U.S. Department of the Interior

U.S. Geological Survey Circular 1265

Water Quality in the Nation’s Streams and Aquifers—

Overview of Selected Findings, 1991–2001
Front cover: Photo by Phillip J. Redman, USGS
Water Quality in the Nation’s Streams and Aquifers—

Overview of Selected Findings, 1991–2001

By Pixie A. Hamilton, Timothy L. Miller, and Donna N. Myers

Circular 1265

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

Free on application

U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.
Contents

Information to Manage, Protect, and Restore Water Quality ....................................... 2

Water Quality and its Connection to Land Use—Agricultural and Urban Sources 

of Nonpoint Pollution ........................................................................... 4

Effects of Natural Features and Land-Management Practices .................................... 6

Complex Contaminant Patterns—Mixtures, Breakdown Products, and Seasonality ............ 8

Interactions Among Water, Air, and Aquatic Ecosystems .......................................... 10

Changes in Water Quality Over Time .................................................................. 16

The NAWQA Program .................................................................................... 18

For Additional Information .............................................................................. 20

This report accompanies the publication of the last 15 of 51 river 

basin and aquifer assessments by the USGS National WaterQuality Assessment (NAWQA) Program during 1991–2001. 

It highlights selected water-quality findings of regional and 

national interest through examples from river basins and 

aquifer systems across the Nation. Forthcoming reports in the 

USGS series “The Quality of Our Nation’s Waters” will present 

comprehensive national syntheses of information collected in 

the 51 study units on pesticides in water, sediment, and fish; 

volatile organic compounds in major aquifers used for domestic 

and public supply; nutrients and trace elements in streams and 

ground water; and aquatic ecology. This report, summaries of 

the 51 water-quality assessments, and a 1999 national synthesis 

of information on nutrients and pesticides, are available free of 

charge as USGS Circulars and on the World Wide Web at 

water.usgs.gov/nawqa/nawqa_sumr.html.

Photo by Phillip J. Redman, USGS

Water Quality in the Nation’s Streams and Aquifers—

Overview of Selected Findings, 1991–2001

By Pixie A. Hamilton, Timothy L. Miller, and Donna N. Myers

The U.S. Geological Survey (USGS) serves 

the Nation by providing reliable and timely 

scientific information that helps enhance 

and protect our quality of life, and facilitates 

effective management of water, biological, 

energy, and mineral resources.

Photo by Gregory K. Boughton, USGS

Photo by Phillip J. Redman, USGS
2

The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) assesses the quality of 

streams, ground water, and aquatic ecosystems in major river basins and aquifer systems 

across the Nation (known as “study units”; see 

map on p. 19). These assessments characterize 

the ambient water resource—the source for 

more than 60 percent of the Nation’s drinking 

water and water for irrigation and industry.

During its first decade (1991–2001), 

NAWQA completed assessments in 51 study 

units, which provided baseline data and information on the occurrence of pesticides, nutrients, volatile organic compounds (VOCs), 

trace elements, and radon in water, and on 

the condition of aquatic habitats and fish, 

insect, and algal communities. Conditions are 

compared to selected benchmarks, such as for 

drinking-water quality and the protection of 

aquatic organisms (see p. 18). Each assessment follows a nationally consistent study 

design and methodology, thereby providing 

information about local water-quality conditions as well as providing insight on where 

and when water quality varies regionally and 

nationally. This document contains findings 

of regional and national interest along with 

examples from the study units illustrating 

these findings.

During its second decade (2002–2012), 

NAWQA plans to reassess 42 of the 51 study 

units. These assessments will fill critical gaps 

in the characterization of water-quality conditions; determine trends at many of the monitoring sites; and build upon earlier assessments that link water-quality conditions and 

trends to natural and human factors (see p. 18 

for more details about the NAWQA Program).

The first round of NAWQA assessments 

indicates that while many of our Nation’s 

waters are suitable for most uses, contaminants from nonpoint and point sources continue to affect our streams and ground water 

in parts of every study unit. Findings from the 

51 study units show that

• contamination of streams and ground 

water is widespread in agricultural and 

urban areas, and is characterized by 

complex mixtures of nutrients, trace 

elements, pesticides, VOCs, and their 

chemical breakdown products, and

• water quality and aquatic-ecosystem 

health are controlled by a combination 

of factors, including chemical use, 

land use, land-management practices, 

and natural features, such as geology, 

hydrology, soils, and climate.

Information to Manage, Protect, and Restore Water Quality

Local, State, Tribal, and national stakeholders use NAWQA information to design and 

implement strategies for managing, protecting, and monitoring water resources in many different hydrologic and land-use settings across the Nation, such as to:

• support development of regulations, standards, and guidelines that reflect actual contaminant occurrence, including contaminant mixtures, breakdown products, seasonal 

patterns, and variability among different settings;

• identify key sources of nonpoint pollution in agricultural and urban areas;

• prioritize geographic areas and basins in which water resources and aquatic ecosystems are most vulnerable to contamination and where improved treatment or 

management can have the greatest benefits;

• improve strategies and protocols for monitoring, sampling, and analysis of all 

hydrologic components, including the atmosphere, surface water, ground water, and 

biological communities;

• contribute to State assessments of beneficial uses and impaired waters (Total Maximum Daily Loads or TMDLs), strategies for source-water protection and management, pesticide and nutrient management plans, and fish-consumption advisories; 

and,

• sustain the health of aquatic ecosystems through improved stream protection and 

restoration management.

“The USGS provides local, 

State, and Federal agencies 

with top quality data and 

accurate reporting that both 

the farming community and 

the environmental community can trust. NAWQA’s 

ability to look at water quality over the long term helps 

to evaluate the effectiveness of water-management 

decisions, conservation 

activities, and certain farming practices that are used to 

reduce sediment and runoff 

of agricultural nutrients and 

chemicals from fields.”

Jeff Loser, 

National Leader for Clean 

Water Programs, 

USDA Natural Resources 

Conservation Service

Photo by Phillip J. Redman, USGS
“Data from the NAWQA Program supplied critical 

information for Ohio EPA’s Total Maximum Daily 

Load (TMDL) effort in the Stillwater River Basin, 

and will continue to provide valuable data for 

future TMDLs in other sub-basins of the Great 

Miami River. Additionally, the NAWQA study 

has helped further our understanding of linkages 

between nutrients, land use, and impairment of 

aquatic life.”

Robert Miltner, 

Aquatic Ecologist, 

Ohio Environmental Protection Agency

“Properly balancing competing water-resource 

demands while conserving our significant fish 

and wildlife resources for future generations is 

one of the most critical environmental management issues facing the Service today. The 

NAWQA Program provides an objective scientific 

foundation to assist resource agencies charged 

with making difficult management decisions. 

It synthesizes surface-water, ground-water, and 

biological data in an accessible and understandable way for a wide variety of readers.”

Larry E. Goldman, 

Field Supervisor, 

U.S. Fish and Wildlife Service

“The New England Coastal Basins NAWQA study 

has been very valuable to the U.S. Environmental 

Protection Agency’s New England regional water 

programs. The study has provided contaminated 

sediment data, which will be incorporated into 

our National and regional sediment inventories; 

has highlighted the importance of arsenic in 

drinking water wells in New England; and has 

established relationships between land use 

and environmental quality of rivers and streams, 

including flow, nutrient status, and biological 

communities. The data from, and the monitoring 

approaches of, the study will help the USEPA in 

its monitoring and regulatory roles.”

Matthew Liebman, 

Environmental Biologist, 

U.S. Environmental Protection AgencyNew England

“The NAWQA Program has filled a tremendous 

void in the pesticide data that the State of 

Alabama must acquire in the development of the 

USEPA-mandated State Pesticide Management 

Plan... The NAWQA data are used to make 

important determinations and the plan can target 

the areas of greatest importance.”

Tony Cofer, 

Program Director—

Pesticide Division, 

Alabama Department of Agriculture and Industries

3

Photo by Dennis K. Demcheck, USGS
NAWQA studies indicate that contaminants 

are widespread, albeit often at low concentrations, in river basins and aquifer systems 

across a wide range of landscapes and land 

uses. In the mostly agricultural Lower Tennessee River Basin, for example, 52 different 

pesticides were detected in streams and rivers, 

and VOCs were detected in about 67 percent 

of sampled springs and wells that tap underlying carbonate aquifers. Nationally, at least 

one pesticide was found in about 94 percent 

of water samples and in 90 percent of fish 

samples from streams, and in about 55 percent 

of shallow wells sampled in agricultural and 

urban areas.

