science for a changing world 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 A COORDINATED EFFORT

Coordination among agencies and organizations is an integral part of the NAWQA Program. We thank the following 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 design and results. District of Columbia Department of Consumer and Resources for the Future Regulatory Affairs U.S. Army Corps of Engineers District of Columbia Water Resources Research Institute, U.S. Department of Agriculture, Agricultural Research Service University of the District of Columbia U.S. Department of Agriculture, Natural Resources Interstate Commission on the Potomac River Basin Conservation Service Johns Hopkins University U.S. Environmental Protection Agency, Maryland Department of the Environment Chesapeake Bay Program Maryland Department of Natural Resources, U.S. Environmental Protection Agency, Region III Maryland Geological Survey U.S. Fish and Wildlife Service Maryland Water Resources Research Institute, Virginia Department of Environmental Quality University of Maryland Virginia Division of Mineral Resources Metropolitan Washington Council of Governments Virginia Water Resources Research Institute, Virginia National Park Service Polytechnic Institute and State University Pennsylvania Department of Conservation & Natural Resources, West Virginia Department of Environmental Protection Bureau of Topographic and Geologic Survey West Virginia Geological and Economic Survey Pennsylvania Department of Environmental Resources, West Virginia Water Resources Institute, Division of Assessments and Standards West Virginia University Pennsylvania Environmental Resources Research Institute, Pennsylvania State University

Data for this report were collected by many people, including John Battista, Bruce Bernard, Amy Derosier, Gary Fisher, James Gerhart, Liz Gno, Michael Hackney, Kalman Illyefalvi, Phyllis Illyefalvi, James Jeffries, Jon Kaye, Sarah Kelley, 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 Gerhart, U.S. Geological Survey

FOR ADDITIONAL INFORMATION ON THE NATIONAL WATER-QUALITY ASSESSMENT (NAWQA) PROGRAM: Potomac River Study Unit, contact: District Chief Chief, NAWQA Program U.S. Geological Survey U.S. Geological Survey Water Resources Division Water Resources Division 8987 Yellow Brick Road 12201 Sunrise Valley Drive, M.S. 413 Baltimore, MD 21237 Reston, VA 20192

Information on the NAWQA Program is also available on the Internet via the World Wide Web. You may connect to the NAWQA Home Page using the Universal Resources Locator (URL): http://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/ Water Quality in the Potomac River Basin, Maryland, Pennsylvania, Virginia, West Virginia, and the District of Columbia, 1992–96

By Scott W. Ator, Joel D. Blomquist, John W. Brakebill, Janet M. Denis, Matthew J. Ferrari, Cherie V. Miller, and Humbert Zappia U.S. GEOLOGICAL SURVEY CIRCULAR 1166

CONTENTS

National Water-Quality Assessment Program...... 1 Summary of major issues and findings ...... 2 Environmental setting ...... 4 Hydrologic conditions...... 5 Major issues and findings ...... 6 Nutrients and pesticides in streams and ground water ...... 6 Nutrients ...... 6 Pesticides...... 10 Organic contaminants and metals in streams...... 16 Streambed sediment ...... 17 Aquatic tissues...... 18 Radon in ground water ...... 20 Recent water-quality trends and outlook ...... 21 Water-quality conditions in a national context...... 22 Study design and data collection...... 26 Summary of compound detections and concentrations...... 28 References...... 34 Glossary...... 37 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY Thomas J. Casadevall, Acting Director

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

1998

Free on application to the U.S. Geological Survey Information Services Box 25286 Federal Center Denver, CO 80225

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 NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

“Potomac NAWQA studies are contributing valuable EXPLANATION information on water quality/ Began in 1991 land use issues vital to Began in 1994 Began in 1997 effective management of the Not scheduled yet Chesapeake Bay ecosys- tem.”

—Dr. Emery Cleaves, Knowledge of the quality of the Nation's streams and aquifers is important because Director, Maryland of the implications to human and aquatic health and because of the significant costs associated with decisions involving land and water management, conservation, and Geological Survey, regulation. In 1991, the U.S. Congress appropriated funds for the U.S. Geological Baltimore, Maryland 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 under- “As one involved in sharing standing of the effects of human actions and natural factors on water quality condi- information with both the tions. public and other agencies The NAWQA Program is assessing the water-quality conditions of more than 50 of addressing water resources 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 issues in the Shenandoah drinking water used by about 70 percent of the U.S. population. Comprehensive River Basin, the Potomac assessments of about one-third of the Study Units are ongoing at a given time. Each NAWQA study has been Study Unit is scheduled to be revisited every decade to evaluate changes in water- quite helpful. This particular quality conditions. NAWQA assessments rely heavily on existing information col- publication, summarizing a lected by the USGS and many other agencies as well as the use of nationally consis- considerable amount of tent study designs and methods of sampling and analysis. Such consistency simulta- neously provides information about the status and trends in water-quality conditions water quality data through in a particular stream or aquifer and, more importantly, provides the basis to make informative graphics and comparisons among watersheds and improve our understanding of the factors that excellent maps, should affect water-quality conditions regionally and nationally. serve as a convenient refer- This report is intended to summarize major findings that emerged between 1992 ence to others interested in and 1995 from the water-quality assessment of the Potomac River Basin Study Unit knowing more about our and to relate these findings to water-quality issues of regional and national concern. valuable water resources.” 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, pub- —Thomas Mizell, lic officials, and members of stakeholder groups who provided advice and input to the Virginia Department of USGS during this NAWQA Study-Unit investigation. Yet, the information contained Environmental Quality, here may also interest those who simply wish to know more about the quality of water Harrisonburg, Virgina. in the rivers and aquifers in the area where they live.

Robert M. Hirsch, Chief Hydrologist

U.S. Geological Survey Circular 1166 1 SUMMARY OF MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

PENNSYLVANIA

MARYLAND

WEST VIRGINIA D.C.

VIRGINIA

Nutrients and pesticides in Pesticides can make water unfit to drink and streams and ground water cause adverse ecological effects in streams. Com- monly used pesticides are present in ground A regional perspective water in the Potomac River Basin, but in most cases at concentrations that are not threatening Although nitrogen and phosphorus occur natu- to human health. rally and are essential for the growth of plants (p. 10) and animals, excessive nutrients in water can adversely affect human health and the environ- More pesticides were detected in streams than in ment. Elevated concentrations of nitrogen and ground water, but only rarely at concentrations phosphorus in streams and ground water of the threatening to aquatic life. Potomac River Basin often result from human (p. 11) activities such as manure and fertilizer applica- Pesticides were commonly detected in agricul- tions. tural areas of the Potomac River Basin, particu- (p. 6) larly in areas of intense crop production such as Nutrient inputs to the Potomac River Basin are the corn-producing northeastern counties and in related to land use. Agricultural areas receive the the Great Valley. Samples from forested areas largest amounts of nutrients because manure and rarely contained detectable pesticides. fertilizer applications comprise 45 percent of (p. 12-13) nitrogen and 93 percent of phosphorus inputs. Pesticides were frequently present in streams in (p. 6) urban areas; insecticide concentrations were greatest in urban streams. In most waters of the Potomac River Basin, con- (p. 13) centrations of nutrients do not pose a threat to human health or wildlife. Maximum concentrations of most pesticides (p. 7) occur in streams during the spring and early sum- mer months, coincident with their application to Elevated nitrogen concentrations in streams and fields, although atrazine and metolachlor are ground water are common in areas of intensive present year round in streams in agricultural row cropping, such as the northeastern part of the areas. Potomac River Basin, and areas underlain by car- (p. 14) bonate bedrock, such as the Great Valley. (p. 8) Spring floods carry large amounts of nutrients and pesticides. A June 1996 flood on the Poto- Organic nitrogen and phosphorus concentrations mac River at Washington, D.C., carried an esti- are typically low, except in streams during high mated 3,300 pounds of atrazine and 3,300,000 flows. pounds of nitrogen. (p. 9) (p. 14) Tributary streams draining agricultural areas Higher concentrations of agricultural chemicals yield the greatest quantities of nitrogen to the are found in streams in the Great Valley than in Potomac River; streams draining agricultural and other agricultural areas, presumably because car- urban areas yield the greatest quantities of phos- bonate bedrock permits relatively rapid move- phorus. ment of these chemicals through ground water to (p. 9) streams. (p. 15)

2 Water Quality in the Potomac River Basin SUMMARY OF MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN

Organic contaminants and metals Radon in ground water in streams Radon is present in ground water throughout the Chlorinated organic compounds, mercury, and Potomac River Basin. lead are present in streambed sediment at con- (p. 20) centrations that have some potential to adversely The Federal drinking-water standard for radon is affect aquatic life. currently under review by the U.S. Environmen- (p. 16) tal Protection Agency; however, radon levels in Although its use was banned in 1988, chlordane 69 percent of ground-water samples were greater was detected in streambed sediment from 13 of than a previously proposed standard of 300 pico- 26 sites, including 4 sites at which concentrations curies per liter. pose a high potential for adverse effects on (p. 20) aquatic life. (p. 17) Radon in ground water is related to rock type, and levels are highest in eastern parts of the basin The use of DDT was banned in 1972 but it was underlain by crystalline and siliciclastic rocks. detected in streambed sediment at most sites, (p. 20) although concentrations typically pose little risk to aquatic life. (p. 17) Recent water-quality trends Mercury from an industrial plant in Waynesboro, and outlook Va., possibly over a period of decades, has Despite an estimated 44-percent increase in pop- caused elevated concentrations of mercury in ulation in the Potomac River Basin from 1970 to sediments downstream from the plant in the 1990, total phosphorus concentrations in the Shenandoah River, a major Potomac tributary. Potomac River at Washington, D.C., have (p. 18) decreased since 1979, and nitrogen concentra- tions have apparently stabilized. The organic compounds and metals present in (p. 21) streambed sediment have been incorporated into the food chain. Different forms of nitrogen show differing pat- (p. 18) terns in long-term trends in the Potomac River at Washington, D.C.; ammonia plus organic nitro- gen concentrations have decreased, whereas nitrate concentrations have increased. (p. 21)

Photograph by James Gerhart, U.S. Geological Survey

U.S. Geological Survey Circular 1166 3 ENVIRONMENTAL SETTING IN THE POTOMAC RIVER BASIN

78° Figure 1. Generalized land use in the 40° Cr Potomac River Basin (modified from e u g ea Vogelmann and others, 1997; and Hitt, h r c C o 77° ° c m 1994). The basin is predominantly 79 R o ta e n tl y

o n c forested, with smaller areas of C a A c n o n agriculture and urban development. o

h M nc ra r C B h th c n Poto r n o m o a R a r u c N n q R R B o e h p p h t a a u p O o o a d S n a C a i

n t s R

e r o ° h e C c 39 S os R o a n c k G A a r k Accot o r i m F o n to F k WASHINGTON, D.C. th o r th C 60 P o u o r r N S B R S O n r c a 50 k C co q u F y S d d u 40

M 30 EXPLANATION Poto mac R 20 Urban

38° Agriculture 38° 10 0 Forest AREA OF BASIN PERCENTAGE 0 1020304050MILES Water

0 1020304050KILOMETERS Other Urban Forest Agriculture LAND USE Figure 2. Major land use in the Potomac River Basin, 1990-94 (modified from Vogelmann and others, 1997; and Hitt, 78° 40° 1994).

° 79° 77 2,998 2,794 93 2,130 71

700 22 (3,856) GROUND WATER 600 20 SURFACE WATER 18 500 (3,856) POPULATION SERVED, ° 16 39 IN THOUSANDS WASHINGTON, D.C. 14 400 12 300 10 8 200 6 WATER WITHDRAWALS, WATER

EXPLANATION 4 WATER WITHDRAWALS 100 (798) PERCENTAGE OF TOTAL

Rock Types IN MILLIONS OF GALLONS PER DAY 2 Unconsolidated 0 0 Carbonate TOTAL MINING Siliciclastic SUPPLY THERMO-

° ° ELECTRIC

38 38 DOMESTIC Crystalline LIVESTOCK COMMERCIAL PUBLIC SUPPLY

0 1020304050MILES AND IRRIGATION INDUSTRIAL AND INDUSTRIAL 0 1020304050KILOMETERS ESTIMATED WATER WITHDRAWALS IN 1990

Figure 3. Generalized geology and physiography in the Figure 4. Freshwater withdrawals in the Potomac Potomac River Basin (modified from Fenneman and Johnson, River Basin (data from H.A. Perlman, U.S. 1946; Milici and others, 1963; Cardwell and others, 1968; Geological Survey, written commun., 1993). Most Cleaves and others, 1968; King and Beikman, 1974; and Berg, of the surface water withdrawn from the Potomac 1980). Unconsolidated deposits occur mainly in the Coastal River Basin is used for the generation of electricity Plain and in isolated areas of alluvial deposits along stream and for public supply. Ground water in the basin is channels in the Valley and Ridge. Crystalline rocks underlie used mainly for domestic and public supply. Water only the Piedmont and Blue Ridge in the central and eastern is also withdrawn from the basin for various parts of the basin. The entire basin west of the Blue Ridge is commercial, industrial, and agricultural purposes. underlain by sedimentary rocks; these rocks are mainly siliciclastic, with areas of extensive carbonate rocks, particularly in the Great Valley.

4 Water Quality in the Potomac River Basin HYDROLOGIC CONDITIONS IN THE POTOMAC RIVER BASIN, 1992-96

100 25,000 100,000 Precipitation at Eisenhower National Historic Site, Pa. Period of most intensive stream sampling 80 20,000 10,000 Flow in Monocacy River at Bridgeport, Md. 15,000 60 1 1,000 LTA 11,710 10,000 23,760 18,830 40 17,460 100 5,000 8,832 8,698 ANNUAL MEAN FLOW,

10 20 IN CUBIC FEET PER SECOND 0

FLOW, IN CUBIC FEET PER SECOND PER FEET CUBIC IN FLOW, WY1992 WY1993 WY1994 WY1995 WY1996

MONTHLY PRECIPITATION, IN INCHES 1 1 0 LTA - Long term average discharge for period of record (1959-96) WY- Water Year (WY1992— October 1991- September 1992) 12 100 Precipitation at Savage River Dam, Md. 13 Period of ground-water sampling 80 Figure 6. Mean annual streamflow of the Potomac River at 14 Water level in well "AL Ca 19", Allegany County, Md. Washington, D.C. Streamflow can vary considerably from 15 year to year. Flow of the Potomac River at Washington, D.C., 60 16 did not exceed flood level in 1992 or 1995; however, 17 occasional flooding did occur in 1993, 1994, and 1996 and

18 40 locally on some tributaries throughout the study period.

