U.S. Department of the Interior

U.S. Geological Survey

Data Series 987

Version 1.1, January 2017

Prepared in cooperation with the California State Water Resources Control Board

Groundwater-Quality Data in the Monterey–Salinas 

Shallow Aquifer Study Unit, 2013: Results from the 

California GAMA Program
1

2

3

4

5

Cover. 1. Well near Santa Cruz, California. (Photograph taken by Christine Lawrence, U.S. Geological Survey.)

2. Field near Pajaro, California. (Photograph taken by George L. Bennett, U.S. Geological Survey.)

3. Salinas Valley, California. (Photograph taken by George L. Bennett, U.S. Geological Survey.)

4. Well near Santa Margarita, California. (Photograph taken by Dara A. Goldrath, U.S. Geological Survey.)

5. Salinas Valley, California. (Photograph taken by George L. Bennett, U.S. Geological Survey.)

Cover photographs
Groundwater-Quality Data in the 

Monterey–Salinas Shallow Aquifer Study 

Unit, 2013: Results from the California 

GAMA Program

By Dara A. Goldrath, Justin T. Kulongoski, and Tracy A. Davis

Prepared in cooperation with the California State Water Resources Control 

Board

Data Series 987

Version 1.1, January 2017

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, Director

U.S. Geological Survey, Reston, Virginia: 2016

First release: 2016

Revised: January 2017 (ver 1.1)

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

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

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

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

Suggested citation:

Goldrath, D.A., Kulongoski, J.T., and Davis, T.A., 2015, Groundwater-quality data in the Monterey–Salinas shallow 

aquifer study unit, (ver. 1.1, January 2017): Results from the California GAMA Program: U.S. Geological Survey Data 

Series 987, 132 p., http://dx.doi.org/10.3133/ds987.

ISSN 2327-638X (online)
iii

Contents

Acknowledgments........................................................................................................................................ix

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

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

Methods...........................................................................................................................................................5

Study Design..........................................................................................................................................5

Sample Collection and Analysis.......................................................................................................16

Data Reporting.....................................................................................................................................16

Comparison Benchmarks ..................................................................................................................16

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

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

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

Groundwater-Quality Data ................................................................................................................19

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

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

Constituents of Special Interest..............................................................................................20

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

Isotopic Tracers .........................................................................................................................21

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

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

References Cited..........................................................................................................................................23

Tables ...........................................................................................................................................................26

Appendix A..................................................................................................................................................107

Sample Collection and Analysis.....................................................................................................107

Data Reporting...................................................................................................................................109

Reporting Levels.......................................................................................................................109

Notation.....................................................................................................................................110

Constituents Measured in the Field and the Laboratory...................................................110

Quality-Control Methods and Results ...........................................................................................111

Assessment of Blank Results and Study Reporting Levels ..............................................111

Blank Collection and Analysis ......................................................................................111

Determining Study Reporting Levels ...........................................................................111

Detections in Field Blanks and Application of Study Reporting Levels.................112

Replicates..................................................................................................................................113

Assessment of Replicate Samples ..............................................................................113

Variability in Replicate Samples...................................................................................113

Matrix Spikes............................................................................................................................114

Assessment of Matrix Spikes .......................................................................................114

Matrix-Spike Recoveries...............................................................................................115

Surrogate Compound Recoveries................................................................................115

Other Quality-Control Results ................................................................................................115

References Cited...............................................................................................................................116
iv

Figures

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

Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project................................................................4

2. Map showing the boundaries of the Monterey–Salinas Shallow Aquifer study unit 

of the California Groundwater Ambient Monitoring and Assessment Priority Basin 

Project; the Santa Cruz, Pajaro Valley, Salinas River Valley, and Highlands study 

areas; major cities; topographic features; and hydrologic features....................................6

3. Map showing the distribution of grid cells, location of grid wells, and topographic 

features in the Santa Cruz study area of the Monterey–Salinas Shallow Aquifer study 

unit, California Groundwater Ambient Monitoring and Assessment Priority Basin 

Project ............................................................................................................................................7

4. Map showing the distribution of grid cells, the location of grid wells, and 

topographic features in the Pajaro Valley study area of the Monterey–Salinas Shallow 

