U.S. Department of the Interior

U.S. Geological Survey

Data Series 874 

Prepared in cooperation with the California State Water Resources Control Board

Groundwater-Quality Data in the Santa Cruz, San Gabriel, 

and Peninsular Ranges Hard Rock Aquifers Study Unit, 

2011–2012: Results from the California GAMA Program

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

Basin and Range

Central

Valley

Desert

Transverse Ranges and

selected Peninsular Ranges

Southern Coast

Ranges

Sierra

Nevada

San Diego

Drainages

Bakersfield

San

Francisco

Sacramento

NEVADA

MEXICO

Los Angeles

San Diego

P a c i f i c O c e a n

Hard Rock - Santa Cruz

Hard Rock - San Gabriel

Hard Rock - Peninsular Ranges
Cover photographs:

Top right: Well in San Jacinto Valley, California. (Photograph taken by Franklin Moseanko, U.S. Geological Survey).

Bottom right: Wellhouse on mountainside in Angeles National Forest. (Photograph taken by Tyler Evans, U.S. Geological Survey.)
Groundwater-Quality Data in the Santa Cruz, 

San Gabriel, and Peninsular Ranges Hard Rock 

Aquifers Study Unit, 2011–2012: Results from the 

California GAMA Program

By Tracy A. Davis and Jennifer L. Shelton

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 874

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:

Davis, T.A., and Shelton, J.L., 2014, Groundwater-quality data in the Santa Cruz, San Gabriel, and Peninsular Ranges 

Hard Rock Aquifers study unit, 2011–2012—Results from the California GAMA Program: U.S. Geological Survey Data 

Series 874, 142 p., http://dx.doi.org/10.3133/ds874.

ISSN 2327-638X (Online)

ISSN 2327-0271 (Print)

ISBN 978-1-4113-3861-6
iii

Contents

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

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

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

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

Santa Cruz Study Area (SC) ................................................................................................................5

San Gabriel Study Area (SG).............................................................................................................12

Peninsular Ranges Study Area (PR) ................................................................................................12

Methods.........................................................................................................................................................13

Study Design........................................................................................................................................13

Sample Collection and Analysis.......................................................................................................17

Data Reporting.....................................................................................................................................17

Comparative Benchmarks.................................................................................................................17

Quality-Assurance Methods.............................................................................................................18

Water-Quality Results .................................................................................................................................18

Quality-Control Results ......................................................................................................................18

Groundwater-Quality Data ................................................................................................................18

Water-Quality Indicators ..........................................................................................................19

Organic Constituents.................................................................................................................19

Constituent of Special Interest................................................................................................20

Inorganic Constituents..............................................................................................................20

Geochemical and Age-Dating Tracers...................................................................................21

Radioactive Constituents and Uranium..................................................................................22

Future Work ..................................................................................................................................................22

Summary........................................................................................................................................................22

Acknowledgments.......................................................................................................................................24

References....................................................................................................................................................24

Tables.............................................................................................................................................................31

Appendix......................................................................................................................................................115
iv

Figures

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

of the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock 

Aquifers study unit, California GAMA Priority Basin Project ........................................4

2. Maps of the Santa Cruz, San Gabriel, and Peninsular Ranges study areas 

showing selected hydrologic and geologic features, Hard Rock study unit, 

California GAMA Priority Basin Project ............................................................................6

3. Maps of the Santa Cruz, San Gabriel, and Peninsular Ranges study 

areas showing the 3-kilometer buffers, locations of wells in the California 

Department of Public Health database, counties, major roads and cities, 

and hydrologic and topographic features, Hard Rock study unit, 

California GAMA Priority Basin Project ............................................................................9

4. Maps of the Santa Cruz, San Gabriel, and Peninsular Ranges study areas 

showing the distribution of the grid cells, locations of sampled wells, 

major cities, and hydrologic and topographic features, Hard Rock 

study unit, California GAMA Priority Basin Project.......................................................14

Tables

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

Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers study unit, 

March 2011 through March 2012, California GAMA Priority Basin Project ..............31

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

the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers study 

unit, March 2011 through March 2012, California GAMA Priority Basin Project .....35

3A. Volatile organic compounds, primary uses or sources, reporting information, 

and comparative benchmarks for the U.S. Geological Survey 

National Water Quality Laboratory Schedule 2020 .......................................................36

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

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

National Water Quality Laboratory Schedule 2003 .......................................................40

3C. Constituent of special interest, primary uses or sources, 

reporting information, and comparative benchmark for 

analysis performed by Weck Laboratories, Inc. ............................................................42

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

U.S. Geological Survey National Water Quality Laboratory Schedule 1948 .............42

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

U.S. Geological Survey National Water Quality Laboratory Schedule 2755 .............43

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

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

Survey National Water Quality Laboratory Schedule 1948..........................................43

3G. Arsenic, chromium, and iron species, reporting information, and 

comparative benchmarks for the U.S. Geological Survey Trace 

Metal Laboratory, Boulder, Colorado, analyses.............................................................44
v

3H. Isotopic and radioactive constituents, reporting information, 

and comparative benchmarks for laboratory analyses................................................45

3I. Dissolved noble gases and tritium, reporting information, and comparative 

benchmarks for the Lawrence Livermore National Laboratory analyses.................46

4. Water-quality indicators in samples collected for the Santa Cruz, San Gabriel, 

and Peninsular Ranges Hard Rock Aquifers study unit, March 2011 through 

March 2012, California GAMA Priority Basin Project ...................................................47

5. Volatile organic compounds detected in samples collected for the Santa 

Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers study unit, 

March 2011 through March 2012, California GAMA Priority Basin Project ..............55

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

Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers study unit, 

March 2011 through March 2012, California GAMA Priority Basin Project ..............64

7. Perchlorate detected in samples collected for the Santa Cruz, San Gabriel, 

and Peninsular Ranges Hard Rock Aquifers study unit, March 2011 through 

March 2012, California GAMA Priority Basin Project ...................................................67

8. Trace elements detected in the samples collected for the Santa Cruz, 

San Gabriel, and Peninsular Ranges Hard Rock Aquifers study unit, 

March 2011 through March 2012, California GAMA Priority Basin Project ..............68

9. Nutrients detected in samples collected for the Santa Cruz, San Gabriel, and 

Peninsular Ranges Hard Rock Aquifers study unit, March 2011 through 

March 2012, California GAMA Priority Basin Project ...................................................81

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

in samples collected for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers study unit, March 2011 through March 2012, 

California GAMA Priority Basin Project ..........................................................................86

11. Arsenic, chromium, and iron species detected in samples collected for the 

Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers study unit, 

March 2011 through March 2012, California GAMA Priority Basin Project ..............92

12. Results for analyses of stable isotope ratios, carbon-14 abundance, and tritium 

activity in samples collected for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers study unit, March 2011 through March 2012, 

California GAMA Priority Basin Project ..........................................................................97

13. Results for analyses of dissolved noble gases by the Lawrence Livermore 

National Laboratory for samples collected for the Santa Cruz, San Gabriel, 

and Peninsular Ranges Hard Rock Aquifers study unit, March 2011 through 

March 2012, California GAMA Priority Basin Project .................................................102

14A. Radon-222 detected in samples collected for the Santa Cruz, San Gabriel, 

and Peninsular Ranges Hard Rock Aquifers study unit, March 2011 

through March 2012, California GAMA Priority Basin Project ..................................106

14B. Gross alpha and gross beta radioactivity detected in samples collected for the 

Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers study unit, 

March 2011 through March 2012, California GAMA Priority Basin Project ............108

14C. Uranium activities detected in samples collected for the Santa Cruz, San 

Gabriel, and Peninsular Ranges Hard Rock Aquifers study unit, March 2011 

through March 2012, California GAMA Priority Basin Project ..................................113

Tables—Continued
vi

Conversion Factors and Datums

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2) 

quart (qt) 0.95 liter (L)

ounce, avoirdupois (oz) 28.35 gram (g)

pound, avoirdupois (lb) 0.4536 kilogram (kg)

picocurie per liter (pCi/L) 0.037 becquerel per liter (Bq/L)

SI to Inch/Pound

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) 1.057 quart (qt)

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound, avoirdupois (lb)

becquerel per liter (Bq/L) 27.03 picocurie per liter (pCi/L)

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).

Turbidity is given in nephelometric turbidity units (NTU).

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 dissolved noble gases are given as the atom ratio (for helium-3/helium-4) or 

as cubic centimeters of gas at standard temperature and pressure per gram of water (cm3 

STP/g).

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

Datums

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

(NAVD 88). Land-surface datum (LSD), as used in this report, refers to a horizontal plane that is 

approximately at land surface at each site, at a specific altitude relative to NAVD 88.

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

Selected Terms and Symbols

α significance level

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

and 1 atmosphere of pressure) per gram of water

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

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

expressed as per mil

= equal to

> greater than 

≥ greater than or equal to

< less than

≤ less than or equal to

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

— not detected

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

± plus or minus

* value is greater than benchmark level

** value is greater than upper benchmark level

Abbreviations and Acronyms

AL-US action level (USEPA)

APE Alternate Place Entry program designed for USGS sampling

BBP Blind Blank Project (USGS Branch of Quality Systems)

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

CSU combined standard uncertainty

E estimated or having a higher degree of uncertainty 

GAMA Groundwater Ambient Monitoring and Assessment Program

GPS global positioning system

HAL-US lifetime health advisory level (USEPA)

HPLC high-performance liquid chromatography

IBSP Inorganic Blind Sample Project (USGS Branch of Quality Systems)

IRL interim reporting level

LRL laboratory reporting level
viii

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 

NFM National Field Manual (USGS)

NFQA National Field Quality Assurance Program (USGS Branch of Quality Systems)

NL-CA notification level (CDPH)

nv no measured value or no value in category

NWIS National Water Information System (USGS)

PBP Priority Basin Project (USGS GAMA)

PCFF Personal Computer Field Form program designed for USGS sampling

QA quality assurance

QC quality control

RPD relative percent difference

RSD relative standard deviation

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

SAFZ San Andreas Fault Zone

SD standard deviation

SMCL-CA secondary maximum contaminant level (CDPH)

SMCL-US secondary maximum contaminant level (USEPA)

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

results)

ssLC sample-specific critical level

UV-Vis ultraviolet-visible

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

BQS Branch of Quality Systems (USGS)

CDPH California Department of Public Health

CDPR California Department of Pesticide Regulation

CDWR California Department of Water Resources

LLNL Lawrence Livermore National Laboratory

NAWQA National Water-Quality Assessment Program (USGS)

NELAP National Environmental Laboratory Accreditation Program

Abbreviations and Acronyms—Continued
ix

NWQL National Water Quality Laboratory (USGS)

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 Constituent Names

B boron

C carbon

CaCO3 calcium carbonate

CFC chlorofluorocarbon

CO3

2– carbonate ion

H hydrogen

HCO3– bicarbonate ion

MTBE methyl tert-butyl ether

O oxygen

PCE perchloroethene (tetrachloroethene)

PVC polyvinyl chloride

Sr strontium

TDS total dissolved solids

THM trihalomethane

VOC volatile organic compound

Organizations—Continued

Groundwater-Quality Data in the Santa Cruz, San Gabriel, 

and Peninsular Ranges Hard Rock Aquifers Study Unit, 

2011–2012: Results from the California GAMA Program

By Tracy A. Davis and Jennifer L. Shelton

Abstract

Groundwater quality in the 2,400-square-mile Santa 

Cruz, San Gabriel, and Peninsular Ranges Hard Rock 

Aquifers (Hard Rock) study unit was investigated by the 

U.S. Geological Survey (USGS) from March 2011 through 

March 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-PBP was developed in response to the 

California Groundwater Quality Monitoring Act of 2001 and 

is being conducted in collaboration with the SWRCB and 

Lawrence Livermore National Laboratory (LLNL). The Hard 

Rock study unit was the 35th study unit to be sampled as part 

of the GAMA-PBP.

The GAMA Hard Rock study was designed to 

provide a spatially unbiased assessment of untreatedgroundwater quality in the primary aquifer system and to 

facilitate statistically consistent comparisons of untreatedgroundwater quality throughout California. The primary 

aquifer system is defined as those parts of the aquifers 

corresponding to the perforation intervals of wells listed in 

the California Department of Public Health (CDPH) waterquality-monitoring database for the Hard Rock study unit. 

Groundwater quality in the primary aquifer system may differ 

from the quality in the shallower or deeper water-bearing 

zones; shallow groundwater may be more vulnerable to 

surficial contamination.

In the Hard Rock study unit, groundwater samples were 

collected from 112 wells and springs in 3 study areas (the 

Santa Cruz, the San Gabriel, and the Peninsular Ranges) in 

San Mateo, Santa Clara, Santa Cruz, San Benito, Los Angeles, 

Orange, Riverside, San Bernardino, and San Diego Counties. 

Eighty-three wells and 11 springs were selected by using a 

spatially distributed, randomized grid-based method to provide 

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

15 wells and 3 springs were selected to aid in evaluation of 

water-quality issues (understanding wells).

The groundwater samples were analyzed for field waterquality indicators; organic constituents; one constituent of 

special interest (perchlorate); naturally occurring inorganic 

constituents; and radioactive constituents. Naturally occurring 

isotopes and dissolved noble gases were also measured to help 

identify the sources and ages of the sampled groundwater. 

In total, 209 constituents and water-quality indicators were 

measured.

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

and matrix spikes) were collected at approximately 10 percent 

of the wells in the Hard Rock study unit, and the results 

for these samples were used to evaluate the quality of the 

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. Median matrixspike recoveries were within the acceptable range (70 to 

130 percent) for approximately 92 percent of the compounds.

This study did not attempt to evaluate the quality of water 

delivered to consumers; after withdrawal from the ground, 

untreated groundwater typically is treated, disinfected, and 

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

Regulatory benchmarks apply to water that is served to the 

consumer, not to untreated groundwater. However, to provide 

some context for the results, concentrations of constituents 

measured in the untreated groundwater were compared with 

regulatory and nonregulatory health-based benchmarks 

established by the U.S. Environmental Protection Agency 

(USEPA) and CDPH, and to nonregulatory benchmarks 

established for aesthetic concerns by the CDPH. Comparisons 

between data collected for this study and benchmarks for 

drinking water are for illustrative purposes only and are 

not indicative of compliance or non-compliance with those 

benchmarks.
2 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

All organic constituents and most inorganic constituents 

that were detected in groundwater samples from the 112 wells 

in the Hard Rock study unit were detected at concentrations 

less than drinking-water benchmarks.

Of the 149 organic and special-interest constituents, 

34 were detected in groundwater samples; concentrations 

of all detected constituents were less than regulatory and 

nonregulatory health-based benchmarks. In total, VOCs were 

detected in 44 percent of the 94 grid wells sampled, pesticides 

and pesticide degradates were detected in 18 percent, and 

perchlorate was detected in 48 percent.

Trace elements, nutrients, major and minor ions, and 

radioactive constituents were sampled for at 94 grid wells; 

most detected concentrations were less than health-based 

benchmarks. Exceptions in the Hard Rock study unit grid 

wells include 3 detections of arsenic greater than the USEPA 

maximum contaminant level (MCL-US) of 10 micrograms 

per liter (μg/L), 3 detections of boron greater than the CDPH 

notification level (NL-CA) of 1,000 μg/L, 2 detections of 

molybdenum greater than the USEPA lifetime health advisory 

level (HAL-US) of 40 μg/L, 2 detections of nitrite plus nitrate 

(as nitrogen) greater than the MCL-US of 10 milligrams 

per liter (mg/L), 3 detections of fluoride greater than the 

CDPH maximum contaminant level (MCL-CA) of 2 mg/L, 

5 detections of radon-222 greater than the proposed MCL-US 

of 4,000 picocuries per liter (pCi/L), and 11 detections of 

unadjusted gross alpha radioactivity greater than the MCL-US 

of 15 pCi/L. Seven of the 11 samples having unadjusted gross 

alpha activity greater than the MCL-US also had total uranium 

concentrations greater than the MCL-US of 30 μg/L and (or) 

uranium activities greater than the MCL-CA of 20 pCi/L.

Results for constituents with nonregulatory benchmarks 

set for aesthetic concerns showed that iron concentrations 

greater than the CDPH secondary maximum contaminant 

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

from 19 grid wells. Manganese concentrations greater than 

the SMCL-CA of 50 μg/L were detected in 27 grid wells. 

Chloride was detected at a concentration greater than the 

SMCL-CA upper benchmark of 500 mg/L in one grid well. 

TDS concentrations in three grid wells were greater than the 

SMCL-CA upper benchmark of 1,000 mg/L.

Introduction

About one-half of the water used for public and 

domestic drinking-water supply in California is groundwater 

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

groundwater in aquifers used for public drinking-water supply 

and to establish a baseline groundwater-quality monitoring 

program, the California State Water Resources Control Board 

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

(USGS) and Lawrence Livermore National Laboratory 

(LLNL), implemented the Groundwater Ambient Monitoring 

and Assessment (GAMA) Program (California State Water 

Resources Control Board, 2011). The GAMA Program was 

initiated by the SWRCB in 2000 and later expanded by 

the Groundwater Quality Monitoring Act of 2001 (State of 

California, 2001a, 2001b, Sections 10780–10782.3 of the 

California Water Code, Assembly Bill 599). 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 

GAMA-PBP primarily focuses on the deep part of the 

groundwater resource, which is typically used for public 

drinking-water supply. The GAMA Domestic Well Project 

generally focuses on the shallow aquifer systems, which may 

be particularly at risk as a result of surficial contamination. 

The GAMA Special Studies Project focuses on using research 

methods to help explain the source, fate, transport, and 

occurrence of chemicals that can affect groundwater quality. 

GeoTracker GAMA is a web-based system that displays 

groundwater information using Google Maps and includes 

analytical tools and reporting features to assess water quality. 

The Geotracker GAMA database stores groundwater-quality 

data and related reports collected by other State agencies, 

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

the California Department of Water Resources (CDWR), and 

the California Department of Pesticide Regulation (CDPR), 

and data collected by the SWRCB and Regional Boards from 

environmental monitoring wells at contaminated or remediated 

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

The GAMA-PBP assesses groundwater quality in key 

groundwater basins and other areas that account for more than 

95 percent of groundwater used for public supply in the State. 

The USGS, in collaboration with the SWRCB, developed 

the monitoring plan for the project to assess groundwater 

basins through direct and other statistically reliable sample 

approaches (Belitz and others, 2003; California State Water 

Resources Control Board, 2003). Additional partners in the 

GAMA-PBP include LLNL, CDPH, CDWR, CDPR, local 

water agencies, and well owners (Kulongoski and Belitz, 

2004). Participation in the project is entirely voluntary.

In order to delineate areas for evaluation as part of the 

GAMA-PBP, the range of hydrologic, geologic, and climatic 
Introduction 3

conditions in California needed to be considered. Belitz and 

others (2003) partitioned the State into 10 hydrogeologic 

provinces, each with distinctive hydrologic, geologic, and 

climatic characteristics: Modoc Plateau and Cascades, 

Klamath Mountains, Northern Coast Ranges, Central Valley, 

Sierra Nevada, Basin and Range, Southern Coast Ranges, 

Transverse and Selected Peninsular Ranges, Desert, and San 

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

include groundwater basins and subbasins designated by 

the CDWR (California Department of Water Resources, 

2003). Groundwater basins and subbasins generally consist 

of relatively permeable, unconsolidated deposits of alluvial 

origin. Eighty percent of California’s approximately 

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

statewide water-quality monitoring database maintained by the 

CDPH (hereinafter referred to as CDPH wells) are located in 

groundwater basins and subbasins within the 10 hydrogeologic 

provinces. Groundwater basins and subbasins were prioritized 

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

the basin, with secondary consideration given to municipal 

groundwater use, agricultural pumping, the number of 

formerly leaking underground fuel tanks, and the number of 

square-mile sections with registered pesticide applications 

(Belitz and others, 2003). Of the 472 basins and subbasins 

designated by the CDWR, 116 were identified as priority 

basins. These priority basins contain approximately 95 percent 

of the CDPH wells located in groundwater basins. In addition, 

some areas outside of the defined groundwater basins were 

included to achieve representation of the 20 percent of the 

CDPH wells not located in the groundwater basins. The 

priority basins, selected other basins, and selected areas 

outside of basins were grouped into 35 study units for 

sampling. The Santa Cruz, San Gabriel, and Peninsular Ranges 

Hard Rock Aquifers study unit (hereinafter referred to as the 

Hard Rock study unit) contains a large number of CDPH 

wells outside of the CDWR-defined groundwater basins. The 

Hard Rock study unit includes hard rock areas located in the 

Southern Coast Ranges, Transverse and Selected Peninsular 

Ranges, San Diego Drainages, and Desert hydrogeologic 

provinces (fig. 1).

The data collected in each study unit are used for three 

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

of the current quality of the groundwater resource; 

(2) Understanding: identification of the natural and human 

factors affecting groundwater quality; and (3) Trends: 

detection of changes in groundwater quality over time 

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

to characterize the quality of groundwater in the primary 

aquifer system of the study units, not the treated drinking 

water delivered to consumers by water purveyors. The 

primary aquifer system is defined as that part of the aquifers 

corresponding to the perforated depth intervals of wells listed 

in the CDPH database for the study units. The CDPH database 

lists wells used for public drinking-water supplies and includes 

wells from systems classified as community (such as those 

in cities, towns, and mobile-home parks), non-transient and 

non-community (such as those in schools, workplaces, and 

restaurants), and transient and non-community (such as those 

in campgrounds and parks). Collectively, the CDPH refers 

to these wells as “public-supply” wells. Groundwater quality 

in the primary aquifer system may differ from the quality in 

the shallow or deep parts of the aquifer systems. In particular, 

shallow groundwater may be more vulnerable to surface 

contamination. As a result, samples from shallow wells (such 

as many private domestic wells and environmental monitoring 

wells) can have higher concentrations of constituents (such 

as volatile organic compounds [VOCs] and nitrate) from 

anthropogenic sources than samples from wells screened in 

the underlying primary aquifer system (for example, Landon 

and others, 2010).

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 300 chemical 

constituents by using methods with lower detection limits 

than required by the CDPH for regulatory monitoring of 

drinking-water wells. These analyses will be especially useful 

for providing an early indication of changes in groundwater 

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

a suite of constituents more extensive than that required by 

CDPH and for a suite of chemical and isotope tracers for 

exploring hydrologic and geochemical processes. A broad 

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.

Published and quality-assured data collected for the 

GAMA Program are stored in the web-based Geotracker 

GAMA database (California State Water Resources Control 

Board, 2009) and in the web-based USGS National Water 

Information System (U.S. Geological Survey, 2014).

This USGS Data Series Report is similar to other USGS 

Data Series Reports written for the GAMA-PBP study units 

sampled to date. Data Series Reports and additional reports 

(Scientific Investigations Reports and Fact Sheets) addressing 

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

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

projects/gama/includes/GAMA_publications.html.
4 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Basin and Range

Central

Valley

Klamath

Mountains

Desert

Cascades and

Modoc Plateau

Transverse Ranges and

selected Peninsular Ranges

Southern Coast

Ranges

Sierra

Nevada

Northern

Coast

Ranges

San Diego

Drainages

Bakersfield

San

Francisco

Sacramento

OREGON

NEVADA

MEXICO

ARIZONA

Redding

Los Angeles

San Diego

P a c i f i c O c e a n

0 200 MILES

0 200 KILOMETERS

100

100

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Provinces from Belitz and others, 2003

sac14-0529_Figure 01 loc map

Hard Rock - Santa Cruz

Hard Rock - San Gabriel

Hard Rock - Peninsular Ranges

Figure 1. Hydrogeologic provinces of California and the location of the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock 

Aquifers (Hard Rock) study unit, California GAMA Priority Basin Project.
Hydrogeologic Setting 5

Purpose and Scope

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

design, including the hydrogeologic setting of the Hard 

Rock study unit and the study methods; (2) the analytical 

results for groundwater samples collected in the Hard Rock 

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

samples were collected and analyzed for field water-quality 

indicators; organic, special-interest, inorganic, and radioactive 

constituents; naturally occurring isotopes; and dissolved noble 

gases. The water-quality data presented in this report were 

compared to State and Federal drinking-water regulatory 

and other nonregulatory standards that are applied to treated 

drinking water. Regulatory and nonregulatory benchmarks 

considered for this report are those established by the 

U.S. Environmental Protection Agency (USEPA) and the 

CDPH. Discussion of the factors that influence the distribution 

and occurrence of the constituents detected in groundwater 

samples will be the subject of subsequent publications.

Hydrogeologic Setting

The Hard Rock study unit consists of selected portions 

of California’s mountainous regions outside of the CDWRdefined groundwater basins. Separated by up to 200 miles of 

land, the three study areas of the Hard Rock study unit—Santa 

Cruz (SC), San Gabriel (SG), and Peninsular Ranges (PR)—

each form distinct hydrogeologic settings (fig. 2). The San 

Andreas Fault Zone (SAFZ) forms the eastern boundary and 

structurally dominates the geology for all three of the study 

areas in the study unit. Groundwater is used extensively for 

public and domestic drinking-water supplies in the Hard Rock 

study unit, and much of this groundwater comes from aquifers 

in granitic, metamorphic, or lithified sedimentary rocks, rather 

than from sediment deposits in groundwater basins. These 

rocks typically have low permeability except where they are 

extensively fractured. The three-dimensional complexity and 

variability of fracture systems can cause well yields and water 

quality to vary widely on a local scale. Recharge to hard-rock 

aquifers occurs by direct infiltration of precipitation and snow 

melt and by infiltration from lakes and streams (California 

Department of Water Resources, 2011).

Santa Cruz Study Area (SC)

The Santa Cruz study area of the Hard Rock study unit is 

located in the Southern Coast Ranges hydrogeologic province 

(fig. 1) and includes parts of San Mateo, Santa Clara, Santa 

Cruz, and San Benito Counties (fig. 3A). The study area 

contains the Santa Cruz Mountains, which are approximately 

75 miles in length and up to 15 miles wide. The study area 

boundaries were defined primarily by the extent of the 

igneous, metamorphic, and Tertiary-age sedimentary rocks that 

compose the mountains (fig. 2A). Areas mapped as Quaternary 

alluvium and surficial deposits or Plio-Pleistocene sediments 

were excluded. Several small areas of rock along the eastern 

boundary were excluded because they were included in the 

GAMA-PBP San Francisco Bay study unit (Ray and others, 

2009), and a large area of rock along the southern boundary 

was excluded because it was included in the GAMA-PBP 

Monterey Bay and Salinas Valley study unit (Kulongoski and 

Belitz, 2007).

The SC study area is divided into two geologically 

distinct regions by the SAFZ and Sargent fault (fig. 2A). 

Rocks to the west of these faults are mostly lithified marine 

sediments of Tertiary age with lesser amounts of granitic rocks 

of Mesozoic age and older metamorphic rocks, whereas rocks 

to the east of these faults are primarily Mesozoic metavolcanic 

and metasedimentary rocks of the Franciscan Complex. 

Sub-parallel to the SAFZ, the Butano and Zayante-Vergeles 

faults cut into the marine sediment. The western edge of the 

study area is intersected by the San Gregorio fault, which 

originates off the coast of San Francisco and extends south 

where it terminates in Big Sur (U.S. Geological Survey, 2010). 

The sources of surface-water discharge for the study area are 

several creeks flowing from the mountains out to the Pacific 

Ocean, Monterey Bay, or San Francisco Bay; most notably are 

the Pescadero Creek, San Lorenzo River, and Pajaro River.

The SC study area is characterized as a temperate 

rainforest, with a cool, wet climate conducive to redwood 

forests. The National Climatic Data Center (NCDC) station 

located in Ben Lomond (fig. 2A) measured an average annual 

temperature of 55 degrees Fahrenheit (°F) (13 degrees Celsius 

[°C]) for 2011. Average annual precipitation was 38 inches 

(U.S. Department of Commerce, National Climatic Data 

Center, 2011). Precipitation primarily occurs as rain during 

the winter and early spring and as fog cover in the summer 

months. Snow may occur in the winter months at the higher 

elevations. The highest peak in the Santa Cruz Mountains is 

the Loma Prieta Peak at an elevation of about 3,800 feet.
6 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

San Francisco

San Jose

Santa Cruz

?

?

sac14-0529_Figure 2a Map of the Santa Cruz study area showing selected hydrologic and geologic features, 

Hard Rock study unit, California GAMA Priority Basin Project.

122°30’ 122° 121°30’

37°

30’

37°

0 10 20 MILES

0 10 20 KILOMETERS

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Pacific Ocean

Monterey Bay

San Francisco Bay

San Lorenzo River

Pescadero Creek

EXPLANATION

San Andreas Fault Zone

Zayante-Vergeles Fault

Butano Fault

San Gregorio Fault

Sargent Fault

Pajaro Valley

Santa Cruz Mtns

Loma Prieta Peak

Ben Lomond Stn

Pajaro River

Geologic units and faults available from the California 

Geological Survey (Saucedo and others, 2000)

A

Geologic description and Age

Alluvial and surficial deposits

 (Holocene and upper Pleistocene)

Nonmarine sediments 

 (Plio-Pleistocene) 

Marine metasediments

 (Mesozoic) 

Lithified marine

 sediments (Tertiary)

Granitic rocks

 (Mesozoic) 

Franciscan Complex

 (Mesozoic)

Igneous and metamorphic

 rocks (Precambrian)

Schist

National Climatic

 Data Center

 station

Metasedimentary and meta-

 volcanic rocks (Pre-Cenozoic)

Generalized boundary of

the Santa Cruz study area

of the Hard Rock study unit

Figure 2. (A) Santa Cruz, (B) San Gabriel, and (C) Peninsular Ranges study areas showing selected hydrologic and geologic features, 

Hard Rock study unit, California GAMA Priority Basin Project.
Hydrogeologic Setting 7

14

58

138

138

60

57

91

210

210

10

10

15

15

605

110 710

405

5

5

101

395

118°30’ 118° 117°30’

34°30’ 34°

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Pacific Ocean

KERN CO

LOS ANGELES CO

SAN BERNARDINO CO

RIVERSIDE CO

VENTURA CO

Azusa

Acton

Ontario

Castaic

Palmdale

Big Pines

San Gabriel

Los Angeles

Lake Hughes

sac14-0529_Figure02b Map of the San Gabriel study area showing selected hyrologic and geologic features,

Hard Rock study unitCalifornia GAMA Priority Basin Project

Geologic units and faults available from the California 

Geological Survey (Saucedo and others, 2000)

Santa Clara River

San Andreas Fault Zone

San Gabriel Fault

Sierra Madre Fault

Los Angeles River

San Gabriel River

Santa Ana River

Antelope Valley

Mt 

San Antonio

Mt Wilson Stn

San Fernando Valley

Upper Santa

Ana Valley

Los Angeles 

Coastal Plain

San Gabriel Mts

Castaic Mts

Santa Monica Mtns

Santa Clarita 

Valley

Cajon Pass

San Bernardino

Mts

EXPLANATION

Geologic description and Age

Alluvial and surficial deposits

 (Holocene and upper Pleistocene)

Nonmarine sediments 

 (Plio-Pleistocene) 

Marine metasediments

 (Mesozoic) 

Lithified marine sediments 

 (Tertiary)

Pyroclastic and volcanic

 mudflow (Cenozoic)

Granitic rocks

 (Mesozoic) 

Igneous and metamorphic

 rocks (Precambrian)

Schist

Marine metasedimentary

 rocks (Paleozoic) 

Metasedimentary and metavolcanic rocks

 (Pre-Cenozoic)

B

Generalized boundary of

the San Gabriel study area

of the Hard Rock study unit

National Climatic

 Data Center

 station

Piru Creek

Castaic Creek

Lytle Creek

Figure 2. —Continued
8 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

SAN BERNARDINO CO

RIVERSIDE CO

IMPERIAL

CO

SAN DIEGO CO

ORANGE CO

LOS

ANGELES

CO

sac14-0529_Figure 2c Map of the Peninsular Ranges study area showing selected hydrologic and geologic features, 

Hard Rock study unit, California GAMA Priority Basin Project.

117°30' 117° 116°30' 116°

34°

33°

30’33°

0

0 5 10 15 20 KILOMETERS

5 10 15 20 MILES

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Pacific Ocean

Salton Sea

San Andreas Fault Zone

Orange County 

Coastal Plain

San Jacinto Fault

Anza-Borrego

Elsinore Fault

Coachella 

Valley

EXPLANATION

Upper Santa 

Ana Valley

Mexico

Cuyamaca Mts

Palomar Mtn 

Observatory

San Diego

 Bay

San Jacinto

Peak

San Ysidro 

Mts

Santa Ana Mtns

San Luis Rey River

Santa Margarita River

San Diego River

Sweetwater River

Santa Ysabel Creek

San Jacinto River

San Felipe Creek

San Jacinto

Valley

Palomar Mtn

San Jacinto Mtn 

Geologic units and faults available from the California 

Geological Survey (Saucedo and others, 2000)

San Diego

C

Geologic description and Age

Alluvial and surficial deposits

 (Holocene and upper

 Pleistocene)

Nonmarine sediments 

 (Plio-Pleistocene) 

Marine metasediments

 (Mesozoic) 

Lithified marine

 sediments 

 (Tertiary)

Granitic rocks

 (Mesozoic) 

Santiago Peak

 volcanic rocks

 (Mesozoic)

Igneous and metamorphic

 rocks (Precambrian)

Schist

Gabbroic

 rocks

 (Mesozoic)

Granitic and metamorphic

 rocks (Pre-Cenozoic) 

Generalized boundary

of the Peninsular Ranges

study area

of the Hard Rock

study unit

National Climatic

 Data Center

 station

Metasedimentary and

 metavolcanic rocks

 (Pre-Cenozoic)

Figure 2. —Continued
Hydrogeologic Setting 9

San Francisco

Santa Cruz

84 35

17

1

1

92

84

238

237

152

82

85 87

101

101

880

280

680

580

580

205

SANTA CLARA CO

SAN MATEO CO

SAN FRANCISCO CO

ALAMEDA CO

SAN JOAQUIN CO

STANISLAUS CO

CONTRA COSTA CO

SANTA CRUZ CO

SAN BENITO CO

MONTEREY CO

0 10 20 Miles

0 10 20 Kilometers

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Pacific Ocean

Monterey Bay

San Francisco Bay

San Lorenzo River

Pescadero Creek

EXPLANATION

Pajaro Valley

Santa Cruz Mtns

Pajaro River

Santa Cruz 

 3-kilometer buffer

CDPH well

Gilroy

Lompico

San Jose

Millbrae

Pescadero

Palo Alto

Los Gatos

Half Moon Bay

sac14-0529_Figure 3a Map of the Santa Cruz study area showing the 3-kilometer buffers, locations of wells in the California 

Department of Public Health (CDPH) database, counties, major roads and cities, and hydrologic and topographic features, 

Hard Rock study unit, California GAMA Priority Basin Project.

A

122°30’ 122° 121°30’

37°

30’

37°

Santa Cruz study area

Figure 3. (A) Santa Cruz, (B) San Gabriel, and (C) Peninsular Ranges study areas showing the 3-kilometer buffers, locations of wells in 

the California Department of Public Health (CDPH) database, counties, major roads and cities, and hydrologic and topographic features, 

Hard Rock study unit, California GAMA Priority Basin Project.
10 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

14

58

138

138

60

57

91

210

210

10

10

15

15

605

110 710

405

5

5

101

395

118°30’ 118° 117°30’

34°30’ 34°

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Pacific Ocean

KERN CO

LOS ANGELES CO

SAN BERNARDINO CO

RIVERSIDE CO

VENTURA CO

Azusa

Acton

Ontario

Castaic

Palmdale

Big Pines

San Gabriel

Los Angeles

Lake Hughes

Geologic units and faults available from the California 

Geological Survey (Saucedo and others, 2000)

Santa Clara River

Los Angeles River

San Gabriel River

Santa Ana River

Antelope Valley

San Fernando Valley

Upper Santa

Ana Valley

Los Angeles 

Coastal Plain

San Gabriel Mtns

Santa Monica Mtns

Santa Clarita 

Valley

Cajon Pass

San Bernardino

Mtns

San Gabriel study area CDPH well

San Gabriel

 3-kilometer buffer

EXPLANATION

B

Figure 3. —Continued
Hydrogeologic Setting 11

1

73

78

74

71

91

60

74

111

86

62

94

10

15

15

5

5

8

805

405

15

215

SAN BERNARDINO CO

RIVERSIDE CO

SAN DIEGO CO

ORANGE CO

Campo

Orange

Julian

Jacumba

Temecula

San Diego

San Marcos

San Jacinto

Palm Desert

San Clemente

Mount Laguna

Lake Elsinore

Borrego Springs

117°30’ 117° 116°30’

34° 33°30’ 33°

0 5 10 15 20 MILES

0 10 15 20 5 KILOMETERS

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

sac14-0529_fig03c. Map of the Peninsular Ranges study area showing the 3-kilometer buffers, locations of wells in the California 

Department of Public Health (CDPH) database, counties, major roads and cities, and hydrologic and topographic features, 

Hard Rock study unit, California GAMA Priority Basin Project.

Peninsular Ranges study area CDPH well

Peninsular Ranges

 3-kilometer buffer

EXPLANATION

Pacific Ocean

San Diego

 Bay

C

Figure 3. —Continued
12 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

San Gabriel Study Area (SG)

The San Gabriel study area of the Hard Rock study unit 

is located in the Transverse and Selected Peninsular Ranges 

hydrogeologic province (fig. 1) and includes parts of Los 

Angeles and San Bernardino Counties (fig. 3B). The study 

area contains the San Gabriel and Castaic Mountains, is 

approximately 85 miles in length and up to 20 miles wide, 

and is wedged between major fault zones (fig. 2B). Along the 

northeast flank, the SAFZ separates the mountains from the 

Antelope Valley. The study area is bounded in the east by the 

boundary of the San Gabriel and San Bernardino Mountains, 

known as the Cajon Pass area (California Department of 

Water Resources, 2004a). The Sierra Madre and San Gabriel 

faults meet on the southwest flank and extend northwest up to 

Piru Creek, almost connecting with the SAFZ. The study unit 

boundaries were defined primarily by the extent of Mesozoic 

granitic rocks, Mesozoic and older metamorphic rocks, and 

lithified Tertiary sedimentary rocks in the mountain block. 

Alluvial valleys within the mountain block were excluded. The 

alluvial valleys of the Santa Clarita Valley in the southwestern 

part of the mountain block were part of the GAMA-PBP Santa 

Clara River Valley study unit (Montrella and Belitz, 2009). 

The basins along the southern margin of the mountain block 

composed the GAMA-PBP San Fernando–San Gabriel (Land 

and Belitz, 2008) and Upper Santa Ana Watershed (Kent and 

Belitz, 2009) study units; the Antelope Valley and small basins 

in the SAFZ were included in the GAMA-PBP Antelope 

Valley study unit (Schmitt and others, 2009).

The SG study area consists primarily of granitic, 

plutonic rocks (Mesozoic through Precambrian) and schist 

(fig. 2B). Tertiary, lithified sediments and mafic volcanics are 

interstratified with schist in the Castaic Mountains located in 

the northwestern portion of the study area. Several streams, 

including the San Gabriel River, Castaic Creek, and Lytle 

Creek, cut through the mountains and flow outside the study 

area into local reservoirs or into rivers that travel south 

through the coastal valleys and eventually terminate in the 

Pacific Ocean (California Department of Water Resources, 

2004c). The streams are the main sources of surface-water 

discharge for the study area. In some areas, water stored in 

fractured hard rock forms springs or recharges local waterbearing formations for nearby groundwater alluvial basins 

(California Department of Water Resources, 2004b).

The climate in the San Gabriel study area is characterized 

as Mediterranean, with warm, dry summers and cool, wet 

winters. The NCDC station located on Mount Wilson (fig. 2B) 

measured an average annual temperature of 55 °F (13 °C) 

for 2011; total annual precipitation was measured at about 

14 inches (U.S. Department of Commerce, National Climatic 

Data Center, 2011). Precipitation primarily occurs as rain 

during the winter and early spring. Snow occurs in the winter 

months at the higher elevations. The highest peak in the San 

Gabriel Mountains is Mount San Antonio at an elevation of 

about 10,000 feet.

Peninsular Ranges Study Area (PR)

The Peninsular Ranges study area of the Hard Rock 

study unit is located in the southwest corner of California, in 

San Diego, Riverside, and Orange Counties (fig. 3C). The PR 

study area is primarily composed of the mountainous regions 

of the San Diego Drainages hydrogeologic province and 

includes portions of the Transverse and Selected Peninsular 

Ranges hydrogeologic province to the north and the Desert 

hydrogeologic province to the east (fig. 1).

The PR mountain ranges include the Santa Ana, San 

Jacinto, Palomar, Cuyamaca, and San Ysidro Mountains. 

The PR study area consists primarily of Mesozoic granitic 

rocks, which in some regions are intermixed with Santiago 

Peak volcanic rocks and gabbroic plutons (fig. 2C). The 

Santiago Peak volcanics are metavolcanic, volcaniclastic, 

and sedimentary rocks located along the western zone of the 

Peninsular Ranges batholith, which extends south to Baja 

California (Tanaka and others, 1984). Toward the coast, 

the mountains give way to younger (Mesozoic to Tertiary) 

lithified sediments. The boundaries of the study area were 

defined by the extent of these igneous, metamorphic, and 

lithified sedimentary rocks; areas of Quaternary alluvium were 

excluded from the study area. Alluvial valleys within and 

surrounding the study area were included in the GAMA-PBP 

San Diego Drainages (Wright and others, 2005), Upper Santa 

Ana Watershed (Kent and Belitz, 2009), Los Angeles Coastal 

Plain (Mathany and others, 2008), and Coachella Valley 

(Goldrath and others, 2009) study units. The SAFZ branches 

out to two parallel systems in the area: the Elsinore and San 

Jacinto faults. Several rivers and creeks flow through the 

mountains and eventually terminate in the San Diego Bay in 

the southwest, the Pacific Ocean in the west, or the Salton Sea 

in the east. Major surface-water drainage features in the study 

area include the San Luis Rey, San Jacinto, Santa Margarita, 

San Diego, and Sweetwater Rivers and Santa Ysabel Creek.

The climate in the Peninsular Ranges study area is 

characterized as Mediterranean, with warm, dry summers 

and cool, wet winters. The NCDC station located at the 

Palomar Mountain Observatory (fig. 2C) measured an 

average annual temperature of 56 °F (13 °C) for 2011; total 

annual precipitation was about 25 inches (U.S. Department 

of Commerce, National Climatic Data Center, 2011). 

Precipitation primarily occurs as rain during the winter and 

early spring. Snow may occur in the winter months at the 

higher elevations. The highest peak in the Peninsular Ranges 

study area is San Jacinto Peak at an elevation of about 

10,800 feet.
Methods 13

Methods

Methods used for the GAMA-PBP were selected to 

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

for suitable statistical representation; (2) collect samples in 

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

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

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

relevant documentation. The appendix contains detailed 

descriptions of the sample collection protocols, analytical 

methods, quality-assurance (QA) methods, and results of 

analyses of quality-control (QC) samples.

Study Design

Public-supply wells in the CDPH database located 

outside of CDWR-defined groundwater basins were mapped 

to determine the areas with relatively high well density. Wells 

that supply drinking water in the hard rock regions of the 

Klamath (Mathany and Belitz, 2014), North San Francisco 

Bay (Kulongoski and others, 2006), Sierra Nevada (Fram and 

Belitz, 2007; Ferrari and others, 2008; Fram and others, 2009; 

Shelton and others, 2010), Big Bear (Mathany and Belitz, 

2013), and San Diego (Wright and others, 2005) study units 

have been sampled as part of previous GAMA-PBP studies. 

Of the remaining regions that are outside groundwater basins, 

three study areas with high densities of CDPH wells were 

selected: the Santa Cruz, San Gabriel, and Peninsular Ranges 

study areas.

CDPH wells were not distributed evenly over the 

study areas, and only the parts of the study areas in which 

groundwater resources are currently used for public drinkingwater supply were assessed in this study. The areas to 

be assessed were defined by drawing 3-kilometer (km) 

(1.86-mile) radius circles around the locations of wells in the 

CDPH database, referred to as “buffers” (figs. 3A–C). Buffers 

around wells near the study area margins may not be circular 

because only areas within the study unit boundaries are 

included.

The collective area encompassed by the buffers was then 

divided into equal-area grid cells using a randomized gridbased method (Scott, 1990) (figs. 4A–C). The SC study area 

has a total buffer area of 450 square miles (mi2), which was 

divided into 25 grid cells, each with an average area of 18 mi2 

(fig. 4A). The SG study area has a total buffer area of 546 mi2, 

which was divided into 40 grid cells, each with an average 

area of 13 mi2 (fig. 4B). The PR study area has a total buffer 

area of 1,405 mi2 which was divided into 41 grid cells, each 

with an average area of 34 mi2 (fig. 4C). Because the total 

buffered area in each study area consists of many irregularlyshaped pieces and the sizes of the grid cells are much larger 

than the size of a buffer around an individual well, each cell 

generally includes several non-continuous areas.

Some of the sites listed in the CDPH database for the 

SC and SG study areas are springs. Springs are sites where 

groundwater naturally flows from below ground to above 

land surface, sometimes through a horizontal well bore. In 

the CDPH database, a spring with a horizontal well bore may 

have been given a name that identifies it as a well. All sites 

are referred to as wells in this report, unless the difference 

between a well and a spring is important to the discussion.

Sites were randomly selected to provide a statistically 

unbiased, spatially distributed assessment of the quality of 

the groundwater that is used for public drinking-water supply 

within each study area. The objective was to sample one 

CDPH well in each grid cell. If a grid cell contained more 

than one CDPH well, each well randomly was assigned a 

rank. The highest-ranking well that met basic sampling criteria 

(for example, sampling point located prior to treatment or 

capability to pump for several hours) was sampled. If a CDPH 

well was not accessible, then other types of wells, such as 

irrigation wells, domestic wells, or commercial wells, were 

considered for sampling. These “alternative” wells were 

identified from wells listed in the USGS National Water 

Information System database or by door-to-door canvassing. 

Wells with depths and screened intervals similar to those in 

CDPH wells in the area were selected. In this fashion, 1 well 

was selected for sampling in 94 of the 106 grid cells to provide 

a spatially distributed, randomized monitoring network. The 

remaining 12 cells contained no accessible wells.

The 94 wells sampled as part of the spatially distributed, 

randomized grid-cell network, hereinafter, are referred to 

as “grid wells.” Eighteen additional, non-randomized wells 

(hereinafter referred to as “understanding wells”) were 

selected to aid in the understanding of groundwater sources 

and flow through hard rock aquifers in the Hard Rock study 

unit. The understanding wells were not included in the 

statistical characterization of water quality in the Hard Rock 

study unit because inclusion of these wells would lead to the 

over-representation of some cells.

All 112 grid and understanding wells in the Hard 

Rock study unit were named by using the prefix “HR.” The 

94 grid wells sampled were named by using a suffix “SC,” 

“SG,” or “PR” depending on the study area, followed by a 

number representing the order in which they were sampled 

for each study area (figs. 4A–C). The 18 understanding wells 

sampled were named by adding “U” or “FP” to the study 

area abbreviation (“U” indicating “understanding” and “FP” 

indicating “flow path”) followed by a number representing the 

order in which they were sampled for each study area. Flowpath wells are a subset of the understanding wells sampled 

for the PR study area and are located in the Sweetwater River 

watershed of San Diego County.
14 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

San Francisco

Santa Cruz

84 35

17

1

1

92

84

238

237

152

82

85 87

101

101

880

280

680

580

580

205

SANTA CLARA CO

SAN MATEO CO

SAN FRANCISCO CO

ALAMEDA CO

SAN JOAQUIN CO

STANISLAUS CO

CONTRA COSTA CO

SANTA CRUZ CO

SAN BENITO CO

MONTEREY CO

SC-25

SC-17

SC-24

SC-23

SC-22

SC-21

SC-20

SC-19 SC-18

SC-16

SC-15

SC-14

SC-13

SC-12

SC-11

SC-10

SC-08 SC-09

SC-07

SC-06

SC-05

SC-04

SC-03

SC-02

SC-01

0 10 20 Miles

0 10 20 Kilometers

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Pacific Ocean

Monterey Bay

San Francisco Bay

San Lorenzo River

Pescadero Creek

EXPLANATION

Pajaro Valley

Santa Cruz Mtns

Loma Prieta Peak

Ben Lomond Stn

Pajaro River

Santa Cruz grid cell

USGS-grid well

 and identifier

Gilroy

Lompico

San Jose

Millbrae

Pescadero

Palo Alto

Los Gatos

Half Moon Bay

SC-24

A

sac14-0529_Figure 4a Map of the Santa Cruz study area showing the distribution of the grid cells, locations of sampled wells, 

major cities, and hydrologic and topographic features, Hard Rock study unit, California GAMA Priority Basin Project.

