Water Quality in the

South Platte River Basin

Colorado, Nebraska, and Wyoming, 1992–95

U.S. Department of the Interior

U.S. Geological Survey Circular 1167

science for a changing world
Information on the NAWQA Program is also available on the Internet via the World Wide Web. You may

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

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

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

http://webserver.cr.usgs.gov/nawqa/splt/splt_home.html

•Central Colorado Water Conservancy

District

•Colorado Division of Water Resources

•Colorado Division of Wildlife

•Colorado Geological Survey

•Colorado State University

•Colorado Water Conservation Board

•Colorado Water Resources Research

Institute

•Denver Regional Council of

Governments

•Denver Water Department

•Colorado Division of Minerals and

Geology

•Environmental Defense Fund

•Lower South Platte Water Conservancy

District

•Metro Wastewater Reclamation District

•Natural Resources Conservation Service

•Nebraska Department of Environmental

Control

•Nebraska Department of Water Resources

•Nebraska Natural Resources Commission

•Northern Front Range Water Quality

Planning Association

•Northern Colorado Water Conservancy

District

•National Park Service

•St. Vrain and Left Hand Water Conservation District

•Twin Platte Natural Resources District

•University of Nebraska Water Center

•Urban Drainage and Flood Control

District

•U.S. Army Corps of Engineers

•U.S. Bureau of Land Management

•U.S. Bureau of Reclamation

•U.S. Environmental Protection Agency

•U.S. Fish and Wildlife Service

•U.S. Forest Service

•Water Quality Control Division -

Colorado Department of Health and

Environment

•Wyoming Department of

Environmental Quality

•Wyoming State Engineer’s Office

•Wyoming Water Development

Commission

•Wyoming Water Research Center

A COORDINATED EFFORT

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

agencies and organizations who contributed data used in this report.

FOR ADDITIONAL INFORMATION ON THE NATIONAL

WATER-QUALITY ASSESSMENT (NAWQA) PROGRAM:

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Division

12201 Sunrise Valley Drive, MS 413

Reston, VA 20192

Data for this report were collected by many people, including Dennis Smits, Jonathan Evans, Karla Pfenning, Jorge Ortiz,

Jeff Deacon, Nancy Bauch, Lori Martin, John Crittenden, Dana Strength, and Chris Sagebiel.

Front cover photograph: The Denver skyline looking west from the plains, by Michael Mauro©, (published with

permission).

Back cover photograph: Siphon irrigation in a sugar beet field, by David W. Litke, U.S. Geological Survey.

South Platte River Basin Study Unit, contact:

District Chief

U.S. Geological Survey

Water Resources Division

P.O. Box 25046, MS 415

Lakewood, CO 80225
Water Quality in the South Platte River

Basin, Colorado, Nebraska, and Wyoming,

1992–95

By Kevin F. Dennehy, David W. Litke, Cathy M. Tate,

Sharon L. Qi, Peter B. McMahon, Breton W. Bruce, Robert

A. Kimbrough, and Janet S. Heiny

U.S. GEOLOGICAL SURVEY CIRCULAR 1167

CONTENTS

National Water-Quality Assessment Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

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

Welcome to the South Platte River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Environmental setting and hydrologic conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Major issues and findings:

How has water development affected water quality in the South Platte River Basin? . . . . . . . . . . . . . . . . . . 8

Does land use contribute to contaminant inputs and affect habitat characteristics and biological

communities in streams?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

What factors control the occurrence of uranium and radon, and are the reported concentrations

a concern? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Have mining and residential development in the mountains affected water quality? . . . . . . . . . . . . . . . . . 13

Does urban land use affect water quality? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Have agricultural chemicals affected water quality?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

How do discharges from permitted municipal wastewater-treatment plants affect nutrient levels

in streams?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

What are the cumulative effects of mixed (urban/agriculture) land use on water quality? . . . . . . . . . . . . . 19

What is the relative status of water quality by land use in the South Platte River Basin? . . . . . . . . . . . . . . . 20

Water-quality conditions in a national context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Study design and data collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Summary of compound detections and concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Water-quality assessment of the South Platte River basin, Colorado,

Nebraska, and Wyoming, 1992-95 / by Kevin F. Dennehy ... [et al.].

p. cm. — (U.S. Geological Survey circular; 1167)

Includes bibliographic references.

1. Water quality — South Platte River Watershed (Colo. and Neb.)

I. Dennehy, Kevin F. II. Series.

TD225.S52W38 1998

363.739'42'097887 — dc21 98-14453

 CIP

ISBN 0-607-89362-1

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

Library of Congress Cataloging in Publication Data
U.S. Geological Survey Circular 1167 1

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

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

and aquatic health and because of the significant costs associated with decisions involving land and water management, conservation, and regulation. In 1991, the U.S. Congress appropriated funds for the U.S. Geological Survey

(USGS) to begin the National Water-Quality Assessment (NAWQA) Program to help meet the continuing need for

sound, scientific information on the areal extent of the water-quality problems, how these problems are changing with

time, and an understanding of the effects of human actions and natural factors on water quality conditions.

The NAWQA Program is assessing the water-quality conditions of more than 50 of the Nation's largest river basins

and aquifers, known as Study Units. Collectively, these Study Units cover about one-half of the United States and

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

about one-third of the Study Units are ongoing at a given time. Each Study Unit is scheduled to be revisited every

decade to evaluate changes in water-quality 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 waterquality 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 South Platte River Basin Study Unit and to relate these findings to water-quality issues of regional

and national concern. The information is primarily intended for those who are involved in water-resource management. Indeed, this report addresses many of the concerns raised by regulators, water-utility managers, industry representatives, and other scientists, engineers, public officials, and members of stakeholder groups who provided advice

and input to the USGS during this NAWQA Study-Unit investigation. Yet, the information contained here may also

interest those who simply wish to know more about the quality of water in the rivers and aquifers in the area where

they live.

 Robert M. Hirsch, Chief Hydrologist

Began in 1991

Began in 1994

Began in 1997

Not scheduled yet

EXPLANATION
2 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

How has water development affected water quality in the South Platte River Basin? Page 8

• Withdrawals of large volumes of water from streams in the basin for agricultural and urban use result in less water to

dilute contaminants in streams.

• Alteration of the natural flow regime has degraded native aquatic habitat along streams.

• Ground water (subsurface irrigation return flow) is a major nonpoint source of nitrate, dissolved solids, and pesticides

(atrazine and prometon) in the lower reaches of the South Platte River.

• Reuse of surface and ground water for irrigation has resulted in increased salinity in the lower South Platte River and surrounding alluvial aquifer. High salinity can be detrimental to irrigation and drinking-water supplies.

• Stream water having high concentrations of nitrate can be stored in agricultural reservoirs, where nitrate concentrations

decrease during the summer; thus, reservoirs could be part of a nitrate management strategy.

Does land use contribute to contaminant inputs and affect habitat characteristics and biological

communities in streams? Page 10

• Concentrations of contaminants, such as organochlorine pesticides and polychlorinated biphenyls (PCBs) in bed sediment and whole fish tissue were related to land use.

- Lowest concentrations and fewest number of these compounds were measured in forested mountains or rangeland

sites; highest concentrations and greatest number of compounds were measured in urban and mixed (urban/agriculture) areas.

• A habitat degradation index (HDI) and an index of biotic integrity (IBI), indicates that most sites were moderately

degraded and that human activities and local site characteristics had a greater effect on habitat and fish communities than

basin-scale characteristics such as land use.

• The relative abundance of families of fish were altered and the number of invertebrate taxa were lower in mining-affected

sites and urban, agricultural and mixed land-use settings compared to minimally affected areas such as forest and rangeland.

What factors control the occurrence of uranium and radon, and are the reported concentrations

a concern? Page 12

• High concentrations of uranium and radon in the South Platte River Basin are directly related to local geology.

• Median uranium concentrations were highest in shallow ground water from the alluvial aquifer in the plains, whereas,

median radon concentrations were highest in ground water from the crystalline aquifer in the forested mountain areas.

• There currently are no Federal drinking-water standards for uranium or radon, although standards for both are under

review by USEPA. Naturally occurring concentrations of both these elements were high compared to proposed and/or

historical standards in most areas of the basin.

Have mining and residential development in the mountains affected water quality? Page 13

• Ground-water quality in the forested mountain areas generally was better than in other land-use areas. However, the

potential for degraded ground-water quality is likely to increase as mountain communities grow.

• Surface-water quality generally was better in forested mountain areas than in other land uses. Development in mountain

drainages correlated with elevated concentrations of dissolved solids, suspended sediment, and nutrients in surface water.

• Volatile organic compounds (VOCs) were detected in ground water in forested mountain areas. Ground water in crystalline bedrock is susceptible to contamination from surface sources.

• Bed sediments in forested mountain streams affected by mining or development had the highest concentrations of trace

elements.

• Biological communities were less diverse and had fewer fish species in tributaries affected by mining or development

compared to undeveloped mountain streams.

SUMMARY OF MAJOR ISSUES AND FINDINGS
U.S. Geological Survey Circular 1167 3

Does urban land use affect water quality? Page 14

• Pesticides were frequently detected in surface water and shallow ground water in the urban setting. However, pesticide

concentrations were generally low, with only seven pesticides having median values above the method detection limit.

• VOCs, derived from gasoline and cleaning solvents, were detected in 86 percent of shallow urban ground-water samples.

• Nutrient concentrations in urban streams have many potential sources and generally were highest immediately downstream from wastewater treatment plants. Nutrient concentrations in streams did not exceed any existing USEPA drinkingwater standards. However, three ground-water samples from the alluvial aquifer had nitrate concentrations that exceeded

the drinking-water standard.

• Banned compounds, such as PCBs and chlordane, widely used historically in the urban setting, were detected in fish tissue. Stream-channel modifications for flood control and bank stabilization in the urban setting have altered the habitat

available to biological communities.

Have agricultural chemicals affected water quality? Page 16

• Pesticides were detected in ground water, surface water, fish tissue, and bed sediment. Several pesticides were detected

throughout the agricultural areas of the basin during the growing season. Although concentrations of individual pesticides

generally were low compared to established criteria, the ecological and human-health effects of long-term exposure to

pesticide mixtures are unknown.

• Nitrate concentrations in alluvial ground water were high in areas where agricultural fertilizers and manure were applied.

These high nitrate concentrations have degraded the use of ground water as a rural drinking-water supply. Nitrate concentrations in surface water were smaller than in ground water because microbial activity in streambed sediments removes a

substantial portion of the nitrate from the incoming ground-water return flows.

How do discharges from permitted municipal wastewater treatment plants affect nutrient levels in

streams? Page 18

• Treated wastewater effluent can account for as much as 100 percent of streamflow downstream from Denver and is the primary source of nitrate, ammonia, and phosphorus to Front Range streams.

• Total nitrogen concentrations in streams along the Front Range urban corridor increased substantially downstream from

wastewater treatment plants.

• Phosphorus concentrations in the South Platte River from Denver to Balzac, Colo., were higher than USEPA recommended limits for control of eutrophication.

What are the cumulative effects of mixed (urban/agriculture) land use on water quality? Page 19

• The average number of pesticides detected in surface-water samples from the South Platte River were greater in mixed

land-use areas than in land-use settings that were exclusively urban or agriculture.

• Federally banned compounds, DDT and dieldrin, were detected more often and at higher concentrations in bed sediment

and fish tissue collected from mixed land-use sites than in urban or agricultural settings.

• Because of the cumulative effects of contaminants from point and nonpoint sources and habitat alteration, the number of

aquatic invertebrate taxa generally was lower in mixed land-use areas than in either urban or agricultural land-use areas

alone, and the IBI for fish indicated moderately to significantly degraded conditions.

What is the relative status of water quality by land use in the South Platte River Basin? Page 20

• Water quality in surface and ground water in the forested mountain region of the basin generally was of good quality and

was relatively unaffected by humans.

• In contrast, water quality in the agricultural areas of the basin was the most degraded, primarily from nitrate and salinity in

ground water and salinity and suspended sediment in surface water.

• Water quality in the ground water beneath urban areas and surface water within mixed land-use areas are degraded, as

indicated by the highest relative ranking for VOCs and organochlorines and PCBs in fish within the basin, respectively.

SUMMARY OF MAJOR ISSUES AND FINDINGS
4 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

WELCOME TO THE SOUTH PLATTE RIVER BASIN

Agricultural setting, north of Greeley,

Colo.

Mixed (urban/agriculture) setting, Dacono,

Colo.

Urban setting, Denver, Colo.

Forested mountain setting, Loch Vale, Colo. (photograph by John Turk, U.S. Geological Survey).

these areas has occurred. This area exhibited a 22-percent

increase in population during 1990-93 (Denver Regional

Council of Governments, 1997). Between the mountains

and the plains is a transition zone where the largest population centers of the basin are located, including Denver

(2.2 million in 1997 in the Denver metropolitan area).

The basin extends eastward across the Great Plains where

agriculture is the predominant land use and water is used

primarily for irrigation of crops. On the plains, the topography of the basin continues to slope gently to the mouth

of the basin at North Platte, Nebr., at an altitude of

2,788 feet, thus resulting in an altitude change of slightly

more than 11,000 vertical feet.

The physical and cultural diversity has a profound

effect on water-quality conditions within the basin. The

goal of data-collection activities and information from

This circular is intended for Federal, State, and local

water professionals and anyone who has an interest in the

water-quality conditions of the South Platte River Basin. All

of us have a stake in our water resources, and perhaps more

important, we have an interest in maintaining the resources

for future residents of the basin.

The physical and cultural (land use) characteristics of the

South Platte River Basin are quite diverse. The headwaters of

the basin begin at an altitude of more than 14,000 feet along

the Continental Divide. The population in the forested mountain areas lives primarily in single-family residences and

small residential communities; however, rapid growth in
U.S. Geological Survey Circular 1167 5

studies presented in this report is to characterize, in a consistent manner, the broad scale geographic and seasonal

distributions of water-quality conditions in relation to

major contaminant sources and background conditions

(Gilliom and others, 1995). These activities and studies

also serve as the basis for the design of future assessments

of long-term water-quality trends and changes in the

basin.

Future demands on the water resources within the

basin likely will be high; some of the issues include: (1)

Allocating water between urban and agricultural demands;

(2) managing growth without deterioration of water

quality; (3) restoring degraded riparian habitat and fisheries

in the plains; (4) developing future water supplies without

affecting the environment; and (5) protecting existing

drinking-water supplies. The pressures of growth present

challenges that we need to be ready to address. By knowing

the current water-quality conditions and identifying environmental factors that affect those conditions, we can meet

the challenges of the future. Sufficient knowledge can help

us (individually or collectively) make the right decisions.

