U.S. Department of the Interior

U.S. Geological Survey

Data Series 659

Prepared in cooperation with the California State Water Resources Control Board

Groundwater-Quality Data in the Borrego Valley, Central 

Desert, and Low-Use Basins of the Mojave and Sonoran

Deserts Study Unit, 2008–2010: Results from the California 

GAMA Program

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

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Top Right:

Borrego Valley at sunset, California. (Photograph taken by Michael Solt, U.S. Geological Survey)

Bottom:

Joshua Tree and public supply well, Yucca Valley, California. (Photograph taken by Dara Goldrath, U.S. Geological Survey) 
Groundwater-Quality Data in the Borrego Valley, 

Central Desert, and Low-Use Basins of the 

Mojave and Sonoran Deserts Study Unit, 

2008–2010: Results from the California 

GAMA Program

By Timothy M. Mathany, Michael T. Wright, Brandon S. Beuttel, 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

Data Series 659

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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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:

Mathany, T.M., Wright, M.T., Beuttel, B.S., and Belitz, Kenneth, 2012, Groundwater-quality data in the Borrego Valley, 

Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts study unit, 2008–2010—Results from the 

California GAMA Program: U.S. Geological Survey Data Series 659, 100 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................5

Hydrogeologic Setting ..................................................................................................................................5

CLUB Study Unit—Borrego Valley Study Area................................................................................5

CLUB Study Unit—Central Desert Study Area ................................................................................8

CLUB Study Unit—Low-Use Basins of the Mojave and Sonoran Deserts Study Area ..........10

Low-Use Basins of the Mojave and Sonoran Deserts Study Area—Mojave Desert 

Region ............................................................................................................................10

Low-Use Basins of the Mojave and Sonoran Deserts Study Area—Sonoran Desert 

Region ............................................................................................................................10

Methods ........................................................................................................................................................19

Study Design........................................................................................................................................19

Sample Collection and Analysis.......................................................................................................20

Data Reporting.....................................................................................................................................20

Quality-Assurance Methods ............................................................................................................20

Water-Quality Results ................................................................................................................................21

Quality-Control Results ......................................................................................................................21

Comparison Benchmarks ..................................................................................................................21

Groundwater-Quality Data ................................................................................................................22

Water-Quality Indicators .........................................................................................................23

Organic Constituents.................................................................................................................23

Constituents of Special Interest..............................................................................................23

Inorganic Constituents..............................................................................................................24

Isotopic Tracers and Dissolved Noble Gases .......................................................................25

Radioactive Constituents..........................................................................................................25

Future Work ..................................................................................................................................................26

Summary .......................................................................................................................................................26

Acknowledgments.......................................................................................................................................27

References Cited..........................................................................................................................................27

Appendix .......................................................................................................................................................77
iv

Figures

Figure 1. Map showing the hydrogeologic provinces of California and the location of the

Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran

Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) 

study unit and study areas.................................................................. 4

Figure 2. Map showing the location of the Borrego Valley, Central Desert, and 

Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater 

Ambient Monitoring and Assessment (GAMA) study units ........................... 6

Figure 3. Map showing the Borrego Valley study area (BV), the boundaries of the 

California Department of Water Resources (CDWR) defined groundwater 

basins, the distribution of the Central Desert study area grid cells, the location 

of California Department of Public Health (CDPH) wells, and the location of 

sampled grid wells........................................................................... 7

Figure 4. Map showing the Central Desert study area (CD), the boundaries of the 

California Department of Water Resources (CDWR) defined groundwater 

basins, the distribution of the CD study area grid cells, the location of 

California Department of Public Health (CDPH) wells, and the location of 

sampled grid wells........................................................................... 9

Figure 5. Map showing the northwestern part, the northern part, the northeastern part, 

the western part, the central part, the eastern part, the southwestern part, 

and the southeastern part of the Low-Use Basins of the Mojave and Sonoran 

Deserts study area (LUB), the boundaries of the California Department of 

Water Resources (CDWR) defined groundwater basins, the distribution of the 

LUB study-area grid cells, the location of California Department of Public 

Health (CDPH) wells, and the location of sampled grid and understanding wells... 11

Tables

Table 1. Identification, sampling, and construction information for wells sampled for the

Borrego, Central Desert, and Low-Use Basins of the Mojave and Sonoran

Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA)

study, California, December 2008 to March 2010. ....................................... 37

Table 2. Classes of chemical constituents and water-quality indicators collected for the

slow and the fast well sampling schedules in the Borrego, Central Desert, and

Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater

Ambient Monitoring and Assessment (GAMA) study, California, December 2008 

to March 2010 .............................................................................. 39

Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparative

benchmarks, and reporting information for the U.S. Geological Survey (USGS)

National Water Quality Laboratory (NWQL) Schedule 2020 ........................... 40

Table 3B. Pesticides and pesticide degradates, primary uses or sources, comparative

benchmarks, and reporting information for the U.S. Geological Survey (USGS)

National Water Quality Laboratory (NWQL) Schedule 2003 ........................... 43

Table 4. Water-quality indicators in samples collected for the Borrego Valley, Central

Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB)

Groundwater Ambient Monitoring and Assessment (GAMA) study, California,

December 2008 to March 2010 ............................................................ 53
v

Tables—Continued

Table 5. Volatile organic compounds (VOCs) detected in samples collected for the

Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran

Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA)

study, California, December 2008 to March 2010. ....................................... 56

Table 6. Pesticides and pesticide degradates detected in samples collected for the

Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran

Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA)

study, California, December 2008 to March 2010. ....................................... 58

Table 7. Perchlorate detected in the samples collected for the Borrego Valley, Central

Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB)

Groundwater Ambient Monitoring and Assessment (GAMA) study, California,

December 2008 to March 2010 ............................................................ 59

Table 8. Trace elements detected in the samples collected for the Borrego Valley,

Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB)

Groundwater Ambient Monitoring and Assessment (GAMA) study, California,

December 2008 to March 2010 ............................................................ 60

Table 9. Nutrients detected in samples collected for the Borrego Valley, Central Desert,

and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater

Ambient Monitoring and Assessment (GAMA) study, California, December 2008 

to March 2010 .............................................................................. 66

Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples

collected for the Borrego Valley, Central Desert, and Low-Use Basins of the

Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and

Assessment (GAMA) study, California, December 2008 to March 2010............... 68

Table 11. Species of inorganic chromium detected in samples collected for the Borrego

Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts

(CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study,

California, December 2008. ............................................................... 71

Table 12. Hexavalent chromium (chromium-VI, Cr-VI) detected in samples collected for the

Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran

Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA)

study, California, October 2009 to March 2010. .......................................... 71

Table 13. Results for analyses of stable isotope ratios, tritium activity, and carbon-14

abundance detected in samples collected for the Borrego Valley, Central Desert,

and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater

Ambient Monitoring and Assessment (GAMA) study, California, December 2008 

to March 2010 .............................................................................. 72

Table 14A. Radon-222 detected in samples collected for the Borrego Valley , Central Desert,

and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater

Ambient Monitoring and Assessment (GAMA) study, California, December 2008 

to March 2010. .............................................................................. 74

Table 14B. Radium isotopes detected in samples collected for the Borrego Valley, Central

Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB)

Groundwater Ambient Monitoring and Assessment (GAMA) study, California,

December 2008 to March 2010 ............................................................ 75

Table 14C. Gross alpha and beta radioactivity detected in samples collected for the Borrego

Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts

(CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study,

California, December 2008 to March 2010 ................................................ 76
vi

Conversion Factors and Datums

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2) 2.590 square kilometer (km2) 

quart (qt) 0.9464 liter (L)

pound, avoirdupois (lb) 0.4536 kilogram (kg)

SI to Inch/Pound

Multiply By To obtain

centimeter (cm) 0.3937 inch (in.)

micrometer (μm) 3.3 × 10–6 foot (ft)

kilometer (km) 0.6214 mile (mi)

square kilometer (km2) 0.3861 square mile (mi2)

liter (L) 1.0567 quart (qt)

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound, avoirdupois (lb)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8 ×°C)+32.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm 

at 25°C).

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

or micrograms per liter (μg/L). 

Milligrams per liter is equivalent to parts per million (ppm), and micrograms per liter is 

equivalent to parts per billion (ppb). 

Concentrations of radioactive constituents in water are given in picocuries per liter (pCi/L). 

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).

Land-surface altitude, as used in this report, refers to distance above the vertical datum and is 

reported as feet above mean sea level (ft above msl) and feet below mean sea level (ft below 

msl).
vii

Selected Terms and Symbols

α confidence level

cm3 STP/g cubic centimeters of gas at standard temperature and pressure (0 degrees 

Celsius and 1 atmosphere of pressure) per gram of water

δ iE delta notation, the ratio of a heavier isotope of an element (iE) to the more 

common lighter isotope of that element, relative to a standard reference 

material, expressed as per mil

= equal to

> greater than

≥ greater than or equal to

< less than

≤ less than or equal to

N Normal (1-gram-equivalent per liter of solution)

– not detected

p significant level

pH measure of the acidity of water

pK1,2 acid dissociation constants of carbonic acid

pKw acid dissociation constant of water

R result

z test statistic

± plus or minus

* value is at a concentration greater than benchmark level

** value is at a concentration greater than upper benchmark level

Abbreviations and Acronyms

AL action level

AL-US action level (USEPA)

APE Alternate Place Entry Form program designed for USGS sampling

BV Borrego Valley study area

BVU Borrego Valley study area understanding (well)

CAS Chemical Abstract Service (American Chemical Society)

CASRN Chemical Abstract Service (American Chemical Society) Registry Number®

CD Central Desert study area

CLUB Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran 

Deserts study unit

CSU combined standard uncertainty

DWP Domestic Well Project (SWRCB)

E estimated or having a higher degree of uncertainty

GAMA Groundwater Ambient Monitoring and Assessment Program

GPS Global Positioning System

HAL lifetime health advisory level

HAL-US lifetime health advisory level (USEPA)

HPLC high-performance liquid chromatography

IBSP Inorganic Blind Sample Project (USGS)
viii

LRL laboratory reporting level

LSD land surface datum

LT-MDL long-term method detection level

LUB Low-Use Basins of the Mojave and Sonoran Deserts study area

LUBU Low-Use Basins of the Mojave and Sonoran Deserts study area understanding 

(well)

MCL maximum contaminant level

MCL-US maximum contaminant level (USEPA)

MCL-CA maximum contaminant level (CDPH)

MDL method detection limit

MRL minimum reporting level

MU method uncertainty

na not available

nc not collected

NELAP National Environmental Laboratory Accreditation Program

NFM National Field Manual (USGS)

NFQA National Field Quality Assurance Program (USGS)

NL notification level

NL-CA notification level (CDPH)

nv no measured value or no value in category

np no preference

NRP National Research Program (USGS)

NWIS National Water Information System (USGS)

OBSP Organic Blind Sample Program (USGS)

PBP Priority Basin Project

PCFF Personal Computer Field Form program designed for USGS sampling

QA quality assurance

QC quality control

RL reporting level

RPD relative percent difference

RSD relative standard deviation

RSD5 risk-specific dose at 10–5 (USEPA)

SD standard deviation

SMCL secondary maximum contaminant level

SMCL-CA secondary maximum contaminant level (CDPH)

SMCL-US secondary maximum contaminant level (USEPA)

SRL study reporting level (concentration cutoff for applying the ≤ symbol)

ssLC sample-specific critical level

U.S. United States

UV ultraviolet

VPDB Vienna Pee Dee Belemnite (the international reference standard for carbon 

isotopes)

VSMOW Vienna Standard Mean Ocean Water (an isotopic water standard defined in 1968 

by the International Atomic Energy Agency)

Abbreviations and Acronyms—Continued
ix

Organizations

BQS Branch of Quality Systems (USGS)

CDPH California Department of Public Health

CDPR California Department of Pesticide Regulation

CDWR California Department of Water Resources

LLNL Lawrence Livermore National Laboratory

NAWQA National Water-Quality Assessment Program (USGS)

NIST National Institute of Standards and Technology

NWQL National Water Quality Laboratory (USGS)

SITL Stable Isotope and Tritium Laboratory, Menlo Park, California (USGS)

SWRCB California State Water Resources Control Board

TALIR TestAmerica Laboratories, Inc., Irvine, California

TML Trace Metal Laboratory, Boulder, Colorado (USGS)

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

Selected Chemical Names

CaCO3 calcium carbonate

CO3

2– carbonate

CFC chlorofluorocarbon

Cr-VI hexavalent chromium (chromium-VI)

DIPE diisopropyl ether

H2

O water

HCl hydrochloric acid

HCO3

– bicarbonate

MTBE methyl tert-butyl ether

NDMA N-nitrosodimethylamine

PCE perchloroethene (tetrachloroethene)

PVC polyvinyl chloride

SiO2 silicon dioxide

TCE trichloroethene

TDS total dissolved solids

THM trihalomethane

VOC volatile organic compound

Abbreviations and Acronyms—Continued
x

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Abstract 

Groundwater quality in the 12,103-square-mile Borrego 

Valley, Central Desert, and Low-Use Basins of the Mojave 

and Sonoran Deserts (CLUB) study unit was investigated by 

the U.S. Geological Survey (USGS) from December 2008 to 

March 2010, as part of the California State Water Resources 

Control Board (SWRCB) Groundwater Ambient Monitoring 

and Assessment (GAMA) Program’s Priority Basin Project 

(PBP). The GAMA-PBP was developed in response to the 

California Groundwater Quality Monitoring Act of 2001 and 

is being conducted in collaboration with the SWRCB and 

Lawrence Livermore National Laboratory (LLNL). The CLUB 

study unit was the twenty-eighth study unit to be sampled as 

part of the GAMA-PBP.

The GAMA CLUB study was designed to provide a 

spatially unbiased assessment of untreated-groundwater 

quality in the primary aquifer systems, and to facilitate 

statistically consistent comparisons of untreated-groundwater 

quality throughout California. The primary aquifer systems 

(hereinafter referred to as primary aquifers) are defined as 

parts of aquifers corresponding to the perforation intervals 

of wells listed in the California Department of Public Health 

(CDPH) database for the CLUB study unit. The quality 

of groundwater in shallow or deep water-bearing zones 

may differ from the quality of groundwater in the primary 

aquifers; shallow groundwater may be more vulnerable to 

surficial contamination.

In the CLUB study unit, groundwater samples were 

collected from 52 wells in 3 study areas (Borrego Valley, 

Central Desert, and Low-Use Basins of the Mojave and 

Sonoran Deserts) in San Bernardino, Riverside, Kern, 

San Diego, and Imperial Counties. Forty-nine of the wells 

were selected by using a spatially distributed, randomized 

grid-based method to provide statistical representation of the 

study unit (grid wells), and three wells were selected to aid in 

evaluation of water-quality issues (understanding wells).

The groundwater samples were analyzed for organic 

constituents (volatile organic compounds [VOCs], 

pesticides and pesticide degradates, and pharmaceutical 

compounds), constituents of special interest (perchlorate 

and N-nitrosodimethylamine [NDMA]), naturally-occurring 

inorganic constituents (trace elements, nutrients, major and 

minor ions, silica, total dissolved solids [TDS], alkalinity, and 

species of inorganic chromium), and radioactive constituents 

(radon-222, radium isotopes, and gross alpha and gross beta 

radioactivity). Naturally-occurring isotopes (stable isotopes 

of hydrogen, oxygen, boron, and strontium in water, stable 

isotopes of carbon in dissolved inorganic carbon, activities 

of tritium, and carbon-14 abundance) and dissolved noble 

gases also were measured to help identify the sources and 

ages of sampled groundwater. In total, 223 constituents and 

12 water-quality indicators were investigated.

Three types of quality-control samples (blanks, replicates, 

and matrix spikes) were collected at up to 10 percent of 

the wells in the CLUB study unit, and the results for these 

samples were used to evaluate the quality of the data for 

the groundwater samples. Field blanks rarely contained 

detectable concentrations of any constituent, suggesting 

that contamination from sample collection procedures 

was not a significant source of bias in the data for the 

groundwater samples. Replicate samples generally were 

within the limits of acceptable analytical reproducibility. 

Median matrix-spike recoveries were within the acceptable 

range (70 to 130 percent) for approximately 85 percent of 

the compounds.

This study did not attempt to evaluate the quality of water 

delivered to consumers; after withdrawal from the ground, 

untreated groundwater typically is treated, disinfected, and 

(or) blended with other waters to maintain water quality. 

Regulatory benchmarks apply to water that is delivered to the 

consumer, not to untreated groundwater. However, to provide 

some context for the results, concentrations of constituents 

measured in the untreated groundwater were compared with 

Groundwater-Quality Data in the Borrego Valley, 

Central Desert, and Low-Use Basins of the Mojave and 

Sonoran Deserts Study Unit, 2008–2010: Results from the 

California GAMA Program

By Timothy M. Mathany, Michael T. Wright, Brandon S. Beuttel, and Kenneth Belitz
2 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

regulatory and non-regulatory health-based benchmarks 

established by the U.S. Environmental Protection Agency 

(USEPA) and CDPH, and to non-regulatory benchmarks 

established for aesthetic concerns by CDPH. Comparisons 

between data collected for this study and benchmarks 

for drinking water are for illustrative purposes only and 

are not indicative of compliance or non-compliance with 

those benchmarks.

Most inorganic constituents detected in groundwater 

samples from the 49 grid wells were detected at concentrations 

less than drinking-water benchmarks. In addition, all 

detections of organic constituents from the CLUB study-unit 

grid-well samples were less than health-based benchmarks.

In total, VOCs were detected in 17 of the 49 grid wells 

sampled (approximately 35 percent), pesticides and pesticide 

degradates were detected in 5 of the 47 grid wells sampled 

(approximately 11 percent), and perchlorate was detected in 

41 of 49 grid wells sampled (approximately 84 percent). 

Trace elements, major and minor ions, and nutrients were 

sampled for at 39 grid wells, and radioactive constituents were 

sampled for at 23 grid wells; most detected concentrations 

were less than health-based benchmarks. Exceptions in the 

grid-well samples include seven detections of arsenic greater 

than the USEPA maximum contaminant level (MCL-US) of 

10 micrograms per liter (μg/L); four detections of boron 

greater than the CDPH notification level (NL-CA) of 

1,000 μg/L; six detections of molybdenum greater than the 

USEPA lifetime health advisory level (HAL-US) of 40 μg/L; 

two detections of uranium greater than the MCL-US of 

30 μg/L; nine detections of fluoride greater than the CDPH 

maximum contaminant level (MCL-CA) of 2 milligrams per 

liter (mg/L); one detection of nitrite plus nitrate (NO2

–+NO3–), 

as nitrogen, greater than the MCL-US of 10 mg/L; and four 

detections of gross alpha radioactivity (72-hour count), and 

one detection of gross alpha radioactivity (30-day count), 

greater than the MCL-US of 15 picocuries per liter. 

Results for constituents with non-regulatory benchmarks 

set for aesthetic concerns showed that a manganese 

concentration greater than the CDPH secondary maximum 

contaminant level (SMCL-CA) of 50 μg/L was detected 

in one grid well. Chloride concentrations greater than the 

recommended SMCL-CA benchmark of 250 mg/L were 

detected in three grid wells, and one of these wells also had 

a concentration that was greater than the upper SMCL-CA 

benchmark of 500 mg/L. Sulfate concentrations greater than 

the recommended SMCL-CA benchmark of 250 mg/L were 

measured in six grid wells. TDS concentrations greater than 

the SMCL-CA recommended benchmark of 500 mg/L were 

measured in 20 grid wells, and concentrations in 2 of these 

wells also were greater than the SMCL-CA upper benchmark 

of 1,000 mg/L. 

Introduction 

About one-half of the water used for public and 

domestic drinking-water supply in California is groundwater 

(Kenny and others, 2009). To assess the quality of ambient 

groundwater in aquifers used for public drinking-water supply 

and to establish a baseline groundwater-quality monitoring 

program, the California State Water Resources Control Board 

(SWRCB) in cooperation with the U.S. Geological Survey 

(USGS) and Lawrence Livermore National Laboratory 

(LLNL) implemented the Groundwater Ambient Monitoring 

and Assessment (GAMA) Program (California Environmental 

Protection Agency, 2011, website at http://www.waterboards.

ca.gov/water_issues/programs/gama/). The main goals of 

the GAMA Program are to improve groundwater monitoring 

and to increase the availability of groundwater-quality data 

to the public. The GAMA Program currently consists of 

three projects: (1) the GAMA Priority Basin Project (PBP) 

conducted by the USGS (U.S. Geological Survey, 2011a, 

California Water Science Center website at http://ca.water.

usgs.gov/gama/); (2) the GAMA Domestic Well Project 

(DWP) conducted by the SWRCB; and (3) GAMA Special 

Studies conducted by LLNL. The GAMA-PBP primarily 

focuses on the deep part of the groundwater resource, 

which is typically used for public drinking-water supply. 

The GAMA-DWP generally focuses on the shallow aquifer 

systems, which may be particularly at risk as a result of 

surficial contamination. The GAMA Special Studies Project 

focuses on using research methods to help explain the source, 

fate, transport, and occurrence of chemicals that can affect 

groundwater quality. 

All published and quality-assurance/quality-control 

(QA/QC) approved analytical data collected for the GAMA 

Program are stored in the web-based Geotracker Database 

(California State Water Resources Control Board, 2009a, 

website at https://geotracker.waterboards.ca.gov/gama/). 

The Geotracker Database also stores groundwater-quality 

data and related reports collected by other State agencies, 

such as the California Department of Public Health (CDPH), 

California Department of Water Resources (CDWR), and 

California Department of Pesticide Regulation (CDPR), and 

data collected by the SWRCB and Regional Boards from 

environmental monitoring wells at contaminated and (or) 

remediated sites.

The GAMA Program was initiated by the SWRCB 

in 2000 and later expanded by the Groundwater Quality 

Monitoring Act of 2001 (State of California, 2001a,b; Sections 

10780–10782.3 of the California Water Code, Assembly Bill 

599). The GAMA-PBP assesses groundwater quality in key 

groundwater basins that account for more than 90 percent 
Introduction 3

of all groundwater in the State. For the GAMA-PBP, 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; California State Water Resources Control 

Board, 2003). Additional partners in the GAMA-PBP include 

LLNL, CDPH, CDWR, CDPR, local water agencies, and well 

owners (Kulongoski and Belitz, 2004). Participation in the 

GAMA-PBP is entirely voluntary.

The GAMA-PBP is unique in California because it 

includes many chemical analyses that are not otherwise 

available in the statewide water-quality monitoring datasets. 

Groundwater samples collected for the GAMA-PBP 

are typically analyzed for approximately 300 chemical 

constituents using analytical methods with lower detection 

limits than required by the CDPH for regulatory monitoring 

of water from drinking-water wells. These analyses will 

be especially useful for providing an early indication of 

changes in groundwater quality. In addition, the GAMA-PBP 

analyzes samples for a suite of constituents more extensive 

than required by CDPH and for a suite of chemical and 

isotopic tracers for understanding hydrologic and geochemical 

processes. This understanding of groundwater composition is 

useful for identifying the natural and human factors affecting 

water quality. Understanding the occurrence and distribution 

of chemical constituents of significance to water quality is 

important for the long-term management and protection of 

groundwater resources.

The range of hydrologic, geologic, and climatic 

conditions in California must 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: 

Cascades and Modoc Plateau, Klamath Mountains, 

Northern Coast Ranges, Central Valley, Sierra Nevada, 

Basin and Range, Southern Coast Ranges, Transverse 

Ranges and selected Peninsular Ranges, Desert, and San 

Diego Drainages (fig. 1). These 10 hydrogeologic provinces 

include groundwater basins and subbasins designated by the 

CDWR (California Department of Water Resources, 2003a). 

Groundwater basins and subbasins generally consist of 

relatively permeable, unconsolidated deposits of alluvial or 

volcanic origin. Eighty percent of California’s approximately 

16,000 active and standby drinking-water wells listed in the 

statewide database maintained by the CDPH (hereinafter 

referred to as CDPH wells) are located in groundwater 

basins and subbasins within the 10 hydrogeologic provinces. 

Groundwater basins and subbasins were prioritized for 

sampling on the basis of the number of CDPH wells in the 

basin, with secondary consideration given to municipal 

groundwater use, agricultural pumping, the number of 

formerly leaking underground fuel tanks, and the number of 

registered pesticide applications (Belitz and others, 2003). 

Of the 472 basins and subbasins designated by the CDWR, 

116 priority basins were selected and grouped into 35 

GAMA study units, representing approximately 95 percent 

of the CDPH wells in California. In addition, some areas 

outside of the defined groundwater basins were included in 

the nearest respective study unit to achieve representation 

of the 20 percent of the CDPH wells not located in the 

groundwater basins. 

The data collected in each study unit is used for three 

types of water-quality assessments: (1) Status: assessment 

of the current quality of the groundwater resource; 

(2) Understanding: identification of the natural and human 

factors affecting groundwater quality; and (3) Trends: 

detection of changes in groundwater quality over time 

(Kulongoski and Belitz, 2004). The assessments are intended 

to characterize the quality of groundwater in the primary 

aquifer systems of the study units, not the treated drinking 

water delivered to consumers by water purveyors. The 

primary aquifer systems (hereinafter referred to as primary 

aquifers) are defined as parts of aquifers corresponding 

to the perforation intervals of wells listed in the CDPH 

database for the study units. The CDPH database lists wells 

used for municipal and community drinking-water supplies, 

and includes wells from systems classified as non-transient 

(such as those in cities, towns, and mobile-home parks) 

and transient (such as those in schools, campgrounds, and 

restaurants). Collectively, the CDPH refers to these wells as 

“public-supply” wells. Groundwater quality in shallow or 

deep parts of the aquifer systems may differ from that in the 

primary aquifers. In particular, shallow groundwater may 

be more vulnerable to surface contamination. As a result, 

samples from shallow wells (such as many private domestic 

wells and environmental monitoring wells) can have greater 

concentrations of constituents (such as volatile organic 

compounds [VOCs] and nitrate) from anthropogenic sources 

than samples from wells screened in the underlying primary 

aquifers (Landon and others, 2010).

The Borrego Valley, Central Desert, and Low-Use 

Basins of the Mojave and Sonoran Deserts study unit 

(hereinafter referred to as the CLUB study unit) lies in the 

Desert hydrogeologic province as described by Belitz and 

others (2003) (fig. 1). Groundwater is a major source of 

public drinking-water supply for many of the cities located 

in the CLUB study unit (Water Education Foundation, 2006); 

therefore, the CLUB study unit was considered high priority 

for sampling to provide adequate representation of the Desert 

hydrogeologic province. This USGS Data Series Report is 

the first in a series of reports presenting the water-quality 

data collected by the USGS in the CLUB study unit for the 

GAMA-PBP. Other Data Series Reports and additional reports 

addressing the status, understanding, and trends aspects of 

the water-quality assessments of each study unit are available 

from the U.S. Geological Survey (2011b) at http://ca.water.

usgs.gov/projects/gama/includes/GAMA_publications.html.
4 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Basin and Range

Central

Valley

Klamath

Mountains

Desert

Cascades and

Modoc Plateau

Transverse Ranges and

selected Peninsular Ranges

Southern Coast

Ranges

Sierra

Nevada

Northern

Coast

Ranges

San Diego

Drainages

Borrego Valley, Central Desert,

and the Low-Use Basins

of the Mojave and Sonoran

Deserts Study Unit

(figure 2)

Bakersfield

San

Francisco

Sacramento

OREGON

NEVADA

MEXICO

ARIZONA

Redding

Los Angeles

San Diego

PA C I F I C O C E A N

0 200 MILES

0 200 KILOMETERS

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

Provinces from Belitz and others, 2003.

Borrego Valley

 study area

Central Desert

 study area

Low-Use Basins

 study area

EXPLANATION

IP021385_Fig01_CLUB_locmap.ai

Figure 1. The hydrogeologic provinces of California and the location of the Borrego Valley, Central Desert, and 

Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit and study areas.
Hydrogeologic Setting 5

Purpose and Scope

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

design, the hydrogeologic setting of the CLUB study unit, and 

the study methods; (2) the analytical results for groundwater 

samples collected in the CLUB study unit, and (3) the results 

of QC analyses. Groundwater samples were analyzed for 

water-quality indicators; organic, special-interest, inorganic, 

and radioactive constituents; naturally-occurring isotopes; 

and dissolved gases. The chemical data presented in this 

report were evaluated by comparison to State and Federal 

drinking-water regulatory and other non-regulatory standards 

that are applied to treated drinking water. Regulatory and 

non-regulatory benchmarks considered for this report are those 

established by the U.S. Environmental Protection Agency 

(USEPA) and (or) the CDPH. Discussion of the factors that 

influence the distribution and occurrence of the constituents 

detected in groundwater samples will be the subject of 

subsequent publications.

Hydrogeologic Setting 

The CLUB study unit contains 47 groundwater basins 

and subbasins delineated by CDWR and is located in 

the South Lahontan and Colorado River hydrogeologic 

regions (California Department of Water Resources, 

2003b,c, 2004a–ss). The three study areas (Borrego Valley, 

Central Desert, and Low-Use Basins of the Mojave and 

Sonoran Deserts) of the CLUB study unit cover an area of 

12,103 square miles (mi2) in San Bernardino, Riverside, Kern, 

San Diego, and Imperial Counties, California (fig. 2).

CLUB Study Unit—Borrego Valley Study Area

The Borrego Valley study area (hereinafter referred 

to as the BV study area) is 238 mi2 in area and lies in the 

westernmost part of the Sonoran Desert, about 80 miles (mi) 

east of San Diego (fig. 2). The BV study area is located within 

the Borrego Valley groundwater basin (California Department 

of Water Resources, 2004a) and encompasses a large section 

of the Anza-Borrego Desert State Park. The study area is 

bounded on the west by the San Ysidro, Vallecito, Fish Creek, 

and Coyote Mountains and on the north by the Santa Rosa 

Mountains. The eastern boundary of the study area is defined 

by the Coyote Creek and Superstition Mountain faults. The 

southernmost border of the study area is a large unnamed 

wash that stretches from the Coyote Mountains northeast to 

Superstition Mountain (fig. 3).

Land-surface altitudes in the study area range from 

approximately 30 feet below mean sea level (ft below msl) 

in the Lower Borrego Valley, to over 4,500 feet above mean 

sea level (ft above msl) in the San Ysidro Mountains, located 

just west of the village of Borrego Springs. The major surface 

drainage features of the study area are the Coyote and San 

Felipe Creeks, both of which have their headwaters in the 

mountains to the north and west and drain to the Salton Sea. 

There is also a large surface drainage feature in the northern 

part of the study area named Borrego Sink, which is a major 

collection point for surficial runoff from Coyote Creek (fig. 3). 

The climate in the study area is classified as subtropical 

desert (due to the land-surface altitude), with very hot 

summers and cool winters (PRISM Climate Group, 2010; 

U.S. Department of Commerce, National Climatic Data 

Center, 2010). Rainfall is predominantly derived from storms 

originating in the Pacific Ocean in the winter and to a lesser 

extent from the North American Monsoon, which is drawn 

northward through Mexico from the Pacific Ocean and (or) 

the Gulf of Mexico in the summer (Adams, 1997). Average 

annual precipitation in the study area is less than 7 inches 

(in.) (PRISM Climate Group, Oregon State University, 2010; 

Western Regional Climate Center, 2010). 

The primary aquifer in the study area is the upper 

aquifer of a three-tiered alluvium-filled aquifer system that 

is underlain by crystalline bedrock. The upper aquifer is 

composed of alluvial, playa, eolian, and fan deposits of 

Holocene to Pleistocene age. The middle and lower aquifers 

consist of continental deposits of moderately consolidated 

gravel, sand, and boulders of Pleistocene age (California 

Department of Water Resources, 2004a). 

The general groundwater-flow direction in the study 

area is from the western and northern sides of the study area 

toward the center, then southward, following the topography 

of the Borrego and Lower Borrego Valleys. The study area has 

two major northwest trending faults (Superstition Mountain 

and Coyote Creek), which act as hydrologic barriers to 

groundwater movement (California Department of Water 

Resources, 2004a) (fig. 3). 

Groundwater recharge in the study area primarily occurs 

from the infiltration of runoff from the surrounding mountains 

into Coyote Creek, San Felipe Creek, and Borrego Sink. To a 

lesser extent, ambient recharge also occurs from the seepage 

of small intermittent streams and washes originating from 

the mountains west and north of the study area (California 

Department of Water Resources, 2004a).
6 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

8

10

10

15

5

5

215

210

405

15

40

78

74

91

62

58

14

86

111

395

95

Los Angeles

San Diego

San

Bernardino

Victorville

Palm Springs

El Centro

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

0 25 50 Miles

0 25 50 Kilometers

Area shown on

figure 3

Area shown

on figure 4

Area shown

on figure 5A

Area shown

on figure 5C Area shown

on figure 5B

Area shown

on figure 5D

Area shown on figure 5E

Area shown

on figure 5F

Area shown

on figure 5G

Area shown

on figure 5H

Colorado

River

IP021385_Fig02_CLUB_overall.ai

Tehachapi Mts

Garlock Fault Zone Panamint Mts

San Bernardino Mts

Little San Bernardino Mts

Laguna Mts

Salton

Sea

Approximate boundary of

 the Sonoran Desert

Approximate boundary of

 the Mojave Desert

MEXICO

ARIZONA

Pacific Ocean

NEVADA

EXPLANATION

San Diego

Co

Orange

Co

Los Angeles

Co

Kern

Co

Inyo

Co

Riverside

Co

San Bernardino 

Co

Imperial

Co

Figure 2. The location of the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts 

(CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study units.
Hydrogeologic Setting 7

Figure 3. The Borrego Valley study area (BV), the boundaries of the California Department of Water Resources (CDWR) defined 

groundwater basins, the distribution of the Central Desert study area grid cells, the location of California Department of Public 

Health (CDPH) wells, and the location of sampled grid wells.

Salton Sea

Clark

Lake

(Dry) Coyote Creek

San Felipe Creek

Caririzo Creek

86

78

0 5 10 Miles

0 5 10 Kilometers

SAN DIEGO CO

IMPERIAL CO

Ocotillo

Wells

Borrego

Springs

BV-07

BV-06

BV-05

BVU-01

BV-04

BV-03

BV-02

BV-01

BV-02 Borrego Valley grid well and identifier

Borrego Valley

 grid cell

Borrego Valley

 groundwater basin

Borrego Valley understanding well and identifier

California Department of Public Health

 (CDPH) well

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

EXPLANATION

BVU-01

Desert Lodge

Boundary of Anza-Borrego

 Desert State Park

San Ysidro Mts

Vallecito Mts

Coyote Mts

Superstition Mtn

Unnamed Wash

Santa Rosa Mts

Fish

Creek

 Mts

Superstition Mountain Fault

Coyote Creek Fault

IP021385_Fig03_BorregoV.ai

Borrego

Sink
8 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

CLUB Study Unit—Central Desert Study Area

The Central Desert study area (hereinafter referred to 

as the CD study area) is 353 mi2 in area and contains six 

CDWR‐defined basins and subbasins (California Department 

of Water Resources, 2003b, 2004b–f). The CD study area 

lies within the southern part of the Mojave Desert about 

30 mi north of the city of Palm Springs and includes the 

northernmost section of the Joshua Tree National Park (fig. 4). 

The study area is bounded on the west by the uplands of the 

San Bernardino Mountains and the northern reaches of the 

Emerson fault. It is bounded to the north by the Johnson 

Valley fault zone and Iron Ridge. The eastern boundary of 

the study area is defined by the Surprise Spring fault and the 

Hidalgo, Copper, and Pinto Mountains. The southernmost 

borders of the study area are Lower Morongo Canyon, the 

Little San Bernardino Mountains, and the uplands areas of the 

Joshua Tree National Park (California Department of Water 

Resources, 2003b, 2004b–f).

Land-surface altitudes in the study area range from 

approximately 2,300 ft above msl near Emerson Lake in the 

northern part of the study area, to over 5,000 ft above msl 

in the Little San Bernardino Mountains, located south of the 

town of Yucca Valley. The northern and western portions of 

the study area are drained by Pipes Wash to Emerson Lake. 

The southernmost reaches of the study area are drained by 

the Big and Little Morongo Creeks. Small ephemeral streams 

drain the eastern parts of the study area towards Emerson and 

Deadman Lakes (California Department of Water Resources, 

2003b, 2004b–f) (fig. 4). 

The climate in the study area is classified as high arid 

desert (due to the land-surface altitude), with hot, dry summers 

and cold winters (PRISM Climate Group, Oregon State 

University, 2010; U.S. Department of Commerce, National 

Climatic Data Center, 2010). Rainfall in the study area 

primarily stems from storms originating in the Pacific Ocean 

and is fairly evenly distributed throughout the year. Average 

annual precipitation in the study area is approximately 6.5 in. 

(PRISM Climate Group, Oregon State University, 2010; 

Western Regional Climate Center, 2010).

