San Gorgonio Pass

 subbasin

Indio subbasin

Mission Creek subbasin

Desert

Hot

Springs

subbasin

Palm Springs

Indio

Mecca

Data Series 373

U.S. Geological Survey

U.S. Department of the Interior

Ground-Water Quality Data in the Coachella Valley Study Unit, 2007:

Results from the California GAMA Program

In cooperation with the California State Water Resources Control Board

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

Salton

Sea

Desert Hot

Springs

Banning
Cover Photographs:

Top: Wind farm, San Gorgonio Pass, California. Photograph taken by Dara Goldrath, U.S. Geological Survey (USGS).

Middle: Coachella Canal with citrus orchard in background, Coachella Valley, California. Photograph taken by Michael T. Wright, (USGS).

Bottom left: “Mr. Rex”, Cabazon, California. Photograph taken by Dara Goldrath, (USGS).

Bottom right: Irrigation well on Golf course used for sampling near Indio, California. Photograph taken by Timothy Mathany, (USGS). 
Ground-Water Quality Data in the 

Coachella Valley Study Unit, 2007:

Results from the California GAMA Program 

By Dara A. Goldrath, Michael T. Wright, and Kenneth Belitz

Prepared in cooperation with the California State Water Resources Control Board

Data Series 373

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

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

reproduce any copyrighted materials contained within this report.

Suggested citation:

Goldrath, Dara A., Wright, Michael T., and Belitz, Kenneth, 2009, Ground-water quality data in the Coachella Valley 

study unit, 2007: Results from the California GAMA Program: U.S. Geological Survey Data Series 373, 70 p. 

Available at http://pubs.usgs.gov/ds/373
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................4

Hydrogeologic Setting ........................................................................................................................4

Methods ..........................................................................................................................................................6

Study Design..........................................................................................................................................6

Sample Collection and Analysis.........................................................................................................8

Data Reporting.......................................................................................................................................8

Quality Assurance.................................................................................................................................8

Water Quality Results ...................................................................................................................................8

Quality-Control-Sample Results .........................................................................................................9

Comparison Thresholds.......................................................................................................................9

Ground-Water Quality Data...............................................................................................................10

Field Parameters........................................................................................................................10

Organic Constituents ................................................................................................................10

Constituents of Special Interest..............................................................................................11

Inorganic Constituents..............................................................................................................11

Isotopic Tracers ........................................................................................................................11

Radioactive Constituents..........................................................................................................12

Microbial Indicators..................................................................................................................12

Future Work .........................................................................................................................................12

Summary .......................................................................................................................................................12

Acknowledgments.......................................................................................................................................13

References Cited..........................................................................................................................................13

Appendix .......................................................................................................................................................51
iv

Figures

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

Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study unit .......................................................................................................................................3

Figure 2. Map of the Coachella Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit showing the California Department of Water 

Resources defined groundwater subbasins within the study unit, locations 

of major cities, roads, rivers, and faults....................................................................................5

Figure 3. Map of the Coachella Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit showing the distribution of study area grid cells, 

and the grid wells and understanding wells sampled............................................................7

Tables

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

Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, February and March 2007...........................................................................19

Table 2. Classes of chemical and microbial constituents and water-quality indicators 

collected for the slow and intermediate well sampling schedules in the 

Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, February and March, 2007..........................................................................20

Table 3A. Volatile organic compounds, primary uses or sources, comparative thresholds, 

and reporting information for the U.S. Geological Survey (USGS) National Water 

Quality Laboratory schedule 2020............................................................................................21

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

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

National Water Quality Laboratory schedule 2060 ...............................................................23

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

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

National Water Quality Laboratory schedule 2003 ...............................................................25

Table 3D. Pharmaceutical compounds, primary uses or sources, comparative thresholds, 

and reporting information for the U.S. Geological Survey (USGS) National Water 

Quality Laboratory schedule 2080............................................................................................27

Table 3E. Potential wastewater indicator compounds, primary uses or sources, comparative 

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

National Water Quality Laboratory schedule 4433 ...............................................................28

Table 3F. Constituents of special interest, primary uses or sources, comparative thresholds, 

and reporting information for the Montgomery Watson-Harza Laboratory .....................30

Table 3G.Nutrients and dissolved organic carbon, comparative thresholds, and reporting 

information for the U.S. Geological Survey (USGS) National Water Quality 

Laboratory schedule 2755 and lab code 2613 ........................................................................30

Table 3H. Major and minor ions and trace elements, comparative thresholds, and reporting 

information for the U.S. Geological Survey (USGS) National Water Quality 

Laboratory schedule 1948 .........................................................................................................31

Table 3I. Arsenic, chromium, and iron species, comparative thresholds, and reporting 

information for the U.S. Geological Survey (USGS) Trace Metal Laboratory, 

Boulder, Colorado .......................................................................................................................32
v

Tables—Continued

Table 3J. Isotopic, tritium, and radioactive constituents, comparative thresholds, and 

reporting information for laboratories.....................................................................................33

Table 3K. Noble gas constituents, comparison thresholds, and reporting information for 

the Lawrence Livermore National Laboratory.......................................................................34

Table 3L. Microbial constituents, comparison thresholds, and reporting information for 

the U.S. Geological Survey Ohio Microbiology Laboratory parameter codes 90901, 

90900, 99335, and 99332 .............................................................................................................34

Table 4. Water-quality indicators in samples collected for the Coachella Valley 

Ground-Water Ambient Monitoring and Assessment (GAMA) study, California, 

February and March 2007..........................................................................................................35

Table 5. Volatile organic compounds (VOC) detected in ground-water samples collected 

for the Coachella Valley Ground-Water Ambient Monitoring and Assessment 

(GAMA) study, California, February and March 2007 ...........................................................36

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

Coachella Valley Ground-Water Ambient Monitoring and Assessment (GAMA) 

study, California, February and March 2007...........................................................................37

Table 7. Potential wastewater indicator compounds detected in samples collected for 

the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, February and March 2007...........................................................................38

Table 8. Constituents of special interest (Perchlorate, and 1,2,3-Trichloropropane 

[1,2,3-TCP]) detected in samples collected for the Coachella Valley Groundwater 

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

March 2007 ..................................................................................................................................39

Table 9. Nutrients and dissolved organic carbon detected in samples collected for the 

Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, February and March 2007...........................................................................40

Table 10. Major and minor ions and total dissolved solids detected in samples collected 

for the Coachella Valley Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, February and March 2007 ...........................................................41

Table 11. Trace elements detected in ground-water samples collected for the Coachella 

Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, February and March 2007 ......................................................................................43

Table 12. Species of inorganic arsenic, iron, and chromium in samples collected for the 

Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, February and March 2007...........................................................................47

Table 13. Stable isotopic ratios, tritium, uranium and carbon-14 activities in samples 

collected for the Coachella Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, February and March 2007 ....................................48

Table 14. Radioactive constituents detected in samples collected for the Coachella Valley 

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

February to March 2007.............................................................................................................49

Table 15. Microbial indicators detected in samples collected for the Coachella Valley 

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

February and March 2007..........................................................................................................50
vi

Appendix Tables

Table A1. Analytical methods used to determine organic, inorganic, and microbial 

constituents by the U.S. Geological Survey (USGS) National Water Quality 

Laboratory (NWQL) and contract laboratories......................................................................58

Table A2. Preferred analytical schedules for constituents appearing on multiple schedules 

for samples collected for the Coachella Valley Groundwater Ambient Monitoring 

and Assessment (GAMA) study, California, February and March 2007.............................60

Table A3. Constituents detected in field blanks collected for the Coachella Valley 

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

February and March 2007..........................................................................................................60

Table A4. Quality-control summary for replicate analyses of constituents detected in 

samples collected for the Coachella Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, February and March 2007 ...................................61

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic 

compounds (VOCs) in samples collected for the Coachella Valley Groundwater 

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

March 2007 ..................................................................................................................................62

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide 

degradates from schedules 2060 in samples collected for the Coachella Valley 

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

February and March 2007..........................................................................................................64

Table A5C. Quality-control summary for matrix-spike recoveries of pesticides and pesticide 

degradates from schedule 2003 in samples collected for the Coachella Valley 

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

February to March 2007.............................................................................................................66

Table A5D. Quality-control summary for matrix-spike recoveries of pharmaceutical 

compounds in samples collected for the Coachella Valley Groundwater 

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

March 2007 ..................................................................................................................................68

Table A5E. Quality-control summary for matrix-spike recoveries of potential wastewaterindicator compounds in samples collected for the Coachella Valley Groundwater 

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

March 2007 ..................................................................................................................................69

Table A6. Quality-control summary for surrogate recoveries of volatile organic compounds, 

pesticides and pesticide degradates, pharmaceutical compounds, potential 

wastewater-indicator compounds, and constituents of special interest in samples 

collected for the Coachella Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, February and March 2007 ....................................70
vii

Abbreviations and Acronyms

AB Assembly Bill (through the California State Assembly)

AL-US action level (USEPA, see “Organizations”)

CAS Chemical Abstracts Service (American Chemical Society)

COA Study Unit Coachella Valley study unit

CSU combined standard uncertainty

E estimated or having a higher degree of uncertainty

GAMA Groundwater Ambient Monitoring and Assessment program

GPS Global Positioning System

HAL-US Lifetime Health Advisory Level (USEPA)

HCI hydrochloric acid

HPLC high-performance liquid chromatography

LRL laboratory reporting level

LSD land-surface datum

LT-MDL long-term method detection level

MCL-CA maximum contaminant level (CDPH, see “Organizations”)

MCL-US maximum contaminant level (USEPA)

MDL method detection limit

MIMS Membrane Inlet Mass Spectrometry

MRL minimum reporting level

MU method uncertainty

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

na not available

nc not collected

– not detected

NL-CA California notification level (CDPH)

NWIS National Water Information System (USGS, see “Organizations”)

PCFF-GAMA personal computer field forms program designed for GAMA sampling

QC quality control

RPD relative percent difference

RSD relative standard deviation

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

SMCL-CA secondary maximum contaminant level (CDPH)

SMCL-US secondary maximum contaminant level (USEPA)

SSMDC sample-specific minimum detectable concentration

DS total dissolved solids

TT-US Treatment Technique (USEPA)

V analyte detected in sample and an associated blank; thus, data are not 

included in ground-water quality assessment
viii

Abbreviations and Acronyms—Continued

Organizations

CDPH California Department of Public Health

CDWR California Department of Water Resources

LLNL Lawrence Livermore National Laboratory

MWH Montgomery Watson-Harza laboratory

NAWQA National Water Quality Assessment (USGS)

NWQL National Water Quality Laboratory (USGS)

SWRCB State Water Resources Control Board (California)

TML National Research Program Trace Metal Laboratory (USGS)

USEPA U.S. Environmental Protection Agency

USGS U. S. Geological Survey

UWCD United Water Conservation District

Selected Chemical Names

CaCO3 calcium carbonate

CFC chlorofluorocarbon

CO3

–2 carbonate

DOC dissolved organic carbon

HCl hydrochloric acid

HCO3

– bicarbonate

MTBE methyl tert-butyl ether

NDMA N-nitrosodimethylamine

PCE tetrachloroethene

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

TDS total dissolved solids

THM trihalomethane

VOC volatile organic compound
ix

Abbreviations and Acronyms—Continued

Units of Measure

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

and 1 atmosphere of pressure per gram of water) 

δi

E delta notation, the ratio of a heavier isotope of an element (i

E) to the more 

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

expressed as per mil

ft foot (feet)

in. inch

kg kilogram

L liter

mg milligram

mg/L milligrams per liter (parts per million)

mi mile

mL milliliter

μg/L micrograms per liter (parts per billion)

μL microliter

μm micrometer

μS/cm microsiemens per centimeter

pCi/L picocurie per liter

per mil parts per thousand

pmc percent modern carbon

TU tritium unit

> greater than

< less than

oC degrees Celsius

oF degrees Fahrenheit

Notes

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

°F = (1.8 × °C) + 32

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

°C=(°F-32)/1.8

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).

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 million (ppm) and micrograms per liter is 

equivalent to parts per billion (ppb) .
x

This page intentionally left blank.
Ground-Water Quality Data in the Coachella Valley Study 

Unit, 2007: Results from the California GAMA Program

By Dara A. Goldrath, Michael T. Wright, and Kenneth Belitz

Abstract 

Ground-water quality in the approximately 820 squaremile Coachella Valley Study Unit (COA) was investigated 

during February and March 2007 as part of the Priority 

Basin Project of the Groundwater Ambient Monitoring and 

Assessment (GAMA) Program. The GAMA Priority Basin 

Project was developed in response to the Groundwater Quality 

Monitoring Act of 2001, and is being conducted by the U.S. 

Geological Survey (USGS) in cooperation with the California 

State Water Resources Control Board (SWRCB).

The study was designed to provide a spatially unbiased 

assessment of raw ground water used for public-water supplies 

within the Coachella Valley, and to facilitate statistically 

consistent comparisons of ground-water quality throughout 

California. Samples were collected from 35 wells in Riverside 

County. Nineteen of the wells were selected using a spatially 

distributed, randomized grid-based method to provide 

statistical representation of the study unit (grid wells). Sixteen 

additional wells were sampled to evaluate changes in water 

chemistry along selected ground-water flow paths, to examine 

land use effects on ground-water quality, and to collect waterquality data in areas where little exists. These wells were 

referred to as “understanding wells.”

The ground-water samples were analyzed for a large 

number of organic constituents (volatile organic compounds 

[VOC], pesticides and pesticide degradates, pharmaceutical 

compounds, and potential wastewater-indicator 

compounds), constituents of special interest (perchlorate 

and 1,2,3-trichloropropane [1,2,3-TCP]), naturally occurring 

inorganic constituents (nutrients, major and minor ions, 

and trace elements), radioactive constituents, and microbial 

indicators. Naturally occurring isotopes (uranium, tritium, 

carbon-14, and stable isotopes of hydrogen, oxygen, and 

boron), and dissolved noble gases (the last in collaboration 

with Lawrence Livermore National Laboratory) also were 

measured to help identify the source and age of the sampled 

ground water. 

A quality-control sample (blank, replicate, or matrix 

spike) was collected at approximately one quarter of the wells, 

and the results for these samples were used to evaluate the 

quality of the data for the ground-water samples. Assessment 

of the quality-control information resulted in V-coding less 

than 0.1 percent of the data collected.

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 (or) blended with 

other waters to maintain acceptable water quality. Regulatory 

thresholds apply to treated water that is supplied to the 

consumer, not to raw ground water. However, to provide 

some context for the results, concentrations of constituents 

measured in the raw ground water were compared with 

health-based thresholds established by the U.S. Environmental 

Protection Agency (USEPA) and the California Department 

of Public Health (CDPH) and thresholds established for 

aesthetic purposes (secondary maximum contaminant levels, 

SMCL-CA) by CDPH.

Most constituents detected in ground-water samples 

were at concentrations below drinking-water thresholds. 

Volatile organic compounds, pesticides, and pesticide 

degradates were detected in less than one-third of the grid 

well samples collected. All VOC and pesticide concentrations 

measured were below health-based thresholds. Potential 

waste-water indicators were detected in less than half of 

the wells sampled, and no detections were above healthbased thresholds. Perchlorate was detected in seven grid 

wells; concentrations from two wells were above the CDPH 

maximum contaminant level (MCL-CA). Most detections 

of trace elements in samples collected from COA Study 

Unit wells were below water-quality thresholds. Exceptions 

include five samples of arsenic that were above the USEPA 

maximum contaminant level (MCL-US), two detections 

of boron above the CDPH notification level (NL-CA), and 

two detections of molybdenum and strontium above USEPA 

maximum contaminant levels (HAL-US). Concentrations 

of nitrite plus nitrate as nitrogen in two understanding well 

samples were above the USEPA maximum contaminant 

level (MCL-US). Activities of radon-222 in samples from 

seven wells were above the proposed MCL-US of 300 pCi/L; 

however, no samples had an activity above the proposed 

alternative MCL-US of 4,000 pCi/L. Most samples collected 

in the COA Study Unit had concentrations of major ions and 

total dissolved solids below the non-enforceable thresholds set 

for aesthetic purposes. Major ions detected at concentrations 

above the SMCL-CA thresholds included chloride, fluoride, 

sulfate, manganese, and total dissolved solids. 
2 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Introduction 

Ground water comprises nearly half of the water used 

for public-supply in California (Hutson and others, 2004). 

To assess the quality of ground water in aquifers used 

for drinking-water supply and to establish a program for 

monitoring trends in ground-water quality, the State Water 

Resources Control Board (SWRCB), in collaboration with 

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

National Laboratory (LLNL), implemented the Groundwater 

Ambient Monitoring and Assessment (GAMA) Program 

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

consists of three projects: Priority Basin Project, conducted 

by the USGS (http://ca.water.usgs.gov/gama/); Voluntary 

Domestic Well Assessment, conducted by the SWRCB; and 

Special Studies, conducted by LLNL. 

The SWRCB initiated the GAMA Priority Basin Project 

in response to the Ground-Water Quality Monitoring Act of 

2001 (Sections 10780-10782.3 of the California Water Code, 

Assembly Bill 599). AB 599 is a public mandate to assess and 

monitor the quality of ground water used as public supply for 

municipalities in California. The project is a comprehensive 

assessment of Statewide ground-water quality designed to help 

better understand and identify risks to ground-water resources 

and to increase the availability of information about groundwater quality to the public. As part of the AB 599 process, 

the USGS, in collaboration with the SWRCB, developed the 

monitoring plan for the project (Belitz and others, 2003; State 

Water Resources Control Board, 2003). Key aspects of the 

project are inter-agency collaboration, and cooperation with 

local water agencies and well owners. Local participation in 

the project is entirely voluntary.

The GAMA Priority Basin Project is unique to California 

because the data are derived from the analyses of over three 

hundred chemical constituents using analytical methods 

capable of detecting very small concentrations, analyses 

that are not normally available. A broader understanding 

of ground-water composition will be especially useful for 

providing an early indication of changes in water quality, 

and for identifying the natural and human factors affecting 

water quality. Additionally, the GAMA Priority Basin Project 

will analyze a broader suite of constituents than required 

by the California Department of Public Health (CDPH). 

Understanding the occurrence and distribution of these 

constituents is important for the long-term management and 

protection of ground-water resources.

 The range of hydrologic, geologic, and climatic 

conditions that exists in California must be considered 

when assessing ground-water quality. Belitz, and others 

(2003) partitioned the state into 10 hydrogeologic provinces, 

each with distinctive hydrologic, geologic, and climatic 

characteristics; representative regions in all 10 provinces 

were included in the project design (fig. 1). Eighty percent of 

California’s approximately 16,000 public-supply wells are in 

ground-water basins within these hydrologic provinces. These 

ground-water basins, defined by the California Department 

of Water Resources (CDWR), generally consist of relatively 

permeable, unconsolidated deposits of alluvial or volcanic 

origin (California Department of Water Resources, 2003). 

Ground-water basins were prioritized for sampling according 

to the number of public-supply wells in the basin, with 

secondary consideration given to municipal ground-water use, 

agricultural pumping, the number of leaking underground fuel 

tanks, and pesticide applications within the basins (Belitz, 

and others, 2003). In addition, some ground-water basins, or 

groups of adjacent similar basins with relatively few publicsupply wells, were assigned high priority status so that all 

hydrogeologic provinces would be represented in the subset 

of basins sampled. The 116 priority basins were grouped into 

35 study units. Some areas not in the defined ground-water 

basins were included in several of the study units to represent 

the 20 percent of public-supply wells not located in the 

ground-water basins. The Coachella Valley GAMA Study Unit 

(hereinafter referred to as the COA Study Unit) contains four 

ground-water subbasins. The COA Study Unit was considered 

high priority for sampling in order to adequately represent the 

Desert hydrogeologic province (Belitz, and others, 2003). 

Three types of water-quality assessments are being 

made using the data collected in each study unit: (1) Status: 

assessing the current quality of the ground-water resource, 

(2) Trends: detection of changes in ground-water quality and 

(3) Understanding: identification of the natural and human 

factors affecting ground-water quality (Kulongoski and Belitz, 

2004). This report is one of a series of reports presenting 

water-quality data collected in each study unit (Wright and 

others, 2005; Bennett and others, 2006; Kulongoski and 

others, 2006; Kulongoski and Belitz, 2007; Dawson and 

others, 2008). Subsequent reports will present the status, 

trends, and understanding assessments of water-quality in the 

study units.
Introduction 3

Figure 1. Map of the hydrogeologic provinces of California and the location of the Coachella Valley 

Groundwater Ambient Monitoring and Assessment (GAMA) study unit. 

Basin and Range

Klamath

Mountains

Desert

Cascades and

Modoc Plateau

Southern 

Coast

 Ranges

Sierra

Nevada

Central

Valley

Northern

Coast

Ranges

San Diego

Drainages

Bakersfield

San Francisco

OREGON

NEVADA

MEXICO

ARIZONA

Redding

Los Angeles

San Diego

Pacific Ocean

0 200 MILES

0 200 KILOMETERS

40

42 124 122 120 118 116 114

38

36

34

Base from U.S. Geological Survey digital elevation

data, 1999, Albers Equal Area Projection

Provinces from Belitz and others, 2003

Sacramento

Coachella Valley Basin 

GAMA Study Unit
4 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Purpose and Scope

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

design, including the hydrogeologic setting of the COA 

Study Unit, (2) to detail the sampling and analytical methods, 

and quality assurance methods used during the study, (3) to 

present the results of quality-control tests, and (4) to present 

the analytical results for ground-water samples collected in 

the COA. Ground-water samples were analyzed for organic, 

inorganic, and microbial constituents, field parameters, and 

chemical tracers. The chemical and microbial data presented 

in this report were evaluated by comparing them with state 

and federal drinking water regulatory and other health-based 

standards that are applied to treated drinking water. Regulatory 

thresholds considered for this report are those established 

by the United States Environmental Protection Agency 

(USEPA) and the CDPH. The data presented in this report are 

intended to characterize the quality of untreated ground-water 

resources within the study unit, not the treated drinking water 

delivered to consumers by water purveyors. Discussion of 

the factors that influence the distribution and occurrence of 

the constituents detected in ground-water samples will be the 

subject of subsequent publications.

Hydrogeologic Setting 

Knowledge of the hydrogeologic setting is important 

in the design of a ground-water-quality investigation. The 

Coachella Valley, approximately 820 square-miles, is located 

within the Desert Hydrogeologic Province (fig. 1) and extends 

from near the city of Banning to the northwestern shore of 

the Salton Sea (fig. 2). The COA Study Unit is positioned 

almost entirely in Riverside County, but sections extend 

into San Bernardino, San Diego, and Imperial Counties. The 

Coachella Valley is the northern expression of the Salton 

Trough, a landward extension of the Gulf of California. The 

Salton Trough formed in the late Cenozoic and is part of the 

tectonically active San Andreas Fault system (Loeltz and 

others, 1975). The San Bernardino Mountains, the Little San 

Bernardino Mountains, and the Mecca Hills form the north 

and the eastern boundaries of the valley and are composed of 

pre-Tertiary plutonic and metamorphic rocks. The San Jacinto 

and Santa Rosa Mountains bound the valley to the west and 

are composed of folded Tertiary sediments underlain by preTertiary shist (Mendenhall, 1909). The Salton Sea occupies the 

Coachella Valley at its southern end.

The Coachella Valley has a desert climate; the mean 

total annual precipitation is less than five inches, on the 

valley floor (National Climate Data Center, 2005a or b). 

The mountainous areas bordering the valley to the north and 

west receive as much as forty inches of precipitation a year. 

Temperatures range from 120°F in the summer on the valley 

floor to below freezing during the winter in the surrounding 

mountains (Reichard and Meadows, 1992); the average annual 

temperature is 67.5°F (National Climate Data Center, 2005a 

or b). Topographic relief in the area ranges from more than 

10,000 feet above sea level in the surrounding mountains to 

200 feet below sea level near the Salton Sea. 

Ground-water recharge in the Coachella Valley comes 

from several sources including (1) precipitation on the 

valley floor, (2) stream-flow infiltration from the runoff of 

precipitation that falls on the surrounding mountains; this 

runoff is transported and flows to the valley floor by way of 

several ephemeral rivers and creeks, including the Whitewater 

and San Gorgonio Rivers and Mission Creek, (3) engineered 

recharge using Colorado River and local surface water via 

recharge ponds in the Indio and the Mission Creek groundwater subbasins, and (4) percolation of irrigation water in the 

agricultural areas of the southern Coachella Valley. Groundwater is discharged primarily through ground-water pumping.

The Coachella Valley ground-water basin has been 

hydrogeologically divided by the San Andreas Fault into four 

ground-water subbasins defined by structural boundaries: 

the San Gorgonio Pass subbasin, the Indio subbasin, the 

Mission Creek subbasin, and the Desert Hot Springs subbasin 

(California’s Groundwater Bulletin 118, 2003). 

The San Gorgonio Pass subbasin, 60 square miles in 

area, lies in the north-western limb of the Coachella Valley, 

bounded by the San Bernardino Mountains to the north 

and the San Jacinto Mountains to the south. Water-bearing 

formations include Holocene and Pleistocene age alluvium 

and the Pliocene to Pleistocene age San Timoteo Formation 

(California Department of Water Resources, 2007d). 

The Indio subbasin, 525 square-miles in area, lies in the 

western side of the Coachella Valley. It is bounded by the San 

Jacinto Mountains on the west, the Santa Rosa Mountains 

on the southwest and the Salton Sea on the south, and the 

Banning Fault and the Indio Hills on the northeast. Water 

bearing formations in this subbasin include late Pleistocene 

and Holocene alluvial deposits (California Department of 

Water Resources, 2007a).

The Mission Creek subbasin, 76 square-miles in area, lies 

in the northern part of the Coachella Valley and is bounded 

by the San Bernardino Mountains on the west, the Banning 

fault on the southwest, the Indio Hills on the southeast, and 

the Mission Creek fault on the northeast. Water bearing 

formations include late Pleistocene Ocotillo Conglomerate 

and Holocene alluvial fan and terrace deposits (California 

Department of Water Resources, 2007b). 
Introduction 5

Figure 2. Map of the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing the 

California Department of Water Resources defined groundwater subbasins within the study unit, locations of major cities, roads, 

rivers, and faults.

Salton

Sea

Coachella Canal

Gorgonio San

River

Whitewater River

Whitewater River

Mission

Creek

Whitewater River

Colorado River

Aqueduct

Fault (Modified from Matti and

 others, 1992)

10

10

74

86

62

111

San Andreas Fault

Mission Creek Fault

Indio

Fault Hills

Banning Fault

Desert Hot

Springs

Mecca

Banning

INDIO HILLS

MECCA

HILLS

SAN JACINTO MOUNTAINS

SANTA ROSA MOUNTAINS

SAN BERNARDINO

MOUNTAINS

LITTLE

SAN BERNARDINO

MOUNTAINS

0 5 15

15

10

10

20 MILES

0 5 20 KILOMETERS

Area outside of study area

 (Not included in Study)

SAN DIEGO COUNTY

RIVERSIDE COUNTY

RIVERSIDE COUNTY

IMPERIAL

COUNTY

SAN BERNARDINO COUNTY

Ground-water basin boundary

 (from California Department of

 Water Resources)

116 45’ 116 30’ 116 15’ 116 00’

34

00’

34

45’

34

30’

Base from U.S. Geological Survey National Elevation

Dataset, 2006, Albers Equal-Area Conic Projection

EXPLANATION

Desert Hot Springs

subbasin

Mission Creek

subbasin

San Gorgonio Pass

subbasin

Indio

subbasin

Recharge Ponds

Whitewater Recharge Ponds

Palm Springs

Indio
6 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

The Desert Hot Springs subbasin, 158 square-miles in 

area, lies in the northern and eastern parts of the Coachella 

Valley and is bounded on the northeast by the relatively 

nonpermeable Little San Bernardino Mountains and on the 

southwest by the semipermeable rocks of the Indio Hills 

and the Banning and Mission Creek faults. Water-bearing 

formations include late Pleistocene and Holocene alluvial 

fan deposits of the Ocotillo Conglomerate that underlie the 

Dillon Road Piedmont Slope. The slope is being actively 

deposited by weathering forces upon the Little San Bernardino 

Mountains. Hot thermal waters are near active fault areas, 

such as the Mission Creek fault (California Department of 

Water Resource, 2007c). 

Methods 

Methods used for the GAMA program were selected 

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

plan suitable for statistical analysis, (2) collect samples in 

a consistent manner, (3) analyze samples using proven and 

reliable laboratory methods, (4) assure the quality of the 

ground-water data, and (5) maintain data securely and provide 

relevant documentation. The Appendix to this report contains 

detailed descriptions of the sample collection protocols and 

analytical methods, the quality-assurance methods, and the 

results of analyses of quality-control samples.

