Water Quality in the Santa Ana Basin

California, 1999–2001

U.S. Department of the Interior

U.S. Geological Survey

Circular 1238
Points of Contact and Additional Information

The companion Web site for NAWQA summary reports:

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

Other NAWQA summary reports

River Basin Assessments

Acadian-Pontchartrain Drainages (Circular 1232)

Albemarle-Pamlico Drainage Basin (Circular 1157)

Allegheny and Monongahela River Basins (Circular 1202)

Apalachicola-Chattahoochee-Flint River Basin (Circular 1164)

Central Arizona Basins (Circular 1213)

Central Columbia Plateau (Circular 1144)

Central Nebraska Basins (Circular 1163)

Connecticut, Housatonic and Thames River Basins (Circular 1155)

Cook Inlet Basin (Circular 1240)

Delaware River Basin (Circular 1227)

Delmarva Peninsula (Circular 1228)

Eastern Iowa Basins (Circular 1210)

Georgia-Florida Coastal Plain (Circular 1151)

Great and Little Miami River Basins (Circular 1229) 

Great Salt Lake Basins (Circular 1236)

Hudson River Basin (Circular 1165)

Island of Oahu (Circular 1239)

Kanawha - New River Basins (Circular 1204)

Lake Erie - Lake Saint Clair Drainages (Circular 1203)

Long Island - New Jersey Coastal Drainages (Circular 1201)

Lower Illinois River Basin (Circular 1209)

Lower Susquehanna River Basin (Circular 1168)

Lower Tennessee River Basin (Circular 1233)

Las Vegas Valley Area and the Carson and Truckee River Basins (Circular 1170)

Mississippi Embayment (Circular 1208)

Mobile River Basin (Circular 1231)

New England Coastal Basins (Circular 1226)

Northern Rockies Intermontane Basins (Circular 1235)

Ozark Plateaus (Circular 1158)

Potomac River Basin (Circular 1166)

Puget Sound Basin (Circular 1216)

Red River of the North Basin (Circular 1169)

Rio Grande Valley (Circular 1162)

Sacramento River Basin (Circular 1215)

San Joaquin-Tulare Basins (Circular 1159)

Santee River Basin and Coastal Drainages (Circular 1206)

South-Central Texas (Circular 1212)

South Platte River Basin (Circular 1167)

Southern Florida (Circular 1207)

Trinity River Basin (Circular 1171)

Upper Colorado River Basin (Circular 1214)

Upper Illinois River Basin (Circular 1230)

Upper Mississippi River Basin (Circular 1211)

Upper Snake River Basin (Circular 1160)

Upper Tennessee River Basin (Circular 1205)

Western Lake Michigan Drainages (Circular 1156)

White River Basin (Circular 1150)

Willamette Basin (Circular 1161)

Yakima River Basin (Circular 1237)

Yellowstone River Basin (Circular 1234)

National Assessments

The Quality of Our Nation‘s Waters—Nutrients and Pesticides (Circular 1225)

Santa Ana Basin contact and Web site:

USGS State Representative

U.S. Geological Survey

Water Resources Discipline

5735 Kearny Villa Road, Suite O

San Diego, CA 92123

e-mail: gs-w_nawqa_soca_chief@usgs.gov

http://ca.water.usgs.gov/sana_nawqa

National NAWQA Program:

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Discipline

12201 Sunrise Valley Drive, M.S. 413

Reston, VA 20192

http://water.usgs.gov/nawqa/

Front cover: State highway 91 runs through the city of Corona, through the gap between the Santa Ana Mountains and Chino Hills, 

and westward toward the ocean (photograph by Eagle Aerial Imaging, Costa Mesa, California). 

Back cover: Left, Prado Dam (Photograph by U.S. Army Corps of Engineers); center, monitoring-well installation in the Coastal 

Basin (photograph by Scott Hamlin, U.S. Geological Survey); right, flowers, Santa Ana River at Featherly Regional Park (photograph 

by Carmen Burton, U.S. Geological Survey).
Water Quality in the Santa Ana Basin,

California, 1999–2001

By Kenneth Belitz, Scott N. Hamlin, Carmen A. Burton, Robert Kent, 

Ronald G. Fay, and Tyler Johnson

Circular 1238

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

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

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

endorsement by the U.S. Government

U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

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

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

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

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

endorsement by the U.S. Government.

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

reproduce any copyrighted materials contained within this report.

Library of Congress Cataloging-in-Publication Data

Water quality in the Santa Ana Basin, California, 1999-2001 / by Kenneth Belitz . . . [ et al. ].

 p. cm. - - (Circular; 1238)

 Includes bibliographical references.

 ISBN 0-607-96407-3 (alk. paper)

 1. Water quality- -California- -Santa Ana River Watershed. I. Belitz, Kenneth. II.

 Geological Survey (U.S.) III. U.S. Geological Survey circular; 1238.

 TD224,C3W3683 2004

 363.739’42’09794- -dc22 2004041399
iii

Contents

National Water-Quality Assessment Program ......................................................... iv

What kind of water-quality information does the NAWQA Program provide? ............... v

Introduction to this Report .............................................................................. vi

Summary of Major Findings .............................................................................. 1

Stream and River Highlights ..................................................................... 1

Ground-Water Highlights ........................................................................... 2

Introduction to the Santa Ana Basin .................................................................. 3

The hydrologic cycle in the Santa Ana Basin is dominated by human activities ............ 3

Water quality in the Santa Ana Basin reflects the influence of urbanization ............... 4

Major Findings ............................................................................................. 5

Concentrations of nitrate and dissolved solids are elevated in surface water 

and ground water in the Santa Ana Basin ............................................. 5

Nitrate and dissolved-solids concentrations in streams are related to 

water source and location ............................................................... 6

Nitrate and dissolved-solids concentrations are higher in ground water 

recharged since the 1950s than in older ground water .............................. 8

Pesticides and volatile organic compounds are commonly present in surface 

water and ground water .................................................................. 9

Some pesticides are detected more frequently in streams, and at higher concentrations, 

during and after storms than during dry periods ....................................... 10

Volatile organic compounds in Santa Ana Basin streams can come from the air, 

treated wastewater, or ground water or can be washed in by storms ............ 12

Pesticides and volatile organic compounds are more frequently detected in 

ground water recharged since the 1950s than in older ground water ............... 14

Organochlorine and semivolatile organic compounds are detected more frequently 

in bed sediment and fish tissue at urban sites than at undeveloped sites ......... 17

Detection frequencies of organic compounds at Santa Ana River sites are different 

than detection frequencies at tributary sites .......................................... 18

Sediment cores from reservoir and retention basins provide a historical record of 

pesticides and semivolatile organic compounds ....................................... 18

Trace-element concentrations sometimes exceed aquatic-life guidelines in 

bed sediment and reservoir-sediment cores .......................................... 20

Urbanization has altered stream channels and the sources of water reaching 

stream channels; these changes have degraded aquatic ecosystems ............ 21

Today’s surface water is tomorrow’s ground water ............................................. 24

Study Unit Design ....................................................................................... 26

Stream Chemistry ................................................................................. 26

Aquatic Ecology and Sediment .................................................................. 26

Ground-Water Quality .............................................................................. 26

References Cited .......................................................................................... 28

Glossary ................................................................................................... 30

Appendix—Water Quality Data from the Santa Ana Basin in a National Context ............... 32
National Water-Quality Assessment Program

The quality of the Nation’s water resources is integrally linked to the long-term availability of 

water that is clean and safe for drinking and recreation and also suitable for industry, irrigation, 

and habitat for fish and wildlife. Recognizing the need for long-term, nationwide assessments 

of water resources, the U.S. Congress has appropriated funds since 1991 for the USGS to conduct the National Water-Quality Assessment (NAWQA) Program. Scientists in the NAWQA 

Program work with partners in government, research, and public interest groups to assess 

the spatial extent of water-quality conditions, how water quality changes with time, and how 

human activities and natural factors affect water quality. This information is useful for guiding 

water-management and protection strategies, research, and monitoring in different hydrologic 

and land-use settings across the Nation.

The Santa Ana River Basin is one of 51 water-quality assessments initiated since 1991. 

Together, the 51 major river basins and aquifer systems, referred to as “Study Units,” include 

water resources used by more than 60 percent of the population in watersheds that cover about 

half of the land areas of the conterminous United States. Timing of the assessments varies 

because of the Program’s rotational design in which one-third of all Study Units are intensively 

investigated for 3 to 4 years, with trends assessed every 10 years. As indicated on the map, the 

Santa Ana River Basin is part of the third set of intensive investigations that began in 1997.

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iv
What kind of water-quality information does the NAWQA 

Program provide?

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

water-resources needs and issues. Therefore, it is necessary to define the context within which 

NAWQA information is most useful. 

• Total resource assessment—NAWQA assessments are long-term and interdisciplinary, 

and include information on water chemistry, hydrology, land use, stream habitat, and 

aquatic life. Assessments are not limited to a specific geographic area or water-resource 

problem at a specific time. Therefore, the findings describe the general health of the total 

water resource, as well as emerging water issues, thereby helping managers and decision 

makers to set priorities.

• Source-water characterization—Assessments focus on the quality of the available, 

untreated resource and thereby complement (rather than duplicate) Federal, State, and 

local programs that monitor drinking water. Findings are compared to drinking-water 

standards and health advisories as a way to characterize the resource.

• Compounds studied—Assessments focus on chemical compounds that have well-established methods of investigation. It is not financially or technically feasible to assess all 

the contaminants in our Nation’s waters. In general, the NAWQA Program investigates 

those pesticides, nutrients, volatile organic compounds, and metals that have been or are 

currently used commonly in agricultural and urban areas across the Nation. A complete 

list of compounds studied is on the NAWQA Web site at water.usgs.gov/nawqa.

• Detection relative to risk—Compounds are measured at very low concentrations, often 

10 to 100 times lower than Federal or State standards and health advisories. Detection of 

compounds, therefore, does not necessarily translate to risks to human health or aquatic 

life. However, these analyses are useful for identifying and evaluating emerging issues, 

as well as for tracking contaminant levels over time.

• Multiple scales—Assessments are guided by a nationally consistent study design and 

uniform methods of sampling and analysis. Findings thereby pertain not only to water 

quality of a particular stream or aquifer, but also contribute to the larger picture of how 

and why water quality varies regionally and nationally. This consistent, multi-scale 

approach helps to determine if a water-quality issue is isolated or pervasive. It also 

allows direct comparisons of how human activities and natural processes affect water 

quality in the Nation’s diverse environmental settings. 

v
vi

Introduction to this Report

This report contains the major findings of a 1999–2001 assessment of water quality in the Santa 

Ana River Basin. It is one of a series of reports by the National Water-Quality Assessment 

(NAWQA) Program that present major findings in 51 major river basins and aquifer systems 

across the Nation. 

In these reports, water quality is discussed in terms of local, State, and regional issues. Conditions in a particular basin or aquifer system are compared to conditions found elsewhere and 

to selected national benchmarks, such as those for drinking-water quality and the protection of 

aquatic organisms. 

This report is intended for individuals working with water-resource issues in Federal, State, or 

local agencies, universities, public interest groups, or in the private sector. The information will 

be useful in addressing a number of current issues, such as the effects of agricultural and urban 

land use on water quality, human health, drinking water, source-water protection, hypoxia and 

excessive growth of algae and plants, pesticide registration, and monitoring and sampling strategies. This report is also for individuals who wish to know more about the quality of streams 

and ground water in areas near where they live and how that water quality compares to other 

areas across the Nation.

The water-quality conditions in the Santa Ana River Basin summarized in this report are discussed in detail in other reports that can be accessed from http://ca.water.usgs.gov/

sana_nawqa/. Detailed technical information, data and analyses, collection and analytical methodology, models, graphs, and maps that support the findings presented in this report in addition 

to other reports in this series from other basins can be accessed from the national NAWQA Web 

site (water.usgs.gov/nawqa). 

Urbanization has resulted in 

channelization of streams in 

the Santa Ana Basin. In many 

cases channels are concrete 

lined. Warm Creek, near San 

Bernardino, is an example. (photograph by Carmen Burton, U.S. 

Geological Survey)

“California’s State Water 

Resources Control Board 

(SWRCB) has worked 

with other State, local and 

Federal agencies, as well 

as with representatives of 

industry and nongovernmental agencies, to develop 

a $50 million comprehensive monitoring and assessment program for California’s groundwater basins. 

The approach, methods, 

and results from NAWQA 

studies are important elements of California’s plans 

to evaluate ground-water 

quality on a statewide basis. 

The USGS will work with 

the SWRCB to implement 

this program.”

Arthur G. Baggett, Jr., 

Chair State Water Resources 

Control Board
Summary of Major Findings

1

Stream and River Highlights

Urbanization in the Santa Ana Basin has resulted in alteration of stream channels and the sources of water reaching those 

channels. The primary source of base flow in the Santa Ana 

River, and many of its tributaries, is treated wastewater effluent. 

Secondary sources include mountain runoff, urban runoff, and 

ground-water influx. During storms, base flow is supplemented 

primarily by runoff from urban areas, and secondarily by runoff 

from undeveloped and agricultural areas. The quality of water 

in the Santa Ana River and its tributaries reflects the quantity 

and quality of the different sources of water.

• Concentrations of nitrate were high in the Santa Ana 

River and Cucamonga Creek, a tributary receiving 

treated wastewater, with values occasionally higher 

than the U.S. Environmental Protection Agency 

(USEPA) drinking-water standard (10 mg/L as nitrogen, p. 6). 

• Volatile organic compounds (VOCs) were detected in 

100 percent of 106 surface-water samples collected 

from three sites in urban areas (Warm Creek, Santa 

Ana River below Prado Dam, and Santa Ana River 

below Imperial Highway) and in 5 of 8 samples collected from a site in an undeveloped area (Santa Ana 

River near Mentone)(p. 9). Although the concentrations 

of these compounds were generally low, the concentration of chloroform, a byproduct of water disinfection, 

sometimes exceeded the aquatic life guideline (p. 10).

