A COORDINATED EFFORT

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Division

12201 Sunrise Valley Drive, M.S. 413

Reston, VA 20192

FOR ADDITIONAL INFORMATION ON THE 

NATIONAL WATER-QUALITY ASSESSMENT (NAWQA) PROGRAM:

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

acknowledge the significant contribution by members of these organizations through their regular participation 

in the study liaison committee:

Much appreciation is extended to several U.S. Geological Survey employees for their significant contributions to 

this report: Robert F. Breault, Jonathan Morrison, John R. Mullaney, Peter A. Steeves, and Britt O. Stock. 

Special appreciation is extended to volunteer Peter Mitchell for his help and support.

Illustrations by Luis E. Menoyo; Rerendered by Mark V. Bonito

Edited by Linda S. Rogers

Hardcopy manuscript prepared by Luis E. Menoyo; PDF version prepared by Mark V. Bonito

Front cover: The Connecticut River near Sunderland, Massachusetts; photograph by Peter A. Steeves

Back cover: (left) White River near West Hartford, Vermont; photograph by Britt O. Stock;

(right) White River near West Hartford, Vermont; photograph by Britt O. Stock

Connecticut, Housatonic, and Thames River 

Basins Study Unit, contact:

District Chief

U.S. Geological Survey

MA-RI District Office

10 Bearfoot Road, Suite 6

Northborough, MA 01532

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

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

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

The Connecticut, Housatonic, and Thames River Basins Study Unit’s Home Page 

can be accessed at URL:

http://mass1.er.usgs.gov

or

http://ma.water.usgs.gov

Federal and Interstate Organizations

U.S. Fish and Wildlife Service

U.S. Environmental Protection Agency

New England Interstate Water Pollution Control 

Commission

Connecticut River Joint River Commission (New 

Hampshire, Vermont)

State Agencies

Connecticut Department of Environmental Protection

Massachusetts Department of Environmental Protection

New Hampshire Department of Environmental Services

Vermont Department of Environmental Conservation

Local Agencies

Pioneer Valley Planning Commission

Middlesex County Soil and Water Conservation District

Universities

University of Massachusetts

University of Connecticut

Private Organizations

Connecticut River Watershed Council

Housatonic River Valley Association

Nature Conservancy

River Watch Network
U.S. GEOLOGICAL SURVEY CIRCULAR

Water Quality in the Connecticut, 

Housatonic, and Thames River Basins, 

Connecticut, Massachusetts, New Hampshire, 

New York, and Vermont, 1992–95

1155

By S.P. Garabedian, J.F. Coles, S.J. Grady, E.C.T. Trench, and

M.J. Zimmerman

CONTENTS

National Water-Quality Assessment 

Program.................................................... 1

Summary of major issues and findings........ 2

Environmental setting and hydrologic

conditions ................................................. 4

Major issues and findings:

Contaminants in streambed sediments and

 fish tissue ............................................. 6

Nutrients in surface water......................... 8

Pesticides in surface water....................... 10

Pesticides in ground water ....................... 12

Volatile organic compounds in

 ground water ........................................ 14

Nitrate in ground water ............................. 16

Radon in ground water ............................. 17

Water-quality conditions in a

national context ........................................ 18

Study design and data collection................. 22

Summary of compound detections and

concentrations .......................................... 24

References .................................................. 30

Glossary ...................................................... 31
Library of Congress Cataloging in Publications Data

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

does not constitute endorsement by the U.S. Government

Free on application to the

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, CO 80225–0286

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Thomas J. Casadevall, Acting Director

Garabedian, Stephen P.

Water Quality in the Connecticut, Housatonic, and Thames River Basins, Connecticut, Massachusetts, 

New Hampshire, New York, and Vermont, 1992-95 / by Stephen P. Garabedian.

p. cm. -- (U.S. Geological Survey circular ; 1155)

Includes bibliographical references.

1. Water quality--Connecticut River Watershed. 2.Water Quality-Housatonic River Watershed (Mass. and 

Conn.) 3. Water quality-Connecticut--Thames river watershed. I. Title. II. Series.

TD223.15.g37 1998

363.739.42.0974--dc21

ISBN 0-607-89366-4

Printed version 1998

PDF (web) version 2001
U.S. Geological Survey Circular 1155 1

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

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

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

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

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

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

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

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

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

conditions. 

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

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

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

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

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

Study Unit is scheduled to be revisited every decade to evaluate changes in waterquality conditions. NAWQA assessments rely heavily on existing information collected by the USGS and many other agencies as well as the use of nationally consistent study designs and methods of sampling and analysis. Such consistency simultaneously provides information about the status and trends in water-quality conditions

in a particular stream or aquifer and, more importantly, provides the basis to make

comparisons among watersheds and improve our understanding of the factors that

affect water-quality conditions regionally and nationally. 

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

and 1995 from the water-quality assessment of the Connecticut, Housatonic, and

Thames River Basins Study Unit and to relate these findings to water-quality issues of

regional and national concern. The information is primarily intended for those who

are involved in water-resource management. Indeed, this report addresses many of the

concerns raised by regulators, water-utility managers, industry representatives, and

other scientists, engineers, public officials, and members of stakeholder groups who

provided advice and input to the USGS during this NAWQA Study-Unit investigation. Yet, the information contained here may also interest those who simply wish to

know more about the quality of water in the rivers and aquifers in the area where they

live. 

 Robert M. Hirsch, Chief Hydrologist
SUMMARY OF MAJOR ISSUES AND FINDINGS

2 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

Toxic contaminants have accumulated in some Study Unit streambed 

sediments and fish.

Concentrations of polychlorinated biphenyls (PCBs) in streambed sediments and fish 

in the Housatonic River were among some of the highest detected in NAWQA Study 

Units across the Nation. Concentrations of trace elements and organic contaminants 

in streambed sediment and fish generally were highest in the southern part of the 

Study Unit (Massachusetts and Connecticut). Because of the presence of these 

contaminants, fish consumption advisories have been issued for a number of rivers 

and lakes throughout the Study Unit. These advisories recommend limiting the 

number of fish of certain species that should be consumed by people, particularly by 

children and pregnant women.

Nutrient (nitrogen and phosphorus) concentrations are a concern for 

surface-water quality.

The large amount of nitrogen entering Long Island Sound from streams, precipitation, 

and coastal communities has stimulated algal blooms. Decay of the algae then 

produces low dissolved-oxygen conditions in the Sound, creating poor habitat for fish 

and other marine animals. Nitrogen and phosphorus concentrations are highest in 

urban streams, primarily because of wastewater discharges from sewage-treatment 

facilities.

Pesticides were frequently detected in Study Unit streams.

The herbicides atrazine, metolachlor, prometon, and simazine, and the insecticides 

diazinon and carbaryl were the most frequently detected compounds. Concentrations 

of atrazine, metolachlor, and simazine were highest in surface water draining from 

agricultural areas. Concentrations of prometon, diazinon, and carbaryl were highest in 

surface water draining from urban areas. However, current drinking-water standards 

were not exceeded. None of the pesticides were detected at concentrations greater 

than the U.S. Environmental Protection Agency’s maximum contaminant level 

(MCL) or the health advisory limit (HAL), and few pesticide concentrations exceeded 

1 microgram per liter (1 μg/L). Current drinking-water standards, however, do not 

include some detected pesticides (or breakdown products), and do not include 

consideration of more than one pesticide in the water. Thus, the actual health concern 

posed by these results is somewhat uncertain.

Several classes of contaminants were detected in ground water.

These contaminants included pesticides, volatile organic compounds (VOCs), and 

nitrate. Twenty-four different pesticides (or their breakdown products) were detected 

in shallow ground water beneath the Study Unit. Atrazine, prometon, and simazine 

were the most commonly detected pesticides in ground water. VOCs were detected in 

70 percent of the shallow ground-water samples collected in urban areas. Methyl tertbutyl ether (MTBE), a gasoline additive, was the most frequently detected VOC, and 

chloroform, a byproduct of water disinfection, was the second most frequently 

detected. Median nitrate concentrations in shallow ground water beneath agricultural 

fields (3.8 mg/L) were nearly 30 times higher than background concentrations 

(0.14 mg/L).
U.S. Geological Survey Circular 1155 3

SUMMARY OF MAJOR ISSUES AND FINDINGS

Some contaminant MCLs were exeeded in ground water.

The pesticides atrazine and ethylene dibromide were detected at concentrations 

greater than their MCLs in a few samples collected from agricultural areas. The 

VOCs—tetrachloroethene, trichloroethene, benzene, and naphthalene—exceeded 

their MCLs in some samples collected from urban areas. Nitrate concentrations 

exceeded the MCL in 15 percent of the samples of shallow ground water collected in 

agricultural areas.

Radon is present in ground water across the Study Unit.

Radon is a naturally occurring, colorless, odorless radioactive gas derived from 

uranium. Exposure to radon has been recognized as a health risk, primarily as a cause 

of lung cancer. Radon concentrations exceeded the previously proposed limit of 

300 picocuries per liter in 97 percent of water samples collected from bedrock supply 

wells, and in 88 percent of water samples collected from the shallow monitoring wells 

in the Study Unit.

VT.

N.H.

MASS.

CONN. R.I.

Quabbin Reservoir, which is within the Study Unit in central Massachusetts, supplies most of the drinking water for Boston, 

Massachusetts (photograph by Stephen Garabedian, U.S. Geological Survey).
4 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95.

ENVIRONMENTAL SETTING AND HYDROLOGIC CONDITIONS

EXPLANATION

LAND USE—From Mitchell and 

others (1997)

Urban

Agriculture

Forest

BOUNDARY OF MAJOR BASINS 

BOUNDARY OF STUDY UNIT

0 20

0 20

40MILES

40 KILOMETERS

VERMONT

CANADA

NEW YORK

NEW YORK

LONG ISLAND SOUND

NEW

HAMPSHIRE

MASSACHUSETTS

RHODE

ISLAND

CONNECTICUT

Base from U.S. Geological Survey Digital Line Graphs, 1989

Universal Transverse Mercator

1:100,000

UNITED STATES

QUEBEC

ATLANTIC OCEAN

73 ̊ 72 ̊

71 ̊

45 ̊

44 ̊

43 ̊

42 ̊

41 ̊

AREA OF STUDY UNIT

EXPLANATION

0 20 40

0 20 40

MILES

KILOMETERS

VERMONT

CANADA

NEW YORK

NEW YORK

NEW

HAMPSHIRE

MASSACHUSETTS

RHODE

ISLAND

LONG ISLAND SOUND

ATLANTIC OCEAN

CONNECTICUT

Base from U.S. Geological Survey Digital Line Graphs, 1989

Universal Transverse Mercator

1:100,000

UNITED STATES

QUEBEC 73 ̊ 72 ̊

71 ̊

45 ̊

44 ̊

43 ̊

42 ̊

41 ̊

Bridgeport

New Haven

Hartford

Springfield

✪

. .

.

Housatonic

River

Connecticut

River

Thames River

Mt.

Washington

The Connecticut, Housatonic, and 

Thames River Basins Study Unit, 15,760 square 

miles in extent, includes eastern Vermont, 

western New Hampshire, west-central 

Massachusetts, nearly all of Connecticut, and 

small parts of New York, Rhode Island, and the 

Province of Quebec, Canada. Altitudes in the 

Study Unit range from sea level in coastal 

Connecticut to 6,288 feet at the peak of Mount 

Washington in the White Mountains of New 

Hampshire.

The population in the Study Unit is about 

4.5 million people, about 2 percent of the 

Nation’s population. Population density varies 

from the sparsely populated, rural agrarian and 

wilderness areas of northern Vermont and New 

Hampshire to the densely populated urban areas 

of southwestern Connecticut and the southcentral part of the Connecticut River Valley.

Most of the area is forested undeveloped land, 

agriculture covers about 12 percent of the total 

area of the Study Unit, and urban areas cover 

about 8 percent of the Study Unit. All major 

cities, including Hartford, Springfield, 

Bridgeport, and New Haven, are in the southern 

part of the area.

Total freshwater use in the Study Unit 

during 1990 was estimated to be about 

2,300 Mgal/d (million gallons per day). The 

dominant surface-water use is for thermoelectric 

power generation, and the next largest use is for 

public supply. Ground water supplied about 

12 percent (270 Mgal/d) of the freshwater used 

in the Study Unit. Ground water is used 

primarily for public supply and self-supplied 

domestic use. Discharges of treated sewage, 

amounting to about 520 Mgal/d, are released 

from 145 wastewater-treatment facilities, most 

of which are in the densely populated southern 

part of the area.

