U.S. Department of the Interior

U.S. Geological Survey

Data Series 463

Version 1.1 

In cooperation with the California State Water Resources Control Board 

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

Groundwater-Quality Data in the South Coast Interior Basins Study

Unit, 2008: Results from the California GAMA Program

680

680

580

580

Arroyo de la Laguna

Pleasanton

Canal

Canal

Arroyo Mocho

Alamo Canal

Dublin

Livermore

Pleasanton

Valle de

San Jose

Rocky Ridge

Tassajara

Hills

Collier Canyon

Altamont Hills

Dougherty Hills

Harlan Hill

Pleasanton Ridge

Cedar Mountain Ridge

Crane Ridge

Lake del Valle

Contra Costa County

Alameda

County

101

101

101

Gilroy

Hollister

Hollister Hills

Diablo

Range

MTS

Range

Cherry Peak

San Benito

Pajaro River

River

San Benito

County

Merced

County

Monterey

County

Santa Clara

County Santa Cruz

County

Stanislaus

County

SANTA CRUZ

Soda Lake

Kern

County

Ventura

County Los Angeles

County

Santa Barbara County

San Luis Obispo County

Sierra Madre Mountains

Caliente Range

Tehachapi Mts

Cuyama

New Cuyama

Lebec

Cuyama

River

5

5

99

1

152

5
Cover Photographs:

Top right: Golf course irrigation well, Pleasonton, California. (Photograph taken by Tracy Davis, U.S. Geological Survey.)

Bottom left: Farm in Gilroy , California. (Photograph taken by Michael Land, U.S. Geological Survey.)
Groundwater-Quality Data in the South 

Coast Interior Basins Study Unit, 2008: 

Results from the California GAMA Program

By Timothy M. Mathany, Justin T. Kulongoski, Mary C. Ray, and Kenneth Belitz

Prepared in cooperation with the California State Water Resources Control Board

Data Series 463

Version 1.1 

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

Revised 2010 

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Mathany, T.M., Kulongski, J.T., Ray, M.C., and Belitz, Kenneth, 2009, Groundwater-quality data in the South Coast 

Interior Basins study unit, 2008: Results from the California GAMA program: U.S. Geological Survey Data Series 463, 

82 p. Available at http://pubs.usgs.gov/ds/463.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................3

Hydrogeologic Setting ........................................................................................................................3

Methods ........................................................................................................................................................10

Study Design........................................................................................................................................10

Sample Collection and Analysis.......................................................................................................11

Data Reporting.....................................................................................................................................11

Quality Assurance...............................................................................................................................11

Water-Quality Results ................................................................................................................................11

Quality-Control Results ......................................................................................................................11

Comparison Thresholds.....................................................................................................................12

Groundwater-Quality Data ................................................................................................................13

Water-Quality Indicators (Field Parameters) ........................................................................13

Organic Constituents.................................................................................................................13

Constituents of Special Interest..............................................................................................14

Inorganic Constituents..............................................................................................................14

Isotopic Tracers and Noble Gases..........................................................................................15

Radioactive Constituents..........................................................................................................16

Future Work .........................................................................................................................................16

Summary .......................................................................................................................................................16

Acknowledgments.......................................................................................................................................17

References Cited..........................................................................................................................................17

Tables ...........................................................................................................................................................23

Appendix .......................................................................................................................................................61
iv

Figures

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

South Coast Interior Basins Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit....................................................................................................................4

Figure 2. Map of the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit showing the three study areas (Livermore, Gilroy, 

and Cuyama), the location of public-supply wells with a record in the California 

Department of Public Health (CDPH) Database, major cities, topographic features, 

and hydrologic features ..........................................................................................................5

Figure 3. Map of the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit showing the distribution of the Livermore studyarea grid cells, the location of sampled grid wells and understanding wells, the 

Livermore Valley groundwater-basin boundary (as defined by the California 

Department of Water Resources, CDWR), major cities, major roads, 

topographic features, and hydrologic features ..................................................................7

Figure 4. Map of the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit showing the distribution of the Gilroy study-area 

grid cells, the location of sampled grid wells and understanding wells, the GilroyHollister groundwater-basin boundary (as defined by the California Department 

of Water Resources, CDWR), major cities, major roads, topographic features, and 

hydrologic features..................................................................................................................8

Figure 5. Map of the South Coast Interior Basins Groundwater Ambient Monitoring 

and Assessment (GAMA) study unit showing the distribution of the Cuyama 

study area-grid cells, the location of sampled grid wells and understanding 

wells, the Cuyama Valley, Castaic Lake Valley, Cuddy Canyon Valley, Cuddy 

Ranch Area, Cuddy Valley, and Mil Potrero groundwater-basin boundaries 

(as defined by the California Department of Water Resources, CDWR), 

major cities, major roads, topographic features, and hydrologic features....................9

Tables

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

South Coast Interior Basins Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, August to December 2008.......................................................24

Table 2. Classes of chemical consistuents and water-quality indicators (field parameters) 

collected for the slow and fast well sampling schedules in the South Coast 

Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, June to November 2008..........................................................................26

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

thresholds, and reporting information for the U.S. Geological Survey National 

Water Quality Laboratory Schedule 2020...........................................................................27
v

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

thresholds, and reporting information for the U.S. Geological Survey National 

Water Quality Laboratory Schedule 2003...........................................................................30

Table 3C. Polar pesticides and metabolites, primary uses or sources, comparative 

thresholds, and reporting information for the U.S. Geological Survey National 

Water Quality Laboratory Schedule 2060...........................................................................32

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

and reporting information for the U.S. Geological Survey National Water Quality 

Laboratory Schedule 2080 ....................................................................................................34

Table 3E. Constituents of special interest (perchlorate and N-nitrosodimethylamine 

[NDMA]), primary uses or sources, comparative thresholds, and reporting 

information for Weck Laboratories, Inc. analyses ...........................................................34

Table 3F. Trace elements, comparative thresholds, and reporting information for the 

U.S. Geological Survey National Water Quality Laboratory Schedule 1948 ...............35

Table 3G. Nutrients, comparative thresholds, and reporting information for the U.S. 

Geological Survey National Water Quality Laboratory Schedule 2755.........................36

Table 3H. Major and minor ions, silica, total dissolved solids (TDS), and alkalinity, 

comparative thresholds, and reporting information for the U.S. Geological 

Survey National Water Quality Laboratory Schedule 1948.............................................36

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

information for the U.S. Geological Survey Trace Metal Laboratory, Boulder, 

Colorado, analyses.................................................................................................................37

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

information for laboratory analyses....................................................................................37

Table 3K. Noble gases and tritium, comparison thresholds, and reporting information for 

the Lawrence Livermore National Laboratory analyses .................................................38

Table 4. Water-quality indicators (field parameters) in samples collected for the South 

Coast Interior Basins Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, August to December 2008...............................................39

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

South Coast Interior Basins Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, August to December 2008.......................................................41

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

 South Coast Interior Basins Groundwater Ambient Monitoring and Assessment 

 (GAMA) study unit, California, August to December 2008...............................................45

Table 6B. Polar pesticides and metabolites detected in samples collected for the 

South Coast Interior Basins Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, August to December 2008.......................................................46

Table 7. Constituents of special interest ([perchlorate and N-nitrosodimethylamine 

[NDMA]) collected for the South Coast Interior Basins Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, August to December 2008...47

Table 8. Trace elements collected for the South Coast Interior Basins Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, August to 

December 2008 .......................................................................................................................48
vi

Table 9. Nutrients detected in samples collected for the South Coast Interior Basins 

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

August to December 2008.....................................................................................................52

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

collected for the South Coast Interior Basins Groundwater Ambient Monitoring 

and Assessment (GAMA) study, California, August to December 2008........................54

Table 11. Species of inorganic arsenic, chromium, and iron detected in samples collected 

for the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, August to December 2008................................56

Table 12. Results for analyses of stable isotope ratios and tritium and carbon-14 activities 

detected in samples collected for the South Coast Interior Basins 

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

August to December 2008. ...................................................................................................57

Table 13A. Gross alpha and gross beta radioactivity detected in samples collected for 

the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, August to December 2008 ...............................59

Table 13B. Radon-222 detected in samples collected for the South Coast Interior Basins 

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

August to December 2008 ....................................................................................................60

Appendix Tables

Table A1. Analytical methods used for the determination of organic and inorganic 

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

Laboratory (NWQL) and additional contract laboratories...............................................71

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

for samples collected for the South Coast Interior Basins Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, August to 

December 2008 .......................................................................................................................73

Table A3. Constituents detected in field blanks collected for the South Coast Interior 

Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, August to December 2008..................................................................................73

Table A4A. Quality-control summary for replicate analyses of organic constituents 

detected in samples collected for the South Coast Interior Basins Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, August to 

December 2008 .......................................................................................................................74

Table A4B. Quality-control summary for replicate analyses of trace elements, major and 

minor ions, silica, total dissolved solids (TDS), nutrients, and isotope tracers 

detected in samples collected for the South Coast Interior Basins Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, August to 
vii

Table A4B. Quality-control summary for replicate analyses of trace elements, major and 

minor ions, silica, total dissolved solids (TDS), nutrients, and isotope tracers 

detected in samples collected for the South Coast Interior Basins Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, August to 

December 2008 .......................................................................................................................75

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

compounds (VOCs) in samples collected for the South Coast Interior Basins 

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

August to December 2008.....................................................................................................77

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

pesticide degradates in samples collected for the South Coast Interior Basins 

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

August to December 2008.....................................................................................................79

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

 metabolites in samples collected for the South Coast Interior Basins 

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

 August to December 2008....................................................................................................80

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

N-nitrosodimethylamine (NDMA) in samples collected for the South Coast 

Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, August to December 2008......................................................................81

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

compounds (VOCs), pesticides and pesticide degradates, and polar pesticides 

and metabolites in samples collected for the South Coast Interior Basins 

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

August to December 2008.....................................................................................................81
viii

Conversion Factors 

Inch/Pound to SI

Multiply By To obtain

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2) 

SI to Inch/Pound

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

square kilometer (km2

) 0.3861 square mile (mi2)

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

 °F = (1.8×°C) + 32

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).

Altitude, as used in this report, refers to distance above the vertical datum.

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

25°C).

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

or micrograms per liter (μg/L). Milligrams per liter is equivalent to parts per million (ppm) and 

micrograms per liter is equivalent to parts per billion (ppb).
ix

AL-US action level (USEPA)

CAS Chemical Abstract Service (American Chemical Society)

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

CSU combined standard uncertainty

CUY Cuyama study area

CUYU Cuyama study area understanding (well)

E estimated or having a higher degree of uncertainty

GAMA Groundwater Ambient Monitoring and Assessment Program

GIL Gilroy study area

GILU Gilroy study area understanding (well)

GPS Global Positioning System

HAL-US lifetime health advisory level (USEPA)

HPLC high-performance liquid chromatography

LIV Livermore study area

LIVU Livermore study area understanding (well)

LRL laboratory reporting level

LSD land surface datum

LT-MDL long-term method detection level

MCL-US maximum contaminant level (USEPA)

MCL-CA maximum contaminant level (CDPH)

MDL method detection limit

MRL minimum reporting level

MU method uncertainty

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

na not available

nc not collected

NL-CA notification level (CDPH)

nv no measured value or no value in category

np no preference

NWIS National Water Information System (USGS)

PCFF portable computer field forms program designed for USGS sampling

QC quality control

RL reporting level

RPD relative percent difference

RSD relative standard deviation

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

SCI South Coast Interior Basins study unit

SD standard deviation

SMCL-CA secondary maximum contaminant level (CDPH)

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

ssLC sample-specific critical level

U.S. United States

UV ultraviolet

V analyte detected in sample and associated blank, thus data are not included in groundwater quality assessment

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

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

International Atomic Energy Agency)

Abbreviations and Acronyms
x

Symbols

= equal to

> greater than 

≥ greater than or equal to

< less than

≤ less than or equal to

— not detected

± plus or minus

* value is above threshold level

** value is above upper threshold level

Organizations

CDPH California Department of Public Health

CDWR California Department of Water Resources

LLNL Lawrence Livermore National Laboratory

NAWQA National Water Quality Assessment (USGS)

NELAP National Environmental Laboratory Accreditation Program

NWQL National Water Quality Laboratory (USGS)

NRP National Research Program (USGS)

SWRCB State Water Resources Control Board

TML Trace Metal Laboratory (USGS)

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

Selected Chemical Names

CaCO3 calcium carbonate

CO3

–2 carbonate

CFC chlorofluorocarbon

HCl hydrochloric acid

HCO3

– bicarbonate

MTBE methyl tert-butyl ether

Na2

S2O3 sodium thiosulfate

NDMA N-nitrosodimethylamine

NO2

–

+NO3

– nitrite plus nitrate, as nitrogen

PCE perchloroethene (tetrachloroethene)

SiO2 silicon dioxide

TCE trichloroethene

TCP trichloropropane

TDS total dissolved solids

THM trihalomethane

VOC volatile organic compound

Units of Measurement

C Celsius

cm3

 STP/g cubic centimeters of gas at standard temperature and pressure (0 degrees Celsius and 1 

atmosphere of pressure) per gram of water

f.a.s.l. feet above sea level

ft foot (feet)

km kilometer

km2 square kilometer

L liter
xi

mg/L milligrams per liter (parts per million)

mi mile

mi2 square mile

mL milliliter

μg/L micrograms per liter (parts per billion)

μm micrometer

NTU nephelometric turbidity unit

pCi/L picocuries per liter

pH measure of the acidity or basicity of water

pK1,2 acid dissociation constants of carbonic acid

pKw acid dissociation constant of water

ppb parts per billion

ppm parts per million

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

lighter isotope of that element, relative to a standard reference material, expressed as 

per mil
This page intentionally left blank.
Abstract 

Groundwater quality in the approximately 

653-square-mile South Coast Interior Basins (SCI) study 

unit was investigated from August to December 2008, as part 

of the Priority Basins Project of the Groundwater Ambient 

Monitoring and Assessment (GAMA) Program. The GAMA 

Priority Basins Project was developed in response to Legislative mandates (Supplemental Report of the 1999 Budget Act 

1999-00 Fiscal Year and the Groundwater-Quality Monitoring 

Act of 2001 [Sections 10780-10782.3 of the California Water 

Code, Assembly Bill 599]) to assess and monitor the quality of groundwater used as public supply for municipalities 

in California, and is being conducted by the U.S. Geological Survey (USGS) in cooperation with the California State 

Water Resources Control Board (SWRCB). SCI was the 27th 

study unit to be sampled as part of the GAMA Priority Basins 

Project.

This study was designed to provide a spatially unbiased 

assessment of the quality of untreated groundwater used for 

public water supplies within SCI, and to facilitate statistically 

consistent comparisons of groundwater quality throughout 

California. Samples were collected from 54 wells within the 

three study areas [Livermore, Gilroy, and Cuyama] of SCI in 

Alameda, Santa Clara, San Benito, Santa Barbara, Ventura, 

and Kern Counties. Thirty-five of the wells were selected 

using a spatially distributed, randomized grid-based method 

to provide statistical representation of the study unit (grid 

wells), and 19 were selected to aid in evaluation of specific 

water-quality issues (understanding wells).

The groundwater samples were analyzed for organic 

constituents (volatile organic compounds [VOCs], pesticides 

and pesticide degradates, polar pesticides and metabolites, and 

pharmaceutical compounds), constituents of special interest 

(perchlorate and N-nitrosodimethylamine [NDMA]), naturally 

occurring inorganic constituents (trace elements, nutrients, 

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

and alkalinity), and radioactive constituents (gross alpha and 

gross beta radioactivity and radon-222). Naturally occurring 

isotopes (stable isotopes of hydrogen, oxygen, and carbon, 

and activities of tritium and carbon-14) and dissolved noble 

gases also were measured to help identify the sources and ages 

of the sampled groundwater. In total, 288 constituents and 

water-quality indicators (field parameters) were investigated.

Three types of quality-control samples (blanks, replicates, and matrix spikes) each were collected at approximately 

4–11 percent of the wells, and the results for these samples 

were used to evaluate the quality of the data for the groundwater samples. Field blanks rarely contained detectable concentrations of any constituent, suggesting that contamination was 

not a significant source of bias in the data obtained from the 

groundwater samples. Differences between replicate samples 

generally were less than 10 percent relative standard deviation, 

indicating acceptable analytical reproducibility. Matrix 

spike recoveries were within the acceptable range (70 to 

130 percent) for most compounds.

This study did not attempt to evaluate the quality of water 

delivered to consumers; after withdrawal from the ground, 

untreated groundwater typically is treated, disinfected, and/or 

blended with other waters to maintain water quality. Regulatory thresholds apply to water that is served to the consumer, 

not to untreated groundwater. However, to provide some context for the results, concentrations of constituents measured in 

the untreated groundwater were compared with regulatory and 

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

Environmental Protection Agency (USEPA) and California 

Department of Public Health (CDPH) and to nonregulatory 

thresholds established for aesthetic and technical concerns by 

CDPH. Comparisons between data collected for this study and 

thresholds for drinking water are for illustrative purposes only, 

and are not indicative of compliance or noncompliance with 

those thresholds.

Most inorganic constituents that were detected in groundwater samples from the 35 grid wells in the SCI study unit 

were found at concentrations below drinking-water thresholds; 

additionally, all detections of organic constituents in SCI grid 

well samples were below health-based thresholds. 

Groundwater-Quality Data in the South Coast Interior 

Basins Study Unit, 2008: Results from the California GAMA 

Program

By Timothy M. Mathany, Justin T. Kulongoski, Mary C. Ray, and Kenneth Belitz
2 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

In total, VOCs and pesticides and pesticide degradates 

were detected in approximately 23 percent of the 35 grid wells 

sampled in the SCI study. In the Livermore study area, VOCs 

were detected in approximately 67 percent and pesticides 

and pesticide degradates were detected in 50 percent of the 

6 grid wells. In the Gilroy study area, VOCs were detected in 

approximately 18 percent and pesticides and pesticide degradates were detected in approximately 29 percent of the 17 grid 

wells. In the Cuyama study area, VOCs were detected in 

approximately 8 percent of the grid wells, while pesticides and 

pesticide degradates were not detected in any of the 12 grid 

wells. 

Trace elements and nutrients were sampled for at the 

35 grid wells in the SCI study unit and most detections were 

below health-based thresholds. Exceptions in SCI grid wells 

include: two detections of arsenic above the USEPA maximum contaminant level (MCL-US) of 10 μg/L, two detections of boron above the CDPH notification level (NL-CA) of 

1,000 μg/L, three detections of molybdenum above 

the USEPA lifetime health advisory level (HAL-US) of 

40 μg/L, and five detections of nitrite plus nitrate, as nitrogen 

(NO2

– + NO3–

) above the MCL-US of 10 mg/L. All detections 

of gross alpha and gross beta radioactivity from SCI grid 

wells were below health-based thresholds. 

Results for the nonenforceable thresholds set for aesthetic 

and technical concerns for trace elements, major ions, and 

TDS from SCI grid wells showed that 8 grid wells (of 35 sampled) had detections of manganese above the CDPH secondary maximum contaminant level (SMCL-CA) of 50 μg/L. 

Twelve grid wells (of 35 sampled) had sulfate measured at a 

concentration above the recommended SMCL-CA threshold of 

250 mg/L and 9 of these detections also were above the upper 

SMCL-CA threshold of 500 mg/L. Twenty-five grid wells 

(of 35 sampled) had measured TDS concentrations above the 

SMCL-CA-recommended threshold of 500 mg/L, and 10 of 

these wells also were above the SMCL-CA upper threshold of 

1,000 mg/L. 

Introduction 

Groundwater comprises nearly half of the water used 

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

assess the quality of ambient groundwater in aquifers used for 

public supply and to establish a baseline groundwater-quality 

monitoring program, the State Water Resources Control 

Board (SWRCB), in cooperation with the U.S. Geological 

Survey (USGS) and Lawrence Livermore National Laboratory 

(LLNL), implemented the Groundwater Ambient Monitoring 

and Assessment (GAMA) Program (http://www.waterboards.

ca.gov/gama). The GAMA Program currently consists of three 

Projects: GAMA Priority Basins Project, conducted by the 

USGS (http://ca.water.usgs.gov/gama/); GAMA Domestic 

Well Project, conducted by the SWRCB; and GAMA Special 

Studies, conducted by LLNL. 

The SWRCB initiated the GAMA Priority Basins 

Project in response to Legislative mandates (Supplemental 

Report of the 1999 Budget Act 1999–2000 Fiscal Year; and, 

the Groundwater-Quality Monitoring Act of 2001 {Sections 

10780–10782.3 of the California Water Code, Assembly Bill 

599}) to assess and monitor the quality of groundwater used 

as public supply for municipalities in California. The GAMA 

Priority Basins Project is a comprehensive assessment of statewide groundwater quality designed to help better understand 

and identify risks to groundwater resources, and to increase 

the availability of information about groundwater quality to 

the public. For the Priority Basins Project, the USGS, in collaboration with the SWRCB, developed the monitoring plan to 

assess groundwater basins through direct and other statistically 

reliable sampling approaches (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 Basins Project is unique because 

it includes many chemical analyses that otherwise are not 

available in statewide water-quality monitoring datasets. 

Groundwater samples collected for the project are analyzed 

for 288 chemical constituents using analytical methods with 

much lower detection limits than required by the California 

Department of Public Health (CDPH). These analyses will be 

especially useful for providing an early indication of changes 

in groundwater quality. In addition, the GAMA Priority 

Basins Project analyzes samples for a suite of constituents 

more extensive than that required by CDPH, and for a suite 

of chemical and isotopic tracers for exploring hydrologic and 

geochemical processes. A broader understanding of groundwater composition is useful for identifying the natural and human 

factors affecting water quality. Understanding the occurrence 

and distribution of chemical constituents of significance to 

water quality is important for the long-term management and 

protection of groundwater resources.
Introduction 3

 The range of hydrologic, geologic, and climatic conditions that exist in California must be considered in an assessment of groundwater quality. Belitz and others (2003) partitioned the State into 10 hydrogeologic provinces, each with 

distinctive hydrologic, geologic, and climatic characteristics 

(fig. 1), and representative regions in all 10 provinces were 

included in the project design. Eighty percent of California’s 

approximately 16,000 public-supply wells are located in 

groundwater basins within these hydrologic provinces. These 

groundwater 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). Groundwater basins were prioritized for sampling on the basis of the 

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

consideration given to municipal groundwater use, agricultural pumping, the number of formerly leaking underground 

fuel tanks, and pesticide applications within the basins (Belitz 

and others, 2003). In addition, some groundwater basins or 

groups of adjacent similar basins with relatively few publicsupply wells were assigned high priority so that all hydrogeologic provinces would be represented in the subset of basins 

sampled as part of the project. The 116 priority basins were 

grouped into 37 study units. Some areas not in the defined 

groundwater basins were included in the nearest respective study unit to achieve representation of the 20 percent of 

public-supply wells not located in the groundwater basins. 

Three types of water-quality assessments are being conducted with the data collected in each study unit: (1) Status: 

assessment of the current quality of the groundwater resource; 

(2) Trends: detection of changes in groundwater quality; and 

(3) Understanding: identification of the natural and human 

factors affecting groundwater quality (Kulongoski and Belitz, 

2004). This status 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; Fram and Belitz, 2007; Kulongoski and Belitz, 

2007; Burton and Belitz, 2008; Dawson and others, 2008; 

Ferrari and others, 2008; Land and Belitz, 2008; Landon and 

Belitz, 2008; Mathany and others, 2008; Schmitt and others, 

2008; Shelton and others, 2008; Fram and others, 2009; Kent 

and Belitz, 2009; Mathany and Belitz, 2009; Montrella and 

Belitz, 2009; and, Ray and others, 2009). Subsequent reports 

will address the trends and understanding aspects of the 

water-quality assessments of each study unit.

The South Coast Interior Basins GAMA study unit, 

hereafter referred to as SCI, contains 11 groundwater basins 

and subbasins delineated by CDWR. SCI was considered high 

priority for sampling to provide adequate characterization of 

the South Coast Ranges Hydrologic Province (Belitz and 

others, 2003). 

Purpose and Scope

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

design, including the hydrogeologic setting of SCI and the 

study methods; (2) the results of quality-control tests; and (3) 

the analytical results for groundwater samples collected in 

SCI. Groundwater samples were analyzed for water-quality 

indicators (field parameters), organic and inorganic constituents, radioactive constituents, naturally occurring isotopes, 

and dissolved noble gases. The chemical data presented in 

this report were evaluated by comparison to State and Federal 

drinking water regulatory and other nonregulatory healthbased standards that are applied to treated drinking water. 

Regulatory and nonregulatory thresholds considered for 

this report are those established by the U.S. Environmental 

Protection Agency (USEPA) and/or the CDPH. The data presented in this report are intended to characterize the quality 

of untreated groundwater 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 groundwater samples will be the subject of subsequent 

publications.

Hydrogeologic Setting 

The South Coast Interior Basins study unit lies within 

the Southern Coast Ranges Hydrogeologic Province described 

by Belitz and others (2003), and includes 11 CDWR-defined 

groundwater basins and subbasins (California Department of 

Water Resources,2004a,b,c,d,e,f,g,h,i,j; 2006). The three study 

areas of the SCI study unit (Livermore, Gilroy, and Cuyama) 

cover an area of approximately 653 mi2

, in Alameda, Contra Costa, Santa Clara, San Benito, San Luis Obispo, Santa 

Barbara, Ventura, Kern, and Los Angeles Counties, California 

(fig. 2). 
4 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Figure 1. The hydrogeologic provinces of California and the location of the South Coast Interior Basins 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

Cuyama Study Area

Livermore Study Area

Gilroy Study Area

Transverse Ranges and selected Peninsular Ranges
Introduction 5

Figure 2. The South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing the three study areas 

(Livermore, Gilroy, and Cuyama), the location of public-supply wells with a record in the California Department of Public Health (CDPH) Database, 

major cities, topographic features, and hydrologic features.

Southern Coast

Ranges

0 100 200 MILES 50

0 100 200 KILOMETERS

Cuyama Study Area

Livermore Study Area

Gilroy Study Area

Cuyama Study Area

Livermore Study Area Gilroy Study Area

Public-supply well-With a record in California

 Department of Public Health (CDPH) Database

EXPLANATION

Groundwater basin (from California Department

 of Water Resources, CDWR)

Soda Lake

Kern

County

Ventura

County Los Angeles

County

Santa Barbara

County

San Luis Obispo

County

0 5 10 20 MILES

0 10 20 KILOMETERS 5

Sierra Madre Mountains

Caliente Range

Tehachapi Mts

Cuyama

New Cuyama

Lebec

Cuyama

River

101

101

101

Gilroy

Hollister

Hollister Hills

Diablo

Range

MTS

Diablo

Range

Cherry Peak

Pajaro

San Benito

River

River

San Benito

County

Merced

County

Monterey

County

Santa Clara

County Santa Cruz

County

Stanislaus

County

0 5 10 20 MILES

0 10 20 KILOMETERS 5

SANTA CRUZ

5

5

5

152

1

99

680

680

580

580

Arroyo de la Laguna

Pleasanton Canal

Canal

Arroyo Mocho

Alamo Canal

0 2 4 6 MILES

0 4 6 KILOMETERS 2

Dublin

Livermore

Pleasanton

Valle de

San Jose Rocky Ridge

Tassajara

Hills

Collier Canyon

Altamont Hills

Dougherty Hills

Harlan Hill

Pleasanton Ridge

Cedar Mountain Ridge

Crane Ridge

Lake del Valle

Contra Costa

County

Alameda

County

Dublin

Canyon

Bases from U.S. Geological Survey National Elevation

Dataset, 2006, Albers Equal-Area Conic Projection
6 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

The Livermore (LIV) study area is approximately 

109 mi2 in area and lies about 40 mi east of San Francisco 

within a structural trough of the Diablo Range. The LIV study 

area is located within the Livermore Valley Groundwater 

Basin (California Department of Water Resources, 2006), 

and is bounded on the west by the Pleasanton Ridge, Dublin 

Canyon, and Harlan Hill. It is bordered to the north by the 

Dougherty and Tassajara Hills, Collier Canyon, and the Contra 

Costa County boundary. The eastern boundary of the study 

area is the Altamont Hills. The southernmost border of LIV 

includes: the Crane, Cedar Mountain, and Rocky Ridges, Lake 

del Valle, and Valle de San Jose. The main surface drainage 

features of the LIV study area include four major canals, the 

Alamo, Arroyo Mocho, and Pleasanton, which converge to 

form the Arroyo de la Laguna canal on the west side of the 

basin (fig. 3). Elevations within LIV range from about 280 ft 

above sea level (f.a.s.l.) in the southwest, where Arroyo de la 

Laguna exits the study area, to about 600 f.a.s.l. in the east, 

near the Altamont Hills. Average annual precipitation in LIV 

ranges from more than 20 inches along the southeast and 

northwest study area margins to 16 inches on the valley floor 

(California Department of Water Resources, 2006).

Primary water-bearing formations in the LIV study area 

occur in the Livermore Valley and portions of the upland areas 

surrounding the valley. These formations include Holocene 

age valley-fill materials, the Plio-Pleistocene age Livermore 

Formation in the south and southwest, and the Pliocene-age 

Tassajara Formation in the northern region of LIV (California 

Department of Water Resources, 2006). 

The LIV study area has three major faults (the Pleasanton, Parks, and Livermore fault zone), each acting as a 

barrier to the lateral movement of groundwater (California 

Department of Water Resources, 2006) (fig. 3). Groundwater 

recharge in LIV occurs from a mixture of ambient recharge 

(percolation of precipitation and irrigation waters), subsurface 

inflow, and engineered recharge (percolation ponds and lakes) 

(California Department of Water Resources, 2006).

The Gilroy (GIL) study area is approximately 287 mi2

 in 

area and lies within the Gilroy–Hollister Groundwater Basin, 

which contains four CDWR-defined subbasins: Llagas, Bolsa 

Area, Hollister Area, and San Juan Bautista Area (not shown 

in figure 4) (California Department of Water Resources, 

2004a,b,c,d). The GIL study area is bordered on the west by 

the San Andreas Rift Zone, the Hollister Hills, and the Santa 

Cruz Mountains. It is bounded in the north, east, and south by 

the Diablo Range. The Pájaro River and its major tributaries 

(Llagas and Uvas Creeks) drain the northern portion of GIL to 

the Pacific Ocean through Monterey Bay. The southern portion 

of the GIL study area is drained by the San Benito River and 

its major tributaries (Tres Pinos and Pescadero Creeks) (fig. 4). 

Elevations within the basin range from about 140 f.a.s.l in the 

north, along the Santa Clara County and San Benito County 

border, to approximately 2,400 f.a.s.l. in the south, near 

Cherry Peak, in the Diablo Range. Average annual precipitation in GIL ranges from 17 inches in the northern reaches of 

the study area to 13 inches in the south (California Department 

of Water Resources, 2004a,b,c,d). 

