Prepared in cooperation with the California State Water Resources Control Board

Ground-Water Quality Data in the Middle Sacramento 

Valley Study Unit, 2006—Results from the California 

GAMA Program

Data Series 385

U.S. Department of the Interior

U.S. Geological Survey
Cover Photographs:

Top: Rice field and grain silos in Colusa County, California, July 2008. (Photograph taken by Cathy Munday, U.S. Geological Survey.)

Bottom: Irrigation well in Butte County, California, July 2008. (Photograph taken by Michael Judd, U.S. Geological Survey.)
Ground-Water Quality Data in the Middle 

Sacramento Valley Study Unit, 2006—Results 

from the California GAMA Program

By Stephen J. Schmitt, Miranda S. Fram, Barbara J. Milby Dawson, and Kenneth Belitz

Prepared in cooperation with the California State Water Resources Control Board

Data Series 385

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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

reproduce any copyrighted materials contained within this report.

Suggested reference:

Schmitt, S.J., Fram, M.S., Milby Dawson, B.J., Belitz, K., 2008, Ground-water quality data in the middle Sacramento 

Valley study unit, 2006—results from the California GAMA program: U.S. Geological Survey Data Series 385, 100 p. 

Available at http://pubs.usgs.gov/ds/385
iii

Contents

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

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

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

Acknowledgments ...............................................................................................................................4

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

West Study Area—Corning and Colusa Subbasins........................................................................6

East Study Area—Vina, W. Butte, E. Butte, N. Yuba, S. Yuba, and Sutter Subbasins...............6

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

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

Sample Collection and Analysis.........................................................................................................9

Data Reporting.......................................................................................................................................9

Quality Assurance...............................................................................................................................10

Water-Quality Results .................................................................................................................................10

Quality-Control Sample Results........................................................................................................10

Comparison Thresholds.....................................................................................................................10

Ground-Water-Quality Data ..............................................................................................................11

Water-Quality Indicators ..........................................................................................................12

Organic Constituents.................................................................................................................12

Constituents of Special Interest..............................................................................................12

Inorganic Constituents..............................................................................................................12

Inorganic Tracer Constituents .................................................................................................13

Radioactive Constituents..........................................................................................................13

Microbial Indicators..................................................................................................................14

Future Work .........................................................................................................................................14

Summary........................................................................................................................................................14

References Cited..........................................................................................................................................15

Appendix........................................................................................................................................................78
iv

Figures

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

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit ........................................................................ 3

Figure 2. Map showing the Middle Sacramento Groundwater Ambient Monitoring and 

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

Resources defined ground-water basins and major hydrologic features within 

the study unit................................................................................. 5

Figure 3. Map showing the East and West study areas of the Middle Sacramento 

Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing 

the distribution of study area grids cells, the locations of sampled grid cell wells, 

and the study area boundaries ............................................................ 7

Figure 4. Map showing the East and West study areas of the Middle Sacramento 

Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing 

the distribution of study area grid cells, the locations of sampled flow-path (FP) 

and RICE (R) wells, and the study area boundaries .................................... 8

Tables

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

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June to September, 2006 .................................... 20

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

constituents collected for the slow, intermediate, fast, and RICE well sampling 

schedules in the Middle Sacramento Valley Groundwater Ambient Monitoring 

and Assessment (GAMA) study, California, June to September, 2006 ............... 23

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

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

Quality Laboratory Schedule 2020 ......................................................... 24

Table 3B. Gasoline oxygenates and their degradates, primary uses or sources, comparative 

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

National Water Quality Laboratory Schedule 4024 .................................... 26

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

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

National Water Quality Laboratory Schedules 2032 and 2033 ........................ 27

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

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

National Water Quality Laboratory Schedule 2060 .................................... 29

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

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

Water Quality Laboratory Schedule 2080 ................................................ 30

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

thresholds, and reporting information for the Montgomery Watson Harza 

laboratory .................................................................................... 31

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

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

Laboratory Schedule 2755 and parameter code 2613 ................................. 31
v

Tables—Continued

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

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

Laboratory Schedule 1948 .................................................................. 32

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

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

Boulder, Colorado ........................................................................... 33

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

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

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

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

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

the U.S. Geological Survey’s (USGS) Ohio Microbiology Laboratory parameter 

codes 90901, 90900, 99335, and 99332 ................................................... 35

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

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

June to September, 2006 .................................................................. 36

Table 5. Volatile organic compounds (VOCs), and gasoline oxygenates and degradates 

detected in samples collected for the Middle Sacramento Valley Groundwater 

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

September, 2006 ........................................................................... 41

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

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June to September, 2006 .................................... 45

Table 7. Constituents of special interest (perchlorate, N-nitrosodimethylamine [NDMA], 

and 1,2,3-trichloropropane [1,2,3-TCP]) detected in samples collected in the 

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June to September, 2006 .................................... 54

Table 8. Nutrients and dissolved organic carbon detected in samples collected for the 

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June to September, 2006 .................................... 55

Table 9. Major and minor ions and total dissolved solids detected in samples collected 

for the Middle Sacramento Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, June to September, 2006 ..................... 58

Table 10. Trace elements detected in samples collected for the Middle Sacramento Valley 

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

June to September, 2006 .................................................................. 61

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

for the Middle Sacramento Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, June to September, 2006 ..................... 69

Table 12. Stable isotope ratios of water and tritium detected in samples collected for the 

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June to September, 2006 .................................... 72

Table 13. Nitrogen and oxygen isotopes in nitrate, nitrogen isotopes in nitrogen gas, and 

carbon-14 activities detected in samples collected for the Middle Sacramento 

Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, June to September, 2006 ...................................................... 75
vi

Tables—Continued

Table 14. Radioactive constituents detected in samples collected for the Middle 

Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

Program, California, June to September, 2006 .......................................... 77

Appendix Tables

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

microbial constituents by the U.S. Geological Survey’s (USGS) National Water 

Quality Laboratory (NWQL) and additional contract laboratories ..................... 87

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

schedules/methods for samples collected for the Middle Sacramento Valley 

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

June to September 2006 .................................................................. 89

Table A3. Constituents detected in field blanks collected for the Middle Sacramento 

Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, June to September, 2006 ...................................................... 90

Table A4. Quality-control summary of replicate samples for constituents collected for the 

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, June to September, 2006 .................................... 91

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

compounds (VOCs) and gasoline oxygenates and their degradates in samples 

collected for the Middle Sacramento Valley Groundwater Ambient Monitoring 

and Assessment (GAMA) study, California, June to September, 2006 ............... 93

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

pesticide degradates in samples collected for the Middle Sacramento Valley 

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

June to September, 2006 .................................................................. 95

Table A5C. Quality-control summary for matrix-spike recoveries of constituents of special 

interest in samples collected for the Middle Sacramento Valley Groundwater 

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

September, 2006 ........................................................................... 98

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

constituents in samples collected for the Middle Sacramento Valley 

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

June to September, 2006 .................................................................. 98

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

compounds, and gasoline oxygenates and their degradates, pesticides and 

pesticide degradates, and constituents of special interest in samples collected 

for the Middle Sacramento Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, June to September, 2006 ..................... 99
vii

Abbreviations and Acronyms

(Additional information or clarification given in parentheses)

AB Assembly Bill (through the California State Assembly)

AL action level

AL-US action level (USEPA)

CAS Chemical Abstracts Service (American Chemical Society)

CSU combined standard uncertainty

D detected

DLR detection level for the purpose of reporting (CDPH)

E estimated or having a higher degree of uncertainty

ESAC East study area of the Middle Sacramento Valley study unit

FP flow path

GAMA Groundwater Ambient Monitoring and Assessment (program)

GPS global positioning system

HAL-US Lifetime Health Advisory Level (USEPA)

HPLC high-performance liquid chromatography

IBW inorganic blank water

LRL laboratory reporting level

LSD land-surface datum

LT-MDL long-term method detection level

MCL maximum contaminant level

MCL-CA maximum contaminant level (CDPH)

MCL-US maximum contaminant level (USEPA)

MDL method detection limit

MRL minimum reporting level

MSACV Middle Sacramento Valley study unit

MU method uncertainty

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

na not available

NAWQA National Water Quality Assessment (USGS)

nc sample not collected

NL notification level

NL-CA California notification level (CDPH)

NRP National Research Program (USGS)

NWIS National Water Information System (USGS)

P probability

PCFF-GAMA Personal Computer Field Forms program designed for GAMA sampling

pK logarithm of the reciprocal of the equilibrium constant for a specified reaction 

under specific conditions

QC quality control

RICE rice agriculture

RPD relative percent difference

RSD relative standard deviation

RSD5 risk-specific dose at 10–5
viii

Abbreviations and Acronyms—Continued

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

SMCL secondary maximum contaminant level

SMCL-CA secondary maximum contaminant level (CDPH)

SMCL-US secondary maximum contaminant level (USEPA)

SSMDC sample-specific minimum detectable concentration

TT treatment technique

TT-US treatment technique (USEPA)

U.S. United States

V analyte detected in sample and an associated blank—thus data are not included 

in ground-water quality analysis results

VBW VOC-free (nitrogen-purged) blank water

VPDB Vienna Peedee 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)

WSAC West study area of the Middle Sacramento Valley study unit

Organizations

CDPH California Department of Public Health (formerly the California Department of 

Health Services until July 1, 2007)

LLNL Lawrence Livermore National Laboratory

MWH Montgomery Watson Harza (laboratory)

NELAP National Environmental Laboratory Accreditation Program

NWQL National Water Quality Laboratory (USGS)

SWRCB State Water Resources Control Board (California)

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

DOC dissolved organic carbon

HCl hydrochloric acid

HCO3

– bicarbonate

MTBE methyl tert-butyl ether

NDMA N-Nitrosodimethylamine

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

TDS total dissolved solids

THM trihalomethane

VOC volatile organic compound
ix

Notes

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).

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).

Units of Measurement

ft foot (feet)

in. inch

L liter

mg milligram

mg/L milligrams per liter (parts per million)

mi mile

mL milliliter

mm of Hg millimeters of mercury

μg/L micrograms per liter (parts per billion)

μL microliter

μm micrometer

NTU nephelometric turbidity units

pCi/L picocuries per liter

per mil parts per thousand

δi

E standard 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 in per mil

Abbreviations and Acronyms—Continued
x

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Ground-Water Quality Data in the Middle Sacramento 

Valley Study Unit, 2006—Results from the California 

GAMA Program 

By Stephen J. Schmitt, Miranda S. Fram, Barbara J. Milby Dawson, and Kenneth Belitz

Abstract

Ground-water quality in the approximately 3,340 mi2

Middle Sacramento Valley study unit (MSACV) was 

investigated from June through September, 2006, as part of the 

California Groundwater Ambient Monitoring and Assessment 

(GAMA) program. The GAMA Priority Basin Assessment 

project was developed in response to the Groundwater Quality 

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

Geological Survey (USGS) in cooperation with the California 

State Water Resources Control Board (SWRCB).

The Middle Sacramento Valley study was designed to 

provide a spatially unbiased assessment of raw ground-water 

quality within MSACV, as well as a statistically consistent 

basis for comparing water quality throughout California. 

Samples were collected from 108 wells in Butte, Colusa, 

Glenn, Sutter, Tehama, Yolo, and Yuba Counties. Seventy-one 

wells were selected using a randomized grid-based method to 

provide statistical representation of the study unit (grid wells), 

15 wells were selected to evaluate changes in water chemistry 

along ground-water flow paths (flow-path wells), and 22 were 

shallow monitoring wells selected to assess the effects of rice 

agriculture, a major land use in the study unit, on groundwater chemistry (RICE wells). 

The ground-water samples were analyzed for a large 

number of synthetic organic constituents (volatile organic 

compounds [VOCs], gasoline oxygenates and degradates, 

pesticides and pesticide degradates, and pharmaceutical 

compounds), constituents of special interest (perchlorate, 

N-nitrosodimethylamine [NDMA], and 1,2,3-trichloropropane 

[1,2,3-TCP]), inorganic constituents (nutrients, major and 

minor ions, and trace elements), radioactive constituents, and 

microbial indicators. Naturally occurring isotopes (tritium, and 

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

and carbon), and dissolved noble gases also were measured 

to help identify the sources and ages of the sampled ground 

water. 

Quality-control samples (blanks, replicates, laboratory 

matrix spikes) were collected at approximately 10 percent 

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

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

Field blanks rarely contained detectable concentrations of 

any constituent, suggesting that contamination was not a 

noticeable source of bias in the data for the ground-water 

samples. Differences between replicate samples were within 

acceptable ranges, indicating acceptably low variability. 

Matrix spike recoveries were within acceptable ranges for 

most constituents.

This study did not attempt to evaluate the quality of water 

delivered to consumers; after withdrawal from the ground, 

water typically is treated, disinfected, or blended with other 

waters to maintain acceptable water quality. Regulatory 

thresholds apply to treated water that is served to the 

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

context for the results, concentrations of constituents measured 

in the raw ground water were compared with health-based 

thresholds established by the U.S. Environmental Protection 

Agency (USEPA) and California Department of Public Health 

(CDPH) and thresholds established for aesthetic concerns 

(secondary maximum contaminant levels, SMCL-CA) by 

CDPH. Comparisons between data collected for this study and 

drinking-water thresholds are for illustrative purposes only 

and are not indicative of compliance or noncompliance with 

regulatory thresholds.

Most constituents that were detected in ground-water 

samples were found at concentrations below drinking-water 

thresholds. VOCs were detected in less than one-third and 

pesticides and pesticide degradates in just over one-half of 

the grid wells, and all detections of these constituents in 

samples from all wells of the MSACV study unit were below 

health-based thresholds. All detections of trace elements 

in samples from MSACV grid wells were below healthbased thresholds, with the exceptions of arsenic and boron. 
2 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Arsenic concentrations were above the USEPA maximum 

contaminant level (MCL-US) threshold in eight grid wells, 

and boron concentrations were above the CDPH notification 

level (NL-CA) in two grid wells. Arsenic was detected above 

the MCL-US in two flow-path wells. Arsenic, barium, boron, 

molybdenum, strontium, and vanadium were detected above 

health-based thresholds in a few of the RICE wells; these 

wells are not used to supply drinking water. All detections of 

radioactive constituents were below health-based thresholds, 

although six samples had activities of radon-222 above the 

lower proposed MCL-US threshold. Most of the samples from 

the MSACV wells had concentrations of major elements, total 

dissolved solids, and trace elements below the non-enforceable 

thresholds set for aesthetic concerns. Chloride and sulfate 

concentrations exceeded SMCL-CA thresholds in two and one 

grid well, respectively. Iron, manganese, and total dissolved 

solids concentrations were above the SMCL-CA thresholds 

in 1, 12, and 6 grid wells, respectively. Nitrate (nitrite plus 

nitrate, as dissolved nitrogen) concentrations from two grid 

wells were above the MCL-US threshold. There were no 

detections of microbial indicators in MSACV. 

Introduction

Ground water comprises nearly half of the public water 

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

assess the quality of ground water from public-supply wells 

and establish a program for monitoring trends in groundwater quality, the California State Water Resource Control 

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

Survey (USGS) and Lawrence Livermore National Laboratory 

(LLNL), implemented a statewide Groundwater Ambient and 

Monitoring and Assessment (GAMA) program (http://www.

waterboards.ca.gov/gama). The GAMA program consists of 

three projects: Priority Basin Assessment, conducted by the 

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

Well Assessment, conducted by the SWRCB; and Special 

Studies, conducted by LLNL.

The SWRCB initiated the GAMA Priority Basin 

Assessment project in response to the Ground-Water Quality 

Monitoring Act of 2001 (Sections 10780–10782.3 of the 

California Water Code, Assembly Bill 599). AB 599 is a 

public mandate to assess and monitor the quality of ground 

water used as public supply for municipalities in California. 

The project is a comprehensive assessment of statewide 

ground-water quality designed to help better understand 

and identify risks to ground-water resources and to increase 

the availability of information about ground-water quality 

to the public. As part of the AB 599 process, the USGS, in 

collaboration with the SWRCB, developed the monitoring 

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

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

are interagency collaboration and cooperation with local water 

agencies and well owners. Local participation in the project is 

entirely voluntary.

The GAMA Priority Basin Assessment project is 

unique in California because the data collected during the 

study include analyses for an extensive number of chemical 

constituents at very low concentrations—analyses that are not 

normally available. A broader understanding of ground-water 

composition will be especially useful for providing an early 

indication of changes in water quality and for identifying 

the natural and human factors affecting water quality. 

Additionally, the GAMA Priority Basin Assessment project 

will analyze a broader suite of constituents than required 

by the California Department of Public Health (CDPH, 

formerly the California Department of Health Services). An 

understanding of the occurrence and distribution of these 

constituents is important for the long-term management and 

protection of ground-water resources.

The range of hydrologic, geologic, and climatic 

conditions that exist in California must be considered in 

an assessment of ground-water 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 ground-water basins within these hydrologic 

provinces. These ground-water basins, defined by the 

California Department of Water Resources, generally consist 

of relatively permeable, unconsolidated deposits of alluvial or 

volcanic origin (California Department of Water Resources, 

2003). Ground-water basins were prioritized for sampling on 

the basis of the number of public-supply wells in the basin, 

with secondary consideration given to municipal ground-water 

use, agricultural pumping, the number of leaking underground 

fuel tanks, and pesticide applications within the basins 

(Belitz, and others, 2003). In addition, some ground-water 

basins or groups of adjacent similar basins with relatively few 

public-supply wells were assigned high priority so that all 

hydrogeologic provinces would be represented in the subset 

of basins sampled. The 116 priority basins were grouped into 

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

basins were included in several of the study units to achieve 

representation of the 20 percent of public-supply wells not 

located in the ground-water basins. 
Introduction 3

Figure 1. The hydrogeologic provinces of California and the location of the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit (black area).

Sacramento

Redding

Los Angeles

Bakersfield

San Diego 0 50 100 200 MILES

0 100 200 KILOMETERS 50

Shaded relief derived from U.S. Geological Survey Provinces from Belitz and others, 2003

National Elevation Dataset, 2006 

Albers Equal Area Conic Projection

124° 122° 120° 118° 116° 114°

42°

40°

38°

36°

34°

32°

Transverse

and Selected

Peninsular Range

Desert

Southern

Coast

Ranges

Basin

and Range

Sierra

Nevada

Central

Valley

Modoc

Plateau and

Cascades

Klamath

Mountains

Northern

Coast

Ranges

San

Diego

MEXICO

ARIZONA

NEVADA

OREGON

Middle Sacramento

Valley Basin Study Unit

Pacific

Ocean

San Francisco
4 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

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 ground-water quality 

(Kulongoski and Belitz, 2004). This report is one of a series 

of status reports presenting water-quality data collected in 

each study unit; previous reports in this series include Wright 

and others (2005), Kulongoski and others (2006), Bennett and 

others (2006), Fram and Belitz (2007), Dawson and others 

(2008), and Kulongoski and Belitz (2007). Subsequent GAMA 

reports will address the trends and understanding aspects of 

the water-quality assessments.

The Middle Sacramento Valley GAMA study unit, 

hereinafter referred to as “MSACV,” lies in the Central Valley 

hydrogeologic province (Belitz and others, 2003). MSACV 

contains eight subbasins of the Sacramento Valley groundwater basin (California Department of Water Resources, 2003) 

(fig. 2). MSACV was considered high priority for sampling 

because of the number of public-supply wells, basin area, 

number of sections with pesticide applications, and the amount 

of agricultural pumping (Belitz and others, 2003).

Purpose and Scope

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

study design and study methods; (2) to present the sampling, 

analytical, and quality assurance methods used during the 

study; (3) to present the results of quality-control (QC) tests; 

and (4) to present the analytical results for ground-water 

samples collected in MSACV. 

Ground-water samples were analyzed for organic, 

inorganic, and microbial constituents, field parameters, and 

chemical tracers. The chemical and microbial data presented 

in this report were evaluated by comparison with state and 

federal drinking-water regulatory thresholds and other healthbased standards that are applied to treated drinking water. 

Regulatory thresholds considered for this report are those 

established by the U.S. Environmental Protection Agency 

(USEPA) and the California Department of Public Health 

(CDPH) (U.S. Environmental Protection Agency, 2008a, 

2008b, 2008c; California Department of Public Health, 2008a, 

2008b). 

The data presented in this report are intended to 

characterize the quality of untreated ground-water resources 

within the study unit, not the treated drinking water delivered 

to consumers by water purveyors. Discussions of the 

factors that influence the distribution and occurrence of the 

constituents detected in ground-water samples will be the 

subject of subsequent publications. 

Acknowledgments 

The authors thank the following cooperating agencies 

for their support: the State Water Resources Control Board 

(SWRCB), California Department of Public Health, California 

Department of Water Resources, and Lawrence Livermore 

National Laboratory. We especially thank the well owners 

and water purveyors for their generosity in allowing the U.S. 

Geological Survey (USGS) to collect samples from their 

wells. Three reviewers, Jan Stepek (SWRCB), George Bennett 

(USGS), and Jacob Fleck (USGS) provided comments to 

improve this report. Funding for this work was provided by 

state bonds authorized by Proposition 50 and administered by 

the SWRCB.

Hydrogeologic Setting 

Knowledge of the hydrogeologic setting is important in 

the design of a ground-water-quality investigation. MSACV 

lies within the Central Valley hydrogeologic province of 

California and covers approximately 3,340 mi2 in Butte, 

Colusa, Glenn, Sutter, Tehama, Yolo, and Yuba Counties 

(fig. 2). The long axis of the study unit trends north-south 

for a distance of approximately 90 mi along the Sacramento 

River, and the short axis is approximately 40 mi long and 

corresponds to the width of the Central Valley between the 

Coast Ranges to the west and the Sierra Nevada to the east 

(fig. 2). MSACV contains eight subbasins of the Sacramento 

Valley ground-water basin (California Department of Water 

Resources, 2003) (fig. 2). For the purposes of this study, these 

eight subbasins were grouped into the East and West study 

areas, separated by the Sacramento River (fig. 3). The East 

study area includes the subbasins of Vina, West Butte, East 

Butte, North Yuba, South Yuba, and Sutter, whereas the West 

study area includes the Colusa and Corning subbasins. 

The main water-bearing deposits of MSACV are 

primarily composed of continental and marine sediments 

overlying the consolidated Sierra Nevada block (California 

Department of Water Resources, 2003). These recent 

Quaternary (Holocene) to Late Tertiary (Miocene) deposits 

have a cumulative thickness of several hundred feet near 

the foothills of the Coast Ranges and Sierra Nevada and 

deepen to approximately 2,000 ft near the valley center. 

Sources of ground-water recharge include deep infiltration of 

precipitation, river and stream flow, and agricultural irrigation 

return flow. 

The primary surface-water features of MSACV include 

the Sacramento River and smaller rivers and their principal 

tributaries. The rivers and tributaries include Stony Creek 

and Cache Creek in the West study area, and Butte Creek, the 

Feather, Yuba, and Bear Rivers in the East study area (fig. 2). 
Hydrogeologic Setting 5

Figure 2. The Middle Sacramento Groundwater Ambient Monitoring and Assessment (GAMA) study unit 

showing the California Department of Water Resources defined ground-water basins and major hydrologic 

features within the study unit.

Corning

Vina

West

Butte

Colusa

East Butte

Sutter

North

Yuba

South

Yuba

70

49

505

70

149

29

99

80

20

49

99

20

65

5

TEHAMA CO

TEHAMA CO

BUTTE CO

GLENN CO

GLENN CO

PLUMAS CO

BUTTE CO

COLUSA CO

COLUSA CO

SUTTER CO

Sutter

 Buttes

YOLO CO

SACRAMENTO CO

PLACER CO

PLACER CO

EL DORADO CO

NEVADA CO

YUBA CO

LAKE CO

NAPA CO

SONOMA

CO

122°30’ 122°

40°

39°30’

39°

121°30’

0 105 20 MILES

0 10 20 5 KILOMETERS

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Colusa

Coast

Ranges

Sierra

Nevada

Oroville

Chico

Corning Vina

Willows

Yuba City Marysville

Yolo City

Colusa

EXPLANATION

Limited access highway

Highway

Counties

Water bodies

Stream or river Chico Monocline

Thomes Creek

Stony Creek

Butte Creek

Deer Creek

Cache Creek

Sutter Bypass Bear River

YubaRiver

Fea ht er River

Sacramento

River

Black 

Butte

Lake

Thermalito

Afterbay 

Lake

Oroville

Thermalito

Forebay 
6 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

West Study Area—Corning and Colusa 

Subbasins

The West study area is bounded to the north by Thomes 

Creek, to the south by Cache Creek, to the west by the Coastal 

Ranges, and to the east by the Sacramento River (fig. 3). It 

covers an area of approximately 1,756 mi2 and includes parts 

of Colusa, Glenn, Tehama, and Yolo Counties (California 

Department of Water Resources, 2003). The average annual 

precipitation ranges from 17 to 27 in., increasing to the north 

and west. The main water-bearing aquifer within this study 

area is the Tehama formation (Pliocene). The formation 

consists of unconsolidated to moderately consolidated 

coarse- and fine-grained sediments, indicative of floodplain 

deposits. The Tehama formation is up to 2,000 ft thick and 

varies in depth from a few feet to several hundred feet below 

the land surface with depth generally increasing to the east. 

The Tehama formation is confined by the Tertiary-age Tuscan 

formation, which contains low permeability lahar layers 

(California Department of Water Resources, 2003).

East Study Area—Vina, W. Butte, E. Butte, N. 

Yuba, S. Yuba, and Sutter Subbasins

The East study area is bounded to the north by Deer 

Creek, to the south by Sutter Bypass and Bear River, to the 

west by the Sacramento River, and to the east by the Chico 

Monocline and the Sierra Nevada (fig. 3). It covers an area 

of approximately 1,584 mi2 and includes parts of Butte, 

Colusa, Glenn, Sutter, Tehama and Yuba Counties (California 

Department of Water Resources, 2003). The average annual 

precipitation is 17 to 32 in., with increasing rainfall to the 

north and east. Aquifers within this study area are composed 

of Tertiary to late Quaternary age deposits, with the younger 

Quaternary deposits typically representing the unconfined 

portion of the aquifer system. The Quaternary portion of 

the aquifer system is largely composed of unconsolidated 

gravel, sand, silt, and clay stream channel and alluvial fan 

deposits. South and east of the Sutter Buttes, the deposits 

contain Pleistocene alluvium, which is composed of loosely 

compacted silts, sands, and gravels that are moderately 

permeable; however, nearly impermeable hardpans and 

claypans do exist in this deposit, which restrict the vertical 

movement of ground water. The confined portion of the 

aquifer system includes the Tertiary-age Tuscan and Laguna 

formations. The Tuscan formation consists of volcanic 

mudflows, tuff breccia, tuffaceous sandstone, and volcanic 

ash deposits up to 1,250 ft thick. The Laguna formation 

consists of moderately consolidated and poorly to well 

cemented interbedded alluvial sand, gravel, and silt with a 

low permeability, overall (California Department of Water 

Resources, 2003).

Methods

The methods used for the GAMA program were selected 

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

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

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

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

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

relevant documentation.

Study Design

The wells selected for sampling in this study reflect 

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

spatially distributed assessment of the quality of ground-water 

resources used for public drinking-water supply (fig. 3), and 

37 additional wells were selected to provide greater sampling 

density in several areas to address specific ground-water 

quality issues in the study unit (fig. 4).

The spatially distributed wells were selected using a 

randomized grid-based method (Scott, 1990). Each of the 

study areas was subdivided into grid cells that were 38.6 mi2

(100 km2) in area. This grid-cell size met GAMA objectives 

for the Central Valley hydrogeologic province of a sampling 

density of at least one well per 38.6 mi2 and having at least 10 

grid cells per study area. For this assessment, the East study 

area was divided into 41 grid cells and the West study area 

into 46 grid cells.

 Seventy-one of the 87 grid cells in MSACV contained 

wells that could be sampled; the other 16 grid cells did not 

contain accessible wells. If a grid cell contained more than 

one public-supply well, each well was randomly assigned a 

rank. The highest ranking well that met basic sampling criteria 

(for example, sampling point prior to treatment, capability 

to pump for several hours, and available well-construction 

information), and for which permission to sample could 

be obtained was then sampled. If a grid cell contained no 

accessible public-supply wells, domestic and irrigation wells 

were considered for sampling. An attempt was made to 

select domestic and irrigation wells with depths and screened 

intervals similar to those in public-supply wells in the area. 

Wells sampled as part of the randomized grid-cell network 

are hereinafter referred to as “grid wells.” Grid wells sampled 

in MSACV were numbered in the order of sample collection, 

with the following prefixes that are based on study area: 

“ESAC” for the East study area of the Middle Sacramento 

Valley study unit, and “WSAC” for the West study area of the 

Middle Sacramento Valley study unit.
Methods 7

Figure 3. The East and West study areas of the Middle Sacramento Groundwater Ambient Monitoring 

and Assessment (GAMA) study unit showing the distribution of study area grids cells, the locations of 

sampled grid cell wells, and the study area boundaries.

36

35

34

33

32

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

15

14

13

12

11

10

09

08 07

06

05

04

03

02

01

35

34 33

32

31

30

29

28

27

26

25

24

23

22

21

20 19

18

17

16

15

14

13

12

11

10

09

08 07

06

05

04

03

02 01

Sutter

 Buttes

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

West 

study 

area

Coast

Ranges

Sierra

Nevada

East 

study 

area

39°30’

39°

40°

122°30’ 122° 121°30’

0 5 10 20 MILES

0 10 20 5 KILOMETERS

EXPLANATION

Grid well

Cell boundary Chico Monocline

Thomes Creek

Deer Creek

Cache Creek

Sutter

Bypass

Bear River

Sacra

mento

River
8 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Figure 4. The East and West study areas of the Middle Sacramento Groundwater Ambient Monitoring 

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

sampled flow-path (FP) and RICE (R) wells (RICE wells are part of a well network monitoring the shallow 

ground-water quality associated with rice agriculture), and the study area boundaries.

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

R-22

R-21

R-20

R-19

R-18

R-17

R-16

R-15

R-14

R-13

R-12 R-11

R-10 R-09

R-08

R-07

R-06

R-05

R-04

R-03

R-02

R-01

Sutter

 Buttes

0 5 10 20 MILES

0 10 20 5 KILOMETERS

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

FP-01

FP-01

FP-07

FP-08

FP-03

FP-04

FP-02

FP-02

FP-03

FP-04

FP-06

FP-05

FP-05

FP-06

FP-07

39°30’

39°

40°

122°30’ 122° 121°30’

EXPLANATION

Rice well

Cell boundary

Single well

Two well cluster

Three well cluster

Flow-path well

!

!

!!

!!!

Chico Monocline

Thomes Creek

Deer Creek

Cache Creek

Sutter

Bypass

Bear River

West 

study 

area

Coast

Ranges

Sierra

Nevada

East 

study 

area

Sacramento

River
Methods 9

In addition to the 71 grid wells, two types of 

nonrandomized wells were sampled in the East and West study 

areas. The first type of nonrandomized wells included 15 

wells to evaluate changes in water chemistry along groundwater flow paths; these wells are referred to as “flow-path 

wells.” Flow-path wells were numbered in the order of sample 

collection, with the prefixes ESAC-FP for wells in the East 

Sacramento Valley study area and WSAC-FP for wells in 

the West Sacramento Valley study area. The second type of 

nonrandomized wells consisted of 22 shallow monitoring 

wells selected to assess the effects of rice agriculture, a major 

land-use in the study unit, on shallow ground-water chemistry. 

In 1997, the USGS installed and sampled a set of monitoring 

wells in rice-growing areas of the Sacramento Valley as part 

of the National Water-Quality Assessment Program (Milby 

Dawson, 2001). Many of those monitoring wells are in the 

MSACV area and were resampled as part of this study. 

The monitoring wells are numbered in the order of sample 

collection with the prefix “RICE.” Flow-path wells and RICE 

wells sampled as part of this study for better understanding 

were not included in the statistical characterization of water 

quality in MSACV, as the inclusion of these wells would have 

caused overrepresentation of certain grid wells and of shallow 

ground water.

Table 1 provides the GAMA alphanumeric identification 

number for each well, along with the date sampled, sampling 

schedule, well elevation, and well-construction information.

Well locations and identifications were verified using 

a global positioning system (GPS) receiver, 1:24,000 scale 

USGS topographic maps, comparison with existing well 

information in USGS and CDPH databases, and information 

provided by well owners. Drillers’ logs for wells were 

obtained when available. Well information was recorded 

by hand on field sheets and electronically using specialized 

software on field laptop computers. All information was 

verified and then uploaded into the USGS’s National Water 

Information System (NWIS). Well owner information is 

confidential. Well location information and all chemical data 

are currently inaccessible from NWIS’s public website.

The wells in MSACV were sampled using a tiered 

analytical approach. All wells were sampled for a standard 

set of constituents, including field water-quality indicators, 

volatile organic compounds (VOCs), pesticides and pesticide 

degradates, perchlorate, stable isotopes of water, and dissolved 

noble gases and tritium and helium age dates. The standard 

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

Wells on the intermediate schedule were sampled for all 

the constituents on the fast schedule, plus pharmaceuticals, 

N-nitrosodimethylamine (NDMA), 1,2,3-trichloropropane 

(1,2,3-TCP), nutrients, stable isotopes of oxygen and nitrogen 

in nitrate, major and minor ions, trace elements, species of 

arsenic, iron, and chromium, and carbon isotopes. Wells on 

the slow schedule were sampled for all the constituents on 

the intermediate schedule, plus dissolved organic carbon, 

radium 226/228, radon-222, gross alpha and beta radiation, 

coliform, coliphage, alkalinity, and turbidity (table 2). Fast, 

intermediate, and slow refer to the time required to sample the 

well for all the analytes on the schedule. Generally, one slow, 

two intermediate, or three fast wells could be sampled in one 

day. RICE wells were sampled on a modified intermediate 

schedule. In MSACV, 26 wells were sampled on the fast 

schedule, 52 were sampled on the intermediate schedule, 8 

on the slow schedule, and 22 on the RICE monitoring-well 

schedule (table 2).

Sample Collection and Analysis

Samples were collected in accordance with the protocols 

established by the USGS’s National Water Quality Assessment 

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

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

dated). These sampling protocols ensure that a representative 

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

samples are collected and handled in a way that minimizes 

the potential for contamination. The methods used for sample 

collection are described in the Appendix section “Sample 

Collection and Analysis.”

Tables 3A–L list the compounds analyzed in each 

constituent class. Raw (untreated) ground-water samples were 

analyzed for 85 VOCs (table 3A) and 8 gasoline additives 

(table 3B), 135 pesticide and pesticide degradates (tables 3C, 

3D), 14 pharmaceutical compounds (table 3E), 3 constituents 

of special interest (table 3F), 5 nutrients and dissolved organic 

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

solids (table 3H), 25 trace elements (table 3H), 6 species of 

arsenic, iron, and chromium (table 3I), 5 stable isotope ratios 

and 7 radioactive constituents, tritium, and carbon-14 (table 

3J), 5 dissolved noble gases, helium stable isotope ratios, and 

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

The methods used for sample analysis are described in the 

Appendix section “Sample Collection and Analysis.”

Data Reporting

The methods and conventions used for reporting the data 

are described in the Appendix. Thirteen constituents analyzed 

in this study were measured by more than one method at 

the USGS’s National Water Quality Laboratory (NWQL), 

but only the results from the preferred method for each of 

the constituents are reported. Arsenic, iron, and chromium 

concentrations, and tritium activities were analyzed by more 

than one laboratory, and both sets of results are reported.
10 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Quality Assurance

The protocols used for this study are those used by the 

NAWQA program (U.S. Geological Survey, variously dated; 

Koterba and others, 1995), and the quality assurance protocols 

are described in the NWQL quality assurance plan (Maloney, 

2005; Pirkey and Glodt, 1998). QC samples collected in the 

MSACV study include source-solution blanks, field blanks, 

replicates, and matrix and surrogate spikes. QC samples were 

collected to evaluate contamination, bias, and variability of 

the water-quality data that may have resulted from sample 

collection, processing, storage, transportation, and laboratory 

analysis. Quality-assurance methods and results are described 

in the Appendix section “Quality Assurance.”

Water-Quality Results

Quality-Control Sample Results

Results of QC analyses (blanks, replicates, matrix 

spikes, and surrogates) were used to evaluate the quality 

of the data for the ground-water samples (see Appendix). 

Assessment of the QC data from blanks resulted in some 

ground-water samples being censored, as indicated with 

“V” codes in tables 5–14. Of the 300 constituents analyzed, 

35 were detected in at least one field blank. For 15 of these 

constituents, concentrations detected in the field blanks were 

below the lowest concentration detected in ground-water 

samples, or the constituent was not detected in ground-water 

samples; thus, no data were affected. Some reported detections 

for five organic constituents in ground-water samples were 

flagged as potentially contaminated, and, therefore, were not 

considered as detections for ground-water quality assessment. 

Some low concentration detections of 12 inorganic 

constituents were flagged because contamination may have 

raised the concentrations sufficiently to have changed a 

nondetection into a low-level detection relative to the stated 

reporting limit. 

Data from replicates indicate that variability between 

measurements generally was low, with relative standard 

deviations (RSD) below 5 percent for most replicate pairs 

for most constituents. Of the 30 pairs with RSDs above 

the acceptable limit of 20 percent, 29 had data that were 

estimated concentrations at or below the laboratory reporting 

level (LRL) for the constituent analyzed. At these low 

concentrations, small differences in the measured values in the 

replicate pairs account for the large RSDs. These results from 

the replicates confirm that the procedures used to collect and 

analyze the samples were consistent. 

Median matrix-spike recoveries for 35 of the 232 

constituents analyzed were lower than the acceptable limits, 

which may indicate that these constituents might not have 

been detected in some samples if they were present at very 

low concentrations. 

More than 90 percent of the samples analyzed with 

surrogates had surrogate recoveries within acceptable 

limits. The QC results are described in the Appendix section 

“Quality-Control Sample Results.”