The climate in the Connecticut, 

Housatonic, and Thames River Basins generally 

is temperate and humid. Mean annual 

precipitation averages about 43 inches over the 

entire Study Unit but ranges from about 

34 inches at places in the northern end of the 

Connecticut River Valley to more than 

65 inches in adjacent mountainous regions. In 

general, average precipitation is evenly 

distributed throughout the year. Precipitation 

generally was close to average during 1992-95, 

with a slightly dry condition from March 

through June 1995.

All streams in the Study Unit flow to Long Island Sound, with a 

combined drainage area of nearly 16,000 square miles.

Land use across the Study Unit varies from primarily forest in the 

northern areas to a mix of urban and agricultural uses to the south.
U.S. Geological Survey Circular 1155 5

ENVIRONMENTAL SETTING AND HYDROLOGIC CONDITIONS

The Connecticut River is the principal river in the Study Unit, extending about 400 miles from its source in 

northern New Hampshire to the mouth at Old Saybrook, Connecticut, on Long Island Sound. The drainage area of 

the Connecticut River is 11,260 square miles, or about 72 percent of the Study Unit; average discharge at the 

mouth of the river is estimated to be 19,200 cubic feet per second. The Connecticut River is heavily regulated, with 

at least 125 reservoirs within the basin used for power generation and 16 flood-control reservoirs. Other major 

streams include the Housatonic and Thames Rivers, which together drain 3,420 square miles, or about 20 percent 

of the Study Unit.

Average monthly discharge for an unregulated stream (that is, not dammed) show that peak streamflow 

generally is in late winter and early spring, but discharges in mid-1995 were uniformly lower than average because 

of below-average precipitation. The average annual discharge for the Connecticut River in 1995 was the sixth 

lowest discharge for 1930-95 owing to the dry conditions that year.

The aquifers that yield the most water in the Study Unit are sand and gravel deposits within the glacial 

stratified drift that fills many of the valleys in the region. Water levels in wells are typically at their highest 

elevations in early spring and lowest elevations in late summer. Ground-water levels generally were close to 

average during 1992-95 but were slightly lower during mid-1995 as a result of the dry conditions that year.

 

100

90

80

70

60

50

40

30

20

10

0

FRESHWATER WITHDRAWALS,

IN MILLION GALLONS PER DAY

PERCENTAGE OF TOTAL

FRESHWATER WITHDRAWALS

2,000

1,500

1,000

500

0

2,500

GROUND WATER

SURFACE WATER

POPULATION SERVED,

IN THOUSANDS

TOTAL

PUBLIC

SUPPLY

DOMESTIC

SUPPLY

COMMERCIAL

INDUSTRIAL

AND MINING

IRRIGATION AND

LIVESTOCK

THERMOELECTRIC

(3,655)

(3,655)

(924)

6

14

4

8

10

12

WATER LEVEL, IN FEET BELOW LAND SURFACE

WATER LEVEL, IN FEET ABOVE SEA LEVEL

AVERAGE MONTHLY WATER 

LEVEL NOVEMBER 1966-

SEPTEMBER 1995

WATER LEVEL DURING 

WATER YEARS 1992-95

1992 1993 1994 1995

DATE

26

34

36

28

30

32

South Windsor,

Connecticut

SW 64

1992 1993 1994 1995

DATE

8,000

10,000

0

2,000

4,000

6,000

DISCHARGE, IN CUBIC FEET PER SECOND

White River at W. Hartford, Vermont

MONTHLY AVERAGE DISCHARGE

WATER YEARS 93-95

AVERAGE MONTHLY DISCHARGE,

PERIOD OF RECORD

0

10

1

2

3

4

5

6

7

8

9

PRECIPITATION, IN INCHES

MONTHLY PRECIPITATION (1992-95)

AVERAGE MONTHLY PRECIPITATION (1961-90)

Windsor Locks, Connecticut

44.14 inches average annual precipitation

1992 1993 1994 1995

DATE

Precipitation was close to average during 

1992-95, except for slightly dry conditions in 

spring 1995.

Discharge in Study Unit streams without dams is 

highest in the spring and lowest in late summer. Note 

the effect of decreased precipitation on discharge in 

1995.

About 80 percent of all freshwater used in the 

Study Unit is from surface sources. Most of this 

water is used for cooling in thermoelectric power 

generation and for public supply.

Ground-water levels vary seasonally and from year to 

year. Note the effect of decreased precipitation on 

water levels in 1995.
6 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

MAJOR ISSUES AND FINDINGS

CONTAMINANTS IN STREAMBED SEDIMENTS AND FISH TISSUE

Toxic contaminants have 

accumulated in some Study 

Unit streambed sediments 

and fish

Samples collected at selected 

sites show that toxic contaminants 

have accumulated in streambed 

sediment and fish in many parts of 

the Study Unit (Coles, 1996; 

Breault and Harris, 1997). These are 

contaminants that do not easily 

dissolve in water but instead tend to 

accumulate in streambed sediments 

and aquatic animals. The most 

common contaminants detected in 

bed sediment were the trace 

elements chromium, copper, lead, 

mercury, nickel, and zinc, and the 

organic compounds chlordane, 

dichlorodiphenyltrichloroethane 

(DDT), polychlorinated biphenyls 

(PCBs), and polycyclic aromatic 

hydrocarbons (PAHs). The most 

commonly detected organic 

compounds detected in whole fish 

samples included chlordane, DDT 

(and its breakdown product DDE), 

and PCBs. These trace elements and 

organic compounds are on the U.S. 

Environmental Protection Agency’s 

Priority Pollutant List and have 

been given high priority in waterquality monitoring and pollution 

abatement programs. 

Trace elements and organic 

compounds in streambed sediments 

and fish generally were detected at 

lowest concentrations in the 

northern forested drainage basins 

and at highest concentrations in the 

southern urban drainage basins 

because of an increased number of 

sources in the southern basins. In 

addition, streams that drain large 

basins typically had more frequent 

detections of toxic contaminants 

because these streams generally 

drain large urban areas, providing 

more potential contaminant sources. 

The highest percentages of traceelement concentrations exceeding 

naturally occurring concentrations 

were in samples collected from 

streambed sediments in the Thames 

River Basin. The highest 

percentages of organic-compound 

detections were in streambed 

sediments from smaller streams that 

drain to Long Island Sound. 

Concentrations of PCBs in 

streambed sediments and fish in the 

Housatonic River are some of the 

highest for NAWQA Study Units in 

the Nation; several of these 

concentrations exceeded 

10,000 parts per billion.

Aquatic organisms can 

concentrate contaminants, and 

adverse effects on bottom-dwelling 

organisms (for example, aquatic 

insects, clams, crayfish) can be 

related to elevated trace-element 

and organic-compound 

concentrations in streambed 

sediments (Breault and Harris, 

1997). Adverse effects can include 

decreased numbers of species and 

death of contaminant-sensitive 

species (Ecosystem Conservation 

Directorate, 1995). Trace elements 

represent the most geographically 

widespread concern to aquatic 

organisms, exceeding sedimentquality guidelines over a wider 

geographical area than the organic 

compounds. However, some organic 

compounds (chlordane and PCBs) 

pose the greatest biological concern 

in terms of exceeding sedimentquality aquatic life guidelines; they 

are present at sufficiently high 

concentrations to cause severe 

effects at several locations in the 

Study Unit (see map at right).

Once bottom-dwelling organisms 

have become contaminated, they 

become a source of contaminants to 

fish. Many of the contaminants are 

readily stored in the fatty tissue of 

fish where they tend to accumulate. 

Fish-eating mammals and birds can 

then consume the contaminated 

fish, and so pass contaminants up 

the food chain. National Academy 

of Science and National Academy 

of Engineering guidelines (1973) 

for fish tissue, issued for the 

protection of fish-eating wildlife, 

were exceeded at many sampling 

sites because of high concentrations 

of PCBs, total chlordane, and 

dieldrin (see map at right).

Contaminants in fish tissue are a 

concern not only because of hazards 

to wildlife but also because of 

human health concerns. U.S. 

Environmental Protection Agency 

guidelines and U.S. Food and Drug 

Administration standards have been 

established for contaminant 

concentrations in fish tissue for 

human consumption. The possible 

risks to human health through the 

consumption of contaminated fish 

have resulted in advisories to 

restrict the consumption of some 

species of fish in the Study Unit. 

These advisories recommend 

limiting the number of fish of 

certain species that are consumed 

by people, particularly by children 

and pregnant women. Fish 

consumption advisories now in 

effect include those issued for 

mercury contamination in 

Connecticut (Department of 

Environmental Protection, 1994, 

1996), Massachusetts (Department 

Some fish collected for this study had 

open sores from either injury or disease 

(photograph by Michael Turtora, U.S. 

Geological Survey).

Spills and leaks of PCBs have led to 

contamination of streambed sediment 

and fish in many streams across the 

Study Unit (photograph by Michael 

Turtora, U.S. Geological Survey).
U.S. Geological Survey Circular 1155 7

MAJOR ISSUES AND FINDINGS

CONTAMINANTS IN STREAMBED SEDIMENTS AND FISH TISSUE

LAND USE—From Mitchell and others (1977)

Urban

Agriculture

Forest

NATIONAL ACADEMY OF SCIENCE AND 

NATIONAL ACADEMY OF ENGINEERING

GUIDELINES FOR ORGANOCHLORINES IN 

WHOLE FISH FOR THE PROTECTION OF 

FISH-EATING WILDLIFE

Exceeds total PCB guideline

Exceeds total chlordane 

and dieldrin guideline

Sampled - No exceedance 

of guidelines

EXPLANATION

STUDY UNIT BOUNDARY

BED SEDIMENT SITES

POTENTIAL FREQUENCY OF OCCURRENCE 

OF ADVERSE EFFECTS ON 

BENTHIC ORGANISMS

(Ecosystem Conservation, 1995)

Not detected

Rare

Occasional

Frequent

Not sampled

TOTAL CHLORDANE

TOTAL PCBs

LEAD

MERCURY

70 ̊

71 ̊

73 ̊ 72 ̊

45 ̊

44 ̊

43 ̊

42 ̊

41 ̊

0 10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

CANADA

MAINE

NEW HAMPSHIRE

VERMONT

NEW YORK

MASSACHUSETTS

RHODE

ISLAND ATLANTIC OCEAN

LONG ISLAND SOUND

Base from U.S. Geological Survey Digital Line Graphs, 1989

Universal Transverse Mercator Projection, 1:100,000 scale

of Environmental Protection, 1995), 

New Hampshire (Department of 

Environmental Services, 1996) and 

Vermont (Department of 

Environmental Conservation, 

1996). Other consumption 

advisories include those issued for 

selected fish species from specific 

stream reaches because of 

contamination by PCB. These 

stream reaches include lengths 

along the Connecticut, Housatonic, 

Millers, and Otter Rivers in 

Massachusetts, (Department of 

Environmental Protection, 1995); 

and the Connecticut and Housatonic 

Rivers in Connecticut (Connecticut 

Department of Environmental 

Protection, 1994). Information on 

fish consumption advisories is 

available in pamphlets distributed 

with fishing licenses and on signs 

posted along affected stream 

reaches.

The potential for adverse effects on wildlife from toxic contaminants in either streambed sediment or fish is greatest in the 

southern part of the Study Unit.
8 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

MAJOR ISSUES AND FINDINGS

NUTRIENTS IN SURFACE WATER

FORESTED

(17 stations)

AGRICULTURAL

(21 stations)

URBAN

(23 stations)

0

0.3

0.6

0.9

1.2

1.5

Nitrite plus nitrate (as N)

Ammonia (as N)

Phosphorus (total as P)

MEDIAN NUTRIENT

CONCENTRATIONS

CONCENTRATION, IN MILLIGRAMS PER LITER

Nutrient (nitrogen and 

phosphorus) concentrations 

are a concern for surfacewater quality

Streams, lakes, and estuaries in 

the Study Unit have been adversely 

affected by eutrophication caused 

by above-background nutrient 

concentrations, primarily 

downstream from major urban 

wastewater-treatment facilities.

Nutrients are compounds 

containing nitrogen and 

phosphorus. Nutrients in streams 

are derived from natural sources and 

human activities, including 

decaying plants, animal wastes, 

fertilizers, municipal and industrial 

wastewater, and atmospheric 

deposition. Many of these nutrient 

sources are quite large; for example, 

about 58 million pounds of nitrogen 

and 11 million pounds of 

phosphorus are applied each year as 

chemical fertilizer and manure in 

the Study Unit . Although nitrogen 

and phosphorus are essential for 

plant growth, high concentrations of 

these nutrients can cause 

eutrophication, a condition in which 

aquatic plant and algal growth is 

excessive. Decomposition of the 

plants and algae reduces dissolvedoxygen concentrations in the water, 

creating poor habitat for fish and 

other aquatic animals. In addition, 

nitrogen in the form of ammonia 

can be toxic to aquatic life, the 

toxicity level depending on the 

temperature and pH of the water.

