U.S. Department of the Interior

U.S. Geological Survey

Data Series 865

Prepared in cooperation with the California State Water Resources Control Board

Groundwater-Quality Data in the North San Francisco Bay 

Shallow Aquifer Study Unit, 2012: Results from the California 

GAMA Program

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

Cloverdale

Healdsburg

Calistoga

Guerneville

Sonoma Napa

Petaluma

Sebastopol

Santa Rosa

PACIFIC OCEAN
Cover photographs:

Top photo: Well pump in field near Petaluma, California. (Photograph by Sarmad Al-Kayssi, U.S. Geological Survey)

Bottom photo: Scenic photograph near Petaluma, California. (Photograph by George Bennett, U.S. Geological Survey)
Groundwater-Quality Data in the North 

San Francisco Bay Shallow Aquifer Study Unit, 

2012: Results from the California GAMA Program

By George L. Bennett V and Miranda S. Fram

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

Prepared in cooperation with the California State Water Resources Control Board

Data Series 865

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Bennett, G.L.,V, and Fram, M.S., 2014, Groundwater-quality data in the North San Francisco Bay Shallow Aquifer 

study unit, 2012—Results from the California GAMA Program: U.S. Geological Survey Data Series 865, 94 p., 

http://dx.doi.org/10.3133/ds865.

ISSN 2327-638X (online)

ISSN 2327-0271 (print)

ISBN 978-1-4113-3806-7
iii

Contents

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

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

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

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

Valley and Plains Study Area..............................................................................................................5

Highlands Study Area...........................................................................................................................5

Methods...........................................................................................................................................................7

Study Design..........................................................................................................................................7

Sample Collection and Analysis.........................................................................................................7

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

Quality-Assurance Methods...............................................................................................................9

Water-Quality Results ...................................................................................................................................9

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

Comparison Benchmarks ....................................................................................................................9

Groundwater-Quality Data ................................................................................................................11

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

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

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

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

Geochemical and Age-Dating Tracers...................................................................................13

Radioactive Constituents..........................................................................................................14

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

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

Acknowledgments.......................................................................................................................................15

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

Appendix A....................................................................................................................................................71

Appendix B....................................................................................................................................................93
iv

Figures

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

North San Francisco Bay Shallow Aquifer study unit, California GAMA 

Priority Basin Project................................................................................................................3

2. Map showing the location and boundaries of the North San Francisco Bay Shallow 

Aquifer study unit, the Primary Aquifer study unit, and the Highlands and 

Valley and Plains study areas, and the location of major cities, topographic features, 

and hydrologic features, California GAMA Priority Basin Project....................................6

3. Map showing the distribution of the Highlands and Valley and Plains study area 

grid cells, the location of sampled grid and understanding wells, and topographic 

features, North San Francisco Bay Shallow Aquifer study unit, California GAMA 

Priority Basin Project................................................................................................................8

4. Hierarchies showing the California GAMA Priority Basin Project select 

benchmarks used for comparison with groundwater-quality data.................................10

Tables

1. Identification, sampling, construction, and water-level information for wells sampled 

for the North San Francisco Bay Shallow Aquifer study unit, California 

GAMA Priority Basin Project, April to August 2012 ...........................................................21

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

North San Francisco Bay Shallow Aquifer study unit, California GAMA 

Priority Basin Project, April to August 2012 ........................................................................23

3A. Volatile organic compounds, primary uses or sources, comparison benchmarks, 

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

Quality Laboratory (NWQL) Schedule 2020.........................................................................24

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

benchmarks, and reporting information for the USGS National Water 

Quality Laboratory Schedule 2003 ........................................................................................28

3C. Constituents of special interest, primary uses or source, comparison benchmarks, 

and reporting information for analyses performed by Weck Laboratories, 

Inc., City of Industry, California .............................................................................................30

3D. Trace elements, comparison benchmarks, and reporting information for the 

U.S. Geological Survey National Water Quality Laboratory Schedule 1948..................30

3E. Nutrients, comparison benchmarks, and reporting information for the 

U.S. Geological Survey National Water Quality Laboratory Schedule 2755..................31

3F. Major and minor ions, silica, total dissolved solids, and alkalinity, comparison 

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

National Water Quality Laboratory Schedule 1948............................................................31

3G. Isotopic tracers, radioactive constituents, comparison benchmarks, and reporting 

information for laboratory analyses .....................................................................................32

4. Water-quality indicators in samples collected for the North San Francisco Bay 

Shallow Aquifer study unit, California GAMA Priority Basin Project, 

April to August 2012.................................................................................................................33
v

Tables—Continued

5. Volatile organic compounds detected in samples collected for the North San 

Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin Project, 

April to August 2012.................................................................................................................37

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

North San Francisco Bay Shallow Aquifer study unit, California GAMA 

Priority Basin Project, April to August 2012 ........................................................................46

7. Constituents of special interest detected in samples collected for the North 

San Francisco Bay Shallow Aquifer study unit, California GAMA Priority 

Basin Project, April to August 2012 ......................................................................................47

8. Trace elements detected in samples collected for the North San Francisco 

Bay Shallow Aquifer study unit, California GAMA Priority Basin Project, 

April to August 2012.................................................................................................................48

9. Nutrients detected in samples collected for the North San Francisco Bay 

Shallow Aquifer study unit, California GAMA Priority Basin Project, 

April to August 2012.................................................................................................................56

10. Major and minor ions, silica, and total dissolved solids detected in samples 

collected for the North San Francisco Bay Shallow Aquifer study unit, 

California GAMA Priority Basin Project, April to August 2012.........................................59

11. Isotopic tracers detected in samples collected for the North San Francisco Bay 

Shallow Aquifer study unit, California GAMA Priority Basin Project, 

April to August 2012.................................................................................................................63

12. Radioactive constituents detected in samples collected for the North San 

Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin 

Project, April to August 2012 .................................................................................................66
vi

Conversion Factors and Datums

Inch/foot/mile to International System of Units (SI)

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2)

quart (qt) 0.95 liter (L)

ounce, avoirdupois (oz) 28.35 gram (g)

pound, avoirdupois (lb) 0.4536 kilogram (kg)

SI to Inch/foot/mile

Multiply By To obtain

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.28 foot (ft)

kilometer (km) 0.6214 mile (mi)

square kilometer (km2

) 0.3861 square mile (mi2)

liter (L) 1.0567 quart (qt)

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound, avoirdupois (lb)

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

°F=(1.8×°C)+32.

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

25 °C).

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

or micrograms per liter μg/L). 

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

equivalent to parts per billion (ppb). 

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

Datums

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

(NAVD 88).

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

Altitude, as used in this report, refers to distance above or below the vertical datum and 

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

below msl).
vii

Selected Terms and Symbols

α significance level

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

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

expressed as per mil

= equal to

> greater than 

≥ greater than or equal to

< less than

≤ less than or equal to

meq/L milliequivalents per liter

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

— not detected

pH a measure of the acidity or basicity of a solution

pK1,2 negative logarithms of the acid dissociation constants for carbonic acid

pKw negative logarithm of the acid dissociation constant of water, Kw

R result 

± plus or minus

* value is at a concentration greater than benchmark level

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

Abbreviations and Acronyms

AL-US action level (USEPA)

APE Alternate Place Entry program designed for USGS sampling

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

CSU combined standard uncertainty

E estimated or having a higher degree of uncertainty

GPS Global Positioning System

HAL-US lifetime health advisory level (USEPA)

HBSL Health-Based Screening Level

HPLC high-performance liquid chromatography

LRL laboratory reporting level

LSD land-surface datum

LT-MDL long-term method detection level

MCL-CA maximum contaminant level (CDPH)

MCL-US maximum contaminant level (USEPA)

MDL method detection limit

MRL minimum reporting level

MU method uncertainty

na not available

NAD normalized absolute difference

nc not collected

NFM National Field Manual (USGS)
viii

Abbreviations and Acronyms—Continued

NL-CA notification level (CDPH)

np no preference

NSF-SA North San Francisco Bay Shallow Aquifer study unit

nv no measured value or no value in category

NWIS National Water Information System (USGS)

PBP Priority Basin Project

PCFF Personal Computer Field Form program designed for USGS sampling

QA quality assurance

QC quality control

RL reporting level

RSD relative standard deviation

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

SD standard deviation

SMCL-CA secondary maximum contaminant level (CDPH)

SMCL-US secondary maximum contaminant level (USEPA)

S-NSF-H North San Francisco Bay Shallow Aquifer study unit Highlands study 

area grid well

S-NSF-HU North San Francisco Bay Shallow Aquifer study unit Highlands study area 

understanding well

S-NSF-VP North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area 

grid well

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

in reporting results)

ssLC sample-specific critical level

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

isotopes)

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

by the International Atomic Energy Agency)

Organizations

BBP Blind Blank Program 

BQS Branch of Quality Systems (USGS)

CDPH California Department of Public Health

CDPR California Department of Pesticide Regulation

CDWR California Department of Water Resources

GAMA Groundwater Ambient Monitoring and Assessment Program

IBSP Inorganic Blind Sample Program (USGS)

LLNL Lawrence Livermore National Laboratory, Livermore, California

NAWQA National Water-Quality Assessment Program (USGS)

NELAP National Environmental Laboratory Accreditation Program

NJDEP New Jersey Department of Environmental Protection
ix

Organizations—Continued

NFQA National Field Quality Assurance Program (USGS)

NWQL National Water Quality Laboratory (USGS)

OSSU Oregon Health & Science University

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

SWRCB California State Water Resources Control Board

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

Selected Chemical Names

CaCO3 calcium carbonate

CO3

2– carbonate

H2O water

HCl hydrochloric acid

HCO3

– bicarbonate

NDMA N-nitrosodimethylamine

PVC polyvinyl chloride

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

TDS total dissolved solids

THM trihalomethane

VOC volatile organic compound
x
Groundwater-Quality Data in the North San Francisco 

Bay Shallow Aquifer Study Unit, 2012: Results from the 

California GAMA Program

By George L. Bennett V and Miranda S. Fram

Abstract strontium, and inorganic carbon in water, tritium activities, 

and carbon-14 abundances) were measured to help identify 

the sources and ages of the sampled groundwater. In total, Groundwater quality in the 1,850-square-mile North San 207 constituents and water-quality indicators were measured. Francisco Bay Shallow Aquifer (NSF-SA) study unit was Three types of quality-control samples (blanks, replicates, investigated by the U.S. Geological Survey (USGS) from and matrix spikes) were collected at up to 13 percent of April to August 2012, as part of the California State Water the wells in the NSF-SA study unit, and the results for Resources Control Board (SWRCB) Groundwater Ambient these samples were used to evaluate the quality of the Monitoring and Assessment (GAMA) Program’s Priority data for the groundwater samples. Blanks rarely contained Basin Project (PBP). The GAMA-PBP was developed in detectable concentrations of any constituent, suggesting that response to the California Groundwater Quality Monitoring contamination from sample-collection procedures was not Act of 2001 and is being conducted in collaboration with a significant source of bias in the data for the groundwater the SWRCB and Lawrence Livermore National Laboratory samples. Replicate samples generally were within the limits of (LLNL). The NSF-SA study unit was the first study unit to be acceptable analytical reproducibility. Matrix-spike recoveries sampled as part of the second phase of the GAMA-PBP, which were within the acceptable range (70 to 130 percent) for focuses on the shallow aquifer system. approximately 91 percent of the compounds. The GAMA NSF-SA study was designed to provide Most of the wells sampled for this study were private a spatially unbiased assessment of untreated-groundwater domestic wells. Private domestic wells are not regulated quality in the shallow aquifer systems and to facilitate in California, and groundwater from these wells is rarely statistically consistent comparisons of untreated-groundwater analyzed for water-quality constituents. Although regulatory quality throughout California. The shallow aquifer system in benchmarks for drinking-water quality do not apply to the NSF-SA study unit was defined as the part of the aquifer private domestic wells, to provide some context for the system that is used by many private domestic wells and is results, concentrations of constituents measured in the shallower than the primary aquifer system used by many untreated groundwater were compared with regulatory and public-supply wells. non-regulatory health-based benchmarks established by In the NSF-SA study unit located in Marin, Mendocino, the U.S. Environmental Protection Agency (USEPA) and 

Napa, Solano, and Sonoma Counties, groundwater samples California Department of Public Health (CDPH), to nonwere collected from 71 wells. Seventy of the wells were regulatory health-based benchmarks established by the 

selected by using a spatially distributed, randomized grid- USGS in cooperation with the USEPA, and to non-regulatory 

based method to provide statistical representation of the benchmarks established for aesthetic concerns by the CDPH. 

study unit (grid wells), and one well was selected to aid in Comparisons between data collected for this study and 

evaluation of water-quality issues (understanding well). benchmarks for drinking water are for illustrative purposes 

The groundwater samples were analyzed for organic only and are not indicative of compliance or non-compliance 

constituents (volatile organic compounds [VOCs], pesticides, with those benchmarks. Most of the organic and inorganic 

and pesticide degradates); constituents of special interest constituents that were detected in groundwater samples from 

(perchlorate and 1,2,3-trichloropropane [1,2,3-TCP]); the 70 grid wells in the NSF-SA study unit were detected at 

naturally occurring inorganic constituents (trace elements, concentrations less than drinking-water benchmarks.

nutrients, major and minor ions, silica, and total dissolved Of the 149 organic and special-interest constituents 

solids [TDS]); and radioactive constituents (radon-222 and analyzed for in groundwater samples, 31 were detected; 

gross alpha and gross beta radioactivity). Naturally occurring concentrations of most detected constituents were less than 

isotopes (stable isotopes of hydrogen, oxygen, boron, regulatory and non-regulatory health-based benchmarks. 
2 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

One VOC, benzene, and one insecticide, dieldrin, were 

detected at concentrations above their respective health-based 

benchmarks. In total, VOCs were detected in 40 percent of 

the grid wells sampled, pesticides and pesticide degradates 

were detected in 13 percent, and perchlorate was detected in 

27 percent of the 70 grid wells sampled.

Groundwater samples from 70 grid wells were analyzed 

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

radioactive constituents; most detected concentrations were less 

than health-based benchmarks. Exceptions are 12 detections 

of manganese greater than the USGS Health-Based Screening 

Level (HBSL), 7 detections of arsenic greater than the USEPA 

maximum contaminant level (MCL-US) of 10 micrograms 

per liter (μg/L), 2 detections of boron greater than the HBSL 

of 6,000 μg/L, 2 detections of fluoride greater than the CDPH 

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

liter (mg/L), 2 detections of nitrate greater than the MCL-US 

of 10 mg/L, and two detections of radon-222 greater than the 

proposed MCL-US of 4,000 picocuries per liter.

Results for constituents with non-regulatory benchmarks 

set for aesthetic concerns from the grid wells showed that iron 

concentrations greater than the CDPH secondary maximum 

contaminant level (SMCL-CA) of 300 μg/L were detected 

in 13 grid wells. Chloride was detected at a concentration 

greater than the SMCL-CA recommended benchmark of 

250 mg/L in two grid wells. Sulfate concentrations greater 

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

were measured in two grid wells, and the concentration in 

one of these wells was also greater than the SMCL-CA upper 

benchmark of 500 mg/L. TDS concentrations greater than 

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

measured in 15 grid wells, and concentrations in 4 of these 

wells were also greater than the SMCL-CA upper benchmark 

of 1,000 mg/L.

Introduction

About one-half of the water used for public and 

domestic drinking-water supply in California is groundwater 

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

groundwater in shallow aquifers used for drinking-water 

supply and to establish a baseline groundwater-quality 

monitoring program, the California State Water Resources 

Control Board (SWRCB), in cooperation with the 

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

National Laboratory (LLNL), implemented the Groundwater 

Ambient Monitoring and Assessment (GAMA) Program 

(California State Water Resources Control Board, 2013). 

The main goals of the GAMA Program are to improve 

groundwater monitoring and to increase the availability of 

groundwater-quality data to the public. 

The GAMA Program currently consists of four projects: 

(1) the GAMA Priority Basin Project (PBP) conducted by 

the USGS (U.S. Geological Survey, 2013a); (2) the GAMA 

Domestic Well Project conducted by the SWRCB; (3) the 

GAMA Special Studies Project conducted by LLNL; and 

(4) GeoTracker GAMA conducted by the SWRCB. The first 

phase of the GAMA-PBP (2004–2012) primarily focused on 

the deeper aquifer system, which is typically used for public 

drinking-water supply. The second phase of the GAMAPBP focuses on the shallow aquifer system, typically used 

by domestic and small-system wells (2012–present). The 

GAMA Domestic Well Project samples domestic wells in 

selected counties, and the GAMA Special Studies Project 

focuses on using research methods to help explain the 

source, fate, transport, and occurrence of chemicals that can 

affect groundwater quality. GeoTracker GAMA is an online 

groundwater information system that serves groundwaterquality data and other groundwater information collected for 

programs operated by many agencies including the SWRCB, 

the Regional Water Quality Control Boards, and the California 

Departments of Public Health (CDPH), Water Resources 

(CDWR), Toxic Substances Control (CDTSC), and Pesticide 

Regulation (CDPR).

The SWRCB initiated the GAMA Program in 2000 

in response to a legislative mandate (State of California, 

2001a, b). The GAMA-PBP was initiated in response to the 

Groundwater Quality Monitoring Act of 2001 to assess and 

monitor the quality of groundwater in California (State of 

California, 2001b). The GAMA-PBP is a comprehensive 

assessment of statewide groundwater quality designed to 

help better understand and identify risks to groundwater 

resources and to increase the availability of information 

about groundwater quality to the public. For the first phase 

of the GAMA-PBP, the USGS, in collaboration with the 

SWRCB, developed a monitoring plan to assess groundwater 

basins through direct sampling of groundwater and other 

statistically reliable sampling approaches (Belitz and others, 

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

Building on the first phase, the second phase expands the 

monitoring plan to include shallow aquifer systems. Additional 

partners in the GAMA-PBP include the CDPH, CDWR, 

CDPR, and local water agencies and well owners (Kulongoski 

and Belitz, 2004; U.S. Geological Survey, 2013b).

Hydrologic and geologic conditions and land-use patterns 

in California were considered in this statewide assessment of 

groundwater quality. Belitz and others (2003) partitioned the 

State into 10 hydrogeologic provinces, each with distinctive 

hydrologic, geologic, and land-use characteristics: Cascades 

and Modoc Plateau, Klamath Mountains, Northern Coast 

Ranges, Central Valley, Sierra Nevada, Basin and Range, 

Southern Coast Ranges, Transverse Ranges and selected 

Peninsular Ranges, Desert, and San Diego Drainages (fig. 1). 

These 10 hydrogeologic provinces include groundwater basins 

designated by the CDWR (California Department of Water 

Resources, 2003). Groundwater basins generally consist of 

relatively permeable, unconsolidated deposits of alluvial 

origin. Areas outside of basins generally consist of fractured 

hard-rock aquifers and are an important source of drinking 

water in some of the hydrogeologic provinces.
Introduction 3

sac14-0532_fig 01

Valley

North San Francisco

Bay Shallow Aquifer

 Study Unit (figure 2)

Klamath

Mountains

Cascades and

Modoc Plateau

Transverse Ranges and

selected Peninsular Ranges

Southern Coast

Ranges

Sierra

Nevada

Northern

Coast

Ranges

Central

Basin and Range

Desert

San Diego

Drainages

OREGON IDAHO

NEVADA

MEXICO

ARIZONA

Los Angeles

Bakersfield

San Diego

0 200 MILES

0 200 KILOMETERS

40°

42°

124° 122° 120° 118° 116° 114°

38°

36°

34°

Sacramento

Redding

San

Francisco

PACIFIC OCEAN

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006. 

Albers Equal Area Conic Projection

North American Datum of 1983 (NAD 83)

Hydrogeologic provinces from Belitz and others, 2003

Figure 1. Hydrogeologic provinces of California and the location of the North San Francisco Bay Shallow Aquifer study unit, California 

GAMA Priority Basin Project.
4 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

The first phase of the GAMA-PBP assessed 

approximately 95 percent of the groundwater resource used 

for public supply. Basins were prioritized for sampling on the 

basis of number of public-supply wells listed in the CDPH 

database, with secondary consideration given to municipal 

groundwater use, agricultural pumping, the number of 

historically leaking underground fuel tanks, and the number of 

square-mile sections having registered pesticide applications 

(Belitz and others, 2003). The 35 study units sampled in this 

first phase (2004–2012) included all of the priority basins, a 

subset of low-use basins, and selected areas outside of basins.

For the second phase of the GAMA-PBP, a different 

method of prioritization was required because shallow aquifer 

systems typically are used by private domestic wells, and no 

statewide database of these wells was available. The State 

was divided into 938 groundwater units, corresponding to the 

463 alluvial groundwater basins defined by the CDWR and 

475 areas outside of basins (hereinafter referred to as highland 

areas) (Johnson and Belitz, 2014). The estimated number of 

households relying on domestic wells in each groundwater 

unit was calculated from U.S. Census data (U.S. Census 

Bureau, 1990), and water-use information was compiled from 

drillers’ logs submitted to CDWR (Johnson and Belitz, in 

press). The groundwater units were prioritized for sampling 

on the basis of the number and density of households relying 

on domestic wells. Groundwater units are grouped into study 

units designed to facilitate comparison of groundwater quality 

between the shallow aquifer systems being assessed in this 

second phase of the GAMA-PBP and the deeper aquifer 

systems assessed in the first phase.

The North San Francisco Bay Shallow Aquifer (NSF-SA) 

study unit is the first study unit to be sampled in the second 

phase of the GAMA-PBP and is located in the Northern Coast 

Ranges hydrogeologic province (fig. 1).

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) Understanding: identification of 

the natural and human factors affecting groundwater quality; 

and (3) Trends: detection of changes in groundwater quality 

over time (Kulongoski and Belitz, 2004). The assessments 

include comparison between the shallow aquifer system and 

the deeper primary aquifer system assessed in the first phase. 

These assessments are intended to characterize the quality of 

groundwater in the aquifer systems of the study units, not the 

quality of drinking water used by consumers. Groundwater 

may be treated prior to use as drinking water.

In groundwater basins, domestic and small-system wells 

typically are shallower than public-supply wells listed in the 

CDPH database. In the first phase of the GAMA-PBP, the 

primary aquifer system in a study unit was defined by the 

depths of the screened or open intervals of public-supply 

wells listed in the CDPH database for the study unit. The 

shallow aquifer system assessed in this second phase of the 

GAMA‐PBP is defined as shallower than the primary aquifer 

system. In highland areas, the differences in depth zones used 

by public-supply wells and domestic and small-system wells 

may be less distinct.

The GAMA-PBP is unique in California because it 

includes many chemical analyses that are not otherwise 

available in statewide water-quality monitoring datasets. 

Groundwater samples collected for the GAMA-PBP 

are typically analyzed for approximately 200 chemical 

constituents, and the analytical methods used have lower 

detection limits than required by the CDPH for regulatory 

monitoring of public-supply wells. These analyses are useful 

for providing an early indication of changes in groundwater 

quality. In addition, the GAMA-PBP analyzes samples for a 

suite of chemical and isotope tracers for exploring hydrologic 

and geochemical processes. A broader understanding of 

groundwater composition is useful for identifying the natural 

and human factors affecting water quality. Understanding 

the occurrence and distribution of chemical constituents of 

significance to water quality is important for the long-term 

management and protection of groundwater resources.

All published and quality-assured data collected for the 

GAMA Program are available through the USGS National 

Water Information System (NWIS) web interface (U.S. 

Geological Survey, 2013c) and the SWRCB GeoTracker 

groundwater information system (California State Water 

Resources Control Board, 2009). 

This USGS Data Series Report is similar to other USGS 

Data Series Reports written for the GAMA-PBP study units 

sampled to date and is the first in a series of reports presenting 

the water-quality data collected in the NSF-SA study unit. 

Data Series Reports and additional reports addressing the 

status, understanding, and trends aspects of the waterquality assessments of each study unit are available from the 

U.S. Geological Survey (2013d) at http://ca.water.usgs.gov/

gama/includes/GAMA_publications.html.
Hydrogeologic Setting 5

Purpose and Scope

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

hydrogeologic setting of the NSF-SA study unit, the study 

design, and the study methods; (2) the analytical results 

for groundwater samples collected in the NSF-SA study 

unit, and (3) the results of QC analyses. Groundwater 

samples were collected and analyzed for field waterquality indicators; organic, special-interest, inorganic, and 

radioactive constituents; and geochemical and age-dating 

tracers. The chemical data presented in this report were 

compared to California State and Federal drinking-water 

regulatory benchmarks that are applied to treated drinking 

water, and to non-regulatory benchmarks established for 

constituents without regulatory benchmarks. Regulatory and 

non-regulatory benchmarks considered for this report are 

those established by the USEPA, the CDPH, and the USGS. 

Discussion of the factors that influence the distribution 

and occurrence of the constituents detected in groundwater 

samples will be the subject of subsequent publications.

Hydrogeologic Setting

The NSF-SA study unit lies within the Northern Coast 

Ranges hydrogeologic province described by Belitz and 

others (2003). The study unit covers 1,850 square miles (mi2) 

in Napa, Sonoma, Mendocino, Marin, and Solano Counties. 

The NSF-SA study unit is larger than the North San Francisco 

Bay Primary Aquifer study unit defined by Kulongoski and 

others (2006) for the GAMA-PBP assessment of public-supply 

aquifers (fig. 2). The NSF-SA study unit is divided into two 

study areas, the Valley and Plains study area and the Highlands 

study area.

The climate in the NSF-SA study unit is characterized 

by warm, dry summers and cool, moist winters. The average 

annual temperature in Sonoma is 59 degrees Fahrenheit (°F), 

and the average annual precipitation is 30 inches, occurring 

as rain during the winter and early spring (Western Regional 

Climate Center, 2013).

The study unit is drained by several rivers and their 

principal tributaries, including the Napa River, Sonoma Creek, 

and Petaluma River, which flow into San Pablo Bay, and the 

Laguna de Santa Rosa and Russian Rivers, which flow out to 

the Pacific Ocean. The highland areas are drained primarily by 

tributaries of the larger rivers and creeks listed here (fig. 2).

Valley and Plains Study Area

The Valley and Plains study area covers the same 

area as the Valley and Plains study area of Kulongoski and 

others (2006) and was defined by the extent of six CDWR 

groundwater basins: the Alexander, Kenwood, Napa-Sonoma, 

Petaluma, Santa Rosa, and Sonoma Valleys (California 

Department of Water Resources, 2003) (fig. 2). These basins 

result from a series of northwest-southeast–trending structural 

depressions in the southern part of the Northern Coast 

Ranges (Cardwell, 1958; Farrar and others, 2006; Metzger 

and others, 2006). The main water-bearing units in the basins 

are the alluvial sediments that range in age from Tertiary 

to Quaternary (California Department of Water Resources, 

2003, 2004a–f). The thickness of the sediments progressively 

increases from north to south and from the valley margins 

towards the rivers in the centers of the valleys. Sediment 

thickness within the valleys ranges from 10 feet (ft) to more 

than 300 ft. Groundwater recharge to the alluvial aquifers 

occurs primarily by stream-channel infiltration beneath 

major rivers and their tributaries and by direct infiltration 

of precipitation, with only minor recharge resulting from 

irrigation or other sources (Farrar and others, 2006; Metzger 

and others, 2006).

Highlands Study Area

The Highlands study area consists of the CDWR Wilson 

Grove Formation Highlands groundwater basin and the areas 

surrounding the Valley and Plains study area (fig. 2). Johnson 

and Belitz (in press) divided the State into 938 groundwater 

units: the 463 alluvial groundwater basins defined by the 

CDWR, and 475 areas outside of these groundwater basins, 

hereinafter identified as highland areas. The highland areas 

associated with groundwater basins were delineated based 

upon the surficial contributing area (watershed) immediately 

adjacent to and upslope of each groundwater basin (Johnson 

and Belitz, in press). The Highlands study area includes 

the highland groundwater units associated with the CDWR 

groundwater basins located in the Valley and Plains study 

area. Although it is defined as a groundwater basin by CDWR, 

the Wilson Grove Formation Highlands groundwater basin 

was defined by Johnson and Belitz (in press) as an associated 

highland groundwater unit and is included in the Highlands 

study area. The Highlands study area is larger than the Wilson 

Grove Formation and Volcanic Highlands study areas of 

Kulongoski and others (2006).

The Highlands study area covers about 940 mi2, with 

topography ranging from rolling hills and rounded hill tops 

to mountainous; mountain elevations are from 1,000 to 

more than 4,000 ft. The study area is composed of a variety 

of geologic units, with Tertiary volcanic (primarily the 

Sonoma Volcanics) and Cretaceous marine rocks (primarily 

the Franciscan Complex) predominating. Important waterbearing units within these rocks are often those with the 

highest porosities and transmissivities, which for the volcanic 

rocks are the tuffs (consolidated volcanic ash) and breccias 

(angular broken rock fragments), and for marine rocks are the 

conglomerates and sandstones.
6 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

sac14-0532_fig 02

EXPLANATION

North San Francisco Bay Shallow Aquifer

study unit

North San Francisco Bay Primary Aquifer

study unit boundary (Kulongoski and others, 2006)

Highlands study area

Valley and Plains study area

Volcanic Highlands study area

(Kulongoski and others, 2006)

Wilson Grove Formation

Highlands study area

(Kulongoski and others, 2006)

Clear Lake

LAKE CO

LAKE CO

NAPA CO

MARIN CO

YOLO CO

MENDOCINO CO

SONOMA CO

SOLANO CO

COLUSA CO

CONTRA

COSTA CO

80 680

780

Russian River

Dry Creek

Clear Lake

Napa River Napa River

Russian RiverRussian River

Sonoma CreekSonoma Creek

Petaluma

River PetalumaRiver

Laguna

de Santa Rosa River

Laguna

de Santa Rosa River

122°30'

38°45'

38°30'

38°15'

123°

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

29

29

20

1

128

101

101

San Pablo

Bay

0 5 10 20 Miles

0 5 10 20 Kilometers

Cloverdale

Healdsburg

Calistoga

Guerneville

Sonoma Napa

Petaluma

Sebastopol

Santa Rosa

PACIFIC OCEAN

Figure 2. Location and boundaries of the North San Francisco Bay Shallow Aquifer study unit, the Primary Aquifer study unit

(Kulongoski and others, 2006), and the Highlands and Valley and Plains study areas, and the location of major cities, topographic 

features, and hydrologic features, California GAMA Priority Basin Project.
Methods 7

Methods

Methods used for the GAMA-PBP were selected to 

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

for suitable statistical representation; (2) collect samples in 

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

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

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

with relevant documentation. Appendix A contains detailed 

descriptions of the sample-collection protocols, analytical 

methods, the QA methods, and the results of analyses of QC 

samples.

Study Design

Seventy wells were selected to provide a statistically 

unbiased, spatially distributed assessment of the quality of 

groundwater resources within the shallow aquifer system. 

Wells sampled as part of the spatially distributed, randomized 

grid-cell network, hereinafter, are referred to as “grid wells.” 

One additional, non-randomized well (hereinafter referred 

to as the “understanding well”) was selected to aid in the 

understanding of specific issues associated with vertical 

changes in groundwater quality and age.

The grid wells were selected by using a randomized 

grid-based method (Scott, 1990). The study unit was divided 

into equal-area grid cells as part of the randomized grid-based 

method; however, geographic features may force a grid cell 

to be divided into multiple pieces to obtain the designated 

coverage area for each cell. For example, parts of a grid 

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

the grid cell is still considered one grid cell. The Valley and 

Plains study area was divided into thirty 12-mi2

 grid cells, 

and the Highlands study area was divided into forty 23-mi2

grid cells. To avoid having grid cells in the Highlands study 

area that did not contain any wells suitable for this study, only 

sections of land with at least one drillers’ log for a domestic or 

public-supply well were included in the area divided into grid 

cells. The population of wells in each section statewide was 

estimated from a statistical evaluation of the CDWR’s library 

of 750,000 scanned images of drillers’ logs (Johnson and 

Belitz, in press). Sections without drillers logs lack the green 

color of the Highlands study area and are most often in the 

northern portions of the study unit.

The objective was to sample one shallow well in each 

grid cell (fig. 3). Shallow wells were targeted by using drillers’ 

log information obtained from the CDWR. Drillers’ logs of 

shallow wells (generally private domestic and small-system 

wells) that contained location information were compiled 

for each cell. To ensure that wells were randomly selected, a 

random latitude/longitude point was defined in each cell, and 

wells located closest to the random point were given highest 

priority. Locations were visited in descending order of priority 

while waiting for permission from the well owner to sample 

an appropriate well. Basic sampling criteria (for example, 

a sampling point located prior to any treatment, such as 

chlorination, or the capability to pump for an extended period 

of time) were considered prior to sampling.

The 70 grid wells sampled in the NSF-SA study unit 

were named by using the prefix “S-NSF-H” for wells in the 

Highlands study area or “S-NSF-VP” for wells in the Valley 

and Plains study area (fig. 3). A sequence number defined 

by the number of the grid cell in which the samples were 

collected in each study area was then added, creating a unique 

alphanumeric GAMA identification number.

The one understanding well sampled as part of the study 

was not included in the statistical characterization of water 

quality in the NSF-SA study unit because inclusion of this 

well would lead to the overrepresentation of one cell. The 

additional well was named by using the prefix “S-NSF-HU” 

(“U” indicating “understanding”).

The GAMA identification number for each well, the date 

sampled, well type, well altitude, available well-construction 

information, and depth to water level are listed in table 1. 

Groundwater samples were collected during the time period 

from April to August 2012. Well types in table 1 are identified 

as production, spring, or unused. Any site with a pump that 

brought groundwater to the land surface was considered 

a production well, whereas any site where groundwater 

intersected the land surface was considered a spring. Grid 

wells included 64 production wells, 4 springs, and 2 unused 

wells. The understanding well was a production well. Unless 

the distinction is important, for the remainder of the report, all 

sampled sites will be referred to as wells even though some 

are springs.

Well locations were verified by using a global positioning 

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

existing well information in USGS and CDPH databases, and 

information provided by well owners, drillers’ logs, or other 

sources of site information. Well locations and information 

were recorded by hand on field sheets and electronically on 

field laptop computers using the Alternate Place Entry (APE) 

program designed by the USGS. All information was verified 

and then uploaded into the USGS NWIS. Well owner and well 

use information is confidential.

Sample Collection and Analysis

Samples were collected in accordance with the USGS 

National Field Manual (NFM) (U.S. Geological Survey, 

variously dated) and modified USGS National Water Quality 

Assessment (NAWQA) Program sampling protocols (Koterba 

and others, 1995). These sampling protocols were followed 

so that representative samples of groundwater were collected 

at each well and to ensure that the samples were collected 

and handled in a manner that minimized the potential for 

contamination.
8 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

sac14-0532_fig 03

122°30'

38°45'

38°30'

38°15'

123°

H07

H06

H08

H05

H09

H19

H21

H22

H33

H34

H35

H36

H37

H32

H31

H30

H29

H28

VP21

VP22

VP23

VP26

VP27

VP24

VP25

VP12

VP01

VP13

H38

H39

H40

H23

H24

H25

VP14

VP20 VP30

VP29

VP28

HU30

VP16

VP06

VP08

VP09

VP05

VP15

VP02

VP11

VP03

VP04 VP10

H10

H11

H01

H12

H17

H13

H14

H15

H16

H26

H27

H04

H03

H02

H18

H20

VP18

VP07

VP19

VP17

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

0 5 10 20 Miles

0 5 10 20 Kilometers

EXPLANATION

Highlands study area understanding well

Highlands study area grid well

Valley and Plains study area grid well

Highlands study area

Valley and Plains study area

Study unit boundary 

PACIFIC OCEAN

Figure 3. Distribution of the Highlands and Valley and Plains study area grid cells, the location of sampled grid and understanding 

wells, and topographic features, North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin Project.
Water-Quality Results 9

All 71 wells in the NSF-SA study unit were sampled for 

a standard set of constituents (table 2). Tables 3A–G list the 

compounds analyzed in each constituent class. Groundwater 

samples were analyzed for 85 volatile organic compounds 

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

(table 3B); 2 constituents of special interest (table 3C); 

23 trace elements (table 3D); 5 nutrients (table 3E); 9 major 

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

laboratory alkalinity (table 3F); and 5 isotopic tracers and 

5 radioactive constituents, including tritium and carbon-14 

abundance (table 3G). The methods used for sample collection 

and analysis are described in the section in appendix A titled 

“Sample Collection and Analysis.”

Data Reporting

The methods and conventions used for reporting the 

data are described in the section in appendix A titled “Data 

Reporting.” Five constituents analyzed in this study were 

measured by more than one method at the USGS National 

Water Quality Laboratory (NWQL), four of which only have 

results reported from the preferred method (see the section 

in appendix A titled “Constituents on Multiple Analytical 

Schedules” for the preferred method selection procedure). 

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

specific conductance—were measured in the field and at the 

NWQL. The VOC 1,2,3-trichloropropane (1,2,3-TCP) was 

measured at the NWQL and Weck Laboratories, Inc.

Quality-Assurance Methods

The QA/QC procedures used for this study followed the 

protocols used by the NAWQA Program (Koterba and others, 

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

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

primary laboratory used to analyze samples for this study, is 

described in Pirkey and Glodt (1998) and Maloney (2005). 