Comparison Thresholds

Concentrations in ground-water samples were 

compared with CDPH and USEPA drinking-water healthbased thresholds. Concentrations were also compared with 

thresholds established for aesthetics—secondary maximum 

contaminant levels (SMCLs) (California Department of 

Health Services, 2007a; California Department of Public 

Health, 2008a, 2008b; U.S. Environmental Protection Agency, 

2006, 2008a, 2008b, 2008c). CDPH became the California 

Department of Health Services (CDHS) on July 1, 2007. 

The chemical and microbial data presented in this report are 

meant to characterize the quality of the untreated groundwater resources within MSACV, and are not intended to 

represent the treated drinking water delivered to consumers 

by water purveyors. The chemical and microbial composition 

of treated drinking water may differ from untreated ground 

water because treated drinking water may be subjected to 

disinfection, filtration, mixing with other waters, and exposure 

to the atmosphere prior to its delivery to consumers. 

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. National MCLs established 

by the USEPA are the minimum standards with which states 

are required to comply, and individual states may choose to 

set more stringent standards. CDPH has established MCLs 

for additional constituents not regulated by the USEPA, as 

well as lowered the threshold concentration for a number of 

constituents with MCLs established by the USEPA. In this 

report, a threshold set by the USEPA is labeled “MCL-US,” 

and one set by CDPH that is different from the MCL-US is 

labeled “MCL-CA.” CDPH is notified when constituents are 

detected at concentrations exceeding MCL-US or MCL-CA 

thresholds in samples collected for the GAMA Priority Basin 

Assessment, 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 actionlevel 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 these thresholds are labeled “AL-US” in this report.

TT—Treatment Technique. Legally enforceable 

standards that apply to public-water systems and are designed 

to protect public health by limiting the levels of microbial 

constituents in drinking water. Detections of microbial 
Water-Quality Results 11

constituents above the treatment-technique thresholds trigger 

requirements for mandatory additional disinfection during 

water treatment. The action levels established by the USEPA 

and CDPH are the same, thus these thresholds are labeled “TTUS” in this report.

SMCL—Secondary Maximum Contaminant Level. 

Non-enforceable standards applied to constituents that affect 

the aesthetic qualities of drinking water, such as taste, odor, 

and color, or technical qualities of drinking water, such as 

scaling and staining. Both the USEPA and CDPH define 

SMCLs, but unlike MCLs, SMCLs established by CDPH are 

not required to be at least as stringent as those established by 

USEPA. SMCLs established by CDPH are used in this report 

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

The SMCL-US is used for pH because no SMCL-CA has been 

defined.

NL—Notification Level. Health-based notification 

levels established by CDPH for some of the constituents in 

drinking water that lack MCLs (NL-CA). If a constituent 

is detected above its NL-CA, California state law requires 

timely notification of local governing bodies and recommends 

consumer notification.

HAL—Lifetime Health Advisory Level. The maximum 

concentration of a constituent at which its presence in drinking 

water is not expected to cause any adverse carcinogenic 

effects for a lifetime of exposure. HALs are established by the 

USEPA (HAL-US) and are calculated assuming consumption 

of two liters of water per day over a 70-year lifetime by a 

70-kilogram 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 concentrations established by 

the USEPA by ten (RSD5-US).

For constituents with MCLs, detections in ground-water 

samples were compared with 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 ground-water 

samples were compared with both levels. The SMCL-US 

for these constituents corresponds to the recommended 

SMCL-CA. Detected concentrations of constituents that 

lack MCLs and SMCLs were compared with NL-CAs. 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-CA, 

detected concentrations were compared with the RSD5-US. 

Note this hierarchy of selection of comparison thresholds 

means that for constituents with multiple types of established 

thresholds, the threshold used for comparison purposes may 

not be the one with the lowest concentration. The comparison 

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

constituents and in tables 4–14 for constituents detected in 

ground-water samples from the MSACV. Not all constituents 

analyzed for this study have established thresholds. 

Concentrations greater than the selected comparison threshold 

are marked with asterisks in tables 4–14.

Ground-Water-Quality Data

Results from analyses of raw (untreated) ground-water 

samples from MSACV are presented in tables 4–14. Groundwater samples collected in MSACV were analyzed for up 

to 280 constituents, and 195 of those constituents were not 

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

tables present only the constituents that were detected and list 

only samples that had at least one constituent detected. For 

constituent classes that were analyzed at all of the grid wells, 

the tables include 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), and the total number of 

constituents detected at each well. Results from the flow-path 

and RICE 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 

these wells.

Table 4 includes water-quality indicators measured in the 

field and at NWQL. Tables 5–14 present the results of groundwater laboratory analyses organized by compound classes: 

• Organic constituents

•	 VOCs and gasoline oxygenates and degradates 

(table 5)

•	 Pesticides and pesticide degradates (table 6)

• Constituents of special interest (table 7)

• Inorganic constituents

•	 Nutrients and dissolved organic carbon (table 8)

•	 Major and minor ions (table 9)

•	 Trace elements (table 10)

•	 Species of inorganic arsenic, iron, and chromium 

(table 11)

• Inorganic tracer constituents

•	 Hydrogen and oxygen isotopes and tritium (table 12)

•	 Stable isotopes of nitrogen and carbon and 

carbon-14 (table 13)

• Radioactive constituents (table 14)

Results for pharmaceutical compounds, dissolved 

noble gases, and tritium/helium age dates are not presented 

in this report; they will be included in subsequent GAMA 
12 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

publications. No summary table is presented for microbial 

constituents because none were detected in any of the samples 

analyzed. 

Water-Quality Indicators

Field and laboratory measurements of water-quality 

indicators, including dissolved oxygen, pH, specific 

conductance, alkalinity, and associated parameters (turbidity 

and water temperature) are presented in table 4. Dissolved 

oxygen and alkalinity are used as indicators of natural 

processes that control water chemistry. Specific conductance is 

the unit electrical conductivity of the water and is proportional 

to the amount of total dissolved solids (TDS) in the water. 

The pH value indicates the acidity or basicity of the water. Six 

wells (3 grid wells, 2 flow-path wells, and 1 RICE well) had 

pH values outside of the SMCL-CA range for pH. Laboratory 

pH values may be higher than field pH values because the 

pH of ground water often increases upon exposure to the 

atmosphere (see Appendix). Twenty-two wells (11 grid, 1 

flow-path well, and 10 RICE wells) had specific conductance 

values above the recommended SMCL-CA, with 9 of those 

wells (4 grid wells and 5 RICE wells) above the upper 

threshold. 

Organic Constituents

VOCs are widely used and can be found in paints, 

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

disinfected water and are characterized by their tendency to 

evaporate. VOCs generally persist longer in ground water than 

in surface water because ground water is isolated from the 

atmosphere. 

Of the 85 VOCs analyzed, 24 were detected in groundwater samples; all detections were below health-based 

thresholds and most were less than one-hundredth of the 

threshold values (table 5). The only VOC detected in more 

than 10 percent of the grid wells was chloroform, a byproduct 

of drinking-water disinfection. Chloroform was the most 

frequently detected VOC in ground water nationally (Zogorski 

and others, 2006).

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 135 pesticides and pesticide degradates analyzed, 30 were 

detected in ground-water samples; all detections were below 

health-based thresholds and all were less than one-hundredth 

of the threshold values (table 6). The only pesticides detected 

in more than 10 percent of the grid wells were the herbicides 

bentazon, simazine, atrazine, and deethylatrazine, a degradate 

of atrazine. Simazine, atrazine, and deethlyatrazine are among 

the most commonly detected pesticide compounds in ground 

water nationally (Gilliom and others, 2006). Bentazon is 

primarily used in rice agriculture. 

Constituents of Special Interest

Perchlorate, 1,2,3-TCP, 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 Health Services, 

2007b). Perchlorate is used as an oxidizer in rocket fuel and 

explosives, 1,2,3-TCP is used as a chemical synthesis product, 

and NDMA is an industrial by-product. Perchlorate was 

detected in approximately 6 percent of the grid wells, and all 

concentrations measured in the MSACV wells were less than 

one-third of the NL-CA (table 7). 1,2,3-TCP and NDMA were 

not detected in any samples.

Inorganic Constituents

Unlike the organic constituents and the constituents 

of special interest, most of the inorganic constituents 

are naturally present in ground water, although their 

concentrations may be influenced by human activities.

The nutrients, nitrogen and phosphorus, and dissolved 

organic carbon present in ground water can affect biological 

activity in aquifers and in surface water bodies that receive 

ground-water discharge. Nitrogen may be present in the form 

of ammonia, nitrite, or nitrate depending on the oxidation–

reduction state of the ground water. High concentrations of 

nitrate can adversely affect human health, particularly the 

health of infants. Ground-water samples from two grid wells 

in MSACV had concentrations of nitrate (nitrite plus nitrate, 

dissolved as nitrogen) above the health-based threshold (table 

8). All concentrations of nitrite and ammonia measured in 

ground-water samples were below health-based thresholds. 

Concentrations of orthophosphate (as phosphorus) and 

dissolved organic carbon were also low.

The major-ion composition, total dissolved solids (TDS) 

content, and levels of certain trace elements in ground water 

may produce undesirable effects on the aesthetic and technical 

properties of the water. Undesirable aesthetic properties 

include poor taste, color, or odor, and staining. Undesirable 

technical properties include scaling, and reduced effectiveness 

of treatment for other contaminants. CDPH has established 

non-enforceable thresholds (SMCL-CAs) that are based on 

aesthetic or technical properties rather than on health-based 

concerns for the major ions chloride and sulfate, TDS, and 

several trace elements. Chloride was detected in two grid 

wells above the recommended SMCL-CA, with one of those 

detections above the upper SMCL-CA. Sulfate was detected in 

one grid well above the lower SMCL-CA. Samples from six 

grid wells contained TDS above the recommended SMCL-CA, 

although only two of these samples were also above the upper 

SMCL-CA for TDS (table 9). 
Water-Quality Results 13

Iron and manganese are trace elements whose 

concentrations are affected by the oxidation–reduction state 

of the ground water. Precipitation of minerals containing iron 

or manganese may cause orange or black staining of surfaces. 

Samples from 12 grid wells had manganese concentrations 

above the SMCL-CA, and one of these samples also had an 

iron concentration above the MCL-CA (table 10).

Eighteen of the 25 trace elements analyzed in this study 

have health-based thresholds. Of the 18 trace elements with 

health-based thresholds, 2 were not detected in any samples, 

and all detections of 16 trace elements were below healthbased thresholds (table 10). Samples from eight grid wells had 

arsenic concentrations above the MCL-US and samples from 

two grid wells had concentrations of boron above the NL-CA. 

Arsenic, iron, and chromium occur in different species 

depending on the oxidation–reduction state of the ground 

water. The oxidized and reduced species have different 

solubilities in ground water and may have different effects 

on human health. The relative proportions of the oxidized 

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

interpretation of the oxidation–reduction state of the aquifer. 

Table 11 reports measured concentrations of total arsenic, 

iron, and chromium, and the concentrations of the oxidized 

or the reduced species of each element. The concentration 

of the other species can be calculated by difference. For 

example, chromium(III) is equal to chromium(total) minus 

chromium(VI). The concentrations of arsenic, iron, and 

chromium reported in table 11 may be different than those 

reported in table 10 because different analytical methods were 

used (see Appendix). The concentrations reported in table 10

are considered more accurate.

Inorganic Tracer Constituents

Stable isotope ratios, tritium and carbon-14 activities, 

and noble gas concentrations are used as tracers of natural 

processes affecting ground-water composition. The stable 

isotope ratios of oxygen and hydrogen in water (table 12) 

may aid in interpretation of ground-water recharge sources. 

These stable isotope ratios reflect the altitude, latitude, and 

temperature of precipitation and the extent of evaporation of 

surface water or soil water. The nitrogen and oxygen stable 

isotope ratios in nitrate (table 13) may aid in interpretation 

of sources and processes affecting nitrate concentrations in 

ground water. Concentrations of dissolved noble gases are 

used to estimate the conditions of ground-water recharge, 

particularly the temperature of the recharge water. Noble 

gases from air dissolve in water that is in contact with the 

atmosphere, and the solubilities of the different noble gases 

vary with temperature. Results of noble gas analyses were 

not available in time for inclusion in this report; they will be 

presented in a subsequent GAMA report.

Tritium activities (table 12), carbon-14 activities 

(table 13), and helium isotope ratios provide information 

about the age of the ground water. Tritium is a short-lived 

radioactive isotope of hydrogen that is incorporated into 

the water molecule. Low levels of tritium are continuously 

produced by interaction of cosmic radiation with the earth’s 

atmosphere, and a large amount of tritium was produced by 

atmospheric testing of nuclear weapons between 1952 and 

1963. Thus, concentrations of tritium above background levels 

generally indicate the presence of water recharged since the 

early 1950s (Thatcher and others, 1977). Helium isotope ratios 

are used in conjunction with tritium concentrations to estimate 

ages for young ground water. Helium isotope analyses were 

not completed in time for inclusion in this report; they will be 

presented in a subsequent GAMA report.

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

Low levels of carbon-14 are continuously produced by 

interaction of cosmic radiation with the earth’s atmosphere 

and incorporated into atmospheric carbon dioxide. The carbon 

dioxide dissolves in precipitation and water that is in contact 

with the atmosphere. Because carbon-14 decays with a halflife of approximately 5,700 years, low activities of carbon-14 

relative to modern values generally indicate presence of 

ground water that is several thousand years old. 

Of the inorganic tracer constituents analyzed for this 

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

All measured tritium activities in samples from MSACV wells 

were less than one-thousandth of the MCL-CA (table 12).

Radioactive Constituents

Radioactivity is the release of energy or energetic 

particles during changes in the structure of the nucleus of an 

atom. Most of the radioactivity in ground water comes from 

decay of naturally occurring isotopes of uranium and thorium 

that are present in minerals in the sediments or fractured rocks 

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

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

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

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

the decay series, one radioactive element turns into a different 

radioactive element by emitting an alpha or a beta particle 

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

particle and, therefore, turns into radon-222. Radium-228 

decays to form actinium-228 by emission of a beta particle. 

The alpha and beta particles emitted during radioactive 

decay are hazardous to human health because these energetic 

particles may damage cells. Radiation damage to cell DNA 

may increase the cancer risk in humans.

Activity is often used instead of concentration for 

reporting the presence of radioactive constituents. Activity 

of radioactive constituents in ground water is measured in 

units of picocuries per liter (pCi/L), 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.
14 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

 The eight MSACV samples analyzed for radioactive 

constituents had activities of radium and of gross alpha and 

beta emitters less than established health-based thresholds 

(table 14). Activities of radon-222 in samples from six grid 

wells were above the proposed MCL-US of 300 pCi/L, but all 

were below the proposed alternative MCL-US of 4,000 pCi/L. 

The alternative MCL-US will apply if the state or local water 

agency has an approved multimedia mitigation program 

to address radon levels in indoor air (U.S. Environmental 

Protection Agency, 1999a).

Microbial Indicators

Water is disinfected during drinking-water treatment to 

prevent diseases that may be spread by water-borne microbial 

constituents derived from human or animal wastes. The 

specific viruses and bacteria responsible for diseases generally 

are not measured because routine analytical methods are not 

available. Measurements are made of more easily analyzed 

microbial constituents that serve as indicators of the presence 

of human or animal waste in water. Drinking-water purveyors 

respond to detections of microbial indicators by applying 

additional disinfection techniques to the water.

Samples from eight MSACV wells were analyzed 

for microbial indicators. None of the samples contained 

viral indicators F-specific and somatic coliphage, and none 

contained the bacterial indicator Escherichia coliform (E. coli) 

or total coliforms. 

Future Work

Subsequent reports will focus on assessment of the 

data presented in this report using a variety of statistical, 

qualitative, and quantitative approaches to evaluate the natural 

and human factors affecting ground-water quality. Waterquality data contained in the CDPH and NWIS databases, 

and water-quality data available from other state and local 

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

combination with the data presented in this report.

Summary

Ground-water quality in the approximately 3,340 mi2

Middle Sacramento Valley study unit (MSACV) was 

investigated from June to September, 2006, as part of 

the Priority Basin Assessment project of Ground-Water 

Ambient Monitoring and Assessment (GAMA) program. The 

California State Water Resources Control Board (SWRCB), 

in collaboration with the U.S. Geological Survey and the 

Lawrence Livermore National Laboratory, is implementing 

the GAMA program (http://www.waterboards.ca.gov/gama/). 

The Priority Basin Assessment project was designed by the 

SWRCB and the USGS in response to the Ground-Water 

Quality Monitoring Act of 2001 (Belitz and others, 2003; 

State Water Resources Control Board, 2003). The project is a 

comprehensive assessment of statewide ground-water quality 

designed to identify and characterize risks to ground-water 

resources and to increase the availability of information about 

ground-water quality to the public. MSACV was the twelfth 

study unit sampled as part of the project. 

MSACV is in the Central Valley hydrogeologic province, 

and includes within it eight ground-water basins, as defined 

by the California Department of Water Resources (California 

Department of Water Resources, 2003). The MSACV study 

included assessment of ground-water quality from 108 wells 

in Butte, Colusa, Glenn, Sutter, Tehama, Yolo, and Yuba 

Counties. Seventy-one of the wells (grid wells) were selected 

using a spatially distributed, randomized grid-based method 

to achieve statistically unbiased representation of the portion 

of the ground-water resource used for public drinking-water 

supplies. Fifteen of the wells (flow-path wells) were selected 

to provide additional sampling density to aid in understanding 

processes affecting ground-water quality. Twenty-two of the 

wells (RICE wells) were sampled for better understanding of 

the contribution of rice agriculture land use to ground-water 

conditions. 

Ground-water samples were analyzed for volatile organic 

compounds (VOCs), pesticides and pesticide degradates, 

constituents of special interest, pharmaceutical compounds, 

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

and microbial indicators. Naturally occurring isotopes (stable 

isotopes of hydrogen, oxygen, nitrogen, and carbon, and 

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

also were measured to provide a dataset that will be used to 

help interpret the source and age of the sampled ground water. 

This report describes the hydrogeologic setting of the MSACV 

region, details the sampling, analytical, and quality-assurance 

methods used in the study, and presents the results of the 

chemical and microbial analyses made of the ground-water 

samples collected during June to September, 2006.

QC samples (blanks, replicates, samples for matrix 

spikes) were collected at approximately 10 percent of 

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

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

Field blanks rarely contained detectable concentrations of 

any constituent, suggesting that contamination was not a 

noticeable source of bias in the data for the ground-water 

samples. Most of the differences between replicate samples 

were within acceptable ranges, indicating acceptably low 

variability. Matrix spike recoveries were within acceptable 

ranges for most compounds.

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 
References Cited 15

thresholds apply to treated water that is served to the 

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in the raw ground water were compared with health-based 

thresholds established by the U.S. Environmental Protection 

Agency (USEPA) and the California Department of Public 

Health (CDPH). 

All detections of VOCs, pesticides, and pesticide 

degradates were below health-based thresholds, and most 

were less than one-hundredth of the threshold values. All 

detections of perchlorate, and radioactive constituents were 

below established thresholds. Arsenic, nitrate, and boron 

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health-based thresholds in samples from the grid wells. Total 

dissolved solids, specific conductance, pH, iron, chloride, 

sulfate, and manganese were detected at concentrations above 

the SMCL-CA, a non-enforceable threshold set for aesthetic 

concerns, in samples from several of the grid wells.

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20 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 1. Identification, sampling, and construction information for wells sampled for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; ft, foot 

(feet); LSD, land surface datum; mm/dd/yy, month/day/year; na, not available; no., number; RICE, rice agriculture; WSAC, West study area of the middle 

Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path]

GAMA 

identification 

no.

Sampling information

Well type

Construction information

Date 

(mm/dd/yy)

Sampling

schedule1

Elevation of LSD 

(ft above 

NAVD88)2

Well depth 

(ft below LSD)

Top perforation

(ft below LSD)

Bottom 

perforation 

(ft below LSD)

Grid wells

ESAC-01 6/29/06 Fast Production 76 278 150 252

ESAC-02 6/29/06 Fast Production 38 160 140 160

ESAC-03 7/10/06 Intermediate Production 176 272 110 150

ESAC-04 7/10/06 Fast Production 154 200 140 200

ESAC-05 7/10/06 Intermediate Production 77 410 207 395

ESAC-06 7/12/06 Intermediate Production 182 260 148 260

ESAC-07 7/12/06 Fast Production 153 220 80 220

ESAC-08 7/12/06 Fast Production 89 108 68 108

ESAC-09 7/13/06 Fast Production 129 554 140 554

ESAC-10 7/13/06 Intermediate Production 60 316 96 303

ESAC-11 7/13/06 Intermediate Production 68 520 220 510

ESAC-12 7/17/06 Intermediate Production 107 375 0 370

ESAC-13 7/17/06 Fast Production 207 355 na na

ESAC-14 7/17/06 Fast Production 47 280 140 280

ESAC-15 7/20/06 Intermediate Production 197 500 200 480

ESAC-16 7/20/06 Intermediate Production 297 560 240 540

ESAC-17 7/20/06 Intermediate Production 52 200 150 na

ESAC-18 7/20/06 Intermediate Production 220 560 240 540

ESAC-19 7/20/06 Intermediate Production 48 265 185 265

ESAC-20 7/25/06 Fast Production 84 354 212 354

ESAC-21 7/25/06 Intermediate Production 53 na na na

ESAC-22 7/26/06 Intermediate Production 105 90 na na

ESAC-23 7/26/06 Fast Production 93 72 na na

ESAC-24 7/26/06 Fast Production 94 327 84 318

ESAC-25 7/27/06 Slow Production 264 570 290 550

ESAC-26 7/31/06 Slow Production 37 200 160 200

ESAC-27 8/2/06 Slow Production 54 135 65 125

ESAC-28 8/3/06 Slow Production 92 360 102 360

ESAC-29 8/3/06 Intermediate Production 31 223 199 215

ESAC-30 8/7/06 Intermediate Production 43 na na na

ESAC-31 8/7/06 Intermediate Production 62 235 48 235

ESAC-32 8/17/06 Intermediate Production 66 140 64 124

ESAC-33 8/17/06 Fast Production 212 335 na na

ESAC-34 8/17/06 Intermediate Production 102 60 na na

ESAC-35 8/24/06 Intermediate Production 114 558 74 558

WSAC-01 7/10/06 Fast Production 446 na na na

WSAC-02 7/11/06 Fast Production 179 na na na

WSAC-03 7/11/06 Slow Production 274 na 115.5 253

WSAC-04 7/11/06 Intermediate Production 452 880 320 880

WSAC-05 7/12/06 Fast Production 367 236 136 236

WSAC-06 7/12/06 Intermediate Production 485 na na na

WSAC-073 7/18/06, 8/10/06 Fast Production 152 220 71 200

WSAC-08 7/18/06 Slow Production 248 180 56 170

WSAC-093 7/18/06, 8/10/06 Fast Production 222 na na na

WSAC-103 7/18/06, 8/10/06 Intermediate Production 187 225 145 225

WSAC-113 7/19/06, 8/9/06 Intermediate Production 142 570 240 561

WSAC-12 7/19/06 Slow Production 52 490 na na

WSAC-13 7/24/06 Fast Production 87 na na na
Table 1 21

Table 1. Identification, sampling, and construction information for wells sampled for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; ft, foot 

(feet); LSD, land surface datum; mm/dd/yy, month/day/year; na, not available; no., number; RICE, rice agriculture; WSAC, West study area of the middle 

Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path]

GAMA 

identification 

no.

Sampling information

Well type

Construction information

Date 

(mm/dd/yy)

Sampling

schedule1

Elevation of LSD 

(ft above 

NAVD88)2

Well depth 

(ft below LSD)

Top perforation

(ft below LSD)

Bottom 

perforation 

(ft below LSD)

WSAC-14 7/24/06 Intermediate Production 62 159 157 159

WSAC-15 7/31/06 Intermediate Production 147 610 280 610

WSAC-16 7/31/06 Fast Production 30 332 313 na

WSAC-17 8/1/06 Intermediate Production 32 260 230 260

WSAC-18 8/1/06 Slow Production 85 402 160 380

WSAC-19 8/1/06 Fast Production 37 364 348 356

WSAC-20 8/2/06 Fast Production 81 340 253 340

WSAC-21 8/2/06 Intermediate Production 168 369 237 256

WSAC-22 8/8/06 Intermediate Production 358 870 408 870

WSAC-23 8/8/06 Fast Production 43 56 31 56

WSAC-24 8/9/06 Fast Production 75 185 165 185

WSAC-25 8/9/06 Intermediate Production 45 na na na

WSAC-26 8/14/06 Intermediate Production 413 330 110 330

WSAC-27 8/15/06 Fast Production 65 300 140 300

WSAC-28 8/15/06 Intermediate Production 292 165 145 165

WSAC-29 8/16/06 Intermediate Production 142 759 173 651

WSAC-30 8/16/06 Intermediate Production 121 na na na

WSAC-31 8/21/06 Intermediate Production 60 260 145 245

WSAC-32 8/21/06 Fast Production 93 180 110 180

WSAC-33 8/22/06 Fast Production 88 205 na na

WSAC-34 8/22/06 Intermediate Production 144 197 60 180

WSAC-35 8/23/06 Intermediate Production 143 410 100 410

WSAC-36 8/23/06 Intermediate Production 82 260 160 260

Flow-path wells

ESAC-FP-01 7/13/06 Intermediate Production 51 750 580 720

ESAC-FP-02 8/21/06 Intermediate Monitoring 181 na na na

ESAC-FP-03 8/23/06 Intermediate Monitoring 105 130 98.8 109

ESAC-FP-04 8/23/06 Intermediate Monitoring 107 583 509 562

ESAC-FP-05 8/24/06 Intermediate Monitoring 105 100 80 90

ESAC-FP-06 8/24/06 Intermediate Monitoring 105 380 340 350

ESAC-FP-07 8/25/06 Intermediate Monitoring 105 555 520 530

WSAC-FP-01 8/14/06 Intermediate Monitoring 312 na na na

WSAC-FP-02 8/15/06 Intermediate Monitoring 257 421 390 400

WSAC-FP-03 8/15/06 Intermediate Monitoring 257 310 270 290

WSAC-FP-04 8/16/06 Intermediate Monitoring 131 200 138 180

WSAC-FP-05 8/16/06 Intermediate Production 94 625 540 625

WSAC-FP-06 8/16/06 Intermediate Monitoring 131 540 445 525

WSAC-FP-07 8/17/06 Intermediate Monitoring 99 490 415 470

WSAC-FP-08 8/17/06 Intermediate Monitoring 99 280 190 260

RICE wells

RICE-01 7/17/06 RICE Monitoring 24 50 40 45

RICE-02 7/18/06 RICE Monitoring 38 44 34 39

RICE-03 7/18/06 RICE Monitoring 43 35 25 30

RICE-04 7/18/06 RICE Monitoring 88 35 25 30

RICE-05 7/19/06 RICE Monitoring 126 35 25 30

RICE-06 7/19/06 RICE Monitoring 138 35 25 30

RICE-07 7/20/06 RICE Monitoring 91 45 35 40

RICE-08 7/20/06 RICE Monitoring 88 35 25 30

RICE-09 7/24/06 RICE Monitoring 70 34 24 28
22 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 1. Identification, sampling, and construction information for wells sampled for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; ft, foot 

(feet); LSD, land surface datum; mm/dd/yy, month/day/year; na, not available; no., number; RICE, rice agriculture; WSAC, West study area of the middle 

Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path]

GAMA 

identification 

no.

Sampling information

Well type

Construction information

Date 

(mm/dd/yy)

Sampling

schedule1

Elevation of LSD 

(ft above 

NAVD88)2

Well depth 

(ft below LSD)

Top perforation

(ft below LSD)

Bottom 

perforation 

(ft below LSD)

RICE-10 7/24/06 RICE Monitoring 80 35 25 30

RICE-11 7/25/06 RICE Monitoring 127 35 25 30

RICE-12 7/25/06 RICE Monitoring 98 35 25 30

RICE-13 7/26/06 RICE Monitoring 110 35 25 30

RICE-14 7/26/06 RICE Monitoring 82 36 26 30

RICE-15 7/27/06 RICE Monitoring 100 35 25 30

RICE-16 7/27/06 RICE Monitoring 82 35 25 30

RICE-17 8/15/06 RICE Monitoring 57 35 25 30

RICE-18 8/16/06 RICE Monitoring 99 38 28 34

RICE-19 8/16/06 RICE Monitoring 74 38 28 34

RICE-20 8/17/06 RICE Monitoring 24 29 19 24

RICE-21 9/12/06 RICE Monitoring 76 35 25 30

RICE-22 9/13/06 RICE Monitoring 51 35 25 30

1

 Sampling schedules are described in table 2.

2

 Land-surface datum (LSD) is a datum plane that is approximately at land surface at each well. The elevation of the LSD is described in feet above the North 

American Vertical Datum 1988.

3

 Well sampled twice (well was partially resampled to replace some sample containers lost in shipping prior to analysis).
Table 2 23

Analyte classes Analyte list 

table

Slow 

schedule

Intermediate

schedule

Fast 

schedule

RICE 

schedule

Water-quality indicators

DO, SC, pH, temperature X X X X

Alkalinity, turbidity X X

Organic constituents

Volatile organic compounds 3A X X X X

Gasoline additives and oxygenates 3B X

Pesticides and pesticide degradates 3C, 3D X X X X

Pharmaceutical compounds 3E X X X

Constituents of special interest

Perchlorate 3F X X X X

N-Nitrosodimethylamine (NDMA) 3F X X

1,2,3-Trichloropropane (1,2,3-TCP) 3F X X

Inorganic constituents

Nutrients 3G X X X

Dissolved organic carbon (DOC) 3G X X

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

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

Stable isotopes

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

Stable isotopes of nitrogen and oxygen in nitrate 3J X X

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

Radioactivity and gases

Tritium 3J X X X

Tritium and noble gases 3K X X X X

Radium isotopes 3J X

Radon-222 3J X

Gross alpha and beta radiation 3J X

Microbial constituents

Escherichia coliform and total coliform 3L X

F-specific and somatic coliphage 3L X

Table 2. Classes of water-quality indicators, chemical constituents, and microbial constituents collected for the slow, intermediate, 

fast, and RICE well sampling schedules in the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, June to September, 2006.

[DO, dissolved oxygen; NDMA, N-nitrosodimethylamine; SC, specific conductance]
24 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

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

Geological Survey’s (USGS) National Water Quality Laboratory Schedule 2020.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. CAS, Chemical Abstracts Service; CDPH, California 

Department of Public Health; D, detected; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum 

contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; NL-CA, notification level (CDPH); RSD5-US, U.S. 

Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk concentration established 

by the USEPA by 10); THM, trihalomethane; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; —, analyzed but not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

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

Acrylonitrile Organic synthesis 34215 107-13-1 0.8 RSD5-US 0.6 —

Benzene Gasoline hydrocarbon 34030 71-43-2 0.021 MCL-CA 1 D

Bromobenzene Solvent 81555 108-86-1 0.028 na na —

Bromochloromethane Fire retardant 77297 74-97-5 0.12 HAL-US 90 —

Bromodichloromethane Disinfection by-product (THM) 32101 75-27-4 0.028 MCL-US1 80 D

Bromoform (Tribromomethane) Disinfection by-product (THM) 32104 75-25-2 0.10 MCL-US1 80 D

2-Butanone (MEK, Methyl ethyl 

ketone)

Solvent 81595 78-93-3 2 HAL-US 4,000 D

n-Butylbenzene Gasoline hydrocarbon 77342 104-51-8 0.12 NL-CA 260 —

sec-Butylbenzene Gasoline hydrocarbon 77350 135-98-8 0.06 NL-CA 260 —

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

Carbon disulfide Organic synthesis 77041 75-15-0 0.038 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 0.028 MCL-CA 70 —

Chloroethane Solvent 34311 75-00-3 0.12 na na —

Chloroform (Trichloromethane) Disinfection by-product (THM) 32106 67-66-3 0.024 MCL-US1 80 D

Chloromethane Refrigerant/organic synthesis 34418 74-87-3 0.17 HAL-US 30 D

3-Chloro-1-propene Organic synthesis 78109 107-05-1 0.5 na na —

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

4-Chlorotoluene Solvent 77277 106-43-4 0.05 NL-CA 140 —

Dibromochloromethane Disinfection by-product (THM) 32105 124-48-1 0.10 MCL-US1 80 D

1,2-Dibromo-3-chloropropane 

(DBCP)

Fumigant 82625 96-12-8 0.51 MCL-US 0.2 —

1,2-Dibromoethane (EDB) Fumigant 77651 106-93-4 0.036 MCL-US 0.05 —

Dibromomethane Solvent 30217 74-95-3 0.050 na na —

1,2-Dichlorobenzene Solvent 34536 95-50-1 0.048 MCL-CA 600 —

1,3-Dichlorobenzene Solvent 34566 541-73-1 0.03 HAL-US 600 —

1,4-Dichlorobenzene Fumigant 34571 106-46-7 0.034 MCL-CA 5 —

trans-1,4-Dichloro-2-butene Organic synthesis 73547 110-57-6 0.70 na na —

Dichlorodifluoromethane (CFC-12) Refrigerant 34668 75-71-8 0.18 NL-CA 1,000 —

1,1-Dichloroethane Solvent 34496 75-34-3 0.035 MCL-CA 5 D

1,2-Dichloroethane Solvent 32103 107-06-2 0.13 MCL-CA 0.5 —

1,1-Dichloroethene (DCE) Organic synthesis 34501 75-35-4 0.024 MCL-CA 6 —

cis-1,2-Dichloroethene Solvent 77093 156-59-2 0.024 MCL-CA 6 D

trans-1,2-Dichloroethene Solvent 34546 156-60-5 0.032 MCL-CA 10 D

Dichloromethane (Methylene 

chloride)

Solvent 34423 75-09-2 0.06 MCL-US 5 —

1,2-Dichloropropane Fumigant 34541 78-87-5 0.029 MCL-US 5 —

1,3-Dichloropropane Fumigant 77173 142-28-9 0.06 na na —

2,2-Dichloropropane Fumigant 77170 594-20-7 0.05 na na —

1,1-Dichloropropene Organic synthesis 77168 563-58-6 0.026 na na —

cis-1,3-Dichloropropene Fumigant 34704 10061-01-5 0.05 RSD5-US2 4 —

trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.09 RSD5-US2 4 —

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

Diisopropyl ether (DIPE) Gasoline oxygenate 81577 108-20-3 0.10 na na —

Ethylbenzene Gasoline hydrocarbon 34371 100-41-4 0.030 MCL-CA 300 —

Ethyl tert-butyl ether (ETBE) Gasoline oxygenate 50004 637-92-3 0.030 na na —

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

Geological Survey’s (USGS) National Water Quality Laboratory Schedule 2020.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. CAS, Chemical Abstracts Service; CDPH, California 

Department of Public Health; D, detected; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum 

contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; NL-CA, notification level (CDPH); RSD5-US, U.S. 

Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk concentration established 

by the USEPA by 10); THM, trihalomethane; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; —, analyzed but not detected]
Table 3A 25

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

Geological Survey’s (USGS) National Water Quality Laboratory Schedule 2020.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. CAS, Chemical Abstracts Service; CDPH, California 

Department of Public Health; D, detected; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum 

contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; NL-CA, notification level (CDPH); RSD5-US, U.S. 

Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk concentration established 

by the USEPA by 10); THM, trihalomethane; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; —, analyzed but not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Ethyl methacrylate Organic synthesis 73570 97-63-2 0.18 na na —

1-Ethyl-2-methylbenzene (o-Ethyl 

toluene)

Gasoline hydrocarbon 77220 611-14-3 0.06 na na D

Hexachlorobutadiene Organic synthesis 39702 87-68-3 0.14 RSD5-US 90 —

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

2-Hexanone (n-Butyl methyl ketone) Solvent 77103 591-78-6 0.4 na na —

Isopropylbenzene (Cumene) Gasoline hydrocarbon 77223 98-82-8 0.038 NL-CA 770 —

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

Methyl acrylate Organic synthesis 49991 96-33-3 1.0 na na —

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

Methyl bromide (Bromomethane) Fumigant 34413 74-83-9 0.33 HAL-US 10 —

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

Methyl iodide (Iodomethane) Organic synthesis 77424 74-88-4 0.50 na na —

Methyl isobutyl ketone (MIBK) Solvent 78133 108-10-1 0.37 NL-CA 120 —

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

Methyl tert-pentyl ether (tert-Amyl 

methyl ether, TAME)

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

Naphthalene Gasoline hydrocarbon 34696 91-20-3 0.52 NL-CA 17 —

n-Propylbenzene Solvent 77224 103-65-1 0.042 NL-CA 260 —

Styrene Gasoline hydrocarbon 77128 100-42-5 0.042 MCL-US 100 —

1,1,1,2-Tetrachloroethane Solvent 77562 630-20-6 0.03 HAL-US 70 —

1,1,2,2-Tetrachloroethane Solvent 34516 79-34-5 0.08 MCL-CA 1 —

Tetrachloroethene (PCE) Solvent 34475 127-18-4 0.030 MCL-US 5 D

Tetrahydrofuran Solvent 81607 109-99-9 1.2 na na —

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

1,2,3,5-Tetramethylbenzene Gasoline hydrocarbon 50000 527-53-7 0.18 na na D

Toluene Gasoline hydrocarbon 34010 108-88-3 0.02 MCL-CA 150 D

1,2,3-Trichlorobenzene Organic synthesis 77613 87-61-6 0.18 na na —

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

1,1,1-Trichloroethane (TCA) Solvent 34506 71-55-6 0.032 MCL-US 200 —

1,1,2-Trichloroethane Solvent 34511 79-00-5 0.04 MCL-US 5 —

Trichloroethene (TCE) Solvent 39180 79-01-6 0.038 MCL-US 5 D

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 0.18 NL-CA 0.005 —

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

(CFC-113)

Refrigerant 77652 76-13-1 0.038 MCL-CA 1,200 —

1,2,3-Trimethylbenzene Gasoline hydrocarbon 77221 526-73-8 0.09 na na —

1,2,4-Trimethylbenzene Gasoline hydrocarbon 77222 95-63-6 0.056 NL-CA 330 D

1,3,5-Trimethylbenzene Organic synthesis 77226 108-67-8 0.044 NL-CA 330 D

Vinyl bromide (Bromoethene) Fire retardant 50002 593-60-2 0.10 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

0.06 MCL-CA 1,750 D

o-Xylene Gasoline hydrocarbon 77135 95-47-6 0.038 MCL-CA 1,750 —

1

 The MCL-US and MCL-CA thresholds for trihalomethanes are 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).
26 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL

 (μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Acetone Degradate 81552 67-64-1 1.8 na na D

tert-Amyl alcohol Gasoline oxygenate 77073 75-85-4 1 na na —

tert-Butyl alcohol (TBA) Oxygenate/degradate 77035 75-65-0 1 NL-CA 12 —

Diisopropyl ether Gasoline oxygenate 81577 108-20-3 0.04 na na —

Ethyl tert-butyl ether (ETBE) Gasoline oxygenate 50004 637-92-3 0.06 DLR-CA 3 —

Methyl acetate Degradate 77032 79-20-9 0.43 na na —

Methyl tert-butyl ether (MTBE) Gasoline oxygenate 78032 1634-04-4 0.05 MCL-US 13 D

Methyl tert-pentyl ether Gasoline oxygenate 50005 994-05-8 0.05 DLR-CA 3 —

Table 3B. Gasoline oxygenates and their degradates, primary uses or sources, comparative thresholds, and reporting information for 

the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedule 4024.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. CAS, Chemical Abstracts Service; CDPH, California 

Department of Public Health; D, detected; DLR-CA, detection level for the purpose of reporting (CDPH); LRL, laboratory reporting level; MCL-US, maximum 

contaminant level (USEPA); na, not available; NL-CA, notification level (CDPH); USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; 

—, analyzed but not detected]
Table 3C 27

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

Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032 and 2033.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Rice wells were sampled for Schedule 2033, whereas all 

other wells were sampled for Schedule 2032. CAS, Chemical Abstracts Service; CDPH, California Department of Public Health; D, detected; HAL-US, Lifetime 

Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level 

(USEPA); na, not available; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing 

the 10–4 cancer risk concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; —, analyzed 

but not detected]

Constituent1 Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Type of 

comparison 

threshold

Threshold 

(μg/L) Detection

Acetochlor Herbicide 49260 34256-82-1 0.006 na na D

Alachlor Herbicide 46342 15972-60-8 0.005 MCL-US 2 —

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

Azinphos-methyl Insecticide 82686 86-50-0 0.05 na na —

Azinphos-methyl-oxon Degradate 61635 961-22-8 0.042 na na —

Benfluralin Herbicide 82673 1861-40-1 0.01 na na —

Carbaryl Insecticide 82680 63-25-2 0.041 RSD5 400 D

Carbofuran Herbicide 82674 1563-66-2 0.02 MCL-CA 18 —

2-Chloro-2,6-diethylacetanilide Degradate 61618 6967-29-9 0.0065 na na —

2-Chloro-4-isopropylamino-6-

amino-s-triazine (deethylatrazine)

Degradate 04040 6190-65-4 0.014 na na D

4-Chloro-2-methylphenol Degradate 61633 1570-64-5 0.005 na na —

Chlorpyrifos Insecticide 38933 2921-88-2 0.005 HAL-US 2 D

Chlorpyrofos, oxygen analog Degradate 61636 5598-15-2 0.0562 na na —

Cyanazine2 Herbicide 04041 21725-46-2 0.018 HAL-US 1 —

Cyfluthrin Insecticide 61585 68359-37-5 0.053 na na —

λ-Cyhalothrin Insecticide 61595 91465-08-6 0.014 na na —

Cypermethrin Insecticide 61586 52315-07-8 0.046 na na —

DCPA (Dacthal) monoacid Herbicide 82682 1861-32-1 0.003 HAL-US 70 —

Desulfinylfipronil Degradate 62170 na 0.012 na na D

Desulfinylfipronil amide Degradate 62169 na 0.029 na na —

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

3,4-Dichloroaniline Degradate 61625 95-76-1 0.0045 na na D

3,5-Dichloroaniline2 Degradate 61627 626-43-7 0.012 na na —

Dichlorvos Fumigant 38775 62-73-7 0.013 na na —

Dicrotophos Insecticide 38454 141-66-2 0.0843 na na —

Dieldrin Insecticide 39381 60-57-1 0.009 RSD5 0.2 —

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

Dimethoate Insecticide 82662 60-51-5 0.0061 na na —

Disulfoton2 Insecticide 82677 298-04-4 0.021 HAL-US 0.7 —

Disulfoton sulfone2 Degradate 61640 218208 0.014 na na —

α-Endosulfan2 Insecticide 34362 959-98-8 0.011 na na —

Endosulfan sulfate2 Degradate 61590 1031-07-8 0.022 na na —

EPTC2 Herbicide 82668 759-94-4 0.004 na na —

Ethion Insecticide 82346 563-12-2 0.016 na na —

Ethion monoxon Degradate 61644 17356-42-2 0.021 na na —

Ethoprophos2 Insecticide 82672 13194-48-4 0.012 na na —

2-Ethyl-6-methylaniline Degradate 61620 24549-06-2 0.01 na na —

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

Fenamiphos sulfone Degradate 61645 31972-44-8 0.053 na na —

Fenamiphos sulfoxide Degradate 61646 31972-43-7 0.04 na na —

Fipronil Insecticide 62166 120068-37-3 0.016 na na D

Fipronil sulfide Degradate 62167 120067-83-6 0.013 na na D

Fipronil sulfone Degradate 62168 120068-36-2 0.024 na na D

Fonofos Insecticide 04095 944-22-9 0.0053 HAL-US 10 —

Hexazinone Herbicide 04025 51235-04-2 0.026 HAL-US 400 D

Isofenphos Insecticide 61594 25311-71-1 0.011 na na —

Malaoxon Degradate 61652 1634-78-2 0.039 na na —

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

U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032 and 2033.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Rice wells were sampled for Schedule 2033, whereas 

all other wells were sampled for Schedule 2032. CAS, Chemical Abstracts Service; CDPH, California Department of Public Health; D, detected; HAL-US, 

Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant 

level (USEPA); na, not available; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by 

dividing the 10–4 cancer risk concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; —, 

analyzed but not detected]
28 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

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

Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032 and 2033.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Rice wells were sampled for Schedule 2033, whereas all 

other wells were sampled for Schedule 2032. CAS, Chemical Abstracts Service; CDPH, California Department of Public Health; D, detected; HAL-US, Lifetime 

Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level 

(USEPA); na, not available; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing 

the 10–4 cancer risk concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; —, analyzed 

but not detected]

Constituent1 Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Type of 

comparison 

threshold

Threshold 

(μg/L) Detection

Malathion Insecticide 39532 121-75-5 0.027 HAL-US 100 —

Metalaxyl Fungicide 61596 57837-19-1 0.0069 na na —

Methidathion Insecticide 61598 950-37-8 0.0087 na na —

Methyl paraoxon2 Degradate 61664 950-35-6 0.019 na na —

Methyl parathion Insecticide 82667 298-00-0 0.015 HAL-US 1 —

Metolachlor Herbicide 39415 51218-45-2 0.006 HAL-US 700 D

Metribuzin Herbicide 82630 21087-64-9 0.028 HAL-US 70 —

Molinate Herbicide 82671 2212-67-1 0.003 MCL-CA 20 D

Myclobutanil Fungicide 61599 88671-89-0 0.033 na na —

1-Naphthol Degradate 49295 90-15-3 0.0882 na na —

Oxyfluorfen2 Herbicide 61600 42874-03-3 0.017 na na —

Pendimethalin Herbicide 82683 40487-42-1 0.022 na na —

cis-Permethrin Insecticide 82687 54774-45-7 0.006 na na —

Phorate Insecticide 82664 298-02-2 0.055 na na —

Phorate oxygen analog Degradate 61666 2600-69-3 0.027 na na —

Phosmet Insecticide 61601 732-11-6 0.0079 na na D

Phosmet oxon Degradate 61668 3735-33-9 0.0511 na na D

Prometon Herbicide 04037 1610-18-0 0.01 HAL-US 100 —

Prometryn Herbicide 04036 7287-19-6 0.0059 na na —

Pronamide Herbicide 82676 23950-58-5 0.004 RSD5 200 —

Propargite2 Insecticide 82685 2312-35-8 0.023 na na —

Propanil Herbicide 82679 709-98-8 0.011 na na D

cis-Propiconazole Fungicide 79846 60207-90-1 0.013 na na D

trans-Propiconazole Fungicide 79847 60207-90-1 0.034 na na D

Simazine Herbicide 04035 122-34-9 0.005 MCL-US 4 D

Tebuconazole2 Fungicide 62852 107534-96-3 0.0136 na na —

Tebuthiuron Herbicide 82670 34014-18-1 0.016 HAL-US 500 D

Tefluthrin2 Insecticide 61606 79538-32-2 0.0033 na na —

Terbufos Insecticide 82675 13071-79-9 0.017 HAL-US 0.4 —

Terbufos oxygen analog sulfone Degradate 61674 56070-15-6 0.045 na na —

Terbuthylazine Herbicide 04022 5915-41-3 0.0083 na na —

Thiobencarb Herbicide 82681 28249-77-6 0.01 MCL-CA 70 —

Tribufos Herbicide 61610 78-48-8 0.035 na na —

Trifluralin Herbicide 82661 1582-09-8 0.009 HAL-US 10 —

 1 Constituents on both Schedules 2032 and 2033 unless noted otherwise.

2

 Constituent on Schedule 2033 only.
Table 3D 29

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

Geological Survey’s (USGS) National Water Quality Laboratory Schedule 2060.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. CAS, Chemical Abstracts Service; CDPH, California 

Department of Public Health; D, detected; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum 

contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk 

factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk concentration established by the USEPA by 10); USEPA, U.S. Environmental 

Protection Agency; μg/L, micrograms per liter; —, analyzed but not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Type of 

comparison 

threshold

Threshold 

(μg/L) Detection

Acifluorfen Herbicide 49315 50594-66-6 0.028 na na —

Aldicarb Insecticide 49312 116-06-3 0.15 MCL-US 3 —

Aldicarb sulfone Insecticide/degradate 49313 1646-88-4 0.018 MCL-US 2 —

Aldicarb sulfoxide Degradate 49314 1646-87-3 0.1 MCL-US 4 —

Atrazine Herbicide 39632 1912-24-9 0.008 MCL-CA 1 D

Bendiocarb Insecticide 50299 22781-23-3 0.08 na na —

Benomyl Fungicide 50300 17804-35-2 0.022 na na —

Bensulfuron-methyl Herbicide 61693 83055-99-6 0.018 na na D

Bentazon Herbicide 38711 25057-89-0 0.024 MCL-CA 18 D

Bromacil Herbicide 04029 314-40-9 0.018 HAL-US 70 —

Bromoxynil Herbicide 49311 1689-84-5 0.044 na na —

Caffeine Beverages 50305 58-08-2 0.018 na na —

Carbaryl Insecticide 49310 63-25-2 0.018 RSD5 400 D

Carbofuran Herbicide 49309 1563-66-2 0.016 MCL-CA 18 —

Chloramben, methyl ester Herbicide 61188 7286-84-2 0.024 na na —

Chlorimuron-ethyl Herbicide 50306 90982-32-4 0.032 na na D

2-Chloro-6-ethylamino-4-amino-striazine (deisopropylatrazine)

Degradate 04038 1007-28-9 0.08 na na D

2-Chloro-4-isopropylamino-6-amino-striazine (deethylatrazine)

Degradate 04040 6190-65-4 0.028 na na D

3-(4-Chlorophenyl)-1-methyl urea Degradate 61692 5352-88-5 0.036 na na —

Clopyralid Herbicide 49305 1702-17-6 0.067 na na —

Cycloate Herbicide 04031 1134-23-2 0.014 na na —

DCPA (Dactal) monoacid Degradate 49304 887-54-7 0.028 na na —

Dicamba Herbicide 38442 1918-00-9 0.036 HAL-US 400 —

2,4-D and 2,4-D methyl ester, summed 

on molar basis, reported as 2,4-D

Herbicide 66496 94-75-7 0.009 MCL-US 70 D

4-(2,4-Dichlorophenoxy)butyric acid 

(2,4-DB)

Herbicide 38746 94-82-6 0.020 na na —

Dichlorprop Herbicide 49302 120-36-5 0.028 na na —

Dinoseb Herbicide 49301 88-85-7 0.038 MCL-US 7 D

Diphenamid Herbicide 04033 957-51-7 0.010 HAL-US 200 —

Diuron Herbicide 49300 330-54-1 0.016 RSD5 200 D

Fenuron Herbicide 49297 101-42-8 0.01 na na —

Flumetsulam Herbicide 61694 98967-40-9 0.04 na na —

Fluometuron Herbicide 38811 2164-17-2 0.016 HAL-US 90 —

3-Hydroxycarbofuran Degradate 49308 16655-82-6 0.008 na na —

2-Hydroxy-4-isopropylamino6-ethylamino-s-triazine 

(hydroxyatrazine)

Degradate 50355 2163-68-0 0.032 na na D

Imazaquin Herbicide 50356 81335-37-7 0.036 na na —

Imazethapyr Herbicide 50407 81335-77-5 0.038 na na —

Imidacloprid Insecticide 61695 138261-41-3 0.02 na na —

Linuron Herbicide 38478 330-55-2 0.014 na na —

Metalaxyl Fungicide 50359 57837-19-1 0.03 na na —

Methiocarb Insecticide 38501 2032-65-7 0.034 na na —

Methomyl Insecticide 49296 16752-77-5 0.07 HAL-US 200 —

2-Methyl-4-chlorophenoxyacetic acid 

(MCPA) 

Herbicide 38482 94-74-6 0.07 HAL-US 4 D
30 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

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

Geological Survey’s (USGS) National Water Quality Laboratory Schedule 2060.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. CAS, Chemical Abstracts Service; CDPH, California 

Department of Public Health; D, detected; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum 

contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk 

factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk concentration established by the USEPA by 10); USEPA, U.S. Environmental 

Protection Agency; μg/L, micrograms per liter; —, analyzed but not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Type of 

comparison 

threshold

Threshold 

(μg/L) Detection

4-(2-Methyl-4-chlorophenoxy) butyric 

acid (MCPB) 

Herbicide 38487 94-81-5 0.1 na na —

Metsulfuron methyl1 Herbicide 61697 74223-64-6 0.067 na na —

Neburon Herbicide 49294 555-37-3 0.012 na na —

Nicosulfuron Herbicide 50364 111991-09-4 0.04 na na —

Norflurazon Herbicide 49293 27314-13-2 0.02 na na —

Oryzalin Herbicide 49292 19044-88-3 0.023 na na —

Oxamyl Insecticide 38866 23135-22-0 0.05 MCL-CA 50 —

Picloram Herbicide 49291 1918-02-01 0.032 MCL-US 500 —

Propham Herbicide 49236 122-42-9 0.03 HAL-US 100 —

Propiconazole Fungicide 50471 60207-90-1 0.01 na na D

Propoxur Insecticide 38538 114-26-1 0.008 na na —

Siduron Herbicide 38548 1982-49-6 0.02 na na —

Sulfometuron-methyl Herbicide 50337 74222-97-2 0.09 na na —

Tebuthiuron Herbicide 82670 34014-18-1 0.026 HAL-US 500 D

Terbacil Herbicide 04032 5902-51-2 0.026 HAL-US 90 —

Triclopyr Herbicide 49235 55335-06-3 0.026 na na D

1

 These constituents were reported using method reporting levels (MRLs) during the period of this study.

Table 3E. Pharmaceutical compounds, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey’s (USGS) National Water Quality Laboratory Schedule 2080.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold values as of February 10, 2007. 

CAS, Chemical Abstracts Service; MDL, method detection limit; na, not available; μg/L, micrograms per liter]

Constituent Primary use 

or source

USGS 

parameter

code

CAS 

number

MDL1

(μg/L)

Threshold 

type

Threshold 

value

(μg/L)

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; 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

Paraxanthine Caffeine metabolite 62030 611-59-6 0.10 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

 1The California Groundwater Ambient Monitoring and Assessment (GAMA) program uses more conservative reporting limits for the pharmaceutical 

compounds than recommended by the USGS’s 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’s Branch 

of Quality Systems in October 2007 (BQS LT-MDL). For acetaminophen, caffeine, cotinine, diphenhydramine, and paraxanthine, the MDL corresponds to the 

effective method detection limit determined from assessment of quality-control data associated with GAMA samples collected from May 2004 to September 

2007 (GAMA E-MDL). The GAMA E-MDL is higher than the BQS LT-MDL for those compounds. Detections reported by the USGS’s National Water Quality 

Laboratory with concentrations lower than the BQS LT-MDL or GAMA E-MDL are reported as nondetections by the GAMA program. 
Table 3G 31

Table 3F. Constituents of special interest, primary uses or sources, comparative thresholds, and reporting information for the 

Montgomery Watson Harza laboratory.

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

as of October 18, 2007. The laboratory entity code for the Montgomery Watson Harza laboratory in the USGS’s National Water Information System (NWIS) 

is CA-MWHL. CAS, Chemical Abstracts Service; CDPH, California Department of Public Health; D, detected; HAL-CA, Lifetime Health Advisory Level 

(CDPH); MCL-CA, maximum contaminant level (CDPH); MRL, minimum reporting level; NL-CA, notification level (CDPH); μg/L, micrograms per liter; 

—, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 MRL 

(μg/L)

Threshold 

type

Threshold 

value 

(μg/L)

Detection

Perchlorate Rocket fuel, fireworks, flares 61209 14797-73-0 0.5 MCL-CA 6 D

1,2,3-Trichloropropane (1,2,3-

TCP)

Fumigant, solvent 77443 96-18-4 0.005 HAL-CA 40 —

N-Nitrosodimethylamine 

(NDMA)

Rocket fuel, plasticizer 64176 62-75-9 0.002 NL-CA 10 —

Table 3G. Nutrients and dissolved organic carbon, comparative thresholds, and reporting information for the U.S. Geological Survey’s 

(USGS) National Water Quality Laboratory Schedule 2755 and parameter code 2613.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. CAS, Chemical Abstracts Service; D, detected; HAL-US, 

Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-US, maximum contaminant level (USEPA); mg/L, milligrams per liter; na, not 

available; USEPA, U.S. Environmental Protection Agency]

Constituent

USGS 

parameter 

code

CAS 

number

 LRL 

(mg/L)

Threshold 

type

Threshold 

value 

(mg/L)

Detection

Ammonia (as nitrogen) 00608 7664-41-7 0.01 HAL-US 30 D

Nitrate plus nitrite (as nitrogen) 00631 na 0.06 MCL-US 10 D

Nitrite (as nitrogen) 00613 14797-65-0 0.002 MCL-US 1 D

Total nitrogen (ammonia + nitrate + nitrite + organic nitrogen as 

nitrogen)

62854 17778-88-0 0.06 na na D

Orthophosphate (as phosphorus) 00671 14265-44-2 0.006 na na D

Dissolved organic carbon (DOC) 00681 na 0.33 na na D
32 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 3H. Major and minor ions and trace elements, comparative thresholds, and reporting information for the U.S. Geological 

Survey’s (USGS) National Water Quality Laboratory Schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. AL-US, action level (USEPA); CAS, Chemical Abstracts 

Service; CDPH, California Department of Public Health; D, detected; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; 

MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); mg/L, milligrams per liter; na, not available; NL-CA, 

notification level (CDPH); SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per 

liter; —, not detected] 

Constituent

USGS 

parameter 

code

CAS 

number LRL Threshold type

Threshold 

value Detection

Major and minor ions (mg/L)

Bromide 71870 24959-67-9 0.02 na na D

Calcium 00915 7440-70-2 0.02 na na D

Chloride 00940 16887-00-6 0.2 SMCL-CA 250 (500)1 D

Fluoride 00950 16984-48-8 0.1 MCL-CA 2 D

Iodide 78165 7553-56-2 0.002 na na D

Magnesium 00925 7439-95-4 0.008 na na D

Potassium 00935 7440-09-7 0.16 na na D

Silica 00955 7631-86-9 0.04 na na D

Sodium 00930 7440-23-5 0.2 na na D

Sulfate 00945 14808-79-8 0.18 SMCL-CA 250 (500)1 D

Total dissolved solids (TDS) 70300 na 10 SMCL-US 500 (1,000)1 D

Trace elements (μg/L)

Aluminum 01106 7429-90-5 1.6 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.2 MCL-US 6 D

Arsenic 01000 7440-38-2 0.12 MCL-US 10 D

Barium 01005 7440-39-3 0.2 MCL-CA 1,000 D

Beryllium 01010 7440-41-7 0.06 MCL-US 4 —

Boron 01020 7440-42-8 8 NL-CA 1,000 D

Cadmium 01025 7440-43-9 0.04 MCL-US 5 D

Chromium 01030 7440-47-3 0.4 MCL-CA 50 D

Cobalt 01035 7440-48-4 0.04 na na D

Copper 01040 7440-50-8 0.4 AL-US 1,300 D

Iron 01046 7439-89-6 6 SMCL-CA 300 D

Lead 01049 7439-92-1 0.08 AL-US 15 D

Lithium 01130 7439-93-2 0.6 na na D

Manganese 01056 7439-96-5 0.2 SMCL-CA 50 D

Mercury 71890 7439-97-6 0.01 MCL-US 2 —

Molybdenum 01060 7439-98-7 0.4 HAL-US 40 D

Nickel 01065 7440-02-0 0.06 MCL-CA 100 D

Selenium 01145 7782-49-2 0.8 MCL-US 50 D

Silver 01075 7440-22-4 0.2 SMCL-CA 100 —

Strontium 01080 7440-24-6 0.4 HAL-US 4,000 D

Thallium 01057 7440-28-0 0.04 MCL-US 2 D

Tungsten 01155 7440-33-7 0.06 na na D

Uranium 22703 7440-61-1 0.04 MCL-US 30 D

Vanadium 01085 7440-62-2 0.1 NL-CA 50 D

Zinc 01090 7440-66-6 0.6 SMCL-US 5,000 D

 1 The recommended SMCL-CA thresholds for chloride, sulfate, and TDS are listed with the upper SMCL-CA thresholds in parentheses.
Table 3I 33

Table 3I. Arsenic, chromium, and iron species, comparative thresholds, and reporting information for the U.S. Geological Survey’s 

(USGS) Trace Metal Laboratory, Boulder, Colorado.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. The laboratory entity code for the USGS Trace Metal 

Laboratory in the USGS’s National Water Information System (NWIS) is USGSTMCO. CAS, Chemical Abstracts Service; CDPH, California Department of 

Public Health; D, detected; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); MDL, method detection limit; 

na, not available; SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter]

Constituent (valence state)

USGS 

parameter 

code

CAS 

number

MDL 

(μg/L)

Threshold 

type

Threshold 

level 

(μg/L)

Detection

Inorganic Arsenic(III) 99034 22569-72-8 1 na na D

Inorganic 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-CA 300 D

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

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. The laboratory entity codes for the 

laboratories in the USGS’s National Water Information System (NWIS) listed in the footnotes are shown in parentheses following the laboratory name. 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. CAS, Chemical Abstracts Service; CDPH, California Department of Public Health; D, detected; hr, hour; MCL-CA, maximum contaminant 

level (CDPH); MCL-US, maximum contaminant level (USEPA); MRL, minimum reporting level; MU, method uncertainty; na, not available; pCi/L, picocuries 

per liter; SSMDC, sample-specific minimum detectable concentration; USEPA, U.S. Environmental Protection Agency; —, not detected]

Constituent

USGS 

parameter 

code

CAS 

number

Reporting 

level 

type

Reporting 

level or 

uncertainty

Threshold 

type1

Threshold 

value Detection

Stable isotope ratios (per mil)

δ2

H of water2 82082 na MU 2 na na D

δ18O of water2 82085 na MU 0.20 na na D

δ15N of nitrate2 82690 na MU 0.50 na na D

δ18O of nitrate2 63041 na MU 1.00 na na D

δ13O of dissolved carbonates3 82081 na 1 sigma 0.05 na na D

Radioactive constituents (percent modern)

Carbon-144 49933 14762-75-5 1 sigma 0.0015 na na D

Radioactive constituents (pCi/L)

Radon-2225 82303 14859-67-7 SSMDC see table 14 Proposed 

MCL-US2

6

300 (4,000) D

Tritium7 07000 10028-17-8 MRL 1 MCL-CA 20,000 D

Gross-alpha radioactivity, 72-hr count 

and 30-day counts8

62636, 62639 12587-46-1 SSMDC see table 14 MCL-US 15 D

Gross-beta radioactivity, 72-hr count 

and 30-day counts8

62642, 62645 12587-47-2 SSMDC see table 14 MCL-CA 50 D

Radium-2268 09511 13982-63-3 SSMDC see table 14 MCL-US9 5 D

Radium-2288 81366 15262-20-1 SSMDC see table 14 MCL-US9 5 D

 1 Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

 USGS Stable Isotope Laboratory, Reston, Virginia (USGSSIVA).

3

 University of Waterloo (contract laboratory) (CAN-UWIL).

4

 University of Arizona, Accelerator Mass Spectrometry Laboratory (contract laboratory) (AZ-UAMSL).

5

 USGS National Water Quality Laboratory (USGSNWQL).

6

 Two MCLs have been proposed for radon-222. The proposed alternaltive MCL is given in parentheses.

7

 USGS Stable Isotope and Tritium Laboratory, Menlo Park, California (USGSH3CA).

8

 Eberline Analytical Services (contract laboratory) (CA-EBERL).

9

 The MCL-US threshold for radium is the sum of radium-226 and radium-228.
34 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 3K. Noble gases and tritium, comparison thresholds and reporting information for the Lawrence Livermore National Laboratory.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. The laboratory entity code for the 

Lawrence Livermore National Laboratory in the USGS’s National Water Information System (NWIS) is CA-LLNL. CAS, Chemical Abstracts Service; CDPH, 

California Department of Public Health; cm3 STP/g H2O, cubic centimeters of gas at standard temperature and pressure per gram of water; MCL-CA, maximum 

contaminant level (CDPH); na, not available; pCi/L, picocuries per liter]

Constituent

USGS 

parameter 

code

CAS 

number

MU 

(percent)

Reporting 

units

Threshold 

type

Threshold 

value 

(pCi/L)

Detection

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 H2O na na na

Helium-4 85561 7440-59-7 2 cm3

STP/g H2O na na na

Krypton 85565 7439-90-9 2 cm3

STP/g H2O na na na

Neon 61046 7440-01-09 2 cm3

STP/g H2O na na na

Xenon 85567 7440-63-3 2 cm3

STP/g H2O na na na

Tritium 07000 10028-17-8 1 pCi/L MCL-CA 20,000 na
Table 3L

35

Table 3L. Microbial constituents, comparison thresholds, and reporting information for the U.S. Geological Survey’s (USGS) Ohio Microbiology Laboratory parameter codes 90901, 90900, 99335, and 99332.[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. The laboratory entity code for the USGS’s Ohio Microbiology Laboratory in the USGS’s National Water Information System (NWIS) is given in footnote 3. MCL-US, maximum contaminant level (USEPA); MDL, method detection limit; mL, milliliters; na, not available; TT-US, U.S. Environmental Protection Agency treatment technique—a required process intended to reduce the level of contamination in drinking water; USEPA, U.S. Environmental Protection Agency; —, analyzed but not detected] 

Constituent

USGS 

parameter 

code

Primary source MDL Threshold type1 Threshold value Detection

Escherichia coliform2 90901 Sewage and animal waste 

indicator/intestinal tracts of humans and animals

1 colony/100 mL TT-US No fecal coliforms are 

allowed.

—

Total coliform (including 

fecal coliform and E. coli)2

90900 Water-quality indicator/

soil, water and intestinal tracts of animals

1 colony/100 mL MCL-US No more then 5 percent 

samples total coliformpositives in a month. Every sample that has total coloforms must be analyzed for fecal coliforms; no fecal coliforms are allowed.

—

F-specific coliphage3 99335 Viral indicator/intestinal 

tracts of warm-blooded animals

na TT-US 99.99 percent killed/

inactivated

—

Somatic coliphage3 99332 Viral indicator/fecal 

contaminated waters

na TT-US 99.99 percent killed/

inactivated

—

1 Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.2 Analyzed in the field.3 Analyzed by the USGS’s Ohio Microbiology Laboratory (laboratory entity code USGSOHML).
36 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program Table 4.

Water-quality indicators in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, June to September, 2006.—Continued[The five-digit number below the constituent name in the headings is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a specific constituent or property; °C, degrees Celsius; CDPH, California Department of Public Health; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; mg/L, milligrams per liter; mm, millimeter; na, not available; nc, sample not collected; no., number; NTU, nephelometric turbidity unit; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); SMCL-U.S., secondary maximum contaminant level (USEPA); WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μS/cm, microsiemens per centimeter; *, value above recommended threshold level; **, value above upper threshold level; <, less than] 

GAMA identification no.

Turbidity 

(NTU) 

(63676)

Dissolved 

oxygen 

(mg/L) 

(00300) 

Water 

temperature 

(oC) 

(00010)

pH, lab 

(standard units) 

(00403)

pH, field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm at 25oC) 

(90095)

Specific 

conductance, 

field 

(μS/cm at 25oC) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3

)

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

Reporting limit or range 0.1 0.2 0.0-38.5 0-14 0-14 5 5 1 1

Threshold type na1 na na SMCL-US SMCL-US SMCL-CA2 SMCL-CA2 na na

Threshold level na1 na na 6.5–8.5 6.5–8.5 900 (1,600) 900 (1,600) na na

Grid wells

ESAC-01 nc 2.4 19.0 nc nc nc 372 nc nc

ESAC-02 nc <0.2 19.0 nc nc nc ** 2,040 nc ncESAC-03 nc 3.2 23.0 7.8 7.8 432 417 146 nc

ESAC-04 nc 6.8 19.5 nc 7.5 nc 422 nc nc

ESAC-05 nc 1.6 19.0 7.7 7.1 511 507 195 nc

ESAC-06 nc 6.9 21.0 7.5 7.1 209 208 106 nc

ESAC-07 nc 4.7 21.5 nc 7.7 nc 255 nc ncESAC-08 nc 1.9 16.5 nc 7.7 nc 459 nc ncESAC-09 nc 2.6 19.0 nc * 6.3 nc 418 nc ncESAC-10 nc 0.4 19.5 7.6 7.3 511 513 210 nc

ESAC-11 nc 0.4 21.0 7.7 7.4 212 220 111 nc

ESAC-12 nc nc 18.5 7.9 nc 338 341 179 ncESAC-13 nc 3.9 16.5 nc nc nc 322 nc ncESAC-14 nc 2.5 19.5 nc 7.0 nc 373 nc ncESAC-15 nc 10.1 18.0 7.8 7.6 281 280 118 nc

ESAC-16 nc 9.9 20.0 7.7 7.5 385 380 134 nc

ESAC-17 nc <0.2 19.0 7.7 7.3 * 959 898 304 nc

ESAC-18 nc 8.7 19.0 7.9 7.7 227 227 111 nc

ESAC-19 nc 2.3 21.0 7.6 7.0 429 421 191 nc

ESAC-20 nc <0.2 20.6 nc 7.5 nc 321 nc nc

ESAC-21 nc <0.2 17.5 7.9 7.6 ** 2,380 ** 2,370 218 nc

ESAC-22 nc 8.9 18.5 7.0 * 6.5 312 314 81 nc

ESAC-23 nc 3.4 17.0 nc * 6.3 nc 254 nc ncESAC-24 nc nc 19.5 nc 7.5 nc 281 nc nc

ESAC-25 0.2 6.9 21.5 7.8 7.2 205 207 106 98

ESAC-26 0.1 <0.2 16.0 7.9 7.9 306 292 162 148

ESAC-27 0.1 0.8 19.0 7.3 7.1 497 486 221 212

Table 4.

Water-quality indicators in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, June to September, 2006.[The five-digit number below the constituent name in the headings is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a specific constituent or property. °C, degrees Celsius; CDPH, California Department of Public Health; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; mg/L, milligrams per liter; mm, millimeter; na, not available; nc, sample not collected; no., number; NTU, nephelometric turbidity unit; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); SMCL-U.S., secondary maximum contaminant level (USEPA); WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μS/cm, microsiemens per centimeter; *, value above recommended threshold level; **, value above upper threshold level; <, less than]
Table 4

37

Table 4. Water-quality indicators in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued[The five-digit number below the constituent name in the headings is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a specific constituent or property. °C, degrees Celsius; CDPH, California Department of Public Health; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; mg/L, milligrams per liter; mm, millimeter; na, not available; nc, sample not collected; no., number; NTU, nephelometric turbidity unit; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); SMCL-U.S., secondary maximum contaminant level (USEPA); WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μS/cm, microsiemens per centimeter; *, value above recommended threshold level; **, value above upper threshold level; <, less than] 

GAMA identification no.

Turbidity 

(NTU) 

(63676)

Dissolved 

oxygen 

(mg/L) 

(00300) 

Water 

temperature 

(oC) 

(00010)

pH, lab 

(standard units) 

(00403)

pH, field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm at 25oC) 

(90095)

Specific 

conductance, 

field 

(μS/cm at 25oC) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3)

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

Reporting limit or range 0.1 0.2 0.0-38.5 0-14 0-14 5 5 1 1

Threshold type na1 na na SMCL-US SMCL-US SMCL-CA2 SMCL-CA2 na na

Threshold level na1 na na 6.5–8.5 6.5–8.5 900 (1,600) 900 (1,600) na na

ESAC-28 0.1 2.1 20.0 7.4 7.4 371 368 186 180

ESAC-29 nc <0.2 17.0 8.0 nc 473 465 225 nc

ESAC-30 nc 0.2 15.5 7.9 7.8 432 408 121 nc

ESAC-31 nc <0.2 18.5 7.8 7.6 642 613 297 nc

ESAC-32 nc 1.0 18.0 7.4 7.2 356 362 174 nc

ESAC-33 nc 4.1 20.0 nc 7.0 nc 367 nc nc

ESAC-34 nc 2.5 17.5 7.6 7.2 593 591 273 nc

ESAC-35 nc nc 17.5 7.7 7.4 331 324 168 nc

WSAC-01 nc 2.0 22.5 nc 8.1 nc 367 nc ncWSAC-02 nc 6.3 19.0 nc 7.3 nc 476 nc nc

WSAC-03 0.1 7.7 20.0 7.5 7.3 338 337 133 122

WSAC-04 nc <0.2 24.5 8.2 7.9 318 321 173 nc

WSAC-05 nc <0.2 19.0 nc 7.9 nc 354 nc nc

WSAC-06 nc 2.7 19.5 7.3 7.0 572 574 275 nc

WSAC-07 nc 7.0 18.0 nc nc nc 500 nc ncWSAC-07 nc 5.4 18.0 nc 7.1 nc 481 nc nc

WSAC-08 0.2 4.1 20.5 7.4 7.0 535 536 221 202

WSAC-09 nc 6.3 19.0 nc nc nc 392 nc ncWSAC-09 nc 5.9 18.5 nc 6.9 nc 387 nc nc

WSAC-10 nc 6.9 19.5 7.5 7.4 597 602 231 nc

WSAC-10 nc 6.2 19.5 nc 7.2 nc 562 nc nc

WSAC-11 nc 7.1 23.5 7.8 7.8 652 649 189 nc

WSAC-11 nc 5.6 20.5 nc 7.7 nc 625 nc ncWSAC-12 0.3 <0.2 20.5 8.1 7.6 719 729 213 nc

WSAC-13 nc 2.1 20.0 nc 7.1 nc 782 nc ncWSAC-14 nc <0.2 17.5 7.8 7.2 ** 2,040 ** 2,100 324 nc

WSAC-15 nc 6.9 18.0 7.6 7.1 * 938 * 931 388 nc
38 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program Table 4.

Water-quality indicators in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, June to September, 2006.—Continued[The five-digit number below the constituent name in the headings is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a specific constituent or property. °C, degrees Celsius; CDPH, California Department of Public Health; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; mg/L, milligrams per liter; mm, millimeter; na, not available; nc, sample not collected; no., number; NTU, nephelometric turbidity unit; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); SMCL-U.S., secondary maximum contaminant level (USEPA); WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μS/cm, microsiemens per centimeter; *, value above recommended threshold level; **, value above upper threshold level; <, less than] 

GAMA identification no.