We can prepare now for the future if we can coordinate

water-quality activities among agencies at all levels to create an integrated approach to problem resolution. Information exchange and coordination help ensure that the waterquality information produced is relevant to all interests.

This circular summarizes the results of the occurrence

and distribution assessment (high-intensity sampling

phase) of the National Water-Quality Assessment

(NAWQA) Program’s South Platte River Basin Study Unit

investigation. The circular presents: (1) Information on the

environmental setting and the hydrologic conditions during

1992-95; (2) a summary of major water-quality issues and

findings; (3) a comparison of local water-quality results with

national NAWQA findings; (4) a description of water-quality

data-collection sites; and (5) tables summarizing the analysis

and detections of compounds determined during the course of

the study. The primary emphasis of NAWQA data collection

is to provide information needed for an integrated assessment

of water quality. Results presented in this circular and data

available on the internet will provide information that can

foster collaborative efforts within the water-resources community and continued evaluation and critical review of status

and trends in water quality in the South Platte River Basin.

Providing sufficient and safe drinking-water supplies is a goal of water

managers within the basin.

Irrigation in eastern plains.

Recreational water use in mountain areas of the basin.

WELCOME TO THE SOUTH PLATTE RIVER BASIN
6 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Water quality in the South Platte River Basin is a product of its environmental setting and hydrologic

conditions. Environmental conditions that affect water quality include natural factors such as

physiography, climate, geology, and soils and human factors such as water use, population, land use,

and water-management practices. However, in the South Platte River Basin, the largest population center

in the Rocky Mountain Region is in a predominantly semi-arid environment, so human factors have an

especially large effect on water quality.

ENVIRONMENTAL SETTING AND HYDROLOGIC CONDITIONS

Land use provides many of the

chemical and sediment inputs that

affect water quality. Forest and

rangeland are sources of nutrients,

suspended sediment, dissolved

solids, and metals. However, urban

and agricultural land uses are

larger sources of these same conRANGELAND

IRRIGATED

DRY LAND

FALLOW FOREST URBAN

OTHER

LANDS

FARMING

FARM LAND

LAND USE

Total area = 24,300 square miles

WATER USE

Total use = 4 billion gallons per day

IRRIGATION

(SURFACE WATER)

IRRIGATION

(GROUND

WATER)

POWER

GENERATION

URBAN

OTHER

The South Platte River Basin is characterized by a continental-type

climate having a wide temperature range (–30 to 100o

F) and irregular

seasonal and annual precipitation. Precipitation patterns across the

basin depend on altitude (mountains to plains). The greatest amount of

precipitation (more than 30 inches annually) falls in the mountains as

snow. In contrast, annual precipitation on the plains is less than

15 inches. Most of the precipitation on the plains occurs from April to

September as thunderstorms.

Population density in the South Platte River Basin ranges from

sparsely populated mountain areas in the headwaters region and

rural agricultural areas downstream from Denver to the densely

populated Denver metropolitan area and Front Range urban

corridor in the central part of the basin.

stituents, as well as other chemicals such as pesticides and volatile organic compounds. In the South Platte River Basin, stream-water quality generally is dependent

more on adjacent land use than on upstream land use because upstream water often is

removed from the river by diversions. In terms of area, rangeland is the largest land

use (41 percent), but has a relatively small effect on water quality because of the lack

of water and minimal water use. Irrigated agriculture comprises only 8 percent of the

basin but accounts for 71 percent of the water use. Urban lands comprise only 3 percent of the basin but account for 12 percent of the water use (or 27 percent if power

generation is considered an urban water use).

Mean-annual precipitation (1951-80) in the

South Platte River Basin. Precipitation data

are from the Colorado Climate

Center (1984).

Major land uses, 1975-80, in the South Platte River Basin (modified from Fegeas and others, 1983).

Population growth areas in the

South Platte River Basin, during 1979-90.

Water use in the South Platte River Basin for

1990. Data are from the U.S. Geological

Survey’s National Water Information System

(NWIS).

EXPLANATION

1979urbanarea

(Fegeas andothers,

1983)

Urban growth

(U.S. Dep t. of

Commerce,1991)

Front Range

urban corridor

Fort Collins

Denver

EXPLANATION

Urban

Agricultural

Forest

Rangeland

Other

EXPLANATION

Greater than 30

inches/year

20 to 30 inches/year

15 to 20 inches/year

Less than 15

inches/year

Wyo. Nebr.

Colo.
U.S. Geological Survey Circular 1167 7

chemical constituents compared to the previous

2 years. Results from water-quality samples collected during 1995 would likely be atypical.

The hydrograph for the Cache La Poudre River

showed a consistent seasonal pattern of streamflow.

Streamflow was high only during the annual snowmelt-runoff peak, which occurred during April

through August. In contrast, the hydrograph at a

plains site, such as the South Platte River at Cooper

Bridge, near Balzac, Colo., showed more monthly

variability. This variability was caused by two

factors: precipitation and water use. The high-flow

peak during May-August 1995 at the Balzac site

was caused by unusually large rainfall amounts in

the foothills and the plains that coincided with the

annual snowmelt peak. The remaining monthly

variability at the Balzac site primarily was due to

the effects of irrigation water diversions along the

river.

Ground-water levels in the mountains and

plains during the study period showed seasonal

patterns. Ground-water levels in the mountains

fluctuated in response to snowmelt and the subsequent infiltration of water, which resulted in the

highest water levels occurring between March

and June. The crystalline-bedrock aquifer in the

forested mountains primarily is used to supply

small quantities of water to individual households,

so water use usually does not drawdown water

levels except during extreme dry periods. Groundwater levels in the alluvial aquifer in the plains

fluctuated in response to the application of irrigation water to fields, which resulted in the highest

water levels occurring between July and September. The South Platte alluvial aquifer in the plains

primarily is used for irrigation but also is used as a

drinking-water supply.

Water quality is affected by hydrologic conditions such as the

quantity of water in streams and aquifers and the source of that

water. In the South Platte River Basin, the primary sources of

water are snowmelt from the mountains and rainfall on the plains.

Streamflow in a typical mountain stream, the Cache La

Poudre River, during the study period showed year-to-year variability. Snowfall, and the resulting streamflow, was about average

during 1993. Mountain streamflow during 1993 helped to fill reservoirs, which had been at low levels during the prolonged dry

spell of 1985-92. Mountain snowfall and streamflow were below

average during 1994. The plains climate also was drier than

normal during 1994, and the combined effect of dry mountains

and dry plains made 1994 the driest year of the study period. This

was followed during 1995 by

a wet year in the mountains

and the plains, which produced near-record high

streamflows in some areas and

localized flooding. The large

flows during 1995 resulted in

increased loads for many

Streamflow at plains sites was about 10 times larger during

1995 than during the previous 2 years.

The snowmelt peak at

mountain

sites was

about twice

as large during 1995 as

during the

previous 2

years.

Groundwater-level

fluctuations

occur in

response to

different

factors

depending if

wells are

located in

mountains

(snowmelt)or

in the plains

(irrigation).

ENVIRONMENTAL SETTING AND HYDROLOGIC CONDITIONS

Surface-water

sites

Ground-water

sites

A

C

D

B

South Platte River

EXPLANATION

18

6

8

10

12

14

16

1993 1994 1995 1996 1997

22

8

10

12

14

16

18

20

DEPTH TO WATER, in feet

C

D

Mountain Well-crystalline aquifer

Plains Well-alluvial aquifer
8 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Water development in the South Platte River Basin

began in 1870 when the first irrigation ditches were dug

in the vicinity of Greeley, Colo. Today, hundreds of structures withdraw more than 3 million acre-feet of water

from streams each year, dozens of water storage reservoirs store more than 2 million acre-feet of water each

year, 12 transmountain diversions import 400,000

acre-feet of water into the basin each year, and several

thousand wells pump an estimated 1 million acre-feet of

water each year (Dennehy and others, 1993).

These alterations of the natural hydrologic system

have affected the quantity and quality of water in the

South Platte River. For example, at several locations

along the river, there exist “dry points”—locations where

water diversions remove all the water from the river.

Withdrawals of water for urban and agricultural use have

resulted in less water available to dilute contaminants in

the river. The existence of dry points (lack of streamflow)

upstream from wastewater-treatment plant discharges has

led to nutrient concentrations in the South Platte River

that are substantially higher than elsewhere in the Nation

(Litke, 1996).

Alterations of the natural hydrologic system also

have resulted in less water in the river during spring

snowmelt runoff and more water in the river during fall

and winter. Historically, the South Platte River ran dry in

the plains when the supply of mountain snowmelt was

exhausted. Now, seepage of irrigation water from ditches

and fields replenishes the alluvial aquifer during spring

and summer, and the aquifer slowly drains during fall and

winter by discharging ground water to the South Platte

River. This altered flow regime has changed native

aquatic habitat along the river. For example, because

scouring high flows are less common, vegetation along

the channel has increased (Knopf, 1991), and the active

channel is narrower than in the past.

Ground water contributes substantially to streamflow

in the South Platte River in the plains (Litke, 1996). As a

result, nitrate, dissolved solids, and the pesticides

atrazine and prometon, which can be mobilized in irrigation water as it infiltrates from agricultural fields into

ground water, are subsequently transported into streams

(Litke, 1996; Bruce and McMahon, 1998; Kimbrough

and Litke, in press). Improvements in water quality,

therefore, depend on management of agricultural nonpoint sources, which are a long-term concern because

ground water and its associated dissolved chemical constituents can take as long as 25 years to migrate from

beneath fields to the river (McMahon, 1995).

The Burlington Canal can remove all the flow from the South Platte

River near Denver, Colo.

The importance of ground-water discharge to the South Platte River is

shown in the river water balance during April 1994. Large amounts of

water withdrawn from the river for irrigation are replaced by large

amounts of ground-water discharge into the river.

Alteration of natural streamflow for development has resulted in a

substantial decrease in channel width along the South Platte River

from 1865 to the present. Most of the change occurred prior to 1938.

0

200

100

GROUND-WATER

DISCHARGE INTO THE

per second (ft3/s)

200 400

RIVER MILES

0

200

100

SURFACE-WATER

feet per second (ft3/s)

MAJOR ISSUES AND FINDINGS: How Has Water Development Affected Water Quality in

the South Platte River Basin?

0

0 300 100 200

RIVER MILES

2,000

1,000

2,000

1,000

1865 1993

CHANNEL WIDTH, in feet

DENVER

JULESBURG

0

WITHDRAWALS FROM

, in cubic feet RIVER in cubic THE RIVER,

DENVER

JULESBURG

KERSEY

NORTH

PLATTE
U.S. Geological Survey Circular 1167 9

Because surface water was withdrawn all along the river

and was replaced by ground water, there was a recycling

effect on the water as it moved downstream. This reuse

resulted in increasing salinity in a downstream direction in

shallow alluvial ground water (Bruce and McMahon, 1998)

and in surface water (Litke and Kimbrough, 1998). Salinity

increases are related to water reuse and are caused by evaporation, dissolving soil minerals, and the concentration of salts

in the soil zone as plants utilize soil water. Deterioration of the

quality of the water resource from increased salinity can affect

its suitability for irrigation and as a drinking-water supply.

 Offstream reservoirs are an important part of the water

development infrastructure. About 30 percent of the streamRecreational land developed along an agricultural reservoir in Loveland, Colo.,

shows that use of water resources can be shared.

Specific conductance (a measure of salinity) in ground water from

the alluvial aquifer adjacent to the South Platte River and in surface

water from the South Platte River indicates that salinity increases

from Denver to Sterling, Colo., as water is reused. Salinity then

decreases near the mouth of the basin, probably due to dilution by

discharge of higher quality ground water from the Ogallala aquifer.

Nitrate concentrations in water from an agricultural reservoir during

monthly sampling in 1994 decreased steadily during the summer,

most likely due to biological uptake.

March June July September

MONTH

0

4

1

2

3

NITRATE CONCENTRATION,

in milligrams per liter (mg/L)

0 200 400

RIVER MILES

0

5,000

2,000

4,000

SPECIFIC CONDUCTANCE,

in microsiemens per centimeter (μS/cm)

GROUND WATER SURFACE WATER DENVER KERSEY NORTH PLATTE STERLING

Water development has led to

the extensive use and reuse of

water in the South Platte River

Basin, and urban and agricultural

water development have contributed to some degradation of water

quality. However, the existence of

the water-development infrastructure allows for the possibility of

improvement of water quality by

careful management.

flow in the South Platte River at Kersey, Colo., is stored in

offstream reservoirs during fall and winter for use the following irrigation season. Total nitrogen concentrations,

more specifically nitrate, decreased in reservoir water during summer (R. Kimbrough, U.S. Geological Survey, written commun., 1997), most likely due to biological uptake.

The practice of storing streamflows in agricultural reservoirs could reduce nitrate concentrations before flows are

released for irrigation in summer. Expanded use of this

management strategy could reduce nitrate levels throughout the basin.

(alluvial aquifer

adjacent to river)

(South Platte River)

Nitrate below detection limit

MAJOR ISSUES AND FINDINGS: How Has Water Development Affected Water Quality in

the South Platte River Basin?
10 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

MAJOR ISSUES AND FINDINGS: Does Land Use Contribute to Contaminant Inputs and

Affect Habitat Characteristics and Biological Communities in Streams?

Biological communities vary naturally with

elevation (mountains compared to plains) and corresponding changes in the physical habitat. Land

use can affect biological communities directly by

introduction of contaminants and indirectly by

altering the physical habitat. Humans also can

alter biological communities by stocking nonnative fish. Evaluation of invertebrate and fish

communities provides the opportunity to assess

responses to changes in environmental conditions

using organisms with different life spans. Collection of these data can provide some of the multiple lines of evidence needed to assess waterquality conditions.

An indicator of how land use can contribute

contaminants to streams is the measurement of

organochlorine pesticides and PCBs in bed sediment, and fish tissue at a site offers a clearer

picture of the persistence of these compounds in

the environment and their relation to land-use settings (Tate and Heiny, 1996). Although most of

these compounds have been banned since the

Engineering (NAE) (1973) guidelines for the protection of

aquatic life and wildlife. Concentrations of PCBs and chlordane exceeded guidelines primarily in urban areas, whereas

total DDT exceeded guidelines in mixed and agricultural

land-use areas (Tate and Heiny, 1996).

