U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the California State Water Resources Control Board

A product of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program

Status of Groundwater Quality in the California Desert Region, 

2006–2008: California GAMA Priority Basin Project

Photo placement

Scientific Investigations Report 2012–5040
Front Cover Map: Groundwater basins categorized by sampling priority. Location of groundwater basin 

boundaries from California Department of Water Resources (CDWR, 2003).

Cover photographs:

Front cover: Looking east from Owens Valley to the Sierra Nevada Mountains, near Cartago, California. 

(Photograph taken by Isabel Pimentel, U.S. Geological Survey.)

Back cover: Supply well near Lancaster, California. (Photograph taken by Stephen Schmitt, U.S. Geological 

Survey.) 

Sampling priority

Study area

Low-use basins

Priority basins

Areas that are outside CDWR-defined

 groundwater basins
Status of Groundwater Quality in the 

California Desert Region, 2006–2008: 

California GAMA Priority Basin Project

By Barbara J.M. Dawson and Kenneth Belitz

A product of the California Groundwater Ambient Monitoring and Assessment 

(GAMA) Program

Prepared in cooperation with the California State Water Resources Control Board

Scientific Investigations Report 2012–5040

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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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.

Suggested citation:

Dawson, B.J.M., and Belitz, Kenneth, 2012, Status of groundwater quality in the California Desert Region, 

2006–2008—California GAMA Priority Basin Project: U.S. Geological Survey Scientific Investigations Report 

2012–5040, 110 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction ....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Hydrogeologic Setting and Description of Study Areas ...............................................................4

Owens Valley ................................................................................................................................7

Antelope .......................................................................................................................................7

Mojave...........................................................................................................................................7

Coachella ....................................................................................................................................16

Colorado River............................................................................................................................16

Indian Wells ...............................................................................................................................16

Methods ...............................................................................................................................................18

Relative-Concentrations and Water-Quality Benchmarks .................................................18

Data Used for Status Assessment ..........................................................................................19

Grid Values: USGS Data...................................................................................................19

Grid Values: CDPH Data...................................................................................................19

Selection of Constituents for Status Assessment................................................................20

Calculation of Aquifer-Scale Proportions..............................................................................24

Grid-Based Aquifer-Scale Proportions .........................................................................24

Spatially Weighted Aquifer-Scale Proportions............................................................24

Raw Detection Frequencies............................................................................................24

Area Correction Factors ..................................................................................................24

Status of Groundwater Quality .................................................................................................................25

Inorganic Constituents.......................................................................................................................30

Inorganic Constituents with Health-Based Benchmarks ...................................................30

Trace Elements..................................................................................................................30

Radioactive Constituents.................................................................................................40

Nutrients.............................................................................................................................40

Special-Interest Constituent: Perchlorate....................................................................40

Inorganic Constituents with Non- Health-Based Benchmarks .........................................40

Organic Constituents..........................................................................................................................50

Volatile Organic Compounds....................................................................................................50

Pesticides and Pesticide Degradates ....................................................................................50

Special-Interest Constituents..................................................................................................57

Summary .......................................................................................................................................................59

Acknowledgments.......................................................................................................................................59

References....................................................................................................................................................59

Appendix A. Use of Data From the CDPH Database ..............................................................................65

Appendix B. Data For Individual Desert Study Areas............................................................................67

Appendix C. Comparison of CDPH and USGS-GAMA Data ................................................................103
iv

Figures

Figure 1. Map showing locations of the California Desert Region Groundwater Ambient

Monitoring and Assessment (GAMA) study areas and California hydrogeologic

provinces .................................................................................... 3

Figure 2. Ternary diagram showing proportions of urban, agricultural, and natural land use

in the California Desert Region Groundwater Ambient Monitoring and

Assessment (GAMA) study areas and within a 500-meter radius of data points in

those study areas ........................................................................... 5

Figure 3. Maps showing general land use from the 1990s in the California Desert Region

Groundwater Ambient Monitoring and Assessment (GAMA) study areas ......... 6

Figure 4. Maps showing geology and locations of grid cells and grid wells used for the

Groundwater Ambient Monitoring and Assessment (GAMA) Program in the

California Desert Region study areas, 2006–2008: Owens Valley, Antelope Valley,

Mojave, Coachella Valley, Colorado River, and Indian Wells Valley .................. 8

Figure 5. Maps showing generalized directions of groundwater flow in the California

Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study

areas, 2006–2008 ........................................................................... 17

Figure 6. Graphs showing aquifer-scale proportions for inorganic and organic constituent

classes in the California Desert Region as a whole and for the individual

California Desert Region Groundwater Ambient Monitoring and Assessment

(GAMA) study areas, 2006–2008 ......................................................... 25

Figure 7. Graph showing maximum concentrations relative to health-based and

non-health-based benchmarks in grid wells for classes of constituents detected

in the California Desert Region Groundwater Ambient Monitoring and

Assessment (GAMA) study areas, 2006–2008 .......................................... 26

Figure 8. Graph showing detected concentrations of arsenic, boron, fluoride, molybdenum,

and vanadium in grid wells relative to health-based benchmarks in the California

Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study

areas, 2006–2008 ........................................................................... 32

Figure 9. Maps showing concentrations of arsenic in grid wells relative to health-based

benchmarks in the California Desert Region Groundwater Ambient Monitoring

and Assessment (GAMA) study areas, 2006–2008....................................... 33

Figure 10. Maps showing concentrations of boron in grid wells relative to health-based

benchmarks in the California Desert Region Groundwater Ambient Monitoring

and Assessment (GAMA) study areas, 2006–2008....................................... 34

Figure 11. Maps showing concentrations of fluoride in grid wells relative to health-based

benchmarks in the California Desert Region Groundwater Ambient Monitoring

and Assessment (GAMA) study areas, 2006–2008....................................... 35

Figure 12. Maps showing concentrations of molybdenum in grid wells relative to

health-based benchmarks in the California Desert Region Groundwater Ambient

Monitoring and Assessment (GAMA) study areas, 2006–2008 ........................ 36

Figure 13. Maps showing concentrations of vanadium in grid wells relative to health-based

benchmarks in the California Desert Groundwater Ambient Monitoring and

Assessment (GAMA) study areas, 2006–2008 .......................................... 37

Figure 14. Graph showing concentrations of strontium, uranium, gross-alpha radioactivity,

nitrate, and perchlorate in grid wells relative to health-based benchmarks in the

California Desert Groundwater Ambient Monitoring and Assessment (GAMA)

study areas, 2006–2008 ..................................................................... 38
v

Figures—Continued

Figure 15. Maps showing concentrations of strontium in grid wells relative to health-based

benchmarks in the California Desert Region Groundwater Ambient Monitoring

and Assessment (GAMA) study areas, 2006–2008....................................... 39

Figure 16. Maps showing concentrations of gross-alpha radioactivity in grid wells relative

to health-based benchmarks in the California Desert Region Groundwater

Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008 ............ 41

Figure 17. Maps showing concentrations of uranium in grid wells relative to health-based

benchmarks in the California Desert Region Groundwater Ambient Monitoring

and Assessment (GAMA) study areas, 2006–2008....................................... 42

Figure 18. Maps showing concentrations of perchlorate in grid wells relative to

health-based benchmarks in the California Desert Region Groundwater 

Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008 ............ 43

Figure 19. Graph showing concentrations of chloride, iron, manganese, sulfate, and total

dissolved solids in grid wells relative to non-health-based benchmarks in the

California Desert Groundwater Ambient Monitoring and Assessment (GAMA)

study areas, 2006–2008 ..................................................................... 44

Figure 20. Maps showing concentrations of total dissolved solids in grid wells relative to

non-health-based benchmarks in the California Desert Region Groundwater

Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008 ............ 45

Figure 21. Maps showing concentrations of manganese in grid wells relative to

non-health-based benchmarks in the California Desert Region Groundwater

Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008 ............ 46

Figure 22. Maps showing concentrations of sulfate in grid wells relative to

non-health-based benchmarks in the California Desert Region Groundwater

Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008 ............ 47

Figure 23. Maps showing concentrations of iron in grid wells relative to non-health-based

benchmarks in the California Desert Region Groundwater Ambient Monitoring

and Assessment (GAMA) study areas, 2006–2008....................................... 48

Figure 24. Maps showing concentrations of chloride in grid wells relative to

non-health-based benchmarks in the California Desert Region Groundwater

Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008 ............ 49

Figure 25. Graph showing detection frequencies and maximum relative-concentrations

for organic constituents detected in grid wells in the California Desert Region

Groundwater Ambient Monitoring and Assessment (GAMA) study areas,

2006–2008 .................................................................................... 52

Figure 26. Graphs showing concentrations relative to health-based benchmarks and

detection frequencies of volatile organic compounds in grid wells in the

California Desert Region Groundwater Ambient Monitoring and Assessment

(GAMA) study areas, 2006–2008 ......................................................... 53

Figure 27. Maps showing concentrations of chloroform relative to health-based

benchmarks in the California Desert Region Groundwater Ambient Monitoring

and Assessment (GAMA) study areas, 2006–2008....................................... 54

Figure 28. Graphs showing concentrations relative to health-based benchmarks and

detection frequencies of pesticide compounds in grid wells in the California

Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study

areas, 2006–2008 ........................................................................... 55
vi

Figures—Continued

Figure 29. Maps showing concentrations of dieldrin and simazine relative to health-based

benchmarks in the California Desert Region Groundwater Ambient Monitoring

and Assessment (GAMA) study areas, 2006–2008....................................... 56

Figure 30. Graph showing detection frequency and concentrations of

N-nitrosodimethylamine in 77 grid wells relative to health-based benchmarks in

the California Desert Region Groundwater Ambient Monitoring and Assessment

(GAMA) study areas, 2006–2008 ......................................................... 57

Figure 31. Maps showing concentrations of N-nitrosodimethylamine relative to

health-based benchmarks in the California Desert Region Groundwater Ambient

Monitoring and Assessment (GAMA) study areas, 2006–2008 ........................ 58

Tables

Table 1. Historical and current periods of record available in the California Department

of Public Health database in the California Desert Region Groundwater Ambient

Monitoring and Assessment (GAMA) study areas. .................................... 20

Table 2. Number of grid wells used for assessment of status of inorganic constituents in

the California Desert Region Groundwater Ambient Monitoring and Assessment

(GAMA) study areas. ........................................................................ 21

Table 3. Constituents historically reported in the California Department of Public Health

database with high maximum relative-concentrations (above benchmarks) in the

California Desert Region Groundwater Ambient Monitoring and Assessment

(GAMA) study areas. ........................................................................ 23

Table 4. Number of constituents analyzed and number detected by the U.S. Geological

Survey in grid wells, with associated benchmarks for each constituent class,

California Desert Region Groundwater Ambient Monitoring and Assessment

(GAMA) study areas, September 2006 to April 2008. .................................... 27

Table 5. Current aquifer proportions from grid-based and spatially weighted methods for

constituents with moderate or high relative-concentrations, California Desert

Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas,

September 2006 to April 2008. ............................................................ 28

Table 6. Summary of aquifer-scale proportions for inorganic constituent classes in the

California Desert Region Groundwater Ambient Monitoring and Assessment

(GAMA) study areas. ........................................................................ 31

Table 7. Summary of grid-based aquifer-scale proportions for organic constituent classes

in the California Desert Groundwater Ambient Monitoring and Assessment

(GAMA) study areas. ........................................................................ 51
vii

Conversion Factors, Datums, and Abbreviations and 

Acronyms

Conversion Factors

Inch/foot/mile to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L). One milligram per liter is equivalent to 1 part per million (ppm); 

1 microgram per liter is equivalent to 1 part per billion (ppb); 1 nanogram per liter (ng/L) is 

equivalent to 1 part per trillion (ppt); 1 per mil is equivalent to 1 part per thousand.

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
viii

Conversion Factors, Datums, and Abbreviations and 

Acronyms—Continued

Abbreviations and Acronyms

AL-US U.S. Environmental Protection Agency action level 

GAMA Groundwater Ambient Monitoring and Assessment Program

HAL-US U.S. Environmental Protection Agency lifetime health advisory level 

LRL laboratory reporting level

MCL-CA California Department of Public Health maximum contaminant level 

MCL-US U.S. Environmental Protection Agency maximum contaminant level 

NL-CA California Department of Public Health notification level

RC relative concentration

RSD5-US U.S. Environmental Protection Agency risk-specific dose at a risk factor of 10–5

SMCL-CA California Department of Public Health secondary maximum contaminant level 

SMCL-US U.S. Environmental Protection Agency secondary maximum contaminant level 

U.S. United States

> greater than

< less than

≤ less than or equal to 

Organizations

CDPH California Department of Public Health (Department of Health Services prior to July 1, 2007)

CDWR California Department of Water Resources

LLNL Lawrence Livermore National Laboratory

SWRCB State Water Resources Control Board (California)

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

Selected Chemical Names

NDMA N-nitrosodimethylamine

1,2,3-TCP 1,2,3-trichloropropane

TDS total dissolved solids

VOC volatile organic compound
Status of Groundwater Quality in the California 

Desert Region, 2006–2008: California GAMA 

Priority Basin Project

By Barbara J.M. Dawson and Kenneth Belitz

Abstract

Groundwater quality in six areas in the California 

Desert Region (Owens, Antelope, Mojave, Coachella, 

Colorado River, and Indian Wells) was investigated as part 

of the Priority Basin Project of the Groundwater Ambient 

Monitoring and Assessment (GAMA) Program. The GAMA 

Priority Basin Project is being conducted by the California 

State Water Resources Control Board in collaboration with the 

U.S. Geological Survey (USGS) and the Lawrence Livermore 

National Laboratory. 

The six Desert studies were designed to provide a 

spatially unbiased assessment of the quality of untreated 

groundwater in parts of the Desert and the Basin and Range 

hydrogeologic provinces, as well as a statistically consistent 

basis for comparing groundwater quality to other areas in 

California and across the Nation. Samples were collected 

by the USGS from September 2006 through April 2008 

from 253 wells in Imperial, Inyo, Kern, Los Angeles, Mono, 

Riverside, and San Bernardino Counties. Two-hundred wells 

were selected using a spatially distributed, randomized gridbased method to provide a spatially unbiased representation of 

the study areas (grid wells), and fifty-three wells were sampled 

to provide additional insight into groundwater conditions 

(additional wells).

The status of the current quality of the groundwater 

resource was assessed based on data from samples analyzed 

for volatile organic compounds (VOCs), pesticides, and 

inorganic constituents such as major ions and trace elements. 

Water-quality data from the California Department of Public 

Health (CDPH) database also were incorporated in the 

assessment. The status assessment is intended to characterize 

the quality of untreated groundwater resources within the 

primary aquifer systems of the Desert Region, not the treated 

drinking water delivered to consumers by water purveyors. 

The primary aquifer systems (hereinafter, primary aquifers) 

in the six Desert areas are defined as that part of the aquifer 

corresponding to the perforation intervals of wells listed in the 

CDPH database.

Relative-concentrations (sample concentration 

divided by the benchmark concentration) were used as the 

primary metric for evaluating groundwater quality for those 

constituents that have Federal and (or) California benchmarks. 

A relative-concentration (RC) greater than (>) 1.0 indicates 

a concentration above a benchmark, and an RC less than or 

equal to (≤) 1.0 indicates a concentration equal to or below 

a benchmark. Organic and special-interest constituent RCs 

were classified as “low” (RC ≤ 0.1), “moderate” (0.1 < RC 

≤ 1.0), or “high” (RC > 1.0). Inorganic constituent RCs were 

classified as “low” (RC ≤ 0.5), “moderate” (0.5 < RC ≤ 1.0), 

or “high” (RC > 1.0). A lower threshold value RC was used 

to distinguish between low and moderate RCs for organic 

constituents because these constituents are generally less 

prevalent and have smaller RCs than inorganic constituents.

Aquifer-scale proportion was used as the primary metric 

for evaluating regional-scale groundwater quality. High 

aquifer-scale proportion was defined as the percentage of the 

area of the primary aquifers with an RC greater than 1.0 for 

a particular constituent or class of constituents; percentage 

is based on an areal rather than a volumetric basis. Moderate 

and low aquifer-scale proportions were defined as the 

percentage of the primary aquifers with moderate and low 

RCs, respectively. Two statistical approaches—grid-based 

and spatially weighted—were used to evaluate aquiferscale proportions for individual constituents and classes of 

constituents. Grid-based and spatially weighted estimates 

were comparable in the Desert Region (within 90 percent 

confidence intervals). 

The status assessment determined that one or more 

inorganic constituents with health-based benchmarks had high 

RCs in 35.4 percent of the Desert Region’s primary aquifers, 

moderate RCs in 27.4 percent, and low RCs in 37.2 percent. 

The inorganic constituents with health-based benchmarks 

having the largest high aquifer-scale proportions were arsenic 

(17.8 percent), boron (11.4 percent), fluoride (8.9 percent), 

gross-alpha radioactivity (6.6 percent), molybdenum 

(5.7 percent), strontium (3.7 percent), vanadium (3.6 percent), 

uranium (3.2 percent), and perchlorate (2.4 percent). Inorganic 

constituents with non-health-based benchmarks were also 

detected at high RCs in 18.6 percent and at moderate RCs in 

16.0 percent of the Desert Region’s primary aquifers.
2 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

In contrast, organic constituents had high RCs in only 

0.3 percent of the Desert Region’s primary aquifers, moderate 

in 2.0 percent, low in 48.0 percent, and were not detected in 

49.7 percent of the primary aquifers in the Desert Region. 

Of 149 organic constituents analyzed for all six study areas, 

42 constituents were detected. Six organic constituents, 

carbon tetrachloride, chloroform, 1,2-dichloropropane, 

dieldrin, 1,2-dichloroethane, and tetrachloroethene, were 

found at moderate RCs in one or more of the grid wells. One 

constituent, N-nitrosodimethylamine, a special-interest VOC, 

was detected at a high RC in one well. Thirty-nine organic 

constituents were detected only at low concentrations. Three 

organic constituents were frequently detected (in more than 

10 percent of samples from grid wells): chloroform, simazine, 

and deethylatrazine. 

Introduction 

Groundwater composes nearly half of the water used for 

drinking-water supply in California (Hutson and others, 2004). 

To assess the quality of ambient groundwater in aquifers 

used for drinking-water supply and to establish a baseline 

groundwater-quality monitoring program, the State Water 

Resources Control Board (SWRCB), in collaboration with 

the U.S. Geological Survey (USGS) and Lawrence Livermore 

National Laboratory (LLNL), implemented the Groundwater 

Ambient Monitoring and Assessment (GAMA) Program 

(http://www.waterboards.ca.gov/gama). The statewide GAMA 

Program currently consists of three projects: GAMA Priority 

Basin Project, conducted by the USGS (http://ca.water.usgs.

gov/gama/); GAMA Domestic Well Project, conducted by the 

SWRCB; and GAMA Special Studies, conducted by LLNL. 

On a statewide basis, the Priority Basin Project focused 

primarily on the deeper portion of the groundwater resource, 

and the SWRCB Domestic Well Project generally focused on 

the shallower aquifer systems. The primary aquifer systems in 

some areas may be at less risk of contamination than shallower 

or deeper parts of the groundwater systems. As a result, 

concentrations of some contaminants in wells screened in the 

(deeper) primary aquifer system could be lower or higher than 

those in shallower (Nolan and Hitt, 2006; Zogorski and others, 

2006) or deeper wells. 

The SWRCB initiated the GAMA Program in 2000 in 

response to a legislative mandate (Supplemental Report of the 

1999 Budget Act 1999–00 Fiscal Year). The GAMA Priority 

Basin Project was initiated in response to the Groundwater 

Quality Monitoring Act of 2001 {Section 10780-10782.3 

of the California Water Code, Assembly Bill 599} to assess 

and monitor the quality of groundwater in California. The 

GAMA Priority Basin Project is a comprehensive assessment 

of statewide groundwater quality designed to help better 

understand and identify risks to groundwater resources, and 

to increase the availability of information about groundwater 

quality to the public. For the Priority Basin Project, the USGS, 

in collaboration with the SWRCB, developed the monitoring 

plan to assess groundwater basins through direct and other 

statistically reliable sample approaches (Belitz and others, 

2003; State Water Resources Control Board, 2003). Additional 

partners in the GAMA Priority Basin Project include the 

California Department of Public Health (CDPH), California 

Department of Pesticide Regulation (CDPR), California 

Department of Water Resources (CDWR), local water 

agencies, and well owners (Kulongoski and Belitz, 2004). 

The range of hydrologic, geologic, and climatic 

conditions that exist in California should be considered in 

an assessment of groundwater quality. Belitz and others 

(2003) partitioned the State into 10 hydrogeologic provinces, 

each with distinctive hydrologic, geologic, and climatic 

characteristics (fig. 1). All of these hydrogeologic provinces 

include groundwater basins and subbasins designated by the 

CDWR (California Department of Water Resources, 2003). 

Groundwater basins generally consist of relatively permeable, 

unconsolidated deposits of alluvial or volcanic origin. Eighty 

percent of California’s approximately 16,000 public-supply 

wells are located in designated groundwater basins (Belitz 

and others, 2003). Groundwater basins and subbasins were 

prioritized for sampling on the basis of the number of 

public-supply wells, with secondary consideration given 

to municipal groundwater use, agricultural pumping, the 

number of historically leaking underground fuel tanks, and 

registered pesticide applications (Belitz and others, 2003). The 

116 priority basins, plus additional areas outside of defined 

groundwater basins, were grouped into 35 study units, which 

include approximately 95 percent of public-supply wells 

in California. 

Purpose and Scope

The purposes of this report are to (1) describe the 

hydrogeologic setting of six Desert areas (refered to in this 

report as the Desert Region) studied as part of the Priority 

Basin Project (fig. 1), and (2) provide a status assessment of 

the current quality of groundwater in the primary aquifers in 

the Desert Region.

This report is one in a series of USGS reports presenting 

the status of current water-quality conditions in GAMA study 

areas. Five USGS data-series reports (Densmore and others, 

2009; Goldrath and others, 2009, 2010; Mathany and Belitz, 

2009; Schmitt and others, 2009) provide tabulated results of 

water-quality analyses for samples collected by the Priority 

Basin Project in the Desert Region. 

Subsequent reports will address the relation of 

groundwater quality to selected explanatory factors and to the 

change in groundwater quality over time with respect to these 

water-quality assessments. This report describes water-quality 

conditions in the Owens Valley, Antelope, Mojave, Coachella, 

Colorado River, and Indian Wells GAMA study areas (fig. 1). 
Introduction 3

sac11-0428_fig 01

124° 122° 120° 118° 116° 114°

42°

40°

38°

36°

34°

32°

Cascades and

Modoc Plateau

Sierra

Nevada

Central

Valley

South

Coast

Ranges Basin and Range

Desert

San Diego

Drainages

Transverse and Selected 

Peninsular Ranges

North

Coast

Ranges

Klamath

Mountains

PACIFIC OCEAN

OREGON

NEVADA

MEXICO

ARIZONA

Sacramento

San Francisco

Los Angeles

San Diego

Coachella

Colorado

River

Colorado

River

Colorado

River

Mojave

Owens Valley

Antelope

Indian Wells

0

0 50 100 200 Kilometers

50 100 200 Miles

Shaded relief derived from from U.S. Geological Survey

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Provinces from Belitz and others, 2003

Figure 1. Locations of the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study 

areas and California hydrogeologic provinces.
4 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

Three additional study areas in the Desert hydrogeologic 

province, the Central Desert, Low-Use Basins, and the 

Borrego Springs areas, will be discussed in a future report. 

The status assessment in this report includes analyses 

of water-quality data from 200 wells selected for sampling 

by the USGS within spatially distributed grid cells across the 

Desert Region, referred to as USGS-grid wells (table B1). 

Most of these are public water-supply wells (PSWs), but the 

USGS-grid wells also include other well types with similar 

perforation depth intervals. Samples were collected from these 

wells for analysis of constituents such as volatile organic 

compounds (VOCs) and pesticides, and inorganic constituents 

such as major ions and trace elements. Water-quality data 

from the CDPH database were also used to supplement data 

collected by USGS for the GAMA Program. The 200 USGSgrid-well samples were supplemented with 51 samples from 

the CDPH database to provide data in 251 grid cells (table B1) 

for the status assessment. The resulting set of USGS-grid data 

and selected CDPH data was considered to be representative 

of the primary aquifers in the Desert Region; the primary 

aquifers are defined as that part of the aquifer corresponding 

to the perforation intervals of wells listed in the CDPH 

database for the Desert Region. GAMA status assessments are 

designed to provide a statistically robust characterization of 

groundwater quality in the primary aquifers at the basin scale 

(Belitz and others, 2003). The statistically robust design also 

allows for comparison between basins and for synthesis of 

results at regional and statewide scales.

 For the purposes of providing context, the water-quality 

data discussed in this report were compared to State and 

Federal health-based and non-health-based drinking-water 

benchmarks. The assessments in this report are intended to 

characterize the quality of untreated groundwater resources 

in the primary aquifers within the GAMA study areas, 

not the drinking water delivered to consumers by water 

purveyors. After withdrawal from the ground, water typically 

is treated, disinfected, and (or) blended with other waters 

to maintain acceptable water quality. Benchmarks apply to 

treated drinking water that is served to the consumer, not to 

untreated groundwater. 

Water-quality data for samples collected by the USGS 

for the GAMA Program in the Desert Region and details of 

sample collection, analysis, and quality-assurance procedures 

are presented by Densmore and others (2009), Goldrath 

and others (2009, 2010), Mathany and Belitz (2009), and 

Schmitt and others (2009). Utilizing that same data, this report 

describes methods used in designing the sampling network, 

identifying CDPH data for use in the status assessment, and 

estimating aquifer-scale proportions (Belitz and others, 2010).

Hydrogeologic Setting and Description of 

Study Areas 

The study areas discussed in this report cover 

approximately 6,050 square miles (mi2) (15,670 square 

kilometers, km2) in the Desert and the Basin and Range 

hydrogeologic provinces defined by Belitz and others (2003) 

(fig. 1). Together, these areas compose the Desert Region 

that is the subject of this report. The Desert hydrogeologic 

province occupies the southeastern corner of California and 

is the largest of the 10 hydrogeologic provinces in California 

(Belitz and others, 2003). It is bounded on the north by the 

Sierra Nevada and Basin and Range hydrogeologic provinces, 

to the east by the Colorado River, to the south by the U.S./

Mexico border, and to the west by the crystalline rocks of 

the San Gabriel Mountains, San Bernardino Mountains, and 

the Peninsular Ranges of Southern California. The Basin and 

Range hydrogeologic province (Belitz and others, 2003) is 

located in the eastern part of California (fig. 1). It is bounded 

to the northeast by the California-Nevada State line, to the 

west by the crystalline rocks of the Sierra Nevada, and to the 

south by the Desert hydrogeologic province. 

The climate varies from semiarid to arid, with average 

precipitation amounts ranging from 8 inches per year in the 

north (Owens Valley) to less than 1 inch per year in the south 

(Yuma area in the Colorado River study area) (PRISM Group, 

Oregon State University, 2007). Northern Owens Valley is 

in the Great Basin Desert; southern Owens Valley and the 

Indian Wells, Antelope, and Mojave study areas are located 

in the Mojave Desert (Duell, 1987; Berenbrock and Martin, 

1991; Putnam and Smith, 1995, p. 4; Izbicki and others, 

2000). The Coachella and Colorado River study areas are 

located in the Sonoran Desert, in the part locally known as the 

Colorado Desert (Phillips and Comus, 2000, p. 14). Except 

for the Colorado River, all of the study areas have internal 

surface-water drainages, with streamflow originating in the 

surrounding mountains or along valley edges and flowing to 

dry lake beds. The Colorado River study area includes three 

separate groundwater basins along the Colorado River. The 

Desert study areas are dominated by natural land use, but 

include some urban and agricultural areas (figs. 2 and 3). 

The aquifers are made up of alluvium with highly variable 

lithology from surrounding mountains. 
Introduction 5

sac11-0428_fig 02

All grid points with USGS data. Land use within a 500-meter radius.

All grid points with CDPH data. Land use within a 500-meter radius.

All additional data points with USGS data. Land use within a 500-meter radius.

Owens Valley

Indian Wells

Coachella

Colorado River

Antelope

Mojave

Percent Natural

Percent Urban

Percent Agricultural

100 80 60 40 20 0

0

20

40

60

80

100 0

20

40

60

80

100

Study Area

EXPLANATION

Grid data points,

land use within a 

500-meter radius 

All CDPH data points,

land use within a 

500-meter radius

Figure 2. Proportions of urban, agricultural, and natural land use in the California Desert Region Groundwater 

Ambient Monitoring and Assessment (GAMA) study areas and within a 500-meter radius of data points in those 

study areas.
6 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 03

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

NEVADA

CALIFORNIA

ARIZONA

ARIZONA

Figure 3. General land use from the 1990s in the California Desert Region Groundwater Ambient Monitoring and 

Assessment (GAMA) study areas.
Introduction 7

Owens Valley

The Owens Valley study area (OV) covers about 

1,030 mi2 in Mono and Inyo Counties and includes the Owens 

Valley CDWR groundwater basin (California Department of 

Water Resources, 2003). OV is bounded on the west by the 

Sierra Nevada Mountains, on the east by the Inyo and White 

Mountains, on the south by the Coso Range, and on the north 

by the Volcanic Tablelands (California Department of Water 

Resources, 2004a) (fig. 4A). 

