene

9H-Fluorene

1-Methyl-9H-Fluorene

Dibenzothiophene

Phenanthrene

Anthracene

Acridine

9H-Carbazol

2-Methylanthracene

4,5-Methylenephenanthrene

1-Methylphenanthrene

Anthraquinone

Pyrene

1-Methylpyrene

Benz(a)anthracene

Chrysene

Benzo(b)fluoranthene

Benzo(a)pyrene

Fluoranthene

EXPLANATION

Trinity River downstream from Dallas

West Fork Trinity River 

White Rock Creek

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

PAHs were frequently detected in SPMDs deployed in urban streams.

Hazardous PAHs detected in 

SPMDs

[ASTDR, Agency for Toxic Substances 

and Disease Registry]

PAH ASTDR

ranking

Benzo(a)pyrene 8

Benzo(b)fluoranthene 10

Benz(a)anthracene 35

Fluoranthene 100

Chrysene 110

Acenaphthene 140

Phenanthrene 188

Pyrene 201

Anthracene 235
U.S. Geological Survey Circular 1171 19

MAJOR ISSUES AND FINDINGS

Fish-Community Changes Reflect Water-Quality Improvements in the

Trinity River Downstream from Dallas

Fossil

Little

C

Bear

a l loway

Creek

Br.

Creek Creek

Cr.

Johnson

Combs

Rush Cr.

Creek

Creek

Bear Creek

Sycamore

Big On ion

T RINITY

Chambers

RIVER

Creek

Creek

Mill Creek

White Rock

97 96o o

33o

32 30’ o

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

Trinity River 

downstream 

from Dallas

DALLAS 

A timeline of change for the Trinity River downstream from Dallas.

1900 1920 1940 1960 1980 2000

“Mythological river of death”

Primary wastewatertreatment processes begin

Secondary wastewatertreatment processes beginFederal Clean Water Act, 1972

Upper Trinity River Basin Comprehensive

13 fishkills during 1970–85

Trinity River NAWQA started

Sewage Plan, 1971

In 1925, the Trinity River in the 

Dallas-Fort Worth area was characterized by the Texas Department of 

Health as a “mythological river of 

death.” With a rapid expansion of 

industry and population and only primary wastewater treatment beginning 

in the late 1920s and secondary treatment in the mid-1930s, water-quality 

conditions in the area were poor. They 

did not substantially improve until 

State and Federal pollution control 

laws, like the Federal Clean Water Act 

of 1972, stimulated efforts to address 

degraded water-quality conditions. 

The Upper Trinity River Basin Comprehensive Sewage Plan of 1971 

resulted in the construction of large, 

regional wastewater-treatment plants, 

elimination of many small, industrial 

and municipal wastewater-treatment 

plants, and the upgrading of existing 

wastewater-treatment plants. 

During 1970–85, 13 fishkills were 

documented in the Trinity River from a 

reach just downstream from Dallas to 

Lake Livingston in the lower part of 

the Trinity River Basin. The magnitude and frequency of the fishkills 

resulted in a depleted fish community, 

particularly in the reach of the Trinity 

River immediately downstream from 

Dallas. An estimated 1.04 million fish 

died in these 13 kills. Twelve of the 

During 1970–85, more than 

1 million fish were killed by 

water pollution in the Trinity 

River downstream from Dallas.

13 fishkills were associated with minor 

flooding on the Trinity River from 

rainfall in the Dallas-Fort Worth metropolitan area. According to the Texas 

Parks and Wildlife Department 

(TPWD), the probable cause of the 

kills was the resuspension of bottom 

sediments and associated organic 

material during floods that caused an 

increase in biochemical oxygen 

demand and a corresponding rapid 

drop in dissolved oxygen (Davis, 

1987). Ironically, improvements in 

water quality during the 1970s set the 

stage for the fishkills by allowing 

appreciable fish populations to live in 

this reach of the Trinity River.

How Has the Water Quality

Improved?

Dissolved oxygen, measured as 

milligrams of oxygen per liter of 

water, has increased from lows of near 

zero in the early 1970s to highs of 

more than 10 milligrams per liter in 

1996. Notable improvement in dissolved oxygen concentrations in the 

Trinity River downstream from Dallas 

began in the late 1970s and continued 

through the 1980s and into the 1990s. 

Dissolved oxygen was consistently 

recorded above the TNRCC (Texas 

Natural Resource Conservation 

Commission, 1996) dissolved oxygen 

criterion for the support of aquatic 

life (5.0 milligrams per liter) beginning 

in the late 1980s. The improvement 

in dissolved oxygen concentrations 

is attributable to improvements in 

wastewater-treatment practices and the 

corresponding reduction in the discharge of oxygen-demanding materials 

The Trinity River downstream from Dallas data-collection site.
20 Water Quality in the Trinity River Basin, Texas, 1992–95

Ammonia nitrogen

0 0 0

1970

Families identified, Families identified, Families identified,

Shad

Temperate bass 25%

25%

Minnows

25%

Suckers

25%

Sunfishes

27%

Shad

9.1%

Drums

9.1%

Minnows

18% Suckers

18%

Livebearers

9.1%

Sunfishes

28%

Silversides

4.0%

Temperate bass

4.0%

Drums

4.0%

Livebearers

4.0%

Gars

12%

Catfishes

12%

from wastewater-treatment plants and 

industry.

Advanced wastewater-treatment 

processes that include nitrification 

(conversion of ammonia nitrogen to 

nitrate) have been implemented at the 

large wastewater-treatment plants that 

discharge into the Trinity River in the 

Dallas-Fort Worth area. Ammonia 

consumes oxygen when it is converted 

to nitrate, and large concentrations of 

ammonia are toxic to fish and other 

aquatic organisms. Ammonia levels in 

the Trinity River downstream from 

Dallas exceeded the TNRCC criterion 

for dissolved ammonia in freshwater 

streams and reservoirs (1.0 milligram 

per liter) consistently until the late 

1980s. Since then, the nitrification process used in wastewater-treatment 

plants has reduced the amount of 

ammonia nitrogen that is discharged to 

the river.

How Has the Fish Community 

Changed as a Result?

The fish community in the Trinity 

River immediately downstream from 

Dallas was almost nonexistent in the 

early 1970s (Texas Parks and Wildlife 

Department, 1974). Only four species 

of fish were collected by the TPWD 

during 1972–74—smallmouth buffalo, gizzard shad, common carp, and 

yellow bass. Four of the six surveys 

yielded no fish from this reach of the 

river. Two of the species, gizzard shad 

and common carp, generally are classified as tolerant taxa and could be 

expected to tolerate the water-quality 

conditions in this reach in the 1970s. 

The TPWD collected 11 species of 

fish from this reach in 1987. Although 

the 1987 survey yielded more species 

than the 1972–74 surveys, the TPWD 

still considered the species richness 

low and attributed the condition to 

the fishes’ exposure to ammonia nitrogen and heavy trace elements introduced from the upstream wastewatertreatment plants (Davis, 1991).

1970 2000 1970 1975 1980 1985 1990 1995

SAMPLING YEAR

14

2

4

6

8

10

12

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

30

5

10

15

20

25

FISH SPECIES

Fish

Dissolved oxygen

DISSOLVED OXYGEN AND FISH SPECIES

TNRCC

1975 1980 1985 1990 1995 2000

SAMPLING YEAR

18

2

4

6

8

10

12

14

16

AMMONIA, IN MILLIGRAMS PER LITER AS NITROGEN

FISH SPECIES

Fish

AMMONIA NITROGEN AND FISH SPECIES

TNRCC

standard for

Fish species have increased as water quality improved in the Trinity River downstream from Dallas.

ammonia 

30

5

10

15

20

25

In slightly more than two decades, the fish community in a reach of the Trinity River downstream from Dallas has 

markedly improved. Improvement is most evident in the number of fish caught and the number of species, including 

those that are not tolerant of polluted water.

MAJOR ISSUES AND FINDINGS

Fish-Community Changes Reflect Water-Quality Improvements in the 

Trinity River Downstream from Dallas

Silversides

9.1%

Minnows

8.0%

Suckers

8.0%

Shad

8.0%

Darters

8.0%

nitrogen

standard for

dissolved

oxygen

0

1972–74 surveys 1987 survey 1993–95 surveys
U.S. Geological Survey Circular 1171 21

The USGS conducted fishcommunity surveys on the reach 

at Trinity River downstream from 

Dallas during 1993–95. The methods 

used by the USGS—seining, boat 

electrofishing, and gill netting—are 

identical to the methods used by the 

TPWD in 1987. A cumulative total 

of 25 species of fish were collected in 

this reach during the 3-year period. 

Fish surveys during 1993–95 

indicate that the Trinity River 

downstream from Dallas is 

typical of a large stream in the 

region.