The number and diversity of aquatic biological communities are directly related to the available stream habitat and

concentrations of suspended sediment. A habitat degradation

The status of biological

integrity, habitat, and suspended-sediment concentrations in different landuse areas in the South

Platte River Basin.

index (HDI) was developed by the

NAWQA Program to indicate

habitat conditions at a site

(Gilliom and others, in press). An

HDI score for a site was calculated

by summing the ranks of three

parameters; the amount of stream

modification, bank erosion, and

bank vegetative stability. Site

scores were then grouped into

three degradation classes; significantly degraded, moderately

degraded, and minimally

degraded. HDI scores varied The highest number of compounds and highest concentrations were

detected in the urban and mixed (urban/agriculture) land-use areas.

1970’s, they can persist in the environment for decades,

which is important because of the multiple pathways for

these contaminants to become part of the natural food

chain. Assessing the effects of organochlorines on fish and

wildlife is becoming increasingly important because many

organochlorine pesticides and PCBs have been linked to

hormone disruption and reproductive problems in aquatic

invertebrates, fish, birds, and mammals (Colborn and

others, 1993; Goodbred and others, 1997).

Organochlorine pesticides and PCBs in bed sediment

and fish tissue were related to land use. Few organochlorine pesticides and PCBs were detected, and concentrations

were low in bed sediment or fish tissue in forested or

rangeland areas. Concentrations of organochlorine pesticides and PCBs in whole

fish tissue did not exceed

U.S. Food and Drug

Administration (U.S.

Food and Drug Administration, 1989) standards

for human consumption

of fish fillets. However,

concentrations of several

organochlorine pesticides

and PCBs in whole fish

exceeded National Academy of Sciences (NAS)

and National Academy of

EXPLANATION

Index of Biotic Integrity (IBI)

Habitat Degradation Index (HDI)

Mean suspended-sediment

concentration

CONCERNS ASSOCIATED WITH HABITAT

Stream modification Bank vegetative stability Bank erosion

Agricultural

Mountains

Urban

Mixed

(Urban/Agriculture)

IBI

< 25

25-45

> 45

SEDIMENT

> 275 mg/L

100-275 mg/L

< 100 mg/L

HDI

>14

9-14

<9

Significantly degraded

Moderately degraded

Minimally degraded

CATEGORY

Rangeland site

Miningaffected

site
U.S. Geological Survey Circular 1167 11

throughout the basin and showed the effect of human activities on a site-by-site basis. Most forested sites in the mountain area had HDI scores indicating moderately degraded

conditions with the exception of one site which was minimally degraded. Forested mountain sites had suspended-sediment concentrations indicating minimally degraded

conditions, whereas, the mining-affected site had concentrations indicating moderately degraded conditions. Most plains

sites had HDI scores and suspended-sediment concentrations

indicating moderately degraded conditions; however, the

rangeland site had HDI scores and suspended-sediment concentrations indicating minimally degraded conditions. Two

sites in the agricultural area had HDI scores and suspendedsediment concentrations indicating significantly degraded

conditions and only one urban site had suspended-sediment

concentrations indicating significantly degraded conditions.

These results indicate that human activities local to a site has

a greater affect on habitat characteristics and suspended-sediment concentrations than basin-scale characteristics such as

land use.

An index of biotic integrity (IBI) developed for fish in

the South Platte River Basin (Schrader, 1989) can be used as

a biological indicator of habitat and water-quality conditions.

An IBI for a site was calculated by summing the ranks of

three categories of fish-community characteristics; the

number and types of fish, fish feeding habits, and fish abundance and health. The ranks were determined by comparing a

fish-community characteristic at a site to those expected

under natural conditions. The site scores were then grouped

into three classes; significantly degraded, moderately

degraded, and minimally degraded. IBI scores varied

throughout the basin and showed the effect of human activities on a site-by-site basis. Forested sites in the mountain

areas had IBI scores indicating moderately degraded conditions, whereas a mining site in the mountains had an IBI indicating a significantly degraded condition. Most plains sites

had IBI scores indicating moderately degraded conditions;

however, two sites in the plains were significantly degraded:

one immediately downstream from Denver and one farther

downstream in an agricultural area. Only two sites in the

plains had IBI scores indicating minimally degraded conditions: the rangeland site and one agricultural site. These

results indicate that local site characteristics had a greater

effect on fish communities than basin-scale characteristics

such as land use.

The relative abundance of dominant families of fish was

affected by natural environmental factors (elevation) and

human activities (land use). Trout were present only in

mountain streams; however, the relative abundance of trout

was lower in areas affected by mining than in minimally

affected forest settings. Suckers, which are tolerant of

The composition and health of biological

communities are the integrated result of the

physical and chemical environment at a site.

Human activities associated with land use

directly (introduction of chemicals) and indirectly (alteration of physical habitat) affect

local invertebrate and fish communities.

The highest number of invertebrate taxa are present in the minimally degraded land-use (forest and rangeland) area.

Minnows are the dominant fish family present at the rangeland

site and a majority of the agricultural sites in the plains areas of

the basin.

MAJOR ISSUES AND FINDINGS: Does Land Use Contribute to Contaminant Inputs and

Affect Habitat Characteristics and Biological Communities in Streams?

contaminants, were dominant in urban environments.

Mixed (urban/agriculture) land-use settings had a similar

composition of fish families to urban and agricultural settings but had smaller relative abundance for each family.

Invertebrate taxa also vary naturally with elevation and

in response to human activities (land use). The decreased

numbers of invertebrate taxa in mining, agricultural, urban,

and mixed land-use areas compared to minimally affected

areas (forest and rangeland) in the mountains and plains,

showed the effect of human activity on the invertebrate

communities. The decline in the number of taxa was not a

result of natural variability (Tate and Heiny, 1995).
12 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

MAJOR ISSUES AND FINDINGS: What Factors Control the Occurrence of Uranium and

Radon, and Are the Reported Concentrations a Concern?

Uranium is a naturally occurring radioactive element that is

present in rocks throughout the South Platte River Basin. Radon

gas is a product of the radioactive decay of uranium. Both of

these constituents could be a health concern in the South Platte

River Basin because of the radiotoxicity effects in humans.

Uranium also is a heavy metal, which can cause liver damage.

Radon may be a concern in drinking water, and radon also can

enter indoor air from household water use, leading to exposure

through inhalation. Uranium was detected in a majority of

ground-water and bed-sediment samples and in some surfacewater samples during the NAWQA study (Bruce and McMahon,

1998; Heiny and Tate, 1997). Radon also was detected in all

ground-water samples (Bruce and McMahon, 1998).

High concentrations of uranium and radon in the South

Platte River Basin are directly related to the local geology. The

local bedrock, particularly the crystalline rocks (primarily granitic) in the mountains and marine shales and coal deposits in

the plains, are naturally high in uranium. Sediments derived

from crystalline rocks in the mountains are transported by the

streams eastward onto the plains. Uranium concentrations in

bed sediments were higher in the mountain streams than in the

plains streams. There was no relation between mining impacts

to the streams and uranium concentration in bed sediment. The

highest uranium concentration in bed sediment (25 μg/g) was

detected in the North St. Vrain Creek (naturally occurring), a

mountain drainage that is relatively unaffected by humans.

Median uranium concentrations in shallow ground water

were higher in the plains than in the mountains, indicating a secondary source of dissolved uranium in the eastern part of the

Uranium occurs naturally in the South Platte River Basin as

a result of weathering of crystalline and some sedimentary

rocks.

Uranium and radon levels in groundwater resources of the South Platte River

Basin were high compared to proposed

and historical USEPA drinking-water

standards. Revised standards for both

constituents are pending.

The source of the elevated radon and uranium concentrations is

linked to the local geology.

Uranium concentrations in streambed sediments

are highest in

mountain

streams.

basin other than the mountain-derived alluvial sediments. Preliminary evidence points to the presence of natural uranium in

coal deposits and shale bedrock of marine origin that are in contact with alluvial ground water. Samples from at least 10 wells

exceeded the proposed USEPA maximum contaminant level

(MCL) of 20 μg/L (equal to parts per billion) in each of the three

study areas.

Radon

Uranium

Mountain Plains

MEDIAN URANIUM CONCENTRATION,

Wells

Plains

50

40

30

20

10

0

MEDIAN RADON CONCENTRATION,

4,000

3,000

2,000

1,000

0

in micrograms per liter (μg/L)

in picocuries per liter (pCi/L)

Median radon concentrations in shallow ground

water in the forested mountains were higher than in the

plains. Currently (1998), there is no standard for radon

in drinking water. USEPA withdrew the previous standard of 300 pCi/L pending further review. Median

radon concentrations in ground water of the basin

exceeded the previous USEPA standard. Once new

standards for uranium and radon are finalized

(expected by the year 2001), ground water in the South

Platte River Basin may require special treatment before

it can be used for human consumption. Analysis of fish

liver tissue from numerous points in the basin indicated

that uranium does not bioaccumulate (Heiny and Tate,

1997).

Wells (Urban) (Agricultural)

Wells

Mountain Streams

Tributary

Plains Streams

South Platte

25

20

15

10

5

URANIUM CONCENTRATION, in

0

micrograms per gram (μg/g)

Trib.

Streams Streams Main Stem
U.S. Geological Survey Circular 1167 13

MAJOR ISSUES AND FINDINGS: Have Mining and Residential Development in the

Mountains Affected Water Quality?

occurrence of VOCs in the mountain wells indicates that ground water is susceptible to contamination from development and human activity.

Geology and proximity to the source rocks are

important factors affecting the concentration of

trace elements in bed sediments. Higher concentrations of most elements were present in bed sediment in the mountains, and concentrations

generally exceeded basin background levels (Heiny

and Tate, 1997). Elevated concentrations of some

elements in Clear Creek bed sediments were attributed to the effects of mining or development.

The numbers of invertebrate and fish taxa at

forested mountain sites were related to past mining

activity and the level of urban development. Clear

Creek (mining/development-affected) had fewer

invertebrate taxa (10) and lower invertebrate density (1,980 individuals per square meter) than the

Cache La Poudre River above Fort Collins, Colo.

(less developed; 19 taxa and 3,300 individuals per

square meter) (Tate and Heiny, 1995). Clear Creek

also had fewer fish species, more unstable banks,

more channelization, and less available habitat than

the Cache La Poudre or Big Thompson Rivers.

As population has increased in the Denver metropolitan area,

many mountain tributary basins have changed from forested areas

with little or no development to high-volume traffic corridors with

suburban and recreational development.

Throughout the mountains, alteration of land use for the everincreasing numbers of new homes may increase the probability of

contaminants being introduced to the ground-water system. Wells are

the primary drinking-water source for most mountain communities.

Data from wells and stream sites indicated that ground- and surfacewater quality in the mountains generally was representative of natural background conditions. Most chemical concentrations were lower

in the forested mountains than in urban, agricultural, and rangeland

areas. For example, pesticide compounds were not detected in

ground water from the forested mountain areas, but often were

detected in other land-use areas (Bruce and McMahon, 1998).

Among the mountain tributaries sampled, concentrations of dissolved solids, suspended sediment, nitrate, and phosphorus correlated with the degree of development in the basin. There were higher

concentrations of these constituents in Clear Creek (a more developed area) and lower concentrations in the Cache La Poudre and Big

Thompson Rivers (less developed areas) (Litke and Kimbrough,

1998). In ground water, only 1 of 27 mountain wells had a nitrate

concentration above the drinking-water standard of 10 mg/L as nitrogen, and 5 of those 27 wells had nitrate concentrations that might be

affected by septic systems (more than 2 mg/L) (Mueller and Helsel,

1996).

Volatile organic compounds (VOCs) are manufactured chemicals

such as organic solvents, by-products of chlorinated disinfectants,

and many petroleum-based derivatives that are components of gasoline, fuel oil, and lubricants. VOCs were detected in 8 of 27 groundwater wells sampled, but none of the concentrations exceeded

drinking-water standards (Bruce and McMahon, 1998). The

Undeveloped mountain drainage and residential development in mountain areas.

Median

concentrations of

selected

constituents in

forested

mountain

areas of

the South

Platte

River

Basin.

Water quality in the forested mountain setting generally represents background conditions; however,

surface water, ground water, bed sediment, and fish communities have been minimally affected by mining

activities and residential development. Because continued development is anticipated in mountain communities, long-term monitoring of water quality is important.

ClearCreek

Poudre

Cache La

Thompson

Big Ground water 0.001

1,000

0.01

0.1

1

10

100

CONCENTRATION, in milligrams per liter (mg/L)

Dissolved solids Suspended sediment

Nitrate Phosphorus

(greatest degree of development)
14 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Color indicates type of pesticide: Herbicide and Insecticide.

List of pesticides that comprise eighty percent of all pesticides

detected in surface and ground water within the urban setting. [<, less

than indicated value]

Pesticide

Percent detection

Maximum

concentration

(μg/L)

Surface

water

Ground

water

Surface

water

Ground

water

Carbaryl 97 0 5.2 < 0.003

Atrazine 86 43 0.2 0.2

Prometon 86 63 0.16 1.4

Diazinon 69 0 0.24 < 0.002

Simazine 64 30 0.048 0.068

DCPA 61 0 0.029 < 0.002

Tebuthiuron 53 17 0.17 0.79

Chlorpyrifos 31 0 0.11 < 0.004

Malathion 25 0 0.089 < 0.005

Land-use practices in the Denver metropolitan area

can affect the quality of streams and shallow ground

water in various ways. For example, fertilizers and pesticides applied to lawns, parks, and roadways can wash

into streams. Sediment from construction sites also can

wash into streams. Fuels and solvents used throughout

the urban area can migrate into shallow aquifers.

diazinon for one surface-water sample, and aquatic-life criteria were commonly exceeded for carbaryl, diazinon, and chlorpyrifos. No ground-water sample had a pesticide

concentration in excess of a regulatory criteria. The frequent

detection of pesticides, however, indicates that pesticide use in

Denver does affect water quality.

Volatile organic compounds derived from substances

commonly used in urban areas, such as gasoline and cleaning

solvents, were detected in 86 percent of the wells sampled

from the alluvial aquifer in Denver (Bruce and McMahon,

1996; McMahon and Bruce, 1997). Sixty-two percent of the

samples had more than one VOC present. The most frequently

detected VOC was methyl tert-butyl ether (MTBE), a gasoline

additive used to reduce carbon monoxide emissions from

vehicles during winter. The second most frequently detected

VOC was tetrachloroethene (PCE), a common cleaning

MAJOR ISSUES AND FINDINGS: Does Urban Land Use Affect Water Quality?

Surface water and shallow ground water in Denver, Colo., are susceptible to

contamination by urban activities.

All 36 of the surface water samples collected at two urban sites in the Denver metropolitan area contained at least one pesticide

(Kimbrough and Litke, in press), and water

from 90 percent of the wells (27 of 30 wells)

sampled in the urban alluvial aquifer contained

at least one pesticide (Bruce and McMahon,

1996, 1998). Twenty-eight different pesticides

were detected in surface water, but only 9 pesticides were detected in ground water. Atrazine,

prometon, and simazine were frequently

detected in both surface water and ground

water.