• Pesticides were detected in 104 of 105 surface-water 

samples collected from three sites in urban areas (p. 9). 

The concentrations of several pesticides (diuron, diazinon, 

carbaryl, chlopyrifos, lindane, malathion, and chlorothalonil) were occasionally above either nonenforceable drinking water guidelines or aquatic life criteria. In contrast to 

their detections at urban sites, pesticides were not detected 

in samples from a site in an undeveloped area. 

• Organochlorine compounds and semivolatile organic 

compounds (SVOCs) were frequently detected in bed 

sediment from streams draining urban and undeveloped 

areas. The number of compounds detected and the concentrations of those compounds were higher for urban 

sites (p. 17). 

• Trace-element concentrations in bed sediment exceeded 

guidelines for the protection of aquatic life in three 

streams draining urban areas: Chino Creek, Warm 

Creek, and the San Jacinto River. Trace elements with 

concentrations exceeding guidelines were zinc, lead, and 

arsenic (p. 20).

• Aquatic invertebrate and algal communities were more 

degraded in streams receiving treated wastewater than 

in streams receiving either urban runoff or groundwater influx. Aquatic communities were least degraded 

in streams receiving mountain runoff (p. 21).

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The Santa Ana Basin is highly urbanized, with nearly 5 million 

people living within the 2,700-square-mile watershed. About onehalf of the basin consists of steep mountains that are difficult to 

develop.
2 Water Quality in the Santa Ana Basin, California, 1999–2001

• Pesticides and volatile organic compounds (VOCs) 

were detected more frequently in younger ground water 

than in older ground water (p. 14). While the concentrations of these compounds were generally low, the 

concentrations of three VOCs (PCE, TCE, and DBCP) 

exceeded USEPA drinking-water standards in four 

irrigation wells in the Inland Basin (p. 10). 

• Pesticides and VOCs were detected more frequently 

in the aquifers of the Santa Ana Basin than in aquifers 

assessed by NAWQA nationwide (p. 15). The higher 

detection frequencies are notable because the supply 

wells in the Santa Ana Basin are relatively deep, typically drilled to depths of 200 to 1,000 feet.

• Nearly 80 percent of the public supply and irrigation 

wells sampled in the Santa Ana Basin had concentrations of radon higher than the drinking water standard of 

300 picocuries per liter proposed by the USEPA (p. 16). 

Trends in Ground-Water Quality

Major aquifer systems in the Santa Ana Basin are 

recharged by the diversion of the Santa Ana River and its tributaries to engineered recharge facilities. Water managers also 

use water imported from the Colorado River and northern California for recharge. Therefore, the quality of water in aquifers 

in the Santa Ana Basin reflects the quality of the surface water 

diverted during the past 50 years. Similarly, the future quality 

of ground water will be affected by the quality of surface water 

currently being used to recharge these aquifers (p. 24).

• Aquatic invertebrate and fish communities were more 

degraded in concrete-lined channels than in natural 

channels or channelized streams with natural bottoms. 

Aquatic communities in channelized streams with 

natural bottoms were more similar to those in natural 

channels than those in concrete channels (p, 22).

Trends in Surface-Water Quality

Pesticides and SVOCs can persist in the environment for 

long periods of time. For example, DDT and chlordane have 

not been used for 15 to 30 years, yet they are still detected 

in stream-bed sediment (p. 17). However, analyses of sediment cores obtained from the West Street Basin, located 

in the Coastal Basin, indicate that concentrations of these 

compounds are lower in younger sediment than in older sediment (p. 18). Analyses of sediment cores also indicate that the 

concentrations of lead and zinc in sediment at the West Street 

Basin have been persistently above aquatic-life guidelines, 

but are lower in more recent sediment (p. 20). The concentrations of some pesticides, SVOCs, and trace elements fluctuate 

with climate: higher during wet periods and lower during dry 

periods (p. 19, 20). 

Ground-Water Highlights

Ground-water pumping and artificial recharge have 

accelerated the movement of water through the aquifers of 

the Santa Ana Basin. To a large extent, native water in these 

aquifers has been replaced by water recharged since the early 

1950s (p. 8). The quality of younger ground water (recharged 

since the early 1950s) is generally different from the quality of 

the older, native ground water. In the Inland and San Jacinto 

Basins, younger ground water tends to be shallower than older, 

native ground water. In the Coastal Basin, younger ground 

water tends to be closer to recharge facilities along the Santa 

Ana River and Santiago Creek.

• Ground water recharged since the 1950s has higher 

concentrations of nitrate and dissolved solids than older 

ground water (p. 8). Nitrate concentrations in younger 

water from aquifers that provide drinking-water supply 

exceed the USEPA drinking-water standard of 10 mg/L 

(as nitrogen) in some areas of the Inland and San Jacinto 

Basins. Dissolved-solids concentrations in younger 

water from aquifers used for public supply frequently 

exceed the USEPA nonenforceable drinking-water 

guideline (500 mg/L) in the Coastal Basin. 

Major Influences on Streams and Rivers

• Routing and rerouting of water through the urban 

landscape affects water quality

• Channelization and concrete lining of streams 

degrades aquatic ecosystems

Major Influences on Ground Water

• Artificial recharge and ground-water pumping 

have accelerated the movement of water and dissolved consituents in aquifers.

• Historical and present-day land uses introduce 

nitrate, volatile organic compounds, pesticides, 

and other constituents into ground water. 

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Selected Indicators of Ground-Water Quality

Public Supply and Irrigation Wells

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Introduction to the Santa Ana Basin

3

The Santa Ana Basin, located in 

southern California, is characterized by 

prominent mountains that rise steeply 

from the relatively flat-lying coastal plain 

and inland valleys. The tallest peaks in 

the San Gabriel, San Bernardino, and 

San Jacinto Mountains exceed 10,000 

feet in elevation. These mountain ranges 

are drained by the Santa Ana River and 

its tributaries. The drainage area of the 

Santa Ana River is about 2,700 square 

miles, making it the largest stream system in southern California. 

The Santa Ana Basin includes 

parts of Orange, San Bernardino, 

Riverside, and Los Angeles Counties, 

and is home to nearly 5 million people 

who rely not only on water resources 

that originate within the basin but 

also on water imported from northern 

California and the Colorado River. The 

population is expected to increase to 

about 7 million people by 2025 and to 

10 million by 2050 (Santa Ana Water 

Project Authority, 2003).

Land use in the basin is about 35 

percent urban, 10 percent agricultural, 

and 55 percent undeveloped (fig. 1). 

Urban and agricultural land uses occur 

primarily in the relatively flat valleys 

and coastal plain. The mountains are 

generally steep and remain undeveloped. 

Population density for the entire study 

area is 1,500 people per square mile; 

excluding the land area that is steep, the 

population density is about 3,000 per 

square mile. The most densely populated 

part of the basin is in the city of Santa 

Ana, where the population density is as 

high as 20,000 per square mile.

The Santa Ana Basin can be 

subdivided into three primary subunits: 

the San Jacinto, the Inland, and the 

Coastal Basins (fig. 2). Within these 

subunits, water-bearing deposits lie 

within the alluvium-filled valleys and 

coastal plain, which are bounded by 

relatively impervious mountains and 

hills. Ground water pumped from the 

alluvial deposits is the primary source 

of municipal water supply. Public supply wells are typically drilled to depths 

ranging from 200 to 1,000 feet.

The hydrologic cycle 

in the Santa Ana Basin 

is dominated by 

human activities

The climate of the Santa Ana Basin 

is Mediterranean with hot, dry summers and cool, wet winters. Average 

annual precipitation ranges from 10 to 

24 inches in the coastal plain and inland 

valleys and from 24 to 48 inches in the 

San Gabriel and San Bernardino MounFigure 2. The hydrologic cycle in the Santa Ana Basin is dominated by artificial recharge, 

ground-water pumping, and discharge of treated wastewater. Water-bearing deposits, 

used for municipal supply, lie within the alluvium filled valleys and coastal plain.

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tains. As a consequence of the semiarid 

climate and the water demands of the 

urban population, the hydrologic cycle is 

dominated by human activities. Streams 

and rivers draining the San Gabriel, San 

Bernardino, and San Jacinto Mountains 

are diverted to ground-water recharge 

facilities (fig. 2). In turn, pumped ground 

water is the major source of water supply 

in the watershed, providing about twothirds of the total water demand 

(1.2 million acre-feet per year acre 

feet per year, or about 1 billion gallons 

per day). Water imported from north-

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Figure 1. The Santa Ana Basin is characterized by prominent mountains that rise steeply 

from the flat-lying coastal plain and inland valleys. Almost all of the urban and agricultural 

land uses occur on the coastal plain and inland valleys.
4 Water Quality in the Santa Ana Basin, California, 1999–2001

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ern California and the Colorado River 

accounts for about one-quarter of the 

total consumptive demand. Imported 

water is delivered directly to consumers and is also used as a supplementary 

water source at ground-water recharge 

facilities.

From a mass-balance perspective, 

water is cycled twice in the Inland and 

Coastal Basins before it is discharged 

to the ocean. In the first cycle, tributaries exiting the San Gabriel and San 

Bernardino Mountains are diverted to 

ground-water recharge facilities in the 

Inland Basin. In turn, ground water is 

extracted for use and then discharged 

as treated wastewater to the Santa Ana 

River. In the second cycle, the Santa 

Ana River enters the Coastal Basin, 

where water managers utilize almost 

all of the base flow and most of the 

stormflow to recharge the coastal aquifer 

system. Base flow consists primarily 

of treated wastewater (Mendez and 

Belitz, 2002) and stormflow includes 

runoff from urban and agricultural land. 

Artificially recharged water accounts for 

about three-quarters of the ground water 

pumped from the coastal aquifer system 

(about 300,000 acre feet per year, or 

about 270 million gallons per day). 

Urban water use exceeds agricultural water use in the Study Unit

(75 percent as compared to 25 percent). 

After delivery to consumers, the water is 

typically used for landscape irrigation and 

for indoor purposes. Water used for landscape irrigation can be used by plants, run 

off into storm drains and then streams, or 

recharge ground-water aquifers. Water 

used indoors is routed to wastewatertreatment facilities and then discharged, 

primarily to surface-water bodies: in the 

San Jacinto Basin, to constructed ponds; 

in the Inland Basin, to the Santa Ana 

River, its tributaries, and ponds; and in 

the Coastal Basin, to the ocean. In the 

Coastal Basin, reclaimed wastewater is 

also injected into aquifers along the coast 

as a barrier to seawater intrusion.

During the period of this study 

(October 1998 to September 2001), precipitation was less than the 30-year average. Streamflow in Warm Creek, a small 

urban watershed in the Inland Basin, 

was generally near historical lows during 

base-flow conditions; high flows occurred 

only during storms (fig. 3). In contrast, 

streamflow in the Santa Ana River was 

higher than the 30-year average (fig. 4). 

The high streamflow resulted from discharges of treated wastewater to the Santa 

Ana River (Burton and others, 1998). 

During the past 30 years, increasing 

urbanization has led to a steady increase 

in the volume of these discharges.

Water quality in the 

Santa Ana Basin 

reflects the influence 

of urbanization

The best quality water in the Santa 

Ana watershed occurs in streams flowing from surrounding mountains and in 

ground water recharged by those streams. 

As the water flows away from the mountains, either in the surface or subsurface, 

its quality is affected by mineral dissolution, urban runoff, discharge of treated 

wastewater, dairy operations in the Chino 

Dairy preserve (fig. 1), landscape irrigation, and the use of high-salinity imported 

surface water. Water quality can also be 

affected by the legacy of previous activities including spills and leaks of industrial 

solvents, and by agricultural production. 

The purpose of the NAWQA study 

in the Santa Ana Basin was to assess 

water quality in streams and aquifers. 

In this report, particular emphasis is 

placed on understanding the influence of 

urbanization on water quality. The Santa 

Ana Basin is the most densely populated of the NAWQA study areas and is 

among the more arid. The large population places a high demand on the limited 

water resources. Therefore, the Santa Ana 

Basin provides an ideal opportunity for 

assessing the effects of human activities 

on water quality.

Figure 3. Base flow 

in Warm Creek was 

near historical lows 

during the period of 

study (October 1998 

to September 2001) 

due to below-average 

precipitation.

Figure 4. The base 

flow of the Santa Ana 

River was high during 

the period of study 

(October 1998 to September 2001) due to 

the steady increase in 

the volume of treated 

wastewater discharged to the river.
Concentrations of nitrate 

and dissolved solids are 

elevated in surface water 

and ground water in the 

Santa Ana Basin

Concentrations of nitrate above 

10 milligrams per liter (mg/L), the 

USEPA drinking-water standard, can 

adversely affect human health, particularly the health of infants. In the Santa 

Ana River and some of its tributaries 

(for example Cucamonga Creek and San 

Timoteo Creek), the concentrations of 

nitrate can exceed the USEPA drinking-water standard. In some areas of 

the Inland and San Jacinto Basins, the 

concentrations of nitrate in ground-water 

can also exceed the drinking-water standard. For example, water from agricultural wells located in the Chino Dairy 

Preserve (fig. 1) have nitrate concentrations generally above 25 mg/L (Wildermuth Environmental Inc., 2002).

Concentrations of dissolved 

solids above 500 mg/L are of secondary concern, affecting mainly the odor, 

taste, or color of water. In the Santa Ana 

River and some tributaries (for example, 

Warm Creek and Little Chino Creek), 

the concentrations can exceed 500 mg/L. 

In ground water, concentrations are 

generally below 500 mg/L but are higher 

in some areas. For example, dissolvedsolids concentrations in ground water 

from the Chino Dairy Preserve (Wildermuth Environmental Inc., 2000; 2002) 

and from many areas of the San Jacinto 

Basin (Kaehler and Belitz, 2003) are 

generally above 1,000 mg/L. 