The type and concentrations of contaminants that are found in urban and agricultural 

water resources are closely related to the 

chemicals that are used (such as fertilizers 

and pesticides) or that are released with waste 

products (such as sewage or manure). For 

example, phosphorus and many insecticides, 

such as diazinon, carbaryl, chlorpyrifos, and 

malathion, were detected more frequently 

and usually at higher concentrations in urban 

streams than in agricultural streams (see

Thornton Creek near Seattle, Washington

example). Nationally, at least one pesticide 

guideline established to protect aquatic life 

was exceeded in nearly all (about 93 percent) 

of the urban streams sampled.

Nitrogen and many herbicides—most 

commonly atrazine and its breakdown product 

deethylatrazine (DEA), metolachlor, alachlor, 

and cyanazine—generally were detected more 

frequently and usually at higher concentrations in streams and shallow ground water in 

agricultural areas than in urban areas. Occurrence is linked to use; these herbicides rank in 

the top five used for agriculture. Concentrations of nitrate exceeded the U.S. Environmental Protection Agency (USEPA) drinkingwater standard of 10 milligrams per liter in 

samples collected from about 20 percent of 

shallow wells in agricultural areas (versus 

about 3 percent in urban areas).

VOCs were detected frequently in 

shallow ground water beneath urban areas 

(in about 90 percent of monitoring wells 

sampled) and less frequently in shallow 

ground water beneath agricultural areas (in 

20 percent of monitoring wells). Some of the 

most common VOCs in urban areas, such 

as in the Delaware River Basin, were the 

solvents trichloroethene (TCE), tetrachloroethene (PCE), 1,1,1-trichloroethane (TCA), 

and trichloromethane (also known as chloroform), which is also a disinfection by-product 

of water treatment; and the gasoline-related 

compounds benzene, toluene, xylene, and 

methyl tert-butyl ether (MTBE).

New pesticides, VOCs, and other synthetic chemicals are introduced into the environment every year as products are approved 

for agricultural or urban use. USGS has 

expanded its laboratory methods to analyze 

for these “emerging” contaminants, testing 

new methods in areas where their use is the 

greatest (see southern Louisiana example).

Water Quality and Its Connection to Land Use — 

Agricultural and Urban Sources of Nonpoint Pollution

Implications

Reducing chemical use 

and improving disposal 

practices can help reduce 

contaminant concentrations in both urban and 

agricultural settings. More 

information about chemical use—data that are 

virtually unavailable in 

urban areas—is critical 

to linking contaminants to 

their sources, thus helping 

individuals, businesses, 

and industry as well as 

local, State, and Federal 

governments to improve 

water quality.

4
Insecticides are frequently detected in the urban 

stream Thornton Creek near Seattle, Washington

Insecticides in Thornton Creek, which drains urban areas in King 

County outside of Seattle, were typical of those detected in urban 

streams across the Nation. Diazinon, carbaryl, chlorpyrifos, and malathion were frequently detected; diazinon concentrations exceeded the 

guideline established to protect aquatic life in 20 percent of the samples 

from Thornton Creek. These pesticide detections are strongly related 

to pesticide use. For example, diazinon is the number one insecticide 

sold to King County residents. (King County provided data on pesticide 

sales in 10 large home and garden stores.) Moreover, in a USGS study 

done with Washington State Department of Ecology and King County, 

23 of 98 pesticides were detected in King County urban streams—

homeowner use was identified as the probable source of diazinon and 

the herbicide 2,4-D. Almost half of the pesticides detected, however, 

had no known or identified retail sales, indicating other possible 

sources such as applications in commercial areas, along road rights-ofway, and in parks and recreational areas (USGS Circular 1216).

Fipronil is widely detected in southern Louisiana

streams

Fipronil was licensed for use in 1996 as a replacement for carbofuran to 

control organisms such as fleas, termites, water weevils, and fire ants. 

Its use became widespread in Louisiana in 1999, particularly on rice 

fields in the Mermentau River Basin. Fipronil was detected in about 

72 percent of water samples from agricultural streams in the Mermentau River Basin. Concentrations of fipronil reached a maximum of 

6.41 micrograms per liter and exceeded Total Maximum Daily Load 

(TMDL) numeric freshwater targets at 17 sites (U.S. Environmental 

Protection Agency, 2002). Fipronil and some of its breakdown products, particularly fipronil sulfone and fipronil sulfide, are of concern 

because of their possible effects on crawfish and other aquatic life 

(USGS Circular 1232). 

Photo by Phillip J. Redman, USGS

Photo by Sandra Embrey, USGS

“The Acadian-Pontchartrain Drainages NAWQA 

program has contributed valuable information to 

the U.S. EPA’s Office of Pesticide Programs’ (OPP) 

understanding of the occurrence of pesticides in 

ground and surface water in one of the Nation’s 

major rice and sugarcane production areas. As 

a reliable source of comprehensive information, 

results from the USGS study unit have been used 

in pesticide exposure and risk assessments. The 

OPP has found the data useful in understanding the 

relationship between land use (e.g., agriculture) and 

the frequency and levels of pesticide detections in 

water.” 

Sid Abel, Environmental Fate and Effects Division, 

Office of Pesticide Programs, 

U.S. Environmental Protection Agency

5
6

The effects of natural features, such as geology, climate, hydrology, and soils, on the 

transport of chemicals from land to water 

often result in different contaminant concentrations among basins that have similar landuse settings and chemical use. For example, 

ground water is vulnerable to nitrate contamination in well-drained areas with permeable 

soils that are underlain by sand and gravel, 

such as in the Platte River Valley in Colorado 

and Nebraska, or in karst (fractured carbonate 

rocks) in parts of Florida and the Susquehanna and Potomac River Basins in Pennsylvania, Maryland, and Virginia.

In contrast, streams are most vulnerable to contamination in basins with poorly 

drained clay soils, steep slopes, or where 

sparse vegetation does not slow runoff. 

Streams also are vulnerable in agricultural 

areas where tile drains and ditches quickly 

transport runoff from fields to streams, such 

as in the Eastern Iowa Basins and the White 

River Basin in Indiana. Stream hydrology and 

basin characteristics also affect contaminant 

movement. Small streams respond quickly to 

rainfall or irrigation and, therefore, contaminants usually peak at higher concentrations, 

and these peaks rise and fall more quickly 

than in larger rivers. In large rivers, peak 

concentrations of contaminants generally are 

lower than in small streams because of dilution; however, concentrations remain moderate in large rivers for longer periods (see 

Mississippi River example).

A comparison of findings in the 

NAWQA study units shows that water-quality 

conditions are similar over large regions that 

have similar natural features and land-management practices. For example, throughout 

much of the Upper Midwest, ground water 

underlying intensive agriculture generally has 

low concentrations of agricultural chemicals 

where the water is protected by low-permeability soils and glacial till. As demonstrated 

in the White River Basin, local hotspots of 

contamination occur where ancient glacial 

streams deposited sand and gravel, which 

enable rapid infiltration and downward 

movement of water and chemicals. In parts 

of the Southeast, streams and ground water 

contain low concentrations of nitrate, in part 

because the high organic content of the soils 

and aquifers favors the conversion of nitrate 

into nitrogen gas (denitrification). In contrast, 

concentrations of nitrate are relatively high 

in streams and shallow ground water in the 

Central Valley of California and parts of the 

Northwest, Great Plains, and Mid-Atlantic 

regions where permeable, well-drained soils 

having a lower organic content favor rapid 

transport of water and chemicals and limited 

denitrification.

Geology, soils, and climate can affect 

concentrations of constituents that occur 

naturally in water, such as dissolved solids, 

nutrients, radon, and trace elements (see 

Yellowstone River Basin example). For 

example, phosphatic limestone deposits are 

a major source of phosphorus in the Duck 

and Elk Rivers draining the Lower Tennessee 

River Basin; concentrations of phosphorus in 

these rivers were in the upper 10 percent of 

the concentrations in 473 streams and rivers 

sampled nationwide even though phosphorus from point and nonpoint sources in these 

basins is relatively low. Radon, a radioactive 

gas that forms in rocks and soils through the 

decay of uranium, is often present in ground 

water, in large part depending on rock characteristics. For example, the median concentration of radon in wells tapping the EdwardsTrinity aquifers beneath parts of central Texas 

was relatively low at 170 picocuries per liter 

(pCi/L), whereas the median concentration 

in wells tapping the crystalline-rock aquifers 

underlying New York and New England was 

2,200 pCi/L (which exceeds the USEPA proposed drinking-water standard of 300 pCi/L). 