The primary aquifers in the study area are located in 

unconsolidated to partly consolidated continental deposits 

and alluvium of Miocene to Quaternary age. These 

unconfined water-bearing formations consist of interbedded 

conglomerates, gravels, sands, and silts deposited into alluvial 

fan systems. To a lesser extent, groundwater in the study 

area is found in deposits of clays, sandy-clays, distal silts, 

and dune sand (California Department of Water Resources, 

2003b, 2004b–f). 

The general direction of groundwater flow in the study 

area is from the southern, western, and eastern parts, towards 

the center, then northward to the Emerson Lake area. In the 

southwesternmost part of the study area, the direction of 

groundwater flow follows Morongo Canyon to the southwest 

then exits the study area by way of Lower Morongo Canyon. 

The east-west trending Pinto Mountain fault is the most 

influential hydrologic barrier to groundwater movement in 

the study area, with water table differences across the fault 

of more than 125 ft in some locations. Additionally, the 

Emerson, Surprise Spring, and Morongo Valley faults and the 

Johnson Valley fault zone act as impediments to groundwater 

movement (Mendez and Christensen, 1997; California 

Department of Water Resources, 2003b, 2004b–f; U.S. 

Geological Survey, 2009) (fig. 4). 

Groundwater recharge in the study area occurs from 

a mixture of ambient recharge (infiltration of runoff from 

surrounding mountains and hills into Little and Big Morongo 

Creeks, Pipes Wash, and Emerson Lake, seepage from 

ephemeral streams, and direct percolation of precipitation), 

subsurface inflow (from non-alluvial geologic units that bound 

the alluvial basins), and engineered recharge (percolation 

ponds and septic tank effluent) (California Department of 

Water Resources, 2003b, 2004b–f; U.S. Geological Survey, 

2009) (fig. 4). 
Hydrogeologic Setting 9

Deadman

Lake

(Dry)

Mesquite

Lake

(Dry)

Emerson

Lake

(Dry)

Pipes

Pipes

Big

Litle

Morongo

Morongo

Creek 

Creek 

Wash

Wash

62

247

CD-15

CD-14

CD-13

CD-12

CD-11

CD-10

CD-08

CD-07

CD-06

CD-04 CD-05

CD-03

CD-09

CD-02

CD-01

Landers

Joshua

Tree

Yucca

Valley

Morongo Valley

Twentynine Palms

0 5 10 Miles

0 5 10 Kilometers

CD-02

Central Desert grid well and identifier

Central Desert grid cell

Central Desert

 groundwater basins

California Department of Public Health

 (CDPH) well

EXPLANATION

Fault-Dashed where

 approximate, dotted

 where concealed

Melville

Lake

(Dry)

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

SAN

BERNARDINO

CO

RIVERSIDE

CO

San Bernardino Mts

Lower

Morongo

Canyon

Little San Bernardino Mts

Pinto Mts

Copper Mt

Hidalgo Mt

Iron Ridge

Joshua Tree

National Park

Surprise Spring Fault

Mountain Fault

Pinto

Emerson Fault

Johnson Valley Fault Zone

Morongo

Valley Fault

Figure 4. The Central Desert study area (CD), the boundaries of the California Department of Water Resources (CDWR) 

defined groundwater basins, the distribution of the CD study area grid cells, the location of California Department of Public 

Health (CDPH) wells, and the location of sampled grid wells.
10 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

CLUB Study Unit—Low-Use Basins of the 

Mojave and Sonoran Deserts Study Area

The Low-Use Basins of the Mojave and Sonoran Deserts 

study area (hereinafter referred to as the LUB study area) is 

11,512 mi2 in area and contains a total of 40 CDWR-defined 

basins and subbasins (California Department of Water 

Resources, 2003c, 2004g–ss). These basins and subbasins 

are spread over a large area in southeastern California that 

encompasses portions of the Mojave and Sonoran Deserts 

(fig. 2). The LUB study area is bounded on the west by 

the Laguna, San Bernardino, and Little San Bernardino 

Mountains. The northern border of the study area is bounded 

by the Garlock fault zone and the Tehachapi, Chuckwalla, 

El Paso, Panamint, Soda, and Clark Mountains. The eastern 

border of the study area is bounded by the state of Nevada 

and the Colorado River, and the southern boundary is the 

international border with Mexico (fig. 5A–H). 

Low-Use Basins of the Mojave and Sonoran 

Deserts Study Area—Mojave Desert Region

In the LUB study area, 24 CDWR-defined basins and 

subbasins are located in the Mojave Desert (hereinafter 

referred to as the LUB Mojave Desert region). The LUB 

Mojave Desert region consists of the CDWR-defined basins 

and subbasins located along and to the north of California 

State Route 62 (fig. 2). Land-surface altitudes in the region 

range from approximately 600 ft above msl near Bristol 

Lake, to over 7,900 ft above msl on the flanks of the Clark 

Mountains located northeast of the city of Baker (fig. 5C). 

The major surface drainage features in the region are the Los 

Angeles Aqueduct, Mojave River, and numerous ephemeral 

streams, creeks, and washes that flow towards dry lake beds 

located inside or adjacent to the groundwater basins and (or) 

subbasins (fig. 5A–E). 

The climate in this region is classified as high arid desert 

(due to the land-surface altitude), with hot, dry summers and 

cold winters (PRISM Climate Group, Oregon State University, 

2010; U.S. Department of Commerce, National Climatic 

Data Center, 2010). The region lies in the rain shadow of the 

Tehachapi and the Sierra Nevada Mountains with rainfall 

principally occurring in the winter months from storms 

originating in the Pacific Ocean. Average annual precipitation 

in the region is approximately 6 inches per year (in/yr). Some 

basins and subbasins can potentially receive no annual rainfall 

(PRISM Climate Group, Oregon State University, 2010; 

Western Regional Climate Center, 2010). 

Aquifers in the region are found in alluvial deposits 

of Miocene to Holocene age. The primary aquifers in the 

region are located in alluvium of Quaternary age. To a lesser 

extent, groundwater is found in Tertiary alluvium primarily 

underlying the alluvial deposits of Quaternary age, which are 

composed largely of unconsolidated to semi-consolidated 

clays, silts, sands, and gravels. Water-bearing formations in 

the region are on average about 2,000-ft thick (California 

Department of Water Resources, 2003c, 2004g–r, u–bb). 

The general direction of groundwater flow in the region 

is from the surrounding mountains and hills towards dry 

lake beds located inside or adjacent to the basins and (or) 

subbasins. Nearly every basin and subbasin that makes up 

the region has faults present. Some faults act as hydrologic 

barriers, while the effect of other faults on groundwater flow is 

unknown (California Department of Water Resources, 2003c, 

2004g–r, u–bb). In addition, an anticline is present north and 

west of the city of Twentynine Palms, limiting groundwater 

interaction between the LUB Mojave Desert region and the 

CD study area (California Department of Water Resources, 

2004w–y) (fig. 5C and 5E). 

Groundwater recharge in the region occurs from a 

mixture of ambient recharge (infiltration of runoff from 

the surrounding mountains into alluvial fan deposits, direct 

percolation of precipitation, and seepage from ephemeral 

rivers, streams, and washes) and subsurface inflow (from 

non-alluvial geologic units that bound the alluvial basins) 

(California Department of Water Resources, 2003c, 

2004g–r, u–bb).

Low-Use Basins of the Mojave and Sonoran 

Deserts Study Area—Sonoran Desert Region

In the LUB study area, 16 CDWR-defined basins are 

situated in the Sonoran Desert (hereinafter referred to as the 

LUB Sonoran Desert region). The LUB Sonoran Desert region 

is composed of CDWR-defined basins located to the south of 

California State Route 62 (fig. 2). Land-surface altitudes in 

this region range from approximately 230 ft below msl in the 

basins surrounding the Salton Sea, to approximately 9,700 ft 

above msl in the Santa Rosa Mountains just north of the BV 

study area (figs. 3 and 5F–H). The major surface drainage 

features of the region are the Salton Sea and the Colorado 

River. The Salton Sea is fed by the New and Alamo Rivers, 

San Felipe, Vallecitos, and Caririzo Creeks, and unnamed 

ephemeral streams. The Colorado River supplies water to the 

Colorado Aqueduct, the All American, Coachella, and East 

Highline Canals, and the New and Alamo Rivers (fig. 5F–H). 

The climate in the region is classified as subtropical 

desert (due to the land-surface altitude), with very hot 

summers and cool winters (PRISM Climate Group, Oregon 

State University, 2010; U.S. Department of Commerce, 

National Climatic Data Center, 2010). Rainfall in these basins 

follows a bimodal pattern similar to that of the BV study 

area. The winter storms originating in the Pacific Ocean have 

a greater influence on precipitation in the western parts of 

the LUB Sonoran Desert region, and the North American 

Monsoon accounts for most of the rainfall in the central and 

eastern parts (Adams, 1997). Annual rainfall in the region 

is approximately 4 in/yr, while some basins can receive 

little to no precipitation per year (PRISM Climate Group, 

Oregon State University, 2010; Western Regional Climate 

Center, 2010).
Hydrogeologic Setting 11

Rogers

Lake

(Dry)

Koehn

Lake

(Dry)

Rosamond

Lake (Dry)

Los Angeles 

Aqueduct

58

14

LUB-02

Low-Use Basins of the Mojave and

 Sonoran Deserts grid well and identifier

Low-Use Basins

 of the Mojave and

 Sonoran Deserts grid cell

Low-Use Basins

 of the Mojave and

 Sonoran Deserts

 groundwater basin California Department of Public Health

 (CDPH) well

EXPLANATION

Fault-Dashed where

 approximate, dotted

 where concealed

0 5 10 Miles

0 5 10 Kilometers

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

KERN CO

SAN

BERNARDINO

CO

Mojave

Cantil

California City

LUB-11

LUB-04

LUB-03

LUB-02

LUB-01

A

T e h a c h a p i M t s

Rand Mts

El Paso Mts

Chuckwalla Mt

Garlock Fault Zone

Garlock Fault Zone

IP021385_Fig05a_LUBWest.ai

Figure 5. (A) The northwestern part, (B) the northern part, (C) the northeastern part, (D) the western part, (E) the central part, (F) the 

eastern part, (G) the southwestern part, and (H) the southeastern part of the Low-Use Basins of the Mojave and Sonoran Deserts study 

area (LUB), the boundaries of the California Department of Water Resources (CDWR) defined groundwater basins, the distribution of 

the LUB study-area grid cells, the location of California Department of Public Health (CDPH) wells, and the location of sampled grid and 

understanding wells.
12 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Searles

Lake

(Dry)

Harper

Lake

(Dry)

Coyote

Lake

(Dry)

Superior

Lake

(Dry)

15

LUB-07

LUBU-02 Low-Use Basins of the Mojave and

 Sonoran Deserts understanding well and identifier

Low-Use Basins of the Mojave and

 Sonoran Deserts grid well and identifier

Low-Use Basins

 of the Mojave and

 Sonoran Deserts grid cell

Low-Use Basins

 of the Mojave and

 Sonoran Deserts

 groundwater basin

EXPLANATION

Fault-Dashed where

 approximate, dotted

 where concealed

0 5 10 Miles

0 5 10 Kilometers

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

?

SAN

BERNARDINO

CO

B

Goldstone

LUBU-02

LUB-08

LUB-07

LUB-06

Fort Irwin

G r a n i t e M t s

California Department of Public Health

 (CDPH) well

Garlock Fault Zone

Garlock Fault Zone Panamint Mts

IP021385_Fig05b_LUBWest2.ai

Figure 5.—Continued
Hydrogeologic Setting 13

Soda

Lake

(Dry)

Bristol

Lake

(Dry)

Ivanpah

Lake

(Dry)

Silver

Lake

(Dry)

15

40

EXPLANATION

Fault-Dashed where

 approximate, dotted

 where concealed

0 10 20 Miles

0 10 20 Kilometers

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

SAN

BERNARDINO

CO

Baker

Midway

Ludlow

Chambless LUB-27

LUB-26

LUB-25

LUB-09

LUB-24

LUB-10

C

NEVADA

Cady Mts

Soda Mts

Clark Mts

LUB-24

California Department of Public Health

 (CDPH) well

Rand Mts

Mojave River

Low-Use Basins

 of the Mojave and

 Sonoran Deserts grid cell

Low-Use Basins

 of the Mojave and

 Sonoran Deserts

 groundwater basin

Low-Use Basins of the Mojave and

 Sonoran Deserts grid well 

IP021385_Fig05c_LUBEast.ai Figure 5.—Continued
14 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Lucerne

Lake

(Dry)

247

247

18

18

EXPLANATION

Fault-Dashed where

 approximate, dotted

 where concealed

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

0 5 10 Miles

0 5 10 Kilometers

SAN

BERNARDINO

CO

LUB-13

LUB-12

LUB-05

Lucerne Valley

Big Bear Lake

Baldwin Lake

D

LUB-05

Low-Use Basins of the Mojave and

 Sonoran Deserts grid well and identifier

California Department of Public Health

 (CDPH) well

San Bernardino Mts

Graniter Mts

Ord Mts

Bighorn Mts

H e l e n d a l e F a u l t Z o n e

Low-Use Basins

 of the Mojave and

 Sonoran Deserts grid cell

Low-Use Basins

 of the Mojave and

 Sonoran Deserts

 groundwater basin

IP021385_Fig05d_LUBMiddle.ai Figure 5.—Continued
Hydrogeologic Setting 15

Dale

Lake

(Dry)

Mesquite

Lake

(Dry)

Deadman

Lake

(Dry)

62

Twentynine Palms

34°

15'

34°

0 5 10 Miles

0 5 10 Kilometers

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

EXPLANATION

Fault-Dashed where

 approximate, dotted

 where concealed

E

SAN

BERNARDINO

CO

RIVERSIDE CO

LUBU-01

LUBU-01

California Department of Public Health

 (CDPH) well

P i n t o M t s

Low-Use Basins of the Mojave and

 Sonoran Deserts understanding well

 and identifier

Low-Use Basins

 of the Mojave and

 Sonoran Deserts grid cell

Low-Use Basins

 of the Mojave and

 Sonoran Deserts

 groundwater basin

IP021385_Fig05e_LUBMiddle3.ai

B u l l i o n M t s

Figure 5.—Continued
16 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Aqueduct

Colorado

Palen

Lake

(Dry)

Ford

Lake

(Dry)

10

111

62

0 10 20Miles

0 10 20 Kilometers

EXPLANATION

Fault-Dashed where

 approximate, dotted

 where concealed

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

?

?

?

?

?

?

SAN

BERNARDINO

CO

RIVERSIDE CO

IMPERIAL CO

Salton Sea

34°

15'

34°

33°

45'

33°

30'

LUB-23

LUB-22

LUB-21

Desert Center

F

LUB-21 Grid cell shown on

 figure 5E

California Department of Public Health

 (CDPH) well

C h u c k w a l l a M t s

C o t t o n w o o d M t s

C o x c o m b M t s

Low-Use Basins of the Mojave and

 Sonoran Deserts grid well and identifier

Low-Use Basins

 of the Mojave and

 Sonoran Deserts grid cell

Low-Use Basins

 of the Mojave and

 Sonoran Deserts

 groundwater basin

IP021385_Fig05f_LUBMiddle2.ai Figure 5.—Continued
Hydrogeologic Setting 17

8

86

94

78

EXPLANATION

Fault-Dashed where

 approximate, dotted

 where concealed

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

0 5 10 Miles

0 5 10 Kilometers

SAN DIEGO CO

IMPERIAL CO

Salton Sea

Jacumba

Ocotillo

Ocotillo Wells

LUB-20

LUB-19

LUB-18

LUB-15

LUB-14

G

MEXICO

LUB-15

California Department of Public Health

 (CDPH) well

Fish

Creek

 Mts

San Ysidro

 Mts

Vallecito Mts

Laguna Mts

Coyote Mts

Jacumba Mts

San Felipe

San Felipe Creek

Caririzo Creek

Vallecitos Creek

Creek

Superstition Mountain Fault

Coyote Creek

Fault

Low-Use Basins of the Mojave and

 Sonoran Deserts grid well and identifier

Low-Use Basins

 of the Mojave and

 Sonoran Deserts grid cell

Low-Use Basins

 of the Mojave and

 Sonoran Deserts

 groundwater basin

IP021385_Fig05g_LUBSouth2.ai Figure 5.—Continued
18 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

8

86

111

78

MEXICO

0 10 20 Miles

0 10 20 Kilometers

EXPLANATION

Fault-Dashed where

 approximate, dotted

 where concealed

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

IMPERIAL CO

LUB-17

LUB-16

Imperial

El Centro

Date City

H

ARIZONA

Cargo Muchacho Mts

Sand Hills

C h o c o l a t e M t s

New River

Alamo River

Coachella Canal

East Highline Canal

Colorado

River

All American Canal

LUB-16

California Department of Public Health

 (CDPH) well

IP021385_Fig05h_LUBSouth.ai

Low-Use Basins of the Mojave and

 Sonoran Deserts grid well and identifier

Low-Use Basins

 of the Mojave and

 Sonoran Deserts grid cell

Low-Use Basins

 of the Mojave and

 Sonoran Deserts

 groundwater basin

Figure 5.—Continued
Methods 19

The primary aquifers in the region are located in alluvium 

of Quaternary age. To a lesser extent, groundwater is found in 

Tertiary-aged alluvium that is usually overlain by the alluvium 

of Quaternary age. Both the Quaternary and Tertiary deposits 

are composed of unconsolidated to semi-consolidated gravels, 

sands, silts, and clays. Water-bearing formations in the study 

area are, on average, 850 ft thick (California Department of 

Water Resources 2004s, t, cc–ss). 

The general direction of groundwater flow in most of 

the basins that make up the LUB Sonoran Desert region is 

towards rivers, creeks, and streams that eventually discharge 

into the Salton Sea. In the remaining basins, the direction of 

groundwater flow is from the surrounding hills and mountains 

towards dry lake beds. The region has numerous faults 

associated with the San Andreas fault zone that act as the 

major barriers to groundwater flow. To a lesser extent, clay 

deposits and bedrock act as impediments to groundwater 

movement (California Department of Water Resources,

2004s, t, cc–ss).

Groundwater recharge in the region occurs from a variety 

of sources: ambient recharge (infiltration of run off from 

the surrounding mountains into alluvial fan deposits, direct 

percolation of precipitation, seepage from ephemeral rivers, 

streams, and washes, agricultural return, and leaching along 

canals) and subsurface inflow (from non-alluvial geologic 

units that bound the alluvial basins) (California Department of 

Water Resources 2004s, t, cc–ss).

Methods 

Methods used for the GAMA-PBP were selected to 

achieve the following objectives: (1) design a sampling plan 

for suitable statistical representation; (2) collect samples in 

a consistent manner; (3) analyze samples by using proven 

and reliable laboratory methods; (4) assure the quality 

of the groundwater data; and (5) maintain data securely 

and with relevant documentation. The appendix contains 

detailed descriptions of the sample-collection protocols and 

analytical methods, the QA plan, and the results of analyses of 

QC samples.

Study Design

The wells selected for sampling in this study reflect 

the combination of two well-selection strategies. Fortynine wells were selected to provide a statistically unbiased, 

spatially distributed assessment of the quality of groundwater 

resources used for public drinking-water supply. Wells 

sampled as part of the spatially distributed, randomized 

grid-cell network, hereinafter, are referred to as “grid 

wells.” Three additional, non-randomized wells (hereinafter 

referred to as “understanding wells”) were sampled in the 

BV and LUB study areas to aid in the understanding of 

groundwater-quality issues.

The spatially distributed wells were selected by using a 

randomized grid-based method (Scott, 1990). The randomized 

grid-based method divides the study areas into equal-area grid 

cells; however, geographic features may force a grid cell to be 

divided into multiple pieces to obtain the designated coverage 

area for each cell. For instance, a portion of a grid cell may be 

located on either side of a mountain range, but the grid cell is 

still considered one grid cell. 

In the CLUB study unit, the approach was to sample one 

available CDPH well located within each grid cell. If a grid 

cell contained more than one CDPH well, each well randomly 

was assigned a rank. The highest ranking well that met basic 

sampling criteria (for example, sampling point located prior 

to treatment, or capability to pump for several hours) was 

sampled. If a grid cell contained no accessible CDPH wells, 

then other types of wells, such as domestic, irrigation, and (or) 

industrial, were considered for sampling. These “alternative” 

wells were identified from wells listed in USGS databases or 

by door-to-door canvassing. Wells with depths and screened 

intervals similar to those in CDPH wells in the area were 

selected. In this fashion, one well was selected for possible 

sampling in each cell to provide a spatially distributed, 

randomized monitoring network. 

The BV study area was divided into nine equal-area grid 

cells, each approximately 9.7 mi2 (25 square kilometers [km2]) 

in area; wells in seven of the nine grid cells were sampled 

(fig. 3). The CD study area was divided into 17 equal-area 

grid cells, approximately 9.2 mi2 (24 km2) in area; wells in 

15 of the 17 grid cells were sampled (fig. 4). The LUB study 

area was divided into 30 equal-area grid cells, approximately 

20 mi2 (52 km2) in area; wells in 27 of the 30 grid cells were 

sampled (fig. 5A–H).

The design of the grid cells differed within the CLUB 

study unit because of differences in the distribution of CDPH 

wells and the overall size of each study area. A direct sampling 

approach involving use of circular buffers around each CDPH 

well was used, as has been used in other GAMA-PBP study 

units with few and (or) unevenly distributed CDPH wells 

(Wright and others, 2005; Kulongoski and others, 2006; 

Fram and Belitz, 2007; Ferrari and others, 2008; Land and 

Belitz, 2008; Densmore and others, 2009; Fram and others, 

2009; Bennett and others, 2009; Mathany and Belitz, 2009; 

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

and others, 2010). These buffers have a radius of about 

3 kilometers (km), and the combined area was divided into the 

equal-area grid cells. In the BV and CD study areas, the CDPH 

wells were clustered in and around population centers, and the 

two study areas were relatively similar in size (BV = 238 mi2 

and CD = 353 mi2); therefore, the size of the grid cells were 

similar (figs. 3 and 4). In the LUB study area, the CDPH 

wells were distributed sporadically, and the study area was 

much larger than the other study areas (LUB = 11,512 mi2); 

consequently, the size of each grid cell was much larger than 

the grid cells in other study areas (fig. 5A–H).
20 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

The 49 grid wells sampled in the CLUB study unit were 

numbered in the order in which samples were collected in each 

study area with the prefix varying by study area; “BV” for 

the Borrego Valley, “CD” for the Central Desert, and “LUB” 

for the Low-Use Basins of the Mojave and Sonoran Deserts 

(figs. 3, 4, and 5A–H).

The three understanding wells sampled as part of the 

study were not included in the statistical characterization of 

water quality in the CLUB study unit because inclusion of 

these wells would lead to the overrepresentation of some cells. 

These additional wells were numbered in the order of sample 

collection with the prefix modified from those used by the grid 

cells: “BVU” or “LUBU” (“U” indicates “understanding”) 

(figs. 3, 5B and 5E).

The GAMA alphanumeric identification number for 

each well, along with the date sampled, sampling schedule, 

land-surface altitude, well type, and available wellconstruction information, is shown in table 1. Groundwater 

samples were collected from 42 CDPH wells, 4 domestic 

wells, 2 irrigation wells, 2 unused wells, 1 industrial well, and 

1 institutional well during the period from December 2008 to 

March 2010. 

Well locations were verified by using a global positioning 

system (GPS), 1:24,000-scale USGS topographic maps, 

comparison with existing well information in USGS 

and CDPH databases, and information provided by well 

owners, drillers’ logs, and (or) other sources of construction 

information. Well location and information were recorded 

by hand on field sheets and electronically on field laptop 

computers using the Alternate Place Entry Form (APE) 

program designed by the USGS. All information was verified 

and then uploaded into the USGS National Water Information 

System (NWIS) database. Well location, well owner, and 

well-use information is confidential.

The wells in the CLUB study unit were sampled by 

using a tiered analytical approach. All wells were sampled 

for a standard set of constituents: water-quality indicators, 

VOCs, pesticides and pesticide degradates, perchlorate, stable 

isotopes of hydrogen and oxygen in water, stable isotopes 

of carbon in dissolved inorganic carbon and carbon-14 

abundance, tritium, and dissolved noble gases. The standard 

set of constituents was termed the “fast” schedule (table 2). 

Wells on the “slow” schedule were sampled for all constituents 

on the fast schedule, plus pharmaceutical compounds, 

N-nitrosodimethylamine (NDMA), trace elements, nutrients, 

major and minor ions, silica, total dissolved solids (TDS), 

stable isotopes of boron and strontium in water, radon-222, 

radium isotopes, and gross alpha and gross beta radioactivity. 

Species of inorganic chromium were sampled for on the 

CLUB study-unit slow sampling schedule in December 2008. 

Hexavalent chromium (chromium-VI, Cr-VI) analysis from 

a second laboratory was added to the CLUB study-unit slow

sampling schedule starting in October 2009. Additionally, 

the 18 wells on the fast schedule in the LUB study area were 

sampled for trace elements, nutrients, major and minor ions, 

silica, and TDS (table 2). 

Fast and slow refers to the relative time required to 

sample the well for all analytes on the schedule. Two slow

or three fast wells generally could be sampled in 1 day. 

In the CLUB study unit, 28 of the wells were sampled 

on the fast schedule (26 grid and 2 understanding), and 

24 wells were sampled on the slow schedule (23 grid and 

1 understanding) (table 1).

Sample Collection and Analysis

Samples were collected with modified USGS National 

Water-Quality Assessment (NAWQA) Program (Koterba 

and others, 1995) and USGS National Field Manual (NFM) 

(U.S. Geological Survey, variously dated) sampling protocols. 

These sampling protocols were followed so that representative 

samples of groundwater were collected at each site, and so 

that the samples were collected and handled in ways that 

minimized the potential for contamination.

Table 3A–K lists the compounds analyzed in each 

constituent class. Groundwater samples were analyzed for 

85 VOCs (table 3A); 63 pesticides and pesticide degradates 

(table 3B); 13 pharmaceutical compounds (table 3C); 

2 constituents of special interest (table 3D); 24 trace 

elements (table 3E); 5 nutrients (table 3F); 9 major and 

minor ions, silica, TDS, and alkalinity (table 3G); species of 

inorganic chromium (table 3H and 3I); 4 stable isotopes and 

7 radioactive constituents, including tritium and carbon-14 

abundance (table 3J); and 6 dissolved noble gases and helium 

isotope ratios (table 3K). The methods used for sample 

collection and analysis are described in the appendix section 

titled “Sample Collection and Analysis.”

Data Reporting

The methods and conventions used for reporting the data 

are described in the appendix section titled “Data Reporting.” 

Three water-quality indicators—alkalinity, pH, and specific 

conductance—were measured in the field and at the USGS 

National Water Quality Laboratory (NWQL), and both results 

are reported (see the appendix section titled “Constituents on 

Multiple Analytical Schedules”). Total chromium and Cr-VI 

were measured by two different laboratories, and all results 

are reported (tables 8, 11, and 12). Tritium activities were 

measured by two different laboratories, but only one set of 

results were available at the time this report was published.

Quality-Assurance Methods 

The QA/QC procedures used for this study followed the 

protocols used by the NAWQA Program (Koterba and others, 

1995) and described in the NFM (U.S. Geological Survey, 

variously dated). The QA plan followed by the USGS NWQL, 

the primary laboratory used to analyze samples for this study, 

is described in Pirkey and Glodt (1998) and Maloney (2005). 
Water-Quality Results 21

QC samples collected in the CLUB study unit are blanks, 

replicates, and matrix and surrogate spikes. QC samples were 

collected to evaluate potential contamination, as well as bias 

and variability of the data that may have resulted from sample 

collection, processing, storage, transportation, and laboratory 

analysis. QA/QC procedures and results are described in the 

appendix section titled “Quality-Assurance Methods.”

Water-Quality Results 

Quality-Control Results

Results of QC analyses (blanks, replicates, and matrix 

and surrogate spikes) were used to evaluate the quality of the 

data for the groundwater samples. On the basis of detections 

in NWQL blanks and QC samples collected for this and 

previous GAMA-PBP study units, the reporting levels for 

10 VOCs and 13 trace elements were raised. Detections of the 

10 VOCs with concentrations less than the raised reporting 

limits were removed from the set of groundwater-quality data 

presented in this report. Detections of the 13 trace elements 

with concentrations less than the raised reporting limits are 

flagged with a less than or equal to symbol (≤) in this report 

(see table A3 and additional discussion in the appendix section 

titled “Detections in Field Blanks and Application of SRLs”). 

Results from the replicates confirm that the procedures used 

to collect and analyze the samples were consistent. Variability 

for nearly 100 percent of the replicate pairs for constituents 

detected in samples was within the acceptable limits 

(table A4A–C). Median matrix-spike recoveries for 25 of the 

150 organic and special-interest constituents analyzed were 

outside the acceptable range of between 70 and 130 percent 

(tables 3B and A5B). Constituents for which low recoveries 

occurred might not have been detected in some samples if they 

were present at concentrations near the laboratory reporting 

levels (LRLs), and constituents with high recoveries may 

indicate that reported values could be greater than what is 

in the sample. The QC results are described in the appendix 

section titled “Quality-Control Results.”

Comparison Benchmarks

Concentrations of constituents detected in groundwater 

samples were compared with CDPH and USEPA regulatory 

and non-regulatory drinking-water health-based benchmarks 

and benchmarks established for aesthetic purposes (California 

Department of Public Health, 2008a,b; U.S. Environmental 

Protection Agency, 2008a–c). The chemical data presented 

in this report are meant to characterize the quality of the 

untreated groundwater within the primary aquifers of the 

CLUB study unit and are not intended to represent the treated 

drinking water delivered to consumers by water purveyors. 

The chemical composition of treated drinking water may 

differ from untreated groundwater because treated drinking 

water may be subjected to disinfection, filtration, mixing 

with other waters, and (or) exposure to the atmosphere prior 

to its delivery to consumers. Comparisons of untreated 

groundwater to benchmarks are for illustrative purposes only 

and are not indicative of compliance or non-compliance with 

drinking-water regulations. The following benchmarks were 

used for comparisons:

• MCL–Maximum Contaminant Level. Legally 

enforceable standards that apply to public-water 

systems and are designed to protect public health by 

limiting the levels of contaminants in drinking water. 

MCLs established by the USEPA are the minimum 

standards with which States are required to comply, 

and individual States may choose to set more stringent 

standards. CDPH has established MCLs for additional 

constituents not regulated by the USEPA, as well as 

lowered the benchmark concentration for a number of 

constituents with MCLs established by the USEPA. 

In this report, a benchmark set by the USEPA and 

adopted by CDPH is labeled “MCL-US,” and one set 

by CDPH that is more stringent than the MCL-US is 

labeled “MCL-CA.” Well owners are notified when 

constituents are detected at concentrations greater than 

an MCL-US or an MCL-CA benchmark in samples 

collected for the GAMA-PBP, but these detections do 

not constitute violations of CDPH regulations.

• AL–Action Level. Legally enforceable standards that 

apply to public-water systems and are designed to 

protect public health by limiting the levels of copper 

and lead in drinking water. Detections of copper or 

lead greater than the action-level benchmarks trigger 

requirements for mandatory water treatment to reduce 

the corrosiveness of water to water pipes. The action 

levels established by the USEPA and CDPH are the 

same; thus, the benchmarks are labeled “AL-US” in 

this report.

• SMCL–Secondary Maximum Contaminant Level. 

Non-enforceable standards applied to constituents that 

affect the aesthetic qualities of drinking water, such 

as taste, odor, and color, or the technical qualities of 

drinking water, such as scaling and staining. Both the 

USEPA and CDPH define SMCLs, but unlike MCLs, 

SMCLs established by CDPH are not required to be 

at least as stringent as those established by USEPA. 

SMCLs established by CDPH are used in this report 

(SMCL-CA) for all constituents that have SMCL-CA 

values. The SMCL-US is used for pH because no 

SMCL-CA has been defined.
22 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

• NL–Notification Level. Health-based notification 

levels established by CDPH for some of the 

constituents in drinking water that lack MCLs 

(NL-CA). If a constituent is detected at concentrations 

greater than its NL-CA, California State law requires 

timely notification of local governing bodies and 

recommends consumer notification.

• HAL–Lifetime Health Advisory Level. The 

maximum concentration of a constituent at which its 

presence in drinking water is not expected to cause any 

adverse carcinogenic effects for a lifetime of exposure. 

HALs are established by the USEPA (HAL-US) and 

are calculated assuming consumption of 2 liters (L) 

(2.1 quarts) of water per day over a 70-year lifetime by 

a 70-kilogram (154-pound) adult and that 20 percent of 

a person’s exposure comes from drinking water.

• RSD5–Risk-Specific Dose. The concentration of a 

constituent in drinking water corresponding to an 

excess estimated lifetime cancer risk of 1 in 100,000. 

RSD5 is an acronym for risk-specific dose at 10–5. 

RSD5s are calculated by dividing the 10–4 cancer 

risk concentration established by the USEPA by 

10 (RSD5-US).

For constituents with MCLs, detections in groundwater 

samples were compared to the MCL-US or MCL-CA. 

Constituents with SMCLs were compared with the SMCL-CA. 

For chloride, sulfate, specific conductance, and TDS, CDPH 

defines a “recommended” and an “upper” SMCL-CA; 

detections of these constituents in groundwater samples 

were compared with both levels. The SMCL-US for these 

constituents corresponds to the recommended SMCL-CA. 

Detected concentrations of constituents without an MCL or 

SMCL were compared to the NL-CA. For constituents without 

an MCL, SMCL, or NL-CA, detected concentrations were 

compared with the HAL-US. For constituents without an 

MCL, SMCL, NL-CA, or HAL-US, detected concentrations 

were compared with the RSD5-US. For constituents without 

an MCL, SMCL, NL-CA, HAL-US, or RSD5-US, detected 

concentrations were compared with the AL-US. Note that 

using this hierarchy to select the comparison benchmark for a 

constituent with more than one type of established benchmark 

will not necessarily result in selection of the benchmark 

with the lowest concentration. For example, for zinc the 

SMCL-CA is 5,000 μg/L and the HAL-US is 2,000 μg/L, but 

the comparison benchmark selected by this hierarchy is the 

SMCL-CA. The comparison benchmarks used in this report 

are listed in table 3A–K for all constituents and in tables 4–14

for constituents detected in groundwater samples from the 

CLUB study unit. Established benchmarks are not available 

for all constituents analyzed for this study. Detections of 

constituents at concentrations greater than the selected 

comparison benchmark are marked with asterisks in tables 4, 

8–10, and 14C. 

Groundwater-Quality Data

Results from analyses of untreated-groundwater samples 

from the CLUB study unit are presented in tables 4–14. These 

results are separated into the three study areas that make 

up the CLUB study unit (BV, CD, and LUB). Groundwater 

samples collected in the CLUB study unit were analyzed for 

221 constituents; 134 of those constituents were not detected 

in any of the samples, and 68 constituents were detected 

(table 3A–K). The LLNL results for dissolved noble gases, 

tritium, and helium isotope ratios have not been received yet 

and are not presented in this report; they will be included in a 

subsequent publication. 

For organic and special-interest constituent classes 

that were analyzed at all of the grid wells, the results tables 

include the following summary statistics: the number of wells 

at which each analyte was detected, the frequency at which 

it was detected (in relation to the number of grid wells in the 

study unit and in each study area), and the total number of 

constituents detected at each well. For the inorganic, isotopic, 

and radioactive constituent classes, the tables include all of the 

wells, constituents, and samples analyzed. 

Water-quality indicators measured in the field and at the 

NWQL are included in table 4. The results of groundwater 

analyses organized by compound classes are presented 

in tables 5–14: 

• Organic constituents

• Volatile organic compounds (table 5)

• Pesticides and pesticide degradates (table 6)

• Perchlorate (table 7)

• Inorganic constituents

• Trace elements (table 8)

• Nutrients (table 9)

• Major and minor ions, silica, and total dissolved 

solids (table 10)

• Species of inorganic chromium (table 11)

• Hexavalent chromium (chromium-VI) (table 12)

• Isotopic tracers (table 13)

• Radioactive constituents 

• Radon-222 (table 14A)

• Radium isotopes (table 14B)

• Gross alpha and gross beta radioactivity (table 14C)
Water-Quality Results 23

Water-Quality Indicators 

Field measurements of dissolved oxygen and water 

temperature and field and laboratory measurements of pH, 

specific conductance, and alkalinity are presented in table 4. 

Bicarbonate and carbonate concentrations are calculated from 

the pH and alkalinity results. Dissolved oxygen, alkalinity, 

and bicarbonate and carbonate concentrations are used as 

indicators of natural processes that affect water chemistry. 

The pH value indicates the acidity of the water. Specific 

conductance is the measure of electrical conductivity of the 

water and is proportional to the amount of total dissolved 

solids in the water. 