Major Findings

The USGS has been monitoring 

the Santa Ana River for more 

than 100 years. Here, at the 

MWD Crossing site, discharge 

has been monitored since 

1969. The NAWQA Program 

has been monitoring the Santa 

Ana River since 1998. (photograph by Carmen Burton, U.S. 

Geological Survey)

The USGS NAWQA Program works with local 

water districts and municipalities to sample 

ground-water supply wells. (photograph by 

Barbara Dawson, U.S. Geological Survey)

Water samples must be handled carefully to ensure the accuracy of laboratory 

analyses. (photograph by Carmen Burton, 

U.S. Geological Survey)

5

These findings are supported by 

the Study-Unit Design described 

on pages 26–27.
6 Water Quality in the Santa Ana Basin, California, 1999–2001

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Figure 5. Nitrate concentrations in streams receiving treated wastewater are higher than 

streams that do not have wastewater inflows. (SAR = Santa Ana River)

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Figure 6. Concentrations of dissolved solids 

were relatively high in the Santa Ana River 

and valley floor tributaries (Warm Creek 

and Cucamonga Creek), and relatively low 

in mountain streams and in storm runoff. 

Concentrations of dissolved solids in storm 

runoff were calculated from records of 

continuously monitored discharge and 

conductivity (Kent and Belitz, 2004)

Nitrate and dissolved 

solids concentrations in 

streams are related to 

water source and location

Concentrations of nitrate and dissolved solids in streams in the Santa Ana 

Basin are controlled to a large extent 

by the sources of water reaching the 

streams. During base-flow conditions, 

these sources include treated wastewater, mountain runoff, urban runoff, and 

ground-water influx. During stormflow 

conditions, stream discharge includes 

additional runoff from mountain and 

urban areas. Treated wastewater and 

urban runoff represent the indoor and outdoor use of water delivered to consumers. Delivered water consists of pumped 

ground water and imported water. The 

sources of mountain runoff and storm 

runoff are precipitation. The sources 

of ground-water influx to streams vary, 

reflecting the complexities of the hydrologic cycle in the Santa Ana Basin.

The highest concentrations of 

nitrate were in streams receiving treated 

wastewater. For example, nitrate concentrations in Cucamonga Creek and 

the Santa Ana River (sites at MWD 

Crossing, below Prado Dam, and below 

Imperial Highway) typically ranged from 

4 to 8 mg/L (fig. 5). In contrast, nitrate 

concentrations in mountain streams and 

in Warm Creek, which receives urban 

runoff and ground-water influx, were 

usually less than 1 mg/L (fig. 5). Nitrate 

concentrations in samples consisting 

predominantly of storm runoff typically 

ranged from 1 to 3 mg/L.

The highest dissolved-solids 

concentrations were in the Santa Ana 

River and valley-floor tributaries 

during base-flow conditions (fig. 6). 

Concentrations typically ranged from 

400 to 600 mg/L. The lowest dissolved-solids concentrations were in 

mountain streams and storm runoff, 

with values typically ranging from 

100 to 300 mg/L.

The concentrations of dissolved 

solids in streams receiving treated 

wastewater were comparable to dissolved-solids concentrations in Warm 

Creek, which receives urban runoff 

and ground-water influx. This indicates that the indoor use of delivered 

water and subsequent treatment of that 

water do not substantially increase dissolved-solids concentrations. 

Concentrations of fluoride, a minor 

component of dissolved solids, were 

above the USEPA drinking-water standard (4 mg/L) in four of eight samples 

collected from East Twin Creek, a small 

stream located in the San Bernardino 

Mountains. Over a long period of time, 

drinking water with elevated concentrations of fluoride can lead to bone disease 

in some people. The high concentrations 

likely result from geothermal water 

discharging to East Twin Creek.

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Collecting water samples on the Santa Ana 

River near Imperial Highway, just upstream 

from facilities used to recharge aquifers in 

the coastal plain. (photograph by Carmen 

Burton, U.S. Geological Survey)
Major Findings 7

The Santa Ana Basin is one of 

the few urban areas in the country 

sampled by NAWQA (60 urban 

sites) where total nitrogen concentrations in streams commonly 

exceed 3 mg/L. In most streams 

sampled by NAWQA (a total of 479 

sites), elevated nitrogen concentrations come from applications of 

fertilizer and manure in agricultural 

areas (Fuhrer and others, 1999). In 

contrast, elevated concentrations in 

the Santa Ana Basin come primarily from wastewater-treatment-plant 

effluent. In the Santa Ana Basin, 

all base-flow samples (about 120) 

collected at four sites downstream 

from wastewater-treatment plants 

had total nitrogen concentrations 

above 3 mg/L, placing these sites 

in the upper 10 percent of urban 

sites sampled by NAWQA. In contrast, base-flow samples collected 

upstream from the wastewater-treatment plants in the Santa Ana Basin 

had total nitrogen concentrations 

below 2 mg/L. The predominant 

form of nitrogen in streams in the 

Santa Ana Basin is nitrate because 

modern wastewater-treatment plants 

convert ammonia to nitrate to protect 

aquatic life from the toxic effects of 

un-ionized ammonia.

National Perspective—The primary source of elevated nitrogen concentrations in surface water in the Santa Ana Basin 

differs from most areas sampled by NAWQA in the Nation

In the urbanized Santa Ana Basin, the median concentration of nitrogen in streams is about 6 milligrams per liter, 

and results from discharge of treated wastewater effluent. Nitrate is the predominant form of nitrogen in the 

Santa Ana Basin.

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8 Water Quality in the Santa Ana Basin, California, 1999–2001

including the importation of high-salinity water from the Colorado River. The 

Colorado River has been an important 

source of engineered recharge in the 

Coastal Basin since the 1950s.

In the San Jacinto Basin, the difference in the concentrations of dissolved 

solids between younger and older 

ground water is not as apparent as that 

observed in the two other ground-water 

basins. This difference is due to several 

factors including less human activity, higher concentrations of dissolved 

solids in the native ground water, and 

greater variability in concentrations in 

the native ground water. In many parts 

of the San Jacinto Basin, the native 

ground water has dissolved-solids 

concentrations exceeding 1,000 mg/L 

(Burton and others, 1996; Kaehler and 

others, 1998; Kaehler and Belitz, 2003); 

there are relatively few water-supply 

wells in these areas. 

Additional Information

Additional information and data 

on nitrate, dissolved solids, and 

sampling protocols in the Santa 

Ana Basin are provided by Kent 

and Belitz (2004) and Hamlin and 

others (2002). Additional data are 

also available at http://water.usgs.

gov/pubs/wri/wri02-4243/text.html

Figure 7. Concentrations of nitrate are higher in ground water 

recharged during the past 50 years (younger ground water) than 

in older ground water in many areas of the Santa Ana Basin.

Figure 8. Concentrations of dissolved solids are higher in 

younger ground water than older ground water in the Inland

and Coastal Basins.

Nitrate and dissolvedsolids concentrations 

are higher in ground 

water recharged since 

the 1950s than in older 

ground water

In the Santa Ana Basin, ground 

water recharged since the early 1950s 

typically has higher concentrations of 

nitrate and dissolved solids than ground 

water recharged before the early 1950s. 

The water quality of younger ground 

water has generally been affected by 

activities such as agriculture, landscape 

irrigation, and wastewater generation 

and disposal. These activities typically 

increase the concentrations of nitrate 

and dissolved solids. As aquifers are 

recharged with water associated with 

these activities, the concentrations of 

nitrate and dissolved solids increase in 

ground water. 

In the Santa Ana Basin, the concentration of nitrate in younger ground water 

typically ranges from 2 to 10 mg/L 

(fig. 7). In general, nitrate concentrations greater than 2 mg/L in ground 

water are indicative of contamination by 

human activities (Mueller and Helsel, 

1996). In the San Jacinto and Coastal 

Basins, concentrations of nitrate in older 

ground water typically range from less 

than 0.05 mg/L to about 3 mg/L, with 

most less than 0.1 mg/L (fig. 7). In the 

Inland Basin, only three wells tap older 

ground water; the nitrate concentrations 

range from 0.8 to 8 mg/L. 

Of the 52 public supply and irrigation wells sampled in the San Jacinto 

and Inland Basins, 6 public supply wells 

and 3 irrigation wells produced water 

with nitrate concentrations that exceeded 

the USEPA drinking-water standard 

(10 mg/L as nitrogen). Ground water 

from eight of those nine wells is young. 

Water from the public supply wells with 

high nitrate concentrations is blended 

with other water sources with lower 

nitrate concentrations to comply with 

drinking-water standards. 

Concentrations of dissolved solids 

are generally higher in ground water 

recharged since the early 1950s than in 

older ground water in the Coastal and 

Inland Basins (fig. 8). In the Coastal 

Basin, the median concentration of 

dissolved solids in younger ground 

water exceeded 500 mg/L (the USEPA 

nonenforceable drinking-water guideline). In contrast, the median concentration in older ground water was less 

than 300 mg/L. In the Inland Basin, the 

concentrations of dissolved solids in 

younger ground water ranged from 200 

to 800 mg/L, whereas the samples of 

older water had concentrations less than 

300 mg/L. The higher concentrations 

in younger ground water in both basins 

are primarily due to human activity, 

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Major Findings 9

Figure 9. Pesticides and volatile organic 

compounds (VOCs ) were detected frequently in urbanized streams (Warm Creek, 

Santa Ana River below Prado Dam, and 

Santa Ana River below Imperial Highway) 

and in ground water (72 wells in the San 

Jacinto, Inland, and Coastal Basins).

Tritium analyses are used to 

assess whether ground water has 

been recharged since the early 

1950s

Tritium, a radioactive isotope 

of hydrogen that is incorporated into 

molecules of water, is generated by 

natural and human activities. The 

primary natural source is the interaction of cosmic rays with water in 

the Earth’s atmosphere (Thatcher, 

1962). The primary human source 

was the testing of nuclear weapons 

in the atmosphere from 1952 until 

1963; atmospheric testing elevated 

the concentration of tritium by 

several orders of magnitude in the 

Northern Hemisphere. Since the ban 

on atmospheric testing in 1963, the 

amount of tritium in the atmosphere 

and in rainfall has been decreasing 

due to radioactive decay. Presently 

(2003), the amount of tritium in the 

atmosphere is approaching natural 

concentrations, and as a consequence, concentrations of tritium in 

precipitation and modern recharge 

are also approaching background 

levels. Concentrations of tritium 

above background levels generally indicate the presence of water 

recharged since the early 1950s. 

NAWQA studies routinely include 

the analysis of tritium concentrations 

in ground water. These analyses provide a basis for identifying the presence of “young” (recharged since 

the early 1950s) water in aquifers.

Pesticides and volatile 

organic compounds 

are commonly present 

in surface water and 

ground water

Pesticides—including herbicides, 

insecticides, and fungicides—are synthetic organic compounds used throughout the Nation to control weeds, insects, 

fungi, and other pests. Volatile organic 

compounds (VOCs) — present in paints, 

solvents, fuels, fuel additives, refrigerants, 

fumigants, and disinfected water – tend 

to evaporate under normal environmental 

conditions. Both classes of compounds 

were frequently detected in surface and 

ground water in the Santa Ana Basin 

(fig. 9). VOCs were detected in 100 

percent of 106 samples collected at three 

stream sites located in urban areas: Warm 

Creek, Santa Ana River below Prado 

Dam, and Santa Ana River below Imperial Highway. Pesticides were detected 

in 104 of the 105 samples. In contrast, 

VOCs were detected in 5 of 8 samples 

collected at a stream site draining an 

undeveloped area (Santa Ana River near 

Mentone); pesticides were not detected 

there (fig. 9). 

Pesticides and VOCs were detected 

less frequently in ground water than in 

urban streams (fig. 9). However, at least 

one pesticide or one VOC was detected 

in about 85 percent of the wells sampled 

in the San Jacinto, Inland, and Coastal 

Basins. VOCs were detected more frequently (80 percent) than pesticides 

(60 percent). Fewer pesticides were 

detected than VOCs because many pesticides do not have the chemical stability 

or mobility that allows them to move and 

persist in the ground-water flow system 

long enough to reach a well. Of the 72 

wells sampled as part of the aquifer system 

studies, 57 were used for public supply.

A large number of different pesticides and VOCs were detected in surface 

and ground-water samples from the Santa 

Ana Basin. Of the 103 pesticides and pesticide degradates routinely analyzed for in 

both surface water and ground water, 58 

were detected. Of the 85 VOCs routinely 

analyzed for, 49 were detected.

Pesticide concentrations are 

generally low

All detections of pesticides were at 

concentrations less than USEPA drinking-water standards (enforceable) and 

almost all were less than USEPA drinking-water guidelines (nonenforceable). 

Diuron, a herbicide, and diazinon, an 

insecticide, were detected at concentrations above their USEPA health advisory 

limits (10 and 0.6 μg/L [micrograms per 

liter], respectively) in a few samples. 

These exceedances occurred at four 

streams; water from these streams is not 

directly used for drinking-water supply.

Six pesticides were detected at 

concentrations above aquatic life criteria. 

Four of these (carbaryl, chlorpyrifos, 

malathion, and chlorathalonil) were only 

in exceedance in stormflow samples 

collected at three stream sites located 

in urban areas, suggesting that aquatic 

organisms are not chronically exposed 

at concentrations of concern at these 

locations. Two compounds (diazinon and 

lindane) were detected at concentrations 

above aquatic life criteria in base-flow 

samples from eight stream sites located 

in urban areas, suggesting that aquatic 

organisms may be chronically exposed 

at concentrations of concern at these 

locations. Diazinon was also detected 

in storm samples above aquatic life 

criteria at three stream sites located in 

urban areas. At one site (Santa Ana River 

below Imperial Highway), diazinon was 

detected at concentrations above these 

levels in all storm samples.