122°30’ 122° 121°30’

37°

30’

37°

Figure 4. (A) Santa Cruz, (B) San Gabriel, and (C) Peninsular Ranges study areas showing the distribution of the grid cells, locations of 

sampled wells, major cities, and hydrologic and topographic features, Hard Rock study unit, California GAMA Priority Basin Project.
Methods 15

The GAMA alphanumeric identification number for each 

well, along with the date sampled, well altitude, well type, and 

available well-construction information are shown in table 1. 

Groundwater samples were collected from March 28, 2011, 

through March 8, 2012. Grid wells included 83 production 

wells (74 CDPH, 4 domestic, 3 irrigation, 1 fire, and 1 unused) 

and 11 springs (all CDPH springs). Understanding wells 

included 15 production wells (5 CDPH, 6 domestic, and 

4 irrigation) and 3 springs (1 CDPH, 1 domestic, and 1 spring 

used for bottling water).

Well locations were verified by using a global positioning 

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

information in USGS and CDPH databases, and information 

provided by well owners, driller’s logs, or other sources. 

Well locations and information were recorded by hand on 

field sheets, and electronically on field computers using the 

Alternate Place Entry (APE) program designed by the USGS. 

All information was verified and then uploaded into the USGS 

National Water Information System (NWIS). Well owner and 

water-use information is confidential.

14

58

138

138

60

57

91

210

210

10

10

15

15

605

110 710

405

5

5

101

395

118°30’ 118° 117°30’

34°30’ 34°

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Pacific Ocean

KERN CO

LOS ANGELES CO

SAN BERNARDINO CO

RIVERSIDE CO

VENTURA CO

Azusa

Acton

Ontario

Castaic

Palmdale

Big Pines

San Gabriel

Los Angeles

Lake Hughes

Geologic units and faults available from the California 

Geological Survey (Saucedo and others, 2000)

Santa Clara River

Los Angeles River

San Gabriel River

Santa Ana River

Antelope Valley

Mt 

San Antonio

Mt Wilson Stn

San Fernando Valley

Upper Santa

Ana Valley

Los Angeles 

Coastal Plain

San Gabriel Mtns

Santa Monica Mtns

Santa Clarita 

Valley

Cajon Pass

San Bernardino

Mtns

SG-16

San Gabriel grid cell

USGS-grid well and identifier

SGU-01 USGS-understanding well and identifier

EXPLANATION

B

SG-33

SG-32

SG-31

SG-30

SG-28

SG-27

SG-26 SG-25

SG-24

SG-23

SG-22

SG-21

SG-20

SG-19

SG-18

SG-16

SG-15

SG-14

SG-12

SG-11

SG-10

SG-09

SG-08

SG-07

SG-06

SG-05

SG-04

SG-02

SG-01

SG-29

SG-17

SG-13

SG-03

SGU-04

SGU-03

SGU-02

SGU-01

Figure 4. —Continued
16 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

PR-36

PR-35

PR-34

PR-33

PR-32

PR-31

PR-30

PR-29 PR-28

PR-27

PR-26

PR-25

PR-24

PR-23

PR-22

PR-21

PR-20

PR-19

PR-18

PR-17

PR-16

PR-15

PR-14

PR-14

PR-13

PR-12

PR-11 PR-10

PR-09

PR-08

PR-07

PR-06

PR-05

PR-04

PR-03

PR-02

PR-01

RIVERSIDE CO

SAN DIEGO CO

ORANGE

CO

Julian

Dulzura

Temecula

San Diego

Fallbrook

San Marcos

San Jacinto

Palm Desert

Mount Laguna

Lake Elsinore

Borrego Springs

117°30' 117° 116°30'

33°30' 33°

Shaded relief derived from U.S. Geological Survey 

National Elevation Dataset, 2006, 

Albers Equal Area Conic Projection

Figure 4c. Map of the Peninsular Ranges study area showing the distribution of the grid cells, locations of sampled wells, 

major cities, and topographic and hydrologic features, Hard Rock study unit, California GAMA Priority Basin Project.

Pacific Ocean

San Diego Bay

USGS-grid well

 and identifier

USGS-flow-path well

 and identifier

USGS-understanding well

 and identifier

PRU-01

FP-13

FP-12

FP-11

FP-10

FP-09

FP-09

FP-08 FP-07

FP-06

FP-05 FP-04 FP-03 FP-01

PRU-01

FP-02

0 5 10 15 MILES

0 10 15 5 KILOMETERS

EXPLANATION

Peninsular Ranges

 grid cell

C

Figure 4. —Continued
Methods 17

Sample Collection and Analysis

Samples were collected in accordance with the protocols 

established by the USGS National Water-Quality Assessment 

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

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

variously dated). These sampling protocols were followed so 

that representative samples of groundwater were collected at 

each site and so that the samples were collected and handled 

in ways that minimized the potential for contamination. Use 

of the sampling protocols also allows comparison with data 

collected by the GAMA-PBP throughout California and with 

other USGS projects in California and the Nation.

All 112 wells in the Hard Rock study unit were sampled 

for a standard set of constituents (table 2); the 37 SG grid 

and understanding wells were also sampled for chromium 

species. Tables 3A–I list the compounds analyzed in each 

constituent class. Groundwater samples were analyzed for 

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

(table 3B); 1 constituent of special interest (table 3C); 

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

and minor ions, silica, total dissolved solids, and laboratory 

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

(table 3G); 5 isotopic tracers and 6 radioactive constituents, 

including tritium and carbon-14 abundance (table 3H); and 

stable isotope ratios of helium, 5 dissolved noble gases, and 

tritium (table 3I). The methods used for sample collection and 

analysis are described in the appendix section titled “Sample 

Collection and Analysis.”

Data Reporting

The methods and conventions used for reporting the data 

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

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

conductance—were measured in the field and at the 

National Water Quality Laboratory (NWQL), and four other 

constituents—tritium and total arsenic, chromium, and iron—

were each measured by two different laboratories. Both sets 

of results for each constituent (except tritium) were reported, 

with preference given to one set according to the method of 

analysis; tritium does not have a preferred method; however, 

only one set of results was available at the time this report was 

published (see the appendix section titled “Constituents on 

Multiple Analytical Schedules”).

Comparative Benchmarks

Concentrations of constituents detected in groundwater 

samples were compared with CDPH and USEPA regulatory 

and nonregulatory drinking-water health-based benchmarks 

and benchmarks established for aesthetic purposes (California 

Department of Public Health, 2012a,b; U.S. Environmental 

Protection Agency, 2009, 2012a,b). The water-quality data 

presented in this report are meant to characterize the quality 

of the untreated groundwater within the aquifers of the Hard 

Rock study unit and are not intended to represent the treated 

drinking water delivered to consumers by water purveyors. 

The chemical composition of treated drinking water may 

differ from untreated groundwater because treated drinking 

water may be subjected to disinfection, filtration, mixing with 

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

delivery to consumers. Comparisons of untreated groundwater 

to benchmarks are for illustrative purposes only and are not 

indicative of compliance or non-compliance with drinkingwater regulations. The benchmarks used for each constituent 

were selected in the following order of priority:

1. 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. The 

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 the CDPH 

is labeled “MCL-US,” and one set by the 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 MCL-CA 

benchmark in samples collected for the GAMA-PBP, but 

these detections do not constitute violations of CDPH 

regulations.

2. AL–Action Level. Legally enforceable standards that 

apply to public water systems and are designed to protect 

public health by limiting the levels of copper and lead 

in drinking water. Detections of copper or lead greater 

than the action-level benchmarks trigger requirements for 

mandatory water treatment to reduce the corrosiveness of 

water to water pipes. The action levels established by the 

USEPA and CDPH are the same; thus, these benchmarks 

are labeled “AL-US” in this report.

3. SMCL–Secondary Maximum Contaminant Level. 

Non-enforceable standards applied to constituents that 

affect the aesthetic qualities of drinking water, such 

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

drinking water, such as scaling and staining. Both the 

USEPA and CDPH define SMCLs, but unlike MCLs, 

SMCLs established by the CDPH are not required 

to be at least as stringent as those established by the 

USEPA. SMCLs established by the CDPH are used in 

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

SMCL-CA values. The SMCL established by the USEPA 

(SMCL-US) is used for pH because no SMCL-CA has 

been defined.
18 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

4. NL–Notification Level. Health-based standards 

established by the CDPH (NL-CA) for some of the 

constituents in drinking water that lack MCLs. 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.

5. HAL–Lifetime Health Advisory Level. The maximum 

concentration of a constituent at which its presence in 

drinking water is not expected to cause any adverse 

carcinogenic effects for a lifetime of exposure. HALs are 

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

assuming consumption of 2 liters (1 quart) 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.

6. 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).

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, 

for zinc the SMCL-CA is 5,000 micrograms per liter 

(μg/L) and the HAL-US is 2,000 μg/L, but the comparative 

benchmark selected by this hierarchy is the SMCL-CA. 

The comparative benchmarks used in this report are listed 

in tables 3A–I for all constituents and in tables 4–14 for 

constituents detected in groundwater samples from the Hard 

Rock 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 asterisks (*) in 

tables 4, 8, 9, 10, 11, and 14.

Quality-Assurance Methods

The QA methods used for this study followed the 

protocols used by the NAWQA Program (Koterba and others, 

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

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

primary laboratory used to analyze samples for this study, 

is described by Stevenson (2013). QC samples collected in 

the Hard Rock 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 appendix section 

titled “Quality-Assurance and Quality-Control Methods and 

Results” and are summarized in the following section.

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, as well as a review of available 

QA/QC information, reporting levels in this study unit were 

raised from the USGS NWQL levels for three volatile organic 

compounds (1,2,4-trimethylbenzene, carbon disulfide, and 

toluene), eight trace elements (copper, iron, lead, manganese, 

molybdenum, nickel, tungsten, and zinc), and three nutrients 

(ammonia, nitrite, and nitrite plus nitrate). The raised reporting 

levels are referred to as “study reporting levels” (SRLs). 

Detections of the 14 constituents with concentrations less 

than their SRLs were coded with a less than or equal to (≤) 

symbol in this report and the NWIS database. Additionally, 

all groundwater detections for three VOCs (2-butanone, 

acetone, and tetrahydrofuran) and all results for one trace 

element (cobalt) were coded as “reviewed and rejected.” For 

blank results for this study unit and references for additional 

information, see table A3 and the appendix section titled 

“Detections in Blanks and Application of SRLs.”

Results from the replicates confirm that the procedures 

used to collect and analyze the samples were consistent. 

Variability for about 98 percent of the replicate pairs for 

constituents detected in samples was within acceptable 

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

are described in the appendix section titled “Methods of 

Assessment of Replicate Samples.” Of the 148 organic 

constituents analyzed, 11 pesticides or pesticide degradates 

had median matrix-spike recoveries lower than the acceptable 

limit of 70 percent, and 1 pesticide had a median recovery 

greater than the acceptable limit of 130 percent (tables 3A–B

and A5A–B). The constituents with low recoveries might not 

have been detected in some samples if they were present in 

the samples at concentrations near laboratory reporting levels 

(LRLs). Constituents with high recoveries may indicate that 

reported values could be greater than what is in the sample. 

The QC results are described in the appendix section titled 

“Matrix-Spike Recoveries.”

Groundwater-Quality Data

Results from analyses of untreated groundwater samples 

from the Hard Rock study unit are presented in tables 4–14. 

These results are separated into the three study areas (SC, SG, 

and PR) that make up the Hard Rock study unit. Groundwater 

samples collected in the Hard Rock study unit were analyzed 

for 209 unique constituents; 115 of those constituents were 

not detected in any of the samples, and 92 constituents were 

detected at least once. The results for stable isotopes of 

dissolved boron, isotope ratios for dissolved strontium, and 
Water-Quality Results 19

tritium (analyzed at the LLNL) were not available at the time 

this report was written; they will be included in subsequent 

publications. Tritium data analyzed at the USGS Stable Isotope 

and Tritium Laboratory (SITL) are presented in this report. 

For organic and special-interest constituents, the results 

listed in the tables include only those constituents that were 

detected, and the following summary statistics are presented 

only for the grid wells: the number of wells at which each 

constituent 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 that were analyzed, as 

all constituents were detected in at least one well sample.

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 5–14:

• Organic constituents

• Volatile organic compounds (table 5)

• Pesticides and pesticide degradates (table 6)

• Perchlorate (table 7)

• Inorganic constituents

• Trace elements (table 8)

• Nutrients (table 9)

• Major and minor ions, silica, and total dissolved 

solids (table 10)

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

• Isotope tracers (table 12)

• Dissolved noble gases (table 13)

• Radioactive constituents 

• Radon-222 (table 14A)

• Gross alpha and gross beta radioactivity (table 14B)

• Uranium-234, -235, and -238 (table 14C)

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 total 

dissolved solids (TDS) in the water.

Field pH values were outside of the SMCL-US range 

(6.5 to 8.5) for 14 of the 94 Hard Rock study unit grid-well 

samples: 10 well samples had field pH values less than 6.5; 

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

One understanding-well sample in the PR study area had 

a field pH value greater than 8.5. 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 18 of the gridwell samples, three of which were also greater than the upper 

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

six understanding wells in the PR study area were greater than 

the recommended SMCL-CA, three of which were also greater 

than the upper SMCL-CA.

Organic Constituents

VOCs are present in paints, solvents, fuels, fuel 

additives, refrigerants, fumigants, and disinfected water, 

and are characterized by their tendency to evaporate. VOCs 

generally persist longer in groundwater than in surface water 

because groundwater is isolated from the atmosphere. Of the 

85 VOCs analyzed for the Hard Rock study unit, 19 were 

detected in grid-well samples (table 5). All concentrations 

were less than health-based benchmarks. One or more VOCs 

were detected in 41 of the 94 grid-well samples (44 percent 

detection frequency). The trihalomethane chloroform was the 

most frequently detected VOC in the study unit. 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). The detection frequency of chloroform was greater 

than 10 percent. Other than chloroform, no other VOCs had 

detection frequencies greater than 10 percent in the grid wells 

for all three study areas; however, two VOCs had detection 

frequencies greater than 10 percent in at least one study area. 

The detection frequency of the solvent 1,1-dichloroethene 

(1,1-DCE) was greater than 10 percent in samples from the SC 

study area. The detection frequency of the gasoline oxygenate 

methyl tert-butyl ether (MTBE) was greater than 10 percent 

in the PR study area. One or more VOCs were detected in 7 of 

the 18 understanding-well samples, all of which were from the 

PR study area.

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 for the Hard Rock study 

unit, 14 were detected in grid-well samples (table 6). All 
20 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

concentrations were less than health-based benchmarks. One 

or more pesticides were detected in 17 of the 93 grid-well 

samples (18 percent detection frequency). There were no 

pesticide results for one grid well (HR-PR-01) because the 

sample was ruined during analysis. None of the pesticides 

had detection frequencies greater than 10 percent in the study 

unit as a whole; however, the herbicide simazine and the 

herbicide degradate deethylatrazine had detection frequencies 

greater than 10 percent in the PR study area. Simazine and 

deethylatrazine are among the most commonly detected 

pesticide compounds in groundwater nationally (Gilliom and 

others, 2006). One or more pesticides were detected in 4 of 

the 18 understanding wells, all of which were in the PR study 

area.

Constituent of Special Interest

Perchlorate was classified as a special-interest constituent 

because at the inception of the GAMA-PBP in 2003, 

perchlorate had recently been detected in public-supply wells 

in several areas of the State and the CDPH was evaluating 

whether or not an MCL-CA should be established (California 

Department of Public Health, 2012c). The MCL-CA of 6 μg/L 

was promulgated in 2007. Perchlorate was detected in 45 of 

94 grid-well samples (48 percent detection frequency) and 

in 9 of the understanding-well samples (table 7). The three 

study areas of the Hard Rock study unit had different detection 

frequencies of perchlorate: 36 percent for SC, 55 percent for 

SG, and 50 percent for PR. Perchlorate was not detected at 

concentrations greater than the MCL-CA of 6 μg/L at any of 

the grid or understanding wells in the Hard Rock study unit.

Inorganic Constituents

Unlike the organic and special-interest constituents, most 

of the inorganic constituents generally are naturally present in 

groundwater, although their concentrations may be influenced 

by human activities.

Seventeen of the trace elements (table 3D) and 1 of the 

major and minor ions (table 3F) analyzed and detected in the 

Hard Rock study unit have regulatory or nonregulatory healthbased benchmarks. Of these 18 constituents with health-based 

benchmarks, concentrations were less than their respective 

benchmarks in all grid-well detections for 13 constituents 

(tables 8, 10). The remaining five inorganic constituents 

(arsenic, boron, molybdenum, uranium, and fluoride) were 

each detected at concentrations greater than their health-based 

benchmarks in one or more grid-well samples.

Arsenic concentrations greater than the MCL-US of 

10 μg/L were detected in grid-well samples from two wells 

in the SC study area and one well in the SG study area 

(table 8). Boron concentrations greater than the NL-CA of 

1,000 μg/L were detected in grid-well samples from two 

wells in the SC study area and one well in the SG study area. 

Molybdenum concentrations greater than the HAL-US of 

40 μg/L were detected in grid-well samples from one well in 

the SC study area and one well in the SG study area. Fluoride 

concentrations greater than the MCL-CA of 2 milligrams 

per liter (mg/L) were detected in grid-well samples from 

one well in the SC study area and two wells in the SG study 

area (table 10). Uranium concentrations are discussed in the 

“Radioactive Constituents and Uranium” section.

Arsenic, strontium, and fluoride were detected at 

concentrations greater than their health-based benchmarks 

in one or more understanding wells (tables 8, 10). Arsenic 

concentrations greater than the benchmark level were detected 

in two understanding-well samples. A strontium concentration 

greater than the HAL-US of 4,000 μg/L was detected in one 

understanding-well sample. A fluoride concentration greater 

than the benchmark level was detected in one understandingwell sample.

Nutrients (nitrogen and phosphorus) 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 (California Department of 

Public Health, 2012d). Most concentrations of ammonia, 

nitrite, and nitrate in samples from the 94 Hard Rock study 

unit grid wells were less than health-based benchmarks 

(table 9). Exceptions are detections of nitrite plus nitrate 

(as nitrogen) at concentrations greater than the MCL-US of 

10 mg/L in grid-well samples from two wells in the PR study 

area. Of the 18 understanding-well samples, nitrite plus nitrate 

concentrations were greater than the benchmark in 4 samples, 

all of which came from flow-path wells in the PR study area.

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) for iron, manganese, silver, zinc, chloride, 

sulfate, and TDS that are based on aesthetic properties rather 

than on human-health concerns. Iron and manganese are trace 

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

containing iron or manganese may cause orange, brown, or 

black staining of surfaces.

Iron concentrations greater than the SMCL-CA of 

300 μg/L were detected in grid-well samples from eight 

wells in the SC study area, three wells in the SG study area, 

and eight wells in the PR study area (table 8). Manganese 
Water-Quality Results 21

concentrations greater than the SMCL-CA of 50 μg/L were 

detected in grid-well samples from 13 wells in the SC study 

area, 3 wells in the SG study area, and 11 wells in the PR 

study area. Chloride concentrations were greater than the 

recommended SMCL-CA of 250 mg/L in grid-well samples 

from one well in the SC study area and two wells in the 

PR study area; one of the PR grid-well samples also had a 

concentration greater than the upper SMCL-CA of 500 mg/L 

(table 10). Sulfate concentrations were greater than the 

recommended SMCL-CA of 250 mg/L for grid-well samples 

from one well in the SC study area and three wells in the 

PR study area; none of these concentrations were greater 

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

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

for grid-well samples from 8 wells in the SC study area, 

4 wells in the SG study area, and 15 wells in the PR study 

area; one of the SC and two of the PR grid-well samples had 

TDS concentrations greater than the upper SMCL-CA of 

1,000 mg/L.

Iron was detected at concentrations greater than the 

benchmark level in two understanding-well samples, and 

manganese was detected at concentrations greater than 

the benchmark level in eight understanding-well samples 

(table 8). Chloride was detected at concentrations greater 

than the recommended benchmark in four understandingwell samples; two of these concentrations were greater than 

the upper benchmark (table 10). Sulfate was detected at 

concentrations greater than the recommended benchmark 

in two understanding-well samples. TDS was detected at 

concentrations greater than the recommended benchmark in 

nine understanding-well samples; three of these concentrations 

were greater than the upper benchmark.

Geochemical and Age-Dating Tracers

The geochemical and age-dating tracers may be used 

to help interpret hydrologic processes affecting groundwater 

quality (Clark and Fritz, 1997). Arsenic, chromium, and 

iron occur as different species depending on the oxidation–

reduction state of the groundwater. The oxidized and reduced 

species have different solubilities in groundwater and 

may have different effects on human health. The relative 

proportions of the oxidized and reduced species of each 

element can be used to aid in interpretation of the oxidation–

reduction conditions of the aquifer, which affect the mobility 

of many constituents. Concentrations of total arsenic, 

chromium, and iron and the dissolved concentration of either 

the reduced or the oxidized species of these elements are 

reported in table 11.

Stable-isotope ratios of hydrogen and oxygen in water 

reflect the altitude, latitude, and temperature of precipitation 

and also the extent of evaporation of the water in surfacewater bodies or soils prior to infiltration into the aquifer. These 

data aid in the interpretation of the sources of groundwater 

recharge. Results for stable isotopes of hydrogen, oxygen, 

and carbon are reported in table 12 (see appendix section 

“Notation” for reporting methods for stable isotope data).

Carbon-14 is a radioactive isotope used for age-dating 

(time since recharge). Low levels of carbon-14 are produced 

continuously by interaction of cosmic radiation with the 

Earth’s atmosphere and are 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 thousands 

of years old or more. Carbon-14 results, as percent modern 

carbon, are reported in table 12.

Tritium activities and dissolved noble gases also provide 

information about the age of groundwater. Tritium is a shortlived 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 levels 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 healthbased benchmark. All measured tritium activities in samples 

from the Hard Rock study unit were less than 1/1,000 of the 

MCL-CA benchmark (table 12).

Gases dissolve in water that is in contact with the 

atmosphere, and the solubilities of the different gas species 

vary with temperature. Concentrations of dissolved noble 

gases are used to estimate the conditions of groundwater 

recharge, particularly the temperature of the water at the time 

of recharge. Results for analyses of dissolved noble gases 

(argon, helium, krypton, neon, and xenon) are reported in 

table 13. These results are stored in a database separate from 

the NWIS database and maintained by GAMA-PBP project 

staff.
22 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Radioactive Constituents and Uranium

Radioactivity is the release of energy or energetic 

particles during changes in the structure of the nucleus of 

an atom. Most of the radioactivity in groundwater comes 

from decay of naturally occurring isotopes of uranium and 

thorium that can be present in minerals in the sediments or 

fractured rocks of an 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 number of particles emitted is equal to 

the number of atoms decaying. Concentrations of radioactive 

constituents in groundwater are expressed in picocuries per 

liter; 1 picocurie per liter (pCi/L) is approximately equal to 

two atoms decaying per minute.

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 

(U.S. Environmental Protection Agency, 2013). For that 

reason, MCLs were set by the USEPA and CDPH to regulate 

concentrations of gross alpha and beta radioactivity and 

uranium in drinking water. The MCL-US for gross alpha 

radioactivity applies to adjusted gross alpha radioactivity, 

which is equal to measured gross alpha activity minus uranium 

activity. The proposed MCL-US for radon-222 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, 2012b). 

Of the 112 wells in the Hard Rock study unit, samples 

from 105 wells were analyzed for radon-222, samples from 

110 wells were analyzed for gross alpha and beta activities, 

and samples from 29 wells were analyzed for uranium 

isotopes (uranium-234, uranium-235, and uranium-238). 

Radon-222 activities were less than the proposed MCL-US 

of 4,000 pCi/L in most of the sampled wells; exceptions were 

grid-well samples from two wells in the SG study area and 

three wells in the PR study area (table 14A). Gross alpha 

activity was greater than the MCL-US of 15 pCi/L in gridwell samples from four wells in the SG study area and seven 

wells in the PR study area (table 14B). Two of the SG and four 

of the PR grid-well samples having unadjusted gross alpha 

activity greater than the benchmark also had total uranium 

concentrations greater than the MCL-US of 30 μg/L; the same 

wells plus one PR grid-well sample had uranium activities 

greater than the MCL-CA of 20 pCi/L (tables 8, 14C).

Radon-222 was greater than the proposed MCL-US 

in five understanding-well samples (table 14A). Gross 

alpha activities were greater than the benchmark in seven 

understanding-well samples. One of these samples also had 

gross beta activity (30-day count) greater than the MCL-CA 

of 50 pCi/L (table 14B). Five of the seven understandingwell samples having unadjusted gross alpha activity greater 

than the MCL-US also had total uranium concentrations 

greater than the MCL-US and uranium activities greater than 

the MCL-CA. One additional understanding-well sample 

had uranium concentration and activity greater than the 

benchmarks, but gross alpha and beta activities were not 

analyzed for this sample (tables 8, 14C).

Future Work

Subsequent reports for the Hard Rock 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 Hard Rock study unit. 

Water-quality data contained in the CDPH databases will be 

compiled, evaluated, and used in combination with the data 

that are presented in this report.

Summary

Groundwater quality in the 2,400-square-mile Santa Cruz, 

San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard 

Rock) study unit was investigated by the U.S. Geological 

Survey (USGS) from March 2011 through March 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 of California. 

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.

The GAMA Hard Rock study was designed to provide 

a spatially unbiased assessment of untreated-groundwater 

quality within the primary aquifer system and to facilitate 

statistically consistent comparisons of untreated groundwater 

quality throughout California. The primary aquifer system 

is defined as the depth intervals of the wells listed in the 

California Department of Public Health (CDPH) database 

for the Hard Rock study unit. The quality of groundwater in 

the primary aquifer system may differ from that in shallow 

or deeper water-bearing zones; shallow groundwater may be 

more vulnerable to surficial contamination.

This study did not attempt to evaluate the quality of 

water delivered to consumers; after withdrawal from the 

ground, water typically is treated, disinfected, and blended 

with other waters to maintain acceptable water quality. 

Regulatory benchmarks apply to treated water that is served 

to the consumer, not to untreated groundwater. However, 

to provide some context for the results, concentrations of 
Summary 23

constituents measured in the untreated groundwater samples 

were compared with regulatory and nonregulatory healthbased benchmarks established by the U.S. Environmental 

Protection Agency (USEPA) and the CDPH and nonregulatory 

benchmarks established for aesthetic concerns by the CDPH.

The Hard Rock study unit is located within the Southern 

Coast Ranges, Transverse and Selected Peninsular Ranges, 

San Diego Drainages, and Desert hydrogeologic provinces. 

The study unit includes areas outside of the groundwater 

basins defined by the California Department of Water 

Resources. The Hard Rock study included assessment of the 

groundwater quality from 112 wells and springs in 3 study 

areas (the Santa Cruz, San Gabriel, and Peninsular Ranges) 

in San Mateo, Santa Clara, Santa Cruz, San Benito, Los 

Angeles, Orange, Riverside, San Bernardino, and San Diego 

Counties. All sites are referred to as wells in this report unless 

the difference between a well and a spring is important to 

the discussion. Ninety-four sites were selected by using a 

randomized grid approach to achieve a statistically unbiased 

representation of groundwater used for public drinkingwater supplies (grid wells): 25 in the Santa Cruz (SC) study 

area, 33 in the San Gabriel (SG) study area, and 36 in the 

Peninsular Ranges (PR) study area. Eighteen additional wells 

were selected to aid in the evaluation of water-quality issues 

(understanding wells).

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

constituent, inorganic constituents, geochemical and 

age-dating tracers, and radioactive constituents. In total, 

209 different constituents and water-quality indicators were 

measured in this study. This report describes the sampling, 

analytical, and quality-assurance methods used in the study 

and presents the results of the chemical analyses of the 

groundwater samples.

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

and matrix spikes) were collected at approximately 10 percent 

of the wells in the Hard Rock study unit, and the results 

for these samples were used to evaluate the quality of the 

data for the groundwater samples. Blanks rarely contained 

detectable concentrations of most constituents, suggesting 

that contamination from sample collection procedures was 

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

samples. Replicate samples generally were within the limits 

of acceptable analytical reproducibility. Median matrixspike recoveries were within the acceptable range (70 to 

130 percent) for approximately 92 percent of the organic 

compounds.

All constituents were analyzed for in samples from the 

112 wells in the Hard Rock study unit, except for chromium 

species, which were analyzed for the San Gabriel study area 

only. Of the 149 organic and special-interest constituents 

analyzed, 34 were detected in groundwater samples; 

concentrations of all detected constituents were less than 

regulatory and nonregulatory health-based benchmarks. One 

or more organic constituents were detected in 51 percent of the 

grid wells in the Hard Rock study unit: VOCs were detected 

in 44 percent and pesticides and pesticide degradates were 

detected in 18 percent. Perchlorate was detected in 48 percent 

of the Hard Rock grid wells.

Most of the grid-well samples analyzed for inorganic 

constituents had concentrations less than the regulatory and 

the nonregulatory health-based benchmarks. Arsenic was 

detected at concentrations greater than the USEPA maximum 

contaminant level (MCL-US) in three grid-well samples. 

Boron was detected at concentrations greater than the CDPH 

notification level (NL-CA) in three grid-well samples. 

Molybdenum was detected at a concentration greater than the 

USEPA lifetime health advisory level (HAL-US) in two gridwell samples. Nitrite plus nitrate (as nitrogen) was detected at 

concentrations greater than the CDPH maximum contaminant 

level (MCL-CA) in two grid-well samples. Fluoride was 

detected at concentrations greater than the MCL-CA in three 

grid-well samples.

Most of the grid-well samples analyzed for inorganic 

constituents had concentrations less than the non-enforceable 

benchmarks set for aesthetic concerns (secondary maximum 

contaminant levels [SMCLs]). Iron was detected at 

concentrations greater than the CDPH SMCL (SMCL-CA) 

in 19 grid-well samples, and manganese was detected at 

concentrations greater than the SMCL-CA in 27 grid-well 

samples. Chloride was detected at a concentration greater than 

the recommended SMCL-CA in three grid-well samples, one 

of which was also greater than the upper benchmark. Sulfate 

was detected at concentrations greater than the recommended 

SMCL-CA in four grid-well samples, none of which were 

greater than the upper benchmark. Total dissolved solids 

(TDS) concentrations were greater than the recommended 

SMCL-CA in 27 grid-well samples, 3 of which were also 

greater than the upper benchmark.

Radon-222 was detected at activities greater than the 

proposed MCL-US in five grid-well samples. Unadjusted 

gross alpha radioactivity was detected at activities greater than 

the MCL-US in 11 grid-well samples, 7 of which also had 

total uranium concentrations greater than the MCL-US and 

(or) uranium activities greater than the MCL-CA. 

For the understanding-well samples, two detections 

of arsenic and one detection of fluoride had concentrations 

greater than the respective MCL-CA, one detection of 

strontium had a concentration greater than the HAL-US, 

and four detections of nitrite plus nitrate (as nitrogen) had 

concentrations greater than the MCL-US. Two detections of 

iron and eight detections of manganese were at concentrations 

greater than the respective SMCL-CA. Four detections of 

chloride were at concentrations greater than the recommended 

SMCL-CA, two of which were also greater than the upper 

benchmark. Two detections of sulfate were at concentrations 

greater than the recommended SMCL-CA. Nine detections 

of TDS were at concentrations greater than the recommended 

SMCL-CA, three of which were greater than the upper 

benchmark.
24 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Five understanding-well samples had radon-222 activities 

greater than the proposed MCL-US. One understandingwell sample had gross beta radioactivity greater than the 

MCL-CA. Seven understanding-well samples had gross alpha 

radioactivity greater than the MCL-US, five of which also 

had total uranium concentrations greater than the MCL-US 

and uranium activities greater than the MCL-CA. One 

understanding-well sample had uranium concentration and 

activity greater than the benchmarks, but gross alpha and beta 

activities were not analyzed for this sample.

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. Funding for this work 

was provided by State of California bonds authorized by 

Proposition 50 and administered by the State Water Resources 

Control Board.

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Tables 31 Tables

Table 1. Identification, sampling, and construction information for wells sampled for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.

[GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area 

understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study 

area understanding well. Other abbreviations: ft, feet; LSD, land-surface datum; NAVD 88, North American Vertical Datum of 1988; na, not available]

GAMA well 

identification 

number

Date sampled 

(mm/dd/yyyy)

Altitude of LSD 

(ft above NAVD 88)1 Well type Well depth 

(ft below LSD)

Top of perforated 

interval 

(ft below LSD)

Bottom of 

perforated interval 

(ft below LSD)

Santa Cruz study area (25 wells)

HR-SC-01 3/28/2011 482 Production 776 370 776

HR-SC-02 3/29/2011 483 Spring na na na

HR-SC-03 3/29/2011 361 Production 140 80 140

HR-SC-04 3/30/2011 1,785 Production 300 60 280

HR-SC-05 3/31/2011 2,450 Production 310 50 310

HR-SC-06 4/4/2011 2,082 Production 260 na na

HR-SC-07 4/4/2011 445 Production 300 90 280

HR-SC-08 4/5/2011 1,398 Production 152 16 152

HR-SC-09 4/5/2011 728 Production 420 120 420

HR-SC-10 4/6/2011 2,942 Production 200 130 190

HR-SC-11 4/6/2011 1,679 Production 110 60 110

HR-SC-12 4/7/2011 826 Production 226 126 226

HR-SC-13 4/18/2011 1,000 Production 160 50 160

HR-SC-14 4/19/2011 1,779 Production 180 160 180

HR-SC-15 4/19/2011 622 Production 320 220 320

HR-SC-16 4/20/2011 1,142 Production 293 60 280

HR-SC-17 4/20/2011 1,013 Production 320 na na

HR-SC-18 4/21/2011 767 Production 790 560 770

HR-SC-19 4/21/2011 103 Production 180 60 180

HR-SC-20 5/2/2011 75 Production 65 na na

HR-SC-21 5/2/2011 888 Production 234 na na

HR-SC-22 5/3/2011 2,053 Production 460 na na

HR-SC-23 5/3/2011 1,683 Production 480 90 480

HR-SC-24 5/4/2011 134 Production 90 70 90

HR-SC-25 5/5/2011 525 Production 174 124 164

San Gabriel study area (37 wells)

HR-SG-01 5/16/2011 1,829 Production na na na

HR-SG-02 5/16/2011 2,717 Production na 22 62

HR-SG-03 5/17/2011 2,154 Production na na na

HR-SG-04 5/18/2011 2,364 Production 90 na na

HR-SG-05 5/19/2011 3,319 Production 805 238 805
32 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 1. Identification, sampling, and construction information for wells sampled for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—

Continued

[GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area 

understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study 

area understanding well. Other abbreviations: ft, feet; LSD, land-surface datum; NAVD 88, North American Vertical Datum of 1988; na, not available]

GAMA well 

identification 

number

Date sampled 

(mm/dd/yyyy)

Altitude of LSD 

(ft above NAVD 88)1 Well type Well depth 

(ft below LSD)

Top of perforated 

interval 

(ft below LSD)

Bottom of 

perforated interval 

(ft below LSD)

San Gabriel study area (37 wells)—Continued

HR-SG-06 5/23/2011 2,817 Spring na na na

HR-SG-07 5/23/2011 3,363 Spring na na na

HR-SG-08 5/24/2011 1,998 Production 800 na na

HR-SG-09 5/25/2011 1,474 Production 600 na na

HR-SG-10 5/25/2011 3,436 Production na na na

HR-SG-11 5/26/2011 4,121 Production 600 na na

HR-SG-12 7/11/2011 5,118 Spring na na na

HR-SG-13 7/12/2011 6,165 Production 367 121 367

HR-SG-14 7/12/2011 7,290 Production 265 245 265

HR-SG-15 7/13/2011 5,644 Production 250 235 250

HR-SG-16 7/13/2011 2,712 Production 350 250 350

HR-SG-17 7/14/2011 6,203 Spring na na na

HR-SG-18 7/18/2011 3,337 Production 112 72 112

HR-SG-19 7/18/2011 4,726 Spring na na na

HR-SG-20 7/19/2011 4,267 Production na 10 50

HR-SG-21 7/20/2011 4,405 Spring na na na

HR-SG-22 7/21/2011 1,661 Production 84 na na

HR-SG-23 7/25/2011 2,874 Production na na na

HR-SG-24 7/26/2011 2,368 Production na na na

HR-SG-25 7/27/2011 2,332 Spring na na na

HR-SG-26 7/28/2011 1,495 Production na na na

HR-SG-27 8/1/2011 6,048 Production 800 80 800

HR-SG-28 8/2/2011 na Spring na na na

HR-SG-29 8/3/2011 na Spring na na na

HR-SG-30 8/3/2011 6,559 Spring na na na

HR-SG-31 8/17/2011 2,623 Production 60 na na

HR-SG-32 8/18/2011 4,923 Production 88 na na

HR-SG-33 1/31/2012 2,320 Production 188 na na

HR-SGU-01 5/18/2011 2,704 Production na na na

HR-SGU-02 8/2/2011 na Spring na na na

HR-SGU-03 8/15/2011 4,493 Spring na na na

HR-SGU-04 8/16/2011 6,884 Spring na na na
Tables 33

Table 1. Identification, sampling, and construction information for wells sampled for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—

Continued

[GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area 

understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study 

area understanding well. Other abbreviations: ft, feet; LSD, land-surface datum; NAVD 88, North American Vertical Datum of 1988; na, not available]

GAMA well 

identification 

number

Date sampled 

(mm/dd/yyyy)

Altitude of LSD 

(ft above NAVD 88)1 Well type Well depth 

(ft below LSD)

Top of perforated 

interval 

(ft below LSD)

Bottom of perforated 

interval 

(ft below LSD)

Peninsular Ranges study area (50 wells)

HR-PR-01 8/22/2011 2,081 Production 46 41 na

HR-PR-02 8/23/2011 3,884 Production 222 na na

HR-PR-03 8/23/2011 4,757 Production 315 na na

HR-PR-04 8/24/2011 2,857 Production 280 119 280

HR-PR-05 8/24/2011 3,894 Production 400 97 400

HR-PR-06 8/25/2011 3,121 Production 500 60 500

HR-PR-07 8/29/2011 342 Production 450 60 345

HR-PR-08 8/30/2011 2,282 Production 560 320 560

HR-PR-09 8/31/2011 4,813 Production 600 76 600

HR-PR-10 9/13/2011 4,107 Production 500 na 500

HR-PR-11 9/13/2011 1,542 Production 979 820 979

HR-PR-12 9/14/2011 1,003 Production 93.5 na na

HR-PR-13 9/14/2011 1,751 Production 59.5 na na

HR-PR-14 9/15/2011 1,650 Production 350 50 350

HR-PR-15 9/20/2011 4,937 Production na na na

HR-PR-16 9/21/2011 658 Production 500 0 500

HR-PR-17 9/21/2011 2,786 Production 340 na na

HR-PR-18 9/22/2011 1,518 Production 455 na na

HR-PR-19 10/3/2011 4,128 Production 200 31 200

HR-PR-20 10/4/2011 933 Production 104 20 104

HR-PR-21 10/17/2011 1,622 Production 330 na na

HR-PR-22 10/31/2011 4,035 Production 570 0 570

HR-PR-23 10/31/2011 3,182 Production 703 120 703

HR-PR-24 11/1/2011 529 Production 215 100 200

HR-PR-25 11/1/2011 2,239 Production 280 240 280

HR-PR-26 11/2/2011 425 Production 305 282 305

HR-PR-27 11/3/2011 3,757 Production 186 60 186

HR-PR-28 11/14/2011 2,866 Production 416 336 416

HR-PR-29 11/15/2011 4,058 Production 1,400 na na

HR-PR-30 11/16/2011 5,172 Production 355 175 335
34 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 1. Identification, sampling, and construction information for wells sampled for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—

Continued

[GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area 

understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study 

area understanding well. Other abbreviations: ft, feet; LSD, land-surface datum; NAVD 88, North American Vertical Datum of 1988; na, not available]

GAMA well 

identification 

number

Date sampled 

(mm/dd/yyyy)

Altitude of LSD 

(ft above NAVD 88)1 Well type Well depth 

(ft below LSD)

Top of perforated 

interval 

(ft below LSD)

Bottom of 

perforated interval 

(ft below LSD)

Peninsular Ranges study area (50 wells)—Continued

HR-PR-31 11/16/2011 5,695 Production 645 50 545

HR-PR-32 11/17/2011 3,853 Production 310 160 310

HR-PR-33 11/28/2011 3,562 Production na na na

HR-PR-34 11/28/2011 3,475 Production 75 30 75

HR-PR-35 11/29/2011 3,481 Production 1,000 na na

HR-PR-36 11/29/2011 5,795 Production 500 na na

HR-PRFP-01 1/9/2012 3,430 Production 465 50 465

HR-PRFP-02 1/9/2012 876 Production na na na

HR-PRFP-03 1/10/2012 3,265 Production na na na

HR-PRFP-04 1/10/2012 1,536 Production 1,600 na na

HR-PRFP-05 1/11/2012 1,808 Production 720 na na

HR-PRFP-06 1/11/2012 1,996 Production 750 20 750

HR-PRFP-07 1/12/2012 4,145 Production 500 380 500

HR-PRFP-08 1/24/2012 4,109 Production 980 100 980

HR-PRFP-09 1/25/2012 426 Production na na na

HR-PRFP-10 1/26/2012 3,714 Production 500 na na

HR-PRFP-11 2/21/2012 198 Production 350 305 345

HR-PRFP-12 2/22/2012 532 Production 128 38 128

HR-PRFP-13 3/8/2012 868 Production 200 0 200

HR-PRU-01 9/20/2011 4,931 Production 340 107 340

1

 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 of 1988.
Tables 35

Table 2. Classes of chemical constituents and field water-quality indicators collected for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.

Constituent classes Constituent list table Results table

Field water-quality indicators 

Dissolved oxygen, temperature, pH, and specific conductance none 4

Field alkalinity, bicarbonate, and carbonate 1 none 4

Organic constituents

Volatile organic compounds (VOCs) 3A 5

Pesticides and pesticide degradates 3B 6

Constituent of special interest

Perchlorate 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

Arsenic, chromium, and iron species 2 3G 11

Isotopic tracers, dissolved noble gases, and radioactive constituents

Stable isotopes of hydrogen and oxygen in water 3H 12

Stable isotopes of dissolved boron and strontium in water 3H none 3

Stable isotopes of carbon in dissolved inorganic carbon and carbon-14 abundance 3H 12

Tritium 3H 12

Stable isotope ratios of helium, dissolved noble gases, and tritium 3I 3

 13

Radon-222 3H 14A

Gross alpha and gross beta radioactivity (72-hour and 30-day counts) 3H 14B

Uranium isotopes (234, 235, and 238) 4 3H 14C

1

 Field alkalinity was collected at approximately 10 percent of all sampled sites.

2

 Chromium species were collected at sites in the San Gabriel study area only.

3

 Results for stable isotopes of dissolved boron and strontium and for tritium analyzed at the Lawrence Livermore National Laboratory were not completed in 

time for inclusion in this report; results will be presented in a subsequent publication.

4

 Uranium isotopes only analyzed for samples with uranium concentrations greater than or equal to 10 micrograms per liter.
Table 3A. Volatile organic compounds (VOCs), primary uses or sources, reporting information, and comparative benchmarks for the U.S. Geological 

Water Quality Laboratory Schedule 2020. [The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. 

contaminant levels 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. Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximuCDPH notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstracts Service; LRL, laboratory reporting level; 

THM, trihalomethane; na, not available; —, not detected; D, detected in groundwater samples (table 5)] Constituent (synonym or abbreviation) Primary use or source USGS parameter code CAS registry number® 1 LRL (μg/L) 2 Benchmark type B

Acetone Solvent 81552 67-64-1 3.4 na 

Acrylonitrile Organic synthesis 34215 107-13-1 0.8, 0.48 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 HAL-US 

Bromochloromethane Fire retardant 77297 74-97-5 0.06 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 0.20 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 0.060 NL-CA 

Carbon disulfide Organic synthesis 77041 75-15-0 0.08, 0.1 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 0.14, 0.1 na 

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

2-Chlorotoluene Solvent 77275 95-49-8 0.028 NL-CA 

4-Chlorotoluene Solvent 77277 106-43-4 0.042 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 0.40 MCL-US 

1,2-Dibromoethane (EDB) Fumigant 77651 106-93-4 0.028 MCL-US 

Dibromomethane Solvent 30217 74-95-3 0.050 na 

1,2-Dichlorobenzene Solvent 34536 95-50-1 0.028 MCL-CA 1,3-Dichlorobenzene Solvent 34566 541-73-1 0.024 HAL-US 
Table 3A. Volatile organic compounds (VOCs), primary uses or sources, reporting information, and comparative benchmarks for the U.S. Geological Water Quality Laboratory Schedule 2020.—Continued[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. 

contaminant levels 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. Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximuCDPH notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstracts Service; LRL, laboratory reporting level; 

THM, trihalomethane; na, not available; —, not detected; D, detected in groundwater samples (table 5)]

Constituent 

(synonym or abbreviation) Primary use or source

USGS 

parameter 

code

CAS registry 

number® 1

 LRL 

(μg/L) 2

Benchmark 

type

B

1,4-Dichlorobenzene Solvent 34571 106-46-7 0.026 MCL-CA 

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

Dichlorodifluoromethane (CFC-12) Refrigerant 34668 75-71-8 0.1 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 0.040 na 

cis-1,3-Dichloropropene Fumigant 34704 10061-01-5 0.1 RSD5-US 

trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.14 RSD5-US Diethyl ether Solvent 81576 60-29-7 0.1 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 0.20 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 RSD5-US 

Hexachloroethane Solvent 34396 67-72-1 0.22, 0.1 HAL-US 

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

Iodomethane (Methyl iodide) Organic synthesis 77424 74-88-4 0.26 na 

Isopropylbenzene Gasoline hydrocarbon 77223 98-82-8 0.042 NL-CA 

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 
Table 3A. Volatile organic compounds (VOCs), primary uses or sources, reporting information, and comparative benchmarks for the U.S. Geological Water Quality Laboratory Schedule 2020.—Continued [The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. 

contaminant levels 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. Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximuCDPH notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstracts Service; LRL, laboratory reporting level; 

THM, trihalomethane; na, not available; —, not detected; D, detected in groundwater samples (table 5)] Constituent (synonym or abbreviation) Primary use or source USGS parameter code CAS registry number® 1 LRL (μg/L) 2 Benchmark type B

Methyl acrylonitrile Organic synthesis 81593 126-98-7 0.26 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 Methyl ethyl ketone (2-butanone, MEK) Solvent 81595 78-93-3 1.6 HAL-US 

Methyl methacrylate Organic synthesis 81597 80-62-6 0.22 na 

Methylene chloride (Dichloromethane) Solvent 34423 75-09-2 0.04 MCL-US 

Naphthalene Gasoline hydrocarbon 34696 91-20-3 0.18 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 0.040 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, 0.02 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 0.030 MCL-US 

1,1,2-Trichloroethane (1,1,2-TCA) Solvent 34511 79-00-5 0.028, 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 HAL-US 6 

Trichlorotrifluoroethane (CFC-113) Refrigerant 77652 76-13-1 0.034, 0.022 MCL-CA 

1,2,3-Trimethylbenzene Gasoline hydrocarbon 77221 526-73-8 0.060 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 
Table 3A. Volatile organic compounds (VOCs), primary uses or sources, reporting information, and comparative benchmarks for the U.S. Geological Water Quality Laboratory Schedule 2020.—Continued[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. 

contaminant levels 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. Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximuTHM, trihalomethane; na, not available; —, not detected; D, detected in groundwater samples (table 5)]CDPH notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstracts Service; LRL, laboratory reporting level; 

Constituent 

(synonym or abbreviation) Primary use or source

USGS 

parameter 

code

CAS registry 

number® 1

 LRL 

(μg/L) 2

Benchmark 

type

B

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- and 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 CAS Registry Numbers® (CASRNs), which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS

ServicesSM.