QC samples collected in the NSF-SA study unit were blanks, 

replicates, and matrix and surrogate spikes. QC samples were 

collected to evaluate potential contamination, as well as bias 

and variability of the data that may have resulted from sample 

collection, processing, storage, transportation, and laboratory 

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

section in appendix A titled “Quality-Assurance Methods and 

Results.”

Water-Quality Results

Quality-Control Results

Results of QC analyses (blanks, replicates, and matrix 

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

data for the groundwater samples. On the basis of detections 

in field blanks collected for this and for previous GAMA-PBP 

study units, the study reporting levels (SRLs) for ten volatile 

organic compounds and eight trace elements were raised (see 

table A3 and additional discussion in the section in appendix A

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

Detections of these constituents with concentrations less 

than their SRLs were reported as a non-detection (VOCs) or 

flagged with a less than or equal to symbol (≤) (trace elements) 

in this report and in the NWIS database (tables 5 and 8).

Results from the replicates confirm that the procedures 

used to collect and analyze the samples were consistent. 

Variability for nearly 100 percent of the replicate pairs for 

constituents detected in samples was within the acceptable 

limits (tables A4A–C). The criteria for acceptable replication 

is described in the section in appendix A titled “Quality 

Assurance Methods and Results.” Median matrix-spike 

recoveries for 28 of the 148 organic constituents analyzed 

were lower than the acceptable limit of 70 percent, and 

11 were greater than the acceptable limit of 130 percent 

(tables 3B and A5A–B). The constituents for which low 

recoveries occurred might not have been detected in some 

samples if they were present in the samples at concentrations 

near the laboratory reporting levels (LRLs). High recoveries of 

constituents may indicate that reported values could be greater 

than what is in the sample. The QC results are described in 

the section in appendix A titled “Quality-Control Methods and 

Results.”

Comparison Benchmarks

The chemical data presented in this report are meant to 

characterize the quality of the untreated groundwater within 

the shallow aquifers of the NSF-SA study unit and are not 

intended to represent the drinking water used by consumers. 

The chemical composition of treated drinking water may 

differ from untreated groundwater because treated drinking 

water may be subjected to disinfection, filtration, mixing with 

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

use. To place the results in a human-health context, however, 

concentrations of constituents measured in the untreated 

groundwater were compared to regulatory and non-regulatory 

benchmarks that are used to assess drinking-water quality.
10 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

In the first phase of the GAMA-PBP (primary 

aquifer system), concentrations of constituents detected 

in groundwater samples were compared with CDPH 

and U.S. Environmental Protection Agency (USEPA) 

regulatory and non-regulatory drinking-water health-based 

benchmarks and benchmarks established for aesthetic 

purposes (California Department of Public Health, 2010, 

2013a; U.S. Environmental Protection Agency, 2012). For the 

second phase (shallow aquifer system) of the GAMA-PBP, 

an additional non-regulatory health-based drinking-water 

benchmark was included: the Health-Based Screening Level 

(HBSL) (Toccalino and others, 2012). A constituent may 

have values for more than one type of benchmark, and the 

different benchmarks must be prioritized in order to develop 

a consistent set of comparison benchmarks. In both phases 

of the GAMA-PBP, highest priority was given to regulatory, 

health-based benchmarks (fig. 4). The prioritization of 

benchmarks used for constituents without regulatory healthbased benchmarks was changed between the first and second 

phases of the GAMA-PBP. In the first phase, non-regulatory 

aesthetic-based and health-based benchmarks established by 

the CDPH were given priority over non-regulatory healthbased benchmarks established by the USEPA; whereas, in 

the second phase, non-regulatory health-based benchmarks 

were given priority over non-regulatory aesthetic-based 

benchmarks (fig. 4). The comparison benchmarks used in 

this study are described in order of priority. The effects of the 

change in prioritization are described in appendix B. Boron 

and manganese are the only constituents detected in the 

NSF-SA study unit for which the change in the prioritization 

of the benchmarks and addition of the HBSLs changed the 

presentation of the results.

MCL–Maximum Contaminant Level. Legally enforceable 

standards that apply to public-water systems and are designed 

to protect public health by limiting the levels of contaminants 

in drinking water. MCLs established by the USEPA are the 

minimum standards with which States are required to comply, 

and individual States may choose to set more stringent 

standards. CDPH has established MCLs for additional 

constituents not regulated by the USEPA, as well as lowered 

the benchmark concentrations for a number of constituents 

with MCLs established by the USEPA. In this report, a 

benchmark set by the USEPA and adopted by CDPH is labeled 

“MCL-US,” and one set by CDPH that is more stringent than 

the MCL-US is labeled “MCL-CA.” Well owners are notified 

when constituents are detected at concentrations greater than 

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

for the GAMA-PBP, but these detections do not constitute 

violations of CDPH regulations.

AL–Action Level. Legally enforceable standards that apply 

to public-water systems and are designed to protect public 

health by limiting the levels of copper and lead in drinking 

water. Detections of copper or lead greater than the actionlevel benchmarks trigger requirements for mandatory water 

treatment to reduce the corrosiveness of water to water pipes. 

The action levels established by the USEPA and CDPH are 

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

report.

Increasing order of priority

MCL-CA

MCL-US

AL-US

NL-CA

HAL-US

RSD5-US

HBSL

SMCL-CA

MCL-CA

MCL-US

AL-US

NL-CA

HAL-US

RSD5-US

SMCL-CA

Regulatory, health-based

Non-regulatory, aesthetic-based

Non-regulatory, health-based

Type of benchmark

Hierarchies used by GAMA-PBP to select benchmarks for 

comparison with groundwater-quality data

EXPLANATION

First phase 

(2004–2012)

Second phase 

(2012–ongoing)

Figure 4. Hierarchies showing the California GAMA Priority 

Basin Project select benchmarks used for comparison with 

groundwater-quality data.
Water-Quality Results 11

HBSL–Health-Based Screening Level. Non-enforceable 

water-quality benchmarks developed by the USGS in 

collaboration with the USEPA, New Jersey Department of 

Environmental Protection (NJDEP), and Oregon Health & 

Science University (OHSU). HBSLs are established by using 

the same methodologies implemented by the USEPA when 

establishing drinking-water guidelines and are based on the 

most recent human-health toxicity information available 

(Toccalino and others, 2012). HBSLs are not established for 

constituents that have MCL-US benchmarks. HBSLs have 

been established for many constituents that also have USEPA 

non-regulatory health-based benchmarks and for a large 

number of organic constituents for which USEPA has not 

yet established benchmarks. For carcinogenic constituents, 

the HBSL range represents the constituent concentration 

in drinking water that represents an excess estimated 

lifetime cancer risk of 1 chance in 1 million to 1 chance in 

10 thousand. For noncarcinogens, the HBSL concentration is 

the maximum concentration in drinking water that a lifetime of 

exposure is not expected to cause any adverse effect. HBSLs 

follow USEPA assumptions about lifetime ingestion and are 

calculated assuming consumption of 2 liters (L) (2.1 quarts) 

of water per day over a 70-year lifetime by a 70-kilogram 

(154-pound) adult and that 20 percent of a person’s exposure 

comes from drinking water.

HAL–Lifetime Health Advisory Level. The maximum 

concentration of a constituent at which its presence in drinking 

water is not expected to cause any adverse carcinogenic 

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

USEPA (HAL-US) and are calculated assuming consumption 

of 2 L (2.1 quarts) of water per day over a 70-year lifetime 

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

person’s exposure comes from drinking water. Because the 

methods used to calculate HAL-US and HBSL benchmarks 

are the same, for constituents having a HAL-US, the HBSL 

and the HAL-US generally have the same value.

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 the 10–5 risk level (10–5 equals 1/100,000). 

RSD5s are calculated by dividing the 10–4 cancer risk 

concentration established by the USEPA by 10 (RSD5-US).

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 

in drinking water at concentrations greater than its NL-CA, 

California State law requires timely notification of local 

governing bodies and recommends consumer notification.

SMCL–Secondary Maximum Contaminant Level. Nonenforceable standards applied to constituents that affect the 

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

color, or the technical qualities of drinking water, such as scaling 

and staining. Both the USEPA and CDPH define SMCLs, but 

unlike MCLs, SMCLs established by CDPH are not required 

to be at least as stringent as those established by USEPA. For 

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

a “recommended” and an “upper” SMCL-CA; detections of 

these constituents in groundwater samples were compared 

with both levels. The SMCL-US levels for these constituents 

correspond to their recommended SMCL-CAs. 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.

Note that using this hierarchy to select the comparative 

benchmark for a constituent with more than one type of 

established benchmark will not necessarily result in selection 

of the benchmark with the lowest concentration. For example, 

the HBSL for boron is 6,000 micrograms per liter (μg/L), and 

the NL-CA is 1,000 μg/L, but the comparative benchmark 

selected by this hierarchy is the HBSL. The comparative 

benchmarks used in this report are listed in tables 3A–G for 

all constituents and in tables 4–12 for constituents detected in 

groundwater samples from the NSF-SA study unit. Established 

benchmarks are not available for all constituents analyzed for 

this study. Detections of constituents at concentrations greater 

than the selected comparative benchmarks are marked with an 

asterisk (*) in tables.

Groundwater-Quality Data

Results from analyses of untreated-groundwater samples 

from the NSF-SA study unit are presented in tables 4–12. 

Groundwater samples collected in the NSF-SA study unit were 

analyzed for 207 constituents and water-quality indicators; 

118 of those constituents were not detected in any of the 

samples, and 89 constituents or water-quality indicators were 

detected.

For organic and special-interest constituents, the results 

tables include only those constituents that were detected. For 

the organic constituents, the following summary statistics 

are presented for all of the grid wells: the number of wells at 

which each analyte was detected, the frequency at which it 

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

study unit), and the total number of constituents detected 

at each well. For the inorganic, isotopic, and radioactive 

constituents, the tables include all of the constituents and wells 

that were analyzed.
12 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Water-quality indicators measured in the field and at the 

NWQL are included in table 4. The results of groundwater 

analyses, organized by constituent class, are presented in 

tables 5–12:

• Organic constituents

• Volatile organic compounds (table 5)

• Pesticides and pesticide degradates (table 6)

• Constituents of special interest (table 7)

• Inorganic constituents

• Trace elements (table 8)

• Nutrients (table 9)

• Major and minor ions, silica, and total dissolved 

solids (table 10)

• Isotope tracers (table 11)

• Radioactive constituents (table 12)

Water-Quality Indicators

Field measurements of dissolved oxygen and water 

temperature and field and laboratory measurements of pH, 

specific conductance, and alkalinity are presented in table 4. 

Bicarbonate and carbonate concentrations were calculated 

from the pH and alkalinity results. Dissolved oxygen and 

alkalinity are used as indicators of natural processes that affect 

water chemistry. The pH value indicates the acidity or basicity 

of the water. Specific conductance is the measure of electrical 

conductivity of the water and is proportional to amount of 

TDS in the water.

Field pH values were outside of the SMCL-US range 

for 14 percent of the NSF-SA study unit grid wells: eight 

well samples had field pH values less than 6.5, and two well 

samples had field pH values greater than 8.5 (table 4). Low pH 

in water may contribute to corrosion of pipes, and high pH in 

water may contribute to scaling. Laboratory pH values may 

differ from field pH values because the pH of groundwater 

may change upon removal from the ambient environment and 

exposure to the atmosphere.

Field specific-conductance values were greater than the 

recommended SMCL-CA of 900 microsiemens per centimeter 

at 25 degrees Celsius (μS/cm at 25 °C) for 9 of the 70 gridwell samples, 2 of which were also greater than the upper 

benchmark of 1,600 μS/cm at 25 °C (table 4).

Organic Constituents

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

refrigerants, fumigants, and disinfected water and are 

characterized by their tendency to evaporate. VOCs generally 

persist longer in groundwater than in surface water because 

groundwater is isolated from the atmosphere.

Of the 85 VOCs analyzed for the NSF-SA study unit, 

22 were detected in groundwater samples, and all but 1 of 

the concentrations detected were less than health-based 

benchmarks (table 5). The VOC benzene was detected in one 

well at a concentration of 4.41 μg/L, which is greater than 

the MCL-CA of 1 μg/L. One or more VOCs were detected 

in 28 of the 70 grid-well samples (about 40 percent detection 

frequency). One VOC had a detection frequency above 

10 percent. The trihalomethane chloroform (trichloromethane) 

was the most frequently detected VOC in the study unit (about 

19 percent detection frequency). Chloroform is among the 

most commonly detected VOCs in groundwater nationally, 

and its source is attributed, in part, to the recycling of 

chlorinated waters to aquifers (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 63 pesticides 

and pesticide degradates analyzed at 70 grid wells in the 

NSF-SA study unit, 8 were detected in groundwater samples, 

and all but 1 of the concentrations detected were less than 

health-based benchmarks (table 6). The insecticide dieldrin 

was detected in one well at a concentration of 0.065 μg/L 

which is greater than the HBSL of 0.02 μg/L. One or more 

pesticides or pesticide degradates were detected in 9 of the 

70 NSF-SA study unit grid well samples (about 13 percent 

detection frequency). The herbicide simazine was detected 

in more than 10 percent of the samples from the Valley 

and Plains study area. Simazine is among the nation’s most 

commonly detected pesticide compounds in groundwater 

(Gilliom and others, 2006).

Constituents of Special Interest

Perchlorate and 1,2,3-TCP were classified as constituents 

of special interest at the inception of the GAMA-PBP in 

2003 because they had recently been detected in some 

drinking-water supplies in California and the CDPH was 

considering whether or not to pursue future regulation of 

these constituents. The CDPH promulgated an MCL-CA for 

perchlorate in 2007 and is currently (as of 2013) developing 

an MCL-CA for 1,2,3-TCP (California Department of Public 

Health, 2013b). Perchlorate was detected in 19 of 70 gridwell samples (about 27 percent detection frequency), and all 

detections had concentrations less than the MCL-CA of 6 μg/L 

(table 7). 1,2,3-TCP was not detected.
Water-Quality Results 13

Inorganic Constituents

Unlike the organic constituents, most of the inorganic 

constituents generally are naturally present in groundwater, 

although their concentrations may be influenced by human 

activities.

Nineteen of the 23 trace elements and 1 of the major and 

minor ions analyzed and detected in the NSF-SA study unit 

have regulatory or non-regulatory health-based benchmarks 

(tables 3D, F). Of these 19 constituents with health-based 

benchmarks, 4 constituents were detected at concentrations 

greater than benchmarks; all detections of 15 constituents 

had concentrations less than their respective benchmarks. 

Manganese concentrations greater than the HBSL of 300 μg/L 

were detected in samples from 13 grid wells, arsenic 

concentrations greater than the MCL-US of 10 μg/L were 

detected in samples from 7 grid wells, boron concentrations 

greater than the HBSL of 6,000 μg/L were detected in samples 

from 2 grid wells, and fluoride concentrations greater than the 

MCL-CA of 2 milligrams per liter (mg/L) were detected in 

samples from 2 grid wells (tables 8 and 10).

Nutrients (nitrogen and phosphorus) present in 

groundwater can affect biological activity in aquifers and 

in surface-water bodies that receive groundwater discharge. 

Inorganic nitrogen may be present in the form of ammonia, 

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

the groundwater. High concentrations of nitrate can adversely 

affect human health, particularly the health of infants. 

Groundwater samples from two grid wells (S-NSF-VP11 and 

S-NSF-VP25) had nitrate concentrations equal to or greater 

than the MCL-US of 10 mg/L (table 9). All other nutrient 

concentrations in NSF-SA were less than health-based 

benchmarks.

The levels of certain trace elements, major-ion 

composition, and TDS content in groundwater affect the 

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

and the technical properties of water, such as scaling and 

staining. Although there are no adverse health effects directly 

associated with these properties, they may reduce consumer 

satisfaction with the water or may have economic effects. 

The CDPH has established non-enforceable benchmarks 

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

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

chloride, sulfate, and TDS. Manganese, silver, and zinc also 

have HBSLs, which are used as the comparison benchmarks in 

this study (table 3D). Iron and manganese are trace elements 

whose concentrations are affected by the oxidation-reduction 

state of the groundwater. Precipitation of minerals containing 

iron or manganese may cause orange, brown, or black staining 

of surfaces.

Iron concentrations greater than the SMCL-CA of 

300 μg/L were detected in 13 grid-well samples (table 8). 

Chloride concentrations were greater than the recommended 

SMCL-CA of 250 mg/L in two grid-well samples (table 10). 

Chloride was not detected at a concentration greater than the 

upper SMCL-CA of 500 mg/L. Sulfate concentrations were 

greater than the recommended SMCL-CA of 250 mg/L in 

two grid-well samples, one of which was also greater than the 

upper SMCL-CA of 500 mg/L (table 10). TDS concentrations 

were greater than the recommended SMCL-CA of 500 mg/L 

for 15 grid-well samples, 4 of which were also greater than the 

upper SMCL-CA of 1,000 mg/L (table 10).

Geochemical and Age-Dating Tracers

Geochemical and age-dating tracers may be used to help 

interpret hydrologic processes affecting groundwater quality 

(Clark and Fritz, 1997).

The stable isotopic ratios of hydrogen and oxygen 

in water (table 11) aid in the interpretation of the sources 

of groundwater recharge (see section in appendix A titled 

“Notation” for description of how stable isotopic ratios are 

reported). These stable isotopic ratios reflect the altitude, 

latitude, and temperature of precipitation and also the extent 

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

prior to infiltration into the aquifer. The stable isotopic ratio 

of boron in water may be useful in distinguishing the sources 

of boron in aquifers. In regions that have diverse geology, 

strontium isotope ratios may aid in estimating groundwaterflow paths.

Tritium activities (table 12) and helium isotope ratios 

provide information about the age (time since recharge) of 

groundwater. Tritium is a short-lived radioactive isotope of 

hydrogen that is incorporated into the water molecule. Low 

levels of tritium are produced continuously by interaction 

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

amount of tritium was produced as a result of atmospheric 

testing of nuclear weapons between 1952 and 1963. Thus, 

concentrations of tritium greater than background generally 

indicate the presence of water recharged after the early 1950s. 

Helium isotope ratios are used in conjunction with tritium 

concentrations to estimate ages for young groundwater. Of 

the isotope-tracer constituents analyzed for this study, tritium 

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

measured tritium activities in samples from the NSF-SA 

study unit were less than 1/100 of the MCL-CA benchmark 

(table 12).

Carbon-14 (table 11), a radioactive isotope of carbon, 

is also an age-dating tracer. Low levels of carbon-14 are 

produced continuously by interaction of cosmic radiation with 

the Earth’s atmosphere and incorporated into atmospheric 

carbon dioxide. Carbon dioxide dissolves in precipitation, 

surface water, and groundwater exposed to the atmosphere, 

thereby entering the hydrologic cycle. Because carbon-14 

decays with a half-life of approximately 5,700 years, low 

activities of carbon-14, relative to modern values, generally 

indicate a presence of groundwater that is several thousand 

years old or more.
14 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Radioactive Constituents

Radioactivity is the release of energy or energetic 

particles during changes in the structure of the nucleus of an 

atom. Most radioactivity in groundwater comes from decay 

of naturally occurring isotopes of uranium and thorium that 

are present in minerals in the sediments or fractured rocks of 

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

eventually forming stable isotopes of lead (Soddy, 1913; Faure 

and Mensing, 2005). In each step in the decay series, one 

radioactive element turns into a different radioactive element 

by emitting an alpha or a beta particle from its nucleus. The 

alpha and beta particles emitted during radioactive decay may 

be hazardous to human health because these energetic particles 

may damage cells. Radiation damage to cell DNA may 

increase the risk of getting cancer.

Activity often is used instead of concentration for 

reporting the presence of radioactive constituents. Activity of 

radioactive constituents in groundwater is measured in units 

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

equal to two atoms decaying per minute. The number of atoms 

decaying is equal to the number of alpha or beta particles 

emitted.

Radon-222 was collected and analyzed in samples 

from 68 of the 70 grid wells. Radon-222 activity was greater 

than the proposed MCL-US of 4,000 pCi/L in two of the 

grid wells (table 12). The proposed MCL-US will apply if 

the State or local water agency has an approved multimedia 

mitigation program to address radon levels in indoor air 

(U.S. Environmental Protection Agency, 1999). Gross alpha 

and gross beta particle activities were less than established 

health-based benchmarks in all samples (table 12).

Future Work

Subsequent reports for the NSF-SA study unit will be 

focused on assessment of the data presented in this report 

by using a variety of statistical, qualitative, and quantitative 

approaches to evaluate the natural and human factors affecting 

groundwater quality in the NSF-SA study unit. If available, 

additional water-quality data will be compiled, evaluated, 

and used in combination with the data that are presented in 

this report.

Summary

Groundwater quality in the 1,850-square-mile North 

San Francisco Bay Shallow Aquifer (NSF-SA) study unit 

was investigated by the U.S. Geological Survey (USGS) 

from April to August 2012, as part of the California State 

Water Resources Control Board (SWRCB) Groundwater 

Ambient Monitoring and Assessment (GAMA) Program’s 

Priority Basin Project (PBP). The GAMA Program was 

created to provide a comprehensive baseline of groundwater 

quality in the State. The GAMA-PBP was created as a 

result of the Groundwater Quality Monitoring Act of 2001 

(Sections 10780–10782.3 of the California Water Code, 

Assembly Bill 599) to assess and monitor the quality of 

groundwater. The GAMA-PBP is being conducted by the 

USGS in cooperation with the SWRCB and Lawrence 

Livermore National Laboratory (LLNL).

The GAMA NSF-SA study was designed to provide 

a spatially unbiased assessment of untreated-groundwater 

quality within the shallow aquifer system and to facilitate 

statistically consistent comparisons of untreated-groundwater 

quality throughout California. The shallow aquifer system is 

defined as the part of the aquifer system that is used by many 

private domestic wells and is shallower than the primary 

aquifer system used by many public-supply wells.

This assessment characterized the quality of groundwater 

in the NSF-SA study. Most of the wells sampled for this study 

were private domestic wells. Private domestic wells are not 

regulated in California and groundwater from these wells 

is rarely analyzed for water-quality constituents. Although 

regulatory benchmarks for drinking water quality do not 

apply to private domestic wells, to provide some context for 

the results, concentrations of constituents measured in the 

untreated groundwater were compared with regulatory and 

non-regulatory health-based benchmarks established by the 

U.S. Environmental Protection Agency (USEPA), CDPH, 

and USGS and non-regulatory benchmarks established for 

aesthetic concerns by CDPH.

The NSF-SA study unit is located within the Northern 

Coast Ranges hydrogeologic province and includes 

12 groundwater basins or subbasins defined by the California 

Department of Water Resources and surrounding highland 

areas outside of the groundwater basins. The NSF-SA study 

included assessment of the groundwater quality from 71 wells 

in Marin, Mendocino, Napa, Solano, and Sonoma Counties. 

Seventy wells were selected by using a randomized grid 

approach to achieve a statistically unbiased representation 

of groundwater in shallow aquifer systems used for private, 

domestic drinking-water supplies (grid wells), and one 

additional well was selected to aid in the evaluation of waterquality issues (understanding well).

Groundwater samples were analyzed for field waterquality indicators, organic constituents, special-interest 

constituents, inorganic constituents, and radioactive 

constituents. Naturally occurring isotopes were measured to 

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

ages of the sampled groundwater. In total, 207 constituents 

and water-quality indicators were measured for this study. 

This report describes the sampling, analytical, and qualityassurance methods used in the study and presents the results of 

the chemical analyses made of the groundwater samples.

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

and matrix spikes) were collected at up to 13 percent of 

the wells in the NSF-SA study unit, and the results for 

these samples were used to evaluate the quality of the 
References Cited 15

data for the groundwater samples. Blanks rarely contained 

detectable concentrations of any constituent, suggesting that 

contamination from sample collection procedures was not 

a significant source of bias in the data for the groundwater 

samples. Replicate samples generally were within the limits of 

acceptable analytical reproducibility. Matrix-spike recoveries 

were within the acceptable range (70 to 130 percent) for 

approximately 91 percent of the compounds.

In the grid-well samples, 1 detection of benzene 

was greater than the CDPH maximum contaminant level 

(MCL-CA), 1 detection of dieldrin was greater than the 

USGS Health-Based Screening Level (HBSL), 13 detections 

of manganese were greater than the HBSL, 7 detections of 

arsenic were greater than the USEPA maximum contaminant 

level (MCL-US), 2 detections of boron were greater than 

the HBSL, 2 detections of fluoride were greater than the 

MCL-CA, 2 detections of nitrate were greater than the 

MCL-US, and 2 detections of radon-222 were greater than 

the proposed MCL-US. The following constituents had 

concentrations greater than the CDPH secondary maximum 

contaminant level (SMCL-CA): 13 detections of iron, 

2 detections of chloride, 2 detections of sulfate (1 of which 

was also greater than the SMCL-CA upper benchmark), and 

15 detections of total dissolved solids (4 of which were also 

greater than the SMCL-CA upper benchmark).

Acknowledgments

The authors thank the following cooperators for their 

support: the California State Water Resources Control 

Board, California Department of Public Health, California 

Department of Water Resources, and Lawrence Livermore 

National Laboratory. We especially thank the well owners and 

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

collect samples from their wells.

References Cited

American Public Health Association, 1998, Standard 

methods for the examination of water and wastewater 

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

Association, American Water Works Association, and Water 

Environment Federation, p. 3-37–3-43.

American Society for Testing and Materials, 1998, Water 

and environmental technology, in Annual Book of ASTM 

Standards: Philadelphia, Pa., American Society for Testing 

and Materials, section 11.02 (Water II), p. 664–666.

Anderson, R.L., 1987, Practical statistics for analytical 

chemists: New York, Van Nostrand Reinhold Company, 

Inc., 315 p.

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

Bryant, and Johnson, Tyler, 2003, Framework for a 

groundwater quality monitoring and assessment program 

for California: U.S. Geological Survey Water-Resources 

Investigations Report 03–4166, 78 p.

Bullen, T.D., Krabbenhoft, D.P., and Kendall, Carol, 1996, 

Kinetic and mineralogic controls on the evolution of 

groundwater chemistry and 87Sr/86Sr in a sandy silicate 

aquifer, northern Wisconsin, USA: Geochimica et 

Cosmochimica Acta, v. 60, no. 10, p. 1807–1821.

California Department of Public Health, 2010, Drinking 

water notification levels and response levels—An 

overview: California Department of Public Health, 

accessed February 18, 2014, at http://www.cdph.ca.gov/

certlic/drinkingwater/Documents/Notificationlevels/

notificationlevels.pdf.

California Department of Public Health, 2011, Certificates and 

licenses—Drinking water systems—1,4-Dioxane, accessed 

February 18, 2014, at http://www.cdph.ca.gov/certlic/

drinkingwater/Pages/1,4-dioxane.aspx.

California Department of Public Health, 2013a, California 

regulations related to drinking water—Title 22: California 

Department of Public Health, accessed February 18, 

2014, at http://www.cdph.ca.gov/certlic/drinkingwater/

Documents/Lawbook/dwregulations-2013-07-01.pdf.

California Department of Public Health, 2013b, 

Certificates and licenses—Drinking water systems—

1,2,3-Trichloropropane, accessed February 18, 2014, 

at http://www.cdph.ca.gov/certlic/drinkingwater/

Pages/123TCP.aspx.

California Department of Public Health, 2014, Chromium-6 

drinking water MCL, accessed August 29, 2014, at http://

www.cdph.ca.gov/certlic/drinkingwater/Pages/Chromium6.

aspx.

California Department of Water Resources, 2003, California’s 

groundwater update 2003: California Department of Water 

Resources Bulletin 118, 246 p., accessed October 27, 

2011, at http://www.water.ca.gov/groundwater/bulletin118/

update2003.cfm.

California Department of Water Resources, 2004a, California’s 

groundwater—Individual basin descriptions, Alexander 

Valley, Alexander subbasin: California Department of 

Water Resources Bulletin 118, accessed August 6, 2013, at 

http://www.water.ca.gov/pubs/groundwater/bulletin_118/

basindescriptions/1-54.01.pdf.

California Department of Water Resources, 2004b, 

California’s groundwater—Individual basin descriptions, 

Alexander Valley groundwater basin, Cloverdale subbasin: 

California Department of Water Resources Bulletin 118, 

accessed August 6, 2013, at http://www.water.ca.gov/pubs/

groundwater/bulletin_118/basindescriptions/1-54.02.pdf.
16 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

California Department of Water Resources, 2004c, California’s 

groundwater—Individual basin descriptions, Lower Russian 

River Valley groundwater basin: California Department of 

Water Resources Bulletin 118, accessed August 6, 2013, at 

http://www.water.ca.gov/pubs/groundwater/bulletin_118/

basindescriptions/1-60.pdf.

California Department of Water Resources, 2004d, 

California’s groundwater—Individual basin descriptions, 

Santa Rosa Valley, Santa Rosa Plain subbasin: California 

Department of Water Resources Bulletin 118, accessed 

August 6, 2013, at http://www.water.ca.gov/pubs/

groundwater/bulletin_118/basindescriptions/1-55.01.pdf.

California Department of Water Resources, 2004e, California’s 

groundwater—Individual basin descriptions, Santa Rosa 

Valley, Healdsburg Area subbasin: California Department 

of Water Resources Bulletin 118, accessed August 6, 2013, 

at http://www.water.ca.gov/pubs/groundwater/bulletin_118/

basindescriptions/1-55.02.pdf.

California Department of Water Resources, 2004f, California’s 

groundwater—Individual basin descriptions, Santa Rosa 

Valley, Rincon Valley subbasin: California Department of 

Water Resources Bulletin 118, accessed August 6, 2013, at 

http://www.water.ca.gov/pubs/groundwater/bulletin_118/

basindescriptions/1-55.03.pdf.

California State Water Resources Control Board, 2003, 

Report to the Governor and Legislature, A comprehensive 

groundwater quality monitoring program for California: 

Assembly Bill 599, March 2003, 121 p., accessed 

October 27, 2011, at http://www.waterboards.ca.gov/gama/

docs/final_ab_599_rpt_to_legis_7_31_03.pdf.

California State Water Resources Control Board, 2009, 

Geotracker GAMA: State Water Resources Control 

Board database, accessed June 11, 2013, at 

https://geotracker.waterboards.ca.gov/gama/.

California State Water Resources Control Board, 2013, 

GAMA—Groundwater Ambient Monitoring and 

Assessment Program, accessed June 6, 2013, at http://www.

waterboards.ca.gov/water_issues/programs/gama/.

Cardwell, G.T., 1958, Geology and ground water in the 

Santa Rosa and Petaluma Valley areas, Sonoma County, 

California: U.S. Geological Survey Water-Supply 

Paper 1427, 273 p., 5 pls.

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

T.J., 1999, New reporting procedures based on longterm method-detection levels and some considerations 

for interpretations of water-quality data provided by the 

U.S. Geological Survey National Water Quality Laboratory: 

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

Clark, I.D., and Fritz, P., 1997, Environmental isotopes in 

hydrogeology: Boca Raton, Fla., CRC Press LLC, 328 p.

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

L.K., and Abney, S.R., 1998, Methods of analysis by 

the U.S. Geological Survey National Water Quality 

Laboratory—Determination of 86 volatile organic 

compounds in water by gas chromatography/mass 

spectrometry, including detections less than reporting limits: 

U.S. Geological Survey Open-File Report 97–829, 78 p.

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

oxygen isotopic abundances: Pure and Applied Chemistry, 

v. 66, p. 273–276.

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

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

Vocke, R.D., Jr., Revesz, K.M., Lamberty, A., Taylor, P., 

and DeBierve, P., 2002, Compilation of minimum and 

maximum isotope ratios of selected elements in naturally 

occurring terrestrial materials and reagents: U.S. Geological 

Survey Water-Resources Investigations Report 01–4222, 

98 p.

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

Improvements in the gaseous hydrogen-water equilibrium 

technique for hydrogen isotope analysis: Analytical 

Chemistry, v. 63, p. 910–912.

Donahue, D.J., Linick, T.W., and Jull, A.J.T., 1990, Isotoperatio and background corrections for accelerator mass 

spectrometry radiocarbon measurements: Radiocarbon, 

v. 32, book 2, p. 135–142.

Dwyer, G.S., and Vengosh, A., 2008, Alternative filament 

loading solution for accurate analysis of boron isotopes 

by negative thermal ionization mass spectrometry: Eos, 

Transactions, American Geophysical Union, v. 89, no. 53, 

abstract H51C-0824.

Epstein, Samuel, and Mayeda, T.K., 1953, Variation of O18

content of water from natural sources: Geochimica et 

Cosmochimica Acta, v. 4, p. 213–224.

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

U.S. Geological Survey National Water Quality 

Laboratory—Determination of metals in water by 

inductively coupled plasma-mass spectrometry: 

U.S. Geological Survey Open-File Report 92–634, 28 p.

Farrar, C.D., Metzger, L.F., Nishikawa, Tracy, Koczot, K.M., 

and Reichard, E.G., 2006, Geohydrological characterization, 

water-chemistry, and ground-water flow simulation model 

of the Sonoma Valley area, Sonoma County, California, with 

a section on Basement rock configuration interpreted from 

gravity data by Victoria E. Langenheim: U.S. Geological 

Survey Scientific Investigations Report 2006–5092, 167 p.
References Cited 17

Farrar, J.W., and Long, H.K., 1997, Report on the 

U.S. Geological Survey’s evaluation program for standard 

reference samples distributed in September 1996—T-143 

(trace constituents), T-145 (trace constituents), M-140 

(major constituents), N-51 (nutrient constituents), P-27 

(low ionic strength constituents), and Hg-23 (mercury): 

U.S. Geological Survey Open-File Report 97–20, 145 p.

Faure, Gunter, and Mensing, T.M., 2005, Isotopes—Principles 

and applications (3d ed.): Hoboken, New Jersey, John Wiley 

& Sons, Inc., 897 p.

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

U.S. Geological Survey National Water Quality 

Laboratory—Determination of inorganic and organic 

constituents in water and fluvial sediments: U.S. Geological 

Survey Open-File Report 93–125, 217 p.

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

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A1, 545 p.

Fram, M.S., Munday, Cathy, and Belitz, Kenneth, 2009, 

Groundwater quality data for the Tahoe–Martis study 

unit, 2007—Results from the California GAMA Program: 

U.S. Geological Survey Data Series 432, 88 p. (Also 

available at http://pubs.usgs.gov/ds/432/.)

Fram, M.S., Olsen, L.D., and Belitz, Kenneth, 2012, 

Evaluation of volatile organic compound (VOC) 

blank data and application of study reporting levels to 

groundwater data collected for the California GAMA 

Priority Basin Project, May 2004 through September 

2010: U.S. Geological Survey Scientific Investigations 

Report 2012–5139, 94 p.

Gagnon, A.R., and Jones, G.A., 1993, AMS-graphite target 

production methods at the Woods Hole Oceanographic 

Institution during 1986–1991: Radiocarbon, v. 35, book 

2, p. 301–310, https://journals.uair.arizona.edu/index.php/

radiocarbon/article/viewFile/18070/17800#page=65.

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

U.S. Geological Survey National Water Quality 

Laboratory—Determination of dissolved arsenic, boron, 

lithium, selenium, strontium, thallium, and vanadium 

using inductively coupled plasma-mass spectrometry: 

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

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

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

and soil samples using collision/reaction cell inductively 

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

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

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

P.A., Martin, J.D., Nakagaki, N., Nowell, L.H., Scott, 

J.C., Stackelberg, P.E., Thelin, G.P., and Wolock, D.M., 

2006, The quality of our Nation’s waters—Pesticides 

in the Nation’s streams and ground water, 1992–2001: 

U.S. Geological Survey Circular 1291, 172 p.

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

potentiometric titration, Part II: Analyst, v. 77, p. 661–671.

Hahn, G.J., and Meeker W.Q., 1991, Statistical intervals—A 

guide for practitioners: New York, John Wiley & Sons, 

392 p.

Hawaii Department of Health, 2005, Rules relating to 

public water systems: Hawaii Administrative Rules, 

Title 11, Chapter 20, 346 p., accessed April 30, 2014, at 

http://oeqc.doh.hawaii.gov/sites/har/AdmRules1/11-20.pdf.

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 4, chap. A3, 510 p. 

(Also available at http://water.usgs.gov/pubs/twri/twri4a3/.)

Hem, J.D., 1985, Study and interpretation of the chemical 

characteristics of natural water: U.S. Geological Survey 

Water-Supply Paper 2254, 263 p., 3 pls.

Hoaglin, D.C., 1983, Letter values—A set of selected order 

statistics, in Hoaglin, D.C., Mosteller, F., and Tukey, J.W., 

eds., Understanding robust and exploratory data analysis: 

New York, John Wiley & Sons, p. 33–54.

Hooker, E.P., Fulcher, K.G., and Gibb, H.J., 2012, Report 

to the Hawaii Department of Health, Safe Drinking 

Water Branch, regarding the human health risks of 

1,2,3-trichloropropane in tap water: Tetra Tech Services, 

101 p., accessed June 12, 2013, at http://eha-web.doh.

hawaii.gov/eha-cma/documents/fd65a6d2-73d1-4d5c-88c6-

97a47ba36650.