Nitrogen and phosphorus 

compounds have different effects in 

freshwater and saltwater bodies. 

Nitrogen concentrations are rarely 

low enough to limit aquatic plant 

growth in fresh-water, whereas 

phosphorus concentrations 

generally are low enough to limit 

plant growth. Hence, excessive 

aquatic plant growth and 

eutrophication in freshwater 

generally result from high 

phosphorus concentrations 

(typically greater than 0.1 mg/L). In 

contrast, nitrogen is typically the 

limiting nutrient for aquatic plant 

growth in saltwater, and excess 

nitrogen can lead to algal blooms 

and low concentrations of dissolved 

oxygen in coastal waters. For 

example, Long Island Sound 

ultimately receives all the water 

(and wastewater) from streams in 

the Study Unit, and algal blooms 

created by excess nutrients have 

caused low concentrations of 

dissolved oxygen and poor habitat 

for fish and other marine animals in 

the sound (U.S. Environmental 

Protection Agency, 1997).

Land use and nutrient 

concentrations in streams are 

related

Nutrient concentrations are 

substantially higher in streams 

draining urban areas than in streams 

draining either agricultural or 

forested areas in the Study Unit 

(Zimmerman and others, 1996). The 

median concentration of nitrate in 

water samples from urban streams 

was more than twice that of streams 

in agricultural areas and more than 

10 times that in streams draining 

forested areas. Ammonia and 

phosphorus concentrations are 

much higher in urban water-quality 

samples than in samples from either 

agricultural or forested areas. The 

median phosphorus concentration 

for urban streams was three times 

that of streams in agricultural areas 

and nine times the median for 

streams in forested areas (see graph 

at right).

Wastewater-treatment facilities 

are major sources of nutrients in 

surface water in urban areas. 

Nutrient concentrations at four 

urban-area streams sampled as part 

of the NAWQA program were 

examined to determine the effect of 

wastewater in these streams. 

Median concentrations of ammonia, 

nitrate, and total phosphorus for two 

streams with wastewater effluent 

greater than 10 percent of the flow 

at the sampling site were from 2 to 

more than 10 times the median 

concentrations for two urban 

streams without large upstream 

wastewater discharges. The median 

nutrient concentrations at the urban 

streams without large upstream 

wastewater discharges were 

comparable to stream 

concentrations in agricultural areas. 

The highest nitrate concentration 

(10 mg/L) measured in surface 

water during this study was 

collected from a station downstream 

from a wastewater-treatment 

facility. In contrast, the highest 

concentration of nitrate detected in 

an agricultural-area stream was 

Algal blooms can occur in streams 

downstream from wastewatertreatment facilities (Hockanum River at 

East Hartford, Connecticut. Photograph 

by Britt Stock, U.S. Geological Survey).

Concentrations of nitrogen and 

phosphorus are substantially higher in 

streams draining urban areas than in 

streams draining either agricultural or 

forested areas.
U.S. Geological Survey Circular 1155 9

MAJOR ISSUES AND FINDINGS

NUTRIENTS IN SURFACE WATER

Map

No. Station name Drainage

basin area

(square miles)

Drainage

basin area

(square miles)

1 w W 0 illimantic River at Merro 94.

2 m S 8 hetucket River at South Windha 40

3 g Q 5 uinebaug River at Quinebau 15

4 y Q 3 uinebaug River at Jewett Cit 71

5 Connecticut River at Thompsonville 0 9,66

6 n S 2 till River at Riverto 86.

7 e F 8 armington River at Unionvill 37

8 n P 2 equabuck River at Farmingto 57.

Map

No. Station name

9 e F 7 armington River at Tariffvill 57

1 n 0 S 0 almon River near East Hampto 10

1 d 1 Q 5 uinnipiac River at Wallingfor 11

1 d 2 H 2 ousatonic River near New Milfor 1,02

1 n 3 H 4 ousatonic River at Stevenso 1,54

1 s 4 N 0 augatuck River at Beacon Fall 26

1 g 5 S 0 augatuck River near Reddin 21.

1 k 6 N 0 orwalk River at Winnipau 33.

 

9 16

14

EXPLANATION

LAND USE

Urban

Agriculture

Forest

Upward or downward trend

—arrowhead indicates 

location of gaging station

No trend—dot indicates 

location of gaging station

GAGING STATION AND NUMBER

0 20 MI

0 20 KM

9 6 5 3

1

7

8

12

15

16

13

14 11

10

2

4

6

9

5 3

1

7

8

12

15

16

13

14 11

10

2

4

6

9

5 3

1

7

8

12

15

16

13

14 11

10

2

4

6 5 3

1

7

8

12

15

16

13

14 11

10

2

4

9

41 ̊

73 ̊ 72 ̊ 73 ̊ 72 ̊

42 ̊

41 ̊

42 ̊

41 ̊

42 ̊

41 ̊

42 ̊

Total Nitrogen

Ammonia-Nitrogen

Nitrate-Nitrogen

Total Phosphorus

Total Nitrogen

Ammonia-Nitrogen

Nitrate-Nitrogen

Total Phosphorus

one-half the highest concentration 

detected in an urban-area stream. 

Nutrient concentrations are 

changing with time

Nitrate concentrations in streams 

commonly increased during 1980-

92, whereas ammonia and total 

phosphorus concentrations 

commonly decreased (Zimmerman, 

1997). Decreases in ammonia 

concentrations were generally 

associated with increases in nitrate 

concentrations, resulting primarily 

from improved wastewatertreatment processes, which convert 

ammonia to nitrate (Trench, 1996). 

Decreases in total phosphorus 

concentrations also are likely due to 

improvements in wastewater 

treatment and to the elimination or 

reduction of phosphate in 

detergents. Although more effective 

wastewater treatment has improved 

surface-water-quality conditions in 

many parts of the Study Unit, the 

total amount of nutrients 

(particularly nitrogen) discharged to 

Long Island Sound is still 

considered an environmental 

concern (U.S. Environmental 

Protection Agency, 1997).

The MCL for nitrate (10 mg/L as 

N) was rarely exceeded in the Study 

Unit, indicating that nutrient 

concentrations generally are not a 

concern for surface-water supplies 

used for drinking water.

Concentrations of nutrients in Connecticut from 1980 to 1992 were generally unchanged for total nitrogen, increased for nitrate, 

and decreased for ammonia and phosphorus. These changes were primarily the result of more effective wastewater treatment, 

which has significantly improved the water quality in streams over this period (Zimmerman, 1997).
10 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

MAJOR ISSUES AND FINDINGS

PESTICIDES IN SURFACE WATER

 

PESTICIDES DETECTED

Herbicides Insecticides

PERCENTAGE OF PESTICIDE DETECTIONS AT

SURFACE-WATER STATION

Carbaryl

Diazinon

Atrazine

Metolachlor

Prometon

Simazine

0

10

20

30

40

50

60

70

80

90

100

TOTAL

(56 stations)

INTEGRATOR

FORESTED

(20 stations)

(7 stations)

AGRICULTURAL

(16 stations)

URBAN

(13 stations)

 

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

PESTICIDES DETECTED - Number in parenthesis is the 

MCL or HAL in micrograms per liter for each pesticide.

* indicates pesticide exceeded the noted 

aquatic-life criteria.

Herbicides

EXPLANATION

Insecticides

AGRICULTURAL

Carbaryl (700)(*0.02)

Diazinon (0.6)(*0.009)

Atrazine (3)

Metolachlor (100)

Prometon (100)

Simazine (4)

URBAN

INTEGRATOR

FORESTED

MAXIMUM PESTICIDE CONCENTRATION,

IN MICROGRAMS PER LITER

Pesticides were frequently 

detected in Study Unit 

streams

Nationally, more than 1.1 billion 

pounds of pesticides are applied 

each year to control rodents, 

insects and grubs, weeds, fungi, 

and other pests in urban centers, 

suburbs, rural communities, and 

farms. The occurrence and 

distribution of pesticides in water 

draining from various land-use 

types were investigated as part of 

the NAWQA program by collecting 

and analyzing samples from 56 

stream sites across the Study Unit. 

Streams were sampled after spring 

applications of pesticides and 

during low-flow conditions (late 

summer). 

The pesticides most frequently 

detected in streams in the Study 

Unit include the herbicides 

atrazine, metolachlor, simazine, 

and prometon. Atrazine and 

metolachlor are used for selective 

weed control, typically in the 

cultivation of feed corn, which is 

grown in New England primarily 

for dairy cattle. Simazine is used 

for weed control in agricultural and 

urban areas (lawn care), and 

prometon is a broad-band 

(nonselective) weed control 

commonly used along highways 

and railroads. Other commonly 

detected pesticides included the 

insecticides diazinon (for crops and 

home applications) and carbaryl 

(for crops and other plants). Each 

of these pesticides was detected at 

20 percent or more of the stream 

sites.

Land use and pesticide 

concentrations in streams 

are related

Different numbers and types of 

pesticides were detected in samples 

collected from streams draining 

urban, agricultural, and forested 

areas, and streams draining large 

basin areas. Twenty-seven 

pesticides or breakdown products 

were detected in samples collected 

in urban areas. Diazinon was the 

most commonly detected pesticide 

in urban stream sites; it was 

detected in one or more samples at 

92 percent of these sites. Other 

commonly detected pesticides at 

urban streams were atrazine and 

prometon. The maximum 

concentrations of carbaryl, 

diazinon, and prometon were 

detected at urban streams, but these 

concentrations did not exceed their 

HALs. However, carbaryl and 

diazinon concentrations did exceed 

the aquatic-life criteria in samples 

collected from a stream draining an 

urban area.

A study was conducted at a site 

on the Norwalk River (Winnipauk, 

Connecticut) to investigate 

pesticide concentrations in a 

stream draining an urban/suburban 

setting. Samples were collected 

weekly from March through 

October and monthly from 

November through February 

during 1993 and 1994, for a total of 

59 pesticide samples in this period. 

Twenty-two pesticides or 

breakdown products were detected 

at the Norwalk River site; however, 

only prometon and atrazine were 

detected in more than 50 percent of 

the samples. Prometon was 

detected in more than 90 percent of 

the Norwalk River samples. The 

highest prometon concentration 

was 0.14 μg/L, about 1,000 times 

lower than the MCL for this 

compound. Other commonly 

detected pesticides included 

simazine, carbaryl, metolachlor, 

and DCPA (another herbicide); 

these pesticides were detected in 

more than 20 percent of the 

samples collected at this site.

Fourteen pesticides or 

breakdown products were detected 

in streams draining agricultural 

basins in the Study Unit. Three 

herbicides—atrazine, metolachlor, 

and simazine—were the most 

frequently detected pesticides at 

agricultural stream sites; the 

maximum concentrations for these 

compounds were in samples 

collected at agricultural sites. 

Atrazine was detected at 88 percent 

of the agricultural sites, and was 

the most commonly detected 

pesticide for the study overall. 

Although none of the atrazine 

The concentrations of most common 

herbicides were highest in streams 

draining agricultural areas in the Study 

Unit, whereas concentrations of most 

common insecticides were highest in 

urban-area streams.

The proportion and variety of pesticide 

detections at stream sites differed 

considerably among land-use types 

across the Study Unit. Although the 

highest proportion of detections were in 

high pesticide use areas, pesticides 

were still detected in forested 

(background) areas.
U.S. Geological Survey Circular 1155 11

MAJOR ISSUES AND FINDINGS

PESTICIDES IN SURFACE WATER

70 ̊

71 ̊

73 ̊ 72 ̊

45 ̊

44 ̊

43 ̊

42 ̊

41 ̊

0 10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

CANADA

MAINE

NEW HAMPSHIRE

VERMONT

NEW YORK

NEW YORK

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND ATLANTIC OCEAN

LONG ISLAND SOUND

Base from U.S. Geological Survey Digital Line Graphs, 1989

Universal Transverse Mercator

1:100,000 scale

EXPLANATION

NUMBER OF PESTICIDES DETECTED

0

1 to 4

5 or more

LAND-USE TYPE

Mixture of land use (integrator)

Agriculture

Urban

Forest 

BOUNDARY OF STUDY UNIT

Norwalk River

concentrations exceeded the MCL, 

atrazine was frequently detected in 

combination with other pesticides 

and with desethylatrazine, a 

breakdown product of atrazine.

Pesticide detections generally 

were fewer in streams draining 

forested basins than in streams 

draining urban and agricultural 

areas, and pesticide concentrations 

also were low in streams in 

forested basins. The greatest 

variety of pesticides generally was 

detected in samples collected from 

large rivers (see map at right). The 

most commonly detected 

pesticides in samples collected 

from large rivers were atrazine and 

metolachlor, with mixtures of 

several pesticides common. 