The primary aquifer system in OV is contained in the 

alluvial valley-fill deposits (fig. 4A), and consists of an 

upper unconfined unit that is up to 100 feet thick and a lower 

confined unit that is from 10 to 500 feet (ft) thick; along the 

edges of the valley, there is no confining unit, and both units 

form one aquifer. Groundwater recharge is primarily from 

tributary streams, mountain-front runoff, canals, ditches, 

ponds, and irrigation drainage. The general direction of 

groundwater flow is from north to south (Danskin, 1998) 

(fig. 5). South of the city of Big Pine, a bedrock high separates 

the northern Bishop Basin from the Owens Lake Basin to 

the south; groundwater from the Bishop Basin discharges 

over the bedrock high into the Owens Lake Basin. Several 

faults and volcanic deposits restrict groundwater flow locally. 

Groundwater discharge is primarily through pumping or 

flowing wells, evapotranspiration, and underflow to the Owens 

Lake dry lakebed (Danskin, 1998). 

Antelope 

The Antelope study area (ANT) covers approximately 

1,600 mi2 in Kern and Los Angeles Counties with small 

portions in San Bernardino County, at the northwestern part of 

the Desert hydrogeologic province (figs. 1 and 4B). The study 

area includes one groundwater basin (the Antelope Valley 

groundwater basin), as defined by the CDWR (California 

Department of Water Resources, 2003). ANT is bounded to 

the northwest by the Tehachapi Mountains, to the south by the 

San Gabriel Mountains, and to the north and east by several 

fault systems and low-lying bedrock hills (Londquist and 

others, 1993; Rewis, 1995; California Department of Water 

Resources, 2004b) (fig. 4B). 

The primary aquifers in ANT are in alluvium of Pliocene 

and Pleistocene age (Durbin, 1978; Duell, 1987; Sneed and 

Galloway, 2000; Nishikawa and others, 2001; Leighton and 

Phillips, 2003). In the southern part of the study area, near 

the mountain front, the primary aquifer is the upper aquifer 

described by Leighton and Phillips (2003); in previous work 

(such as Durbin, 1978, and Duell, 1987), this was referred 

to as the “principal aquifer.” The upper aquifer consists of 

interbedded clay, silt, sand, and gravel and is unconfined. In 

the northern part of the study area, the primary aquifer is the 

confined middle aquifer, which is below the upper aquifer 

and a confining layer of lacustrine deposits (Sneed and 

Galloway, 2000; Nishikawa and others, 2001; Leighton and 

Phillips, 2003). The main source of groundwater recharge 

is runoff from the San Gabriel and Tehachapi Mountains; 

additional sources are drainage from irrigation and septic 

systems. Imported water from the California State Water 

Project is used for irrigation (Duell, 1987). The general 

direction of groundwater flow is north and east, away from 

the mountains, toward the dry lakebeds and pumping (fig. 5) 

(Leighton and Phillips, 2003). Several faults in the study 

area act as partial barriers to groundwater flow (Leighton and 

Phillips, 2003). Groundwater discharge currently is mainly to 

pumping wells; prior to the start of groundwater pumping in 

the late 1800s, groundwater discharge was predominantly by 

evapotranspiration and as subsurface flow into Fremont Valley 

to the north (Nishikawa and others, 2001). 

Mojave

The Mojave study area (MOJ) includes four contiguous 

CDWR-defined groundwater basins: the Upper, Middle, 

and Lower Mojave River Basins, and the El Mirage Valley 

Basin (California Department of Water Resources, 2004c–f). 

These basins define the extent of MOJ and cover an area of 

approximately 1,500 mi2 in San Bernardino County, with 

small portions in Kern and Los Angeles Counties (figs. 1

and 4C). The MOJ study area is bounded on the west by the 

Antelope groundwater basin, the Shadow Mountains, and 

the Kramer Hills. It is bordered to the north by the Harper 

Valley groundwater basin, Iron Mountain, the Coyote Lake 

Valley groundwater basin, and the Calico Mountains. The 

eastern boundaries of the study area include the Coyote Lake 

groundwater basin and the Cady, Newberry, Ord, and Granite 

Mountains. The southernmost border of MOJ is formed by the 

San Gabriel and San Bernardino Mountains. 

The primary aquifers in MOJ are the flood-plain aquifer 

and the regional aquifer. The flood-plain aquifer consists of 

Holocene-age deposits located in and adjacent to the current 

flood plain of the Mojave River. The regional aquifer consists 

of older Pleistocene–Pliocene-age deposits of the Mojave 

River that extend throughout the study area and are beneath 

the flood-plain aquifer. The main source of recharge to both 

aquifers is runoff from the San Bernardino and San Gabriel 

Mountains, mostly through the Mojave River channel; 

additional sources are irrigation, treated sewage effluent, 

septic systems, and imported water from Northern California 

delivered by the California aqueduct. Groundwater flow 

is generally north and then east, away from the mountain 

front and following the Mojave River (fig. 5). Groundwater 

discharge is mainly through pumping and evapotranspiration, 

and possibly as underflow through Afton Canyon. Historically, 

groundwater discharged to the dry lakebeds, but pumping 

beginning in the late 1800s has changed flow directions away 

from the dry lakes and decreased the amount of groundwater 

discharging to the dry lakebeds (Stamos and others, 2001).
8 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 04a

EXPLANATION

Lake

Dry Lake Bed

Alluvium

Hard Rock

Owens grid cells

Water bodies

Stream or river

Grid wells

USGS data

USGS and CDPH data

CDPH data

Additional wells

USGS data

CDPH data

119°15’ 118°45’ 118°30’ 118°15’ 117°45’

38°

37°45’

37°15’

36°45’

36°15’

36°30’

37°

37°30’

119° 118° 117°30’ 117°15’

0

0 5 10 20 KILOMETERS

5 10 20 MILES

INYO MOUNTAINS

SIERRA NEVADA

MOUNTAINS

TABLELANDS

VOLCANIC

WHITE

MOUNTAINS

NEVADA

Bishop

Big Pine

COSO

RANGE

Owens Lake Basin

Bishop Basin

Owens Dry Lake Bed

TUOLUMNE

CO

MONO CO

INYO CO

TULARE CO

FRESNO CO

MADERA CO

Owens River Owens River

A

Figure 4. Geology and locations of grid cells and grid wells used for the Groundwater Ambient Monitoring and 

Assessment (GAMA) Program in the California Desert Region study areas, 2006–2008: (A) Owens Valley, 

(B) Antelope Valley, (C) Mojave, (D) Coachella Valley, (E–G) Colorado River, and (H) Indian Wells Valley. 
Introduction 9

Figure 4.—Continued

sac11-0428_fig 04b

0

0 5 10 20 KILOMETERS

5 10 20 MILES

TEHACHAPI MOUNTAINS

SAN GABRIEL MOUNTAINS

KERN CO

LOS ANGELES CO

SAN BERNARDINO CO

EXPLANATION

Lake

Dry Lake Bed

Alluvium

Hard Rock

Antelope grid cells

Antelope Valley 

groundwater basin

Water bodies

Stream or river

Grid wells

USGS data

USGS and CDPH data

CDPH data

Additional wells

USGS data

CDPH data

118°45’

35°15’

34°45’

34°30’

34°15’

35°

B 118°30’ 118°15’ 118° 117°45’
10 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 04c

C

1050 20 KILOMETERS

50 10 20 MILES

EXPLANATION

Lake

Dry Lake Bed

Alluvium

Hard Rock

Mojave grid cells

Mojave groundwater 

basin

Water bodies

Stream or river

Grid wells

USGS data

USGS and CDPH data

CDPH data

Additional wells

USGS data

CDPH data

117°45’

35°15’

34°45’

34°30’

34°15’

35°

117°30’ 117°15’ 117° 116°45’ 116°30’

NEWBERRY

MOUNTAINS

MOUNTAINS

CALICO

MOUNTAINS

CADY

MOUNTAINS

ORD

GRANITE

MOUNTAINS

SHADOW

MOUNTAINS

IRON

MOUNTAIN

KRAMER

HILLS

SAN BERNARDINO

MOUNTAINS

SAN GABRIEL

MOUNTAINS

KERN CO SAN BERNARDINO CO

LOS ANGELES

CO

Harper Valley 

Groundwater Basin

Coyote Lake Valley 

Groundwater Basin

Lower Mojave Groundwater Basin

Middle Mojave

Groundwater Basin

Antelope

Groundwater 

Basin El Mirage

Groundwater 

Basin

Upper 

Mojave

Groundwater 

Basin

Mojave RiverMojave River

Mojave RiverMojave River

AFTON

CANYON

Figure 4.—Continued
Introduction 11

sac11-0428_fig 04d

D

0 5 10 20 KILOMETERS

0 5 10 20 MILES

EXPLANATION

Lake

Dry Lake Bed

Alluvium

Hard Rock

Coachella grid cells

Water bodies

Stream or river

Grid wells

USGS data

USGS and CDPH data

CDPH data

Additional wells

USGS data

CDPH data

116°45’ 116°30’

33°45’

33°30’

33°15’

34°

116°15’ 116°

RIVERSIDE CO

SAN DIEGO CO IMPERIAL CO

SAN BERNARDINO CO

SALTON 

SEA

Palm Springs

Whitewater RiverWhitewater River

SAN BERNARDINO

MOUNTAINS

MECCA

SAN JACINTO

HILLS

MOUNTAINS

SANTA ROSA

MOUNTAINS

Figure 4.—Continued
12 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 04e

10 MILES

0 52.5 10 KILOMETERS

0 2.5 5

35°

34°45'

E

EXPLANATION

Lake

Alluvium

Hard Rock

Colorado River grid cells

Colorado River 

Groundwater basin

Water bodies

Stream or river

Grid wells

USGS data

Additional wells

USGS data

CDPH data

114°45’ 114°30’

SAN BERNARDINO CO

SACRAMENTO MOUNTAINS

DEAD

MOUNTAINS

CHEMEHUEVI

MOUNTAINS

Needles Valley 

Groundwater Basin

Colorado River Colorado River

ARIZONA

Figure 4.—Continued
Introduction 13

sac11-0428_fig 04f

52.50 10 KILOMETERS

52.50 10 MILES

EXPLANATION

Dry Lake Bed

Alluvium

Hard Rock

Colorado River grid cells

Colorado River 

Groundwater basin

Stream or river

Grid wells

USGS data

Additional wells

USGS data

CDPH data

114°45’

33°45’

33°30’

115° 114°30’

Blythe

BIG MARIA

MOUNTAINS

MCCOY MOUNTAINS

MULE MOUNTAINS

Palo Verde Mesa 

Groundwater Basin

Palo Verde Valley 

Groundwater Basin

Colorado River Colorado River

RIVERSIDE CO

IMPERIAL CO

PALO VERDE

MOUNTAINS

ARIZONA

F

Figure 4.—Continued
14 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 04g

0 2.5 5 10 MILES

2.50 5 10 KILOMETERS

EXPLANATION

Lake

Alluvium

Hard Rock

Colorado River grid cells

Colorado River 

groundwater basin

Water bodies

Stream or river

Grid wells

USGS data

Additional wells

CDPH data

33°

32°45’

114°45’ 114°30’

CHOCOLATE MOUNTAINS

Yuma Valley 

Groundwater Basin

Ogilby Valley 

Groundwater Basin

Ogilby Valley 

Groundwater Basin

Colorado

River ColoradoRiver

IMPERIAL CO

CARGO

MUCHACHO

MOUNTAINS

ARIZONA

MEXICO

G

Figure 4.—Continued
Introduction 15

sac11-0428_fig 04h

10 MILES

0 52.5 10 KILOMETERS

52.50

EXPLANATION

Lake

Dry Lake Bed

Alluvium

Hard Rock

Indian Wells grid cells

Indian Wells 

groundwater basin

Water bodies

Stream or river

Grid wells

USGS data

USGS and CDPH data

CDPH data

Additional wells

USGS data

CDPH data

118° 117°45' 117°30'

35°45'

35°30'

Ridgecrest

SIERRA NEVADA

 MOUNTAINS

ARGUS RANGE

COSO RANGE

EL PASO MOUNTAINS

TULARE CO INYO CO

KERN CO

SAN BERNARDINO CO

China

Lake

H

Figure 4.—Continued
16 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

Coachella 

The Coachella study area (COA), approximately 

820 mi2, is located almost entirely in Riverside County, but 

sections extend into San Bernardino, San Diego, and Imperial 

Counties (fig. 4D). COA includes the Coachella Valley 

CDWR-defined groundwater basin, which is made up of the 

Desert Hot Springs, Indio, Mission Creek, and San Gorgornio 

Pass subbasins (California Department of Water Resources, 

2004g–j). The Coachella Valley is the northern expression 

of the Salton Trough, a landward extension of the Gulf of 

California (Goldrath and others, 2009). The San Bernardino 

Mountains and the Mecca Hills form the northern and the 

eastern boundaries of the valley; the San Jacinto and Santa 

Rosa Mountains bound the valley to the south and west; the 

southeastern boundary for the COA is the Salton Sea.

The primary aquifer system in the COA is in the 

unconsolidated, Pleistocene-Holocene valley fill. Throughout 

the valley, many faults in the San Andreas Fault system act 

as barriers to groundwater flow (Tyley, 1974). Groundwater 

flow is generally from the northwest to the southeast 

(fig. 5). Groundwater recharge is primarily runoff from the 

surrounding mountains, local precipitation, irrigation return, 

streamflow from the Whitewater River and other rivers and 

creeks (Tyley, 1974), and from imported Colorado River water 

supplied to the Whitewater River spreading grounds near Palm 

Springs (California Department of Water Resources, 2004h). 

Groundwater discharge is to evapotranspiration, to underflow 

to the Salton Sea and Imperial Valley areas, and to pumping 

wells (Tyley, 1974).

Colorado River

The Colorado River study area (COL) includes 

three separate subareas: Needles, Palo Verde, and Yuma 

(figs. 4E–G). The exterior boundaries of the study area 

correspond to four CDWR-delineated groundwater basins: 

Needles Valley, Palo Verde Mesa, Palo Verde Valley, and 

Yuma Valley (California Department of Water Resources, 

2004k–n). The Needles Valley groundwater basin is 138 mi2

and underlies the Mohave Valley in the eastern portion of San 

Bernardino County (fig. 4E). The basin is bounded by the 

Colorado River on the east, the non-water-bearing rocks of the 

Dead Mountains to the northwest, the Sacramento Mountains 

to the southwest, and the Chemehuevi Mountains to the south 

(Bishop, 1963). The Palo Verde groundwater basins, which 

include the CDWR Palo Verde Mesa and Palo Verde Valley 

groundwater basins, occupy 553 mi2 and underlie Parker 

Valley in the eastern portion of Riverside County (fig. 4F). 

The basin is bounded by the Colorado River to the east, the 

non-water-bearing rocks of the Big Maria Mountains to the 

north, the McCoy and Mule Mountains to the west, and the 

Palo Verde Mountains to the South (Jennings, 1967; California 

Department of Water Resources, 1979). The Yuma Valley 

groundwater basin is approximately 193 mi2 and underlies 

a southeast-trending valley in Imperial County (California 

Department of Water Resources, 2004n) (fig. 4G). The basin is 

bounded by the Colorado River to the east and south, the nonwater-bearing rocks of the Cargo Muchacho Mountains on the 

west, and the Chocolate Mountains to the north and northeast. 

The primary aquifers in each of the COL subareas 

are contained in alluvial deposits of the Colorado River 

(figs. 4E–G). These deposits consist of sand, gravel, silt, and 

clay laid down by the Colorado River, ranging from 100 to 

600 ft thick. In the Palo Verde basins, near Blythe, CA, some 

deep wells tap the Bouse Formation beneath the alluvium, 

which is made up of interbedded clay, silt, and sand from 

the Colorado River. In the Needles and Palo Verde basins, 

the main source of groundwater recharge is the Colorado 

River (fig. 5). Minor recharge is from irrigation return flows, 

local precipitation/runoff, and underflow from basins to the 

west (Metzger and Loeltz, 1973; California Department of 

Water Resources, 2004k–m). Groundwater discharge is to 

pumping wells, evapotranspiration, and occasionally to the 

Colorado River. In the Yuma basin, groundwater recharge is 

from subsurface inflow from the Ogilby Valley groundwater 

basin to the west and from mountain runoff; groundwater 

generally flows southeast and discharges to the Colorado River 

(California Department of Water Resources, 2004n) (fig. 5). 

Indian Wells 

The Indian Wells study area (IW) covers about 597 mi2

in Inyo, Kern, and San Bernardino Counties and includes the 

Indian Wells Valley CDWR groundwater basin (California 

Department of Water Resources, 2004o). Indian Wells Valley 

is bounded on the west by the southern terminus of the Sierra 

Nevada, on the north by a low ridge of volcanic rocks and the 

Coso Range, on the east by the Argus Range, and on the south 

by the El Paso Mountains (fig. 4H). 

The primary aquifer in IW is the “deep aquifer” described 

in Berenbrock and Schroeder (1994), which consists of 

alluvial deposits that occupy most of the valley (fig. 4H) 

and are up to 1,000 ft thick. In the center of the valley, 

beneath China Lake and other dry lakebeds, the deep aquifer 

is overlain by a shallow aquifer that consists of lacustrine, 

alluvial, playa, and sand-dune deposits. Groundwater flow 

is generally from the sides of the valley toward the dry lake 

beds (Berenbrock and Schroeder, 1994) (fig. 5). Groundwater 

recharge is primarily from infiltration of surface runoff from 

the Sierra Nevada to the west, with minor contribution by 

runoff from the mountains to the north, east, and south, 

and locally from irrigation. Prior to groundwater pumping 

in the 1920s, groundwater discharge from the deep aquifer 

was to the shallow aquifer. Starting in the late 1900s and 

continuing to the present, discharge was also to pumping wells 

in the southern parts of the Valley, and cones of depression 

have formed in the deep aquifer near Ridgecrest. Because 

of this increase in pumping, the shallow aquifer is now a 

source of recharge to the deep aquifer (Berenbrock and 

Schroeder, 1994). 
Introduction 17

sac11-0428_fig 05

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 0 10 MILES

0 10 KILOMETERS 0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Direction of groundwater flow

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

EXPLANATION

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 5. Generalized directions of groundwater flow in the California Desert Region Groundwater Ambient Monitoring 

and Assessment (GAMA) study areas, 2006–2008.
18 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

Methods 

The status assessment was designed to provide a 

spatially unbiased assessment of untreated groundwater 

quality in the primary aquifer systems. This section describes 

the methods used for (1) defining levels of groundwater 

quality, (2) assembling the datasets used for the assessment, 

(3) determining which constituents will be discussed in this 

assessment, and (4) calculating aquifer-scale proportions for 

particular constituents or classes of constituents. 

The primary metric for defining levels of groundwater 

quality in this report is relative concentration (RC), which 

compares groundwater chemistry to regulatory and nonregulatory benchmarks used to evaluate drinking-water 

quality. A subset of constituents was selected for this 

assessment on the basis of objective criteria using these 

RCs. Groundwater-quality data collected by the USGS for 

the GAMA Program (USGS-GAMA) and data compiled in 

the CDPH database were used in the status assessment. Two 

statistical methods based on spatially unbiased grids with 

equal-area cells in each study area were used to calculate 

aquifer-scale proportions (Belitz and others, 2010): (1) 

the “grid-based” method, which uses one value per cell to 

represent groundwater quality, and (2) the “spatially weighted” 

method, which uses all available values per cell.

The CDPH database contains historical records from 

more than 25,000 wells, necessitating targeted retrievals to 

effectively access water-quality data. The CDPH data were 

used in three ways in the status assessment: (1) to fill in 

gaps in USGS-GAMA data for the grid-based calculations 

of aquifer-scale proportions, (2) to identify constituents 

for inclusion in the status assessment, and (3) to provide 

most of the data used in the spatially weighted calculations 

of aquifer-scale proportions. Methods used for selection 

of CDPH data for these three purposes are described 

in appendix A.

Relative-Concentrations and 

Water-Quality Benchmarks

Concentrations of constituents in the status assessment

are presented as RCs:

Sampleconcentration Relative-concentration

Benchmark concentration =

Relative-concentrations less than 1.0 indicate sample 

concentrations that are less than the benchmark, and RCs 

greater than 1.0 indicate sample concentrations greater than 

the benchmark. The use of RCs standardized to the benchmark 

of each constituent facilitates comparisons between 

constituents that have water-quality benchmarks at different 

concentrations, even for benchmarks that differ by several 

orders of magnitude.

Regulatory and non-regulatory benchmarks used 

for drinking water apply to the water that is served to the 

consumer, not to the untreated groundwater that was analyzed 

in this study. However, to provide some context for the results, 

concentrations of constituents measured in the untreated 

groundwater were compared with benchmarks established 

by the U.S. Environmental Protection Agency (USEPA) and 

CDPH (California Department of Public Health, 2008, 2010a, 

2010b; U.S. Environmental Protection Agency, 2011), which 

are listed in appendix B, tables B2A–F. The benchmarks 

used for each constituent were selected in the following order 

of priority:

1. Regulatory, health-based CDPH and USEPA maximum 

contaminant levels (MCL-CA and MCL-US) and action 

levels (AL-US). 

2. Non-regulatory CDPH and USEPA secondary maximum 

contaminant levels (SMCL-CA and SMCL-US). 

For constituents with both recommended and upper 

SMCL-CA levels, the values for the upper levels were 

used. 

3. Non-regulatory, health-based CDPH notification levels 

(NL-CA), USEPA lifetime health advisory levels 

(HAL-US), and USEPA cancer risk-specific doses for 

1:100,000 (RSD5-US).

For constituents with multiple types of benchmarks, this 

hierarchy may not result in selection of the benchmark with 

the lowest concentration. Additional information on the 

types of benchmarks and listings of the benchmarks for all 

constituents analyzed is provided by Densmore and others 

(2009), Goldrath and others (2009, 2010), Mathany and Belitz 

(2009), and Schmitt and others (2009).

Toccalino and others (2004), Toccalino and Norman 

(2006), and Rowe and others (2007) previously used the ratio 

of measured concentration to a benchmark [either MCLs or 

Health-Based Screening Levels (HBSLs)] and defined this 

ratio as the benchmark quotient. Relative-concentrations 

used in this report are equivalent to the benchmark quotient 

of Toccalino and others (2004) for constituents with 

water-quality benchmarks; however, HBSLs were not 

used in this report because they are not currently used as 

benchmarks by California drinking-water regulatory agencies. 

Relative-concentrations can be computed only for constituents 

with water-quality benchmarks; therefore, constituents lacking 

water-quality benchmarks were not included in the status 

assessment. 

In this report, RCs of constituents were classified into 

high, moderate, and low categories:
Introduction 19

Category

Relative-concentrations 

for organic and 

special-interest 

constituents

Relative-concentrations 

for inorganic 

constituents

High > 1.0 > 1.0

Moderate > 0.1 and < 1.0 > 0.5 and < 1.0

Low < 0.1 < 0.5

The boundary between moderate and low RCs was 

set at 0.1 for organic and special-interest constituents for 

consistency with other studies and reporting requirements 

(U.S. Environmental Protection Agency, 1998; Toccalino and 

others, 2004). In a national survey of water quality in aquifers 

used for public drinking-water supply, Toccalino and others 

(2004) found that organic constituents (pesticides and VOCs) 

were detected at high or moderate benchmark quotients (>0.1) 

in about 10 percent of samples and that, in contrast, inorganic 

constituents (trace elements and radioactive constituents) were 

detected at high or moderate benchmark quotients in about 

80 percent of samples. Therefore, to provide an indication of 

the potential groundwater contamination issues that are of the 

highest and most immediate concern, the boundary between 

“moderate” and “low” RCs was set at 0.5 for inorganic 

constituents in this report.

Concentrations of the man-made organic constituents 

may change rapidly in groundwater; thus, early warning is 

vital for planning and implementing measures to protect 

aquifer systems from further contamination and to mitigate 

existing contamination. Inorganic constituents generally are 

naturally occurring in groundwater, and their concentrations 

generally are stable or change slowly compared to 

concentrations of organic constituents; thus, early warning of 

potential groundwater contamination may be less critical for 

management of potential water-quality problems. By choosing 

a boundary between low and moderate RCs (or benchmark 

quotient) that is greater than 0.1, inorganic constituents can 

be identified from among the many that may be present at 

concentrations approaching benchmarks that may warrant 

more immediate attention from water-resource managers.

Data Used for Status Assessment

 Two datasets were used in the status assessment: data 

from wells sampled by the USGS for the GAMA PBP, and 

data from the CDPH database. Each dataset is described and 

summarized here, with a discussion comparing the USGS and 

CDPH sources presented in appendix C.

Grid Values: USGS Data

The primary data used for the grid-based calculations of 

aquifer-scale proportions were data from grid wells sampled 

by USGS-GAMA. Detailed descriptions of the methods used 

to identify samples and wells are given in Densmore and 

others (2009), Goldrath and others (2009, 2010), Mathany and 

Belitz (2009), and Schmitt and others (2009). Briefly, each 

study area was divided into equal-area grid cells; one well 

was randomly selected to represent each cell (Scott, 1990). 

Wells were selected from the population of wells in statewide 

databases maintained by CDPH and USGS. 

The six Desert study areas contained 251 grid cells, and 

the USGS sampled wells in 200 of those cells (USGS-grid 

wells). Of the 200 USGS-grid wells, 159 were public-supply 

wells also listed in the CDPH database. The other 41 

USGS-grid wells were domestic, irrigation, monitoring, 

industrial, aquaculture, commercial, and recreation-use wells 

perforated at depths similar to the depths of CDPH wells in the 

specified cell or neighboring cells. USGS-grid samples were 

named with an alphanumeric GAMA_ID consisting of a prefix 

identifying the study area and a number indicating the order 

of sample collection (fig. B1A–F, table B1). In the Desert 

Region, the following prefixes were used to indicate study 

areas: ANT, Antelope Valley study area; COA, Coachella 

study area; COL, Colorado River study area; IW, Indian Wells 

study area; MOJ, Mojave study area; and OV, Owens Valley 

study area. 

Groundwater samples collected from USGS-grid wells 

were analyzed for up to 207 constituents (tables B2A–F). 

VOCs, pesticides, tritium, noble gases, perchlorate, and stable 

isotopes of hydrogen and oxygen were analyzed in water 

samples from all wells. Major and minor inorganic ions, 

trace elements, and nutrients were analyzed in samples from 

most wells, and radiochemical constituents, carbon isotopes, 

and NDMA were analyzed in samples from some wells. The 

sample-collection methods, analysis methods, and qualitycontrol data for the constituents listed in tables B2A–F are 

described by Densmore and others (2009), Goldrath and others 

(2009, 2010), Mathany and Belitz (2009), and Schmitt and 

others (2009).

Grid Values: CDPH Data

Of the 251 grid cells in the 6 study areas, 51 cells did 

not have a USGS-grid sample, 71 cells had a USGS-grid 

sample but did not have USGS data for major ions, trace 

elements, nutrients, and radiochemical constituents, and 

129 cells had a USGS-grid sample but did not have USGS 

data for radiochemical constituents. The CDPH database 

was queried to identify wells that could provide the missing 

inorganic and radiochemical data. CDPH wells with samples 

collected within 3 years of the USGS-GAMA sampling 

periods were considered (table 1). If more than one analysis 

for a constituent in a well was available in the 3-year interval, 

then the most recent data were selected. Using this method, 

an additional 15 grid cells were populated with data from the 

CDPH database, and USGS data were supplemented with 

CDPH data in 89 grid cells.
20 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

The decision tree used to identify suitable CDPH samples 

is described in detail in appendix A. Briefly, the first choice 

was to use CDPH data from the same well that was sampled 

by the USGS (“DG” CDPH-grid samples; fig. B1, table B1). 

If the CDPH sample did not have all of the needed data or if 

there was no well sampled by the USGS, another well was 

randomly selected from the CDPH database if it had data for 

the missing constituents (“DPH” CDPH-grid samples). No 

more than one CDPH-grid sample was selected for each cell. 

The combination of the USGS-grid data and the CDPH-grid 

data produced a grid-data network covering 215 of the 

251 grid cells in the 6 study units. 

The CDPH database generally did not contain data for 

all of the missing inorganic constituents for every CDPH-grid 

sample; therefore, the number of values used for the gridbased assessment differed for various inorganic constituents 

(table 2). Although other organizations also collect waterquality data, the CDPH database is the only statewide database 

of groundwater-chemistry data available during this study for 

comprehensive analysis. 