Turbidity 

(NTU) 

(63676)

Dissolved 

oxygen 

(mg/L) 

(00300) 

Water 

temperature 

(oC) 

(00010)

pH, lab 

(standard units) 

(00403)

pH, field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm at 25oC) 

(90095)

Specific 

conductance, 

field 

(μS/cm at 25oC) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3

)

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

Reporting limit or range 0.1 0.2 0.0-38.5 0-14 0-14 5 5 1 1

Threshold type na1 na na SMCL-US SMCL-US SMCL-CA2 SMCL-CA2 na na

Threshold level na1 na na 6.5–8.5 6.5–8.5 900 (1,600) 900 (1,600) na na

WSAC-16 nc <0.2 19.0 nc 7.5 nc * 1,240 nc ncWSAC-17 nc 1.3 18.0 7.5 7.2 428 429 204 nc

WSAC-18 0.1 <0.2 20.5 7.8 7.8 * 1,080 * 1,050 320 295

WSAC-19 nc 0.7 20.5 nc 7.6 nc 567 nc nc

WSAC-20 nc 5.9 17.0 nc 7.0 nc * 958 nc ncWSAC-21 nc 7.8 20.0 7.6 7.0 416 415 172 nc

WSAC-22 nc 5.1 21.0 7.8 7.7 516 523 211 nc

WSAC-23 nc 5.4 19.0 nc 7.2 nc * 1,210 nc ncWSAC-24 nc 6.8 20.0 nc 7.2 nc * 1,470 nc ncWSAC-25 nc <0.2 19.5 8.0 7.8 465 449 222 nc

WSAC-26 nc 10.8 20.0 7.7 7.6 325 325 158 nc

WSAC-27 nc 0.5 18.5 nc 7.8 nc * 914 nc ncWSAC-28 nc 4.8 19.5 7.4 7.2 433 425 168 nc

WSAC-29 nc 3.2 20.0 8.1 8.0 423 422 201 nc

WSAC-30 nc 2.2 19.0 7.7 7.4 ** 1680 ** 1,670 204 nc

WSAC-31 nc 1.8 19.0 8.2 8.0 279 280 129 nc

WSAC-32 nc 1.8 18.0 nc 7.8 nc 409 nc nc

WSAC-33 nc 5.4 19.5 nc 7.6 nc 733 nc ncWSAC-34 nc 20.4 18.5 7.4 7.1 835 816 259 nc

WSAC-35 nc 13.3 18.5 7.6 7.3 475 478 206 nc

WSAC-36 nc nc 18.5 7.9 7.6 424 461 216 nc

Flow-path wells

ESAC-FP-01 nc <0.2 23.5 7.7 7.6 547 553 75 nc

ESAC-FP-02 6.6 4.0 23.5 7.5 7.2 441 449 202 nc

ESAC-FP-03 0.3 0.3 20.5 7.5 7.5 379 379 197 nc

ESAC-FP-04 1.0 0.5 20.5 8.2 8.3 206 206 108 nc

ESAC-FP-05 0.2 1.5 22.0 7.7 7.5 742 742 355 nc

ESAC-FP-06 3.1 0.2 22.0 * 8.9 * 8.8 315 316 134 nc
Table 5

39

Table 4. Water-quality indicators in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued[The five-digit number below the constituent name in the headings is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a specific constituent or property. °C, degrees Celsius; CDPH, California Department of Public Health; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; mg/L, milligrams per liter; mm, millimeter; na, not available; nc, sample not collected; no., number; NTU, nephelometric turbidity unit; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); SMCL-U.S., secondary maximum contaminant level (USEPA); WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μS/cm, microsiemens per centimeter; *, value above recommended threshold level; **, value above upper threshold level; <, less than] 

GAMA identification no.

Turbidity 

(NTU) 

(63676)

Dissolved 

oxygen 

(mg/L) 

(00300) 

Water 

temperature 

(oC) 

(00010)

pH, lab 

(standard units) 

(00403)

pH, field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm at 25oC) 

(90095)

Specific 

conductance, 

field 

(μS/cm at 25oC) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3)

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

Reporting limit or range 0.1 0.2 0.0-38.5 0-14 0-14 5 5 1 1

Threshold type na1 na na SMCL-US SMCL-US SMCL-CA2 SMCL-CA2 na na

Threshold level na1 na na 6.5–8.5 6.5–8.5 900 (1,600) 900 (1,600) na na

ESAC-FP-07 2.9 0.2 21.5 8.5 8.3 405 407 158 nc

WSAC-FP-01 0.7 5.7 24.0 7.9 7.6 342 338 182 nc

WSAC-FP-02 2.6 2.7 22.5 8.2 8.2 315 323 143 nc

WSAC-FP-03 3.6 5.8 23.0 8.0 7.8 416 421 176 nc

WSAC-FP-04 1.1 <0.2 20.0 * 8.6 * 8.6 315 312 148 nc

WSAC-FP-05 nc 0.2 21.5 8.0 8.0 * 928 * 934 250 nc

WSAC-FP-06 2.1 <0.2 21.0 8.5 8.4 349 344 142 nc

WSAC-FP-07 0.6 0.2 20.5 8.4 8.2 326 330 145 nc

WSAC-FP-08 1.4 1.4 20.5 7.9 7.6 403 409 185 nc

RICE wells

RICE-01 4.0 <0.2 19.0 7.0 6.8 ** 13,600 ** 13,800 nc nc

RICE-02 0.3 <0.2 18.5 7.8 7.3 591 593 nc 335

RICE-03 0.2 <0.2 19.5 7.5 7.0 853 875 nc 432RICE-04 0.7 0.4 17.5 7.4 6.8 630 644 nc 328RICE-05 0.3 0.2 18.0 7.0 * 6.4 890 * 930 nc 426RICE-06 0.2 <0.2 18.0 7.1 6.6 720 756 nc 384RICE-07 1.1 0.2 20.0 7.8 7.3 784 803 nc 421RICE-08 0.1 0.4 18.0 7.7 7.3 780 796 nc 378

RICE-09 1.8 <0.2 19.5 7.9 7.2 239 267 nc 128

RICE-10 0.4 <0.2 21.0 8.0 7.4 330 363 nc 169RICE-11 0.9 0.2 20.0 7.3 7.0 *937 * 968 nc 414RICE-12 0.9 <0.2 21.5 7.7 7.3 798 818 nc 397RICE-13 1.0 <0.2 19.0 7.5 7.1 *915 * 944 nc 416RICE-14 0.5 <0.2 18.5 7.3 7.0 823 844 nc 401RICE-15 0.5 <0.2 17.0 7.8 7.3 * 947 * 944 nc 436RICE-16 0.6 1.5 20.0 7.8 7.3 ** 1,870 ** 1840 nc 596
40 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program Table 4.

Water-quality indicators in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, June to September, 2006.—Continued[The five-digit number below the constituent name in the headings is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a specific constituent or property. °C, degrees Celsius; CDPH, California Department of Public Health; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; mg/L, milligrams per liter; mm, millimeter; na, not available; nc, sample not collected; no., number; NTU, nephelometric turbidity unit; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); SMCL-U.S., secondary maximum contaminant level (USEPA); WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μS/cm, microsiemens per centimeter; *, value above recommended threshold level; **, value above upper threshold level; <, less than] 

GAMA identification no.

Turbidity 

(NTU) 

(63676)

Dissolved 

oxygen 

(mg/L) 

(00300) 

Water 

temperature 

(oC) 

(00010)

pH, lab 

(standard units) 

(00403)

pH, field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm at 25oC) 

(90095)

Specific 

conductance, 

field 

(μS/cm at 25oC) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3

)

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

Reporting limit or range 0.1 0.2 0.0-38.5 0-14 0-14 5 5 1 1

Threshold type na1 na na SMCL-US SMCL-US SMCL-CA2 SMCL-CA2 na na

Threshold level na1 na na 6.5–8.5 6.5–8.5 900 (1,600) 900 (1,600) na na

RICE-17 0.5 <0.2 18.5 7.7 7.4 ** 4,770 ** 4750 nc 350

RICE-18 0.4 <0.2 19.0 7.7 7.3 855 863 nc 343RICE-19 0.2 <0.2 18.5 7.8 7.4 481 489 nc 245RICE-20 0.2 <0.2 18.0 7.7 7.3 * 1,000 * 1,010 nc 407

RICE-21 0.1 0.2 18.5 7.6 7.3 ** 1,650 ** 1,680 nc 347RICE-22 0.6 0.2 18.0 7.5 7.3 ** 3,290 ** 3,310 nc 415

1A TT-US threshold of 5 NTU does exist, but it applies to surface water and, therefore, is not included with this table.2 Specific conductance has a recommended and an upper threshold value. The upper value is shown in parentheses.
Table 541

Table 5. Volatile organic compounds (VOCs), and gasoline oxygenates and degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued [Samples from all 108 wells were analyzed, but only wells with detections are listed. Constituents are grouped by primary use or source, and within each group are listed in order of decreasing detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property.CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; NL-CA, notification level (CDPH); no., number; RICE, RICE well; USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected]

GAMA 

identification 

no.

Trihalomethanes Gasoline Hydrocarbons and Oxygenates

Chloroform 

(Trichloromethane)

(μg/L) 

(32106)

Bromodichloromethane

(μg/L) 

(32101)

Bromoform 

(μg/L) 

(32104)

Methyl tertbutyl ether 

(MTBE)

(μg/L)

(78032)

1,2,4-Trimethylbenzene 

(μg/L) 

(77222)

1,3,5-Trimethylbenzene 

(μg/L) 

(77226)

1,2,3-Trimethylbenzene 

(μg/L) 

(77221)

1,2,3,4-

Tetramethylbenzene 

(μg/L) 

(49999)

1,2,3,5-

Tetramethylbenzene 

(μg/L) 

(50000)

2-Ethyltoluene 

(μg/L) 

(77220)

4-Isopropyltoluene 

(μg/L) 

(77356)

Benzene

(μg/L) 

(34030)

m- and 

p-Xylene

(μg/L) 

(85795)

Toluene 

(μg/L) 

(34010)

[LRL] [0.024] [0.028] [0.1] [0.1] [0.056] [0.044] [0.09] [0.14] [0.18] [0.06] [0.08] [0.021] [0.06] [0.02]

Threshold type1 MCL-US MCL-US MCL-US MCL-CA NL-CA NL-CA na na na na na MCL-CA MCL-CA MCL-CA

Threshold (μg/L) 280 280 280 13 330 330 na na na na na 1 1750 150

Grid wells

ESAC-01 V0.01 — — — — — — — — — — — — —

ESAC-02 V0.01 — — — — — — — — — — — — —

ESAC-03 0.14 — — E0.1 — — — — — — — — — —

ESAC-07 E0.06 — — — — — — — — — — — — —

ESAC-15 E0.06 — — — — — — — — — — — — —

ESAC-17 — — — — — — — — — — — — — —

ESAC-21 — — — — — — — — — — — — — —

ESAC-22 — — — — E0.07 E0.02 — — — — — — — —

ESAC-25 — — — — 0.1 — — — — — — — — —

ESAC-27 — — — 0.1 — — — — — — — — — —

ESAC-28 E0.09 — — — V0.05 — — — — — — — — —

ESAC-32 — — — — — — — — — — — — — —

ESAC-33 0.86 E0.04 — 0.1 — — — — — — — — — —

WSAC-03 0.2 E0.03 0.11 — — — — — — — — — — —

WSAC-05 — — — E0.1 — — — — — — — — — —

WSAC-11 E0.08 — — — — — — — — — — — — —

WSAC-12 — — — — V0.02 — — — — — — — — —

WSAC-16 0.16 E0.02 — — — — — — — — — — — —

WSAC-17 E0.05 — — — — — — — — — — — — —

Table 5. Volatile organic compounds (VOCs), and gasoline oxygenates and degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006. [Samples from all 108 wells were analyzed, but only wells with detections are listed. Constituents are grouped by primary use or source, and within each group are listed in order of decreasing detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; NL-CA, notification level (CDPH); no., number; RICE, RICE well; USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected]
42 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program Table 5.

Volatile organic compounds (VOCs), and gasoline oxygenates and degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued [Samples from all 108 wells were analyzed, but only wells with detections are listed. Constituents are grouped by primary use or source, and within each group are listed in order of decreasing detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; NL-CA, notification level (CDPH); no., number; RICE, RICE well; USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected]

GAMA 

identification 

no.

Trihalomethanes Gasoline Hydrocarbons and Oxygenates

Chloroform 

(Trichloromethane)

(μg/L) 

(32106)

Bromodichloromethane

(μg/L) 

(32101)

Bromoform 

(μg/L) 

(32104)

Methyl tertbutyl ether 

(MTBE)

(μg/L)

(78032)

1,2,4-Trimethylbenzene 

(μg/L) 

(77222)

1,3,5-Trimethylbenzene 

(μg/L) 

(77226)

1,2,3-Trimethylbenzene 

(μg/L) 

(77221)

1,2,3,4-

Tetramethylbenzene 

(μg/L) 

(49999)

1,2,3,5-

Tetramethylbenzene 

(μg/L) 

(50000)

2-Ethyltoluene 

(μg/L) 

(77220)

4-Isopropyltoluene 

(μg/L) 

(77356)

Benzene

(μg/L) 

(34030)

m- and 

p-Xylene

(μg/L) 

(85795)

Toluene 

(μg/L) 

(34010)

[LRL] [0.024] [0.028] [0.1] [0.1] [0.056] [0.044] [0.09] [0.14] [0.18] [0.06] [0.08] [0.021] [0.06] [0.02]

Threshold type1 MCL-US MCL-US MCL-US MCL-CA NL-CA NL-CA na na na na na MCL-CA MCL-CA MCL-CA

Threshold (μg/L) 280 280 280 13 330 330 na na na na na 1 1750 150

WSAC-18

—

—

—

— 0.15

—

—

—

—

—

—

—

—

—

WSAC-24 V0.02

—

—

—

—

—

—

—

—

—

—

—

—

—

WSAC-27

—

—

—

— V0.06 E0.04 E0.1 E0.1 E0.1 E0.02 E0.01

—

—

—

WSAC-28

—

—

—

— V0.04

—

—

—

—

—

—

—

—

—

WSAC-33 E0.08

—

—

—

—

—

—

—

—

—

—

—

—

—

Number of wells with detections 10 3 1 4 3 2 1 1 1 1 1 0 0 0

Detection frequency (percent) 14 4 1 6 4 3 1 1 1 1 1

Flow-path wells

ESAC-FP-02

—

—

—

—

—

—

—

—

—

—

—

—

—

—

ESAC-FP-03

—

—

—

—

—

—

—

—

—

—

—

—

— V0.02

ESAC-FP-06

—

—

—

—

—

—

—

—

—

—

—

—

—

—

ESAC-FP-07

—

—

—

— V0.02

—

—

—

—

—

—

—

—

—

WSAC-FP-04

—

—

—

—

—

—

—

— E0.1

—

—

—

—

—

WSAC-FP-05

—

—

—

— V0.03

—

—

—

—

—

—

—

—

—

WSAC-FP-06

—

—

—

—

—

—

—

— E0.2

—

—

—

—

—

RICE wells

RICE-01

—

—

—

—

—

—

—

—

—

—

— E0.02

—

—

RICE-05

—

—

—

—

—

—

—

—

—

—

—

— V0.01

—
Table 543

Table 5. Volatile organic compounds (VOCs), and gasoline oxygenates and degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Contined [Samples from all 108 wells were analyzed, but only wells with detections are listed. Constituents are grouped by primary use or source, and within each group are listed in order of decreasing detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; NL-CA, notification level (CDPH); no., number; RICE, RICE well; USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected]

GAMA 

identification 

no.

Solvents Organic synthesis Refrigerant

VOC 

detections 

per well

Perchloro

ethene 

(PCE)

(μg/L) 

(34475)

1,1-

Dichloroethane

(μg/L) 

(34496)

cis-1,2-

Dichloroethene

(μg/L) 

(77093)

Carbon 

tetrachloride

(μg/L) 

(32102)

trans-1,2-

Dichloroethene

(μg/L) 

(34546)

Trichloroethene 

(TCE)

(μg/L) 

(39180)

Acetone

(μg/L) 

(81552)

2-Butanone 

(MEK, 

Methyl ethyl 

ketone)

(μg/L)

(81595)

Carbon 

disulfide

(μg/L) 

(77041)

Trichlorofluoromethane 

(CFC-11)

(μg/L) 

(34488)

[LRL] [0.03] [0.035] [0.024] [0.06] [0.032] [0.038] [6] [2] [0.038] [0.08]

Threshold type1 MCL-US MCL-CA MCL-CA MCL-CA MCL-CA MCL-US na HAL-US NL-CA MCL-CA

Threshold (μg/L) 5 5 6 0.5 10 5 na 4000 160 150

Grid wells

ESAC-01 — — — — — — — — — — 0

ESAC-02 — — — — — — — — — — 0

ESAC-03 E0.02 E0.03 — — — — — — — — 4

ESAC-07 — — — — — — — — — — 1

ESAC-15 0.51 0.11 2.06 — E0.01 0.11 — — — — 6

ESAC-17 — — — — — — — — 0.15 — 1

ESAC-21 — — — — — — — — E0.05 — 1

ESAC-22 — — — — — — — — — — 2

ESAC-25 — — — — — — — — — — 1

ESAC-27 — — — — — — — — — — 1

ESAC-28 — — — — — — — — — — 1

ESAC-32 E0.05 — — — — — — — — — 1

ESAC-33 0.96 — — — — — — — — 0.11 5

WSAC-03 — — — — — — — — — — 3

WSAC-05 — — — — — — — — — — 1

WSAC-11 — — — — — — — — — — 1

WSAC-12 — — — — — — — — — — 0

WSAC-16 — — — — — — — — — — 2

WSAC-17 — — — — — — — — — — 1
44 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program Table 5.

Volatile organic compounds (VOCs), and gasoline oxygenates and degradates detected in samples collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006. —Contined[Samples from all 108 wells were analyzed, but only wells with detections are listed. Constituents are grouped by primary use or source, and within each group are listed in order of decreasing detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; NL-CA, notification level (CDPH); no., number; RICE, RICE well; USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected]

GAMA 

identification 

no.

Solvents Organic synthesis Refrigerant

VOC 

detections 

per well

Perchloro

ethene 

(PCE)

(μg/L) 

(34475)

1,1-

Dichloroethane

(μg/L) 

(34496)

cis-1,2-

Dichloroethene

(μg/L) 

(77093)

Carbon 

tetrachloride

(μg/L) 

(32102)

trans-1,2-

Dichloroethene

(μg/L) 

(34546)

Trichloroethene 

(TCE)

(μg/L) 

(39180)

Acetone

(μg/L) 

(81552)

2-Butanone 

(MEK, 

Methyl ethyl 

ketone)

Carbon 

disulfide

(μg/L) 

(77041)

Trichlorofluoromethane 

(CFC-11)

(μg/L) 

(34488)

[LRL] [0.03] [0.035] [0.024] [0.06] [0.032] [0.038] [6] [2] [0.038] [0.08]

Threshold type1 MCL-US MCL-CA MCL-CA MCL-CA MCL-CA MCL-US na HAL-US NL-CA MCL-CA

Threshold (μg/L) 5 5 6 0.5 10 5 na 4000 160 150

WSAC-18

—

—

—

—

—

—

—

—

—

— 1

WSAC-24

—

—

— E0.04

—

—

—

—

—

— 1

WSAC-27

—

—

—

—

—

—

—

—

—

— 6

WSAC-28

—

—

—

—

—

—

—

—

—

— 0

WSAC-33

—

—

—

—

—

—

—

—

—

— 1

Number of wells with detections 4 2 1 1 1 1 0 0 2 1

Detection frequency (percent) 6 3 1 1 1 1 3 1 328

Flow-path wells

ESAC-FP-02 E0.03

—

— 0.18

—

—

—

—

—

— 2

ESAC-FP-03

—

—

—

—

—

—

—

—

—

— 0

ESAC-FP-06

—

—

—

—

—

—

—

— E0.03

— 1

ESAC-FP-07

—

—

—

—

—

— E2 6.4 E0.03

— 3

WSAC-FP-04

—

—

—

—

—

—

—

—

—

— 1

WSAC-FP-05

—

—

—

—

—

—

—

—

—

— 0

WSAC-FP-06

—

—

—

—

—

—

—

—

—

— 1

RICE wells

RICE-01

—

—

—

—

—

—

—

—

—

— 1

RICE-05

—

—

—

—

—

—

—

—

—

— 0

1Maximum contaminant level thresholds are listed as MCL-US when MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than 

the MCL-US or no MCL-US exists.

2 The MCL-US threshold for trihalomethanes is the sum of chloroform, bromodichloromethane, dibromochloromethane, and bromoform.3 Frequency of detection of at least one VOC in the grid wells. Detections with V remark codes are not included.
Table 6 45

Table 6. Pesticides and pesticide degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[Results are from the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032, 2033, and 2060. Samples from all 108 wells were 

analyzed, but only wells with detections are listed. Constituents are grouped by primary use of source and within each group are listed in order of decreasing 

detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name is used by the USGS to uniquely identify a specific 

constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study 

unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory 

reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; no., number; RICE, RICE 

well; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus 

data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area 

of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected] 

GAMA 

identification 

no.

Herbicides

Bentazon

(μg/L) 

(38711)

Atrazine

(μg/L)

(39632)

Simazine

(μg/L)

(04035)

Metolachlor

(μg/L) 

(39415)

Hexazinone

(μg/L) 

(04025)

Dinoseb 

(μg/L) 

(49301)

Molinate

(μg/L) 

(82671)

Prometon

(μg/L) 

(04037)

Acetochlor

(μg/L) 

(49260)

Metribuzin

(μg/L) 

(82630)

Tebuthiuron

(μg/L) 

(82670)

Propanil

(μg/L)

(82679)

[LRL] [0.024] [0.008] [0.005] [0.006] [0.026] [0.038] [0.003] [0.01] [0.006] [0.028] [0.026] [0.011]

Threshold 

type1 MCL-CA MCL-CA MCL-US HAL-US HAL-US MCL-US MCL-CA HAL-US na HAL-US HAL-US na

Threshold 

value 18 1 4 700 400 7 20 100 na 70 500 na

Grid wells

ESAC-01 — E0.004 E0.003 — — — — — — — — —

ESAC-05 — — — — — — — — — — — —

ESAC-09 0.09 — E0.004 — — — E0.02 — — — — 0.097

ESAC-10 0.47 0.008 — — — — — — — — — —

ESAC-20 0.02 — — — — — 0.013 — — — — —

ESAC-22 — E0.004 E0.004 — — — — — — — — —

ESAC-23 — 0.077 — 0.028 — — — 0.02 0.059 — — —

ESAC-24 — E0.007 E0.005 — — — — — — — — —

ESAC-26 — — 0.011 — — — — — — — — —

ESAC-27 0.03 0.011 0.024 — — — — — — — — —

ESAC-28 0.05 E0.005 — — — — — — — — — —

ESAC-31 0.43 — — — — — — — — — — —

ESAC-32 0.04 — — — — — — — — — — —

ESAC-33 0.04 E0.004 — — — E0.004 — — — — — —

ESAC-34 0.1 — — — — E0.01 — — — — — —

ESAC-35 0.08 — — — — — — — — — — —

WSAC-02 — 0.04 E0.005 — — — — — — — — —

WSAC-06 — E0.004 E0.004 — — — — — — — — —

WSAC-07 — E0.005 E0.005 — — — — — — — — —

WSAC-08 — — — — — — — — — — — —

WSAC-09 — E0.007 E0.004 — — — — — — — — —

WSAC-11 — — E0.005 — — — — — — — — —

WSAC-12 0.09 — — — — — — — — — — —

WSAC-13 0.08 — — — — — — — — — — —

WSAC-14 E0.01 — — — — — — — — — — —

WSAC-15 — — 0.009 E0.005 E0.009 — — — — — 0.03 —

WSAC-16 E0.005 — — — — — — — — — — —
46 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 6. Pesticides and pesticide degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006. —Continued

[Results are from the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032, 2033, and 2060. Samples from all 108 wells were 

analyzed, but only wells with detections are listed. Constituents are grouped by primary use of source and within each group are listed in order of decreasing 

detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name is used by the USGS to uniquely identify a specific 

constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study 

unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory 

reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; no., number; RICE, RICE 

well; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus 

data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area 

of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected] 

GAMA 

identification 

no.

Herbicides

Bentazon

(μg/L) 

(38711)

Atrazine

(μg/L)

(39632)

Simazine

(μg/L)

(04035)

Metolachlor

(μg/L) 

(39415)

Hexazinone

(μg/L) 

(04025)

Dinoseb 

(μg/L) 

(49301)

Molinate

(μg/L) 

(82671)

Prometon

(μg/L) 

(04037)

Acetochlor

(μg/L) 

(49260)

Metribuzin

(μg/L) 

(82630)

Tebuthiuron

(μg/L) 

(82670)

Propanil

(μg/L)

(82679)

[LRL] [0.024] [0.008] [0.005] [0.006] [0.026] [0.038] [0.003] [0.01] [0.006] [0.028] [0.026] [0.011]

Threshold 

type1 MCL-CA MCL-CA MCL-US HAL-US HAL-US MCL-US MCL-CA HAL-US na HAL-US HAL-US na

Threshold 

value 18 1 4 700 400 7 20 100 na 70 500 na

WSAC-17 — — E0.006 — E0.008 — — — — — — —

WSAC-18 E0.02 — — — — — — — — — — —

WSAC-20 — E0.004 0.01 E0.005 — — — — — 0.113 — —

WSAC-23 — — 0.008 — — — — — — — — —

WSAC-27 0.29 — — — — — — — — — — —

WSAC-28 — — — — — — — — — — — —

WSAC-29 E0.004 E0.006 — — — — — — — — — —

WSAC-31 0.09 — — — — — — — — — — —

WSAC-32 E0.01 E0.005 E0.004 — — — — — — — — —

WSAC-34 — E0.008 — — — — — — — — — —

WSAC-35 E0.005 E0.005 E0.004 — E0.016 — — — — — — —

WSAC-36 0.11 — — — — — — — — — — —

Number of 

wells with 

detections

21 17 17 3 3 2 2 1 1 1 1 1

Detection 

frequency 

(percent)

30 24 24 4 4 3 3 1 1 1 1 1

Flow-path wells

ESAC-FP-03 0.15 — — — — — — — — — — —

ESAC-FP-05 E0.01 — — — — — — — — — — —

ESAC-FP-06 — — — — — — — — — — — —

ESAC-FP-07 — — — — — — — — — — — —

WSAC-FP-06 — — — — — — — — — — — —

WSAC-FP-08 0.13 — — — — — — — — — — —
Table 6 47

Table 6. Pesticides and pesticide degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006. —Continued

[Results are from the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032, 2033, and 2060. Samples from all 108 wells were 

analyzed, but only wells with detections are listed. Constituents are grouped by primary use of source and within each group are listed in order of decreasing 

detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name is used by the USGS to uniquely identify a specific 

constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study 

unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory 

reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; no., number; RICE, RICE 

well; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus 

data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area 

of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected] 

GAMA 

identification 

no.

Herbicides

Bentazon

(μg/L) 

(38711)

Atrazine

(μg/L)

(39632)

Simazine

(μg/L)

(04035)

Metolachlor

(μg/L) 

(39415)

Hexazinone

(μg/L) 

(04025)

Dinoseb 

(μg/L) 

(49301)

Molinate

(μg/L) 

(82671)

Prometon

(μg/L) 

(04037)

Acetochlor

(μg/L) 

(49260)

Metribuzin

(μg/L) 

(82630)

Tebuthiuron

(μg/L) 

(82670)

Propanil

(μg/L)

(82679)

[LRL] [0.024] [0.008] [0.005] [0.006] [0.026] [0.038] [0.003] [0.01] [0.006] [0.028] [0.026] [0.011]

Threshold 

type1 MCL-CA MCL-CA MCL-US HAL-US HAL-US MCL-US MCL-CA HAL-US na HAL-US HAL-US na

Threshold 

value 18 1 4 700 400 7 20 100 na 70 500 na

RICE wells

RICE-01 — — — — — — 0.008 — — — — —

RICE-03 — E0.007 E0.005 — — — — — — — — E0.006

RICE-04 0.11 — — — — — — — — — — —

RICE-06 0.04 — E0.003 — — — — — — — — —

RICE-07 1.46 — — — — — — — — — — —

RICE-08 E0.02 — — — — — — — — — — —

RICE-09 — — E0.004 — E0.013 — — — — — — —

RICE-10 — — 0.082 — — — — — — — — —

RICE-11 0.03 E0.007 E0.005 — — — — — — — — —

RICE-12 0.42 E0.005 E0.008 — — — — — — — — —

RICE-13 0.32 — — — — — — — — — — —

RICE-14 0.14 — — — — — — — — — 0.02 —

RICE-15 0.32 E0.007 — — — — — — — — — —

RICE-16 0.29 — — — — — — — — — — —

RICE-17 1.7 — — — — — — — — — — —

RICE-18 1.82 — — — — — — — — — — —

RICE-19 0.08 0.008 — — — — — — — — — —

RICE-20 0.21 — E0.004 — — — — — — — — —

RICE-21 0.45 — — — — — — — — — — —

RICE-22 0.23 — — — E0.014 — — — — — — —
48 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

GAMA 

identification 

no.

Herbicides—continued Insecticides

Bensulfuronmethyl

(μg/L) 

(61693)

MCPA

(μg/L) 

(38482)

Triclopyr

(μg/L) 

(49235)

2,4-D,

(μg/L)

(39732)

Chlorimuron

(μg/L) 

(50306)

Bromacil 

(μg/L) 

(04029)

Chlorpyrifos

(μg/L) 

(38933)

Carbaryl

(μg/L) 

(82680)

Fipronil

(μg/L) 

(62166)

[LRL] [0.018] [0.07] [0.026] [0.038] [0.032] 0.018 [0.005] [0.041] [0.016]

Threshold type1 na HAL-US na MCL-US na HAL-US HAL-US RSD5-US na

Threshold value na 30 na 70 na 70 2 400 na

Grid wells

ESAC-01 — — — — — — — —

ESAC-05 — — — — — V0.01 — — —

ESAC-09 E0.01 E0.02 0.12 — — — — E0.007 —

ESAC-10 — — na — — — — — —

ESAC-20 — — na — — — — — —

ESAC-22 — — — — — V0.03 — — —

ESAC-23 — — na — — — 0.008 — E0.017

ESAC-24 — — na — — — — — —

ESAC-26 — — na — — — — — —

ESAC-27 — — na — — — — — —

ESAC-28 — — — — — — — — —

ESAC-31 — — — — — — — — —

ESAC-32 — — — — — — — — —

ESAC-33 — — — — — — — — —

ESAC-34 — — — — — — — — —

ESAC-35 — — — — — — — — —

WSAC-02 — — — — — — — — —

WSAC-06 — — — — — — — — —

WSAC-07 — — — — — V0.004 — — —

WSAC-08 — — na — — — — — —

WSAC-09 — — — — — — — — —

WSAC-11 — — — — — — — — —

WSAC-12 — — — — — — — — —

WSAC-13 — — na — — — — — —

WSAC-14 — — na — — — — — —

WSAC-15 — — — — — — — — —

WSAC-16 — — na — — — — — —

WSAC-17 — — na — — — — — —

Table 6. Pesticides and pesticide degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006. —Continued

[Results are from the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032, 2033, and 2060. Samples from all 108 wells were 

analyzed, but only wells with detections are listed. Constituents are grouped by primary use of source and within each group are listed in order of decreasing 

detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name is used by the USGS to uniquely identify a specific 

constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study 

unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory 

reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; no., number; RICE, RICE 

well; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus 

data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area 

of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected] 
Table 6 49

GAMA 

identification 

no.

Herbicides—continued Insecticides

Bensulfuronmethyl

(μg/L) 

(61693)

MCPA

(μg/L) 

(38482)

Triclopyr

(μg/L) 

(49235)

2,4-D,

(μg/L)

(39732)

Chlorimuron

(μg/L) 

(50306)

Bromacil 

(μg/L) 

(04029)

Chlorpyrifos

(μg/L) 

(38933)

Carbaryl

(μg/L) 

(82680)

Fipronil

(μg/L) 

(62166)

[LRL] [0.018] [0.07] [0.026] [0.038] [0.032] 0.018 [0.005] [0.041] [0.016]

Threshold type1 na HAL-US na MCL-US na HAL-US HAL-US RSD5-US na

Threshold value na 30 na 70 na 70 2 400 na

WSAC-18 — — — — — — — — —

WSAC-20 — — — — — — — — —

WSAC-23 — — — — — — — — —

WSAC-27 — — — — — — — — —

WSAC-28 — — — — — — — — —

WSAC-29 — — — — — — — — —

WSAC-31 — — — — — — — — —

WSAC-32 — — — — — — — — —

WSAC-34 — — — — — — — — —

WSAC-35 — — — — — — — — —

WSAC-36 — — — — — — — — —

Number of wells with 

detections

1 1 1 0 0 0 1 1 1

Detection frequency 

(percent)

1 1 1 1 1 1

Flow-path wells

ESAC-FP-03 — — — — — — — — —

ESAC-FP-05 — — — E0.004 — — — — —

ESAC-FP-06 — — E0.02 — — — — — —

ESAC-FP-07 — — E0.01 — — — — — —

WSAC-FP-06 — — — — — — — — —

WSAC-FP-08 — — — — — — — — —

Table 6. Pesticides and pesticide degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006. —Continued

[Results are from the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032, 2033, and 2060. Samples from all 108 wells were 

analyzed, but only wells with detections are listed. Constituents are grouped by primary use of source and within each group are listed in order of decreasing 

detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name is used by the USGS to uniquely identify a specific 

constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study 

unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory 

reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; no., number; RICE, RICE 

well; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus 

data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area 

of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected] 
50 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

GAMA 

identification 

no.

Herbicides—continued Insecticides

Bensulfuronmethyl

(μg/L) 

(61693)

MCPA

(μg/L) 

(38482)

Triclopyr

(μg/L) 

(49235)

2,4-D,

(μg/L)

(39732)

Chlorimuron

(μg/L) 

(50306)

Bromacil 

(μg/L) 

(04029)

Chlorpyrifos

(μg/L) 

(38933)

Carbaryl

(μg/L) 

(82680)

Fipronil

(μg/L) 

(62166)

[LRL] [0.018] [0.07] [0.026] [0.038] [0.032] 0.018 [0.005] [0.041] [0.016]

Threshold type1 na HAL-US na MCL-US na HAL-US HAL-US RSD5-US na

Threshold value na 30 na 70 na 70 2 400 na

RICE wells

RICE-01 — — — — — — — — —

RICE-03 — — — — — — — — —

RICE-04 — — — — — — — — —

RICE-06 — — — — — — — — —

RICE-07 — — — — — — — — —

RICE-08 — — — — — — — — —

RICE-09 — — — — — — — — —

RICE-10 — — — — 1.57 — — — —

RICE-11 — — — — — — — — —

RICE-12 — — — — — — — — —

RICE-13 — — — — — — — — —

RICE-14 — — — — — — — — —

RICE-15 — — — — — — — — —

RICE-16 — — — — — — — — —

RICE-17 — — — — — — — — —

RICE-18 — — — — — — — — —

RICE-19 — — — — — — — — —

RICE-20 — — — — — — — — —

RICE-21 — — — — — — — — —

RICE-22 — — — — — — — — —

Table 6. Pesticides and pesticide degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006. —Continued

[Results are from the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032, 2033, and 2060. Samples from all 108 wells were 

analyzed, but only wells with detections are listed. Constituents are grouped by primary use of source and within each group are listed in order of decreasing 

detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name is used by the USGS to uniquely identify a specific 

constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study 

unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory 

reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; no., number; RICE, RICE 

well; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus 

data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area 

of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected] 
Table 6 51

Table 6. Pesticides and pesticide degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006. —Continued

[Results are from the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032, 2033, and 2060. Samples from all 108 wells were 

analyzed, but only wells with detections are listed. Constituents are grouped by primary use of source and within each group are listed in order of decreasing 

detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name is used by the USGS to uniquely identify a specific 

constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study 

unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory 

reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; no., number; RICE, RICE 

well; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus 

data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area 

of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected] 

GAMA 

identification 

no.

Fungicides Degradates

Pesticide 

detections

per well

cisPropiconazole

 (μg/L) 

(79846)

transPropiconazole

(μg/L) 

(79847)

Deethylatrazine

(μg/L) 

(04040)

3,4-

Dichloroaniline

(μg/L) 

(61625)

Hydroxyatrazine

 (μg/L) 

(50355)

Desulfinylfipronil

(μg/L) 

(62170)

Fipronil 

sulfide

(μg/L) 

(62167)

Fipronil 

sulfone

(μg/L) 

(62168)

Deisopropylatrazine

(μg/L) 

(04038)

[LRL] [0.013] [0.034] [0.028] [0.0045] [0.032] [0.012] [0.013] [0.024] [0.08]

Threshold 

type1 na na na na na na na na na

Threshold 

value na na na na na na na na na

Grid wells

ESAC-01 — — E0.006 — — — — — — 3

ESAC-05 — — — — — — — — — 0

ESAC-09 — — — E0.541 — — — — — 9

ESAC-10 — — E0.008 — — — — — — 3

ESAC-20 — — — — — — — — — 2

ESAC-22 — — — — — — — — — 2

ESAC-23 — — E0.022 — — E0.008 E0.006 E0.008 — 10

ESAC-24 — — E0.007 — — — — — — 3

ESAC-26 — — — — — — — — — 1

ESAC-27 — — E0.011 — — — — — — 4

ESAC-28 — — E0.009 — — — — — — 3

ESAC-31 — — — — — — — — — 1

ESAC-32 — — — — — — — — — 1

ESAC-33 — — E0.01 — — — — — — 4

ESAC-34 — — — — — — — — — 2

ESAC-35 — — — — — — — — — 1

WSAC-02 — — E0.057 E0.006 E0.003 — — — — 5

WSAC-06 — — E0.007 — na — — — — 3

WSAC-07 — — E0.006 — — — — — — 3

WSAC-08 — — E0.007 — — — — — — 1

WSAC-09 — — E0.009 — — — — — — 3

WSAC-11 — — — — — — — — — 1

WSAC-12 — — — — — — — — — 1

WSAC-13 — — — — — — — — — 1

WSAC-14 — — — — — — — — — 1

WSAC-15 — — E0.005 — — — — — — 5

WSAC-16 — — — — — — — — — 1
52 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 6. Pesticides and pesticide degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006. —Continued

[Results are from the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032, 2033, and 2060. Samples from all 108 wells were 

analyzed, but only wells with detections are listed. Constituents are grouped by primary use of source and within each group are listed in order of decreasing 

detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name is used by the USGS to uniquely identify a specific 

constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study 

unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory 

reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; no., number; RICE, RICE 

well; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus 

data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area 

of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected] 

GAMA 

identification 

no.