Processing of ground-water samples 

in a mobile laboratory, including 

samples for analysis of tritium. 

(photograph by Carmen Burton, U.S. 

Geological Survey)

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10 Water Quality in the Santa Ana Basin, California, 1999–2001

VOC concentrations are also

generally low

Like pesticides, most detections of 

VOCs were at low concentrations relative to drinking water standards, drinking-water guidelines, and aquatic life 

criteria. Two solvents, tetrachloroethylene 

(PCE) and trichloroethylene (TCE), and 

a soil fumigant, dibromochloropropane 

(DBCP), were detected in ground water 

at concentrations exceeding USEPA 

drinking-water standards (5 μg/L, 5 μg/L, 

and 0.2 μg/L respectively). These exceedances occurred in samples from four 

irrigation wells in the Inland Basin. Chloroform, a byproduct of the disinfection 

of water, was detected at concentrations 

higher than its aquatic life criterion (1.8 

μg/L) in 2 of 14 samples collected from 

the Santa Ana River below Prado Dam.

A comprehensive analysis of possible 

risks implied by findings in the Santa Ana 

River Basin is not possible because many 

of the compounds do not have established 

standards, guidelines, or criteria. Of the 

58 pesticides detected in water samples 

from the Santa Ana Basin, the USEPA 

has established drinking-water standards 

(enforceable) or guidelines (nonenforceable) for only 30 compounds; only 23 of 

the 58 have established aquatic life criteria. Similarly, of the 49 VOCS detected, 

the USEPA has established standards or 

guidelines for 34; only 13 of the 49 have 

established aquatic life criteria. Moreover, 

existing standards, guidelines, and criteria 

do not account for the possible synergistic effects of exposure to mixtures of 

pesticides and VOCs. A detailed listing 

of detected and nondetected compounds, 

along with selected graphical summaries, 

is provided in the Appendix. 

Some pesticides are 

detected more frequently 

in streams, and at higher 

concentrations, during 

and after storms than 

during dry periods

Pesticide concentrations in Santa 

Ana Basin streams can increase during 

storms (Izbicki and others, 2000), and 

elevated concentrations can persist for 

several days or weeks after the storm. 

The elevated concentrations of pesticides persist even though the stream 

discharge has returned to base-flow 

conditions. Because it rains more during 

the winter than during the other seasons, 

pesticides were detected more frequently 

during the winter. However, extended 

dry periods are common throughout the 

year. It is therefore more appropriate to 

characterize samples on the basis of how 

long it has been since a storm rather than 

by the season.

The influence of storms was 

evaluated by grouping samples into four 

categories: samples collected during 

and within 1 day of a storm (or peak 

flow); samples collected 1 to 7 days after; 

samples collected more than 7 and up to 

14 days after; and samples collected more 

than 14 days after. The period within 1 

day of storms can be defined as wet conditions and the period more than 14 days 

after can be defined as dry conditions.

Warm Creek is a concrete-lined 

channel that drains a small urban area. 

As a result, discharge in Warm Creek 

increases rapidly in response to storms, 

and decreases rapidly after the storms 

pass. During the period of this study 

(October 1998 to September 2001), 

few storms lasted more than a few 

hours, and the discharge at Warm Creek 

usually returned to prestorm conditions within a few hours after the rain 

stopped. In contrast, some pesticide 

compounds persisted at elevated concentrations for nearly 2 weeks after the 

rain stopped. For example, the insecticide diazinon (fig. 10A) was detected 

in more than 90 percent of samples 

collected within 1 day of storms (wet 

conditions) and in less than 40 percent 

of samples collected more than 14 days 

after storms (dry conditions); detection 

frequencies for samples collected in the 

two intermediate time categories were 

transitional between wet and dry conditions. The herbicide simazine 

(fig. 10B) behaved similarly. The systematic decrease in detection frequency 

suggests that these pesticides are 

washed off the landscape by storms and 

that concentrations in the stream can 

persist for weeks afterward.

The Santa Ana River drains a large 

watershed with mixed land use. Many 

pesticides were detected in the Santa Ana 

River below Imperial Highway during 

both base-flow and storm conditions. For 

example, diazinon and simazine were 

detected in all samples collected at this 

site (figs. 10A,B). However, the concentration of these compounds is higher 

during wet conditions than during dry 

conditions (figs. 11A,B). 

The discharge of the Santa Ana River 

increases after storms. Photograph 

taken below Prado Dam. (photograph by 

Michael Wright, California State 

University Sacramento Foundation)
Major Findings 11

Analyses of water samples, collected before and after drinking-water treatment at 

Canyon Lake in Elsinore Valley, show that the treatment process reduces the concentrations of many pesticides below laboratory detection levels.

ing three compounds—prometon, 

simazine, and atrazine (all herbicides)—were detected just as 

frequently in the treated water as in 

the untreated water.

Of the 20 compounds detected 

in the reservoir water samples, 

drinking-water standards (enforceable) or guidelines (nonenforceable) 

have been established for only 12. 

Concentrations of these 12 compounds were less than the applicable 

standards or guidelines. Concentrations of the other 8 compounds were 

similar to the concentrations of the 

12 with standards or guidelines. 

Figure 11. Diazinon (A) and simazine (B) 

concentrations, decrease with time after 

storms in the Santa Ana River below Imperial Highway. 

Drinking-water treatment can 

reduce concentrations of many 

pesticides

In 1999, NAWQA and the 

USEPA initiated a 2-year pilot monitoring program to assess human exposure to pesticides in drinking water 

derived from surface-water reservoirs 

(Blomquist and others, 2001). Reservoirs were sampled because they are 

important sources of drinking water 

and because they integrate pesticide 

loadings within their watersheds. 

Canyon Lake in Elsinore Valley, 

Calif., was 1 of 12 reservoirs sampled 

in the national assessment. From July 

to December 1999, water samples 

were collected from a drinking-water 

treatment facility both before (8 samples) and after treatment (8 samples). 

The water samples were analyzed for 

186 pesticides and pesticide degradation products: 20 were detected 

(see figure). All 20 compounds were 

detected in untreated water, whereas 

only 8 were detected in treated water. 

Five of the eight were detected less 

frequently in the treated water than 

in the untreated water. The remainFigure 10. At Warm Creek, diazinon (A) and 

simazine (B) are washed into the stream by 

storms, and detections can persist for days 

or weeks after storms.

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12 Water Quality in the Santa Ana Basin, California, 1999–2001

Figure 12. The atmosphere is the 

primary source of MTBE detected in 

surface water at Warm Creek and the 

Santa Ana River below Imperial Highway. (A) MTBE is detected frequently 

in surface water and the atmosphere 

at both sites. (B) Concentrations of 

MTBE measured in water are less than 

or equal to concentrations predicted 

by equilibrium with the atmosphere; 

predicted values in water are based 

on concentrations of MTBE measured 

in air samples collected at the same 

time as stream samples. (C) MTBE is 

detected less frequently during storms 

than during other time periods.

Volatile organic compounds in Santa Ana 

Basin streams can come 

from the air, treated 

wastewater, or ground 

water or can be washed 

in by storms

Volatile organic compounds (VOCs) 

can enter streams in a variety of ways. 

MTBE (Methyl tert-butyl ether), chloroform, and TCE (trichloroethylene) 

were among the most frequently detected 

VOCs in surface water in the Santa Ana 

Basin, but each comes primarily from 

a different source. MTBE and other 

gasoline components are present in 

the atmosphere in the Santa Ana Basin 

and can enter streams due to exchange 

between air and water. Chloroform and 

other byproducts of the disinfection of 

water are present in streams receiving 

treated wastewater and in streams receiving runoff of chlorinated tapwater used 

outdoors. TCE and other solvents are 

present in ground water in many parts 

of the Santa Ana Basin due to improper 

disposal or to inadvertent leaks and spills 

and can enter streams through groundwater influx. To a large extent, the 

frequency of occurrence and concentrations of MTBE, chloroform, and TCE in 

the Santa Ana River and in Warm Creek 

reflect the sources of these compounds.

MTBE was detected frequently in 

surface-water samples collected from 

Warm Creek (94 percent of 49 samples, 

fig. 12A) and from the Santa Ana River 

below Imperial Highway (93 percent 

of 43 samples, fig. 12A), and in all air 

samples collected at both sites (9 samples at each site, fig. 12A). At both sites, 

the concentrations in surface water were 

generally less than or equal to the concentrations predicted for a water sample 

in equilibrium with the atmosphere 

(fig. 12B), indicating the likely transfer 

of MTBE from the atmosphere to the 

streams. In addition, the concentrations 

(fig. 12B) and detection frequencies 

(fig. 12C) of MTBE in water samples 

from Warm Creek were similar to those 

from the Imperial Highway site, providing additional evidence that the atmosphere is the likely source of MTBE in 

surface water at the two sites. 

Chloroform primarily enters the 

Santa Ana River and some tributaries 

with discharges of treated wastewater. 

At the Santa Ana River below Imperial 

Highway, streamflow consists primarily of treated wastewater (Mendez and 

Belitz, 2002), and chloroform was 

detected in all samples collected there 

(fig. 13A). The concentrations of 

chloroform in samples collected from the 

Imperial Highway site were higher than 

concentrations predicted by equilibrium 

with the atmosphere. (fig. 13B), indicating the likely transfer of chloroform from 

the water to the air. 

At the Warm Creek site, streamflow does not contain treated wastewater, and chloroform was detected 

less frequently than at the Imperial 

Highway site (fig. 13A). Chloroform 

in Warm Creek was detected more 

frequently in samples collected during 

and shortly after storms than during 

dry conditions (more than 14 days after 

storms, fig. 13C), suggesting that chloroform is associated with storm runoff 

from this urbanized basin. Although 

chloroform was detected in all nine air 

samples collected at Warm Creek 

 (fig. 13B), it was detected in water in 

only two of the water samples collected 

at the same time. 

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Discharge of treated municipal wastewater is the single largest source of base flow 

to the Santa Ana River. Photograph looking 

down toward the point of discharge from 

a large treatment facility. (photograph by 

Carmen Burton, U.S. Geological Survey)
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Major Findings 13

Large TCE plumes are present in 

ground water in many areas of the Santa 

Ana basin, including areas near Warm 

Creek (Hamlin and others, 2002). At 

Warm Creek, ground-water influx is a 

major source of base flow, and TCE was 

present in all samples collected more 

than 1 day after storms (fig. 14C). In 

contrast, detection frequency was only 

63 percent during storms (fig. 14C), 

suggesting dilution of concentrations 

in ground-water influx by storm runoff. 

The concentrations of TCE in samples 

collected from Warm Creek were higher 

than concentrations predicted by equilibrium with the atmosphere (fig. 14B), 

indicating that the atmosphere is not a 

likely source of TCE at Warm Creek.

At the Imperial Highway site, 

ground water is not a major source of 

base flow, and TCE is detected less frequently than at Warm Creek (fig. 14A). 

In fact, TCE was never detected during 

dry conditions (>14 days) at Imperial 

Highway (fig. 14C), suggesting that 

TCE in the Santa Ana River may come 

from storm runoff. Although TCE was 

detected in all nine air samples collected at Imperial Highway (fig. 14B), 

it was detected in only one of the water 

samples collected at the same time. 

Figure 13. Treated wastewater is the 

primary source of chloroform in the 

Santa Ana River. Urban runoff can 

also contribute chloroform to streams. 

(A) Chloroform was detected in surface water more frequently in water 

samples from the Santa Ana River 

below Imperial Highway than from 

Warm Creek. (B) Chloroform was 

detected in water samples from the 

Imperial Highway and Warm Creek 

sites at concentrations higher than 

would be expected if the atmosphere 

were the source of chloroform. (C) 

Chloroform was detected more 

frequently in Warm Creek during wet 

conditions than during dry conditions.

Figure 14. Ground water is the 

primary source of TCE in streams 

during base-flow conditions. (A) 

TCE is detected frequently in water 

samples from Warm Creek, but not 

in water samples from Santa Ana 

River below Imperial Highway. (B) 

TCE was detected in water samples 

from Warm Creek at concentrations 

higher than would be expected if the 

atmosphere were the source of TCE. 

(C) At Warm Creek TCE is detected 

less frequently during wet periods 

because of dilution from storm runoff.

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Low-volume air samplers are used to monitor VOCs in the atmosphere. (photograph 

by Greg Mendez, U.S. Geological Survey)
14 Water Quality in the Santa Ana Basin, California, 1999–2001

Figure 15. Pesticides (A) and VOCs (B) are 

detected more frequently in ground water 

recharged during the past 50 years than in 

older ground water.

Pesticides and volatile 

organic compounds 

are more frequently 

detected in ground 

water recharged since 

the 1950s than in older 

ground water

In the Santa Ana Basin, pesticides 

and VOCs are detected more frequently 

in ground water recharged during the 

past 50 years than in older ground water 

(fig. 15). In the San Jacinto Basin, pesticides and VOCs were detected in more 

than 70 percent of the younger samples 

but were detected in only 20 percent of 

the older samples. In the Inland Basin, 

these compounds were detected in more 

than 80 percent of the younger samples 

and in only one of the three older 

samples. In the Coastal Basin, pesticides 

were detected in almost 40 percent of 

the younger samples but in none of the 

older samples; VOCs were detected in 

more than 90 percent of the younger 

samples but in only 50 percent of the 

older samples. 

The age of ground water reflects 

proximity to sources of recharge. In the 

San Jacinto and Inland Basins, shallower ground water is younger than 

deeper ground water, indicating the 

predominance of recharge from the 

overlying land surface rather than by 

lateral flow from more distant areas. 

In the Coastal Basin, ground water in 

the unconfined area, located closer to 

the Santa Ana Mountains, is younger 

than ground water in the confined area, 

located farther from the mountains. The 

age distribution is consistent with the 

dynamics of the flow system: recharge 

in the unconfined area and lateral flow 

toward the confined areas. The detection frequencies of pesticides and VOCs 

reflect these age distributions.