CDPH data were not used to supplement USGS-grid data 

for VOCs, pesticides, or perchlorate for the status assessment. 

A larger number of VOCs and pesticide compounds were 

analyzed for the USGS-GAMA Program than are available 

from the CDPH database. USGS-GAMA collected data for 

84 VOCs and 64 pesticides and pesticide degradates at every 

well (tables B2A and B2B). Laboratory reporting levels used 

for USGS-GAMA analyses of organic constituents typically 

were one to two orders of magnitude lower than the reporting 

levels used for analyses compiled by the CDPH. 

Selection of Constituents for Status Assessment

As many as 207 constituents were analyzed in 

groundwater samples from the Desert study areas; however, 

only a subset of these constituents is evaluated in this report. 

Three criteria were used to select constituents for further 

analysis in the status assessment:

Table 1. Historical and current periods of record available in the California Department of Public Health database in the California 

Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.

Study area Full period of record 

available for use in this report

Current period

(3-year interval prior to 

USGS-GAMA sample collection)

Owens Valley and Indian Wells 08-15-1980 to 09-11-2006 09-11-03 to 09-11-06

Coachella 01-04-1984 to 02-25-2007 02-25-04 to 02-25-07

Colorado River 03-04-1982 to 01-11-2006 01-11-03 to 01-11-06

Antelope Valley 05-02-1980 to 01-27-2008 01-27-05 to 01-27-08

Mojave 04-04-1983 to 02-30-2008 02-03-05 to 02-03-08

1. Constituents detected at high or moderate RCs in the 

CDPH database within the 3-year intervals prior to 

USGS-GAMA sampling periods,

2. Constituents detected at high or moderate RCs in the 

USGS-grid wells or USGS-understanding wells used in 

the status assessment, or

3. Organic constituents with detection frequencies greater 

than 10 percent in the USGS-grid well dataset for a 

particular study unit.

These criteria resulted in the identification of 14 inorganic 

constituents and 3 organic constituents for further evaluation 

in the status assessment. An additional 43 organic 

constituents and 36 inorganic constituents were detected by 

USGS-GAMA and were not selected for further evaluation 

in the status assessment because they either have no 

established benchmarks, or they were only detected at low 

RCs. The remaining constituents that were not detected 

by USGS-GAMA in any of the six study units are listed 

in Densmore and others (2009), Goldrath and others 

(2009, 2010), Mathany and Belitz (2009), and Schmitt and 

others (2009). 

The CDPH database also was used to identify 

constituents that have been reported at high RCs historically. 

The historical period was defined as the earliest record 

maintained in the CDPH database to just prior to the 3-year 

intervals used for the status assessments. Constituent 

concentrations in the CDPH database may have decreased 

from historically high values because of improvement in 

groundwater quality or because of abandonment of wells 

with high concentrations. Historically high constituent 

concentrations in wells in the Desert Region are shown 

in table 3. Constituents with high concentrations only in 

the historical time period (and that were not detected at 

high concentrations in current samples) did not meet the 

criteria for further evaluation in the status assessment and 

are not considered representative of current concerns about 

groundwater quality in the study areas. 
Introduction 21

Table 2. Number of grid wells used for assessment of status of inorganic constituents in the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.[Abbreviations: USGS, U.S. Geological Survey; CDPH, California Department of Public Health]

Constituent

Owens Valley study area 

(60 cells)

Indian Wells study area 

(20 cells)

Coachella study area 

(20 cells)

Colorado River basins study 

area (20 cells)

Antelope study area 

(66 cells)

Mojave study area 

(65 cells)

Number of 

grid cells 

for which 

USGS data 

were used

Number of 

grid cells 

for which 

CDPH data 

were used

Number of 

grid cells 

for which 

USGS data 

were used

Number of 

grid cells 

for which 

CDPH data 

were used

Number of 

grid cells

 for which 

USGS data 

were used

Number of 

grid cells 

for which 

CDPH data 

were used

Number of 

grid cells 

for which 

USGS data 

were used

Number of 

grid cells 

for which 

CDPH data 

were used

Number of 

grid cells 

for which 

USGS data 

were used

Number of 

grid cells 

for which 

CDPH data 

were used

Number of 

grid cells 

for which 

USGS data 

were used

Number of 

grid cells 

for which 

CDPH data 

were used

Trace element, health-based benchmarkAluminum 40 0 13 0 19 0 20 0 18 32 19 22

Antimony 40 0 13 0 19 0 20 0 18 31 19 22

Arsenic 40 0 13 0 19 0 20 0 18 34 19 24

Barium 40 0 13 0 19 0 20 0 18 31 19 22

Beryllium 40 0 13 0 19 0 20 0 18 30 19 22Boron 40 0 13 0 19 0 20 0 18 15 19 17Cadmium 40 0 13 0 19 0 20 0 18 32 19 22Chromium 40 0 13 0 19 0 20 0 18 32 18 20Copper 40 0 13 0 19 0 20 0 18 32 19 23Fluoride 40 0 13 0 19 0 20 0 18 33 19 27Lead 40 0 13 0 19 0 20 0 18 24 19 21Mercury 40 0 13 0 7 3 20 0 0 0 0 0Molybdenum 40 0 13 0 19 0 20 0 18 0 19 0Nickel 40 0 13 0 19 0 20 0 18 32 19 22

Selenium 40 0 13 0 19 0 20 0 18 32 19 22Strontium 40 0 13 0 19 0 20 0 18 0 19 0Thallium 40 0 13 0 19 0 20 0 18 30 19 22Vanadium 40 0 13 0 19 0 20 0 18 14 19 17Radioactive, health-based benchmarkGross-alpha radioactivity 7 10 0 6 7 4 20 0 18 29 19 19Gross-beta radioactivity 7 4 0 0 7 0 20 0 18 3 19 4Radium-226 7 7 0 0 7 0 20 0 18 0 19 0Radium-228 7 0 0 4 7 1 20 0 18 24 19 15Radon-222 7 0 0 0 7 0 19 0 18 0 19 3Uranium 40 0 13 0 19 0 20 0 18 21 19 12
22 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Constituent Owens Valley study area (60 cells) Indian Wells study area (20 cells) Coachella study area (20 cells) Colorado River basins study area (20 cells) Antelope study area (66 cells) Mojave study area (65 cells) Number of grid cells for which USGS data were used Number of grid cells for which CDPH data were used Number of grid cells for which USGS data were used Number of grid cells for which CDPH data were used Number of grid cells for which USGS data were used Number of grid cells for which CDPH data were used Number of grid cells for which USGS data were used Number of grid cells for which CDPH data were used Number of grid cells for which USGS data were used Number of grid cells for which CDPH data were used Number of grid cells for which USGS data were used Number of grid cells for which CDPH data were used Nutrient, health-based benchmark Ammonia, as nitrogen 40 0 13 0 19 0 20 0 18 3 19 0 Nitrate, as nitrogen 40 0 13 0 19 0 20 0 18 36 19 34 Nitrite, as nitrogen 40 0 13 0 19 0 20 0 18 30 19 22 Inorganic, non-health-based benchmarks Chloride 40 0 13 0 19 0 20 0 18 33 19 23 Iron 40 0 13 0 19 0 20 0 18 32 19 24 Manganese 40 0 13 0 19 0 20 0 18 32 19 24 Silver 40 0 13 0 19 0 20 0 18 31 19 21 Sulfate 40 0 13 0 19 0 20 0 18 33 19 23 Total dissolved solids 40 0 13 0 19 0 20 0 18 33 19 23 Zinc 40 0 13 0 19 0 20 0 18 32 19 23 Table 2. Number of grid wells used for assessment of status of inorganic constituents in the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued

[Abbreviations: USGS, U.S. Geological survey; CDPH, California Department of Public Health]
Introduction 23

Table 3. Constituents historically reported in the California Department of Public Health database with high maximum relative-concentrations (above benchmarks) in the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.[The historical period was defined as the earliest record maintained in the CDPH database to just prior to the 3-year intervals sampled by the USGS GAMA Program. Benchmarks and benchmark values as of June 1, 2008. Benchmark type: RSD5-US, U.S. Environmental Protection Agency risk-specific dose at a risk factor of 10–5; MCL-CA, California Department of Public Health maximum contaminant level; 

MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. Relative-concentration equals measured concentration divided by benchmark value; relative-concentration greater than 1.0 is defined as high. Other abbreviations: pCi/L, picocuries per liter; –, none]

Constituent 1 Benchmark type Benchmark value Units Date of most recent high value (by study area) Number of wells that had high relative- concentrations (by study area) Number of wells that had analyses (by study area) Study area

Organic constituents with health-based benchmarksAldrin RSD5-US 0.02 μg/L 02-26-03 1 56 Owens Valley

Atrazine MCL-CA 1 μg/L 07-12-89 1 214 Coachella

Benzene MCL-CA 1 μg/L 10-21-87, 05-11-88 1, 2 265, 166 Mojave, Owens Valley

Bis(2-ethylhexyl)phthalate, also 

Di(2-ethylhexyl)phthalate

MCL-CA 4 μg/L 04-02-92 6 165 Mojave

cis-1,2-Dichloroethene MCL-CA 6 μg/L 08-24-94 8 229 Coachella

1,2-Dibromo-3-chloropropane (DBCP) MCL-US 0.2 μg/L 01-03-91, 08-03-93 2, 1 215, 182 Antelope, Mojave

Dichloromethane (Methylene chloride) MCL-US 5 μg/L 03-30-88 1 265 Mojave

Ethylene dibromide (EDB) MCL-US 0.05 μg/L 02-15-91 1 206 AntelopeHeptachlor MCL-CA 0.01 μg/L 01-28-93 2 165 Mojave

tert-Butyl alcohol NL-CA 12 μg/L 07-16-02 7 182 AntelopeTrichloroethene MCL-US 5 μg/L 11-08-89, 09-03-91 2, 7 272, 265 Antelope, MojaveVinyl chloride MCL-CA 0.5 μg/L 07-13-04 1 265 Mojave

Inorganic constituents with health-based benchmarksCadmium MCL-US 5 μg/L 12-04-87, 02-09-87, 

07-10-90, 10-12-90

1, 1, 4, 1 286, 252, 236, 135 Antelope, Coachella, 

Mojave, Owens Valley

Gross-beta radioactivity MCL-CA 5 pCi/L 10-09-91 1 52 Owens Valley

Mercury MCL-US 2 μg/L 02-09-87, 08-21-02 2, 2 252, 31 Coachella, Colorado River

Nitrite MCL-US 1 μg/L 11-12-96, 06-10-98 2, 1 237, 221 Antelope, Mojave

Thallium MCL-US 2 μg/L 09-12-94 3 236 AntelopeZinc SMCL-US 5,000 μg/L 11-23-99 2 285 Antelope

1 Constituents that had high relative-concentrations in 2006–2008 are not included in this table.
24 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

Calculation of Aquifer-Scale Proportions

Aquifer-scale proportions are defined as the percentage 

of the area (rather than the volume) of the primary aquifer 

system with concentrations greater than or less than specified 

thresholds relative to water-quality benchmarks. This 

status assessment is intended to characterize the quality of 

groundwater resources in the primary aquifers of the Desert 

Region study areas. The primary aquifers are defined by the 

depth intervals over which wells listed in the CDPH database 

are perforated. The use of the term “primary aquifer” does 

not imply that there is a single discrete aquifer unit. The 

primary aquifer corresponds to the portion of the aquifer 

system tapped by municipal and community supply wells. 

To the extent that domestic wells in the six study areas are 

perforated over the same depth intervals as the CDPH wells, 

the assessments presented in this report also may be applicable 

to the portions of the aquifer systems used for domestic 

drinking-water supplies.

Two approaches, grid-based and spatially weighted 

(Belitz and others, 2010), were selected to determine the areal 

proportions of the primary aquifers in the six study areas with 

high and moderate RCs of constituents. These proportions are 

referred to as “high” and “moderate” aquifer-scale proportions. 

Calculations of aquifer-scale proportions were made for 

individual constituents meeting the criteria for inclusion in 

the status assessment and for classes of constituents. Classes 

of constituents with health-based benchmarks included 

VOCs, pesticides, special-interest constituents, any organic 

constituent (combination of all VOCs, pesticides, and organic 

special-interest constituents), radioactive constituents, 

trace elements, nutrients, and any inorganic constituent 

(combination of all radioactive constituents, trace elements, 

nutrients, and inorganic special-interest constituents).

Grid-Based Aquifer-Scale Proportions

The grid-based calculation used the grid-well dataset 

assembled from the USGS-grid and CDPH-grid samples as 

described in the section “Data Used for Status Assessment.” 

For each constituent, the high aquifer-scale proportion was 

calculated by dividing the number of cells with a high RC for 

that constituent by the total number of grid cells with data for 

that constituent. The moderate aquifer-scale proportion was 

calculated similarly for each constituent. Confidence intervals 

for the high aquifer-scale proportions were computed using 

the Jeffreys interval for the binomial distribution (Brown and 

others, 2001; Belitz and others, 2010). The grid-based estimate 

is designed to be spatially unbiased. However, the grid-based 

approach may not detect constituents that are present at high 

concentrations in small proportions of the primary aquifers. 

Additionally, estimates of aquifer-scale proportion for 

constituents based on a smaller number of wells have a larger 

error associated with the 90 percent confidence intervals. 

For classes of constituents, the high aquifer-scale 

proportion was calculated by dividing the number of cells 

with a high concentration for any of the constituents in that 

class by the total number of cells with data for that class 

of constituents. The moderate aquifer-scale proportion was 

calculated by dividing the number of cells with a moderate 

concentration for any of the constituents (not counting cells 

that also had high concentrations) by the total number of cells 

with data for that class of constituents. 

Spatially Weighted Aquifer-Scale Proportions

The spatially weighted calculation used a larger, 

non-gridded dataset assembled from CDPH and USGS 

samples, including 53 additional samples collected by 

USGS-GAMA, and all wells in the CDPH database that have 

water-quality data from the 3-year intervals prior to USGSGAMA sampling periods (for wells with USGS and CDPH 

data, only the USGS data were used). For each constituent, 

the high aquifer-scale proportion was calculated by computing 

the proportion of “high” wells in each cell and then averaging 

together the proportions for all cells for a particular study unit 

(Isaaks and Srivastava, 1989). The resulting proportions are 

spatially unbiased (Isaaks and Srivastava, 1989). Confidence 

intervals for spatially weighted estimates of aquifer-scale 

proportion are not described in this report. The moderate 

aquifer-scale proportion was calculated similarly. 

For the calculation of high aquifer-scale proportion for a 

class of constituents, a class was considered high if the RC of 

any constituents in that class was high in any sample. A class 

was considered moderate if the RC of any constituent in that 

class was moderate for any sample and if the RC of none of 

the constituents was high. 

Raw Detection Frequencies

In addition, for each constituent, the raw detection 

frequencies (number of detections above a specified 

concentration divided by number of analyses) for high and 

moderate RCs were calculated using the same dataset as was 

used for the spatially weighted calculations. However, these 

raw detection frequencies are not spatially unbiased because 

the wells in the CDPH database are not uniformly distributed 

(figs. 4A–H). For example, if a constituent was present at 

high RCs in a small region of the aquifer with a high density 

of wells, the raw detection frequency of high RCs would be 

greater than the grid-based high aquifer-scale proportion. Raw 

detection frequencies are provided for reference but were not 

used to assess aquifer-scale proportions. 

Area Correction Factors

For the calculation of the grid-based and spatially 

weighted aquifer proportions for the entire Desert Region, 

an area correction factor was applied to the results of the 
Status of Groundwater Quality 25

individual study areas. This was done so that results from 

the smaller study areas would not be over-represented when 

combined with results from the larger study areas. The 

correction factors were calculated as the area of each study 

area, defined as the area covered by grid cells, divided by 

the sum of all grid cell areas in all of the study areas. These 

area correction factors were as follows: Owens Valley, 0.22; 

Antelope, 0.19; Mojave, 0.18; Coachella, 0.23; Colorado 

River, 0.06; Indian Wells, 0.13. Area correction factors for 

NDMA, which was not analyzed for in all six study areas, 

were calculated using a similar process for only the four study 

areas where samples were analyzed for NDMA. Similarly, 

area correction factors for radon-222 were calculated for the 

five study areas where samples were collected for radon-222 

analysis. 

Status of Groundwater Quality 

The RCs for the inorganic and organic constituent classes 

for grid samples for the Desert Region as a whole and in each 

study area are shown in figure 6. The maximum RCs in grid 

wells for each detected constituent in the Desert Region are 

shown in figure 7; the results for the individual study areas are 

shown in figures B2 and B3. As shown in all of these figures, 

there is a large contrast between the inorganic constituents 

compared to organic constituents. For the inorganic classes, 

a larger proportion of the aquifers in each study area and a 

higher number of constituents had high or moderate RCs; for 

organic classes, much smaller proportions of the aquifers and 

fewer constituents had high or moderate RCs. 

Figure 6. Aquifer-scale proportions for inorganic and organic constituent classes in the California Desert Region as a whole 

and for the individual California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 

2006–2008.

Pie charts illustrate the proportions of the primary aquifers with concentrations in specified categories. 

Values on pie chart may not equal 100 due to rounding of percentages

Aquifer-scale proportions

EXPLANATION

High – At least one constituent in any 

grid well had a high relative-concentration, 

greater than 1.0 of their respective 

benchmarks

Low or not detected – No constituents in 

any grid well had high or moderate relativeconcentrations; all concentrations were 

below 0.5 (for inorganic constituents) or 

below 0.1 (for organic and special-interest 

constituents) of their respective 

benchmarks

Moderate – No constituents in any grid 

well had high relative-concentrations, and at 

least one constituent had a moderate 

relative-concentration, between 0.1 (for 

organic and special-interest constituents) 

or 0.5 (for inorganic constituents) and 1.0 of 

their respective benchmarks

Inorganic consituents with health-based benchmarks

Number of constituents: 29

Organic constituents with health-based benchmarks

Number of constituents: 78

Indian Wells

Coachella

Owens

Desert

Antelope

Colorado Mojave

River

Colorado Mojave

River

Indian Wells

Owens

Antelope

Coachella

Desert

23 62

15

42

26

32

45

35

20

22

20 58

1

99

10

90

2

98

2 6

92

2

98

100

100 0.3

35

27

37

28

36

36

30

30

41
26 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 7

10

1

0.1

0.01

0.001

0.0001

100

Volatile

organic

compounds

Pesticides Specialinterest

constituents

Nutrients Trace

elements

Inorganic

constituents

with non-healthbased benchmarks

Radioactive

constituents

Maximum relative-concentration

Nitrite

Strontium

Vanadium

Fluoride

Molybdenum

Uranium

Arsenic

Boron

Barium

Selenium

Aluminum

Nickel

Copper

Antimony

Beryllium Cadmium

Sulfate

Total dissolved solids

Chloride

Manganese

Zinc

Iron

Radium-226

Radon-222

Radium-228 Gross-beta

Gross-alpha

Lead Chromium

Nitrate

Silver

Ammonia

Thallium

Mercury

N-nitrosodimethylamine

Perchlorate

Dieldrin

Atrazine

Simazine

Metolachlor

Chloroform

Bromodichloromethane

Tetrachloroethene

1,1-Dichloroethane

Bromoform

Dibromochloromethane

1,1-Dichloroethene

1,2-Dichloroethane

cis-1,2-Dichloroethene

Dichloromethane

Trichloroethene

trans-1,2-Dichloroethene

Trichlorofluoromethane

Chlorobenzene

1,2-Dichloropropane Carbon Tetrachloride

Methyl tert-butyl ether

1,4-Dichlorobenzene

Chloromethane

Carbon Disulfide

Bromochloromethane

Styrene

Moderate

High

Low

Figure 7. Maximum concentrations relative to health-based and non-health-based benchmarks in 

grid wells for classes of constituents detected in the California Desert Region Groundwater Ambient 

Monitoring and Assessment (GAMA) study areas, 2006–2008.

Of the 149 organic constituents analyzed in the Desert 

Region, 78 have a health-based benchmark. Forty-two organic 

constituents were detected, most of which (32 of the 42) 

have health-based benchmarks (tables 4 and B2A–B2C). Of 

the 10 detected constituents that did not have benchmarks, 

two (desethylatrazine and 3,4-dichloroanaline) are possible 

degradates of pesticides (atrazine and diuron) that do have 

benchmarks. The other detected organic constituents that 

did not have benchmarks were four solvents (chloroethane, 

chloromethane, dibromomethane, and tetrahydrofuran), 

two herbicides (prometryn and terbuthylazine), and an 

insecticide and two of its degradation products (fipronil, 

desulfinylfipronil, and fipronil sulfide). 

In contrast to organic constituents, all inorganic 

constituents (48 of 48) analyzed in the Desert Region were 

detected in at least one study area (tables 4 and B2C–B2F). 

Twenty-nine of these inorganic constituents have health-based 

benchmarks. Most of the constituents without benchmarks 

are major or minor ions that are present naturally in 

most groundwater.

The inorganic constituents that were detected in 

grid wells at high concentrations relative to health-based 

thresholds in the Desert Region are arsenic, boron, fluoride, 

aluminum, gross-alpha radioactivity, molybdenum, nitrate, 

strontium, uranium, and vanadium (fig. 7; table 5). The 

inorganic constituents that were detected in grid wells at 

high concentrations relative to non-health-based thresholds 

are chloride, iron, manganese, sulfate, and total dissolved 

solids (TDS) (fig. 7; table 5). No VOC or pesticide 

constituents were detected at high RCs in grid wells in 

any of the Desert Region study areas; however, the VOCs 

carbon tetrachloride (tetrachoromethane), chloroform 

(trichloromethane), 1,2-dichloropropane, 1,2-dichloroethane, 

and tetrachloroethene and the pesticide dieldrin were detected 

at moderate RCs. The special-interest constituents perchlorate 

and NDMA were detected at high RCs in one or more of the 

USGS-grid wells.

Spatially weighted high aquifer-scale proportions fell 

within the 90 percent confidence intervals for their respective 

grid-based high aquifer-scale proportions, showing that 

the grid-based and spatially weighted approaches yield 

statistically equivalent results (table 5). 
Status of Groundwater Quality 27

Table 4. Number of constituents analyzed and number detected by the U.S. Geological Survey in grid wells, with associated benchmarks for each constituent class, California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas, September 2006 to April 2008.[Abbreviations: USEPA, U.S. Environmental Protection Agency; CDPH, California Department of Public Health; AL-US, USEPA action level; MCL, USEPA or CDPH Maximum Contaminant Level; HAL-US, USEPA Lifetime Health Advisory Level; NL-CA, CDPH Notification Level; RSD5-US, USEPA Risk-Specific Dose at 10–5; SMCL, USEPA or CDPH 

Secondary Maximum Contaminant Level]

Sum of organic 

constituents

Organic Constituent Classes

Volatile organic 

compounds

Pesticides and 

degradates 

Special-interest 

constituents

Benchmark type Analyzed Detected Analyzed Detected Analyzed Detected Analyzed Detected

MCL 35 22 32 20 3 2 0 0

HAL-US 23 7 8 2 14 4 1 1

NL-CA 13 2 12 1 0 0 1 1

RSD5-US 7 1 4 0 3 1 0 0

None 71 10 27 4 44 7 0 0

Total: 149 42 83 27 64 14 2 2

Sum of inorganic 

constituents

Inorganic Constituent Classes

Major and minor 

ions and total 

dissolved solids

Trace elements Nutrients Radioactive constituents Special-interest constituents

Benchmark type Analyzed Detected Analyzed Detected Analyzed Detected Analyzed Detected Analyzed Detected Analyzed Detected

MCL 22 22 1 1 12 12 2 2 6 6 1 1HAL-US 3 3 0 0 2 2 1 1 0 0 0 0AL-US 2 2 0 0 2 2 0 0 0 0 0 0NL-CA 2 2 0 0 2 2 0 0 0 0 0 0RSD5-US 0 0 0 0 0 0 0 0 0 0 0 0SMCL 7 7 3 3 4 4 0 0 0 0 0 0None 12 12 7 7 3 3 2 2 0 0 0 0

Total: 48 48 11 11 25 25 5 5 6 6 1 1

Organic and 

inorganic 

constituents 

combined:

197 90
28 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table 5. Current aquifer proportions from grid-based and spatially weighted methods for constituents with moderate or high relative-concentrations, California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas, September 2006 to April 2008. [Moderate, relative-concentration between 0.5 (for trace elements, radioactive constituents, nutrients, and inorganic constituents) or 0.1 (for volatile organic compounds, pesticides, and special-interest constituents) and 1; High, relative-concentration greater than 1.0] Raw detection frequency Spatially weighted aquifer-scale proportions Grid-based aquifer-scale proportions 90 percent confidence interval for grid-based high proportion (percent) Constituent Number of wells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Lower Upper Trace elements with health-based benchmarks Aluminum 682 0.0 0.3 187 0.0 0.2 182 0.0 0.4 0.0 0.7 Antimony 675 0.0 0.1 186 0.0 0.1 180 0.0 0.0 0.0 0.7 Arsenic 700 9.4 12.9 189 10.3 16.9 188 8.0 17.8 12.6 21.6 Boron 472 4.7 5.9 167 5.5 11.1 161 6.1 11.4 6.7 14.6 Chromium 676 0.7 0.0 186 1.5 0.0 182 1.6 0.0 0.0 0.7 Fluoride 705 7.2 4.5 189 11.2 9.3 189 13.2 8.9 4.9 11.3 Lead 630 0.5 1.0 181 0.4 0.2 175 0.4 0.0 0.0 0.8 Molybdenum 177 11.9 4.5 148 15.3 6.4 129 12.5 5.7 2.8 9.5 Strontium 175 6.9 3.4 131 5.7 3.7 129 6.5 3.7 3.4 10.4 Vanadium 467 9.0 2.8 165 7.5 3.6 160 8.3 3.6 1.9 7.0 Radioactive constituents with health-based benchmarks Gross-alpha radioactivity1 532 9.6 3.6 152 9.7 7.0 142 5.4 6.6 3.2 9.8 Radon-222 91 1.1 0.0 71 2.6 0.0 73 11.1 0.0 0.0 1.8 Uranium 445 5.2 2.9 168 6.9 3.8 162 6.9 3.2 1.9 6.9 Nutrients with health-based benchmarks Nitrate 843 4.5 1.2 200 3.7 1.1 199 3.3 0.4 0.1 2.0 Inorganic constituents with non-health-based benchmarks Chloride 683 2.8 1.5 186 4.0 2.3 185 3.8 2.9 0.9 4.6 Iron 698 7.0 7.7 187 6.7 6.0 186 5.2 4.4 3.2 8.8 Manganese 694 2.3 7.2 187 2.2 8.2 185 2.1 9.3 6.7 14.0 Sulfate 682 8.2 1.9 186 10.4 3.4 185 12.4 4.4 2.4 7.4 Total dissolved solids (TDS) 685 14.9 5.8 186 20.2 9.8 185 18.0 11.3 8.6 16.5
Status of Groundwater Quality 29

Raw detection frequency Spatially weighted aquifer-scale proportions Grid-based aquifer-scale proportions

90 percent confidence 

interval for grid-based 

high proportion 

(percent)

Constituent Number of wells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Lower Upper

Volatile organic constituents with health-based benchmarks

1,2-Dibromo-3-chloropropane 528 0.2 0.0 202 0.2 0.0 200 0.0 0.0 0.0 0.7

1,2-Dichloroethane 670 0.1 0.0 202 0.3 0.0 200 0.3 0.0 0.0 0.7

1,2-Dichloropropane 671 0.3 0.0 202 0.5 0.0 200 0.6 0.0 0.0 0.7

1,4-Dichlorobenzene 664 0.3 0.0 202 0.1 0.0 200 0.0 0.0 0.0 0.7

Bromodichloromethane 671 0.3 0.0 203 0.1 0.0 200 0.0 0.0 0.0 0.7

Chloroform (trichloromethane) 672 0.4 0.0 203 0.3 0.0 200 0.4 0.0 0.0 0.7

Dibromochloromethane 671 0.4 0.0 203 0.1 0.0 200 0.0 0.0 0.0 0.7

Ethylbenzene 671 0.1 0.0 202 0.3 0.0 200 0.0 0.0 0.0 0.7

Tetrachloroethene (PCE) 672 0.6 0.0 202 0.5 0.0 200 0.3 0.0 0.0 0.7

Carbon tetrachloride 

(tetrachloromethane)

671 0.1 0.0 202 0.3 0.0 200 0.3 0.0 0.0 0.7

Pesticides with health-based benchmarks

Dieldrin 363 0.3 0.0 197 0.3 0.0 194 0.3 0.0 0.0 0.7

Special-interest constituents with health-based benchmarks

1,2,3-Trichloropropane 487 0.2 0.0 200 0.2 0.0 199 0.0 0.0 0.0 0.7

N-Nitrosodimethylamine 

(NDMA)

100 0.0 1.0 80 0.0 1.2 77 0.0 1.4 0.2 5.0

Perchlorate 422 11.4 0.7 202 10.9 2.5 195 17.2 2.4 0.3 2.7

1Gross alpha radioactivities were not adjusted for uranium activity. The MCL-US applies to adjusted gross alpha radioactivity which is gross alpha activity minus uranium activity.