Study Design

The wells selected for sampling in this study reflect 

the combination of two well selection strategies. Nineteen 

wells were selected using a randomized grid-based method 

(Scott, 1990) in order to provide a statistically unbiased, 

spatially-distributed assessment of the quality of groundwater resources used for public drinking water supply. Sixteen 

additional wells were selected to aid in the understanding of 

specific ground-water-quality issues in the COA Study Unit. 

To select an unbiased, spatially distributed network of 

wells, the locations of wells listed in the statewide databases 

maintained by the CDPH and USGS were plotted on a 

regional map. A grid of 20 equal-area cells (about 40 mi2

each) was then drawn over the COA Study Unit, with the 

objective to sample at least one public-supply well per grid 

cell (fig. 3). Wells in 18 of the 20 grid cells were sampled. 

Two grid cells had either no wells or no permission to sample 

wells in that cell. If a grid cell contained more than one 

public-supply well, each well was randomly assigned a rank. 

The highest ranking well that met basic sampling criteria (for 

example, capability of the well to pump for several hours and 

availability of well-construction information) and for which 

permission to sample could be obtained was then sampled. 

If a grid cell did not contain accessible public-supply wells, 

domestic and irrigation wells were considered for sampling.

In this way, one well was selected for 18 of the 20 qualifying 

grid cells to provide a spatially distributed, randomized 

monitoring network for the study unit. Wells sampled as part 

of the randomized grid-cell network are hereinafter referred 

to as “grid wells.” Grid wells in the COA Study Unit were 

numbered in the order of sample collection and assigned the 

prefix “COA” (fig. 1). One well, COA-10, is located next to 

the boundary of two grid-cells and is considered to have water 

quality representative of both cells (fig. 3). With this additional 

cell coverage, 19 of the 20 grid cells are considered to be 

represented in the grid cell network.

Sixteen additional wells (fig. 3) were sampled to evaluate 

changes in water chemistry along selected ground-water flow 

paths, to examine land use effects on ground-water quality, 

and to collect water-quality data in areas where little exists. 

Wells sampled as part of these studies were not included in 

the statistical characterization of water quality in the COA 

Study Unit because they were not randomly selected. These 

additional (nonrandomized) wells are collectively referred 

to as understanding wells in this report and have the prefix 

“COAU.” 

Table 1 provides the GAMA alphanumeric identification 

number for each well, along with the sampling schedule, well 

type, date sampled and well-construction information. Well 

locations were verified using GPS, 1:24,000 scale USGS 

topographic maps, comparison with existing well information 

in USGS and CDPH databases, and information provided by 

well owners.

The wells in the COA Study Unit were sampled using 

a tiered analytical approach. All wells were sampled for a 

standard set of constituents, including VOCs, pesticides and 

pesticide degradates, pharmaceutical compounds, perchlorate, 

uranium, stable isotopes of hydrogen and oxygen of water, 

tritium, nutrients, hexavalent chromium, major ions, and 

trace elements. This standard set of constituents was termed 

the “intermediate” schedule (table 2). Wells sampled for 

additional constituents are termed the “slow” schedule and 

include all of the constituents on the intermediate schedule 

plus mercury, wastewater indicator compounds, 1,2,3 TCP, 

radium, gross/alpha beta, radon, dissolved organic carbon, and 

microbial constituents (table 2). Intermediate and slow refer to 

the time required to sample the well for all the analytes on the 

associated schedule. Generally, one slow or two intermediate 

schedules could be sampled in one day. In the COA, 24 wells 

were sampled using the intermediate schedule and 11 wells 

were sampled using the slow schedule (table 1). Other GAMA 

study units use a “fast” schedule, which involved collecting 

fewer constituents. 
Methods 7

Figure 3. Map of the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing the 

distribution of study area grid cells, and the grid wells and understanding wells sampled.

Salton

Sea

Coachella Canal

Gorgonio San

River

Whitewater River

Whitewater River

Whitewater River

Aqueduct Colorado River

Aqueduct

Mission

Cr

10

10

74

86

62

111

11

10

07 18

08

04 06 05

16

03

15

17

13

01

14

09

19

12

02

02

09

09

16

14

13

02

11

01

06

12

07 05

10

03

08

04

15

Understanding well

(COAU)

Grid well (COA)

Palm Springs

Indio

Mecca

Banning

INDIO HILLS

SAN JACINTO MOUNTAINS

SANTA ROSA MOUNTAINS

SAN BERNARDINO

MOUNTAINS

0 5 15

15

10

10

20 MILES

0 5 20 KILOMETERS

Area outside of study area

(Not included in Study)

116 45’ 116 30’ 116 15’ 116 00’

34

00’

34

45’

34

30’

Base from U.S. Geological Survey National Elevation

Dataset, 2006, Albers Equal-Area Conic Projection

EXPLANATION

SAN DIEGO COUNTY

RIVERSIDE COUNTY

RIVERSIDE COUNTY

IMPERIAL

COUNTY

SAN BERNARDINO COUNTY

MECCA

HILLS

LITTLE

SAN BERNARDINO

MOUNTAINS

Desert Hot

Springs

Randomized sampling

 grid cell
8 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Sample Collection and Analysis

Samples were collected in accordance with the protocols 

established by the USGS National Water Quality Assessment 

(NAWQA) program (Koterba and others, 1995) and the USGS 

National Field Manual (U.S. Geological Survey, variously 

dated). These sampling protocols ensure that a representative 

sample of ground water is collected at each site, and that the 

samples are collected and handled in a way that minimizes the 

potential for contamination of samples. The methods used for 

sample collection are described in the Sample Collection and 

Analysis section of the Appendix.

Tables 3A–L (see back of report) list the compounds 

analyzed in each constituent class. Ground-water samples 

were analyzed for 85 VOCs (table 3A), 58 polar pesticides 

and pesticide degradates (table 3B), 62 pesticides and 

pesticide degradates (table 3C), 14 pharmaceutical compounds 

(table 3D), 69 wastewater-indicator compounds (table 3E), 

2 constituents of special interest (table 3F), 6 nutrients and 

dissolved organic carbon (table 3G), 10 major and minor ions 

and total dissolved solids and 25 trace elements (table 3H), 

arsenic, iron, and chromium species (table 3I), stable isotopes 

of hydrogen and oxygen of water, 9 radioactive constituents, 

including tritium and carbon-14 (table 3J), noble gases 

(table 3K), and 4 microbial constituents (table 3L). The 

methods used for sample analysis are described in the Sample 

Collection and Analysis section of the Appendix.

Data Reporting

The methods and conventions used for reporting the data 

are described in the Data Reporting section of the Appendix. 

Twenty-two constituents analyzed in this study were measured 

by more than one method at the USGS National Water Quality 

Laboratory (NWQL). For these constituents, only the results 

from the preferred method are reported. The preferredmethod selection is described in the Constituents on Multiple 

Analytical Schedules section of the Appendix. Arsenic, iron, 

and chromium concentrations, and uranium activities were 

measured by more than one laboratory; both sets of results are 

reported. 

Quality Assurance

The quality-assurance methods used for this study 

followed the protocols used by the USGS NAWQA program 

(Koterba and others, 1995), and are described in the USGS 

National Field Manual (U.S. Geological Survey, variously 

dated). The quality assurance method followed by the NWQL, 

the primary laboratory used to analyze samples for this study, 

is described by Maloney (2005) and Pirkey and Glodt (1998). 

Quality-control (QC) samples collected in the COA Study 

Unit included source-solution blanks, field blanks, replicates, 

and matrix and surrogate spikes. QC samples were collected 

to evaluate possible bias and variability of water-quality data 

that may have resulted from sample collection, processing, 

storage, transportation, and (or) laboratory analysis. A qualitycontrol sample was collected at approximately one quarter 

of the wells, and the results for these samples were used to 

evaluate the quality of the results of sampling and analysis for 

the ground-water samples. Assessment of the quality-control 

information resulted in V-coding less than 0.1 percent of the 

data collected. The quality-assurance method is described in 

the Quality-Assurance method of the Appendix.

Water Quality Results 

Results from analyses of raw (untreated) ground-water 

samples from the COA Study Unit are given in tables 4

through 15. Ground-water samples were analyzed for up 

to 370 constituents, and 278 of those constituents were not 

detected in any of the samples (tables 3A–L). The results 

tables present only the constituents that were detected, and 

list only samples that had at least one constituent detected. 

The tables summarizing detections of constituents analyzed 

using USGS NWQL schedules 2020, 2060, 2003 and 4433 

(tables 3A–C, E) include the number of wells at which each 

analyte was detected, the frequency at which it was detected, 

and the total number of constituents detected at each well. 

Results from understanding wells were excluded from these 

calculations to avoid statistically over-representing the areas 

near these wells. 

Table 4 includes water-quality indicators measured in 

the field and at the NWQL, and tables 5 through 15 present 

the results of ground-water analyses organized by compound 

classes: 

• Organic Constituents

• VOCs (table 5)

• Pesticides and pesticide degradates (table 6)

• Potential wastewater-indicator compounds (table 7)

• Constituents of special interest (table 8)

• Inorganic constituents

• Nutrients and dissolved organic carbon (table 9)

• Major and minor ions (table 10)

• Trace elements (table 11)

• Arsenic, iron, and chromium species (table 12)

• Isotopic tracers 

• Stable isotopes and tritium and carbon-14 activities 

(table 13) 

• Radioactive constituents (table 14)

• Microbial indicators (table 15)
Water Quality Results 9

Pharmaceutical compounds have no summary table 

because the only compound detected was acetaminophen and 

the detected concentration is reported in the Ground-Water 

Quality Data section. 

Quality-Control-Sample Results

Results of quality-control analyses (blanks, replicates, 

matrix spikes, and surrogates) were used to evaluate the 

quality of the data for the ground-water samples. Matrixspike recoveries for most organic constituents were below 

acceptable limits, which may indicate that these constituents 

might not have been detected in some samples if they were 

present at very low concentrations. The quality-control results 

are described in the Quality-Control-Sample Results section in 

the Appendix.

Comparison Thresholds

Concentrations of constituents detected in groundwater samples were compared with CDPH and USEPA 

drinking-water health-based and aesthetically-based 

thresholds (California Department of Public Health 2007a; 

U.S. Environmental Protection Agency, 2006). The chemical 

and microbial data presented in this report characterize the 

quality of the untreated ground-water resources within the 

COA Study Unit, and are not intended to represent the treated 

drinking water delivered to consumers by water purveyors. 

The chemical and microbial composition of treated drinking 

water may differ from untreated ground water because treated 

drinking water may be disinfected, filtered, mixed with other 

waters, and exposed to the atmosphere before being delivered 

to consumers.

The following thresholds were used for comparisons:

• MCL– Maximum Contaminant Level. Legally 

enforceable standards that apply to public-water 

systems and 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 and lowered the threshold 

concentration for constituents with MCLs established 

by the USEPA. In this report, a threshold 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”. CDPH is notified 

when constituents are detected at concentrations 

exceeding MCL-US or MCL-CA thresholds in samples 

collected for the GAMA Priority Basin Project.

• AL – Action Level. Legally enforceable standards that 

apply to public water systems and protect public health 

by limiting the levels of copper and lead in drinking 

water. Detection concentrations of copper or lead 

above thresholds 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 thresholds 

are labeled “AL-US” in this report.

• TT – Treatment Technique. Legally enforceable 

standards that apply to public-water systems and 

protect public health by limiting the levels of microbial 

constituents in drinking water. Detections of microbial 

constituents above thresholds trigger requirements 

for mandatory additional disinfection during water 

treatment. The action levels established by the USEPA 

and CDPH are the same, thus the thresholds are labeled 

“TT-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 technical qualities of drinking 

water, such as scaling and staining. Both the USEPA 

and the 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.

• 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 above its 

NL-CA, State law requires timely notification of 

local governing bodies and recommends consumer 

notification.

• HAL – Lifetime Health Advisory Level. The 

maximum concentration of a constituent in drinking 

water which 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 2 liters (2.1 quarts) of water 

per day are consumed 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.
10 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

• 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 ten 

(RSD5-US).

For constituents having an MCL, detection 

concentrations in ground-water samples were compared to the 

MCL-US or the MCL-CA. If a constituent has an SMCL, its 

concentration was compared to the SMCL-CA. For chloride, 

sulfate, specific conductance, and total dissolved solids, CDPH 

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

concentrations of these constituents in ground-water samples 

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

constituents corresponds to the recommended SMCL-CA. 

Detected concentrations of constituents that lack an MCL or 

SMCL were compared to the NL-CA. Detected concentrations 

of constituents that lack an MCL, SMCL, or NL-CA were 

compared with the HAL-US. Detected concentrations of 

constituents that lack an MCL, SMCL, NL-CA, or HAL-CA 

were compared with the RSD5-US. Note that the result 

of this hierarchy of selecting comparison thresholds for 

constituents that have multiple types of established thresholds 

may not be a threshold that has the lowest concentration. 

The comparison thresholds used in this report are listed in 

tables 3A–L for all constituents analyzed and in tables 4–15 

for constituents detected in ground-water samples from 

the COA. Not all constituents analyzed for this study have 

established thresholds. Constituents detected at concentrations 

above established thresholds are marked with asterisks in the 

associated results table.

Ground-Water Quality Data

Field Parameters

Field and laboratory measurements of pH, specific 

conductance, alkalinity, and field measurements of turbidity, 

dissolved oxygen, and water temperature are presented in 

table 4. Dissolved oxygen and alkalinity are used as indicators 

of natural processes that control water chemistry. Specific 

conductance is the unit electrical conductivity of the water and 

is proportional to the amount of total dissolved solids (TDS) 

in the water. The pH value indicates the acidity or basicity 

of the water. Specific conductance measured in the field 

and in the laboratory samples was above the recommended 

SMCL-CA for six grid wells, three of which were above the 

upper threshold. Two grid wells had field pH values above the 

SMCL-US. Laboratory pH values may be higher than field pH 

values because the pH of ground water often increases when 

exposed to the atmosphere (see Appendix).

Organic Constituents 

Volatile organic compounds (VOCs) are in paints, 

solvents, fuels, fuel additives, refrigerants, fumigants, and 

disinfected water, and are characterized by their tendency to 

evaporate. VOCs generally persist longer in ground water than 

in surface water because ground water is isolated from the 

atmosphere. All concentrations of VOCs detected in samples 

from the COA Study Unit were below health-based thresholds. 

Concentrations ranged from less than one one-hundredth to 

less than one one-thousandth of the threshold values (table 5). 

At least one VOC was detected in 21 percent of the grid wells 

sampled. The only VOC detected in more than 10 percent 

of the grid wells was trichloromethane, also known as 

chloroform. Trichloromethane, a byproduct of drinking-water 

disinfection, tetrachloroethene (PCE), a solvent used for dry 

cleaning, and bromodichloromethane, another byproduct of 

disinfection, were detected in more than 10 percent of the 

understanding wells. Toluene was detected in 10 samples, but 

these detections were V-coded because toluene was detected 

in blanks also. V-coded values were not used in calculating 

summary statistics, and are preceded by a V in table 5. 

Pesticides include herbicides, insecticides, and 

fungicides. Pesticides are used to control weeds, insects, fungi, 

and other pests in agricultural, urban, and suburban settings. 

All detections of pesticides in samples from the COA Study 

Unit were at concentrations below health-based thresholds; 

all were less than one one-hundredth of the threshold values 

(table 6). There were 15 detections of pesticides and pesticide 

degradates in grid wells and 13 detections in understanding 

wells. At least one compound was detected in 32 percent of 

the grid wells sampled. Compounds detected in more than 

10 percent of the wells were the herbicides atrazine and 

simazine, and the atrazine degradate deethylatrazine (CIAT). 

These three compounds are among the most commonly 

detected pesticides and pesticide degradates in ground water in 

the Nation (Gilliom and others, 2006). 

Potential wastewater-indicator compounds were collected 

at wells sampled on a slow schedule (table 3E). Compounds 

include a wide variety of constituents, compounds analyzed 

for included caffeine, pyrene (a component of coal, tar and 

asphalt), and menthol (cigarettes, cough drops, liniment, 

mouthwash). All detections of potential wastewater-indicator 

compounds were below health-based thresholds. Phenol was 

detected at 29 percent of grid wells (table 7). Eleven potential 

wastewater-indicator compounds were detected in grid wells, 

and at least one potential wastewater-indicator compound was 

detected in 57 percent of the grid wells. 

Acetaminophen, a pharmaceutical compound, was 

detected in one understanding well, COAU-03, at an estimated 

laboratory value of 0.02 μg/L. Acetaminophen is a known 

analgesic commonly found in many over-the-counter pain 

relievers. 
Water Quality Results 11

Constituents of Special Interest

Perchlorate and 1,2,3-TCP are constituents of special 

interest in California because they recently have been found to 

be widely distributed in water supplies (California Department 

of Public Health, 2007b). Perchlorate was detected in 7 grid 

wells and 5 understanding wells in the COA; 2 of the grid 

wells contained concentrations above the MCL-CA (table 8). 

1,2,3-TCP was not detected in any samples.

Inorganic Constituents

Unlike the organic constituents and the constituents 

of special interest, most of the inorganic constituents 

are naturally present in ground water, although their 

concentrations may be influenced by human activities.

Nitrogen, phosphorus, and dissolved organic carbon 

present in ground water can affect biological activity in 

aquifers and in surface water bodies that receive ground-water 

discharge. Nitrogen may be present in the form of ammonia, 

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

the ground water. High concentrations of nitrate can adversely 

affect human health, particularly the health of infants. All 

concentrations of nitrate, nitrite, and ammonia measured in 

samples from the COA Study Unit were below health-based 

thresholds except nitrite plus nitrate as nitrogen concentrations 

from two understanding wells (table 9). Concentrations of 

phosphorus and dissolved organic carbon were also low.

The major-ion composition, total dissolved solids 

(TDS) content, and levels of certain trace elements in ground 

water can affect the aesthetic properties of water, such as 

taste, color, and odor, and the technical properties, such as 

scaling and staining. Although there are no adverse health 

effects associated with these properties, they may reduce 

consumer satisfaction with the water or may have economic 

impacts. CDPH has established non-enforceable thresholds 

(SMCL-CA) that are based on aesthetic or technical properties 

rather than health-based concerns for the major ions chloride 

and sulfate, TDS, and several trace elements.

Samples for the analysis of major and minor ions and 

total dissolved solids (TDS) were collected at 35 wells in the 

COA Study Unit (table 10). The concentrations of chloride 

in all the COA Study Unit wells, except one, were below the 

recommended SMCL-CAs. Fluoride concentrations in five 

samples were above the SMCL-CAs. Sulfate concentrations 

in seven samples were above the SMCL-CAs recommended 

threshold, and one above the upper threshold (table 10). TDS 

concentrations in nine samples were above the recommended 

SMCL-CA, and one sample was above the upper SMCL-CA. 

Samples for the analysis of trace elements were collected at 35 

wells in the COA Study Unit (table 11). Iron and manganese 

are trace elements whose concentrations are affected by the 

oxidation-reduction state of the ground water. Precipitation 

of minerals containing iron or manganese may stain surfaces 

orange, brown, or black. Concentrations of manganese in all 

but one sample were below the SMCL-CA. All concentrations 

of iron were below the SMCL-CA. 

Seventeen of the 23 trace elements analyzed in this study 

have health-based thresholds. Mercury was the only trace 

element not detected in at least one sample. Detections of trace 

elements in all samples from the COA Study Unit were below 

health-based thresholds, except five samples with arsenic 

concentrations above the MCL-US, two samples with boron 

above the NL-CA, two samples with molybdenum above the 

HAL-US, and two samples with strontium above the HAL-US 

(table 11). 

Arsenic, iron, and chromium occur in different species 

depending on the oxidation-reduction state of the ground 

water. The oxidized and reduced species have different 

solubilities in ground water and may have different effects 

on human health. The relative proportions of the oxidized 

and reduced species of each element can be used to aid in 

interpretation the oxidation–reduction state of the aquifer. 

Concentrations of total arsenic, iron, and chromium, and the 

concentrations of either the reduced or the oxidized species 

of each element are reported on table 12. The concentration 

of the other species can be calculated by difference. The 

concentrations of arsenic, iron, and chromium reported on 

table 12 may be different than those reported on table 11

because different analytical methods were used (see 

Appendix). The concentrations reported on table 11 are 

considered to be more accurate.

Isotopic Tracers 

The isotopic ratios of oxygen and hydrogen of water, 

tritium, and carbon-14 activities may be used as tracers of 

hydrologic processes. The isotopic ratios of oxygen and 

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

ground-water recharge location. These stable isotopic ratios 

reflect the altitude, latitude, and temperature of precipitation, 

and the extent of evaporation of recharge water. 

Tritium activities, carbon-14 activities, and helium 

isotopic ratios provide information about the age (time 

since recharge) of the ground-water. Tritium is a short-lived 

radioactive isotope of hydrogen that is incorporated into the 

water molecule. Tritium is produced in the atmosphere by the 

interaction of cosmic-ray produced neutrons with nitrogen-14 

(Craig and Lal, 1961), by atmospheric nuclear explosions, 

and by the operation of nuclear reactors. Carbon-14 

(table 13) is a radioactive isotope of carbon. Low levels of 

carbon-14 are continuously produced by interaction of cosmic 

radiation with the Earth’s atmosphere, and incorporated 

into atmospheric carbon dioxide. When carbon dioxide 

dissolved in precipitation, surface water, and ground water 

is exposed to the atmosphere, it enters the hydrologic cycle. 
12 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Because carbon-14 decays with a half-life of approximately 

5,700 years, low activities of carbon-14 relative to modern 

values generally indicate presence of ground water that is 

several thousand years old.

 Tritium is the only isotopic tracer that has a health-based 

threshold. All measured tritium activities in samples from the 

COA Study Unit wells were less than one one-hundredth of 

the MCL-CA (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 of the radioactivity in ground water comes from 

decay of naturally-occurring isotopes of uranium and thorium 

in minerals in the sediments or fractured rocks that comprise 

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

steps, eventually forming stable isotopes of lead. Radium-226, 

radium-228, and radon-222 are radioactive isotopes formed 

during the uranium and thorium decay series. In each step in 

the decay series, one radioactive element turns into a different 

radioactive element by emitting an alpha particle or a beta 

particle from its nucleus. For example, radium-226 emits an 

alpha particle and becomes radon-222. Radium-228 emits 

a beta particle to form actinium-228. 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.

Activity is often used instead of concentration for 

reporting the presence of radioactive constituents. Activity of 

radioactive constituents in ground water is measured in units 

of picocuries per liter (pCi/L); one picocurie approximately 

equals two atoms decaying per minute. The number of atoms 

decaying is equal to the number of alpha or beta particles 

emitted. 

All thirty-five wells sampled in Coachella were analyzed 

for uranium activities, and all reported activities were less than 

half of the regulatory threshold (table 13). The eleven slowschedule samples analyzed for all radioactive constituents had 

activities of radium and of gross alpha/beta emitter detections 

less than established health-based standards. Activities of 

radon-222 in samples from seven wells were above the 

proposed MCL-US of 300 pCi/L (table 14); however, no 

samples had an activity above the proposed alternative 

MCL-US of 4,000 pCi/L. The alternative MCL-US will apply 

if the State or local water agency has an approved multimedia 

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

Environmental Protection Agency, 1999a). 

Microbial Indicators

Water is disinfected during drinking-water treatment to 

prevent diseases that may be spread by water-borne microbial 

constituents derived from human or animal wastes. The 

specific viruses and bacteria responsible for diseases generally 

are not measured because routine analytical methods are not 

available. Measurements are made of more easily analyzed 

microbial constituents that serve as indicators of the presence 

of human or animal waste in water. Drinking water purveyors 

respond to detections of microbial indicators by applying 

additional disinfectants to the water.

Eleven samples were analyzed for microbial indicators. 

No samples contained the viral indicators F-specific 

and somatic coliphage and none contained the bacterial 

indicator Escherichia coli (E. coli). The bacterial indicator 

total coliforms was detected at a low level in one grid well 

(table 15). The threshold for total coliforms is based on 

recurring detections, thus the detection reported here does not 

necessarily exceed the MCL-US. 

Future Work

Subsequent reports will be focused on assessment of 

the data presented in this report using a variety of statistical, 

qualitative, and quantitative approaches to evaluate the 

natural and human factors affecting ground-water quality. 

Water-quality data contained in the CDPH and USGS NWIS 

databases and water-quality data available from other State 

and local water agencies will be compiled, evaluated, and used 

to complement the data presented in this report.

Summary 

Ground-water quality in the approximately 820 squaremile Coachella Valley was investigated in February and 

March 2007 as part of the Priority Basin Project of the 

Ground-Water Ambient Monitoring and Assessment (GAMA) 

Program. The project is a comprehensive assessment of 

statewide ground-water quality designed to identify and 

characterize risks to ground-water resources and to increase 

the amount of information available about ground-water 

quality to the public. The COA Study Unit was the sixteenth 

study unit sampled as part of the project. 

Thirty-five ground-water samples were analyzed for a 

combination of VOCs, pesticides and pesticide degradates, 

pharmaceutical compounds, potential wastewater-indicator 

compounds, nutrients, major and minor ions, trace elements, 

radioactive constituents, and microbial indicators. Naturally 

occurring isotopes (stable-isotopic ratios of hydrogen, oxygen, 

and carbon, and activities of tritium, carbon-14, and dissolved 

noble gases) were measured to provide a data set that will be 

used to help assess the source and age of the sampled ground 

water. A quality-control sample (blank, replicate, or matrix 

spike) was collected at approximately a quarter of the wells to 

evaluate the quality of the results from the analysis of groundwater samples.
References Cited 13

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 

thresholds apply to treated water that is served to the 

consumer, not to raw ground water. However, to provide some 

context for the results, concentrations of constituents measured 

in the raw ground water were compared with health-based 

thresholds established by the U.S. Environmental Protection 

Agency (USEPA) and California Department of Public Health 

(CDPH). 

Concentrations of VOCs were detected in 4 samples from 

grid wells and pesticides were detected in 6 samples from 

grid wells. All detections were less than one one-hundredth 

of health-based threshold concentrations. Potential wastewater indicators were detected in 4 grid well samples at 

levels below health-based thresholds. The pharmaceutical 

acetaminophen was detected in one sample in the COA study 

unit, but at a very low level. Perchlorate was detected in two 

grid wells at concentrations above the MCL-CA threshold. 

Two understanding wells contained concentrations of nitrite as 

nitrogen above established health-based thresholds. Chloride, 

fluoride, sulfate, manganese, and total dissolved solids were 

detected above the aesthetic thresholds in several samples. 

Several samples had concentrations of the trace elements 

arsenic, boron, molybdenum, and strontium above healthbased thresholds. All activities of the radioactive constituents 

uranium and gross alpha/beta were below established 

thresholds, but radon-222 was detected in four grid wells and 

three understanding wells at activities above both the proposed 

and the alternative maximum contaminant levels (MCL-US). 

The field parameters specific conductance and pH were 

detected above maximum contaminant levels (SMCL-CA 

and SMCL-US). Future work will include assessment of the 

data presented in this report, using a variety of statistical, 

qualitative, and quantitative approaches to help determine 

the influences of natural and human factors on ground-water 

quality.

Acknowledgments

The authors thank the following cooperators for 

their support: the State Water Resources Control Board 

(SWRCB), California Department of Public Health, California 

Department of Water Resources, and Lawrence Livermore 

National Laboratory. We especially thank the participating 

well owners for their generosity in allowing the USGS to 

collect samples from their wells. We also thank the reviewers 

who provided comments to improve this work. Funding 

for this work was provided by State bonds authorized by 

Proposition 50 and administered by the SWRCB.

References Cited

American Public Health Association, 1998, Standard 

methods for the examination of water and wastewater 

(20th ed.): Washington, D.C., American Public Health 

Association, American Water Works Association, and Water 

Environment Federation, p. 3-37–3-43.

American Society for Testing and Materials, 1998, Annual 

book of ASTM standards - water and environmental 

technology: Philadelphia, Pennsylvania, American Society 

for Testing and Materials, v. 11.02 (Water II), p. 664–666.

American Society for Testing and Materials, D 3972, 

“Standard Test Method for Isotopic Uranium in Water 

by Radiochemistry,” American Society for Testing and 

Materials International. 

Ball, J.W., and McCleskey, R.B., 2003a, A new cationexchange method for accurate field speciation of hexavalent 

chromium: U.S. Geological Survey Water-Resources 

Investigations Report 03-4018, 17 p.

Ball, J.W., and McCleskey, R.B., 2003b, A new cationexchange method for accurate field speciation of hexavalent 

chromium: Talanta, v. 61, p. 305–313.