19 Floods occurred mostly during the months of winter and early spring. Near-drought conditions occurred for short periods in 20 20 the late summer or fall of 1992, 1993, and 1995. 21

MONTHLY PRECIPITATION, IN INCHES 22 0

WATER LEVEL , IN FEET BELOW LAND SURFACE Hydrologic conditions affect the quality of streams NOV JAN MAR MAY JUL SEP NOV JAN MAR MAY JUL SEP NOV JAN MAR MAY JUL SEP NOV JAN MAR MAY JUL SEP and ground water in the Potomac River Basin. Fertilizers, 1991 1992 1993 1994 1995 pesticides, and other chemicals that are applied to the land Figure 5. Streamflow, ground-water levels, and precipitation surface may infiltrate to ground water or run off to streams at selected sites in the Potomac River Basin. Streamflow and during rainfall depending on the season, soil properties, and ground-water levels in the basin typically vary seasonally with the intensity and duration of precipitation. During dry peri- rates of precipitation and evapotranspiration. ods, flow in most streams of the Potomac River Basin is sus- tained by discharge from ground water (fig. 7) and streamwater quality is similar to that of ground water. When flows are elevated during storms, streams of the basin typi- cally become concentrated in chemicals that are washed from the land (fig. 8), although streams in some areas may become diluted.

600 10,000 9 Total flow Mean daily flow Nitrate 8 500 Estimated ground-water contribution to flow 7 1,000 400 6

5 300 100 4

200 3 AS NITROGEN

10 2 100 1 FLOW, IN CUBIC FEET PER SECOND Some dry periods NITRATE, IN MILLIGRAMS PER LITER 0 1 0 JULY AUGUST SEPTEMBER OCTOBER MEAN DAILY FLOW, IN CUBIC FEET PER SECOND MAR MAY JUL SEP NOV JAN MAR MAY JUL SEP NOV JAN MAR MAY JUL SEP 1993 1993 1994 1995

Figure 7. Total streamflow and estimated ground-water Figure 8. Streamflow and nitrate concentrations in Muddy contribution to flow in the South Branch Potomac River near Creek at Mount Clinton, Va. Nitrate concentrations are Springfield, W. Va., during part of 1993. Ground water typically higher during periods of high flow than during drier contributes virtually all flow to the river during dry periods but periods. some of the flow during wetter periods.

U.S. Geological Survey Circular 1166 5 MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Nutrients and pesticides in streams and ground water — A regional perspective

In the Potomac River Basin, the River Basin focused on nutrients and Nutrients (Nitrogen and quality of streams and ground water is pesticides because these compounds Phosphorus) affected by a variety of natural and are of primary concern to environmen- human processes. Several major types tal managers within the basin. Elevated Although nitrogen and phospho- of chemicals found in water in the concentrations of nutrients and pesti- rus occur naturally, elevated concen- basin include nutrients, trace elements, cides can render water unsafe to drink trations of these nutrients in streams pesticides, chlorinated industrial com- and can have adverse environmental and ground water of the Potomac pounds, and volatile organic com- effects. In 1987, Maryland, Pennsylva- River Basin often result from human pounds. Agricultural and urban land- nia, Virginia, the District of Columbia, activities. Major sources of nitrogen use practices broadly characterize the and the Federal government estab- and phosphorus to the basin in 1990 distribution of these sources, because lished a goal of reducing nutrient loads included commercial fertilizers and most contamination results from the to Chesapeake Bay. The Potomac manure. Atmospheric deposition from disposal of human and animal wastes River is the second largest tributary to the combustion of fossil fuels accounts or from the use and disposal of other Chesapeake Bay, and information from for an additional 32 percent of nitrogen chemical compounds. Water, sediment, the NAWQA Program can be used to inputs. Municipal wastewater-treat- and tissue samples were collected monitor progress toward this goal. ment plants are locally important throughout the basin and analyzed for Only a small amount of data was avail- sources of nutrients to many streams, nutrients, pesticides, metals, or other able for pesticides in the Potomac but they contributed about 12 percent potential contaminants that are associ- River Basin prior to the NAWQA Pro- of nitrogen and 4 percent of phospho- ated with urban and agricultural gram. Data collection was designed to rus inputs to the basin in 1990 (fig. 9). sources. fill this gap in information. Nutrient inputs to the Potomac Much of the analysis done by the River Basin are related to land use. NAWQA Program within the Potomac The Great Valley (fig.3), which is 45 percent cropland, received the largest

A. NITROGEN B. PHOSPHORUS 4 percent 3 percent EXPLANATION

Atmospheric deposition 26 percent 32 percent Municipal and industrial 48 percent wastewater discharges 45 percent Septic systems 29 percent 12 percent Animal manure Commercial fertilizer

Less than 2 percent

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).

A. NITROGEN B. PHOSPHORUS 35 8 Atmospheric deposition 7 Commercial fertilizer 30 Commercial fertilizer Animal manure Animal manure 6 25 Septic systems Figure 10. Inputs of (A) Septic systems 5 20 nitrogen and (B) 4 phosphorus from non- 15 3 point sources to areas of 10 2 the Potomac River Basin, POUNDS PER SQUARE MILE 5 POUNDS PER SQUARE MILE 1 1990 (modified from

NITROGEN INPUTS, IN THOUSANDS OF 0 0 Blomquist and others,

PHOSPHORUS INPUTS, IN THOUSANDS OF 1996).

PLAIN

PLAIN COASTAL

RIDGE COASTAL RIDGE PIEDMONT PIEDMONT BLUE RIDGE PLATEAUS VALLEY AND BLUE RIDGE PLATEAUS VALLEY AND APPALACHIAN APPALACHIAN GREAT VALLEY GREAT VALLEY

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

estimated inputs from non-point grams per liter (mg/L) as nitrogen has block sunlight from the water, and pro- sources of both nitrogen and phospho- been established for nitrate (U.S. Envi- duce toxins that are harmful to other rus per unit area in 1990, followed by ronmental Protection Agency, 1994a). aquatic life (Allaby, 1989). To control the Piedmont (including the Triassic Drinking water containing nitrate in eutrophication, the U.S. Environmen- Lowlands), which is 43 percent agri- excess of this concentration may cause tal Protection Agency (1986) recom- cultural and 25 percent urban (Vogel- health problems in infants and small mends that total phosphorus mann and others, 1997; Hitt, 1994). children. Nitrate concentrations in concentrations in flowing waters not Inputs to these areas were mostly sampled streams of the Potomac River exceed 0.1 mg/L, a concentration attributed to commercial fertilizers and Basin were generally well below the exceeded in only 12 percent of sam- manure. Dominantly forested areas of MCL, even during high flows. Ground ples from small streams in the Poto- the basin received smaller inputs of water in agricultural areas of the basin mac River Basin at low flow but in a nitrogen (mostly from atmospheric underlain by carbonate rock, however, greater percentage of samples from deposition) and phosphorus per unit is particularly susceptible to nitrate larger streams at varying flow condi- area in 1990. (fig. 10). contamination (Ferrari and Ator, tions. In most waters of the Potomac 1995). Nearly 25 percent of ground- Nutrients are present in waters of River Basin, concentrations of nutri- water samples from domestic wells in the Potomac River Basin in many ents do not pose a threat to human such areas contained nitrate in excess forms, often at concentrations sug- health or wildlife. A Maximum Con- of 10 mg/L. Excessive nitrogen or gestive of human-derived sources taminant Level1 (MCL) of 10 milli- phosphorus in streams can cause (figs. 11, 12). Maximum natural or eutrophication, a condition whereby “background” concentrations of nutri- 1MCLs are standards for levels of contaminants in aquatic plants and algae are overpro- ents in ground water of the basin are finished public water supplies and are not directly applica- duced. This algae can smother larger estimated at 0.4 mg/L (as nitrogen) for ble to untreated streams or ground water. MCLs are cited in this report for reference only. plants, consume dissolved oxygen, nitrate, 0.1 mg/L (as nitrogen) for

Estimated maximum natural level (ground water) Estimated maximum natural level (streams) Federal maximum contaminant level ENVIRONMENTAL SETTING Agriculture 29 underlain by carbonate rock Agriculture underlain by Ground water non-carbonate rock Agriculture Small streams at low flow underlain by carbonate rock

Agriculture Median underlain by Minimum Maximum non-carbonate rock

0 5 10 15 20

NITRATE, IN MILLIGRAMS PER LITER AS NITROGEN 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.

WATERSHED Estimated maximum natural level (streams) Conococheague Cr. at Fairview, Md. (Predominantly agriculture, carbonate, basin)

Monocacy River near Frederick, Md. (Predominantly agriculture, non-carbonate, basin)

S. Br. Potomac River at Moorefield, W.Va. (Predominantly forested, Median non-carbonate, basin) Minimum Maximum Figure 12. Time-series data show a wide variation in nitrate concentrations in selected Potomac River tributaries from 1993 through 1995, but 0 5 10 concentrations typically are highest in those tributaries draining agricultural land and carbonate NITRATE, IN MILLIGRAMS PER LITER AS NITROGEN OCTOBER, 1993 - SEPTEMBER, 1995 bedrock.

U.S. Geological Survey Circular 1166 7 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 phospho- seasonal variations in precipitation and greater in shallower than in deeper rus) for orthophosphate, the most com- inputs, but they generally exceed natu- ground water (Blomquist and others, mon form of dissolved phosphorus in ral concentrations more often in 1996). This is not evident from the natural waters (Ator and Denis, 1997). streams and ground water in agricul- data, however, likely because mostly On the basis of data from across the tural areas of the basin than in areas shallow wells were sampled. United States, maximum natural con- with other land uses. This is particu- Nitrate concentrations that centrations of nutrients in streams have larly evident in areas underlain by car- exceed natural concentrations are been estimated at 0.6 mg/L for nitrate bonate bedrock, where natural waters more common in streams and and 0.1 mg/L for ammonia (Mueller are more susceptible to such contami- ground water in agricultural areas and others, 1995). nation (figs. 11, 12). Elevated nitrate in the northeastern part of the Poto- Elevated nitrogen concentrations concentrations in streams and ground mac River Basin than in other agri- in streams and ground water are water in some urban areas indicate that cultural areas that contain lesser common in the Potomac River Basin urban sources also contribute nutrients percentages of row cropping (fig. 13) in areas of intensive row cropping to the basin, although relatively few (Ator and Denis, 1997; Miller and oth- and carbonate bedrock. Nitrate is the samples were collected in these areas ers, 1997). In 1992, row crops most common form of nitrogen in during this study (Ator and Denis, accounted for less than 20 percent of waters of the basin. Nitrate concentra- 1997; Miller and others, 1997). agricultural land in most counties of tions may vary considerably during the Because nitrogen sources are typically the basin, but as much as 47 percent of year at any given location because of surficial, concentrations are often such land in counties in the northeast-

78° EXPLANATION 77° 40° County agricultural land planted in corn, barley, oats, wheat, sorghum, or soybeans, in percent

79° Greater than 20 Less than or equal to 20

Nitrate concentrations at selected sites in agricultural areas, in milligrams per liter as nitrogen Ground water Less than or equal to 3

39° 3.01 Ð 7 Greater than 7

Streams, low flow Less than or equal to 2 2.01 Ð 4 Greater than 4

° ° 38 0 1020304050MILES 38 0 1020304050KILOMETERS

Figure 13. Within agricultural areas, most elevated nitrate 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.

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 ern part (U.S. Department of Com- Organic nitrogen and phosphorus cheague Creek, Muddy Creek, and the merce, 1995). Nitrogen is typically concentrations are typically low in Monocacy River, which drain prima- applied in greater quantities to crops in waters of the basin, except in rily agricultural watersheds, yield the the form of fertilizer and manure than streams during high flows. Organic largest loads of total nitrogen per to pastures in the form of manure. nitrogen (fig. 14) and phosphorus con- square mile. Accotink Creek, an urban Ammonia concentrations are typ- centrations can be elevated for short stream, yields the largest loads of total ically lower than nitrate concentra- periods in streams during high flow, phosphorus per square mile, followed tions but occasionally exceed natural but they were detected at low concen- by Muddy and Conococheague Creeks concentrations. Elevated ammonia trations or were undetectable in most and the Monocacy River (fig. 15). concentrations in small streams during ground-water samples. Phosphorus is less soluble than most low flow in carbonate areas were likely Streams draining primarily agri- forms of nitrogen and is often bound to related to agricultural and urban land cultural or urban areas yield the stream sediment. Accotink Creek uses (Miller and others, 1997). Ammo- greatest quantities of nutrients to yields the most sediment per square nia in ground water in forested areas the Potomac River. Although the mile among Potomac tributaries at may form from nitrogen that is depos- Shenandoah River contributes the which data were collected over time ited from the atmosphere or from greatest loads of total nitrogen and (Lizarraga, in press). organic nitrogen in leaves and other phosphorus among streams at which natural debris (Ator and Denis, 1997). data were collected over time, Conoco-

4 Figure 14. Organic nitro- gen concentrations were elevated for a short time 3 during high flow in Cono- cocheague Creek in June 2 1996 but quickly decreased as the flow subsided. Concentrations 1 of nitrate, a much more soluble form of nitrogen, DISSOLVED NITROGEN, DISSOLVED

IN MILLIGRAMS PER LITER were slightly depressed 0 during the high flow.