Johnson, T.D., and Belitz, Kenneth, 2014, California 

Groundwater Units: U.S. Geological Survey Data Series 

796, 34 p. (Also available at http://dx.doi.org/10.3133/

ds796.)

Johnson, T.D., and Belitz, Kenneth, in press, Domestic wells 

in California—Mapping their location and population 

served: Journal of Hydrology: Regional Studies.

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

Lovelace, J.K., and Maupin, M.A., 2009, Estimated use of 

water in the United States in 2005: U.S. Geological Survey 

Circular 1344, 52 p.
18 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

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

Groundwater data-collection protocols and procedures 

for the National Water-Quality Assessment Program—

Collection and documentation of water-quality samples 

and related data: U.S. Geological Survey Open-File 

Report 95–399, 113 p.

Krieger, H.L., and Whittaker, E.L., 1980, Prescribed 

procedures for measurement of radioactivity in drinking 

water: U.S. Environmental Protection Agency 

EPA-600-4-80-032, 142 p. (Also available as PB80-224744 

at http://www.ntis.gov.)

Kulongoski, J.T., and Belitz, K., 2004, Groundwater Ambient 

Monitoring and Assessment Program: U.S. Geological 

Survey Fact Sheet 2004–3088, 2 p.

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

Ground-water quality data in the North San Francisco Bay 

hydrologic provinces, California, 2004—Results from 

the California Ground-Water Ambient Monitoring and 

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

Data Series Report 167, 100 p.

Landon, M.K., Belitz, Kenneth, Jurgens, B.C., 

Kulongoski, J.T., and Johnson, T.D., 2010, Status and 

understanding of groundwater quality in the Central–

Eastside San Joaquin Basin, 2006—California GAMA 

Priority Basin Project: U.S. Geological Survey Scientific 

Investigations Report 2009–5266, 97 p.

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

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

Survey Techniques of Water-Resources Investigations, 

book 9, chap. A2, accessed October 27, 2011, at 

http://pubs.water.usgs.gov/twri9A2/.

Lewis, M.E., 2006, Dissolved oxygen (ver. 2.1): 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 9, chap. A6.2, accessed October 27, 

2011, at http://pubs.water.usgs.gov/twri9A6.2/.

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

Determination of low concentrations of acetochlor in 

water by automated solid-phase extraction and gas 

chromatography with mass selective detection: Journal of 

AOAC International, v. 79, no. 4, p. 962–966.

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

Methods of analysis by the U.S. Geological Survey 

National Water Quality Laboratory—A method supplement 

for the determination of fipronil and degradates in water by 

gas chromatography/mass spectrometry: U.S. Geological 

Survey Open-File Report 02–462, 11 p.

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

U.S. Geological Survey National Water Quality 

Laboratory: U.S. Geological Survey Open-File 

Report 2005–1263, accessed October 27, 2011, at 

http://pubs.usgs.gov/of/2005/1263/.

McCurdy, D.E., Garbarino, J.R., and Mullin, A.H., 2008, 

Interpreting and reporting radiological water-quality data: 

U.S. Geological Survey Techniques and Methods, book 5, 

chap. B6, 33 p.

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

Survey National Water Quality Laboratory—Determination 

of chromium in water by graphite furnace atomic absorption 

spectrophotometry: U.S. Geological Survey Open-File 

Report 93–449, 16 p.

McNichol, A.P., Gagnon, A.R., Jones, G.A., and Osborne, 

E.A., 1992, Illumination of a black box—Analysis of gas 

composition during graphite target preparation, in Long, A., 

and Kra, R.S., eds., Proceedings of the 14th International 

14C Conference: Radiocarbon, v. 34, book 3, p. 321–329.

McNichol, A.P., Jones, G.A., Hutton, D.L., and Gagnon, 

A.R., 1994, The rapid preparation of seawater ∑CO2 for 

radiocarbon analysis at the National Ocean Sciences AMS 

Facility: Radiocarbon, v. 36, book 2, p. 237–246.

Metzger, L.F., Farrar, C.D., Koczot, K.M., and Reichard, E.G., 

2006, Geohydrology and water chemistry of the Alexander 

Valley, Sonoma County, California: U.S. Geological Survey 

Scientific Investigations Report 2006–5115, 83 p.

Mueller, D.K., and Titus, C.J., 2005, Quality of nutrient data 

from streams and ground water sampled during water 

years 1992–2001: U.S. Geological Survey Scientific 

Investigations Report 2005–5106, 27 p.

Okamoto, H.S., Steeber, W.R., Remoy, R., Hill, P., and Perera, 

S.K., eds., 2002, Determination of 1,2,3-trichloropropane 

in drinking water by purge and trap gas chromatography/

mass spectrometry (February 2002): California Department 

of Health Services, Division of Drinking Water and 

Environmental Management, Sanitation and Radiation 

Laboratories Branch, accessed June 6, 1013, at 

http://www.cdph.ca.gov/certlic/drinkingwater/Documents/

Drinkingwaterlabs/TCPbyPT-GCMS.pdf.

Olsen, L.D., Fram, M.S., and Belitz, Kenneth, 2010, 

Review of trace-element field-blank data collected for 

the California Groundwater Ambient Monitoring and 

Assessment (GAMA) Program, May 2004–January 2008: 

U.S. Geological Survey Scientific Investigations 

Report 2009–5220, 47 p.
References Cited 19

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

by the U.S. Geological Survey National Water Quality 

Laboratory—Evaluation of alkaline persulfate digestion 

as an alternative to Kjeldahl digestion for determination 

of total and dissolved nitrogen and phosphorous in water: 

U.S. Geological Survey Water-Resources Investigations 

Report 03–4174, 33 p.

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

the U.S. Geological Survey National Water Quality 

Laboratory: U.S. Geological Survey Fact Sheet 026–98, 

4 p., accessed October 27, 2011, at 

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

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

electrical conductance (ver. 1.2): U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 9, chap. A6.3, accessed October 27, 2011, at 

http://pubs.water.usgs.gov/twri9A6.3/.

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

and Schroeder, M.P., 2001, Methods of analysis by 

the U.S. Geological Survey National Water Quality 

Laboratory—Determination of moderate-use pesticides 

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

extraction and gas chromatography/mass spectrometry: 

U.S. Geological Survey Water-Resources Investigations 

Report 01–4098, 70 p.

Schneider, R.J., Jones, G.A., McNichol, A.P., von Reden, K.F., 

Elder, K.A., Huang, K., and Kessel, E.D., 1994, 

Methods for data screening, flagging, and error analysis 

at the National Ocean Sciences AMS Facility: Nuclear 

Instruments and Methods in Physics Research, book 92, 

p. 172–175.

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

selection approaches for design of a ground-water-quality 

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

Investigations Report 90–4101, 109 p.

Shelton, J.L., Burow, K.R., Belitz, Kenneth, Dubrovsky, 

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

volatile organic compounds in active public supply wells as 

groundwater tracers in the Los Angeles physiographic basin, 

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

Investigations Report 01–4188, 29 p.

Soddy, F., 1913, Radioactivity: Annual Reports on the 

Progress of Chemistry, v. 10, p. 262–288.

State of California, 2001a, Assembly Bill No. 599, 

Chapter 522, accessed October 27, 2011, at 

http://www.swrcb.ca.gov/gama/docs/ab_599_

bill_20011005_chaptered.pdf.

State of California, 2001b, Groundwater Monitoring Act of 

2001: California Water Code, part 2.76, Sections 10780–

10782.3, accessed October 27, 2011, at http://www.leginfo.

ca.gov/cgi-bin/displaycode?section=wat&group=10001-

11000&file=10780-10782.3.

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

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

New York, John Wiley & Sons, 1022 p.

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

Methods for the determination of radioactive substances 

in water: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A5, 95 p.

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

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

Report 95–352, 120 p.

Toccalino, P.L., Norman, J.E., Booth, N.L., Thompson, J.L., 

and Zogorski, J.S., 2012, Health-Based Screening 

Levels—Benchmarks for evaluating water-quality data: 

U.S. Geological Survey, accessed February 19, 2014, at 

http://water.usgs.gov/nawqa/HBSL/.

U.S. Census Bureau, 1990, Census of population and 

housing, summary tape file 3A, accessed June 6, 2013, at 

ftp://ftp2.census.gov/census_1990/.

U.S. Environmental Protection Agency, 1989, 

1,2,3-Trichloropropane—Drinking water health advisory: 

Office of Water, 15 p., accessed February 18, 2014, at http://

nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=60001XkV.txt.

U.S. Environmental Protection Agency, 1999, National 

primary drinking water regulations, Radon-222: Federal 

Register, v. 64, no. 211, p. 59, 245–259, and 294.

U.S. Environmental Protection Agency, 2002, Guidelines 

for establishing procedures for the analysis of pollutants: 

U.S. Code of Federal Regulations, Title 40, 136 p.

U.S. Environmental Protection Agency, 2005, Method 331.0—

Determination of perchlorate in drinking water by liquid 

chromatography electrospray ionization mass spectrometry 

(Revision 1.0, January 2005): Office of Groundwater 

and Drinking Water, EPA Document #815-R-05-007, 

34 p., accessed October 27, 2011, at http://www.epa.gov/

safewater/methods/pdfs/methods/met331_0.pdf.

U.S. Environmental Protection Agency, 2012, 2012 Edition of 

the drinking water standards and health advisories, accessed 

February 18, 2014, at http://water.epa.gov/action/advisories/

drinking/upload/dwstandards2012.pdf.
20 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

U.S. Environmental Protection Agency, 2013, Technical fact 

sheet—1,2,3-Trichloropropane: Office of Solid Waste 

and Emergency Response, EPA 505-F-11-008, accessed 

February 18, 2014, at http://www2.epa.gov/sites/production/

files/2014-03/documents/ffrrofactsheet_contaminant_tcp_

january2014_final.pdf.

U.S. Geological Survey [variously dated], National 

field manual for the collection of water-quality data: 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 9, chap. A1–A9, accessed October 27, 

2011, at http://water.usgs.gov/owq/FieldManual/.

U.S. Geological Survey, 2006, National Elevation Dataset 

(NED): U.S. Geological Survey database, accessed 

October 27, 2011, at http://ned.usgs.gov/.

U.S. Geological Survey, 2009, Preferred method selection 

procedure, National Water Quality Laboratory website, 

accessed October 27, 2011, at http://wwwnwql.cr.usgs.gov/

dyn.shtml?Preferred_method_selection_procedure.

U.S. Geological Survey, 2013a, What is the Priority Basin 

Project?: California Water Science Center website, accessed 

June 6, 2013, at http://ca.water.usgs.gov/gama/.

U.S. Geological Survey, 2013b, California Groundwater 

Ambient Monitoring and Assessment (GAMA) Program 

Priority Basin Project—Shallow aquifer assessment: 

U.S. Geological Survey Fact Sheet 2012–3136, 2 p.

U.S. Geological Survey, 2013c, National Water 

Information System—Web interface, USGS water 

data for California, accessed June 6, 2013, at 

http://waterdata.usgs.gov/ca/nwis/.

U.S. Geological Survey, 2013d, Publications: California Water 

Science Center website, accessed June 6, 2013, at http://

ca.water.usgs.gov/gama/includes/GAMA_publications.html.

U.S. Geological Survey, 2013e, Branch of Quality 

Systems, Inorganic Blind Sample Project (IBSP) 

QADATA summaries, accessed June 6, 2013, at 

http://bqs.usgs.gov/ibsp/qadata.shtml.

U.S. Geological Survey, 2013f, Branch of Quality Systems, 

Inorganic Blind Sample Project (IBSP) NWQL control 

charts for fiscal year 2011 analytes, accessed June 6, 2013, 

at http://bqs.usgs.gov/ibsp/FY11charts.shtml.

Vengosh, A., Chivas, A.R., and McCulloch, M.T., 1989, Direct 

determination of boron and chlorine isotopes in geological 

materials by negative thermal ionization mass spectrometry: 

Chemical Geology, v. 79, p. 333–343.

Vogel, J.S., Nelson, D.E., and Southon, J.R., 1987, 14C 

background levels in an accelerator mass spectrometry 

system: Radiocarbon, v. 29, book 3, p. 323–333.

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

sealed water samples: Deep Sea Research, v. 15, p. 721–735.

Western Regional Climate Center, 2013, Western 

Regional Climate Center, Summary climate data 

for Northern California, average monthly precipitation 

data, accessed October 24, 2013, at 

http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca8351.

Wetzel, R.G., and Likens, G.E., 2000, Limnological analyses 

(3d ed.): New York, Springer, 429 p.

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

sampling (ver. 2.0): U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 9, chap. A3, accessed 

October 27, 2011, at http://pubs.water.usgs.gov/twri9A3/.

Wilde, F.D., 2006, Temperature (ver. 2): U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 9, chap. A6.1, accessed October 27, 2011, at 

http://pubs.water.usgs.gov/twri9A6.1/.

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

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

October 27, 2011, at http://pubs.water.usgs.gov/twri9A6.4/.

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

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

Techniques of Water-Resources Investigations, book 9, 

chap. A6.0, accessed October 27, 2011, at 

http://pubs.water.usgs.gov/twri9A6.0/.

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

1999, Collection of water samples: U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 9, chap. A4, accessed October 27, 2011, at 

http://pubs.water.usgs.gov/twri9A4/.

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

2004, Processing of water samples: U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 9, chap. A5, accessed October 27, 2011, at 

http://pubs.water.usgs.gov/twri9A5/.

Wright, M.T., Belitz, Kenneth, and Burton, C.A., 2005, 

California GAMA Program—Ground-water quality in the 

San Diego Drainages hydrogeologic province, California, 

2004: U.S. Geological Survey Data Series 129, 91 p. (Also 

available at http://pubs.usgs.gov/ds/2005/129.)

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

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

Survey National Water Quality Laboratory—Determination 

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

capillary-column gas chromatography/mass spectrometry: 

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

Zogorski, J.S., Carter, J.M., Ivahnenko, T., Lapham, W.W., 

Moran, M.J., Rowe, B.L., Squillace, P.J., and 

Toccalino, P.L., 2006, Volatile organic compounds in the 

Nation’s ground water and drinking-water supply wells: 

U.S. Geological Survey Circular 1292, 101 p.
Tables Tables 21

Table 1. Identification, sampling, construction, and water-level information for wells sampled for the North San Francisco Bay Shallow 

Aquifer study unit, California GAMA Priority Basin Project, April to August 2012.

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

American Vertical Datum 1988 (NAVD 88). GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands 

study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study area understanding well; S-NSF-VP, North San Francisco 

Bay Shallow Aquifer study unit Valley and Plains study area well. Other abbreviations: ft, feet; na, not available]

Sampling information Construction information1 Depth to 

water 

level 

(ft below LSD)

GAMA well 

identification 

number

Date 

sampled 

(mm/dd/ yyyy)

Well 

type

Altitude 

of LSD 

(ft above NAVD 88)

Well 

depth 

(ft below LSD)

Depth to top 

perforation 

(ft below LSD)

Depth to bottom 

perforation 

(ft below LSD)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)

Highlands study area wells (40 wells sampled)

S-NSF-H01 7/23/2012 Production 1,073 80 na na 17.16

S-NSF-H02 7/23/2012 Production 65 30 11 30 16.88

S-NSF-H03 7/16/2012 Spring 1,175 at LSD at LSD at LSD na

S-NSF-H04 7/17/2012 Production 801 240 80 240 na

S-NSF-H05 7/25/2012 Production 1,150 160 60 160 41.45

S-NSF-H06 7/30/2012 Production 1,254 na na na 127.80

S-NSF-H07 7/30/2012 Production 1,144 200 60 200 36.30

S-NSF-H08 8/2/2012 Production 1,781 300 201 299 na

S-NSF-H09 8/2/2012 Production 387 141 61 141 70.37

S-NSF-H10 8/1/2012 Production 1,366 168 80 168 122.51

S-NSF-H11 6/19/2012 Production 226 22 11 22 11.81

S-NSF-H12 7/16/2012 Spring 710 at LSD at LSD at LSD na

S-NSF-H13 7/24/2012 Production 77 na na na 12.22

S-NSF-H14 7/24/2012 Production 90 104 60 104 12.21

S-NSF-H15 6/18/2012 Production 99 116 na na 8.05

S-NSF-H16 4/25/2012 Production 231 315 115 315 na

S-NSF-H17 4/23/2012 Production 232 180 60 180 31.97

S-NSF-H18 7/18/2012 Production 111 98 58 98 17.81

S-NSF-H19 8/23/2012 Spring 315 at LSD at LSD at LSD na

S-NSF-H20 8/21/2012 Production 1,872 170 30 170 57.53

S-NSF-H21 7/31/2012 Production 490 270 110 270 na

S-NSF-H22 7/11/2012 Production 1,071 240 160 240 na

S-NSF-H23 6/13/2012 Production 482 92 70 92 34.20

S-NSF-H24 7/31/2012 Unused 461 382 112 382 71.18

S-NSF-H25 7/12/2012 Spring 1,571 at LSD at LSD at LSD na

S-NSF-H26 4/18/2012 Production 89 189 na na 79.25

S-NSF-H27 8/30/2012 Production 103 26 na na na

S-NSF-H28 6/20/2012 Production 263 102 na na 64.55

S-NSF-H29 7/10/2012 Production 1,022 480 80 480 na

S-NSF-H30 8/20/2012 Production 672 345 na na 2

 229.24

S-NSF-H31 8/22/2012 Production 1,099 74 34 74 na

S-NSF-H32 7/2/2012 Production 1,125 550 210 550 na

S-NSF-H33 7/11/2012 Production 803 529 389 529 na

S-NSF-H34 4/11/2012 Production 371 155 40 155 7.30

S-NSF-H35 4/10/2012 Production 175 190 40 190 56.54
22 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Table 1. Identification, sampling, construction, and water-level information for wells sampled for the North San Francisco Bay Shallow 

Aquifer study unit, California GAMA Priority Basin Project, April to August 2012.—Continued

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

American Vertical Datum 1988 (NAVD 88). GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands 

study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study area understanding well; S-NSF-VP, North San Francisco 

Bay Shallow Aquifer study unit Valley and Plains study area well. Other abbreviations: ft, feet; na, not available]

Sampling information Construction information1 Depth to 

water 

level 

(ft below LSD)

GAMA well 

identification 

number

Date 

sampled 

(mm/dd/ yyyy)

Well 

type

Altitude 

of LSD 

(ft above NAVD 88)

Well 

depth 

(ft below LSD)

Depth to top 

perforation 

(ft below LSD)

Depth to bottom 

perforation 

(ft below LSD)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued

Highlands study area wells (40 wells sampled)—Continued

S-NSF-H36 4/17/2012 Production 1,264 400 180 400 103.73

S-NSF-H37 8/23/2012 Production 1,230 345 20 345 na

S-NSF-H38 6/14/2012 Production 648 275 200 275 132.31

S-NSF-H39 6/20/2012 Production 582 620 420 620 183.26

S-NSF-H40 7/19/2012 Production 185 175 40 175 na

Valley and Plains study area wells (30 wells sampled)

S-NSF-VP01 6/18/2012 Production 38 64 24 64 na

S-NSF-VP02 4/24/2012 Production 117 80 40 80 na

S-NSF-VP03 4/25/2012 Production 85 87 27 87 11.76

S-NSF-VP04 4/23/2012 Production 79 217 204 214 60.48

S-NSF-VP05 6/11/2012 Production 104 160 140 160 29.07

S-NSF-VP06 8/22/2012 Production 63 90 30 90 16.12

S-NSF-VP07 8/1/2012 Production 267 360 100 360 87.72

S-NSF-VP08 6/11/2012 Production 161 147 107 147 72.55

S-NSF-VP09 8/22/2012 Production 95 200 40 200 20.14

S-NSF-VP10 6/19/2012 Production 123 134 74 134 15.69

S-NSF-VP11 4/24/2012 Production 142 183 83 183 na

S-NSF-VP12 4/18/2012 Production 159 280 100 280 na

S-NSF-VP13 4/26/2012 Production 60 620 440 620 73.57

S-NSF-VP14 6/13/2012 Production 210 68 60 68 21.81

S-NSF-VP15 7/13/2012 Unused 173 80 38 44 17.02

S-NSF-VP16 7/25/2012 Production 236 107 87 107 37.62

S-NSF-VP17 6/12/2012 Production 150 50 20 50 21.70

S-NSF-VP18 7/26/2012 Production 308 28 8 28 17.53

S-NSF-VP19 8/23/2012 Production 213 200 60 200 82.30

S-NSF-VP20 7/17/2012 Production 543 157 57 157 56.15

S-NSF-VP21 8/22/2012 Production 201 755 395 755 255.24

S-NSF-VP22 7/10/2012 Production 53 250 90 250 27.70

S-NSF-VP23 7/9/2012 Production 107 500 80 500 na

S-NSF-VP24 7/26/2012 Production 94 201 95 205 na

S-NSF-VP25 4/19/2012 Production 36 80 na na 24.57

S-NSF-VP26 4/9/2012 Production 41 150 40 150 24.45

S-NSF-VP27 4/9/2012 Production 44 190 30 190 9.64

S-NSF-VP28 4/11/2012 Production 83 255 77 255 10.93

S-NSF-VP29 4/12/2012 Production 161 455 180 455 49.71
Tables 23

Table 1. Identification, sampling, construction, and water-level information for wells sampled for the North San Francisco Bay Shallow 

Aquifer study unit, California GAMA Priority Basin Project, April to August 2012.—Continued

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

American Vertical Datum 1988 (NAVD 88). GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands 

study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study area understanding well; S-NSF-VP, North San Francisco 

Bay Shallow Aquifer study unit Valley and Plains study area well. Other abbreviations: ft, feet; na, not available]

Sampling information Construction information1 Depth to 

water 

level 

(ft below LSD)

GAMA well 

identification 

number

Date 

sampled 

(mm/dd/ yyyy)

Well 

type

Altitude 

of LSD 

(ft above NAVD 88)

Well 

depth 

(ft below LSD)

Depth to top 

perforation 

(ft below LSD)

Depth to bottom 

perforation 

(ft below LSD)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued

Valley and Plains study area wells (30 wells sampled)—Continued

S-NSF-VP30 8/21/2012 Production 273 410 60 410 42.83

North San Francisco Bay Shallow Aquifer study unit understanding well (1 well sampled)

S-NSF-HU30 8/20/2012 Production 592 47 na na na

1

 Some wells may have multiple perforation intervals; only the shallowest and deepest perforations are listed for those wells.

2

 Water-level measurement for this well was taken on 6/20/2012 and may not be representative of the water level in the well at the time of sampling. 

Table 2. Classes of chemical constituents and field water-quality indicators collected for the North San Francisco Bay Shallow Aquifer 

study unit, California GAMA Priority Basin Project, April to August 2012.

[na, not applicable]

Constituent classes Constituent list table Results table

Field water-quality indicators 

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

Field alkalinity, bicarbonate, and carbonate na 4

Organic constituents

Volatile organic compounds (VOCs) 3A 5

Pesticides and pesticide degradates 3B 6

Constituents of special interest

Perchlorate 3C 7

1,2,3-Trichloropropane 3C 7

Inorganic constituents

Trace elements 3D 8

Nutrients 3E 9

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

Laboratory alkalinity, bicarbonate, and carbonate 3F 4

Isotopic tracers

Stable isotopes of hydrogen and oxygen in water 3G 11

Stable isotopes of carbon in dissolved inorganic carbon and carbon-14 abundance 3G 11

Stable isotopes of boron in water 3G 11

Stable isotopes of strontium in water 3G 11

Radioactive constituents

Radon-222 3G 12

Gross alpha and gross beta radioactivity (72-hour and 30-day counts) 3G 12

Tritium 3G 12
Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparison benchmarks, and reporting information for the U.S. Geological S

Water Quality Laboratory (NWQL) Schedule 2020. [The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. LRL, benchmark type, and benchmark level as of August 30, 2012. Benchm

level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HScreening Level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; MCL-HI, Hawaii Dcontaminant level; NL-CA, CDPH notification level; HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; RSD5-US, USEPA risk-specific 

Other abbreviations: CAS, Chemical Abstracts Service; CASRN®, Chemical Abstracts Service Registry Number®; LRL, laboratory reporting level; SRL, study reporting level; 

D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; —, not detected] Constituent (synonym or abbreviation) Primary use or source USGS parameter code CASRN® 1 LRL (μg/L) Benchmark type 2 

Acetone Solvent 81552 67-64-1 3.4 HBSL (na) Acrylonitrile Organic synthesis 34215 107-13-1 0.48 HBSL (RSD5-US) tert-Amyl methyl ether (TAME) Gasoline oxygenate 50005 994-05-8 0.06 na Benzene Gasoline hydrocarbon 34030 71-43-2 0.026 MCL-CA 

Bromobenzene Solvent 81555 108-86-1 0.022 HBSL (HAL-US) 

Bromochloromethane Fire retardant 77297 74-97-5 0.06 HBSL (HAL-US) 

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

Bromoform (Tribromomethane) Disinfection byproduct (THM) 32104 75-25-2 0.1 MCL-US Bromomethane (Methyl bromide) Fumigant 34413 74-83-9 0.2 HBSL (HAL-US) 

n-Butylbenzene Gasoline hydrocarbon 77342 104-51-8 0.08 NL-CA sec-Butylbenzene Gasoline hydrocarbon 77350 135-98-8 0.034 NL-CA tert-Butylbenzene Gasoline hydrocarbon 77353 98-06-6 0.06 NL-CA Carbon disulfide Organic synthesis 77041 75-15-0 0.1 HBSL (NL-CA) 

Carbon tetrachloride (Tetrachloromethane) Solvent 32102 56-23-5 0.06 MCL-CA 

Chlorobenzene Solvent 34301 108-90-7 0.026 MCL-CA 

Chloroethane Solvent 34311 75-00-3 0.06 na 

Chloroform (Trichloromethane) Disinfection byproduct (THM) 32106 67-66-3 0.03 MCL-US 

Chloromethane Solvent 34418 74-87-3 0.1 na 3-Chloropropene Organic synthesis 78109 107-05-1 0.08 na 2-Chlorotoluene Solvent 77275 95-49-8 0.028 HBSL (NL-CA) 4-Chlorotoluene Solvent 77277 106-43-4 0.042 HBSL (NL-CA) Dibromochloromethane Disinfection byproduct (THM) 32105 124-48-1 0.12 MCL-US 1,2-Dibromo-3-chloropropane (DBCP) Fumigant 82625 96-12-8 0.4 MCL-US 1,2-Dibromoethane (EDB) Fumigant 77651 106-93-4 0.028 MCL-US Dibromomethane Solvent 30217 74-95-3 0.05 na 

1,2-Dichlorobenzene Solvent 34536 95-50-1 0.028 MCL-US 
Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparison benchmarks, and reporting information for the U.S. Geological SWater Quality Laboratory (NWQL) Schedule 2020.—Continued[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. LRL, benchmark type, and benchmark level as of August 30, 2012. Benchmlevel benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HScreening Level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; MCL-HI, Hawaii Dcontaminant level; NL-CA, CDPH notification level; HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; RSD5-US, USEPA risk-specific 

Other abbreviations: CAS, Chemical Abstracts Service; CASRN®, Chemical Abstracts Service Registry Number®; LRL, laboratory reporting level; SRL, study reporting level; 

D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent 

(synonym or abbreviation)

Primary use 

or source

USGS 

parameter 

code

CASRN® 1 LRL (μg/L) Benchmark type 2 

1,3-Dichlorobenzene Solvent 34566 541-73-1 0.024 HBSL (HAL-US) 

1,4-Dichlorobenzene Fumigant 34571 106-46-7 0.026 MCL-CA trans-1,4-Dichloro-2-butene Organic synthesis 73547 110-57-6 2 na 

Dichlorodifluoromethane (CFC-12) Refrigerant 34668 75-71-8 0.1 HBSL (NL-CA) 1,1-Dichloroethane (1,1-DCA) Solvent 34496 75-34-3 0.044 MCL-CA 

1,2-Dichloroethane (1,2-DCA) Solvent 32103 107-06-2 0.08 MCL-CA 1,1-Dichloroethene (1,1-DCE) Organic synthesis 34501 75-35-4 0.022 MCL-CA cis-1,2-Dichloroethene (cis-1,2-DCE) Solvent 77093 156-59-2 0.022 MCL-CA trans-1,2-Dichloroethene (trans-1,2-DCE) Solvent 34546 156-60-5 0.018 MCL-CA 

1,2-Dichloropropane Fumigant 34541 78-87-5 0.026 MCL-US 1,3-Dichloropropane Fumigant 77173 142-28-9 0.06 na 2,2-Dichloropropane Fumigant 77170 594-20-7 0.06 na 1,1-Dichloropropene Organic synthesis 77168 563-58-6 0.04 na 

cis-1,3-Dichloropropene Fumigant 34704 10061-01-5 0.1 MCL-CA trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.14 MCL-CA Diethyl ether Solvent 81576 60-29-7 0.1 HBSL (na) Diisopropyl ether (DIPE) Gasoline oxygenate 81577 108-20-3 0.06 na 

Ethylbenzene Gasoline hydrocarbon 34371 100-41-4 0.036 MCL-CA Ethyl tert-butyl ether (ETBE) Gasoline oxygenate 50004 637-92-3 0.032 na Ethyl methacrylate Organic synthesis 73570 97-63-2 0.2 na o-Ethyl toluene (1-Ethyl-2-methyl benzene) Gasoline hydrocarbon 77220 611-14-3 0.032 na 

Hexachlorobutadiene Organic synthesis 39702 87-68-3 0.08 HBSL (RSD5-US) Hexachloroethane Solvent 34396 67-72-1 0.1 HBSL (HAL-US) 

2-Hexanone (n-Butyl methyl ketone) Solvent 77103 591-78-6 0.4 HBSL (na) Iodomethane (Methyl iodide) Organic synthesis 77424 74-88-4 0.26 na Isopropylbenzene Gasoline hydrocarbon 77223 98-82-8 0.042 HBSL (NL-CA) 
Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparison benchmarks, and reporting information for the U.S. Geological SWater Quality Laboratory (NWQL) Schedule 2020.—Continued [The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. LRL, benchmark type, and benchmark level as of August 30, 2012. Benchmlevel benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HScreening Level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; MCL-HI, Hawaii Dcontaminant level; NL-CA, CDPH notification level; HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; RSD5-US, USEPA risk-specific 

Other abbreviations: CAS, Chemical Abstracts Service; CASRN®, Chemical Abstracts Service Registry Number®; LRL, laboratory reporting level; SRL, study reporting level; 

D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; —, not detected] Constituent (synonym or abbreviation) Primary use or source USGS parameter code CASRN® 1 LRL (μg/L) Benchmark type 2 

4-Isopropyl-1-methyl benzene Gasoline hydrocarbon 77356 99-87-6 0.06 na Methyl acrylate Organic synthesis 49991 96-33-3 0.8 na Methyl acrylonitrile Organic synthesis 81593 126-98-7 0.26 HBSL (na) Methyl tert-butyl ether (MTBE) Gasoline oxygenate 78032 1634-04-4 0.1 MCL-CA 

Methyl iso-butyl ketone (MIBK) Solvent 78133 108-10-1 0.32 NL-CA Methylene chloride (Dichloromethane) Solvent 34423 75-09-2 0.04 MCL-US Methyl ethyl ketone (2-butanone, MEK) Solvent 81595 78-93-3 1.6 HBSL (HAL-US) 4

Methyl methacrylate Organic synthesis 81597 80-62-6 0.22 HBSL (na) Naphthalene Gasoline hydrocarbon 34696 91-20-3 0.18 HBSL (NL-CA) 

Perchloroethene (PCE, Tetrachloroethene) Solvent 34475 127-18-4 0.026 MCL-US 

n-Propylbenzene Solvent 77224 103-65-1 0.036 NL-CA Styrene Gasoline hydrocarbon 77128 100-42-5 0.042 MCL-US 

1,1,1,2-Tetrachloroethane Solvent 77562 630-20-6 0.04 HBSL (HAL-US) 

1,1,2,2-Tetrachloroethane Solvent 34516 79-34-5 0.14 MCL-CA Tetrahydrofuran Solvent 81607 109-99-9 1.4 na 1,2,3,4-Tetramethylbenzene Gasoline hydrocarbon 49999 488-23-3 0.1 na 1,2,3,5-Tetramethylbenzene Gasoline hydrocarbon 50000 527-53-7 0.08 na Toluene Gasoline hydrocarbon 34010 108-88-3 0.018 MCL-CA 

1,2,3-Trichlorobenzene Organic synthesis 77613 87-61-6 0.06 na 1,2,4-Trichlorobenzene Solvent 34551 120-82-1 0.08 MCL-CA 1,1,1-Trichloroethane (1,1,1-TCA) Solvent 34506 71-55-6 0.03 MCL-US 1,1,2-Trichloroethane (1,1,2-TCA) Solvent 34511 79-00-5 0.046 MCL-US 

Trichloroethene (TCE) Solvent 39180 79-01-6 0.022 MCL-US 

Trichlorofluoromethane (CFC-11) Refrigerant 34488 75-69-4 0.06 MCL-CA 

1,2,3-Trichloropropane (1,2,3-TCP) Solvent/organic synthesis 77443 96-18-4 0.12 MCL-HI 5 (NL-CA) 

Trichlorotrifluoroethane (CFC-113) Refrigerant 77652 76-13-1 0.022 MCL-CA 
Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparison benchmarks, and reporting information for the U.S. Geological SWater Quality Laboratory (NWQL) Schedule 2020.—Continued[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. LRL, benchmark type, and benchmark level as of August 30, 2012. Benchmlevel benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HScreening Level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; MCL-HI, Hawaii Dcontaminant level; NL-CA, CDPH notification level; HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; RSD5-US, USEPA risk-specific 

Other abbreviations: CAS, Chemical Abstracts Service; CASRN®, Chemical Abstracts Service Registry Number®; LRL, laboratory reporting level; SRL, study reporting level; 

D, detected in groundwater samples (table 5); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent 

(synonym or abbreviation)

Primary use 

or source

USGS 

parameter 

code

CASRN® 1 LRL (μg/L) Benchmark type 2 

1,2,3-Trimethylbenzene Gasoline hydrocarbon 77221 526-73-8 0.06 na 1,2,4-Trimethylbenzene Gasoline hydrocarbon 77222 95-63-6 0.032 NL-CA 1,3,5-Trimethylbenzene Organic synthesis 77226 108-67-8 0.032 NL-CA Vinyl bromide (Bromoethene) Fire retardant 50002 593-60-2 0.12 na Vinyl chloride (Chloroethene) Organic synthesis 39175 75-01-4 0.06 MCL-CA m- plus p-Xylene Gasoline hydrocarbon 85795 108-38-3 / 106-42-3 0.08 MCL-CA 

o-Xylene Gasoline hydrocarbon 77135 95-47-6 0.032 MCL-CA 

1 This report contains CASRNs®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs® through CAS Clien2 Constituents with HBSLs also can have other non-regulatory, health-based benchmarks. The type and value of these other benchmarks are shown in parentheses.3 Detected above MCL-CA.4 The MCL-US benchmark for trihalomethanes is the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.5 Currently (2014) Hawaii is the only jurisdiction that has an enforcable maximum contaminant level for 1,2,3-TCP (Hooker and others, 2012).6 The MCL-CA benchmark for m- plus p-xylene and o-xylene is the sum of all three xylene compounds.
28 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

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

USGS National Water Quality Laboratory Schedule 2003.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. LRL, benchmark type, and benchmark level as of August 30, 

2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the 

MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS Health-Based Screening Level; MCL-CA, California Department of Public Health (CDPH) 

maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; HAL-US, U.S. Environmental Protection Agency 

(USEPA) lifetime health advisory level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. Other abbreviations: CASRN®, Chemical Abstracts Service 

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

Constituent 

(synonym or abbreviation)

Primary use 

or source

USGS 

parameter 

code

CASRN® LRL 

(μg/L)

Benchmark 

type 1

Benchmark 

level 

(μg/L) 1

Detection

Acetochlor Herbicide 49260 34256-82-1 0.01 HBSL (na) 10 (na) —

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

Atrazine Herbicide 39632 1912-24-9 0.008 MCL-CA 1 D

Azinphos-methyl Insecticide 82686 86-50-0 0.12 HBSL (na) 10 (na) — (2)

Azinphos-methyl oxon Insecticide degradate 61635 961-22-8 0.042 na na — (2)

Benfluralin Herbicide 82673 1861-40-1 0.014 HBSL (na) 4 (na) — (2)

Carbaryl Insecticide 82680 63-25-2 0.06 HBSL 3 (RSD5-US) 400 (400) —

2-Chloro-2,6-

diethylacetanilide 

Herbicide degradate 61618 6967-29-9 0.01 na na —

4-Chloro-2-methylphenol Herbicide degradate 61633 1570-64-5 0.008 na na — (2)

Chlorpyrifos Insecticide 38933 2921-88-2 0.0036 HBSL (HAL-US) 2 (2) —

Chlorpyrifos oxon Insecticide degradate 61636 5598-15-2 0.08 HBSL (na) 0.8 (na) — (2)