Several game species were collected 

including largemouth bass, white 

crappie, and white bass. None of these 

game species were collected in the 

reach during the 1972–74 or 1987 surveys. Two darter species, bigscale 

logperch and slough darter, also were 

collected. The presence of these 

indigenous species suggests a return of 

this reach to a more natural condition. 

Other species characteristic of warmwater southeastern streams—alligator, 

spotted, and longnose gars and 

flathead, blue, and channel catfish—

frequently were collected during the 

USGS surveys of 1993–95. None of 

these gar or catfish species were 

reported in the reach downstream from 

Dallas in the 1972–74 or 1987 TPWD 

surveys. The change since 1972–74 is 

a likely consequence of improvements 

in water quality, particularly improvements in the quality of discharges from 

wastewater-treatment plants in the 

Dallas-Fort Worth area.

MAJOR ISSUES AND FINDINGS

Fish-Community Changes Reflect Water-Quality Improvements in the

Trinity River Downstream from Dallas

Catching fish with a backpack electrofishing device.

White bass being measured and examined.
22 Water Quality in the Trinity River Basin, Texas, 1992–95

o

31

95

33

96

98

97

32

o

o

o

o

o

o

o

30

Trinity

Woodbine

Gulf

 Coast

Dallas Fort

 Worth

Carrizo−

 Wilcox

0 20 40 60 MILES

0 20 40 60 KILOMETERS

The Trinity, Woodbine, CarrizoWilcox, and Gulf Coast aquifers (and

intervening confining units and minor

aquifers) in the Trinity River Basin

occur as a series of sloping layers that

begin at land surface and become more

deeply buried toward the gulf coast.

The aquifer outcrops delineated on a

map of the basin appear as generally

coast-parallel bands. The Trinity,

Carrizo-Wilcox, and Gulf Coast are

major aquifers, on the basis of the

quantity of water that can be supplied

to wells. The Woodbine is a minor

aquifer, but it is important to the study

of water-quality conditions in the basin

because it underlies the urban DallasFort Worth metropolitan area.

Ground-water samples were collected from wells in the outcrops of the

four aquifers from August 1993 to

August 1994 and analyzed for nutrients, major inorganic compounds,

trace elements, pesticides, organic carbon, and VOCs.

Trinity Aquifer

On the basis of samples from 24

wells less than 200 feet deep in the

Trinity aquifer outcrop, ground water

in the uppermost zone of the aquifer

did not exceed 1996 EPA primary

drinking-water standards (MCLs) for

the analyzed constituents but has

higher than acceptable dissolved solids

concentration (salinity) in water from

one-half of the wells. (Salinity has an

EPA secondary MCL [SMCL]. An

SMCL is based on factors such as taste

and odor that affect the potability of

water but do not pose a health concern.) The salinity could occur naturally or it could be from brines

associated with oil and gas production.

Pesticides were detected in Trinity

aquifer wells. The insecticide diazinon

was detected in nearly one-half the

samples, and the DDT derivative

p,p'-DDE was detected in samples

from four wells. None of the concentrations exceeded the 1996 EPA lifetime HA for diazinon. The herbicide

atrazine or its metabolite deethylatrazine was detected in two wells. Benzene, a component of gasoline, was

detected in one well at a concentration

Trace concentrations of organic

compounds, such as pesticides

and solvents, show the vulnerability of these aquifers to

contamination.

less than the 1996 MCL. The pesticide

and VOC detections show the vulnerability of shallow ground water in the

Trinity aquifer to contamination. The

pathway of such compounds into shallow ground water could be through

natural recharge or recharge along the

outside of well casings that are not

completely sealed at the land surface.

Woodbine Aquifer

Analyses of samples from the

outcrop of the Woodbine aquifer

could indicate shallow ground-water

contamination associated with urban

land use. Twenty-eight specially constructed monitoring wells less than

50 feet deep were used to sample water

in the uppermost aquifer zone. Ten

Diagrammatic section showing aquifer configuration in the

Trinity River Basin.

Ground-water sampling sites in outcrops of aquifers in the Trinity River

Basin.

Gulf Coast

Carrizo-Wilcox Trinity

Land surface

Gulf of

Confining units

Confining units

Confining units and

Confining units

Woodbine

Northwest Southeast

Mexico

minor aquifers

MAJOR ISSUES AND FINDINGS

Quality of Ground Water in Aquifer Outcrops

aquifer aquifer aquifer

aquifer
U.S. Geological Survey Circular 1171 23

domestic wells were used to sample

water in the deeper aquifer zone (50

to 150 feet deep). The water in the

Woodbine aquifer (Reutter, 1996) can

be naturally saline and high in iron

and sulfate—71 percent of the 38

Woodbine water samples exceeded the

EPA SMCL for dissolved solids, and

61 percent of the samples exceeded the

SMCLs for both iron and sulfate. Five

of the 38 samples exceeded the EPA

MCL for nitrate.

Herbicides were detected in 11 of

the 38 wells; p,p'-DDE was detected in

samples from two wells. None of the

sample concentrations of pesticides for

which EPA has established MCLs or

HAs exceeded those standards.

Samples from seven wells have

detectable concentrations of VOCs.

The most commonly detected VOC

was MTBE (methyl tert-butyl ether), a

gasoline additive, in the urban part of

the Woodbine aquifer. The sample

from one shallow monitoring well has

concentrations of several VOCs

greater than 10 micrograms per liter.

Tetrachloroethylene and trichloroethylene, solvents for which the 1996

MCL is 5 micrograms per liter, were

detected at concentrations of 6,000 and

230 micrograms per liter, respectively.

Chloroethylene (vinyl chloride), a

compound used as a solvent and as

a refrigerant, for which the 1996 MCL

is 2 micrograms per liter, was detected

at a concentration of 32 micrograms

per liter; and cis-1,2-dichloroethylene,

a solvent for which the 1996 MCL is

70 micrograms per liter, was detected

at a concentration of 82 micrograms

per liter.

Carrizo-Wilcox Aquifer

In the outcrop of the CarrizoWilcox aquifer, 23 wells less than

300 feet deep were sampled. Samples

from seven wells had dissolved solids

or iron concentrations that exceeded

EPA SMCLs. As in the Trinity aquifer,

higher than acceptable salinity could

occur naturally or be related to historical brine disposal from oil and gas production; the higher than acceptable

iron concentrations occur naturally.

Herbicides were detected in samples

from two wells and insecticides in

samples from five wells. Trichlorofluoromethane, a VOC used as solvent,

was detected in the sample from one

well. None of the pesticides or VOCs

for which EPA has established MCLs

or HAs had concentrations that

exceeded those standards.

Gulf Coast Aquifer

In the outcrop of the Gulf Coast

aquifer, 24 wells less than 250 feet

deep were sampled. Samples from

six wells had dissolved solids concentrations that exceeded the EPA SMCL.

The excess salinity probably is related

to historical brine disposal from oil

and gas production. Herbicides were

detected in samples from three wells

and insecticides in samples from two

wells. Trichloromethane, a VOC used

as a refrigerant or a solvent, was

detected in the sample from one well.

As in the Carrizo-Wilcox aquifer, none

of the pesticides or VOCs for which

the EPA has established MCLs or HAs

had concentrations that exceeded those

standards.

Water samples from wells in the

outcrops of major aquifers did

not exceed EPA drinking-water

MCLs or SMCLs for trace elements, except for iron at some

locations.

A comparison of pesticides detected

in shallow ground water in the outcrops with those detected in streams in

the outcrops (excluding the main-stem

Trinity River sites) indicates that

stream water generally contains a

greater number of pesticides at higher

concentrations than shallow ground

water. A larger pesticide presence in

streams than in ground water implies

that pesticides applied to the land are

more readily transported into the

streams by runoff than into the shallow

ground water by natural recharge or

recharge associated with well construction (Brown, 1995).