Table 5. Current aquifer proportions from grid-based and spatially weighted methods for constituents with moderate or high relative-concentrations, California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, September 2006 to April 2008.—Continued

[Moderate, relative-concentration between 0.5 (for trace elements, radioactive constituents, nutrients, and inorganic constituents) or 0.1 (for volatile organic compounds, pesticides, and special-interest constituents) and 1; High, relative-concentration greater than 1.0]
30 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

Inorganic Constituents

Data for 48 inorganic constituents were used for this 

study (11 major or minor ions, 25 trace elements, 5 nutrients, 

6 radioactive constituents, and 1 special-interest constituent). 

All 48 inorganic constituents were detected at least once in 

the Desert Region (table 4). Of these, 29 have health-based 

benchmarks, and 7 have non-health-based benchmarks. 

Eighteen inorganic constituents—arsenic, boron, 

chloride, chromium, fluoride, gross-alpha radioactivity, iron, 

lead, molybdenum, manganese, nitrate, perchlorate, radon222, strontium, sulfate, uranium, vanadium, and TDS—had 

moderate RCs in the grid-based aquifer proportions (table 5). 

Of these, 14 also had high RCs in more than 2 percent 

of the primary aquifers in the Desert Region (arsenic, 

boron, chloride, fluoride, gross-alpha radioactivity, iron, 

molybdenum, manganese, perchlorate, strontium, sulfate, 

uranium, vanadium, and TDS); maps showing the areal 

distributions of these constituents are presented later in 

the report. 

Inorganic Constituents with 

Health-Based Benchmarks

Inorganic constituents with health-based benchmarks 

were the constituent class with the largest aquifer proportion 

of high RCs in the Desert Region. High RCs of one or more 

inorganic constituents with health-based benchmarks were 

found in 35.4 percent of the primary aquifers (table 6; fig. 6). 

Several inorganic constituents with health-based benchmarks 

were detected at high RCs in each of the Desert Region study 

areas (appendix B; tables B3A–F). This constituent class had 

moderate RCs in 27.4 percent of the Desert Region’s primary 

aquifers, and low RCs in 37.2 percent (table 6; fig. 6).

Trace Elements

Trace elements, as a class, had high RCs for one or 

more constituents in 32.5 percent of the primary aquifers, 

moderate RCs in 20.2 percent, and low RCs in 47.3 percent 

of the Desert Region’s primary aquifers (table 6). High RCs 

of trace elements reflected high arsenic, boron, fluoride, 

molybdenum, strontium, vanadium, and aluminum (table 5). 

Two trace elements, chromium and lead, were detected only 

at moderate RCs. The trace elements antimony and lead were 

not detected in grid wells, but had spatially weighted, high 

RCs in 0.1 percent and 0.2 percent of the primary aquifers, 

respectively; these detections were within the 90 percent 

confidence intervals for these trace elements for the grid-based 

approach. The spatially weighted approach includes data from 

a larger number of wells than used in the grid-based approach 

and, therefore, is more sensitive to constituents present in very 

small proportions of the primary aquifers.

Arsenic was detected at high RCs in 17.8 percent 

of the Desert Region’s primary aquifers and at moderate 

concentrations in 8.0 percent (table 5). All six Desert Region 

study areas had high-relative concentrations of arsenic (figs. 8

and 9; tables B3A–F). The highest RC was in the ANT study 

area (fig. 8). The high RCs are distributed throughout some 

study areas (OV, ANT, and MOJ,), but occur only in parts of 

other study areas (IW, COA, and COL) (fig. 9). 

Boron was detected at high RCs in 11.4 percent of 

Desert Region grid wells, and at moderate RCs in 6.1 percent 

(table 5). High RCs of boron occurred in all six study areas 

(figs. 8 and 10; tables B3A–F). The highest RC was detected 

in IW (fig. 8). High boron concentrations were found in wells 

near the downgradient parts of the regional groundwater flow 

systems (identified in fig. 5) in every study area (fig. 10). 

Fluoride was detected at high RCs in 8.9 percent and at 

moderate RCs in 13.2 percent of the Desert Region’s primary 

aquifers (table 5). It was detected at high RCs in COA, COL, 

MOJ, OV, and ANT; it was detected at moderate RCs in IW 

(tables B3A–F). The highest RC was in COA (fig. 8). The 

distributions of high fluoride concentrations varied in the 

study areas (fig. 11). In COA, OV, and IW, high and moderate 

concentrations were found in upgradient and downgradient 

areas. In ANT and MOJ, high concentrations were mostly 

in downgradient areas; in COL, high concentrations of 

fluoride were in the Needles and Palo Verde basins, but not in 

the Yuma basin.

Molybdenum was detected at high RCs in 5.7 percent 

and at moderate RCs in 12.5 percent of the primary aquifers 

in the Desert Region (table 5). It was detected at high RCs 

in all the study areas except ANT, where it was detected at 

moderate RCs (figs. 8 and 12; tables B3A–F). The highest RC 

was in COL (fig. 8). Moderate and high RCs were distributed 

throughout OV, IW, MOJ, and COA. A high RC was in 

the Palo Verde basin in COL; moderate RCs were only in 

downgradient wells in ANT (fig. 12). 

Vanadium was detected at high RCs in 3.6 percent of 

the Desert Region’s primary aquifers and at moderate RCs in 

8.3 percent (table 5). It was detected at high RCs in MOJ, IW, 

and ANT; at moderate RCs in COA; and at low RCs in OV 

and COL (tables B3A–F). The highest RC was in IW; this RC 

was similar to the highest RCs in ANT and MOJ (fig. 8). The 

high RCs in IW and MOJ were in the middle or upper parts 

of the flow systems; in ANT, the highest concentrations were 

in downgradient wells (fig. 13). Moderate RCs were in the 

middle and downgradient areas in COA; only low RCs were in 

OV and COL.

Strontium was detected at high RCs in 3.7 percent 

of the Desert Region’s primary aquifers and at moderate 

RCs in 6.5 percent (table 5). It was detected at high RCs in 

MOJ, COA, IW, and COL, and at low RCs in ANT and OV 

(fig. 14; tables B3A–F). The highest RC was in MOJ (fig. 14). 

High and moderate RCs of strontium were generally in the 

downgradient areas of the groundwater flow systems of the six 

study areas (fig. 15). 
Status of Groundwater Quality 31

Table 6. Summary of aquifer-scale proportions for inorganic constituent classes in the California Desert Region Groundwater Ambient 

Monitoring and Assessment (GAMA) study areas.

[Low, relative-concentration less than 0.5 (or 0.1 for perchlorate); Moderate, relative-concentration between 0.5 (or 0.1 for perchlorate) and 1; High, 

relative-concentration greater than 1.0; Values are grid-based except where footnoted]

Study area Number of grid 

cells with data

Aquifer-scale proportion (percent)

Not detected Low Moderate High

Trace elements with health-based benchmarks

Desert Region (all study areas) 192 0.0 47.3 20.2 32.5

Owens Valley 40 0.0 72.5 12.5 15.0

Antelope 54 0.0 51.8 16.7 31.5

Mojave 46 0.0 45.7 21.7 32.6

Coachella 19 0.0 42.1 21.1 36.8

Colorado River 20 0.0 30.0 30.0 40.0

Indian Wells 13 0.0 15.4 30.8 53.8

Radioactive constituents with health-based benchmarks 2

Desert Region (all study areas) 182 0.0 81.9 11.1 1 7.1

Owens Valley 40 0.0 75.0 15.0 10.0

Antelope 50 0.0 90.0 6.0 4.0

Mojave 40 0.0 82.5 15.0 2.5

Coachella 19 0.0 85.6 10.5 1 3.9

Colorado River 20 0.0 75.0 10.0 15.0

Indian Wells 13 0.0 76.9 7.7 15.4

Nutrient constituents with health-based benchmarks

Desert Region (all study areas) 199 3.0 92.8 3.4 1 0.8

Owens Valley 40 0.0 100.0 0.0 0.0

Antelope 54 7.3 81.5 9.3 1.9

Mojave 53 3.8 94.3 1.9 0.0

Coachella 19 0.0 92.8 5.3 1 1.9

Colorado River 20 0.0 99.0 1.01 0.0

Indian Wells 13 7.7 92.3 0.0 0.0

Inorganic constituents with non-health-based benchmarks

Desert Region (all study areas) 187 0.0 65.4 16.0 18.6

Owens Valley 40 0.0 77.5 7.5 15.0

Antelope 51 0.0 72.6 9.8 17.6

Mojave 44 0.0 77.3 13.6 9.1

Coachella 19 0.0 63.1 21.1 15.8

Colorado River 20 0.0 10.0 25.0 65.0

Indian Wells 13 0.0 46.1 30.8 23.1

Special-interest constituent: Perchlorate

Desert Region (all study areas) 195 58.3 22.1 17.2 2.4

Owens Valley 40 97.5 2.5 0.0 0.0

Antelope 56 14.3 57.1 28.6 0.0

Mojave 50 40.0 38.0 22.0 0.0

Coachella 19 63.2 10.5 15.8 10.5

Colorado River 20 55.0 10.0 35.0 0.0

Indian Wells 13 84.6 0.0 15.4 0.0

Any inorganic constituents with health-based benchmarks 2

Desert Region (all study areas) 206 0.0 37.2 27.4 35.4

Owens Valley 40 0.0 57.5 20.0 22.5

Antelope 61 0.0 41.0 29.5 29.5

Mojave 53 0.0 35.9 35.8 28.3

Coachella 19 0.0 31.6 26.3 42.1

Colorado River 20 0.0 20.0 35.0 45.0

Indian Wells 13 0.0 15.4 23.1 61.5

1

Spatially weighted value.

2

Aquifer-scale proportions for radioactive constituents and for any inorganic constituents with health-based benchmarks were calculated using unadjusted 

gross alpha activity. The MCL-US applies to adjusted gross alpha radioactivity which is gross alpha activity minus uranium activity.
32 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 08

Low

Moderate

High

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

0.0001

0.001

0.01

0.1

1

10

100

Relative-concentration

Arsenic Boron Fluoride Molybdenum Vanadium

Figure 8. Detected concentrations of arsenic, boron, fluoride, molybdenum, and vanadium in grid wells 

relative to health-based benchmarks in the California Desert Region Groundwater Ambient Monitoring and 

Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 33

sac11-0428_fig 09

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

EXPLANATION

USGS-Grid Data CDPH-Grid Data

Arsenic, relative-concentration

Not Detected

Low

Moderate

High

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 9. Concentrations of arsenic in grid wells relative to health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
34 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 10

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Boron, relative-concentration

Not Detected

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 10. Concentrations of boron in grid wells relative to health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 35

sac11-0428_fig 11

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Fluoride, relative-concentration

Not Detected

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 11. Concentrations of fluoride in grid wells relative to health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
36 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 12

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data

Molybdenum, relative-concentration

Low

Moderate

High

Not Detected

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 12. Concentrations of molybdenum in grid wells relative to health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 37

Figure 13. Concentrations of vanadium in grid wells relative to health-based benchmarks in the California Desert 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.

sac11-0428_fig 13

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Vanadium, relative-concentration

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA
38 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 14

Low

Moderate

High

0.0001

0.001

0.01

0.1

1

10

100

Relative-concentration

Strontium Uranium Gross-Alpha Nitrate Perchlorate

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Figure 14. Concentrations of strontium, uranium, gross-alpha radioactivity, nitrate, and perchlorate in grid 

wells relative to health-based benchmarks in the California Desert Groundwater Ambient Monitoring and 

Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 39

Figure 15. Concentrations of strontium in grid wells relative to health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.

sac11-0428_fig 15

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Strontium, relative-concentration

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°
40 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

Radioactive Constituents

Radioactive constituents had high RCs for one or more 

constituents in 7.1 percent of the Desert Region’s primary 

aquifers, moderate RCs in 11.1 percent, and low RCs in 

81.9 percent (table 6). The high RCs reflect detections of 

gross-alpha radioactivity and uranium (table 5). Radon-222 

was detected at moderate concentrations in OV and COL, and 

at low RCs in COA, ANT, and MOJ; no data were available 

for IW. The other radioactive constituents were found only at 

low RCs in the primary aquifers in the Desert Region. 

Gross-alpha radioactivity was found at high RCs in 

6.6 percent of the Desert Region’s primary aquifers and at 

moderate RCs in 5.4 percent (table 5). It was found at high 

RCs in all Desert Region study areas, except COA, where 

it was only found at low RCs (tables B3A–F). The highest 

RC was found in COL (fig. 14). The distributions of high 

RCs varied among the study areas. In OV, high RCs were 

in upgradient and downgradient wells; in ANT and MOJ, in 

downgradient wells; in IW, only in an upgradient well; and 

in COL, in the Palo Verde basin (fig. 16). These RCs were 

calculated using unadjusted gross-alpha radioactivity; the 

MCL-US applies to adjusted gross-alpha radioactivity, which 

is equal to the measured gross-alpha activity minus uranium 

activity (U.S. Environmental Protection Agency, 2000). 

Uranium was detected at high RCs in 3.2 percent and 

moderate RCs in 6.9 percent of the Desert Region’s primary 

aquifers (table 5); it was detected at high RCs in OV, IW, 

and COL, and at moderate RCs in ANT, COA, and MOJ 

(fig. 14; tables B3A–F). The highest RC was in IW (fig. 14). 

The distribution of high RCs varied in the study areas. In OV, 

high RCs of uranium were in the upgradient areas (fig. 17). 

In ANT and MOJ, the moderate uranium RCs were in the 

downgradient wells. In IW and COA, high RCs were in 

upgradient and downgradient areas; in COL, high RCs were 

only in the Palo Verde basin. 

Nutrients

Nutrient constituents had high RCs in 0.8 percent of 

the Desert Region’s primary aquifers and moderate RCs 

in 3.4 percent (table 6), reflecting the detections of nitrate 

(table 5). Ammonia and nitrite were detected only at low 

concentrations or were below reporting levels. Note that 

the high RC calculated for the Desert Region (0.8 percent) 

includes high nitrate values that were in wells used to calculate 

the spatially weighted aquifer proportion in COA (table 6).

Nitrate was detected at high RCs in grid wells in ANT, 

at moderate RCs in MOJ and COA, and at low RCs or not 

detected in OV, IW, and COL (fig. 14; tables B3A–F). The 

highest RC was in ANT (fig. 14). 

Special-Interest Constituent: Perchlorate

Perchlorate was detected at high RCs in 2.4 percent 

of the primary aquifers in the Desert Region, moderate in 

17.2 percent, and low in 22.1 percent; it was not detected in 

58.3 percent of the primary aquifers (tables 5 and 6). The high 

RCs occurred in COA, in two grid wells on the southwestern 

side of the study area (fig. 18). Moderate RCs were detected 

in grid wells in IW, ANT, MOJ, and COL (fig. 14). Perchlorate 

was detected at low RCs in one grid well in OV. Moderate 

or high RCs occurred in all parts of the groundwater flow 

systems in COA, ANT, MOJ, and COL; moderate RCs were 

detected on the west side of IW (fig. 18).

Inorganic Constituents with NonHealth-Based Benchmarks

The inorganic constituents that have non-health-based 

benchmarks (SMCLs), as a class, had high RCs for one or 

more constituents in 18.6 percent of the primary aquifers in 

the Desert Region, moderate RCs in 16.0 percent, and low 

RCs in 65.4 percent (table 6). High RCs of three or more of 

these constituents were detected in all of the Desert Region 

study areas (appendix B, tables B3A–F). High RCs for this 

class of constituents reflected high RCs for TDS, manganese, 

sulfate, iron, and chloride (table 5). 

Total dissolved solids were detected at high RCs in 

11.3 percent of the Desert Region’s primary aquifers and at 

moderate RCs in 18.0 percent (table 5). TDS was detected 

at high RCs in all of the Desert Region study areas (fig. 19; 

tables B3A–F). The highest RC was in COA (fig. 19). The 

high RCs of TDS were in the downgradient areas of the 

groundwater flow systems all six study areas (fig. 20). 

Manganese was detected at high RC in 9.3 percent of 

the Desert Region’s primary aquifers and at moderate RCs 

in 2.1 percent (table 5). High RCs occurred in all study areas 

(fig. 19). The highest RC was detected in COL. High RCs of 

manganese were in the downgradient areas of OV, IW, COA, 

and ANT (fig. 21). A high RC was detected in the upgradient 

area of MOJ. High RCs were in the Palo Verde and Yuma 

basins in COL.

Sulfate was detected at high RCs in 4.4 percent of the 

Desert Region’s primary aquifers and at moderate RCs in 

12.4 percent (table 5). High RCs occurred in MOJ, COA, and 

COL, moderate RCs occurred in ANT and IW, and low RCs 

occurred in OV. The highest RC was in MOJ (fig. 19). High 

and moderate RCs were generally in the downgradient areas 

within each of the study areas except OV (fig. 22).

Iron was detected at high RCs in 4.4 percent of the 

Desert Region’s primary aquifers and at moderate RCs in 

5.2 percent (table 5). High RCs were in OV, COL, ANT, and 

MOJ; iron was low or not detected in IW and COA (figs. 19

and 23). The highest RC was in OV (fig. 19). 

Chloride was detected at high RCs in 2.9 percent of 

the Desert Region’s primary aquifers and at moderate RCs 

in 3.8 percent (table 5). High RCs occurred in IW, COA, 

COL, and MOJ; moderate RCs occurred in ANT, and low 

RCs occurred in OV (figs. 19 and 24). The highest RC was in 

IW (fig. 19). 
Status of Groundwater Quality 41

sac11-0428_fig 16

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS Grid-Data CDPH Grid-Data

Gross alpha radioactivity, relative concentration—

Gross alpha radioactivities were not adjusted for 

uranium activity. The MCL-US applies to adjusted 

gross alpha radioactivity which is gross alpha minus 

uranium activity.

Not Detected

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 16. Concentrations of gross-alpha radioactivity in grid wells relative to health-based benchmarks in the California 

Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
42 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 17

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Uranium, relative-concentration

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 17. Concentrations of uranium in grid wells relative to health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 43

sac11-0428_fig 18

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Perchlorate, relative-concentration

Not Detected

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 18. Concentrations of perchlorate in grid wells relative to health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
44 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 19

Chloride Iron Manganese Sulfate Total Dissolved Solids

Low

Moderate

High

0.0001

0.001

0.01

0.1

1

10

100

Relative-concentration

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Figure 19. Concentrations of chloride, iron, manganese, sulfate, and total dissolved solids in grid wells 

relative to non-health-based benchmarks in the California Desert Groundwater Ambient Monitoring and 

Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 45

sac11-0428_fig 20

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

NEVADA

NEVADA

NEVADA

CALIFORNIA

ARIZONA

ARIZONA

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Total dissolved solids, relative-concentration

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

Figure 20. Concentrations of total dissolved solids in grid wells relative to non-health-based benchmarks in the California 

Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
46 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 21

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Manganese, relative-concentration

Not Detected

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

NEVADA

CALIFORNIA

ARIZONA

ARIZONA

Figure 21. Concentrations of manganese in grid wells relative to non-health-based benchmarks in the California Desert 

Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 47

sac11-0428_fig 22

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Sulfate, relative-concentration

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

NEVADA

CALIFORNIA

ARIZONA

ARIZONA

Figure 22. Concentrations of sulfate in grid wells relative to non-health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
48 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 23

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES 10 MILES

0 10 KILOMETERS

0

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Iron, relative-concentration

Not Detected

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 23. Concentrations of iron in grid wells relative to non-health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 49

sac11-0428_fig 24

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES

0 10 KILOMETERS

0 10 MILES

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Chloride, relative-concentration

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 24. Concentrations of chloride in grid wells relative to non-health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
50 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

Organic Constituents

Data for 149 organic compounds were used in this 

report, including 83 volatile organic compounds (VOCs), 

64 pesticides and pesticide degradates, and 2 special-interest 

constituents (NDMA and 1,2,3-trichloropropane) (tables 4 and 

B2A–C). Of these, 42 were detected in at least one grid well 

in the Desert Region’s primary aquifers. Of the 200 grid wells 

sampled in the Desert Region, 49.7 percent had no detections 

of any organic constituents, and 48.0 percent of the primary 

aquifer systems had RCs that were considered low (≤ 0.1 of 

benchmarks) (table 7).

Among all organic constituents with health-based 

benchmarks (78 constituents), the proportion of the Desert 

Region’s primary aquifers with high concentrations was 

0.3 percent (table 7), which reflects one detection of NDMA 

(table 7) in the Mojave study unit. This was the only detection 

of an organic constituent at a concentration greater than a 

health-based benchmark. 

The proportion of the Desert primary aquifers having 

moderate RCs of organic constituents was 2.0 percent 

(table 7). Five VOCs were detected at moderate concentrations 

in grid wells: carbon tetrachloride (tetrachloromethane), 

chloroform (trichloromethane), 1,2-dichloropropane, 

tetrachoroethylene (PCE), and 1,2-dichloroethane (table 5). 

One pesticide constituent, dieldrin, was detected at a moderate 

RC. Of these six constituents detected at moderate RCs, only 

chloroform was detected (at low and moderate RCs) in more 

than 10 percent of the grid wells in the Desert Region (fig. 25). 

Twenty-five organic constituents having health-based 

benchmarks were detected at only low RCs (fig. 25). Of 

these, only one pesticide, simazine, was detected in more 

than 10.0 percent of the grid wells in the Desert Region. The 

proportion of the Desert Region’s primary aquifers having low 

RCs of organic constituents was 48.0 percent. The proportion 

of the Desert Region’s primary aquifers having no detections 

of organic constituents with health-based benchmarks was 

49.7 percent (table 7). 

Nine organic constituents that have no health-based 

benchmarks were detected in grid wells in the Desert Region. 

Of these, desethylatrazine, a degradation product of the 

herbicide atrazine and other triazine pesticides, was detected 

in more than 10 percent of the 200 grid wells (fig. 25).

Volatile Organic Compounds

Of the 83 VOCs analyzed, 27 were detected in at least 

one grid well in the Desert Region (table 4 and table B2A). 

The detection frequency for VOCs in the 200 grid wells 

was 32.5 percent. Four VOCs were detected that do not 

have health-based benchmarks: tetrahydrofuran (detected 

in two grid wells), chloroethane (detected in one grid 

well), chloromethane (detected in one grid well), and 

dibromomethane (detected in one grid well). 

In grid wells in the Desert Region, 23 VOCs were 

detected that have health-based benchmarks. Of these, 18 

were detected only at low RCs. None of these were detected 

in more than 10 percent of the grid wells. Five VOCs were 

detected in grid wells at moderate RCs: carbon tetrachloride, 

chloroform, 1,2-dichloroethane, 1,2-dichloropropane, and 

tetrachloroethene. Of these, only chloroform was detected 

in more than 10 percent of the grid wells. No VOCs were 

detected above a health-based benchmark (figs. 25 and 26). 

Chloroform was detected at moderate RCs in 

0.4 percent of the Desert Region’s primary aquifers

(table 5), at low concentrations in 20.2 percent, and not 

detected in 79.4 percent. It was detected in all six study 

areas, with the highest RC in ANT (fig. 26). Chloroform was 

detected in 23 percent of 200 grid wells in the Desert Region 

study areas. The one moderate RC was in a downgradient grid 

well in ANT; low RCs were distributed throughout most study 

areas (fig. 27). No chloroform was detected in grid wells in the 

Yuma subbasin in COL. 

Pesticides and Pesticide Degradates

Of the 64 pesticides and pesticide degradates analyzed in 

all study areas, 14 were detected; 7 were parent compounds 

with benchmarks, 3 were parent compounds without 

benchmarks, and 4 were degradates without benchmarks 

(table B2B). Pesticides or pesticide degradates were detected 

in 17.1 percent of the Desert Region’s primary aquifers at 

low RCs and in 0.3 percent (one grid well) at moderate RCs 

(table 7). The moderate RC was found in MOJ. All detected 

concentrations of pesticides were below health-based 

benchmarks (fig. 28). The individual constituents that were 

not detected and the wells sampled in the Desert Region are 

listed in Densmore and others (2009), Goldrath and others 

(2009, 2010), Mathany and Belitz (2009), and Schmitt and 

others (2009).

Dieldrin, an insecticide, was detected at a moderate RC 

in 0.3 percent of the Desert Region’s primary aquifers. The 

detection was in one well in MOJ (figs. 28 and 29; table 5). 

This was the only detection of dieldrin.

Simazine, an herbicide, was detected at low RCs 

in 13.9 percent of the grid wells and was not detected in 

the remaining 86.1 percent of the grid wells, resulting in 

100 percent of the wells being in the “low” category for the 

Desert Region’s primary aquifers (fig. 28). It was detected in 

one or more wells within every study area except IW (fig. 29). 

Atrazine was detected at low RCs in 9.8 percent of the 

grid wells and was not detected in the remaining 90.2 percent 

of the grid wells (fig. 25). Atrazine was detected in one or 

more of the wells in all study areas except IW (fig. 28). 

Desethylatrazine, a degradate of atrazine and other triazine 

pesticides, was detected in 12.3 percent of the grid wells 

(fig. 25). The combined detection frequency of atrazine and 

desethylatrazine in grid wells was 13.9 percent. 
Status of Groundwater Quality 51

Table 7. Summary of grid-based aquifer-scale proportions for organic constituent classes in the California Desert Groundwater 

Ambient Monitoring and Assessment (GAMA) study areas.

[Low, relative-concentration less than 0.1; Moderate, relative-concentration between 0.1 and 1; High, relative-concentration greater than 1.0; Values are gridbased except where footnoted]

Study area Number of grid 

cells with data

Aquifer-scale proportion (percent)

Not detected Low Moderate High

Volatile organic compounds

Desert Region (all study areas) 200 61.6 37.4 0.9 0.0

Owens Valley 40 67.5 32.5 0.0 0.0

Antelope 56 60.7 37.5 1.8 0.0

Mojave 52 67.3 28.8 3.8 0.0

Coachella 19 47.4 52.6 11.0 0.0

Colorado River 20 65.0 25.0 10.0 0.0

Indian Wells 13 69.2 30.8 0.0 0.0

Pesticides and pesticide degradates

Desert Region (all study areas) 195 82.5 17.1 0.3 0.0

Owens Valley 35 88.2 11.8 0.0 0.0

Antelope 56 75.0 25.0 0.0 0.0

Mojave 52 80.8 17.3 1.9 0.0

Coachella 19 73.7 26.3 0.0 0.0

Colorado River 20 90.0 10.0 0.0 0.0

Indian Wells 13 100.0 0.0 0.0 0.0

Special-interest constituent: 1,2,3-Trichloropropane

Desert Region (all study areas) 200 99.7 0.3 0.0 0.0

Owens Valley 40 100.0 0.0 0.0 0.0

Antelope 56 100.0 0.0 0.0 0.0

Mojave 52 100.0 0.0 0.0 0.0

Coachella 19 100.0 0.0 0.0 0.0

Colorado River 20 95.0 5.0 0.0 0.0

Indian Wells 13 100.0 0.0 0.0 0.0

Special-interest constituent: N-Nitrosodimethylamine

Desert Region (all study areas) 77 99.0 0.0 0.0 1.4

Owens Valley 32 100.0 0.0 0.0 0.0

Antelope 18 100.0 0.0 0.0 0.0

Mojave 19 94.7 0.0 0.0 5.3

Indian Wells 8 100.0 0.0 0.0 0.0

Any organic constituents with health-based benchmarks

Desert Region (all study areas) 200 49.7 48.0 2.0 0.3

Owens Valley 40 62.5 37.5 0.0 0.0

Antelope 56 21.4 76.8 1.8 0.0

Mojave 52 53.8 38.5 5.8 1.9

Coachella 19 47.4 52.6 11.0 0.0

Colorado River 20 55.0 35.0 10.0 0.0

Indian Wells 13 69.2 30.8 0.0 0.0

1

Spatially weighted value.
52 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 25

Low

Moderate

High

10

1

0.1

0.01

0.001

0.0001

0.00001

0.1% 1.0% 10.0% 100.0%

Detection frequency

Maximum relative-concentration

N-Nitrosodimethylamine

Dieldrin

Atrazine

Simazine

Metolachlor

Chloroform

Bromodichloromethane

Dibromochloromethane

Desethylatrazine

1,1-Dichloroethane Bromoform

1,1-Dichloroethene

1,2-Dichloroethane

Carbon Tetrachloride

cis-1,2-Dichloroethene Dichloromethane

trans-1,2-Dichloroethene

Trichlorofluoromethane

Chlorobenzene

1,2-Dichloropropane

Methyl tert-butyl ether

1,2-Dichlorobenzene

Chloromethane

Carbon Disulfide

Bromochloromethane

Styrene

Tetrachloroethene

Prometon

Trichloroethylene

1,3-Dichlorobenzene

1,4-Dichlorobenzene

Chloromethane

Tebuthiuron Hexazinone

3,4-Dichloroaniline

Fipronil

Desulfinylfipronil Fipronil Sulfide

Prometryn No Health-Based 

Benchmarks

Tetrahydrofuran Chloroethane Dibromomethane

Figure 25. Detection frequencies and maximum relative-concentrations for organic constituents detected 

in grid wells in the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study 

areas, 2006–2008.
Status of Groundwater Quality 53

sac11-0428_fig 26

Low

Moderate

High

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

0.0001

0.001

0.01

0.1

1

10

Relative-concentration

1,2-Dichloroethane 1,2-Dichloropropane Carbon Tetrachloride Chloroform Tetrachloroethene

0.00001

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

Detection frequency

10 percent

Figure 26. Concentrations relative to health-based benchmarks and detection frequencies 

of volatile organic compounds in grid wells in the California Desert Region Groundwater 

Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
54 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 27

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES

0 10 KILOMETERS

0 10 MILES

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data CDPH-Grid Data

Chloroform, relative-concentration

Not Detected

Low

Moderate

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

Figure 27. Concentrations of chloroform relative to health-based benchmarks in the California Desert Region Groundwater 

Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 55

sac11-0428_fig 28

Atrazine Dieldrin Simazine

0.0001

0.001

0.01

0.1

1

Relative-concentration

10

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

Detection frequency

Low

Moderate

High

10 percent

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Figure 28. Concentrations relative to health-based benchmarks and detection frequencies of 

pesticide compounds in grid wells in the California Desert Region Groundwater Ambient Monitoring and 

Assessment (GAMA) study areas, 2006–2008.
56 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 29

EXPLANATION

0 10 MILES

0 10 MILES

0 10 KILOMETERS

0 10 KILOMETERS

Colorado River

Antelope

Coachella

Owens Valley

Indian Wells

Mojave

0 10 MILES

0 10 KILOMETERS

0 10 MILES

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data

Simazine and Dieldrin, relative-concentration

Not Detected

Simazine, Low

Simazine, Low; Dieldrin, Moderate

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

117° 116°30’ 116°

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

33°30’

34°

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

115° 114°30’

34°30’

33°30’

34°

33°

117°

NEVADA

NEVADA

ARIZONA

ARIZONA

CALIFORNIA

NEVADA

Figure 29. Concentrations of dieldrin and simazine relative to health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
Status of Groundwater Quality 57

Special-Interest Constituents

Two organic special-interest constituents were analyzed 

in samples from the Desert Region. 1,2,3-Trichloropropane 

was sampled at all wells and was analyzed at laboratory 

reporting levels of 0.12 to 0.18 micrograms per liter 

(Densmore and others, 2009; Goldrath and others, 2009, 

2010; Mathany and Belitz, 2009; Schmitt and others, 

2009). At 94 wells, additional samples were analyzed 

for 1,2,3-trichloropropane at a method detection level of 

0.005 microgram per liter. It was detected in one well in COL 

at a low RC. 