Fungicides Degradates

Pesticide 

detections

per well

cisPropiconazole

 (μg/L) 

(79846)

transPropiconazole

(μg/L) 

(79847)

Deethylatrazine

(μg/L) 

(04040)

3,4-

Dichloroaniline

(μg/L) 

(61625)

Hydroxyatrazine

 (μg/L) 

(50355)

Desulfinylfipronil

(μg/L) 

(62170)

Fipronil 

sulfide

(μg/L) 

(62167)

Fipronil 

sulfone

(μg/L) 

(62168)

Deisopropylatrazine

(μg/L) 

(04038)

[LRL] [0.013] [0.034] [0.028] [0.0045] [0.032] [0.012] [0.013] [0.024] [0.08]

Threshold 

type1 na na na na na na na na na

Threshold 

value na na na na na na na na na

WSAC-17 — — — E0.005 E0.024 — — — — 4

WSAC-18 — — — — — — — — — 1

WSAC-20 — — E0.006 — — — — — — 5

WSAC-23 — — — — — — — — — 1

WSAC-27 — — — — — — — — — 1

WSAC-28 — — E0.005 — — — — — — 1

WSAC-29 — — E0.005 — — — — — — 3

WSAC-31 — — — — — — — — — 1

WSAC-32 — — E0.006 — — — — — — 4

WSAC-34 — — E0.007 — — — — — — 2

WSAC-35 — — E0.006 E0.006 — — — — — 6

WSAC-36 — — — — — — — — — 1

Number of 

wells with 

detections

0 0 19 4 3 1 1 1 0

Detection 

frequency 

(percent)

27 6 4 1 1 1 2

54

Flow-path wells

ESAC-FP-03 — — — — — — — — — 1

ESAC-FP-05 — — — — — — — — — 2

ESAC-FP-06 E0.001 E0.01 — — — — — — — 3

ESAC-FP-07 — — — — — — — — — 1

WSAC-FP-06 — — — — — — — — E0.04 1

WSAC-FP-08 — — — — — — — — — 1
Table 6 53

Table 6. Pesticides and pesticide degradates detected in samples collected for the Middle Sacramento Valley Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, June to September, 2006. —Continued

[Results are from the U.S. Geological Survey’s (USGS) National Water Quality Laboratory Schedules 2032, 2033, and 2060. Samples from all 108 wells were 

analyzed, but only wells with detections are listed. Constituents are grouped by primary use of source and within each group are listed in order of decreasing 

detection frequency in the 71 grid wells. The five-digit number in parentheses below the constituent name is used by the USGS to uniquely identify a specific 

constituent or property. CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study 

unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory 

reporting level; MCL-CA; maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; no., number; RICE, RICE 

well; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5 μg/L (RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus 

data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area 

of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected] 

GAMA 

identification 

no.

Fungicides Degradates

Pesticide 

detections

per well

cisPropiconazole

 (μg/L) 

(79846)

transPropiconazole

(μg/L) 

(79847)

Deethylatrazine

(μg/L) 

(04040)

3,4-

Dichloroaniline

(μg/L) 

(61625)

Hydroxyatrazine

 (μg/L) 

(50355)

Desulfinylfipronil

(μg/L) 

(62170)

Fipronil 

sulfide

(μg/L) 

(62167)

Fipronil 

sulfone

(μg/L) 

(62168)

Deisopropylatrazine

(μg/L) 

(04038)

[LRL] [0.013] [0.034] [0.028] [0.0045] [0.032] [0.012] [0.013] [0.024] [0.08]

Threshold 

type1 na na na na na na na na na

Threshold 

value na na na na na na na na na

RICE wells

RICE-01 — — — — — — — — — 1

RICE-03 — — E0.006 — — — — — — 4

RICE-04 — — — — — — — — — 1

RICE-06 — — — E0.004 — — — — — 3

RICE-07 — — — — — — — — — 1

RICE-08 — — — — — — — — — 1

RICE-09 — — — — — — — — — 2

RICE-10 — — — E0.091 — — — — 0.15 4

RICE-11 — — E0.006 — — — — — — 4

RICE-12 — — E0.006 E0.006 — — — — — 5

RICE-13 — — — — — — — — — 1

RICE-14 — — — — — — — — — 2

RICE-15 — — — — — — — — — 2

RICE-16 — — — — — — — — — 1

RICE-17 — — — E0.005 — — — — — 2

RICE-18 — — — — — — — — — 1

RICE-19 — — E0.006 — — — — — — 3

RICE-20 — — — — — — — — — 2

RICE-21 — — — — — — — — — 1

RICE-22 — — — — — — — — — 2

1

 Maximum contaminant level thresholds are listed as MCL-US when MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than 

the MCL-US or no MCL-US exists.

2

 Frequency of detection of at least one pesticide in the grid wells. Detections with V remark codes are not included.
54 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

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

[NDMA], and 1,2,3-trichloropropane [1,2,3-TCP]) detected in samples collected in the 

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, June to September, 2006.

[Samples from all 108 wells were analyzed for perchlorate; samples from 45 grid wells and 15 

flow-path wells were sampled for NDMA and 1,2,3-TCP; only wells with at least one detection are 

listed. Analyses done by the Mongomery Watson Harza laboratory. The laboratory entity code for the 

Montgomery Watson Harza laboratory in the U. S. Geological Survey’s National Water Information 

System (NWIS) is CA-MWHL. CDPH, California Department of Public Health; ESAC, East study 

area of the middle Sacramento Valley study unit; MCL-CA, maximum contaminant level (CDPH); 

MRL, minimum reporting level; no., number; RICE, RICE well; WSAC, West study area of the middle 

Sacramento Valley study unit; μg/L, micrograms per liter]

GAMA identification no. Perchlorate (μg/L)

Threshold Type MCL-CA

Threshold (μg/L) 6

[MRL] [0.5]

Grid wells

ESAC-03 0.6

ESAC-04 1.4

WSAC-20 0.6

WSAC-24 1.4

Number of wells with detections 4

Detection frequency (percent) 6

RICE wells

RICE-10 1.3
Table 8 55

Table 8. Nutrients and dissolved organic carbon detected in samples collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed for nutrients; samples from all slow grid wells 

and all RICE wells were analyzed for dissolved organic carbon. The five-digit number in parentheses below the constituent name in the headings is used by the 

U.S. Geological Survey (USGS) to uniquely identify a specific constituent or property. E, estimated value; ESAC, East study area of the middle Sacramento 

Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, 

laboratory reporting level; MCL-US, maximum contaminant level (USEPA); mg/L, milligrams per liter; na, not available; nc, not collected; no., number; RICE, 

RICE well; USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water 

quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study 

unit–flow path; —, analyzed but not detected; *, value above threshold level]

GAMA

identification no.

Ammonia

(mg/L) 

as nitrogen

(00608)

Nitrite plus 

nitrate

(mg/L) 

as nitrogen 

(00631)

Nitrite

(mg/L) 

as nitrogen

(00613)

Total nitrogen 

(nitrate + 

nitrite + 

ammonia +

 organic-N)

(mg/L) 

(62854)

Orthophosphate

(mg/L) 

as phosphorus

(00671)

Dissolved

organic 

carbon

(DOC)

(mg/L) 

(00681)

[LRL] [0.01] [0.06] [0.002] [0.06] [0.006] [0.33]

Threshold type1 HAL-US MCL-US MCL-US na na na

Threshold value 2

24.7 10 1 na na na

Grid wells

ESAC-03 — 2.46 — 2.50 0.075 nc

ESAC-05 — 6.25 — 6.25 0.168 nc

ESAC-06 — 0.79 — 0.82 0.118 nc

ESAC-10 0.016 0.30 0.005 0.34 0.095 nc

ESAC-11 — — — — 0.100 nc

ESAC-12 — 0.82 — 3

0.81 0.058 nc

ESAC-15 E0.008 — — 4

— V0.003 nc

ESAC-16 E0.008 0.78 — 5

0.71 0.092 nc

ESAC-17 0.075 — — V0.07 0.167 nc

ESAC-18 E0.006 0.74 — 5

0.67 0.086 nc

ESAC-19 — 0.50 — 5

0.45 0.090 nc

ESAC-21 0.117 — — V0.16 0.120 nc

ESAC-22 — *10.4 — 8.81 0.053 nc

ESAC-25 — 0.54 — 0.54 0.112 E0.2

ESAC-26 0.056 — — V0.04 0.499 0.5

ESAC-27 E0.008 0.86 — 0.92 0.100 0.8

ESAC-28 — 1.62 — 3

1.58 0.194 E0.3

ESAC-29 0.095 — — V0.12 0.240 nc

ESAC-30 — 0.13 0.011 V0.16 0.256 nc

ESAC-31 E0.006 0.13 E0.001 V0.14 0.101 nc

ESAC-32 — 0.92 — 0.95 0.090 nc

ESAC-34 — 0.89 — 0.91 0.108 nc

ESAC-35 — 0.76 — 0.78 0.066 nc

WSAC-03 — 3.38 — 3

3.3 0.036 E0.2

WSAC-04 E0.005 — — 4

— 0.040 nc

WSAC-06 — 1.03 — 1.10 0.028 nc

WSAC-08 E0.006 3.43 — 3

3.23 0.031 E0.3

WSAC-10 — 6.49 — 3

6.35 0.027 nc

WSAC-11 — 2.27 — 3

2.13 0.065 nc

WSAC-12 0.124 — — V0.17 0.200 0.5

WSAC-14 0.011 1.29 0.003 3

1.26 0.077 nc

WSAC-15 — *13 — 13.50 0.047 nc

Table 8. Nutrients and dissolved organic carbon detected in samples collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed for nutrients; samples from all slow grid wells 

and all RICE wells were analyzed for dissolved organic carbon. The five-digit number in parentheses below the constituent name in the headings is used by the 

U.S. Geological Survey (USGS) to uniquely identify a specific constituent or property. E, estimated value; ESAC, East study area of the middle Sacramento 

Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, 

laboratory reporting level; MCL-US, maximum contaminant level (USEPA); mg/L, milligrams per liter; na, not available; nc, not collected; no., number; RICE, 

RICE well; USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water 

quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study 

unit–flow path; —, analyzed but not detected; *, value above threshold level]
56 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 8. Nutrients and dissolved organic carbon detected in samples collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed for nutrients; samples from all slow grid wells 

and all RICE wells were analyzed for dissolved organic carbon. The five-digit number in parentheses below the constituent name in the headings is used by the 

U.S. Geological Survey (USGS) to uniquely identify a specific constituent or property. E, estimated value; ESAC, East study area of the middle Sacramento 

Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, 

laboratory reporting level; MCL-US, maximum contaminant level (USEPA); mg/L, milligrams per liter; na, not available; nc, not collected; no., number; RICE, 

RICE well; USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water 

quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study 

unit–flow path; —, analyzed but not detected; *, value above threshold level]

GAMA

identification no.

Ammonia

(mg/L) 

as nitrogen

(00608)

Nitrite plus 

nitrate

(mg/L) 

as nitrogen 

(00631)

Nitrite

(mg/L) 

as nitrogen

(00613)

Total nitrogen 

(nitrate + 

nitrite + 

ammonia +

 organic-N)

(mg/L) 

(62854)

Orthophosphate

(mg/L) 

as phosphorus

(00671)

Dissolved

organic 

carbon

(DOC)

(mg/L) 

(00681)

[LRL] [0.01] [0.06] [0.002] [0.06] [0.006] [0.33]

Threshold type1 HAL-US MCL-US MCL-US na na na

Threshold value 2

24.7 10 1 na na na

WSAC-17 — 0.73 — 3

0.72 0.257 nc

WSAC-18 — 0.57 0.003 0.59 0.070 E0.2

WSAC-21 — 6.04 — 3

5.73 0.081 nc

WSAC-22 E0.008 1.24 — 3

1.22 0.047 nc

WSAC-25 E0.006 E0.05 — V0.06 0.101 nc

WSAC-26 E0.005 3.02 — 3.15 0.049 nc

WSAC-28 — 2.54 — 2.64 0.097 nc

WSAC-29 E0.005 1.84 — 1.89 0.043 nc

WSAC-30 E0.005 7.38 — 3

7.36 0.037 nc

WSAC-31 — 0.77 — 3

0.75 0.077 nc

WSAC-34 — 9.10 — 3

8.99 0.032 nc

WSAC-35 — 0.97 — 1.04 0.036 nc

WSAC-36 — 0.45 — 0.51 0.103 nc

Flow-path wells

ESAC-FP-01 0.320 — — V0.33 0.031 nc

ESAC-FP-02 — 2.37 0.010 3

2.20 0.033 nc

ESAC-FP-03 — 0.33 0.018 V0.35 0.084 nc

ESAC-FP-04 — 0.16 0.002 V0.14 0.056 nc

ESAC-FP-05 — 6.01 E0.002 3

5.61 0.100 nc

ESAC-FP-06 0.027 — — 4

— 0.062 nc

ESAC-FP-07 0.028 — — 4

— 0.077 nc

WSAC-FP-01 V0.007 1.32 — 1.42 0.050 nc

WSAC-FP-02 V0.007 0.76 — 0.76 0.038 nc

WSAC-FP-03 V0.009 2.82 E0.001 2.78 0.040 nc

WSAC-FP-04 0.014 — — 4

— 0.063 nc

WSAC-FP-05 E0.009 E0.03 E0.002 V0.07 0.064 nc

WSAC-FP-06 — 0.27 0.008 V0.27 0.034 nc

WSAC-FP-07 V0.009 — — 4

— 0.055 nc

WSAC-FP-08 — 1.89 — 1.97 0.052 nc
Table 8 57

Table 8. Nutrients and dissolved organic carbon detected in samples collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed for nutrients; samples from all slow grid wells 

and all RICE wells were analyzed for dissolved organic carbon. The five-digit number in parentheses below the constituent name in the headings is used by the 

U.S. Geological Survey (USGS) to uniquely identify a specific constituent or property. E, estimated value; ESAC, East study area of the middle Sacramento 

Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, 

laboratory reporting level; MCL-US, maximum contaminant level (USEPA); mg/L, milligrams per liter; na, not available; nc, not collected; no., number; RICE, 

RICE well; USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water 

quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study 

unit–flow path; —, analyzed but not detected; *, value above threshold level]

GAMA

identification no.

Ammonia

(mg/L) 

as nitrogen

(00608)

Nitrite plus 

nitrate

(mg/L) 

as nitrogen 

(00631)

Nitrite

(mg/L) 

as nitrogen

(00613)

Total nitrogen 

(nitrate + 

nitrite + 

ammonia +

 organic-N)

(mg/L) 

(62854)

Orthophosphate

(mg/L) 

as phosphorus

(00671)

Dissolved

organic 

carbon

(DOC)

(mg/L) 

(00681)

[LRL] [0.01] [0.06] [0.002] [0.06] [0.006] [0.33]

Threshold type1 HAL-US MCL-US MCL-US na na na

Threshold value 2

24.7 10 1 na na na

RICE wells

RICE-01 0.517 — — 0.51 0.109 —

RICE-02 — 0.88 — 0.86 0.149 V0.8

RICE-03 — 1.72 — 1.67 0.057 V0.9

RICE-04 V0.007 0.47 — 0.55 0.093 1.1

RICE-05 V0.013 — — V0.13 0.099 2.4

RICE-06 V0.005 0.27 — V0.32 0.079 1.6

RICE-07 V0.006 0.11 — V0.11 0.098 1.0

RICE-08 — 1.83 — 1.78 0.082 V0.5

RICE-09 — E0.04 — V0.07 0.101 V0.7

RICE-19 V0.008 — — V0.06 0.106 1.1

RICE-20 V0.005 3.77 0.005 3.80 0.326 1.4

RICE-10 — 0.36 — V0.37 0.160 1.0

RICE-11 V0.008 4.93 0.006 4.98 0.058 2.6

RICE-12 V0.01 0.40 0.006 0.47 0.115 1.4

RICE-13 — 3.82 0.026 3.75 0.104 2.3

RICE-14 — — — V0.1 0.051 2.3

RICE-15 — 0.30 — V0.31 0.097 1.3

RICE-16 V0.007 0.08 0.003 V0.1 0.086 1.2

RICE-17 V0.005 0.88 — 0.99 0.100 2.1

RICE-18 V0.006 0.71 — 0.78 0.076 V0.7

RICE-21 V0.011 0.17 — V0.21 0.041 V0.8

RICE-22 V0.011 — — V0.08 0.048 1.3

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

 The HAL-US is 30 mg/L “as ammonia.” To facilitate comparison to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L “as 

nitrogen.”

3

Total nitrogen in these samples is less than the sum of the filtered nitrogen analytes, but falls within the USGS’s National Water Quality Laboratory 

acceptance criteria of a 10 percent relative percent difference.

4

Total nitrogen in these samples is less than the sum of the filtered nitrogen analytes and exceeds the USGS’s National Water Quality Laboratory acceptance 

criteria of 10 percent relative difference, but the sum of the filtered nitrogen analytes is less than the LRL for total nitrogen.

5

Total nitrogen in these samples is less than the sum of the filtered nitrogen analytes and exceeds the USGS’s National Water Quality Laboratory acceptance 

criteria of 10 percent relative difference. Values were verified by the laboratory.
58 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 9. Major and minor ions and total dissolved solids detected in samples collected for the Middle Sacramento Valley 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the 

constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. CDPH, California Department 

of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento 

Valley study unit–flow path; LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); mg/L, milligrams per liter; na, not available; 

no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); WSAC, West study area of the middle Sacramento Valley study 

unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; —, analyzed but not detected; *, value above threshold level; **, value 

above upper threshold level] 

GAMA 

identification 

no.

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 

(mg/L) 

(00955) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

Total 

dissolved 

solids 

(TDS) 

(mg/L) 

(70301)

Bicarbonate1

(mg/L as

CaCO3)

Carbonate1

(mg/L as

CaCO3)

Threshold type2 na na SMCL-CA3 MCL-CA na na na na na SMCL-CA3 SMCL-CA3 na na

Threshold 

(mg/L) na na 250 (500) 2.00 na na na na na 250 (500) 500 (1,000) na na

[LRL] [0.02] [0.02] [0.2] [0.1] [0.002] [0.008] [0.16] [0.04] [0.2] [0.18] [10] [1] [1]

Grid wells

ESAC-03 0.06 29.1 21.5 E0.09 0.002 16.4 1.39 34.2 38.1 33.5 274 177 1

ESAC-05 0.11 32.7 7.85 E0.07 0.002 36.8 3.51 63.6 19.1 44.1 353 237 1

ESAC-06 — 18.1 2.26 E0.08 — 12.1 1.75 71.7 7.33 1.5 183 129 —

ESAC-10 0.11 40.6 36.6 0.15 0.036 28.1 1.73 42.7 23.6 13.9 316 255 —

ESAC-11 0.03 13.6 4.62 E0.07 0.019 10.5 3.73 75.7 17.1 2.0 194 135 —

ESAC-12 0.05 23.9 12.9 0.12 E0.001 12.5 1.59 34.9 30 9.5 237 217 1

ESAC-15 0.03 22.4 8.13 E0.07 — 14.4 1.17 60.0 11.9 6.3 195 143 —

ESAC-16 0.08 18.9 36.3 E0.08 — 14.0 3.25 63.7 35.9 10.3 267 163 —

ESAC-17 0.23 55.4 124 0.11 0.079 48.9 5.10 50.3 61.7 22.0 * 552 369 1

ESAC-18 — 17.9 5.12 E0.09 — 11.3 2.38 59.1 10.7 2.6 179 134 —

ESAC-19 E0.01 38.1 9.65 0.24 — 17.8 3.46 69.5 24.7 25.0 306 232 —

ESAC-21 1.71 58.2 ** 626 — 1.110 25.0 8.28 36.8 401 — **1,290 264 1

ESAC-22 0.05 23.0 11.4 — E0.001 17.4 0.31 60.6 12 21.0 240 99 —

ESAC-25 — 17.2 2.07 E0.09 — 11.3 1.35 67.4 8.43 2.5 177 129 —

ESAC-26 — 8.84 4.12 0.14 0.025 7.85 1.20 47.4 47.7 4.0 212 196 1

ESAC-27 0.14 39.6 19.6 E0.06 0.037 29.0 1.68 50.1 20.6 20.6 312 269 —

ESAC-28 0.02 24.1 5.55 0.14 E0.001 26.4 2.62 61.2 15.2 6.8 259 226 —

ESAC-29 0.07 24.5 15.0 E0.08 0.068 15.6 2.44 37.1 54.8 10.6 297 272 1

ESAC-30 0.16 18.7 58.5 0.11 0.040 21.7 1.67 48.6 36.6 7.3 268 146 1

ESAC-31 0.09 50.1 27.9 E0.08 0.105 32.2 2.49 50.3 49.5 17.4 410 360 1

ESAC-32 E0.02 32.5 4.62 — — 21.7 1.45 52.1 9.17 12.6 243 212 —

ESAC-34 0.08 50.3 13.5 0.11 0.003 34.4 1.83 62.4 26.9 38.6 397 332 1

ESAC-35 — 28.8 2.60 — — 19.2 1.55 57.0 10.2 8.4 232 204 —

WSAC-03 — 32.3 7.11 0.10 — 16.2 0.70 28.9 12.8 20.8 207 162 —

WSAC-04 0.03 16.5 5.11 0.18 0.021 15.9 0.56 24.9 34.2 1.2 203 208 2

WSAC-06 0.05 40.5 15.2 0.29 0.003 37.7 0.57 30.3 24.4 24.7 344 335 —

WSAC-08 0.05 67.5 21.4 E0.09 E0.001 19.7 0.84 19.5 17.9 25.8 310 269 —

WSAC-10 0.06 66.5 23.1 E0.08 E0.002 23.8 0.87 21.8 21.8 31.8 329 281 —

WSAC-11 0.28 29.4 87.4 0.21 0.006 29.9 1.05 30.0 51.9 10.5 365 229 1

WSAC-12 0.25 22.8 50.8 0.11 0.125 16.2 1.50 41.3 115 62.3 440 257 1

WSAC-14 0.81 84.5 236 0.42 0.524 70.4 2.12 42.0 259 * 429 ** 1,330 393 1

WSAC-15 0.12 48.6 27.1 0.29 0.010 35.6 1.80 26.0 101 49.5 * 584 472 1

Table 9. Major and minor ions and total dissolved solids detected in samples collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the 

constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. CDPH, California Department 

of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento 

Valley study unit–flow path; LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); mg/L, milligrams per liter; na, not available; no., 

number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); WSAC, West study area of the middle Sacramento Valley study unit; 

WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; —, analyzed but not detected; *, value above threshold level; **, value above 

upper threshold level]
Table 9 59

Table 9. Major and minor ions and total dissolved solids detected in samples collected for the Middle Sacramento Valley 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the 

constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. CDPH, California Department 

of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento 

Valley study unit–flow path; LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); mg/L, milligrams per liter; na, not available; 

no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); WSAC, West study area of the middle Sacramento Valley study 

unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; —, analyzed but not detected; *, value above threshold level; **, value 

above upper threshold level] 

GAMA 

identification 

no.

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 

(mg/L) 

(00955) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

Total 

dissolved 

solids 

(TDS) 

(mg/L) 

(70301)

Bicarbonate1

(mg/L as

CaCO3)

Carbonate1

(mg/L as

CaCO3)

Threshold type2 na na SMCL-CA3 MCL-CA na na na na na SMCL-CA3 SMCL-CA3 na na

Threshold 

(mg/L) na na 250 (500) 2.00 na na na na na 250 (500) 500 (1,000) na na

[LRL] [0.02] [0.02] [0.2] [0.1] [0.002] [0.008] [0.16] [0.04] [0.2] [0.18] [10] [1] [1]

WSAC-17 E0.01 27.3 7.38 0.12 0.008 23.4 1.62 37.6 29.7 20.6 275 248 —

WSAC-18 0.40 50.5 96.4 0.47 0.420 37.6 1.26 28.2 117 110 * 623 388 1

WSAC-21 0.04 27.6 14.0 0.30 0.003 19.8 0.50 29.9 26.9 7.0 257 209 —

WSAC-22 0.16 29.8 34.1 0.20 0.026 24.5 1.05 22.4 39.9 12.0 297 256 1

WSAC-25 0.08 23.0 17.5 0.18 0.013 22.4 2.35 41.5 44.1 8.3 294 268 1

WSAC-26 0.03 33.3 2.80 0.43 — 16.3 0.56 30.0 11.7 3.9 208 192 —

WSAC-28 0.04 43.8 20.1 E0.08 — 22.1 0.69 26.1 10.9 21.0 258 204 —

WSAC-29 0.05 20.9 8.49 0.29 0.008 21.5 0.80 23.3 36.2 11.9 253 242 1

WSAC-30 1.29 79.5 * 358 0.64 — 68.5 0.53 21.4 136 87.0 * 910 248 1

WSAC-31 0.03 18.9 4.23 0.19 E0.002 11.3 0.74 28.2 25 11.1 181 155 1

WSAC-34 0.08 88.9 74.0 E0.09 E0.002 38.5 1.10 23.4 23.4 39.4 486 315 —

WSAC-35 0.02 45.2 16.9 E0.07 0.003 18.9 0.86 22.9 23.6 19.9 277 250 —

WSAC-36 — 24.6 4.41 0.17 0.020 22.5 1.03 30.7 31.7 8.0 256 262 1

Flow-path wells

ESAC-FP-01 0.31 45.3 124 E0.09 0.026 9.09 1.87 65.1 39 — 331 91 —

ESAC-FP-02 0.03 40.3 13.5 E0.06 E0.002 26.0 1.54 60.2 18.5 11.3 304 246 —

ESAC-FP-03 — 33.0 2.43 E0.05 0.008 23.5 1.34 56.4 10.3 9.2 257 240 —

ESAC-FP-04 — 14.3 1.79 — E0.002 11.2 2.29 57.7 10.9 2.1 166 130 1

ESAC-FP-05 — 66.1 9.43 E0.08 0.006 41.5 2.75 51.0 22.4 26.5 460 431 1

ESAC-FP-06 0.07 13.5 19.4 E0.09 0.054 3.99 2.88 41.8 51.7 1.4 216 152 6

ESAC-FP-07 0.13 14.6 35.9 E0.09 0.101 4.69 2.73 46.9 68.8 0.3 270 187 3

WSACFP-01E0.02 24.7 2.33 0.33 — 20.5 0.76 31.1 19.9 1.7 217 220 1

WSACFP-020.04 20.6 11.1 0.15 0.002 16.7 0.75 27.3 21.8 8.9 197 172 1

WSACFP-030.05 35.4 15.7 0.13 E0.001 24.8 0.75 30.2 16.4 16.7 259 213 1

WSACFP-040.05 19.9 13.9 0.13 0.032 7.34 1.89 21.3 34.5 0.6 189 174 3

WSACFP-050.41 28.7 100 0.29 0.227 25.3 2.38 40.4 128 88.4 * 565 302 1

WSACFP-060.10 16.0 22.4 0.18 0.055 15.8 0.87 21.1 30.4 7.6 202 168 2

WSACFP-070.07 15.9 15.1 0.12 0.041 7.21 1.56 37.1 41.1 7.2 213 173 2

WSACFP-080.04 36.9 10.5 0.12 E0.002 18.6 0.73 25.5 18.5 12.6 244 224 1
60 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 9. Major and minor ions and total dissolved solids detected in samples collected for the Middle Sacramento Valley 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the 

constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. CDPH, California Department 

of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento 

Valley study unit–flow path; LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); mg/L, milligrams per liter; na, not available; 

no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); WSAC, West study area of the middle Sacramento Valley study 

unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; —, analyzed but not detected; *, value above threshold level; **, value 

above upper threshold level] 

GAMA 

identification 

no.

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 

(mg/L) 

(00955) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

Total 

dissolved 

solids 

(TDS) 

(mg/L) 

(70301)

Bicarbonate1

(mg/L as

CaCO3)

Carbonate1

(mg/L as

CaCO3)

Threshold type2 na na SMCL-CA3 MCL-CA na na na na na SMCL-CA3 SMCL-CA3 na na

Threshold 

(mg/L) na na 250 (500) 2.00 na na na na na 250 (500) 500 (1,000) na na

[LRL] [0.02] [0.02] [0.2] [0.1] [0.002] [0.008] [0.16] [0.04] [0.2] [0.18] [10] [1] [1]

RICE wells

RICE-01 12.60 814 ** 4730 — nc 447 11.50 24.3 1250 4

— ** 7,390 135 —

RICE-02 0.05 41.5 8.07 E0.08 nc 36.5 0.87 52.4 33.3 23.3 402 406 1

RICE-03 0.19 67.4 34.4 E0.08 nc 43.9 2.54 58.4 53.3 37.8 * 566 525 1

RICE-04 — 63.3 7.05 0.18 nc 40.2 2.05 57.3 16.9 17.7 404 399 —

RICE-05 0.07 85.1 16.9 0.13 nc 54.7 1.66 70.2 35.5 48.0 * 569 519 —

RICE-06 — 68.7 2.44 0.11 nc 51.9 1.36 67.9 16.1 15.2 456 468 —

RICE-07 0.04 73.0 3.88 0.15 nc 52.4 1.36 52.3 23.1 28.1 488 511 1

RICE-08 0.05 68.2 9.57 E0.1 nc 49.0 1.12 52.4 34.3 36.4 487 459 1

RICE-09 — 22.5 3.05 E0.09 nc 15.1 0.77 39.6 11 5.1 174 155 1

RICE-10 0.03 36.8 3.85 0.24 nc 18.8 0.69 28.5 11.2 7.8 212 204 1

RICE-11 0.10 91.3 26.8 0.18 nc 60.6 0.62 33.4 27.8 49.4 * 562 504 —

RICE-12 0.08 59.9 14.0 0.32 nc 45.6 0.50 30.5 55 20.4 468 482 1

RICE-13 0.10 66.5 26.7 0.12 nc 50.2 0.91 32.7 56.7 37.4 * 539 506 1

RICE-14 0.07 59.5 9.67 0.19 nc 50.9 0.49 28.8 47.7 38.4 478 488 —

RICE-15 0.04 39.2 7.10 0.89 nc 47.7 0.45 21.9 105 79.5 * 566 529 2

RICE-16 0.15 29.2 23.9 1.70 nc 31.9 0.56 17.6 356 * 375 ** 1,200 723 2

RICE-17 0.60 92.8 147 1.70 nc 114 0.72 21.5 838 ** 2,080 ** 3,510 423 2

RICE-18 0.05 59.4 9.18 0.26 nc 38.3 0.81 27.4 72.8 104.0 * 522 416 1

RICE-19 0.04 38.0 3.56 E0.07 nc 25.4 1.23 42.3 27.4 8.5 294 297 1

RICE-20 0.21 47.9 46.9 0.41 nc 64.1 0.85 46.6 81 63.2 * 614 494 1

RICE-21 0.42 77.2 106 0.62 nc 44.3 0.54 19.9 232 * 359 ** 1,050 422 1

RICE-22 0.65 73.1 156 0.90 nc 50.0 0.53 16.7 603 ** 1,080 ** 2,240 505 1

1

Bicarbonate and carbonate concentrations were calculated from the laboratory alkalinity and pH values (table 4) using the advance speciation method (http://

or.water.usgs.gov/alk/methods.html).

2

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.

3

The SMCL-CA for chloride, sulfate, and total dissolved solids have recommended and upper threshold values. The upper value is shown in parentheses.

4

Laboratory reporting level is 4.5 mg/L.
Table 10

61

Table 10. Trace elements detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. AL-US, action level (USEPA); CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; nc, not collected; NL-CA, notification level (CDPH); no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in groundwater quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level]

GAMA 

identification 

no.

Aluminum 

(μg/L) 

(01106)

Antimony 

(μg/L) 

(01095)

Arsenic 

(μg/L) 

(01000)

Barium 

(μg/L) 

(01005)

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)

[LRL] [1.6] [0.2] [0.12] [0.2] [8] [0.04] [0.04] [0.04] [0.4] [6] [0.08]

Threshold type1 MCL-CA MCL-US MCL-US MCL-CA NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US

Threshold level 1000 6 10 1000 1000 5 50 na 1300 300 15

Grid wells

ESAC-03 — — 0.83 56 808 — 1.1 0.078 7.6 — 1.37

ESAC-05 — E0.1 *19.6 104 26 — 4.9 0.084 1.2 — 0.24

ESAC-06 E1.5 — 0.97 15 — — 1.2 — 3.3 — 2.11

ESAC-10 — — 5 99 20 — 0.16 — — 30 0.19

ESAC-11 — 0.87 *70 130 53 — V0.02 E0.03 — 7 0.19

ESAC-12 4.5 — 4.4 87 107 — 6.0 — 3.2 E4 1.03

ESAC-15 E0.8 — 0.47 16 83 — 6.7 — E0.21 — 0.14

ESAC-16 E1.1 — 0.78 25 316 — 0.58 — — — 0.1

ESAC-17 — — *15.9 385 379 — V0.02 — — *355 0.2

ESAC-18 E1.4 — 0.73 21 70 — 0.94 — — — 0.09

ESAC-19 E1.1 0.38 9.2 147 96 — 6.9 — 0.72 8 0.43

ESAC-21 E1.5 — *80.6 461 *1,010 E0.03 V0.04 E0.02 — 221 0.51

ESAC-22 — — 0.39 19 13 — 1.1 0.07 1.7 — 0.86

ESAC-25 E1.3 — 0.83 13 16 — 0.73 — 0.57 — 0.15

ESAC-26 1.7 E0.11 *23.1 39 237 — V0.02 — — 6 0.26

ESAC-27 — — 6.5 78 37 — 1.1 0.27 1.8 — 1.12

ESAC-28 — — *10.1 52 24 — 6.9 — 0.62 — 0.31

ESAC-29 E1.2 — 9.2 141 712 — V0.03 — — 295 0.08

ESAC-30 E1 E0.15 *17 38 111 — V0.03 E0.02 E0.25 E4 E0.15

ESAC-31 E0.8 — *12 124 140 — 0.12 E0.03 — 19 E0.1

ESAC-32 E1 — 2.6 29 14 — 3.0 — 1.9 E5 0.74

ESAC-34 E1.2 — 5.6 90 E6 — 4.6 — E0.25 — 0.21

ESAC-35 1.9 — 0.8 23 27 — 4.5 — E0.25 — 0.1
62 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program Table 10. Trace elements detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued [Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. AL-US, action level (USEPA); CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; nc, not collected; NL-CA, notification level (CDPH); no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground- water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level] GAMA identification no. Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) 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) [LRL] [1.6] [0.2] [0.12] [0.2] [8] [0.04] [0.04] [0.04] [0.4] [6] [0.08] Threshold type1 MCL-CA MCL-US MCL-US MCL-CA NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US Threshold level 1000 6 10 1000 1000 5 50 na 1300 300 15 WSAC-03

—

— 0.48 66 16

— 1.2 0.081 0.8

— 0.2

WSAC-04

—

— 3.6 98 33

—

— 0.041 E0.2 43

—

WSAC-06

—

— 0.63 86 87

— 0.72

— 2.6 E3 1.67

WSAC-08

—

— 0.24 103 160

— 1.1

— 0.56 E3 3.43

WSAC-10

—

— 0.36 123 197

— 1.6

— 2 — 0.16

WSAC-11 E1

— 2.6 232 599

— 11.1

— 0.47

— 0.27

WSAC-12 1.8

— 2.2 126 212

— V0.04

— E0.28 53

—

WSAC-14 E1.3

— 2.6 29 364 0.04 V0.05 0.09 2 E4 0.62

WSAC-15 E1

— 1.3 295 *2330

— 7.3 0.04 0.47

— 0.08

WSAC-17 E1 E0.17 6.7 48 344

— 0.80 E0.02 1.4

— 0.69

WSAC-18 E1.2

— 1.3 74 447

— 0.07 0.04 E0.24

— 1.37

WSAC-21 E1

— 1.4 198 193

— 8.0

— E0.26

— 0.1

WSAC-22 E0.8

— 7.9 268 105

— 2.5

— 0.93 14 0.68

WSAC-25 E1

— 4 106 762

— 0.48

—

—

— 0.32

WSAC-26 E1.4

— 1.1 106 11

— 4.3 0.06 0.46

— 0.35

WSAC-28

—

— 0.33 63 36

— 1.3

— E0.24

—

—

WSAC-29 E1

— 3.1 145 64

— 11.5

— E0.25

— 0.42

WSAC-30 E0.8

— 0.39 58 339

— 6.0

— 2.7 E5 0.43

WSAC-31 E1.3

— 4.7 61 71 3.54 10.8

— E0.22

— 0.17

WSAC-34 E0.9

— 0.46 197

—

— 2.7 E0.03 0.47

—

—

WSAC-35 E1.1

— 1.2 117 128

— 2.2

— 0.66

— 0.17

WSAC-36 E1.2

— 4.5 142 117

— 4.3

— 0.47 E4 0.32
Table 10

63

Table 10. Trace elements detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. AL-US, action level (USEPA); CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; nc, not collected; NL-CA, notification level (CDPH); no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in groundwater quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level]

GAMA 

identification 

no.