Cyfluthrin Insecticide 61585 68359-37-5 0.016 HBSL (na) 200 (na) — (2)

Cypermethrin Insecticide 61586 52315-07-8 0.02 HBSL (na) 40 (na) — (2)

Dacthal (DCPA) Herbicide 82682 1861-32-1 0.0076 HBSL (HAL-US) 70 (70) —

Deethylatrazine (2-Chloro4-isopropylamino-6-

amino-s-triazine)

Herbicide degradate 04040 6190-65-4 0.006 na na D (2)

Desulfinylfipronil Insecticide degradate 62170 na 0.012 na na —

Desulfinylfipronil amide Insecticide degradate 62169 na 0.029 na na —

Diazinon Insecticide 39572 333-41-5 0.006 HBSL (NL-CA) 1 (1.2) —

3,4-Dichloroaniline Herbicide degradate 61625 95-76-1 0.006 na na D

Dichlorvos Insecticide 38775 62-73-7 0.04 na na — (2)

Dicrotophos Insecticide 38454 141-66-2 0.08 HBSL (na) 0.05 (na) — (2)

Dieldrin Insecticide 39381 60-57-1 0.008 HBSL (RSD5-US) 0.02 (0.02) D

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

Dimethoate Insecticide 82662 60-51-5 0.006 HBSL (na) 2 (na) — (2)

Ethion Insecticide 82346 563-12-2 0.01 HBSL (na) 4 (na) — (2)

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

2-Ethyl-6-methylaniline Herbicide degradate 61620 24549-06-2 0.01 na na —

Fenamiphos Insecticide 61591 22224-92-6 0.03 HBSL (HAL-US) 0.7 (0.7) —

Fenamiphos sulfone Insecticide degradate 61645 31972-44-8 0.054 na na —

Fenamiphos sulfoxide Insecticide degradate 61646 31972-43-7 0.08 na na — (2)

Fipronil Insecticide 62166 120068-37-3 0.018 HBSL (na) 0.1 (na) —

Fipronil sulfide Insecticide degradate 62167 120067-83-6 0.012 na na D

Fipronil sulfone Insecticide degradate 62168 120068-36-2 0.024 na na —

Fonofos Insecticide 04095 944-22-9 0.0048 HBSL (HAL-US) 10 (10) —

Hexazinone Herbicide 04025 51235-04-2 0.012 HBSL (HAL-US) 400 (400) — (2)
Tables 29

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

USGS National Water Quality Laboratory Schedule 2003.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. LRL, benchmark type, and benchmark level as of August 30, 

2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the 

MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS Health-Based Screening Level; MCL-CA, California Department of Public Health (CDPH) 

maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; HAL-US, U.S. Environmental Protection Agency 

(USEPA) lifetime health advisory level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. Other abbreviations: CASRN®, Chemical Abstracts Service 

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

Constituent 

(synonym or abbreviation)

Primary use 

or source

USGS 

parameter 

code

CASRN® LRL 

(μg/L)

Benchmark 

type 1

Benchmark 

level 

(μg/L) 1

Detection

Iprodione Fungicide 61593 36734-19-7 0.014 HBSL (na) 80 (na) — (2)

Isofenphos Insecticide 61594 25311-71-1 0.008 HBSL (na) 6 (na) —

Malaoxon Insecticide degradate 61652 1634-78-2 0.022 na na —

Malathion Insecticide 39532 121-75-5 0.016 HBSL (HAL-US) 500 (500) —

Metalaxyl Fungicide 61596 57837-19-1 0.014 HBSL (na) 500 (na) —

Methidathion Insecticide 61598 950-37-8 0.012 HBSL (na) 1 (na) —

Metolachlor Herbicide 39415 51218-45-2 0.02 HBSL (HAL-US) 700 (700) —

Metribuzin Herbicide 82630 21087-64-9 0.012 HBSL (HAL-US) 90 (70) —

Myclobutanil Fungicide 61599 88671-89-0 0.01 HBSL (na) 200 (na) —

1-Naphthol Insecticide degradate 49295 90-15-3 0.036 na na — (2)

Paraoxon-methyl Insecticide degradate 61664 950-35-6 0.014 na na — (2)

Parathion-methyl Insecticide 82667 298-00-0 0.008 HBSL (HAL-US) 1 (1) —

Pendimethalin Herbicide 82683 40487-42-1 0.012 HBSL (na) 20 (na) —

cis-Permethrin Insecticide 82687 54774-45-7 0.01 HBSL (na) 400 (na) — (2)

Phorate Insecticide 82664 298-02-2 0.02 HBSL (na) 4 (na) — (2)

Phorate oxon Insecticide degradate 61666 2600-69-3 0.027 na na —

Phosmet Insecticide 61601 732-11-6 0.08 HBSL (na) 4 (na) — (2)

Phosmet oxon Insecticide degradate 61668 3735-33-9 0.0511 na na — (2)

Prometon Herbicide 04037 1610-18-0 0.012 HBSL (HAL-US) 400 (400) D (2)

Prometryn Herbicide 04036 7287-19-6 0.01 HBSL (na) 300 (na) —

Pronamide (Propyzamide) Herbicide 82676 23950-58-5 0.0036 HBSL (RSD5-US) 10 (10) —

Simazine Herbicide 04035 122-34-9 0.006 MCL-US 4 D

Tebuthiuron Herbicide 82670 34014-18-1 0.028 HBSL (HAL-US) 1,000 (500) D

Terbufos Insecticide 82675 13071-79-9 0.018 HBSL (HAL-US) 0.4 (0.4) — (2)

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 0.045 na na — (2)

Terbuthylazine Herbicide 04022 5915-41-3 0.008 HBSL (na) 2 (na) —

Tribufos Defoliant 61610 78-48-8 0.018 HBSL (na) 7 (na) — (2)

Trifluralin Herbicide 82661 1582-09-8 0.018 HBSL (HAL-US) 20 (10) —

1

 Constituents with HBSLs also can have other non-regulatory, health-based benchmarks. The type and value of these other benchmarks are shown in 

parentheses.

2

 One or more median matrix-spike recoveries were less than 70 percent. Low recoveries may indicate that the compound might not have been detected in some 

samples if it was present at very low concentrations.

3

 An HBSL range of 40 to 4,000 μg/L is defined; 400 μg/L is selected as the comparison benchmark in this report.
30 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Table 3C. Constituents of special interest, primary uses or source, comparison benchmarks, and reporting information for analyses 

performed by Weck Laboratories, Inc. (Weck), City of Industry, California.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. MRL, benchmark type, and benchmark level as of August 30, 

2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when 

the MCL-CA is lower than the MCL-US or no MCL-US exists. MCL-CA, California Department of Public Health maximum contaminant level. MCL-HI, 

Hawaii Department of Health maximum contaminant level. Other abbreviations: CASRN®, Chemical Abstracts Service Registry Number®; MRL, minimum 

reporting level; D, detected in groundwater samples (table 7); μg/L, micrograms per liter; —, not detected] 

Constituent 

(synonym or 

abbreviation)

Primary use 

or source

USGS 

parameter 

code

CASRN® MRL 

(μg/L)

Benchmark 

type

Benchmark 

level 

(μg/L)

Detection

Perchlorate Rocket fuel, fireworks, 

flares, natural

63790 14797-73-0 0.10 MCL-CA 6 D

1,2,3-Trichloropropane Fumigant, solvent 77443 96-18-4 0.005 MCL-HI 1 0.6 —

1

 Currently (2014) Hawaii is the only jurisdiction that has an enforcable maximum contaminant level for 1,2,3-TCP (Hooker and others, 2012). Previous 

GAMA-PBP reports used the NL-CA of 0.005 μg/L or the HAL-US of 40 μg/L (no longer in existance as of 2006) as the comparison benchmark.

Table 3D. Trace elements, comparison benchmarks, and reporting information for the U.S. Geological Survey (USGS) National Water 

Quality Laboratory (NWQL) Schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. LRL, benchmark type, and benchmark level as of August 30, 

2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when 

the MCL-CA is lower than the MCL-US or no MCL-US exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS HealthBased Screening Level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant 

level; NL-CA, CDPH notification level; HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; SMCL-CA, CDPH secondary 

maximum contaminant level. Other abbreviations: CASRN®, Chemical Abstracts Service Registry Number®; LT-MDL, long-term method detection limit; 

D, detected in groundwater samples (table 8); na, not available; μg/L, micrograms per liter]

Constituent USGS 

parameter code CASRN® LT-MDL 

(μg/L)

Benchmark 

type 1

Benchmark level 

(μg/L) 1 Detection

Aluminum 01106 7429-90-5 2.2 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.027 MCL-US 6 D

Arsenic 01000 7440-38-2 0.03 MCL-US 10 D

Barium 01005 7440-39-3 0.07 MCL-CA 1,000 D

Beryllium 01010 7440-41-7 0.006 MCL-US 4 D

Boron 01020 7440-42-8 3 HBSL (NL-CA) 6,000 (1,000) D

Cadmium 01025 7440-43-9 0.016 MCL-US 5 D

Chromium 01030 7440-47-3 0.07 MCL-CA 50 D

Cobalt 01035 7440-48-4 0.021 na na D

Copper 01040 7440-50-8 0.08 AL-US 1,300 D

Iron 01046 7439-89-6 3.2 SMCL-CA 300 D

Lead 01049 7439-92-1 0.025 AL-US 15 D

Lithium 01130 7439-93-2 0.22 na na D

Manganese 01056 7439-96-5 0.13 HBSL (SMCL-CA) 300 (50) D

Molybdenum 01060 7439-98-7 0.014 HBSL (HAL-US) 40 (40) D

Nickel 01065 7440-02-0 0.09 MCL-CA 100 D

Selenium 01145 7782-49-2 0.03 MCL-US 50 D

Silver 01075 7440-22-4 0.005 HBSL (SMCL-CA) 100 (100) D

Strontium 01080 7440-24-6 0.2 HBSL (HAL-US) 4,000 (4,000) D

Thallium 01057 7440-28-0 0.01 MCL-US 2 D

Uranium 22703 7440-61-1 0.003 MCL-US 30 D

Vanadium 01085 7440-62-2 0.08 NL-CA 50 D

Zinc 01090 7440-66-6 1.4 HBSL (SMCL-CA) 2,000 (5,000) D

1

 Constituents with HBSLs also can have other non-regulatory, health-based benchmarks. The type and value of these other benchmarks are shown in parentheses.
Table 3E. Nutrients, comparison benchmarks, and reporting information for the U.S. Geological Survey (USGS) National Water Quality Laboratory (N[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. LT-MDL, benchmark type, and benchmark level as of August 30, 2012. Benccontaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCLHAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant lecontaminant level. Other abbreviations: CASRN®, Chemical Abstracts Service Registry Number®; LT-MDL, long-term method detection limit; D, detected in groundwater sammg/L, milligrams per liter]

Constituent USGS parameter code CASRN® LT-MDL (mg/L) Benchmark type Benchma

(mg/

Ammonia (as nitrogen) 00608 7664-41-7 0.01 HAL-US 1 24

Nitrite (as nitrogen) 00613 14797-65-0 0.001 MCL-US 1 

Nitrate plus nitrite (as nitrogen)2 00631 na 0.04 MCL-US 10 

Total nitrogen (ammonia + nitrite + nitrate + organic nitrogen) 62854 17778-88-0 0.05 na na 

Phosphate, orthophosphate (as phosphorus) 00671 14265-44-2 0.004 na na 

1 The HAL-US is 30 mg/L “as ammonia.” To facilitate comparison to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L “as nitrogen.”2 Nitrite plus nitrate (as nitrogen) is referred to as nitrate in the text for clarity.

Table 3F. Major and minor ions, silica, total dissolved solids (TDS), and alkalinity, comparison benchmarks, and reporting information for the U.S. Ge

National Water Quality Laboratory (NWQL) Schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. LT-MDL, benchmark type, and benchmark level as of August 30, 2012. Benc

contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCLDepartment of Public Health (CDPH) maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; SMCL-CA, CDPH secondaOther abbreviations: CASRN®, Chemical Abstracts Service Registry Number®; LT-MDL, long-term method detection limit; D, detected in groundwater samples (table 10); na, 

per liter; SiO2, silicon dioxide; CaCO3, calcium carbonate]

Constituent 

(synonym or abbreviation)

USGS 

parameter code CASRN® LT-MDL (mg/L) Benchmark type Benchmark le

(mg/L) 

Bromide 71870 24959-67-9 0.01 na na 

Calcium 00915 7440-70-2 0.022 na na 

Chloride 00940 16887-00-6 0.06 SMCL-CA 1 250 (500) 

Fluoride 00950 16984-48-8 0.04 MCL-CA 2 Iodide 71865 7553-56-2 0.001 na na Magnesium 00925 7439-95-4 0.011 na na Potassium 00935 7440-09-7 0.03 na na Sodium 00930 7440-23-5 0.06 na na Sulfate 00945 14808-79-8 0.09 SMCL-CA 1 250 (500) Silica (as SiO2) 00955 7631-86-9 0.018 na na 

Total dissolved solids (TDS) 70300 na 10 SMCL-CA 1 500 (1,000

Laboratory alkalinity (as CaCO3) 2 29801 na 4.6 na na 

1 The SMCL-CA for chloride, sulfate, and TDS have recommended and upper benchmark values. The upper benchmark value is shown in parentheses.2 Laboratory alkalinity results are presented in table 4.
Table 3G. Isotopic tracers, radioactive constituents, comparison benchmarks, and reporting information for laboratory analyses. [The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Stable isotope ratios are reported in the standard delta notation (δ), the ratio o

the more common lighter isotope of that element, relative to a standard reference material. Laboratory entity codes in the USGS National Water Information System (NWIS) for the USGS National Water Quality Laboratory (NWQL) are given in parentheses after the laboratory names in table footnotes. Benchmark type and benchmark value as of Augustype: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCMCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant level. Elements: H, h

Sr, strontium; C, carbon. Reporting units: pCi/L, picocuries per liter. Other abbreviations: CASRN®, Chemical Abstracts Service Registry Number®; CSU, 1-sigma combined 

in groundwater samples (tables 11 and 12); na, not available; NRP, National Research Program; pmc, percent modern carbon; ssLC, sample-specific critical level; USGS, U.S. G

Constituent USGS param- eter code CASRN® Reporting level Reporting uncertainty Reporting units Benchmark type 

Isotopic tracers 11B/10B of dissolved boron 1 62648 na na 2 per mil na 

δ2H in water 2 82082 na na 2 per mil na δ18O in water 2 82085 na na 0.20 per mil na δ13C in dissolved inorganic carbon 3 82081 na na 0.05 per mil na 

87Sr/86Sr of dissolved strontium 1 75978 na na 0.00005 atom ratio na 

Radioactive constituents Carbon-14 3 49933 14762-75-5 na 0.0015 pmc na 

Tritium 5 07000 10028-17-8 ssLC CSU pCi/L MCL-CA 

Radon-222 4 82303 14859-67-7 ssLC CSU pCi/L MCL-US (Proposed) 

Gross alpha radioactivity, 72-hour and 30-day counts 6 62636, 62639 12587-46-1 ssLC CSU pCi/L MCL-US 

Gross beta radioactivity, 72-hour and 30-day counts 6 62642, 62645 12587-47-2 ssLC CSU pCi/L MCL-CA 

1 USGS-NRP Metals Isotope Research Laboratory, Menlo Park, California (USGSMICA). 2 USGS Stable Isotope Laboratory, Reston, Virginia (USGSSIVA). 3 Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry Facility [NOMAS], Woods Hole, Massachusetts (MA-WHAMS). 4 USGS National Water Quality Laboratory (USGSNWQL). 5 USGS Stable Isotope and Tritium Laboratory [SITL], Menlo Park, California (USGSH3CA). 6 Eberline Analytical Services, Richmond, California (CA-EBERL). 7 The MCL-US benchmark for gross alpha activity applies to adjusted gross alpha, which is equal to measured gross alpha activity minus uranium activity.
Table 4. Water-quality indicators in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin P[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification number: S-NSF-H, Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study area understanding well; S-NSF-VP, NAquifer study unit Valley and Plains study area well. Benchmark type, benchmark level, and RL as of August 30, 2012. Benchmark type: SMCL-US, U.S. Environmental Protemaximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological Surveymg/L, milligrams per liter; nc, not collected; na, not available; RL, reporting level or range; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium c

greater than (or outside of range of) the benchmark level; **, concentration greater than the upper benchmark level; —, not detected]

GAMA 

well identification 

number

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

Water 

temperature, 

field 

(°C) 

(00010)

pH, 

field 

(standard 

units) 

(00400)

pH, 

laboratory 

(standard 

units) 

(00403)

Specific 

conductance, 

field 

(μS/cm at 25 °C) 

(00095)

Specific 

conductance, 

laboratory 

(μS/cm at 25 °C) 

(90095)

Alkalinity, 

field (mg/L 

as 

CaCO3) 

(29802)

Alkalinity, 

laboratory 

(mg/L as 

CaCO3) 

(29801)

Bicarbonate, 

field 

(mg/L) 

(63786)

Bicarbonate

laboratory 

(mg/L)

Benchmark type

na na SMCL-US SMCL-US SMCL-CA SMCL-CA na na na na 

Benchmark level

na na <6.5 or >8.5 <6.5 or >8.5 1 900 (1,600) 1 900 (1,600) na na na na 

[RL] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [1] [1] [1] [1] 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)Highlands study area wells (40 wells sampled)S-NSF-H01 1.1 14.5 6.5 7.0 304 305 nc 84 nc 102 

S-NSF-H02 5.3 12.0 6.5 7.1 310 315 nc 160 nc 195 

S-NSF-H03 8.9 17.0 7.0 7.5 182 186 nc 87 nc 106 

S-NSF-H04 0.4 16.5 7.7 7.9 841 844 nc 452 nc 551 

S-NSF-H05 0.4 18.0 7.1 7.6 513 517 nc 243 nc 296 

S-NSF-H06 0.7 17.0 7.0 7.4 750 752 nc 362 nc 441 

S-NSF-H07 4.8 13.0 7.0 7.4 404 403 nc 218 nc 266 

S-NSF-H08 <0.2 19.0 *8.7 *8.8 719 729 nc 351 nc 428 

S-NSF-H09 0.8 26.0 7.5 7.8 394 387 nc 160 nc 195 

S-NSF-H10 7.6 24.0 6.8 7.3 140 143 nc 58 nc 70 

S-NSF-H11 3.6 14.0 *6.2 6.8 193 191 80.1 85 97.6 104 

S-NSF-H12 <0.2 14.0 *6.2 6.7 313 308 nc 63 nc 76 

S-NSF-H13 <0.2 20.0 *9.4 *9.4 567 566 nc 217 nc 263 

S-NSF-H14 0.4 15.0 7.8 8.1 564 566 nc 159 nc 194 

S-NSF-H15 5.8 17.0 7.2 7.7 324 328 nc 110 nc 134 
Table 4. Water-quality indicators in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification number: S-NSF-H, Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study area understanding well; S-NSF-VP, NAquifer study unit Valley and Plains study area well. Benchmark type, benchmark level, and RL as of August 30, 2012. Benchmark type: SMCL-US, U.S. Environmental Protemaximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological Surveymg/L, milligrams per liter; nc, not collected; na, not available; RL, reporting level or range; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium c

greater than (or outside of range of) the benchmark level; **, concentration greater than the upper benchmark level; —, not detected] GAMA well iden- tification number Dissolved oxygen, field (mg/L) (00300) Water temperature, field (°C) (00010) pH, field (standard units) (00400) pH, laboratory (standard units) (00403) Specific conductance, field (μS/cm at 25 °C) (00095) Specific conductance, laboratory (μS/cm at 25 °C) (90095) Alkalinity, field (mg/L as CaCO3) (29802) Alkalinity, laboratory (mg/L as CaCO3) (29801) Bicarbonate, field (mg/L) (63786) Bicarbonate

laboratory 

(mg/L) 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Highlands study area wells (40 wells sampled)—Continued S-NSF-H16 <0.2 17.5 6.8 7.2 325 321 nc 81 nc 99 

S-NSF-H17 1.3 18.0 7.8 8.0 710 717 nc 122 nc 149 

S-NSF-H18 0.6 19.5 6.5 6.9 599 622 nc 234 nc 285 

S-NSF-H19 6.7 17.0 6.8 7.4 319 322 nc 160 nc 195 

S-NSF-H20 4.2 18.5 *6.4 6.9 162 164 nc 80 nc 98 

S-NSF-H21 0.2 21.5 6.6 7.0 464 398 nc 180 nc 219 

S-NSF-H22 <0.2 20.5 7.9 8.2 *903 *910 nc 427 nc 521 

S-NSF-H23 6.4 16.0 *6.2 6.7 197 198 nc 88 nc 108 

S-NSF-H24 4.8 24.5 6.5 7.0 151 147 nc 65 nc 79 

S-NSF-H25 7.3 16.0 6.7 7.2 286 285 nc 144 nc 176 

S-NSF-H26 <0.2 19.5 7.2 7.4 733 731 nc 209 nc 255 

S-NSF-H27 1.4 16.5 6.8 7.2 *1,420 *1,450 nc 262 nc 319 

S-NSF-H28 6.1 20.0 6.6 7.0 170 168 nc 76 nc 93 

S-NSF-H29 6.9 21.0 *6.1 *6.4 *1,480 *1,480 nc 90 nc 109 

S-NSF-H30 2.5 24.0 6.6 7.0 123 121 nc 51 nc 62 

S-NSF-H31 0.8 16.0 7.2 7.8 *958 *944 324 335 394 408 

S-NSF-H32 5 17.0 *6.3 6.8 175 177 nc 88 nc 108 

S-NSF-H33 2.6 23.0 *6.3 6.8 170 169 nc 77 nc 94 

S-NSF-H34 0.2 15.5 6.8 7.3 716 796 nc 327 nc 399 

S-NSF-H35 5.7 20.0 7.0 7.3 312 308 140 142 170 173 
Table 4. Water-quality indicators in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification number: S-NSF-H, Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study area understanding well; S-NSF-VP, NAquifer study unit Valley and Plains study area well. Benchmark type, benchmark level, and RL as of August 30, 2012. Benchmark type: SMCL-US, U.S. Environmental Protemaximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological Surveymg/L, milligrams per liter; nc, not collected; na, not available; RL, reporting level or range; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium c

greater than (or outside of range of) the benchmark level; **, concentration greater than the upper benchmark level; —, not detected]

GAMA 

well identification 

number

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

Water 

temperature, 

field 

(°C) 

(00010)

pH, 

field 

(standard 

units) 

(00400)

pH, 

laboratory 

(standard 

units) 

(00403)

Specific 

conductance, 

field 

(μS/cm at 25 °C) 

(00095)

Specific 

conductance, 

laboratory 

(μS/cm at 25 °C) 

(90095)

Alkalinity, 

field (mg/L 

as 

CaCO3) 

(29802)

Alkalinity, 

laboratory 

(mg/L as 

CaCO3) 

(29801)

Bicarbonate, 

field 

(mg/L) 

(63786)

Bicarbonate

laboratory 

(mg/L)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedHighlands study area wells (40 wells sampled)—ContinuedS-NSF-H36 5.9 18.5 *6.0 *6.3 173 180 37.8 46 46.1 56 

S-NSF-H37 5.4 20.5 6.5 7.2 123 120 nc 55 nc 67 

S-NSF-H38 <0.2 18.0 8.2 8.4 *1,170 *1,370 nc 668 nc 814 

S-NSF-H39 5.6 20.5 6.5 7.0 144 140 nc 59 nc 72 

S-NSF-H40 0.9 18.0 6.9 7.2 **1,620 **1,640 223 363 272 443 

Valley and Plains study area wells (30 wells sampled)S-NSF-VP01 0.2 17.0 7.2 7.4 **1,750 **1,780 nc 427 nc 521 

S-NSF-VP02 1.2 16.5 6.8 7.2 799 780 nc 340 nc 415 

S-NSF-VP03 <0.2 16.5 7.5 7.8 *1,080 *1,030 nc 242 nc 295 

S-NSF-VP04 <0.2 18.5 6.6 7.0 361 350 nc 76 nc 93 

S-NSF-VP05 <0.2 23.0 7.5 7.8 526 516 nc 199 nc 243 

S-NSF-VP06 <0.2 20.5 7.2 7.9 502 499 230 245 279 299 

S-NSF-VP07 0.4 20.5 7.2 7.5 678 666 258 276 314 336 S-NSF-VP08 1.8 20.5 6.8 7.2 400 399 177 105 216 128 

S-NSF-VP09 <0.2 20.0 6.9 7.3 437 434 nc 138 nc 168 

S-NSF-VP10 <0.2 18.0 7.3 7.7 406 405 nc 140 nc 171 

S-NSF-VP11 3.2 17.5 6.9 7.3 867 827 nc 237 nc 289 

S-NSF-VP12 <0.2 20.0 8.0 8.1 625 621 nc 245 nc 299 

S-NSF-VP13 <0.2 23.5 8.3 8.3 582 564 258 269 308 328 

S-NSF-VP14 <0.2 19.5 7.1 7.4 771 763 nc 387 nc 472 

S-NSF-VP15 3.5 18.0 6.6 7.0 558 544 nc 258 nc 315 
Table 4. Water-quality indicators in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification number: S-NSF-H, Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study area understanding well; S-NSF-VP, NAquifer study unit Valley and Plains study area well. Benchmark type, benchmark level, and RL as of August 30, 2012. Benchmark type: SMCL-US, U.S. Environmental Protemaximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: USGS, U.S. Geological Surveymg/L, milligrams per liter; nc, not collected; na, not available; RL, reporting level or range; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium c

greater than (or outside of range of) the benchmark level; **, concentration greater than the upper benchmark level; —, not detected] GAMA well iden- tification number Dissolved oxygen, field (mg/L) (00300) Water temperature, field (°C) (00010) pH, field (standard units) (00400) pH, laboratory (standard units) (00403) Specific conductance, field (μS/cm at 25 °C) (00095) Specific conductance, laboratory (μS/cm at 25 °C) (90095) Alkalinity, field (mg/L as CaCO3) (29802) Alkalinity, laboratory (mg/L as CaCO3) (29801) Bicarbonate, field (mg/L) (63786) Bicarbonate

laboratory 

(mg/L) 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Valley and Plains study area wells (30 wells sampled)—Continued S-NSF-VP16 0.3 19.0 7.2 7.5 502 505 nc 212 nc 258 

S-NSF-VP17 4.5 16.0 6.5 6.9 568 570 nc 255 nc 311 

S-NSF-VP18 4.8 16.0 6.9 7.2 406 410 149 172 182 210 S-NSF-VP19 0.9 21.5 6.5 7.0 314 307 nc 101 nc 123 

S-NSF-VP20 0.8 18.5 6.7 7.1 224 225 nc 94 nc 115 

S-NSF-VP21 0.4 25.0 7.4 7.9 660 669 nc 237 nc 289 

S-NSF-VP22 0.3 17.5 6.6 7.1 460 456 134 158 163 193 S-NSF-VP23 0.4 22.0 7.3 7.6 893 854 nc 388 nc 473 

S-NSF-VP24 nc 19.0 8.1 8.2 897 892 nc 401 nc 489 

S-NSF-VP25 0.2 19.0 7.0 7.3 *1,420 *1,520 nc 165 nc 201 

S-NSF-VP26 0.3 18.5 6.5 6.9 316 317 nc 78 nc 95 

S-NSF-VP27 0.3 17.0 6.6 6.9 500 513 nc 151 nc 184 

S-NSF-VP28 <0.2 18.5 6.9 7.2 465 463 nc 185 nc 226 

S-NSF-VP29 3.8 18.0 7.0 7.4 499 497 nc 214 nc 261 

S-NSF-VP30 nc 22.0 6.9 7.3 434 409 nc 173 nc 211 

North San Francisco Bay Shallow Aquifer study unit understanding well (1 well sampled)S-NSF-HU30 4 21 6.8 7.1 325 327 nc 163 nc 199 

1 The SMCL-CA for specific conductance has recommended and upper benchmark values. The upper value is shown in parentheses.2 Bicarbonate and carbonate concentrations were calculated from the laboratory alkalinity and pH values using the advanced speciation method (http://or.water.usgs.gov/alk/m

pK2 = 10.33, and pKW = 14.
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GA

April to August 2012.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onlisted. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in table 3A

number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Benchmark type, benchmark level, and LRL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS health-based screening level; MCL-US, U.S. Environmental Protection Agency mMCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher laboratory reporting level; na, not available; SRL, study reporting level; ≤, less than or equal to; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —

Primary use 

or 

source

Trihalomethanes

Natural, 

organic 

synthesis

Gasoline 

oxygenate

GAMA 

well identification number

Chloroform (trichloromethane) (μg/L) 

(32106)

Bromodichloromethane 

(μg/L) 

(32101)

Dibromochloromethane 

(μg/L) 

(32105)

Tribromomethane 

(μg/L) 

(32104)

Carbon 

disulfide 

(μg/L) 

(77041)

Methyl tertbutyl ether 

(μg/L) 

(78032)

Diisopropyl 

ether 

(μg/L) 

(81577)

Benchmark type MCL-US MCL-US MCL-US MCL-US HBSL MCL-CA na Benchmark level 1 80 1 80 1 80 1 80 700 13 na 

[LRL or SRL] [0.03] [0.034] [0.12] [0.1] [0.03] 2 [0.1] [0.06] 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)Number of wells 

with detections

13 1 1 1 6 4 3 

Detection 

frequency (percent)

19 1.4 1.4 1.4 9 5.7 4.3 

Total detections 

(number)

Highlands study area wells (40 wells sampled)S-NSF-H01 — — — — — 0.3 0.1 

S-NSF-H03 0.01 — — — — — — 

S-NSF-H08 — — — — E0.5 — — 

S-NSF-H10 0.02 — — — — — — 

S-NSF-H11 — — — — — — — 

S-NSF-H13 — — — — E0.1 — — 

S-NSF-H18 — — — — — — 2.24 

S-NSF-H22 — — — — — — — S-NSF-H23 0.16 — — — — — — 

S-NSF-H28 0.01 — — — — — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAApril to August 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onlisted. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in table 3Anumber: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Benchmark type, benchmark level, and LRL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS health-based screening level; MCL-US, U.S. Environmental Protection Agency mMCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher laboratory reporting level; na, not available; SRL, study reporting level; ≤, less than or equal to; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —

Primary use or source Trihalomethanes Natural, organic synthesis Gasoline oxygenate 

GAMA well identifica- tion number Chloroform (trichlo- romethane) (μg/L) (32106) Bromodichloromethane (μg/L) (32101) Dibromochloromethane (μg/L) (32105) Tribromomethane (μg/L) (32104) Carbon disulfide (μg/L) (77041) Methyl tert- butyl ether (μg/L) (78032) Diisopropyl ether (μg/L) (81577) 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Highlands study area wells (40 wells sampled)—Continued S-NSF-H34 0.05 — — — — — — 

S-NSF-H36 3 2.1 — — — — — — 

S-NSF-H38 4 — — — — E3.6 — — 

S-NSF-H39 0.04 — — — — — — 

S-NSF-H40 0.01 — — — — — — 

Number of wells with detections 8 0 0 0 3 1 2 

Detection frequency (percent) 20 0 0 0 7.5 2.5 5 

Total detections (number)Valley and Plains study area wells (30 wells sampled)S-NSF-VP01 3 1.6 0.372 0.38 0.33 < 0.01 5 — 0.14 

S-NSF-VP02 — — — — — — — 

S-NSF-VP03 — — — — — 0.13 — 

S-NSF-VP08 0.03 — — — — — — 

S-NSF-VP09 — — — — E0.1 — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAApril to August 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onlisted. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in table 3Anumber: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Benchmark type, benchmark level, and LRL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS health-based screening level; MCL-US, U.S. Environmental Protection Agency mMCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher laboratory reporting level; na, not available; SRL, study reporting level; ≤, less than or equal to; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —

Primary use 

or 

source

Trihalomethanes

Natural, 

organic 

synthesis

Gasoline 

oxygenate

GAMA 

well identification number

Chloroform (trichloromethane) (μg/L) 

(32106)

Bromodichloromethane 

(μg/L) 

(32101)

Dibromochloromethane 

(μg/L) 

(32105)

Tribromomethane 

(μg/L) 

(32104)

Carbon 

disulfide 

(μg/L) 

(77041)

Methyl tertbutyl ether 

(μg/L) 

(78032)

Diisopropyl 

ether 

(μg/L) 

(81577)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedValley and Plains study area wells (30 wells sampled)—ContinuedS-NSF-VP10 — — — — E0.1 — — 

S-NSF-VP11 0.06 — — — — — — 

S-NSF-VP14 — — — — E0.1 0.65 — 

S-NSF-VP15 0.03 — — — — — — 

S-NSF-VP20 — — — — < 0.03 5 — — 

S-NSF-VP25 0.03 — — — — — — 

S-NSF-VP29 — — — — — — — 

S-NSF-VP30 — — — — — 0.06 — 

Number of wells 

with detections

5 1 1 1 3 3 1 

Detection 

frequency (percent)

17 3.3 3.3 3.3 10 10 3.3 

Total detections 

(number)
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAApril to August 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onlisted. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in table 3Anumber: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Benchmark type, benchmark level, and LRL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS health-based screening level; MCL-US, U.S. Environmental Protection Agency mMCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher laboratory reporting level; na, not available; SRL, study reporting level; ≤, less than or equal to; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —

Primary use or source Gasoline hydrocarbon Solvent GAMA well identification number Benzene (μg/L) (34030) Isopropylbenzene (μg/L) (77223) Naphthalene (μg/L) (34696) Perchloroethene (μg/L) (34475) 1,1-Dichloroethane (μg/L) (34496) Chlorobenzene (μg/L) (34301) Dibromomethane (μg/L) (30217) Tetrachlo

(μg

(32

Benchmark type MCL-CA HBSL HBSL MCL-US MCL-CA MCL-CA na MCBenchmark level 1 700 100 5 5 70 na 0

[LRL or SRL] [0.026] [0.042] [0.18] [0.026] [0.044] [0.016] [0.05] [0.0

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Number of wells with detections 1 1 1 2 1 1 1 1 

Detection frequency (percent) 1.4 1.4 1.4 2.9 1.4 1.4 1.4 1.4 

Total detections (number) Highlands study area wells (40 wells sampled)—Continued S-NSF-H01 — — — — — — — — 

S-NSF-H03 — — — — — — — — 

S-NSF-H08 — — — — — — — — 

S-NSF-H10 — — — — — — — — 

S-NSF-H11 — — — — — — — — 

S-NSF-H13 — — — — — — — — 

S-NSF-H18 — — — — — — — — 

S-NSF-H22 — — — — — — — — 

S-NSF-H23 — — — — — — — — 

S-NSF-H28 — — — — — — — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAApril to August 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onlisted. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in table 3Anumber: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Benchmark type, benchmark level, and LRL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS health-based screening level; MCL-US, U.S. Environmental Protection Agency mMCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher laboratory reporting level; na, not available; SRL, study reporting level; ≤, less than or equal to; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —

Primary use 

or source

Gasoline 

hydrocarbon Solvent

GAMA well 

identification 

number

Benzene 

(μg/L) 

(34030)

Isopropylbenzene 

(μg/L) 

(77223)

Naphthalene 

(μg/L) 

(34696)

Perchloroethene 

(μg/L) 

(34475)

1,1-Dichloroethane 

(μg/L) 

(34496)

Chlorobenzene 

(μg/L) 

(34301)

Dibromomethane 

(μg/L) 

(30217)

Tetrachlo

(μg

(32

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedHighlands study area wells (40 wells sampled)—ContinuedS-NSF-H34 — — — — — — — — 

S-NSF-H36 — — — — — — — — 

S-NSF-H38 3 *4.41 0.023 0.1 — — — — — 

S-NSF-H39 — — — — — — — — 

S-NSF-H40 — — — — — — — — 

Number of 

wells with detections

1 1 1 0 0 0 0 0 

Detection 

frequency (percent)

2.5 2.5 2.5 0 0 0 0 0 

Total detections 

(number)

Valley and Plains study area wells (30 wells sampled)—ContinuedS-NSF-VP01 — — — — — — 0.022 — S-NSF-VP02 — — — 0.017 — — — — S-NSF-VP03 — — — — — 0.054 — — 

S-NSF-VP08 — — — — — — — — 

S-NSF-VP09 — — — — — — — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAApril to August 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onlisted. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in table 3Anumber: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Benchmark type, benchmark level, and LRL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS health-based screening level; MCL-US, U.S. Environmental Protection Agency mMCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher laboratory reporting level; na, not available; SRL, study reporting level; ≤, less than or equal to; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —

Primary use or source Gasoline hydrocarbon Solvent GAMA well identification number Benzene (μg/L) (34030) Isopropylbenzene (μg/L) (77223) Naphthalene (μg/L) (34696) Perchloroethene (μg/L) (34475) 1,1-Dichloroethane (μg/L) (34496) Chlorobenzene (μg/L) (34301) Dibromomethane (μg/L) (30217) Tetrachlo

(μg

(32

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Valley and Plains study area wells (30 wells sampled)—Continued S-NSF-VP10 — — — — — — — — 

S-NSF-VP11 — — — — — — — — 

S-NSF-VP14 — — — — — — — — 

S-NSF-VP15 — — — — — — — 0.04 S-NSF-VP20 — — — — 0.042 — — — 

S-NSF-VP25 — — — — — — — — 

S-NSF-VP29 — — — 0.023 — — — — S-NSF-VP30 — — — — — — — — 

Number of wells with detections 0 0 0 2 1 1 1 1 

Detection 

frequency (percent)

0 0 0 6.7 3.3 3.3 3.3 3.3 

Total detections 

(number)
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAApril to August 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onlisted. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in table 3Anumber: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Benchmark type, benchmark level, and LRL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS health-based screening level; MCL-US, U.S. Environmental Protection Agency mMCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher laboratory reporting level; na, not available; SRL, study reporting level; ≤, less than or equal to; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —

Primary use 

or source Refrigerant Fire retardant Detections 

per 

well

GAMA well identification 

number Trichlorotrifluoroethane (μg/L) (77652) Trichlorofluoromethane (μg/L) (34488) Bromochloromethane (μg/L) (77297)

Benchmark type MCL-CA MCL-CA HBSLBenchmark level 1200 150 90[LRL or SRL] [0.034] [0.08] [0.06]North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedNumber of wells with detections 1 1 1 

Detection frequency (percent) 1.4 1.4 1.4 Total detections (number) Highlands study area wells (40 wells sampled)—ContinuedS-NSF-H01 — — — 2

S-NSF-H03 — — — 1

S-NSF-H08 — — — 1

S-NSF-H10 — — — 1

S-NSF-H11 — — — 1

S-NSF-H13 — — — 1

S-NSF-H18 — — — 2

S-NSF-H22 — — — 1

S-NSF-H23 — — — 1

S-NSF-H28 — — — 1

S-NSF-H34 — — — 1

S-NSF-H36 — — — 1

S-NSF-H38 3 — — — 7

S-NSF-H39 — — — 1

S-NSF-H40 0.191 0.35 — 3
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAApril to August 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onlisted. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in table 3Anumber: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Benchmark type, benchmark level, and LRL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS health-based screening level; MCL-US, U.S. Environmental Protection Agency mMCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher laboratory reporting level; na, not available; SRL, study reporting level; ≤, less than or equal to; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —

Primary use or source Refrigerant Fire retardant Detections per well 

GAMA well identification 

number Trichlorotrifluoroethane (μg/L) (77652) Trichlorofluoromethane (μg/L) (34488) Bromochloromethane (μg/L) (77297) North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Highlands study area wells (40 wells sampled)—Continued Number of wells with detections 1 1 0 

Detection frequency (percent) 2.5 2.5 0 Total detections (number) Valley and Plains study area wells (30 wells sampled)—Continued S-NSF-VP01 — — 0.03 7 S-NSF-VP02 — — — 1 S-NSF-VP03 — — — 2 S-NSF-VP08 — — — 1 S-NSF-VP09 — — — 1 S-NSF-VP10 — — — 1 S-NSF-VP11 — — — 1 S-NSF-VP14 — — — 2 S-NSF-VP15 — — — 2

S-NSF-VP20 — — — 2

S-NSF-VP25 — — — 1

S-NSF-VP29 — — — 1

S-NSF-VP30 — — — 1
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAApril to August 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onlisted. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in table 3Anumber: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Benchmark type, benchmark level, and LRL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HBSL, USGS health-based screening level; MCL-US, U.S. Environmental Protection Agency mMCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher laboratory reporting level; na, not available; SRL, study reporting level; ≤, less than or equal to; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —

Primary use 

or source Refrigerant Fire retardant Detections 

per 

well

GAMA well identification 

number Trichlorotrifluoroethane (μg/L) (77652) Trichlorofluoromethane (μg/L) (34488) Bromochloromethane (μg/L) (77297)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedValley and Plains study area wells (30 wells sampled)—ContinuedNumber of wells with detections 0 0 1 

Detection frequency (percent) 0 0 3.3 Total detections (number) 

1 The MCL-US threshold for trihalomethanes is for the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.2 The SRLs for acetone (all detections censored), carbon disulfide (0.03 μg/L), ethylbenzene (0.1 μg/L), toluene (0.69 μg/L), tetrahydrofuran (all detections censored), 1,2,4-tr

m-xylene plus p-xylene (0.33 μg/L), and o-xylene (0.56 μg/L) were defined by Fram and others (2012). Detections of acetone (S-NSF-H38: 27.8 μg/L) and tetrahydrofuran (S-N

2.1 μg/L; S-NSF-H16: 0.4 μg/L; S-NSF-H34: 0.6 μg/L; S-NSF-H38: 3 μg/L; S-NSF-VP06: 5.2 μg/L; S-NSF-VP12: 0.4 μg/L; S-NSF-VP23: 0.8 μg/L) have been reclassified as presented in this report. Detections of ethylbenzene (S-NSF-H38: E0.073 μg/L), 1,2,4-trimethylbenzene (S-NSF-H38: 0.046 μg/L; S-NSF-V29: 0.14 μg/L), m-xylene plus p-xyl

and o-xylene (S-NSF-H38: 0.046 μg/L) have been reclassified as less than or equal to the SRL and are not presented in this report.