N-Nitrosodimethylamine (NDMA) was analyzed 

in samples collected in four study areas (OV, IW, ANT, 

MOJ). NDMA was detected at a high RC in one grid 

well in MOJ (figs. 30 and 31), equivalent to 1.4 percent 

of the Desert Region’s primary aquifers (table 7). This 

was the only detection of an organic constituent above a 

health-based benchmark. 

sac11-0428_fig 30

0.001

0.01

0.1

1

Relative-concentration

10

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

Detection frequency

No Data Available

No Data Available

N-Nitrosodimethylamine

Low

Moderate

High

10 percent

Owens Valley

Indian Wells

Colorado River

Antelope

Mojave

Coachella

Figure 30. Detection frequency and concentrations 

of N-nitrosodimethylamine in 77 grid wells relative 

to health-based benchmarks in the California Desert 

Region Groundwater Ambient Monitoring and 

Assessment (GAMA) study areas, 2006–2008.
58 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig 31

EXPLANATION

0 10 MILES

0 10 KILOMETERS

Owens Valley Antelope

Indian Wells

Mojave

0 10 MILES

0 10 KILOMETERS

0 8 MILES

0 8 KILOMETERS

Aqueduct

Canal

Stream, perennial

Stream, intermittent

Study area boundary

Lake

Dry lake bed

Urban land use

Agricultural land use

Natural land use

USGS-Grid Data

N-nitrosodimethylamine, relative-concentration

Not Detected

High

118°30’

119° 118° 117° 116° 115° 114°

118°30’

118° 117°30’

37°30’

36°30’

38°

37°

38°

35°

34°

33°

35°30’

36°

37°

118° 118° 117°30’ 116°30’

35°

34°30’

117°

NEVADA

ARIZONA

CALIFORNIA

NEVADA

Figure 31. Concentrations of N-nitrosodimethylamine relative to health-based benchmarks in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
References 59

Summary 

Groundwater quality in six California Desert Region 

study areas, covering approximately 6,050 square miles 

(mi2) [15,670 square kilometers (km2)] was investigated by 

the U.S. Geological Survey (USGS) as part of the Priority 

Basin Project of the Groundwater Ambient Monitoring and 

Assessment (GAMA) Program. Samples were collected 

from September 2006 through April 2008 from 253 wells in 

the Owens, Indian Wells, Coachella, Antelope, and Mojave 

Valleys, and in three Colorado River Basins. 

The GAMA Priority Basin Project is designed to 

provide a statistically robust characterization of untreated 

groundwater quality in the primary aquifer at the basin-scale. 

Two-hundred grid wells were selected within spatially 

distributed, randomized grid cells in the Desert Region study 

areas to assess the quality of the groundwater; fifty-three wells 

were sampled to provide additional insight into groundwater 

conditions. Current (2003–2008) California Department of 

Public Health (CDPH) data in each study area were used to 

complement USGS-grid-well data and provide additional 

information about groundwater quality. Because of the large 

number of constituents, relative-concentrations (RCs) (sample 

concentration divided by benchmark concentration) were 

used as the primary metric for comparing concentrations in 

groundwater, for those constituents that have Federal and (or) 

California benchmarks. An RC greater than (>) 1.0 indicates 

a concentration above a benchmark, and an RC less than or 

equal to (≤) 1.0 indicates a concentration equal to or below 

a benchmark. Organic and special-interest constituent RCs 

were classified as “low” (RC ≤ 0.1), “moderate” (0.1 < RC 

≤ 1.0), or “high” (RC > 1.0). Inorganic constituent RCs were 

classified as “low” (RC ≤ 0.5), “moderate” (0.5 < RC ≤ 1.0), 

or “high” (RC > 1.0). A lower threshold value RC was used 

to distinguish between low and moderate RCs for organic 

constituents because these constituents are generally less 

prevalent and have smaller RCs than inorganic constituents.

Grid-based and spatially weighted statistical approaches 

were used to assess aquifer-scale proportions of constituents 

at high, moderate, and low RCs in the primary aquifers 

to characterize the quality of untreated groundwater. The 

grid-based aquifer proportions, which were based on 

sampling one randomly selected well per grid cell, were 

verified by checking that the spatially weighted results, 

which incorporated the CDPH data from every well in each 

grid cell, fell within 90 percent confidence intervals of the 

grid-based values. 

For inorganic constituents with health-based benchmarks, 

35.4 percent of the Desert Region’s primary aquifers had high 

RCs of at least one constituent, 27.4 percent had moderate 

RCs, and 37.2 percent had low RCs. Inorganic constituents 

detected at high concentrations relative to health-based 

benchmarks were arsenic, boron, fluoride, gross-alpha 

radioactivity, molybdenum, nitrate, strontium, uranium, 

and vanadium. Inorganic constituents detected at high 

concentrations relative to non-health-based benchmarks were 

chloride, iron, manganese, sulfate, and total dissolved solids. 

A special-interest constituent, perchlorate, was also detected at 

high RCs. 

In contrast to the aquifer-scale proportions for high 

inorganic constituents, organic constituents were detected 

at high concentrations in only 0.3 percent of the Desert 

Region’s primary aquifers. The proportion of the Desert 

Region’s primary aquifers having moderate concentrations of 

organic constituents was 2 percent, and 48 percent had low 

concentrations or no detections. No organic constituents with 

health-based benchmarks were detected in 49.7 percent of the 

Desert Region’s primary aquifers. 

Acknowledgments

The authors thank the following cooperators for their 

support: the California State Water Resources Control 

Board, Lawrence Livermore National Laboratory, California 

Department of Public Health, and California Department 

of Water Resources. We especially thank the well owners 

and water purveyors for their generosity in allowing the 

U.S. Geological Survey to collect samples from their wells. 

Funding for this work was provided by State of California 

bonds authorized by Proposition 50 and administered by the 

California State Water Resources Control Board. 

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and simulations—The Holly site, Edwards Air Force Base, 

Antelope Valley, California: U.S. Geological Survey WaterResources Investigations Report 00-4015, 65 p. 

Stamos, C.L., Martin, P., Nishikawa, T., and Cox, B.F., 2001, 

Simulation of ground-water flow in the Mojave River 

basin, California: U.S. Geological Survey Water-Resources 

Investigations Report 01-4002, 129 p. 

State Water Resources Control Board, 2003, A comprehensive 

groundwater quality monitoring program for California: 

Assembly Bill 99 Report to the Governor and Legislature, 

March 2003, 100 p, Accessed on April 10, 2012, at http://

www.waterboards.ca.gov/gama/docs/final_ab_599_rpt_to_

legis_7_31_03.pdf.

Toccalino, P.L., and Norman, J.E., 2006, Health-based 

screening levels to evaluate U.S. Geological Survey 

ground-water quality data: Risk Analysis, v. 26, no. 5, 

p. 1339–1348.

Toccalino, P.L., Norman, J.E., Phillips, R.H., Kauffman, 

L.J., Stackelberg, P.E., Nowell, L.H., Krietzman, S.J., and 

Post, G.B., 2004, Application of health-based screening 

levels to ground-water quality data in a state-scale pilot 

effort: U.S. Geological Survey Scientific Investigations 

Report 2004-5174, 64 p. 

Tyley, S.J., 1974, Analog model study of the ground-water 

basin of the Upper Coachella Valley, California: U.S. 

Geological Survey Water-Supply Paper 2027, 77 p. 

U.S. Environmental Protection Agency, 1998, Code of 

Federal Regulations, title 40—protection of environment, 

chapter 1—Environmental Protection Agency, 

subchapter E—pesticide programs, part 159—statements 

of policies and interpretations, subpart D—reporting 

requirements for risk/benefit information, 40 CFR 

159.184: National Archives and Records Administration, 

September 19, 1997; amended June 19, 1998, Accessed 

September 5, 2008, at http://www.epa.gov/EPA-PEST/1997/

September/Day-19/p24937.htm. 

U.S. Environmental Protection Agency, 2000, National 

primary drinking water regulations; radionuclides; final 

rule, accessed February 2012 at https://federalregister.

gov/a/00-30421.
References 63

U.S. Environmental Protection Agency, 2011, 2011 Edition 

of the Drinking Water Standards and Health Advisories, 

updated January 2011: U.S. Environmental Protection 

Agency, Office of Water EPA/822-R-11-002, accessed 

March 14, 2012, at http://water.epa.gov/action/advisories/

drinking/upload/dwstandards2011.pdf.

U.S. Geological Survey, 2011, USGS water data for the Nation 

help system, parameter help, accessed March 14, 2012, at 

http://waterdata.usgs.gov/nwis/help?parameters_help. 

Zogorski, J.S., Carter, J.M., Ivahnenko, T., Lapham, W.W., 

Moran, M.J., Rowe, B.L., Squillace, P.J., and Toccalino, 

P.L., 2006, Volatile organic compounds in the Nation’s 

ground water and drinking-water supply wells: U.S. 

Geological Survey Circular 1292, 101 p. 
64 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

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Appendix A 65

Appendix A. Use of Data From the CDPH Database

California requires regular sampling of public-supply 

wells under Title 22, and historical data are available from the 

CDPH database. The GAMA Program used CDPH’s existing 

monitoring data along with data collected by USGS-GAMA 

to characterize the primary aquifers. The CDPH database 

provided additional water-quality data for the grid-based and 

statistically weighted approaches to estimating aquifer-scale 

proportions for constituents. Methods for the selection and use 

of CDPH data are described in the following sections.

Spatially Weighted Assessment

For each constituent, the spatially weighted approach 

(Belitz and others, 2010) used the most recent CDPH data 

within the current 3-year period (table 1) for every well in 

a grid cell. The average of all of the data selected in a grid 

cell, including the USGS-grid and USGS-additional data, 

was calculated; this average was used as the value of that 

constituent for that grid cell. This average value was then 

divided by the constituent’s respective benchmark in order to 

calculate that constituent’s RC for the grid cell. The aquifer 

proportion was then calculated as the percentage of grid cells 

with high, moderate, or low RCs.

Grid-Based Assessment

The grid-based approach is based on a single value 

from a well in each grid cell. Not all inorganic constituents 

sampled by the USGS were sampled in every grid cell, and 

for some grid cells, no well was available for sampling by 

the USGS. To supplement the USGS dataset, the CDPH 

database was used to fill in the missing constituents. The 

CDPH wells in each cell were ranked using the same method 

as for the selection of the USGS-grid wells (Scott, 1990). For 

cells that had no USGS-grid well, the highest ranked CDPH 

well that had data from the current sampling period in each 

study area (table 1) and a cation/anion balance of less than 

10 percent, a commonly used quality-assurance check for 

water-sample analysis (Hem, 1989), was selected to complete 

the grid dataset. This step resulted in the selection of CDPHgrid data to fill 14 empty grid cells. For cells that did not 

have a complete set of inorganic data, two selection methods 

were used: 

1. CDPH data were selected from the same well sampled by 

the USGS, if it met the selection criteria used to fill empty 

grid cells. This step resulted in the selection of inorganic 

data from the CDPH database for 59 grid cells that also 

contain USGS data. 

2. If no acceptable CPDH data were available from the same 

well sampled by the USGS, data from the highest ranking 

well located in the same grid cell, that met the same 

criteria, were selected. This step resulted in the selection 

of CDPH-grid wells for 29 grid cells. 

These selection methods resulted in one set of inorganic data 

per cell from either the USGS database or from the CDPH 

database, or a combination of data from both sources for 197 

of the 251 grid cells (table B1, figs. 4A–H). 

Analysis of the combined USGS and CDPH datasets 

for the evaluation of the occurrence of relatively high or 

moderate concentrations was not affected by differences in 

laboratory reporting levels or method detection levels between 

USGS-collected and CDPH data because concentrations 

high enough to be relevant to benchmarks were generally 

substantially higher than the highest reporting levels. Several 

types of comparisons between USGS-collected and CDPH 

data are described in appendix C.
66 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

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Appendix B 67

Appendix B. Data For Individual Desert Study Areas
68 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas. [No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well] Grid cell number USGS GAMA well identification number CDPH GAMA well identification number Well type Land use categories (percent) Land use classification Construction information (ft below LSD) Agricultural land use within 500 m of the well Natural land use within 500 m of the well Urban land use within 500 m of the well Well depth Top of perforations Bottom of perforations Antelope study area

1 ANT-09 na PSW 60 37 3 Agricultural 213 93 213

2 No USGS well ANT-DPH-02 PSW 3 97 0 Natural na na na

3 ANT-56 No CDPH well DOM 93 7 0 Agricultural 340 170 340

4 ANT-44 na PSW 66 34 0 Agricultural 320 na na

4 na ANT-DPH-04 PSW 52 47 1 Agricultural na na na

5 ANT-15 na PSW 81 19 0 Agricultural 680 na na

6 No USGS well ANT-DPH-06 PSW 62 38 0 Agricultural na na na

7 No USGS well ANT-DPH-07 PSW 32 68 0 Natural na na na

8 ANT-54 No CDPH well IRR 87 13 1 Agricultural 821 na na

9 No USGS well ANT-DPH-09 PSW 76 24 0 Agricultural na na na

10 ANT-28 na PSW 0 100 0 Natural na na na

10 na ANT-DPH-10 PSW 0 64 36 Natural na na na

11 ANT-29 na PSW 1 99 0 Natural na na na

11 na ANT-DPH-11 PSW 50 50 0 Agricultural na na na

12 ANT-04 na PSW 86 14 0 Agricultural 765 350 765

13 ANT-42 na PSW 93 7 0 Agricultural na na na

13 na ANT-DPH-13 PSW 82 18 0 Agricultural 680 360 680

14 ANT-08 ANT-DPH-14 PSW 77 20 3 Agricultural 500 na na

15 ANT-41 ANT-DPH-15 PSW 79 21 0 Agricultural na na na

16 ANT-46 na PSW 69 28 3 Agricultural 475 250 475

17 ANT-31 ANT-DPH-17 PSW 18 76 6 Natural na na na

18 ANT-53 No CDPH well PSW 0 34 66 Urban 232 70 209

19 ANT-01 ANT-DPH-19 PSW 39 31 30 Mixed na na na

20 ANT-03 na PSW 13 6 81 Urban 570 390 560

20 na ANT-DPH-20 PSW 2 32 66 Urban 610 260 600

21 ANT-47 na PSW 1 84 16 Natural 1,100 115 1,10022 ANT-16 ANT-DPH-22 PSW 0 85 15 Natural 300 120 300

23 ANT-14 No CDPH well PSW 1 92 7 Natural 470 270 470

24 ANT-07 na PSW 0 100 0 Natural 527 260 527

25 ANT-48 na PSW 83 15 2 Agricultural na na na

26 ANT-22 ANT-DPH-26 PSW 0 95 5 Natural 365 na na
Appendix B 69

Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued[No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well]

Grid

cell

number

USGS

GAMA well 

identification

number

CDPH

GAMA well 

identification

number

Well 

type

Land use categories

(percent)

Land use 

classification

Construction information

(ft below LSD)

Agricultural 

land use 

within 500 m of 

the well

Natural 

land use 

within 500 m 

of the well

Urban 

land use 

within 500 m 

of the well

Well

depth 

Top of 

perforations

Bottom of 

perforations 

Antelope study area—Continued

27 ANT-27 ANT-DPH-27 PSW 0 96 4 Natural 220 na na

28 ANT-06 na PSW 0 80 20 Natural 1,000 240 1,000

28 na ANT-DPH-28 PSW 0 60 40 Natural 1,104 180 na29 ANT-17 na PSW 0 13 87 Urban 552 192 552

30 ANT-05 na PSW 0 78 22 Natural 770 350 762

30 na ANT-DPH-30 PSW 0 80 20 Natural 740 350 728

31 ANT-49 na PSW 0 81 19 Natural 801 500 801

32 ANT-55 ANT-DPH-32 PSW 70 12 18 Agricultural 800 420 800

33 ANT-21 ANT-DPH-33 PSW 0 92 8 Natural 400 na na

34 ANT-20 ANT-DPH-34 PSW 0 100 0 Natural 350 80 350

35 ANT-02 na PSW 0 73 27 Natural 400 190 400

36 ANT-18 na PSW 86 13 0 Agricultural 920 570 900

36 na ANT-DPH-36 PSW 87 12 1 Agricultural 694 na na

37 ANT-30 ANT-DPH-37 PSW 55 30 15 Agricultural 700 400 700

38 ANT-12 na PSW 86 11 3 Agricultural 1,200 na na

39 ANT-10 ANT-DPH-39 PSW 91 8 0 Agricultural 1,200 360 1,200

40 No USGS well ANT-DPH-40 PSW 0 91 8 Natural 154 70 na41 ANT-11 ANT-DPH-41 PSW 0 100 0 Natural 125 80 102

42 ANT-37 ANT-DPH-42 PSW 0 100 0 Natural 700 270 690

43 ANT-38 ANT-DPH-43 PSW 0 100 0 Natural 700 290 690

44 ANT-40 na PSW 0 100 0 Natural 843 583 833

45 ANT-13 ANT-DPH-45 PSW 33 11 56 Urban 600 350 600

46 No USGS well ANT-DPH-46 PSW 75 5 20 Agricultural na na na

47 ANT-19 ANT-DPH-47 PSW 0 97 3 Natural 410 200 410

48 ANT-26 na PSW 0 100 0 Natural 320 160 300

49 ANT-43 na PSW 2 48 50 Urban 550 210 540

50 No USGS well No CDPH well na na na na na na na na

51 ANT-23 ANT-DPH-51 PSW 8 89 3 Natural 150 na 150

52 No USGS well ANT-DPH-52 PSW 0 69 31 Natural na na na

53 ANT-25 No CDPH well PSW 0 100 0 Natural 360 na na

54 No USGS well ANT-DPH-54 PSW 0 87 13 Natural na na na
70 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued [No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well] Grid cell number USGS GAMA well identification number CDPH GAMA well identification number Well type Land use categories (percent) Land use classification Construction information (ft below LSD) Agricultural land use within 500 m of the well Natural land use within 500 m of the well Urban land use within 500 m of the well Well depth Top of perforations Bottom of perforations Antelope study area—Continued 55 ANT-39 ANT-DPH-55 PSW 1 99 0 Natural 750 238 738 56 ANT-35 ANT-DPH-56 PSW 0 100 0 Natural 534 155 505 57 ANT-45 na PSW 0 86 14 Natural na na na 58 ANT-51 na PSW 0 49 51 Urban 328 188 328 59 ANT-32 ANT-DPH-59 PSW 27 41 31 Mixed 715 na na 60 ANT-33 ANT-DPH-60 PSW 0 100 0 Natural 530 281 530 61 ANT-34 na PSW 0 93 7 Natural 606 96 606 62 No USGS well No CDPH well na na na na na na na na 63 ANT-36 ANT-DPH-63 PSW 0 100 0 Natural 548 148 548 64 ANT-52 ANT-DPH-53 PSW 0 80 20 Natural 300 200 300 65 ANT-24 na PSW 0 100 0 Natural 795 545 785 65 na ANT-DPH-65 PSW 0 100 0 Natural na na na 66 ANT-50 ANT-DPH-66 PSW 0 94 6 Natural na na na Coachella study area

1 COA-13 COA-DG-13 PSW 1 79 20 Natural 890 510 870

2 COA-01 na PSW 2 97 0 Natural 1,200 900 1,200

3 COA-17 na PSW 0 100 0 Natural na na na

4 COA-15 na PSW 0 67 33 Natural 400 180 380

5 COA-19 na PSW 0 45 55 Urban na na na

6 COA-16 na IND 0 98 2 Natural 650 300 650

7 COA-03 na PSW 94 6 0 Agricultural na na na

8 COA-05 na IRR 1 11 87 Urban 1090 710 1,090

8 na COA-DPH-22 PSW 1 77 22 Natural na na na

9 COA-14 na PSW 2 34 64 Urban 820 420 820

10 COA-09 na PSW 1 30 69 Urban na na na

11 COA-04 COA-DG-04 PSW 1 62 37 Natural 1,070 500 1,060

12 COA-06 na PSW 4 34 62 Urban 654 203 654

13 COA-08 na IRR 86 13 1 Agricultural 342 258 342

14 COA-18 na PSW 31 69 0 Natural 790 280 790
Appendix B 71

Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued[No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well]

Grid

cell

number

USGS

GAMA well 

identification

number

CDPH

GAMA well 

identification

number

Well 

type

Land use categories

(percent)

Land use 

classification

Construction information

(ft below LSD)

Agricultural 

land use 

within 500 m of 

the well

Natural 

land use 

within 500 m 

of the well

Urban 

land use 

within 500 m 

of the well

Well

depth 

Top of 

perforations

Bottom of 

perforations 

Coachella study area—Continued

15 No USGS well No CDPH well na na na na na na na na

16 COA-12 na DOM 94 5 1 Agricultural 525 445 525

17 COA-02 na AQU 43 57 0 Natural 550 230 480

18 COA-11 na PSW 87 9 4 Agricultural na na na

19 COA-10 COA-DG-10 PSW 70 10 20 Agricultural na na na

20 COA-07 na PSW 5 95 1 Natural 240 na na

Colorado River study area

1 COLOR-11 na PSW 0 95 5 Natural na na na

2 COLOR-04 na PSW 42 57 1 Natural 90 30 90

3 COLOR-08 na PSW 0 88 12 Natural 500 140 480

4 COLOR-20 na DOM 0 61 39 Natural 700 na na

5 COLOR-13 na PSW 0 90 10 Natural 195 na na

6 COLOR-12 na PSW 0 100 0 Natural 420 300 420

7 COLOR-18 na IND 8 90 3 Natural 600 150 580

8 COLOR-09 na PSW 70 30 0 Agricultural na na na

9 COLOR-10 na PSW 66 13 21 Agricultural 1,000 na na

10 COLOR-14 na DOM 0 90 10 Natural na na na

11 COLOR-03 na PSW 53 13 34 Agricultural 512 437 497

12 COLOR-07 na PSW 43 56 1 Natural 438 20 438

13 COLOR-06 na PSW 0 13 86 Urban 505 421 na14 COLOR-05 na PSW 80 7 12 Agricultural 610 380 590

15 COLOR-17 na PSW 0 98 2 Natural 210 80.2 200

16 COLOR-16 na PSW 26 40 34 Mixed 600 378 486

17 COLOR-01 na PSW 0 100 0 Natural na na na

18 COLOR-02 na PSW 1 94 5 Natural na na na

19 COLOR-15 na DOM 59 23 17 Agricultural na na na

20 COLOR-19 na IRR 85 11 4 Agricultural 143 118 140
72 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued [No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well] Grid cell number USGS GAMA well identification number CDPH GAMA well identification number Well type Land use categories (percent) Land use classification Construction information (ft below LSD) Agricultural land use within 500 m of the well Natural land use within 500 m of the well Urban land use within 500 m of the well Well depth Top of perforations Bottom of perforations Indian Wells study area

1 No USGS well No CDPH well na na na na na na na na

2 OIW-03 No CDPH well PSW 0 91 9 Natural na na na

3 No USGS well No CDPH well na na na na na na na na

4 OIW-09 No CDPH well DOM 30 69 1 Natural na na na

5 OIW-04 OIW-DG-04 PSW 0 98 2 Natural 400 320 400

6 OIW-12 No CDPH well PSW 0 100 0 Natural 200 100 na7 na OIW-DPH-21 PSW 19 81 0 Natural na na na

7 OIW-08 na PSW 0 18 82 Urban 190 na na

8 OIW-10 OIW-DG-10 PSW 0 100 0 Natural 260 200 260

9 OIW-02 OIW-DG-02 PSW 0 70 30 Natural 480 310 470

10 na OIW-DPH-22 PSW 0 100 0 Natural na na na

10 OIW-05 na PSW 0 99 1 Natural 1,020 560 1,000

11 OIW-07 OIW-DG-07 PSW 0 91 9 Natural 620 260 600

12 OIW-01 OIW-DG-01 PSW 0 95 5 Natural 850 320 830

13 No USGS well No CDPH well na na na na na na na na

14 No USGS well No CDPH well na na na na na na na na

15 No USGS well No CDPH well na na na na na na na na

16 OIW-13 No CDPH well MW 0 100 0 Natural 70 60 70

17 No USGS well No CDPH well na na na na na na na na

18 No USGS well No CDPH well na na na na na na na na

19 OIW-11 No CDPH well MW 0 57 43 Natural 77 75 77

20 OIW-06 OIW-DG-06 PSW 0 100 0 Natural 232 135 181

Mojave study area

1 MOJO-28 na PSW 1 88 12 Natural 230 50 165

1 na MOJO-DPH-01 PSW 0 76 24 Natural na na na

2 MOJO-31 na PSW 0 100 0 Natural 1,130 660 1,120

3 No USGS well No CDPH well na na na na na na na na

4 MOJO-07 na PSW 0 100 0 Natural 660 na na

4 na MOJO-DPH-04 PSW 0 100 0 Natural na na na

5 No USGS well MOJO-DPH-05 PSW 0 100 0 Natural 691 379 691
Appendix B 73

Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued[No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well]

Grid

cell

number

USGS

GAMA well 

identification

number

CDPH

GAMA well 

identification

number

Well 

type

Land use categories

(percent)

Land use 

classification

Construction information

(ft below LSD)