Belitz, K., Dubrovsky, N.M., Burow, K.R., Jurgens, B., 

and Johnson, T., 2003, Framework for a ground-water 

quality monitoring and assessment program for California: 

U.S. Geological Survey Water-Resources Investigations 

Report 03-4166, 78 p.

Bennett, G.L., V, Belitz, K., and Milby Dawson, B.J., 2006, 

California GAMA Program - Ground-water quality data 

in the northern San Joaquin basin study unit, 2005: U.S. 

Geological Survey Data Series 196, 122 p.

Brenton, R.W., and Arnett, T.L., 1993, Methods of analysis 

by the U.S. Geological Survey National Water-Quality 

Laboratory - determination of dissolved organic carbon 

by UV-promoted persulfate oxidation and infrared 

spectrometry: U.S. Geological Survey Open-File 

Report 92-480, 12 p.

Bushon, R.N., 2003, Fecal indicator viruses: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chap. A7.2, accessed June 28, 2007 at http://pubs.water.

usgs.gov/twri9A7.2/

California Department of Water Resources, 2003, California’s 

groundwater: California Department of Water Resources 

Bulletin 118, 246 p, available at http://www.dpla2.water.

ca.gov/publications/groundwater/ bulletin118/Bulletin118_

Entire.pdf
14 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

California Department of Water Resources, 2007a, California 

Department of Water Resources Bulletin 118, individual 

basin descriptions, Indio subbasin, accessed December 1, 

2007 at http://www.dpla2.water.ca.gov/publications/

groundwater/bulletin118/basins/pdfs_desc/7-21.01.pdf

California Department of Water Resources, 2007b, California 

Department of Water Resources Bulletin 118, individual 

basin descriptions, Mission Creek subbasin, accessed 

December 1, 2007 at http://www.dpla2.water.ca.gov/

publications/groundwater/bulletin118/basins/pdfs_desc/7-

21.02.pdf

California Department of Water Resources, 2007c, California 

Department of Water Resources Bulletin 118, individual 

basin descriptions, Dessert Hot Springs subbasin, accessed 

December 1, 2006 at http://www.dpla2.water.ca.gov/

publications/groundwater/bulletin118/basins/pdfs_desc/7-

21.03.pdf

California Department of Water Resources, 2007d, California 

Department of Water Resources Bulletin 118, individual 

basin descriptions, San Gorgonio Pass subbasin, accessed 

December 1, 2007 at http://www.dpla2.water.ca.gov/

publications/groundwater/bulletin118/basins/pdfs_desc/7-

21.04.pdf

Childress, C.J.O., Foreman, W.T., Connor, B.F., and Maloney, 

T.J., 1999, New reporting procedures based on long-term 

method detection levels and some considerations for 

interpretations of water-quality data provided by the U.S. 

Geological Survey National Water Quality Laboratory: U.S. 

Geological Survey Open-File Report 99-193, 19 p.

Connor, B.F., Rose, D.L., Noriega, M.C., Murtagh, L.K., 

and Abney, S.R., 1998, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory - 

determination of 86 volatile organic compounds in water 

by gas chromatography/mass spectrometry, including 

detections less than reporting limits: U.S. Geological 

Survey Open-File Report 97-829, 78 p.

Coplen, T.B., Wildman, J.D., and Chen, J., 1991, 

Improvements in the gaseous hydrogen-water equilibrium 

technique for hydrogen isotope analysis: Analytical 

Chemistry, v. 63, p. 910–912. 

Coplen, T.B., 1994, Reporting of stable hydrogen, carbon, and 

oxygen isotopic abundances: Pure and Applied Chemistry, 

v. 66, p. 273–276.

Coplen, T.B., Hopple, J.A., Bohlke, J.K., Peiser, H.S., Rieder, 

S.E., Krouse, H.R., Rosman, K.J.R., Ding, T., Vocke, R.D., 

Jr., Revesz, K.M., Lamberty, A., Taylor, P., and DeBierve, 

P., 2002, Compilation of minimum and maximum 

isotope ratios of selected elements in naturally occurring 

terrestrial materials and reagents: U.S. Geological Survey 

Water-Resources Investigations Report 01-4222, 98 p. 

Craig, H.D., and Lal,, D. , 1961, The production rate of natural 

tritium: Tellus, v. 13, p. 85–105,

Dawson, B.J., Bennett, G.L., V, and Belitz, K., 2008, Groundwater quality data in the southern Sacramento Valley study 

unit, California, 2005—Results from the California GAMA 

Program: U.S. Geological Survey Data Series 285, 93 p.

Donahue, D.J., Linick, T.W., and Jull, A.J.T., 1990, Ratio and 

background corrections for accelerator mass spectrometry 

radiocarbon measurements: Radiocarbon, v. 32, p. 135–142.

Eaton, G.F., Hudson, G.B., and Moran, J.E., 2004, Tritiumhelium-3 age-dating of groundwater in the Livermore Valley 

of California: American Chemical Society ACS Symposium 

Series, v. 868, p. 235–245.

Epstein, S., and Mayeda, T.K., 1953, Variation of O-18 

content of water from natural sources: Geochimica et 

Cosmochimica Acta, v. 4, p. 213–224.

Faires, L.M., 1993, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory - 

determination of metals in water by inductively coupled 

plasma-mass spectrometry: U.S. Geological Survey 

Open-File Report 92-634, 28 p.

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and 

fluvial sediments: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 5, chap. A1, 545 p.

Fishman, M.J., 1993, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory - 

determination of inorganic and organic constituents in water 

and fluvial sediments: U.S. Geological Survey Open-File 

Report 93-125, 217 p.

Firestone, R.B., Shirley, V.S., Baglin, C.M., Chu, S.Y.F., and 

Zipkin, J., 1996, Table of Isotopes (8th ed.): New York, John 

Wiley & Sons, 3168 p., available at http://ie.lbl.gov/toipdf/

toi20.pdf

Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., 

Coffey, L.J., and Burkhardt, M.R., 2001, Methods of 

Analysis by the U.S. Geological Survey National Water 

Quality Laboratory-Determination of Pesticides in Water 

by Graphitized Carbon-Based Solid-Phase Extraction 

and High-Performance Liquid Chromatography/Mass 

Spectrometry: U.S. Geological Survey Water-Resources 

Investigations Report 01-4134, 73 p.
References Cited 15

Furlong, E.T., Werner, S.L., Anderson, B.D., and Cahill, 

J.D., 2008, Methods of Analysis by the U.S. Geological 

Survey National Water Quality Laboratory – Determination 

of human-health pharmaceuticals in filtered water by 

chemically modified styrene-divinylbenzene resin-based 

solid-phase extraction and high-performance liquid 

chromatography/mass spectrometry. U.S. Geological 

Survey Techniques and Methods, book 5, chap. A9, 56 p.

Garbarino, J.R., 1999, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory 

- determination of dissolved arsenic, boron, lithium, 

selenium, strontium, thallium, and vanadium using 

inductively coupled plasma-mass spectrometry: U.S. 

Geological Survey Open-File Report 99–093, 31 p.

Garbarino, J.R., and Damrau, D.L., 2001, Methods of analysis 

by the U.S. Geological Survey National Water Quality 

Laboratory - determination of organic plus inorganic 

mercury in filtered and unfiltered natural water with cold 

vapor - atomic fluorescence spectrometry: U.S. Geological 

Survey Water-Resources Investigations Report 01-4132, 

16 p.

Garbarino, J.R., Kanagy, J.R., and Cree, M.E., 2006, 

Determination of elements in natural-water, biota, sediment, 

and soil samples using collision/reaction cell inductively 

coupled plasma-mass spectrometry: U.S. Geological Survey 

Techniques and Methods, book 5, chap. B1, 88 p.

Gilliom, R.J., Barbash, J.E., Crawford, C.G., Hamilton, P.A., 

Martin, J.D., Nakagaki, N., Nowell, L.H., Scott, J.C., 

Stackelberg, P.E., Thelin, G.P., and Wolock, D.M., 2006, 

The quality of our Nation’s waters: Pesticides in the nation’s 

streams and ground water, 1992-2001: U.S. Geological 

Survey Circular 1291, 172 p.

Gran, G,. 1952, Determination of the equivalence point in 

potentiometric titrations—Part II: The Analyst: v. 77, 

p. 661-671.

Grob, R.L, ed., 1995, Modern practice of gas chromatography 

(3rd ed.): New York, John Wiley & Sons, 888 p.

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

2002, Ground-water quality in the Santa Ana watershed, 

California: Overview and data summary: U.S. Geological 

Survey Water-Resources Investigations Report 02-4243, 

137 p.

Hautman, D.P., Munch, D.J., Eaton, A.D., and Haghani, 

A.W., 1999, Method 314.0 Determination of perchlorate in 

drinking water using ion chromatography, revision 1.0: U.S. 

Environmental Protection Agency, accessed June 22, 2004 

at http://www.epa.gov/safewater/methods/pdfs/met314.pdf.

Hutson, S.S., Barber, N.L., Kenny, J.F., Linsey, K.S., Lumia, 

D.S., and Maupin, M.A., 2004, Estimated use of water 

in the United States in 2000: U.S. Geological Survey 

Circular 1268, 46 p.

Jull, A.J.T., Burr, G.S., McHargue, L.R., Lange, T.E., Lifton, 

N.A., Beck, J.W., Donahue, D.J., and Lal, D., 2004, 

New frontiers in dating of geological, paleoclimatic, 

and anthropological applications using accelerator mass 

spectrometric measurements of 14C and 10Be in diverse 

samples: Global and Planetary Change, v. 41, p. 309–323.

Kolpin, D.W., Furlong, E.T., Meyer, M.T., Thurman, E.M., 

Zaugg, S.D., Barber, L.B., and Buxton, H.T., 2002, 

Pharmaceuticals, hormones and other organic wastewater 

contaminants in U.S. streams, 1999–2000: Environmental 

Science & Technology, v. 36, no. 6, p. 1202–1211. 

Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995, 

Ground-water data-collection protocols and procedures for 

the National Water-Quality Assessment Program - collection 

and documentation of water-quality samples and related 

data: U.S. Geological Survey Open-File Report 95-399, 

113 p.

Kulongoski, J.T., and Belitz, K., 2004, Ground-water ambient 

monitoring and assessment program: U.S. Geological 

Survey Fact Sheet 2004-3088, 2 p.

Kulongoski, J.T., Belitz, K., and Dawson, B.J., 2006, 

Ground-water quality data in the North San Francisco Bay 

Hydrogeologic provinces, California, 2004: Results from 

the California Ground-Water Ambient Monitoring and 

Assessment (GAMA) Program: U.S. Geological Survey 

Data Series 167, 100 p.

Kulongoski, J.T., and Belitz, K., 2007, Ground-water quality 

data in the Monterey Bay and Salinas Valley Basins, 

California, 2005 – Results from the California GAMA 

Program: U.S. Geological Survey Data Series DS-258, 84 p.

Lane, S.L., Flanagan, S., and Wilde, F.D., 2003, Selection of 

equipment for water sampling (ver. 2.0): U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 9, chap. A2, accessed June 28, 2007, at http://pubs.

water.usgs.gov/twri9A2/

Lewis, M.E., 2006, Dissolved Oxygen (ver. 2.1): U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 9, chap. A6.2, accessed June 28, 2007 

at http://pubs.water.usgs.gov/twri9A6.2/

Lindley, C.E., Stewart, J.T., and Sandstrom, M.W., 1996, 

Determination of low concentrations of acetochlor in 

water by automated solid-phase extraction and gas 

chromatography with mass selective detection: Journal of 

AOAC International, v. 79, no. 4, p. 962–966.
16 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Loeltz, O.J., Irelan, Burdge, Robinson, J.H., and Olmsted, 

F.H., 1975, Geohydrologic reconnaissance of the Imperial 

Valley, California: U.S. Geological Survey Professional 

Paper 486-K, 54 p.

Madsen, J.E., Sandstrom, M.W., and Zaugg, S.D., 2003, 

Methods of analysis by the U.S. Geological Survey 

National Water Quality Laboratory - A method supplement 

for the determination of fipronil and degradates in water by 

gas chromatography/mass spectrometry: U.S. Geological 

Survey Open-File Report 02-462, 11 p.

Maloney, T.J., ed., 2005, Quality management system, U.S. 

Geological Survey National Water Quality Laboratory: 

U.S. Geological Survey Open-File Report 2005-1263, 

93 p., available at http://pubs.usgs.gov/of/2005/1263/pdf/

OFR2005-1263.pdf

McCleskey, R.B., Nordstrom, D.K., and Ball, J.W., 2003, 

Metal interferences and their removal prior to the 

determination of As(T) and As(III) in acid mine waters 

by hydride generation atomic absorption spectrometry: 

U.S. Geological Survey Water-Resources Investigations 

Report 03-4117.

McLain, B., 1993, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory - determination 

of chromium in water by graphite furnace atomic absorption 

spectrophotometry: U.S. Geological Survey Open-File 

Report 93-449, 16 p.

Mendenhall, W.C., 1909, Ground waters of the Indio region, 

California, with a sketch of the California desert: U.S. 

Geological Survey Water Supply Paper 225, 56 p.

Moran, J.E., Hudson, G.B., Eaton, G.F., and Leif, R., 

2002, A contamination vulnerability assessment for the 

Livermore-Amador and Niles Cone Groundwater Basins: 

Lawrence Livermore National Laboratory internal report, 

UCRL-AR-148831, 25 p.

Myers, D.N., 2004, Fecal indicator bacteria (ver. 1.2): 

U.S. Geological Survey Techniques of Water-Resources 

Investigations Report, book 9, chap. A7.1, accessed June 28, 

2007, at http://pubs.water.usgs.gov/twri9A7.1/

National Climate Data Center, 2005a, Annual mean daily 

average temperature: National Oceanic and Atmospheric 

Administration, accessed March 5, 2008, at http://cdo.ncdc.

noaa.gov/climaps/temp0313.pdf

National Climate Data Center, 2005b, Annual mean 

total precipitation: National Oceanic and Atmospheric 

Administration, accessed March 5, 2008, at http://cdo.ncdc.

noaa.gov/climaps/prec0113.pdf

Patton, C.J., and Kryskalla, J.R., 2003, Methods of analysis 

by the U.S. Geological Survey National Water Quality 

Laboratory - evaluation of alkaline persulfate digestion 

as an alternative to Kjeldahl digestion for determination 

of total and dissolved nitrogen and phosphorous in water: 

U.S. Geological Survey Water-Resources Investigations 

Report 03-4174, 33 p.

Pirkey, K.D., and Glodt, S.R., 1998, Quality control at the 

U.S. Geological Survey National Water Quality Laboratory: 

U.S. Geological Survey Fact-Sheet FS-026-98, 4 p., http://

pubs.er.usgs.gov/usgspubs/fs/fs02698

Radtke, D.B., Davis, J.V., and Wilde, F.D., 2005, Specific 

electrical conductance (ver. 1.2), in National Field 

Manual for the Collection of Water-Quality Data, Field 

Measurements: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 9, chap. A6, sec. 

6.3, accessed June 28, 2007, at http://pubs.water.usgs.gov/

twri9A6.3/

Reichard, E.G. and Meadows, K.J., 1992, Evaluation of 

a ground-water flow and transport model of the upper 

Coachella Valley, California: U.S. Geological Survey 

Water-Resources Investigation Report 91-4142, 101 p.

Rose, D.L., and Sandstrom, M.W., 2003, Methods of analysis 

by the U.S. Geological Survey National Water Quality 

Laboratory - determination of gasoline oxygenates, selected 

degradates, and BTEX in water by heated purge and trap/

gas chromatography/mass spectrometry: U.S. Geological 

Survey Water-Resources Investigations Report 03-4079, 

31 p.

Rounds, S.A., 2006, Alkalinity and acid neutralizing capacity 

(ver. 3): U.S. Geological Survey Techniques of WaterResources Investigations, in National Field Manual for the 

Collection of Water-Quality Data, Field Measurements: 

book 9, chap. A6, sec 6.6, accessed June 28, 2007, at http://

pubs.water.usgs.gov/twri9A6.6/

Sandstrom, M.W., Stroppel, M.E., Foreman, W.T., and 

Schroeder, M.P., 2001, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory 

- determination of moderate-use pesticides and selected 

degradates in water by C-18 solid-phase extraction and 

gas chromatography/mass spectrometry: U.S. Geological 

Survey Water-Resources Investigations Report 01-4098, 

70 p.

Scott, J.C., 1990, Computerized stratified random site 

selection approaches for design of a ground-water quality 

sampling network: U.S. Geological Survey Water-Resources 

Investigations Report 90-4101, 109 p.
References Cited 17

Shelton, J.L., Burow, K.R., Belitz, K., Dubrovsky, N.M., 

Land, M.T., and Gronberg, J.M., 2001, Low-level volatile 

organic compounds in active public supply wells as groundwater tracers in the Los Angeles physiographic basin, 

California, 2000: U.S. Geological Survey Water-Resources 

Investigations Report 01-4188, 29 p.

State Water Resources Control Board, 2003, A comprehensive 

groundwater quality monitoring program for California: 

Assembly Bill 599 Report to the Governor and Legislature, 

March 2003, 100 p., available at http://www.waterboards.

ca.gov/gama/docs/final_ab_599_rpt_to_legis_7_31_03.pdf

Stookey, L.L., 1970, FerroZine - a new spectrophotometric 

reagent for iron: Analytical Chemistry, v. 42, p. 779–781.

Stumm, W., and Morgan, J.J., 1996, Aquatic chemistry: 

Chemical equilibria and rates in natural waters (3rd ed.): 

New York, John Wiley & Sons, 1022 p.

Thatcher, L.L., Janzer, V.J., and Edwards, K.W., 1977, 

Methods for the determination of radioactive substances 

in water: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 5, chap. A5, 95 p., 

available at http://pubs.usgs.gov/twri/twri5a5/

Timme, P.J., 1995, National Water Quality Laboratory 1995 

services catalog: U.S. Geological Survey Open-File 

Report 95-352, 120 p.

To, T.B., Nordstrom, D.K., Cunningham, K.M., Ball, J.W., 

and McCleskey, R.B., 1998, New method for the direct 

determination of dissolved Fe(III) concentration in acid 

mine waters: Environmental Science and Technology, v. 33, 

p. 807813.

U.S. Environmental Protection Agency, 1980, Prescribed 

procedures for measurement of radioactivity in drinking 

water: U.S. Environmental Protection Agency EPA-600-4-

80-032.

U.S. Environmental Protection Agency, 1995, Method 524.2, 

Measurement of purgeable organic compounds in water by 

capillary column gas chromatography/mass spectrometry: 

U.S. Environmental Protection Agency EPA/600/R-95-131.

U.S. Environmental Protection Agency, 1996, Method 8270C 

- Semivolatile organic compounds by gas chromatography/

mass spectrometry (rev 3), available at http://www.nemi.

gov/

U.S. Environmental Protection Agency, 1999a, National 

primary drinking water regulations, radon-222: Federal 

Register, v. 64, no. 211, p. 59245–59294.

U.S. Environmental Protection Agency, 2001, Method 1601 

- Male-specific (F+) and somatic Coliphage in water by 

two-step enrichment procedure - April 2000 Draft: U.S. 

Environmental Protection Agency EPA 821-R-00-009.

U.S. Environmental Protection Agency, 2002b, Method 1604 - 

total coliforms and Escherichia coli in water by membrane 

filtration using a simultaneous detection technique (MI 

medium): U.S. Environmental Protection Agency EPA 821-

R-02-024.

U.S. Environmental Protection Agency, 2002a, Guidelines for 

establishing procedures for the analysis of pollutants: U.S. 

Code of Federal Regulations, Title 40, 136 p.

U.S. Environmental Protection Agency, 2004, National 

primary drinking water regulations - analytical method for 

uranium: U.S. Code of Federal Regulations, Title 40, part 

141, p. 31008-31013.

U.S. Environmental Protection Agency, 2006, 2006 Edition 

of the drinking water standards and health advisories: U.S. 

Environmental Protection Agency, Office of Water EPA 

822-R-06-013. Accessed June 21, 2007, at http://www.epa.

gov/waterscience/criteria/drinking/dwstandards.pdf

U.S. Geological Survey, variously dated, National field manual 

for the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 9, chap. A1-A9, available at http://water.usgs.gov/

owq/FieldManual/ 

Weiss, R.F., 1968, Piggyback sampler for dissolved gas 

studies on sealed water samples: Deep Sea Research, v. 15, 

p. 721-735.

Wilde, F.D., 2006, Temperature (ver. 2) , in National Field 

Manual for the Collection of Water-Quality Data, Field 

Measurements: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 9, chap. A6, sec. 

6.1, accessed June 28, 2007, at http://pubs.water.usgs.gov/

twri9A6.1/

Wilde, F.D., ed., 2004, Cleaning of equipment for water 

sampling (ver. 2.0), in National Field Manual for the 

Collection of Water-Quality Data: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 9, 

chap. A3, accessed June 28, 2007, at http://pubs.water.usgs.

gov/twri9A3/

Wilde, F.D., Busenberg, E., and Radtke, D.B., 2006, pH 

(ver. 1.3): U.S. Geological Survey Techniques of WaterResources Investigations, book 9, chap. A6.4, accessed 

June 28, 2007 at http://pubs.water.usgs.gov/twri9A6.4/

Wilde, F.D., and Radtke, D.B., 2005, General information and 

guidelines (ver. 1.2): U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 9, chap. A6.0, 

accessed June 28, 2007, at http://pubs.water.usgs.gov/

twri9A6.0/
18 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Wilde, F.D., Radtke, D.B., Gibs, J., and Iwatsubo, R.T., 1999, 

Collection of water samples: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 9, 

chap. A4, accessed June 28, 2007, at http://pubs.water.usgs.

gov/twri9A4/

Wilde, F.D., Radtke, D.B., Gibs, J., and Iwatsubo, R.T., 2004, 

Processing of water samples: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 9, 

chap. A5, accessed June 28, 2007, at http://pubs.water.usgs.

gov/twri9A5/

Wright, M.T., Belitz, K., and Burton, C.A., 2005, California 

GAMA program - ground-water quality in the San Diego 

drainages hydrologic province, California, 2004: U.S. 

Geological Survey Data Series 129, 91 p.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory - Determination 

of pesticides in water by C-18 solid-phase extraction and 

capillary-column gas chromatography/mass spectrometry: 

U.S. Geological Survey Open-File Report 95-181, 60 p.

Zaugg, S.D., Smith, S.G., Schroeder, M.P., Barber, L.B., and 

Burkhardt, M.R., 2002, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory - 

determination of wastewater compounds by polystyrene 

divinylbenzene solid-phase extraction and capillary-column 

gas chromatography/mass spectrometry: U.S. Geological 

Survey Water-Resources Investigations Report 01-4186, 

37 p.
Table 1 19

GAMA well

identification 

No.

Sampling information

Well type

Construction information

Date Sampling

schedule

Elevation of LSD 

(ft above 

NAVD 88)

Well depth 

(ft below 

LSD)

Top

perforation

(ft below 

LSD)

Bottom 

perforation 

(ft below 

LSD)

Grid wells

COA-01 02-27-07 Slow 1,993 Production 1,200 900 1,200 

COA-02 02-28-07 Slow -211 Production na 230 480 

COA-03 02-28-07 Slow 147 Production na na na 

COA-04 03-01-07 Intermediate 79 Production 1,070 500 1,060 

COA-05 03-05-07 Intermediate 237.23 Production 1,090 710 1,090 

COA-06 03-05-07 Intermediate 52.20 Production 654 203 654 

COA-07 03-06-07 Intermediate 2 Production 240 na na 

COA-08 03-06-07 Slow -16 Production 342 258 342 

COA-09 03-07-07 Slow 392 Production na na na 

COA-10 03-08-07 Intermediate 106 Production na na na 

COA-11 03-08-07 Intermediate -110 Production na na na 

COA-12 03-08-07 Intermediate -173 Production 525 445 525 

COA-13 03-12-07 Intermediate 1,953 Production 890 510 870 

COA-14 03-12-07 Intermediate 232 Production 820 420 820 

COA-15 03-14-07 Slow 872 Production 400 180 380 

COA-16 03-15-07 Slow 477 Production 650 300 650 

COA-17 03-15-07 Intermediate 2,475 Production na na na 

COA-18 03-19-07 Intermediate 43 Production 790 280 790 

COA-19 03-29-07 Intermediate 1,063 Production na na na 

Understanding wells

COAU-01 02-26-07 Slow 2,218 Production 96 12 43 

COAU-02 02-27-07 Intermediate 382 Production 600 288 600 

COAU-03 03-01-07 Slow 332 Production na na na 

COAU-04 03-06-07 Intermediate 2 Production 400 280 400 

COAU-05 03-07-07 Slow 1,175 Production 909 306 906 

COAU-06 03-13-07 Slow 2,297.83 Production 1,130 580 1,110 

COAU-07 03-13-07 Intermediate 1,353 Production 553 225 553 

COAU-08 03-14-07 Intermediate 499.42 Production 730 476 726 

COAU-09 03-19-07 Intermediate 183 Production na na na 

COAU-10 03-20-07 Intermediate 1,016 Production 1,070 410 1,050 

COAU-11 03-20-07 Intermediate 589 Production 400 220 400 

COAU-12 04-11-01 Intermediate 4,469.99 Production 160 55 155 

COAU-13 03-26-07 Intermediate 171 Production na na na 

COAU-14 03-27-07 Intermediate 62 Production 550 330 530 

COAU-15 03-28-07 Intermediate 344 Production 700 400 700 

COAU-16 03-28-07 Intermediate -3 Production na na na

Table 1. Identification, sampling, and construction information for wells sampled for the Coachella Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, February and March 2007.