Field pH values for 5 of the 49 grid wells sampled 

(1 in the BV study area, 1 in the CD study area, and 3 in the 

LUB study area) in the CLUB study unit were outside of the 

SMCL-US range for pH (<6.5 or >8.5) (table 4). Laboratory 

pH values may be dissimilar to field pH values because the pH 

of groundwater may change upon removal from the ambient 

environment and exposure to the atmosphere.

Field specific-conductance values for 18 of 49 of 

the CLUB study-unit grid-well samples were greater than 

the recommended SMCL-CA of 900 microsiemens per 

centimeter (μS/cm) (approximately 37 percent) (table 4). 

Field specific‐conductance values for five of seven 

grid-well samples in the BV study area were greater than 

the recommended SMCL-CA, and two of these values also 

were greater than the upper SMCL-CA of 1,600 μS/cm. Field 

specific-conductance values for 1 of 15 grid-well samples 

in the CD study area were greater than the recommended 

SMCL-CA. Field specific-conductance values for 12 of 27 

grid-well samples in the LUB study area were greater than 

the recommended SMCL-CA, and 3 of these values also were 

greater than the upper SMCL-CA. 

Organic Constituents

VOCs are present in paints, solvents, fuels, fuel additives, 

refrigerants, fumigants, and disinfected water and are 

characterized by their tendency to evaporate. VOCs generally 

persist longer in groundwater than in surface water because 

groundwater is isolated from the atmosphere. 

Of the 85 VOCs analyzed, 8 were detected in the CLUB 

study-unit groundwater samples; all detections in samples 

were less than health-based benchmarks (table 5). One or 

more VOCs were detected in 17 of the 49 CLUB study-unit 

grid wells sampled (about 35 percent detection frequency). 

Three VOCs, including chloroform (trichloromethane), were 

detected in two of the seven grid wells sampled in the BV 

study area (approximately 29 percent). Chloroform is among 

the most commonly detected VOCs in groundwater nationally 

(Zogorski and others, 2006). VOCs were detected in 3 of 

the 15 grid wells sampled in the CD study area (20 percent); 

chloroform was detected in all 3 grid wells in which VOCs 

were detected. VOCs were detected in 12 of the 27 grid wells 

sampled in the LUB study area (approximately 44 percent). 

Chloroform and perchloroethene (PCE) were detected in 

more than 10 percent of the grid wells sampled in the LUB 

study area. Chloroform and 1,2,4-trimethylbenzene were the 

only VOCs detected in one of the three understanding well 

samples (table 5).

Pesticides include herbicides, insecticides, and fungicides 

and are used to control weeds, insects, fungi, and other pests in 

agricultural, urban, and suburban settings. Of the 63 pesticides 

and pesticide degradates analyzed at 47 of the 49 grid wells 

in the CLUB study unit, 3 pesticides (atrazine, simazine, and 

metolachlor) and 3 pesticide degradates (3,4-dichloroaniline, 

deethylatrazine, and dieldrin) were detected in groundwater 

samples; all detections were less than health-based 

benchmarks (table 6). Atrazine, simazine, and deethylatrazine 

are among the nation’s most commonly detected pesticide 

compounds in groundwater (Gilliom and others, 2006). One or 

more pesticide compounds were detected in 5 of 47 grid wells 

sampled in the CLUB study unit (about 11 percent detection 

frequency). Four pesticide compounds were detected in 1 grid 

well sampled in the CD study area. Pesticide and (or) pesticide 

degradates were detected in 4 of 27 grid wells sampled in the 

LUB study area (approximately 15 percent). No pesticides 

and (or) pesticide degradates were detected in any of the 

seven grid wells sampled in the BV study area or in the three 

understanding wells sampled in the CLUB study unit. 

Pharmaceutical compounds were not detected at 

concentrations greater than or equal to method detection limits 

in the CLUB study unit. Fram and Belitz (2011) present all 

results for pharmaceutical compounds in groundwater samples 

collected for the first 28 GAMA-PBP study units (May 2004 

through March 2010).

Constituents of Special Interest

Perchlorate and NDMA are constituents of special 

interest in California because they may adversely affect water 

quality and recently have been detected in water supplies 

(California Department of Public Health, 2008b). Perchlorate 

was analyzed for at all 52 wells in the CLUB study unit and 

was detected in 41 of 49 grid wells sampled (about 84 percent 

detection frequency; table 7). Perchlorate was detected in 4 of 

7 grid wells sampled in the BV study area (approximately 

57 percent). Perchlorate was detected in 14 of 15 grid wells 

sampled in the CD study area (approximately 93 percent). 

Perchlorate was detected in 23 of 27 grid wells sampled in 

the LUB study area (approximately 85 percent). Perchlorate 

was not measured at concentrations greater than the MCL-CA 

of 6 micrograms per liter (μg/L) in any of the grid or 

understanding wells sampled in the CLUB study unit. NDMA 

was sampled for at the 24 slow wells in the CLUB study unit 

and was not detected in any of the wells. As a result, NDMA is 

not included in table 7. 
24 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Inorganic Constituents

Unlike the organic constituents and the constituents of 

special interest, inorganic constituents are naturally present in 

groundwater, although their concentrations may be influenced 

by human activities. Inorganic constituents were sampled for 

on the slow sampling schedule in the CLUB study unit and the 

fast sampling schedule in the LUB study area. 

Regulatory health-based or non-regulatory health-based 

benchmarks have been established for 18 of 24 trace 

elements and for one of the major and minor ions analyzed 

in this study (table 3E, G). Of these 18 constituents with 

health-based benchmarks, all detections of 13 constituents 

had concentrations less than their respective benchmarks 

(table 8). Arsenic, boron, molybdenum, uranium, and 

fluoride were detected at concentrations greater than healthbased benchmarks in samples from the CD and LUB study 

areas. Trace elements were not detected at concentrations 

greater than established health-based benchmarks in the BV 

study area well samples (table 8). 

Arsenic concentrations greater than the MCL-US of 

10 μg/L were detected in seven grid wells sampled (one in the 

CD study area and six in the LUB study area; table 8). Arsenic 

was measured at a concentration greater than the MCL-US in 

one LUBU well sample. 

Boron concentrations greater than the CDPH notification 

level (NL-CA) of 1,000 μg/L were detected in four grid wells 

sampled in the LUB study area (table 8). 

Molybdenum concentrations greater than the HAL-US 

of 40 μg/L were detected in six grid wells sampled (one in 

the CD study area and five in the LUB study area; table 8). 

Additionally, molybdenum was measured at a concentration 

greater than the HAL-US in one LUBU well sample. 

Uranium concentrations greater than the MCL-US of 

30 μg/L were detected in two grid wells sampled (one in the 

CD study area and one in the LUB study area; table 8).

Fluoride is the only major ion with a regulatory 

health-based benchmark (MCL-CA of 2 milligrams per liter 

[mg/L]); it was detected at a concentration greater than the 

MCL-CA in nine grid wells sampled (one in the CD study 

area and eight in the LUB study area; table 10). Fluoride was 

detected at a concentration greater than the MCL-CA in one 

LUBU well sample.

Nutrients (nitrogen and phosphorus) present in 

groundwater can affect biological activity in aquifers and 

in surface-water bodies that receive groundwater discharge. 

Inorganic nitrogen may be present in the form of ammonia, 

nitrite, or nitrate, depending on the oxidation-reduction state of 

the groundwater. High concentrations of nitrate can adversely 

affect human health, particularly the health of infants. 

All concentrations of ammonia, nitrite, and nitrate 

measured in the CLUB study-unit wells were less than 

health-based benchmarks, with the exception of nitrite plus 

nitrate (NO2

–+NO3–), as nitrogen, detected at a concentration 

greater than the MCL-US of 10 mg/L in one grid well sampled 

in the LUB study area (table 9). 

The levels of certain trace elements, major-ion 

composition, and TDS content in groundwater affect the 

aesthetic properties of water, such as taste, color, and odor, 

and the technical properties of water, such as scaling and 

staining. Although there are no adverse health effects directly 

associated with these properties, they may reduce consumer 

satisfaction with the water or may have economic effects. 

The CDPH has established non-enforceable benchmarks 

(SMCL-CAs) that are based on aesthetic properties rather 

than on human-health concerns for iron, manganese, silver, 

zinc, chloride, sulfate, and TDS. Iron and manganese are trace 

elements whose concentrations are affected by the oxidationreduction state of the groundwater. Precipitation of minerals 

containing iron or manganese may cause orange, brown, or 

black staining of surfaces. 

Iron concentrations greater than the SMCL-CA of 

300 μg/L were not detected in any of the wells in the CLUB 

study unit (table 8). Manganese concentrations greater than the 

SMCL-CA of 50 μg/L were detected in one LUB study-area 

grid-well sample (table 8). 

Chloride concentrations greater than the recommended 

SMCL-CA benchmark of 250 mg/L were detected in three grid 

wells sampled in the LUB study area (table 10). One of these 

three well samples also had chloride concentrations greater 

than the upper SMCL-CA benchmark of 500 mg/L.

Sulfate concentrations greater than the recommended 

SMCL-CA benchmark of 250 mg/L were detected in six grid 

wells sampled (one in the BV study area and five in the LUB 

study area; table 10). 

TDS concentrations greater than the recommended 

SMCL-CA benchmark of 500 mg/L were detected in 20 grid 

wells sampled (3 in the BV study area, 1 in the CD study area, 

and 16 in the LUB study area; table 10). TDS concentrations 

greater than the upper SMCL-CA benchmark of 1,000 mg/L 

were detected in 2 of the 16 grid wells sampled in the LUB 

study area. 

Silver and zinc were not detected at concentrations 

greater than the corresponding SMCL-CA in any of wells 

in the CLUB study unit (table 8). Additionally, all iron, 

manganese, chloride, sulfate, and TDS concentrations in the 

three understanding wells in the CLUB study unit were less 

than the SMCL-CA (tables 8, 10).

Chromium occurs as different species depending on the 

oxidation-reduction state of the groundwater. The oxidized 

and reduced species have different solubilities in groundwater 

and may have different effects on human health. The relative 

proportions of the species can be used to aid in interpretation 

of the oxidation–reduction state of the aquifer. Concentrations 

of chromium (total) and (or) the concentrations of Cr-VI are 

reported in tables 11 and 12.

Species of inorganic chromium were sampled for at 

seven slow wells (three CD study-area grid wells and four 

LUB study-area grid wells) in December 2008. Chromium 

(total) and Cr-VI were detected in five grid-well samples in 

the CLUB study unit (three in the CD study area and two in 

the LUB study area; table 11). Concentrations of chromium 
Water-Quality Results 25

(total) reported by the NWQL in table 8 are considered to 

be more accurate than the concentrations reported by the 

USGS National Research Program (NRP) Trace Metal 

Laboratory (TML), Boulder, Colorado, in table 11 (see 

the appendix section titled “Constituents on Multiple 

Analytical Schedules”). 

Cr-VI is a heavy metal that is frequently detected at 

low levels in California’s drinking-water supply (California 

Environmental Protection Agency, 2009). Cr-VI has a 

variety of natural sources (oxidation of chromium-III, 

serpentine-containing rocks, and chromium-containing 

geologic formations) and anthropogenic sources 

(chrome-plating liquid wastes, dye and paint pigments, wood 

preservatives, chemical manufacturing, and the combustion 

of natural gas, oil, and coal) (California Environmental 

Protection Agency, 2009; California State Water Resources 

Control Board, 2009b). In January 2001, CDPH identified 

Cr-VI as an unregulated chemical requiring monitoring 

(California State Water Resources Control Board, 2009b). 

Cr-VI was sampled for at 17 slow wells (3 BV study-area 

grid wells, 6 CD study-area grid wells, 7 LUB study-area grid 

wells, and the BVU well) in the CLUB study unit starting in 

October 2009. These samples were analyzed at TestAmerica 

Laboratories, Inc. (TALIR), Irvine, California, rather than at 

the NRP-TML in order to fulfill a contractual obligation with 

the NWQL. Cr-VI was detected in seven grid wells sampled 

in the CLUB study unit (four in the CD study and three in 

the LUB study area; table 12). Cr-VI also was detected in the 

BVU well sampled.

Isotopic Tracers and Dissolved Noble Gases

The isotopic ratios, activities, and abundances of many 

elements and the concentrations of dissolved gases (including 

noble gases) may be used as tracers of hydrologic processes 

(Clark and Fritz, 1997). 

The isotopic ratios of hydrogen and oxygen in 

water (table 13) aid in the interpretation of the sources of 

groundwater recharge. These stable-isotope ratios reflect the 

altitude, latitude, and temperature of precipitation and also the 

extent of evaporation of the water in surface-water bodies or 

soils prior to infiltration into the aquifer. 

Stable-isotope ratios of boron in water may be useful 

in distinguishing the sources of boron in aquifers. A 

geochemically-based classification of the source of boron 

in groundwater could potentially determine the similarity of 

boron to known sources or mixtures between known sources, 

or classify whether the relative age of the groundwater 

predated potential sources.

Stable-isotope ratios of strontium in water reflect the 

amount of strontium (and other inorganic constituents) the 

aquifer materials are contributing to the groundwater system. 

In regions that have diverse geology, strontium isotope ratios 

may aid in estimating groundwater-flow paths.

Tritium activities (table 13), helium isotope ratios, and 

carbon-14 abundance (table 13) also provide information 

about the age (time since recharge) of groundwater. Tritium 

is a short-lived radioactive isotope of hydrogen that is 

incorporated into the water molecule. Low levels of tritium 

are produced continuously by interaction of cosmic radiation 

with the Earth’s atmosphere, and a large amount of tritium was 

produced as a result of atmospheric testing of nuclear weapons 

between 1952 and 1963. Thus, concentrations of tritium 

greater than background generally indicate the presence of 

water recharged after the early 1950s. Helium isotope ratios 

are used in conjunction with tritium concentrations to estimate 

ages for young groundwater. 

Carbon-14 (table 13) is a radioactive isotope of carbon. 

Low levels of carbon-14 are produced continuously by 

interaction of cosmic radiation with the Earth’s atmosphere 

and incorporated into atmospheric carbon dioxide. Carbon 

dioxide dissolves in precipitation, surface water, and 

groundwater exposed to the atmosphere, thereby entering the 

hydrologic cycle. Because carbon-14 decays with a half-life 

of approximately 5,700 years, low activities of carbon-14, 

relative to modern values, generally indicate a presence of 

groundwater that is several thousand years old or more. 

Gases dissolve in water that is in contact with the 

atmosphere, and the solubilities of the different gas species 

vary with temperature. Concentrations of dissolved noble 

gases are used to estimate the conditions of groundwater 

recharge, particularly the temperature of the recharge water. 

Of the isotopic tracer constituents analyzed for this study, 

tritium is the only one with a health-based benchmark. All 

measured tritium activities in samples from the well samples 

in the CLUB study unit were more than three orders of 

magnitude less than the MCL-CA benchmark (table 13).

Radioactive Constituents

Radioactivity is the release of energy or energetic 

particles during changes in the structure of the nucleus of an 

atom. Most radioactivity in groundwater comes from decay 

of naturally-occurring isotopes of uranium and thorium that 

are present in minerals in the sediments or fractured rocks of 

the aquifer. Uranium and thorium decay in a series of steps 

eventually forming stable isotopes of lead (Soddy, 1913; 

Faure and Mensing, 2005). Radium-226, radium-228, and 

radon-222 are radioactive isotopes formed during the uranium 

or thorium decay series. In each step in the decay series, 

one radioactive element turns into a different radioactive 

element by emitting an alpha or a beta particle from its 

nucleus. For example, radium-226 emits an alpha particle and 

therefore turns into radon-222. Radium-228 decays to form 

actinium-228 by emission of a beta particle. The alpha and 

beta particles emitted during radioactive decay are hazardous 

to human health because these energetic particles may damage 

cells. Radiation damage to cell DNA may increase the risk of 

getting cancer.
26 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Activity often is used instead of concentration for 

reporting the presence of radioactive constituents. Activity of 

radioactive constituents in groundwater is measured in units 

of picocuries per liter (pCi/L), and 1 pCi/L is approximately 

equal to two atoms decaying per minute. The number of 

atoms decaying is equal to the number of alpha or beta 

particles emitted. 

Radon-222 was sampled for at 22 slow grid wells and 1 

slow understanding well in the CLUB study unit (table 14A). 

Radium isotopes (radium-226 and radium-228) and gross 

alpha and gross beta radioactivity were sampled for at 23 slow

grid wells and 1 slow understanding well (table 14B, C). 

Radon-222 activities for all wells sampled in the 

CLUB study unit were less than the proposed MCL-US of 

4,000 pCi/L (table 14A). The proposed MCL-US will apply 

if the state or local water agency has an approved multimedia 

mitigation program to address radon levels in indoor air (U.S. 

Environmental Protection Agency, 1999).

Radium isotope (radium-226 and radium-228) 

activities for all of the wells sampled in the CLUB study 

unit were less than the MCL-US of 5 pCi/L (table 14B). The 

MCL-US benchmark for radium is the sum of radium-226 

and radium-228.

Gross alpha and gross beta radioactivity activities for 

most of the wells sampled in the CLUB study unit were 

less than established health-based benchmarks (table 14C). 

Exceptions include two detections of gross alpha radioactivity 

(72-hour count) and one detection of gross alpha radioactivity 

(30-day count) greater than the MCL-US of 15 pCi/L in two 

grid wells sampled in the CD study area and two detections 

of gross alpha radioactivity (72-hour count) in two grid wells 

sampled in the LUB study area.

Future Work

Subsequent reports for the CLUB study unit will be 

focused on assessment of the data presented in this report 

by using a variety of statistical, qualitative, and quantitative 

approaches to evaluate the natural and human factors affecting 

groundwater quality in the CLUB study unit. Water-quality 

data contained in the CDPH databases will be compiled, 

evaluated, and used in combination with the data that are 

presented in this report. Additionally, these subsequent reports 

will include the results for the analysis of stable isotopes of 

boron and strontium in water and the LLNL results (dissolved 

noble gases, tritium, and helium isotope ratios) for the CLUB 

study unit.

Summary 

Groundwater quality in the 12,103-square-mile Borrego 

Valley, Central Desert, and Low-Use Basins of the Mojave 

and Sonoran Deserts (CLUB) study unit was investigated by 

the U.S. Geological Survey (USGS) from December 2008 to 

March 2010, as part of the California State Water Resources 

Control Board (SWRCB) Groundwater Ambient Monitoring 

and Assessment (GAMA) Program’s Priority Basin Project 

(PBP). The GAMA Program was created to provide a 

comprehensive baseline of groundwater quality in the state. 

The GAMA-PBP was created as a result of the Groundwater 

Quality Monitoring Act of 2001 (Sections 10780–10782.3 of 

the California Water Code, Assembly Bill 599) to assess and 

monitor the quality of groundwater. The GAMA-PBP is being 

conducted by the USGS in cooperation with the SWRCB and 

Lawrence Livermore National Laboratory (LLNL).

The GAMA CLUB study was designed to provide a 

spatially unbiased assessment of untreated-groundwater 

quality in the primary aquifer systems and to facilitate 

statistically consistent comparisons of untreated-groundwater 

quality throughout California. The primary aquifer systems 

(hereinafter referred to as primary aquifers) are defined as 

parts of aquifers corresponding to the perforation intervals 

of wells listed in the California Department of Public Health 

(CDPH) database for the CLUB study unit. The quality of 

groundwater in shallow or deep water-bearing zones may 

differ from that in the primary aquifers; shallow groundwater 

may be more vulnerable to surficial contamination.

This study did not attempt to evaluate the quality of 

water delivered to consumers; after withdrawal from the 

ground, water typically is treated, disinfected, and blended 

with other waters to maintain acceptable water quality. 

Regulatory benchmarks apply to treated water that is served 

to the consumer, not to untreated groundwater. However, 

to provide some context for the results, concentrations of 

constituents measured in the untreated groundwater were 

compared with regulatory and non-regulatory health-based 

benchmarks established by the U.S. Environmental Protection 

Agency (USEPA) and CDPH and non-regulatory benchmarks 

established for aesthetic concerns by the CDPH.

The CLUB study unit is located within the Mojave 

and Sonoran Deserts in the Desert hydrologic province and 

includes 47 groundwater basins and subbasins defined by 

the California Department of Water Resources. The CLUB 

study included assessment of the groundwater quality 

from 52 wells in San Bernardino, Riverside, San Diego, 

and Imperial Counties, California. Forty-nine of the wells 

were selected using a randomized grid approach to achieve 

statistically unbiased representation of groundwater used 

for public drinking-water supplies (grid wells). Three of the 

wells were selected to provide additional sampling density to 

aid in understanding processes affecting groundwater quality 

(understanding wells). 
References Cited 27

Groundwater samples were analyzed for water-quality 

indicators, organic constituents, naturally-occurring inorganic 

constituents, and radioactive constituents. Naturally-occurring 

isotopes and dissolved noble gases also were measured to 

provide a dataset that will be used to interpret the sources and 

ages of the sampled groundwater. In total, 223 constituents 

and 12 water-quality indicators were measured for this 

study. This report describes the sampling, analytical, and 

quality-assurance methods used in the study and presents the 

results of the chemical analyses of the groundwater samples. 

Three types of quality-control samples (blanks, replicates, 

and matrix spikes) were collected at up to 10 percent of 

the wells in the CLUB study unit, and the results for these 

samples were used to evaluate the quality of the data for 

the groundwater samples. Field blanks rarely contained 

detectable concentrations of any constituent, suggesting 

that contamination from sample collection procedures 

was not a significant source of bias in the data for the 

groundwater samples. Replicate samples generally were 

within the limits of acceptable analytical reproducibility. 

Median matrix-spike recoveries were within the acceptable 

range (70 to 130 percent) for approximately 85 percent of 

the compounds.

Organic constituents were sampled for at all 49 grid 

wells in the CLUB study unit, and all detected concentrations 

were less than health-based benchmarks. Trace elements, 

nutrients, and major and minor ions were sampled for at 

39 grid wells, and radioactive constituents were sampled for at 

23 grid wells. Most detections were at concentrations less than 

health-based benchmarks. 

In the Borrego Valley study area, all detected 

concentrations of trace elements, major and minor ions, 

and radioactive constituents were less than health-based 

benchmarks. 

In the Central Desert study area, one detection of 

arsenic was greater than the USEPA maximum contaminant 

level (MCL-US), one detection of molybdenum was greater 

than the USEPA lifetime health advisory level (HAL-US), 

one detection of uranium was greater than the MCL-US, 

one detection of fluoride measured greater than the CDPH 

maximum contaminant level (MCL-CA), and two detections 

of gross alpha radioactivity (72-hour count) and one detection 

of gross alpha radioactivity (30-day count) were greater than 

the MCL-US.

In the Low-Use Basins of the Mojave and Sonoran 

Deserts study area, detections of arsenic were greater than 

the MCL-US, four detections of boron were greater than 

the CDPH notification level (NL-CA), five detections of 

molybdenum were greater than the HAL-US, one detection 

of uranium was at a concentration greater than the MCL-US, 

eight detections of fluoride were greater than the MCL-CA, 

one detection of nitrite plus nitrate (NO2

–+NO3–), as nitrogen, 

was greater than the MCL-US, and two detections of gross 

alpha radioactivity (72-hour count) were greater than 

the MCL-US. 

Most of the samples from the CLUB study-unit wells 

collected for trace elements and major ions had measured 

concentrations less than the non-enforceable benchmarks set 

for aesthetic concerns. 

In the Borrego Valley study area, one detection 

of sulfate was greater than the recommended CDPH 

secondary maximum contaminant level (SMCL-CA), 

and three detections of TDS were greater than the 

recommended SMCL-CA.

In the Central Desert study area, one detection of TDS 

was greater than the recommended SMCL-CA.

In the Low-Use Basins of the Mojave and Sonoran 

Deserts study area, 1 detection of manganese was greater than 

the SMCL-CA, 3 detections of chloride were greater than the 

recommended SMCL-CA (1 of the detections was greater than 

the upper SMCL-CA), 5 detections of sulfate were greater 

than the recommended SMCL-CA, and 16 detections of TDS 

were greater than the recommended SMCL-CA (2 of the 

detections were greater than the upper SMCL-CA).

In the three understanding wells in the CLUB study unit, 

one detection of arsenic was greater than the MCL-US, one 

detection of molybdenum was greater than the HAL-US, and 

one detection of fluoride was greater than the MCL-CA. 

Acknowledgments

The authors thank the following cooperators for their 

support: the California State Water Resources Control 

Board, California Department of Public Health, California 

Department of Water Resources, and Lawrence Livermore 

National Laboratory. We especially thank the well owners and 

water purveyors for allowing the U.S. Geological Survey to 

collect samples from their wells.

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Table 1 37

Table 1. Identification, sampling, and construction information for wells sampled for the Borrego, Central Desert, and Low-Use Basins 

of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 

2008 to March 2010. 

[Sampling schedule is described in table 2. Land-surface datum (LSD) is a datum plane that is approximately at land surface at each well. The altitude of the 

LSD is described in feet above the North American Vertical Datum 1988 (NAVD 88). Numbered suffix indicates the order of sample collection within each 

study area. GAMA well identification number: BV, Borrego study-area grid well; BVU, Borrego study-area understanding well; CD, Central Desert study-area 

grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts studyarea understanding well. Other abbreviations: ft, foot; na, not available]

Sampling information Construction information

GAMA well 

identification 

number

Date

sampled 

Sampling

schedule

Altitude of LSD 

(ft above 

NAVD 88) 

Well type

Well depth 

(ft below

LSD)

Depth to top 

perforation 

(ft below LSD)

Depth to bottom 

perforation 

(ft below LSD)

CLUB grid wells

Borrego Valley study area 

BV-01 10-19-09 Fast 526 Production na na na

BV-02 10-20-09 Fast 731 Production 490 na na

BV-03 10-20-09 Slow 929 Production 350 150 350

BV-04 10-26-09 Slow 830 Production 630 420 630

BV-05 10-29-09 Fast 533 Production 580 248 568

BV-06 11-03-09 Fast 383 Production 391 252 285

BV-07 12-03-09 Slow 559 Production 95 na na

Central Desert study area 

CD-01 12-15-08 Slow 3,062 Production na na na

CD-02 12-15-08 Fast 3,471 Production 358 na na

CD-03 12-16-08 Slow 3,974 Production na na na

CD-04 12-17-08 Slow 2,512 Production 350 195 345

CD-05 12-17-08 Fast 2,160 Production 430 220 420

CD-06 12-18-08 Fast 2,839 Production na na na

CD-07 10-05-09 Slow 2,628 Production 740 470 720

CD-08 10-05-09 Fast 2,467 Production 425 na na

CD-09 10-06-09 Slow 3,233 Production 1,115 550 1,115

CD-10 10-06-09 Fast 3,285 Production 604 220 580

CD-11 10-07-09 Slow 2,858 Production na na na

CD-12 10-07-09 Slow 2,793 Production 550 na na

CD-13 11-16-09 Slow 2,083 Production 260 147 247

CD-14 11-17-09 Slow 2,524 Production 600 390 580

CD-15 11-17-09 Fast 2,512 Production 600 390 580

Low-Use Basins of the Mojave and Sonoran Deserts study area 

LUB-01 12-02-08 Slow 2,663 Production 381 205 381

LUB-02 12-02-08 Fast 2,423 Unused 543 na na

LUB-03 12-03-08 Slow 2,028 Production 456 na na

LUB-04 12-03-08 Fast 2,443 Production na na na

LUB-05 12-04-08 Fast 3,224 Production 490 322 480

LUB-06 12-08-08 Fast 2,464 Production 490 220 475

LUB-07 12-09-08 Slow 2,181 Production 660 160 440

LUB-08 12-09-08 Fast 2,378 Production 800 300 780

LUB-09 12-10-08 Fast 1,040 Production 224 184 224

LUB-10 12-10-08 Slow 1,737 Production 300 190 300

LUB-11 12-11-08 Fast 2,288 Production 600 452 590

LUB-12 12-16-08 Fast 3,279 Production 840 650 800

LUB-13 10-08-09 Slow 2,957 Production 500 100 500

LUB-14 10-21-09 Fast 2,375 Production 240 na na

LUB-15 10-26-09 Fast 386 Production 312 212 312
38 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Sampling information Construction information

GAMA well 

identification 

number

Date

sampled 

Sampling

schedule

Altitude of LSD 

(ft above 

NAVD 88) 

Well type

Well depth 

(ft below

LSD)

Depth to top 

perforation 

(ft below LSD)

Depth to bottom 

perforation 

(ft below LSD)

CLUB grid wells—Continued

Low-Use Basins of the Mojave and Sonoran Deserts study area—Continued

LUB-16 10-28-09 Fast 88 Production 105 0 105

LUB-17 10-28-09 Fast 495 Production 584 484 584

LUB-18 11-02-09 Slow 2,851 Production 36 15 36

LUB-19 11-03-09 Slow 177 Production na na na

LUB-20 11-04-09 Slow 282 Production 100 70 na

LUB-21 11-18-09 Fast 627 Production 400 300 400

LUB-22 11-19-09 Fast 459 Production 1,200 690 1,190

LUB-23 12-07-09 Slow 2,978 Production 403 200 400

LUB-24 12-08-09 Fast 1,175 Production 788 235 na

LUB-25 12-08-09 Fast 3,057 Production 866 534 864

LUB-26 12-09-09 Slow 4,625 Production 711 na na

LUB-27 03-04-10 Slow 242 Production 400 140 400

CLUB understanding wells

BVU-01 10-27-09 Slow 595 Production 392 162 372

LUBU-01 12-17-08 Fast 1,819 Production 1,010 350 940

LUBU-02 03-03-10 Fast 3,041 Unused 400 140 380

Table 1. Identification, sampling, and construction information for wells sampled for the Borrego, Central Desert, and Low Use Basins 

of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 

to March 2010.—Continued

[Sampling schedule is described in table 2. Land-surface datum (LSD) is a datum plane that is approximately at land surface at each well. The altitude of the 

LSD is described in feet above the North American Vertical Datum 1988 (NAVD 88). Numbered suffix indicates the order of sample collection within each study 

area. GAMA well identification number: BV, Borrego study-area grid well; BVU, Borrego study-area understanding well; CD, Central Desert study-area grid 

well; LUB, Low Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low Use Basins of the Mojave and Sonoran Deserts study-area 

understanding well. Other abbreviations: ft, foot; na, not available]
Table 2 39

Table 2. Classes of chemical constituents and water-quality indicators collected for the slow and the fast well sampling schedules 

in the Borrego, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, December 2008 to March 2010. 

Analyte classes Slow

schedule

Fast

schedule

Analyte list 

table

Results

table

Water-quality indicators 

Dissolved oxygen, temperature, pH, and specific conductance X X 4

Field alkalinity, bicarbonate, and carbonate X 4

Organic constituents

Volatile organic compounds (VOC) X X 3A 5

Pesticides and pesticide degradates X X 3B 6

Pharmaceutical compounds X 3C none 1

Constituents of special interest

Perchlorate X X 3D 7

N-nitrosodimethylamine (NDMA) X 3D none 2

Inorganic constituents

Trace elements X X 3 3E 8

Nutrients X X 3 3F 9

Major and minor ions, silica, and total dissolved solids (TDS) X X 3 3G 10

Laboratory alkalinity, bicarbonate, and carbonate X X 3G 4

Species of inorganic chromium X 4 3H, 3I 11, 12

Stable isotopes

Stable isotopes of hydrogen and oxygen in water X X 3J 13

Stable isotopes of carbon in dissolved inorganic carbon and carbon-14 abundance X X 3J 13

Stable isotopes of boron in water X 3J none 5

Stable isotopes of strontium in water X 3J none 5

Radioactivity and dissolved noble gases

Tritium X X 3J 13

Radon-222 X 3J 14A

Radium isotopes (radium-226 and radium-228) X 3J 14B

Gross alpha and gross beta radioactivity (72-hour and 30-day) X 3J 14C

Dissolved noble gases, tritium, and helium isotope ratios X X 3K none 6

1

 Pharmaceutical compounds were not detected at concentrations greater than or equal to method detection limits in the CLUB study unit.

2

 Constituent was not detected in groundwater samples.

3

 Wells sampled on the fast schedule in the Low-Use Basins of the Mojave and Sonoran Deserts study area included these constituents.

4

 Hexavalent chromium analysis from TestAmerica Laboratories, Inc., Irvine, California, was added to the slow sampling schedule starting in October 2009.

5

 Results for the stable isotopes of boron and strontium in water analyzed by U.S. Geological Survey National Research Program Metals Isotope Research 

Laboratory, Menlo Park, California, were not completed in time for inclusion in this report; results will be presented in a subsequent publication.

6

 Results for dissolved noble gases, tritium, and helium isotope ratios analyzed by Lawrence Livermore National Laboratory, Livermore, California, were not 

completed in time for inclusion in this report; results will be presented in a subsequent publication.
40 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 Table 3A.