Summary of ground-water-quality data

Trinity

aquifer

(24 samples)

Woodbine

aquifer

(38 samples)

CarrizoWilcox

aquifer

(23 samples)

Gulf

Coast

aquifer

(24 samples)

Percentage of samples in which concentrations exceeded

1996 EPA drinking-water standards

Major constituents (1996 EPA SMCL in milligrams per liter)

Chloride (250) 12 18 0 4

Fluoride (2.0) 0 5 0 0

Sulfate (250) 4 61 0 0

Dissolved solids (500) 50 71 17 25

Nutrients (1996 EPA MCL in milligrams per liter)

Nitrate nitrogen (10) 0 13 0 0

Trace elements (1996 EPA MCL or SMCL [iron, zinc] in milligrams per liter)

Arsenic (0.05) 0 0 0 0

Chromium (0.1) 0 0 0 0

Iron (0.3) 12 61 17 17

Lead (0.015) 0 0 0 0

Nickel (0.1) 0 10 0 0

Selenium (0.05) 0 0 0 0

Zinc (5) 0 0 0 0

Percentage of samples in which pesticides and

volatile organic compounds were detected

Pesticides

Herbicides 8 29 9 12

Insecticides 54 5 22 8

Volatile organic compounds 4 18 4 4

MAJOR ISSUES AND FINDINGS

Quality of Ground Water in Aquifer Outcrops
24 Water Quality in the Trinity River Basin, Texas, 1992–95

FORT WORTH DALLAS

FORT WORTH DALLAS

FORT WORTH DALLAS

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Comparison of Trinity River Basin Study Unit Surface-Water Results

with Nationwide NAWQA Findings

The median nutrient concentration 

at a Trinity River site downstream 

from large wastewater discharges 

is in the highest category of all 

NAWQA stream sites, and one 

sample from the site exceeded 

the EPA MCL. Otherwise, all the 

sites except one in a rural area are 

less than the national median. As 

expected, the median concentrations at reference sites are in the 

lowest quartile of all NAWQA 

Study Units across the Nation.

Concentrations of organochlorine pesticides and PCBs in bed 

sediments and biota (clam and fish tissue) at two sites on the 

Trinity River in the Dallas-Fort Worth area are in the highest 

category of all NAWQA Study Units. Sites in watersheds with 

little development are in the lowest category.

Seven major water-quality characteristics were evaluated for stream sites in each NAWQA 

Study Unit. Summary scores for each characteristic were computed for all sites that have 

adequate data. Scores for each site in the Trinity River Basin were compared with scores for 

all sites sampled in the 20 NAWQA Study Units during 1992–95. Results are summarized by 

percentiles; higher percentiles generally indicate poorer quality compared with other 

NAWQA sites. Water-quality conditions at each site also are compared to established criteria 

for protection of aquatic life. Applicable criteria are limited to nutrients and pesticides in 

water and semivolatile organic compounds (SVOCs), organochlorine pesticides, and PCBs in 

sediment. (Methods used to compute rankings and evaluate aquatic-life criteria are described 

in Gilliom and others, in press.)

Median pesticide concentrations are 

greater than the national NAWQA 

median at all three sites for which there 

were adequate data to make the comparison. Sites with urban watersheds 

are in the highest category. A site with 

croplands in the watershed is in the second highest category. Exceedances of 

drinking-water standards are most often 

attributed to diazinon in urban streams 

and atrazine in agricultural streams. 

EXPLANATION

Ranking relative to national conditions—

Darker colored circles generally indicate poorer 

quality. Bold outline of circle indicates one or 

more drinking-water standards or aquatic-life 

criteria are exceeded

Greater than the 75th percentile

(among the highest 25 percent nationally)

Between the median and the 75th percentile

Between the 25th percentile and the median

Less than the 25th percentile

(among the lowest 25 percent nationally)

NUTRIENTS in water

PESTICIDES in water

ORGANOCHLORINES

in streambed sediments and biota
U.S. Geological Survey Circular 1171 25

FORT WORTH DALLAS

FORT WORTH DALLAS

FORT WORTH DALLAS

FORT WORTH DALLAS

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Comparison of Trinity River Basin Study Unit Surface-Water Results

with Nationwide NAWQA Findings

SEMIVOLATILE ORGANIC COMPOUNDS 

in streambed sediments

Concentrations of trace elements in sediments at a site on the West 

Fork Trinity River near downtown Fort Worth are in the highest 

category of all NAWQA sites. The next-highest concentrations are 

in the Trinity River downstream from Dallas. All other sites have 

concentrations less than the national median.

STREAM HABITAT

Habitat degradation is greater than the 

national median at one site on the Trinity 

River. Leveeing of the streams and bank 

erosion are the most influential factors 

for this degraded habitat. All the sites on 

relatively small rural streams are in the 

least-degraded category.

A fish-community index based 

on the number of diseased, 

pollution-tolerant, omnivorous, 

and nonnative fish is greater 

than the national NAWQA 

median at 4 of the 10 sites evaluated. The two most degraded 

sites are on the Trinity River; 

one is downstream from DallasFort Worth, and the other is near 

the mouth of the Trinity River.

TRACE ELEMENTS 

in streambed sediments

Concentrations of SVOCs 

(primarily PAHs) in sediments 

at two sites on the Trinity River 

in the Dallas-Fort Worth area 

are in the highest category of 

all NAWQA sites. However, 

no compounds exceeded an 

aquatic-life criterion. Surprisingly, SVOCs at the reference 

site on Menard Creek are above 

the national median. 

FISH COMMUNITIES

CONCLUSIONS

Nutrient concentrations in most streams in 

the Trinity River Basin were below national 

median concentrations for NAWQA Study 

Units. Two exceptions are the Trinity River 

downstream from Dallas and a rural site. 

Pesticide concentrations at two urban sites 

were in the highest category, and concentrations at an agricultural site were in the 

second highest category, all above the 

national NAWQA median.

In general, concentrations of trace elements, PCBs, organochlorine pesticides, 

and PAHs in streambed sediments and 

aquatic biota exceeded national medians 

(highest two categories) or 75th percentiles 

(highest category) at urban sites and were 

below national medians at more rural sites.

One urban site, one agricultural site, and 

two sites on the Trinity River downstream 

from Dallas had fish-community indices 

greater than the national median. One of 

those sites also had habitat degradation 

greater than the national median. 
26 Water Quality in the Trinity River Basin, Texas, 1992–95

EXPLANATION

Drinking-water aquifers

Trinity

Carrizo-Wilcox

Gulf Coast

Shallow ground-water area

Woodbine aquifer (urban area)

FORT WORTH

DALLAS

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Comparison of Trinity River Basin Study Unit Ground-Water Results

with Nationwide NAWQA Findings

Four major water-quality characteristics were evaluated for ground-water studies in each 

NAWQA Study Unit. Ground-water resources were divided into two categories: 

(1) drinking-water aquifers, and (2) shallow ground water underlying agricultural or urban 

areas. Summary scores were computed for each characteristic for all aquifers and shallow 

ground-water areas that have adequate data. Scores for each aquifer and shallow groundwater area in the Trinity River Basin were compared with scores for all aquifers and 

shallow ground-water areas sampled in the 20 NAWQA Study Units during 1992–95. 

Results are summarized by percentiles; higher percentiles generally indicate poorer quality 

compared with other NAWQA ground-water studies. Water-quality conditions for each 

drinking-water aquifer also are compared to established drinking-water standards and 

criteria for protection of human health. (Methods used to compute rankings and evaluate 

standards and criteria are described in Gilliom and others, in press.)

The median nitrate nitrogen concentrations are 

less than the median of comparable aquifers in 

NAWQA Study Units nationwide except for the 

Trinity aquifer, which has a median only slightly 

greater than the national median. The only sample 

that exceeded the drinking-water standard was 

from a shallow monitoring well in the Woodbine 

aquifer in an urban area. This part of the aquifer is 

not used for drinking-water supply.

Ranking relative to national conditions—

Darker colored circles generally indicate poorer 

quality. Bold outline of circle indicates one or 

more drinking-water standards or criteria are 

exceeded

Greater than the 75th percentile

(among the highest 25 percent nationally)

Between the median and the 75th percentile

Between the 25th percentile and the median

Less than the 25th percentile

(among the lowest 25 percent nationally)

NITRATE
U.S. Geological Survey Circular 1171 27

FORT WORTH

DALLAS

FORT WORTH

DALLAS

FORT WORTH

DALLAS

CONCLUSIONS

No samples of ground water in aquifers used 

for drinking water exceeded EPA MCLs and 

HAs for nutrients, pesticides, and VOCs; however, dissolved solids concentrations commonly exceed the SMCL. Dissolved solids in 

all four aquifers, nitrate in the Trinity aquifer, 

and VOCs in the Woodbine aquifer were at 

greater concentrations or were detected more 

frequently than national medians for comparable aquifers. The avenues of contamination 

could be natural recharge or recharge along 

the outside of well casings that are not completely sealed at the surface. 

The percentages of pesticide detections in the 

Trinity, Carrizo-Wilcox, and Gulf Coast aquifers 

are less than the median of all NAWQA groundwater surveys nationwide. Although pesticides 

were detected in 29 percent of the wells sampled 

in the Woodbine aquifer, that percentage is in the 

lowest category relative to nationwide results 

for shallow ground water underlying urban and 

agricultural areas.

One or more VOCs were detected in less than 5 percent of the wells in 

the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers. The percentage 

of detections in all three aquifers is less than the median percentage of 

detections for all comparable aquifers in NAWQA Study Units nationwide. These results are in contrast to a detection rate of 18 percent for 

the network of shallow wells in the Woodbine aquifer in an urban area. 