[Sampling schedules are described in table 2. Land surface datum (LSD) is a datum plane that is approximately at land surface at each well. The elevation of 

the LSD is described in feet above the North American Vertical Datum 1988 (NAVD 88). Abbreviations: COA, Coachella Valley study unit grid well; COAU, 

Coachella Valley study unit understanding well. ft, foot; na, not available]
20 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Analyte classes Analyte list 

table

Sampling schedule

Slow Intermediate

Water-quality indicators

Dissolved oxygen, temperature, specific conductance X X

pH, alkalinity X X

Turbidity X

Organic constituents

Volatile organic compounds 3A X X

Polar pesticides and pesticide degredates 3B X X

Pesticides and pesticide degredates 3C X X

Pharmaceutical compounds 3D X X

Dissolved organic carbon 3G X

Wastewater-indicator compounds 3E X

Constituents of special interest

Perchlorate 3F X X

1,2,3-Trichloropropane 3F X

Inorganic constituents

Nutrients 3G X X

Major and minor ions and trace elements including mercury 3H X

Major and minor ions and trace elements without mercury X

Arsenic, chromium, and iron abundances and speciation 3I X X

Isotopes

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

Stable isotopes of carbon and carbon-14 abundance 3J X X

Uranium isotopes 3J X X

Radioactivity and noble gases

Tritium 3J X X

Radium isotopes 3J X

Radon-222 3J X

Gross alpha and beta radiation 3J X

Noble gases 3K X X

Microbial constituents

Bacterial indicators 3L X

Viral indicators 3L X

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

for the slow and intermediate well sampling schedules in the Coachella Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, February and March, 2007.
Table 3A 21

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Acetone Solvent 81552 67-64-1 6 na na –

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

Benzene Gasoline hydrocarbon 34030 71-43-2 0.016 MCL-CA 1 –

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

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

Bromodichloromethane Disinfection by-product 

(THM)

32101 75-27-4 0.04 MCL-US1 80 D 

Bromoform (Tribromomethane) Disinfection by-product 

(THM)

32104 75-25-2 0.08 MCL-US1 80 –

2-Butanone (MEK, Methyl ethyl 

ketone)

Solvent 81595 78-93-3 1.6 HAL-US 4,000 –

n-Butylbenzene Gasoline hydrocarbon 77342 104-51-8 0.14 NL-CA 260 –

sec-Butylbenzene Gasoline hydrocarbon 77350 135-98-8 0.04 NL-CA 260 –

tert-Butylbenzene Gasoline hydrocarbon 77353 98-06-6 0.08 NL-CA 260 –

Carbon disulfide Organic synthesis 77041 75-15-0 0.06 NL-CA 160 –

Carbon tetrachloride 

(Tetrachloromethane)

Solvent 32102 56-23-5 0.08 MCL-CA 0.5 –

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

Chloroethane Solvent 34311 75-00-3 0.1 na na –

Chloroform (Trichloromethane) Disinfection by-product 

(THM)

32106 67-66-3 0.04 MCL-US1 80 D 

Chloromethane Refrigerant/organic synthesis 34418 74-87-3 0.1 HAL-US 30 –

3-Chloro-1-propene Organic synthesis 78109 107-05-1 0.08 na na –

2-Chlorotoluene Solvent 77275 95-49-8 0.04 NL-CA 140 –

4-Chlorotoluene Solvent 77277 106-43-4 0.04 NL-CA 140 –

Dibromochloromethane Disinfection by-product 

(THM)

32105 124-48-1 0.12 MCL-US1 80 –

1,2-Dibromo-3-chloropropane 

(DBCP)

Fumigant 82625 96-12-8 0.5 MCL-US 0.2 –

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

Dibromomethane Solvent 30217 74-95-3 0.004 na na –

1,2-Dichlorobenzene Solvent 34536 95-50-1 0.04 MCL-US 600 –

1,3-Dichlorobenzene Solvent 34566 541-73-1 0.04 HAL-US 600 –

1,4-Dichlorobenzene Fumigant 34571 106-46-7 0.04 MCL-CA 5 –

trans-1,4-Dichloro-2-butene Organic synthesis 73547 110-57-6 0.6 na na –

Dichlorodifluoromethane (CFC-12) Refrigerant 34668 75-71-8 0.14 NL-CA 1,000 –

1,1-Dichloroethane Solvent 34496 75-34-3 0.06 MCL-CA 5 D

1,2-Dichloroethane Solvent 32103 107-06-2 0.1 MCL-CA 0.5 –

1,1-Dichloroethene Organic synthesis 34501 75-35-4 0.02 MCL-CA 6 –

cis-1,2-Dichloroethene Solvent 77093 156-59-2 0.02 MCL-CA 6 –

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

Dichloromethane (Methylene 

chloride)

Solvent 34423 75-09-2 0.04 MCL-US 5 –

1,2-Dichloropropane Fumigant 34541 78-87-5 0.02 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 na na –

cis-1,3-Dichloropropene Fumigant 34704 10061-01-5 0.06 RSD5-US2 4 –

trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.1 RSD5-US2 4 –

Diethyl ether Solvent 81576 60-29-7 0.08 na na –

Diisopropyl ether (DIPE) Gasoline oxygenate 81577 108-20-3 0.06 na na –

Table 3A. Volatile organic compounds, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey (USGS) National Water Quality Laboratory schedule 2020.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which

 is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client 

ServicesSM. Threshold type: Maximum contaminant level thresholds 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 Lifetime Health Advisory; MCL-CA, 

California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, 

California Department of Public Health notification level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10-5. Other 

abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; THM, trihalomethane; D, detected in ground-water samples (table 5); na, not 

available; μg/L, micrograms per liter; –, not detected]
22 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Ethylbenzene Gasoline hydrocarbon 34371 100-41-4 0.02 MCL-CA 300 –

Ethyl tert-butyl ether (ETBE) Gasoline oxygenate 50004 637-92-3 0.04 DLR 3 –

Ethyl methacrylate Organic synthesis 73570 97-63-2 0.14 na na –

1-Ethyl-2-methylbenzene (o-Ethyl 

toluene)

Gasoline hydrocarbon 77220 611-14-3 0.04 na na –

Hexachlorobutadiene Organic synthesis 39702 87-68-3 0.1 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 0.4 na na –

Isopropylbenzene (Cumene) Gasoline hydrocarbon 77223 98-82-8 0.04 NL-CA 770 –

4-Isopropyl-1-methylbenzene Gasoline hydrocarbon 77356 99-87-6 0.08 na na –

Methyl acrylate Organic synthesis 49991 96-33-3 0.4 na na –

Methyl acrylonitrile Organic synthesis 81593 126-98-7 0.40 na na –

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

Methyl tert-butyl ether (MTBE) Gasoline oxygenate 78032 1634-04-4 0.10 MCL-CA 13 –

Methyl iodide (Iodomethane) Organic synthesis 77424 74-88-4 0.4 na na –

Methyl isobutyl ketone (MIBK) Solvent 78133 108-10-1 0.2 NL-CA 120 –

Methyl methacrylate Organic synthesis 81597 80-62-6 0.20 na na –

Methyl tert-pentyl ether (tert-Amyl 

methyl ether, TAME)

Gasoline oxygenate 50005 994-05-8 0.04 na na –

Naphthalene Gasoline hydrocarbon 34696 91-20-3 0.4 NL-CA 17 –

n-Propylbenzene Solvent 77224 103-65-1 0.04 NL-CA 260 –

Styrene Gasoline hydrocarbon 77128 100-42-5 0.04 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 0.1 MCL-CA 1 –

Tetrachloroethene (PCE) Solvent 34475 127-18-4 0.04 MCL-US 5 D

Tetrahydrofuran Solvent 81607 109-99-9 1.0 na na –

1,2,3,4-Tetramethylbenzene Gasoline hydrocarbon 49999 488-23-3 0.14 na na –

1,2,3,5-Tetramethylbenzene Gasoline hydrocarbon 50000 527-53-7 0.12 na na –

Toluene Gasoline hydrocarbon 34010 108-88-3 0.018 MCL-CA 150 D

1,2,3-Trichlorobenzene Organic synthesis 77613 87-61-6 0.12 na na –

1,2,4-Trichlorobenzene Solvent 34551 120-82-1 0.12 MCL-CA 5 –

1,1,1-Trichloroethane Solvent 34506 71-55-6 0.04 MCL-CA 200 –

1,1,2-Trichloroethane Solvent 34511 79-00-5 0.04 MCL-CA 5 –

Trichloroethene (TCE) Solvent 39180 79-01-6 0.02 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 NL-CA 0.005 –

1,1,2-Trichloro-1,2,2-trifluoroethane 

(CFC-113)

Refrigerant 77652 76-13-1 0.04 MCL-CA 1,200 –

1,2,3-Trimethylbenzene Gasoline hydrocarbon 77221 526-73-8 0.08 na na –

1,2,4-Trimethylbenzene Gasoline hydrocarbon 77222 95-63-6 0.04 NL-CA 330 –

1,3,5-Trimethylbenzene Organic synthesis 77226 108-67-8 0.04 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 MCL-CA 0.5 –

m- and p-Xylene Gasoline hydrocarbon 85795 108-38-3 / 106-42-3 0.08 MCL-CA 3 1,750 –

o-Xylene Gasoline hydrocarbon 77135 95-47-6 0.04 MCL-CA 3

1,750 –

1The MCL-US, and MCL-CA thresholds for trihalomethanes are the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.

2The RSD5 threshold for 1,3-dichloropropene is the sum of its isomers (cis and trans).

3The MCL value is the sum of all three xylene compounds.

Table 3A. Volatile organic compounds, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey (USGS) National Water Quality Laboratory schedule 2020.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which

 is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client 

ServicesSM. Threshold type: Maximum contaminant level thresholds 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 Lifetime Health Advisory; MCL-CA, 

California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, 

California Department of Public Health notification level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10-5. Other 

abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; THM, trihalomethane; D, detected in ground-water samples (table 5); na, not 

available; μg/L, micrograms per liter; –, not detected]
Table 3B 23

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Acifluorfen Herbicide 49315 50594-66-6 0.06 na na –

Aldicarb Insecticide 49312 116-06-3 0.04 MCL-US 4 –

Aldicarb sulfone Degradate 49313 1646-88-4 0.08 MCL-US 3 –

Aldicarb sulfoxide Degradate 49314 1646-87-3 0.04 MCL-US 3 –

Atrazine Herbicide 39632 1912-24-9 0.04 MCL-CA 1 D

Bendiocarb Insecticide 50299 22781-23-3 0.04 na na –

Benomyl Fungicide 50300 17804-35-2 0.02 na na –

Bensulfuron-methyl Herbicide 61693 83055-99-6 0.06 na na –

Bentazon Herbicide 38711 25057-89-0 0.02 MCL-CA 18 –

Bromacil Herbicide 04029 314-40-9 0.04 HAL-US 70 –

Bromoxynil Herbicide 49311 1689-84-5 0.12 na na –

Caffeine Stimulant 50305 58-08-2 0.04 na na –

Carbaryl Herbicide 49310 63-25-2 0.02 HAL-US 700 –

Carbofuran Herbicide 49309 1563-66-2 0.06 MCL-CA 18 –

Chloramben methyl ester Herbicide 61188 7286-84-2 0.1 na na –

Chlorimuron-ethyl Herbicide 50306 90982-32-4 0.08 na na –

2-Chloro-4-isopropylamino-6-

amino-s-triazine (Deethylatrazine, 

CIAT)

Degradate 04040 6190-65-4 0.02 na na D

2-Choro-6-ethylamino-4-aminos-triazine (Deisopropylatrazine, 

CEAT)

Degradate 04038 1007-28-9 0.08 na na D

3-(4-Chlorophenyl)-1-methyl urea Degradate 61692 5352-88-5 0.06 na na –

Clopyralid Herbicide 49305 1702-17-6 0.06 na na –

Cycloate Herbicide 04031 1134-23-2 0.06 na na –

2,4-D plus 2,4-D methyl ester Herbicide 66496 – 0.02 MCL-US 70 –

2,4-DB (4-(2,4-Dichlorophenoxy)

butyric acid)

Herbicide 38746 94-82-6 0.02 na na –

DCPA (Dacthal) monoacid Degradate 49304 887-54-7 0.02 na na –

Dicamba Herbicide 38442 1918-00-9 0.08 HAL-US 4,000 –

Dichlorprop Herbicide 49302 120-36-5 0.04 na na –

Dinoseb Herbicide 49301 88-85-7 0.04 MCL-CA 7 –

Diphenamid Herbicide 04033 957-51-7 0.04 HAL-US 200 –

Diuron Herbicide 49300 330-54-1 0.04 HAL-US 10 D

Fenuron Herbicide 49297 101-42-8 0.04 na na –

Flumetsulam Herbicide 61694 98967-40-9 0.06 na na –

Fluometuron Herbicide 38811 2164-17-2 0.04 HAL-US 90 –

2-Hydroxy-4-isopropylamino6-ethylamino-s-triazine 

(Hydroxyatrazine)

Degradate 50355 2163-68-0 0.08 na na –

3-Hydroxy carbofuran Degradate 49308 16655-82-6 0.02 na na –

Imazaquin Herbicide 50356 81335-37-7 0.04 na na –

Imazethapyr Herbicide 50407 81335-77-5 0.04 na na –

Imidacloprid Insecticide 61695 138261-41-3 0.06 na na –

Linuron Herbicide 38478 330-55-2 0.04 na na –

MCPA (2-Methyl-4-

chlorophenoxyacetic acid)

Herbicide 38482 94-74-6 0.06 HAL-US 30 –

MCPB (4-(2-Methyl-4-

chlorophenoxy) butyric acid)

Herbicide 38487 94-81-5 0.2 na na –

Table 3B. Polar pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for 

the U.S. Geological Survey (USGS) National Water Quality Laboratory schedule 2060.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which 

is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client 

ServicesSM. Threshold type: Maximum contaminant level thresholds 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 Lifetime Health Advisory; MCL-CA, 

California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other 

abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples (table 6); na, not available; μg/L, 

micrograms per liter; –, not detected]
24 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Metalaxyl Fungicide 50359 57837-19-1 0.04 na na –

Methiocarb Insecticide 38501 2032-65-7 0.04 na na –

Methomyl Insecticide 49296 16752-77-5 0.06 HAL-US 200 –

Metsulfuron methyl Herbicide 61697 74223-64-6 0.14 na na –

Neburon Herbicide 49294 555-37-3 0.02 na na –

Nicosulfuron Herbicide 50364 111991-09-4 0.1 na na –

Norflurazon Herbicide 49293 27314-13-2 0.04 na na –

Oryzalin Herbicide 49292 19044-88-3 0.04 na na –

Oxamyl Insecticide 38866 23135-22-0 0.04 MCL-CA 50 –

Picloram Herbicide 49291 06607 0.12 MCL-US 500 –

Propham Herbicide 49236 122-42-9 0.06 HAL-US 100 –

Propiconazole Fungicide 50471 60207-90-1 0.06 na na –

Propoxur Insecticide 38538 114-26-1 0.04 HAL-US 3 –

Siduron Herbicide 38548 1982-49-6 0.04 na na –

Sulfometuron methyl Herbicide 50337 74222-97-2 0.06 na na –

Tebuthiuron Herbicide 82670 34014-18-1 0.016 HAL-US 500 –

Terbacil Herbicide 04032 5902-51-2 0.04 HAL-US 90 –

Triclopyr Herbicide 49235 55335-06-3 0.04 na na –

Table 3B. Polar pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for 

the U.S. Geological Survey (USGS) National Water Quality Laboratory schedule 2060.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which 

is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client 

ServicesSM. Threshold type: Maximum contaminant level thresholds 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 Lifetime Health Advisory; MCL-CA, 

California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other 

abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples (table 6); na, not available; μg/L, 

micrograms per liter; –, not detected]
Table 3C 25

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Acetochlor Herbicide 49260 34256-82-1 0.006 na na –

Alachlor Herbicide 46342 15972-60-8 0.005 MCL-US 2 –

Atrazine Herbicide 39632 1912-24-9 0.007 MCL-CA 1 D 

Azinphos-methyl Insecticide 82686 86-50-0 0.08 na na –

Azinphos-methyl-oxon Insecticide degradate 61635 961-22-8 0.042 na na –

Benfluralin Herbicide 82673 1861-40-1 0.01 na na –

Carbaryl Insecticide 82680 63-25-2 0.06 RSD5-US 400 –

2-Chloro-2,6-diethylacetanilide Herbicide degradate 61618 6967-29-9 0.0065 na na –

4-Chloro-2-methylphenol Herbicide degradate 61633 1570-64-5 0.0050 na na –

Chlorpyrifos Insecticide 38933 2921-88-2 0.005 HAL-US 2 –

Chlorpyrifos, oxygen analog Insecticide degradate 61636 5598-15-2 0.0562 na na –

Cyfluthrin Insecticide 61585 68359-37-5 0.053 na na –

Cypermethrin Insecticide 61586 52315-07-8 0.046 na na –

Dacthal (DCPA) Herbicide 82682 1861-32-1 0.003 HAL-US 70 –

Deethylatrazine (2-Chloro-4-

isopropylamino-6-amino-striazine)

Herbicide degradate 04040 6190-65-4 0.014 na na D

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 0.0045 na na –

Dichlorvos Insecticide 38775 62-73-7 0.013 na na –

Dicrotophos Insecticide 38454 141-66-2 0.0843 na na –

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 0.0061 na na –

Ethion Insecticide 82346 563-12-2 0.016 na na –

Ethion monoxon Insecticide degradate 61644 17356-42-2 0.021 na na –

2-Ethyl-6-methylaniline Herbicide degradate 61620 24549-06-2 0.010 na na –

Fenamiphos Insecticide 61591 22224-92-6 0.029 HAL-US 0.7 –

Fenamiphos sulfone Insecticide degradate 61645 31972-44-8 0.053 na na –

Fenamiphos sulfoxide Insecticide degradate 61646 31972-43-7 0.040 na na –

Fipronil Insecticide 62166 120068-37-3 0.016 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 –

Fonofos Insecticide 04095 944-22-9 0.06 HAL-US 10 –

Hexazinone Herbicide 04025 51235-04-2 0.026 HAL-US 400 –

Iprodione Fungicide 61593 36734-19-7 0.026 na na –

Isofenphos Insecticide 61594 25311-71-1 0.011 na na –

Malaoxon Insecticide degradate 61652 1634-78-2 0.039 na na –

Malathion Insecticide 39532 121-75-5 0.016 HAL-US 100 –

Metalaxyl Fungicide 61596 57837-19-1 0.0069 na na –

Methidathion Insecticide 61598 950-37-8 0.0087 na na –

Metolachlor Herbicide 39415 51218-45-2 0.01 HAL-US 700 –

Metribuzin Herbicide 82630 21087-64-9 0.12 HAL-US 70 –

Myclobutanil Fungicide 61599 88671-89-0 0.033 na na –

1-Naphthol Insecticide degradate 49295 90-15-3 0.0882 na na –

Paraoxon-methyl Insecticide degradate 61664 950-35-6 0.019 na na –

Parathion-methyl Insecticide 82667 298-00-0 0.008 HAL-US 1 –

Pendimethalin Herbicide 82683 40487-42-1 0.02 na na –

Table 3C. Pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory schedule 2003.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

Threshold type: Maximum contaminant level thresholds 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 Lifetime Health Advisory; MCL-CA, California 

Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. 

Environmental Protection Agency risk specific dose at a risk factor of 10-5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting 

level; D, detected in ground-water samples (table 6); na, not available; μg/L, micrograms per liter; –, not detected]
26 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

cis-Permethrin Insecticide 82687 54774-45-7 0.01 na na –

Phorate Insecticide 82664 298-02-2 0.02 na na –

Phorate oxon Insecticide degradate 61666 2600-69-3 0.027 na na –

Phosmet Insecticide 61601 732-11-6 0.0079 na na –

Phosmet oxon Insecticide degradate 61668 3735-33-9 0.0511 na na –

Prometon Herbicide 04037 1610-18-0 0.01 HAL-US 100 D

Prometryn Herbicide 04036 7287-19-6 0.0059 na na –

Pronamide (Propyzamide) Herbicide 82676 23950-58-5 0.004 RSD5-US 20 –

Simazine Herbicide 04035 122-34-9 0.006 MCL-US 4 D

Tebuthiuron Herbicide 82670 34014-18-1 0.016 HAL-US 500 –

Terbufos Insecticide 82675 13071-79-9 0.012 HAL-US 0.4 –

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 0.045 na na –

Terbuthylazine Herbicide 04022 5915-41-3 0.0083 na na –

Trifluralin Herbicide 82661 1582-09-8 0.009 HAL-US 10 –

Table 3C. Pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory schedule 2003.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

Threshold type: Maximum contaminant level thresholds 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 Lifetime Health Advisory; MCL-CA, California 

Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. 

Environmental Protection Agency risk specific dose at a risk factor of 10-5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting 

level; D, detected in ground-water samples (table 6); na, not available; μg/L, micrograms per liter; –, not detected]
Table 3D 27

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Acetaminophen Analgesic 62000 103-90-2 0.024 na na D 

Albuterol Anti-inflammatory; bronchodilator 62020 18559-94-9 0.14 na na –

Caffeine Stimulant 50305 58-08-2 0.01 na na –

Carbamazapine Anticonvulsant; analgesic; mood 

stabilizer

62793 298-46-4 0.0179 na na –

Codeine Opioid narcotic 62003 76-57-3 0.022 na na –

Cotinine Nicotine metabolite 62005 486-56-6 0.03 na na –

Dehydronifedipine Antianginal metabolite 62004 67035-22-7 0.022 na na –

Diltiazem Antianginal; antihypertensive 62008 42399-41-7 0.18 na na –

Diphenhydramine Antihistamine 62796 58-73-1 0.023 na na –

1,7-Dimethylxanthine Caffeine metabolite 62030 611-59-6 0.021 na na –

Sulfamethoxazole Antibacterial, antiprotozoal 62021 723-46-6 0.024 na na –

Thiabendazole Anthelmintic 62801 148-79-8 0.025 na na –

Trimethoprim Antibacterial 62023 738-70-5 0.020 na na –

Warfarin Anticoagulant 62024 81-81-2 0.019 na na –

Table 3D. Pharmaceutical compounds, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey (USGS) National Water Quality Laboratory schedule 2080.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples; na, not available; μg/L, micrograms per 

liter; –, not detected]
28 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Acetophenone Fragrance in detergent and tobacco, 

flavor in beverages 

62811 98-86-2 0.2 na na –

Acetyl hexamethyl 

tetrahydro naphthalene 

(AHTN)

Musk fragrance 62812 21145-77-7 0.2 na na –

Anthracene Wood preservative, tar, diesel, 

crude oil, combustion product 

34220 120-12-7 0.2 na na D 

9,10-Anthraquinone Manufactured dye/textiles, seed 

treatment, bird repellant

62813 84-65-1 0.2 na na D

Atrazine Herbicide 39630 1912-24-9 0.2 MCL-CA 1 –

Benzo[a]pyrene Cancer research, combustion 

product 

34247 50-32-8 0.2 MCL-US 0.2 D

Benzophenone Fixative for perfumes and soaps 62814 119-61-9 0.2 na na –

Bisphenol A Manufactured polycarbonate resins, 

antioxidant, flame retardant

62816 80-05-7 0.4 na na –

Bromacil Herbicide, greater than 80 percent 

noncrop usage on grass/brush 

30234 314-40-9 0.2 HAL-US 70 –

Bromoform 

(tribromomethane)

Byproduct waste water treatment, 

military/explosives 

32104 75-25-2 0.08 MCL-US 80 –

3-tert-Butyl-4-hydroxy 

anisole (BHA) 

Antioxidant, general preservative 61702 25013-16-5 0.2 na na –

Caffeine Beverages 81436 58-08-2 0.2 na na D

Camphor Flavor, odorant, ointments 62817 76-22-2 0.2 na na –

Carbaryl Insecticide, crop and garden uses 39750 63-25-2 0.2 RSD5-US 400 –

Carbazole Insecticide, manuf. dyes, 

explosives, and lubricants 

77571 86-74-8 0.2 na na –

Chlorpyrifos Insecticide, domestic pest and 

termite control 

38932 2921-88-2 0.2 HAL-US 2 –

Cholesterol Fecal indicator, plant sterol 62818 57-88-5 0.8 na na –

3-ß-Coprostanol Carnivore fecal indicator 62806 360-68-9 0.8 na na –

Cotinine Primary nicotine metabolite 61945 486-56-6 0.8 na na –

p-Cresol Wood preservative 77146 106-44-5 0.2 na na –

4-Cumylphenol Nonionic detergent metabolite 62808 599-64-4 0.2 na na –

Diazinon Insecticide, greater than 40 percent 

nonagricultural usage, ants, flies 

39570 333-41-5 0.2 HAL-US 1 –

Dichlorvos Insecticide 30218 62-73-7 0.2 na na –

N,N-diethyl-m-toluamide 

(DEET) 

Insecticide, urban uses, mosquito 

repellent 

61947 134-62-3 0.2 na na –

1,4-Dichlorobenzene Moth repellant, fumigant, deodorant 34571 106-46-7 0.04 MCL-CA 5 –

3,4-Dichlorophenyl 

isocyanate

Intermediate for the synthesis of 

organic compounds

63145 102-36-3 2 na na D

Diethyl phthalate Wood stains and varnishes, 

plasticizer, softener

34336 84-66-2 0.2 na na D

2,6-Dimethylnaphthalene Diesel/kerosene (trace in gasoline) 62085 581-42-0 0.2 na na D

Bis(2-ethylhexyl)phthalate Plasticizer, softener 39100 117-81-7 2 MCL-CA 4 –

4-Nonylphenol 

monoethoxylates

Nonionic detergent metabolite 61704 na 2 na na –

4-Nonylphenol diethoxylates Nonionic detergent metabolite 61703 na 3.2 na na –

4-Octylphenol diethoxylates Nonionic detergent metabolite 61705 na 0.32 na na –

Table 3E. Potential wastewater indicator compounds, primary uses or sources, comparative thresholds, and reporting information for 

the U.S. Geological Survey (USGS) National Water Quality Laboratory schedule 4433.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

Threshold type: Maximum contaminant level thresholds 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 Lifetime Health Advisory; NL-CA, California 

Department of Public Health notification level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Abbreviations: CAS, Chemical 

Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples (table 7); na, not available; μg/L, micrograms per liter; –, not detected]
Table 3E 29

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

4-Octylphenol 

monoethoxylates

Nonionic detergent metabolite 61706 na 1 na na –

Fluoranthene Component of coal tar and asphalt 34376 206-44-0 0.2 na na D

Hexahydrohexamethylcyclopentabenzopyran (HHCB) Musk fragrance 62823 1222-05-5 0.2 na na –

Indole Pesticide ingredient, fragrance in 

coffee 

62824 120-72-9 0.2 na na –

Isoborneol Fragrance in perfumery, in 

disinfectants 

62825 124-76-5 0.2 na na –

Isophorone Solvent for lacquer, plastic, oil, 

silicon, resin 

34409 78-59-1 0.2 HAL-US 100 –

Isopropylbenzene Manufactured phenol/acetone, fuels 

and paint thinner 

77223 98-82-8 0.04 NL-CA 770 –

Isoquinoline Flavors and fragrances 62826 119-65-3 0.2 na na –

d-Limonene Fungicide, antimicrobial, antiviral, 

fragrance in aerosols 

62819 5989-27-5 0.2 na na –

Menthol Cigarettes, cough drops, liniment, 

mouthwash 

62827 89-78-1 0.2 na na –

Metalaxyl Herbicide, fungicide, mildew, 

blight, pathogens, golf/turf 

04254 57837-19-1 0.2 na na –

3-Methyl-1(H)-indole 

(Skatole) 

Fragrance, stench in feces and coal 

tar 

62807 83-34-1 0.2 na na –

5-Methyl-1H-benzotriazole Antioxidant in antifreeze and 

deicers 

61944 136-85-6 1.6 na na D

1-Methylnaphthalene Gasoline, diesel fuel, or crude oil 81696 90-12-0 0.2 na na –

2-Methylnaphthalene Gasoline, diesel fuel, or crude oil 30194 91-57-6 0.2 na na –

Methyl salicylate Liniment, food, beverage, UVabsorbing lotion 62828 119-36-8 0.2 na na

Metolachlor Herbicide, indicator of agricultural 

drainage 

82612 51218-45-2 0.2 HAL-US 700 –

Naphthalene Fumigant, moth repellent, major 

component of gasoline 

34696 91-20-3 0.4 NL-CA 17 –

4-Nonylphenol (total) Nonionic detergent metabolite 62829 84852-15-3 1.6 na na –

4-n-Octylphenol Nonionic detergent metabolite 62809 1806-26-4 0.2 na na –

4-tert-Octylphenol Nonionic detergent metabolite 62810 140-66-9 0.2 na na –

Pentachlorophenol Herbicide, fumigant, wood 

preservative, termite control 

39032 87-86-5 0.8, 2 MCL-US 1 D

Phenanthrene Manufactured explosives, tar, 

diesel, crude oil, combustion 

product 

34461 85-01-8 0.2 na na D

Phenol Disinfectant, product 

manufacturing, leachate 

34694 108-95-2 0.2 HAL-US 2,000 D

Prometon Herbicide (non-crop only) applied 

prior to blacktop 

39056 1610-18-0 0.2 HAL-US 100 –

Pyrene Component of coal tar and asphalt 34469 129-00-0 0.2 na na D

ß-Sitosterol Plant sterol 62815 83-46-5 0.8 na na –

ß-Stigmastanol Plant sterol 61948 19466-47-8 0.8 na na –

2,2',4,4'-Tetrabromodiphenyl 

ether

Brominated flame retardant 63147 5436-43-1 0.2 na na –

Table 3E. Potential wastewater indicator compounds, primary uses or sources, comparative thresholds, and reporting information for 

the U.S. Geological Survey (USGS) National Water Quality Laboratory schedule 4433.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

Threshold type: Maximum contaminant level thresholds 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 Lifetime Health Advisory; NL-CA, California 

Department of Public Health notification level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Abbreviations: CAS, Chemical 

Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples (table 7); na, not available; μg/L, micrograms per liter; –, not detected]
30 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Tetrachloroethene (PCE) Solvent, degreaser 34476 127-18-4 0.5 MCL-US 5 D 

Tributyl phosphate Antifoaming agent, flame retardant 62832 126-73-8 0.2 na na D

Triclosan Disinfectant, antimicrobial 61708 3380-34-5 0.2 na na –

Triethyl citrate (ethyl citrate) Cosmetics, pharmaceuticals 62833 77-93-0 0.2 na na –

Triphenyl phosphate Plasticizer, resin, wax, finish, 

roofing paper, flame retardant

62834 115-86-6 0.2 na na –

Tris(2-butoxyethyl)

phosphate 

Flame retardant 62830 78-51-3 0.2 na na –

Tris(2-chloroethyl)

phosphate 

Plasticizer, flame retardant 62831 115-96-8 0.2 na na –

Tris(dichlorisopropyl)

phosphate 

Flame retardant 61707 13674-87-8 0.2 na na –

Table 3E. Potential wastewater indicator compounds, primary uses or sources, comparative thresholds, and reporting information for 

the U.S. Geological Survey (USGS) National Water Quality Laboratory schedule 4433.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

Threshold type: Maximum contaminant level thresholds 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 Lifetime Health Advisory; NL-CA, California 

Department of Public Health notification level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Abbreviations: CAS, Chemical 

Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples (table 7); na, not available; μg/L, micrograms per liter; –, not detected]

Constituent Primary use 

or source

CAS 

number

MRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Perchlorate Rocket fuel, fireworks, flares 14797-73-0 0.5 MCL-CA 6 D

1,2,3-Trichloropropane (TCP) Industrial solvent, organic synthesis 96-18-4 0.005 NL-CA 0.005 –

Table 3F. Constituents of special interest, primary uses or sources, comparative thresholds, and reporting information for the 

Montgomery Watson-Harza Laboratory.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

Threshold type: MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification 

level. Abbreviations: CAS, Chemical Abstract Service;MRL, minimum reporting level; D, detected in ground-water samples (table 8); μg/L, micrograms per 

liter; –, not detected]

Constituent

USGS 

parameter 

code

CAS 

number

 LRL

 (mg/L)

Threshold 

type

Threshold 

value 

(mg/L)

Detection

Ammonia (as nitrogen) 00608 7664-41-7 0.02 HAL-US 1 30 D

Nitrite (as nitrogen) 00613 14797-65-0 0.002 MCL-US 1 D

Nitrite plus nitrate (as nitrogen) 00631 na 0.06 MCL-US 10 D

Total nitrogen (ammonia, nitrite, nitrate, organic 

nitrogen)

62854 17778-88-0 0.06 na na D

Orthophosphate (as phosphorus) 00671 14265-44-2 0.006 na na D

Dissolved organic carbon (DOC) 00681 na 0.4 na na D

1Threshold is as ammonia; data and LRL are reported as nitrogen.

