U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3098

January 2013 Printed on recycled paper

U.S. Geological Survey and the California State Water Resources Control Board

Groundwater Quality in Coachella Valley, 

California

Groundwater provides more than 40 percent of California’s drinking water. To protect this vital 

resource, the State of California created the Groundwater Ambient Monitoring and Assessment 

(GAMA) Program. The Priority Basin Project of the GAMA Program provides a comprehensive 

assessment of the State’s groundwater quality and increases public access to groundwater-quality 

information. Coachella Valley is one of the study areas being evaluated. 

GAMA’s Priority Basin Project 

evaluates the quality of untreated 

groundwater. However, for context, 

benchmarks established for drinking-water 

quality are used for comparison. Benchmarks 

and definitions of high, moderate, and low 

concentrations are discussed in the inset box 

on page 3. The USGS sampled 19 wells for 

this assessment; data from the California 

Department of Public Health database were 

used to supplement USGS data.

Many inorganic constituents occur 

naturally in groundwater. The concentrations 

of the inorganic constituents can be affected 

by natural processes as well as by human 

activities. In the Coachella study area, one 

or more inorganic constituents were present 

at high concentrations in 42% of the primary 

aquifers and at moderate concentrations in 

26%.

Organic constituents are found in 

products used in the home, business, 

industry, and agriculture. Organic 

constituents can enter the groundwater 

system through normal usage, spills, or 

improper disposal. In the Coachella study 

area, organic constituents were present 

at moderate concentrations in 1% of the 

primary aquifers.

The Coachella study area is approximately 820 square miles (2,124 square 

kilometers) and includes the Coachella Valley groundwater basin (California 

Department of Water Resources, 2003). Coachella Valley has an arid climate, with 

average annual rainfall of about 6 inches (15 centimeters). The runoff from the 

surrounding mountains drains to rivers that flow east and south out of the study area to 

the Salton Sea. Land use in the study area is approximately 67 percent (%) natural, 

21% agricultural, and 12% urban. The primary natural land cover is shrubland. The 

largest urban areas are the cities of Indio and Palm Springs (2010 populations of 76,000 

and 44,000, respectively).

Groundwater in this basin is used for public and domestic water supply and for 

irrigation. The main water-bearing units are gravel, sand, silt, and clay derived from 

surrounding mountains. The primary aquifers in Coachella Valley are defined as those 

parts of the aquifers corresponding to the perforated intervals of wells listed in the 

California Department of Public Health database. Public-supply wells in Coachella 

Valley are completed to depths between 490 and 900 feet (149 to 274 meters), consist 

of solid casing from the land surface to a depth of 260 to 510 feet (79 to 155 meters), 

and are screened or perforated below the solid casing. Recharge to the groundwater 

system is primarily runoff from the surrounding mountains, and by direct infiltration of 

irrigation. The primary sources of discharge are pumping wells, evapotranspiration, and 

underflow to the Salton Sea and Imperial Valley areas.

The Coachella Study Area Overview of Water Quality

High Moderate

CONSTITUENT CONCENTRATIONS

Low or not detected 

Pie charts illustrate the percentages of the primary 

aquifers, on an areal basis, with concentrations in the 

three specified categories.

42

26

32

Organic

constituents

Inorganic

constituents

Number analyzed: 27 Number analyzed: 79

1

99

116°45’

34°

33°45’

33°30’

116°30’ 116°15’ 116°

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Salton

Sea

IMPERIAL

COUNTY

SAN DIEGO COUNTY

RIVERSIDE COUNTY

SAN BERNARDINO COUNTY

Colorado River AqueductColorado River Aqueduct

Palm Springs

Indio

Coachella Valley Groundwater Basin

EXPLANATION

Lake

Urban area

Alluvium

Hard rock

Study area 

boundary
RESULTS: Groundwater Quality in the Coachella Study Area

Inorganic Constituents with Human-Health Benchmarks

Trace elements are naturally present in the minerals in rocks and 

soil, and in the water that comes into contact with those materials. In the Coachella 

study area, trace elements with human-health benchmarks were present at high 

concentrations in 37% of the primary aquifers. Trace elements were present at moderate 

concentrations in 21% of the primary aquifers. Of the 17 trace elements with humanhealth benchmarks analyzed in this study, 5 were detected at high concentrations: 

arsenic, boron, fluoride, molybdenum, and strontium. Vanadium was present at 

moderate concentrations.