The primary water-bearing formation in GIL is a sedimentary sequence consisting mainly of clays, silts, sands, 

and gravels ranging in age from Tertiary to Holocene (California Department of Water Resources, 2004a,b,c,d). The 

major faults that bound the GIL study area (Calaveras, San 

Andreas, and Sargent) are relatively impermeable barriers to 

groundwater flow (California Department of Water Resources, 

2004b,c,d). There also is an unnamed clay confining layer 

in the Llagas Subbasin that restricts groundwater flow in 

the northern region of GIL (California Department of Water 

Resources, 2004a). 

Groundwater recharge in the GIL study area occurs from 

a variety of sources: ambient recharge (infiltration losses along 

the Pájaro and San Benito Rivers and their tributaries, percolation of precipitation and irrigation waters, and seepage along 

canals), subsurface inflow, and engineered recharge. A number 

of engineered-recharge facilities (percolation ponds and channels) enhance ambient recharge to the northern portion of 

GIL. In the southern region of the GIL study area, engineered 

recharge occurs from the San Benito River as a result of 

river regulation at the Hernandez Reservoir, which is located 

approximately 20 mi southeast of the study area boundary 

(California Department of Water Resources, 2004a,b,c,d) 

(fig. 4).

The Cuyama (CUY) study area is approximately 257 mi2

in area, comprised largely of the Cuyama Valley Groundwater 

Basin (230 mi2), but also includes five small CDWR-defined 

groundwater basins [Castaic Lake Valley (6 mi2), Cuddy 

Canyon Valley (5 mi2), Cuddy Ranch Area (7 mi2), Cuddy Valley (5 mi2

), and Mil Potrero (4 mi2)] (California Department 

of Water Resources, 2004e,f,g,h,i,j). The CUY study area is 

bounded on the west and the south by the Sierra Madre Mountains and on the north and east by the Caliente Range. The 

study area is drained by the Cuyama River and its major tributaries (Alamo and Reyes Creeks and the New River) (fig. 5). 

Elevations within CUY range from about 1,400 f.a.s.l. in the 

west, where the Cuyama River exits the Cuyama study unit, 

to about 6,400 f.a.s.l. in the east, in the Tehachapi Mountains. 

Average annual precipitation in the CUY study area ranges 

from 15 inches in the southern mountains to 7 inches in the 

north (California Department of Water Resources, 2004e). 

The primary water-bearing formations in CUY mainly 

are unconfined and are composed of Holocene age alluvium 

(consisting of alternating layers of sands, gravels, silts, and 

clays) and older terrestrial deposits (consisting of Pleistoceneaged poorly consolidated clays, silts, and gravels) (California 

Department of Water Resources, 2004e). Groundwater flow 

in the Cuyama Valley groundwater basin is controlled by a 

series of small faults (Morales, Ozena, and South Cuyama), 

which act as barriers to groundwater movement. Groundwater 

recharge in CUY occurs almost exclusively from seepage from 

the Cuyama River (California Department of Water Resources, 

2004e).
Introduction 7

Figure 3. The South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing the distribution of the 

Livermore study-area grid cells, the location of sampled grid wells and understanding wells, the Livermore Valley groundwater-basin boundary 

(as defined by the California Department of Water Resources, CDWR), major cities, major roads, topographic features, and hydrologic features. 

Alphanumeric identification numbers for grid wells have the prefix “LIV”, and understanding wells have “LIVU.”

680

680

580

580

Parks Fault

Fault

Livermore Fault Zone

Pleasanton

Arroyo de la Laguna

Pleasanton

Canal

Canal

Arroyo Mocho

Alamo Canal

LIV-01

LIV-03

LIVU-03

LIVU-08

LIVU-07

LIVU-01

LIVU-04

LIVU-02

LIV-04

LIV-02

LIV-06

LIVU-05, 06 LIV-05

Southern Coast

Ranges

Livermore

California

Location of groundwater

basins in this study

Cuyama

Gilroy

121 55’ 121 50’ 121 45’ 121 40’

37 35’

37 40’

37 45’

0 2 4 6 MILES

0 2 4 6 KILOMETERS

Base from U.S. Geological Survey National Elevation

Dataset, 2006, Albers Equal-Area Conic Projection

Dublin

Livermore

Pleasanton

Valle de

San Jose

Rocky Ridge

Tassajara Hills

Collier Canyon

Altamont Hills

Dougherty Hills

Harlan Hill

Pleasanton Ridge

Cedar Mountain Ridge

Crane Ridge

Lake del Valle

Contra Costa

County

Alameda

County

Fault

Dublin

Canyon

Livermore Valley groundwater

 basin (from California Department

 of Water Resources, CDWR)

Grid well

Water bodies

Stream or river

Randomized sampling

 grid cell

LIVU-05

LIV-05

Understanding well
8 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Figure 4. The South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing the distribution of 

the Gilroy study-area grid cells, the location of sampled grid wells and understanding wells, the Gilroy-Hollister groundwater-basin boundary 

(as defined by the California Department of Water Resources, CDWR), major cities, major roads, topographic features, and hydrologic features. 

Alphanumeric identification numbers for grid wells have the prefix “GIL”, and understanding wells have “GILU.”

SAN ANDREAS

Sargent Fault

RIFT ZONE

Calaveras Fault

Canal

Miller’s

101

Southern Coast

Ranges

Livermore

California

Location of groundwater

basins in this study

Cuyama

Gilroy

Gilroy-Hollister groundwater

 basin (from California Department

 of Water Resources, CDWR)

Randomized sampling

 grid cell

EXPLANATION

Water bodies

Fault Stream or river

Grid well

Understanding well

GIL-05

GILU-05

GIL-15

GIL-16

GIL-03

GIL-14

GIL-05

GIL-12

GIL-04

GIL-17

GIL-13

GIL-06

GIL-11

GIL-07

GILU-02, GIL-02

GILU-03, 04, 05

GIL-09

GIL-08

GIL-10

GILU-01

GIL-01

121 45’ 121 30’ 121 15’ 121

36 45’

37

Base from U.S. Geological Survey National Elevation

Dataset, 2006, Albers Equal-Area Conic Projection

0 5 10 20 MILES

0 10 20 KILOMETERS 5

Gilroy

Hollister

Diablo

Range

SANTA CRUZ

MOUNTAINS

Hollister Hills

Diablo

Range

Cherry Peak

Hernandez

Reservoir

aproximately

20 miles

To: 

Monterey

Bay and

the Pacific 

Ocean

+

Liagas

Uvas

Creek

Creek

Pajaro

River

San Benito

River

Pescadero

Creek

Tres Pinos

Creek

San Benito

County

Merced

County

Monterey

County

Santa Clara

Santa Cruz County

County

Stanislaus

County

101

101

5

152

1
Introduction 9

Figure 5. The South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing the distribution of 

the Cuyama study-area grid cells, the location of sampled grid wells and understanding wells, the Cuyama Valley, Castaic Lake Valley, Cuddy 

Canyon Valley, Cuddy Ranch Area, Cuddy Valley, and Mil Potrero groundwater-basin boundaries (as defined by the California Department of Water 

Resources, CDWR), major cities, major roads, topographic features, and hydrologic features. Alphanumeric identification numbers for grid wells 

have the prefix “CUY”, and understanding wells have “CUYU.”

Southern Coast

Ranges

Livermore

California

Location of groundwater

basins in this study

Gilroy

Cuyama

Big Pine

Ozena

Fault

Garlock

Fault

Fault

San Andreas

Morales

Fault

Fault

Fault South Cuyama

5

5

99

Soda Lake

Cuyama

New Cuyama

Kern

County

Ventura

County

Los Angeles

County

Santa Barbara

County

San Luis Obispo

County

Lebec

CUY-01

CUY-02

CUY-05

CUY-04

CUY-07

CUY-08

CUY-06

CUY-12

CUY-03

CUY-11

Cuyama Valley groundwater

 basin (from California Department

 of Water Resources, CDWR)

EXPLANATION

Understanding

 well

Grid well

Castaic Lake Valley, Cuddy Canyon

 Valley, Cuddy Ranch Area, Cuddy

 Valley, and Mil Potrero groundwater

 basins included in this study (from

 California Department of Water

 Resources, CDWR)

Water bodies

Stream or river

Fault

Randomized sampling

 grid cell

CUY-09

CUYU-02

5

5

San Andreas Fault

Garlock Fault

Big Pine Fault

Castac

Lake

0 5 10 MILES

0 5 10 KILOMETERS

Lebec

CUY-09

CUYU-02

CUYU-04

CUYU-03

CUYU-01

CUYU-05

CUYU-06

CUY-10

Los Angeles

County

Ventura

County

Kern

County

0 5 10 20 MILES

0 10 20 KILOMETERS 5

120 119 40’ 119 20’ 119

34 40’

35 00’

Base from U.S. Geological Survey National Elevation

Dataset, 2006, Albers Equal-Area Conic Projection

Sierra Madre Mountains

Tehachapi Mts

See inset map below

Cuyama

River

Caliente Range
10 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Five small CDWR-defined groundwater basins (Castaic 

Lake Valley, Cuddy Canyon Valley, Cuddy Ranch Area, Cuddy 

Valley, and Mil Potrero) located east of the Cuyama Valley groundwater basin were included in the CUY study area 

to gain information on the quality of groundwater in active 

fault zones (the Big Pine, Garlock, and San Andreas) (fig. 5, 

inset map). These groundwater basins lie in the Tehachapi 

Mountains, contain Tertiary, Pleistocene, or Quaternary-aged 

alluvial fill material, and are drained by a series of streams and 

creeks. Groundwater recharge in these basins occurs from the 

percolation of precipitation, spring flows, and septic tank 

effluent (California Department of Water Resources, 

2004f,g,h,i,j).

Methods 

Methods used for the GAMA Priority Basins Project 

were selected to achieve the following objectives: (1) design a 

sampling plan for suitable statistical representation; (2) collect 

samples in a consistent manner; (3) analyze samples using 

proven and reliable laboratory methods; (4) assure the quality 

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

with relevant documentation. The Appendix to this report contains detailed descriptions of the sample-collection protocols 

and analytical methods, the quality-assurance plan, 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. Thirty-five 

“grid” wells were selected to provide a statistically unbiased, 

spatially distributed assessment of the quality of groundwater 

resources used for public drinking-water supply, while 19 

additional “understanding” wells were selected to provide 

greater sampling density in several areas to aid in the understanding of specific groundwater-quality issues in the study 

areas.

The spatially distributed wells were selected using a 

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

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

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

divided into multiple pieces in order to obtain the designated 

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

cell may be located on either side of a mountain range, but 

the grid cell still is considered one grid cell. The objective 

for the SCI study unit within the GAMA South Coast Ranges 

Hydrologic Province was to sample at least one well per 

10 mi2 (about 25 km2). SCI was subdivided into 44 grid cells 

(LIV study area, 7 grid cells; GIL study area, 19 grid cells; 

CUY study area, 18 grid cells) (figs. 3,4,5). If a grid cell contained more than one public-supply well, each well randomly 

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

sampling criteria (for example, sampling point located prior 

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

which permission to sample could be obtained, was sampled. 

If a grid cell contained no accessible public-supply wells, then 

other types of wells, such as domestic or irrigation wells, were 

considered for sampling. An attempt was made to select “alternative” wells that had depths and screened intervals similar to 

those in public-supply wells in the area. In this fashion, one 

well was selected in each cell to provide a spatially distributed, randomized monitoring network. Wells sampled as part 

of the spatially distributed, randomized grid-cell network, 

hereafter, are referred to as “grid wells.” The 35 grid wells 

sampled in SCI were named for the study area where they 

were located by using the prefix “LIV”, “GIL”, or “CUY” and 

numbered in the order of sample collection within each study 

area (figs. 3,4,5).

Nineteen additional, nonrandomized wells were sampled 

throughout the three study areas of SCI to collect more information for various water-quality issues within each study area. 

Wells sampled as part of these studies were not included in 

the statistical characterization of water quality in SCI because 

inclusion of these wells would lead to the overrepresentation 

of some cells. These additional, nonrandomized wells were 

named for the study area where they were located by using the 

prefix “LIVU”, “GILU”, or “CUYU” (“U” indicating “understanding”) and numbered in the order of sample collection 

within each study area (figs. 3,4,5).

The GAMA alphanumeric identification number for each 

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

elevation, well type, and available well-construction information is shown in table 1 (all tables shown in back of report). 

Groundwater samples were collected from 31 public-supply 

wells, 8 domestic wells, 7 irrigation wells, 7 monitoring 

(observation) wells, and 1 well used for industrial activities, 

during the period from August to December 2008. 

Well locations and identifications were verified using 

global positioning system (GPS), 1:24,000-scale USGS 

topographic maps, comparison with existing well information 

in USGS and CDPH Databases, and information provided 

by well owners. Driller’s logs for wells were obtained, when 

available. Well information was recorded by hand on field 

sheets and electronically on field laptop computers using 

the portable computer field forms (PCFF) program designed 

for USGS sampling. All information was verified and then 

uploaded into the USGS National Water Information System 

(NWIS). Well owner information is confidential.
Water-Quality Results 11

The wells in SCI were sampled using a tiered analytical approach. All wells were sampled for a standard set of 

constituents, including volatile organic compounds (VOCs), 

pesticides and pesticide degradates, perchlorate, trace elements, nutrients, major and minor ions, silica, total dissolved 

solids (TDS), alkalinity, stable isotopes of hydrogen and 

oxygen in water, tritium, dissolved noble gases, stable isotopes 

of carbon, and carbon-14 abundance. The standard set of 

constituents was termed the “fast” schedule (table 2). Wells on 

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

the fast schedule, plus polar pesticides and metabolites, pharmaceutical compounds, N-nitrosodimethylamine (NDMA), 

arsenic, chromium, and iron speciation, and gross alpha and 

gross beta radioactivity (table 2). There also were five wells 

on the fast schedule (one grid and four understanding wells) 

for which radon-222 was added to the sampling schedule; this 

addition coincided with a special study being conducted in 

the GIL study area. Fast and slow refer to the time required to 

sample the well for all the analytes on the schedule. Generally, 

two slow or three fast wells could be sampled in 1 day. In SCI, 

43 of the wells were sampled on the fast schedule (28 grid and 

15 understanding wells) and 11 wells were sampled on the 

slow schedule (7 grid and 4 understanding wells) (table 1).

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 representative 

samples of groundwater are collected at each site and that the 

samples are collected and handled in ways that minimize the 

potential for contamination. 

Tables 3A–K list the compounds analyzed in each 

constituent class. Groundwater samples were analyzed for 

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

(table 3B); 60 polar pesticides and metabolites (table 3C); 

14 pharmaceutical compounds (table 3D); 2 constituents of 

special interest (table 3E); 24 trace elements (table 3F); 5 

nutrients (table 3G); 9 major and minor ions, silica, TDS, and 

alkalinity (table 3H); arsenic, chromium, and iron species 

(table 3I); stable isotopes of hydrogen, oxygen, and carbon, 

and 5 radioactive constituents, including carbon-14 (table 3J); 

and 5 dissolved noble gases, tritium, and helium stable isotope 

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

and analysis are described in the Appendix section of this 

report “Sample Collection and Analysis.” 

Data Reporting

The methods and conventions used for reporting the 

data are described in the Appendix section “Data Reporting.” 

Eleven constituents analyzed in this study were measured by 

more than one analytical schedule or more than one laboratory. 

Four constituents analyzed in this study were measured by 

more than one method at the USGS National Water Quality 

Laboratory (NWQL), but only the results from the preferred 

method are reported (see Appendix section “Constituents on 

Multiple Analytical Schedules”). Four other constituents—

arsenic, chromium, and iron concentrations and tritium activities—were measured by two different laboratories, and both 

sets of results are reported for these constituents. 

Quality Assurance

The quality-assurance and quality-control procedures 

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 plan followed 

by the USGS National Water Quality Laboratory (NWQL), 

the primary laboratory used to analyze samples for this 

study, is described in Maloney (2005) and Pirkey and Glodt 

(1998). Quality-control (QC) samples collected in the SCI 

study include: field blanks, replicates, and matrix and surrogate spikes. QC samples were collected to evaluate potential 

contamination, as well as bias and variability of the data that 

may have resulted from sample collection, processing, storage, transportation, and laboratory analysis. Quality-control 

procedures and quality-control sample results are described in 

the Appendix section “Quality Assurance.”

Water-Quality Results 

Quality-Control Results

Results of quality-control analyses (blanks, replicates, 

matrix spikes, and surrogates) were used to evaluate the 

quality of the data for the groundwater samples. On the basis 

of detections in field blanks collected for this and previous 

GAMA Priority Basins Project study units, some detections 

reported by the laboratory for two organic compounds were 

considered suspect and, therefore, were removed from the 

set of groundwater-quality data presented in this report (see 

table A3 and additional discussion in Appendix). Results from 

the replicates confirm that the procedures used to collect and 

analyze the samples were consistent. Ninety-eight percent of 

the replicate pairs for constituents detected in samples had 

variability within acceptable limits. Median matrix-spike 

recoveries for 40 of the 210 organic constituents analyzed 

were lower than the acceptable limits (tables 3B and 3C), 

which may indicate that these constituents might not have 

been detected in some samples if they were present in the 

samples at concentrations near the laboratory reporting 

levels (LRLs). The quality-control results are described in the 

Appendix section “Quality-Control Results.”
12 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Comparison Thresholds

Concentrations of constituents detected in groundwater 

samples were compared with CDPH and USEPA regulatory 

and nonregulatory drinking-water health-based thresholds 

and thresholds established for aesthetic purposes (California 

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

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

in this report are meant to characterize the quality of the 

untreated groundwater resources within SCI, and are not 

intended to represent the treated drinking water delivered to 

consumers by water purveyors. The chemical composition of 

treated drinking water may differ from untreated groundwater 

because treated drinking water may be subjected to disinfection, filtration, mixing with other waters, and/or exposure to 

the atmosphere prior to its delivery to consumers. Comparisons of untreated groundwater to thresholds are for illustrative 

purposes only and are not indicative of compliance or noncompliance with drinking-water regulations.

The following thresholds were used for comparisons:

• MCL—Maximum Contaminant Level. Legally 

enforceable standards that apply to public water systems and are designed to protect public health by limiting the levels of contaminants in drinking water. MCLs 

established by the USEPA are the minimum standards 

with which states are required to comply, and individual states may choose to set more stringent standards. 

CDPH has established MCLs for additional constituents not regulated by the USEPA and has lowered the 

threshold concentration for a number of 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 “MCLCA.” CDPH is notified when constituents are detected 

at concentrations greater than MCL-US or MCL-CA 

thresholds in samples collected for the GAMA Priority 

Basins Project, but these detections do not constitute 

violations of CDPH regulations.

• AL—Action Level. Legally enforceable standards that 

apply to public water systems and are designed to protect public health by limiting the levels of copper and 

lead in drinking water. Detections of copper or lead 

above the action-level 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.

• SMCL—Secondary Maximum Contaminant Level.

Nonenforceable standards applied to constituents that 

affect the aesthetic qualities of drinking water, such 

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

drinking water, such as scaling and staining. Both the 

USEPA and CDPH define SMCLs, but unlike MCLs, 

SMCLs established by CDPH are not required to be 

as stringent as those established by USEPA. SMCLs 

established by CDPH are used in this report (SMCLCA) 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, California 

state law requires timely notification of local governing 

bodies and recommends consumer notification.

• HAL—Lifetime Health Advisory Level. The 

maximum concentration of a constituent at which its 

presence in drinking water is not expected to cause 

any adverse carcinogenic effects for a lifetime of 

exposure. HALs are established by the USEPA (HALUS) and are calculated assuming consumption of 2 L 

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

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

a person’s exposure comes from drinking water.

• RSD5—Risk-Specific Dose. The concentration of 

a constituent in drinking water corresponding to an 

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

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

RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by ten 

(RSD5-US).

For constituents with MCLs, detections in groundwater 

samples were compared to the MCL-US or MCL-CA. Constituents with SMCLs were compared with the SMCL-CA. 

For chloride, sulfate, specific conductance, and total dissolved 

solids, CDPH defines a “recommended” and an “upper” 

SMCL-CA; detections of these constituents in groundwater 

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

these constituents corresponds to the recommended SMCLCA. Detected concentrations of constituents that lack an MCL 

or SMCL were compared to the NL-CA. For constituents that 

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

compared with the HAL-US. For constituents that lack an 

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

were compared with the RSD5-US. Note that if a constituent 

has more than one type of established threshold, using this 

hierarchy to select the comparison threshold will not necessarily result in selection of the threshold with the lowest concentration. For example, zinc has an SMCL-CA of 5,000 μg/L 

and a HAL-US of 2,000 μg/L, and the comparison threshold 

selected by this hierarchy is the SMCL-CA. The comparison 

thresholds used in this report are listed in tables 3A–3K for 

all constituents and in tables 4–13 for constituents detected in 

groundwater samples from SCI. Not all constituents analyzed 

for this study have established thresholds available. Detections of constituents at concentrations greater than the selected 

comparison threshold are marked with asterisks in tables 4, 5, 

and 7–11. 
Water-Quality Results 13

Groundwater-Quality Data

Results from analyses of untreated groundwater samples 

from SCI are presented in tables 4–13. These results are separated into the three study areas that make up the SCI study unit 

(LIV, GIL, and CUY). Groundwater samples collected in SCI 

were analyzed for 288 constituents, and 219 of those constituents were not detected in any of the samples (tables 3A–K). 

For organic constituent classes that were analyzed at all of the 

grid wells, the results tables include the following summary 

statistics for all 35 SCI grid wells, and for the grid wells in 

each study area (LIV, GIL, and CUY), the number of wells 

at which each analyte was detected, the frequency at which 

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

study area), and the total number of constituents detected at 

each well. For the constituents of special interest, inorganic, 

isotopic, and radioactive constituent classes, the summary 

tables include all wells, constituents, and samples analyzed. 

Results from the understanding wells are presented in the 

tables, but these results were excluded from the detection 

frequency calculations to avoid statistically over-representing 

the areas in the vicinity of the understanding wells.

Table 4 includes water-quality indicators (field parameters) measured in the field and at the NWQL. Tables 5–13

present the results of groundwater analyses organized by 

compound classes: 

• Organic constituents

• Volatile organic compounds (VOCs) (table 5)

• Pesticides and pesticide degradates (table 6A)

• Polar pesticides and metabolites (table 6B)

• Constituents of special interest (table 7)

• Inorganic constituents

• Trace elements (table 8)

• Nutrients (table 9)

• Major and minor ions, silica, and total dissolved 

solids (TDS) (table 10)

• Arsenic, chromium, and iron speciation (table 11)

• Isotopic tracers (table 12)

• Radioactive constituents (tables 13A,B)

Results for pharmaceutical compounds are not presented 

in this report; they will be included in a subsequent publication. In addition, as of the publishing date of this data report, 

the results of analyses of samples collected in SCI for noble 

gases and helium isotope ratios were not available; results will 

be presented in a subsequent publication. 

Water-Quality Indicators (Field Parameters)

Field and laboratory measurements of dissolved oxygen, 

pH, specific conductance, alkalinity, and associated parameters 

(turbidity, water temperature, and bicarbonate and carbonate 

concentrations) are presented in table 4. Alkalinity, dissolved 

oxygen, and bicarbonate and carbonate concentrations are 

used as indicators of natural processes that affect water chemistry. Specific conductance is the measure of 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 of the water. 

Sixty percent of SCI’s grid wells (21 of 35 wells) (2 of 

6 LIV grid wells, 9 of 17 GIL grid wells, and 10 of 12 CUY 

grid wells) had field specific conductance values above the 

recommended SMCL-CA of 900 μS/cm; 9 of these grid wells 

(3 GIL wells and 6 CUY wells) also were above the upper 

threshold of 1,600 μS/cm. 

Nine of the 19 understanding wells (6 of 8 LIVU wells 

and 3 of 6 CUYU wells) had field specific conductance values 

above the recommended SMCL-CA. Additionally, 4 of the 

8 LIVU wells were above the SMCL-CA upper threshold. 

None of the 54 wells sampled in the SCI study unit 

had field pH values outside of the SMCL-US range for pH 

(table 4). (Laboratory pH values may be dissimilar to field 

pH values because the pH of groundwater may change upon 

exposure to the atmosphere [see Appendix]).

Organic Constituents

Volatile organic compounds (VOCs) may be present in 

paints, solvents, fuels, fuel additives, refrigerants, fumigants, 

and disinfected water, and are characterized by their tendency 

to evaporate. VOCs generally persist longer in groundwater 

than in surface water because groundwater is isolated from the 

atmosphere. 

Of the 85 VOCs analyzed, 13 were detected in SCI 

groundwater samples; all detections were below health-based 

thresholds (table 5). VOCs that were detected in more than 

10 percent of the six LIV grid wells were: chloroform (trichloromethane); dichlorodifluoromethane (CFC-12); perchloroethene (PCE, tetrachloroethene); 1,1-dichloroethene (1,1-DCE); 

methyl ethyl ketone (2-butanone, MEK); carbon tetrachloride 

(tetrachloromethane); and tetrahydrofuran. No VOCs were 

detected in more than 10 percent of the 17 GIL grid wells or 

the 12 CUY grid wells. One or more VOCs were detected in 

8 of the 35 grid wells in SCI and in 8 of the 19 understanding 

wells sampled.
14 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Pesticides include herbicides, insecticides, and fungicides, and are used to control weeds, insects, fungi, and other 

pests in agricultural, urban, and suburban settings. Of the 63 

pesticides and pesticide degradates analyzed at all of the grid 

and understanding wells in the SCI study, 4 pesticides were 

detected in groundwater samples; all detections were below 

health-based thresholds (table 6A). The herbicides—simazine, 

deethylatrazine (a degradate of atrazine), prometon, and/or 

tebuthiuron—were detected in more than 10 percent of the 

six LIV grid well samples. Simazine and deethylatrazine are 

among the nation’s most commonly detected pesticide compounds in groundwater (Gilliom and others, 2006). Simazine 

was detected in more than 10 percent of the 17 GIL grid well 

samples. No pesticides and pesticide degradates were detected 

in any of the 12 grid wells in the CUY study area. One or more 

pesticide compounds were detected in 8 of the 35 grid wells in 

SCI and in 3 of the 19 understanding wells sampled. 

In addition, groundwater samples for 60 polar pesticides 

and metabolites were collected at the 11 slow wells in SCI. 

Of the 60 polar pesticides and metabolites analyzed, only 

bentazon (an herbicide) was detected (table 6B). This single 

detection occurred in a LIV study area grid well (LIV-06), and 

it was below the health-based threshold.

Constituents of Special Interest

Perchlorate and NDMA are constituents of special 

interest in California because they may adversely affect 

water quality and recently have been found in water supplies 

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

was analyzed for at all 54 wells in SCI and was detected in 

approximately 77 percent of the grid wells (27 of 35 wells) (5 

of 6 LIV grid wells, 13 of 17 GIL grid wells, and 9 of 12 CUY 

grid wells); however, none of these detections were above the 

MCL-CA (table 7). In SCI’s 19 understanding wells, 1 well 

(GILU-01) had perchlorate measured just above the MCL–

CA. NDMA was analyzed for at the 11 slow wells in SCI and 

was not detected. 

Inorganic Constituents

Unlike the organic constituents and the constituents of 

special interest, most of the inorganic constituents are naturally present in groundwater, although their concentrations 

may be influenced by human activities. Inorganic constituents 

were sampled on both the fast and slow sampling schedule 

(35 grid and 19 understanding wells) in SCI, while arsenic, 

chromium, and iron species were sampled only on the slow 

schedule (7 grid and 4 understanding wells). 

Twenty-one of 24 trace elements analyzed in this study 

have regulatory health-based or nonregulatory aesthetic 

thresholds. Of the 17 trace elements with health-based 

thresholds, most detections of the trace elements in SCI grid 

wells had concentrations below the thresholds (table 8). The 

exceptions were a few detections of arsenic, molybdenum, 

and boron above thresholds. In the 12 CUY grid well samples, there were two detections of arsenic above the USEPA 

maximum contaminant level (MCL-US) of 10 μg/L and three 

detections of molybdenum above the USEPA lifetime health 

advisory level (HAL-US) of 40 μg/L. Two LIV grid wells 

samples (of 6) and one GIL grid well sample (of 17) had 

concentrations of boron above the NL-CA of 1,000 μg/L 

(table 8). 

Results for trace elements for the 19 understanding wells 

in SCI include detections of five constituents above their 

respective health-based thresholds. Of the eight LIVU wells 

sampled, there were two detections of uranium and one detection of arsenic that were above the MCL-US thresholds for 

these constituents. Additionally, out of the eight LIVU wells, 

there were two understanding wells that had strontium and 

one understanding well that had molybdenum measured above 

their respective HAL-US. Four of the eight LIVU understanding wells and one of the six CUYU understanding wells had 

boron above the NL-CA. For the understanding wells sampled 

in the GIL study area, there were no detections of trace elements measured above established health-based thresholds 

(table 8).

Nutrients (nitrogen and phosphorus) present in groundwater can affect biological activity in aquifers and in surfacewater bodies that receive groundwater discharge. Inorganic 

nitrogen may be present in the form of ammonia, nitrite, or 

nitrate, depending on the oxidation-reduction state of the 

groundwater. High concentrations of nitrate can affect human 

health adversely, particularly the health of infants. Concentrations of nitrate, nitrite, and ammonia measured in samples 

from the 54 wells in the SCI study unit were below healthbased thresholds, with the exception of five detections of 

nitrite plus nitrate, as nitrogen (NO2

– + NO3–

) above the MCLUS of 10 mg/L. These detections occurred in 5 of the 35 SCI 

grid wells (1 of 6 LIV grid wells, 2 of 17 GIL grid wells, and 2 

of 12 CUY grid wells) (table 9). 

Fluoride is the only major ion with a regulatory healthbased threshold (MCL-CA of 2 mg/L); it was detected at a 

concentration above this threshold in one CUYU understanding well (table 10).

The levels of certain trace elements, major-ion composition, and total dissolved solids (TDS) content in groundwater 

affect the aesthetic properties of water such as taste, color, and 

odor, and the technical properties of water such as scaling and 

staining. Although there are no adverse health effects directly 

associated with these properties, they may reduce consumer 

satisfaction with the water or may have economic impacts. 

CDPH has established nonenforceable thresholds (SMCLCAs) that are based on aesthetic or technical properties rather 

than on health-based concerns for several trace elements, the 

ions; chloride and sulfate, and TDS. 
Water-Quality Results 15

Iron and manganese are trace elements with concentrations affected by the oxidation-reduction state of the groundwater. Precipitation of minerals containing iron or manganese 

may cause orange, brown, or black staining of surfaces. Iron 

was detected in 31 of the 54 samples in SCI wells (22 grid 

and 9 understanding), but only one of these detections (in 

understanding well LIVU-06) had concentrations above the 

SMCL-CA (table 8). 

Manganese was detected in 45 of the 54 samples in 

SCI wells (27 grid and 18 understanding). There were eight 

grid wells (one LIV grid well, five GIL grid wells, and two 

CUY grid wells) having manganese concentrations above the 

SMCL-CA of 50 μg/L. In the SCI study unit there were four 

understanding wells (three LIVU understanding wells and one 

GILU understanding well) where manganese was measured 

above the SMCL-CA (table 8).