This detection rate is in the worst category for all comparable aquifers. 

Only one well in the urban area had a VOC concentration that exceeded 

the drinking-water standards.

The median dissolved solids concentration of the 

Carrizo-Wilcox aquifer was slightly less than the 

median concentration of comparable aquifers in 

NAWQA Study Units nationwide. However, the 

medians of the Gulf Coast, Trinity, and Woodbine 

aquifers were greater than the national median. The 

percentage of wells with samples that exceeded the 

SMCL ranges from 17 percent in the Carrizo-Wilcox 

aquifer to 71 percent in the Woodbine aquifer.

DISSOLVED SOLIDS

VOLATILE ORGANIC COMPOUNDS

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Comparison of Trinity River Basin Study Unit Ground-Water Results

with Nationwide NAWQA Findings

PESTICIDES
28 Water Quality in the Trinity River Basin, Texas, 1992–95

95

96

98

97

31

33

o

o 30

o

o

32

o

o

o

o

95

96

98

97

31

33

o

o 30

o

o

32

o

o

o

o

95

96

98

97

31

33

o

o 30

o

o

32

o

o

o

o

95

96

98

97

31

33

o

o 30

o

o

32

o

o

o

o

0 40 80 120 MILES

0 40 80 120 KILOMETERS

Location of data-collection sites.

Chemistry of Surface Water

and Bed Sediment

Aquatic Biology

Chemistry of Ground Water Special Studies

Bed-sediment site

Basic Fixed site

Intensive Fixed site

Basinwide synoptic site

Aquatic-biota site

Basic Fixed site

Aquifer outcrop

Urban land

Basinwide survey site

Land-use study site

Semipermeable

 membrane device site

Urban point- and

 nonpoint-source site

Richland-Chambers

 watershed site

Coastal Prairie site

Reservoir sediment core site

EXPLANATION EXPLANATION

EXPLANATION EXPLANATION

STUDY DESIGN AND DATA COLLECTION

IN THE TRINITY RIVER BASIN

Intensive Fixed site
U.S. Geological Survey Circular 1171 29

Summary of data collection in the Trinity River Basin Study Unit, 1992–95 

Study component Objectives Brief description and

water-quality measures

Number

of sites

Frequency

during 1993–95

Chemistry of surface water and bed sediment

Water chemistry—

Basic and Intensive 

Fixed sites

Describe concentrations and loads of 

water-quality constituents at 

selected stream sites. 

Sample at or near streamflow-gaging stations. 

Basic sites are sampled for major ions, organic 

carbon, suspended sediment, and nutrients. 

Intensive sites are a subset of the Basic sites 

and include sampling for pesticides.

8 Basic;

2 

Intensive

~14 per year 

at Basic; 

~25 per year 

at Intensive

Water chemistry—

Basinwide synoptic 

studies

Describe short-term presence and 

distribution of contamination over 

the entire basin and how well the 

Basic and Intensive sites represent 

the Trinity River Basin.

Sample streams during winter base-flow and 

spring runoff conditions for major ions, organic 

carbon, suspended sediment, nutrients, and 

pesticides.

43 2

Bed-sediment 

contamination—

Presence and distribution survey

Determine presence of potentially 

toxic compounds attached to sediment deposited on streambeds.

Sample depositional zones of streams for 

trace elements and hydrophobic organic 

compounds.

16 1

Aquatic biology

Ecological assessments—Basic and 

Intensive Fixed 

sites

Assess in detail biological communities and habitat in streams representing primary ecological and 

land-use regions.

Sample and quantify fish, macroinvertebrates, 

and algae in streams at stream-chemistry sites 

and describe stream habitat. Intensive sites are 

a subset of the Basic sites where there is replicate sampling over three stream reaches.

7 Basic;

5 

Intensive

1 at Basic; 1 per 

year and 

multiple 

reaches at 

Intensive

Aquatic-biota contamination—Presence 

and distribution survey

Determine presence of contaminants 

that can accumulate in tissues of 

aquatic biota.

Collect clam and fish species that are present in 

most streams of the Trinity River Basin. Sample composites of clams or fish for organic 

compounds and trace elements.

16 1 

Chemistry of ground water

Water chemistry—

Basinwide survey

Describe the overall water quality 

and natural chemical patterns of 

water in aquifers.

Sample existing supply wells in the outcrop of 

three major aquifers for major ions, nutrients, 

pesticides, trace elements, and VOCs.

71 1

Water chemistry—

Land-use study

Determine the effects of urban land 

use on the quality of shallow 

ground water.

Sample shallow monitoring and supply wells 

where there is residential and commercial 

development for major ions, nutrients, pesticides, trace elements, and VOCs.

38 1

Water chemistry—

Flow-path study

Describe changes in water quality in 

an urban area along flow paths 

from a shallow aquifer to small 

streams.

Sample clusters of wells in land-use effects 

survey and a nearby small stream for major 

ions, nutrients, pesticides, and age-dating 

constituents.

3 1

Special studies

Water chemistry—

Use of SPMDs

Determine presence of organic contaminants in water and sediment 

by deploying caged clams and 

SPMDs and comparing the results 

of the two approaches.

Deploy caged native clams and SPMDs side by 

side for 1 month and determine the presence 

and concentration of PCBs and PAHs in each 

medium.

3 1

Water chemistry—

Comparison of 

urban point- and 

nonpoint-source 

contaminants

Compare the presence and distribution of nutrients and pesticides in 

small urban streams and in effluent from regional wastewatertreatment plants in the same service area.

Sample streams and effluent from regional 

wastewater-treatment plants during late winter 

to summer for major ions, nutrients, and 

pesticides.

6 streams: 

3 wastewatertreatment 

plants

6

Water chemistry—

Richland-Chambers

watershed

Describe presence and distribution of 

agricultural chemicals in streams 

and reservoirs in a major cropproducing area.

Sample streams from late winter to late summer 

for major ions, nutrients, pesticides, and suspended sediment. Reservoirs sampled at beginning or end of study, or both.

5 streams; 

11 reservoirs

7 at streams; 

1 or 2 at 

reservoirs

Water chemistry— 

Coastal Prairie 

agricultural area

Describe presence and distribution of 

agricultural chemicals in streams 

in a major crop-producing area 

with irrigation.

Sample streams for 1 year for major inorganic 

ions, nutrients, pesticides, and suspended sediment. Sampling much more frequent during 

late spring and summer than fall and winter.

3 ~25

Water-quality 

trends—Reservoir 

sediment cores

Determine temporal trends of trace 

elements, organochlorine compounds, and PAHs in streams.

Collect sediment cores at Lake Livingston and 

White Rock Lake. Horizontal slices analyzed 

for age-dating elements, trace elements, 

organochlorine compounds, and PAHs.

2 reservoirs 1

STUDY DESIGN AND DATA COLLECTION

IN THE TRINITY RIVER BASIN
30 Water Quality in the Trinity River Basin, Texas, 1992–95

Herbicide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

The following tables summarize data collected for NAWQA studies from 1992–95 by showing results for the Trinity River Basin

Study Unit compared to the NAWQA national range for each compound detected. The data were collected at a wide variety of places and

times. In order to represent the wide concentration ranges observed among Study Units, logarithmic scales are used to emphasize the

general magnitude of concentrations (such as 10, 100, or 1,000), rather than the precise number. The complete dataset used to construct

these tables is available upon request.

Concentrations of herbicides, insecticides, volatile organic compounds, and nutrients detected in ground and surface waters of the Trinity

River Basin Study Unit

[μg/L, micrograms per liter; %, percent; <, less than; --, not measured; mg/L, milligrams per liter; trade names might vary]

EXPLANATION

Range of surface-water detections in all 20 Study Units

Detection in the Trinity River Basin Study Unit

Range of ground-water detections in all 20 Study Units

Drinking-water standard or guideline a

Freshwater-chronic criterion for the protection of aquatic life a

Herbicide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

Dicamba (Banvel,

Mediben, dianat)

1%

0%

Dichlorprop (2,4-DP,

Seritox 50, Kildip)

3%

0%

Dinoseb (DNBP, DN

289, Premerge, Aretit)

1%

0%

Diuron (Karmex,

Direx, DCMU)

7%

0%

EPTC (Eptam) 1%

0%

Fluometuron (FloMet, Cotoran)

17%

0%

Linuron (Lorox,

Linex, Sarclex)

1%

0%

MCPA (Agritox,

Agroxone)

3%

0%

MCPB (Can-Trol,

Thistrol, Tropotox)

<1%

0%

Metolachlor (Dual,

Pennant)

69%

0%

Metribuzin (Lexone,

Sencor)

10%

2%

Molinate (Ordram) 18%

0%

Napropamide

(Devrinol)

