Water Quality in the

Potomac River Basin

Maryland, Pennsylvania, Virginia, West Virginia

and the District of Columbia, 1992–96

U.S. Department of the Interior

U.S. Geological Survey Circular 1166

science for a changing world
A COORDINATED EFFORT

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Division

12201 Sunrise Valley Drive, M.S. 4

Reston, VA 20192

FOR ADDITIONAL INFORMATION ON THE

NATIONAL WATER-QUALITY ASSESSMENT (NAWQA) PROGRAM:

Data for this report were collected by many people, including John Battista, Bruce Bernard, Amy Derosier, Gar

James Gerhart, Liz Gno, Michael Hackney, Kalman Illyefalvi, Phyllis Illyefalvi, James Jeffries, Jon Kaye, Sarah 

Stephen Maskol, Mastin Mount, Michael Shackelford, Gianni Venturi, and William Werkheiser.

Cover photograph credits:

Front: The Potomac River at Great Falls, Virginia, by James Gerhart, U.S. Geological Survey

Back, left: The Potomac River at Washington, D.C., by James Gerhart, U.S. Geological Survey

Back, right: Confluence of the Shenandoah (left) and Potomac Rivers at Harpers Ferry, W.Va., by James Ger

U.S. Geological Survey

Potomac River Study Unit, contact:

District Chief

U.S. Geological Survey

Water Resources Division

8987 Yellow Brick Road

Baltimore, MD 21237

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

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

http://water.usgs.gov/lookup/get?nawqa/

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

http://water.usgs.gov/lookup/get?mdwater/pnawqa/

District of Columbia Department of Consumer and

 Regulatory Affairs

District of Columbia Water Resources Research Institute,

 University of the District of Columbia

Interstate Commission on the Potomac River Basin

Johns Hopkins University

Maryland Department of the Environment

Maryland Department of Natural Resources,

 Maryland Geological Survey

Maryland Water Resources Research Institute,

 University of Maryland

Metropolitan Washington Council of Governments

National Park Service

Pennsylvania Department of Conservation & Natural Resources,

 Bureau of Topographic and Geologic Survey

Pennsylvania Department of Environmental Resources,

 Division of Assessments and Standards

Pennsylvania Environmental Resources Research Institute,

 Pennsylvania State University

Resources for the Future

U.S. Army Corps of Engineers

U.S. Department of Agriculture, Agricultural Res

U.S. Department of Agriculture, Natural Resource

 Conservation Service

U.S. Environmental Protection Agency,

 Chesapeake Bay Program

U.S. Environmental Protection Agency, Region II

U.S. Fish and Wildlife Service

Virginia Department of Environmental Quality

Virginia Division of Mineral Resources

Virginia Water Resources Research Institute, Virg

 Polytechnic Institute and State University

West Virginia Department of Environmental Prote

West Virginia Geological and Economic Survey

West Virginia Water Resources Institute,

 West Virginia University

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

agencies and organizations who contributed data used in this report.

Interstate Commission on the Potomac River Basin Metropolitan Washington Council of Governments

We also thank the following agencies and organizations for contributing advice and comments on study desig

 and results.
U.S. GEOLOGICAL SURVEY CIRCULAR

Water Quality in the Potomac River Basin,

Maryland, Pennsylvania, Virginia, West

Virginia, and the District of Columbia, 1992–

1166

By Scott W. Ator, Joel D. Blomquist, John W. Brakebill,

Janet M. Denis, Matthew J. Ferrari, Cherie V. Miller, and

Humbert Zappia

CONTENTS

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

Summary of major issues and findings ......................................

Environmental setting ...................................................................

Hydrologic conditions...................................................................

Major issues and findings .............................................................

 Nutrients and pesticides in streams and ground water .......

 Nutrients .................................................................................

 Pesticides .................................................................................

 Organic contaminants and metals in streams........................

 Streambed sediment ..............................................................

 Aquatic tissues........................................................................

 Radon in ground water .............................................................

 Recent water-quality trends and outlook ...............................

Water-quality conditions in a national context..........................

Study design and data collection.................................................

Summary of compound detections and concentrations...........

References........................................................................................

Glossary...........................................................................................
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

1998

Library of Congress Cataloging-in-Publication Data

Water Quality in the Potomac River Basin, Maryland, Pennsylvania, Virginia, West Virginia,

and the District of Columbia, 1992–96

by Scott W. Ator ... [et al.].

p. cm. -- (U.S. Geological Survey Circular : 1166)

1. Water Quality--Potomac River Basin. I. Ator, Scott W. II. Series.

TD225.P74W35 1998

363.739’42’09752--dc21 98-4567

 CIP

ISBN 0-607-89112-2
U.S. Geological Survey Circular 1166 

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 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 assessments 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 water-quality 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 Potomac 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 may 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

“Potomac NAWQA s

are contributing valu

information on wate

land use issues vita

effective manageme

Chesapeake Bay ec

tem.”

—Dr. Emery Cleave

Director, Maryland

Geological Survey

Baltimore, Maryla

“As one involved in 

information with bot

public and other age

addressing water re

issues in the Shena

River Basin, the Pot

NAWQA study has 

quite helpful. This p

publication, summa

considerable amoun

water quality data t

informative graphics 

excellent maps, sho

serve as a convenie

ence to others intere

knowing more abou

valuable water reso

—Thomas Mizell,

Virginia Departme

Environmental Qu

Harrisonburg, Virg
2 Water Quality in the Potomac River Basin

SUMMARY OF MAJOR ISSUES AND FINDINGS

IN THE POTOMAC RIVER BASIN

WEST

VIRGINIA

VIRGINIA

PENNSYLVANIA

MARYLAND

D.C.

Nutrients and pesticides in

streams and ground water

A regional perspective

Although nitrogen and phosphorus occur naturally and are essential for the growth of plants

and animals, excessive nutrients in water can

adversely affect human health and the environment. Elevated concentrations of nitrogen and

phosphorus in streams and ground water of the

Potomac River Basin often result from human

activities such as manure and fertilizer applications.

(p. 6)

Nutrient inputs to the Potomac River Basin are

related to land use. Agricultural areas receive the

largest amounts of nutrients because manure and

fertilizer applications comprise 45 percent of

nitrogen and 93 percent of phosphorus inputs.

(p. 6)

In most waters of the Potomac River Basin, concentrations of nutrients do not pose a threat to

human health or wildlife.

(p. 7)

Elevated nitrogen concentrations in streams and

ground water are common in areas of intensive

row cropping, such as the northeastern part of the

Potomac River Basin, and areas underlain by carbonate bedrock, such as the Great Valley.

(p. 8)

Organic nitrogen and phosphorus concentrations

are typically low, except in streams during high

flows.

(p. 9)

Tributary streams draining agricultural areas

yield the greatest quantities of nitrogen to the

Potomac River; streams draining agricultural and

urban areas yield the greatest quantities of phosphorus.

(p. 9)

Pesticides can make water unfit to drink and

cause adverse ecological effects in streams. Commonly used pesticides are present in ground

water in the Potomac River Basin, but in most

cases at concentrations that are not threatening

to human health.

(p. 10)

More pesticides were detected in streams than in

ground water, but only rarely at concentrations

threatening to aquatic life.

(p. 11)

Pesticides were commonly detected in agricultural areas of the Potomac River Basin, particularly in areas of intense crop production such as

the corn-producing northeastern counties and in

the Great Valley. Samples from forested areas

rarely contained detectable pesticides.

(p. 12-13)

Pesticides were frequently present in streams in

urban areas; insecticide concentrations were

greatest in urban streams.

(p. 13)

Maximum concentrations of most pesticides

occur in streams during the spring and early summer months, coincident with their application to

fields, although atrazine and metolachlor are

present year round in streams in agricultural

areas.

(p. 14)

Spring floods carry large amounts of nutrients

and pesticides. A June 1996 flood on the Potomac River at Washington, D.C., carried an estimated 3,300 pounds of atrazine and 3,300,000

pounds of nitrogen.

(p. 14)

Higher concentrations of agricultural chemicals

are found in streams in the Great Valley than in

other agricultural areas, presumably because carbonate bedrock permits relatively rapid movement of these chemicals through ground water to

streams.

(p. 15)
U.S. Geological Survey Circular 1166 

SUMMARY OF MAJOR ISSUES AND FI

IN THE POTOMAC RIVER 

Organic contaminants and metals

in streams

Chlorinated organic compounds, mercury, and

lead are present in streambed sediment at concentrations that have some potential to adversely

affect aquatic life.

(p. 16)

Although its use was banned in 1988, chlordane

was detected in streambed sediment from 13 of

26 sites, including 4 sites at which concentrations

pose a high potential for adverse effects on

aquatic life.

(p. 17)

The use of DDT was banned in 1972 but it was

detected in streambed sediment at most sites,

although concentrations typically pose little risk

to aquatic life.

(p. 17)

Mercury from an industrial plant in Waynesboro,

Va., possibly over a period of decades, has

caused elevated concentrations of mercury in

sediments downstream from the plant in the

Shenandoah River, a major Potomac tributary.

(p. 18)

The organic compounds and metals present in

streambed sediment have been incorporated into

the food chain.

(p. 18)

Radon in ground water

Radon is present in ground water throughout the

Potomac River Basin.

(p. 20)

The Federal drinking-water standard for radon is

currently under review by the U.S. Environmental Protection Agency; however, radon levels in

69 percent of ground-water samples were greater

than a previously proposed standard of 300 picocuries per liter.

(p. 20)

Radon in ground water is related to rock type,

and levels are highest in eastern parts of the basin

underlain by crystalline and siliciclastic rocks.

(p. 20)

Recent water-quality trends

and outlook

Despite an estimated 44-percent increase in population in the Potomac River Basin from 1970 to

1990, total phosphorus concentrations in the

Potomac River at Washington, D.C., have

decreased since 1979, and nitrogen concentrations have apparently stabilized.

(p. 21)

Different forms of nitrogen show differing patterns in long-term trends in the Potomac River at

Washington, D.C.; ammonia plus organic nitrogen concentrations have decreased, whereas

nitrate concentrations have increased.

(p. 21)

Photograph by James Gerhart, U.S. Geological Survey
ENVIRONMENTAL SETTING IN THE POTOMAC RIVER BASIN

4 Water Quality in the Potomac River Basin

0

100

200

300

400

500

600

700

0

2

4

6

8

10

12

14

16

18

20

22

2,130

2,794

2,998

TOTAL

PUBLIC SUPPLY

DOMESTIC 

SUPPLY

COMMERCIAL

INDUSTRIAL AND 

MINING

IRRIGATION AND 

LIVESTOCK

THERMOELECTRIC

GROUND WATER

SURFACE WATER

POPULATION SERVED,

IN THOUSANDS

(3,856)

(798)

(3,856)

PERCENTAGE OF TOTAL

ESTIMATED WATER WITHDRAWALS IN 1990

WATER WITHDRAWALS,

IN MILLIONS OF GALLONS PER DAY

93

71

Urban

Agriculture

Forest

Other

0

10

20

30

40

50

60

LAND USE

PERCENTAGE OF BASIN AREA

0 10 20 30 40 50

0 10 20 30 40 50

MILES

KILOMETERS

South Branch

C apapon R

Opequon Cr Conococheague Cr

Oc co q u an R

Accotink Cr

An a costia

R

Potomac R

Antletam Cr

78°

40°

79°

39°

38° 38°

77°

Mononcacy R

Potoma c R

Goose Cr

She nand oah R

South Fork

North Fork Muddy Cr

S Fk S Br Potomac R

North Branch

WASHINGTON, D.C.

Urban

Agriculture

Forest

Water

EXPLANATION

78°

40°

79°

39°

38° 38°

77°

0 10 20 30 40 50

0 10 20 30 40 50

MILES

KILOMETERS

Unconsolidated

Carbonate

Siliciclastic

Crystalline

EXPLANATION

Rock Types

WASHINGTON, D.C.

Figure 1. Generalized land use in the

Potomac River Basin (modified from

Vogelmann and others, 1997; and Hitt,

1994). The basin is predominantly

forested, with smaller areas of

agriculture and urban development.

Figure 2. Major land use in the Potomac

River Basin, 1990-94 (modified from

Vogelmann and others, 1997; and Hitt,

1994).

Figure 3. Generalized geology and physiography in the

Potomac River Basin (modified from Fenneman and Johnson,

1946; Milici and others, 1963; Cardwell and others, 1968;

Cleaves and others, 1968; King and Beikman, 1974; and Berg,

1980). Unconsolidated deposits occur mainly in the Coastal

Plain and in isolated areas of alluvial deposits along stream

channels in the Valley and Ridge. Crystalline rocks underlie

only the Piedmont and Blue Ridge in the central and eastern

parts of the basin. The entire basin west of the Blue Ridge is

underlain by sedimentary rocks; these rocks are mainly

siliciclastic, with areas of extensive carbonate rocks,

particularly in the Great Valley.

Figure 4. Freshwater withdrawals in the Potom

River Basin (data from H.A. Perlman, U.S.

Geological Survey, written commun., 1993). Mo

of the surface water withdrawn from the Potoma

River Basin is used for the generation of electric

and for public supply. Ground water in the basin 

used mainly for domestic and public supply. Wa

is also withdrawn from the basin for various

commercial, industrial, and agricultural purpose
U.S. Geological Survey Circular 1166 

HYDROLOGIC CONDITIONS IN THE POTOMAC RIVER BASIN, 

MEAN DAILY FLOW, IN CUBIC FEET PER SECOND

Mean daily flow

Nitrate

1993 1994 1995

10,000

1,000

100

10

1

MARMAYJULSEPNOVJANMARMAYJULSEPNOVJANMARMAYJUL

1991 1992 1993 1994 1995

WATER LEVEL , IN FEET BELOW LAND SURFACE FLOW, IN CUBIC FEET PER SECOND

MONTHLY PRECIPITATION, IN INCHES MONTHLY PRECIPITATION, IN INCHES

100

0

20

40

60

80

100

0

20

40

60

80

100,000

10,000

1,000

100

10

1

22

21

20

19

18

17

16

15

14

13

12

Precipitation at Eisenhower National Historic Site, Pa.