20,000

10,000 FLOW, SECOND 0 19 20 21 22 23 IN CUBIC FEET PER DATE (JUNE 1996)

14 1.0 Figure 15. Estimated yields of Nitrogen nitrogen and phosphorus for 12 Phosphorus 0.8 selected streams in the Potomac 10 River Basin, 1994-95 (Lizarraga, in press). The Monocacy River and 8 0.6 Conococheague and Muddy 6 0.4 Creeks, which drain primarily agricultural watersheds, and 4 Accotink Creek, which drains a 0.2 2 small urban watershed, yield the greatest amounts of nitrogen and 0 0.0 TOTAL NITROGEN YIELD, PER YEAR, YIELD, PER NITROGEN TOTAL IN 1000 POUNDS PER SQUARE MILE IN 1,000 POUNDS PER SQUARE MILE phosphorus per square mile to the

TOTAL PHOSPHORUS YIELD, PER YEAR, YIELD, PER PHOSPHORUS TOTAL Potomac River.

Monocacy River Muddy Creek at Monocacy River at Bridgeport, Md. Catoctin Creek at Accotink Creek at Mount Clinton, Va. Shenandoah River near Frederick, Md. Taylorstown, Va. Annandale, Va. Potomac River at at Millville, W. Va. Conococheague Washington, D.C. Creek at Fairview, Md.

S. Branch Potomac River near Springfield, W. Va. STREAM

U.S. Geological Survey Circular 1166 9 MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Nutrients and pesticides in streams and ground water — A regional perspective

Pesticides control insects and fungi, respectively. the heaviest average rate of pesticide Pesticides are also used for non-agri- application, followed by potatoes and Each year, 4.94 million pounds of cultural purposes such as maintenance peaches. The agricultural areas with synthetic organic pesticides are applied of golf courses, lawns, and gardens; the lowest average rates of pesticide to agricultural lands within the Poto- defoliation of rights-of-way; and con- application are pastures and hayfields. mac River Basin, including 2.88 mil- trol of disease-carrying or defoliating Commonly used pesticides are lion pounds of herbicides, 1.09 million insects. Application rates for these present in ground water of the Poto- pounds of insecticides, and 0.97 mil- uses are not as well documented. mac River Basin, typically at low lion pounds of fungicides. Addition- Cornfields and apple orchards concentrations. Pesticide compounds ally, 1.24 million pounds of oil and receive nearly 75 percent of agricul- were detectable2 in ground-water sam- 0.47 million pounds of sulfur are used tural pesticides applied in the Potomac ples from throughout the basin, primarily on apples and peaches to River Basin (table 2). Apples receive although concentrations rarely

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

Estimated Sample result amount Estimated Major target Pesticide (Trade names1) Type applied2 acres treated crops Ground Streams (lb/yr) water

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

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).

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

exceeded 1 microgram per liter (µg/L). were usually less than 1 µg/L. Atrazine lected during this study of the Potomac Atrazine was the most commonly (fig. 17), metolachlor, simazine, and River Basin, most commonly during detected pesticide in ground water, in prometon were each detected in more storms. The MCL of 70 µg/L for 2,4-D 34 percent of samples (fig. 16). than half of these samples. In addition, was never exceeded. There are cur- Simazine, metolachlor, and prometon tebuthiuron, diazinon, and carbaryl rently no established drinking-water were also detected in at least 15 per- were each detected in at least 10 per- criteria for the other pesticides in com- cent of samples, and 10 other com- cent of samples, and 18 other pesticide mon use in the basin, although estab- pounds (p,p’-DDE, EPTC, metribuzin, compounds were detected in less than lished lifetime health-advisory levels tebuthiuron, DCPA, pebulate, dichlor- 10 percent of the samples. Only atra- (U.S. Environmental Protection benil, dicamba, terbacil, and propoxur) zine and metolachlor were measured at Agency, 1996) for cyanazine and diaz- were detected in less than 10 percent concentrations greater than 1 µg/L. inon were infrequently exceeded. of samples. Deethylatrazine (a byprod- Deethylatrazine was detected in 67 Although criteria for the protection of uct of atrazine degradation) was percent of samples from small streams aquatic life do not reflect all possible detected in nearly all ground-water at low flow and in 86 percent of such effects of pesticides in streams and samples that contained detectable atra- samples that contained detectable atra- have not been established for many zine, often at higher concentrations. zine. compounds, degradation products, and A wider variety of pesticides was Concentrations of pesticides in mixtures, established criteria (Interna- detected more frequently in small streams and ground water of the tional Joint Commission Canada and streams than in ground-water sam- Potomac River Basin are usually not United States, 1977; Canadian Council ples. Pesticides were commonly threatening to human health or most of Resource and Environment Minis- detected in samples from small ecosystems, based on current stan- ters, 1991; U.S. Environmental Protec- streams of the basin that were col- dards and understanding. Estab- tion Agency, 1991a) were exceeded for lected during periods of low flow in lished MCLs (U.S. Environmental atrazine, chlorpyrifos, cyanazine, diaz- late summer, although concentrations Protection Agency, 1994a) for atra- inon, malathion, methylazinphos, and zine (3 µg/L), simazine (4 µg/L), and metolachlor. Aquatic-life criteria were µ 2Using methods employed by the NAWQA Program, alachlor (2 g/L) were only occasion- exceeded almost exclusively in sam- most pesticide compounds were detectable in water samples ally exceeded in stream samples col- ples collected during storms in May, at concentrations as low as 0.001 µg/L to 0.01 µg/L.

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

Estimated amounts of pesticides used (lb/yr)2 Most heavily applied Crop 1 Estimated acres pesticide Fungicides Herbicides Insecticides Total

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

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

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

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

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

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

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 Mancozeb

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

1Based on 1992 agricultural census data (U.S. Department of Commerce, 1995). 2Based on Gianessi and Puffer, 1990, 1992a, 1992b. 3No reported use.

U.S. Geological Survey Circular 1166 11 MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Nutrients and pesticides in streams and ground water — A regional perspective

1.2 1.1 25 Number of samples 1.0 (12) Number of samples with concentrations 0.9 less than 0.001 micrograms per liter 0.8 0.7 0.6 0.5

ATRAZINE, ATRAZINE, 0.4 0.3 0.2

IN MICROGRAMS PER LITER 0.1 0.0 25(24) 3(3) 29(4) 25(20) 23(18) Valley and Ridge Valley and Ridge Great Valley Carbonate Piedmont Triassic Lowlands (agricultural) (forest) (agricultural)

Figure 16. Concentrations of atrazine in ground water in sampled areas of the Potomac River Basin. Atrazine was most commonly detected in ground water in agricultural areas of the Great Valley.

2.5 2.4 25 Number of samples (5) Number of samples with concentrations 2.3 less than 0.001 micrograms per liter 2.2 2.1 2.0 1.0 0.9 0.8 0.7

ATRAZINE, ATRAZINE, 0.6 0.5 0.4 0.3 IN MICROGRAMS PER LITER IN MICROGRAMS 0.2 0.1 0.0 25(12) 27(0) 25(5) 12(2) Valley and Ridge Great Valley Carbonate Piedmont Triassic Lowlands

Figure 17. Concentrations of atrazine in small streams during low flow in sampled areas of the Potomac River Basin. The highest concentrations of atrazine were typically detected in streams of the Great Valley, although the highest concentration was detected in the Triassic Lowlands.

June, or July from Accotink Creek, the deethylatrazine, simazine, prometon, detected in four samples. Only atra- Monocacy River, or Muddy Creek. and metolachlor were each detected in zine, deethylatrazine, metolachlor, These streams drain predominantly more than half of the samples from prometon, simazine, and tebuthiuron urban or agricultural areas and were ground water and small streams. Pesti- were detected in small-stream samples among the most intensely sampled for cides were also commonly detected in from the Valley and Ridge. pesticides within the Potomac River ground water and streams of the Pied- Basin by the NAWQA Program. mont and Triassic Lowlands. In the Pesticides were commonly mostly forested Valley and Ridge, detected in streams and ground however, detections of pesticide com- water in agricultural areas of the pounds in streams were much less fre- Potomac River Basin; samples from quent, and there were virtually no forested areas rarely contained detections in ground water. Six com- detectable pesticides. Much of the pounds (atrazine, deethylatrazine, p,p’- agriculture in the basin is in the Great DDE, metribuzin, prometon, and Valley, Piedmont, and Triassic Low- simazine) were each detected in a sin- lands (fig. 3). In carbonate areas of the gle ground-water sample from the Val- Great Valley, atrazine (figs. 16, 17), ley and Ridge, and dichlorbenil was

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

Pesticide concentrations in Streams in the Potomac River malathion measured in the Potomac streams and ground water of the Basin are affected by pesticide appli- River Basin and the highest concentra- Potomac River Basin are greatest in cations in urban as well as agricul- tions of oryzalin and MCPA measured areas of intense crop production – tural areas. Many pesticides have by the NAWQA Program. Pesticides particularly in the corn-producing been detected in samples from found in Accotink Creek are generally northeastern counties and in the Accotink Creek, which drains a small, used on rights-of-way, turf, golf Great Valley. Pesticide concentra- urban watershed near Washington, courses, and for landscaping, and as tions in ground water and small D.C. Herbicides detected at this site additives to asphalt and other building streams were typically higher in sam- include atrazine, metolachlor, MCPA, materials. ples from the more heavily cropped oryzalin, and prometon. Simazine was areas than other agricultural areas (fig. detected most often and at the highest 18). Among larger streams, the highest concentrations, occasionally exceeding incidence of detections and elevated the MCL of 4 µg/L. Insecti- concentrations of atrazine and meto- cides—including diazinon, carbaryl, lachlor also occurred predominantly in and chlorpyrifos—were also detected, these areas, particularly in the Mono- year-round. Samples from Accotink cacy River and Opequon, Conoco- Creek contained the highest concentra- cheague, and Antietam Creeks. tions of the insecticides diazinon and

78° EXPLANATION 77° 40° County agricultural land planted in corn, barley, oats, wheat, sorghum, or soybeans, in percent

79° Greater than 20 Less than or equal to 20

Atrazine concentrations at selected sites in agricultural areas, in micrograms per liter Ground water Less than 0.001 0.001 - 0.009 39° 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

° ° 38 0 1020304050MILES 38 0 1020304050KILOMETERS

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.

U.S. Geological Survey Circular 1166 13 MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Nutrients and pesticides in streams and ground water — A regional perspective

Maximum concentrations of most 100,000 25 Atrazine pesticides occur in streams during the Metolachlor Flow spring and early summer months, 10,000 20 although atrazine and metolachlor are present year round in agricultural 1,000 15 areas. The Monocacy River at Bridge- port, Md., for example, drains 173 100 10 square miles, almost 80 percent of which

is agricultural. Pesticide concentrations IN MICROGRAMS PER LITER 10 5 PESTICIDE CONCENTRATION,

in this stream are related to flow, but the PER SECOND IN CUBIC FEET FLOW, major controlling factor is the seasonal 1 0 application (fig. 19). During a storm in MARCHMAY JULY SEPT NOV JAN MARCHMAY JULY SEPT May 1994, concentrations of alachlor 1994 1995 (3.1 µg/L), atrazine (25 µg/L), cyana- Figure 19. In the Monocacy River at Bridgeport, Md., atrazine and metolachlor zine (3.0 µg/L), and metolachlor (23 µ were present at detectable concentrations during most of the year but g/L) in the Monocacy River were the concentrations were typically highest during the late spring following application. highest measured in any water sample during this study. Other pesticides fre- were detected at least once during the Concentrations declined through the quently detected in the Monocacy River period of most intensive sampling in summer months and were nearly unde- included simazine, prometon, and linu- 1994. Pesticide concentrations in the tectable in late fall and winter. ron. Of the 45 pesticides for which sam- Potomac River also were highest in the ples from this site were analyzed, 19 spring, during the time of applications.

Three major floods occurred in the Potomac River Basin in STORM FLOW 1996 and had different effects on water quality because they 600 occurred during different seasons (fig. 20). Record high flow for a 500 single day occurred in January in the Potomac River at Washington,

400 D.C., due to intense rainfall and rapid snowmelt caused by unseason- ably warm weather following a blizzard. In June, basins of the Mono- 300 cacy River and Conococheague Creek, which are dominantly 200 agricultural, received intense rainfall over a 5-day period. Flow from TOTAL FLOW, IN FLOW, TOTAL BILLION GALLONS 100 the June storm in the Monocacy River at Bridgeport, Md., reached a level expected to occur only once in 200 years. Intensive rainfall from 0 a tropical storm caused flooding in September in the mostly agricul- tural Shenandoah River Basin and points west. TOTAL NITROGEN LOAD Nitrogen loads in the Potomac River at Washington, D.C., were 20 greater during the January flood than during June or September.

15 Record flow, including runoff from previously frozen land, carried an estimated 18 million pounds of nitrogen, including large amounts of

10 ammonia and organic nitrogen which are typically associated with

OF POUNDS manure and wastewater discharges.

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

NITROGEN, IN MILLIONS NITROGEN, much atrazine during the June flood as in September, even though 0 the flow was three times greater in September. Over a 5-day period, the river carried an estimated 3,300 pounds of atrazine and 3.3 mil- ATRAZINE LOAD lion pounds of nitrogen. On two consecutive days following the June 5,000 storm, atrazine was measured in the river at concentrations greater than the MCL of 3 g/L.Pesticides and fertilizers are generally applied 4,000 to the land in the spring, whereas nitrogen may be applied in the form 3,000 of manure throughout the year. Long-term impacts of the unprecedented flooding within the Poto- 2,000 mac River Basin during 1996 have yet to be determined; however, the 1,000 USGS is currently studying aquatic vegetation downstream in the ATRAZINE, IN POUNDS ATRAZINE, NOT MEASURED NOT Potomac estuary, and State and local governments are planning to 0 January June September sample drinking-water sources for pesticides more frequently during (19-23) (19-24) (7-10) 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.