Arsenic, a mineral present in certain rocks 

and soils, also is naturally elevated in ground 

water in parts of the Nation, and generally 

highest in the West and parts of the Midwest 

and Northeast (Welch and others, 2000).

Effects of Natural Features and Land-Management Practices

Implications

A better understanding of 

natural features controlling the occurrence and 

movement of contaminants 

allows water-resource 

managers to identify 

streams and aquifers most 

vulnerable to contamination. Because vulnerability 

to contamination can 

differ from place to place, 

a national strategy for 

managing nonpoint source 

pollution should consider 

local and regional differences in natural features. 
7

Contamination extends deep in the ground-water system underlying the Island of Oahu, Hawaii

elevated nutrients were prevalent in ground 

water beneath central Oahu agricultural 

lands. Concentrations of only a few contaminants, however, exceeded Federal and State 

drinking-water standards. To the southeast 

in urban Honolulu, few contaminants were 

detected in drinking-water wells due to a century of urban planning and watershed protection that has directed intensive chemical use 

and storage away from upland recharge areas 

of Honolulu (USGS Circular 1239).

Mississippi River hydrology affects atrazine concentrations in Louisiana’s streams and rivers

In the Yellowstone River at Corwin Springs, 

Montana (see photo), near the relatively 

pristine headwaters, the average concentration of ammonia (also adjusted for flow) was 

0.04 milligrams per liter as nitrogen, which 

was about twice that in streams sampled by 

NAWQA in other undeveloped areas across 

the Nation. Elevated ammonia at Corwin 

Springs most likely results from organic-rich 

sedimentary rocks in contact with hightemperature geothermal waters that flow into 

the river. Arsenic, also present in geothermal waters, was 

elevated in the Yellowstone 

River at Corwin Springs; concentrations in 78 percent of 

samples exceeded the USEPA 

drinking-water standard of 10 

micrograms per liter (USGS 

Circular 1234). 

The deep volcanic-rock aquifer in central 

Oahu and Honolulu supplies more than 90 

percent of the island’s public-water supply 

and is a designated Sole Source DrinkingWater Aquifer. The aquifer is highly permeable and unconfined except near the coast, 

and is vulnerable to contamination despite 

the deep water table (100-1,000 feet deep). 

Solvents were detected in the drinking-water 

aquifer throughout central Oahu, with highest 

concentrations beneath urban areas and military installations. Fumigants, herbicides, and 

Atrazine concentrations in streams and rivers 

in the Acadian-Pontchartrain Drainages in 

Louisiana are affected by hydrology. In the 

Mississippi River at Baton Rouge, which 

receives runoff (referred to as the “spring 

flush”) from agricultural areas throughout 

the Midwest, atrazine concentrations peaked 

during May and June 1999 and 2000. Atrazine 

concentrations peaked earlier (in April 1999 

and 2000) and were much higher in Bayou 

Grosse Tete at Rosedale, a relatively small 

and hydrologically isolated system dominated 

by local inputs from urban and agricultural 

lands in the Terrebonne Basin. Peak atrazine 

concentrations in Bayou Boeuf at Amelia are 

of longer duration than in the other two systems because the bayou receives water from 

Mississippi River by way of the Atchafalaya 

River and water draining nearby sugarcane 

fields, and because of tide-induced backwater 

effects (USGS Circular 1232).

Naturally occurring contaminants are elevated in Yellowstone River Basin streams

Geology and climate affect concentrations of 

dissolved solids, nutrients, and trace elements 

in streams in the Yellowstone River Basin. 

Naturally occurring phosphorus in igneous 

and marine sedimentary rocks results in high 

concentrations of phosphorus in water at 

some sites in the Yellowstone River; average 

concentrations of total phosphorus (adjusted 

for flow) ranged up to 2.1 milligrams per 

liter, which is more than 20 times the USEPA 

goal for minimizing nuisance plant growth. 

Copyrighted photo by Douglas Peebles. Used with permission

Photo by Gregory K. Boughton, USGS

������������

�������������

�����������������������������

���������������������

��������������������������������

���������������������

����������������

��������

���� ���� ����

�

�

��

��

��

��

� � � � � � � � � � � � � � � � � � � � � � � �

���������������

�����������������������

Atrazine concentrations were as much as 10 times higher 

and increased more rapidly in the relatively small Bayou 

Grosse Tete than in the larger Mississippi River and in 

Bayou Boeuf that receive water from multiple sources.
8

NAWQA studies show that although the concentrations of many contaminants in streams 

and ground water often do not exceed USEPA 

drinking-water standards, the risk to human 

and aquatic health is unclear for several reasons. In almost all 51 study units, contaminant 

exposure varies with the seasons, with long 

periods of low or non-detectable concentrations punctuated by brief periods of much 

higher concentrations. Seasonal patterns in 

concentrations of pesticides and nutrients are 

related primarily to the timing and amount of 

chemical use, the frequency and magnitude of 

runoff from rainstorms or snowmelt, and landmanagement practices such as soil tillage, 

irrigation, and the use of tile drains. Concentrations in agricultural streams are generally 

highest during runoff following chemical 

applications (see Lake Erie-Lake St. Clair 

Drainages example). Water temperature can 

have a significant effect on seasonal VOC 

concentrations, as shown in Deer Creek in the 

Pittsburgh area, where VOCs were detected 

in samples collected in February, November, 

and December, but not in samples collected in 

July, August, and September. VOCs are more 

likely to be stable and detectable in cold water 

because warm temperatures can cause VOCs 

to volatilize.

Individual compounds seldom occur 

alone—streams and ground water in basins 

with significant agriculture or urban development almost always contain mixtures of 

VOCs, nutrients, pesticides, and their chemical breakdown products (Squillace and others, 

2002). In Oahu, for example, combinations 

of VOCs and pesticides were detected in 

53 percent of sampled public-supply wells, 

and some individual samples contained as 

many as 10 herbicide compounds. Nationally, 

about 15 percent of samples collected from 

urban streams contained at least 10 VOCs. 

Similarly, about 23 percent of urban stream 

samples contained 10 or more pesticides. Possible cumulative effects on human and aquatic 

health from low concentrations of multiple 

compounds are unknown.

Breakdown products frequently are as 

common in the environment as parent compounds (see Eastern Iowa Basin example). 

Ground-water samples collected on the 

Delmarva Peninsula, for example, contained 

breakdown products of the pesticides alachlor 

and metolachlor at median concentrations 

generally higher than 0.1 micrograms per liter, 

whereas median concentrations of their parent 

compounds were about 10 times lower. Atrazine, the most heavily used herbicide in the 

Nation, and its breakdown product deethylatrazine (DEA), were found together in about 

75 percent of stream samples and about 40 

percent of ground-water samples collected in 

agricultural areas across the Nation. DDT was 

detected in whole fish collected from about 30 

percent of agricultural stream sites, whereas 

its stable breakdown products DDE and DDD 

were detected in fish at up to 90 percent 

(for DDE) of agricultural sites. Standards or 

guidelines to protect human health or aquatic 

life have not been established for breakdown 

products, yet they can be as toxic, or even 

more toxic, than parent compounds.

Complex Contaminant Patterns — 

Mixtures, Breakdown Products, and Seasonality

Implications

Effective water-resource 

management and watershed protection may 

require monitoring 

programs that analyze 

samples for breakdown 

products and multiple 

compounds, and that 

evaluate patterns related 

to seasons and storms 

when peak contaminant 

concentrations could possibly affect drinking-water 

supplies and critical life 

stages of aquatic organisms. 

“The California State Water Resources 

Control Board has worked closely with 

the U.S. Geological Survey to develop a 

comprehensive monitoring and assessment program for California’s groundwater 

basins. The approach, methods, and 

results from NAWQA studies have been 

fully integrated into California’s plans 

to evaluate ground-water quality on a 

statewide basis.”

Arthur G. Baggett, Jr., 

Chair, State Water Resources 

Control Board
9

Most pesticide compounds in Eastern Iowa Basin streams are 

breakdown products

Seasonal patterns of contamination are related to chemical use, land use, 

and precipitation in the Lake Erie-Lake St. Clair Drainages

breakdown products and parent compounds 

in ground water used for city water supplies 

(USGS Circular 1210). 