2 For constituents with two LRLs listed, the first value was in use before October 1, 2011, and the second value was in use starting October 1, 2011. The higher LRL is used fo3 Study reporting levels (SRLs) determined on the basis of the quality-control data collected between May 2004 and September 2010 for the first 32 study uints of the Californ

Monitoring and Assessment (GAMA) Priority Basin Project (Fram and others, 2012) resulted in censoring all groundwater detections when applied to four VOCs for the Hard Racetone, 2-butanone, and tetrahydrofuran were censored from this dataset and coded in the USGS database as “reviewed and rejected.” All groundwater detections of 1,2,4 -trimas nondetections and are reported with the following comment in the USGS National Water Information System database: Result is < or = reported value, based on quality-contrSee appendix table A3 for more information.

4 The MCL-US benchmark for trihalomethanes is for the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.5 The RSD5 benchmark for 1,3-dichloropropene is for the sum of its isomers (cis and trans).6 In earlier reports in this series, the NL-CA (0.005 μg/L) was used as the comparative benchmark for 1,2,3-TCP.7 The MCL-CA benchmark for m- and p-xylene and o-xylene is for the sum of all three xylene compounds.
40 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

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

U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2003.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels 

as of July 6, 2012. Benchmark type: Maximum contaminant levels are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA 

when the MCL-CA is lower than the MCL-US or no MCL-US exists. HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; 

MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, USEPA maximum contaminant level; RSD5-US, USEPA riskspecific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstracts Service; LRL, laboratory reporting level; μg/L, micrograms per liter; na, 

not available; —, not detected; D, detected in groundwater samples (table 6)]

Constituent 

(synonym or abbreviation)

Primary use or 

source

USGS 

parameter 

code

CAS 

registry 

number®

 LRL 

(μg/L) 1

Benchmark 

type

Benchmark 

level 

(μg/L)

Detection

Acetochlor Herbicide 49260 34256-82-1 0.010 na 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 na na —

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

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

Carbaryl Insecticide 82680 63-25-2 0.06 RSD5-US 400 D

2-Chloro-2,6-diethylacetanilide Herbicide degradate 61618 6967-29-9 0.010 na na —

4-Chloro-2-methylphenol Herbicide degradate 61633 1570-64-5 0.0046, 0.008 na na —

Chlorpyrifos Insecticide 38933 2921-88-2 0.0036 HAL-US 2 —

Chlorpyrifos oxon Insecticide degradate 61636 5598-15-2 0.06, 0.08 na na — 2

Cyfluthrin Insecticide 61585 68359-37-5 0.016 na na —

Cypermethrin Insecticide 61586 52315-07-8 0.020 na na —

Dacthal (DCPA) Herbicide 82682 1861-32-1 0.0076 HAL-US 70 —

Deethylatrazine (2-Chloro4-isopropylamino-6-amino-striazine)Herbicide degradate 04040 6190-65-4 0.006 na na D

Desulfinylfipronil Insecticide degradate 62170 na 0.012 na na D

Desulfinylfipronil amide Insecticide degradate 62169 na 0.029 na na —

Diazinon Insecticide 39572 333-41-5 0.0060 HAL-US 1 —

3,4-Dichloroaniline Herbicide degradate 61625 95-76-1 0.0042, 0.006 na na D

Dichlorvos Insecticide 38775 62-73-7 0.04 na na — 2

Dicrotophos Insecticide 38454 141-66-2 0.08 na na — 2

Dieldrin Insecticide 39381 60-57-1 0.008 RSD5-US 0.02 —

2,6-Diethylaniline Herbicide degradate 82660 579-66-8 0.0060 na na D

Dimethoate Insecticide 82662 60-51-5 0.006 na na — 2

Ethion Insecticide 82346 563-12-2 0.008, 0.010 na na —

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

2-Ethyl-6-methylaniline Herbicide degradate 61620 24549-06-2 0.010 na na —

Fenamiphos Insecticide 61591 22224-92-6 0.030 HAL-US 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 na 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 D

Fonofos Insecticide 04095 944-22-9 0.0048 HAL-US 10 —

Hexazinone Herbicide 04025 51235-04-2 0.008, 0.012 HAL-US 400 D 2
Tables 41

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

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

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels 

as of July 6, 2012. Benchmark type: Maximum contaminant levels are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA 

when the MCL-CA is lower than the MCL-US or no MCL-US exists. HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; 

MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, USEPA maximum contaminant level; RSD5-US, USEPA riskspecific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstracts Service; LRL, laboratory reporting level; μg/L, micrograms per liter; na, 

not available; —, not detected; D, detected in groundwater samples (table 6)]

Constituent 

(synonym or abbreviation)

Primary use or 

source

USGS 

parameter 

code

CAS 

registry 

number®

 LRL 

(μg/L) 1

Benchmark 

type

Benchmark 

level 

(μg/L)

Detection

Iprodione Fungicide 61593 36734-19-7 0.014 na na —

Isofenphos Insecticide 61594 25311-71-1 0.006, 0.008 na na —

Malaoxon Insecticide degradate 61652 1634-78-2 0.022 na na —

Malathion Insecticide 39532 121-75-5 0.016 HAL-US 500 —

Metalaxyl Fungicide 61596 57837-19-1 0.014 na na —

Methidathion Insecticide 61598 950-37-8 0.012 na na —

Metolachlor Herbicide 39415 51218-45-2 0.020 HAL-US 700 D

Metribuzin Herbicide 82630 21087-64-9 0.012 HAL-US 70 D

Myclobutanil Fungicide 61599 88671-89-0 0.010 na 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 —

Parathion-methyl Insecticide 82667 298-00-0 0.008 HAL-US 1 —

Pendimethalin Herbicide 82683 40487-42-1 0.012 na na —

cis-Permethrin Insecticide 82687 54774-45-7 0.010 na na —

Phorate Insecticide 82664 298-02-2 0.020 na na —

Phorate oxon Insecticide degradate 61666 2600-69-3 0.027 na na —

Phosmet Insecticide 61601 732-11-6 0.14, 0.08 na na — 2

Phosmet oxon Insecticide degradate 61668 3735-33-9 0.0511 na na — 2

Prometon Herbicide 04037 1610-18-0 0.012 HAL-US 400 D

Prometryn Herbicide 04036 7287-19-6 0.006, 0.010 na na —

Pronamide (Propyzamide) Herbicide 82676 23950-58-5 0.0036 RSD5-US 10 —

Simazine Herbicide 04035 122-34-9 0.006 MCL-US 4 D

Tebuthiuron Herbicide 82670 34014-18-1 0.028 HAL-US 500 D 3

Terbufos Insecticide 82675 13071-79-9 0.018 HAL-US 0.4 —

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 0.045 na na — 2

Terbuthylazine Herbicide 04022 5915-41-3 0.0060, 0.008 na na —

Tribufos Defoliant 61610 78-48-8 0.018 na na — 2

Trifluralin Herbicide 82661 1582-09-8 0.018 HAL-US 10 —

1

 For constituents with two LRLs listed, the first value was in use before October 1, 2011, and the second value was in use starting October 1, 2011. The 

highest LRL is used for this report. 

2

 The median matrix-spike recovery was less than 70 percent. Low recoveries may indicate that the compound might not have been detected in some samples 

if it was present at very low concentrations.

3

 The median matrix-spike recovery was greater than 130 percent. High recoveries may indicate that the reported concentrations were greater than what were 

in the samples.
42 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 3C. Constituent of special interest, primary uses or sources, reporting information, and comparative benchmark for analysis 

performed by Weck Laboratories, Inc.

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

and benchmark level as of July 6, 2012. Benchmark type: Maximum contaminant levels are listed as MCL-US when the MCL-US and MCL-CA are identical, 

and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. MCL-US, USEPA maximum contaminant level; MCL-CA, California 

Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: CAS, Chemical Abstracts Service; MRL, minimum reporting level; 

μg/L, micrograms per liter; D, detected in groundwater samples (table 7)] 

Constituent Primary uses or sources

USGS 

parameter 

code

CAS 

registry 

number®

MRL 

(μg/L)

Benchmark 

type

Benchmark 

level 

(μg/L)

Detection

Perchlorate Rocket fuel, fireworks, flares 63790 14797-73-0 0.10 MCL-CA 6 D

Table 3D. Trace elements, reporting information, and comparative benchmarks for the U.S. Geological Survey (USGS) National Water 

Quality Laboratory Schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels 

as of July 6, 2012. Benchmark type: Maximum contaminant levels 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. Secondary maximum contaminant level benchmarks are listed as SMCL-CA when 

the SMCL-CA exists, and as the SMCL-US when no SMCL-CA exists. AL-US, U.S. Environmental Protection Agency (USEPA) action level; HAL-US, 

USEPA lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum 

contaminant level; NL-CA, CDPH notification level; SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: CAS, Chemical 

Abstracts Service; LT-MDL, long-term method detection level; na, not available; μg/L, micrograms per liter; D, detected in groundwater samples (table 8)]

Constituent USGS parameter 

code

CAS Registry 

Number®

 LT-MDL 

(μg/L) 1

Benchmark 

type

Benchmark level 

(μg/L) Detection

Aluminum 01106 7429-90-5 1.7, 2.2 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.027 MCL-US 6 D

Arsenic 01000 7440-38-2 0.022, 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 NL-CA 1,000 D

Cadmium 01025 7440-43-9 0.016 MCL-US 5 D

Chromium 01030 7440-47-3 0.06, 0.07 MCL-CA 50 D

Cobalt 01035 7440-48-4 0.02, 0.021 na na na 2

Copper 01040 7440-50-8 0.5, 0.8 AL-US 1,300 D

Iron 01046 7439-89-6 3.2 SMCL-CA 300 D

Lead 01049 7439-92-1 0.015, 0.025 AL-US 15 D

Lithium 01130 7439-93-2 0.22 na na D

Manganese 01056 7439-96-5 0.13 SMCL-CA 50 D

Molybdenum 01060 7439-98-7 0.014 HAL-US 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 SMCL-CA 100 D

Strontium 01080 7440-24-6 0.2 HAL-US 4,000 D

Thallium 01057 7440-28-0 0.010 MCL-US 2 D

Tungsten 01155 7440-33-7 0.010 na na D

Uranium 22703 7440-61-1 0.004 MCL-US 30 D

Vanadium 01085 7440-62-2 0.08 NL-CA 50 D

Zinc 01090 7440-66-6 1.4 SMCL-CA 5,000 D

1

 For constituents with two LT-MDLs listed, the first value was in use before October 1, 2011, and the second value was in use starting October 1, 2011. The 

highest LT-MDL is used for this report. 

2

 Evaluation of quality-control data collected from October 2009 through March 2013 for the California Groundwater Ambient Monitoring and Assessment 

(GAMA) Priority Basin Project resulted in censoring all groundwater results for cobalt for the Hard Rock study unit (Davis and others, 2014). All results for 

cobalt were censored from this dataset and coded in the USGS database as “reviewed and rejected.” See appendix table A3 for more information.
Tables 43

Table 3E. Nutrients, reporting information, and comparative benchmarks for the U.S. Geological Survey (USGS) National Water Quality 

Laboratory Schedule 2755.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels 

as of July 6, 2012. Benchmark type: HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-US, USEPA maximum 

contaminant level. Other abbreviations: CAS, Chemical Abstracts Service; LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, 

milligrams per liter; na, not available; D, detected in groundwater samples (table 9)]

Constituent

USGS 

parameter 

code

CAS 

registry 

number®

 LT-MDL 

or MDL 

(mg/L)

Benchmark 

type

Benchmark 

level 

(mg/L)

Detection

Ammonia (as nitrogen) 00608 7664-41-7 0.010 HAL-US 1

 24.7 D

Nitrate plus nitrite (as nitrogen) 00631 na 2

 0.02, 0.04 MCL-US 10 D

Nitrite (as nitrogen) 00613 14797-65-0 0.0010 MCL-US 1 D

Total nitrogen (ammonia, nitrite, nitrate, 

organic nitrogen)

62854 17778-88-0 0.05 na na D

Phosphate, orthophosphate (as phosphorus) 00671 14265-44-2 0.004 na na D

1

 The HAL-US is 30 mg/L “as ammonia.” To facilitate comparson to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L “as 

nitrogen.”

2

 For nitrate plus nitrite, the first value was the MDL in use before October 17, 2011, and the second value was the interim reporting level (IRL) in use starting 

October 17, 2011. 

Table 3F. Major and minor ions, silica, total dissolved solids (TDS), and laboratory alkalinity, reporting information, and comparative 

benchmarks for the U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels 

as of July 6, 2012. Benchmark type: Maximum contaminant levels 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. Secondary maximum contaminant level benchmarks are listed as SMCL-CA when the 

SMCL-CA exists, and as the SMCL-US when no SMCL-CA exists. MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; 

SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: CAS, Chemical Abstracts Service; LT-MDL, long-term method detection 

level; MDL, method detection limit; MRL, minimum reporting level; mg/L, milligrams per liter; na, not available; D, detected in groundwater samples 

(table 10)]

Constituent

USGS 

parameter 

code

CAS 

registry 

number®

 LT-MDL, 

MDL, or MRL 

(mg/L) 1

Benchmark 

type

Benchmark 

level 

(mg/L)

Detection

Bromide 71870 24959-67-9 0.010 na na D

Calcium 00915 7440-70-2 0.022 na na D

Chloride 00940 16887-00-6 0.06 SMCL-CA 2

 250 (500) D

Fluoride 00950 16984-48-8 0.04 MCL-CA 2 D

Iodide 71865 7553-56-2 0.0010, 0.001 na na D

Magnesium 00925 7439-95-4 0.008, 0.011 na na D

Potassium 00935 7440-09-7 0.022, 0.03 na na D

Silica (as SiO2

) 00955 7631-86-9 0.029, 0.018 na na D

Sodium 00930 7440-23-5 0.06 na na D

Sulfate 00945 14808-79-8 0.09 SMCL-CA 2

 250 (500) D

Residue on evaporation (total 

dissolved solids, TDS)

70300 na 12, 20 SMCL-CA 2

 500 (1,000) D

Laboratory alkalinity (as CaCO3

) 29801 na 4.0, 4.6 na na D 3

1

 For constituents with two reporting levels (LT-MDL, MDL, or MRL) listed, the first value was in use before October 1, 2011, and the second value was in 

use starting October 1, 2011. The highest reporting level is used for this report. 

2

 The recommended SMCL-CA benchmarks for chloride, sulfate, and TDS are listed with the upper SMCL-CA benchmarks in parentheses.

3

 Laboratory alkalinity results are presented in table 4.
44 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 3G. Arsenic, chromium, and iron species, reporting information, and comparative benchmarks for the U.S. Geological Survey 

(USGS) Trace Metal Laboratory, Boulder, Colorado, analyses.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Reporting levels, benchmark types, and benchmark levels 

as of July 6, 2012. Benchmark type: maximum contaminant levels 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. Secondary maximum contaminant level benchmarks are listed as SMCL-CA when the 

SMCL-CA exists, and as the SMCL-US when no SMCL-CA exists. MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; 

SMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: CAS, Chemical Abstracts Service; MDL, method detection limit; na, not 

available; μg/L, micrograms per liter; D, detected in groundwater samples (table 11)]

Constituent USGS 

parameter code

CAS registry 

number®

MDL 

(μg/L)

Benchmark 

type

Benchmark level 

(μg/L) Detection

Arsenic (total) 99033 7440-38-2 0.2 MCL-US 10 D

Arsenic (III) 99034 22569-72-8 0.5 na na D

Chromium (total) 01030 7440-47-3 1 MCL-CA 50 D

Chromium (VI) 01032 18540-29-9 1 na na D

Iron (total) 01046 7439-89-6 2 SMCL-CA 300 D

Iron (II) 01047 7439-89-6 2 na na D
Tables 45

Table 3H. Isotopic and radioactive constituents, reporting information, and comparative benchmarks for laboratory analyses.

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Stable isotope ratios are reported in 

the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard reference material. Reporting 

levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant levels are listed as MCL-US when the MCL-US 

and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection 

Agency maximum contaminant level; MCL-CA, California Department of Public Health maximum contaminant level. Other abbreviations: CAS, Chemical 

Abstracts Service; pCi/L, picocuries per liter; H, hydrogen; O, oxygen; B, boron; C, carbon; Sr, strontium; MU, method uncertainty; ssLC, sample-specific 

critical level; CSU, 1-sigma combined standard uncertainty; na, not available; D, detected in groundwater samples (tables 12 and 14A–C)]

Constituent

USGS 

parameter 

code

CAS 

registry 

number®

Reporting 

level 

type

Reporting 

level or 

uncertainty 

Benchmark 

type

Benchmark 

level Detection

Stable isotope ratios (per mil)

δ2

H in water 1 82082 na MU 2 na na D

δ18O in water 1 82085 na MU 0.20 na na D

δ11B of boron dissolved in water 2 62648 na MU na na na na 3

δ13C in dissolved inorganic carbon 4 82081 na MU 0.05 na na D

Isotope ratios (atom ratio)

87Sr/86Sr of strontium dissolved in water 2 75978 na MU 0.00005 na na na 3

Radioactive constituents (percent modern)

Carbon-14 4 49933 14762-75-5 MU CSU na na D

Radioactive constituents (pCi/L)

Radon-222 5 82303 14859-67-7 ssLC CSU Proposed 

MCL-US

4,000 D

Tritium 6 07000 10028-17-8 ssLC CSU MCL-CA 20,000 D

Gross alpha radioactivity, 72-hour and 

30-day counts 7

62636, 62639 12587-46-1 ssLC CSU MCL-US 15 D

Gross beta radioactivity, 72-hour and 

30-day counts 7

62642, 62645 12587-47-2 ssLC CSU MCL-CA 50 D

Uranium-234, -235, and -238 7 22610, 22620, 

22603

na ssLC CSU MCL-CA 8 20 D

1

 USGS Stable Isotope Laboratory, Reston, Virginia (USGSSIVA).

2

 USGS NRP Metals Isotope Research Laboratory, Menlo Park, California (USGSMICA).

3

 Stable isotopes of dissolved boron and strontium in water data will be included in a subsequent report.

4

 Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS), Woods Hole, Massachusetts 

(MA-WHAMS).

5

 USGS National Water Quality Laboratory (USGSNWQL).

6

 USGS Stable Isotope and Tritium Laboratory, Menlo Park, California (USGSH3CA).

7

 Eberline Analytical Services, Richmond, California (CA-EBERL).

8

 The MCL-CA benchmark for uranium is the sum of uranium-234, -235, and -238.
46 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 3I. Dissolved noble gases and tritium, reporting information, and comparative benchmarks for the Lawrence Livermore National 

Laboratory (LLNL) analyses.

[Results for noble gas and tritium analyses by the LLNL are stored in a database maintained by Groundwater Ambient Monitoring and Assessment (GAMA) 

Priority Basin Project project staff. Benchmark types and benchmark values as of July 6, 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: CAS, Chemical Abstracts Service; na, not available; 

cm3 STP/g, cubic centimeters of gas at standard temperature and pressure per gram of water; D, detected in groundwater samples (table 13)]

Constituent

CAS 

registry 

number®

Reporting 

units

Method 

uncertainty 

(percent)

Benchmark 

type

Benchmark 

level Detection

Argon 7440-37-1 cm3

 STP/g 2 na na D

Helium-3/Helium-4 na / 7440-59-7 atom ratio 1

 1.5 na na D

Helium-4 7440-59-7 cm3

 STP/g 2 na na D

Krypton 7439-90-9 cm3

 STP/g 3 na na D

Neon 7440-01-09 cm3

 STP/g 2 na na D

Tritium 10028-17-8 pCi/L 1 MCL-CA 20,000 na 2

Xenon 7440-63-3 cm3 STP/g 1 na na D

1

 Helium-3/Helium-4 results for the Hard Rock study unit had uncertainties ranging from 1 to 9 percent of the reported concentrations (the median was 

1.5 percent).

2

 Results for tritium analyzed at the LLNL were not available at the time of this report.
Table 4. Water-quality indicators in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study 

March 2012, California GAMA Priority Basin Project.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Field alkalinities were mof the Hard Rock sites. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study arePeninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benlevel as of July 6, 2012. Benchmark type: Maximum contamination level benchmarks are listed as SMCL-CA when the SMCL-CA exists, and as the SMCL-US when no SMCLU.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Oth

Celsius; mg/L, milligrams per liter; na, not available; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; HCO3–, bicarbonate; CO32–, ca

benchmark level or outside range; **, value greater than 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, 

laboratory 

(mg/L as 

CaCO3) 

(29801)

Bicarbonate, 

laboratory 

(mg/L as 

HCO3–) 1

Carbonate, 

laboratory 

(mg/L as 

CO32–) 1

Alkalinit

field 

(mg/L as 

CaCO3) 

(29802)

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 2 900 (1,600) 2 900 (1,600) na na na na 

[Reporting level 

or range]

[0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [4.6] [1] [0.1] [1] 

Santa Cruz study area (25 wells sampled)HR-SC-01 5.2 18.5 8.1 8.1 289 282 69.5 83.6 0.5 na 

HR-SC-02 7.5 14.0 6.9 7.1 394 429 95 116 — na 

HR-SC-03 0.2 15.0 7.2 7.2 704 695 204 248 0.2 209 

HR-SC-04 1.3 13.5 6.9 7.2 889 872 227 277 0.2 na 

HR-SC-05 — 14.0 7.1 7.4 264 263 112 137 0.2 na 

HR-SC-06 5.5 14.0 6.5 6.9 411 412 176 214 — na 

HR-SC-07 — 19.5 7.1 7.3 ** 1,690 ** 1,700 322 392 0.4 na 

HR-SC-08 0.6 16.0 6.5 6.8 412 419 166 203 — na 

HR-SC-09 — 19.5 8.2 8.5 * 1,060 * 991 521 617 9.0 453 

HR-SC-10 1.0 13.0 6.5 7.0 291 291 132 161 — na 

HR-SC-11 6.0 15.5 6.9 7.2 710 717 324 394 0.3 na 

HR-SC-12 0.2 17.5 7.2 7.4 868 873 457 556 0.7 na 

HR-SC-13 8.2 14.5 6.9 7.4 264 269 120 146 0.2 na 

HR-SC-14 0.3 14.5 * 6.1 6.5 527 540 160 196 — na 

HR-SC-15 — 17.0 * 8.6 * 8.8 504 510 220 253 7.0 na 
Table 4. Water-quality indicators in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study uMarch 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Field alkalinities were meof the Hard Rock sites. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area uPeninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benclevel as of July 6, 2012. Benchmark type: Maximum contamination level benchmarks are listed as SMCL-CA when the SMCL-CA exists, and as the SMCL-US when no SMCL-CU.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other 

Celsius; mg/L, milligrams per liter; na, not available; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; HCO3–, bicarbonate; CO32–, carb

benchmark level or outside range; **, value greater than 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, laboratory (mg/L as CaCO3) (29801) Bicarbonate, laboratory (mg/L as HCO3–) 1 Carbonate, laboratory (mg/L as CO32–) 1 Alkalinity, field (mg/L as CaCO3) (29802) 

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 2 900 (1,600) 2 900 (1,600) na na na na 

[Reporting level or range] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [4.6] [1] [0.1] [1] 

Santa Cruz study area (25 wells sampled)—Continued HR-SC-16 2.2 13.0 7.7 8.1 252 250 119 143 0.8 na 

HR-SC-17 5.9 16.0 * 5.7 * 3 6.1 89 3 87 25.8 31.5 — 22.2 

HR-SC-18 0.6 18.0 7.0 7.4 195 192 54.7 66.5 — na 

HR-SC-19 — 17.0 7.3 7.6 782 790 334 406 0.7 na 

HR-SC-20 5.8 16.0 6.7 7.0 * 1,480 * 1,530 319 388 0.2 na 

HR-SC-21 0.2 19.0 7.2 7.4 * 1,120 * 1,170 265 323 0.4 na 

HR-SC-22 — 15.0 6.6 6.9 839 862 369 450 0.2 364 

HR-SC-23 0.2 18.0 7.1 7.4 792 791 349 425 0.4 na 

HR-SC-24 0.8 17.5 7.0 7.4 * 1,470 * 1,480 544 662 0.7 na 

HR-SC-25 9.8 15.0 * 6.4 6.8 134 135 41.7 50.8 — na 

San Gabriel study area (37 wells sampled) HR-SG-01 3.4 14.0 7.4 7.6 739 736 256 311 0.5 na 

HR-SG-02 1.4 15.0 7.2 7.5 654 664 273 332 0.5 na 

HR-SG-03 1.5 14.5 7.3 7.6 630 622 265 322 0.6 na 

HR-SG-04 6.2 20.0 7.2 7.5 * 1,080 * 1,050 330 401 0.6 na 

HR-SG-05 6.9 16.0 7.3 7.5 663 660 291 354 0.5 na 
Table 4. Water-quality indicators in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study uMarch 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Field alkalinities were meof the Hard Rock sites. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area uPeninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benclevel as of July 6, 2012. Benchmark type: Maximum contamination level benchmarks are listed as SMCL-CA when the SMCL-CA exists, and as the SMCL-US when no SMCL-CU.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other 

Celsius; mg/L, milligrams per liter; na, not available; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; HCO3–, bicarbonate; CO32–, carb

benchmark level or outside range; **, value greater than 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, 

laboratory 

(mg/L as 

CaCO3) 

(29801)

Bicarbonate, 

laboratory 

(mg/L as 

HCO3–) 1

Carbonate, 

laboratory 

(mg/L as 

CO32–) 1

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

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 2 900 (1,600) 2 900 (1,600) na na na na 

[Reporting level 

or range]

[0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [4.6] [1] [0.1] [1] 

San Gabriel study area (37 wells sampled)—ContinuedHR-SG-06 6.2 17.0 7.3 7.6 338 332 140 170 0.3 na 

HR-SG-07 0.2 15.5 7.6 7.8 349 344 165 200 0.6 na 

HR-SG-08 — 16.0 7.4 7.5 830 822 333 405 0.6 na 

HR-SG-09 0.5 22.5 * 8.9 * 8.9 * 1,220 * 1,210 281 318 11.6 251 

HR-SG-10 7.3 17.0 6.9 7.2 625 625 243 296 0.2 na 

HR-SG-11 6.5 20.0 * 8.8 * 8.8 337 338 126 145 4.2 na 

HR-SG-12 5.1 10.0 6.7 7.4 349 358 190 231 0.3 na 

HR-SG-13 2.8 11.0 6.9 7.3 546 547 258 314 0.3 265 

HR-SG-14 0.4 12.0 6.7 7.2 615 633 258 314 0.2 na 

HR-SG-15 3.2 19.0 6.8 7.1 303 289 142 173 0.1 na 

HR-SG-16 1.9 18.5 7.3 7.5 418 420 181 220 0.3 na 

HR-SG-17 2.3 10.5 6.7 7.4 305 313 168 204 0.2 na 

HR-SG-18 0.8 14.5 7.0 7.4 540 539 252 307 0.4 na 

HR-SG-19 2.1 13.0 7.0 7.3 559 559 259 315 0.3 na 

HR-SG-20 2.8 17.0 7.3 7.3 686 702 304 370 0.3 301 
Table 4. Water-quality indicators in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study uMarch 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Field alkalinities were mof the Hard Rock sites. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benlevel as of July 6, 2012. Benchmark type: Maximum contamination level benchmarks are listed as SMCL-CA when the SMCL-CA exists, and as the SMCL-US when no SMCL-U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Othe

Celsius; mg/L, milligrams per liter; na, not available; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; HCO3–, bicarbonate; CO32–, ca

benchmark level or outside range; **, value greater than 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, laboratory (mg/L as CaCO3) (29801) Bicarbonate, laboratory (mg/L as HCO3–) 1 Carbonate, laboratory (mg/L as CO32–) 1 Alkalinity

field (mg/L as CaCO3) (29802) 

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 2 900 (1,600) 2 900 (1,600) na na na na 

[Reporting level or range] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [4.6] [1] [0.1] [1] 

San Gabriel study area (37 wells sampled)—Continued HR-SG-21 6.4 11.5 6.8 7.2 454 464 240 292 0.2 na 

HR-SG-22 0.2 16.0 7.4 7.8 546 555 218 264 0.8 na 

HR-SG-23 6.9 11.5 7.0 7.5 268 273 132 160 0.2 na 

HR-SG-24 5.4 19.0 6.9 7.4 458 459 165 201 0.2 na 

HR-SG-25 6.5 16.5 * 6.4 7.3 248 249 110 134 0.1 na 

HR-SG-26 3.5 15.5 7.2 7.7 378 374 178 216 0.5 na 

HR-SG-27 5.9 15.0 7.0 7.3 232 245 124 151 0.1 118 

HR-SG-28 7.7 15.0 6.6 7.1 300 305 141 172 0.1 na 

HR-SG-29 0.8 11.5 7.1 7.5 444 455 213 259 0.4 na 

HR-SG-30 9.4 12.0 7.2 7.6 372 388 199 242 0.4 na 

HR-SG-31 0.6 15.5 * 6.3 7.1 654 665 257 313 0.2 249 

HR-SG-32 — 16.0 * 6.2 4 8.4 207 186 82.2 98 1.1 na 

HR-SG-33 6.2 19.0 7.4 7.5 858 872 213 259 0.4 na 

HR-SGU-01 1.6 22.0 7.4 7.7 844 866 361 438 1.0 na 

HR-SGU-02 5 16.3 15.5 7.6 7.8 192 198 96.9 117 0.3 na 

HR-SGU-03 8.9 13.0 7.4 8.2 248 254 96.1 115 0.8 na 

HR-SGU-04 6.3 14.5 6.6 7.4 394 401 168 204 0.2 na 
Table 4. Water-quality indicators in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study uMarch 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Field alkalinities were mof the Hard Rock sites. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benlevel as of July 6, 2012. Benchmark type: Maximum contamination level benchmarks are listed as SMCL-CA when the SMCL-CA exists, and as the SMCL-US when no SMCL-U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Othe

Celsius; mg/L, milligrams per liter; na, not available; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; HCO3–, bicarbonate; CO32–, ca

benchmark level or outside range; **, value greater than 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, 

laboratory 

(mg/L as 

CaCO3) 

(29801)

Bicarbonate, 

laboratory 

(mg/L as 

HCO3–) 1

Carbonate, 

laboratory 

(mg/L as 

CO32–) 1

Alkalinity

field 

(mg/L as 

CaCO3) 

(29802)

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 2 900 (1,600) 2 900 (1,600) na na na na 

[Reporting level 

or range]

[0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [4.6] [1] [0.1] [1] 

Peninsular Ranges study area (50 wells sampled)HR-PR-01 0.4 17.5 6.7 7.0 840 860 276 336 0.2 na 

HR-PR-02 5.2 17.5 7.0 7.2 560 559 158 192 0.2 na 

HR-PR-03 — 13.5 7.1 7.4 206 211 84.8 103 0.1 na 

HR-PR-04 — 18.0 6.7 7.1 327 337 129 157 — na 

HR-PR-05 1.7 16.5 7.5 7.9 232 235 96.4 117 0.4 92.2 

HR-PR-06 — 20.5 7.3 7.7 888 888 231 281 0.7 na 

HR-PR-07 0.7 20.0 6.8 7.2 ** 2,360 ** 2,310 323 393 0.3 na 

HR-PR-08 1.3 22.0 7.6 7.9 409 409 125 151 0.5 na 

HR-PR-09 0.5 13.0 7.1 7.4 347 354 139 169 0.2 139 

HR-PR-10 7.4 15.0 * 5.8 * 6.3 726 764 85.8 105 — na 

HR-PR-11 0.4 24.0 7.1 7.5 724 700 136 165 0.2 na 

HR-PR-12 3.1 19.5 6.6 7.2 * 901 * 906 118 144 — na 

HR-PR-13 0.3 19.0 6.8 7.3 * 1,450 * 1,450 311 379 0.4 na 

HR-PR-14 3.5 20.5 6.6 7.2 647 650 177 216 0.1 177 

HR-PR-15 3.4 11.0 * 6.2 6.7 201 206 78.5 95.7 — na 
Table 4. Water-quality indicators in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study uMarch 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Field alkalinities were mof the Hard Rock sites. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benclevel as of July 6, 2012. Benchmark type: Maximum contamination level benchmarks are listed as SMCL-CA when the SMCL-CA exists, and as the SMCL-US when no SMCL-U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Othe

Celsius; mg/L, milligrams per liter; na, not available; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; HCO3–, bicarbonate; CO32–, car

benchmark level or outside range; **, value greater than 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, laboratory (mg/L as CaCO3) (29801) Bicarbonate, laboratory (mg/L as HCO3–) 1 Carbonate, laboratory (mg/L as CO32–) 1 Alkalinity

field (mg/L as CaCO3) (29802) 

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 2 900 (1,600) 2 900 (1,600) na na na na 

[Reporting level or range] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [4.6] [1] [0.1] [1] 

Peninsular Ranges study area (50 wells sampled)—Continued HR-PR-16 0.4 22.5 6.9 7.2 * 1,260 * 1,240 186 226 0.2 185 

HR-PR-17 3.5 18.5 7.0 7.2 597 595 193 235 0.2 na 

HR-PR-18 0.3 22.0 6.8 7.1 * 918 * 926 346 421 0.2 na 

HR-PR-19 0.8 16.5 * 6.0 6.8 422 458 164 199 — na 

HR-PR-20 5.1 19.0 6.8 7.0 526 539 150 182 — na 

HR-PR-21 0.6 22.0 6.9 7.2 * 1,090 * 1,160 215 261 0.2 na 

HR-PR-22 0.5 18.0 7.1 7.3 832 882 267 325 0.3 na 

HR-PR-23 0.4 20.0 7.0 7.2 525 533 177 215 0.2 na 

HR-PR-24 3.4 21.5 * 6.4 6.6 * 1,190 * 1,210 132 161 — na 

HR-PR-25 6.5 21.0 7.3 7.5 * 967 * 988 289 351 0.6 278 

HR-PR-26 0.4 18.0 6.7 7.0 ** 2,760 ** 2,800 320 390 0.2 na 

HR-PR-27 5.6 15.0 6.9 7.3 211 215 81.6 99.3 — na 

HR-PR-28 0.7 21.0 7.5 7.3 * 1,220 * 1,220 192 233 0.2 na 

HR-PR-29 — 25.5 * 9.5 * 9.2 303 311 58.3 61.8 4.1 56.2 

HR-PR-30 3.1 15.0 6.5 6.9 299 304 123 150 — na 
Table 4. Water-quality indicators in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study uMarch 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Field alkalinities were mof the Hard Rock sites. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benclevel as of July 6, 2012. Benchmark type: Maximum contamination level benchmarks are listed as SMCL-CA when the SMCL-CA exists, and as the SMCL-US when no SMCL-U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Othe

Celsius; mg/L, milligrams per liter; na, not available; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; HCO3–, bicarbonate; CO32–, car

benchmark level or outside range; **, value greater than 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, 

laboratory 

(mg/L as 

CaCO3) 

(29801)

Bicarbonate, 

laboratory 

(mg/L as 

HCO3–) 1

Carbonate, 

laboratory 

(mg/L as 

CO32–) 1

Alkalinity

field 

(mg/L as 

CaCO3) 

(29802)

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 2 900 (1,600) 2 900 (1,600) na na na na 

[Reporting level 

or range]

[0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [4.6] [1] [0.1] [1] 

Peninsular Ranges study area (50 wells sampled)—ContinuedHR-PR-31 3.6 13.0 6.6 7.0 167 170 68 82.8 — na 

HR-PR-32 0.7 19.0 7.3 7.5 * 1,120 * 1,160 256 312 0.5 na 

HR-PR-33 3.5 17.5 6.7 6.9 645 682 179 218 — na 

HR-PR-34 4.6 17.0 7.4 7.6 762 775 275 334 0.6 na 

HR-PR-35 2.8 17.0 7.4 7.7 297 308 130 158 0.3 na 

HR-PR-36 1.3 11.0 6.9 7.2 218 224 110 134 — na 

HR-PRFP-01 0.6 17.5 7.3 7.4 539 552 140 170 0.2 na 

HR-PRFP-02 4.2 24.0 7.1 7.2 * 1,370 * 1,390 193 235 0.2 na 

HR-PRFP-03 0.3 19.0 7.1 7.3 794 802 164 200 0.2 160 

HR-PRFP-04 3.2 23.0 6.9 7.1 835 836 137 167 — na 

HR-PRFP-05 0.8 22.5 7.1 7.2 * 1,310 * 1,350 296 361 0.3 na 

HR-PRFP-06 1.0 22.5 7.3 7.4 864 888 216 263 0.3 na 

HR-PRFP-07 0.3 17.0 7.5 7.7 441 445 108 131 0.3 na 

HR-PRFP-08 0.2 18.0 * 9.1 * 8.9 211 206 55.5 62.0 2.5 na 

HR-PRFP-09 2.1 23.0 7.0 7.3 ** 2,020 ** 1,940 322 393 0.3 na 
Table 4. Water-quality indicators in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study uMarch 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Field alkalinities were meof the Hard Rock sites. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benclevel as of July 6, 2012. Benchmark type: Maximum contamination level benchmarks are listed as SMCL-CA when the SMCL-CA exists, and as the SMCL-US when no SMCL-U.S. Environmental Protection Agency secondary maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Othe

Celsius; mg/L, milligrams per liter; na, not available; μS/cm, microsiemens per centimeter; <, less than; >, greater than; CaCO3, calcium carbonate; HCO3–, bicarbonate; CO32–, car

benchmark level or outside range; **, value greater than 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, laboratory (mg/L as CaCO3) (29801) Bicarbonate, laboratory (mg/L as HCO3–) 1 Carbonate, laboratory (mg/L as CO32–) 1 Alkalinity, field (mg/L as CaCO3) (29802) 

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 2 900 (1,600) 2 900 (1,600) na na na na 

[Reporting level or range] [0.2] [0.0–38.5] [0–14] [0–14] [5] [5] [4.6] [1] [0.1] [1] 

Peninsular Ranges study area (50 wells sampled)—Continued HR-PRFP-10 0.5 17.5 6.7 7.1 484 488 138 168 0.1 136 

HR-PRFP-11 4.4 22.0 6.9 7.0 ** 4,400 ** 4,750 281 342 0.2 na 

HR-PRFP-12 6.6 22.0 7.1 7.3 * 1,570 * 1,580 250 304 0.3 na 

HR-PRFP-13 0.7 16.5 6.5 6.8 ** 3,480 ** 3,530 240 292 — na 

HR-PRU-01 1.2 12.0 6.9 7.3 232 238 102 124 0.1 na 

1 Laboratory carbonate and bicarbonate results were calculated from laboratory alkalinity and pH, according to the advanced speciation method. Results are stored in a separate d

GAMA Program. 2 The SMCL-CA for specific conductance has recommended and upper benchmark values. The upper value is shown in parentheses. 3 Values estimated by laboratory: high variability exists for pH when specific conductance is <100 μS/cm at 25 °C. 4 High laboratory pH compared to field value. Field pH is considered more representative of aquifer conditions; laboratory pH can be affected by reactions that occur in the samp

collection and analysis, which was 60 days for this sample. 5 Sample was collected from a spring and was highly oxic, likely indicating exposure to the atmosphere prior to sampling.
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquife

March 2011 through March 2012, California GAMA Priority Basin Project.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3A. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San GabriHR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public HealNL-CA, CDPH notification level. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, micrograms per liter; na, n

GAMA 

well 

identification 

number

Disinfection byproducts Solvents

Chloroform 

(trichloromethane) 

(μg/L) 

(32106)

Bromodichloromethane 

(μg/L) 

(32101)

Dibromochloromethane 

(μg/L) 

(32105)

Bromoform 

(tribromomethane) 

(μg/L) 

(32104)

Tetrachloroethene 

(μg/L) 

(34475)

Trichloroethene 

(μg/L) 

(39180)

1,1,1-Trichloroethane 

(μg/L) 

(34506)

1,2,4-Trichlorobenzene 

(μg/L) 

(34551)

1,3-Dichlorobenzene 

(μg/L) 

(34566)

1,4-Dichlorobenzene 

(μg/L) 

(34571)

Ca

Benchmark type MCL-US MCL-US MCL-US MCL-US MCL-US MCL-US MCL-US MCL-CA HAL-US MCL-CA Benchmark level 2 80 2 80 2 80 2 80 5 5 200 5 600 5 

[LRL] [0.03] [0.034] [0.12] [0.1] [0.026] [0.022] [0.030] [0.08] [0.024] [0.026] 

Hard Rock study unit (94 grid wells sampled)Number of wells with 

detections

28 4 3 2 7 3 2 1 1 1 

Detection frequency (percent) 30 4.3 3.2 2.1 7.4 3.2 2.1 1.1 1.1 1.1 

Santa Cruz study area (25 grid wells sampled)HR-SC-02 0.02 — — — — — — — — — 

HR-SC-04 0.02 — — — — — — — — — 

HR-SC-08 0.72 — — — — — — — — — 

HR-SC-11 — — — — — — 0.018 — — — 

HR-SC-13 — — — — — — — — — — 

HR-SC-14 0.02 — — — — — — — — — 

HR-SC-16 4 20.4 6.59 2.00 0.22 — — — — — — 

HR-SC-17 0.12 — — — — — — — — — 

HR-SC-20 0.43 0.043 — — — — — — — — 

HR-SC-21 — — — — — — — — — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquifeMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3A. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San GabriHR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public HealNL-CA, CDPH notification level. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, micrograms per liter; na, n

GAMA well identification number Disinfection byproducts Solvents Chloroform (trichloro- methane) (μg/L) (32106) Bromo- dichloro- methane (μg/L) (32101) Dibromo- chloro- methane (μg/L) (32105) Bromoform (tribromo- methane) (μg/L) (32104) Tetra- chloro- ethene (μg/L) (34475) Trichloro- ethene (μg/L) (39180) 1,1,1-Tri- chloro- ethane (μg/L) (34506) 1,2,4-Tri- chloro- benzene (μg/L) (34551) 1,3-Di- chloro- benzene (μg/L) (34566) 1,4-Di- chloro- benzene (μg/L) (34571) Ca

Benchmark type MCL-US MCL-US MCL-US MCL-US MCL-US MCL-US MCL-US MCL-CA HAL-US MCL-CA Benchmark level 2 80 2 80 2 80 2 80 5 5 200 5 600 5 

[LRL] [0.03] [0.034] [0.12] [0.1] [0.026] [0.022] [0.030] [0.08] [0.024] [0.026] 

Santa Cruz study area (25 grid wells sampled)—Continued HR-SC-22 — — — — — — — — — — 

HR-SC-23 — — — — — — — — — — 

HR-SC-24 0.02 — — — — — — — — — 

HR-SC-25 0.10 — — — 0.014 0.084 0.043 — — — 

Number of wells with detections 9 2 1 1 1 1 2 0 0 0 

Detection frequency (percent) 36 8.0 4.0 4.0 4.0 4.0 8.0 0 0 0 

San Gabriel study area (33 grid wells sampled) HR-SG-02 0.08 — — — — — — — — — 

HR-SG-04 — — — — 0.019 0.040 — — — — 

HR-SG-05 — — — — 0.027 — — — — — 

HR-SG-08 0.04 0.035 0.06 — — — — — — — 

HR-SG-15 0.03 0.039 0.08 0.06 — — — — — — 

HR-SG-27 0.02 — — — 0.024 0.428 — 0.17 0.078 0.016 

HR-SG-28 0.20 — — — — — — — — — 

HR-SG-31 0.08 — — — — — — — — — 

HR-SG-33 0.32 — — — — — — — — — 

Number of wells with 

detections

7 2 2 1 3 2 0 1 1 1 

Detection frequency (percent) 21 6.1 6.1 3.0 9.1 6.1 0 3.0 3.0 3.0 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquifeMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3A. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San GabriHR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public HealNL-CA, CDPH notification level. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, micrograms per liter; na, n

GAMA 

well 

identification 

number

Disinfection byproducts Solvents

Chloroform 

(trichloromethane) 

(μg/L) 

(32106)

Bromodichloromethane 

(μg/L) 

(32101)

Dibromochloromethane 

(μg/L) 

(32105)

Bromoform 

(tribromomethane) 

(μg/L) 

(32104)

Tetrachloroethene 

(μg/L) 

(34475)

Trichloroethene 

(μg/L) 

(39180)

1,1,1-Trichloroethane 

(μg/L) 

(34506)

1,2,4-Trichlorobenzene 

(μg/L) 

(34551)

1,3-Dichlorobenzene 

(μg/L) 

(34566)

1,4-Dichlorobenzene 

(μg/L) 

(34571)

Ca

Benchmark type MCL-US MCL-US MCL-US MCL-US MCL-US MCL-US MCL-US MCL-CA HAL-US MCL-CA Benchmark level 2 80 2 80 2 80 2 80 5 5 200 5 600 5 

[LRL] [0.03] [0.034] [0.12] [0.1] [0.026] [0.022] [0.030] [0.08] [0.024] [0.026] 

Peninsular Ranges study area (36 grid wells sampled)HR-PR-01 0.08 — — — — — — — — — 

HR-PR-02 0.03 — — — 5 0.012 — — — — — 

HR-PR-07 0.02 — — — — — — — — — 

HR-PR-08 — — — — 0.058 — — — — — 

HR-PR-12 1.4 — — — — — — — — — 

HR-PR-13 0.06 — — — — — — — — — 

HR-PR-15 0.11 — — — — — — — — — 

HR-PR-17 0.12 — — — 5 0.012 — — — — — 

HR-PR-18 — — — — — — — — — — 

HR-PR-20 0.14 — — — — — — — — — 

HR-PR-22 — — — — — — — — — — 

HR-PR-24 — — — — — — — — — — 

HR-PR-25 — — — — — — — — — — 

HR-PR-28 — — — — — — — — — — 

HR-PR-30 0.12 — — — — — — — — — 

HR-PR-31 0.10 — — — — — — — — — 

HR-PR-33 0.02 — — — — — — — — — 

HR-PR-35 1.4 — — — — — — — — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquifeMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3A. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San GabriHR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public HealNL-CA, CDPH notification level. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, micrograms per liter; na, n

GAMA well identification number Disinfection byproducts Solvents Chloroform (trichloro- methane) (μg/L) (32106) Bromo- dichloro- methane (μg/L) (32101) Dibromo- chloro- methane (μg/L) (32105) Bromoform (tribromo- methane) (μg/L) (32104) Tetra- chloro- ethene (μg/L) (34475) Trichloro- ethene (μg/L) (39180) 1,1,1-Tri- chloro- ethane (μg/L) (34506) 1,2,4-Tri- chloro- benzene (μg/L) (34551) 1,3-Di- chloro- benzene (μg/L) (34566) 1,4-Di- chloro- benzene (μg/L) (34571) Ca

Benchmark type MCL-US MCL-US MCL-US MCL-US MCL-US MCL-US MCL-US MCL-CA HAL-US MCL-CA Benchmark level 2 80 2 80 2 80 2 80 5 5 200 5 600 5 

[LRL] [0.03] [0.034] [0.12] [0.1] [0.026] [0.022] [0.030] [0.08] [0.024] [0.026] 

Peninsular Ranges study area (36 grid wells sampled)—Continued Number of wells with detections 12 0 0 0 3 0 0 0 0 0 

Detection frequency (percent) 33 0 0 0 8.3 0 0 0 0 0 

Hard Rock understanding wells (16 wells sampled) 6 HR-PRFP-02 1.1 0.173 — — — — — — — — 

HR-PRFP-08 — — — — — — — — — — 

HR-PRFP-09 0.06 — — — — — — — — — 

HR-PRFP-11 0.10 — — — 0.022 — — — — — 

HR-PRFP-12 — — — — 5 0.011 — — — — — 

HR-PRFP-13 — — — — — — — — — — 

HR-PRU-01 0.02 — — — — — — — — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquifeMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3A. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San GabriHR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public HealNL-CA, CDPH notification level. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, micrograms per liter; na, n

GAMA well 

identification 

number

Organic synthesis Gasoline oxygenate

Organic 

synthesis or 

natural

Refrigerants Fire retarda

1,1-Dichloroethene 

(μg/L) 

(34501)

1,2,3-Trichlorobenzene 

(μg/L) 

(77613)

Methyl tert-butyl ether 

(MTBE) 

(μg/L) 

(78032)

Carbon 

disulfide 

(μg/L) 

(77041)

Trichlorotrifluoroethane 

(CFC-113) 

(μg/L) 

(77652)

Trichlorofluoromethane 

(CFC-11) 

(μg/L) 

(34488)

Bromochlo

methane 

(μg/L) 

(77297)

Benchmark type

MCL-CA na MCL-CA NL-CA MCL-CA MCL-CA HAL-US

Benchmark level

6 na 13 160 1,200 150 90

[LRL] [0.022] [0.06] [0.1] 3 [0.1] [0.034] [0.06] [0.06]