<1%

0%

Neburon (Neburex,

Noruben, Kloben)

<1%

0%

Oryzalin (Surflan,

Dirimal, Ryzelan)

3%

0%

Pendimethalin

(Prowl, Stomp)

10%

0%

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS

Acetochlor 7%

0%

Acifluorfen (Blazer,

Tackle 2S)

1%

0%

Alachlor (Lasso) 15%

0%

2,6-Diethylaniline

(Alachlor metabolite)

<1%

0%

Atrazine (AAtrex,

Gesaprim)

88%

3%

Deethylatrazinec

(Atrazine metabolite)

71%

4%

Bentazon (Basagran,

bentazone)

4%

1%

Bromacil (Hyvar X,

Urox B, Bromax)

<1%

1%

Bromoxynil (Buctril,

Brominal, Torch)

<1%

0%

Butylate (Sutan,

Genate Plus, butilate)

<1%

0%

Chloramben

(Amiben, Vegiben)

<1%

0%

Clopyralid (Stinger,

Lontrel, Dowco 290)

1%

0%

Cyanazine (Bladex,

Fortrol)

5%

0%

2,4-D (2,4-PA) 17%

2%

DCPA (Dacthal,

chlorthal-dimethyl)

<1%

<1%

Dacthal, mono-acid

(Dacthal metabolite)

<1%

0%
U.S. Geological Survey Circular 1171 31

Picloram (Tordon,

Amdon)

1%

0%

Prometon (Gesagram, prometone)

50%

4%

Pronamide (Kerb,

propyzamid)

2%

0%

Propachlor (Ramrod,

propachlore)

1%

0%

Propanil (Stampede,

Surcopur)

5%

0%

Propham (Chem-Hoe,

IPC, prophame)

1%

0%

Simazine (Aquazine,

Princep, Gesatop)

63%

<1%

Tebuthiuron (Spike,

Perflan)

42%

2%

Thiobencarb (Bolero,

Saturn, benthiocarb)

8%

0%

Triclopyr (Garlon,

Grazon, Crossbow)

1%

0%

Trifluralin (Treflan,

Trinin, Elancolan)

3%

0%

Insecticide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

Aldicarbc (Temik) <1%

0%

Aldicarb sulfonec

(Standak)

<1%

0%

Aldicarb sulfoxidec

(Aldicarb metabolite)

<1%

0%

Azinphos-methylc

(Guthion)

1%

0%

Carbarylc (Sevin,

Savit)

24%

0%

Carbofuranc

(Furadan, Curaterr)

7%

0%

Chlorpyrifos (Dursban, Lorsban)

21%

<1%

p,p’-DDE (p,p’-DDT

metabolite)

<1%

<1%

Diazinon 47%

10%

Dieldrin (Panoram

D-31, Octalox)

2%

1%

0.001 0.01 0.1 1 10 100 1,000

Disulfotonc (Disyston, Dithiosystox)

<1%

0%

Fonofos (Dyfonate) 1%

0%

alpha-HCH (alphaBHC, alpha-lindane)

<1%

0%

gamma-HCH 5%

0%

3-Hydroxycarbofuran <1%

0%

Malathion (maldison,

malathon, Cythion)

10%

0%

Methiocarb (Grandslam, Mesurol,Draza)

<1%

0%

Methomyl (Lannate,

Nudrin)

2%

0%

Methyl parathion

(Penncap-M)

1%

0%

cis-Permethrinc

(Ambush, Pounce)

<1%

0%

Volatile organic

compound

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

1,1-Dichloroethene

(Vinylidene chloride)

--

1%

1,2,4-Trimethylbenzene (Pseudocumene)

--

1%

Benzene --

1%

Chlorobenzene

(Monochlorobenzene)

--

1%

Chloroethene (Vinyl

Chloride)

--

1%

Dimethylbenzenes

(Xylenes (total))

--

1%

total Trihalomethanes --

3%

Trichloroethene

(TCE)

--

3%

Trichlorofluoromethane (CFC 11)

--

1%

cis-1,2-Dichloroethene)

--

1%

trans-1,2-Dichloroethene)

--

1%

0.01 0.1 1 10 100 1,000

Insecticide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

Herbicide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
32 Water Quality in the Trinity River Basin, Texas, 1992–95

Herbicides

2,4,5-T

2,4,5-TP (Silvex, Fenoprop)

2,4-DB (Butyrac, Butoxone, Embutox Plus, Embutone)

Benfluralin (Balan, Benefin, Bonalan, Benefex)

Ethalfluralin (Sonalan, Curbit)

Fenuron (Fenulon, Fenidim)

Norflurazon (Evital, Predict, Solicam, Zorial)

Pebulate (Tillam, PEBC)

Terbacil (Sinbar)

Triallate (Far-Go, Avadex

BW, Tri-allate)

Insecticides

Ethoprop (Mocap, Ethoprophos)

Oxamyl (Vydate L, Pratt)

Parathion (Roethyl-P, Alkron, Panthion, Phoskil)

Phorate (Thimet, Granutox, Geomet, Rampart)

Propargite (Comite, Omite,

Ornamite)

Propoxur (Baygon, Blattanex, Unden, Proprotox)

Terbufos (Contraven,

Counter, Pilarfox)

Volatile organic

compounds

1,1,1,2-Tetrachloroethane

(1,1,1,2-TeCA)

1,1,1-Trichloroethane

(Methylchloroform)

1,1,2,2-Tetrachloroethane

1,1,2-Trichloro-1,2,2-trifluoroethane (Freon 113, CFC

113)

1,1,2-Trichloroethane

(Vinyl trichloride)

1,1-Dichloroethane (Ethylidene dichloride)

1,1-Dichloropropene

1,2,3-Trichlorobenzene

(1,2,3-TCB)

1,2,3-Trichloropropane

(Allyl trichloride)

1,2,4-Trichlorobenzene

1,2-Dibromo-3-chloropropane (DBCP, Nemagon)

1,2-Dibromoethane (EDB,

Ethylene dibromide)

1,2-Dichlorobenzene (oDichlorobenzene, 1,2-

DCB)

1,2-Dichloroethane (Ethylene dichloride)

1,2-Dichloropropane (Propylene dichloride)

1,3,5-Trimethylbenzene

(Mesitylene)

1,3-Dichlorobenzene (mDichlorobenzene)

1,3-Dichloropropane (Trimethylene dichloride)

1,4-Dichlorobenzene (pDichlorobenzene, 1,4-

DCB)

1-Chloro-2-methylbenzene

(o-Chlorotoluene)

1-Chloro-4-methylbenzene

(p-Chlorotoluene)

2,2-Dichloropropane

Bromobenzene (Phenyl

bromide)

Bromochloromethane

(Methylene chlorobromide)

Bromomethane (Methyl

bromide)

Chloroethane (Ethyl

chloride)

Chloromethane (Methyl

chloride)

Dibromomethane (Methylene dibromide)

Dichlorodifluoromethane

(Freon 12, CFC 12)

Dichloromethane (Methylene chloride)

Ethenylbenzene (Styrene)

Ethylbenzene (Phenylethane)

Hexachlorobutadiene

Isopropylbenzene

(Cumene)

Methylbenzene (Toluene)

Naphthalene

Tetrachloromethane (Carbon tetrachloride)

cis-1,3-Dichloropropene

((Z)-1,3-Dichloropropene)

n-Butylbenzene (1-Phenylbutane)

n-Propylbenzene (Isocumene)

p-Isopropyltoluene (pCymene)

sec-Butylbenzene

tert-Butylbenzene

trans-1,3-Dichloropropene

((E)-1,3-Dichloropropene)

Nutrients

No nondetects

Methyl tert-butyl

etherd (MTBE)

--

4%

Tetrachloroethene

(Perchloroethene)

--

1%

Dissolved ammonia 90%

92%

Dissolved ammonia

plus organic nitrogen

as nitrogen

91%

41%

Dissolved phosphorus as phosphorus

77%

66%

Dissolved nitrite plus

nitrate

87%

50%

Nutrient Rate

of

detection b

Concentration, in mg/L

0.01 1 10 100 1,000 10,000100,00 0.1 0

Volatile organic

compound

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.01 1 10 100 1,000 10,000100,00 0.1 0

Herbicides, insecticides, volatile organic compounds, and nutrients not detected in ground and surface waters of the Trinity River Basin

Study Unit.