3 Well periodically treated with downhole chlorination, which may have affected the trihalomethane results.4 This well had a vehicle parked next to the well head for long periods of time, and the vehicle is suspected to have leaked oil onto the ground which may account for the suite 

detections.

5 Carbon disulfide concentration is less than the SRL (Fram and others, 2012).
Table 6. Pesticides and pesticide degradates detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GApril to August 2012. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed, but onare listed. Detected constituents are grouped by primary use or source and then listed in order of decreasing detection frequency in the 70 grid wells. All constituents are listed in identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark level, and LRL as of Augustype: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCHBSL, USGS Health-Based Screening Level; MCL-US, U.S. Environmental Protection Agency (USEPA) maximum contaminant level; MCL-CA, California Department of Pucontaminant level. Other abbreviations: USGS, U.S. Geological Survey; E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, microgra*, concentration greater than the benchmark level; —, not detected] Primary use or source Herbicide Herbicide degradate Insecticide Insecticide degradate 

GAMA well identification number Simazine (μg/L) (04035) Atrazine (μg/L) (39632) Prometon (μg/L) (04037) Tebuthiuron (μg/L) (82670) Deethylatrazine (μg/L) (04040) 3,4-Dichloroaniline (μg/L) (61625) Dieldrin (μg/L) (39381) Fipronil sulfid

(μg/L) (62167) Benchmark type MCL-US MCL-CA HBSL HBSL na na HBSL na Benchmark level 4 1 400 1,000 na na 0.02 na [LRL] [0.006] [0.008] [0.012] [0.028] [0.006] [0.006] [0.008] [0.012] North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled) Number of wells with detections 6 4 1 1 4 1 1 1 

Detection frequency (percent) 8.6 5.7 1.4 1.4 5.7 1.4 1.4 1.4 

Total detections (number) Highlands study area wells (40 wells sampled) S-NSF-H27 — — — E0.013 — — — — 

S-NSF-H28 — — — — E0.004 — — — 

S-NSF-H30 0.005 0.007 — — E0.005 — — — 

S-NSF-H36 — — — — — — — 0.007 

Number of wells with detections 1 1 0 1 2 0 0 1 

Detection frequency (percent) 2.5 2.5 0 2.5 5 0 0 2.5 

Total detections (number) Valley and Plains study area wells (30 wells sampled)S-NSF-VP01 0.007 0.005 0.01 — E0.006 — — — 

S-NSF-VP02 0.028 0.004 — — E0.004 — — — 

S-NSF-VP17 0.006 — — — — — — — 

S-NSF-VP18 0.009 — — — — — — — 

S-NSF-VP25 0.01 0.007 — — — E0.0894 *0.065 — 

Number of wells with detections 5 3 1 0 2 1 1 0 

Detection frequency (percent) 17 10 3.3 0 6.7 3.3 3.3 0 

Total detections (number) North San Francisco Bay Shallow Aquifer study unit understanding well (1 well sampled)S-NSF-HU30 0.005 — 0.004 — — — — —
Tables 47

Table 7. Constituents of special interest detected in samples 

collected for the North San Francisco Bay Shallow Aquifer study 

unit, California GAMA Priority Basin Project, April to August 2012.

[1,2,3-Trichloropropane (1,2,3-TCP) was not detected and is therefore 

not presented in this table. The five-digit USGS parameter code below the 

constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 71 wells were analyzed, but only samples with detections 

are listed. Information about the constituents given in table 3C. GAMA well 

identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer 

study unit Highlands study area well; S-NSF-HU, North San Francisco 

Bay Shallow Aquifer study unit Highlands study area understanding well; 

S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and 

Plains study area well. Benchmark type, benchmark level, and LT-MDL as of 

August 30, 2012. Benchmark type: Maximum contaminant level benchmarks 

are listed as MCL-US when the MCL-US and MCL-CA are identical, and as 

MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. 

MCL-CA, California Department of Public Health maximum contaminant 

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

level. Other abbreviations: USGS, U.S. Geological Survey; LT-MDL, longterm method detection limit; μg/L, micrograms per liter]

GAMA well 

identification 

number

Perchlorate 

(μg/L) 

(63790)

Benchmark type MCL-CA

Benchmark level 6

[LT-MDL] [0.10] 

North San Francisco Bay Shallow Aquifer study unit grid wells 

(70 wells sampled)

Highlands study area wells (40 wells sampled)

S-NSF-H23 0.19

S-NSF-H24 0.25

S-NSF-H27 1.36

S-NSF-H28 0.19

S-NSF-H30 0.13

S-NSF-H33 0.14

S-NSF-H35 0.25

S-NSF-H36 0.46

S-NSF-H37 0.11

S-NSF-H39 0.17

S-NSF-H40 0.37

Valley and Plains study area wells (30 wells sampled)

S-NSF-VP02 0.53

S-NSF-VP08 0.38

S-NSF-VP11 0.38

S-NSF-VP15 0.31

S-NSF-VP17 0.17

S-NSF-VP25 1.62

S-NSF-VP27 0.58

S-NSF-VP29 0.17

North San Francisco Bay Shallow Aquifer study unit understanding 

well (1 well sampled)

S-NSF-HU30 0.11
Table 8. Trace elements detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin P[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3D. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Franc

study unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchm

of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when th

MCL-US or no MCL-US exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California Departmaximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Oth

U.S. Geological Survey; LT-MDL, long-term method detection limit; SRL, study reporting level; μg/L, micrograms per liter; na, not available; —, not detected; ≤, less than or ethan the benchmark level; nc, not collected] GAMA well identifi- cation number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01030) Cobalt (μg/L) (01035) Coppe

(μg/L

(0104

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US HBSL MCL-US MCL-CA na AL-U

Benchmark level 1,000 6 10 1,000 4 6,000 5 50 na 1,300 [LT-MDL or SRL] [2.2] [0.027] [0.03] [0.36] 1 [0.006] [3] [0.016] [0.42] 1 [0.05] 2 [3.2] 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled) Highlands study area wells (40 wells sampled) S-NSF-H01 — — 0.18 4.23 — 7 — ≤0.07 0.10 — 

S-NSF-H02 — — 0.13 49 — 38 — 1.3 — ≤1.1 

S-NSF-H03 — 0.039 1.8 150 — 12 — — ≤0.04 ≤1.9 

S-NSF-H04 2.3 0.765 — 18 0.011 *8,270 0.062 2.5 ≤0.05 — 

S-NSF-H05 7.3 0.086 0.58 112 — 45 — — ≤0.04 ≤0.86 

S-NSF-H06 — 0.039 0.24 52.4 0.006 205 — — ≤0.04 ≤1.8 

S-NSF-H07 — 0.027 0.12 17.3 — 49 — 3.7 ≤0.03 ≤2.1 

S-NSF-H08 — — — 316 0.295 *10,400 — — — — S-NSF-H09 — 0.103 0.95 6.62 0.011 183 — — ≤0.03 — 

S-NSF-H10 11.8 0.034 0.14 29.6 — 8 — 0.98 — 12 S-NSF-H11 39.4 — 0.12 62.3 — 68 — ≤0.15 ≤0.04 7.8 

S-NSF-H12 14.9 0.048 1.9 15.2 0.018 16 — ≤0.29 0.18 — S-NSF-H13 38.4 — — 12.9 — 146 — 4.7 0.05 — 

S-NSF-H14 — — 0.09 182 — 37 — — 0.08 — 

S-NSF-H15 — — 6.4 0.54 — 8 — — ≤0.02 — 
Table 8. Trace elements detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3D. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Franc

unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark l30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-Cno MCL-US exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California Department of Pubcontaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbrev

Survey; LT-MDL, long-term method detection limit; SRL, study reporting level; μg/L, micrograms per liter; na, not available; —, not detected; ≤, less than or equal to; *, concenbenchmark level; nc, not collected] 

GAMA well identification number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01030) Cobalt (μg/L) (01035) Coppe

(μg/L

(0104

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedHighlands study area wells (40 wells sampled)—ContinuedS-NSF-H16 2.6 — 1.7 6.9 — 27 — — 0.06 — 

S-NSF-H17 — — — 5.35 — 12 — — 0.08 — S-NSF-H18 — — 0.42 60.2 — 62 — — 0.07 — 

S-NSF-H19 4.1 — — 75.5 — 53 0.025 — — ≤0.93 S-NSF-H20 6.2 — — 51.5 0.033 17 — — — — 

S-NSF-H21 2.8 0.03 7 98.1 — 81 — — 0.12 — 

S-NSF-H22 8.5 — 1.5 81.6 0.019 803 0.02 0.55 ≤0.04 — 

S-NSF-H23 — — 0.21 2.15 0.006 5 — 1.1 ≤0.03 ≤2.3 

S-NSF-H24 9.4 0.032 2.7 3.55 — 12 — 3.3 — — 

S-NSF-H25 11.8 — 0.76 7.24 — 24 — 2.1 — — 

S-NSF-H26 — — 5.7 55.3 — 18 — — 0.15 ≤1.1 

S-NSF-H27 — — 0.2 37.5 — 240 — ≤0.16 0.05 ≤1.2 

S-NSF-H28 — 0.046 2.9 4.43 — 50 — 1.1 ≤0.03 ≤1.2 

S-NSF-H29 — — 0.31 23.2 0.052 9 — — 0.49 — 

S-NSF-H30 6.2 0.054 2.3 23.2 — 16 — ≤0.09 ≤0.02 ≤2.5 

S-NSF-H31 2.7 0.333 6.9 143 0.053 3 2,650 0.029 — 0.38 ≤0.86 

S-NSF-H32 2.4 0.095 4.5 23.2 0.006 13 — 3.9 — ≤1.3 S-NSF-H33 2.3 0.052 7.2 7.45 0.044 26 — ≤0.18 — ≤2.1 

S-NSF-H34 3.1 0.05 1.6 532 — 364 — — 0.19 — 

S-NSF-H35 — 0.058 3.6 17.9 — 106 — 2.6 0.08 14.2 
Table 8. Trace elements detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3D. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Franc

unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark l30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-Cno MCL-US exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California Department of Pubcontaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbrev

Survey; LT-MDL, long-term method detection limit; SRL, study reporting level; μg/L, micrograms per liter; na, not available; —, not detected; ≤, less than or equal to; *, concenbenchmark level; nc, not collected] GAMA well identifi- cation number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01030) Cobalt (μg/L) (01035) Coppe

(μg/L

(0104

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Highlands study area wells (40 wells sampled)—Continued S-NSF-H36 42.1 0.118 1.7 42.7 0.127 153 0.029 — 0.18 8.4 

S-NSF-H37 16.5 0.055 0.7 17.4 0.007 16 — 1.7 ≤0.03 3.9 S-NSF-H38 29.3 0.075 0.7 110 0.057 3 3,560 — ≤0.11 ≤0.03 — 

S-NSF-H39 2.3 0.037 3.8 6.74 0.016 24 — 0.42 — ≤1.6 

S-NSF-H40 — 0.22 0.21 74 0.009 76 — — 0.14 — 

Valley and Plains study area wells (30 wells sampled) S-NSF-VP01 — 0.097 2.5 251 — 84 — ≤0.12 0.16 ≤3.1 

S-NSF-VP02 — 0.089 4.5 40.8 — 49 — 2.3 0.11 6.3 

S-NSF-VP03 2.7 0.045 *19.2 299 — 190 0.035 — 0.12 ≤0.92 S-NSF-VP04 — — 0.85 57.4 — 13 — ≤0.09 0.14 ≤1.2 

S-NSF-VP05 — — *58.1 58.6 0.011 465 — ≤0.11 — ≤0.92 

S-NSF-VP06 7.9 0.034 1 194 — 120 0.018 — 0.17 ≤2.3 S-NSF-VP07 2.3 — 0.09 1.29 — 109 — — ≤0.03 — 

S-NSF-VP08 — — 6.2 44 — 20 — ≤0.32 — ≤1.7 

S-NSF-VP09 2.3 — *43.6 170 0.007 55 — — ≤0.03 — 

S-NSF-VP10 — — 5.7 144 — 53 — — 0.10 — 

S-NSF-VP11 3.6 0.086 5.4 180 — 42 — 3.7 0.06 — 

S-NSF-VP12 2.3 — *11.5 49.6 — 378 — ≤0.11 0.11 — 

S-NSF-VP13 7.3 — 0.72 52.6 0.024 3 1,300 0.021 ≤0.08 ≤0.03 5.4 

S-NSF-VP14 — — 6.1 145 — 98 0.041 — ≤0.03 — 

S-NSF-VP15 — 0.039 0.43 122 — 205 — 1 0.16 — 
Table 8. Trace elements detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3D. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Franc

unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark l30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-Cno MCL-US exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California Department of Pubcontaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbrev

Survey; LT-MDL, long-term method detection limit; SRL, study reporting level; μg/L, micrograms per liter; na, not available; —, not detected; ≤, less than or equal to; *, concenbenchmark level; nc, not collected] 

GAMA well identification number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01030) Cobalt (μg/L) (01035) Coppe

(μg/L

(0104

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedValley and Plains study area wells (30 wells sampled)—ContinuedS-NSF-VP16 2.6 0.028 6.6 223 0.014 432 0.024 ≤0.12 0.06 — 

S-NSF-VP17 8.6 0.034 0.32 200 — 118 — 3.8 ≤0.04 4.5 

S-NSF-VP18 6.7 0.106 0.32 127 0.007 267 — 1.5 ≤0.04 3.5 

S-NSF-VP19 2.3 — 1.5 72.4 — 26 — — — — 

S-NSF-VP20 179 1.36 6.3 44.2 0.027 53 0.067 1.3 1.47 18 

S-NSF-VP21 — 0.043 *20.4 92 0.018 766 0.049 — ≤0.04 — 

S-NSF-VP22 — 0.095 3.4 111 — 50 — 1.1 — ≤1.7 

S-NSF-VP23 2.5 — *43 65.8 0.019 604 0.024 — — — 

S-NSF-VP24 6.9 0.028 4.2 67.4 0.01 277 0.072 — 0.09 — 

S-NSF-VP25 13.7 0.18 1.7 420 0.006 112 0.029 ≤0.16 0.19 3.4 

S-NSF-VP26 — 0.036 1.2 70.8 — 42 — ≤0.15 ≤0.02 — 

S-NSF-VP27 7.1 — 0.3 83.3 — 49 — — 0.09 ≤2.3 

S-NSF-VP28 — 0.054 3 165 — 68 — — 0.35 — 

S-NSF-VP29 — 0.041 0.63 95 — 140 — 4.2 ≤0.03 — 

S-NSF-VP30 3.8 0.118 *22.6 17.7 — 109 — — 0.09 ≤1.4 North San Francisco Bay Shallow Aquifer study unit understanding well (1 well sampled)S-NSF-HU30 4.1 0.072 0.59 46.7 — 45 — 7.7 ≤0.04 4.3 
Table 8. Trace elements detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3D. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Franc

unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark l30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-Cno MCL-US exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California Department of Pubcontaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbrev

Survey; LT-MDL, long-term method detection limit; SRL, study reporting level; μg/L, micrograms per liter; na, not available; —, not detected; ≤, less than or equal to; *, concenbenchmark level; nc, not collected] GAMA well identifi- cation number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Uranium (μg/L) (22703) 

Benchmark type na HBSL HBSL MCL-CA MCL-US HBSL HBSL MCL-US MCL-US 

Benchmark level na 300 40 100 50 100 4,000 2 30 

[LT-MDL or SRL] [0.22] [0.2] 1 [0.014] [0.2] 2 [0.03] [0.005] [0.2] [0.01] [0.003] 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled) Highlands study area wells (40 wells sampled) S-NSF-H01 10.3 4 94.5 0.359 3.9 — — 95.4 — — 

S-NSF-H02 0.75 — 0.142 8.8 0.14 — 143 — 0.010 

S-NSF-H03 13.1 33.4 0.725 — — — 424 — 0.686 

S-NSF-H04 11.9 0.6 15 1.7 1.5 0.006 271 — 11.8 

S-NSF-H05 11.3 21.2 1.35 0.5 — — 545 — 0.128 

S-NSF-H06 15.3 12.7 0.604 0.8 — 0.007 3,700 — 0.217 

S-NSF-H07 0.41 — 0.192 1.6 0.04 — 144 — 0.060 

S-NSF-H08 54.8 3.5 0.073 — — — 408 0.02 0.008 

S-NSF-H09 12.1 35.2 2.64 ≤0.2 0.07 — 333 — 0.032 

S-NSF-H10 4 0.4 0.127 1.2 0.24 — 105 — 0.021 

S-NSF-H11 5.78 0.3 0.069 1 0.07 — 179 — 0.023 

S-NSF-H12 15.6 4 212 3.02 0.3 0.13 — 88.1 — 0.235 

S-NSF-H13 13.9 1.5 0.539 1.4 — — 27.4 — 0.007 

S-NSF-H14 20.3 25.1 0.471 0.2 — — 933 — 0.010 S-NSF-H15 17.3 4 285 0.599 ≤0.1 — — 13.6 — — 
Table 8. Trace elements detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3D. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Franc

unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark l30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-Cno MCL-US exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California Department of Pubcontaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbrev

Survey; LT-MDL, long-term method detection limit; SRL, study reporting level; μg/L, micrograms per liter; na, not available; —, not detected; ≤, less than or equal to; *, concenbenchmark level; nc, not collected] 

GAMA well identification number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Uranium (μg/L) (22703) 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedHighlands study area wells (40 wells sampled)—ContinuedS-NSF-H16 11.3 4 82.2 1.34 0.8 — — 191 — — 

S-NSF-H17 42 4 202 0.381 0.6 — — 247 — 0.011 

S-NSF-H18 8.76 *625 0.372 3.7 — — 282 — 0.332 

S-NSF-H19 8.82 0.5 0.019 0.4 0.08 — 143 — 0.030 

S-NSF-H20 0.76 0.6 0.954 ≤0.15 0.07 — 209 — — 

S-NSF-H21 20.6 4 159 1.32 0.6 — — 299 — 0.019 

S-NSF-H22 81.7 18.8 7.88 0.3 — — 36.1 — — 

S-NSF-H23 0.64 0.4 — 0.2 — — 72.4 — 0.019 

S-NSF-H24 3.63 0.7 0.727 0.8 0.53 — 30.3 — 0.014 

S-NSF-H25 3.96 0.3 0.600 0.4 0.09 — 72.4 — 0.476 

S-NSF-H26 15.8 4 64 2.31 0.7 — — 285 0.02 0.102 

S-NSF-H27 20.4 12.6 0.565 3.2 0.20 0.005 1,100 — 1.37 

S-NSF-H28 21 1.1 0.591 ≤0.2 0.06 — 29.3 — 0.038 

S-NSF-H29 9.88 *2,800 0.440 1.5 — — 2,110 — — 

S-NSF-H30 7.79 0.2 0.348 ≤0.1 0.18 — 27.1 — 0.051 

S-NSF-H31 19.7 12.8 8.86 10.2 0.05 — 618 0.04 0.212 

S-NSF-H32 14.8 ≤0.2 0.100 3.7 0.36 — 38.8 — 0.053 

S-NSF-H33 10.4 0.6 0.371 — 0.08 — 69.8 — 0.157 

S-NSF-H34 35.8 *773 0.680 3.6 0.26 — 412 0.01 0.378 

S-NSF-H35 20.9 ≤0.2 0.449 0.9 0.29 — 78.9 — 0.411 
Table 8. Trace elements detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3D. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Franc

unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark l30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-Cno MCL-US exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California Department of Pubcontaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbrev

Survey; LT-MDL, long-term method detection limit; SRL, study reporting level; μg/L, micrograms per liter; na, not available; —, not detected; ≤, less than or equal to; *, concenbenchmark level; nc, not collected] GAMA well identifi- cation number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Uranium (μg/L) (22703) 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Highlands study area wells (40 wells sampled)—Continued S-NSF-H36 10.7 1.2 0.086 1.8 0.04 — 73.5 0.04 0.269 

S-NSF-H37 6.01 — 0.074 7.8 0.08 — 43.2 — 0.079 

S-NSF-H38 21.6 48 1.53 ≤0.2 — — 52.1 — 0.043 

S-NSF-H39 20.2 — 0.367 ≤0.1 0.23 — 26.8 — 0.035 

S-NSF-H40 22.6 1.1 1.11 3 0.18 — 942 — 1.00 

Valley and Plains study area wells (30 wells sampled) S-NSF-VP01 29 *623 1.70 3.1 0.45 — 838 — 5.37 

S-NSF-VP02 11.1 ≤0.1 0.209 1.6 0.13 0.006 256 — 4.20 

S-NSF-VP03 12.2 *560 12.1 0.7 0.10 — 448 — 0.448 

S-NSF-VP04 13 4 62.7 0.157 3 — — 154 — 0.007 

S-NSF-VP05 20.5 30.7 4.24 0.3 0.05 — 59.9 — 0.025 

S-NSF-VP06 2.93 *509 0.878 0.7 — — 258 — 0.298 

S-NSF-VP07 8.96 1.8 0.225 0.4 — — 178 — 0.014 

S-NSF-VP08 14.4 0.7 0.542 0.8 0.12 — 93 — 0.025 

S-NSF-VP09 23.6 *1,570 0.243 ≤0.1 — — 139 0.02 — 

S-NSF-VP10 13 *485 0.731 0.4 — — 146 — — 

S-NSF-VP11 37.4 15.5 0.582 1.2 0.83 — 369 — 2.79 

S-NSF-VP12 34.9 45.4 2.80 0.2 — — 332 0.09 0.060 

S-NSF-VP13 87.9 21.6 4.75 ≤0.1 — — 37.1 — 0.020 

S-NSF-VP14 47.1 *942 10.5 0.7 — — 237 — 0.005 

S-NSF-VP15 4.08 4 104 0.632 3.4 0.24 — 221 — 0.281 
Table 8. Trace elements detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin PAugust 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3D. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Franc

unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark l30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-Cno MCL-US exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California Department of Pubcontaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbrev

Survey; LT-MDL, long-term method detection limit; SRL, study reporting level; μg/L, micrograms per liter; na, not available; —, not detected; ≤, less than or equal to; *, concenbenchmark level; nc, not collected] 

GAMA well identification number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Uranium (μg/L) (22703) 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedValley and Plains study area wells (30 wells sampled)—ContinuedS-NSF-VP16 213 *542 5.74 0.4 — — 94.1 — 0.008 

S-NSF-VP17 16.9 1.2 0.511 6.4 3.6 — 214 — 1.08 

S-NSF-VP18 6.01 0.4 0.332 2.3 0.10 — 300 — 0.108 

S-NSF-VP19 42.6 *1,080 0.626 — — — 121 — — 

S-NSF-VP20 0.49 2.4 1.50 14.7 2.9 0.006 100 0.02 0.178 

S-NSF-VP21 32.3 4 139 19.4 0.5 0.04 — 74.4 — 0.096 

S-NSF-VP22 16.8 0.5 0.274 2.2 1.2 — 157 — 0.648 

S-NSF-VP23 58.3 4 230 10.7 ≤0.1 — — 50.1 0.02 0.004 

S-NSF-VP24 31.1 5.1 14.7 0.4 0.16 — 114 — 1.89 

S-NSF-VP25 43.6 17.3 1.10 2 2.5 — 1,110 — 0.986 

S-NSF-VP26 23.2 22.7 0.235 1.4 0.06 — 142 — 0.009 

S-NSF-VP27 27 4 183 0.292 0.6 0.06 — 294 — 0.185 

S-NSF-VP28 21.7 *1,470 0.982 1.3 0.10 — 196 — 0.177 

S-NSF-VP29 8.06 — 0.446 1.3 0.24 — 285 — 0.429 

S-NSF-VP30 23.3 *978 4.42 0.8 — — 107 0.02 0.279 

North San Francisco Bay Shallow Aquifer study unit understanding well (1 well sampled)S-NSF-HU30 3.11 — 0.371 8.8 0.11 — 86.6 — 0.130 

1 The SRL was defined by Olsen and others (2010). 2 The SRL was defined by Tracy Davis and is based on an updated assessment of field blank detections of trace elements (Tracy Davis, U.S. Geological Survey, written comm3 Concentration of boron greater than the California notification level of 1,000 μg/L.4 Concentration greater than California secondary maximum contaminant level for manganese of 50 μg/L.
56 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Table 9. Nutrients detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority 

Basin Project, April to August 2012.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were 

analyzed, but only samples with detections are listed. Information about the constituents given in table 3E. GAMA well identification number: S-NSF-H, North 

San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study 

area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark level, 

and LT-MDL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are 

identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HAL-US, U.S. Environmental Protection Agency (USEPA) 

lifetime health advisory level; MCL-US, USEPA maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; LT-MDL, long-term 

method detection limit; mg/L, milligrams per liter; *, concentration greater than the benchmark level; na, not available; —, not detected]

GAMA 

well 

identification 

number

Ammonia 

(as nitrogen) 

(mg/L) 

(00608)

Nitrite 

(as nitrogen) 

(mg/L) 

(00613)

Nitrite plus nitrate 

(as nitrogen) 1

(mg/L) 

(00631)

Total nitrogen 

(ammonia + nitrate + nitrite 

+ organic nitrogen) 

(mg/L) 

(62854)

Phosphate, 

orthophosphate 

(as phosphorus) 

(mg/L) 

(00671)

Benchmark type HAL-US MCL-US MCL-US na na

Benchmark level 2

 24.7 1 10 na na

[LT-MDL] [0.01] [0.001] [0.04] [0.05] [0.004]

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)

Highlands study area wells (40 wells sampled)

S-NSF-H01 — — — — 0.021

S-NSF-H02 — — 0.14 0.11 0.019

S-NSF-H03 — — — — 0.042

S-NSF-H04 — — — — 0.004

S-NSF-H05 0.04 0.001 — — 0.007

S-NSF-H06 0.09 — 0.08 0.15 0.01

S-NSF-H07 — — 0.09 0.09 0.014

S-NSF-H08 0.14 — — 0.15 0.006

S-NSF-H09 0.01 — — — 0.014

S-NSF-H10 — — 0.05 — 0.065

S-NSF-H11 0.01 — — — 0.028

S-NSF-H12 0.03 — — — 0.097

S-NSF-H13 0.24 — — 0.26 0.039

S-NSF-H14 0.22 — — 0.24 0.008

S-NSF-H15 0.04 — — — 0.129

S-NSF-H16 0.02 — — — 0.739

S-NSF-H17 0.09 0.017 0.14 0.18 0.034

S-NSF-H18 — 0.012 0.28 0.30 0.038

S-NSF-H19 — — — — 0.004

S-NSF-H20 — — 0.19 0.19 0.042

S-NSF-H21 0.03 — — — 0.066

S-NSF-H22 0.17 — — 0.18 0.181

S-NSF-H23 — — 1.28 1.30 0.081

S-NSF-H24 — — 0.80 0.82 0.439

S-NSF-H25 — — 0.07 0.08 0.077
Tables 57

Table 9. Nutrients detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority 

Basin Project, April to August 2012.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were 

analyzed, but only samples with detections are listed. Information about the constituents given in table 3E. GAMA well identification number: S-NSF-H, North 

San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study 

area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark level, 

and LT-MDL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are 

identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HAL-US, U.S. Environmental Protection Agency (USEPA) 

lifetime health advisory level; MCL-US, USEPA maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; LT-MDL, long-term 

method detection limit; mg/L, milligrams per liter; *, concentration greater than the benchmark level; na, not available; —, not detected]

GAMA 

well 

identification 

number

Ammonia 

(as nitrogen) 

(mg/L) 

(00608)

Nitrite 

(as nitrogen) 

(mg/L) 

(00613)

Nitrite plus nitrate 

(as nitrogen) 1

(mg/L) 

(00631)

Total nitrogen 

(ammonia + nitrate + nitrite 

+ organic nitrogen) 

(mg/L) 

(62854)

Phosphate, 

orthophosphate 

(as phosphorus) 

(mg/L) 

(00671)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued

Highlands study area wells (40 wells sampled)—Continued

S-NSF-H26 — — 0.07 — 0.038

S-NSF-H27 — — 4.64 4.63 0.034

S-NSF-H28 0.01 — 0.40 0.41 0.293

S-NSF-H29 1.5 0.002 0.05 1.62 0.045

S-NSF-H30 — — 0.38 0.4 0.216

S-NSF-H31 0.01 — — — 0.021

S-NSF-H32 — — 0.05 — 0.272

S-NSF-H33 — — 0.06 0.06 0.186

S-NSF-H34 1.02 0.006 0.12 1.41 0.101

S-NSF-H35 — — 0.47 0.46 0.198

S-NSF-H36 — — 2.07 1.99 0.152

S-NSF-H37 — — 0.56 0.59 0.152

S-NSF-H38 0.60 — — 0.70 0.052

S-NSF-H39 0.01 — 0.46 0.47 0.443

S-NSF-H40 — 0.004 5.37 6.20 0.007

Valley and Plains study area wells (30 wells sampled)

S-NSF-VP01 0.10 0.003 0.94 1.22 0.13

S-NSF-VP02 — — 7.53 7.59 0.191

S-NSF-VP03 0.18 0.003 0.21 0.46 0.358

S-NSF-VP04 — 0.002 0.46 0.44 0.042

S-NSF-VP05 0.11 0.004 0.72 0.79 0.443

S-NSF-VP06 0.13 — — 0.15 0.126

S-NSF-VP07 0.01 — — — 0.032

S-NSF-VP08 — — 1.98 1.90 0.225

S-NSF-VP09 0.40 — — 0.42 0.219

S-NSF-VP10 0.05 — — 0.06 0.267
58 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Table 9. Nutrients detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority 

Basin Project, April to August 2012.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were 

analyzed, but only samples with detections are listed. Information about the constituents given in table 3E. GAMA well identification number: S-NSF-H, North 

San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer study unit Highlands study 

area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmark level, 

and LT-MDL as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are 

identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. HAL-US, U.S. Environmental Protection Agency (USEPA) 

lifetime health advisory level; MCL-US, USEPA maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; LT-MDL, long-term 

method detection limit; mg/L, milligrams per liter; *, concentration greater than the benchmark level; na, not available; —, not detected]

GAMA 

well 

identification 

number

Ammonia 

(as nitrogen) 

(mg/L) 

(00608)

Nitrite 

(as nitrogen) 

(mg/L) 

(00613)

Nitrite plus nitrate 

(as nitrogen) 1

(mg/L) 

(00631)

Total nitrogen 

(ammonia + nitrate + nitrite 

+ organic nitrogen) 

(mg/L) 

(62854)

Phosphate, 

orthophosphate 

(as phosphorus) 

(mg/L) 

(00671)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued

Valley and Plains study area wells (30 wells sampled)—Continued

S-NSF-VP11 — — *14 13 0.099

S-NSF-VP12 0.16 — — 0.14 0.045

S-NSF-VP13 0.20 — — 0.16 0.184

S-NSF-VP14 0.30 — — 0.32 0.332

S-NSF-VP15 — 0.001 1.87 2.01 0.071

S-NSF-VP16 0.79 0.002 — 0.85 0.223

S-NSF-VP17 — — 1.12 1.20 0.046

S-NSF-VP18 — — 1.94 1.99 0.018

S-NSF-VP19 0.04 — — — 0.043

S-NSF-VP20 0.04 — — — 0.425

S-NSF-VP21 0.18 — — 0.21 0.663

S-NSF-VP22 — — 3.2 3.29 0.178

S-NSF-VP23 0.15 — — 0.15 1.61

S-NSF-VP24 0.06 0.001 0.10 0.26 0.129

S-NSF-VP25 — 0.007 *10 10.1 0.09

S-NSF-VP26 — — 4.41 4.22 0.237

S-NSF-VP27 — 0.007 4.72 5.17 0.093

S-NSF-VP28 0.07 — — 0.10 0.329

S-NSF-VP29 — — 1.53 1.53 0.063

S-NSF-VP30 0.09 — — 0.11 0.512

North San Francisco Bay Shallow Aquifer study unit understanding well (1 well sampled)

S-NSF-HU30 — — 0.38 0.42 0.086

1

 Nitrite plus nitrate (as nitrogen) is referred to as nitrate in the text for clarity.

