Water Quality in the

Central Columbia Plateau

Washington and Idaho, 1992–95

U.S. Department of the Interior

U.S. Geological Survey

science for a changing world
Coordination among agencies and organizations is an integral part of the NAWQA program. We thank the 

following agencies and organizations who directly participated in the Central Columbia Plateau program.

Federal Organizations

U.S. Bureau of Reclamation

U.S. Department of Agriculture, Natural Resources Conservation Service

U.S. Environmental Protection Agency

U.S. Fish and Wildlife Service

Yakama Indian Nation

Universities and State Agencies

University of Idaho

University of Washington

Washington State University Cooperative Extension

Idaho Department of Health & Division of Environmental Quality

Washington Department of Agriculture

Washington Department of Ecology

Washington Department of Fisheries

Washington Department of Health

Washington Department of Natural Resources

Washington Department of Transportation

Washington Department of Wildlife

Washington State Conservation Commission

Local Agencies

Kittitas County Conservation District

Lake Roosevelt Forum

Lincoln County Conservation District

Palouse Conservation District

Palouse-Clearwater Environmental Institute

Quincy-Columbia Irrigation District

South Columbia Basin Irrigation District

Spokane County Conservation District

Thurston County Health Department

Washington PUD Association

Whitman County Conservation District

Private Organizations

Battelle-Pacific Northwest Laboratory

Best Test Analytical Services

Columbia Basin Institute

Columbia Foods, Inc.

DowElanco

Far West Fertilizer & Agrichemical Association

Lincoln County Wheat Growers Association

Northwest Food Processor Association

Qualls Agricultural Labs

Soiltest Farm Consultants, Inc.

Washington Farm Bureau

Washington Toxics Coalition

Central Columbia Plateau Study Unit contact: NAWQA Program contact:

District Chief Chief, NAWQA Program

U.S. Geological Survey U.S. Geological Survey

Water Resources Division Water Resources Division

1201 Pacific Ave., Suite 600 12201 Sunrise Valley Drive, M.S. 413

Tacoma WA 98402 Reston VA 20192

Phone: (253) 428-3600

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

The Central Columbia Plateau Study Unit’s Home Page is: The NAWQA Program’s Home Page is:

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

Email: nawqa_ccpt_wa@usgs.gov

This circular is also available on the Internet via the World Wide Web, at URL:

http://water.usgs.gov/lookup/get?circ1144

FOR ADDITIONAL INFORMATION ON THE 

NATIONAL WATER-QUALITY ASSESSMENT (NAWQA) PROGRAM:

Much appreciation is extended to the following U.S. Geological Survey employees: 

Martha L. Erwin, Technical editor Joseph L. Jones, Ground-water specialist

Moon H. Kim, Hydrologist Alan L. Haggland, Computer assistant 

Brett A. Smith, O. Gary Holloway, and Jeanette F. O’Neil, Hydrologic technicians 

Appreciation is also extended to those individuals and agencies that reviewed this report: 

Stuart W. McKenzie, U.S. Geological Survey Karen Dinicola, U.S. Geological Survey

Phillip Crawford, Washington State University (WSU) Coop. Extension John Holmes, Franklin County Conservation District

Scott Downey, U.S. Environmental Protection Agency, Ground Water Div. Cliff Carstens, Lincoln County Wheat Growers Assoc.

Front cover: Rolling hills near Pullman, Washington. The Palouse basin is almost entirely cropped in wheat and other dry-farmed grains. Strip

cropping (alternating bands of different crops or fallow) is a best management practice (BMP) designed to reduce soil erosion. (Photograph © by Phil Schofield. Used with permission)

Back cover: Front cover photograph and a second photograph, looking south from where I-90 crosses the Columbia River, showing the mouth

of Crab Creek, and irrigated circles on both the Royal Slope in front of the Saddle Mountains and on the Wahluke Slope beyond. (Second

photograph by Dennis Cline, U.S. Geological Survey)
Library of Congress Cataloging in Publications Date

ISBN 0-607-89116-5

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

does not constitute endorsement by the U.S. Government

1998

Free on application to the

U.S. Geological Survey

Information Services

Box 25286 Federal Center

Denver, CO 80225

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Thomas J. Casadevall, Acting Director
By Alex K. Williamson, Mark D. Munn, Sarah J. Ryker, 

Richard J. Wagner, James C. Ebbert, and Ann M. Vanderpool

A contribution of the National Water-Quality Assessment (NAWQA) Program

Water Quality in the Central Columbia Plateau, 

Washington and Idaho, 1992–95

U.S. GEOLOGICAL SURVEY CIRCULAR 1144

CONTENTS

National Water-Quality Assessment 

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

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

Environmental setting and hydrologic

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

Major issues and findings:

Nitrate in ground water..................................... 6

Nitrate trends in ground water .......................... 9

Pesticides and radon in ground water ............... 10

Pesticides in surface water................................ 12

The influence of ground water on 

surface-water quality..................................... 13

Sediment in surface water................................. 14

Nutrients in surface water................................. 16

The influence of land use on aquatic life.......... 18

Water-quality conditions in a national 

context ............................................................. 20

Study design and data collection......................... 24

Summary of compound detections

and concentrations........................................... 26

References........................................................... 32

Glossary .............................................................. 34

Numbers in [ ] refer to References. Words in italics are defined in the Glossary.
U.S. Geological Survey Circular 1144 1

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

Began in 1991

Began in 1994

Began in 1997

Not scheduled yet

EXPLANATION

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

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

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

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

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

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

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

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

conditions. 

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

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

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

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

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

Study Unit is scheduled to be revisited every decade to evaluate changes in waterquality conditions. NAWQA 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 Central Columbia Plateau 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 waterresource 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
2 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Palouse

subunit

NorthCentral

subunit

Washington

Idaho

Central Columbia Plateau

study unit

QuincyPasco

subunit

which is the U.S. Environmental Protection Agency maximum contaminant level (MCL). The highest exceedance rates 

occur where fertilizer use and irrigation are greatest.

• The primary source of nitrate in ground water is agricultural fertilizers. Other sources include cattle feedlots, food processing plants, septic tanks, and wastewater discharges.

• Nitrate concentrations are generally highest in shallow wells in irrigated areas, including many domestic wells and shallow 

public supply wells.

• Nitrate concentrations in shallow wells are among the highest in the Nation (p. 22).

Pesticides are frequently detected, although generally at concentrations below drinking water criteria (p. 10–11).

• Pesticides were detected in 60 percent of shallow wells and 46 percent of deeper public supply wells.

• Concentrations of only three pesticides exceed the MCL or a health advisory: dieldrin, EDB, and 1,2-dichloropropane. 

These pesticides have been discontinued from use, and the exceedances occur in only 2 percent of the wells.

• Herbicides were detected most often, especially atrazine and its breakdown products. However, no concentrations of an herbicide exceed MCLs or health advisories.

• Shallow wells in irrigated agricultural areas of the Quincy-Pasco subunit have the most pesticide detections and the largest 

number of different pesticides detected per well. Pesticide detections also correlate with elevated nitrate concentrations.

• In the Palouse subunit, none of the commonly used pesticides were detected in ground water, although 10 were detected in 

surface water.

• Sixty-four percent of public supply wells with detections of pesticides contain more than one detectable pesticide. The 

human health significance of very low concentrations of several pesticides is uncertain because drinking water standards do 

not exist for 40 percent of the pesticides detected or for occurrences of multiple pesticides. 

• Pesticides were detected more frequently than the national average, with the exception of those in shallow ground water 

associated with dryland farming (p. 22).

Radon, a naturally occurring gas, is not increased by agricultural practices. Neither radon nor trace elements are a 

major concern in the Central Columbia Plateau.

Is ground-water quality improving?

Improvements from best management practices (BMPs) take decades or longer to be seen.

• However, as a result of fertilizer use leveling off since 1985, nitrate concentrations may be beginning to level off in some 

areas. In many areas, concentrations continue to rise.

It is difficult to determine trends for pesticides because there are not enough data, but the patterns of detection may 

give some clues (p. 10).

• The newer pesticides, which are less persistent in the environment than the discontinued ones, were not detected at concentrations above MCLs or health advisories. EDB, discontinued in the late 1970s, was detected more frequently in deeper 

wells, possibly indicating that it is moving down into deeper ground water. This is another indication that ground-water 

quality improvements take decades or longer.

• Concentrations of nitrate and pesticides are generally similar in shallow ground water and in surface water at base flow, 

which occurs in winter. Trends in pesticides in ground water are most cost effectively monitored by sampling surface water 

at base flow, though sampling very shallow wells gives the most current picture of ground-water quality (p. 13).

GROUND WATER: Ground water, the main source of drinking 

water, is substantially affected by agricultural practices.

Concentrations of nitrate in many wells exceed the drinking water standard (p. 6–8). 

• Nitrate concentrations in about 20 percent of all wells exceed the drinking water standard, 

SUMMARY OF MAJOR ISSUES AND FINDINGS
U.S. Geological Survey Circular 1144 3

SURFACE WATER: The health of the aquatic ecosystems is substantially affected by 

agricultural practices and, in a few streams, by wastewater discharges.

Eutrophication, caused by high concentrations of nutrients, is degrading streams (p. 17, 18).

• Eutrophication results in excessive plant growth, sometimes reducing dissolved oxygen below levels that some fish species 

require.

• Improving the health of aquatic ecosystems may require reducing nitrate concentrations in ground water. At one site in the 

Quincy-Pasco subunit, over 60 percent of the nitrogen comes from ground water (p. 13).

Sediment erosion and runoff are degrading streams (p. 14–15, 19).

• In most streams, sediment loading has reduced instream habitat needed by fish and other aquatic life (p. 19). Moreover, 

eroded soil particles carry pesticides that accumulate in streambeds and also in fish tissue.

• Concentrations of some long-banned but persistent organochlorine pesticides (such as DDT) or total PCBs exceed environmental guidelines for streambed sediment at 22 percent of the sites sampled.

• However, concentrations of trace elements are not elevated above naturally occurring levels in soils.

Riparian (streamside) habitat has been seriously reduced, and present-day agricultural practices limit natural 

recovery of the vegetation (p. 19).

• Loss of riparian habitat causes stream temperatures to increase and stream banks to become more unstable, and thus more 

likely to erode. Increased temperatures and sediment in streams can alter resident fish communities.

• Grazing practices also contribute to erosion of destabilized stream banks.

Concentrations of agricultural pesticides occasionally exceed criteria for the protection of aquatic life in several 

streams (p. 12).

• Highest concentrations and exceedances of freshwater-chronic criteria generally occur within a month or two of pesticide 

application.

• Most exceedances of freshwater-chronic criteria are for currently used organophosphate insecticides.

• Carp in a small lake in the Quincy-Pasco subunit showed nervous system abnormalities, possibly indicating exposure to 

organophosphate insecticides; long-term effects are uncertain (p. 19).

Is surface-water quality improving?

Soil erosion is decreasing as a result of best management practices (BMPs) (p. 14–15).

• Changing from furrow to sprinkler irrigation is reducing the loss of soil from irrigated cropland in the Quincy- Pasco subunit.

• Soil erosion from irrigated cropland and DDT concentrations in sediment and fish correlate with the percentage of furrowirrigated land, so changing to sprinklers also improves sediment quality.

• Improved farming practices may have reduced soil erosion from dry-farmed cropland in the Palouse subunit.

Although concentrations of nutrients are commonly still increasing, at some sites they have decreased slightly or begun 

to level off (p. 9, 17).
4 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Figure 1. Most of the land in the Central Columbia Plateau is used for agriculture.

Palouse

subunit

North-Central

subunit

Quincy-Pasco

subunit

(Columbia Basin

Irrigation Project)

120

118

48

46 30’

0 20 40 mi

0 20 40 km

Moscow

Palouse

Quincy

Pullman

Pasco

Hooper

Ritzville

Othello Beverly

Coulee

City

Nonirrigated (dryland)

agriculture

Surface-water 

irrigated agriculture

Ground-water 

irrigated agriculture

Barren or rangeland

Forest

Subunit boundary

County boundary

State boundary

EXPLANATION WASHINGTON IDAHO

DOUGLAS

GRANT

LINCOLN

WHITMAN

ADAMS

FRANKLIN

LATAH

SPOKANE

Potholes

Reservoir Cow Creek

Moses

Lake

Banks

Lake

Palouse River Rock Lake

Crab Creek

Columbia

River

Snake

River

ENVIRONMENTAL SETTING AND HYDROLOGIC CONDITIONS

Table 1. Summary of subunit characteristics [mi2, square mile; %, percent]

Quincy-Pasco subunit (2,500 mi2) North-Central subunit (8,100 mi2) Palouse subunit (2,500 mi2)

Total croplanda

Major cropsb

(approximate percentage of total cropland)

896,000 acres

alfalfa (30%) wheat (20%)

field crops (15%) corn (11%)

potatoes (10%) orchard (7%)

3,210,000 acres 

cereal grains (wheat, barley, oats) 

(93%)

1,260,000 acres

cereal grains (78%) 

field crops (19%)

Hydrology

Controlled during irrigation season (Mar.–Oct.)

Nearly all surface water is canals and agricultural 

drains

Storm runoff is rare

Intermittent streams with few 

disconnected perennial stream 

segments

Perennial streams in larger 

basins

Major point and 

localized nonpoint 

sources of pollutants

Feedlots, pesticide handling areas

Land-applied food-processing effluent

Land-applied wastewater-treatment effluent

Some feedlots Wastewater-treatment effluent

discharged to streams

Surficial geology

Topography

Varied thickness of sediments over basalt

Nearly flat basins between bluffs

0-20 feet of loess over basalt

Channeled scablands

5-100 feet of loess over basalt

Rolling hills

Water table change, 

1950 to present

Rise of 50 to 500 feet Decline of more than 150 feet in 

some locations

Slightly declining

a [1]; b [2, 3]

Rich grasslands and forested canyons inspired 19th-century cattle ranchers to make the Central Columbia Plateau their 

home. As overgrazing devalued the land for ranching, farming became more important. Today it is an area of national agricultural importance and home to about 300,000 people. The region is one of the Nation’s top two producers of potatoes and 

wheat, is a significant producer of apples and many other crops, and supports much rangeland grazing. 

The Study Unit was divided into three subunits on the basis of hydrologic and geologic differences affecting land and water 

use (see p. 24–25). Thick loess and moderate precipitation allow for dryland farming in the Palouse subunit, while the Columbia Basin Irrigation Project has made the Quincy-Pasco subunit also productive for farming. The North-Central subunit supports rangeland grazing and, where conditions allow, irrigated and dryland farming.
U.S. Geological Survey Circular 1144 5

Irrigation has greatly altered the Quincy-Pasco subunit

Irrigation in the Quincy-Pasco subunit increased significantly 

during 1955–75 as the Columbia Basin Irrigation Project made 

more water available. Water diverted from the Columbia River, 

conveyed through irrigation canals, and applied to agricultural 

lands has raised the water table tens to hundreds of feet, creating or 

increasing base flow to many of the streams and wasteways. The 

result is an overall annual increase in streamflow, controlled mostly 

by irrigation, with base flow in the winter and high flows in the 

summer (fig. 4).