Volatile organic compounds (VOCs), primary uses or sources, comparative benchmarks, and reporting information for the U.S. Geological Survey (USGS) National 

Water Quality Laboratory (NWQL) Schedule 2020.[USGS parameter code: The five-digit code is used to uniquely identify a specific constituent or property. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; SRL, study 

reporting level; THM, trihalomethane; D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; –, not detected; ≤, less than or equal to; NWIS, USGS National 

Water 

Information System]

Constituent

(synonym or abbreviation) Primary use or source

USGS 

parameter

code

CAS number 1 LRL 3 or SRL (μg/L) Benchmark type Benchmark level (μg/L) Detection

Acetone Solvent 81552 67-64-1 4, 3.4 na na – (2)

Acrylonitrile Organic synthesis 34215 107-13-1 0.4, 0.8 RSD5-US 0.6 –

tert-Amyl methyl ether (TAME) Gasoline oxygenate 50005 994-05-8 0.06 na na –

Benzene Gasoline hydrocarbon 34030 71-43-2 0.016, 0.026 MCL-CA 1 D

Bromobenzene Solvent 81555 108-86-1 0.02, 0.022 na na –

Bromochloromethane Fire retardant 77297 74-97-5 0.06 HAL-US 90 –

Bromodichloromethane Disinfection byproduct (THM) 32101 75-27-4 0.04, 0.034 MCL-US 4 80

D

Bromoform (Tribromomethane) Disinfection byproduct (THM) 32104 75-25-2 0.1 MCL-US 4 80

D

Bromomethane (Methyl bromide) Fumigant 34413 74-83-9 0.4, 0.2 HAL-US 10 –

n-Butylbenzene Gasoline hydrocarbon 77342 104-51-8 0.08 NL-CA 260 –

sec-Butylbenzene Gasoline hydrocarbon 77350 135-98-8 0.02, 0.034 NL-CA 260 –

tert-Butylbenzene Gasoline hydrocarbon 77353 98-06-6 0.06 NL-CA 260 –

Carbon disulfide Organic synthesis 77041 75-15-0 2 0.03 NL-CA 160 –

Carbon tetrachloride (Tetrachloromethane) Solvent 32102 56-23-5 0.06, 0.052 MCL-CA 0.5 –

Chlorobenzene Solvent 34301 108-90-7 0.02, 0.016 MCL-CA 70 –

Chloroethane Solvent 34311 75-00-3 0.10, 0.06 na na –

Chloroform (Trichloromethane) Disinfection byproduct (THM) 32106 67-66-3 0.04, 0.03 MCL-US 4 80

D

Chloromethane Solvent 34418 74-87-3 0.14 HAL-US 30 –

3-Chloropropene Organic synthesis 78109 107-05-1 0.08 na na –

2-Chlorotoluene Solvent 77275 95-49-8 0.02, 0.028 NL-CA 140 –

4-Chlorotoluene Solvent 77277 106-43-4 0.02, 0.042 NL-CA 140 –

Dibromochloromethane Disinfection byproduct (THM) 32105 124-48-1 0.12 MCL-US 4 80 –

1,2-Dibromo-3-chloropropane (DBCP) Fumigant 82625 96-12-8 1, 0.34 MCL-US 0.2 –

1,2-Dibromoethane (EDB) Fumigant 77651 106-93-4 0.04, 0.05 MCL-US 0.05 –

Dibromomethane Solvent 30217 74-95-3 0.04, 0.05 na na –

1,2-Dichlorobenzene Solvent 34536 95-50-1 0.02, 0.028 MCL-CA 600 –

1,3-Dichlorobenzene Solvent 34566 541-73-1 0.02, 0.024 HAL-US 600 –

1,4-Dichlorobenzene Fumigant 34571 106-46-7 0.02, 0.026 MCL-CA 5 –

trans-1,4-Dichloro-2-butene Organic synthesis 73547 110-57-6 0.4, 0.36 na na –

Dichlorodifluoromethane (CFC-12) Refrigerant 34668 75-71-8 0.1 NL-CA 1,000 –

1,1-Dichloroethane (1,1-DCA) Solvent 34496 75-34-3 0.04, 0.044 MCL-CA 5 –

1,2-Dichloroethane (1,2-DCA) Solvent 32103 107-06-2 0.06, 0.08 MCL-CA 0.5 –

1,1-Dichloroethene (1,1-DCE) Organic synthesis 34501 75-35-4 0.02, 0.022 MCL-CA 6 –
Table 3A 41

Constituent

(synonym or abbreviation) Primary use or source

USGS 

parameter

code

CAS number 1 LRL 3 or SRL (μg/L) Benchmark type Benchmark level (μg/L) Detection

cis-1,2-Dichloroethene (cis-1,2-DCE) Solvent 77093 156-59-2 0.02, 0.022 MCL-CA 6 –

trans-1,2-Dichloroethene (trans-1,2-DCE) Solvent 34546 156-60-5 0.018 MCL-CA 10 –

1,2-Dichloropropane Fumigant 34541 78-87-5 0.02, 0.026 MCL-US 5 –

1,3-Dichloropropane Fumigant 77173 142-28-9 0.06 na na –

2,2-Dichloropropane Fumigant 77170 594-20-7 0.06 na na –

1,1-Dichloropropene Organic synthesis 77168 563-58-6 0.04, 0.03 na na –

cis-1,3-Dichloropropene Fumigant 34704 10061-01-5 0.1 RSD5-US 5 4 –

trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.10, 0.14 RSD5-US 5 4 –Diethyl ether Solvent 81576 60-29-7 0.12, 0.08 na na –

Diisopropyl ether (DIPE) Gasoline oxygenate 81577 108-20-3 0.06 na na D

Ethylbenzene Gasoline hydrocarbon 34371 100-41-4 2 0.1 MCL-CA 300 –

Ethyl tert-butyl ether (ETBE) Gasoline oxygenate 50004 637-92-3 0.04, 0.032 na na –

Ethyl methacrylate Organic synthesis 73570 97-63-2 0.14 na na –

o-Ethyl toluene (1-Ethyl-2-methyl benzene) Gasoline hydrocarbon 77220 611-14-3 0.02, 0.032 na na –

Hexachlorobutadiene Organic synthesis 39702 87-68-3 0.06 RSD5-US 9 –

Hexachloroethane Solvent 34396 67-72-1 0.14 HAL-US 1 –

2-Hexanone (n-Butyl methyl ketone) Solvent 77103 591-78-6 0.6, 0.46 na na –

Iodomethane (Methyl iodide) Organic synthesis 77424 74-88-4 0.8, 0.26 na na –

Isopropylbenzene Gasoline hydrocarbon 77223 98-82-8 0.04, 0.042 NL-CA 770 –

4-Isopropyl-1-methyl benzene Gasoline hydrocarbon 77356 99-87-6 0.06 na na –

Methyl acrylate Organic synthesis 49991 96-33-3 0.6, 0.56 na na –

Methyl acrylonitrile Organic synthesis 81593 126-98-7 0.2, 0.26 na na –

Methyl tert-butyl ether (MTBE) Gasoline oxygenate 78032 1634-04-4 0.10, 0.1 MCL-CA 13 –

Methyl iso-butyl ketone (MIBK) Solvent 78133 108-10-1 0.4, 0.32 NL-CA 120 –

Methylene chloride (Dichloromethane) Solvent 34423 75-09-2 0.04, 0.038 MCL-US 5 –

Methyl ethyl ketone (2-butanone, MEK) Solvent 81595 78-93-3 1.6 HAL-US 4,000 –

Methyl methacrylate Organic synthesis 81597 80-62-6 0.20, 0.22 na na –

Naphthalene Gasoline hydrocarbon 34696 91-20-3 0.2, 0.18 NL-CA 17 –

Perchloroethene (PCE, Tetrachloroethene) Solvent 34475 127-18-4 6 0.02 MCL-US 5 D

n-Propylbenzene Solvent 77224 103-65-1 0.04, 0.036 NL-CA 260 –

Styrene Gasoline hydrocarbon 77128 100-42-5 0.04, 0.03 MCL-US 100 –

1,1,1,2-Tetrachloroethane Solvent 77562 630-20-6 0.04 HAL-US 70 –

1,1,2,2-Tetrachloroethane Solvent 34516 79-34-5 0.10, 0.14 MCL-CA 1 –

Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparative benchmarks, and reporting information for the U.S. Geological Survey (USGS) National 

Water Quality Laboratory (NWQL) Schedule 2020.—Continued

[USGS parameter code: The five-digit code is used to uniquely identify a specific constituent or property. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; SRL, study 

reporting level; THM, trihalomethane; D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; –, not detected; ≤, less than or equal to; NWIS, USGS National Water 

Information System]
42 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 Constituent (synonym or abbreviation) Primary use or source USGS parameter code CAS number 1 LRL 3 or SRL (μg/L) Benchmark type Benchmark level (μg/L) Detection Tetrahydrofuran Solvent 81607 109-99-9 1.4 na na – 1,2,3,4-Tetramethylbenzene Gasoline hydrocarbon 49999 488-23-3 0.08 na na – 1,2,3,5-Tetramethylbenzene Gasoline hydrocarbon 50000 527-53-7 0.08 na na – Toluene Gasoline hydrocarbon 34010 108-88-3 2 0.69 MCL-CA 150 – (2) 1,2,3-Trichlorobenzene Organic synthesis 77613 87-61-6 0.06 na na – 1,2,4-Trichlorobenzene Solvent 34551 120-82-1 0.04, 0.08 MCL-CA 5 – 1,1,1-Trichloroethane (1,1,1-TCA) Solvent 34506 71-55-6 0.02, 0.03 MCL-CA 200 – 1,1,2-Trichloroethane (1,1,2-TCA) Solvent 34511 79-00-5 0.06, 0.046 MCL-CA 5 – Trichloroethene (TCE) Solvent 39180 79-01-6 0.02, 0.022 MCL-US 5 D Trichlorofluoromethane (CFC-11) Refrigerant 34488 75-69-4 0.08 MCL-CA 150 – 1,2,3-Trichloropropane (1,2,3-TCP) Solvent/organic synthesis 77443 96-18-4 0.12 HAL-US 7 40 – Trichlorotrifluoroethane (CFC-113) Refrigerant 77652 76-13-1 0.04, 0.034 MCL-CA 1,200 – 1,2,3-Trimethylbenzene Gasoline hydrocarbon 77221 526-73-8 0.08, 0.06 na na – 1,2,4-Trimethylbenzene Gasoline hydrocarbon 77222 95-63-6 2 0.56 NL-CA 330 D (2) 1,3,5-Trimethylbenzene Organic synthesis 77226 108-67-8 0.04, 0.032 NL-CA 330 – Vinyl bromide (Bromoethene) Fire retardant 50002 593-60-2 0.12 na na – Vinyl chloride (Chloroethene) Organic synthesis 39175 75-01-4 0.08, 0.06 MCL-CA 0.5 –

m- and 

p-Xylene Gasoline hydrocarbon 85795 108-38-3 / 106-42-3 2 0.4 MCL-CA 8 1,750 –

o-Xylene Gasoline hydrocarbon 77135 95-47-6 2 0.1 MCL-CA 8 1,750 –

1 This report contains CAS Registry Numbers® (CASRNs), which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client 

ServicesSM.

2 SRLs were defined on the basis of examination of quality-control samples collected between May 2004 and September 2010 for the first 32 study units of the California GAMA Priority Basin Project (M.S. 

Fram, L.D. Olsen, and K. Belitz, U.S. Geological Survey, written commun., 2011). Values measured at concentrations less than the SRLs have been reclassified as non-detections and are not presented on table 5.

3 For constituents with two LRLs listed, the first value was in use before 09-30-10, and the second value was in use after 10-01-10. The highest LRL is used for this report.4 The MCL-US benchmark for trihalomethanes is the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.5 The RSD5 benchmark for 1,3-dichloropropene is the sum of its isomers (cis and trans).6 SRL was defined based on a detection in a field blank. Values measured at concentrations less than the SRL are noted with a ≤ symbol in the USGS NWIS database and were not included in the calculations 

of detection frequencies.

7 In earlier reports in this series, the NL-CA (0.005 μg/L) was used as the comparison benchmark for 1,2,3-TCP.8 The MCL-CA benchmarks for 

m- and p-xylene and o-xylene are the sum of all three xylene compounds.

Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparative benchmarks, and reporting information for the U.S. Geological Survey (USGS) National 

Water Quality Laboratory (NWQL) Schedule 2020.—Continued

[USGS parameter code: The five-digit code is used to uniquely identify a specific constituent or property. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; SRL, study 

reporting level; THM, trihalomethane; D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; –, not detected; ≤, less than or equal to; NWIS, USGS National 

Water 

Information System]
Table 3B 43

Table 3B. Pesticides and pesticide degradates, primary uses or sources, comparative benchmarks, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) Schedule 2003.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Benchmark type and benchmark level as of October 1, 2008. 

Benchmark type: Maximum 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. HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, 

California Department of Public Health maximum contaminant level; MCL-US, USEPA maximum contaminant level; RSD5-US, USEPA risk-specific dose at 

a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (table 6); na, 

not available; μg/L, micrograms per liter; –, not detected]

Constituent 

(synonym or abbreviation) Primary use or source

USGS 

parameter 

code

CAS

number

 LRL 1

(μg/L)

Benchmark 

type

Benchmark

level 

(μg/L)

Detection

Acetochlor Herbicide 49260 34256-82-1 0.01, 0.010 na na –

Alachlor Herbicide 46342 15972-60-8 0.008 MCL-US 2 –

Atrazine Herbicide 39632 1912-24-9 0.007 MCL-CA 1 D

Azinphos-methyl Insecticide 82686 86-50-0 0.12 na na –

Azinphos-methyl oxon Insecticide degradate 61635 961-22-8 0.042 na na –

Benfluralin Herbicide 82673 1861-40-1 0.014 na na – (2)

Carbaryl Insecticide 82680 63-25-2 0.2, 0.06 RSD5-US 400 –

2-Chloro-2,6-diethylacetanilide Herbicide degradate 61618 6967-29-9 0.01, 0.010 na na –

4-Chloro-2-methylphenol Herbicide degradate 61633 1570-64-5 0.0050, 0.0032 na na – (2)

Chlorpyrifos Insecticide 38933 2921-88-2 0.01, 0.010 HAL-US 2 – (2)

Chlorpyrifos oxon Insecticide degradate 61636 5598-15-2 0.05 na na – (2)

Cyfluthrin Insecticide 61585 68359-37-5 0.016 na na – (2)

Cypermethrin Insecticide 61586 52315-07-8 0.02, 0.020 na na – (2)

Dacthal (DCPA) Herbicide 82682 1861-32-1 0.006, 0.0076 HAL-US 70 –

Deethylatrazine (2-Chloro-4-

isopropylamino-6-amino-striazine)

Herbicide degradate 04040 6190-65-4 0.014 na na D (2)

Desulfinylfipronil Insecticide degradate 62170 na 0.012 na na –

Desulfinylfipronil amide Insecticide degradate 62169 na 0.029 na na –

Diazinon Insecticide 39572 333-41-5 0.005 HAL-US 1 –

3,4-Dichloroaniline Herbicide degradate 61625 95-76-1 0.004, 0.0042 na na D

Dichlorvos Insecticide 38775 62-73-7 0.02 na na – (2)

Dicrotophos Insecticide 38454 141-66-2 0.08 na na – (2)

Dieldrin Insecticide 39381 60-57-1 0.009 RSD5-US 0.02 –

2,6-Diethylaniline Herbicide degradate 82660 579-66-8 0.006 na na –

Dimethoate Insecticide 82662 60-51-5 0.006 na na – (2)

Ethion Insecticide 82346 563-12-2 0.012, 0.008 na na – (2)

Ethion monoxon Insecticide degradate 61644 17356-42-2 0.021 na na –

2-Ethyl-6-methylaniline Herbicide degradate 61620 24549-06-2 0.010, 0.0098 na na –

Fenamiphos Insecticide 61591 22224-92-6 0.029, 0.030 HAL-US 0.7 –

Fenamiphos sulfone Insecticide degradate 61645 31972-44-8 0.053 na na –

Fenamiphos sulfoxide Insecticide degradate 61646 31972-43-7 0.08 na na – (2)

Fipronil Insecticide 62166 120068-37-3 0.04, 0.018 na na –

Fipronil sulfide Insecticide degradate 62167 120067-83-6 0.013 na na –

Fipronil sulfone Insecticide degradate 62168 120068-36-2 0.024 na na – (2)

Fonofos Insecticide 04095 944-22-9 0.01, 0.0044 HAL-US 10 –

Hexazinone Herbicide 04025 51235-04-2 0.008 HAL-US 400 – (2)

Iprodione Fungicide 61593 36734-19-7 0.014 na na –

Isofenphos Insecticide 61594 25311-71-1 0.006 na na –

Malaoxon Insecticide degradate 61652 1634-78-2 0.08 na na –

Malathion Insecticide 39532 121-75-5 0.02, 0.016 HAL-US 100 –

Metalaxyl Fungicide 61596 57837-19-1 0.0069, 0.007 na na –

Methidathion Insecticide 61598 950-37-8 0.006 na na –

Metolachlor Herbicide 39415 51218-45-2 0.014 HAL-US 700 D

Metribuzin Herbicide 82630 21087-64-9 0.016, 0.012 HAL-US 70 –

Myclobutanil Fungicide 61599 88671-89-0 0.01, 0.010 na na –

1-Naphthol Insecticide degradate 49295 90-15-3 0.04, 0.036 na na – (2)
44 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Constituent 

(synonym or abbreviation) Primary use or source

USGS 

parameter 

code

CAS

number

 LRL 1

(μg/L)

Benchmark 

type

Benchmark

level 

(μg/L)

Detection

Paraoxon-methyl Insecticide degradate 61664 950-35-6 0.01, 0.010 na na – (2)

Parathion-methyl Insecticide 82667 298-00-0 0.008 HAL-US 1 – (2)

Pendimethalin Herbicide 82683 40487-42-1 0.012 na na –

cis-Permethrin Insecticide 82687 54774-45-7 0.014 na na – (2)

Phorate Insecticide 82664 298-02-2 0.02 na na – (2)

Phorate oxon Insecticide degradate 61666 2600-69-3 0.027 na na –

Phosmet Insecticide 61601 732-11-6 0.2, 0.034 na na – (2)

Phosmet oxon Insecticide degradate 61668 3735-33-9 0.0511 na na – (2)

Prometon Herbicide 04037 1610-18-0 0.012 HAL-US 100 –

Prometryn Herbicide 04036 7287-19-6 0.0059, 0.006 na na –

Pronamide (Propyzamide) Herbicide 82676 23950-58-5 0.004, 0.0036 RSD5-US 20 –

Simazine Herbicide 04035 122-34-9 0.01, 0.006 MCL-US 4 D

Tebuthiuron Herbicide 82670 34014-18-1 0.02, 0.028 HAL-US 500 – (3)

Terbufos Insecticide 82675 13071-79-9 0.018 HAL-US 0.4 – (2)

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 0.045 na na –

Terbuthylazine Herbicide 04022 5915-41-3 0.006 na na –

Tribufos Defoliant 61610 78-48-8 0.035, 0.018 na na – (2)

Trifluralin Herbicide 82661 1582-09-8 0.012, 0.018 HAL-US 10 – (2)

1

 For constituents with two LRLs listed, the first value was in use before 09-30-10, and the second value was in use after 10-01-10. The highest LRL is used 

for this report.

2

 The median matrix-spike recovery was less than 70 percent. Low recoveries may indicate that the compound might not have been detected in some samples 

if it was present at very low concentrations.

3

 The median matrix-spike recovery was greater than 130 percent. High recoveries may indicate that reported values could be greater than what is detected in 

the sample.

Table 3B. Pesticides and pesticide degradates, primary uses or sources, comparative benchmarks, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) Schedule 2003.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Benchmark type and benchmark level as of October 1, 2008. 

Benchmark type: Maximum 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. HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, 

California Department of Public Health maximum contaminant level; MCL-US, USEPA maximum contaminant level; RSD5-US, USEPA risk-specific dose at 

a risk factor of 10-5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (table 6); na, 

not available; μg/L, micrograms per liter; –, not detected]
Table 3C 45

Table 3C. Pharmaceutical compounds, primary uses or sources, comparative benchmarks, and reporting information for the U.S. 

Geological Survey (USGS) National Water Quality Laboratory (NWQL) Schedule 2080.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Abbreviations: CAS, Chemical Abstract Service; SRL, 

study reporting level; na, not available; μg/L, micrograms per liter]

Constituent Primary use or source

USGS

parameter 

code

CAS

number

SRL 1

(μg/L)

Benchmark

type

Benchmark 

level Detection

Acetaminophen Analgesic 62000 103-90-2 0.06 na na –

Albuterol Bronchodilator 62020 18559-94-9 0.04 na na –

Caffeine Stimulant 50305 58-08-2 0.10 na na –

Carbamazapine Anticonvulsant; mood stabilizer 62793 298-46-4 0.03 na na –

Codeine Opiod narcotic 62003 76-57-3 0.023 na na –

Cotinine Nicotine metabolite 62005 486-56-6 0.019 na na –

Dehydronifedipine Antianginal metabolite 62004 67035-22-7 0.04 na na –

Diltiazem Antianginal; antihypertensive 62008 42399-41-7 0.04 na na –

1,7-Dimethylxanthine Caffeine metabolite 62030 611-59-6 0.06 na na –

Diphenhydramine Antihistamine 62796 147-25-0 0.02 na na –

Sulfamethoxazole Antibacterial 62021 723-46-6 0.08 na na –

Thiabendazole Anthelmintic 62801 148-79-8 0.03 na na –

Trimethoprim Antibacterial 62023 738-70-5 0.017 na na –

Warfarin Anticoagulant 62024 81-81-2 0.05 na na –

1

 The California Groundwater Ambient Monitoring and Assessment (GAMA) Program uses more conservative reporting limits for the pharmaceutical 

compounds than are used by the USGS National Water Quality Laboratory (NWQL) (Fram and Belitz, 2011). The SRL corresponds to the highest long-term 

method detection limit (LT-MDL) or interim method detection limit (I-MDL) used by the NWQL during the period GAMA samples were analyzed 

(May 2004 through June 2010). Results reported by the NWQL with concentrations less than the SRLs are reported as non-detections by GAMA. Data are stored 

in the USGS National Water Information System (NWIS) database as reported by GAMA: results initially reported as detections with concentrations below the 

SRLs or as non-detections less than LRLs have been recoded as non-detections less than SRLs. Results for pharmaceutical compounds in groundwater samples 

from the GAMA Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) study unit are presented in Fram and Belitz 

(2011).
46 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table 3D. Constituents of special interest, primary uses or sources, comparative benchmarks, and reporting information for Weck 

Laboratories, Inc., analyses.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Minimum reporting level, benchmark type, and benchmark 

level as of October 1, 2008. Benchmark type: Maximum 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. MCL-CA, California Department of Public Health (CDPH) maximum 

contaminant level; NL-CA, CDPH notification level. Other abbreviations: CAS, Chemical Abstract Service; MRL, minimum reporting level; D, detected in 

groundwater samples (table 7); μg/L, micrograms per liter; –, not detected]

Constituent

(synonym or

abbreviation)

Primary use or source

USGS

parameter 

code

CAS

number

MRL

(μg/L)

Benchmark

type

Benchmark 

level Detection

Perchlorate Rocket fuel, fireworks, flares 63790 14797-73-0 0.10 MCL-CA 6 D

N-nitrosodimethylamine 

(NDMA)

Disinfection byproduct 34438 62-75-9 0.0020 NL-CA 0.010 –
Table 3E 47

Table 3E. Trace elements, comparative benchmarks, and reporting information for the U.S. Geological 

Survey (USGS) National Water Quality Laboratory (NWQL) Schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Benchmark type and 

benchmark level as of October 1, 2008. Benchmark type: Maximum 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. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HAL-US, USEPA lifetime health advisory 

level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum 

contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other 

abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; SRL, study reporting level; D, detected in 

groundwater samples (table 8); na, not available; μg/L, micrograms per liter; ≤, less than or equal to; NWIS, USGS National 

Water Information System; NWQL, USGS National Water Quality Laboratory; BQS, USGS Branch of Quality Systems]

Constituent

USGS

parameter 

code

CAS

number

LRL 1 or SRL

(μg/L)

Benchmark

type

Benchmark 

level Detection

Aluminum 01106 7429-90-5 2 1.6 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.04, 0.054 MCL-US 6 D

Arsenic 01000 7440-38-2 0.06, 0.044 MCL-US 10 D

Barium 01005 7440-39-3 2 0.36 MCL-CA 1,000 D

Beryllium 01010 7440-41-7 0.02, 0.012 MCL-US 4 D

Boron 01020 7440-42-8 4, 2.8 NL-CA 1,000 D

Cadmium 01025 7440-43-9 0.02 MCL-US 5 D

Chromium 01030 7440-47-3 2 0.42 MCL-CA 50 D

Cobalt 01035 7440-48-4 3 0.18 na na D

Copper 01040 7440-50-8 2 1.7 AL-US 1,300 D

Iron 01046 7439-89-6 2 6 SMCL-CA 300 D

Lead 01049 7439-92-1 2 0.65 AL-US 15 D

Lithium 01130 7439-93-2 1, 0.44 na na D

Manganese 01056 7439-96-5 2 0.2 SMCL-CA 50 D

Molybdenum 01060 7439-98-7 3 0.32 HAL-US 40 D

Nickel 01065 7440-02-0 2 0.36 MCL-CA 100 D

Selenium 01145 7782-49-2 0.06, 0.040 MCL-US 50 D

Silver 01075 7440-22-4 0.008, 0.010 SMCL-CA 100 D

Strontium 01080 7440-24-6 0.8, 0.40 HAL-US 4,000 D

Thallium 01057 7440-28-0 0.04, 0.020 MCL-US 2 D

Tungsten 01155 7440-33-7 2 0.11 na na D

Uranium 22703 7440-61-1 0.006, 0.008 MCL-US 30 D

Vanadium 01085 7440-62-2 2 0.11 NL-CA 50 D

Zinc 01090 7440-66-6 2 4.8 4SMCL-CA 5,000 D

1

 For constituents with two LRLs listed, the first value was in use before 09-30-10, and the second value was in use after 

10-01-10. The highest LRL is used for this report.

2

 SRL was defined based on examination of GAMA quality-control samples collected from May 2004 through January 2008 

(Olsen and others, 2010). Values less than the SRL are reported as less than or equal to the value reported by the laboratory. In 

the USGS NWIS database, the result is accompanied with the following comment: Result is < or = reported value, based on QC 

data (may include: field blanks, source-solution blanks, trip blanks, NWQL set blanks, NWQL blank water certificates, and USGS 

BQS Blind Blank Program data).

3

 SRL was defined based on a detection in a field blank. Values less than the SRL are reported as ≤ the value reported by the 

laboratory. In the USGS NWIS database, the result is accompanied with the following comment: Result is < or = reported value, 

based on a detection in a field blank.

4

 The secondary maximum contaminant level for zinc is listed as SMCL-CA because SMCLs established by the CDPH are 

used in this report for all constituents that have SMCL-CA values.
48 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table 3F. Nutrients, comparative benchmarks, and reporting information for the U.S. Geological Survey 

(USGS) National Water Quality Laboratory (NWQL) Schedule 2755.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Benchmark type and 

benchmark level as of October 1, 2008. Benchmark type: Maximum 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. HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-US, USEPA maximum 

contaminant level. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in 

groundwater samples (table 9); na, not available; mg/L, milligrams per liter]

Constituent

USGS

parameter 

code

CAS

number

LRL 1

(mg/L)

Benchmark

type

Benchmark 

level Detection

Ammonia (as nitrogen) 00608 7664-41-7 0.02 HAL-US 2 24.7 D

Nitrate plus nitrite (as 

nitrogen)

00631 na 0.04 MCL-US 10 D

Nitrite (as nitrogen) 00613 14797-65-0 0.002 MCL-US 1 D

Total nitrogen (ammonia, 

nitrite, nitrate, organic 

nitrogen)

62854 17778-88-0 0.1, 0.10 na na D

Phosphate, orthophosphate 

(as phosphorus)

00671 14265-44-2 0.006 na na D

1

 For constituents with two LRLs listed, the first value was in use before 09-30-10, and the second value was in use after 

10-01-10. The highest LRL is used for this report.

2

 The 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.”
Table 3G 49

Table 3G. Major and minor ions, silica, total dissolved solids (TDS), and alkalinity, comparative benchmarks, 

and reporting information for the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL)

Schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Benchmark type and benchmark 

level as of October 1, 2008. Benchmark type: Maximum 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. MCL-CA, 

California Department of Public Health (CDPH) maximum contaminant level; SMCL-CA, CDPH secondary maximum contaminant 

level. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples 

(table 10); na, not available; mg/L, milligrams per liter]

Constituent

USGS

parameter 

code

CAS

number

LRL 1

(mg/L)

Benchmark

type

Benchmark 

level Detection

Bromide 71870 24959-67-9 0.02 na na D

Calcium 00915 7440-70-2 0.02, 0.044 na na D

Chloride 00940 16887-00-6 0.12 SMCL-CA 2 250 (500) D

Fluoride 00950 16984-48-8 0.08 MCL-CA 2 D

Iodide 71865 7553-56-2 0.002 na na D

Magnesium 00925 7439-95-4 0.012, 0.016 na na D

Potassium 00935 7440-09-7 0.06, 0.064 na na D

Sodium 00930 7440-23-5 0.12, 0.10 na na D

Sulfate 00945 14808-79-8 0.18 SMCL-CA 2 250 (500) D

Silica (as SiO2) 00955 7631-86-9 0.02, 0.058 na na D

TDS 70300 na 10 SMCL-CA 2 500 (1,000) D

Laboratory alkalinity 

(as CaCO3) 3

29801 na 1 na na D

1

 For constituents with two LRLs listed, the first value was in use before 09-30-10, and the second value was in use after 10-01-10. 

The highest LRL is used for this report.

2

 The recommended SMCL-CA benchmarks for chloride, sulfate, and TDS are listed with the upper SMCL-CA benchmarks in 

parentheses.

3

 Laboratory alkalinity results are presented in table 4.
50 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table 3H. Species of inorganic chromium, comparative benchmarks, and reporting information for the U.S. 

Geological Survey Trace Metal Laboratory, Boulder, Colorado, analyses.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Method detection limit, 

benchmark type, and benchmark level as of November 17, 2008. Benchmark type: Maximum 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. MCL-CA, California Department of Public Health maximum contaminant level. Other abbreviations: CAS, 

Chemical Abstract Service; MDL, method detection limit; Cr-VI, hexavalent chromium (chromium-VI); na, not available; μg/L, 

micrograms per liter; D, detected in groundwater samples (table 11); NWIS, USGS National Water Information System]

Constituent

USGS

parameter 

code 1

CAS

number

MDL

(μg/L)

Benchmark

type

Benchmark 

level 

(μg/L)

Detection

Chromium (total) 01030 7440-47-3 1 MCL-CA 50 D

Cr-VI 01032 18540-29-9 1 na na D

1

 Data are generated from research methods and not stored in the USGS NWIS database under the listed parameter code.

Table 3I. Hexavalent chromium (chromium-VI, Cr-VI), comparative benchmark, and reporting information for the 

TestAmerica Laboratories, Inc., Irvine, California, analyses.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Method detection limit as 

of October 5, 2009. Abbreviations: CAS, Chemical Abstract Service; MDL, method detection limit; na, not available; μg/L, 

micrograms per liter; D, detected in groundwater samples (table 12)]

Constituent

USGS

parameter 

code

CAS

number

MDL

(μg/L)

Benchmark

type

Benchmark 

level Detection

Cr-VI 01032 18540-29-9 1 na na D
Table 3J 51

Table 3J. Isotopic and radioactive constituents, comparative benchmarks, and reporting information for laboratory analyses.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Stable isotope ratios are reported in the standard delta 

notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard reference material. Reporting level, benchmark 

type, and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-US, U.S. Environmental Protection Agency 

maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant level. Other abbreviations: USGS, U.S. Geological 

Survey; CAS, Chemical Abstract Service; CSU, combined standard uncertainty; ssLC, sample-specific critical level; MRL, minimum reporting level; na, not 

available; H, hydrogen; O, oxygen; B, boron; Sr, strontium; pCi/L, picocuries per liter; D, detected in groundwater samples (tables 13 and 14A through 14C); 

NRP, USGS National Research Program]

Constituent

USGS

parameter 

code 

CAS

number

Reporting 

level type

Reporting 

level or 

uncertainty

Benchmark

type

Benchmark 

level Detection

Stable isotope ratios (per mil)

δ2H in water 1 82082 na MU 2 na na D

δ18O in water 1 82085 na MU 0.20 na na D

δ11B in water 2 62648 na MU na na na D

δ13C in dissolved inorganic 

carbon 3

82081 na 1-sigma 0.05 na na D

Isotope ratios (atom ratio)

Strontium isotope ratio 

(87Sr/86Sr) 2

75978 na MU 0.00005 na na D

Radioactive constituents (percent modern)

Carbon-14 3 49933 14762-75-5 1-sigma 0.0015 na na D

Radioactive constituents (pCi/L)

Radon-222 4 82303 14859-67-7 ssLC CSU MCL-US (Proposed) 4,000 D

Tritium 5 07000 10028-17-8 ssLC CSU MCL-CA 20,000 D

Radium-226 6 09511 13982-63-3 ssLC CSU MCL-US 7 5 D

Radium-228 6 81366 15262-20-1 ssLC CSU MCL-US 7 5 D

Gross alpha radioactivity, 

72-hour and 30-day counts 6 62636, 62639 12587-46-1 ssLC CSU MCL-US 15 D

Gross beta radioactivity, 

72-hour and 30-day counts 6 62642, 62645 12587-47-2 ssLC CSU MCL-CA 50 D

1

 USGS Stable Isotope Laboratory, Reston, Virginia (USGSSIVA).

2

 USGS NRP Metals Isotope Research Laboratory, Menlo Park, California (USGSMICA).

3

 Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry Facility (contract laboratory, MA-WHAMS).

4

 USGS National Water Quality Laboratory (USGSNWQL).

5

 USGS Stable Isotope and Tritium Laboratory, Menlo Park, California (USGSH3CA).

6

 Eberline Analytical Services, Richmond, California (contract laboratory, CA-EBERL).

7

 The MCL-US benchmark for radium is the sum of radium-226 and radium-228.
52 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table 3K. Dissolved noble gases and tritium, comparison benchmarks, and reporting information for the Lawrence Livermore National 

Laboratory, Livermore, California, analyses.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Method uncertainty, benchmark type, and benchmark values 

as of October 1, 2008. Benchmark type: Maximum 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. MCL-CA, California Department of Public Health maximum contaminant level. 

Other abbreviations: CAS, Chemical Abstract Service; MU, method uncertainty; na, not available; cm3 STP/g, cubic centimeters of gas at standard temperature 

and pressure per gram of water; pCi/L, picocuries per liter]

Constituent

USGS

parameter

code 

CAS

number

MU

(percent)

Reporting 

units

Benchmark

type

Benchmark 

level

(pCi/L)

Detection

Argon 85563 7440-37-1 2 cm3 STP/g na na na

Helium-4 85561 7440-59-7 2 cm3 STP/g na na na

Krypton 85565 7439-90-9 2 cm3 STP/g na na na

Neon 61046 7440-01-09 2 cm3 STP/g na na na

Xenon 85567 7440-63-3 2 cm3 STP/g na na na

Tritium 07000 10028-17-8 1 pCi/L MCL-CA 20,000 na

Helium-3 / Helium-4 61040 na / 7440-59-7 0.75 atom ratio na na na
Table 4 53

Table 4. Water-quality indicators in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Reporting level, benchmark type, and benchmark level as of October 1, 2008. Benchmark type: SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: USGS, 

U.S. Geological Survey; °C, degrees Celsius; mg/L, milligrams per liter; nc, not collected; na, not available; RL, reporting limit or range; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; *, value at a concentration greater than benchmark level; **, value at a concentration greater than upper benchmark level; –, not detected]

GAMA well 

identification 

number

Dissolved 

oxygen, 

field

(mg/L)

(00300) 

Water 

temperature, 

field 

(°C) 

(00010)

pH, lab 

(standard 

units) 

(00403)

pH, field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm at 25°C) 

(90095)

Specific

conductance, 

field 

(μS/cm at 25°C) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3) 

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

Bicarbonate, 

field 

(mg/L) 

(63786)

Bicarbonate 2

(mg/L)

Carbonate, 

field 

(mg/L) 

(63788)

Carbonate 2

(mg/L)

Benchmark type na na SMCL-US SMCL-US SMCL-CA SMCL-CA na na na na na naBenchmark level na na <6.5 or >8.5 <6.5 or >8.5 1 900 (1,600) 1 900 (1,600) na na na na na na

[RL] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [1] [1] [1] [1] [0.1] [0.1]

CLUB grid wells (49 wells sampled)

Borrego Valley study area

BV-01 4.1 28.0 nc 7.9 nc **2,060 69.0 nc nc 83.5 nc 0.3BV-02 7.1 22.5 nc 7.2 nc 715 147 nc nc 179 nc 0.1BV-03 6.2 25.0 7.6 7.4 *1,080 *1,080 171 nc nc 208 nc 0.4BV-04 4.4 31.5 7.5 7.3 *910 *912 174 nc nc 212 nc 0.3BV-05 1.1 26.5 nc 8.4 nc 490 61.0 nc nc 72.6 nc 0.8BV-06 3.3 30.5 nc 7.7 nc **1,810 110 nc nc 134 nc 0.3BV-07 2.0 28.5 *8.9 *8.9 *974 *956 79.0 nc nc 89.3 nc 3.3

Central Desert study area

CD-01 6.2 20.5 8.0 7.8 448 438 159 nc nc 192 nc 0.9CD-02 4.8 23.0 nc 7.8 nc 547 nc nc nc nc nc ncCD-03 6.6 17.5 7.9 7.6 227 221 82.0 nc nc 99.3 nc 0.4CD-04 7.0 23.5 8.1 7.9 198 196 73.0 nc nc 87.9 nc 0.5CD-05 5.8 24.5 nc 7.8 nc 251 nc nc nc nc nc ncCD-06 6.2 20.0 nc 7.6 nc 682 nc nc nc nc nc ncCD-07 4.5 24.5 8.0 8.1 319 312 105 nc nc 127 nc 0.6CD-08 2.4 23.5 nc 7.9 nc *1,160 47.0 nc nc 56.9 nc 0.2CD-09 6.3 21.0 7.7 7.6 429 413 84.0 80.1 97.3 102 0.1 0.2CD-10 4.4 23.0 nc 7.8 nc 426 179 nc nc 217 nc 0.6CD-11 7.2 21.5 7.5 7.4 863 844 284 nc nc 345 nc 0.5CD-12 3.3 26.0 8.5 8.5 310 309 92.0 nc nc 109 nc 1.6CD-13 5.1 25.5 8.3 8.5 455 440 81.0 nc nc 96.9 nc 0.9CD-14 1.1 25.5 8.4 *8.6 332 334 60.0 nc nc 71.4 nc 0.8CD-15 5.1 25.0 nc 8.3 nc 307 79.0 75 91.5 94.5 -- 0.9
54 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 GAMA well identification number Dissolved oxygen, field (mg/L) (00300) Water temperature, field 

(°C) 

(00010)

pH, lab 

(standard 

units) 

(00403)

pH, field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm at 25°C) 

(90095)

Specific

conductance, 

field 

(μS/cm at 25°C) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3) 

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

Bicarbonate, 

field 

(mg/L) 

(63786)

Bicarbonate 2

(mg/L)

Carbonate, 

field 

(mg/L) 

(63788)

Carbonate 2

(mg/L)

Benchmark type na na SMCL-US SMCL-US SMCL-CA SMCL-CA na na na na na naBenchmark level na na <6.5 or >8.5 <6.5 or >8.5 1 900 (1,600) 1 900 (1,600) na na na na na na

[RL] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [1] [1] [1] [1] [0.1] [0.1]

CLUB grid wells (49 wells sampled)—Continued

Low-Use Basins of the Mojave and Sonoran Deserts study area 

LUB-01 6.1 24.5 7.7 7.7 *941 *944 91.0 65.1 79.2 110 0.1 0.3LUB-02 5.5 25.0 8.0 7.9 767 777 193 nc nc 233 nc 1.1LUB-03 <0.2 23.5 7.9 7.7 721 740 225 219 266 272 0.4 1.0LUB-04 4.2 26.0 7.9 7.8 777 792 195 nc nc 236 nc 0.9LUB-05 6.8 22.0 7.8 7.8 677 689 213 nc nc 258 nc 0.7LUB-06 3.4 26.0 8.2 8.2 876 875 117 nc nc 141 nc 1.0LUB-07 1.9 24.5 8.3 8.1 886 893 229 219 262 274 2.6 2.5LUB-08 2.6 28.0 7.8 7.6 *1,340 *1,370 118 nc nc 143 nc 0.4LUB-09 3.9 27.0 8.0 7.8 **1,950 **1,980 254 nc nc 307 nc 1.4LUB-10 <0.2 25.5 *9.0 *9.2 849 855 279 293 312 311 21.9 14.3LUB-11 1.2 26.5 7.7 7.7 694 700 171 nc nc 208 nc 0.5LUB-12 2.3 30.0 8.1 8.1 579 592 126 nc nc 152 nc 0.9LUB-13 3.5 23.5 8.1 7.9 398 393 170 nc nc 205 nc 1.2LUB-14 2.1 24.0 7.2 7.3 *1,270 *1,230 78.0 nc nc 95.0 nc 0.1LUB-15 2.9 29.0 7.5 8.0 605 635 125 nc nc 152 nc 0.2LUB-16 2.0 22.5 7.7 7.6 *1,220 *1,220 155 149 182 188 -- 0.4LUB-17 1.9 35.0 7.9 7.8 **2,210 **2,250 69.0 nc nc 83.5 nc 0.3LUB-18 1.2 24.5 7.1 6.9 598 599 120 nc nc 146 nc 0.1LUB-19 0.4 36.0 8.4 8.4 *1,580 **1,620 29.0 23.9 26.5 34.4 1.0 0.4LUB-20 3.6 28.5 7.2 7.7 *1,140 *1,120 131 nc nc 160 nc 0.1

Table 4.

