Water Quality in the

Rio Grande Valley

Colorado, New Mexico, and Texas, 1992–95

U.S. Department of the Interior

U.S. Geological Survey Circular 1162

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

following agencies and organizations who directly participated in the Rio Grande Valley program.

•Bureau of Land Management •Bureau of Reclamation

•City of Albuquerque •City of Las Cruces

•City of Sante Fe •Colorado Department of Health

•Colorado Division of Water Resources, Division III •Colorado Division of Wildlife

•Colorado State University •Elephant Butte Irrigation District

•International Boundary and Water Commission •Los Alamos National Laboratory

•Middle Rio Grande Conservancy District •National Park Service

•Natural Resources Conservation Service •New Mexico Environment Department

•New Mexico Game and Fish Department •New Mexico Highlands University

•New Mexico State Engineer •New Mexico Water Resources Research Institute

•Pueblo of Isleta •Pueblo of Santa Clara

•Rio Grande Water Conservation District •Texas Natural Resources Conservation Commission

•Town of Sunland Park •University of New Mexico

•U.S. Environmental Protection Agency •U.S. Fish and Wildlife Service

Front cover: Rio Grande at Taos Junction Bridge near Taos, New Mexico.

 (Photograph by Lisa F. Carter, U.S. Geological Survey)

Back cover: Electro fishing on the Rio Grande near Del Norte, Colorado.

 (Photograph by Denis F. Healy, U.S. Geological Survey)

 Installing monitoring wells in the Rincon Valley, New Mexico.

 (Photograph by Scott K. Anderholm, U.S. Geological Survey)

Rio Grande Valley Study Unit, contact:

District Chief

U.S. Geological Survey

Water Resources Division

4501 Indian School Road NE, Suite 200

Albuquerque, NM 87110-3929

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Division

12201 Sunrise Valley Drive, M.S. 4

Reston, VA 20192

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

connect to the NAWQA home page using the Universal Resources Locator (URL):

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

The Rio Grande Valley Study Unit’s home page is at URL:

http://water.usgs.gov/lookup/get?nmwater/riognawqa/riognawqa4.html

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

http://water.usgs.gov/lookup/get?circ1162

A COORDINATED EFFORT

FOR ADDITIONAL INFORMATION ON THE

NATIONAL WATER-QUALITY ASSESSMENT (NAWQA) PROGRAM:
Water Quality in the Rio Grande Valley,

Colorado, New Mexico, and Texas, 1992-95

U.S. GEOLOGICAL SURVEY CIRCULAR 1162

By Gary W. Levings, Denis F. Healy, Steven F. Richey,

and Lisa F. Carter

CONTENTS

National Water-Quality Assessment

Program ........................................................

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

Environmental setting and hydrologic

conditions .....................................................

Major issues and findings..............................

Welcome to the Rio Grande Valley ...........

Organics in ground water, surface

 water, bed sediment, and fish tissue .....

Nutrients in ground water and surface

water ...........................................................

Radon in ground water and dissolved

solids in surface water..............................

Trace elements..............................................

Fish communities and stream

habitat.........................................................

Water quality conditions in a

national context ...........................................

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

Summary of compound detections

and concentrations ......................................

References ........................................................

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

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

does not constitute endorsement by the U.S. Government

 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

Levings, Gary W.

 Water quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992–95

 p. cm. -- (U.S. Geological Survey circular ; 1162)

 Includes bibliographical references.

 1. Water quality--Rio Grande Valley I. Levings, Gary W. II. Geological Survey (U.S.) III. Series: U.S.

Geological Survey circular : 1162-G.

TD225.R53W38 1998

363.739’42’097644--dc21

98-11972

CIP

ISBN 0-607-89113-0
U.S. Geological Survey Circular 1162 

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 water-quality conditions in a particular

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

comparisons among watersheds and improve our understanding of the

factors that affect water-quality conditions regionally and nationally.

This report is intended to summarize major findings that emerged

between 1992 and 1995 from the water-quality assessment of the Rio

Grande Valley 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

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

“In New Mexico, we are

particularly pleased with

the NAWQA effort on the

Rio Grande. We were in

great need of reliable, scientific data from which to

assess the health of the

river system. Now we are

able to use these data to

improve our management

of this vital water

resource.”

Bobby J. Creel,

Assistant Director,

New Mexico Water

Resources Research

Institute
2 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

COLORADO

NEW

MEXICO

Issue: Ground water is the main source of drinking water in the Rio Gra

Valley Study Unit; its quality is a major concern.

A variety of chemicals used in human activities, including pesticides, vola

organic compounds (VOCs), and nitrate, were detected in ground-water

samples from shallow wells (within the top 10-15 feet of the water table).

Samples from deeper ground water underlying the Rio Grande flood pla

which is more typically used as a drinking-water source, contained one

pesticide, no VOCs, and nitrates (pages 10, 13, and 14).

• Nitrate concentrations exceeded the U.S. Environmental Protection Agency (EPA) 

ing-water standard in 31 percent of shallow wells in the San Luis Valley and 17 per

shallow wells in the Rincon Valley. Both of these areas are predominantly agricultu

use.

• Pesticides were detected in both agricultural and urban land-use areas, with 29 percent of shallow wel

taining at least one pesticide. Prometon and metolachlor were the most frequently detected, yet neithe

pound exceeded EPA drinking-water standards, although standards do not exist for all pesticides detec

Only one pesticide was detected in the deeper ground water.

• Six VOCs were detected in shallow ground water from 11 percent of the wells sampled, most common

urban land-use area. No VOCs were found in deeper ground water. No concentrations exceeded EPA d

ing-water standards; however, standards exist for only three of the six compounds detected.

• Radon, a naturally occurring radionuclide in the Rio Grande Valley, was detected in all ground-water s

in concentrations that ranged from 190 to 2,300 picocuries per liter. The highest median concentration

occurred in shallow wells in the San Luis Valley and in the deeper ground water. About 57 percent of t

ples exceeded 300 picocuries per liter, the proposed EPA drinking-water standard that has recently bee

drawn for further evaluation.

Issue: Pesticides are present in surface water, bed sediment, and whole-body fish at sites samp

the Rio Grande and its tributaries and drains.

No pesticide concentration detected in surface water exceeded EPA drinking-water standard

applicable Federal or State ambient criterion or guideline. One or more pesticides were detec

94 percent of the sites sampled in the Rio Grande, its tributaries, or drains; most concentrat

however, were at or only slightly above the laboratory level of detection (pages 10, 11, and 12

• In the Mesilla Valley, there were more detections of more different pesticides during the nonirrigation 

than during the irrigation season; as many as 27 percent of the pesticide detections attributed to pestic

in the Mesilla Valley may be from urban sources.

• In the Rincon Valley, more pesticide compounds were detected more frequently in agricultural drains i

than in October or January; some individual pesticides detected in agricultural drains were not detecte

shallow ground water.

• Concentrations of DDE were detected in composited samples of fish collected at 10 of 11 sites; these 

trations, however, are below the national median reported by the U.S. Fish and Wildlife Service (FWS

National Contaminant Biomonitoring Program.

• The presence of DDT and its metabolites, DDE and DDD, in bed sediment and whole-body fish confi

persistence of this pesticide in the environment.

• Cis-chlordane, trans-chlordane, and trans-nonachlor were detected in whole-body fish samples; conc

tions, however, were below the national median reported by the FWS National Contaminant Biomonit

Program.

SUMMARY OF MAJOR ISSUES AND FINDINGS
U.S. Geological Survey Circular 1162 

SUMMARY OF MAJOR ISSUES AND FIND

Issue: Have elevated trace-element concentrations impaired reaches of the Rio Grande and i

tributaries and, if so, can the sources be identified?

The water quality in reaches of the Rio Grande and some of its tributaries has been impaire

elevated concentrations of trace elements; however, data indicate that the concentrations ten

decrease downstream from the source. A combination of natural conditions and human activ

appears to be associated with elevated trace-element concentrations (page 19).

• Highly elevated concentrations of antimony, arsenic, cadmium, copper, lead, mercury, silver, and zinc 

detected in bed sediment from Willow Creek and the Rio Grande, downstream from the Creede, Color

Mining District.

• Elevated concentrations of arsenic, cadmium, copper, lead, and zinc were detected in fish tissue (liver) 

Rio Grande downstream from the Creede, Colorado, Mining District.

• Analysis of data collected using transplanted bryophytes (moss) indicates that concentrations of cadm

copper, lead, and zinc in bryophytes increased at sites on the Rio Grande immediately downstream fro

taries that drain mining districts but decreased with distance from the tributaries. Concentrations of mo

elements in bryophytes were lower in a tributary stream downstream from urban land use than at sites 

mining or agricultural land use.

• Dissolved concentrations of beryllium, cadmium, cobalt, lithium, manganese, molybdenum, nickel, an

were moderately higher at a site on the lower Red River than in the Rio Grande downstream of its con

with the Red River.

• Highly elevated concentrations of dissolved cadmium, cobalt, copper, iron, manganese, nickel, strontiu

nium, and vanadium were detected in the Alamosa River where it enters the San Luis Valley.

• Maximum total recoverable concentrations of most trace elements in bed sediment were detected near 

mouth of the Rio Puerco, an indication of the importance of sediment in trace-element transport.

Issue: Is the fish community structure in the Rio Grande Valley an indication that sites are

environmentally stressed?

Based on the number of introduced, omnivorous, pollution-tolerant fish and the number of fi

with external anomalies, six of the ten sites sampled appear to show some indications of

environmental perturbation (page 20).

• Fish community-structure data indicate that introduced species predominate at four of the six sites sam

during 1994. Stocking introduced species has probably resulted in the displacement of native species t

competition or predation.

• The number of introduced, omnivorous, pollution-tolerant, and anomalous fish at sites sampled in the 

Grande indicate that sites are environmentally stressed.

Issue: Is significant habitat degradation occurring in the Rio Grande Valley?

Six of the 10 sites sampled appear to have significant habitat degradation based on stream

modification, bank erosion, bank vegetation stability, and riparian vegetation density (page 2

• Rio Grande near Del Norte, Colorado; Conejos River near Lasauses, Colorado; Rio Chama near Cham

New Mexico; Santa Fe River above Cochiti Lake, New Mexico; Rio Grande at Isleta, New Mexico; an

Grande at El Paso, Texas, appear to have significant habitat degradation.
4 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

ENVIRONMENTAL SETTING AND HYDROLOGIC CONDITIONS

Socorro

El Paso, Texas

Santa Fe

Alamosa

Albuquerque

Taos

Las Cruces

Colorado

New Mexico

Southern Rocky

Mountains Province

Colorado

Plateaus

Province

Basin and Range

Province

Mexico

United States

0 30 60 MILES

0 30 60 KILOMETERS

0 30 60 MILES

0 30 60 KILOMETERS

Urban

Agriculture

Forest

Barren and

Other

Rangeland

EXPLANATIO

LAND USE

0 0

10

20

30

40

50

60

70

80

90

100

PERCENTAGE OF TOTAL

WATER WITHDRAWALS

500

1,000

1,500

2,000

2,500

3,000

3,500

GROUND WATER

SURFACE WATER

WATER WITHDRAWALS,

IN MILLIONS OF GALLONS PER DAY

TOTAL

PUBLIC SUPPLY

(911,000 served)

DOMESTIC SUPPLY

(193,000 served)

COMMERCIAL AND

LIVESTOCK

INDUSTRIAL AND

MINING

IRRIGATION

ESTIMATED WATER WITHDRAWAL IN 1990

URBAN AGRICULTURERANGELANDFOREST BARREN

AND

OTHER

LAND USE

30,000

0

5,000

10,000

15,000

20,000

25,000

AREA, IN SQUARE MILES

TOTAL AREA =

45,900 SQUARE

MILES

(430)

(1820) (880)

(16,500)

(26,300)

Rangeland is dominant in the Basin and Range

Province, and forest is dominant in the Southern

Rocky Mountains and Colorado Plateaus Provin

Agricultural land use is limited primarily to areas w

surface water or shallow ground water is availab

irrigation.

The Rio Grande Valley Study Unit is located in three

physiographic provinces. Extreme contrasts in

precipitation, runoff, and temperature characteristics

exist between the Southern Rocky Mountains and the

Basin and Range Provinces. These characteristics

strongly affect land and water use in the Study Unit.

Approximately 5 percent of the land use is agricultural and urban; however, agricultural and urban land uses account 

percent and 8 percent, respectively, of the water used in the study area. Almost all public and domestic supplies rely 

ground water, primarily from deeper aquifers. Surface-water availability typically is necessary for agriculture with the

exception of a few areas where ground water is available in sufficient quantities.
U.S. Geological Survey Circular 1162 

ENVIRONMENTAL SETTING AND HYDROLOGIC COND

EXPLANATION

MONTHLY TOTAL

PRECIPITATION

HISTORICAL MEDIAN For

precipitation, it is the median

of monthly total precipitation.

For streamflow, it is the

median of monthly median

streamflow. Period of

record is 1960-90

PRECIPITATION, IN INCHES

0

5

10

15

JAN 1993

JAN 1994

JAN 1995

Wolf Creek Pass

Red River

0

5

10

15

JAN 1993

JAN 1994

JAN 1995

PRECIPITATION, IN INCHES

Elephant Butte Dam

0

5

10

15

JAN 1993

JAN 1994

JAN 1995

PRECIPITATION, IN INCHES PRECIPITATION, IN INCHES

0

5

10

15

JAN 1993

JAN 1994

JAN 1995

Albuquerque

Socorro

El Paso, Texas

Santa Fe

Alamosa

Albuquerque

Taos

Las Cruces

Colorado

New Mexico

JAN 1993

JAN 1994

JAN 1995

0

5,000

1,000

2,000

3,000

4,000

STREAMFLOW, IN CUBIC FEET

PER SECOND

JAN 1993

JAN 1994

JAN 1995

5,000

0

1,000

2,000

3,000

4,000

STREAMFLOW, IN CUBIC FEET

PER SECOND

JAN 1993

JAN 1994

JAN 1995

5,000

0

1,000

2,000

3,000

4,000

STREAMFLOW, IN CUBIC FEET

PER SECOND

JAN 1993

JAN 1994

JAN 1995

STREAMFLOW, IN CUBIC FEET

PER SECOND

5,000

0

1,000

2,000

3,000

4,000

Rio Grande near Del Norte

Rio Grande near Lobatos

Rio Grande Conveyance Channel

and Floodway at San Marcial

Rio Grande at El Paso

MONTHLY MEDIAN

STREAMFLOW

A comparison of precipitation and streamflow at selected sites for the study period 1992-95 with the historical period 19

shown above. Monthly total precipitation during the study period was generally higher than the monthly median at the t

northern sites, whereas precipitation at the two southern sites was near the median. The monthly median streamflow a

northern sites was generally about the same as the historical median monthly streamflow except during spring runoff w

monthly median during the study period exceeded the historical median streamflow. The streamflow at the two southern 

controlled primarily by reservoir releases, but did exceed the historical median during the irrigation season. The impac

above average precipitation and streamflow on the water quality of the Study Unit cannot be generalized, it must be ev

on a site by site basis. This detailed evaluation is necessary because of the complexity of the interaction of surface wa

ground water, irrigation withdrawal and return, and reservoir storage and release.
6 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

MAJOR ISSUES AND FINDINGS

Welcome to the Rio Grande Valley

The Rio Grande is the only river I ever saw that needed irrigation.