Pesticide concentrations were generally

low, with only seven pesticides having median

values above the method detection limit. However, the health advisory limit was exceeded for Thirty-one (ten most frequently detected VOCs shown) of 59 VOCs were detected in

shallow urban ground water.
U.S. Geological Survey Circular 1167 15

solvent. Benzene and PCE were the only VOCs

whose concentrations exceeded drinking-water standards (see Summary of Compound Detections and

Concentrations section, p. 28-34 for range of concentrations). These findings indicate that gasoline and

solvents used in the urban area affect water quality.

Nutrients such as ammonia, nitrate, and phosphorus have many potential sources in the Denver

metropolitan area, including fertilizers applied to

lawn areas and discharges from wastewater treatment

plants. However, nutrient concentrations in urban

streams did not exceed any existing USEPA drinking-water standard (Litke, 1996). Three of 30 samples of shallow alluvial ground water had nitrate

concentrations that exceeded the 10-mg/L drinkingwater standard (Bruce and McMahon, 1996). Nutrient concentrations in urban streams generally were

highest immediately downstream from wastewater

treatment plants. The effect of wastewater discharges

on water quality are discussed on page 18 of this

report.

Urban sources of surface water and alluvial

ground water are not currently (1998) used for drinking water in the Denver metropolitan area. However,

it is possible that these supplies could become drinking-water sources as demand for water increases.

The NAWQA study determined

that streams and shallow ground

water in the urban area are susceptible to contamination from pesticides and VOCs, indicating that

better management of potentially

toxic substances may be needed to

protect water resources for possible future use as drinking-water

supplies.

Channel modification has a direct effect on stream habitat and biological communities in the South Platte River.

MAJOR ISSUES AND FINDINGS: Does Urban Land Use Affect Water Quality?

Fish and stream habitat in the urban environment have been

affected by land-use activities. For example, tissue from common

carp and white sucker from urban streams contained the banned

compounds, PCBs and chlordane, both of which were widely

used historically in the urban environment (Tate and Heiny,

1996). Fish communities also were dominated by suckers, a

family of fish that is tolerant of degraded water-quality conditions. Channel modifications for flood control and bank stabilization in Cherry Creek and the South Platte River have resulted in

high suspended-sediment concentrations and degraded habitat for

biotic communities. Despite these negative effects of urban land

use on fish communities and habitat, an IBI developed for fish

communities in the South Platte River Basin as a tool to assess the

ecological health of streams across the basin indicated waterquality conditions were only moderately degraded.

Development of areas along the South Platte River is ongoing.
16 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

PESTICIDE

OCCURRENCE AT

AGRICULTURAL SITES

Ground Water Surface Water Fish Tissue Bed Sediment

What pesticides were

detected?

Fifteen pesticides were

detected. Atrazine and

prometon were most frequently detected. A greater

variety of pesticides was

detected in agricultural

wells than in urban wells.

Twenty-five pesticides were

detected. Atrazine, prometon, DCPA, metolachlor,

cyanazine, and EPTC were

detected in at least one-half

of the samples collected.

DDT or DDT metabolites

were detected in all samples. Dieldrin and dacthal

also were commonly

detected.

DDT was detected in about

one-half of the samples.

Where do pesticides

occur?

Pesticides were detected in

29 of the 30 wells sampled

between Fort Lupton, Colo.,

and North Platte, Nebr.

Atrazine and prometon were

detected at all 10 sites sampled between Kersey, Colo.,

and North Platte, Nebr. All

sites had at least five pesticides detected.

DDT was detected at all

sites from Henderson,

Colo., to North Platte, Nebr.

Dieldrin and dachthal

occurred primarily between

Henderson and Fort

Morgan, Colo.

DDT was detected primarily

from Henderson to Fort

Morgan, Colo.

When were pesticides

detected?

Wells were sampled once

(summer of 1994).

Pesticide detections were

more frequent in June than

in May or August 1994.

Atrazine and prometon persisted throughout the growing season.

Fish samples were collected once, during 1992 or

1993.

Bed sediment samples were

collected once, during 1992

or 1993.

MAJOR ISSUES AND FINDINGS: Have Agricultural Chemicals Affected Water Quality?

Agriculture accounts for about 37 percent of the land

use in the South Platte River Basin, and agricultural chemicals (fertilizers and pesticides) are used to enhance production. It is estimated that more than 2 million pounds of

active pesticide ingredients are applied in the basin each

year. Eleven chemicals account for about 90 percent of the

pesticide usage: eight herbicides, which are applied predominantly on corn during spring planting; and three

insecticides, which are applied as needed throughout the

growing season (Dennehy and others, 1995). Fertilizer use

is predominantly nitrogen and phosphorus compounds

applied in the form of chemical fertilizer or manure. It is

Irrigated fields south of Greeley, Colo. Corn, hay, dry beans, and

other small grains are the principal irrigated crops in the basin.

Feedlot near Fort Lupton, Colo. Feedlots generate substantial quantities of manure, which are applied to nearby fields as supplemental fertilizer. 

estimated that about 40,000 tons of phosphorus and 200,000

tons of nitrogen are applied in the basin each year (Litke,

1996). Residual chemicals migrate into the hydrologic system by ground- and surface-water irrigation return flows or

storm runoff.

Pesticides were detected in surface-water (Kimbrough

and Litke, in press), ground-water (Bruce and McMahon,

1998), bed-sediment, and fish-tissue (Tate and Heiny, 1996)

samples collected as part of NAWQA studies during

1992-95. Generally, the most commonly detected pesticides

were those that were most commonly used. DDT, which was

banned in 1972, was detected in bed sediment and fish tissue;
U.S. Geological Survey Circular 1167 17

and dieldrin, which also was banned in the 1970’s, was

detected in all four media. The common occurrence of some

pesticides, and the persistence of others, can be an ecological

and human health concern. Although individual pesticide

concentrations were small, generally less than MCLs, the

effects of long-term exposure to pesticide mixtures are

unknown.

Nitrate was the predominant form of nitrogen in ground

and surface water within the basin. Nitrate concentrations in

alluvial ground water were high in some areas where agricultural fertilizers and manure were applied to the land. Previous

work has shown that the location of nitrate “hot spots” is

related to soil texture and to the locations of combined

organic/inorganic fertilizer applications (Wylie and others,

1993). At nitrate hot spots, nitrate concentrations exceeded

the drinking-water standard (10 mg/L), and have resulted in

the restricted use of ground water as a rural drinking-water

supply. Nitrate-contaminated ground water generally cannot

be avoided by drilling deeper wells because nitrate concentrations typically are similar throughout the depth of the alluvial

aquifer, most likely due to mixing of water in the aquifer

caused by irrigation pumpage. Mixing was documented by

age-dating of the ground water, which showed small age differences between the top and bottom of the aquifer

(McMahon and Böhlke, 1996).

Ground water contributes substantially to the flow of the

South Platte River in the agricultural part of the basin, but

nitrate concentrations in surface water were much smaller

than in ground water and did not exceed the USEPA drinking-water standard. Studies have shown that microbial activity in streambed sediments removes a substantial portion of

the nitrate in the incoming ground water (McMahon and

Nitrate concentrations exceeded the U.S. Environmental Protection Agency

drinking-water standard of 10 milligrams per liter in about one-half of the

wells sampled. Locations of exceedances are scattered and depend on fertilizer application rates and soil leaching potential.

Nitrate concentrations in surface water are substantially lower than

concentrations in wells adjacent to the South Platte River. Microbial

action removes some nitrate from ground water as it moves from the

aquifer to the river.

Drinking water

for sale near

Greeley, Colo.,

in an area

where the

ground-water

supply is contaminated by

high nitrate

concentrations.

Böhlke, 1996), and that as much as 90 percent of the nitrate

can be removed from surface water over short distances

(Sjodin, and others, 1997). This natural removal process

does much to improve nitrate concentrations in the South

Platte River, but concentrations are still large enough that,

when excessive phosphorus concentrations also are present,

increased growth of nuisance algae and other aquatic plants

can occur in streams and reservoirs.

Agricultural pesticides were detected

at low concentrations throughout the

agricultural land-use area, but the

effects of long-term exposure to pesticide mixtures are unknown.

The use of agricultural fertilizers and

manure has affected the use of ground

water as a drinking-water supply in

some areas.

MAJOR ISSUES AND FINDINGS: Have Agricultural Chemicals Affected Water Quality?

0 200 400

RIVER MILES

0

45

20

40

NITRATE

CONCENTRATION, in

milligrams per liter (mg/L)

SURFACE WATER GROUND WATER DENVER KERSEY BALZAC NORTH PLATTE

(data collected from April 12 to (data collected from June 8 to

May 3, 1994) August 4, 1994)

EXPLANATION

NITRATE*, in milligrams

per liter (mg/L)

Less than 5

5 to10

Greater than 10

Alluvial aquifer

* Data collected from June 8 to August 4, 1994
18 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

There are more than 100 permitted municipal wastewater

treatment plants (WWTPs) in the South Platte River Basin.

Twenty-five plants located along the Front Range urban corridor

discharge about 275 million gallons of effluent per day or about

95 percent of the total daily effluent discharge in the basin. Most

plants discharge into streams, and in some locations, effluent can

make up a substantial part of the streamflow. For example,

Metro Wastewater Reclamation District annually contributes

about 69 percent of the streamflow and at times 100 percent

of the streamflow in the South Platte River downstream from

Denver, Colo. (Dennehy and others, 1995). About 7,000 tons

of nitrogen and 1,200 tons of phosphorus enter the South

Platte River Basin every year from WWTPs (Litke, 1996).

Nitrate and ammonia were the primary forms of nitrogen

present in WWTP effluent in the basin (Litke, 1996). Elevated

levels of these constituents can lead to excessive growth of

algae and other aquatic plants. Also, high nitrate levels can be

a health concern to infants, and high levels of ammonia in its

un-ionized form can be toxic to fish. Data collected from synoptic sites indicated that for most streams along the Front

Range urban corridor, total nitrogen concentrations were substantially higher downstream from WWTPs.

Phosphorus is the nutrient that often is the controlling

factor in causing eutrophication in reservoirs and aquatic

plant growth in streams, and the USEPA has recommended a

limit of 0.1 mg/L for total phosphorus in streams (U.S. Environmental Protection Agency, 1986). NAWQA synoptic data

showed that total phosphorus concentrations in the main stem

South Platte River generally exceeded this limit in the

150-mile reach of the river from Denver to Balzac, Colo. On

the main stem, total nitrogen and total phosphorus concentrations were largest just downstream from Denver and generally

decreased in a downstream direction.

Elevated nutrient concentrations in streams have the

potential to affect oxygen and food supplies for aquatic

MAJOR ISSUES AND FINDINGS: How Do Discharges from Permitted Municipal

Wastewater Treatment Plants Affect Nutrient Levels in Streams?

Wastewater-treatment plant effluent can contribute almost all of the

flow in the South Platte River downstream from Denver.

Total nitrogen and total phosphorus concentrations in the South Platte

River were largest just downstream from Denver and then generally

decreased in a downstream direction.

Total nitrogen concentrations in streams along the Front Range were

substantially larger downstream from WWTPs.

Nutrient concentrations were

elevated downstream from WWTPs.

Phosphorus concentrations were

consistently in excess of USEPA

recommended limits.

communities through eutrophication. Among the five

main-stem sites monitored for IBI, the South Platte River

at Henderson, Colo., had an IBI score of 24, which was the

lowest for all sites considered and indicated significantly

degraded conditions. Elevated nutrient concentrations in

the South Platte River at Henderson, primarily caused by

effluent from Denver’s WWTPs, contribute to degraded

conditions at this site.

0 100 200 300 400

15

5

10

TOTAL NITROGEN, in milligrams

3

0

1

2

TOTAL PHOSPHORUS, in milligrams

per liter (mg/L)

Total nitrogen, as N

Total phosphorus, as P

DenverHenderson

Kersey

Balzac

Julesburg

North Platte

RIVER MILES

0

per liter (mg/L)

[Data from synoptic

study, April 1994]

EXPLANATION

*TOTAL NITROGEN, in

milligrams per liter (mg/L)

Greater than 7

2 to 7

Less than 2

Wastewater treatment

plant

South

Platte

River

*Nitrogen data from a nutrient

synoptic study, April 1994

Kersey

Ft. Collins

Henderson

Denver
U.S. Geological Survey Circular 1167 19

MAJOR ISSUES AND FINDINGS: What Are the Cumulative Effects of Mixed

(Urban/Agriculture) Land Use on Water Quality?

Mixed (urban/agriculture)

land use has developed along the

Front Range urban corridor starting just north of Denver, Colo.,

and extending to the Fort Collins,

Colo., area. Water quality in this

mixed land-use setting is the product of combined urban and agricultural land-use practices. For

example, nitrate in surface water

can be attributed in part to the

large number of permitted discharges of WWTP effluent (point

sources) in the urban area. Howpesticides exceeded MCLs, the

ecological or human health

effects of long-term exposure to

low concentrations of multiple

pesticides is unknown.

The organochlorine compounds DDT, chlordane,

dacthal, dieldrin, and PCB in

bed sediment and fish tissue

were detected in the greatest

number and at the highest concentrations in streams affected

by urban and mixed land use

(see Summary of Compound

ever, ground-water irrigation return flows (nonpoint sources)

from agricultural lands also contribute to the nitrate load in

the river (McMahon and Böhlke, 1996).

The average number of pesticides detected in surfacewater samples at main-stem synoptic sites was greater in

mixed land-use areas than in land-use settings that were

exclusively urban or agricultural. The types of pesticides

detected were a combination of the types of pesticides generally associated with urban settings (prometon, simazine, carbaryl, and diazinon) and those used commonly in agricultural

areas (atrazine, metolachlor, cyanazine, and EPTC)

(Kimbrough and Litke, in press). Pesticide concentrations

measured at mixed land-use sites did exceed aquatic life criteria for three pesticides (Gilliom and others, in press); however, no drinking-water criteria were exceeded. Although no

Detections and Concentrations section, p. 28-34 for range

of concentrations). This result represents a cumulative

effect of multiple land uses (urban/agriculture) (Tate and

Heiny, 1996). Furthermore, the highest mean concentrations of federally banned compounds (DDT and its metabolites, dieldrin, and total PCBs) in bed sediment and fish

tissue throughout the basin occurred in the mixed land-use

setting. Although these compounds have been restricted or

banned for 20 to 25 years, they still are present in the environment and in a few samples persist at concentrations

above levels of concern for the protection of fish-eating

wildlife (Tate and Heiny, 1996).