Most water withdrawals are for irrigation

About 94 percent of combined ground- and surface-water withdrawals are for irrigation [5]. Eighty-four percent of public and 

domestic supplies comes from ground water (fig. 5).

Figure 5. Most of the water in the Central Columbia Plateau 

is used for irrigation. Ground water is the main source of 

drinking water (1990 data shown; graphs have different 

vertical scales) [5].

EXPLANATION

Ground

water

Surface

water

(234) Population

served, in

thousands

3,000

2,000

1,000

0

TOTAL

Irrigation

Water withdrawals,

in millions of gallons per day

Public

supply

Domestic

supply

Food processing

100

80

60

40

20

0

(234)

(58)

Figure 4. In the Quincy-Pasco subunit, irrigation has 

increased and stabilized streamflows throughout the 

year.

ON D J F MAMJ J AS

Streamflow, in cubic feet per second

Water year (Oct. - Sept.)

Crab Creek at Beverly

1993

1995 1994

400

100

200

300

0

Interquartile range (middle 

50 percent of the values) 

of daily streamflow, water 

years 1970-95

Interquartile range of daily 

streamflow, water years 1961-64

Figure 3. Conditions in the Palouse subunit were 

typical during 1993–95, the sampling period, with 

variable streamflows in dry, average, and wet years.

Interquartile range (middle 

50 percent of the values) 

of daily streamflow, water 

years 1952-95

O ND J FMAMJ J AS

Streamflow, in cubic feet per second

Water year (Oct. - Sept.)

8,000

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0

Palouse River at Hooper

1995 (wet)

1994 (dry)

1993

Figure 2. Average annual precipitation is highest in the Palouse subunit; 

average monthly figures for Pullman, Wash., show that precipitation mostly 

occurs in the winter (years of record 1956–77). Modified from [4].

11

8

11

9

12 13

14

15

16

18

7

10

8

20

8

25

18

0 40 mi

0 40 km

120 ̊ 118 ̊

48 ̊

46 ̊

30’

WA

ID

EXPLANATION

Subunit boundary

State boundary

Line of equal average 

annual precipitation, 

in inches. Contour 

interval is variable

8 Precipitation,

in inches

Month

4

3

2

1

0 JFMAMJJASOND

Pullman

The climate is arid to 

semiarid

The arid to semiarid climate is evident in the hydrology. Only the Palouse subunit receives enough rainfall 

(fig. 2) to support perennial streams

that have high flows in the wetter winter months and low base flows in the 

dry, hot summer months (fig. 3). 

Before increased irrigation, the 

remainder of the Study Unit mostly 

supported intermittent streams that 

only had substantial streamflows following storms; this is still true for most 

of the North-Central subunit.
6 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Nitrate concentrations in 

many drinking water 

wells exceed the 

maximum contaminant 

level (MCL).

In the Central Columbia Plateau, 

84 percent of drinking water comes 

from ground water. Both public 

supply and domestic water systems 

depend largely on ground water [5, 

6] (fig. 5). Current nitrate data are 

generally available for public supply wells, which must be sampled 

regularly. Domestic wells, however, are generally sampled only for 

special studies. About 20 percent of 

wells in the Study Unit exceed the 

MCL for nitrate in drinking water 

[1, 7]; the MCL is set by the U.S. 

Environmental Protection Agency 

at 10 milligrams per liter (mg/L) 

[8]. Reducing nitrate in ground 

water has been the focus of cooperative efforts between Federal, State, 

and local agencies.

Nitrate concentration has been 

suggested as an indicator of overall 

ground-water quality [9, 10], and 

drinking water with high nitrate 

concentrations is a potential health 

risk, particularly for infants [7, 8, 

11]. 

Figure 6. Most public supply wells [13] and domestic wells that exceed the maximum 

contaminant level (MCL) for nitrate are in the Quincy-Pasco subunit. (Wells were 

sampled from 1985 to 1996; for wells sampled more than once, the most recent value 

was used.)

118

46 30’

120

48

CrabCreek

CowCreek

Banks

Lake

PalouseRiver Rock

Lake

DOUGLAS

GRANT

LINCOLN

WHITMAN

ADAMS

FRANKLIN

LATAH

NEZ PERCE

SPOKANE

North-Central 

subunit

Palouse

subunit

Quincy-Pasco

subunit

Columbia River

Snake River

0 20 40 mi

0 20 40 km

Potholes

Reservoir

Moses

Lake

Pasco

Quincy

Pullman

EXPLANATION

0 - 2.5 mg/L

2.6 - 5.0 mg/L

5.1 - 9.9 mg/L

Greater than or

equal to 10.0 mg/L

Naturally occurring

[12]

Elevated

At or above the MCL

Nitrate concentration, in milligrams per liter

(mg/L) as nitrogen

a

 For wells sampled more than once, the most recent value was used. b 411 public water systems with at 

least 15 hook-ups; average depth 270 feet [9]. c 270 public water systems with less than 15 hook-ups; average depth 210 feet. d

 67 domestic wells sampled for the NAWQA Land Use Study component (p. 24); average depth 140 feet [3]. e Percentages were not calculated for counties that fall partly outside the study area. f

 Most wells are deep, averaging 500 feet (see Moses Lake area, fig. 6).

Table 2. Percentage of drinking water wells sampled in 1985–96 with nitrate 

concentrationsa

 exceeding the U.S. Environmental Protection Agency maximum 

contaminant level of 10 milligrams per liter [--, insufficient data; %, percent]

Class A public supply 

wells b

Class B public supply 

wells c

Shallow

domestic 

wells d

County e Adams 3% 25% - -

Douglas 7% - - - -

Franklin 28% 29% 33%

Grant 1% f 3% 35%

Whitman 7% 4% 6%

Subunit Quincy-Pasco 9% 15% 35%

North-Central 3% 5% - -

Palouse 7% 5% 5%

Study Unit 6% 12% - -

The Quincy-Pasco subunit has 

the highest percentage of wells 

exceeding the MCL

The Columbia Basin Irrigation 

Project brings more than 2,500,000 

acre-feet (800 billion gallons) of 

water per year from the Columbia 

River to the Quincy-Pasco subunit, 

enabling intensive irrigated agriculture.

In much of the North-Central 

subunit, deep ground water is the 

only source of water. Most of this 

subunit’s high nitrate concentrations are in the shallower wells bordering the Quincy-Pasco subunit.

The Palouse subunit, dominated 

by nonirrigated agriculture, has 

generally lower nitrate concentrations than the rest of the Study Unit.

MAJOR ISSUES AND FINDINGS -

NITRATE IN GROUND WATER
U.S. Geological Survey Circular 1144 7

Intensive application of 

fertilizers and irrigation 

water causes high nitrate 

concentrations in the 

Quincy-Pasco subunit

Synthetic fertilizers became widely 

available after World War II. Fertilizers are the source of 84 percent of 

nitrate inputs to the Central Columbia 

Plateau [16]. Other sources of nitrate 

include cattle feedlots, food processing 

plants, septic tanks, and treated wastewater; these are local and thus less 

important sources in most of the Study 

Unit.

Agricultural acreage continues to 

increase in the plateau, but nationally 

recommended application rates for fertilizer have been lowered in the last 

few years. As a result, fertilizer sales 

(fig. 7) and application have leveled 

off [12]. Irrigation, however, continues 

to increase in the plateau [fig. 8].

Two primary factors contribute to 

the Quincy-Pasco subunit’s high 

nitrate concentrations: high rates of 

fertilizer application [fig. 9] and irrigation water. Ninety-four percent of all 

the water used in the plateau supports 

agricultural irrigation in the arid 

Quincy-Pasco subunit [5]. This extensive irrigation has greatly increased 

rates of recharge (fig. 10), which is 

water moving from the land surface to 

ground water. Recharge, especially at 

higher rates, moves nitrate into shallow ground water.

Figure 9. Annual application rates of 

nitrogen fertilizer are highest in the 

Quincy-Pasco subunit (rates are in 

pounds per acre (lb/acre)), (1991 data 

shown) [16]. 

50

lb/acre

55

lb/acre

Columbia River

Snake River

Pasco

Wenatchee

Pullman

Spokane

Quincy-Pasco subunit

140

lb/acre

Figure 8. The amount of irrigation 

water diverted from the Columbia River 

has steadily increased [16].

1945 1955 1965 1975 1985 1995

0

1

2

3

4

Irrigation water, in 

millions of acre-feet

Irrigation

water

Figure 7. Sales of nitrogen fertilizer in 

the United States have leveled off [14, 

15]. Graph modified from [12].

1945 1965 1975 1985 1955 1995

10

6

2

4

0

8

12

Nitrogen fertilizer sales,

in millions of tons per year

Nitrogen

fertilizer

Figure 11. Nitrate concentrations may 

have leveled off at Ringold Springs, a 

large spring in the Study Unit (site A, 

fig. 14), from 1957 to 1994 [18]. 

However, data are limited and the 

peak concentration in 1986 may have 

been unusual.

1945 1955 1965 1975 1985 1995

Nitrate as nitrogen,

in milligrams per liter

Nitrate

concentration

MCL 10

9

8

7

6

5

4

3

2

1

0

Figure 10. Average rates of recharge 

are highest in the Quincy-Pasco 

subunit (rates are in inches per year 

(in/yr)) [17].

2 in/yr

12

in/yr 4 in/yr

Columbia River

Snake River

Pasco

Wenatchee

Pullman

Spokane

Columbia Basin

Irrigation Project

area

Trends in nitrate 

concentrations vary 

across the Study Unit

Nitrate concentrations in the Central 

Columbia Plateau’s ground water have 

generally increased since the 1950s. 

Although fertilizer application leveled 

off in about 1985, it is too early to be 

certain of any corresponding leveling 

off or decrease in nitrate concentrations in the regional ground-water system.

Individual wells may show trends 

that reflect only local conditions. For 

example, at Ringold Springs, one of 

the largest springs in the Study Unit, 

nitrate concentrations may have leveled off. However, the improvement is 

probably not as dramatic as is suggested by the decrease shown in 

figure 11.

Across the plateau, nitrate concentrations continue to increase in most 

areas. Examples of varying nitrate 

trends in ground- and surface-water 

systems are discussed on page 9.
8 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Figure 14. Sites in the Quincy-Pasco 

subunit (also the Columbia Basin 

Irrigation Project area) used to describe 

trends in nitrate concentrations.

Irrigated areas

Waterways

0

0

20

20

40 mi

40 km

EXPLANATION

Pasco

Quincy

Columbia River

Moses 

Lake

D

A

C B

E

G

F

A Ringold Springs

B Well, fig. 12

C Area, fig. 13

D EL68D Wasteway

E Frenchman Hills Wasteway

F Crab Creek at Beverly

G Crab Creek Lateral

Figure 13. In an irrigated area in 

western Franklin County (area C, 

fig. 14), PE 59.4 Lateral has a nitrate 

concentration of 1.3 milligrams per 

liter. Most wells close to the canal 

have lower nitrate concentrations [18].

0.5

0.5

16

PE 59.4

PE 59.4D

14

6.8

1.3

20

2.4

2.4

0.6

13

EXPLANATION

Canal lateral

Well

Nitrate concentration, in

milligrams per liter as nitrogen

Irrigation increases the variability 

of nitrate concentrations

Trends in individual wells may not 

reliably represent trends for a large 

area. In the Quincy-Pasco subunit, 

samples from springs and surfacewater sites can give further insight into 

trends and variability of nitrate in 

ground water.

In the Quincy-Pasco subunit, nitrate 

concentrations in ground water can be 

much higher during the irrigation 

season (fig. 12). In some parts of the 

subunit, however, low-nitrate water 

leaking from irrigation canals may 

dilute nitrate in ground water, so that 

summer concentrations are close to 

naturally occurring levels (2–3 mg/L) 

[12].

Figure 15. Nitrate concentrations are 

lower at greater depths; however, in 

irrigated areas (see fig. 14) some deep 

wells have elevated nitrate 

concentrations. Nitrate as nitrogen, in milligrams per liter

Depth to sample, in feet

0 250 500 750 1,000 1,250 1,500

>30

10

20

30

0

Figure 12. In a well in western Franklin 

County (site B, fig. 14), nitrate 

concentrations are higher during the 

peak irrigation season (Mar.–Oct.) 

[18].

1987 1988 July Jan. Jan. July June 1986

14

16

18

20

22

Date of sample

Nitrate

concentration

Nitrate as nitrogen,

in milligrams per liter

summer winter

The average nitrate concentration in 

regional shallow ground water is 

6 mg/L or more. In fresh water 

diverted from the Columbia River for 

irrigation, nitrate concentrations are 

1 mg/L or lower. As shown in 

figure 13, some wells close to canals 

have below-average nitrate concentrations due to dilution by water leaking 

from canals [18].

Deeper ground water, which is farther from sources of nitrate applied on 

the land surface, is less susceptible to 

contamination. Also, when irrigation 

raises the water table significantly, as 

has occurred in the Quincy-Pasco subunit, recently recharged ground water 

flows rapidly to surface waters instead 

of to deeper ground water. This prevents some of the nitrate present in 

recently recharged ground water from 

moving to deeper ground water. 

Figure 15 shows that nitrate concentrations are generally lower at greater 

depths. Many public supply wells are 

relatively deep, so have lower nitrate 

concentrations and exceed the MCL 

less frequently than do the shallower 

domestic wells (table 2).
U.S. Geological Survey Circular 1144 9

Sampling surface water at 

base flow is a cost-effective 

way to monitor trends in 

ground-water quality

Nitrate concentrations vary considerably in wells, requiring many samples to determine trends. However, in 

the Quincy-Pasco subunit many irrigation wasteways and other surface drains 

receive large contributions from 

ground-water discharge. For example, 

about 60 percent of total nitrogen discharged annually by EL68D Wasteway 

(site D, fig. 14) comes from groundwater discharges to the wasteway. 

From November to February, irrigation 

water is not delivered and storms large 

enough to produce runoff are rare. During this time, streamflow is low and 

ground water is the predominant source 

of nitrate in surface water conveyed by 

wasteways (fig. 16). Therefore, in the 

Quincy-Pasco subunit, samples of surface water during winter can be used to 

monitor nitrate trends in ground water 

for a large area. Base-flow surfacewater sampling can also be used to 

track occurrence and trends in other 

dissolved constituents in ground water, 

including pesticides such as atrazine 

(p. 13). 

Base-flow sampling in Palouse subunit streams is less indicative of 

ground water for several reasons. Base 

flow in the Palouse subunit occurs during the summer when plant growth is 

high; uptake of nitrogen by aquatic 

plants can greatly decrease nitrate concentrations in surface water. In addition, a substantial percentage of 

Palouse River flow in the summer is 

high-nitrate discharge from wastewater-treatment plants.