In the San Jacinto Basin, pesticides and VOCs were detected more 

frequently in water from shallower 

wells than in water from deeper wells 

(fig. 16A). In this basin, wells are 

typically drilled to depths ranging from 

about 300 to more than 1,500 feet. The 

top one-third of a typical well is solid 

casing, and the bottom two-thirds is usually screened (open to the aquifer). Pesticides and VOCs were detected more 

frequently in wells in which the top of 

the well screen is within 250 feet of land 

surface than in deeper wells (fig. 16A). 

The differences in detection frequency 

based on depth are comparable to the 

differences based on age.

In the Inland Basin, as in the San 

Jacinto Basin, pesticides and VOCs 

were detected more frequently in the 

shallower wells (fig. 16B). These compounds were detected in all wells 

(100 percent) in which the top of the 

screen is within 150 feet of land surface, 

but in less than two-thirds of the wells 

in which the top of the screen is more 

than 350 feet deep. As in the San Jacinto 

Basin, the differences in detection 

frequency are consistent with recharge 

from the overlying land surface. The 

detection frequencies for pesticides and 

VOCs were higher in the Inland Basin 

than in the San Jacinto Basin and reflect 

more intensive land use, more pumping of ground water, and higher rates of 

recharge in the Inland Basin. In addition, 

the Inland Basin has been developed for 

a longer period of time.

Figure 16. Detection frequency for pesticides and volatile organic compounds is 

related to proximity to recharge sources. 

(A) Shallow and deep ground water in 

the San Jacinto Basin; recharge is from 

the overlying land surface. (B) Shallow, 

intermediate-depth, and deep ground 

water in the Inland Basin; recharge is from 

the overlying land surface. (C) Unconfined 

and confined areas of the Coastal Basin; 

recharge is in the unconfined area.

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Major Findings 15

In the Coastal Basin, pesticides and 

VOCs were detected more frequently 

in ground water in the unconfined area 

than in the confined area (fig. 16C). 

The differences in detection frequencies based on location are similar to the 

differences based on age, and reflect the 

fact that ground water is recharged in the 

unconfined area and moves laterally into 

the confined area. 

Herbicides and VOCs were 

detected in aquifers of the Santa 

Ana Basin more frequently than in 

other aquifers sampled by NAWQA 

across the Nation (84 aquifer studies). The higher detection frequencies 

are notable because the supply wells 

in the Santa Ana Basin are relatively 

deep, typically drilled to depths of 

200 to 1,000 feet. Detection frequencies of herbicides in the San Jacinto 

and Inland Basins ranked in the upper 

10 percent of all aquifers sampled by 

NAWQA from 1991 to 2001. Detections of 55 selected VOCs (at concentrations above 0.2 μg/L) in the Inland 

ground-water basin ranked in the upper 

5 percent of all aquifers sampled, 

and detections in the San Jacinto and 

Coastal Basins ranked in the upper 

20 percent. All of the aquifers sampled 

in the Santa Ana Basin are used for 

public supply. The high detection 

frequencies of herbicides and VOCs in 

aquifers of the Santa Ana Basin reflect 

the intensive land use and management of ground water. Engineered 

recharge, ground-water pumping, and 

incidental recharge from landscape and 

agricultural irrigation act to accelerate 

the movement of water through the 

aquifer system and to widely distribute 

anthropogenic compounds.

National Perspective—Herbicides and volatile 

organic compounds occur more frequently in the 

deep aquifers of the Santa Ana Basin than in other 

aquifers sampled by NAWQA nationwide

SAN

JACINTO

BASIN

NAWQA

NATIONWIDE

AVERAGE

INLAND

BASIN

COASTAL

BASIN

SAN

JACINTO

BASIN

NAWQA

NATIONWIDE

AVERAGE

INLAND

BASIN

COASTAL

BASIN

0

10

20

30

40

50

60

70

80

90

100

HERBICIDES �����������������

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The USGS NAWQA Program sampled public supply and irrigation wells in the Santa Ana 

Basin. Photograph of an irrigation well in the San Jacinto Basin. (photograph by Sarah 

Kraja, California State University Sacramento Foundation) 

Additional Information

Additional information and data 

on pesticides and volatile organic 

compounds in the Santa Ana 

Basin, are provided by Hamlin 

and others (2002). Additional 

data are also available at http://

water.usgs.gov/pubs/wri/

wri02-4243/text.html
16 Water Quality in the Santa Ana Basin, California, 1999–2001

Radon is a colorless, odorless, 

radioactive gas that enters air and 

water from the decay of uranium 

that occurs naturally in rocks and 

soils. Of the estimated 160,100 lung 

cancer deaths in the United States 

in 1998, an estimated 19,000 were 

attributed to radon in air and to the 

combination of radon and smoking 

(National Research Council, 1999). 

In response, the U.S. Environmental 

Protection Agency (USEPA) has 

proposed drinking water standards to 

address radon levels in indoor air. In 

communities with programs to mitigate radon in air, the proposed drinking-water standard is 4,000 pCi/L 

(picocurie per liter). In communities 

without such programs, the proposed 

standard is 300 pCi/L. In the Santa 

Ana Basin, 50 of 63 wells sampled 

by NAWQA had concentrations of 

radon exceeding the proposed 300 

pCi/L standard (samples from 9 wells 

were not analyzed for radon); one 

well had a concentration exceeding 

the proposed 4,000-pCi/L standard. 

Nationwide, two-thirds of the wells 

sampled by NAWQA had concentrations of radon exceeding the proposed 

300 pCi/L standard. 

Arsenic is a trace element derived 

from naturally occurring minerals. 

Arsenic can occur naturally in soils 

and rocks, can be used as a component in pesticides, and has been 

detected in some fertilizers. The 

USEPA drinking-water standard for 

arsenic is 10 micrograms per liter; 

nationwide, 7 percent of the wells 

sampled by NAWQA had concentrations higher than the standard. In the 

Santa Ana Basin, 3 percent of the 

72 wells sampled had concentrations 

of arsenic exceeding the USEPA 

drinking-water standard.

USGS scientists work with 

colleagues from other 

institutions to sample fish in 

the Santa Ana River below 

Prado Dam. (photograph 

by Carmen Burton, U.S. 

Geological Survey)

 In the Santa Ana Basin, about 80 percent of the public supply wells sampled 

by NAWQA had radon concentrations 

above 300 pCi/L, a drinking-water standard proposed by the USEPA. Nationwide, about 65 percent of the wells 

sampled had concentrations exceeding 

the proposed standard. 

National Perspective—Radon and arsenic 

concentrations in ground water may be of

concern as drinking-water regulations change

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Major Findings 17

Figure 17. Organochlorine compounds and 

semivolatile organic compounds (SVOCs) 

were detected more frequently in bed sediment and fish tissue at urban sites than at 

undeveloped sites.

Figure 18. Organochlorine compounds were detected at higher concentrations at urban 

sites (8 sites) than at undeveloped sites (4 sites) in both bed sediment (A) and fish tissue 

(B). Concentrations of chlordane, p,p’-DDE, and p,p’-DDT in bed sediment occasionally 

exceeded guidelines for the protection of aquatic life (probable-effect level, Canadian 

Council of Ministers of the Environment, 1999). Concentrations in fish tissue were lower 

than guidelines developed for protection of fish-eating wildlife (Newell and others, 1987).

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Organochlorine and 

semivolatile organic 

compounds are detected 

more frequently in bed 

sediment and fish tissue 

at urban sites than at 

undeveloped sites

Organochlorine compounds have 

been used historically as insecticides on 

crops and to control termites and insectborne diseases. These compounds can 

be detrimental to the health of aquatic 

organisms. Some compounds, such as 

DDT and chlordane, are no longer used 

but continue to be present in bed sediment and fish tissue (Wong and others, 

2000). More organochlorine compounds 

were detected in bed sediment and fish 

tissue, and at higher concentrations at 

urban sites in the Santa Ana Basin 

(8 sites) than at undeveloped sites 

(4 sites)(figs. 17 and 18). 

Semivolatile organic compounds 

(SVOCs) include polycyclic aromatic 

hydrocarbons (PAHs), phenols, and 

phthalates, and have a variety of sources 

including vehicle exhaust, petroleum 

refining, forest fires, asphalt, solvents, 

and plasticizers. The number of SVOCs 

detected and the concentrations of 

SVOCs were greater at urban sites than 

at undeveloped sites. (figs. 17 and 18). 

DDT (p,p’-DDT) and one of its 

breakdown products (p,p’-DDE) and 

chlordane, a pesticide used for termite 

control, were detected in bed sediment 

at concentrations exceeding guidelines 

established to protect aquatic life (probable-effect level, Canadian Council of 

Ministers of the Environment, 1999) 

(fig. 18A). These elevated concentrations 

occurred at urban sites on the Santa Ana 

River (4 sites) but not at an undeveloped 

site on the Santa Ana River nor at any 

tributary sites (4 urban and 3 undeveloped sites). Other organochlorine compounds detected in bed sediment were 

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present at concentrations lower than the 

guidelines. SVOCs were not detected in 

bed sediment at concentrations exceeding guidelines; however, guidelines have 

been established for only 13 of the 77 

SVOCs analyzed. In addition, all detections of organochlorine compounds in 

fish tissue were at concentrations lower 

than guidelines developed for fish-eating 

wildlife (Newell and others, 1987).
18 Water Quality in the Santa Ana Basin, California, 1999–2001

Sediment cores from 

reservoir and retention 

basins provide a historical record of pesticides 

and semivolatile organic 

compounds

Cores of sediment that accumulates 

at the bottom of reservoirs and stormflow 

retention basins were collected at three 

locations in the Santa Ana Basin to assess 

historical concentrations of selected pesticides and SVOCs. West Street Basin is a 

small stormflow-retention basin located in 

an area that began urban development after 

World War II and was fully urbanized by 

the middle of the 1960s. Canyon Lake is 

located in an area that has been undergoing 

active urbanization since the 1970s. Hemet 

Lake is located in a relatively undeveloped mountain area. Chemical analyses of 

age-dated sediment cores (Van Metre and 

others, 1997) from the West Street Basin 

and Canyon Lake define historical trends 

(early 1950s to 1998) in the presence and 

concentrations of selected organic compounds, which are related to factors such as 

land use, traffic density, and chemical use.

Analyses of sediment cores indicate 

that concentrations of DDT, used to control 

mosquitoes and other insects, decreased 

significantly in Canyon Lake and West 

Street Basin after discontinuation of its use 

in 1972 (fig. 20). For example, concentrations decreased in West Street Basin 

from its peak of about 500 micrograms 

per kilogram (μg/kg) in the late 1960s to 

less than 100 μg/kg in 1975. However, 

DDT continues to be present in sediment 

deposited since 1975, indicating that the 

compound is still being transported with 

sediment. Similar results have been found 

elsewhere in the Nation (Ging and others, 

1999; Van Metre and others, 1997).

Sediment cores also show that concentrations of chlordane, used to control 

termites and other insects, decreased significantly in West Street Basin since its partial 

termination in 1978 (fig. 20). Chlordane use 

was completely terminated in the United 

States in 1988. However, chlordane concentrations at West Street Basin remain above 

100 μg/kg, which is more than 10 times 

greater than the sediment guideline for 

Figure 19. (A) More organochlorine compounds were detected in bed sediment 

and fish tissue from the Santa Ana River 

than from its tributaries. (B) In contrast, 

generally more semivolatile organic compounds were detected in samples from 

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Detection frequencies 

of organic compounds 

at Santa Ana River sites 

are different than detection frequencies at 

tributary sites

More organochlorine compounds 

were detected in bed sediment and fish 

tissue collected at urban sites on the 

Santa Ana River than at urban sites on 

tributaries. At the Santa Ana River sites, 

the number of compounds detected in 

bed sediment ranged from four to nine 

at any single site, compared to zero 

to three compounds detected at any 

single tributary site (fig. 19A). The total 

number of compounds detected in bed 

sediment at all Santa Ana River sites 

was also higher than the total number 

for tributary sites: 12 compared to 4. 

The occurrence of organochlorine compounds in fish tissue showed a similar 

pattern. The greater occurrence of 

organochlorine compounds in bed sediment and fish tissue in the Santa Ana 

River may have resulted from the persistent nature of these compounds, which 

facilitates transport to and accumulation 

in the Santa Ana River.

In contrast to organochlorine compounds, generally fewer SVOCs were 

detected in bed-sediment samples from 

urban sites on the Santa Ana River than 

from urban sites on tributaries (fig. 19B). 

Nine compounds were detected at Santa 

Ana River sites as compared to 

19 compounds at tributary sites. The 

number of compounds detected at any 

single site showed a similar pattern: 

2 to 5 at Santa Ana River sites compared 

to 1 to 19 at tributary sites. The less frequent occurrence in the Santa Ana River 

may be due to a greater distance of the 

Santa Ana River sites from sources of 

SVOCs, thus allowing more time for 

degradation to nondetectable levels. 

Santa Ana River at MWD Crossing. Pipeline conveys imported surface-water deliveries. 

(photograph by Carmen Burton, U.S. Geological Survey)
Major Findings 19

Figure 20. Chlordane and DDT are decreasing in concentration but continue to be 

detected in sediment decades after the use of these compounds was discontinued. The 

concentrations of these pesticides tend to be higher during wet periods and lower during 

dry periods (Burton, 2002). 

Figure 21. Concentrations of polycyclic aromatic hydrocarbons (PAHs) are 

decreasing at West Street Basin, located 

in a well-established urban area, but are 

increasing at Canyon Lake, in an area of 

active urban development.

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Collection of sediment cores from Hemet Lake. (photograph by Jennifer Wilson, 

U.S. Geological Survey)

protection of aquatic life (probable-effect 

level, Canadian Council of Ministers of 

the Environment, 1999). Concentrations 

are lower at Canyon Lake than at West 

Street Basin but are near the guideline. 