Streams in the mixed land-use setting are slow moving

with meandering to straight channels composed of runs

and point bars. Channel bottoms are composed of gravel,

More pesticides

were detected in

surface-water

samples from

mixed (urban/

agriculture) landuse areas.

The cumulative effects on water quality from urban and agricultural land uses in the mixed landuse setting were greater for selected constituents than in either land use alone.

the canopy is open with some overhanging

vegetation, and streambanks are eroding or

lined with rip-rap. Bank erosion and vegetation instability, which result in increased suspended sediment and less favorable habitat

conditions for biological communities, are

common in mixed land-use streams. The

cumulative effect of contaminants from point

and nonpoint sources and habitat alterations

generally decreased the number of insect

(invertebrate) species (Tate and Heiny, 1995)

and also resulted in fish populations representative of moderately to significantly

affected water-quality conditions based on

an IBI.

An example of a mixed (urban/agriculture) land-use setting,

Dacono, Colo.
20 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

MAJOR ISSUES AND FINDINGS: What Is the Relative Status of Water Quality by Land Use

in the South Platte River Basin?

fish IBI can be affected by localized channel conditions as

well as the land use in the immediate vicinity of the site.

The urban and mixed (urban/agriculture) land uses

are very similar in overall water quality, with almost all

measures ranked as moderately affected. There is considerable site-to-site variability in surface-water quality

within urban land use, depending primarily on the magnitude of WWTP discharges near a site (Litke and

Kimbrough, 1998). There is less variability in surfacewater quality within the mixed (urban/agriculture) land

use because sites in this land use integrate land-use

effects. This integration was particularly evident for pesticides: concentrations of organochlorine pesticides and

PCBs in fish were higher in mixed land use than elsewhere; and the largest variety of pesticides detected at a

site occurred at a mixed (urban/agriculture) site. The significantly affected rankings for trace elements in surface

water and radon in ground water within the forested land

Previous sections of this report have

examined the effects of different land

uses on water quality using a combination of physical, chemical, and biological information from streams and

aquifers. In this section, the status of

water quality for each of four land uses

will be compared and contrasted, and the

role of land use as the primary factor in

determining water quality will be discussed. A determination of the relative

status of water quality will be accomplished by aggregating NAWQA data by

land use and then summarizing the

results in a single graphical display.

Median values are used to characterize

each land use, which places a greater

emphasis on average characteristics for a

land use rather than on extreme values

that might occur at individual sites. The

graphical display consists of nine

measures of water quality for surface

water and six measures of water quality

for ground water. The surface-water

measures include information on water,

but also include information about

stream habitat, fish communities, and

suspended sediment. Each measure is

ranked as to whether it is significantly

affected, moderately affected, or minimally affected by land use. Details on

how the 15 measures were classified and

Relative ranking of water-quality indicators by land use in surface and ground water of the South

Platte River Basin.

ranked are shown in the chart on the following page.

In the forested mountains, most measures rank as minimally affected by land use, but there are six measures that rank

as more than minimally affected. Of these, four are affected by

factors other than the dominant land use: trace elements in surface water are affected by mining, radon in ground water is

affected by bedrock geology, and nitrate and VOCs in ground

water are affected by low-density residential development.

These exceptions indicate that other factors (such as geology)

and minor land uses can have a larger effect on water quality

than the dominant land use.

In the forested mountains, the habitat index (HDI) and fish

index (IBI) also are ranked as moderately affected by land use.

However, these two measures are ranked as moderately

affected in all of the land uses. This situation arises because in

each land use, there are sites that rank as minimally affected

and sites that rank as more significantly affected; that is, there

is as much variability among sites within the same land use as

there is variability in sites between land uses. Habitat HDI and

SW GW

SW GW

SW GW

NA

NA

NA

NA

NA

NA

NA

SW GW

Agricultural

Mixed

(Urban/Agriculture)

Forested

(Mountains)

Urban

Significantly affected

Moderately affected

Minimally affected

NA Not applicable

Surface

Water

Ground

Water

Total Nitrogen

Total Phosphorus

Pesticides

Specific Conductance (salinity)

Organochlorines

and PCBs in fish

Trace Elements

Suspended Sediment

Habitat Degradation

Index (HDI)

Fish Index of Biotic

Integrity (IBI)

Nitrate

Pesticides

Specific Conductance

(salinity)

VOCs

Uranium

Radon

EXPLANATION
U.S. Geological Survey Circular 1167 21

1

 Classification breakpoints are 25th and 75th percentiles of data sets. For trace elements, exceedances are above background levels determined by Heiny and Tate, 1997.

2 Classification breakpoints were selected to bracket mean land-use concentrations.

3 Classification breakpoints modified from Schrader, 1989.

CLASSIFICATION RANKINGS

[mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees celsius; μg/L, micrograms per liter; pCi/L, picocuries per liter; <, less

than; >, greater than]

Water-quality indicators Minimally affected Moderately affected Significantly affected

SURFACE WATER

Total nitrogen1 < 1.6 mg/L 1.6 - 7.3 mg/L > 7.3 mg/L

Total phosphorus1 < 0.1 mg/L 0.1 - 0.87 mg/L > 0.87 mg/L

Pesticides1 < 6 detections 6 - 10 detections > 10 detections

Specific conductance (salinity)1 < 397 μS/cm 397 - 1,350 μS/cm > 1,350 μS/cm

Organochlorines and PCBs in fish1 < 2 detections 2 - 7 detections > 7 detections

Trace elements1 < 3 exceedances 3 - 12 exceedances > 12 exceedances

Suspended sediment2 < 14 mg/L 14 - 131 mg/L > 131 mg/L

Habitat degradation index (HDI)1 < 9 = minimally degraded 9 - 14 = moderately degraded > 14 = significantly degraded

Fish index of biotic integrity (IBI)3 > 45 = minimally degraded 25 - 45 = moderately degraded < 25 = significantly degraded

GROUND WATER

Nitrate1 < 0.4 mg/L 0.4 - 9.0 mg/L > 9.0 mg/L

Pesticides1 No detections 1 - 3 detections > 3 detections

Specific conductance (salinity)1 < 590 μS/cm 590 - 1,918 μS/cm > 1,918 μS/cm

VOCs1 No detections 1 detection > 1 detection

Uranium1 < 10 μg/L 10 - 49 μg/L > 49 μg/L

Radon1 < 450 pCi/L 450 - 2,500 pCi/L > 2,500 pCi/L

irrigation return flows predominate, water quality is related

primarily to agricultural land use. But the mix of sources

leads to considerable geographic and temporal variability

in agricultural water quality.

An integrated assessment of water-quality

conditions using multiple lines of evidence is a

valuable tool for examining the physical, chemical, and biological factors affecting surfaceand ground-water resources in the basin.

Results from the NAWQA study demonstrate

that natural and human factors can affect the

quality of ground water and surface water and

the biological communities at a given site.

Moreover, water quality can vary depending on

the physical features (mountains compared to

plains), hydrologic conditions, land use in the

immediate vicinity of the site, water-management practices, and the land use

upstream/upgradient from the site.

use do not carry through to the urban or mixed (urban/agricultural) land use. Much of the surface water from mountain

streams is removed before it reaches the plains, and the crystalline mountain aquifers and plains alluvial aquifers are not

hydrologically connected.

Agricultural land use has the most significant relative

effect on water quality because it is a source for three constituents: nitrate in ground water, specific conductance (salinity)

in surface water and ground water, and suspended sediment

in surface water. Ground water in the agricultural land use is

derived almost entirely from irrigation return flows, which

infiltrate into the aquifer. Therefore, ground water is very representative of agricultural land use: it is highly affected by

nitrate and salinity, but minimally affected by VOCs and

radon. Surface water in the agricultural area, however, has

three primary sources: upstream urban water, surface return

flows from agricultural lands (irrigation return flows and

occasional storm runoff), and ground-water recharge from the

aquifer. When upstream urban water predominates, urban

contaminants are carried to the agricultural users. When

MAJOR ISSUES AND FINDINGS: What Is the Relative Status of Water Quality by Land Use

in the South Platte River Basin?
22 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Denver

South

Platte

River

ORGANOCHLORINE PESTICIDES AND PCBs

in bed sediment and fish tissue

Denver

NUTRIENTS in water

South

Platte

River

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT: Comparison of Stream

Quality in the South Platte River Basin Study Unit with Nationwide NAWQA Findings.

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 South Platte River Basin Study Unit

were compared with scores for all sites in the 20 NAWQA Study Units sampled during

1992–95. Results are summarized by percentiles; higher percentile values generally indicate poorer quality compared with other NAWQA sites. Water-quality conditions at each

site also are compared to established criteria for protection of aquatic life. Applicable criteria are limited to nutrients and pesticides in water and semivolatile organic compounds,

organochlorine pesticides and PCBs in sediment. (Methods used to compute rankings and

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

Pesticide concentrations in the Denver urban area and in

an agricultural area near Greeley, Colo., are among the highest of all NAWQA Study-Unit sites. Both urban sites

exceeded the aquatic-life criteria for three compounds during

the summer.

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)

Insufficient data for analysis

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.

Concentrations of organochlorine pesticides and PCBs including

DDT, chlordane, and dieldrin in the South Platte River Basin in

urban, agricultural, and mixed (urban/agriculture) land uses rank

among the highest of all sites sampled in NAWQA Study Units.

Nutrient concentrations in

urban, mixed (urban/agriculture), and agricultural land-use

areas were some of the highest

compared to other NAWQA

Study-Unit sites. Ammonia concentrations exceeded aquatic-life

criteria for fish (salmonids)

toxicity at most sites in these

land uses. In contrast, nutrient

levels in mountain and rangeland

sites were among the lowest

nationally.

Denver

PESTICIDES in water

South

Platte

River
U.S. Geological Survey Circular 1167 23

Denver

FISH COMMUNITY DEGRADATION

No fish present at

time of sampling

South

Platte

River

SEMIVOLATILE ORGANIC COMPOUNDS (SVOCs)

in bed sediment

Denver

South

Platte

River

Denver

TRACE ELEMENTS in bed sediment

South

Platte

River

CONCLUSIONS

Physical, chemical, and biological

measures indicate that urban, mixed

(urban/agriculture), and agricultural

land-use areas generally have poorer

water quality not only within the South

Platte River Basin but also compared to

all sites sampled for the NAWQA program. In contrast, sites in forested mountain and rangeland areas have good

water quality both within the basin and in

comparison to all Study Units.

Though some trace elements occur naturally in soils,

South Platte River Basin sites in

urban areas and sites affected by

mining were ranked among the

highest compared to sites in

other NAWQA Study Units.

A majority of the sites

in the South Platte River

Basin sampled for SVOCs

were ranked above the

national median for all

NAWQA sites sampled.

Only two urban sites had

compounds that exceeded

threshold concentrations

known to have adverse

effects on aquatic life.

Physical characteristics of stream channels (natural

compared to modified) and streambanks (vegetation

cover, bank erosion) strongly affect water quality and

the ability of streams to support biological communities. In the South Platte River Basin, the physical condition of most stream habitat assessed was lower than

the national median; the exceptions occurred at sites

located in agricultural and urban areas, which also had

degraded fish communities.

Fish communities are directly related to the habitat available and the chemistry of the

environment in which they live. Sites in urban, agricultural, and mixed (urban/agriculture)

land-use types have fish communities that are among the most severely degraded of all

NAWQA Study-Unit sites. These degraded fish communities are characterized by a large

percentage of contaminant-tolerant species and correlated to stream habitat degradation and

high concentrations of chemicals in water, sediment, and fish. In contrast, fish communities

in forested mountain and rangeland sites were ranked lower than the national median; the

exception occurs at a mountain site having high concentrations of trace elements in sediment

as a result of upstream mining.

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT: Comparison of Stream

Quality in the South Platte River Basin Study Unit with Nationwide NAWQA Findings.

STREAM HABITAT DEGRADATION

Denver

South

Platte

River
24 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

NITRATE

Denver

RADON

Denver

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 South Platte River Basin Study Unit were compared with

scores for all aquifers and shallow ground-water areas sampled in the 20 NAWQA Study

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

generally indicate poorer quality compared with other NAWQA ground-water studies.

Radon concentrations measured in

wells completed in the crystalline bedrock of forested mountain areas and the

alluvial aquifer in the Denver urban area

were among the highest of all NAWQA

ground-water sites nationwide. Wells

completed in agricultural areas (alluvium) had comparatively low concentrations and were ranked below the national

median (50th percentile).

Nitrate concentrations in shallow ground water underlying irrigated agricultural lands were among the highest of all NAWQA

ground-water sites, and water from about one-half the wells sampled exceeded drinking-water standards. Ground water sampled

from wells in the forested mountain areas had nitrate concentrations that were below the national median. Only one well exceeded

drinking-water standards in the mountain area. Ten percent of the

samples collected from the shallow alluvial ground water in the

urban area exceeded the USEPA drinking-water standard.

EXPLANATION

Drinking-water aquifers

Forested mountain area

Shallow ground-water areas

Agricultural area (irrigated cropland)

Urban area

Ranking of ground-water quality relative

to all NAWQA ground-water studies —

Darker colored circles generally indicate

poorer quality. Bold outline of circle

indicates one or more standards or criteria

were exceeded.

Greater than the 75th percentile

(among the highest 25 percent

of NAWQA ground-water 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 ground-water sites)

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT: Comparison of GroundWater Quality in the South Platte River Basin Study Unit with Nationwide NAWQA Findings.

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

by Gilliom and others, in press).
U.S. Geological Survey Circular 1167 25

DISSOLVED SOLIDS

Denver

CONCLUSIONS

In the South Platte River Basin, compared to

other NAWQA Study Units:

Radon and VOCs in the urban land-use setting and developed areas in the forested

mountain setting were among the top 25

percent.

Dissolved solids and pesticides in the urban

and agricultural land-use settings were

among the top 25 percent.

Nitrate concentrations in the urban and agricultural land-use settings were higher

than the national median (50th percentile).

The median dissolved-solids concentrations in the urban and agricultural areas of the basin ranked in the

top 25 percent of all NAWQA groundwater sites; no drinking-water wells

were sampled in these areas. Although

dissolved-solids concentrations in the

mountain area were among the lowest

for NAWQA sites, they exceeded

drinking-water standards in 2 of the 27

household wells sampled.

No VOCs were detected in ground water underlying agricultural areas. In contrast, more than 86 percent of urban wells sampled contained VOCs, placing

it in the top 25 percent of all NAWQA ground-water

sites nationwide. Only 30 percent of mountain wells

sampled contained VOCs, but national NAWQA rankings were such that VOC detections in drinking-water

wells sampled in the mountain areas of the basin were

also among the highest for all NAWQA ground-water

sites nationwide.