In the Quincy-Pasco subunit, nitrate 

concentrations are generally 

increasing . . .

In most parts of the Quincy-Pasco 

subunit, base-flow concentrations of 

nitrate in wasteways and other surface 

drains have increased since the 1960s 

— indicating an increase in nitrate 

concentrations in ground water. Best 

management practices (BMPs) in use 

in parts of the subunit may in time 

decrease these concentrations. However, changes in ground-water quality 

may not be apparent for decades or 

longer.

. . . but trends vary.

In Frenchman Hills Wasteway, 

base-flow nitrate concentrations doubled from about 3 to about 6 mg/L 

between 1966 and 1990 and appear 

still to be increasing (fig. 17). Ground 

water is the source of nearly 100 percent of base flow in the wasteway, so 

nitrate concentrations in nearby 

ground water have likely followed the 

same trend.

Base-flow nitrate concentrations are 

still increasing in Crab Creek at Beverly, but the increase has slowed since 

1980. This trend is similar to trends 

that occurred in fertilizer sales (fig. 7) 

and irrigation (fig. 8) in much of the 

drainage basin. In addition, concentrations may be leveling off at this site 

because of contributions from the Crab 

Creek Lateral subbasin, where concentrations are decreasing.

In Crab Creek Lateral, base-flow 

concentrations of nitrate decreased 

from about 8 mg/L in 1966 to about 

6 mg/L in 1991. This decrease may be 

partially explained by changing farming practices. For example, although 

the total amount of irrigated cropland 

draining to Crab Creek Lateral has not 

decreased, from 1974 to 1990 the proportion of this land used for orchards 

increased from 9 to 29 percent. 

Orchards require less applied nitrogen 

than do many of the row crops that 

they replaced [16].

Figure 17. Three sites in the Quincy-Pasco subunit show varying 

trends in nitrate concentrations at base flow (Nov.-Feb.) from 1960–91. 

In Frenchman Hills Wasteway (site E, fig. 14), concentrations doubled. 

At Crab Creek at Beverly (site F), the increase has slowed since 1980. 

In Crab Creek Lateral (site G), there has been a decrease.

1955 1965 1975 1985 1995

Nitrate as nitrogen,

in milligrams per liter

2

0

4

6

8

10

Crab Creek Lateral (G)

Crab Creek

at Beverly

(F)

Frenchman Hills 

Wasteway

(E) 

Figure 16. Nitrate concentrations at 

EL68D Wasteway (site D, fig. 14) are 

highest during the winter when the main 

source is ground-water discharge and 

there is little dilution by canals or return 

flows [2].

Daily average streamflow,

in cubic feet per second

Nitrate as nitrogen,

in milligrams per liter

400

0

200

ON D J FM A MJ J A S

1993 1994

10

0

5

Nitrate

concentration

Streamflow

MAJOR ISSUES AND FINDINGS -

NITRATE TRENDS IN GROUND WATER
10 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Figure 18. Locations of wells sampled for pesticides and volatile organic 

compounds in the Central Columbia Plateau.

Quincy-Pasco

subunit

North-Central

subunit

Palouse

subunit

0 20 40 mi

0 20 40 km

GRANT

DOUGLAS

LINCOLN

WHITMAN

ADAMS

FRANKLIN

SPOKANE

Beverly

Pasco

Ritzville

Hooper

Quincy

Pullman

Moscow

118

48

120

46 30’

EXPLANATION

County boundary

Monitoring or 

domestic well

Public supply well

Subunit boundary

Without

detection Withdetection

Samples from 255 wells in the Central Columbia Plateau were analyzed 

for 145 pesticides and volatile organic 

compounds (figs. 18, 20). Volatile 

organic compounds (VOCs) are used 

as solvents or metal degreasers and as 

pesticides (as inert ingredients or 

active ingredients to kill nematodes, 

insects, bacteria, or rodents). There 

were 24 pesticides and 15 VOCs 

detected; concentrations were mostly 

well below drinking water standards, 

ranging from the method detection 

limit (as low as 0.001 microgram per 

liter) to a maximum of 7.3 micrograms 

per liter for 1,2-dichloropropane (see 

p. 26). The significance of such low 

concentrations in drinking water is not 

clear; and in addition, no drinking 

water standards or guidelines have 

been established for 40 percent of the 

pesticides or VOCs analyzed. In the 

Quincy-Pasco subunit, four of the 

commonly used pesticides (herbicides

or insecticides) were detected in 

ground water [19, 20]. In the Palouse 

subunit, none of the commonly used 

pesticides were detected in ground 

water [21].

Only discontinued 

compounds exceed 

drinking water standards 

Only concentrations of 1,2-dichloropropane in one well and 1,2-dibromoethane (EDB) in two wells exceed 

the MCL. Both of these compounds 

are VOCs used as soil fumigants that 

were phased out in the late 1970s and 

1980s, respectively. Herbicides, 

though applied in greater amounts and 

detected more frequently than other 

types of pesticides, were not detected 

at concentrations that exceed MCLs. 

Most of the newer pesticides break 

down more rapidly and thus are less 

persistent in the environment than the 

discontinued ones; they were not 

detected at concentrations above 

drinking water standards or guidelines 

[19, 20, 45].

Most drinking water is from 

deeper wells, which are 

somewhat less susceptible

to contamination

Shallower wells have a greater number and percentage of pesticide detections [44]. Most people in the Central 

Columbia Plateau drink water from 

public supply wells (fig. 5), which are 

generally deeper than domestic wells 

(and deeper than this study’s monitoring wells), and therefore contain water 

that is less susceptible to contamination. However, similar pesticides at 

similar concentrations have been 

detected in public supply wells, shallow domestic wells, and very shallow 

monitoring wells (fig. 20), indicating 

that some contamination does reach 

deeper wells. This could be due to 

faulty well construction, high pumpage 

rates, or local ground-water pathways 

(relatively common in fractured basalt 

aquifers) that allow water to move 

quickly to greater depths. 

Samples from five public supply 

wells contained only p,p′-DDE, a 

breakdown product of DDT, which 

was discontinued for sale in the 

United States in the early 1970s. More 

modern pesticides were not detected, 

suggesting that these deeper wells are 

probably withdrawing older ground 

water that predates the use of newer 

pesticides.

Low concentrations of pesticides 

and VOCs were detected in 60 percent 

of samples from 117 shallow domestic 

and monitoring wells and in 46 percent 

of samples from 138 deeper public supply wells. Modern pesticides may get 

to shallow ground water before they 

have had time to break down; therefore, shallow wells tend to have a 

higher rate of detections. Thirty-one 

pesticides and VOCs were detected in 

samples from shallow domestic and 

monitoring wells, whereas 18 pesticides and VOCs were detected in samples from public supply wells.

Figure 19. Shallow wells have a 

greater number and percentage of 

pesticide detections.

0

10

20

30

40

50

60

70

100

90

80

0-25

25-50

50-100

>200

100-200

0

1

2

3

4

Well depth, in feet

Percentage of wells

with pesticide detections

Average number of pesticide

detections per well

Percentage

Number

MAJOR ISSUES AND FINDINGS -

PESTICIDES AND RADON IN GROUND WATER
U.S. Geological Survey Circular 1144 11

Radon, a naturally occurring, 

radioactive decay product of radium, 

is a water-soluble gas from bedrock 

that emits high-energy alpha particles that can damage lung tissue. 

The primary health risk from radon 

and its decay products appears to be 

from inhalation of the gas, although 

there is an increased health risk from 

drinking water with high concentrations of radon. Dissolved radon is 

easily released into the air when 

water is used for showering and 

other purposes. In 151 ground-water 

samples, radon concentrations 

ranged from 110 to 4,100 picocuries 

per liter (pCi/L); the median concentration was 530 pCi/L, similar to the 

median in many parts of the United 

States (p. 23).

Monitoring

well

Domestic

well

Public supply

well

Irrigation canal

Wasteway / drain

Older ground water

Younger ground water

Sprinkler irrigation fields

Water table

Multiple pesticides were detected in 

some wells, especially shallow wells

Of samples with detections, 66 percent contained more than one pesticide. Generally, the highest frequency 

of multiple detections occurred in samples from very shallow monitoring 

wells (fig. 21). Current drinking 

water standards or guidelines are 

only for individual compounds; no 

standards or guidelines have been 

established for multiple pesticides in 

drinking water. Health effects of 

combinations of pesticides in drinking 

water are not clearly understood. 

Figure 22. Pesticide detections 

correlate with nitrate concentrations.

0-2.5

2.5-5

5-7.5

>10

7.5-10

0

10

20

30

40

50

60

70

100

90

80

Nitrate concentration, in milligrams per liter

Percentage of wells

with pesticide detections

Figure 21. Most detections of more than one pesticide occurred in 

samples from very shallow monitoring wells.

Percentage of well type

1 23456 7

0

5

10

15

20

25

Number of pesticides per well

Deeper public supply wells

Very shallow monitoring wells

Shallow domestic wells

Pesticides were frequently detected 

in wells with elevated nitrate 

Many chemicals, including nitrate 

and pesticides, can leach through the 

soil to ground water. Pesticides are 

present in more than one-half of wells 

in the plateau that contain elevated 

nitrate concentrations (above the “natural” or background level of 2-3 mg/L 

[12]). Indeed, the higher the nitrate 

concentration, the greater the percentage of wells with pesticides (fig. 22). 

Because of this consistent correlation, 

sampling for nitrate may be cost effective for identifying wells that may be 

at risk of pesticide contamination. 

Nitrate testing is far less expensive 

than pesticide testing, and the latter 

could then be targeted more carefully. 

Figure 20. Idealized cross section of groundwater system in the Quincy-Pasco subunit. 

Three types of wells were sampled for 

pesticides and VOCs: very shallow monitoring 

wells installed for sampling purposes near the 

water table, shallow domestic wells, and 

deeper public supply wells. Median depths of 

the wells were 36 feet, 119 feet, and 197 feet, 

respectively.
12 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Figure 25. Concentrations of six pesticides (mostly insecticides) in surface water sometimes exceed guidelines for the 

protection of aquatic life. No concentrations exceed existing drinking water standards (see p. 26).

Azinphos-methyl (Guthion) QP,NC 12%

Triallate (Far-go) P,NC 3%

Diazinon (several) P, QP

Pesticide (trade or

common name)

Detected

in

subunit *

(p. 10)

Chlorpyrifos (Lorsban) QP 4%

gamma-HCH (Lindane) P,NC

less than 1%

less than 1%

Parathion (several) QP

0.001 0.01 0.1 1 10 100 1,000

Concentration, in micrograms per liter (μg/L)

NC - North Central

P - Palouse

QP - Quincy/Pasco

*

less than 1%

Herbicide

Maximum contaminant

level or health advisory

Freshwaterchronic criterionPesticide

detection

Insecticides

Of 226 samples,

percentage

exceeding

criterion

Figure 24. In the Palouse subunit, concentrations of gammaHCH (Lindane) are highest during periods of storm runoff [2, 

22]; gamma-HCH is not applied to crops but is registered for 

use as a livestock spray and as a seed treatment.

Concentration of Lindane,

in micrograms per liter

Streamflow, in cubic feet per second

M A M J J A SO N DJ FM AM J

1993 1994

0.04

0

0.01

0.02

0.03

5,000

0

1,000

2,000

3,000

4,000

Palouse River

Pesticides were detected in 

streams all over the plateau

Thirty-one surface-water sites representing agricultural land use with different crops, irrigation methods, and other 

agricultural practices were sampled for 

pesticides. Pesticides were detected in 

samples from all sites except for Palouse River at Laird Park, a headwaters

site in a forested area (see map, p. 24). 

Pesticide detections are usually related 

to pesticide applications (fig. 23) but are 

also influenced by agricultural practices, such as the rate of application, the 

rate at which the pesticide breaks down 

in the soil and water, and the ability of 

the pesticide to dissolve and be transported by water (fig. 24).

Figure 23. In the Quincy-Pasco subunit, concentrations of 

pendimethalin are highest during or shortly after reported 

periods of application, April to June (shaded areas).

Concentration of pendimethalin,

in micrograms per liter

Streamflow, in cubic feet per second

400

0

100

200

300

0.20

0

0.05

0.10

0.15

M A MJ J A SO N DJ FM AM J

1993 1994

Streamflow

Compound detected

Compound not detected

Method detection limit (MDL)

EL68D Wasteway

Concentrations of some 

pesticides may be harmful 

to aquatic life

Many pesticides were detected in surface water at very low concentrations. 

Concentrations of six pesticides in one 

or more surface-water samples exceed 

freshwater-chronic criteria for the protection of aquatic life in some samples 

(fig. 25). No pesticide concentrations 

exceed drinking water standards (however, surface water is not a drinking 

water source in the Central Columbia 

Plateau).

MAJOR ISSUES AND FINDINGS -

PESTICIDES IN SURFACE WATER
U.S. Geological Survey Circular 1144 13

Some pesticides in surface 

water come from ground 

water

Like nitrate, soluble pesticides such 

as atrazine, metribuzin, and simazine 

can leach to ground water in the 

Quincy-Pasco subunit and later be 

transported to agricultural wasteways

[2, 20]. Atrazine present in EL68D 

Wasteway during base flow comes 

from ground-water discharges to the 

wasteway (fig. 26). 

Ground-water discharges make up a 

large percentage of the total load of 

some compounds transported by a 

wasteway. About 40 percent of the 

atrazine discharged annually by 

EL68D Wasteway enters via the 

ground water. For Crab Creek Lateral, 

the percentages for atrazine and other 

compounds are somewhat lower 

(table 3). 

In summer, the wasteways also 

carry unused irrigation water and runoff of excess irrigation water that contains additional pesticides from the 

fields.

Figure 27. Median concentrations of pesticides, nitrate, and chloride are similar in 

ground water, subsurface drains, and surface water sampled during base flow.

Deethylatrazine

Atrazine

Metribuzin

Simazine

Nitrate

Chloride

Concentration 

(nitrate and chloride in milligrams per liter, pesticides in micrograms per liter)

SW

DR

GW

SW

DR

GW

SW

DR

GW

SW

DR

GW

SW

DR

GW

SW

DR

GW

0.001 0.01 0.1 1 10 100 1,000

50th percentile of 

detections

Surface water sampled

during base flow

Subsurface drain

Ground water

SW

DR

GW

Sampling surface water 

monitors ground-water 

quality cost-effectively

Ground-water quality is highly variable, requiring many samples to detect 

trends; therefore, it may be advantageous to sample surface drains during 

winter to monitor trends in groundwater quality. Sampling discharges 

from subsurface field drains, which 

collect and drain ground water to prevent waterlogging of fields, may also 

be useful. Figure 27 shows median

concentrations of pesticides, nitrate, 

and chloride were similar (and usually 

not statistically different) among samples from monitoring wells, subsurface 

drains, and wasteways sampled during 

winter base flow. Concentrations in 

samples from wells usually varied the 

most because these samples represent 

only a small part of the aquifer. 