Chloride was detected at concentrations above the upper 

SMCL-CA threshold of 500 mg/L in two LIVU understanding 

wells (table 10).

Sulfate was detected above the recommended SMCL-CA 

threshold of 250 mg/L in 17 of the 54 samples in the SCI wells 

(12 of 35 grid wells and 5 of 19 understanding wells). There 

were nine grid wells (one GIL grid well and eight CUY grid 

wells) also having measured sulfate concentrations above the 

upper SMCL-CA threshold of 500 mg/L. Three LIVU understanding wells had measured sulfate concentrations above the 

upper SMCL-CA (table 10). 

TDS was detected above the recommended SMCL-CA 

threshold of 500 mg/L in 36 of the 54 samples in the SCI wells 

(25 of 35 grid wells and 11 of 19 understanding wells). There 

were 10 grid wells (3 GIL grid wells and 7 CUY grid wells) 

having TDS concentrations above upper SMCL-CA threshold 

of 1,000 mg/L. Four LIVU understanding wells had TDS 

measured at concentrations above the upper SMCL-CA 

(table 10). 

Arsenic, chromium, and iron occur as different species, 

depending on the oxidation-reduction state of the groundwater. 

The oxidized and reduced species have different solubilities in 

groundwater and may have different effects on human health. 

The relative proportions of the oxidized and reduced species 

of each element can be used to aid in interpretation of the oxidation–reduction state of the aquifer. Concentrations of total 

arsenic, chromium, and iron and the concentration of either the 

reduced or the oxidized species of each element are reported in 

table 11. The concentration of the other species can be calculated by difference. The concentrations of arsenic, chromium, 

and iron reported in table 11 may be different than those 

reported in table 8 because different analytical methods were 

used (see Appendix). The concentrations reported in table 8

are considered to be more accurate. Some arsenic, chromium, 

and iron species analyses were not completed in time for 

inclusion in this report; complete results will be presented in a 

subsequent publication.

Isotopic Tracers and Noble Gases

The isotopic ratios of oxygen and hydrogen in water, the 

tritium and carbon-14 activities, and the concentrations of dissolved noble gases may be used as tracers of hydrologic processes. The isotopic ratios of hydrogen and oxygen in water 

(table 12) aid in the interpretation of the sources of groundwater recharge. These stable isotopic ratios reflect the altitude, 

latitude, and temperature of precipitation and also the extent of 

evaporation of the water in surface water bodies or soils prior 

to infiltration into the aquifer. Concentrations of dissolved 

noble gases are used to estimate the conditions of groundwater 

recharge, particularly the temperature of the recharge water. 

All noble gas analyses and some isotopic ratios of oxygen and 

hydrogen in water measurements were not completed in time 

for inclusion in this report; complete results will be presented 

in a subsequent publication. 

Tritium and carbon-14 activities and helium isotope ratios 

also provide information about the age (time since recharge) 

of groundwater. Tritium is a short-lived radioactive isotope of 

hydrogen that is incorporated into the water molecule. Low 

levels of tritium are produced continuously by interaction 

of cosmic radiation with the Earth’s atmosphere, and a large 

amount of tritium was produced as a result of atmospheric 

testing of nuclear weapons between 1952 and 1963. Thus, 

concentrations of tritium above background generally indicate 

the presence of water recharged since the early 1950s. Helium 

isotope ratios are used in conjunction with tritium concentrations to estimate ages for young groundwater. Some tritium 

activities and all helium isotope ratio analysis were not completed in time for inclusion in this report; complete results will 

be presented in a subsequent publication.

Carbon-14 (table 12) is a radioactive isotope of carbon. 

Low levels of carbon-14 are produced continuously by interaction of cosmic radiation with the Earth’s atmosphere, and 

incorporated into atmospheric carbon dioxide. Carbon dioxide 

dissolves in precipitation, surface water, and groundwater 

exposed to the atmosphere, thereby entering the hydrologic 

cycle. Because carbon-14 decays with a half-life of approximately 5,700 years, low activities of carbon-14, relative to 

modern values, generally indicate a presence of groundwater 

that is several thousand years old. Some carbon-14 activity analyses were not completed in time for inclusion in this 

report; complete results will be presented in a subsequent 

publication. 

Of the isotopic tracer constituents analyzed for this study, 

tritium is the only one with a health-based threshold. Thus far, 

all measured tritium activities in samples from SCI wells have 

been about one one-thousandth of the MCL-CA (table 12).
16 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

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 groundwater comes from 

decay of naturally occurring isotopes of uranium and thorium 

that are present in minerals in the sediments or fractured rocks 

of the aquifer. Both uranium and thorium decay in a series of 

steps, eventually forming stable isotopes of lead. Radon-222 

is a radioactive isotope formed during the uranium or thorium 

decay series. In each step in the decay series, one radioactive 

element turns into a different radioactive element by emitting 

an alpha or a beta particle from its nucleus. The alpha and beta 

particles emitted during radioactive decay are hazardous to 

human health because these energetic particles may damage 

cell DNA and may increase the risk of getting cancer.

Activity often is used instead of concentration for 

reporting the presence of radioactive constituents. Activity of 

radioactive constituents in groundwater is measured in units 

of picocuries per liter (pCi/L), and one picocurie is approximately equal to two atoms decaying per minute. The number 

of atoms decaying is equal to the number of alpha or beta 

particles emitted. The 11 slow samples in SCI were analyzed 

for gross alpha and gross beta radioactivity and all samples 

had activities less than established health-based thresholds 

(table 13A). Five of the 11 samples collected for gross alpha 

and gross beta radioactivity activities were either counted after 

72 hours or recounted several days after the original count 

at the laboratory. A delay in the counting by the laboratory 

may result in lower activities than may have been observed 

if the count had been preformed within the 72-hour/30-day 

time period; the results for these five samples are footnoted in 

table 13A.

Samples were collected for the analysis of radon-222 

from five special studies wells (one grid well and four understanding wells) in the GIL study area. No samples had activities above the proposed alternative MCL-US of 4,000 pCi/L 

(table 13B). The proposed alternative MCL-US will apply if 

the state or local water agency has an approved multimedia 

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

Environmental Protection Agency, 1999). 

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 groundwater quality. Waterquality data contained in the CDPH Databases will be compiled, evaluated, and used in combination with the data that 

are presented in this report.

Summary 

Groundwater quality in the approximately 653-squaremile South Coast Interior Basins (SCI) study unit was investigated from August to December 2008, as part of the Priority 

Basins Project of the Groundwater Ambient Monitoring and 

Assessment (GAMA) Program. The GAMA Priority Basins 

Project was developed in response to Legislative mandates 

(Supplemental Report of the 1999 Budget Act 1999-2000 

Fiscal Year; and, the Groundwater-Quality Monitoring Act 

of 2001 {Sections 10780-10782.3 of the California Water 

Code, Assembly Bill 599}) to assess and monitor the quality of groundwater used as public supply for municipalities 

in California, and is being conducted by the U.S. Geological Survey (USGS) in cooperation with the California State 

Water Resources Control Board (SWRCB). SCI was the 27th 

study unit to be sampled as part of the GAMA Priority Basins 

Project.

SCI is located in the South Coast Ranges Hydrologic 

Province and includes 11 groundwater basins and subbasins defined by the California Department of Water 

Resources (California Department of Water Resources, 2006; 

2004a,b,c,d,e,f,g,h,i,j). The SCI study included assessment 

of the groundwater quality from 54 wells in Alameda, Santa 

Clara, San Benito, Santa Barbara, Ventura, and Kern Counties, California. Thirty-five of the wells were selected using 

a randomized grid approach to achieve statistically unbiased 

representation of groundwater used for public drinking-water 

supplies. Nineteen of the wells were selected to provide 

additional sampling density to aid in understanding processes 

affecting groundwater quality. 

Groundwater samples were analyzed for volatile organic 

compounds (VOCs), pesticides and pesticide degradates, polar 

pesticide and metabolites, pharmaceutical compounds, perchlorate, NDMA, trace elements, nutrients, major and minor 

ions, silica, total dissolved solids (TDS), alkalinity, and radioactivity (gross alpha and gross beta radiation and radon-222). 

Naturally occurring isotopes [stable isotopes of hydrogen, 

oxygen, and carbon, and activities of tritium and carbon-14] 

and dissolved noble gases also were measured to provide a 

data set that will be used to help interpret the sources and ages 

of the sampled groundwater. In total, 288 constituents and 

water-quality indicators (field parameters) were investigated 

for this study. This report describes the sampling, analytical, 

and quality-assurance methods used in the study, and presents 

the results of the chemical analyses made of the groundwater 

samples.
References Cited 17

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 untreated groundwater. However, to provide 

some context for the results, concentrations of constituents 

measured in the untreated groundwater were compared with 

regulatory and nonregulatory health-based thresholds established by the U.S. Environmental Protection Agency (USEPA) 

and California Department of Public Health (CDPH) and 

nonregulatory thresholds established for aesthetic and 

technical concerns by CDPH.

All detections of VOCs and pesticides in samples from 

the 54 SCI grid and understanding wells were below healthbased thresholds; additionally, all of the detections of organic 

and special interest constituents from SCI grid and understanding wells were below health-based thresholds, with the exception of a single understanding well detection of perchlorate 

above the CDPH maximum contaminant level (MCL-CA). 

Results from SCI grid wells showed that most detections 

of trace elements and nutrients in samples from the 35 grid 

wells were below health-based thresholds. Exceptions include: 

two detections of arsenic and five detections of nitrite plus 

nitrate, as nitrogen (NO2

– + NO3–

) above the USEPA maximum 

contaminant level (MCL-US), three detections of boron and 

three detections of molybdenum that were above the USEPA 

lifetime health advisory level (HAL-US). All detections of 

gross alpha and gross beta radioactivity in SCI grid wells were 

below health-based thresholds. 

Most of the samples from SCI grid wells collected for 

trace elements, major ions, and TDS had concentrations measured below the nonenforceable thresholds set for aesthetic 

concerns. Eight grid wells (of 35 sampled) in SCI had detections of manganese above the SMCL-CA of 50 μg/L. Twelve 

grid wells had sulfate measured at a concentration above the 

recommended SMCL-CA threshold of 250 mg/L and nine 

of these also were above the upper SMCL-CA threshold of 

500 mg/L. Twenty-five grid wells (of 35 sampled) had TDS 

concentrations above the SMCL-CA recommended threshold 

and 10 of these wells also were above the SMCL-CA upper 

threshold (SMCL-CA threshold for TDS has a recommended 

value of 500 mg/L and an upper value of 1,000 mg/L). 

Results from the 19 understanding wells in SCI showed 

one detection of arsenic and two detections of uranium that 

were above the USEPA maximum contaminant levels (MCLUS). Two understanding wells had strontium and one understanding well had molybdenum, measured above the USEPA 

lifetime health advisory levels (HAL-US). One understanding 

well had a fluoride concentration above the MCL-CA, and 

five wells had concentrations of boron above the NL-CA. 

One understanding well had iron measured at a concentration above the SMCL-CA of 300 μg/L. One understanding 

well had sulfate measured above the recommended SMCLCA threshold of 250 mg/L and two understanding wells 

had chloride levels above the upper SMCL-CA threshold of 

500 mg/L. Twelve understanding wells (of 19 sampled) had 

TDS concentrations above the SMCL-CA recommended lower 

threshold and four of these wells also had concentrations 

above the upper threshold. Samples were collected for the 

analysis of radon-222 from five special studies wells (one grid 

well and four understanding wells) in the GIL study area, and 

all had activities of radon-222 below the proposed alternative 

MCL-US of 4,000 pCi/L.

Acknowledgments

The authors thank the following cooperators for their 

support: the State Water Resources Control Board, California 

Department of Public Health, California Department of Water 

Resources, and Lawrence Livermore National Laboratory. We 

especially thank the well owners and water purveyors for their 

generosity in allowing the USGS to collect samples from their 

wells. 

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Tables 23

Tables
24 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table 1. Identification, sampling, and construction information for wells sampled for the South Coast Interior Basins Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.—Continued

[Sampling schedule: described in table 2. Elevation of LSD: 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). GAMA well identification number: LIV, Livermore study area grid well; LIVU, 

Livermore study area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; 

CUYU, Cuyama study area understanding well. Abbreviations: ft, foot; LSD, land surface datum; na, not available]

GAMA well 

identification 

number

Sampling information Construction information

Date

sampled

Sampling 

schedule

Elevation of LSD 

(ft above 

NAVD 88)

Well type Well depth 

(ft below LSD)

Top perforation 

(ft below LSD)

Bottom 

perforation 

(ft below LSD)

SCI Grid wells

LIV-01 08-25-08 Fast 359 Production 500 200 490

LIV-02 08-25-08 Fast 316 Production 113 37 107

LIV-03 08-25-08 Fast 348 Production 650 149 650

LIV-04 08-26-08 Fast 422 Production 147 101 146

LIV-05 10-28-08 Slow 416 Production na na na

LIV-06 10-28-08 Slow 574 Production na na na

GIL-01 08-11-08 Fast + Radon 353 Production 484 157 480

GIL-02 08-12-08 Fast 193 Production 470 240 460

GIL-03 08-13-08 Fast 273 Production na na na

GIL-04 08-13-08 Fast 290 Production 500 147 500

GIL-05 08-13-08 Fast 203 Production na na na

GIL-06 08-14-08 Fast 203 Production na na na

GIL-07 08-14-08 Fast 183 Production na na na

GIL-08 08-14-08 Fast 273 Production na na na

GIL-09 08-18-08 Slow 241 Production na na na

GIL-10 08-18-08 Fast 360 Production 378 na na

GIL-11 08-19-08 Fast 174 Production na na na

GIL-12 08-19-08 Fast 155 Production 700 na na

GIL-13 08-19-08 Fast 503 Production 460 100 460

GIL-14 08-20-08 Fast 294 Production na na na

GIL-15 08-21-08 Fast 254 Production na na na

GIL-16 08-21-08 Fast 232 Production 339 282 337

GIL-17 08-21-08 Fast 317 Production na na na

CUY-01 09-15-08 Fast 1,908 Production 188 45 125

CUY-02 09-15-08 Slow 2,258 Production 790 340 790

CUY-03 09-16-08 Fast 2,756 Production na na na

CUY-04 09-17-08 Slow 2,279 Production na na na

CUY-05 09-17-08 Fast 2,194 Production na na na

CUY-06 09-17-08 Fast 2,552 Production 800 640 800

CUY-07 09-18-08 Fast 2,394 Production 695 na na

CUY-08 09-18-08 Fast 2,463 Production na na na

CUY-09 09-22-08 Slow 5,370 Production 361 80 361

CUY-10 09-23-08 Slow 5,400 Production 298 146 288

CUY-11 09-25-08 Fast 3,682 Production 357 na na

CUY-12 09-25-08 Fast 2,743 Production na na na

Table 1. Identification, sampling, and construction information for wells sampled for the South Coast Interior Basins Groundwater 

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

[Sampling schedule: described in table 2. Elevation of LSD: 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). GAMA well identification number.: LIV, Livermore study area grid well; LIVU, 

Livermore study area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; 

CUYU, Cuyama study area understanding well. Abbreviations: ft, foot; LSD, land surface datum; na, not available]
Tables 25

Table 1. Identification, sampling, and construction information for wells sampled for the South Coast Interior Basins Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.—Continued

[Sampling schedule: described in table 2. Elevation of LSD: 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). GAMA well identification number: LIV, Livermore study area grid well; LIVU, 

Livermore study area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; 

CUYU, Cuyama study area understanding well. Abbreviations: ft, foot; LSD, land surface datum; na, not available]

GAMA well 

identification 

number

Sampling information Construction information

Date

sampled

Sampling 

schedule

Elevation of LSD 

(ft above 

NAVD 88)

Well type Well depth 

(ft below LSD)

Top perforation 

(ft below LSD)

Bottom 

perforation 

(ft below LSD)

SCI Understanding wells

LIVU-01 08-26-08 Fast 328 Production 315 235 310

LIVU-02 08-27-08 Slow 345 Production 530 150 510

LIVU-03 08-27-08 Slow 338 Production 745 515 730

LIVU-04 08-28-08 Fast 381 Production 420 200 410

LIVU-05 10-29-08 Fast 325 Monitoring 35 20 35

LIVU-06 10-29-08 Fast 325 Monitoring 70 45 65

LIVU-07 10-30-08 Fast 324 Monitoring 52 42 52

LIVU-08 10-30-08 Fast 326 Monitoring 50 30 50

GILU-01 08-11-08 Fast + Radon 332 Production 420 190 420

GILU-02 08-12-08 Slow 193 Production 800 530 790

GILU-03 10-27-08 Fast + Radon 203 Monitoring 285 225 280

GILU-04 10-27-08 Fast + Radon 203 Monitoring 395 350 390

GILU-05 10-27-08 Fast + Radon 203 Monitoring 615 560 610

CUYU-01 09-22-08 Fast 4,752 Production 193 39 193

CUYU-02 09-23-08 Fast 5,196 Production 270 51 256

CUYU-03 09-24-08 Fast 5,097 Production 212 na na

CUYU-04 09-24-08 Fast 6,038 Production na na na

CUYU-05 11-17-08 Fast 4,004 Production 351 191 351

CUYU-06 11-17-08 Slow 3,578 Production 295 na na
26 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table 2. Classes of chemical consistuents and water-quality indicators (field parameters) collected for the slow and fast well sampling 

schedules in the South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to 

December 2008.

Analyte classes

Schedule Analyte list 

table

Results 

table Slow Fast

Water-quality indicators (field parameters)

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

Field alkalinity, bicarbonate, and carbonate X 4

Turbidity X 4

Organic constituents

Volatile organic compounds (VOCs) X X 3A 5

Pesticides and pesticide degradates X X 3B 6A

Polar pesticides and metabolites X 3C 6B

Pharmaceutical compounds X 3D None1

Constituents of special interest

Perchlorate X X 3E 7

N-nitrosodimethylamine (NDMA) X 3E 7

Inorganic constituents

Trace elements X X 3F 8

Nutrients X X 3G 9

Major and minor ions, silica, total dissolved solids (TDS), and laboratory 

alkalinity

X X 3H 4, 10

Arsenic, chromium, and iron speciation X 3I 11

Stable isotopes

Stable isotopes of hydrogen and oxygen in water X X 3J 12

Stable isotopes of carbon and carbon-14 abundance X X 3J 12

Radioactivity and noble gases

Tritium X X 3J 12

Gross alpha and gross beta radioactivity X 3J 13A

Radon-222 X2 3J 13B

Tritium and noble gases X X 3K None3

1

Results for pharmaceutical compounds will be published in a subsequent publication.

2

Radon-222 collected at five fast wells in the Gilroy study area as part of a special study.

3

As of the publishing date of this data report, results for the analyses of noble gases and tritium by Lawrence Livermore National Laboratory (LLNL) were not 

available for publication.
Tables 27

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

Geological Survey National Water Quality Laboratory Schedule 2020.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold level 

as of November 17, 2008. 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 level; 

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

RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. This report contains CAS Registry Numbers®, which are a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM. Abbreviations: CAS, 

Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; 

—, not detected]

Constituent Primary use 

or source

USGS

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold

Detection Type Level

(μg/L)

Acetone Solvent 81552 67-64-1 4 na na —

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

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

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

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-US 1

80 D

Bromoform (Tribromomethane) Disinfection by-product 

(THM)

32104 75-25-2 0.1 MCL-US 1

80 —

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

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

sec-Butylbenzene Gasoline hydrocarbon 77350 135-98-8 0.02 NL-CA 260 —

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

Carbon disulfide Organic synthesis 77041 75-15-0 0.04 NL-CA 160 D

Carbon tetrachloride 

(Tetrachloromethane)

Solvent 32102 56-23-5 0.06 MCL-CA 0.5 D

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

Chloroethane Solvent 34311 75-00-3 0.10 na na —

Chloroform (Trichloromethane) Disinfection by-product 

(THM)

32106 67-66-3 0.04 MCL-US 1

80 D

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

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

2-Chlorotoluene Solvent 77275 95-49-8 0.02 NL-CA 140 —

4-Chlorotoluene Solvent 77277 106-43-4 0.02 NL-CA 140 —

Dibromochloromethane Disinfection by-product 

(THM)

32105 124-48-1 0.12 MCL-US 1

80 —

1,2-Dibromo-3-chloropropane 

(DBCP)

Fumigant 82625 96-12-8 1 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 0.04 na na —

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

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

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

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

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

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

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

Geological Survey National Water Quality Laboratory Schedule 2020.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold level 

as of November 17, 2008. 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 level; 

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

RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. This report contains CAS Registry Numbers®, which are a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM. Abbreviations: CAS, 

Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; 

—, not detected]
28 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

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

Geological Survey National Water Quality Laboratory Schedule 2020.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold level 

as of November 17, 2008. 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 level; 

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

RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. This report contains CAS Registry Numbers®, which are a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM. Abbreviations: CAS, 

Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; 

—, not detected]

Constituent Primary use 

or source

USGS

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold

Detection Type Level

(μg/L)

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

1,1-Dichloroethene (1,1-DCE) Organic synthesis 34501 75-35-4 0.02 MCL-CA 6 D

cis-1,2-Dichloroethene 

(cis-1,2-DCE)

Solvent 77093 156-59-2 0.02 MCL-CA 6 —

trans-1,2-Dichloroethene 

(trans-1,2-DCE)

Solvent 34546 156-60-5 0.018 MCL-CA 10 —

1,2-Dichloropropane Fumigant 34541 78-87-5 0.02 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 0.1 RSD5-US 2

4 —

trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.10 RSD5-US 2

4 —

Diethyl ether Solvent 81576 60-29-7 0.12 na na —

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

Ethylbenzene Gasoline hydrocarbon 34371 100-41-4 0.04 MCL-CA 300 —

Ethyl tert-butyl ether (ETBE) Gasoline oxygenate 50004 637-92-3 0.04 na na —

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

o-Ethyl toluene (1-Ethyl-2-methyl 

benzene)

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

Hexachlorobutadiene Organic synthesis 39702 87-68-3 0.06 RSD5-US 9 —

Hexachloroethane Solvent 34396 67-72-1 0.14 HAL-US 1 —

2-Hexanone (n-Butyl methyl ketone) Solvent 77103 591-78-6 0.6 na na —

Iodomethane (Methyl iodide) Organic synthesis 77424 74-88-4 0.8 na na —

Isopropylbenzene Gasoline hydrocarbon 77223 98-82-8 0.04 NL-CA 770 —

4-Isopropyl-1-methyl benzene Gasoline hydrocarbon 77356 99-87-6 0.06 na na —

Methyl acrylate Organic synthesis 49991 96-33-3 0.6 na na —

Methyl acrylonitrile Organic synthesis 81593 126-98-7 0.2 na na —

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

Methyl iso-butyl ketone (MIBK) Solvent 78133 108-10-1 0.4 NL-CA 120 —

Methylene chloride 

(Dichloromethane)

Solvent 34423 75-09-2 0.04 MCL-US 5 —

Methyl ethyl ketone (2-butanone, 

MEK)

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

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

Naphthalene Gasoline hydrocarbon 34696 91-20-3 0.2 NL-CA 17 —
Tables 29

1

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

2

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

In earlier reports in this series, the NL-CA (0.005 μg/L) was used as the comparison threshold for 1,2,3-TCP.

4

The MCL-CA thresholds for m- and p-Xylene and o-Xylene is the sum all three xylene compounds.

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

Geological Survey National Water Quality Laboratory Schedule 2020.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold level 

as of November 17, 2008. 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 level; 

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

RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. This report contains CAS Registry Numbers®, which are a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM. Abbreviations: CAS, 

Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; 

—, not detected]

Constituent Primary use 

or source

USGS

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold

Detection Type Level

(μg/L)

Perchloroethene (PCE, 

Tetrachloroethene)

Solvent 34475 127-18-4 0.04 MCL-US 5 D

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 0.10 MCL-CA 1 —

Tetrahydrofuran Solvent 81607 109-99-9 1.4 na na D

1,2,3,4-Tetramethylbenzene Gasoline hydrocarbon 49999 488-23-3 0.08 na na —

1,2,3,5-Tetramethylbenzene Gasoline hydrocarbon 50000 527-53-7 0.08 na na —

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

1,2,3-Trichlorobenzene Organic synthesis 77613 87-61-6 0.06 na na —

1,2,4-Trichlorobenzene Solvent 34551 120-82-1 0.04 MCL-CA 5 —

1,1,1-Trichloroethane (1,1,1-TCA) Solvent 34506 71-55-6 0.02 MCL-CA 200 —

1,1,2-Trichloroethane (1,1,2-TCA) Solvent 34511 79-00-5 0.06 MCL-CA 5 —

Trichloroethene (TCE) Solvent 39180 79-01-6 0.02 MCL-US 5 —

Trichlorofluoromethane (CFC-11) Refrigerant 34488 75-69-4 0.08 MCL-CA 150 D

1,2,3-Trichloropropane (1,2,3-TCP) Solvent/organic 

synthesis

77443 96-18-4 0.12 HAL-US3 40 —

Trichlorotrifluoroethane (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 4

1,750 —

o-Xylene Gasoline hydrocarbon 77135 95-47-6 0.04 MCL-CA 4

1,750 —
30 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table 3B. Pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for the 

U.S. Geological Survey National Water Quality Laboratory Schedule 2003.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold level 

as of November 17, 2008. 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 level; 

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

RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; D, detected in groundwater samples (table 6A); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent

(synonym or abbreviation)

Primary use

or source

USGS

parameter 

code

CAS

number

 LRL

 (μg/L)

Threshold

Detection

Type Level

(μg/L)

Acetochlor Herbicide 49260 34256-82-1 0.01 na na —

Alachlor Herbicide 46342 15972-60-8 0.008 MCL-US 2 —

Atrazine Herbicide 39632 1912-24-9 0.007 MCL-CA 1 —

Azinphos-methyl Insecticide 82686 86-50-0 0.12 na na —(1)

Azinphos-methyl oxon Insecticide degradate 61635 961-22-8 0.042 na na —(1)

Benfluralin Herbicide 82673 1861-40-1 0.014 na na —(1)

Carbaryl Insecticide 82680 63-25-2 0.2 RSD5-US 400 —

2-Chloro-2,6-diethylacetanilide Herbicide degradate 61618 6967-29-9 0.01 na na —

4-Chloro-2-methylphenol Herbicide degradate 61633 1570-64-5 0.0050 na na —

Chlorpyrifos Insecticide 38933 2921-88-2 0.01 HAL-US 2 —

Chlorpyrifos oxon Insecticide degradate 61636 5598-15-2 0.05 na na —(1)

Cyfluthrin Insecticide 61585 68359-37-5 0.016 na na —(1)

Cypermethrin Insecticide 61586 52315-07-8 0.02 na na —(1)

Dacthal (DCPA) Herbicide 82682 1861-32-1 0.006 HAL-US 70 —

Deethylatrazine (2-Chloro-4-isopropylamino-6-amino-s-triazine)Herbicide degradate 04040 6190-65-4 0.014 na na D1

Desulfinylfipronil Insecticide degradate 62170 na 0.012 na na —

Desulfinylfipronil amide Insecticide degradate 62169 na 0.029 na na —

Diazinon Insecticide 39572 333-41-5 0.005 HAL-US 1 —

3,4-Dichloroaniline Herbicide degradate 61625 95-76-1 0.004 na na —

Dichlorvos Insecticide 38775 62-73-7 0.02 na na —(1)

Dicrotophos Insecticide 38454 141-66-2 0.08 na na —(1)

Dieldrin Insecticide 39381 60-57-1 0.009 RSD5-US 0.02 —

2,6-Diethylaniline Herbicide degradate 82660 579-66-8 0.006 na na —

Dimethoate Insecticide 82662 60-51-5 0.006 na na —(1)

Ethion Insecticide 82346 563-12-2 0.012 na na —(1)

Ethion monoxon Insecticide degradate 61644 17356-42-2 0.021 na na —(1)

2-Ethyl-6-methylaniline Herbicide degradate 61620 24549-06-2 0.0049 na na —

Fenamiphos Insecticide 61591 22224-92-6 0.029 HAL-US 0.7 —(1)

Fenamiphos sulfone Insecticide degradate 61645 31972-44-8 0.053 na na —(1)

Fenamiphos sulfoxide Insecticide degradate 61646 31972-43-7 0.08 na na —(1)

Fipronil Insecticide 62166 120068-37-3 0.04 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 —(1)

Fonofos Insecticide 04095 944-22-9 0.01 HAL-US 10 —

Hexazinone Herbicide 04025 51235-04-2 0.008 HAL-US 400 —

Iprodione Fungicide 61593 36734-19-7 0.014 na na —(1)

Isofenphos Insecticide 61594 25311-71-1 0.006 na na —

Malaoxon Insecticide degradate 61652 1634-78-2 0.08 na na —

Malathion Insecticide 39532 121-75-5 0.02 HAL-US 100 —

Metalaxyl Fungicide 61596 57837-19-1 0.0069 na na —

Methidathion Insecticide 61598 950-37-8 0.006 na na —

Metolachlor Herbicide 39415 51218-45-2 0.014 HAL-US 700 —

Metribuzin Herbicide 82630 21087-64-9 0.016 HAL-US 70 —

Myclobutanil Fungicide 61599 88671-89-0 0.01 na na —

Table 3B. Pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for the 

U.S. Geological Survey National Water Quality Laboratory Schedule 2003.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold level 

as of November 17, 2008. 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 level; 

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

RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; D, detected in groundwater samples (table 6A); na, not available; μg/L, micrograms per liter; —, not detected]
Tables 31

Table 3B. Pesticides and pesticide degradates, primary uses or sources, comparative thresholds, and reporting information for the 

U.S. Geological Survey National Water Quality Laboratory Schedule 2003.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold level 

as of November 17, 2008. 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 level; 

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

RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; D, detected in groundwater samples (table 6A); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent

(synonym or abbreviation)

Primary use

or source

USGS

parameter 

code

CAS

number

 LRL

 (μg/L)

Threshold

Detection

Type Level

(μg/L)

1-Naphthol Insecticide degradate 49295 90-15-3 0.04 na na —(1)

Paraoxon-methyl Insecticide degradate 61664 950-35-6 0.01 na na —(1)

Parathion-methyl Insecticide 82667 298-00-0 0.008 HAL-US 1 —(1)

Pendimethalin Herbicide 82683 40487-42-1 0.012 na na —

cis-Permethrin Insecticide 82687 54774-45-7 0.014 na na —(1)

Phorate Insecticide 82664 298-02-2 0.02 na na —(1)

Phorate oxon Insecticide degradate 61666 2600-69-3 0.027 na na —

Phosmet Insecticide 61601 732-11-6 0.2 na na —(1)

Phosmet oxon Insecticide degradate 61668 3735-33-9 0.0511 na na —(1)

Prometon Herbicide 04037 1610-18-0 0.012 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 0.01 MCL-US 4 D

Tebuthiuron Herbicide 82670 34014-18-1 0.02 HAL-US 500 D

Terbufos Insecticide 82675 13071-79-9 0.018 HAL-US 0.4 —(1)