The concentrations of polycyclic 

aromatic hydrocarbons (PAHs) have 

decreased at West Street Basin and 

increased at Canyon Lake since the 

1950s (fig. 21). These trends correlate 

with historical land use: West Street 

Basin is in an area that has long been 

urbanized, whereas Canyon Lake is in 

an area of active urbanization. This correlation in the Santa Ana Basin suggests 

that PAHs may be decreasing with time 

in well-established urbanized areas and 

increasing with time in areas of active 

urban development. One possible explanation is that controls on industrial and 

automobile emissions have resulted in 

a decrease in PAHs in well-established 

urban areas, but these reductions at the 

source can be offset by an increased 

number of cars and increased road density in more recently urbanizing areas. 

Sediment cores also show that 

the concentrations of pesticides and 

SVOCs can fluctuate with climate 

(Burton, 2002). Some pesticides, such 

as chlordane and DDT, are present at 

higher concentrations in reservoir sediment deposited during wet periods than 

sediment deposited during dry periods 

(fig. 20). Similarly, some SVOCs 

(for example, total PAHs) also have higher 

concentrations in sediment deposited during wet periods than that deposited during 

dry periods (fig. 21). These results suggest 

that some pesticides and SVOCs accumulate and persist on the landscape during 

dry periods and are subsequently mobilized and transported to receiving waters 

during wet periods. 
20 Water Quality in the Santa Ana Basin, California, 1999–2001

Table 1. Guidelines for trace-element concentrations in sediment, established to protect 

aquatic life, were exceeded at three stream sites in the Santa Ana Basin.

Additional Information

A detailed description of trace 

elements in bed sediment and 

reservoir cores is given by 

Burton (2002). 

Figure 22. Trace-element concentrations in reservoir-sediment cores often exceeded 

guidelines established for protecting aquatic life at West Street Basin. Concentrations of 

lead and zinc in sediment core at Canyon Lake are lower than at West Street Basin.

Trace-element concentrations sometimes exceed 

aquatic-life guidelines in 

bed sediment and 

reservoir-sediment cores

In the Santa Ana Basin, trace element concentrations exceeded guidelines 

established for the protection of aquatic 

life (probable-effect levels, Canadian 

Council of Ministers of the Environment, 1999) at three sites, all of which are 

urban. At Warm Creek, the concentrations 

of two trace elements (lead and zinc) 

exceeded guidelines (table 1). At Chino 

Creek, the concentration of one trace element (zinc) exceeded a guideline (table 

1). Sediment from the San Jacinto River 

also had one trace element (arsenic) with 

a concentration higher than a guideline 

(table 1). Thirty-eight of the 46 trace elements, for which samples were analyzed, 

do not have guidelines established to 

protect aquatic life. Sediment samples 

analyzed for trace element concentrations 

by the NAWQA Program are sieved and 

are relatively fine-grained (less than 

63 micrometers); therefore, the detected 

concentrations may be higher than concentrations in a whole-sediment sample. 

Sediment cores collected from West 

Street Basin and Canyon Lake provide a 

historical record of trace-element concenTrace

element

Median

(micrograms

per gram)

Maximum

(micrograms

per gram)

Probable-effect

level (micrograms

per gram)1

Location of

exceedances 

Arsenic 4.8 45 17 San Jacinto River

Cadmium 0.35 2.8 3.5 no exceedances

Chromium 55 72 90 no exceedances

Copper 52.5 86 197 no exceedances

Lead 28.5 100 91.3 Warm Creek

Mercury 0.055 0.20 0.486 no exceedances

Selenium 0.4 2.7 4.022 no exceedances

Zinc 160 550 315 Chino Creek, Warm Creek

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trations (fig. 22). At West Street Basin, 

concentrations of lead and zinc equaled 

or exceeded guidelines throughout the 

historical record (fig. 22). The concentrations of four of the six other trace 

elements with established guidelines 

also exceeded guidelines at some point 

during the historical record; concentrations of cadmium, chromium, copper, 

and mercury exceeded guidelines at least 

once, but concentrations of arsenic and 

selenium did not (Burton, 2002). Concentrations of trace elements in the sediment 

core from Canyon Lake were generally 

lower than those in the core from West 

Street Basin, and with the exception of 

copper (fig. 22), were lower than established guidelines (Burton, 2002).

The concentrations of lead in sediment at West Street Basin decreased 

from older to younger sediment (fig. 22). 

Similar trends have been observed in 

sediment cores obtained from reservoirs in urban areas elsewhere in the 

Nation (Burton, 2002; Ging and others, 

1999; Van Metre and others, 1997). 

At West Street Basin, other trace elements, including zinc (fig. 22), show a 

decrease in concentration from 1952 to 

about 1970. The decrease in concentration during that time period may reflect 

changes in land use in the surrounding 

area (Van Metre and others, 2003).

Concentrations of some trace elements (for example, arsenic, cadmium, 

copper, and zinc) in sediment cores 

tend to be higher during wet periods 

and lower during dry periods (Burton, 

2002). One possible explanation is that 

these trace elements behave similarly to 

pesticides and many SVOCs: accumulating on the landscape during dry 

periods and washing off into receiving 

waters during wet periods. 

1Sediment-quality guideline from Canadian Interim Sediment Quality Guidelines, Freshwater (Canadian Council of Ministers of 

 the Environment, 1999). 2Toxicity threshold obtained from the National Irrigation Water Quality Program Information Report (U.S. Department of the 

Interior, 1998).
Major Findings 21

aquatic ecosystems are less degraded in 

streams receiving ground water than in 

streams receiving urban runoff. 

The drainage basins of streams 

receiving mountain runoff are less 

urbanized than those of streams receiving other sources of water (table 2). This 

partly explains why aquatic ecosystems 

were least degraded in streams receiving 

mountain runoff. However, the percentage of urbanization did not vary among 

the drainage basins of streams receiving 

water from the other sources. One can 

therefore conclude that the observed 

differences in aquatic communities are 

related more to water source than to 

percentage of urbanization.

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Figure 23. (A) Larger numbers of invertebrate taxa indicate healthier ecosystems. (B) Larger percentages of pollution-tolerant diatom species indicate 

ecosystem degradation.

Little Chino Creek is one of many tributaries that have been channelized for flood 

control. (photograph by Carmen Burton, 

U.S. Geological Survey)

Urbanization has altered 

stream channels and the 

sources of water reaching 

stream channels; these 

changes have degraded 

aquatic ecosystems

Urbanization has resulted in channelization of streams in the Santa Ana 

Basin and, in many cases, channels are 

concrete lined. The water in these channels also reflects a hydrologic system 

that is highly engineered. Streamflow 

from the mountains is typically diverted 

for ground-water recharge, and streamflow is reestablished on the valley floor 

by discharge from wastewater-treatment 

plants, urban runoff, and ground-water 

influx. The health of aquatic ecosystems 

has been affected by these changes.

Some organisms thrive in undisturbed ecosystems, whereas others 

thrive in degraded systems. The richness 

(number of species or other taxa) and 

relative abundance of the different types 

of organisms (invertebrates, algae, and 

fish) were used as a measure of ecosystem 

health. In the summer of 2000, ecological 

assessments were conducted at 19 sites 

that included a range of water sources 

and channel types. Four sources of water 

were sampled: mountain runoff, ground 

water, urban runoff, and treated wastewater. Three channel types were sampled: 

natural channels, channelized streams 

with natural bottoms, and concrete-lined 

channels. Artificial substrates were used 

to collect invertebrates and algae. 

Water source affects the health

of aquatic ecosystems

The source of water to a stream 

channel affects water chemistry and 

many of the physical characteristics 

of the aquatic ecosystem. Stream sites 

receiving treated wastewater have higher 

concentrations of dissolved solids, 

nutrients, iron, and suspended sediment 

than do other stream sites. In addition, 

streams receiving treated wastewater 

have relatively high and stable discharge 

and low variability in other physical 

characteristics, such as temperature, 

stream depth, and stream width. Aquatic 

communities at these sites are more 

degraded than in streams receiving other 

sources of water. Stream sites receiving urban runoff or ground water have 

more dissolved solids and higher water 

temperatures than do streams receiving 

mountain runoff; aquatic communities 

in these streams are degraded relative to 

streams receiving mountain runoff.

Richness (number) of invertebrate 

taxa (fig. 23A) is lowest in streams 

receiving treated wastewater and highest 

in streams receiving mountain runoff. 

The median number of taxa was 9 in 

streams receiving wastewater, 

14 in streams receiving urban runoff or 

ground-water influx, and 19 in streams 

receiving mountain runoff. Moreover, 

the abundance of pollution-tolerant diatom species (a group of alga, fig. 23B) 

is highest in streams receiving treated 

wastewater, intermediate in streams 

receiving urban runoff or ground-water 

influx, and lowest in streams receiving 

mountain runoff. 

The results of the ecosystem assessment indicate that aquatic ecosystems 

are most degraded in streams receiving 

treated wastewater and least degraded 

in streams receiving mountain runoff. 

Aquatic ecosystems in streams receiving 

urban runoff or ground water are intermediate between these two extremes; 

Water source Percentage of urbanization

Minimum Maximum Median

Mountain runoff 0 65 20

Ground water 45 95 55

Urban runoff 50 100 80

Treated wastewater 45 100 69

Table 2. Percentage 

of urbanization in 

relation to stream 

sites studied during 

the summer of 2000.
22 Water Quality in the Santa Ana Basin, California, 1999–2001

Figure 25. The percentage of native fish is 

highest in streams with natural channels 

and lowest in concrete channels.

Figure 24. The richness (A) and relative abundance (B) of different types of 

organisms indicate that concrete-lined 

channels are the most degraded. Streams 

with natural banks are the least degraded. 

Channelized streams are slightly more 

degraded than natural streams.

Table 3. Percentage of urbanization in relation to stream sites studied during the summer of 2000.���������������������������������

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Channel type Percentage of urbanization

Minimum Maximum Median

Natural channels 0 65 20

Channelized streams 

with natural bottoms 45 95 55

Concrete-lined channels 50 100 80

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NUMBER OF CADDISFLY

AND MAYFLY TAXA

0

2

4

6

8

10

RELATIVE ABUNDANCE OF

NONINSECT INVERTEBRATE

TAXA, IN PERCENT

0

20

40

60

80

100

B

A

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Cajon Creek is located in the pass between 

the San Gabriel and San Bernardino Mountains. (photograph by Carmen Burton, U.S. 

Geological Survey)

Aquatic ecosystems are more 

degraded in concrete channels than in either channelized 

streams or natural channels

Physical habitat for aquatic communities differs substantially among natural 

channels, channelized streams with natural bottoms, and concrete-lined channels. 

In the Santa Ana Basin, natural streams 

have the most bank shading, allowing the 

least penetration of sunlight and coolest 

temperatures. Concrete-lined channels 

have minimal to no bank shading and are 

generally wide and shallow, resulting in 

the most exposure to sunlight and highest water temperatures. Bank shading in 

channelized streams encompasses the 

extremes, ranging from complete canopy 

cover to minimal shading. Streambed 

substrates in natural channels and channelized streams are composed of sand, 

gravel, and (or) cobbles, along with leaf 

litter and woody debris. These substrates 

provide habitat for invertebrates and 

other aquatic life. In contrast, suitable 

habitat is minimal to absent in smooth 

concrete-lined channels. 

Aquatic communities were most 

degraded at sites located in concretelined channels and least degraded at 

sites located in natural channels. The 

median number of insect taxa sensitive 

to pollution and habitat degradation 

(caddisfly and mayfly, fig. 24A) is highest in natural channels and lowest in 

concrete-lined channels; the number in 

channelized streams (four taxa) is more 

similar to that in natural channels (five 

taxa) than in concrete-lined channels 

(two taxa). Moreover, the abundance of 

noninsect invertebrates (such as snails 

and worms) was highest in concretelined channels; the abundance in channelized streams was similar to the abundance in natural channels (fig. 24B). 

These noninsect taxa tend to thrive in 

degraded ecosystems. Similarly, the 

percentage of native fish species was 

highest in natural channels and lowest 

in concrete-lined channels (fig. 25), with 

the percentage in channelized streams 

intermediate between the two.

In this study, the health of aquatic 

ecosystems appears to be related more 

to streambed substrate materials than to 

stream-channel shape or percentage of 

urbanization. Channelized streams have 

aquatic ecosystems that are more similar 

to those in natural channels than to those 

in concrete-lined channels. Similarly, 

channelized streams have streambed 

substrate materials that are more similar 

to those in natural channels than to those 

in concrete-lined channels. In contrast, 

channelized streams are more similar 

to concrete-lined channels in terms of 

shape and percentage of urbanization 

(table 3). These results suggest that 

lining of channels with concrete has a 

greater effect on ecosystem health than 

does channelization of streams in the 

urbanized Santa Ana Basin. 
Major Findings 23

Shallow water depth and 

high nitrate concentrations in 

Cucamonga Creek support a 

highly productive ecosystem

Cucamonga Creek in Ontario, 

Calif. is a wide, concrete-lined flood 

control channel receiving effluent from a wastewater-treatment 

plant. The treated effluent has high 

concentrations of nitrate, typically 

ranging from 5 to 10 mg/L. During 

nonstorm conditions, the stream is 

shallow (typically less than 

4 inches), exposed to direct sunlight 

most of the day, and relatively 

warm. Such conditions promote the 

growth of algae, which blanket the 

channel bottom throughout the year. 

These algae assimilate nitrate as a 

consequence of their productivity. 

The productivity and assimilative 

capacity of the algae were evaluated 

during a 24-hour study conducted 

in August 2001.