—Will Rogers

A discussion of water-quality

issues, results, or findings in the Rio

Grande Valley Study Unit (fig. 1) necessarily emphasizes the historical

importance of surface water in this arid

to semiarid environment. Surface

water has been the “lifeblood of the

Rio Grande Valley.” Records from the

sixteenth-century Spanish expeditions

into the area report that irrigated agriculture was in use by some of the

indigenous peoples. Where surface

water and springs existed, people

could exist. As European colonization

of the area occurred, the introduction

of new crops, such as wheat, barley,

and oats, required the expansion of

irrigation systems. As a result, settlements were established on the flood

plains of the streams where agricultural land could be irrigated. Only

when technological developments

facilitated access to water in deep

aquifers did settlements begin to

appear throughout the Study Unit.

Grande flood plain. Limited work also

was conducted on tributary and nontributary streams in the northern part

of the Study Unit. The only exception

was an agricultural land-use study

component assessing shallow ground

water in basin-fill deposits in the San

Luis Valley located primarily outside

the flood plain. For a discussion of the

objectives, a brief description, and the

water-quality measures of these study

components, see the Study Design and

Data Collection section (page 26).

Selected results and interpretations

based on these study components are

discussed in the following sections.

Detailed data interpretation for

selected study components is reported

in individual reports (see References

section, page 34).

The following discussion includes

interpretation of data collected for

analysis of pesticides, nutrients, radon,

volatile organic compounds, dissolved

solids, and trace elements and results

Not all data collected as par

NAWQA Program have been c

in reports. These data have bee

lected at specific sites through

Study Unit and are available in 

files. For example, ground-wat

were collected at two sites in A

querque and at one site in the M

Valley to determine the age of 

water with depth. Biological c

nity surveys conducted at selec

face-water sites include quanti

and qualitative sampling meth

algae and benthic invertebrates

characterization including stre

reach characterization, instream 

0 30 60 MILES

0 30 60 KILOMETERS

Rio

Puerco

37

UNIT

STUDY

BOUNDARY

Colorado

106

32

New Mexico

33

34

35

36

107

38

108

MEXICO

UNITED STATES

Albuquerq

Elephant

Butte Res

Caballo

Res

Conejos R

Cochiti

Lake

El Paso,

Texas

Las

Cruces

Del

Norte Rio

Grande

Reservoir

Rio Chama

Rio Grande

Saguache C

Rio

Gra

d

San

Luis

Va

Rincon

Valley

Mesilla Valley

Alamosa R

Creede

Figure 1.—Rio Grande Valley 

Unit.

For the people living in the Rio

Grande Valley, the importance of

water—both quantity and quality—is

an ongoing issue. Water-resource

issues of a local or regional nature

appear in the news virtually everyday.

As competition for the limited water

resource intensifies, major economic

decisions, both locally and regionally,

will be controlled by the availability

of usable quantities of ground and surface water.

The objective of the NAWQA Program is to assess the status of and

trends in the Nation’s water quality. In

the Rio Grande Valley Study Unit, a

series of interrelated but separate

study components were conducted

during 1992-95 to assess the quality of

ground and surface water (fig. 2). The

primary focus was along the Rio

of ecological studies of biological communities and stream habitat. Where

applicable, these constituents are compared to EPA maximum contaminant

levels (MCLs), secondary maximum

contaminant levels (SMCLs), or health

advisories (HAs) for public water systems (U.S. Environmental Protection

Agency, 1996a). For ambient water, the

EPA, National Academy of Sciences,

and Environment Canada have established water-quality criteria or guidelines for aquatic organisms. These

criteria may be used by State agencies

to establish local ambient criteria. The

FWS has reported median values for

organochlorine compounds and polychlorinated biphenyls as part of their

National Biomonitoring Program

(Schmitt and others, 1985, 1990;

Schmitt and Brumbaugh, 1990).
U.S. Geological Survey Circular 1162 

MAJOR ISSUES AND FI

Welcome to the Rio Grand

bank vegetation species, density, and

species dominance along transects perpendicular to the stream; and stream

meandering, gradient, elevation, and

water-management features (dams,

bridges, canals, or diversions).

The Study Unit, approximately

45,900 square miles, contains diverse

hydrologic and climatological regimes.

Altitudes range from peaks exceeding

14,000 feet in the northern part of the

Study Unit to approximately 3,700 feet

at the lower basin boundary. The climate in the high mountain headwater

areas of the Rio Grande and its northern tributaries is alpine tundra where

average annual precipitation may

exceed 50 inches; most of this precipitation is in the form of snow. Annual

runoff in mountainous areas may

exceed 30 inches. In contrast, 750

miles downstream near the lower basin

boundary of the Study Unit, the Rio

Grande flows through a portion of the

Chihuahuan Desert where average

annual precipitation is less than 8

inches; most of this precipitation is in

the form of summer thunderstorms.

Annual runoff is less than 0.01 inch. In

the mountainous headwater areas,

annual potential evaporation is less

than 70 percent of annual precipitation,

whereas in the southern part of the

Study Unit, annual potential evaporation may exceed 1,000 percent of

annual precipitation.

The existence of a reliable source of

surface water in the southern part of

the Study Unit is the result of human

alteration of the river system by the

construction of reservoirs to control

runoff. The storage of runoff in the

springtime allows for a dependable

source of water to support irrigation

needs throughout the long growing

season. This alteration of the river system has affected the water quality of

the Rio Grande.

Within the Study Unit, two groundwater land-use studies and one aquifer

subunit survey focused on the flood

plain of the Rio Grande from Cochiti

Lake in New Mexico, to El Paso,

Figure 2.—Land-use studies, aquifer subunit survey, and surface-water site
8 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

MAJOR ISSUES AND FINDINGS

Welcome to the Rio Grande Valley

Texas. One land-use study was conducted in the basin-fill deposits in the

San Luis Valley in Colorado. Only

when the hydrologic system along the

Rio Grande is understood can the complexity of the many influences that

affect water quality throughout the

Study Unit be appreciated. A detailed

discussion of the ground-water system

in the Study Unit is presented in Ellis

and others (1993). The following is a

brief description of the ground-water

system to aid in understanding the following water-quality discussions.

Complex interactions occur

between ground water and surface

water in the Rio Grande flood plain. A

system of canals distributes surface

water for agricultural irrigation and a

system of drains intercepts shallow

ground water and returns it to 

Grande. Surface water leaks fr

Rio Grande and canals to rech

shallow ground-water system. 

places, deeper ground water fl

upward to recharge the shallow

ground-water system and/or to 

ute flow to the Rio Grande. In a

excess applied irrigation water 

trates and recharges the shallo

ground-water system. Evapotr

tion losses from vegetation, la

water surfaces, can have a maj

on the quality of ground water

Two land-use studies, in the 

querque area and in the Rincon 

focused on the upper 10-15 fee

ground water in the flood-plain 

vium (referred to as shallow g

water in this report). This wate

ally is not used for domestic su

However, because of the intera

with surface water and, in isol

areas, because declines in the 

level in the deeper aquifer have 

the shallow aquifer to be a rec

source in some areas, knowing 

quality of the shallow ground 

important in making managem

decisions.

 The aquifer subunit survey

Cochiti Lake to El Paso, focus

deeper water underlying the fl

plain (referred to as deeper gro

water in this report). This wate

for domestic supply in some a

The land-use study in the S

Valley was not entirely in the R

Grande flood plain. Most of th

in the San Luis Closed Basin, 

both a ground-water and surfac

closed basin. Neither ground w

surface water flows out of the 

Basin. The shallow ground wa

unconsolidated basin-fill depo

water in these basin-fill deposi

used extensively for irrigation 

a limited basis, for domestic su

However, these wells generally 

several tens of feet of the aqui

study wells were completed in 

upper 10-15 feet of the saturat

fill deposits.

 Table 1.—Rio Grande Valley Study Unit Basic Fixed Sites

[Main-stem sites shown in blue]

Site number Station name

1 Rio Grande near Del Norte, Colo.

2 Saguache Creek near Saguache, Colo.

3 Medano Creek near Mosca, Colo.

4 Rio Grande above mouth of Trinchera Creek, near Lasauses, Colo.

5 Conejos River near Lasauses, Colo.

6 Rio Grande near Lobatos, Colo.

7 Rio Grande below Taos Junction Bridge, near Taos, N. Mex.

8 Rio Chama near Chamita, N. Mex.

9 Rio Grande at Otowi Bridge near San Ildefonso, N. Mex.

10 Rito de los Frijoles in Bandelier National Monument, N. Mex.

11 Santa Fe River above Cochiti Lake, N. Mex.

12 Rio Grande at Isleta, N. Mex.

13 Rio Puerco near Bernardo, N. Mex.

14 Rio Grande Conveyance Channel at San Marcial, N. Mex.

15 Rio Grande Floodway at San Marcial, N. Mex.

16 Rio Grande below Leasburg Dam near Leasburg, N. Mex.

17 Rio Grande at El Paso, Tex.

Rio Grande Reservoir, in the headwaters of the Rio Grande, is used to store

runoff for irrigation at surface-water diversions in the San Luis Valley (photograph

by Sherman R. Ellis, U.S. Geological Survey).
U.S. Geological Survey Circular 1162 

MAJOR ISSUES AND FI

Welcome to the Rio Grand

Historically, streamflow in the Rio

Grande was caused by spring snowmelt (April through June) and summer

monsoon thunderstorms (July and

August). This natural streamflow pattern has been altered and regulated by

the construction of reservoirs on the

main stem and tributaries that impound

and store water for later use, primarily

irrigation.

All surface water in the Rio Grande

is appropriated by various compacts,

treaties, and individual water rights.

Appropriated surface-water rights on

the Rio Grande in Colorado and New

Mexico usually exceed the annual

mean flow of the river (Ellis and others, 1993).

As the discussion of the water-quality data is presented, it is important to

realize that 89 percent of water use in

the Study Unit in 1990 was for irrigation, 8 percent for public supply, and 3

percent for all other uses. The effect

that irrigation and urban use has on the

quality of surface water is related to

the processes to which the water is

subjected as it moves downstream. It is

repeatedly diverted, applied to fields,

returned to the Rio Grande directly or

through drains, impounded in reservoirs, lost to evapotranspiration, or

consumptively used. Urban areas contribute wastewater and anthropogenic

organic chemicals such as volatile

organic compounds and pesticides;

agricultural areas contribute chemicals

from fertilizers and pesticides; mining

areas contribute trace elements; atmospheric deposition contributes chemicals such as nitrate and phosphorus;

and the use and reuse of water

increases dissolved-solids concentrations because of evapotranspiration.

All of these processes can contribute to

deterioration in surface-water quality

of the Rio Grande as it moves through

the basin.

Typical ephemeral tributary channel to the Rio Grande in the lower part o

Study Unit. Runoff occurs in response to precipitation (photograph by She

R. Ellis, U.S. Geological Survey).

San Acacia Diversion Dam on the Rio Grande about 55 miles downstream 

Albuquerque is one of several diversion dams established on the Rio Grand

surface-water irrigation (photograph by Sherman R. Ellis, U.S. Geological S
10 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

MAJOR ISSUES AND FINDINGS

Organics in Ground Water, Surface Water, Bed Sediment, and Fish Tissue

Synthetic organic compounds have

been detected in ground and surface

water, sediment, and biota of the aquifers, rivers, and lakes throughout the

United States. These organic compounds enter the hydrologic system in

point-source discharges, nonpointsource runoff, atmospheric deposition,

and ground-water discharges.

Why are Pesticides of

Interest?

Pesticides are used to control many

different types of weeds, insects, and

other pests in a wide variety of agricultural and urban settings. Concerns

have grown steadily about the potential

adverse effects of pesticides on the

environment and human health

through contamination of the hydrologic system. Water is one of the primary means by which pesticides are

transported from their application

areas to other parts of the environment.

Through physical processes such as

erosion, surface runoff, and groundwater recharge, trace amounts of pesticides used on lawns, gardens, road

rights-of-way, and crops can eventually end up in the ground-water system

and in streams. Although many modern pesticides are designed to degrade

rapidly, the short distance between the

land surface and shallow water table

makes shallow wells more susceptible

to contamination than deeper wells.

Organochlorine pesticides are synthetic hydrophobic organic chemicals

that pose a threat to the environment

because of their persistence (their use

has been banned in the U.S. since the

early 1970’s) and toxicity to most

organisms. They tend to adsorb to

organic carbon in suspended or bed

sediments rather than dissolve in the

water column. Because of this characteristic, these compounds can be

present in sediments in concentrations

that are much larger than those in the

water column. Sediments can provide

a mechanism by which organochlorine

pesticides remain in a surface-water

system many years after their initial

introduction and are available for

downstream transport and bioaccumulation in aquatic organisms.

Pesticides in Ground Water

During 1993-95, 65 wells that tap

shallow ground water were sampled in

two agricultural land-use studies (table

2). Eighteen wells had detectable pesticides, with 6 different pesticides

detected a total of 23 times. Of the 24

wells that represent urban land use

overlying shallow ground water, 8

wells had detectable pesticides, with 5

different pesticides detected a total of

nine times. The aquifer subunit survey,

which sampled water from existing

wells that are completed in the deeper

aquifer, yielded only 1 pesticide detection for 30 wells. The pesticides

detected most often were prometon

(12) and metolachlor (10) (table 2). No

concentrations of pesticides exceeded

any EPA MCL or HA.

The small number of differe

cides detected and the small co

tions of those pesticides indica

leaching of pesticides from lan

face to shallow ground water i

land-use areas. The detection o

one pesticide in the samples fr

aquifer subunit survey suggest

shallow ground water containi

cides has not moved into deep

of the aquifer.