Period of most intensive stream sampling

Flow in Monocacy River at Bridgeport, Md.

Precipitation at Savage River Dam, Md.

Period of ground-water sampling

Water level in well "AL Ca 19", Allegany County, Md.

NOVJANMARMAYJULSEPNOVJANMARMAYJULSEPNOVJANMARMAYJULSEPNOVJANMARMAYJULSEP

1993

FLOW, IN CUBIC FEET PER SECOND

Some dry periods

JULY AUGUST SEPTEMBER OCTOBER

0

100

200

300

400

500

600

Total flow

Estimated ground-water

contribution to flow

Figure 5. Streamflow, ground-water levels, and precipitation

at selected sites in the Potomac River Basin. Streamflow and

ground-water levels in the basin typically vary seasonally with

rates of precipitation and evapotranspiration.

Figure 6. Mean annual streamflow of the Potomac R

Washington, D.C. Streamflow can vary considerably 

year to year. Flow of the Potomac River at Washingto

did not exceed flood level in 1992 or 1995; however,

occasional flooding did occur in 1993, 1994, and 199

locally on some tributaries throughout the study perio

Floods occurred mostly during the months of winter a

spring. Near-drought conditions occurred for short pe

the late summer or fall of 1992, 1993, and 1995.

Figure 7. Total streamflow and estimated ground-water

contribution to flow in the South Branch Potomac River near

Springfield, W. Va., during part of 1993. Ground water

contributes virtually all flow to the river during dry periods but

some of the flow during wetter periods.

Hydrologic conditions affect the quality of 

and ground water in the Potomac River Basin. Fe

pesticides, and other chemicals that are applied to th

surface may infiltrate to ground water or run off to s

during rainfall depending on the season, soil propert

the intensity and duration of precipitation. During dr

ods, flow in most streams of the Potomac River Basi

tained by discharge from ground water (fig. 7) and

streamwater quality is similar to that of ground wate

flows are elevated during storms, streams of the basi

cally become concentrated in chemicals that are was

from the land (fig. 8), although streams in some area

become diluted.

Figure 8. Streamflow and nitrate concentrations in M

Creek at Mount Clinton, Va. Nitrate concentrations a

typically higher during periods of high flow than durin

periods.

LTA1 11,710 

8,832

17,460 18,830

8,698

23,760

ANNUAL MEAN FLOW,

IN CUBIC FEET PER SECOND

WY1992 WY1993 WY1994 WY1995 WY1996

1

LTA - Long term average discharge for period of record (1959-9

WY- Water Year (WY1992— October 1991- September 1992)

0

5,000

10,000

15,000

20,000

25,000
6 Water Quality in the Potomac River Basin

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

Nutrients and pesticides in streams and ground water — A regional perspective

3 percent

4 percent

48 percent

32 percent

29 percent

26 percent

12 percent

Less than 2 percent

A. NITROGEN B. PHOSPHORUS

45 percent

Atmospheric deposition

Municipal and industrial 

wastewater discharges

Septic systems

Animal manure

Commercial fertilizer

EXPLANATION

In the Potomac River Basin, the

quality of streams and ground water is

affected by a variety of natural and

human processes. Several major types

of chemicals found in water in the

basin include nutrients, trace elements,

pesticides, chlorinated industrial compounds, and volatile organic compounds. Agricultural and urban landuse practices broadly characterize the

distribution of these sources, because

most contamination results from the

disposal of human and animal wastes

or from the use and disposal of other

chemical compounds. Water, sediment,

and tissue samples were collected

throughout the basin and analyzed for

nutrients, pesticides, metals, or other

potential contaminants that are associated with urban and agricultural

sources.

Much of the analysis done by the

NAWQA Program within the Potomac

River Basin focused on nutrients and

pesticides because these compounds

are of primary concern to environmental managers within the basin. Elevated

concentrations of nutrients and pesticides can render water unsafe to drink

and can have adverse environmental

effects. In 1987, Maryland, Pennsylvania, Virginia, the District of Columbia,

and the Federal government established a goal of reducing nutrient loads

to Chesapeake Bay. The Potomac

River is the second largest tributary to

Chesapeake Bay, and information from

the NAWQA Program can be used to

monitor progress toward this goal.

Only a small amount of data was available for pesticides in the Potomac

River Basin prior to the NAWQA Program. Data collection was designed to

fill this gap in information.

Nutrients (Nitrogen and

Phosphorus)

Although nitrogen and ph

rus occur naturally, elevated 

trations of these nutrients in 

and ground water of the Pot

River Basin often result from 

activities. Major sources of ni

and phosphorus to the basin in 

included commercial fertilizer

manure. Atmospheric depositi

the combustion of fossil fuels 

for an additional 32 percent of 

inputs. Municipal wastewater-

ment plants are locally import

sources of nutrients to many s

but they contributed about 12 

of nitrogen and 4 percent of p

rus inputs to the basin in 1990 

Nutrient inputs to the Pot

River Basin are related to la

The Great Valley (fig.3), whic

percent cropland, received the 

Figure 9. Major inputs of (A) nitrogen and (B) phosphorus to the Potomac River Basin, 1990. Most

nitrogen and phosphorus inputs are derived from commercial fertilizers and manure, although a large

percentage of nitrogen is derived from atmospheric deposition as well (Blomquist and others, 1996).

Figure 10. Inputs 

nitrogen and (B)

phosphorus from 

point sources to a

the Potomac Rive

1990 (modified fr

Blomquist and ot

1996). 0 0

1

2

3

4

5

6

7

8

5

10

15

20

25

30

35

APPALACHIAN

PLATEAUS

VALLEY AND

 RIDGE

GREAT VALLEY

BLUE RIDGE

PIEDMONT

COASTAL

PLAIN

VALLEY AND

 RIDGE

GREAT VALLEY

BLUE RIDGE

PIEDMONT

COASTAL

PLAIN

A. NITROGEN B. PHOSPHORUS

NITROGEN INPUTS, IN THOUSANDS OF 

POUNDS PER SQUARE MILE

PHOSPHORUS INPUTS, IN THOUSANDS OF 

POUNDS PER SQUARE MILE

APPALACHIAN

PLATEAUS

Atmospheric deposition

Commercial fertilizer

Animal manure

Septic systems

Commercial fertilizer

Animal manure

Septic systems
U.S. Geological Survey Circular 1166 

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER 

Nutrients and pesticides in streams and ground water — A regional pers

estimated inputs from non-point

sources of both nitrogen and phosphorus per unit area in 1990, followed by

the Piedmont (including the Triassic

Lowlands), which is 43 percent agricultural and 25 percent urban (Vogelmann and others, 1997; Hitt, 1994).

Inputs to these areas were mostly

attributed to commercial fertilizers and

manure. Dominantly forested areas of

the basin received smaller inputs of

nitrogen (mostly from atmospheric

deposition) and phosphorus per unit

area in 1990. (fig. 10).

In most waters of the Potomac

River Basin, concentrations of nutrients do not pose a threat to human

health or wildlife. A Maximum Contaminant Level1 (MCL) of 10 milligrams per liter (mg/L) as nitrogen has

been established for nitrate (U.S. Environmental Protection Agency, 1994a).

Drinking water containing nitrate in

excess of this concentration may cause

health problems in infants and small

children. Nitrate concentrations in

sampled streams of the Potomac River

Basin were generally well below the

MCL, even during high flows. Ground

water in agricultural areas of the basin

underlain by carbonate rock, however,

is particularly susceptible to nitrate

contamination (Ferrari and Ator,

1995). Nearly 25 percent of groundwater samples from domestic wells in

such areas contained nitrate in excess

of 10 mg/L. Excessive nitrogen or

phosphorus in streams can cause

eutrophication, a condition whereby

aquatic plants and algae are overproduced. This algae can smother larger

plants, consume dissolved oxygen,

block sunlight from the water, 

duce toxins that are harmful to 

aquatic life (Allaby, 1989). To 

eutrophication, the U.S. Enviro

tal Protection Agency (1986) r

mends that total phosphorus

concentrations in flowing wate

exceed 0.1 mg/L, a concentrat

exceeded in only 12 percent of 

ples from small streams in the 

mac River Basin at low flow b

greater percentage of samples 

larger streams at varying flow 

tions.

Nutrients are present in w

the Potomac River Basin in m

forms, often at concentration

gestive of human-derived sou

(figs. 11, 12). Maximum natur

“background” concentrations o

ents in ground water of the bas

estimated at 0.4 mg/L (as nitro

nitrate, 0.1 mg/L (as nitrogen) 

1MCLs are standards for levels of contaminants in

finished public water supplies and are not directly applicable to untreated streams or ground water. MCLs are cited in

this report for reference only.

Agriculture

underlain by

carbonate rock

Agriculture

underlain by

non-carbonate rock

Agriculture

underlain by

non-carbonate rock

Agriculture

underlain by

carbonate rock

29 

ENVIRONMENTAL

SETTING

0 5 10 15 20

NITRATE, IN MILLIGRAMS PER LITER AS NITROGEN

Minimum

Median

Maximum

Ground water

Small streams at low flow

Estimated maximum natural level (ground water)

Federal maximum contaminant level

Estimated maximum natural level (streams)

Figure 11. Among samples from small streams at low flow and ground water in the Potomac River Basin, the

highest nitrate concentrations were found in areas of agriculture and carbonate bedrock.

0 5 10

NITRATE, IN MILLIGRAMS PER LITER AS NITROGEN

OCTOBER, 1993 - SEPTEMBER, 1995

Minimum

Median

Maximum

Estimated maximum natural level (streams)

S. Br. Potomac River

at Moorefield, W.Va.

(Predominantly forested,

 non-carbonate, basin)

Monocacy River

near Frederick, Md.

(Predominantly agriculture,

 non-carbonate, basin)

Conococheague Cr. at Fairview, Md.

(Predominantly agriculture,

carbonate, basin)

WATERSHED

Figure 12. Time-series data show a wide variation in

nitrate concentrations in selected Potomac River

tributaries from 1993 through 1995, but

concentrations typically are highest in those

tributaries draining agricultural land and carbonate

bedrock.
8 Water Quality in the Potomac River Basin

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

Nutrients and pesticides in streams and ground water — A regional perspective

ammonia, and 0.07 mg/L (as phosphorus) for orthophosphate, the most common form of dissolved phosphorus in

natural waters (Ator and Denis, 1997).

On the basis of data from across the

United States, maximum natural concentrations of nutrients in streams have

been estimated at 0.6 mg/L for nitrate

and 0.1 mg/L for ammonia (Mueller

and others, 1995).

Elevated nitrogen concentrations

in streams and ground water are

common in the Potomac River Basin

in areas of intensive row cropping

and carbonate bedrock. Nitrate is the

most common form of nitrogen in

waters of the basin. Nitrate concentrations may vary considerably during the

year at any given location because of

seasonal variations in precipitation and

inputs, but they generally exceed natural concentrations more often in

streams and ground water in agricultural areas of the basin than in areas

with other land uses. This is particularly evident in areas underlain by carbonate bedrock, where natural waters

are more susceptible to such contamination (figs. 11, 12). Elevated nitrate

concentrations in streams and ground

water in some urban areas indicate that

urban sources also contribute nutrients

to the basin, although relatively few

samples were collected in these areas

during this study (Ator and Denis,

1997; Miller and others, 1997).

Because nitrogen sources are typically

surficial, concentrations are often

greater in shallower than in de

ground water (Blomquist and 

1996). This is not evident from 

data, however, likely because m

shallow wells were sampled.

Nitrate concentrations tha

exceed natural concentration

more common in streams an

ground water in agricultural 

in the northeastern part of th

mac River Basin than in othe

cultural areas that contain le

percentages of row cropping 

(Ator and Denis, 1997; Miller 

ers, 1997). In 1992, row crops

accounted for less than 20 perc

agricultural land in most coun

the basin, but as much as 47 pe

such land in counties in the no

78°

40°

79°

39°

38° 38°

77°

0 10 20 30 40 50

0 10 20 30 40 50

MILES

KILOMETERS

Greater than 20

Less than or equal to 2

Nitrate concentrations at selec

sites in agricultural areas, i

milligrams per liter as nitrog

Ground water

Less than or equal to 3

3.01 – 7

Greater than 7

Streams, low flow

Less than or equal to 2

2.01 – 4

Greater than 4

EXPLANATION

County agricultural land plante

in corn, barley, oats, wheat, so

or soybeans, in percent 

Figure 13. Within agricultural areas, most elevated nitrate concentrations in ground water and in small streams at low f

found in counties with the highest percentages of agricultural land devoted to row crops.
U.S. Geological Survey Circular 1166 

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER 

Nutrients and pesticides in streams and ground water — A regional pers

0

1

2

3

4

20,000

10,000

0

19 20 21 22 23

DATE (JUNE 1996)

DISSOLVED NITROGEN,

 IN MILLIGRAMS PER LITER

FLOW,

IN CUBIC FEET PER

SECOND 14

12

10

8

6

4

2

0

1.0

0.8

0.6

0.4

0.2

0.0

TOTAL NITROGEN YIELD, PER YEAR,

IN 1,000 POUNDS PER SQUARE MILE

TOTAL PHOSPHORUS YIELD, PER YEAR,

IN 1000 POUNDS PER SQUARE MILE

STREAM

Potomac River at

Washington, D.C. 

Shenandoah River 

at Millville, W. Va.

S. Branch Potomac River 

near Springfield, W. Va.

Monocacy River 

near Frederick, Md.

Monocacy River 

at Bridgeport, Md.

Conococheague

Creek at Fairview, Md. 

Catoctin Creek at

Taylorstown, Va.

Accotink Creek at

Annandale, Va.

Muddy Creek at

Mount Clinton, Va.

Nitrogen

Phosphorus

Figure 14. Organic nitrogen concentrations were

elevated for a short time

during high flow in Conococheague Creek in June

1996 but quickly

decreased as the flow

subsided. Concentrations

of nitrate, a much more

soluble form of nitrogen,

were slightly depressed

during the high flow.