Aquifer study unit, California Groundwater Ambient Monitoring and Assessment 

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

5. Maps showing the distribution of grid cells, location of sampled grid wells, and 

topographic features in the Salinas Valley and Paso Robles study areas of the 

Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project................................................................9

6. Map showing the distribution of the study-area cells, the location of sampled grid 

wells, and topographic features in the Highlands study area of the Monterey–

Salinas Shallow Aquifer study unit, California Groundwater Ambient Monitoring 

and Assessment Priority Basin Project ..................................................................................11

7. Map showing the distribution of the grid cells and subcells, the location of 

shallow-well tap sites, and topographic features in the Pajaro Valley study area 

of the Monterey–Salinas Shallow Aquifer study unit, California Groundwater 

Ambient Monitoring Assessment Priority Basin Project .....................................................13

8. Maps showing the distribution of the grid cells and subcells, the location of 

shallow-well tap sites, and topographic features in the Salinas Valley and Paso 

Robles study area of the Monterey–Salinas Shallow Aquifer study unit, California 

Groundwater Ambient Monitoring Assessment Priority Basin Project: A, northern 

part, and B, southern part .........................................................................................................14

9. Hierarchies used by the California Groundwater Ambient Monitoring Assessment 

Priority Basin Project to select benchmarks for comparison with groundwaterquality data ..................................................................................................................................18

Tables

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

wells sampled for the Monterey–Salinas Shallow Aquifer study unit, California 

Groundwater Ambient Monitoring and Assessment Priority Basin Project, 

October 2012 to May 2013 .........................................................................................................26

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

in groundwater samples from the Monterey–Salinas Shallow Aquifer study unit, 

California Groundwater Ambient Monitoring and Assessment Priority Basin 

Project, October 2012 to May 2013 ..........................................................................................30

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

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

Laboratory Schedule 2020.........................................................................................................31
v

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

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

Water Quality Laboratory Schedule 2003 ...............................................................................35

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

and reporting information for analyses performed by Weck Laboratories, Inc., City 

of Industry, California.................................................................................................................37

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

U.S. Geological Survey National Water Quality Laboratory Schedule 1948.....................37

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

U.S. Geological Survey National Water Quality Laboratory Schedule 2755.....................38

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

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

Water Quality Laboratory Schedule 1948 ...............................................................................38

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

information for laboratory analyses ........................................................................................39

3H. Noble gases, comparative thresholds, and reporting information for dissolved 

gases analyzed by the Lawrence Livermore National Laboratory.....................................39

4A. Water-quality indicators in grid-well samples collected for the Monterey–Salinas 

Shallow Aquifer study unit, California Groundwater Ambient Monitoring and 

Assessment Priority Basin Project, October 2012 to May 2013 ..........................................40

4B. Water-quality indicators in shallow-well tap-site samples collected for the 

Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project, October 2012 to May 2013..............46

5. Volatile organic compounds detected in grid-well samples collected for the 

Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project, October 2012 to May 2013..............49

6. Pesticides and pesticide degradates detected in grid-well samples collected for 

the Monterey-Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project, October 2012 to May 2013..............52

7. Constituents of special interest detected in grid-well samples collected for the 

Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project, October 2012 to May 2013..............54

8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas 

Shallow Aquifer study unit, California Groundwater Ambient Monitoring and 

Assessment Priority Basin Project, October 2012 to May 2013 ..........................................56

8B. Trace elements detected in shallow-well tap-site samples collected for the 

Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project, October 2012 to May 2013..............68

9A. Nutrients detected in grid-well samples collected for the Monterey–Salinas 

Shallow Aquifer study unit, California Groundwater Ambient Monitoring and 

Assessment Priority Basin Project, October 2012 to May 2013 ..........................................76

9B. Nutrients detected in shallow-well tap-site samples collected for the Monterey–

Salinas Shallow Aquifer study unit, California Groundwater Ambient Monitoring 

and Assessment Priority Basin Project, October 2012 to May 2013 ..................................80

10A. Major and minor ions, silica, and total dissolved solids detected in grid-well 

samples collected for the Monterey–Salinas Shallow Aquifer study unit, California 

Groundwater Ambient Monitoring and Assessment Priority Basin Project, 

October 2012 to May 2013 .........................................................................................................82