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.”
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the North San Francisco Bay Shallow Aquif

GAMA Priority Basin Project, April to August 2012.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3F. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francstudy unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmas of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when than the MCL-US or no MCL-US exists. The SMCL-CA benchmark for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark level MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: US

LT-MDL, long-term method detection limit; mg/L, milligrams per liter; SiO2, silicon dioxide; na, not available; —, not detected; *, concentration greater than the recommended 

concentration greater than upper benchmark level]

GAMA 

well 

identification 

number

Bromide 

(mg/L) 

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Iodide 

(mg/L) 

(71865)

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

Benchmark type na na SMCL-CA MCL-CA na na na na SMCL-CA 

Benchmark level na na 250 (500) 2 na na na na 250 (500) 

[LT-MDL] [0.01] [0.022] [0.06] [0.04] [0.001] [0.011] [0.03] [0.06] [0.09] 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)Highlands study area wells (40 wells sampled)S-NSF-H01 0.11 13.4 20.1 0.1 0.002 20.9 1.13 16.6 39.7 S-NSF-H02 0.02 19.4 6.53 0.06 — 27.9 0.64 7.19 6.08 S-NSF-H03 0.02 18.1 4.78 0.24 — 6.05 0.6 13.1 3.94 S-NSF-H04 0.03 17.6 4.68 *5.2 0.009 13.9 0.91 175 14 

S-NSF-H05 0.03 64.9 6.39 0.37 — 21.7 1.46 20.4 34.9 

S-NSF-H06 0.04 71 5.57 0.54 — 38.9 2.85 48.1 63.9 

S-NSF-H07 0.04 12.6 5.67 — — 48.3 0.35 4.4 8.2 

S-NSF-H08 0.06 2.17 19 1.87 0.016 1.5 1.11 183 21.6 

S-NSF-H09 0.03 37.4 6.08 0.42 0.007 13.5 0.51 31.2 37.9 

S-NSF-H10 0.03 15.5 4.33 0.07 — 3.06 0.85 10 9.23 

S-NSF-H11 0.03 19 7.58 0.08 0.001 6.08 1.24 11.5 4.1 

S-NSF-H12 0.06 15 24.5 0.27 0.003 17.1 1.43 18.6 47.2 

S-NSF-H13 0.11 0.922 41.3 0.23 0.009 0.046 0.36 126 13.1 

S-NSF-H14 0.14 32.8 48.4 0.09 0.003 13.1 0.58 70 58.9 

S-NSF-H15 0.12 21.4 21.7 0.1 0.014 17.4 0.28 19.6 26.6 
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the North San Francisco Bay Shallow AquifGAMA Priority Basin Project, April to August 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3F. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francstudy unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmas of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when than the MCL-US or no MCL-US exists. The SMCL-CA benchmark for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark level MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: US

LT-MDL, long-term method detection limit; mg/L, milligrams per liter; SiO2, silicon dioxide; na, not available; —, not detected; *, concentration greater than the recommended 

concentration greater than upper benchmark level] GAMA well identification number Bromide (mg/L) (71870) Calcium (mg/L) (00915) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Iodide (mg/L) (71865) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Highlands study area wells (40 wells sampled)—Continued S-NSF-H16 0.08 22.6 17.9 0.11 0.011 12.2 1.38 26.7 54.1 S-NSF-H17 0.08 64.8 23.7 0.07 0.002 46.2 2.97 23.3 240 S-NSF-H18 0.22 33.5 27.7 0.17 0.07 42.2 0.8 38.9 58.5 S-NSF-H19 0.02 28.3 4.86 0.14 — 23.5 1.3 6.4 11.3 S-NSF-H20 0.02 17.1 2.49 0.09 — 6.4 1.62 8.05 2.12 S-NSF-H21 0.04 31.7 10.2 0.21 0.002 21.6 4.36 23.1 23.1 

S-NSF-H22 0.19 3.86 50.1 0.75 0.206 1.1 7.78 210 — 

S-NSF-H23 0.04 17.3 8.41 — — 9.35 0.83 10.9 1.25 

S-NSF-H24 0.03 11.1 5.19 0.27 — 5.46 1.02 12.4 1.08 

S-NSF-H25 0.02 28.4 5.31 0.12 — 13.9 2.92 12.1 2.83 

S-NSF-H26 0.26 95.5 97.7 0.15 0.012 14.2 1.19 36.9 26.6 

S-NSF-H27 0.34 91.3 135 0.36 0.045 82.4 0.35 114 *360 S-NSF-H28 0.03 9.66 8.07 0.21 — 6.66 3.44 14.9 2.45 

S-NSF-H29 0.23 254 54.1 0.14 0.01 37.2 8.83 39.4 **667 S-NSF-H30 0.02 7.6 4.5 0.14 — 4.19 2.55 10.7 2.93 

S-NSF-H31 0.03 89.4 7.28 0.2 0.028 82.6 1.77 13.9 228 

S-NSF-H32 0.03 10.2 4.17 0.1 — 10.5 3.75 10.5 0.92 

S-NSF-H33 0.02 13 4.75 0.12 — 5.72 3.34 13.5 4.18 

S-NSF-H34 — 31.4 71 0.22 0.095 29.3 5.27 110 32.9 

S-NSF-H35 0.04 18.8 9.6 0.17 — 20.6 3.11 15.3 7.44 
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the North San Francisco Bay Shallow AquifGAMA Priority Basin Project, April to August 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3F. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francstudy unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmas of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when than the MCL-US or no MCL-US exists. The SMCL-CA benchmark for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark level MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: US

LT-MDL, long-term method detection limit; mg/L, milligrams per liter; SiO2, silicon dioxide; na, not available; —, not detected; *, concentration greater than the recommended 

concentration greater than upper benchmark level]

GAMA 

well 

identification 

number

Bromide 

(mg/L) 

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Iodide 

(mg/L) 

(71865)

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedHighlands study area wells (40 wells sampled)—ContinuedS-NSF-H36 0.02 10.1 16.5 0.05 0.004 6.03 4.92 14.2 9.89 S-NSF-H37 0.03 8.77 4.63 0.08 0.001 5.78 1.73 7.6 1.13 S-NSF-H38 — 3.37 121 *2.1 0.388 0.375 1.08 384 6.89 

S-NSF-H39 0.03 7.7 7.4 0.17 — 4.7 3 13.9 2.04 S-NSF-H40 0.89 152 212 0.26 0.005 75.1 3.32 92.8 166 Valley and Plains study area wells (30 wells sampled)S-NSF-VP01 — 121 *278 0.17 0.065 69.7 3.22 155 104 

S-NSF-VP02 0.01 84.7 31.5 0.12 0.008 41.2 1.32 36.2 30.4 S-NSF-VP03 0.30 52.2 198 0.15 0.094 45.5 2.14 107 32.8 S-NSF-VP04 0.15 21.4 51.2 0.09 0.007 9.17 1.28 36.1 19.2 S-NSF-VP05 0.12 7.19 42.7 0.19 0.032 5.74 1.36 103 3.41 S-NSF-VP06 0.15 25.8 9.09 0.09 0.038 35.7 0.71 32.5 23.1 S-NSF-VP07 0.12 59 28.7 0.2 0.003 37.9 0.55 35 47.9 S-NSF-VP08 0.19 19 56.3 0.26 — 21.3 4.26 26.1 3.95 S-NSF-VP09 0.15 22 50.9 0.09 0.018 18.6 14.2 31.6 2.59 S-NSF-VP10 0.12 27.2 40.5 0.13 0.01 19.6 1.4 26 8.8 S-NSF-VP11 0.22 70.9 72.8 0.21 0.013 28.2 1.89 63.8 32.7 S-NSF-VP12 0.09 20.6 47.4 0.24 0.013 14.6 1.72 100 20 S-NSF-VP13 0.07 3.95 26.2 0.42 0.037 1.13 2.47 134 8.18 

S-NSF-VP14 — 64.4 22.6 0.21 0.019 41.5 8.33 51.8 22.3 

S-NSF-VP15 0.08 37 18.3 0.12 0.002 42.4 1.06 20.4 18.6 
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the North San Francisco Bay Shallow AquifGAMA Priority Basin Project, April to August 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3F. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francstudy unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type, benchmas of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when than the MCL-US or no MCL-US exists. The SMCL-CA benchmark for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark level MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: US

LT-MDL, long-term method detection limit; mg/L, milligrams per liter; SiO2, silicon dioxide; na, not available; —, not detected; *, concentration greater than the recommended 

concentration greater than upper benchmark level] GAMA well identification number Bromide (mg/L) (71870) Calcium (mg/L) (00915) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Iodide (mg/L) (71865) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Valley and Plains study area wells (30 wells sampled)—Continued S-NSF-VP16 0.07 14.6 18.7 0.13 0.006 10.7 20.1 70 24.7 S-NSF-VP17 0.14 21.6 32.7 0.14 0.002 47.6 2.37 39.4 34.3 S-NSF-VP18 0.14 34.6 8.64 0.11 — 29.8 0.74 9.51 30.8 S-NSF-VP19 0.09 22.3 15.5 0.08 0.003 16.2 4.51 15.2 31.9 S-NSF-VP20 0.04 13.3 6.61 0.09 0.002 13.2 6.37 10 13.1 S-NSF-VP21 0.20 7.25 73.6 0.24 0.142 3.66 3.24 147 14.6 

S-NSF-VP22 0.14 24.1 32.6 0.14 0.005 30.2 2.05 27.7 23.2 

S-NSF-VP23 0.29 5.77 59 0.52 0.259 2.42 9.67 202 1.9 

S-NSF-VP24 0.16 10.3 36.3 0.23 0.085 3.97 1.23 192 36.4 

S-NSF-VP25 0.66 116 *369 0.25 0.034 49.9 2.41 122 37 S-NSF-VP26 0.08 17.2 22.7 0.21 0.003 11.1 1.46 28.4 25.4 S-NSF-VP27 0.10 35.7 33.5 0.2 0.01 23.6 1.28 36.4 40.7 

S-NSF-VP28 1.25 26.7 15 0.14 0.022 34.4 3.07 19.8 47.6 

S-NSF-VP29 0.08 31.7 11.4 0.11 — 39.1 1.71 16 34.2 

S-NSF-VP30 0.05 27.7 17.2 0.2 0.02 16.8 8.23 31.4 12.6 

North San Francisco Bay Shallow Aquifer study unit understanding well (1 well sampled)S-NSF-HU30 0.02 20.3 7.1 0.08 — 27.1 1.93 10.5 6.81 
Tables 63

Table 11. Isotopic tracers detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA 

Priority Basin Project, April to August 2012.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about the 

constituents given in table 3G. Samples from all 71 wells were analyzed. Stable isotope ratios of hydrogen, oxygen, and carbon 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. GAMA well identification 

number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer 

study unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. 

Benchmark type and benchmark level as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the 

MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. MCL-CA, California Department 

of Public Health maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; B, boron; C, Carbon; H, hydrogen; O, oxygen; Sr, 

strontium; na, not available]

GAMA well identification number

11B/10B in water

(per mil)

(62648)

δ13C in dissolved 

inorganic carbon 

(per mil) 

(82081)

Carbon-14 in 

water 

(percent modern) 

(49933)

δ2

H in water 

(per mil) 

(82082)

δ18O in water 

(per mil) 

(82085)

87Sr/86Sr 

(atom ratio) 

(75978)

Benchmark type na na na na na na

Benchmark level na na na na na na

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)

Highlands study area wells (40 wells sampled)

S-NSF-H01 na –21.00 95.97 –32.5 –5.71 0.71947

S-NSF-H02 na –17.76 100.3 –33.8 –5.88 0.71257

S-NSF-H03 na –16.19 101.4 –38.8 –6.59 0.70891

S-NSF-H04 4.14 –16.18 11.96 –44.5 –6.84 0.70651

S-NSF-H05 na –17.77 52.94 –45.6 –7.11 0.70726

S-NSF-H06 3.98 –12.67 33.80 –46.8 –7.29 0.70637

S-NSF-H07 na –15.56 106.5 –44.1 –7.07 0.70703

S-NSF-H08 4.11 –15.26 18.88 –54.0 –8.14 0.70611

S-NSF-H09 4.06 –18.89 42.9 –43.9 –6.83 0.70651

S-NSF-H10 na –16.95 103.3 –40.0 –6.69 0.70634

S-NSF-H11 4.15 –18.13 100.9 –36.0 –6.06 0.70906

S-NSF-H12 na –20.06 94.70 –34.0 –5.69 0.70638

S-NSF-H13 4.00 –21.52 16.42 –35.8 –5.81 0.70738

S-NSF-H14 na –21.79 96.35 –35.1 –5.58 0.70730

S-NSF-H15 na –21.24 90.18 –36.3 –5.78 0.70542

S-NSF-H16 4.05 –21.75 102 –36.9 –5.81 0.70598

S-NSF-H17 3.98 –21.03 56.87 –35.2 –5.62 0.70565

S-NSF-H18 4.06 –19.68 101.9 –38.8 –6.10 0.70681

S-NSF-H19 na –12.78 36.89 –41.1 –6.58 0.70650

S-NSF-H20 na –15.88 96.83 –42.8 –6.47 0.70511

S-NSF-H21 na –15.59 33.18 –42.4 –6.70 0.70601

S-NSF-H22 4.11 –3.43 5.21 –50.7 –8.00 0.70580

S-NSF-H23 na –21.71 98.10 –39.5 –6.31 0.70371

S-NSF-H24 na –17.58 66.90 –39.5 –6.04 0.70425

S-NSF-H25 na –17.69 89.66 –43.4 –6.87 0.70414
64 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Table 11. Isotopic tracers detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA 

Priority Basin Project, April to August 2012.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about the 

constituents given in table 3G. Samples from all 71 wells were analyzed. Stable isotope ratios of hydrogen, oxygen, and carbon 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. GAMA well identification 

number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer 

study unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. 

Benchmark type and benchmark level as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the 

MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. MCL-CA, California Department 

of Public Health maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; B, boron; C, Carbon; H, hydrogen; O, oxygen; Sr, 

strontium; na, not available]

GAMA well identification number

11B/10B in water

(per mil)

(62648)

δ13C in dissolved 

inorganic carbon 

(per mil) 

(82081)

Carbon-14 in 

water 

(percent modern) 

(49933)

δ2

H in water 

(per mil) 

(82082)

δ18O in water 

(per mil) 

(82085)

87Sr/86Sr 

(atom ratio) 

(75978)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued

Highlands study area wells (40 wells sampled)—Continued

S-NSF-H26 4.07 –16.14 53.22 –39.3 –6.07 0.70653

S-NSF-H27 4.10 –18.27 99.63 –31.0 –4.01 0.70639

S-NSF-H28 na –19.13 76.25 –40.7 –6.43 0.70435

S-NSF-H29 na –18.95 78.31 –41.2 –6.62 0.70449

S-NSF-H30 –18.41 72.57 –41.0 –6.49 0.70421

S-NSF-H31 4.09 –16.15 55.95 –44.1 –6.94 0.70642

S-NSF-H32 na –20.57 90.42 –44.7 –7.12 0.70519

S-NSF-H33 na –18.83 66.66 –44.8 –7.00 0.70476

S-NSF-H34 4.11 –19.86 81.71 –41.3 –6.20 0.70686

S-NSF-H35 4.08 –14.88 75.15 –42.6 –6.37 0.70522

S-NSF-H36 na –21.14 101.8 –40.0 –6.50 0.70522

S-NSF-H37 na –19.93 87.58 –41.5 –6.53 0.70529

S-NSF-H38 4.13 –11.03 22.70 –37.3 –6.06 0.70706

S-NSF-H39 na –18.40 58.76 –40.2 –6.35 0.70439

S-NSF-H40 3.99 –17.84 70.60 –42.2 –6.14 0.70741

Valley and Plains study area wells (30 wells sampled)

S-NSF-VP01 4.01 –17.75 100.7 –38.4 –5.81 0.70607

S-NSF-VP02 4.09 –20.72 105.4 –37.0 –5.76 0.70492

S-NSF-VP03 4.02 –19.34 49.42 –39.5 –6.09 0.70596

S-NSF-VP04 na –22.38 80.54 –36.3 –5.90 0.70618

S-NSF-VP05 4.02 –15.89 37.39 –41.0 –6.28 0.70591

S-NSF-VP06 4.09 –18.17 97.76 –37.1 –6.01 0.70665

S-NSF-VP07 3.98 –17.95 73.11 –38.4 –5.92 0.70484

S-NSF-VP08 na –20.63 84.08 –38.5 –6.14 0.70557

S-NSF-VP09 na –20.47 84.19 –36.7 –5.92 0.70537

S-NSF-VP10 4.04 –18.49 96.27 –38.6 –5.85 0.70537
Tables 65

Table 11. Isotopic tracers detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA 

Priority Basin Project, April to August 2012.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about the 

constituents given in table 3G. Samples from all 71 wells were analyzed. Stable isotope ratios of hydrogen, oxygen, and carbon 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. GAMA well identification 

number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Shallow Aquifer 

study unit Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. 

Benchmark type and benchmark level as of August 30, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the 

MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. MCL-CA, California Department 

of Public Health maximum contaminant level. Other abbreviations: USGS, U.S. Geological Survey; B, boron; C, Carbon; H, hydrogen; O, oxygen; Sr, 

strontium; na, not available]

GAMA well identification number

11B/10B in water

(per mil)

(62648)

δ13C in dissolved 

inorganic carbon 

(per mil) 

(82081)

Carbon-14 in 

water 

(percent modern) 

(49933)

δ2

H in water 

(per mil) 

(82082)

δ18O in water 

(per mil) 

(82085)

87Sr/86Sr 

(atom ratio) 

(75978)

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued

Valley and Plains study area wells (30 wells sampled)—Continued

S-NSF-VP11 4.05 –20.46 103.6 –37.1 –5.52 0.70636

S-NSF-VP12 3.98 –16.47 56.96 –39.9 –6.08 0.70609

S-NSF-VP13 3.96 –16.63 4.60 –51.0 –7.61 0.70566

S-NSF-VP14 4.00 –21.09 87.64 –40.9 –6.05 0.70506

S-NSF-VP15 4.05 –19.91 102.2 –40.2 –6.29 0.70602

S-NSF-VP16 3.98 –18.96 41.48 –45.7 –6.85 0.70569

S-NSF-VP17 4.07 –17.99 98.97 –40.2 –6.31 0.70635

S-NSF-VP18 4.02 –17.21 94.67 –44.4 –6.79 0.70631

S-NSF-VP19 na –19.85 75.04 –38.1 –5.89 0.70503

S-NSF-VP20 na –21.3 93.11 –39.5 –6.29 0.70673

S-NSF-VP21 4.09 –19.36 7.24 –48.3 –7.48 0.70565

S-NSF-VP22 na –19.45 104 –38.5 –5.86 0.70552

S-NSF-VP23 4.15 –13.60 1.18 –50.7 –7.73 0.70611

S-NSF-VP24 4.02 –15.88 63.41 –35.3 –4.70 0.70621

S-NSF-VP25 4.05 –16.18 79.37 –37.5 –5.83 0.70704

S-NSF-VP26 4.10 –18.62 85.88 –38.9 –5.96 0.70680

S-NSF-VP27 4.08 –20.09 97.17 –39.4 –5.85 0.70684

S-NSF-VP28 4.02 –20.30 99.18 –40.0 –6.12 0.70603

S-NSF-VP29 4.05 –16.70 96.13 –39.0 –5.76 0.70648

S-NSF-VP30 na –19.77 89.31 –42.5 –6.62 0.70459

North San Francisco Bay Shallow Aquifer study unit understanding well (1 well sampled)

S-NSF-HU30 na –15.8 102.8 –39.5 –6.51 0.70516
Table 12. Radioactive constituents detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA PrioAugust 2012. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). Tritium activities were not measured less than the ssLC; 

reported. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type and benchmark leBenchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant leveU.S. Geological Survey; RL, reporting level; CSU, 1-sigma combined standard uncertainty; pCi/L, picocuries per liter; —, not detected; *, concentration greater than the benchmnot collected] GAMA well identification number 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 rad

30-day c

(pCi/L

(62645

Benchmark type Proposed MCL-US MCL-US MCL-US MCL-CA MCL-CBenchmark level 4,000 15 15 50 50 [RL] Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU 

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled) Highlands study area wells (40 wells sampled) S-NSF-H01 127 ± 12 12 — 0.49 — 0.51 — 0.75 1.04 ± 0.55 

S-NSF-H02 300 ± 21 12 — 0.64 — 0.63 0.75 ± 0.46 0.72 0.8 ± 0.5 S-NSF-H03 — 13 0.67 ± 0.47 0.50 — 0.48 — 0.65 — S-NSF-H04 157 ± 14 12 — 1.10 — 1.20 1.02 ± 0.35 0.54 — S-NSF-H05 104 ± 12 13 2.88 ± 0.71 0.63 — 0.66 1.80 ± 0.43 0.64 1.63 ± 0.41 

S-NSF-H06 300 ± 21 11 1.66 ± 0.87 0.93 — 1.20 1.74 ± 0.61 0.90 2.46 ± 0.57 

S-NSF-H07 55 ± 8.8 11 — 0.57 — 0.71 — 0.85 — 

S-NSF-H08 45 ± 8.1 11 1.68 ± 0.92 0.98 — 1.10 1.83 ± 0.61 0.96 — 

S-NSF-H09 163 ± 13 11 2.94 ± 0.63 0.45 — 0.75 1.07 ± 0.34 0.51 — 

S-NSF-H10 — 12 0.8 ± 0.5 0.62 — 0.64 1.45 ± 0.45 0.66 — 

S-NSF-H11 980 ± 56 12 0.48 ± 0.24 0.30 1.17 ± 0.46 0.39 0.49 ± 0.29 0.46 — 

S-NSF-H12 220 ± 18 14 — 0.62 — 0.55 1.12 ± 0.48 0.74 1.14 ± 0.45 

S-NSF-H13 204 ± 15 11 1.39 ± 0.76 0.88 — 0.89 — 0.75 — 

S-NSF-H14 93 ± 10 12 0.93 ± 0.61 0.66 — 0.76 — 0.84 — 

S-NSF-H15 165 ± 15 14 — 0.65 — 0.63 — 0.59 — 
Table 12. Radioactive constituents detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA PrioAugust 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). Tritium activities were not measured less than the ssLC; 

reported. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type and benchmark leBenchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant leveU.S. Geological Survey; RL, reporting level; CSU, 1-sigma combined standard uncertainty; pCi/L, picocuries per liter; —, not detected; *, concentration greater than the benchmnot collected]

GAMA 

well 

identification 

number

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 rad

30-day c

(pCi/L

(62645

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedHighlands study area wells (40 wells sampled)—ContinuedS-NSF-H16 400 ± 26 11 — 0.48 — 0.60 0.95 ± 0.39 0.60 1.08 ± 0.42 S-NSF-H17 176 ± 16 15 — 1.20 — 0.83 2.78 ± 0.57 0.85 2.11 ± 0.56 S-NSF-H18 460 ± 29 12 2.3 ± 1.1 1.00 — 1.10 — 1.30 — 

S-NSF-H19 280 ± 20 11 — 0.61 — 0.66 0.90 ± 0.48 0.74 — 

S-NSF-H20 3,070 ± 170 13 2.13 ± 0.46 0.41 — 0.58 1.9 ± 0.3 0.40 2.09 ± 0.56 

S-NSF-H21 560 11 1 ± 0.5 0.58 — 0.81 3.74 ± 0.52 0.71 3.88 ± 0.54 

S-NSF-H22 *14,700 ± 790 11 — 1.30 — 1.30 7.40 ± 0.59 0.51 7.01 ± 0.57 

S-NSF-H23 158 ± 15 14 — 0.44 — 0.51 0.74 ± 0.29 0.45 — S-NSF-H24 460 ± 31 16 — 0.52 — 0.43 1.31 ± 0.49 0.72 — S-NSF-H25 540 ± 33 11 — 0.45 — 0.56 2.12 ± 0.43 0.61 2.20 ± 0.37 

S-NSF-H26 *16,700 ± 890 11 — 0.88 2.42 ± 0.93 1.10 — 1.10 1.55 ± 0.66 S-NSF-H27 nc nc nc nc nc 

S-NSF-H28 890 ± 51 12 — 0.55 — 0.54 2.36 ± 0.49 0.69 1.38 ± 0.51 S-NSF-H29 nc 8.1 ± 2.1 1.80 — 2.00 7.89 ± 0.91 1.10 6.7 ± 0.7 

S-NSF-H30 1,420 ± 80 14 0.97 ± 0.56 0.55 — 0.57 2.08 ± 0.56 0.83 — 

S-NSF-H31 41 ± 8.3 11 — 1.20 — 1.30 2.15 ± 0.41 0.57 2.60 ± 0.81 

S-NSF-H32 940 ± 56 16 0.60 ± 0.31 0.40 — 0.52 1.94 ± 0.35 0.51 1.36 ± 0.42 

S-NSF-H33 2,250 ± 120 12 1.27 ± 0.46 0.47 — 0.62 2.87 ± 0.37 0.48 3.05 ± 0.58 

S-NSF-H34 165 ± 15 13 1.53 ± 0.82 1.10 — 1.00 4.98 ± 0.66 0.86 3.86 ± 0.73 

S-NSF-H35 810 ± 49 16 0.93 ± 0.34 0.33 — 0.54 2.75 ± 0.46 0.64 1.7 ± 0.4 
Table 12. Radioactive constituents detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA PrioAugust 2012.—Continued [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). Tritium activities were not measured less than the ssLC; 

reported. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type and benchmark leBenchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant leveU.S. Geological Survey; RL, reporting level; CSU, 1-sigma combined standard uncertainty; pCi/L, picocuries per liter; —, not detected; *, concentration greater than the benchmnot collected] GAMA well identification number 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 rad

30-day c

(pCi/L

(62645

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—Continued Highlands study area wells (40 wells sampled)—Continued S-NSF-H36 1,170 ± 67 14 0.83 ± 0.31 0.34 0.82 ± 0.43 0.47 4.47 ± 0.45 0.51 4.69 ± 0.54 

S-NSF-H37 380 ± 24 11 — 0.55 — 0.55 1.0 ± 0.6 0.94 1.54 ± 0.48 S-NSF-H38 34 ± 8.3 12 — 2.20 — 2.60 1.78 ± 0.61 0.93 — 

S-NSF-H39 1,140 ± 64 11 0.42 ± 0.24 0.28 — 0.33 — 0.64 0.67 ± 0.39 

S-NSF-H40 270 ± 22 18 3.0 ± 1.6 1.90 — 2.40 3.80 ± 0.68 0.93 2.84 ± 0.62 

Valley and Plains study area wells (30 wells sampled) S-NSF-VP01 760 ± 45 14 6.6 ± 2.4 2.70 — 2.40 3.19 ± 0.67 0.98 4.87 ± 0.75 

S-NSF-VP02 780 ± 46 13 2.76 ± 0.99 1.10 1.50 ± 0.82 1.00 0.8 ± 0.3 0.46 1.90 ± 0.46 

S-NSF-VP03 520 ± 32 12 — 1.70 — 1.20 1.88 ± 0.35 0.50 2.03 ± 0.39 S-NSF-VP04 137 ± 15 15 — 0.49 — 0.44 1.08 ± 0.39 0.60 1.2 ± 0.4 S-NSF-VP05 790 ± 47 13 — 0.90 — 0.67 — 0.68 1.29 ± 0.45 

S-NSF-VP06 310 ± 21 13 1.69 ± 0.53 0.61 — 0.80 0.6 ± 0.3 0.48 — 

S-NSF-VP07 72 ± 9.7 12 1.28 ± 0.71 0.77 — 1.50 — 0.97 — S-NSF-VP08 540 ± 34 13 1.02 ± 0.56 0.60 — 0.52 3.25 ± 0.63 0.86 3.02 ± 0.52 

S-NSF-VP09 770 ± 46 13 1.1 ± 0.5 0.60 — 0.91 10.9 ± 0.78 0.60 11.6 ± 0.95 

S-NSF-VP10 600 ± 37 13 0.93 ± 0.41 0.49 — 0.56 — 0.69 1.15 ± 0.46 S-NSF-VP11 520 ± 33 13 3.3 ± 1.2 1.30 — 1.10 1.98 ± 0.38 0.53 2.56 ± 0.41 

S-NSF-VP12 400 ± 25 11 — 1.10 — 0.73 1.08 ± 0.42 0.66 1.54 ± 0.61 

S-NSF-VP13 1,770 ± 98 11 1.96 ± 0.82 0.99 — 1.20 2.6 ± 0.52 0.76 2.03 ± 0.56 

S-NSF-VP14 480 ± 31 14 1.12 ± 0.76 0.99 — 0.86 9.39 ± 0.68 0.55 7.38 ± 0.58 

S-NSF-VP15 700 ± 43 16 1 1.12 ± 0.61 0.72 — 0.84 1 1.48 ± 0.61 0.90 — 
Table 12. Radioactive constituents detected in samples collected for the North San Francisco Bay Shallow Aquifer study unit, California GAMA PrioAugust 2012.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 71 wells were analyzed. Informgiven in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). Tritium activities were not measured less than the ssLC; 

reported. GAMA well identification number: S-NSF-H, North San Francisco Bay Shallow Aquifer study unit Highlands study area well; S-NSF-HU, North San Francisco Bay Highlands study area understanding well; S-NSF-VP, North San Francisco Bay Shallow Aquifer study unit Valley and Plains study area well. Benchmark type and benchmark leBenchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant leveU.S. Geological Survey; RL, reporting level; CSU, 1-sigma combined standard uncertainty; pCi/L, picocuries per liter; —, not detected; *, concentration greater than the benchmnot collected]

GAMA 

well 

identification 

number

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 rad

30-day c

(pCi/L

(62645

North San Francisco Bay Shallow Aquifer study unit grid wells (70 wells sampled)—ContinuedValley and Plains study area wells (30 wells sampled)—ContinuedS-NSF-VP16 490 ± 31 14 2.49 ± 0.65 0.45 — 0.69 20.2 ± 1.3 0.66 18.5 ± 1.2 

S-NSF-VP17 280 ± 20 12 2.6 ± 0.8 0.80 3.62 ± 0.93 0.71 2.85 ± 0.82 1.20 1.94 ± 0.61 

S-NSF-VP18 234 ± 17 11 2.03 ± 0.45 0.28 — 0.57 1.34 ± 0.34 0.52 1.31 ± 0.46 

S-NSF-VP19 720 ± 42 11 1.13 ± 0.61 0.56 — 0.58 3.26 ± 0.63 0.83 2.92 ± 0.57 

S-NSF-VP20 480 ± 30 13 0.87 ± 0.28 0.24 0.6 ± 0.3 0.34 3.74 ± 0.41 0.52 3.0 ± 0.36 

S-NSF-VP21 780 ± 46 12 — 1.10 — 1.00 3.62 ± 0.82 1.20 2.54 ± 0.57 

S-NSF-VP22 1,100 ± 62 11 1.06 ± 0.61 0.68 — 0.87 1.68 ± 0.61 0.92 1.0 ± 0.55 

S-NSF-VP23 1,220 ± 68 11 — 1.60 — 1.20 7.71 ± 0.63 0.59 8.18 ± 0.56 

S-NSF-VP24 590 ± 35 11 6.3 ± 1.4 0.98 3.4 ± 1.2 1.20 1.88 ± 0.61 0.95 1.2 ± 0.6 

S-NSF-VP25 660 ± 39 11 — 2.10 — 2.30 3.25 ± 0.58 0.78 2.40 ± 0.61 

S-NSF-VP26 1,040 ± 59 11 — 0.50 — 0.48 1.11 ± 0.39 0.60 1.37 ± 0.35 

S-NSF-VP27 1,220 ± 69 11 — 0.57 — 0.74 1.26 ± 0.41 0.62 0.68 ± 0.39 

S-NSF-VP28 790 ± 47 14 0.79 ± 0.34 0.36 — 0.60 2.78 ± 0.47 0.64 1.75 ± 0.45 

S-NSF-VP29 510 ± 31 12 1.0 ± 0.4 0.45 — 0.59 1.84 ± 0.32 0.45 1.27 ± 0.55 

S-NSF-VP30 690 ± 41 12 0.72 ± 0.56 0.72 — 0.64 7.20 ± 0.68 0.73 7.38 ± 0.72 

North San Francisco Bay Shallow Aquifer study unit understanding well (1 well sampled)S-NSF-HU30 1,290 ± 74 14 0.83 ± 0.61 0.67 — 0.57 1.18 ± 0.55 0.81 1.65 ± 0.56 

1 Counted 4–6 days after sample collection.

Appendix A 71

This appendix includes discussions of the methods used 

to collect and analyze groundwater samples and report the 

resulting water-quality data. These methods were selected to 

obtain representative samples of the groundwater from each 

well and to minimize the potential for contamination of the 

samples or bias in the data. Procedures used to collect and 

assess QC data and the results of the QC assessments also are 

discussed.

In the NSF-SA study unit, groundwater samples 

were collected, and QA procedures were implemented by 

using standard and modified USGS protocols from the 

NAWQA Program (Koterba and others, 1995) and the NFM 

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

described by Shelton and others (2001) and Wright and others 

(2005). The QA plan followed by the NWQL, the primary 

laboratory used to analyze samples for this study, is described 

in Maloney (2005) and Pirkey and Glodt (1998).

Sample Collection and Analysis

Samples were collected from two types of sites: 

production wells and springs (“springs” in this study unit 

include horizontal wells). Sites classified as production 

wells are vertically drilled into the ground and have pumps 

that bring the groundwater from the aquifer to a distribution 

system. Sites were classified as springs if groundwater could 

discharge from the aquifer into the distribution system without 

a pump and if the well was either drilled horizontally or 

had no drilled hole. A few springs had pumps to transport 

groundwater from the spring to a storage tank at a higher 

elevation.

In most cases, wells were pumped continuously to purge 

at least three casing volumes of water from the well prior 

to sampling (Wilde and others, 1999). Drought conditions 

during the period of sampling for the NSF-SA study unit 

(April through August 2012) resulted in limitations on the 

amount of groundwater that could be pumped from some of 

the wells. In some cases, continuous pumping was limited to 2 

hours, either because of limited space in storage tanks for the 

pumped water or because of drawdown of the water table. A 

minimum of one casing volume of groundwater was pumped 

from each well before sampling. The limitation on pumping 

did not allow sufficient time to complete the sampling of a 

few wells, and some constituent groups were not collected 

from these wells. Wells were sampled by using Teflon® tubing 

with brass and stainless-steel fittings attached to a sampling 

point (usually a hose-bib fitting) on the well discharge pipe 

as close to the well head as possible. The sampling point was 

located upstream from water-storage tanks and from the wellhead treatment system (if a system existed). If a chlorinating 

system was attached to the well, the chlorinator was shut 

off, when possible, before the well was purged and sampled, 

in order to clear all chlorine out of the system. The absence 

of free chlorine was verified by using a Hach® field test kit. 

All samples were collected outdoors by connecting a 1- to 

3-ft length of Teflon® tubing to the sampling point (Lane and 

others, 2003). All fittings and lengths of tubing were cleaned 

between samples (Wilde, 2004).

For the field measurements, groundwater was pumped 

through a flow-through chamber that was attached to the 

sampling point and fitted with a multi-probe meter that 

simultaneously measures the field water-quality indicators—

dissolved oxygen, temperature, pH, and specific conductance. 

Field measurements were made in accordance with protocols 

in the NFM (Radtke and others, 2005; Wilde and Radtke, 

2005; Lewis, 2006; Wilde, 2006; Wilde and others, 2006). 

All sensors on the multi-probe meter were calibrated daily. 

Measured dissolved oxygen, temperature, pH, and specificconductance values were recorded at 3- to 5-minute (min) 

intervals, and when these values remained stable, samples for 

laboratory analyses then were collected.

Field measurements and instrument calibrations were 

recorded by hand on field record sheets and electronically 

in the Personal Computer Field Form (PCFF) program. 

Analytical service requests also were managed by PCFF, 

whereas analytical service requests for non-NWQL 

analysis were entered into laboratory-specific spreadsheets. 

Information from PCFF was uploaded directly into the USGS 

NWIS at the end of every week of sample collection.

Prior to sample collection, polyethylene sample bottles 

were pre-rinsed three times with deionized water and then 

once with native sample water before sample collection. 

Samples requiring acidification were acidified to a pH of 

between 2 and 1 with the appropriate acids using ampoules 

of certified, traceable concentrated acids obtained from the 

NWQL.

Temperature-sensitive samples were stored on ice prior 

to and during daily shipping to the various laboratories. The 

non-temperature-sensitive samples for tritium and stable 

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

were shipped monthly. Temperature-sensitive or time-sensitive 

samples for VOCs, pesticides and pesticide degradates, 

1,2,3-TCP, perchlorate, trace elements, nutrients, major and 

minor ions, silica, TDS, laboratory alkalinity, radon-222, 

and gross alpha and gross beta radioactivity were shipped 

daily whenever possible. The temperature-sensitive samples 

for stable isotopes of carbon in dissolved inorganic carbon 

and carbon-14 abundance were stored on ice, archived in a 

laboratory refrigerator, and shipped after all of the laboratory 

alkalinity measurements were received.