Hard Rock study unit (94 grid wells sampled)Number of 

wells with detections

7 1 7 2 2 1 1 

Detection 

frequency (percent)

7.4 1.1 7.4 2.1 2.1 1.1 1.1 

Santa Cruz study area (25 grid wells sampled)HR-SC-02 — — — — — — — HR-SC-04 0.031 — — — — — — HR-SC-08 — — — — — — — HR-SC-11 — — — — — — — HR-SC-13 0.034 — — — — — — HR-SC-14 — — — — — — — HR-SC-16 4 — — — — — — 5 0.02 HR-SC-17 — — 0.05 — — — — HR-SC-20 5 0.010 — — — — — — HR-SC-21 0.030 — — — — — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquifeMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3A. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San GabriHR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public HealNL-CA, CDPH notification level. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, micrograms per liter; na, n

GAMA well 

identification 

number

Organic synthesis Gasoline oxygenate

Organic 

synthesis or 

natural

Refrigerants Fire retarda

1,1-Dichloroethene 

(μg/L) 

(34501)

1,2,3-Trichlorobenzene 

(μg/L) 

(77613)

Methyl tert-butyl ether 

(MTBE) 

(μg/L) 

(78032)

Carbon 

disulfide 

(μg/L) 

(77041)

Trichlorotrifluoroethane 

(CFC-113) 

(μg/L) 

(77652)

Trichlorofluoromethane 

(CFC-11) 

(μg/L) 

(34488)

Bromochlo

methane 

(μg/L) 

(77297)

Benchmark type

MCL-CA na MCL-CA NL-CA MCL-CA MCL-CA HAL-US

Benchmark level

6 na 13 160 1,200 150 90

[LRL] [0.022] [0.06] [0.1] 3 [0.1] [0.034] [0.06] [0.06]

Santa Cruz study area (25 grid wells sampled)—ContinuedHR-SC-22 0.019 — — — — — — 

HR-SC-23 0.019 — — — — — — HR-SC-24 — — — — 0.021 — — HR-SC-25 — — 0.06 — — — — Number of 

wells with detections

6 0 2 0 1 0 1 

Detection 

frequency (percent)

24 0 8.0 0 4.0 0 4.0 

San Gabriel study area (33 grid wells sampled)HR-SG-02 — — — — — — — HR-SG-04 0.035 — — — 0.1 0.06 — HR-SG-05 — — — — — — — HR-SG-08 — — — — — — — HR-SG-15 — — — — — — — HR-SG-27 — 1.24 — — — — — HR-SG-28 — — — — — — — HR-SG-31 — — — — — — — HR-SG-33 — — — — — — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquifeMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3A. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San GabriHR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public HealNL-CA, CDPH notification level. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, micrograms per liter; na, n

GAMA well 

identification 

number

Organic synthesis Gasoline oxygenate

Organic 

synthesis or 

natural

Refrigerants Fire retarda

1,1-Dichloroethene 

(μg/L) 

(34501)

1,2,3-Trichlorobenzene 

(μg/L) 

(77613)

Methyl tert-butyl ether 

(MTBE) 

(μg/L) 

(78032)

Carbon 

disulfide 

(μg/L) 

(77041)

Trichlorotrifluoroethane 

(CFC-113) 

(μg/L) 

(77652)

Trichlorofluoromethane 

(CFC-11) 

(μg/L) 

(34488)

Bromochlo

methane 

(μg/L) 

(77297)

Benchmark type

MCL-CA na MCL-CA NL-CA MCL-CA MCL-CA HAL-US

Benchmark level

6 na 13 160 1,200 150 90

[LRL] [0.022] [0.06] [0.1] 3 [0.1] [0.034] [0.06] [0.06]

San Gabriel study area (33 grid wells sampled)—ContinuedNumber of 

wells with detections

1 1 0 0 1 1 

Detection 

frequency (percent)

3.0 3.0 0 0 3.0 3.0 

Peninsular Ranges study area (36 grid wells sampled)HR-PR-01 — — — — — — — HR-PR-02 — — — — — — — HR-PR-07 — — — — — — — HR-PR-08 — — — — — — — HR-PR-12 — — — — — — — HR-PR-13 — — — — — — — HR-PR-15 — — — — — — — HR-PR-17 — — — — — — — HR-PR-18 — — 0.07 — — — — HR-PR-20 — — — — — — — 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquifeMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3A. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San GabriHR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public HealNL-CA, CDPH notification level. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, micrograms per liter; na, n

GAMA well identification number Organic synthesis Gasoline oxygenate Organic synthesis or natural Refrigerants Fire retarda

1,1-Dichloro- ethene (μg/L) (34501) 1,2,3-Trichloro- benzene (μg/L) (77613) Methyl tert-butyl ether (MTBE) (μg/L) (78032) Carbon disulfide (μg/L) (77041) Trichlorotrifluoroethane (CFC-113) (μg/L) (77652) Trichlorofluoromethane (CFC-11) (μg/L) (34488) Bromochlo

methane (μg/L) (77297) Benchmark type MCL-CA na MCL-CA NL-CA MCL-CA MCL-CA HAL-US Benchmark level 6 na 13 160 1,200 150 90 [LRL] [0.022] [0.06] [0.1] 3 [0.1] [0.034] [0.06] [0.06] Peninsular Ranges study area (36 grid wells sampled)—Continued HR-PR-22 — — 5 0.02 E0.05 — — — 

HR-PR-24 — — 0.14 — — — — HR-PR-25 — — 5 0.03 — — — — HR-PR-28 — — 0.53 E0.13 — — — HR-PR-30 — — — — — — — HR-PR-31 — — — — — — — HR-PR-33 — — — — — — — HR-PR-35 — — — — — — — Number of wells with detections 0 0 5 2 0 0 Detection frequency (percent) 0 0 14 5.6 0 0 
Table 5. Volatile organic compounds (VOCs) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquifeMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3A. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San GabriHR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California Department of Public HealNL-CA, CDPH notification level. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; μg/L, micrograms per liter; na, n

GAMA well 

identification 

number

Organic synthesis Gasoline oxygenate

Organic 

synthesis or 

natural

Refrigerants Fire retarda

1,1-Dichloroethene 

(μg/L) 

(34501)

1,2,3-Trichlorobenzene 

(μg/L) 

(77613)

Methyl tert-butyl ether 

(MTBE) 

(μg/L) 

(78032)

Carbon 

disulfide 

(μg/L) 

(77041)

Trichlorotrifluoroethane 

(CFC-113) 

(μg/L) 

(77652)

Trichlorofluoromethane 

(CFC-11) 

(μg/L) 

(34488)

Bromochlo

methane 

(μg/L) 

(77297)

Benchmark type

MCL-CA na MCL-CA NL-CA MCL-CA MCL-CA HAL-US

Benchmark level

6 na 13 160 1,200 150 90

[LRL] [0.022] [0.06] [0.1] 3 [0.1] [0.034] [0.06] [0.06]

Hard Rock understanding wells (16 wells sampled) 6

HR-PRFP-02 — — — — — — — HR-PRFP-08 — — — E0.08 — — — HR-PRFP-09 — — 0.07 — — — — HR-PRFP-11 — — — — — — — HR-PRFP-12 — — — — — — — HR-PRFP-13 — — — — — 0.04 — HR-PRU-01 — — — — — — — 

1 Study reporting levels (SRLs) determined on the basis of the quality-control data collected between May 2004 and September 2010 for the first 32 study units of the Californ

(Fram and others, 2012) were applied to three VOCs. Detections of 1,2,4-trimethylbenzene, carbon disulfide, and toluene at concentrations less than the respective SRL were recreported with the following comment in the USGS National Water Information System (NWIS) database: Result is < or = reported value, based on quality-control data (see Fram not be determined for three other VOCs, and instead all detections for acetone, 2-butanone, and tetrahydrofuran were censored from this dataset and coded in the USGS database appendix table A3 for more information.

2 The MCL-US benchmark for trihalomethanes is the sum of chloroform, bromodichloromethane, dibromochloromethane, and bromoform.3 The highest LRL for carbon disulfide during March 2011 through March 2012 was greater than the established SRL of 0.03 μg/L and therefore is used in this table. 4 The HR-SC-16 groundwater well pumps to a nearby storage tank that is sometimes chlorinated.5 Result is below long-term method detection level.6 Understanding wells were not included in statistical calculations. Due to high concentrations of known contaminants 2-butanone, acetone, and tetrahydrofuran (31.0, 19.8, an

sample HR-PRFP-04, all VOC results for that sample were coded as “reviewed and rejected” and omitted from this dataset; the coding caused one chloroform detection at a conomitted from this report. For HR-SGU-01, all results for organic constituents were coded as “reviewed and rejected” and omitted from this dataset due to suspected chlorination 
Table 6. Pesticides and pesticide degradates detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aqui

March 2011 through March 2012, California GAMA Priority Basin Project. [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 wel

samples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3B. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabri

HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-CA; California Department of Public Health maximum contaminant level. Other abbreviations: E, estimated or having a 

LRL, laboratory reporting level; μg/L, micrograms per liter; na, not available; —, not detected] GAMA well identification number Herbicide degradate Herbicide Insecticide degradates 

Deethyl- atrazine (μg/L) (04040) 3,4-Dichloro- aniline (μg/L) (61625) 2,6-Diethyl- aniline (μg/L) (82660) Sima- zine (μg/L) (04035) Atrazine (μg/L) (39632) Tebuthi- uron (μg/L) (82670) Hexazi- none (μg/L) (04025) Metola- chlor (μg/L) (39415) Prome- ton (μg/L) (04037) Me- tribuzin (μg/L) (82630) Desulfinyl- fipronil (μg/L) (62170) Fipronil sulfide (μg/L) (62167) Fiproni

sulfone (μg/L) (62168) 

Benchmark type na na na MCL-US MCL-CA HAL-US HAL-US HAL-US HAL-US HAL-US na na na 

Benchmark level na na na 4 1 500 400 700 400 70 na na na 

[LRL] [0.006] [0.006] [0.0060] [0.006] [0.008] [0.028] [0.012] [0.020] [0.012] [0.012] [0.012] [0.012] [0.024] 

Hard Rock study unit (93 grid wells sampled) 1 Number of wells with detections 8 2 1 7 4 3 2 2 2 1 2 1 1 

Detection frequency (percent) 8.6 2.2 1.1 7.5 4.3 3.2 2.2 2.2 2.2 1.1 2.2 1.1 1.1 

Santa Cruz study area (25 grid wells sampled) HR-SC-01 — — — — — — — — — — — — — 

HR-SC-11 — — — 0.010 — — — — — — — — — 

Number of wells with detections 0 0 0 1 0 0 0 0 0 0 0 0 0 

Detection frequency (percent) 0 0 0 4.0 0 0 0 0 0 0 0 0 0 
Table 6. Pesticides and pesticide degradates detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquiMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3B. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabri

HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-CA; California Department of Public Health maximum contaminant level. Other abbreviations: E, estimated or having a 

LRL, laboratory reporting level; μg/L, micrograms per liter; na, not available; —, not detected]

GAMA 

well 

identification 

number

Herbicide degradate Herbicide Insecticide degradates 

Deethylatrazine 

(μg/L) 

(04040)

3,4-Dichloroaniline 

(μg/L) 

(61625)

2,6-Diethylaniline 

(μg/L) 

(82660)

Simazine 

(μg/L) 

(04035)

Atrazine 

(μg/L) 

(39632)

Tebuthiuron 

(μg/L) 

(82670)

Hexazinone 

(μg/L) 

(04025)

Metolachlor 

(μg/L) 

(39415)

Prometon 

(μg/L) 

(04037)

Metribuzin 

(μg/L) 

(82630)

Desulfinylfipronil 

(μg/L) 

(62170)

Fipronil 

sulfide 

(μg/L) 

(62167)

Fiproni

sulfone 

(μg/L) 

(62168)

Benchmark type

na na na MCL-US MCL-CA HAL-US HAL-US HAL-US HAL-US HAL-US na na na 

Benchmark level

na na na 4 1 500 400 700 400 70 na na na 

[LRL] [0.006] [0.006] [0.0060] [0.006] [0.008] [0.028] [0.012] [0.020] [0.012] [0.012] [0.012] [0.012] [0.024] 

San Gabriel study area (33 grid wells sampled) HR-SG-04 E0.006 — — 0.011 — — — — — — — — — 

HR-SG-06 E0.029 — — — — — — — — — — — — 

HR-SG-15 — — — — — — 0.011 — — — — — — 

HR-SG-18 — — — 0.007 — — — — — — — — — 

HR-SG-21 — — — — 0.009 — — 2 0.008 — — — — — 

Number of 

wells with detections

2 0 0 2 1 0 1 1 0 0 0 0 0 

Detection 

frequency (percent)

6.1 0 0 6.1 3.0 0 3.0 3.0 0 0 0 0 0 

Peninsular Ranges study area (35 grid wells sampled) HR-PR-03 E0.014 E0.029 0.0031 — 0.040 E0.023 0.015 0.019 0.007 0.007 0.006 0.007 2 E0.00

HR-PR-06 — — — — — 2 0.009 — — — — — — — 

HR-PR-07 E0.005 — — 0.006 — — — — — — 2 0.003 — — 

HR-PR-12 E0.006 — — 0.008 0.005 — — — — — — — — 

HR-PR-17 E0.276 — — 0.010 0.005 — — — — — — — — 
Table 6. Pesticides and pesticide degradates detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock AquiMarch 2011 through March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from 110 welsamples with detections of at least one constituent are listed. Constituents are grouped by primary use or source and listed in order of decreasing detection frequency for each groAll analytes are listed in table 3B. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabri

HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting benchmark levels as of July 6, 2012. Benchmark type: Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as Mlower than the MCL-US or no MCL-US exists. MCL-CA; California Department of Public Health maximum contaminant level. Other abbreviations: E, estimated or having a 

LRL, laboratory reporting level; μg/L, micrograms per liter; na, not available; —, not detected] GAMA well identification number Herbicide degradate Herbicide Insecticide degradates 

Deethyl- atrazine (μg/L) (04040) 3,4-Dichloro- aniline (μg/L) (61625) 2,6-Diethyl- aniline (μg/L) (82660) Sima- zine (μg/L) (04035) Atrazine (μg/L) (39632) Tebuthi- uron (μg/L) (82670) Hexazi- none (μg/L) (04025) Metola- chlor (μg/L) (39415) Prome- ton (μg/L) (04037) Me- tribuzin (μg/L) (82630) Desulfinyl- fipronil (μg/L) (62170) Fipronil sulfide (μg/L) (62167) Fiproni

sulfone (μg/L) (62168) 

Benchmark type na na na MCL-US MCL-CA HAL-US HAL-US HAL-US HAL-US HAL-US na na na 

Benchmark level na na na 4 1 500 400 700 400 70 na na na 

[LRL] [0.006] [0.006] [0.0060] [0.006] [0.008] [0.028] [0.012] [0.020] [0.012] [0.012] [0.012] [0.012] [0.024] 

Peninsular Ranges study area (35 grid wells sampled)—Continued HR-PR-21 E0.006 — — — — E0.031 — — — — — — — 

HR-PR-24 E0.005 — — — — — — — — — — — — 

HR-PR-26 — — — 0.006 — — — — — — — — — 

HR-PR-28 — E0.0036 — — — — — — — — — — — 

HR-PR-33 — — — — — — — — 2 0.005 — — — — 

Number of wells with detections 6 2 1 4 3 3 1 1 2 1 2 1 1 

Detection frequency (percent) 17 5.7 2.9 11 8.6 8.6 2.9 2.9 5.7 2.9 5.7 2.9 2.9 

Hard Rock understanding wells (17 wells sampled) 3 HR-PRFP-05 — — — 0.006 — — — — 0.007 — — — — 

HR-PRFP-11 — — — — — — — — 0.006 — — — — HR-PRFP-12 E0.035 — — 0.015 0.009 — — — 0.007 — — — — 

HR-PRFP-13 — — — — — E0.015 — — — — — — — 

1 One grid-well pesticide sample (HR-PR-01) was ruined during analysis. 2 Result is below long-term method detection level.3 For sample HR-SGU-01, all results for organic constituents were coded as “reviewed and rejected” and omitted from this dataset due to suspected chlorination of sample.
Tables 67

Table 7. Perchlorate detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard 

Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Information about the constituent is given in table 3C. Samples from all 112 wells were analyzed, but only samples with detections are listed. GAMA well 

identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; 

HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding 

well. Reporting level, benchmark type, and benchmark level as of July 6, 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: MRL, minimum reporting level; μg/L, micrograms per liter]

GAMA well 

identification 

number

Perchlorate 

(μg/L) 

(63790)

Benchmark type MCL-CA

Benchmark level 6

[MRL] [0.10]

Hard Rock study unit (94 grid wells sampled)

Number of wells with detections 45

Detection frequency (percent) 48

Santa Cruz study area (25 grid wells sampled)

HR-SC-01 0.11

HR-SC-03 0.31

HR-SC-04 0.35

HR-SC-11 0.25

HR-SC-13 0.10

HR-SC-14 0.10

HR-SC-20 0.14

HR-SC-24 0.58

HR-SC-25 0.12

Number of wells with detections 9

Detection frequency (percent) 36

San Gabriel study area (33 grid wells sampled)

HR-SG-01 0.12

HR-SG-04 2.95

HR-SG-05 0.33

HR-SG-06 0.14

HR-SG-07 0.25

HR-SG-12 0.19

HR-SG-13 0.46

HR-SG-15 0.11

HR-SG-16 0.20

HR-SG-19 0.18

HR-SG-20 0.16

HR-SG-23 5.26

HR-SG-24 2.27

HR-SG-25 0.25

HR-SG-26 0.10

HR-SG-27 0.19

HR-SG-28 0.13

GAMA well 

identification 

number

Perchlorate 

(μg/L) 

(63790)

Benchmark type MCL-CA

Benchmark level 6

[MRL] [0.10]

San Gabriel study area (33 grid wells sampled)—Continued

HR-SG-33 1.38

Number of wells with detections 18

Detection frequency (percent) 55

Peninsular Ranges study area (36 grid wells sampled)

HR-PR-01 0.20

HR-PR-02 0.90

HR-PR-07 0.61

HR-PR-08 0.61

HR-PR-11 0.16

HR-PR-12 0.85

HR-PR-13 1.31

HR-PR-14 0.52

HR-PR-17 0.76

HR-PR-19 0.13

HR-PR-21 0.17

HR-PR-24 0.68

HR-PR-25 1.47

HR-PR-27 0.41

HR-PR-28 0.12

HR-PR-33 0.54

HR-PR-34 0.13

HR-PR-35 0.10

Number of wells with detections 18

Detection frequency (percent) 50

Hard Rock understanding wells (18 wells sampled)

HR-SGU-01 1.20

HR-PRFP-02 2.25

HR-PRFP-03 0.16

HR-PRFP-04 1.01

HR-PRFP-08 0.18

HR-PRFP-09 1.05

HR-PRFP-11 5.39

HR-PRFP-12 2.37

HR-PRFP-13 1.10
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) s

through March 2012, California GAMA Priority Basin Project. [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identifica

Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level] GAMA well identification number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01030) Copper (μg/L) (01040) Iron (μg/L) (01046) 

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA AL-US SMCL-CA 

Benchmark level 1,000 6 10 1,000 4 1,000 5 50 1,300 300 

[LT-MDL] or [SRL] [2.2] [0.027] [0.03] [0.07] [0.006] [3] [0.016] [0.07] 1 [2.1] 1 [6] 

Santa Cruz study area (25 wells sampled) HR-SC-01 2.2 — 7.9 26.2 — 13 0.045 — ≤ 1.0 — HR-SC-02 291 0.034 0.23 44.0 0.019 83 0.023 0.30 3.4 266 HR-SC-03 — — * 20.0 95.7 0.026 * 1,980 0.205 0.07 ≤ 0.52 * 8,390 HR-SC-04 — 0.358 0.13 38.8 0.006 142 — 0.07 ≤ 1.2 ≤ 4.

HR-SC-05 — — 0.05 15.2 0.018 10 — — — * 1,010 

HR-SC-06 2 1.7 — 0.08 13.9 0.006 54 — — 2.4 5.

HR-SC-07 3.0 0.067 0.20 23.6 0.011 425 — 0.10 — 276 HR-SC-08 3.4 0.046 0.11 190 0.019 52 0.035 — 5.5 * 447 

HR-SC-09 54.0 — 1.0 116 0.217 * 7,920 — — — 42.

HR-SC-10 2 2.0 0.037 0.24 0.66 — 9 — — — 7.

HR-SC-11 — 0.039 0.12 281 — 43 — 0.09 4.1 — 

HR-SC-12 — — 0.05 194 0.010 897 — — ≤ 0.50 166 

HR-SC-13 4.3 0.136 0.30 1.48 — 151 — 0.10 ≤ 1.9 13.

HR-SC-14 2.3 0.034 0.16 39.1 — 31 0.019 0.08 — * 940 

HR-SC-15 6.4 3.63 * 19.1 2.35 — 101 — — ≤ 1.1 — 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level]

GAMA well 

identification 

number

Aluminum 

(μg/L) 

(01106) 

Antimony 

(μg/L) 

(01095) 

Arsenic 

(μg/L) 

(01000) 

Barium 

(μg/L) 

(01005) 

Beryllium 

(μg/L) 

(01010)

Boron 

(μg/L) 

(01020) 

Cadmium 

(μg/L) 

(01025) 

Chromium 

(μg/L) 

(01030) 

Copper 

(μg/L) 

(01040) 

Iron 

(μg/L) 

(01046) 

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA AL-US SMCL-CA 

Benchmark level 1,000 6 10 1,000 4 1,000 5 50 1,300 300 

[LT-MDL] or [SRL] [2.2] [0.027] [0.03] [0.07] [0.006] [3] [0.016] [0.07] 1 [2.1] 1 [6] 

Santa Cruz study area (25 wells sampled)—ContinuedHR-SC-16 — 0.550 1.2 10.7 — 14 — — ≤ 0.77 — 

HR-SC-17 2.3 — 0.27 10.9 0.032 7 0.537 0.24 4.9 37.

HR-SC-18 — — 8.9 18.3 — 15 — 0.11 ≤ 0.67 * 341 

HR-SC-19 2.2 — 0.25 59.4 0.018 491 — — — * 1,250 

HR-SC-20 — 0.055 0.47 12.2 — 221 0.029 1.4 4.0 8.

HR-SC-21 — — 1.1 9.94 0.015 786 — — — * 2,330 

HR-SC-22 — 0.030 0.07 110 0.017 53 — — — * 1,490 

HR-SC-23 — — 0.63 73.9 0.008 329 — — — 99.

HR-SC-24 — 0.061 0.62 132 0.011 418 0.019 2.4 ≤ 1.9 83.HR-SC-25 8.9 0.112 1.8 1.17 — 15 0.185 0.28 5.4 — 

San Gabriel study area (37 wells sampled)HR-SG-01 — 0.065 0.51 58.0 — 101 0.021 0.07 ≤ 1.8 ≤ 5.

HR-SG-02 — — 0.12 48.1 — 46 0.023 0.07 — 84.

HR-SG-03 4.3 0.050 0.58 75.5 — 144 — 0.08 ≤ 1.9 ≤ 3.

HR-SG-04 — — 0.35 124 — 138 — 0.64 — ≤ 5.

HR-SG-05 3 — — — 44.5 — 44 — 0.56 — 6.

HR-SG-06 2.2 0.502 4.5 7.52 — 42 — 0.08 — — 

HR-SG-07 2.5 — 0.64 4.06 0.029 23 — — — * 484 

HR-SG-08 — 0.029 0.87 99.6 — 210 — — ≤ 1.1 35.

HR-SG-09 2 1.8 0.086 * 14.7 4.49 — 411 — 0.11 ≤ 0.84 16.

HR-SG-10 — — 0.07 21.8 — 44 0.023 0.46 ≤ 1.1 ≤ 4.
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level] GAMA well identification number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01030) Copper (μg/L) (01040) Iron (μg/L) (01046) 

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA AL-US SMCL-CA 

Benchmark level 1,000 6 10 1,000 4 1,000 5 50 1,300 300 

[LT-MDL] or [SRL] [2.2] [0.027] [0.03] [0.07] [0.006] [3] [0.016] [0.07] 1 [2.1] 1 [6] 

San Gabriel study area (37 wells sampled)—Continued HR-SG-11 23.7 — 0.09 29.0 — 39 — 0.12 — 9.

HR-SG-12 — 0.238 0.55 25.0 — 23 — 0.16 ≤ 1.1 — 

HR-SG-13 — — 0.13 33.0 — 37 — 0.21 ≤ 1.2 ≤ 5.

HR-SG-14 — — 0.03 5.91 0.017 13 — — ≤ 2.0 * 457 

HR-SG-15 — 1.25 0.11 44.7 — 50 0.082 0.07 ≤ 1.8 — 

HR-SG-16 2 2.0 3.85 2.6 77.7 — 92 0.020 0.08 3.8 — 

HR-SG-17 — 0.033 0.06 2.63 0.042 5 — — 2.6 — 

HR-SG-18 — 0.070 0.58 24.1 — 17 — — 4.2 ≤ 5.

HR-SG-19 2.2 — — 77.4 — 16 — — ≤ 1.7 10.

HR-SG-20 — 0.154 0.07 82.2 — 110 0.044 0.11 2.4 8.

HR-SG-21 — — 0.07 0.92 — 4 0.021 — ≤ 1.2 73.

HR-SG-22 — 0.278 1.3 72.2 — 418 0.031 — ≤ 1.7 ≤ 4.

HR-SG-23 2 1.8 0.041 0.26 10.7 — 11 0.018 0.10 — — 

HR-SG-24 2 2.0 0.117 2.4 18.9 0.022 *1,530 0.147 0.07 — ≤ 3.

HR-SG-25 5.0 — 0.32 23.9 — 4 — 0.10 — ≤ 5.

HR-SG-26 3.7 0.404 3.3 89.1 — 28 — 0.16 — — 

HR-SG-27 — 0.097 0.28 8.82 — 4 — 0.07 5.3 15.

HR-SG-28 — — — 7.62 — 9 — 0.12 2.2 — 

HR-SG-29 — 0.222 2.2 60.3 0.011 — 0.036 — ≤ 1.3 72.

HR-SG-30 — 0.106 0.93 63.8 — 3 — 0.19 ≤ 1.3 — 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level]

GAMA well 

identification 

number

Aluminum 

(μg/L) 

(01106) 

Antimony 

(μg/L) 

(01095) 

Arsenic 

(μg/L) 

(01000) 

Barium 

(μg/L) 

(01005) 

Beryllium 

(μg/L) 

(01010)

Boron 

(μg/L) 

(01020) 

Cadmium 

(μg/L) 

(01025) 

Chromium 

(μg/L) 

(01030) 

Copper 

(μg/L) 

(01040) 

Iron 

(μg/L) 

(01046) 

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA AL-US SMCL-CA 

Benchmark level 1,000 6 10 1,000 4 1,000 5 50 1,300 300 

[LT-MDL] or [SRL] [2.2] [0.027] [0.03] [0.07] [0.006] [3] [0.016] [0.07] 1 [2.1] 1 [6] 

San Gabriel study area (37 wells sampled)—ContinuedHR-SG-31 — — 0.12 52.2 — 74 0.029 — ≤ 0.74 52.HR-SG-32 2 1.8 0.107 0.35 7.95 — 4 — 0.08 ≤ 0.55 * 5,970 

HR-SG-33 2.2 0.029 0.92 78.2 0.008 449 — 2.2 10.6 74.

HR-SGU-01 — 0.118 0.12 109 0.014 201 0.037 0.14 4.4 — HR-SGU-02 3.0 0.143 0.05 8.02 — 23 — 0.15 ≤ 1.0 — 

HR-SGU-03 — 0.295 1.6 6.19 — 18 — 0.18 — ≤ 3.

HR-SGU-04 2 2.1 0.167 * 24.7 28.4 — 4 — 0.09 ≤ 0.88 271 

Peninsular Ranges study area (50 wells sampled)HR-PR-01 — 0.052 1.7 204 — 58 0.055 — 3.8 ≤ 5.

HR-PR-02 28.3 — 0.14 753 — 58 0.018 — 3.2 23.HR-PR-03 — — 0.08 1.65 — 3 0.017 — — * 475 HR-PR-04 — — 0.13 73.2 0.008 19 — — — * 679 

HR-PR-05 — — 0.49 160 — 21 0.021 — 2.6 6.HR-PR-06 2.4 — 0.62 15.5 0.008 252 0.028 — ≤ 0.99 ≤ 5.

HR-PR-07 — 0.340 4.0 44.1 — 163 0.103 — 6.8 14.

HR-PR-08 — 1.30 4.5 0.61 — 10 — — ≤ 0.82 — 

HR-PR-09 — — 0.11 1.62 — 6 — 0.11 — 245 

HR-PR-10 — — 0.31 48.1 0.155 10 — — 0.58 * 4,040 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level] GAMA well identification number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01030) Copper (μg/L) (01040) Iron (μg/L) (01046) 

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA AL-US SMCL-CA 

Benchmark level 1,000 6 10 1,000 4 1,000 5 50 1,300 300 

[LT-MDL] or [SRL] [2.2] [0.027] [0.03] [0.07] [0.006] [3] [0.016] [0.07] 1 [2.1] 1 [6] 

Peninsular Ranges study area (50 wells sampled)—Continued HR-PR-11 — — 0.89 5.76 — 35 0.032 — 0.68 — 

HR-PR-12 — 0.033 0.44 44.4 — 103 0.019 — 3.1 ≤ 4.

HR-PR-13 — — 0.71 149 — 170 0.043 — ≤ 0.53 ≤ 4.

HR-PR-14 — — 0.33 14.2 — 41 0.018 0.15 3.1 — 

HR-PR-15 3.1 — 0.13 45.9 — 4 — 0.11 7.5 12.

HR-PR-16 — 0.043 0.24 13.5 0.031 84 — — — * 1,220 

HR-PR-17 2 2.0 — 0.25 60.1 — 55 0.047 — ≤ 0.89 ≤ 3.

HR-PR-18 — 0.121 0.50 10.9 0.113 45 0.025 — — * 1,530 HR-PR-19 — 0.048 0.59 29.6 — 24 0.029 — — 40.

HR-PR-20 — 0.182 2.0 18.5 — 15 0.033 — 3.1 21.

HR-PR-21 — 0.031 0.57 36.9 — 65 0.078 — 4.2 9.

HR-PR-22 — 0.044 0.51 5.72 — 42 0.016 — — * 362 

HR-PR-23 3.6 — 6.8 61.4 0.022 155 — — — * 1,700 

HR-PR-24 4.4 — 0.35 26.7 — 31 0.054 0.83 8.0 14.HR-PR-25 — — 0.76 4.79 — 53 — 0.34 — — 

HR-PR-26 3 — 0.063 0.20 32.5 — 181 0.597 — 2.5 43.

HR-PR-27 — — 0.05 17.1 — 10 — — ≤ 1.2 — 

HR-PR-28 — — — 16.1 0.049 49 — — — * 1,770 

HR-PR-29 23.7 — 0.48 0.12 — 52 0.036 — — 6.

HR-PR-30 5.8 — 0.18 29.9 — 9 — — ≤ 0.94 — 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level]

GAMA well 

identification 

number

Aluminum 

(μg/L) 

(01106) 

Antimony 

(μg/L) 

(01095) 

Arsenic 

(μg/L) 

(01000) 

Barium 

(μg/L) 

(01005) 

Beryllium 

(μg/L) 

(01010)

Boron 

(μg/L) 

(01020) 

Cadmium 

(μg/L) 

(01025) 

Chromium 

(μg/L) 

(01030) 

Copper 

(μg/L) 

(01040) 

Iron 

(μg/L) 

(01046) 

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA AL-US SMCL-CA 

Benchmark level 1,000 6 10 1,000 4 1,000 5 50 1,300 300 

[LT-MDL] or [SRL] [2.2] [0.027] [0.03] [0.07] [0.006] [3] [0.016] [0.07] 1 [2.1] 1 [6] 

Peninsular Ranges study area (50 wells sampled)—ContinuedHR-PR-31 6.0 0.034 0.84 16.7 — 19 0.020 — — ≤ 4.

HR-PR-32 — — 0.54 11.7 0.008 43 0.028 — 6.6 ≤ 3.

HR-PR-33 — — 0.15 218 — 71 0.027 — — 10.

HR-PR-34 — 0.036 1.1 148 — 82 — — ≤ 1.5 11.

HR-PR-35 — — 0.32 28.2 — 11 — — — — 

HR-PR-36 — 0.029 — 3.03 — 6 0.017 — ≤ 1.7 8.HR-PRFP-01 — — 0.58 4.44 0.019 75 — — — * 1,410 

HR-PRFP-02 3 — — 0.94 39.2 — 86 — — 4.5 7.

HR-PRFP-03 3 — — 1.1 35.0 — 25 — — — 8.

HR-PRFP-04 3 — — 0.96 11.9 — 94 — — 11.3 ≤ 4.

HR-PRFP-05 — — 5.0 9.94 0.012 146 0.063 — — 21.

HR-PRFP-06 — — * 13.7 2.16 0.007 222 0.112 — — 129 

HR-PRFP-07 — — 0.11 3.83 0.012 30 — — — * 481 

HR-PRFP-08 14.0 — 0.06 2.37 — 104 — — — ≤ 3.

HR-PRFP-09 — 0.097 1.9 50.2 — 198 0.073 0.23 7.0 — 

HR-PRFP-10 — — 0.48 10.1 — 13 0.055 — 3.9 161 

HR-PRFP-11 3 — 0.073 0.76 221 0.018 314 — 0.18 7.5 10.

HR-PRFP-12 3 — — 0.36 25.7 — 87 — 0.18 — ≤ 5.

HR-PRFP-13 3 — 1.61 5.9 16.9 0.093 308 0.851 — 3.6 257 HR-PRU-01 2.3 — 0.31 23.2 — 7 — — ≤ 1.5 12.
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level] GAMA well identification number Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) 

Benchmark type SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US Benchmark level 50 40 100 50 100 4,000 2 na 30 

[LT-MDL] or [SRL] 1 [0.66] 1 [0.023] 1 [0.21] [0.03] [0.005] [0.2] [0.010] 1 [0.023] [0.004] 

Santa Cruz study area (25 wells sampled) HR-SC-01 — 24.8 ≤ 0.14 0.26 — 40.7 — 0.806 0.104 

HR-SC-02 * 59.6 1.34 0.95 0.16 — 230 — — 0.116 HR-SC-03 * 469 * 113 1.5 0.08 — 213 — — 0.049 

HR-SC-04 * 93 0.637 1.1 0.07 — 1,220 0.018 ≤ 0.022 0.170 

HR-SC-05 * 204 0.724 ≤ 0.09 — — 91.6 — ≤ 0.014 — 

HR-SC-06 3.32 0.091 0.24 0.22 — 295 — — 0.074 

HR-SC-07 * 83.9 0.821 0.84 — — 331 — — 0.087 

HR-SC-08 * 561 0.113 2.1 0.24 — 302 — — 0.006 

HR-SC-09 2.89 0.735 — — 0.005 351 — 4.25 0.063 

HR-SC-10 9.29 0.430 0.45 0.22 — 162 — ≤ 0.010 0.031 HR-SC-11 — 0.482 0.57 0.34 — 432 — — 0.107 HR-SC-12 12.9 0.653 1.6 0.04 — 2,020 — — 0.304 

HR-SC-13 0.81 0.356 11.0 0.33 — 80.9 — ≤ 0.021 0.016 

HR-SC-14 * 897 0.237 1.7 0.30 — 181 — — 0.013 

HR-SC-15 1.93 4.77 — 0.06 — 73.2 0.010 4.92 6.19 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level]

GAMA well 

identification 

number

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

Benchmark type SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US Benchmark level 50 40 100 50 100 4,000 2 na 30 

[LT-MDL] or [SRL] 1 [0.66] 1 [0.023] 1 [0.21] [0.03] [0.005] [0.2] [0.010] 1 [0.023] [0.004] 

Santa Cruz study area (25 wells sampled)—ContinuedHR-SC-16 ≤ 0.34 3.24 ≤ 0.11 — — 111 — ≤ 0.016 0.120 HR-SC-17 * 56.3 0.271 5.6 0.22 — 70.4 — — 0.032 HR-SC-18 30.2 4.90 ≤ 0.14 — — 122 — 0.027 — HR-SC-19 * 199 1.77 ≤ 0.11 — — 166 0.015 0.036 — 

HR-SC-20 2.55 1.42 1.3 0.11 — 321 — — 0.765 

HR-SC-21 * 359 5.03 ≤ 0.09 — — 119 — 0.086 0.004 

HR-SC-22 * 528 0.109 1.3 — — 568 — — 0.054 HR-SC-23 * 62.5 0.291 0.25 — — 1,900 — 0.079 0.031 

HR-SC-24 * 396 4.12 6.2 1.8 — 957 — — 8.61 

HR-SC-25 — 0.298 2.6 0.75 — 69.3 — — 0.006 

San Gabriel study area (37 wells sampled)HR-SG-01 — 6.85 ≤ 0.16 0.57 — 594 — — 2.62 HR-SG-02 1.52 7.26 ≤ 0.13 0.28 — 473 — — 11.9 

HR-SG-03 ≤ 0.13 1.74 ≤ 0.18 0.10 — 776 — ≤ 0.012 0.495 

HR-SG-04 ≤ 0.14 2.32 0.34 3.42 — 777 — 0.065 8.96 

HR-SG-05 3 ≤ 0.57 8.10 — 0.60 — 829 — 0.077 7.24 

HR-SG-06 — 4.66 — 0.41 — 192 — 0.043 10.3 

HR-SG-07 7.12 7.19 — — — 328 — 0.028 * 66.0 

HR-SG-08 * 219 1.75 0.43 0.05 — 1,010 — 0.099 0.373 

HR-SG-09 3.66 5.65 — 0.64 — 73.3 — 2.23 5.49 

HR-SG-10 ≤ 0.54 7.56 ≤ 0.15 0.48 — 308 — 0.046 29.3 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level] GAMA well identification number Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) 

Benchmark type SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US Benchmark level 50 40 100 50 100 4,000 2 na 30 

[LT-MDL] or [SRL] 1 [0.66] 1 [0.023] 1 [0.21] [0.03] [0.005] [0.2] [0.010] 1 [0.023] [0.004] 

San Gabriel study area (37 wells sampled)—Continued HR-SG-11 ≤ 0.33 4.36 ≤ 0.13 0.05 — 275 — 0.384 16.0 HR-SG-12 — 0.043 — 0.10 — 201 — 0.025 1.16 HR-SG-13 3.34 1.19 1.1 0.19 — 637 — 0.137 0.976 HR-SG-14 40.5 0.596 0.56 0.08 — 495 — 0.037 0.584 

HR-SG-15 4.54 2.01 0.40 0.16 — 355 — — 1.40 

HR-SG-16 ≤ 0.22 0.512 — 0.52 — 905 — — 11.8 

HR-SG-17 — 0.054 — — 0.009 267 — ≤ 0.014 * 36.8 

HR-SG-18 ≤ 0.17 2.70 0.29 0.12 — 540 — 0.090 1.32 HR-SG-19 ≤ 0.49 3.00 ≤ 0.18 1.9 — 326 — 0.864 2.19 HR-SG-20 ≤ 0.29 11.7 ≤ 0.13 1.1 — 1,350 — — 3.62 HR-SG-21 2.64 0.225 ≤ 0.18 0.15 — 335 — — 0.011 

HR-SG-22 ≤ 0.46 13.9 0.22 0.07 — 380 — 0.034 3.05 HR-SG-23 — 3.81 0.27 0.15 — 176 — 0.419 5.37 HR-SG-24 ≤ 0.63 * 83.2 ≤ 0.09 0.21 — 481 — 2.57 4.06 

HR-SG-25 — 0.347 — 0.20 0.006 91.4 — ≤ 0.011 4.99 

HR-SG-26 — 3.54 — 0.25 — 534 — 0.224 1.67 

HR-SG-27 ≤ 0.29 0.042 ≤ 0.11 0.09 0.005 167 — ≤ 0.020 13.7 HR-SG-28 — 1.54 ≤ 0.14 0.38 — 200 — ≤ 0.014 2.54 HR-SG-29 * 55.6 6.47 1.8 — — 419 — 0.025 6.42 

HR-SG-30 — 2.61 ≤ 0.10 0.25 — 385 — 0.158 1.88 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level]

GAMA well 

identification 

number

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

Benchmark type SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US Benchmark level 50 40 100 50 100 4,000 2 na 30 

[LT-MDL] or [SRL] 1 [0.66] 1 [0.023] 1 [0.21] [0.03] [0.005] [0.2] [0.010] 1 [0.023] [0.004] 

San Gabriel study area (37 wells sampled)—ContinuedHR-SG-31 ≤ 0.63 9.19 ≤ 0.13 0.11 — 334 — ≤ 0.017 2.47 HR-SG-32 * 93.4 1.62 0.61 — — 214 — — 0.714 HR-SG-33 6.52 4.46 0.65 6.2 — 466 — ≤ 0.015 4.54 HR-SGU-01 — 11.9 ≤ 0.17 0.65 0.009 1,530 — 0.032 17.8 

HR-SGU-02 ≤ 0.16 1.27 — 0.08 — 163 — ≤ 0.016 7.99 HR-SGU-03 ≤ 0.21 3.87 — 0.62 — 121 — 0.251 2.74 

HR-SGU-04 2.46 2.04 ≤ 0.16 0.34 — 479 — — 3.40 

Peninsular Ranges study area (50 wells sampled) HR-PR-01 * 290 8.93 0.80 0.30 0.007 355 — 0.027 11.6 HR-PR-02 15.9 2.09 0.39 0.40 0.012 536 — 0.037 0.733 

HR-PR-03 30.5 5.98 — 0.16 — 68.2 — 0.096 0.028 

HR-PR-04 * 102 1.42 ≤ 0.14 0.14 — 109 — 0.179 0.159 HR-PR-05 * 10.7 5.49 — 0.05 — 112 — 0.622 0.466 HR-PR-06 * 87.8 8.01 0.21 0.05 — 285 — 12.7 3.60 HR-PR-07 5.21 20.4 1.7 0.97 0.019 718 0.014 0.942 * 30.7 

HR-PR-08 — 4.13 0.22 7.7 — 223 — 0.023 0.156 

HR-PR-09 17.7 0.652 0.30 0.18 — 141 — 0.965 0.568 

HR-PR-10 * 335 0.676 1.4 — — 426 — 0.117 0.022 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level] GAMA well identification number Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) 

Benchmark type SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US 

Benchmark level 50 40 100 50 100 4,000 2 na 30 

[LT-MDL] or [SRL] 1 [0.66] 1 [0.023] 1 [0.21] [0.03] [0.005] [0.2] [0.010] 1 [0.023] [0.004] 

Peninsular Ranges study area (50 wells sampled)—Continued HR-PR-11 18.5 6.38 0.25 0.19 — 240 — 0.127 0.890 

HR-PR-12 ≤ 0.15 3.00 0.26 1.3 0.024 286 — ≤ 0.012 0.724 

HR-PR-13 ≤ 0.57 17.0 0.32 2.2 — 868 — 0.031 8.62 

HR-PR-14 — 8.47 0.36 1.1 0.010 189 — 0.029 6.10 

HR-PR-15 0.94 1.21 ≤ 0.13 0.25 — 70.4 — — 0.148 

HR-PR-16 * 207 3.13 0.50 — — 338 — ≤ 0.018 0.280 

HR-PR-17 — 20.3 ≤ 0.11 0.70 0.027 260 — 0.570 * 34.8 

HR-PR-18 * 690 4.90 0.23 — — 294 0.011 0.996 28.8 

HR-PR-19 0.70 6.58 0.40 1.3 — 106 — 0.174 7.86 

HR-PR-20 ≤ 0.57 4.3 0.43 0.33 — 259 — — 1.58 

HR-PR-21 * 214 14.0 0.68 0.44 — 252 0.011 0.196 * 66.6 

HR-PR-22 * 254 6.44 1.9 0.05 — 164 — 0.731 * 61.2 

HR-PR-23 * 116 2.46 0.40 — — 104 0.015 1.99 0.093 

HR-PR-24 — 9.28 1.6 0.61 0.113 509 — — 1.06 

HR-PR-25 — 0.734 0.80 1.2 0.005 297 — 0.225 1.18 

HR-PR-26 3 45.9 2.77 1.3 0.18 0.098 738 — — 4.53 

HR-PR-27 — 0.322 0.21 0.17 0.007 221 — — 0.158 

HR-PR-28 * 161 4.57 1.8 — — 508 — 3.03 0.252 

HR-PR-29 ≤ 0.32 16.6 — — — 21.7 — 0.857 0.586 

HR-PR-30 ≤ 0.14 3.05 0.85 0.07 — 164 — ≤ 0.019 5.14 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level]

GAMA well 

identification 

number

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

Benchmark type SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US Benchmark level 50 40 100 50 100 4,000 2 na 30 

[LT-MDL] or [SRL] 1 [0.66] 1 [0.023] 1 [0.21] [0.03] [0.005] [0.2] [0.010] 1 [0.023] [0.004] 

Peninsular Ranges study area (50 wells sampled)—ContinuedHR-PR-31 1.52 9.26 0.20 0.04 — 98.0 — 0.096 21.7 HR-PR-32 3.00 5.28 1.8 0.07 — 1,220 — 0.054 0.796 HR-PR-33 28.4 0.359 0.37 0.84 0.015 492 — 0.030 2.85 HR-PR-34 ≤ 0.21 1.93 0.49 0.96 — 763 — ≤ 0.014 4.82 

HR-PR-35 ≤ 0.33 1.45 ≤ 0.14 0.26 — 197 — ≤ 0.012 1.26 

HR-PR-36 * 376 0.119 0.31 — — 107 — — 2.13 

HR-PRFP-01 * 226 1.58 ≤ 0.09 — — 137 0.054 4.57 0.242 HR-PRFP-02 3 0.90 7.12 — 4.2 — 179 — — 12.0 

HR-PRFP-03 3 * 136 0.369 — 0.29 — 152 — 0.952 1.47 HR-PRFP-04 3 1.09 5.95 2.4 6.9 — 152 — 0.190 * 35.6 HR-PRFP-05 * 129 11.6 0.95 0.09 0.014 136 0.010 1.26 * 35.8 

HR-PRFP-06 * 160 18.7 0.33 0.04 — 59.6 — 3.30 17.8 

HR-PRFP-07 * 107 12.3 ≤ 0.12 — — 114 — 2.65 0.283 

HR-PRFP-08 2.73 1.71 — — — 10.9 — 17.2 0.445 HR-PRFP-09 * 50.6 16.8 0.31 2.8 0.022 332 0.013 0.090 * 45.2 
Table 8. Trace elements detected in the samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) sthrough March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as MCL-US when the SMCL-CA does not exist. AL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CASMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; SRL, study reporting level; μg/L, micrograms pethan or equal to; *, value above benchmark level] GAMA well identification number Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) 

Benchmark type SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US MCL-US na MCL-US Benchmark level 50 40 100 50 100 4,000 2 na 30 

[LT-MDL] or [SRL] 1 [0.66] 1 [0.023] 1 [0.21] [0.03] [0.005] [0.2] [0.010] 1 [0.023] [0.004] 

Peninsular Ranges study area (50 wells sampled)—Continued HR-PRFP-10 * 337 2.91 0.32 0.07 — 112 0.016 0.036 * 286 HR-PRFP-11 3 7.31 0.458 2.4 3.8 0.348 * 4,050 — — * 64.6 

HR-PRFP-12 3 ≤ 0.30 6.56 0.61 1.2 0.071 600 0.037 0.340 8.28 

HR-PRFP-13 3 * 425 6.05 4.4 4.5 0.027 741 — 0.042 * 48.9 

HR-PRU-01 1.25 3.92 — 0.04 — 47.0 — — 0.305 

1 SRL defined based on examination of quality-control results from October 2009 through March 2013 (Davis and others, 2014). All results for cobalt were censored from this 

National Water Information System (NWIS) database as “reviewed and rejected.” All detections of aluminum, copper, iron, lead, manganese, molybdenum, nickel, tungsten, and the respective SRL are reported as greater than or equal to (≤) the value reported by the laboratory. In the NWIS database, results are accompanied with the following comment: based on quality-control data (Davis and others, 2014). 2 Value is below the highest LT-MDL used by the NWQL during the time in which samples were analyzed for the Hard Rock study unit. 3 LT-MDLs reported by the NWQL were raised due to dilution during analyses for all trace elements for the following Hard Rock samples: HR-SG-05 (by factor of 3); HR-PRHR-PRFP-02, 03, and 04 (by factor of 5); and HR-PRFP-11, 12, and 13 (by factor of 2).
Tables 81

