U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3033

January 2013 Printed on recycled paper

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

Groundwater Quality in the Antelope 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. Antelope 

Valley is one of the study areas being evaluated. 

The Antelope Study Area Overview of Water Quality

GAMA’s Priority Basin Project 

evaluates the quality of untreated 

groundwater. However, for context, 

benchmarks established for drinkingwater 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 56 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 Antelope Valley 

study area, one or more inorganic constituents were present at high concentrations in 

30% of the primary aquifers and at moderate concentrations in 30%.

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 Antelope Valley 

study area, organic constituents were 

present at moderate concentrations in 2% 

of the primary aquifers.

The Antelope study area is approximately 1,600 square miles (4,144 square kilometers) and includes the Antelope Valley groundwater basin (California Department of Water 

Resources, 2003). Antelope Valley has an arid climate and is part of the Mojave Desert. 

Average annual rainfall is about 6 inches (15 centimeters). The study area has internal 

drainage, with runoff from the surrounding mountains draining towards dry lakebeds in 

the lower parts of the valley. Land use in the study area is approximately 68 percent (%) 

natural (mostly shrubland and grassland), 24% agricultural, and 8% urban. The primary 

crops are pasture and hay. The largest urban areas are the cities of Palmdale and Lancaster 

(2010 populations of 152,000 and 156,000, 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 Antelope 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 Antelope Valley are 

completed to depths between 360 and 700 feet (110 to 213 meters), consist of solid casing 

from the land surface to a depth of 180 to 350 feet (55 to 107 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 and sewer and 

septic systems. The primary sources of discharge are pumping wells and evapotranspiration near the dry lakebeds.

High Moderate

CONSTITUENT CONCENTRATIONS

Low or not detected 

Pie charts illustrate the proportion of the primary 

aquifers, on an areal basis, with concentrations in the

three specified categories.

30

30

40

Organic

constituents

Inorganic

constituents

Number analyzed: 27 Number analyzed: 79

98

2

118°45’

35°15’

34°45’

34°30’

35°

118°30’ 118°15’ 118° 117°45’

0 5 10 20 MILES

0 5 10 20 KILOMETERS

EXPLANATION

Lake

Dry lake bed

Urban area

Alluvium

Hard rock

Study area 

boundary

Lancaster

Rosamond

Dry Lake

Rogers

Dry Lake

Palmdale

KERN COUNTY

LOS ANGELES COUNTY

SAN BERNARDINO COUNTY

Antelope Valley

Groundwater Basin

Los Angeles AqueductLos Angeles Aqueduct

California Aqueduct California Aqueduct
RESULTS: Groundwater Quality in the Antelope Study Area

Inorganic Constituents with Human-Health Benchmarks

Trace elements are naturally present in the minerals in rocks and soils, and in the 

water that comes into contact with those materials; their concentrations can be affected 

by human activities. In the Antelope study area, trace elements were present at high 

concentrations in 32% of the primary aquifers, on an areal basis, and at moderate concentrations in 17%. Of the 17 trace elements with human-health benchmarks analyzed 

in this study, 5 were detected at high concentrations: aluminum, arsenic, vanadium, 

boron, and fluoride. Chromium, lead, and molybdenum were 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 Antelope study area, radioactive constituents were detected at 

concentrations above benchmarks in 4% of the primary aquifers, and at moderate values 

in 6%. Six radioactive constituents were analyzed; of these, gross alpha radioactivity was detected above human-health benchmarks. Uranium was present at moderate 

concentrations.

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.

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 iron, affect the 

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

these constituents were present at high concentrations in 18% of the primary aquifers, 

and at moderate concentrations in 10%. Of the seven constituents with non-healthbased benchmarks that were analyzed, three (iron, manganese, and total dissolved 

solids) were detected above benchmarks. Sulfate and chloride were detected at 

modertate concentrations.

Special Interest: Perchlorate

Perchlorate is an inorganic constituent which 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 Antelope study area, perchlorate was found at moderate 

concentrations in 29% of the primary aquifers.

Other

inorganic

constituents

Perchlorate

17

32

2 9

51

90

89

72

29

18

10

71

6 4

Trace 

elements

Radioactive

constituents

Nutrients

INORGANIC CONSTITUENTS
RESULTS: Groundwater Quality in the Antelope Study Area

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 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 can form during the disinfection of water supplies; they are characterized 

by their tendency to volatilize into the air. Of 56 VOCs with health-based benchmarks 

analyzed in the Antelope Valley study area, only the VOC trichloromethane (chloroform) was detected at moderate concentrations in 2% of the primary aquifers. No VOCs 

were detected at high concentrations in the 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 Antelope Valley study area, pesticides were not detected or were only detected at 

low concentrations. Of the 20 pesticides with health-based benchmarks that were analyzed, none were detected at high or moderate concentrations in the primary aquifers.

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

Pesticides

Volatile

organic

compounds

100

98

2

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 primary 

aquifers. In Antelope, they were high in 32% of the primary aquifers, on an areal basis; 

the range of high trace element percentages in the Desert Region study areas was 15 

to 54% (Milby Dawson and Belitz, 2012). The highest percentages in Antelope valley 

were arsenic (high in 28% of the primary aquifers), vanadium (6%), and boron (3%). 

Arsenic and boron were detected at high concentrations in all of the Desert primary 

aquifers; vanadium was detected at high concentrations in three of the six Desert 

Region study areas. Arsenic was high in a larger portion of the Antelope Valley primary 

aquifers than in any of the other Desert Region study areas.

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 human-health 

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/

Milby Dawson, B.J., and, Belitz, K., 2010, 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.

Schmitt, S.J., Milby Dawson, B.J., and Belitz, K., 2009, Groundwater quality 

 data in the Antelope Valley Study Unit, 2008—Results from the California GAMA 

 Program: U.S. Geological Survey Data Series 479, 79 p., available at

http://pubs.usgs.gov/ds/479/

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/

0 25 50

0 25 50 100 KILOMETERS

100 MILES

Owens

Valley

Indian Wells

Mojave

Coachella

Antelope

NEVADA

ARIZONA

MEXICO

CALIFORNIA

Colorado

River

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

Owens

Indian Wells

Coachella

Colorado River

Antelope

Mojave

High aquifer proportion

EXPLANATION

Moderate aquifer proportion

Trace Elements

Vanadium

Arsenic

Boron

Desert Region Study Areas

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

Owens

Indian Wells

Coachella

Colorado River

Antelope

Mojave

High aquifer proportion

EXPLANATION

Moderate aquifer proportion

Trace Elements

Vanadium

Arsenic

Boron

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