Pesticides in Surface Wat

During 1994-95, 156 water 

were collected at 40 stream an

sites to study the occurrence a

sonal variability of pesticides. 

samples were collected as part 

separate study components (ta

Collectively, 322 detections of 

ticides occurred in 125 of the 

ples. The most commonly dete

pesticides were DCPA (65 sam

metolachlor (53), prometon (3

simazine (36). The pesticides d

1

Pesticide identified but concentration was not determined at a 99-percent confidence 

Table 2.—Pesticide detections in ground water

[μg/L, micrograms per liter; MCL, U.S. Environmental Protection Agenc

maximum contaminant level; HA, U.S. Environmental Protection Agency

lifetime health advisory; E, estimated;1 --, no MCL or HA established]

Pesticide Number of

detections

Detection

concentration

(μg/L)

MCL

(μg/L)

HA

(μg/L)

San Luis Valley agricultural land-use study (35 samples)

Metribuzin 3 E0.005 - 0.017 -- 100

Metolachlor 1 0.072 -- 70

p,p’-DDE 1 E0.002 -- --

Prometon 1 0.01 -- 100

Albuquerque urban land-use study (24 samples)

Prometon 5 E0.005 - 0.27 -- 100

Atrazine 1 0.016 3 3

Bromacil 1 0.52 -- 90

Carbaryl 1 E0.021 -- 700

Carbofuran 1 E0.010 40 40

Rincon Valley agricultural land-use study (30 samples)

Metolachlor 9 E0.005 - 5.4 -- 70

Prometon 5 E0.005 - 0.32 -- 100

Diazinon 1 0.077 -- --

Napropamide 1 0.014 -- --

p,p’-DDE 1 E0.002 -- --

Aquifer subunit survey (30 samples)

Prometon 1 0.038 -- 100
U.S. Geological Survey Circular 1162 

MAJOR ISSUES AND FI

Organics in Ground Water, Surface Water, Bed Sediment, and Fish 

at the largest number of sites were

DCPA (25 sites), metolachlor (23),

prometon (14), and carbofuran (14).

The maximum pesticide concentration

detected was an estimated 0.75 microgram per liter carbofuran. The presence of pesticides in surface water is

erratic and probably highly dependent

on the amount applied and the timing,

location, and method of application.

On the basis of data collected, pesticide concentrations are usually small

and do not presently appear to be a

major concern in the surface waters of

the Rio Grande Valley. Table 4 lists the

eight pesticides with the largest concentrations; all but one site is located

in the Rincon or Mesilla Valley. Of

these pesticides, only carbofuran has

an established EPA MCL and it was

not exceeded. No pesticide concentration exceeded EPA MCLs, HAs, or any

applicable Federal or State ambient

criteria or exposure guidelines. The

relatively frequent detection of pesticides at low levels, however, indicates

ongoing exposure that merits careful

monitoring. Water-quality standards

have not been set for many pesticides

and existing standards do not consider

cumulative effects of several pesticides

in the water at the same time.

The pesticide synoptic study conducted in the Mesilla Valley enabled

pesticide concentrations during the

irrigation and the nonirrigation seasons

to be compared. There were more

detections of different pesticides during the nonirrigation season than during the irrigation season. The synoptic

study also allowed comparison

between urban contributions (samples

from wastewater-treatment plant effluent) and agricultural contributions

(drains). About one- fourth of the pesticide detections in the Mesilla Valley

may be from urban sources.

During the temporal study of drains

in the Rincon Valley, pesticides were

detected more frequently in drains in

April than in October or January. Also,

some pesticides were detected 

drains but not in shallow groun

This may mean that pesticides 

entering drains as a result of su

runoff from fields or that the ti

ground-water sampling in the 

(April-May) was not represent

ground-water quality througho

year.

Pesticides in Bed Sedime

Whole-Body Fish Tissue

As part of the pesticide sam

the Mesilla and Rincon Valley

sediment also was sampled ne

mouths of nine drains. Sample

sediment from all nine drains c

tained detectable concentration

DDT, DDD, and DDE.

Bed sediment was sampled 

sites between September 1992 

March 1993 to characterize th

graphic distribution of organoc

pesticides and polychlorinated 

nyls (PCBs). Six of the bed-se

samples had detectable concen

of at least one DDT-related com

No other organochlorine pestic

were reported in bed sediment

As part of the whole-body fi

sue contaminant study, fish we

lected at 11 of the 18 bed-sedi

sites and analyzed for organoc

pesticides and PCBs. Concent

of DDE were detected in comp

samples of fish collected at 10 

11 sites; these concentrations, 

ever, were below the median r

 Table 3.—Surface-water pesticide study components

Study-Unit

component

Number

of sites

Number of

samples

Number of

detections

Mesilla Valley pesticide

synoptic study

19 51 100

Rincon Valley temporal

drain study

11 37 93

Basic Fixed Site study 9 45 120

Intensive Fixed Site study 1 23 9

Ground-water sampling at one of the monitoring wells in the San Luis Valley

(photograph by Sherman R. Ellis, U.S. Geological Survey).
12 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

MAJOR ISSUES AND FINDINGS

Organics in Ground Water, Surface Water, Bed Sediment, and Fish Tissue

by the FWS National Contaminant

Biomonitoring Program. Cis-chlordane, trans-chlordane, and trans-nonachlor were other compounds detected

in whole-body samples of fish from at

least one site; these concentrations also

were below the median reported by the

FWS National Contaminant Biomonitoring Program.

Comparison of pesticide data for

bed sediment and whole-body fish tissue indicates (1) organochlorine pesticides were reported more frequently in

fish samples and (2) more types of pesticides were detected in fish samples.

The presence of DDT and its metabo10.5 μg/kg in sediments depo

the late 1960s, then decreased 

nentially, indicating the gradu

removal of residual total DDT 

watershed. The largest concen

detected in the core does not e

sediment-quality guidelines p

for aquatic life (Environment 

1995, and Environmental Pro

Agency, 1996b).

Volatile Organic Comp

in Ground Water

Volatile organic compound

are carbon-containing chemic

readily evaporate at normal ai

ature and pressure. They are c

in many commercial products 

gasoline, paints, adhesives, so

wood preservatives, dry-clean

agents, pesticides, fertilizers, 

ics, and refrigerants. Some VO

suspected carcinogens and are 

humans or wildlife.

Improper disposal of VOC

result in the leaching or infiltr

these compounds to the shallo

ground-water system. VOCs c

be removed from ground wate

adsorption onto clays or organ

rials, or they can be broken do

bacteria and other microbes in 

The detection of VOCs in gro

water indicates compounds ge

associated with human activit

ing into ground water.

1

Pesticide identified, but concentration was not determined at a 99-percent confidence level.

 Table 4.—Eight largest pesticide concentrations detected in surface water

 [μg/L, micrograms per liter; MCL, U.S. Environmental Protection Agency maximum contaminant

level; E, estimated;1 --, no MCL; WWTP, wastewater-treatment plant]

Pesticide Concentration

(μg/L) Date Location MCL(μg/L)

Carbofuran E0.75 04/27/94 East Side Drain at levee road near Anthony, Tex. 40

Metolachlor 0.41 01/04/95 Hatch Drain at Rio Grande, near Hatch, N. Mex. --

DCPA 0.21 10/26/94 Rincon Drain at Rio Grande, near Rincon, N. Mex. --

Diazinon 0.21 09/06/95 Santa Fe River above Cochiti Lake, N. Mex. --

Chlorpyrifos 0.19 04/26/94 Las Cruces WWTP outflow at levee road, Las Cruces, N. Mex. --

DCPA 0.17 04/22/94 Rincon Drain at Rio Grande, near Rincon, N. Mex. --

Diazinon 0.16 04/28/94 Sunland Park WWTP at Sunland Park, N. Mex. --

Carbofuran E0.15 04/20/94 Garfield Drain at Road 391, near Salem, N. Mex. 40

A site in Elephant Butte Reservoir, one of four major reservoirs on the main stem

of the Rio Grande, was cored for analysis of selected pesticides (photograph by

Sherman R. Ellis, U.S. Geological Survey).

lites, DDD and DDE, in bed sediment

and whole-body fish confirms the persistence of this pesticide in the environment.

Pesticides in Elephant Butte

Reservoir Sediment Core

In July 1995, a site in Elephant

Butte Reservoir was cored and analyzed for DDT metabolites (Van

Metre and others, 1997). The core was

age-dated by correlating sample depth

with the radioactive isotope cesium137. Total DDT concentrations in the

core reached a maximum of about
U.S. Geological Survey Circular 1162 

MAJOR ISSUES AND FI

Organics in Ground Water, Surface Water, Bed Sediment, and Fish 

Samples were collected from 79

shallow wells and 30 deeper wells for

analysis of 60 VOCs. No concentrations exceeded an EPA MCL or HA

(table 5).

Water from 9 of the 79 wells sampled had detectable concentrations of

one or more VOCs. In the Albuquerque urban land-use study, five different

VOCs, two of which were found in

more than one sample, were detected

in water from 5 of the 24 shallow wells

(table 5). Four of the VOCs detected

are solvents or metal degreasers. The

other is methyl tert-butyl ether

(MTBE), a gasoline additive that was

detected at a concentration of 7.9 μg/L,

which was the largest VOC concentration measured in the Study Unit. In the

Rincon Valley agricultural land-use

study, only one VOC, xylene, was

detected in 3 of 20 samples. In the San

Luis Valley agricultural land-use study,

MTBE was detected in one well.

Although few VOCs were detected

and the concentrations were relatively

small, their presence in shallow ground

water means that shallow groundwater quality has been adversely

affected by human activities. VOCs

were detected more frequently in the

Albuquerque urban land-use study

than in the agricultural land-use studies, perhaps because urban areas have

more sources of VOCs.

The wells sampled in the aquifer

subunit survey had no VOC detections.

This may mean that VOCs have not

moved into deeper parts of the aquifer.

Semivolatile Organic

Compounds in Bed Sediment

Semivolatile organic compounds are

a large group of environmentally

important organic compounds. Three

groups of compounds, polycyclic aromatic hydrocarbons (PAHs), phenols,

and phthalate esters, were included in

the analysis of bed sediment collected

at 17 sites in the Study Unit. These

compounds are abundant in the environment, are toxic and often carcinogenic to organisms, and could

represent a long-term source of contamination.

The analysis of the PAH data show

one or more PAH compounds were

detected at 14 sites. Four of these sites

had about 60 percent of the detections;

three sites had no detections. Two of

the four sites are downstream from

urban land-use areas, one is downstream from a mining area, an

in a forested area.

Phenol compounds were de

13 sites with 50 percent of the 

tions at 5 sites. Two sites had n

tions. No relation to land use w

apparent for the phenol compo

detections.

Four phthalate ester compou

were detected at 10 sites. Only 

site, downstream from an urba

use area, had detections of mo

one phthalate ester.

 Table 5.—Volatile organic compounds detected in

shallow ground water

[μg/L, micrograms per liter; MCL, U.S. Environmental Protection Agency

maximum contaminant level; HA, U.S. Environmental Protection Agency

lifetime health advisory; --, no MCL or HA]

Volatile organic

compound

Number of

detections

Detection

concentration

(μg/L)

MCL

(μg/L)

HA

(μg/L)

San Luis Valley agricultural land-use study (35 samples)

Methyl tert-butyl ether 1 0.6 -- 20 - 200

Albuquerque urban land-use study (24 samples)

Methyl tert-butyl ether 1 7.9 -- 20 - 200

Trichloroethene 1 1.1 5.0 --

1,1-Dichloroethane 2 0.2 - 0.5 -- --

p-Isopropyltoluene 1 0.4 -- --

cis-1,2-Dichloroethene 2 0.3 70 --

Rincon Valley agricultural land-use study (20 samples)

Xylene 3 0.3 - 2.8 10,000 10,000
14 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

MAJOR ISSUES AND FINDINGS

Nutrients in Ground Water and Surface Water

Nutrients include nitrogen and

phosphorus compounds that are necessary components for the growth of

plants and animals. However, in excessive concentrations, nutrients are a

water-quality concern in drinking

water and are a major contributor to

eutrophication in rivers, lakes, and reservoirs. Large nutrient concentrations

can contribute to excessive growth of

algae and other aquatic plants that can

cause destruction of habitat and depletion of dissolved oxygen, which usually results in the disappearance of

intolerant aquatic insect species and

fish. Major sources of nutrients are fertilizers, sewage effluent, precipitation,

and dissolution of naturally occurring

minerals (Mueller and Helsel, 1996, p.

10). Fertilizers, which include commercial fertilizers and animal manure,

are applied in urban and agricultural

areas. Sewage effluent includes municipal WWTP discharge to streams and

wastewater from septic tanks or cesspools. An estimate of nutrient loads to

the entire Study Unit indicated that

loading from fertilizers and WWTP

effluent is considerably larger than

loading from precipitation (Anderholm

and others, 1995, p. 127). As a result

of human activities in the Rio Grande

Valley Study Unit, nutrient concentrations in both ground water and surface

water have exceeded established Federal and State standards.

The EPA has established an MCL

for nitrate in drinking water of 10 milligrams per liter (mg/L) as nitrogen.

The EPA recommends that total (not

dissolved) phosphorus concentrations

should be less than 0.1 mg/L in rivers

and less than 0.05 mg/L where rivers

enter lakes and reservoirs because concentrations greater than this could contribute to eutrophication. The States of

Colorado, New Mexico, and Texas

have also established individual

aquatic-life criteria for selected nutrients that apply to specific river reaches

within the Study Unit.

Nutrients in Ground Water

In the San Luis Valley agricultural

land-use study, water from 11 of the 35

wells sampled contained nitrate concentrations greater than the EPA MCL;

the largest concentration was 58 mg/L

(table 6). In the Rincon Valley agricultural land-use study, water from 5 of

the 30 wells sampled exceeded the

EPA MCL; the largest concentration

was 33 mg/L. These elevated nitrate

concentrations are indicative of leaching of fertilizers into shallow ground

water. However, the spatial variation in

nitrate concentrations indicates that

leaching of fertilizer is not uniform

throughout these areas. The spatial

variation may be the result of variable

fertilizer application rates, timing of

fertilizer application, timing of application of irrigation water, and recharge

rates controlled by soil type, texture,

permeability, precipitation, and biological/geochemical processes in the

unsaturated zone.

In the Albuquerque urban land-use

study, the largest nitrate concentration

was 2.8 mg/L, which is considerably

below the EPA MCL. Although infiltration of septic tank effluent results in

considerable loading of nutrients to the

shallow aquifer in this area, the small

nitrate concentrations suggest that

nitrogen compounds in the effluent are

not being converted to nitrate. This is

probably due to the lack of dissolved

oxygen and the relatively large dissolved organic carbon concentrations

in shallow ground water in the 

Large ammonia concentration

would be expected, are not pre

shallow ground water because 

nia is adsorbed on clays in the 

or soil zone.

Nitrate concentrations in wa

deep wells sampled during the 

subunit survey ranged from les

0.05 to 1.9 mg/L. Throughout 

the area of the aquifer subunit 

the small nitrate concentration

water from deeper parts of the 

fill aquifers probably indicate 

shallow ground-water recharge 

deeper parts of the aquifer is li

Nutrients in Surface Wa

Dissolved Nutrients

Dissolved nutrient concentr

are shown in Table 7. The larg

centrations of dissolved nutrie

surface water were detected at 

downstream from urban land u

erally, a WWTP was associate

the urban area and was located

upstream from the sampling si

general, dissolved nutrient con

tions were larger at Basic Fixe

downstream from Cochiti Lake

probably the result of the incre

urban land use along the Rio G

and the associated WWTPs.