Water-quality indicators in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Reporting level, benchmark type, and benchmark level as of October 1, 2008. Benchmark type: SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: USGS, 

U.S. Geological Survey; °C, degrees Celsius; mg/L, milligrams per liter; nc, not collected; na, not available; RL, reporting limit or range; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; *, value at a concentration greater than benchmark level; **, value at a concentration greater than upper benchmark level; –, not detected]
Table 4 55

GAMA well 

identification 

number

Dissolved 

oxygen, 

field

(mg/L)

(00300) 

Water 

temperature, 

field 

(°C) 

(00010)

pH, lab 

(standard 

units) 

(00403)

pH, field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm at 25°C) 

(90095)

Specific

conductance, 

field 

(μS/cm at 25°C) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3) 

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

Bicarbonate, 

field 

(mg/L) 

(63786)

Bicarbonate 2

(mg/L)

Carbonate, 

field 

(mg/L) 

(63788)

Carbonate 2

(mg/L)

Benchmark type na na SMCL-US SMCL-US SMCL-CA SMCL-CA na na na na na naBenchmark level na na <6.5 or >8.5 <6.5 or >8.5 1 900 (1,600) 1 900 (1,600) na na na na na na

[RL] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [1] [1] [1] [1] [0.1] [0.1]

CLUB grid wells (49 wells sampled)—Continued

Low-Use Basins of the Mojave and Sonoran Deserts study area—Continued 

LUB-21 2.6 28.5 *8.9 *8.9 *1,330 *1,320 40.0 nc nc 45.0 nc 1.6LUB-22 <0.2 41.0 *8.9 *8.8 *1,370 *1,420 70.0 nc nc 79.0 nc 2.9LUB-23 7.6 15.0 7.8 7.7 442 428 123 120 146 149 0.4 0.4LUB-24 1.3 23.0 7.6 7.5 852 857 156 nc nc 190 nc 0.3LUB-25 3.6 31.0 8.1 8.2 *907 *935 125 nc nc 151 nc 0.9LUB-26 3.8 24.5 7.7 7.6 *1,420 *1,430 175 166 201 212 0.8 0.5LUB-27 2.5 33.0 8.0 8.0 570 558 112 nc nc 135 nc 0.6

CLUB understanding wells (3 wells sampled)

BVU-01 2.0 27.0 8.2 8.3 445 448 88.0 nc nc 106 nc 0.8LUBU-01 2.4 27.0 8.2 8.4 565 572 165 nc nc 198 nc 1.4LUBU-02 2.9 25.5 7.9 7.8 365 367 102 nc nc 123 nc 0.5

1 The SMCL-CA for specific conductance has recommended and upper benchmark values. The upper value is shown in parentheses.2 Bicarbonate and carbonate concentrations were calculated from the laboratory alkalinity and pH values using the advanced speciation method (http://or.water.usgs.gov/alk/methods.html) with 

pK1 = 6.35, pK2 = 10.33, and pKW = 14.

Table 4. Water-quality indicators in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Reporting level, benchmark type, and benchmark level as of October 1, 2008. Benchmark type: SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations:USGS, U.S. Geological Survey; °C, degrees Celsius; mg/L, milligrams per liter; nc, not collected; na, not available; RL, reporting limit or range; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; *, value at a concentration greater than benchmark level; **, value at a concentration greater than upper benchmark level; –, not detected]
56 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed, but only samples with detections are listed. Analytes are listed in order of decreasing detection frequency in the 49 grid wells. All analytes are listed in table 3A. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting level; μg/L, micrograms per liter; na, not available; –, not detected; ≤, less than or equal to; NWIS, USGS National 

Water Information System]

Primary use or source Trihalomethane Solvent Gasoline Gasoline Trihalomethane Trihalomethane Solvent

Detections 

per well

VOC

detection 

summary 1

GAMA

well

 identification

number

Chloroform 

(Trichloromethane)

(μg/L)

(32106)

Perchloroethene

(PCE, Tetrachloroethene)

(μg/L)

(34475)

1.2.4-

trimethylbenzene

(μg/L)

(77222)

Benzene

(μg/L)

(34030)

Bromodichloromethane

(μg/L)

(32101)

Bromoform, 

(Tribromethane) 

(μg/L) 

(32104)

Trichloroethane 

(TCE)

(μg/L)

(39180)

Benchmark type MCL-US MCL-US NL-CA MCL-CA MCL-US MCL-US MCL-US

Benchmark level 2 80 5 330 1 2 80 2 80 5

[LRL or SRL] [0.04] 4 [0.02] 1 [0.56] [0.026] [0.04] [0.1] [0.022]

CLUB grid wells (49 wells sampled)

Number of wells with detections 13 4 2 1 1 1 1 17

Detection frequency (percent) 26.5 8.2 4.1 2.0 2.0 2.0 2.0 35

Total detections 25Borrego Valley study area (7 grid wells sampled)BV-03 – ≤0.01 – – – – – 0

BV-04 E0.07 – – – E0.03 – – 2

BV-07 – – 1.60 – – – – 1

Number of wells with detections 1 0 1 0 1 0 0 2

Detection frequency (percent) 14.3 0 14 0 14.3 0 0 29

Total detections 3Central Desert study area (15 grid wells sampled)CD-03 E0.05 – – – – – – 1

CD-11 E0.08 – – – – – – 1

CD-12 E0.03 – – – – 0.11 – 2

Number of wells with detections 3 0 0 0 0 1 0 3

Detection frequency (percent) 20.0 0 0 0 0 6.7 0 20

Total detections 4Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)LUB-01 E0.04 E0.03 – – – – – 2

LUB-06 E0.05 – – E0.03 – – 0.17 4

LUB-09 E0.02 – – – – – – 2

LUB-12 E0.03 – – – – – – 1
Table 5 57

Primary use or source Trihalomethane Solvent Gasoline Gasoline Trihalomethane Trihalomethane Solvent

Detections 

per well

VOC

detection 

summary 1

GAMA

well

 identification

number

Chloroform 

(Trichloromethane)

(μg/L)

(32106)

Perchloroethene

(PCE, Tetrachloroethene)

(μg/L)

(34475)

1.2.4-

trimethylbenzene

(μg/L)

(77222)

Benzene

(μg/L)

(34030)

Bromodichloromethane

(μg/L)

(32101)

Bromoform, 

(Tribromethane) 

(μg/L) 

(32104)

Trichloroethane 

(TCE)

(μg/L)

(39180)

Benchmark type MCL-US MCL-US NL-CA MCL-CA MCL-US MCL-US MCL-US

Benchmark level 2 80 5 330 1 2 80 2 80 5

[LRL or SRL] [0.04] 4 [0.02] 1 [0.56] [0.026] [0.04] [0.1] [0.022]

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)—ContinuedLUB-13 – E0.02 – – – – – 1

LUB-14 – E0.02 – – – – – 1

LUB-16 E0.02 E0.02 – – – – – 2

LUB-18 E0.07 – – – – – – 1

LUB-20 – – 0.98 – – – – 1

LUB-23 E0.02 – – – – – – 1

LUB-25 – ≤0.01 – – – – – 0

LUB-26 E0.01 – – – – – – 1

LUB-27 0.06 – – – – – – 1

Number of wells with detections 9 4 1 1 0 0 1 12

Detection frequency (percent) 33.3 14.8 3.7 3.7 0 0 3.7 44

Total detections 18

CLUB understanding wells (3 wells sampled) 4

BVU-01 E0.04 1.82 – – – – – 2

1 SRLs for acetone (all data), toluene (0.69 μg/L), and 1,2,4-trimethylbenzene (0.56 μg/L) were defined on the basis of examination of quality-control samples collected between May 2004 and 

September 2010 for the first 32 study units of the California GAMA Priority Basin Project (M.S. Fram, L.D. Olsen, and K. Belitz, U.S. Geological Survey, written commun., 2011). Detections 

of these three constituents in samples from the CLUB study unit had concentrations less than the SRLs: acetone (LUB-06: 7 μg/L), toluene (BV-07: E0.01 μg/L; LUB-01: E0.02 μg/L), and 1,2,4-trimethylbenzene (BV-03: E0.02 μg/L; CD-13: 0.24 μg/L; CD-14: E0.08 μg/L; LUB-16: E0.03 μg/L; LUB-22: E0.08 μg/L; LUB-23: 0.23 μg/L; LUB-25: 0.14 μg/L; LUB-26: 0.19 μg/L; LUB27: 0.24 μg/L) and have been reclassified as non-detections.

2 The MCL-US benchmark for trihalomethanes is for the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.3 SRL was defined based on a detection in a field blank. Values measured at concentrations less than the SRL are noted with a ≤ symbol in the USGS NWIS database and were not included in the 

calculations of detection frequencies.

4 Understanding wells were not included in statistical calculations.

Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 52 wells were analyzed, but only samples with detections are listed. Analytes are listed in order of decreasing detection frequency in the 49 grid wells. All analytes are listed in table 3A. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting level; μg/L, micrograms per liter; na, not available; –, not detected; ≤, less than or equal to; NWIS, USGS National Water Information System]
58 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table 6. Pesticides and pesticide degradates detected in samples collected for the Borrego Valley, Central Desert, and Low-Use 

Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

December 2008 to March 2010. 

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 50 wells were 

analyzed, but only samples with detections are listed. Analytes are listed in order of decreasing detection frequency in the 47 grid wells sampled. All analytes 

are listed in table 3B. GAMA well identification number: CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts 

study-area grid well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-CA, 

California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency (USEPA) maximum contaminant level; 

HAL-US, USEPA lifetime health advisory level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher degree of uncertainty; 

LRL, laboratory reporting level; μg/L, micrograms per liter; na, not available; –, not detected]

Primary use or source Herbicide Herbicide

degradate Herbicide Herbicide degradate Herbicide Insecticide 

degradate

Pesticide 

detections 

per well

Pesticide 

detection 

summary GAMA well 

identification number

Atrazine 

(μg/L) 

(39632)

Deethylatrazine 

(2-Chloro4-isopropylamino-6-aminos-triazine) 

(μg/L)

(04040)

Simazine 

(μg/L) 

(04035)

3,4-Dichloroaniline

(μg/L)

(61625)

Metolachlor 

(μg/L)

(39415)

Dieldrin 

(μg/L) 

(39381)

Benchmark type MCL-CA na MCL-US na HAL-US RSD5-US

Benchmark level 1 na 4 na 700 0.02

[LRL] [0.007] [0.014] [0.01] [0.0042] [0.014] [0.009]

CLUB grid wells (47 wells sampled) 1

Number of wells with detections 3 2 2 2 1 1 5

Detection frequency (percent) 6.4 4.3 4.3 4.3 2.1 2.1 11

Total detections 11

Central Desert study area (13 grid wells sampled) 1

CD-09 0.011 – 0.022 E0.018 E0.011 – 2

Number of wells with detections 1 0 1 1 1 0 1

Detection frequency (percent) 7.7 0 7.7 7.7 7.7 0 8

Total detections 4

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)

LUB-01 E0.007 E0.009 0.025 E0.005 – – 4

LUB-06 – – – – – E0.004 1

LUB-16 – E0.007 – – – – 1

LUB-27 E0.006 – – – – – 1

Number of wells with detections 2 2 1 1 0 1 4

Dectection frequency (percent) 7.0 7.0 3.7 3.7 0 3.7 15

Total detections 7

1Samples from CD-10 and CD-12 were ruined during sample preparation at the USGS National Water Quality Laboratory.
Table 7 59

Table 7. Perchlorate detected in the samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and 

Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010. 

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about the analyte 

given in table 3D. Samples from all 52 wells were analyzed for perchlorate, but only samples with detections are listed. GAMA well identification number:

BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins 

of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Minimum 

reporting level, benchmark type, and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-CA, California 

Department of Public Health maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; MRL, minimum reporting level; μg/L, 

micrograms per liter]

GAMA well 

identification 

number

Perchlorate

(μg/L)

(63790)

Benchmark type MCL-CA

Benchmark level 6

[MRL] [0.10]

CLUB grid wells (49 wells sampled)

Number of wells with detections 41

Detection frequency (percent) 84

CLUB Borrego Valley study area (7 grid wells sampled)

BV-01 0.19

BV-04 0.57

BV-06 0.88

BV-07 0.30

Number of wells with detections 4

Detection frequency (percent) 57

CLUB Central Desert study area (15 grid wells sampled)

CD-01 0.48

CD-02 0.59

CD-03 0.30

CD-04 0.39

CD-05 0.44

CD-06 0.19

CD-07 0.43

CD-09 0.19

CD-10 0.38

CD-11 0.52

CD-12 0.50

CD-13 0.26

CD-14 0.29

CD-15 0.59

Number of wells with detections 14

Detection frequency (percent) 93

GAMA well 

identification 

number

Perchlorate

(μg/L)

(63790)

Benchmark type MCL-CA

Benchmark level 6

[MRL] [0.10]

CLUB Low-Use Basins of the Mojave and Sonoran Deserts study 

area (27 grid wells sampled)

LUB-01 0.28

LUB-02 0.17

LUB-04 0.14

LUB-05 0.55

LUB-06 0.67

LUB-07 0.28

LUB-08 1.12

LUB-09 1.83

LUB-11 0.64

LUB-12 0.35

LUB-13 0.33

LUB-14 0.37

LUB-15 0.28

LUB-16 1.29

LUB-17 1.87

LUB-19 0.10

LUB-20 0.33

LUB-21 0.87

LUB-23 0.95

LUB-24 0.47

LUB-25 1.48

LUB-26 3.59

LUB-27 0.71

Number of wells with detections 23

Detection frequency (percent) 85

CLUB understanding wells (3 wells sampled)

BVU-01 0.27

LUBU-02 0.83
60 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 Table 8. Trace elements detected in the samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 42 wells were analyzed. Information about the analytes given in table 3E. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HAL-US, USEPA lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting level; μg/L, micrograms per liter; na, not available; –, not detected; ≤, less than or equal to; *, value at a concentration greater than benchmark level; NWIS, USGS National Water Information System; NWQL, USGS National Water Quality Laboratory; QC, quality control; BQS, USGS Branch of Quality Systems; QA, quality assurance] GAMA well identification number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01025) Cobalt (μg/L) (01035) Copper (μg/L) (01040) Iron (μg/L) (01046) Lead (μg/L) (01049) Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US Benchmark level 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 15 [LRL or SRL] 1 [1.6] [0.054] [0.06] 1 [0.36] [0.02] [4.0] [0.02] 1 [0.42] 2 [0.18] 1 [1.7] 1 [6] 1 [0.65] CLUB grid wells (39 wells sampled) Borrego Valley study area (3 grid wells sampled) BV-03 – – 0.70 25.0 – 183 E0.05 ≤0.41 ≤0.14 – 15 ≤0.09 BV-04 – – 0.76 342 – 56.0 0.03 ≤0.12 ≤0.13 2.3 ≤5 ≤0.22 BV-07 10.3 E0.03 6.2 30.0 – 113 0.02 ≤0.34 0.22 – 7 ≤0.05 Central Desert study area (9 grid wells sampled) CD-01 E2.3 – 2.9 40.0 – 97.0 0.03 3.2 ≤0.04 ≤0.72 – ≤0.15 CD-03 – – *123 13.0 – 174 E0.01 0.68 ≤0.02 ≤0.51 18 ≤0.04 CD-04 – – 5.1 14.0 – 57.0 – 0.75 ≤0.01 ≤1.3 – ≤0.43 CD-07 – – 1.1 41.0 – 60.0 0.02 17.1 ≤0.03 ≤0.81 – ≤0.12 CD-09 – – 2.9 48.0 – 42.0 E0.01 1.6 ≤0.09 ≤1.1 20 ≤0.20 CD-11 – – 0.13 46.0 – 47.0 0.12 0.65 ≤0.12 – – ≤0.07 CD-12 4.1 E0.03 6.2 5.0 – 177 E0.02 ≤0.16 ≤0.03 ≤1.1 – ≤0.33 CD-13 4.8 – 7.0 17.0 – 307 0.26 9.7 ≤0.06 2.5 – 0.90 CD-14 E2.6 – 1.6 16.0 – 39.0 0.02 2.5 ≤0.05 ≤0.75 ≤4 1.0 Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled) LUB-01 – 0.10 1.6 64.0 – 84.0 E0.01 5.7 ≤0.05 ≤0.69 40 ≤0.53 LUB-02 – 0.26 5.9 27.0 – 397 0.42 9.5 ≤0.01 – ≤2 ≤0.16 LUB-03 9.1 0.10 3.7 147 – 391 0.08 – ≤0.04 ≤0.79 22 0.82 LUB-04 – 0.41 6.4 26.0 – 423 0.45 7.4 ≤0.01 ≤0.56 8 0.86 LUB-05 – 0.08 3.3 52.0 – 105 0.04 1.2 ≤0.03 ≤1.1 18 1.7
Table 8 61

GAMA well

identification number

Aluminum 

(μg/L) 

(01106) 

Antimony 

(μg/L) 

(01095) 

Arsenic 

(μg/L) 

(01000) 

Barium 

(μg/L) 

(01005) 

Beryllium 

(μg/L) 

(01010)

Boron

(μg/L) 

(01020) 

Cadmium

(μg/L)

(01025) 

Chromium 

(μg/L) 

(01025) 

Cobalt

(μg/L) 

(01035) 

Copper 

(μg/L) 

(01040) 

Iron

(μg/L) 

(01046) 

Lead

(μg/L) 

(01049) 

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US

Benchmark level 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 15

[LRL or SRL] 1 [1.6] [0.054] [0.06] 1 [0.36] [0.02] [4.0] [0.02] 1 [0.42] 2 [0.18] 1 [1.7] 1 [6] 1 [0.65]

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)—ContinuedLUB-06 – 0.20 *39.3 27.0 – *1,350 0.17 6.0 ≤0.01 – 6 ≤0.22

LUB-07 – 0.06 7.3 13.0 – 828 0.13 2.3 – – ≤2 ≤0.21

LUB-08 – 0.07 3.4 35.0 – 719 0.04 2.7 ≤0.04 – 9 ≤0.21

LUB-09 – 0.05 6.1 61.0 – *2,670 0.04 17.6 ≤0.02 1.7 – 0.88

LUB-10 4.4 – *42.0 6.0 – *2,070 0.04 ≤0.06 ≤0.01 – – –

LUB-11 – 0.11 *10.2 58.0 – 539 0.02 0.73 ≤0.02 – 13 ≤0.07

LUB-12 5.6 E0.02 2.5 18.0 – 169 0.05 3.9 ≤0.02 ≤0.51 23 ≤0.09

LUB-13 – 0.11 6.6 49.0 – 62.0 0.02 2.6 ≤0.04 ≤0.79 6 ≤0.09

LUB-14 – – 0.6 18.0 – 203 0.06 1.7 ≤0.11 – 9 ≤0.52

LUB-15 E2.1 E0.05 4.1 79.0 – 460 0.04 2.5 ≤0.08 – 7 ≤0.20

LUB-16 – 0.07 1.8 32.0 – 175 0.02 ≤0.14 ≤0.15 ≤1.5 – ≤0.53

LUB-17 E2.0 – 6.4 69.0 E0.01 921 0.04 8.2 ≤0.12 ≤1.0 E11 ≤0.57

LUB-18 20.0 0.09 2.0 85.0 E0.01 323 E0.02 – 1.5 4.9 17 ≤0.57

LUB-19 7.9 – 3.2 30.0 – 377 0.08 0.49 ≤0.07 – – ≤0.08

LUB-20 – – 3.0 77.0 – 742 0.03 2.5 ≤0.09 ≤1.3 – ≤0.11

LUB-21 9.5 0.13 *66.2 32.0 E0.01 998 0.25 7.9 ≤0.08 – 9 ≤0.57

LUB-22 9.3 0.11 *37.5 39.0 0.01 *1,580 0.28 ≤0.10 ≤0.10 – 7 ≤0.25

LUB-23 – – 2.1 43.0 – 162 0.05 ≤0.10 ≤0.12 – 9 ≤0.04

LUB-24 – 0.13 1.8 20.0 – 71.0 E0.02 ≤0.14 0.31 ≤0.55 25 ≤0.19

LUB-25 – E0.04 4.6 42.0 – 400 0.06 18.5 ≤0.15 – 45 ≤0.07

LUB-26 – 0.18 0.58 29.0 – 299 E0.02 ≤0.16 0.42 – 16 ≤0.26

LUB-27 6.6 0.12 *16.5 95.0 – 385 0.09 11.4 ≤0.09 – ≤5 ≤0.05

Table 8. Trace elements detected in the samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 42 wells were analyzed. Information about the analytes given in table 3E. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins 

of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HAL-US, USEPA lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological 

Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting level; μg/L, micrograms per liter; na, not available; –, not detected; ≤, less than or equal to; *, value at a concentration greater than benchmark level; NWIS, USGS National Water Information System; NWQL, USGS National Water Quality Laboratory; QC, quality control; BQS, USGS Branch of Quality Systems; QA, quality assurance]
62 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 GAMA well identification number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01025) Cobalt (μg/L) (01035) Copper (μg/L) (01040) Iron (μg/L) (01046) Lead (μg/L) (01049) Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US Benchmark level 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 15 [LRL or SRL] 1 [1.6] [0.054] [0.06] 1 [0.36] [0.02] [4.0] [0.02] 1 [0.42] 2 [0.18] 1 [1.7] 1 [6] 1 [0.65] CLUB understanding wells (3 wells sampled) BVU-01 E3.3 E0.03 9.9 55.0 – 90.0 0.05 1.1 ≤0.04 ≤0.84 – ≤0.03 LUBU-01 8.3 – 5.3 26.0 – 325 0.26 5.5 – 2.8 – 2.3 LUBU-02 – 0.13 *15.0 59.0 – 309 0.07 1.6 ≤0.08 – 16 ≤0.02 Table 8. Trace elements detected in the samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 42 wells were analyzed. Information about the analytes given in table 3E. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HAL-US, USEPA lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting level; μg/L, micrograms per liter; na, not available; –, not detected; ≤, less than or equal to; *, value at a concentration greater than benchmark level; NWIS, USGS National Water Information System; NWQL, USGS National Water Quality Laboratory; QC, quality control; BQS, USGS Branch of Quality Systems; QA, quality assurance]
Table 8 63

Table 8. Trace elements detected in the samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 42 wells were analyzed. Information about the analytes given in table 3E. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins 

of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HAL-US, USEPA lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological 

Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting level; μg/L, micrograms per liter; na, not available; –, not detected; ≤, less than or equal to; *, value at a concentration greater than benchmark level; NWIS, USGS National Water Information System; NWQL, USGS National Water Quality Laboratory; QC, quality control; BQS, USGS Branch of Quality Systems; QA, quality assurance]

GAMA well 

identification number

Lithium 

(μg/L) 

(01130) 

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L)

(01060) 

Nickel

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium

(μg/L)

(22703)

Vanadium 

(μg/L) 

(01085) 

Zinc

(μg/L) 

(01090)

Benchmark type na SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US NL-CA SMCL-CA

Benchmark level na 50 40 100 50 100 4,000 2 na 30 50 5,000

[LRL or SRL] [1.0] 1 [0.2] 2 [0.32] 1 [0.36] [0.06] [0.010] [0.8] [0.04] 1 [0.11] [0.008] 1 [0.11] 1 [4.8]

CLUB grid wells (39 wells sampled)

Borrego Valley study area (3 grid wells sampled)BV-03 22.8 1.1 10.3 0.61 1.6 – 426 – 0.69 9.86 11.3 80.5BV-04 16.4 ≤0.1 5.0 0.62 2.3 0.02 642 – 0.14 0.91 18.0 ≤4.7BV-07 10.1 0.8 9.2 ≤0.35 4.1 – 460 – 1.1 0.67 44.2 5.5

Central Desert study area (9 grid wells sampled)CD-01 9.7 – 8.0 ≤0.33 0.76 – 219 – 0.89 9.60 6.0 ≤2.4

CD-03 25.1 1.3 5.4 ≤0.18 0.21 – 246 – 0.21 0.79 19.8 26.5

CD-04 10.2 E0.2 2.9 ≤0.12 0.45 – 166 – 2.2 2.67 9.2 ≤1.6

CD-07 8.2 – 11.2 ≤0.27 0.91 – 129 E0.01 0.30 2.64 14.5 ≤2.1

CD-09 24.3 0.8 2.5 0.46 0.51 – 346 – 0.79 9.44 4.2 ≤4.1

CD-11 2.8 – 37.4 1.1 0.88 – 742 – 0.21 *33.9 5.9 13.7CD-12 12.4 – 4.9 ≤0.23 1.1 – 108 E0.01 2.5 17.4 14.8 ≤2.1

CD-13 6.2 ≤0.1 *46.3 ≤0.16 0.74 – 297 – 46.8 7.19 22.8 –

CD-14 3.0 0.5 3.8 ≤0.19 0.59 – 420 – 0.41 1.49 10.1 –

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)LUB-01 14.3 1.5 2.0 0.69 0.48 – 899 – ≤0.06 1.96 9.2 10.5LUB-02 32.3 ≤0.1 *153 ≤0.15 0.67 – 252 – 0.25 8.38 19.6 ≤2.0

LUB-03 11.6 *376 19.3 0.41 0.06 0.03 846 – 0.34 15.0 2.4 27.5

LUB-04 35.5 ≤0.1 *157 ≤0.20 0.66 – 296 – 0.34 8.99 13.2 ≤4.1

LUB-05 5.9 1.2 9.5 ≤0.32 1.9 – 511 – 0.40 7.35 14.3 218
64 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 GAMA well identification number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) Vanadium (μg/L) (01085) Zinc (μg/L) (01090) Benchmark type na SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US NL-CA SMCL-CA Benchmark level na 50 40 100 50 100 4,000 2 na 30 50 5,000 [LRL or SRL] [1.0] 1 [0.2] 2 [0.32] 1 [0.36] [0.06] [0.010] [0.8] [0.04] 1 [0.11] [0.008] 1 [0.11] 1 [4.8] Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)—Continued LUB-06 43.2 0.4 *55.8 ≤0.13 0.75 – 108 – 18.0 4.94 23.4 ≤2.1 LUB-07 42.1 E0.2 *42.9 ≤0.08 0.51 – 238 – 1.3 12.6 30.0 ≤2.6 LUB-08 57.1 0.6 10.0 0.55 2.0 – 688 – 0.60 12.2 7.1 ≤2.4 LUB-09 107 ≤0.1 11.6 ≤0.21 2.8 – 1,690 – 0.30 *30.8 23.0 ≤3.2 LUB-10 18.4 3.7 16.6 ≤0.08 – – 45.0 – 13.5 0.22 0.50 – LUB-11 36.6 0.6 6.7 0.36 3.1 – 697 – 0.29 4.33 12.9 14.2 LUB-12 3.3 5.0 17.0 ≤0.30 1.3 – 349 – 13.5 5.67 21.2 ≤2.4 LUB-13 3.7 0.3 11.6 0.36 1.1 – 177 – 0.88 2.35 12.8 22.9 LUB-14 61.7 E0.6 13.8 0.73 3.2 0.05 328 – 0.19 0.50 8.6 – LUB-15 8.6 0.5 7.6 ≤0.21 0.97 – 187 – 3.3 0.40 27.4 ≤2.3 LUB-16 76.6 8.0 5.9 1.7 2.5 – 1,560 E0.01 ≤0.04 8.83 2.6 63.4 LUB-17 128 0.3 15.0 ≤0.35 6.8 E0.01 1,970 – 3.5 7.90 9.4 12.7 LUB-18 77.2 8.1 2.9 0.84 2.3 E0.01 335 – 3.8 2.52 13.7 20.1 LUB-19 23.5 ≤0.1 28.5 ≤0.25 13.2 E0.01 491 – 12.7 0.08 30.9 ≤4.7 LUB-20 21.3 – 9.8 ≤0.30 3.0 – 347 – 3.9 2.92 18.4 ≤2.5 LUB-21 191 0.7 37.1 ≤0.25 2.6 – 477 – 89.7 0.16 33.5 208 LUB-22 146 1.2 *56.7 ≤0.11 0.04 – 188 – 48.6 0.02 1.3 – LUB-23 15.0 2.0 16.7 0.85 2.6 – 324 – 0.58 3.46 5.8 237 LUB-24 10.3 3.5 5.0 2.4 0.48 – 1,230 – 0.52 1.38 1.6 ≤3.2 LUB-25 52.3 3.9 22.1 0.40 2.2 – 376 – 0.59 2.69 7.5 – LUB-26 7.2 3.7 5.8 2.8 6.2 – 903 – 0.71 14.2 3.9 148 LUB-27 48.4 E0.2 13.1 ≤0.26 1.0 – 411 – 1.3 3.63 12.9 ≤3.9 Table 8. Trace elements detected in the samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 42 wells were analyzed. Information about the analytes given in table 3E. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HAL-US, USEPA lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting level; μg/L, micrograms per liter; na, not available; –, not detected; ≤, less than or equal to; *, value at a concentration greater than benchmark level; NWIS, USGS National Water Information System; NWQL, USGS National Water Quality Laboratory; QC, quality control; BQS, USGS Branch of Quality Systems; QA, quality assurance]
Table 8 65

GAMA well 

identification number

Lithium 

(μg/L) 

(01130) 

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L)

(01060) 

Nickel

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium

(μg/L)

(22703)

Vanadium 

(μg/L) 

(01085) 

Zinc

(μg/L) 

(01090)

Benchmark type na SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US NL-CA SMCL-CA

Benchmark level na 50 40 100 50 100 4,000 2 na 30 50 5,000

[LRL or SRL] [1.0] 1 [0.2] 2 [0.32] 1 [0.36] [0.06] [0.010] [0.8] [0.04] 1 [0.11] [0.008] 1 [0.11] 1 [4.8]

CLUB understanding wells (3 wells sampled)

BVU-01 4.4 – 9.6 ≤0.19 1.3 – 171 – 4.2 0.43 67.3 8.8

LUBU-01 14.6 – *94.8 ≤0.10 0.52 – 242 – 19.4 16.8 21.7 ≤2.1

LUBU-02 15.0 1.6 11.8 ≤0.25 0.92 – 186 – 1.0 0.58 30.2 6.8

Table 8. Trace elements detected in the samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 42 wells were analyzed. Information about the analytes given in table 3E. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins 

of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HAL-US, USEPA lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological 

Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting level; μg/L, micrograms per liter; na, not available; –, not detected; ≤, less than or equal to; *, value at a concentration greater than benchmark level; NWIS, USGS National Water Information System; NWQL, USGS National Water Quality Laboratory; QC, quality control; BQS, USGS Branch of Quality Systems; QA, quality assurance]
66 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table 9. Nutrients detected in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the 

Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

December 2008 to March 2010.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 

42 wells were analyzed. Information about the analytes given in table 3F. GAMA well identification number: BV, Borrego Valley studyarea grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the 

Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. 

Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. HAL-US, 

U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-US, USEPA maximum contaminant level. Other 

abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; mg/L, 

milligram per liter; na, not available; –, not detected; *, value is at a concentration greater than benchmark level]

GAMA well

identification

number

Ammonia, 

as nitrogen

(mg/L)

(00608)

 Nitrite, as 

nitrogen

(mg/L)

(00613)

Nitrite

plus nitrate, 

as nitrogen

(mg/L)

(00631)

Total nitrogen

(ammonia + 

nitrate + nitrite + 

organic-nitrogen) 

(mg/L)

(62854)

Phosphate, 

orthophosphate

(as phosphorus)

(mg/L)

(00671)

Benchmark type HAL-US MCL-US MCL-US na na

Benchmark level 1

 24.7 1 10 na na

[LRL] [0.02] [0.002] [0.04] [0.10] [0.006]

CLUB grid wells (39 wells sampled)

Borrego Valley study area (3 grid wells sampled)

BV-03 – – 0.28 2 0.27 0.019

BV-04 – – 2.44 2.46 0.033

BV-07 – E0.001 0.99 1.01 0.013

Central Desert study area (9 grid wells sampled)

CD-01 – – 1.55 2 1.51 0.016

CD-03 – – 2.03 2.06 0.025

CD-04 – – 1.41 1.42 0.018

CD-07 – – 2.62 2.68 0.027

CD-09 – – 2.20 2.25 0.027

CD-11 – – 1.24 1.30 0.027

CD-12 – E0.001 1.90 2.00 0.014

CD-13 – – 1.63 1.91 0.009

CD-14 – E0.001 1.19 1.20 0.009

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)

LUB-01 – – *12.1 12.3 0.011

LUB-02 – – 0.41 2 0.39 0.022

LUB-03 0.04 0.011 0.09 2 E0.10 0.051

LUB-04 – – 0.38 2 0.36 0.017

LUB-05 – – 1.03 1.04 0.012

LUB-06 – 0.014 3.60 2 3.55 0.015

LUB-07 – – 1.57 2 1.50 0.011

LUB-08 – – 4.94 4.96 0.029

LUB-09 – – 5.11 5.22 0.018

LUB-10 0.16 – – 0.21 0.096

LUB-11 – E0.001 4.10 2 4.06 0.017

LUB-12 – 0.006 1.50 1.56 1.35

LUB-13 – – 0.92 0.94 0.014

LUB-14 – – 0.60 2 0.58 0.024

LUB-15 – – 2.06 2.09 0.013
Table 9 67

GAMA well

identification

number

Ammonia, 

as nitrogen

(mg/L)

(00608)

 Nitrite, as 

nitrogen

(mg/L)

(00613)

Nitrite

plus nitrate, 

as nitrogen

(mg/L)

(00631)

Total nitrogen

(ammonia + 

nitrate + nitrite + 

organic-nitrogen) 

(mg/L)

(62854)

Phosphate, 

orthophosphate

(as phosphorus)

(mg/L)

(00671)

Benchmark type HAL-US MCL-US MCL-US na na

Benchmark level 1

 24.7 1 10 na na

[LRL] [0.02] [0.002] [0.04] [0.10] [0.006]

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)—Continued

LUB-16 – – 0.35 0.42 0.009

LUB-17 – – 1.35 1.41 E0.008

LUB-18 – – 0.25 0.28 0.160

LUB-19 – – 1.22 2 1.18 E0.007

LUB-20 – – 1.71 1.77 0.018

LUB-21 – 0.005 4.51 4.68 0.008

LUB-22 0.093 E0.001 – 0.21 0.010

LUB-23 – – 1.47 1.48 0.014

LUB-24 – E0.002 0.65 0.66 0.011

LUB-25 – 0.002 3.03 2 3.02 E0.008

LUB-26 – – 4.55 2 4.32 0.010

LUB-27 – – 2.69 2.72 0.021

CLUB understanding wells (3 wells sampled)

BVU-01 – – 2.02 2.07 0.016

LUBU-01 – – 0.33 0.34 0.011

LUBU-02 – 0.004 2.48 2.52 0.042

1

 The HAL-US is 30 mg/L “as ammonia.” To facilitate comparison to the analytical results, we have converted and reported this HAL-US as 

24.7 mg/L “as nitrogen.”

2

 Total nitrogen in these samples is less than the sum of the filtered nitrogen analytes, but falls within the U.S. Geological Survey National 

Water Quality Laboratory acceptance criteria of a 10 percent relative percent difference.