Concentrations of the pesticides prometon 

and diazinon typically increased in streams 

draining urban areas in the Lake Erie-Lake 

St. Clair Drainages (Ohio, Michigan, Indiana, 

Pennsylvania, and New York) following summertime applications. Herbicides such as atrazine, metolachlor, cyanazine, and acetochlor 

were elevated in streams draining row-crop 

agriculture in the Lake Erie-Lake St. Clair 

Drainages for 4 to 6 weeks after rainfall and 

runoff in the spring and early summer (USGS 

Circular 1203). Elevated concentrations of 

herbicides and nutrients during spring runoff 

following agricultural applications were typical of streams that drain much of the farmland 

in the Midwest. Different seasonal patterns, 

however, were noted in other agricultural 

areas. For example, concentrations of diazinon in streams in the San Joaquin-Tulare 

Basins were highest during winter because 

of high rainfall and use of sprays on dormant 

orchards (USGS Circular 1159).

Breakdown products were some of the most 

frequently detected pesticide compounds in 

streams in the Eastern Iowa Basin in Iowa. On 

average, nearly 85 percent of the total amount 

of pesticides in stream samples was composed 

of 10 breakdown products of the agricultural 

herbicides acetochlor, alachlor, atrazine, 

cyanazine, and metolachlor. Concentrations of 

breakdown products acetochlor ESA, alachlor 

ESA, and metolachlor ESA commonly were 

more than 10 times higher than the concentrations of their parent compounds. Thus, breakdown products make up the largest amount of 

pesticides that are transported from the basin 

to the Mississippi River, accounting for more 

than 80 percent of the yearly pesticide load 

in the Iowa River at Wapello. Pumping from 

public-supply wells near Cedar Rapids, Iowa, 

induces infiltration from the Cedar River, 

which has allowed pesticides and their breakdown products to enter ground water. City 

officials are pursuing additional research on 

Elevated concentrations of herbicides during spring runoff 

following agricultural applications were typical of streams 

that drain much of the farmland in the Midwest.

Breakdown products were some of the most frequently detected 

pesticide compounds in streams in the Eastern Iowa Basin.

���� ���� ����

����

����

�����

������

��

���

�����

������

�������

����������������������

������������������������

�������������������������

����������������

����������������������

������������������������

��������������

�����������������������

� ���� � � � ���� � ���� � � � ���� � ���� � � � ����

���� ���� ����

�

��

��

��

��

��

�

���

���

���

���

������������������������

������������������������������

��������������

�������������������������������������

�������������

����������������������������������������

��������

��������

���������������

� � � � � � � � � � � � � � � � � � � � � � � �
10

Interactions among surface water, ground 

water, land, and the atmosphere govern the 

occurrence and movement of water and 

contaminants, and thus affect the health of 

aquatic ecosystems. NAWQA studies therefore include assessments of multiple components of the hydrologic system, including 

streams, rivers, and ground water within the 

study units; the atmosphere; and biological 

communities (primarily fish, aquatic invertebrates, and algae) and stream habitat.

Interactions between surface 

water and ground water

Ground-water discharge can influence the 

quality of streams and ultimately the receiving water. For example, ground water supplies about half of the water and nitrogen to 

streams in the Chesapeake Bay watershed and 

is therefore an important source of nitrogen 

to the Chesapeake Bay (Phillips and Lindsey, 

2003). Streams, in turn, can influence the 

quality of ground water. Contaminants generally are more prevalent and detected at higher 

concentrations in streams than in ground 

water. This is largely determined by chemical 

properties of contaminants and flow conditions—ground water typically is not vulnerable to contamination by compounds that 

attach to soils or that are unstable in water, 

and relatively long residence times along 

ground-water flow paths allow many chemicals to degrade, disperse, or be diluted before 

reaching a well.

Interactions between surface water and 

ground water are affected by natural features 

such as soils, geology, and hydrology, and by 

human activities such as ground-water pumping. Exchanges of water and contaminants can 

be rapid in areas underlain by carbonate rocks 

(see Edwards aquifer near San Antonio, 

Texas example) or by permeable and welldrained soils and sediment, such as sand and 

gravel (see North Carolina example). Pumping ground water can accelerate exchanges 

between streams and ground water (see Great 

Miami River Basin example). In some areas, 

concentrations of contaminants can decrease 

during these exchanges, such as when chemicals are sorbed onto soil particles or are transformed by chemical or biological processes 

(see southern New Jersey example).

Exchanges are substantial in the 

Edwards aquifer near San Antonio, 

Texas

Ground-water and surface-water exchanges 

are substantial in carbonate aquifers near San 

Antonio, Texas. Major streams lose water to 

the Edwards aquifer as they flow across the 

highly permeable, faulted and fractured carbonate rocks of the aquifer outcrop. Although 

streams that recharge the aquifer originate in 

and flow through mostly undeveloped rangeland, some of them also flow through urbanized northern San Antonio. Urban contamiInteractions Among Water, Air, and Aquatic Ecosystems

Implications

Ground-water contributions to streams and rivers 

can be substantial. For 

this reason, ground-water 

flow and quality should be 

considered in making decisions for stream protection, such as in establishing Total Maximum Daily 

Loads (TMDLs). Surfacewater recharge to ground 

water also is important, 

particularly where publicsupply wells are located 

near streams, and should 

be considered in sourcewater management and 

well-head protection 

programs.

Ground-water and 

surface-water exchanges 

are substantial in 

carbonate aquifers near 

San Antonio, Texas.
11

nants, such as chloroform and commonly used 

herbicides (including atrazine, and its breakdown product DEA, simazine, and prometon) 

are transported to wells in the recharge zone 

of the Edwards aquifer, the principal source 

of water supply for the greater San Antonio 

region (USGS Circular 1212).

Phosphorus in ground-water 

discharge affects streams in 

North Carolina

Ground-water and surface-water interactions 

in sand and gravel aquifers of the AlbemarlePamlico Drainage Basin in North Carolina 

help to explain elevated concentrations of 

phosphorus in selected streams. Deep ground 

water underlying parts of the Atlantic Coastal 

Plain contains naturally high concentrations of 

phosphorus (a median concentration of 0.25 

milligrams per liter), which likely originates 

from phosphate minerals in the aquifer sands. 

Upward discharge of the ground water results 

in elevated phosphorus in streams, particularly 

in the Tar River and Neuse River Basins, as 

shown by similarities in phosphorus concentrations in discharging ground water and in 

streams. Documenting this natural source 

of phosphorus has increased the accuracy of 

TMDLs for some North Carolina streams 

(USGS Circular 1157).

Pumping induces contamination in 

the Great Miami River Basin

Pesticides such as bentazon, atrazine, metolachlor, and prometon were detected frequently 

in public-supply wells near streams in the 

“The combined surface- and 

ground-water quality and 

ecological assessments 

of the Flint River Basin by 

the Lower Tennessee River 

Basin NAWQA Program have 

heightened our awareness 

of how vulnerable our water 

resources are due to karst 

features of the watershed. 

These technical, interdisciplinary assessments of 

watershed conditions have 

helped focus our watershed 

restoration efforts within the 

Flint River Basin.”

Susan Weber,

Flint River Conservation 

Association

Great Miami River Basin in Ohio and Indiana. 

At least one pesticide was detected in about 

60 percent of samples from public-supply 

wells (about 80 feet deep) versus about 15 

percent of samples from shallow domestic 

wells (about 60 feet deep). The most likely 

source of the pesticides was pumping-induced 

infiltration of stream water, which can reach 

the high-capacity public-supply wells near 

streams within weeks or even days. These 

wells may be vulnerable to contaminants 

discharged to the river upstream of the well 

fields (USGS Circular 1229).

Nitrate is reduced naturally in 

southern New Jersey

NAWQA scientists studied denitrification 

(conversion of nitrate to nitrogen gas) in 

southern New Jersey using a three-dimensional model of ground-water flow that 

simulated the movement of nitrate through 

the shallow aquifer system to streams and 

public-supply wells. Modeled concentrations of nitrate generally matched measured 

concentrations in public-supply wells, indicating that nitrate remains relatively stable as it 

moves through the aquifer. Measured nitrate 

concentrations in three streams during baseflow (when most streamflow is derived from 

ground water) were about 60 percent of the 

modeled concentrations over a 9-year period. 

The apparent loss of nitrate in streams indicates that about 40 percent of the nitrate was 

removed by processes, such as denitrification 

and biological uptake, as ground water moves 

upward through the organic-rich sediment 

(USGS Circular 1201).

Ground-water and surface-water interactions 

in sand and gravel aquifers of the AlbemarlePamlico Drainage Basin in North Carolina help to 

explain elevated concentrations of phosphorus 

in selected streams.