Tables—Continued
vi

10B. Major and minor ions, silica, and total dissolved solids detected in shallow-well 

tap-site samples collected for the Monterey–Salinas Shallow Aquifer study 

unit, California Groundwater Ambient Monitoring and Assessment Priority Basin 

Project, October 2012 to May 2013 ..........................................................................................88

11. Radioactive constituents detected in grid-well samples collected for the 

Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project, October 2012 to May 2013..............92

12. Isotopic tracers detected in grid-well samples collected for the Monterey–Salinas 

Shallow Aquifer study unit, California Groundwater Ambient Monitoring and 

Assessment Priority Basin Project, October 2012 to May 2013 ..........................................98

13. Dissolved noble gases detected in grid-well samples collected for the Monterey–

Salinas Shallow Aquifer study unit, California Groundwater Ambient Monitoring 

and Assessment Priority Basin Project, October 2012 to May 2013 ................................102

A–1. Analytical methods used for the determination of organic and inorganic 

constituents by the U.S. Geological Survey National Water Quality Laboratory 

and contract laboratories........................................................................................................121

A–2. Constituents detected in field blanks and study reporting levels used for the 

Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project, October 2012 to May 2013............123

A–3A. Quality-control summary for replicate pair analyses of organic constituents and 

special-interest constituents in samples collected for the Monterey–Salinas Shallow 

Aquifer study unit, California Groundwater Ambient Monitoring and Assessment 

Priority Basin Project, October 2012 to May 2013 ...............................................................124

A–3B. Quality-control summary for replicate pair analyses of inorganic constituents in 

samples collected for the Monterey–Salinas Shallow Aquifer study unit, California 

Groundwater Ambient Monitoring and Assessment Priority Basin Project, 

October 2012 to May 2013 .......................................................................................................125

A–3C. Quality-control summary for replicate pair analyses of radioactive constituents 

in samples collected for the Monterey–Salinas Shallow Aquifer study unit, 

California Groundwater Ambient Monitoring and Assessment Priority Basin 

Project, October 2012 to May 2013 ........................................................................................127

A–4A. Quality-control summary for matrix-spike recoveries of volatile organic 

compounds and the special interest constituent N-nitrosodimethylamine in 

samples collected for the Monterey–Salinas Shallow Aquifer study unit, California 

Groundwater Ambient Monitoring and Assessment Priority Basin Project, 

October 2012 to May 2013 .......................................................................................................127

A–4B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide 

degradates in samples collected for the Monterey–Salinas Shallow Aquifer study 

unit, California Groundwater Ambient Monitoring and Assessment Priority Basin 

Project, October 2012 to May 2013. .......................................................................................130

A–5. Quality-control summary for surrogate compound recoveries of volatile organic 

compounds and pesticides and pesticide degradates in samples collected for the 

Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient 

Monitoring and Assessment Priority Basin Project, October 2012 to May 2013............132

Tables—Continued
vii

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)

SI to Inch/foot/mile

Multiply By To obtain

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.28 foot (ft)

kilometer (km) 0.6214 mile (mi)

square kilometer (km2) 0.3861 square mile (mi2)

liter (L) 1.0567 quart (qt)

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound, avoirdupois (lb)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × 

°C) + 32.

Supplemental Information

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

25 °C).

Concentrations of chemical constituents in water are given in either 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).

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

Delta notation (δiE) represents the ratio of a heavier isotope of an element (δ) to the more 

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

per mil.

Datum

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

Abbreviations and Acronyms

AL-US action level (USEPA)

BBP Blind Blank Program

BQS Branch of Quality Systems (USGS)

CDWR California Department of Water Resources

DDW State Water Resources Control Board-Division of Drinking Water 

 (formerly the Department of Public Health, or CDPH)

GAMA Groundwater Ambient Monitoring and Assessment Program

GPS Global Positioning System

HAL-US lifetime health-advisory level (USEPA)

HBSL health-based screening level

IBSP Inorganic Blind Sample Project

LLNL Lawrence Livermore National Laboratory 

LRL laboratory reporting level

LT-MDL long-term method detection level

MCL-CA maximum contaminant level (SWRCB-DDW)

MCL-US maximum contaminant level (USEPA)