Table 9. Nutrients detected in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the 

Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

December 2008 to March 2010.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 

42 wells were analyzed. Information about the analytes given in table 3F. GAMA well identification number: BV, Borrego Valley studyarea grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the 

Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding 

well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-US, USEPA maximum contaminant 

level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting 

level; mg/L, milligram per liter; na, not available; –, not detected; *, value is at a concentration greater than benchmark level]
68 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 42 wells were analyzed. Information about the analytes given in table 3G. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; LRL, laboratory reporting level; mg/L, milligrams per liter; SiO2, silicon dioxide; E, estimated or having a higher degree of uncertainty; na, not available; –, not detected; *, value is at a concentration greater than recommended benchmark level, **, value is at a concentration greater than upper benchmark level; BQS, USGS Branch of Quality Systems; NWQL, USGS National 

Water Quality 

Laboratory; QA, quality assurance]

GAMA well 

identification

number

Bromide 

(mg/L)

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride

(mg/L)

(00940) 

Fluoride 

(mg/L) 

(00950) 

Iodide 

(mg/L) 

(71865)

Magnesium

(mg/L)

(00925) 

Potassium 

(mg/L)

(00935) 

Sodium

(mg/L)

 (00930) 

Sulfate

(mg/L)

(00945) 

Silica 

(as SiO2) 

(mg/L)

 (00955) 

TDS

(mg/L)

(70300)

Benchmark type na na SMCL-CA MCL-CA na na na na SMCL-CA na SMCL-CA

Benchmark level na na 1 250 (500) 2 na na na na 1 250 (500) na 1 500 (1,000)

[LRL] [0.02] [0.044] [0.12] [0.08] [0.002] [0.016] [0.064] [0.12] [0.18] [0.058] [10]

CLUB grid wells (39 wells sampled) 

Borrego Valley study area (3 grid wells sampled)BV-03 0.24 103 61.3 0.82 – 19.6 11.6 103 *299 26.7 *734

BV-04 0.52 63.5 158 0.41 – 11.7 5.93 95.9 25.7 32.4 *512

BV-07 0.50 20.0 135 0.41 0.019 0.67 2.58 168 169 12.2 *571

Central Desert study area (9 grid wells sampled)CD-01 0.14 37.3 19.1 0.78 – 6.2 2.42 47.9 35.6 22.7 271

CD-03 0.04 14.0 8.1 1.6 E0.002 1.9 1.69 33.4 14.1 37.5 161

CD-04 0.05 19.9 8.4 0.58 – 2.2 1.28 17.7 8.6 33.2 139

CD-07 0.10 15.4 14.7 0.64 – 3.7 2.14 43.3 22.6 22.3 199

CD-09 0.20 38.8 49.5 0.30 0.003 5.4 1.43 30.4 31.3 30.5 254

CD-11 0.11 86.3 17.5 1.1 – 31.6 7.74 47.8 163 21.3 *553

CD-12 0.10 7.2 15.9 0.96 – 0.08 1.41 58.0 29.6 17.2 186

CD-13 0.13 13.6 19.8 *7.1 0.015 2.5 2.72 79.2 79.2 14.8 281

CD-14 0.11 15.9 31.2 0.54 0.006 0.37 3.08 53.0 42.5 15.6 203

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)LUB-01 0.35 106 123 0.17 0.006 15.8 2.33 61.5 134 26.5 *588

LUB-02 0.17 22.1 67.8 1.4 0.003 6.0 2.53 149 85.1 25.4 466

LUB-03 0.13 62.6 26.4 0.74 0.068 11.4 2.08 83.6 120 28.7 475

LUB-04 0.18 26.7 70.0 1.2 0.003 6.6 2.83 134 90.5 24.7 472

LUB-05 0.21 44.9 30.0 0.66 – 36.8 4.75 46.0 104 28.1 443
Table 10 69

GAMA well 

identification

number

Bromide 

(mg/L)

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride

(mg/L)

(00940) 

Fluoride 

(mg/L) 

(00950) 

Iodide 

(mg/L) 

(71865)

Magnesium

(mg/L)

(00925) 

Potassium 

(mg/L)

(00935) 

Sodium

(mg/L)

 (00930) 

Sulfate

(mg/L)

(00945) 

Silica 

(as SiO2) 

(mg/L)

 (00955) 

TDS

(mg/L)

(70300)

Benchmark type na na SMCL-CA MCL-CA na na na na SMCL-CA na SMCL-CA

Benchmark level na na 1 250 (500) 2 na na na na 1 250 (500) na 1 500 (1,000)

[LRL] [0.02] [0.044] [0.12] [0.08] [0.002] [0.016] [0.064] [0.12] [0.18] [0.058] [10]

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)—Continued LUB-06 0.33 15.7 76.5 *8.5 0.017 1.7 10.3 158 145 65.2 *590

LUB-07 0.26 8.1 51.0 *8.5 0.027 2.3 3.08 188 111 26.1 *556

LUB-08 0.25 67.4 248 1.0 0.007 10.7 9.35 186 137 43.6 *798

LUB-09 0.52 21.9 *277 1.2 0.017 23.2 8.51 365 245 30.5 **1,170

LUB-10 0.12 1.3 73.7 *5.0 0.069 0.10 1.95 196 35.0 65.2 *564

LUB-11 0.32 40.2 45.8 0.33 0.004 13.9 6.13 88.6 89.1 36.6 438

LUB-12 0.30 19.7 40.2 0.76 0.004 4.5 4.93 98.5 91.8 14.5 354

LUB-13 0.04 22.9 8.2 0.71 – 11.2 1.78 43.5 25.8 20.4 247

LUB-14 0.63 92.0 142 0.59 E0.001 26.3 9.28 136 *327 39.3 *836

LUB-15 0.26 21.0 82.8 1.5 0.003 3.3 4.36 93.8 31.4 29.8 356

LUB-16 0.11 84.7 112 0.44 0.004 33.6 4.30 125 *295 14.6 *796

LUB-17 0.53 62.1 **555 1.9 0.013 1.1 5.77 367 141 19.4 **1,220

LUB-18 0.33 37.8 81.5 1.6 0.019 8.4 1.83 64.2 38.3 39.1 369

LUB-19 0.56 44.1 *271 0.72 0.010 1.8 5.55 244 *295 13.2 *953

LUB-20 0.61 42.9 199 0.85 0.012 11.5 5.31 163 85.5 41.9 *675

LUB-21 0.48 19.5 203 *12.6 0.019 0.12 1.50 225 213 17.8 *763

LUB-22 0.29 8.0 226 *9.6 0.069 0.16 1.56 251 213 30.6 *805

LUB-23 0.22 36.5 40.1 *2.9 E0.002 6.9 1.75 39.5 26.9 33.3 304

LUB-24 0.10 96.0 12.8 0.45 – 39.4 4.09 27.4 *292 29.7 *637

LUB-25 0.35 16.7 160 *3.2 0.005 5.2 2.63 159 70.1 24.2 *542

LUB-26 1.0 128 167 0.63 0.008 28.7 3.17 122 *292 26.4 *928

LUB-27 0.13 20.5 62.1 *3.6 0.004 4.1 5.54 81.3 46.8 39.7 356

Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 42 wells were analyzed. Information about the analytes given in table 3G. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: USGS, U.S. 

Geological Survey; LRL, laboratory reporting level; mg/L, milligrams per liter; SiO2, silicon dioxide; E, estimated or having a higher degree of uncertainty; na, not available; –, not detected; *, value is at a 

concentration greater than recommended benchmark level, **, value is at a concentration greater than upper benchmark level; BQS, USGS Branch of Quality Systems; NWQL, USGS National Water Quality 

Laboratory; QA, quality assurance]
70 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 GAMA well identification number Bromide (mg/L) (71870) Calcium (mg/L) (00915) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Iodide (mg/L) (71865) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) Silica (as SiO2) (mg/L) (00955) TDS (mg/L) (70300) Benchmark type na na SMCL-CA MCL-CA na na na na SMCL-CA na SMCL-CA Benchmark level na na 1 250 (500) 2 na na na na 1 250 (500) na 1 500 (1,000) [LRL] [0.02] [0.044] [0.12] [0.08] [0.002] [0.016] [0.064] [0.12] [0.18] [0.058] [10] CLUB understanding wells (3 wells sampled) BVU-01 0.20 15.0 44.3 0.43 E0.002 1.9 3.02 71.4 46.9 16.6 271 LUBU-01 0.14 15.2 22.0 *5.6 0.031 3.2 2.45 105 70.5 17.4 347 LUBU-02 0.12 17.2 20.5 0.60 E0.002 2.8 8.29 47.5 35.9 71.5 289

1 The SMCL-CAs for chloride, sulfate, and TDS have recommended and upper bechmark values. The upper value is shown in parentheses.

Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 42 wells were analyzed. Information about the analytes given in table 3G. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: USGS, U.S. 

Geological Survey; LRL, laboratory reporting level; mg/L, milligrams per liter; SiO2, silicon dioxide; E, estimated or having a higher degree of uncertainty; na, not available; –, not detected; *, value is at a 

concentration greater than recommended benchmark level, **, value is at a concentration greater than upper benchmark level; BQS, USGS Branch of Quality Systems; NWQL, USGS National 

Water Quality 

Laboratory; QA, quality assurance]
Table 12 71

GAMA well 

identification 

number

Chromium

(μg/L)

Cr-VI

(μg/L) 

Benchmark type MCL-CA na

Benchmark level 50 na

[MDL] [1] [1]

CLUB grid wells (7 wells sampled)

Borrego Valley study area (3 grid wells sampled)

CD-01 3.0 2.3

CD-03 E0.6 E0.5

CD-04 E0.6 E0.6

Low-Use Basins of the Mojave and Sonoran Deserts study area 

(4 grid wells sampled)

LUB-01 6.4 5.3

LUB-03 – –

LUB-07 2.1 1.9

LUB-10 – –

Table 11. Species of inorganic chromium detected in samples 

collected for the Borrego Valley, Central Desert, and Low-Use 

Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, 

December 2008. 

[Data in this table was generated at the USGS Trace Metals Laboratory, 

Boulder, Colorado, using research methods and are not stored in the USGS 

National Water Information System database. Information about the analytes 

given in table 3H. Samples from 7 slow wells in December 2008 were 

analyzed. GAMA well identification number: CD, Central Desert studyarea grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts 

study-area grid well. Method detection limit, benchmark type, and benchmark 

level as of October 1, 2008. Benchmark type: Maximum 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. MCL-CA, California Department of Public Health 

maximum contaminant level. Other abbreviations: USGS, U.S. Geological 

Survey; Cr-VI, hexavalent chromium, chromium-VI; MDL, method detection 

limit; μg/L, micrograms per liter; na, not available; E, estimated or having a 

high degree of uncertianty; –, not detected] GAMA well 

identification 

number

Cr-VI

(μg/L)

Benchmark type na

Benchmark level na

[MDL] [1]

CLUB grid wells (16 wells sampled)

Borrego Valley study area (3 grid wells sampled)

BV-01 3.0

BV-03 E0.6

BV-04 E0.6

Central Desert study area (6 grid wells sampled)

CD-07 18.0

CD-09 1.9

CD-11 –

CD-12 –

CD-13 10.0

CD-14 2.4

Low-Use Basins of the Mojave and Sonoran Deserts study area 

(7 grid wells sampled)

LUB-13 3.1

LUB-18 –

LUB-19 –

LUB-20 2.8

LUB-23 –

LUB-26 –

LUB-27 13.0

CLUB understanding wells (1 well sampled)

BVU-01 1.1

Table 12. Hexavalent chromium (chromium-VI, Cr-VI) 

detected in samples collected for the Borrego Valley, 

Central Desert, and Low-Use Basins of the Mojave and 

Sonoran Deserts (CLUB) Groundwater Ambient Monitoring 

and Assessment (GAMA) study, California, October 2009 to 

March 2010. 

[The five-digit USGS parameter code below the constituent name is used 

to uniquely identify a specific constituent or property. Data in this table 

were generated at TestAmerica Laboratories, Inc., Irvine, California. 

Samples from 17 slow wells were analyzed. Information about the 

analyte given in table 3I. GAMA well identification number: BV, 

Borrego Valley study-area grid well; BVU, Borrego Valley study-area 

understanding well; CD, Central Desert study-area grid well; LUB, LowUse Basins of the Mojave and Sonoran Deserts study-area grid well. 

Method detection limit as of October 5, 2009. Other abbreviations: 

USGS, U.S. Geological Survey; na, not available; MDL, method 

detection limit; μg/L, micrograms per liter; –, not detected]
72 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table 13. Results for analyses of stable isotope ratios, tritium activity, and carbon-14 abundance detected in samples 

collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about 

the analytes given in table 3J. Samples from all 52 wells were analyzed for stable isotopes of hydrogen and oxygen in water and tritium activities. 

Samples from 51 wells were analyzed for stable isotopes of carbon in dissolved inorganic carbon and carbon-14 abundance. Stable isotope ratios 

are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard 

reference material. Tritium values less than the sample-specific critical level (ssLC) are reported as non-detections (–). GAMA well identification 

number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; 

LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts studyarea understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL–CA, California Department of Public Health maximum contaminant level. Other abbreviations: USGS, U.S. Geological 

Survey; H, hydrogen; O, oxygen; C, carbon; CSU, 1-sigma combined standard uncertainty; pCi/L, picocuries per liter; –, not detected; ±, plus or 

minus; na, not available]

GAMA well 

identification 

number

δ2H

(per mil) 

(82082)

δ18O

(per mil) 

(82085)

Tritium 

(pCi/L) 

(07000)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent 

modern) 

(49933)

Benchmark type na na MCL–CA

20,000

na na

Benchmark level na na na na

Result ± CSU ssLC

CLUB grid wells (49 wells sampled)

Borrego Valley study area (7 grid wells sampled)

BV–01 –56.90 –8.17 0.4 ± 0.32 0.32 –9.48 42.41

BV–02 –56.40 –8.34 3.8 ± 0.35 0.32 –10.64 112.6

BV–03 –60.90 –8.73 2.5 ± 0.32 0.32 –13.10 99.29

BV–04 –64.00 –8.90 – 0.32 –12.78 79.08

BV–05 –59.90 –8.83 0.5 ± 0.32 0.32 –11.30 27.45

BV–06 –73.10 –8.57 – 0.32 –10.94 4.390

BV–07 –67.30 –9.45 – 0.35 na 1 na 1

Central Desert study area (15 grid wells sampled)

CD–01 –83.80 –11.4 – 0.35 –8.81 85.11

CD–02 –82.30 –11.0 – 0.45 –9.44 84.73

CD–03 –78.70 –11.1 4.5 ± 0.38 0.35 –12.13 75.81

CD–04 –80.60 –11.5 2.8 ± 0.45 0.41 –12.40 87.65

CD–05 –81.60 –11.5 0.5 ± 0.45 0.45 –11.85 79.42

CD–06 –78.70 –11.1 4.4 ± 0.45 0.38 –10.50 92.91

CD–07 –77.80 –11.0 – 0.32 –11.10 59.77

CD–08 –89.50 –11.9 0.5 ± 0.32 0.32 –10.03 12.69

CD–09 –73.90 –9.98 6.9 ± 0.41 0.32 –10.92 91.04

CD–10 –80.50 –11.2 2.5 ± 0.35 0.32 –9.99 90.55

CD–11 –73.50 –10.6 4.6 ± 0.41 0.35 –12.27 107.1

CD–12 –77.00 –10.7 – 0.32 –12.21 26.62

CD–13 –83.40 –11.3 – 0.32 –9.59 31.86

CD–14 –83.10 –11.3 – 0.32 –11.03 26.31

CD–15 –82.20 –11.3 – 0.32 –8.52 54.81

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)

LUB–01 –69.00 –8.67 2.7 ± 0.38 0.35 –9.23 45.07

LUB–02 –78.30 –10.9 – 0.35 –6.74 21.29

LUB–03 –82.70 –11.1 0.7 ± 0.38 0.38 –11.66 50.48

LUB–04 –78.50 –10.9 – 0.38 –6.82 19.27

LUB–05 –88.50 –11.9 – 0.38 –9.24 60.23
Table 13 73

GAMA well 

identification 

number

δ2H

(per mil) 

(82082)

δ18O

(per mil) 

(82085)

Tritium 

(pCi/L) 

(07000)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent 

modern) 

(49933)

Benchmark type na na MCL–CA

20,000

na na

Benchmark level na na na na

Result ± CSU ssLC

Low-Use Basins of the Mojave and Sonoran Deserts study area (27 grid wells sampled)—Continued

LUB–06 –93.40 –11.4 0.5 ± 0.38 0.35 –8.64 22.24

LUB–07 –95.90 –11.9 – 0.35 –5.82 6.020

LUB–08 –97.50 –12.4 – 0.35 –8.31 8.220

LUB–09 –85.90 –10.6 – 0.38 –3.27 22.04

LUB–10 –69.10 –9.49 – 0.35 –7.30 14.51

LUB–11 –102.0 –13.1 – 0.35 –9.33 6.820

LUB–12 –90.20 –11.9 – 0.35 –9.97 25.31

LUB–13 –89.70 –12.4 – 0.32 –8.85 15.90

LUB–14 –65.00 –9.17 – 0.32 –12.80 56.20

LUB–15 –73.10 –10.2 – 0.32 –10.13 31.76

LUB–16 –94.30 –11.4 17.8 ± 0.67 0.32 –7.89 89.60

LUB–17 –54.40 –7.26 – 0.32 –8.52 9.440

LUB–18 –57.30 –8.27 1.2 ± 0.32 0.32 –14.97 89.61

LUB–19 –67.50 –8.55 – 0.32 –10.30 30.84

LUB–20 –73.00 –10.2 – 0.32 –10.41 34.20

LUB–21 –79.80 –10.6 – 0.32 –10.07 14.74

LUB–22 –73.70 –9.69 – 0.32 –5.43 3.040

LUB–23 –70.80 –9.78 0.3 ± 0.35 0.35 –9.88 53.99

LUB–24 –88.00 –12.1 0.6 ± 0.35 0.35 –6.46 4.230

LUB–25 –79.50 –10.5 0.6 ± 0.32 0.32 –8.11 9.790

LUB–26 –75.20 –10.1 3.9 ± 0.41 0.35 –8.98 99.20

LUB–27 –83.70 –11.4 – 0.35 –8.37 10.44

CLUB understanding wells (3 wells sampled)

BVU–01 –70.40 –9.73 – 0.32 –11.27 18.51

LUBU–01 –79.40 –11.1 – 0.38 –10.33 38.49

LUBU–02 –98.30 –12.7 – 0.35 –9.48 18.50

1

 Sample bottle broken during shipment to the laboratory. 

Table 13. Results for analyses of stable isotope ratios, tritium activity, and carbon-14 abundance detected in samples 

collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about 

the analytes given in table 3J. Samples from all 52 wells were analyzed for stable isotopes of hydrogen and oxygen in water and tritium activities. 

Samples from 51 wells were analyzed for stable isotopes of carbon in dissolved inorganic carbon and carbon-14 abundance. Stable isotope ratios 

are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard 

reference material. Tritium values less than the sample-specific critical level (ssLC) are reported as non-detections (–). GAMA well identification 

number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; 

LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts studyarea understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL–CA, California Department of Public Health maximum contaminant level. Other abbreviations: USGS, U.S. Geological 

Survey; H, hydrogen; O, oxygen; C, carbon; CSU, 1-sigma combined standard uncertainty; pCi/L, picocuries per liter; –, not detected; ±, plus or 

minus; na, not available]
74 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

GAMA well 

identification 

number

Radon-222 

(pCi/L) 

(82303)

Result ± CSU ssLC

Benchmark type Proposed MCL-US

Benchmark level 4,000

CLUB Grid wells (22 wells sampled) 1

Borrego Valley study area (3 grid wells sampled)

BV-03 390 ± 26 13

BV-04 175 ± 15 13

BV-07 600 ± 36 12

Central Desert study area (8 grid wells sampled)1

CD-01 630 ± 38 12

CD-03 1,090 ± 61 10

CD-04 1,700 ± 95 12

CD-07 510 ± 32 12

CD-09 1,080 ± 61 11

CD-11 810 ± 47 11

CD-12 810 ± 47 13

CD-14 670 ± 40 12

Table 14A. Radon-222 detected in samples collected for the Borrego Valley , Central Desert, and Low-Use Basins of the Mojave and 

Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010. 

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 23 slow wells 

were analyzed. Information about the analytes given in table 3J. GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego 

Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid 

well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-US, U.S. Environmental 

Protection Agency maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; CSU, combined standard uncertainty; pCi/L, picocuries 

per liter; ssLC, sample-specific critical level; ±, plus or minus]

GAMA well 

identification 

number

Radon-222 

(pCi/L) 

(82303)

Result ± CSU ssLC

Benchmark type Proposed MCL-US

Benchmark level 4,000

Low-Use Basins of the Mojave and Sonoran Deserts study area 

(11 grid wells sampled)

LUB-01 400 ± 26 13

LUB-03 570 ± 35 13

LUB-07 830 ± 48 11

LUB-10 1,540 ± 86 12

LUB-13 660 ± 39 11

LUB-18 240 ± 19 14

LUB-19 270 ± 20 13

LUB-20 340 ± 22 11

LUB-23 1,400 ± 79 15

LUB-26 760 ± 45 14

LUB-27 490 ± 30 11

CLUB understanding wells (1 well sampled)

BVU-01 330 ± 22 12

1

 Sample from CD-13 was not collected.
Table 14B 75

GAMA well 

identification 

number

Radium-226

(pCi/L) 

(09511)

Radium-228

(pCi/L) 

(81366)

Result ± CSU ssLC Result ± CSU ssLC

Benchmark type MCL-US MCL-US

Benchmark level 1

 5 1 5

CLUB grid wells (22 wells sampled) 1

Borrego Valley study area (3 grid wells sampled)

BV-03 0.08 ± 0.011 0.013 0.55 ± 0.085 0.17

BV-04 0.07 ± 0.015 0.017 – 0.20

BV-07 0.036 ± 0.011 0.016 0.29 ± 0.13 0.20

Central Desert study area (8 grid wells sampled)

CD-01 0.048 ± 0.013 0.015 0.82 ± 0.11 0.22

CD-03 0.103 ± 0.017 0.014 0.48 ± 0.098 0.22

CD-04 0.097 ± 0.016 0.014 – 0.27

CD-07 0.068 ± 0.011 0.010 – 0.18

CD-09 0.188 ± 0.021 0.017 0.27 ± 0.12 0.24

CD-11 0.09 ± 0.016 0.016 0.57 ± 0.12 0.23

CD-12 0.035 ± 0.012 0.015 – 0.18

CD-13 0.0331 ± 0.0084 0.015 – 0.18

CD-14 0.05 ± 0.01 0.016 – 0.17

Low-Use Basins of the Mojave and Sonoran Deserts study area (11 grid wells sampled)

LUB-01 0.035 ± 0.01 0.014 – 0.20

LUB-03 0.114 ± 0.016 0.011 0.344 ± 0.092 0.21

LUB-07 0.04 ± 0.013 0.015 – 0.21

LUB-10 0.018 ± 0.011 0.015 – 0.22

LUB-13 0.067 ± 0.015 0.016 – 0.17

LUB-18 0.137 ± 0.016 0.014 – 0.20

LUB-19 0.058 ± 0.011 0.015 0.244 ± 0.096 0.22

LUB-20 0.085 ± 0.016 0.017 – 0.20

LUB-23 0.114 ± 0.019 0.016 0.78 ± 0.14 0.18

LUB-26 0.088 ± 0.013 0.013 0.355 ± 0.077 0.16

CLUB understanding wells (1 well sampled)

BVU-01 0.03 ± 0.01 0.015 0.26 ± 0.13 0.26

1

 The MCL-US benchmark for radium is the sum of radium-226 and radium-228. 

Table 14B. Radium isotopes detected in samples collected for the Borrego Valley, Central Desert, 

and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, December 2008 to March 2010. 

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from the 24 slow wells were analyzed. Information about the analytes given in table 3J. Values less than the samplespecific critical level (ssLC) are reported as non-detections. GAMA well identification number: BV, Borrego Valley study-area 

grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert study-area grid well; LUB, Low-Use Basins 

of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran Deserts study-area 

understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-US, U.S. Environmental Protection Agency maximum contaminant level. 

Other abbreviations: USGS, U.S. Geological Survey; CSU, combined standard uncertainty; pCi/L, picocuries per liter; ±, plus 

or minus; –, not detected]
76 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table 14C. Gross alpha and beta radioactivity detected in samples collected for the Borrego Valley, Central Desert, and Low-Use 

Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

December 2008 to March 2010. 

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from the 24 slow 

wells were analyzed. Information about the analytes given in table 3J. The reference nuclide for measurement of gross alpha is thorium-230, and the reference 

nuclide for measurement of gross beta is cesium-137. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections. 

GAMA well identification number: BV, Borrego Valley study-area grid well; BVU, Borrego Valley study-area understanding well; CD, Central Desert 

study-area grid well; LUB, Low-Use Basins of the Mojave and Sonoran Deserts study-area grid well; LUBU, Low-Use Basins of the Mojave and Sonoran 

Deserts study-area understanding well. Benchmark type and benchmark level as of October 1, 2008. Benchmark type: Maximum 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. MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; CSU, 

1-sigma combined standard uncertainty; pCi/L, picocuries per liter; –, not detected; ±, plus or minus; *, value is at a concentration greater than benchmark 

level]

GAMA well 

identification

number

Gross alpha

radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha 

radioactivity, 

30-day count 

(pCi/L)

(62639)

Gross beta 

radioactivity, 

72-hour count 

(pCi/L) 

(62642)

Gross beta 

radioactivity, 

30-day count 

(pCi/L) 

(62645)

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

Benchmark type MCL-US MCL-US MCL-CA MCL-CA

Benchmark level 15 15 50 50

CLUB grid wells (23 wells sampled)

Borrego Valley study area (3 grid wells sampled)

BV-03 9.4 ± 1.7 1.2 6.3 ± 1.5 1.3 1 10.7 ± 0.76 0.51 21.4 ± 1.4 0.84

BV-04 – 1.4 – 1.2 5.8 ± 0.72 0.89 5.35 ± 0.71 0.91

BV-07 2.54 ± 0.89 0.97 – 0.94 2.61 ± 0.57 0.83 1.87 ± 0.56 0.83

Central Desert study area (9 grid wells sampled)

CD-01 12.7 ± 1.7 0.83 8.2 ± 1.2 0.60 4.76 ± 0.45 0.46 6.27 ± 0.52 0.46

CD-03 3.2 ± 1.0 1.3 1.21 ± 0.81 1.2 1.99 ± 0.34 0.48 2.12 ± 0.35 0.48

CD-04 3.92 ± 0.68 0.46 4.33 ± 0.75 0.60 1.46 ± 0.31 0.43 2.19 ± 0.46 0.71

CD-07 7.0 ± 1.0 0.51 3.42 ± 0.83 0.62 2.85 ± 0.38 0.48 3.14 ± 0.52 0.68

CD-09 10.8 ± 1.7 1.4 3.5 ± 1.2 1.5 1.97 ± 0.46 0.66 3.75 ± 0.51 0.66

CD-11 * 28.7 ± 3.7 1.2 14.4 ± 2.3 1.4 8.32 ± 0.68 0.66 17.0 ± 1.2 0.86

CD-12 * 20.8 ± 2.4 0.36 * 21.0 ± 2.5 1.2 1.09 ± 0.33 0.46 6.09 ± 0.51 0.47

CD-13 10.5 ± 1.4 0.64 9.1 ± 1.3 0.60 3.17 ± 0.48 0.65 3.67 ± 0.44 0.52

CD-14 2.23 ± 0.51 0.43 2.23 ± 0.51 0.46 2.43 ± 0.36 0.48 2.74 ± 0.34 0.43

Low-Use Basins of the Mojave and Sonoran Deserts study area (11 grid wells sampled)

LUB-01 – 2.2 – 1.5 1.64 ± 0.39 0.58 2.09 ± 0.50 0.75

LUB-03 * 17.3 ± 2.5 1.3 13.5 ± 2.0 1.2 3.44 ± 0.63 0.82 5.21 ± 0.94 1.4

LUB-07 1 10.5 ± 2.1 1.9 14.3 ± 2.4 1.7 3.11 ± 0.40 0.48 6.24 ± 0.65 0.83

LUB-10 3.0 ± 1.4 2.0 – 1.5 3.26 ± 0.42 0.54 0.64 ± 0.33 0.53

LUB-13 4.72 ± 0.85 0.49 2.02 ± 0.59 0.60 2.5 ± 0.40 0.54 2.03 ± 0.33 0.45

LUB-18 5.0 ± 1.0 0.75 3.65 ± 0.88 0.73 2.49 ± 0.48 0.66 2.28 ± 0.48 0.67

LUB-19 – 1.6 – 1.6 5.4 ± 0.62 0.83 4.47 ± 0.51 0.60

LUB-20 4.0 ± 1.2 1.3 3.3 ± 1.2 1.3 4.3 ± 0.52 0.67 6.4 ± 0.53 0.49

LUB-23 13.4 ± 1.8 0.55 4.9 ± 0.9 0.66 1.88 ± 0.39 0.54 2.68 ± 0.41 0.54

LUB-26 1 * 19.1 ± 3.1 1.9 13.7 ± 2.6 1.9 1 4.31 ± 0.55 0.68 7.41 ± 0.68 0.68

LUB-27 6.6 ± 1.1 0.54 5.6 ± 0.99 0.73 4.96 ± 0.66 0.87 5.5 ± 0.58 0.74

CLUB understanding wells (1 well sampled)

BVU-01 0.7 ± 0.44 0.59 – 1.3 2.67 ± 0.42 0.58 2.6 ± 0.37 0.49

1

 72-hour holding time exceeded by 4 to 7 days. A delay in the counting by the laboratory may result in lower activities than may have been observed for 

these analytes if the count had been performed within the 72-hour time period
Appendix 77

Appendix 

This appendix includes discussions of the methods used 

to collect and analyze groundwater samples and to report the 

resulting water-quality data. These methods were selected to 

obtain representative samples of the groundwater from each 

well and to minimize the potential for contamination of the 

samples or bias in the data. Procedures used to collect and 

assess QC data, and the results of the QC assessments also 

are discussed. 

In the CLUB study unit, groundwater samples were 

collected and QA/QC procedures were implemented by 

using standard and modified USGS protocols from the 

NAWQA Program (Koterba and others, 1995), the NFM (U.S. 

Geological Survey, variously dated), and protocols described 

by Shelton and others (2001) and Wright and others (2005). 

The QA plan followed by the NWQL, the primary laboratory 

used to analyze samples for this study, is described in Maloney 

(2005) and Pirkey and Glodt (1998). 

Sample Collection and Analysis

Prior to sampling, each well was pumped continuously 

to purge at least three casing-volumes of water from the well 

(Wilde and others, 1999). Wells were sampled using Teflon®

tubing with brass and stainless-steel fittings attached to a 

sampling point on the well discharge pipe as close to the well 

head as possible. The sampling point was located upstream 

from water-storage tanks and upstream from the well-head 

treatment system (if a system existed). If a chlorinating system 

was attached to the well, the chlorinator was shut off, when 

possible, before the well was purged and sampled, in order 

to clear all chlorine out of the system. The absence of free 

chlorine was verified using a Hach® field test kit. For the 

fast schedule, samples were collected at the well head using 

a foot-long length of Teflon® tubing. For the slow schedule, 

the samples were either collected in the same manner as the 

fast schedule or collected inside an enclosed chamber located 

inside a mobile laboratory and connected to the well head 

by a 10–50 ft length of the Teflon® tubing (Lane and others, 

2003). All fittings and lengths of tubing were cleaned between 

samples (Wilde, 2004).

For the field measurements, groundwater was pumped 

through a flow-through chamber (that was attached to 

the sampling point) fitted with a multi-probe meter that 

simultaneously measures the field water-quality indicators—

dissolved oxygen, temperature, pH, and specific conductance. 

Field measurements were made in accordance with protocols 

in the NFM (Radtke and others, 2005; Wilde and Radtke, 

2005; Lewis, 2006; Wilde, 2006; Wilde and others, 2006). 

All sensors on the multi-probe meter were calibrated daily. 

Measured temperature, dissolved oxygen, pH, and 

specific-conductance values were recorded at 

5-minute (min) intervals, and when these values remained 

stable for a minimum of 30 min, samples for laboratory 

analyses then were collected. 

Field measurements and instrument calibrations 

were recorded on field record sheets and electronically 

in the Personal Computer Field Form (PCFF) program. 

Analytical service requests for the NWQL were generated by 

PCFF, whereas analytical service requests for non-NWQL 

analysis were entered into laboratory-specific spreadsheets. 

Information from PCFF was uploaded directly into the USGS 

NWIS database at the end of every week of sample collection. 

Prior to sample collection, polyethylene sample bottles 

were pre-rinsed two times using deionized water, and then 

once with native sample water before sample collection. 

Samples requiring acidification were acidified to a pH of 

between 2 and 1 with the appropriate acids using ampoules 

of certified, traceable concentrated acids obtained from 

the NWQL.

Temperature-sensitive samples were stored on ice prior 

to and during daily shipping to the various laboratories. The 

non-temperature sensitive samples for species of inorganic 

chromium, tritium, stable isotopes of hydrogen and oxygen 

in water, stable isotopes of boron and strontium in water, and 

dissolved noble gases were shipped monthly. Temperature- or 

time-sensitive samples for VOCs, pesticides and pesticide 

degradates, pharmaceutical compounds, perchlorate, 

NDMA, trace elements, nutrients, major and minor ions, 

silica, TDS, laboratory alkalinity, chromium-IV, radon-222, 

radium isotopes, and gross alpha and gross beta radioactivity 

were shipped daily. The temperature-sensitive samples for 

stable isotopes of carbon in dissolved inorganic carbon 

and carbon-14 abundance were stored on ice, archived in a 

laboratory refrigerator, and shipped after all of the alkalinity 

measurements were collected.

Detailed sampling protocols for individual analyses 

and groups of analytes are described in Koterba and others 

(1995), the NFM (Wilde and others, 1999, 2004), and in the 

references for analytical methods listed in table A1; only brief 

descriptions are given here. VOC samples were collected in 

three 40-mL sample vials that were purged with three vial 

volumes of groundwater before bottom filling to eliminate 

atmospheric contamination. One to one (1:1) hydrochloric acid 

to water (HCl/H2O) solution was added as a preservative to the 

VOC samples. Each sample to be analyzed for perchlorate was 

collected in a 125-milliliter (mL) polystyrene bottle and then 

filtered in two or three 20-mL aliquots of groundwater through 

a 0.20-micrometer (μm) pore-size Corning® syringe-tip 

disk filter into a sterilized 125-mL bottle. Tritium samples 

were collected by bottom filling one 1-L polyethylene bottle 

and one 1-L glass bottle with unfiltered groundwater, after 

first overfilling the bottles with three volumes of unfiltered 
78 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

groundwater. Samples for analysis of stable isotopes of 

hydrogen and oxygen in water were collected in a 60-mL clear 

glass bottle filled with unfiltered groundwater, sealed with a 

conical cap, and secured with electrical tape to prevent leakage 

and evaporation.

Pesticides and pesticide degradates, pharmaceutical 

compounds, and NDMA samples were collected in 1-L baked 

amber glass bottles. Pesticide and pharmaceutical samples 

were filtered through a 0.7-μm nominal pore-size glass 

fiber filter during collection, whereas the NDMA samples 

were filtered at Weck Laboratories, Inc., City of Industry, 

California, prior to analysis. NDMA sample containers, treated 

with 0.05 gram (g) of sodium thiosulfate (Na2S2O3) as a 

preservative, were provided by Weck Laboratories, Inc.

Groundwater samples for trace elements, major and 

minor ions, silica, and TDS analyses required filling one 

250-mL polyethylene bottle with unfiltered groundwater and 

one 500-mL and one 250-mL polyethylene bottle with filtered 

groundwater (Wilde and others, 2004). Filtration was done 

using either a 0.45-μm pore-size Whatman® vented capsule 

filter or a 0.45-μm pore-size PALL® unvented capsule filter 

that was pre-rinsed with 2-L of deionized water, then rinsed 

with 1-L of groundwater prior to sampling. The 250-mL 

filtered sample then was preserved with 7.5-Normal (N) nitric 

acid. Nutrient samples were collected by filtering groundwater 

into a 125-mL brown polyethylene bottle. Cr-VI samples for 

analysis at TALIR were collected by filtering groundwater 

into a 500-mL polyethylene bottle and buffering to a pH range 

of 9.3 to 9.7 with a solution consisting of ammonium sulfate, 

ammonium hydroxide, and ultrapure water. Stable isotopes of 

boron and strontium in water samples were filtered into one 

250-mL polyethylene bottle and secured with electrical tape 

to prevent leakage and evaporation. Radium isotope and gross 

alpha and gross beta radioactivity samples were each filtered 

into individual 1-L polyethylene bottles and then preserved 

with 7.5-N nitric acid. Stable isotopes of carbon in dissolved 

inorganic carbon and carbon-14 abundance samples were 

filtered and bottom filled into 500-mL glass bottles that first 

were overfilled with three bottle volumes of groundwater. 