Radioactivity is the release of energy or energetic particles during structural 

changes in the nucleus of an atom. Most of the radioactivity in groundwater comes

from decay of naturally occurring isotopes of uranium and thorium that are present 

in minerals in the aquifer. In the Coachella study area, radioactive constituents 

were detected at concentrations above benchmarks in 4% of the primary aquifers, and 

at moderate concentrations in 10%. Six radioactive constituents were analyzed; of 

these, uranium and gross alpha radioactivity were detected at concentrations above 

benchmarks.

Nutrients, such as nitrate and nitrite, are naturally present at low concentrations in 

groundwater. High and moderate concentrations generally occur as a result of human 

activities, such as fertilizer application, livestock waste, or septic-system seepage. Of 

the three nutrients with health-based benchmarks analyzed, one, nitrate, was detected at 

concentrations above benchmarks in the Coachella primary aquifers.

Inorganic Constituents with Non-Health Benchmarks

(Not included in water-quality overview charts shown on the front page)

Other inorganic constituents, such as total dissolved solids and manganese, affect 

the aesthetic properties of water, such as taste, color, or odor. In the Coachella study 

area, these constituents were present at high concentrations in 16% of the primary 

aquifers, and at moderate concentrations in 21%. Of the seven constituents with 

non-health-based benchmarks analyzed, four were detected at concentrations above 

benchmarks: chloride, manganese, total dissolved solids, and sulfate.

Special Interest: Perchlorate

Perchlorate is an inorganic constituent that has been regulated in California 

drinking water since 2007. It is an ingredient in rocket fuel, fireworks, safety flares, 

may be present in some fertilizers, and also occurs naturally at low concentrations in 

groundwater. In the Coachella study area, perchlorate was found at high concentrations 

in 10% and at moderate concentrations in 16% of the primary aquifers.

Other

inorganic

constituents

Perchlorate

37 42

21

86

93

63

10

16

16

21

74

5

4 10

2

Trace 

elements

Radioactive

constituents

Nutrients

INORGANIC CONSTITUENTS
BENCHMARKS FOR EVALUATING GROUNDWATER QUALITY

GAMA’s Priority Basin Project uses benchmarks established for drinking 

water to provide context for evaluating the quality of untreated groundwater. After 

withdrawal, groundwater may be disinfected, filtered, mixed, or exposed to the 

atmosphere before being delivered to consumers. Federal and California regulatory 

benchmarks for protecting human health (Maximum Contaminant Level, MCL) are 

used when available. Otherwise, nonregulatory benchmarks for protecting human 

health (Notification Level, NL, and Lifetime Health Advisory, HAL) and nonregulatory 

benchmarks for protecting aesthetic properties such as taste and odor (Secondary 

Maximum Contaminant Level, SMCL) are used. 

High, moderate, and low concentrations are defined relative to benchmarks

Concentrations are considered high if they are greater than a benchmark. For inorganic constituents, concentrations are moderate

if they are greater than one-half of a benchmark. For organic and special-interest constituents, concentrations are considered moderate

if they are greater than one-tenth of a benchmark; this lower threshold was used because organic constituents are generally less 

prevalent and have smaller concentrations relative to benchmarks than inorganic constituents. Low concentrations include nondetections and values less than moderate concentrations. Methods for evaluating water quality are discussed by Milby Dawson and 

Belitz (2012).

Organic Constituents with Human-Health Benchmarks

The Priority Basin Project uses laboratory methods that can detect the presence 

of volatile organic compounds (VOCs) and pesticides at very low concentrations, far 

below human-health benchmarks. VOCs and pesticides detected at these very low 

concentrations can be used to help trace water from the land surface into the aquifer 

system.

Volatile Organic Compounds

VOCs are present in many household, commercial, industrial, and agricultural 

products, and are characterized by their tendency to volatilize into the air. Of 56 VOCs 

with health-based benchmarks analyzed in the Coachella study area, none were detected 

above benchmarks. The VOCs trichloromethane and tetrachloroethene were detected at 

moderate concentrations in 1% of the Coachella primary aquifers.

Pesticides

Pesticides are used on lawns, in gardens, around buildings, along roads, and in 

agriculture to help control unwanted vegetation (weeds), insects, fungi, and other 

pests. In the Coachella study area, pesticides were not detected or only detected at 

low concentrations. Of the 20 pesticides with health-based benchmarks that were 

analyzed in the Coachella primary aquifers, none were detected at high or moderate 

concentrations in the primary aquifers.