Figure 15. Estimated yields 

nitrogen and phosphorus fo

selected streams in the Pot

River Basin, 1994-95 (Lizar

press). The Monocacy Rive

Conococheague and Muddy

Creeks, which drain primari

agricultural watersheds, and

Accotink Creek, which drain

small urban watershed, yiel

greatest amounts of nitroge

phosphorus per square mile 

Potomac River.

ern part (U.S. Department of Commerce, 1995). Nitrogen is typically

applied in greater quantities to crops in

the form of fertilizer and manure than

to pastures in the form of manure.

Ammonia concentrations are typically lower than nitrate concentrations but occasionally exceed natural

concentrations. Elevated ammonia

concentrations in small streams during

low flow in carbonate areas were likely

related to agricultural and urban land

uses (Miller and others, 1997). Ammonia in ground water in forested areas

may form from nitrogen that is deposited from the atmosphere or from

organic nitrogen in leaves and other

natural debris (Ator and Denis, 1997).

Organic nitrogen and phosphorus

concentrations are typically low in

waters of the basin, except in

streams during high flows. Organic

nitrogen (fig. 14) and phosphorus concentrations can be elevated for short

periods in streams during high flow,

but they were detected at low concentrations or were undetectable in most

ground-water samples.

Streams draining primarily agricultural or urban areas yield the

greatest quantities of nutrients to

the Potomac River. Although the

Shenandoah River contributes the

greatest loads of total nitrogen and

phosphorus among streams at which

data were collected over time, Conococheague Creek, Muddy Creek

Monocacy River, which drain 

rily agricultural watersheds, y

largest loads of total nitrogen 

square mile. Accotink Creek, 

stream, yields the largest loads 

phosphorus per square mile, fo

by Muddy and Conococheagu

and the Monocacy River (fig. 

Phosphorus is less soluble tha

forms of nitrogen and is often b

stream sediment. Accotink Cr

yields the most sediment per s

mile among Potomac tributari

which data were collected ove

(Lizarraga, in press).
10 Water Quality in the Potomac River Basin

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

Nutrients and pesticides in streams and ground water — A regional perspective

Pesticides

Each year, 4.94 million pounds of

synthetic organic pesticides are applied

to agricultural lands within the Potomac River Basin, including 2.88 million pounds of herbicides, 1.09 million

pounds of insecticides, and 0.97 million pounds of fungicides. Additionally, 1.24 million pounds of oil and

0.47 million pounds of sulfur are used

primarily on apples and peaches to

control insects and fungi, respectively.

Pesticides are also used for non-agricultural purposes such as maintenance

of golf courses, lawns, and gardens;

defoliation of rights-of-way; and control of disease-carrying or defoliating

insects. Application rates for these

uses are not as well documented.

Cornfields and apple orchards

receive nearly 75 percent of agricultural pesticides applied in the Potomac

River Basin (table 2). Apples receive

the heaviest average rate of pe

application, followed by potat

peaches. The agricultural area

the lowest average rates of pes

application are pastures and ha

Commonly used pesticides 

present in ground water of th

mac River Basin, typically at 

concentrations. Pesticide com

were detectable2 in ground-wa

ples from throughout the basin

although concentrations rarely

1Use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

2Amount of active ingredient (Gianessi and Puffer, 1990, 1992a, 1992b).

Table 1: Major agricultural pesticides used in the Potomac River Basin and results of pesticide analyses

[F, fungicide; H, herbicide, I, insecticide; A, alfalfa; Ap, apples; C, corn; Ch, cherries; O, other hay; P, pasture; Pe, peaches; S, soybeans; T, to

wheat; D, detected; N, not detected, ---, not analyzed]

Pesticide (Trade names1) Type

Estimated

amount

applied2

(lb/yr)

Estimated

acres treated

Major target

crops

Sample result

Ground

water Stream

Atrazine (AAtrex, Gesaprim) H 697,000 492,000 C D D

Metolachlor (Dual, Pennant) H 539,000 323,000 C, S D D

Captan (Clomitane, Captanex) F 319,000 37,600 Ap, Pe --- ---

Alachlor (Lasso, Alanox) H 295,000 165,000 C, S N D

Chlorpyrifos (Dursban, Lorsban) I 281,000 253,000 C, A, Ap D D

2,4-D (Weed-B-Gon, Chloroxone) H 205,000 376,000 P, O, C, W N D

Mancozeb (Dithane DF, Nemispor) F 202,000 43,300 Ap --- ---

Simazine (Aquazine, Princep) H 168,000 126,000 C, Ap, Pe D D

Cyanazine (Bladex, Fortrol) H 167,000 113,000 C N D

Metiram (Carbatene, Polyram DF) F 148,000 8,230 Ap, Pe --- ---

Paraquat (Cyclone, Total) H 133,000 336,000 C, A, Ap, S --- ---

Carbofuran (Furadan, Curaterr) I 132,000 143,000 C, A, S N D

Butylate (Genate Plus, Sutan) H 121,000 28,000 C N D

Glyphosate (Roundup, Rattler) H 120,000 108,000 C, P, S, Ap --- ---

Ziram (Corozate, Thionic) F 109,000 16,000 Ap, Pe --- ---

Azinphos-methyl (Guthion, Carfene) I 88,000 49,800 Ap, Pe N D

EPTC (Eptam, Alirox) H 83,300 19,700 C, A D D

Dicamba (Banvel, Metambane) H 77,100 253,000 P, C, O N N

Pendimethalin (Prowl, Stomp) H 73,700 79,300 C, S, T N D

Methomyl (Lannate, Methomex) I 67,800 75,000 Ap, C, W N N
U.S. Geological Survey Circular 1166 

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER 

Nutrients and pesticides in streams and ground water — A regional pers

1Based on 1992 agricultural census data (U.S. Department of Commerce, 1995).

2Based on Gianessi and Puffer, 1990, 1992a, 1992b.

3No reported use.

Table 2: Pesticide application to major crops in the Potomac River Basin

Crop Estimated acres1

Estimated amounts of pesticides used (lb/yr)2

Most heav

pest

Fungicides Herbicides Insecticides Total

Corn 416,000 2,500 2,090,000 354,000 2,450,000 Atra

Apples 50,000 812,000 110,000 372,000 1,300,000 Capt

Alfalfa 247,00 03 102,000 212,000 314,000 Chlo

Soybeans 157,000 583 275,000 38,400 314,000 Meto

Pasture 1,510,000 03 149,000 03 149,000 2,4-D

Peaches 8,790 79,600 11,300 31,900 123,000 Capt

Other Hay 545,000 03 73,800 1,260 75,000 2,4-D

Wheat 123,000 1,880 21,000 22,400 45,300 2,4-D

Potatoes 1,220 9,310 6,410 13,600 29,400 Man

Cherries 1,600 16,600 721 2,090 19,400 Capt

exceeded 1 microgram per liter (μg/L).

Atrazine was the most commonly

detected pesticide in ground water, in

34 percent of samples (fig. 16).

Simazine, metolachlor, and prometon

were also detected in at least 15 percent of samples, and 10 other compounds (p,p’-DDE, EPTC, metribuzin,

tebuthiuron, DCPA, pebulate, dichlorbenil, dicamba, terbacil, and propoxur)

were detected in less than 10 percent

of samples. Deethylatrazine (a byproduct of atrazine degradation) was

detected in nearly all ground-water

samples that contained detectable atrazine, often at higher concentrations.

A wider variety of pesticides was

detected more frequently in small

streams than in ground-water samples. Pesticides were commonly

detected in samples from small

streams of the basin that were collected during periods of low flow in

late summer, although concentrations

were usually less than 1 μg/L. Atrazine

(fig. 17), metolachlor, simazine, and

prometon were each detected in more

than half of these samples. In addition,

tebuthiuron, diazinon, and carbaryl

were each detected in at least 10 percent of samples, and 18 other pesticide

compounds were detected in less than

10 percent of the samples. Only atrazine and metolachlor were measured at

concentrations greater than 1 μg/L.

Deethylatrazine was detected in 67

percent of samples from small streams

at low flow and in 86 percent of such

samples that contained detectable atrazine.

Concentrations of pesticides in

streams and ground water of the

Potomac River Basin are usually not

threatening to human health or most

ecosystems, based on current standards and understanding. Established MCLs (U.S. Environmental

Protection Agency, 1994a) for atrazine (3 μg/L), simazine (4 μg/L), and

alachlor (2 μg/L) were only occasionally exceeded in stream samples collected during this study of the P

River Basin, most commonly 

storms. The MCL of 70 μg/L f

was never exceeded. There are 

rently no established drinking

criteria for the other pesticides 

mon use in the basin, although 

lished lifetime health-advisory 

(U.S. Environmental Protectio

Agency, 1996) for cyanazine a

inon were infrequently exceed

Although criteria for the prote

aquatic life do not reflect all p

effects of pesticides in streams 

have not been established for m

compounds, degradation produ

mixtures, established criteria (

tional Joint Commission Cana

United States, 1977; Canadian 

of Resource and Environment 

ters, 1991; U.S. Environmenta

tion Agency, 1991a) were exce

atrazine, chlorpyrifos, cyanazi

inon, malathion, methylazinph

metolachlor. Aquatic-life crite

exceeded almost exclusively in 

ples collected during storms in 

2

Using methods employed by the NAWQA Program,

most pesticide compounds were detectable in water samples

at concentrations as low as 0.001 μg/L to 0.01 μg/L.
12 Water Quality in the Potomac River Basin

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

Nutrients and pesticides in streams and ground water — A regional perspective

Valley and Ridge Great Valley Carbonate Piedmont Triassic Lo

ATRAZINE, 

IN MICROGRAMS PER LITER 

25(12) 27(0) 25(5) 1

2.5

2.4

2.3

2.2

2.1

2.0

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

 Number of samples

 Number of samples with concentrations less than 0.001 micrograms per liter

25

(5)

June, or July from Accotink Creek, the

Monocacy River, or Muddy Creek.

These streams drain predominantly

urban or agricultural areas and were

among the most intensely sampled for

pesticides within the Potomac River

Basin by the NAWQA Program.

Pesticides were commonly

detected in streams and ground

water in agricultural areas of the

Potomac River Basin; samples from

forested areas rarely contained

detectable pesticides. Much of the

agriculture in the basin is in the Great

Valley, Piedmont, and Triassic Lowlands (fig. 3). In carbonate areas of the

Great Valley, atrazine (figs. 16, 17),

deethylatrazine, simazine, prometon,

and metolachlor were each detected in

more than half of the samples from

ground water and small streams. Pesticides were also commonly detected in

ground water and streams of the Piedmont and Triassic Lowlands. In the

mostly forested Valley and Ridge,

however, detections of pesticide compounds in streams were much less frequent, and there were virtually no

detections in ground water. Six compounds (atrazine, deethylatrazine, p,p’-

DDE, metribuzin, prometon, and

simazine) were each detected in a single ground-water sample from the Valley and Ridge, and dichlorbenil was

detected in four samples. Only 

zine, deethylatrazine, metolach

prometon, simazine, and tebut

were detected in small-stream 

from the Valley and Ridge.

Figure 17. Concentrations of atrazine in small streams during low flo

sampled areas of the Potomac River Basin. The highest concentrati

atrazine were typically detected in streams of the Great Valley, altho

highest concentration was detected in the Triassic Lowlands.

Valley and Ridge

(agricultural)

Great Valley Carbonate

(agricultural)

Valley and Ridge

(forest)

Piedmont Triassic Low

ATRAZINE, 

IN MICROGRAMS PER LITER 

 Number of samples

 Number of samples with concentrations

less than 0.001 micrograms per liter

25

(12)

25(24) 3(3) 29(4) 25(20) 23(

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

Figure 16. Concentrations of atrazine in ground water in sampled areas of the Potomac R

Atrazine was most commonly detected in ground water in agricultural areas of the Great V
U.S. Geological Survey Circular 1166 

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER 

Nutrients and pesticides in streams and ground water — A regional pers

78°

40°

79°

39°

38° 38°

77°

0 10 20 30 40 50

0 10 20 30 40 50

MILES

KILOMETERS

Greater than 20

Less than or equal to 20

Atrazine concentrations at selec

sites in agricultural areas, in 

micrograms per liter

Ground water

Less than 0.001

0.001 - 0.009

0.01 - 0.099

Greater than or equal to 0.1

Streams, low flow

Less than 0.001

0.001 - 0.009

0.01 - 0.099

 Greater than or equal to 0.1

EXPLANATION

County agricultural land planted 

in corn, barley, oats, wheat, sor

or soybeans, in percent 

Pesticide concentrations in

streams and ground water of the

Potomac River Basin are greatest in

areas of intense crop production –

particularly in the corn-producing

northeastern counties and in the

Great Valley. Pesticide concentrations in ground water and small

streams were typically higher in samples from the more heavily cropped

areas than other agricultural areas (fig.

18). Among larger streams, the highest

incidence of detections and elevated

concentrations of atrazine and metolachlor also occurred predominantly in

these areas, particularly in the Monocacy River and Opequon, Conococheague, and Antietam Creeks.

Streams in the Potomac River

Basin are affected by pesticide applications in urban as well as agricultural areas. Many pesticides have

been detected in samples from

Accotink Creek, which drains a small,

urban watershed near Washington,

D.C. Herbicides detected at this site

include atrazine, metolachlor, MCPA,

oryzalin, and prometon. Simazine was

detected most often and at the highest

concentrations, occasionally exceeding

the MCL of 4 μg/L. Insecticides—including diazinon, carbaryl,

and chlorpyrifos—were also detected,

year-round. Samples from Accotink

Creek contained the highest concentrations of the insecticides diazinon and

malathion measured in the Pot

River Basin and the highest co

tions of oryzalin and MCPA m

by the NAWQA Program. Pes

found in Accotink Creek are g

used on rights-of-way, turf, go

courses, and for landscaping, a

additives to asphalt and other b

materials.