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

Within the Potomac River Basin, streams and ground 30 Samples from carbonate rocks water in the Great Valley show the greatest water-qual- ity effects from agricultural sources (fig. 21) because Samples from noncarbonate rocks the valley is intensely used for crop and animal pro- Lines indicate results of LOWESS smoothing duction and because carbonate bedrock permits rapid (Helsel and Hirsch, 1992) transportation of constituents to ground water and 20 streams. Much of the Great Valley is underlain by carbon- ate rock which commonly contains open conduits (solution channels) created and enlarged by the action of acidic water moving through rock fractures. Rain is naturally acid- ified by the dissolution of carbon dioxide in the atmosphere AS NITROGEN 10 and can be further acidified by the introduction of nitric and sulfuric acids into the atmosphere from the combustion of fossil fuels. Chemicals at the land surface in agricultural NITRATE, IN MILLIGRAMS PER LITER NITRATE, areas such as the Great Valley can be quickly and easily carried to ground water through conduits in bedrock. Once 0 chemical constituents reach the ground water in carbonate 025 50 75 100 rocks, they may move quickly with ground-water flow to PERCENTAGE OF CROPLAND WITHIN 0.25 MILES streams, springs, or water-supply wells. Nutrient and pesti- UPGRADIENT OF SAMPLED WELL cide concentrations in ground water of carbonate areas are often highly variable because the ground water responds Figure 21. Nitrate concentrations in ground-water so quickly to precipitation and the application of fertilizers samples from the Potomac River Basin increase with and pesticides. In addition, soils derived from carbonate increasing percentages of cropland, but are typically rocks tend to contain little organic carbon and therefore higher in samples from carbonate rocks like those of the have a reduced ability to bind to organic chemicals, such Great Valley than in samples from rocks of other types. as pesticides (Barbash and Resek, 1996).

Photograph by James Gerhart, U.S. Geological Survey

U.S. Geological Survey Circular 1166 15 MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Organic contaminants and metals in streams

Chlordane,3 DDT,4 PCBs,5 mer- cury, and lead are present in streambed Screening thresholds for organic compounds and trace metals sediment and aquatic tissues in the in streambed sediment Potomac River Basin (fig. 22). Each of A three-tiered system is used for screening measured concentrations of potentially these compounds or metals can directly toxic compounds in streambed sediment. Concentrations in tier 1 (greater than the impair aquatic organisms living in or upper screening value) have a high probability of causing adverse effects on aquatic near the streambed and can be detri- life; concentrations in tier 2 (between the upper and lower screening values) have an mental to the health of humans or other intermediate probability of causing adverse effects on aquatic life; and concentra- animals through the food chain. Lead, tions in tier 3 (less than both screening values) have a low probability of causing mercury, chlordane, and DDT have adverse effects on aquatic life (Gilliom and others, in press). Screening levels for been designated as “toxics of concern” mercury, lead, DDT (Long and others,1995) and chlordane (Long and Morgan, 1990) to the Chesapeake Bay (U.S. Environ- are the ERL (effects range - low) and ERM (effects range - median) developed for mental Protection Agency, 1991b,c). bottom sediments in estuarine waters. Screening levels for PCBs are the PEL (Prob- able Effect Level) and TEL (Threshold Effect Level) developed by the Florida Depart- ment of Environmental Protection (1994). Because these values were developed for screening purposes, measurements within tiers 1 and 2 do not indicate that adverse 3 Chlordane concentrations presented are the sum of effects have occurred at particular sampling sites. trans-chlordane, cis-chlordane, cis-nonachlor, trans-non- achlor, 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. EXPLANATION Probability of organic contaminants or metals in streambed sediment causing Chambersburg adverse effects on aquatic life — Gettysburg Mercury and lead concentrations were adjusted for particle-size distribution for Bridgeport screening purposes Cumberland Hagerstown High

Martinsburg Intermediate Frederick Low Not detected Winchester Not sampled Leesburg Moorefield Strasburg Site location and number

Front Royal Annandale WASHINGTON 30 Alexandria Chlordane 66.6 Manassas 25

20

15 Harrisonburg 10

5 Staunton 0 Waynesboro 30 41.9 25 DDT

20 2 Mercury 14.5 15 1.5 10 1 5 0.5 0 200 0 408 120 PCBs 150 100 Lead 80 100 60

40 50 20 CONCENTRATIONS IN STREAMBED SEDIMENT, IN PARTS PER BILLION IN PARTS IN STREAMBED SEDIMENT, CONCENTRATIONS SEDIMENT, IN PARTS PER MILLION IN PARTS SEDIMENT, CONCENTRATIONS IN STREAMBED CONCENTRATIONS 0 0 135 719921111315 17 23 25 135 719921111315 17 23 25 SITE SITE 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.

16 Water Quality in the Potomac River Basin MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Organic contaminants and metals in streams

CHLORDANE DDT EXPLANATION Probability of chlordane or DDT in 8 8 streambed sediment causing 4 19 4 19 adverse effects on aquatic life 3 7 3 7 2 10 2 10 6 6 High 9 11 20 9 11 20 1 1 Intermediate 17 18 17 18 Low 5 16 21 5 16 21 15 22 15 22 Not detected 23 23 24 25 24 25 19 Site number

12 12 26 26 13 14 13 14

Figure 23. Chlordane and DDT were frequently found in streambed sediment in the Potomac River Basin, even though these insecticides are now banned. The greatest chlordane concentrations were measured near the Washington, D.C., urban areas and Cumberland, Md.; whereas the greatest DDT concentrations were measured in streams in the Great Valley.

The use of chlordane, DDT, and soil particles and to degrade slowly— in 1992 and 1996. DDT is an insecti- PCBs has been banned or restricted for offering long-term protection from cide used to control mosquitoes and nearly two decades. The occurrence of pests. These chemical properties, how- other pests. Its use was banned in 1972 these compounds in streambed sedi- ever, render chlordane a persistent because of its harmful effects on birds ment indicates a persistent potential problem in many streams in the Poto- and other wildlife and its potential to for toxic effects from regional and mac River Basin. cause cancer and damage the human point sources of contamination in parts At least a moderate potential for nervous system, liver, kidney, and skin of the Potomac River Basin occasional adverse effects to aquatic (U.S. Environmental Protection organisms exists at all sites where Agency, 1992). Its widespread occur- Streambed sediment chlordane was detected in stream- rence in the Potomac River Basin two bed sediment. Seven of these sites are decades since its ban is attributable to Chlorinated organic compounds in the Great Valley (fig. 23). Although both widespread use and chemical sta- and trace metals are present in the Great Valley is largely agricultural bility. streambed sediment of the Potomac (including row crops, pasture, and Although DDT was present at a River and its tributaries at concen- orchards), several urban and industrial large proportion of sampled sites, trations that have some potential to centers extend through the valley from concentrations at most sites indicate adversely affect aquatic life. Sedi- Waynesboro, Va., to Chambersburg, little potential for adverse effects on ment from 14 of 25 sites contained Pa. Chlordane in this region could be aquatic biota. DDT concentrations in chlordane, DDT, PCBs, lead, or mer- derived from a wide variety of sources sediment at seven sites indicate a mod- cury at concentrations that pose an and applications. erate potential for adverse effects on intermediate probability of causing Concentrations of chlordane in aquatic life. Of these, five are in the adverse effects on aquatic life; concen- streambed sediment indicate a high Great Valley. The application of DDT trations at six sites indicate a high probability for adverse effects on to orchards has been identified as one probability of causing adverse effects aquatic biota at four sites down- potential source of DDT in several on aquatic life. stream from urban areas (fig. 23). streams in the central Great Valley Chlordane was detected in The maximum concentration (66.6 (Gerhart and Blomquist, 1995). As streambed sediment from 13 of 26 ppb, parts per billion) was measured in with chlordane, sediment from the sites in the Potomac River Basin, a sample from the Anacostia River Anacostia River near Washington, even though most uses of chlordane (site 22) in a tidal area near Washing- D.C. (fig. 23) had the highest concen- were banned in 1978 and a total ban ton, D.C. This concentration was more tration of DDT (41.9 ppb). was implemented in 1988 (U.S. Envi- than 10 times the upper screening PCB concentrations in sediment ronmental Protection Agency, 1991c, threshold. The second highest concen- from the South Fork Shenandoah 1992, 1994a). Chlordane is a synthetic tration was measured in sediment from River at Front Royal, Va., indicate a organic compound that was primarily the North Branch Potomac River, at a high potential for adverse effects on applied to soil surrounding building site downstream from a heavily indus- aquatic life. The high levels of PCBs foundations as an insecticide to control trialized area of Cumberland, Md. at this site are attributable to a textile termites and ants. For this application, DDT was detected in streambed plant immediately upstream (Virginia chlordane was developed to adhere to sediment from 23 of 26 sites sampled Water Control Board, 1992). This plant

U.S. Geological Survey Circular 1166 17 MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Organic contaminants and metals in streams 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 EXPLANATION six sites (Gerhart and Blomquist, Known source of mercury 1995). Although it occurs naturally in Sites with mercury concentration trace amounts in the Earth’s crust, Proportional bar showing mercury concentration in streambed sediment, mercury may be introduced as a con- in parts per million taminant to the environment as a con- sequence of human activities. Mercury is used in the manufacture of paints, paper, and vinyl chloride, and it can Figure 24. Mercury contamination from an industrial source in Waynesboro, Va. also be found in batteries and fungi- (possibly lasting over a period of decades), has led to widespread contamination of the South Fork Shenandoah and Shenandoah Rivers (to about 171 river miles cides. downstream). It is possible that contamination from this source has spread as far High levels of mercury at three downstream as the Potomac River at Washington, D.C. sites are directly attributable to a long-term industrial source of mer- Each of the sediment samples con- urban areas may accumulate lead from cury contamination on the South taining lead at concentrations poten- any of these sources. River in Waynesboro, Va. (fig. 24). tially harmful to aquatic life were In 1977, mercury was found in soils at collected in urban and industrial areas. Aquatic tissues the Waynesboro plant, where it was Although lead occurs naturally in used in industrial processes until 1950. trace amounts, many potential sources Contaminants present in stream- Mercury contamination may have con- of lead contamination exist, including bed sediment are bioavailable and tinued at this site for several decades batteries, vehicle emissions, solder, have been incorporated into the food prior to its discovery (Brooks, 1977). and corroding brass, pipes, and chain. Chlordane, DDT, PCBs, mer- This potentially long-term source has plumbing. Other sources include cury, and lead were detected in Asiatic led to measurable mercury contamina- paints, gasoline, and lead shot, clam (Corbicula fluminea) tissue and tion as far as 171 miles downstream, although uses of lead for these pur- fish tissue samples collected in 1992 near Harpers Ferry, W.Va. (fig. 24). It poses has been restricted. Sediment in and 1996 (Zappia, 1996). Organochlo- is possible that the Waynesboro plant is a contributing source of mercury measured as far downstream as Wash- 140 10 Fish sampled ington, D.C., although more detailed 9 120 Yellow bullhead study would be necessary to make this Shorthead redhorse 8 White sucker 100 7 link. Streambed sediment ND Not detected 6 Lead was detected in streambed 80 5 sediment at all 25 sampled sites in 60 the Potomac River Basin. The high- 4 40 3 IN PARTS PER BILLION IN PARTS est lead concentration (110 ppm, parts 2 PER BILLION IN PARTS 20 ND ND ND per million) was measured in sediment ND 1 ND ND ND ND collected from the Anacostia River TISSUE, CHLORDANE IN WHOLE-FISH 0 0

6812 13 16 19 20 24 25 CHLORDANE IN STREAMBED SEDIMENT, near Washington, D.C., which also SAMPLED STREAMS, BY SITE NUMBER (ON FIGURE 22) contained the highest concentrations of chlordane and DDT. Sediment from Figure 25. Chlordane concentrations in whole-fish samples of bottom-feeding fish two other sites in the Washington, are correlated with concentrations in streambed sediment (Gerhart and Blomquist, D.C., area and one in Cumberland, 1995). These sediments apparently serve as a source of chlordane in the food chain. One sample of shorthead redhorse (a carp-like fish) shows chlordane Md., contained lead at concentrations contamination near Frederick, Md., where none exists in the streambed sample. indicating a moderate potential for This contamination may be from exposure to contamination in other locations or adverse effects on aquatic life. from historical exposure.