Algal photosynthesis during 

the day produced concentrations 

of dissolved oxygen (DO) three 

times greater than concentrations 

predicted by equilibrium with the 

atmosphere. This magnitude of 

DO production is rare in natural 

streams. During the night, concentrations of DO in Cucamonga 

Creek were not as low as might be 

expected in a stream with abundant algal growth (Caduto, 1985) 

because the shallow stream depth 

permits replenishment of oxygen 

from the atmosphere. The high 

levels of algal productivity were 

accompanied by nitrate assimilation, which resulted in the lowering 

of stream-nitrate concentrations 

by about 1 mg/L per hour during daylight hours. The lowering 

of nitrate concentrations by algal 

assimilation is an important factor 

affecting nitrate concentrations 

in Cucamonga Creek where the 

discharge consists primarily of 

treated-wastewater effluent.

Abundant algae in Cucamonga Creek produce high levels of oxygen during the day. 

The high levels are not followed by correspondingly low concentrations at night due 

to the shallow stream depth, which facilitates replenishment of oxygen from the 

atmosphere. The algae assimilate nitrate as a consequence of their high productivity. 

(photograph by Carmen Burton, U.S. Geological Survey)

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24 Water Quality in the Santa Ana Basin, California, 1999–2001

Water managers utilize the 

flow of the Santa Ana River for 

recharging the ground-water 

basin. An inflatable rubber dam 

across the Santa Ana River 

impounds water to facilitate 

diversion into recharge ponds. 

(photograph by Carmen Burton, 

U.S. Geological Survey)

Today’s surface water is

tomorrow’s ground water

In many parts of the Nation, an 

important source of surface water is 

ground water. In the Santa Ana Basin 

and elsewhere in the Western United 

States, the converse is often true: 

surface water is the primary source of 

ground-water recharge. For example, 

in the Santa Ana Basin, ground-water 

recharge facilities are located along 

rivers and streams draining the San 

Gabriel, San Bernardino, and San 

Jacinto Mountains. In addition, largescale recharge facilities are located along 

and adjacent to the Santa Ana River in 

the Coastal Basin. Recharge facilities 

throughout the Santa Ana Basin are used 

to enhance replenishment of aquifers 

used for public supply.

At the large-scale 

recharge facilities in 

the Coastal Basin, 

water managers capture almost all of the 

base flow and most of 

the stormflow of the 

Santa Ana River. This 

engineered or artificial 

recharge, averaging 

about 225,000 acrefeet per year (about 

200 million gallons per 

day), helps balance the 

total amount of ground 

water pumped from the aquifer system 

and used for public supply. These facilities have been used since the late 1940s.

 The distribution of anthropogenic 

compounds in ground water in the 

Coastal Basin illustrates the extent to 

which native ground water has been 

replaced by artificial recharge (fig. 26). 

Tritium, an isotope of hydrogen that is 

incorporated into the water molecule, is 

an indicator of ground water recharged 

since the early 1950s (see sidebar, 

p. 9). Tritium is widespread in the 

aquifer system, indicating widespread 

replacement of older, native ground 

water with water recharged during the 

past 50 years. Chloroform, a byproduct 

of water disinfection, is also widely distributed in the aquifer system, although 

it is not as widespread as is tritium. 

MTBE, a compound added to gasoline 

to reduce air pollution, has been used 

extensively since the early 1990s (Squillace and Moran, 2000). MTBE is not as 

widespread in the aquifer system as is 

chloroform, which has been generated 

for a longer period of time. The concentrations of chloroform and MTBE are 

below USEPA drinking-water standards.

These results indicate that yesterday’s surface water is today’s ground 

water and therefore remind us of the 

importance of protecting surface-water 

quality. Protection of today’s surface 

water will ensure the future quality of 

the ground-water resource. 

Lake Elsinore in the spring. 

(photograph by Mark Dennis, 

City of Lake Elsinore)

Surface-water drain, 

Riverside, California. 

(photograph by 

Phil Contreras, 

U.S. Geological Survey)
Major Findings 25

Figure 26. The areal distribution of anthropogenic compounds in the Coastal ground-water basin illustrates the displacement of native 

ground water by artificial recharge. (LRL, laboratory reporting level)

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26 Water Quality in the Santa Ana Basin, California, 1999–2001

Study Unit Design

Stream Chemistry

In the Santa Ana Basin, stream-chemistry studies were 

designed to broadly assess water quality using a nationally 

consistent approach (Gilliom and others, 1995; Wilde and 

Radtke, 1998) and to assess the effects of urbanization. Sampling sites were established on streams that receive a variety 

of water sources, including mountain runoff, urban runoff, 

ground water, and treated wastewater. Two of the sites were 

sampled more frequently than the other sites to assess the 

influence of seasonality on water quality; samples from these 

sites were also analyzed for pesticides and volatile organic 

compounds (VOCs). Air samples were also collected and analyzed for VOCs; these data helped to identify the sources of 

VOCs in streams. In addition to the regularly scheduled sampling, a tracer test was conducted along the Santa Ana River; 

the tracer study was designed to determine how much of the 

base flow is from treated wastewater and how much is from 

other sources. Sampling for pesticides was also conducted at 

a drinking-water treatment facility as part of a national study 

conducted by NAWQA in collaboration with the U.S. Environmental Protection Agency (Blomquist and others, 2001).

Aquatic Ecology and Sediment

Surface-water studies also included characterization of 

ecological conditions and sampling of bed sediment and fish 

tissue. These studies were implemented to provide a nationally consistent assessment of conditions. In addition to these 

broad-scale assessments, an intensive study of algae and invertebrates was conducted at 19 sites to assess the effect of urbanization on ecosystem health. The sites were selected on the 

basis of channel type and water source. Two additional studies 

were also implemented. One was a study of the role of algae 

in the lowering of nitrate concentrations along a 2-mile reach 

of Cucamonga Creek. The other study, conducted as part of 

a national study (http://tx.usgs.gov/coring/), was of sediment 

cores obtained from two lakes and a storm-retention basin; 

these cores provide a historical record of the concentrations of 

organochlorine compounds, semivolatile organic compounds, 

and trace elements.

Ground-Water Quality

The quality of ground water in deep aquifers used for 

public supply in the Santa Ana Basin was assessed using nationally consistent approaches. Broad-scale assessments of major 

aquifers were conducted in the San Jacinto, Inland, and Coastal 

Basins. These assessments were supplemented by two flowpath 

studies that were designed to evaluate changes in water quality 

as water moves through the aquifer system. The flowpath studies, as well as additional sampling, were done in collaboration 

with the California State Water Resources Control Board as part 

of their California Aquifer Susceptibility program.

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Study Unit Design 27

Study 

component What data were collected and why Types and number of sites sampled Sampling frequency and period

Stream chemistry

Streams and 

rivers

Streamflow, dissolved oxygen, pH, alkalinity, 

specific conductance, temperature, nutrients, major 

ions, organic carbon, and suspended sediment; to 

determine concentration and variability of a constituent over seasons or time.

4 sites—Santa Ana River (SAR) at Mentone (reference); Cucamonga Creek (urban, 

treated wastewater); SAR at MWD Crossing and SAR below Prado Dam (mixed 

urban, predominantly treated wastewater).

Monthly plus 6 

storms, October 

1998–September 

2001.

Organic 

compounds in 

streams and 

rivers

Same as streams and rivers plus pesticides and 

volatile organic compounds (VOC); to determine the occurrence, concentration over time, 

and seasonality of organic compounds. VOCs 

collected in air.

2 sites—Warm Creek (urban, ground 

water); and SAR below Imperial Highway (mixed urban, predominantly treated 

wastewater) discontinued, April 2001. 

(Prado added July 2000, Mentone added 

February 2001)

Semimonthly to 

monthly plus 6 

storms, October 

1998–September 

2001. 

Mountain 

streams

Same as streams and rivers; to determine if SAR at 

Mentone is representative of mountain runoff.

5 sites located at the base of the mountains 

and 1 alpine site.

Quarterly, January 

2000–July 2001

Drinkingwater 

reservoirs

Pesticides; to assess pesticide occurrence from 

drinking-water reservoirs before and after treatment as part of a nationwide study.

2 sites—at a drinking-water treatment plant 

located near Canyon Reservoir, one site 

before treatment and one site after. 

16 samples, 

July–December 

1999

Tracer study Same as stream and rivers plus bromide, isotopes, 

and rhodamine dye; to assess how much of the 

base flow is from treated wastewater and how 

much is from other sources.

9 sites on the Santa Ana River from the 

Rapid Infiltration/Extraction treatment facility to the wetlands behind Prado Dam, and 7 

sites on other water sources to the river.

Hydrograph sampling in May 2001

Stream ecology, streambed sediment and fish tissue, and reservoir sediment

Ecology in 

streams and 

rivers 

Invertebrate, algal, and fish communities and 

stream habitat conditions; to assess the temporal 

variability in contrasting stream environments.

4 sites—2 collocated with the 2 mixed 

urban river sites. 1 site located upstream 

from dam construction and 1 site located in 

the mountains.

Annually, single 

reach, 1999–2000; 

3 reaches, 2001

Urban landuse study 

Same as ecology and streams and rivers, but used 

artificial substrates for algal and invertebrate communities; to assess water source and channel type 

as factors affecting biological communities.

19 sites—3 reference, 16 urban, representing 4 sources of water and 3 channel types. 

Sites were collocated with stream and river 

sites or bed-sediment sites when possible.

July—September 

2001

Cucamonga 

Creek study

Streamflow, nutrients, organic carbon, pH, temperature, dissolved oxygen, specific conductance, 

alkalinity, carbon dioxide, bicarbonate and carbonate; to assess nitrate uptake by algae.

2 sites in the concrete-lined Cucamonga Creek located below treated-wastewater outfall.25 samples in a diel 

study, August 2001

Streambed 

sediment and 

fish tissue 

Organochlorine compounds, semivolatile-organic 

compounds and trace elements in sediment and fish 

tissue to determine occurrence and distribution and 

to compare urban and undeveloped land use.

12 sediment and 10 fish tissue sites—8 

urban sites located on the basin floor and 4 

undeveloped sites. 

Once, September 

1998

Reservoirsediment 

coring sites

Same as for streambed sediment but at multiple 

depths in sediment cores to evaluate changes in 

concentration in relation to time and historical 

land- and chemical-use patterns.

3 reservoirs representing 3 types of land 

use; undeveloped, actively urbanizing, and 

a well-established urban area.

Once, November 

1998

National 

mercury study

Mercury, methylmercury, and acid-volatile sulfides 

in bed sediment and fish fillets; to evaluate factors 

for mercury occurrence and methylation potential.

4 urban and 1 undeveloped sites as part of a 

larger national mercury study.

Once, September 

1998

Ground-water quality

Major aquifer 

survey 

Major ions, nutrients, pesticides, volatile organic 

compounds, trace elements, stable isotopes, tritium, and radon analyzed to assess occurrence in 

the Coastal, Inland, and San Jacinto Basins.

Spatially distributed randomized deep 

public supply, irrigation, and domestic 

wells in the Coastal (20 wells), Inland (29 

wells), and San Jacinto (23 wells) groundwater basins.

Coastal—spring 1999 

Inland—Spring 2000 

San Jacinto —

winter 2001

Urban landuse study

Same constituents as above, to assess shallow 

ground-water quality in the Coastal Basin.

Monitoring wells installed at 30 randomly chosen sites in commercial and 

residential areas.

Summer 2000

Flow-path 

study 

Same constituents as for the major aquifer survey, 

to assess replacement of ground water by engineered recharge.

23 deep production wells. 20 deep monitoring wells and 1 production well.Summer 2000
28 Water Quality in the Santa Ana Basin, California, 1999–2001

References Cited

Blomquist, J.D., Denis, J.M., Cowles, J.L., Hetrick, J.A., 

Jones, R.D., and Birchfield, N.B., 2001, Pesticides in 

selected water-supply reservoirs and finished drinking 

water, 1999–2000. Summary of results from a pilot monitoring program: U.S. Geological Survey Open-File Report 01-

456, in cooperation with the U.S. Environmental Protection 

Agency Baltimore, Maryland, accessed March 28, 2003, at 

URL http://md.water.usgs.gov/nawqa

Burton, C.A., 2002, Effects of urbanization and long-term 

rainfall on the occurrence of organic compounds and trace 

elements in reservoir sediment cores, streambed sediment, 

and fish tissue from the Santa Ana River Basin, California, 

1998: U.S. Geological Survey Water-Resources Investigations Report 02-4175, 73 p.

Burton, C.A., Izbicki, J.A., and Paybins, K.S., 1998, Waterquality trends in the Santa Ana River at MWD Crossing 

and below Prado Dam, Riverside County, California: U.S. 

Geological Survey Water-Resources Investigations Report 

97-4173, 36 p. 

Burton, C.A., Kaehler, C.A., and Christensen, A.H., 1996, 

Well-construction, water-quality, and water-level data, and 

pond-infiltration estimates, for three ground-water subbasins, Riverside County, California: U.S. Geological Survey 

Water-Resources Investigations Report 96-4294, 114 p.

Caduto, M.J., 1985, Pond and brook—A guide to nature in 

freshwater environments: Englewood Cliffs, N.J., PrenticeHall, 276 p. 

Canadian Council of Ministers of the Environment, 1999, 

Canadian sediment quality guidelines for the protection for 

aquatic life. Summary tables, in Canadian environmental 

quality guidelines, 1999: Canadian Council of Ministers of 

the Environment, Winnipeg, publication no. 1299.

Fuher, G.J., Gilliom, R.J., Hamilton, P.A., Morace, J.L., 

Nowell, L.H., Rinella, J.F., Stoner, J.D. and Wentz, D.A., 

1999, The quality of our Nation’s waters—Nutrients and 

pesticides: U.S. Geological Survey Circular 1225, 82 p., 

accessed 03/05/2003 at URL http://water.usgs.gov/pubs/

circ/circ1225/

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.

Ging, P.B., Van Metre, P.C., and Callender, E., 1999, Bottom 

sediments of Lorence Creek Lake, San Antonio, Texas, 

reflect contaminant trends in an urbanizing watershed: U.S. 