Dissolved nutrient concentr

agricultural drains in the Mesi

Rincon Valleys were small. Th

centrations could be small bec

 Table 6.—Nitrate detected in ground water

 [mg/L, milligrams per liter; <, less than]

Ground-water study

component

Number of

samples

Range in

concentration

(mg/L)

Median

(mg/L)

San Luis Valley agricultural

land-use study

35 <0.05 - 58 2.7

Albuquerque urban land-use

study

24 <0.05 - 2.8 <0.05

Rincon Valley agricultural

land-use study

30 <0.05 - 33 0.48

Aquifer subunit survey 30 <0.05 - 1.9 <0.05
U.S. Geological Survey Circular 1162 

MAJOR ISSUES AND FI

Nutrients in Ground Water and Surfac

biological uptake of nutrients and no

widespread excessive nitrate concentrations in ground water that is discharging to drains. Comparison of data

for the Mesilla Valley synoptic study

shows that the inflow of nutrient loads

to the Rio Grande from urban sources

(WWTPs) may equal or exceed the

inflow from agricultural sources

(drains).

Of 455 samples at sites where

aquatic-life criteria apply, un-ionized

ammonia concentrations exceeded the

applicable criterion only twice. No

other dissolved nutrient concentration

in surface water exceeded any applicable Federal or State criterion or standard.

The EPA has recommended total

phosphorus concentrations for streams

not discharging to a lake and for

streams near where they discharge to a

lake. These recommendations are not

criteria or standards. Out of 526 samples from these sites, 250 equaled or

exceeded the recommended concentrations.

Total Nutrients

Total nutrient concentration in surface water is affected significantly by

suspended-sediment concentration

because nutrients adsorb to suspended

sediment and are transported by water.

The largest concentrations of total

nutrients were detected at the Basic

Fixed Site on the Rio Puerco (fig. 2)

and were associated with runoff from

summer thunderstorms, which historically have transported large loads of

suspended sediment.

Approximately 35 percent of the

samples from the Basic Fixed Sites

have total phosphorus and total nitrogen concentrations in the eutro

highly eutrophic range of mos

classification systems. Among 

environmental effects of eutro

tion are large diurnal dissolved

(DO) fluctuations. In addition, 

decay of large amounts of dead 

tion puts a demand upon avail

concentrations. During this stu

concentrations less than the EP

ommended minimum ambient 

rion of 5 mg/L for the health o

aquatic ecosystem were detect

than 7 percent of the time at si

Colorado.

Nutrients in Reservoirs

The effect that reservoirs ca

on water quality is evident wh

solved and total nutrient conce

tions are compared at sites ups

and downstream from reservoi

Although not directly addresse

this study, historical data for s

the Rio Grande show nutrient 

trations in water decreasing sig

cantly while stored in reservoi

(Anderholm and others, 1995)

decrease downstream from res

is attributed to biological uptak

nutrients and suspended sedim

tling out of the water column.

Table 7—Nutrients detected in surface water

[mg/L, milligrams per lite; <, less than]

Nutrient Number of

analyses

Range in

concentration,

(mg/L)

Median

(mg/L)

Nitrite, dissolved 584 <0.01 - 1.2 <0.01

Nitrite plus nitrate,

dissolved

582 <0.05 - 15 0.11

Ammonia, dissolved 584 <0.015 - 27 0.02

Ammonia plus organic

nitrogen, dissolved

566 <0.2 - 29 0.2

Ammonia plus organic

nitrogen, total

556 <0.2 - 57 0.3

Phosphorus, dissolved 579 <0.01 - 3.9 0.03

Phosphorus, total 555 <0.01 - 45 0.08

Orthophosphate,

dissolved

577 <0.01 - 3.4 0.03

Wastewater-treatment plants affect nutrient concentrations in the Rio Gra

(photograph by Sherman R. Ellis, U.S. Geological Survey).
16 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

MAJOR ISSUES AND FINDINGS

Radon in Ground Water and Dissolved Solids in Surface Water

Radon in Ground Water

Radon, which can cause lung cancer, is a radioactive, odorless, and

chemically inert gas that occurs naturally in the air, soil, and ground water.

Radon is a decay product of radium,

which in turn is a decay product of uranium. Rocks break down mechanically

and chemically to form sediments that

contain differing amounts of uranium,

depending on the source rocks. The

higher the uranium concentration is in

the source rocks, the greater the

chances are for radon in the air, soil, or

ground water. Other potential sources

of uranium in the environment are

improper disposal of uranium mining

waste and nuclear fuel processing,

combustion of wood and fossil fuels,

or roasting of rocks in metal extraction

or cement industries.

Radon in ground water affects radon

concentrations in indoor air in homes

because it escapes to the indoor air as

people use water. Open water-distribution systems allow ground water to

aerate and radon to escape. In small,

closed water-distribution systems with

short transit times, radon cannot

escape from the system; therefore, it

escapes into the indoor air. Research

suggests that ingestion of water with

high radon concentrations also may

pose risks, although these risks are

believed to be much lower than those

from inhalation of radon.

Until late 1996, the EPA had proposed an MCL of 300 pCi/L for radon

in drinking water. However, this proposed MCL was withdrawn by EPA

for further evaluation; thus, no proposed MCL currently exists. Radon

concentrations measured during this

study were larger than the previously

proposed MCL in 57 percent of the

wells.

Radon concentrations were equal to

or greater than 512 pCi/L in water

from all shallow wells sampled in the

San Luis Valley land-use study (table

8). Although the range in concentration is not as large in the Albuquerque

land-use study, values for seven samples were greater than 300 pCi/L. In

the Rincon Valley land-use study, only

three samples exceeded 300 pCi/L.

The largest range in concentration was

from the aquifer subunit survey (table

8), which also had the largest radon

concentration measured, 2,300 pCi/L.

More than one-half the wells sampled

from the deeper aquifer have water

with a radon concentration greater than

300 pCi/L.

On the basis of these reported concentrations, it is apparent that radon in

both shallow and deeper ground water

is a potential human health concern.

The likely source for the elevated concentrations of dissolved radon in

ground water is from naturally occurring minerals that contain uranium in

the sediments that compose th

fer. There is no direct evidence 

land use has affected radon co

tions in shallow ground water 

Study Unit.

Dissolved Solids in Sur

Water

A knowledge of the dissolve

concentration in irrigation wat

be useful to water users in dete

application rates for different s

crop types and drainage requir

Dissolved-solids concentration 

measure of the dissolved const

in water and is commonly used 

general indicator of salinity or 

quality. Although dissolved-so

concentration has an importan

on the use of irrigation water, 

no Federal or State standard.

Evaporation, transpiration, 

solution of minerals are the thr

major processes that result in a

increase of dissolved-solids co

tion. All of these processes are 

contributors to the increases in 

solved solids measured in the 

Unit.

In general, the dissolved-so

centration in surface water inc

with the length of time that the 

has been in the hydrologic sys

This is illustrated by data from 

Basic-Fixed-Site network. The 

dissolved-solids concentration

the northern part of the study a

generally represent runoff deri

from snowmelt or water that h

subjected to limited irrigation 

3 and table 9). The median dis

solids concentration for main-

sites increases downstream fro

to site 17, with the exception o

(sites are highlighted in blue in 

9). The cause of the anomalou

median concentration at site 4 

unknown. Possible causes are 

water recharge to the Rio Gran

introduction of ground water p

from the sump area of the Clo

Basin, or discharge from the A

WWTP. The downstream incre

 Table 8.—Radon detected in ground water

 [pCi/L, picocuries per liter]

Ground-water study component Number of

detections

Range in

concentration

(pCi/L)

Median

(pCi/L)

San Luis Valley agricultural

land-use study (29 samples)

29 512 - 1,798 1,190

Albuquerque urban land-use

study (22 samples)

22 198 - 397 280

Rincon Valley agricultural landuse study (18 samples)18 210 - 440 260

Aquifer subunit survey (29

samples)

29 190 - 2,300 380
U.S. Geological Survey Circular 1162 

MAJOR ISSUES AND FI

Radon in Ground Water and Dissolved Solids in Surfac

0 30 60 MILES

0 30 60 KILOMETERS

Rio

Puerco

Rio

Jose

Rio Chama

Santa Fe

River

37

UNIT

STUDY

BOUNDARY

Colorado

106

32

New Mexico

Rio

33

34

35

36

107

38

108

Grande

Rio

San

MEXICO

UNITED STATES

Albuquerque

Cr

Saguache

Medano

Creek

Grande

15

298

17

634

16

430

14

528

13

1,180

12

245

11

376

10

113

9

194

8

174

7

192

6

191

5

92

4

292

3

56

2

96

1

67

1

67

Elephant

Butte Res

Caballo

Res

Conejos R

Rito de 

los Frijoles Cochiti

Lake

BASIC FIXED SITE Top number is

site number (table 9); bottom

number is median dissolved-solids

concentration, in milligrams per liter

SAN LUIS CLOSED BASIN

BOUNDARY

Franklin Eddy

Canal

EXPLANATION

Figure 3.—Median dissolved-solids

concentrations at Basic Fixed Sites.

dissolved-solids concentration at the

Basic Fixed Sites illustrates the effect

that evaporation, transpiration, and dissolution of minerals can have on water

as it moves through the system. All

three of these processes occur extensively along the Rio Grande as a result

of the most significant water use, irrigation.

 Table 9.—Dissolved-solids concentration at Basic Fixed Site

[Main-stem sites shown in blue; mg/L,milligrams per liter]

Site

number

(fig. 2)

Station name

Median

dissolvedsolids

concentration

(mg/L)

Rang

dissol

soli

concent

(mg

1 Rio Grande near Del Norte, Colo. 67 39 - 

2 Saguache Creek near Saguache, Colo. 96 72 - 

3 Medano Creek near Mosca, Colo. 56 31 - 

4 Rio Grande above mouth of Trinchera Creek,

near Lasauses, Colo.

292 161 - 

5 Conejos River near Lasauses, Colo. 92 62 - 

6 Rio Grande near Lobatos, Colo. 191 118 - 

7 Rio Grande below Taos Junction Bridge, near

Taos, N. Mex.

192 113 - 

8 Rio Chama near Chamita, N. Mex. 174 138 - 

9 Rio Grande at Otowi Bridge near San

Ildefonso, N. Mex.

194 124 - 

10 Rito de los Frijoles in Bandelier National

Monument, N. Mex.

113 96 - 

11 Santa Fe River above Cochiti Lake, N. Mex. 376 117 - 

12 Rio Grande at Isleta, N. Mex. 245 142 - 

13 Rio Puerco near Bernardo, N. Mex. 1,180 274 - 2

14 Rio Grande Conveyance Channel at San

Marcial, N. Mex.

528 452 - 

15 Rio Grande Floodway at San Marcial, N. Mex. 298 169 - 

16 Rio Grande below Leasburg Dam near

Leasburg, N. Mex.

430 353 - 

17 Rio Grande at El Paso, Tex. 634 472 - 1

The largest median dissolv

ids concentration for the Basi

Sites was at site 13 on the Rio 

The Rio Puerco, a typical trib

the Rio Grande in the souther

the basin, was the only ephem

stream sampled in this area. I

trates the importance that eph

streams in semiarid environm

have on dissolved-solids conc

tions, particularly in load calcu

In one or two storm-runoff ev

from these tributaries, most o

culated dissolved-solids load 

year can occur.
18 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

MAJOR ISSUES AND FINDINGS

Trace Elements

Many trace elements are essential

nutrients; however, certain trace elements such as arsenic, cadmium, and

mercury are known to be persistent

environmental contaminants and toxic

to most forms of life (Schmitt and

Brumbaugh, 1990). Trace elements are

generally present in small concentrations in natural water systems. Their

occurrence in ground and surface

water can be due to natural sources

such as dissolution of naturally occurring minerals containing trace elements in the soil zone or the aquifer

material or to human activities such as

mining, application of pesticides,

burning of fossil fuels, smelting of

ores, and improper disposal of industrial wastes.

The EPA has established primary

and secondary MCLs, HAs, and issued

guidelines for the establishment of

aquatic-life criteria as they apply to

trace elements. The States of Colorado, New Mexico, and Texas have

also established individual aquatic-life

criteria for selected trace elements that

apply to specific river reaches within

the Study Unit. Acute exposure (short

term, high concentration) to certain

metals can kill organisms directly,

whereas chronic exposure (long term,

low concentration) can result in either

mortality or nonlethal effects such as

stunted growth, reduced reproductive

success, deformities, or lesions.

Trace Elements in Ground

Water

During 1992-95, ground-water samples were collected for analysis of

trace elements during three land-use

studies and the aquifer subunit survey.

Most trace-element concentrations in

ground water ranged from less than 1

to 10 micrograms per liter (μg/L).

Only four trace elements exceeded

EPA MCLs, SMCLs, or HAs (table

10). Uranium concentrations in water

from 15 of 119 wells exceeded the

EPA-proposed MCL of 20 μg/L (U.S.

Environmental Protection Agency,

1996a). Water from two wells

exceeded the EPA HA of 40 μg/L for

molybdenum. The relatively low number of detections and small concentrations of most trace elements indicate

that they are influenced more by natural processes and less by land use.

Two trace elements that consistently

exceeded SMCLs were manganese and

iron, which can stain plumbing fixtures

or impart a metallic taste to the water.

Manganese concentrations in water

from 62 wells and iron concentrations

in water from 14 wells exceeded EPA

SMCLs. Large manganese and iron

concentrations are often associated

with small dissolved-oxygen concentrations. Where oxygen has been consumed, microorganisms will reduce

manganese and iron, resulting in large

concentrations. This commonly occurs

in areas of septic-system effluent discharge.

On the basis of analysis of the spatial distribution and range of traceelement concentrations (table 10),

human activities have not caused widespread trace-element contamination in

ground water. The majority of trace

elements detected are likely the result

of dissolution of naturally occ

minerals in the aquifer.

Trace Elements in the

Surface-Water Environm

Since the late 1800’s, minin

ties have been prevalent in the 

part of the Study Unit in Color

New Mexico. Most mining act

have ceased, and several areas 

various stages of remediation. 

ument the surface-water qualit

immediately adjacent to the R

Grande, a synoptic study focu

trace elements in the water col

suspended sediment, and bed m

was conducted in June and Sep

1994. In January 1995, selecte

elements were analyzed in sam

collected in the Mesilla and Ri

Valleys as part of a pesticide a

ent synoptic study.

Water column

Analysis of trace-element d

lected in the northern part of th

area confirmed previous study 

Moderately to highly elevated 

Table 10.—Trace elements in ground water that exceed U.S

Environmental Protection Agency standards or guidelines

[μg/L, micrograms per liter; MCL, U.S. Environmental Protection Agenc

(EPA) maximum contaminant level; SMCL, EPA secondary maximum

contaminant level; HA, EPA lifetime health advisory; --, no data]

Trace

element

Number of

wells

sampled

Number of

detections

Detection

concentration

(μg/L)

Proposed

MCL

(μg/L)

SMCL

(μg/L)(μ

San Luis Valley agricultural land-use study

Uranium 35 5 23 - 84 20 -- 

Manganese 35 6 69 - 682 -- 50 

Molybdenum 35 1 52 -- -- 

Albuquerque urban land-use study

Uranium 24 5 21 - 89 20 -- 

Iron 24 7 340 - 3,800 -- 300 

Manganese 24 21 130 - 3,600 -- 50 

Rincon Valley agricultural land-use study

Uranium 30 4 26 - 62 20 -- 

Iron 30 5 980 - 1,900 -- 300 

Manganese 30 25 77 - 2,130 -- 50 

Aquifer subunit survey

Uranium 30 1 102 20 -- 

Iron 30 2 360 - 550 -- 300 

Manganese 30 10 58 - 654 -- 50 

Molybdenum 30 1 59 -- -- 
U.S. Geological Survey Circular 1162 

MAJOR ISSUES AND FI

Trace E

element concentrations were detected

in the Creede, Colorado, and Red

River, New Mexico, mining areas and

in the Alamosa River, which drains a

mining area and also contains several

areas of naturally occurring minerals

that contribute trace elements to the

water column.