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
U.S. Geological Survey Circular 1171 33

1,2-Dimethylnaphthalene

--

4%

1,6-Dimethylnaphthalene

--

15%

1-Methylphenanthrene

--

27%

1-Methylpyrene --

35%

2,2-Biquinoline --

4%

2,3,6-Trimethylnaphthalene

--

4%

2,6-Dimethylnaphthalene

--

58%

2,6-Dinitrotoluene --

2%

2-Ethylnaphthalene --

8%

2-Methylanthracene --

35%

4,5-Methylenephenanthrene

--

35%

9H-Carbazole --

46%

9H-Fluorene --

39%

Acenaphthene --

15%

Acenaphthylene --

22%

Acridine --

35%

Anthracene --

46%

Concentrations of semivolatile organic compounds, organochlorine compounds, and trace elements detected in fish and clam tissue and

bed sediment of the Trinity River Basin Study Unit

[μg/kg, micrograms per kilogram; --, not measured; %, percent; μg/g, micrograms per gram; trade names may vary]

EXPLANATION

Range of detections in fish and clam tissue in all 20 Study Units

Detection in fish tissue or bed sediment in the Trinity River Basin Study Unit

Range of detections in bed sediment in all 20 Study Units

Guideline for the protection of aquatic life e

Detection in clam tissue in the Trinity River Basin Study Unit

Semivolatile organic

compound

Rate of

detection b

Concentration, in μg/kg

0.1 1 10 100 1,000 10,000 100,000

Semivolatile organic

compound

Rate of

detection b

Concentration, in μg/kg

0.1 1 10 100 1,000 10,000 100,000

Anthraquinone --

50%

Benz(a)anthracene --

51%

Benzo(a)pyrene --

49%

Benzo(b)fluoranthene --

51%

Benzo(g,h,i)perylene --

37%

Benzo(k)fluoranthene --

51%

Butylbenzylphthalate --

88%

Chrysene --

51%

Di-n-butylphthalate --

95%

Di-n-octylphthalate --

15%

Dibenz(a,h)

anthracene

--

27%

Dibenzothiophene --

12%

Diethylphthalate --

61%

Dimethylphthalate --

32%

Fluoranthene --

85%

Indeno(1,2,3-cd)

pyrene

--

46%

Isoquinoline --

19%

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
34 Water Quality in the Trinity River Basin, Texas, 1992–95

Naphthalene --

8%

Phenanthrene --

69%

Phenanthridine --

12%

Phenol --

50%

Pyrene --

81%

bis(2-Ethylhexyl)phthalate

--

100%

p-Cresol --

50%

Organochlorine

compound

(Trade name)

Rate

of

detection b

Concentration, in μg/kg

Aldrin (HHDN,

Octalene)

3%

0%

total Chlordane 60%

20%

DCPA (dacthal,

chlorthal-dimethyl)

3%

0%

p,p’-DDE 61%

49%

total DDT 67%

49%

Dieldrin (Panoram D31, Octalox)

42%

18%

gamma-HCH (lindane, gamma-BHC)

11%

0%

Heptachlor epoxide 14%

2%

Heptachlor (heptachlore, Velsicol 104)

3%

0%

Mirex (Dechlorane) 0%

2%

PCB, total 28%

4%

Pentachloroanisole 8%

0%

Toxaphene (camphechlor, Hercules)

3%

0%

0.01 1 10 100 1,000 10,000100,000 0.1

Arsenic 73%

100%

Cadmium 73%

98%

Chromium 93%

100%

Copper 100%

100%

Lead 67%

100%

Mercury 67%

67%

Nickel 73%

100%

Selenium 100%

100%

Zinc 100%

96%

Semivolatile organic

compound

Rate of

detection b

Concentration, in μg/kg

0.1 1 10 100 1,000 10,000 100,000

Trace element Rate

of

detection b

Concentration, in μg/g

0.01 0.1 1 10 100 1,000 10,000

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
U.S. Geological Survey Circular 1171 35

Semivolatile organic compounds, organochlorine compounds, and trace elements not detected in fish and clam tissue and bed sediment of

the Trinity River Basin Study Unit.

a

 Selected water-quality standards and guidelines (Gilliom and others, in press).

b

 Rates of detection are based on the number of analyses and detections in the Study Unit, not on national data. Rates of detection for herbicides

and insecticides were computed by counting only detections equal to or greater than 0.01 μg/L to facilitate equal comparisons among compounds, which

had widely varying detection limits. For herbicides and insecticides, a detection rate of “<1%” means that all detections are less than 0.01 μg/L, or the

detection rate rounds to less than 1%. For other compound groups, all detections were counted and minimum detection limits for most compounds were

similar to the lower end of the national ranges shown. Method detection limits for all compounds in these tables are summarized in

(Gilliom and others, in press).

c

 Detections of these compounds are reliable, but concentrations are determined with greater uncertainty than for the other compounds and are

reported as estimated values (Zaugg and others, 1995).

d The guideline for methyl tert-butyl ether is between 20 and 40 μg/L; if the tentative cancer classification C is accepted, the lifetime health advisory

will be 20 μg/L (Gilliom and others, in press).

e

 Selected sediment-quality guidelines (Gilliom and others, in press).

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS

Semivolatile organic

compounds

1,2,4-Trichlorobenzene

1,2-Dichlorobenzene

(o-Dichlorobenzene,

1,2-DCB)

1,3-Dichlorobenzene

(m-Dichlorobenzene)

1,4-Dichlorobenzene

(p-Dichlorobenzene,

1,4-DCB)

1-Methyl-9H-fluorene

2,4-Dinitrotoluene

2-Chloronaphthalene

2-Chlorophenol

3,5-Dimethylphenol

4-Bromophenyl-phenylether

4-Chloro-3-methylphenol

4-Chlorophenyl-phenylether

Azobenzene

Benzo(c)cinnoline

C8-Alkylphenol

Isophorone

N-Nitrosodi-n-propylamine

N-Nitrosodiphenylamine

Nitrobenzene

Pentachloronitrobenzene

Quinoline

bis(2-Chloroethoxy)

methane

Organochlorine

compounds

Chloroneb (chloronebe,

Demosan, Soil Fungicide

1823)

Endosulfan I (alphaEndosulfan, Thiodan,

Cyclodan, Beosit, Malix,

Thimul, Thifor)

Endrin (Endrine)

Hexachlorobenzene (HCB)

Isodrin (Isodrine, Compound 711)

alpha-HCH (alpha-BHC,

alpha-lindane, alphahexachlorocyclohexane,

alpha-benzene hexachloride)

beta-HCH (beta-BHC,

beta-hexachlorocyclohexane, alpha-benzene

hexachloride)

cis-Permethrin (Ambush,

Astro, Pounce, Pramex,

Pertox, Ambushfog, Kafil,

Perthrine, Picket, Picket G,

Dragnet, Talcord, Outflank,

Stockade, Eksmin, Coopex,

Peregin, Stomoxin, Stomoxin P, Qamlin, Corsair,

Tornade)

delta-HCH (delta-BHC,

delta-hexachlorocyclohexane, delta-benzene

hexachloride)

o,p’-Methoxychlor

p,p’-Methoxychlor

(Marlate, methoxychlore)

trans-Permethrin (Ambush,

Astro, Pounce, Pramex,

Pertox, Ambushfog, Kafil,

Perthrine, Picket, Picket G,

Dragnet, Talcord, Outflank,

Stockade, Eksmin, Coopex,

Peregin, Stomoxin, Stomoxin P, Qamlin, Corsair,

Tornade)

Trace elements

No nondetects
36 Water Quality in the Trinity River Basin, Texas, 1992–95

Agency for Toxic Substances and 

Disease Registry, 1994, 1993 

CERCLA priority list of hazardous substances that will be the 

subject of toxicological profiles 

and support document: U.S. 

Public Health Service, 34 p.

Brown, M.F., 1995, Water-quality 

assessment of the Trinity River 

Basin, Texas—Pesticides in a 

suburban watershed, Arlington, 

1993–94: U.S. Geological Survey Fact Sheet FS–159–95, 4 p.

Crawford, K.S., and Luoma, S.N., 

1993, Guidelines for studies of 

contaminants in biological tissues for the National Water Quality Assessment Program: U.S. 

Geological Survey Open-File 

Report 92–494, 69 p.

Davis, J.R., 1987, Analysis of fish kills 

and associated water quality 

conditions in the Trinity River, 

Texas, I: Review of historical 

data, 1970–1985: Texas Water 

Commission LP 87–02, 107 p.

______1991, Analysis of fish kills and 

associated water quality conditions in the Trinity River, Texas, 

IV: Assessment of biotic integrity: Texas Water Commission 

LP 91–03, 169 p.

Gilliom, R.J., Mueller, D.K., and 

Nowell, L.H., in press, Methods 

for comparing water-quality 

conditions among National 

Water-Quality Assessment Study 

Units, 1992–95: U.S. Geological 

Survey Open-File Report 97–589.