Appendix A
72 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Detailed sampling protocols for individual analyses 

and groups of analytes are described in Koterba and others 

(1995), the NFM (Wilde and others, 1999, 2004), and in the 

references for analytical methods listed in table A1; only brief 

descriptions are given here. Samples for analyses of VOCs 

and 1,2,3-TCP were collected in 40-milliliter (mL) sample 

vials that were purged with three vial volumes of unfiltered 

groundwater before bottom filling to eliminate atmospheric 

contamination. One to one (1:1) hydrochloric acid to water 

(HCl/H2O) solution was added as a preservative to the VOC 

samples but not to the 1,2,3-TCP samples. Each sample 

to be analyzed for perchlorate was collected in a 125-mL 

polystyrene bottle and then filtered in two or three 20-mL 

aliquots of groundwater through a 0.20-micrometer (μm) poresize Corning® syringe-tip disk filter into a sterilized 125‐mL 

bottle. Samples for analysis of tritium were collected by 

bottom filling one 1-L polyethylene bottle and one 1-L glass 

bottle with unfiltered groundwater, after first overfilling the 

bottles with three volumes of unfiltered groundwater. Samples 

for analysis of stable isotopes of hydrogen and oxygen in 

water were collected in a 60-mL clear glass bottle filled with 

unfiltered groundwater, sealed with a conical cap, and secured 

with electrical tape to prevent leakage and evaporation.

Samples for analysis of pesticides and pesticide 

degradates were collected in 1-L baked amber glass bottles. 

These samples were filtered through a 0.7-μm nominal poresize glass fiber filter during collection.

Groundwater samples for trace elements, major and 

minor ions, silica, laboratory alkalinity, and TDS analyses 

required filling one 250-mL polyethylene bottle with unfiltered 

groundwater and one 500-mL and one 250-mL polyethylene 

bottle with filtered groundwater (Wilde and others, 2004). 

Filtration was done by using a 0.45-μm pore-size PALL®

unvented capsule filter that was pre-rinsed with 2 L of 

deionized water and then rinsed with 1 L of groundwater 

prior to sampling. Each 250-mL filtered sample then was 

preserved with 7.5-Normal (N) nitric acid. Nutrient samples 

were collected by filtering groundwater into 125-mL brown 

polyethylene bottles. Samples for analyses of stable isotopes 

of boron and strontium were filtered into one 250‐mL 

polyethylene bottle and secured with electrical tape to prevent 

leakage and evaporation. Samples to be analyzed for gross 

alpha and gross beta particle activities were filtered into 1-L 

polyethylene bottles and acidified with 7.5-N nitric acid. 

Stable isotopes of carbon in dissolved inorganic carbon and 

carbon-14 abundance samples were filtered and bottom filled 

into 500-mL glass bottles that first were overfilled with three 

bottle volumes of filtered groundwater. These samples had 

no headspace and were sealed with conical caps to avoid 

atmospheric contamination.

For the collection of samples for radon-222 analysis, a 

stainless-steel and Teflon® valve assembly was attached to 

the sampling port at the well head (Wilde and others, 2004). 

The valve was closed partially to create back pressure, and 

a 10-mL groundwater sample was taken through a Teflon®

septum on the valve assembly by using a glass syringe affixed 

with a stainless-steel needle. The sample was then injected 

into a 25-mL vial partially filled with a scintillation mixture 

(mineral oil and 1,2,4-trimethylbenzene) and shaken. The vial 

then was placed in an insulated cardboard tube to protect the 

sample during shipping. 

Field alkalinity was measured in the mobile laboratory 

at the well site. Samples for field alkalinity titrations were 

collected by filtering groundwater into a 500-mL polyethylene 

bottle. Alkalinity was measured on filtered samples by 

using the Gran titration method (Gran, 1952). Titration data 

were entered directly into PCFF, and the concentrations of 

bicarbonate (HCO3

–

) and carbonate (CO3

2–) were automatically 

calculated from the titration data by using the advanced 

speciation method (http://or.water.usgs.gov/alk/methods.html) 

with pK1 = 6.35, pK2 = 10.33, and pKW = 14. Concentrations 

of HCO3

–

 and CO3

2– also were calculated from the laboratory 

alkalinity and laboratory pH measurements. 

Seven laboratories performed chemical analyses for 

this study (table A1), although most of the analyses were 

performed at the NWQL or by laboratories contracted by the 

NWQL. The NWQL maintains a rigorous QA program (Pirkey 

and Glodt, 1998; Maloney, 2005). Laboratory QC samples, 

including method blanks, continuing calibration verification 

standards, standard reference samples, reagent spikes, external 

certified reference materials, and external blind proficiency 

samples are analyzed regularly. Method detection limits 

are tested continuously, and laboratory reporting levels 

are updated accordingly. The NWQL maintains National 

Environmental Laboratory Accreditation Program (NELAP) 

and other certifications (http://www.nelac-institute.org/

accred-labs.php). The USGS Branch of Quality Systems 

(BQS) maintains independent oversight of QA at the NWQL 

and laboratories contracted by the NWQL. The BQS also 

runs the National Field Quality Assurance Program (NFQA) 

that includes annual testing of all USGS field personnel for 

proficiency in making field water-quality measurements 

(http://bqs.usgs.gov/nfqa/). Results for analyses made at 

the NWQL or by laboratories contracted by the NWQL are 

uploaded directly into NWIS. Results of analyses made at 

other laboratories are compiled in a project database and 

uploaded from there into NWIS.
Appendix A 73

Data Reporting

The following section gives details for the laboratory 

reporting conventions and the constituents that are determined 

by multiple methods or by multiple laboratories.

Reporting Limits

The USGS NWQL uses different conventions for 

reporting results for organic and inorganic constituents. For 

organic constituents, a laboratory reporting level (LRL) and 

a long-term method detection level (LT-MDL) are used as 

thresholds for reporting analytical results. The LRL is set to 

minimize the reporting of false negatives (not detecting a 

compound when it actually is present in a sample) to less than 

1 percent (Childress and others, 1999). The LRL usually is 

set at two times the LT-MDL. The LT-MDL is derived from 

the standard deviation of at least 24 method detection limit 

(MDL) determinations made over an extended period of time. 

The MDL is the minimum concentration of a substance that 

can be measured and reported with 99-percent confidence 

that the concentration is greater than zero (at the MDL there 

is less than 1-percent chance of a false positive) (Childress 

and others, 1999; U.S. Environmental Protection Agency, 

2002). Concentrations less than the LT-MDL are reported as 

non-detections with a dash (–) in the data tables. The USGS 

NWQL updates LRL and LT-MDL values regularly, and the 

values listed in this report were in effect during the period 

that analyses were made for groundwater samples from the 

NSF-SA study unit (April to August 2012).

For organic constituents, concentrations between the 

LRL and the LT-MDL are reported as having a higher degree 

of uncertainty (coded by the letter “E” preceding the values in 

the tables and text). For information-rich methods, detections 

less than the LT-MDL have a high certainty of presence, but 

the precise concentration is uncertain. These values are also 

E-coded. Information-rich methods are those that utilize gas 

chromatography or high-performance liquid chromatography 

(HPLC) with mass spectrometry detection, such as those 

methods used to analyze VOCs and pesticides. Compounds 

are identified by presence of characteristic fragmentation 

patterns in their mass spectra in addition to being 

quantified by measurement of peak areas at their associated 

chromatographic retention times. E-coded values also 

may result from detections outside the range of calibration 

standards, from detections that did not meet all laboratory QC 

criteria, and from samples that were diluted prior to analysis 

(Childress and others, 1999).

For most inorganic constituents, the LT-MDL is the only 

threshold used by the NWQL for reporting analytical results. 

All non-detections for inorganics constituents are reported 

in the NWIS database as less than the LT-MDL (except for 

non-detections of bromide which are reported as less than 

the MDL); E-codes are not used to designate results with 

concentrations less than LRLs or LT-MDLs.

Total dissolved solids and perchlorate are reported by 

using minimum reporting levels (MRLs). The MRL is the 

smallest measurable concentration of a constituent that may 

be reliably reported using a given analytical method (Timme, 

1995).

Isotopes of hydrogen, oxygen, and carbon are reported 

using method uncertainties (MUs). The MU generally 

indicates the precision of a particular analytical measurement; 

it gives a range of values wherein the true value will be found.

Results for most constituents are presented using the 

LRL, LT-MDL, MDL, MRL, or MU values provided by the 

analyzing laboratories. Results for some organic and inorganic 

constituents are presented using study reporting levels (SRLs) 

derived from assessment of data from QC samples associated 

with groundwater samples collected as part of the GAMAPBP [see the section in this appendix titled “Blanks: Study 

Reporting Levels (SRLs)”].

The reporting limits for radiochemical constituents 

(carbon-14, tritium, radon-222, and gross alpha and gross 

beta radioactivity) are based on sample-specific critical 

levels (ssLC) (McCurdy and others, 2008). The critical level 

is analogous to the LT-MDL used for reporting analytical 

results for organic and non-radioactive inorganic constituents. 

Here, the critical level is defined as the minimum measured 

activity that indicates a positive detection of the radionuclide 

in the sample with less than a 5-percent probability of a false 

positive detection. Sample-specific critical levels are used 

for radiochemical measurements because the critical level is 

sensitive to sample size and sample yield during analytical 

processing and is dependent on instrument background, on 

counting times for the sample and background, and on the 

characteristics of the instrument being used and the nuclide 

being measured. An ssLC is calculated for each sample, and 

the measured activity in the sample is compared to the ssLC

associated with that sample. Measured activities less than the 

ssLC are reported as non-detections with a dash (–) in the data 

tables.

The analytical uncertainties associated with measurement 

of activities are also sensitive to sample-specific parameters, 

including sample size, sample yield during analytical 

processing, and time elapsed between sample collection and 

various steps in the analytical procedure, as well as parameters 

associated with the instrumentation. Therefore, measured 

activities of radioactive constituents are reported with samplespecific combined standard uncertainties (CSUs). The CSU 

is reported at the 68-percent confidence level (1-sigma). The 

ssLC was not reported by the laboratory for some tritium 

results, in which case the CSU was used as an estimated 

reporting level.
74 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Notation

Stable isotopic compositions of oxygen, carbon, and 

hydrogen are reported as relative isotope ratios in units of 

per mil using the standard delta notation (Coplen and others, 

2002):

δi sample

reference

E

R

R = −

















1 1× 000, per mil , (A1)

where i is the atomic mass of the heavier isotope of 

the element,

E is the element (H for hydrogen, O for oxygen, 

C for carbon),

Rsample is the ratio of the abundance of the heavier 

isotope of the element (2H, 18O, 13C) to the 

lighter isotope of the element (1H, 16O, 12C) 

in the sample, and

Rreference is the ratio of the abundance of the heavier 

isotope of the element to the lighter isotope 

of the element in the reference material.

The reference material for oxygen and hydrogen is 

Vienna Standard Mean Ocean Water (VSMOW), which is 

assigned δ18O and δ2H values of 0 per mil (note that δ2H 

is sometimes written as δD because the common name of 

the heavier isotope of hydrogen, hydrogen-2, is deuterium) 

(Coplen and others, 2002). The reference material for carbon 

is Vienna Pee Dee Belemnite (VPDB), which is assigned a 

δ13C value of 0 per mil (Coplen and others, 2002). Positive 

values indicate enrichment of the heavier isotope, and negative 

values indicate depletion of the heavier isotope, compared to 

the ratios observed in the standard reference material.

Constituents on Multiple Analytical Schedules

Four constituents targeted in this study were measured 

by more than one analytical method or by more than one 

laboratory (table A2). Preferred analytical methods generally 

were selected on the basis of better performance or sensitivity 

for the constituent, or (in some cases) to provide consistency 

with historical data from the same method (U.S. Geological 

Survey, 2009). One organic constituent (1,2,3-TCP; table 3C) 

was analyzed by two analytical methods for the NSF-SA study 

unit; however, 1,2,3-TCP was not detected by either method.

The field water-quality indicators—pH, specific 

conductance, and alkalinity—were measured in the field 

and at the NWQL. The field measurements are generally 

preferred for all three constituents, although results from 

field and laboratory measurements were reported. The field 

and laboratory results were compared statistically to assess 

potential bias in datasets consisting of field values for some 

samples and laboratory values for other samples.

The field and laboratory data were compared by using 

the Wilcoxon signed-rank or rank-sum tests, which are 

nonparametric statistical tests that are analogous to the 

parametric paired Student’s t or Student’s t-tests, respectively 

(Helsel and Hirsch, 2002). A nonparametric test was used 

because the data were 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, 

and the Wilcoxon rank-sum test evaluates the null hypothesis 

that the difference between the medians of the two datasets is 

zero. Results are reported as the probability, p, of obtaining the 

observed distribution of data or a distribution even less likely 

when the null hypothesis is true. Tests yielding a p-value 

of less than 0.05 were considered significant and indicate a 

greater than 95-percent confidence that the two datasets are 

different.

For specific conductance, all 71 samples were measured 

in the field and the laboratory, and no significant differences 

were observed between the field and laboratory values 

(p = 0.56). The values measured in the field were used to 

describe and assess groundwater quality because field values 

were available for all samples, and they are considered more 

representative of groundwater conditions (Hem, 1985).

For pH, all 71 samples were measured in the field and 

the laboratory, and there was a systematic difference between 

the field and laboratory values (p < 0.001). Laboratory pH 

values were higher than field pH values by a median of 0.4 pH 

units. Laboratory pH values ranged from 0.7 pH units higher 

than the field pH values to the same as the field pH values; no 

samples had laboratory pH values that were lower than field 

pH values. The increase in pH of the groundwater samples 

between field and laboratory measurements may be explained 

by equilibration of the samples with the atmosphere after 

collection and by analytical methods that may introduce bias 

in the laboratory values (Fram and others, 2009). The field 

values for pH were used to describe and assess groundwater 

quality because field values are available for all samples, and 

field values are preferred because they are considered more 

representative of groundwater conditions (Hem, 1985).

For alkalinity, 10 samples were measured in both the 

field and the laboratory; the other 61 samples were measured 

only in the laboratory. Analyzing alkalinity in the field is 

time-consuming and can limit the number of wells that can 

reasonably be visited in a single day. The following evaluation 

of paired field and laboratory alkalinity data demonstrates 

that use of laboratory alkalinity data yields data of acceptable 

quality.

The evaluation of paired field and laboratory alkalinity 

data was made by using data from all of the GAMA-PBP 

studies between May 2004 and October 2012 to have sufficient 

data for a robust statistical assessment. Between May 2004 

and October 2012, 616 groundwater samples collected by the 

GAMA-PBP had alkalinity measurements made in the field by 

using the Gran titration method and made in the laboratory by 

using the fixed-endpoint titration method. Also, 187 replicate 

pairs were analyzed in the laboratory by using the fixedendpoint titration method, and 43 replicate pairs were analyzed 

in the field by using the Gran titration method.
Appendix A 75

The three types of paired alkalinity values first were 

evaluated by using the same methods used to evaluate 

replicate pairs for other constituents (see section in this 

appendix titled “Replicates”). Briefly, for samples with 

alkalinity values less than 40 mg/L as CaCO3 (5 times the 

laboratory reporting limit of 8 mg/L as CaCO3), percent 

relative standard deviation (RSD) was used to assess 

agreement between the paired values, and RSDs less than 

10 percent were considered to indicate acceptable agreement 

between the paired values. For values less than 40 mg/L as 

CaCO3, standard deviation (SD) was used, and SDs less than 

4 mg/L as CaCO3 (half of the reporting limit) were considered 

to indicate acceptable agreement between the paired values. 

Of the 28 samples with alkalinity values less than 40 mg/L, 

21 samples (75 percent) had SDs less than 4 mg/L as 

CaCO3. Of the 588 samples with alkalinity values greater 

than 40 mg/L, 548 samples (93 percent) had RSDs less than 

10 percent. These results indicate that the agreement between 

paired laboratory and field measurements of alkalinity 

generally was within the range of variability for replicate pairs 

considered acceptable for this study. For comparison, of the 

187 replicate pairs consisting of 2 laboratory measurements, 

185 pairs (99 percent) had RSDs less than 10 percent. All 

43 of the replicate pairs consisting of 2 field measurements 

had RSDs less than 10 percent.

Despite the apparent acceptable agreement between 

laboratory and field alkalinity data when the data were 

evaluated by using the methods used to assess agreement 

between replicate pairs for other constituents, the laboratory 

and field alkalinity data were significantly different. 

Laboratory alkalinity values were systematically greater 

than field alkalinity values for samples with alkalinity less 

than 40 mg/L as CaCO3 (p < 0.001) and for samples with 

alkalinity greater than 40 mg/L as CaCO3 (p < 0.001). Of 

the 616 groundwater samples with both field and laboratory 

alkalinity values, 542 samples (88 percent) had a laboratory 

alkalinity value greater than the field alkalinity value. The 

median difference between the field and laboratory alkalinity 

values is +4.3 mg/L as CaCO3 for samples with alkalinity less 

than 40 mg/L and +4.0 percent for samples with alkalinity 

greater than 40 mg/L as CaCO3

 (fig. A1).

The greater alkalinity values from laboratory 

measurements compared with those from field measurements 

likely were due to differences between the fixed-endpoint 

titration method and the Gran titration method rather than to 

chemical changes in the groundwater sample during the time 

between the two measurements.

For the fixed-endpoint method, alkalinity is determined 

by using an automatic titrator that measures the amount 

of acid required to lower the pH of the sample to 4.5. For 

the Gran titration method, alkalinity is determined from 

the amount of acid required to lower the pH of the sample 

to the equivalence point where the buffering capacity of 

the sample from weak bases is exhausted, and the volume 

of acid to reach the equivalence point is calculated from a 

linear regression that uses multiple points from the titration 

(Gran, 1952; Stumm and Morgan, 1996). The pH at this 

equivalence point is inversely correlated with the dissolved 

inorganic carbon content of the sample and usually occurs at 

a pH between 4.2 and 5.1 in freshwater (Wetzel and Likens, 

2000); the fixed-endpoint method therefore may overestimate 

alkalinity in samples with low dissolved inorganic carbon. 

The fixed-endpoint method also may overestimate alkalinity 

because the amount of acid required to reach a pH of 4.5 may 

be overestimated by up to one of the increments used by the 

titrator.

Absolute difference, in milligrams per liter, or relative difference, in percent, between laboratory and field alkalinity values

20

15

10

5

0

-5

-10

-15

Six samples

above 20%

Alkalinity, <40 milligrams per liter

(absolute difference)

n=28

(relative difference)

n=588

Outlier

Outlier

 90th percentile

Interquartile

range

50th percentile

(median)

25th percentile

10th percentile

75th percentile

EXPLANATION

Figure A1. Absolute difference or percent relative difference 

of replicate alkalinity pairs. Replicate pairs are composed of an 

alkalinity measurement made at a field site by using the Gran 

titration method and a measurement made at the USGS National 

Water Quality Laboratory by using the fixed-endpoint titration 

method, North San Francisco Bay Shallow Aquifer study unit, 

California Groundwater Ambient Monitoring and Assessment 

(GAMA) Priority Basin Project.
76 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Chemical changes that may occur in the sample 

during the time between the field and laboratory alkalinity 

measurements either do not affect alkalinity or likely would 

result in a decrease in alkalinity. Equilibration of the sample 

with the atmosphere by loss or gain of carbon dioxide does not 

change alkalinity (although pH and dissolved inorganic carbon 

concentration will change) (Stumm and Morgan, 1996). 

Oxygenation of anoxic groundwater samples likely would 

decrease alkalinity because oxidation of dissolved iron (II), 

manganese (II), sulfide, or ammonium consumes oxygen and 

produces acidity, thereby reducing the buffering capacity of 

the sample (Stumm and Morgan, 1996). 

The systematic difference between the field and 

laboratory alkalinity values is unlikely to affect interpretation 

of the chemical data because the difference is too small to 

significantly disrupt the cation-anion balances. The balance 

between cations and anions is commonly used as an indicator 

of data quality for major-ion analyses of water samples. 

A cation-anion balance of plus or minus 2 percent or less 

suggests that the major-ion data are of high quality (Hem, 

1985), and a balance of plus or minus 10 percent or less 

may be considered acceptable (for example, Landon and 

others, 2010). The cations included in the sum are calcium, 

magnesium, potassium, and sodium, and the anions included 

in the sum are chloride, sulfate, bicarbonate, carbonate, 

fluoride, bromide, and nitrate.

Cation-anion balances calculated by using the 

bicarbonate and carbonate concentrations determined from 

the field alkalinity and pH values were compared to those 

calculated by using the bicarbonate and carbonate values 

determined from the laboratory alkalinity and pH values, and 

to those calculated by using the bicarbonate and carbonate 

values determined from the laboratory alkalinity and field 

pH values. The bicarbonate and carbonate concentrations 

were calculated from alkalinity and pH values assuming 

the carbonate system was the only source of alkalinity 

and equilibrium constants of pK1

 = 6.35, pK2 = 10.33, and 

pKW = 14. The median cation-anion balance calculated by 

using the field alkalinity and pH values, +0.68 percent, was 

significantly different from the median cation-anion balance 

calculated by using the laboratory alkalinity and pH values, 

–0.77 percent, or laboratory alkalinity and field pH values, 

–0.74 percent (p < 0.001 for both comparisons; fig. A2). The 

difference between cation-anion balances calculated by using 

laboratory alkalinity values and laboratory or pH values was 

not significant (p = 0.74).

Among the 616 groundwater samples, 70 percent had 

a cation-anion balance within plus or minus 2 percent when 

using the laboratory alkalinity values, and 67 percent had a 

cation-anion balance within plus or minus 2 percent when 

using the field alkalinity values (fig. A2). Ninety-seven percent 

had a cation-anion balance within plus or minus 5 percent 

when using either alkalinity value. These results indicate that 

the field and laboratory alkalinity values both yield highquality major-ion data.

sac14-0532_fig A02

12

8

4

0

-4

-8

Cation-anion balance, in percent

Calculated using

field alkalinity 

Calculated using

laboratory alkalinity 

2 samples

above 12%

1 sample

above 12%

1 sample

below -10%

n=616

1 sample

below -10%

Outlier

Outlier

 90th percentile

Interquartile

range

50th percentile

(median)

25th percentile

10th percentile

75th percentile

EXPLANATION

Figure A2. Cation-anion balance calculated using alkalinity 

values obtained from field sites by using the Gran titration method 

and cation-anion balances calculated by using laboratory 

alkalinity values and the fixed-endpoint titration method, North 

San Francisco Bay Shallow Aquifer study unit, California 

Groundwater Ambient Monitoring and Assessment (GAMA) 

Priority Basin Project.

Quality-Control Methods and Results

The purpose of QC is to identify which data best 

represent environmental conditions and which may have been 

affected by contamination or bias during sample collection, 

processing, storage, transportation, and (or) laboratory 

analysis. Four types of QC measurements were evaluated in 

this study: (1) blank samples were collected to assess positive 

bias as a result of contamination during sample handling 

or analysis, (2) replicate samples were collected to assess 

variability, (3) matrix-spike tests were done to assess positive 

or negative bias, and (4) surrogate compounds were added to 

samples analyzed for organic constituents to assess potential 

bias of laboratory analytical methods.
Appendix A 77

Blanks

The primary purposes of collecting blanks are to evaluate 

the magnitude of potential contamination of samples with 

compounds of interest during sample handling or analysis and 

to identify and mitigate the sources of sample contamination. 

Results from blanks collected for the NSF-SA study unit and 

for previous GAMA study units were used to establish SRLs 

for some constituents detected in blanks. SRLs have higher 

concentrations than the reporting levels used by the laboratory. 

Detections reported by the laboratory with concentrations less 

than SRLs may have significant contamination bias. These 

data were flagged with an appropriate remark code (described 

in subsequent sections).

Blank Collection and Analysis

Blanks were collected by using blank water certified 

by the NWQL to contain less than the reporting levels for 

selected constituents investigated in the study (James A. 

Lewis, National Water Quality Laboratory, written commun., 

2012). Nitrogen-purged, organic-free blank water was used for 

blanks of organic constituents, and inorganic-free blank water 

was used for blanks of other constituents.

Source-solution blanks are collected at the beginning 

of a study or when using a new lot of blank water to assess 

potential contamination of samples during transport and 

analysis and potential contamination of the certified blank 

water obtained from the NWQL. A “lot” is a unique batch 

of blank water with defined production and expiration 

dates. Source-solution blanks were collected in the USGS 

Sacramento Projects Office laboratory by pouring blank water 

directly into sample containers that were preserved, stored, 

shipped, and analyzed in the same manner as the groundwater 

samples. Source-solution blanks were analyzed for VOCs, 

1,2,3-TCP, perchlorate, trace elements, major and minor ions, 

silica, and TDS. One additional source-solution blank was 

collected at a sampling site for perchlorate analysis.

Field blanks were collected to assess potential 

contamination of samples during collection, processing, 

transport, and analysis. To collect field blanks at the sampling 

sites, blank water was either pumped or poured through the 

sampling equipment (fittings and tubing) used to collect 

groundwater samples, then processed and transported 

using the same protocols used for the groundwater samples. 

Four liters of blank water were pumped or poured through the 

sampling equipment before each field blank was collected. 

Field blanks were analyzed for VOCs, pesticides and pesticide 

degradates, 1,2,3-TCP, perchlorate, trace elements, nutrients, 

major and minor ions, silica, and TDS.

Field or source-solution blanks were not collected for 

gross alpha and gross beta radioactivity or radon because the 

laboratory determines an ssLC value for each sample. The 

ssLC is the minimum measured value that indicates a non-zero 

amount of the radionuclide in the sample, in other words, an 

amount of the radionuclide that is statistically significantly 

greater than the amount in a blank. Blanks were not collected 

for tritium. Tritium is in the atmosphere and would dissolve 

into any solution used in collecting a blank, making it 

impractical to collect a blank for these analytes. Isotopic ratios 

of carbon, hydrogen, and oxygen are an intrinsic property of 

any of these elements; therefore, the concept of a blank does 

not apply to these ratios.

Study Reporting Levels (SRLs)

SRLs for VOCs detected in field blanks collected for 

the first 32 GAMA-PBP study units (May 2004 through 

September 2010) were defined by Fram and others (2012) 

on the basis of assessment of results from field blanks, 

source-solution blanks, laboratory instrument blanks, 

and groundwater samples. Detections of VOCs having 

concentrations less than the SRLs are reported as nondetections in table 5.

SRLs for trace elements detected in field blanks collected 

in the first 20 GAMA-PBP study units (May 2004 through 

January 2008) were defined by Olsen and others (2010) on 

the basis of statistical assessment of results from the field 

blanks. The assessment used order statistics and binomial 

probabilities to construct an upper confidence limit (Hahn 

and Meeker, 1991) for the maximum concentration of 

constituents possibly introduced while groundwater samples 

were collected, handled, transported, and analyzed. Since the 

publication of trace element SRLs by Olsen and others (2010), 

SRLs for some of the constituents have been updated. The 

updated SRLs were calculated by using the same methods 

and techniques that Olsen and others (2010) used, but 

more recent GAMA-PBP field blank data were used in the 

calculations (January 2008 through September 2012; Tracy 

Davis, U.S. Geological Survey, written commun., 2013). If 

the SRL changed based on the analyses of the more recent 

blank data, the newer SRL is used in this report. Detections 

of trace elements having concentrations less than the SRLs 

are marked with a ≤ symbol preceding the reported value in 

table 8 to indicate that the true value may be less than or equal 

to the reported value (including the possibility of being a 

non-detection).

SRLs for other classes of constituents detected in field 

blanks collected for the NSF-SA study unit were defined as 

equal to the highest concentration measured in the field blanks.

Detections in Field Blanks and Application of SRLs

Table A3 presents a summary of detections in the field 

blanks and the SRLs applied for the NSF-SA study unit. 

Eight field blanks (representing approximately 11 percent of 

the sampled wells) were collected in the NSF-SA study unit. 

No constituents were detected in the source-solution blanks 

collected during the NSF-SA study.
78 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

VOCs were not detected in the field blanks for the 

NSF-SA study unit (table A3). Of the 10 VOCs with SRLs 

defined by Fram and others (2012), 8 were detected in 

groundwater samples from the NSF-SA study unit: acetone, 

carbon disulfide, ethylbenzene, tetrahydrofuran, toluene, 

1,2,4-trimethylbenzene, m-xylene plus p-xylene, and o-xylene. 

All detections of acetone, ethylbenzene, tetrahydrofuran, 

1,2,4-trimethylbenzene, m-xylene plus p-xylene, and 

o-xylene had concentrations less than the SRL and were thus 

reclassified as non-detections in the NSF-SA study unit dataset 

(tables 5 and A3). For the GAMA-PBP, concentrations of 

1,2,4-trimethylbenzene in blanks and groundwater samples 

below 0.56 μg/L were found to be correlated with the presence 

of equipment in field vehicles used for collecting radon 

samples (Fram and others, 2012). The vials used to collect 

radon samples contain a scintillation cocktail made of mineral 

oil and 1,2,4-trimethylbenzene. 1,2,4-Trimethylbenzene was 

detected in two wells in the NSF-SA, and both detections were 

below the SRL (table 5). Acetone and tetrahydrofuran were 

found to be associated with contamination of equipment by 

the methanol used to clean equipment and with the cement 

used on polyvinyl chloride (PVC) piping that is sometimes 

found in distribution systems connected to domestic wells 

(Fram and others, 2012). Samples from eight NSF-SA wells 

had detections of tetrahydrofuran, one of which also had a 

detection of acetone (table 5). A sample from one NSF-SA 

well had detections of ethylbenzene, m-xylene plus p-xylene, 

and o-xylene with concentrations less than the SRLs (table 5).

The SRL of 0.02 μg/L for chloroform was defined by 

Fram and others (2012) for wells that required the use of a 

portable submersible pump. The portable submersible pump 

is lowered into wells that do not have a permanent pump 

installed in them. The length and complexity of the lines used 

with the portable submersible pump are much greater than 

for the short line sampling configurations. Two wells sampled 

in the NSF-SA study unit required the use of the portable 

submersible pump. One of the wells (S-NSF-VP15) had a 

detection of chloroform at a concentration greater than the 

SRL, thus no censoring of the data was required. One of the 

seven detections of carbon disulfide had a concentration less 

than the SRL of 0.03 μg/L and was censored. The application 

and concentration of an SRL for each trace element were 

determined primarily by guidance from Olsen and others 

(2010) with more recent updates provided by Tracy Davis 

(U.S. Geological Survey, written commun., 2013) based 

on a statistical assessment of quality-control results during 

2004–2012. GAMA SRLs from Olsen and others (2010) were 

used for barium, chromium, iron, and manganese; updated 

SRLs from Tracy Davis were used for cobalt, copper, lead, 

nickel, and zinc (table A3). Seven of these trace elements 

were detected in at least one NSF-SA field blank: chromium, 

cobalt, copper, lead, manganese, nickel, and zinc. Detections 

in field blanks were typically at concentrations below the SRL 

for each constituent, with the following three exceptions: six 

detections of cobalt ranging from 0.08 μg/L to 0.22 μg/L, 

one detection of lead at 1.67 μg/L, and five detections of 

manganese ranging from 0.21 to 0.44 μg/L (table A3).

Between October 2009 and September 2012, a marked 

increase in the detection frequency of cobalt and manganese 

in GAMA-PBP field blanks was observed (Tracy Davis, 

U.S. Geological Survey, written commun., 2013). Cobalt and 

manganese were detected in about 96 and 79 percent of field 

blanks, respectively, during this period. It is hypothesized that 

the same source of contamination is responsible, and the filter 

used to filter groundwater for collection of trace elements is a 

likely source of the detections (Tracy Davis, U.S. Geological 

Survey, written commun., 2013).

Three trace elements, arsenic, molybdenum, and 

silver, were detected at low concentrations in field blanks. 

The concentrations in blanks were below the range of 

concentrations observed in groundwater samples and therefore 

were not considered to have affected groundwater results.

Aluminum was detected in one field blank in the 

NSF-SA study unit at a concentration of 29.9 μg/L (table A3). 

Aluminum has rarely been detected in GAMA-PBP field 

blanks, with the last recorded detection occurring in 

January 2008. Olsen and others (2010) assigned an SRL 

of 1.6 μg/L for aluminum; however, the NWQL has since 

raised the detection level to 1.7 μg/L based on laboratory 

performance. See the appendix A section titled “Other QualityControl Results” for analysis of BQS data for aluminum. 

Applying an SRL based on the concentration observed in the 

field blank would be overly conservative in this case, given 

that the median aluminum concentration in groundwater 

samples collected in the NSF-SA study unit was 6.2 μg/L. 

At this time, the aluminum detection in the field blank has no 

explanation and is considered anomalous. It is not considered 

to have affected the groundwater samples, and no SRL was 

defined for aluminum for the NSF-SA study unit.

Calcium was detected in one field blank at a 

concentration of 0.027 mg/L (table A3). The minimum 

concentration detected in groundwater samples in the NSF-SA 

study unit was 0.922 mg/L, or about 30 times greater than 

the concentration detected in the blank; therefore, the blank 

detection is not considered to have an effect on the quality 

of the measured concentrations observed in groundwater 

samples.

Constituents were not detected in field blanks for the 

following analyte groups or analytes: VOCs, pesticides and 

pesticide degradates, perchlorate, 1,2,3-TCP, and TDS.
Appendix A 79

Replicates

Sequential replicate samples were collected to assess 

the precision of the water-quality data. Estimates of data 

precision are needed to assess whether differences between 

concentrations in samples are because of differences in 

groundwater quality or because of variability that may result 

from collecting, processing, and analyzing the samples.

Assessment of Replicate Samples

Two methods for measuring variability were needed to 

adequately assess precision over the broad range of measured 

concentrations of most constituents. The variability between 

measured concentrations in the pairs of sequential replicate 

samples was represented by the standard deviation (SD) 

for low concentrations and by relative standard deviation 

(RSD) for high concentrations (Anderson, 1987; Mueller and 

Titus, 2005). The RSD is defined as the SD divided by the 

mean concentration for each replicate sample expressed as a 

percentage. The boundary between concentrations for which 

variability is assessed with SD and concentrations for which 

variability is assessed with RSD was defined as five times the 

reporting level (RL) for each constituent. The RL may be an 

LRL, SRL, MDL, or MRL for each constituent.

Replicate samples for all constituents except for 

radiochemical constituents were evaluated as follows:

• If both values were reported as detections, the SD 

was calculated if the mean concentration was < 5 RL 

for the constituent, or the RSD was calculated if the 

mean concentration was ≥ 5 RL for the constituent. 

Acceptable precision is defined as an SD of less 

than 1⁄2 RL or an RSD of less than 10 percent. For 

comparison, an RSD of 10 percent is equivalent to a 

relative percent difference (RPD) of 14 percent.

• If both values were reported as non-detections, the 

variability was set to zero by definition.

• If one value was reported as a non-detection, and the 

other value was reported as a detection less than the 

RL, then a value of zero was substituted for the nondetection and the SD calculated. Substituting zero for 

the non-detection yielded the maximum estimate of 

variability for the replicate sample.

• If one value for a sample pair was reported as a nondetection and the other value was reported as a ≤-coded 

value (less than or equal to the SRL), or if both values 

were reported as ≤-coded values (less than or equal to 

the SRL), the SD was not calculated because the values 

may be analytically identical. The ≤ code indicates that 

the value is a maximum potential concentration, and 

that concentration may be low enough to be reported as 

a non-detection.

• If one value was reported as a non-detection and the 

other value was reported as a detection greater than 

the RL, the variability for the pair was considered 

unacceptable.

Replicate samples of radiochemical constituents were 

evaluated by using the following equation (McCurdy and others, 

2008) to calculate the normalized absolute difference (NAD):

NAD

R R

CSU CSU

= −

( ) +

1 2

1

2

2

2 , (A2)

where 

R1 and R2 are the results for the two samples in the 

replicate sample, and

CSU1 and CSU2 are the combined standard uncertainties 

associated with the results.

Values < 1.65 for the NAD correspond to a significance level 

(α) of 5 percent (α = 0.05), indicating differences that are 

acceptably small and not statistically significant.

If results from replicate samples indicate that precision 

is unacceptable for a constituent and no specific reason can 

be identified, then this greater variability must be considered 

when interpreting the data. If measured concentrations are 

slightly greater than a water-quality benchmark, then actual 

concentrations could be slightly less than that benchmark. 

Similarly, if measured concentrations are slightly less than a 

water-quality benchmark, then actual concentrations could be 

slightly greater than a benchmark. Also, if a constituent has 

high variability in replicate samples, then a larger difference 

between concentrations measured in two samples is required 

to conclude that the two samples have significantly different 

concentrations.

Variability in Replicate Samples

Tables A4A–C summarize the results of replicate samples 

for constituents detected in groundwater samples collected 

in the NSF-SA study unit. Replicate samples were made at 

seven wells, representing approximately 10 percent of all the 

samples collected.

Of the 1,344 replicate samples analyzed, 227 pairs had a 

detection in 1 or both samples of the pair. Of these 227 pairs, 

5 pairs (nitrate, total nitrogen, gross alpha radioactivity [72-

hour and 30-day count], and gross beta radioactivity) were 

outside the limits for acceptable precision. Results for replicate 

samples for constituents that were not detected in groundwater 

samples are not reported in tables A4A–C. All replicate 

samples for VOCs, 1,2,3-TCP, perchlorate, and pesticides and 

pesticide degradates were within acceptable precision. 