For the entire reach of the Rio

Grande sampled in 1994, the largest

concentrations of dissolved antimony,

beryllium, cadmium, cobalt, copper,

iron, lead, mercury, nickel, silver, and

zinc were detected at sites downstream

from areas of known mineral extraction. Dissolved concentrations of

beryllium, cadmium, cobalt, lithium,

manganese, molybdenum, nickel, and

zinc were moderately higher at a site

on the lower Red River than in the Rio

Grande downstream of its confluence.

At the site on the Alamosa River where

it enters the San Luis Valley, highly

elevated concentrations of dissolved

cadmium, cobalt, copper, iron, manganese, nickel, strontium, uranium, and

vanadium were detected.

The largest concentrations of dissolved arsenic, barium, boron, chromium, lithium, molybdenum, and

uranium were detected at sites in the

Mesilla and Rincon Valleys. The elevated concentrations of these trace elements may be related to discharges

from geothermal springs, the return

flow of irrigation water, or urban landuse discharges.

Concentrations of dissolved cadmium, copper, manganese, iron, silver, and zinc in the water column

exceeded the following applicable

standards at one or more sites. Dissolved concentrations of cadmium,

copper, iron, and zinc exceeded the

Colorado chronic aquatic-life standard

(Colorado Water Quality Control

Commission, 1989) at the site on the

Alamosa River and dissolved silver

concentrations exceeded the Colorado

chronic aquatic-life standard for trout

at four sites in Colorado . The copper

concentration at one site on the Red

River exceeded the New Mexico coldwater fishery chronic standard (New

Mexico Water Quality Control Commission, 1991).

Bed sediment

Bed-sediment samples were collected to characterize the occurrence

and distribution of trace elements in

the Study Unit. Because of the large

areal extent of naturally occurring

mineralized areas in the Study Unit,

particularly in the northern one-third,

the source of trace-element concentrations detected in bed-sediment samples

may be natural rather than anthropogenic.

Trace-element concentrations in bed

sediment closely reflect the same pattern as water-column concentrations.

Highly elevated concentrations of antimony, arsenic, cadmium, copper, lead,

mercury, silver, and zinc were detected

in bed-sediment material from Willow

Creek and the Rio Grande downstream

from the Creede mining area compared

to the rest of the study area. Concentrations of these elements in samples

from the Alamosa River and Red River

areas were elevated compared with the

rest of the study area. At present, no

Federal or State guidelines have been

established for trace-element concentrations in bed sediment.

Fish tissue (liver)

As part of the fish-tissue contaminant study, fish were collected at 12

sites and their livers analyzed for traceelements. The bioavailability of trace

elements is an important factor in

assessing threats to aquatic organisms,

ecosystems, and public health. As with

water-column and bed-sediment samples, the sample from the Rio Grande

near Creede contained elevated concentrations of arsenic, cadmium, copper, lead, and zinc. Some trace

elements were detected at higher concentrations in liver samples than in

bed-sediment samples from the same

site.

Accumulation of trace elem

fish appears to be species depe

Zinc concentrations in liver sam

common carp liver at certain si

three to four times those in sam

white sucker at other sites. A b

trout sample contained signific

higher concentrations of arsen

per, mercury, and selenium tha

other fish samples. To differen

between environmental and sp

dependent factors, however, th

tion of multiple species at a nu

individual sites would be nece

Bryophytes (moss)

Transplanted bryophytes (m

were used to determine the spa

tribution of trace elements in r

to land-use practices, compare 

mulation rates of trace elemen

bryophytes at sites known to b

taminated by trace elements, a

uate transplanted bryophytes a

for examining the bioavailabil

trace elements in relation to co

tions in water and bed sedimen

Thirteen sites on the Rio Gr

and tributary streams in southe

rado and northern New Mexic

sampled for determination of 1

elements in transplanted bryop

Analysis of the data indicates 

concentrations of cadmium, co

lead, and zinc in bryophytes in

at sites on the Rio Grande imm

downstream from tributaries th

the mining districts, (2) concen

of these metals in bryophytes

decreased with distance from t

taries, and (3) concentrations o

trace elements in bryophytes w

lower in a tributary stream dow

from an urban area than at site

mining or agricultural land use
20 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

MAJOR ISSUES AND FINDINGS

Fish Communities and Stream Habitat

Fish communities and stream habitat (instream and riparian) were

assessed at selected sites in three major

physiographic provinces and three of

four ecoregions of the Rio Grande Valley Study Unit. The structure of a community can be influenced by natural

and human changes to physical and

chemical characteristics of the stream.

A stream reach, or section of stream,

was selected to assess fish communities and stream habitat that best represented the condition of a longer river

segment. This allows for an integrated

approach to characterizing surfacewater quality. A combination of qualitative and quantitative sampling methods was used to determine the species

present in a reach and to provide a

measure of structure, which can be

expressed in a variety of ways including species richness, relative abundance, trophic complexity, native/nonnative composition, and tolerance to

human disturbance. Samples of fish

were collected primarily during the

summer low-flow period in 1993-95.

These samples, in addition to more

than 30 instream and riparian characteristics of stream habitat (including

stream modification, bank erosion,

bank vegetation stability, and riparian

vegetation density) were used to

describe water-quality conditions.

Fish Communities

Fish communities were assessed at

10 sites in the Study Unit. In 25 samples, 29 species representing 10 families were identified. Species richness

ranged from 1 to 13. Species richness

was lowest at Medano Creek near

Mosca, Colorado, where the Colorado

Division of Wildlife removed all other

species from the stream in an effort to

reintroduce the Rio Grande cutthroat

trout. Species richness increased

downstream with increasing contributing drainage area; the Rio Grande at El

Paso site had the most species. Warmwater fisheries generally support more

species than cold-water fisheries; however, the site at El Paso may have the

most species because it is downstream

from a very large warm-water reservoir which could provide seed populations that are present downstream.

Fish, which are relatively long lived

and can travel long distances, integrate

water-quality conditions over a longer

period of time and at a relatively larger

spatial scale than algae and benthic

invertebrates. Four indicators of biotic

integrity (percentages of introduced

species, omnivores, tolerant species,

and anomalies) were used to provide a

broad overview of the fish community

structure.

At sites sampled during this study,

13 native and 16 introduced species of

fish were identified. Introduced fish

species predominate at four of six sites

sampled in 1994, probably because of

stocking of some of these fish species.

The dominance of omnivores in samples from the Rio Grande below Taos

Junction Bridge, Rio Chama near

Chamita, Rio Grande at Isleta, and Rio

Grande at El Paso (fig. 2) can be an

indication of environmental stress at

these sites. However, omnivores can

also be an indication of increasing

stream size. In 1994, tolerant species

accounted for the entire fish community at Rio Grande at Isleta.

The occurrence of external anomalies on all fish samples was less than 2

percent except for the sample from Rio

Grande at Isleta, which was 14 percent. Based on the relative percentages

of introduced, omnivorous, tolerant

fish and the number of fish with external anomalies, six of the sampled sites

appear to show some indications of

environmental perturbation. The biotic

integrity at the Rio Grande at Isleta site

appears to be the most impaired of all

sites.

In 1995, fish communities were

sampled in three separate reaches in

both the Santa Fe River above Cochiti

Lake and the Rio Grande near Isleta

sites to assess small-scale spatial patterns in the structure of fish communities among the reaches at each site and

to determine the influence of physical

and chemical characteristics of each

reach on the fish communities 

stream. The fish communities 

some variability among reache

of these sites. The variability i

spatial pattern at both sites mi

because of natural variability; 

ever, at the Santa Fe River site

variability also could be relate

presence or absence of such im

habitat features as shallow poo

stream physical or chemical ch

istics among each reach at each 

not seem to influence the spati

tern of fish communities. No s

cant correlation existed betwee

communities at each reach and 

the physical variables (such as 

width, depth, and substrate com

tion) or the chemical variables 

water temperature, DO, and sp

conductance).

The relative abundance of fi

cies and the total number of in

als varied in samples collected 

sampled annually. All sites, ex

Rio Grande near Del Norte, ha

decline in the total number of i

als in a sample from 1993 to 1

This temporal decline also cou

caused by natural variability w

fish community or some artifa

sampling.

Stream Habitat

Stream habitat characteristi

used to describe the environme

ting at sites selected for ecolog

veys. At the spatial scales of b

stream segment, stream reach, 

microhabitat, physical charact

of streams strongly influence w

quality and the capacity of a st

support healthy biological com

ties. Basin factors, such as phy

graphic province, ecoregion, a

climate, can be used to evaluat

influence on biological commu

Stream segments are a more d

unit that should have relatively 

geneous physical, chemical, an

logical characteristics. Within 

segment, a stream reach was s

for an intensive site evaluation

habitat features, such as macro
U.S. Geological Survey Circular 1162 

MAJOR ISSUES AND FI

Fish Communities and Stream 

beds, woody debris, and bed substrate,

also were evaluated within each stream

reach. The presence or absence of different biological communities at

Study-Unit sites is influenced to varying degrees by the environmental setting at a particular site. For instance,

fish communities are more influenced

by climate, which is considered a basin

factor, than by specific microhabitat

conditions.

Principal component analysis was

used to determine the overall variance

in the combination of various stream

habitat characteristics. Physiographic

province and ecoregion were the physical variables that explained most variance among sites. Physiographic

provinces are distinct areas that have

common topography, rock types and

structure, and geologic and geomorphic history. Ecoregions are relatively

homogeneous ecological regions and

are classified by spatially variable

combinations of geomorphology, soils,

physiography, land use and land cover,

and potential natural vegetation.

Because a combination of physical

variables define both physiographic

province and ecoregion, most variance

among sites is explained by these two

habitat characteristics.

A habitat degradation index also

was used to describe the physical condition of the sites selected for ecological surveys. The index included four

habitat characteristics: stream modification, bank erosion, bank vegetation

stability, and riparian vegetation density. Use of these four habitat characteristics revealed that 6 of 10 sites

sampled appear to have significant

habitat degradation. These sites are

Rio Grande near Del Norte, Colorado;

Conejos River near Lasauses, Colorado; Rio Chama near Chamita, New

Mexico; Santa Fe River above Cochiti

Lake, New Mexico; Rio Grande at

Isleta, New Mexico; and Rio Grande at

El Paso, Texas. Saguache Creek near

Saguache, Colorado; Medano Creek

near Mosca, Colorado; and Rio Grande

below Taos Junction Bridge near Taos,

New Mexico, were sites that have

moderate to minimal habitat degradation. Rito de los Frijoles in Bandelier

National Monument, New Mexico,

was the only site that had minimal habitat degradation. The habitat at 

los Frijoles was characterized 

stream modification, very little 

erosion, highly stable banks, an

riparian vegetation.

Stream habitat changes significantly from the upper to the lower part of the 

Top photograph is Rio Grande near Del Norte, Colorado; lower photograph 

Grande at El Paso, Texas (photographs by Lisa F. Carter, U.S. Geological S
22 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

Nutrient concentrations

downstream from urban

areas and in a sedimentladen tributary were

among the highest in the

Nation. The impact of

reservoirs on reducing

nutrient concentrations

is shown by the reduced

concentrations at the two

lower sites.

Pesticide concentrations

in surface water ranked

among the lowest of all

NAWQA sites nationwide. Within the Study

Unit, the two sites with

the highest concentrations were below urban

land-use areas.

Albuquerque

El Paso

Rio Grande

NUTRIENTS in water

Albuquerq

El Paso

Rio Grande

PESTICIDES in water

Albuquerque

El Paso

Rio Grande

ORGANOCHLORINE PESTICIDES and PCBs

in bed sediment and biological tissue

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Comparison of Stream Quality in the Rio Grande Valley

with Nationwide NAWQA Findings

Greater than the 75th percentile

(among the highest 25 percent

of NAWQA stream sites)

Between the median and the 75th percentile

Between the 25th percentile and the median

Less than the 25th percentile

(among the lowest 25 percent

of NAWQA stream sites)

EXPLANATION

Ranking of stream quality relative to all

NAWQA stream sites — Darker colored

circles generally indicate poorer quality.

Bold outline of circle indicates one or more

aquatic-life criteria were exceeded.

Seven major water-quality characteristics were evaluated for stream sites i

NAWQA Study Unit. Summary scores for each characteristic were compute

sites that had adequate data. Scores for each site in the Rio Grande Valley 

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

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

indicate poorer quality compared with other NAWQA sites. Water-quality

conditions at each site also are compared to established criteria for protect

aquatic life. Applicable criteria are limited to nutrients and pesticides in wa

semivolatile organic compounds, organochlorine pesticides and PCBs in se

(Methods used to compute rankings and evaluate aquatic-life criteria are d

by Gilliom and others, in press.)

The largest concentrations of organochlorines and PCBs were

at sites downstream

from urban areas.

Three sites had levels

above the national

NAWQA median.
U.S. Geological Survey Circular 1162 

For the trace elements

measured for this comparison, one site was in the

highest 25 percent nationwide. Two sites in the lower part of the Study Unit

have levels greater than the

median for all NAWQA

sites.

On the basis of attributes used to

provide a broad overview of the fish

community structure—introduced

species, omnivorous species, percent tolerant species, and external

anomalies—all of the sites were

above the national median. The

ranking was strongly influenced by

the predominance of introduced and

omnivorous species at many of the

sites.

CONCLUSIONS

Compared to other NAWQA Stud

Units, in the Rio Grande Valley

 • Based on the water-quality data co

lected and presented here, land 

the middle part of the Study Un

a major impact on nutrient conc

tions.

 • Pesticide concentrations have not

affected the quality of surface w

at the sampled sites.

 • Fish community rankings were str

influenced by the predominanc

introduced and omnivorous spe

Albuquerque

El Paso

Rio Grande

TRACE ELEMENTS in bed sediment

Albuqu

El Paso

Rio Grande

STREAM HABITAT DEGR

Albuquerque

El Paso

Rio Grande

SEMIVOLATILE ORGANIC COMPOUNDS

in bed sediment

Albuquerque

El Paso

Rio Grande

FISH COMMUNITY DEGRADATION

Four of 10 sites in the

Study Unit were above the

national median; however,

all sites showed some signs

of degradation. Two sites

ranked as highly degraded

compared with other sites.

The rankings were influenced most by the lack of

dense riparian vegetation.