Agricultural 

land use 

within 500 m of 

the well

Natural 

land use 

within 500 m 

of the well

Urban 

land use 

within 500 m 

of the well

Well

depth 

Top of 

perforations

Bottom of 

perforations 

Mojave study area—Continued

6 MOJO-48 No CDPH well IRR 18 82 0 Natural 520 200 540

7 MOJO-20 MOJO-DPH-07 PSW 0 95 5 Natural na na na

8 MOJO-13 na PSW 25 57 17 Natural na na na

9 MOJO-12 na PSW 20 60 19 Natural 360 110 360

10 MOJO-25 na PSW 12 88 0 Natural na na na

11 MOJO-30 na PSW 0 60 40 Natural 650 430 630

12 no USGS well MOJO-DPH-12 PSW 0 95 5 Natural na na na

13 MOJO-11 MOJO-DPH-13 PSW 0 47 53 Urban 630 310 610

14 MOJO-10 No CDPH well PSW 0 65 35 Natural 1,010 600 na

15 MOJO-27 na PSW 1 43 56 Urban 1,110 850 1,110

16 MOJO-08 MOJO-DPH-16 PSW 0 100 0 Natural 660 na na

17 no USGS well No CDPH well na na na na na na na na

18 MOJO-32 MOJO-DPH-18 PSW 0 71 29 Natural 800 na na

19 MOJO-16 na PSW 0 68 32 Natural 1,000 515 1,000

20 MOJO-04 MOJO-DPH-20 PSW 0 66 34 Natural 877 445 865

21 MOJO-14 na PSW 0 8 92 Urban 530 365 505

22 MOJO-15 na PSW 0 54 46 Natural 720 495 700

23 MOJO-26 MOJO-DPH-23 PSW 1 84 15 Natural 390 180 390

24 MOJO-09 MOJO-DPH-24 PSW 8 79 13 Natural 425 150 415

25 MOJO-02 MOJO-DPH-25 PSW 0 100 0 Natural 330 133 330

26 MOJO-19 na PSW 0 77 23 Natural 420 160 180

27 MOJO-01 MOJO-DPH-27 PSW 17 68 15 Natural 393 168 373

28 MOJO-06 MOJO-DPH-28 PSW 4 76 20 Natural 334 164 334

29 MOJO-18 na PSW 0 79 21 Natural na na na

30 MOJO-46 MOJO-DPH-30 PSW 0 45 55 Urban 606 258 565

31 MOJO-17 na PSW 0 61 39 Natural 810 410 810

32 MOJO-05 MOJO-DPH-32 PSW 0 90 10 Natural 700 420 700

33 MOJO-34 No CDPH well PSW 0 100 0 Natural na na na

34 MOJO-29 na PSW 0 92 8 Natural 480 na na

35 MOJO-21 na PSW 1 92 8 Natural na na na
74 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued [No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well] Grid cell number USGS GAMA well identification number CDPH GAMA well identification number Well type Land use categories (percent) Land use classification Construction information (ft below LSD) Agricultural land use within 500 m of the well Natural land use within 500 m of the well Urban land use within 500 m of the well Well depth Top of perforations Bottom of perforations Mojave study area—Continued 35 na MOJO-DPH-35 PSW 0 94 6 Natural na na na 36 MOJO-03 na PSW 0 72 28 Natural 310 221 310 36 na MOJO-DPH-36 PSW 0 75 25 Natural na na na 37 No USGS well MOJO-DPH-37 PSW 0 58 42 Natural na na na 38 MOJO-43 MOJO-DPH-38 PSW 0 100 0 Natural na na na 39 MOJO-39 na PSW 0 93 7 Natural na na na 40 MOJO-40 na IRR 0 97 3 Natural 350 190 350 40 na MOJO-DPH-40 PSW 0 61 39 Natural na na na 41 MOJO-45 na DOM 0 65 35 Natural 200 na na 41 na MOJO-DPH-41 PSW 0 70 30 Natural na na na 42 MOJO-50 na IRR 11 89 0 Natural 150 na na 42 na MOJO-DPH-42 PSW 0 60 39 Natural 174 na na 43 No USGS well No CDPH well na na na na na na na na 44 MOJO-44 MOJO-DPH-44 PSW 1 96 3 Natural 700 na na 45 MOJO-33 na PSW 0 83 17 Natural 140 105 140 45 na MOJO-DPH-45 PSW 0 74 26 Natural na na na 46 No USGS well No CDPH well na na na na na na na na 47 MOJO-47 na DOM 0 100 0 Natural na na na 47 na MOJO-DPH-47 PSW 0 92 8 Natural 420 na 396 48 MOJO-23 na PSW 0 100 0 Natural na na na 48 na MOJO-DPH-48 PSW 0 100 0 Natural 195 74 144 49 No USGS well No CDPH well na na na na na na na na 50 MOJO-22 No CDPH well PSW 0 100 0 Natural na na na 51 MOJO-24 na PSW 0 74 26 Natural 300 120 300 51 na MOJO-DPH-51 PSW 0 83 17 Natural na na na 52 No USGS well No CDPH well na na na na na na na na 53 MOJO-42 na PSW 0 89 11 Natural 388 242 na 54 na MOJO-DPH-54 PSW 0 99 1 Natural na na na

55 MOJO-35 na PSW 0 83 17 Natural 400 160 400

56 No USGS well MOJO-DPH-56 PSW 1 99 0 Natural na na na

57 MOJO-49 na PSW 0 100 0 Natural 400 200 390
Appendix B 75

Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued[No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well]

Grid

cell

number

USGS

GAMA well 

identification

number

CDPH

GAMA well 

identification

number

Well 

type

Land use categories

(percent)

Land use 

classification

Construction information

(ft below LSD)

Agricultural 

land use 

within 500 m of 

the well

Natural 

land use 

within 500 m 

of the well

Urban 

land use 

within 500 m 

of the well

Well

depth 

Top of 

perforations

Bottom of 

perforations 

Mojave study area—Continued

58 No USGS well No CDPH well na na na na na na na na

59 MOJO-51 na IRR 0 100 0 Natural 300 na na

59 na MOJO-DPH-59 PSW 0 100 0 Natural na na na

60 MOJO-41 na PSW 0 100 0 Natural na na na

61 MOJO-52 na DOM 5 95 0 Natural na na na

61 na MOJO-DPH-61 PSW 4 96 0 Natural na na na

62 MOJO-38 MOJO-DPH-62 PSW 3 97 0 Natural 110 na na

63 No USGS well No CDPH well na na na na na na na na

64 MOJO-36 MOJO-DPH-65 PSW 1 93 7 Natural 140 na na

65 MOJO-37 No CDPH well PSW 3 97 0 Natural na na na

Owens Valley study area

1 OV-11 na PSW 0 75 25 Natural 161 121 161

2 na OV-DPH-61 PSW 30 9 62 Urban na na na

2 OV-37 na PSW 36 24 40 Mixed 400 100 390

3 OV-10 na PSW 8 92 0 Natural na na na

4 OV-08 OV-DG-08 PSW 26 55 19 Natural 800 240 800

5 OV-04 OV-DG-04 PSW 0 100 0 Natural 340 na na

6 na OV-DPH-62 PSW 2 71 27 Natural na na na

6 OV-29 na PSW 2 85 12 Natural 200 180 200

7 No USGS well No CDPH well na na na na na na na na

8 No USGS well No CDPH well na na na na na na na na

9 No USGS well No CDPH well na na na na na na na na

10 OV-20 No CDPH well IRR 32 68 0 Natural na na na

11 OV-18 No CDPH well IRR 94 6 0 Agricultural 642 210 640

12 OV-28 No CDPH well PSW 4 48 48 Mixed 150 130 150

13 OV-01 OV-DG-01 PSW 48 11 42 Mixed 217 70 na14 OV-26 OV-DG-26 PSW 11 39 51 Urban 128 70 120

15 OV-09 OV-DG-09 PSW 2 57 41 Natural na na na

16 No USGS well No CDPH well na na na na na na na na

17 OV-02 na PSW 48 19 33 Mixed 126 60 120
76 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued [No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well] Grid cell number USGS GAMA well identification number CDPH GAMA well identification number Well type Land use categories (percent) Land use classification Construction information (ft below LSD) Agricultural land use within 500 m of the well Natural land use within 500 m of the well Urban land use within 500 m of the well Well depth Top of perforations Bottom of perforations Owens Valley study area—Continued 18 No USGS well No CDPH well na na na na na na na na 19 No USGS well No CDPH well na na na na na na na na 20 OV-17 No CDPH well MW 43 57 0 Natural 616 47 322 21 OV-27 No CDPH well PSW 32 47 21 Mixed 200 100 200 22 OV-30 No CDPH well IRR 0 100 0 Natural 388 143 360 23 OV-03 OV-DG-03 PSW 0 100 0 Natural 250 50 250 24 na OV-DPH-63 PSW 10 75 15 Natural na na na 24 OV-24 na PSW 9 86 5 Natural 305 120 300 25 OV-16 No CDPH well AQU 1 99 0 Natural 185 20 130 26 No USGS well No CDPH well na na na na na na na na 27 OV-06 na PSW 0 99 1 Natural 196 155 196 28 OV-35 No CDPH well MW 0 100 0 Natural 290 250 290 29 OV-07 No CDPH well PSW 0 95 5 Natural 650 290 650 30 OV-13 OV-DG-13 PSW 0 100 0 Natural 114 69 109 31 OV-12 OV-DG-12 PSW 0 100 0 Natural 126 96 116 32 OV-34 No CDPH well MW 0 100 0 Natural na 660 700 33 No USGS well No CDPH well na na na na na na na na 34 OV-22 OV-DG-22 PSW 10 79 11 Natural 650 300 640 35 OV-14 na DOM 39 55 6 Natural 237 40 220 36 OV-23 No CDPH well PSW 0 100 0 Natural 188 na na 37 No USGS well No CDPH well na na na na na na na na 38 No USGS well No CDPH well na na na na na na na na 39 no USGS well No CDPH well na na na na na na na na 40 OV-15 No CDPH well MW 0 100 0 Natural 202 150 180 41 OV-21 No CDPH well PSW 0 99 1 Natural 255 140 240 42 No USGS well No CDPH well na na na na na na na na 43 No USGS well No CDPH well na na na na na na na na 44 OV-19 No CDPH well DOM 0 58 42 Natural na na na

45 No USGS well No CDPH well na na na na na na na na

46 OV-38 No CDPH well DOM 0 100 0 Natural 232 80 232

47 OV-31 na PSW 7 68 26 Natural 240 150 180
Appendix B 77

Table B1. Grid cell number, USGS and CDPH well identification numbers, land use categories, land use classification, and well construction information for wells sampled September 2006 to April 2008, in the California Desert Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued[No CDPH well, no water-quality data available from the CDPH database in that cell; No USGS well, USGS grid well not sampled in that cell; USGS data, USGS-grid well with inorganic data; GAMA identification numbers: ANT, Antelope study area; COA, Coachella study area; COL, Colorado River study area; MOJO, Mojave study area; OIW, Indian Wells study area; OV, Owens Valley study area; ft, feet; m, meter; LSD, land surface datum; na, not available; USGS, U.S. Geological Survey; PSW, public supply well; DOM, domestic well; IRR, irrigation well; IND, industrial well]

Grid

cell

number

USGS

GAMA well 

identification

number

CDPH

GAMA well 

identification

number

Well 

type

Land use categories

(percent)

Land use 

classification

Construction information

(ft below LSD)

Agricultural 

land use 

within 500 m of 

the well

Natural 

land use 

within 500 m 

of the well

Urban 

land use 

within 500 m 

of the well

Well

depth 

Top of 

perforations

Bottom of 

perforations 

Owens Valley study area—Continued

48 No USGS well No CDPH well na na na na na na na na

49 No USGS well OV-DPH-64 PSW 0 99 1 Natural na na na

49 OV-39 OV-DG-39 PSW 0 99 1 Natural 272 55 272

50 No USGS well OV-DPH-65 PSW 28 64 7 Natural na na na

50 OV-05 OV-DG-05 PSW 34 54 12 Natural na na na

51 na OV-DPH-66 PSW 0 100 0 Natural na na na

51 OV-25 OV-DG-25 PSW 19 81 0 Natural 390 70 390

52 No USGS well No CDPH well na na na na na na na na

53 OV-33 No CDPH well MW 0 100 0 Natural 319 258 298

54 OV-32 No CDPH well PSW 0 100 0 Natural 125 51 108

55 OV-40 No CDPH well MW 0 99 1 Natural 775 644 774

56 No USGS well No CDPH well na na na na na na na na

57 No USGS well No CDPH well na na na na na na na na

58 No USGSw ell No CDPH well na na na na na na na na

59 OV-36 No CDPH well IRR 66 34 0 Agricultural na na na

60 No USGS well No CDPH well na na na na na na na na
78 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B2A. Volatile organic compounds analyzed in grid wells the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas. [The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; RSD5-US, U.S. Environmental Protection Agency risk-specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; THM, trihalomethane; D, detected in USGS groundwater samples from grid wells, no benchmark available for this constituent; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.1 × benchmark value and the benchmark value; μg/L, micrograms per liter; na, not applicable; –, not detected] Constituent (synonym or abbreviation) Primary use or source USGS parameter code CAS number1 LRL (μg/L) Benchmark type2 Benchmark level (μg/L) Owens Valley Antelope Mojave Coachella Colorado River Indian Wells 1,1,1,2-Tetrachloroethane Solvent 77562 630-20-6 0.04 HAL-US 70 – – – – – – 1,1,1-Trichloroethane (TCA) Solvent 34506 71-55-6 0.02 MCL-CA 200 – – – na – – 1,1,2,2-Tetrachloroethane Solvent 34516 79-34-5 0.10 MCL-CA 1 – – – – – – 1,1,2-Trichloroethane Solvent 34511 79-00-5 0.06 MCL-CA 5 – – – – – – 1,1-Dichloroethane (1,1-DCA) Solvent 34496 75-34-3 0.04 MCL-CA 5 – L

L – – –

1,1-Dichloroethene (1,1-DCE) Organic synthesis 34501 75-35-4 0.02 MCL-CA 6 – L

L – – –

1,1-Dichloropropene Organic synthesis 77168 563-58-6 0.04 na na – – – – – –

1,2,3,4-Tetramethylbenzene Gasoline hydrocarbon 49999 488-23-3 0.14 na na – – – – – –

1,2,3,5-Tetramethylbenzene Gasoline hydrocarbon 50000 527-53-7 0.12 na na – – – – – –

1,2,3-Trichlorobenzene Organic synthesis 77613 87-61-6 0.08 na na – – – – – –

1,2,3-Trichloropropane (1,2,3-TCP) Solvent/organic synthesis 77443 96-18-4 0.12 HAL-US 40 – – – – – –

1,2,3-Trimethylbenzene Gasoline hydrocarbon 77221 526-73-8 0.08 na na – – – – – –

1,2,4-Trichlorobenzene Solvent 34551 120-82-1 0.08 MCL-CA 5 – – – – – –

1,2-Dibromo-3-chloropropane 

(DBCP)

Fumigant 82625 96-12-8 0.5 MCL-US 0.2 – – – – – –

1,2-Dibromoethane (EDB) Fumigant 77651 106-93-4 0.04 MCL-US 0.05 – – – – – –

1,2-Dichlorobenzene Solvent 34536 95-50-1 0.02 MCL-CA 600 – L – – – –1,2-Dichloroethane (1,2-DCA) Solvent 32103 107-06-2 0.5 MCL-CA 0.5 – – M – – –1,2-Dichloropropane (1,2-DCP) Fumigant 34541 78-87-5 0.02 MCL-US 5 – – – – M –

1,3,5-Trimethylbenzene Organic synthesis 77226 108-67-8 0.04 NL-CA 330 – – – – – –

1,3-Dichlorobenzene Solvent 34566 541-73-1 0.04 HAL-US 600

L

L

L – – –

1,3-Dichloropropane Fumigant 77173 142-28-9 0.06 na na – – – – – –

1,4-Dichlorobenzene Fumigant 34571 106-46-7 0.02 MCL-CA 5 – L – – – –

2,2-Dichloropropane Fumigant 77170 594-20-7 0.06 na na – – – – – –

2-Chlorotoluene Solvent 77275 95-49-8 0.04 NL-CA 140 – – – – – –

2-Hexanone (n-Butyl methyl ketone) Solvent 77103 591-78-6 0.6 na na – – – – – –

3-Chloropropene Organic synthesis 78109 107-05-1 0.08 na na – – – – – –

4-Chlorotoluene Solvent 77277 106-43-4 0.04 NL-CA 140 – – – – – –

4-Isopropyl-1-methyl benzene Gasoline hydrocarbon 77356 99-87-6 0.08 na na – – – – – –

Acetone Solvent 81552 67-64-1 4 na na – – – – – –

Acrylonitrile Organic synthesis 34215 107-13-1 0.4 RSD5-US 0.6 – – – – – –

Benzene Gasoline hydrocarbon 34030 71-43-2 0.016 MCL-CA 1 – – – – – –

Bromobenzene Solvent 81555 108-86-1 0.02 HAL-US 70 – – – – – –

Bromochloromethane Fire retardant 77297 74-97-5 0.06 HAL-US 90 – L – – – –Bromodichloromethane Disinfection byproduct 

(THM)

32101 75-27-4 0.04 MCL-US 3 80 – L

L – – –
Appendix B 79

Constituent

(synonym or abbreviation) Primary use or source

USGS 

parameter 

code

CAS number1 LRL (μg/L) Benchmark type2 Benchmark level (μg/L) Owens Valley Antelope Mojave Coachella Colorado River Indian Wells

Bromoform (Tribromomethane) Disinfection byproduct 

(THM)

32104 75-25-2 0.08 MCL-US 3 80 – L L – – –

Bromomethane (Methyl bromide) Fumigant 34413 74-83-9 0.4 HAL-US 10 – – – – – –

Carbon disulfide Organic synthesis 77041 75-15-0 0.06 NL-CA 160 L – – – – L

Carbon tetrachloride 

(Tetrachloromethane)

Solvent 32102 56-23-5 0.08 MCL-CA 0.5 – L M – – –

Chlorobenzene Solvent 34301 108-90-7 0.02 MCL-CA 70 – – L – – –

Chloroethane Solvent 34311 75-00-3 0.10 na na – D – – – –

Chloroform (Trichloromethane) Disinfection byproduct 

(THM)

32106 67-66-3 0.02 MCL-US 3 80 L M M L L L

Chloromethane Solvent 34418 74-87-3 0.10 na na – D – – – –

cis-1,2-Dichloroethene (cis-1,2-DCE) Solvent 77093 156-59-2 0.02 MCL-CA 6 – – L – – –

cis-1,3-Dichloropropene Fumigant 34704 10061-01-5 0.1 RSD5-US 4 4 – – – – – –

Dibromochloromethane Disinfection byproduct 

(THM)

32105 124-48-1 0.12 MCL-US 3 80 – L L – – –

Dibromomethane Solvent 30217 74-95-3 0.04 na na – D – – – –Dichlorodifluoromethane (CFC-12) Refrigerant 34668 75-71-8 0.14 NL-CA 1,000 – – – – – –

Diethyl ether Solvent 81576 60-29-7 0.12 na na – – – – – –

Diisopropyl ether (DIPE) Gasoline oxygenate 81577 108-20-3 0.06 na na – – – – – –

Ethyl methacrylate Organic synthesis 73570 97-63-2 0.14 na na – – – – – –

Ethyl tert-butyl ether (ETBE) Gasoline oxygenate 50004 637-92-3 0.04 na na – – – – – –

Ethylbenzene Gasoline hydrocarbon 34371 100-41-4 0.04 MCL-CA 300 – – – – – –

Hexachlorobutadiene Organic synthesis 39702 87-68-3 0.06 RSD5-US 9 – – – – – –

Hexachloroethane Solvent 34396 67-72-1 0.14 HAL-US 1 – – – – – –

Iodomethane (Methyl iodide) Organic synthesis 77424 74-88-4 0.4 na na – – – – – –

Isopropylbenzene Gasoline hydrocarbon 77223 98-82-8 0.04 NL-CA 770 – – – – – –

m- and p-Xylene Gasoline hydrocarbon 85795 108-38-3 / 106-42-3 0.08 MCL-CA 5 1,750 – – – – – –

Methyl acrylate Organic synthesis 49991 96-33-3 0.6 na na – – – – – –

Methyl acrylonitrile Organic synthesis 81593 126-98-7 0.2 na na – – – – – –

Methyl ethyl ketone (2-butanone, 

MEK)

Solvent 81595 78-93-3 1.6 HAL-US 4,000 – – – – – –

Methyl iso-butyl ketone (MIBK) Solvent 78133 108-10-1 0.4 NL-CA 120 – – – – – –

Methyl methacrylate Organic synthesis 81597 80-62-6 0.2 na na – – – – – –

Methyl tert-butyl ether (MTBE) Gasoline oxygenate 78032 1634-04-4 0.1 MCL-CA 13 L L – – – –

Methylene chloride (Dichloromethane) Solvent 34423 75-09-2 0.04 MCL-US 5 – L L – – –Naphthalene Gasoline hydrocarbon 34696 91-20-3 0.2 NL-CA 17 – – – – – –

Table B2A. Volatile organic compounds analyzed in grid wells the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; RSD5-US, U.S. Environmental Protection Agency risk-specific dose at a risk factor of 10–5; Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; THM, trihalomethane; D, detected in USGS groundwater samples from grid wells, no benchmark available 

for this constituent; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.1 × benchmark value and the benchmark value; μg/L, micrograms per liter; na, not applicable; –, not detected]
80 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Constituent (synonym or abbreviation) Primary use or source USGS parameter code CAS number1 LRL (μg/L) Benchmark type2 Benchmark level (μg/L) Owens Valley Antelope Mojave Coachella Colorado River Indian Wells

n-Butylbenzene Gasoline hydrocarbon 77342 104-51-8 0.14 NL-CA 260 – – – – – –n-Propylbenzene Solvent 77224 103-65-1 0.04 NL-CA 260 – – – – – –o-Ethyl toluene (1-Ethyl-2-methyl 

benzene)

Gasoline hydrocarbon 77220 611-14-3 0.04 na na – – – – – –

o-Xylene Gasoline hydrocarbon 77135 95-47-6 0.04 MCL-CA 5 1,750 – – – – – –

sec-Butylbenzene Gasoline hydrocarbon 77350 135-98-8 0.04 NL-CA 260 – – – – – –

Styrene Gasoline hydrocarbon 77128 100-42-5 0.04 MCL-US 100 – L – – – –tert-Amyl methyl ether (TAME) Gasoline oxygenate 50005 994-05-8 0.06 na na – – – – – –

tert-Butylbenzene Gasoline hydrocarbon 77353 98-06-6 0.06 NL-CA 260 – – – – – –

Tetrachloroethene (PCE) Solvent 34475 127-18-4 0.04 MCL-US 5 L

L

M

L – –

Tetrahydrofuran Solvent 81607 109-99-9 1.4 na na

D – D – – –

trans-1,2-Dichloroethene 

(trans-1,2-DCE)

Solvent 34546 156-60-5 0.018 MCL-CA 10 – – L – – –

trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.10 RSD5-US 4 4 – – – – – –

trans-1,4-Dichloro-2-butene Organic synthesis 73547 110-57-6 0.6 na na – – – – – –

Trichloroethene (TCE) Solvent 39180 79-01-6 0.02 MCL-US 5 – L

L – – –

Trichlorofluoromethane (CFC-11) Refrigerant 34488 75-69-4 0.08 MCL-CA 150 – – L – – –Trichlorotrifluoroethane (CFC-113) Refrigerant 77652 76-13-1 0.04 MCL-CA 1,200 – – – – – –

Vinyl bromide (Bromoethene) Fire retardant 50002 593-60-2 0.12 na na – – – – – –

Vinyl chloride (Chloroethene) Organic synthesis 39175 75-01-4 0.08 MCL-CA 0.5 – – – – – –

1This report contains CAS Registry Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM.2Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.3The MCL-US benchmark for trihalomethanes is the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.4The RSD5 benchmark for 1,3-dichloropropene is the sum of its isomers (cis and trans).5The MCL-CA benchmarks for 

m- and p-Xylene and o-Xylene is the sum all three xylene compounds.

Table B2A. Volatile organic compounds analyzed in grid wells the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; RSD5-US, U.S. Environmental Protection Agency risk-specific dose at a risk factor of 10–5; 

Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; THM, trihalomethane; D, detected in USGS groundwater samples from grid wells, no benchmark available for this constituent; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.1 × benchmark value and the benchmark value; μg/L, micrograms per liter; na, not applicable; –, not detected]
Appendix B 81

Table B2B. Pesticides and pesticide degradates analyzed in samples from the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk-specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract 

Service; LRL, laboratory reporting level; D, detected in USGS groundwater samples from grid wells, no benchmark available; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.1 × benchmark value and the benchmark value; μg/L, micrograms per liter; na, not applicable; –, not detected]

Constituent (synonym or abbreviation) Primary use or source

USGS 

parameter 

code

CAS number1 LRL (μg/L) Benchmark type2 Benchmark level (μg/L) Owens Valley Antelope Mojave Coachella Colorado River Indian Wells

1-Naphthol Insecticide degradate 49295 90-15-3 0.04 na na –3 – 3 – 3 – – 3 – 3

2,6-Diethylaniline Herbicide degradate 82660 579-66-8 0.006 na na – – – – – –

2-Chloro-2,6-diethylacetanilide Herbicide degradate 61618 6967-29-9 0.01 na na – – – – – –

2-Ethyl-6-methylaniline Herbicide degradate 61620 24549-06-2 0.010 na na – – – 3 – – –

3,4-Dichloroaniline Herbicide degradate 61625 95-76-1 0.006 na na – D D – – –4-Chloro-2-methylphenol Herbicide degradate 61633 1570-64-5 0.0050 na na – – 3 – 3 – – 3 –Acetochlor Herbicide 49260 34256-82-1 0.006 na na – – – – – –

Alachlor Herbicide 46342 15972-60-8 0.006 MCL-US 2 – – – – – –

Atrazine Herbicide 39632 1912-24-9 0.007 MCL-CA 1 L L L L L LAzinphos-methyl Insecticide 82686 86-50-0 0.12 na na – – 3 – 3 – – –

Azinphos-methyl-oxon Insecticide degradate 61635 961-22-8 0.042 na na – – 3 – 3 – – –Benfluralin Herbicide 82673 1861-40-1 0.004 na na – – 3 – 3 – – 3 –Carbaryl Insecticide 82680 63-25-2 0.06 RSD5-US 400 – – – – – –

Chlorpyrifos Insecticide 38933 2921-88-2 0.005 HAL-US 2 – – 3 – 3 – – –

Chlorpyrifos oxon Insecticide degradate 61636 5598-15-2 0.0562 na na – – 3 – 3 – – 3 –cis-Permethrin Insecticide 82687 54774-45-7 0.01 na na – – 3 – 3 – – 3 –Cyfluthrin Insecticide 61585 68359-37-5 0.016 na na – – 3 – 3 – – 3 –Cypermethrin Insecticide 61586 52315-07-8 0.014 na na – – 3 – 3 – – 3 –Dacthal (DCPA) Herbicide 82682 1861-32-1 0.003 HAL-US 70 – – – – – –

Deethylatrazine (2-Chloro-4-

isopropylamino-6-amino-s-triazine)

Herbicide degradate 04040 6190-65-4 0.014 na na – D 3 D 3 L L –

Desulfinylfipronil Insecticide degradate 62170 na 0.012 na na – – D – – –Desulfinylfipronil amide Insecticide degradate 62169 na 0.029 na na – – – – – –

Diazinon Insecticide 39572 333-41-5 0.005 HAL-US 1 – – – – ns –

Diazinon, oxon Insecticide degradate 61638 962-58-3 0.006 na na – ns ns – ns –Dichlorvos Insecticide 38775 62-73-7 0.013 na na – – 3 – 3 – – 3 –

Dicrotophos Insecticide 38454 141-66-2 0.0843 na na – – 3 – 3 – – 3 –Dieldrin Insecticide 39381 60-57-1 0.05 RSD5-US 0.02 – – M – – –Dimethoate Insecticide 82662 60-51-5 1.006 na na – 3 – 3 – 3 – – 3 – 3Ethion Insecticide 82346 563-12-2 0.01 na na – – 3 – – – –

Ethion monoxon Insecticide degradate 61644 17356-42-2 0.010 na na – – 3 – 3 – – –

Fenamiphos Insecticide 61591 22224-92-6 0.006 HAL-US 0.7 – – – – – –

Fenamiphos sulfone Insecticide degradate 61645 31972-44-8 0.0050 na na – – 3 – – – –

Fenamiphos sulfoxide Insecticide degradate 61646 31972-43-7 1.006 na na – 3 – – 3 – – – 3

Fipronil Insecticide 62166 120068-37-3 0.007 na na – – 3 D 3 – – –Fipronil sulfide Insecticide degradate 62167 120067-83-6 1.007 na na – – 3 D 3 – ns –
82 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Constituent (synonym or abbreviation) Primary use or source USGS parameter code CAS number1 LRL (μg/L) Benchmark type2 Benchmark level (μg/L) Owens Valley Antelope Mojave Coachella Colorado River Indian Wells Fipronil sulfone Insecticide degradate 62168 120068-36-2 0.12 na na – – 3 – 3 – – 3 – Fonofos Insecticide 04095 944-22-9 0.042 HAL-US 10 – – – – – – Hexazinone Herbicide 04025 51235-04-2 0.004 HAL-US 400

L – 3 – 3 – – –

Iprodione Fungicide 61593 36734-19-7 0.06 na na – 3 – 3 – 3 – – – 3Isofenphos Insecticide 61594 25311-71-1 1.005 na na – – – – – –

Malaoxon Insecticide degradate 61652 1634-78-2 0.0562 na na – – 3 – 3 – – –

Malathion Insecticide 39532 121-75-5 0.01 HAL-US 500 – – 3 – – – –Metalaxyl Fungicide 61596 57837-19-1 0.016 na na – – – – – –

Methidathion Insecticide 61598 950-37-8 0.014 na na – – – – – –

Metolachlor Herbicide 39415 51218-45-2 1.003 HAL-US 700 – L

L – – –

Metribuzin Herbicide 82630 21087-64-9 0.015 HAL-US 70 – – – – – –

Myclobutanil Fungicide 61599 88671-89-0 0.008 na na – – – – – –

Paraoxon-methyl Insecticide degradate 61664 950-35-6 0.0048 na na – 3 – 3 – 3 – – 3 – 3

Parathion-methyl Insecticide 82667 298-00-0 0.001 HAL-US 1 – – 3 – 3 – – –Pendimethalin Herbicide 82683 40487-42-1 0.006 na na – – 3 – – – –

Phorate Insecticide 82664 298-02-2 0.013 na na – 3 – 3 – 3 – – – 3

Phorate oxon Insecticide degradate 61666 2600-69-3 0.0843 na na – – 3 – – – –

Phosmet Insecticide 61601 732-11-6 0.06 na na – 3 – 3 – 3 – – 3 – 3

Phosmet oxon Insecticide degradate 61668 3735-33-9 2.006 na na – 3 – 3 – 3 – – 3 – 3Prometon Herbicide 04037 1610-18-0 0.01 HAL-US 400 – L

L – –

Prometryn Herbicide 04036 7287-19-6 0.010 na na – – – – L –

Pronamide (Propyzamide) Herbicide 82676 23950-58-5 0.006 RSD5-US 10 – – – – – –

Simazine Herbicide 04035 122-34-9 0.005 MCL-US 4 L

L

L

L

L –

Tebuthiuron Herbicide 82670 34014-18-1 2.006 HAL-US 500

L – – – – –

Terbufos Insecticide 82675 13071-79-9 0.008 HAL-US 0.4 – – 3 – – – –

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 2.007 na na – – 3 – 3 – – –

Terbuthylazine Herbicide 04022 5915-41-3 0.12 na na – – – – – –

Tribufos Defoliant 61610 78-48-8 0.042 na na ns – 3 – ns ns ns

Trifluralin Herbicide 82661 1582-09-8 0.004 HAL-US 10 – – 3 – 3 – – –

11This report contains CAS Registry Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM.2Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.3The median matrix-spike recovery was less than 70 percent. Low recoveries may indicate that the constituent might not have been detected in some samples if it was present at very low concentrations.