Figure 18. Within agricultural areas, most elevated atrazine concentrations in

ground water and in small streams at low flow were found in counties with the

highest percentages of agricultural land devoted to row crops.
14 Water Quality in the Potomac River Basin

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

Nutrients and pesticides in streams and ground water — A regional perspective

Maximum concentrations of most

pesticides occur in streams during the

spring and early summer months,

although atrazine and metolachlor

are present year round in agricultural

areas. The Monocacy River at Bridgeport, Md., for example, drains 173

square miles, almost 80 percent of which

is agricultural. Pesticide concentrations

in this stream are related to flow, but the

major controlling factor is the seasonal

application (fig. 19). During a storm in

May 1994, concentrations of alachlor

(3.1 μg/L), atrazine (25 μg/L), cyanazine (3.0 μg/L), and metolachlor (23

μg/L) in the Monocacy River were the

highest measured in any water sample

during this study. Other pesticides frequently detected in the Monocacy River

included simazine, prometon, and linuron. Of the 45 pesticides for which samples from this site were analyzed, 19

Atrazine

Metolachlor

Flow

100,000

10,000

1,000

100

10

1

FLOW, IN CUBIC FEET PER SECOND

1994 1995

MARCH JULY MAY NOV SEPT MARCH JULY JAN MAY 

Figure 19. In the Monocacy River at Bridgeport, Md., atrazine and m

were present at detectable concentrations during most of the year bu

concentrations were typically highest during the late spring following 

STORM FLOW

TOTAL NITROGEN LOAD

ATRAZINE LOAD

January

(19-23)

June

(19-24)

September

(7-10)

TOTAL FLOW, IN

 BILLION GALLONS

NITROGEN, IN MILLIONS 

OF POUNDS ATRAZINE, IN POUNDS

NOT MEASURED

0

1,000

2,000

3,000

4,000

5,000

0

20

15

10

5

0

600

500

300

200

100

400

were detected at least once during the

period of most intensive sampling in

1994. Pesticide concentrations in the

Potomac River also were highest in the

spring, during the time of applications.

Concentrations declined throu

summer months and were near

tectable in late fall and winter.

Three major floods occurred in the Potomac River Bas

1996 and had different effects on water quality because th

occurred during different seasons (fig. 20). Record high flow 

single day occurred in January in the Potomac River at Washin

D.C., due to intense rainfall and rapid snowmelt caused by uns

ably warm weather following a blizzard. In June, basins of the 

cacy River and Conococheague Creek, which are dominantly

agricultural, received intense rainfall over a 5-day period. Flow 

the June storm in the Monocacy River at Bridgeport, Md., reac

level expected to occur only once in 200 years. Intensive rainfa

a tropical storm caused flooding in September in the mostly ag

tural Shenandoah River Basin and points west.

Nitrogen loads in the Potomac River at Washington, D.C., w

greater during the January flood than during June or Septemb

Record flow, including runoff from previously frozen land, carri

estimated 18 million pounds of nitrogen, including large amoun

ammonia and organic nitrogen which are typically associated w

manure and wastewater discharges.

The Potomac River at Washington, D.C., carried 25 times a

much atrazine during the June flood as in September, even tho

the flow was three times greater in September. Over a 5-day p

the river carried an estimated 3,300 pounds of atrazine and 3.

lion pounds of nitrogen. On two consecutive days following the 

storm, atrazine was measured in the river at concentrations gr

than the MCL of 3 g/L.Pesticides and fertilizers are generally a

to the land in the spring, whereas nitrogen may be applied in th

of manure throughout the year.

Long-term impacts of the unprecedented flooding within th

mac River Basin during 1996 have yet to be determined; howev

USGS is currently studying aquatic vegetation downstream in 

Potomac estuary, and State and local governments are planni

sample drinking-water sources for pesticides more frequently d

peak application periods.

Figure 20. Three major floods in the Potomac River Basin during 1996

had different effects on water quality in the Potomac River at

Washington, D.C., because they occurred at different times of the year.
U.S. Geological Survey Circular 1166 

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER 

Nutrients and pesticides in streams and ground water — A regional pers

Samples from carbonate rocks

Samples from noncarbonate rocks

Lines indicate results of 

LOWESS smoothing 

(Helsel and Hirsch, 1992) 

30

20

10

0

NITRATE, IN MILLIGRAMS PER LITER

 AS NITROGEN

PERCENTAGE OF CROPLAND WITHIN 0.25 MILES 

UPGRADIENT OF SAMPLED WELL

0 75 100 25 50

Within the Potomac River Basin, streams and gro

water in the Great Valley show the greatest water-

ity effects from agricultural sources (fig. 21) beca

the valley is intensely used for crop and animal p

duction and because carbonate bedrock permits 

transportation of constituents to ground water an

streams. Much of the Great Valley is underlain by ca

ate rock which commonly contains open conduits (so

channels) created and enlarged by the action of acid

water moving through rock fractures. Rain is naturally 

ified by the dissolution of carbon dioxide in the atmosp

and can be further acidified by the introduction of nitri

sulfuric acids into the atmosphere from the combustio

fossil fuels. Chemicals at the land surface in agricultu

areas such as the Great Valley can be quickly and ea

carried to ground water through conduits in bedrock. 

chemical constituents reach the ground water in carb

rocks, they may move quickly with ground-water flow 

streams, springs, or water-supply wells. Nutrient and 

cide concentrations in ground water of carbonate area

often highly variable because the ground water respo

so quickly to precipitation and the application of fertili

and pesticides. In addition, soils derived from carbon

rocks tend to contain little organic carbon and therefo

have a reduced ability to bind to organic chemicals, s

as pesticides (Barbash and Resek, 1996).

Figure 21. Nitrate concentrations in ground-water

samples from the Potomac River Basin increase with

increasing percentages of cropland, but are typically

higher in samples from carbonate rocks like those of the

Great Valley than in samples from rocks of other types.

Photograph by James Gerhart, U.S. Geological Survey
16 Water Quality in the Potomac River Basin

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

Organic contaminants and metals in streams

EXPLANATION

Probability of organic contaminants or 

metals in streambed sediment causing 

adverse effects on aquatic life — 

Mercury and lead concentrations were 

adjusted for particle-size distributi

screening purposes

 High

 Intermediate

 Low

 Not detected

 Not sampled

Site location and number

41.9

66.6 30

25

20

15

10

5

0

30

25

20

15

10

5

0

200

150

100

50

0

Chlordane

DDT

PCBs

CONCENTRATIONS IN STREAMBED SEDIMENT, IN PARTS PER BILLION

1 3 5 7 19 9 21 11 23 13 25 15 17

SITE

408

14.5

120

100

80

40

20

60

0

1 3 5 7 19 9 21 11 23 13 25 15 17

2

Mercury

Lead

0

0.5

1

1.5

CONCENTRATIONS IN STREAMBED

 SEDIMENT, IN PARTS PER MILLION

SITE

Chlordane,3 DDT,4 PCBs,5 mercury, and lead are present in streambed

sediment and aquatic tissues in the

Potomac River Basin (fig. 22). Each of

these compounds or metals can directly

impair aquatic organisms living in or

near the streambed and can be detrimental to the health of humans or other

animals through the food chain. Lead,

mercury, chlordane, and DDT have

been designated as “toxics of concern”

to the Chesapeake Bay (U.S. Environmental Protection Agency, 1991b,c).

3

Chlordane concentrations presented are the sum of

trans-chlordane, cis-chlordane, cis-nonachlor, trans-nonachlor, and oxychlordane.

4DDT concentrations presented are the sum of

o,p’-DDT, p,p’-DDT, o,p’-DDD, p,p’-DDD, o,p’-DDE,

p,p’-DDE.

5PCB concentrations presented are the sum of all

PCB congeners.

Chambersburg

Hagerstown

Bridgeport

Gettysburg

Frederick

Leesburg

Alexandria

Annandale

Manassas

WASHINGTON

Winchester

Strasburg

Front Royal

Moorefield

Harrisonburg

Staunton

Waynesboro

Cumberland

Martinsburg

Screening thresholds for organic compounds and trace met

in streambed sediment

 A three-tiered system is used for screening measured concentrations of potent

toxic compounds in streambed sediment. Concentrations in tier 1 (greater than 

upper screening value) have a high probability of causing adverse effects on aq

life; concentrations in tier 2 (between the upper and lower screening values) hav

intermediate probability of causing adverse effects on aquatic life; and concentr

tions in tier 3 (less than both screening values) have a low probability of causing

adverse effects on aquatic life (Gilliom and others, in press). Screening levels fo

mercury, lead, DDT (Long and others,1995) and chlordane (Long and Morgan, 1

are the ERL (effects range - low) and ERM (effects range - median) developed f

bottom sediments in estuarine waters. Screening levels for PCBs are the PEL (P

able Effect Level) and TEL (Threshold Effect Level) developed by the Florida De

ment of Environmental Protection (1994). Because these values were develope

screening purposes, measurements within tiers 1 and 2 do not indicate that adv

effects have occurred at particular sampling sites.

Figure 22. Chlordane, DDT, PCBs, lead, and mercury were detected in streambed sediment at many sites throughout the

Potomac River Basin. Many concentrations were greater than screening levels, indicating that there is some potential for

these contaminants to adversely affect aquatic life.
U.S. Geological Survey Circular 1166 

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER 

Organic contaminants and metals in s

The use of chlordane, DDT, and

PCBs has been banned or restricted for

nearly two decades. The occurrence of

these compounds in streambed sediment indicates a persistent potential

for toxic effects from regional and

point sources of contamination in parts

of the Potomac River Basin

Streambed sediment

Chlorinated organic compounds

and trace metals are present in

streambed sediment of the Potomac

River and its tributaries at concentrations that have some potential to

adversely affect aquatic life. Sediment from 14 of 25 sites contained

chlordane, DDT, PCBs, lead, or mercury at concentrations that pose an

intermediate probability of causing

adverse effects on aquatic life; concentrations at six sites indicate a high

probability of causing adverse effects

on aquatic life.

Chlordane was detected in

streambed sediment from 13 of 26

sites in the Potomac River Basin,

even though most uses of chlordane

were banned in 1978 and a total ban

was implemented in 1988 (U.S. Environmental Protection Agency, 1991c,

1992, 1994a). Chlordane is a synthetic

organic compound that was primarily

applied to soil surrounding building

foundations as an insecticide to control

termites and ants. For this application,

chlordane was developed to adhere to

soil particles and to degrade slowly—

offering long-term protection from

pests. These chemical properties, however, render chlordane a persistent

problem in many streams in the Potomac River Basin.

 At least a moderate potential for

occasional adverse effects to aquatic

organisms exists at all sites where

chlordane was detected in streambed sediment. Seven of these sites are

in the Great Valley (fig. 23). Although

the Great Valley is largely agricultural

(including row crops, pasture, and

orchards), several urban and industrial

centers extend through the valley from

Waynesboro, Va., to Chambersburg,

Pa. Chlordane in this region could be

derived from a wide variety of sources

and applications.

Concentrations of chlordane in

streambed sediment indicate a high

probability for adverse effects on

aquatic biota at four sites downstream from urban areas (fig. 23).

The maximum concentration (66.6

ppb, parts per billion) was measured in

a sample from the Anacostia River

(site 22) in a tidal area near Washington, D.C. This concentration was more

than 10 times the upper screening

threshold. The second highest concentration was measured in sediment from

the North Branch Potomac River, at a

site downstream from a heavily industrialized area of Cumberland, Md.

DDT was detected in streambed

sediment from 23 of 26 sites sampled

in 1992 and 1996. DDT is an 

cide used to control mosquitoe

other pests. Its use was banned 

because of its harmful effects 

and other wildlife and its poten

cause cancer and damage the h

nervous system, liver, kidney, 

(U.S. Environmental Protectio

Agency, 1992). Its widespread 

rence in the Potomac River Ba

decades since its ban is attribu

both widespread use and chem

bility.

Although DDT was presen

large proportion of sampled 

concentrations at most sites i

little potential for adverse ef

aquatic biota. DDT concentra

sediment at seven sites indicat

erate potential for adverse effe

aquatic life. Of these, five are 

Great Valley. The application o

to orchards has been identified 

potential source of DDT in sev

streams in the central Great Va

(Gerhart and Blomquist, 1995

with chlordane, sediment from 

Anacostia River near Washing

D.C. (fig. 23) had the highest c

tration of DDT (41.9 ppb).

PCB concentrations in sed

from the South Fork Shenan

River at Front Royal, Va., in

high potential for adverse eff

aquatic life. The high levels o

at this site are attributable to a 

plant immediately upstream (V

Water Control Board, 1992). T

Figure 23. Chlordane and DDT were frequently found in streambed sediment in the Potomac River Basin, even though 

insecticides are now banned. The greatest chlordane concentrations were measured near the Washington, D.C., urba

and Cumberland, Md.; whereas the greatest DDT concentrations were measured in streams in the Great Valley.

4

2 3

1

 5

12

13 14

1615

6

7

8 19

10

9 11 20

18 17

21

25 24 23

22

26

4

2 3

1

 5

12

13 14

1615

6

7

8 19

10

9 11 20

18 17

21

25 24 23

22

26

19

High

Intermediate

Low

Not detected

Site number

EXPLANATION

Probability of chlordane or DDT in

streambed sediment causing 

adverse effects on aquatic life

CHLORDANE DDT
18 Water Quality in the Potomac River Basin

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

Organic contaminants and metals in streams

,

Known source of mercury

Sites with mercury concentration

Proportional bar showing mercury 

concentration in streambed sediment, 

in parts per million

EXPLANATION

has been closed since 1989, when the

PCB releases were discovered. Other

high levels of PCBs were measured in

sediment from the Potomac River at

Shepherdstown, W. Va. (site 11), but

no local sources have been identified

(Gerhart and Blomquist, 1995).

Mercury was detected in all

streambed sediment samples from

the Potomac River Basin and poses

a potential threat to aquatic life at

six sites (Gerhart and Blomquist,

1995). Although it occurs naturally in

trace amounts in the Earth’s crust,

mercury may be introduced as a contaminant to the environment as a consequence of human activities. Mercury

is used in the manufacture of paints,

paper, and vinyl chloride, and it can

also be found in batteries and fungicides.