Six of the nine sites have

concentrations lower than

the national median. Two

sites located downstream

from urban areas ranked

among the highest in the

Nation for semivolatile organic compounds in sediment.

WATER-QUALITY CONDITIONS IN A NATIONAL CO

Comparison of Stream Quality in the Rio Grand

with Nationwide NAWQA F
24 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

Nitrate concentrations throughout most

of the Study Unit were among the lowest

in the Nation. However, in the San Luis

Valley, nitrate concentrations were higher than the national median and, along

with the Rincon Valley area, exceeded

drinking-water standards in some wells.

Radon concentrations in the San Luis

Valley were among the highest measured

nationwide. However, radon concentrations in the rest of the Study Unit were

smaller than the national median value.

Alamosa

Albuquerque

El Paso

RADON

(RV)

(SUS)

(ALB)

(SLV)

Alamosa

Albuquerque

El Paso

NITRATE

(RV)

(SUS)

(ALB)

(SLV)

EXPLANATION

Aquifer subunit survey (SUS)

Agricultural area; Rincon Val

Cropland area; San Luis Vall

Urban area; Albuquerque are

Drinking-water aquifers

Shallow ground-water areas

Ranking of ground-water quality

relative to all NAWQA groundwater studies Darker colored cir

generally indicate poorer quality.

Bold outline of circle indicates

one or more standards or criteria

were exceeded

Greater than the 75th percentile

Between the median and the 75th p

Between the 25th percentile and th

Less than the 25th percentile

(Among the lowest 25 percent of

NAWQA ground-water studies)

(Among the highest 25 percent of

NAWQA ground-water studies)

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Comparison of Ground-Water Quality in the Rio Grande Valley

with Nationwide NAWQA Findings

Five major water-quality characteristics were evaluated for ground-water studie

NAWQA Study Unit. Ground-water resources were divided into two categorie

(1) drinking-water aquifers, and (2) shallow ground water underlying agricultu

urban areas. Summary scores were computed for each characteristic for all aqui

shallow ground-water areas that had adequate data. Scores for each aquifer and 

ground-water area in the Rio Grande Valley were compared with scores for all 

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

95. Results are summarized by percentiles; higher percentile values generally 

poorer quality compared with other NAWQA ground-water studies. Water-qu

conditions for each drinking-water aquifer also are compared to established

drinking-water standards and criteria for protection of human health. (Methods 

compute rankings and evaluate standards and criteria are described by Gilliom 

others, in press.)
U.S. Geological Survey Circular 1162 

Pesticide detections for the San Luis Valley and aqu

subunit survey were among the lowest of all NAWQ

ground-water studies and were only slightly higher 

the Albuquerque area and Rincon Valley. No standa

were exceeded in any samples from the four areas.

The percentage of wells with VOC detections in urban

and agricultural areas ranked in the middle categories

nationwide. No VOCs were detected in aquifer subunit

survey samples.

CONCLUSIONS

Compared to other NAWQA Study Units, in

the Rio Grande Valley

 • Pesticide concentrations detected in shallow

ground water in the agricultural and

urban land-use areas have not exceeded

any drinking-water standards.

• Radon concentrations in the San Luis Valley

and in parts of the aquifer subunit survey

area may be high enough to be of potential health concern.

• Dissolved-solids concentrations are higher in

the middle to lower parts of the study

area. This may indicate interaction of

ground water and surface water along th

Rio Grande and deeper water has been

recharged at basin boundaries and traveled large distances.

The median dissolved-solids concentration in water

from the Albuquerque and Rincon land-use studies and

aquifer subunit survey ranked in the top 25 percent nationwide. Drinking-water standards were exceeded in

some wells in all areas.

Alamosa

Albuquerque

El Paso

VOLATILE ORGANIC

COMPOUNDS

(RV)

(SUS)

(ALB)

(SLV)

Alamosa

Albuquerque

El Paso

PESTICIDES

(RV)

(SUS)

(ALB)

(SLV)

Alamosa

Albuquerque

El Paso

DISSOLVED SOLIDS

(RV)

(SUS)

(ALB)

(SLV)

WATER-QUALITY CONDITIONS IN A NATIONAL CO

Comparison of Stream Quality in the Rio Grand

with Nationwide NAWQA F
26 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

STUDY DESIGN AND DATA COLLECTION

EXPLANATION

0 30 60 MILES

0 30 60 KILOMETERS

SURFACE-WATER SITE

WHERE CHEMICAL DATA

WERE COLLECTED

0 30 60 MILES

0 30 60 KILOMETERS

EXPLANATION

SURFACE-WATER SITE WHERE

ECOLOGICAL DATA WERE

COLLECTED

0 30 60 MILES

0 30 60 KILOMETERS

EXPLANATION

URBAN LAND-USE STUDY

AQUIFER SUBUNIT

SURVEY

AGRICULTURAL LAND-USE

STUDY

Stream Chemistry

The primary objective of the

stream chemistry component was to

assess the relationship between land

use and chemical constituents of

surface water. Surface-water sites

were distributed among land uses;

site types include basic, intensive,

and synoptic sites for pesticides,

nutrients, and trace elements.

Ground-Water Chemistry

The primary objective of the

ground-water chemistry component was to determine if the chemical constituents in the shallow

aquifer were related to urban and

irrigated agricultural land use. A

subunit survey of a deeper aquifer

used for domestic supply was also

conducted.

Stream Ecology

The primary objective of the

stream ecology component was to

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

biological factors. Ecology sites

were distributed among forest, irrigated agriculture, urban, and rangeland. Sites were classified as either

intensive or synoptic on the basis of

the level of the sampling effort or

the number of years data were collected. A special study on the applicability of transplanted bryophytes

(moss) for trace-element accumulation was also conducted.
U.S. Geological Survey Circular 1162 

STUDY DESIGN AND DATA COLL

SUMMARY OF DATA COLLECTION IN THE RIO GRANDE VALLEY STUDY UNIT, 1992-95

Study

 component

What data were

 collected and Why Types of sites sampled

Number

of sites

Stream Chemistry

Bed-sediment study Determine presence of potentially toxic

compounds attached to sediments in

major streams.

Sample depositional zones of the Rio Grande and selected tributaries and non-tributaries for trace elements and hydrophobic

organic compounds.

18 

Water chemistry —

Basic Fixed Site study

Describe concentrations and loads of chemicals, suspended sediment, and nutrients

at selected sites throughout the Study

Unit.

Sample at or near sites where streamflow is measured continuously

for major constituents, nutrients, and suspended sediment.

17 

Water chemistry —

Intensive Fixed Site

study

Determine concentration and timing of pesticides transported by runoff to streams.Select an agricultural basin where pesticides, dissolved solids,

major constituents, and nutrients were sampled weekly and during selected runoff events.

1 

Water chemistry —

Trace-element synoptic study

Describe presence and distribution of trace

elements in the water column, suspended

sediment, and bed material in the Rio

Grande and tributaries in the northern

part of the Study Unit.

Sample water column and suspended sediment during high flow

(June) and water column and bed material during low flow (September) for trace elements and major constituents.

34 

Water chemistry—

Mesilla Valley pesticide and nutrient synoptic study

Describe presence and distribution of pesticides and nutrients in the water column

in the Rio Grande and drains in the

Mesilla Valley.

Sample water column during high flow (irrigation season) for pesticides, nutrients, dissolved solids, and major constituents and

during low flow (nonirrigation season) for pesticides, nutrients,

dissolved solids, major constituents, and trace elements. Sample

bed material in drains during low flow for pesticides.

19 

Water chemistry—Rincon Valley temporal

drain study

Describe temporal water-quality variation

in surface drains and Rio Grande in an

agricultural area flood irrigated with surface water.

Sample selected sites twice during nonirrigation season (low flow)

and at the beginning and end of the irrigation season (high flow).

Water analyzed for dissolved solids, major constituents, nutrients, organic carbon, trace elements, and pesticides.

11 

Stream Ecology

Fish-tissue contaminant

study

Determine the presence of contaminants in

fish tissue from species that can be found

in most streams of the Study Unit.

Sample composites of whole-body fish for:

hydrophobic organic contaminants

fish livers for trace elements.

11

12

Intensive ecological

assessments

Assess fish, macroinvertebrates, and algae

communities and habitat in streams representing three ecological regions.

Sample aquatic communities at a subset of water-chemistry basic

sites; quantitatively describe stream habitat for these organisms.

Sample aquatic communities at a subset of water-chemistry basic

sites; quantitatively describe stream habitat for these organisms.

2

8

Ecological synoptic

studies

Assess aquatic and terrestrial communities

and habitat in representative streams

throughout the Study Unit.

Sample macroinvertebrates and algae at or near water-chemistry

sites and describe habitat.

Sample adult insects using ultraviolet light traps at or near waterchemistry sites.

16

14

Transplanted aquatic

bryophyte study

Determine spatial distribution of trace elements in the upper Rio Grande Valley

Study Unit using transplanted aquatic

bryophytes.

Transplant bryophyte samples (Hygrohypnum ochraceum) for variable lengths of time and analyze samples for trace-element concentration.13 

Ground-water Chemistry

Land-use studies Examine natural and human factors that

affect the quality of shallow ground

water that underlies areas of urban land,

overhead, center-pivot sprinkler-irrigated

agriculture land, or flood-irrigated agricultural land.

Install shallow wells and sample water from wells for analysis of

dissolved solids, major constituents, nutrients, dissolved organic

carbon, trace elements, pesticides, volatile organic compounds,

and radionuclides.

(1) San Luis Valley agricultural land-use study of an area irrigated

with ground water by overhead, center-pivot sprinklers.

(2) Albuquerque urban land-use study.

(3) Rincon Valley agricultural land-use study of an area flood irrigated with surface water.

35

24

30

Aquifer subunit survey Describe the overall water quality in the

part of the basin-fill aquifer used for

domestic supply, public supply, or irrigation.

Randomly select and sample existing wells located in the Rio

Grande flood plain from Cochiti Lake, New Mexico, to El Paso,

Texas, for analysis of major constituents, nutrients, dissolved

organic carbon, trace elements, pesticides, volatile organic compounds, and radionuclides.

30 
28 Water-Quality Assessment of the Rio Grande Valley, 1992-95

Herbicide

(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

The following tables summarize data collected for NAWQA studies from 1992-95 by showing results for the Rio G

Study Unit compared to the NAWQA national range for each compound detected. The data were collected at a wide varie

tions and times. In order to represent the wide concentration ranges observed among Study Units, logarithmic scales are us

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

construct these tables is available upon request.

Concentrations of pesticides, volatile organic compounds, and nutrients detected in ground and surface waters of the Rio G

Study Unit. [mg/L, milligrams per liter; μg/L, micrograms per liter; pCi/L, picocuries per liter; %, percent; <, less than; - -, not 

trade names may vary]

EXPLANATION

Range of surface-water detections in all 20 Study Units

Range of ground-water detections in all 20 Study Units

Drinking water standard or guideline a

Freshwater-chronic criterion for the protection of aquatic life a

Atrazine (AAtrex,

Gesaprim)

<1%

1%

Deethylatrazinec

(Atrazine metabolite)

<1%

0%

Bentazon (Basagran,

bentazone)

1%

1%

Bromacil (Hyvar X,

Urox B, Bromax)

0%

1%

Cyanazine (Bladex,

Fortrol)

<1%

0%

2,4-D (2,4-PA) 1%

0%

DCPA (Dacthal, chlorthal-dimethyl)

10%

0%

Dacthal, mono-acid

(Dacthal metabolite)

2%

0%

Diuron (Karmex,

Direx, DCMU)

1%

0%

EPTC (Eptam) 3%

0%

Metolachlor (Dual,

Pennant)

11%

6%

Metribuzin (Lexone,

Sencor)

2%

2%

Napropamide

(Devrinol)

0%

1%

Pendimethalin

(Prowl, Stomp, Herb1%

0%

Prometon (Gesagram, prometone)

7%

8%

Simazine (Aquazine,

Princep, GEsatop,

12%

0%

Tebuthiuron (Spike,

Perflan)

3%

0%

Trifluralin (Treflan,

Trinin, Elancolan)

1%

0%

Insecticide

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

Azinphos-methylc

(Guthion, Gusathion

1%

0%

Carbarylc (Sevin,

Savit)

6%

1%

Carbofuranc

(Furadan, Curaterr,

11%

1%

Chlorpyrifos (Dursban, Lorsban, Dowco

3%

0%

p,p’-DDE (p,p’-DDT

metabolite)

<1%

<1%

Diazinon 10%

1%

gamma-HCH 2%

0%

Malathion (maldison,

malathon, Cythion)

1%

0%

Propargite (Comite,

Omite, BPPS)

1%

0%

Terbufos (Counter) 1%

0%

0.001 0.01 0.1 1 

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
U.S. Geological Survey Circular 1162 

Trichloroethene

(TCE)

--

1%

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

--

2%

p-Isopropyltoluene

(p-Cymene)

--

1%

1,1-Dichloroethane

(Ethylidene dichloride)

--

2%

Dimethylbenzenes

(Xylenes, total)

--

3%

Volatile organic

compound

(Trade or common

name)

Rate

of

detection b

Concentration, in μg/L

Methyl tert-butyld

ether (MTBE)

--

2%

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

Dissolved ammonia 75%

78%

Dissolved ammonia

plus organic nitrogen

as nitrogen

53%

39%

Dissolved phosphorus as phosphorus

82%

72%

Dissolved nitrite plus

nitrate

66%

65%

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 CONCE
30 Water-Quality Assessment of the Rio Grande Valley, 1992-95

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

Study Unit.