RESULTS: Groundwater Quality in the Coachella Study Area

ORGANIC CONSTITUENTS

Pesticides

Volatile

organic

compounds

1

99

100

High

Moderate

EX

Low or not detected

AMPLE Values are a percentage of the area of the primary aquifers 

with concentrations in the three specified categories.

CONSTITUENT CONCENTRATIONS
Trace Element Concentrations Throughout the 

California Desert Region

Trace elements were present at high concentrations in all of the Desert Region 

primary aquifers. In the Coachella study area, they were high in 37% of the primary 

aquifers, on an areal basis; the range of high trace element percentages in the Desert 

Region primary aquifers was 15 to 54% (Milby Dawson and Belitz, 2012). The trace 

elements with the highest percentages in Coachella were arsenic (high in 21% of the 

primary aquifers) and fluoride (21%). Arsenic was found at high concentrations in all 

of the primary aquifers in the Desert region. Fluoride was found at high concentrations 

in five of the six Desert Region study areas and in the highest proportion in Coachella.

Priority Basin Assessments 

GAMA’s Priority Basin Project 

(PBP) assesses water quality in that part 

of the aquifer system used for drinking 

water, primarily public supply. Water 

quality in shallower and deeper parts 

may differ from water quality in the 

primary aquifers. GAMA’s Domestic 

Well Project assesses water quality 

in the shallower parts of the aquifer 

system. Ongoing assessments are being 

conducted in more than 120 basins 

throughout California.

The PBP assessments are based 

on a comparison of constituent 

concentrations in untreated groundwater 

with benchmarks established for the 

protection of human health and for 

aesthetic concerns. The PBP does not 

evaluate the quality of drinking water 

delivered to consumers.

The PBP uses two approaches for 

assessing groundwater quality. The first 

approach uses a network of wells to 

provide a statistically based assessment 

of the status of groundwater quality. The 

second approach uses additional wells 

to help assess the factors that affect 

water quality. Both approaches use 

data routinely collected for regulatory 

compliance, as well as data collected 

by the PBP. The PBP includes chemical 

analyses not generally available 

as part of regulatory compliance 

monitoring, including measurements at 

concentrations much lower than humanhealth benchmarks, and measurement of 

constituents that can be used to trace the 

sources and movement of groundwater.

By Barbara J. Milby Dawson and Kenneth Belitz

SELECTED REFERENCES

California Department of Water Resources, 2003, California’s groundwater: California 

Department of Water Resources Bulletin 118, 246 p., available at

http://www.water.ca.gov/groundwater/bulletin118/update2003.cfm

Goldrath, D.A., Wright, M.T., and Belitz, K., 2009, Ground-water quality data in the 

Coachella Valley study unit, 2007—Results from the California GAMA Program: 

U.S. Geological Survey Data Series 373, 70 p., available at 

http://pubs.usgs.gov/ds/373

 Milby Dawson, B.J., and Belitz, K., 2012, Status of groundwater quality in the 

California Desert Region, 2006–2008—California GAMA Program Priority Basin 

Project: U.S. Geological Survey Scientific Investigations Report 2012-5040, 100 p. 

For more information

Technical reports and hydrologic 

data collected for the GAMA Program 

may be obtained from:

GAMA Program Unit

U.S. Geological Survey

California Water Science Center

4165 Spruance Road, Suite 200

San Diego, CA 92101

Telephone number: (619) 225-6100

WEB: http://ca.water.usgs.gov/gama

GAMA Program Unit

State Water Resources Control Board

Division of Water Quality

PO Box 2231, Sacramento, CA 95812

Telephone number: (916) 341-5779

WEB: http://www.waterboards.ca.gov/gama/

Desert Region Study Areas

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

Percentage of area of primary aquifers with concentrations in the specified categories 100%

0%

20%

40%

60%

80%

100%

Owens

Indian Wells

Coachella

Colorado River

Antelope

Mojave

High aquifer proportion

EXPLANATION

Moderate aquifer proportion

Trace Elements

Arsenic

Fluoride

0 25 50

0 25 50 100 KILOMETERS

100 MILES

Owens

Valley

Indian Wells

Mojave

Colorado River

Coachella

Antelope

NEVADA

ARIZONA

MEXICO

CALIFORNIA