These samples had no headspace and were sealed with 

conical caps to avoid atmospheric contamination. Samples 

for laboratory or field alkalinity titrations were collected by 

filtering groundwater into a 500-mL polyethylene bottle.

Species of inorganic chromium, radon-222, and noble 

gases samples were collected from the hose bib at the well 

head, regardless of the sampling schedule (fast or slow). 

Species of inorganic chromium samples for analysis at 

the NRP-TML were collected using a 10-mL syringe with an 

attached 0.45-μm pore-size MILLEX®HA disk filter. After the 

syringe was rinsed thoroughly and filled with groundwater, 

4 mL of sample water was forced through the disk filter; the 

next 2 mL of the groundwater was filtered slowly into a small 

centrifuge vial for analysis of total chromium. Cr-VI then 

was collected by attaching a small cation-exchange column 

to the syringe filter and, after conditioning the column with 

2 mL of sample water, an additional 2 mL of sample water 

was collected in a second centrifuge vial. Both vials were 

preserved with 10 microliters (μL) of 7.5-N nitric acid (Ball 

and McClesky, 2003a,b).

For the collection of radon-222 samples, a stainless-steel 

and Teflon® valve assembly was attached to the sampling 

port at the well head (Wilde and others, 2004). The valve 

was partially closed to create back pressure, and a 10-mL 

groundwater sample was taken through a Teflon® septum 

on the valve assembly using a glass syringe affixed with a 

stainless-steel needle. The sample was then injected into a 

25-mL vial partially filled with a scintillation mixture (mineral 

oil) and shaken. The vial then was placed in an insulated 

cardboard tube to protect the sample during shipping. 

Dissolved noble gases were collected in 3⁄8-inch-diameter 

copper tubes using reinforced nylon tubing connected to 

the hose bib at the well head. Groundwater was flushed 

through the tubing to dislodge bubbles before the flow was 

restricted with a back pressure valve. Clamps on either side 

of the copper tube then were tightened, trapping a sample 

of groundwater for analyses of dissolved noble gases 

(Weiss, 1968). 

Field alkalinity was measured in the mobile laboratory 

at the well site. Alkalinity was measured on filtered samples 

by Gran’s titration method (Gran, 1952). Titration data 

were entered directly into PCFF, and the concentrations of 

bicarbonate (HCO3

–) and carbonate (CO32–) automatically 

were calculated from the titration data using the advanced 

speciation method (http://or.water.usgs.gov/alk/methods.html) 

with pK1 = 6.35, pK2 = 10.33, and pKW = 14. Concentrations 

of HCO3

– and CO32– also were calculated from the laboratory 

alkalinity and laboratory pH measurements. 

Nine laboratories performed chemical analyses for 

this study (table A1), although most of the analyses were 

performed at the NWQL or by laboratories contracted by the 

NWQL. The NWQL maintains a rigorous QA program (Pirkey 

and Glodt, 1998; Maloney, 2005). Laboratory QC samples, 

including method blanks, continuing calibration verification 

standards, standard reference samples, reagent spikes, external 

certified reference materials, and external blind proficiency 

samples are analyzed regularly. Method detection limits 

are tested continuously, and laboratory reporting levels 

are updated accordingly. NWQL maintains the National 

Environmental Laboratory Accreditation Program (NELAP) 

and other certifications (http://www.nelac-institute.org/accredlabs.php). In addition, the USGS Branch of Quality Systems 

(BQS) maintains independent oversight of QA at the NWQL 

and laboratories contracted by the NWQL. The BQS also 

runs the National Field Quality Assurance Program (NFQA) 

that includes annual testing of all USGS field personnel for 

proficiency in making field water-quality measurements 

(http://qadata.cr.usgs.gov/nfqa/). Results for analyses made 

at the NWQL or by laboratories contracted by the NWQL are 

uploaded directly into the USGS NWIS database. Results of 

analyses made at other laboratories are compiled in a project 
Appendix 79

database and uploaded from there into the USGS NWIS 

database. Some laboratory QC data are stored in the USGS 

NWIS database also.

Data Reporting

The following section gives details for the laboratory 

reporting conventions and the constituents that are determined 

by multiple methods or by multiple laboratories.

Reporting Limits

The NWQL uses the LRL as a benchmark for reporting 

analytical results. The LRL is set to minimize the reporting 

of false negatives (not detecting a compound when it actually 

is present in a sample) to less than 1 percent (Childress and 

others, 1999). The NWQL updates LRL values regularly, 

and the values listed in this report were in effect during the 

period groundwater samples from the CLUB study unit were 

analyzed (December 2008 to March 2010). LRL values for 

some constituents changed on October 1, 2009; therefore, two 

LRLs are reported (table 3A, 3B, 3E–G): the LRL for samples 

collected before October 1, 2009, and the LRL for samples 

collected on or after October 1, 2009. The highest LRL is used 

for this report.

The LRL usually is set at two times the long-term 

method detection level (LT-MDL). The LT-MDL is derived 

from the standard deviation of at least 24 method detection 

level (MDL) determinations made over an extended period 

of time. The MDL is the minimum concentration of a 

substance that can be measured and reported with 99-percent 

confidence that the concentration is greater than zero (at the 

MDL there is less than 1 percent chance of a false positive). 

LT-MDLs continually are monitored and updated (Childress 

and others, 1999; U.S. Environmental Protection Agency, 

2002). Concentrations less than the LT-MDL are reported as 

non-detections with a dash (–) in the data tables.

Concentrations between the LRL and the LT-MDL are 

reported as estimated concentrations (coded by the letter “E” 

preceding the values in the tables and text). For informationrich methods, detections less than the LT-MDL have high 

certainty of detection, but the precise concentration is 

uncertain. These values are also E-coded. Information-rich 

methods are those that utilize gas chromatography or 

high-performance liquid chromatography (HPLC) with mass 

spectrometry detection, such as those methods used to analyze 

VOCs and pesticides. Compounds are identified by presence 

of characteristic fragmentation patterns in their mass spectra 

in addition to being quantified by measurement of peak areas 

at their associated chromatographic retention times. E-coded 

values also may result from detections outside the range of 

calibration standards, from detections that did not meet all 

laboratory QC criteria, and from samples that were diluted 

prior to analysis (Childress and others, 1999).

Some constituents in this study are reported by using 

minimum reporting levels (MRLs) or method uncertainties 

(MU). The MRL is the smallest measurable concentration 

of a constituent that may be reliably reported using a given 

analytical method (Timme, 1995). The MU generally indicates 

the precision of a particular analytical measurement; it gives a 

range of values wherein the true value will be found. 

Results for most constituents are presented using the 

LRL, MDL, or MRL values provided by the analyzing 

laboratories. Results for some organic and inorganic 

constituents are presented using study reporting levels (SRL) 

derived from assessment of data from QC samples associated 

with groundwater samples collected as part of the GAMA-PBP 

(see the appendix section titled “Assessment of Blank Results 

and SRLs”).

The methods used for analysis of radiochemical 

constituents (tritium, radon-222, radium isotopes, and gross 

alpha and gross beta radioactivity) measure activities by 

counting techniques (table A1). The reporting limits for 

radiochemical constituents are based on sample-specific 

critical levels (ssLC) (McCurdy and others, 2008). The critical 

level is analogous to the LT-MDL used for reporting analytical 

results for organic and non-radioactive inorganic constituents. 

Here, the critical level is defined as the minimum measured 

activity that indicates a positive detection of the radionuclide 

in the sample with less than a 5-percent probability of a false 

positive detection. Sample-specific critical levels are used 

for radiochemical measurements because the critical level is 

sensitive to sample size and sample yield during analytical 

processing and is dependent on instrument background, on 

counting times for the sample and background, and on the 

characteristics of the instrument being used and the nuclide 

being measured. An ssLC is calculated for each sample, and 

the measured activity in the sample is compared to the ssLC

associated with that sample. Measured activities less than 

the ssLC are reported as non-detections with a dash (–) in the 

data tables. 

The analytical uncertainties associated with measurement 

of activities also are sensitive to sample-specific parameters, 

including sample size, sample yield during analytical 

processing, and time elapsed between sample collection and 

various steps in the analytical procedure, as well as parameters 

associated with the instrumentation. Therefore, measured 

activities of radioactive constituents are reported with 

sample‐specific combined standard uncertainties (CSU). The 

CSU is reported at the 68-percent confidence level (1-sigma). 

Notation

Stable isotopic compositions of oxygen, boron, carbon, 

and hydrogen are reported as relative isotope ratios in units 

of per mil using the standard delta notation (Coplen and 

others, 2002):
80 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

1 1,000 per mil,

where

is the atomic mass of the heavier isotope of

the element,

is the element (O for oxygen, B for boron, 

C for carbon, H for hydrogen),

is the rati

i sample

reference

sample

R

E

R

i

E

R

 

δ = −×      

18 11 13

2

16 10 12 1

o of the abundance of the heavier

isotope of the element ( O, B, C,

H) to the lighter isotope of the element

( O, B, C, H) in the sample, and

is the ratio of the abundance of the hea Rreference vier

isotope of the element to the lighter

isotope of the element in the reference

material.

 (A1)

The reference material for oxygen and hydrogen is 

Vienna Standard Mean Ocean Water (VSMOW), which is 

assigned δ18O and δ2H values of 0 per mil (note than δ2H 

is sometimes written as δD because the common name of 

the heavier isotope of hydrogen, hydrogen-2, is deuterium) 

(Coplen and others, 2002). The reference material for boron 

is the National Institute of Standards and Technology (NIST) 

reference material SRM 951 boric acid, which is assigned a 

δ11B value of 0 per mil. The reference material for carbon is 

Vienna Pee Dee Belemnite (VPDB), which is assigned a δ13C 

value of 0 per mil (Coplen and others, 2002). Positive values 

indicate enrichment of the heavier isotope, and negative values 

indicate depletion of the heavier isotope, compared to the 

ratios observed in the standard reference material. 

Stable isotopic composition of strontium is presented as 

the abundance of atoms of the heavier isotope (87Sr) to the 

lighter isotope (86Sr) of the element.

Constituents on Multiple Analytical Schedules

Six constituents targeted in this study were measured 

by more than one analytical method or by more than one 

laboratory (table A2). The preferred methods for these 

constituents were selected on the basis of the procedure 

recommended by the NWQL (http://wwwnwql.cr.usgs.gov/

dyn.shtml?Preferred_method_selection_procedure). 

The water-quality indicators—alkalinity, pH, and specific 

conductance—were measured in the field and at the NWQL. 

The field measurements are the preferred method for all three 

constituents; however, both measurements are reported on 

table 4. Field values are generally preferred because field 

conditions are considered more representative of groundwater 

conditions (Hem, 1985).

For total chromium concentrations, the approved method 

(Schedule 1948, which is used by the NWQL) is preferred 

over the research methods used by the NRP-TML; however, 

both measurements are reported (tables 8 and 11). The 

concentrations measured by the NRP-TML only are used to 

calculate ratios of the abundance of the oxidized species to the 

abundance of the reduced species for the element. 

For example,

Cr(III) Cr(T) Cr(VI) , Cr(VI) Cr(VI)

where

Cr(T) is the total chromium concentration

(measured),

Cr(VI) is the concentration of hexavalent chromium

(measured), and

Cr(III) is the concentration of trivalent chromi

− =

um

(calculated).

 (A2)

Cr-VI was measured at two laboratories―NRP-TML and 

TALIR―and both sets of results are reported. 

Additionally, tritium was measured at two laboratories: 

LLNL and USGS Stable Isotope and Tritium Laboratory, 

Menlo Park, California (SITL). Only tritium data from 

the SITL was available for reporting at the time of 

this publication. 

Quality-Assurance Methods

The purpose of QA is to identify which data best 

represent environmental conditions and which may have been 

affected by contamination or bias during sample collection, 

processing, storage, transportation, and (or) laboratory 

analysis. Four types of QC tests were used in this study: 

(1) blank samples were collected to assess positive bias as a 

result of contamination during sample handling or analysis, 

(2) replicate samples were collected to assess variability, 

(3) matrix-spike tests were done to assess positive or negative 

bias, and (4) surrogate compounds were added to samples 

analyzed for organic constituents to assess bias of laboratory 

analytical methods. Results that were found to have significant 

contamination bias, on the basis of the QC data collected 

from this study and previous studies, were flagged with an 

appropriate remark code (described in subsequent sections) 

and rejected from subsequent use, including calculations of 

detection frequency. 

Blanks

The primary purposes of collecting blanks are to evaluate 

the magnitude of potential contamination of samples with 

compounds of interest during sample collection, processing, 

transport, and (or) analysis, and to identify and mitigate these 

sources of sample contamination. 
Appendix 81

Blank Collection and Analysis

Field blanks were collected using blank water certified 

by the NWQL to contain less than the LRL, MDL, or MRL of 

the analytes investigated in the study (http://wwwnwql.cr.usgs.

gov/USGS/OBW/obw.html). Nitrogen-purged, organic-free 

blank water was used for field blanks of organic constituents, 

and inorganic-free blank water was used for field blanks of 

other constituents. 

Field blanks were analyzed for VOCs, pesticides and 

pesticide degradates, perchlorate, NDMA, trace elements, 

nutrients, major and minor ions, silica, TDS, species of 

inorganic chromium, radium isotopes, and gross alpha and 

gross beta radioactivity. Field blanks were not collected 

for tritium or dissolved noble gases. Tritium and dissolved 

noble gases are in the atmosphere and would dissolve into 

any solution used in collecting a blank, making it impractical 

to collect a blank for these analytes. Stable-isotopic ratios 

of boron, carbon, hydrogen, oxygen, and strontium are an 

intrinsic property of any of these elements; therefore, the 

concept of a blank does not apply to these ratios.

To collect field blanks, blank water either was pumped 

or poured through the sampling equipment (fittings and 

tubing) used to collect groundwater samples, then processed 

and transported using the same protocols as were used for 

the groundwater samples. Twelve liters of blank water were 

pumped or poured through the sampling equipment before 

each field blank was collected.

Assessment of Blank Results and SRLs

Contamination in blanks may originate from several 

different types of sources that require different strategies 

for assessment of potential contamination of groundwater 

samples during sample collection, handling, and analysis. 

Four primary modes of contamination are assessed in the 

event of detections in blanks or atypical results in groundwater 

samples: (1) impurities in the water used to collect the blanks, 

(2) contamination during sample collection and handling 

from a known source or condition present at the field site, 

(3) carry-over of material on the sampling equipment from 

one sample to the next sample, (4) systematic and random 

contamination from field and laboratory equipment and 

processes. The fourth source of contamination (systematic and 

random) is being addressed using a larger set of blank results 

from multiple studies, in addition to the results from the field 

blanks collected from the CLUB study unit. The development 

of this approach and its methods are described by M.S. Fram, 

L.D. Olsen, and K. Belitz, U.S. Geological Survey, written 

commun. (2011) for VOCs and by Olsen and others (2010) for 

trace elements.

The first potential mode that was evaluated is the 

presence of impurities in the water used to collect the blank. 

Because the blanks were collected using blank water certified 

by the NWQL to contain less than the LRL, MDL, or MRL of 

the analytes investigated in the study, the blank water is rarely 

the source of constituents detected in blanks. However, blank 

water sometimes is used before the certification process has 

been completed; thus, the certificates of analysis always must 

be checked. Blank water used in the CLUB study unit was 

certified by the NWQL prior to field blank collection.

The second potential mode that was evaluated is 

contamination from identifiable, known sources present at 

a specific field site. Contamination from specific sources 

may produce distinctive patterns of detections in blanks and 

groundwater samples, particularly for the VOCs. Substances 

that may be encountered at the field site contain recognizable 

associations of VOC constituents. For example, cements used 

on polyvinyl chloride (PVC) piping are primarily composed 

of tetrahydrofuran with lesser amounts of acetone and methyl 

ethyl ketone (2-butanone). However, detection of these 

recognizable associations of VOC constituents in groundwater 

samples does not necessarily indicate contamination during 

sample collection because these VOC constituents also may 

occur together in groundwater.

If a recognizable association of VOC constituents was 

detected in a field blank or in a groundwater sample, the 

field notes and photographs from the site at which the field 

blank or groundwater sample was collected were examined 

for conditions that may have caused the field blank or the 

groundwater sample to be contaminated. If such conditions 

were present, the detections of VOC constituents in the field 

blank or groundwater sample were considered suspect. 

The third potential mode of contamination that was 

evaluated was carry-over from the previous groundwater 

sample or blank collected with the same equipment. 

Carry-over between samples is rare because the procedures 

used to clean the equipment between samples have been 

developed and extensively tested to assure that carry-over 

is mitigated as much as possible. Potential carry-over was 

evaluated using time-series analysis to look for patterns 

suggestive of carry-over of constituents from a sample with 

high concentrations to the next groundwater sample or 

blank collected with the same equipment. If non-detections 

were reported in blanks or groundwater samples collected 

after the collection of groundwater samples containing high 

concentrations of the constituent, then carry-over as a mode of 

contamination was ruled out. 

The fourth potential mode of contamination that was 

evaluated was random or systematic contamination from 

field or laboratory equipment or processes. All detections in 

blanks that could not be accounted for by impurities in the 

source-solution water, by specific known conditions at field 

sites, or by carry-over between samples were evaluated for 

random contamination. Random contamination in field and 

laboratory processes has an equal chance of affecting each 

groundwater sample; thus, strategies for flagging detections of 

constituents that are subject to random contamination in field 

and laboratory processes must be applied to all groundwater 

samples. Random or systematic contamination in field and 

laboratory processes generally is the most common of the four 

modes of contamination and is addressed by applying SRLs. 
82 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

The SRLs for some VOCs were defined on the basis of 

concentrations and detection frequencies in field blanks and 

source-solution blanks collected for the first 32 GAMA‐PBP 

study units (May 2004 through September 2010) and in 

NWQL instrument and preparation blanks analyzed during the 

same time period as the samples (M.S. Fram, L.D. Olsen, and 

K. Belitz, U.S. Geological Survey, written commun., 2011). 

SRLs were defined for five hydrocarbons (ethylbenzene, 

toluene, 1,2,4-trimethylbenzene, m- and p-xylenes, and 

o-xylene), three solvents (acetone, 2-butanone, and 

tetrahydrofuran), and one VOC that occurs naturally and also 

is used in industrial processes (carbon disulfide). 

For organic and special-interest constituents detected 

less frequently in blanks than in groundwater samples, 

the concentration corresponding to the 95th percentile of 

the cumulative frequency distribution of the field blanks, 

source-solution blanks, or laboratory blanks, whichever was 

highest, was defined as the SRL. For most constituents, the 

95th percentiles of the cumulative frequency distributions were 

non-detections (values below the RL); thus, no SRLs were 

required. Concentrations of those constituents reported by 

the laboratory that were less than the SRL are flagged with a 

less than or equal to (≤) symbol preceding the reported value. 

Organic and special-interest constituent results flagged with 

a ≤ symbol were not considered detections in the GAMAPBP study and were not included in the calculations of 

detection frequencies.

The SRLs for all trace elements except cobalt and 

molybdenum were determined by statistical assessment 

of results from the field blanks collected in the first 

20 GAMA-PBP study units (May 2004 through January 2008) 

(Olsen and others, 2010). The assessment used order 

statistics and binomial probabilities to construct an upper 

confidence limit (Hahn and Meeker, 1991) for the maximum 

concentration of constituents possibly introduced while 

groundwater samples were collected, handled, transported, 

and analyzed. The resulting SRLs for trace elements were set 

at concentrations representing a confidence limit of 90 percent 

for the 90th percentile of the 86 field blanks used in the 

assessment. Concentrations of those constituents reported 

by the NWQL that were less than the SRL are flagged with a 

≤ symbol preceding the reported value.

For all other inorganic constituents, the SRL for applying 

the ≤ symbol was determined from assessment of the field 

blanks collected in the CLUB study unit and was defined as 

equal to the highest concentration measured in the field blanks. 

Replicates

Sequential replicate samples were collected to assess 

the precision of the water-quality data. Estimates of data 

precision are needed to assess whether differences between 

concentrations in samples are because of differences in 

groundwater quality or because of variability that may result 

from collecting, processing, and analyzing the samples. 

Two methods for measuring variability were needed to 

adequately assess precision over the broad range of measured 

concentrations of most constituents. The variability between 

measured concentrations in the pairs of sequential replicate 

samples was represented by the standard deviation (SD) for 

low concentrations and by relative standard deviation (RSD) 

for high concentrations (Anderson, 1987; Mueller and Titus, 

2005). The RSD is defined as the SD divided by the mean 

concentration for each replicate pair of samples expressed as 

a percentage. The boundary between concentrations for which 

variability is assessed with SD and concentrations for which 

variability is assessed with RSD was defined as five times the 

reporting level (RL) for each constituent. The RL may be an 

LRL, SRL, MDL, or MRL for each constituent. 

 For this study, acceptable precision for replicate sample 

pairs is defined as follows.

• For concentrations less than five times the RL (<5 RL), 

an SD of <1⁄2 the RL is acceptable.

• For concentrations greater than (or equal to) five times 

the RL (≥5 RL), an RSD of <10 percent is acceptable. 

For comparison, an RSD of 10 percent is equivalent to 

a relative percent difference (RPD) of 14 percent. 

• For activities of radiochemical constituents (except 

carbon-14), replicate pairs with values that are 

statistically indistinguishable at a confidence level (α) 

of α = 0.05 are defined as acceptable. 

If results from replicate sample pairs indicate that 

precision is unacceptable for a constituent and no specific 

reason can be identified, then this greater variability must 

be considered when interpreting the data. If measured 

concentrations are slightly greater than a water-quality 

benchmark, then actual concentrations could be slightly less 

than that benchmark. Similarly, if measured concentrations 

are slightly less than a water-quality benchmark, then actual 

concentrations could be slightly greater than a benchmark. 

Also, if a constituent has high variability in replicate sample 

pairs, then a larger difference between concentrations 

measured in two samples is required to conclude that the two 

samples have significantly different concentrations. 

Replicate pairs of analyses of all constituents except for 

radiochemical constituents were evaluated as follows. 

• If both values were reported as detections, the SD was 

calculated if the mean concentration was <5 RL for 

the constituent, or the RSD was calculated if the mean 

concentration was ≥5 RL for the constituent. 

• If both values were reported as non-detections, the 

variability was set to zero by definition. 

• If one value was reported as a non-detection, and 

the other value was reported as a detection less than 

the RL, then a value of zero was substituted for the 

non-detection, and the SD was calculated. Substituting 

zero for the non-detection yielded the maximum 

estimate of variability for the replicate pair. 
Appendix 83

• If one value for a sample pair was reported as a 

non-detection and the other value was reported as a 

≤-coded value (less than or equal to the SRL), or if 

both values were reported as ≤-coded values (less 

than or equal to the SRL), the SD was not calculated 

because the values may be analytically identical. The 

≤-code indicates that the value is a maximum potential 

concentration and that concentration may be low 

enough to be reported as a non-detection. 

• If one value was reported as a non-detection 

and the other value was reported as a detection 

greater than the RL, the variability for the pair was 

considered unacceptable.

Replicate pairs of analyses of radiochemical constituents 

were evaluated using the following equation (McCurdy and 

others, 2008):

( )

1 2

2 2

1 2

1 2

2 2

1 2

,

where

is the test statistic,

 and are the results for the two samples

in the replicate pair, and

and are the combined standard

uncertainties associated with 

the results.

R R

z

CSU CSU

z

R R

CSU CSU

− =

+

(A3)

Values of z <1.65 correspond to significant levels (p) <α = 

0.05, and thus indicate replicate pairs with acceptable 

precision.

Matrix Spikes

Addition of a known concentration of a constituent 

(spike) to a replicate environmental sample enables the 

analyzing laboratory to determine the effect of the matrix, 

in this case groundwater, on the analytical technique used 

to measure the constituent. The known compounds added 

in matrix spikes are the same as those being analyzed in the 

method. This enables an analysis of matrix interferences on a 

compound-by-compound basis. For this study, matrix spikes 

were added by the laboratory performing the analysis. Low 

matrix-spike recovery may indicate that the compound might 

not be detected in some samples if it were present at very low 

concentrations. Low and high matrix-spike recoveries may be 

a potential concern if the concentration of a compound in a 

groundwater sample is close to the health-based benchmark; a 

low recovery could result in a falsely measured concentration 

less than the health-based benchmark, whereas a high recovery 

could result in a falsely measured concentration greater than 

the health-based benchmark.

The GAMA-PBP defined the data-quality objective range 

for acceptable matrix-spike recoveries as 70 to 130 percent. 

Only constituents with median matrix-spike recoveries 

outside of this range were flagged as having unacceptable 

recoveries. For many constituents, an acceptable range 

of 70 to 130 percent for matrix-spike recovery was more 

restrictive than the acceptable control limits for laboratory-set 

spike recoveries. Laboratory-set spikes are aliquots of 

laboratory blank water to which the same spike solution 

used for the matrix spikes has been added. One set spike is 

analyzed with each set of samples. Acceptable control limits 

for set spikes are defined relative to the long-term variability 

in recovery. For example, for many NWQL schedules, 

acceptable set-spike recovery is within ±3 F-pseudosigma 

of the median recovery for at least 30 set spikes (Conner and 

others, 1998). The F-pseudosigma is calculated by dividing 

the fourth-spread (analogous to interquartile range) by 1.349; 

therefore, the smaller the F-pseudosigma, the more precise the 

determinations (Hoaglin, 1983). 

 Matrix spikes were performed for VOCs, pesticides and 

pesticide degradates, pharmaceutical compounds, perchlorate, 

and NDMA because the analytical methods for these 

constituents may be susceptible to matrix interferences. 

Surrogates

Surrogate compounds are added to groundwater samples 

in the laboratory prior to analysis to evaluate the recovery 

of similar constituents. Surrogate compounds were added 

in the laboratory to all groundwater and QC samples that 

were analyzed by the NWQL for VOCs, pesticides, and 

pharmaceutical compounds. Most of the surrogate compounds 

are deuterated analogs of compounds being analyzed. For 

example, the surrogate toluene-d8 that is used for the VOC 

analytical method has the same chemical structure as toluene, 

except that the eight hydrogen-1 atoms on the molecule have 

been replaced by deuterium (hydrogen-2). Toluene-d8 and 

toluene behave very similarly in the analytical procedure, but 

the small mass difference between the two results in slightly 

different chromatographic retention times; thus, the use of a 

toluene-d8 surrogate does not interfere with the analysis of 

toluene (Grob, 1995). Only 0.015 percent of hydrogen atoms 

are deuterium (Firestone and others, 1996); thus, deuterated 

compounds such as toluene-d8 do not occur naturally and are 

not detected in groundwater samples. Surrogates are used to 

identify general problems that may arise during laboratory 

sample analysis that could affect the analysis results for all 

compounds in that sample. Potential problems include matrix 

interferences (such as high levels of DOC) that produce a 

positive bias or incomplete laboratory recovery (possibly 

because of improper maintenance and calibration of analytical 

equipment) that produces a negative bias. A 70 to 130 percent 

recovery of surrogates, in general, is considered acceptable; 

values outside this range indicate possible problems with the 

processing and analysis of samples (Connor and others, 1998; 

Sandstrom and others, 2001).
84 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Quality-Control Results

Detections in Field Blanks and Application 

of SRLs

Table A3 presents a summary of detections in the field 

blanks and the SRLs applied for the CLUB study unit. Field 

blanks were collected at approximately 2 to 10 percent of the 

sites sampled in the CLUB study unit.

Of the five field blanks analyzed for VOCs, PCE was 

detected in one blank. The PCE detection was considered 

to be random contamination, likely from a field process, but 

the exact source could not be identified. This blank detection 

had an equal chance of affecting each groundwater sample. 

PCE was detected in the field blank at a concentration of 

E0.02 μg/L, creating an SRL of 0.02 μg/L. PCE was detected 

at concentrations less than the SRL in two groundwater 

samples, and these concentrations were flagged with a 

≤ symbol. These groundwater samples were reclassified as 

non-detections and were not included in the calculations of 

PCE detection frequencies (tables 5 and A3). 

GAMA SRLs from M.S. Fram, L.D. Olsen, and K. 

Belitz, U.S. Geological Survey, written commun. (2011) were 

used for nine VOCs. Of these VOCs with SRLs, three were 

detected in field blanks and (or) groundwater samples from 

the CLUB study unit. Toluene was detected in 1 of 5 field 

blanks at a concentration of E0.02 μg/L (table A3) and in 

two groundwater samples at concentrations of E0.01 μg/L 

and E0.02 μg/L (table 5). Both detections were measured 

at concentrations less than the SRL of 0.69 μg/L and were 

reclassified as non-detections. The source of the toluene 

contamination is uncertain. 

1,2,4-trimethylbenzene was detected in 12 of 

52 groundwater samples at concentrations ranging from 

E0.01 μg/L to 1.82 μg/L (median 0.21 μg/L) (table 5). 

Nine of the detections were measured at concentrations 

less than the SRL of 0.56 μg/L and were reclassified as 

non-detections. The three remaining detections were 

considered to be representative of groundwater quality and 

are presented on table 5. For the GAMA-PBP, detections of 

1,2,4-trimethylbenzene in blanks and groundwater samples 

are correlated with the presence in field vehicles of equipment 

used for collecting radon samples (M.S. Fram, L.D. Olsen, and 

K. Belitz, U.S. Geological Survey, written commun., 2011). 

The vials used to collect radon samples contain a scintillation 

cocktail made of mineral oil and 1,2,4-trimethylbenzene. 

Radon samples were collected at 22 wells in the CLUB study 

unit; therefore, there was a potential for the contamination of 

groundwater samples.

Acetone was detected in one groundwater sample 

at a concentration of 7 μg/L (table 5). Contamination 

of groundwater samples and field blanks by acetone, 

tetrahydrofuran, and (or) 2-butanone is associated with 

presence of PVC-cement at sample collection sites (some 

wells are plumbed with PVC piping) and with contamination 

of sample collection equipment by the methanol used for 

cleaning equipment (M.S. Fram, L.D. Olsen, and K. Belitz, 

U.S. Geological Survey, written commun., 2011). Field blanks 

with contamination from either of these two sources were 

not considered representative; therefore, no QC assessment 

could be made for these three solvents, and no concentration 

threshold could be established for the SRL. The SRL consists 

of reclassifying these three solvents as “not analyzed” and 

detections in groundwater samples as non-detections. 

Five field blanks were collected for analysis of trace 

elements. Five trace elements were detected in at least one 

field blank―cobalt, copper, iron, lead, and molybdenum 

(table A3). The detections of copper, iron, and lead were 

measured at concentrations less than the SRL assigned by 

Olsen and others (2010). SRLs for cobalt (0.18 μg/L) and 

molybdenum (0.32 μg/L) were established on the basis of 

the highest detected concentration in the two field blanks. 

Measured concentrations that were less than the SRL were 

flagged with a ≤ symbol (table 8). There were no other trace 

elements detected in any of the field blanks in the CLUB 

study unit.

GAMA SRLs from Olsen and others (2010) were 

used for aluminum, barium, chromium, copper, iron, lead, 

manganese, nickel, tungsten, vanadium, and zinc. Measured 

concentrations that were less than the SRL were flagged with a 

≤ symbol in table 8. 

Two field blanks were collected for analysis of 

radioactive constituents. Results from field blanks were not 

used to define SRLs for radiochemical constituents because 

the low activities of these constituents occasionally reported 

in GAMA-PBP blanks are thought to be an artifact of the 

algorithms used to convert instrument response to activities 

for blank samples, rather than to reflect presence of these 

constituents in blank samples (Sylvia Stork, U.S. Geological 

Survey, written commun., 2010). Activities of radiochemical 

constituents reported in field blanks were lower than most of 

the activities reported in the CLUB study-unit groundwater 

samples, indicating that groundwater samples likely were 

not significantly contaminated by these constituents during 

collection, handling, or analysis (tables 14 and A3). 

Constituents were not detected in the field blanks for the 

following analyte groups: pesticides and pesticide degradates 

(five field blanks); perchlorate (three field blanks); NDMA 

(two field blanks); nutrients (five field blanks); major and 

minor ions, silica, and TDS (five field blanks); species of 

inorganic chromium (one field blank); Cr-VI from TALIR 

(one field blank); radium-228 (two field blanks); gross alpha 

radioactivity (30-day count, two field blanks); and gross beta 

radioactivity (72-hour and 30-day counts, two field blanks). 

Variability in Replicate Samples

Table A4A–C summarizes the results of replicate 

analyses for constituents detected in groundwater samples 

collected in the CLUB study unit. Replicate analyses 

were made on approximately 4 to 10 percent of the 

samples collected. 
Appendix 85

Of the 944 replicate pairs of constituents analyzed, 269 

were for constituents detected in at least one groundwater 

sample. Of these 269 pairs, 2 pairs (tritium) were outside the 

limits for acceptable precision. Results for replicate analyses 

for constituents that were not detected in groundwater samples 

are not reported in table A4A–C. 

Five replicate pairs of samples were analyzed for 

the 85 VOCs, and all pairs were composed of two values 

reported as non-detections or two values ≤-coded with the 

exception of two replicate pairs of chloroform and PCE and 

one replicate pair of diisopropyl ether (DIPE), benzene, and 

trichloroethene (TCE) (table A4A). These replicate pairs 

either yielded two values reported as detections or one value 

reported as a detection and one reported as a non-detection. 

All replicate pair analyses resulted in SDs and RSDs within 

acceptable precision. 

Five replicate pairs of samples were analyzed for the 

63 pesticide and pesticide degradate compounds and all pairs 

were composed of two values reported as non-detections with 

the exception of one replicate pair of atrazine, deethylatrazine, 

3,4-dichloroaniline, and dieldrin (table A4A). The replicate 

pairs all yielded two values reported as detections, 

and all replicate pair analyses resulted in SDs within 

acceptable precision. 

Five replicate pairs for perchlorate and two replicate 

pairs for NDMA were analyzed at Weck Laboratories, 

Inc., for variability (table A4A). One of the replicate pairs 

for perchlorate and both replicate pairs for NDMA were 

composed of two values reported as non-detections. The other 

four replicate pairs for perchlorate yielded two values reported 

as detections, and all replicate pair analyses resulted in SDs or 

RSDs within acceptable precision. 

Replicate pairs of samples were analyzed for the 

24 trace elements (four pairs); 5 nutrients (four pairs); 

9 major and minor ions, silica, and TDS (four pairs); Cr-VI 

from TALIR (two pairs); and 4 isotope tracers (four pairs). 

The SD or RSD values for all pairs were within acceptable 

precision (table A4B). 

Five replicate pairs for tritium were analyzed for 

variability (table A4C). Two of these replicate pairs resulted in 

values of p >0.05, which indicates that these replicate pairs do 

not have acceptable precision. However, these samples were 

reported as non-detections and (or) concentrations more than 

four orders of magnitude less than the corresponding MCL-CA 

(tables 3J and 13). For tritium concentrations less than 

health-based benchmarks, precision that is less than acceptable 

will not affect the assessments of groundwater quality being 

made by the GAMA-PBP.

Two replicate pairs for radon-222, radium isotopes, and 

gross alpha and gross beta radioactivity were analyzed for 

variability (table A4C). All replicate pairs for these radioactive 

constituents yielded statistically similar results (p ≤0.05) and 

were, therefore, considered acceptable. 

Environmental detections were not modified on the basis 

of the replicate analysis.

Matrix-Spike Recoveries

Table A5A–C presents a summary of matrix-spike 

recoveries for the CLUB study unit. Replicate samples 

for spike additions were collected at approximately 2 to 

10 percent of the wells sampled. 

Five groundwater samples were spiked with VOCs 

to calculate matrix-spike recoveries (table A5A). Median 

matrix-spike recoveries for all 85 VOC spike compounds were 

between 70 and 130 percent. Eight VOC spike compounds 

had one matrix-spike recovery greater than 130 percent. Of 

these VOC spike compounds, one constituent, chloroform, 

also was detected in groundwater samples (tables 3A and 5). 

Three VOC spike compounds had one matrix-spike recovery 

less than 70 percent, and none of these VOC spike compounds 

were detected in groundwater samples (tables 3A and A5A). 

Five groundwater samples were spiked with pesticide 

and pesticide degradate compounds to calculate matrix-spike 

recoveries (table A5B). Median matrix-spike recoveries 

for 40 of the 63 spike compounds were between 70 and 

130 percent. Twenty-four of the compounds had median 

matrix-spike recoveries less than 70 percent. One compound 

(tebuthiuron) had a median matrix-spike recovery greater than 

130 percent. 

Two of the three compounds detected in groundwater 

samples (3,4-dichloroaniline and atrazine) had median 

matrix-spike recoveries within the acceptable range (tables 3B

and 6). 

The median matrix-spike recovery for the third 

compound detected in groundwater samples, deethylatrazine, 

had a median matrix-spike recovery less than the acceptable 

range (63 percent). Deethylatrazine was detected at 

concentrations (E0.009 μg and E0.007 μg) less than the LRL 

of 0.014 μg in two grid wells in the LUB study area (table 6). 