Table B2B. Pesticides and pesticide degradates analyzed in samples from the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study 

areas.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk-specific dose at a risk factor of 10-5. Other abbreviations: CAS, Chemical Abstract Service; LRL, 

laboratory reporting level; D, detected in USGS groundwater samples from grid wells, no benchmark available; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.1 × benchmark value and the benchmark value; μg/L, micrograms per liter; –, not detected]
Appendix B 83

Table B2C. Constituents of special interest analyzed in samples from the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; NL-CA, California Department of Public Health notification level. Other abbreviations: CAS, Chemical Abstract Service; MRL, minimum reporting level; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.1 × benchmark value and the benchmark value; H, detected in USGS groundwater samples from grid wells at greater than the benchmark value; μg/L, micrograms per liter; –, not detected; ns, not sampled in this study area]

Constituent (synonym or abbreviation) Primary use or source

USGS 

parameter 

code

CAS number1 MRL (μg/L) Benchmark type2 Benchmark level (μg/L) Owens Valley Antelope Mojave Coachella Colorado River Indian Wells

Perchlorate Rocket fuel, fireworks, 

flares

63790 14797-73-0 0.1, 0.5 MCL-CA 6 – M M H M M

1,2,3-Trichloropropane (1,2,3-TCP) Fumigant, solvent 77443 96-18-4 0.005 HAL-US 40 – – – – L –N-Nitrosodimethylamine (NDMA) Disinfection byproduct 34438 62-75-9 0.002 NL-CA 0.01 – – H ns ns –

1This report contains CAS Registry Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM.2Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.

Table B2D. Nutrients analyzed in samples from the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in USGS groundwater samples from grid wells, no benchmark available; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.5 × benchmark value and the benchmark value; H, detected in USGS groundwater samples from grid wells at greater than the benchmark value; na, not available; mg/L, milligrams per liter]

Constituent

USGS 

parameter 

code

CAS number1 LRL (mg/L) Benchmark type2 Benchmark level (mg/L) Owens Valley Antelope Mojave Coachella Colorado River Indian Wells

Ammonia (as nitrogen) 00608 7664-41-7 0.020 HAL-US 3 24.7 L – L L L L

Nitrite (as nitrogen) 00613 14797-65-0 0.002 MCL-US 1 L L L L L L

Nitrate plus nitrite (as nitrogen) 00631 na 0.040 MCL-US 10 L H M M L L

Total nitrogen (ammonia, nitrite, 

nitrate, organic nitrogen)

62854 17778-88-0 0.06 na na D D D D D D

Phosphorus, phosphate, orthophosphate 

(as phosphorus)

00671 14265-44-2 0.006 na na D D D D D D

1This report contains CAS Registry Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS 

Client ServicesSM.

2Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no 

MCL-US exists.

3The HAL-US is 30 mg/L “as ammonia.” To facilitate comparson to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L “as nitrogen.”
84 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B2E. Major, minor, and trace inorganic elements analyzed in samples from the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas. [The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in USGS groundwater samples from grid wells, no benchmark available; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.5 × benchmark value and the benchmark value; H, detected in USGS groundwater samples from grid wells at greater than the benchmark value; SRL, Study reporting level; na, not available; mg/L, milligrams per liter; μg/L, micrograms per liter; na, not applicable; –, not detected] Constituent USGS parameter code CAS number1 LRL/SRL Benchmark type2 Benchmark level Owens Valley Antelope Mojave Coachella Colorado River Indian Wells Inorganic constituents: major and minor elements (mg/L) Bromide 71870 24959-67-9 0.02 na na

D

D

D

D

D

D

Calcium 00915 7440-70-2 0.04 na na

D

D

D

D

D

D

Chloride 00940 16887-00-6 0.12 SMCL-CA, upper 500

L

M

H

H

H

H

Fluoride 00950 16984-48-8 0.12 MCL-CA 2 H

H

H

H

H

M

Iodide 71865 7553-56-2 0.002 na na

D

D

D

D

D

D

Magnesium 00925 7439-95-4 0.02 na na

D

D

D

D

D

D

Potassium 00935 7440-09-7 0.02 na na

D

D

D

D

D

D

Silica 00955 7631-86-9 0.018 na na

D

D

D

D

D

D

Sodium 00930 7440-23-5 0.12 na na

D

D

D

D

D

D

Sulfate 00945 14808-79-8 0.18 SMCL-CA, upper 500

L

M

H

H

H

M

Total dissolved solids (TDS) 70300 na 10 SMCL-CA, upper 1,000

H

H

H

H

H

H

Inorganic constituents: trace elements (μg/L)

Aluminum 01106 7429-90-5 1.6 MCL-CA 1,000

L

H

L

L

L

L

Antimony 01095 7440-36-0 0.14 MCL-US 6 L

L

L

L

L

L

Arsenic 01000 7440-38-2 0.06 MCL-US 10

H

H

H

H

H

H

Barium 01005 7440-39-3 0.4 MCL-CA 1,000

L

L

L

L

L

L

Beryllium 01010 7440-41-7 0.008 MCL-US 4 L

L

L

L

L

L

Boron 01020 7440-42-8 6 NL-CA 1,000

H

H

H

H

H

H

Cadmium 01025 7440-43-9 0.04 MCL-US 5 L

L

L

L

L

L

Chromium 01030 7440-47-3 0.12 MCL-CA 50

L

L

L

L

L

M

Cobalt 01035 7440-48-4 0.02 na na

D

L

L

L

L

L

Copper 01040 7440-50-8 1 AL-US 1,300

L

L

L

L

L

L

Iron 01046 7439-89-6 8 SMCL-CA 300

H

H

H

L

H

L

Lead 01049 7439-92-1 0.08 AL-US 15

L

M

L

L

L

L

Lithium 01130 7439-93-2 1 na na

D

D

D

D

D

D

Manganese 01056 7439-96-5 0.2 SMCL-CA 50

H

H

H

H

H

H

Mercury 71890 7439-97-6 0.010 MCL-US 2 L – – – – L

Molybdenum 01060 7439-98-7 0.2 HAL-US 40

H

M

H

H

H

H

Nickel 01065 7440-02-0 0.2 MCL-CA 100

L

L

L

L

L

L
Appendix B 85

Constituent

USGS 

parameter

 code

CAS number1 LRL/SRL Benchmark type2 Benchmark level Owens Valley Antelope Mojave Coachella Colorado River Indian Wells

Inorganic constituents: trace elements (μg/L)—Continued

Selenium 01145 7782-49-2 0.04 MCL-US 50 L L L L L L

Silver 01075 7440-22-4 0.1 SMCL-CA 100 L L L L L L

Strontium 01080 7440-24-6 0.8 HAL-US 4,000 L L H H H H

Thallium 01057 7440-28-0 0.04 MCL-US 2 L – – – L L

Tungsten 01155 7440-33-7 0.06 na na D D D D D D

Uranium 22703 7440-61-1 0.02 MCL-US 30 H M M M H H

Vanadium 01085 7440-62-2 0.04 NL-CA 50 L H H M L H

Zinc 01090 7440-66-6 1.8 SMCL-CA3 5,000 L L L L L L

1This report contains CAS Registry Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM.2Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.3The secondary maximum contaminant level for zinc is listed as SMCL-CA because SMCLs established by CDPH are used in this report for all constituents that have SMCL-CA values.

Table B2E. Major, minor, and trace inorganic elements analyzed in samples from the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health zdvisory; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level;D, detected inUSGS groundwater samples from grid wells, no benchmark available; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.5 × benchmark value and the benchmark value; H, detected in USGS groundwater samples from grid wells at greater than the benchmark value; SRL, Study reporting level; na, not available; mg/L, milligrams per liter; μg/L, micrograms per liter; na, not applicable; –, not detected]
86 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B2F. Radioactive constituents analyzed in samples from the California Desert Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas. [The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property (U.S. Geological Survey, 2011). Benchmark types and levels as of July 5, 2011. Benchmark type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CAS, Chemical Abstract Service; CSU, combined standard uncertainty; ssLc, sample-specific critical level; MRL, minimum reporting level; MU, method uncertainty; na, not available; pCi/L, picocuries per liter; 2SCU, 2-sigma combined uncertainty; L, detected in USGS groundwater samples from grid wells at less than 0.1 × benchmark value; M, detected in USGS groundwater samples from grid wells between 0.5 × benchmark value and the benchmark value; H, detected in USGS groundwater samples from grid wells at greater than the benchmark value; μg/L, micrograms per liter; na, not applicable; –, not detected] Constituent USGS parameter code CAS number1 Reporting level type Reporting level or uncertainty Benchmark type2 Benchmark level (μg/L) Owens Valley Antelope Mojave Coachella Colorado River Indian Wells Gross-alpha radioactivity, 30-day count 62639 12587-46-1 ssLC CSU MCL-US 15

H

H

H

L

H

H

Gross-beta radioactivity, 30-day count 62645 12587-47-2 ssLC CSU MCL-CA 50

L

L

L

L

L

L

Radium-226 09511 13982-63-3 ssLC CSU MCL-US 3 5

L

L

L

L

L

L

Radium-228 81366 15262-20-1 ssLC CSU MCL-US 3 5

L

L

L

L

L

L

Radon-222 82303 14859-67-7 na 2SCU MCL-US4 4,000

M

L

L

L

M

L

Tritium 07000 10028-17-8 MRL 1 MCL-CA 20,000

L

L

L

L

L

L

1This report contains CAS Registry Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM.2Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.3The MCL-US threshold for radium is the sum of radium-226 and radium-228.4Proposed.
Appendix B 87

Table B3A. Current aquifer-scale proportions in the Owens Valley Groundwater Ambient Monitoring and Assessment (GAMA) study area, California.[Moderate, relative concentration between 0.5 (for trace elements, radioactive constituents, nutrients, and inorganic constituents) or 0.1 (for volatile organic compounds, pesticides, and special-interest constituents) and 1; High, relative concentration greater than 1.0; Values are grid-based except where footnoted]

Constituent

Raw detection frequency 1 Spatially weighted aquifer-scale proportions 1 Grid-based aquifer-scale proportions

90 percent confidence

interval for grid-based 

high proportion

(percent) 2

Number 

of wells

Moderate 

(percent)

High 

(percent)

Number 

of cells

Moderate 

(percent)

High 

(percent)

Number 

of cells

Moderate 

(percent)

High 

(percent)

Lower

limit

Upper

limit

Trace and minor elements with health-based benchmarks

Arsenic 82 1.2 8.5 40 2.5 10.5 40 2.5 7.5 2.8 16.6

Boron 79 6.3 7.6 40 4.4 9.0 40 0.0 10.0 4.3 19.9

Fluoride 84 11.9 7.1 40 10.9 4.3 40 10.0 2.5 0.4 9.4

Molybdenum 53 7.5 3.8 40 6.3 5.0 40 5.0 5.0 1.4 13.2

Inorganic constituents with non-health-based benchmarks

Chloride 80 1.3 1.3 40 0.0 0.8 40 0.0 0.0 0.0 3.3

Iron 82 6.1 3.7 40 7.1 4.6 40 10.0 2.5 0.4 9.4

Manganese 82 2.4 13.4 40 3.8 14.4 40 2.5 15.0 7.6 26.0

Total dissolved solids (TDS) 80 6.3 3.8 40 9.0 2.5 40 7.5 2.5 0.4 9.4

Radioactive constituents with health-based benchmarks

Gross-alpha radioactivity 53 9.4 5.7 23 10.1 13.4 16 6.3 12.5 3.5 28.9

Radon-222 8 37.5 0.0 9 33.3 0.0 7 42.9 0.0 0.0 17.0

Uranium 70 5.7 8.6 40 6.3 9.2 40 5.0 7.5 2.8 16.6

1Based on most recent analysis for each CDPH well during September 11, 2003–September 11, 2006, combined with USGS grid data.2Based on the Jeffreys interval for the binomial distribution (Brown and others, 2001). 
88 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B3B. Current aquifer-scale proportions in the Antelope Groundwater Ambient Monitoring and Assessment (GAMA) study area. [Moderate, relative concentration between 0.5 (for trace elements, radioactive constituents, nutrients and inorganic constituents) or 0.1 (for volatile organic compounds, pesticides, and special-interest constituents) and 1; High, relative concentration greater than 1.0; Values are grid-based except where footnoted] Constituent Raw detection frequency 1 Spatially weighted aquifer-scale proportions 1 Grid-based aquifer-scale proportions 90 percent confidence interval for grid-based high proportion (percent) 2 Number of wells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Lower limit Upper limit Trace elements with health-based benchmarks Aluminum 185 0.0 0.5 53 0.3 0.0 50 0.0 2.0 0.0 2.7 Arsenic 200 16.0 21.5 54 17.2 28.6 53 13.2 28.3 15.0 34.2 Boron 95 1.1 1.1 38 2.6 2.6 33 0.0 3.0 0.6 12.3 Chromium 184 0.5 0.0 53 0.3 0.0 50 2.0 0.0 0.0 2.7 Fluoride 189 4.8 0.5 52 6.4 1.0 51 5.9 2.0 0.4 7.7 Lead 151 0.7 0.0 48 1.0 0.0 43 2.3 0.0 0.0 3.3 Molybdenum 19 15.8 0.0 18 16.7 0.0 18 16.7 0.0 0.0 7.1 Vanadium 86 9.3 2.3 37 5.5 5.4 32 6.3 6.3 1.9 17.3 Radioactive constituents with health-based benchmarks Gross-alpha 123 5.7 4.1 50 5.7 3.9 49 6.1 4.1 1.3 12.3 Uranium 113 3.5 0.9 40 0.6 5.0 39 5.1 0.0 0.0 6.8 Nutrients with health-based benchmarks Nitrate 212 8.5 1.9 55 9.0 3.3 54 9.3 1.9 0.3 7.3 Inorganic constituents with non-health-based benchmarks Chloride 190 1.1 0.0 52 2.9 0.0 51 3.9 0.0 0.0 2.7 Iron 192 8.3 14.1 52 7.7 12.5 51 5.9 11.8 4.8 19.0 Manganese 185 5.3 3.7 52 6.2 2.5 50 8.0 4.0 0.4 7.9 Sulfate 190 6.3 0.5 52 5.6 0.4 51 7.8 0.0 0.0 2.7 Total dissolved solids (TDS) 192 15.6 2.6 52 16.1 2.9 51 11.8 3.9 1.2 10.8 Volatile organic constituents with health-based thresholds Chloroform 182 1.1 0.0 56 1.1 0.0 56 1.9 0.0 0.0 2.4 Trichloroethene (TCE) 183 0.5 0.0 56 0.2 0.0 56 0.0 0.0 0.0 2.4 Special-interest constituents with health-based benchmarks Perchlorate 99 17.2 0.0 59 16.2 0.0 56 28.6 0.0 0.0 2.4

1 Based on most recent analysis for each CDPH well during January 27, 2005–January 27, 2008, combined with USGS GAMA grid-based data.2 Based on the Jeffreys interval for the binomial distribution (Brown and others, 2001). 
Appendix B 89

Table B3C. Current aquifer-scale proportions for constituents detected at high or moderate aquifer-scale proportions in the Mojave Groundwater Ambient Monitoring and Assessment (GAMA) study area.[Moderate, relative-concentration between 0.5 (for trace elements, radioactive constituents, nutrients, and inorganic constituents) or 0.1 (for volatile organic compounds, pesticides and special-interest constituents) and 1; High, relative-concentration greater than 1.0; Values are grid-based except where footnoted]

Constituent

Raw detection frequency 1 Spatially weighted aquifer-scale proportions 1 Grid-based aquifer-scale proportions

90 percent confidence

interval for grid-based 

high proportion

(percent) 2

Number 

of wells

Moderate 

(percent)

High 

(percent)

Number 

of cells

Moderate 

(percent)

High 

(percent)

Number 

of cells

Moderate 

(percent)

High 

(percent)

Lower

limit

Upper

limit

Trace elements with health-based benchmarks

Arsenic 144 12.5 11.1 43 8.1 11.6 43 0.0 20.9 12.6 33.1

Boron 101 8.9 3.0 37 11.6 4.6 36 16.7 5.6 1.6 14.5

Chromium 133 1.5 0.0 41 1.1 0.0 40 0.0 0.0 0.0 3.4

Fluoride 158 5.7 5.1 45 8.6 10.9 46 10.9 10.9 4.0 18.6

Lead 139 0.7 3.6 41 0.6 0.9 40 0.0 0.0 0.0 3.4

Molybdenum 22 0.0 4.5 21 0.0 4.8 19 0.0 5.3 0.9 18.8

Strontium 21 9.5 4.8 21 9.5 4.8 19 10.5 5.3 0.9 18.8

Vanadium 103 26.2 7.8 37 19.2 6.4 36 13.9 8.3 3.2 18.8

Radioactive constituents with health-based benchmarks

Gross-alpha radioactivity 123 11.4 1.6 46 10.3 2.2 40 12.5 2.5 0.4 9.1

Uranium 77 6.5 0.0 37 2.9 0.0 31 3.2 0.0 0.0 4.4

Nutrients with health-based benchmarks

Nitrate 214 2.8 0.0 53 3.2 0.0 53 1.9 0.0 0.0 2.5

Inorganic constituents with non-health-based benchmarks

Chloride 142 3.5 2.1 42 3.5 2.1 42 0.0 2.4 0.4 9.1

Iron 153 5.9 7.2 43 5.7 4.5 43 2.3 2.3 0.0 3.2

Manganese 153 0.7 3.3 43 0.0 1.3 43 0.0 2.3 0.0 3.2

Sulfate 142 7.0 1.4 42 8.9 1.7 42 11.9 2.4 0.4 9.1

Total dissolved solids (TDS) 142 14.8 4.9 42 16.3 6.3 42 14.3 7.1 2.7 16.2

Volatile organic constituents with health-based thresholds

1,2-Dibromo-3-chloropropane 

(DBCP)

137 0.7 0.0 55 1.8 0.0 52 0.0 0.0 0.0 2.6

1,2-Dichloroethane 127 0.8 0.0 55 1.8 0.0 52 1.9 0.0 0.0 2.6

Bromodichloromethane 127 0.8 0.0 55 0.3 0.0 52 0.0 0.0 0.0 2.6

Dibromochloromethane 127 0.8 0.0 55 0.3 0.0 52 0.0 0.0 0.0 2.6

Ethylbenzene 127 0.8 0.0 55 0.3 0.0 52 0.0 0.0 0.0 2.6

Tetrachloroethene (PCE) 127 0.8 0.0 55 1.8 0.0 52 1.9 0.0 0.0 2.6
90 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Constituent Raw detection frequency 1 Spatially weighted aquifer-scale proportions 1 Grid-based aquifer-scale proportions 90 percent confidence interval for grid-based high proportion (percent) 2 Number of wells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Lower limit Upper limit Pesticides with health-based thresholds Dieldrin 93 1.1 0.0 54 1.9 0.0 52 1.9 0.0 0.0 2.6 Special-interest constituents with health-based benchmarks

N-Nitrosodimethylamine 22 0.0 4.5 21 0.0 4.8 19 0.0 5.3 0.9 18.8

Perchlorate 73 13.7 0.0 52 15.6 0.0 50 22.0 0.0 0.0 2.7

1,2,3-Trichloropropane 

(1,2,3-TCP)3

74 1.4 0.0 54 0.9 0.0 52 0.0 0.0 0.0 2.6

1Based on most recent analysis for each CDPH well during February 3, 2005–February 3, 2008, combined with USGS GAMA grid-based data.2Based on the Jeffreys interval for the binomial distribution (Brown and others, 2001).31,2,3-Trichloropropane was only analyzed in USGS samples at the higher laboratory reporting limit of 0.12 microgram per liter in the Mojave study area.

Table B3C. Current aquifer-scale proportions for constituents detected at high or moderate aquifer-scale proportions in the Mojave Groundwater Ambient Monitoring and Assessment (GAMA) study area.—Continued[Moderate, relative concentration between 0.5 (for trace elements, radioactive constituents, nutrients and inorganic constituents) or 0.1 (for volatile organic compounds, pesticides and special interest constituents) and 1; High, relative-concentration greater than 1.0; Values are grid-based except where footnoted]
Appendix B 91

Table B3D. Current aquifer-scale proportions in the Coachella Groundwater Ambient Monitoring and Assessment (GAMA) study area.[Moderate, relative-concentration between 0.5 (for trace elements, radioactive constituents, nutrients, and inorganic constituents) or 0.1 (for volatile organic compounds, pesticides and special-interest constituents) and 1; High, relative-concentration greater than 1.0; Values are grid-based except where footnoted]

Constituent

Raw detection frequency 1 Spatially weighted aquifer-scale proportions 1 Grid-based aquifer-scale proportions

90 percent confidence

interval for grid-based 

high proportion

(percent) 2

Number 

of wells

Moderate 

(percent)

High 

(percent)

Number 

of cells

Moderate 

(percent)

High 

(percent)

Number 

of cells

Moderate 

(percent)

High 

(percent)

Lower

limit

Upper

limit

Trace elements with health-based benchmarks

Aluminum 187 0.0 0.5 19 0.0 0.5 19 0.0 0.0 0.0 6.8

Arsenic 188 1.1 5.9 19 0.0 15.5 19 0.0 21.1 9.2 39.0

Boron 124 2.4 1.6 19 3.7 7.0 19 5.3 10.5 3.1 26.2

Chromium 133 1.5 0.0 41 1.1 0.0 19 0.0 0.0 0.0 6.8

Fluoride 188 6.4 5.3 19 14.4 20.2 19 15.8 21.1 9.2 39.0

Lead 173 0.6 0.0 19 0.2 0.0 19 0.0 0.0 0.0 6.8

Molybdenum 36 25.0 5.6 19 30.3 10.5 19 26.3 10.5 3.1 26.2

Strontium 35 2.9 5.7 19 5.3 4.4 19 5.3 5.3 0.9 18.8

Vanadium 129 3.9 0.8 19 13.0 1.8 19 15.8 0.0 0.0 6.8

Radioactive constituents with health-based benchmarks

Gross-alpha radioactivity 162 13.6 3.7 13 13.4 3.9 11 0.0 0.0 0.0 11.3

Uranium 131 5.3 2.3 19 7.5 1.5 19 10.5 0.0 0.0 6.8

Nutrients with health-based benchmarks

Nitrate 208 6.3 2.9 19 5.7 1.9 19 5.3 0.0 0.0 6.8

Inorganic constituents with non-health-based benchmarks

Chloride 187 0.0 0.5 19 0.0 0.6 19 0.0 5.3 0.9 18.8

Iron 186 3.2 2.7 19 3.7 1.7 19 0.0 0.0 0.0 6.8

Manganese 186 1.1 0.5 19 0.7 0.7 19 0.0 5.3 0.9 18.8

Sulfate 186 5.9 1.1 19 18.9 5.8 19 21.1 10.5 3.1 26.2

Total dissolved solids 187 9.1 2.7 19 20.7 11.8 19 21.1 15.8 5.9 32.8

Volatile organic constituents with health-based thresholds

Chloroform 189 0.5 0.0 19 0.2 0.0 19 0.0 0.0 0.0 6.8

Tetrachloroethene 190 1.6 0.0 19 0.8 0.0 19 0.0 0.0 0.0 6.8

Special-interest constituents with health-based benchmarks

Perchlorate 130 7.7 2.3 19 8.5 10.7 19 15.8 10.5 3.1 26.2

1Based on most recent analysis for each CDPH well during February 25, 2004–February 25, 2007, combined with USGS GAMA grid-based data.2Based on the Jeffreys interval for the binomial distribution (Brown and others, 2001).
92 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project Table B3E. Current aquifer-scale proportions in the Colorado River Groundwater Ambient Monitoring and Assessment (GAMA) study areas. [Moderate, relative-concentration between 0.5 (for trace elements, radioactive constituents, nutrients, and inorganic constituents) or 0.1 (for volatile organic compounds, pesticides, and special-interest constituents) and 1; High, relative-concentration greater than 1.0; Values are grid-based except where footnoted] Constituent Raw detection frequency 1 Spatially weighted aquifer-scale proportions 1 Grid-based aquifer-scale proportions 90 percent confidence interval for grid-based high proportion (percent) 2 Number of wells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Number of cells Moderate (percent) High (percent) Lower limit Upper limit Trace and minor elements with health-based benchmarks Arsenic 39 10.3 5.1 20 11.3 7.5 20 20.0 5.0 0.9 18.0 Boron 30 3.3 10.0 20 1.3 10.0 20 0.0 10.0 2.9 25.0 Chromium 39 2.6 0.0 20 5.0 0.0 20 5.0 0.0 0.0 6.5 Fluoride 39 7.7 15.4 20 8.8 21.3 20 10.0 20.0 8.7 37.3 Molybdenum 27 11.1 3.7 20 10.0 5.0 20 5.0 5.0 0.9 18.0 Strontium 27 22.2 7.4 20 22.5 7.5 20 25.0 10.0 2.9 25.0 Radioactive constituents with health-based benchmarks Gross-alpha radioactivity 38 5.3 5.3 20 10.0 5.0 20 10.0 10.0 2.9 25.0 Radon-222 26 3.8 0.0 19 2.6 0.0 19 5.3 0.0 0.0 9.5 Uranium 28 0.0 7.1 20 0.0 5.0 20 0.0 10.0 2.9 25.0 Nutrients with health-based benchmarks Nitrate 41 2.4 0.0 20 1.0 0.0 20 0.0 0.0 0.0 6.5 Inorganic constituents with non-health-based benchmarks Chloride 38 23.7 5.3 20 38.8 5.0 20 35.0 5.0 0.9 18.0 Iron 39 25.6 17.9 20 25.8 19.3 20 25.0 20.0 8.7 37.3 Manganese 39 2.6 61.5 20 0.0 48.8 20 0.0 45.0 28.0 63.0 Sulfate 38 57.9 21.1 20 51.0 27.5 20 50.0 25.0 12.2 42.9 Total dissolved solids (TDS) 38 52.6 42.1 20 39.0 53.5 20 35.0 55.0 37.0 72.0 Volatile organic constituents with health-based thresholds 1,2-Dichloropropane (1,2-DCP) 46 4.3 0.0 20 7.5 0.0 20 10.0 0.0 0.0 6.5 1,4-Dichlorobenzene 39 5.1 0.0 20 2.3 0.0 20 0.0 0.0 0.0 6.5 Special-interest constituents with health-based benchmarks Perchlorate 30 30.0 0.0 20 28.4 0.0 20 35.0 0.0 0.0 6.5