Because waters in wasteways and subsurface drains represent the largest 

ground-water volumes, concentrations 

in these samples usually varied the 

least; therefore, fewer samples are necessary for trend analysis. 

For examples using nitrate concentrations in wasteways to infer trends in 

nitrate in ground water, see page 9.

Table 3. Estimated contributions of 

ground-water discharges to annual 

load [N, Nitrogen; %, percent]

Compound EL68D

Wastewa

Crab 

Creek

Atrazine 40% 10%

Metribuzin 20% 10%

Simazine 10% 5%

N-total 65% 30%

Figure 26. Concentrations of atrazine, a soluble pesticide, do 

not decrease during base flow.

EL68D Wasteway

0.025

0.030

0

0.005

0.010

0.015

0.020

M A MJ J AS O ND J F MA M J

1993 1994

400

500

0

100

200

300

M J

Streamflow

Method detection limit (MDL)

Compound detected

Compound not detected

Reported period of

application to crops

Concentration of atrazine,

in micrograms per liter

Streamflow, in cubic feet per second

MAJOR ISSUES AND FINDINGS -

THE INFLUENCE OF GROUND WATER ON SURFACE-WATER QUALITY
14 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Figure 29. Concentrations of organochlorine compounds in streambed 

sediments sometimes exceed guidelines for the protection of aquatic life [24]. Concentration, in micrograms per kilogram, dry weight

0.1

10,000

1

10

100

1,000

Total

DDT

Heptachlor

epoxide

ChlordaneDDE Dieldrin Total

PCBs

Sample

Sample that exceeds guideline

Guideline

Minimum reporting level

gamma-HCH

(p,p’) (Lindane)

Erosion depletes cropland 

of fertile soil and nutrients

Over the last 100 years, about 40 

percent of the topsoil in the drylandfarming Palouse subunit has been lost 

because of erosion [23]. Most soil erosion in this region is caused by storm 

runoff. In the Quincy-Pasco subunit 

where irrigated farming predominates, 

most soil erosion is caused by runoff 

of excess irrigation water from cropland.

Erosion carries 

compounds like DDT into 

streams

Even though most organochlorine 

pesticides (DDT, for example) are no 

longer used, they break down slowly 

and are still present in the environment. Because they bind strongly to 

soils, they are carried with eroded soils 

into streams. The most persistent 

breakdown product of DDT, p,p′-

DDE, was found in all parts of the 

Study Unit except in the headwaters of 

the Palouse River Basin and upper 

Crab Creek (fig. 28). Concentrations 

of p,p′-DDE exceed guidelines for the 

protection of aquatic life [24] at 22 

percent of the sites sampled [25]. 

Other organochlorine pesticides found 

in streambed sediments at concentrations exceeding guidelines were heptachlor epoxide, dieldrin, and Lindane 

(fig. 29).

Figure 28. p,p′-DDE concentrations in streambed sediments commonly exceed 

the guideline for protection of aquatic life [24] in dryland farming areas.

Potholes

Reservoir

Moses

Lake

Banks

Lake

Columbia River

Pullman

Moscow

Pasco

Quincy

Palouse River

Lind Coulee

Upper Crab Creek

Snake River

Douglas Creek

Lower CrabCreek

0 20 40 mi

0 20 40 km

46 30’

48

120

118

EXPLANATION

Not detected

Detected below guideline

(6.75 μg/kg) 

Exceeds guideline 

(p,p’) -DDE detections

Polychlorinated biphenyls (PCBs) 

are organochlorine compounds that 

were detected only at sites sampled 

downstream from the cities of Moscow 

and Pullman in the Palouse subunit 

[25]. PCBs, which were widely used in 

electrical transformers, have not been 

manufactured in the United States 

since the 1970s because they are toxic 

and persistent in the environment.

Irrigation can increase 

erosion

Furrow irrigation causes more erosion than sprinkler or drip irrigation 

[26]. DDT is carried with eroded soils 

[27], and highest concentrations of 

DDT in streambed sediment and fish 

tissue were detected in watersheds 

with more furrow irrigation (fig. 30).

Figure 30. DDT concentrations in 

streambed sediment and fish increase 

as the percentage of furrow irrigation 

increases. 

Fraction of irrigated cropland in 

furrow irrigation, in percent

1

10

100

1,000

10,000

100,000

0 10 20 30 40 50 60 70 80 90 100

Streambed sediment

Fish tissue

Total DDT,

in micrograms per kilogram

MAJOR ISSUES AND FINDINGS -

SEDIMENT IN SURFACE WATER
U.S. Geological Survey Circular 1144 15

Figure 32. The average sediment load 

per unit volume of water discharged by 

the Palouse River has decreased 

(comparing 1993–96 with 1962–71 

data).

7.0

Water Year (October through September)

Average = 2.8 tons/acre-ft

Average =

1.4 tons/acre-ft

Sediment load / water discharge, in tons per acre-foot

0

1.0

2.0

3.0

4.0

5.0

6.0

8.0

9.0

10.0

11.0

1962

1963

1964

1965

1966

1967

19681969

1970

1971

1993

1994

1995

1996

Beginning in the 1970s, the use of 

sprinkler irrigation in the QuincyPasco subunit increased; with this 

change in irrigation method came 

reports of reduced erosion. A good 

indicator of the severity of erosion in a 

drainage basin is the concentration of 

suspended solids in streams. Figure 31 

shows the relation between irrigation 

method and average daily yields of 

suspended solids discharged by Lower 

Crab Creek to the Columbia River.

Figure 31. Average daily yields of 

suspended solids discharged by Lower 

Crab Creek to the Columbia River 

decreased from 1975 to 1988, 

coinciding with a decrease in the use of 

furrow irrigation [28, 29].

Data collected from 1993 to 1995 

also show the relation between irrigation method and erosion. For nine 

drainage basins sampled in 1994, average daily yields of suspended sediment

(which is collected and analyzed differently than suspended solids) ranged 

from 0.4 pound per acre from a basin 

with no furrow irrigation to about 20 

pounds per acre from a basin where 

about 60 percent of cropland is irrigated by the furrow method [28, 29].

Fraction of irrigated cropland in 

furrow irrigation, in percent

Yield of suspended solids, in pounds per acre per day

1975

1975

1976

19771978

1979

1980

1981

1982

1983

1984

1985

1987

1988

40 45 50 55 60 65 70 0.1

0.5

0.2

0.3

0.4 Average daily yield

for year indicated

Crab Creek near Beverly

Erosion may be decreasing in 

dryland farming areas

Studies by the U.S. Department of 

Agriculture indicate that improved 

farming practices that began in the 

1970s have reduced erosion of soil 

from cropland in the United States by 

up to 25 percent [30]. Field observations and studies indicate that a 

reduction in erosion of about the 

same magnitude has occurred in the 

Palouse subunit [31]. The decrease in 

suspended sediment discharged by 

the Palouse River may be indicative 

of less erosion (fig. 32). However, 

the average sediment concentration 

for the period from 1962 to 1971 is 

skewed by a very wet year (1963), 

which did not occur in 1993–96. 

Therefore, the difference between the 

two periods is probably exaggerated 

on the graph.

Trace elements are not elevated in streambed sediments

Because trace elements bind to sediments, and sediments accumulate on the 

streambed during low flows, analysis of streambed sediments is a good way to 

relate concentrations to the effects of land use. In the Central Columbia Plateau, 

streambed sediments are derived mostly from eroded soils. If the concentration 

of a trace element in streambed sediments is greater than the concentration in 

undisturbed soils, a source related to land use is probable. However, most trace 

element concentrations in streambed sediments were not commonly above concentrations in undisturbed soils of the Study Unit (fig. 33) [32].

Figure 33. Except for selenium, concentrations of trace elements in streambed 

sediments and soils were not commonly above concentrations in undisturbed 

soils in the Central Columbia Plateau. Trace element

Concentration, in micrograms per gram (parts per million)

Minimum and median values in soil

are less than 0.1; maximum value is 0.1

Minimum value in sediment is

less than 0.02; median value is 0.02

All concentrations

in soil were less than 2 

Zinc

Selenium

Nickel

Mercury

Lead

Copper

Chromium

Cadmium

Arsenic

0.01 0.1 1 10 100 1,000

Sediment concentration range

Median value

Soil concentration 

range
16 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Nutrient concentrations 

vary over time and space

Seasonal variations in concentrations of nutrients are influenced by 

land use and by natural and human 

factors that cause variations in streamflow. For example, in the QuincyPasco subunit, high streamflows are 

from April through October, coinciding with the delivery of large quantities of irrigation water withdrawn 

from the Columbia River. Excess irrigation water, which contains low concentrations of nitrate, discharging to 

wasteways and drains dilutes nitrate 

present at high concentrations in 

ground water discharging to surface 

waters (see p. 8). Therefore, concentrations in surface waters are lowest in 

summer when delivery of irrigation 

water is at a peak (fig. 34). 

Figure 34. Nitrate concentrations in the 

Quincy-Pasco subunit are lowest in 

summer and highest in winter when 

irrigation water is not being delivered.

200

0

100

Daily average streamflow,

in cubic feet per second

15

0

5

10

Nitrate as nitrogen,

in milligrams per liter

Nitrate

concentration

Sand Hollow Wasteway

Streamflow

ON D J FM A MJ J A S

1993 1994

Figure 36. Inorganic nitrogen concentrations vary widely in streams in the dryland and irrigated agricultural 

and urban land use areas. In contrast, phosphorus concentrations are less variable throughout the year 

except at the urban land use sites, which are downstream from wastewater-treatment plant discharge to the 

South Fork of the Palouse River. (Each bar represents an annual range of concentrations at one site within 

that land use.)

0

2

4

6

8

10

12

14

Land Use

Inorganic nitrogen,

in milligrams per liter

FOR DLF URB IRG DLF/SP DLF/SP

0

0.5

1

1.5

2

2.5

3

Land Use

Phosphorus,

in milligrams per liter

FOR DLF URB IRG

FOR: forest

DLF: dryland farming

URB: urban

DLF/SP: dryland 

farming/desert spring

IRG: irrigated land use

In the Palouse subunit, concentrations of nitrate in surface waters are 

highest during winter when storm runoff transports nitrogen from fields to 

streams (fig. 35). Lower concentrations of nitrate in surface waters during 

the summer are caused by lower nitrate 

concentrations in ground water discharging to streams and uptake by 

plants.

Figure 35. Nitrate concentrations in the 

Palouse subunit are highest in winter 

because of fall fertilizer applications 

and storm runoff.

As shown in figure 36, annual variation of inorganic nitrogen and phosphorus concentrations is related to land 

use. Phosphorus concentrations are 

generally less variable than nitrogen 

concentrations and are also generally 

lower in agricultural streams because 

phosphorus is applied to crops at a 

much lower rate and it binds with soil 

particles, thereby reducing its transport 

to surface waters.

1,000

0

500

3

0

1

2

Nitrate

concentration

Palouse River at Hooper

Streamflow

Daily average streamflow,

in cubic feet per second

Nitrate as nitrogen,

in milligrams per liter

O N DJ FM AM J J A S

1993 1994

Concentrations of 

nutrients have increased 

in streams

Nutrients are an important indicator 

of surface water quality because inorganic nitrogen (nitrate and ammonia) 

and phosphorus control the growth of 

aquatic plants (p. 18). Excessive 

growth of aquatic plants can cause 

dissolved oxygen concentrations in 

streams to decrease during the night to 

levels that may not sustain certain species of fish. 

In streams of the Central Columbia 

Plateau, naturally occurring levels of 

these essential nutrients have been 

increased as a result of land use practices. Inorganic nitrogen, which is 

water soluble, enters surface waters 

directly in runoff from agricultural 

fields treated with fertilizer, or indirectly via ground water. Phosphorus, 

also used as a fertilizer, is relatively 

insoluble and binds to soil particles, 

entering surface waters as a result of 

erosion. Nutrients also enter surface 

waters from feedlots and wastewatertreatment plants, either through runoff 

or via ground water in the case of landapplied waste.

Understanding the distribution of 

nutrients in surface waters permits 

managers to better identify best management practices (BMPs) that can 

improve water quality. 

MAJOR ISSUES AND FINDINGS -

NUTRIENTS IN SURFACE WATER
U.S. Geological Survey Circular 1144 17

8

0

2

4

6

Nitrate as nitrogen,

in milligrams per liter

180 100 60 20 140 0

Distance, in river miles from 

the mouth of the Palouse River

Palouse River

South Fork 

Location of 

wastewater 

treatment plant

(a)

Figure 38. Summertime 

concentrations of (a) nitrogen and (b) 

phosphorus in the South Fork of the 

Palouse River (sampled August 1994) 

are elevated above levels at other sites 

on the river.

(b)

0

3.0

0.5

1.0

1.5

2.0

2.5

Distance, in river miles from 

the mouth of the Palouse River

Orthophosphate as phosphorus,

in milligrams per liter

180 100 60 20 140 0

Nitrate trends are tied to 

land use

Concentrations of nitrate in the Palouse River have not changed significantly since 1965, which reflects the 

consistent land use (dryland agriculture) over time [33].

Figure 39. Nitrate trends in Palouse 

River at Hooper, Palouse subunit.

Nitrate has increased in Crab Creek 

because the acreage of irrigated land 

and therefore fertilizer application has 

increased.

Figure 40. Nitrate trends in Crab Creek 

at Beverly, Quincy-Pasco subunit.

Nitrate in Crab Creek Lateral has 

decreased, probably because of an 

increase in acreage of orchards, which 

require less fertilizer than row crops.

Figure 41. Nitrate trends in Crab Creek 

Lateral, Quincy-Pasco subunit. Nitrate as nitrogen, in milligrams per liter 14

0

2

-2

4

6

8

10

12

1965 1970 1975 1980 1985 1990

Nitrate as nitrogen,

in milligrams per liter 14

0

2

-2

4

6

8

10

12

1965 1970 1975 1980 1985 1990

Nitrate as nitrogen,

in milligrams per liter 14

0

2

-2

4

6

8

10

12

1965 1970 1975 1980 1985 1990

Figure 37. Sites with the highest summertime concentrations of inorganic nitrogen 

are in the South Fork of the Palouse River, which is dominated by wastewater 

discharge, and several streams in the Quincy-Pasco subunit [33].

48

118

46 30’

120

0 20 40 mi

0 20 40 km

0.1 - 1.2 (25th - 50th percentile)

EXPLANATION

3.1 - 12.0 (greater than 75th percentile)

Inorganic nitrogen, in milligrams per liter

1.6 - 2.9 (50th - 75th percentile)

non-detect - 0.1 (less than 25th percentile)

South Fork

Palouse River

Concentrations of nitrogen are most 

critical to aquatic life during the summer when aquatic plant growth is highest. Sites with the highest summertime 

concentrations include the wastewaterdominated South Fork of the Palouse 

River in the Palouse subunit and several irrigated streams in the QuincyPasco subunit (fig. 37) [33].