Table 3G. Nutrients and dissolved organic carbon, comparative thresholds, and reporting information for the U.S. Geological Survey 

(USGS) National Water Quality Laboratory schedule 2755 and lab code 2613.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. Abbreviations: CAS, Chemical Abstract Service;LRL, laboratory reporting level; D, detected in ground-water samples (table 9); μg/L, 

micrograms per liter]
Table 3H 31

Constituent

USGS 

parameter 

code

CAS 

number LRL Threshold type

Threshold 

value Detection

Major and minor ions (mg/L)

Bromide 71870 24959-67-9 0.02 na na D

Calcium 00915 7440-70-2 0.02 na na D

Chloride 00940 16887-00-6 0.12 SMCL-CA 1250 (500) D

Fluoride 00950 16984-48-8 0.10 MCL-CA 2 D

Iodide 78165 7553-56-2 0.002 na na D

Magnesium 00925 7439-95-4 0.014 na na D

Potassium 00935 7440-09-7 0.04 na na D

Silica 00955 7631-86-9 0.018 na na D

Sodium 00930 7440-23-5 0.20 na na D

Sulfate 00945 14808-79-8 0.18 SMCL-CA 1 250 (500) D

Residue on evaporation (total dissolved solids, TDS) 70300 na 10 SMCL-CA 1500 (1,000) D

Trace elements (μg/L)

Aluminum 01106 7429-90-5 1.6 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.06 MCL-US 6 D

Arsenic 01000 7440-38-2 0.12 MCL-US 10 D

Barium 01005 7440-39-3 0.08 MCL-CA 1,000 D

Beryllium 01010 7440-41-7 0.06 MCL-US 4 D

Boron 01020 7440-42-8 8 NL-CA 1,000 D

Cadmium 01025 7440-43-9 0.04 MCL-US 5 D

Chromium 01030 7440-47-3 0.12 MCL-CA 50 D

Cobalt 01035 7440-48-4 0.04 na na D

Copper 01040 7440-50-8 0.4 AL-US 1,300 D

Iron 01046 7439-89-6 6 SMCL-CA 300 D

Lead 01049 7439-92-1 0.12 AL-US 15 D

Lithium 01130 7439-93-2 0.6 na na D

Manganese 01056 7439-96-5 0.2 SMCL-CA 50 D

Mercury 71890 7439-97-6 0.010 MCL-US 2 –

Molybdenum 01060 7439-98-7 0.12 HAL-US 40 D

Nickel 01065 7440-02-0 0.06 MCL-CA 100 D

Selenium 01145 7782-49-2 0.08 MCL-US 50 D

Silver 01075 7440-22-4 0.1 SMCL-CA 100 –

Strontium 01080 7440-24-6 0.4 HAL-US 4,000 D

Thallium 01057 7440-28-0 0.04 MCL-US 2 –

Tungsten 01155 7440-33-7 0.06 na na D

Uranium 22703 7440-61-1 0.04 MCL-US 30 D

Vanadium 01085 7440-62-2 0.04 NL-CA 50 D

Zinc 01090 7440-66-6 0.6 SMCL-CA 5,000 D

1

The recommended SMCL-CA thresholds for chloride, sulfate, and TDS are listed with the upper SMCL-CA thresholds in parentheses.

Table 3H. Major and minor ions and trace elements, comparative thresholds, and reporting information for the U.S. Geological Survey 

(USGS) National Water Quality Laboratory schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which 

is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client 

ServicesSM. Threshold type: Maximum contaminant level thresholds 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. SMCL-CA, California Department of Public Health secondary maximum contaminant 

level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant 

level; NL-CA, California Department of Public Health notification level; AL-US, U.S. Environmental Protection Agency action level. Abbreviations: CAS, 

Chemical Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples (table 10 and 11); μg/L, micrograms per liter; –, not detected]
32 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent

(valance state)

USGS 

parameter 

code

CAS 

number

MDL

 (μg/L)

Threshold 

type

Threshold 

level 

(μg/L)

Detection

Arsenic(III) 99034 22569-72-8 1 na na D

Arsenic (total) 01000 7440-38-2 0.5 MCL-US 10 D

Chromium(VI) 01032 18540-29-9 1 na na D

Chromium (total) 01030 7440-47-3 1 MCL-CA 50 D

Iron(II) 01047 7439-89-6 2 na na D

Iron (total) 01046 7439-89-6 2 HAL-US 300 D

Table 3I. Arsenic, chromium, and iron species, comparative thresholds, and reporting information for the U.S. Geological 

Survey (USGS) Trace Metal Laboratory, Boulder, Colorado.

[The five-digit USGS parameter code is used to uniquely identify a specific constituents or property. This report contains CAS Registry 

Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry 

Numbers through CAS Client ServicesSM. Threshold type: Maximum contaminant level thresholds 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; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level. Abbreviations: CAS, Chemical Abstract Service; MDL, 

method detection limit; D, detected in ground-water samples (table 12); mg/L, micrograms per liter; na, not available]
Table 3J 33

Constituent

USGS 

parameter 

code

CAS 

number

Reporting 

level type

Reporting 

level or 

uncertainty

Threshold 

type

Threshold 

value

Reporting 

units Detection

Stable isotope ratios (per mil)

δ2H of water 1 82082 na MU 2 na na per mil D

δ18O of water 1 82085 na MU 0.20 na na per mil D

δ13C of dissolved carbonates 2 82081 na 1 sigma 0.05 na na D

Radioactive constituents (percent modern)

14Carbon-143 49933 14762-75-5 1 sigma 0.0015 na na percent 

modern

D

Radioactive constituents (pCi/L)

Radon-2224 82303 14859-67-7 SSMDC CSU and CV Proposed 

MCL-US

5300 (4,000) pCi/L D

Tritium6,7 07000 10028-17-8 MRL 1 MCL-CA 20,000 pCi/L D

Gross-alpha radioactivity, 

72 hr count 8

62636 12587-46-1 SSMDC CSU and CV MCL-US 15 pCi/L D

Gross-alpha radioactivity, 

30 day count 8

62639 12587-46-1 SSMDC CSU and CV MCL-US 15 pCi/L D

Gross-beta radioactivity, 

72 hr count 8

62642 12587-47-2 SSMDC CSU and CV MCL-CA 50 pCi/L D

Gross-beta radioactivity, 

30 day count 8

62645 12587-47-2 SSMDC CSU and CV MCL-CA 50 pCi/L D

Radium-2268 09511 13982-63-3 SSMDC CSU and CV MCL-US 95 pCi/L D

Radium-2288 81366 15262-20-1 SSMDC CSU and CV MCL-US 95 pCi/L D

Uranium-2348 22610 13966-29-5 SSMDC 0.1 MCL-CA 20 pCi/L D

Uranium-2358 22620 15117-96-1 SSMDC 0.1 MCL-CA 20 pCi/L D

Uranium-2388 22603 7440-61-1 SSMDC 0.1 MCL-CA 20 pCi/L D

1USGS Stable Isotope Laboratory, Reston, Virginia.

2

 University of Waterloo (contract laboratory).

3University of Arizona, Accelerator Mass Spectrometry Laboratory (contract laboratory).

4USGS National Water Quality Laboratory.

5Two MCLs have been proposed for Radon-222. The proposed alternative MCL is in parentheses.

6USGS Stable Isotope and Tritium Laboratory, Menlo Park, California.

7Lawrence Livermore National Laboratory.

8Eberline Analytical Services (contract laboratory).

9The MCL-US threshold for radium is the sum of radium-226 and radium-228.

Table 3J. Isotopic, tritium, and radioactive constituents, comparative thresholds, and reporting information for laboratories.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

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. Threshold type: Maximum contaminant level thresholds 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 maximum contaminant level. Abbreviations: CAS, Chemical Abstract Service; CSU, combined 

standard uncertainty; CV, critical value; MU, method uncertainty; SSMDC, sample specific minimum detectable concentration; MRL, minimum reporting level; 

na, not available; pCi/L, picocuries per liter; D, detected in ground-water samples (tables 13 and 14)]
34 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent

USGS 

parameter 

code

CAS 

number

MU

 (percent)

Reporting 

units

Threshold 

type

Threshold 

value

(pCi/L)

Detection

Argon na 7440-37-1 2 cm3STP/g na na No data

Helium-3 / Helium-4 ratio na na/7440-59-7 0.75 na na na No data

Helium-4 na 7440-59-7 2 cm3STP/g na na No data

Krypton na 7439-90-9 2 cm3STP/g na na No data

Neon na 7440-01-09 2 cm3STP/g na na No data

Xenon na 7440-63-3 2 cm3STP/g na na No data

Table 3K. Noble gas constituents, comparison thresholds, and reporting information for the Lawrence Livermore National Laboratory.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which is a 

Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client ServicesSM. 

Abbreviations: CAS, Chemical Abstract Service; cm3 STP/g, cubic centimeters of gas at standard temperature and pressure per gram of water; pCi/L, picocurie 

per liter, na, not applicable]

Constituent

USGS 

parameter 

code

Primary source MDL Threshold 

type

Threshold 

value Detection

Escherichia coli 90901 Sewage and animal waste 

indicator / intestinal tracts of 

humans and animals

1 colony / 

100 mL

TT-US Zero –

Total coliform, including 

fecal coliform and E. coli

90900 Water-quality indicator / soil, 

water and intestinal tracts of 

animals

1 colony / 

100 mL

MCL-US 5 percent of samples 

positive per month

D

F-specific coliphage 99335 Viral indicator / intestinal tracts 

of warm-blooded animals

na TT-US 99.99 percent killed / 

inactivated

–

Somatic coliphage 99332 Viral indicator / fecal 

contaminated waters

na TT-US 99.99 percent killed / 

inactivated

–

Table 3L. Microbial constituents, comparison thresholds, and reporting information for the U.S. Geological Survey Ohio Microbiology 

Laboratory parameter codes 90901, 90900, 99335, and 99332. 

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. This report contains CAS Registry Numbers®, which 

is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client 

ServicesSM. Threshold type: TT-US, U.S. Environmental Protection Agency treatment technique: a required process intended to reduce the level of 

contamination in drinking water; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Abbreviations: CAS, Chemical Abstract 

Service; MDL, method detection level; mL, milliliter; D, detected in groundwater samples (table 15); –, not detected]
Table 4 35

GAMA well 

identification 

No.

Turbidity,

field 

(NTU) 

(63676)

Dissolved 

oxygen,

field 

(mg/L) 

(00300) 

Water 

temperature,

field

(oC) 

(00010)

pH, lab 

(standard 

units) 

(00403)

pH, field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm at 

25oC) 

(90095)

Specific 

conductance, 

field 

(μS/cm at 

25oC) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3

)

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3

) 

(29802)

Threshold type TT/MCL-CA na na SMCL-US SMCL-US SMCL-CA1 SMCL-CA1 na na

Threshold level 1/5 na na 6.5 - 8.5 6.5 - 8.5 900 (1,600) 900 (1,600) na na

Grid wells

COA-01 0.1 10.9 18.8 7.6 7.6 411 411 178 174

COA-02 0.1 0.4 35.2 7.4 8.0 *5,570 *5,580 40 37.6

COA-03 0.1 1.5 20.5 7.3 8.0 649 649 96 90.8

COA-04 nc 6.2 21.5 8.0 8.1 304 300 123 nc

COA-05 nc 6.4 21.1 7.8 8.0 315 297 133 nc

COA-06 nc 0.3 23.6 7.7 7.7 605 617 162 nc

COA-07 nc 19.5 24.8 7.5 7.4 *1,759 *1,760 98 nc

COA-08 0.1 0.6 26.5 8.0 8.0 702 703 84 81.3

COA-09 0.1 9.7 19.0 7.7 7.6 369 316 111 110

COA-10 nc 0.1 25.2 *9.2 *9.2 230 232 62 nc

COA-11 nc 0.1 33.0 *9.1 *9.1 701 733 35 nc

COA-12 nc <0.2 26.2 *8.6 8.5 746 710 123 nc

COA-13 nc 7.4 19.0 7.7 7.7 382 357 169 nc

COA-14 nc 7.1 21.1 7.9 7.9 409 392 137 nc

COA-15 0.1 4.9 26.5 7.8 7.8 478 487 125 121

COA-16 0.5 2.7 34.9 8.1 8.1 *1,330 *1,340 90 87.3

COA-17 nc 7.9 20.9 7.6 7.5 * 1,113 *1,120 218 nc

COA-18 nc 4.1 33.0 8.0 8.0 *1,487 *1,490 87 nc

COA-19 nc 0.2 44.4 8.4 8.4 *1,639 *1,670 38 nc

Understanding wells

COAU-01 0.1 7.3 16.8 7.9 7.5 393.5 389 165 160

COAU-02 nc 6.5 24.9 7.8 7.8 557 552 127 nc

COAU-03 0.1 10.5 20.5 7.4 7.7 422.9 425 150 146

COAU-04 nc 0.3 29.2 7.9 8.0 *1,482 *1,550 84 nc

COAU-05 0.1 7.2 20.4 7.8 7.6 451 442 189 221

COAU-06 0.4 6.1 21.5 7.8 7.7 370 360 152 149

COAU-07 nc 6.9 21.8 7.7 7.3 406 382 164 nc

COAU-08 nc 9.2 18.3 6.4 7.1 451 447 145 nc

COAU-09 nc 0.4 24.5 *8.9 *9.1 231 229 70 nc

COAU-10 nc 6.0 29.0 7.9 7.6 735 702 144 nc

COAU-11 nc 6.8 26.7 7.9 7.7 432 437 127 nc

COAU-12 nc 6.0 12.5 7.4 7.2 367 350 167 nc

COAU-13 nc 6.7 21.7 8.0 7.9 339 335 133 nc

COAU-14 nc 4.5 23.4 7.9 7.8 776 780 98 nc

COAU-15 nc 6.0 24.3 7.6 7.5 *1,015 *1,000 212 nc

COAU-16 nc 5.6 21.6 8.0 7.9 357 372 111 nc

*Value was above threshold.

1The SMCL-CA for specific conductance has recommended and upper threshold values. The upper value is shown in parentheses.

Table 4. Water-quality indicators in samples collected for the Coachella Valley Ground-Water Ambient Monitoring and Assessment 

(GAMA) study, California, February and March 2007.

[The five digit number below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or 

property. Samples from all 35 wells were analyzed (19 grid wells and 16 understanding wells), but only samples with detections are listed. Abbreviations:

COA, Coachella Valley study unit grid well; COAU, Coachella Valley study unit understanding well; oC, degrees Celsius; mg/L, milligram per liter; TT, 

treatment technique; MCL-CA, maxium contaminant level California Department of Public Health; SMCL-US, secondary maximum contaminant level U.S. 

Environmental Protection Agency; na, not applicable; nc, sample not collected; NTU, nephelometric turbidity unit; μS/cm, microsiemens per centimeter; 

CaCO3, calcium carbonate]
36 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

GAMA well

identification 

No.

Cloroform

(Trichloromethane)C

(μg/L) 

(32106)

Toluene

(μg/L)

(34010)

Tetrachloroethene 

(μg/L) 

(34475)

Bromodichloromethane 

(μg/L)

(32101)

1,1-Dichloroethane

(μg/L) 

(34496)

Trichloroethene

(μg/L) 

(39180)

VOC 

detections 

per well

LRL [0.04] [0.018] [0.04] [0.04] [0.06] [0.02]

Threshold type1 MCL-US MCL-CA MCL-US MCL-US MCL-CA MCL-US

Threshold level 2 80 150 5 80 5 5

Grid wells

COA-01 – V0.01 – – – – 0

COA-02 – V0.01 – – – – 0

COA-05 – V0.01 – – – – 0

COA-07 – V0.01 – – – – 0

COA-08 – V0.07 – – – – 0

COA-09 0.13 – – – – – 1

COA-11 – V0.01 – – – – 0

COA-14 E0.06 – E0.04 – – – 2

COA-15 0.37 V0.02 – – – – 1

COA-18 E0.03 V0.01 – – – – 1

Number of detections 4 0 1 0 0 0 4

Detection frequency 

(percent) 

21 0 5 0 0 0 3 21 

Understanding wells

COAU-03 E0.02 V0.08 – – – – 1

COAU-05 – V0.01 – – – – 0

COAU-07 E0.09 – 0.19 – E0.04 E0.01 4

COAU-11 0.23 – – E0.05 – – 2

COAU-15 0.54 – 0.31 E0.07 – – 3

1Maximum contaminant level thresholds 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.

2The MCL-US threshold for trihalomethanes is the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.

3Frequency of detection of at least one VOC in the grid wells. Detections with V remark codes are not included in calculation for frequency of detection.

Table 5. Volatile organic compounds (VOC) detected in ground-water samples collected for the Coachella Valley Ground-Water 

Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all 35 wells were analyzed (19 grid wells and 16 understanding wells), but only samples with detections are listed. Abbreviations:

COA, Coachella Valley study unit grid well; COAU, Coachella Valley study unit understanding well; LRL, laboratory reporting level; MCL-US, U.S. 

Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant level; E, estimated 

value; V, analyte detected in sample and an associated blank—thus data are not included in ground-water-quality assessment; μg/L, microgram per liter; –, not 

detected; percentage values are detection frequencies in the grid wells]
Table 6 37

GAMA well

identification 

No.

2-Chloro-4-

isopropylamino6-aminos-triazine 

(μg/L)

(04040)

Atrazine

(μg/L)

(39632)

Simazine 

(μg/L) 

(04035)

Diuron 

(μg/L) 

(49300)

2-Chloro-6-

ethylamino-4-

amino-s-triazine 

(μg/L) 

(04038)

Prometon 

(μg/L) 

(04037)

Pesticide 

detections per 

well

LRL [0.02] [0.04] [0.006] [0.04] [0.08] [0.01]

Threshold type1 na MCL-CA MCL-US RSD5-US na HAL-US

Threshold level na 1 4 20 na 100

Grid wells

COA-01 E0.012 E0.006 E0.004 – – – 3

COA-07 E0.005 – – – – – 1

COA-09 E0.006 0.008 0.016 0.05 E0.01 – 5

COA-14 E0.007 E0.006 0.013 – – – 3

COA-15 – E0.005 – – – – 1

COA-18 E0.006 – E0.004 – – – 2

Number of detections 5 4 4 1 1 0 6

Detection frequency 

(percent) 

26 21 21 5 5 0 232

Understanding wells

COAU-04 E0.007 – – – – – 1

COAU-05 E0.005 E0.006 E0.005 – – – 3

COAU-06 E0.008 0.008 E0.005 – – – 3

COAU-07 E0.008 0.019 0.011 – – – 3

COAU-15 E0.006 – 0.015 – – E0.01 3

1Maximum contaminant level thresholds 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.

2Frequency of detection of at least one pesticide in the grid wells.

Table 6. Pesticides and pesticide degradates detected in samples collected for the Coachella Valley Ground-Water Ambient 

Monitoring and Assessment (GAMA) study, California, February and March 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all 35 wells were analyzed (19 grid wells and 16 understanding wells), but only samples with detections are listed. Abbreviations:

COA, Coachella Valley study unit grid well; COAU, Coachella Valley study unit understanding well; HAL-US, U.S. Environmental Protection Agency Lifetime 

Health Advisory; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum 

contaminant level; E, estimated value; LRL, laboratory reporting level; μg/L, microgram per liter; –, not detected; percentage values are detection frequencies 

for grid wells]
38 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program Table 7. Potential wastewater indicator compounds detected in samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007. [The five-digit number below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from eleven slow wells were analyzed, but only samples with detections are listed. Abbreviations: COA Coachella Valley grid well; COAU, Coachella Valley Understanding well; HAL, U.S. Environmental Protection Agency Lifetime Health Advisory; MCL-US, U.S. Environmental Protection Agency defined maximum contaminant level; MCL-CA, California Department of Public Health defined maximum contaminant level; E, estimated value; LRL, laboratory reporting level; μg/L, microgram per liter; –, not detected; percentage values are detection frequencies] GAMA well identification No. Anthracene (μg/L) (34220) Phe- nanthrene (μg/L) (34461) Phenol (μg/L) (34694) 2,6-Di- methyl- naphthalene (μg/L) (62805) 3,4-Di- chloro- phenyl isocyanate (μg/L) (63145) 9,10-Anthra- quinone (μg/L) (62813) Diethyl phthalate (μg/L) (34336) Fluoran- thene (μg/L) (34376) Penta- chloro- phenol (μg/L) (39032) Pyrene (μg/L) (34469) Tributyl phosphate (μg/L) (62832) Benzo[a] pyrene (μg/L) (34247) Number of detections LRL [0.2] [0.2] [0.2] [0.2] [2] [0.2] [0.2] [0.2] [0.8] [0.2] [0.2] [0.2] Threshold type1 na na HAL-US na na na na na MCL-US na na MCL-US Threshold level na na 2000 na na na na na 1 na na 0.2 Grid wells COA-03 – – E0.1 – – – – – – – – – 1 COA-09 0.01 0.05 – – E0.26 – – E0.1 – E0.1 – – 5 COA-15 – – E0.1 – – 0.005 0.5 – 0.02 – 0.02 – 5 COA-16 – – – 0.007 – – – – – – – – 1 Number of detections 1 1 2 1 1 1 1 1 1 1 1 0 4 Detection frequency (percent) 14 14 29 14 14 14 14 14 14 14 14 0 257 Understanding wells COAU-05 – 0.03 – – – – – E0.1 – E0.1 – 0.03 4 COAU-06 – – E0.1 – – – – – – – – – 1

1 Maximum contaminant level thresholds 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.2 Frequency of detection of at least one potential wastewater indicator compound in grid wells.
Table 8 39

Table 8. Constituents of special interest (Perchlorate, and 

1,2,3-Trichloropropane [1,2,3-TCP]) detected in samples collected for the 

Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, February and March 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey 

parameter code used to uniquely identify a specific constituent or property. Samples from all 35 

wells were analyzed for perchlorate; samples from the 11 slow wells were analyzed for 1,2,3-

TCP; only wells with at least one detection are listed. Abbreviations: COA, Coachella Valley 

study unit grid well; COAU, Coachella Valley study unit understanding well; MRL, method 

reporting level; MCL-CA, California Department of Public Health maximum contaminant 

level; μg/L, microgram per liter]

GAMA

identification 

No.

Perchlorate 

(μg/L)

(61209)

Threshold type1 MCL-CA

Threshold level 6

MRL 0.5

Grid wells

COA-07 *9.0

COA-08 0.54

COA-09 0.58

COA-11 *6.1

COA-15 0.85

COA-16 0.62

COA-18 2.0

Number of wells with detections 7

Detection frequency (percent) 2 37

Understanding wells

COAU-03 0.85

COAU-06 0.8

COAU-14 0.7

COAU-15 1.2

COAU-16 0.67

* Indicates value above threshold level.

1Maximum contaminant level thresholds 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.

2Frequency of detection of percholorate in the grid wells.
40 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

GAMA well

identification 

No.

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite plus 

nitrate, as 

nitrogen 

(mg/L) 

(00631)

Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Total nitrogen 

(nitrate + nitrite + 

ammonia + organicnitrogen) as nitrogen 

(mg/L) 

(62854)

Orthophosphate 

as phosphorus 

(mg/L) 

(00671)

Dissolved 

organic carbon 

(DOC) 

(mg/L) 

(00681)

Threshold type1 HAL-US MCL-US MCL-US na na na

Threshold level 2 24.7 10 1 na na na

LRL [0.02] [0.06] [0.002] [0.06] [0.006] [0.4]

Grid wells

COA-01 – 2.02 – 2.02 0.019 E0.2

COA-02 1.42 0.12 0.033 1.57 0.007 –

COA-03 – 1.26 – 1.28 0.01 –

COA-04 – 0.60 – 0.60 0.011 NC

COA-05 – 0.63 – 0.62 0.011 NC

COA-06 – 0.50 – 0.54 0.015 NC

COA-07 – 7.12 – 7.19 0.006 NC

COA-08 – 0.61 – 0.61 0.01 –

COA-09 – 2.38 – 2.32 0.02 E0.2

COA-10 – 0.23 0.005 0.26 0.012 NC

COA-11 0.054 1.36 0.033 1.39 0.006 NC

COA-12 0.133 – E0.002 0.19 0.02 NC

COA-13 – 1.81 – 1.73 0.022 NC

COA-14 – 4.54 – 4.57 0.012 NC

COA-15 – 1.23 – 1.19 0.018 –

COA-16 – 3.98 – 4.04 E0.006 E0.4

COA-17 – 0.39 – 0.36 0.008 NC

COA-18 – 2.93 E0.001 2.89 E0.005 NC

COA-19 – 0.08 E0.002 0.11 0.006 NC

Understanding wells

COAU-01 – 0.46 – 0.46 0.008 E0.2

COAU-02 – 0.64 – 0.66 0.022 NC

COAU-03 – 1.06 – 1.08 0.015 E0.2

COAU-04 – 1.18 – 1.23 0.006 NC

COAU-05 – 0.82 – 0.85 0.021 E0.2

COAU-06 – 2.02 – 1.98 0.03 –

COAU-07 – 2.81 – 2.81 0.017 NC

COAU-08 – 0.92 – 0.91 0.022 NC

COAU-09 0.03 E0.04 0.003 0.09 0.017 NC

COAU-10 – 0.95 – 1.04 0.015 NC

COAU-11 – 0.57 – 0.60 0.04 NC

COAU-12 – 0.56 – 0.60 E0.005 NC

COAU-13 – 0.60 – 0.69 0.013 NC

COAU-14 – * 14.3 – 14.80 0.012 NC

COAU-15 – * 13.8 – 14.40 0.022 NC

COAU-16 – 0.82 – 0.83 0.014 NC

*Value above regulatory threshold.

1

Maximum contaminant level thresholds 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.

2The 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.”

Table 9. Nutrients and dissolved organic carbon detected in samples collected for the Coachella Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, February and March 2007.

[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all 35 wells were analyzed (19 grid wells and 16 understanding wells), but only samples with detections are listed. Abbreviations:

COA, Coachella Valley study unit grid well; COAU, Coachella Valley study unit understanding well; HAL-US, U.S. Environmental Protection Agency Lifetime 

Health Advisory; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; E, estimated value; LRL, laboratory reporting level; mg/L, 

milligram per liter; na, not available; nc, not collected; –, not detected]
Table 10

41

Table 10. Major and minor ions and total dissolved solids detected in samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 35 wells were analyzed (19 grid wells and 16 understanding wells), but only samples with detections are listed. Abbreviations: COA, Coachella Valley study unit grid well; COAU, Coachella Valley study unit understanding well; MCL-CA, California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level; LRL, laboratory reporting level; mg/L, milligram per liter; nc, not collected; na, not available; –, not detected]

GAMA 

identification 

No.