Herbicides

2,4,5-T

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

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

2,6-Diethylaniline (Metabolite of Alachlor)

Acetochlor (Harness Plus,

Surpass)

Acifluorfen (Blazer, Tackle

2S)

Alachlor (Lasso, Bronco,

Lariat, Bullet)

Benfluralin (Balan, Benefin,

Bonalan, Benefex)

Bromoxynil (Buctril, Brominal)

Butylate (Sutan +, Genate

Plus, Butilate)

Chloramben (Amiben,

Amilon-WP, Vegiben)

Clopyralid (Stinger, Lontrel, Reclaim, Transline)

Dicamba (Banvel, Dianat,

Scotts Proturf)

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

Dinoseb (Dinosebe)

Ethalfluralin (Sonalan, Curbit)

Fenuron (Fenulon, Fenidim)

Fluometuron (Flo-Met,

Cotoran, Cottonex, Meturon)

Linuron (Lorox, Linex, Sarclex, Linurex, Afalon)

MCPA (Rhomene, Rhonox,

Chiptox)

MCPB (Thistrol)

Molinate (Ordram)

Neburon (Neburea, Neburyl, Noruben)

Norflurazon (Evital, Predict, Solicam, Zorial)

Oryzalin (Surflan, Dirimal)

Pebulate (Tillam, PEBC)

Picloram (Grazon, Tordon)

Pronamide (Kerb, Propyzamid)

Propachlor (Ramrod, Satecid)

Propanil (Stam, Stampede,

Wham, Surcopur, Prop-Job)

Propham (Tuberite)

Terbacil (Sinbar)

Thiobencarb (Bolero, Saturn, Benthiocarb, Abolish)

Triallate (Far-Go, Avadex

BW, Tri-allate)

Triclopyr (Garlon, Grandstand, Redeem, Remedy)

Insecticides

3-Hydroxycarbofuran (Carbofuran metabolite)

Aldicarb sulfone (Standak,

aldoxycarb, aldicarb metabolite)

Aldicarb sulfoxide (Aldicarb metabolite)

Aldicarb (Temik, Ambush,

Pounce)

Dieldrin (Panoram D-31,

Octalox, Compound 497,

Aldrin epoxide)

Disulfoton (Disyston, DiSyston, Frumin AL,

Solvirex, Ethylthiodemeton)

Ethoprop (Mocap, Ethoprophos)

Fonofos (Dyfonate, Capfos,

Cudgel, Tycap)

Methiocarb (Slug-Geta,

Grandslam, Mesurol)

Methomyl (Lanox, Lannate, Acinate)

Methyl parathion (PenncapM, Folidol-M, Metacide,

Bladan M)

Oxamyl (Vydate L, Pratt)

Parathion (Roethyl-P, Alkron, Panthion, Phoskil)

Phorate (Thimet, Granutox, Geomet, Rampart)

Propoxur (Baygon, Blattanex, Unden, Proprotox)

alpha-HCH (alpha-BHC,

alpha-lindane, alphahexachlorocyclohexane,

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)

Volatile organic

compounds

1,1,1,2-Tetrachloroethane

(1,1,1,2-TeCA)

1,1,1-Trichloroethane

(Methylchloroform)

1,1,2,2-Tetrachloroethane

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

CFC 113)

1,1,2-Trichloroethane

(Vinyl trichloride)

1,1-Dichloroethene

(Vinylidene chloride)

1,1-Dichloropropene

1,2,3-Trichlorobenzene

(1,2,3-TCB)

1,2,3-Trichloropropane

(Allyl trichloride)

1,2,4-Trichlorobenzene

1,2,4-Trimethylbenzene

(Pseudocumene)

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

1,2-Dibromoethane (EDB,

Ethylene dibromide)

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

DCB)

1,2-Dichloroethane (Ethylene dichloride)

1,2-Dichloropropane (Propylene dichloride)

1,3,5-Trimethylbenzene

(Mesitylene)

1,3-Dichlorobenzene (mDichlorobenzene)

1,3-Dichloropropane (Trimethylene dichloride)

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

DCB)

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

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

2,2-Dichloropropane

Benzene

Bromobenzene (Phenyl

bromide)

Bromochloromethane

(Methylene chlorobromide)

Bromomethane (Methyl

bromide)

Chlorobenzene

(Monochlorobenzene)

Chloroethane (Ethyl chloride)

Chloroethene (Vinyl Chloride)

Chloromethane (Methyl

chloride)

Dibromomethane (Methylene dibromide)

Dichlorodifluoromethane

(CFC 12, Freon 12)

Dichloromethane (Methylene chloride)

Ethenylbenzene (Styrene)

Ethylbenzene (Phenylethane)

Hexachlorobutadiene

Isopropylben

(Cumene)

Methylbenze

Naphthalene

Tetrachloroe

chloroethene

Tetrachlorom

bon tetrachlo

Total Trihalo

(Trichlorome

roform), Dib

romethane,

Bromodichlo

Tribromome

form))

Trichlorofluo

(CFC 11, Fre

cis-1,3-Dich

((Z)-1,3-Dic

n-Butylbenz

nylbutane)

n-Propylben

umene)

sec-Butylben

tert-Butylbe

trans-1,2-Di

((E)-1,2-Dic

trans-1,3-Di

((E)-1,3-Dic

Nutrients

No non-dete

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
U.S. Geological Survey Circular 1162 

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

sediment of the Rio Grande Valley Study Unit. [μg/g, micrograms per gram; μg/kg, micrograms per kilogram; %, percent; <

, not measured; trade names may vary]

EXPLANATION

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

Detection in bed sediment or fish tissue in the Rio Grande Valley Study Unit

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

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

Semivolatile

organic compound

Rate

of

detection b

Concentration, in μg/kg

0.1 10 100 11

1,6-Dimethylnaphthalene

--

13%

1-Methylphenanthrene

--

6%

1-Methylpyrene --

6%

2,3,6-Trimethylnaphthalene

--

13%

2,6-Dimethylnaphthalene

--

81%

2-Methylanthracene --

6%

3,5-Dimethylphenol --

13%

4,5-Methylenephenanthrene

--

6%

9H-Carbazole --

19%

9H-Fluorene --

6%

Acenaphthylene --

13%

Anthracene --

38%

Anthraquinone --

13%

Benz[ a ]anthracene --

38%

Benzo[ a ]pyrene --

31%

Benzo[ b ]fluoranthene

--

19%

Benzo[ ghi ]perylene --

13%

Benzo[ k ]fluoranthene

--

19%

Butylbenzylphthalate --

69%

Chrysene --

50%

Di- n -butylphthalate --

88%

Di- n -octylphthalate --

6%

Dibenz[ a,h ]

anthracene

--

6%

Dibenzothiophene --

13%

Diethylphthalate --

81%

Dimethylphthalate --

19%

Fluoranthene --

62%

Indeno[1,2,3- cd ]

pyrene

--

13%

Phenanthrene --

62%

Phenanthridine --

13%

Phenol --

50%

Pyrene --

56%

bis(2-Ethylhexyl)phthalate

--

100%

p-Cresol --

69%

SUMMARY OF COMPOUND DETECTIONS AND CONCE
32 Water-Quality Assessment of the Rio Grande Valley, 1992-95

total-Chlordane 9%

0%

PCB, total 45%

0%

p,p’-DDE 91%

31%

total-DDT 91%

31%

gamma-HCH (lindane, gamma-BHC,

9%

--

Hexachlorobenzene 9%

--

Arsenic 92%

100%

Cadmium 83%

100%

Chromium 75%

100%

Copper 100%

100%

Lead 17%

100%

Mercury 75%

73%

Nickel 50%

100%

Selenium 100%

100%

Zinc 100%

100%

Organochlorine

compound

(Trade name)

Rate

of

detection b

Concentration, in μg/kg

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

Trace element Rate

of

detection b

Concentration, in μg/g

0.01 0.1 1 10 1

SUMMARY OF COMPOUND DETECTIONS AND CONCENTRATIONS
U.S. Geological Survey Circular 1162 

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

Grande Valley Study Unit.

Semivolatile organic

compounds

1,2,4-Trichlorobenzene

1,2-Dichlorobenzene

(o-Dichlorobenzene,

1,2-DCB)

1,2-Dimethylnaphthalene

1,3-Dichlorobenzene

(m-Dichlorobenzene)

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

DCB)

1-Methyl-9H-fluorene

2,2-Biquinoline

2,4-Dinitrotoluene

2,6-Dinitrotoluene

2-Chloronaphthalene

2-Chlorophenol

2-Ethylnaphthalene

4-Bromophenyl-phenylether

4-Chloro-3-methylphenol

4-Chlorophenyl-phenylether

Acenaphthene

Acridine

Azobenzene

Benzo [c] cinnoline

C8-Alkylphenol

Isophorone

Isoquinoline

N-Nitrosodi-n-propylamine

N-Nitrosodiphenylamine

Naphthalene

Nitrobenzene

Pentachloronitrobenzene

Quinoline

bis (2-Chloroethoxy)methane

Organochlorine

compounds

Aldrin (HHDN, Octalene)

Chloroneb (chloronebe,

Demosan, Soil Fungicide 1823)

DCPA (Dacthal, chlorthal-dimethyl)

Dieldrin (Panoram D31, Octalox, Compound

497, Aldrin epoxide)

Endosulfan I (alphaEndosulfan, Thiodan,

Cyclodan, Beosit,

Malix, Thimul, Thifor)

Endrin (Endrine)

Heptachlor epoxide

(Heptachlor metabolite)

Heptachlor (Heptachlore, Velsicol 104)

Isodrin (Isodrine, Compound 711)

Mirex (Dechlorane)

Oxychlordane (Chlordane metabolite)

Pentachloroanisole

(PCA, pentachlorophenol metabolite)

Total Trihalomethanes

(Trichloromethane

(Chloroform), Dibromochloromethane, Bromodichloromethane,

Tribromomethane (Bromoform))

Toxaphene (Camphechlor, Hercules

3956)

alpha-HCH (alphaBHC, alpha-lindane,

alpha-hexachlorocyclohexane, alpha-benzene

hexachloride)

beta-HCH (beta-BHC,

beta-hexachlorocyclohexane, 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

p,p’-Methoxychlor

(Marlate, methoxychlore)

trans-Permethrin

(Ambush, Astro,

Pounce, Pramex, Pertox, Ambushfog, Kafil,

Perthrine, Picket, Picket

G, Dragnet, Talcord,

Outflank, Stockade,

Eksmin, Coopex, Peregin, Stomoxin, Stomoxin P, Qamlin,

Corsair, Tornade)

Trace elements

No non-detects

a

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

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

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 

reported as estimated values (Zaugg and others, 1995).

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

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 CONCE
34 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

REFERENCES

Anderholm, S.K., 1996, Water-quality

assessment of the Rio Grande

Valley, Colorado, New Mexico,

and Texas—Shallow groundwater quality of a land-use area in

the San Luis Valley, south-central

Colorado, 1993: U.S. Geological

Survey Water-Resources Investigations Report 96-4144, 94 p.

———1997, Water-quality assessment

of the Rio Grande Valley, Colorado, New Mexico, and

Texas—Shallow ground-water

quality and land use in the Albuquerque area, central New Mexico, 1993: U.S. Geological

Survey Water-Resources Investigations Report 97-4067, 73 p.

Anderholm, S.K., Radell, M.J., and

Richey, S.F., 1995, Water-quality

assessment of the Rio Grande

Valley study unit, Colorado, New

Mexico, and Texas—Analysis of

selected nutrient, suspended-sediment, and pesticide data: U.S.

Geological Survey WaterResources Investigations Report

94-4061, 203 p.

Barbash, J.E., and Resek, E.A., 1996,

Pesticides in ground water—Distribution, trends, and governing

factors: Chelsea, Mich., Ann

Arbor Press, Inc., Pesticides in

the hydrologic system series, v. 2,

588 p.

Bexfield, L.M., and Anderholm, S.K.,

1997, Water-quality assessment

of the Rio Grande Valley, Colorado, New Mexico, and

Texas—Ground-water quality in

the Rio Grande flood plain,

Cochiti Lake, New Mexico, to El

Paso, Texas, 1995: U.S. Geological Survey Water-Resources

Investigations Report 96-4249, 93

p.

Carter, L.F., 1997a, Water-quality

assessment of the Rio Grande

Valley, Colorado, New Mexico,

and Texas—Fish communities at

selected sites, 1993-95: U.S. Geological Survey Water-Resources

Investigations Report 97-4017,

27 p.

———1997b, Water-quality assessment of the Rio Grande Valley,

Colorado, New Mexico, and

Texas—Organic compounds and

trace elements in bed sediment

and fish tissue, 1992-93: U.S.

Geological Survey WaterResources Investigations Report

97-4002, 23 p.

Carter, L.F., and Porter, S.D., 1997,

Trace-element accumulation by

Hygrohypnum ochraceum in the

upper Rio Grande Basin, Colorado and New Mexico: Environmental Toxicology and

Chemistry, v. 16, no. 12,

p. 2521-2528.

Colorado Water Quality Control Commission, 1989, Classifications and

numeric standards Rio Grande

River Basin: Denver, 50 p.

Ellis, S.R., 1991, National WaterQuality Assessment Program—The Rio Grande Valley:

U.S. Geological Survey OpenFile Report 91-160, 2 p.

Ellis, S.R., Levings, G.W., Carter, L.F.,

Richey, S.F., and Radell, M.J.,

1993, Rio Grande Valley, Colorado, New Mexico, and Texas, in

Leahy, P.P., Ryan, B.J., and

Johnson, A.I., eds., American

Water Resources Association

Monograph Series no. 19,

p. 617-646.

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-

1995: U.S. Geological Survey

Open-File Report 97-589.

Healy, D.F., 1996, Water-quality

assessment of the Rio Grande

Valley, Colorado, New Mexico,

and Texas—Occurrence and distribution of selected pesticides

and nutrients at selected s

water sites in the Mesilla 

1994-95: U.S. Geologica

Water-Resources Investig

Report 96-4069, 85 p.

———1997, Water-quality ass

of the Rio Grande Valley, 

rado, New Mexico, and

Texas—Summary and an

water-quality data for the 

fixed-site network, 1993-

Geological Survey Water

Resources Investigations 

97-4212, 82 p.

Larson, S.J., Capel, P.D., and M

ski, M.S., 1997, Pesticide

face waters—Distribution

and governing factors: Ch

Mich., Ann Arbor Press, 

Pesticides in the hydrolog

tem series, v. 3, 373 p.

Majewski, M.S., and Capel, P.

1995, Pesticides in the atm

sphere—Distribution, tren

governing factors: Chelse

Mich., Ann Arbor Press, 

Pesticides in the hydrolog

tem series, v. 1, 214 p.

Miller, L.K., Moquino, R.L., a

B.A., 1997, Water-quality 

ment of the Rio Grande V

Colorado, New Mexico, a

Texas—Water-quality dat

water-column, suspended

ment, and bed-material sa

collected at selected surfa

water sites in the upper R

Grande Basin, June and S

ber, 1994: U.S. Geologica

vey Open-File Report 97-

18 p.

Mueller, D.K., Hamilton, P.A.

D.R., Hitt, K.J., and Rudd

1995, Nutrients in ground 

and surface water of the U

States—An analysis of da

through 1992: U.S. Geolo

Survey Water-Resources 

gations Report 95-4031, 7

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

Nutrients in the nation’s

waters—Too much of a g

thing?: U.S. Geological S

Circular 1136, 24 p.
U.S. Geological Survey Circular 1162 

REFER

New Mexico Water Quality Control

Commission, 1991, Water-quality standards for interstate and

intrastate streams in New Mexico:

Santa Fe, 49 p.

Nolan, B.T., and Ruddy, B.C., 1996,

Nitrate in ground waters of the

United States—Assessing the

risk: U.S. Geological Survey Fact

Sheet 092-96, 4 p.

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

National standards and guidelines

for pesticides in water, sediment,

and aquatic organisms—Application to water-quality assessments, in Ware, G.W., ed.,

Reviews of environmental contamination and toxicology, v. 140:

New York, Springer-Verlag,

p. 1-164.

Richey, S.F., and Ellis, S.R., 1993,

National Water-Quality Assessment Program—Water use in the

Rio Grande Valley, 1990: U.S.

Geological Survey Open-File

Report 93-456, 2 p.