Aluminum 

(μg/L) 

(01106)

Antimony 

(μg/L) 

(01095)

Arsenic 

(μg/L) 

(01000)

Barium 

(μg/L) 

(01005)

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)

[LRL] [1.6] [0.2] [0.12] [0.2] [8] [0.04] [0.04] [0.04] [0.4] [6] [0.08]

Threshold type1 MCL-CA MCL-US MCL-US MCL-CA NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US

Threshold level 1000 6 10 1000 1000 5 50 na 1300 300 15

Flow-path wells

ESAC-FP-01 1.3 — 1.1 73 171 — V0.02 — — 106 0.08

ESAC-FP-02 2.1 — 0.71 35 108 — 1.3 0.28 V0.2 65 0.13

ESAC-FP-03 V0.8 — 2.4 47 19 — 1.2 E0.03 — 134 0.11

ESAC-FP-04 V1.7 — 3.2 16 67 — 1.3 — — 67 —

ESAC-FP-05 2.7 0.23 6.5 116 55 — 5.3 E0.03 — — —

ESAC-FP-06 39.4 E0.18 *12.7 17 208 — 0.70 E0.02 — 14 E0.07

ESAC-FP-07 17.2 — 9 35 243 — 0.22 E0.03 — 10 E0.05

WSAC-FP-01 V1.4 — 2.4 128 28 — 16.1 E0.02 — — —

WSAC-FP-02 2.2 E0.11 3.3 132 101 — 18.4 — — V6 —

WSAC-FP-03 3.7 E0.13 1.6 173 81 — 4.8 E0.02 V0.55 — —

WSAC-FP-04 11.1 — 5.5 91 80 — 0.16 0.04 — V6 —

WSAC-FP-05 4.5 — 8.3 42 230 E0.02 — — 0.35 9 0.8

WSAC-FP-06 3.0 E0.15 4 167 98 — 0.33 — — 15 —

WSAC-FP-07 4.4 — *10.6 8 99 — V0.07 — — 40 —

WSAC-FP-08 V1.4 — 1.1 99 114 — 4.8 — — 10 —
64 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program Table 10. Trace elements detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued [Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. AL-US, action level (USEPA); CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; nc, not collected; NL-CA, notification level (CDPH); no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground- water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level] GAMA identification no. Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) 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) [LRL] [1.6] [0.2] [0.12] [0.2] [8] [0.04] [0.04] [0.04] [0.4] [6] [0.08] Threshold type1 MCL-CA MCL-US MCL-US MCL-CA NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US Threshold level 1000 6 10 1000 1000 5 50 na 1300 300 15 RICE wells RICE-01

—2 —2 4.9 *5,900 *1,260

—2 0.42 E0.18

—2 *4,610

—2

RICE-02 V1.3 E0.11 *10.4 39 55

— 2.4 0.09

— V3

—

RICE-03 V0.8 E0.14 6.2 188 117

— 2.0 E0.02 V0.31 V5

—

RICE-04

—

— 4.7 154 16

— 1.7 E0.03 V0.54 57

—

RICE-05

—

— 1.4 160 9 E0.02 0.14 0.27 V0.97 28

—

RICE-06

—

— 1.8 85 16

— 0.41 0.04 V0.62 V4

—

RICE-07 V1.0

— 6.2 78 25

— 1.6 E0.02 V0.24

—

—

RICE-08 V1.0

— 6 96 35

— 4.1

—

—

—

—

RICE-09 1.8 E0.18 4.6 26 62

— V0.07 0.15 V0.28 V6

—

RICE-10 V1.1 E0.16 3.1 87 57

— 0.37 E0.02 V0.32

—

—

RICE-11 V1.1 E0.1 1.6 552 92 E0.02 1.3 0.21 V1.1 V4

—

RICE-12 V1.0 E0.1 3.2 408 223

— 0.08 0.31

— 218 E0.04

RICE-13 V1.2 E0.11 2.3 286 199

— 3.1 0.44 V1.1

— 0.08

RICE-14 V1.2

— 1.1 357 174

— V0.10 0.39 V0.27 110

—

RICE-15

—

— 1.1 65 551

— 0.77 0.04 V0.48

—

—

RICE-16 V1.3

— 0.57 20 945

— V0.05 0.13

— *304

—

RICE-17 E2.4

— 1.6 15 *1,640 0.05 13.1 0.13 V0.83

—

—

RICE-18 2.9

— 1 81 204

— 7.8 0.06 V0.53

—

—

RICE-19 V1.6 E0.11 4.1 61 68

— V0.08 0.05 V0.69

—

—

RICE-20 V1.4 E0.14 7.5 46 195 0.04 V0.02 0.6 V0.80

—

—

RICE-21 2.2

— 0.38 46 97

— 0.13 0.13 V0.29 155 0.13

RICE-22

—

— 1.9 15 *4,630

— 0.85 1.6

— 166

—
Table 10

65

Table 10. Trace elements detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. AL-US, action level (USEPA); CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; nc, not collected; NL-CA, notification level (CDPH); no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level]

GAMA 

identification no.

Lithium 

(μg/L) 

(01130)

Manganese 

(μg/L) 

(01056)

Molybdenum 

(μg/L) 

(01060)

Nickel 

(μg/L) 

(01065)

Selenium 

(μg/L) 

(01145)

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057)

Tungsten 

(μg/L) 

(01155)

Vanadium 

(μg/L) 

(01085)

Zinc 

(μg/L) 

(01090)

Uranium 

(μg/L) 

(22703)

[LRL] [0.6] [0.2] [0.4] [0.06] [0.08] [0.4] [0.04] [0.06] [0.1] [0.6] [0.04]

Threshold type1 na SMCL-CA HAL-US MCL-CA MCL-US HAL-US MCL-US na NL-CA SMCL-CA MCL-US

Threshold level na 50 40 100 50 4000 2 na 50 5000 30

Grid wells

ESAC-03 14.1 E0.1 0.5 1.19 0.09 254 — 0.35 9.7 3.6 0.37

ESAC-05 E0.4 — 1.8 1.38 0.61 214 — 0.06 28.8 2.8 2.76

ESAC-06 2.1 E0.2 E0.2 0.26 E0.05 112 — — 28.8 10.7 0.12

ESAC-10 E0.4 *95.1 0.6 0.18 1.0 319 — E0.05 6.5 1.7 6.07

ESAC-11 20.9 *112 2.0 V0.04 — 138 — 0.27 40.4 V0.42 0.69

ESAC-12 2.8 0.2 2.3 0.13 0.40 290 — 0.11 12.2 4.4 0.45

ESAC-15 — — — V0.07 0.16 145 — — 17.7 V0.73 0.08

ESAC-16 6.5 E0.1 E0.2 0.14 E0.06 123 — — 21.1 V0.52 0.23

ESAC-17 0.7 *568 1.8 0.22 — 488 — 0.23 E0.05 3.2 —

ESAC-18 1.6 — E0.2 0.09 E0.04 116 — E0.03 19.8 V0.58 0.35

ESAC-19 4.8 — 1.1 0.14 0.6 342 — 0.07 22.7 3.2 1.50

ESAC-21 3.8 *257 16.5 V0.07 — 460 — 0.1 0.11 1.3 —

ESAC-22 0.7 E0.2 — 0.58 0.09 111 — — 6.8 6.3 0.04

ESAC-25 4.1 — E0.3 0.12 E0.06 115 — — 30.6 V1.2 0.07

ESAC-26 1.0 *80.2 4.2 — — 112 — 0.53 9.6 1.3 0.21

ESAC-27 0.7 *110 0.8 0.57 0.24 258 — — 8.4 V0.93 2.24

ESAC-28 E0.6 1.3 1.1 0.11 0.12 179 — 0.07 26.2 1.3 1.41

ESAC-29 2.4 *219 E4 0.09 — 276 — 0.23 0.42 12.2 —

ESAC-30 1.7 *99.6 1.4 0.08 0.31 195 — 0.28 35 V0.97 0.39

ESAC-31 1.9 *72.2 2.6 0.13 0.10 388 — 0.08 13.9 V0.92 1.88

ESAC-32 0.7 E0.1 — 0.17 0.16 227 — — 9.5 4.5 1.09
66 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program Table 10. Trace elements detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued [Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. AL-US, action level (USEPA); CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; nc, not collected; NL-CA, notification level (CDPH); no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level] GAMA identification no. Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Vanadium (μg/L) (01085) Zinc (μg/L) (01090) Uranium (μg/L) (22703) [LRL] [0.6] [0.2] [0.4] [0.06] [0.08] [0.4] [0.04] [0.06] [0.1] [0.6] [0.04] Threshold type1 na SMCL-CA HAL-US MCL-CA MCL-US HAL-US MCL-US na NL-CA SMCL-CA MCL-US Threshold level na 50 40 100 50 4000 2 na 50 5000 30 ESAC-34 0.8

— 0.5 0.10 0.36 360

— E0.03 38.5 137 3.71

ESAC-35 1.3

—

—

— E0.05 197

— E0.05 22.4 V0.84 1.05

WSAC-03 3.7

— 1.0 1.32 0.10 368

—

— 3.9 6.6 0.14

WSAC-04 4.4 43.3 1.6 0.59

— 199

— E0.03

— V1.2

—

WSAC-06 11.5

— 0.5 0.21 0.08 506

—

— 5.0 62.9 0.40

WSAC-08 3.9 0.2 1.0 0.12 0.09 841

—

— 1.8 10.2 0.54

WSAC-10 6.4

— E0.7 E0.14 0.09 849

—

— 2.8 13.3 0.78

WSAC-11 21.6

—

—

— 0.50 360

—

— 8.3 V0.51 0.28

WSAC-12 3.8 *106 7.8 V0.05

— 256

— 0.42 0.53 V0.67 0.07

WSAC-14 24.8 *89.8 4.5 0.36 10.8 1570 E0.02 0.08 10.7 8.6 2.57WSAC-15 37 E0.1 0.5 0.66 1.4 641

— 0.18 5.7 V0.68 2.61

WSAC-17 1.3 0.2 4.0 0.17 0.57 234

— 0.07 18.5 36.4 1.16

WSAC-18 18.6 *84.6 3.7 V0.05 1.2 877

— E0.05 8.4 V0.37 E0.14

WSAC-21 14.9 E0.1 E0.3 0.08 0.36 276

—

— 5.5 28.1 0.18

WSAC-22 15 36.6 0.6 0.11 0.16 435

— E0.03 2.6 16.4 0.25

WSAC-25 26.9 1.8 3.5 V0.05 0.31 332

— 0.19 10.8 5.4 0.64

WSAC-26 14.9

— 0.9 V0.07 0.10 254

—

— 3.8 8.9 0.33

WSAC-28 4.1

— E0.4 0.12 E0.04 428

—

— 2.8 V0.43 0.10

WSAC-29 9.8 3.1 1.0 0.18 0.77 395

—

— 10.8 3.4 0.43

WSAC-30 22 E0.1 1.0 0.30 0.75 1480

—

— 3.7 4.5 1.06

WSAC-31 2.7

— 2.0 V0.03 0.77 226

— 0.06 17.9 V0.53 0.19

WSAC-34 6.9

— 0.7 0.33 0.08 1130

—

— 3.0 2.0 0.79

WSAC-35 5.5

— 0.8 0.11 0.17 619

—

— 3.8 3.3 0.46

WSAC-36 4.6 0.5 3.1 V0.06 0.30 439

— E0.05 9.4 1.5 0.72
Table 10

67

Table 10. Trace elements detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. AL-US, action level (USEPA); CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; nc, not collected; NL-CA, notification level (CDPH); no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level]

GAMA 

identification no.

Lithium 

(μg/L) 

(01130)

Manganese 

(μg/L) 

(01056)

Molybdenum 

(μg/L) 

(01060)

Nickel 

(μg/L) 

(01065)

Selenium 

(μg/L) 

(01145)

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057)

Tungsten 

(μg/L) 

(01155)

Vanadium 

(μg/L) 

(01085)

Zinc 

(μg/L) 

(01090)

Uranium 

(μg/L) 

(22703)

[LRL] [0.6] [0.2] [0.4] [0.06] [0.08] [0.4] [0.04] [0.06] [0.1] [0.6] [0.04]

Threshold type1 na SMCL-CA HAL-US MCL-CA MCL-US HAL-US MCL-US na NL-CA SMCL-CA MCL-US

Threshold level na 50 40 100 50 4000 2 na 50 5000 30

Flow-path wells

ESAC-FP-01 0.6 *184 0.8 V0.05 — 455 — 0.22 E0.05 6.4 —

ESAC-FP-02 — 14.5 0.7 2.2 E0.07 261 — V0.05 7.5 6.3 0.46

ESAC-FP-03 — 16.8 E0.2 0.31 — 225 — 0.09 23.4 — 0.70

ESAC-FP-04 — 3.5 0.4 0.30 0.12 100 — 0.21 10.0 V0.68 0.09

ESAC-FP-05 1.3 V0.3 0.6 0.57 0.38 534 — 0.31 26.3 — 5.44

ESAC-FP-06 0.7 8.4 4.9 0.47 — 127 — 1.1 2.9 — 0.07

ESAC-FP-07 E0.4 16.4 8.3 0.76 — 96.7 — 0.69 0.7 — 0.05

WSAC-FP-01 12.7 — 0.8 0.31 0.57 439 — 0.03 8.9 — 0.36

WSAC-FP-02 8.5 V0.5 0.8 0.33 0.39 379 — 0.07 10.3 V0.6 0.20

WSAC-FP-03 13.4 V0.8 0.6 0.72 0.11 410 — 0.09 6.4 V1.2 0.12

WSAC-FP-04 16.9 8.4 1.9 1.1 — 635 — 1.4 0.19 — 0.07

WSAC-FP-05 5.6 *60.6 3.9 0.09 E0.06 758 — 0.21 0.82 2.4 0.56

WSAC-FP-06 7.6 7.2 1.1 0.33 0.20 449 — 0.36 8 V1.2 0.07

WSAC-FP-07 4 22.6 2.1 V0.17 — 296 — 0.33 — — 0.04

WSAC-FP-08 5.5 V0.4 1.3 0.27 0.08 475 — V0.03 6 V1.4 0.22
68 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program Table 10. Trace elements detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued [Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey to uniquely identify a specific constituent or property. AL-US, action level (USEPA); CDPH, California Department of Public Health; E, estimated value; ESAC, East study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; HAL-US, Lifetime Health Advisory Level (USEPA); LRL, laboratory reporting level; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); na, not available; nc, not collected; NL-CA, notification level (CDPH); no., number; RICE, RICE well; SMCL-CA, secondary maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level] GAMA identification no. Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Vanadium (μg/L) (01085) Zinc (μg/L) (01090) Uranium (μg/L) (22703) [LRL] [0.6] [0.2] [0.4] [0.06] [0.08] [0.4] [0.04] [0.06] [0.1] [0.6] [0.04] Threshold type1 na SMCL-CA HAL-US MCL-CA MCL-US HAL-US MCL-US na NL-CA SMCL-CA MCL-US Threshold level na 50 40 100 50 4000 2 na 50 5000 30 RICE wells RICE-01 E3.3 *3,420 E1.6 1.3

—2 *7,880

—2 nc 1.1 4.7

—2

RICE-02 E0.4 14.2 1.3 0.46 E0.06 354

— nc *51.3 V0.48 4.29

RICE-03 1.1 2.6

— 0.38 E0.04 800

— nc 34.4 V0.56 4.44

RICE-04 0.8 19.9 0.6 0.96 0.09 449

— nc 25.7 V0.75 3.36

RICE-05 0.7 *75.4

— 1.9

— 618

— nc 27.1 V1.1 3.52

RICE-06 E0.3 34.1

— 0.86 E0.04 420

— nc 40.9 V0.75 2.67

RICE-07

— 3.4 E0.4 0.28

— 660

— nc *57.4 V0.34 5.19

RICE-08 0.7 V0.2 E0.3 0.22 0.20 666

— nc 38 V0.52 3.27

RICE-09 1.0 41.9 1.3 0.29

— 179

— nc 18.4

— 0.34

RICE-10 2.5 7.9 2.5 0.22 E0.05 359

— nc 10.9

— 0.64

RICE-11 18.3 9.1 0.5 1.6

— 1,340

— nc 5.8 V1.0 1.13

RICE-12 14.3 *55.2 1.7 0.56

— 1,000

— nc 2.2 V1.1 1.57

RICE-13 19.9 26.6 0.8 1.1

— 1,010

— nc 8.4 V0.57 1.48

RICE-14 11.5 *379 1.2 1.3

— 919

— nc 0.55 V0.99 1.65

RICE-15 23.3 1.3 5.4 0.40 0.43 812

— nc 5.5 V0.47 4.44

RICE-16 26.1 *434 9.8 V0.20 11 795

— nc 0.54 V0.53 7.76

RICE-17 31.2 27.5 *46.2 0.61 7.8 1,900

— nc 8.5 V1.6 10.20

RICE-18 18.9 7.7 0.9 0.28 0.55 772

— nc 5.2 V0.88 2.04

RICE-19 0.8 6.1 1.2 0.32

— 370

— nc 24.8 V1.2 1.25

RICE-20 0.9 *216 10.9 1.3 0.32 461

— nc 29.6 V0.44 4.90

RICE-21 19.7 *156 2.4 0.31 0.45 1200

— nc 0.42 V0.8 2.38

RICE-22 102 *602 9.6 2.3 E0.77 *4,540

— nc E0.74 E4 4.81

1 Maximum contaminant level thresholds are listed as MCL-US when MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.2 Laboratory reporting level is four times the LRL stated above.
Table 11 69

Table 11. Species of inorganic arsenic, iron, and chromium detected in samples collected for the Middle Sacramento Valley 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed for iron, arsenic, and chromium; only wells with 

at least one detection are listed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey (USGS)

to uniquely identify a specific constituent or property. Analyses made by the USGS’s Trace Metals Laboratory. The laboratory entity code for the USGS’s Trace 

Metals Laboratory in the USGS’s National Water Information System (NWIS) is USGSTMCO. CDPH, California Department of Public Health; ESAC, East 

study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; MCL-CA, maximum 

contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); MDL, method detection limit; na, not available; no., number; NRP, National 

Research Program (USGS); NWQL, National Water Quality Laboratory (USGS); RICE, RICE well; RSD, relative standard deviation; SMCL-CA, secondary 

maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not 

included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle 

Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level]

GAMA 

identification no.

Iron(Total)2

(μg/L) 

(01046)

Iron(II) 

(μg/L) 

(01047)

Inorganic 

Arsenic(Total)2

(μg/L) 

(99033)

Inorganic 

Arsenic(III) 

(μg/L) 

(99034)

Chromium(Total) 

(μg/L) 

(01030)

Chromium(VI) 

(μg/L) 

(01032)

Threshold type1 SMCL-CA na MCL-US na MCL-CA na

Threshold (μg/L) 300 na 10 na 50 na

[MDL] [2] [2] [0.5] [1] [1] [1]

Grid wells

ESAC-03 — — — — 1 —

ESAC-05 — — * 17 — 4 4

ESAC-06 — — V3.6 — — —

ESAC-10 28 17 4.9 — — —

ESAC-11 6 4 3

* 35 — — —

ESAC-12 3 — 3.6 — 6 5

ESAC-15 — — V0.7 — 2 —

ESAC-16 — — V1.2 — — —

ESAC-17 * 359 238 * 14 13 — —

ESAC-18 — — V1.7 — — —

ESAC-19 6 — 8.0 — 5 5

ESAC-21 198 57 * 70 70 — —

ESAC-22 — — — — 1 1

ESAC-25 — — V4.3 — — —

ESAC-26 6 4 * 19 4 — —

ESAC-27 — — 6.2 — — —

ESAC-28 — — 7.8 — 5 4

ESAC-29 * 304 26 8.7 7 — —

ESAC-30 4 3 * 15 — — —

ESAC-31 21 18 * 11 4 — —

ESAC-32 — — 2.0 — 2 2

ESAC-34 — — 5.1 — 4 3

ESAC-35 — — V1.7 — 3 2

WSAC-03 — — — — — —

WSAC-04 36 23 V5.0 — — —

WSAC-06 — — V1.5 — — —

WSAC-08 2 — V0.8 — — —

WSAC-10 4 — — — 1 1

WSAC-11 2 — 1.9 — 9 8

WSAC-12 54 36 1.9 1 — —

WSAC-14 4 4 2.0 — — —

Table 11. Species of inorganic arsenic, iron, and chromium detected in samples collected for the Middle Sacramento Valley 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed for iron, arsenic, and chromium; only wells with 

at least one detection are listed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey (USGS)

to uniquely identify a specific constituent or property. Analyses made by the USGS’s Trace Metals Laboratory. The laboratory entity code for the USGS’s Trace 

Metals Laboratory in the USGS’s National Water Information System (NWIS) is USGSTMCO. CDPH, California Department of Public Health; ESAC, East 

study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; MCL-CA, maximum 

contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); MDL, method detection limit; na, not available; no., number; NRP, National 

Research Program (USGS); NWQL, National Water Quality Laboratory (USGS); RICE, RICE well; RSD, relative standard deviation; SMCL-CA, secondary 

maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not 

included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle 

Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; * , value above threshold level]
70 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 11. Species of inorganic arsenic, iron, and chromium detected in samples collected for the Middle Sacramento Valley 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed for iron, arsenic, and chromium; only wells with 

at least one detection are listed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey (USGS)

to uniquely identify a specific constituent or property. Analyses made by the USGS’s Trace Metals Laboratory. The laboratory entity code for the USGS’s Trace 

Metals Laboratory in the USGS’s National Water Information System (NWIS) is USGSTMCO. CDPH, California Department of Public Health; ESAC, East 

study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; MCL-CA, maximum 

contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); MDL, method detection limit; na, not available; no., number; NRP, National 

Research Program (USGS); NWQL, National Water Quality Laboratory (USGS); RICE, RICE well; RSD, relative standard deviation; SMCL-CA, secondary 

maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not 

included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle 

Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level]

GAMA 

identification no.

Iron(Total)2

(μg/L) 

(01046)

Iron(II) 

(μg/L) 

(01047)

Inorganic 

Arsenic(Total)2

(μg/L) 

(99033)

Inorganic 

Arsenic(III) 

(μg/L) 

(99034)

Chromium(Total) 

(μg/L) 

(01030)

Chromium(VI) 

(μg/L) 

(01032)

Threshold type1 SMCL-CA na MCL-US na MCL-CA na

Threshold (μg/L) 300 na 10 na 50 na

[MDL] [2] [2] [0.5] [1] [1] [1]

WSAC-15 — — 1.6 — 6 5

WSAC-17 — — 5.9 — — —

WSAC-18 — — 1.3 — — —

WSAC-21 2 — 1.5 — 6 5

WSAC-22 11 — 6.5 — 2 1

WSAC-25 — — 3

2.6 — — —

WSAC-26 — — V1.8 — 3 2

WSAC-28 — — V0.9 — — —

WSAC-29 — — 3.6 — 11 10

WSAC-30 4 — — — 7 5

WSAC-31 — — 4.1 — 9 5

WSAC-34 — — V1.0 — 2 2

WSAC-35 — — V3.5 — 1 1

WSAC-36 4 3 5.7 — 3 2

Flow-path wells

ESAC-FP-01 103 82 V1.8 — — —

ESAC-FP-02 61 10 V1.4 — 4 2

ESAC-FP-03 130 69 1.8 — 2 —

ESAC-FP-04 62 — 3.5 — 2 1

ESAC-FP-05 — — 6.0 — 5 4

ESAC-FP-06 12 6 * 12 — — —

ESAC-FP-07 8 2 8.0 — — —

WSAC-FP-01 — — 1.5 — 17 17

WSAC-FP-02 5 — 2.7 — 21 19

WSAC-FP-03 3 — 1.1 — 4 3

WSAC-FP-04 6 — 5.4 4 — —

WSAC-FP-05 10 — 6.9 — — —

WSAC-FP-06 13 3 4.3 — — —

WSAC-FP-07 39 11 9.3 9 — —

WSAC-FP-08 6 — 0.7 — 4 4
Table 11 71

Table 11. Species of inorganic arsenic, iron, and chromium detected in samples collected for the Middle Sacramento Valley 

Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from the 45 slow and intermediate grid wells, 15 flow-path wells, and 22 RICE wells were analyzed for iron, arsenic, and chromium; only wells with 

at least one detection are listed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. Geological Survey (USGS)

to uniquely identify a specific constituent or property. Analyses made by the USGS’s Trace Metals Laboratory. The laboratory entity code for the USGS’s Trace 

Metals Laboratory in the USGS’s National Water Information System (NWIS) is USGSTMCO. CDPH, California Department of Public Health; ESAC, East 

study area of the middle Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; MCL-CA, maximum 

contaminant level (CDPH); MCL-US, maximum contaminant level (USEPA); MDL, method detection limit; na, not available; no., number; NRP, National 

Research Program (USGS); NWQL, National Water Quality Laboratory (USGS); RICE, RICE well; RSD, relative standard deviation; SMCL-CA, secondary 

maximum contaminant level (CDPH); USEPA, U.S. Environmental Protection Agency; V, analyte detected in sample and an associated blank—thus data are not 

included in ground-water quality analysis results; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle 

Sacramento Valley study unit–flow path; μg/L, micrograms per liter; —, analyzed but not detected; *, value above threshold level]

GAMA 

identification no.

Iron(Total)2

(μg/L) 

(01046)

Iron(II) 

(μg/L) 

(01047)

Inorganic 

Arsenic(Total)2

(μg/L) 

(99033)

Inorganic 

Arsenic(III) 

(μg/L) 

(99034)

Chromium(Total) 

(μg/L) 

(01030)

Chromium(VI) 

(μg/L) 

(01032)

Threshold type1 SMCL-CA na MCL-US na MCL-CA na

Threshold (μg/L) 300 na 10 na 50 na

[MDL] [2] [2] [0.5] [1] [1] [1]

RICE wells

RICE-01 * 4,790 4,720 3.7 4 1 —

RICE-02 3 — 8.8 — — —

RICE-03 4 2 3

4 — 1 1

RICE-04 3

4 4 4.0 — 1 —

RICE-05 28 28 0.9 — — —

RICE-06 4 3 1.5 — — —

RICE-07 2 2 5.5 — 1 —

RICE-08 3 3 5.3 — 4 4

RICE-09 3 2 3.8 — — —

RICE-10 2 2 2.8 — — —

RICE-11 — — V2.5 — — —

RICE-12 207 126 3.0 — — —

RICE-13 — — V3.5 — 2 2

RICE-14 112 96 0.7 — — —

RICE-15 — — V1.5 — — —

RICE-16 * 309 250 0.6 — — —

RICE-17 2 — V3.0 — 12 9

RICE-18 — — 1.1 — 6 5

RICE-19 — — 3.5 — — —

RICE-20 — — 6.8 — — —

RICE-21 140 130 — — — —

RICE-22 3

6 3 0.7 — — —

1

 Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2

 V codes were applied to ground-water samples for which the concentration measured by the NRP laboratory was greater than the concentration measured by 

the NWQL preferred method (table 10), and the difference between the results was greater than 20 percent RSD.

3

 Concentration measured by the NRP laboratory was less than the concentration measured by the NWQL preferred method (table 10), and the difference 

between the results was greater than 20 percent RSD.
72 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 12. Stable isotope ratios of water and tritium detected in samples collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[Samples from 70 of the grid wells (WSAC-14 not analyzed), the 15 flow-path wells, and 2 of the RICE wells were analyzed for stable isotopes of water; 

samples from 70 of the grid wells (WSAC-13 not analyzed), and the 15 flow-path wells were analyzed for tritium. The five-digit number in parentheses below 

the constituent name in the headings is used by the U.S. Geological Survey (USGS) to uniquely identify a specific constituent or property. Stable isotope ratios 

are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard reference

material. The laboratory entity codes for the laboratories in the USGS’s National Water Information System (NWIS) listed in the footnotes are shown in 

parentheses following the laboratory name. CDPH, California Department of Public Health; ESAC, East study area of the middle Sacramento Valley study unit; 

ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; MCL-CA, maximum contaminant level (CDPH); nc, sample not collected; no., 

number; pCi/L, picocuries per liter; RICE, RICE well; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the 

middle Sacramento Valley study unit–flow path; <, less than]

GAMA 

identification 

no.

δ2H of water1

(per mil) 

(82082)

δ18O of water1

(per mil) 

(82085)

Tritium2

(pCi/L) 

(07000)

Threshold type na na MCL-CA

Threshold na na 20,000

Grid wells

ESAC-01 –63.1 –8.81 1.9

ESAC-02 –63.4 –8.68 11.5

ESAC-03 –63.4 –8.80 8

ESAC-04 –59.8 –8.19 2.8

ESAC-05 –63.8 –8.88 8

ESAC-06 –59.0 –8.25 1.3

ESAC-07 –56.6 –7.92 4.2

ESAC-08 –78.9 –11.02 9.9

ESAC-09 –56.6 –7.83 3.8

ESAC-10 –48.7 –6.65 2.9

ESAC-11 –60.0 –8.47 <1

ESAC-12 –71.1 –10.11 1

ESAC-13 –80.0 –11.35 3.5

ESAC-14 –57.0 –8.10 2.6

ESAC-15 –67.0 –9.73 1

ESAC-16 –60.0 –8.80 2.9

ESAC-17 –60.8 –8.28 3.5

ESAC-18 –66.1 –9.58 <1

ESAC-19 –56.3 –7.91 <1

ESAC-20 –54.3 –7.78 <1

ESAC-21 –75.2 –10.31 <1

ESAC-22 –53.0 –7.51 12.2

ESAC-23 –72.5 –10.43 10.2

ESAC-24 –57.9 –8.25 <1

ESAC-25 –61.2 –8.72 <1

ESAC-26 –82.2 –11.52 <1

ESAC-27 –55.2 –7.51 9.3

ESAC-28 –67.5 –9.48 7.4

ESAC-29 –59.2 –8.10 2.9

ESAC-30 –83.0 –11.74 <1

ESAC-31 –70.2 –9.41 8.6

ESAC-32 –67.6 –9.47 9.6

ESAC-33 –61.2 –8.70 12.5

ESAC-34 –55.9 –7.37 13.4

ESAC-35 –70.6 –9.88 4.2
Table 12 73

Table 12. Stable isotope ratios of water and tritium detected in samples collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from 70 of the grid wells (WSAC-14 not analyzed), the 15 flow-path wells, and 2 of the RICE wells were analyzed for stable isotopes of water; 

samples from 70 of the grid wells (WSAC-13 not analyzed), and the 15 flow-path wells were analyzed for tritium. The five-digit number in parentheses below 

the constituent name in the headings is used by the U.S. Geological Survey (USGS) to uniquely identify a specific constituent or property. Stable isotope ratios 

are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard reference

material. The laboratory entity codes for the laboratories in the USGS’s National Water Information System (NWIS) listed in the footnotes are shown in 

parentheses following the laboratory name. CDPH, California Department of Public Health; ESAC, East study area of the middle Sacramento Valley study unit; 

ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; MCL-CA, maximum contaminant level (CDPH); nc, sample not collected; no., 

number; pCi/L, picocuries per liter; RICE, RICE well; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the 

middle Sacramento Valley study unit–flow path; <, less than]

GAMA 

identification 

no.

δ2H of water1

(per mil) 

(82082)

δ18O of water1

(per mil) 

(82085)

Tritium2

(pCi/L) 

(07000)

Threshold type na na MCL-CA

Threshold na na 20,000

WSAC-01 –72.1 –9.98 <1

WSAC-02 –63.0 –8.41 6.4

WSAC-03 –68.1 –9.64 7.4

WSAC-04 –67.4 –9.24 <1

WSAC-05 –65.0 –8.90 7.7

WSAC-06 –66.2 –9.46 8.6

WSAC-07 –66.9 –9.24 13.4

WSAC-08 –62.6 –8.61 11.8

WSAC-09 –63.3 –8.83 6.7

WSAC-10 –63.7 –8.82 7.4

WSAC-11 –59.5 –8.60 <1

WSAC-12 –76.3 –10.35 <1

WSAC-13 –63.9 –8.91 nc

WSAC-14 nc nc <1

WSAC-15 –44.7 –5.81 8.3

WSAC-16 –52.1 –6.93 2.6

WSAC-17 –75.9 –10.61 8.6

WSAC-18 –62.2 –8.45 1.6

WSAC-19 –58.7 –8.37 <1

WSAC-20 –44.4 –5.90 4.5

WSAC-21 –59.0 –8.38 1.9

WSAC-22 –59.5 –8.53 5.8

WSAC-23 –60.5 –8.15 7.7

WSAC-24 –59.1 –8.54 1.3

WSAC-25 –51.7 –7.14 <1

WSAC-26 –64.2 –9.08 3.8

WSAC-27 –65.4 –8.84 9.3

WSAC-28 –63.6 –8.75 11.8

WSAC-29 –64.4 –8.87 <1

WSAC-30 –66.9 –9.21 14.7

WSAC-31 –64.8 –9.21 <1

WSAC-32 –74.3 –10.51 8.3

WSAC-33 –62.0 –8.88 <1

WSAC-34 –64.8 –9.04 9.6

WSAC-35 –68.8 –9.37 7.4

WSAC-36 –66.6 –9.26 1.6
74 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 12. Stable isotope ratios of water and tritium detected in samples collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[Samples from 70 of the grid wells (WSAC-14 not analyzed), the 15 flow-path wells, and 2 of the RICE wells were analyzed for stable isotopes of water; 

samples from 70 of the grid wells (WSAC-13 not analyzed), and the 15 flow-path wells were analyzed for tritium. The five-digit number in parentheses below 

the constituent name in the headings is used by the U.S. Geological Survey (USGS) to uniquely identify a specific constituent or property. Stable isotope ratios 

are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard reference

material. The laboratory entity codes for the laboratories in the USGS’s National Water Information System (NWIS) listed in the footnotes are shown in 

parentheses following the laboratory name. CDPH, California Department of Public Health; ESAC, East study area of the middle Sacramento Valley study unit; 

ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; MCL-CA, maximum contaminant level (CDPH); nc, sample not collected; no., 

number; pCi/L, picocuries per liter; RICE, RICE well; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the 

middle Sacramento Valley study unit–flow path; <, less than]

GAMA 

identification 

no.

δ2H of water1

(per mil) 

(82082)

δ18O of water1

(per mil) 

(82085)

Tritium2

(pCi/L) 

(07000)

Threshold type na na MCL-CA

Threshold na na 20,000

Flow-path wells

ESAC-FP-01 –53.6 –7.34 <1

ESAC-FP-02 –69.4 –10.06 3.5

ESAC-FP-03 –72.9 –10.11 6.4

ESAC-FP-04 –64.0 –9.14 <1

ESAC-FP-05 –61.7 –8.01 12.8

ESAC-FP-06 –75.5 –10.58 <1

ESAC-FP-07 –80.8 –11.08 <1

WSAC-FP-01 –65.3 –9.13 <1

WSAC-FP-02 –67.7 –9.55 <1

WSAC-FP-03 –63.5 –8.96 9.0

WSAC-FP-04 –66.6 –9.43 1.3

WSAC-FP-05 –71.6 –9.63 <1

WSAC-FP-06 –69.7 –9.66 <1

WSAC-FP-07 –72.9 –10.22 <1

WSAC-FP-08 –69.2 –9.70 12.8

RICE wells

RICE-07 –54.1 –6.63 nc

RICE-11 –63.0 –8.47 nc

 1 USGS Stable Isotope Laboratory, Reston, Virginia (USGSSIVA).

2

 USGS Stable Isotope and Tritium Laboratory, Menlo Park, California (USGSH3CA). 
Table 13 75

Table 13. Nitrogen and oxygen isotopes in nitrate, nitrogen isotopes in nitrogen gas, and carbon-14 activities detected in samples 

collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to 

September, 2006.

[Samples from 42 of the slow and intermediate grid wells (ESAC-35, WSAC-10, and WSAC-11 not analyzed) and the 15 flow-path wells were analyzed for 

isotopes of nitrate; samples from 43 of the slow and intermediate grid wells (ESAC-35 and WSAC-11 not analyzed) and the 15 flow-path wells were analyzed 

for carbon-14 activities. Nitrogen and oxygen 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. The five-digit number in parentheses below the constituent name in the headings is used by 

the U.S. Geological Survey (USGS) to uniquely identify a specific constituent or property. The laboratoroy entity codes for the laboratories in the USGS’s 

National Water Information System (NWIS) listed in the footnotes are shown in parentheses following the laboratory name. ESAC, East study area of the middle 

Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; na, not available; nc, sample not collected; no., 

number; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; 

—, nitrate not detected, therefore sample was not analyzed for nitrate isotopes]

GAMA identification no.

δ18O of nitrate1

(per mil) 

(63041)

δ15N of nitrate1

(per mil) 

(82690)

δ13O of dissolved 

carbonates2

(per mil) 

(82081)

3

Carbon-14 

(percent modern) 

(49933)

Threshold type na na na na

Threshold na na na na

Grid wells

ESAC-03 2.76 8.43 –16.37 89

ESAC-05 4.00 6.41 –15.53 98

ESAC-06 2.58 3.92 –17.02 91

ESAC-10 5.28 11.76 –14.19 106

ESAC–11 — — –16.57 25

ESAC-12 0.46 4.59 –15.62 62

ESAC-15 — — –14.19 95

ESAC-16 1.00 4.38 –17.44 88

ESAC-17 — — –14.18 81

ESAC-18 1.39 4.59 –14.84 93

ESAC-19 –0.55 4.55 –15.46 82

ESAC-21 — — 5.57 11

ESAC-22 3.99 3.52 –18.13 111

ESAC-25 0.01 2.71 –16.03 90

ESAC-26 — — –12.79 50

ESAC-27 3.54 9.35 –17.24 93

ESAC-28 2.86 6.38 –15.29 99

ESAC-29 — — –15.00 53

ESAC-30 11.21 26.65 –12.86 56

ESAC-31 16.33 24.47 –17.50 82

ESAC-32 6.60 7.46 –19.37 108

ESAC-34 5.64 9.88 –17.47 100

WSAC-03 2.28 4.23 –16.32 103

WSAC-04 — — –8.58 34

WSAC-06 3.57 11.54 –16.17 102

WSAC-08 1.02 5.82 –14.29 23

WSAC-10 nc nc –14.04 114

WSAC-11 nc nc –15.69 66

WSAC-12 — — nc nc

WSAC-14 14.65 25.43 –12.09 40

WSAC-15 3.37 4.53 –15.09 104
76 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table 13. Nitrogen and oxygen isotopes in nitrate, nitrogen isotopes in nitrogen gas, and carbon-14 activities detected in samples 

collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to 

September, 2006.—Continued

[Samples from 42 of the slow and intermediate grid wells (ESAC-35, WSAC-10, and WSAC-11 not analyzed) and the 15 flow-path wells were analyzed for 

isotopes of nitrate; samples from 43 of the slow and intermediate grid wells (ESAC-35 and WSAC-11 not analyzed) and the 15 flow-path wells were analyzed 

for carbon-14 activities. Nitrogen and oxygen 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. The five-digit number in parentheses below the constituent name in the headings is used by 

the U.S. Geological Survey (USGS) to uniquely identify a specific constituent or property. The laboratoroy entity codes for the laboratories in the USGS’s 

National Water Information System (NWIS) listed in the footnotes are shown in parentheses following the laboratory name. ESAC, East study area of the middle 

Sacramento Valley study unit; ESAC-FP, East study area of the middle Sacramento Valley study unit–flow path; na, not available; nc, sample not collected; no., 

number; WSAC, West study area of the middle Sacramento Valley study unit; WSAC-FP, West study area of the middle Sacramento Valley study unit–flow path; 

—, nitrate not detected, therefore sample was not analyzed for nitrate isotopes]

GAMA identification no.