Wastewater is a significant point 

source of nutrients in the Palouse 

River

Discharge of treated wastewater 

during summer low flow elevates concentrations of nitrogen and phosphorus, resulting in eutrophication of the 

South Fork of the Palouse River 

(fig. 38). During the summer, plants in 

the South Fork increase to excessive 

amounts. Nitrogen is reduced in the 

lower river because of uptake by these 

aquatic plants whereas phosphorus 

concentrations are greater than what is 

required by plants, so concentrations in 

water remain high. The high phosphorus can be due to low oxygen conditions during the summer, which cause 

sediments to release phosphorus. 
18 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

This eutrophication cycle has 

occurred in the wastewater-dominated 

South Fork of the Palouse River 

(fig. 38). This overgrowth resulted in 

dissolved oxygen concentrations 

decreasing below the level (5 mg/L) 

required for many fish species 

(fig. 42) [34].

Figure 42. Dissolved oxygen 

concentrations decreased at night at 

three sites on the Palouse River; the 

decrease was greatest in the 

wastewater-dominated stream.

Oxygen also decreased in the dryland streams, but the decrease was less 

severe: the dryland reach has less plant 

growth than the wastewater-dominated 

reach. The Palouse River at Hooper, a 

site affected by a combination of both 

dryland farming and urban land uses, 

had dissolved oxygen concentrations 

that remained at or above the 5 mg/L 

level for sustaining fish. 

18

0

2

4

6

8

10

12

14

16

0800 1600 2400 0800 1600

Wastewater-dominated stream

Dryland-dominated stream

Mixed stream

Dissolved oxygen,

in milligrams per liter

Time of day

Range of saturation during 

the study

Minimum level

required to sustain

fish

Land use influences the 

chemical and physical 

characteristics of streams

Land use influences both the chemical and physical characteristics of 

streams, thereby affecting aquatic life. 

Assessing the relative importance of 

potential impacts to streams helps 

water resource managers allocate 

resources to better protect and manage 

streams. Most impacts on streams in 

the Central Columbia Plateau result 

from agricultural practices such as fertilizer and pesticide application and 

sediment from agricultural runoff. 

While grazing was more pervasive historically, it still occurs in localized 

areas and therefore influences riparian

and instream habitat, especially in the 

North-Central subunit. The dominant 

impact from urban land use is point 

source discharge of nutrient-rich, 

treated wastewater from wastewatertreatment plants; however, urban 

impacts are overall less significant 

than agricultural impacts. Biological 

communities, including fish, that presently reside in streams of the Central 

Columbia Plateau are influenced by 

cumulative impacts from all these land 

use activities and are therefore influenced by three of the dominant water 

resource issues: eutrophication from 

excessive nutrient inputs, physical 

habitat alteration, and pesticides. 

Eutrophication of many streams has 

increased

Eutrophication is a natural process 

which can be accelerated by human 

activities that increase inputs of nutrients, primarily nitrogen and phosphorus, to surface waters, thereby causing 

excessive growth of aquatic plants. 

This overgrowth causes a wide swing 

in oxygen concentrations over a 24-

hour period; because of respiration and 

decay night-time oxygen can decrease 

to levels that will not sustain some 

aquatic life. Aquatic plant growth also 

alters physical habitat by slowing the 

flow of water and reducing sunlight 

penetration.

Concentrations of nitrogen during 

the growing season were highest in the 

irrigated and urban land use and lowest 

in the forest and dryland farming/spring sites (fig. 36). The dryland 

sites were intermediate in nitrogen 

concentrations. 

Algae are indicators of water 

quality

Understanding the relation between 

algae and nutrients is important for the 

development of integrated water- quality assessment and monitoring programs. Along with influencing 

dissolved oxygen in surface waters, 

individual species of algae respond to 

specific nutrient conditions and therefore serve as indicators of water quality. Indicator species can be either 

positively or negatively correlated 

with nutrient concentrations.

In streams where nutrient concentrations are low, such as in the forested 

land use, nutrient-poor species dominated (fig. 43); because these algae fix 

their own nitrogen, high nutrient levels 

need not be present in their environment. A dominance of nutrient-rich 

algae, as documented in the urban land 

use stream that has high inputs of 

nutrients during summer, indicates a 

high concentration of nutrients.

Figure 43. Algal communities in the forested land 

use streams (FOR) were dominated by nutrient-poor 

species, most of which were blue-green algae, while 

the urban stream (URB) was dominated by nutrientrich species. Communities varied in streams in the 

dryland and irrigated land uses (DLF, DLF/SP, and 

IRG), but nutrient-rich species dominated. 

(Percentages do not add up to 100 because many 

FOR URB DLF DLF/SP IRG

Land Use

Percentage of species

Nutrient-poor algae

Nutrient-rich algae

50

40

30

20

10

0

MAJOR ISSUES AND FINDINGS -

THE INFLUENCE OF LAND USE ON AQUATIC LIFE
U.S. Geological Survey Circular 1144 19

Columbia Basin Irrigation Project had 

reduced concentrations of an important 

nervous system enzyme in their brains 

[37]. Organophosphate pesticides, 

which are used in the Central Columbia 

Plateau and were detected, are known to 

cause this effect. While the implications 

for sportfish are unclear, this finding 

indicates that modern pesticides may 

have a negative influence on some fish 

species. 

Fish communities have 

been altered

Fish communities reflect cumulative 

effects of land use activities. Streams in 

the Palouse subunit, which once contained rainbow trout, are presently dominated by minnows (fig. 45). These 

streams have been impacted by elevated 

stream temperatures, extensive soil erosion from both agricultural runoff and 

bank destabilization, and reduced oxygen levels caused by eutrophication. The 

spring-fed Crab Creek in the North-Central subunit is able to sustain rainbow 

trout, likely due to cooler water temperatures and better water quality. Fish 

communities in the irrigated QuincyPasco subunit vary because of the diversity of stream conditions. Even with little riparian shading, stream temperatures 

remain low as a result of the input of 

cold irrigation water from the Columbia 

River. Furthermore, fish communities in 

the irrigation streams may be influenced 

by lakes downstream. Pesticides may 

also have an effect on fish species 

(p. 12, 14).

algal species are not correlated with 

nutrient concentrations.) 

Physical habitat has been altered

In the Central Columbia Plateau, 

agriculture, grazing, and urban practices have singly, or in combination, 

impaired the riparian vegetation and 

bank stability, and have increased sediment erosion (p. 14), thereby affecting 

instream habitat. 

Historically, much of the land in the 

Central Columbia Plateau was dominated by grasslands with an established riparian community, which 

maintained cooler water temperatures, 

provided food and cover for fish, and 

stabilized stream banks. Vegetated 

banks commonly have less bank erosion [35]. Current conditions, however, are greatly altered. Most streams 

lack a riparian community; average 

canopy cover is less than 20 percent, 

with most of this in isolated reaches. 

There is also substantial bank erosion 

(about 70 percent), which may be partially due to the reduction of riparian 

vegetation and agricultural practices 

[35].

Lack of a riparian community 

results in higher water temperatures 

(fig. 44); temperatures in urban and 

dryland streams in the Palouse subunit 

exceed levels that protect aquatic life 

(22 degrees Celsius) [34]. These 

higher temperatures may partially 

explain the lack of rainbow trout, 

which were historically present [36]. 

Figure 44. Stream temperature 

ranges in August 1994 and 1995 

show that temperatures in urban 

(URB) and dryland (DLF) streams in 

the Palouse subunit exceed levels for 

protection of aquatic life (22 

degrees Celsius).

Pesticides may be a 

concern for aquatic life

Organochlorine pesticides, most 

of which are banned in the U.S., are 

stored in streambed sediment and 

fatty tissue in fish. Some of these 

compounds were found at concentrations that may be detrimental to 

aquatic life. This is particularly true 

for p,p′-DDE in streambed sediments 

(p. 14) and fish tissue [25, 27].

Modern pesticides are more watersoluble and therefore less prone to be 

stored in sediment or accumulate in 

fish tissue. Concentrations in surface 

waters only occasionally exceed 

freshwater-chronic criteria (see 

p. 12, 26). However, regardless of 

criteria, these pesticides may influence aquatic life. For example, carp 

collected from Royal Lake within the 

URB

DLF

0

5

10

15

20

25

30

35

FORDLF/

SP

IRG

Land Use (see fig. 45)

Stream temperature,

in degrees Celsius

Maximum temperature

for the protection 

of aquatic life

Figure 45. Composition of fish communities in various land uses. Minnows and sculpin are the dominant 

species. 

minnows suckers

South Fork Palouse River (URB)

minnows

Pine Creek (DLF)

suckers

minnows

sculpin suckers

other

Palouse River at Hooper (DLF)

minnows

sculpin

suckers

trout

Crab Creek at Marcellus (DLF/SP)

minnows

sculpin

trout

other

Lind Coulee Wasteway (IRG)

sculpin

Sand Hollow Wasteway (IRG)

EXPLANATION

Land use types

Nonirrigated

agriculture

Surface-waterirrigated agriculture

Ground-waterirrigated agriculture

Barren or rangeland

Forest

URB urban

DLF dryland farming

DLF/ dryland farming/desert

SP spring

IRG irrigated farming
20 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

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)

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. 

Comparison of Stream Quality in the Central Columbia Plateau with Nationwide NAWQA 

Findings

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

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

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

sites that had adequate data. Scores for each site in the Central Columbia Plateau 

were compared with scores for all sites sampled in the 20 NAWQA Study Units during 1992–95 (see map at left). 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 in reference 38.)

Many pesticides (12–45) were detected at four sites; the 

detection frequency at one of the sites is in the upper 25 

percent of NAWQA sites. The two sites with the highest 

detection frequencies are in the Quincy-Pasco subunit, 

where irrigation and high chemical use combine to increase transport of pesticides to surface waters. Pesticide 

detection frequencies at sites in the dryland farming areas of the North-Central and Palouse subunits are below 

the national median for NAWQA sites. All of the sites 

had at least one pesticide concentration that exceeded a 

water-quality standard or guideline. 

NUTRIENTS in water

ORGANOCHLORINE PESTICIDES and PCBs in 

bed sediment and biological tissue

PESTICIDES in water

Yellow areas indicate other NAWQA 

Study Units sampled during 1992–95.

Central Columbia Plateau Study Unit

Concentrations of 

organochlorine 

pesticides and 

PCBs are higher 

than the national 

median (50th percentile) at 7 of 11 

sites, with 4 sites 

in the upper 25 

percent of all 

NAWQA sites. 

Elevated concentrations were observed in dryland farming areas as well as in irrigated areas. One 

or more environmental guidelines were exceeded at one of the sites 

in the Palouse River basin that is affected by urban wastewater as 

well as at Lind Coulee. Although most of these compounds have 

been banned, they still persist in the environment. 

Nutrient levels are greater than 

the national median at all but 

one site, with 5 of 13 sites in the 

upper 25 percent of NAWQA 

sites. Elevated nutrient concentrations, primarily caused by 

fertilizer application on fields 

upstream of most sites and municipal wastewater at a few 

sites, are causing eutrophication. Effects of eutrophication 

include reduced dissolved oxygen, which can adversely affect 

fish, and nuisance growth of 

aquatic plants. 
U.S. Geological Survey Circular 1144 21

All 16 sites for which stream habitat degradation was evaluated in the Central Columbia Plateau showed some signs of habitat degradation; 44 percent are in the upper 25 percent. Streams in this Study Unit area have an 

average of only 20 percent canopy cover, with most having far less. The 

loss of riparian vegetation, combined with other land use practices, has resulted in streams having an average of 70 percent bank erosion. These factors, combined with high nutrient and sediment loading, have resulted in 

the majority of streams in this Study Unit having habitat conditions that are 

unsuitable for many native species. 

CONCLUSIONS

In the Central Columbia Plateau, 

compared to other NAWQA Study 

Units:

• High levels of nutrients, primarily 

from fertilizer, are causing 

eutrophication.

• Levels of pesticides in water and 

organochlorine compounds in bed 

sediment and fish tissue are relatively high: at all four sites where 

pesticides in water were measured 

over one year, a median concentration exceeded a freshwater-chronic 

criterion in at least one month; at 2 

of 11 bed sediment sites, one or 

more organochlorine compounds 

exceeded an aquatic-life guideline.

• Habitat degradation is relatively high: 

seven of sixteen sites are in the 

upper 25th percentile, mainly 

because of reduced canopy cover 

and increased bank erosion.

• Fish community degradation is moderate.

• Levels of trace elements and semivolatile organic compounds in bed 

sediment are relatively low.

TRACE ELEMENTS in bed sediment

SEMIVOLATILE ORGANIC COMPOUNDS in bed 

sediment

STREAM HABITAT DEGRADATION

FISH COMMUNITY DEGRADATION

Fish community degradation in the Central Columbia Plateau varies 

across the national range. Fish communities can be influenced by multiple factors, including pesticides, increased aquatic plant growth due 

to nutrients, reduced riparian habitat, and sediment runoff from agricultural practices. The two sites with the most impacted fish communities were a wastewater-dominated urban stream and a large dryland 

farming stream. Small dryland streams associated with spring systems 

contained the most trout. 

At 7 of 11 sites, concentrations of semivolatile organic compounds are 

lower than the national 

median. Three of four sites 

in the Palouse River drainage basin have levels in the 

lowest 25 percent of 

NAWQA sites. At Crab 

Creek near Beverly in the 

Quincy-Pasco subunit, levels are in the upper 25 percent of NAWQA sites. 

Trace elements, such as the 

metals lead and chromium, 

are low in the Central Columbia Plateau compared 

to other NAWQA Study 

Units because of the minimal influence of mining 

and urban sources and the 

low natural background 

concentrations in soils. All 

sites have trace element 

levels below the national 

median for NAWQA sites. 
22 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Median nitrate concentrations in deeper public 

supply wells are below 

the national median 

(50th percentile) for 

NAWQA drinking water 

sites. Shallow ground 

water associated with 

agricultural land use 

(wheat, orchards, and 

potatoes) have median 

nitrate concentrations 

NITRATE

Pasco

Pullman

ps

w

p

o

that are in the upper 25 percent of NAWQA study median values. In the Central Columbia Plateau, high nitrate concentrations are due primarily to high 

rates of fertilizer application. Grazing and application of food processingplant wastes are lesser influences.

PESTICIDES

Pasco

Pullman

ps

w

p

o

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)

Wheat and small grains (w) 

(domestic wells)

(For detailed land use map, see p. 4)

EXPLANATION

Public supply wells (ps) were sampled 

across the entire Study Unit - see p. 24

Shallow wells were sampled in:

Potatoes and corn (p)

(domestic and very shallow monitoring wells)

Orchards (o)

(domestic and very shallow monitoring wells)

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 drinking-water 

standards or criteria were exceeded in at 

least one well.