Although many pesticides were 

detected in samples collected from 

large rivers, the concentrations 

were low, and none of the 

concentrations were maximums for 

these compounds for this study. 

These results reflect the mixed 

nature of the upstream land use in 

larger basins and the dilution of 

pesticide concentrations in these 

rivers by large flows. Rivers with 

the highest percentage of pesticide 

detections generally were in the 

southern part of the Study Unit, 

where population density is 

greatest and agricultural activity 

generally is most intensive.

Current drinking-water 

standards were not exceeded. None 

of the pesticides were detected at 

concentrations greater than the 

U.S. Environmental Protection 

Agency’s MCL or HAL for the 

compound, and few pesticide 

concentrations exceeded 1 μg/L. 

Current drinking-water standards, 

however, do not include some of 

the detected pesticides (or 

breakdown products) and do not 

include consideration of more than 

one pesticide in the water. Thus, 

there is some uncertainty in the 

actual health concern posed by 

these results.

The greatest variety of pesticide detections at stream sites generally was in the 

southern part of the Study Unit, where there are large urban areas and agricultural 

activity is most intensive.

Pesticides, particularly herbicides, were frequently detected in water draining from 

agricultural areas (photograph by Stephen Grady, U.S. Geological Survey).
12 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

MAJOR ISSUES AND FINDINGS

PESTICIDES IN GROUND WATER

Desethylatrazine

Atrazine

Metolachlor

Simazine

Terbacil

Trifluralin

Carbofuran

p,p' DDE

Permethrin

Aldicarb sulfoxide

Benfluralin

DCPA

Dichlobenil

Dichlorprop

Ethalfluralin

Napropamide

Prometon

Propargite

Triallate

Bromacil

Metribuzin

Propanil

Tebuthiuron

Carbaryl

0

20

40

HERBICIDE

0

80

20

40

60

PERCENTAGE OF WELLS WITH DETECTIONS

0

20

INSECTICIDE

URBAN (40 samples)

AGRICULTURAL (40 samples)

FORESTED (23 samples)

Pesticides were frequently 

detected in ground water

Twenty-four pesticide compounds 

or breakdown products were 

detected in shallow monitoring wells 

across the Study Unit (Grady and 

Mullaney, 1998). Although 

pesticides were frequently detected, 

the concentrations generally were 

low, and more than 75 percent of all 

pesticide detections reported in this 

study were at trace-level 

concentrations of less than 0.1 μg/L.

The pesticides (or breakdown 

products) were detected in water 

samples collected from 103 

monitoring wells in the Study Unit. 

The depths of these monitoring 

wells ranged from 7 to 54 ft below 

land surface and generally were 

screened in the upper 10 ft of the 

aquifer. Herbicides comprised 90 

percent of the pesticide detections in 

these wells. Atrazine, 

desethylatrazine, prometon, and 

simazine alone accounted for 

72 percent of all pesticide 

detections. Metolachlor also was 

frequently detected, comprising 

9 percent of the total. Carbaryl was 

the most frequently detected 

insecticide. The only other 

insecticide detected in more than 

two wells was DDE, a breakdown 

product of DDT.

A few of the most heavily applied 

pesticides in the Study Unit were not 

detected in shallow ground-water 

samples, for example, alachlor and 

chlorpyrifos. Important factors in the 

mobility and detection of a pesticide 

include solubility (the compound’s 

ability to dissolve in water), 

persistence (how slowly it breaks 

down), and the soil characteristics in 

the area where it is applied. Low 

solubility pesticides tend to stay 

adsorbed to the soil and thus do not 

leach into ground water. Pesticides 

that degrade quickly also are less 

likely to be detected in ground water. 

Pesticides applied in areas of finegrained soils will move slowly 

through these materials and make it 

less likely that the pesticide will be 

detected in ground water. Thus, the 

Sampling ground water at a monitoring 

well with an electric submersible pump 

(photograph by Stephen Garabedian, 

U.S. Geological Survey).

Atrazine, a herbicide used in the cultivation of corn, and its breakdown product desethylatrazine, were 

the most commonly detected pesticide compounds in ground water in the Study Unit.
U.S. Geological Survey Circular 1155 13

MAJOR ISSUES AND FINDINGS

PESTICIDES IN GROUND WATER

probability that a pesticide will be 

detected in shallow ground water is 

highest for pesticides that are highly 

soluble in water, relatively stable, 

and applied in large amounts to 

highly permeable soils. An 

additional factor is the sensitivity of 

the chemical analysis for the 

pesticide; this varies depending on 

the actual concentration of the 

pesticide (low concentrations 

generally are less likely to be 

detected), and the characteristics 

inherent to the analytical method 

used for each pesticide.

Land use and pesticide 

concentrations in ground 

water are related

A comparison of pesticide 

detection frequencies by land-use 

category indicates that the 

proportions of wells with pesticide 

detections differed among the three 

major land-use categories. Water 

samples from 80 percent of 

agricultural wells contained at least 

one pesticide as compared to 

60 percent of the water samples from 

wells in urban areas and 48 percent 

of water samples from wells in 

forested areas. Of the 24 compounds 

detected in samples from all well 

types, 19 were detected in samples 

from agricultural wells, including 12 

compounds that were detected 

exclusively in these wells. Atrazine, 

desethylatrazine, and metolachlor 

were detected in water samples from 

agricultural wells more often than in 

samples from wells in forested or 

urban areas. More than 70 percent of 

the agricultural wells contained 

either atrazine and or 

desethylatrazine, and metolachlor 

was detected in 28 percent of these 

wells. More than 50 percent of the 

water samples from agricultural 

wells contained two or more 

pesticides.

In contrast to other herbicides, 

prometon was detected primarily in 

water samples from wells in urban 

areas, with about 33 percent of these 

samples containing this compound.

Similarly, simazine was most 

frequently detected in water samples 

from wells in urban areas. 

Pesticide concentrations generally 

were highest in water samples from 

wells in agricultural areas; more 

than 33 percent of the concentrations 

were greater than or equal to 

0.1 μg/L. In contrast, most of the 

pesticide detections in ground water 

beneath urban and forested areas 

were at concentrations less than 

0.1 μg/L. Only two pesticides, 

atrazine and ethylene dibromide 

(EDB), were detected at 

concentrations that exceeded their 

MCLs (although several detected 

pesticides do not have MCLs). An 

atrazine concentration of 3.6 μg/L in 

a sample from a cornfield well was 

slightly greater than the MCL of 

3.0 μg/L. An EDB concentration of 

1.4 μg/L in a sample from an area of 

ornamental plant cultivation was 

substantially greater than the MCL 

of 0.05 μg/L. The area of ornamental 

plant cultivation had recently been in 

tobacco production. Although 

banned for use now, EDB was used 

as a pesticide in the cultivation of 

tobacco in the Study Unit.

Some of the most productive farms in the Study Unit are on the Connecticut River flood plain (photograph by Stephen 

Garabedian, U.S. Geological Survey).
14 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

MAJOR ISSUES AND FINDINGS

VOLATILE ORGANIC COMPOUNDS IN GROUND WATER

Manchester

Hamden

URBAN LAND USE

MONITORING WELLS

VOCs not detected

VOCs detected

WATER-SUPPLY WELLS

 VOCs not detected

 VOCs detected

EXPLANATION

VOCs were also frequently 

detected in ground water

Volatile organic compounds are 

frequently detected in shallow 

ground water beneath urban areas in 

the Study Unit. These compounds 

are used in paints, adhesives, petroleum products (fuels), pharmaceuticals, refrigerants, solvents, hydraulic 

fluids, dry cleaning agents, and some 

pesticides, and they can contaminate ground water by way of industrial use and release, leaking 

underground fuel tanks and pipelines, accidental surface spills and 

leaks, and infiltration of runoff from 

paved urban areas.

Twenty-five different VOCs were 

detected in water from wells sampled in the Study Unit (Grady, 

1997). The gasoline additive MTBE 

was detected in about 25 percent of 

all wells and was the most commonly detected compound. Chloroform (a trihalomethane) can form 

during disinfection of drinkingwater supplies and was the second 

most frequently detected compound. Chloroform was present in a 

little less than 25 percent of all 

wells. Tetrachloroethene and trichloroethene, solvents commonly used 

in industrial and commercial activities (for example as degreasers), also 

were commonly detected in wells in 

the Study Unit.

Land use and VOC 

concentrations in ground 

water are related

Of the 133 wells sampled for 

VOCs, most of the 61 wells with 

VOC detections were in the southern 

part of the Study Unit (Grady, 1997). 

VOCs were most commonly 

detected in samples from wells in 

urban areas, with 70 percent of monitoring wells in urban areas containing one or more compounds. 

Twenty-three of the 25 VOCs 

present in ground-water samples 

were detected at least once in monitoring wells in urban areas, and 19 of 

the 23 compounds were detected 

exclusively or most frequently in 

Volatile organic compounds were detected in ground water most 

frequently in the urban areas of the southern part of the Study Unit.

Methyl tert-butyl ether and chloroform were the most frequently detected volatile 

organic compounds.

Methyl tert-butyl ether

Choroform

Tetrachloroethene

Trichloroethene

Naphthalene

cis -1,2-Dichloroethene

1,1-Dichloroethane

Toluene

Dichlorodifluoromethane

Methylene chloride

1,2,4-Trimethylbenzene

1,1,1-Trichloroethane

Benzene

Bromodichloromethane

p-Isopropyltoluene

Bromobenzene

n-Butylbenzene

sec-Butylbenzene

Carbon tetrachloride

1,2-Dibromoethane (EDB)

Ethylbenzene

Isopropylbenzene

n-Propylbenzene

1,3,5-Trimethylbenzene

Xylenes

0

5

10

15

20

25

PERCENTAGE OF WELLS WITH DETECTIONS

HALOGENATED ALKANE

HALOGENATED ALKENE

ETHER

ALKYLATED BENZENE

HALOGENATED BENZENE
U.S. Geological Survey Circular 1155 15

MAJOR ISSUES AND FINDINGS

VOLATILE ORGANIC COMPOUNDS IN GROUND WATER

Forest

Agricultural

Urban

No urban land use

Some urban land use

MONITORING 

WELLS

0

20

40

60

80

PERCENTAGE OF WELLS WITH VOC DETECTIONS

WATER-SUPPLY 

WELLS

(22) (24) (57) (15) (15)

NUMBER OF WELLS SAMPLED

The proportion of detections of volatile organic compounds was highest in urban 

areas, regardless of well type.

wells in urban areas. VOCs were 

detected in 37 percent of the samples 

collected from monitoring wells in 

agricultural areas; nine compounds 

were detected, due in part to the use 

of some VOCs (EDB and naphthalene) as pesticides. The fewest number of VOC detections (9 percent) 

were in samples from monitoring 

wells in forested areas, and only 

three compounds were detected. 

VOCs also were detected in domestic water-supply wells drilled into 

bedrock; most in wells within a 

0.25 mile distance of an urban 

land-use area.

Although most VOC concentrations measured in ground-water 

samples were low, concentrations 

were as high as 300 μg/L. High concentrations of tetrachlorethane 

(250 μg/L), trichloroethene 

(63 μg/L), benzene (73 μg/L), and 

total xylenes (300 μg/L) were 

detected in samples from three monitoring wells in an urban area; these 

VOC concentrations are indicative 

of nearby point sources. Most of the 

VOC detections (64 percent), however, were at concentrations less 

than 1.0 μg/L; these concentrations 

are more indicative of nonpoint 

sources.

Volatile organic compound contamination of drinking-water supplies is a health concern because 

many of these compounds are toxic 

and are known or suspected human 

carcinogens. Concentrations of benzene, EDB, naphthalene, tetrachloroethene, and trichloroethene 

exceeded their MCLs or HALs in 

samples from five monitoring wells; 

all but one of which were in urban 

areas. Public-supply wells are completed in several of the same aquifers 

that were sampled in this study. 

Therefore, these study results indicate that high VOC concentrations 

are of potential health concern with 

regard to drinking-water supplies, 

particularly for ground water in 

urban areas, where10 percent of the 

monitoring wells exceeded a VOC 

MCL.

MTBE and its effect on 

ground-water quality

The Clean Air Act Amendments 

of 1990 mandated use of oxygenated 

or reformulated gasoline in specific 

parts of the United States where carbon monoxide and ozone concentrations do not meet air-quality 

standards. As a result, MTBE is 

added to gasoline as an oxygenate 

across the Northeastern United 

States, including most of New 

England, to help meet these standards. As a consequence of its extensive use and persistence, MTBE was 

the most commonly detected VOC in 

ground water in the Study Unit. 

MTBE was detected in water samples in 33 of the 133 wells sampled, 

at concentrations ranging from 

0.2 to 5.8 μg/L. Most of the 

detectable MTBE concentrations 

were in water samples from wells in 

Connecticut and Massachusetts, 

where use of oxygenated or reformulated gasoline is required.