Schmitt, C.J., and Brumbaugh, W.G.,

1990, National Contaminant

Biomonitoring Program—Concentrations of arsenic, cadmium,

copper, lead, mercury, selenium,

and zinc in U.S. freshwater fish,

1976-1984: Archives of Environmental Contamination and Toxicology, v. 19, p. 731-747.

Schmitt, C.J., Zajicek, J.L., and Peterman, P.H., 1990, National Contaminant Biomonitoring

Program—Residues of organochlorine chemicals in U.S.

freshwater fish, 1976-1984:

Archives of Environmental Contamination and Toxicology, v. 19,

p. 748-781.

Schmitt, C.J., Zajicek, J.L., and

Ribick, M.A., 1985, National

Contaminant Biomonitoring Program—Residues of organochlorine chemicals in freshwater fish,

1980-1981: Archives of Environmental Contamination and Toxicology, v. 14, p. 225-260.

Smith, J.A., Witowski, P.J., and

Fusillo, T.V., 1988, Manmade

organic compounds in the surface

waters of the United States—A

review of current understanding:

U.S. Geological Survey Circular

1007, 92 p.

U.S. Environmental Protection

Agency, 1996a, Drinking water

regulations and health advisories:

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

of Water, 11 p.

———1996b,(Draft) National sediment contaminant point-source

inventory: EPA-823-D-96-001.

———1996c,The National Sediment

Quality Survey—A report to Congress on the extent and severity of

sediment contamination in surface waters of the United States:

U.S. Environmental Protection

Agency, Office of Science and

Technology, Draft Report EPA

823-D-96-002.

Van Metre, P.C., Mahler, B.J., and Callender, Edward, 1997, Waterquality trends in the Rio

Grande/Río Bravo Basin using

sediment cores from reservoirs:

U.S. Geological Survey Fact

Sheet 221-96, 8 p.

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

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

Methods of analysis by the U.S.

Geological Survey National

Water Quality Laboratory—Determination of pesticides in water by C-18 solidphase extraction and capillarycolumn gas chromatography/mass spectrometry with

selected ion monitoring: U.S.

Geological Survey Open-File

Report 95-181, 54 p.
36 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

GLOSSARY

The terms in this glossary were compiled from numerous sources. Some

definitions have been modified and

may not be the only valid ones for

these terms.

Alluvial aquifer - A water-bearing

deposit of unconsolidated material

(sand and gravel) left behind by a river

or other flowing water.

Anomalies - As related to fish, externally visible skin or subcutaneous disorders, including deformities, eroded

fins, lesions, and tumors.

Anthropogenic - Occurring because

of, or influenced by, human activity.

Aquatic-life criteria - Water-quality

guidelines for protection of aquatic

life. Often refers to U.S. Environmental Protection Agency water-quality

criteria for protection of aquatic organisms. See also Water-quality guidelines and Water-quality criteria.

Aquifer - A water-bearing layer of

soil, sand, gravel, or rock that will

yield usable quantities of water to a

well.

Basic Fixed Sites - 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 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.

Benthic - Refers to plants or animals

that live on the bottom of lakes,

streams, or oceans.

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.

Bioavailability - The capacity of a

chemical constituent to be taken up by

living organisms either through physical contact or by ingestion.

Biodegradation - Transformation of a

substance into new compounds

through biochemical reactions or the

actions of microorganisms such as bacteria.

Community - In ecology, the species

that interact in a common area.

Concentration - The amount or mass

of a substance present in a given volume or mass of sample. Usually

expressed as microgram per liter

(water sample) or micrograms per

kilogram (sediment or tissue sample).

Confluence - The flowing together of

two or more streams; the place where a

tributary joins the main stream.

Constituent - A chemical or biological substance in water, sediment, or

biota that can be measured by an analytical method.

Contamination - Degradation of

water quality compared to original or

natural conditions due to human activity.

Criterion - A standard rule or test on

which a judgment or decision can be

based.

Degradation products - Com

resulting from transformation 

organic substance through che

photochemical, and/or biochem

reactions.

Detection limit - The concent

below which a particular analy

method cannot determine, with 

degree of certainty, a concentr

DDT - Dichloro-diphenyl-trich

hane. An organochlorine insec

longer registered for use in the 

States.

Dissolved solids - Amount of 

als, such as salt, that are dissol

water; amount of dissolved sol

indicator of salinity or hardnes

Diversion - A turning aside or 

ation of the natural course of a 

water, normally considered ph

to leave the natural channel. In 

States, this can be a consumpt

direct from another stream, su

livestock watering. In other St

diversion must consist of such 

as taking water through a cana

or conduit.

Drainage basin - The portion 

surface of the Earth that contri

water to a stream through over

run-off, including tributaries a

impoundments.

Drinking-water standard or 

line - A threshold concentratio

public drinking-water supply, d

to protect human health. As de

here, standards are U.S. Enviro

Protection Agency regulations 

specify the maximum contami

levels for public water systems

required to protect the public w

guidelines have no regulatory 

and are issued in an advisory c

Ecological studies - Studies o

ical communities and habitat c

teristics to evaluate the effects 

physical and chemical charact
U.S. Geological Survey Circular 1162 

GLO

of water and hydrologic conditions on

aquatic biota and to determine how

biological and habitat characteristics

differ among environmental settings in

NAWQA Study Units.

Ecoregion - An area of similar climate, landform, soil, potential natural

vegetation, hydrology, or other ecologically relevant variables.

Ecosystem - The interacting populations of plants, animals, and microorganisms occupying an area, plus their

physical environment.

Effluent - Outflow from a particular

source, such as a stream that flows

from a lake or liquid waste that flows

from a factory or sewage-treatment

plant.

Environmental setting - Land area

characterized by a unique combination of natural and human-related factors, such as row-crop cultivation or

glacial-till soils.

Ephemeral stream - A stream or part

of a stream that flows only in direct

response to precipitation or snowmelt.

Its channel is above the water table at

all times.

Eutrophication - The process by

which water becomes enriched with

plant nutrients, most commonly phosphorus and nitrogen.

Evapotranspiration - A collective

term that includes water lost through

evaporation from the soil and surfacewater bodies and by plant transpiration.

FDA action level - A regulatory level

recommended by the U.S. Environmental Protection Agency for enforcement by the FDA when pesticide

residues occur in food commodities for

reasons other than the direct application of the pesticide. Action levels are

set for inadvertent pesticide residues

resulting from previous legal use or

accidental contamination. Applies to

edible portions of fish and shellfish in

interstate commerce.

Fixed Sites - NAWQA's most comprehensive monitoring sites. See also

Basic Fixed Sites and Intensive Fixed

Sites.

Flood irrigation - The application of

irrigation water where the entire surface of the soil is covered by ponded

water.

Flood plain - The relatively level area

of land bordering a stream channel and

inundated during moderate to severe

floods.

Ground water - In general, any water

that exists beneath the land surface, but

more commonly applied to water in

fully saturated soils and geologic formations.

Habitat - The part of the physical

environment where plants and animals

live.

Health advisory - Nonregulatory levels of contaminants in drinking water

that may be used as guidance in the

absence of regulatory limits. Advisories consist of estimates of concentrations that would result in no known or

anticipated health effects (for carcinogens, a specified cancer risk) determined for a child or for an adult for

various exposure periods.

Herbicide - A chemical or other agent

applied for the purpose of killing undesirable plants. See also Pesticide.

Human health advisory - Guidance

provided by U.S. Environmental Protection Agency, State agencies or scientific organizations, in the absence of

regulatory limits, to describe acceptable contaminant levels in drinking

water or edible fish.

Index of Biotic Integrity (IBI

aggregated number, or index, b

several attributes or metrics of 

community that provides an as

ment of biological conditions.

Indicator sites- Stream sampl

located at outlets of drainage b

with relatively homogeneous l

and physiographic conditions; 

indicator-site basins have drain

areas ranging from 20 to 200 s

miles.

Infiltration - Movement of wa

ically downward, into soil or p

rock.

Insecticide - A substance or m

of substances intended to destr

repel insects.

Integrator or Mixed-use site 

sampling site located at an out

drainage basin that contains m

environmental settings. Most i

tor sites are on major streams 

atively large drainage areas.

Intensive Fixed Sites - Basic 

Sites with increased sampling 

quency during selected season

ods and analysis of dissolved

pesticides for 1 year. Most NA

Study Units have one to two in

Intensive Fixed Sites and one t

indicator Intensive Fixed Sites

Intermittent stream - A strea

flows only when it receives wa

rainfall runoff or springs, or fro

surface source such as melting 

Intolerant organisms - Organ

that are not adaptable to huma

ations to the environment and 

decline in numbers where hum

ations occur. See also Tolerant 

Irrigation return flow - The p

irrigation applied to the surfac

not consumed by evapotranspi
38 Water Quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95

GLOSSARY

uptake by plants and that migrates to

an aquifer or surface-water 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 Study-Unit

Survey and have the goal of relating

the quality of shallow ground water to

land use. See also Study-Unit Survey.

Main stem - The principal course of a

river or a stream.

Major ions - Constituents commonly

present in concentrations exceeding

1.0 milligram per liter. Dissolved cations generally are calcium, magnesium, sodium, and potassium; the

major anions are sulfate, chloride, fluoride, nitrate, and those contributing to

alkalinity, most generally assumed to

be bicarbonate and carbonate.

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.

Mean discharge (MEAN) - The arithmetic mean of individual daily mean

discharges during a specific period,

usually daily, monthly, or annually.

Median - The middle or central value

in a distribution of data ranked in order

of magnitude. The median is also

known as the 50th percentile.

Method detection limit - The minimum concentration of a substance that

can be accurately identified and measured with present laboratory technologies.

Micrograms per liter (μg/L) - A unit

expressing the concentration of constituents in solution as weight (micrograms) of solute per unit volume (liter)

of water; equivalent to one part per billion in most streamwater and ground

water. One thousand micrograms per

liter equals 1 mg/L.

Milligrams per liter (mg/L) - A unit

expressing the concentration of chemical constituents in solution as weight

(milligrams) of solute per unit volume

(liter) of water; equivalent to one part

per million in most streamwater and

ground water. One thousand micrograms per liter equals 1 mg/L.

Minimum reporting level (MRL) -

The smallest measured concentration

of a constituent that may be reliably

reported using a given analytical

method. In many cases, the MRL is

used when documentation for the

method detection limit is not available.

Monitoring well - A well designed for

measuring water levels and testing

ground-water quality.

Nonpoint source - A pollution source

that cannot be defined as originating

from discrete points such as pipe discharge. Areas of fertilizer and pesticide applications, atmospheric

deposition, manure, and natural inputs

from plants and trees are types of nonpoint source pollution.

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 broadscale 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, and some sol

containing chlorine.

Pesticide - A chemical applied 

crops, rights of way, lawns, or 

dences to control weeds, insect

nematodes, rodents or other "p

Point-source contaminant - A

stance that degrades water qua

originates from discrete locatio

as discharge pipes, drainage di

wells, concentrated livestock o

tions, or floating craft.

Pollutant - Any substance tha

present in a hydrologic system 

cient concentration, degrades w

quality in ways that are or cou

become harmful to human and

logical health or that impair th

water for recreation, agricultur

industry, commerce, or domes

poses.

Polychlorinated biphenyls (P

A mixture of chlorinated deriv

biphenyl, marketed under the t

name Aroclor with a number d

ing the chlorine content (such 

clor 1260). PCBs were used in

transformers and capacitors fo

lating purposes and in gas pipe

tems as a lubricant. Further sa

new use was banned by law in 

Polycyclic aromatic hydroca

(PAH) - A class of organic com

with a fused-ring aromatic stru

PAHs result from incomplete c

tion of organic carbon (includi

wood), municipal solid waste, 

sil fuels, as well as from natur

anthropogenic introduction of 

busted coal and oil. PAHs incl

benzo(a)pyrene, fluoranthene, 

pyrene.

Radon - A naturally occurring

less, odorless, radioactive gas 

by the disintegration of the ele

radium; damaging to human lu

when inhaled.
U.S. Geological Survey Circular 1162 

GLO

Riparian - Areas adjacent to rivers

and streams with a high density, diversity, and productivity of plant and animal species relative to nearby uplands.

Secondary maximum contaminant

level (SMCL) - The maximum contamination level in public water systems that, in the judgment of the U.S.

Environmental Protection Agency, are

required to protect the public welfare.

SMCLs are secondary (nonenforceable) drinking water regulations established by the USEPA for contaminants

that may adversely affect the odor or

appearance of such water.

Sediment quality guideline - Threshold concentration above which there is

a high probability of adverse effects on

aquatic life from sediment contamination, determined using modified EPA

(1996c) procedures.

Semivolatile organic compound

(SVOC) - Operationally defined as a

group of synthetic organic compounds

that are solvent-extractable and can be

determined by gas chromatography/mass spectrometry. SVOCs

include phenols, phthalates, and polycyclic aromatic hydrocarbons (PAHs).

Species diversity - An ecological concept that incorporates both the number

of species in a particular sampling area

and the evenness with which individuals are distributed among the various

species.

Specific conductance - A measure of

the ability of a liquid to conduct an

electrical current.

Stream-aquifer interactions - Relations of water flow and chemistry

between streams and aquifers that are

hydraulically connected.

Stream reach - A continuous part of a

stream between two specified points.

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 surfacewater 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.

Subsurface drain - A shallow drain

installed in an irrigated field to intercept the rising ground-water level and

maintain the water table at an acceptable depth below the land surface.

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.

Synoptic sites - Sites sampled during a

short-term investigation of specific

water-quality conditions during

selected seasonal or hydrologic conditions to provide improved spatial resolution for critical water-quality

conditions.

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.

Urban Site - A site that has gr

than 50 percent urbanized and 

than 25 percent agricultural ar

Volatile organic compounds 

- Organic chemicals that have 

vapor pressure relative to their 

solubility. VOCs include comp

of gasoline, fuel oils, and lubri

well as organic solvents, fumig

some inert ingredients in pesti

and some by-products of chlor

infection.

Wasteway - A waterway used 

excess irrigation water dumpe

the irrigation delivery system.

Water-quality criteria - Spec

els of water quality which, if r

are expected to render a body 

unsuitable for its designated u

monly refers to water-quality c

established by the U.S. Enviro

Protection Agency. Water-qua

teria are based on specific leve

pollutants that would make the 

harmful if used for drinking, s

ming, farming, fish production

industrial processes.

Water-quality guidelines - Sp

levels of water quality which, 

reached, may adversely affect 

health or aquatic life. These ar

forceable guidelines issued by 

ernmental agency or other inst

Water-quality standards - St

adopted and U.S. Environmen

tection Agency-approved amb

standards for water bodies. Sta

include the use of the water bo

the water-quality criteria that m

met to protect the designated u

uses.

Water table - The point below 

land surface where ground wa

first encountered and below w

earth is saturated. Depth to the 

table varies widely across the 
Levings and others • Water Quality in the Rio Grande Valley

USGS Circular 1162 • 1998

NEW

MEXICO

El Paso, Texas

Rio Grande Albuquerque

COLORADO

National Water-Quality Assessment (NAWQA) Program

Rio Grande Valley

NAWQA