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 0.045 na na —(1)

Terbuthylazine Herbicide 04022 5915-41-3 0.006 na na —

Tribufos Defoliant 61610 78-48-8 0.035 na na —(1)

Trifluralin Herbicide 82661 1582-09-8 0.012 HAL-US 10 —(1)

1

The median matrix-spike recovery was less than 70 percent. Low recoveries may indicate that the compound might not have been detected in some samples 

if it was present at very low concentrations.
32 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table 3C. Polar pesticides and metabolites, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey National Water Quality Laboratory Schedule 2060.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold and threshold values 

as of November 17, 2008. 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. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; IRL, interim reporting level; D, detected in groundwater samples (table 6B); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent Primary use 

or source

USGS

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold

Detection

Type Level

(μg/L)

Acifluorfen Herbicide 49315 50594-66-6 0.04 na na —(1)

Aldicarb Insecticide 49312 116-06-3 0.12 MCL-US 3 —(1)

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

Aldicarb sulfoxide Degradate 49314 1646-87-3 0.06 MCL-US 4 —

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

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

Benomyl Fungicide 50300 17804-35-2 0.06 na na —

Bensulfuron-methyl Herbicide 61693 83055-99-6 0.06 na na —(2)

Bentazon Herbicide 38711 25057-89-0 0.06 MCL-CA 18 D

Bromacil Herbicide 04029 314-40-9 0.02 HAL-US 70 —

Bromoxynil Herbicide 49311 1689-84-5 0.12 na na —(1)

Caffeine Beverages 50305 58-08-2 0.08 na na —

Carbaryl Herbicide 49310 63-25-2 0.04 RSD5-US 400 —

Carbofuran Herbicide 49309 1563-66-2 0.04 MCL-CA 18 —

Chloramben, methyl ester Herbicide 61188 7286-84-2 0.10 na na —

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

3-(4-Chlorophenyl)-1-methyl 

urea 

Degradate 61692 5352-88-5 0.06 na na —(1)

Clopyralid Herbicide 49305 1702-17-6 0.06 na na —(1)

Cycloate Herbicide 04031 1134-23-2 0.04 na na —

2,4-D Herbicide 39732 298-00-0 0.02 HAL-US 70 —

2,4-D methyl ester Herbicide 50470 na 0.04 na na —

2,4-D plus 2,4-D methyl ester Herbicides 66496 na 3

0.02 na na —

2,4-DB (4-(2,4-Dichlorophenoxy)butyric acid)Herbicide 38746 94-82-6 0.02 na na —(1)

DCPA (Dacthal) monoacid Degradate 49304 887-54-7 0.04 na na —

Deethylatrazine (2-Chloro-4-

isopropylamino-6-amino-striazine)

Degradate 04040 6190-65-4 0.06 na na —

Deisopropyl atrazine (2-Chloro-6-ethylamino-4-amino-striazine)Degradate 04038 1007-28-9 0.06 na na —

Dicamba Herbicide 38442 1918-00-9 0.04 HAL-US 4,000 —(1)

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

Dinoseb (Dinitrobutyl phenol) Herbicide 49301 88-85-7 0.04 MCL-CA 7 —(1)

Diphenamid Herbicide 04033 957-51-7 0.04 HAL-US 200 —

Diuron Herbicide 49300 330-54-1 0.04 HAL-US 10 —(2)

Fenuron Herbicide 49297 101-42-8 0.06 na na —

Flumetsulam Herbicide 61694 98967-40-9 0.06 na na —(2)

Fluometuron Herbicide 38811 2164-17-2 0.04 HAL-US 90 —

Hydroxyatrazine (2-Hydroxy4-isopropylamino-6-ethylamino-s-triazine)Degradate 50355 2163-68-0 0.06 na na —

3-Hydroxycarbofuran Degradate 49308 16655-82-6 0.04 na na —

Imazaquin Herbicide 50356 81335-37-7 0.06 na na —(2)

Imazethapyr Herbicide 50407 81335-77-5 0.06 na na —

Table 3C. Polar pesticides and metabolites, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey National Water Quality Laboratory Schedule 2060.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold and threshold values 

as of November 17, 2008. 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. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; IRL, interim reporting level; D, detected in groundwater samples (table 6B); na, not available; μg/L, micrograms per liter; —, not detected]
Tables 33

Table 3C. Polar pesticides and metabolites, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey National Water Quality Laboratory Schedule 2060.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold and threshold values 

as of November 17, 2008. 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. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; IRL, interim reporting level; D, detected in groundwater samples (table 6B); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent Primary use 

or source

USGS

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold

Detection

Type Level

(μg/L)

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 0.04 HAL-US 30 —

MCPB (4-(2-Methyl-4-chlorophenoxy) butyric acid)Herbicide 38487 94-81-5 0.2 na na —(1)

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 0.12 HAL-US 200 —

Metsulfuron methyl Herbicide 61697 74223-64-6 10.14 na na —

Neburon Herbicide 49294 555-37-3 0.02 na na —

Nicosulfuron Herbicide 50364 111991-09-4 0.10 na na — (2)

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 0.12 MCL-CA 50 —

Picloram Herbicide 49291 1918-02-01 0.12 MCL-US 500 —(1)

Propham Herbicide 49236 122-42-9 0.04 HAL-US 100 —

Propiconazole Fungicide 50471 60207-90-1 0.04 na na —

Propoxur Insecticide 38538 114-26-1 0.06 na na —

Siduron Herbicide 38548 1982-49-6 0.04 na na —

Sulfometuron-methyl Herbicide 50337 74222-97-2 0.06 na na —(2)

Tebuthiuron Herbicide 82670 34014-18-1 0.06 HAL-US 500 —

Terbacil Herbicide 04032 5902-51-2 0.04 HAL-US 90 —

Triclopyr Herbicide 49235 55335-06-3 0.08 na na —

1

Value is an IRL rather than an LRL.

2

The median matrix-spike recovery was less than 70 percent. Low recoveries may indicate that the compound might not have been detected in some samples 

if it was present at very low concentrations.

3

The median laboratory matrix-spike recovery was greater than 130 percent. High recoveries may indicate that reported values could be higher than what is in 

the sample.
34 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Constituent Primary use 

or source

USGS

parameter 

code

CAS 

number

 MDL

 (μg/L)

Threshold

Type Level

(μg/L)

1,7-Dimethylxanthine Caffeine metabolite 62030 611-59-6 0.10 na na

Acetaminophen Analgesic 62000 103-90-2 0.60 na na

Albuterol Anti-inflammatory; bronchodilator 62020 18559-94-9 0.03 na na

Caffeine Stimulant 50305 58-08-2 0.40 na na

Carbamazapine Anticonvulsant; analgesic; mood 

stabilizer

62793 298-46-4 0.02 na na

Codeine Opiod narcotic 62003 76-57-3 0.02 na na

Cotinine Nicotine metabolite 62005 486-56-6 0.03 na na

Dehydronifedipine Antianginal metabolite 62004 67035-22-7 0.03 na na

Diltiazem Antianginal; antihypertensive 62008 42399-41-7 0.02 na na

Diphenhydramine Antihistamine 62796 58-73-1 0.03 na na

Sulfamethoxazole Antibacterial, antiprotozoal 62021 723-46-6 0.05 na na

Thiabendazole Anthelmintic 62801 148-79-8 0.02 na na

Trimethoprim Antibacterial 62023 738-70-5 0.01 na na

Warfarin Anticoagulant 62024 81-81-2 0.03 na na

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 MRL 

(μg/L)

Threshold

Detection

Type Level 

(μg/L)

Perchlorate Rocket fuel, fireworks, flares

63790 14797-73-0 0.10 MCL-CA 6 D

N-nitrosodimethylamine 

(NDMA)

Disinfection byproduct

34438 62-75-9 0.0020 NL-CA 0.010 —

Table 3E. Constituents of special interest (perchlorate and N-nitrosodimethylamine [NDMA]), primary uses or sources, comparative 

thresholds, and reporting information for Weck Laboratories, Inc. analyses.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold level 

as of November 17, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; NL-CA, California Department 

of Public Health notification level. Abbreviations: CAS, Chemical Abstract Service; MRL, minimum reporting level; D, detected in groundwater samples 

(table 7); μg/L, micrograms per liter; —, not detected]

Table 3D. Pharmaceutical compounds, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey National Water Quality Laboratory Schedule 2080.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. The California Groundwater Ambient Monitoring and Assessment (GAMA) program uses more conservative reporting limits for the pharmaceutical compounds than recommended by the USGS 

National Water Quality Laboratory. For albuterol, carbamazepine, codeine, dehydronifedipine, diltiazem, sulfamethoxazole, thiabendazole, trimethoprim, and 

warfarin, the MDL corresponds to the long-term method detection limit determined by the USGS Branch of Quality Systems in October 2007 (BQS LT-MDL). 

For acetaminophen, caffeine, cotinine, diphenhydramine, and xanthine, the MDL corresponds to the study reporting levels determined from assessment of 

quality-control data associated with GAMA samples collected from May 2004 through September 2007 (GAMA SRL). The GAMA SRLs are higher than the 

BQS LT-MDL for those compounds. Detections reported by the USGS National Water Quality Laboratory with concentrations lower than the BQS LT-MDL or 

GAMA SRL are reported as non-detections by the GAMA program. Results for pharmaceutical compounds from the GAMA SCI study unit will be included in a 

subsequent report. Abbreviations: CAS, Chemical Abstract Service; MDL, method detection limit; μg/L, micrograms per liter; na, not available]
Tables    35

Constituent

USGS

parameter

code

CAS

number

LRL/SRL

(μg/L)

Threshold

Detection

Type Level

(μg/L)

Aluminum 01106 7429-90-5 4 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.04 MCL-US 6 D

Arsenic 01000 7440-38-2 0.06 MCL-US 10 D

Barium 01005 7440-39-3 0.4 MCL-CA 1,000 D

Beryllium 01010 7440-41-7 0.02 MCL-US 4 D

Boron 01020 7440-42-8 4 NL-CA 1,000 D

Cadmium 01025 7440-43-9 0.02 MCL-US 5 D

Chromium 01030 7440-47-3 0.12 MCL-CA 50 D

Cobalt 01035 7440-48-4 0.02 na na D

Copper 01040 7440-50-8 1 AL-US 1,300 D

Iron 01046 7439-89-6 4 SMCL-CA 300 D

Lead 01049 7439-92-1 0.06 AL-US 15 D

Lithium 01130 7439-93-2 1 na na D

Manganese 01056 7439-96-5 0.2 SMCL-CA 50 D

Molybdenum 01060 7439-98-7 0.02 HAL-US 40 D

Nickel 01065 7440-02-0 0.12 MCL-CA 100 D

Selenium 01145 7782-49-2 0.06 MCL-US 50 D

Silver 01075 7440-22-4 0.008 SMCL-CA 100 D

Strontium 01080 7440-24-6 0.8 HAL-US 4,000 D

Thallium 01057 7440-28-0 0.04 MCL-US 2 —

Tungsten 01155 7440-33-7 0.02 na na D

Uranium 22703 7440-61-1 0.006 MCL-US 30 D

Vanadium 01085 7440-62-2 0.16 NL-CA 50 D

Zinc 01090 7440-66-6 2 SMCL-CA1 5,000 D

1

The secondary maximum contaminant level for zinc is listed as SMCL-CA since SMCLs established by California 

Department of Public Health are used in this report for all constituents that have SMCL-CA values.

Table 3F.  Trace elements, comparative thresholds, and reporting information for the U.S. Geological

Survey National Water Quality Laboratory Schedule 1948.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold level as of November 17, 2008. 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. AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

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

Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum 

contaminant level. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; SRL, study reporting 

limit; D, detected in groundwater samples (table 8); na, not available; μg/L, micrograms per liter; —, not detected]
36 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Constituent

USGS

parameter 

code

CAS 

number

 LRL

 (mg/L)

Threshold

Detection

Type Level

(mg/L)

Ammonia (as nitrogen) 00608 7664-41-7 0.02 HAL-US 124.7 D

Nitrate plus nitrite (as nitrogen) 00631 na 0.04 MCL-US 10 D

Nitrite (as nitrogen) 00613 14797-65-0 0.002 MCL-US 1 D

Total nitrogen (ammonia, nitrite, nitrate, organic 

nitrogen)

62854 17778-88-0 0.06 na na D

Phosphate, orthophosphate (as phosphorus) 00671 14265-44-2 0.006 na na D

1

The HAL-US is 30 mg/L “as ammonia.” To facilitate comparson to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L “as 

nitrogen.”

Constituent

USGS

parameter 

code

CAS 

number

 LRL

 (mg/L)

Threshold

Detection

Type Level

(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 1

250 (500) D

Fluoride 00950 16984-48-8 0.08 MCL-CA 2 D

Iodide 71865 7553-56-2 0.002 na na D

Magnesium 00925 7439-95-4 0.012 na na D

Potassium 00935 7440-09-7 0.06 na na D

Silica (as SiO2

) 00955 7631-86-9 0.02 na na D

Sodium 00930 7440-23-5 0.12 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 1

500 (1,000) D

Laboratory alkalinity (as CaCO3

)2 29801 na 1 na na D

1

 The recommended SMCL-CA thresholds for chloride, sulfate, and TDS are listed with the upper SMCL-CA thresholds in parentheses.

2

 Laboratory alkalinity results are presented in table 4.

Table 3H. Major and minor ions, silica, total dissolved solids (TDS), and alkalinity, comparative thresholds, and reporting information 

for the U.S. Geological Survey National Water Quality Laboratory Schedule 1948.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold 

level as of November 17, 2008. 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; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Abbreviations: CAS, Chemical Abstract Service; 

LRL, laboratory reporting level; D, detected in groundwater samples (table10); na, not available; mg/L, milligrams per liter]

Table 3G. Nutrients, comparative thresholds, and reporting information for the U.S. Geological Survey National Water Quality 

Laboratory Schedule 2755.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold 

level as of November 17, 2008. 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 level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; D, detected in groundwater samples (table 9); na, not available; mg/L, milligrams per liter]
Tables 37

Constituent

USGS

parameter 

code

CAS 

number

MDL

 (μg/L)

Threshold

Detection

Type Level

(μg/L)

Arsenic(III) 99034 22569-72-8 1 na na D

Arsenic (total) 99033 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 SMCL-US 300 D

Table 3I. Arsenic, chromium, and iron species, comparative thresholds, and reporting information for the U.S. Geological 

Survey Trace Metal Laboratory, Boulder, Colorado, analyses.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and 

threshold level as of November 17, 2008. 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; SMCL-US, U.S. 

Environmental Protection Agency secondary maximum contaminant level. Abbreviations: CAS, Chemical Abstract Service; MDL, method detection limit; na, not available; μg/L, micrograms per liter; D, detected in groundwater samples (table 11)]

Constituent

USGS

parameter 

code

CAS 

number

Reporting 

level type

Reporting 

level or uncertainty

Threshold

Detection

Type Level

Stable isotope ratios (per mil)

δ2

H of water 1 82082 na MU 2 na na D

δ18O of water 1 82085 na MU 0.20 na na D

δ13C of dissolved carbonates2 82081 na 1 sigma 0.05 na na D

Radioactive constituents (percent modern)

Carbon-142 49933 14762-75-5 1 sigma 0.0015 na na D

Radioactive constituens (pCi/L)

Radon-2223 82303, 14859-67-7 na 2SCU Prop. MCL-US 4,000 D

Tritium4 07000 10028-17-8 MRL 1 MCL-CA 20,000 D

Gross alpha radioactivity, 72-hour 

and 30-day counts5

62636, 

62639

12587-46-1 ssLC CSU MCL-US 15 D

Gross beta radioactivity, 72-hour 

and 30-day counts5

62642, 

62645

12587-47-2 ssLC CSU MCL-CA 50 D

1

U.S. Geological Survey Stable Isotope Laboratory, Reston, Virginia.

2

Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) (contract laboratory). 3

U.S. Geological Survey National Water Quality Laboratory.

4

U.S. Geological Survey Stable Isotope and Tritium Laboratory, Menlo Park, California.

5

Eberline Analytical Services (contract laboratory).

Table 3J. Isotopic and radioactive constituents, comparative thresholds, and reporting information for laboratory analyses.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Stable isotope ratios are reported 

in the standard delta notation (δ), the ratio of a heavier isotope to a more common lighter isotope of that element, relative to a standard reference material. 

Threshold type and threshold level as of November 17, 2008. Threshold type: Maximum contaminant level thresholds are listed as MCL-US when the MCLUS 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; ssLC, sample-specific critical level; MRL, minimum reporting level; MU, method uncertainty; na, not 

available; pCi/L, picocuries per liter; 2SCU, 2-sigma combined uncertainty; D, detected in groundwater samples (tables 12 and 13]
38 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Constituent

USGS

parameter 

code

CAS 

number

MU

(percent)

Reporting

units

Threshold

Detection

Type Level

(pCi/L)

Helium-3/Helium-4 61040 na/7440-59-7 0.75 atom ratio na na na

Argon 85563 7440-37-1 2 cm3

 STP/g na na na

Helium-4 85561 7440-59-7 2 cm3

 STP/g na na na

Krypton 85565 7439-90-9 2 cm3

 STP/g na na na

Neon 61046 7440-01-09 2 cm3

 STP/g na na na

Xenon 85567 7440-63-3 2 cm3

 STP/g na na na

Tritium 07000 10028-17-8 1 pCi/L MCL-CA 20,000 na

Table 3K. Noble gases and tritium, comparison thresholds, and reporting information for the Lawrence Livermore National Laboratory 

analyses.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Threshold type and threshold 

values as of November 17, 2008. 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. Abbreviations: CAS, Chemical Abstract Service; MU, method uncertainty; na, not available; cm3

 STP/g, cubic centimeters of gas at standard 

temperature and pressure per gram of water; pCi/L, picocuries per liter]
Tables 39

GAMA well 

identification 

number

Turbidity,

field 

(NTU) 

(63676)

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

pH

(standard units)

Water 

temperature,

field 

(°C) 

(00010)

Specific conductance

(μS/cm at 25°C)

Alkalinity

(mg/L as CaCO3

) Bicarbonate,

field

(63786)

Bicarbonate

Carbonate,

field

(63788)

Carbonate Lab 

(00403)

Field

(00400)

Lab 

(90095)

Field 

(00095)

Lab 

(29801)

Field 

(29802)

Threshold type na na SMCL-US SMCL-US na SMCL-CA SMCL-CA na na na na na na

Threshold level na na <6.5–8.5> <6.50–8.5> na 1 900 (1,600) 1 900 (1,600) na na na na na na

[LRL] [0.1] [0.2] [0–14] [0–14] [0.0–38.5] [5] [5] [1] [1] [1] [1] [1] [1]

SCI Grid wells (35 wells sampled)

LIV-01 1.1 3.5 7.5 7.2 17.6 683 654 224 nc nc 272 nc <1

LIV-02 nc 0.2 7.3 6.9 18.5 *1,270 *1,180 390 nc nc 475 nc <1

LIV-03 nc 4.0 7.4 7.0 18.5 *953 873 325 nc nc 396 nc <1

LIV-04 nc 4.5 7.7 7.4 19.5 *905 862 311 nc nc 378 nc <1

LIV-05 nc 5.1 7.8 7.7 21.0 726 715 281 268 327 341 <1 1.0

LIV-06 nc 5.3 7.3 7.1 18.0 *1,560 *1,590 375 362 441 457 <1 <1

GIL-01 0.2 3.7 7.6 7.3 21.0 534 510 185 nc nc 225 nc <1

GIL-02 1.1 4.6 7.6 7.3 19.5 587 531 208 nc nc 253 nc <1

GIL-03 0.1 5.9 7.5 7.2 17.5 **3,320 **3,230 582 nc nc 708 nc 1.0

GIL-04 0.8 0.7 8.0 7.8 24.0 *1,080 *1,070 242 nc nc 292 nc 1.3

GIL-05 0.2 2.4 7.2 7.0 17.0 *968 869 338 nc nc 412 nc <1

GIL-06 0.4 <0.2 7.5 7.2 18.5 755 734 266 nc nc 324 nc <1

GIL-07 0.7 5.6 7.2 6.7 17.0 518 469 176 nc nc 214 nc <1

GIL-08 0.4 2.3 7.3 7.1 18.0 454 453 187 nc nc 228 nc <1

GIL-09 0.2 2.0 7.4 7.1 18.0 477 467 188 182 221 229 <1 <1

GIL-10 nc 5.8 7.5 7.1 19.5 *1,110 *1,060 252 nc nc 307 nc <1

GIL-11 nc 5.4 7.3 6.9 18.0 *1,010 *980 270 nc nc 329 nc <1

GIL-12 nc <0.2 8.0 7.8 22.0 595 596 223 nc nc 269 nc 1.2

GIL-13 nc 0.2 7.4 7.2 19.0 *1,340 *1,350 384 nc nc 467 nc <1

GIL-14 nc <0.2 7.9 7.8 23.0 **1,960 **1,890 403 nc nc 488 nc 1.8

GIL-15 nc <0.2 7.3 7.0 20.5 **1,820 **1,820 542 nc nc 660 nc <1

GIL-16 nc 1.1 7.8 7.5 21.0 *1,150 *1,150 294 nc nc 357 nc 1.0

GIL-17 nc 4.7 7.7 7.5 20.5 *1,130 *1,100 266 nc nc 323 nc <1

CUY-01 nc 3.8 7.5 7.3 22.0 *1,260 *1,270 220 nc nc 268 nc <1

CUY-02 nc 1.3 7.7 7.5 26.0 *1,320 *1,320 153 148 179 186 <1 <1

CUY-03 nc 8.8 7.4 7.2 15.5 **1,960 **1,910 181 nc nc 220 nc <1

CUY-04 nc 6.2 7.4 7.2 17.5 **2,080 **2,080 148 nc nc 180 nc <1

CUY-05 nc 1.8 7.3 7.3 21.5 **2,070 **2,070 133 nc nc 162 nc <1

CUY-06 nc 5.6 7.4 7.2 17.0 **1,810 **1,810 145 nc nc 176 nc <1

CUY-07 nc 9.4 7.5 7.2 17.0 **2,360 **2,380 129 nc nc 157 nc <1

CUY-08 nc 10 7.5 7.2 16.5 *1,470 *1,480 157 nc nc 191 nc <1

CUY-09 0.4 1.4 7.9 7.6 16.0 636 637 182 172 209 220 <1 <1

CUY-10 0.3 1.9 7.4 7.2 15.0 *973 *965 338 314 382 411 <1 <1

CUY-11 nc 3.4 7.5 7.3 16.0 836 829 174 nc nc 212 nc <1

CUY-12 nc 6.7 7.4 7.2 16.5 **1,920 **1,870 171 nc nc 208 nc <1

Table 4. Water-quality indicators (field parameters) in samples collected for the South Coast Interior Basins Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, August to December 2008.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

GAMA identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; 

GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. Threshold type: SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, 

California Department of Public Health secondary maximum contaminant level. Bicarbonate and carbonate concentrations were calculated from the field and 

laboratory alkalinity and pH values using the advanced speciation method (http://or.water.usgs.gov/alk/methods.html) with pK1 = 6.35, pK2 = 10.33, and 

pKW = 14. Abbreviations: C, Celsius; E, estimated or having a higher degree of uncertainty; mg/L, milligrams per liter; nc, not collected; na, not available; 

NTU, nephelometric turbidity unit; RL, reporting limit or range; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; 

*, value above threshold level; **, value above upper threshold level]
40 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

GAMA well 

identification 

number

Turbidity,

field 

(NTU) 

(63676)

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

pH

(standard units)

Water 

temperature,

field 

(°C) 

(00010)

Specific conductance

(μS/cm at 25°C)

Alkalinity

(mg/L as CaCO3

) Bicarbonate,

field

(63786)

Bicarbonate

Carbonate,

field

(63788)

Carbonate Lab 

(00403)

Field

(00400)

Lab 

(90095)

Field 

(00095)

Lab 

(29801)

Field 

(29802)

Threshold type na na SMCL-US SMCL-US na SMCL-CA SMCL-CA na na na na na na

Threshold level na na <6.5–8.5> <6.50–8.5> na 1 900 (1,600) 1 900 (1,600) na na na na na na

[LRL] [0.1] [0.2] [0–14] [0–14] [0.0–38.5] [5] [5] [1] [1] [1] [1] [1] [1]

SCI Understanding wells (19 wells sampled)

LIVU-01 0.8 5.0 7.7 7.2 17.5 793 755 286 nc nc 347 nc <1

LIVU-02 6.9 3.8 7.6 7.2 17.5 *1,180 *1,160 355 340 414 431 <1 <1

LIVU-03 0.4 3.2 7.7 7.4 21.0 *1,200 *1,180 374 356 434 454 <1 1.0

LIVU-04 3.2 5.1 7.5 7.2 23.0 677 647 214 nc nc 260 nc <1

LIVU-05 nc 4.7 7.0 6.8 20.5 **E34,800 **40,300 680 nc nc 829 <1 <1

LIVU-06 nc 0.6 7.0 6.9 18.0 **E17,900 **17,800 310 nc nc 378 <1 <1

LIVU-07 nc 0.3 7.0 6.8 20.0 **2,970 **2,980 819 nc nc 998 nc <1

LIVU-08 nc 0.3 7.3 7.1 19.5 **2,690 **2,690 830 nc nc 1,011 nc <1

GILU-01 0.1 5.3 6.8 7.0 19.5 500 473 146 nc nc 178 nc <1

GILU-02 0.7 1.5 7.8 7.6 23.5 533 533 191 183 222 232 <1 <1

GILU-03 nc 3.4 7.5 7.3 19.0 524 526 193 nc nc 235 nc <1

GILU-04 nc 4.1 7.5 7.4 20.0 502 505 181 nc nc 220 nc <1

GILU-05 nc <0.2 8.0 7.9 22.0 539 546 204 nc nc 247 nc 1.1

CUYU-01 nc 4.5 7.6 7.3 14.5 *1,160 *1,150 352 nc nc 428 nc <1

CUYU-02 0.3 6.4 7.3 7.1 11.0 *964 *953 413 nc nc 503 nc <1

CUYU-03 nc 5.2 7.5 7.2 12.5 *1,340 *1,290 382 nc nc 465 nc <1

CUYU-04 nc 2.5 7.5 7.2 13.0 575 567 291 nc nc 354 nc <1

CUYU-05 nc 6.3 7.7 7.4 15.5 903 890 283 nc nc 344 nc <1

CUYU-06 2.0 6.3 7.6 7.4 17.0 911 891 297 287 348 361 <1 <1

1

The SMCL-CA for specific conductance has recommended and upper threshold values. The upper value is shown in parentheses.