18 Water Quality in the Potomac River Basin MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Organic contaminants and metals in streams rine compounds were detected less fre- Jones, Commonwealth of Virginia, mercury in Asiatic clams (0.71 ppm) quently in clam tissue than in Department of Game and Inland Fish- was detected at site 14, downstream streambed sediment, as chlordane and eries, written commun., 1996; Hamid from Waynesboro, Va. Mercury was DDT were detected in only 3 of 16 sites Karimi, District of Columbia Depart- also detected at five sites (8, 13, 16, 19, and PCBs were detected in 4 sites ment of Consumer and Regulatory and 20) in fish livers, although FDA (table 3). Chlordane was generally Affairs, written commun., 1994). action levels and NAS/NAE criteria found in higher concentrations in Mercury was detected in tissue are not applicable to fish livers. whole-fish tissue than in clams. samples from nine sites, including The Virginia Department of Health Streambed sediment apparently four sites in the Shenandoah River has established warnings to restrict serves as a source of chlordane to the watershed downstream from the consumption of fish from the South food chain, because chlordane concen- contamination source in Waynes- River and the South Fork of the tration in fish tissue is correlated with boro, Va. Mercury was detected in Shenandoah River because of concen- concentration in sediment (fig. 25). Asiatic clams from seven sites, but no trations of mercury in fish tissue Chlordane concentrations in fish concentrations exceeded the FDA (Vickie Odell, Virginia Department of tissue pose a threat to fish-eating action level for the protection of Health, written and oral commun., wildlife at two sites in the Potomac human health in edible-shellfish tissue. 1997). River Basin. Whole-fish tissues from The highest measured concentration of two streams in Virginia, Bull Run (site 25) and Accotink Creek (site 24), con- Table 3. Summary of chlordane, DDT, PCB, lead and mercury concentrations in Asiatic tained chlordane at concentrations clam tissues and relation to standards for the protection of human health exceeding the National Academy of [ppb, parts per billion; also equivalent to micrograms per kilogram] Sciences, National Academy of Engi- Number of U.S. Food and neering (NAS/NAE) (1973) recom- Minimum Maximum sites where Drug Number of sites Compound or detected detected mended maximum concentration for detected Administration exceeding metal concentration concentration the protection of fish-eating wildlife. (16 sites action level1 standard (ppb) (ppb) These sites are in the heavily urbanized sampled) (ppb) Washington, D.C., area. A human Chlordane 3 8.8 31.1 300 0 health advisory including chlordane DDT 3 5.1 12.9 5,000 0 currently exists for the consumption of PCBs 4 140 162 2,000 0 fish caught in Washington, D.C., Lead 14 300 1,200 no standard -- waters, “due to PCBs and other com- Mercury 7 89 710 1,000 0 pounds” (Hamid Karimi, District of Columbia Department of Consumer 1 U.S. Food and Drug Administration, 1992. and Regulatory Affairs, written com- All samples of Asiatic clams (Corbicula fluminea) contained chlordane, DDT, and PCB at mun., 1994). Possible effects of chlor- concentrations well below the U.S. Food and Drug Administration action levels for protection of dane on human health include cancer, human health. Mercury concentrations approached the FDA action level in a sample from the dizziness, headache, fatigue, and con- South River near Waynesboro, where the greatest concentration was measured in streambed sediment . vulsions. No Asiatic clam samples con- tained chlordane at concentrations Table 4. Summary of chlordane, DDT, and PCB concentrations in whole-fish tissue and threatening to humans or wildlife. relation to criteria for the protection of fish-eating wildlife No Asiatic-clam or whole-fish [ppb, parts per billion, also equivalent to micrograms per kilogram] samples contained PCBs at concen- trations threatening to human health NAS/NAE Number of recommended or wildlife, although human health Minimum Maximum sites where maximum Number of sites detected detected advisories have been issued for some Compound detected concentration for exceeding concentration concentration streams. Asiatic clams from the South (8 sites the protection of standard (ppb) (ppb) Fork Shenandoah River at Front Royal, sampled) fish-eating Va. (site 15), contained the highest wildlife1 (ppb) measured concentration of PCBs in the Chlordane 4 9.6 127 100 2 basin. Human-health advisories for DDT 4 6.4 12 1,000 0 PCBs in fish exist in this part of the PCBs 5 75 146 500 0 South Fork Shenandoah River. Human- 1 health advisories also exist for other National Academy of Sciences, National Academy of Engineering, 1973. reaches of the North Fork, South Fork, Two samples of bottom-feeding fish contained chlordane at concentrations greater than the and mainstem Shenandoah River and NAS/NAE recommended maximum concentration for the protection of fish-eating wildlife. These samples, collected in 1992, show a persistence in the food chain because chlordane for Washington, D.C., waters (Emily use was restricted in 1978 and banned in 1988.

U.S. Geological Survey Circular 1166 19 MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Radon in ground water

Radon is present in ground water Figure 26. Radon activities throughout the Potomac River Basin. in ground water in the The Federal drinking-water standard 78° Potomac River Basin are for radon is currently under review 40° generally higher in sampled by the U.S. Environmental Protection areas of the Piedmont ° Agency; however, radon levels in 69 79° 77 Province than in those of the Valley and Ridge percent of ground-water samples (modified from Lindsey and were greater than a previously pro- Ator, 1996). posed standard of 300 picocuries per liter. Of 104 ground-water samples, 103 contained detectable levels of radon and EXPLANATION Median radon activity, in ° levels ranged from among the lowest to 39 picocuries per liter among the highest in the Nation. greater than 1,000 A colorless, odorless, radioactive gas, 300 Ð 1,000 radon forms naturally in rocks and soils through the radioactive decay of radium, less than 300 a product of uranium decay. Radon com- unsampled areas monly enters buildings through founda- tion cracks and may dissolve in ground water and be carried into buildings served by water supply wells. Radon 38° 38° from ground water is released into 0 1020304050MILES household air when water is used for 0 1020304050KILOMETERS showering, washing, and other every- average, than do granitic or carbonate from the primarily granitic rocks of day purposes. According to the U.S. rocks (Faure, 1986). the Piedmont (figs. 26, 27). Surgeon General, exposure to airborne Ground-water radon activities in Ground-water radon activities in radon is second only to cigarette smok- the Triassic Lowlands are among the Valley and Ridge are generally ing as a cause of lung cancer. The risk of the highest detected in the basin. very low. The Valley and Ridge cov- cancer increases with exposure to The rocks of the Triassic Lowlands ers most of the basin from the area of increasing levels of airborne radon (U.S. are mainly siliciclastic and extend western Maryland through eastern Environmental Protection Agency, south from the area of Gettysburg, West Virginia and is underlain prima- 1994b). Pa., to the west of Washington, D.C., rily by siliciclastic rocks. Unlike sam- Radon activities in ground water of through Maryland and Virginia. ples from the siliciclastic rocks of the the Potomac River Basin are related Ground-water samples from these Triassic Lowlands, however, samples to rock type. Ground-water radon activ- 6 rocks contained radon activities com- from these rocks typically contained ities are highly variable in all areas but parable to those measured in samples very little radon (figs. 26, 27). are typically higher in areas underlain by crystalline rocks of the Piedmont than in areas underlain by carbonate EXPLANATION 10,000 rocks (figs. 26, 27). Crystalline rocks of Predominant rock type predominantly granitic composition, Crystalline like many of those in the Piedmont, con- Carbonate 1,000 tain more uranium, on average, than do Siliciclastic carbonate rocks (Faure, 1986). The part Maximum 75th percentile of the Piedmont west of the Triassic Lowlands is an exception; ground-water Median 100 radon activities in this area are typically lower than in carbonate areas. This area 25th percentile Minimum contains some granitic rocks, but many 10 RADON ACTIVITY IN PICOCURIES PER LITER ACTIVITY RADON of the crystalline rocks of this area are Background colors in graph correspond to colors in figure 26 above not predominantly granitic like those of Province the rest of the Piedmont. Rocks of this Provinces Piedmont and Valley and Ridge Valley Valley and Ridge Valley (western portion) type contain much less uranium, on Lowlands Triassic Piedmont Province Piedmont Province

6Amounts of radioactive elements (such as radon) are Figure 27. Radon activities in ground water vary widely within each sampled area of the often reported in terms of activities rather than concentrations. Potomac River Basin but are generally higher in sampled areas of the Piedmont Pro- vince than in those underlain by carbonate rocks (modified from Lindsey and Ator, 1996).

20 Water Quality in the Potomac River Basin MAJOR ISSUES AND FINDINGS IN THE POTOMAC RIVER BASIN Recent water-quality trends and outlook

The quality of water in aquifers and ground water underlying agricultural detected in tissues and sediment and streams of the Potomac River Basin lands in the Potomac River Basin will likely remain present at low con- likely will continue to be stressed by already contains elevated concentra- centrations in urban and suburban population growth and associated pres- tions of nitrate and detectable concen- areas for the foreseeable future. Mer- sures well into the 21st century. Basin trations of herbicides; and small cury and PCBs will likely continue to population will increase by an estimated streams at base flow contain concen- be carried downstream in sediments 19 percent to 6.2 million between the trations of nitrate and pesticides simi- of the Shenandoah River from their years 2000 and 2020 (Carlton Haywood, lar to those found in ground water. At industrial sources until the reservoir Interstate Commission on the Potomac this point, it is impossible to predict of the contaminants is depleted. Many River Basin, oral commun., 1998). the long-term effect(s) that BMPs newly developed pesticides and indus- Analysis of data collected by the may have on ground-water quality or trial compounds are being released NAWQA Program suggests that, resulting effects on the Potomac River into the environment. The occurrence although water quality in the basin is and its tributaries. of these compounds can be tracked improving in some respects, water man- Contamination by pesticides and only with continued monitoring initia- agers will continue to wrestle with sev- industrial compounds will likely per- tives. eral long-term water-quality problems sist in the Potomac River Basin for while addressing the pressures and con- years to come. Chlordane and DDT, sequences of population growth and two long-banned insecticides, were associated land-use changes.

Despite an estimated 44 percent 1.000 increase in population in the Potomac Total Phosphorus River Basin from 1970 to 1990, total phosphorus concentrations in the 0.100 Potomac River at Washington, D.C., have decreased since 1979, and nitro- 0.010 gen concentrations have apparently stabilized (fig. 28). Large-scale water- 0.001 quality-management practices such as 4.0 Total Nitrogen improving municipal wastewater-treat- ment facilities and widespread imple- 3.0 mentation of phosphate-detergent bans 2.0 and agricultural best-management prac- tices (BMPs) are apparently working 1.0 effectively to curb nutrient concentra- 0.0 tions in the Potomac River. 4.0 Different forms of nitrogen show Dissolved Nitrate as Nitrogen conflicting patterns in long-term 3.0 trends in the Potomac River at Wash- ington, D.C., which complicates the 2.0 forecasting of trends in nutrient con- centrations (fig. 28). Improved treat- 1.0 ment of municipal wastewater is likely 0.0 FLOW-ADJUSTED CONCENTRATION, IN MILLIGRAMS PER LITER CONCENTRATION, FLOW-ADJUSTED to decrease discharges of both ammonia 4.0 Ammonia plus Organic Nitrogen as Nitrogen and organic nitrogen significantly but increase nitrate discharge to streams. 3.0

Agricultural BMPs that minimize field 2.0 runoff and increase infiltration to ground water may cause similar nitrate 1.0 increases in surface water by diverting 0.0 nitrogen through the ground-water sys- 1979 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 tem prior to its discharging to streams. These practices may delay the move- ment of nitrogen to streams by years or even decades (Focazio and others, in Figure 28. Flow-adjusted nutrient concentrations in the Potomac River at Washington, D.C., 1979-96. Total phosphorus concentrations have press) as well as increase contamination decreased over this period. Recent trends in nitrogen concentrations are of ground water by nitrogen and other more complicated; ammonia plus organic nitrogen concentrations have agricultural chemicals. Much of the decreased, whereas nitrate concentrations have increased, resulting in apparently stable total nitrogen concentrations since about 1985

U.S. Geological Survey Circular 1166 21 WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT Comparison of Stream Quality in the Potomac River Basin with Nationwide NAWQA Findings

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, organo- chlorine pesticides, and PCBs in sediment. (Methods used to compute rankings and evaluate aquatic-life criteria are described by Gilliom and others, in press.) EXPLANATION Ranking of stream quality relative to all NUTRIENTS in water Among sites at which long- NAWQA stream sites - Darker colored cir- term data were collected, cles generally indicate poorer quality. Bold nutrient concentrations in the outline of circle indicates one or more Potomac River Basin were aquatic life criteria were exceeded. consistently highest in streams

P draining mostly agricultural o t Greater than the 75th percentile o m (among the highest 25 percent of NAWQA ac areas, particularly in Conoco- stream sites) R cheague and Muddy Creeks iv er and the Shenandoah River, Between the median and the 75th percentile which drain areas underlain by carbonate rocks. Nutrient con- centrations in these streams Between the 25th percentile and the median and the Monocacy River ranked among the highest in Less than the 25th percentile the Nation, although no appli- (among the lowest 25 percent of NAWQA cable criteria for the protec- stream sites) tion of aquatic life were exceeded. ORGANOCHLORINE PESTICIDES and PCBs in streambed sediment and aquatic tissues PESTICIDES in water Accotink Creek, which drains a small urban basin near Wash- ington, D.C., had the highest concentrations of pesticides measured in the Potomac River P o t o m Basin and ranked among the ac highest observed, nationwide. R iv er Agricultural basins (particu- larly cropped) also contribute relatively large amounts of pesticides to the Potomac River, but less so than Ac- cotink Creek. Concentrations of pesticides at these sites are PCBs or organochlorine pesticides were detected in streambed sediment similar to many sites across the or aquatic tissues at all sampled sites and the levels of these compounds Nation. Similar concentrations at four sites rank among the highest in the Nation. Chlordane concentra- of herbicides were detected tions in streambed sediment at sites on the North Branch Potomac River among agricultural and urban and Accotink Creek exceeded threshold levels that indicate a potential to sites, but insecticide concentra- cause adverse effects on aquatic organisms. Further sampling would be tions were higher at the urban necessary to determine possible dangers of consuming fish from these site. Aquatic-life criteria were sites (for more information, see pages 16-19). exceeded only in Accotink Creek.

22 Water Quality in the Potomac River Basin WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT Comparison of Stream Quality in the Potomac River Basin with Nationwide NAWQA Findings

TRACE ELEMENTS in streambed sediment Trace element concentrations CONCLUSIONS in streambed sediment were among highest in the Nation at Elevated concentrations of nutrients two of ten sampled sites in the and pesticides in streams of the Poto- Potomac River Basin. Rela- mac River Basin are among the highest

P tively high concentrations of in the Nation at several sites and are o t o m ac mercury and zinc were detect- generally related to agricultural or ur-

R ed in the North Branch Poto- ban land in the contributing water- iv er mac River at Cumberland, sheds. Stream habitat and fish Md. This site drains a coal- communities are also most degraded in mining region as well as near- streams draining intensively agricultur- by urban and industrial land. al or urban areas. Mercury concentrations in the Shenandoah River at Mill- Concentrations of PCBs, organochlo- ville, W. Va., were greater rines, trace elements, and SVOCs in than seven times the National streambed sediment or aquatic tissues median (for more informa- at several sites are also among the tion, see page 18). highest measured by the NAWQA Pro- SEMIVOLATILE ORGANIC COMPOUNDS gram. The most affected streams, in- in streambed sediment Concentrations of semivola- cluding the North Branch Potomac, tile organic compounds Shenandoah, and Monocacy Rivers, (SVOCs) in streambed sedi- as well as Accotink Creek, typically ment were among the highest drain intensely agricultural or urban in the Nation at four sites in areas. Criteria for the protection of

P o the Potomac River Basin. aquatic life were exceeded at some of t o m ac Two of these sites are near these sites.