Pesticides were detected in greater than 90 percent of the wells sampled in urban and agricultural

areas. Pesticides were detected in 27 of 30 wells sampled in the urban area and 29 of 30 wells sampled in

the agricultural area, which ranks these areas among

the highest of all NAWQA ground-water sites nationwide. No pesticides were detected in the mountain

area.

VOLATILE ORGANIC COMPOUNDS (VOCs)

Denver

PESTICIDES

Denver

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT: Comparison of GroundWater Quality in the South Platte River Basin Study Unit with Nationwide NAWQA Findings.
26 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Land Use and Stream-Chemistry Sites

20 40 MILES

0 20 40 KILOMETERS

0

Stream Chemistry Sites

Land Use

Basic Fixed Sites

Intensive Fixed Sites

Synoptic sites

Bed sediment and tissue

sites

Urban

Agricultural

Rangeland

Forest

Other

EXPLANATION

STUDY DESIGN AND DATA COLLECTION

The goal of the data collection for this study

was to characterize, in a nationally consistent

manner, the broad-scale geographic and seasonal

distribution of water-quality conditions in relation to major contaminant sources and background conditions (Gilliom and others, 1995).

The study design was multidisciplinary in nature,

examining the stream chemistry, stream ecology,

and ground-water chemistry across the basin. To

the extent possible, sampling sites represent

homogeneous combinations of land use, ecoregions, and hydrogeology that generally are relevant to surface- and ground-water quality. An

environmental framework of the basin was developed and a stratification process followed in

which sampling sites were selected that address

the most important water-quality issues and concerns within the basin. Physiographic province,

ecoregion, geology, and land use were the strata

used in the site selection process.

One of the advantages of the NAWQA

design is the use of multiple lines of evidence to

describe water-quality conditions (Gilliom and

others, 1995). The multiyear (April 1993-September 1995), intensive data collection phase of

the South Platte River Basin study provided

information on stream chemistry, chemistry of

bed sediment and fish tissue, stream ecology, and

ground-water chemistry. The sampling sites

associated with the various study components are

plotted on the appropriate maps, and the designs

of the individual study components are described

in the table on the following page.

Finally, study design and data collection

activities during the intensive multiyear

sampling effort yielded 104 surface-water sites

on 24 streams, 35 sampling locations in 5 reservoirs, and 159 wells throughout the basin.

Stream Ecology Sites and Ecoregions

20 40 MILES

0 20 40 KILOMETERS

0

Stream Ecology Sites

*Ecoregions

Intensive assessments

Synoptic sites

Southern Rockies

Western High Plains

Southwestern Tablelands

Nebraska Sand Hills

EXPLANATION

* Ecoregions modified from Gallant and

others, 1989; and Omernik, 1987

Stream-Chemistry Sites and Land Use

Ground-Water Chemistry Sites and Hydrogeology

20 40 MILES

0 20 40 KILOMETERS

0

Ground-Water Sites

Hydrogeology

Urban land-use study

Agricultural land-use

study

Crystalline/forested/urban

Study-unit survey

South Platte Alluvium

High Plains Aquifer

Denver Basin Aquifer

Crystalline Bedrock Aquifer

Other bedrock

EXPLANATION
U.S. Geological Survey Circular 1167 27

SUMMARY OF DATA COLLECTION IN THE SOUTH PLATTE RIVER BASIN STUDY UNIT, 1992-95

Study

component What data were collected and why Types of sites sampled

Number

of

sites

Sampling frequency

and period

Stream Chemistry

Basic Fixed Sites

— water column

Continuous streamflow, major ions, nutrients, organic carbon,

suspended sediment, and physical parameters: Describe

concentration, seasonal variability, and loads.

Streams draining predominant land-use types

across basin: forest, urban, mixed, agriculture, and rangeland.

12 Monthly plus storms;

April 1993-Sept. 1995

Intensive Fixed

Sites — water

column

In addition to the above constituents, 83 dissolved pesticides

were analyzed to determine concentration and timing of

occurrence.

A subset of basic sites draining agricultural

and urban land-use areas.

3 Minimum monthly plus

storms and more often

during high use period;

~20 per year, 1993-94

Synoptic sites —

water column

Streamflow, nutrients or pesticides, and physical parameters

were determined during high or low flow conditions to

describe short-term presence and distribution of constituents over broad scale in basin.

Streams draining a variety of land-use types; 5

synoptics for nutrients and 3 synoptics for

pesticides.

20-64

16-20

April, May, June, Aug.,

1994, Jan., 1995

May, June, Aug., 1994

Contaminants —

bed sediments

Trace elements and hydrophobic pesticides and other organic

compounds were analyzed in streambed sediments to

determine occurrence and spatial distribution.

Depositional zones for all basic and intensive

sites and several synoptic sites.

23 Summer 1992 (17) and

1993(6)

Contaminants —

fish tissue

Trace elements in fish livers and organic compounds in composites of whole fish were sampled and analyzed to determine occurrence and spatial distribution.All basic and intensive sites and some synoptic sites. Samples were taken from fish

species common to and across Study Unit.

23;

only 19

had fish

Summer 1992 (17) and

1993 (7); one site sampled twice

Stream Ecology

Intensive assessmentsFish, macroinvertebrates, algae, and aquatic and riparian

habitat were sampled and described to assess biological

communities in different land uses.

Stream reaches were co-located with basic

sites. Sites represent the variety of land

uses within the basin.

11

1

Once in 1993-95; 3

reaches sampled at each

of 4 sites in 1994

Once in 1995

Synoptic sites Macroinvertebrates, algae, nutrients, and aquatic and riparian

habitat were sampled to assess spatial distribution of biological communities in predominant land uses.

Stream reaches were co-located with basic

sites and a sub-set of synoptic stream

chemistry sites. Sites represent urban, agricultural, and mixed land uses.

26 Once in summer 1993

(Aug.-Sept.)

Ground-Water Chemistry

Land-use effects

— alluvial/urban

Major ions, nutrients, pesticides, VOCs, radon, trace elements, and DOC were sampled and analyzed to determine

effects of Denver metro area on the quality of recently

recharged ground water in the alluvial aquifer.

Existing non-drinking water wells screened

near the water table in the urban area were

located using a statistically random selection process.

30 Once in 1993 (July-Sept.)

Land-use effects

— alluvial/agricultural

Major ions, nutrients, pesticides, VOCs, radon, trace elements, tritium, DOC, and isotopes of nitrogen and uranium

were sampled and analyzed to determine effects of irrigated agriculture on the quality of recently recharged

ground water in the alluvial aquifer.

Newly installed monitoring wells completed

at water table were located using a statistically random selection process. Predominant crops: Corn, wheat and grains >20

percent.

30 Once in 1994 (June-Aug.)

Aquifer Studyunit survey —

crystalline/forest/urban

Major ions, nutrients, pesticides, VOCs, radon, trace elements, tritium, and DOC were sampled and analyzed to

assess condition of ground-water quality in forested urbanized crystalline bedrock aquifer.

Existing domestic wells completed in bedrock

(<400 ft deep) located using a statistically

random selection process.

27 Once in 1995 (July-Sept.)

Special Studies

Reservoir sites —

water column

(Five agricultural reservoirs

downstream

from Kersey,

Colo.)

Nutrients and physical parameters were determined from vertical profiles in agricultural reservoirs during one reservoir

irrigation season. Nutrient budgets computed to determine

if reservoirs are a source/sink of nutrients to irrigation supply water. Sampled for algae and chlorophyll.

Five reservoirs (Riverside, Jackson, Jumbo,

Prewitt, and Sterling) were selected in agricultural land-use areas.

35 (7

sites

per reservoir)

March, June, July, Sept.,

1995

Stream-aquifer

interaction

(south of Greeley, Colo.)

Major ions, nutrients, dissolved gases, stable isotopes of carbon, nitrogen, and sulfur, chlorofluorocarbons, tritium, and

DOC were collected and analyzed to describe the processes

controlling the fate of nitrogen-contaminated ground water

near areas of discharge to the South Platte River.

Monitoring wells were installed along flow

paths from recharge to discharge area.

Wells were nested and sampled top,

middle, and bottom of aquifer.

47 1 round of sampling

(1992); 2 rounds in 1993;

2 rounds in 1994

Degradation

study (Denver,

Colo.)

Major ions, nutrients, dissolved gases, VOCs, stable isotopes

of carbon, and DOC were collected and analyzed to determine the transport and degradation of VOCs in the alluvial

aquifer.

Monitoring wells were installed and sampled

along flow paths from a known VOC contaminant source to its discharge to South

Platte River. Wells were nested and completed at multiple depths.

25 2 rounds in 1994; 1 round

in 1995; 1 round in 1996

STUDY DESIGN AND DATA COLLECTION
28 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Herbicide

(Trade or common

name)

Rate of

detection b

Concentration, in μg/L

The following tables summarize data collected for NAWQA studies from 1992–95 by listing results for t

Platte River Basin Study Unit compared to the NAWQA national range for each compound detected. The data 

lected at a wide variety of places and times. In order to represent the wide concentration ranges observed amon

Units, logarithmic scales are used to emphasize the general magnitude of concentrations (such as 10, 100, or 1,

than the precise number. The complete data set used to construct these tables is available upon request.

Concentrations of pesticides, volatile organic compounds, and nutrients detected in ground and surfa

of the South Platte River Basin Study Unit. [mg/L, milligrams per liter; μg/L, micrograms per liter; pCi/

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 South Platte River Basin Study Unit

Range of ground-water detections in all 20 Study Units

Drinking-water standard or guideline a

Freshwater-chronic criterion for the protection of aquatic life a

Acetochlor 6%

0%

Alachlor (Lasso) 21%

1%

2,6-Diethylaniline <1%

0%

Atrazine (AAtrex) 90%

61%

Deethylatrazinec

(Atrazine metabolite)

61%

54%

Benfluralin (Balan,

Benefin)

1%

0%

Bentazon (Basagran) 1%

1%

Bromacil (Bromax

90, Urox B)

0%

2%

Bromoxynil (Buctril,

Brominal)

5%

0%

Butylate (Sutan +) 4%

0%

Cyanazine (Bladex) 45%

5%

2,4-D (2,4-D and

many others)

24%

1%

DCPA (Dacthal) 50%

1%

Dacthal, mono-acid

(Dacthal metabolite)

5%

1%

Dicamba (Banvel) 2%

0%

Dichlorprop (2,4-DP) 1%

0%

Herbicide

(Trade or common

name)

Rate of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 

Diuron (Direx and

many others)

2%

2%

EPTC (Eptam) 41%

2%

Ethalfluralin (Sonalan)

6%

0%

Linuron (Lorox) 10%

0%

Metolachlor (Dual,

Bicep)

50%

10%

Metribuzin (Lexone,

Sencor)

4%

1%

Molinate (Ordram) 1%

0%

Napropamide

(Devrinol)

1%

0%

Oryzalin (Surflan) 1%

0%

Pebulate (Tillam) 1%

0%

Pendimethalin

(Prowl)

20%

0%

Prometon (Pramitol) 93%

64%

Pronamide (Kerb) 1%

0%

Propachlor (Ramrod) 1%

0%

Propanil (Stampede) 1%

0%

Propham (IPC) 1%

0%

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS: Compou

Detected in Surface and Ground Water in the South Platte River Basin.

0.001 0.01 0.1 1 10 100 1,000
U.S. Geological Survey Circular 116

Simazine (Aquazine,

Princep)

43%

13%

Tebuthiuron (Spike,

Graslan)

26%

15%

Terbacilc (Sinbar) 1%

0%

Triallate (Far-Go) 1%

0%

Trifluralin (Treflan

and many others)

5%

0%

Insecticide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

Aldicarbc (Temik) 1%

0%

Aldicarb sulfoxidec

(Aldicarb metabolite)

1%

1%

Azinphos-methylc

(Guthion)

1%

0%

Carbarylc (Sevin) 48%

3%

Carbofuranc

(Furadan)

25%

2%

Chlorpyrifos (Dursban, Lorsban)

15%

0%

p,p’-DDE (p,p’-DDT

metabolite)

<1%

<1%

Diazinon 48%

3%

Dieldrin (Dieldrex,

Dieldrite)

9%

3%

Disulfotonc (Disyston and many others)

1%

0%

Ethoprop (Mocap) 1%

0%

Fonofos (Dyfonate) 2%

0%

alpha-HCH (alphaBHC, alpha-lindane)

1%

0%

gamma-HCH (Lindane)

2%

0%

Malathion

(Malathion)

13%

0%

Methyl parathion

(Penncap-M)

4%

0%

0.001 0.01 0.1 1 10 100 1,000

Parathion (Alkron and

many others)

1%

0%

cis-Permethrinc

(Ambush, Pounce)

1%

0%

Phorate (Thimet and

many others)

1%

0%

Propargite (Comite,

Omite)

11%

0%

Propoxur (Baygon) 1%

0%

Terbufos (Counter) 4%

0%

Volatile organic

compound

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

1,1,1-Trichloroethane

(Methylchloroform)

--

5%

1,1-Dichloroethane

(Ethylidene dichloride)

--

5%

1,1-Dichloroethene

(Vinylidene chloride)

--

1%

1,2,4-Trimethylbenzene (Psudocumene)

--

2%

1,2-Dichlorobenzene (oDichlorobenzene)--

4%

1,2-Dichloropropane

(Propylene dichloride)

--

2%

1,3,5-Trimethylbenzene (Mesitylene)

--

2%

1,4-Dichlorobenzene (pDichlorobenzene)

--

3%

Benzene --

6%

Chlorobenzene

(Monochlorobenzene)

--

3%

Chloroethane (Ethyl

chloride)

--

2%

Chloroethene (Vinyl

Chloride)

--

3%

Chloromethane

(Methyl chloride)

--

2%

Dichlorodifluoromethane (CFC 12)--

2%

Dichloromethane

(Methylene chloride)

--

1%

0.01 0.1 1 10 

Insecticide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 

Herbicide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.001 0.01 0.1 1 10 100 1,000

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS: Compounds

Detected in Surface and Ground Water in the South Platte River Basin.
30 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Dimethylbenzenes

(Xylenes (total))

--

4%

Ethylbenzene (Phenylethane)

--

3%

Isopropylbenzene

(Cumene)

--

5%

Methylbenzene (Toluene)

--

3%

Naphthalene --

3%

total Trihalomethanes --

6%

Trichloroethene

(TCE)

--

4%

cis-1,2-Dichloroethene ((Z)-

1,2-Dichloroethene)

--

6%

n-Butylbenzene (1-

Phenylbutane)

--

3%

n-Propylbenzene

(Isocumene)

--

3%

p-Isopropyltoluene

(p-Cymene)

--

1%

sec-Butylbenzene --

4%

tert-Butylbenzene --

2%

trans-1,2-Dichloroethene

((E)-1,2-Dichlorothene)

--

1%

Volatile organic

compound

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

Methyl tert-butyld

ether (MTBE)

--

26%

Tetrachloroethene

(Perchloroethene)

--

11%

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

Dissolved ammonia 91%

88%

Dissolved ammonia

plus organic nitrogen

as nitrogen

82%

74%

Dissolved phosphorus as phosphorus

77%

80%

Dissolved nitrite plus

nitrate

97%

78%

Other Rate

of

detection b

Concentration, in pCi/L

Radon 222 --

100%

1 10 100 1,000 

Nutrient

(Trade or common

name)

Rate

of

detection b

Concentration, in mg/L

0.01 0.1 1 10 100 

Volatile organic

compound

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

0.01 0.1 1 10 100 1,000

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS: Compou

Detected in Surface and Ground Water in the South Platte River Basin.
U.S. Geological Survey Circular 116

Pesticides, volatile organic compounds, and nutrients not detected in ground and surface waters of t

Platte River Basin Study Unit.