Table 4. Water-quality indicators (field parameters) in samples collected for the South Coast Interior Basins Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, August to December 2008.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

GAMA identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; 

GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. Threshold type: SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, 

California Department of Public Health secondary maximum contaminant level. Bicarbonate and carbonate concentrations were calculated from the field and 

laboratory alkalinity and pH values using the advanced speciation method (http://or.water.usgs.gov/alk/methods.html) with pK1 = 6.35, pK2 = 10.33, and 

pKW = 14. Abbreviations: C, Celsius; E, estimated or having a higher degree of uncertainty; mg/L, milligrams per liter; nc, not collected; na, not available; 

NTU, nephelometric turbidity unit; RL, reporting limit or range; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; 

*, value above threshold level; **, value above upper threshold level]
Tables 41

 GAMA well 

identification 

number

Trihalomethane Refrigerant Solvent Organic 

synthesis Solvent

Chloroform 

(Trichloromethane) 

(μg/L) 

(32106)

Dichlorodifluoromethane 

(CFC-12) 

(μg/L) 

(34668)

Perchloroethene 

(PCE, Tetrachloroethene) 

(μg/L) 

(34475)

1,1-Dichloroethene 

(1,1-DCE) 

(μg/L) 

(34501)

Carbon 

disulfide 

(μg/L) 

(77041)

Carbon tetra

chloride 

(Tetrachloromethane) 

(μg/L) 

(32102)

Tetrahydrofuran 

(μg/L) 

(81607)

Threshold type MCL-US NL-CA MCL-US MCL-CA HAL-US MCL-CA na

Threshold level 1 80 1,000 5 6 4,000 0.5 na

[LRL] [0.04] [0.1] [0.04] [0.02] [1.6] [0.06] [1.4]

SCI Grid wells (35 wells sampled)

Number of wells with 

detections

4 2 1 1 1 1 1

Detection frequency 

(percent)

11.4 5.7 2.9 2.9 2.9 2.9 2.9

Total Detections

SCI Livermore study area (6 grid wells sampled)

LIV-02 — — — — E1.5 — 2

LIV-03 0.15 — — — — — —

LIV-04 0.10 E0.17 — — — E0.05 —

LIV-06 0.24 — E0.03 E0.02 — — —

Number of wells with 

detections

3 1 1 1 1 1 1

Detection frequency 

(percent)

50.0 16.7 16.7 16.7 16.7 16.7 16.7

Total Detections

SCI Gilroy study area (17 grid wells sampled)

GIL-02 — E0.10 — — — — —

GIL-05 — — — — — — —

GIL-09 — — — — — — —

Number of wells with 

detections

0 1 0 0 0 0 0

Detection frequency 

(percent)

0 5.8 0 0 0 0 0

Total Detections

SCI Cuyama study area (12 grid wells sampled)

CUY-09 V0.04 — — — — — —

CUY-10 E0.06 — — — — — —

Number of wells with 

detections

1 0 0 0 0 0 0

Detection frequency 

(percent)

8.3 0 0 0 0 0 0

Total Detections

Table 5. Volatile organic compounds (VOCs) detected in samples collected for the South Coast Interior Basins Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, August to December 2008.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were analyzed, but only samples with detections are listed. Analytes are listed in order of decreasing detection frequency in the 35 grid 

wells. All analytes are listed in table 3A. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding 

well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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 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. Abbreviations: E, estimated or having 

a higher degree of uncertainty; LRL, laboratory reporting level; V, analyte detected in sample and an associated blank, thus data are not included in groundwater 

quality assessment; μg/L, microgram per liter; na, not available; –, not detected]
42 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

 GAMA well 

identification 

number

Trihalomethane Refrigerant Solvent Organic 

synthesis Solvent

Chloroform 

(Trichloromethane) 

(μg/L) 

(32106)

Dichlorodifluoromethane 

(CFC-12) 

(μg/L) 

(34668)

Perchloroethene 

(PCE, Tetrachloroethene) 

(μg/L) 

(34475)

1,1-Dichloroethene 

(1,1-DCE) 

(μg/L) 

(34501)

Carbon 

disulfide 

(μg/L) 

(77041)

Carbon tetra

chloride 

(Tetrachloromethane) 

(μg/L) 

(32102)

Tetrahydrofuran 

(μg/L) 

(81607)

Threshold type MCL-US NL-CA MCL-US MCL-CA HAL-US MCL-CA na

Threshold level 1 80 1,000 5 6 4,000 0.5 na

[LRL] [0.04] [0.1] [0.04] [0.02] [1.6] [0.06] [1.4]

SCI Understanding wells2

 (19 wells sampled)

LIVU-01 V0.04 — — — — — —

LIVU-02 E0.09 — — — — — —

LIVU-03 0.14 — — — — — —

LIVU-06 V0.03 — — — — — —

LIVU-07 — — — — — — —

GILU-02 — E0.14 — — — — —

CUYU-04 — — E0.06 — — — —

CUYU-05 V0.01 — E0.04 — — — —

CUYU-06 — — E0.02 — — — —

Table 5. Volatile organic compounds (VOCs) detected in samples collected for the South Coast Interior Basins Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, August to December 2008.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were analyzed, but only samples with detections are listed. Analytes are listed in order of decreasing detection frequency in the 35 grid 

wells. All analytes are listed in table 3A. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding 

well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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 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. Abbreviations: E, estimated or having 

a higher degree of uncertainty; LRL, laboratory reporting level; V, analyte detected in sample and an associated blank, thus data are not included in groundwater 

quality assessment; μg/L, microgram per liter; na, not available; –, not detected]
Tables 43

 GAMA well

identification 

number

Gasoline Refrigerant Gasoline Trihalomethane

Organic

synthesis Gasoline

Detections 

per well

Any 

Toluene VOC

(μg/L) 

(34010)

Trichlorofluoromethane 

(CFC-11) 

(μg/L) 

(34488)

Benzene 

(μg/L) 

(34030)

Bromodichloromethane 

(μg/L) 

(32101)

Carbon 

disulfide 

(μg/L) 

(77041)

Methyl 

tert-butyl 

ether 

(MTBE) 

(μg/L) 

(78032)

Threshold type MCL-CA MCL-CA MCL-CA MCL-US NL-CA MCL-CA

Threshold level 150 150 1 1

 80 160 13

[LRL] [0.018] [0.08] [0.016] [0.04] [0.04] [0.10]

SCI Grid wells (35 wells sampled)

Number of wells with 

detections

1 1 0 0 0 0 8

Detection frequency 

(percent)

2.9 2.9 0 0 0 0 23

Total Detections 13

SCI Livermore study area (6 grid wells sampled)

LIV-02 — — — — — — 2

LIV-03 — — — — — — 1

LIV-04 — — — — — — 3

LIV-06 — — — — — — 3

Number of wells with 

detections

0 0 0 0 0 0 4

Detection frequency 

(percent)

0 0 0 0 0 0 67

Total Detections 9

SCI Gilroy study area (17 grid wells sampled)

GIL-02 — — — — — — 1

GIL-05 E0.04 — — — — — 1

GIL-09 — E0.07 — — — — 1

Number of wells with 

detections

1 1 0 0 0 0 3

Detection frequency 

(percent)

5.8 5.8 0 0 0 0 18

Total Detections 3

SCI Cuyama study area (12 grid wells sampled)

CUY-09 — — — — — — 0

CUY-10 — — — — — — 1

Number of wells with 

detections

0 0 0 0 0 0 1

Detection frequency 

(percent)

0 0 0 0 0 0 8

Total Detections 1

Table 5. Volatile organic compounds (VOCs) detected in samples collected for the South Coast Interior Basins Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, August to December 2008.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were analyzed, but only samples with detections are listed. Analytes are listed in order of decreasing detection frequency in the 35 grid 

wells. All analytes are listed in table 3A. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding 

well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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 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. Abbreviations: E, estimated or having 

a higher degree of uncertainty; LRL, laboratory reporting level; V, analyte detected in sample and an associated blank, thus data are not included in groundwater 

quality assessment; μg/L, microgram per liter; na, not available; –, not detected]
44 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

 GAMA well

identification 

number

Gasoline Refrigerant Gasoline Trihalomethane

Organic

synthesis Gasoline

Detections 

per well

Any 

Toluene VOC

(μg/L) 

(34010)

Trichlorofluoromethane 

(CFC-11) 

(μg/L) 

(34488)

Benzene 

(μg/L) 

(34030)

Bromodichloromethane 

(μg/L) 

(32101)

Carbon 

disulfide 

(μg/L) 

(77041)

Methyl 

tert-butyl 

ether 

(MTBE) 

(μg/L) 

(78032)

Threshold type MCL-CA MCL-CA MCL-CA MCL-US NL-CA MCL-CA

Threshold level 150 150 1 1

 80 160 13

[LRL] [0.018] [0.08] [0.016] [0.04] [0.04] [0.10]

SCI Understanding wells2

 19 wells sampled)

LIVU-01 — — — — — — 0

LIVU-02 — — — E0.07 — — 2

LIVU-03 — — — — — — 1

LIVU-06 — — E0.02 — E0.02 — 2

LIVU-07 — — — — — 0.1 1

GILU-02 — — — — — — 1

CUYU-04 — — — — — — 1

CUYU-05 — — — — — — 1

CUYU-06 — — — — — 0.4 2

1

 The MCL-US threshold for trihalomethanes is for the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.

2

 Understanding wells were not included in statistical calculations.

Table 5. Volatile organic compounds (VOCs) detected in samples collected for the South Coast Interior Basins Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, August to December 2008.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were analyzed, but only samples with detections are listed. Analytes are listed in order of decreasing detection frequency in the 35 grid 

wells. All analytes are listed in table 3A. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding 

well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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 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. Abbreviations: E, estimated or having 

a higher degree of uncertainty; LRL, laboratory reporting level; V, analyte detected in sample and an associated blank, thus data are not included in groundwater 

quality assessment; μg/L, microgram per liter; na, not available; –, not detected]
Tables 45

GAMA well

identification 

number

Simazine 

(μg/L) 

(04035)

Deethylatrazine

(2-Chloro-4-

isopropylamino6-amino-striazine) 

(μg/L) 

(04040)

Prometon

(μg/L) 

(04037)

Tebuthiuron

(μg/L) 

(82670)

Atrazine 

(μg/L) 

(39632)

Pesticide 

detections 

per well

Any 

pesticide

Threshold type MCL-US na HAL-US HAL-US MCL-CA

Threshold level 4 na 100 500 1

[LRL] [0.01] [0.014] [0.012] [0.02] [0.007]

SCI grid wells (35 grid wells sampled)

Number of wells with 

detections

7 2 2 1 0 8

Detection frequency 

(percent)

20.0 5.7 5.7 2.9 0 23

Total Detections 12

SCI Livermore study area (6 grid wells sampled)

LIV-02 E0.005 — E0.005 E0.03 V0.007 3

LIV-03 E0.006 E0.005 — — V0.006 2

LIV-06 E0.009 — 0.021 — — 2

Number of wells with 

detections

3 1 2 1 0 3

Detection frequency 

(percent)

50.0 16.7 33.3 16.7 0 50

Total Detections 7

SCI Gilroy study area (17 grid wells sampled)

GIL-03 — E0.008 — — — 1

GIL-05 E0.006 — — — — 1

GIL-07 E0.005 — — — — 1

GIL-08 E0.005 — — — — 1

GIL-13 E0.006 — — — — 1

Number of wells with 

detections

4 1 0 0 0 5

Detection frequency 

(percent)

23.5 5.9 0 0 0 29

Total Detections 5

SCI Understanding wells1 (19 wells sampled)

LIVU-04 E0.006 — — — — 1

CUYU-05 E0.005 E0.006 — — — 2

CUYU-06 0.014 E0.011 — — V0.008 2

1

 Understanding wells were not included in statistical calculations.

Table 6A. Pesticides and pesticide degradates detected in samples collected for the South Coast Interior Basins 

Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, August to December 2008.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or 

property. Samples from all 54 wells were analyzed, but only samples with detections are listed. Analytes are listed in order of decreasing detection frequency in the 35 grid wells. All analytes are listed in table 3B. GAMA well identification number: LIV, Livermore study area grid well; 

LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUYU, Cuyama 

study area understanding well. Threshold type and threshold level as of November 17, 2008. 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 level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA; California Department of Public Health maximum contaminant level. Abbreviations: E, 

estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; V, analyte detected in sample and an associated blank, thus 

data are not included in groundwater quality assessment; μg/L, microgram per liter; na, not available; —, not detected]
46 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

GAMA well

identification 

number

Bentazon

(μg/L) 

(38711)

Threshold type MCL-CA

Threshold level 18

[LRL] [0.06]

SCI slow wells (11 wells sampled)

LIV-06 0.11

Table 6B. Polar pesticides and metabolites detected in samples 

collected for the South Coast Interior Basins Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, 

August to December 2008.

[The five-digit U.S. Geological Survey (USGS) parameter code below the 

constituent name is used to uniquely identify a specific constituent or property. 

Samples from the 11 slow wells were analyzed, but only the sample with a 

detection is listed. All analytes are listed in table 3C. GAMA well identification number: LIV, Livermore study area grid well. Threshold type 

and threshold level as of November 17, 2008. 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. Abbreviations: LRL, laboratory reporting level; μg/L, microgram per liter]
Tables 47

GAMA well

identification 

number

Perchlorate 

(μg/L)

(63790) 

N-nitrosodimethylamine

(NMDA)

(ug/L)

(34438)

Threshold type MCL-CA NL-CA

Threshold level 6 0.010

[MRL] [0.10] [0.0020]

SCI Grid wells (35 wells sampled)

Number of wells with detections 27

Detection frequency (percent) 77

SCI Livermore study area (6 grid wells sampled)

LIV-01 0.43 nc

LIV-02 – nc

LIV-03 0.61 nc

LIV-04 1.31 nc

LIV-05 0.23 –

LIV-06 0.99 –

Number of wells with detections 5

Detection frequency (percent) 83

SCI Gilroy study area (17 grid wells sampled)

GIL-01 2.84 nc

GIL-02 2.11 nc

GIL-03 1.17 nc

GIL-04 – nc

GIL-05 0.15 nc

GIL-06 0.17 nc

GIL-07 0.37 nc

GIL-08 0.72 nc

GIL-09 0.60 –

GIL-09 1.74 nc

GIL-11 4.14 nc

GIL-12 – nc

GIL-13 – nc

GIL-14 – nc

GIL-15 0.91 nc

GIL-16 0.22 nc

GIL-17 0.44 nc

Number of wells with detections 13

Detection frequency (percent) 77

Table 7. Constituents of special interest (perchlorate and N-nitrosodimethylamine [NDMA]) collected for the South Coast Interior 

Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were 

analyzed for perchlorate; samples from the 11 slow wells were sampled for NDMA; detection frequency presented for perchlorate only. Information about 

the analytes given in table 3E. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding well; 

GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding 

well. Threshold type and threshold level as of November 17, 2008. 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; NL-CA, California Department of Public Health notification level. Summary statistics were not calculated for 

NDMA because it was not sampled at all grid wells. Abbreviations: MRL, method reporting level; μg/L, microgram per liter; nc, not collected; –, not detected; 

*, value above threshold level]

GAMA well

identification 

number

Perchlorate 

(μg/L)

(63790) 

N-nitrosodimethylamine

(NMDA)

(ug/L)

(34438)

Threshold type MCL-CA NL-CA

Threshold level 6 0.010

[MRL] [0.10] [0.0020]

SCI Cuyama study area (12 grid wells sampled)

CUY-01 0.31 nc

CUY-02 – –

CUY-03 0.40 nc

CUY-04 0.77 –

CUY-05 – nc

CUY-06 0.36 nc

CUY-07 0.85 nc

CUY-08 0.22 nc

CUY-09 – –

CUY-10 0.28 –

CUY-11 0.42 nc

CUY-12 0.25 nc

Number of wells with detections 9

Detection frequency (percent) 75

SCI Understanding wells1

 (19 wells sampled)

LIVU-01 0.30 nc

LIVU-02 0.95 –

LIVU-03 0.42 –

LIVU-04 0.47 nc

LIVU-05 – nc

LIVU-06 – nc

LIVU-07 – nc

LIVU-08 – nc

GILU-01 *6.37 nc

GILU-02 0.41 –

GILU-03 3.53 nc

GILU-04 5.05 nc

GILU-05 0.22 nc

CUYU-01 0.38 nc

CUYU-02 0.12 nc

CUYU-03 0.30 nc

CUYU-04 0.21 nc

CUYU-05 0.30 nc

CUYU-06 0.49 –

1

Understanding wells were not included in statistical calculations.
48 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table 8. Trace elements collected for the South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, August to December 2008.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 54 wells were analyzed. Information about the analytes given in table 3F. GAMA well identification number: LIV, Livermore study area grid 

well; LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area 

grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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. AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; 

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

NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. 

Abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting limit; μg/L, microgram per liter; 

na, not available; —, not detected; ≤ less than or equal to; *, value above threshold level]

GAMA well

identification 

number

Aluminum 

(μg/L) 

(01106) 

Antimony 

(μg/L) 

(01095) 

Arsenic 

(μg/L) 

(01000) 

Barium 

(μg/L) 

(01005) 

Beryllium 

(μg/L) 

(01010)

Boron 

(μg/L) 

(01020) 

Cadmium 

(μg/L) 

(01025) 

Chromium 

(μg/L) 

(01030) 

Cobalt 

(μg/L) 

(01035) 

Copper 

(μg/L) 

(01040) 

Iron

(μg/L) 

(01046) 

Lead, 

(μg/L) 

(01049)

Threshold type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US

Threshold 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 15

[LRL/SRL] 1

[1.6] [0.04] [0.06] 1[0.36] [0.02] [4] [0.02] 1[0.42] [0.02] 1[1.7] 1[6] 1[0.65]

SCI grid wells (35 wells sampled)

LIV-01 2.5 — 0.33 157 — 281 — 5.0 0.03 ≤0.80 — ≤0.22

LIV-02 — — 2.0 338 0.01 124 — — 0.24 — 155 1.51

LIV-03 — — 0.33 265 — 304 — 3.8 0.04 11.9 ≤5 4.09

LIV-04 — — 0.56 311 — 284 — 8.2 0.03 ≤1.4 — ≤0.24

LIV-05 — 0.04 0.80 255 — 309 — 8.9 0.04 ≤1.3 ≤5 2.00

LIV-06 — 0.06 0.75 377 — *1,880 — 4.7 0.11 ≤0.73 ≤5 ≤0.05

GIL-01 — — 0.32 61 — 101 — 1.2 0.02 3.6 — ≤0.52

GIL-02 — — 0.26 138 — 90 — 1.1 0.02 ≤1.2 — ≤0.09

GIL-03 — — 1.1 31 — *1,080 — 32.2 0.13 2.1 — ≤0.32

GIL-04 ≤1.5 — 8.0 74 0.01 869 E0.03 2.4 0.03 ≤0.84 14 ≤0.19

GIL-05 — E0.08 0.49 55 — 135 — ≤0.4 0.07 — 58 —

GIL-06 — 0.17 0.86 150 E0.004 490 — — 0.07 — — ≤0.20

GIL-07 — — 0.12 73 — 52 — 0.78 0.04 ≤0.80 — ≤0.29

GIL-08 — — 0.13 56 — 130 — 1.1 0.02 2.3 — ≤0.25

GIL-09 — — 0.17 62 — 165 — 1.4 0.04 ≤1.5 — ≤0.62

GIL-10 — — 0.36 306 — 96 — 4.5 0.07 2.7 11 ≤0.62

GIL-11 — — 0.50 262 — 103 — 1.1 0.07 2.4 — ≤0.32

GIL-12 ≤1.6 — 1.5 74 — 166 — ≤0.07 0.03 — 78 ≤0.11

GIL-13 — 0.17 1.3 27 E0.01 886 E0.03 ≤0.06 0.28 ≤0.78 ≤6 4.46

GIL-14 ≤1.5 — 0.13 35 E0.01 727 — — 0.05 — 223 ≤0.06

GIL-15 ≤1.1 1.5 7.7 290 0.02 E31 E0.02 6.8 0.11 4.1 16 4.73

GIL-16 ≤0.9 E0.13 2.8 30 E0.01 981 — 20.6 0.03 1.9 — ≤0.30

GIL-17 ≤1.6 E0.13 2.3 28 — E10 — 15.9 0.04 2.7 19 ≤0.37

CUY-01 — — 0.64 18 — 117 0.08 ≤0.35 0.06 3.4 22 5.68

CUY-02 E2.9 — *44.0 19 — 207 0.14 — E0.06 — 102 ≤0.60

CUY-03 — — E0.18 11 — 180 — ≤0.37 0.13 — 13 ≤0.29

CUY-04 — — 0.18 10 — 153 — 1.3 0.14 4.7 — 1.20

CUY-05 — — 1.6 10 — 151 0.17 — 0.12 — E14 ≤0.24

CUY-06 — — 0.32 11 — 148 — ≤0.30 0.13 — 34 2.11

CUY-07 — — 0.19 13 E0.005 152 — 0.53 0.16 2.4 41 0.83

CUY-08 — — 0.18 8.0 — 137 — ≤0.31 0.09 ≤0.89 ≤5 ≤0.08

CUY-09 2.7 E0.11 9.3 98 — 41 — — 0.05 — 31 2.70

CUY-10 — E0.08 *10.8 72 — 53 0.08 ≤0.08 0.07 — 46 ≤0.09

CUY-11 3.2 — 0.12 33 — 36 — 1.5 0.09 ≤0.97 — 0.85

CUY-12 — — 0.37 11 — 135 — ≤0.34 0.17 1.8 ≤4 ≤0.48
Tables 49

Table 8. Trace elements collected for the South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, August to December 2008.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 54 wells were analyzed. Information about the analytes given in table 3F. GAMA well identification number: LIV, Livermore study area grid 

well; LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area 

grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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. AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; 

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

NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. 

Abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting limit; μg/L, microgram per liter; 

na, not available; —, not detected; ≤ less than or equal to; *, value above threshold level]

GAMA well

identification 

number

Aluminum 

(μg/L) 

(01106) 

Antimony 

(μg/L) 

(01095) 

Arsenic 

(μg/L) 

(01000) 

Barium 

(μg/L) 

(01005) 

Beryllium 

(μg/L) 

(01010)

Boron 

(μg/L) 

(01020) 

Cadmium 

(μg/L) 

(01025) 

Chromium 

(μg/L) 

(01030) 

Cobalt 

(μg/L) 

(01035) 

Copper 

(μg/L) 

(01040) 

Iron

(μg/L) 

(01046) 

Lead, 

(μg/L) 

(01049)

Threshold type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US

Threshold 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 15

[LRL/SRL] 1

[1.6] [0.04] [0.06] 1[0.36] [0.02] [4] [0.02] 1[0.42] [0.02] 1[1.7] 1[6] 1[0.65]

SCI Understanding wells (19 wells sampled)

LIVU-01 — — 0.94 200 — 301 — 7.3 0.03 2.4 — ≤0.17

LIVU-02 E2.5 — 1.0 162 — 800 — 8.1 0.05 — — —

LIVU-03 ≤0.9 — 1.3 365 — 406 — 4.5 0.04 ≤1.7 — 0.66

LIVU-04 — — 0.30 170 — 274 — 4.4 0.04 ≤1.6 18 ≤0.21

LIVU-05 — E0.52 9.0 20 — *10,800 1.68 E2.1 27.3 — — —

LIVU-06 — 0.44 *15.9 688 — *1,070 E0.09 E0.91 6.8 — *1,340 —

LIVU-07 — 0.11 1.4 58 — *3,280 0.06 ≤0.18 0.34 — — —

LIVU-08 — 0.13 3.0 40 E0.02 *6,240 0.05 ≤0.26 0.66 — — —

GILU-01 — — 0.37 84 — 42 — 1.7 E0.02 ≤1.5 — ≤0.36

GILU-02 — — 0.57 88 — 122 — ≤0.41 0.03 ≤0.67 — ≤0.18

GILU-03 — E0.02 0.26 145 — 77 — 1.2 0.04 ≤0.61 ≤6 0.99

GILU-04 — E0.03 0.36 132 — 86 — 1.1 0.04 ≤0.65 ≤5 2.75

GILU-05 — 0.04 0.61 125 — 105 E0.02 ≤0.17 0.04 — 50 1.60

CUYU-01 ≤0.8 E0.07 1.4 40 E0.01 *1,110 E0.04 0.71 0.07 2.1 — ≤0.37

CUYU-02 — — E0.04 55 — 132 — 0.52 0.06 — 8 ≤0.21

CUYU-03 ≤0.9 E0.08 2.6 43 — 781 E0.03 0.54 0.09 5.3 — 0.75

CUYU-04 — E0.12 E0.04 76 — 60 — ≤0.26 0.06 2.0 E8 ≤0.65

CUYU-05 — 0.20 1.1 26 — 652 0.11 ≤0.30 0.07 ≤1.5 ≤4 ≤0.54

CUYU-06 — 0.16 0.54 58 — 393 0.08 0.55 0.09 1.8 ≤4 ≤0.24

CUYU-04 — E0.12 E0.04 76 — 60 — ≤0.26 0.06 2.0 E8 ≤0.65

CUYU-05 — 0.20 1.1 26 — 652 0.11 ≤0.30 0.07 ≤1.5 ≤4 ≤0.54

CUYU-06 — 0.16 0.54 58 — 393 0.08 0.55 0.09 1.8 ≤4 ≤0.24
50 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

GAMA well

identification 

number

Lithium

(μg/L)

(01130)

Manganese 

(μg/L) 

(01056) 

Molyb 

denum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075)

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057)

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

Vanadium 

(μg/L) 

(01085) 

Zinc

(μg/L) 

(01090)

Threshold type na SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US NL-CA SMCL-CA

Threshold na 50 40 100 50 100 4,000 2 na 30 50 5,000

[LRL/SRL] [1] 1

[0.2] [0.02] 1[0.36] [0.06] [0.008] [0.8] [0.04] 1[0.11] [0.006] 1[0.11] 1[4.8]

SCI grid wells (35 wells sampled)

LIV-01 6.7 ≤0.2 0.8 0.38 0.28 — 799 — — 1.12 1.6 ≤3.2

LIV-02 23.2 *450 4.2 1.5 0.60 — 1,210 — ≤0.11 0.27 ≤0.4 47.1

LIV-03 8.2 — 0.7 0.48 1.5 — 1,150 — — 2.01 1.7 ≤4.5

LIV-04 7.5 — 0.8 0.44 0.14 — 743 — — 1.01 2.1 ≤3.3

LIV-05 8.2 ≤0.2 0.8 0.84 0.52 — 689 — ≤0.01 0.76 3.1 101

LIV-06 17.1 0.9 0.9 2.6 0.10 E0.008 820 — — 2.26 2.4 ≤2.2

GIL-01 7.8 0.3 1.0 ≤0.21 0.34 — 492 — — 0.37 3.5 ≤4.7

GIL-02 7.5 — 0.7 ≤0.27 0.36 — 499 — — 0.49 3.8 ≤2.8

GIL-03 35.1 E0.4 2.5 2.0 35.6 — 2,020 — — 14.0 6.6 ≤2.9

GIL-04 14.7 30.3 8.1 ≤0.36 1.0 — 811 — ≤0.10 1.65 2.9 13.9

GIL-05 14.0 16.6 2.6 0.58 0.74 — 512 — — 5.31 1.4 ≤3.1

GIL-06 5.6 *58.6 2.3 0.43 0.37 — 966 — — 1.20 1.2 ≤1.4

GIL-07 2.7 — 0.4 1.3 0.60 — 225 — — 0.17 1.4 ≤4.1

GIL-08 2.4 ≤0.1 0.3 ≤0.36 0.05 — 247 — — 0.15 2.8 ≤2.4

GIL-09 4.2 ≤0.2 0.5 0.51 0.06 — 274 — — 0.21 3.0 5.0

GIL-10 18.8 0.3 0.8 0.62 1.3 — 735 — — 1.19 1.8 9.3

GIL-11 23.7 — 0.8 0.85 1.6 — 642 — — 1.24 1.9 ≤1.1

GIL-12 8.8 *140 4.7 ≤0.25 — — 270 — 0.12 0.02 ≤0.09 ≤1.8

GIL-13 34.8 *390 4.0 20.0 2.3 — 1,240 — ≤0.05 6.76 8.1 24.2

GIL-14 14.5 *58.8 8.0 1.1 E0.03 — 753 — 0.32 0.07 0.25 ≤1.9

GIL-15 35.9 *63.0 6.5 1.4 1.2 — 1,220 — — 4.92 10.7 18.4

GIL-16 21.2 — 3.1 1.3 2.4 — 759 — — 3.75 7.9 5.3

GIL-17 18.4 0.7 2.3 0.61 3.1 — 882 — — 3.61 6.6 9.6

CUY-01 29.9 4.8 *49.1 6.2 2.1 — 1,400 — — 5.67 1.1 22.1

CUY-02 55.0 34.8 *95.6 5.4 E0.07 — 1,390 — — 0.45 ≤0.07 —

CUY-03 34.1 — 1.5 3.3 1.8 — 1,830 — — 4.56 0.30 —

CUY-04 28.3 — 0.9 3.4 11.1 — 2,000 — — 4.79 0.64 6.8

CUY-05 49.1 7.3 *58.5 3.2 0.79 — 2,540 — — 6.71 2.7 —

CUY-06 30.7 4.9 2.1 3.0 1.6 — 1,710 — E0.18 3.60 0.80 452

CUY-07 32.4 1.2 1.0 4.0 3.4 — 2,380 — ≤0.03 4.34 0.47 21.7

CUY-08 29.1 0.3 0.9 0.90 1.8 — 1,430 — — 4.04 0.48 7.3

CUY-09 3.3 *137 7.8 0.45 E0.03 — 504 — ≤0.10 2.69 0.32 ≤2.2

CUY-10 10.3 *80.6 14.4 0.55 5.1 — 1,200 — — 7.65 0.25 6.4

CUY-11 17.8 ≤0.1 0.8 0.75 0.97 — 1,480 — — 5.53 0.46 —

CUY-12 25.6 1.1 2.2 1.5 2.2 — 1,820 — — 4.32 0.47 ≤4.7

Table 8. Trace elements collected for the South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, August to December 2008.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 54 wells were analyzed. Information about the analytes given in table 3F. GAMA well identification number: LIV, Livermore study area grid 

well; LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area 

grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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. AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; 

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

NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. 

Abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting limit; μg/L, microgram per liter; 

na, not available; —, not detected; ≤, less than or equal to; *, value above threshold level]
Tables 51

GAMA well

identification 

number

Lithium

(μg/L)

(01130)

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075)

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057)

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

Vanadium 

(μg/L) 

(01085) 

Zinc

(μg/L) 

(01090)

Threshold type na SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US NL-CA SMCL-CA

Threshold na 50 40 100 50 100 4,000 2 na 30 50 5,000

[LRL/SRL] [1] 1

[0.2] [0.02] 1[0.36] [0.06] [0.008] [0.8] [0.04] 1[0.11] [0.006] 1[0.11] 1[4.8]

SCI Understanding wells (19 wells sampled)

LIVU-01 8.1 ≤0.2 1.4 ≤0.33 4.8 — 855 — — 2.00 3.6 ≤1.4

LIVU-02 9.5 ≤0.2 1.0 0.99 1.0 — 774 — — 2.44 3.6 —

LIVU-03 11.0 — 1.1 0.68 8.2 — 1,230 — — 2.87 5.1 ≤1.5

LIVU-04 5.7 0.9 0.7 0.47 0.13 — 854 — — 0.77 1.2 334

LIVU-05 146 *17,500 *123 29.0 E1.0 E0.1 *20,000 — — *138 27.9 —

LIVU-06 91.2 *26,600 9.8 16.7 0.57 0.1 *15,000 — — 5.56 10.8 —

LIVU-07 66.7 46.2 2.5 7.4 0.17 E0.009 2,530 — — 19.5 5.1 —

LIVU-08 76.0 *308 11.2 3.7 E0.09 E0.008 2,170 — — *33.0 15.3 —

GILU-01 7.0 ≤0.1 0.4 ≤0.21 0.22 — 225 — — 0.10 2.6 ≤2.8

GILU-02 9.2 5.8 6.3 1.8 0.76 — 363 — — 0.53 4.9 ≤2.5

GILU-03 7.7 2.0 0.6 0.65 0.13 — 419 — ≤0.01 0.35 2.6 45.2

GILU-04 9.4 2.3 0.7 0.59 0.22 — 436 — — 0.33 2.3 32.7

GILU-05 10.8 *148 5.2 0.78 0.74 — 556 — ≤0.07 0.56 2.9 30.8

CUY-01 27.4 <0.2 20.7 0.76 1.1 — 1,240 — — 23.9 0.96 48.3

CUYU-02 20.5 ≤0.2 4.3 1.2 0.76 — 1,920 — — 6.03 0.12 35.4

CUYU-03 18.9 ≤0.1 8.0 0.80 1.5 — 1,440 — ≤0.04 16.7 1.8 11.5

CUYU-04 3.6 ≤0.1 0.5 0.85 0.32 — 783 — — 4.83 0.57 12.2

CUYU-05 26.0 0.4 36.0 0.65 0.57 — 1,120 — ≤0.03 26.4 0.61 61.6

CUYU-06 22.5 ≤0.2 23.6 0.87 0.47 E0.006 1,030 — ≤0.06 20.3 1.0 8.3

Table 8. Trace elements collected for the South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, August to December 2008.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 54 wells were analyzed. Information about the analytes given in table 3F. GAMA well identification number: LIV, Livermore study area grid 

well; LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area 

grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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. AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; 

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

NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. 

Abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; SRL, study reporting limit; μg/L, microgram per liter; 

na, not available; —, not detected; ≤, less than or equal to; *, value above threshold level]

1

Study reporting limit (SRL) defined based on examination of GAMA quality-control samples collected from May 2004 through January 2008 (L.D. Olsen 

and M.S. Fram, U.S. Geological Survey, written commun., 2009). Values below SRL are reported as less than or equal to the value reported by the laboratory 

(≤). In the USGS NWIS database, the result is accompanied with the following comment: Result is < or = reported value, based on QC data (may include: field 

blanks, source-solution blanks, trip blanks, NWQL set blanks, NWQL blank water certificates, and USGS BQS Blind Blank Program data). 
52 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

GAMA well

identification 

number

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 + 

organic-nitrogen) 

as nitrogen 

(mg/L) 

(62854)

Phosphate, 

orthophosphate 

(as phosphorus) 

(mg/L) 

(00671)

Threshold type HAL-US MCL-US MCL-US na na

Threshold level 1

24.7 10 1 na na

[MRL] [0.02] [0.04] [0.002] [0.06] [0.006]

SCI grid wells (35 wells sampled)

LIV-01 — 2.08 — 2.12 0.029

LIV-02 0.165 0.48 0.053 0.69 0.033

LIV-03 — 4.18 — 4.24 0.031

LIV-04 — 7.81 — 7.93 0.044

LIV-05 — 2.79 — 2

2.63 0.050

LIV-06 — *13.4 — 14.0 0.084

GIL-01 — 4.11 — 4.23 0.039

GIL-02 — 8.39 — 8.68 0.037

GIL-03 0.038 *22.0 — 23.2 0.076

GIL-04 0.033 0.26 E0.002 0.31 0.071

GIL-05 — 2.21 — 2

2.19 0.049

GIL-06 — 2.25 — 2.26 0.068

GIL-07 — 5.94 — 6.10 0.033

GIL-08 — 2.57 — 2.64 0.036

GIL-09 — 4.18 — 4.30 0.036

GIL-10 — 9.91 — 10.3 0.033

GIL-11 — *28.3 — 29.7 0.047

GIL-12 E0.016 — — — 0.064

GIL-13 E0.014 0.20 0.009 0.24 0.027

GIL-14 4.16 — — 2

4.05 0.122

GIL-15 — 6.22 0.014 6.41 0.128

GIL-16 — 0.67 — 2

0.63 0.056

GIL-17 — 3.01 — 2

2.98 0.040

CUY-01 — 2.51 — 2

2.48 0.023

CUY-02 0.411 E0.02 0.004 0.46 0.018

CUY-03 — 4.60 — 2

4.55 0.013

CUY-04 — *10.3 — 2

10.2 0.013

CUY-05 0.077 1.1 E0.001 2

1.09 0.01

CUY-06 — 3.99 — 2

3.98 0.01

CUY-07 — *15.1 — 2

15.2 0.012

CUY-08 — 0.84 — 2

0.82 0.011

CUY-09 0.398 0.30 0.031 0.74 0.066

CUY-10 0.151 1.20 — 1.36 0.049

CUY-11 — 0.67 — 2

0.66 0.018

CUY-12 — 2.10 — 2

2.08 0.05

Table 9. Nutrients detected in samples collected for the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, August to December 2008.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were 

analyzed. Information about the analytes given in table 3G. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study 

area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama 

study area understanding well. Threshold type and threshold level as of November 17, 2008. 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 level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. 

Abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; mg/L, milligram per liter; na, not available; —, not 

detected; *, value above threshold level]
Tables 53

GAMA well

identification 

number

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 + 

organic-nitrogen) 

as nitrogen 

(mg/L) 

(62854)

Phosphate, 

orthophosphate 

(as phosphorus) 

(mg/L) 

(00671)

Threshold type HAL-US MCL-US MCL-US na na

Threshold level 1

24.7 10 1 na na

[MRL] [0.02] [0.04] [0.002] [0.06] [0.006]

SCI understanding wells (19 grid wells sampled)

LIVU-01 — 3.33 — 2

3.20 0.053

LIVU-02 — 7.41 — 7.54 0.066

LIVU-03 — 4.37 — 4.46 0.072

LIVU-04 — 2.15 — 2.25 0.019

LIVU-05 0.916 E0.02 E0.002 1.26 0.212

LIVU-06 1.42 — E0.001 2

1.34 0.186

LIVU-07 — — — 0.10 0.128

LIVU-08 E0.017 — — 0.13 0.132

GILU-01 — 6.65 — 7.20 0.063

GILU-02 — 4.19 0.007 4.31 0.063

GILU-03 — 5.98 0.003 2

5.79 0.043

GILU-04 — 5.80 0.017 2

5.76 0.029

GILU-05 0.25 2.25 0.08 2

2.43 0.063

CUYU-01 — 2.62 — 2.67 0.009

CUYU-02 — 0.65 — 0.65 E0.004

CUYU-03 — 1.64 — 1.65 0.051

CUYU-04 — 0.48 — 0.48 0.007

CUYU-05 — 4.20 — 2 3.96 E0.006

CUYU-06 — 4.17 — 2 4.10 E0.008

Table 9. Nutrients detected in samples collected for the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, August to December 2008.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were 

analyzed. Information about the analytes given in table 3G. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study 

area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama 

study area understanding well. Threshold type and threshold level as of November 17, 2008. 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 level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. 

Abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; mg/L, milligram per liter; na, not available; —, not 

detected; *, value above threshold level]

 1The HAL-US is 30 mg/L “as ammonia.” To facilitate comparson to the analytical results, we have converted and reported this HAL-US 

as 24.7 mg/L “as nitrogen.”

2.Total nitrogen in these samples is less than the sum of the filtered nitrogen analytes, but falls within the U.S. Geological Survey National 

Water Quality Laboratory acceptance criteria of a 10 percent or less relative percent difference.
54 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the South Coast Interior 

Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 were 

analyzed. Information about the analytes given in table 3H. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study 

area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama 

study area understanding well. Threshold type and threshold level as of November 17, 2008. 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; SMCL-CA, California Department of Public Health secondary maximum contaminant 

level. Abbreviations: LRL, laboratory reporting level; mg/L, milligrams per liter; E, estimated or having a higher degree of uncertainty; na, not available; —, 

not detected; *, value above threshold level; **, value above upper threshold level]

GAMA well 

identification 

number

Bromide 

(mg/L) 

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Iodide 

(mg/L) 

(71865) 

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935)) 

Silica 

(as SiO2

) 

(mg/L) 

(00955) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

Residue on 

evaporation [Total 

dissolved 

solids 

(TDS) 

 (mg/L) 

(70300)

Threshold type na na SMCL-CA MCL-CA na na na na na SMCL-CA SMCL-CA

Threshold level na na 1

250 (500) 2 na na na na na 1250 (500) 1500 (1,000)

[LRL] [0.02] [0.04] [0.12] [0.08] [0.002] [0.012] [0.06] [0.02] [0.12] [0.18] [10]

SCI Grid wells (35 wells sampled)

LIV-01 0.18 64.8 53.7 0.15 E0.001 27.4 1.75 18.6 35.9 43.5 396

LIV-02 0.56 78.9 159 E0.12 0.397 33.0 2.04 30.6 156 56.0 *760

LIV-03 0.30 89.5 79.8 0.13 E0.001 42.9 2.16 19.9 48.6 54.6 *569

LIV-04 0.21 57.4 68.5 0.12 E0.001 65.2 1.99 23.2 29.1 50.1 *524

LIV-05 0.12 49.5 41.0 0.14 E0.001 45.0 1.93 22.9 35.6 42.1 426

LIV-06 0.50 72.4 199 0.20 0.010 86.5 1.22 32.0 131 129 *952

GIL-01 0.11 44.9 29.8 0.18 — 21.5 1.57 23.8 30.6 34.5 312

GIL-02 0.14 55.0 26.7 0.16 — 26.2 1.45 27.1 26.2 34.0 372

GIL-03 1.09 171 429 0.36 0.007 233 4.75 26.9 252 **666 **2,410

GIL-04 0.36 39.8 109 0.20 0.089 25.3 2.54 18.1 161 156 *665

GIL-05 0.21 122 70.3 0.73 0.004 24.0 1.84 24.0 52.3 70.4 *600

GIL-06 0.20 66.2 47.8 0.18 0.039 27.9 1.65 18.5 50.9 57.6 456

GIL-07 0.06 43.2 21.1 0.15 — 29.4 0.65 26.5 17.6 42.4 316

GIL-08 0.08 40.1 16.5 0.13 — 26.6 0.63 25.5 12.7 24.8 281

GIL-09 0.12 40.4 14.9 0.13 E0.001 24.5 0.71 26.1 12.6 27.0 284

GIL-10 0.45 76.4 146 0.18 0.002 65.3 1.82 25.9 38.4 33.2 *591

GIL-11 0.35 73.3 63.9 0.26 E0.002 56.1 1.27 26.4 45.1 64.6 *602

GIL-12 0.12 32.6 37.0 0.29 0.016 24.2 2.14 31.6 56.5 37.7 364

GIL-13 0.22 87.0 73.9 0.30 0.008 60.4 3.40 33.6 122 242 *865

GIL-14 0.49 49.9 150 E0.10 0.057 48.1 4.50 33.4 309 *403 **1,270

GIL-15 0.62 101 233 0.46 0.051 80.7 1.41 33.7 168 84.9 **1,070

GIL-16 0.30 43.4 92.9 0.33 0.006 48.6 2.96 26.7 134 179 *703

GIL-17 0.26 53.5 91.4 0.28 0.004 45.8 3.04 27.4 117 185 *705

CUY-01 0.13 130 33.0 0.38 0.003 37.7 2.97 23.3 100 *399 *928

CUY-02 0.13 105 17.6 0.18 0.035 19.3 5.23 34.6 173 **508 *972

CUY-03 0.03 246 11.9 0.87 E0.002 99.1 4.02 14.6 87.1 **971 **1,690

CUY-04 0.11 268 24.5 0.65 — 106 4.30 18.5 87.1 **1,050 **1,810

CUY-05 0.08 227 13.8 0.28 0.012 97.4 6.30 34.2 135 **1,080 **1,820

CUY-06 0.03 226 11.5 0.92 E0.001 93.4 3.92 15.5 72.3 **911 **1,530

CUY-07 0.06 323 16.0 0.93 E0.002 128 4.46 15.8 84.1 **1,270 **2,170

CUY-08 0.02 182 6.39 0.92 — 67.2 3.87 15.6 64.1 **683 **1,200

CUY-09 0.08 74.0 21.1 1.94 0.007 7.33 2.88 14.5 51.9 107 394

CUY-10 0.05 118 10.6 1.38 0.002 38.7 4.54 16.1 44.2 193 *659

CUY-11 0.02 115 5.79 0.22 — 21.2 2.10 22.3 41.2 *268 *602

CUY-12 0.03 245 11.7 0.87 — 96.1 3.86 14.8 86.2 **976 **1,680

Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the South Coast Interior 

Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 were 

analyzed. Information about the analytes given in table 3H. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study 

area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama 

study area understanding well. Threshold type and threshold level as of November 17, 2008. 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; SMCL-CA, California Department of Public Health secondary maximum contaminant 

level. Abbreviations: LRL, laboratory reporting level; mg/L, milligrams per liter; E, estimated or having a higher degree of uncertainty; na, not available; —, 

not detected; *, value above threshold level; **, value above upper threshold level]
Tables 55

Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the South Coast Interior 

Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 were 

analyzed. Information about the analytes given in table 3H. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study 

area understanding well; GIL, Gilroy study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama 

study area understanding well. Threshold type and threshold level as of November 17, 2008. 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; SMCL-CA, California Department of Public Health secondary maximum contaminant 

level. Abbreviations: LRL, laboratory reporting level; mg/L, milligrams per liter; E, estimated or having a higher degree of uncertainty; na, not available; —, 

not detected; *, value above threshold level; **, value above upper threshold level]

GAMA well 

identification 

number

Bromide 

(mg/L) 

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Iodide 

(mg/L) 

(71865) 

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935)) 

Silica 

(as SiO2

) 

(mg/L) 

(00955) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

Residue on 

evaporation [Total 

dissolved 

solids 

(TDS) 

 (mg/L) 

(70300)

Threshold type na na SMCL-CA MCL-CA na na na na na SMCL-CA SMCL-CA

Threshold level na na 1

250 (500) 2 na na na na na 1250 (500) 1500 (1,000)

[LRL] [0.02] [0.04] [0.12] [0.08] [0.002] [0.012] [0.06] [0.02] [0.12] [0.18] [10]

SCI Understanding wells (19 wells sampled)

LIVU-01 0.16 65.1 53.6 E0.12 0.004 41.1 1.86 20.8 35.7 46.2 461

LIVU-02 0.37 72.4 124 E0.12 0.008 65.6 2.27 23.5 84.5 68.9 *683

LIVU-03 0.39 88.6 123 E0.07 0.005 59.0 2.97 22.9 79.1 82.5 *716

LIVU-04 0.19 59.9 61.5 0.16 E0.001 28.5 1.66 17.2 33.0 41.2 405

LIVU-05 19.0 704 **11,300 0.74 2.80 1,900 4.54 11.4 6,050 **7,660 **30,400

LIVU-06 11.0 1,060 **6,020 0.16 1.49 636 5.01 20.0 1,800 **720 **11,100

LIVU-07 1.31 225 254 0.26 0.98 182 2.72 26.8 234 **599 **2,080

LIVU-08 1.14 134 179 0.42 1.51 107 1.84 23.3 365 *464 **1,790

GILU-01 0.16 32.5 38.0 0.17 — 28.9 0.86 33.8 18.7 27.9 294

GILU-02 0.10 49.1 26.3 E0.1 0.008 8.33 1.39 25.8 50.2 33.7 340

GILU-03 0.17 50.7 24.4 0.14 — 24.2 1.31 25.7 22.7 28.2 326

GILU-04 0.15 46.8 24.3 0.11 — 21.2 1.35 24.4 23.7 25.7 315

GILU-05 0.08 43.6 22.5 E0.06 0.007 14.5 3.05 24.1 48.6 36.8 333

CUYU-01 0.14 100 35.5 1.58 0.002 42.4 4.53 17.8 99.2 226 *752

CUYU-02 E0.01 94.7 4.17 0.70 — 56.9 9.34 11.9 36.5 134 *613

CUYU-03 0.22 95.0 67.0 1.42 0.003 53.7 3.07 20.1 139 *256 *864

CUYU-04 0.02 69.1 5.27 0.17 — 22.0 3.06 15.7 24.8 20.9 328

CUYU-05 0.07 75.4 26.9 *2.22 E0.001 34.0 5.04 15.3 75.5 148 *562

CUYU-06 0.11 95.0 36.7 1.27 — 29.5 4.96 17.3 63.8 126 *583

1

 The SMCL-CA for chloride, sulfate, and total dissolved solids (TDS) have recommended and upper threshold values. The upper value is shown in 

parentheses.
56 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table 11. Species of inorganic arsenic, chromium, and iron detected in samples collected for the South 

Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to 

December 2008.

[Data in this table analyzed at U.S. Geological Survey Trace Metals Laboratory using research methods and are not stored in the USGS 

NWIS database. Information about the analytes given in table 3I. Samples from the 11 slow wells were analyzed; only wells with at 

least one detection are listed. GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area 

understanding well; GIL, Gilroy study area grid well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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; SMCL-CA, California Department of Public Health secondary maximum contaminant 

level. Abbreviations: MDL, method detection limit; μg/L, microgram per liter; na, not available; —, not detected]

GAMA well

identification 

number

Arsenic 

(μg/L) 

Arsenic (III) 

(μg/L) 

Chromium 

(μg/L) 

Chromium (VI) 

(μg/L)

Iron 

(μg/L) 

Iron (II) 

(μg/L)

Threshold type MCL-US na MCL-CA na SMCL-CA na

Threshold level 10 na 50 na 300 na

[MDL] [0.5] [1] [1] [1] [2] [2]

SCI Grid wells (7 wells sampled)

LIV-05 0.59 — 9 8 12 —

LIV-06 — — 5 5 8 —

GIL-09 — — 1 — 4 —

CUY-02 na1 na1 na1 na1 na1 na1

CUY-04 na1 na1 na1 na1 na1 na1

CUY-09 na1 na1 na1 na1 na1 na1

CUY-10 na1 na1 na1 na1 na1 na1

SCI Understanding wells (4 wells sampled)

LIVU-02 0.74 — 10 10 — —

LIVU-03 0.89 — 6 5 — —

CUYU-06 na1 na1 na1 na1 na1 na1

1

Analyses at the U.S. Geological Survey Trace Metals Laboratory were not completed in time for inclusion in this report; complete 

results will be presented in a subsequent publication.
Tables 57

Table 12. Results for analyses of stable isotope ratios and tritium and carbon-14 activities detected in samples collected for the 

South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 

2008.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were 

analyzed for stable isotopes of water, tritium, and carbon and carbon activities. 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. Information about the analytes given in table 3J. 

GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; 

GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold 

level as of November 17, 2008. 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. Abbreviations: na, not available; —, not detected; pCi/L, picocuries per liter]

GAMA well 

identification 

number

δ2H 

(per mil) 

(82082)

δ18O 

(per mil) 

(82085)

Tritium 

(pCi/L)

(07000)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent modern) 

(49933)

Threshold type na na MCL-CA na na

Threshold level na na 20,000 na na

SCI Grid wells (35 wells sampled)

LIV-01 –47.20 –6.50 11.13 –16.36 98.45

LIV-02 –46.10 –6.50 8.52 –11.98 80.76

LIV-03 –46.40 –6.13 15.47 –11.94 66.10

LIV-04 –56.50 –7.89 20.64 –14.29 94.88

LIV-05 –55.30 –7.70 na1 na1 na1

LIV-06 –57.90 –7.48 na1 na1 na1

GIL-01 na2 na2 3.67 –13.82 73.50

GIL-02 –38.90 –5.84 5.68 –15.68 86.06

GIL-03 –43.90 –5.96 4.18 –15.80 94.88

GIL-04 –49.40 –6.81 — –13.53 38.26

GIL-05 –42.10 –6.44 7.27 –15.37 98.12

GIL-06 –43.20 –6.10 8.80 –15.80 93.85

GIL-07 –36.40 –5.66 8.58 –16.40 103.2

GIL-08 –36.60 –5.28 8.04 –14.31 109.7

GIL-09 –35.40 –5.12 9.41 –14.68 109.9

GIL-10 –43.80 –6.34 3.99 –15.73 88.31

GIL-11 –38.80 –5.79 9.51 –15.93 101.9

GIL-12 –40.00 –6.00 — –16.05 58.95

GIL-13 –45.30 –5.80 5.90 –14.11 97.66

GIL-14 –51.40 –6.91 — –14.82 20.30

GIL-15 –42.70 –5.88 — –17.26 86.29

GIL-16 –47.60 –6.63 na1 –13.46 65.78

GIL-17 –49.00 –6.67 0.73 –13.75 76.92

CUY-01 na1 na1 na1 –11.33 72.07

CUY-02 na1 na1 na1 –7.11 1.57

CUY-03 na1 na1 na1 –12.03 92.81

CUY-04 na1 na1 na1 –10.03 63.88

CUY-05 na1 na1 na1 –5.70 4.03

CUY-06 na1 na1 na1 –11.07 86.37

Table 12. Results for analyses of stable isotope ratios and tritium and carbon-14 activities detected in samples collected for the South 

Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008. 

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were 

analyzed for stable isotopes of water, tritium, and carbon and carbon activities. 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. Information about the analytes given in table 3J. 

GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; 

GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold 

level as of November 17, 2008. 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. Abbreviations: na, not available; —, not detected; pCi/L, picocuries per liter]
58 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table 12. Results for analyses of stable isotope ratios and tritium and carbon-14 activities detected in samples collected for the 

South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 

2008.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 54 wells were 

analyzed for stable isotopes of water, tritium, and carbon and carbon activities. 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. Information about the analytes given in table 3J. 

GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding well; GIL, Gilroy study area grid well; 

GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold 

level as of November 17, 2008. 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. Abbreviations: na, not available; —, not detected; pCi/L, picocuries per liter]

GAMA well 

identification 

number

δ2H 

(per mil) 

(82082)

δ18O 

(per mil) 

(82085)

Tritium 

(pCi/L)

(07000)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent modern) 

(49933)

Threshold type na na MCL-CA na na

Threshold level na na 20,000 na na

CUY-07 na1 na1 na1 –9.55 70.22

CUY-08 na1 na1 na1 –9.67 73.59

CUY-09 –83.10 –11.51 na1 –14.53 49.06

CUY-10 –80.70 –11.38 na1 na1 na1

CUY-11 –70.80 –9.93 na1 –12.61 64.56

CUY-12 –69.20 –9.66 na1 –11.49 86.72

SCI Understanding wells (19 wells sampled)

LIVU-01 –50.80 –7.30 1.15 –11.26 92.49

LIVU-02 –52.20 –7.19 32.86 –9.26 37.57

LIVU-03 –50.60 –7.02 8.52 –4.40 1.54

LIVU-04 3.20 –7.03 10.14 –14.38 92.23

LIVU-05 –32.50 –4.20 na1 na1 na3

LIVU-06 –42.20 –6.17 na1 na1 na3

LIVU-07 –47.80 0.67 na1 na1 na3

LIVU-08 –51.00 0.20 na31 na1 na3

GILU-01 –44.80 –6.54 6.51 –15.75 86.67

GILU-02 –40.30 –6.16 3.80 –15.08 47.79

GILU-03 –36.70 –5.49 na1 na1 na1

GILU-04 –40.30 –5.97 na1 na1 na1

GILU-05 –41.70 –6.34 na1 na1 na1

CUYU-01 –80.30 –11.22 na1 –11.97 93.55

CUYU-02 –80.50 –11.68 na1 –10.78 76.92

CUYU-03 –80.50 –10.83 na1 –12.34 97.08

CUYU-04 –83.20 –11.88 na1 –11.90 80.92

CUYU-05 –80.40 –11.19 na1 na1 na1

CUYU-06 –77.70 –11.01 na1 na1 na1

1

Analyses of stable isotopic ratios and tritium and carbon-14 activities were not completed in time for inclusion in this report; complete results will be presented in a subsequent publication.

2

Sample arrived at the USGS Stable Isotope Laboratory broken.
Tables 59

GAMA well identification number

Gross alpha radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha radioactivity, 

30-day count 

(pCi/L) 

(62639)

Gross beta radioactivity, 

72-hour count 

(pCi/L) 

(62642)

Gross beta radioactivity, 

30-day count 

(pCi/L) 

(62645)

Threshold type MCL-US MCL-US MCL-CA MCL-CA

Threshold level 15 15 50 50

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

SCI Grid wells (7 wells sampled)

LIV-05 1.34 ± 0.66 0.80 — 1.4 1.84 ± 0.61 0.95 1.84 ± 0.56 0.87

LIV-06 —(1) 3.0 — 3.3 1

1.34 ± 0.60 0.93 — 1.4

GIL-09 — 0.47 — 0.85 — 1.0 — 1.2

CUY-02 4.5 ± 1.9 2.4 4.8 ± 1.7 2.0 5.81 ± 0.55 0.57 5.27 ± 0.71 1.0

CUY-04 1

13.0 ± 3.5 3.9 —2 4.5 15.66 ± 0.95 1.4 26.33 ± 0.96 1.3

CUY-09 1

2.6 ± 1.1 1.2 3.9 ± 1.0 1.1 13.67 ± 0.82 1.1 2.77 ± 0.67 1.0

CUY-10 1

6.8 ± 1.8 2.0 5.0 ± 3.1 3.9 14.69 ± 0.61 0.76 7.02 ± 0.71 0.73

SCI Understanding wells (4 wells sampled)

LIVU-02 5.3 ± 1.7 2.0 2.6 ± 1.4 1.8 4.78 ± 0.66 0.86 4.45 ± 0.79 1.2

LIVU-03 5.1 ± 1.6 1.7 8.8 ± 1.9 1.4 2.94 ± 0.57 0.78 2.72 ± 0.57 0.81

GILU-02 1.39 ± 0.62 0.77 — 1.1 1.44 ± 0.45 0.68 — 1.1

CUYU-06 1

13.4 ± 2.3 1.7 13.9 ± 1.9 1.0 16.36 ± 0.54 0.48 10.5 ± 0.83 0.82

1

Counted 4-6 days after collection.

2

Counted 44-46 days after initial count.

Table 13A. Gross alpha and gross beta radioactivity detected in samples collected for the South Coast Interior Basins Groundwater 

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

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from the 11 slow wells were analyzed. Information about the analytes given in table 3J. The reference nuclide for measurement of gross alpha is thorium-230 and the reference nuclide for measurement of gross beta is cesium-137. Measured values less than the sample-specific critical level (ssLC) are reported 

as non-detections (—). GAMA well identification number: LIV, Livermore study area grid well; LIVU, Livermore study area understanding well; GIL, Gilroy 

study area grid well; GILU, Gilroy study area understanding well; CUY, Cuyama study area grid well; CUYU, Cuyama study area understanding well. Threshold type and threshold level as of November 17, 2008. 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: CSU, 1-sigma combined 

standard uncertainty; pCi/L, picocurie per liter; —, not detected; ±, plus or minus]
60 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table 13B. Radon-222 detected in samples collected for the 

South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, August to December 2008.

[The five-digit U.S. Geological Survey (USGS) parameter code below the 

constituent name is used to uniquely identify a specific constituent or property. 

Samples from five Gilroy study area wells were analyzed. Information about 

the analytes given in table 3J. GAMA well identification number: GIL, 

Gilroy study area grid well; GILU, Gilroy study area understanding well. 

Threshold type and threshold level as of November 17, 2008. 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. Abbreviations: 2SCU, 

2-sigma combined uncertainty; pCi/L, picocurie per liter]

GAMA well 

identification 

number

Radon-222 

(pCi/L)

(82303) 

Threshold type Proposed MCL-US

Threshold level 4,000

Result ± 2SCU

SCI Grid wells (1 well sampled)

GIL-01 720 ± 43

SCI Understanding wells (4 wells sampled)

GILU-01 700 ± 41

GILU-03 690 ± 41

GILU-04 520 ± 32

GILU-05 670 ± 40
Appendix 61

Appendix 

This Appendix includes discussions of the methods used 

to collect and analyze groundwater samples and report the 

resulting water-quality data. These methods were selected 

to obtain representative samples of the groundwater from 

each well and to minimize the potential for contamination 

of the samples or bias in the data. Procedures used to 

collect and assess quality-control data, and the results of the 

quality-control assessments also are discussed.

Sample Collection and Analysis

Groundwater samples were collected using standard and 

modified USGS protocols from the USGS NAWQA program 

(Koterba and others, 1995), the USGS National Field Manual 

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

described by Weiss (1968), Shelton and others (2001), Ball 

and McClesky (2003a, 2003b), and Wright and others (2005). 

Prior to sampling, each well was pumped continuously 

to purge at least three casing-volumes of water from the well 

(Wilde and others, 1999). Wells were sampled using Teflon©

tubing with brass and stainless-steel fittings attached to a sampling point on the well discharge pipe as close to the well-head 

as possible. The sampling point always was located upstream 

of any well-head treatment system or water storage tank. If a 

chlorinating system was attached to the well, the chlorinator 

was shut off at least 24 hours prior to purging and sampling 

the well to clear all chlorine out of the system. For the fast

schedule, samples were collected at the well head using a 

foot-long length of Teflon© tubing. For the slow schedule, the 

samples were collected inside an enclosed chamber located 

inside a mobile laboratory and connected to the well head 

by a 10–50 ft length of the Teflon© tubing (Lane and others, 

2003). All fittings and lengths of tubing were cleaned between 

samples (Wilde, 2004).

For the field measurements, groundwater was pumped 

through a flow-through chamber fitted with a multi-probe 

meter that simultaneously measures the water-quality indicators (field parameters)—dissolved oxygen, temperature, pH, 

and specific conductance. Turbidity was measured in the field 

with a calibrated turbidity meter. Field measurements were 

made in accordance with protocols in the USGS National 

Field Manual (Radtke and others, 2005; Wilde and Radtke, 

2005; Lewis, 2006; Wilde, 2006; Wilde and others, 2006). All 

sensors on the multi-probe meter were calibrated daily. Measured temperature, dissolved oxygen, pH, specific conductance 

and turbidity values were recorded at 5-minute intervals for at 

least 30 minutes, and when these values remained stable for 

20 minutes, samples for laboratory analyses then were 

collected. 

Field measurements and instrument calibrations were 

recorded by hand on field record sheets and electronically in 

PCFF, a software package designed by the USGS with support from the GAMA Program. Analytical service requests 

also were managed by PCFF. Information from PCFF was 

uploaded directly into NWIS at the end of every week of 

sample collection. 

For analyses requiring filtered water, groundwater 

was diverted through a disk filter, a baked 0.3-μm nominal 

pore-size glass-fiber filter, or a 0.45-μm pore-size Whatman© vented capsule filter, depending on the protocol for 

the analysis (Wilde and others, 1999, 2004). Prior to sample 

collection, polyethylene sample bottles were pre-rinsed two 

times using deionized water, and then once with sample 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 NWQL.

Temperature-sensitive samples were stored on ice prior 

to, and during daily shipping to the various laboratories. The 

nontemperature-sensitive samples for chromium speciation, 

stable isotopes of hydrogen and oxygen in water, tritium, 

and noble gases were shipped monthly, while temperaturesensitive samples for volatile organic compounds, pesticides, 

polar pesticides, perchlorate, NDMA, trace elements, nutrients, major and minor ions, silica, TDS, gross alpha and gross 

beta radioactivity, and radon-222 were shipped daily. The 

temperature-sensitive samples for arsenic and iron speciation were stored on ice, archived in a laboratory refrigerator, 

and shipped after results for the metal concentrations were 

received from the NWQL.

Detailed sampling protocols for individual analyses 

and groups of analytes are described in Koterba and others 

(1995), the USGS National Field Manual (Wilde and others, 

1999, 2004) and in the references for analytical methods listed 

in table A1; only brief descriptions are given here. Volatile 

organic compounds (VOCs) 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. Each sample 

to be analyzed for perchlorate was collected in a 125-mL 

polystyrene bottle and then filtered in two or three 20-mL 

aliquots through a 0.20-μm pore-size CORNING® syringetip disk filter into a sterilized 125-mL bottle. Tritium samples 

were collected by bottom filling one 1-L polyethylene bottle 

and one 1-L glass bottle with unfiltered groundwater, after first 

overfilling the bottles with three volumes of water. Samples 

for analysis of stable isotopes of hydrogen and oxygen in 

water were collected in a 60-mL clear glass bottle filled with 

unfiltered water, sealed with a conical cap, and secured with 

electrical tape to prevent leakage and evaporation.
62 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Pesticides and pesticide degradation products, polar 

pesticides and metabolites, pharmaceutical compounds, and 

NDMA samples were collected in 1-L baked amber bottles. 

Pesticide and pharmaceutical samples were filtered through a 

0.3-μm nominal pore-size glass fiber filter during collection, 

whereas the NDMA samples were filtered at Weck Laboratories, Inc. prior to analysis. Samples of NDMA were collected 

in containers treated with 0.05 grams of sodium thiosulfate 

(Na2S2O3).

Groundwater samples for trace elements, major and 

minor ions, silica, TDS, and alkalinity analyses required filling 

one 250-mL polyethylene bottle with untreated groundwater, 

and one 500-mL and one 250-mL polyethylene bottle with 

filtered groundwater (Wilde and others, 2004). Filtration was 

done using a 0.45-μm pore-size Whatman© vented capsule filter. The 250-mL filtered sample then was preserved with 7.5-N 

nitric acid. Arsenic and iron speciation samples were filtered 

into a 250-mL polyethylene bottle that was covered with tape 

to prevent light exposure and preserved with 6-N hydrochloric 

acid. The nutrient samples were filtered into 125-mL brown 

polyethylene bottles. Gross alpha and gross beta radiation 

samples were filtered into 1-L polyethylene bottles and acidified with nitric acid. Carbon isotope samples were filtered and 

bottom filled into 500-mL glass bottles that first were overfilled with three bottle volumes of groundwater. These samples 

had no headspace and were sealed with a conical cap to avoid 

atmospheric contamination. Samples for alkalinity titrations 

were collected by filtering groundwater into 500-mL polyethylene bottles.

Chromium, radon-222, and noble gases were collected 

from the hose bib at the well head, regardless of the sampling 

schedule (fast or slow). 

 Chromium speciation samples were collected using 

a 10-mL syringe with an attached 0.45-μm pore-size 

MILLEX®HAdisk filter. After the syringe was rinsed thoroughly and filled with groundwater, 4-mL of sample water 

were forced through the disk filter; the next 2-mL of the 

groundwater were filtered slowly into a small centrifuge vial 

for analysis of total chromium. Hexavalent chromium, Cr 

(VI), then was collected by attaching a small cation-exchange 

column to the syringe filter and, after conditioning the column 

with 2-mL of sample water, an additional 2-mL of sample 

water were collected in a second centrifuge vial. Both vials 

were preserved with 10-μL of 7.5-N nitric acid (Ball and 

McClesky, 2003a, b).