Huckins, J.N., Tubergen, M.W., and 

Manuweera, G.K., 1990, Semipermeable membrane devices 

containing model lipid—A new 

approach to monitoring the 

bioavailability of lipophilic contaminants and estimating their 

bioconcentration potential: 

Chemosphere, v. 20, no. 5, 

p. 533–552.

Land, L.F., 1997, Water-quality 

assessment of the Trinity River 

Basin, Texas—Nutrients and 

pesticides in the watersheds of 

Richland and Chambers Creeks, 

1993–95: U.S. Geological Survey Water-Resources Investigations Report 97–4132, 22 p.

Land, L.F., and Brown, M.F., 1996, 

Water-quality assessment of 

the Trinity River Basin, Texas—

Pesticides in streams draining an 

urban and an agricultural area, 

1993–95: U.S. Geological Survey Water-Resources Investigations Report 96–4114, 22 p.

Land, L.F., and Shipp, A.A., 1996, 

Water-quality assessment of the 

Trinity River Basin, Texas—

Nutrients in streams draining an 

agricultural and an urban area, 

1993–95: U.S. Geological Survey Open-File Report 96–322, 6 

p.

Moring, J.B., 1997, Occurrence and 

distribution of organochlorine 

compounds in biological tissue 

and bed sediment from streams in 

the Trinity River Basin, Texas, 

1992–93: U.S. Geological Survey Water-Resources Investigations Report 97–4057, 19 p.

Omernik, J.N., 1987, Ecoregions of the 

conterminous United States: 

Annals of the Association of 

American Geographers, v. 77, 

p. 118–125.

Reutter, D.C., 1996, Water-quality 

assessment of the Trinity River 

Basin, Texas—Well and waterquality data from the outcrop of 

the Woodbine aquifer in urban 

Tarrant County, 1993: U.S. 

Geological Survey Open-File 

Report 96–413, 32 p.

Shipp, A.A., 1995a, Water-quality 

assessment in the Trinity River 

Basin, Texas—Nutrient concentrations in streams, winter and 

spring 1994: U.S. Geological Survey Fact Sheet FS–231–95, 2 p.

______1995b, Water-quality assessment in the Trinity River Basin, 

Texas—Pesticide occurrence in 

streams, winter and spring 1994: 

U.S. Geological Survey Fact 

Sheet FS–160–95, 2 p.

Texas Natural Resource Conservation 

Commission, 1996, Surface water 

monitoring program—Supplementary information manual: 

Texas Natural Resource Conservation Commission [variously 

paged].

Texas Parks and Wildlife Department, 

1974, Trinity River study—A 

comparison of fish collections 

and water quality in the Trinity 

River between Dallas County and 

Lake Livingston, July, 1972 

through April, 1974: Austin, 

Inland Fisheries and Environmental Branches, 47 p.

Ulery, R.L., and Brown, M.F., 1995, 

Water-quality assessment of the 

Trinity River Basin, Texas—

Review and analysis of available 

pesticide information, 1968–91: 

U.S. Geological Survey WaterResources Investigations Report 

94–4218, 88 p.

Ulery, R.L., Van Metre, P.C., and 

Crossfield, A.S., 1993, Trinity 

River Basin, Texas: American 

Water Resources Association, 

Water Resources Bulletin, v. 29, 

no. 4, p. 685–711. 

U.S. Environmental Protection 

Agency, 1996, Drinking water 

regulations and health advisories: 

EPA 822–R–96–001, 14 p.

Van Metre, P.C., and Callender, 

Edward, 1997, Water-quality 

trends in White Rock Creek Basin 

from 1912–1994 identified using 

sediment cores from White Rock 

Lake reservoir, Dallas, Texas: 

Journal of Paleolimnology 17, 

p. 239–249.

Van Metre, P.C., and Reutter, D.C., 

1995, Water-quality assessment 

of the Trinity River Basin, 

Texas—Analysis of available 

information on nutrients and 

suspended sediment, 1974–91: 

U.S. Geological Survey WaterResources Investigations Report 

94–4086, 71 p.

Zaugg, S.D., Sandstrom, M.W., Smith, 

S.G., and Fehlberg, K.M., 1995, 

Methods of analysis by the U.S. 

Geological Survey National 

Water Quality Laboratory—

Determination of pesticides in 

water by C–18 solid-phase extraction and capillary-column gas 

chromatography/mass 

spectrometry with selected-ion 

monitoring: U.S. Geological Survey Open-File Report 95–181, 

49 p.

REFERENCES
U.S. Geological Survey Circular 1171 37

The terms in this glossary were compiled from numerous sources. Some definitions have been modified and may not be 

the only valid ones for these terms.

Algae - Chlorophyll-bearing, nonvascular, primarily aquatic species that have no true roots, stems, or leaves; most algae are 

microscopic, but some species can be as large as vascular plants. 

Ammonia - A compound of nitrogen and hydrogen (NH3) that is a common by-product of animal waste. Ammonia readily 

converts to nitrate in soils and streams. 

Anomalies - As related to fish, externally visible skin or subcutaneous disorders, including deformities, eroded fins, lesions, 

and tumors. 

Aquifer - A water-bearing layer of soil, sand, gravel, or rock that will yield usable quantities of water to wells. 

Bank - The sloping ground that borders a stream and confines the water in the natural channel when the water level, or flow, is 

normal. 

Basic Fixed sites - Sites on streams at which streamflow is measured and samples are collected for temperature, salinity, suspended sediment, major ions and trace elements, nutrients, and organic carbon to assess the broad-scale spatial and temporal character and transport of inorganic constituents of stream water in relation to hydrologic conditions and 

environmental settings. 

Bed sediment - The material that temporarily is stationary in the bottom of a stream or other watercourse. 

Bioaccumulation - The biological sequestering of a substance at a higher concentration than that at which it occurs in the surrounding environment or medium. Also, the process whereby a substance enters organisms through the gills, epithelial 

tissues, dietary, or other sources.

Biochemical oxygen demand (BOD) - The amount of oxygen, measured in milligrams per liter, that is removed from aquatic 

environments by the life processes of microorganisms. 

Bioconcentration - A process by which there is a net accumulation of a chemical directly from water into aquatic organisms 

resulting from simultaneous uptake (for example, by gill or epithelial tissue) and elimination. 

Biota - Living organisms. 

Channelization - Modification of a stream, typically by straightening the channel, to provide more uniform flow; often done 

for flood control or for improved agricultural drainage or irrigation. 

Chlordane - Octachloro-4,7-methanotetrahydroindane. An organochlorine insecticide no longer registered for use in the 

United States. Technical chlordane is a mixture in which the primary components are cis- and trans-chlordane, cis- and 

trans-nonachlor, and heptachlor. 

Concentration - The amount or weight of a substance present in a given volume or weight of sample. Usually expressed as 

micrograms per liter (water sample) or micrograms per kilogram (sediment or tissue sample). 

Constituent - A chemical or biological substance in water, sediment, or biota that can be measured by analytical methods. 

Contamination - Degradation of water quality compared to original or natural conditions due to human activity. 

Cubic foot per second - The rate of water discharge representing a volume of 1 cubic foot passing a given point during 1 second, approximately equivalent to 7.48 gallons per second or 448.8 gallons per minute or 0.02832 cubic meter per second. 

DDT - Dichlorodiphenyltrichloroethane. An organochlorine insecticide no longer registered for use in the United States. 

Detection limit - The concentration below which a particular analytical method cannot determine, with a high degree of certainty, a concentration. 

Dieldrin - An organochlorine insecticide no longer registered for use in the United States. Also a degradation product of the 

insecticide aldrin. 

Discharge - Rate of fluid flow passing a given point at a given moment in time, expressed as volume per unit of time. 

Dissolved constituent - Operationally defined as a constituent that passes through a 0.45-micrometer filter. 

Ecoregion - An area of similar climate, landform, soil, potential natural vegetation, hydrology, or other ecologically relevant 

variables. 

Effluent - Outflow from a particular source, such as a stream that flows from a lake or liquid waste that flows from a factory or 

sewage-treatment plant. 

Environmental setting - Land area characterized by a unique combination of natural and human-related factors, such as rowcrop cultivation or glacial-till soils. 

Eutrophication - The process by which water becomes enriched with plant nutrients, most commonly nitrogen and 

phosphorus. 

Fish community - A group of populations of fish that interact in a common area. 

Fixed sites - NAWQA’s most comprehensive monitoring sites. See Basic Fixed sites and Intensive Fixed sites. 

Flow-path study - Network of clustered wells located along a flow path extending from a recharge zone to a discharge zone, 

preferably a shallow stream. The studies examine the relations of land-use practices, ground-water flow, and contaminant 

occurrence and transport. The studies are located in the area of one of the land-use studies. 

GLOSSARY
38 Water Quality in the Trinity River Basin, Texas, 1992–95

Fumigant - A substance or mixture of substances that produce gas, vapor, fume, or smoke intended to destroy insects, bacteria, or rodents. 