Table 9. Nutrients detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard 

Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 112 wells were analyzed, but only samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, 

Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges 

study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, 

benchmark type, and benchmark level as of July 6, 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: SRL, study reporting level; IRL, interim 

reporting level; LT-MDL, long-term method detection level; mg/L, milligrams per liter; *, value above benchmark level; na, not available; —, not detected; 

≤, less than or equal to]

GAMA 

well 

identification 

number

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Nitrite plus nitrate, 

as nitrogen 

(mg/L) 

(00631)

Total nitrogen 1

(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

[SRL], [IRL], or [LT-MDL] 3

 [0.015] 3 [0.0014] 4 [0.04] [0.05] [0.004]

Santa Cruz study area (25 wells sampled)

HR-SC-01 — — 0.27 0.29 0.006

HR-SC-02 0.02 0.008 0.94 1.1 0.096

HR-SC-03 0.61 0.002 — 0.82 0.457

HR-SC-04 — 0.006 4.5 4.6 0.007

HR-SC-05 0.08 — — 0.05 —

HR-SC-06 — — ≤ 0.03 — 0.012

HR-SC-07 2.8 0.005 0.07 3.0 0.025

HR-SC-08 0.14 — 0.27 0.43 0.036

HR-SC-09 0.28 — 0.09 0.28 0.007

HR-SC-10 — — 0.10 — 0.166

HR-SC-11 — — 2.2 2.2 0.008

HR-SC-12 ≤ 0.01 — 0.07 — 0.013

HR-SC-13 — — 0.05 — 0.013

HR-SC-14 ≤ 0.01 ≤ 0.001 0.35 0.37 0.172

HR-SC-15 0.74 — — 0.88 0.012

HR-SC-16 0.02 0.013 0.09 0.07 0.013

HR-SC-17 0.05 — 0.04 — 0.219

HR-SC-18 0.02 — — — 0.672

HR-SC-19 7.6 — 5 — 8.0 0.265

HR-SC-20 — — 0.41 0.49 0.048

HR-SC-21 2.9 — ≤ 0.03 2.9 0.143

HR-SC-22 0.04 — — 0.05 0.024

HR-SC-23 0.88 0.002 0.04 0.91 0.031

HR-SC-24 0.13 0.002 2.6 2.9 0.063

HR-SC-25 — — 1.5 1.6 0.878
82 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 9. Nutrients detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard 

Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 112 wells were analyzed, but only samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, 

Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges 

study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, 

benchmark type, and benchmark level as of July 6, 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: SRL, study reporting level; IRL, interim 

reporting level; LT-MDL, long-term method detection level; mg/L, milligrams per liter; *, value above benchmark level; na, not available; —, not detected; 

≤, less than or equal to]

GAMA 

well 

identification 

number

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Nitrite plus nitrate, 

as nitrogen 

(mg/L) 

(00631)

Total nitrogen 1

(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

[SRL], [IRL], or [LT-MDL] 3

 [0.015] 3 [0.0014] 4 [0.04] [0.05] [0.004]

San Gabriel study area (37 wells sampled) 6

HR-SG-01 ≤ 0.01 — 0.25 0.25 0.027

HR-SG-02 ≤ 0.01 ≤ 0.001 0.32 0.30 0.027

HR-SG-03 ≤ 0.01 ≤ 0.001 0.47 0.51 0.058

HR-SG-04 ≤ 0.01 — 6.0 6.2 0.041

HR-SG-05 — — 3.2 3.4 0.019

HR-SG-06 — — 0.47 0.44 0.005

HR-SG-08 0.02 ≤ 0.001 — 0.08 0.115

HR-SG-09 0.07 0.003 1.2 1.25 0.034

HR-SG-10 — — 3.5 3.5 0.010

HR-SG-11 — — ≤ 0.02 — 0.006

HR-SG-12 — — 0.04 — 0.014

HR-SG-13 — ≤ 0.001 0.11 0.09 0.012

HR-SG-14 — 0.002 0.16 0.16 0.013

HR-SG-15 — — 0.86 0.9 0.006

HR-SG-16 — — 1.0 1.1 0.011

HR-SG-17 — — 0.07 — 0.019

HR-SG-18 — — 0.35 0.34 0.028

HR-SG-19 — 0.003 0.41 0.40 0.016

HR-SG-20 — — 0.38 0.35 0.009

HR-SG-21 — ≤ 0.001 0.18 0.15 0.023

HR-SG-22 — — 0.13 0.17 0.045

HR-SG-23 — — 0.48 0.48 0.015

HR-SG-24 — — 0.22 0.21 0.012

HR-SG-25 — — 1.3 1.2 0.044

HR-SG-26 — — 0.38 0.37 0.012
Tables 83

Table 9. Nutrients detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard 

Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 112 wells were analyzed, but only samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, 

Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges 

study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, 

benchmark type, and benchmark level as of July 6, 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: SRL, study reporting level; IRL, interim 

reporting level; LT-MDL, long-term method detection level; mg/L, milligrams per liter; *, value above benchmark level; na, not available; —, not detected; 

≤, less than or equal to]

GAMA 

well 

identification 

number

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Nitrite plus nitrate, 

as nitrogen 

(mg/L) 

(00631)

Total nitrogen 1

(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

[SRL], [IRL], or [LT-MDL] 3

 [0.015] 3 [0.0014] 4 [0.04] [0.05] [0.004]

San Gabriel study area (37 wells sampled) 6

—Continued

HR-SG-27 — — 0.38 0.39 0.038

HR-SG-28 — — 0.83 0.86 0.008

HR-SG-30 — — 0.07 — —

HR-SG-31 — — 0.13 0.13 0.015

HR-SG-33 ≤ 0.01 0.002 6.6 6.5 0.091

HR-SGU-01 — — 1.3 1.3 0.015

HR-SGU-02 — — 0.74 0.79 0.010

HR-SGU-03 — — 0.19 0.18 0.007

HR-SGU-04 — — ≤ 0.03 — 0.004

Peninsular Ranges study area (50 wells sampled)

HR-PR-01 — — 1.3 1.5 0.174

HR-PR-02 — — 5.0 4.9 0.040

HR-PR-03 — — ≤ 0.03 — 0.013

HR-PR-04 — — ≤ 0.03 — 0.020

HR-PR-05 — — 0.08 — 0.027

HR-PR-06 — — 0.06 — 0.009

HR-PR-07 — 0.004 1.3 1.4 0.060

HR-PR-08 — — 3.4 3.7 0.015

HR-PR-09 — — 0.08 0.07 0.008

HR-PR-10 — — — — 0.010

HR-PR-11 — — 1.1 1.1 0.017

HR-PR-12 0.02 — 1.2 1.2 0.042

HR-PR-13 — ≤ 0.001 * 11.8 12.5 0.104

HR-PR-14 — — 1.7 1.8 0.027

HR-PR-15 — — — — 0.019
84 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 9. Nutrients detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard 

Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 112 wells were analyzed, but only samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, 

Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges 

study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, 

benchmark type, and benchmark level as of July 6, 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: SRL, study reporting level; IRL, interim 

reporting level; LT-MDL, long-term method detection level; mg/L, milligrams per liter; *, value above benchmark level; na, not available; —, not detected; 

≤, less than or equal to]

GAMA 

well 

identification 

number

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Nitrite plus nitrate, 

as nitrogen 

(mg/L) 

(00631)

Total nitrogen 1

(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

[SRL], [IRL], or [LT-MDL] 3

 [0.015] 3 [0.0014] 4 [0.04] [0.05] [0.004]

Peninsular Ranges study area (50 wells sampled)—Continued

HR-PR-16 — — — — 0.007

HR-PR-17 — — 7.2 7.4 0.017

HR-PR-18 — — — 0.07 0.012

HR-PR-19 — — 0.29 0.35 0.017

HR-PR-20 — — 0.05 0.07 0.020

HR-PR-21 — 0.003 0.46 0.53 0.014

HR-PR-22 — — — — 0.009

HR-PR-23 — — — — 0.014

HR-PR-24 — — 2.7 2.7 0.146

HR-PR-25 — — 8.8 9.2 0.020

HR-PR-26 ≤ 0.01 0.002 0.22 0.33 0.019

HR-PR-27 ≤ 0.01 ≤ 0.001 3.4 3.8 0.035

HR-PR-28 0.02 — — — 0.014

HR-PR-30 0.02 — 0.82 1.00 0.018

HR-PR-31 0.02 — 0.74 0.75 0.012

HR-PR-32 — — — — 0.008

HR-PR-33 0.03 0.004 * 14.7 15.4 0.068

HR-PR-34 — — 1.1 1.1 0.140

HR-PR-35 — — 1.1 1.1 0.021

HR-PR-36 ≤ 0.01 — — — —

HR-PRFP-01 — — — — 0.020

HR-PRFP-02 — — 6.4 6.6 0.102

HR-PRFP-03 0.02 — 4.0 3.8 0.014

HR-PRFP-04 — — * 13.4 12.7 0.026

HR-PRFP-05 — — 0.26 0.31 0.029
Tables 85

Table 9. Nutrients detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard 

Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from all 112 wells were analyzed, but only samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, 

Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges 

study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, 

benchmark type, and benchmark level as of July 6, 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: SRL, study reporting level; IRL, interim 

reporting level; LT-MDL, long-term method detection level; mg/L, milligrams per liter; *, value above benchmark level; na, not available; —, not detected; 

≤, less than or equal to]

GAMA 

well 

identification 

number

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Nitrite plus nitrate, 

as nitrogen 

(mg/L) 

(00631)

Total nitrogen 1

(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

[SRL], [IRL], or [LT-MDL] 3

 [0.015] 3 [0.0014] 4 [0.04] [0.05] [0.004]

Peninsular Ranges study area (50 wells sampled)—Continued

HR-PRFP-06 — — — — 0.030

HR-PRFP-07 — — — — 0.007

HR-PRFP-08 — — — — 0.008

HR-PRFP-09 — 0.002 1.5 1.8 0.039

HR-PRFP-10 — 0.003 0.15 0.18 0.014

HR-PRFP-11 — ≤ 0.001 * 33.9 29.8 0.035

HR-PRFP-12 — — * 11.0 10.5 0.046

HR-PRFP-13 0.03 0.118 * 20.4 20.3 0.018

HR-PRU-01 — — — — 0.007

1

 Total nitrogen concentration (T) was compared with the sum of ammonia, nitrite, and nitrate concentrations (S) for each sample, using the same criteria used 

to evaluate acceptibility of replicates: for T greater than 0.25 mg/L (5 times the LT-MDL), relative percent difference less than 10 percent indicates acceptable 

replication; for T less than 0.25 mg/L, standard deviation less than 0.025 mg/L indicates acceptable precision. There were five samples (HR-SC-09, HR-SC-10, 

HR-SC-12, HR-SC-16, and HR-SC-17) with T less than S, and precision between the two parameters was considered unacceptable. For T greater than S and 

unacceptable replication by these criteria, organic nitrogen may be present. 

2

 The HAL-US is 30 mg/L “as ammonia.” To facilitate comparson to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L “as 

nitrogen.”

3

 SRLs were defined for nutrients based on the highest detected concentrations in field blanks for the Hard Rock study unit. Values less than the SRL are 

reported as greater than or equal to (≤) the value reported by the laboratory. In the USGS National Water Information System (NWIS) database, the result is 

accompanied by the following comment: Result is < or = reported value, based on quality-control data. See appendix table A3 for more information.

4

 The interim reporting level is the highest reporting level for nitrite plus nitrate during March 2011 to March 2012 and therefore is used in this table. The SRL 

applied to nitrite plus nitrate, based on the highest concentration detected in field blanks for the Hard Rock study unit, is 0.031 mg/L.

5

 Sample HR-SC-19 was diluted during analysis, increasing the LT-MDL of nitrite by a factor of two (0.002 mg/L).

6

 Nutrients were not detected in sample HR-SG-32. However, the sample was diluted, increasing the LT-MDLs for ammonia and orthophosphate by a factor of 

two (0.020 mg/L and 0.008 mg/L, respectively).
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the Santa Cruz, San Gabriel, and Peninsula

Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project. [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identifica

Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as SMCL-US when the SMCL-CA does not exist. MCL-CA, California Department of Public Health (CDPSMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; MRL, minimum reporting level; mg/L, milligram

na, not available; —, not detected; *, value above benchmark level, **, value above 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) Silica (as SiO2) (mg/L) (00955) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

Benchmark type na na SMCL-CA MCL-CA na na na na na SMCL-CA 

Benchmark level na na 1 250 (500) 2 na na na na na 1 250 (500) 

[LT-MDL] or [MRL] [0.010] [0.022] [0.06] [0.04] [0.001] [0.011] [0.03] [0.029] [0.06] [0.09] 

Santa Cruz study area (25 wells sampled) HR-SC-01 0.138 28.7 40.2 0.57 — 3.48 0.36 16.8 23.9 10.3 

HR-SC-02 0.138 26.3 33.2 0.18 — 2 11.2 1.61 33.8 45.5 58.0 

HR-SC-03 0.549 20.4 76.9 1.74 0.195 15.9 2.56 16.3 107 32.0 

HR-SC-04 0.054 146 31.7 0.14 — 20.3 2.06 18.7 22.9 203 

HR-SC-05 0.043 33.4 8.40 0.11 0.003 8.72 2.46 30.7 9.75 16.7 

HR-SC-06 0.046 60.4 13.6 0.18 0.001 10.1 1.36 28.4 16.3 26.2 

HR-SC-07 0.904 86.4 *258 0.21 0.094 68.8 5.15 29.4 174 175 

HR-SC-08 0.039 56.6 13.5 0.16 0.003 10.4 1.70 32.2 18.9 36.9 

HR-SC-09 0.039 3.01 13.8 *2.42 0.039 0.298 1.63 11.5 240 13.3 

HR-SC-10 0.028 50.5 4.32 0.17 — 3.25 0.80 35.8 9.78 17.2 

HR-SC-11 0.080 128 34.0 0.11 — 15.9 0.71 16.9 14.3 13.3 

HR-SC-12 0.059 87.2 17.6 0.24 0.002 64.8 0.90 40.6 22.9 35.4 

HR-SC-13 0.010 31.4 3.74 0.19 — 10.2 0.52 18.2 10.8 17.8 

HR-SC-14 0.063 65.6 20.8 0.35 0.007 19.7 1.84 46.7 21.4 91.2 

HR-SC-15 0.043 4.07 10.6 0.72 0.004 1.99 3.34 14.3 112 33.8 
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the Santa Cruz, San Gabriel, and PeninsulaAquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as SMCL-US when the SMCL-CA does not exist. MCL-CA, California Department of Public Health (CDPSMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; MRL, minimum reporting level; mg/L, milligram

na, not available; —, not detected; *, value above benchmark level, **, value above 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) 

Silica 

(as SiO2) 

(mg/L) 

(00955) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

Benchmark type na na SMCL-CA MCL-CA na na na na na SMCL-CA 

Benchmark level na na 1 250 (500) 2 na na na na na 1 250 (500) 

[LT-MDL] or [MRL] [0.010] [0.022] [0.06] [0.04] [0.001] [0.011] [0.03] [0.029] [0.06] [0.09] 

Santa Cruz study area (25 wells sampled)—ContinuedHR-SC-16 0.015 29.8 6.35 0.12 0.002 10.5 2.33 15.7 15.9 14.9 

HR-SC-17 0.020 6.22 7.27 0.06 0.001 1.21 0.95 45.2 8.72 7.51 

HR-SC-18 0.025 22.0 8.36 0.10 0.005 1.47 1.28 37.8 16.6 27.7 

HR-SC-19 0.200 37.5 41.7 0.32 0.059 37.6 4.67 36.3 71.1 35.6 

HR-SC-20 0.491 50.6 236 0.24 0.004 64.5 1.17 26.2 192 152 

HR-SC-21 0.138 45.6 64.0 0.19 0.003 37.2 11.6 56.9 150 *268 

HR-SC-22 0.092 118 30.1 0.10 0.009 36.6 1.46 30.8 20.4 70.3 

HR-SC-23 0.060 80.0 19.6 0.31 0.003 28.4 3.81 29.6 60.3 59.8 

HR-SC-24 0.206 133 119 0.29 0.028 89.0 2.43 25.1 81.8 142 

HR-SC-25 0.016 16.5 7.73 0.18 — 1.02 0.97 33.2 10.6 8.19 

San Gabriel study area (37 wells sampled)HR-SG-01 0.054 71.1 20.2 0.90 0.003 36.1 1.80 21.1 36.9 134 

HR-SG-02 0.055 73.4 20.3 0.84 0.002 28.8 2.52 23.6 29.9 67.3 

HR-SG-03 0.103 70.3 24.4 0.32 0.004 18.0 1.96 28.1 40.5 47.4 

HR-SG-04 0.278 118 79.1 0.39 0.001 48.2 1.62 28.1 45.4 141 

HR-SG-05 0.041 80.0 13.1 0.58 0.001 23.8 2.40 18.1 31.8 52.2 

HR-SG-06 0.029 36.4 6.39 0.19 — 12.3 4.27 20.2 17.2 29.4 

HR-SG-07 0.022 45.5 4.50 0.88 0.005 8.92 0.60 22.6 17.3 18.7 

HR-SG-08 0.177 90.5 46.3 0.33 0.019 23.7 2.48 30.0 62.0 56.7 

HR-SG-09 0.209 4.10 62.0 1.47 0.038 0.199 0.88 37.7 274 232 

HR-SG-10 0.054 67.0 13.5 1.51 0.001 25.6 2.82 24.1 31.8 64.8 
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the Santa Cruz, San Gabriel, and PeninsulaAquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as SMCL-US when the SMCL-CA does not exist. MCL-CA, California Department of Public Health (CDPSMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; MRL, minimum reporting level; mg/L, milligram

na, not available; —, not detected; *, value above benchmark level, **, value above 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) Silica (as SiO2) (mg/L) (00955) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

Benchmark type na na SMCL-CA MCL-CA na na na na na SMCL-CA 

Benchmark level na na 1 250 (500) 2 na na na na na 1 250 (500) 

[LT-MDL] or [MRL] [0.010] [0.022] [0.06] [0.04] [0.001] [0.011] [0.03] [0.029] [0.06] [0.09] 

San Gabriel study area (37 wells sampled)—Continued HR-SG-11 0.058 18.4 13.1 *8.67 0.006 8.28 0.84 24.4 46.4 17.7 

HR-SG-12 — 49.0 2.64 0.21 — 12.0 2.28 20.9 6.55 2.35 

HR-SG-13 0.014 71.4 3.00 0.25 — 20.5 2.18 14.7 17.9 26.7 

HR-SG-14 0.013 102 2.51 0.09 — 20.3 2.80 18.9 4.15 16.0 

HR-SG-15 — 44.3 0.83 0.57 — 6.79 3.30 9.38 3.65 7.66 

HR-SG-16 0.038 58.6 7.46 0.90 — 12.0 0.22 19.9 13.8 9.70 

HR-SG-17 — 52.9 1.49 0.13 — 3.86 1.53 25.7 9.34 2.38 

HR-SG-18 0.072 62.1 11.4 0.21 0.002 16.0 2.25 31.1 34.6 34.0 HR-SG-19 0.089 75.3 13.5 0.38 0.003 13.6 3.92 18.9 25.8 33.0 

HR-SG-20 — 69.6 3.04 0.45 — 35.3 4.27 12.7 29.7 85.1 

HR-SG-21 — 66.6 4.08 — 0.001 13.0 0.65 24.3 12.8 14.9 

HR-SG-22 0.065 49.1 30.4 0.76 0.038 16.2 3.36 21.6 44.8 34.5 

HR-SG-23 — 38.2 1.97 0.27 0.001 6.25 2.14 18.3 6.86 9.11 

HR-SG-24 0.039 38.8 9.59 *3.49 0.005 16.2 1.76 24.8 33.8 58.1 

HR-SG-25 0.040 16.8 6.92 0.34 — 11.1 2.59 27.8 18.4 8.80 

HR-SG-26 0.017 52.3 2.74 0.39 — 12.7 3.14 12.7 8.53 24.0 

HR-SG-27 0.017 31.3 3.24 0.16 — 5.36 2.24 29.5 11.2 3.85 

HR-SG-28 — 40.8 2.37 0.10 — 7.70 2.19 21.0 8.28 16.9 

HR-SG-29 — 83.2 0.80 0.09 — 6.12 1.79 11.8 4.16 38.4 

HR-SG-30 — 69.5 0.89 0.14 — 7.30 1.12 9.69 3.67 13.9 
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the Santa Cruz, San Gabriel, and PeninsulaAquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as SMCL-US when the SMCL-CA does not exist. MCL-CA, California Department of Public Health (CDPSMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; MRL, minimum reporting level; mg/L, milligram

na, not available; —, not detected; *, value above benchmark level, **, value above 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) 

Silica 

(as SiO2) 

(mg/L) 

(00955) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

Benchmark type na na SMCL-CA MCL-CA na na na na na SMCL-CA 

Benchmark level na na 1 250 (500) 2 na na na na na 1 250 (500) 

[LT-MDL] or [MRL] [0.010] [0.022] [0.06] [0.04] [0.001] [0.011] [0.03] [0.029] [0.06] [0.09] 

San Gabriel study area (37 wells sampled)—ContinuedHR-SG-31 0.066 62.5 17.1 1.02 0.004 34.4 1.81 29.9 30.3 61.1 

HR-SG-32 0.042 18.6 4.98 0.06 0.004 5.02 0.88 24.0 12.6 3.01 

HR-SG-33 0.471 87.4 87.0 0.54 0.002 27.3 1.81 32.9 53.2 82.8 

HR-SGU-01 0.040 39.1 61.0 1.06 0.002 46.5 4.12 22.2 76.8 35.7 

HR-SGU-02 — 27.2 1.53 0.09 — 3.44 1.84 15.1 6.80 3.55 

HR-SGU-03 — 34.6 0.78 0.36 — 7.58 2.18 14.5 3.13 24.6 

HR-SGU-04 — 74.0 0.61 — — 4.16 1.63 9.17 3.13 31.5 

Peninsular Ranges study area (50 wells sampled)HR-PR-01 0.329 55.8 91.0 0.27 0.038 38.5 2.82 48.5 57.7 21.9 

HR-PR-02 0.312 38.8 58.0 0.31 0.004 11.0 5.23 38.9 53.2 6.44 

HR-PR-03 0.020 15.0 6.31 0.05 0.005 7.82 3.20 35.5 14.6 9.50 

HR-PR-04 0.069 25.2 19.8 0.15 0.007 10.5 6.43 55.6 24.5 19.7 

HR-PR-05 0.043 18.5 10.7 0.23 0.005 6.48 2.79 27.7 18.7 12.6 

HR-PR-06 0.296 79.3 114 0.37 0.037 7.05 1.30 21.8 97.6 64.6 

HR-PR-07 0.607 151 *328 0.44 0.067 100 5.06 50.8 210 *481 

HR-PR-08 0.080 41.5 21.7 0.11 0.001 8.92 0.57 30.2 27.6 34.7 

HR-PR-09 0.069 35.9 24.2 0.11 0.003 8.69 1.33 25.8 22.1 5.26 

HR-PR-10 0.143 64.1 46.8 0.06 0.009 29.0 3.51 46.2 36.7 212 
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the Santa Cruz, San Gabriel, and PeninsulaAquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued [The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as SMCL-US when the SMCL-CA does not exist. MCL-CA, California Department of Public Health (CDPSMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; MRL, minimum reporting level; mg/L, milligram

na, not available; —, not detected; *, value above benchmark level, **, value above 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) Silica (as SiO2) (mg/L) (00955) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

Benchmark type na na SMCL-CA MCL-CA na na na na na SMCL-CA 

Benchmark level na na 1 250 (500) 2 na na na na na 1 250 (500) 

[LT-MDL] or [MRL] [0.010] [0.022] [0.06] [0.04] [0.001] [0.011] [0.03] [0.029] [0.06] [0.09] 

Peninsular Ranges study area (50 wells sampled)—Continued HR-PR-11 0.373 46.6 107 0.34 0.015 22.0 2.52 40.0 54.3 37.2 

HR-PR-12 0.133 58.7 93.4 0.19 0.002 32.5 1.88 39.0 73.7 191 

HR-PR-13 0.536 98.1 222 0.32 0.014 43.8 4.23 37.0 129 66.9 

HR-PR-14 0.333 47.6 70.9 0.29 0.005 14.8 4.28 39.7 55.2 31.1 

HR-PR-15 0.015 15.2 13.4 — — 7.56 3.82 30.2 12.8 5.25 

HR-PR-16 0.817 65.7 241 0.33 0.128 32.0 4.65 37.8 135 72.3 

HR-PR-17 0.210 47.5 43.0 0.32 0.002 16.4 3.07 34.3 47.4 17.7 

HR-PR-18 0.528 94.9 67.8 0.44 0.601 21.4 3.35 42.4 69.2 35.8 

HR-PR-19 0.143 34.0 27.9 0.34 0.004 17.5 3.34 46.0 32.3 21.9 

HR-PR-20 0.099 59.1 23.6 0.26 0.002 14.7 1.46 43.0 28.9 81.8 

HR-PR-21 0.511 91.3 194 0.64 0.037 35.7 4.24 41.5 89.7 83.8 

HR-PR-22 0.252 106 77.0 0.17 0.016 24.0 5.38 32.0 42.7 88.3 

HR-PR-23 0.159 40.3 51.0 0.36 0.029 17.0 6.75 68.2 41.3 24.6 

HR-PR-24 0.375 106 197 0.28 0.006 37.1 6.04 79.1 78.9 149 

HR-PR-25 0.237 89.7 89.9 — 0.004 63.5 2.74 65.0 25.3 71.4 

HR-PR-26 1.84 185 **639 0.28 0.065 131 0.47 34.8 213 228 

HR-PR-27 0.052 18.1 12.2 0.19 — 5.52 1.34 36.3 19.4 1.77 

HR-PR-28 0.370 138 93.7 0.35 0.021 35.4 9.90 40.3 74.0 *327 

HR-PR-29 0.247 3.94 39.3 0.36 0.019 0.037 0.73 13.8 56.9 23.7 

HR-PR-30 0.061 28.9 17.9 0.18 0.005 5.07 3.62 39.8 28.3 7.25 
Table 10. Major and minor ions, silica, and total dissolved solids (TDS) detected in samples collected for the Santa Cruz, San Gabriel, and PeninsulaAquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identificaCruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 2012. Benchmark typebenchmarks 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. Seconbenchmarks are listed as SMCL-CA when the SMCL-CA exists, and as SMCL-US when the SMCL-CA does not exist. MCL-CA, California Department of Public Health (CDPSMCL-CA, CDPH secondary maximum contaminant level. Other abbreviations: LT-MDL, long-term method detection level; MRL, minimum reporting level; mg/L, milligram

na, not available; —, not detected; *, value above benchmark level, **, value above 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) 

Silica 

(as SiO2) 

(mg/L) 

(00955) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

Benchmark type na na SMCL-CA MCL-CA na na na na na SMCL-CA 

Benchmark level na na 1 250 (500) 2 na na na na na 1 250 (500) 

[LT-MDL] or [MRL] [0.010] [0.022] [0.06] [0.04] [0.001] [0.011] [0.03] [0.029] [0.06] [0.09] 

Peninsular Ranges study area (50 wells sampled)—ContinuedHR-PR-31 — 13.7 9.80 0.07 — 1.41 1.27 23.8 20.0 2.98 

HR-PR-32 0.312 129 55.1 0.21 0.018 61.5 0.56 37.5 53.8 *308 

HR-PR-33 0.298 57.0 60.9 0.45 0.006 16.1 1.51 54.6 64.2 22.6 

HR-PR-34 0.373 65.8 72.3 0.84 0.004 18.1 1.05 47.2 82.1 26.9 

HR-PR-35 0.082 31.3 15.6 0.23 0.002 7.05 2.61 40.6 21.9 5.02 

HR-PR-36 0.023 18.8 5.56 0.08 0.004 7.89 1.83 26.8 14.8 0.75 

HR-PRFP-01 0.157 57.1 45.9 0.50 0.016 13.1 3.57 52.5 34.7 64.5 

HR-PRFP-02 0.256 74.7 171 0.37 0.009 57.9 2.71 51.1 121 226 

HR-PRFP-03 0.294 79.0 88.6 0.45 0.015 20.5 5.35 49.7 51.9 97.2 

HR-PRFP-04 0.360 60.6 131 0.25 0.003 17.9 2.63 39.5 79.4 34.3 

HR-PRFP-05 0.502 130 187 0.30 0.083 40.8 6.08 45.1 91.4 152 

HR-PRFP-06 0.317 88.3 115 0.23 0.084 19.6 4.85 44.9 64.0 67.5 

HR-PRFP-07 0.107 45.8 30.8 0.39 0.006 10.7 2.77 26.7 27.9 69.8 

HR-PRFP-08 0.065 7.69 17.1 *2.93 0.008 0.518 0.70 24.3 34.4 14.7 

HR-PRFP-09 0.603 121 *288 0.51 0.042 73.4 9.74 39.5 184 *256 

HR-PRFP-10 0.126 43.6 48.3 0.28 0.015 12.9 4.07 42.9 31.6 36.4 

HR-PRFP-11 3.43 448 **1,290 0.17 0.034 133 3.39 30.7 325 223 

HR-PRFP-12 0.718 128 *259 0.41 0.011 43.5 4.06 47.3 120 128 

HR-PRFP-13 2.59 149 **753 0.71 0.530 117 2.10 45.1 414 *444 

HR-PRU-01 0.033 19.6 9.11 — 0.002 9.47 5.24 22.7 11.6 6.25 

1 The SMCL-CAs for chloride, sulfate, and TDS have recommended and upper benchmark values. The upper value is shown in parentheses.2 The LT-MDL for iodide was raised by a factor of two (0.002 mg/L) for HR-SC-02 due to sample dilution during analysis.
92 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 11. Arsenic, chromium, and iron species detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges 

Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed for arsenic and iron species. Samples from all 37 San Gabriel study area wells were analyzed for chromium species. Only 

samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel 

study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study 

area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Secondary maximum contaminant level benchmarks are listed as SMCL-CA when the SMCL-CA 

exists, and as the SMCL-US when the SMCL-CA does not exist. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, 

California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant 

level. Other abbreviations: MDL, method detection limit; μg/L, micrograms per liter; —, not detected; na, not available; *, greater than the benchmark level]

GAMA well 

identification 

number

Arsenic 

(μg/L) 

(99033) 

Arsenic (III) 

(μg/L) 

(99034)

Chromium 

(μg/L) 

(01030)

Chromium (VI) 

(μg/L) 

(01032)

Iron 

(μg/L) 

(01046)

Iron (II) 

(μg/L) 

(01047) 

Benchmark type MCL-US na MCL-CA na SMCL-CA na

Benchmark level 10 na 50 na 300 na

[MDL] [0.2] [0.5] [1] [1] [2] [2]

Santa Cruz study area (25 wells sampled)

HR-SC-01 7.5 — na na — na 1

HR-SC-02 0.3 — na na 140 30

HR-SC-03 *18.5 17.5 na na * 8,570 7,370

HR-SC-05 — — na na * 1,060 1,040

HR-SC-07 — — na na 272 229

HR-SC-08 — — na na * 444 344

HR-SC-09 0.8 0.8 na na 42 41

HR-SC-10 0.3 — na na 5 4

HR-SC-11 — — na na 5 —

HR-SC-12 — — na na 202 198

HR-SC-13 0.2 — na na 9 7

HR-SC-14 — 0.5 na na * 891 872

HR-SC-15 *17.8 2.3 na na — na 1

HR-SC-16 1 — na na 7 4

HR-SC-17 0.2 — na na 28 10

HR-SC-18 8.6 7.2 na na * 327 325

HR-SC-19 0.5 0.5 na na * 1,220 1,220

HR-SC-20 0.4 — na na 10 3

HR-SC-21 0.9 0.7 na na * 2,320 2,200

HR-SC-22 — — na na *1,500 1,500

HR-SC-23 0.6 — na na 100 93

HR-SC-24 0.5 — na na 88 65

HR-SC-25 1.7 — na na — —
Tables 93

Table 11. Arsenic, chromium, and iron species detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges 

Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed for arsenic and iron species. Samples from all 37 San Gabriel study area wells were analyzed for chromium species. Only 

samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel 

study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study 

area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Secondary maximum contaminant level benchmarks are listed as SMCL-CA when the SMCL-CA 

exists, and as the SMCL-US when the SMCL-CA does not exist. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, 

California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant 

level. Other abbreviations: MDL, method detection limit; μg/L, micrograms per liter; —, not detected; na, not available; *, greater than the benchmark level]

GAMA well 

identification 

number

Arsenic 

(μg/L) 

(99033) 

Arsenic (III) 

(μg/L) 

(99034)

Chromium 

(μg/L) 

(01030)

Chromium (VI) 

(μg/L) 

(01032)

Iron 

(μg/L) 

(01046)

Iron (II) 

(μg/L) 

(01047) 

Benchmark type MCL-US na MCL-CA na SMCL-CA na

Benchmark level 10 na 50 na 300 na

[MDL] [0.2] [0.5] [1] [1] [2] [2]

San Gabriel study area (37 wells sampled)

HR-SG-01 na 2 na 2 — — na 2 na 2

HR-SG-02 — — — — 86 82

HR-SG-03 0.5 — — — — —

HR-SG-04 0.3 — — — 5 —

HR-SG-05 — — — — 5 —

HR-SG-06 4.3 — — — 3 —

HR-SG-07 0.6 — — — * 473 245

HR-SG-08 0.8 — — — 34 26

HR-SG-09 * 14.1 2.2 — — 15 4

HR-SG-10 — — — — 4 —

HR-SG-11 — — — — 7 2

HR-SG-12 0.5 — — — — —

HR-SG-13 — — — — 7 5

HR-SG-14 — — — — * 471 455

HR-SG-15 — — — — 4 —

HR-SG-16 2.2 — — — — —

HR-SG-17 — — — — 3 —

HR-SG-18 0.5 — — — 3 3

HR-SG-19 — — — — 7 5

HR-SG-20 — — — — 5 3

HR-SG-21 — — — — 87 38

HR-SG-22 1.1 — — — 3 3

HR-SG-23 0.2 — — — — —

HR-SG-24 2.3 0.8 — — 5 —

HR-SG-25 0.3 — — — 6 4
94 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 11. Arsenic, chromium, and iron species detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges 

Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed for arsenic and iron species. Samples from all 37 San Gabriel study area wells were analyzed for chromium species. Only 

samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel 

study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study 

area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Secondary maximum contaminant level benchmarks are listed as SMCL-CA when the SMCL-CA 

exists, and as the SMCL-US when the SMCL-CA does not exist. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, 

California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant 

level. Other abbreviations: MDL, method detection limit; μg/L, micrograms per liter; —, not detected; na, not available; *, greater than the benchmark level]

GAMA well 

identification 

number

Arsenic 

(μg/L) 

(99033) 

Arsenic (III) 

(μg/L) 

(99034)

Chromium 

(μg/L) 

(01030)

Chromium (VI) 

(μg/L) 

(01032)

Iron 

(μg/L) 

(01046)

Iron (II) 

(μg/L) 

(01047) 

Benchmark type MCL-US na MCL-CA na SMCL-CA na

Benchmark level 10 na 50 na 300 na

[MDL] [0.2] [0.5] [1] [1] [2] [2]

San Gabriel study area (37 wells sampled)—Continued

HR-SG-26 3.2 — — — — —

HR-SG-27 0.3 — — — 2 —

HR-SG-29 2 1.3 — — 73 64

HR-SG-30 1 — — — — —

HR-SG-31 — — — — 46 33

HR-SG-32 0.3 — — — *6,080 6,080

HR-SG-33 0.8 — 2.8 1.1 76 4

HR-SGU-01 na 2 na 2 — — na 2 na 2

HR-SGU-03 1.9 — — — — —

HR-SGU-04 * 26.6 1 — — 267 15

Peninsular Ranges study area (50 wells sampled)

HR-PR-01 1.5 — na na — —

HR-PR-02 — — na na 4 3

HR-PR-03 — — na na * 494 471

HR-PR-04 0.3 — na na * 722 678

HR-PR-05 0.4 — na na — —

HR-PR-06 0.4 — na na 4 2

HR-PR-07 3.7 — na na 4 —

HR-PR-08 3.4 — na na — —

HR-PR-09 — — na na 256 233

HR-PR-10 0.3 — na na *3,920 3,920

HR-PR-11 0.6 — na na 4 —

HR-PR-12 0.4 — na na 3 —

HR-PR-13 0.4 — na na — —

HR-PR-14 0.3 — na na — —

HR-PR-15 0.2 — na na 10 5
Tables 95

Table 11. Arsenic, chromium, and iron species detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges 

Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed for arsenic and iron species. Samples from all 37 San Gabriel study area wells were analyzed for chromium species. Only 

samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel 

study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study 

area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Secondary maximum contaminant level benchmarks are listed as SMCL-CA when the SMCL-CA 

exists, and as the SMCL-US when the SMCL-CA does not exist. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, 

California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant 

level. Other abbreviations: MDL, method detection limit; μg/L, micrograms per liter; —, not detected; na, not available; *, greater than the benchmark level]

GAMA well 

identification 

number

Arsenic 

(μg/L) 

(99033) 

Arsenic (III) 

(μg/L) 

(99034)

Chromium 

(μg/L) 

(01030)

Chromium (VI) 

(μg/L) 

(01032)

Iron 

(μg/L) 

(01046)

Iron (II) 

(μg/L) 

(01047) 

Benchmark type MCL-US na MCL-CA na SMCL-CA na

Benchmark level 10 na 50 na 300 na

[MDL] [0.2] [0.5] [1] [1] [2] [2]

Peninsular Ranges study area (50 wells sampled)—Continued

HR-PR-16 — — na na *1,210 1,190

HR-PR-17 0.3 — na na — —

HR-PR-18 0.3 — na na *1,620 1,610

HR-PR-19 0.5 — na na 43 39

HR-PR-20 2 — na na 20 19

HR-PR-21 0.4 — na na 9 6

HR-PR-22 0.4 — na na * 372 355

HR-PR-23 6.5 6.5 na na *1,710 1,670

HR-PR-24 0.3 — na na 10 5

HR-PR-25 0.7 — na na 2 —

HR-PR-26 — — na na 33 29

HR-PR-28 — — na na *1,790 850

HR-PR-29 0.5 — na na 6 4

HR-PR-30 — — na na 4 4

HR-PR-31 0.9 — na na 4 4

HR-PR-32 0.5 — na na 3 3

HR-PR-33 — — na na 12 7

HR-PR-34 1.1 — na na 9 7

HR-PR-35 0.3 — na na — —

HR-PR-36 — — na na 9 4

HR-PRFP-01 0.5 0.5 na na *1,460 1,420

HR-PRFP-02 0.9 — na na 4 4

HR-PRFP-03 1.3 — na na 4 4

HR-PRFP-04 1 — na na 6 4

HR-PRFP-05 4.1 — na na 18 15
96 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 11. Arsenic, chromium, and iron species detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges 

Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed for arsenic and iron species. Samples from all 37 San Gabriel study area wells were analyzed for chromium species. Only 

samples with detections of at least one constituent are listed. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel 

study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study 

area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Secondary maximum contaminant level benchmarks are listed as SMCL-CA when the SMCL-CA 

exists, and as the SMCL-US when the SMCL-CA does not exist. MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, 

California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant 

level. Other abbreviations: MDL, method detection limit; μg/L, micrograms per liter; —, not detected; na, not available; *, greater than the benchmark level]

GAMA well 

identification 

number

Arsenic 

(μg/L) 

(99033) 

Arsenic (III) 

(μg/L) 

(99034)

Chromium 

(μg/L) 

(01030)

Chromium (VI) 

(μg/L) 

(01032)

Iron 

(μg/L) 

(01046)

Iron (II) 

(μg/L) 

(01047) 

Benchmark type MCL-US na MCL-CA na SMCL-CA na

Benchmark level 10 na 50 na 300 na

[MDL] [0.2] [0.5] [1] [1] [2] [2]

Peninsular Ranges study area (50 wells sampled)—Continued

HR-PRFP-06 * 12.8 8.4 na na 132 127

HR-PRFP-07 — — na na * 480 469

HR-PRFP-08 — — na na 2 2

HR-PRFP-09 1.8 — na na — —

HR-PRFP-10 0.4 — na na 176 148

HR-PRFP-11 0.6 — na na 6 5

HR-PRFP-12 0.3 — na na — —

HR-PRFP-13 5.2 — na na 240 9

HR-PRU-01 0.3 — na na 13 3

1

 Iron (II) is frequently not measured if iron (total) is not detected. 

2

 HR-SG-01 and HR-SGU-01 samples were not analyzed for arsenic and iron speciation due to sample mix-up.
Tables 97

Table 12. Results for analyses of stable isotope ratios, carbon-14 abundance, and tritium activity in samples collected for the Santa 

Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA 

Priority Basin Project.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Stable 

isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard 

reference material. Measured values of tritium less than the sample-specific critical level (ssLC) are reported as not detected (—). GAMA well identification 

number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, 

Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. 

Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Elements: H, hydrogen; O, oxygen; C, carbon. Other abbreviations: CSU, 1-sigma combined 

standard uncertainty; ssLC, sample-specific critical level; ±, plus or minus; pCi/L, picocuries per liter; na, not available]

GAMA well 

identification 

number

δ2H 

(per mil) 

(82082)

δ18O 

(per mil) 

(82085)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent modern carbon) 

(49933)

Tritium 

(pCi/L) 

(07000)

Benchmark type na na na na MCL-CA

Benchmark level na na na na 20,000

Result ± CSU ssLC

Santa Cruz study area (25 wells sampled)

HR-SC-01 –33.7 –5.56 –19.01 78.70 1.28 ± 0.29 0.27

HR-SC-02 –32.7 –5.34 –14.38 59.37 3.03 ± 0.32 0.27

HR-SC-03 –32.3 –5.36 –19.21 33.73 0.64 ± 0.44 0.43

HR-SC-04 –37.1 –6.29 –13.73 67.12 4.63 ± 0.46 0.4

HR-SC-05 –36.9 –6.37 –16.48 74.80 3.87 ± 0.44 0.39

HR-SC-06 –35.7 –6.28 –17.88 72.78 4.56 ± 0.33 0.27

HR-SC-07 –33.9 –5.29 –10.27 35.34 1.21 ± 0.26 0.26

HR-SC-08 –41.2 –6.59 –19.84 83.64 5.93 ± 0.35 0.25

HR-SC-09 –43.0 –6.81 –14.33 8.83 0.75 ± 0.3 0.29

HR-SC-10 –43.3 –7.12 –18.23 70.93 4.95 ± 0.32 0.41

HR-SC-11 –43.6 –6.70 –13.89 78.86 5.22 ± 0.41 0.31

HR-SC-12 –43.4 –6.52 –12.16 31.90 2.02 ± 0.36 0.32

HR-SC-13 –41.5 –6.69 –18.89 71.12 6.14 ± 0.48 0.36

HR-SC-14 –39.7 –6.61 –19.66 84.22 5.83 ± 0.45 0.34

HR-SC-15 –34.5 –5.92 –14.27 47.89 1.09 ± 0.38 0.36

HR-SC-16 –37.6 –6.44 –17.18 91.13 5.28 ± 0.43 0.33

HR-SC-17 –35.6 –6.04 –20.50 106.98 4.75 ± 0.46 0.37

HR-SC-18 –36.0 –6.14 –15.52 60.37 1.54 ± 0.38 0.35

HR-SC-19 –32.9 –5.25 –11.65 9.77 0.31 ± 0.26 0.26

HR-SC-20 –32.6 –4.86 –16.85 88.24 3.38 ± 0.3 0.26

HR-SC-21 –37.7 –5.70 –13.34 33.22 0.81 ± 0.26 0.26

HR-SC-22 –41.2 –6.71 –17.07 67.00 3.97 ± 0.32 0.26

HR-SC-23 –39.8 –6.34 –12.94 41.79 2.88 ± 0.33 0.28

HR-SC-24 –41.1 –6.32 –16.62 94.67 4.68 ± 0.36 0.28

HR-SC-25 –36.1 –5.85 –18.33 105.14 3.98 ± 0.34 0.28
98 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 12. Results for analyses of stable isotope ratios, carbon-14 abundance, and tritium activity in samples collected for the Santa 

Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA 

Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Stable 

isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard 

reference material. Measured values of tritium less than the sample-specific critical level (ssLC) are reported as not detected (—). GAMA well identification 

number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, 

Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. 

Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Elements: H, hydrogen; O, oxygen; C, carbon. Other abbreviations: CSU, 1-sigma combined 

standard uncertainty; ssLC, sample-specific critical level; ±, plus or minus; pCi/L, picocuries per liter; na, not available]

GAMA well 

identification 

number

δ2H 

(per mil) 

(82082)

δ18O 

(per mil) 

(82085)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent modern carbon) 

(49933)

Tritium 

(pCi/L) 

(07000)

Benchmark type na na na na MCL-CA

Benchmark level na na na na 20,000

Result ± CSU ssLC

San Gabriel study area (37 wells sampled)

HR-SG-01 –55.5 –8.10 –13.39 100.26 10.62 ± 0.47 0.26

HR-SG-02 –55.9 –8.51 –14.61 104.04 7.59 ± 0.5 0.34

HR-SG-03 –59.8 –8.35 –14.40 103.94 9.83 ± 0.54 0.32

HR-SG-04 –58.3 –8.65 –14.03 96.43 3.57 ± 0.38 0.31

HR-SG-05 –60.2 –8.94 –13.40 103.11 8.06 ± 0.51 0.34

HR-SG-06 –50.5 –8.06 –17.38 88.88 3.42 ± 0.34 0.29

HR-SG-07 –54.8 –8.53 –17.58 89.95 1.96 ± 0.34 0.3

HR-SG-08 –60.3 –8.20 –15.81 104.04 6.93 ± 0.45 0.31

HR-SG-09 –54.6 –7.65 –11.33 60.03 0.64 ± 0.31 0.3

HR-SG-10 –65.6 –9.61 –14.89 102.93 5.61 ± 0.33 0.25

HR-SG-11 –67.0 –9.97 –15.40 83.10 — 0.27

HR-SG-12 –57.5 –8.86 –17.68 89.20 6.44 ± 0.39 0.28

HR-SG-13 –76.7 –11.14 –14.74 80.00 5.03 ± 0.33 0.25

HR-SG-14 –74.2 –10.96 –16.16 77.51 10.19 ± 0.63 0.38

HR-SG-15 –69.8 –10.45 –15.60 95.83 13.74 ± 0.76 0.41

HR-SG-16 –47.8 –7.68 –17.41 78.60 9.15 ± 0.61 0.39

HR-SG-17 –72.5 –10.74 –17.24 77.89 8.91 ± 0.63 0.42

HR-SG-18 –61.4 –8.78 –14.94 104.58 16.46 ± 1.05 0.6

HR-SG-19 –71.1 –10.34 –16.52 80.35 3.32 ± 0.52 0.44

HR-SG-20 –76.0 –10.71 –11.63 80.56 7.43 ± 0.55 0.37

HR-SG-21 –63.8 –9.62 –17.23 94.76 5.3 ± 0.53 0.41

HR-SG-22 –98.0 –12.58 –12.08 91.40 11.67 ± 0.66 0.36

HR-SG-23 –60.8 –9.30 –12.56 94.22 8.67 ± 0.59 0.38

HR-SG-24 –50.4 –7.76 –15.60 101.75 8.47 ± 0.59 0.38

HR-SG-25 –49.6 –7.92 –19.82 95.70 3.55 ± 0.45 0.37
Tables 99

Table 12. Results for analyses of stable isotope ratios, carbon-14 abundance, and tritium activity in samples collected for the Santa 

Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA 

Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Stable 

isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard 

reference material. Measured values of tritium less than the sample-specific critical level (ssLC) are reported as not detected (—). GAMA well identification 

number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, 

Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. 

Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Elements: H, hydrogen; O, oxygen; C, carbon. Other abbreviations: CSU, 1-sigma combined 

standard uncertainty; ssLC, sample-specific critical level; ±, plus or minus; pCi/L, picocuries per liter; na, not available]

GAMA well 

identification 

number

δ2H 

(per mil) 

(82082)

δ18O 

(per mil) 

(82085)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent modern carbon) 

(49933)

Tritium 

(pCi/L) 

(07000)

Benchmark type na na na na MCL-CA

Benchmark level na na na na 20,000

Result ± CSU ssLC

San Gabriel study area (37 wells sampled)—Continued

HR-SG-26 –63.7 –9.54 –10.67 93.95 11.9 ± 0.6 0.39

HR-SG-27 –70.5 –10.34 –16.94 84.69 6.66 ± 0.48 0.35

HR-SG-28 –58.1 –8.94 –16.25 94.70 9.59 ± 0.69 0.47

HR-SG-29 –73.8 –10.86 –15.16 56.32 9.97 ± 0.61 0.37

HR-SG-30 –72.4 –10.63 –14.64 79.31 11.73 ± 0.66 0.38

HR-SG-31 –56.9 –8.26 –14.12 79.14 8.87 ± 0.57 0.35

HR-SG-32 –65.3 –9.56 –16.36 99.84 8.95 ± 0.58 0.37

HR-SG-33 –62.0 –8.45 –13.64 84.08 2.56 ± 0.44 0.40

HR-SGU-01 –60.9 –8.58 –9.18 36.06 3.41 ± 0.41 0.34

HR-SGU-02 –63.2 –9.59 –15.38 90.95 7.06 ± 0.65 0.49

HR-SGU-03 –68.1 –10.20 –11.59 80.24 9.28 ± 0.58 0.36

HR-SGU-04 –72.4 –10.64 –15.10 106.76 10.87 ± 0.61 0.34

Peninsular Ranges study area (50 wells sampled)

HR-PR-01 –38.8 –5.87 –15.44 107.49 6.13 ± 0.43 0.32

HR-PR-02 –58.1 –8.16 –12.44 102.37 2.32± 0.39 0.35

HR-PR-03 –52.9 –8.34 –19.15 97.25 3.87 ± 0.36 0.3

HR-PR-04 –47.2 –7.64 –17.64 97.22 2.08 ± 0.33 0.29

HR-PR-05 –50.2 –7.90 –18.23 86.39 1.35 ± 0.31 0.28

HR-PR-06 –51.8 –7.81 –14.00 98.69 2.52 ± 0.32 0.28

HR-PR-07 –49.4 –6.65 –16.08 103.08 9.42 ± 0.49 0.31

HR-PR-08 –39.4 –6.27 –15.80 61.34 2.09 ± 0.34 0.31

HR-PR-09 –53.8 –8.49 –16.74 102.22 4.79 ± 0.39 0.32

HR-PR-10 –47.2 –7.33 –21.32 95.96 5.15 ± 0.36 0.28
100 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 12. Results for analyses of stable isotope ratios, carbon-14 abundance, and tritium activity in samples collected for the Santa 

Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA 

Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Stable 

isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard 

reference material. Measured values of tritium less than the sample-specific critical level (ssLC) are reported as not detected (—). GAMA well identification 

number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, 

Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. 

Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Elements: H, hydrogen; O, oxygen; C, carbon. Other abbreviations: CSU, 1-sigma combined 

standard uncertainty; ssLC, sample-specific critical level; ±, plus or minus; pCi/L, picocuries per liter; na, not available]

GAMA well 

identification 

number

δ2H 

(per mil) 

(82082)

δ18O 

(per mil) 

(82085)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent modern carbon) 

(49933)

Tritium 

(pCi/L) 

(07000)

Benchmark type na na na na MCL-CA

Benchmark level na na na na 20,000

Result ± CSU ssLC

Peninsular Ranges study area (50 wells sampled)—Continued

HR-PR-11 –39.6 –6.03 –16.79 77.06 3.23 ± 0.34 0.28

HR-PR-12 –72.9 –8.62 –9.83 96.91 14.61 ± 0.66 0.36

HR-PR-13 –54.7 –7.45 –15.86 106.67 7.32 ± 0.49 0.38

HR-PR-14 –42.9 –6.33 –15.13 110.61 5.23 ± 0.51 0.44

HR-PR-15 –50.4 –8.15 –19.86 104.18 5.11 ± 0.43 0.36

HR-PR-16 –35.1 –5.49 –15.62 78.08 1.27 ± 0.41 0.4

HR-PR-17 –46.9 –7.28 –15.64 110.35 5.92 ± 0.49 0.41

HR-PR-18 –34.2 –5.17 –13.95 89.44 3.27 ± 0.45 0.41

HR-PR-19 –49.0 –7.83 –17.38 107.38 6.81 ± 0.47 0.37

HR-PR-20 –36.7 –6.00 –16.73 102.05 6.74 ± 0.49 0.39

HR-PR-21 –36.7 –5.95 –16.76 102.74 3.57 ± 0.4 0.36

HR-PR-22 –50.7 –7.86 –15.79 98.30 2.61 ± 0.44 0.41

HR-PR-23 –47.5 –7.40 –15.90 76.70 1.56 ± 0.42 0.41

HR-PR-24 –41.1 –6.13 –17.11 105.48 4.6 ± 0.52 0.44

HR-PR-25 –43.4 –6.48 –14.60 105.03 4.02 ± 0.5 0.43

HR-PR-26 –34.2 –5.20 –15.94 107.97 7.79 ± 0.53 0.38

HR-PR-27 –52.1 –8.08 –16.83 100.04 2.41 ± 0.42 0.38

HR-PR-28 –55.4 –8.13 –15.22 86.35 0.77 ± 0.41 0.4

HR-PR-29 –73.7 –9.67 na 1 na 1 0.59 ± 0.37 0.37

HR-PR-30 –60.0 –8.86 –17.09 105.69 5.99 ± 0.43 0.32

HR-PR-31 –68.6 –10.24 –18.39 95.32 3.42 ± 0.41 0.35

HR-PR-32 –68.8 –9.40 –11.80 91.41 2.65 ± 0.37 0.32

HR-PR-33 –52.8 –7.96 –15.91 103.84 4.74 ± 0.58 0.5

HR-PR-34 –53.0 –7.73 –13.72 104.99 4.03 ± 0.56 0.49

HR-PR-35 –58.9 –8.57 –15.62 84.14 2.06 ± 0.49 0.46
Tables 101

Table 12. Results for analyses of stable isotope ratios, carbon-14 abundance, and tritium activity in samples collected for the Santa 

Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA 

Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. Stable 

isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard 

reference material. Measured values of tritium less than the sample-specific critical level (ssLC) are reported as not detected (—). GAMA well identification 

number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, 

Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. 

Reporting levels, benchmark types, and benchmark levels as of July 6, 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. Elements: H, hydrogen; O, oxygen; C, carbon. Other abbreviations: CSU, 1-sigma combined 

standard uncertainty; ssLC, sample-specific critical level; ±, plus or minus; pCi/L, picocuries per liter; na, not available]

GAMA well 

identification 

number

δ2H 

(per mil) 

(82082)

δ18O 

(per mil) 

(82085)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent modern carbon) 

(49933)

Tritium 

(pCi/L) 

(07000)

Benchmark type na na na na MCL-CA

Benchmark level na na na na 20,000

Result ± CSU ssLC

Peninsular Ranges study area (50 wells sampled)—Continued

HR-PR-36 –64.1 –9.70 –18.06 100.17 5.1 ± 0.58 0.49

HR-PRFP-01 –49.1 –7.58 –16.07 72.67 0.67 ± 0.48 0.47

HR-PRFP-02 –51.6 –6.85 –17.37 97.44 8.08 ± 0.62 0.47

HR-PRFP-03 –46.8 –7.37 –17.98 58.49 1.28 ± 0.48 0.46

HR-PRFP-04 –38.6 –6.02 –17.15 92.69 2.44 ± 0.5 0.46

HR-PRFP-05 –41.2 –5.97 –15.27 105.73 6.26 ± 0.6 0.49

HR-PRFP-06 –43.5 –6.50 –14.54 97.79 1.49 ± 0.49 0.49

HR-PRFP-07 –51.8 –8.11 –16.51 99.39 5.25 ± 0.55 0.46

HR-PRFP-08 –57.0 –8.92 –17.85 43.08 0.93 ± 0.35 0.33

HR-PRFP-09 –44.8 –6.08 –16.97 103.39 7.29 ± 0.45 0.31

HR-PRFP-10 –47.3 –7.48 na 1 na 1 1.00 ± 0.37 0.35

HR-PRFP-11 –34.1 –5.24 –15.58 93.70 2.55 ± 0.27 0.24

HR-PRFP-12 –37.1 –5.60 –14.85 106.25 4.96 ± 0.27 0.18

HR-PRFP-13 –41.1 –6.16 –17.02 104.79 8.18 ± 0.39 0.23

HR-PRU-01 –52.1 –8.41 –18.54 98.45 1.99 ± 0.44 0.38

1

 No results for samples HR-PR-29 (valve malfunction during analysis) and HR-PRFP-10 (broken during storage).
102 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 13. Results for analyses of dissolved noble gases by the Lawrence Livermore National Laboratory (LLNL) for samples collected 

for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, 

California GAMA Priority Basin Project.

[Results for noble gas analyses from the LLNL are stored in a separate database maintained by the GAMA Program. Information about the analytes given in 

table 3I. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study 

area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges 

study area understanding well. Other abbreviations: cm3STP/g, cubic centimeters per gram at standard temperature and pressure]

GAMA well 

identification number

Argon 

(104

 cm3STP/g) 

Helium-3/Helium-4 

(106 atom ratio)

Helium-4 

(108 cm3STP/g) 

Krypton 

(108 cm3STP/g) 

Neon 

(107 cm3STP/g) 

Xenon 

(108 cm3STP/g) 

Santa Cruz study area (23 wells sampled) 1

HR-SC-01 3.745 1.42 5.83 8.62 2.49 1.16

HR-SC-02 3.756 1.43 5.85 8.46 2.44 1.17

HR-SC-03 9.632 1.39 28.4 18.73 10.29 2.12

HR-SC-04 na 0.97 8.00 8.04 2.40 1.13

HR-SC-05 3.932 1.34 7.28 7.90 2.78 1.09

HR-SC-06 3.62 1.37 4.57 8.51 1.97 1.23

HR-SC-07 4.06 1.32 6.06 8.85 2.60 1.29

HR-SC-08 4.35 1.41 8.96 9.07 3.58 1.28

HR-SC-10 4.37 1.5 8.75 9.09 3.61 1.32

HR-SC-11 3.45 1.4 5.01 7.78 2.14 1.14

HR-SC-12 4.54 1.38 8.19 9.63 3.41 1.28

HR-SC-14 4.51 1.41 7.99 9.60 3.44 1.34

HR-SC-15 7.90 1.14 25.2 13.73 8.46 1.85

HR-SC-16 6.90 1.38 19.8 12.18 8.12 1.58

HR-SC-17 3.49 1.43 4.71 7.76 2.06 1.08

HR-SC-18 4.24 1.42 7.77 8.97 3.12 1.24

HR-SC-19 3.76 0.51 18.5 8.48 2.35 1.17

HR-SC-20 4.02 1.40 6.45 8.94 2.71 1.13

HR-SC-21 3.82 1.29 5.95 8.97 2.40 1.19

HR-SC-22 5.06 1.40 10.8 10.28 4.45 1.39

HR-SC-23 4.61 1.28 9.99 9.61 3.73 1.39

HR-SC-24 3.34 1.40 3.36 7.77 1.62 1.14

HR-SC-25 4.15 1.46 7.26 8.97 2.95 1.17

San Gabriel study area (32 wells sampled) 1

HR-SG-01 4.39 1.37 9.43 8.88 3.58 1.17

HR-SG-02 3.93 1.30 7.08 8.22 3.72 1.12

HR-SG-03 4.38 1.21 13.96 8.17 4.31 1.09

HR-SG-04 2.80 1.18 5.08 6.20 1.78 0.82

HR-SG-05 3.46 1.38 5.10 7.81 2.14 1.34

HR-SG-07 3.63 0.49 18.25 7.77 2.58 1.19

HR-SG-08 3.37 0.79 11.51 7.52 2.06 1.27

HR-SG-09 4.83 1.26 10.37 9.63 3.73 1.33

HR-SG-10 3.19 1.11 6.03 7.08 2.00 1.08

HR-SG-11 3.49 1.07 8.41 7.65 2.61 1.28
Tables 103

Table 13. Results for analyses of dissolved noble gases by the Lawrence Livermore National Laboratory (LLNL) for samples collected 

for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, 

California GAMA Priority Basin Project.—Continued

[Results for noble gas analyses from the LLNL are stored in a separate database maintained by the GAMA Program. Information about the analytes given in 

table 3I. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study 

area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges 

study area understanding well. Other abbreviations: cm3STP/g, cubic centimeters per gram at standard temperature and pressure]

GAMA well 

identification number

Argon 

(104

 cm3STP/g) 

Helium-3/Helium-4 

(106 atom ratio)

Helium-4 

(108 cm3STP/g) 

Krypton 

(108 cm3STP/g) 

Neon 

(107 cm3STP/g) 

Xenon 

(108 cm3STP/g) 

San Gabriel study area (32 wells sampled) 1

—Continued

HR-SG-12 4.39 1.46 8.51 9.25 3.39 1.31

HR-SG-13 3.71 1.31 7.38 8.10 2.81 1.13

HR-SG-14 5.97 1.48 13.27 11.15 6.14 1.50

HR-SG-15 2.90 1.36 3.01 6.89 1.44 0.99

HR-SG-16 4.01 1.20 7.91 9.04 2.80 1.20

HR-SG-17 3.76 0.84 11.54 8.18 2.59 1.15

HR-SG-18 3.04 1.39 4.77 6.76 1.99 0.90

HR-SG-19 3.31 1.41 4.54 7.52 2.02 1.02

HR-SG-20 3.02 1.20 5.41 6.83 2.02 0.94

HR-SG-23 3.01 1.33 4.08 7.00 1.77 0.95

HR-SG-24 3.03 0.20 28.87 6.92 1.95 0.94

HR-SG-26 2.90 1.24 4.46 6.60 1.69 0.92

HR-SG-27 5.10 1.34 11.33 9.55 4.93 1.24

HR-SG-28 3.15 1.37 4.06 7.32 1.81 1.02

HR-SG-29 3.85 1.51 7.34 8.01 2.96 1.10

HR-SG-30 4.50 1.39 8.97 9.03 3.45 1.19

HR-SG-31 3.44 1.34 6.36 7.26 2.60 0.99

HR-SG-32 3.78 1.48 5.42 7.24 2.25 1.03

HR-SG-33 6.69 1.35 16.38 11.82 6.54 1.40

HR-SGU-01 4.30 0.95 13.39 8.67 3.61 1.09

HR-SGU-03 5.66 1.35 17.10 10.03 7.13 1.22

HR-SGU-04 2.76 1.35 3.44 6.55 1.55 0.91

Peninsular Ranges study area (49 wells sampled) 1

HR-PR-01 3.38 1.11 6.27 7.34 2.26 1.03

HR-PR-02 3.27 1.22 5.74 7.26 2.12 0.97

HR-PR-03 4.16 1.52 7.18 9.09 2.72 1.24

HR-PR-04 4.25 0.66 13.58 8.59 3.07 1.21

HR-PR-05 3.72 0.89 8.39 7.78 3.41 1.05

HR-PR-06 3.71 0.16 555 8.07 2.72 1.09

HR-PR-07 3.88 0.89 10.17 7.95 3.00 1.12

HR-PR-08 4.36 1.38 9.47 8.66 3.76 1.16

HR-PR-09 3.95 0.94 9.50 8.56 2.68 1.22

HR-PR-10 9.48 1.30 32.15 18.03 11.66 1.90
104 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 13. Results for analyses of dissolved noble gases by the Lawrence Livermore National Laboratory (LLNL) for samples collected 

for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, 

California GAMA Priority Basin Project.—Continued

[Results for noble gas analyses from the LLNL are stored in a separate database maintained by the GAMA Program. Information about the analytes given in 

table 3I. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study 

area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges 

study area understanding well. Other abbreviations: cm3STP/g, cubic centimeters per gram at standard temperature and pressure]

GAMA well 

identification number

Argon 

(104

 cm3STP/g) 

Helium-3/Helium-4 

(106 atom ratio)

Helium-4 

(108 cm3STP/g) 

Krypton 

(108 cm3STP/g) 

Neon 

(107 cm3STP/g) 

Xenon 

(108 cm3STP/g) 

Peninsular Ranges study area (49 wells sampled) 1

—Continued

HR-PR-06 3.71 0.16 555 8.07 2.72 1.09

HR-PR-07 3.88 0.89 10.17 7.95 3.00 1.12

HR-PR-08 4.36 1.38 9.47 8.66 3.76 1.16

HR-PR-09 3.95 0.94 9.50 8.56 2.68 1.22

HR-PR-10 9.48 1.30 32.15 18.03 11.66 1.90

HR-PR-11 5.16 1.23 12.83 9.58 4.45 1.21

HR-PR-12 4.04 1.40 8.03 7.85 3.20 1.08

HR-PR-13 3.51 1.43 5.43 7.33 2.59 1.01

HR-PR-14 3.30 1.38 5.35 6.98 2.18 0.94

HR-PR-15 4.20 1.31 7.18 9.32 2.93 1.26

HR-PR-16 3.54 0.24 39.64 7.76 2.56 0.98

HR-PR-17 3.19 0.19 37.60 7.13 2.12 0.92

HR-PR-18 4.31 0.27 58.62 8.54 4.12 1.03

HR-PR-19 3.28 0.96 6.46 7.59 1.96 1.02

HR-PR-20 3.19 1.36 4.67 7.37 1.96 0.96

HR-PR-21 4.58 1.06 12.30 8.97 3.94 1.12

HR-PR-22 3.88 0.68 23.29 7.82 3.17 1.08

HR-PR-23 3.65 0.58 261 7.81 2.49 1.05

HR-PR-24 3.34 1.14 7.15 7.24 2.22 0.96

HR-PR-25 3.29 1.38 5.58 7.16 2.33 0.92

HR-PR-26 3.88 1.35 6.75 8.50 2.89 1.11

HR-PR-27 4.42 1.41 27.98 9.28 3.33 1.28

HR-PR-28 3.60 1.30 8.57 8.12 2.42 1.13

HR-PR-29 4.03 0.30 39.88 7.83 3.17 1.00

HR-PR-30 3.80 1.06 7.08 7.57 2.43 1.03
Tables 105

Table 13. Results for analyses of dissolved noble gases by the Lawrence Livermore National Laboratory (LLNL) for samples collected 

for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, 

California GAMA Priority Basin Project.—Continued

[Results for noble gas analyses from the LLNL are stored in a separate database maintained by the GAMA Program. Information about the analytes given in 

table 3I. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study 

area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges 

study area understanding well. Other abbreviations: cm3STP/g, cubic centimeters per gram at standard temperature and pressure]

GAMA well 

identification number

Argon 

(104

 cm3STP/g) 

Helium-3/Helium-4 

(106 atom ratio)

Helium-4 

(108 cm3STP/g) 

Krypton 

(108 cm3STP/g) 

Neon 

(107 cm3STP/g) 

Xenon 

(108 cm3STP/g) 

Peninsular Ranges study area (49 wells sampled) 1

—Continued

HR-PR-31 3.66 0.40 17.91 7.78 2.43 1.15

HR-PR-32 4.77 1.36 13.15 9.37 4.64 1.16

HR-PR-33 4.07 1.37 9.31 7.81 4.02 1.05

HR-PR-34 3.12 1.39 28.02 6.58 2.14 0.94

HR-PR-35 3.74 1.36 4.50 7.79 2.20 1.12

HR-PR-36 3.63 1.22 8.40 8.33 2.24 1.24

HR-PRFP-01 3.68 0.31 135 8.07 2.49 1.08

HR-PRFP-02 4.41 0.91 15.59 7.87 4.58 1.03

HR-PRFP-03 4.16 0.25 42.69 8.19 3.63 1.08

HR-PRFP-04 3.90 0.69 13.41 7.76 2.85 1.03

HR-PRFP-05 3.74 0.33 36.33 6.80 3.81 0.96

HR-PRFP-06 4.02 0.19 147 7.62 3.41 1.01

HR-PRFP-07 4.57 0.39 36.31 9.30 3.35 1.25

HR-PRFP-08 3.70 0.09 248 8.28 2.41 1.17

HR-PRFP-09 3.95 0.24 58.91 7.83 3.22 1.02

HR-PRFP-10 4.71 0.73 14.16 9.41 3.79 1.21

HR-PRFP-11 3.89 1.29 6.97 8.06 2.70 1.04

HR-PRFP-12 3.35 1.11 10.81 7.15 2.41 0.92

HR-PRU-01 10.00 1.31 59.07 20.47 19.76 2.08

1

 Samples were not collected for analyses of dissolved noble gases at HR-SC-13, HR-SG-06, HR-SG-21, and HR-SGU-02, due to lack of back pressure, at 

HR-SC-09 and HR-SG-25 due to suspected aeration at sample point, and at HR-PRFP-13 due to short run time at the well. No result reported for HR-SG-22.
106 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 14A. Radon-222 detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard 

Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 105 wells were analyzed. Information about the analytes are given in table 3H. The reporting levels for radioactive constituents are given as 

sample-specific critical levels (ssLC). GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; 

HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path 

well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benchmark type, and benchmark level as of July 6, 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-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CSU, 1-sigma 

combined standard uncertainty; pCi/L, picocuries per liter; ±, plus or minus; *, value above benchmark level]

GAMA well 

identification 

number

Radon-222 

(pCi/L) 

(82303)

Benchmark type Proposed MCL-US

Benchmark level 4,000

Result ± CSU ssLC

Santa Cruz study area (23 wells sampled) 1

HR-SC-01 92 ± 10 11

HR-SC-02 412 ± 26 10

HR-SC-03 1,633 ± 90 10

HR-SC-04 343 ± 23 13

HR-SC-05 1,169 ± 66 11

HR-SC-06 808 ± 48 13

HR-SC-07 178 ± 15 13

HR-SC-08 476 ± 30 12

HR-SC-09 107 ± 11 12

HR-SC-10 1,116 ± 63 11

HR-SC-11 58.1 ± 9.5 12

HR-SC-12 160 ± 13 11

HR-SC-14 1,084 ± 61 11

HR-SC-15 691 ± 41 11

HR-SC-16 792 ± 47 13

HR-SC-17 915 ± 53 13

HR-SC-18 395 ± 25 11

HR-SC-20 405 ± 27 14

HR-SC-21 633 ± 38 13

HR-SC-22 177 ± 15 14

HR-SC-23 142 ± 14 13

HR-SC-24 433 ± 27 12

HR-SC-25 292 ± 20 10

San Gabriel study area (33 wells sampled) 2

HR-SG-01 571 ± 36 14

HR-SG-02 446 ± 29 14

HR-SG-03 42.9 ± 8.8 12

HR-SG-04 720 ± 43 14

HR-SG-05 804 ± 47 12

GAMA well 

identification 

number

Radon-222 

(pCi/L) 

(82303)

Benchmark type Proposed MCL-US

Benchmark level 4,000

Result ± CSU ssLC

San Gabriel study area (33 wells sampled) 2—Continued

HR-SG-07 * 4,590 ± 250 11

HR-SG-08 72.3 ± 9.1 11

HR-SG-09 319 ± 21 11

HR-SG-10 1,330 ± 74 11

HR-SG-11 1,245 ± 70 11

HR-SG-12 330 ± 22 11

HR-SG-13 724 ± 42 11

HR-SG-14 526 ± 32 11

HR-SG-15 247 ± 19 13

HR-SG-16 648 ± 39 13

HR-SG-17 * 10,540 ± 560 12

HR-SG-18 930 ± 0.53 12

HR-SG-19 227 ± 17 12

HR-SG-20 302 ± 23 16

HR-SG-22 375 ± 24 12

HR-SG-23 582 ± 35 12

HR-SG-24 1,099 ± 62 11

HR-SG-26 369 ± 24 11

HR-SG-27 3,350 ± 180 11

HR-SG-28 243 ± 17 11

HR-SG-29 1,508 ± 84 12

HR-SG-30 225 ± 17 12

HR-SG-31 539 ± 33 12

HR-SG-32 2,190 ± 120 11

HR-SG-33 706 ± 42 14

HR-SGU-01 1,810 ± 180 14

HR-SGU-02 138 ± 12 11

HR-SGU-04 478 ± 30 12
Tables 107

Table 14A. Radon-222 detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard 

Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 105 wells were analyzed. Information about the analytes are given in table 3H. The reporting levels for radioactive constituents are given as 

sample-specific critical levels (ssLC). GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San Gabriel study area grid well; 

HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular Ranges study area flow-path 

well; HR-PRU, Peninsular Ranges study area understanding well. Reporting level, benchmark type, and benchmark level as of July 6, 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-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CSU, 1-sigma 

combined standard uncertainty; pCi/L, picocuries per liter; ±, plus or minus; *, value above benchmark level]

GAMA well 

identification 

number

Radon-222 

(pCi/L) 

(82303)

Benchmark type Proposed MCL-US

Benchmark level 4,000

Result ± CSU ssLC

Peninsular Ranges study area (49 wells sampled) 3

HR-PR-01 1,850 ± 100 13

HR-PR-02 190 ± 16 13

HR-PR-03 1,028 ± 59 13

HR-PR-04 2,270 ± 130 13

HR-PR-05 394 ± 26 14

HR-PR-06 1,480 ± 82 12

HR-PR-07 996 ± 58 16

HR-PR-08 54 ± 10 14

HR-PR-09 876 ± 51 13

HR-PR-10 799 ± 47 14

HR-PR-11 525 ± 33 14

HR-PR-12 168 ± 14 12

HR-PR-13 162 ± 14 12

HR-PR-14 780 ± 45 11

HR-PR-15 3,490 ± 190 14

HR-PR-16 1,725 ± 96 12

HR-PR-17 2,510 ± 140 12

HR-PR-18 3,370 ± 180 11

HR-PR-19 * 5,780 ± 310 14

HR-PR-20 1,427 ± 80 12

HR-PR-21 * 7,740 ± 420 13

HR-PR-22 3,240 ± 180 11

HR-PR-23 2,420 ± 130 11

HR-PR-24 1,084 ± 62 13

HR-PR-25 224 ± 17 13

HR-PR-26 1,584 ± 88 11

HR-PR-27 431 ± 27 11

GAMA well 

identification 

number

Radon-222 

(pCi/L) 

(82303)

Benchmark type Proposed MCL-US

Benchmark level 4,000

Result ± CSU ssLC

Peninsular Ranges study area (49 wells sampled) 3—Continued

HR-PR-28 603 ± 37 13

HR-PR-29 3,090 ± 170 11

HR-PR-30 2,190 ± 120 11

HR-PR-31 * 4,170 ± 230 11

HR-PR-32 259 ± 18 12

HR-PR-33 842 ± 49 12

HR-PR-34 85 ± 10 12

HR-PR-35 809 ± 47 11

HR-PR-36 75.0 ± 9.5 11

HR-PRFP-01 1,363 ± 77 14

HR-PRFP-02 934 ± 54 13

HR-PRFP-03 * 4,870 ± 260 12

HR-PRFP-04 * 4,280 ± 230 11

HR-PRFP-05 2,340 ± 130 14

HR-PRFP-06 * 5,070 ± 270 14

HR-PRFP-07 1,742 ± 96 12

HR-PRFP-08 876 ± 51 13

HR-PRFP-09 * 4,990 ± 270 13

HR-PRFP-10 * 17,200 ± 920 11

HR-PRFP-11 394 ± 27 16

HR-PRFP-12 441 ± 28 13

HR-PRU-01 1,910 ± 110 14

1

 Samples for HR-SC-13 and HR-SC-19 could not be collected with 

equipment available onsite.

2

 Samples for HR-SG-06, HR-SG-21, and HR-SG-25, could not be 

collected due to low groundwater flow or significant interaction between 

groundwater and atmosphere. Sample for HR-SGU-03 was not analyzed due 

to shipping error.

3

 Sample for HR-PRFP-13 could not be collected before well shut off.
108 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 14B. Gross alpha and gross beta radioactivity detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed. Information about the analytes given in table 3H. The reference nuclide for measurement of gross alpha radioactivity is 

thorium-230, and the reference nuclide for measurement of gross beta radioactivity is cesium-137. The reporting levels for radioactive constituents are given as 

sample-specific critical levels (ssLC). Measured values less than the ssLC are reported as not detected (—). GAMA well identification number: HR-SC, Santa 

Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area 

grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark 

types, and benchmark levels as of July 6, 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-US, U.S. Environmental Protection Agency 

maximum contaminant level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: CSU, 1-sigma 

combined standard uncertainty; pCi/L, picocuries per liter; ±, plus or minus; na, not available; *, value above benchmark level]

GAMA 

well 

identification 

number

Gross alpha radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha radioactivity, 

30-day count 

(pCi/L) 

(62639)

Gross beta radioactivity, 

72-hour count 

(pCi/L) 

(62642)

Gross beta radioactivity, 

30-day count 

(pCi/L) 

(62645)

Benchmark type MCL-US 1 MCL-US 1 MCL-CA MCL-CA

Benchmark level 15 15 50 50

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

Santa Cruz study area (25 wells sampled)

HR-SC-01 — 0.27 — 0.48 — 0.47 0.5 ± 0.3 0.47

HR-SC-02 0.8 ± 0.4 0.46 — 0.51 2.64 ± 0.43 0.61 1.95 ± 0.38 0.53

HR-SC-03 — 1.1 2.55 ± 0.84 0.88 2.54 ± 0.38 0.53 2.4 ± 0.35 0.47

HR-SC-04 2.17 ± 0.93 2 1.1 2.1 ± 0.97 1.1 2.5 ± 0.39 0.52 2.66 ± 0.39 0.52

HR-SC-05 10.5 ± 1.3 0.28 0.76 ± 0.36 0.44 4.84 ± 0.48 0.53 2.65 ± 0.37 0.51

HR-SC-06 1.18 ± 0.37 0.32 0.91 ± 0.39 0.45 1.5 ± 0.33 0.48 0.70 ± 0.32 0.49

HR-SC-07 4.5 ± 1.6 1.7 — 2 4.3 ± 0.6 0.74 3.99 ± 0.73 1

HR-SC-08 3 ± 0.63 0.5 0.70 ± 0.37 0.45 2.08 ± 0.34 0.46 1.45 ± 0.34 0.49

HR-SC-09 — 1.3 — 3 1.8 1.04 ± 0.36 0.56 1.3 ± 0.4 4 0.6

HR-SC-10 — 0.4 — 0.36 — 0.43 — 0.45

HR-SC-11 2.47 ± 0.65 0.49 — 0.97 1.16 ± 0.48 0.74 0.9 ± 0.5 0.84

HR-SC-12 — 0.75 — 0.89 — 0.83 — 0.91

HR-SC-13 — 0.38 — 0.4 — 0.47 — 0.49

HR-SC-14 1.24 ± 0.45 0.46 1.16 ± 0.47 0.5 1.65 ± 0.48 0.73 1.71 ± 0.56 0.85

HR-SC-15 11.2 ± 1.6 0.68 10.1 ± 1.5 0.64 3.62 ± 0.47 0.59 5.3 ± 0.56 0.62

HR-SC-16 2.63 ± 0.49 0.27 — 0.34 2.94 ± 0.35 0.42 2 ± 0.32 0.43

HR-SC-17 — 0.23 — 0.25 — 0.42 0.92 ± 0.27 0.41

HR-SC-18 1.29 ± 0.37 0.35 0.51 ± 0.28 0.37 1.2 ± 0.31 0.46 1.41 ± 0.29 0.41

HR-SC-19 2.2 ± 0.78 0.9 — 0.77 4.5 ± 0.6 0.78 4.51 ± 0.84 1.2

HR-SC-20 — 1.9 — 2.1 0.95 ± 0.55 0.84 0.84 ± 0.42 0.66

HR-SC-21 — 1.6 — 1.5 11.9 ± 0.86 0.62 9.92 ± 0.74 0.62

HR-SC-22 — 2, 3 1.5 — 3 1.5 1.69 ± 0.37 2 0.54 1.48 ± 0.46 0.69

HR-SC-23 — 2 1.2 — 1.3 4.36 ± 0.48 2 0.58 4.1 ± 0.42 0.48

HR-SC-24 6.2 ± 2.1 2.4 — 2.3 2.33 ± 0.66 0.97 3.55 ± 0.58 0.8

HR-SC-25 1.25 ± 0.31 0.25 — 0.36 0.89 ± 0.28 0.42 0.54 ± 0.27 0.42
Tables 109

Table 14B. Gross alpha and gross beta radioactivity detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—

Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed. Information about the analytes given in table 3H. The reference nuclide for measurement of gross alpha radioactivity is 

thorium-230, and the reference nuclide for measurement of gross beta radioactivity is cesium-137. The reporting levels for radioactive constituents are given as 

sample-specific critical levels (ssLC). Measured values less than the ssLC are reported as not detected (—). GAMA well identification number: HR-SC, Santa 

Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area 

grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark 

types, and benchmark levels as of July 6, 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-US, U.S. Environmental Protection Agency 

maximum contaminant level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: CSU, 1-sigma 

combined standard uncertainty; pCi/L, picocuries per liter; ±, plus or minus; na, not available; *, value above benchmark level]

GAMA 

well 

identification 

number

Gross alpha radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha radioactivity, 

30-day count 

(pCi/L) 

(62639)

Gross beta radioactivity, 

72-hour count 

(pCi/L) 

(62642)

Gross beta radioactivity, 

30-day count 

(pCi/L) 

(62645)

Benchmark type MCL-US 1 MCL-US 1 MCL-CA MCL-CA

Benchmark level 15 15 50 50

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

San Gabriel study area (36 wells sampled) 5

HR-SG-01 — 1.2 — 1.3 1.82 ± 0.32 0.44 1.96 ± 0.38 0.53

HR-SG-02 6.8 ± 1.3 0.86 5.2 ± 1.1 0.8 3.06 ± 0.49 0.66 5.05 ± 0.46 0.47

HR-SG-03 0.7 ± 0.5 0.68 — 0.96 1.4 ± 0.7 1.1 1.49 ± 0.47 0.71

HR-SG-04 5.8 ± 1.7 1.9 4.7 ± 1.2 1.1 0.84 ± 0.38 0.58 3.31 ± 0.48 0.64

HR-SG-05 6.0 ± 1.2 0.86 6 ± 1.1 0.72 1.92 ± 0.66 0.99 3.01 ± 0.62 0.88

HR-SG-06 7 ± 1 0.56 7 ± 1 0.44 4.58 ± 0.47 0.54 6.2 ± 0.5 0.42

HR-SG-07 *58.9 ± 6.4 0.46 *43.6 ± 4.8 0.44 2.8 ± 0.5 0.64 18 ± 1.1 0.45

HR-SG-08 5.5 ± 1.6 6 1.8 2.3 ± 1.3 6 1.7 8.68 ± 0.69 6 0.65 9.86 ± 0.72 6 0.53

HR-SG-09 6.4 ± 1.7 1.7 8.5 ± 1.9 1.5 — 0.63 2.69 ± 0.43 0.57

HR-SG-10 *19.5 ± 2.5 2 0.73 *15.5 ± 2.2 0.98 4.66 ± 0.61 2 0.76 10.5 ± 0.91 0.86

HR-SG-11 14.3 ± 1.8 0.42 8.4 ± 1.2 0.58 1.29 ± 0.35 0.5 4.53 ± 0.45 0.48

HR-SG-12 0.63 ± 0.35 0.43 — 0.86 1.6 ± 0.33 0.46 2.21 ± 0.51 0.8

HR-SG-13 — 0.79 — 0.77 2.83 ± 0.52 0.78 2.09 ± 0.47 0.73

HR-SG-14 3.37 ± 0.78 0.65 1.0 ± 0.5 0.59 3.22 ± 0.49 0.66 2.57 ± 0.52 0.78

HR-SG-15 2.17 ± 0.52 0.47 — 0.56 2.52 ± 0.51 0.73 2.58 ± 0.71 1

HR-SG-16 7.2 ± 1.1 0.5 4.94 ± 0.87 0.5 — 0.65 2.59 ± 0.57 0.79

HR-SG-17 *18.6 ± 2.2 0.43 12.1 ± 1.6 0.45 2.95 ± 0.39 0.46 12.1 ± 0.8 0.46

HR-SG-18 1.18 ± 0.61 0.75 1.37 ± 0.57 0.62 1.39 ± 0.44 0.67 2.29 ± 0.45 0.64

HR-SG-19 — 0.71 — 0.73 3.3 ± 0.5 0.67 3.51 ± 0.52 0.69

HR-SG-20 1.41 ± 0.72 0.95 1.95 ± 0.63 0.66 4.22 ± 0.51 0.61 4.9 ± 0.7 0.91

HR-SG-21 — 0.6 — 3 0.58 — 0.42 — 0.44

HR-SG-22 4.56 ± 0.97 0.78 1.94 ± 0.63 0.64 2.46 ± 0.62 0.86 3.71 ± 0.73 1

HR-SG-23 2.46 ± 0.61 0.55 2.32 ± 0.51 0.37 1.58 ± 0.36 0.52 2.93 ± 0.39 0.54

HR-SG-24 2.98 ± 0.76 0.8 2.3 ± 0.6 0.5 1.9 ± 0.43 0.62 2.04 ± 0.51 0.79

HR-SG-25 3.72 ± 0.63 0.43 2.36 ± 0.52 0.45 2.59 ± 0.35 0.45 3.49 ± 0.38 0.45
110 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 14B. Gross alpha and gross beta radioactivity detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—

Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed. Information about the analytes given in table 3H. The reference nuclide for measurement of gross alpha radioactivity is 

thorium-230, and the reference nuclide for measurement of gross beta radioactivity is cesium-137. The reporting levels for radioactive constituents are given as 

sample-specific critical levels (ssLC). Measured values less than the ssLC are reported as not detected (—). GAMA well identification number: HR-SC, Santa 

Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area 

grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark 

types, and benchmark levels as of July 6, 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-US, U.S. Environmental Protection Agency 

maximum contaminant level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: CSU, 1-sigma 

combined standard uncertainty; pCi/L, picocuries per liter; ±, plus or minus; na, not available; *, value above benchmark level]

GAMA 

well 

identification 

number

Gross alpha radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha radioactivity, 

30-day count 

(pCi/L) 

(62639)

Gross beta radioactivity, 

72-hour count 

(pCi/L) 

(62642)

Gross beta radioactivity, 

30-day count 

(pCi/L) 

(62645)

Benchmark type MCL-US 1 MCL-US 1 MCL-CA MCL-CA

Benchmark level 15 15 50 50

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

San Gabriel study area (36 wells sampled) 5—Continued

HR-SG-26 — 0.73 0.68 ± 0.38 0.46 — 0.53 3.05 ± 0.48 0.67

HR-SG-27 11.3 ± 1.4 0.51 11.1 ± 1.7 0.62 2.18 ± 0.37 0.49 6.77 ± 0.62 0.59

HR-SG-28 1.8 ± 0.77 0.77 — 0.93 2.14 ± 0.56 0.76 3.0 ± 0.5 0.65

HR-SG-29 *15.4 ± 2.1 0.83 6.8 ± 1.2 0.69 4.37 ± 0.69 0.9 5.83 ± 0.91 1.2

HR-SG-30 1.92 ± 0.73 0.93 1.32 ± 0.57 0.62 — 0.81 1.05 ± 0.65 1

HR-SG-31 3 ± 0.86 0.79 1.32 ± 0.76 0.94 1.75 ± 0.56 0.89 2.06 ± 0.66 1

HR-SG-32 1.25 ± 0.37 0.4 1.21 ± 0.49 0.53 1 ± 0.29 0.43 0.7 ± 0.4 0.61

HR-SG-33 6.1 ± 1.5 1.4 2.7 ± 1.3 1.6 1.9 ± 0.35 0.49 2.56 ± 0.42 0.58

HR-SGU-01 *18.9 ± 2.7 0.93 9.1 ± 1.6 0.91 7.6 ± 1.1 1.4 9.23 ± 0.75 0.68

HR-SGU-02 4.7 ± 1.1 0.74 2.5 ± 0.7 0.64 1.2 ± 0.5 0.74 2.85 ± 0.48 0.63

HR-SGU-04 1.14 ± 0.56 0.71 3.0 ± 0.9 0.77 1.2 ± 0.4 0.59 2.78 ± 0.57 0.81

Peninsular Ranges study area (49 wells sampled) 5

HR-PR-01 7.2 ± 1.2 0.99 4.7 ± 1.2 1.1 3.06 ± 0.39 0.48 6.02 ± 0.64 0.69

HR-PR-02 — 0.99 — 0.81 4.05 ± 0.64 0.9 4.95 ± 0.84 1.2

HR-PR-03 0.62 ± 0.25 0.27 — 0.55 2.64 ± 0.38 0.51 2.2 ± 0.5 0.71

HR-PR-04 2.98 ± 0.86 0.76 0.96 ± 0.51 0.58 6.1 ± 0.6 0.62 5.51 ± 0.58 0.62

HR-PR-05 — 0.74 0.62 ± 0.36 0.38 1.94 ± 0.44 0.63 1.78 ± 0.45 0.68

HR-PR-06 9.5 ± 1.5 0.77 1.26 ± 0.66 0.85 2.57 ± 0.57 0.81 — 1

HR-PR-07 *31 ± 5.3 3.8 14.7 ± 3.1 2 5.96 ± 0.96 1.3 11.6 ± 1.2 1.3

HR-PR-08 0.45 ± 0.33 0.43 — 0.62 — 0.64 — 0.63

HR-PR-09 — 0.5 — 0.52 1 ± 0.32 0.49 1.43 ± 0.43 0.63

HR-PR-10 — 0.95 — 0.99 2.59 ± 0.52 2 0.74 3.27 ± 0.58 0.79
Tables 111

Table 14B. Gross alpha and gross beta radioactivity detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—

Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed. Information about the analytes given in table 3H. The reference nuclide for measurement of gross alpha radioactivity is 

thorium-230, and the reference nuclide for measurement of gross beta radioactivity is cesium-137. The reporting levels for radioactive constituents are given as 

sample-specific critical levels (ssLC). Measured values less than the ssLC are reported as not detected (—). GAMA well identification number: HR-SC, Santa 

Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area 

grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark 

types, and benchmark levels as of July 6, 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-US, U.S. Environmental Protection Agency 

maximum contaminant level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: CSU, 1-sigma 

combined standard uncertainty; pCi/L, picocuries per liter; ±, plus or minus; na, not available; *, value above benchmark level]

GAMA 

well 

identification 

number

Gross alpha radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha radioactivity, 

30-day count 

(pCi/L) 

(62639)

Gross beta radioactivity, 

72-hour count 

(pCi/L) 

(62642)

Gross beta radioactivity, 

30-day count 

(pCi/L) 

(62645)

Benchmark type MCL-US 1 MCL-US 1 MCL-CA MCL-CA

Benchmark level 15 15 50 50

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

Peninsular Ranges study area (49 wells sampled) 5—Continued

HR-PR-11 3 ± 1 1.1 — 1.1 7.96 ± 0.78 0.8 2.21 ± 0.66 0.99

HR-PR-12 1.55 ± 0.77 0.96 1.4 ± 0.91 1.2 — 1.3 — 1.1

HR-PR-13 4.3 ± 1.9 2.2 3.2 ± 1.7 2.2 5.06 ± 0.71 0.89 6.03 ± 0.82 1

HR-PR-14 3.82 ± 0.98 0.98 3.56 ± 0.93 0.95 2.72 ± 0.67 0.99 4.92 ± 0.61 0.8

HR-PR-15 — 0.62 0.72 ± 0.44 0.52 3.38 ± 0.52 0.67 3.94 ± 0.51 0.61

HR-PR-16 5.3 ± 1.5 1.6 — 2 4.2 ± 0.5 0.65 3.9 ± 0.43 0.5

HR-PR-17 *27.1 ± 3.3 0.83 *17.2 ± 2.3 0.76 4.2 ± 0.6 0.76 11.9 ± 0.89 0.68

HR-PR-18 *73.9 ± 8.5 1.6 *28.6 ± 3.8 1.4 14.8 ± 1.1 0.7 15.6 ± 0.99 0.5

HR-PR-19 5.1 ± 1.1 0.8 3.18 ± 0.86 0.75 3.74 ± 0.53 0.65 6.82 ± 0.71 0.75

HR-PR-20 1.86 ± 0.54 0.5 2.79 ± 0.85 0.77 1.42 ± 0.33 0.48 1.44 ± 0.47 0.69

HR-PR-21 *97 ± 11 2.1 *44 ± 5.6 2 10.1 ± 0.78 0.57 23.4 ± 1.4 0.54

HR-PR-22 *75 ± 8.4 0.97 *33.8 ± 4.1 0.79 8.9 ± 0.9 0.9 21 ± 1.5 1

HR-PR-23 *18.1 ± 2.3 0.67 1.79 ± 0.68 0.79 12.1 ± 0.9 0.64 8.19 ± 0.75 0.75

HR-PR-24 1.9 ± 1.2 1.6 — 1.7 6 ± 0.68 0.83 6.08 ± 0.64 0.66

HR-PR-25 1.47 ± 0.91 1.2 — 1.3 1.97 ± 0.66 1 2.62 ± 0.71 1.1

HR-PR-26 — 3.8 — 4.1 — 1.3 1.82 ± 0.71 1.1

HR-PR-27 1.04 ± 0.47 0.51 0.61 ± 0.26 0.29 1.08 ± 0.41 0.61 1.67 ± 0.33 0.48

HR-PR-28 1.4 ± 1.1 1.4 1.37 ± 0.76 0.86 8.13 ± 0.62 2 0.5 7.25 ± 0.58 0.51

HR-PR-29 3.76 ± 0.84 0.53 3.1 ± 0.6 0.46 — 0.62 1.01 ± 0.33 0.5

HR-PR-30 3.26 ± 0.87 0.75 1.49 ± 0.57 0.58 2.99 ± 0.51 0.68 4.2 ± 0.6 0.75
112 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 14B. Gross alpha and gross beta radioactivity detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular 

Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—

Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 110 wells were analyzed. Information about the analytes given in table 3H. The reference nuclide for measurement of gross alpha radioactivity is 

thorium-230, and the reference nuclide for measurement of gross beta radioactivity is cesium-137. The reporting levels for radioactive constituents are given as 

sample-specific critical levels (ssLC). Measured values less than the ssLC are reported as not detected (—). GAMA well identification number: HR-SC, Santa 

Cruz study area grid well; HR-SG, San Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area 

grid well; HR-PRFP, Peninsular Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark 

types, and benchmark levels as of July 6, 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-US, U.S. Environmental Protection Agency 

maximum contaminant level; MCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: CSU, 1-sigma 

combined standard uncertainty; pCi/L, picocuries per liter; ±, plus or minus; na, not available; *, value above benchmark level]

GAMA 

well 

identification 

number

Gross alpha radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha radioactivity, 

30-day count 

(pCi/L) 

(62639)

Gross beta radioactivity, 

72-hour count 

(pCi/L) 

(62642)

Gross beta radioactivity, 

30-day count 

(pCi/L) 

(62645)

Benchmark type MCL-US 1 MCL-US 1 MCL-CA MCL-CA

Benchmark level 15 15 50 50

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

Peninsular Ranges study area (49 wells sampled) 5—Continued

HR-PR-31 *21.1 ± 2.6 0.58 *18.8 ± 2.4 0.59 1.34 ± 0.43 0.58 7.58 ± 0.73 0.67

HR-PR-32 0.51 ± 0.32 0.4 0.46 ± 0.28 0.32 — 0.59 — 0.57

HR-PR-33 5.7 ± 1.1 0.68 4 ± 1 1.1 1.56 ± 0.56 0.83 1.97 ± 0.66 0.97

HR-PR-34 6.7 ± 1.3 0.95 5.2 ± 1.2 1.1 1.1 ± 0.6 0.93 1.71 ± 0.56 0.87

HR-PR-35 3.72 ± 0.84 0.5 0.79 ± 0.56 0.71 3.53 ± 0.54 0.7 1.78 ± 0.46 0.72

HR-PR-36 2.14 ± 0.64 0.59 1.33 ± 0.51 0.54 2.95 ± 0.53 0.71 2.0 ± 0.5 0.72

HR-PRFP-01 4.31 ± 0.96 0.85 0.88 ± 0.56 0.68 3.6 ± 0.58 0.84 3.58 ± 0.52 0.69

HR-PRFP-02 *15.5 ± 2.8 2.1 *15.1 ± 2.6 1.5 4.1 ± 0.52 0.65 8.17 ± 0.66 0.58

HR-PRFP-03 9.6 ± 1.7 1.1 6.9 ± 1.3 0.99 6.97 ± 0.84 1 6.9 ± 0.8 1

HR-PRFP-04 *56.6 ± 6.5 1.2 *36.9 ± 4.6 1 3.71 ± 0.78 1.1 14.1 ± 1.2 1

HR-PRFP-05 *29.7 ± 4.3 2.1 14.1 ± 2.5 1.3 6.97 ± 0.67 0.71 13.9 ± 0.97 0.71

HR-PRFP-06 15 ± 2.4 1.6 7.6 ± 1.6 1.2 5.2 ± 0.62 0.7 8.82 ± 0.65 0.49

HR-PRFP-07 14.8 ± 1.9 0.57 2.01 ± 0.73 0.69 7.04 ± 0.58 0.52 4 ± 0.59 0.76

HR-PRFP-08 0.81 ± 0.42 0.47 — 0.67 — 0.69 0.75 ± 0.44 0.68

HR-PRFP-09 *35.1 ± 5.3 2.8 *33 ± 5 2.5 10.4 ± 0.94 0.96 20.7 ± 1.5 1.1

HR-PRFP-10 *378 ± 39 0.5 *214 ± 23 0.78 7.81 ± 0.78 0.59 *94.9 ± 5.3 0.51

HR-PRFP-11 *48 ± 9 6.5 *20.9 ± 6.4 6.3 9.0 ± 1.6 2.2 24 ± 2 1.9

HR-PRFP-12 2.6 ± 1.9 2.6 5.6 ± 1.9 2.1 4.38 ± 0.69 0.94 5.73 ± 0.63 0.71

HR-PRU-01 1.2 ± 0.52 0.54 0.68 ± 0.48 0.62 4.72 ± 0.65 0.85 5.1 ± 0.55 0.59

1

 The MCL-US applies to adjusted gross alpha radioactivity, which is equal to gross alpha activity minus uranium activity. Results were not adjusted for 

uranium activity.