The presence of MTBE in ground 

water appears to be related to urban 

land use, as it was detected in nearly 

50 percent of the wells sampled in 

urban areas but was undetected or 

rarely detected in ground water 

beneath forested and agricultural 

areas. Most MTBE detections 

(69 percent) have been in shallow 

monitoring wells that are within 

0.25 mile of gasoline stations. All 

MTBE concentrations were less than 

the current U.S. Environmental 

Protection Agency drinking-water 

health advisory (U.S. Environmental 

Protection Agency, 1996) for this 

compound (20 to 40 μg/L).

Urban areas include many possible 

sources of volatile organic compounds, 

including gasoline stations, commercial 

establishments, and manufacturing 

operations (photograph by Stephen 

Grady, U.S. Geological Survey).
16 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

MAJOR ISSUES AND FINDINGS

NITRATE IN GROUND WATER

Agriculture Urban Forest

LAND-USE CATEGORY

0

5.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

MEDIAN NITRITE PLUS NITRATE CONCENTRATION (MG/L)

Nitrate concentrations can be 

a ground-water quality 

concern

The widespread application of 

chemical fertilizers, manure, and 

sewage sludge to some agricultural 

fields has caused high nitrate concentrations in shallow ground water 

in the Study Unit (Grady and 

Mullaney, 1998).

Reported total applications of 

nitrogen in chemical fertilizer and 

manure are estimated to be about 

58 million pounds in the Study Unit. 

Much of the nitrogen is applied to 

agricultural fields, but fertilizers also 

are commonly used on lawns and 

turf in urban and suburban areas. 

Other sources of nitrogen in urban 

areas are from septic system and 

sanitary-sewer effluents, domestic 

animal wastes, and infiltration of 

runoff from urban streets and 

parking lots. Significant amounts of 

nitrogen also are deposited by 

precipitation in the Study Unit, with 

2,200 to 2,400 kilograms per year 

per square mile estimated for most 

of the area. Although nitrogen is 

deposited and applied in various 

forms, the most common form of 

nitrogen in ground water is nitrate.

Concentrations of nitrate were 

measured in samples from 120 monitoring wells across the Study Unit. 

Results from this investigation 

showed nitrogen concentrations in 

samples from wells in agricultural 

areas were significantly higher than 

in samples collected from wells in 

either urban or forested areas. The 

median nitrate concentration in samples from agricultural wells is 

3.8 mg/L, which is nearly 30 times 

the median concentration for wells 

in forested areas (0.14 mg/L) and 

more than 3 times the median concentration in urban areas (1.1 mg/L).

Nitrate concentrations in ground 

water in urban areas generally are 

low because average nitrogen fertilizer application rates are less than 

the fertilizer and manure applications in agricultural areas. The highest nitrate concentration for urban 

ground water is 9.7 mg/L, 

significantly lower than the maximum concentration in ground water 

beneath agricultural areas (22 

mg/L). Nitrate concentrations in 

ground-water samples from urban 

areas are substantially higher than 

those in samples from forested areas, 

but less than those in agricultural 

areas. The median concentration of 

nitrate in ground-water samples 

from forested areas is only 0.14 

mg/L; this represents the expected 

natural background concentration of 

nitrate in ground water. Only two 

samples from wells in forested areas 

contained more than 1.0 mg/L of 

nitrate, and these samples were from 

sites where transport of nitrogen 

from nearby agricultural fields was 

possible.

Drinking water that contains 

nitrate concentrations that exceed 

the MCL (10 mg/L) is a health concern, particularly for infants. In this 

study, 15 percent of the water collected from wells in agricultural 

areas yielded water with nitrate concentrations that exceeded the MCL. 

Although the wells sampled as part 

of this study are not used for 

drinking water, many of the aquifers 

that were sampled are used for 

drinking-water supplies. These 

results indicate a potential health 

concern, particularly for shallow 

wells used for rural domestic supply 

in agricultural areas.

Nitrate concentrations were highest in 

shallow ground water beneath 

agricultural areas.

Fertilizers are often heavily applied to row crops like corn and, if soils are 

permeable, cause higher nitrate concentrations in ground water beneath the fields 

(photograph by Stephen Grady, U.S. Geological Survey).
U.S. Geological Survey Circular 1155 17

MAJOR ISSUES AND FINDINGS

RADON IN GROUND WATER

Radon is present in ground 

water across the Study Unit

Almost all monitoring and supply 

wells sampled as part of this study 

exceeded the previously proposed 

limit for radon.

Radon is a naturally occurring, 

colorless, odorless radioactive gas, 

which can be a health risk for lung 

cancer when people are exposed to 

high concentrations over an 

extended period of time. Exposures 

to radon gas occur primarily through 

the movement of soil gas into a 

home, but radon also can enter 

homes from ground water pumped 

from private wells. Radon concentrations are reported as a measure of 

its radioactivity, an “activity” in picocuries per liter. The previously proposed limit on the activity of radon 

gas was 300 picocuries per liter of 

water (pCi/L) (U.S. Environmental 

Protection Agency, 1996).

All rocks in the Study Unit contain some uranium, the first element 

in the radioactive decay series that 

leads to the formation of radon gas, 

but the distribution is not even. 

Some types of igneous and metamorphic rocks (granites, for example) have high uranium content and 

are frequently associated with high 

radon activities. After radon gas is 

produced in the rock, some of it can 

become dissolved in the water passing through the rock, and the water 

(with the radon in it) may be 

pumped from a well and used in a 

home. Use of the water for washing, 

cooking, or drinking exposes people 

to the radon gas, creating a health 

risk.

Analyses of ground-water samples collected in the Study Unit indicate that almost all water samples 

(94 percent of samples from 47 

wells) exceeded the previously proposed limit. Two types of wells were 

sampled for radon as part of this 

study—bedrock supply wells and 

shallow monitoring wells in stratified-drift aquifers. Median radon 

activity was high in the water samples from the bedrock-supply wells 

(2,150 pCi/L); 97 percent of these 

samples exceeded the previously 

proposed limit. Median radon activity was low for water samples from 

shallow monitoring wells in stratified-drift aquifers (520 pCi/L), but 

88 percent of samples from these 

wells still exceeded the previously 

proposed limit. Water from a few 

shallow monitoring wells exceeded 

1,000 pCi/L, but radon activities of 

most samples (88 percent) from 

crystalline bedrock wells were 

greater than 1,000 pCi/L and samples from two bedrock wells 

exceeded 10,000 pCi/L. Although 

these radon levels in bedrock wells 

are high in comparison to levels in 

other NAWQA Study Units (see 

Water-Quality Conditions in a 

National Context), they are similar 

to ranges of radon levels reported for 

ground water from bedrock in other 

areas of the United States (Brill, 

1994).

Almost all of the sampled bedrock wells, like the one pictured above, had radon concentrations that exceeded 

the previously proposed limit (photograph by Stephen Garabedian, U.S. Geological Survey).
18 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

Comparison of Stream Quality in the Connecticut, Housatonic, and Thames River Basins with 

Nationwide NAWQA Findings

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ORGANOCHLORINE PESTICIDES and PCBs

in bed sediment and biological tissue

Greater than the 75th percentile

(among the highest 25 percent

of NAWQA stream sites)

Between the median and the 75th percentile

Between the 25th percentile and the median

Less than the 25th percentile

(among the lowest 25 percent

of NAWQA stream sites)

Concentrations of PCBs and organochlorine compounds were among 

some of the highest of the NAWQA 

Study Units. Organochlorine compound 

and PCB concentrations exceeded 

aquatic life criteria at several sites. 

Although most of these compounds are 

presently banned, they still persist.

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Water-quality characteristics were evaluated for stream sites in each NAWQA 

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

had adequate data. Scores for each site in the Connecticut, Housatonic, and Thames 

River Basins were compared with scores for all sites sampled in the 20 NAWQA 

Study Units during 1992–95. Results are summarized by percentiles; higher 

percentile values generally indicate poorer quality compared with other NAWQA 

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

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

pesticides in water, and semivolatile organic compounds, organochlorine pesticides 

and PCBs in sediment. (Methods used to compute rankings and evaluate aquatic-life 

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

EXPLANATION

Ranking of stream quality relative to all 

NAWQA stream sites — Darker colored 

circles generally indicate poorer quality. 

Bold outline of circle indicates one or more 

aquatic life criteria were exceeded.

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Trace elements in sediment were 

high compared to other NAWQA 

Study Units. Many sites contained 

at least one trace element that 

exceeded aquatic life criteria. 

Though some trace elements occur 

naturally in soils, sites shaded 

darkest show the effects of point 

and nonpoint waste-discharge 

sources of these elements.

TRACE ELEMENTS in bed sediment

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Several sites sampled for SVOCs were ranked 

among some of the highest of the NAWQA 

Study Units. These compounds are commonly 

associated with the byproducts of fuel combustion. Several sites exceeded the aquatic life 

criteria for SVOCs.

SEMIVOLATILE ORGANIC COMPOUNDS

 in bed sediment
U.S. Geological Survey Circular 1155 19

CONCLUSIONS

In the Connecticut, Housatonic, and 

Thames River Basins, compared to other 

NAWQA Study Units:

• High concentrations of nutrients, primarily 

from wastewater-treatment facilities in 

urban areas, are causing eutrophication in 

some lakes, streams, and ponds.

• Pesticide concentrations in water are 

relatively low. Guidelines for the protection 

of aquatic life are exceeded by pesticide 

concentrations only infrequently.

• Concentrations of PCBs and 

organochlorine pesticides in bed sediment 

and fish are among the highest for NAWQA 

Study Units, and concentrations exceeded 

guidelines for the protection of wildlife in 

several places.

• Degradation of stream habitat and fish 

communities, as indicated at the limited 

number of NAWQA stream sites, is 

moderate in the Study Unit.

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Physical characteristics of streams 

and streambanks, including the 

amount of bank vegetation, stability 

of bank soils, and stream depth and 

shape, strongly influence water 

quality and the ability of streams to 

support biological communities. The 

physical condition of most stream 

habitat was about average compared 

to conditions at other NAWQA Study 

Units.

The number of diseased, pollutiontolerant, omnivorous, and non-native 

fish at several sites is higher than what 

would be expected in a healthy fish 

community. Fish communities in urban 

areas generally were in worse 

condition than those found in other 

NAWQA Study Units. There are no 

standards with which to evaluate the 

long-term ecological effects of these 

conditions.

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

FISH COMMUNITY DEGRADATION

STREAM HABITAT DEGRADATION

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Nutrient levels downstream from urban 

and agricultural areas were among some 

of the highest of the NAWQA Study 

Units. Nutrient concentrations in some 

streams were high enough to contribute 

to eutrophication and low dissolvedoxygen conditions, particularly in lakes 

and estuaries downstream from major 

urban areas.

NUTRIENTS in water
20 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

 

EXPLANATION

Fractured crystalline–bedrock aquifer (FC)

Agriculture (AG)

Urban (UR)

Forest (FO)

Comparison of Ground-Water Quality in the Connecticut, Housatonic, and Thames River Basins with 

Nationwide NAWQA Findings

 

(FC)

(FO)

(UR)

(AG)

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

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 Connecticut, Housatonic, and Thames River Basins 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.)

Nitrate concentrations in shallow ground 

water under agricultural areas generally 

were greater than the national median 

concentration, and 15 percent of these 

wells exceeded the drinking-water 

standard for nitrate. In contrast, nitrate 

concentrations in other shallow ground 

water and bedrock wells generally were 

less than the national median for 

NAWQA sites.

Ranking of ground-water quality relative 

to all NAWQA ground-water studies —

Darker colored circles generally indicate 

poorer quality. Bold outline of circle 

indicates one or more standards or criteria 

were exceeded.

Greater than the 75th percentile

(among the highest 25 percent

of NAWQA ground-water studies)

Between the median and the 75th percentile

Between the 25th percentile and the median

Less than the 25th percentile

(among the lowest 25 percent

of NAWQA ground-water studies)

NITRATE

 

(FC)

(FO)

(UR)

(AG)

Pesticide detection was common from 

wells in agricultural areas, with detection 

in more than 80 percent of wells 

sampled. Concentrations were generally 

low, with only two samples exceeding the 

drinking water standards. Pesticides were 

also commonly detected in urban wells, 

but were detected much less frequently in 

forested areas and drinking-water 

(bedrock) wells.

PESTICIDES
U.S. Geological Survey Circular 1155 21

 

(FC) (UR)

(AG)

Volatile organic compounds were frequently 

detected in study area wells, with more than 70 

percent of urban wells sampled containing VOCs, 

placing them among the top 25 percent of all 

NAWQA ground-water samples. VOCs also were 

frequently detected in bedrock wells used for 

drinking water; however, VOCs were not 

frequently detected in wells in agricultural areas.