High levels of mercury at three

sites are directly attributable to a

long-term industrial source of mercury contamination on the South

River in Waynesboro, Va. (fig. 24).

In 1977, mercury was found in soils at

the Waynesboro plant, where it was

used in industrial processes until 1950.

Mercury contamination may have continued at this site for several decades

prior to its discovery (Brooks, 1977).

This potentially long-term source has

led to measurable mercury contamination as far as 171 miles downstream,

near Harpers Ferry, W.Va. (fig. 24). It

is possible that the Waynesboro plant

is a contributing source of mercury

measured as far downstream as Washington, D.C., although more detailed

study would be necessary to make this

link.

Lead was detected in streambed

sediment at all 25 sampled sites in

the Potomac River Basin. The highest lead concentration (110 ppm, parts

per million) was measured in sediment

collected from the Anacostia River

near Washington, D.C., which also

contained the highest concentrations

of chlordane and DDT. Sediment from

two other sites in the Washington,

D.C., area and one in Cumberland,

Md., contained lead at concentrations

indicating a moderate potential for

adverse effects on aquatic life.

Figure 24. Mercury contamination from an industrial source in Waynesbo

(possibly lasting over a period of decades), has led to widespread contam

the South Fork Shenandoah and Shenandoah Rivers (to about 171 river 

downstream). It is possible that contamination from this source has sprea

downstream as the Potomac River at Washington, D.C. ND ND ND ND NDNDNDND

ND

140

120

100

80

60

40

20

0

10

9

8

7

6

5

4

3

2

1

CHLORDANE IN WHOLE-FISH TISSUE,

0

 IN PARTS PER BILLION

CHLORDANE IN STREAMBED SEDIMENT,

 IN PARTS PER BILLION

SAMPLED STREAMS, BY SITE NUMBER (ON FIGURE 22)

6 8 12 13 16 19 20 24 25

Fish sampled

 Yellow bullhead

 Shorthead redhorse

 White sucker

Streambed sediment

Not detected

Figure 25. Chlordane concentrations in whole-fish samples of bottom

are correlated with concentrations in streambed sediment (Gerhart an

1995). These sediments apparently serve as a source of chlordane in 

chain. One sample of shorthead redhorse (a carp-like fish) shows chl

contamination near Frederick, Md., where none exists in the streamb

This contamination may be from exposure to contamination in other lo

from historical exposure.

Each of the sediment samples containing lead at concentrations potentially harmful to aquatic life were

collected in urban and industrial areas.

Although lead occurs naturally in

trace amounts, many potential sources

of lead contamination exist, including

batteries, vehicle emissions, solder,

and corroding brass, pipes, and

plumbing. Other sources include

paints, gasoline, and lead shot,

although uses of lead for these purposes has been restricted. Sediment in

urban areas may accumula

any of these sources.

Aquatic tissues

Contaminants present 

bed sediment are bioavai

have been incorporated i

chain. Chlordane, DDT, P

cury, and lead were detecte

clam (Corbicula fluminea) 

fish tissue samples collecte

and 1996 (Zappia, 1996). O
U.S. Geological Survey Circular 1166 

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER 

Organic contaminants and metals in s

rine compounds were detected less frequently in clam tissue than in

streambed sediment, as chlordane and

DDT were detected in only 3 of 16 sites

and PCBs were detected in 4 sites

(table 3). Chlordane was generally

found in higher concentrations in

whole-fish tissue than in clams.

Streambed sediment apparently

serves as a source of chlordane to the

food chain, because chlordane concentration in fish tissue is correlated with

concentration in sediment (fig. 25).

Chlordane concentrations in fish

tissue pose a threat to fish-eating

wildlife at two sites in the Potomac

River Basin. Whole-fish tissues from

two streams in Virginia, Bull Run (site

25) and Accotink Creek (site 24), contained chlordane at concentrations

exceeding the National Academy of

Sciences, National Academy of Engineering (NAS/NAE) (1973) recommended maximum concentration for

the protection of fish-eating wildlife.

These sites are in the heavily urbanized

Washington, D.C., area. A human

health advisory including chlordane

currently exists for the consumption of

fish caught in Washington, D.C.,

waters, “due to PCBs and other compounds” (Hamid Karimi, District of

Columbia Department of Consumer

and Regulatory Affairs, written commun., 1994). Possible effects of chlordane on human health include cancer,

dizziness, headache, fatigue, and convulsions. No Asiatic clam samples contained chlordane at concentrations

threatening to humans or wildlife.

No Asiatic-clam or whole-fish

samples contained PCBs at concentrations threatening to human health

or wildlife, although human health

advisories have been issued for some

streams. Asiatic clams from the South

Fork Shenandoah River at Front Royal,

Va. (site 15), contained the highest

measured concentration of PCBs in the

basin. Human-health advisories for

PCBs in fish exist in this part of the

South Fork Shenandoah River. Humanhealth advisories also exist for other

reaches of the North Fork, South Fork,

and mainstem Shenandoah River and

for Washington, D.C., waters (Emily

Table 3. Summary of chlordane, DDT, PCB, lead and mercury concentrations in A

clam tissues and relation to standards for the protection of human health

 [ppb, parts per billion; also equivalent to micrograms per kilogram]

Compound or

metal

Number of

sites where

detected

(16 sites

sampled)

Minimum

detected

concentration

(ppb)

Maximum

detected

concentration

(ppb)

U.S. Food and

Drug

Administration

action level1

(ppb)

1

 U.S. Food and Drug Administration, 1992.

Numb

exc

sta

Chlordane 3 8.8 31.1 300 

DDT 3 5.1 12.9 5,000 

PCBs 4 140 162 2,000 

Lead 14 300 1,200 no standard 

Mercury 7 89 710 1,000 

 All samples of Asiatic clams (Corbicula fluminea) contained chlordane, DDT, and PC

concentrations well below the U.S. Food and Drug Administration action levels for pro

human health. Mercury concentrations approached the FDA action level in a sample 

South River near Waynesboro, where the greatest concentration was measured in s

sediment .

Table 4. Summary of chlordane, DDT, and PCB concentrations in whole-fish tissu

relation to criteria for the protection of fish-eating wildlife

 [ppb, parts per billion, also equivalent to micrograms per kilogram]

Compound

Number of

sites where

detected

(8 sites

sampled)

Minimum

detected

concentration

(ppb)

Maximum

detected

concentration

(ppb)

NAS/NAE

recommended

maximum

concentration for

the protection of

fish-eating

wildlife1 (ppb)

1 National Academy of Sciences, National Academy of Engineering, 1973.

Numb

exc

sta

Chlordane 4 9.6 127 100 

DDT 4 6.4 12 1,000 

PCBs 5 75 146 500 

 Two samples of bottom-feeding fish contained chlordane at concentrations greater 

NAS/NAE recommended maximum concentration for the protection of fish-eating wi

These samples, collected in 1992, show a persistence in the food chain because ch

use was restricted in 1978 and banned in 1988.

Jones, Commonwealth of Virginia,

Department of Game and Inland Fisheries, written commun., 1996; Hamid

Karimi, District of Columbia Department of Consumer and Regulatory

Affairs, written commun., 1994).

Mercury was detected in tissue

samples from nine sites, including

four sites in the Shenandoah River

watershed downstream from the

contamination source in Waynesboro, Va. Mercury was detected in

Asiatic clams from seven sites, but no

concentrations exceeded the FDA

action level for the protection of

human health in edible-shellfish tissue.

The highest measured concentration of

mercury in Asiatic clams (0.7

was detected at site 14, downs

from Waynesboro, Va. Mercur

also detected at five sites (8, 13

and 20) in fish livers, although 

action levels and NAS/NAE cr

are not applicable to fish livers

The Virginia Department of 

has established warnings to re

consumption of fish from the S

River and the South Fork of th

Shenandoah River because of 

trations of mercury in fish tiss

(Vickie Odell, Virginia Depart

Health, written and oral comm

1997).
20 Water Quality in the Potomac River Basin

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

Radon in ground water

Piedmont Province

Triassic Lowlands

Piedmont and

Valley and Ridge

Provinces

Piedmont Province

(western portion)

Valley and Ridge

Province

EXPLANATION

Predominant rock type

Crystalline

Carbonate

Siliciclastic

Maximum

75th percentile

Median

25th percentile

Minimum

Background colors in graph 

correspond to colors in 

figure 26 above

10,000

1,000

100

10

RADON ACTIVITY IN PICOCURIES PER LITER

78°

40°

79°

39°

38° 38°

77°

0 10 20 30 40 50

0 10 20 30 40 50

MILES

KILOMETERS

EXPLANATION

Median radon act

picocuries per lite

greater than 1

300 – 1,000

less than 300

unsampled a

Radon is present in ground water

throughout the Potomac River Basin.

The Federal drinking-water standard

for radon is currently under review

by the U.S. Environmental Protection

Agency; however, radon levels in 69

percent of ground-water samples

were greater than a previously proposed standard of 300 picocuries per

liter. Of 104 ground-water samples, 103

contained detectable levels of radon and

levels ranged from among the lowest to

among the highest in the Nation.

A colorless, odorless, radioactive gas,

radon forms naturally in rocks and soils

through the radioactive decay of radium,

a product of uranium decay. Radon commonly enters buildings through foundation cracks and may dissolve in ground

water and be carried into buildings

served by water supply wells. Radon

from ground water is released into

household air when water is used for

showering, washing, and other everyday purposes. According to the U.S.

Surgeon General, exposure to airborne

radon is second only to cigarette smoking as a cause of lung cancer. The risk of

cancer increases with exposure to

increasing levels of airborne radon (U.S.

Environmental Protection Agency,

1994b).

Radon activities in ground water of

the Potomac River Basin are related

to rock type. Ground-water radon activities6 are highly variable in all areas but

are typically higher in areas underlain

by crystalline rocks of the Piedmont

than in areas underlain by carbonate

rocks (figs. 26, 27). Crystalline rocks of

predominantly granitic composition,

like many of those in the Piedmont, contain more uranium, on average, than do

carbonate rocks (Faure, 1986). The part

of the Piedmont west of the Triassic

Lowlands is an exception; ground-water

radon activities in this area are typically

lower than in carbonate areas. This area

contains some granitic rocks, but many

of the crystalline rocks of this area are

not predominantly granitic like those of

the rest of the Piedmont. Rocks of this

type contain much less uranium, on

6Amounts of radioactive elements (such as radon) are

often reported in terms of activities rather than concentrations.

Figure 26. Rad

in ground wate

Potomac River 

generally highe

areas of the Pi

Province than i

the Valley and 

(modified from 

Ator, 1996).

Figure 27. Radon activities in ground water vary widely within each sample

Potomac River Basin but are generally higher in sampled areas of the Pied

vince than in those underlain by carbonate rocks (modified from Lindsey and 

average, than do granitic or carbonate

rocks (Faure, 1986).

Ground-water radon activities in

the Triassic Lowlands are among

the highest detected in the basin.

The rocks of the Triassic Lowlands

are mainly siliciclastic and extend

south from the area of Gettysburg,

Pa., to the west of Washington, D.C.,

through Maryland and Virginia.

Ground-water samples from these

rocks contained radon activities comparable to those measured in samples

from the primarily granitic ro

the Piedmont (figs. 26, 27).

Ground-water radon acti

the Valley and Ridge are gen

very low. The Valley and Rid

ers most of the basin from the 

western Maryland through ea

West Virginia and is underlain 

rily by siliciclastic rocks. Unl

ples from the siliciclastic rock

Triassic Lowlands, however, s

from these rocks typically con

very little radon (figs. 26, 27)
U.S. Geological Survey Circular 1166 

MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER 

Recent water-quality trends and 

1.000

0.100

0.010

0.001

4.0

3.0

2.0

1.0

0.0

4.0

3.0

2.0

1.0

0.0

4.0

3.0

2.0

1.0

0.0

FLOW-ADJUSTED CONCENTRATION, IN MILLIGRAMS PER LITER

Total Phosphorus

Total Nitrogen

Dissolved Nitrate as Nitrogen

Ammonia plus Organic Nitrogen as Nitrogen

1979 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 

The quality of water in aquifers and

streams of the Potomac River Basin

likely will continue to be stressed by

population growth and associated pressures well into the 21st century. Basin

population will increase by an estimated

19 percent to 6.2 million between the

years 2000 and 2020 (Carlton Haywood,

Interstate Commission on the Potomac

River Basin, oral commun., 1998).

Analysis of data collected by the

NAWQA Program suggests that,

although water quality in the basin is

improving in some respects, water managers will continue to wrestle with several long-term water-quality problems

while addressing the pressures and consequences of population growth and

associated land-use changes.

Despite an estimated 44 percent

increase in population in the Potomac

River Basin from 1970 to 1990, total

phosphorus concentrations in the

Potomac River at Washington, D.C.,

have decreased since 1979, and nitrogen concentrations have apparently

stabilized (fig. 28). Large-scale waterquality-management practices such as

improving municipal wastewater-treatment facilities and widespread implementation of phosphate-detergent bans

and agricultural best-management practices (BMPs) are apparently working

effectively to curb nutrient concentrations in the Potomac River.

Different forms of nitrogen show

conflicting patterns in long-term

trends in the Potomac River at Washington, D.C., which complicates the

forecasting of trends in nutrient concentrations (fig. 28). Improved treatment of municipal wastewater is likely

to decrease discharges of both ammonia

and organic nitrogen significantly but

increase nitrate discharge to streams.

Agricultural BMPs that minimize field

runoff and increase infiltration to ground

water may cause similar nitrate

increases in surface water by diverting

nitrogen through the ground-water system prior to its discharging to streams.

These practices may delay the movement of nitrogen to streams by years or

even decades (Focazio and others, in

press) as well as increase contamination

of ground water by nitrogen and other

agricultural chemicals. Much of the

Figure 28. Flow-adjusted nutrient concentrations in the Potomac River at

Washington, D.C., 1979-96. Total phosphorus concentrations have

decreased over this period. Recent trends in nitrogen concentrations are

more complicated; ammonia plus organic nitrogen concentrations have

decreased, whereas nitrate concentrations have increased, resulting in

apparently stable total nitrogen concentrations since about 1985

ground water underlying agricultural

lands in the Potomac River Basin

already contains elevated concentrations of nitrate and detectable concentrations of herbicides; and small

streams at base flow contain concentrations of nitrate and pesticides similar to those found in ground water. At

this point, it is impossible to predict

the long-term effect(s) that BMPs

may have on ground-water quality or

resulting effects on the Potomac River

and its tributaries.