Photo by J.R. Gilhousen, USGS

Photos by Douglas Harned, USGS
12

Atmospheric contributions

The atmosphere can be a major source of contaminants. For example, as much 

as 25 percent of the nitrogen entering the Chesapeake Bay comes from the 

atmosphere (Fisher and Oppenheimer, 1991). Nearly every pesticide that has 

been investigated has been detected in air, rain, snow, or fog throughout the 

Nation at different times of the year (Majewski, 1995). Atmospheric deposition also is a major source of mercury to most ecosystems; mercury enters 

the atmosphere from natural and human-related sources, mostly coal combustion, waste incineration, industrial uses, and mining (Krabbenhoft and others, 

1999). NAWQA findings indicate that concentrations of methylmercury (the 

most toxic form of mercury) are strongly related to the amount of wetlands in a 

watershed, and are increased by the presence of sulfur, carbon, organic matter, 

and dissolved oxygen (see New England example).

The interconnection of water and the atmosphere can lead to unintended 

consequences. For example, methyl tert-butyl ether (MTBE)—a chemical that 

allows gasoline to burn cleaner—was not regarded as a water contaminant 

when its use as an oxygenate in gasoline was increased in the 1990s to help 

improve air quality in many cities. MTBE’s high solubility in water, persistence, and widespread usage has led to its occurrence at low concentrations in 

ground water and community water supplies, especially in those areas where it 

is used in reformulated gasoline (Grady, 2003; Moran and others, 2003). The 

USEPA has issued a drinking-water advisory on MTBE (U.S. Environmental 

Protection Agency, 1997), and 17 States, including California and New York, 

have passed legislation to ban or limit its use in gasoline (Tancred Lidderdale, 

Energy Information Administration, written communication, 2004). Such 

legislation is pending in other states, such as 

Maine and New Hampshire, where MTBE is 

commonly detected in ground water.

Mercury contamination in New 

England is typical of national patterns

NAWQA findings on mercury in the New 

England Coastal Basins were typical of patterns documented at many geographic scales. 

Specifically, concentrations of total mercury 

in sediment were highest in urban watersheds 

in the Boston metropolitan area, where there 

are many urban sources, including historical 

point-source discharges, nonpoint sources, 

and atmospheric deposition. Concentrations were lowest in sediment in adjacent, 

more forested watersheds in Maine and New 

Hampshire. In contrast, concentrations of 

total mercury in fish (more than 95 percent of 

which is methylmercury, the most toxic form) 

were higher in the forested watersheds near 

the Boston metropolitan area than in fish in 

the more urban watersheds. Elevated conImplications

Water quality cannot be 

fully protected without 

consideration of atmospheric deposition of contaminants. Water quality 

can be impaired by emissions from both local and 

distant sources; therefore, 

water-management strategies require coordination 

at the State, regional, and 

national levels.

� ���� ���� ���� ���� ���� ����

�������������������������������

������������������������������������

����������������������

���������������������������

��������������

����������������������

�������������������

��������������������������������������

������������������

������������������������������������

����������������������

����������������

��������������������

�����������������������������������

��������������������������

�����������������������

�������������������������������

���������������

����������������������������������������

��������������������������

��������������������������

����������������

������������������

�����������������

Interactions Among Water, Air, and Aquatic Ecosystems

Samples from the Santee River Basin in 

South Carolina had the highest ratios of methylmercury to total mercury in the Nation.
���������

���������

������������

� �� ��������

� �� �������������

�����������

��������

���������

���������������

���������������

����������������

���������������������

����������������������������

������������������������������������

������������������������

�����������������������

��������������������

��������������������������

����������������

�����������������������

��������������������

��������������������������

������������������������������≥�����

�����������������������

��������������������������������

������������� �

�������

���

���������

�����

����

��������

�������������

�����

������

������

������� �

� ����

�����

���

���������

����

��

������

�����

���

���������

����

��

������

centrations in fish in the forested watersheds 

result largely from natural factors, such as the 

presence of wetlands that enhance the process 

of converting total mercury to methylmercury. 

Nationwide, study units that had the highest 

ratios of methylmercury to total mercury were 

along the East Coast (Krabbenhoft and others, 

1999), with the highest ratios in samples from 

the Santee River Basin in South Carolina. The 

Santee River Basin sites represent primarily blackwater streams, which typically have 

large amounts of dissolved organic carbon 

and low concentrations of dissolved oxygen. 

Nationwide, concentrations of methylmercury 

in fish tissue exceeded the USEPA human 

health criterion of 0.3 milligrams per kilogram (U.S. Environmental Protection Agency, 

2001) in about 40 percent of sampled game 

fish, two-thirds of which were bass. Concentrations of methylmercury were highest in fish 

collected from southeastern streams, such as 

those in South Carolina, Georgia, and Florida, 

and in streams locally contaminated by mining (Brumbaugh and others, 2001).

13
14

Condition of biological 

communities and stream habitat

Potentially toxic compounds, such as DDT, 

chlordane, dieldrin, polychlorinated biphenyls (PCBs), and mercury, were commonly 

detected in fish in sampled urban streams, 

often at higher concentrations than in the sediment. Nationally, one or more organochlorine compounds (including organochlorine 

pesticides and PCBs) were detected in about 

95 percent of whole-fish samples collected at 

urban sites. Concentrations of organochlorine 

compounds in fish tissue exceeded guidelines 

to protect wildlife at nearly 75 percent of 

urban sites.

Activities associated with agriculture, 

urban areas, and (or) forests can affect streamhabitat conditions and fish, aquatic invertebrate, and algal communities. Degraded 

water and sediment, and physical alterations 

to streams that result in changes to streamflow, temperature, and channel morphology, 

commonly result in degraded stream habitat, 

reduced biological diversity, and an increase 

in the number of species tolerant of disturbance, such as worms, midges, and omnivorous fish communities. The most profound 

effects can be seen in urbanizing areas (see 

Birmingham, Alabama example).

NAWQA stream-ecology studies in the 

metropolitan areas of Anchorage, Birmingham, Boston, Chicago, Dayton-Cincinnati, 

Los Angeles, Philadelphia-Trenton, and Salt 

Lake City show that changes in aquatic communities are noticeable at low levels of urbanization within a basin (Couch and Hamilton, 

2002). For example, in Anchorage, changes in 

aquatic communities are evident when watersheds reach about 5 percent impervious area, 

which in Anchorage correlates with a population density as low as 125 to 250 people per 

square mile. Findings also indicate that physical characteristics are altered with increasing urbanization, which can greatly affect 

aquatic communities. Specifically, increased 

residential and commercial development 

and road density often are associated with 

less tree canopy for shading, increased water 

temperatures, and more impervious surfaces, 

storm drains, and other artificial controls, all 

of which can increase the amount and rate of 

runoff during storms. As a result, increases 

Implications

Information on the effects 

of urbanization on aquatic 

life can help planners 

and decision makers 

to design and prioritize 

cost-effective strategies 

for stream protection 

and restoration (such as 

managing chemical use, 

controlling storm runoff, or 

restoring riparian habitat). 

Information on links 

between water quality 

and aquatic communities 

can improve biological 

monitoring and methods 

for assessing results 

of water-management 

strategies.

in the magnitude and volume of peak streamflows can destroy fish-spawning beds, remove 

woody debris, transport large amounts of sediment, and remove natural substrates. These 

physical alterations are not typically tolerated 

by sensitive aquatic communities. Water temperatures often are increased in urban streams 

as a result of runoff flowing over impervious 

areas, such as parking lots and buildings. 

Many aquatic organisms can survive only 

within a narrow temperature range.

Aquatic communities do not respond 

uniformly to changes in water quality and 

habitat conditions; rather, responses can 

differ among species and among streams. 

For example, aquatic invertebrate and fish 

communities in streams draining the Mobile 

River Basin were degraded with increasing 

urbanization in a constant or linear fashion; 

degradation continued in watersheds with 

about 75 percent urban land and about 4,000 

people per square mile and did not level off or 

reach a “threshold” point. In contrast, changes 

in aquatic invertebrate and fish communities 

in streams draining the New England Coastal 

Basins continued in watersheds associated 

with about 20 percent urban land and less 

than 3,000 people per square mile, at which 

point the changes began to level off. Thresholds can be useful for understanding where 

water-quality management actions are likely 

to have the most benefit. Thresholds are not 

applicable to all streams, however, and an 

understanding of individual stream ecosystems is necessary before making decisions on 

the most appropriate and beneficial actions for 

individual systems.

Studies on the relation of biological communities to physical and chemical characteristics of streams that vary in 

degree of urbanization were conducted in the metropolitan 

areas of Anchorage (USGS Circular 1240), Birmingham 

(USGS Circular 1231), Boston (USGS Circular 1226), Chicago 

(USGS Circular 1230), Dayton-Cincinnati (USGS Circular 

1229), Los Angeles (USGS Circular 1238), PhiladelphiaTrenton (USGS Circular 1227), and Salt Lake City (USGS 

Circular 1236).