Herbicides

2,4,5-T

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

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

Acifluorfen (Blazer, Tackle

2S)

Chloramben (Amiben,

Amilon-WP, Vegiben)

Clopyralid (Stinger, Lontrel,

Reclaim, Transline)

Dinoseb (Dinosebe)

Fenuron (Fenulon, Fenidim)

Fluometuron (Flo-Met,

Cotoran, Cottonex, Meturon)

MCPA (Rhomene, Rhonox,

Chiptox)

MCPB (Thistrol)

Neburon (Neburea, Neburyl,

Noruben)

Norflurazon (Evital, Predict,

Solicam, Zorial)

Picloram (Grazon, Tordon)

Thiobencarb (Bolero, Saturn, Benthiocarb, Abolish)

Triclopyr (Garlon, Grandstand, Redeem, Remedy)

Insecticides

3-Hydroxycarbofuran

(Carbofuran metabolite)

Aldicarb sulfone (Standak,

aldoxycarb, aldicarb

metabolite)

Methiocarb (Slug-Geta,

Grandslam, Mesurol)

Methomyl (Lanox, Lannate, Acinate)

Oxamyl (Vydate L, Pratt)

Volatile organic

compounds

1,1,1,2-Tetrachloroethane

(1,1,1,2-TeCA)

1,1,2,2-Tetrachloroethane

1,1,2-Trichloro-1,2,2-trifluoroethane (Freon 113,

CFC 113)

1,1,2-Trichloroethane

(Vinyl trichloride)

1,1-Dichloropropene

1,2,3-Trichlorobenzene

(1,2,3-TCB)

1,2,3-Trichloropropane

(Allyl trichloride)

1,2,4-Trichlorobenzene

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

1,2-Dibromoethane (EDB,

Ethylene dibromide)

1,2-Dichloroethane (Ethylene dichloride)

1,3-Dichlorobenzene (mDichlorobenzene)

1,3-Dichloropropane (Trimethylene dichloride)

1-Chloro-2-methylbenzene

(o-Chlorotoluene)

1-Chloro-4-methylbenzene

(p-Chlorotoluene)

2,2-Dichloropropane

Bromobenzene (Phenyl bromide)

Bromochloromethane

(Methylene chlorobromide)

Bromomethane (Methyl

bromide)

Dibromomethane (Methylene dibromide)

Ethenylbenzene (Styrene)

Hexachlorobutadiene

Tetrachloromethane

(Carbon tetrachloride)

Trichlorofluoromethane

(CFC 11, Freon 11)

cis-1,3-Dichlo

((Z)-1,3-Dich

trans-1,3-Dich

((E)-1,3-Dich

Nutrients

No non-detect

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS: Compounds Not

Detected in Surface and Ground Water in the South Platte River Basin.
32 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Concentrations of semivolatile organic compounds, organochlorine compounds, and trace elements d

fish tissue and bed sediment of the South Platte River Basin Study Unit. [μg/g, micrograms per gram

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

EXPLANATION

Range of detections in fish tissue in all 20 Study Units

Detection in bed sediment or fish tissue in the South Platte River Basin Study Un

Range of detections in bed sediment in all 20 Study Units

Guideline for the protection of aquatic life e

Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg

0.1 10 100 1,1

1,2-Dimethylnaphthalene

--

5%

1,3-Dichlorobenzene --

5%

1,6-Dimethylnaphthalene

--

20%

1-Methyl-9H-fluorene --

10%

1-Methylphenanthrene

--

30%

1-Methylpyrene --

32%

2,2-Biquinoline --

40%

2,3,6-Trimethylnaphthalene

--

10%

2,6-Dimethylnaphthalene

--

90%

2,6-Dinitrotoluene --

5%

2-Chloronaphthalene --

10%

2-Methylanthracene --

30%

3,5-Dimethylphenol --

20%

4,5-Methylenephenanthrene

--

30%

9H-Carbazole --

30%

9H-Fluorene --

30%

Acenaphthene --

30%

Acenaphthylene --

35%

Acridine --

30%

Anthracene --

65%

Anthraquinone --

35%

Benz[ a ]anthracene --

63%

Benzo[ a ]pyrene --

75%

Benzo[ b ]fluoranthene

--

75%

Benzo[ ghi ]perylene --

45%

Benzo[ k ]fluoranthene

--

70%

Butylbenzylphthalate --

42%

Chrysene --

65%

Di- n -butylphthalate --

85%

Di- n -octylphthalate --

40%

Dibenz[ a,h ]

anthracene

--

25%

Dibenzothiophene --

25%

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS: Concent

Compounds In Fish Tissue and Streambed Sediment in the South Platte River Basi

0.1 10 100 1,000 10,000 100,000 1
U.S. Geological Survey Circular 116

Diethylphthalate --

5%

Fluoranthene --

74%

Indeno[1,2,3- cd ]

pyrene

--

45%

Isophorone --

5%

Isoquinoline --

25%

Naphthalene --

10%

Pentachloronitrobenzene

--

10%

Phenanthrene --

70%

Phenanthridine --

20%

Phenol --

100%

Pyrene --

68%

bis(2-Chloroethoxy)methane

--

15%

bis(2-Ethylhexyl)phthalate

--

100%

p-Cresol --

70%

Organochlorine

compound

(Trade name)

Rate

of

detection b

Concentration, in μg/kg

total-Chlordane 38%

30%

Dieldrin (Panoram D31)

42%

25%

Endosulfan I (alphaendosulfan)

--

10%

Endrin (endrine) 12%

0%

PCB, total 62%

0%

DCPA (dacthal, chlorthal-dimethyl)

27%

5%

p,p’-DDE 85%

45%

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

total-DDT 85%

45%

gamma-HCH (lindane)

8%

--

Heptachlor epoxide

(heptachlor metabolite)

15%

0%

Hexachlorobenzene 12%

--

p,p’-Methoxychlor

(Marlate)

4%

33%

Pentachloroanisole 8%

0%

Toxaphene (camphechlors)

4%

0%

Trace element Rate

of

detection b

Concentration, in μg/g

Arsenic 70%

100%

Cadmium 91%

100%

Chromium 65%

100%

Copper 100%

100%

Lead 39%

100%

Mercury 83%

92%

Nickel 70%

100%

Selenium 100%

100%

Zinc 100%

100%

0.01 0.1 1 10 1

Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg

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

Organochlorine

compound

(Trade name)

Rate

of

detection b

Concentration, in μg/kg

0.01 0.1 1 10 100 

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS: Concentration Of

Compounds In Fish Tissue and Streambed Sediment in the South Platte River Basin.

Summary of Compound Detections and C

tions tables were designed and built by 

Ryker, Jonathon Scott, and Alan Hagg

Geological Survey.
34 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Semivolatile organic compounds, organochlorine compounds, and trace elements not detected in fis

and bed sediment of the South Platte River Basin Study Unit.

Semivolatile organic

compounds

1,2,4-Trichlorobenzene

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

DCB)

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

DCB)

2,4-Dinitrotoluene

2-Chlorophenol

2-Ethylnaphthalene

4-Bromophenyl-phenylether

4-Chloro-3-methylphenol

4-Chlorophenyl-phenylether

Azobenzene

Benzo [c] cinnoline

C8-Alkylphenol

Dimethylphthalate

N-Nitrosodi-n-propylamine

N-Nitrosodiphenylamine

Nitrobenzene

Quinoline

Organochlorine

compounds

Aldrin (HHDN, Octalene)

Chloroneb (chloronebe,

Demosan, Soil Fungicide

1823)

Endrin (Endrine)

Heptachlor (Heptachlore,

Velsicol 104)

Isodrin (Isodrine, Compound 711)

Mirex (Dechlorane)

alpha-HCH (alpha-BHC,

alpha-lindane, alphahexachlorocyclohexane,

alpha-benzene hexachloride)

beta-HCH (beta-BHC, betahexachlorocyclohexane,

alpha-benzene hexachloride)

cis-Permethrin (Ambush,

Astro, Pounce, Pramex,

Pertox, Ambushfog, Kafil,

Perthrine, Picket, Picket G,

Dragnet, Talcord, Outflank, Stockade, Eksmin,

Coopex, Peregin, Stomoxin, Stomoxin P, Qamlin, Corsair, Tornade)

delta-HCH (delta-BHC,

delta-hexachlorocyclohexane, delta-benzene

hexachloride)

o,p’-Methoxychlor

trans-Permethrin (Ambush,

Astro, Pounce, Pramex,

Pertox, Ambushfog, Kafil,

Perthrine, Picket, Picket G,

Dragnet, Talco

flank, Stockade

Coopex, Peregi

moxin, Stomox

lin, Corsair, To

Trace element

No non-detects

a

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

b

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

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

had varying detection limits; a value of <1% signifies that there were only detections below, or <1% above, the 0.01 μg/L level. So

and insecticides were not reliably detected as low as the 0.01 μg/L level, so frequencies may be underestimated for some compound

compound groups, all detections were counted and detection limits for most compounds were similar to the lower end of the nation

shown. Method detection limits for all compounds in all groups are summarized in (Gilliom and others, in press).

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

as estimated values (Zaugg and others, 1995).

d

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

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

e

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

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS: Compou

Detected in Fish Tissue and Streambed Sediment in the South Platte River Basin.
U.S. Geological Survey Circular 1167 35

REFERENCES

This Report was Based on the

Following Publications:

Bruce, B.W., and McMahon, P.B., 1996,

Shallow ground-water quality

beneath a major urban center—Denver, Colorado, USA: Journal of Hydrology, v. 186, p. 129-

151.

Bruce, B.W., and McMahon, P.B., 1998,

Shallow ground-water quality of

selected land-use/aquifer settings

in the South Platte River Basin,

Colorado and Nebraska 1993-95:

U.S. Geological Survey WaterResources Investigations Report

97-4229, 48 p.

Colborn, T., VomSaal, F.S., and Soto,

A.M., 1993, Developmental effects

of endocrine-disrupting chemicals

in wildlife and humans: Environmental Health Perspectives, v. 101,

p. 378-384.

Colorado Climate Center, 1984, Colorado average annual precipitation

1950-80: Fort Collins, Colorado,

1 pl.

Dennehy, K.F., Litke, D.W., McMahon,

P.B., Heiny, J.S., and Tate, C.M.,

1995, Water-quality assessment of

the South Platte River Basin, Colorado, Nebraska, and Wyoming—Analysis of available

nutrient, suspended-sediment, and

pesticide data, water years 1980-

92: U.S. Geological Survey WaterResources Investigations Report

94-4095, 145 p.

Dennehy, K.F., Litke, D.W., Tate. C.M.,

and Heiny, J.S., 1993, South Platte

River Basin—Colorado, Nebraska,

and Wyoming: Water Resources

Bulletin, v. 29, no. 4, p. 647-683.

Denver Regional Council of Governments, 1997, Regional population

and household estimates: Regional

Report, v. 30, no. 7.

Fegeas, R.G., Claire, R.W., Guptill,

S.C., Anderson, K.E., and Hallam,

C.A., 1983, Land use and land

cover digital data: U.S. Geological

Survey Circular 895-E, 21 p.

Gallant, A.L., Whittier, T.R., Larsen,

D.P., Omernick, J.M., and Hughes,

R.M., 1989, Regionalization as a

tool for managing environmental

resources: EPA/600/3-89/060, 152

p.

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

M.E., 1995, Design of the national

water-quality assessment program: occurrence and distribution

of water-quality conditions: U.S.

Geological Survey Circular 1112,

33 p.

Gilliom, R.J., Mueller, D.K., and Nowell, L.H., in press, Methods for

comparing water-quality conditions among national water-quality assessment study units 1992-

95: U.S. Geological Survey OpenFile Report 97-5890.

Goodbred, S.L., Gilliom, R.J., Gross,

T.S., Denslow, N.P., Bryant, W.L.,

and Schoeb, T.R., 1997, Reconnaissance of 17β-estradiol, 11-

ketotestosterone, vitellogenin, and

gonad histopathology in common

carp of United States

streams—Potential for contaminant-induced endocrine disruption: U.S. Geological Survey

Open-File Report 96-627, 47 p.

Heiny, J.S., and Tate, C.M., 1997, Concentration, distribution, and comparison of selected trace elements

in bed sediment and fish tissue in

the South Platte River Basin,

USA, 1992-93: Archives of Environmental Contamination and

Toxicology, v. 32,

p. 246-259.

Kimbrough, R.A., and Litke, D.W.,

1996, Pesticides in streams draining agricultural and urban areas in

Colorado: Environmental Science

and Technology,

v. 30, no. 3, p. 908-916.

Kimbrough, R.A., and Litke, D.W., in

press, Pesticides in the South

Platte River from Henderson, Colorado to North Platte, Nebraska

during the 1994 growing season,

and comparison of pesticide

occurrence in two nested urban

basins in Denver, Colorado: U.S.

Geological

Survey Water-Resources Investigations Report 97-4230.

Knopf, F., 1991, Ecological succession

and conservation confusion in the

South Platte floodplain, in South

Platte River Resource Management: Finding a balance (Conference Proceeding),

R.C. Woodring, ed., Colorado

Water Resources Research Institute, Information Series no. 66, 27

p.

Litke, D.W., 1996, Sources and loads

of nutrients in the South Platte

River, Colorado and Nebraska,

1994-95: U.S. Geological Survey

Water-Resources Investigations

Report 96-4029, 57 p.