δ18O of nitrate1

(per mil) 

(63041)

δ15N of nitrate1

(per mil) 

(82690)

δ13O of dissolved 

carbonates2

(per mil) 

(82081)

3

Carbon-14 

(percent modern) 

(49933)

Threshold type na na na na

Threshold na na na na

WSAC-17 5.58 13.78 –15.50 81

WSAC-18 12.82 27.24 –13.10 34

WSAC-21 0.29 1.58 –17.09 88

WSAC-22 0.34 7.46 –15.13 78

WSAC-25 16.81 28.19 –14.14 39

WSAC-26 1.29 2.55 –14.62 74

WSAC-28 0.40 3.67 –13.78 114

WSAC-29 0.06 4.85 –15.03 44

WSAC-30 6.20 10.21 –13.42 84

WSAC-31 –0.20 5.00 –15.56 41

WSAC-34 1.96 5.07 –15.62 114

WSAC-35 2.63 7.86 –14.93 94

WSAC-36 7.25 13.64 –15.42 65

Flow-path wells

ESAC-FP-01 — — –15.25 27

ESAC-FP-02 0.38 8.30 –14.82 100

ESAC-FP-03 11.89 19.89 –17.50 93

ESAC-FP-04 2.17 4.07 –17.45 58

ESAC-FP-05 0.98 5.65 –22.23 100

ESAC-FP-06 — — –14.98 9

ESAC-FP-07 — — –11.63 5

WSAC-FP-01 0.47 4.18 –13.49 43

WSAC-FP-02 –3.09 2.52 –13.19 23

WSAC-FP-03 0.07 4.49 –17.89 85

WSAC-FP-04 — — –14.00 18

WSAC-FP-05 10.56 20.26 –16.50 14

WSAC-FP-06 6.69 9.76 –14.40 15

WSAC-FP-07 — — –14.82 15

WSAC-FP-08 3.42 7.43 –15.22 93

1

 USGS Stable Isotope Laboratory, Reston, Virginia (USGSSIVA).

2

 University of Waterloo (contract laboratory) (CAN-UWIL).

3

 University of Arizona, Accelerator Mass Spectrometry Laboratory (contract laboratory) (AZ-UAMSL).
Table 14 77

Table 14. Radioactive constituents detected in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring 

and Assessment (GAMA) Program, California, June to September, 2006.

[Samples from the eight slow grid wells were analyzed. The five-digit number in parentheses below the constituent name in the headings is used by the U.S. 

Geological Survey (USGS) to uniquely identify a specific constituent or property. Analyses by Eberline Analytical Services. The laboratory entity code for 

Eberline Analytical Services in the USGS’s National Water Information System (NWIS) is CA-EBERL. CDPH, California Department of Public Health; E, 

estimated value; ESAC, East study area of the middle Sacramento Valley study unit; MCL-CA, maximum contaminant level (CDPH); MCL-US, maximum 

contaminant level (USEPA); no., number; pCi/L, picocuries per liter; USEPA, U.S. Environmental Protection Agency; WSAC, West study area of the middle 

Sacramento Valley study unit; <, nondetection; L<, nondetection, however, result may be biased low on the basis of matrix-spike results with the potential for a 

false nondetection; *, value above lower threshold]

GAMA identification no.

Radium-226

(pCi/L) 

(09511)

Radium-228

(pCi/L) 

(81366)

Radon-222

(pCi/L) 

(82303)

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 type1 MCL-US2 MCL-US2 proposed 

MCL-US3 MCL-US MCL-US MCL-CA MCL-CA

Threshold value 5 5 300 (4,000) 15 15 50 50

Grid wells

ESAC-25 E0.02 <0.46 78 <2.2 <2.1 E1.1 E1.6

ESAC-26 E0.03 <0.46 *307 <1.2 <2.5 E1.9 E2.0

ESAC-27 E0.05 <0.51 *972 E1.5 E1.2 E1.6 E1.4

ESAC-28 E0.03 <0.62 *343 E1.1 <2.2 2.7 E3.2

WSAC-03 E0.03 <0.44 *447 E0.6 <3.3 <1.9 <2.8

WSAC-084 E0.03 <0.54 *463 L<2.2 L<2.1 E1.7 <1.7

WSAC-12 0.09 E0.45 *411 <1.7 <2.7 <2.0 E1.0

WSAC-184 E0.05 <0.54 214 L<4.9 L<3.1 E1.2 E1.6

1 Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

2 The MCL-US threshold for radium is the sum of radium-226 and radium-228.

3 Two MCL-US thresholds have been proposed: 300 pCi/L and 4,000 pCi/L.

4

 Potential to be biased low for gross alpha 72-hour and gross alpha 30-day radioactivity counts because of relatively high concentration of calcium.
78 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Appendix

The appendix discusses methods used to collect and 

analyze ground-water samples and to report the data for the 

MSACV study unit. These methods were selected to obtain 

representative samples of the ground water used for drinkingwater supplies in the study and to minimize potential bias of 

the data. Procedures to analyze and interpret QC data collected 

as part of the ground-water sampling are also discussed.

Sample Collection and Analysis

Ground-water samples were collected using standard 

and modified USGS protocols (Koterba and others, 1995), 

the National Field Manual for the collection of water quality 

data (U.S. Geological Survey, variously dated) and protocols 

described by Weiss (1968), Shelton and others (2001), Ball 

and McClesky (2003a,b), 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 

as possible. The sampling point was always 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 and intermediate schedules, 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- to 50-ft length of 

Teflon tubing (Lane and others, 2003). 

For intermediate monitoring schedules (flow-path and 

RICE wells), samples were collected using a portable, 2-in. 

diameter submersible pump (Grundfos RediFlo2 pump) 

attached to reels of approximately 300 ft of Teflon tubing. The 

10- to 50-ft Teflon tubing used to sample slow schedules was 

attached to the outflow section of the reels and samples were 

collected inside an enclosed chamber in a mobile laboratory. 

Two separate submersible pumps and reels were used to 

collect samples from monitoring wells in MSACV. All fittings 

and lengths of tubing were cleaned between samples (Wilde, 

2004). 

For the field measurements, ground water was pumped 

through a flow-through chamber fitted with a multiprobe meter 

that simultaneously measures the water-quality indicators 

dissolved oxygen, temperature, pH, turbidity, and specific 

conductance. Field measurements were made in accordance 

with protocols in the USGS’s National Field Manuals (Lewis, 

2006; Radtke and others, 2005; Wilde, 2006; Wilde and others, 

2006; Wilde and Radtke, 2005). All sensors on the multiprobe 

meter were calibrated daily. Measurements of temperature, 

dissolved oxygen, pH, and specific conductance 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 were then collected. Field measurements 

and instrument calibrations were recorded by hand on field 

record sheets and electronically in PCFF (“Personal Computer 

Field Forms”)-GAMA, a software package designed by the 

USGS with support from the GAMA program. Analytical 

service requests were also managed by PCFF-GAMA. Chain 

of custody documentation forms were completed by hand or 

electronically. Information from PCFF-GAMA was uploaded 

directly into NWIS at the end of every week of sample 

collection. 

For analyses requiring filtered water, ground water was 

diverted through a 0.45-μm pore size vented capsule filter,

a disk filter, or a baked glass-fiber filter depending on the 

protocol for the analysis (Wilde, 2004; Wilde and others, 

1999). Prior to sample collection, polyethylene sample 

bottles were prerinsed twice using dionized water and once 

with sample water before 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 NWQL.

Temperature-sensitive samples were stored on ice prior 

to, and during, daily shipping to the various laboratories. 

The nontemperature-sensitive samples, tritium, noble gases, 

chromium speciation, and stable isotopes were shipped 

monthly, whereas VOCs, pesticides and pesticide degradates, 

constituents of special interest, dissolved organic carbon, 

radium isotopes, gross alpha and beta radioactivity, and radon222 samples were shipped daily. 

Detailed sampling protocols for individual analyses and 

groups of analytes are described in Koterba and others (1995) 

and the USGS’s National Field Manuals (Wilde, 2004; Wilde 

and others, 1999) and in the references for analytical methods 

listed in table A1; only brief descriptions are given here. 

VOCs and gasoline oxygenates and degradates, and 1,2,3-TCP 

samples were collected in 40-mL baked amber glass sample 

vials that were purged with three vial volumes of sample water 

before bottom-filling to eliminate atmospheric contamination. 

Six normal (6 N) hydrochloric acid (HCl) was added as a 

preservative to the VOC samples, but not to the gasoline 

oxygenate and degradate samples, or the 1,2,3-TCP samples. 

Perchlorate samples were collected in 125-mL polyethylene 

bottles. Tritium samples were collected by bottom-filling 

two 1-L polyethylene bottles with unfiltered ground water, 

after first overfilling the bottle with three volumes of water. 

Stable isotopes of water were collected in 60-mL clear glass 

bottles filled with unfiltered water, sealed with a conical 

cap, and secured with electrical tape to prevent leakage and 

evaporation.
Appendix 79

Pesticides and pesticide degradation products, 

pharmaceutical compounds, and NDMA samples were 

collected in 1-L baked amber glass bottles. Pesticide and 

pharmaceutical samples were filtered with a glass-fiber filter 

during collection, whereas the NDMA samples were filtered at 

the Montgomery Watson Harza laboratory prior to analysis. 

Ground-water samples for major and minor ions, trace 

elements, alkalinity, and total dissolved solids analyses 

required filling one 250-mL polyethylene bottle with raw 

ground water, and one 500-mL and one 250-mL polyethylene 

bottles with filtered ground water (Wilde, 2004). A Whatman 

capsule filter was used for filtration. Each 250-mL filtered 

sample was then preserved with an ampoule of 7.5 N nitric 

acid. Mercury samples were collected by filtering ground 

water into a 250-mL glass bottle and preserving with an 

ampoule of 6 N HCl. Arsenic and iron speciation samples 

were filtered into 250-mL polyethylene bottles that were 

covered with tape to prevent light exposure and preserved with 

6 N HCl. Nutrient samples were filtered into 125-mL brown 

polyethylene bottles. Nitrate isotope samples were filtered into 

125-mL polyethylene bottles. Radium isotopes and gross alpha 

and beta radiation samples were filtered into 1-L polyethylene 

bottles and acidified with nitric acid. Carbon isotope samples 

were filtered and bottom-filled into two 500-mL glass bottles 

that were first overfilled with three bottle volumes of ground 

water. These samples had no headspace and were sealed with 

a conical cap to avoid atmospheric contamination. Samples for 

alkalinity titrations were collected by filtering ground water 

into 500-mL polyethylene bottles.

Dissolved organic carbon (DOC), chromium, radon-222, 

dissolved gases, and microbial constituents were collected 

from the hose bib at or near the well head, regardless of 

the sampling schedule (fast, intermediate, or slow). DOC 

was collected after rinsing the sampling equipment with 

universal blank water (Wilde, 2004). Using a 50-mL syringe 

and 0.45-μm disk filter, ground-water samples were filtered

into 125-mL baked amber glass bottles and preserved with 

4.5 N sulfuric acid. Chromium speciation samples were 

collected using a 10-mL syringe with an attached 0.45-μm

disk filter. After the syringe was thoroughly rinsed and filled 

with ground water, 4 mL was forced through the disk filter; 

the next 2 mL of the ground water was then slowly filtered 

into a small centrifuge vial for analysis of total chromium. 

Hexavalent chromium, Cr(VI), was then collected by attaching 

a small cation-exchange column to the syringe filter, and after 

conditioning the column with 2 mL of sample water, 2 mL 

was collected in a second centrifuge vial. Both vials were 

preserved with 10 μL of 7.5 N nitric acid (Ball and McClesky,

2003a,b).

For the collection of radon-222, a stainless steel and 

Teflon valve assembly was attached to the sampling port at 

the well head (Wilde, 2004). The valve was partially closed to 

create back pressure, and a 10-mL sample was taken through 

a Teflon septum on the value assembly using a glass syringe 

affixed with a stainless-steel needle. The sample was then 

injected into a 25-mL vial partially filled with scintillation 

mixture (mineral oil) and shaken. The vial was then placed in 

a cardboard tube to shield it from light during shipping. 

Noble gases were collected in 3/8-in. copper tubes 

using reinforced nylon tubing connected to the hose bib at 

the wellhead. Ground water was flushed through the tubing 

to dislodge bubbles before flow was restricted with a back 

pressure valve. Clamps on either side of the copper tube were 

then tightened, trapping a sample of ground water for analyses 

of noble gases (Weiss, 1968). 

Samples for analysis of microbial constituents also were 

collected at the well head (Bushon, 2003; Myers, 2004). Prior 

to the collection of samples, the sampling port was sterilized 

using isopropyl alcohol, and ground water was run through 

the sampling port for at least three minutes to remove any 

traces of the sterilizing agent. One sterilized 3-L carboy 

was filled for coliphage analyses (F-specific and somatic 

coliphage determinations), and two sterilized 250-mL bottles 

were filled with ground water for coliform (total coliforms 

and Escherichia coliform) analyses. Total coliforms and 

Escherichia coliform (E. coli) plates were prepared using 

sterilized equipment and reagents (Myers, 2004). Plates were 

counted under an ultraviolet light, following a 22- to 24-hour 

incubation time.

Turbidity and alkalinity were measured in the mobile 

laboratory at the well site. Turbidity was measured in the field 

with a calibrated turbidity meter. Alkalinity concentrations 

were measured on filtered samples by Gran’s titration method 

(Rounds, 2006). Titration data were entered directly into 

PCFF-GAMA, and the concentrations of bicarbonate (HCO3

–

) 

and carbonate (CO3

2–) were automatically calculated from 

the titration data using the advanced speciation method. 

Concentrations of HCO3

–

 and CO3

2– were also 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. 

Ten laboratories performed chemical and microbial 

analyses for this study (see table A1), with most of the 

analyses being performed at NWQL or by laboratories 

contracted by NWQL. NWQL maintains a rigorous qualityassurance program (Maloney, 2005; Pirkey and Glodt, 1998). 

Laboratory QC samples, including method blanks, continuing 

calibration verification standards, standard reference samples, 

reagent spikes, external certified reference materials, and 

external blind proficiency samples, are analyzed regularly. 

Method detection limits are continuously tested and laboratory 

reporting levels updated accordingly. NWQL maintains 

National Environmental Laboratory Accreditation Program 
80 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

(NELAP) and other certifications (http://nwql.usgs.gov/

Public/lab_cert.shtml). In addition, the Branch of Quality 

Systems within the USGS’s Office of Water Quality maintains 

independent oversight of quality assurance at NWQL and 

laboratories contracted by NWQL. The Branch of Quality 

Systems also runs a National Field Quality Assurance program 

that includes annual testing of all USGS field personal for 

proficiency in making field water-quality measurements 

(http://bqs.usgs.gov/nfqa/). Results for analyses made at 

NWQL or by laboratories contracted by NWQL are uploaded 

directly into NWIS by NWQL.

Data Reporting

Laboratory Reporting Conventions

NWQL uses the LRL as a threshold for reporting 

analytical results. The LRL is set to minimize the reporting of 

false negatives (not detecting a compound when it is actually 

present in a sample) to less than 1 percent (Childress and 

others, 1999). The LRL is 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 

continually monitored and updated. 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, 2002a). 

NWQL updates LRL values regularly, and the values listed in 

this report were in effect during the period analyses were made 

for ground-water samples from the MSACV study (June to 

September, 2006).

Detections between the LRL and the LT-MDL are 

reported as estimated concentrations (designated with an 

“E” before the value 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, gasoline 

oxygenates and degradates, and pesticides and pesticide 

degradates). For these methods, 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 QC criteria and for samples that were diluted 

prior to analysis (Childress and others, 1999).

Some compound concentrations in this study are 

reported using minimum reporting levels (MRLs) or 

method uncertainties. 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.

The reporting levels for radiochemical constituents 

(gross-alpha radioactivity, gross-beta radioactivity, 

radium-226, and radium-228) are based on a sample-specific 

minimum detectable concentration (SSMDC), a samplespecific critical value, and the combined standard uncertainty 

(CSU) (Bennett and others, 2006; U.S. Environmental 

Protection Agency, 2004). A result above the critical value 

represents a greater-than-95-percent certainty that the result is 

greater than zero (significantly different from the instrument’s 

background response to a blank sample), and a result above 

the SSMDC represents a greater-than-95-percent certainty 

that the result is greater than the critical value. Using these 

reporting level elements, three unique cases were possible 

when screening the raw analytical data, as described in 

Bennett and others (2006). If the analytical result was less 

than the critical value (case 1), the analyte was considered 

not detected, and the concentration was reported as less than 

the SSMDC. If the analytical result was greater than the 

critical value, the ratio of the CSU to the analytical result 

was calculated as a percent (percent relative CSU). For those 

samples with percent relative CSU greater than 20 percent 

(case 2), concentrations were reported as estimated values 

(designated by an “E” preceding the value). For those samples 

with percent relative CSU less than 20 percent, concentrations 

were reported unqualified (case 3). For table clarity, only the 

screened results were reported in table 14; the raw analytical 

results with their corresponding SSMDCs, critical values, 

and CSUs, are on file at the USGS California Water Science 

Center.

Stable isotopic compositions of oxygen, hydrogen, 

carbon, and nitrogen are reported as relative isotope ratios in 

units of per mil using the standard delta notation δiE (Coplen 

and others, 2002):

18 13 2

16 12

1

1 1,000 per mil,

where

is the heavier isotope ( C, C, or H),

is the ratio of the abundance of the heavier

 isotope to the lighter isotope ( O, C,

or H) in the

i sample

reference

i

sample

R

E

R

E

R

 

δ = −      

16 12

1

 sample, and

is the ratio of the abundance of the heavier

isotope to the lighter isotope ( O, C,

or H) in the reference material.

Rreference

(1)
Appendix 81

The reference material for oxygen and hydrogen is 

Vienna Standard Mean Ocean Water (VSMOW), which is 

assigned δ18O and δ2H values of 0 per mil (note than δ2H is 

also written as δD because the common name of the heavier

isotope of hydrogen, hydrogen-2, is deuterium). The reference 

material for carbon is Vienna Peedee Belemnite (VPDB), 

which is assigned a δ13C value of 0 per mil. Positive values 

indicate enrichment of the heavier isotope and negative values 

indicate depletion of the heavier isotope, compared with the 

ratios observed in the standard reference material.

Constituents on Multiple Analytical Schedules

 Eighteen constituents targeted in this study are 

measured by more than one analytical schedule or more than 

one laboratory (table A2). The preferred methods for these 

constituents were selected on the basis of the procedure 

recommended by NWQL (http://wwwnwql.cr.usgs.gov/

USGS/Preferred_method_selection_procedure.html). 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 is generally 

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.

Five constituents appear on NWQL Schedules 2020 and 

4024, and the preferred method is Schedule 2020 to provide 

consistency. All samples collected for the GAMA Priority 

Basin Assessment project are analyzed using Schedule 2020, 

whereas, only a subset are analyzed using Schedule 4024. Six 

constituents appear on NWQL Schedules 2032/2033 and 2060, 

and the preferred method is Schedule 2032/2033 because it 

has greater precision and accuracy for the six overlapping 

constituents. For constituents that appear on two NWQL 

schedules, only the values determined by the preferred method 

are reported. 

The water-quality indicators pH, specific conductance, 

and alkalinity were measured in the field and at NWQL. 

The field measurements are the preferred method for all 

three constituents; however, both are reported because the 

laboratory alkalinity measurements were made on a greater 

number of samples. 

The field and laboratory data were compared using the 

Wilcoxon signed-rank test, a nonparametric statistical test that 

is analogous to the parametric statistical test the paired t-test 

(Helsel and Hirsch, 2002). A nonparametric test was used 

because the data are not normally distributed. The Wilcoxon 

signed-rank test evaluates the null hypothesis that the median 

of the paired differences between the two datasets is zero. 

Results are reported as the probability, P, of obtaining the 

observed distribution of data, or one even less likely, when the 

null hypothesis is true. Therefore, a P value of 0.01 indicates 

99 percent confidence that the two datasets are different. 

Specific conductance was measured in both the field 

and the laboratory for 82 samples, and there was no statistical 

significance between the two datasets (P = 0.1035). Both 

laboratory and field pH measurements were made for 80 

samples, and the two datasets were systematically different 

(P = <0.0001). Field pH values were lower by a median of 

0.3 pH units. The increase in pH between field and laboratory 

measurement may be explained by equilibration of the sample 

with the atmosphere after collection. The partial pressure of 

CO2

 in ground water is often greater than the atmospheric 

partial pressure (Appelo and Postma, 2005); thus, CO2

degasses from the ground water when it is brought in contact 

with the atmosphere. CO2 loss results in increased pH. Field 

and laboratory alkalinities were measured for seven samples, 

and the two datasets were significantly different (P = 0.0156). 

Field alkalinity values were lower by a median of 11 mg/L 

as CaCO3. The differences between the field and laboratory 

values were greater than 5 percent for all but two samples.

For arsenic, chromium, and iron concentrations, the 

standard methods used by NWQL are preferred over the 

research methods used by the USGS National Research 

Program (NRP) Trace Metal Laboratory (TML) in Boulder, 

Colorado. The concentrations measured by TML are used only 

to

calculated ratios of redox species for each element, As(V)

As(III)

for arsenic, Cr(VI)

Cr(III)

for chromium, and Fe(III)

Fe(II)

 for iron. For 

example:

Fe(III) Fe(T) – Fe(II) , Fe(II) Fe(II)

where

Fe(T) is the total iron concentration (measured),

Fe(II) is the concentration of ferrous iron (measured), 

and

Fe(III)is the concentration of ferric iron (calculated

=

).

(2)

Quality Assurance 

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 QC tests were used in this study: blank 

samples were collected to assess contamination; replicate 

samples were collected to assess reproducibility; matrix spike 

tests were done to assess accuracy of laboratory analytical 

methods; and surrogate compounds were added to samples 

analyzed for organic constituents to assess bias of laboratory 

analytical methods. In the tables of this report, detections of 

organic constituents in ground-water samples that may have 

resulted from contamination were flagged with a “V” remark 

code, and were not considered detections for calculations 
82 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

of detection frequencies in water-quality assessments. 

Detections of inorganic constituents in ground-water samples 

that may have resulted from contamination were flagged 

with a “V” 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.

The quality-assurance used for this study followed the 

protocols used by the USGS’s NAWQA program (Koterba and 

others, 1995) and described in the National Field Manual (U.S. 

Geological Survey, variously dated). The quality assurance 

plan followed by NWQL, the primary laboratory used to 

analyze samples for this study, is described in Maloney (2005) 

and Pirkey and Glodt (1998).

Blanks

Blank samples (blanks) were collected using two types 

of water certified by NWQL to contain less than the LRL or 

MRL of the analytes investigated in the study. First, inorganic 

blank water (IBW) was used to collect sample blanks of 

perchlorate, major ions and trace elements, nutrients, arsenic 

and iron speciation, and chromium speciation. All other blanks 

were collected using VOC-free (nitrogen-purged) blank water 

(VBW). Two types of blanks were collected: source-solution 

and field blanks. Source-solution blanks were collected to 

verify that the blank water used for the field blanks was free 

of analytes. Field and source solution blanks were collected at 

approximately 10 percent of the wells sampled to determine 

if equipment or procedures used in the field or laboratory 

introduced contamination. Field blanks were analyzed for 

VOCs, gasoline oxygenates and their degradates, pesticides 

and pesticide degradates, pharmaceuticals, perchlorate, 

NDMA, 1,2,3-TCP, nutrients, DOC, major and minor ions, 

trace elements, iron, arsenic, and chromium speciation, 

and radioactive constituents (table A3). NWQL-certified 

blank water is not available for tritium or noble gases; thus, 

source solution and field blanks were not collected for these 

constituents.

Field blanks were collected by pumping or pouring blank 

water through the sampling equipment (fittings and tubing) 

used to collect ground water, then processing and transporting 

the blank samples using the same protocols for the groundwater samples. The equipment used to collect samples from 

monitoring wells was significantly different than that used 

to collect samples from production wells; thus, the field 

blanks were separated into monitoring well and production 

well groups for comparison with ground-water data. Sourcesolution blanks were collected at the sampling site by 

pouring blank water directly into sample containers that were 

preserved, stored, shipped, and analyzed in the same manner 

as the ground-water samples. Source-solution blanks were not 

divided into two classes because they were not collected using 

the field sampling equipment.

If a constituent was detected in field or source-solution 

blanks, the data for that constituent in ground-water samples 

were examined for potential contamination. Detections in 

ground-water samples with concentrations less than the 

highest concentration measured in a blank plus the LT-MDL 

were marked with a “V” in the data tables (LRL equals 

twice the LT-MDL). The highest concentration measured 

in a blank was assumed to represent the highest potential 

amount of contamination. Thus, the V remark code flags 

results that could have changed from a nondetection to a 

detection relative to the LT-MDL because of contamination. 

For example, if the LT-MDL for a constituent is 0.10 μg/L, 

the measured concentration in a ground-water sample 

with a true concentration of 0.05 μg/L would be reported 

as a nondetection. But, if the ground-water sample was 

contaminated with 0.20 μg/L of the constituent, the measured 

concentration would be reported as 0.25 μg/L, a detection. If 

the maximum potential amount of contamination is 0.20 μg/L, 

then ground-water samples with measured concentrations less 

than 0.30 μg/L may actually have true concentrations less than 

the LT-MDL. 

For organic constituents, results with V codes are not 

considered to be detections of the constituent when calculating 

detection frequencies for ground-water quality assessments. 

For inorganic constituents, results with V codes are considered 

to have concentrations less than the reported value (including 

the possibility of the concentration being less than the 

LT-MDL).

Replicates 

Sequential replicate samples were collected to assess 

variability that may result from the processing and analyses 

of inorganic and organic constituents. RSD of the measured 

values was used to express the variability between replicate 

pairs for each compound (table A4). The RSD is defined as 

the standard deviation divided by the mean concentration for 

each replicate pair of samples, multiplied by 100 percent. If 

one value in a sample pair was reported as a nondetection and 

the other value was reported as an estimated value below the 

LRL or MRL, the RSD was set to zero because the values 

are analytically identical. If one value in a sample pair was 

reported as a nondetection and the other value was greater 

than the LRL or MRL, then the nondetection value was set 

equal to one-quarter of the LRL, and the RSD was calculated 

(Hamlin and others, 2002). Values of RSD less than 20 percent 

are considered acceptable in this study. An RSD value of 

20 percent corresponds to a relative percent difference (RPD) 

value of 29 percent. High RSD values for a compound 

may indicate analytical uncertainty at low concentrations, 

particularly for concentrations within an order of magnitude of 

LT-MDL or MDL. Sequential replicate samples were collected 

at approximately 10 percent of the wells sampled. 
Appendix 83

Matrix Spikes

Addition of a known concentration of a constituent 

(“spike”) to a replicate environmental sample enables the 

laboratory to determine the effect of the matrix, in this case 

ground water, on the analytical technique used to measure the 

constituent. The compounds added as 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. Matrix spikes were added at the laboratory performing 

the analysis. Compounds with low recoveries are of particular 

concern if environmental concentrations are close to the 

MCLs; a concentration below an MCL could be above this 

threshold. Conversely, compounds with high recoveries are of 

potential concern if the environmental concentrations exceed 

MCLs; a high recovery could falsely indicate a concentration 

above the MCL. 

Acceptable ranges for matrix-spike recoveries are 

based on the acceptable ranges established for laboratory 

“set” spike recoveries. Laboratory set spikes are aliquots 

of laboratory blank water to which the same spike solution 

used for the matrix spikes has been added. One set spike is 

analyzed with each set of samples. Acceptable ranges for set 

spike recoveries are 70 to 130 percent for NWQL Schedules 

2020 and 4024 (VOCs and gasoline additives; Connor and 

others, 1998; Rose and Sandstrom, 2003; Zaugg and others, 

2002), 60 to 120 percent for NWQL Schedules 2032, 2033, 

and 2060 (pesticides; Sandstrom and others, 2001), and 60 

to 130 percent for Schedule 2080 (pharmaceuticals; Kolpin 

and others, 2002). On the basis of these ranges, we defined 

70 to 130 percent as the acceptable range for matrix-spike 

recoveries for organic compounds in this study.

Laboratory matrix spikes were performed for VOCs, 

gasoline oxygenate and their degradates, pesticide compounds, 

pharmaceutical compounds, NDMA, and 1,2,3-TCP 

because the analytical methods for these constituents are 

chromatographic methods that may be susceptible to matrix 

interferences. Replicate samples for matrix-spike additions 

were collected at approximately 10 percent of the wells 

sampled, although not all analyte classes were tested for every 

well (tables A5A–D).

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 ground-water and QC samples that were analyzed 

for VOCs, gasoline oxygenates and their degradates, pesticide 

compounds, NDMA, and 1,2,3-TCP (table A6). Most of the 

surrogate compounds are deuterated analogs of compounds 

being analyzed. For example, the surrogate toluene-d8 used in 

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. 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 attributed to improper maintenance and calibration 

of analytical equipment) that produces a negative bias. A 70 

to 130 percent recovery of surrogates is generally considered 

acceptable. Values outside this range indicate possible 

problems with the processing and analysis of samples (Connor 

and others, 1998; Sandstrom and others, 2001).

Quality-Control Sample Results

Detections in Field and Source-Solution Blanks

Field blanks were collected at approximately 10 percent 

of the sites sampled in MSACV. Table A3 presents a summary 

of compound detections in field blanks. Field blank results 

were grouped according to sampling methods (see “Sample 

Collection and Analysis” section) and analyzed to determine 

how field blank detections affected environmental data. 

Seven source-solution blanks, seven field blanks at 

production wells, and five field blanks at monitoring wells 

were collected for analysis of VOCs. Eleven VOC constituents 

were detected in field blanks collected at production wells 

or in source-solution blanks (table A3). Only 2 of these 11 

VOCs—chloroform and 1,2,4-trimethylbenzene—were 

detected in ground-water samples collected at production 

wells. Chloroform was detected in one field blank at a 

concentration of E0.04 μg/L. Three detections in groundwater samples with concentrations less than 0.05 μg/L 

(E0.04 μg/L plus one-half of the LRL of 0.02 μg/L) were 

flagged with a V code (table 5). 1,2,4-trimethlybenzene was 

detected in one source-solution blank at a concentration of 

E0.04 μg/L. Four detections in production well samples 

with concentrations less than 0.07 μg/L (E0.04 μg/L plus 

one-half the LRL of 0.056 μg/L) were flagged with a V code 

(table 5). The V-coded results were counted as nondetections 

for calculation of the detection frequency of chloroform and 

1,2,4-trimethylbenzene in the grid wells.
84 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Three VOC constituents were detected in field blanks 

collected at monitoring wells or in source-solution blanks 

(table A3), and all three were detected in ground-water 

samples collected at monitoring wells. 1,2,4-trimethlybenzene 

was detected in one source-solution blank and one field 

blank with a maximum concentration of E0.04 μg/L. A single 

detection in a ground-water sample with a concentration 

less than 0.07 μg/L (E0.04 μg/L plus one-half the LRL of 

0.056 μg/L) was flagged with a V code (table 5). m- and 

p-Xylene was detected was detected in two fields with a 

maximum concentration of E0.07 μg/L. m- and p-Xylene

was detected in one ground-water sample collected from 

a monitoring well. The concentration of m- and p-Xylene

detected in the sample was less than 0.10 μg/L (0.07 μg/L plus 

one-half the LRL of 0.06 μg/L) and was, therefore, flagged 

with a V code. Toluene was detected in three source solution 

blanks and three field blanks with a maximum concentration 

of E0.07 μg/L. Low levels of toluene were detected in 

source-solution and field blanks in many of the earlier GAMA 

study units (Bennett and others, 2006; Dawson and others, 

2008; Fram and Belitz, 2007; Kulongoski and Belitz, 2007; 

Kulongoski and others, 2006; Wright and others, 2005). 

Toluene was detected in one ground-water sample collected 

from a monitoring well. The concentration of toluene detected 

in the sample was less than 0.08 μg/L (0.07 μg/L plus one-half 

the LRL of 0.02 μg/L), and was, therefore, flagged with a V 

code. Seven field blanks were collected at production wells 

and four field blanks were collected at monitoring wells for 

analysis of pesticides and pesticide degradates. Three pesticide 

compounds were detected in one field blank collected at a 

production well (table A3), and one of these compounds, 

bromacil, was detected in ground-water samples collected 

from production wells. The concentration of bromacil detected 

in the field blank was E0.11 μg/L. All three detections of 

bromacil in ground-water samples were less than 0.012 μg/L 

(0.11 μg/L plus one-half the LRL of 0.018 μg/L), and were, 

therefore, flagged with a V code (table 6). The V-coded results 

were counted as nondetections for calculation of the detection 

frequency of bromacil in the grid wells.

Constituents of special interest (perchlorate, 1,2,3-TCP, 

and NDMA) and radioactive constituents (radium isotopes 

and gross alpha and beta radiation) were not detected in any 

source-solution or field blanks. One field blank was collected 

at a production well for analysis of radium isotopes and gross 

alpha and beta radiation. Eleven source-solution blanks, 

seven field blanks at production wells, and four field blanks 

at monitoring wells were collected for analysis of perchlorate. 

Six source solution-blanks, five field blanks at production 

wells, and one field blank at a monitoring well were collected 

for analysis of 1,2,3-TCP and NDMA.

 DOC was analyzed in one field blank collected at a 

production well and three field blanks collected at monitoring 

wells. DOC was detected in all three field blanks collected at 

monitoring wells, with a maximum concentration of 0.7 mg/L. 

Six ground-water samples collected at monitoring wells 

had detections of DOC at concentrations less than 0.9 mg/L 

(0.7 mg/L plus one-half the LRL of 0.33 mg/L). These six 

samples were flagged with V codes (table 8), indicating that 

the concentration of DOC in the samples may be as high as 

the reported value, but may also be as low as a nondetection 

relative to the stated detection limit (one-half the LRL).

Nutrients were analyzed in five field blanks collected at 

production wells and four field blanks collected at monitoring 

wells. Nitrate and nitrite were not detected in any of the field 

blanks. Orthophosphate was detected at a concentration of 

E0.003 mg/L in one field blank collected at a production well, 

and in two field blanks collected at monitoring wells. One 

production well sample had an orthophosphate concentration 

less than 0.006 mg/L (0.003 plus one-half the LRL of 

0.006 μg/L); this result was flagged with a V code. Ammonia 

was detected in two field blanks collected at monitoring wells, 

with a maximum concentration of E0.007 mg/L. Seventeen 

ground-water samples collected from monitoring wells had 

ammonia concentrations less than 0.012 mg/L (E0.007 mg/L 

plus one-half the LRL of 0.01 mg/L). These results 

were flagged with V codes, indicating that the ammonia 

concentration in the samples could be as high as the reported 

value if no contamination had occurred, but also be as low as 

a nondetection relative to the LT-MDL of 0.005 mg/L if the 

maximum potential amount of contamination (0.003 mg/L) 

had occurred. Total nitrogen was detected in three field blanks 

collected at production wells, with a maximum concentration 

of 0.26 mg/L, and in two field blanks collected at monitoring 

wells with a maximum concentration of 0.45 mg/L. The 

LRL for total nitrogen is 0.06 mg/L; thus, the threshold 

concentration for flagging results with V codes was 0.29 mg/L 

for ground-water samples collected at production wells and 

0.48 mg/L for ground-water sampled collected at monitoring 

wells. Total nitrogen results for the 10 ground-water samples 

collected from production wells and the 14 collected from 

monitoring wells with concentrations less than these threshold 

concentrations were flagged with V codes. 

Major ions were analyzed in five field blanks collected 

at production wells and four collected at monitoring wells. 

Calcium, chloride, magnesium, and silica were each detected 

in at least one field blank (table A3). However, for all four 

ions, the maximum concentration detected in the field 

blanks plus one-half the LRL was less than the minimum 

concentrations detected in ground-water samples. Therefore, 

no data were flagged with V codes.
Appendix 85

Trace elements were analyzed in five field blanks 

collected at production wells and in five field blanks 

collected at monitoring wells. Maximum concentrations for 

the three trace elements detected in field blanks collected 

at production wells were: chromium, 0.04 μg/L; nickel, 

0.05 μg/L; and zinc, 1.0 μg/L (table A3). The threshold 

concentration for flagging results with V codes in table 10

was the maximum concentration of the constituent detected 

in a field blank plus one-half the LRL for that constituent. 

Nine detections of chromium with concentrations less than 

0.06 μg/L, 10 detections of nickel with concentrations less 

than 0.08 μg/L, and 16 detections of zinc with concentrations 

less than 1.3 μg/L in ground-water samples collected from 

production wells were flagged with V codes, indicating that 

the concentration in the ground-water sample may be as high 

as the reported concentration, but also may be as low as a 

nondetection. In all cases, the results flagged with V codes had 

concentrations far below health-based or other drinking-water 

quality thresholds (the MCL-CA for chromium is 50 μg/L; the 

MCL-CA for nickel is 100 μg/L; and the SMCL-CA for zinc is 

5,000 μg/L).

Maximum concentrations for the 11 trace elements 

detected in at least one field blank collected at a monitoring 

well were: aluminum, E1 μg/L; barium, E0.9 μg/L; chromium, 

0.10 μg/L; copper, 1.80 μg/L; iron, 8 μg/L; manganese, 

0.7 μg/L; nickel, 0.20 μg/L; strontium, 0.55 μg/L; tungsten, 

E0.04 μg/L; vanadium, E0.08 μg/L; and zinc, 2.4 μg/L 

(table A3). The threshold concentration for flagging results 

with V codes in table 10 was the maximum concentration 

of the constituent detected in a field blank plus one-half the 

LRL for that constituent. Sixteen detections of aluminum, 6 

detections of chromium, 18 detections of copper, 7 detections 

of iron, 5 detections of manganese, 2 detections of nickel, 2 

detections of tungsten, and 23 detections of zinc in groundwater samples collected from monitoring wells were flagged 

with V codes, indicating that the concentration in the groundwater sample may be as high as the reported concentration, but 

also may be as low as a nondetection. In all cases, the results 

flagged with V codes had concentrations far below healthbased or other drinking-water quality thresholds (table 10). 