R urban areas and the others, iv er the Shenandoah River and STREAM HABITAT DEGRADATION Conococheague Creek, drain mixed urban and agricultural areas. Criteria for the protec- tion of aquatic life were not P o t o exceeded. m ac

R i ve FISH COMMUNITY DEGRADATION Of nine sites in the Potomac r River Basin at which fish com- munities were analyzed, only Muddy Creek, in an agricultur- al setting, was highly degraded

P relative to sites nationwide. A o t o m a high percentage of fish found at c Stream habitats at Muddy and Ac-

R this site are pollution tolerant. iv cotink Creeks were among the er Fish communities at two other most degraded in the Nation. A sites were degraded to a lesser majority of sites in the Potomac degree but were also among the River Basin at which stream habi- most degraded in the Nation. tats were assessed exhibited mod- One of these sites, Conoco- erate to high habitat degradation cheague Creek, drains an agri- with typically lower bank stabili- cultural area and the other, ty, increased bank erosion, and Accotink Creek, drains an lower densities of riparian vegeta- urban area near Washington, tion than at less degraded sites. D.C.

U.S. Geological Survey Circular 1166 23 WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT Comparison of Ground-Water Quality in the Potomac RIver Basin with Nationwide NAWQA Findings

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. Water- quality conditions for each drinking-water aquifer also are compared to established drinking-water standards and criteria for protection of human health. (Methods used to compute rankings and evaluate standards and criteria are described by Gilliom and others, in press.)

RADON The occurrence of radon in ground EXPLANATION water is dependent on a number of Shallow drinking-water aquifers geologic and hydrologic factors, Great Valley Carbonate, agricultural especially bedrock composition. areas Ground-water radon levels in the crystalline and siliciclastic rocks Valley and Ridge, agricultural areas of the Piedmont and Triassic Low- Piedmont lands in the eastern part of the Triassic Lowlands basin are among the highest ob- served nationwide. Radon activi- Ranking of ground-water quality relative ties in carbonate rocks of the to all NAWQA ground-water studies — Great Valley are also relatively DW indicates ranking compared to drinking- high, but activities in the western water aquifers (only), nationwide DW part of the Valley and Ridge are SGW indicates ranking compared to shal- among the lowest in the Nation. SGW low ground-water (only), nationwide No label indicates comparison to DW and SGW Nitrate concentrations in ground Darker colored circles generally indicate NITRATE water in carbonate rocks underly- poorer quality. Bold outline of circle indi- ing agricultural areas of the basin cates one or more standards or criteria were exceeded. are among the highest in the Na- tion; nearly 25 percent of samples Greater than the 75th percentile (among the highest 25 percent of NAWQA SGW contained nitrate at concentrations ground-water studies) DW exceeding the Federal drinking- water standard. Nitrate concentra- Between the median and the 75th percentile tions in the Piedmont area of the basin are also relatively high com- pared to other drinking-water Between the 25th percentile and the median sources across the Nation, al- though no samples exceeded the drinking-water standard. Nitrate Less than the 25th percentile DW (among the lowest 25 percent of NAWQA concentrations in the Triassic ground-water studies) SGW Lowlands and under agricultural lands in the Valley and Ridge are relatively low.

24 Water Quality in the Potomac River Basin WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT Comparison of Ground-Water Quality in the Potomac RIver Basin with Nationwide NAWQA Findings

DISSOLVED SOLIDS

CONCLUSIONS

In general, the presence of pesticides, ni- trate, and dissolved solids in ground water is related to agricultural land use—particularly in areas underlain by carbonate rocks. Po- tential 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 sedimen- Concentrations of dissolved solids in ground tary rocks derived from granitic rocks) tend water in carbonate aquifers underlying agricultur- to contain more uranium (Faure, 1986) and, al areas of the basin are among the highest in the therefore, higher activities of radon than Nation; 10 percent of samples exceeded the Fed- rocks of other types. Uranium is often con- eral drinking-water standard. Dissolved solids centrated in carbonate rocks as well. concentrations in other sampled areas of the Poto- mac River Basin are generally lower, although the drinking-water standard was exceeded in 14 per- cent of the samples from the Triassic Lowlands and 4 percent from the Valley and Ridge.

VOLATILE ORGANIC COMPOUNDS PESTICIDES

DW

SGW

Concentrations of volatile organic compounds Pesticide concentrations in agricultural areas of (VOCs) in agricultural areas of the Great Valley the Great Valley Carbonate are among the highest are among the lowest in the Nation. Only 6 percent in the Nation; 85 percent of samples contained of the samples contained detectable VOCs, and no detectable pesticides. Ground water in the Pied- Federal drinking-water standards were exceeded. mont also contains relatively high levels of pesti- No other area of the Potomac River Basin was cides. By contrast, pesticides were detected in sampled for VOCs as part of the NAWQA Pro- only 12 percent of wells in agricultural areas of the gram. Valley and Ridge.

U.S. Geological Survey Circular 1166 25 STUDY DESIGN AND DATA COLLECTION IN THE POTOMAC RIVER BASIN

8 1 4 3 9 6 7

2 10 11

5

Stream monitoring Sites sampled for site streambed sediment aquatic tissues

Figure 29. Stream chemistry was monitored at 11 sites in the Figure 30. Streambed sediment was sampled at 26 basin (see table 5). Of these sites, four (sites 5, 6, 8, and 11) sites in the basin. Of these sites, 21 were also were also monitored more intensively for pesticides, and two sampled for aquatic tissues (Asiatic clams or yellow (sites 5 and 11) were monitored more intensively for ecology. bullhead).

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

Number Name Drainagearea Principal land use(s) (see fig. 29) (square miles)

1 North Branch Potomac River near Cumberland, Md. 875 Forested 2 South Fork South Branch Potomac River near Moorefield, W. Va. 283 Forested, agricultural 3 South Branch Potomac River near Springfield, W. Va. 1,470 Forested, agricultural 4 Conococheague Creek at Fairview, Md. 494 Agricultural 5 Muddy Creek at Mount Clinton, Va. 14.2 Agricultural 6 Shenandoah River at Millville, W. Va. 3,040 Agricultural 7 Catoctin Creek at Taylorstown, Va. 89.6 Forested 8 Monocacy River at Bridgeport, Md. 173 Agricultural 9 Monocacy River near Frederick, Md. 817 Agricultural 10 Potomac River at Chain Bridge at Washington, D.C. 11,600 Forested, agricultural 11 Accotink Creek near Annandale, Va. 23.5 Urban

EXPLANATION Subunit Great Valley Carbonate

Valley and Ridge

Piedmont

Triassic Lowlands

Ground-water basin-wide Sites on major tributaries survey sites Sites on small streams Ground-water land-use effects survey sites (agriculture) Ground-water land-use effects survey sites (forest) Flow-path study site

Figure 31. Stream-chemistry and ecological studies were Figure 32. Ground-water samples were collected at 48 sites done at 89 small streams in four subunits of the basin. A in two subunits and at 57 sites in specific land uses in two synoptic study of water chemistry was also done at 23 larger other subunits. Multiple samples were collected from ground streams throughout the basin. water and streams at a small-scale flow-path study site.

26 Water Quality in the Potomac River Basin. STUDY DESIGN AND DATA COLLECTION IN THE POTOMAC RIVER BASIN

Sampling What data were collected Number Study component1 Types of sites sampled frequency and why of sites and period Stream chemistry Streambed-sediment Concentrations of trace elements and organic compounds in Depositional zones of the 22 1 survey sediment were measured to determine their occurrence and Potomac River and (in 1992) spatial distribution in sediments in streams of the basin. selected tributaries. 4 1 (see fig. 30) (in 1996) Basic sites Concentrations of major ions, suspended sediment, organic Streams of the basin, at or 11 About 14 carbon, and nutrients were measured in water samples col- near sites where stream- samples per lected monthly and during selected high flows to describe flow is measured contin- (see fig. 29, year, the occurrence of those compounds in streams over time. uously. table 5) (1993-95) Intensive sites Concentrations of pesticides were measured in water samples Subset of basic sites, 4 About 24 collected during selected high flows and weekly during a including streams drain- samples per growing season to determine the timing of transportation ing predominantly agri- (see fig. 29, year, of such compounds to streams. cultural or urban areas. table 5) (1993-95) Synoptic study of major Concentrations of major ions, nutrients, pesticides, and sus- Selected tributaries of the 23 1 tributaries pended sediment were measured in water samples col- Potomac River draining lected during stable, intermediate flow to relate the watersheds of greater (in 1994) occurrence and spatial distribution of those chemical com- than about 100 square pounds to potential sources in contributing watersheds. miles. (see fig. 31) Synoptic studies of small Concentrations of nutrients, pesticides, suspended sediment, Small streams draining 25 1 streams and major ions were measured in water samples collected watersheds of less than (in 1993) during low flows to determine the occurrence and spatial 37 square miles. 39 1 distribution of those compounds in streams across the (in 1994) basin and relate the stream chemistry to land use and other 25 1 watershed characteristics. (see fig. 31) (in 1995) Stream ecology Contaminants in aquatic Concentrations of organic compounds in whole fishes and Subset of streambed- 17 1 tissues clams and concentrations of trace metals in fish livers and sediment-survey sites. (in 1992) clams were measured to determine the occurrence and spa- 4 1 tial distribution of metals and organic compounds that can (see fig. 30) (in 1996) accumulate in aquatic tissues. Intensive ecological Fish, macroinvertebrates, and algae were identified and Subset of intensive sites. 2 1 reach per assessments counted and quantitative assessments of stream habitat site per year, were conducted to determine the variability of biological (see fig. 29, (1993-95) communities and habitat representing primary ecological table 5) regions of the basin on a small scale. Ecological synoptic Fish, macroinvertebrates, and algae were identified and Sites sampled during syn- 25 1 studies counted and quantitative assessements of stream habitat optic studies of small (in 1993) were conducted to determine the habitat and community streams. 39 1 structure of aquatic species in representative streams (in 1994) across the basin. 25 1 (see fig. 31) (in 1995) Ground-water chemistry Basin-wide survey Concentrations of nutrients, pesticides, organic carbon, radon, Randomly selected subset 48 1 uranium, tritium, and major ions were measured in water of previously existing samples to describe the chemistry of ground water in the shallow (mostly less than (see fig. 32) (in 1994) Piedmont and Triassic Lowlands (fig. 3). 300 feet deep) wells. Land-use effects survey Concentrations of nutrients, pesticides, organic carbon, Randomly selected subset 54 1 radon, uranium, tritium, and major ions were measured in of previously existing (agricul- (29 in 1993) water samples to describe the chemistry of ground water shallow (mostly less than ture) 1 within particular land-use settings and relate the differ- 300 feet deep) wells 3 (25 in 1995) ences in ground-water chemistry to natural and human fac- within agricultural or (forest) 1 tors. forested areas. (see fig. 32) (3 in 1995) Flow-path study Concentrations of nutrients, pesticides, organic carbon, radon, Streams and shallow 29 1 - 10 uranium, tritium, and major ions were measured in water (mostly less than 50 feet samples to relate their occurrence and distribution on a deep) wells installed (see fig. 32) (1993–1995) small scale to land use and other factors and evaluate their along an approximate transport from the land surface to ground water and from line of ground-water ground water to streams. flow within a small (less than 2 square miles) watershed.

1Gerhart and Brakebill, 1997; Gilliom and others, 1995.

U.S. Geological Survey Circular 1166 27 SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS

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]

a EXPLANATION Freshwater-chronic criterion for the protection of aquatic life Drinking-water standard or guideline a Range of surface-water detections in all 20 Study Units Range of ground-water detections in all 20 Study Units Detection in the Potomac River Basin Study Unit

Herbicide Rate of Concentration, in µg/L Herbicide Rate of Concentration, in µg/L (Trade or common detec- (Trade or common detec- b name) tion 0.001 0.01 0.1 1 10 100 1,000 name) tion b 0.001 0.01 0.1 1 10 100 1,000

Acetochlor 11% Metribuzin (Lexone, 9% 0% Sencor) 2% Alachlor (Lasso) 18% Napropamide <1% 0% (Devrinol) 0% 2,6-Diethylaniline <1% Oryzalin (Surflan, 6% (Alachlor metabolite) 0% Dirimal, Ryzelan) 0% Atrazine (AAtrex, 76% Pebulate (Tillam) 0% Gesaprim) 46% <1% Deethylatrazinec 62% Pendimethalin 13% (Atrazine metabolite) 41% (Prowl, Stomp) 0% Benfluralin (Balan, 1% Prometon (Gesa- 59% Benefin, Bonalan) 0% gram, prometone) 7% Butylate (Sutan, <1% Propachlor (Ramrod, <1% Genate Plus, butilate) 0% propachlore) 0% Cyanazine (Bladex, 21% Simazine (Aquazine, 79% Fortrol) 0% Princep, Gesatop) 38% DCPA (Dacthal, chlo- 1% Tebuthiuron (Spike, 7% rthal-dimethyl) <1% Perflan) 4% Dicamba (Banvel, 0% Terbacilc (Sinbar) 4% Mediben, dianat) 1% <1% Dichlorprop (2,4-DP, 1% Triclopyr (Garlon, 4% Seritox 50, Kildip) 0% Grazon, Crossbow) 0% Diuron (Karmex, 14% Trifluralin (Treflan, <1% Direx, DCMU) 0% Trinin, Elancolan) <1% EPTC (Eptam) 1% <1% Insecticide Rate Concentration, in µg/L (Trade or common of Linuron (Lorox, 9% name) detec- 0.001 0.01 0.1 1 10 100 1,000 Linex, Sarclex) 0% tion b 2% MCPA (Agritox, c 3% Agroxone) 0% Azinphos-methyl (Guthion, Gusathion) 0% 66% Metolachlor (Dual, c 24% Pennant) 17% Carbaryl (Sevin, Savit) 0%