Litke, D.W., and Kimbrough, R.A.,

1998, Water-quality assessment of

the South Platte River Basin, Colorado, Nebraska, and Wyoming—Environmental setting and

water quality of fixed sites, 1993-

95: U.S. Geological Survey

Water-Resources Investigations

Report 97-4220, 61 p.

McMahon, P.B., 1995, Some bacteria

are beneficial!: U.S. Geological

Survey Fact Sheet FS-102-95,

2 p.

McMahon, P.B., and Böhlke, J.K.,

1996, Denitrification and mixing

in a stream-aquifer system—Effects on nitrate loading to

surface water: Journal of Hydrology, v. 186, p. 105-128.

McMahon, P.B., and Bruce, B.W.,

1997, Distribution of terminal

electron-accepting processes in an

aquifer having multiple contaminant sources: Applied Geochemistry, v. 12, p. 507-516.

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

Nutrients in the Nation’s

waters—Too much of a good

thing?: U.S. Geological Survey

Circular 1136, 24 p.

National Academy of Sciences,

National Academy of Engineering, 1973, Water-quality criteria

1972, Ecological Research Series:

EPA-R3-73-033, 594 p.

Omernick, J.M., 1987, Ecoregions of

the conterminous United States:

Annals of the Association of
36 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

American Geographers 77, p. 118-

125.

Schrader, L.H., 1989, Use of the index

of biotic integrity to evaluate fish

communities in Western Great

Plains streams: Fort Collins, Colorado State University, Master’s

thesis.

Sjodin, A.L., Lewis, W.M., Jr., and

Saunders, J.F., III, 1997, Denitrification as a component of the nitrogen budget for a large plains river:

Biochemistry, v. 39, p. 327-342.

Tate, C.M., and Heiny, J.S., 1995, The

ordination of benthic invertebrate

communities in the South Platte

River Basin in relation to environmental factors: Freshwater Biology, v. 33, no. 3, p. 439-454.

Tate, C.M., and Heiny, J.S., 1996, Organochlorine compounds in bed sediments and fish tissue in the South

Platte River Basin, USA, 1992-

1993: Archives of Environmental

Contamination and Toxicology,

v. 30, p. 62-78.

U.S. Department of Commerce, Bureau

of the Census, 1991, 1990 Census

population and housing: Washington D.C., Data on CD-ROM.

U.S. Environmental Protection Agency,

1986, Quality criteria for use,

1986: U.S. Environmental Protection Agency Report 440 14-86-001,

[variously paged].

U.S. Environmental Protection Agency,

1990, Maximum contaminantlevels (subpart B of 141, National

primary drinking-water regulations) (revised July 1, 1990): U.S.

Code of Federal Regulations, Title

40, Parts 100-149, p. 559-563.

U.S. Food and Drug Administration,

1989, Compliance policy guide

7141.01, Pesticide residues in food

of feed—Enforcement criteria,

Attachment B, Action levels for

unavoidable pesticide residues in

food and feed commodities: U.S.

Food and Drug Administration.

Wylie, B.K., Wagner, D.G., Hoffer,

R.M., Maxwell, S., and Shaffer,

M.J., 1993, Spatial distribution of

nitrate leaching ‘hot spots’ and

nitrate contributions to the South

Platte River Basin aquifers: Fort

Collins, Colorado Water

Resources Research Institute

Report 181, 12 p.

Zaugg, S.D. and others, 1995, Methods of analysis by the U.S. Geological Survey National Water

Quality Laboratory—Determination of pesticides in water by

C-18 solid-phase extraction and

capillary-column gas chromatography/mass spectrometry with

selected-ion monitoring: U.S.

Geological Survey Open-File

Report 95-181, 49 p.

South Platte NAWQA Study

Unit Bibliography--Additional

References:

Bradely, P.M., McMahon, P.B., and

Chapelle, 1995, Effects of carbon and nitrate on denitrification

in bottom sediments of an effluent-dominated river: Water

Resources Research, v. 31, no. 4,

p. 1063-1068.

Bruce, B.W., 1995, Denver’s urban

ground-water quality: Nutrients,

pesticides, and volatile organic

compounds: U.S. Geological

Survey Fact Sheet FS-106-95,

2 p.

Dennehy, Kevin F., 1991, National

Water-Quality Assessment Program—South Platte River Basin:

U.S. Geological Survey OpenFile Report 91-155, 2 p.

Dennehy, Kevin F. and Ortiz-Zayas,

Jorge R., 1993, Bibliography of

water-related studies; South

Platte River Basin—Colorado,

Nebraska, and Wyoming: U.S.

Geological Survey Open-File

Report 93-106, 278 p.

Heiny, J.S., 1995, Review of sediment

data in the South Platte River

Basin, Colorado, 1980-92: U.S.

Geological Survey Fact Sheet

FS-153-95, 2 p.

Heiny, J.S., 1997, Organochlorine

compounds and trace metals in

streambed sediment and fish

tissue, South Platte River

Basin—Colorado, Nebraska, and

Wyoming: U.S. Geological Survey Fact Sheet FS-040-97,

4 p.

Kimbrough, R.A., 1995, Are streams

in agricultural and urban areas

contaminated by pesticides?:

U.S. Geological Survey Fact

Sheet FS-104-95, 2 p.

Litke, D.W., 1995, Nutrients in the

South Platte River, 1993-95: U.S.

Geological Survey Fact Sheet

FS-105-95, 2 p.

McMahon, P.B., Litke, D.W., Paschal,

J.E., and Dennehy, K.F., 1994,

Ground water as a source of

nutrients and atrazine to streams

in the South Platte River Basin:

Water Resources Bulletin, v. 30,

no. 3, p. 521-530.

McMahon, P.B., Lull, K.J., Dennehy,

K.F., and Collins, J.A., 1995,

Quantity and quality of groundwater discharge to the South

Platte River, Denver to Fort Lupton, Colorado, August 1992

through July 1993: U.S. Geological Survey Water-Resources

Investigations Report 95-4110,

71 p.

McMahon, P.B., Tindall, J.A., Collins,

J.A., Lull, K.J., and Nuttle, J.R.,

1995, Hydrologic and geochemical effects on oxygen uptake in

bottom sediments of an effluentdominated river: Water

Resources Research, v. 31,

no. 10, p. 2561-2569.

McMahon, P.B., Böhlke, J.K., and

Litke, D.W., 1996, Nitrate in the

South Platte River alluvial aquifer, Colorado: U.S. Geological

Survey Yearbook, p. 39-41.

Minter, J.B., 1996, Comparison of

macroinvertebrate communities

from three substrates in the lower

South Platte River: Fort Collins,

Colorado State University, Master’s thesis.

Pfenning, K.S., and McMahon, P.B.,

1996, Effect of nitrate, organic

carbon, and temperature on

potential denitrification rates in

REFERENCES
U.S. Geological Survey Circular 1167 37

nitrate-rich riverbed sediments:

Journal of Hydrology, v. 187, p.

283-295.

Pocernich, M., and Litke, D.W., 1997,

Nutrient concentrations in wastewater-treatment plant effluents, South

Platte River Basin: Water Resources

Bulletin, v. 33, no. 1, p. 205-214.

Qi, S.L., 1995, Use of ARC/INFO in the

National Water-Quality Assessment Program—South Platte River

Basin Study: Proceedings of the Fifteenth Annual Environmental Systems Research Institute, Inc. (ESRI)

Users Conference, May 22-26,

1995, Palm Springs, California, 9 p.

Qi, S.L., and Dennehy, K.F., 1997, World

Wide Web home page for the South

Platte NAWQA: U.S. Geological

Survey Fact Sheet FS-242-96, 2 p.

Sjodin, A.L., 1996, Nitrogen processing

in a large plains river: Boulder, University of Colorado, Master’s thesis.

Tate, C.M., and Martin, L.M., 1995, Fish

communities in the plains region of

the South Platte River, August 1993

and 1994: U.S. Geological Survey

Fact Sheet FS-154-95, 2 p.

Tate, C.M., and Ortiz-Zayas, J.R.,1995,

An inventory of biological investigations related to streamwater quality in the South Platte River Basin,

Colorado, Nebraska, and Wyoming, 1891-1994: U.S. Geological

Survey Open-File Report 95-379,

12 p.

Wagner, D.G., and Hoffer, R.M., 1994,

Determination of land use by processing satellite images, Lonetree

Creek Basin—Final report: Fort

Collins, Colorado State University,

18 p. [Requisition 93-4608-0437]

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 1

foot in depth and covering

1 acre; equivalent to 43,560 cubic

feet or 325,851 gallons.

Basic Fixed Sites on streams at which

streamflow is measured and

samples are collected for temperature, salinity, suspended sediment,

major ions and metals, nutrients,

and organic carbon to assess the

broad-scale spatial and temporal

character and transport of inorganic

constituents of streamwater in relation to hydrologic conditions and

environmental settings.

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

stream or other watercourse.

Bed sediment and tissue studies -

Assessment of concentrations and

distributions of trace elements and

hydrophobic organic contaminants

in streambed sediment and tissues

of aquatic organisms to identify

potential sources and to assess spatial distribution.

Bioaccumulation - The biological

sequestering of a substance at a

higher concentration than that at

which it occurs in the surrounding

environment or medium. Also, the

process whereby a substance enters

organisms through the gills, epithelial tissues, dietary, or other sources.

Channelization - Modification of a

stream, typically by straightening

the channel, to provide more uniform flow; often done for flood control or for improved agricultural

drainage or irrigation.

Community - In ecology, the species

that interact in a common area.

Denitrification - A process by which

oxidized forms of nitrogen such as

nitrate (NO3

-

) are reduced to form

nitrites, nitrogen oxides, or free

nitrogen: commonly brought about

by the action of denitrifying bacteria and usually resulting in the

escape of nitrogen to the air.

Dissolved solids - Amount of minerals,

such as salt, that are dissolved in

water; amount of dissolved solids is

an indicator of salinity or hardness.

Effluent - Outflow from a particular

source, such as a stream that flows

from a lake or liquid waste that

flows from a factory or sewagetreatment plant.

Eutrophication - The process by which

a body of water becomes, either by

natural means or by pollution,

excessively rich in dissolved nutrients, resulting in extensive algal

growth.

Fish communities - See Community.

Front Range - Eastern slope of the

Rocky Mountains, in Colorado, it

generally extends from Colorado

Springs in the south to the Colorado

State Line to the north. When

referred to as the Front Range urban

corridor in this report, it extends

from Denver to Fort Collins along

the mountain front.

Intensive Fixed Sites - Basic sites with

increased sampling frequency during selected seasonal periods and

analysis of dissolved pesticides for

1 year. Most NAWQA Study Units

have one to two integrator Intensive

Fixed Sites and one to four indicator

Intensive Fixed Sites.

Invertebrate - An animal having no

backbone or spinal column.

Invertebrate density - The number of

individual invertebrates found

within a known area.

Ions - Elements or molecules that have a

positive or negative charge that are

responsible for the salinity of

stream water and can indicate the

source of the water.

Irrigation return flow - The part of irrigation applied to the surface that is

not consumed by evapotranspiration

or uptake by plants and that

migrates to an aquifer or surfacewater body.

Land-use study - A network of existing

shallow wells in an area having a

relatively uniform land use. These

studies are a subset of the StudyUnit Survey and have the goal of

relating the quality of shallow

ground water to land use. See also

Study-Unit Survey.

Load - General term that refers to a

material or constituent in solution,

in suspension, or in transport; usually expressed in terms of mass or

volume.

GLOSSARY
38 Water Quality in the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1992-95

Main stem - The principal course of a

river or a stream.

Maximum contaminant level (MCL) -

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.

Metabolite - A substance produced in or

by biological processes.

Nonpoint-source contaminant - A substance that pollutes or degrades

water that comes from lawn or cropland runoff, the atmosphere, roadways, and other diffuse sources.

Nutrient - Element or compound essential for animal and plant growth.

Common nutrients in fertilizer

include nitrogen, phosphorus, and

potassium.

Occurrence and distribution assessment - Characterization of the

broad-scale spatial and temporal distributions of water-quality conditions in relation to major

contaminant sources and background conditions for surface water

and ground water.

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 (PCBs), and some

solvents containing chlorine.

Pesticide - A chemical applied to crops,

rights of way, lawns, or residences to

control weeds, insects, fungi, nematodes, rodents or other “pests.”

Point source - A source at a discrete

location such as a discharge pipe,

drainage ditch, tunnel, well, concentrated livestock operation, or floating craft.

Polychlorinated biphenyls (PCBs) - A

mixture of chlorinated derivatives of

biphenyl, marketed under the trade

name Aroclor with a number designating the chlorine content (such as

Aroclor 1260). PCBs were used in

transformers and capacitors for insulating purposes and in gas pipeline

systems as a lubricant. Further sale

for new use was banned by law in

1979.

Salinity - The total quantity of dissolved

salts, measured by weight in parts

per thousand.

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).

Species - Populations of organisms that

may interbreed and produce fertile

offspring having similar structure,

habits, and functions.

Specific conductance - A measure of the

ability of a liquid to conduct an electrical current.

Study unit - A major hydrologic system

of the United States in which

NAWQA studies are focused. Study

Units are geographically defined by

a combination of ground- and surface-water features and generally

encompass more than 4,000 square

miles of land area.

Study-unit survey - Broad assessment of

the water-quality conditions of the

major aquifer systems of each Study

Unit. The Study-Unit

Survey relies primarily on sampling

existing wells and, wherever possible, on existing data collected by

other agencies and programs. Typically, 20 to 30 wells are sampled in

each of three to five aquifer subunits.

Suspended (as used in tables of chemical analyses) - The amount (concentration) of undissolved material in a

water-sediment mixture. It is associated with the material retained on a

0.45- micrometer filter.

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 sites - Sites that are sampled

within a selected time period so that

samples represent similar hydrographic conditions.

GLOSSARY

Taxon (plural taxa) - Any identifiable

group of taxonomically related

organisms.

Tissue study - The assessment of concentrations and distributions of trace elements and certain organic

contaminants in tissues of aquatic

organisms.

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.

Volatile organic compounds (VOCs) -

Organic chemicals that have a high

vapor pressure relative to their water

solubility. VOCs include components of gasoline, fuel oils, and lubricants, as well as organic solvents,

fumigants, some inert ingredients in

pesticides, and some by-products of

chlorine disinfection.
Dennehy and others • Water Quality in the South Platte River Basin

USGS Circular 1167 • 1998

National Water-Quality Assessment (NAWQA) Program

South Platte River Basin

NAWQA

Denver

Cheyenne

South

Platte Riv er

Sout h Pl atte River

NEBRASKA WYOMING

COLORADO