1Based on most recent analysis for each CDPH well during January 11, 2003–January 11, 2006, combined with USGS GAMA grid-based data.2Based on the Jeffreys interval for the binomial distribution (Brown and others, 2001).
Appendix B 93

Table B3F. Current aquifer-scale proportions in the Indian Wells Groundwater Ambient Monitoring and Assessment (GAMA) study area.[Moderate, relative-concentration between 0.5 (for trace elements, radioactive constituents, nutrients, and inorganic constituents) or 0.1 (for volatile organic compounds, pesticides and special-interest constituents) and 1; High, relative-concentration greater than 1.0; Values are grid-based except where footnoted]

Constituent

Raw detection frequency 1 Spatially-weighted aquifer-scale proportions 1 Grid-based aquifer-scale proportions

90 percent confidence

interval for grid-based 

high proportion

(percent) 2

Number 

of wells

Moderate 

(percent)

High 

(percent)

Number 

of cells

Moderate 

(percent)

High 

(percent)

Number 

of cells

Moderate 

(percent)

High 

(percent)

Lower

limit

Upper

limit

Trace and minor elements with health-based benchmarks

Antimony 47 0.0 2.1 13 0.0 0.5 13 0.0 0.0 0.0 9.7

Arsenic 47 19.1 23.4 13 36.6 25.9 13 30.8 15.4 4.6 36.5

Boron 43 7.0 30.2 13 8.7 46.2 13 15.4 38.5 19.4 61.0

Chromium 52 1.9 0.0 13 7.7 0.0 13 7.7 0.0 0.0 9.7

Fluoride 47 17.0 2.1 13 18.3 2.6 13 30.8 0.0 0.0 9.7

Lead 46 0.0 2.2 13 0.0 0.5 13 0.0 0.0 0.0 9.7

Molybdenum 20 10.0 10.0 13 15.4 10.3 13 15.4 7.7 1.4 26.4

Strontium 20 15.0 5.0 13 9.0 7.7 13 15.4 7.7 1.4 26.4

Vanadium 39 5.1 5.1 12 0.0 8.9 13 7.7 7.7 1.4 26.4

Inorganic constituents with non-health-based benchmarks

Chloride 46 4.3 6.5 13 4.5 10.9 13 7.7 7.7 1.4 26.4

Iron 46 6.5 2.2 13 1.7 2.6 13 0.0 0.0 0.0 9.7

Manganese 46 0.0 4.3 13 0.0 10.3 13 0.0 7.7 1.4 26.4

Sulfate 46 2.2 0.0 13 2.6 0.0 13 7.7 0.0 0.0 9.7

Total dissolved solids (TDS) 46 19.6 8.7 13 42.3 13.5 13 38.5 15.4 4.6 36.5

Radioactive constituents with health-based benchmarks

Gross-alpha 33 3.0 3.0 6 1.2 16.7 6 0.0 16.7 3.0 49.5

Uranium 26 11.5 3.8 12 19.4 8.3 13 15.4 7.7 1.4 26.4

Special interest constituents with health-based benchmarks

Perchlorate 20 15.0 0.0 13 17.9 0.0 13 15.4 0.0 0.0 9.7

1Based on most recent analysis for each CDPH well during September 11, 2003–September 11, 2006, combined with USGS GAMA grid-based data.2Based on the Jeffreys interval for the binomial distribution (Brown and others, 2001).
94 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig B1a

Alluvium

Hard Rock

Grid Data Points Additional Data Points

USGS Data

CDPH Data

USGS and CDPH Data

OVU-01 USGS Data

OV-12,

OV-31

OV-DG-12

OV-DPH-64

38°

37°45’

37°15’

36°45’

36°15’

36°30’

37°

37°30’

119°15’ 119° 118°45’ 118°30’ 118°15’ 118° 117°45’ 117°30’ 117°15’

NEVADA

1050 20 KILOMETERS

50 10 20 MILES

OV-29

OV-20

OV-28

OV-30

OV-27

OV-17

OVU-08

OVU-02

OVU-01 OVU-04, OVU-05

OVU-03

OVU-13

OVU-12

OVU-06, OVU-07

OVU-09, OVU-10

OVU-11

OV-03,

OV-04,

OV-08

OV-10

OV-37 OV-11

OV-26 OV-29

OV-02

OV-24

OV-16

OV-06

OV-07

OV-21

OV-33

OV-34

OV-19

OV-32

OV-40

OV-31

OV-36

OV-38

OV-13

OV-35

OV-23

OV-14

OV-15

OV-22,

OV-DG-09

OV-DG-22

OV-25, OV-DG-25

OV-39, OV-DG-39

OV-05, OV-DG-05 OV-12, OV-DG-12

OV-DG-13

OV-DG-26

OV-DG-03

OV-DG-04

OV-01

OV-DG-01

OV-DG-08

OV-DPH-61

OV-DPH-63

OV-DPH-66

OV-DPH-64

OV-DPH-65

OV-18

OV-DPH-62

EXPLANATION

B1.A

Figure B1. Maps showing the locations and identification numbers of data points in the California Desert 

Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008: (A) Owens Valley, 

(B) Antelope Valley, (C) Mojave, (D) Coachella Valley, (E) Colorado River, and (F) Indian Wells Valley.
Appendix B 95

sac11-0428_fig B1b

Alluvium

Hard Rock

Grid Data Points Additional Data Points

USGS Data

CDPH Data

USGS and CDPH Data

ANT-U USGS Data

ANT-31,

ANT-03

ANT-DPH-17, ANT-DG-28

ANT-DPH-02

EXPLANATION

118°30’

34°45’

34°30’

35°

118°15’ 118° 117°45’

20 MILES

1050 20 KILOMETERS

0 5 10

ANT-U

ANT-32,

ANT-34

ANT-51

ANT-45

ANT-DG-32

ANT-33, ANT-DG-33

ANT-36, ANT-DG-36

ANT-39, ANT-DG-39

ANT-35, ANT-DG-35 ANT-38,

ANT-40

ANT-48

ANT-14

ANT-54 ANT-07

ANT-04

ANT-42

ANT-47

ANT-22,

ANT-DPH-71

ANT-DPH-69

ANT-DPH-67

ANT-DPH-75

ANT-DPH-82

ANT-DPH-78

ANT-DPH-68

ANT-DPH-72

ANT-DPH-73

ANT-DPH-74

ANT-DPH-77 ANT-DPH-80

ANT-DPH-84 ANT-DPH-81

ANT-DPH-83

ANT-DPH-85

ANT-DPH-76

ANT-DG-38

ANT-28, ANT-DG-22

ANT-15

ANT-56

ANT-09 ANT-46 ANT-03

ANT-49

ANT-12

ANT-06

ANT-52

ANT-26

ANT-50

ANT-43

ANT-21 ANT-02

ANT-17

ANT-DG-28

ANT-29, ANT-DG-29

ANT-08, ANT-DG-08

ANT-41, ANT-DG-41

ANT-16, ANT-DG-16

ANT-11, ANT-DG-11

ANT-10, ANT-DG-10

ANT-13, ANT-DG-13

ANT-24, ANT-DG-24

ANT-19, ANT-DG-19

ANT-23, ANT-DG-23

ANT-30, ANT-DG-30

ANT-25, ANT-DG-25

ANT-27, ANT-DG-27

ANT-05, ANT-DG-05

ANT-01, ANT-DG-01

ANT-53, ANT-DG-53

ANT-31, ANT-DG-31

ANT-20, ANT-DPH-34

ANT-55, ANT-DG-55 ANT-18, ANT-DG-18

ANT-44, ANT-DG-44

ANT-37, ANT-DG-37

B1.B

Figure B1.—Continued
96 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig B1c

Alluvium

Hard Rock

Grid Data Points Additional Data Points

USGS Data

CDPH Data

USGS and CDPH Data

MOJOU-02 USGS Data

MOJO-23,

MOJO-03

MOJO-DG-23

MOJO-DPH-66

EXPLANATION

20 MILES

1050 20 KILOMETERS

0 5 10

MOJOU-07

MOJOU-03

MOJOU-04

MOJOU-05

MOJOU-02

MOJOU-01

MOJOU-06

MOJO-09,

MOJO-26,

MOJO-12

MOJO-21

MOJO-29 MOJO-47

MOJO-24

MOJO-22

MOJO-34

MOJO-16

MOJO-18 MOJO-18

MOJO-17

MOJO-13 MOJO-25

MOJO-48 MOJO-30

MOJO-14

MOJO-39

MOJO-33

MOJO-40

MOJO-45 MOJO-50

MOJO-49

MOJO-36

MOJO-52

MOJO-51 MOJO-41

MOJO-42

MOJO-38,

MOJO-35

MOJO-DG-09

MOJO-DG-26

MOJO-02, MOJO-DG-02

MOJO-01, MOJO-06, MOJO-DG-01

MOJO-DG-06

MOJO-23, MOJO-DG-23

MOJO-46, MOJO-DG-46

MOJO-05, MOJO-DG-05

MOJO-20, MOJO-DG-20

MOJO-37, MOJO-DG-37

MOJO-44, MOJO-DG-44

MOJO-43,

MOJO-03

MOJO-19

MOJO-DG-43

MOJO-11, MOJO-DG-11

MOJO-04, MOJO-DG-04

MOJO-07, MOJO-DG-07

MOJO-32, MOJO-DG-32

MOJO-08,

MOJO-28

MOJO-31

MOJO-15

MOJO-10

MOJO-DG-08

MOJO-DG-38

MOJO-DPH-77

MOJO-DPH-80 MOJO-DPH-78

MOJO-DPH-79

MOJO-DPH-70

MOJO-DPH-71

MOJO-DPH-73

MOJO-DPH-72

MOJO-DPH-69

MOJO-DPH-68

MOJO-DPH-67

MOJO-DPH-66

MOJO-DPH-76

MOJO-DPH-74

MOJO-DPH-75

MOJO-DPH-81

MOJO-DPH-85

MOJO-DPH-84

MOJO-DPH-82

MOJO-DPH-83

117°30’

34°45’

34°30’

34°15’

35°

B 117°15’ 117° 116°45’ 1.C

Figure B1.—Continued
Appendix B 97

sac11-0428_fig B1d

Alluvium

Hard Rock

Lake

Grid Data Points Additional Data Points

USGS Data

CDPH Data

USGS and CDPH Data

COAU-02 USGS Data

COA-04,

COA-03

COA-DG-04

COA-DPH-25

EXPLANATION

116°45’

34°15’

33°45’

33°30’

33°15’

34°

116°30’ 116°15’ 116°

0 5 10 20 MILES

50 10 20 KILOMETERS

COAU-12

COAU-01

COAU-11

COAU-08

COAU-02

COAU-03

COAU-13

COAU-04

COAU-16

COAU-09

COAU-14

COAU-15

COAU-07

COAU-06 COAU-05

COAU-10

COA-19

COA-09 COA-03 COA-16

COA-08

COA-18

COA-11

COA-02

COA-12

COA-07

COA-15

COA-17

COA-01

COA-DPH-21 COA-13,COA-DG-13

COA-04,

COA-05

COA-DG-04

COA-06, COA-DG-06

COA-10, COA-DG-10

COA-14, COA-DG-14

COA-DPH-23

COA-DPH-22

COA-DPH-24

COA-DPH-25

B1.D

Figure B1.—Continued
98 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig B1e

ARIZONA

MEXICO

Alluvium

Hard Rock

Lake

Grid Data Points Additional Data Points

USGS Data COLORU-02 USGS Data COLOR-03

EXPLANATION

115°45’ 115°30’ 115°15’ 115° 114°45’ 114°30’ 114°15’ 114° 113°45’ 113°30’ 113°15’

34°45’

34°30’

34°15’

33°45’

33°30’

33°15’

32°45’

33°

34°

35°

50 MILES

2512.50 50 KILOMETERS

0 12.5 25

COLORU-05

COLORU-02 COLORU-08

COLORU-07

COLORU-01

COLORU-03

COLORU-06

COLORU-04

COLOR-17

COLOR-06

COLOR-16

COLOR-18

COLOR-08

COLOR-09

COLOR-05

COLOR-04

COLOR-11

COLOR-07

COLOR-01

COLOR-15

COLOR-14 COLOR-19

COLOR-02

COLOR-03

COLOR-10

COLOR-12

COLOR-13

COLOR-20

B1.E

Figure B1.—Continued
Appendix B 99

sac11-0428_fig B1f

Alluvium

Hard Rock

Grid Data Points Additional Data Points

USGS Data

CDPH Data

USGS and CDPH Data

OIWU-02 USGS Data

OIW-02,

OIW-03

OIW-DG-02

OIW-DPH-22

EXPLANATION

117°45’

35°45’

35°30’

118° 117°30’

10 MILES

0 52.5 10 KILOMETERS

52.50

OIW-03

OIW-05

OIW-09

OIW-10

OIW-11

OIW-02, OIW-DG-02

OIW-01, OIW-DG-01

OIW-07, OIW-DG-07

OIW-DG-04

OIW-06, OIW-DG-06

OIW-08

OIW-13

OIW-12

OIW-04,

OIWU-04, OIWU-05

OIWU-03

OIWU-01 OIWU-02

OIWU-06

OIWU-07

OIWU-08

OIW-DPH-22

OIW-DPH-21

B.1F

Figure B1.—Continued
100 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig B2

Inorganic constituents

with non-healthbased benchmarks

Trace

elements

Inorganic constituents

with non-healthbased benchmarks

Trace

elements

10

1

0.1

0.01

0.001

100

10

1

0.1

100

10

0.1

0.01

0.001

1

0.01

0.001

100

Indian Wells

Colorado River

Mojave

Owens Valley

Coachella

Antelope

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Nitrate

Ammonia

Nitrite

Molybdenum

Strontium

Fluoride

Barium

Arsenic

Boron

Vanadium

Chromium

Lead

Copper

Nickel

Selenium

Aluminum

Antimony

Cadmium

Mercury

Beryllium

Thallium

Chloride

Sulfate

Total Dissolved Solids

Zinc

Manganese

Iron

Gross-alpha

Gross-beta

Radium-226

Radium-228

Radon-222

Maximum relative-concentrations

Nitrate

Ammonia

Nitrite

Lead

Copper

Strontium

Fluoride

Barium

Aluminum

Nickel

Arsenic

Antimony

Selenium

Mercury

Cadmium

Thallium

Boron

Chloride

Manganese

Iron

Silver

Zinc

Gross-alpha

Radium-228

Molybdenum Sulfate

Chromium

Ammonia

Nitrite

Aluminum

Antimony

Arsenic

Barium

Beryllium

Boron

Cadmium

Chromium

Copper

Fluoride

Lead

Mercury

Molybdenum

Nickel

Selenium

Strontium

Thallium

Vanadium

Chloride

Iron

Manganese

Sulfate

Zinc

Gross-alpha

Gross-beta 

Radium-226

Radium-228

Radon-222 Nitrate

Nitrate

Nitrite

Copper

Molybdenum

Strontium

Barium

Aluminum

Nickel

Arsenic

Selenium

Antimony

Cadmium

Beryllium

Vanadium

Chloride Sulfate

Silver

Zinc

Gross-beta

Gross-alpha

Radium-226

Radium-228

Radon-222

Nitrite

Strontium

Molybdenum

Arsenic Boron

Barium

Nickel

Antimony

Cadmium

Beryllium

Radium-226

Radon-222

Gross-beta

Gross-alpha

Radium-228

Chromium

Nitrate

Nutrients

Total Dissolved Solids

Total Dissolved Solids

Total Dissolved Solids

Perchlorate

Perchlorate

Gross-beta

Radium-226

Radon-222

Gross-alpha

Radium-228

Chloride

Sulfate

Zinc

Manganese

Iron

Total Dissolved Solids

Perchlorate

Perchlorate

Nitrate

Nitrite

Ammonia

Molybdenum Strontium

Fluoride

Aluminum

Barium

Arsenic

Selenium

Boron

Vanadium

Nickel

Chromium

Lead

Cadmium

Copper

Antimony

Beryllium

Perchlorate

Perchlorate

Special-interest

Radioactive

constituent

constituents

Nutrients

Special-interest

Radioactive

constituent

constituents

Iron

Lead

Fluoride Boron

Chromium

Manganese

Uranium

Uranium

Uranium

Uranium

Uranium

Fluoride Vanadium

Uranium

Copper

Zinc

Selenium Aluminum

Lead

Sulfate

Chloride

Manganese Iron

Total Dissolved Solids Vanadium

Figure B2. Graphs showing the maximum relative-concentrations of inorganic constituents with health-based 

or non-health-based benchmarks detected in grid wells by constituent class in the California Desert Region 

Groundwater Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
Appendix B 101

sac11-0428_fig B3 Maximum relative-concentration

Chloroform

Carbon Disulfide

Atrazine

Simazine

Atrazine

Simazine

Atrazine

Simazine

Prometon

Chloroform

Chloromethane

Carbon Tetrachloride

Dichloromethane

Bromoform

Chloroform

Bromochloromethane Styrene

Atrazine

Simazine

1,2,3-Trichloropropane

Dieldrin

Atrazine

Simazine

Metolachlor

Prometon

Chloroform

Carbon Disulfide

Chloroform

Chloroform Bromoform

Carbon Tetrachloride

Dichloromethane

Chlorobenzene

Volatile

organic

compounds

Pesticides Specialinterest

constituents

Volatile

organic

compounds

Pesticides Specialinterest

constituents

Methyl tert-butyl ether

Tetrachloroethene

1,2-Dichloropropane

N-Nitrosodimethylamine

Bromodichloromethane

1,1-Dichloroethane

Dibromochloromethane

1,1-Dichloroethene

1,2-Dichloroethane

cis-1,2-Dichloroethene

trans-1,2-Dichloroethene

Trichlorofluoromethane

Tetrachloroethene

Tetrachloroethene

Trichloroethene

Methyl tert-butyl ether

Bromodichloromethane Dibromochloromethane

1,1-Dichloroethene

1,1-Dichloroethane Trichloroethene

Tetrachloroethene

100

10

0.1

0.01

0.001

0.0001

1

100

10

1

0.1

0.01

0.001

0.0001

10

1

0.1

0.01

0.001

0.0001

100

Indian Wells

Colorado River

Mojave

Owens Valley

Coachella

Antelope

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Figure B3. Graphs showing the maximum relative-concentrations of organic constituents with healthbased benchmarks detected in grid wells by constituent class in the California Desert Region Groundwater 

Ambient Monitoring and Assessment (GAMA) study areas, 2006–2008.
102 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

cis-1,2-Dichloroethene Tetrachloromethane

Trichloroethene

Tetrachloromethane

Trichlorofluoromethane

10

1

0.1

0.01

0.001

0.1

0.01

0.001

0.0001

0.00001

0.0001

0.00001

No benchmarks

No benchmarks

100

10

1

100

0.1

0.01

0.001

0.0001

0.00001

No benchmarks

10

1

100

Indian Wells

Colorado River

Mojave

Owens Valley

Coachella

Antelope

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

Low

Moderate

High

10 100

Detection frequency

1 1 10 100

Maximum relative-concentration

Chloroform

Simazine

Atrazine Bromodichloromethane

Tetrachloroethene

1,1-Dichloroethane

Dibromochloromethane

Bromoform

Dieldrin

1,1-Dichloroethene

1,2-Dichloroethane

Dichloromethane 

trans-1,2-Dichloroethene

Trichloroethene

N-Nitrosodimethylamine

Metolachlor

Chlorobenzene

1,3-Dichlorobenzene

Prometon

Chloroform

Simazine

Bromodichloromethane

Atrazine

Tetrachloroethene Dibromochloromethane Bromoform

1,1-Dichloroethane 1,4-Dichlorobenzene Dichloromethane

1,1-Dichloroethene

Chloromethane

Prometon

Bromochloromethane

Styrene

1,2-Dichlorobenzene

1,3-Dichlorobenzene

Tetrachloroethene Chloroform

Simazine

Atrazine

Chloroform

Tetrachloroethene

Methyl tert-butyl ether

Simazine

Atrazine

Carbon disulfide

1,3-Dichlorobenzene Hexazinone

Tebuthiuron

Chloroform

Carbon disulfide

1,2-Dichloropropane

Chloroform

Simazine

Atrazine

1,2,3-Trichloropropane

Methyl tert-butyl ether

Desethylatrazine Desethylatrazine

Desethylatrazine 3,4-Dichloroaniline

Desethylatrazine Desulfinylfipronil Fipronil

Fipronil Sulfide

Prometryn

sac11-0428_fig B4

Figure B4. Graphs showing the detection frequencies and maximum relative-concentrations of organic 

constituents detected in grid wells in the California Desert Region Groundwater Ambient Monitoring and 

Assessment (GAMA) study areas, 2006–2008.
Appendix C 103

Appendix C. Comparison of CDPH and USGS-GAMA Data

Comparisons of CDPH and USGS-GAMA data were 

done to assess the validity of using data from these different 

sources in combination. Concentrations of inorganic 

constituents (alkalinity, fluoride, magnesium, potassium, 

sodium, sulfate, and total dissolved solids), which generally 

are prevalent at concentrations substantially above laboratory 

reporting levels, were compared for each well with data from 

both sources. Sixty wells had major-ion data from USGS and 

the CDPH databases. Although differences between the paired 

datasets occurred for a few wells, most sample pairs plotted 

close to a 1-to-1 line (fig. C1). Wilcoxon signed-rank tests of 

paired analyses of alkalinity, fluoride, magnesium, potassium, 

sodium, sulfate, and total dissolved solids yielded results of no 

significant differences (p > 0.05) between USGS and CDPH 

data for any of the constituents. 

Major-ion data for Desert Region grid wells were plotted 

on Piper diagrams (Piper, 1944) with all CDPH major-ion 

data to determine if the grid wells represented the range of 

groundwater types that have historically been observed in the 

Desert Region. Piper diagrams show the relative abundance 

of major cations and anions (on a charge-equivalent basis) 

as a percentage of the total ion content of the water and are 

often used to define groundwater type (Hem, 1985). All CDPH 

data having cation/anion data and a cation/anion imbalance of 

less than 10 percent were retrieved and plotted on these Piper 

diagrams for comparison with grid-well data. A similar range 

of water types was evident from grid wells and historical 

CDPH data (fig. C2). This similarity of the range of relative 

abundance of major cations and anions in grid wells compared 

to the set of all CDPH wells indicates that the grid wells 

represent the types of water present within the Desert Region’s 

primary aquifers. 
104 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig C1

EXPLANATION 1,000

100

10

1

0.1

0.1 1 10

Concentration, USGS-GAMA data, in milligrams per liter

100 1,000

Concentration, CDPH data, in milligrams per liter

Calcium

Magnesium

Potassium

Sodium

Alkalinity

Fluoride

Sulfate

Total Dissolved Solids

Figure C1. Graph showing paired inorganic concentrations from USGS-GAMA Program data collected from 

September 2006 to April 2008 and current (2003–2008) California Department of Public Health data in the California Desert 

Region Groundwater Ambient Monitoring and Assessment (GAMA) study areas.
Appendix C 105

Figures C2. Piper diagrams showing water types in USGS-GAMA wells, 2006–2008, and in all wells in the California Department 

of Public Health database with a charge imbalance of less than 10 percent in the California Desert Groundwater Ambient 

Monitoring and Assessment (GAMA) study areas: (A) Owens Valley, (B) Indian Wells Valley, (C) Coachella Valley, (D) Colorado 

River, (E) Antelope Valley, and (F) Mojave.

sac11-0428_fig C2a

Percent

Calcium

 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 

Magnesium

 0 

 20 

 40 

 60 

 80 

 100 

Sodium plus Potassium

Chloride plus Fluoride

 0 

 20 

 40 

 60 

 80 

 100 

 100 

 80 

 60 

 40 

 20 

 0 

Bicarbonate

 100 

 80 

 60 

 40 

 20 

 0 

Sulfate

 0 

 20 

 40 

 60 

 80 

 100 

Sulfate plus Chloride

 0 

 20 

 40 

 60 

 80 

 100 

Calcium plus Magnesium

 100 

 80 

 60 

 40 

 20 

 0 

 100 

 80 

 60 

 40 

 20 

 0 

Percent

Percent

Owens Valley

EXPLANATION

USGS Grid Data

All CDPH Data

C2.A
106 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

Figure C2.—Continued

sac11-0428_fig C2b

Percent

Calcium

 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 

Magnesium

 0 

 20 

 40 

 60 

 80 

 100 

Sodium plus Potassium

Chloride plus Fluoride

 0 

 20 

 40 

 60 

 80 

 100 

 100 

 80 

 60 

 40 

 20 

 0 

Bicarbonate

 100 

 80 

 60 

 40 

 20 

 0 

Sulfate

 0 

 20 

 40 

 60 

 80 

 100 

Sulfate plus Chloride

 0 

 20 

 40 

 60 

 80 

 100 

Calcium plus Magnesium

 100 

 80 

 60 

 40 

 20 

 0 

 100 

 80 

 60 

 40 

 20 

 0 

Percent

Percent

Indian Wells Valley

EXPLANATION

USGS Grid Data

All CDPH Data

C2.B
Appendix C 107

Figure C2.—Continued

sac11-0428_fig C2c

Percent

Calcium

 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 

Magnesium

 0 

 20 

 40 

 60 

 80 

 100 

Sodium plus Potassium

Chloride plus Fluoride

 0 

 20 

 40 

 60 

 80 

 100 

 100 

 80 

 60 

 40 

 20 

 0 

Bicarbonate

 100 

 80 

 60 

 40 

 20 

 0 

Sulfate

 0 

 20 

 40 

 60 

 80 

 100 

Sulfate plus Chloride

 0 

 20 

 40 

 60 

 80 

 100 

Calcium plus Magnesium

 100 

 80 

 60 

 40 

 20 

 0 

 100 

 80 

 60 

 40 

 20 

 0 

Percent

Percent

Coachella Valley

EXPLANATION

USGS Grid Data

All CDPH Data

C2.C
108 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig C2d

Percent

Calcium

 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 

Magnesium

 0 

 20 

 40 

 60 

 80 

 100 

Sodium plus Potassium

Chloride plus Fluoride

 0 

 20 

 40 

 60 

 80 

 100 

 100 

 80 

 60 

 40 

 20 

 0 

Bicarbonate

 100 

 80 

 60 

 40 

 20 

 0 

Sulfate

 0 

 20 

 40 

 60 

 80 

 100 

Sulfate plus Chloride

 0 

 20 

 40 

 60 

 80 

 100 

Calcium plus Magnesium

 100 

 80 

 60 

 40 

 20 

 0 

 100 

 80 

 60 

 40 

 20 

 0 

Percent

Percent

Colorado River

EXPLANATION

USGS Grid Data

All CDPH Data

C2.D

Figure C2.—Continued
Appendix C 109

Figure C2.—Continued

sac11-0428_fig C2e

Percent

Calcium

 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 

Magnesium

 0 

 20 

 40 

 60 

 80 

 100 

Sodium plus Potassium

Chloride plus Fluoride

 0 

 20 

 40 

 60 

 80 

 100 

 100 

 80 

 60 

 40 

 20 

 0 

Bicarbonate

 100 

 80 

 60 

 40 

 20 

 0 

Sulfate

 0 

 20 

 40 

 60 

 80 

 100 

Sulfate plus Chloride

 0 

 20 

 40 

 60 

 80 

 100 

Calcium plus Magnesium

 100 

 80 

 60 

 40 

 20 

 0 

 100 

 80 

 60 

 40 

 20 

 0 

Percent

Percent

Antelope Valley

EXPLANATION

USGS Grid Data

All CDPH Data

C2.E
110 Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project

sac11-0428_fig C2f

Percent

Calcium

 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 

Magnesium

 0 

 20 

 40 

 60 

 80 

 100 

Sodium plus Potassium

Chloride plus Fluoride

 0 

 20 

 40 

 60 

 80 

 100 

 100 

 80 

 60 

 40 

 20 

 0 

Bicarbonate

 100 

 80 

 60 

 40 

 20 

 0 

Sulfate

 0 

 20 

 40 

 60 

 80 

 100 

Sulfate plus Chloride

 0 

 20 

 40 

 60 

 80 

 100 

Calcium plus Magnesium

 100 

 80 

 60 

 40 

 20 

 0 

 100 

 80 

 60 

 40 

 20 

 0 

Percent

Percent

Mojave

EXPLANATION

USGS Grid Data

All CDPH Data

C2. F

Figure C2.—Continued
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For more information concerning the research in this report, contact the

 Director, California Water Science Center

U.S. Geological Survey

6000 J Street, Placer Hall

Sacramento, California 95819

http://ca.water.usgs.gov
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Dawson and Belitz—Status of Groundwater Quality in the California Desert Region, 2006–2008: California GAMA Priority Basin Project—SIR 2012–5040

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