Gaging station - A particular site on a stream, canal, lake, or reservoir where systematic observations of hydrologic data are 

obtained. 

Habitat - The part of the physical environment where plants and animals live. 

Health advisory (HA) - Nonregulatory levels of contaminants in drinking water that can be used as guidance in the absence of 

regulatory limits. They consist of estimates of concentrations that would result in no known or anticipated health effects 

(for carcinogens, a specified cancer risk) determined for a child or for an adult for various exposure periods. 

Herbicide - A chemical or other agent applied for the purpose of killing undesirable plants. See also Pesticide. 

Hydrograph - Graph showing variation of water elevation, velocity, streamflow, or other property of water with respect to 

time. 

Indicator sites - Stream sampling sites located at outlets of drainage basins with relatively homogeneous land-use and physiographic conditions; most indicator-site basins have drainage areas ranging from 20 to 200 square miles. 

Insecticide - A substance or mixture of substances intended to destroy or repel insects. 

Integrator or mixed-use site - Stream sampling site located at an outlet of a drainage basin that contains multiple environmental settings. Most integrator sites are on major streams with relatively large drainage areas. 

Intensive Fixed sites - Basic Fixed sites with increased sampling frequency during selected seasonal periods and analysis 

of dissolved pesticides for 1 year. Most NAWQA Study Units have 1 to 2 integrator Intensive Fixed sites and 1 to 4 

indicator Intensive Fixed sites. 

Invertebrate - An animal with no backbone or spinal column.

Land-use study - A network of existing shallow wells in an area with a relatively uniform land use. These studies are a part of 

the Study Unit Survey and have the goal of relating the quality of shallow ground water to land use. See also Study Unit 

Survey. 

Main stem - The principal course of a river or stream. 

Major ions - Constituents commonly present in concentrations exceeding 1.0 milligram per liter. Major cations generally are 

calcium, magnesium, sodium, and potassium; major anions are sulfate, chloride, fluoride, nitrate, and those contributing 

to alkalinity, generally assumed to be bicarbonate and carbonate. 

Maximum contaminant level (MCL) - Maximum permissible level of a contaminant in water that is delivered to any user of 

a public water system. MCLs are enforceable standards established by the U.S. Environmental Protection Agency. 

Mean - The average of a set of observations, unless otherwise specified. 

Mean discharge - The arithmetic mean of individual daily mean discharges during a specific period, usually daily, monthly, or 

annually. 

Median - The middle or central value in a distribution of data ranked in order of magnitude. The median is also the 50th 

percentile. 

Micrograms per liter - A unit expressing the concentration of constituents in solution as weight (micrograms) of solute per 

unit volume (liter) of water; equivalent to 1 part per billion in most stream water and ground water. One thousand micrograms per liter equals 1 milligram per liter. 

Milligrams per liter - A unit expressing the concentration of chemical constituents in solution as weight (milligrams) of solute per unit volume (liter) of water; equivalent to 1 part per million in most stream water and ground water. One thousand 

micrograms per liter equals 1 milligram per liter. 

Nitrate - An ion consisting of nitrogen and oxygen (NO3

-

). Nitrate is a plant nutrient and is very mobile in soils. 

Nonpoint source - A pollution source that cannot be defined as originating from discrete points such as pipe discharge. Areas 

of fertilizer and pesticide applications, atmospheric deposition, manure, and natural inputs from plants and trees are types 

of nonpoint-source pollution. 

Nutrient - Element or compound essential for animal and plant growth. Common nutrients in fertilizer include nitrogen, phosphorus, and potassium. 

Organochlorine compound - Synthetic organic compounds containing chlorine. As generally used, term refers to compounds 

containing mostly or exclusively carbon, hydrogen, and chlorine. Examples include organochlorine insecticides, polychlorinated biphenyls, and some solvents containing chlorine. 

Organochlorine insecticide - A class of organic insecticides containing a large percentage of chlorine. Includes dichlorodiphenylethanes (such as DDT), chlorinated cyclodienes (such as chlordane), and chlorinated benzenes (such as lindane). 

Most organochlorine insecticides are banned because of their carcinogenicity, tendency to bioaccumulate, and toxicity to 

wildlife. 

Pesticide - A chemical applied to crops, rights of way, lawns, or residences to control weeds, insects, fungi, nematodes, 

rodents or other “pests.” 

GLOSSARY
U.S. Geological Survey Circular 1171 39

pH - The logarithm of the reciprocal of the hydrogen ion concentration (activity) of a solution; a measure of the acidity (pH 

less than 7) or alkalinity (pH greater than 7) of a solution; a pH of 7 is neutral.

Phosphorus - A nutrient essential for growth that can be important in stimulating aquatic growth in lakes and streams. 

Picocurie - One trillionth (10-12) of the amount of radioactivity represented by a curie. A curie is the amount of radioactivity 

that yields 3.7 X 1010 radioactive disintegrations per second. A picocurie yields 2.22 disintegrations per minute. 

Point source - A source at a discrete location such as a discharge pipe, drainage ditch, tunnel, well, concentrated livestock 

operation, or floating craft. 

Polychlorinated biphenyl (PCB) - A mixture of chlorinated derivatives of biphenyl, marketed under the trade name Aroclor 

with a number designating the chlorine content (such as Aroclor 1260). PCBs were used in transformers and capacitors 

for insulation and in gas pipeline systems as a lubricant. Further sale for new use was banned by law in 1979. 

Polycyclic aromatic hydrocarbon (PAH) - A class of organic compounds with a fused-ring aromatic structure. PAHs result 

from incomplete combustion of organic carbon (including wood), municipal solid waste, and fossil fuels, as well as from 

natural or anthropogenic introduction of uncombusted coal and oil. PAHs include benzo(a)pyrene, fluoranthene, and 

pyrene. 

Precipitation - Any or all forms of water particles that fall from the atmosphere, such as rain, snow, hail, and sleet. 

Recharge - Water that infiltrates the ground and reaches the saturated zone. 

Reference site - A NAWQA sampling site selected for its relatively undisturbed conditions. 

Riparian zone - Pertaining to or located on the bank of a body of water, especially a stream. 

Runoff - Excess rainwater or snowmelt that is transported to streams by overland flow, tile drains, or ground-water flow. 

Salinity - In this report, refers to the concentration of dissolved solids in water. 

Secondary maximum contaminant level (SMCL) - The maximum contamination level in public water systems that, in the 

judgment of the U.S. Environmental Protection Agency (EPA), are required to protect the public welfare. SMCLs are secondary (nonenforceable) drinking-water regulations established by the EPA for contaminants that may adversely affect 

the odor or appearance of such water.

Sediment - Particles, derived from rocks or biological materials, that have been transported by a fluid or other natural process, 

suspended or settled in water. 

Semivolatile organic compound (SVOC) - Operationally defined as a group of synthetic organic compounds that are solventextractable and can be determined by gas chromatography/mass spectrometry. SVOCs include phenols, phthalates, and 

PAHs. 

Streamflow - A type of channel flow, applied to that part of surface runoff in a stream whether or not it is affected by diversion 

or regulation. 

Study Unit - A major hydrologic system of the United States in which NAWQA studies are focused. Study Units are geographically defined by a combination of ground- and surface-water features and generally encompass more than 4,000 

square miles of land area. 

Study Unit Survey - Broad assessment of the water-quality conditions of the major aquifer systems of each Study Unit. The 

Study Unit Survey relies primarily on sampling existing wells and, wherever possible, on existing data collected by other 

agencies and programs. Typically, 20 to 30 wells are sampled in each of 3 to 5 aquifer subunits. 

Survey - Sampling of any number of sites during a given hydrologic condition. 

Synoptic sites - Sites sampled during a short-term investigation of specific water-quality conditions during selected seasonal 

or hydrologic conditions to provide improved spatial resolution for critical water-quality conditions. 

Tolerant species - Those species that are adaptable to (tolerant of) human effects on the environment. 

Total concentration - Refers to the concentration of a constituent regardless of its form (dissolved or bound) in a sample. 

Trace element - An element found in only minor amounts (concentrations less than 1.0 milligram per liter) in water or sediment; includes arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc. 

Volatile organic compound (VOC) - Organic chemical that has a high vapor pressure relative to its water solubility. VOCs 

include components of gasoline, fuel oils, and lubricants, as well as organic solvents, fumigants, some inert ingredients in 

pesticides, and some by-products of chlorine disinfection. 

GLOSSARY
Land and others • Water Quality in the Trinity River Basin

 USGS Circular 1171 • 1998

National Water-Quality Assessment (NAWQA) Program

Trinity River Basin

NAWQA

Tri nity Riv er

Dallas Fort Worth