Interactions Among Water, Air, and Aquatic Ecosystems
Aquatic communities are affected by urban development near 

Birmingham, Alabama

-5

0

5

10

15

20

25

NUMBER OF EPT TAXA

20

30

40

50

60

70

NUMBER OF INVERTEBRATE SPECIES

���������������������������������������������������������������������������������

���������������������

0

5

10

15

20

25

30

TOTAL NUMBER OF  FISH SPECIES

0

20

40

60

80

FISH COMMUNITY COMPOSED OFTOLERANT SPECIES, IN PERCENT

�������������������������������������������������������������������������������

�����������

���������

�������

�������

�������

�� ��������

� �� ������������

�

���������

����

��������

�������

����������

������ ��������

����������������

���������

���

���

��� ���

��� ���

���

���

���

���

��� ���

������������������������

�����������������

����������

�����������

������������������

“Urban intensity” ranges along a gradient 

from 0 to 100 and is based on 24 measures, 

including amounts of urban land (residential, 

commercial, industrial, and transportation) 

within a watershed, and socioeconomic factors related to housing, income, and population characteristics. An urban intensity index 

of 60 in the Mobile River Basin, for example, 

is associated with watersheds with about 40 

percent urban land and a population density 

of about 1,870 people per square mile.

NAWQA assessed physical, chemical, and 

biological characteristics in 30 similar-sized 

streams that vary in degree of urbanization 

in the Ridge and Valley ecoregions within 

the Mobile River Basin. The study showed 

that aquatic invertebrate and fish communities change as watersheds become increasingly urbanized. For example, the number of 

invertebrate species intolerant to pollution, 

such as mayflies, caddis flies, and stoneflies 

(referred to as “EPT taxa”) decreased with 

increasing urban intensity. Specifically, the 

number of EPT taxa ranged from 21 species 

per stream site in a relatively undeveloped 

watershed (draining less than 1 percent 

urban land) to 2 species per site in the highly 

urbanized watersheds, such as Valley Creek 

at Birmingham (draining about 73 percent 

urban land). Overall, the number of aquatic 

invertebrate species decreased by about half, 

from about 60 species in the least urbanized 

watersheds to about 30 species in the most 

urbanized watersheds. Similarly, the number 

of different fish species decreased from about 

20 to 5 species. The decreases were mostly in 

pollution-intolerant fish species, such as black 

bass. More tolerant species, including green 

sunfish, blue gill, yellow bullhead, and creek 

cub, dominated the most urbanized streams 

(up to about 70 percent of the fish community). Declines in the types and abundance 

of aquatic invertebrate and fish communities 

were observed in watersheds with less than 5 

percent urban land and a population density 

less than 200 people per square mile (USGS 

Circular 1231). 

15
16

Water quality varies from season to season and from year to year and, therefore, long-term trends are sometimes difficult to distinguish from short-term 

fluctuations. It is too early to tell whether some types of chemical contamination are increasing or decreasing because historical data are either insufficient 

or too inconsistent to measure trends. Some trends and patterns, however, are 

evident from data collected over the last decade of NAWQA studies in 51 

major river basins and aquifer systems.

NAWQA studies document the long-term presence of some contaminants, which in large part depends on their chemical properties. Not many, for 

example, would have anticipated the long-term persistence in some ground 

water of the fumigants 1,2-dibromomethane (EDB) and 1,2-dibromo-3-chloropropane (DBCP), nor the persistence in streams of certain organochlorine 

compounds, such as PCBs and the insecticides DDT, dieldrin, and chlordane. 

Nationally, for example, one or more organochlorine compounds were detected 

in sediment at about 60 and 80 percent of agricultural and urban stream sites, 

and concentrations exceeded sediment-quality guidelines at nearly 20 and 50 

percent of those sites, respectively.

Studies also show that changes in water quality over time frequently are 

controlled by changes in chemical use and land-management practices. For 

example, concentrations of modern, short-lived pesticides such as acetochlor 

change as chemical use changes. Concentrations of acetochlor increased and 

those of alachlor decreased in many streams in the Upper Illinois River Basin 

and other parts of the Upper Midwest, where acetochlor partly replaced alachlor for weed control in corn and soybeans beginning in 1994. The changes 

in chemical use were reflected in stream quality, generally within 1 to 2 years. 

Contaminant concentrations also change with land-management practices. 

For example, conversion from rill (or “furrow”) irrigation to sprinkler or drip 

irrigation in many parts of the Yakima River Basin since the early 1990s has 

reduced runoff from farm fields, resulting in decreases in suspended sediment, 

total phosphorus, dissolved nitrate, and organochlorine compounds in streams 

(see Yakima River Basin example).

Ground-water quality also responds to changes in chemical use and landmanagement practices, but usually more slowly than surface water. Groundwater age-dating techniques developed by USGS within the last decade 

indicate that improvements in ground-water quality can lag behind land-management changes by decades because of the slow rate of ground-water flow 

(see Delmarva Peninsula example). Long-term monitoring is needed to track 

the progress of improvements in ground-water quality.

Analyses of sediment cores (vertical 

tubes of mud) from reservoir and lake bottoms 

provide a quick snapshot of long-term waterquality changes (Van Metre and others, 2000). 

Runoff carries soil, debris, and attached contaminants to lakes and reservoirs, where they 

settle to the bottom; changes in water quality 

are thereby recorded in the successive layers 

of sediment. Studies show common patterns 

in sediment quality, such as decreases in lead 

and increases in polycyclic aromatic hydrocarbons (PAHs), over several decades in 42 

reservoirs and lakes sampled in 20 metropolitan areas from 1996 to 2001 (see Town Lake 

in Austin, Texas example).

Nitrate concentrations are 

increasing in ground water on the 

Delmarva Peninsula

Concentrations of nitrate in ground water used 

for domestic supply (median well depth 45 

feet) on the Delmarva Peninsula (Delaware, 

Maryland, and Virginia) increased by an 

average 2 milligrams per liter between 1988 

and 2001. The median concentration in 2001 

exceeded the USEPA drinking-water standard 

of 10 milligrams per liter. Increases in nitrate 

concentration most likely reflect an increased 

use of nitrogen fertilizers over the last 50 

years. In contrast, the median concentration 

of nitrate in shallow ground water underlying 

agricultural areas (median well depth 25 feet) 

did not change significantly over the same 

period, remaining below the drinking-water 

standard. Lower nitrate concentrations in the 

shallow ground water may reflect positive 

Changes in Water Quality Over Time

Implications

NAWQA findings confirm 

that long-term, systematic, 

and consistent monitoring 

is essential for distinguishing trends from short-term 

fluctuations, anticipating 

unintended consequences, 

and choosing cost-effective 

management strategies.

Photo by David F. Usher, USGS
17

effects of nutrient management practices on 

shallow ground-water quality, implemented in 

many agricultural areas on the Delmarva Peninsula over the last 10 years. These improvements may not be apparent in the deeper parts 

of the aquifer because of the slow movement 

of ground water. Continued monitoring will 

show if trends continue and improvement 

occurs (USGS Circular 1228).

DDT is declining in the Yakima River 

Basin, central Washington

Previous NAWQA assessments (1988-1991) 

showed widespread detections of DDT and 

its breakdown products DDE and DDD (total 

DDT) in agricultural soils, stream water, 

suspended sediment, and fish in the Yakima 

River Basin in central Washington. Elevated 

concentrations of total DDT in bottom fish 

in the lower Yakima River were among the 

highest in the Nation. On the basis of these 

findings, the Washington Department of 

Health recommended that people eat no more 

than one meal per week of bottom fish from 

the lower Yakima River. Concentrations of 

total DDT in fish such as largescale suckers, 

smallmouth bass, and carp from the lower 

Yakima River decreased by about half from 

the late 1980s to 1998, but still exceeded 

guidelines for the protection of fish-eating 

wildlife. Decreases also were noted in stream 

water—total DDT was detected frequently in unfiltered water samples from the 

Yakima River in 1989, but was not detected in the Yakima River samples one 

decade later (1999). Reduced concentrations of total DDT in the Yakima River 

Basin were attributed primarily to the implementation of best-management 

practices (BMPs) that limit runoff of sediment and sorbed DDT, including drip 

and sprinkler irrigation systems, cover crops and ground cover, sediment retention basins, and the use of PAM (polyacrylamide, which causes soil particles to 

adhere to one another) (USGS Circular 1237).