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

NAWQA Study Unit. Ground-water resources were divided into two categories: (1) 

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

areas. Summary scores were computed for each characteristic for all aquifers and shallow ground-water areas that had adequate data. Scores for each aquifer and shallow 

ground-water area in the Central Columbia Plateau were compared with scores for all 

aquifers and shallow ground-water areas sampled in the 20 NAWQA Study Units during 

1992–95 (see map at left). 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 are also compared to 

established drinking-water standards and criteria for protection of human health. (Methods used to compute rankings and evaluate standards and criteria are described in 

reference 38.)

ated with orchards. The lowest pesticide detection frequency in shallow 

ground water was in the Palouse subunit, where wheat is the dominant crop.

Yellow areas indicate other NAWQA 

Study Units sampled during 1992–95.

Central Columbia Plateau Study Unit

Comparison of Ground-Water Quality in the Central Columbia Plateau with Nationwide 

NAWQA Findings

At three of four sites, 

pesticide detection frequencies in ground water 

were greater than the national median. Detection 

frequencies varied in 

shallow wells depending 

on the land use. Pesticide 

detections associated 

with potatoes are above 

the national median, but 

lower than those associ-
U.S. Geological Survey Circular 1144 23

VOLATILE ORGANIC COMPOUNDS 

Pasco

Pullman

ps

w

p

o

Radon, a decay product of radium, occurs naturally in soils (see p. 11). Radon concentrations in 

public supply wells and potato land use wells are 

below the national median for NAWQA sites. 

Wells associated with orchards in the QuincyPasco subunit and dryland wheat in the Palouse 

subunit exceed the national median. 

Dissolved solids in the public supply wells and in 

the more shallow, dryland farming Palouse subunit 

wells are below the national median for NAWQA 

sites. In contrast, dissolved-solids concentrations 

are greater than the national medians for both potatoes and orchards, with orchards in the upper 25 

percent of NAWQA sites. The higher levels in the 

Quincy-Pasco subunit reflect the influence of irrigation water. 

CONCLUSIONS

In the Central Columbia Plateau, compared to other NAWQA Study Units:

• Nitrate concentrations in ground water 

are high, with more than 20 percent of 

the wells exceeding the drinking water 

standard.

• Pesticides, though frequently detected, 

are generally at concentrations less than 

10 percent of drinking water standards. 

However, pesticide-related health risks 

are difficult to assess because standards 

do not exist for about 40 percent of the 

pesticides analyzed, or for combinations of pesticides.

Concentrations of volatile organic compounds (VOCs) in 

both public supply wells and the more shallow land use 

wells are generally higher than the national median. The 

high application rate of fumigants on potatoes may explain 

the high concentrations of VOCs in the irrigated QuincyPasco subunit. Concentrations of several compounds (primarily older, discontinued fumigants) exceed water-quality 

standards or guidelines in land use wells in the Quincy-Pasco subunit.

DISSOLVED SOLIDS

Pasco

Pullman

ps

w

p

o

RADON

Pasco

Pullman

ps

w

p

o
24 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

Basic sites

Intensive sites - 1 year of pesticide 

sampling

Pesticides (4-5 samples)

Pesticides (1 sample) -The number 

represents the number of sites 

sampled at that location

EXPLANATION

(4)

(4)

(3) (4)

46 30’

120

48

118

0 20 40 mi

0 20 40 km

Crab Creek at Marcellus Road

near Ritzville, Wash.

Lind Coulee below SR 17

near Warden, Wash.

Pine Creek at

Pine City, Wash.

Palouse River at Laird Park

near Harvard, Idaho

South Fork Palouse River

at Colfax, Wash.

Palouse River

at Hooper, Wash.

Sand Hollow Wasteway at 

S. SW Road near Vantage, Wash. 

Crab Creek

near Beverly, Wash.

EL68D Wasteway

near Othello, Wash.

Crab Creek Lateral

near Othello, Wash.

EXPLANATION

Synoptic studies

Intensive assessments

Tissue

Sediment

Nonirrigated agriculture

Surface-water-irrigated 

agriculture

Ground-water-irrigated 

agriculture

Forest

Barren or rangeland

Public supply wells

Flow-path well site

Irrigated row crops

Orchards

Dryland farming 

Shallow wells under

EXPLANATION

STUDY DESIGN AND DATA COLLECTION

Stream Chemistry

The primary objective of the 

stream chemistry component 

was to assess the relationship 

between land use and chemical 

constituents of surface water. 

Surface-water sites were distributed among major land uses 

within each subunit; site types 

included basic, intensive, and 

synoptic sites.

Stream Ecology

The primary objective of the 

stream ecology component was to 

assess surface-water quality by integrating the physical, chemical, and 

biological factors. Ecology sites 

were distributed among the four 

dominant land uses: forest, urban, 

dryland, and irrigated farming. The 

number of sites per land use 

depended on the percentage of the 

land use within the Study Unit. Sites 

were classified as either intensive or 

synoptic on the basis of the level of 

the sampling effort or the number of 

years data were collected.

Ground-Water 

Chemistry

The primary objective of the 

ground-water chemistry component was to determine if the 

chemical constituents of ground 

water were related to specific 

land uses such as irrigated, 

orchard, and dryland agricultural 

farming. A survey of public supply wells across the Study Unit 

was also completed. Samples 

were also collected along a short 

ground-water flow path at a site 

near Pullman, Washington.
U.S. Geological Survey Circular 1144 25

Table 4. Summary of data collection in the Central Columbia Plateau Study Unit, 1992–95, see [39] for NAWQA data design 

framework.

Study

component What data were collected and why Types of sites sampled Number

of sites

Sampling frequency 

and period

Stream Chemistry

Basic sites— 

general water 

chemistry

Concentrations, seasonal variation, and annual loads. Data 

included streamflow, nutrients, major ions, organic carbon, 

suspended sediment, water temperature, specific conductance, alkalinity, pH, and dissolved oxygen.

Basic Fixed Sites: representative 

of common land use mixes, as 

well as basin outflow sites

14 Monthly plus storms:

Quincy-Pasco subunit for 

1 year

Palouse subunit, 2–3 

years

Intensive sites—

pesticides

Concentrations and seasonal variations in pesticides. Data 

included 85 dissolved pesticides plus above constituents. 

Subset of basic sites: where land 

use was most homogeneous

4 Weekly to monthly: 

Feb. 1993–Mar. 1994

Synoptic sites— 

water chemistry

Spatial distribution of pesticides and nutrients. Data included 85 

dissolved pesticides plus same constituents as basic sites. 

Basic sites 

Other sites plus reference sites

11 

27

4 times in spring and 

once in summer, 1994

Once in spring, 1994

Contaminants in 

bed sediments

 Occurrence and distribution of contaminants in bed sediment. 

Data included total PCBs, 32 organochlorine pesticides, 63 

semivolatile organic compounds, and 44 trace elements.

Depositional zones of most stream 

sites sampled in other components of study

23 Once, mostly in 1992–93

Contaminants in 

fish and benthic 

invertebrates 

Occurrence and distribution of contaminants in biota. Data 

included total PCBs, 30 organochlorine pesticides in clams 

and whole fish; 24 trace elements in clam tissue, fish livers, 

and caddisflies. 

 Most stream sites sampled in 

other components of study 

where tissue could be collected

17 Once in either 1992 or 

1994

Stream Ecology

Intensive assessmentsRelationship between biological communities and water chemistry, physical habitat, and land use. Includes spatial relationships, along with spatial and temporal variation. Data 

included algae, invertebrates, and fish communities; physical 

habitat all years; nutrients and other constituents in 1993. 

Basic Fixed Sites 10 total

4

5

3

1 reach - 1 year (1993)

1 reach - 3 years(1993–95)

3 reaches -1 year (1994 

or 1995)

Synoptic studies Sites permitted a better spatial and temporal assessment. Data 

collected were same as above except fish communities were 

not sampled. 

Synoptic sites 14 total

11

 3

1 reach - 1 year (1993)

1 reach - 3 years (1993–

95)

Ground-Water Chemistry

Aquifer survey— 

public supply 

wells

 Occurrence and distribution of chemicals in public supply 

wells. Data included major ions, nutrients, 85 pesticides, 60 

volatile organic compounds, dissolved organic carbon, 

and radon.

Estimate risks of pesticide detection. Data included 47 pesticides only.

Public supply wells across Study 

Unit

Public supply wells across Study 

Unit

43

78

Once in 1994

Once in 1994

Land-use 

effects— irrigated row crops

Describe the effects of agricultural land use on shallow ground 

water in the Quincy-Pasco subunit. Data included major ions, 

nutrients, 85 pesticides, 60 volatile organic compounds, dissolved organic carbon, and radon.

Shallow domestic wells

Very shallow monitoring wells

Wells were generally within 100 

feet of row cropped fields

30

19

Once in 1993–95

Land-use 

effects—

orchards

Describe the effects of agricultural land use on shallow ground 

water in the Quincy-Pasco subunit. Data were same as above. 

Shallow domestic wells

Very shallow monitoring wells

Wells were generally within 100 

feet of orchards

18

22

Once in 1994–95

Land-use 

effects—

dryland farming 

(grains) 

Describe effects of agricultural land use on shallow ground 

water in the Palouse subunit. Data were same as row crops 

and orchards above. 

Shallow domestic wells in basalt

Very shallow monitoring wells in 

loess

Wells were generally next to fields 

in the road right-of-way

19

 8

Once in 1993–94

Variation along

flow paths

Describe the processes controlling the fate of nitrogen and pesticides along a 1/4-mile flow path to an intermittent stream. 

Data included major ions, nutrients, 85 pesticides, 60 volatile 

organic compounds, dissolved organic carbon, radon, and 

age-dating constituents.

Cluster of eight wells at various 

depths along an approximate 

line of ground-water flow

Palouse loess near Pullman, Wash.

1 site: 

8 wells

Twice in 1994

Special Studies

Palouse River 

nutrient processes

Processes affecting eutrophication in stream channels below 

wastewater-treatment plants. Data included algae biomass 

and nutrients, dissolved oxygen, and 24-hour temperature.

Palouse River 19

 5

6-week colonization, 1994

3- to 6-hour intervals for 

one day in Aug. 1994

Pesticides from 

ground water at 

base flow

47 more-soluble pesticides and nutrients to compare nutrient 

concentrations and pesticide occurrence with what is found 

in shallow ground water.

Smaller irrigation drains and subsurface tile-drain outflows to 

surface drains

 4

 6

Once in winter 1995

Once in winter 1996
26 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992-95

Alachlor (Lasso) 21%

1%

2,6-Diethylaniline

(Alachlor metabolite)

<1%

<1%

Atrazine (AAtrex,

Gesaprim)

72%

26%

Deethylatrazinec

(Atrazine metabolite)

13%

17%

Benfluralin (Balan,

Benefin, Bonalan)

<1%

0%

Bentazon (Basagran,

bentazone)

14%

4%

Bromacil (Hyvar X,

Urox B, Bromax)

0%

3%

Bromoxynil (Buctril,

Brominal, Torch)

2%

0%

Butylate (Sutan,

Genate Plus, butilate)

<1%

<1%

Clopyralid (Stinger,

Lontrel, Dowco 290)

0%

1%

Cyanazine (Bladex,

Fortrol)

9%

0%

2,4-D (2,4-PA) 27%

2%

2,4-DB (Butyrac,

Embutox)

0%

1%

DCPA (Dacthal, chlorthal-dimethyl)

37%

1%

Dacthal, mono-acid

(Dacthal metabolite)

<1%

0%

Dicamba (Banvel,

Mediben, MDBA)

2%

0%

Herbicide

(Trade or common

name)

Rate of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

Herbicide

(Trade or common

name)

Rate of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

Dinoseb (DNBP,

Dinitro, DN 289)

1%

2%

Diuron (Karmex,

Direx, DCMU)

20%

3%

EPTC (Eptam) 36%

2%

Ethalfluralin (Sonalan, Curbit EC)

7%

<1%

Linuron (Lorox,

Linex, Linurex)

3%

0%

MCPA (Kilsem,

metaxon)

4%

0%

Metolachlor (Dual,

Pennant)

9%

<1%

Metribuzin (Lexone,

Sencor)

25%

6%

Napropamide

(Devrinol)

1%

0%

Norflurazon (Evital,

Solicam)

0%

1%

Pendimethalin

(Prowl, Stomp)

10%

<1%

Prometon (Gesagram, Pramitol)

14%

2%

Pronamide (Kerb,

propyzamid)

<1%

0%

Propachlor (Ramrod,

propachlore)

<1%

0%

Propanil (Stampede,

Surcopur)

<1%

0%

Propham (ChemHoe, IPC, prophame)

<1%

0%

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS

The following tables summarize data collected for NAWQA studies from 1992-1995 by showing results for the Central Columbia Plateau Study Unit compared to the NAWQA national range for each compound detected. The data were collected at a wide variety

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

emphasize the general magnitude of concentrations (such as 10, 100, or 1000), rather than the precise number. The complete dataset

used to construct these tables is available upon request.