CONCLUSIONS

In the Connecticut, Housatonic, and 

Thames River Basins, compared to other 

NAWQA Study Units:

• Pesticide detections were common, but 

concentrations generally were low. 

Samples from only 2 percent of the 

monitoring wells exceeded a pesticide 

MCL, and only in agricultural areas.

• VOCs were commonly detected in urban 

wells; samples from 10 percent of the wells 

in urban areas exceeded a VOC MCL.

• Nitrate concentrations in ground water 

under agricultural areas are 30 times 

higher than background concentrations; 

samples from 15 percent of these wells 

exceeded the nitrate MCL.

• Radon activities are high; activities in 

ground water from almost all bedrock wells 

exceeded the previously proposed limit.

VOLATILE ORGANIC COMPOUNDS

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

 

(FC)

Radon, a decay product of uranium, 

occurs naturally in soils. Radon levels in 

the drinking-water wells completed in 

bedrock were among the highest 

observed nationally. Almost all of these 

wells (97 percent) exceeded the 

previously proposed limit for radon.

RADON
22 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

STUDY DESIGN AND DATA COLLECTION

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Data collection efforts were designed to assess the quality of 

both surface and ground waters across the Study Unit for both 

regional and national needs (Gilliom and others, 1995). This 

design included three components, stream chemistry, stream 

ecology, and ground-water chemistry.

STREAM CHEMISTRY

Sampling sites were selected to assess the occurrence and distribution of dissolved constituents 

in streamwater. Data from basic fixed sites were used to evaluate the effect of upstream land use 

on stream chemistry. Data from the intensive fixed site, which was sampled more frequently, was 

used to evaluate the seasonal variation of stream chemistry at an urban site. Synoptic surveys 

were conducted during two summers to evaluate the distribution of pesticides throughout the 

Study Unit. Samples were collected to assess the distribution of trace elements and organic 

compounds in bed sediments across the Study Unit.

STREAM ECOLOGY

Intensive ecological assessments were 

conducted at basic fixed sites across the 

Study Unit for use in measuring the impact 

water quality has had on aquatic 

communities. These assessments included 

the collection of fish, macroinvertebrate, 

and algae samples for indentification, along 

with habitat characterization at each site. 

Fish tissue samples were collected at 

selected sites across the Study Unit for 

trace element and organic compound 

analysis.

GROUND-WATER CHEMISTRY

Ground-water samples were collected at two 

types of sites across the Study Unit, shallow 

wells in glacial stratified drift, and deeper wells 

in crystalline bedrock. Samples from shallow 

wells in stratified drift were collected to 

characterize the effects of land use on groundwater quality, whereas samples from the deeper 

bedrock wells were collected to characterize 

water-quality from water-supply wells in this 

Study Unit survey.

 



GROUND-WATER CHEMISTRY

Study Unit survey wells

Land use study wells

Stratified-drift deposits

Undifferentiated crystalline

bedrock

EXPLANATION

STREAM ECOLOGY SITES

Intensive

Fish tissue

EXPLANATION

STREAM-CHEMISTRY SAMPLING SITES

Basic

Intensive

Synoptic

Streambed sediment

EXPLANATION
U.S. Geological Survey Circular 1155 23

Summary of Data Collection in the Connecticut, Housatonic, and Thames River Basins, 1992-95

Study component Objectives

Brief description and 

water-quality measures

Number

of sites

Frequency 

during 

1992-95

Stream Chemistry

Bottom-sediment survey Determine the presence of potentially 

toxic compounds within the bed 

sediments of streams.

Sample depositional zones of streams for trace 

elements and hydrophobic organic compounds.

43 1

(1992-94)

Water chemistry -- 

Basic fixed sites

Describe concentrations and loads of 

chemicals, suspended sediment, and 

nutrients at selected sites basin wide.

Sample at or near sites where streamflow is 

measured periodically for major ions, organic 

carbon, suspended sediment, and nutrients.

12 ~15 per year, 

3 years,

(1993-95)

Water chemistry -- 

Intensive fixed sites

Determine concentration and timing of 

urban-related pesticides that run off to 

streams.

Sample one urban station where pesticides are 

sampled at least monthly during winter, weekly in 

other seasons, and during selected runoff events.

1 ~40 per year, 

2 years,

(1993-94)

Water chemistry -- 

Synoptic studies

Describe the short-term presence and 

distribution of contamination over 

broad areas and determine how well 

the water chemistry stations represent 

the Study Unit surface water.

Sample streams during high flow and low flow 

conditions for pesticides and (or) nutrients, 

suspended sediment, organic carbon, and 

streamflow.

56 1

(1994-95)

Stream Ecology

Contaminants in fish 

tissues

Determine the presence of 

contaminants that can accumulate in 

fish tissues.

Collect specific fish species in the study area, 

taking composites of whole fishes for organic 

compounds and fish livers for trace elements.

32 1

(1992-94)

Intensive ecological 

assessments

Assess in detail biological 

communities and habitat in streams 

representing primary ecological 

regions.

Sample and quantify fish, macroinvertebrates, and 

algae at or near a stream-chemistry station; 

describe stream habitat for these organisms; 

replicate sampling for three consecutive years.

10 1 per year, 

3 years,

(1993-95)

Ground-Water Chemistry

Study Unit survey Describe the overall water quality in 

crystalline bedrock aquifers used for 

water supply.

Sample wells within crystalline bedrock across the 

Study Unit for major ions, nutrients, volatile 

organic compounds, pesticides, and radionuclides.

30 1

(1995)

Land-use effects survey Determine the effects of specific land 

use on the quality of shallow ground 

water in unconsolidated surficial 

aquifers.

For surficial aquifers lying beneath major land 

uses, sample wells completed near water table for 

major ions, nutrients, pesticides, volatile organic 

compounds, and radionuclides.

120 1

(1992-95)

Variation along a 

ground-water

flow path

Describe land-use effects in a surficial 

aquifer along a ground-water flow 

path, from recharge areas beneath 

urban land to discharge to a stream.

Sample clusters of wells installed along an 

approximate line of ground-water flow and at 

various depths within a surficial aquifer; analyze 

for major ions, nutrients, trace elements, volatile 

organic compounds, pesticides, nitrogen isotopes, 

and age-dating constituents.

14 4-7

(1994-95)

Ground-water/surfacewater interactionsDetermine the effects of ground-water 

discharge on surface-water quality.

Sample shallow ground water adjacent to two 

streams, and stream water; analyze for major ions, 

nutrients, pesticides, and volatile organic 

compounds.

13 1

(1994-95)

STUDY DESIGN AND DATA COLLECTION
24

Herbicide

(Trade or common

name)

Rate 

of 

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

EXPLANATION

Range of surface-water detections in all 20 Study Units

Range of ground-water detections in all 20 Study Units

Drinking water standard or guideline a

Freshwater-chronic criterion for the protection of aquatic life

Herbicide 

(Trade or common

name)

Rate 

of 

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

Propachlor (Ramrod, 

propachlore)

<1%

0%

Propanil (Stampede, 

Surcopur)

<1%

<1%

Simazine (Aquazine, 

Princep, GEsatop)

13%

6%

Tebuthiuron (Spike, 

Perflan)

0%

1%

Terbacilc (Sinbar) 1%

1%

Triallate (Far-Go) 0%

<1%

Trifluralin (Treflan, 

Trinin, Elancolan)

1%

<1%

Insecticide 

(Trade or common

name)

Rate 

of 

detection b

Concentration, in μg/L

Aldicarb sulfoxidec

(Aldicarb metabolite)

0%

1%

Carbaryl c

(Sevin, Savit)

19%

2%

Carbofuranc

(Furadan, Curaterr)

1%

1%

Chlorpyrifos 

(Dursban, Lorsban)

1%

0%

p,p’-DDE (p,p’-DDT 

metabolite)

<1%

<1%

Diazinon 21%

0%

0.001 0.01 0.1 1 10 100 1,000

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS

Alachlor (Lasso) 3%

0%

Atrazine (AAtrex, 

Gesaprim)

34%

17%

Desethylatrazinec

(Atrazine metabolite)

6%

17%

Benfluralin (Balan, 

Benefin, Bonalan)

1%

<1%

Bromacil (Hyvar X, 

Urox B, Bromax)

0%

1%

Cyanazine (Bladex,

Fortrol)

2%

0%

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

0%

DCPA (Dacthal, 

chlorthal-dimethyl)

<1%

<1%

Dichlorprop (2,4-DP,

Seritox 50, Kildip)

1%

1%

EPTC (Eptam) <1%

<1%

Ethalfluralin 

(Sonalan, Sonalen)

0%

<1%

Metolachlor 

(Dual, Pennant)

17%

2%

Metribuzin 

(Lexone, Sencor) 

4%

<1%

Napropamide 

(Devrinol)

1%

1%

Pendimethalin 

(Prowl, Stomp)

1%

0%

Prometon (Gesagram

prometone)

48%

6%

 The following tables summarize data collected for NAWQA studies from 1992–1995 by showing results for the Connecticut,

Housatonic, and Thames River Basins Study Unit compared to the NAWQA national range for each compound detected. The data were

collected at a 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 the concentrations (such as 10, 100, or 1000), rather than the precise 

number. The complete dataset used to construct these tables is available upon request. 

a

Detection in the Connecticut, Housatonic, and Thames River Basins Study Unit

Water-Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95 

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

Connecticut, Housatonic, and Thames River Basins 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]
U.S. Geological Survey Circular 1155 25

Dieldrin (Panoram 

D-31, Octalox)

<1%

2%

Disulfotonc

(Disyton)

<1%

0%

gamma-HCH <1%

0%

Malathion (Maldison, 

Malathon, Cythion)

4%

0%

cis-Permethrinc

(Ambush, Pounce) 

<1%

<1%

Propargite (Comite, 

Omite, BPPS)

4%

<1%

Volatile organic 

compound

(Trade or common 

name)

Rate 

of 

detection b

Concentration, in μg/L 

1,1,1-Trichloroethane --

2%

1,1-Dichloroethane --

3%

1,2,4-Trimethylbenzene (Pseudocumene)

--

1%

1,2-Dibromoethane 

(EDB)

--

1%

1,3,5-Trimethylbenzene (Mesitylene)

--

1%

Benzene --

1%

Dichlorodifluoromethane (CFC 12)

--

4%

Dichloromethane 

(Methylene chloride)

--

2%

Dimethylbenzenes 

(Xylenes (total))

--

1%

Ethylbenzene 

(Phenylethane)

--

1%

Isopropylbenzene 

(Cumene)

--

1%

Methylbenzene 

(Toluene)

--

3%

Naphthalene --

2%

Tetrachloromethane --

1%

total Trihalomethanes --

29%

0.01 0.1 1 10 100 1,000

Trichloroethene 

(TCE)

--

13%

cis-1,2-

Dichloroethene

--

8%

n-Butylbenzene 

(1-Phenylbutane)

--

1%

n-Propylbenzene 

(Isocumene)

--

1%

p-Isopropyltoluene 

(p-Cymene)

--

1%

sec-Butylbenzene --

1%

Volatile organic 

compound

(Trade or common 

name)

Rate 

of 

detection b

Concentration, in μg/L

Methyl tert-butyl

etherd (MTBE)

--

25%

Tetrachloroethene 

(Perchloroethene)

--

9%

Nutrient

(Trade or common

name)

Rate 

of 

detection b

Concentration, in mg/L

Dissolved ammonia 85%

70%

Dissolved ammonia 

plus organic nitrogen 

as nitrogen

60%

9%

Dissolved phosphorus as phosphorus

68%

36%

Dissolved nitrite plus 

nitrate

97%

85%

Other Rate 

of 

detection b

Concentration, in pCi/L

Radon 222 --

100%

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

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

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

Volatile organic 

compound

(Trade or common 

name)

Rate 

of 

detection b

Concentration, in μg/L 

0.01 0.1 1 10 100 1,000

Insecticide 

(Trade or common

name)

Rate 

of 

detection b

0.001 0.01 0.1 1 10 100 1,000

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS

Concentration, in μg/L 
26 Water-Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

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

Housatonic, and Thames River Basins Study Unit. 