Changes are positive and negative 

in Town Lake in Austin, Texas

Analysis of sediment layers from Town Lake in Austin, Texas, showed changes 

in selected contaminants that are typical of changes in lakes and reservoirs of 

rapidly urbanizing watersheds 

across the Nation. Lead concentrations in the lake sediments peaked in the late 1960s 

and then declined by about 

70 percent, a direct response 

to the elimination of lead in 

gasoline. Concentrations of 

DDT generally followed its 

historical use in the United 

States, which peaked from the 

late 1950s to the mid-1960s and 

then declined substantially after 

its ban in 1972. Concentrations 

of PCBs, which were used 

primarily as insulation fluids in 

transformers and appliances, peaked during the early 1960s and then declined 

by about 70 percent by 1998 (restrictions on PCBs were imposed in 1971). In 

contrast to trends in these regulated or banned contaminants, concentrations of 

total PAHs in Town Lake substantially increased. PAHs result from the burning 

of hydrocarbons and are present in road asphalt and roofing materials. The 

increase in PAHs generally corresponded to increases in automobile use in the 

greater Austin area—both increased by about 2.5 times from 1982 to 1996. The 

relation between PAH concentrations and motor vehicle traffic is evidence of 

the effect of nonindustrial sources, 

such as vehicle emissions, road and tire 

wear, and engine oil 

leaks associated with 

growth on the city 

fringes. This landuse pattern is typical 

of many urban areas 

across the Nation (Van 

Metre and Mahler, 

1999). 

������������������

��������

�������

���������

����������

���������

�����

������������

�����������������������������

�

�

�

��

��

������������������

������������������������

��������

��������������

������������������ ������������������ ��������������

����������������� �������

���� ���� ���� ����

����

�

��

�

�

������

�

�����

������

����

������������

��������������������������

�����������������������������

�����������������������

����

����������������������������

���

����

�������������

���������������

���������

����

����

����

����

����

����

���� � ���� ����� ����� ���

����

����

���

�������������

�����������

��� ���������

����

� ��� � ���
18

Water-quality assessments by a single program cannot possibly address all the Nation’s 

water-resources needs and issues. Therefore, 

it is necessary to define the context within 

which NAWQA information is most useful.

Source-water characterization—NAWQA 

studies characterize the quality of the available, untreated resource (source water), such 

as water upstream from treatment plants and 

water from public-supply and domestic wells. 

In the second round of assessments, NAWQA 

will continue to conduct source-water assessments for critical surface- and ground-water 

supplies and collaborate with other agencies 

and organizations that regulate, manage, and 

supply drinking water.

Strategic monitoring and assessment—

Water quality is assessed in representative 

river basins and aquifers across the Nation. 

Geographic areas represent a wide range of 

hydrologic environments and priority ecological resources; a variety of contaminant 

sources, including agricultural, urban, and 

natural sources; and a high percentage of 

people (about 60 percent) served by municipal 

water supply and irrigated agriculture water 

use. During the second round of assessments, NAWQA will continue to evaluate key 

processes that affect water quality, including 

land use, natural characteristics of the land, 

and hydrologic transport. Such information 

allows improved prediction of water quality in 

unsampled but comparable areas—a critical 

step for cost-effective management of water 

resources.

Total resource assessment—Assessments are 

not limited to a specific site or water-resource 

problem, but rather focus on the condition of 

the total resource. The information provides 

a scientific basis for prioritizing decisions 

involving competing water demands for 

drinking, irrigation, aquatic ecosystem health, 

and recreation.

Comparisons to benchmarks—Concentrations in water are compared to available 

USEPA drinking-water standards and guidelines, and to USEPA chronic water-quality 

criteria, Canadian water-quality guidelines, 

or Great Lakes water-quality objectives for 

protection of aquatic life (in order of priority, as available). Concentrations in sediment 

are compared to Canadian sediment-quality 

guidelines for protection of aquatic life, and 

concentrations in whole fish are compared to 

New York fish flesh criteria for protection of 

fish-eating wildlife (Nowell, 2004).

Detection versus risk—Compounds are 

measured at very low concentrations, often 

10 to 100 times lower than Federal or State 

standards and health advisories. Detection 

of compounds by NAWQA studies, therefore, does not necessarily translate to risks 

to human health or aquatic life; however, the 

findings are useful for identifying emerging 

issues and tracking contaminant concentrations over time.

Trends—Baseline conditions were assessed 

in the first round of NAWQA studies (1991-

2001). A major evaluation of trends is planned 

in the second decade when study units are 

reassessed and an increasing number of 

stream and ground-water sampling sites will 

have had over 10 years of consistent monitoring.

National priorities—The occurrence and 

distribution of nutrients, pesticides, VOCs, 

and trace elements, as well as the condition of 

aquatic habitat and ecological communities, 

are described on a nationwide basis. In addition, national and regional water-quality topics are addressed. Five topics initiated in 2002 

include (1) effects of urbanization on stream 

ecosystems; (2) ecological effects of nutrient 

enrichment; (3) transport of contaminants to 

public-supply wells; (4) sources, transport, 

and fate of agricultural chemicals; and (5) 

mercury in stream ecosystems. Certain topics 

may be emphasized and new topics added as 

the NAWQA Program continues throughout 

the second decade (Gilliom and others, 2001).

The NAWQA Program 

“Alaska’s social and economic 

fabric is inextricably bound 

to the health of our salmon 

habitat and water quality. 

The NAWQA Program has 

played a critical role in 

helping policy makers, businesses and citizens better 

understand the complexities 

of our watersheds, and as a 

result, we now have better 

tools to manage our salmon 

and water resources for 

future generations.”

Bob Shavelson, 

Executive Director, 

Cook Inlet Keeper, Alaska

“NAWQA data on benthic 

invertebrates is a major 

contribution to the State of 

Hawaii because the data 

have never been collected 

in Hawaiian streams and 

never before in conjunction 

with such a wealth of waterquality parameters. The 

information could provide 

the basis for an important 

new component in waterquality monitoring in Hawaii, 

which would be especially 

useful for volunteer monitors 

and educational groups.”

Dr. Carl Evenson, 

University of Hawaii 

at Manoa
19

NAWQA assessed 51 hydrologic basins (referred to as “study units”) from 1991 through 2001. NAWQA plans to reassess 42 

of the 51 study units in the second round of assessments, from 2002 through 2012 (see Gilliom and others, 2001, for map). 

�������

�������

���������

�����������������

��������������������

��������������������

���������

�������������������

�������������������

��

�

�

��

�

�

��

��

�� ��

��

��

��

��

��

��

��

�� ��

��

��

�

�

��

��

��

�� ��

��

��

��

��

��

��

��

��

��

��

�

�

��

�� ��

��

��

��

��

��

��

��

�

��

NAWQA Circulars

Available on the World Wide Web at 

water.usgs.gov/nawqa/nawqa_sumr.html

River Basin Assessments

 1. Acadian-Pontchartrain Drainages (Circular 1232)

 2. Albemarle-Pamlico Drainage Basin (Circular 1157)

 3. Allegheny and Monongahela River Basins (Circular 1202)

 4. Apalachicola-Chattahoochee-Flint River Basin (Circular 1164)

 5. Central Arizona Basins (Circular 1213)

 6. Central Columbia Plateau (Circular 1144)

 7. Central Nebraska Basins (Circular 1163)

 8. Connecticut, Housatonic and Thames River Basins (Circular 1155)

 9. Cook Inlet Basin (Circular 1240)

 10. Delaware River Basin (Circular 1227)

 11. Delmarva Peninsula (Circular 1228)

 12. Eastern Iowa Basins (Circular 1210)

 13. Georgia-Florida Coastal Plain (Circular 1151)

 14. Great and Little Miami River Basins (Circular 1229)

 15. Great Salt Lake Basins (Circular 1236)

 16. Hudson River Basin (Circular 1165)

 17. Island of Oahu (Circular 1239)

 18. Kanawha - New River Basins (Circular 1204)

 19. Lake Erie - Lake Saint Clair Drainages (Circular 1203)

 20. Long Island - New Jersey Coastal Drainages (Circular 1201)

 21. Lower Illinois River Basin (Circular 1209)

 22. Lower Susquehanna River Basin (Circular 1168)

 23. Lower Tennessee River Basin (Circular 1233)

 23. Las Vegas Valley Area and the Carson and Truckee River Basins 

 (Circular 1170)