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

Central Columbia Plateau 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]

EXPLANATION

Range of surface-water detections in all 20 Study Units

Detection in the Central Columbia Plateau Study Unit

Range of ground-water detections in all 20 Study Units

Drinking water standard or guideline a

Freshwater-chronic criterion for the protection of aquatic life a
U.S. Geological Survey Circular 1144 27

Simazine (Aquazine,

Princep, Weedex)

47%

9%

Tebuthiuron (Spike,

Perflan)

7%

<1%

Terbacilc (Sinbar) 30%

2%

Thiobencarb (Bolero,

Saturn, benthiocarb)

<1%

0%

Triallate (Far-Go) 29%

<1%

Triclopyr (Garlon,

Grazon, Crossbow)

<1%

0%

Trifluralin (Treflan,

Trinin, Elancolan)

7%

0%

Insecticide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

Azinphos-methylc

(Guthion, Gusathion)

12%

1%

Carbarylc (Sevin,

Savit)

6%

<1%

Carbofuranc

(Furadan, Yaltox)

5%

0%

Chlorpyrifos (Lorsban, Dursban)

9%

1%

p,p’-DDE (p,p’-DDT

metabolite)

<1%

<1%

Diazinon 4%

0%

Dieldrin (Panoram D31, Octalox)

5%

1%

Disulfotonc (Di-syston, Dithiosystox)

1%

0%

Ethoprop (Mocap,

Prophos)

3%

0%

Fonofos (Dyfonate) <1%

0%

alpha-HCH (alphaBHC, alpha-lindane)

<1%

0%

gamma-HCH (Lindane, gamma-BHC)

12%

0%

Malathion (maldison,

malathon, Cythion)

2%

0%

Methyl parathion

(Penncap-M)

<1%

1%

0.001 0.01 0.1 1 10 100 1,000

Parathion (Thiophos,

Bladan, Folidol)

<1%

0%

cis-Permethrinc

(Ambush, Pounce)

<1%

0%

Propargite (Comite,

Omite, BPPS)

9%

0%

Propoxur (Baygon,

Blattanex, Unden)

<1%

0%

Volatile organic

compound

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

1,1,1-Trichloroethane (Methylchloroform)

--

1%

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

trifluoroethane

(Freon 113, CFC 113)

--

1%

1,2,3-Trichloropropane (Allyl trichloride)

--

3%

1,2,4-Trimethylbenzene (Pseudocumene)

--

1%

1,2-Dibromoethaned

(EDB)

--

1%

1,2-Dichloropropane

(Propylene dichloride)

--

6%

1,3-Dichloropropane

(Trimethylene dichloride)

--

1%

Chloroethane (Ethyl

chloride)

--

1%

Tetrachloromethane

(Carbon tetrachloride)

--

1%

total Trihalomethanes --

2%

Trichloroethene

(TCE)

--

1%

Volatile organic

compound

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

Methyl tert-butyle

ether (MTBE)

--

1%

Tetrachloroethene

(Perchloroethene)

--

1%

0.01 0.1 1 10 100 1,000

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

Insecticide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

Herbicide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000
28 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992-95

Dissolved ammonia 91%

75%

Dissolved ammonia

plus organic nitrogen

as nitrogen

81%

26%

Dissolved phosphorus as phosphorus

89%

77%

Dissolved nitrite plus

nitrate

93%

95%

Radon 222 --

100%

Other Rate

of

detection b

Concentration, in pCi/L

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

Nutrient

(Trade or common

name)

Rate

of

detection b

Concentration, in mg/L

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

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

Plateau Study Unit.

Herbicides

2,4,5-T

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

Acetochlor (Harness Plus,

Surpass)

Acifluorfen (Blazer, Tackle

2S)

Bromacil (Hyvar X, Urox

B, Bromax)

Chloramben (Amiben,

Amilon-WP, Vegiben)

Clopyralid (Stinger, Lontrel, Reclaim, Transline)

Dicamba (Banvel, Dianat,

Scotts Proturf)

Dichlobenil (Barrier, Casoron, Dyclomec, Norosac)

Dichlorprop (2,4-DP, Seritox 50, Kildip, Lentemul)

Dinoseb (Dinosebe)

Fenuron (Fenulon, Fenidim)

Fluometuron (Flo-Met,

Cotoran, Cottonex, Meturon)

MCPB (Can-Trol, Thistrol)

Molinate (Ordram)

Neburon (Neburea, Neburyl, Noruben)

Norflurazon (Evital, Predict, Solicam, Zorial)

Oryzalin (Surflan, Dirimal)

Pebulate (Tillam, PEBC)

Picloram (Grazon, Tordon)

Pronamide (Kerb, Propyzamid)

Triclopyr (Garlon, Grandstand, Redeem, Remedy)

Insecticides

3-Hydroxycarbofuran (Carbofuran metabolite)

Aldicarb sulfone (Standak,

aldoxycarb, aldicarb metabolite)

Aldicarb sulfoxide (Aldicarb metabolite)

Aldicarb (Temik)

Chlorothalonil (Bravo,

Daconil 2787, Exotherm)

Esfenvalerate (Asana XL,

Sumi-alpha)

Methiocarb (Slug-Geta,

Grandslam, Mesurol)

Methomyl (Lanox, Lannate, Nudrin)

Oxamyl (Vydate L, Pratt)

Phorate (Thimet, Granutox,

Geomet, Rampart)

Propoxur (Baygon, Blattanex, Unden, Proprotox)

Terbufos (Contraven,

Counter, Pilarfox)

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

2,2-Dichloropropane

Benzene

Bromobenzene (Phenyl

bromide)

Bromochloromethane

(Methylene chlorobromide)

Bromodichloromethane

(Dichlorobromomethane)

Bromomethane (Methyl

bromide)

Chlorobenzene

(Monochlorobenzene)

Chloroethene (Vinyl Chloride)

Chloromethane (Methyl

chloride)

Dibromochloromethane

(Dibromochloromethane)

Dibromomethane (Methylene dibromide)

Dichlorodifluoromethane

(CFC 12, Freon 12)

Dichloromethane (Methylene chloride)

Dimethylbenzenes

(Xylenes (total))

Ethenylbenzene (Styrene)

Ethylbenzene (Phenylethane)

Hexachlorobutadiene

Volatile organic

compounds

1,1,1,2-Tetrachloroethane

(1,1,1,2-TeCA)

1,1,2,2-Tetrachloroethane

1,1,2-Trichloroethane

(Vinyl trichloride)

1,1-Dichloroethane (Ethylidene dichloride)

1,1-Dichloroethene

(Vinylidene chloride)

1,1-Dichloropropene

1,2,3-Trichlorobenzene

(1,2,3-TCB)

1,2,4-Trichlorobenzene

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

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

DCB)

1,2-Dichloroethane (Ethylene dichloride)

1,3,5-Trimethylbenzene

(Mesitylene)

1,3-Dichlorobenzene (mDichlorobenzene)

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

DCB)

1-Chloro-2-methylbenzene (o-Chlorotoluene)

Isopropylbenzene

(Cumene)

Methylbenzene (Toluene)

Naphthalene

Tribromomethane (Bromoform)

Trichlorofluoromethane

(CFC 11, Freon 11)

cis-1,2-Dichloroethene

((Z)-1,2-Dichloroethene)

cis-1,3-Dichloropropene

((Z)-1,3-Dichloropropene)

n-Butylbenzene (1-Phenylbutane)

n-Propylbenzene (Isocumene)

p-Isopropyltoluene (pCymene)

sec-Butylbenzene

tert-Butylbenzene

trans-1,2-Dichloroethene

((E)-1,2-Dichlorothene)

trans-1,3-Dichloropropene

((E)-1,3-Dichloropropene)

Nutrients

No non-detects
U.S. Geological Survey Circular 1144 29

1,6-Dimethylnaphthalene

--

5%

1-Methylpyrene --

9%

2,3,6-Trimethylnaphthalene

--

5%

2,6-Dimethylnaphthalene

--

45%

2,6-Dinitrotoluene --

5%

2-Methylanthracene --

5%

3,5-Dimethylphenol --

5%

4,5-Methylenephenanthrene

--

5%

9H-Carbazole --

5%

Acenaphthene --

5%

Acenaphthylene --

5%

Acridine --

9%

Anthracene --

9%

Anthraquinone --

9%

Benz[ a ]anthracene --

9%

Benzo[ a ]pyrene --

32%

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

bed sediment of the Central Columbia Plateau 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 Central Columbia Plateau Study Unit

Range of detections in bed sediment in all 20 Study Units

Guideline for the protection of aquatic life f

Detection in clam tissue in the Central Columbia Plateau Study Unit

Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg

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

Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg

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

Benzo[ b ]fluoranthene

--

36%

Benzo[ ghi ]perylene --

9%

Benzo[ k ]fluoranthene

--

36%

Butylbenzylphthalate --

59%

Chrysene --

9%

Di- n -butylphthalate --

95%

Di- n -octylphthalate --

9%

Dibenz[ a,h ]

anthracene

--

5%

Diethylphthalate --

32%

Dimethylphthalate --

27%

Fluoranthene --

9%

Indeno[1,2,3- cd ]

pyrene

--

9%

Isoquinoline --

5%

N-Nitrosodiphenylamine

--

5%

Phenanthrene --

9%

Phenol --

86%
30 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992-95

Pyrene --

9%

Quinoline --

5%

bis(2-Ethylhexyl)phthalate

--

55%

p-Cresol --

91%

Organochlorine

compound

(Trade name)

Rate

of

detection b

Concentration, in μg/kg

Aldrin (HHDN,

Octalene)

0%

4%

total-Chlordane 20%

9%

DCPA (dacthal, chlorthal-dimethyl)

20%

13%

p,p’-DDE (p,p’-DDT

metabolite)

90%

52%

total-DDT 90%

52%

Dieldrin (Panoram D31, Octalox)

45%

22%

Endrin (endrine) 10%

0%

beta-HCH (betaBHC)

5%

0%

gamma-HCH (lindane, gamma-BHC)

0%

13%

Heptachlor epoxide

(heptachlor metabolite)

5%

4%

Hexachlorobenzene 65%

--

PCB, total 10%

4%

cis-Permethrin

(Ambush, Pounce)

--

14%

trans-Permethrin

(Ambush, Pounce)

--

9%

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

Arsenic 73%

100%

Cadmium 64%

100%

Chromium 82%

100%

Copper 100%

100%

Lead 27%

100%

Mercury 0%

57%

Nickel 45%

100%

Selenium 90%

96%

Zinc 100%

100%

Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg

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

Trace element Rate

of

detection b

Concentration, in μg/g

0.01 0.1 1 10 100 1,000 10,000
U.S. Geological Survey Circular 1144 31

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

of the Central Columbia Plateau Study Unit.

Semivolatile

organic

compounds

1,2,4-Trichlorobenzene

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

DCB)

1,2-Dimethylnaphthalene

1,3-Dichlorobenzene (mDichlorobenzene)

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

DCB)

1-Methyl-9H-fluorene

1-Methylphenanthrene

2,2-Biquinoline

2,4-Dinitrotoluene

2-Chloronaphthalene

2-Chlorophenol

2-Ethylnaphthalene

4-Bromophenyl-phenylether

4-Chloro-3-methylphenol

4-Chlorophenyl-phenylether

9H-Fluorene

Azobenzene

Benzo [c] cinnoline

C8-Alkylphenol

Dibenzothiophene

Isophorone

N-Nitrosodi-n-propylamine

Naphthalene

Nitrobenzene

Pentachloronitrobenzene

Phenanthridine

bis (2-Chloroethoxy)methane

Organochlorine

compounds

Chloroneb (chloronebe,

Demosan, Soil Fungicide

1823)

Endosulfan I (alphaEndosulfan, Thiodan,

Cyclodan, Beosit, Malix,

Thimul, Thifor)

Endrin (Endrine)

Heptachlor (Heptachlore,

Velsicol 104)

Isodrin (Isodrine, Compound 711)

Mirex (Dechlorane)

Pentachloroanisole (PCA,

pentachlorophenol metabolite)

Toxaphene (Camphechlor,

Hercules 3956)

alpha-HCH (alpha-BHC,

alpha-lindane, alphahexachlorocyclohexane,

alpha-benzene hexachloride)

delta-HCH (delta-BHC,

delta-hexachlorocyclohexane, delta-benzene

hexachloride)

o,p’-Methoxychlor

p,p’-Methoxychlor (Marlate, methoxychlore)

Trace elements

No non-detects

a

 Selected water-quality standards and guidelines [38].

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

insecticides were computed by only counting detections equal to or greater than 0.01 μg/L 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

0.01 μg/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 [38]. 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 [43].

d In the Central Columbia Plateau Study Unit, several ground-water samples were analyzed for 1,2-dibromoethane (EDB) at a lower detection limit

(0.04 μg/L). The detections shown on page 27 were confirmed, and EDB was detected in one additional well. e

 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 [38].

f

 Selected sediment-quality guidelines [38].
32 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

REFERENCES

* Central Columbia Plateau 

NAWQA products 

1. *Ryker, S.J., and Jones, J.L., 1995, 

Nitrate concentrations in ground 

water of the Central Columbia Plateau: U.S. Geological Survey OpenFile Report 95-445, 4 p.

2. *Wagner, R.J., Ebbert, J.C., Roberts, 

L.M., and Ryker, S.J., 1995, Agricultural pesticide applications and 

observed concentrations in surface 

waters from four drainage basins in 

the Central Columbia Plateau, Washington and Idaho, 1993–94: U.S. 

Geological Survey Water-Resources 

Investigations Report 95-4285, 50 p.

3. *Jones, J.L., and Wagner, R.J., 1995, 

Ground-water quality of the Central 

Columbia Plateau in Washington and 

Idaho-Analysis of available nutrient 

and pesticide data, 1942–1992: U.S. 

Geological Survey Water-Resources 

Investigations Report 94-4258, 119 p.

4. Nelson, L.M., 1991, Surface-water 

resources for the Columbia Plateau, 

Washington, Oregon, and Idaho: U.S. 

Geological Survey Water-Resources 

Investigations Report 88-4105, 4 p.

5. Horn, Marilee, March-May 1997, U.S. 

Geological Survey, written communication.

6. Sabol, M.A., and Downey, S.E., 1997, 

Support document for consideration 

of the Eastern Columbia Plateau aquifer system as a sole source aquifer: 

U.S. Environmental Protection 

Agency 910/R-97-002, 35+p.

7. Washington State Interagency Ground 

Water Committee, 1996, A report on 

nitrate contamination of ground water 

in the mid-Columbia Basin: Washington State Interagency Ground 

Water Committee Publication 

No. 96-17, 15 p.

8. U.S. Environmental Protection Agency, 

1996b, Drinking water regulations 

and health advisories: Washington, 

D.C., U.S. Environmental Protection 

Agency, Office of Water, EPA 822-

B-96-002, 11 p.

9. *Ryker, S.J., and Williamson, A.K., 

1996, Pesticides in public supply 

wells of the Central Columbia Plateau: U.S. Geological Survey Fact 

Sheet 205-96, 4 p.

10. U.S. Environmental Protection Agency, 

1996a, Environmental indicators of 

water quality in the United States: 

Washington, D.C., U.S. Environmental Protection Agency, Office of 

Water, EPA 841-R-96-002, 25 p.

11. Washington State Department of 

Health, June 1995, Nitrate in drinking 

water: Washington State Department 

of Health Fact Sheet, 2 p.

12. Mueller, D.K., and Helsel, D.R., 1996, 

Nutrients in the nation’s water—Too 

much of a good thing?: U.S. Geological Survey Circular 1136, 24 p.

13. Stern, Ginny, June 1997, Washington 

State Department of Health, written 

communication.

14. Alexander, R.B., and Smith, R.A., 

1990, County-level estimates of 

nitrogen and phosphorus fertilizer use 

in the United States, 1945 to 1985: 

USGS Open-File Report 90-130, 

12 p.

15. Battaglin, W.A., and Goolsby, D.A., 

1995, Spatial data in geographic 

information system format on agricultural chemical use, land use, and 

cropping practices in the United 

States: U.S. Geological Survey 

Water-Resources Investigations 

Report 94-4176, 87 p.

16. *Greene, K.E., Ebbert, J.C., and Munn, 

M.D., 1996, Nutrients, suspended 

sediment, and pesticides in streams 

and irrigation systems in the Central 

Columbia Plateau in Washington and 

Idaho, 1959–1991 (revised ed.): U.S. 

Geological Survey Water-Resources 

Investigations Report 94-4215, 125 p.