For the collection of 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 closed 

partially to create back pressure, and a 10-mL sample was 

taken through a Teflon© septum on the valve assembly using a 

glass syringe affixed with a stainless-steel needle. The sample 

then was injected into a 25-mL vial partially filled with a scintillation mixture (mineral oil) and shaken. The vial then was 

placed in an insulated cardboard tube to protect the sample 

during shipping. 

Noble gases were collected in 3⁄8-inch-diameter copper 

tubes using reinforced nylon tubing connected to the hose bib 

at the wellhead. Groundwater was flushed through the tubing 

to dislodge bubbles before flow was restricted with a back 

pressure valve. Clamps on either side of the copper tube then 

were tightened, trapping a sample of groundwater for analyses 

of noble gases (Weiss, 1968). 

Alkalinity was measured in the mobile laboratory at the 

well site on filtered samples by Gran’s titration method (Gran, 

1952). Titration data were entered directly into PCFF and the 

concentrations of bicarbonate (HCO3

-

) and carbonate (CO3

2-) 

automatically were calculated from the titration data using the 

advanced speciation method. Concentrations of HCO3

-

 and 

CO3

2- also were calculated from the laboratory alkalinity and 

pH measurements. Calculations were made in a spreadsheet 

using the advanced speciation method (http://or.water.usgs.

gov/alk/methods.html) with pK1 = 6.35, pK2 = 10.33, and 

pKW = 14. 

Eight laboratories performed chemical analyses for this 

study (table A1), although most of the analyses were performed at the NWQL or by labs contracted by the NWQL. 

The NWQL maintains a rigorous quality-assurance program 

(Pirkey and Glodt, 1998; Maloney, 2005). Laboratory qualitycontrol samples, including method blanks, continuing calibration verification standards, standard reference samples, 

reagent spikes, external certified reference materials, and 

external blind proficiency samples, are analyzed regularly. 

Method detection limits are tested continuously and laboratory 

reporting levels are updated accordingly. NWQL maintains 

National Environmental Laboratory Accreditation Program 

(NELAP) and other certifications (http://nwql.usgs.gov/

Public/Performance/publiclabcertcoverpage.html). 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 the National 

Field Quality Assurance program that includes annual testing 

of all USGS field personnel for proficiency in making field 

water-quality measurements (http://qadata.cr.usgs.gov/nfqa/). 

Results for analyses made at the NWQL or by laboratories 

contracted by the NWQL are uploaded directly into NWIS by 

the NWQL. 

Results from the USGS Branch of Quality Systems 

quality assurance program indicate that boron and iron had 

negative analytical biases (each of 12 percent), cadmium and 

uranium had positive analytical biases (of “developing” and 

9.7 percent, respectively) during the time period that SCI 

samples were analyzed at the NWQL (U.S. Geological 

Survey Branch of Quality Systems, 2008). The results suggest 

that boron and iron concentrations may be underestimated 
Appendix 63

slightly and cadmium and uranium concentrations may be 

overestimated slightly. 

Data Reporting

The following section details the laboratory-reporting 

conventions and the constituents that are determined by multiple methods or by multiple laboratories.

Reporting Limits

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 actually is present in a sample) to 

less than 1 percent (Childress and others, 1999). The LRL 

usually is set at two times the long-term method detection 

level (LT-MDL). The LT-MDL is derived from the standard 

deviation of at least 24 MDL determinations made over an 

extended period of time. LT-MDLs are monitored and updated 

continually. 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 the MDL there is less than 1 percent 

chance of a false positive) (Childress and others, 1999; U.S. 

Environmental Protection Agency, 2002). The USGS NWQL 

updates LRL values regularly and the values listed in this 

report were in effect during the period when analyses were 

made for groundwater samples from the SCI study (August to 

December 2008).

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 LT-MDL have high certainty of detection, but the precise concentration is uncertain. 

Information-rich methods are those that utilize gas chromatography or high-performance liquid chromatography (HPLC) 

with mass spectrometry detection (VOCs, pesticides, and polar 

pesticides). Compounds are identified by presence of characteristic fragmentation patterns in their mass spectra in addition to being quantified by measurement of peak areas at their 

associated chromatographic retention times. E-coded values 

also may result from detections outside the range of calibration standards, for detections that did not meet all laboratory 

quality-control criteria, and for samples that were diluted prior 

to analysis (Childress and others, 1999).

Some constituents in this study are reported using minimum reporting levels (MRLs) or method uncertainties (MU). 

The MRL is the smallest measurable concentration of a constituent that may be reliably reported using a given analytical 

method (Timme, 1995). The method uncertainty generally 

indicates the precision of a particular analytical measurement; 

it gives a range of values wherein the true value will be found. 

Results for most constituents are presented using the 

LRL or MRL values provided by the analyzing laboratories. 

Results for some constituents are presented using raised study 

reporting limits (SRLs) derived from assessment of data from 

quality-control samples associated with groundwater samples 

collected as part of the GAMA Priority Basins Project. The 

SRLs were determined by statistical assessment of results 

from the field blanks collected during the first 21 GAMA 

Priority Basins Project study units (May 2004 through January 

2008) (L.D. Olsen and M.S. Fram, U.S. Geological Survey, 

written commun., 2009). The statistical analysis used order 

statistical and binomial probabilities to construct an upper 

confidence limit for the amount of contamination potentially 

present in field blanks, and by inference, in groundwater 

samples (Hahn and Meeker, 1991). The upper confidence limit 

is the maximum concentration of a constituent for which there 

is a 90-percent confidence level that no more than 10 percent 

of the groundwater samples might have a higher concentration 

of that constituent due solely to contamination of the groundwater sample during sample collection, handling, and analysis. 

This maximum concentration corresponds to the concentration 

in the field blank that is at the 95th percentile of the 86 field 

blanks used in the statistical assessment. For most constituents, this maximum concentration was below the LRL or MRL 

for the constituent. Data for such constituents are reported 

with the LRL or MRL. For some constituents, this maximum 

concentration was greater than the LRL or MRL. An SRL then 

was defined as equal to the concentration in the 95th percentile 

field blank. Detections of those constituents reported by the 

laboratory with concentrations greater than the LRL or MRL 

but less than the SRL are considered nondetections in this 

report and are reported in table 8 with a “less-than-or-equalto” (≤) sign preceding the reported value.

The methods used for analysis of radiochemical constituents (gross alpha radioactivity and gross beta radioactivity) 

measure activities by counting techniques (table A1). The 

reporting limits for radiochemical constituents are based on 

sample-specific critical levels (ssLC) (McCurdy and others, 

2008). The critical level is analogous to the LT-MDL used 

for reporting analytical results for organic and nonradioactive 

inorganic constituents. Here, the critical level is defined as the 

minimum measured activity that indicates a positive detection 

of the radionuclide in the sample with less than a 5-percent 

probability of a false positive detection. Sample-specific critical levels are used for radiochemical measurements because 

the critical level is sensitive to sample size and sample yield 

during analytical processing, as well as being dependent on 

instrument background, counting times for the sample and 

background, and the characteristics of the instrument being 

used and the nuclide being measured. An ssLC is calculated 

for each sample, and the measured activity in the sample is 
64 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

compared to the ssLC associated with that sample. Measured 

activities less than the ssLC are reported as nondetections 

(table 13A). 

The analytical uncertainties associated with measurement 

of activities also are sensitive to sample-specific parameters, 

including sample size, sample yield during analytical processing, time elapsed between sample collection and various steps 

in the analytical procedure, as well as parameters associated 

with the instrumentation. Therefore, measured activities of 

radioactive constituents are reported with sample-specific 

combined standard uncertainties (CSU) (table 13A). Specifically, activities of gross alpha and gross beta radiation are 

reported with sample-specific CSU. The CSU is reported at 

the 68-percent confidence level (1-sigma). Radon activities are 

measured by a different laboratory than the other radioactive 

constituents, and the laboratory reports results with 2-sigma 

(95-percent confidence level) standard combined uncertainties 

(table 13B).

Notation

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):

 i eE

R

R

i

= − 



 



 sampl

reference

 per mil

where 

is the at

1 1 000 i ,

omic mass of the heavier isotope of 

element 

is the ele

the ;

E ment (O for oxygen, C for carbon, 

or H for hydrogen);

Rsample is the ratio of the abundance of the heavier 

isotope of the element ( O, C, or H) to 

the lighter isotope of 

18 213

the element, 

( O, C, or H) in the sample; and, 16 12 1

Rreference is the ratio of the abundance of the heavier 

isotope of the element to the lighter isotope 

of the element in the reference material.

The reference material for oxygen and hydrogen is Vienna 

Standard Mean Ocean Water (VSMOW), which is assigned 

δ18O and δ2H values of zero per mil (note than δ2H is sometimes written as δD because the common name of the heavier 

isotope of hydrogen, hydrogen-2, is deuterium). The reference 

material for carbon is Vienna Pee Dee Belemnite (VPDB), 

which is assigned a δ13C value of zero 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

Eleven constituents targeted in this study were measured by more than one analytical schedule or by more than 

one laboratory (table A2). The preferred methods for these 

constituents were selected on the basis of the procedure 

recommended by the NWQL. Methods with full approval are 

preferred over those with provisional approval and approved 

methods are favored over research methods. The method 

with greater accuracy and precision and lower LRLs for the 

overlapping constituents generally is preferred. However, the 

method with higher LRLs may be selected as the preferred 

method to provide consistency with historical data analyzed 

by the same method.

Some of the water-quality indicators (field parameters)—

pH, specific conductance, and alkalinity—were measured 

in the field and at the NWQL. The field measurements are 

the preferred method for all three constituents (pH, specific 

conductance, and alkalinity) because groundwater samples 

change once they are removed from the ambient environment; 

however, both measurements are reported. 

Tritium also is measured at two laboratories: Lawrence 

Livermore National Laboratory (LLNL) and U.S. Geological Survey Stable Isotope and Tritium Laboratory (SITL), 

although only a limited amount of tritium data from the SITL 

were available for reporting at the time of this publication.

For arsenic, chromium, and iron concentrations, the 

approved method, Schedule 1948 used by the NWQL, is 

preferred over the research methods used by the USGS Trace 

Metal Laboratory. The concentrations measured by the Trace 

Metal Laboratory only are used 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(II)

Fe(T) - Fe(II)

Fe(II)

where 

Fe(T) is the total i

=

ron concentration (measured),

Fe(II) is the concentration of ferrous iron (measured), and

Fe(III) is the concentration of ferric iron (calculated).
Appendix 65

Quality Assurance

The purpose of quality assurance is to identify which 

data best represent environmental conditions and which may 

have been affected by contamination or bias during sample 

collection, processing, storage, transportation, or laboratory 

analysis. Four types of quality-control (QC) tests were used 

in this study: blank samples were collected to assess positive 

bias due to contamination during sample handling or analysis; 

replicate samples were collected to assess variability; matrix 

spike tests were done to assess positive or negative bias; and 

surrogate compounds were added to samples analyzed for 

organic constituents to assess bias of laboratory analytical 

methods. In this report, detections of organic constituents in 

groundwater samples that may have resulted from contamination were flagged with a “V” remark code, and were not 

considered detections for calculations of detection frequencies in water-quality assessments. Detections of inorganic 

constituents in groundwater samples that may have resulted 

from contamination during sample handling or analysis were 

flagged with a “≤” remark code to indicate that the amount of 

potential contamination may have been sufficient to change 

a nondetection into a detection, relative to the stated reporting level. Because of the potential contamination, the actual 

concentration in the groundwater sample may be less than or 

equal to (≤) the measured concentration. The evaluation of 

QC data presented in this report was based on results for QC 

samples collected for the SCI study unit and on results for QC 

samples for the 21 GAMA Priority Basins Project study units 

sampled from May 2004 through January 2008. 

The quality-assurance protocols 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 plan followed by the NWQL, the 

primary laboratory used to analyze samples for this study, is 

described in Maloney (2005) and Pirkey and Glodt (1998). 

Blanks

The primary purposes of collecting blanks are to evaluate 

the magnitude of potential contamination of samples by 

analytes of interest during sample collection, handling, 

or analysis, and to identify and mitigate sources of this 

contamination. 

Blank Collection and Analysis

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 (http://wwwnwql.cr.usgs.gov/USGS/

OBW/obw.html). Nitrogen-purged, organic-free blank water 

was used for field blanks of organic constituents, and inorganic-free blank water was used for field blanks of other constituents. For SCI, field blanks were collected at 11 percent of 

the wells sampled. Field blanks were analyzed for VOCs; pesticides and pesticide degradates; polar pesticides and metabolites; pharmaceuticals; perchlorate; NDMA; trace elements; 

nutrients; major and minor ions; silica; TDS; arsenic, chromium, and iron speciation; and radioactive constituents. Field 

blanks were not collected for tritium or noble gases. Tritium 

and noble gases are in the atmosphere and would dissolve into 

any solution used in collecting a blank, making it impractical 

to collect a field blank for these analytes. Stable-isotopic ratios 

of oxygen, hydrogen, and carbon are an intrinsic property of 

any of these elements; therefore, the concept of a blank does 

not apply to these ratios. 

To collect field blanks, blank water either was pumped or 

poured through the sampling equipment (fittings and tubing) 

used to collect groundwater, then processed and transported 

using the same protocols used for the groundwater samples. 

Eight to 12-L of blank water were pumped or poured through 

the sampling equipment before each field blank was collected.

Assessment of Blank Results

Contamination in blanks may originate from several 

different types of sources that require different strategies for 

assessment of potential contamination of groundwater samples 

during sample collection, handling, and analysis. Four primary 

modes of contamination are assessed in the event of detections 

in field-blanks or atypical results in groundwater samples: (1) 

impurities in the water used to collect the blanks, (2) contamination during sample collection and handling from a known 

source or condition present at the field site, (3) carry-over of 

material on the sampling equipment from one sample to the 

next sample, and (4) systematic and random contamination 

from field and laboratory equipment and processes. The fourth 

source of contamination (systematic and random) is being 

addressed using a larger set of field blank results from multiple 

studies, in addition to the results from field blanks collected 

during SCI. The development of this approach and its methods 

are described by L.D. Olsen and M.S. Fram (U.S. Geological 

Survey, written commun., 2009).

The first potential mode evaluated is the presence of 

impurities in the water used to collect the field blank. Because 

the 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, the blank water itself is very rarely 

the source of constituents detected in field blanks. However, 

blank water sometimes is used before the certification process 

has been completed, thus, the certificates of analysis always 

must be checked. Blank water used in the GAMA SCI study 

unit was certified by the NWQL prior to field blank collection. 
66 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

The second potential mode evaluated is contamination 

from identifiable, known sources present at a specific field site. 

Contamination from specific 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 cements used on PVC-piping, contain 

recognizable associations of VOC constituents. For example, 

cements used on PVC-piping primarily are composed of tetrahydrofuran with lesser amounts of acetone and methyl ethyl 

ketone (2-butanone). However, detection of these recognizable 

associations of VOC constituents in groundwater samples does 

not necessarily indicate contamination during sample collection, because these VOC constituents also may occur together 

in groundwater.

If a recognizable association of VOC constituents was 

detected in a field blank or in a groundwater sample, then the 

field notes and photographs from the site at which the sample 

was collected were examined for presence of conditions that 

may have resulted in contamination of the field blank or 

groundwater sample during sample collection. If the constituents were present in the field blank and groundwater sample 

from the same site at similar concentrations and the field notes 

or photographs indicated that the probable contaminant source 

was present, then the detections of those constituents in the 

groundwater sample were V-coded, and all other groundwater 

samples collected at sites where the same condition may have 

occurred were considered for V-coding. If the constituents 

were present in a groundwater sample and not the associated 

field blank, or a groundwater sample from a site where no 

blanks were collected, and the field notes or photographs indicated that the presence of conditions that may have resulted 

in contamination of the groundwater sample during sample 

collection, the data were considered for V-coding. If no conditions that may have resulted in contamination of the groundwater sample during sample collection were identified in the 

field notes or photographs, then V-codes were not applied. 

The third potential mode of contamination that was evaluated was carry-over from the previous groundwater sample 

or field blank collected with the same equipment. Carry-over 

between samples is very rare because the procedures used to 

clean the equipment between samples have been developed 

and extensively tested to assure that carry-over is mitigated 

as much as possible. Potential carry-over was evaluated using 

time-series analysis to look for patterns suggestive of carryover of constituents from a sample with high concentrations 

to the next groundwater sample or field blank collected with 

the same equipment. If nondetections were reported in field 

blanks or groundwater samples collected after the collection 

of groundwater samples containing high concentrations of the 

constituent, then carry-over as a mode of contamination was 

ruled out. 

The fourth potential mode of contamination that was 

evaluated was random or systematic contamination from field 

or laboratory equipment or processes. All detections in field 

blanks that could not be accounted for by impurities in the 

source-solution water, specific known conditions at field sites, 

or carry-over between samples were evaluated for random 

contamination. Random contamination in field and laboratory 

processes has an equal chance of affecting each groundwater 

sample, thus, strategies for flagging detections of constituents 

that are subject to random contamination in field and laboratory processes must be applied to all groundwater samples. 

Different notation was used for flagging detections of 

organic and inorganic constituents that may have been subjected to contamination during sample collection, handling, 

and analysis. Inorganic constituents naturally are present in 

groundwater, and the concerns about inorganic constituents 

generally are related to concentration, rather than to detection 

(presence or absence). In contrast, concerns about organic constituents generally are related to both detection and concentration. Therefore, different schema are used for assessing and 

flagging data for organic and inorganic constituents.

For organic constituents, V-codes were applied. The 

purpose of V-coding was to flag detections that have a greater 

chance of being false-positive detections. A false-positive 

detection is a detection that is caused by contamination during 

sample collection, handling, and analysis of a groundwater 

sample that would otherwise have a nondetection for that 

constituent. Results with V-codes were not considered detections of the constituent for this study and were not included in 

calculations of detection frequencies for organic constituents.

The V-coding level was defined as the highest concentration of the constituent detected in a field blank plus the 

LT-MDL (equal to one-half the LRL) for that constituent. 

Detections of the constituent in groundwater samples at concentrations less than this V-coding level were flagged with a 

“V” in front of the reported value in the data tables. The highest concentration measured in a blank was assumed to represent the highest potential amount of contamination. Thus, the 

V-code flags the results that could have changed from nondetection to a detection, relative to the LT-MDL, due to contamination. Results with V-codes were not considered detections of 

the constituent for this study and were not included in calculations of detection frequencies for organic constituents.

For inorganic constituents, a “≤” symbol was used to 

identify low-concentration detections of constituents that may 

have been affected by contamination. The ≤ symbol signifies 

that the concentration of the constituent in the groundwater 

sample is less than or equal to the measured concentration 

(including the possibility that it may be less than the LT-MDL 

and, therefore, a nondetection). For select trace elements 

(aluminum, chromium, copper, lead, manganese, nickel, tungsten, vanadium, and zinc), the concentration cutoff, hereafter 

referred to as the study reporting limit, SRL, for applying the ≤ 

symbol was determined from a statistical assessment of results 

for 86 field blanks collected between May 2004 and January 

2008. The concentration threshold for applying the ≤ symbol 

was equal to the concentration of the field blank ranked at the 

90-percent confidence level for the 90th percentile of the binomial distribution of the 86 field blanks (L.D. Olsen and M.S. 

Fram, U.S. Geological Survey, written commun., 2009). 
Appendix 67

For all other inorganic constituents, the SRL for applying the ≤ symbol was determined from assessment of the field 

blanks collected at SCI sites only, and was defined as equal 

to the highest concentration measured in the six field blanks 

collected at SCI sites (field blanks were collected at 11 percent 

of the wells sampled). In the data tables, a ≤ symbol was put in 

front of measured values that were less than the threshold concentration. Future reports in this series will use the approach 

of L.D. Olsen and M.S. Fram (U.S. Geological Survey, written 

commun., 2009) for all inorganic constituents. 

Replicates

Sequential replicate samples were collected to assess the 

precision of the water-quality data. Estimates of data precision 

are needed to assess whether differences between concentrations in samples are due to differences in groundwater quality 

or to variability that may result from collecting, processing, 

and analyzing the samples.

Two methods for measuring variability were needed to 

adequately assess precision over the broad range of measured 

concentrations of most constituents. The variability between 

measured concentrations in the pairs of sequential replicate 

samples was represented by the standard deviation (SD) for 

low concentrations and by relative standard deviation (RSD) 

for high concentrations (Anderson, 1987; Mueller and Titus, 

2005). The RSD is defined as the SD divided by the mean 

concentration for each replicate pair of samples, expressed as 

a percentage. The boundary between concentrations for which 

variability is assessed with SD and concentrations for which 

variability is assessed with RSD was defined as five times the 

LRL for each constituent. 

 For this study, acceptable precision for replicate sample 

pairs is defined as follows:

• For concentrations less than five times the LRL 

(<5 LRL), an SD of less than one-half LRL is acceptable.

• For concentrations greater than (or equal to) five times 

the LRL (≤5 LRL), an RSD of less than 10 percent is 

acceptable. For comparison, an RSD of 10 percent is 

equivalent to a relative percent difference (RPD) of 

14 percent. 

• For activities of radiochemical constituents, the presence of overlap between the results (value ± 1-sigma 

CSU) is acceptable.

If results from replicate sample pairs indicate that precision is unacceptable for a constituent, and no specific reason 

can be identified, this greater variability must be considered 

when the data are used for the purposes of comparison. If 

measured concentrations are slightly above a water-quality 

threshold, then actual concentrations could be slightly below 

that threshold. Similarly, if measured concentrations are 

slightly below a water-quality threshold, then actual concentrations could be slightly above. Also, if a constituent has 

high variability in replicate sample pairs, a larger difference 

between concentrations measured in two samples is required 

to conclude that the two samples have significantly different 

concentrations. 

For organic and inorganic constituents (except for radiochemical constituents), if both values for a replicate sample 

pair were reported as detections, the SD was calculated if the 

mean concentration was <5 LRL for the constituent or the 

RSD was calculated if the mean concentration was ≥5 LRL for 

the constituent. If both values were reported as nondetects, the 

variability was set to zero by definition. Cases other than two 

detections or two nondetects were treated as follows:

• For organic constituents, if one or both values were 

assigned a V-code, neither SD nor RSD was calculated. 

A V-code indicates that the constituent was detected in 

blanks and was excluded from the dataset of groundwater-quality results. The data might not represent the 

concentration of the constituent in the groundwater 

sample.

• For organic and inorganic constituents, if one value 

was reported as a nondetect, and the other value was 

reported as a detection below the LRL, a value of zero 

was substituted for the nondetect and the SD calculated. Substituting zero for the nondetect yields the 

maximum estimate of variability for the replicate pair. 

• For inorganic constituents, if one value for a sample 

pair was reported as a nondetect and the other value 

was reported as a ≤-coded value less than the SRL, 

or if both values were reported as ≤-coded values less 

than the SRL, neither SD nor RSD was calculated 

because the values may be analytically identical. The 

≤-code indicates that the value is a maximum potential 

concentration and that the concentration may be low 

enough to be reported as a nondetect. 

• For organic and inorganic constituents, if one value 

was reported as a nondetect and the other value was 

reported as a detection greater than the LRL, the 

variability for the pair was considered unacceptable.
68 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Matrix Spikes

Addition of a known concentration of a constituent 

(‘spike’) to a replicate environmental sample enables the 

analyzing laboratory to determine the effect of the matrix, 

in this case groundwater, on the analytical technique used 

to measure the constituent. The known compounds added 

in matrix spikes are the same as those being analyzed in the 

method. This enables an analysis of matrix interferences on a 

compound-by-compound basis. For this study, matrix spikes 

were added by the laboratory performing the analysis. Low 

matrix-spike recovery may indicate that the compound might 

not be detected in some samples if it were present at very low 

concentrations. Low and high matrix-spike recoveries may be 

a potential concern if the concentration of a compound in a 

groundwater sample is close to the MCL: a low recovery could 

result in a falsely measured concentration below the MCL, 

whereas, a high recovery could result in a falsely measured 

concentration above the MCL.

The GAMA Priority Basins Project defined the dataquality objective for acceptable matrix spike recoveries as 70 

to 130 percent. Only constituents with matrix spike recoveries outside of this range were flagged as having unacceptable 

recoveries, they were in tables 3B and 3C. For many constituents, an acceptable range of 70 to 130 percent for matrix spike 

recovery was more restrictive than the acceptable control limits for laboratory “set” spike recoveries. Laboratory set spikes 

are aliquots of laboratory blank water to which the same spike 

solution used for the matrix spikes has been added. One set 

spike is analyzed with each set of samples. Acceptable control 

limits for set spikes are defined, relative to the long-term variability in recovery. For example, for many NWQL schedules, 

acceptable set spike recovery is within ± 3 F-pseudosigma of 

the median recovery for at least 30 set spikes (Conner and others, 1998). Matrix spikes were performed for VOCs, pesticides 

and pesticide degradates, polar pesticides and metabolites, 

pharmaceuticals, perchlorate, and NDMA because the analytical methods for these constituents are chromatographic and 

may be susceptible to matrix interferences. Replicate samples 

for matrix-spike additions were collected at approximately 6 

percent of the wells sampled, although not all analyte classes 

were tested at every well (tables A5A–A5D).

Surrogates

Surrogate compounds are added to environmental 

samples in the laboratory prior to analysis to evaluate the 

recovery of similar constituents. Surrogate compounds were 

added to all groundwater and quality-control samples that 

were analyzed for VOCs and pesticides (table A6). Most of the 

surrogate compounds are deuterated analogs of compounds 

being analyzed. For example, the surrogate toluene-d8 that is 

used for the VOC analytical method has the same chemical 

structure as toluene, except that the eight hydrogen-1 atoms on 

the molecule have been replaced by deuterium (hydrogen-2). 

Toluene-d8 and toluene behave very similarly in the analytical procedure, but the small mass difference between the two 

results in slightly different chromatographic retention times, 

thus, the use of a toluene-d8 surrogate does not interfere with 

the analysis of toluene (Grob, 1995). Only 0.015 percent of 

hydrogen atoms are deuterium (Firestone and others, 1996), 

thus, deuterated compounds 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 due to improper maintenance and calibration of 

analytical equipment) that produces a negative bias. A 70- to 

130-percent recovery of surrogates generally is considered 

acceptable; values outside this range indicate possible problems with the processing and analysis of samples (Connor and 

others, 1998; Sandstrom and others, 2001).

Quality-Control Results

Detections in Field Blanks

Field blanks were collected at 11 percent of the sites sampled in SCI. Table A3 presents a summary of detections in field 

blanks. Chloroform (trichloromethane) was the only VOC 

detected in the field blank that also was detected in groundwater samples. This blank detection was considered to be random 

contamination, which has an equal chance of affecting each 

groundwater sample. Therefore, strategies for flagging detections of constituents that are subject to random contamination 

must be applied to all groundwater samples. Due to the detection of chloroform in the field blank, all chloroform detections 

were subject to a V-coding level of 0.04 μg/L (E0.02 μg/L plus 

one-half the LRL of 0.04 μg/L). Chloroform was detected at 

concentrations equal to or below the V-coding level in four 

groundwater samples and all of these detections were V-coded 

as nondetections (tables 5 and A3). 

Field blanks for pesticides and pesticide degradates were 

collected at 6 of the 54 SCI wells sampled. The only pesticide 

or pesticide degradate detected in a field blank was one detection of atrazine. This blank detection also was considered to 

be random contamination and, as a result, all atrazine detections in SCI were subject to a V-coding level of 0.0115 μg/L 

(E0.008 μg/L plus one-half the LRL of 0.007 μg/L). Atrazine 

was detected at concentrations below the V-coding level in 

three groundwater samples and all of these detections were 

V-coded as nondetections (tables 6A and A3).
Appendix 69

Trace-element data were assessed for potential flagging 

of results using the GAMA study reporting limits (SRLs), 

which are based on results for 86 field blanks collected 

between May 2004 and January 2008, in conjunction with the 

six field blanks collected at SCI sites. Aluminum, chromium, 

copper, lead, manganese, nickel, tungsten, vanadium, and zinc 

have SRLs previously determined by the field blank study 

(Appendix: Assessment of Blank Results). Measured values 

that are less than the SRL are flagged with a ≤ symbol in 

table 8. Field blanks were collected at 6 of the 54 sites in SCI 

sampled for analysis of trace elements. Four trace elements 

were detected in one field blank; chromium (0.15 μg/L), copper (1.28 μg/L), nickel (E0.12 μg/L), and zinc (E1.25 μg/L). 

All measured detections of these trace metals less than their 

SRL levels were flagged with a ≤ symbol (tables 8 and A3). 

There were no other trace metals detected in any of the six 

field blanks in SCI.

Field blanks were collected at 6 of the 54 sites sampled 

for analysis of major and minor ions, silica, and TDS. Silica 

was detected in one field blank, resulting in a study reporting 

limit (SRL) at E0.015 mg/L. This blank detection was considered to be random contamination, which has an equal chance 

of affecting each groundwater sample, thus, all groundwater 

samples below the SRL value were subject to flagging. No 

groundwater samples had silica concentrations measured 

below E0.015 mg/L, therefore, no values were flagged with a 

≤ symbol (table 10).

Two field blanks were collected for analysis of radioactive constituents. Gross alpha radioactivity (72-hour count) 

was measured with an activity of 0.19 ± 0.15 pCi/L in one 

field blank. None of the environmental gross alpha radioactivity samples had measured activities less than 0.34 pCi/L, the 

upper confidence limit of the maximum activity measured in 

the blank, therefore, no environmental values were flagged 

with a ≤ symbol as a result of the blank detection (table 13A). 

No constituents were detected in the field blanks for the 

following analyte groups: polar pesticides and metabolites 

(two field blanks), perchlorate (six field blanks), NDMA (two 

field blanks), nutrients (six field blanks), arsenic, chromium, 

and iron species analyzed at the USGS Trace Metal Laboratory (one field blank), gross alpha radioactivity (30-day count) 

and gross beta radioactivity (72-hour and 30-day counts) (two 

field blanks). 

Variability in Replicate Samples

Tables A4A and A4B summarize the results of replicate 

analyses for constituents detected in groundwater samples collected in the SCI study. Of the 379 replicate pairs of constituents analyzed, 63 were for constituents detected in at least one 

groundwater sample. Of these 63 pairs, 1 pair (perchlorate) 

had a result outside the limits for acceptable precision. Results 

for replicate analyses for constituents that were not detected 

are not reported in tables A4A and A4B. 

The replicate pair for perchlorate had a RSD value of 

88 percent, well above the unacceptable 10 percent threshold. 

However, the environmental sample concentration was less 

than one-third and the replicate sample concentration was 

one-twentieth of the concentration of the corresponding MCLCA (tables 3E and 7). The less-than-acceptable precision for 

this constituent at these low concentrations will not affect the 

assessments of groundwater quality being made by the GAMA 

Priority Basins Project.