Calcium 

(mg/L) 

(00915)

Magnesium 

(mg/L) 

(00925)

Potassium 

(mg/L) 

(00935)

Sodium 

(mg/L) 

(00930)

Bicarbonate 

(mg/L) 

(63786)

Carbonate 

(mg/L) 

(63788)

Bromide 

(mg/L) 

(71870)

Chloride 

(mg/L) 

(00940)

Fluoride 

(mg/L) 

(00950)

Iodide 

(mg/L) 

(71865)

Silica 

(mg/L) 

(00955)

Sulfate 

(mg/L) 

(00945)

Total 

dissolved 

solids 

(TDS) 

(mg/L) 

(70300)

Threshold type1 na na na na na na na SMCL-CA2 MCL-CA na na SMCL-CA2 SMCL-CA2

Threshold level na na na na na na na 250 (500) 2 na na 250 (500) 500 (1000)

LRL [0.02] [0.014] [0.04] [0.2] 1 1 [0.02] [0.12] [0.1] [0.002] [0.018] [0.18] [10]

Grid wells

COA-01 48.9 11.5 2.55 20.5 211 0.4 0.04 8.93 0.78 – 21.7 20.0 250

COA-02 250 37.5 8.08 838 45 0.2 1.01 **1,300 *3.60 0.197 13.5 **901 **3,480

COA-03 42.8 8.10 7.33 72.0 110 0.5 0.09 29.3 1.47 – 17.3 163 418

COA-04 28.8 5.54 4.59 25.3 nc nc 0.03 8.28 0.70 – 17.5 19.3 179

COA-05 28.4 7.29 4.26 24.4 nc nc 0.03 7.74 0.65 – 17.5 17.5 187

COA-06 67.2 10.2 6.62 34.3 nc nc 0.11 34.2 0.57 0.002 21.2 94.3 377

COA-07 183 18.5 14.1 157 nc nc 0.25 203 0.16 0.003 17.3 *498 **1,220

COA-08 44.7 9.90 7.79 74.1 98 0.8 0.09 40.7 0.96 – 15.4 181 448

COA-09 43.3 5.23 2.91 17.7 133 0.4 0.1 23 0.15 – 27 30.8 243

COA-10 4.57 0.056 1.07 44.9 nc nc 0.04 11 0.82 0.004 13.2 29.3 155

COA-11 8.87 0.091 1.25 131 nc nc 0.1 90.9 0.73 0.004 15.9 143 422

COA-12 15.6 1.14 1.63 155 nc nc 0.09 50.5 *6.99 0.080 14.9 174 *509

COA-13 49.2 10.6 3.17 14.6 nc nc 0.02 6.27 0.41 – 21.8 19.0 226

COA-14 50.2 8.70 3.69 20.5 nc nc 0.06 12.9 0.53 – 20.6 35.5 259

COA-15 38.3 5.77 7.09 49.5 146 0.7 0.11 29.5 0.57 – 19.4 69.0 302

COA-16 31.7 6.28 8.36 224 104 1 0.3 88.9 *3.21 0.022 16.8 *385 *840

COA-17 106 39.5 8.55 82.2 nc nc 0.08 22.6 1.62 E 0.001 17.6 *348 *797COA-18 53.5 5.41 4.61 239 nc nc 0.19 212 1.03 0.002 15 *287 *909COA-19 39.2 1.00 6.27 280 nc nc 0.14 120 *8.08 0.043 22.5 **514 **1,070
42 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program Table 10. Major and minor ions and total dissolved solids detected in samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.—Continued

[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 35 wells were analyzed (19 grid wells and 16 understanding wells), but only samples with detections are listed. Abbreviations: COA, Coachella Valley study unit grid well; COAU, Coachella Valley study unit understanding well; MCL-CA, California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level; LRL, laboratory reporting level; mg/L, milligram per liter; nc, not collected; na, not available; –, not detected]

GAMA 

identification 

No.

Calcium 

(mg/L) 

(00915)

Magnesium 

(mg/L) 

(00925)

Potassium 

(mg/L) 

(00935)

Sodium 

(mg/L) 

(00930)

Bicarbonate 

(mg/L) 

(63786)

Carbonate 

(mg/L) 

(63788)

Bromide 

(mg/L) 

(71870)

Chloride 

(mg/L) 

(00940)

Fluoride 

(mg/L) 

(00950)

Iodide 

(mg/L) 

(71865)

Silica 

(mg/L) 

(00955)

Sulfate 

(mg/L) 

(00945)

Total 

dissolved 

solids 

(TDS) 

(mg/L) 

(70300)

Threshold type1 na na na na na na na SMCL-CA2 MCL-CA na na SMCL-CA2 SMCL-CA2

Threshold level na na na na na na na 250 (500) 2 na na 250 (500) 500 (1000)

LRL [0.02] [0.014] [0.04] [0.2] 1 1 [0.02] [0.12] [0.1] [0.002] [0.018] [0.18] [10]

Understanding wells

COAU-01 51.5 13.1 4.40 13.9 195 0.3 – 2.28 1.11 – 15.6 37.2 239

COAU-02 41.3 6.11 6.32 62.5 nc nc 0.07 15.6 0.85 – 20.8 125 369

COAU-03 50.0 10.2 4.50 20.6 176 0.6 0.05 14.7 0.74 – 20.1 46.1 267

COAU-04 39.1 5.97 6.93 239 nc nc 0.22 128 *2.33 0.014 13.7 *408 *936

COAU-05 50.3 12.7 3.59 20.4 183 0.6 0.05 12.6 0.98 – 22.7 28.4 281

COAU-06 32.8 8.18 1.58 32.4 181 0.6 0.05 12.7 0.50 – 23.7 15.7 223

COAU-07 44.8 10.1 2.71 24.9 nc nc 0.04 15 0.46 – 26.5 18.9 250

COAU-08 52.2 7.46 3.64 28.4 nc nc 0.07 14.1 0.29 – 30.1 65.4 301

COAU-09 7.79 0.053 0.69 43.0 nc nc 0.03 7.38 1.14 0.011 14.4 28.6 156

COAU-10 48.2 13.4 7.73 78.6 nc nc 0.09 19.6 0.78 – 19.4 199 488

COAU-11 29.2 4.76 5.65 53.8 nc nc – 12.5 0.89 – 22.2 67.2 265

COAU-12 39.7 16.9 3.49 9.4 nc nc – 2.32 0.47 – 13.7 24.5 208

COAU-13 38.0 5.90 4.66 20.4 nc nc 0.04 6.89 0.79 – 18.9 27.2 204

COAU-14 89.1 11.0 5.46 44.7 nc nc 0.27 63.5 0.17 – 18.4 129 490

COAU-15 93.9 19.6 4.93 86.4 nc nc 0.31 74.4 0.48 0.005 25.1 146 *679

COAU-16 35.3 4.82 4.05 28.6 nc nc 0.04 14.2 0.56 – 18.2 37.3 220

*Value exceeds recommended threshold.**Value exceeds upper threshold.1Maximum contaminant level thresholds 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.2 The SMCL-CA for chloride, sulfate, and total dissolved solids have recommended and upper threshold values. The upper value is shown in parentheses.
Table 11

43

Table 11. Trace elements detected in ground-water samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 35 wells were analyzed for all constituents except mercury, which was analyzed for in samples from the 11 slow wells and was not detected. Abbreviations: COA, Coachella Valley study unit gridwell; COAU, Coachella Valley study unit Understanding well; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level; E, estimated value; LRL, laboratory reporting level; μg/L, microgram per liter; –, not detected]

GAMA well 

identification 

No.

Aluminum 

(μg/L) 

(01106)

[1.6]

Antimony 

(μg/L) 

(01095)

[0.06]

Arsenic 

(μg/L) 

(01000)

[0.12]

Barium 

(μg/L) 

(01005)

[0.08]

Beryllium 

(μg/L) 

(01010)

[0.06]

Boron 

(μg/L) 

(01020)

[8]

Cadmium 

(μg/L) 

(01025)

[0.04]

Chromium 

(μg/L) 

(01030)

[0.12]

Cobalt 

(μg/L) 

(01035)

[0.04]

Copper 

(μg/L) 

(01040)

[0.4]

Iron 

(μg/L) 

(01046)

[6]

Threshold type1 MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA

Threshold level 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300

[LRL] [1.6] [0.06] [0.12] [0.08] [0.06] [8] [0.04] [0.12] [0.04] [0.4] [6]

Grid wells

COA-01 E1.1 – 0.23 14 – 16 – 4.8 – 0.49 –

COA-02 10.2 E0.09 *48.8 41 – *1,510 E0.09 – – – 74

COA-03 2.5 – 0.86 39 – 81 0.05 15.5 – – E4

COA-04 2.4 – 0.62 34 – 14 E0.02 15.1 – 1.6 –

COA-05 1.9 – 0.42 28 – 16 E0.02 11.5 – 1.1 –

COA-06 1.6 – 0.52 88 0.1 27 E0.02 3.3 – 1.7 E4

COA-07 E1.4 – 0.39 72 – 151 – 8.0 E0.02 0.72 21

COA-08 3.4 – 1.0 60 – 70 E0.03 10.9 – – 8

COA-09 E0.9 – 0.13 56 – 17 – 2.5 – – –

COA-10 20.7 0.08 *21.3 5 – 27 – 3.5 – – –

COA-11 16.0 0.15 *12.8 26 – 37 – – – – 22COA-12 4.5 0.07 *27.5 40 – 242 0.05 – – – 26COA-13 1.6 – 0.18 19 – 9 E0.02 4.5 – E0.36 –

COA-14 E1.2 – 0.29 38 – 16 E0.03 3.7 – 1.4 E3

COA-15 3.1 – 0.38 46 – 30 0.04 13.4 – 0.87 E4COA-16 6.9 – 0.86 27 – 688 0.08 3.0 – 0.4 45

COA-17 E1.1 – E0.06 30 – 68 0.11 0.76 E0.02 0.52 –

COA-18 E4.7 0.07 1.7 48 – 247 0.04 1.9 – 0.65 6

COA-19 11.8 – 2.7 23 – *1,270 0.06 0.66 – 0.66 11
44 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program GAMA well identification No. Aluminum (μg/L) (01106) [1.6] Antimony (μg/L) (01095) [0.06] Arsenic (μg/L) (01000) [0.12] Barium (μg/L) (01005) [0.08] Beryllium (μg/L) (01010) [0.06] Boron (μg/L) (01020) [8] Cadmium (μg/L) (01025) [0.04] Chromium (μg/L) (01030) [0.12] Cobalt (μg/L) (01035) [0.04] Copper (μg/L) (01040) [0.4] Iron (μg/L) (01046) [6] Threshold type1 MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA Threshold level 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 [LRL] [1.6] [0.06] [0.12] [0.08] [0.06] [8] [0.04] [0.12] [0.04] [0.4] [6] Understanding wells COAU-01

E1.4 – 0.23 19 – 12 0.06 0.61 – 5 –

COAU-02 3.5 – 0.55 35 – 58 0.06 9.6 – 0.65 –COAU-03

E1.5 – 0.26 38 – 14 – 5.2 – 2.0 –

COAU-04 6.1 – 2.3 37 – 677 0.05 3.1 – 0.83 7COAU-05 1.6 – 0.36 21 – 18 – 5.3 – 1.2 8COAU-06

E1.0 – 0.55 25 – 17 – 12.1 – 4.2 –

COAU-07

E1.2 – 0.15 18 – 20 – 4.8 – 0.66 –

COAU-08 2.5 – 0.37 79 – 32

E0.02 0.28 – 1.2 –

COAU-09 14.3

E0.05 *15.5 7 – 31 0.05 – – E0.32 10

COAU-10 2.8 – 0.52 34 – 56 0.04 17 – 3.9 11COAU-11 1.9 0.08 0.87 27 – 44 0.04 7.3 – 3.4 –COAU-12

E0.9 – – 7 – E6 E0.03 0.56 – 4.3

E4

COAU-13 1.7 – 0.34 35 – 14

E0.03 8.6 – 0.96 –

COAU-14 2.9 – 0.47 112 – 27 – 8.3 – 1.4

E4

COAU-15

E1.3 – 0.36 115 – 282 – 3.4 – 2.8

E4

COAU-16 1.6 – 0.70 45 – 18

E0.02 10.1 – 0.57 –

Table 11. Trace elements detected in ground-water samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.—Continued[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 35 wells were analyzed for all constituents except mercury, which was analyzed for in samples from the 11 slow wells and was not detected. Abbreviations: COA, Coachella Valley study unit gridwell; COAU, Coachella Valley study unit Understanding well; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level; E, estimated value; LRL, laboratory reporting level; μg/L, microgram per liter; –, not detected]
Table 11

45

GAMA well 

identification 

No.

Lead 

(μg/L) 

(01049)

[0.12]

Lithium 

(μg/L) 

(01130)

[0.6]

Manganese 

(μg/L) 

(01056)

[0.2]

Molybdenum 

(μg/L) 

(01060)

[0.12]

Nickel 

(μg/L) 

(01065)

[0.06]

Selenium 

(μg/L) 

(01145)

[0.08]

Strontium 

(μg/L) 

(01080)

[0.4]

Tungsten 

(μg/L) 

(01155)

[0.06]

Uranium 

(μg/L) 

(22703)

[0.04]

Vanadium 

(μg/L) 

(01085)

[0.04]

Zinc 

(μg/L) 

(01090)

[0.6]

[LRL] MCL-US na SMCL-CA HAL-US MCL-CA MCL-US HAL-US na MCL-US NL-CA SMCL-CA

Threshold type1 15 na 50 40 100 50 4,000 na 30 50 5,000

Threshold level [0.12] [0.6] [0.2] [0.12] [0.06] [0.08] [0.4] [0.06] [0.04] [0.04] [0.6]

Grid wells

COA-01 0.16 1.2 – 7.3 E0.03 0.41 188 0.3 3.24 7.4 3.7

COA-02 – 352 *57.2 36.1 0.27 0.78 *5,990 15.3 0.33 0.75 5.8

COA-03 E0.06 6.1 E0.1 22.1 E0.04 1.3 530 2.5 4.27 14.6 E0.3

COA-04 0.28 1.3 – 12.8 0.08 0.43 228 3.8 7.28 15.4 1.7

COA-05 1.53 1.3 – 10.0 E0.05 0.37 182 3.9 5.17 12.7 4.6

COA-06 0.73 1.1 0.3 9.9 0.12 3.2 474 2.8 18.3 10.9 5.7

COA-07 0.24 20.2 1.6 0.7 0.25 14.0 3,760 0.69 11.2 8.0 15.8COA-08 0.18 4.4 0.2 20.1 E0.05 1.8 704 13.7 3.36 17.2 1.4

COA-09 – 1.9 E0.1 4.0 0.06 0.81 258 4.4 7.43 5.3 E0.43

COA-10 – 3.0 0.6 10.3 – 0.56 95 1.8 1.52 46.8 1.3

COA-11 – 8.7 4.0 8.0 E0.03 3.6 151 1.4 0.06 13.0 1.4

COA-12 0.12 12.9 5.0 37.7 0.08 0.13 277 21.4 3.62 6.1 1.1

COA-13 E0.07 E0.6 – 6.8 E0.04 0.47 184 E0.04 1.87 5.8 5.8

COA-14 0.32 1.2 – 9.0 E0.05 0.82 210 0.23 8.99 5.6 1.6

COA-15 0.74 1.8 E0.2 17.9 E0.05 1.6 259 1.1 5.58 11.5 2.2

COA-16 0.41 5.9 1.6 *49.4 0.07 2.2 690 0.4 4.78 26.3 73.5

COA-17 E0.08 2.2 E0.1 *54.9 0.14 0.64 893 0.46 28.1 2.8 169.0COA-18 0.67 37.9 E0.1 12.2 0.16 8.0 1,750 0.9 13.5 5.1 5.5

COA-19 0.15 13.2 0.4 32 E0.05 0.12 494 31.4 0.04 34.3 4.7

Table 11. Trace elements detected in ground-water samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.—Continued[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 35 wells were analyzed for all constituents except mercury, which was analyzed for in samples from the 11 slow wells and was not detected. Abbreviations: COA, Coachella Valley study unit gridwell; COAU, Coachella Valley study unit Understanding well; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level; E, estimated value; LRL, laboratory reporting level; μg/L, microgram per liter; –, not detected]
46 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program GAMA well identification No. Lead (μg/L) (01049) [0.12] Lithium (μg/L) (01130) [0.6] Manganese (μg/L) (01056) [0.2] Molybdenum (μg/L) (01060) [0.12] Nickel (μg/L) (01065) [0.06] Selenium (μg/L) (01145) [0.08] Strontium (μg/L) (01080) [0.4] Tungsten (μg/L) (01155) [0.06] Uranium (μg/L) (22703) [0.04] Vanadium (μg/L) (01085) [0.04] Zinc (μg/L) (01090) [0.6] [LRL] MCL-US na SMCL-CA HAL-US MCL-CA MCL-US HAL-US na MCL-US NL-CA SMCL-CA Threshold type1 15 na 50 40 100 50 4,000 na 30 50 5,000 Threshold level [0.12] [0.6] [0.2] [0.12] [0.06] [0.08] [0.4] [0.06] [0.04] [0.04] [0.6] Understanding wells COAU-01 0.21 1.5 – 18.8 0.09 0.35 194 0.09 11.1 3.0 5.2 COAU-02 0.17 2.2

E0.1 28.2 0.07 0.78 271 0.46 8.29 12.0 5.2

COAU-03 0.30 0.8 – 9.9 0.09 0.73 259 1.9 11.5 5.6 3.4

COAU-04 0.51 6.5 0.4 39.1 0.08 1.3 *12,100 24.9 9.19 34.7 15.1

COAU-05 0.55 1.7

E0.2 10.2 0.06 0.46 205 1.9 7.03 7.1 12.3

COAU-06 0.67 3.7

E0.1 3.0

E0.04 0.41 182 0.06 1.36 10.5 2.8

COAU-07 0.31 2.2 – 6.2 0.06 0.55 184 0.4 3.3 5.0

E0.55

COAU-08 0.17 4.9 – 5.5 0.08 0.58 252 0.19 11.1 3.2 12.6

COAU-09 0.23 1.4 0.8 18.1

E0.03 – 104 4.8 1.4 2.0 1.3

COAU-10 1.89 3.2

E0.2 27.3

E0.03 1.1 306 8.6 7.94 13.3 12.9

COAU-11 0.72 1.1

E0.3 36.7

E0.04 0.79 205 11.2 5.61 15.5 6.9

COAU-12 0.67 – 0.4 8.2 0.2 0.27 74.4 0.2 1.24 1.1 3.7

COAU-13 0.18 1.0 – 16.0 – 0.55 219 0.25 10.7 7.5 1.9

COAU-14 1.51 5.0

E0.1 3.2

E0.04 5.9 643 0.25 4.75 9.6 4.1

COAU-15 0.46 7.4 0.2 3.9

E0.05 3.5 574 0.15 8.12 7.8 3.5

COAU-16 – 1.9 – 10.1

E0.04 0.9 295 0.37 5.59 14.4 1.8

*Value exceeds threshold.1 Maximum contaminant level thresholds 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 

Table 11.exists.

 Trace elements detected in ground-water samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, February and March 2007.—Continued[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all 35 wells were analyzed for all constituents except mercury, which was analyzed for in samples from the 11 slow wells and was not detected. Abbreviations: COA, Coachella Valley study unit gridwell; COAU, Coachella Valley study unit Understanding well; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level; E, estimated value; LRL, laboratory reporting level; μg/L, microgram per liter; –, not detected]
Table 12 47

GAMA well

identification 

No.

Iron

(μg/L) 

(01046)

Iron(II) 

(μg/L) 

(01047)

Arsenic 

(μg/L) 

(99033)

Arsenic(III) 

(μg/L) 

(99034)

Chromium 

(μg/L) 

(01030)

Chromium(VI) 

(μg/L) 

(01032)

Threshold type1 SMCL-CA na MCL-US na MCL-CA na

Threshold level 300 na 10 na 50 na

[MDL] [2] [2] [0.5] [1] [1] [1]

Grid wells

COA-01 3 – – – 5 4

COA-02 72 10 * 23 6.9 – –

COA-03 – – – – 17 16

COA-04 – – – – 15 15

COA-05 – – – – 12 10

COA-06 3 3 – – 3 2

COA-07 20 2 – – 9 7

COA-08 – – – – 11 10

COA-09 – – – – 1 1

COA-10 – – 9.9 – 2 2

COA-11 21 – 6.1 – – –

COA-12 25 7 * 20 17 – –

COA-13 – – 1.3 – 6 1

COA-14 – – – – 5 3

COA-15 5 – 0.7 – 15 10

COA-16 48 3 – – 3 2

COA-17 2 – – – – –

COA-18 4 – – – 2 2

COA-19 14 – 1.4 – 1 –

Understanding wells

COAU-02 4 – 2.4 – 9 9

COAU-03 – – – – 5 4

COAU-04 6 4 1.2 – 3 3

COAU-05 5 – – – 4 3

COAU-06 – – – – 16 14

COAU-07 – – – – 5 5

COAU-09 9 3 9.0 – – –

COAU-10 10 – 0.8 – 17 17

COAU-11 2 – – – 8 6

COAU-12 4 – – – – –

COAU-13 – – 1.3 – 9 7

COAU-14 7 – 1.1 – 8 7

COAU-15 5 – – – 3 4

COAU-16 – – – – 10 9

 *Value exceeds threshold.

1Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

Table 12. Species of inorganic arsenic, iron, and chromium in samples collected for the Coachella Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, February and March 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all 35 wells were analyzed for chromium, arsenic, and iron; only wells with at least one detection are listed. Analyses were made 

by the U.S. Geological Survey Trace Metals Laboratory (laboratory entity code USGSTMCO). Abbreviations: COA, Coachella Valley study unit grid well; 

COAU, Coachella Valley study unit understanding well; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California 

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

method detection level; μg/L, microgram per liter; –, not detected]
48 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

GAMA well

identification 

No.

δ2H

(per mil) 

(82082)1

δ18O 

(per mil) 

(82085)2

Tritium

(pCi/L) 

(07000)3

Uranium234 

(per mil) 

(22610)

Uranium235 

(per mil) 

(22620)

Uranium238

(per mil) 

(82081)3

δ13C 

(per mil) 

(82081)4

Carbon-14 

(percent 

modern) 

(49933)5

Threshold type1 na na MCL-CA MCL-CA MCL-CA MCL-CA na na

Threshold level na na 20,000 20 20 20 na na

Grid wells

COA-01 -61.10 -9.11 4.2 1.119 E0.056 1.001 -12.84 89.15

COA-02 -75.50 -10.76 <1 0.188 <0.054 E0.096 -5.58 4.150

COA-03 -75.20 -10.40 <1 1.506 E0.104 1.244 -10.62 59.03

COA-04 -63.70 -9.48 <1 2.580 E0.158 2.410 -14.89 84.86

COA-05 -63.20 -9.49 <1 1.740 E0.092 1.649 -14.10 79.63

COA-06 -68.80 -9.78 <1 6.730 0.560 6.030 -13.26 82.85

COA-07 -91.30 -11.32 52.8 4.310 0.181 3.320 -12.63 80.69

COA-08 -76.50 -10.54 <1 1.183 E0.058 1.245 -11.17 53.13

COA-09 -74.10 -10.54 8.1 2.730 0.114 2.460 -10.72 96.11

COA-10 -64.50 -9.43 <1 0.394 <0.034 0.356 nc nc

COA-11 -75.70 -10.23 8.0 E0.023 <0.034 <0.035 -9.28 11.41

COA-12 -72.20 -10.28 <1 1.458 E0.096 1.090 -4.94 2.430

COA-13 -65.50 -9.53 6.1 0.654 E0.022 0.582 -12.42 84.93

COA-14 -74.40 -10.52 1.0 2.860 0.146 2.760 -11.04 92.86

COA-15 -69.70 -9.74 <1 1.934 E0.116 1.817 -11.96 105.1

COA-16 -79.10 -9.97 <1 1.817 0.111 1.482 -9.74 69.78

COA-17 -78.50 -10.72 4.8 9.530 0.526 9.180 -11.80 11.11

COA-18 -82.20 -10.51 15.0 4.570 0.230 4.100 -11.26 71.18

COA-19 -88.70 -11.17 <1 0.018 <0.04 <0.033 -9.87 10.90

Understanding wells

COAU-01 -75.60 -10.80 6.7 3.330 0.163 3.350 -12.4 101.5

COAU-02 -75.80 -10.56 <1 2.370 0.122 2.410 -10.95 71.62

COAU-03 -71.40 -10.02 5.8 3.950 0.163 3.730 -11.52 88.73

COAU-04 -76.70 -10.32 2.6 3.180 0.174 2.960 -11.98 46.75

COAU-05 -63.70 -9.37 <1 2.800 E0.118 2.740 -13.25 88.00

COAU-06 -58.10 -8.54 <1 0.622 E0.031 0.464 -17.05 68.69

COAU-07 -62.30 -9.05 4.5 1.395 E0.083 0.972 -12.83 87.63

COAU-08 -68.00 -9.59 4.8 4.190 E0.115 3.740 -10.09 113.3

COAU-09 -67.70 -9.76 <1 0.392 E0.016 0.301 -10.89 35.76

COAU-10 -78.00 -10.61 <1 2.420 E0.083 2.620 -10.18 82.14

COAU-11 -74.90 -10.48 <1 1.797 0.142 1.573 -11.02 73.45

COAU-12 -68.40 -10.17 7.0 0.436 E0.014 0.382 nc nc

COAU-13 -69.40 -10.09 <1 3.240 E0.115 3.140 -11.26 83.34

COAU-14 -69.50 -10.05 <1 1.594 E0.039 1.576 -10.17 82.94

COAU-15 -67.10 -9.13 2.9 3.220 E0.106 2.400 -12.61 98.76

COAU-16 -72.20 -10.34 3.5 1.920 0.145 1.669 -11.14 79.36

1Maximum contaminant level thresholds 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. 

2USGS Stable Isotope Laboratory, Reston, Virginia (USGSSIVA).

3USGS Stable Isotope and Tritium Laboratory, Menlo Park, California (USGSH3CA).

4University of Waterloo (contract laboratory) (CAN-UWIL).

5University of Arizona, Accelerator Mass Spectrometry Laboratory (contract laboratory) (AZ-UAMSL).

Table 13. Stable isotopic ratios, tritium, uranium and carbon-14 activities in samples collected for the Coachella Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all 35 wells were analyzed for stable isotopes of water and uranium, tritium and carbon. 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. 

Abbreviations: COA, Coachella Valley study unit grid well; COAU, Coachella Valley study unit understanding well; MCL-CA, California Department of 

Public Health maximum contaminant level; pCi/L, picocurie per liter; nc, not collected]
Table 14 49

Table 14. Radioactive constituents detected in samples collected for the Coachella Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, February to March 2007.

[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from the eleven slow wells were analyzed. Analyses made by Eberline Services (laboratory entity code CA-EBRL). Abbreviations: COA, 

Coachella Valley study unit grid well; COAU, Coachella Valley study unit understanding well; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; E, estimated value; pCi/L, picocurie per liter; <, less than]

GAMA well 

identification 

No.

Radium-226 

(pCi/L) 

(09511)

Radium-228 

(pCi/L) 

(81366)

Radon-222 

(pCi/L) 

(82303)

Alpha 

radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Alpha 

radioactivity, 

30-day count 

(pCi/L) 

(62639)

Beta 

radioactivity, 

72-hour count 

(pCi/L) 

(62642)

Beta 

radioactivity, 

30-day count 

(pCi/L) 

(62645)

Threshold type1 MCL-US MCL-US Proposed 

MCL-US MCL-US MCL-US MCL-US MCL-US

Threshold level 2

 5 2 5 3 300 (4,000) 15 15 50.00 50.00

Grid wells

COA-01 E0.03 <0.49 *540 <2.3 <2.1 2.6 2.9

COA-02 0.24 0.76 230.00 <20 <22.0 6.8 10.5

COA-03 E0.05 0.46 300.00 E3.1 E5.0 7.0 10.5

COA-08 0.08 <0.55 180.00 5.1 E3.6 7.1 8.5

COA-09 E0.04 <0.55 *400 4.7 4.9 2.3 4.6

COA-15 0.11 E0.34 *460 6.8 6.0 7.2 8.5

COA-16 E0.04 E0.33 *620 E5.4 E2.9 8.5 9.3

Understanding wells

COAU-01 E0.05 <0.67 *910 E6.7 E4.2 4.3 7.0

COAU-03 E0.05 E0.23 270.00 8.5 6.3 4.3 6.5

COAU-05 E0.04 <0.44 *460 E3.7 E1.7 3.3 5.4

COAU-06 E0.03 <0.66 *380 E2.6 <2.0 E1.0 E1.8

*Value exceeds lower threshold.

1Maximum contaminant level thresholds 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.

2The MCL-US threshold for radium is the sum of those for radium-226 and radium-228.

3

 Two MCLs have been proposed for Radon-222. The proposed alternative MCL is in parentheses.
50 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Table 15. Microbial indicators detected in samples collected for the Coachella Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.

[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used 

to uniquely identify a specific constituent or property. Samples from the 11 wells analyzed using the slow schedule. 

Abbreviations: COA, Coachella Valley study unit grid well; TT-US, U.S. Environmental Protection Agency treatment 

technique; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; mL, milliliter, –, not detected]

GAMA well 

identification 

No.

Coliphage 

F-specific 

(99335)

Coliphage 

somatic 

(99332)

E. coli 

colonies/100 mL 

(90901)

Total coliforms 

colonies/100mL 

(90900)

Threshold type TT-US TT-US TT-US MCL-US

Threshold level 99.9% 

Killed/Inactive

99.9% 

Killed/Inactive

No fecal coliforms 

are allowed

5%

COA-08 – – – 4
Appendix 51

Appendix 

This appendix includes discussions of the methods used 

to collect and analyze ground-water samples and report the 

data for the COA Study Unit. These methods were selected 

to obtain representative samples of the ground water from 

each well and to minimize the potential for contamination 

of the samples or bias in the data. Procedures used to collect 

and assess quality-control data and the results of the qualitycontrol assessments also are discussed.