 25. Mississippi Embayment (Circular 1208)

 26. Mobile River Basin (Circular 1231)

 27. New England Coastal Basins (Circular 1226)

 28. Northern Rockies Intermontane Basins (Circular 1235)

 29. Ozark Plateaus (Circular 1158)

 30. Potomac River Basin (Circular 1166)

 31. Puget Sound Basin (Circular 1216)

 32. Red River of the North Basin (Circular 1169)

 33. Rio Grande Valley (Circular 1162)

 34. Sacramento River Basin (Circular 1215)

 35. San Joaquin-Tulare Basins (Circular 1159)

 36. Santa Ana Basin (Circular 1238)

 37. Santee River Basin and Coastal Drainages (Circular 1206)

 38. South-Central Texas (Circular 1212)

 39. South Platte River Basin (Circular 1167)

 40. Southern Florida (Circular 1207)

 41. Trinity River Basin (Circular 1171)

 42. Upper Colorado River Basin (Circular 1214)

 43. Upper Illinois River Basin (Circular 1230)

 44. Upper Mississippi River Basin (Circular 1211)

 45. Upper Snake River Basin (Circular 1160)

 46. Upper Tennessee River Basin (Circular 1205)

 47. Western Lake Michigan Drainages (Circular 1156)

 48. White River Basin (Circular 1150)

 49. Willamette Basin (Circular 1161)

 50. Yakima River Basin (Circular 1237)

 51. Yellowstone River Basin (Circular 1234)
20

NAWQA reports and data are 

readily available

The USGS promotes public access 

to scientific information and strives 

to communicate and disseminate 

credible, timely, and relevant information about water resources. USGS 

Circulars referenced in this document, along with hundreds of other 

publications that describe individual 

study-unit and national-scale assessments, are available on the NAWQA 

Web site at water.usgs.gov/nawqa. 

The Web site also includes maps 

and water-quality data. The large 

NAWQA database on national waterquality conditions at water.usgs.

gov/nawqa/data can be used for a 

wide range of analyses at national, 

regional, State, and local scales.

Grady, S.J., 2003, A National Survey of 

Methyl tert-Butyl Ether and Other Volatile 

Organic Compounds in Drinking-Water 

Sources—Results of the Random Survey: 

U.S. Geological Survey Water-Resources 

Investigations Report 02-4079, 85 p.

Krabbenhoft, D.P., Wiener, J.G., Brumbaugh, 

W.G., Olson, M.L., DeWild, J.F., and 

Sabin, T.J., 1999, A National Pilot Study 

of Mercury Contamination of Aquatic 

Ecosystems along Multiple Gradients, 

in Morganwalp, D.W., and Buxton, 

H.T., eds., 1999, U.S. Geological Survey 

Toxics Substances Hydrology Program 

— Proceedings of the Technical Meeting, 

Charleston, S.C., March 8-12, 1999—Volume 2—Contamination of Hydrologic 

Systems and Related Ecosystems: U.S. 

Geological Survey Water-Resources 

Investigations Report 99-4018B, p. 147-

160.

Lidderdale, Tancred, 2003, Motor Gasoline 

Outlook and State MTBE Bans: Energy 

Information Administration, accessed 

April 8, 2004 at http://www.eia.doe.gov/

emeu/steo/pub/special/mtbeban.html

Majewski, M.S., 1995, Pesticides in the 

Atmosphere: Current Understanding of 

Distribution and Major Influences: U.S. 

Geological Survey Fact Sheet 152-95, 4 p.

Moran, M.J., Zogorski, J.S., and Squillace, 

P.J., 2003, Occurrence and Implications 

of Methyl tert-Butyl Ether and Gasoline Hydrocarbons in Ground Water and 

Source Water in the United States and in 

Drinking Water in 12 Northeast and MidAtlantic States, 1993-2002: U.S. Geological Survey Water-Resources Investigations 

Report 03-4200, 26 p.

Nolan, B.T., Hitt, K.J., and Ruddy, B.C., 

2000, Probability of Nitrate Contamination of Recently Recharged Ground 

Waters in the Conterminous United States: 

Environmental Science and Technology, v. 

36, no. 10, p. 2138-2145.

Nowell, Lisa H., 2004, Sources of Information on Standards and Guidelines for 

Pesticides in Water, Bed Sediment, and 

Fish, U.S. Geological Survey information available on the Web, accessed April 

12, 2004 at URL http://ca.water.usgs.

gov/pnsp/source

For Additional Information

Phillips, S.W. and Lindsey, B.D., 2003, The 

Influence of Ground Water on Nitrogen 

Delivery to the Chesapeake Bay: U.S. 

Geological Survey Fact Sheet 091-03, 6 p.

Squillace, P.J., Scott, J.C., Moran, M.J., 

Nolan, B.T., and Kolpin, D.W., 2002, 

VOCs, Pesticides, Nitrate, and Their Mixtures in Groundwater Used for Drinking 

Water in the United States: Environmental 

Science and Technology, v. 36, no. 9, 

1923-1930.

U.S. Environmental Protection Agency 

(USEPA), 1997, Drinking Water Advisory—Consumer Acceptability Advice 

and Health Effects Analysis on Methyl 

Tertiary-Butyl Ether (MtBE): EPA-822-F97-009, Office of Water, USEPA, accessed 

April 8, 2004 at URL http://www.epa.

gov/waterscience/drinking/mtbefact.pdf

U.S. Environmental Protection Agency, 

2001, Water-Quality Criterion for the Protection of Human Health—Mercury: EPA 

823-R-0-001, Office of Water, USEPA, 

accessed April 2, 2004 at URL http://

www.epa.gov/waterscience/criteria/methylmercury/document.html

U.S. Environmental Protection Agency, 

2002, Total Maximum Daily Load for the 

Pesticide Fipronil in the Mermentau River 

Basin, accessed April 7, 2004 at URL 

http://www.epa.gov/earth1r6/6wq/ecopro/

latmdl/fipronil_merm(f).pdf

Van Metre, P.C., and Mahler, B.J., 1999, 

Town Lake Bottom Sediments: A Chronicle of Water-Quality Changes in Austin, 

Texas, 1960-98: U.S. Geological Survey 

Fact Sheet 183-99, 6 p.

Van Metre, P.C., Mahler, B.J., and Furlong, 

E.T., 2000, Urban Sprawl Leaves its PAH 

Signature: Environmental Science and 

Technology, v. 34, no. 19, 4064-4070.

Welch, A.H., Watkins, S.A., Helsel, D.R., 

and Focazio, M.J., 2000, Arsenic in 

Ground-Water Resources of the United 

States: U.S. Geological Survey Fact Sheet 

063-00, 4 p.

References Cited and 

Suggested Readings

Brumbaugh, W.G., Krabbenhoft, D.P., Helsel, D.R., Wiener, J.G., and Echols, K.R., 

2001, A National Pilot Study of Mercury 

Contamination of Aquatic Ecosystems 

along Multiple Gradients—Bioaccumulation in Fish: U.S. Geological Survey Biological Science Report 2001–0009, 25 p.

Couch, C.A. and Hamilton, P.A., 2002, 

Effects of Urbanization on Stream Ecosystems: U.S. Geological Survey Fact Sheet 

042-02, 2 p.

Fisher, D.C. and Oppenheimer, M., 1991, 

Atmospheric Nitrogen Deposition and the 

Chesapeake Bay Estuary: AMBIO, v. 20, 

no. 3-4, p. 102-108.

Gilliom, R.J., Hamilton, P.A., and Miller, 

T.L., 2001, The National Water-Quality 

Assessment Program—Entering a New 

Decade of Investigations: U.S. Geological 

Survey Fact Sheet 071-01, 6 p.
Contacts for additional information or questions:

Chief, NAWQA Program

U.S. Geological Survey

12201 Sunrise Valley Drive, MS 413

Reston, VA 20192

Email: nawqa_info@usgs.gov

Donna N. Myers, 703.648.5715, dnmyers@usgs.gov

Timothy L. Miller, 703.648.6862, tlmiller@usgs.gov 

Pixie A. Hamilton, 804.261.2602, pahamilt@usgs.gov 

Special thanks to the following individuals for contributing to this effort: 

NAWQA personnel in study units across the Nation for their contributions and commitment to the Program

NAWQA’s many partners in the governmental and non-governmental sectors who have helped guide scientific efforts and ensure that NAWQA 

information meets the needs of local, State, regional, and national stakeholders

Reviewers of this publication, including Michael D. Woodside, Judy Campbell-Bird, and Robert J. Gilliom

Technical editors, including Chester Zenone and Martha L. Erwin

Graphic design and layout, Phillip J. Redman
Hamilton and others—Water Quality in the Nations’s Streams and Aquifers—Circular 1265

Printed on recycled paper

National Water-Quality Assessment Program

NAWQA