17. Bauer, H.H., and Vaccaro, J.J., 1990, 

Estimates of ground-water recharge 

to the Columbia Plateau regional 

aquifer system, Washington, Oregon, 

and Idaho, for predevelopment and 

current land-use conditions: U.S. 

Geological Survey Water-Resources 

Investigations Report 88-4108, 37 p., 

2 pl.

18. Ebbert, J.C., Cox, S.E., Drost, B.W., 

and Schurr, K.M., 1995, Distribution 

and sources of nitrate, and presence 

of fluoride and pesticides, in parts of 

the Pasco Basin, Washington, 1986–

88: U.S. Geological Survey WaterResources Investigations Report 93-

4197, 173 p.

19. *Roberts, L.M., and Jones, J.L., 1995, 

Agricultural pesticides found in 

ground water of the Quincy and 

Pasco Basins: U.S. Geological Survey Fact Sheet 240-95, 2 p.

20. *Roberts, L.M., and Jones, J.L., 1996, 

Pesticides found in ground water 

below orchards in the Quincy and 

Pasco Basins: U.S. Geological Survey Fact Sheet 171-96, 4 p.

21. *Roberts, L.M., and Wagner, R.J., 

1996, Pesticides and volatile organic 

compounds in ground and surface 

water of the Palouse Subunit, Washington and Idaho: U.S. Geological 

Survey Fact Sheet 204-96, 2 p.

22. *Wagner, R.J., Ebbert, J.C., and Roberts, L.M., 1995, Are agricultural pesticides in surface waters of the 

Central Columbia Plateau?: U.S. 

Geological Survey Fact Sheet 241-

95, 4 p.

23. Pimentel, D., Harvey, C., Resosudarmo, P., Sinclair, K., Kurz, D., 

McNair, M., Crist, S., Shpritz, L., 

Fitton, L., Saffouri, R., and Blair, R., 

1995, Environmental and economic 

costs of soil erosion and conservation 

benefits: Science, v. 267, no. 5201, 

p. 1117–1123.

24. Environment Canada, 1995, Interim 

sediment quality guidelines: Ottawa, 

Ontario, Ecosystem Conservation 

Directorate Evaluation and Interpretation Branch, 63 p.

25. *Gruber, S.J., and Munn, M.D., 1996, 

Organochlorine pesticides and PCBs 

in aquatic ecosystems of the Central 

Columbia Plateau: U.S. Geological 

Survey Fact Sheet 170-96, 4 p.

26. Raloff, Janet, 1993, Holding on to the 

Earth: Science News, v. 144, p. 280–

281.

27. *Munn, M.D., and Gruber, S.J., 1997, 

The relationship between land use 

and organochlorine compounds in 

streambed sediment and fish in the 

Central Columbia Plateau, Washington and Idaho, USA: Environmental 

Toxicology and Chemistry, v. 16., 

no. 9, p. 1877-1887.

28. *Ebbert, J.C., and Kim, M.H., 1998, 

The relation between irrigation 

method, sediment yields, and losses 

of pesticides and nitrogen: Journal of 

Environmental Quality, v. 27, no. 2, 

about 10 p.
U.S. Geological Survey Circular 1144 33

29. *Kim, M.H. and Ebbert, J.C., 1997, 

Irrigation and surface-water quality in 

the Quincy and Pasco Basins, Washington.: U.S. Geological Survey Fact 

Sheet 080-97, 2 p.

30. Kellogg, R.L., TeSelle, G.W., and 

Goebel, J.J., 1994, Highlights from 

the 1992 National Resources Inventory: Journal of Soil and Water, v. 49, 

no. 6, p. 521–527.

31. Roe, D., 1997, U.S. Department of 

Agriculture, Natural Resources Conservation Service, written communication.

32. Ames, K.C., and Prych, E.A., 1995, 

Background concentrations of metals 

in soils from selected regions in the 

state of Washington: U.S. Geological 

Survey Water-Resources Investigations Report 95-4018, 103 p.

33. *Greene, K.E., Munn, M.D., and 

Ebbert, J.C., 1997, Nutrients, benthic 

algae, and stream quality during low 

streamflow in the Palouse River 

Basin, Washington and Idaho: U.S. 

Geological Survey Water-Resources 

Investigations Report 96-4078, 38 p.

34. State of Washington, 1992, Water 

quality standards for surface waters 

of the state of Washington, in Washington Administrative Code: State of 

Washington, ch. 172-201A, 14 p.

35. Beeson, C.E. and Doyle, P.F., 1995, 

Comparison of bank erosion at vegetated and non-vegetated channel 

bends: Water Resources Bulletin 

v. 31, n. 6, p. 983-990.

36. Block, Elizabeth, 1993, Aquatic biota 

within the Central Columbia Plateau 

NAWQA study unit—A review of 

existing information: Tacoma, Wash., 

prepared for U.S. Geological Survey, 

Water Resources Division, Central 

Columbia Plateau Study Unit, 92 p.

37. *Gruber, S.J., and Munn, M.D., in 

review, Organophosphate and carbamate insecticides in agricultural 

waters and cholinesterase (ChE) inhibition in common carp (Cyprinus carpio): submitted to Archives of 

Environmental Contamination and 

Toxicology.

38. Gilliom, R.J., Mueller, D.K., and Nowell, L.H., in press, Methods for comparing water-quality conditions 

among National Water-Quality 

Assessment study units, 1992–1995: 

U.S. Geological Survey Open-File 

Report 97-589.

39. 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.

40. *Wagner, R.J. and Roberts, L.M., in 

press, Pesticides and volatile organic 

compounds in surface and ground 

water of the Palouse Subunit, Central 

Columbia Plateau, Washington and 

Idaho, 1993-95: U.S. Geological Survey Water-Resources Investigations 

Report, 97-4285, about 30 p.

41. Bortleson, G.C., 1991, Water fact 

sheet, National Water-Quality 

Assessment Program Mid-Columbia 

River Basin, Washington and Idaho: 

U.S. Geological Survey Open-File 

Report 91-164, 2 p.

42. Nowell, L.H. and Resek, E.A., 1994, 

Summary of national standards and 

guidelines for pesticides in water, bed 

sediment, and aquatic organisms and 

their application to water-quality 

assessments: U.S. Geological Survey 

Open-File Report 94-44, 115 p.

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

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

Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory--determination of 

pesticides in water by C-18 solidphase extraction and capillary-column gas chromatography/mass spectrometry with selected-ion 

monitoring: U.S. Geological Survey 

Open-File Report 95-181, 49 p.

44. *Jones, J.L. and Roberts, L.M., in 

review, The relative merits of monitoring and domestic wells for groundwater quality investigations: submitted to Ground Water Monitoring and 

Remediation.

45. *Jones, J.L. and Roberts, L.M., in 

press, Shallow ground-water quality 

beneath row crops and orchards in the 

Columbia Basin Irrigation Project 

area, Washington: U.S. Geological 

Survey Water-Resources Investigations Report, 97-4238, about 30 p.

46. *Ryker, S.J., and Williamson, A.K., 

1996, Pesticides in public supply 

wells of Washington State: U.S. Geological Survey Fact Sheet 122-96, 

2 p.
34 Water Quality in the Central Columbia Plateau, Washington and Idaho, 1992–95

GLOSSARY

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.

Acre-foot - A volume of water equal to one 

foot in depth and covering one acre; 

equivalent to 43,560 cubic feet or 

325,851 gallons.

Algae - Chlorophyll-bearing nonvascular, 

primarily aquatic species that have no 

true roots, stems, or leaves; most 

algae are microscopic, but some 

species can be as large as vascular 

plants.

Base flow - Sustained, low flow in a 

stream; ground-water discharge is the 

source of base flow in most places.

Best management practice (BMP) - An 

agricultural practice that has been 

determined to be an effective, 

practical means of preventing or 

reducing nonpoint source pollution.

Breakdown product - A compound 

derived by chemical, biological, or 

physical action upon a pesticide; also 

called “metabolite.” The breakdown 

is a natural process which may result 

in a compound that is more or less 

toxic and more or less persistent.

Dissolved solids - Amount of minerals, 

such as salt, that are dissolved in 

water; amount of dissolved solids is 

an indicator of salinity or hardness.

Eutrophication - The process by which 

water becomes enriched with plant 

nutrients, most commonly 

phosphorus and nitrogen, thereby 

causing excessive growth of aquatic 

plants.

Flow path - An underground route for 

ground-water movement, extending 

from a recharge (intake) zone such as 

a hill to a discharge (output) zone 

such as a shallow stream.

Freshwater-chronic criteria - The highest 

concentrations of contaminants that 

freshwater aquatic organisms can be 

exposed to for an extended period of 

time (4 days) without adverse effects. 

See also Water-quality criteria.

Fumigant - A substance or mixture of 

substances that produces gas, vapor, 

fume, or smoke intended to destroy 

insects, bacteria, or rodents.

Furrow irrigation - A type of surface 

irrigation where water is applied at 

the upper end of a field and flows in 

furrows to the lower end.

Headwaters - The source and upper part of 

a stream.

Health advisory - A nonregulatory level of 

a contaminant in drinking water or 

edible fish that may be used as 

guidance in the absence of a 

regulatory limit. 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 pesticide that is applied 

primarily for the purpose of killing 

undesirable plants.

Insecticide - A pesticide intended to 

prevent, destroy, or repel insects.

Load - General term that refers to the 

amount of a material or constituent in 

solution, in suspension, or in 

transport; usually expressed in terms 

of mass or volume.

Loess - A homogeneous, fine-grained 

sediment made up primarily of silt 

and clay, and deposited over a wide 

area (probably by wind).

Maximum contaminant level (MCL) -

The maximum permissible level of a 

contaminant in water that is delivered 

to any user of a public water system. 

MCL’s are enforceable standards 

established by the U.S. 

Environmental Protection Agency 

(USEPA).

Median - The middle or central value in a 

distribution of data ranked in order of 

magnitude. The median is equal to 

the 50th percentile.

Metabolite - See breakdown product.

Method detection limit (MDL) - The 

minimum concentration of a 

substance that can be accurately 

identified and measured with present 

laboratory technologies.

Minimum reporting level (MRL) - The 

smallest measured concentration of a 

constituent that may be reliably 

reported using a given analytical 

method. In many cases, the MRL is 

used when documentation for the 

method detection limit is not 

available.

Nonpoint source - A pollution source that 

cannot be defined as originating from 

discrete points such as pipe 

discharge. Areas of fertilizer and 

pesticide applications, atmospheric 

deposition, manure, and natural 

inputs from plants and trees are types 

of nonpoint source pollution. See

point source.

Organochlorine compound - Synthetic 

organic compounds containing 

chlorine. As generally used, term 

refers to compounds containing 

mostly or exclusively carbon, 

hydrogen, and chlorine. Examples 

include organochlorine insecticides, 

polychlorinated biphenyls, and some 

solvents containing chlorine.

Organochlorine pesticide - A class of 

organic pesticides containing a high 

percentage of chlorine. Includes 

dichlorodiphenylethanes (such as 

DDT), chlorinated cyclodienes (such 

as chlordane), and chlorinated 

benzenes (such as lindane). Most 

organochlorine insecticides were 

banned or severely restricted in usage 

because of their carcinogenicity, 

tendency to bioaccumulate, and 

toxicity to wildlife.

Organophosphate pesticide - A class of 

pesticides derived from phosphoric 

acid. They tend to have high acute 

toxicity to vertebrates. Although 

readily metabolized by vertebrates, 

some metabolic products are more 

toxic than the parent compound. 

Perennial stream - A stream that normally 

has water in its channel at all times.
U.S. Geological Survey Circular 1144 35

Pesticide - A chemical applied to crops, 

rights of way, lawns or residences to 

control weeds, insects, fungi, 

nematodes, rodents, or other “pests.” 

See also herbicide, insecticide, 

fumigant.

Point source - A source at a discrete 

location such as a discharge pipe, 

drainage ditch, tunnel, well, 

concentrated livestock operation, or 

floating craft. See nonpoint source.

Riparian - The area adjacent to rivers or 

streams with a high density, diversity, 

and productivity of plant and animal 

species relative to nearby uplands.

Sediment guideline - Threshold 

concentration above which there is a 

high probability of adverse effects on 

aquatic life from sediment 

contamination, determined using 

modified USEPA (1996) procedures.

Semivolatile organic compound (SVOC)

- Operationally defined as a group of 

synthetic organic compounds that are 

solvent-extractable and can be 

determined by gas 

chromatography/mass spectrometry. 

SVOCs include phenols, phthalates, 

and polycyclic aromatic 

hydrocarbons (PAHs).

Subsurface drain - A slotted or porous 

drainage pipe installed in an irrigated 

field to intercept the rising groundwater level and maintain the water 

table at an acceptable depth below the 

land surface.

Suspended sediment - Particles of rock, 

sand, soil, and organic detritus 

carried in suspension in the water 

column, in contrast to sediment that 

moves on or near the streambed.

Synoptic site - A site sampled during a 

short-term investigation of specific 

water-quality conditions during 

selected seasonal or hydrologic 

conditions to provide improved 

spatial resolution for critical waterquality conditions.

Trace element - An element found in only 

minor amounts (concentrations less 

than 1.0 milligram per liter) in water 

or sediment; includes arsenic, 

cadmium, chromium, copper, lead, 

mercury, nickel, and zinc.

Triazine herbicide - A class of herbicides 

containing a symmetrical triazine 

ring. Examples include atrazine, 

propazine, metribuzin, and simazine.

Volatile organic compound (VOC) - An 

organic chemical that has a high 

vapor pressure relative to its water 

solubility. VOCs include components 

of gasoline, fuel oils, and lubricants, 

as well as organic solvents, 

fumigants, some inert ingredients in 

pesticides, and some by-products of 

chlorine disinfection.

Wasteway - A waterway used to drain 

excess irrigation water dumped from 

the irrigation delivery system.

Water-quality criteria - Specific levels of 

water quality which, if reached, are 

expected to render a body of water 

unsuitable for its designated use. 

Commonly refer 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-quality guideline - A specific level 

of water quality which, if reached, 

may adversely affect human health or 

aquatic life. These are 

nonenforceable guidelines issued by 

a governmental agency or other 

institution.

Water-quality standard - A legallyenforceable state-adopted and U.S. 

Environmental Protection Agencyapproved ambient standard for water 

bodies. Standards include the use of 

the water body and the water-quality 

criteria that must be met to protect the 

designated use or uses.

Water table - The point below the land 

surface where ground water is first 

encountered and below which the 

earth is saturated. Depth to the water 

table varies widely across the Study 

Unit.

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. 
Williamson and others • Water Quality in the Central Columbia Plateau

Pasco

Moses

Lake

Spokane

Snake River

Columbia

River

Crab Creek

Palouse River

National Water-Quality Assessment (NAWQA) Program

Central Columbia Plateau

NAWQA