Contamination by pesticides and

industrial compounds will likely persist in the Potomac River Basin for

years to come. Chlordane and DDT,

two long-banned insecticides, were

detected in tissues and sedim

will likely remain present at l

centrations in urban and subu

areas for the foreseeable futu

cury and PCBs will likely co

be carried downstream in sed

of the Shenandoah River from 

industrial sources until the re

of the contaminants is deplete

newly developed pesticides a

trial compounds are being rel

into the environment. The oc

of these compounds can be tr

only with continued monitori

tives.
22 Water Quality in the Potomac River Basin

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

each NAWQA Study Unit. Summary scores for each characteristic were computed

for all sites that had adequate data. Scores for each routine monitoring site in the

Potomac River Basin (fig. 29) were compared with scores for all sites sampled in

the 20 NAWQA Study Units during 1992–95. Results are summarized by

percentiles; higher percentile values 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, organochlorine pesticides, and PCBs in sediment. (Methods used to compute rankings and

evaluate aquatic-life criteria are described by Gilliom and others, in press.)

NUTRIENTS in water

Greater than the 75th percentile

(among the highest 25 percent of NAWQA

 stream sites)

Between the median and the 75th percentile

Between the 25th percentile and the median

Less than the 25th percentile

(among the lowest 25 percent of NAWQA

 stream sites)

Among sites at which longterm data were collected,

nutrient concentrations in the

Potomac River Basin were

consistently highest in streams

draining mostly agricultural

areas, particularly in Conococheague and Muddy Creeks

and the Shenandoah River,

which drain areas underlain by

carbonate rocks. Nutrient concentrations in these streams

and the Monocacy River

ranked among the highest in

the Nation, although no applicable criteria for the protection of aquatic life were

exceeded.

PCBs or organochlorine pesticides were detected in streambed sediment

or aquatic tissues at all sampled sites and the levels of these compounds

at four sites rank among the highest in the Nation. Chlordane concentrations in streambed sediment at sites on the North Branch Potomac River

and Accotink Creek exceeded threshold levels that indicate a potential to

cause adverse effects on aquatic organisms. Further sampling would be

necessary to determine possible dangers of consuming fish from these

sites (for more information, see pages 16-19).

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Comparison of Stream Quality in the Potomac River Basin

with Nationwide NAWQA Findings

Accotink Creek, which drains

a small urban basin near Washington, D.C., had the highest

concentrations of pesticides

measured in the Potomac River

Basin and ranked among the

highest observed, nationwide.

Agricultural basins (particularly cropped) also contribute

relatively large amounts of

pesticides to the Potomac

River, but less so than Accotink Creek. Concentrations

of pesticides at these sites are

similar to many sites across the

Nation. Similar concentrations

of herbicides were detected

among agricultural and urban

sites, but insecticide concentrations were higher at the urban

site. Aquatic-life criteria were

exceeded only in Accotink

Creek.

EXPLANATION

Ranking of stream quality relative to all

NAWQA stream sites - Darker colored circles generally indicate poorer quality. Bold

outline of circle indicates one or more

aquatic life criteria were exceeded.

ORGANOCHLORINE PESTICIDES and PCBs

in streambed sediment and aquatic tissues PESTICIDES in water

Poto mac River

Poto mac River
U.S. Geological Survey Circular 1166 23

Poto mac River

Trace element concentrations

in streambed sediment were

among highest in the Nation at

two of ten sampled sites in the

Potomac River Basin. Relatively high concentrations of

mercury and zinc were detected in the North Branch Potomac River at Cumberland,

Md. This site drains a coalmining region as well as nearby urban and industrial land.

Mercury concentrations in the

Shenandoah River at Millville, W. Va., were greater

than seven times the National

median (for more information, see page 18).

Stream habitats at Muddy and Accotink Creeks were among the

most degraded in the Nation. A

majority of sites in the Potomac

River Basin at which stream habitats were assessed exhibited moderate to high habitat degradation

with typically lower bank stability, increased bank erosion, and

lower densities of riparian vegetation than at less degraded sites.

Of nine sites in the Potomac

River Basin at which fish communities were analyzed, only

Muddy Creek, in an agricultural setting, was highly degraded

relative to sites nationwide. A

high percentage of fish found at

this site are pollution tolerant.

Fish communities at two other

sites were degraded to a lesser

degree but were also among the

most degraded in the Nation.

One of these sites, Conococheague Creek, drains an agricultural area and the other,

Accotink Creek, drains an

urban area near Washington,

D.C.

Concentrations of semivolatile organic compounds

(SVOCs) in streambed sediment were among the highest

in the Nation at four sites in

the Potomac River Basin.

Two of these sites are near

urban areas and the others,

the Shenandoah River and

Conococheague Creek, drain

mixed urban and agricultural

areas. Criteria for the protection of aquatic life were not

exceeded.

CONCLUSIONS

Elevated concentrations of nutrients

and pesticides in streams of the Potomac River Basin are among the highest

in the Nation at several sites and are

generally related to agricultural or urban land in the contributing watersheds. Stream habitat and fish

communities are also most degraded in

streams draining intensively agricultural or urban areas.

Concentrations of PCBs, organochlorines, trace elements, and SVOCs in

streambed sediment or aquatic tissues

at several sites are also among the

highest measured by the NAWQA Program. The most affected streams, including the North Branch Potomac,

Shenandoah, and Monocacy Rivers,

as well as Accotink Creek, typically

drain intensely agricultural or urban

areas. Criteria for the protection of

aquatic life were exceeded at some of

these sites.

TRACE ELEMENTS in streambed sediment

FISH COMMUNITY DEGRADATION

SEMIVOLATILE ORGANIC COMPOUNDS

in streambed sediment

STREAM HABITAT DEGRADATION

Poto mac River

Poto mac River

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Comparison of Stream Quality in the Potomac River Basin

with Nationwide NAWQA Findings

Poto mac River
24 Water Quality in the Potomac River Basin

EXPLANATION

Shallow drinking-water aquifers

Great Valley Carbonate, agricultural

areas

Valley and Ridge, agricultural areas

Piedmont

Triassic Lowlands

The occurrence of radon in ground

water is dependent on a number of

geologic and hydrologic factors,

especially bedrock composition.

Ground-water radon levels in the

crystalline and siliciclastic rocks

of the Piedmont and Triassic Lowlands in the eastern part of the

basin are among the highest observed nationwide. Radon activities in carbonate rocks of the

Great Valley are also relatively

high, but activities in the western

part of the Valley and Ridge are

among the lowest in the Nation.

Ranking of ground-water quality relative

to all NAWQA ground-water studies —

DW indicates ranking compared to drinkingwater aquifers (only), nationwide

SGW indicates ranking compared to shallow ground-water (only), nationwide

No label indicates comparison to DW and

SGW

Darker colored circles generally indicate

poorer quality. Bold outline of circle indicates one or more standards or criteria were

exceeded.

Five 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 had adequate data. Scores for each aquifer and shallow

ground-water area in the Potomac 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 percentile values generally

indicate poorer quality compared with other NAWQA ground-water studies. Waterquality 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 by Gilliom and

others, in press.)

DW

SGW

DW

SGW

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Comparison of Ground-Water Quality in the Potomac RIver Basin

with Nationwide NAWQA Findings

Nitrate concentrations in ground

water in carbonate rocks underlying agricultural areas of the basin

are among the highest in the Nation; nearly 25 percent of samples

contained nitrate at concentrations

exceeding the Federal drinkingwater standard. Nitrate concentrations in the Piedmont area of the

basin are also relatively high compared to other drinking-water

sources across the Nation, although no samples exceeded the

drinking-water standard. Nitrate

concentrations in the Triassic

Lowlands and under agricultural

lands in the Valley and Ridge are

relatively low.

Greater than the 75th percentile

(among the highest 25 percent of NAWQA

ground-water studies)

Between the median and the 75th percentile

Between the 25th percentile and the median

Less than the 25th percentile

(among the lowest 25 percent of NAWQA

ground-water studies)

RADON

NITRATE

DW

SGW
U.S. Geological Survey Circular 1166 

DISSOLVED SOLIDS

VOLATILE ORGANIC COMPOUNDS

Pesticide concentrations in agricultural areas of

the Great Valley Carbonate are among the highest

in the Nation; 85 percent of samples contained

detectable pesticides. Ground water in the Piedmont also contains relatively high levels of pesticides. By contrast, pesticides were detected in

only 12 percent of wells in agricultural areas of the

Valley and Ridge.

Concentrations of volatile organic compounds

(VOCs) in agricultural areas of the Great Valley

are among the lowest in the Nation. Only 6 percent

of the samples contained detectable VOCs, and no

Federal drinking-water standards were exceeded.

No other area of the Potomac River Basin was

sampled for VOCs as part of the NAWQA Program.

CONCLUSIONS

In general, the presence of pesticides, nitrate, and dissolved solids in ground water is

related to agricultural land use—particularly

in areas underlain by carbonate rocks. Potential urban sources of nitrate, pesticides,

and VOCs were not investigated.

Radon occurrence in ground water is related

to rock type. Igneous and metamorphic

rocks of granitic composition (and sedimentary rocks derived from granitic rocks) tend

to contain more uranium (Faure, 1986) and,

therefore, higher activities of radon than

rocks of other types. Uranium is often concentrated in carbonate rocks as well.

Concentrations of dissolved solids in ground

water in carbonate aquifers underlying agricultural areas of the basin are among the highest in the

Nation; 10 percent of samples exceeded the Federal drinking-water standard. Dissolved solids

concentrations in other sampled areas of the Potomac River Basin are generally lower, although the

drinking-water standard was exceeded in 14 percent of the samples from the Triassic Lowlands

and 4 percent from the Valley and Ridge.

DW

SGW

PESTICIDES

WATER-QUALITY CONDITIONS IN A NATIONAL CO

Comparison of Ground-Water Quality in the Potomac RIve

with Nationwide NAWQA F
26 Water Quality in the Potomac River Basin.

STUDY DESIGN AND DATA COLLECTION

IN THE POTOMAC RIVER BASIN

Ground-water basin-wide 

survey sites

Ground-water land-use effects 

survey sites (agriculture)

Ground-water land-use effects 

survey sites (forest)

Flow-path study site

Great Valley Carbonate

Valley and Ridge

Piedmont

Triassic Lowlands

EXPLANATION

Subunit

Sites on major tributaries

Sites on small streams

Table 5. Basic surface-water monitoring sites in the Potomac River Basin

 Number

(see fig. 29)

Name Drainage area

(square miles)

Principal land use(s)

1

2

3

4

5

6

7

8

9

10

11

North Branch Potomac River near Cumberland, Md.

South Fork South Branch Potomac River near Moorefield, W. Va.

South Branch Potomac River near Springfield, W. Va.

Conococheague Creek at Fairview, Md.

Muddy Creek at Mount Clinton, Va.

Shenandoah River at Millville, W. Va.

Catoctin Creek at Taylorstown, Va.

Monocacy River at Bridgeport, Md.

Monocacy River near Frederick, Md.

Potomac River at Chain Bridge at Washington, D.C.

Accotink Creek near Annandale, Va.

 875

283

1,470

494

14.2

3,040

89.6

173

817

11,600

23.5

Forested

Forested, agricultura

Forested, agricultura

Agricultural

Agricultural

Agricultural

Forested

Agricultural

Agricultural

Forested, agricultura

Urban

Figure 29. Stream chemistry was monitored at 11 sites in the

basin (see table 5). Of these sites, four (sites 5, 6, 8, and 11)

were also monitored more intensively for pesticides, and two

(sites 5 and 11) were monitored more intensively for ecology.

Figure 30. Streambed sediment was sampled 

sites in the basin. Of these sites, 21 were also

sampled for aquatic tissues (Asiatic clams or y

bullhead).

Figure 31. Stream-chemistry and ecological studies were

done at 89 small streams in four subunits of the basin. A

synoptic study of water chemistry was also done at 23 larger

streams throughout the basin.

Figure 32. Ground-water samples were collected a

in two subunits and at 57 sites in specific land use

other subunits. Multiple samples were collected fro

water and streams at a small-scale flow-path study 

Stream monitoring 

site

1

2

3

4

5

6 7

8

9

10

11

Sites sampled for

 streambed sediment

 aquatic tissues
U.S. Geological Survey Circular 1166 

STUDY DESIGN AND DATA COLL

IN THE POTOMAC RIVER 

Study component1 What data were collected

 and why Types of sites sampled Numberof sites

Sampling

frequency

and period

Stream chemistry

Streambed-sediment

survey

Concentrations of trace elements and organic compounds in

sediment were measured to determine their occurrence and

spatial distribution in sediments in streams of the basin.

Depositional zones of the

Potomac River and

selected tributaries.

22

4

(see fig. 30)

1

(in 1992)

1

(in 1996)

Basic sites Concentrations of major ions, suspended sediment, organic

carbon, and nutrients were measured in water samples collected monthly and during selected high flows to describe

the occurrence of those compounds in streams over time.

Streams of the basin, at or

near sites where streamflow is measured continuously.

11

(see fig. 29,

table 5)

 About 14

samples per

year,

(1993-95)

Intensive sites Concentrations of pesticides were measured in water samples

collected during selected high flows and weekly during a

growing season to determine the timing of transportation

of such compounds to streams.

Subset of basic sites,

including streams draining predominantly agricultural or urban areas.

4

(see fig. 29,

table 5)

About 24

samples per

year,

(1993-95)

Synoptic study of major

tributaries

Concentrations of major ions, nutrients, pesticides, and suspended sediment were measured in water samples collected during stable, intermediate flow to relate the

occurrence and spatial distribution of those chemical compounds to potential sources in contributing watersheds.