Herbicides

2,4,5-T

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

2,4-DB (Butyrac, 

Butoxone, Embutox Plus, 

Embutone)

2,6-Diethylaniline 

(Metabolite of Alachlor)

Acetochlor (Harness Plus, 

Surpass)

Acifluorfen (Blazer, Tackle 

2S)

Bentazon (Basagran, 

Bentazone, Bendioxide)

Bromoxynil (Buctril, 

Brominal)

Butylate (Sutan +, Genate 

Plus, Butilate)

Chloramben (Amiben, 

Amilon-WP, Vegiben)

Clopyralid (Stinger, 

Lontrel, Reclaim, 

Transline)

Dacthal mono-acid (Dacthal 

metabolite)

Dicamba (Banvel, Dianat, 

Scotts Proturf)

Dinoseb (Dinosebe)

Diuron (Crisuron, Karmex, 

Direx, Diurex)

Fenuron (Fenulon, Fenidim)

Fluometuron (Flo-Met, 

Cotoran, Cottonex, 

Meturon)

Linuron (Lorox, Linex, 

Sarclex, Linurex, Afalon)

MCPA (Rhomene, Rhonox, 

Chiptox)

MCPB (Thistrol)

Molinate (Ordram)

Neburon (Neburea, 

Neburyl, Noruben)

Norflurazon (Evital, 

Predict, Solicam, Zorial)

Oryzalin (Surflan, Dirimal)

Pebulate (Tillam, PEBC)

Picloram (Grazon, Tordon)

Pronamide (Kerb, 

Propyzamid)

Propham (Tuberite)

Thiobencarb (Bolero, 

Saturn, Benthiocarb, 

Abolish)

Triclopyr (Garlon, 

Grandstand, Redeem, 

Remedy)

Insecticides

3-Hydroxycarbofuran 

(Carbofuran metabolite)

Aldicarb sulfone (Standak, 

aldoxycarb, aldicarb 

metabolite)

Aldicarb (Temik, Ambush, 

Pounce)

Azinphos-methyl (Guthion, 

Gusathion M)

Ethoprop (Mocap, 

Ethoprophos)

Fonofos (Dyfonate, Capfos, 

Cudgel, Tycap)

Methiocarb (Slug-Geta, 

Grandslam, Mesurol)

Methomyl (Lanox, 

Lannate, Acinate)

Methyl parathion 

(Penncap-M, Folidol-M, 

Metacide, Bladan M)

Oxamyl (Vydate L, Pratt)

Parathion (Roethyl-P, 

Alkron, Panthion, Phoskil)

Phorate (Thimet, Granutox, 

Geomet, Rampart)

Propoxur (Baygon, 

Blattanex, Unden, 

Proprotox)

Terbufos (Contraven, 

Counter, Pilarfox)

alpha-HCH (alpha-BHC, 

alpha-lindane, alphahexachlorocyclohexane, 

alpha-benzene 

hexachloride)

Bromomethane (Methyl 

bromide)

Chlorobenzene 

(Monochlorobenzene)

Chloroethane (Ethyl 

chloride)

Chloroethene (Vinyl 

chloride)

Chloromethane (Methyl 

chloride)

Dibromomethane 

(Methylene dibromide)

Ethenylbenzene (Styrene)

Hexachlorobutadiene

Trichlorofluoromethane 

(CFC 11, Freon 11)

cis-1,3-Dichloropropene 

((Z)-1,3-Dichloropropene)

tert-Butylbenzene

trans-1,2-Dichloroethene 

((E)-1,2-Dichlorothene)

trans-1,3-Dichloropropene 

((E)-1,3-Dichloropropene)

Volatile organic 

compounds

1,1,1,2-Tetrachloroethane 

(1,1,1,2-TeCA)

1,1,2,2-Tetrachloroethane

1,1,2-Trichloro-1,2,2-

trifluoroethane (Freon 113, 

CFC 113)

1,1,2-Trichloroethane 

(Vinyl trichloride)

1,1-Dichloroethene 

(Vinylidene chloride)

1,1-Dichloropropene

1,2,3-Trichlorobenzene 

(1,2,3-TCB)

1,2,3-Trichloropropane 

(Allyl trichloride)

1,2,4-Trichlorobenzene

1,2-Dibromo-3-

chloropropane 

(DBCP, Nemagon)

1,2-Dichlorobenzene 

(o-Dichlorobenzene, 

1,2-DCB)

1,2-Dichloroethane 

(Ethylene dichloride)

1,2-Dichloropropane 

(Propylene dichloride)

1,3-Dichlorobenzene 

(m-Dichlorobenzene)

1,3-Dichloropropane 

(Trimethylene dichloride)

1,4-Dichlorobenzene 

(p-Dichlorobenzene, 

1,4-DCB)

1-Chloro-2-

methylbenzene 

(o-Chlorotoluene)

1-Chloro-4-

methylbenzene 

(p-Chlorotoluene)

2,2-Dichloropropane

Bromobenzene (Phenyl 

bromide)

Bromochloromethane 

(Methylene 

chlorobromide)

Nutrients

No non-detects

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
0.1 10 100 1,000 10,000 100,000 1 0.1 10 100 1,000 10,000 100,000 1

U.S. Geological Survey Circular 1155 27

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS

1,2,4-

Trichlorobenzene

--

2%

1,2-Dichlorobenzene --

2%

1,2-

Dimethylnaphthalene

--

14%

1,3-Dichlorobenzene --

2%

1,4-Dichlorobenzene --

9%

1,6-

Dimethylnaphthalene

--

59%

1-Methyl-9H-fluorene --

48%

1-

Methylphenanthrene

--

81%

1-Methylpyrene --

81%

2,2-Biquinoline --

21%

2,3,6-

Trimethylnaphthalene

--

55%

2,6-

Dimethylnaphthalene

--

89%

2-Ethylnaphthalene --

23%

2-Methylanthracene --

74%

3,5-Dimethylphenol --

2%

4,5-Methylenephenanthrene

--

84%

4-Chloro-3-

methylphenol

--

2%

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

sediment of the Connecticut, Housatonic, and Thames River Basins Study Unit. [μg/g, micrograms per gram; μg/kg, micrograms per 

kilogram; %, percent; <, less than; - -, not measured; trade names may vary]

EXPLANATION

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

Detection in bed sediment or fish tissue in the Connecticut, Housatonic, and Thames River 

Range of detections in bed sediment in all 20 Study Units

Guideline for the protection of aquatic life e

Semivolatile 

organic compound

Rate of 

detection b

Concentration, in μg/kg Semivolatile 

organic compound

Rate of 

detection b

Concentration, in μg/kg

4-Chlorophenylphenylether

--

2%

9H-Carbazole --

79%

9H-Fluorene --

80%

Acenaphthene --

73%

Acenaphthylene --

89%

Acridine --

45%

Anthracene --

89%

Anthraquinone --

86%

Azobenzene --

2%

Benz[ a ]anthracene --

94%

Benzo[ a ]pyrene --

92%

Benzo[ b ]

fluoranthene

--

96%

Benzo[ ghi ]perylene --

81%

Benzo[ k ]

fluoranthene

--

96%

Butylbenzylphthalate --

66%

Chrysene --

98%

Di- n -butylphthalate --

88%
0.01 0.1 1 10 100 1,000 10,000 100,000

0.01 0.1 1 10 100 1,000 10,000

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

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

28 Water-Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

Di- n -octylphthalate --

31%

Dibenz[ a,h ] 

anthracene

--

67%

Dibenzothiophene --

73%

Diethylphthalate --

32%

Dimethylphthalate --

18%

Fluoranthene --

98%

Indeno[1,2,3- cd ] 

pyrene

--

85%

Isoquinoline --

20%

Naphthalene --

59%

N-Nitrosodiphenylamine

--

7%

Phenanthrene --

91%

Phenanthridine --

26%

Phenol --

93%

Pyrene --

98%

Quinoline --

16%

bis-(2-Ethylhexyl)

phthalate

--

96%

p-Cresol --

70%

Organochlorine 

compound

(Trade name)

Rate 

of 

detection b

Concentration, in μg/kg

total-Chlordane 78%

34%

p,p’-DDE 97%

64%

total-DDT 97%

70%

Dieldrin (Panoram 

D-31, Octalox)

38%

20%

Endosulfan I (alphaendosulfan, Thiodan)

--

7%

Heptachlor epoxide 3%

0%

Hexachlorobenzene 6%

--

p,p’-Methoxychlor 

(Marlate)

0%

2%

Mirex (Dechlorane) 0%

5%

PCB, total 88%

23%

Pentachloroanisole 22%

0%

Trace element Rate 

of 

detection b

Concentration, in μg/g

Arsenic 71%

100%

Cadmium 93%

100%

Chromium 43%

98%

Copper 100%

100%

Lead 36%

100%

Mercury 80%

96%

Nickel 29%

100%

Selenium 100%

98%

Zinc 100%

100%

Semivolatile 

organic compound

Rate of 

detection b

Concentration, in μg/kg Organochlorine 

compound

(Trade name)

Rate 

of 

detection b

Concentration, in μg/kg

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
U.S. Geological Survey Circular 1155 29

Semivolatile organic compounds, organochlorine compounds, and trace elements analyzed for but not detected in fish tissue and bed

sediment of the Connecticut, Housatonic, and Thames River Basins Study Unit. 

Semivolatile 

organic 

compounds

2,4-Dinitrotoluene

2,6-Dinitrotoluene

2-Chloronaphthalene

2-Chlorophenol

4-Bromophenylphenylether

Benzo [c] cinnoline

C8-Alkylphenol

Isophorone

N-Nitrosodi-npropylamine

Nitrobenzene

Pentachloronitrobenzene

bis-(2-Chloroethoxy)

methane

Organochlorine 

compounds

Aldrin (HHDN, Octalene)

Chloroneb (chloronebe, 

Demosan, Soil Fungicide 

1823)

DCPA (Dacthal, 

chlorthal-dimethyl)

Endrin (Endrine)

Heptachlor (Heptachlore, 

Velsicol 104)

Isodrin (Isodrine, 

Compound 711)

Toxaphene (Camphechlor,

Hercules 3956)

alpha-HCH (alpha-BHC, 

alpha-lindane, alphahexachlorocyclohexane, 

alpha-benzene 

hexachloride)

beta-HCH (beta-BHC, 

betahexachlorocyclohexane

alpha-benzene 

hexachloride)

cis-Permethrin (Ambush, 

Astro, Pounce, Pramex, 

Pertox, Ambushfog, Kafil, 

Perthrine, Picket, Picket G, 

Dragnet, Talcord, 

Outflank, Stockade, 

Eksmin, Coopex, Peregin, 

Stomoxin, Stomoxin P, 

Qamlin, Corsair, Tornade)

delta-HCH (delta-BHC, 

deltahexachlorocyclohexane, 

delta-benzene 

hexachloride)

gamma-HCH (Lindane, 

gamma-BHC, 

Gammexane, Gexane, 

Soprocide, 

gammahexachlorocyclohexane, 

gamma-benzene 

hexachloride, gammahexachlorocyclohexane, 

gamma-benzene)

o,p’-Methoxychlor

trans-Permethrin (Ambush, 

Astro, Pounce, Pramex, 

Pertox, 

Ambushfog, Kafil, 

Perthrine, Picket, Picket G, 

Dragnet, Talcord, 

Outflank, Stockade, 

Eksmin, Coopex, Peregin, 

Stomoxin, Stomoxin P, 

Qamlin, Corsair, Tornade)

Trace elements

No non-detects

a

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

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

insecticides were computed by counting only those detections equal to or greater than 0.01μg/L in order to facilitate equal comparisons among compounds, which had widely varying detection limits. For herbicides and insecticides, a detection rate of “<1%” means that all detections are less than

0.01μg/L, or the detection rate rounds to less than one percent. For other compound groups, all detections were counted and minimum detection

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

are summarized in Gilliom and others (in press).

c

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

as estimated values (Zaugg and others, 1995).

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

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

e

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

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
30 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

THIS REPORT WAS BASED ON THE FOLLOWING PUBLICATIONS

Breault, R.F., and Harris, S.L., 1997, 

Geographical distribution and 

potential for adverse biological 

effects of selected trace elements 

and organic compounds in 

streambed sediment in the 

Connecticut, Housatonic, and 

Thames River Basins, 1992-94: 

U.S. Geological Survey WaterResources Investigations Report 

97-4169, 24 p.

Brill, A.B., 1994, Facts concerning 

environmental radon, Journal of 

Nuclear Medicine, v. 35, no. 2.

Coles, J.F., 1996, Organochlorine 

compounds and trace elements in 

fish tissue and ancillary data for 

the Connecticut, Housatonic, and 

Thames River Basins, 1992-94: 

U.S. Geological Survey OpenFile Report 96-358, 26 p.

Connecticut Department of 

Environmental Protection, 1994, 

Water quality report: Hartford, 

Conn., 97 p.

_____1996, Connecticut waterbodies 

not meeting water-quality 

standards in 1996: Hartford, 

Conn., 24 p.

Ecosystem Conservation 

Directorate—Evaluation and 

Interpretation Branch, 1995, 

Interim sediment quality 

guidelines: Ottawa, Ontario, Soil 

and sediment quality section, 

Guidelines Division, 12 p.