Sample Collection and Analysis

Ground-water samples were collected using standard and 

modified USGS protocols from the USGS NAWQA program 

(Koterba and others, 1995) and the USGS National Field 

Manual (U.S. Geological Survey, variously dated), as well 

as protocols described by Weiss (1968), Shelton and others, 

(2001), and Ball and McClesky (2003a,b). Before sampling, 

each well was pumped continuously until at least three casingvolumes of water was purged from the well (Wilde and others, 

1999). Samples were collected using Teflon tubing with brass 

and stainless-steel fittings attached to a sampling point on 

the well discharge pipe as close to the well as possible. The 

sampling point was always located upstream of any wellhead treatment system or water storage tank. If a chlorinating 

system was attached to the well, the chlorinator was shut off at 

least 24 hours before purging and sampling the well in order 

to clear all chlorine out of the system. For the intermediate 

schedules, samples were collected at the well head using a 

foot-long length of Teflon tubing. Samples collected using 

the slow schedule were within an enclosed chamber located 

inside a mobile laboratory and connected to the well head by 

a 10- to 50- foot length of the Teflon tubing (Lane and others, 

2003). All fittings and lengths of tubing were cleaned between 

sampling events (Wilde, 2004).

For the field measurements, ground water was pumped 

through a flow-through chamber fitted with a multi-probe 

meter that simultaneously measures the water-quality 

indicators: dissolved oxygen, temperature, pH, and specific 

conductance. At sites where the slow schedule was used, 

turbidity readings were taken using a Hatch kit. Field 

measurements were made in accordance with protocols in 

the USGS National Field Manual (Wilde and Radtke, 2005; 

Wilde, 2006; Lewis, 2006; Radtke and others, 2005; 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 3- to 

5-minute intervals for at least 30 minutes, and after these 

values remained stable for 20 minutes, samples to be analyzed 

in the laboratory were collected. Field measurements and 

instrument calibrations were recorded by hand on field 

record sheets and electronically in PCFF-GAMA, a software 

package designed by the USGS with support from the 

GAMA program. Analytical service requests and chain of 

custody documentation also were managed by PCFF-GAMA. 

Information from PCFF-GAMA was uploaded directly into 

NWIS at the end of each week that samples were collected. 

For analyses requiring filtered water, ground-water was 

diverted through a 0.45-μm pore size vented capsule filter, 

a disk filter, or a baked glass-fiber filter, depending on the 

protocol for the analysis (Wilde and others, 1999; Wilde and 

others, 2004). Before samples were collected, polyethylene 

sample bottles were pre-rinsed using deionized water three 

times during the bottle set preparation and then once with 

native well water before sample collection. Samples requiring 

acidification were acidified to a pH of 2 or less with the 

appropriate acids using ampoules of certified, traceable 

concentrated acids obtained from the USGS National Water 

Quality Laboratory (NWQL).

Temperature-sensitive samples, VOCs, pesticides, 

pharmaceutical compounds, potential wastewater-indicator 

compounds, compounds of special interest, dissolved 

organic carbon, radium, nutrients, major and minor trace 

elements, and nitrogen and oxygen isotopes were stored on 

ice until they were shipped to the appropriate laboratory. 

The non-temperature sensitive samples for tritium, noble 

gases, chromium speciation, and stable isotopes were 

shipped monthly with the exception of gross alpha and beta 

radioactivity samples and radon-222 samples, which were 

shipped daily. 

Detailed sampling protocols for individual analyses 

and groups of analytes are described by Koterba and others 

(1995) and in the USGS National Field Manual (Wilde and 

others, 1999; Wilde and others, 2004), and the references for 

analytical methods listed in table A1; only brief descriptions 

are given here. Volatile organic compounds (VOCs) and 

1,2,3-trichloropropane (1,2,3-TCP) samples were collected in 

40-mL sample vials that were purged with three vial volumes 

of sample water before bottom filling to eliminate atmospheric 

contamination. Six normal (6 N) hydrochloric acid (HCl) was 

added as a preservative to the VOC samples but not to the 

1,2,3-TCP samples. The perchlorate sample was collected in 

a 125-mL polyethylene bottle. Tritium samples were collected 

by bottom-filling two 1-L polyethylene bottles with unfiltered 

ground water, after first overfilling the bottle with three 

volumes of water. Stable isotopes of hydrogen and oxygen of 

water were collected in 60-mL clear glass bottles filled with 

unfiltered water, sealed with a conical cap, and secured with 

electrical tape to prevent leakage and evaporation.

Samples containing pesticides and pesticide degradation 

products, pharmaceuticals, and potential wastewater indicators 

were collected in 1-L baked amber bottles. Pesticide and 

pharmaceutical samples were filtered through a glass fiber 

filter. 
52 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Ground-water samples for major and minor ions, trace 

elements, alkalinity, and total dissolved solids analyses were 

collected by filling one 250-mL polyethylene bottle with raw 

ground water and one 500-mL and one 250-mL polyethylene 

bottle with filtered ground water (Wilde and others, 2004). 

The filter used was a Whatman capsule filter, pre-rinsed 

with deionized water. The 250-mL filtered sample was then 

preserved with 7.5 N nitric acid. Mercury samples were 

collected by filtering ground water into a 250-mL glass bottle; 

the water was then preserved with 6 N hydrochloric acid. 

Arsenic and iron speciation samples were collected together, 

filtered into one 250-mL polyethylene bottle that was covered 

with tape to prevent light exposure, and preserved with 6 N 

Hydrochloric acid. The nutrient sample was filtered into a 

125-mL brown polyethylene bottle. Radium isotopes, uranium, 

and gross alpha and beta radiation samples were filtered into 

1-L polyethylene bottles and acidified with nitric acid. Carbon 

isotope samples were filtered and bottom filled into two 

500‐mL glass bottles that were first overfilled with three bottle 

volumes of ground water. These samples had no headspace 

and were sealed with a conical cap to avoid atmospheric 

contamination. Samples for field alkalinity titrations were 

collected by filtering ground water into a 500-mL polyethylene 

bottle. 

Chromium, radon-222, dissolved noble gases, and 

microbial constituents were collected from the hose bib at the 

well head, regardless of the sampling schedule (intermediate 

or slow). DOC was collected at slow schedule sites after 

rinsing the sampling equipment with blank water (Wilde and 

others, 2004). Using a 50-mL syringe and 0.45-μm disk filter, 

the ground-water sample was filtered into a 125-mL baked 

glass bottle and preserved with 4.5 N sulfuric acid. Chromium 

speciation samples were collected using a 10-mL syringe 

with an attached 0.45-μm disk filter. After the syringe was 

thoroughly rinsed and filled with ground water, 2 mL was 

forced through the disk filter; the next 2 mL of the ground 

water was slowly filtered into a small centrifuge vial for 

analysis of total chromium. Hexavalent chromium, Cr(VI), 

was then collected by attaching a small cation-exchange 

column to the syringe filter, and after conditioning the column 

with 3 mL of sample water, 2 mL was collected in a second 

centrifuge vial. Both vials were preserved with 10 μL of 7.5 N 

nitric acid (Ball and McClesky, 2003a,b).

To collect radon-222, 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 sample was collected 

through a Teflon septum on the valve assembly using a glass 

syringe rinsed with ground water and affixed with a stainless 

steel needle. The sample was then injected into a 25-mL vial 

partially filled with scintillation mixture (mineral oil) and 

shaken. The vial was then sealed with electrical tape and 

placed in a cardboard tube in order to shield it from light 

during shipping. 

Noble gases were collected in 3/8-in copper tubes using 

reinforced nylon tubing connected to the hose bib at the 

wellhead. Ground water was flushed through the tubing to 

dislodge bubbles before flow was restricted by a back pressure 

valve. Clamps on either side of the copper tube were then 

tightened, trapping a sample of ground water for analyses of 

noble gases (Weiss, 1968). 

Samples for analysis of microbial constituents also 

were collected at the well head (Myers, 2004; Bushon, 

2003). Before samples were collected, the sampling port was 

sterilized using isopropyl alcohol, and ground water was run 

through the sampling port for at least three minutes to remove 

any traces of the sterilizing agent. Two sterilized 250-mL 

bottles were then filled with ground water for coliform 

analyses (total and Escherichia coliform determinations), and 

one sterilized 3-liter carboy was filled for coliphage analyses 

(F specific and somatic coliphage determinations).

Turbidity, alkalinity, total coliforms and Escherichia

coliform (E. coli) were measured in the mobile laboratory 

at the well site. Turbidity was measured in the field with a 

calibrated turbidity meter. Total coliforms and Escherichia

coliform (E. coli) plates were prepared using sterilized 

equipment and reagents (Myers, 2004). The bacteria on the 

plates were counted under an ultraviolet light, following a 

22–24 hour incubation time. Alkalinity and concentrations of 

bicarbonate (HCO3

-

) and carbonate (CO3

2-) were measured 

on filtered samples by Gran’s titration method (Gran, 1952, 

Rounds, 2006, Stumm and Morgan, 1996). 

Concentrations of HCO3

-

 and CO3

2- were also calculated 

from the laboratory alkalinity and pH measurements. 

Calculations were made using the advanced speciation method 

(http://or.water.usgs.gov/alk/methods.html), with pK1 (-log 10

of the first acid dissociation constant for H2CO3) = 6.35, pK2

(-log10 of the second acid dissociation constant for H2CO3) = 

10.33, and pKW (-log10 of the acid dissociation constant for 

water) = 14. 

Ten laboratories analyzed chemical and microbial 

samples for this study (see table A1), although most of the 

samples were analyzed at the NWQL or by laboratories 

contracted by the NWQL. The NWQL maintains a rigorous 

quality assurance program (Maloney, 2005). Laboratory 

quality-control 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 continuously tested and laboratory 

reporting levels updated accordingly. NWQL maintains 

National Environmental Laboratory Accreditation Program 

(NELAP) and other certifications. In addition, the Branch of 

Quality Systems within the USGS Office of Water Quality 

maintains independent oversight of quality assurance at 

the NWQL and laboratories contracted by the NWQL. The 

Branch of Quality Systems also runs a national field quality 

assurance program that includes annual testing of all USGS 
Appendix 53

field personal for proficiency in making field water-quality 

measurements (http://bqs.usgs.gov/nfqa/). Results for analyses 

made at the NWQL or by laboratories contracted by the 

NWQL are uploaded directly into NWIS by the NWQL. 

Laboratory quality-control data are also stored in NWIS or 

available from the NWQL upon request.

Data Reporting

Laboratory Reporting Conventions

The USGS NWQL uses the laboratory reporting level 

(LRL) as a threshold for reporting analytical results. The 

LRL is set to minimize the reporting of false negatives (not 

detecting a compound when it is actually present in a sample) 

to less than 1 percent (Childress and others, 1999). The LRL 

is usually 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 MDL determinations made over an 

extended period of time. The method detection limit (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 MDL there is less than 

1 percent chance of a false positive) (U.S. Environmental 

Protection Agency, 2002a). The USGS NWQL monitors and 

updates LT-MDL and LRL values regularly and the values 

listed in this report were in effect during the period groundwater samples from the COA Study Unit were analyzed 

(February and March, 2007).

Detections between the LRL and the LT-MDL are 

reported as estimated concentrations (designated with an “E” 

before the values in the tables and text). For informationrich methods, detections below the LRL have a high 

certainty of detection, but the precise concentration is 

uncertain. Information-rich methods are those that use gas 

chromatography or high-performance liquid chromatography 

(HPLC) with mass spectrometry detection (for VOCs, 

pesticides, pharmaceuticals, and wastewater-indicators). 

Compounds are identified by the 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-values also 

may result from detections outside the range of calibration 

standards, for detections that did not meet all laboratory 

quality-control criteria, and for samples that were diluted 

before being analyzed (Childress and others, 1999).

Some compound concentrations in this study are 

reported using minimum reporting levels (MRL) 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 in which the true 

value will be found. 

Detections that may have resulted from inadvertent 

sample contamination are reported with a “V” before the 

values in the tables. The potential for sample contamination 

was assessed using results from field, source-solution, and 

laboratory blanks.

The reporting levels for radiochemical constituents 

(gross-alpha radioactivity, gross-beta radioactivity, 

radium-226, radium-228, and uranium) were based on a 

sample-specific minimum detectable concentration (SSMDC), 

a sample-specific critical value, and the combined standard 

uncertainty (CSU) (U.S. Environmental Protection Agency, 

2004; Bennett and others, 2006). A result above the critical 

value represents a greater-than-95-percent certainty that the 

result is greater than zero (significantly different from the 

instrument’s background response to a blank sample), and a 

result above the SSMDC represents a greater-than-95-percent 

certainty that the result is greater than the critical value. 

Using these reporting level elements, three unique cases 

were possible when screening the raw analytical data. If the 

analytical result was less than the critical value (case 1), the 

analyte was considered not detected, and the concentration 

was reported as less than the SSMDC. If the analytical result 

was greater than the critical value, the ratio of the CSU to 

the analytical result was calculated as a percent (percent 

relative CSU). For those samples with percent relative CSU 

greater than 20 percent (case 2), concentrations were reported 

as estimated values (designated by an “E” preceding the 

value). For those samples with percent relative CSU less than 

20 percent (case 3), concentrations were reported as given.

Stable isotopic compositions of oxygen, hydrogen, and 

carbon are reported as relative isotope ratios in units of per mil 

using the standard delta notation (Coplen and others, 2002):

sample

reference

sample

1 1,000 per mil,

where

is the atomic mass of the heavier isotope of

the element,

is the element (O for oxygen, C for carbon, 

or H for hydrogen,

is the ratio of the abund

i R

E

R

i

E

R

  δ = − •    

18 13 2

16 12 1

reference

ance of the heavier

 isotope of the element ( O, C, or H) 

to the lighter isotope of the element 

( O, C, or H) in the sample and,

is the ratio of the abundance of the heavier

isotope of th

R

e element to the lighter isotope 

of the element in the reference material 

hydrogen.

(1)
54 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

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 that δ2H is 

also written as δD because the common name of the heavier 

isotope of hydrogen, hydrogen-2, is deuterium). The reference 

material for carbon is Vienna Peedee Belemnite (VPDB), 

which is assigned a δ13C value of 0 per mil. 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.

Constituents on Multiple Analytical Schedules 

Seventeen constituents targeted in this study were 

determined by more than one USGS NWQL analytical 

schedule or more than one laboratory (table A2). The preferred 

methods for 17 constituents analyzed under multiple analytical 

schedules at the NWQL were selected on the basis of the 

procedure recommended by the NWQL (http://wwwnwql.

cr.usgs.gov/USGS/Preferred_method_selection_procedure.

html). Only constituents determined by the preferred method 

are reported. For example, this report uses Schedule 2060 

(table 3B) as the preferred method for caffeine because it has 

the lower detection limit than the other analytical methods. 

The standard methods used by the NWQL to analyze 

arsenic, chromium, and iron concentrations are preferred 

over the research methods used by the USGS Trace Metal 

Laboratory. The concentrations measured by the Trace Metal 

Laboratory are used only to calculate ratios of redox species 

for each element, As(V)

As(III) for arsenic, Cr(VI)Cr(III) for chromium,

 and Fe(III)

Fe(II) for iron. For example:

Fe(III) Fe(T) - Fe(II) , Fe(II) Fe(II)

where

Fe(T) is the total iron concentration (measured),

Fe(II) is the concentration of ferrous iron (measured), 

and

Fe(III) is the concentration of ferric iron (calculated

=

).

(2)

Quality-Assurance Method

The quality-assurance process used for this study 

followed the protocols used by the USGS NAWQA program 

(Koterba and others, 1995) and described in the USGS 

National Field Manual (U.S. Geological Survey, variously 

dated). The quality-assurance method followed by the NWQL, 

the primary laboratory used to analyze samples for the study, 

is described by Maloney (2005), and Pirkey and Glodt (1998). 

Quality-control (QC) samples collected in the COA Study 

Unit included source-solution blanks, field blanks, replicates, 

and matrix and surrogate spikes. QC samples were collected 

to evaluate contamination, and bias and variability of the data 

that may have resulted from the sample collection, processing, 

storage, transportation, and laboratory analysis.

Blanks

Blank samples (blanks) were collected using blank 

water certified by the NWQL to contain less than the LRL 

or MRL of the analytes investigated in the study. Two types 

of blanks were collected: source-solution and field blanks. 

Source-solution blanks were collected to verify that the blank 

water used for the field blanks was free of analytes. Field 

and source solution blanks were collected at approximately 

10 percent of the wells sampled to determine if equipment 

or procedures used in the field or laboratory introduced 

contamination. Source solution blanks were analyzed only 

if there were detections in the field blank. Field blanks were 

analyzed for VOCs, pesticides, perchlorate, pharmaceuticals, 

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

wastewater compounds, 1,2,3 TCP, radium, and dissolved 

organic carbon. Source-solution blanks were collected at the 

sampling site by pouring blank water directly into sample 

bottles that were preserved, stored, shipped, and analyzed in 

the same manner as the ground-water samples. Field blanks 

were collected by pumping or pouring blank water through the 

sampling equipment (fittings and tubing) that was to be used 

in collecting ground water samples, field blank samples were 

then processed and transported using the same protocols for 

the ground-water samples. 

Contamination in blanks may originate from several 

different types of sources, including the source-solution water, 

the previous sample, known sources specific to a field site, 

and field or laboratory equipment or processes. These different 

sources of contamination require different strategies for 

V-coding detections in environmental samples on the basis of 

detections in field blanks.

Detections in source-solution blanks were used to 

evaluate potential contamination of the source-solution 

water. If a constituent was detected in a source-solution 

blank at a concentration similar to or greater than the 

lowest concentration detected in the paired field blank, the 

source-solution water was considered to be the origin of the 

contamination and the field blank detection was disregarded. 

The equipment used to collect samples from wells 

sampled with the slow schedule was different than the 

equipment used to collect samples from wells sampled with 

intermediate schedules; therefore, detections in field blanks 

collected at slow wells were compared with detections in 

ground-water samples from slow wells, and detections in 
Appendix 55

field blanks collected at intermediate wells were compared 

with detections in ground water samples from intermediate 

wells. If the constituent was not detected in the ground-water 

sample collected prior to the contaminated field blank, then 

contamination of that field blank due to carry-over was ruled 

out. If non-detections were reported in field blanks or groundwater samples collected after ground-water samples containing 

high concentrations of the constituent, then carry-over 

contamination was considered unlikely in the whole dataset. 

If carry-over contamination in the dataset could not be ruled 

out, then all detections in ground-water samples and field 

blanks collected after a ground-water sample containing a high 

concentration of the constituent were examined for potential 

V-coding. V-coded values are indicated by a ‘V’ preceding the 

value in the data tables, and are excluded from the summary 

statistics.

Contamination from known sources may produce 

distinctive patterns of detections in field blanks and groundwater samples, particularly for the VOCs. Substances that 

may be encountered at the field site, such as lubricants (for 

example, WD-40), cements used on PVC-piping, exhaust 

fumes from pump engines, and the methanol used to clean 

sample lines, contain recognizable associations of VOC 

constituents. If a recognizable association of VOC constituents 

was detected in a field blank and the field notes indicated that 

a known source was present and may have affected collection 

of the field blank, the field blank was not used to V-code 

detections of individual VOCs in ground-water samples. If a 

recognizable association of VOC constituents was detected 

in a ground-water sample and the field notes indicated that 

a known source was present and may have affected sample 

collection, the detections in the ground-water sample were 

examined for potential V-coding. However, detecting these 

co-occurring VOC constituents in ground-water samples 

does not necessarily indicate contamination during sample 

collection, because these VOC constituents also may occur 

together in ground water naturally. 

If a field blank detection could not be attributed to the 

source-solution, carryover, or a specific problem recorded 

in the field notes, that field blank was used to V-code 

detections in all ground water samples collected with the 

same equipment. If the concentration of an analyte detected 

in a field blank was greater than the concentration measured 

in a ground-water sample collected before or after the blank 

sample, the ground-water value was V-coded. V-coded values 

are indicated by a ‘V’ preceding the value in the tables, and 

are excluded from the summary statistics. If a compound was 

detected in multiple field blanks and the detections could not 

be attributed to the source-solution water, any ground-water 

sample that had a detection of that compound was evaluated 

for possible inadvertent contamination.

Replicates

Sequential replicate samples were collected to assess 

variability that may result from processing and analyzing 

inorganic and organic constituents. Relative standard deviation 

(RSD) of the measured values was used in determining 

the variability between replicate pairs for each compound 

(table A4). The RSD is defined as the standard deviation 

divided by the mean concentration for each replicate pair of 

samples, multiplied by 100 percent. If one value in a sample 

pair was reported as a non-detection and the other value was 

reported as an estimate below or equal to the LRL or MRL, 

the RSD was set to zero because the values are analytically 

identical. If one value for a sample pair was reported as a 

non-detection and the other value was greater than the LRL 

or MRL, then the non-detection value was set equal to onequarter of the LRL and the RSD was calculated (Hamlin 

and others, 2002). Values of RSD less than 20 percent 

were considered acceptable in this study. An RSD value of 

20 percent corresponds to a relative percent difference (RPD) 

value of 29 percent. High RSD values for a compound at low 

concentrations may indicate analytical uncertainty, particularly 

for concentrations within an order of magnitude of LT-MDL 

or MDL. Sequential replicate samples were collected at 

approximately 10 percent of the wells sampled.

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 for in the 

method. This enables an analysis of matrix interferences on 

a compound by compound basis. Matrix spikes were added 

at the laboratory performing the analysis. Compounds with 

low recoveries are of potential concern if environmental 

concentrations are close to the MCLs; a concentration 

below an MCL could be falsely indicated. Conversely, 

compounds with high recoveries are of potential concern if 

the environmental concentrations were above MCLs: a high 

recovery could falsely indicate a concentration above the 

MCL. 

Matrix spikes were performed for VOCs, pesticide 

compounds, pharmaceutical compounds, potential wastewaterindicator compounds, 1,2,3-TCP, radium and gross alpha/

beta, and coliphage because the analytical methods for these 

constituents are chromatographic methods, which may be 

susceptible to matrix interferences. Acceptable ranges for 

matrix-spike recoveries are based on the acceptable ranges 
56 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

established 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 

ranges for set spike recoveries are 70 to 130 percent for 

NWQL schedules 2020 and 1433 (Connor and others, 1998; 

Rose and Sandstrom, 2003; Zaugg and others, 2002), 60 to 

120 percent for NWQL schedules 2003 and 2060 (Sandstrom 

and others, 2001; Furlong and others, 2008), and 60 to 130 

percent for NWQL schedule 2080 (Kolpin and others, 2002). 

These ranges were used to define 70 to 130 percent as the 

acceptable range for matrix-spike recoveries for organic 

compounds in this study. 

Surrogates

Surrogate compounds are added to environmental 

samples in the laboratory before analysis in order to monitor 

the performance of the analytical methods for each sample. 

Surrogate compounds were added to all ground-water and 

quality-control samples that were analyzed for VOCs, 

pesticide compounds, pharmaceutical compounds, potential 

wastewater-indicator compounds, and 1,2,3-TCP (table A6). 

Most of the surrogate compounds are deuterated analogs 

of compounds being analyzed. For example, the surrogate 

toluene-d8 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); deuterated compounds like toluene-d8 do not 

occur naturally and are not found in environmental samples. 

Surrogates are used to identify general problems that may arise 

during sample analysis that could affect the analysis results 

for all compounds in that sample. Potential problems include 

matrix interferences (such as high levels of dissolved organic 

carbon) 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 is generally 

considered acceptable; values outside this range indicate 

possible problems with the processing and analysis of samples 

(Connor and others, 1998; Sandstrom and others, 2001).

Quality-Control Sample Results

Detections in Field and Source-Solution Blanks

Field and source solution blanks were collected at 

approximately 10 percent of the sites sampled in the COA 

Study Unit. Table A3 gives a summary of detections in field 

blanks. Four VOCs were detected in field blanks; toluene, 

m- and p-xylene, o-xylene and ethylbenzene. Toluene was 

detected in all three source solution and field blanks at 

concentrations equal to or below 0.33 μg/L. Low levels of 

toluene were detected in source-solution and field blanks in 

many of the earlier study units also (Wright and others, 2005; 

Kulongoski and others, 2006; Bennett and others, 2006; 

Dawson and others, 2008; Kulongoski and Belitz, 2007). 

Because of the persistent detections of toluene in blanks, all 

concentrations of toluene detected in environmental samples 

were V-coded. No ethyl-benzene or xylenes were detected in 

the environmental samples; therefore, the blank detections 

were disregarded.

 Three other constituents were detected in field blanks: 

mercury, radium-226 and -228. One field blank contained 

0.01 μg/L of mercury, but mercury was not detected in any 

environmental samples. Radium-226 and -228 was detected at 

activities of 0.016 and 0.01 pCi/L in one field blank (table A3).

No constituents were detected in field blanks for the 

following analyte groups: pesticides and pesticide degradates, 

pharmaceutical compounds, perchlorate and 1,2,3-TCP, major 

and minor ions, nutrients, and dissolved organic carbon. 

Variability in Replicate Samples

Table A4 summarizes the results of replicate analyses 

of constituents detected in ground-water samples collected in 

the COA Study Unit. Constituents not detected by replicate 

analyses are not reported in table A4. Concentrations or 

activities in the environmental and replicate samples are 

reported for all replicate analyses with RSD values greater 

than 20 percent. Most of replicate sample pairs collected 

during the COA Study Unit had RSDs of less than 20 percent. 

Constituent classes with replicate sample pairs with RSDs 

greater than 20 percent were VOCs, pharmaceuticals, and 

trace elements. No data were V-coded as a result of variability 

in replicate analyses. 
Appendix 57

Matrix-Spike Recoveries

Tables A5A–A5D summarize matrix-spike recoveries 

for the COA Study Unit. Addition of a spike or known 

concentration of a constituent to an environmental sample 

enables the analyzing laboratory to determine the effect of the 

matrix, in this case ground water, on the analytical technique 

used to measure the constituent. Three environmental samples 

were spiked with VOCs (table A5A). Most of the spike 

compounds had median recoveries within the acceptable range 

of 70 to 130 percent. Bromomethane had one spike matrix 

recovery greater than 130 percent and hexachlorobutadiene 

had one spike matrix recovery below 70 percent. Neither 

compound was detected in environmental samples. 

Three environmental samples were spiked with polar 

pesticide and pesticide degradate compounds (NWQL 

schedule 2060, table 3B). Most of the spike compounds had 

median recoveries within the acceptable range of 70 through 

130 percent (table A5B). Two compounds, bendiocarb and 

oxamyl, had a recovery greater than 130 percent; however, 

neither compound was detected in ground-water samples. 

Twelve spike compounds had at least one median recovery 

below 70 percent. Of the compounds with low spike 

recoveries, 2-chloro-4-isopropylamino-6-amino-s-triazine 

(CIAT), 2-Chloro-6-ethylamino-4-amino-s-triazine (CEAT), 

and atrazine were detected in ground-water samples. [NOTE – 

low recoveries may indicate that the compound might not have 

been detected in some samples if it was present at very low 

concentrations].

Three ground-water samples were spiked with pesticide 

and pesticide degradate compounds (NWQL schedule 

2003, table 3C). Most of the spike compounds had median 

recoveries within the acceptable range of 70 to 130 percent 

(table A5C). The compound CIAT again had a low recovery. 

One spike compound had a recovery greater than 130 percent. 

The median recovery was below 70 percent for seventeen 

compounds. 

Three ground-water samples were spiked with 

pharmaceutical compounds (NWQL schedule 2080, table 3D). 

All but one pharmaceutical compound had median recoveries 

within the acceptable range of 70 to 130 percent (table A5D). 

The compound acetaminophen, which was detected in a 

ground-water sample, had acceptable recoveries in all three 

spiked samples.

One ground-water sample was spiked with potential 

wastewater-indicator compounds (NWQL schedule 4433, 

table 3E). Fifty-five of the sixty-eight compounds had 

recoveries less than 70 percent and ten had recoveries greater 

than 130 percent (table A5E). Of the compounds detected 

in ground-water samples, eleven had recoveries below 

70 percent, one had an acceptable recovery, and two were 

greater than 130 percent.

Surrogate Compound Recoveries

Surrogate compounds were added to field blanks and 

environmental samples in the laboratory to evaluate the 

recovery of similar constituents. Table A6 lists the surrogate, 

the NWQL analytical schedule on which it was applied, the 

number of analyses for blank and environmental samples, 

the number of surrogate recoveries below 70 percent, and 

the number of surrogate recoveries above 130 percent. Blank 

and environmental samples were considered separately to 

assess whether the matrices of environmental samples affect 

surrogate recoveries.