Selected tributaries of the

Potomac River draining

watersheds of greater

than about 100 square

miles.

23

(see fig. 31)

1

(in 1994)

Synoptic studies of small

streams

Concentrations of nutrients, pesticides, suspended sediment,

and major ions were measured in water samples collected

during low flows to determine the occurrence and spatial

distribution of those compounds in streams across the

basin and relate the stream chemistry to land use and other

watershed characteristics.

Small streams draining

watersheds of less than

37 square miles.

25

39

25

(see fig. 31)

1

(in 1993)

1

(in 1994)

1

(in 1995)

Stream ecology

Contaminants in aquatic

tissues

Concentrations of organic compounds in whole fishes and

clams and concentrations of trace metals in fish livers and

clams were measured to determine the occurrence and spatial distribution of metals and organic compounds that can

accumulate in aquatic tissues.

Subset of streambedsediment-survey sites.17

4

(see fig. 30)

1

(in 1992)

1

(in 1996)

Intensive ecological

assessments

Fish, macroinvertebrates, and algae were identified and

counted and quantitative assessments of stream habitat

were conducted to determine the variability of biological

communities and habitat representing primary ecological

regions of the basin on a small scale.

Subset of intensive sites. 2

(see fig. 29,

table 5)

1 reach per

site per year

(1993-95)

Ecological synoptic

studies

Fish, macroinvertebrates, and algae were identified and

counted and quantitative assessements of stream habitat

were conducted to determine the habitat and community

structure of aquatic species in representative streams

across the basin.

Sites sampled during synoptic studies of small

streams.

25

39

25

(see fig. 31)

1

(in 1993)

1

(in 1994)

1

(in 1995)

Ground-water chemistry

Basin-wide survey Concentrations of nutrients, pesticides, organic carbon, radon,

uranium, tritium, and major ions were measured in water

samples to describe the chemistry of ground water in the

Piedmont and Triassic Lowlands (fig. 3).

Randomly selected subset

of previously existing

shallow (mostly less than

300 feet deep) wells.

48

(see fig. 32)

1

(in 1994)

Land-use effects survey Concentrations of nutrients, pesticides, organic carbon,

radon, uranium, tritium, and major ions were measured in

water samples to describe the chemistry of ground water

within particular land-use settings and relate the differences in ground-water chemistry to natural and human factors.

Randomly selected subset

of previously existing

shallow (mostly less than

300 feet deep) wells

within agricultural or

forested areas.

54

(agriculture)

3

(forest)

(see fig. 32)

1

(29 in 1993

1

(25 in 1995

1

(3 in 1995)

Flow-path study Concentrations of nutrients, pesticides, organic carbon, radon,

uranium, tritium, and major ions were measured in water

samples to relate their occurrence and distribution on a

small scale to land use and other factors and evaluate their

transport from the land surface to ground water and from

ground water to streams.

Streams and shallow

(mostly less than 50 feet

deep) wells installed

along an approximate

line of ground-water

flow within a small (less

than 2 square miles)

watershed.

29

(see fig. 32)

1 - 10

(1993–1995

1Gerhart and Brakebill, 1997; Gilliom and others, 1995.
28 Water Quality in the Potomac River Basin

Acetochlor 11%

0%

Alachlor (Lasso) 18%

0%

2,6-Diethylaniline

(Alachlor metabolite)

<1%

0%

Atrazine (AAtrex,

Gesaprim)

76%

46%

Deethylatrazinec

(Atrazine metabolite)

62%

41%

Benfluralin (Balan,

Benefin, Bonalan)

1%

0%

Butylate (Sutan,

Genate Plus, butilate)

<1%

0%

Cyanazine (Bladex,

Fortrol)

21%

0%

DCPA (Dacthal, chlorthal-dimethyl)

1%

<1%

Dicamba (Banvel,

Mediben, dianat)

0%

1%

Dichlorprop (2,4-DP,

Seritox 50, Kildip)

1%

0%

Diuron (Karmex,

Direx, DCMU)

14%

0%

EPTC (Eptam) 1%

<1%

Linuron (Lorox,

Linex, Sarclex)

9%

0%

MCPA (Agritox,

Agroxone)

2%

0%

Metolachlor (Dual,

Pennant)

66%

17%

Herbicide

(Trade or common

name)

Rate of

detection b

Concentration, in μg/L

The following tables summarize data collected for NAWQA studies from 1992-95 by showing results for the Potomac 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 data set

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

Potomac River Basin Study Unit. [mg/L, milligrams per liter; μg/L, micrograms per liter; pCi/L, picocuries per liter; %, percent; <, less

than; - -, not measured; trade names may vary and are used for identification purposes only]

EXPLANATION

Range of surface-water detections in all 20 Study Units

Detection in the Potomac 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

Metribuzin (Lexone,

Sencor)

9%

2%

Napropamide

(Devrinol)

<1%

0%

Oryzalin (Surflan,

Dirimal, Ryzelan)

6%

0%

Pebulate (Tillam) 0%

<1%

Pendimethalin

(Prowl, Stomp)

13%

0%

Prometon (Gesagram, prometone)

59%

7%

Propachlor (Ramrod,

propachlore)

<1%

0%

Simazine (Aquazine,

Princep, Gesatop)

79%

38%

Tebuthiuron (Spike,

Perflan)

7%

4%

Terbacilc (Sinbar) 4%

<1%

Triclopyr (Garlon,

Grazon, Crossbow)

4%

0%

Trifluralin (Treflan,

Trinin, Elancolan)

<1%

<1%

Insecticide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

Azinphos-methylc

(Guthion, Gusathion)

3%

0%

Carbarylc (Sevin,

Savit)

24%

0%

0.001 0.01 0.1 1 10 100 1,000

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS

0.001 0.01 0.1 1 10 100 1,000
U.S. Geological Survey Circular 1166 29

Carbofuranc

(Furadan, Curaterr)

5%

0%

Chlorpyrifos (Dursban, Lorsban)

8%

<1%

2,4-D (2,4-PA) 20%

0%

p,p’-DDE (p,p’-DDT

metabolite)

<1%

<1%

Diazinon 24%

1%

Dieldrin (Panoram D31, Octalox)

1%

0%

Ethoprop (Mocap,

Prophos)

<1%

0%

Fonofos (Dyfonate) 1%

0%

gamma-HCH <1%

0%

Malathion (maldison,

malathon, Cythion)

4%

<1%

Methyl parathion

(Penncap-M)

2%

0%

Propoxur (Baygon,

Blattanex, Unden)

0%

1%

Volatile organic

compound

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

Methylbenzene (Toluene)

- -

6%

total Trihalomethanes - -

6%

0.01 0.1 1 10 100 1,000

Dissolved ammonia 87%

88%

Dissolved ammonia

plus organic nitrogen

as nitrogen

77%

10%

Dissolved phosphorus as phosphorus

86%

52%

Dissolved nitrite plus

nitrate

99%

74%

Other Rate

of

detection b

Concentration, in pCi/L

Radon 222 - -

99%

1 10 100 1,000 10,0000 100,000

Nutrient

(Trade or common

name)

Rate

of

detection b

Concentration, in mg/L

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

Insecticide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
30 Water Quality in the Potomac River Basin

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

Basin Study Unit.

Herbicides

2,4,5-T

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

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

Acifluorfen (Blazer, Tackle

2S)

Bentazon (Basagran, Bentazone, Bendioxide)

Bromacil (Hyvar X, Urox

B, Bromax)

Bromoxynil (Buctril, Brominal)

Chloramben (Amiben,

Amilon-WP, Vegiben)

Clopyralid (Stinger, Lontrel, Reclaim, Transline)

Dacthal mono-acid (Dacthal

metabolite)

Dinoseb (Dinosebe)

Ethalfluralin (Sonalan, Curbit)

Fenuron (Fenulon, Fenidim)

Fluometuron (Flo-Met,

Cotoran, Cottonex, Meturon)

MCPB (Thistrol)

Molinate (Ordram)

Neburon (Neburea, Neburyl, Noruben)

Norflurazon (Evital, Predict, Solicam, Zorial)

Picloram (Grazon, Tordon)

Pronamide (Kerb, Propyzamid)

Propanil (Stam, Stampede,

Wham, Surcopur, Prop-Job)

Propham (Tuberite)

Thiobencarb (Bolero, Saturn, Benthiocarb, Abolish)

Triallate (Far-Go, Avadex

BW, Tri-allate)

Insecticides

3-Hydroxycarbofuran (Carbofuran metabolite)

Aldicarb sulfone (Standak,

aldoxycarb, aldicarb metabolite)

Aldicarb sulfoxide (Aldicarb metabolite)

Aldicarb (Temik, Ambush,

Pounce)

Disulfoton (Disyston, DiSyston, Frumin AL,

Solvirex, Ethylthiodemeton)

Methiocarb (Slug-Geta,

Grandslam, Mesurol)

Methomyl (Lanox, Lannate, Acinate)

Oxamyl (Vydate L, Pratt)

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

Phorate (Thimet, Granutox,

Geomet, Rampart)

Propargite (Comite, Omite,

Ornamite)

Terbufos (Contraven,

Counter, Pilarfox)

alpha-HCH (alpha-BHC,

alpha-lindane, alphahexachlorocyclohexane,

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)

1-Chloro-4-methylbenzene (p-Chlorotoluene)

2,2-Dichloropropane

Benzene

Bromobenzene (Phenyl

bromide)

Bromochloromethane

(Methylene chlorobromide)

Bromomethane (Methyl

bromide)

Chlorobenzene

(Monochlorobenzene)

Chloroethane (Ethyl chloride)

Chloroethene (Vinyl Chloride)

Chloromethane (Methyl

chloride)

Dibromomethane (Methylene dibromide)

Dichlorodifluoromethane

(CFC 12, Freon 12)

Dichloromethane (Methylene chloride)

Dimethylbenzenes

(Xylenes (total))

Ethenylbenzene (Styrene)

Ethylbenzene (Phenylethane)

Hexachlorobutadiene

Isopropylbenzene

(Cumene)

Methyl tert-butyl ether

(MTBE)

Naphthalene

Tetrachloroethene (Perchloroethene)

Tetrachloromethane (Carbon tetrachloride)

Trichloroethene (TCE)

Trichlorofluoromethane

(CFC 11, Freon 11)

cis-1,2-Dichloroethene

((Z)-1,2-Dichloroethene)

cis-1,3-Dichloropropene

((Z)-1,3-Dichloropropene)

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-Dichloroethene

(Vinylidene chloride)

1,1-Dichloropropene

1,2,3-Trichlorobenzene

(1,2,3-TCB)

1,2,3-Trichloropropane

(Allyl trichloride)

1,2,4-Trichlorobenzene

1,2,4-Trimethylbenzene

(Pseudocumene)

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)

n-Butylbenzene (1-Phenylbutane)

n-Propylbenzene (Isocumene)

p-Isopropyltoluene (pCymene)

sec-Butylbenzene

tert-Butylbenzene

trans-1,2-Dichloroethene

((E)-1,2-Dichlorothene)

trans-1,3-Dichloropropene

((E)-1,3-Dichloropropene)

Nutrients

No non-detects

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
U.S. Geological Survey Circular 1166 31

1,2,4-Trichlorobenzene

- -

20%

1,2-Dimethylnaphthalene

- -

20%

1,4-Dichlorobenzene - -

33%

1,6-Dimethylnaphthalene

- -

67%

1-Methyl-9H-fluorene - -

85%

1-Methylphenanthrene

- -

80%

1-Methylpyrene - -

60%

2,3,6-Trimethylnaphthalene

- -

43%

2,4-Dinitrotoluene - -

43%

2,6-Dimethylnaphthalene

- -

100%

2,6-Dinitrotoluene - -

33%

2-Chlorophenol - -

50%

2-Methylanthracene - -

73%

3,5-Dimethylphenol - -

20%

4,5-Methylenephenanthrene

- -

60%

4-Bromophenyl-phenylether

- -

33%

Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg

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

4-Chloro-3-methylphenol

- -

33%

4-Chlorophenyl-phenylether

- -

33%

9H-Carbazole - -

75%

9H-Fluorene - -

67%

Acenaphthene - -

78%

Acenaphthylene - -

91%

Acridine - -

78%

Anthracene - -

90%

Anthraquinone - -

91%

Azobenzene - -

56%

Benz[ a ]anthracene - -

100%

Benzo[ a ]pyrene - -

96%

Benzo[ b ]fluoranthene

- -

95%

Benzo[ c ]cinnoline - -

56%

Benzo[ ghi ]perylene - -

71%

Benzo[ k ]fluoranthene

- -

95%

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

bed sediment of the Potomac River Basin Study Unit. [μg/g, micrograms per gram; μg/kg, micrograms per kilogram; %, percent; <, less

than; - -, not measured; trade names may vary]

EXPLANATION

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

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

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

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
32 Water Quality in the Potomac River Basin

Butylbenzylphthalate - -

86%

Chrysene - -

100%

Di- n -butylphthalate - -

100%

Di- n -octylphthalate - -

40%

Dibenz[ a,h ]

anthracene

- -

67%

Dibenzothiophene - -

80%

Diethylphthalate - -

100%

Dimethylphthalate - -

67%

Fluoranthene - -

100%

Indeno[1,2,3- cd ]

pyrene

- -

82%

Isophorone - -

20%

Isoquinoline - -

50%

Naphthalene - -

69%

N-Nitrosodi- n -

propylamine

- -

20%

Phenanthrene - -

96%

Phenanthridine - -

81%

Phenol - -

94%

Pyrene - -

100%

bis(2-Chloroethoxy)methane

- -

56%

bis(2-Ethylhexyl)phthalate

- -

100%

p-Cresol - -

95%

Organochlorine

compound

(Trade name)

Rate

of

detection b

Concentration, in μg/kg

total-Chlordane 26%

48%

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

Chloroneb (chloronebe)

- -

4%

Dieldrin (Panoram D31, Octalox)

13%

36%

PCB, total 39%

68%

DCPA (dacthal, chlorthal-dimethyl)

3%

4%

p,p’-DDE 16%

88%

total-DDT 26%

88%

beta-HCH (betaBHC, beta-hexachlo10%

0%

gamma-HCH (lindane, gamma-BHC)

0%

4%

Heptachlor epoxide 13%

12%

Heptachlor (heptachlore, Velsicol)

3%

8%

p,p’-Methoxychlor

(Marlate)

3%

4%

Pentachloroanisole 3%

8%

Toxaphene (camphechlor)

0%

4%

Trace element Rate

of

detection b

Concentration, in μg/g

Arsenic 80%

48%

Cadmium 96%

100%

Chromium 100%

100%

Copper 100%

100%

Lead 72%

100%

Mercury 56%

100%

Nickel 100%

100%

Selenium 96%

100%

Zinc 100%

100%

0.01 0.1 1 10 100 1,000 10,000

Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg

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

Organochlorine

compound

(Trade name)

Rate

of

detection b

Concentration, in μg/kg

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

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
U.S. Geological Survey Circular 1166 33

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

of the Potomac River Basin Study Unit.