Because deethylatrazine was detected at concentrations 

much lower than the LRL, it was determined that the less 

than acceptable median matrix-spike recovery did not affect 

the analysis and results from the NWQL. Tebuthiuron had 

a median matrix-spike recovery of 149 percent, but this 

compound was not detected in groundwater samples. 

At least one matrix-spike recovery for six pesticide 

and pesticide degradate spike compounds was greater 

than 130 percent (table A5B). Of these six, four pesticide 

and pesticide degradate spike compounds had at least one 

matrix-spike recovery greater than 130 percent and one 

matrix-spike recovery less than 70 percent. At least one 

matrix-spike recovery for 48 pesticide and pesticide degradate 

spike compounds was less than 70 percent. Of these pesticide 

and pesticide degradate spike compounds, 3,4-dichloroaniline 

and deethylatrazine were detected in groundwater samples 

(tables 3B, 6, and A5B). A similar pattern of unusually low 

matrix-spike recoveries that started in March 2008 was noted 

in an assessment of method performance by the Organic 

Blind Sample Program (OBSP) of the BQS (http://bqs.usgs.

gov/OBSP/).
86 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

One groundwater sample was spiked with perchlorate, 

and two groundwater samples were spiked with NDMA to 

calculate matrix-spike recoveries at Weck Laboratories, Inc. 

(table A5C). All median matrix-spike recoveries were between 

70 and 130 percent. 

Environmental detections were not modified on the basis 

of the matrix-spike recovery analysis.

Surrogate Compound Recoveries

Table A6 presents a summary of the surrogate recoveries 

for the CLUB study unit. The table lists the surrogate, the 

analytical schedule on which it was applied, the number of 

analyses for blank and environmental samples, the number 

of surrogate recoveries less than 70 percent, and the number 

of surrogate recoveries greater than 130 percent for the 

blank and environmental samples. Blank and environmental 

samples were considered separately to assess whether or 

not the matrixes present in environmental samples affect 

surrogate recoveries. 

Most surrogate recoveries for the blank and 

environmental samples were within the acceptable range 

of 70 to 130 percent. In total, 93 percent of the blank and 

83 percent of the environmental sample surrogate recoveries 

for VOC analyses were within the acceptable range (table A6). 

In addition, 100 percent of the blank and 90 percent of the 

environmental sample surrogate recoveries for pesticide 

and pesticide degradate analyses were within the acceptable 

range (table A6). There were no significant differences 

between VOC and pesticide and pesticide degradate surrogate 

recoveries in blank and environmental samples (Wilcoxon 

rank sum test, p <0.05).

Environmental detections were not modified on the basis 

of the surrogate recovery analysis.

Other Quality-Control Results

Two other laboratory QC matters arose during the 

analysis of samples collected for CLUB study unit: the 

effect of holding time violations on the results of radioactive 

constituent data and the effect of internal laboratory QC tests 

indicating bias on the results of trace element data.

Holding time refers to the time in calendar days from 

sample collection to the analysis of the sample. A holding 

time violation is when a sample is analyzed past the given 

holding time for a particular analysis. The remote sampling 

areas within the CLUB study unit did not allow for immediate 

shipment of a few radioactive samples for the analysis of gross 

alpha and beta radioactivity. This resulted in the later arrival 

times at the laboratory; thus, the analysis was completed after 

the holding time. This may be important because a delay in 

the analysis at the laboratory may result in lower measured 

activities than what may have been present in the groundwater. 

The gross alpha and beta radioactivity reported result is 

the amount measured in the sample. Radioactive decay occurs 

between the time of sample collection and measurement; 

therefore, gross alpha and gross beta change with time. 

Generally, gross alpha decreases during the first 10 days due 

to decay of unsupported members of the thorium-232 decay 

series (in particular, Ra-224 and its progeny). At least one 

result from the analysis of gross alpha and beta radioactivity 

(72-hour count) was analyzed past the holding time for three 

groundwater samples. The results for these three samples are 

footnoted in table 14C. Gross alpha and beta radioactivity 

(72-hour count) will be lower in samples analyzed late. If 

there were samples with a gross alpha or beta radioactivity 

count just over the benchmark (or just over 1⁄2 benchmark) that 

were present in the groundwater, then late analysis could result 

in the reported activities for these samples being below the 

benchmark. One of the late samples in the CLUB study unit 

may be in this category: gross alpha radioactivity (72-hour 

count) in LUB-07 was measured at 10.5 ± 2.1 pCi/L. This 

sample was analyzed 4 days past the holding time.

Laboratory bias as indicated from internal laboratory QC 

tests is another issue that must be investigated to determine 

whether or not the data are affected. The BQS operates an 

independent, external QA project called the Inorganic Blind 

Sample Project (IBSP) to monitor and evaluate the quality 

of results for analyses of trace elements, nutrients, major and 

minor ions, silica, and TDS by the NWQL. The IBSP submits 

standard reference samples consisting of natural matrix water 

samples spiked with reagent chemicals that contain known 

concentrations of the inorganic constituents (Farrar and Long, 

1997). The IBSP samples are disguised as regular groundwater 

samples for submission to the NWQL. The BQS uses results 

from the IBSP samples to evaluate potential bias, positive or 

negative, in the results reported by the NWQL on a continuous 

basis. The BQS IBSP data are readily available on the BQS 

website, and the BQS issues monthly summaries of the results, 

reporting the amount of bias (if any) observed in the results 

(http://bqs.usgs.gov/ibsp/).

The BQS monthly summaries were examined for the 

period of time during which samples were analyzed for the 

CLUB study unit. In summary, the BQS reported that four 

inorganic constituents showed evidence of bias: a positive 

bias for cadmium, sulfate, and zinc and a negative bias for 

magnesium. Examination of the results for the IBSP samples 

for these four constituents indicated that the analytical biases 

reported by the BQS were not significant for the data collected 

for the CLUB study unit. 

The IBSP samples for cadmium had concentrations 

ranging from 0.18 μg/L to 1.8 μg/L. The average difference 

between the measured and expected concentrations was 

0.14 μg/L (standard deviation = 0.08 μg/L), and the average 

relative percent difference between the measured and 

expected concentrations was 16 percent (standard deviation = 

22 percent). The MCL-US for cadmium is 5 μg/L, thus the 
Appendix 87

estimate of bias from the ISBP samples would be relevant for 

assessment of whether groundwater samples have cadmium 

concentrations greater than or less than the MCL-US 

concentration or greater than or less than 1⁄2 of the MCL-US 

concentration. However, the maximum concentration of 

cadmium in samples from the CLUB study unit was 0.45 μg/L 

(table 8); thus, a potential positive bias of 0.14 μg/L or 

16 percent would not result in a measured concentration above 

either threshold when the true concentration would have been 

below the threshold.

The IBSP samples for sulfate had concentrations 

ranging from 14.9 mg/L to 31.3 mg/L. The average difference 

between the measured and expected concentrations was 

0.7 mg/L (standard deviation = 1.1 mg/L), and the average 

relative percent difference between the measured and 

expected concentrations was 4 percent (standard deviation = 

6 percent). The upper SMCL-CA for sulfate is 500 mg/L, a 

concentration much higher than the maximum concentration 

in the IBSP samples. A positive bias of 4 percent or 0.7 mg/L 

for groundwater samples with measured concentrations of 

less than 31.3 mg/L (table 10) does not affect assessment of 

whether groundwater samples in the CLUB study unit have 

sulfate concentrations greater than or less than the upper 

SMCL-CA concentration or greater than or less than 1⁄2 of the 

upper SMCL-CA concentration. Moreover, a determination 

of bias at low concentrations does not imply that there is 

equivalent bias at higher concentrations.

The IBSP samples for zinc had concentrations ranging 

from 5.9 μg/L to 36.4 μg/L. The average difference between 

the measured and expected concentrations was 1.6 μg/L 

(standard deviation = 1.9 μg/L), and the average relative 

percent difference between the measured and expected 

concentrations was 8 percent (standard deviation = 

15 percent). The SMCL-CA for zinc is 5,000 μg/L, a 

concentration much higher than the maximum concentration 

in the IBSP samples. A positive bias of 8 percent or 1.6 μg/L 

for groundwater samples with measured concentrations 

of less than 36.4 μg/L (table 8) does not affect assessment 

of whether groundwater samples in the CLUB study unit 

have sulfate concentrations greater than or less than the 

SMCL-CA concentration or greater than or less than 1⁄2 of the 

SMCL-CA concentration. 

The IBSP samples for magnesium had concentrations 

ranging from 0.05 mg/L to 7.3 mg/L. The average difference 

between the measured and expected concentrations was 

–0.19 mg/L (standard deviation = 0.2 mg/L), and the average 

relative percent difference between the measured and 

expected concentrations was –6 percent (standard deviation = 

3 percent). A negative bias of 6 percent or 0.2 mg/L can only 

potentially affect measured concentrations of less than 

7.3 mg/L in CLUB study unit groundwater samples (table 10). 

Magnesium does not currently have an established regulatory 

or non-regulatory health-based benchmark or a non-regulatory 

benchmark established for aesthetic concerns; therefore, this 

negative bias will not affect the assessments of groundwater 

quality being made by the GAMA-PBP.
88 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 Table A1. Analytical methods used for the determination of organic and inorganic constituents by the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) and additional contract laboratories. [Laboratory entity codes in the USGS National Water Information System (NWIS) database for laboratories other than the USGS NWQL are given in parentheses after the laboratory names. UV, ultraviolet; USEPA, U.S. Environmental Protection Agency; VOC, volatile organic compound; NRP, USGS National Reasearch Program; HPLC, high-performance liquid chromatography]Analyte Analytical method Laboratory and analytical schedule Citation(s) Water-quality indicators Field parameters Calibrated field meters and test kits USGS field measurement U.S. Geological Survey, variously dated Organic constituents VOCs Purge and trap capillary gas chromatography/ mass spectrometry NWQL, Schedule 2020 Connor and others, 1998 Pesticides and degradates Solid-phase extraction and gas chromatography/mass spectrometry NWQL, Schedule 2003 Zaugg and others, 1995; Lindley and others, 1996; Sandstrom and others, 2001; Madsen and others, 2003 Pharmaceuticals Solid-phase extraction and HPLC/mass spectrometry NWQL, Schedule 2080 Kolpin and others, 2002; Furlong and others, 2008 Constituents of special interest Perchlorate Liquid chromatography with mass spectrometry/mass spectrometry (USEPA Method 331.0) Weck Laboratories, Inc., City of Industry, California (CA-WECK), standard operating procedure ORG099.R01 U.S. Environmental Protection Agency, 2005

N-nitrosodimethylamine (NDMA) Isotopic dilution with gas chromatography 

and chemical-ionization mass spectrometry (USEPA Method 1625 modified)

Weck Laboratories, Inc., City of Industry, 

California (CA-WECK), standard operating procedure ORG065.R10

U.S. Environmental Protection Agency, 1989; 

Plomley and others, 1994

Inorganic constituentsNutrients Alkaline persulfate digestion, Kjedahl 

digestion

NWQL, Schedule 2755 Fishman, 1993; Patton and Kryskalla, 2003

Major and minor ions and trace 

elements

Atomic absorption spectrometry, colorimetry, 

ion-exchange chromatography, inductivelycoupled plasma atomic emission spectrometry and mass spectrometry

NWQL, Schedule 1948 Fishman and Friedman, 1989; Fishman, 1993; 

Faires, 1993; McLain, 1993; Garbarino, 1999; American Public Health Association, 1998; Garbarino and others, 2006

Species of inorganic chromium Various techniques of ultraviolet visible 

(UV-VIS) spectrophotometry and atomic absorbance spectroscopy

USGS NRP Trace Metal Laboratory 

[TML], Boulder, Colorado (USGSTMCO)

Ball and McCleskey, 2003a,b

Hexavalent chromium (chromium-VI, 

Cr-VI)

Ion chromatography (USEPA Methods 218.6 

and 7199)

TestAmerica Laboratories Inc. [TALIR], 

Irvine, California (CA-TALIR), standard operating procedure IR-WET-CRIC, Rev. 1

U.S. Environmental Protection Agency, 1994, 

1996
Table A1 89

Analyte Analytical method Laboratory and analytical schedule Citation(s)

Stable isotopesStable isotopes of hydrogen and oxygen 

in water

Gaseous hydrogen and carbon dioxide-water 

equilibration and stable-isotope mass spectrometry

USGS Stable Isotope Laboratory, Reston, 

Virginia (USGSSIVA), NWQL Schedule 1142

Epstein and Mayeda, 1953; Coplen and others, 

1991; Coplen, 1994

Stable isotopes of boron in water Negative thermal-ionization mass 

spectrometry

USGS NRP Metals Isotope Research 

Laboratory, Menlo Park, California (USGSMICA)

Vengosh and others, 1989; Dwyer and

 Vengosh, 2008

Stable isotopes of strontium in water Chemical separations and thermal-ionization 

mass spectrometry

USGS NRP Metals Isotope Research 

Laboratory, Menlo Park, California (USGSMICA)

Bullen and others, 1996

Stable isotopes of carbon in dissolved 

inorganic carbon and carbon-14 abundance

Accelerator mass spectrometry Woods Hole Oceanographic Institution, 

National Ocean Sciences Accelerator Mass Spectrometry Facility [NOSAMS], Woods Hole, Massachusetts (MAWHAMS), NWQL Schedule 2255

Vogel and others, 1987; Donahue and others, 

1990; McNichol and others, 1992; Gagnon and Jones, 1993; McNichol and others, 1994; Schneider and others, 1994

Radioactivity and gasesTritium Electrolytic enrichment-liquid scintillation USGS Stable Isotope and Tritium 

Laboratory [SITL], Menlo Park, California (USGSH3CA), NWQL Schedule 1565

Thatcher and others, 1977

Radon-222 Liquid scintillation counting NWQL, Schedule 1369 American Society for Testing and Materials, 

1998

Radium isotopes Alpha activity counting (USEPA Methods 903 

and 904)

Eberline Analytical Services, Richmond, 

California (CA-EBERL), NWQL Schedule 1262

Kreiger and Whittaker, 1980 

Gross alpha and gross beta radioactivity Alpha and beta activity counting (USEPA 

Method 900.0)

Eberline Analytical Services, Richmond, 

California (CA-EBERL), NWQL Schedule 1792

Kreiger and Whittaker, 1980 

Dissolved noble gases, tritium, and 

helium isotope ratios

Helium-3 in-growth and mass spectrometry Lawrence Livermore National Laboratory 

[LLNL], Livermore, California (CALLNL)

Moran and others, 2002; Eaton and others, 2004

Table A1. Analytical methods used for the determination of organic and inorganic constituents by the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) and additional contract laboratories.—Continued[Laboratory entity codes in the USGS National Water Information System (NWIS) database for laboratories other than the USGS NWQL are given in parentheses after the laboratory names. UV, ultraviolet; USEPA, U.S. Environmental Protection Agency; VOC, volatile organic compound; NRP, USGS National Reasearch Program; HPLC, high-performance liquid chromatography]
90 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table A2. Preferred analytical schedules for selected constituents collected for the Borrego Valley, Central Desert, 

and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, December 2008 to March 2010.

[Preferred analytical schedules/methods are selected on the basis of the procedure recommended by the USGS National Water Quality 

Laboratory (NWQL) (http://wwwnwql.cr.usgs.gov/dyn.shtml?Preferred_method_selection_procedure). Abbreviations: TML, USGS

Trace Metal Laboratory, Boulder, Colorado; TALIR, TestAmerica, Inc., Irvine, California; np, no preference; SITL, USGS Stable Isotope 

Laboratory, Reston, Virginia; LLNL, Lawrence Livermore National Laboratory, Livermore, California; USGS, U.S. Geological Survey]

Constituent Primary constituent 

classification

Analytical

schedules

Preferred analytical 

schedule

Results from both methods reported

Alkalinity Water-quality indicator Field, 1948 Field

pH Water-quality indicator Field, 1948 Field

Specific conductance Water-quality indicator Field, 1948 Field

Chromium, total Trace element 1948, TML 1948

Hexavalent chromium (chromium-VI, Cr-VI) Trace element species TML, TALIR np

Tritium Inorganic tracer SITL, LLNL np
Table A3 91

Table A3. Constituents detected in field blanks and the study reporting level (SRL) analysis for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.[Sources of study reporting level (SRL): CLUB field blanks, the SRL was assigned a value equal to the highest concentration in field blanks collected for this study unit; report by Olsen and others (2010): the SRL was defined on the basis of the examination of quality-control samples collected for the first 20 GAMA study units; Fram and others, written commun. from M.S. Fram, L.D. Olsen, and K. Belitz, U.S. Geological Survey (2011): the SRL was defined on the basis of examination of quality-control samples collected for the first 32 GAMA study units. Abbreviations: ≤, less than or equal to; LRL, laboratory reporting level; E, estimated or having a higher degree of uncertainty; μg/L, micrograms per liter; –, not detected; PCE, perchloroethene (tetrachloroethene); pCi/L, picocuries per liter; ±, plus or minus; ssLC, 

sample-specific critical level]

Constituent

Number of 

field blank 

detections/ 

total number

of field blanks 

Concentrations 

detected in

field blanks

SRL 

concentration Source of SRL

Number of 

groundwater

samples

≤-coded

Number of 

groundwater

samples

excluded from 

dataset

Volatile organic compounds (VOC) (μg/L)Acetone 0/5 – All data Fram and others, 2011 0 1

Carbon disulfide 0/5 – 0.03 Fram and others, 2011 0 0

Ethylbenzene 0/5 – 0.1 Fram and others, 2011 0 0

2-Hexanone (n-Butyl methyl ketone) 0/5 – All data Fram and others, 2011 0 0

PCE 1/5 E0.02 0.02 CLUB field blanks 1 1

Tetrahydrofuran 0/5 – All data Fram and others, 2011 0 0

Toluene 1/5 E0.02 0.69 Fram and others, 2011 0 2

1,2,4-trimethylbenzene 0/5 – 0.56 Fram and others, 2011 0 9

m-Xylene plus p-xylene 0/5 – 0.4 Fram and others, 2011 0 0

o-Xylene 0/5 – 0.1 Fram and others, 2011 0 0Trace elements (μg/L)Aluminum 0/5 – 1.6 Olsen and others, 2010 0 0

Barium 0/5 – 0.36 Olsen and others, 2010 0 0

Chromium 0/5 – 0.42 Olsen and others, 2010 10 0

Cobalt 2/5 0.18, 0.12 0.18 CLUB field blanks 36 0

Copper 1/5 E0.50 1.7 Olsen and others, 2010 18 0

Iron 1/5 E2.7 6 Olsen and others, 2010 5 0

Lead 1/5 0.04 0.65 Olsen and others, 2010 34 0Manganese 0/5 – 0.2 Olsen and others, 2010 6 0

Molybdenum 2/5 0.32, E0.17 0.32 CLUB field blanks 0 0

Nickel 0/5 – 0.36 Olsen and others, 2010 26 0Tungsten 0/5 – 0.11 Olsen and others, 2010 1 0

Vanadium 0/5 – 0.1 Olsen and others, 2010 0 0

Zinc 0/5 – 4.8 Olsen and others, 2010 19 0

Radioactive constiuents (pCi/L)Radium-226 2/2 0.0348 ± 0.0099, ssLC = 0.012; 0.039 ± 0.011, 

ssLC = 0.011

– CLUB field blanks 0 0

Gross alpha radioactivity, 72-hour count 1/2 0.33 ± 0.17, ssLC = 0.20 – CLUB field blanks 0 0
92 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 Table A4A. Quality-control summary for replicate analyses of organic constituents and perchlorate detected in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010. [Abbreviations: SD, percent standard deviation; RSD, percent relative standard deviation; ≤, less than or equal to; >, greater than; <, less than; ≥, greater than or equal to; RL, reporting level; nv, no value in category] Constituent Number of non-detections/ number of replicates Number of 

≤-coded 

replicates

Replicates with concentrations 

<5 times the RL

Replicates with concentrations 

≥5 times the RL

Number of SDs 

>1⁄2 RL /number 

of replicates

Concentrations of 

replicates with 

SDs >1⁄2 the RL

(environmental, 

replicate) 

Number of RSDs 

>10 percent/

number 

of replicates

Concentrations 

of replicates with 

RSDs >10 percent 

(environmental, 

replicate) 

Volatile organic compounds (VOC)Chloroform (Trichloromethane) 3/5 nv 0/2 nv nv nv

Perchloroethene (PCE, tetrachloroethene) 3/5 nv 0/2 nv nv nv

1,2,4-trimethylbenzene 3/5 2/5 nv nv nv nv

Diisopropyl ether (DIPE) 4/5 nv nv nv 0/1 nv

Benzene 4/5 nv 0/1 nv nv nv

Bromodichloromethane 5/5 nv nv nv nv nv

Bromoform (Tribromomethane) 5/5 nv nv nv nv nv

Trichloroethene (TCE) 4/5 nv nv nv 0/1 nv

Pesticides and pesticide degradatesDeethylatrazine (2-Chloro-4-isopropylamino-6-aminos-triazine) 4/5 nv 0/1 nv nv nv

Simazine 5/5 nv nv nv nv nv

3,4-Dichloroaniline 4/5 nv 0/1 nv nv nv

Atrazine 4/5 nv 0/1 nv nv nv

Metolachlor 5/5 nv nv nv nv nv

Dieldrin 4/5 nv 0/1 nv nv nv

Constituent of special interestPerchlorate 1/5 nv 0/1 nv 0/3 nv
Table A4B 93

Table A4B. Quality-control summary for replicate analyses of inorganic constituents and isotope tracers detected in samples 

collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010. 

[Abbreviations: SD, percent standard deviation; RSD, percent relative standard deviation; >, greater than; <, less than; ≥, greater than or equal to; RL, 

reporting level; μg/L, micrograms per liter; Cr-VI, hexavalent chromium (chromium-VI); TALIR, TestAmerica Laboratories, Inc., Irvine, California; SiO2, 

silicon dioxide; H, hydrogen; O, oxygen; C, carbon; ≤, less than or equal to; nv, no value in category]

Constituent

Number of 

non-detections 

or ≤-coded 

replicates/

number of 

replicates 

Replicates with concentrations 

< 5 times the RL

Replicates with concentrations 

≥5 times the RL

Number of 

SDs >1⁄2 the 

RL /number 

of replicates 

Concentrations 

of replicates with 

SDs >1⁄2 the RL 

(environmental, 

replicate) 

Number of RSDs 

>10 percent/number 

of replicates 

Concentrations 

of replicates with 

RSDs >10 percent 

(environmental, 

replicate) 

Trace elements

Aluminum 3/4 0/1 nv nv nv

Antimony 2/4 0/2 nv nv nv

Arsenic 0/4 nv nv 0/4 nv

Barium 0/4 nv nv 0/4 nv

Beryllium 3/4 0/1 nv nv nv

Boron 0/4 nv nv 0/4 nv

Cadmium 0/4 0/3 nv 0/1 nv

Chromium 0/4 0/2 nv 0/2 nv

Cr-VI (TALIR) 1/2 0/1 nv nv nv

Cobalt 0/4 0/3 nv 0/1 nv

Copper 3/4 0/1 nv nv nv

Iron 3/4 0/1 nv nv nv

Lead 4/4 nv nv nv nv

Lithium 0/4 nv nv 0/4 nv

Manganese 1/4 0/2 nv 0/1 nv

Molybdenum 0/4 nv nv 0/4 nv

Nickel 0/4 0/3 nv 0/1 nv

Selenium 0/4 nv nv 0/4 nv

Silver 3/4 0/1 nv nv nv

Strontium 0/4 nv nv 0/4 nv

Thallium 3/4 0/1 nv nv nv

Tungsten 0/4 nv nv 0/4 nv

Uranium 0/4 nv nv 0/4 nv

Vanadium 0/4 nv nv 0/4 nv

Zinc 0/4 0/4 nv nv nv

Nutrients 

Ammonia (as nitrogen) 4/4 nv nv nv nv

Nitrate plus nitrite (as nitrogen) 0/4 nv nv 0/4 nv

Nitrite (as nitrogen) 3/4 nv nv 0/1 nv

Total nitrogen (ammonia + nitrite + 

nitrate + organic nitrogen)

0/4 0/1 nv 0/3 nv

Phosphate, orthophosphate (as 

phosphorus)

0/4 0/4 nv nv nv
94 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Constituent

Number of 

non-detections 

or ≤-coded 

replicates/

number of 

replicates 

Replicates with concentrations 

<5 times the RL

Replicates with concentrations 

≥5 times the RL

Number of 

SDs >1⁄2 the 

RL / number 

of replicates 

Concentrations 

of replicates with 

SDs >1⁄2 the RL 

(environmental, 

replicate) 

Number of RSDs 

>10 percent/number 

of replicates 

Concentrations 

of replicates with 

RSDs >10 percent 

(environmental, 

replicate) 

Major and minor ions, silica, and total dissolved solids (TDS) 

Bromide 0/4 0/4 nv nv nv

Calcium 0/4 nv nv 0/4 nv

Chloride 0/4 nv nv 0/4 nv

Fluoride 0/4 0/3 nv 0/1 nv

Iodide 0/4 0/2 nv 0/2 nv

Magnesium 0/4 nv nv 0/4 nv

Potassium 0/4 nv nv 0/4 nv

Sodium 0/4 nv nv 0/4 nv

Sulfate 0/4 nv nv 0/4 nv

Silica (as SiO2) 0/4 nv nv 0/4 nv

TDS 0/4 nv nv 0/4 nv

Isotope tracers and radioactivity 

δ2H in water 0/4 nv nv 0/4 nv

δ18O in water 0/4 nv nv 0/4 nv

δ13C in dissolved inorganic carbon 0/4 nv nv 0/4 nv

Carbon-14 0/4 nv nv 0/4 nv

Table A4B. Quality-control summary for replicate analyses of inorganic constituents and isotope tracers detected in samples 

collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.—Continued 

[Abbreviations: SD, percent standard deviation; RSD, percent relative standard deviation in percent; >, greater than; <, less than; ≥, greater than or equal to; 

RL, reporting level; μg/L, micrograms per liter; Cr-VI, hexavalent chromium (chromium-VI); TALIR, TestAmerica Laboratories, Inc., Irvine, California; SiO2, 

silicon dioxide; H, hydrogen; O, oxygen; C, carbon; ≤, less than or equal to; nv, no value in category]
Table A4C 95

Table A4C. Quality-control summary for replicate analyses of radioactive constiuents detected in samples 

collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010. 

[For activities of radiochemical constituents, a replicate pair of analyses is defined as acceptable if the p-value for the normalized 

absolute difference is less than the significance level, α = 0.05. Abbreviations: >, greater than; pCi/L, picocuries per liter; ±, plus or 

minus; nv, no value in category; –, not detected]

Constituent

Number of pairs 

with p > 0.05/total

number of replicates 

Activites for replicate 

pairs with p > 0.05

(environmental, replicate)

(pCi/L)

Tritium 2/5 (17.8 ± 0.67, 20.3 ± 0.77), (– , 0.7 ± 0.32)

Radon-222 0/2 nv

Radium-226 0/2 nv

Radium-228 0/2 nv

Gross alpha radioactivity, 72-hour count 0/2 nv

Gross alpha radioactivity, 30-day count 0/2 nv

Gross beta radioactivity, 72-hour count 0/2 nv

Gross beta radioactivity, 30-day count 0/2 nv
96 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOC) in samples collected for the 

Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, December 2008 to March 2010. 

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number of 

spike 

samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetone 5 106 138 122

Acrylonitrile 5 98 124 107

tert-Amyl methyl ether (TAME) 5 89 115 104

Benzene 1 5 91 109 105

Bromobenzene 5 94 109 101

Bromochloromethane 5 106 129 116

Bromodichloromethane 1 5 89 111 108

Bromoform (Tribromomethane) 1 5 96 117 102

Bromomethane (Methyl bromide) 5 100 147 127

n-Butylbenzene 5 75 102 82

sec-Butylbenzene 5 79 100 93

tert-Butylbenzene 5 93 107 99

Carbon disulfide 5 68 97 73

Carbon tetrachloride (Tetrachloromethane) 5 87 123 114

Chlorobenzene 5 94 104 97

Chloroethane 5 81 117 115

Chloroform (Trichloromethane) 1 5 84 131 119

Chloromethane 5 80 115 100

3-Chloropropene 5 94 119 114

2-Chlorotoluene 5 95 108 101

4-Chlorotoluene 5 95 110 98

Dibromochloromethane 5 99 117 105

1,2-Dibromo-3-chloropropane (DBCP) 5 92 125 102

1,2-Dibromoethane (EDB) 5 99 116 112

Dibromomethane 5 94 125 115

1,2-Dichlorobenzene 5 97 120 117

1,3-Dichlorobenzene 5 90 115 104

1,4-Dichlorobenzene 5 89 107 104

trans-1,4-Dichloro-2-butene 5 97 111 104

Dichlorodifluoromethane (CFC-12) 5 53 117 97

1,1-Dichloroethane (1,1-DCA) 1 5 92 120 117

1,2-Dichloroethane (1,2-DCA) 5 88 124 122

1,1-Dichloroethene (1,1-DCE) 5 93 105 103

cis-1,2-Dichloroethene (cis-1,2-DCE) 5 97 113 106

trans-1,2-Dichloroethene (trans-1,2-DCE) 5 93 121 112

1,2-Dichloropropane 5 90 110 102

1,3-Dichloropropane 5 99 117 110

2,2-Dichloropropane 5 83 95 92

1,1-Dichloropropene 5 82 103 93

cis-1,3-Dichloropropene 5 83 98 89

trans-1,3-Dichloropropene 5 84 98 92

Diethyl ether 5 100 124 114

Diisopropyl ether (DIPE) 1 5 88 119 108
Table A5A 97

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOC) in samples collected for the 

Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, December 2008 to March 2010.—Continued 

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number of 

spike 

samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Ethylbenzene 5 80 97 91

Ethyl tert-butyl ether (ETBE) 5 83 110 97

Ethyl methacrylate 5 85 105 99

o-Ethyl toluene (1-Ethyl-2-methyl benzene) 5 82 97 90

Hexachlorobutadiene 5 65 98 86

Hexachloroethane 5 83 119 108

2-Hexanone (n-Butyl methyl ketone) 5 90 130 108

Iodomethane (Methyl iodide) 5 111 137 125

Isopropylbenzene 5 78 98 89

4-Isopropyl-1-methyl benzene 5 82 102 86

Methyl acrylate 5 101 121 116

Methyl acrylonitrile 5 105 137 120

Methyl tert-butyl ether (MTBE) 1 5 103 117 109

Methyl iso-butyl ketone (MIBK) 5 84 114 102

Methylene chloride (Dichloromethane) 5 86 116 110

Methyl ethyl ketone (2-butanone, MEK) 5 103 194 111

Methyl methacrylate 5 83 102 100

Naphthalene 5 81 104 90

Perchloroethene (PCE, Tetrachloroethene) 1 5 98 126 104

n-Propylbenzene 5 85 98 88

Styrene 5 70 97 88

1,1,1,2-Tetrachloroethane 5 92 117 113

1,1,2,2-Tetrachloroethane 5 90 120 110

Tetrahydrofuran 5 94 124 109

1,2,3,4-Tetramethylbenzene 5 74 101 87

1,2,3,5-Tetramethylbenzene 5 81 117 91

Toluene 5 92 102 98

1,2,3-Trichlorobenzene 5 95 110 103

1,2,4-Trichlorobenzene 5 81 94 89

1,1,1-Trichloroethane (1,1,1-TCA) 5 90 127 117

1,1,2-Trichloroethane (1,1,2-TCA) 5 102 122 110

Trichloroethene (TCE) 1 5 90 105 100

Trichlorofluoromethane (CFC-11) 5 83 129 118

1,2,3-Trichloropropane (1,2,3-TCP) 5 95 129 106

Trichlorotrifluoroethane (CFC-113) 5 76 134 98

1,2,3-Trimethylbenzene 5 92 119 99

1,2,4-Trimethylbenzene 1 5 84 108 95

1,3,5-Trimethylbenzene 5 81 99 92

Vinyl bromide (Bromoethene) 5 88 123 96

Vinyl chloride (Chloroethene) 1 5 76 138 115

m- and p-Xylene 5 85 104 100

o-Xylene 5 89 97 89

1 Constituents detected in groundwater samples.
98 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, December 2008 to March 2010. 

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number of 

spike 

samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetochlor 5 67 117 88

Alachlor 5 73 116 90

Atrazine 1 5 80 118 88

Azinphos-methyl 5 67 116 83

Azinphos-methyl oxon 5 37 100 70

Benfluralin 5 53 84 56

Carbaryl 5 66 156 103

2-Chloro-2,6-diethylacetanilide 5 71 125 84

4-Chloro-2-methylphenol 5 34 80 70

Chlorpyrifos 5 54 90 63

Chlorpyrifos-oxon 5 16 40 37

Cyfluthrin 5 39 86 50

Cypermethrin 5 38 75 53

Dacthal (DCPA) 5 93 108 98

Deethylatrazine (2-Chloro-4-isopropylamino-6-

amino-s-triazine) 1

5 30 85 63

Desulfinylfipronil 5 65 128 93

Desulfinylfipronil amide 5 71 112 79

Diazinon 5 73 105 82

3,4-Dichloroaniline 1 5 61 102 70

Dichlorvos 5 5 51 14

Dicrotophos 5 17 76 32

Dieldrin 1 5 65 93 77

2,6-Diethylaniline 5 86 95 95

Dimethoate 5 30 65 42

Ethion 5 50 95 65

Ethion monoxon 5 55 113 82

2-Ethyl-6-methylaniline 5 81 95 91

Fenamiphos 5 72 115 86

Fenamiphos sulfone 5 61 138 91

Fenamiphos sulfoxide 5 7 90 35

Fipronil 5 74 126 96

Fipronil sulfide 5 60 120 80

Fipronil sulfone 5 56 74 67

Fonofos 5 62 103 80

Hexazinone 5 48 95 69

Iprodione 5 50 101 75

Isofenphos 5 61 118 110

Malaoxon 5 53 112 108

Malathion 5 56 116 108

Metalaxyl 5 73 146 114

Methidathion 5 67 103 90

Metolachlor 1 5 68 103 93

Metribuzin 5 60 110 83

Myclobutanil 5 63 134 80

1-Naphthol 5 11 23 19

Paraoxon-methyl 5 30 80 65

Parathion-methyl 5 60 106 70
Table A5C 99

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, December 2008 to March 2010—Continued 

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number of 

spike 

samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Pendimethalin 5 59 107 88

cis-Permethrin 5 36 66 50

Phorate 5 34 81 59

Phorate oxon 5 67 122 95

Phosmet 5 7 89 35

Phosmet oxon 5 12 78 40

Prometon 5 66 103 79

Prometryn 5 67 118 93

Pronamide (Propyzamide) 5 71 111 80

Simazine 1 5 72 118 87

Tebuthiuron 5 94 205 149

Terbufos 5 60 95 67

Terbufos oxon sulfone 5 44 154 102

Terbuthylazine 5 80 116 92

Tribufos 5 34 66 57

Trifluralin 5 60 94 69

1 Constituents detected in groundwater samples.

Table A5C. Quality-control summary for matrix-spike recoveries of constituents of special interest in samples collected for the 

Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, December 2008 to March 2010. 

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number of 

spike 

samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Perchlorate 1 1 2 94

N-nitrosodimethylamine (NDMA) 2 113 120 116.5

1 Constituent detected in groundwater samples.

2

 Median recovery represented by the single spike value.
100 Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts Study Unit, 2008–2010 Table A6. Quality-control summary for surrogate recoveries of volatile organic compounds and pesticides and pesticide degradates in samples collected for the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts (CLUB) Groundwater Ambient Monitoring and Assessment (GAMA) study, California, December 2008 to March 2010.

[Abbreviation: VOC, volatile organic compound]

Surrogate Analytical schedule Constituent or constituent class analyzed Number of blanks analyzed Median recovery in blanks (percent)

Number of 

surrogate 

recoveries 

less than 

70 percent 

in blanks

Number of 

surrogate 

recoveries 

greater than 

130 percent 

in blanks

Number of 

samples 

analyzed

Median 

recovery 

in samples 

(percent)

Number of 

surrogate 

recoveries 

less than 

70 percent 

in samples

Number of 

surrogate 

recoveries 

greater than 

130 percent 

in samples

1-Bromo-4-fluorobenzene 2020 VOC 5 82 0 0 52 81 0 0

1,2-Dichloroethaned4 2020 VOC 5 123 0 1 52 131 0 26

Toluened8 2020 VOC 5 97 0 0 52 94 0 0

Diazinond10 2003 Pesticide 5 80 0 0 49 78 10 0

α-HCHd6 2003 Pesticide 5 85 0 0 49 85 0 0
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Mathany and others—Groundwater-Quality Data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran

Deserts Study Unit, 2008–2010: Results from the California GAMA Program—Data Series 659