 Two replicate pairs for the 85 VOCs and the 63 pesticide and pesticide degradate compounds were all reported as 

nondetections, while replicate pairs for polar pesticides and 

metabolites were not collected in the SCI study unit. 

Two replicate pairs of samples were analyzed for trace 

elements, nutrients, major and minor ions, silica, total dissolved solids (TDS), isotopic tracers, and carbon-14 activities. 

One replicate pair was analyzed for tritium activities. All of 

the replicate pairs had SD or RSD values within the acceptable 

range of less than 10 percent (table A4B). 

No environmental detections were affected as a result of 

the replicate analysis.

Matrix-Spike Recoveries

Tables A5A–D presents a summary of matrix-spike 

recoveries for the SCI study. The 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 groundwater, on the analytical technique 

used to measure the constituent. Three environmental samples 

were spiked with VOCs to calculate matrix-spike recoveries (table A5A). All of the 85 VOC spike compounds had 

median matrix-spike recoveries within the acceptable range 

of 70 to 130 percent. Three VOC spike compounds; 3-chloropropene, diethyl ether, and iodomethane (methyl iodide) had 

one matrix-spike recovery greater than 130 percent, however, 

they were not detected in groundwater samples. One VOC 

spike compound (dichlorodifluoromethane (CFC-12) had one 

matrix-spike recovery below 70 percent, and it was detected 

in three groundwater samples (two grid and one understanding 

wells) (tables 3A and 5). [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 groundwater samples were spiked with pesticide 

and pesticide degradate compounds to calculate matrix-spike 

recoveries. Thirty-three of the 63 spike compounds had 

median matrix-spike recoveries within the acceptable range of 

70 to 130 percent (table A5B). Three of the four compounds 

detected in groundwater samples had median matrix-spike 

recoveries within the acceptable range. Median spike-matrix 

recovery for deethylatrazine (2-Chloro-4-isopropylamino-6-

amino-s-triazine) was below the acceptable range (62 percent). 

No pesticide and pesticide degradate spike compounds had 

recoveries greater than 130 percent. Thirty-nine pesticide and 

pesticide degradate spike compounds had at least one recovery below 70 percent. Of these compounds, deethylatrazine 

(2-chloro-4-isopropylamino-6-amino-s-triazine) and prometon were the only compounds also detected in groundwater 
70 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

samples (tables 3B and 6A). The deethylatrazine (2-chloro4-isopropylamino-6-amino-s-triazine) detections occurred in 

three grid and two understanding wells, and prometon in two 

grid wells. None of the groundwater samples with environmental detections and unacceptable recoveries in matrix spikes 

analyzed at the NWQL were in the same batch. Thus, none of 

the pesticide and pesticide degradate environmental detections 

were flagged (table 6A). [NOTE – low recoveries indicate that 

the compound might not have been detected in some samples 

if it was present at very low concentrations].

One groundwater sample was spiked with polar pesticide 

and metabolite compounds to calculate matrix-spike recoveries. Forty-two of the 60 spike compounds had matrix-spike 

recoveries within the acceptable range of 70 to 130 percent 

(table A5C). Bentazon, the only polar pesticide and metabolite 

compound detected in groundwater samples had a matrixspike recovery within the acceptable range (76 percent). Ten 

polar pesticide and metabolite compounds had matrix-spike 

recoveries below 70 percent, while eight polar pesticide and 

metabolite compounds had recoveries above 130 percent 

(table A5C). [NOTE – low recoveries indicate that the compound might not have been detected in some samples if it was 

present at very low concentrations].

Four groundwater samples were spiked with perchlorate 

and one with NDMA at Weck Laboratories, Inc. For perchlorate, the median matrix-spike was used and for NDMA the 

median matrix-spike was represented by the recovery from 

the single spike sample. All spike recoveries were within the 

acceptable range of 70 to 130 percent (table A5D). 

Surrogate Compound Recoveries

Surrogate compounds were added to environmental samples in the laboratory and analyzed to evaluate the recovery 

of similar constituents. Table A6 lists the surrogate, 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 for the blank and groundwater 

samples. Blank and environmental samples were considered 

separately to assess whether the matrices present in groundwater samples affect surrogate recoveries. 

In SCI, most surrogate recoveries were within acceptable 

range of 70 to 130 percent recovery. In total, 85 percent of 

the surrogate recoveries for VOC, 88 percent of the surrogate 

recoveries for pesticide, and 85 percent of the surrogate recoveries for polar pesticide analyses were within the acceptable 

range. 
Appendix 71

Table A1. Analytical methods used for the determination of organic and inorganic constituents by the U.S. Geological Survey (USGS) 

National Water Quality Laboratory (NWQL) and additional contract laboratories.

[Laboratory entity codes in the U.S. Geological Survey (USGS) National Water Information System (NWIS) for laboratories other than the USGS National 

Water Quality Laboratory (NWQL) are given in parentheses after the laboratory names. Abbreviations: UV, ultraviolet; VOCs, volatile organic compounds]

Analyte Analytical 

method

Laboratory and 

analytical schedule Citation(s)

Water-quality indicators

Field parameters Calibrated field meters and test kits USGS field measurement U.S. Geological Survey, variously dated

Organic constituents

VOCs Purge and trap capillary gas

chromatography/mass spectrometry

NWQL, Schedule 2020 Connor and others, 1998

Pesticides and 

degradates

Solid-phase extraction and gas

chromatography/mass spectrometry

NWQL, Schedule 2003 Zaugg and others, 1995; Lindley and

others, 1996; Madsen and others, 2003;

Sandstrom and others, 2001

Polar pesticides and 

metabolites

Solid-phase extraction and high

performance 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; Furlong and

others, 2008

Constituents of special interest

Perchlorate Liquid chromatography with mass

spectrometry/mass spectrometry

(USEPA Method 331.0)

Weck Laboratories, Inc., 

standard operating 

procedure ORG099.R01

U.S. Environmental Protection Agency,

2005

N-nitrosodimethylamine 

(NDMA)

Isotopic dilution with gas

chromatography and chemicalionization mass spectrometry 

(USEPA Method 1625 modified)

Weck Laboratories, Inc.,

standard operating

procedure ORG065.R10

U.S. Environmental Protection Agency,

1989; Plomley and others, 1994

Inorganic constituents

Nutrients Alkaline persulfate digestion, 

Kjedahl digestion

NWQL, Schedule 2755 Fishman, 1993; Patton and Kryskalla,

2003

Trace elements, major 

and minor ions, 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

Arsenic, chromium, and 

iron speciation

Various techniques of ultraviolet

visible (UV-VIS) spectrophotometry

and atomicabsorbance spectroscopy

USGS Trace Metal

Laboratory, Boulder,

Colorado (USGSTMCO)

Stookey, 1970; To and others, 1998; Ball

and McCleskey, 2003a and 2003b;

McCleskey and others, 2003
72 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Analyte Analytical 

method

Laboratory and 

analytical schedule Citation(s)

Stable isotopes

Stable isotopes of

hydrogen and oxygen in

water

Gaseous hydrogen and carbon dioxide

water equilibration and stable-isotope

mass spectrometry

USGS Stable Isotope

Laboratory, Reston,Virginia

(USGSSIVA), NWQL

Schedule 1142

Epstein and Mayeda, 1953; Coplen and

others, 1991; Coplen, 1994

Carbon isotopes Accelerator mass spectrometry Woods Hole

Oceanographic Institution,

National Ocean Sciences

Accelerator Mass

Spectrometry Facility

(NOSAMS), NWQL

Schedule 2015

Karlen and others, 1964; Olsson, 1970;

Stuiver, 1980; Stuiver and Polach, 1977

Radioactivity and gases

Tritium Electrolytic enrichment-liquid scintillationUSGS Stable Isotope and

Tritium Laboratory,

Menlo Park, California

(USGSH3CA)

Thatcher and others, 1977

Tritium and noble gases Helium-3 in-growth and mass spectrometryLawrence Livermore

National Laboratory 

(CA-LLNL)

Moran and others, 2002; Eaton and

others, 2004

Radon-222 Liquid scintillation counting NWQL, Schedule 1369 American Society for Testing and

Materials, 1998

Gross alpha and gross

beta radioactivity

Alpha and beta activity counting Eberline Analytical

Services, NWQL 

Schedule 1792

Kreiger and Whittaker, 1980 (USEPA

method 900.0)

Table A1. Analytical methods used for the determination of organic and inorganic constituents by the U.S. Geological Survey (USGS) 

National Water Quality Laboratory (NWQL) and additional contract laboratories.—Continued

[Laboratory entity codes in the U.S. Geological Survey (USGS) National Water Information System (NWIS) for laboratories other than the USGS National 

Water Quality Laboratory (NWQL) are given in parentheses after the laboratory names. Abbreviations: UV, ultraviolet; VOCs, volatile organic compounds]
Appendix 73

Constituent Primary constituent 

classification

Analytical 

schedules

Preferred 

analytical 

schedule

Results from preferred method reported

Atrazine Pesticide 2003, 2060 2003

Caffeine Wastewater indicator 2080, 2060 2060

Deethylatrazine (2-Chloro-4-isopropylamino-6-amino-s-triazine)Pesticide degradate 2003, 2060 2003

Tebuthiuron Pesticide 2003, 2060 2003

Results from both methods reported

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

Tritium Inorganic tracer LLNL, SITL np

Table A2. Preferred analytical schedules for constituents appearing on multiple schedules, for samples collected for the South Coast 

Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.

[Preferred analytical schedules are generally the methods of analysis with the greatest accuracy and precision out of the ones used for the compound in question 

except in cases where consistency with historic data analyzed using the same method is preferred. Abbreviations: LLNL, Lawrence Livermore National Laboratory; SITL, U.S. Geological Survey Stable Isotope and Tritium Laboratory; TML, U.S. Geological Survey Trace Metal Laboratory, Boulder, Colorado; np, no 

preference]

Constituent

Number of 

field blank 

detections/

analyses

Concentrations 

detected in

 field blanks 

Number of 

groundwater 

samples 

V-coded

with ≤

Organic constituents (μg/L)

Chloroform (Trichloromethane) 1/6 E0.02 4

Atrazine 1/6 E0.008 3

Major and minor ions (mg/L)

Silica (as SiO2

) 1/6 E0.015 0

Inorganic constituents (μg/L)

Chromium 1/6 0.15 15

Copper 1/6 1.28 18

Nickel 1/6 E0.12 7

Zinc 1/6 E1.25 20

Radioactive constituents (pCi/L)

Gross alpha radioactivity 

(72-hour count) 1/2 0.19 ± 0.15 0

Table A3. Constituents detected in field blanks collected for the South Coast Interior Basins Groundwater 

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

[V-coded data are reported but not used in summary statistics. Abbreviations: E, estimated or having a higher degree of uncertainty; pCi/L, picocuries per liter; mg/L, milligrams per liter; μg/L, micrograms per liter; ≤, less than or equal to]
74 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table A4A. Quality-control summary for replicate analyses of organic constituents detected in samples collected for the South Coast 

Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.

[Abbreviations: SD, percent standard deviation; RSD, percent relative standard deviation; LRL, laboratory reporting limit; V, analyte detected in samples and 

blanks thus result is not considered a detection for groundwater quality assessment; μg/L, micrograms per liter; nv, no value in category]

Constitutent

Number of 

nondetects/ 

number of

replicates

Number of 

V-coded 

replicates

Number of SDs 

greater than 

1⁄2 LRL/number 

of replicates 

with concentration less than 5 

times the LRL 

Number of 

RSDs greater 

than 10 percent/ 

number of 

replicates with 

concentration 

greater than 5 

times the LRL

Concentrations 

of replicates 

with SDs greater than 1⁄2 LRL 

(environmental, 

replicate)

Volatile organic compounds (VOCs) (Schedule 2020)

Chloroform (Trichloromethane) 2/2 1 nv nv nv

Dichlorodifluoromethane (CFC-12) 2/2 nv nv nv nv

Perchloroethene (PCE) (Tetrachloroethene) 2/2 nv nv nv nv

1,1-Dichloroethene (1,1-DCE) 2/2 nv nv nv nv

Methyl ethyl ketone (2-butanone, MEK) 2/2 nv nv nv nv

Carbon tetrachloride (Tetrachloromethane) 2/2 nv nv nv nv

Tetrahydrofuran 2/2 nv nv nv nv

Toluene 2/2 nv nv nv nv

Trichloro-fluoro-methane (CFC-11) 2/2 nv nv nv nv

Benzene 2/2 nv nv nv nv

Bromodichloromethane 2/2 nv nv nv nv

Carbon disulfide 2/2 nv nv nv nv

Methyl tert-butyl ether (MTBE) 2/2 nv nv nv nv

Pesticides and pesticide degradates (Schedule 2003)

Simazine 2/2 nv nv nv nv

Deethylatrazine (2-Chloro-4-isopropylamino-6-amino-striazine)

2/2 nv nv nv nv

Prometon 2/2 nv nv nv nv

Tebuthiuron 2/2 nv nv nv nv

Polar pesticides and metabolies (Schedule 2060)1

Bentazon 0/0

Constituents of special interest

Perchlorate 1/2 nv nv 1/2 (1.3, 0.30)

1

 No replicate analysis were performed for SC2060 samples.
Appendix 75

Table A4B. Quality-control summary for replicate analyses of trace elements, major and minor ions, silica, total dissolved solids (TDS), 

nutrients, and isotope tracers detected in samples collected for the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, August to December 2008.—Continued

[Abbreviations: SD, percent standard deviation; RSD, percent relative standard deviation in percent; LRL, laboratory reporting limit; μg/L, micrograms per 

liter; mg/L, milligrams per liter; ≤ less than or equal to; nv, no value in category]

Constitutent

Number of 

nondetect or 

≤-coded replicates/number of 

replicates 

Number of SDs 

greater than 

1⁄2 LRL/ number 

of replicates 

with concentration less than 5 

times the LRL

Concentrations 

of replicates 

with SDs 

greater than 

1⁄2 LRL

Number of 

RSDs greater 

than 10 percent/ 

number of 

replicates with 

concentration 

greater than 5 

times the LRL

Concentrations 

of replicates 

with RSDs 

greater than 

10 percent 

Trace elements (μg/L)

Aluminum 1/2 0/1 nv nv nv

Antimony 2/2 nv nv nv nv

Arsenic 0/2 nv nv 0/2 nv

Barium 0/2 nv nv 0/2 nv

Beryllium 2/2 nv nv nv nv

Boron 0/2 nv nv 0/2 nv

Cadmium 2/2 nv nv nv nv

Chromium 1/2 nv nv 0/1 nv

Cobalt 0/2 0/2 nv nv nv

Copper 1/2 0/1 nv nv nv

Iron 1/2 nv nv 0/1 nv

Lead 2/2 nv nv nv nv

Lithium 0/2 0/2 nv nv nv

Manganese 0/2 0/1 nv 0/1 nv

Molybdenum 0/2 nv nv 0/2 nv

Nickel 2/2 nv nv nv nv

Selenium 1/2 nv nv 0/1 nv

Silver 2/2 nv nv nv nv

Strontium 0/2 nv nv 0/2 nv

Tungsten 1/2 0/1 nv nv nv

Uranium 0/2 0/1 nv 0/1 nv

Vanadium 1/2 nv nv 0/1 nv

Zinc 2/2 nv nv nv nv

Major and minor ions, silica, and total dissolved solids (TDS) (mg/L)

Bromide 0/2 0/2 nv nv nv

Calcium 0/2 nv nv 0/2 nv

Chloride 0/2 nv nv 0/2 nv

Fluoride 0/2 0/2 nv nv nv

Iodide 0/2 0/2 nv nv nv

Magnesium 0/2 nv nv 0/2 nv

Potassium 0/2 nv nv 0/2 nv

Silica (as SiO2

) 0/2 nv nv 0/2 nv

Sodium 0/2 nv nv 0/2 nv

Sulfate 0/2 nv nv 0/2 nv

Total dissolved solids (TDS) 0/2 nv nv 0/2 nv

Table A4B. Quality-control summary for replicate analyses of trace elements, major and minor ions, silica, total dissolved solids (TDS), 

nutrients, and isotope tracers detected in samples collected for the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, August to December 2008.

[Abbreviations: SD, percent standard deviation; RSD, percent relative standard deviation in percent; LRL, laboratory reporting limit; μg/L, micrograms per 

liter; mg/L, milligrams per liter; ≤ less than or equal to; nv, no value in category]
76 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Table A4B. Quality-control summary for replicate analyses of trace elements, major and minor ions, silica, total dissolved solids (TDS), 

nutrients, and isotope tracers detected in samples collected for the South Coast Interior Basins Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, August to December 2008.—Continued

[Abbreviations: SD, percent standard deviation; RSD, percent relative standard deviation in percent; LRL, laboratory reporting limit; μg/L, micrograms per 

liter; mg/L, milligrams per liter; ≤ less than or equal to; nv, no value in category]

Constitutent

Number of 

nondetect or 

≤-coded replicates/number of 

replicates 

Number of SDs 

greater than 

1⁄2 LRL/ number 

of replicates 

with concentration less than 5 

times the LRL

Concentrations 

of replicates 

with SDs 

greater than 

1⁄2 LRL

Number of 

RSDs greater 

than 10 percent/ 

number of 

replicates with 

concentration 

greater than 5 

times the LRL

Concentrations 

of replicates 

with RSDs 

greater than 

10 percent 

Nutrients (mg/L)

Phosphorus 0/2 0/2 nv nv nv

Total nitrogen 1/2 nv nv 0/1 nv

Nitrate plus nitrite 1/2 nv nv 0/1 nv

Ammonia 1/2 0/1 nv nv nv

Nitrite 2/2 nv nv nv nv

Isotope tracers

δ2

H (per mil) 0/2 0/2 nv nv nv

δ18O (per mil) 0/2 0/2 nv nv nv

δ13C (per mil) 0/2 0/2 nv nv nv

Carbon-14 (percent modern) 0/2 0/2 nv nv nv
Appendix 77

Constituent

Number 

of spike 

samples

Recovery

(percent)

MinimumMaximum

Median

Acetone 3 100 119 111

Acrylonitrile 3 96 114 114

tert-Amyl methyl ether 

(TAME)

3 110 115 113

Benzene1 3 98 120 116

Bromobenzene 3 98 116 115

Bromochloromethane 3 89 120 111

Bromodichloromethane1 3 83 116 101

Bromoform (Tribromomethane)3 90 114 104

 Bromomethane (Methyl 

bromide) 

3 95 111 102

n-Butylbenzene 3 95 98 95

sec-Butylbenzene 3 106 111 110

tert-Butylbenzene 3 110 117 112

Carbon disulfide1 3 71 84 83

Carbon tetrachloride (Tetrachloromethane)1

3 89 117 114

Chlorobenzene 3 108 116 113

Chloroethane 3 86 115 89

Chloroform (Trichloromethane)1

3 83 124 104

Chloromethane 3 84 104 85

3-Chloropropene 3 107 133 125

2-Chlorotoluene 3 105 115 113

4-Chlorotoluene 3 101 112 110

Dibromochloromethane 3 88 110 108

1,2-Dibromo-3-chloropropane (DBCP)3 100 110 109

1,2-Dibromoethane (EDB) 3 98 119 106

Dibromomethane 3 78 125 97

1,2-Dichlorobenzene 3 91 129 117

1,3-Dichlorobenzene 3 94 115 113

1,4-Dichlorobenzene 3 96 113 112

trans-1,4-Dichloro-2-butene 3 84 108 105

Dichlorodifluoromethane 

(CFC-12)1

3 64 77 72

1,1-Dichloroethane (1,1-

DCA)

3 93 123 114

1,2-Dichloroethane (1,2-

DCA)

3 86 115 108

1,1-Dichloroethene (1,1-

DCE)1

3 95 117 111

cis-1,2-Dichloroethene (cis1,2-DCE)

3 100 121 119

trans-1,2-Dichloroethene 

(trans-1,2-DCE)

3 103 124 118

1,2-Dichloropropane 3 95 121 105

1,3-Dichloropropane 3 96 121 117

2,2-Dichloropropane 3 85 100 99

1,1-Dichloropropene 3 100 123 108

Constituent

Number 

of spike 

samples

Recovery

(percent)

MinimumMaximum

Median

cis-1,3-Dichloropropene 3 101 108 102

trans-1,3-Dichloropropene 3 86 101 101

Diethyl ether 3 106 133 122

Diisopropyl ether (DIPE) 3 108 121 116

Ethylbenzene 3 109 112 110

Ethyl tert-butyl ether 

(ETBE)

3 110 117 111

Ethyl methacrylate 3 102 113 109

o-Ethyl toluene (1-Ethyl-2-

methyl benzene)

3 104 106 105

Hexachlorobutadiene 3 77 99 88

Hexachloroethane 3 92 109 108

2-Hexanone (n-Butyl 

methyl ketone)

3 101 112 110

Iodomethane (Methyl 

iodide)

3 110 135 121

Isopropylbenzene 3 108 112 108

4-Isopropyl-1-methyl 

benzene

3 96 105 105

Methyl acrylate 3 103 122 115

Methyl acrylonitrile 3 106 130 118

Methyl tert-butyl ether 

(MTBE)1

3 110 119 110

Methyl iso-butyl ketone 

(MIBK)

3 100 114 105

Methylene chloride (Dichloromethane)3 84 117 92

Methyl ethyl ketone (2-butanone, MEK)1

3 99 116 113

Methyl methacrylate 3 105 116 111

Naphthalene 3 99 118 106

Perchloroethene (PCE, 

Tetrachloroethene)1

3 89 111 109

n-Propylbenzene 3 99 106 105

Styrene 3 100 107 105

1,1,1,2-Tetrachloroethane 3 87 111 99

1,1,2,2-Tetrachloroethane 3 91 120 106

Tetrahydrofuran1 3 107 118 111

1,2,3,4-Tetramethylbenzene 3 91 110 109

1,2,3,5-Tetramethylbenzene 3 100 117 116

Toluene1 3 93 115 115

1,2,3-Trichlorobenzene 3 105 119 114

1,2,4-Trichlorobenzene 3 97 107 97

1,1,1-Trichloroethane 

(1,1,1-TCA)

3 92 118 106

1,1,2-Trichloroethane 

(1,1,2-TCA)

3 87 123 99

Trichloroethene (TCE) 3 94 115 109

Trichlorofluoromethane 

(CFC-11)1

3 82 113 106

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.

[Acceptable recovery range is between 70 and 130 percent]
78 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Constituent

Number 

of spike 

samples

Recovery

(percent)

MinimumMaximum

Median

1,2,3-Trichloropropane 

(1,2,3-TCP)

3 83 114 96

Trichlorotrifluoroethane 

(CFC-113)

3 74 100 85

1,2,3-Trimethylbenzene 3 111 118 114

1,2,4-Trimethylbenzene 3 105 116 113

1,3,5-Trimethylbenzene 3 105 106 106 1

 Constituents detected in groundwater samples.

Constituent

Number 

of spike 

samples

Recovery

(percent)

MinimumMaximum

Median

Vinyl bromide 

(Bromoethene)

3 91 111 102

Vinyl chloride 

(Chloroethene)

3 90 113 102

m- and p-Xylene 3 109 111 111

o-Xylene 3 104 110 109

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.—

Continued

[Acceptable recovery range is between 70 and 130 percent]
Appendix 79

1

Constituents detected in groundwater samples.

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

South Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number 

of spike 

samples

Recovery

(percent)

MinimumMaximum

Median

Acetochlor 3 79 106 94

Alachlor 3 78 109 95

Atrazine 3 86 102 92

Azinphos-methyl 3 51 94 64

Azinphos-methyl oxon 3 22 53 45

Benfluralin 3 39 55 52

Carbaryl 3 76 123 120

2-Chloro-2,6-diethylacetanilide 3 74 94 81

4-Chloro-2-methylphenol 3 70 83 78

Chlorpyrifos 3 59 87 79

Chlorpyrifos oxon 3 26 55 40

Cyfluthrin 3 34 40 36

Cypermethrin 3 34 39 36

Dacthal (DCPA) 3 89 112 101

Deethylatrazine (2-Chloro4-isopropylamino-6-

amino-s-triazine)1

3 51 71 62

Desulfinylfipronil 3 76 118 102

Desulfinylfipronil amide 3 87 94 94

Diazinon 3 67 86 77

3,4-Dichloroaniline 3 81 94 84

Dichlorvos 3 8 42 18

Dicrotophos 3 24 34 28

Dieldrin 3 75 84 79

2,6-Diethylaniline 3 86 100 87

Dimethoate 3 37 62 47

Ethion 3 52 58 57

Ethion monoxon 3 58 65 63

2-Ethyl-6-methylaniline 3 87 102 89

Fenamiphos 3 57 77 59

Fenamiphos sulfone 3 52 100 64

Fenamiphos sulfoxide 3 7 20 14

Constituent

Number 

of spike 

samples

Recovery

(percent)

MinimumMaximum

Median

Fipronil 3 65 92 81

Fipronil sulfide 3 57 82 78

Fipronil sulfone 3 52 68 65

Fonofos 3 73 95 86

Hexazinone 3 48 55 49

Iprodione 3 41 70 58

Isofenphos 3 57 89 87

Malaoxon 3 42 91 72

Malathion 3 59 88 79

Metalaxyl 3 73 109 98

Methidathion 3 81 84 84

Metolachlor 3 73 100 88

Metribuzin 3 65 81 75

Myclobutanil 3 71 77 74

1-Naphthol 3 27 59 39

Paraoxon-methyl 3 35 71 54

Parathion-methyl 3 61 73 69

Pendimethalin 3 66 86 79

cis-Permethrin 3 33 38 36

Phorate 3 45 72 53

Phorate oxon 3 71 102 78

Phosmet 3 8 14 9

Phosmet oxon 3 18 50 20

Prometon1 3 69 89 80

Prometryn 3 77 105 95

Pronamide (Propyzamide) 3 75 93 85

Simazine1 3 78 95 85

Tebuthiuron1

 3 77 96 83

Terbufos 3 56 70 64

Terbufos oxon sulfone 3 42 85 69

Terbuthylazine 3 81 102 92

Tribufos 3 36 37 37

Trifluralin 3 46 62 56
80 Groundwater-Quality Data, South Coast Interior Basins Study Unit, 2008: Results from the California GAMA Program

Constituent

Number 

of spike 

samples

Recovery

(percent)

Acifluorfen 1 59

Aldicarb 1 67

Aldicarb sulfone 1 73

Aldicarb sulfoxide 1 93

Atrazine 1 121

Bendiocarb 1 103

Benomyl 1 85

Bensulfuron-methyl 1 159

Bentazon1 1 76

Bromacil 1 111

Bromoxynil 1 51

Caffeine 1 78

Carbaryl 1 111

Carbofuran 1 114

Chloramben, methyl ester 1 103

Chlorimuron-ethyl 1 195

3-(4-Chlorophenyl)-1-methyl urea 1 62

Clopyralid 1 28

Cycloate 1 81

2,4-D 1 75

2,4-D methyl ester 1 79

2,4-D plus 2,4-D methyl ester 1 75

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

acid)

1 62

DCPA (Dacthal) monoacid 1 75

Deethylatrazine (2-Chloro-4-isopropylamino-6-amino-s-triazine) 1 89

Deisopropyl atrazine (2-Chloro-6-ethylamino-4-amino-s-triazine) 1 85

Dicamba 1 56

Dichlorprop 1 84

Dinoseb (Dinitrobutyl phenol) 1 57

Diphenamid 1 117

Table A5C. Quality-control summary for matrix-spike recoveries of polar pesticides and metabolites in samples collected for the South 

Coast Interior Basins Groundwater Ambient Monitoring and Assessment (GAMA) study, California, August to December 2008.

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number 

of spike 

samples

Recovery

(percent)

Diuron 1 138

Fenuron 1 110

Flumetsulam 1 131

Fluometuron 1 123

Hydroxyatrazine (2-Hydroxy-4-isopropylamino-6-ethylamino-s-triazine)1 113

3-Hydroxycarbofuran 1 98

Imazaquin 1 137

Imazethapyr 1 122

Imidacloprid 1 111

Linuron 1 121

MCPA (2-Methyl-4-chlorophenoxyacetic 

acid) 

1 75

MCPB (4-(2-Methyl-4-chlorophenoxy)

butyric acid)

1 57

Metalaxyl 1 121

Methiocarb 1 122

Methomyl 1 105

Metsulfuron methyl 1 106

Neburon 1 125

Nicosulfuron 1 207

Norflurazon 1 130

Oryzalin 1 85

Oxamyl 1 97

Picloram 1 37

Propham 1 101

Propiconazole 1 129

Propoxur 1 114

Siduron 1 144

Sulfometuron-methyl 1 161

Tebuthiuron 1 123

Terbacil 1 115

Triclopyr 1 84

1

Constituents detected in groundwater samples.
Appendix 81

Constituent

Number 

of spike 

samples

Recovery (percent)

Minimum Maximum Median

Perchlorate1 4 101 112 110

N-nitrosdimethylamine (NDMA)1 1 2

104

1

Constituents detected in groundwater samples.

2

Median recovery represented by the single spike value.

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

N-nitrosodimethylamine (NDMA) in samples collected for the South Coast Interior Basins 

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

December 2008.

[Acceptable recovery range is between 70 and 130 percent]

Table A6. Quality-control summary for surrogate recoveries of volatile organic compounds (VOCs), pesticides and pesticide 

degradates, and polar pesticides and metabolites in samples collected for the South Coast Interior Basins Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, August to December 2008.

[Abbreviation: VOC, volatile organic compound] 

Surrogate Analytical 

schedule

Constituent or 

constituent

class

analyzed

Number of 

blanks 

analyses

Median 

recovery 

in blanks 

(percent)

Number of surrogate 

recoveries in blanks Number of 

sample 

analyses

Median 

recovery in 

samples 

(percent)

Number of surrogate 

recoveries 

in samples

Below 

70 percent

Above 

130 percent

Below 

70 percent

Above 

130 percent

1-Bromo-4-fluorobenzene 2020 VOC 6 82 0 0 54 81 0 0

1,2-Dichloroethane-d4 2020 VOC 6 118 0 0 54 131 0 24

Toluene-d8 2020 VOC 6 95 0 0 54 95 0 0

Diazinon-d10 2003 Pesticide 6 87 1 0 54 87 12 0

α-HCH-d6 2003 Pesticide 6 86 1 0 54 85 1 0

2,4,5-T (2,4,5-trichlorophenoxyacetic acid)

2060 Polar pesticide 2 73 1 0 11 70 5 0

Barban 2060 Polar pesticide 2 83 0 0 11 85 0 0

Caffeine-13C 2060 Polar pesticide 2 87 0 0 11 89 0 0
This page intentionally left blank.
Manuscript approved for publication, August 11, 2009

Prepared by the USGS Enterprise Publishing Network,

Publishing Service Center, Sacramento, California

For more information concerning the research in this report, contact the

California Water Science Center Director,

U.S. Geological Survey, 6000 J Street

Sacramento, California 95819

http://ca.water.usgs.gov
Mathany and Others–Groundwater-Quality Data in the South Coast Interior Basins Study Unit, 2008:

Results from the California GAMA Program–Data Series 463

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