2

 Gross alpha activity (72-hour) holding time exceeded by 4 days from time of sample collection for HR-SC-04 and HR-SG-10; gross beta activity (72-hour) 

holding time exceeded by 4 days from time of sample collection for HR-SG-10, HR-PR-10, and HR-PR-28. Gross alpha and beta activities (72-hour) holding 

times exceeded by 8 days from time of sample collection for HR-SC-22 and HR-SC-23. 

3

 Laboratory comment: negative result may indicate potential negative bias.

4

 Activity for HR-SC-09 was counted 18 days after 72-hour count rather than 30 days.

5

 Samples for HR-SGU-03 and HR-PRFP-13 were not analyzed due to shipping error.

6

 Variability for the HR-SG-08 replicate pair was outside the acceptable limits for all gross alpha and beta radioactivity results. The replicate sample results 

were generally lower than the environmental sample results. See table A4C for results for the replicate pair.
Tables 113

Table 14C. Uranium activities detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock 

Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 29 wells were analyzed. Information about the analytes given in table 3H. The reporting levels for radioactive constituents are given as samplespecific critical levels (ssLC). Measured values less than the ssLC are reported as not detected (—). Only samples with total uranium concentrations (table 8) 

greater than 10 μg/L were analyzed for isotopic composition. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San 

Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular 

Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as 

of July 6, 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-US, U.S. Environmental Protection Agency maximum contaminant level; 

MCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: CSU, 1-sigma combined standard uncertainty; 

pCi/L, picocuries per liter; ±, plus or minus; *, the sum of uranium-234, -235, and -238 concentrations is greater than the benchmark level]

GAMA well 

identification 

number 

Uranium-234 

(pCi/L) 

(22610)

Uranium-235 

(pCi/L) 

(22620)

Uranium-238 

(pCi/L) 

(22603)

Benchmark type MCL-CA MCL-CA MCL-CA

Benchmark level 1

 20 1 20 1 20

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

Santa Cruz study area (5 wells sampled) 2

HR-SC-01 — 0.024 — 0.042 0.045 ± 0.034 0.033

HR-SC-02 — 0.0119 0.018 ± 0.018 0.018 0.03 ± 0.015 0.018

HR-SC-04 0.146 ± 0.041 0.032 — 0.017 0.049 ± 0.025 0.022

San Gabriel study area (9 wells sampled)

HR-SG-02 3.62 ± 0.18 0.019 0.169 ± 0.25 0.013 3.44 ± 0.17 0.016

HR-SG-06 3.13 ± 0.16 0.022 0.13 ± 0.022 0.011 2.97 ± 0.15 0.016

HR-SG-07 * 20.4 ± 0.88 0.034 * 0.975 ± 0.067 0.012 * 19.2 ± 0.83 0.031

HR-SG-10 8.81 ± 0.39 0.025 0.467 ± 0.039 0.011 8.64 ± 0.39 0.023

HR-SG-11 5.04 ± 0.23 0.019 0.245 ± 0.026 0.01 4.4 ± 0.2 0.016

HR-SG-16 3.28 ± 0.16 0.019 0.189 ± 0.024 0.013 3.37 ± 0.16 0.016

HR-SG-17 * 11.5 ± 0.52 0.33 * 0.56 ± 0.05 0.015 * 10.3 ± 0.47 0.031

HR-SG-27 5.8 ± 0.28 0.026 0.187 ± 0.028 0.017 4.33 ± 0.22 0.023

HR-SGU-01 4.91 ± 0.23 0.022 0.281 ± 0.031 0.013 5.2 ± 0.24 0.019

Peninsular Ranges study area (15 wells sampled)

HR-PR-01 4.2 ± 0.2 0.022 0.204 ± 0.024 0.011 3.42 ± 0.17 0.019

HR-PR-07 * 13.7 ± 0.61 0.03 * 0.4 ± 0.043 0.013 * 8.4 ± 0.39 0.027

HR-PR-17 * 10.2 ± 0.47 0.032 * 0.429 ± 0.044 0.018 * 9.55 ± 0.44 0.028

HR-PR-18 * 19.4 ± 0.86 0.031 * 0.422 ± 0.044 0.018 * 8.07 ± 0.38 0.029

HR-PR-21 *29.5 ± 1.2 0.038 * 1.12 ± 0.071 0.012 * 17.8 ± 0.76 0.035

HR-PR-22 * 16.6 ± 0.72 0.036 * 0.825 ± 0.059 0.014 * 17.8 ± 0.77 0.033

HR-PR-31 8.04 ± 0.37 0.027 0.33 ± 0.035 0.017 6.6 ± 0.31 0.024

HR-PRFP-02 6.67 ± 0.31 0.024 0.185 ± 0.029 0.018 4.64 ± 0.25 0.022

HR-PRFP-04 *22.6 ± 0.97 0.031 * 0.922 ± 0.062 0.011 * 12.3 ± 0.54 0.028

HR-PRFP-05 * 11.4 ± 0.5 0.026 * 0.529 ± 0.044 0.012 * 10.2 ± 0.45 0.023
114 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table 14C. Uranium activities detected in samples collected for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock 

Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued

[The five-digit U.S. Geological Survey (USGS) parameter code below the constituent name is used to uniquely identify a specific constituent or property. 

Samples from 29 wells were analyzed. Information about the analytes given in table 3H. The reporting levels for radioactive constituents are given as samplespecific critical levels (ssLC). Measured values less than the ssLC are reported as not detected (—). Only samples with total uranium concentrations (table 8) 

greater than 10 μg/L were analyzed for isotopic composition. GAMA well identification number: HR-SC, Santa Cruz study area grid well; HR-SG, San 

Gabriel study area grid well; HR-SGU, San Gabriel study area understanding well; HR-PR, Peninsular Ranges study area grid well; HR-PRFP, Peninsular 

Ranges study area flow-path well; HR-PRU, Peninsular Ranges study area understanding well. Reporting levels, benchmark types, and benchmark levels as 

of July 6, 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-US, U.S. Environmental Protection Agency maximum contaminant level; 

MCL-CA, California Department of Public Health (CDPH) maximum contaminant level. Other abbreviations: CSU, 1-sigma combined standard uncertainty; 

pCi/L, picocuries per liter; ±, plus or minus; *, the sum of uranium-234, -235, and -238 concentrations is greater than the benchmark level]

GAMA well 

identification 

number 

Uranium-234 

(pCi/L) 

(22610)

Uranium-235 

(pCi/L) 

(22620)

Uranium-238 

(pCi/L) 

(22603)

Benchmark type MCL-CA MCL-CA MCL-CA

Benchmark level 1

 20 1 20 1 20

Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC

Peninsular Ranges study area (15 wells sampled)—Continued

HR-PRFP-06 6.01 ± 0.28 0.026 0.251 ± 0.029 0.017 5.2 ± 0.25 0.023

HR-PRFP-09 * 19.7 ± 0.84 0.026 * 0.59 ± 0.046 0.011 * 13.8 ± 0.6 0.024

HR-PRFP-10 *40.4 ± 1.7 0.035 * 1.35 ± 0.077 0.01 *28.2 ± 1.2 0.033

HR-PRFP-11 *26.7 ± 1.1 0.033 * 1.06 ± 0.07 0.0098 *21.2 ± 0.91 0.03

HR-PRFP-13 * 19.8 ± 0.85 0.029 * 0.716 ± 0.054 0.012 * 15.6 ± 0.68 0.027

1

 The MCL-CA benchmark for uranium is the sum of uranium-234, -235, and -238.

2

 All 25 Santa Cruz study area wells had samples with total uranium concentrations less than 10 micrograms per liter (see table 8). Samples HR-SC-01 

through HR-SC-05 were requested for analysis of uranium isotopic composition by error. HR-SC-01, HR-SC-02, and HR-SC-04 had very low-level uranium 

activities, but are listed in this table for reporting purposes. HR-SC-03 and HR-SC-05 had no detectable uranium activities. 
Appendix 115

Appendix

This appendix includes discussions of the methods used 

to collect and analyze groundwater samples and report the 

resulting water-quality data. These methods were selected to 

obtain representative samples of the groundwater from each 

well and to minimize the potential for contamination of the 

samples or bias in the data. Procedures used to collect and 

assess QC data and the results of the QC assessments also are 

discussed.

In the Hard Rock 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), 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 

by Stevenson (2013).

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, 2006a). 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; in these cases, a minimum of 

one casing volume of groundwater was pumped from each 

well. The limitation on pumping did not allow sufficient time 

to complete the sampling of at least one well, and samples for 

analysis of some constituent groups were not collected from 

these wells (tables 13, 14A). For all sites, field measurements 

of dissolved oxygen, water temperature, pH, and specific 

conductance were recorded at 3 to 5 minute intervals before 

sampling and then checked against the stabilization criteria 

described in the NFM to ensure purging was sufficient (Wilde, 

2008).

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 wellhead as possible. The sampling point was located 

upstream from water-storage tanks and from the wellhead 

treatment system (if present). All samples were collected 

outdoors by connecting a 1- to 3-foot length of Teflon® tubing 

to the sampling point (Lane and others, 2003). All fittings 

and lengths of tubing were cleaned between samples (Wilde, 

2004).

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. In one well, the chlorinator was not shut 

off prior to sampling. In this case, samples for analysis of 

organic constituents (VOCs and pesticides) were collected 

in amber bottles containing ascorbic acid and buffer (Wilde, 

2009).

For the field measurements, groundwater was pumped 

through a flow-through chamber that was attached to the 

sampling point and fitted with a YSI® multi-probe meter that 

simultaneously measured the field water-quality indicators—

dissolved oxygen, temperature, pH, and specific conductance. 

Field measurements were made in accordance with protocols 

in the USGS NFM (Radtke and others, 2005; Lewis, 2006; 

Wilde, 2006b, 2008; Ritz and Collins, 2008). All sensors 

on the multi-probe meter were calibrated daily. Measured 

dissolved oxygen, temperature, pH, and specific conductance 

values were recorded at 5-minute (min) intervals, and when 

these values remained stable for a minimum of 30 min, 

samples for laboratory analyses then were collected. If runtime was limited but the well was used often, then at least five 

values were recorded at 3-min intervals.

Most of the springs were plumbed and had sampling 

points on the discharge pipes similar to the sampling points 

found on discharge pipes from wells. Field water-quality 

indicators were measured and samples were collected by using 

the same protocols as used for wells.

A few springs were not plumbed and discharged into 

pools, from which the water was then pumped into the 

distribution system. For these springs, field water-quality 

parameters were measured by dipping the multi-probe meter 

directly into the water as close to the spring discharge point 

as possible. Groundwater samples were collected by dipping 

bottles into the water as close to the spring discharge point 

as possible. Turbidity was measured in the mobile laboratory 

with a calibrated turbidity meter (Anderson, 2005). For all 

samples collected from springs with pools or low pressure, 

turbidity was less than 0.5 nephelometric turbidity unit (NTU); 

the samples were collected unfiltered, but were marked 

as filtered for analysis. This method was used because the 

alternative—pumping water from a pool with a portable 

peristaltic pump through the filtration apparatus—was not 

logistically possible at most of the unplumbed spring sites.
116 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Field measurements and instrument calibrations were 

recorded by hand on field record sheets and electronically in 

the USGS Personal Computer Field Form (PCFF) program. 

Analytical service requests for the NWQL were generated by 

PCFF, whereas analytical service requests for non-NWQL 

analysis were entered into laboratory-specific spreadsheets. 

Information from PCFF was uploaded into the USGS NWIS 

database 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 by using ampoules 

of certified, traceable concentrated acids obtained from the 

NWQL.

Temperature-sensitive samples were stored on ice prior to 

and during daily shipping to the various laboratories. The nontemperature-sensitive samples for analysis of tritium, stable 

isotopes of hydrogen and oxygen in water, and dissolved 

noble gases were shipped monthly. Temperature-sensitive or 

time-sensitive samples for analysis of VOCs, pesticides and 

pesticide degradates, 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. Temperature-sensitive 

samples to be analyzed for arsenic and iron species and 

non-temperature sensitive samples for analysis of chromium 

species were shipped weekly. 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. Samples 

for analysis of uranium isotopes and isotopes of boron and 

strontium dissolved in water were stored at room temperature 

in the office until all groundwater samples were collected and 

results from the trace-element analyses were obtained; a subset 

of samples was selected for analyses, based on total uranium, 

boron, or strontium concentrations.

Detailed sampling protocols for individual analyses and 

groups of analytes are described in Koterba and others (1995), 

the NFM (Wilde, 2009), and in the references for analytical 

methods listed in table A1; brief descriptions, in the order of 

sample collection, are given here.

Samples for the analysis of VOCs were collected in 

three 40-milliliter (mL) sample vials that were purged with 

three vial volumes of unfiltered groundwater before bottomfilling to eliminate atmospheric contamination. One to one 

(1:1) hydrochloric acid to water solution was added as a 

preservative to these samples. Samples for the analysis of 

pesticides and pesticide degradates were collected in 1-L 

baked amber glass bottles. These samples were filtered 

through a 0.7-micrometer (μm) nominal pore-size glass fiber 

filter during collection.

Samples for the analysis of perchlorate were collected 

in a 125-mL polystyrene bottle and then filtered in two or 

three 20-mL aliquots through a 0.20-μm pore-size Corning®

syringe-tip disk filter into a sterilized 125-mL bottle. 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 the analysis of tritium were collected by bottomfilling 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 the analysis of trace elements, major and 

minor ions, silica, laboratory alkalinity, and TDS required 

filling one 250-mL polyethylene bottle with unfiltered 

groundwater and one 500-mL and one 250-mL polyethylene 

bottle with filtered groundwater. 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 the analysis of gross alpha and gross beta 

particle activities and uranium isotopes were filtered into 

1-L polyethylene bottles and acidified with 7.5-N nitric acid. 

Samples for the analysis of arsenic and iron species were 

filtered into two 250-mL polyethylene bottles that were 

wrapped with black plastic to prevent light exposure and 

preserved with 6-N hydrochloric acid. Samples for the analysis 

of isotopes of dissolved boron and strontium in water were 

filtered into 250-mL polyethylene bottles and secured with 

electrical tape to prevent leakage and evaporation. Samples for 

the analysis of stable isotopes of carbon in dissolved inorganic 

carbon and carbon-14 abundance were filtered and bottomfilled into 500-mL glass bottles that first were overfilled with 

three bottle volumes of filtered groundwater. Carbon isotope 

samples had no headspace and were sealed with conical caps 

to avoid atmospheric contamination.

Samples for field alkalinity titrations were collected 

by filtering groundwater into a 250-mL polyethylene bottle. 

Field alkalinity was measured in the mobile laboratory at 

the well site by using Gran’s titration method (Gran, 1952). 

Titration data were entered into PCFF, and the alkalinity and 

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 

(Stumm and Morgan, 1996).

Samples for the analysis of chromium species were 

collected at the wellhead by using a 10-mL syringe with an 

attached 0.45-μm pore-size Millex-HA disk filter. After the 

syringe was rinsed thoroughly and filled with groundwater, 

the first 4 mL of water were forced through the filter to waste 
Appendix 117

(to condition the filter), and the next 2 mL were filtered slowly 

into a small centrifuge vial for analysis of total chromium. 

Hexavalent chromium then was collected by attaching a 

small cation-exchange column to the syringe filter and, after 

conditioning the column with 2 mL of sample water, an 

additional 2 mL of sample water was collected in a second 

centrifuge vial. Both vials were preserved with 10 microliters 

(μL) of 7.5-N nitric acid (Ball and McClesky, 2003a, b).

For the collection of groundwater samples for the 

analysis of radon-222, a stainless-steel and Teflon® valve 

assembly was attached to the sampling port at the wellhead. 

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 20-mL vial partially filled with a scintillation mixture 

(mineral oil and 1,2,4-trimethylbenzene) and shaken. The vial 

was sealed and placed in an insulated cardboard tube to protect 

the sample during shipping. 

Samples for analysis of dissolved noble gases were 

collected in 3⁄8-inch-diameter copper tubes by using reinforced 

nylon tubing connected to the hose bib at the wellhead. 

Groundwater was flushed through the tubing to dislodge 

bubbles before the flow was restricted with a back-pressure 

valve. Clamps on either side of the copper tube then were 

tightened, trapping a sample of groundwater for analyses of 

dissolved noble gases (Weiss, 1968).

Nine laboratories performed chemical analyses for 

this study (table A1), although most of the analyses were 

performed at the NWQL or by laboratories contracted by 

the NWQL. The NWQL maintains a rigorous QA program 

(Stevenson, 2013). 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 waterquality measurements (http://bqs.usgs.gov/nfqa/). Results for 

analyses made at the NWQL or by laboratories contracted 

by the NWQL are uploaded directly into the USGS NWIS 

database. Results of analyses made at other laboratories are 

compiled in a project database and uploaded from there into 

the USGS NWIS database. The data are available through the 

USGS NWIS website (http://waterdata.usgs.gov/nwis) and 

the SWRCB’s GeoTracker GAMA database (http://geotracker.

waterboards.ca.gov/gama/).

Data Reporting

The following sections give details for the laboratory 

reporting conventions and determination of constituents by 

multiple methods or laboratories.

Reporting Levels

The laboratory reporting level (LRL) and long-term 

method detection level (LT-MDL) are most commonly 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 a 1-percent chance of a false positive) (Childress and 

others, 1999; U.S. Environmental Protection Agency, 2002).

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). Estimated concentrations 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. For 

concentrations of VOCs and pesticides less than the LT-MDL, 

some values are also E-coded because there is a high certainty 

of detection but the precision in the result is uncertain. 

Methods used to analyze VOCs and pesticides are considered 

to be information-rich because they use gas chromatography 

or high-performance liquid chromatography (HPLC) with 

mass spectrometry detection. 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 

(Childress and others, 1999). Organic constituents not detected 

by the NWQL are reported in the NWIS database as less than 

the associated reporting level (<LRL) and as nondetections (–) 

in this report.

E-coding is not applied to results for inorganic 

constituents with concentrations between the LRL and 

LT-MDL. The LT-MDL is generally the level used by the 

NWQL for reporting analytical results of inorganics, with 

the following exceptions: the MDL is used by the NWQL for 

reporting bromide and nitrite and by the USGS Trace Metal 

Laboratory for reporting arsenic, chromium, and iron species. 

Nitrate plus nitrite is reported using the interim reporting level 

(IRL) starting October 17, 2011, following the implementation 

at the NWQL of a new method for determining nitrate 

plus nitrite in filtered water by enzymatic reduction using 
118 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

discrete analysis (Patton and Krystalla, 2011). The minimum 

reporting level (MRL) is used by the NWQL for reporting 

total dissolved solids and by the Weck Laboratory for 

reporting perchlorate. The MRL is the smallest measurable 

concentration of a constituent that may be reliably reported by 

using a given analytical method (Timme, 1995). Constituents 

not detected by the laboratories are reported in the NWIS 

database as less than the associated reporting level (<LT-MDL, 

<MDL, <IRL, or <MRL) and as nondetections (–) in this 

report.

The reporting levels listed in this report were in effect 

during the period that analyses were made for groundwater 

samples from the Hard Rock study unit. The USGS NWQL 

updates reporting level values for each constituent at least 

once a year. On October 1, 2011, reporting levels changed 

for some organic and inorganic constituents. Both values for 

each constituent are reported in tables 3A, B, D, E, and F, and 

the higher of the two values is reported with the groundwater 

quality data in tables 5, 6, 8, 9, and 10.

Results for some organic and inorganic constituents 

are presented by using SRLs derived from assessment of 

data from QC samples associated with groundwater samples 

collected as part of the GAMA-PBP (see the appendix section 

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

Isotopes of hydrogen, oxygen, carbon, boron, and 

strontium are reported by 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 is expected to be found.

The reporting limits for radiochemical constituents 

(carbon-14, tritium, radon-222, gross alpha and gross beta 

radioactivity, and uranium isotopes) are based on samplespecific 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 nondetections.

The analytical uncertainties associated with measurement 

of activities also are sensitive to sample-specific parameters, 

including sample size, sample yield during analytical 

processing, and time elapsed between sample collection and 

various steps in the analytical procedure, as well as parameters 

associated with the instrumentation. Therefore, measured 

activities of radioactive constituents are reported with samplespecific combined standard uncertainties (CSU). 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.

Notation

Stable isotopic compositions of oxygen, carbon, boron, 

and hydrogen are reported as relative isotope ratios in units of 

per mil using the standard delta notation (Coplen and others, 

2002; Coplen, 2011):

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, 

B for boron, C for carbon);

Rsample is the ratio of the abundance of the heavier 

isotope of the element (2H, 18O, 11B, 13C) to 

the lighter isotope of the element (1H, 16O, 10B, 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; Coplen, 2011). 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; Coplen, 2011). 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. The isotopic composition of 

boron is similarly presented as a ratio of the abundance of 

boron-11 to boron-10 relative to the reference material. The 

isotopic composition of strontium is presented as the ratio of 

the abundance of atoms of the heavier isotope (strontium-87) 

to the lighter isotope (strontium-86) of the element. Strontium 

and boron isotope data were not available for inclusion in this 

report and will be presented in a subsequent report.

Constituents on Multiple Analytical Schedules

Seven constituents targeted in this study were measured 

by more than one analytical method or by more than one 

laboratory (table A2). The preferred analytical methods 
Appendix 119

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.

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

specific conductance—were measured in the field and at the 

NWQL (table 4). Field measurements generally are considered 

more representative of groundwater conditions than laboratory 

measurements because the amount of time is limited for 

reactions to occur in the water sample after exposure to the 

atmosphere (Hem, 1985). Field values of pH and specific 

conductance were measured at each Hard Rock site. Field 

alkalinities were measured at only 15 percent of the Hard 

Rock sites due to time constraints; however, the data confirm 

that differences between laboratory and field alkalinity values 

are negligible for the purpose of this study.

For total arsenic, chromium, and iron concentrations, 

the approved method used by the NWQL, Schedule 1948 

(table 3D), is preferred over the research methods used by the 

USGS Trace Metal Laboratory (table 3G). The concentrations 

measured by the Trace Metal Laboratory are only used to 

calculate ratios of redox species for arsenic, chromium, and 

iron. For example,

Cr III

Cr VI

Cr T Cr VI

Cr VI

( )

( )

( ) ( )

( ) = − , (A2)

where Cr(T) is the total chromium concentration 

(measured);

Cr(VI) is the concentration of hexavalent chromium 

(measured); and

Cr(III) is the concentration of trivalent chromium 

(calculated).

Tritium was measured at two laboratories: LLNL and 

SITL. Only tritium data from the SITL were available for 

reporting at the time of this publication.

Quality-Assurance and Quality-Control 

Methods and Results

The purpose of QA/QC is to identify which data best 

represent environmental conditions and which data may 

have been affected by contamination or bias during sample 

collection, processing, storage, transportation, 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 for organic constituents, and (4) surrogate 

compounds were added to samples analyzed for organic 

constituents to assess potential bias of laboratory analytical 

methods.

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 Hard Rock study 

unit and for previous GAMA study units were used to 

establish raised SRLs for some constituents detected in blanks. 

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., 2011). 

Nitrogen-purged, organic-free water was used for blanks of 

organic constituents, and inorganic-free water was used for 

blanks of other constituents.

Source-solution blanks were collected at the beginning of 

the Hard Rock study and whenever a new lot of blank water 

was introduced to assess potential contamination of samples 

during transport and analysis and potential contamination 

of the certified blank water obtained from the NWQL. Two 

source-solution blanks using nitrogen-purged, organic-free 

blank water were collected during the Hard Rock study 

and analyzed for VOCs. Two source-solution blanks using 

inorganic-free blank water were collected for perchlorate, 

trace elements, major and minor ions, silica, TDS, and 

laboratory alkalinity. Source-solution blanks were collected in 

one of the mobile laboratories by pouring blank water directly 

into sample containers, which were then preserved, stored, 

shipped, and analyzed in the same manner as the groundwater 

samples.

Equipment blanks were collected before the start of 

a study unit, or when using sampling equipment (fittings, 

tubings, and filters) that is not frequently used, to assess 

the potential sources and extent of contamination of the 

equipment. One equipment blank was collected during the 

Hard Rock study in one of the mobile laboratories by pumping 

blank water through the groundwater sampling equipment by 

using a portable QC pump. Four liters of blank water were 

pumped through the sampling equipment before the equipment 

blank was collected. The equipment blank was analyzed 

for VOCs, pesticides and pesticide degradates, perchlorate, 

trace elements, nutrients, major and minor ions, silica, TDS, 

laboratory alkalinity, and arsenic, chromium, and iron species.

Field blanks were collected periodically during the 

course of the study to assess potential contamination of 

samples during collection, processing, transport, and analysis. 
120 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Field blanks were collected at sampling sites by pumping 

blank water through the groundwater sampling equipment 

(fittings, tubing, and filters) by using a portable QC pump. 

The samples were then processed and transported using the 

same protocols used for the groundwater samples. Four liters 

of blank water were pumped through the sampling equipment 

before each field blank was collected. Constituents analyzed 

were VOCs, pesticides and pesticide degradates, perchlorate, 

trace elements, nutrients, major and minor ions, silica, TDS, 

laboratory alkalinity, and arsenic, chromium, and iron species.

Blanks were not collected for radon-222, gross alpha 

and gross beta radioactivity, and uranium isotopes 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 and dissolved noble gases. Tritium and dissolved 

noble gases are in the atmosphere and would dissolve into any 

solution used in collecting a blank, making it impractical to 

collect a blank for these analytes. Isotopic ratios of carbon, 

boron, hydrogen, oxygen, and strontium are an intrinsic 

property of any of these elements; therefore, the concept of a 

blank does not apply to these ratios.

Methods for Determining and Applying 

Study Reporting Levels (SRLs)

In some instances in which contamination bias is 

observed in a set of blanks, it may be necessary to use a 

raised reporting level to identify the concentration above 

which a result is unlikely to be significantly affected by 

contamination bias. SRLs for VOCs collected for the 

35 GAMA-PBP study units were defined by Fram and 

others (2012) on the basis of the assessment of results from 

field blanks collected for the GAMA-PBP from May 2004 

through September 2010, 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-element data collected for the 

GAMA‐PBP starting in October 2009 were defined by Davis 

and others (2014) on the basis of statistical assessment of 

results from the field blanks collected for the GAMA-PBP 

study units from October 2009 through March 2013. The 

assessment used order statistics and binomial probabilities to 

construct an upper confidence limit (Hahn and Meeker, 1991; 

Olsen and others, 2010) for the maximum concentration of 

constituents possibly introduced while groundwater samples 

were collected, handled, transported, and analyzed. Detections 

of trace elements having concentrations less than the SRLs 

are marked with a ≤ symbol preceding the reported values 

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 

nondetection).

SRLs for nutrients collected for the Hard Rock study 

unit were defined by the highest concentration measured in 

the field blanks. Detections of nutrients having concentrations 

less than the SRLs are marked with a ≤ symbol preceding 

the reported value in table 9 to indicate that the true value 

may be less than or equal to the reported value (including the 

possibility of being a nondetection).

Detections in Blanks and Application of SRLs

Table A3 presents a summary of detections in the blanks 

and the SRLs applied for the Hard Rock study unit. Blanks 

were collected at approximately 10 percent of the sampled 

sites in the Hard Rock study unit: 1 VOC source-solution 

blank, 2 inorganic source-solution blanks, 1 equipment blank, 

and 12 field blanks. 1,2,4-Trimethylbenzene, barium, and 

ammonia were the only constituents detected in the sourcesolution blanks collected during the Hard Rock study. Sodium, 

five trace elements (barium, cobalt, copper, lead, and zinc), 

and nitrite plus nitrate were detected in the equipment blank. 

Two VOCs (1,2,4-trimethylbenzene and tetrachloroethene), 

eight trace elements (barium, cobalt, copper, iron, lead, 

manganese, nickel, and zinc), and three nutrients (ammonia, 

nitrite plus nitrate, and nitrite) were detected in at least one 

field blank. Constituents were not detected in blanks for the 

following analyte groups: pesticides and pesticide degradates; 

perchlorate; major and minor ions (except for one detection of 

sodium at a concentration equal to the LT-MDL), silica, and 

TDS; and arsenic, chromium, and iron species.

SRLs for Organic Constituents

Fram and others (2012) identified a set of 10 VOCs that 

had a tendency, based on past GAMA studies, to occur in 

blanks as a result of contamination. The SRLs determined 

by Fram and others (2012) were considered in conjunction 

with additional QC data for the Hard Rock study unit, as 

shown in table A3. As discussed below, six VOCs with 

established SRLs (1,2,4-trimethylbenzene, 2-butanone, 

acetone, carbon disulfide, tetrahydrofuran, and toluene) 

were detected in groundwater samples from the Hard Rock 

study unit, and all detections less than the SRLs were 

reclassified as nondetections. Chloroform has an established 

SRL (0.03 μg/L); however, the SRL applies only to samples 

collected using monitoring-well sampling equipment, which 

was not used in the Hard Rock study unit.

Tetrachloroethene does not have an established SRL 

because the detection frequency of the VOC in field blanks for 

previous study units was low. Tetrachloroethene was detected 

in five field blanks collected for the Hard Rock study unit 

at concentrations ranging from 0.025 to 0.094 μg/L during 

March 31 through July 19, 2011. Tetrachloroethene was not 

detected in the source-solution blanks collected on March 15, 

2011, and November 16, 2011, for the two lots of blank water 

used during the Hard Rock study. Tetrachloroethene was 

detected in nine groundwater samples, none of which were 
Appendix 121

samples collected at sites where field blanks were collected. 

The data suggest that contamination of the field blanks was 

introduced not by the handling and analysis of groundwater 

samples but rather by the equipment used to collect field 

blanks. Tetrachloroethene is a solvent used in cleaning agents 

and manufacturing. Contamination of tetrachloroethene in 

field blanks collected for the Hard Rock study unit likely 

did not affect groundwater samples, and determination 

of an SRL was not necessary. No groundwater detections 

of tetrachloroethene were annotated or reclassified as 

nondetections in the Hard Rock study unit.

For GAMA-PBP studies, most concentrations of 

1,2,4-trimethylbenzene in blanks and groundwater samples 

were found to be correlated with the presence of equipment 

used for collecting radon-222 samples in field vehicles. The 

vials used to collect radon-222 samples contain a scintillation 

cocktail made of mineral oil and 1,2,4-trimethylbenzene. 

1,2,4-Trimethylbenzene was detected in five blanks, of 

which the greatest concentration (0.35 μg/L) was detected 

in a source-solution blank. The field blank collected directly 

following the source-solution blank had the greatest detected 

concentration of 1,2,4-trimethylbenzene in field blanks 

(0.33 μg/L; table A3). According to the NWQL certificates 

of analysis for the lots of organic blank water used during 

this study, no VOCs were detected when tested by the 

NWQL (James A. Lewis, National Water Quality Laboratory, 

written commun., October 2010 and April 2011). Detections 

of 1,2,4-trimethylbenzene in groundwater from the Hard 

Rock study unit were below the SRL determined by Fram 

and others (2012) of 0.56 μg/L, with the exception of three 

samples (PR-27 at 0.868 μg/L; PR-33 at 0.755 μg/L; and 

PR-35 at 0.814 μg/L). All 65 groundwater detections were 

likely a result of field sources of contamination based on the 

detection frequency and concentrations in blanks collected by 

the GAMA-PBP since 2004 and therefore were reclassified as 

nondetections in this report and the NWIS database.

Contamination of groundwater samples and field blanks 

by 2-butanone, acetone, and (or) tetrahydrofuran can be 

attributed to presence of PVC-cement at sample collection 

sites (some wells are plumbed with PVC piping) or with 

contamination of sample collection equipment with the 

methanol used for cleaning equipment (Fram and others, 

2012). 2-Butanone was detected in three groundwater samples 

(SC-07, SGU-01, and PRFP-04); acetone was detected in 

four groundwater samples (SC-07, SGU-01, PR-15, and 

PRFP-04). Tetrahydrofuran was detected in four groundwater 

samples (SC-07, SC-09, SGU-01, and PRFP-04) in the Hard 

Rock study unit. Field blanks with contamination from either 

of these two sources were not considered representative 

of the ambient groundwater. Therefore, no quality-control 

assessment could be made for these three solvents, and 

no concentration threshold could be established for the 

SRL. Instead of establishing an SRL, detections of these 

three solvents in groundwater samples were reclassified as 

“not analyzed.” This reclassification is implemented in the 

USGS NWIS database by setting the data quality indicator 

code to “reviewed and rejected.” 2-Butanone, acetone, and 

tetrahydrofuran were detected at such high concentrations 

(31.0, 19.8, and 112 μg/L, respectively) in the PRFP-04 

sample that all VOC results for this sample were considered 

suspect and were coded as “reviewed and rejected.” The 

coding caused one chloroform detection, at a concentration of 

0.244 μg/L, to be omitted from this report.

Carbon disulfide was detected in four groundwater 

samples in the Hard Rock study unit. One of the detections 

was at a concentration less than the SRL of 0.03 μg/L 

determined by Fram and others (2012): PR-10 at 0.028 μg/L. 

The PR-10 result was reclassified as a nondetection in this 

report and the NWIS database. The likely source of carbon 

disulfide contamination is the gloves worn by field and 

laboratory personnel (Worthington and others, 2007). 

Toluene was detected in five groundwater samples in 

the Hard Rock study unit: SC-15 at 0.176 μg/L; SG-33 at 

0.083 μg/L; PR-09 at 0.026 μg/L; PR-10 at 0.045 μg/L; and 

PRFP-08 at 0.264 μg/L. All groundwater concentrations were 

less than the SRL of 0.69 μg/L and therefore were reclassified 

as nondetections in this report and the NWIS database. The 

source of toluene contamination is uncertain.

SRLs for Inorganic Constituents and Nutrients

For the inorganic constituents, SRLs were only needed 

for selected trace elements and nutrients. For previous GAMA 

study units, concentrations of trace-element SRLs were 

determined primarily by Olsen and others (2010) based on 

a statistical assessment of quality-control results collected 

from May 2004 through January 2008. The concentrations 

and detection frequencies in field blanks collected by the 

GAMA-PBP since January 2008 suggest that the dataset 

used by Olsen and others (2010) may not be representative 

of conditions encountered during collection of samples in 

recent studies, including the Hard Rock study. GAMA SRLs 

were updated for results collected starting October 2009 as 

determined by Davis and others (2014) based on a statistical 

assessment similar to that used by Olsen and others (2010) and 

that included NWQL, BQS, and GAMA QC data. Updated 

GAMA SRLs were used for copper (2.1 μg/L), iron (6 μg/L), 

lead (0.82 μg/L), manganese (0.66 μg/L), molybdenum 

(0.023 μg/L), nickel (0.21 μg/L), tungsten (0.023 μg/L), 

and zinc (6.2 μg/L) for the Hard Rock study unit (table A3). 

Additionally, all groundwater results for cobalt were 

“reviewed and rejected” in the NWIS database and therefore 

censored from this dataset. Seven of these nine trace elements 

were detected in at least one Hard Rock field blank, and most 

of the detections in the field blanks were at concentrations less 

than the updated SRLs. 

Barium was detected in three blanks: one source solution 

blank (0.162 μg/L), the equipment blank (0.121 μg/L), and 

one field blank (0.073 μg/L); however, it was not necessary 

to determine an SRL for barium based on the low detection 

frequency in field blanks collected for the Hard Rock study 

unit and previous study units.
122 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Cobalt and manganese were detected frequently in the 

blanks collected during the Hard Rock study; cobalt was 

detected in the equipment blank (0.03 μg/L) and in all 12 field 

blanks (0.09 to 0.53 μg/L), and manganese was detected in 

all 12 field blanks (0.29 to 0.91 μg/L). Contamination bias for 

these two trace elements was attributed to the capsule filters 

used to filter samples for analysis (Davis and others, 2014). 

Copper was detected in the equipment blank (2.6 μg/L) and 

nine of the field blanks (0.62 to 3.2 μg/L). Iron was detected 

in two field blanks (3.35 and 13.3 μg/L), and nickel was 

detected in one field blank (0.19 μg/L), neither of which were 

detected in the equipment blank. Lead was detected in the 

equipment blank (0.35 μg/L) and eight of the field blanks 

(0.03 to 0.82 μg/L). Zinc was detected in the equipment blank 

(6.2 μg/L) and eight of the field blanks (1.56 to 8.38 μg/L). 

Measured concentrations in groundwater samples that were 

less than the SRLs were coded with a ≤ symbol in table 8, 

except for cobalt results which were omitted from this report.

Ammonia was detected in 1 of the 2 source-solution 

blanks at a concentration of 0.0134 mg/L and in 4 of the 

12 field blanks at concentrations 0.011, 0.013, 0.014, and 

0.015 mg/L (table A3). Additional QC data were reviewed 

for ammonia, including 2 source-solution blanks and 12 field 

blanks collected for the GAMA Trends sampling during 

February 2011 through March 2012. Trends samples are 

collected using the same protocols and equipment as used 

for the Hard Rock study unit and are collected by the same 

personnel. Ammonia was detected in 6 of the 12 Trends 

field blanks at concentrations of 0.011 to 0.014 mg/L, 3 of 

which were changed to nondetections when re-analyzed 

by the NWQL. According to NWQL inorganic blank water 

certificates, ammonia was detected at concentrations up 

to 0.011 mg/L in the lots of blank water used between 

March 2011 and March 2012. Additionally, the BQS operates 

a project called the Blind Blank Project (BBP) in which BQS 

samples are disguised as regular blank samples to evaluate 

potential bias in the results reported by the NWQL on a 

continuous basis. A review of all available BBP ammonia 

results (October 2010 to February 2013) shows a 4 percent 

detection frequency, with concentrations ranging from 0.011 

to 0.058 mg/L and all detections occurring in 2011 and 

2012. The data suggest that low concentrations of ammonia 

may be attributable to a combination of contaminated blank 

water, contamination during laboratory analysis, and field 

factors (contamination during the handling and processing of 

samples or equipment); however, the concentrations of the 

contamination are low compared to the HAL-US for ammonia 

(24.7 mg/L). The SRL for ammonia was determined to be 

equal to the highest concentration detected in field blanks for 

the Hard Rock study unit, 0.015 mg/L. Application of the SRL 

resulted in coding 10 groundwater detections as less than or 

equal to the reported values (table 9).

Nitrate plus nitrite was detected in the equipment blank 

(0.024 mg/L) and one field blank (0.031 mg/L), and nitrite was 

detected in three field blanks at concentrations between 0.001 

and 0.0014 mg/L (table A3). A review of the NWQL inorganic 

blank water certificates and BQS BBP data indicated no bias 

from blank water contamination or laboratory analysis. Field 

factors could not be eliminated as a source of contamination 

for groundwater samples; therefore, SRLs were set for the two 

nutrients to the highest concentrations detected in field blanks 

for the Hard Rock study unit: 0.031 mg/L for nitrate plus 

nitrite and 0.0014 mg/L for nitrite. Application of the SRLs 

resulted in coding six nitrite plus nitrate detections and nine 

nitrite detections as less than or equal to the reported values.

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.

Methods of 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 (pairs with mean concentration less 

than [<] 5 times the reporting level) and by relative standard 

deviation (RSD) for high concentrations (pairs with mean 

concentration greater than [>] 5 times the reporting level) 

(Anderson, 1987; Mueller and Titus, 2005). The RSD is 

defined as the SD divided by the mean concentration for 

each replicate pair of samples expressed as a percentage. The 

reporting level (RL) used for this purpose may be an LRL, 

LT-MDL, SRL, MDL, or MRL for each constituent.

Replicate pairs of analyses of all constituents (except 

radiochemical constituents) were evaluated as follows:

• If both values were reported as detections, the SD or 

RSD was calculated. Acceptable precision is defined 

as an SD of less than one-half of the RL (for pairs with 

mean concentration <5 times the RL) or an RSD of 

less than 10 percent (for pairs with mean concentration 

>5 times the RL). For comparison, an RSD of 

10 percent is equivalent to a relative percent difference 

(RPD) of 14 percent. 

• If both values were reported as nondetections, the 

variability was considered to be acceptable by 

definition. 

• If one value was reported as a nondetection, 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 was calculated. Substituting 

zero for the nondetection yielded the maximum 
Appendix 123

estimate of variability for the replicate pair. For some 

discussions, one-half of the RL is substituted for the 

nondetection when calculating the SD. 

• 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 RL), or if both 

values were reported as ≤-coded values, the variability 

was considered acceptable. The SD could not be 

calculated because the ≤-coded results represent a 

range of possible values.

• If one value was reported as a nondetection and the 

other value was reported as a detection greater than 

the RL, the variability for the pair was considered 

unacceptable.

Replicate pairs of analyses of radiochemical constituents 

were evaluated 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

, (A3)

where R1 and R2 are the results for the two samples in the 

replicate pair; and

CSU1 and CSU2 are the combined standard uncertainties 

associated with the results.

Values less than 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 sample pairs indicate that 

precision is unacceptable for a constituent and no specific 

reason can be identified, then this greater variability must 

be considered when interpreting the data. If measured 

concentrations are slightly greater than a water-quality 

benchmark, then actual concentrations could be slightly less 

than that benchmark. Similarly, if measured concentrations 

are slightly less than a water-quality benchmark, then actual 

concentrations could be slightly greater than a benchmark. 

Also, if a constituent has high variability in replicate sample 

pairs, then a larger difference between concentrations 

measured in two samples is required to conclude that the two 

samples have significantly different concentrations.

Until April 2013, the GAMA-PBP generally requested 

re-analyses of replicate pairs for results outside the acceptable 

limits of precision. Requests and rerun results were recorded 

in an Excel spreadsheet maintained by GAMA project staff. If 

the new result was within acceptable precision for the method 

as per the laboratory analysts, the original concentration was 

not updated. However, if the new result was accompanied 

with the laboratory comment, “Use new result. New result 

within method precision based on multiple reruns,” then 

the concentration was updated by GAMA project staff in 

the NWIS database, regardless of whether precision for the 

updated results for the replicate pair was better or worse. 

Because of the longer holding times, trace elements, major and 

minor ions, and nutrients were generally the only constituents 

able to be re-analyzed by the time the data were uploaded 

to the NWIS database; organic constituents or inorganic 

constituents past the holding times could only be verified by 

laboratory analysts. Original and rerun values for replicate 

pairs that were updated per rerun results and for which the 

precision changed to within the acceptable limits (which only 

occurred for trace elements) are included in the footnotes in 

table A4B.

Variability in Replicate Samples

Tables A4A–C summarize the results of replicate 

analyses for constituents detected in groundwater samples 

collected in the Hard Rock study unit. Replicate analyses were 

made on samples from 12 sites, approximately 10 percent 

of all the samples collected, except for chromium species 

(samples from 4 sites) and dissolved noble gases (samples 

from 11 sites).

Of the 2,512 replicate pairs of constituents analyzed, 

1,937 pairs had no detections in either sample and thus had 

good agreement, and 575 pairs had detections in one or 

both samples of the pair. Of these 575 pairs, 37 pairs were 

outside the limits for acceptable precision and are listed in 

tables A4A–C. Results for replicate analyses for constituents 

that were not detected in groundwater samples are not reported.

The 85 VOCs analyzed for the Hard Rock study 

unit represent 1,020 replicate pairs of analyses. Eleven of 

the replicate pairs were composed of at least 1 detection 

(table A4A). All pairs had results within acceptable precision.

The 63 pesticide and pesticide degradates represent 

756 replicate pairs of analyses. Six of the replicate pairs were 

composed of at least one detection (table A4A). Two replicate 

pairs were each composed of a value less than the LRL and 

a nondetection, which had maximum SDs (by substituting 

zeroes for the nondetections) greater than the acceptable 

limits.

Twelve replicate pairs of samples were analyzed for 

perchlorate (table A4A). Seven of the replicate pairs were 

composed of at least one detection. Results for three of 

the seven pairs with a detection were outside the limits of 

acceptable precision. One replicate pair had a concentration 

greater than the LRL and a nondetection. The other two 

replicate pairs had concentrations greater than the LRL, but 

the RSD was greater than 10 percent or the SD was greater 

than one-half of the LRL. The remaining four replicate pairs 

had results within acceptable precision.

The 23 trace elements represent 276 replicate pairs of 

analyses. Of the replicate pairs, 112 were composed of either 

2 values reported as nondetections, a value reported as a 

nondetection and a value reported as less than or equal to the 

SRL, or 2 values reported as less than or equal to the SRL. Of 

the remaining 164 replicate pairs, 8 pairs had results outside 
124 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

the limits of acceptable precision: 2 replicate pairs (iron 

and zinc) consisted of an environmental value less than the 

SRL and a replicate value greater than the SRL, 4 replicate 

pairs (chromium, copper, silver, and tungsten) consisted of 

a nondetection and a value greater than the LT-MDL, and 

2 replicate pairs had aluminum results with an SD or RSD 

greater than the acceptable limit (table A4B). One replicate 

sample was diluted, raising the LT-MDL by a factor of three 

for the replicate sample and not for the environmental sample 

(HR-PRFP-08); precision for concentrations near the LT-MDL 

for the environmental sample could not be evaluated for this 

replicate pair. Of the eight replicate pairs with results for 

trace elements outside the limits of acceptable precision, two 

replicate pairs (aluminum and zinc) originally had results 

within the acceptable limits, yet the samples were requested 

for re-analysis; at least one value in each pair was updated 

per the rerun results, causing the pairs to have precision 

outside acceptable limits. Additionally, four replicate pairs of 

samples analyzed for trace elements (aluminum [two pairs], 

boron, and lithium) were reanalyzed because the results were 

outside the limits of acceptable precision; at least one value 

in each replicate pair was updated per the rerun result, and the 

resulting SDs or RSDs were within acceptable limits. Original 

and rerun results for these six replicate pairs are listed in the 

footnotes in table A4B.

The 5 nutrients analyzed for the Hard Rock study unit 

represent 60 replicate pairs of analyses. Twenty-four of the 

replicate pairs were each composed of either 2 values reported 

as nondetections, a value reported as a nondetection and a 

value less than or equal to the SRL, or 2 values reported as 

less than or equal to the SRL. Of the remaining 36 replicate 

pairs, 5 pairs had results outside the limits of acceptable 

precision: 2 replicate pairs of ammonia results consisted of an 

environmental value greater than the SRL and a replicate value 

less than the SRL; 1 replicate pair of nitrite results consisted 

of a value greater than the LT-MDL and a nondetection; 

and 1 replicate pair of nitrite results and 1 replicate pair of 

orthophosphate results had an RSD or SD value greater than 

the acceptable precision (table A4B).

The 12 major and minor ions, silica, alkalinity, and 

TDS represent 144 replicate pairs of analyses, of which 142 

were composed of 2 detections and had results within the 

limits of acceptable precision. The remaining two replicate 

pairs had the following iodide results: one pair consisted of 

nondetections, and one pair consisted of an environmental 

value greater than the LT-MDL and a replicate value reported 

as a nondetection (table A4B).

Of the 55 replicate pairs of arsenic, chromium, or iron 

species analyses, 26 were composed of at least 1 detection. 