Geological Survey Fact Sheet, FS–149–99, 4 p.

Hamlin, S.N., Belitz, K., Kraja, S., and Dawson, B.J., 2002, 

Ground-water quality in the Santa Ana watershed, California—Overview and data summary: U.S. Geological Survey 

Water-Resources Investigations Report 02-4243, 137 p.

Izbicki, J.A., Mendez, G.O., and Burton, C.A., 2000, Stormflow chemistry in the Santa Ana River below Prado Dam 

and at the diversion downstream from Imperial Highway, 

Southern California, 1995–98: U.S. Geological Survey 

Water-Resources Investigations Report 00-4127, 92 p.

Kaehler, C.A., and Belitz, K., 2003, Tracing reclaimed water 

in the Menifee, Winchester and Perris-South ground-water 

subbasins, Riverside county, California: U.S. Geological 

Survey Water-Resources Investigations Report 03-4039, 

49 p. accessed 03/05/2003 at URL http://water.usgs.gov/

pubs/wri/wri034039/

Kaehler, C.A., Burton, C.A., Rees, T.F., and Christensen, 

A.H., 1998, Geohydrology of the Winchester subbasin, Riverside County, California: U.S. Geological Survey WaterResources Investigations Report 98-4102, 90 p.

Kent, Robert, and Belitz, Kenneth, 2004, Concentrations of 

dissolved solids and nutrients in water sources and selected 

streams of the Santa Ana Basin, California, October 1998 to 

September 2001: U.S. Geological Survey Water-Resources 

Investigations Report 03-4326, 61 p.

Mendez, G.O., and Belitz, Kenneth, 2002, Identifying sources 

of base flow in the Santa Ana River, CA: American Water 

Resources Association 2002 summer specialty conference 

proceedings—Ground water/surface water interactions, 

p. 567–572. 

Mueller, D.K., and Helsel, D.R., 1996, Nutrients in the 

Nation’s waters—Too much of a good thing?: U.S. Geological Survey Circular 1136, 24 p.

National Research Council, 1999, Risk assessment of radon in 

drinking water, National Academy Press, 

269 p.: accessed June 9, 2003, at URL http://www.nap.

edu/books/0309062926/html/index.html

Newell, A.J., Johnson, D.W., and Allen, L.K., 1987, Niagara River 

biota contamination project—Fish-flesh criteria for piscivorous 

wildlife: Albany, New York State Department of Environmental 

Protection, Division of Fish and Wildlife, Bureau of 

Environmental Protection Technical Report 87-3, 182 p.

Santa Ana Watershed Project Authority, 2003, About the 

watershed; population: accessed June 9, 2003, at URL 

http://www.sawpa.org/about/watershed.htm#Population/ 
References Cited 29

Squillace, P.J., and Moran, M.J., 2000, Estimating the likelihood of MTBE occurrence in drinking water supplied by 

ground-water sources in the northeast and mid-Atlantic 

regions of the United States: U.S. Geological Survey OpenFile Report 00-343, 10 p.

Thatcher, L.L., 1962, The distribution of tritium fallout in precipitation over North America: Louvain, Belgium. International Association, Hydrological Sciences, Publication 

no. 7, p. 48–58.

U.S. Department of the Interior, 1998, Guidelines for interpretation of the biological effects of selected constituents in 

biota, water, and sediment: National Irrigation Water Quality Program Information report no. 3, 198 p. 

Van Metre, P.C., Callender, E., and Fuller, C.C., 1997, Historical trends in organochlorine compounds in river basins identified using sediment cores from reservoirs: Environmental 

Science and Technology, v. 32, no. 8, p. 2339–2344.

Van Metre, P.C., Wilson, J.T., Harwell, G.R., Gary, M.O., 

Heitmuller, F.T., and Mahler, B.J., 2003, Occurrence, 

sources, and trends in particle-associated contaminants 

in selected streams and lakes in Fort Worth, Texas: U.S. 

Geological Survey Water-Resources Investigations Report, 

03-4169.

Wilde, F.D., Radtke, D.B., eds., 1998, Techniques of waterresources investigations of the United States Geological 

Survey; book 9, chap. A6, National field manual for the 

collection of water-quality data: accessed June 9, 2003, at 

URL http://water.usgs.gov/owq/FieldManual/

Wildermuth Environmental Inc., 2000, TIN/TDS Phase 2A: 

Tasks 1 through 5. TIN/TDS Study of the Santa Ana watershed, Technical Memorandum, July 2000, various paging.

Wildermuth Environmental Inc., 2002, Chino Basin optimum 

basin management program, initial state of the basin report: 

Technical Memorandum, October 2002, various paging.

Wong, C.S., Capel, P.D., and Nowell, L.H., 2000, Organochlorine pesticides and PCBs in stream sediment and aquatic 

biota—Initial results from the National Water-Quality 

Assessment Program, 1992–1995: U.S. Geological Survey 

Water-Resources Investigations Report 00-4053, 88 p.
30 Water Quality in the Santa Ana Basin, California, 1999–2001

Glossary

Acre-foot

A volume of water equal to 1 foot in depth and covering 1 

acre; equivalent to 43,560 cubic feet or 325,851 gallons. 

Algae

Chlorophyll-bearing nonvascular, primarily aquatic species 

that have no true roots, stems, or leaves; most algae are microscopic, but some species can be as large as vascular plants. 

Alluvium

Deposits of clay, silt, sand, gravel or other particulate rock 

material left by a river in a streambed, on a flood plain, in a 

delta, or at the base of a mountain. 

Aquatic-life guidelines

Specific levels of water quality which, if reached or 

exceeded, may adversely affect aquatic life. These are nonenforceable guidelines issued by a governmental agency or 

other institution. 

Aquifer

A water-bearing layer of soil, sand, gravel, or rock that will 

yield usable quantities of water to a well. 

Base flow

Sustained, low flow in a stream; ground-water discharge is the 

source of base flow in most streams. 

Bed sediment

The material that temporarily is stationary in the bottom of a 

stream or other watercourse. 

Channelization

Modification of a stream, typically by straightening the channel, to provide more uniform flow; often done for flood control 

or for improved agricultural drainage or irrigation. 

Confined area

That part of an aquifer that is overlain by material that restricts 

the movement of water. 

Degradation products

Compounds resulting from transformation of an organic 

substance through chemical, photochemical, and (or) biochemical reactions. 

Diatoms

Single-celled, colonial, or filamentous algae with siliceous cell 

walls constructed of two overlapping parts. 

Discharge

Rate of fluid flow passing a given point at a given moment in 

time, expressed as volume per unit of time. 

Dissolved solids

Amount of minerals, such as salt, that are dissolved in water; 

amount of dissolved solids is an indicator of salinity or hardness. 

30

Diversion

A turning aside or alteration of the natural course of a flow 

of water, normally considered physically to leave the natural 

channel. In some States, this can be a consumptive use direct 

from another stream, such as by livestock watering. In other 

States, a diversion must consist of such actions as taking water 

through a canal, pipe, or conduit. 

Drinking-water standard or guideline

A threshold concentration in a public drinking-water supply, 

designed to protect human health. As defined here, standards 

are U.S. Environmental Protection Agency regulations that 

specify the maximum contamination levels for public water 

systems required to protect the public welfare; guidelines have 

no regulatory status and are issued in an advisory capacity. 

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. 

Engineered recharge

Augmentation of natural replenishment of ground-water storage by some method of construction, by spreading of water, or 

by pumping water directly into an aquifer. 

Flow path

An underground route for ground-water movement, extending from a recharge (intake) zone to a discharge (output) zone 

such as a shallow stream or public supply well. 

Fumigant

A substance or mixture of substances that produces gas, 

vapor, fume, or smoke intended to destroy insects, bacteria, 

or rodents. 

Habitat

The part of the physical environment where plants and 

animals live. 

Hydrograph

Graph showing variation of water elevation, velocity, streamflow, or other property of water with respect to time. 

Hydrologic cycle

The circulation of water from the sea, through the atmosphere, 

to the land, and thence back to the sea by overland and subterranean routes. 

Invertebrate

An animal having no backbone or spinal column, including 

insects, mollusks, crustaceans, and worms. 
Glossary 31

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. 

Nitrate

An ion consisting of nitrogen and oxygen (NO3

–

). Nitrate is a 

plant nutrient and is very mobile in soils. 

Phenols

A class of organic compounds containing phenol (C6H5OH) 

and its derivatives. Used to make resins or weed killers, and 

as a solvent, disinfectant, and chemical intermediate. Some 

phenols occur naturally in the environment. 

Phthalates

A class of organic compounds containing phthalic acid esters 

[C6H4(COOR)2] and derivatives. Used as plasticizers in plastics. Also used in many other products (such as detergents 

and cosmetics) and industrial processes (such as defoaming 

agents during paper and paperboard manufacture, and

dielectrics in capacitors). 

Picocurie (pCi)

One trillionth (10–12) of the amount of radioactivity represented by a curie (Ci). A curie is the amount of radioactivity 

that yields 3.7 × 1010 radioactive disintegrations per second 

(dps). A picocurie yields 2.22 disintegrations per minute 

(dpm) or 0.037 dps. 

Polycyclic aromatic hydrocarbon (PAH)

A class of organic compounds with a fused-ring aromatic 

structure. PAHs result from incomplete combustion of organic 

carbon (including wood), municipal solid waste, and fossil 

fuels, as well as from natural or anthropogenic introduction 

of uncombusted coal and oil. PAHs include benzo(a)pyrene, 

fluoranthene, and pyrene. 

Recharge

Water that infiltrates the ground and reaches the saturated zone. 

Relative abundance

The number of organisms of a particular kind present in a 

sample relative to the total number of organisms in the sample. 

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). 

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. 

Taxon (plural taxa)

Any identifiable group of taxonomically related organisms.

Total DDT

The sum of DDT and its breakdown products, including DDD 

and DDE. 

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. 

Tributary

A river or stream flowing into a larger river, stream, or lake. 

Unconfined area

That part of an aquifer whose upper surface is a water table.

Volatile Organic Compounds (VOCs)

Organic chemicals that have a high vapor pressure relative 

to the their water solubility. VOCs include components of 

gasoline, fuel oils and lubricants, as well as organic solvents, 

fumigants, some inert ingredients in pesticides, and some byproducts of chlorine disinfection. 

Water table

The point below the land surface where ground water is first 

encountered and below which the earth is saturated. Depth to 

the water table varies widely across the country.
32 Water Quality in the Santa Ana Basin

Appendix—Water-Quality Data from the Santa Ana Basin 

in a National Context

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Coordination with agencies and organizations in the Santa Ana Basin study area was integral to the

success of this water-quality assessment. We thank those who served as members of our 

liaison committee. 

Federal Agencies

Bureau of Indian Affairs, Southern

 California Agency

Bureau of Reclamation

State Agencies

California Department of 

 Water Resources

California State Water Resources 

 Control Board

Santa Ana Regional Water Quality 

 Control Board

Local Agencies

City of Lake Elsinore

City of Riverside

City of San Bernardino

Eastern Municipal Water District

Inland Empire Utilities Agency

Metropolitan Water District

 of Southern California

Orange County Sanitation District

Orange County Water District

San Bernardino Valley 

 Municipal Water District

Santa Ana Watershed Project Authority

Southern California Coastal 

 Water Research Project

Western Municipal Water District

Yucaipa Valley Water District

Native American Tribes and Nations

San Manuel Indian Reservation

Universities

University of California at Riverside

Other public and private organizations

Environmental Systems Research

 Institute (ESRI)

Wildermuth Environmental

We thank the following individuals for contributing to this effort:

• Andrea Altmann (USGS, San Diego CA), prepared supplies and equipment for field work and assisted in the collection of ecology and surface-water samples.

• Larry Brown (USGS, Sacramento CA), participated in the design of aquatic ecology studies and in field activities associated with these studies.

• Ted Callender (USGS, Austin TX), collected, processed, and analyzed reservoir core samples.

• Dennis Clark (USGS, San Diego CA), assisted in logging and installation of monitoring wells for a land-use study.

• Robert Fisher (USGS, San Diego CA), assisted in the collection and field identification of fish.

• Steve Goodbred (USGS, Sacramento CA), assisted in the design of aquatic ecology studies and in collection of streambed sediment and fish-tissue samples.

• Jo Ann Gr 

• Mark Johnso eld data.

• Willie Kinsey (USGS, Sacramento CA), assisted in the collection and processing of ground-water samples.

• Sarah Kraja (USGS, San Diego CA), organized and conducted sampling for all NAWQA ground-water studies.

• Barbara Mahler (USGS, Austin TX), collected, processed, and analyzed reservoir core samples.

• sh-tissue samples.

• Greg Mendez ( . 

• Stephen Porter (USGS, Denver CO), assisted in the design of a study of assimilation of nitrate by algae in Cucamonga Creek.

• Larry Shelton (USGS, Sacramento CA), assisted in the collection of streambed sediment and fish-tissue samples.

• Te sh-tissue samples.

• Joe Smoot (USGS, Reston VA), collected, processed, and analyzed reservoir core samples.

• Camm Swift (consultant, Arcadia CA), assisted in the collection and field identification of fish.

• Jennifer Wilson (USGS, Austin TX), collected, processed, and analyzed reservoir core samples.

• Peter Van Metre (USGS, Au .

• Manna Warburton (USGS, San Diego CA), assisted in the collection and field identification of fish.

Appreciation is extended to those individuals who reviewed or helped prepare this report:

Marc Sylvester, USGS, Menlo Park; Laurel Rogers, USGS, San Diego; Phil Contreras, USGS, San Diego
Belitz and others— Water Quality in the Santa Ana Basin 

U.S. Geological Survey Circular 1238

National Water-Quality Assessment (NAWQA) Program

Santa Ana Basin

NAWQA

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