No detections of barium, strontium, or vanadium were flagged 

with V codes because the maximum concentration detected 

in the field blanks plus one-half the LRL was less than the 

minimum concentration detected in ground-water samples.

Arsenic and iron were detected in field blank samples 

analyzed by the NRP (table A3). Arsenic was detected in two 

of five field blanks collected at production wells and in two of 

five field blanks collected at monitoring wells. The maximum 

concentration of arsenic detected in a field blank analyzed by 

the NRP laboratory was 4.5 μg/L. Arsenic was not detected 

in any field blank samples analyzed by NWQL; therefore, the 

arsenic detected in field blanks analyzed at the NRP laboratory 

were considered to have originated in the laboratory. Because 

the arsenic contamination was not related to sampling 

equipment, there was no basis for assessing NRP arsenic data 

differently for the two different types of sampling equipment. 

Because the arsenic concentration data from NWQL Schedule 

1948 are preferred over the concentration data from the NRP 

laboratory, comparisons between the two sets of data were 

used in conjunction with the detections in the field blanks 

analyzed at the NRP laboratory to assess the NRP arsenic 

data. Arsenic concentrations from the NRP were greater than 

those from NWQL for 27 of the 82 ground-water samples 

analyzed, and for 19 of the 27, the difference was greater than 

20 percent RSD, the criteria for acceptable replicate pairs. The 

NRP arsenic concentrations were up to 3.5 μg/L greater than 

the NWQL arsenic concentration in these 19 ground-water 

samples, a difference that is comparable to the maximum 

concentration of arsenic detected in the field blanks. Arsenic 

results from the NRP laboratory for these 19 ground-water 

samples were flagged with V codes (table 11) to indicate 

that disagreement between the NWQL and NRP arsenic 

concentrations may be due to contamination of ground-water 

samples analyzed at the NRP laboratory. The ratio of 

arsenic species, As(V)

As(III)

, for these 19 samples may not be

representative of the redox conditions in the ground water.

Iron was detected in 2 of 10 field blanks analyzed by the 

NRP laboratory, with a maximum concentration of 15 μg/L. 

For eight ground-water samples with iron concentrations 

greater than 6 μg/L (the NWQL LRL for iron), iron 

concentrations measured by the NRP laboratory were higher 

than those measured by NWQL. However, all eight pairs 

differed by less than 10 percent RSD; thus, none of the NRP 

iron results were flagged with V codes.

Variability in Replicate Samples

Most of the replicate sample pairs collected during the 

MSACV study had relative standard deviations (RSDs) of less 

than 20 percent (table A4). Replicate sample pairs for analytes 

not detected in any ground-water samples are not reported 

in table A4. Thirty replicate sample pairs, representing 20 

chemical constituents, had RSDs greater than 20 percent; 

see table A4 for details. However, the replicate sample 

pairs with high RSDs had very low concentrations. At low 

concentrations, small deviations in measured values account 

for large RSDs. Because the variability in measurements 

occurred at low concentrations, well below regulatory 

thresholds, this variability was not of QC concern, and no 

detections were censored as a result of variability in replicate 

samples. 
86 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Matrix Spike Recoveries

Tables A5A–D present a summary of matrix-spike 

recoveries for the MSACV study. The addition of a spike or 

known concentration of a constituent to an environmental 

sample enables the laboratory to determine the effect of the 

matrix, in this case ground water, on the analytical technique 

used to measure the constituent. Thirteen environmental 

samples were spiked with VOCs to calculate matrix-spike 

recoveries (table A5A). Seventy-one of the 85 VOCs had 

matrix-spike recoveries in the acceptable range between 

70 and 130 percent. Eleven VOCs had at least one-matrix 

spike recovery greater than 130 percent; however, of 

these compounds, 6 were not detected in ground-water 

samples. Seven VOCs had a recoveries below 70 percent; 

however, of these compounds, 4 were not detected in 

ground-water samples. The three VOCs that had recoveries 

less than 70 percent and were detected in ground water 

included carbon disulfide, 1,2,3,4-tetramethylbenzene, and 

1,2,3,5-tetramethylbenzene, with recoveries of 67, 69, and 

62 percent, respectively. The four VOCs that had recoveries 

less than 70 percent, but were not detected in ground water 

included dichloromethane, 2,2-dichloropropane, styrene, and 

1,2,3-trichlorobenzene, with recoveries of 28, 62, 69, and 

56 percent, respectively (NOTE: low recoveries may indicate 

that these compounds may not have been detected if they were 

present at very low levels).

Twelve environmental samples were spiked with 

pesticide and pesticide degradate compounds to calculate 

matrix-spike recoveries, although the number of spiked 

samples varied depending on laboratory procedures 

(table A5B). Forty-one of the 136 spike compounds 

had recoveries in the acceptable range between 70 and 

130 percent. Eighteen of the compounds detected in groundwater samples had spike recoveries that exceeded the 

acceptable range. Twenty-three spike compounds had at least 

one recovery greater than 130 percent. Ninety-one spike 

compounds had at least one recovery below 70 percent, with 

recovery of phosmet being particularly poor. (NOTE: low 

recoveries may indicate that the compound might not have 

been detected in some samples if it was present at a very low 

concentration). 

One, 7, and 5 ground-water samples were spiked with 

perchlorate, 1,2,3-TCP, and NDMA, respectively (table A5C). 

All spike recoveries were within the acceptable range of 70 to 

130 percent.

Two ground-water samples were spiked with radium-226 

and radium-228 (table A5D). All spike recoveries were within 

the acceptable range of 70 to 130 percent with the exception 

of gross alpha 72-hour and gross alpha 30-day counts for 

one of the samples. The spiked sample (WSAC-08) that 

had poor recovery of alpha radioactivity had relatively high 

concentration of calcium (table 9). Because calcium is known 

to interfere with alpha counts (Sinojmeri, 1999), this sample 

and WSAC-18, which had similar major-ion chemistry, were 

coded as having the potential to be biased low for gross alpha 

72-hour and gross alpha 30-day counts.

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 each surrogate, 

the analytical schedule on which it was applied, the number 

of analyses for blank and nonblank samples, the number of 

surrogate recoveries below 70 percent, and the number of 

surrogate recoveries above 130 percent for the blanks and 

environmental samples. Blanks and environmental samples 

were considered separately to assess whether the matrices 

present in ground water affect surrogate recoveries. No 

systematic differences between surrogate recoveries in blanks 

and environmental samples were observed. Ninety-one percent 

of the surrogate recoveries in analyses of VOC and gasoline 

oxygenate and degradates were in the acceptable range of 70 

to 130 percent recovery, as were 96 percent of the surrogate 

recoveries for pesticides and pesticide degradates, and 

89 percent for NDMA and 1,2,3-TCP analyses.
Table A1 87

Table A1. Analytical methods used for the determination of organic, inorganic, and microbial constituents by the U.S. Geological 

Survey’s (USGS) National Water Quality Laboratory (NWQL) and additional contract laboratories.

[MI agar, supplemented nutrient agar in which coliforms (total and Escherichia) produce distinctly different fluorescence under ultraviolet lighting; RSIL, 

Reston Stable Isotope Laboratory (USGS); UV, ultraviolet; VOCs, volatile organic compounds]

Analyte Analytical Method Laboratory and analytical 

schedule or lab code Citation(s)

Organic constituents

VOCs Purge and trap capillary gas 

chromatography/mass 

spectrometry

NWQL, Schedule 2020 Connor and others, 1998

Gasoline oxygenates Heated purge and trap/gas 

chromatography/mass 

spectrometry 

NWQL, Schedule 4024 Rose and Sandstrom, 2003

Pesticides Solid-phase extraction and 

gas chromatography/mass 

spectrometry

NWQL, Schedules 2032, 2033, and 

2060

Furlong and others, 2001; 

Lindley and others, 1996; 

Madsen and others, 2003; 

Sandstrom and others, 2001; 

Zaugg and others, 1995 

Pharmaceuticals Solid-phase extraction and HPLC/

mass spectrometry

NWQL, Schedule 2080 Kolpin and others, 2002

Constituents of special interest

Perchlorate Chromatography and mass 

spectrometry 

Montgomery Watson Harza 

laboratory1

Hautman and others, 1999

N-nitrosodimethylamine (NDMA) Chromatography and mass 

spectrometry 

Montgomery Watson Harza 

laboratory1

U.S. Environmental Protection 

Agency, 1996; U.S. 

Environmental Protection 

Agency, 1999b

1,2,3-Trichloropropane Gas chromatography/electron 

capture detector

Montgomery Watson Harza 

laboratory1

U.S. Environmental Protection 

Agency, 1995

Inorganic constituents

Nutrients Alkaline persulfate digestion, 

Kjedahl digestion

NWQL, Schedule 2755 Fishman, 1993; Patton and 

Kryskalla, 2003

Dissolved organic carbon UV-promoted persulfate oxidation 

and infrared spectrometry

NWQL, Lab Code 2613 Brenton and Arnett, 1993

Major and minor ions, trace 

elements and nutrients

Atomic absorption spectrometry, 

colorimetry, ion-exchange 

chromatography, inductivelycoupled plasma atomicemission spectrometry and 

mass spectrometry

NWQL, Schedule 1948 American Public Health 

Association, 1998; Faires, 

1993; Fishman, 1993; 

Fishman and Friedman, 

1989; Garbarino, 1999; 

Garbarino and Damrau, 

2001; Garbarino and others, 

2006; McLain, 1993

Chromium, arsenic and iron 

speciation

Various techniques of 

ultraviolet visible (UV-VIS) 

spectrophotometry and atomicabsorbance spectroscopy

USGS Trace Metal Laboratory, 

Boulder, Colorado1

Ball and McCleskey, 2003a,b; 

McCleskey and others, 

2003; Stookey, 1970; To and 

others, 1998

Stable isotopes

Stable isotopes of water Gaseous hydrogen and carbon 

dioxide-water equilibration 

and stable-isotope mass 

spectrometry

USGS Stable Isotope Laboratory, 

Reston, Virginia, Schedule 1142

Coplen, 1994; Coplen and 

others, 1991; Epstein and 

Mayeda, 1953 

Nitrogen and oxygen isotopes of 

nitrate

Denitrifier method and mass 

spectrometry

USGS Stable Isotope Laboratory, 

Reston, Virginia, RSIL Lab Code 

2900

Révész, K., and Casciotti, K., 

2007

Carbon isotopes Accelerator mass spectrometry University of Waterloo, 

Environmental Isotope Lab1

; 

University of Arizona Accelerator 

Mass Spectrometry Lab1

Donahue and others, 1990; Jull 

and others, 2004
88 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table A1. Analytical methods used for the determination of organic, inorganic, and microbial constituents by the U.S. Geological 

Survey’s (USGS) National Water Quality Laboratory (NWQL) and additional contract laboratories.—Continued

[MI agar, supplemented nutrient agar in which coliforms (total and Escherichia) produce distinctly different fluorescence under ultraviolet lighting; RSIL, 

Reston Stable Isotope Laboratory (USGS); UV, ultraviolet; VOCs, volatile organic compounds]

Analyte Analytical Method Laboratory and analytical 

schedule or lab code Citation(s)

Radioactivity and gases

Tritium Electrolytic enrichment-liquid 

scintillation

USGS Stable Isotope and Tritium 

Laboratory, Menlo Park, 

California, Lab Code 1565

Thatcher and others, 1977

Tritium and noble gases Helium-3 in-growth and mass 

spectrometry

Lawrence Livermore National 

Laboratory1

Eaton and others, 2004; Moran 

and others, 2002 

Radon-222 Liquid scintillation counting NWQL, Schedule 1369 American Society for Testing 

and Materials, 1998; U.S. 

Environmental Protection 

Agency, 1999a

Radium 226/228 Alpha activity counting Eberline Analytical Services, NWQL 

method 1262

U.S. Environmental Protection 

Agency, 1980 (USEPA 

methods 903 and 904)

Gross alpha and beta radioactivity Alpha and beta activity counting Eberline Analytical Services, NWQL 

method 1792

U.S. Environmental Protection 

Agency, 1980 (USEPA 

method 900.0)

Microbial constituents

F-specific and somatic coliphage Single-agar layer (SAL) and twostep enrichment methodsUSGS Ohio Water Microbiology 

Laboratory1

U.S. Environmental Protection 

Agency, 2001

Total and Escherichia coliform Membrane filter technique with 

“MI agar”

USGS field measurement U.S. Environmental Protection 

Agency, 2002b

1

 The analytes have no schedule or lab code assigned to them.
Table A2 89

Table A2. Preferred analytical schedules/methods for constituents appearing on multiple schedules/methods for samples collected for 

the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September 2006.

[Preferred analytical schedules are the methods of analysis with the greatest accuracy and precision out of the ones used for the compound in question. 

MWH, Montgomery Watson Harza laboratory; TML, U.S. Geological Survey’s (USGS) Trace Metal Laboratory in Boulder, Colorado; VOC, volatile organic 

compound]

Constituent Primary constituent 

classification

Analytical 

schedules/method

Preferred analytical 

schedule/method

Results from preferred method reported

Acetone VOC, gasoline degradate 2020, 4024 2020

Diisopropyl ether VOC, gasoline degradate 2020, 4024 2020

Ethyl tert-Butyl ether (ETBE) VOC, gasoline degradate 2020, 4024 2020

Methyl tert-butyl ether (MTBE) VOC, gasoline degradate 2020, 4024 2020

Methyl tert-pentyl ether VOC, gasoline degradate 2020, 4024 2020

Atrazine Pesticide 2032/2033, 2060 2032/2033

Carbaryl Insecticide 2032/2033, 2060 2032/2033

Carbofuran Herbicide 2032/2033, 2060 2032/2033

Deethlyatrazine Pesticide degradate 2032/2033, 2060 2032/2033

Metalaxyl Fungicide 2032/2033, 2060 2032/2033

Tebuthiuron Pesticide 2032/2033, 2060 2032/2033

Results from both methods reported

Alkalinity Water-quality indicator 1948, field field

Arsenic(Total) Trace element 1948, TML1 1948

Chromium(Total) Trace element 1948, TML1 1948

Iron(Total) Trace element 1948, TML1 1948

pH Water-quality indicator 1948, field field

Specific conductance Water-quality indicator 1948, field field

1,2,3-Trichloropropane (1,2,3-TCP) VOC 2020, MWH1 MWH1

1

 In the USGS’s National Water Information System (NWIS), the laboratory entity code for TML is USGSTMCO and for MWH is CA-MWHL.
90 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table A3. Constituents detected in field blanks collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, June to September, 2006.

[E, estimated value; mg/L, milligrams per liter; μg/L, micrograms per liter; —, not detected]

Constituent

Source-solution blanks Field blanks at production wells Field blanks at monitoring wells Number 

of groundwater data 

affected

Number of 

detections/

analyses

Detected 

concentrations

Number of 

detections/

analyses

Detected 

concentrations

Number of 

detections/

analyses

Detected 

concentrations

 Volatile organic compounds (μg/L)

Acetone 0/7 — 3/7 E3, 6, 11 0/5 — 0

Benzene 0/7 — 1/7 E0.01 0/5 — 0

Dichloromethane 0/7 — 1/7 E0.1 0/5 — 0

2-Butanone (MEK, 

Methyl ethyl 

ketone)

0/7 — 2/7 E1.4, 5.9 0/5 — 0

Ethylbenzene 0/7 — 2/7 E0.01, E0.02 0/5 — 0

1,2,4-Trimethylbenzene1/7 E0.04 0/7 — 1/5 E0.02 6

m- and p-Xylene 0/7 — 3/7 E0.04, E0.06, E0.06 2/5 E0.03, E0.07 1

o-Xylene 0/7 — 1/7 E0.03 0/5 — 0

Styrene 0/7 — 3/7 E0.01, E0.02, E0.02 0/5 — 0

Toluene 3/7 E0.01, E0.01, E0.02 3/7 E0.08, 0.10, 0.16 3/5 E0.02, E0.02, E0.07 1

Chloroform 0/7 — 1/7 E0.04 0/5 — 3

 Pesticide and pesticide degradates (μg/L)

Bromacil 1/7 E0.11 0/4 — 3

2,4-D and 2,4-D 

methyl ester

1/7 0.28 0/4 — 0

Diuron 1/7 0.03 0/4 — 0

 Nutrients and dissolved organic carbon (DOC) (mg/L)

Ammonia (as 

nitrogen)

0/5 — 2/4 E0.006, E0.007 17

Dissolved organic 

carbon (DOC)

0/1 — 3/3 E0.2, E0.7, 0.7 6

Orthophosphate (as 

phosphorus)

1/5 E0.003 2/4 E0.003, E0.003 1

Total nitrogen 3/5 E0.04, E0.04, 0.26 2/4 E0.04, 0.45 24

 Major and minor ions (mg/L)

Calcium 0/5 — 2/4 E0.01, 0.08 0

Chloride 0/5 — 1/4 E0.13 0

Magnesium 1/5 E0.005 2/4 E0.004, 0.039 0

Silica 0/5 — 1/4 E0.03 0

 Trace elements (μg/L)

Aluminum 0/5 — 2/5 E0.9, E1 16

Barium 0/5 — 2/5 E0.8, E0.9 0

Chromium 4/5 E0.03, E0.03, 0.04, 

0.04

4/5 0.04, 0.05, 0.08, 

0.10

15

Copper 0/5 — 2/5 0.73, 1.80 18

Iron 0/5 — 1/4 8 7

Manganese 0/5 — 1/5 0.7 5

Nickel 1/5 E0.05 4/5 0.08, 0.16, 0.17, 

0.20

12

Strontium 0/5 — 2/5 E0.23, 0.55 0

Tungsten 0/5 — 2/2 E0.03, E0.04 2

Vanadium 0/5 — 2/5 E0.08, E0.08 0

Zinc 2/5 E0.3, 1.0 3/5 1.2, 1.6, 2.4 39

 Trace element species (μg/L)

Inorganic 

arsenic(Total)

2/5 3.3, 4.5 2/5 0.6, 0.7 19

Iron(Total) 1/5 3 1/5 15 0
Table A4 91

Table A4. Quality-control summary of replicate samples for constituents collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[The laboratory entity codes for the laboratories in the U.S. Geological Survey’s (USGS) National Water Infomation System (NWIS) listed in the footnotes 

are shown in parentheses following the laboratory name. E, estimated value; mg/L, milligrams per liter; pCi/L, picocuries per liter; RSD, relative standard 

deviation; TU, tritium unit; μg/L, micrograms per liter; <, less than; —, no value]

Constitutent

Number of RSDs 

greater than 

20 percent/number 

of replicates

Maximum RSD 

(percent)

Median RSD 

(percent)

Concentrations for replicates 

with RSDs greater than zero 

(environmental, replicate)

 Volatile organic compounds, gasoline oxygenates and additives from Schedules 2020 and 4024

1,2,4-Trimethylbenzene ( g/L) 2/15 40.4 23.6 (E0.07, E0.05), (0.10, 0.18)

Toluene (μg/L) 1/15 47.1 47.1 (E0.02, E0.01)

Chloroform (Trichloromethane) (μg/L) 2/15 28.3 16.5 (E0.08, E0.06), (E0.02, E0.03)

All other VOCs from Schedules 2020 

and 4024

0/15 < 20 — —

 Pesticides and pesticide degradates from Schedules 2032, 2033, and 2060

All pesticides and pesticide degradates 

from Schedule 2032

0/12 < 20 — —

All pesticides and pesticide degradates 

from Schedule 2033

0/2 < 20 — —

All pesticides and pesticide degradates 

from Schedule 2060

0/13 < 20 — —

 Pharmaceuticals

All pharmaceuticals from Schedule 2080 0/9 < 20 — —

 Constituents of special interest1

Perchlorate 0/15 < 20 — —

1,2,3-Trichloropropane (1,2,3-TCP) 0/7 < 20 — —

N-Nitrosodimethylamine (NDMA) 0/5 < 20 — —

 Major ions, minor ions, trace elements, and nutrients 

Ammonia (mg/L) 1/11 23.6 23.6 (E0.005, E0.007)

Dissolved organic carbon (DOC) (mg/L) 1/5 26.2 5.2 (1.6, 1.1)

Bromide (mg/L) 2/10 122.6 1.3 (0.03, E0.02), (0.07, 0.005)

Aluminum (μg/L) 1/6 47.1 47.1 (2, E1)

Cadmium (μg/L) 1/8 47.1 47.1 (0.04, E0.02)

Cobalt (μg/L) 4/8 101 18.0 (0.01, 0.06), (0.07, E0.03), (0.06, 

E0.02), (E0.03, 0.04)

Copper (μg/L) 1/8 32.9 3.4 (E0.28, 0.45)

Iron (μg/L) 2/10 47.1 3.3 (E3, 6), (6, E3)

Lead (μg/L) 1/8 97.9 2.9 (0.10, 0.08)

Nickel (μg/L) 1/8 60.6 1.8 (1.10, 0.44)

Selenium (μg/L) 1/8 20.2 20.2 (0.08, E0.06)

Tungsten (μg/L) 1/8 28.3 28.3 (0.09, 0.06)

Zinc (μg/L) 1/8 41.9 2.2 (E0.51, 0.94)

All other nutrients from Schedule 2755 0/11 < 20 — —

All other major ions from Schedule 1948 0/10 < 20 — —

All other trace elements from Schedule 

1948

0/8 < 20 — —
92 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table A4. Quality-control summary of replicate samples for constituents collected for the Middle Sacramento Valley Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—Continued

[The laboratory entity codes for the laboratories in the U.S. Geological Survey’s (USGS) National Water Infomation System (NWIS) listed in the footnotes 

are shown in parentheses following the laboratory name. E, estimated value; mg/L, milligrams per liter; pCi/L, picocuries per liter; RSD, relative standard 

deviation; TU, tritium unit; μg/L, micrograms per liter; <, less than; —, no value]

Constitutent

Number of RSDs 

greater than 

20 percent/number 

of replicates

Maximum RSD 

(percent)

Median RSD 

(percent)

Concentrations for replicates 

with RSDs greater than zero 

(environmental, replicate)

 Isotopes and radioactivity

δ18O of nitrate2

 (per mil) 1/4 84.8 7.2 (0.01, 0.04)

Tritium3

 (TU) 4/12 141.4 10.9 (0.3, 0), (0.3, 0), (1.3, 1.9), (1.3, 

0.7)

Gross-beta radioactivity, 72-hour count4

(pCi/L)

1/2 39.0 39 (E1.12, E1.97)

Gross-beta radioactivity, 30-day count4

(pCi/L)

1/2 33.8 21.7 (E1.62, 2.64)

All additional isotopes and radioactivity 0/2 < 20 — —

 Microbial indicators

F-specific and somatic coliphage 0/1 < 20 0 —

E. coli, and total coliforms 0/30 < 20 0 —

1 Analyses performed at Montgomery Watson Harza laboratory, Monrovia, California (CA-MWHL).

2 USGS Stable Isotope Laboratory, Reston, Virginia (USGSSIVA).

3 USGS Stable Isotope and Tritium Laboratory, Menlo Park, California (USGSH3CA).

4 Analyses performed at Eberline Analytical Services, Richmond, California (CA-EBERL).
Table A5A 93

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and gasoline oxygenates and 

their degradates in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, June to September, 2006.

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetone1,2 13 83 122 99

Acrylonitrile 13 93 104 102

tert-Amyl alcohol 2 97 107 102

Benzene1 13 91 109 104

Bromobenzene 13 98 115 102

Bromochloromethane1 13 83 115 105

Bromodichloromethane 13 91 130 104

Bromoform (Tribromomethane)1 13 85 123 98

2-Butanone (MEK, Methyl ethyl ketone)1 13 90 112 97

n-Butylbenzene 13 75 108 91

tert-Butyl alcohol (TBA) 2 94 104 99

sec-Butylbenzene 13 83 115 98

tert-Butylbenzene 13 89 126 107

Carbon disulfide1 13 67 125 82

Carbon tetrachloride (Tetrachloromethane)1 13 87 157 106

Chlorobenzene 13 92 115 102

Chloroethane 13 83 128 106

Chloroform (Trichloromethane)1 13 87 130 111

Chloromethane1 13 88 128 113

3-Chloro-1-propene 13 99 131 116

2-Chlorotoluene 13 91 109 102

4-Chlorotoluene 13 84 109 98

Dibromochloromethane1 13 85 122 101

1,2-Dibromo-3-chloropropane (DBCP) 13 84 113 96

1,2-Dibromoethane (EDB) 13 91 126 104

Dibromomethane 13 83 121 104

1,2-Dichlorobenzene 13 87 111 100

1,3-Dichlorobenzene 13 87 109 102

1,4-Dichlorobenzene 13 91 106 100

trans-1,4-Dichloro-2-butene 13 82 114 96

Dichlorodifluoromethane (CFC-12) 13 70 123 106

1,1-Dichloroethane1 13 97 142 112

1,2-Dichloroethane 13 90 132 111

1,1-Dichloroethene (DCE) 13 87 117 104

cis-1,2-Dichloroethene1 13 96 117 106

trans-1,2-Dichloroethene1 13 94 117 106

Dichloromethane (Methylene chloride) 13 28 128 106

1,2-Dichloropropane 13 94 119 106

1,3-Dichloropropane 13 92 126 106

2,2-Dichloropropane 13 62 124 96

1,1-Dichloropropene 13 93 145 104

cis-1,3-Dichloropropene 13 79 108 97

trans-1,3-Dichloropropene 13 80 116 92

Diethyl ether 13 91 118 102

Diisopropyl ether (DIPE)2 13 85 110 102

Ethylbenzene 13 89 115 100

Ethyl tert-butyl ether (ETBE)2 13 81 119 100

Ethyl methacrylate 13 82 107 96

1-Ethyl-2-methylbenzene (o-Ethyl toluene)1 13 82 106 94

Hexachlorobutadiene 13 70 108 85

Hexachloroethane 13 86 118 102
94 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and gasoline oxygenates and 

their degradates in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) 

study, California, June to September, 2006. —Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

2-Hexanone (n-Butyl methyl ketone) 13 92 112 99

Isopropylbenzene (Cumene) 13 91 119 104

4-Isopropyl-1-methylbenzene1 13 81 110 97

Methyl acetate 2 11 112 111

Methyl acrylate 13 95 111 99

Methyl acrylonitrile 13 86 110 104

Methyl bromide (Bromomethane) 13 81 179 111

Methyl tert-butyl ether (MTBE)1,2 13 86 123 102

Methyl iodide (Iodomethane) 13 75 145 108

Methyl isobutyl ketone (MIBK) 13 85 110 96

Methyl methacrylate 13 73 106 94

Methyl tert-pentyl ether (tert-Amyl methyl ether, TAME)2 13 89 124 100

Naphthalene 13 80 117 96

n-Propylbenzene 13 87 111 98

Styrene 13 69 104 94

1,1,1,2-Tetrachloroethane 13 83 121 102

1,1,2,2-Tetrachloroethane 13 89 116 104

Tetrachloroethene (PCE)1 13 91 119 106

Tetrahydrofuran 13 96 112 106

1,2,3,4-Tetramethylbenzene1 13 69 126 98

1,2,3,5-Tetramethylbenzene1 13 62 135 106

Toluene1 13 88 115 104

1,2,3-Trichlorobenzene 13 56 113 106

1,2,4-Trichlorobenzene 13 77 126 99

1,1,1-Trichloroethane (TCA) 13 96 133 106

1,1,2-Trichloroethane 13 84 113 104

Trichloroethene (TCE)1 13 91 121 104

Trichlorofluoromethane (CFC-11)1 13 96 143 118

1,2,3-Trichloropropane (1,2,3-TCP) 13 89 115 103

1,1,2-Trichloro-1,2,2-trifluoroethane (CFC-113) 13 79 113 98

1,2,3-Trimethylbenzene 13 84 116 105

1,2,4-Trimethylbenzene1 13 86 117 102

1,3,5-Trimethylbenzene1 13 85 108 100

Vinyl bromide (Bromoethene) 13 96 128 117

Vinyl chloride (Chloroethene) 13 90 128 117

m- and p-Xylene1 13 86 171 102

o-Xylene 13 82 113 98

1

 Constituents detected in ground-water samples.

2

 Constituents on schedules 2020 and 4024; only values from schedule 2020 are reported because it is the preferred analytical schedule.
Table A5B 95

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median recovery 

(percent)

Acetochlor1,2 11 78 99 87

Acifluorfen 12 42 88 68

Alachlor2 11 83 97 91

Aldicarb 12 57 86 59

Aldicarb sulfone 12 28 103 65

Aldicarb sulfoxide 12 68 112 85

Atrazine1,2,3 11 87 98 92

Azinphos-methyl2 11 63 103 74

Azinphos-methyl oxon2 9 29 104 56

Bendiocarb 11 49 93 73

Benfluralin2 11 48 62 54

Benomyl 12 45 91 72

Bensulfuron-methyl1 12 91 146 108

Bentazon1 12 46 202 70

Bromacil1 12 51 109 86

Bromoxyni1 12 36 62 52

Caffeine 12 55 101 77

Carbaryl1,2,3 11 84 108 98

Carbofuran2,3 11 74 94 86

Chloramben, methyl ester 12 42 91 81

Chlorimuron-ethyl1 12 69 139 108

2-Chloro-2,6-diethylacetanilide2 11 80 98 93

2-Chloro-6-ethylamino-4-amino-s-triazine (deisopropylatrazine)1 12 24 95 76

2-Chloro-4-isopropylamino-6-amino-s-triazine (deethylatrazine)1,2 11 36 51 44

4-Chloro-2-methylphenol2 11 43 74 64

3-(4-Chlorophenyl)-1-methyl urea 12 42 115 76

Chlorpyrifos1,2 11 83 100 90

Chlorpyrifos, oxygen analog2 11 9 80 29

Clopyralid 12 55 81 69

Cyanazine 2 82 110 96

Cycloate 12 23 83 76

Cyfluthrin2 11 31 93 52

λ-Cyhalothrin2 11 16 53 37

Cypermethrin2 11 34 86 50

DCPA (Dacthal) monoacid 12 61 86 72

DCPA 11 88 104 97

Desulfinylfipronil1,2 11 73 97 87

Desulfinylfipronil amide2 11 50 108 76

Diazinon2 11 78 96 85

Dicamba 12 49 79 57

3,4-Dichloroaniline1,2 11 65 89 81

3,5-Dichloroaniline 2 81 95 88

2,4-D and 2,4-D methyl ester, summed on molar basis, reported as 

2,4-D1,4

12 64 172 79

4-(2,4-Dichlorophenoxy)butyric acid (2,4-DB) 12 53 82 64

Dichlorprop 12 57 90 75

Dichlorvos2 11 9 60 30

Dicrotophos2 10 20 37 30

Dieldrin2 11 76 101 83

2,6-Diethylaniline2 11 87 105 96

Dimethoate2 11 27 34 29
96 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—

Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median recovery 

(percent)

Dinoseb1 12 54 73 61

Diphenamid 12 42 101 90

Disulfoton 2 60 98 79

Disulfoton sulfone 2 100 118 109

Diuron1 12 71 97 88

α-Endosulfan 2 89 114 101

Endosulfan sulfate 2 89 125 107

EPTC 2 92 94 93

Ethion2 11 58 80 67

Ethion monoxon2 11 66 80 74

Ethoprophos 2 103 108 105

2-Ethyl-6-methylaniline2 11 81 108 92

Fenamiphos2 11 56 91 77

Fenamiphos sulfone2 11 40 172 70

Fenamiphos sulfoxide2 10 29 70 44

Fenuron 12 38 99 79

Fipronil1,2 11 60 105 81

Fipronil sulfide1,2 11 70 97 81

Fipronil sulfone1,2 11 52 127 71

Flumetsulam 12 75 158 86

Fluometuron 12 53 103 92

Fonofos2 11 77 93 83

Hexazinone1,2 11 61 112 77

3-Hydroxy carbofuran 11 52 95 74

2-Hydroxy-4-isopropylamino-6-ethylamino-s-triazine (hydroatrazine)1 12 13 106 97

Imazaquin 12 50 126 82

Imazethapyr 12 47 99 81

Imidacloprid 12 65 108 80

Isofenphos2 11 86 108 91

Linuron 12 65 97 90

Malaoxon2 11 67 93 80

Malathion2 11 82 103 92

Metalaxyl2,3 11 80 98 88

Methidathion2 11 71 108 93

Methiocarb 11 47 98 82

Methomyl 12 61 105 79

2-Methyl-4-chlorophenoxyacetic acid (MCPA)1 12 61 90 76

4-(2-Methyl-4-chlorophenoxy) butyric acid (MCPB) 12 53 82 65

Methyl paraoxon2 11 38 70 48

Methyl parathion2 11 57 83 65

Metolachlor1,2 11 96 110 102

Metribuzin2 11 57 239 70

Metsulfuron methyl1 12 55 150 80

Molinate1,2 11 87 110 93

Myclobutanil2 11 63 93 85

1-Naphthol2 11 20 70 30

Neburon 12 73 105 82

Nicosulfuron 12 61 154 96

Norflurazon 12 68 113 89

Oryzalin 12 19 85 76

Oxamyl 11 67 102 81
Table A5B 97

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.—

Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median recovery 

(percent)

Oxyfluorfen 2 58 88 73

Pendimethalin2 11 72 91 80

cis-Permethrin2 11 41 71 57

Phorate2 11 58 84 76

Phorate oxygen analog2 11 60 100 80

Phosmet2 6 8 8 8

Phosmet oxon2 6 47 50 50

Picloram 12 44 111 66

Prometon2 11 80 93 85

Prometryn2 11 84 104 94

Pronamide2 11 76 96 82

Propanil1,2 11 73 118 95

Propargite 2 90 137 113

Propham 12 39 99 87

Propiconazole 12 46 122 84

cis-Propiconazole1,2 11 84 109 90

trans-Propiconazole1,2 11 67 94 86

Propoxur 11 51 97 86

Siduron 12 61 105 93

Simazine1,2 11 81 115 94

Sulfometuron-methyl 12 94 141 106

Tebuconazole 2 70 98 84

Tebuthiuron1,2,3 11 56 230 101

Tefluthrin 2 53 67 60

Terbacil 12 55 104 87

Terbufos2 11 77 131 101

Terbufos oxygen analog sulfone2 11 60 101 77

Terbuthylazine2 11 85 102 95

Thiobencarb2 11 89 116 111

Tribuphos2 11 44 68 57

Triclopyr1 9 68 86 75

Trifluralin2 11 52 72 60

 1 Constituents detected in ground-water samples.

2

 Constituents on Schedules 2032 and 2033; only values from Schedule 2032 are reported because it is the preferred analytical schedule. 

3

 Constituents on Schedules 2032 and 2060; only values from Schedule 2032 are reported because it is the preferred analytical schedule.

4

 2,4-D and 2,4-D methyl ester summed on a molar basis and reported as 2,4-D.
98 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

Table A5C. Quality-control summary for matrix-spike recoveries of constituents of special interest in samples collected for the Middle 

Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Perchlorate1 1 99 99 99

1,2,3-Trichloropropane (1,2,3-TCP) 7 88 106 100

N-Nitrosodimethylamine (NDMA) 5 85 106 93

 1 Constituent detected in ground-water samples.

Table A5D. Quality-control summary for matrix-spike recoveries of radioactive constituents in samples collected for the Middle 

Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.

[Acceptable recovery range is between 70 and 130 percent. hr, hour]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Radium-2261 2 102 104 103

Radium-2281 2 105 117 111

Gross-alpha radioactivity, 72-hr count1 2 55 118 86

Gross-alpha radioactivity, 30-day count1 2 85 95 90

Gross-beta radioactivity, 72-hr count1 2 68 100 84

Gross-beta radioactivity, 30-day count1 2 96 98 97

 1 Constituents detected in ground-water samples.
Table A6

99

Table A6. Quality-control summary of surrogate recoveries of volatile organic compounds, and gasoline oxygenates and their degradates, pesticides and pesticide degradates, and constituents of special interest in samples collected for the Middle Sacramento Valley Groundwater Ambient Monitoring and Assessment (GAMA) study, California, June to September, 2006.[The laboratory entity code for the Montgomery Watson Harza laboratory in the U.S. Geological Survey’s National Water Information System (NWIS) is CA-MWHL. 1,2,3-TCP, 1,2,3-Trichloropropane; MWH, Montgomery Watson Harza laboratory; NDMA, N-nitrosodimethylamine; VOC, volatile organic compound]

Surrogate Analytical schedule Constitutent or constituent class analyzed Number of blank analyses Median recovery in blanks (percent)

Number of 

surrogate 

recoveries 

below 

70 percent 

in blanks

Number of 

surrogate 

recoveries 

above 

130 percent 

in blanks

Number of 

environmental 

sample 

analyses

Median 

recovery in 

environmental 

samples 

(percent)

Number of 

surrogate 

recoveries 

below 

70 percent in 

environmental 

samples

Number of 

surrogate 

recoveries 

above 

130 percent in 

environmental 

samples

1-Bromo-4-

fluorobenzene

2020, 4024 VOC 21 98 1 0 139 97 14 0

1,2-Dichloroethane-d4 2020, 4024 VOC 21 116 0 1 139 118 0 27Isobutyl alcohol-d6 4024 VOC 1 132 0 1 10 103 0 1

Toluene-d8 2020, 4024 VOC 21 100 0 0 139 99 0 0Diazinon-d10 2032, 2033 Pesticide 11 106 0 0 137 95 4 1α-HCH-d6 2032, 2033 Pesticide 11 89 0 0 138 92 0 0

2,4,5-T 2060 Pesticide 11 78 1 0 136 81 2 0Barban 2060 Pesticide 11 94 1 0 136 89 4 0Caffeine-13C 2060 Pesticide 11 101 2 0 135 92 15 0

Toluene-d8 MWH Special interest 

(1,2,3-TCP)

12 98 0 0 63 96 0 0

NDMA-d6 MWH Special interest 

(NDMA)

12 86 3 0 59 87 13 0
100 Ground-Water Qality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program

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Schmitt and others—Ground-Water Quality Data in the Middle Sacramento Valley Study Unit, 2006—Results from the California GAMA Program—Data Series 385