Five of these 26 replicate pairs had results outside the limits of 

acceptable precision: 3 replicate pairs (total iron [2 pairs] and 

iron [II]) had results with an RSD or SD value greater than the 

acceptable limits, and 2 replicate pairs were each composed 

of an environmental value greater than the LT-MDL and a 

replicate value reported as a nondetection (table A4B).

The 4 isotopic tracers represent 48 replicate analyses. 

All replicate pairs had results within the limits of acceptable 

precision.

Eleven replicate samples were each analyzed for 5 

dissolved noble gases and 1 atom ratio. Five of the 66 

replicate pairs had results outside the limits of acceptable 

precision: 1 replicate pair of results for helium-3/helium-4 

atom ratio, 2 replicate pairs of helium-4 results, and 2 replicate 

pairs of neon results had RSD values greater than 10 percent 

(table A4B).

Twelve replicate pairs of samples were each analyzed for 

6 radioactive constituents, and 1 replicate pair was analyzed 

for uranium isotopes (3 different isotopes). Most of the 75 

replicate pairs of constituents yielded statistically similar 

results (p ≤ 0.05), and were therefore considered acceptable. 

Eight replicate pairs, however, had results for the following 

constituents outside the limits of acceptable precision: 

tritium, radon-222, gross alpha radioactivity (72-hr count, 

two pairs), gross alpha radioactivity (30-day count), gross 

beta radioactivity (72-hr count, two pairs), and gross beta 

radioactivity (30-day count). The variability of the results for 

the radon-222 replicate pair was likely caused by the incorrect 

volume of sample collected for the replicate sample as 

reported by the NWQL. Replicate pairs of samples collected 

from the grid well SG-08 had results with variability outside 

the limits of acceptable precision for gross alpha and beta 

radioactivity for the 72-hour and 30-day counts. Activities for 

the replicate samples were lower or not detected for all four 

analytes (table A4C).

Detections in environmental samples were not modified 

on the basis of the replicate analyses.

Methods for Assessing 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 and high matrix-spike recoveries may be a potential 

concern if the concentration of a compound in a groundwater 

sample is close to the health-based benchmark; a low recovery 

could result in a falsely measured concentration less than the 

health-based benchmark, whereas a high recovery could result 

in a falsely measured concentration greater than the healthbased benchmark. In addition, a low matrix-spike recovery 

may indicate that the compound might not be detected in some 

samples if it were present at very low concentrations.

The GAMA-PBP defined the data-quality objective 

range for acceptable median matrix-spike recoveries as 70 

to 130 percent. Only constituents with median matrix-spike 
Appendix 125

recoveries outside of this range were flagged as having 

unacceptable recoveries. For some constituents, the 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 smaller the 

F-pseudosigma, the more precise the determinations (Hoaglin, 

1983).

Matrix spikes were performed for VOCs 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 Hard Rock study unit. Samples for the 

addition of the spike mixtures for 85 VOCs were collected 

at 11 sites, which is approximately 10 percent of all the 

wells sampled. Median matrix-spike recoveries were 

between 70 and 130 percent for all VOCs (table A5A). One 

spike sample had three unusually low or high recoveries: 

bromodichloromethane (minimum = 0 percent), chloroform 

(maximum = 1,320 percent), and dibromochloromethane 

(minimum = 20 percent). The recoveries were affected by 

background concentrations of the constituents at values up 

to 100 times the expected spike fortifications. Additionally, 

two spike recoveries were outside the acceptable limit for 

1,2,4-trimethylbenzene (minimum = 0 percent; maximum = 

180 percent). All groundwater detections of the compound 

in the Hard Rock study unit were attributed to contamination 

(Fram and others, 2012), and concentrations varied between 

replicate samples when detected at concentrations less 

than the SRL. Therefore, background concentrations of 

1,2,4-trimethylbenzene could not be subtracted out of the 

spike sample to calculate meaningful spike recoveries.

Samples for the addition of the spike mixtures for 

63 pesticides and pesticide degradates were collected at 

10 sites. Of the 630 spike analyses, 155 (25 percent) were 

outside the range of acceptable recovery (table A5B). Eleven 

pesticides (chlorpyrifos oxon, dichlorvos, dicrotophos, 

dimethoate, fenamiphos sulfoxide, hexazinone, 1-naphthol, 

phosmet, phosmet oxon, terbufos oxon sulfone, and tribufos) 

had median matrix-spike recoveries less than 70 percent, 

1 of which (hexazinone) was detected in groundwater 

samples. Low matrix-spike recoveries may indicate that 

a low concentration in some samples could be reported 

as a nondetection. One compound (tebuthiuron) had a 

median matrix-spike recovery greater than 130 percent and 

was detected in groundwater samples. High matrix-spike 

recoveries may indicate that a detected concentration in some 

samples is greater than the true concentration.

Detections in environmental samples were not modified 

on the basis of the matrix-spike recovery analysis.

Methods for Assessing 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).

Surrogate Compound Recoveries

Table A6 presents a summary of the surrogate recoveries 

for the Hard Rock study unit. The table lists the surrogate 

compound, 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 blank and 

environmental samples were within the acceptable range of 

70 to 130 percent. For VOC analyses, surrogate recoveries for 

93 percent of the blanks (12 field, 1 equipment, and 1 sourcesolution) and 86 percent of the environmental samples 

(111 samples) were within the acceptable range. For pesticides 

and pesticide degradates, surrogate recoveries for 96 percent 

of the blanks (12 field and 1 equipment) and 95 percent of 

the environmental samples (110 samples) were within the 

acceptable range (table A6).

Detections in environmental samples were not modified 

on the basis of the surrogate recovery analysis, except in 

the following case. For the SGU-01 sample, the pesticide 

surrogate diazinon-d10 had a 0 percent recovery. Low 

recoveries of this surrogate may indicate that the sample was 

treated with chlorine prior to collection. When chlorinated, 

organic samples are collected in bottles containing ascorbic 

acid (see appendix section titled Sample Collection and 
126 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Analysis). The unusually low recovery of diazinon-d10 and 

the moderate concentrations of chlorination byproducts 

in the SGU-01 groundwater sample suggests that the 

sample was treated; detected VOCs in the sample included 

bromochloromethane (0.080 μg/L), bromodichloromethane 

(2.9 μg/L), carbon disulfide (0.044 μg/L), chloroethane 

(0.088 μg/L), chloromethane (0.150 μg/L), 

dibromochloromethane (2.16 μg/L), dibromomethane 

(0.228 μg/L), dichloromethane (0.069 μg/L), bromoform 

(2.54 μg/L), and chloroform (5.47 μg/L). Chlorination of 

SGU-01 was not known at the time of sample collection, and 

the samples collected for analyses of organic constituents were 

not treated with ascorbic acid; therefore, all results for VOCs 

and pesticides for this sample are considered suspect and were 

coded as “reviewed and rejected.”

Other Quality-Control Results

Two other laboratory QC issues arose during the analysis 

of samples collected for the Hard Rock study unit: the effect 

of holding-time violations on the results of radioactive 

constituent data and the effect of internal laboratory QC tests 

indicating potential bias for results of trace-element data.

Holding time refers to the time in calendar days from 

sample collection to the analysis of the sample. A holding-time 

violation occurs when a sample is analyzed past the given 

holding time for a particular analysis. Analyses for some 

samples in the Hard Rock study unit were completed after the 

holding time due to a scheduling error at the laboratory or a 

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, and 

therefore gross alpha and gross beta radioactivity can change 

with time. At least one result from the analysis of gross alpha 

and gross beta radioactivity (72-hour counts) was analyzed 

4 days after sample collection for four groundwater samples 

(SC-04, SG-10, PR-10, and PR-28), and 8 days after sample 

collection for two groundwater samples (SC-22 and SC-23). 

Gross alpha radioactivity (72-hour) may be lower and gross 

beta radioactivity (72-hour) may be lower or higher than 

true activities in samples analyzed past the holding time. 

Three gross alpha radioactivity results (for SC-09, SC-22, 

and SG-21) were annotated by the laboratory that the raw 

results may indicate potential negative bias. The gross beta 

radioactivity (30-day) for one sample (SC-09) was analyzed 

early—18 days after the 72-hour count. The results for these 

nine samples are footnoted in table 14B.

Laboratory bias for trace elements as indicated from 

internal laboratory QC tests was investigated to determine 

whether or not environmental data were affected. The 

BQS operates independent, external QA projects called the 

Inorganic Blind Sample Project (IBSP) and Blind Blank 

Project (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 with known concentrations of inorganic constituents 

(Farrar and Long, 1997). The IBSP and BBP samples are 

submitted to the NWQL as regular environmental and blank 

samples, respectively. The BQS issues quarterly summaries, 

reporting the amount of bias (if any) observed in the results 

(U.S. Geological Survey, 2013c, http://bqs.usgs.gov/ibsp/).

BQS summaries from April 2011 to April 2012 include 

data for the period during which samples were analyzed 

for the Hard Rock study unit. Of the inorganic constituents 

analyzed for the Hard Rock study unit, 19 were reported to 

have bias or variability at some point during this period. The 

analytical biases reported by the BQS were not significant for 

the data collected for the Hard Rock study unit in the context 

of regulatory standards. Only the two constituents (aluminum 

and zinc) that showed ongoing (and the greatest) bias or 

variability during the time which samples were analyzed for 

the Hard Rock study unit are discussed below.

The BQS reported high false positive rates (greater 

than 5 percent of samples were greater than the LT-MDL) 

for aluminum in BBP samples analyzed at the NWQL 

from February through June 2011. During the time which 

samples were analyzed for the Hard Rock study unit 

(March 2011 through March 2012), 5 of the 56 blind blanks 

analyzed (9 percent) had aluminum concentrations ranging 

from 1.77 to 40.9 μg/L, all of which are greater than the 

LT-MDL. The positive bias was not seen in blanks collected 

by the GAMA-PBP; however, replicate samples collected 

for the Hard Rock study unit since January 2011 may 

indicate potential positive bias in groundwater samples. 

Two of the 12 replicate pairs for the Hard Rock study unit 

were re-analyzed by the NWQL due to disagreement in 

aluminum concentrations between the environmental and 

replicate samples. The Hard Rock replicate pairs with initial 

concentrations of 2.0 and 3.3 μg/L and 5.4 μg/L and not 

detected were adjusted by the laboratory to nondetections 

upon re-analysis.

Additionally, the BQS reported variability and 

positive bias (measured concentrations greater than 

target by an average of 11 percent) for aluminum in 

IBSP samples analyzed at the NWQL from October 2011 

through March 2012 (U.S. Geological Survey, 2012). The 

IBSP samples analyzed during this period had aluminum 

concentrations ranging from 58.4 to 144 μg/L. The median 

difference between the measured and expected concentrations 

was 3.6 μg/L (SD = 17 μg/L). The maximum concentration 

of aluminum for the Hard Rock study unit was 291 μg/L 

(table 8), and a difference of 11 percent (32 μg/L) does not 

affect assessment of whether groundwater samples in the Hard 

Rock study unit have aluminum concentrations greater than 

or less than one-half of the MCL-CA concentration or greater 

than or less than the MCL-CA concentration (1,000 μg/L).
Appendix 127

The BQS reported slight positive bias for zinc in IBSP 

samples analyzed at the NWQL during December 2010 

through May 2011 and September 2011 through March 2012; 

the greatest positive bias occurred September through 

November 2011, with measured concentrations greater than 

the targets by an average of 15 percent. The summaries 

indicated that the majority of bias occurs at concentrations 

greater than 800 μg/L; the instruments used by the NWQL 

are optimized to achieve lower detection levels. Other 

issues included instrument sensitivity in late 2011, which 

briefly affected samples to varying degrees for zinc and 

other trace elements including aluminum, boron, cadmium, 

molybdenum, chromium, cobalt, copper, nickel, silver, and 

strontium. Additionally, a problem with the pipettes used 

by the NWQL during this time affected zinc and strontium 

analyses. The IBSP samples analyzed September through 

November 2011 had zinc concentrations ranging from 37 to 

1,102 μg/L (U.S. Geological Survey, 2012). The median 

difference between the measured and expected concentrations 

was 44 μg/L (SD = 172 μg/L); the high SD is evidence of 

variability reported by the BQS, particularly during this time 

period and extending through March 2012. For the Hard Rock 

study unit, one measured groundwater concentration of zinc 

(4,530 μg/L) was greater than one-half of the SMCL-CA 

(table 8). A potential positive bias of 15 percent (680 μg/L) 

does not affect assessment of whether groundwater samples 

in the Hard Rock study unit have zinc concentrations greater 

than or less than one-half of the SMCL-CA concentration 

or greater than or less than the SMCL-CA concentration of 

5,000 μg/L.
128 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table A1. Analytical methods used by the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) and contract 

laboratories.

[Laboratory entity codes in the USGS National Water Information System (NWIS) database for laboratories other than the USGS NWQL are given in 

parentheses after the laboratory names. Abbreviations: UV-Vis, ultraviolet; δ, delta notation, the ratio of a heavier isotope of an element (iE) to the more 

common lighter isotope of that element relative to a standard reference material, expressed as per mil; USEPA, U.S. Environmental Protection Agency; NRP, 

National Research Program]

Analyte Analytical 

method Laboratory and analytical schedule Citation(s)

Water-quality indicators

Field parameters Calibrated field meters and test 

kits

USGS field measurement U.S. Geological Survey, 

variously dated

Organic constituents

Volatile organic compounds Purge and trap capillary gas 

chromatography/mass 

spectrometry

NWQL, Schedule 2020 Connor and others, 1998

Pesticides and pesticide 

degradates

Solid-phase extraction and 

gas chromatography/mass 

spectrometry

NWQL, Schedule 2003 Zaugg and others, 1995; Lindley 

and others, 1996; Sandstrom 

and others, 2001; Madsen and 

others, 2003

Constituent of special interest

Perchlorate Liquid chromatography with 

mass spectrometry/mass 

spectrometry (USEPA 

Method 331.0)

Weck Laboratories, Inc., City of 

Industry, California, standard 

operating procedure ORG099.R01

U.S. Environmental Protection 

Agency, 2005

Inorganic constituents

Major and minor ions, trace 

elements

Atomic absorption spectrometry, 

colorimetry, ion-exchange 

chromatography, inductivelycoupled plasma atomicemission spectrometry and 

mass spectrometry

NWQL, Schedule 1948 Fishman and Friedman, 1989; 

Faires, 1993; Fishman, 1993; 

McLain, 1993; American Public Health Association, 1998; 

Garbarino, 1999; Garbarino 

and others, 2006

Nutrients Alkaline persulfate digestion, 

Kjedahl digestion, colorimetry 

by enzymatic reduction 

NWQL, Schedule 2755 Fishman, 1993; Patton and Kryskalla, 2003, 2011

Arsenic, chromium, and iron 

species

Various techniques of ultraviolet 

visible (UV-Vis) spectrophotometry and atomicabsorbance spectroscopy

USGS Trace Metal Laboratory, 

Boulder, Colorado (USGSTMCO)

Stookey, 1970; To and others, 

1998; Ball and McCleskey, 

2003a, b; McCleskey and 

others, 2003

Isotopes

Stable isotopes of hydrogen 

(δ2

H) and oxygen (δ18O) in 

water

Gaseous hydrogen and carbon 

dioxide—water equilibration and stable-isotope mass 

spectrometry

USGS Stable Isotope Laboratory, 

Reston, Virginia (USGSSIVA), 

NWQL Schedule 1142

Epstein and Mayeda, 1953; 

Coplen and others, 1991; 

Coplen, 1994

δ11B of boron dissolved in 

water

Negative thermal-ionization 

mass spectrometry

USGS NRP Metals Isotope Research 

Laboratory, Menlo Park, California (USGSMICA)

Vengosh and others, 1989; 

Dwyer and Vengosh, 2008

87Sr/86Sr of strontium 

dissolved in water

Chemical separations of thermalionization mass spectrometryUSGS NRP Metals Isotope Research 

Laboratory, Menlo Park, California (USGSMICA)

Bullen and others, 1996
Appendix 129

Table A1. Analytical methods used by the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) and contract 

laboratories.—Continued

[Laboratory entity codes in the USGS National Water Information System (NWIS) database for laboratories other than the USGS NWQL are given in 

parentheses after the laboratory names. Abbreviations: UV-Vis, ultraviolet; δ, delta notation, the ratio of a heavier isotope of an element (iE) to the more 

common lighter isotope of that element relative to a standard reference material, expressed as per mil; USEPA, U.S. Environmental Protection Agency; NRP, 

National Research Program]

Analyte Analytical 

method

Laboratory and analytical 

schedule Citation(s)

Isotopes—Continued

δ13C of inorganic carbon dissolved in water 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, 1987; Donahue 

and others, 1990; McNichol 

and others, 1992; Gagnon and 

Jones, 1993; McNichol and 

others, 1994; Schneider and 

others, 1994

Radioactive constituents and noble gases

Tritium Electrolytic enrichment-liquid 

scintillation

USGS Stable Isotope and Tritium 

Laboratory, Menlo Park, California (USGSH3CA)

Thatcher and others, 1977

Tritium and dissolved noble 

gases

Helium-3 in-growth and mass 

spectrometry

Lawrence Livermore National 

Laboratory, Livermore, California (CA-LLNL)

Moran and others, 2002; Eaton 

and others, 2004

Radon-222 Liquid scintillation counting NWQL, Schedule 1369 American Society for Testing 

and Materials, 1998

Gross alpha and gross beta 

radioactivity

Alpha and beta activity counting 

(USEPA Method 900.0)

Eberline Analytical Services, 

Richmond, California (CAEBERL), NWQL Schedule 

1792

Krieger and Whittaker, 1980 

Uranium-234, -235, and -238 Chemical separations and alphaparticle spectrometryEberline Analytical Services, 

Richmond, California (CAEBERL), NWQL Schedule 

1130

American Society for Testing 

and Materials, 2009 (ASTM 

D3972)

Table A2. Preferred analytical schedules for selected constituents collected for the Santa Cruz, San Gabriel, and Peninsular Ranges 

Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.

[Preferred analytical schedules/methods are selected on the basis of the procedure recommended by the USGS National Water Quality Laboratory (NWQL; 

http://wwwnwql.cr.usgs.gov/dyn.shtml?Preferred_method_selection_procedure). Abbreviations: TML, U.S. Geological Survey Trace Metal Laboratory, 

Boulder, Colorado; LLNL, Lawrence Livermore National Laboratory, Livermore, California; SITL, U.S. Geological Survey Stable Isotope and Tritium 

Laboratory, Reston, Virginia; na, not available (no preferred schedule)]

Constituent Primary constituent 

classification Analytical schedules Preferred analytical schedule

Results from both methods reported

Alkalinity Water-quality indicator field, 1948 field

Arsenic, total Trace element 1948, TML 1948

Chromium, total Trace element 1948, TML 1948

Iron, total Trace element 1948, TML 1948

pH Water-quality indicator field, 1948 field

Specific conductance Water-quality indicator field, 1948 field

Tritium Inorganic tracer LLNL, SITL na
Table A3. Constituents detected in field blanks and study reporting levels (SRLs) used for the Santa Cruz, San Gabriel, and Peninsular Ranges Hard R

study unit, March 2011 through March 2012, California GAMA Priority Basin Project. [Sources of the SRLs: each SRL was selected from either: (1) an analysis of quality-control data from May 2004 through September 2010 for volatile organic compounds (Fram 

analysis of quality-control data collected October 2009 through March 2013 for trace elements (Davis and others, 2014). Abbreviations: ≤, less than or equal to; μg/L, micrograper liter; —, not detected; na, not available; NWIS, U.S. Geological Survey (USGS) National Water Information System] Constituent Number of field blank detections/total number of field blanks Concentrations detected in field blanks SRL concentration Source of SRL 

Volatile organic compounds (VOCs) (μg/L) 1,2,4-Trimethylbenzene 4/12 0.027, 0.032, 0.055, 0.33 1 0.87 Fram and others, 2012 

2-Butanone 0/12 — all detections Fram and others, 2012 

Acetone 0/12 — all detections Fram and others, 2012 

Carbon disulfide 0/12 — 0.03 Fram and others, 2012 

Tetrachloroethene 5/12 0.025, 0.034, 0.048, 0.075, 0.094 na 2 Fram and others, 2012 

Tetrahydrofuran 0/12 — all detections Fram and others, 2012 

Toluene 0/12 — 0.69 Fram and others, 2012 

Trace elements (μg/L) Barium 1/12 0.073 na Davis and others, 2014 

Cobalt 12/12 0.09, 0.15, 0.16, 0.18, 0.20, 0.21, 0.23, 0.32, 0.36, 0.37, 0.52, 0.53 all results Davis and others, 2014 

Copper 9/12 0.62, 0.75, 0.82, 0.95, 1.8, 1.8, 2.1, 3.2, 3.2 2.1 Davis and others, 2014 

Iron 2/12 3.35, 13.3 6 Davis and others, 2014 

Lead 8/12 0.03, 0.04, 0.08, 0.10, 0.21, 0.35, 0.48, 0.82 0.82 Davis and others, 2014 

Manganese 12/12 0.29, 0.31, 0.36, 0.38, 0.38, 0.40, 0.43, 0.54, 0.59, 0.64, 0.88, 0.91 0.66 Davis and others, 2014 

Molybdenum 3 0/12 — 0.023 Davis and others, 2014 

Nickel 1/12 0.19 0.21 Davis and others, 2014 

Tungsten 3 0/12 — 0.023 Davis and others, 2014 

Zinc 8/12 1.56, 1.74, 1.89, 2.17, 3.03, 3.70, 7.16, 8.38 6.2 Davis and others, 2014 

Nutrients (mg/L) Ammonia, as nitrogen 4/12 0.011, 0.013, 0.014, 0.015 0.015 Hard Rock field blanks 

Nitrite, as nitrogen 3/12 0.001, 0.0013, 0.0014 0.0014 Hard Rock field blanks 

Nitrite plus nitrate, as nitrogen 1/12 0.031 0.031 Hard Rock field blanks 

1 Groundwater detections of 1,2,4-trimethylbenzene at concentrations less than the established SRL of 0.56 μg/L were censored from this dataset. Additionally, three groundw

(0.755, 0.814, and 0.868 μg/L) greater than the SRL were likely affected by contamination bias and therefore were reclassified as nondetections in this report and the NWIS data

2 Tetrachlorothene was detected in all three Santa Cruz field blanks and two of the four San Gabriel field blanks. Most groundwater detections occurred during sampling in the 

Detections in field blanks were attributed to contamination of field-blank equipment early in the study, which did not affect groundwater samples.

3 SRLs for molybdenum and tungsten were determined based on quality-control results other than field blanks including laboratory blanks and the USGS Branch of Quality Sy

blind blanks (Davis and others, 2014).
Table A4A. Quality-control summary for replicate analyses of organic constituents and perchlorate detected in samples collected for the Santa CruzPeninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.[Abbreviations: SD, standard deviation; RSD, percent relative standard deviation; ≤, less than or equal to; <, less than; >, greater than; RL, reporting level; nv, no value in categ

Constituent

Number of 

replicate pairs with 

nondetections/

number of replicate 

pairs

Number of SDs greater 

than 1⁄2 RL/number of 

replicate pairs with 

mean concentration 

<5 times the RL

Concentrations in replicate pairs 

with SDs >1⁄2 RL, or replicate 

pairs with one detection and one 

nondetection (environmental 

sample, replicate sample) 

Number of RSDs greater 

than 10 percent/number 

of replicate pairs with 

mean concentration 

>5 times the RL

Volatile organic compounds (VOCs) (μg/L)

Bromochloromethane 12/12 nv nv — — nv 

Bromodichloromethane 11/12 0/1 nv — — nv 

Bromoform (Tribromomethane) 12/12 nv nv — — nv 

Carbon disulfide 11/12 0/1 nv — — nv 

Carbon tetrachloride (Tetrachloromethane) 12/12 nv nv — — nv 

Chlorobenzene 12/12 nv nv — — nv 

Chloroform (Trichloromethane) 8/12 0/3 nv — — 0/1 

Dibromochloromethane 11/12 0/1 nv — — nv 

1,3-Dichlorobenzene 12/12 nv nv — — nv 

1,4-Dichlorobenzene 12/12 nv nv — — nv 

1,1-Dichloroethene 11/12 0/1 nv — — nv Methyl tert-butyl ether (MTBE) 12/12 nv nv — — nv 

Tetrachloroethene 11/12 0/1 nv — — nv 

1,2,3-Trichlorobenzene 12/12 nv nv — — nv 

1,2,4-Trichlorobenzene 12/12 nv nv — — nv 

1,1,1-Trichloroethane 12/12 nv nv — — nv 

Trichloroethene 11/12 0/1 nv — — nv Trichlorofluoromethane (CFC-11) 11/12 0/1 nv — — nv Trichlorotrifluoroethane (CFC-113) 12/12 nv nv — — nv 

Pesticides and pesticide degradates (μg/L)

Atrazine 11/12 1/1 <0.008, 

0.008

— — nv 

Carbaryl 11/12 0/1 nv — — nv Deethylatrazine 11/12 1/1 0.006, 

<0.006

— — nv 

Desulfinylfipronil 12/12 nv nv — — nv 

3,4-Dichloroaniline 12/12 nv nv — — nv 
Table A4A. Quality-control summary for replicate analyses of organic constituents and perchlorate detected in samples collected for the Santa CruzPeninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin Project.—Continued [Abbreviations: SD, standard deviation; RSD, percent relative standard deviation; ≤, less than or equal to; <, less than; >, greater than; RL, reporting level; nv, no value in categ

Constituent Number of replicate pairs with nondetections/ number of replicate pairs Number of SDs greater than 1⁄2 RL/number of replicate pairs with mean concentration <5 times the RL Concentrations in replicate pairs with SDs >1⁄2 RL, or replicate pairs with one detection and one nondetection (environmental sample, replicate sample) Number of RSDs greater than 10 percent/number of replicate pairs with mean concentration >5 times the RL 

Pesticides and pesticide degradates (μg/L)—Continued 2,6-Diethylaniline 12/12 nv nv — — nv 

Fipronil sulfide 12/12 nv nv — — nv 

Fipronil sulfone 12/12 nv nv — — nv 

Hexazinone 12/12 nv nv — — nv 

Metolachlor 11/12 0/1 nv — — nv Metribuzin 12/12 nv nv — — nv 

Prometon 11/12 0/1 nv — — nv Simazine 11/12 0/1 nv — — nv Tebuthiuron 12/12 nv nv — — nv 

Constituent of special interest (μg/L) Perchlorate 5/12 3/4 0.11, <0.10 0.19, 0.10 0.46, 0.11 0/3 
Table A4B. Quality-control summary for replicate analyses of inorganic constituents, isotope tracers, and dissolved noble gases detected in sampleCruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin [Abbreviations: SD, standard deviation; RSD, percent relative standard deviation; RL, reporting level; μg/L, micrograms per liter; mg/L, milligrams per liter; ≤, less than or equthan; nv, no value in category; =, equal to; NWIS, U.S. Geological Survey (USGS) National Water Information System; NWQL, USGS National Water Quality Laboratory; —, 

Constituent

Number of 

replicate pairs with 

nondetections or 

≤-coded values/number 

of replicate pairs 

Number of 

SDs >1⁄2 RL/number of 

replicate pairs with 

mean concentration 

<5 times the RL

Concentrations in 

replicate pairs with 

SDs >1⁄2 RL 

(environmental sample, 

replicate sample) 

Number of replicate pair

with RSDs >10 percent/

number of replicate pair

with mean concentration

>5 times the RL

Trace Elements (μg/L)

Aluminum 7/12 1 1/4 5.8, 7.0 — — 1/1 

Antimony 10/12 0/2 nv — — nv Arsenic 1/12 0/5 nv — — 0/6 Barium 0/12 nv nv — — 0/12 

Beryllium 10/12 0/2 nv — — nv Boron 0/12 3 0/2 nv — — 0/10 

Cadmium 8/12 0/4 nv — — nv Chromium 8/12 1/4 0.11, <0.06 — — nv Copper 9/12 1/3 <0.8, 2.4 — — nv Iron 5/12 1/1 ≤5.2, 6.6 — — 0/6 Lead 12/12 nv nv — — nv 

Lithium 0/12 4 0/2 nv — — 0/10 

Manganese 5/12 0/1 nv — — 0/6 Molybdenum 0/12 0/1 nv — — 0/11 Nickel 1/12 0/8 nv — — 0/3 Selenium 2/12 0/2 nv — — 0/8 Silver 9/12 1/3 <0.005, 0.006 — — nv Strontium 0/12 nv nv — — 0/12 

Thallium 12/12 nv nv — — nv 

Tungsten 2/12 1/5 0.03, <0.01 — — 0/5 Uranium 1/12 0/1 nv — — 0/10 Vanadium 2/12 0/3 nv — — 0/7 Zinc 4/12 1/7 ≤6.1, 9.3 5 — — 0/1 
Table A4B. Quality-control summary for replicate analyses of inorganic constituents, isotope tracers, and dissolved noble gases detected in sampleCruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin [Abbreviations: SD, standard deviation; RSD, percent relative standard deviation; RL, reporting level; μg/L, micrograms per liter; mg/L, milligrams per liter; ≤, less than or equthan; nv, no value in category; =, equal to; NWIS, U.S. Geological Survey (USGS) National Water Information System; NWQL, USGS National Water Quality Laboratory; —, 

centimeters of gas at standard temperature and pressure per gram of water] Constituent Number of replicate pairs with nondetections or ≤-coded values/number of replicate pairs Number of SDs >1⁄2 RL/number of replicate pairs with mean concentration <5 times the RL Concentrations in replicate pairs with SDs >1⁄2 RL (environmental sample, replicate sample) Number of replicate pair

with RSDs >10 percent/ number of replicate pair

with mean concentration

>5 times the RL 

Nutrients (mg/L) Ammonia (as nitrogen) 7/12 2/4 0.016, ≤0.013 0.031, ≤0.012 — 0/1 

Nitrate plus nitrite (as nitrogen) 4/12 0/1 nv — — 0/7 Nitrite (as nitrogen) 10/12 2/2 0.003, <0.001 0.004, 0.003 — nv Total nitrogen (ammonia + nitrite + nitrate + organic nitrogen) 3/12 0/2 nv — — 0/7 Orthophosphate (as phosphorus) 0/12 0/5 nv — — 1/7 

Major and minor ions, silica, and total dissolved soilds (TDS) (mg/L) Bromide 0/12 0/3 nv — — 0/9 

Calcium 0/12 nv nv — — 0/12 

Chloride 0/12 nv nv — — 0/12 

Fluoride 0/12 0/4 nv — — 0/8 Iodide 2/12 1/4 0.001, <0.001 — — 0/6 Magnesium 0/12 0/1 nv — — 0/11 Potassium 0/12 nv nv — — 0/12 

Sodium 0/12 nv nv — — 0/12 

Sulfate 0/12 nv nv — — 0/12 

Silica (as SiO2) 0/12 nv nv — — 0/12 

TDS 0/12 nv nv — — 0/12 

Arsenic, chromium, and iron species (μg/L) Arsenic (total) 6/12 0/4 nv — — 0/2 

Arsenic (III) 11/12 nv nv — — 0/1 

Chromium (total) 4/4 nv nv — — nv 

Chromium (VI) 4/4 nv nv — — nv 

Iron (total) 2/12 3/5 2, 4 4, <2 7, 5 0/5 Iron (II) 6 2/11 2/5 2, 4 4, <2 — 0/4 
Table A4B. Quality-control summary for replicate analyses of inorganic constituents, isotope tracers, and dissolved noble gases detected in sampleCruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin [Abbreviations: SD, standard deviation; RSD, percent relative standard deviation; RL, reporting level; μg/L, micrograms per liter; mg/L, milligrams per liter; ≤, less than or equthan; nv, no value in category; =, equal to; NWIS, U.S. Geological Survey (USGS) National Water Information System; NWQL, USGS National Water Quality Laboratory; —, centimeters of gas at standard temperature and pressure per gram of water]

Constituent

Number of 

replicate pairs with 

nondetections or 

≤-coded values/number 

of replicate pairs 

Number of 

SDs >1⁄2 RL/number of 

replicate pairs with 

mean concentration 

<5 times the RL

Concentrations in 

replicate pairs with 

SDs >1⁄2 RL 

(environmental sample, 

replicate sample) 

Number of replicate pair

with RSDs >10 percent/

number of replicate pair

with mean concentration

>5 times the RL

Isotope tracers 

δ2H in water (per mil) 0/12 nv nv — — 0/12 

δ18O in water (per mil) 0/12 nv nv — — 0/12 

δ13C in dissolved inorganic carbon 

(per mil)

0/12 nv nv — — 0/12 

Carbon-14 (percent modern) 0/12 nv nv — — 0/12 

Dissolved noble gases

Argon (104 cm3 STP/gH2O) 0/11 nv nv — — 0/11 

Helium-3/Helium-4 (106 atom ratio) 0/11 nv nv — — 1/11 

Helium-4 (108 cm3 STP/gH2O) 0/11 nv nv — — 2/11 

Krypton (108 cm3 STP/gH2O) 0/11 nv nv — — 0/11 

Neon (107 cm3 STP/gH2O) 0/11 nv nv — — 2/11 

Xenon (108 cm3 STP/gH2O) 0/11 nv nv — — 0/11 

1 Two replicate pairs for aluminum were re-analyzed because they were outside the limits of acceptable precision: 2.0, 3.3 μg/L (SD = 0.87 μg/L) and 5.4, <1.7 μg/L (SD = 3.2 

for the nondetection). All detections for these two replicate pairs were updated by the GAMA Program in the NWIS database to nondetections per the rerun results and accompa“Use new result. New result within method precision based on multiple reruns.”

2 This aluminum replicate pair had original values of 14.0 and 13.4 μg/L (RSD = 3 percent). The replicate pair was randomly requested for re-analysis, and the replicate result 

Program in the NWIS database from 13.4 to 17.0 μg/L (new RSD = 14 percent) per the rerun result and accompanying comment from the NWQL: “Use new result. New result wmultiple reruns.”

3 One replicate pair for boron was re-analyzed because it was outside the limits of acceptable precision: 104, 82 μg/L (RSD = 16 percent). The replicate result was updated by 

NWIS database from 82 to 96 μg/L (new RSD = 5 percent) per the rerun result and accompanying comment from the NWQL: “Use new result. New result within method precis

4 One replicate pair for lithium was re-analyzed because it was outside the limits of acceptable precision: 10.7, 8.33 μg/L (RSD = 17 percent). The replicate result was updated 

the NWIS database from 8.33 to 9.74 μg/L (new RSD = 7 percent) per the rerun result and accompanying comment from the NWQL: “Use new result. New result within methoreruns.”

5 This zinc replicate pair had original values of 6.7 and 9.2 μg/L (SD = 1.8 μg/L), which was inside the limits of acceptable precision when using the study reporting level of 6

replicate pair was requested for re-analysis, and the environmental result was updated by the GAMA Program in the NWIS database from 6.7 to 6.1 μg/L per the rerun result and the NWQL: “Use new result. New result within method precision based on multiple reruns.” Upon application of study reporting levels for trace elements, the new value was up

4.3 μg/L with 3.05 μg/L substituted for the nondetection).

6 One pair was not analyzed for iron (II) because total iron was not detected, giving a total of only 11 pairs.
136 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table A4C. Quality-control summary for replicate analyses of radioactive constituents detected in samples collected for the Santa 

Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA 

Priority Basin Project.

[For activities of radiochemical constituents, a replicate pair of analyses is defined as acceptable if the normalized absolute difference (NAD) is less than 1.65, 

which corresponds to a significance level of 5 percent (α = 0.05). Abbreviations: >, greater than; pCi/L, picocuries per liter; —, not detected, ±, plus or minus; 

nv, no value in category]

Constituent

Number of replicate pairs with 

NAD >1.65/total number of 

replicate pairs

Activities in replicate pairs with NAD >1.65 

(environmental sample, replicate sample)

(pCi/L)

Tritium 1/12 0.93 ± 0.35, — —

Radon-222 1/12 1

 724 ± 42, 594 ± 35 —

Gross alpha radioactivity, 72-hour count 2/12 2

 5.5 ± 1.6, — 3.82 ± 0.98, 7.4 ± 1.3

Gross alpha radioactivity, 30-day count 1/12 2

 2.3 ± 1.3, — —

Gross beta radioactivity, 72-hour count 3

 2/12 0.84 ± 0.38, 1.92 ± 0.39 2 8.68 ± 0.69, 2.78 ± 0.36

Gross beta radioactivity, 30-day count 1/12 2

 9.86 ± 0.72, 2.12 ± 0.35 —

Uranium-234 0/1 nv —

Uranium-235 0/1 nv —

Uranium-238 0/1 nv —

1

 Laboratory reported the replicate sample was received with an incorrect sample volume.

2

 Variability is outside the acceptable limits of precision for the HR-SG-08 replicate pair for gross alpha and beta radioactivity (72-hour and 30-day counts).

3

 One gross beta radioactivity (72-hour count) replicate pair had unacceptable variability based on application of the replicability criteria to the raw results: 

–0.65, 0.66 pCi/L (NAD = 2.1). However, both results were classified as nondetections (ssLC = 0.7) by the Eberline Analytical Services laboratory and therefore 

were not listed in this table.

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California 

GAMA Priority Basin Project.

[Acceptable recovery range is between 70 and 130 percent. Abbreviation: μg/L, micrograms per liter]

Constituent Number of spike 

samples

Minimum recovery 

(percent)

Maximum recovery 

(percent)

Median recovery 

(percent)

Acetone 11 77 124 106

Acrylonitrile 11 88 116 102

tert-Amyl methyl ether (TAME) 11 75 105 91

Benzene 11 87 109 98

Bromobenzene 11 74 105 93

Bromochloromethane 1 11 85 108 93

Bromodichloromethane 1 11 2

 0 119 80

Bromoform (Tribromomethane) 1 11 68 119 82

Bromomethane (Methyl bromide) 11 73 128 108

n-Butylbenzene 11 57 104 85

sec-Butylbenzene 11 69 107 97

tert-Butylbenzene 11 73 107 97

Carbon disulfide 1 11 67 127 78

Carbon tetrachloride (Tetrachloromethane) 1 11 75 131 85

Chlorobenzene 1 11 77 102 92

Chloroethane 1 11 88 122 98

Chloroform (Trichloromethane) 1 11 86 2

 1,320 97

Chloromethane 1 11 83 144 116

3-Chloropropene 11 82 114 92
Appendix 137

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California 

GAMA Priority Basin Project.—Continued

[Acceptable recovery range is between 70 and 130 percent. Abbreviation: μg/L, micrograms per liter]

Constituent Number of spike 

samples

Minimum recovery 

(percent)

Maximum recovery 

(percent)

Median recovery 

(percent)

2-Chlorotoluene 11 80 106 98

4-Chlorotoluene 11 81 112 101

Dibromochloromethane 1 11 2

 20 116 81

1,2-Dibromo-3-chloropropane (DBCP) 11 69 99 85

1,2-Dibromoethane (EDB) 11 82 107 91

Dibromomethane 1 11 80 117 89

1,2-Dichlorobenzene 11 84 112 101

1,3-Dichlorobenzene 1 11 79 104 99

1,4-Dichlorobenzene 1 11 83 111 102

trans-1,4-Dichloro-2-butene 11 81 115 85

Dichlorodifluoromethane (CFC-12) 1 11 50 143 86

1,1-Dichloroethane (1,1-DCA) 1 11 86 118 95

1,2-Dichloroethane (1,2-DCA) 1 11 86 124 96

1,1-Dichloroethene (1,1-DCE) 1 11 81 112 97

cis-1,2-Dichloroethene (cis-1,2-DCE) 11 82 102 93

trans-1,2-Dichloroethene (trans-1,2-DCE) 11 87 112 96

1,2-Dichloropropane 11 79 109 89

1,3-Dichloropropane 11 84 113 96

2,2-Dichloropropane 11 54 115 79

1,1-Dichloropropene 11 77 101 88

cis-1,3-Dichloropropene 11 72 114 81

trans-1,3-Dichloropropene 11 71 105 75

Diethyl ether 11 90 113 99

Diisopropyl ether (DIPE) 11 74 110 98

Ethylbenzene 11 73 106 88

Ethyl tert-butyl ether (ETBE) 11 77 107 96

Ethyl methacrylate 11 75 102 88

o-Ethyl toluene (1-Ethyl-2-methyl benzene) 11 75 108 95

Hexachlorobutadiene 11 53 90 84

Hexachloroethane 11 72 111 86

2-Hexanone (n-Butyl methyl ketone) 11 79 118 95

Iodomethane (Methyl iodide) 11 86 139 108

Isopropylbenzene 11 69 105 87

4-Isopropyl-1-methyl benzene 11 65 103 91

Methyl acrylate 11 73 100 88

Methyl acrylonitrile 11 91 118 101

Methyl tert-butyl ether (MTBE) 1 11 85 106 99

Methyl iso-butyl ketone (MIBK) 11 75 109 93

Methyl ethyl ketone (2-butanone, MEK) 11 86 114 100

Methyl methacrylate 11 73 100 88
138 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California 

GAMA Priority Basin Project.—Continued

[Acceptable recovery range is between 70 and 130 percent. Abbreviation: μg/L, micrograms per liter]

Constituent Number of spike 

samples

Minimum recovery 

(percent)

Maximum recovery 

(percent)

Median recovery 

(percent)

Methylene chloride (Dichloromethane) 1 11 87 115 94

Naphthalene 11 68 103 86

Perchloroethene (PCE, Tetrachloroethene) 1 11 77 126 93

n-Propylbenzene 11 67 102 87

Styrene 11 54 104 87

1,1,1,2-Tetrachloroethane 11 74 104 83

1,1,2,2-Tetrachloroethane 11 77 112 88

Tetrahydrofuran 11 86 114 101

1,2,3,4-Tetramethylbenzene 11 68 107 90

1,2,3,5-Tetramethylbenzene 11 66 110 91

Toluene 11 84 110 101

1,2,3-Trichlorobenzene 1 11 77 106 96

1,2,4-Trichlorobenzene 1 11 74 99 91

1,1,1-Trichloroethane (1,1,1-TCA) 1 11 80 122 93

1,1,2-Trichloroethane (1,1,2-TCA) 11 82 110 91

Trichloroethene (TCE) 1 11 71 106 88

Trichlorofluoromethane (CFC-11) 1 11 92 135 105

1,2,3-Trichloropropane (1,2,3-TCP) 11 82 106 95

Trichlorotrifluoroethane (CFC-113) 1 11 81 126 92

1,2,3-Trimethylbenzene 11 79 108 103

1,2,4-Trimethylbenzene 11 3

 0 3 180 107

1,3,5-Trimethylbenzene 11 73 106 92

Vinyl bromide (Bromoethene) 11 91 122 94

Vinyl chloride (Chloroethene) 11 83 146 89

m- and p-Xylene 11 75 107 96

o-Xylene 11 74 107 87

1

 Constituents detected in groundwater samples.

2

 Recoveries for one spike sample were affected by the high concentrations of three VOCs in the environmental sample relative to the spike concentration: 

bromodichloromethane, dibromochloromethane, and chloroform were detected in the environmental sample at concentrations (6.59 μg/L, 2.00 μg/L, and 

20.5 μg/L, respectively) up to 100 times the expected spike fortifications.

3

 All groundwater detections of 1,2,4-trimethylbenzene in the Hard Rock study unit were determined to be caused by contamination during the sampling 

process (Fram and others, 2012). Detected concentrations varied greatly within the replicate pairs and, therefore, between the environmental and spike samples. 

Background concentrations of the compound could not be subtracted out of the spike sample to calculate meaningful spike recoveries, resulting in two matrixspike recoveries outside the acceptable range.
Appendix 139

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California 

GAMA Priority Basin Project.

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number 

of spike 

samples

Number of recoveries 

outside the acceptable 

range

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetochlor 10 0 76 120 105

Alachlor 10 0 77 117 104

Atrazine 1 10 0 86 127 107

Azinphos-methyl 10 2 65 142 105

Azinphos-methyl oxon 10 3 44 111 74

Benfluralin 10 4 62 94 79

Carbaryl 1 10 3 82 139 111

2-Chloro-2,6-diethylacetanilide 10 0 82 117 100

4-Chloro-2-methylphenol 10 3 55 97 85

Chlorpyrifos 10 1 61 104 89

Chlorpyrifos oxon 10 10 14 67 40

Cyfluthrin 10 5 46 92 70

Cypermethrin 10 5 42 89 70

Dacthal (DCPA) 10 1 91 134 120

Deethylatrazine (2-Chloro-4-isopropylamino-6-amino-s-triazine) 1 10 0 70 114 95

Desulfinylfipronil 1 10 0 80 107 94

Desulfinylfipronil amide 10 0 73 109 90

Diazinon 10 0 83 117 103

3,4-Dichloroaniline 1 10 0 71 107 93

Dichlorvos 10 10 14 56 24

Dicrotophos 10 10 12 47 30

Dieldrin 10 0 90 124 105

2,6-Diethylaniline 1 10 0 82 117 105

Dimethoate 10 7 43 86 67

Ethion 10 2 65 104 77

Ethion monoxon 10 0 73 101 83

2-Ethyl-6-methylaniline 10 0 77 113 97

Fenamiphos 10 0 89 118 104

Fenamiphos sulfone 10 0 81 124 104

Fenamiphos sulfoxide 10 9 6 78 18

Fipronil 10 0 79 120 111

Fipronil sulfide 1 10 0 76 113 102

Fipronil sulfone 1 10 0 72 110 92

Fonofos 10 0 74 111 97

Hexazinone 1 10 7 43 79 65

Iprodione 10 4 58 97 78

Isofenphos 10 1 69 123 99

Malaoxon 10 2 58 104 85

Malathion 10 1 65 108 97

Metalaxyl 10 1 81 131 106
140 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California 

GAMA Priority Basin Project.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number 

of spike 

samples

Number of recoveries 

outside the acceptable 

range

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Methidathion 10 0 77 111 90

Metolachlor 1 10 0 73 119 102

Metribuzin 1 10 0 70 118 97

Myclobutanil 10 1 68 101 85

1-Naphthol 10 8 4 96 29

Paraoxon-methyl 10 4 46 102 72

Parathion-methyl 10 0 71 116 102

Pendimethalin 10 0 73 120 98

cis-Permethrin 10 5 46 91 70

Phorate 10 1 62 95 81

Phorate oxon 10 1 67 116 95

Phosmet 10 10 10 46 25

Phosmet oxon 10 10 10 50 33

Prometon 1 10 1 19 111 96

Prometryn 10 0 73 121 97

Pronamide (Propyzamide) 10 0 73 115 100

Simazine 1 10 0 80 123 100

Tebuthiuron 1 10 7 86 170 142

Terbufos 10 1 62 101 86

Terbufos oxon sulfone 10 6 42 101 69

Terbuthylazine 10 0 86 128 107

Tribufos 10 8 43 75 55

Trifluralin 10 1 68 106 86

1

 Constituent detected in groundwater samples.
Table A6. Quality-control summary for surrogate recoveries of volatile organic compounds (VOCs) and pesticides and pesticide degradates in samp

Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit, March 2011 through March 2012, California GAMA Priority Basin 

Surrogate Analytical schedule

Constitutent 

or constituent 

class 

analyzed

Surrogate information for blank samples Surrogate information for e

Number 

of 

analyses 1

Median 

recovery 

(percent)

Number of 

surrogate 

recoveries below 

70 percent

Number of 

surrogate 

recoveries above 

130 percent 

Number 

of 

analyses 2

Median 

recovery 

(percent)

Num

surro

recoveri

70 pe

1-Bromo-4-fluorobenzene 2020 VOC 14 91 0 0 111 83 0 

1,2-Dichloroethane-d4 2020 VOC 14 123 0 3 111 127 0 

Toluene-d8 2020 VOC 14 90 0 0 111 90 0 

Diazinon-d10 2003 Pesticide 13 88 0 0 110 84 8 

α-HCH-d6 2003 Pesticide 13 101 0 1 110 98 

1 Total number of blank samples for VOC and pesticide analyses includes field, equipment, and source-solution blanks; a source-solution blank was not sampled for pesticide 2 Three samples were omitted from this table: one environmental sample for pesticide analysis was ruined during analysis; environmental samples for VOC and pesticide anal

properly preserved, causing all results for organic constituents to be reviewed and rejected.
142 Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012

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For more information concerning the research in this report, contact the

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ISSN 2327-638X (Online)

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Printed on recycled paper http://dx.doi.org/10.3133/ds874

Davis and Shelton—Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012: 

Results from the California GAMA Program—Data Series 874