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

Insecticide Rate Concentration, in µg/L Nutrient Rate Concentration, in mg/L (Trade or common of (Trade or common of name) detec- 0.001 0.01 0.1 1 10 100 1,000 name) detec- 0.01 0.1 1 10 100 1,000 10,000 100,000 tion b tion b 87% Carbofuranc 5% Dissolved ammonia 88% (Furadan, Curaterr) 0% Chlorpyrifos (Durs- 8% Dissolved ammonia ban, Lorsban) <1% plus organic nitrogen 77% as nitrogen 10% 2,4-D (2,4-PA) 20% 0% Dissolved phospho- 86% p,p’-DDE (p,p’-DDT <1% rus as phosphorus 52% metabolite) <1% Dissolved nitrite plus 99% Diazinon 24% nitrate 74% 1% Dieldrin (Panoram D- 1% 31, Octalox) 0% Ethoprop (Mocap, <1% Prophos) 0% Fonofos (Dyfonate) 1% 0% gamma-HCH <1% 0% Other Rate Concentration, in pCi/L of Malathion (maldison, 4% detec- 1 10 100 1,000 10,0000 100,000 malathon, Cythion) <1% tion b Methyl parathion 2% Radon 222 - - 0% (Penncap-M) 99% Propoxur (Baygon, 0% Blattanex, Unden) 1%

Volatile organic Rate Concentration, in µg/L compound of (Trade or common detec- 0.01 0.1 1 10 100 1,000 name) tion b Methylbenzene (Tolu- - - ene) 6% total Trihalomethanes - - 6%

U.S. Geological Survey Circular 1166 29 SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS

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

Herbicides Insecticides Volatile organic 1-Chloro-4-methylben- n-Butylbenzene (1-Phe- compounds zene (p-Chlorotoluene) nylbutane) 2,4,5-T 3-Hydroxycarbofuran (Car- n-Propylbenzene (Isoc- 1,1,1,2-Tetrachloroethane 2,2-Dichloropropane bofuran metabolite) umene) 2,4,5-TP (Silvex, Fenoprop) (1,1,1,2-TeCA) Benzene Aldicarb sulfone (Standak, p-Isopropyltoluene (p- 2,4-DB (Butyrac, Butox- 1,1,1-Trichloroethane Bromobenzene (Phenyl aldoxycarb, aldicarb metab- Cymene) one, Embutox Plus, Embu- (Methylchloroform) bromide) tone) olite) sec-Butylbenzene 1,1,2,2-Tetrachloroethane Bromochloromethane Acifluorfen (Blazer, Tackle Aldicarb sulfoxide (Aldi- (Methylene chlorobro- tert-Butylbenzene 1,1,2-Trichloro-1,2,2-trif- 2S) carb metabolite) mide) luoroethane (Freon 113, trans-1,2-Dichloroethene Bentazon (Basagran, Benta- Aldicarb (Temik, Ambush, CFC 113) Bromomethane (Methyl ((E)-1,2-Dichlorothene) zone, Bendioxide) Pounce) bromide) trans-1,3-Dichloropropene 1,1,2-Trichloroethane ((E)-1,3-Dichloropropene) Bromacil (Hyvar X, Urox Disulfoton (Disyston, Di- (Vinyl trichloride) Chlorobenzene B, Bromax) (Monochlorobenzene) Syston, Frumin AL, 1,1-Dichloroethane (Eth- Chloroethane (Ethyl chlo- Bromoxynil (Buctril, Bro- Solvirex, Ethylthiodemeton) ylidene dichloride) Nutrients minal) ride) Methiocarb (Slug-Geta, 1,1-Dichloroethene No non-detects Chloroethene (Vinyl Chlo- Chloramben (Amiben, Grandslam, Mesurol) (Vinylidene chloride) Amilon-WP, Vegiben) ride) 1,1-Dichloropropene Methomyl (Lanox, Lan- Chloromethane (Methyl Clopyralid (Stinger, Lon- nate, Acinate) 1,2,3-Trichlorobenzene chloride) trel, Reclaim, Transline) Oxamyl (Vydate L, Pratt) (1,2,3-TCB) Dibromomethane (Methyl- Dacthal mono-acid (Dacthal 1,2,3-Trichloropropane ene dibromide) metabolite) Parathion (Roethyl-P, Alk- ron, Panthion, Phoskil) (Allyl trichloride) Dichlorodifluoromethane Dinoseb (Dinosebe) 1,2,4-Trichlorobenzene (CFC 12, Freon 12) Phorate (Thimet, Granutox, Ethalfluralin (Sonalan, Cur- Geomet, Rampart) 1,2,4-Trimethylbenzene Dichloromethane (Methyl- bit) (Pseudocumene) ene chloride) Propargite (Comite, Omite, Fenuron (Fenulon, Feni- 1,2-Dibromo-3-chloropro- Dimethylbenzenes Ornamite) dim) pane (DBCP, Nemagon) (Xylenes (total)) Fluometuron (Flo-Met, Terbufos (Contraven, 1,2-Dibromoethane (EDB, Ethenylbenzene (Styrene) Counter, Pilarfox) Cotoran, Cottonex, Metu- Ethylene dibromide) Ethylbenzene (Phenyle- ron) alpha-HCH (alpha-BHC, 1,2-Dichlorobenzene (o- thane) MCPB (Thistrol) alpha-lindane, alpha- Dichlorobenzene, 1,2- Hexachlorobutadiene hexachlorocyclohexane, Molinate (Ordram) DCB) Isopropylbenzene alpha-benzene hexachlo- 1,2-Dichloroethane (Ethyl- (Cumene) Neburon (Neburea, Neb- ride) uryl, Noruben) ene dichloride) Methyl tert-butyl ether cis-Permethrin (Ambush, 1,2-Dichloropropane (Pro- (MTBE) Norflurazon (Evital, Pre- Astro, Pounce, Pramex, Per- pylene dichloride) Naphthalene dict, Solicam, Zorial) tox, Ambushfog, Kafil, Per- Picloram (Grazon, Tordon) thrine, Picket, Picket G, 1,3,5-Trimethylbenzene Tetrachloroethene (Per- Dragnet, Talcord, Outflank, (Mesitylene) chloroethene) Pronamide (Kerb, Propyza- Stockade, Eksmin, Coopex, 1,3-Dichlorobenzene (m- Tetrachloromethane (Car- mid) Peregin, Stomoxin, Sto- Dichlorobenzene) bon tetrachloride) Propanil (Stam, Stampede, moxin P, Qamlin, Corsair, 1,3-Dichloropropane (Tri- Trichloroethene (TCE) Wham, Surcopur, Prop-Job) Tornade) methylene dichloride) Trichlorofluoromethane Propham (Tuberite) 1,4-Dichlorobenzene (p- (CFC 11, Freon 11) Thiobencarb (Bolero, Sat- Dichlorobenzene, 1,4- cis-1,2-Dichloroethene urn, Benthiocarb, Abolish) DCB) ((Z)-1,2-Dichloroethene) Triallate (Far-Go, Avadex 1-Chloro-2-methylben- cis-1,3-Dichloropropene BW, Tri-allate) zene (o-Chlorotoluene) ((Z)-1,3-Dichloropropene)

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

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 Guideline for the protection of aquatic life e Range of detections in fish and clam tissue in all 20 Study Units Range of detections in bed sediment in all 20 Study Units Detection in bed sediment or fish tissue in the Potomac River Basin Study Unit Detection in clam tissue in the Potomac River Basin Study Unit

Semivolatile Rate Concentration, in µg/kg Semivolatile Rate Concentration, in µg/kg organic compound of organic compound of detec- 0.1 1 10 100 1,000 10,000 100,000 detec- 0.1 1 10 100 1,000 10,000 100,000 b tion b tion 1,2,4-Trichloroben- - - 4-Chloro-3-meth- - - zene 20% ylphenol 33% 1,2-Dimethylnaphtha- - - 4-Chlorophenyl-phe- - - lene 20% nylether 33% 1,4-Dichlorobenzene - - 9H-Carbazole - - 33% 75% 1,6-Dimethylnaphtha- - - 9H-Fluorene - - lene 67% 67% 1-Methyl-9H-fluorene - - Acenaphthene - - 85% 78% 1-Methylphenan- - - Acenaphthylene - - threne 80% 91% 1-Methylpyrene - - Acridine - - 60% 78% 2,3,6-Trimethylnaph- - - Anthracene - - thalene 43% 90% 2,4-Dinitrotoluene - - Anthraquinone - - 43% 91% 2,6-Dimethylnaphtha- - - Azobenzene - - lene 100% 56% 2,6-Dinitrotoluene - - Benz[ a ]anthracene - - 33% 100% 2-Chlorophenol - - Benzo[ a ]pyrene - - 50% 96% 2-Methylanthracene - - Benzo[ b ]fluoran- - - 73% thene 95% 3,5-Dimethylphenol - - Benzo[ c ]cinnoline - - 20% 56% 4,5-Methyle- - - Benzo[ ghi ]perylene - - nephenanthrene 60% 71% 4-Bromophenyl-phe- - - Benzo[ k ]fluoran- - - nylether 33% thene 95%

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

Semivolatile Rate Concentration, in µg/kg Organochlorine Rate Concentration, in µg/kg organic compound of compound of 0.1 1 10 100 1,000 10,000 100,000 0.01 0.1 1 10 100 1,000 10,000 100,000 detec- (Trade name) detec- tion b tion b

Butylbenzylphthalate - - Chloroneb (chlor- - - 86% onebe) 4% Chrysene - - Dieldrin (Panoram D- 13% 100% 31, Octalox) 36% Di- n -butylphthalate - - PCB, total 39% 100% 68% Di- n -octylphthalate - - DCPA (dacthal, chlo- 3% 40% rthal-dimethyl) 4% Dibenz[ a,h ] - - p,p’-DDE 16% anthracene 67% 88% Dibenzothiophene - - total-DDT 26% 80% 88% Diethylphthalate - - beta-HCH (beta- 10% 100% BHC, beta-hexachlo- 0% Dimethylphthalate - - gamma-HCH (lin- 0% 67% dane, gamma-BHC) 4% Fluoranthene - - Heptachlor epoxide 13% 100% 12% Indeno[1,2,3- cd ] - - Heptachlor (hep- 3% pyrene 82% tachlore, Velsicol) 8% Isophorone - - p,p’-Methoxychlor 3% 20% (Marlate) 4% Isoquinoline - - Pentachloroanisole 3% 50% 8% Naphthalene - - Toxaphene (cam- 0% 69% phechlor) 4% N-Nitrosodi- n - - - propylamine 20% Trace element Rate Concentration, in µg/g of - - Phenanthrene detec- 0.01 0.1 1 10 100 1,000 10,000 96% tion b Phenanthridine - - Arsenic 80% 81% 48% Phenol - - Cadmium 96% 94% 100% Pyrene - - Chromium 100% 100% 100% bis(2-Chloro- - - Copper 100% ethoxy)methane 56% 100% bis(2-Ethyl- - - Lead 72% hexyl)phthalate 100% 100% p-Cresol - - Mercury 56% 95% 100%

Organochlorine Rate Concentration, in µg/kg Nickel 100% of 100% compound 0.01 0.1 1 10 100 1,000 10,000 100,000 (Trade name) detec- Selenium 96% b tion 100% total-Chlordane 26% Zinc 100% 48% 100%

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

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 Organochlorine alpha-HCH (alpha- delta-HCH (delta-BHC, Trace elements organic compounds delta-hexachlorocyclo- BHC, alpha-lindane, No non-detects compounds alpha-hexachlorocyclo- hexane, delta-benzene Aldrin (HHDN, Octal- hexachloride) 1,2-Dichlorobenzene ene) hexane, alpha-benzene (o-Dichlorobenzene, hexachloride) 1,2-DCB) Endosulfan I (alpha- o,p’-Methoxychlor cis-Permethrin 1,3-Dichlorobenzene Endosulfan, Thiodan, Cyclodan, Beosit, (Ambush, Astro, trans-Permethrin (m-Dichlorobenzene) (Ambush, Astro, Malix, Thimul, Thifor) Pounce, Pramex, Pertox, Pounce, Pramex, Pertox, 2,2-Biquinoline Ambushfog, Kafil, Per- Endrin (Endrine) Ambushfog, Kafil, Per- thrine, Picket, Picket G, 2-Chloronaphthalene thrine, Picket, Picket G, Hexachlorobenzene Dragnet, Talcord, Out- 2-Ethylnaphthalene Dragnet, Talcord, Out- (HCB) flank, Stockade, flank, Stockade, C8-Alkylphenol Eksmin, Coopex, Pere- Isodrin (Isodrine, Com- Eksmin, Coopex, Pere- gin, Stomoxin, Sto- N-Nitrosodipheny- pound 711) gin, Stomoxin, Sto- lamine moxin P, Qamlin, moxin P, Qamlin, Mirex (Dechlorane) Corsair, Tornade) Corsair, Tornade) Nitrobenzene Pentachloronitroben- zene Quinoline

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 insecti- cides 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).