Semivolatile

organic

compounds

1,2-Dichlorobenzene

(o-Dichlorobenzene,

1,2-DCB)

1,3-Dichlorobenzene

(m-Dichlorobenzene)

2,2-Biquinoline

2-Chloronaphthalene

2-Ethylnaphthalene

C8-Alkylphenol

N-Nitrosodiphenylamine

Nitrobenzene

Pentachloronitrobenzene

Quinoline

Organochlorine

compounds

Aldrin (HHDN, Octalene)

Endosulfan I (alphaEndosulfan, Thiodan,

Cyclodan, Beosit,

Malix, Thimul, Thifor)

Endrin (Endrine)

Hexachlorobenzene

(HCB)

Isodrin (Isodrine, Compound 711)

Mirex (Dechlorane)

alpha-HCH (alphaBHC, alpha-lindane,

alpha-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

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 non-detects

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 only counting detections equal to or greater than 0.01 μg/L to facilitate equal comparisons among compounds that had

varying detection limits; a value of <1% signifies that there were only detection below, or <1% above, the 1μg/L level. Some herbicides and insecticides were not reliably detected as low as the 0.01μg/L level, so frequencies may be underestimated for some compounds. For other compound

groups, all detections were counted and detection limits for most compounds were similar to the lower end of the national ranges shown. Method

detection limits for all compounds in all groups 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
34 Water Quality in the Potomac River Basin

REFERENCES

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the Environment (3d ed.): New

York, New York University Press,

423 p.

Ator, S.W., and Denis, J.M., 1997,

Relation of nitrogen and phosphorus in ground water to land

use in four subunits of the Potomac River Basin: U.S. Geological

Survey Water-Resources Investigations Report 96-4268, 26 p.

Barbash, J.E., and Resek, E.A., 1996,

Pesticides in ground water – Distribution, trends, and governing

factors: Ann Arbor Press,

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Geologic Survey, 4th Series, 1

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Blomquist, J.D., Fisher, G.T., Denis,

J.M., Brakebill, J.W., and

Werkheiser, W.H., 1996, Waterquality assessment of the Potomac River Basin – Analysis of

available nutrient data, 1970-90:

U.S. Geological Survey WaterResources Investigations Report

95-4221, 88 p.

Brooks, K.M., 1977, Critical areas in

the Potomac River Basin, A mid1977 review of water-pollution

control: Interstate Commission on

the Potomac River Basin Technical Publication 77-3, 77 p.

Canadian Council of Resource and

Environment Ministers, 1991,

Canadian water-quality guidelines: Ottawa, Ontario, Environment Canada, Inland Waters

Directorate, Water Quality

Branch.

Cardwell, D.H., Erwin, R.B., and

Woodward, H.P., compilers.,

1968 (slightly revised 1986),

Geologic map of West Virginia:

West Virginia Geological and

Economic Survey, 2 sheets, scale

1:250,000.

Cleaves, E.T., Edwards, Jonathan, Jr.,

and Glaser, J.D., compilers.,

1968, Geologic map of Maryland:

Maryland Geological Survey, 1

sheet, scale 1:250:000.

Darrell, L.C., Hazelwood, B.K., and

Schwarz, G.W., in press, Comparison of loads and trends in total

nitrogen, total phosphorus, and

suspended material for the Potomac River at Chain Bridge, 1985-

95: Metropolitan Washington

Council of Governments.

Faure, Gunter, 1986, Principles of isotope geology: New York, John

Wiley and Sons, Inc., 589 p.

Fenneman, N.M., and Johnson, D.W.,

1946, Physical divisions of the

United States: U.S. Geological

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Ferrari, M.J., and Ator, S.W., 1995,

Nitrate in ground water of the

Great Valley Carbonate Subunit

of the Potomac River Basin: U.S.

Geological Survey WaterResources Investigations Report

95-4099, 6 p.

Florida Department of Environmental

Protection, 1994, Approach to the

assessment of sediment quality in

Florida coastal waters, Vol. 1,

Development and evaluation of

sediment quality area assessment

guidelines: prep. for FDEP, Office

of Water Policy, Tallahassee,

Florida, by MacDonald Environmental Services, Ltd., Ladysmith,

British Columbia.

Focazio, M.J., Bachman, L.J., 

J.K., Busenberg, E., Plum

L.N., and Powars, D.S., i

Preliminary estimates of 

dence times and apparent 

ground water in the Ches

Bay watershed and water

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97-4225, in press.

Gerhart, J.M., and Blomquist, 

1995, Selected trace-elem

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Geological Survey Water

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95-4267, 12 p.

Gerhart, J.M., and Brakebill, J

1997, Design and implem

of a sampling strategy for 

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Gianessi, L.P, and Puffer, C.A

(revised 1991), Herbicide 

the United States: Resour

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ronment Division, Washin

D.C., 128 p.

____1992a, Fungicide use in U

production: Resources fo

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____1992b, Insecticide use in 

crop production: Resourc

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[variously paged].
U.S. Geological Survey Circular 1166 

REFER

Gilliom, R.J., Alley, W.M., and Gurtz,

M.E., 1995, Design of the

National Water-Quality Assessment program – Occurrence and

distribution of water-quality conditions: U.S. Geological Survey

Circular 1112, 33 p.

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

Nowell, L.H., in press, Methods

for comparing water-quality conditions among National WaterQuality Assessment Study Units.

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Hitt, K.J., 1994, Refining 1970’s landuse data with 1990 population

data to indicate new residential

development: U.S. Geological

Survey Water-Resources Investigations Report 94-4250, 15 p.

Helsel, D.R., and Hirsch, R.M., 1992,

Statistical methods in water

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Publ., 522 p.

International Joint Commission Canada and United States, 1977, New

and revised Great Lakes waterquality objectives, Volume II, An

IJC report to the governments of

the United States and Canada:

IJC, Windsor, Ontario, Canada.

King, P.B. and Beikman, H.M., 1974,

Geologic map of the United

States: U.S. Geological Survey, 3

sheets, scale 1:2,500,000.

Lindsey, B.D., and Ator, S.W., 1996,

Radon in ground water of the

Lower Susquehanna and Potomac

River Basins: U.S. Geological

Survey Water-Resources Investigations Report 96-4156, 6 p.

Lizarraga, J.S., in press, Estimation

and analysis of nutrient and suspended-sediment loads at selected

sites in the Potomac River Basin,

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Water-Resources Investigations

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Long, E.R., MacDonald, D.D., Smith,

S.L., and Calder, F.D., 1995, Incidence of adverse biological

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Long, E.R., and Morgan, L.G., 1990,

The potential for biological

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National Oceanic and Atmospheric Administration, Technical

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Miller, C.V., Denis, J.M., Ator, S.W.,

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D.R., Hitt, K.J., and Ruddy, B.C.,

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36 Water Quality in the Potomac River Basin

REFERENCES

U.S. Food and Drug Administration,

1992, Action levels for poisonous or deleterious substances in

human food and animal feed

(8/92): Department of Health and

Human Services, Washington,

D.C., 16 p.

Virginia Water Control Board, 1992,

Virginia water quality assessment

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Board Information Bulletin #588,

v. 2, 444 p.

Vogelmann, J.E., Sohl, T.L., Campbell,

P.V., and Shaw, D.M., 1997,

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the tools to meet the Nation’s

monitoring needs – The evolution

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Zappia, Humbert, 1996, Chlordane,

DDT, PCB’s and other selected

organic compounds in Asiatic

clams and yellow bullhead in the

Potomac River Basin, 1992: U.S.

Geological Survey WaterResources Investigations Report

96-4210, 12 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

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U.S. Geological Survey OpenFile Report 95-181, 49 p.
U.S. Geological Survey Circular 1166 

GLO

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.

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.

Aquifer - A water-bearing layer of

soil, sand, gravel, or rock that will

yield usable quantities of water to

a well.

Basin - See Drainage basin.

Bedrock - General term for consolidated (solid) rock that underlies

soils or other unconsolidated

material.

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

watercourse.

Carbonate rocks - Rocks (such as

limestone or dolostone) that are

composed primarily of minerals

(such as calcite and dolomite)

containing the carbonate ion

(CO3

2-).

Community - In ecology, the species

that interact in a common area.

Concentration - The amount or mass

of a substance present in a given

volume or mass of sample. Usually expressed as micrograms per

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

tissue sample).

Crystalline rocks - Rocks (igneous or

metamorphic) consisting wholly

of crystals or fragments of crystals.

Degradation products - Compounds

resulting from transformation of

an organic substance through

chemical, photochemical, and(or)

biochemical reactions.

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.

Drainage basin - The portion of the

surface of the Earth that contributes water to a stream through

overland runoff, including tributaries and impoundments.

Ecosystem - The interacting populations of plants, animals, and

microorganisms occupying an

area, plus their physical environment.

Evapotranspiration - A collective

term that includes water lost

through evaporation from the soil

and surface-water bodies and by

plant transpiration.

FDA action level - A regulatory level

recommended by the U.S. Environmental Protection Agency for

enforcement by the FDA when

pesticide residues occur in food

commodities for reasons other

than the direct application of the

pesticide. Action levels are set for

inadvertent pesticide residues

resulting from previous legal use

or accidental contamination.

Applies to edible portions of fish

and shellfish in interstate commerce.

Fish community - See Community.

Ground water - In general, any water

that exists beneath the land surface, but more commonly applied

to water in fully saturated soils

and geologic formations.

Habitat - The part of the phys

environment where plant

animals live.

Health advisory - Nonregulat

els of contaminants in dri

water that may be used as 

ance in the absence of reg

limits. Advisories consist 

mates of concentrations t

would result in no known 

anticipated health effects 

cinogens, a specified canc

determined for a child or 

adult for various exposur

ods.

Herbicide - A chemical or oth

applied for the purpose o

undesirable plants. See al

cide.

Infiltration - Movement of wa

ically downward, into soi

porous rock.

Insecticide - A substance or m

of substances intended to 

or repel insects.

Invertebrate - An animal hav

backbone or spinal colum

Karst - A type of topography 

results from dissolution a

lapse of carbonate rocks s

limestone and dolomite a

acterized by closed depres

sinkholes, caves, and und

ground drainage.

Load - General term that refer

material or constituent in 

or suspension in transpor

ally expressed in terms of 

volume.

Maximum contaminant level 

- Maximum permissible l

contaminant in water that 

ered to any user of a publ

system. MCL's are enforc

standards established by t
38 Water Quality in the Potomac River Basin

GLOSSARY

Environmental Protection

Agency.

Nitrate - An ion consisting of nitrogen

and oxygen (NO3

-

). Nitrate is a

plant nutrient and is very mobile

in soils.

Nutrient - Element or compound

essential for animal and plant

growth. Common nutrients in fertilizer include nitrogen, phosphorus, and potassium.

Pesticide - A chemical applied to

crops, rights of way, lawns, or

residences to control weeds,

insects, fungi, nematodes,

rodents, or other "pests."

Phosphorus - A nutrient essential for

growth that can play a key role in

stimulating aquatic growth in

lakes and streams.

Photosynthesis - Synthesis of chemical compounds by organisms with

the aid of light. Carbon dioxide is

used as raw material for photosynthesis and oxygen is a product.

Physiography - A description of the

surface features of the Earth, with

an emphasis on the origin of landforms.

Picocurie (pCi) - One trillionth (10-12)

of the amount of radioactivity

represented by a curie (Ci). A

curie is the amount of radioactivity that yields 3.7 x 1010 radioactive disintegrations per second

(dps). A picocurie yields 2.22 disintegrations per minute (dpm) or

0.037 dps.

Precipitation - Any or all forms of

water particles that fall from the

atmosphere, such as rain, snow,

hail, and sleet.

Radon - A naturally occurring, colorless, odorless, radioactive gas

formed by the disintegration of

the element radium; damaging to

human lungs when inhaled.

Siliciclastic rocks - Rocks such as

shale and sandstone that are

formed by the compaction and

cementation of quartz-rich mineral grains.

Triazine herbicide - A class of herbicides containing a symmetrical

triazine ring (a nitrogen-heterocyclic ring composed of three nitrogens and three carbons in an

alternating sequence). Examples

include atrazine, propazine, and

simazine.

Triazine pesticide - See Triazine herbicide.

Uranium - A heavy silvery-white

metallic element, highly radioactive and easily oxidized. Of the 14

known isotopes of uranium, 238U

is the most abundant in nature.

Watershed - See Drainage basin.

Water year - The continuous 12-

month period, October 1 through

September 30, in U.S. Geological

Survey reports dealing with the

surface-water supply. The water

year is designated by the calendar

year in which it ends and which

includes 9 of the 12 months.

Thus, the year ending September

30, 1980, is referred to as the

“1980” water year.
Ator and others • Water Quality in the Potomac River Basin

 USGS Circular 1166 • 1998

PENNSYLVANIA

WEST

VIRGINIA

VIRGINIA

Potomac River

MARYLAND

WASHINGTON DC

Baltimore

Potomac River

Annapolis

National Water-Quality Assessment (NAWQA) Program

Potomac River Basin

NAWQA