Differences between surrogate recoveries in blank and 

environmental samples occurred for VOCs, pesticide and 

pesticide degradates, and potential waste-water indicator 

compounds. Surrogate recoveries for these analytical 

classes were lower in the environmental samples (below the 

70 percent lower limit) than they were in the blank samples. 

This result indicates matrix inferences may be biasing analyte 

concentrations lower than they actually are. All surrogates 

recovered in the analyses of pharmaceutical compounds were 

in the acceptable range of 70 to 130 percent recovery. No 

samples had recoveries of surrogates greater than 130 percent. 

A high recovery for a surrogate suggests that the measured 

concentrations of analytes eluting near the surrogate may be 

biased to higher internal laboratory quality-control samples for 

pharmaceutical compounds.
58 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Analyte Analytical Method Laboratory and analytical 

schedule Citation(s)

Water-quality indicators

Field parameters Calibrated field meters and test kits USGS field mesurement 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 pesticide 

degradates

Solid-phase extraction and gas 

chromatography/mass spectrometry

NWQL, schedule 2003 Zaugg and others, 1995; Lindley 

and others, 1996; Madsen and 

others, 2003; Sandstrom and 

others, 2001

Polar pesticides and degradates Solid-phase extraction and highperformance liquid chromatography 

(HPLC)/mass spectrometry with 

selective-ion monitoring

NWQL, Schedule 2060 Furlong and others, 2001

Pharmaceuticals Solid-phase extraction and HPLC/mass 

spectrometry

NWQL, schedule 2080 Kolpin and others, 2002

Potential wastewater-indicators Solid-phase extraction and gas 

chromatography/mass spectrometry

NWQL, schedule 4433 Zaugg and others, 2002

Constituents of special interest

Perchlorate Chromatography and mass spectrometry Montgomery Watson-Harza 

Laboratory

Hautman and others, 1999

1,2,3-Trichloropropane Gas chromatography/electron capture 

detector

Montgomery Watson-Harza 

Laboratory

U.S. Environmental Protection 

Agency, 1995

Inorganic constituents

Nutrients Alkaline persulfate digestion, Kjedahl 

digestion

NWQL, schedule 2755 Fishman and others, 1993; 

Patton and Kryskalla, 2003

Dissolved organic carbon UV-promoted persulfate oxidation and 

infrared spectrometry

NWQL, schedule 2613 Brenton and Arnett, 1993

Major and minor ions, trace 

elements and nutrients

Atomic absorption spectrometry, 

colorimetry, ion-exchange 

chromatography, inductively-coupled 

plasma atomic emission spectrometry 

and mass spectrometry

NWQL, schedule 1948 Fishman and Friedman, 1989; 

Fishman, 1993; Faires, 1993; 

McLain, 1993; Garbarino, 

1999; Garbarino and Damrau, 

2001; American Public Health 

Association, 1998; Garbarino 

and others, 2006

Chromium, arsenic and iron 

speciation

Various techniques of ultraviolet visible 

(UV-VIS) spectrophotometry and 

atomic absorbance spectroscopy

USGS Trace Metal 

Laboratory, Boulder, 

Colorado

Stookey, 1970; To and others, 

1998; Ball and McCleskey, 

2003a and 2003b; McCleskey 

and others, 2003

Table A1. Analytical methods used to determine organic, inorganic, and microbial constituents by the U.S. Geological Survey (USGS) 

National Water Quality Laboratory (NWQL) and contract laboratories.

[MI agar, supplemented nutrient agar in which coliforms (total and Escherichia) produce distinctly different fluorescence under ultraviolet lighting; UV, 

ultraviolet; VOCs, volatile organic compounds]
Table A1 59

Analyte Analytical Method Laboratory and analytical 

schedule Citation(s)

Isotopes

Carbon isotopes Accelerator mass spectrometry University of Waterloo, 

Environmental Isotope 

Lab; University of 

Arizona Accelerator Mass 

Spectrometry Lab

Donahue and others, 1990; 

Jull and others, 2004

Stable isotopes of hydrogen and 

oxygen in water

Gaseous hydrogen and carbon dioxidewater equilibration and stable-isotope 

mass spectrometry

USGS Stable Isotope 

Laboratory, Reston, 

Virginia

Epstein and Mayeda, 1953; 

Coplen and others, 1991 ; 

Coplen, 1994

Uranium Isotopes Chemical separations and alpha-particle 

spectrometry

 Eberline Analytical Services 

(CA-EBERL), NWQL 

Schedule 1130 

American Society for Testing 

Materials, 2002 (D3972)

Radioactivity and gases

Tritium Electrolytic enrichment-liquid 

scintillation

USGS Stable Isotope and 

Tritium Laboratory, Menlo 

Park, California

Thatcher and others, 1977

Tritium and noble gases Helium-3 in-growth and mass 

spectrometry

Lawrence Livermore 

National Laboratory

Moran and others, 2002; 

Eaton and others, 2004

Radon-222 Liquid scintillation counting NWQL, schedule 1369 American Society for Testing 

and Materials, 1998

Radium 226/228 Alpha activity counting Eberline Analytical Services, 

NWQL method 1262

U.S. Environmental Protection 

Agency, 1980 (USEPA 

methods 903 and 904)

Gross alpha and beta radioactivity Alpha and beta activity counting Eberline Analytical Services, 

NWQL method 1792

U.S. Environmental Protection 

Agency, 1980 (USEPA method 

900.0)

Microbial constituents

F-specific and somatic coliphage Single-agar layer (SAL) and two-step 

enrichment methods

USGS Ohio Water 

Microbiology Laboratory

U.S. Environmental Protection 

Agency, 2001

Total and Escherichia coliform Membrane filter technique with 

"MI agar"

USGS field measurement U.S. Environmental Protection 

Agency, 2002

Table A1. Analytical methods used to determine organic, inorganic, and microbial constituents by the U.S. Geological Survey (USGS) 

National Water Quality Laboratory (NWQL) and contract laboratories.—Continued

[MI agar, supplemented nutrient agar in which coliforms (total and Escherichia) produce distinctly different fluorescence under ultraviolet lighting; UV, 

ultraviolet; VOCs, volatile organic compounds]
60 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Table A2. Preferred analytical schedules for constituents appearing on multiple schedules for samples collected for the Coachella 

Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.

[Preferred analytical schedules are the methods of analysis with the greatest accuracy and precision out of the ones used for the compound in question. 

Abbreviations: TML, U.S. Geological Survey Trace Metal Laboratory; VOC, volatile organic compound]

Constituent Primary constituent 

classification

Analytical 

schedules

Preferred 

analytical 

schedule

Results from preferred method reported

Atrazine Pesticide 2003, 2060, 4433 2003

Bromoform (Tribromomethane) VOC 2020, 4433 2020

Caffeine Potential wastewater indicator 4433, 2060, 2080 2060

Carbaryl Pesticide 2003, 2060, 4433 2003

Chlorpyrifos Pesticide 2003, 4433 2003

Cotitine Potential wastewater indicator 2080, 4433 2080

Deethylatrazine (2-Chloro-4-

isopropylamino-6-amino-s-

 triazine)

Pesticide degradate 2003, 2060 2003

Diazinon Pesticide 2003, 4433 2003

1,4-Dichlorobenzene VOC, pesticide 2020, 4433 2020

Dichlorvos Pesticide 2003, 4433 2003

Isopropylbenzene VOC 2020, 4433 2020

Metalaxyl Pesticide 2003, 2060, 4433 2003

Metolachlor Pesticide 2003, 4433 2003

Naphthalene VOC 2020, 4433 2020

Perchloroethene (PCE) VOC 2020, 4433 2020

Prometon Pesticide 2003, 4433 2003

Tebuthiuron Herbicide 2003, 2060 2003

Results from both methods reported (different USGS parameter codes)

Alkalinity Water-quality indicator Field, 1948 Field

Arsenic, total Trace element 1948, TML 1948

Chromium, total Trace element 1948, TML 1948

Iron, total Trace element 1948, TML 1948

pH Water-quality indicator field, 1948 field

Specific conductance Water-quality indicator field, 1948 field

Constituent

Number of source 

solution blank 

detections/analyses

Number of 

field blank 

detections/analyses

Maximum 

concentration 

detected in blanks

Minimum 

concentration 

detected in groundwater samples

Number of groundwater samples 

V-coded

 Organic constituents (μg/L)

Ethylbenzene 1/3 0/3 0.01 0 0

m-Xylene plus p-xylene 2/3 2/3 0.03 0 0

o-Xylene 0/3 1/3 0.01 0 0

Toluene 3/3 3/3 0.33 0.01 10

 Inorganic constituents (mg/L)

Mercury 0/3 1/1 0.01 0 0

Radium-226 (pCi/L) 0/3 1/1 0.02 0.24 0

Radium-228 (pCi/L) 0/3 1/1 0.01 0.76 0

Table A3. Constituents detected in field blanks collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, February and March 2007.

[V-coded data are reported but not used in summary statistics. Abbreviations: pCi/L, picocurie per liter; mg/L, milligram per liter; μg/L, microgram per liter]
Table A4 61

Constituent

Number of 

RSDs greater than 

20 percent /

number of 

replicate pairs

Maximum RSD 

(percent)

Concentrations for replicates 

with RSD greater than zero 

(environmental, replicate)

(mg/L)

Volatile organic compounds, gasoline oxygenates and additives from schedules 2020

n-Butylbenzene 3/3 24 <0.14; 0.1

Hexachloroethane 3/3 24 <0.14; 0.1

Ethyl methacrylate 3/3 24 <0.14; 0.1

1,3-Dichloropropane 3/3 35 <0.06; 0.1

1,2,3,4-Tetramethylbenzene 3/3 24 <0.14; 0.1

All additional VOCs from schedule 2020 0/3 <20 na

Pesticides and pesticide degradates from schedules 2003 and 2060

All additional pesticides and pesticide degradates from schedule 2003 0/3 <20 na

All additional pesticides and pesticide degradates from schedule 2060 0/3 <20 na

Potential wastewater-indicator compounds from schedule 4433

All wastewater-indicator compounds from schedule 4433 0/1 na na

Pharmaceutical compounds

Sulfamethoxazole 1/3 106 0.0237; 0.0034

Consituents of special interest1

Perchlorate and 1,2,3-Trichloropropane 0/3 <20 na

Major ions, minor ions, trace elements, and nutrients

Cadmium (μg/L) 1/3 28 0.09; 0.66

Copper (μg/L) 1/3 24 1.55; 1.1

Lead (μg/L) 1/3 24 0.28; 0.2

Nickel (μg/L) 1/3 33 0.08; 0.05

All additional major ions, minor ions, trace elements, and nutrients 

from schedules 1948 and 2755

0/3 <20 na

Isotopes, radioactivity, and noble gases

2Radium-226 (pCi/L) na na na 2Radium-228 (pCi/L) na na na

Tritium3 (TU) 0/3 <20 na

Alpha radioactivity, 72-hour count2 (pCi/L) na na na

Beta radioactivity, 72-hour count2 (pCi/L) na na na

USGS Trace Metals Laboratory

Iron(II) 1/3 94 10; <2

Microbial indicators

F-specific and somatic coliphage 0/1 <20 na

E. Coli, and total coliforms 0/1 <20 na

1

Analyzed at Montgomery Watson-Harza Laboratories, Monrovia, California.

2

Analyzed at Eberline Analytical Services, Richmond, California.

3

Analyzed at U.S. Geological Survey, Menlo Park, California.

Table A4. Quality-control summary for replicate analyses of constituents detected in samples collected for the Coachella Valley 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007. 

[Abbreviations: na, not applicable; TU, tritium unit; <, less than; mg/L, milligram per liter; μg, microgram per liter; pCi/L, picocurie per liter; RSD, relative 

standard deviation]
62 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent Number of 

spike samples

Recovery (percent)

Minimum Maximum Median 

Acetone 3 94 103 99

Acrylonitrile 3 99 101 99

Benzene 3 98 101 101

Bromobenzene 3 95 99 106

Bromochloromethane 3 101 107 104

Bromodichloromethane1 3 95 117 112

Bromoethene 3 108 112 111

Bromoform (tribromomethane) 3 92 108 92

Bromomethane 3 95 151 137

2-Butanone (ethyl methyl ketone) 3 92 99 97

Butylbenzene (n-Butylbenzene) 3 71 81 75

sec-Butylbenzene 3 89 98 91

tert-Butylbenzene 3 92 104 99

Carbon disulfide 3 75 84 81

Chlorobenzene 3 95 105 100

Chloroethane 3 94 103 100

Chloroform (trichloromethane)1 3 105 108 108

Chloromethane 3 95 104 102

3-Chloropropene 3 112 119 113

2-Chlorotoluene 3 95 101 96

4-Chlorotoluene 3 91 99 91

Dibromochloromethane 3 93 106 101

1,2-Dibromo-3-chloropropane (DBCP) 3 90 96 91

1,2-Dibromoethane (EDB) 3 95 109 108

Dibromomethane 3 99 106 104

1,2-Dichlorobenzene 3 93 101 96

1,3-Dichlorobenzene 3 89 99 92

1,4-Dichlorobenzene 3 89 96 86

trans-1,4-Dichloro-2-butene 3 87 93 93

Dichlorodifluoromethane (CFC-12) 3 71 87 78

1,1-Dichloroethane1 3 101 110 106

1,2-Dichloroethane 3 96 104 102

cis-1,2-Dichloroethene 3 103 109 104

trans-1,2-Dichloroethene 3 96 103 102

1,1-Dichloropropene 3 92 96 92

1,2-Dichloropropane 3 100 107 104

1,3-Dichloropropane 3 99 108 104

cis-1,3-Dichloropropene 3 89 96 93

trans-1,3-Dichloropropene 3 88 92 89

2,2-Dichloropropane 3 77 85 84

Diethyl ether 3 99 105 103

Diisopropyl ether 3 97 99 98

Ethylbenzene 3 94 100 95

Ethyl tert-butyl ether (ETBE, tert-butyl ethyl 

ether)

3 93 94 97

Ethyl methacrylate 3 94 99 95

o-Ethyl toluene (2-Ethyltoluene) 3 89 96 91

Hexachlorobutadiene 3 63 71 67

Hexachloroethane 3 88 99 92

2-Hexanone (n-Butyl methyl ketone) 3 100 104 104

Isopropylbenzene 3 93 107 101

4-Isopropyltoluene (p-isopropyltoluene) 3 82 91 86

Methyl acrylate 3 99 102 100

Methyl acrylonitrile 3 102 105 105

Methyl tert-butyl ether (MTBE) 3 98 104 101

Methyl iodide (iodomethane) 3 107 113 107

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.

[Acceptable recovery range is between 70 and 130 percent.]
Table A5A 63

Constituent Number of 

spike samples

Recovery (percent)

Minimum Maximum Median 

Methyl methacrylate 3 96 100 97

4-Methyl-2-pentanone (MIBK, isobutyl 

methyl ketone)

3 96 102 97

Methyl tert-pentyl ether 3 94 102 97

Naphthalene 3 81 102 91

n-Propylbenzene 3 88 95 89

Styrene 3 89 96 98

1,1,1,2-Tetrachloroethane 3 95 109 106

1,1,2,2-Tetrachloroethane 3 99 105 95

Tetrachloroethene (PCE)1 3 89 101 95

Tetrachloromethane (carbon tetrachloride) 3 95 102 106

Tetrahydrofuran 3 100 106 100

1,2,3,4-Tetramethylbenzene 3 80 97 87

1,2,3,5-Tetramethylbenzene (isodurene) 3 88 103 93

Toluene1 3 83 111 103

1,2,3-Trichlorobenzene 3 86 98 90

1,2,4-Trichlorobenzene 3 79 89 81

1,1,1-Trichloroethane (TCA) 3 97 109 106

1,1,2-Trichloroethane 3 96 105 103

Trichloroethene (TCE)1 3 92 102 99

Trichlorofluoromethane (CFC-11) 3 100 104 103

1,2,3-Trichloropropane (1,2,3-TCP) 3 90 106 102

1,1,2-Trichlorotrifluoroethane (CFC-113) 3 82 85 83

1,2,3-Trimethylbenzene 3 94 105 98

1,2,4-Trimethylbenzene 3 91 101 95

1,3,5-Trimethylbenzene 3 88 97 92

Vinyl chloride 3 102 108 104

m- and p-Xylene 3 92 100 95

o-Xylene 3 91 100 96

1

Constituents detected in ground-water samples.

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.—Continued

[Acceptable recovery range is between 70 and 130 percent.]
64 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent Number of 

spike samples

Recovery (percent)

Minimum Maximum Median 

Acifluorfen 3 73 80 75

Aldicarb sulfone 3 37 74 62

Aldicarb sulfoxide 3 59 100 84

Aldicarb 3 14 85 71

Atrazine1 3 53 83 74

Bendiocarb 3 76 165 76

Benomyl 3 67 79 73

Bensulfuron-methyl 3 67 83 71

Bentazon 3 62 80 75

Bromacil 3 73 86 84

Bromoxynil 3 57 78 78

Caffeine 3 58 87 85

Carbaryl 3 81 109 81

Carbofuran 3 81 95 86

2-Chloro-4-isopropylamino-6-amino-striazine (CIAT)1

3 42 83 61

2-Chloro-6-ethylamino-4-amino-s-triazine 

(CEAT)1

3 33 78 61

Chloramben, methyl ester 3 73 85 81

Chlorimuron-ethyl 3 40 58 55

Chlorodiamino-s-triazine (CAAT) 3 59 98 81

Clopyralid 3 30 87 65

Cycloate 3 61 73 69

2,4-D 3 85 92 91

2,4-D methyl ester 3 63 96 80

2,4-DB 3 59 64 70

Dacthal monoacid 3 73 82 81

Dicamba 3 63 76 69

Dichlorprop 3 79 86 82

Dinoseb 3 68 71 68

Diphenamid 3 85 98 88

Diuron1 3 85 107 89

Fenuron 3 83 93 87

Flumetsulam 3 67 98 84

Fluometuron 3 82 91 83

3-Hydroxycarbofuran 3 83 110 85

2-Hydroxy-4-isopropylamino-6-ethylaminos-triazine (OIET)3 64 94 93

Imazaquin 3 69 98 73

Imazethapyr 3 74 104 79

Imidacloprid 3 71 87 83

Linuron 3 80 86 85

MCPA 3 74 78 83

MCPB 3 62 70 64

Metalaxyl 3 85 87 89

Methiocarb 3 81 124 83

Methomyl 3 71 108 92

Metsulfuron methyl 3 4 49 21

3-(4-Chlorophenyl)-1-methyl urea 3 64 87 67

Neburon 3 76 91 81

Nicosulfuron 3 62 90 81

Norflurazon 3 83 92 87

Oryzalin 3 66 82 81

Oxamyl 3 71 133 85

Picloram 2 70 75 na

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates from schedules 2060 in 

samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and 

March 2007.

[Acceptable recovery range is between 70 and 130 percent.]
Table A5B 65

Constituent Number of 

spike samples

Recovery (percent)

Minimum Maximum Median 

Propham 3 77 88 88

Propiconazole 3 74 83 78

Propoxur (Baygon) 3 80 99 84

Siduron 3 84 91 91

Sulfometuron-methyl 3 59 71 68

Tebuthiuron 3 85 96 85

Terbacil 3 68 87 84

Triclopyr 3 78 84 81

1

Constituent detected in ground-water samples.

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates from schedules 2060 in 

samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and 

March 2007.—Continued

[Acceptable recovery range is between 70 and 130 percent.]
66 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent Number of 

spike samples

Recovery (percent)

Minimum Maximum Median 

Acetochlor 3 98 111 103

Alachlor 3 97 106 102

Atrazine1 3 94 101 95

Azinphos-methyl oxygen analog 3 45 85 64

Azinphos-methyl 3 92 121 113

Benfluralin, water 3 34 76 67

Carbaryl 3 104 122 113

Chlorpyrifos oxygen analog 3 40 48 47

2-Chloro-2',6'-diethylacetanilide 3 91 101 94

2-Chloro-4-isopropylamino-6-amino-striazine (CIAT)1

3 44 50 48

4-Chloro-2-methylphenol 3 46 63 59

Chlorpyrifos 3 91 99 98

cis-Permethrin 3 65 82 67

Cyfluthrin 3 51 72 57

Cypermethrin 3 50 76 60

Dacthal (DCPA) 3 96 103 97

Desulfinylfipronil amide 3 85 110 99

Desulfinyl fipronil 3 84 98 89

Diazinon oxygen analog 3 86 103 86

Diazinon 3 88 96 95

3,4-Dichloroaniline 3 77 85 79

Dicrotophos 3 30 42 38

Dieldrin 3 100 107 107

Dimethoate 3 32 39 34

2,6-Diethylaniline 3 89 99 95

Ethion monoxon 3 86 111 95

Ethion 3 80 98 86

2-Ethyl-6-methylaniline 3 87 96 93

Fenamiphos sulfone 3 68 72 104

Fenamiphos sulfoxide 3 16 38 28

Fenamiphos 3 87 145 96

Fipronil sulfide 3 77 93 80

Fipronil sulfone 3 67 82 74

Fipronil 3 89 113 93

Fonofos 3 87 94 91

Hexazinone 3 65 83 70

Iprodione 3 57 75 65

Isofenphos 3 100 118 108

Malaoxon 3 92 106 101

Malathion 3 89 102 98

Metalaxyl 3 89 99 91

Methidathion 3 92 106 101

Methyl paraoxon 3 52 67 61

Methyl parathion 3 74 89 83

Metolachlor 3 98 108 103

Metribuzin 3 70 82 77

Myclobutanil 3 94 111 97

1-Naphthol 3 23 33 25

Pendimethalin 3 79 101 91

Phorate oxygen analog 3 107 125 117

Phorate 3 78 90 85

Phosmet oxygen analog 3 5 16 6

Phosmet 3 11 27 12

Prometon1 3 88 98 89

Prometryn 3 98 110 102

Table A5C. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates from schedule 2003 in samples 

collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February to March 2007.

[Acceptable recovery range is between 70 and 130 percent.]
Table A5C 67

Constituent Number of 

spike samples

Recovery (percent)

Minimum Maximum Median 

Propyzamide (Pronamide) 3 82 95 87

Simazine1 3 101 111 101

Tebuthiuron 3 79 107 81

Terbufos oxygen analog sulfone 3 80 96 83

Terbufos 3 88 104 98

Terbuthylazine 3 94 102 96

Trifluralin 3 68 82 70

Dichlorvos 3 25 65 32

Tribufos 3 78 98 82

1

Constituents detected in ground-water samples.

Table A5C. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates from schedule 2003 in samples 

collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February to March 

2007.—Continued

[Acceptable recovery range is between 70 and 130 percent.]
68 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program

Constituent Number of 

spike samples

Recovery (percent)

Minimum Maximum Median 

Acetaminophen1 3 89 100 94

Albuterol 3 86 96 90

Caffeine 3 107 117 108

Carbamazepine 3 91 109 106

Codeine 3 78 97 85

Cotinine 3 89 92 90

Dehydronifedipine 3 93 108 106

Diltiazem 3 38 59 44

1,7-Dimethylxanthine 3 83 97 89

Diphenhydramine 3 68 79 73

Sulfamethoxazole 3 58 112 72

Thiabendazole 3 78 91 82

Trimethoprim 3 95 104 101

Warfarin 3 57 92 90

1

Constituent detected in ground-water samples.

Table A5D. Quality-control summary for matrix-spike recoveries of pharmaceutical compounds in samples collected for the Coachella 

Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.

[Acceptable recovery range is between 70 and 130 percent.]
Table A5E 69

Constituent Recovery

(percent)

Acetophenone 42

Acetyl hexamethyl tetrahydro naphthalene 

(AHTN)

54

Anthracene, water1 42

9,10-Anthraquinone1 55

Atrazine 47

Benzo[a]pyrene1 44

Benzophenone 49

ß-Sitosterol 184

ß-Stigmastanol 156

bis(2-Ethylhexyl) phthalate 58

Bisphenol A 68

Bromacil 208

Bromoform 21

3-tert-Butyl-4-hydroxyanisole (BHA) 28

Caffeine1 44

Camphor 38

Carbaryl 40

Carbazole 45

Chlorpyrifos 45

Cholesterol 225

Cotinine 121

3-ß-Coprostanol 290

4-Cumylphenol, water 55

DEET 53

Diazinon 47

1,4-Dichlorobenzene (p-dichlorobenzene) 24

3,4- Dichlorophenyl isocyanate1 81

4-Octylphenol monoethoxylates 101

Dichlorvos 42

Diethyl phthalate1 51

2,6-Dimethylnaphthalene1 35

d-Limonene 8

Fluoranthene1 45

Hexahydrohexamethyl cyclopentabenzopyran 

(HHCB)

51

Table A5E. Quality-control summary for matrix-spike recoveries of potential wastewater-indicator compounds in samples collected for 

the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.

[Acceptable recovery range is between 70 and 130 percent. Only one matrix spike collected from slow wells.]

Constituent Recovery

(percent)

Indole 39

Isoborneol 53

Isophorone 44

Isopropylbenzene 9

Isoquinoline 42

Menthol 58

Metalaxyl 49

1-Methylnaphthalene 36

5-Methyl-1H-benzotriazole1 424

2-Methylnaphthalene 34

3-Methyl-1(H)-indole (Skatole) 43

Methyl salicylate 45

Metolachlor 46

4-n-Octylphenol 52

4-tert-Octylphenol 54

4-Octylphenol diethoxylates 50

Naphthalene 33

4-Nonylphenol diethoxylates 843

Nonylphenol (total) 400

p-Cresol 44

para-Nonylphenol (total) 403

Pentachlorophenol1 140

Phenanthrene1 44

Phenol1 46

Prometon 50

Pyrene1 43

2,2',4,4'- Tetrabromodiphenyl ether 25

Tributyl phosphate1 53

Triclosan 60

Triethyl citrate (ethyl citrate) 49

Triphenyl phosphate 46

Tris(2-butoxyethyl) phosphate 49

Tris(2-chloroethyl) phosphate 48

Tris(dichloroisopropyl) phosphate 41

1

Constituents detected in ground-water samples.
70 Ground-Water Quality Data in the Cochella Valley Study Unit, 2007: Results from the California GAMA Program Table A6. Quality-control summary for surrogate recoveries of volatile organic compounds, pesticides and pesticide degradates, pharmaceutical compounds, potential wastewater-indicator compounds, and constituents of special interest in samples collected for the Coachella Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, February and March 2007.

[Abbreviation: MWH, Montgomery Watson-Harza Laboratory; VOC, volatile organic compound]

Surrogate Analytical schedule Constituent or constituent class analyzed Number of blank analyses Median recovery in blanks (percent)

Number of surrogate 

recoveries Number of 

environmental 

sample 

analyses

Median 

recovery in 

samples 

(percent)

Number of surrogate

recoveries

Below 

70 percent 

in blanks

Above 

130 percent 

in blanks

Below 

70 percent in 

samples

Above 

130 percent in 

samples

1-Bromo-4-

fluorobenzene

2020 VOC 3 86 0 0 35 86 3 0

1,2-Dichloroethane-d4 2020 VOC 3 102 0 0 35 109 0 0

Toluene-d8 2020 VOC 3 98 0 0 35 99 0 0

Diazinon-d10 2003 Pesticide 3 115 0 0 35 101 1 0

alpha-HCH-d6 2003 Pesticide 3 94 0 0 35 84 0 0

2,4,5-T 2060 Pesticide 3 74 0 0 35 75 13 0

Barban 2060 Pesticide 3 86 0 0 35 88 0 0

Caffeine-13

C 2060 Pesticide 3 90 0 0 35 100 3 0

Toluene-d8 MWH 1,2,3-TCP 1 102 0 0 11 103 0 0

Ethyl nicotinate-d4 2080 Pharmaceutical 3 99 0 0 35 96 0 0

Carbamazapine-d10 2080 Pharmaceutical 3 94 0 0 35 96 0 0

Caffeine-13

C 4433 Potential wastewater-indicator 1 35 1 0 12 75 3 0

Bisphenol A-d3, 

surrogate

4433 Potential wastewater-indicator 1 30 1 0 12 70 5 0

Decafluorobiphenyl 4433 Potential wastewater-indicator 1 20 1 0 12 62 8 0

Fluoranthene-d10 4433 Potential wastewater-indicator 1 40 1 0 12 84 1 0
This page intentionally left blank.
Goldrath and Others–Ground-Water Quality Data in the Coachella Valley Study Unit, 2007: Results from the California GAMA Program–Data Series 373

Printed on recycled paper