U.S. Geological Survey Circular 1166 33 REFERENCES

Allaby, Michael, 1989, Dictionary of Cardwell, D.H., Erwin, R.B., and Focazio, M.J., Bachman, L.J., Bohlke, the Environment (3d ed.): New Woodward, H.P., compilers., J.K., Busenberg, E., Plummer, York, New York University Press, 1968 (slightly revised 1986), L.N., and Powars, D.S., in press, 423 p. Geologic map of West Virginia: Preliminary estimates of resi- West Virginia Geological and dence times and apparent ages of Ator, S.W., and Denis, J.M., 1997, Economic Survey, 2 sheets, scale ground water in the Chesapeake Relation of nitrogen and phos- 1:250,000. Bay watershed and water-quality phorus in ground water to land data from a survey of springs: use in four subunits of the Poto- Cleaves, E.T., Edwards, Jonathan, Jr., U.S. Geological Survey Water- mac River Basin: U.S. Geological and Glaser, J.D., compilers., Resources Investigations Report Survey Water-Resources Investi- 1968, Geologic map of Maryland: 97-4225, in press. gations Report 96-4268, 26 p. Maryland Geological Survey, 1 sheet, scale 1:250:000. Gerhart, J.M., and Blomquist, J.D., Barbash, J.E., and Resek, E.A., 1996, 1995, Selected trace-element and Pesticides in ground water – Dis- Darrell, L.C., Hazelwood, B.K., and organic contaminants in stream- tribution, trends, and governing Schwarz, G.W., in press, Compar- bed sediments of the Potomac factors: Ann Arbor Press, ison of loads and trends in total River Basin, August 1992: U.S. Chelsea, Michigan, 588 p. nitrogen, total phosphorus, and Geological Survey Water- suspended material for the Poto- Resources Investigations Report Berg, T.M., chief comp., 1980, Geo- mac River at Chain Bridge, 1985- 95-4267, 12 p. logic map of Pennsylvania: Penn- 95: Metropolitan Washington sylvania Topographic and Council of Governments. Gerhart, J.M., and Brakebill, J.W., Geologic Survey, 4th Series, 1 1997, Design and implementation map on 2 sheets, scale 1:250,000, Faure, Gunter, 1986, Principles of iso- of a sampling strategy for a water- plus 1 sheet of cross sections. tope geology: New York, John quality assessment of the Poto- Wiley and Sons, Inc., 589 p. mac River Basin: U.S. Geological Blomquist, J.D., Fisher, G.T., Denis, Survey Water-Resources Investi- J.M., Brakebill, J.W., and Fenneman, N.M., and Johnson, D.W., gations Report 96-4034, 31 p. Werkheiser, W.H., 1996, Water- 1946, Physical divisions of the quality assessment of the Poto- United States: U.S. Geological Gianessi, L.P, and Puffer, C.A., 1990 mac River Basin – Analysis of Survey map, scale 1:7,000,000. (revised 1991), Herbicide use in available nutrient data, 1970-90: the United States: Resources for U.S. Geological Survey Water- Ferrari, M.J., and Ator, S.W., 1995, the Future, Quality of the Envi- Resources Investigations Report Nitrate in ground water of the ronment Division, Washington, 95-4221, 88 p. Great Valley Carbonate Subunit D.C., 128 p. of the Potomac River Basin: U.S. Brooks, K.M., 1977, Critical areas in Geological Survey Water- ____1992a, Fungicide use in U.S. crop the Potomac River Basin, A mid- Resources Investigations Report production: Resources for the 1977 review of water-pollution 95-4099, 6 p. Future, Washington, D.C. [vari- control: Interstate Commission on ously paged]. the Potomac River Basin Techni- Florida Department of Environmental cal Publication 77-3, 77 p. Protection, 1994, Approach to the ____1992b, Insecticide use in U.S. assessment of sediment quality in crop production: Resources for Canadian Council of Resource and Florida coastal waters, Vol. 1, the Future, Washington, D.C. Environment Ministers, 1991, Development and evaluation of [variously paged]. Canadian water-quality guide- sediment quality area assessment lines: Ottawa, Ontario, Environ- guidelines: prep. for FDEP, Office ment Canada, Inland Waters of Water Policy, Tallahassee, Directorate, Water Quality Florida, by MacDonald Environ- Branch. mental Services, Ltd., Ladysmith, British Columbia.

34 Water Quality in the Potomac River Basin REFERENCES

Gilliom, R.J., Alley, W.M., and Gurtz, Lizarraga, J.S., in press, Estimation National Academy of Sciences, M.E., 1995, Design of the and analysis of nutrient and sus- National Academy of Engineer- National Water-Quality Assess- pended-sediment loads at selected ing, 1973, Water quality criteria, ment program – Occurrence and sites in the Potomac River Basin, 1972: Ecological Research Series distribution of water-quality con- 1993-95: U.S. Geological Survey EPA-R3-73-03, p. 594. ditions: U.S. Geological Survey Water-Resources Investigations Circular 1112, 33 p. Report 97-4154. U.S. Department of Commerce, 1995, 1992 Census of Agriculture Geo- Gilliom, R.J., Mueller, D.K., and Long, E.R., MacDonald, D.D., Smith, graphic Series 1B: Bureau of the Nowell, L.H., in press, Methods S.L., and Calder, F.D., 1995, Inci- Census, Washington, D.C. for comparing water-quality con- dence of adverse biological ditions among National Water- effects within the ranges of chem- U.S. Environmental Protection Quality Assessment Study Units. ical concentrations in marine and Agency, 1986, Quality criteria for 1992-1995: U.S. Geological Sur- estuarine sediments: Environmen- water, 1986: Washington, D.C., vey Open-File Report 97-589. tal Management, v. 19, no. 1, U.S. Environmental Protection p. 81-87. Agency Report 440/5-86-01, Hitt, K.J., 1994, Refining 1970’s land- Office of Water [variously paged]. use data with 1990 population Long, E.R., and Morgan, L.G., 1990, data to indicate new residential The potential for biological ____1991a, Water-quality criteria development: U.S. Geological effects of sediment-sorbed con- summary: Office of Water, Office Survey Water-Resources Investi- taminants tested in the National of Health and Ecological Effects gations Report 94-4250, 15 p. Status and Trends Program: U.S. Division (poster). National Oceanic and Atmo- Helsel, D.R., and Hirsch, R.M., 1992, spheric Administration, Technical ____ 1991b, Chesapeake Bay toxics of Statistical methods in water Memo NOS OMA 52, 175 p. concern list: U.S. Environmental resources: Amsterdam, Elsevier Protection Agency, 9 p. Publ., 522 p. Milici, R.C., Spiker, C.T., Jr., and Wil- son, J.M., compilers, 1963, Geo- ____1991c, Chesapeake Bay toxics of International Joint Commission Can- logic map of Virginia: concern list: U.S. Environmental ada and United States, 1977, New Charlottesville, Virginia, Division Protection Agency, 112 p. and revised Great Lakes water- of Mineral Resources, quality objectives, Volume II, An 1 sheet, scale 1:500,000. ____ 1992, National study of chemical IJC report to the governments of residues in fish – Volume II: [U.S. the United States and Canada: Miller, C.V., Denis, J.M., Ator, S.W., Environmental Protection IJC, Windsor, Ontario, Canada. and Brakebill, J.W., 1997, Nutri- Agency], EPA 823-R-92-008b, ents in streams during baseflow in 263 p. King, P.B. and Beikman, H.M., 1974, selected environmental settings of Geologic map of the United the Potomac River Basin: Journal ____1994a, National primary drinking States: U.S. Geological Survey, 3 of the American Water Resources water standards: EPA 810-F-94- sheets, scale 1:2,500,000. Association, v. 33, no. 6, p. 1155- 001A, 8 p. 1171. Lindsey, B.D., and Ator, S.W., 1996, ____ 1994b, A citizen’s guide to radon Radon in ground water of the Mueller, D.K., Hamilton, P.A., Helsel, (2nd ed.): EPA 402-K92-001, Lower Susquehanna and Potomac D.R., Hitt, K.J., and Ruddy, B.C., 16 p. River Basins: U.S. Geological 1995, Nutrients in ground water Survey Water-Resources Investi- and surface water of the United ____ 1996, Drinking water regulations gations Report 96-4156, 6 p. States – An analysis of data and health advisories: Office of through 1992: U.S. Geological Water, EPA 822-B-96-002, Survey Water-Resources Investi- 11 p. gations Report 95-4031, 74 p.

U.S. Geological Survey Circular 1166 35 REFERENCES

U.S. Food and Drug Administration, 1992, Action levels for poison- ous 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 for 1992: Virginia Water Control Board Information Bulletin #588, v. 2, 444 p.

Vogelmann,J.E., Sohl, T.L., Campbell, P.V., and Shaw, D.M., 1997, Regional land cover characteriza- tion using Landsat and other spa- tial data input [abs.]: Developing the tools to meet the Nation’s monitoring needs – The evolution of EMAP, p. 10.

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 Water- Resources 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 water by C-18 solid-phase extrac- tion and capillary-column gas chromatography/mass spectrome- try with selected ion monitoring: U.S. Geological Survey Open- File Report 95-181, 49 p.

36 Water Quality in the Potomac River Basin GLOSSARY

The terms in this glossary were com- an organic substance through Habitat - The part of the physical piled from numerous sources. Some chemical, photochemical, and(or) environment where plants and definitions have been modified and biochemical reactions. animals live. may not be the only valid ones for these terms. Discharge - Rate of fluid flow passing Health advisory - Nonregulatory lev- a given point at a given moment els of contaminants in drinking Ammonia - A compound of nitrogen in time, expressed as volume per water that may be used as guid- and hydrogen (NH3) that is a unit of time. ance in the absence of regulatory common by-product of animal limits. Advisories consist of esti- waste. Ammonia readily converts Dissolved constituent - Operationally mates of concentrations that to nitrate in soils and streams. defined as a constituent that would result in no known or passes through a 0.45-micrometer anticipated health effects (for car- Aquifer - A water-bearing layer of filter. cinogens, a specified cancer risk) soil, sand, gravel, or rock that will determined for a child or for an yield usable quantities of water to Drainage basin - The portion of the adult for various exposure peri- a well. surface of the Earth that contrib- ods. utes water to a stream through Basin - See Drainage basin. overland runoff, including tribu- Herbicide - A chemical or other agent taries and impoundments. applied for the purpose of killing Bedrock - General term for consoli- undesirable plants. See also Pesti- dated (solid) rock that underlies Ecosystem - The interacting popula- cide. soils or other unconsolidated tions of plants, animals, and material. microorganisms occupying an Infiltration - Movement of water, typ- area, plus their physical environ- ically downward, into soil or Bed sediment - The material that tem- ment. porous rock. porarily is stationary in the bot- tom of a stream or other Evapotranspiration - A collective Insecticide - A substance or mixture watercourse. term that includes water lost of substances intended to destroy through evaporation from the soil or repel insects. Carbonate rocks - Rocks (such as and surface-water bodies and by limestone or dolostone) that are plant transpiration. composed primarily of minerals Invertebrate - An animal having no (such as calcite and dolomite) FDA action level - A regulatory level backbone or spinal column. containing the carbonate ion recommended by the U.S. Envi- 2- Karst - A type of topography that (CO3 ). ronmental Protection Agency for enforcement by the FDA when results from dissolution and col- Community - In ecology, the species pesticide residues occur in food lapse of carbonate rocks such as that interact in a common area. commodities for reasons other limestone and dolomite and char- than the direct application of the acterized by closed depressions or Concentration - The amount or mass pesticide. Action levels are set for sinkholes, caves, and under- of a substance present in a given inadvertent pesticide residues ground drainage. volume or mass of sample. Usu- resulting from previous legal use ally expressed as micrograms per or accidental contamination. Load - General term that refers to a liter (water sample) or micro- Applies to edible portions of fish material or constituent in solution grams per kilogram (sediment or and shellfish in interstate com- or suspension in transport; usu- tissue sample). merce. ally expressed in terms of mass or volume. Crystalline rocks - Rocks (igneous or Fish community - See Community. metamorphic) consisting wholly Maximum contaminant level (MCL) of crystals or fragments of crys- Ground water - In general, any water - Maximum permissible level of a tals. that exists beneath the land sur- contaminant in water that is deliv- face, but more commonly applied ered to any user of a public water Degradation products - Compounds to water in fully saturated soils system. MCL's are enforceable resulting from transformation of and geologic formations. standards established by the U.S.

U.S. Geological Survey Circular 1166 37 GLOSSARY

Environmental Protection the element radium; damaging to Agency. human lungs when inhaled.

Nitrate - An ion consisting of nitrogen Siliciclastic rocks - Rocks such as - and oxygen (NO3 ). Nitrate is a shale and sandstone that are plant nutrient and is very mobile formed by the compaction and in soils. cementation of quartz-rich min- eral grains. Nutrient - Element or compound essential for animal and plant Triazine herbicide - A class of herbi- growth. Common nutrients in fer- cides containing a symmetrical tilizer include nitrogen, phospho- triazine ring (a nitrogen-heterocy- rus, and potassium. clic ring composed of three nitro- gens and three carbons in an Pesticide - A chemical applied to alternating sequence). Examples crops, rights of way, lawns, or include atrazine, propazine, and residences to control weeds, simazine. insects, fungi, nematodes, rodents, or other "pests." Triazine pesticide - See Triazine her- bicide. Phosphorus - A nutrient essential for growth that can play a key role in Uranium - A heavy silvery-white stimulating aquatic growth in metallic element, highly radioac- lakes and streams. tive and easily oxidized. Of the 14 known isotopes of uranium, 238U Photosynthesis - Synthesis of chemi- is the most abundant in nature. cal compounds by organisms with the aid of light. Carbon dioxide is Watershed - See Drainage basin. used as raw material for photo- synthesis and oxygen is a product. Water year - The continuous 12- month period, October 1 through Physiography - A description of the September 30, in U.S. Geological surface features of the Earth, with Survey reports dealing with the an emphasis on the origin of land- surface-water supply. The water forms. year is designated by the calendar year in which it ends and which Picocurie (pCi) - One trillionth (10-12) includes 9 of the 12 months. of the amount of radioactivity Thus, the year ending September represented by a curie (Ci). A 30, 1980, is referred to as the curie is the amount of radioactiv- “1980” water year. ity that yields 3.7 x 1010 radio- active disintegrations per second (dps). A picocurie yields 2.22 dis- integrations 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, color- less, odorless, radioactive gas formed by the disintegration of

38 Water Quality in the Potomac River Basin Ator and others • Water Quality in the Potomac River Basin USGS Circular 1166 • 1998

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