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

M.E., 1995, Design of the 

National Water-Quality 

Assessment Program— 

Occurrence and distribution of 

water-quality conditions: U.S. 

Geological Survey Circular 1112, 

33 p.

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

Nowell, L.H., in press, Methods 

for comparing water-quality 

conditions among National 

Water-Quality Assessment Study 

Units, 1992-1995: U.S. 

Geological Survey Open-File 

Report 97-589.

Grady, S.J., 1997, Occurrence of 

volatile organic compounds in 

ground water in the Connecticut, 

Housatonic, and Thames River 

Basins: U.S. Geological Survey 

Fact Sheet FS-029-97, 6 p.

Grady, S.J., and Mullaney, J.R., 1998, 

Natural and human factors 

affecting shallow water quality in 

surficial aquifers in the 

Connecticut, Housatonic, and 

Thames River Basins: U.S. 

Geological Survey WaterResources Investigations Report 

98-4042, 81 p.

Massachusetts Department of 

Environmental Protection, 1995, 

Summary of water quality: 

Boston, Mass., 97 p.

Mitchell, W.B., Guptill, S.C., 

Anderson, K.E., Fegas, R.G., and 

Hallam, C.A., 1977, GIRAS—A 

geographic information and 

analysis system for handling land 

use and land cover data: U.S. 

Geological Survey Professional 

Paper 1059, 16 p.

National Academy of Sciences and 

National Academy of 

Engineering, 1973 [1974], Waterquality criteria, 1972: U.S. 

Environmental Protection 

Agency, EPA R3-73-033, 594 p.

New Hampshire Department of 

Environmental Services, 1996, 

Water quality report: Concord, 

N.H.

Trench, E.C.T., 1996, Trends in 

surface-water quality in 

Connecticut, 1969-88: U.S. 

Geological Survey WaterResources Investigations Report 

96-4161, 176 p.

U.S. Environmental Protection 

Agency, 1994,Water quality 

standards handbook (2nd ed.): 

U.S. Environmental Protection 

Agency: EPA-823-B-94-005b, 

Appendix P, 3 p.

U.S. Environmental Protection 

Agency, 1996, Drinking water 

regulations and health advisories: 

Office of Water, EPA 822-R-96-

001, 16 p.

_____1997, The Long Island Sound 

Study-Proposal for phase III 

actions for hypoxia management: 

EPA 840-R-97-001, 25 p.

Vermont Department of Environmental 

Conservation, 1996, Water quality 

assessment: Waterbury, Vt.

Zimmerman, M.J., Grady, S.J., Trench, 

E.C.T., Flanagan, S.M., and 

Nielsen, M.G., 1996, Waterquality assessment of the 

Connecticut, Housatonic, and 

Thames River Basins study unit: 

Analysis of available information 

on nutrients, suspended 

sediments, and pesticides, 1972-

92: U.S. Geological Survey 

Water-Resources Investigations 

Report 95-4203, 162 p.

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

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

Methods of analysis by the U.S. 

Geological Survey National 

Water Quality Laboratory— 

Determination of pesticides in 

water by C-18 solid-phase 

extraction and capillary-column 

gas chromatography/mass 

spectrometry with selected-ion 

monitoring: U.S. Geological 

Survey Open-File Report 95-181, 

49 p.

Zimmerman, M.J., 1997, Trends in 

nitrogen and phosphorus 

concentrations in southern New 

England streams, 1974-92: U.S. 

Geological Survey Fact Sheet 

FS-001-97, 4 p.
U.S. Geological Survey Circular 1155 31

GLOSSARY

Ammonia - A compound of nitrogen 

and hydrogen (NH3) that is a 

common by-product of animal 

waste. Ammonia readily converts 

to nitrate in soils and streams.

Aquatic-life criteria - Water-quality 

guidelines for protection of 

aquatic life. Often refers to U.S. 

Environmental Protection Agency 

water-quality criteria for 

protection of aquatic organisms. 

See also Water-quality guidelines, 

Water-quality criteria, and 

Freshwater chronic criteria.

Aquifer - A water-bearing layer of soil, 

sand, gravel, or rock that will yield 

usable quantities of water to a 

well.

Atmospheric deposition - The transfer 

of substances from the air to the 

surface of the Earth, either in wet 

form (rain, fog, snow, dew, frost, 

hail) or in dry form (gases, 

aerosols, particles).

Basic Fixed Sites - Sites on streams at 

which streamflow is measured and 

samples are collected for 

measurement of analysis of 

temperature, salinity, suspended 

sediment, major ions and metals, 

nutrients, and organic carbon to 

assess the broad-scale spatial and 

temporal character and transport 

of inorganic constituents of 

streamwater in relation to 

hydrologic conditions and 

environmental settings. 

Bed sediment - The material that 

temporarily is stationary in the 

bottom of a stream or other 

watercourse.

Benthic - Refers to plants or animals 

that live on the bottom of lakes, 

streams, or oceans.

Breakdown product - A compound 

derived by chemical, biological, or 

physical action upon a pesticide. 

The breakdown is a natural 

process which may result in either 

a more toxic or a less toxic 

compound and either a more 

persistent or less persistent 

compound.

Chlordane - Octachloro-4,7-

methanotetrahydroindane. An 

organochlorine insecticide no 

longer registered for use in the 

U.S. Technical chlordane is a 

mixture in which the primary 

components are cis- and transchlordane, cis- and transnonachlor, and heptachlor.

Concentration - The amount or mass 

of a substance present in a given 

volume or mass of sample. 

Usually expressed in micrograms 

per liter (water sample) or 

micrograms per kilogram 

(sediment or tissue sample).

Detection limit - The concentration 

below which a particular 

analytical method cannot 

determine, with a high degree of 

certainty, a concentration.

DDT - Dichloro-diphenyltrichloroethane. An 

organochlorine insecticide no 

longer registered for use in the 

United States.

Dieldrin - An organochlorine 

insecticide no longer registered for 

use in the United States. Also a 

degradation product of the 

insecticide aldrin.

Drainage basin - The portion of the 

surface of the Earth that 

contributes water to a stream 

through overland run-off, 

including tributaries and 

impoundments.

Effluent - Outflow from a particular 

source, such as a stream that 

flows from a lake or liquid waste 

that flows from a factory or 

sewage-treatment plant.

Eutrophication - The process by 

which water becomes enriched 

with plant nutrients, most 

commonly phosphorus and 

nitrogen.

Fecal bacteria - Microscopic singlecelled organisms (primarily fecal 

coliforms and fecal streptococci) 

found in the wastes of warmblooded animals. Their presence 

in water is used to assess the 

sanitary quality of water for bodycontact recreation or for 

consumption. Their presence 

indicates contamination by the 

wastes of warm-blooded animals 

and the possible presence of 

pathogenic (disease producing) 

organisms.

Health advisory - Nonregulatory levels 

of contaminants in drinking water 

that may be used as guidance in 

the absence of regulatory limits. 

Advisories consist of estimates of 

concentrations that would result in 

no known or anticipated health 

effects (for carcinogens, a 

specified cancer risk) determined 

for a child or for an adult for 

various exposure periods.

Herbicide - A chemical or other agent 

applied for the purpose of killing 

undesirable plants. See also

Pesticide.

Indicator sites - Stream sampling 

sites located at outlets of drainage 

basins with relatively 

homogeneous land use and 

physiographic conditions; most 

indicator-site basins have drainage 

areas ranging from 20 to 

200 square miles.

Insecticide - A substance or mixture of 

substances intended to destroy or 

repel insects.

Integrator or Mixed-use site - Stream 

sampling site located at an outlet 

of a drainage basin that contains 

multiple environmental settings. 

Most integrator sites are on major 

streams with relatively large 

drainage areas.

Intensive Fixed Sites - Basic Fixed 

Sites with increased sampling 

frequency during selected 

seasonal periods and analysis of 

dissolved pesticides for 1 year. 

Most NAWQA Study Units have 

one to two integrator Intensive 

Fixed Sites and one to four 

indicator Intensive Fixed Sites.

Maximum contaminant level 

(MCL) - Maximum permissible 

level of a contaminant in water 

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

only valid ones for these terms.
32 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95

GLOSSARY

that is delivered to any user of a 

public water system. MCLs are 

enforceable standards established 

by the U.S. Environmental 

Protection Agency.

Mean - The arithmetic average of a set 

of observations, unless otherwise 

specified.

Median - The middle or central value 

in a distribution of data ranked in 

order of magnitude. The median 

is also known as the 50th 

percentile.

Micrograms per liter (μg/L) - A unit 

expressing the concentration of 

constituents in solution as weight 

(micrograms) of solute per unit 

volume (liter) of water; equivalent 

to one part per billion in most 

stream water and ground water. 

One thousand micrograms per 

liter equals 1 mg/L.

Milligrams per liter (mg/L) - A unit 

expressing the concentration of 

chemical constituents in solution 

as weight (milligrams) of solute 

per unit volume (liter) of water; 

equivalent to one part per million 

in most stream water and ground 

water. One thousand micrograms 

per liter equals 1 mg/L.

National Academy of 

Sciences/National Academy of 

Engineering (NAS/NAE) 

recommended maximum 

concentration in water - 

Numerical guidelines 

recommended by two joint 

NAS/NAE committees for the 

protection of freshwater and 

marine aquatic life, respectively. 

These guidelines were based on 

available aquatic toxicity studies, 

and were considered preliminary 

even at the time (1972). The 

guidelines used in the NAWQA 

summary reports are for 

freshwater.

Nitrate - An ion consisting of nitrogen 

and oxygen (NO3

-

). Nitrate is a 

plant nutrient and is very mobile 

in soils.

Nutrient - An element or compound 

essential for animal and plant 

growth. Common nutrients in 

fertilizer include nitrogen, 

phosphorus, and potassium.

Organochlorine compound - A 

synthetic organic compound 

containing chlorine. As generally 

used, the term refers to 

compounds containing mostly or 

exclusively carbon, hydrogen, 

and chlorine. Examples include 

organochlorine insecticides, 

polychlorinated biphenyls, and 

some solvents containing 

chlorine.

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

of the amount of radioactivity 

represented by a curie (Ci). 

A curie is the amount of 

radioactivity that yields 3.7 x 1010

radioactive disintegrations per 

second.

Polychlorinated biphenyls (PCBs) - 

A mixture of chlorinated 

derivatives of biphenyl, marketed 

under the trade name Aroclor 

with a number designating the 

chlorine content (such as Aroclor 

1260). PCBs were used in 

transformers and capacitors for 

insulating purposes and in gas 

pipeline systems as a lubricant. 

Further sale for new use was 

banned by law in 1979.

Polycyclic aromatic hydrocarbon 

(PAH) - A class of organic 

compounds with a fused-ring 

aromatic structure. PAHs result 

from incomplete combustion of 

organic carbon (including wood), 

municipal solid waste, and fossil 

fuels, as well as from natural or 

anthropogenic introduction of 

uncombusted coal and oil. PAHs 

include benzo(a)pyrene, 

fluoranthene, and pyrene.

Semivolatile organic compound 

(SVOC) - Operationally defined 

as a group of synthetic organic 

compounds that are solventextractable and can be determined 

by gas chromatography/mass 

spectrometry. SVOCs include 

phenols, phthalates, and 

Polycyclic aromatic hydrocarbons 

(PAHs).

Study Unit - A major hydrologic 

system of the United States in 

which NAWQA studies are 

focused. Study Units are 

geographically defined by a 

combination of ground- and 

surface-water features and 

generally encompass more than 

4,000 square miles of land area.

Synoptic sites - Sites sampled during a 

short-term investigation of 

specific water-quality conditions 

during selected seasonal or 

hydrologic conditions to provide 

improved spatial resolution for 

critical water-quality conditions. 

Volatile organic compounds 

(VOCs) - Organic chemicals that 

have a high vapor pressure 

relative to their water solubility. 

VOCs include components of 

gasoline, fuel oils, and lubricants, 

as well as organic solvents, 

fumigants, some inert ingredients 

in pesticides, and some byproducts of chlorine disinfection.

Water-quality criteria - Specific 

levels or concentrations of 

chemical constituents of organic 

compounds in water, which, if 

exceeded, are considered to 

render a body of water unsuitable 

for its designated use. Commonly 

refers to water-quality criteria 

established by the U.S. 

Environmental Protection 

Agency. Water-quality criteria are 

based on specific levels of 

pollutants that would make the 

water harmful if used for 

drinking, swimming, farming, 

fish production, or industrial 

processes.

Water year - The continuous 12-

month period, October 1 through 

September 30, in U.S. Geological 

Survey reports dealing with the 

surface-water supply. The water 

year is designated by the calendar 

year in which it ends and which 

includes 9 of the 12 months. 

Thus, the year ending September 

30, 1980, is referred to as the 

"1980" water year.