Seven replicate samples were analyzed for the 23 trace 

elements. Of the 154 replicate samples, 55 were composed of 

either two values reported as non-detections, a value reported 

as a non-detection and less than or equal to the SRL, or 

two values reported as less than or equal to the SRL. Of the 
80 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

remaining 99 pairs of constituents, all were within acceptable 

precision (table A4B).

Replicate samples analyzed for nutrients, major ions, 

and TDS resulted in SD and RSD values within acceptable 

precision, with the exceptions of one pair for nitrate and one 

pair for total nitrogen (table A4B).

Replicate samples of radioactive constituents were 

analyzed for variability. Most pairs yielded statistically similar 

results (p ≤ 0.05) and were, therefore, considered acceptable. 

The exceptions were one replicate sample for gross alpha 

radioactivity (72-hour count), two replicate samples for gross 

alpha radioactivity (30-day count), and one replicate sample 

for gross beta radioactivity (30-day count) (table A4C).

Environmental detections were not modified on the basis 

of the replicate samples.

Matrix Spikes

The 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 

groundwater, on the analytical technique used to measure the 

constituent. The known compounds added in matrix spikes are 

the same as those analyzed in the environmental samples. This 

enables an analysis of matrix interferences on a compoundby-compound basis. For this study, matrix spikes were added 

by the laboratory performing the analysis rather than in 

the field. Low matrix-spike recovery may indicate that the 

compound might not be detected in some samples if it were 

present at very low concentrations. Low and high matrix-spike 

recoveries may be a potential concern if the concentration of 

a compound in a groundwater sample is close to the healthbased benchmark; a low recovery could result in a falsely 

measured concentration less than the health-based benchmark, 

whereas a high recovery could result in a falsely measured 

concentration greater than the health-based benchmark.

The GAMA-PBP defined the data-quality objective 

range for acceptable median matrix-spike recoveries as 

70 to 130 percent. Only constituents with median matrixspike recoveries outside of this range were flagged as having 

unacceptable recoveries. For some constituents, an acceptable 

range of 70 to 130 percent for median matrix-spike recovery 

was more restrictive than the acceptable control limits for 

laboratory-set spike recoveries. Laboratory-set spikes are 

aliquots of laboratory blank water to which the same spike 

solution used for the matrix spikes has been added. One 

set spike is analyzed with each set of samples. Acceptable 

control limits for set spikes are defined relative to the 

long-term variability in recovery. For example, for many 

NWQL analyses, acceptable set-spike recovery is within ± 3 

F-pseudosigma of the median recovery for at least 30 set spikes 

(Connor and others, 1998). The F-pseudosigma is calculated 

by dividing the fourth-spread (analogous to interquartile range) 

by 1.349; therefore, the smaller the F-pseudosigma, the more 

precise the determinations (Hoaglin, 1983).

Matrix spikes were performed for VOCs, 1,2,3-TCP, 

and pesticides and pesticide degradates because the analytical 

methods for these constituents may be susceptible to matrix 

interferences.

Matrix-Spike Recoveries

Tables A5A–B present a summary of matrix-spike 

recoveries for the NSF-SA study unit. Replicate samples for 

spike additions of organic constituents were collected at nine 

wells for VOCs and 1,2,3-TCP, representing approximately 

13 percent of all the wells sampled, and at seven wells 

for pesticides and pesticide degradates, representing 

approximately 10 percent of all the wells sampled.

Groundwater samples were spiked with 85 VOCs to 

calculate matrix-spike recoveries. Median matrix-spike 

recoveries were between 70 and 130 percent for all VOCs 

(table A5A). The special-interest constituent 1,2,3-TCP was 

analyzed at Weck Laboratories, Inc., and matrix-spike results 

presented in table A5A for 1,2,3-TCP are from their laboratory.

Groundwater samples were spiked with 63 pesticides 

and pesticide degradates to calculate matrix-spike recoveries. 

Thirteen compounds had median matrix-spike recoveries less 

than 70 percent, none of which were detected in groundwater 

samples (table A5B). One compound, tebuthiuron, had median 

matrix-spike recoveries greater than 130 percent and was 

detected in one groundwater sample (table 6).

Environmental detections were not modified on the basis 

of the matrix-spike recovery analysis.

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 in the laboratory to all groundwater and QC samples 

that were analyzed by the NWQL for VOCs and pesticides and 

pesticide degradates. Surrogates are used to identify general 

problems that may arise during laboratory sample analysis 

that could affect the results for all compounds in that sample. 

Potential problems include matrix interferences (such as high 

levels of dissolved organic carbon) that produce a positive 

bias or incomplete laboratory recovery (possibly because of 

improper maintenance and calibration of analytical equipment) 

that produces a negative bias. A 70 to 130 percent recovery of 

surrogates, in general, is considered acceptable; values outside 

this range indicate possible problems with the processing and 

analysis of samples (Connor and others, 1998; Sandstrom and 

others, 2001).
Appendix A 81

Surrogate Compound Recoveries

Table A6 presents a summary of the surrogate recoveries 

for the NSF-SA study unit. The table lists the surrogates, 

the analytical schedule for which each surrogate was used, 

the number of analyses for field blanks and environmental 

samples, the number of surrogate recoveries less than 70 

percent, and the number of surrogate recoveries greater than 

130 percent for the blank and environmental samples. Field 

blanks and environmental samples were considered separately 

to assess whether or not the matrixes present in environmental 

samples affect surrogate recoveries.

Most surrogate recoveries for the field blanks and 

environmental samples were within the acceptable range of 

70 to 130 percent. For VOC analyses, about 30 percent of 

field blanks and about 36 percent of environmental samples 

had surrogate recoveries for 1,2-dichloroethane-d4 greater 

than 130 percent. For all other VOC surrogates, 100 percent 

were within the acceptable range. For pesticides and pesticide 

degradates, 100 percent of the field blank surrogate recoveries 

and 98 percent of the environmental sample surrogate 

recoveries were within the acceptable range.

Environmental detections were not modified on the basis 

of the surrogate recovery analysis.

Other Quality-Control Results

Two other laboratory QC issues arose during the analysis 

of samples collected for the NSF-SA study unit: the effect 

of holding-time violations on the results of radioactive 

constituent data and the effect of internal laboratory QC tests 

indicating bias on the results of trace element data.

Effect of Holding-Time Violations

Holding time refers to the time in calendar days from 

sample collection to the analysis of the sample. A holding-time 

violation occurs when a sample is analyzed past the given 

holding time for a particular analysis. Analyses for some 

samples in the NSF-SA study unit were completed after the 

holding time due to a scheduling error at the laboratory or 

shipping error. A delay in the analysis at the laboratory may 

result in different measured activities or concentrations than 

what may have been present in the sample.

The gross alpha and beta radioactivity reported result is 

the amount measured in the sample. Radioactive decay occurs 

between the time of sample collection and measurement; 

therefore, gross alpha and gross beta radioactivity can change 

with time. Gross alpha and beta radioactivity (72-hour counts) 

were analyzed past the holding time in one groundwater 

sample. The result for this sample is footnoted in table 12. 

Gross alpha radioactivity (72-hour) may be lower and gross 

beta radioactivity (72-hour) may be lower or higher in samples 

analyzed past the holding time than they would have been if 

analyzed on time.

Laboratory Bias

Laboratory bias as indicated from internal laboratory 

QC tests is another issue that must be investigated to 

determine whether or not the data are affected. The BQS 

operates independent, external quality-assurance projects 

called the Inorganic Blind Sample Project (IBSP) and Blind 

Blank Program (BBP) to monitor and evaluate the quality 

of results for analyses of trace elements, nutrients, major 

and minor ions, silica, and TDS by the NWQL. The IBSP 

submits standard reference samples consisting of natural 

matrix water samples spiked with reagent chemicals to contain 

known concentrations of the inorganic constituents (Farrar 

and Long, 1997). The IBSP samples are disguised as regular 

environmental samples for submission to the NWQL; the 

BBP samples are disguised as regular blank samples. The 

BQS uses results from the IBSP and BBP samples to evaluate 

potential bias in the results reported by the NWQL on a 

continuous basis. The BQS data are readily available on the 

BQS website, and the BQS issues summaries of the results, 

reporting the amount of bias (if any) observed in the results 

(U.S. Geological Survey, 2013e–f, website at http://bqs.usgs.

gov/ibsp/).

The April, June, and August 2012 BQS summaries 

were examined, which includes a review of data for the time 

period March 2, 2012, through October 4, 2012. The BQS 

reported that eight inorganic constituents showed evidence 

of bias during this period: a positive bias for aluminum, 

barium, cadmium, fluoride, lead, and lithium, and a negative 

bias for selenium and zinc. Examination of the results for the 

IBSP samples for these eight constituents indicated that the 

analytical biases reported by the BQS were not significant for 

the data collected for the NSF-SA study unit.
Table A1. Analytical methods used for the determination of organic and inorganic constituents by the U.S. Geological Survey (USGS) National Wate

and contract laboratories. [Laboratory entity codes in the USGS National Water Information System (NWIS) for laboratories other than the USGS National Water Quality Laboratory (NWQL) are given i

names. Abbreviations: USEPA, U.S. Environmental Protection Agency; VOC, volatile organic compound; NRP, USGS National Research Program] Analyte Analytical method Laboratory and analytical schedule 

Water-quality indicators Field parameters Calibrated field meters and test kits USGS field measurement U.S. Geological 

Organic constituents

VOCs Purge and trap capillary gas chromatography/

mass spectrometry

NWQL, Schedule 2020 Connor and other

Pesticides and pesticide 

degradates

Solid-phase extraction and gas 

chromatography/mass spectrometry

NWQL, Schedule 2003 Zaugg and others

1996; SandstroMadsen and ot

Constituents of special interest

Perchlorate Liquid chromatography with mass 

spectrometry/mass spectrometry (USEPA Method 331.0)

Weck Laboratories, Inc. [Weck], City of Industry, 

California (CA-WECK), standard operating procedure ORG099.R01

U.S. Environmen

1,2,3-Trichloropropane 

(1,2,3-TCP)

Isotopic dilution purge and trap/gas 

chromatography/mass spectrometry

Weck Laboratories, Inc., standard operating 

procedure ORG083

Okamoto and oth

Inorganic constituents

Major and minor ions and trace 

elements 

Atomic absorption spectrometry, colorimetry, 

ion-exchange chromatography, inductivelycoupled plasma atomic emission spectrometry, and mass spectrometry

NWQL, Schedule 1948 Fishman and Frie

Fishman, 1993Public Health A1999; Garbarin

Nutrients Alkaline persulfate digestion, Kjedahl 

digestion

NWQL, Schedule 2755 Fishman, 1993; P

Isotopic tracers

Stable isotopes of hydrogen and 

oxygen in water

Gaseous hydrogen and carbon dioxide–water 

equilibration and stable-isotope mass spectrometry

USGS Stable Isotope Laboratory, Reston, Virginia 

(USGSSIVA), NWQL Schedule 1142

Epstein and May

others, 1991; C

Stable isotopes of carbon in 

dissolved inorganic carbon and carbon-14 abundance

Accelerator mass spectrometry Woods Hole Oceanographic Institution, 

National Ocean Sciences Accelerator Mass Spectrometry Facility [NOSAMS], Woods Hole, Massachusetts (MA-WHAMS), NWQL Schedule 2255

Vogel and others

1990; McNichand Jones, 1991994; Schneid

Stable isotopes of boron in water Negative thermal-ionization mass 

spectrometry

USGS NRP Metals Isotope Research Laboratory, 

Menlo Park, California (USGSMICA)

Vengosh and othe

Vengosh, 2008

Stable isotopes of strontium in 

water

Chemical separations and thermal-ionization 

mass spectrometry

USGS NRP Metals Isotope Research Laboratory, 

Menlo Park, California (USGSMICA)

Bullen and others
Table A1. Analytical methods used for the determination of organic and inorganic constituents by the U.S. Geological Survey (USGS) National Wateand contract laboratories.—Continued[Laboratory entity codes in the USGS National Water Information System (NWIS) for laboratories other than the USGS National Water Quality Laboratory (NWQL) are given inames. Abbreviations: USEPA, U.S. Environmental Protection Agency; VOC, volatile organic compound; NRP, USGS National Research Program]

Analyte Analytical method Laboratory and analytical schedule 

Radioactive constituents

Tritium Electrolytic enrichment-liquid scintillation USGS Stable Isotope and Tritium Laboratory 

[SITL], Menlo Park, California (USGSH3CA), NWQL Schedule 1565

Thatcher and oth

Radon-222 Liquid scintillation counting NWQL, Schedule 1369 American Society 

1998

Gross alpha and gross beta 

radioactivity (72-hour and 30-day counts)

Alpha and beta activity counting (USEPA 

Method 900.0)

Eberline Analytical Services, Richmond, California 

(CA-EBERL), NWQL Schedule 1792

Krieger and Whit

Table A2. Preferred analytical methods or laboratories for selected constituents in groundwater samples collected for the North San Francisco Bay California GAMA Priority Basin Project, April to August 2012.[Preferred analytical schedules/methods are selected on the basis of the procedure recommended by the NWQL (http://wwwnwql.cr.usgs.gov/dyn.shtml?Preferred_method_selecAbbreviations: NWQL, USGS National Water Quality Laboratory, Denver, Colorado; VOC, volatile organic compound; Weck, Weck Laboratories, Inc.]

Constituent 

(synonym or abbreviation)

Primary 

constituent classification

Analytical methods 

or laboratory

Preferr

Alkalinity Water-quality indicator field, Schedule 1948 (NWQL) 

pH Water-quality indicator field, Schedule 1948 (NWQL) 

Specific conductance Water-quality indicator field, Schedule 1948 (NWQL) 

1,2,3-Trichloropropane (1,2,3-TCP) VOC Schedule 2020 (NWQL), Weck 
84 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Table A3. Constituents detected in the field blank samples and the study reporting levels (SRLs) used for the North San Francisco Bay 

Shallow Aquifer study unit, California GAMA Priority Basin Project, April to August 2012.

[Abbreviations: RL, reporting level; VOC, volatile organic compound; ≤, less than or equal to; μg/L, micrograms per liter; mg/L, milligrams per liter; na, not 

applicable; nv, no value in category; —, not detected]

Constituent

Number of field 

blank detections 

/ total number of 

field blank samples

RL

Concentration(s) 

detected in field 

blank sample(s)

SRL Source of SRL

Number of groundwater 

samples≤-coded / total 

number of groundwater 

detections

Volatile organic compounds (VOCs) (μg/L)

Acetone 0/8 3.4 — All data Fram and others, 2012 1/1

2-Butanone 0/8 1.6 — All data Fram and others, 2012 0/0

Carbon disulfide 0/8 0.03 — 0.03 Fram and others, 2012 1/7

Chloroform 1 0/8 0.03 — 0.02 Fram and others, 2012 0/13

Ethylbenzene 0/8 0.04 — 0.06 Fram and others, 2012 0/0

Tetrahydrofuran 0/8 1.4 — All data Fram and others, 2012 8/8

Toluene 0/8 0.02 — 0.69 Fram and others, 2012 0/0

1,2,4-Trimethylbenzene 0/8 0.03 — 0.56 Fram and others, 2012 0/0

m- and p-Xylenes 0/8 0.08 — 0.33 Fram and others, 2012 0/0

o-Xylene 0/8 0.03 — 0.12 Fram and others, 2012 0/0

Trace elements (μg/L)

Aluminum 1/8 2.2 29.9 2

 1.6 Olsen and others, 2010 0/40

Arsenic 1/8 0.03 0.04 nv na 0/65

Boron 1/8 3 29 nv na 0/71

Chromium 1/8 0.14 0.08 0.42 Olsen and others, 2010 16/22

Cobalt 8/8 0.021 0.05, 0.05, 0.08, 0.12, 

0.17, 0.18, 0.18, 0.22 

0.05 Tracy Davis 3 24/32

Copper 1/8 0.08 2 3.2 Tracy Davis 3 24/12

Lead 5/8 0.025 0.06, 0.13, 0.19, 

0.25, 1.67 

0.82 Tracy Davis 3 52/7

Manganese 7/8 0.13 0.15, 0.16, 0.21, 0.24, 

0.3, 0.35, 0.44 

0.2 Olsen and others, 2010 3/62

Molybdenum 1/8 0.014 0.019 nv na 0/70

Nickel 1/8 0.09 0.1 0.2 Tracy Davis 3 10/57

Silver 1/8 0.005 0.007 nv na 0/5

Zinc 2/8 1.4 1.6, 6.4 6.4 Tracy Davis 3 36/22

Major and minor ions (mg/L)

Calcium 1/8 0.022 0.027 nv na 0/71

1

 SRL established by Fram and others (2012) for chloroform only applies to samples collected at monitoring wells.

2

 SRL established by Olsen and others (2010) is now lower than current long-term method detection limit of 2.2 μg/L.

3

 Based on written communication with Tracy Davis, U.S. Geological Survey, who is preparing updated SRLs using recent Groundwater Ambient Monitoring 

and Assessment (GAMA) blank data.
Appendix A 85

Table A4A. Quality-control summary for replicate pair analyses of organic constituents in groundwater samples collected for the 

North San Francisco Bay Shallow Aquifer study unit, California GAMA Priority Basin Project, April to August 2012.

[Constituents for which all replicate pairs were non-detections are not listed. Abbreviations: SD, percent standard deviation; >, greater than; <, less than; 

RL, reporting level]

Constituent Number of non-detections / 

number of replicate pairs

Number of SDs > 1⁄2 RL / 

number of replicate pairs 

with concentration < 5 times the RL 

Volatile organic compounds (VOCs) 

Carbon tetrachloride (Tetrachloromethane) 6/7 0/1

Chloroform (Trichloromethane) 4/7 0/3

Perchloroethene (PCE, Tetrachloroethene) 6/7 0/1

Pesticides and pesticide degradates

All replicate pairs considered acceptable for pesticides and pesticide degradates

Constituent of special interest

Perchlorate 3/7 0/4
86 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Table A4B. Quality-control summary for replicate sample analyses of inorganic constituents in samples collected for the North San 

Francisco Bay Shallow Aquifer study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, 

April to August 2012.

[Constituents for which all replicate samples were non-detections are not listed. Abbreviations: SD, percent standard deviation; RSD, percent relative standard 

deviation; RL, reporting level; >, greater than; <, less than; ≤, less than or equal to; nv, no value in category]

Constituent

Number of non-detections 

or ≤-coded replicate 

samples / number of 

replicate samples 

Number of SDs > 1⁄2 RL / 

number of replicate samples 

with concentrations 

< 5 times the RL

Number of RSDs > 10 percent / number of replicate 

samples with concentrations 

> 5 times the RL

Trace Elements

Aluminum 3/7 0/4 nv

Antimony 1/7 0/6 nv

Arsenic 1/7 nv 0/6

Barium 0/7 nv 0/7

Beryllium 4/7 0/2 0/1

Boron 0/7 nv 0/7

Cadmium 6/7 0/1 nv

Chromium 3/7 nv 0/4

Cobalt 2/7 0/5 nv

Copper 2/7 0/3 0/2

Iron 3/7 nv 0/4

Lithium 0/7 0/1 0/6

Manganese 2/7 nv 0/5

Molybdenum 0/7 nv 0/7

Nickel 2/7 nv 0/5

Selenium 1/7 0/2 0/4

Strontium 0/7 nv 0/7

Vanadium 0/7 0/2 0/5

Zinc 4/7 0/1 0/2

Nutrients 

Ammonia (as nitrogen) 4/7 0/2 0/1

Nitrate plus nitrite (as nitrogen) 1 2/7 0/1 1/4

Nitrite (as nitrogen) 6/7 0/1 nv

Total nitrogen (ammonia 

+ nitrite + nitrate + organic nitrogen)

1/7 0/2 1/4

Phosphate, orthophosphate (as phosphorus) 0/7 nv 0/7

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

Calcium 0/7 nv 0/7

Chloride 0/7 nv 0/7

Fluoride 0/7 0/4 0/3

Magnesium 0/7 nv 0/7

Potassium 0/7 nv 0/7

Sodium 0/7 nv 0/7

Sulfate 0/7 nv 0/7

Silica (as SiO2

) 0/7 nv 0/7

TDS 0/7 nv 0/7

1

 Nitrite plus nitrate (as nitrogen) is referred to as nitrate in the text for clarity.
Table A4C. Quality-control summary for replicate pair analyses of radioactive constituents in groundwater samples collected for the North San Franstudy unit, California GAMA Priority Basin Project, April to August 2012.[For activities of radioactive constituents, a replicate pair analyses is defined as acceptable if the p-value for the normalized absolute difference is less than the significance levelthan; >, greater than; —, not detected; ±, plus or minus; nv, no values]

Constituent

Number of non-detections or 

<-coded replicate samples / 

number of replicate samples 

Number of 

detections paired 

with non-detections

Number of replicate 

samples with p > 0.05 /

number of replicate pairs 

Activities 

(groundwater 

Gross alpha radioactivity, 72-hour count 0/7 4 1/7 (0.42 

Gross alpha radioactivity, 30-day count 5/7 2 2/7 (— ± 0.41Gross beta radioactivity, 72-hour count 1/7 1 1/7 (1.48 

Gross beta radioactivity, 30-day count 1/7 0 0/7 

Uranium 1/7 0/1 0/5 

Radon-222 0/7 0 0/7 
88 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and the special-interest 

constituent 1,2,3-trichloropropane in groundwater samples collected for the North San Francisco Bay Shallow Aquifer study unit,

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, April to August 2012.

[Acceptable recovery range is between 70 and 130 percent]

Constituent 

(synonym or abbreviation)

Number of matrixspike samples 

collected

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetone 9 100 127 111

Acrylonitrile 9 103 118 112

tert-Amyl methyl ether (TAME) 9 85 106 97

Benzene 1 9 96 112 104

Bromobenzene 9 91 108 100

Bromochloromethane 1 9 90 116 104

Bromodichloromethane 1 9 80 105 95

Bromoform (Tribromomethane) 1 9 74 106 90

Bromomethane (Methyl bromide) 9 92 135 117

n-Butylbenzene 9 84 105 95

sec-Butylbenzene 9 88 111 102

tert-Butylbenzene 9 96 112 103

Carbon disulfide 1 9 71 97 84

Carbon tetrachloride (Tetrachloromethane) 1 9 85 109 98

Chlorobenzene 1 9 91 109 99

Chloroethane 9 98 126 102

Chloroform (Trichloromethane) 1 9 –88 124 103

Chloromethane 9 97 138 112

3-Chloropropene 9 92 110 100

2-Chlorotoluene 9 95 111 101

4-Chlorotoluene 9 94 113 102

Dibromochloromethane 1 9 82 109 91

1,2-Dibromo-3-chloropropane (DBCP) 9 77 106 92

1,2-Dibromoethane (EDB) 9 92 106 102

Dibromomethane 1 9 82 109 91

1,2-Dichlorobenzene 9 104 126 107

1,3-Dichlorobenzene 9 91 109 103

1,4-Dichlorobenzene 9 97 114 105

trans-1,4-Dichloro-2-butene 9 91 110 103

Dichlorodifluoromethane (CFC-12) 9 98 134 110

1,1-Dichloroethane (1,1-DCA) 1 9 95 122 107

1,2-Dichloroethane (1,2-DCA) 9 94 128 105

1,1-Dichloroethene (1,1-DCE) 9 96 110 106

cis-1,2-Dichloroethene (cis-1,2-DCE) 9 93 109 101

trans-1,2-Dichloroethene (trans-1,2-DCE) 9 96 114 105

1,2-Dichloropropane 9 88 108 103

1,3-Dichloropropane 9 96 113 102

2,2-Dichloropropane 9 56 98 87

1,1-Dichloropropene 9 85 100 94

cis-1,3-Dichloropropene 9 84 103 95
Appendix A 89

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and the special-interest 

constituent 1,2,3-trichloropropane in groundwater samples collected for the North San Francisco Bay Shallow Aquifer study unit,

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, April to August 2012.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent 

(synonym or abbreviation)

Number of matrixspike samples 

collected

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

trans-1,3-Dichloropropene 9 79 103 90

Diethyl ether 9 93 114 108

Diisopropyl ether (DIPE) 1 9 94 111 105

Ethylbenzene 9 89 110 96

Ethyl tert-butyl ether (ETBE) 9 89 107 104

Ethyl methacrylate 9 88 104 95

o-Ethyl toluene (1-Ethyl-2-methyl benzene) 1 9 90 111 101

Hexachlorobutadiene 9 72 98 89

Hexachloroethane 9 71 110 90

2-Hexanone (n-Butyl methyl ketone) 9 90 113 103

Iodomethane (Methyl iodide) 9 91 119 107

Isopropylbenzene 1 9 86 110 92

4-Isopropyl-1-methyl benzene 9 86 108 96

Methyl acrylate 9 87 103 98

Methyl acrylonitrile 9 100 121 109

Methyl tert-butyl ether (MTBE) 1 9 92 109 104

Methyl iso-butyl ketone (MIBK) 9 91 111 102

Methylene chloride (Dichloromethane) 9 94 121 107

Methyl ethyl ketone (2-butanone, MEK) 9 98 122 113

Methyl methacrylate 9 87 103 98

Naphthalene 1 9 79 109 92

Perchloroethene (PCE, Tetrachloroethene) 1 9 94 119 102

n-Propylbenzene 9 86 107 94

Styrene 1 9 89 109 95

1,1,1,2-Tetrachloroethane 9 84 106 97

1,1,2,2-Tetrachloroethane 9 88 118 99

Tetrahydrofuran 9 99 119 108

1,2,3,4-Tetramethylbenzene 9 81 114 92

1,2,3,5-Tetramethylbenzene 9 90 118 97

Toluene 1 9 56 112 105

1,2,3-Trichlorobenzene 9 89 110 101

1,2,4-Trichlorobenzene 9 83 106 92

1,1,1-Trichloroethane (1,1,1-TCA) 9 90 113 104

1,1,2-Trichloroethane (1,1,2-TCA) 9 88 111 103

Trichloroethene (TCE) 1 9 91 107 98

Trichlorofluoromethane (CFC-11) 1 9 105 141 119

1,2,3-Trichloropropane (1,2,3-TCP) 2 9 100 114 107

Trichlorotrifluoroethane (CFC-113) 1 9 94 113 97

1,2,3-Trimethylbenzene 9 98 116 105

1,2,4-Trimethylbenzene 9 96 116 107
90 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and the special-interest 

constituent 1,2,3-trichloropropane in groundwater samples collected for the North San Francisco Bay Shallow Aquifer study unit,

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, April to August 2012.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent 

(synonym or abbreviation)

Number of matrixspike samples 

collected

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

1,3,5-Trimethylbenzene 9 92 112 100

Vinyl bromide (Bromoethene) 9 94 117 104

Vinyl chloride (Chloroethene) 9 98 135 110

m- plus p-Xylene 9 92 112 100

o-Xylene 9 89 109 97

1

 Constituent detected in groundwater sample(s).

2

 Spike results from Weck Laboratories, Inc.

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in groundwater samples 

collected for the North San Francisco Bay Shallow Aquifer study unit, California Groundwater Ambient Monitoring and Assessment 

(GAMA) Priority Basin Project, April to August 2012.

[Acceptable recovery range is between 70 and 130 percent]

Constituent 

(synonym or abbreviation)

Number of 

matrix-spike 

samples 

collected

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetochlor 7 78 112 101

Alachlor 7 87 111 108

Atrazine 1 7 88 117 100

Azinphos-methyl 7 63 135 104

Azinphos-methyl oxon 7 22 189 107

Benfluralin 7 67 85 75

Carbaryl 7 87 131 110

2-Chloro-2,6-diethylacetanilide 7 83 110 99

4-Chloro-2-methylphenol 7 64 73 64

Chlorpyrifos 7 79 99 82

Chlorpyrifos oxon 7 20 65 40

Cyfluthrin 7 56 84 76

Cypermethrin 7 53 82 71

DCPA (Dacthal) 7 99 110 107

Deethylatrazine (2-Chloro-4-isopropylamino-6-amino-s-triazine) 1 7 55 152 70

Desulfinylfipronil 7 83 113 102

Desulfinylfipronil amide 7 96 147 117

Diazinon 7 85 104 100

3,4-Dichloroaniline 1 7 73 95 76

Dichlorvos 7 16 82 45

Dicrotophos 7 7 39 22

Dieldrin 1 7 76 109 94

2,6-Diethylaniline 7 77 97 88

Dimethoate 7 45 73 57

Ethion 7 68 90 80
Appendix A 91

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in groundwater samples 

collected for the North San Francisco Bay Shallow Aquifer study unit, California Groundwater Ambient Monitoring and Assessment 

(GAMA) Priority Basin Project, April to August 2012.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent 

(synonym or abbreviation)

Number of 

matrix-spike 

samples 

collected

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Ethion monoxon 7 75 100 88

2-Ethyl-6-methylaniline 7 81 107 89

Fenamiphos 7 75 90 83

Fenamiphos sulfone 7 78 112 101

Fenamiphos sulfoxide 7 8 40 24

Fipronil 7 77 118 102

Fipronil sulfide 1 7 73 100 91

Fipronil sulfone 7 70 96 82

Fonofos 7 81 98 96

Hexazinone 7 34 76 46

Iprodione 7 59 92 77

Isofenphos 7 81 110 103

Malaoxon 7 81 117 97

Malathion 7 79 108 96

Metalaxyl 7 85 114 100

Methidathion 7 76 97 90

Metolachlor 7 77 114 104

Metribuzin 7 96 108 91

Myclobutanil 7 75 99 90

1-Naphthol 7 24 88 39

Paraoxon-methyl 7 61 100 72

Parathion-methyl 7 79 107 90

Pendimethalin 7 72 111 86

cis-Permethrin 7 54 85 67

Phorate 7 54 83 64

Phorate oxon 7 73 110 83

Phosmet 7 11 78 20

Phosmet oxon 7 12 50 49

Prometon 1 7 69 114 93

Prometryn 7 79 110 98

Pronamide 7 82 107 98

Simazine 1 7 78 116 91

Tebuthiuron 1 7 103 190 133

Terbufos 7 61 93 80

Terbufos oxon sulfone 7 68 121 88

Terbuthylazine 7 93 111 107

Tribufos 7 51 75 61

Trifluralin 7 71 91 78

1

 Constituent detected in groundwater sample(s).
Table A6. Quality-control summary for surrogate compound recoveries of volatile organic compounds (VOCs) and pesticides and pesticide degradate

collected for the North San Francisco Bay Shallow Aquifer study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority BaAugust 2012. [Abbreviations: NWQL, U.S. Geological Survey National Water Quality Laboratory; <, less than; >, greater than] Surrogate compound NWQL analytical schedule Constituent class analyzed Number of blanks analyzed Median recovery in blanks (percent) Number of surrogate recoveries < 70 percent in blanks Number of surrogate recoveries > 130 percent in blanks Number of groundwater samples analyzed Median recovery in groundwater samples (percent) Number o

surrogat

recoverie

< 70 percen

groundwa

samples 

1-Bromo-4-fluorobenzene 2020 VOC 9 93 0 0 71 87 0 

1,2-Dichloroethane-d4 2020 VOC 9 125 0 3 71 128 0 

Toluene-d8 2020 VOC 9 91 0 0 71 95 0 

Diazinon-d10 2003 Pesticide 8 82 0 0 71 86 1 

α-HCH-d6 2003 Pesticide 8 96 0 0 71 95 1 
Appendix B 93

Appendix B

This appendix describes the effects of the change in 

prioritization of comparison benchmarks between the first and 

second phases of the GAMA-PBP (fig. 4).

Of the approximately 350 constituents analyzed by 

USGS-GAMA in one or more GAMA-PBP study units, 

139 constituents had an MCL-CA, MCL-US, proposed 

MCL-US, AL-US, SMCL-CA, NL-CA, HAL-US, or 

RSD5-US benchmark and therefore could be assigned a 

comparison benchmark and assessed during the first phase 

of the GAMA-PBP. HBSLs were available for an additional 

64 constituents, raising the total number of constituents that 

could be assigned a comparison benchmark and assessed 

during the second phase of the GAMA-PBP to 203. These 

64 additional constituents are mostly pesticides or pesticide 

degradates. Of these 64 additional constituents, 25 constituents 

were detected in one or more samples collected by 

USGS-GAMA between May 2004 and October 2012; 

however, none of the detections had concentrations greater 

than the HBSL.

Of the 139 constituents assigned comparison benchmarks 

under the prioritization used in the first phase of the 

GAMA-PBP, 117 constituents were assigned a benchmark 

with the same concentration under the prioritization used in 

the second phase of the GAMA-PBP. Changing the order of 

the prioritization and adding the HBSLs will have no effect on 

the presentation of results for these 117 constituents.

Of the 139 constituents assigned comparison benchmarks 

under the prioritization used in the first phase of the 

GAMA-PBP, 19 constituents were assigned a benchmark 

with a different value under the prioritization used in the 

second phase of the GAMA-PBP. Of these 19 constituents, 

10 have not been detected in any sample collected by 

USGS-GAMA between May 2004 and October 2012, and 

6 were only detected at concentrations below the lower of 

the 2 benchmarks. Changing the order of the prioritization 

and adding the HBSLs likely will have no effect on the 

presentation of results for these 16 constituents.

The three constituents that are affected by changing the 

order of the prioritization of the benchmarks and adding the 

HBSLs and which may have had an effect on the presentation 

of the results are the following inorganic constituents:

• Boron: In the first phase of the GAMA-PBP, boron 

concentrations were compared to the NL-CA of 

1,000 μg/L; in the second phase, boron concentrations 

are compared to the HBSL of 6,000 μg/L. The HBSL is 

equal to the HAL-US. 

• Manganese: In the first phase of the GAMA-PBP, 

manganese concentrations were compared to the 

SMCL-CA of 50 μg/L; in the second phase, manganese 

concentrations are compared to the HBSL of 300 μg/L. 

The HBSL is equal to the HAL-US. The NL-CA for 

manganese is 500 μg/L.

• Chromium (VI): The first phase of the GAMA-PBP 

did not assess chromium (VI) because no comparison 

benchmark was available under the old system during 

that time period. However, in July 2014, CDPH 

announced an MCL-CA for chromium (VI) of 10 μg/L 

(California Department of Public Health, 2014). The 

MCL-CA will be used as the comparison benchmark 

for the second phase of the GAMA-PBP. Note that 

chromium (VI) was not analyzed in the NSF-SA 

study unit. 

Finally, 139 constituents were assigned comparison 

benchmarks under the prioritization used in the first phase of 

the GAMA-PBP; however, the new prioritization order was not 

used to select the comparison benchmark for 3 special-interest 

constituents. All three constituents have NL-CA benchmarks 

and do not have HBSL benchmarks. These constituents 

were assigned a benchmark with a different value under the 

prioritization used in the second phase of the GAMA-PBP.

• 1,2,3-TCP: In first phase of the GAMA-PBP, 

1,2,3-TCP concentrations were compared to the 

HAL-US of 40 μg/L because the NL-CA for 1,2,3-TCP 

of 0.005 μg/L was set at the analytical reporting 

limit. However, the HAL-US, originally developed in 

1989 (U.S. Environmental Protection Agency, 1989), 

no longer appears to be in use (U.S. Environmental 

Protection Agency, 2013). 1,2,3-TCP does not 

have an HBSL. The CDPH is expected to release 

a proposed MCL-CA for 1,2,3-TCP in 2014 

(California Department of Public Health, 2013b). 

Until that proposed MCL-CA is released, 1,2,3-TCP 

concentrations will be compared to the MCL of 

0.6 μg/L established by the State of Hawaii (Hawaii 

Department of Health, 2005). 1,2,3-TCP was not 

detected in the NSF-SA study unit. 

• 1,4-Dioxane: In the first phase of the GAMA-PBP, 

1,4-dioxane concentrations were compared to the 

initial NL-CA of 3 μg/L and then to the new NL-CA 

of 1 μg/L after it was revised in 2010 (California 

Department of Public Health, 2011). 1,4-Dioxane 

does not have an HBSL and has a HAL-US of 

200 μg/L. 1,4-Dioxane concentrations will continue 

to be compared to the NL-CA of 1 μg/L during the 

second phase of the GAMA-PBP. 1,4-Dioxane was not 

analyzed in the NSF-SA study unit.

• N-Nitrosodimethylamine (NDMA): In the first phase 

of the GAMA-PBP, NDMA concentrations were 

compared to the NL-CA of 0.01 μg/L. NDMA has an 

HBSL range of 0.0007 to 0.07 μg/L and an RSD5-US 

of 0.007 μg/L. For consistency with 1,4-dioxane, 

NDMA concentrations will continue to be compared 

to the NL-CA during the second phase of the GAMAPBP. NDMA was not analyzed in the NSF-SA 

study unit.
94 Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012

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Bennett and Fram—Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012: Results from the California GAMA Program—Data Series 865

ISSN 2327-638X (online)

ISSN 2327-0271 (print)

http://dx.doi.org/10.3133/ds865