MDL method detection limit

MRL minimum reporting level

MS-SA Monterey–Salinas Shallow Aquifer study unit

MU method uncertainty

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

NAD normalized absolute difference

NAWQA National Water Quality Assessment Program (USGS)

NDMA N-nitrosodimethylamine 

NFM National Field Manual (USGS)

NL-CA notification level (SWRCB-DDW)

NWIS National Water Information System (USGS)

NWQL National Water Quality Laboratory (USGS)

PBP Priority Basin Project (GAMA)

PCFF Personal Computer Field Form program designed for USGS sampling

PVC polyvinyl chloride 
ix

QA quality assurance

QC quality control

RL reporting level

RSD relative standard deviation

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

SC specific conductance 

SD standard deviation

SMCL-CA Secondary Maximum Contaminant Level (SWRCB-DDW)

SMCL-US Secondary Maximum Contaminant Level (USEPA)

S-MS-H Monterey–Salinas Shallow Aquifer study unit Highlands study area 

S-MS-P Monterey–Salinas Shallow Aquifer study unit Pajaro study area

S-MS-SC Monterey–Salinas Shallow Aquifer study unit Santa Cruz study area 

S-MS-SV Monterey–Salinas Shallow Aquifer study unit Salinas Valley study area

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

 reporting results)

ssLC sample-specific critical level

SWRCB-DDW California State Water Resources Control Board-Division of Drinking Water

TDS total dissolved solids

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey 

VOC volatile organic compound

WCR well-completion report

Acknowledgments

The author thanks the following cooperators for their support: the California State Water 

Resources Control Board, California Department of Water Resources, and Lawrence Livermore 

National Laboratory. We especially thank the well owners for allowing the U.S. Geological 

Survey to collect samples from their wells. 

Thank you to Christine J. Lawrence of the U.S. Geological Survey for obtaining sample 

permissions, project support, and encouragement.

Abbreviations and Acronyms—Continued

Groundwater-Quality Data in the Monterey–Salinas 

Shallow Aquifer Study Unit, 2013: Results from the 

California GAMA Program

By Dara A. Goldrath, Justin T. Kulongoski, and Tracy A. Davis

Abstract

Groundwater quality in the 3,016-square-mile Monterey–

Salinas Shallow Aquifer study unit was investigated by 

the U.S. Geological Survey (USGS) from October 2012 to 

May 2013 as part of the California State Water Resources 

Control Board Groundwater Ambient Monitoring and 

Assessment (GAMA) Program’s Priority Basin Project. 

The GAMA Monterey–Salinas Shallow Aquifer study was 

designed to provide a spatially unbiased assessment of 

untreated-groundwater quality in the shallow-aquifer systems 

in parts of Monterey and San Luis Obispo Counties and to 

facilitate statistically consistent comparisons of untreatedgroundwater quality throughout California. The shallowaquifer system in the Monterey–Salinas Shallow Aquifer study 

unit was defined as those parts of the aquifer system shallower 

than the perforated depth intervals of public-supply wells, 

which generally corresponds to the part of the aquifer system 

used by domestic wells. Groundwater quality in the shallow 

aquifers can differ from the quality in the deeper waterbearing zones; shallow groundwater can be more vulnerable to 

surficial contamination. 

Samples were collected from 170 sites that were selected 

by using a spatially distributed, randomized grid-based 

method. The study unit was divided into 4 study areas, each 

study area was divided into grid cells, and 1 well was sampled 

in each of the 100 grid cells (grid wells). The grid wells were 

domestic wells or wells with screen depths similar to those 

in nearby domestic wells. A greater spatial density of data 

was achieved in 2 of the study areas by dividing grid cells in 

those study areas into subcells, and in 70 subcells, samples 

were collected from exterior faucets at sites where there were 

domestic wells or wells with screen depths similar to those in 

nearby domestic wells (shallow-well tap sites). 

Field water-quality indicators (dissolved oxygen, water 

temperature, pH, and specific conductance) were measured, 

and samples for analysis of inorganic constituents (trace 

elements, nutrients, major and minor ions, silica, total 

dissolved solids, and alkalinity) were collected at all 170 sites. 

In addition to these constituents, the samples from grid wells 

were analyzed for organic constituents (volatile organic 

compounds, pesticides and pesticide degradates), constituents 

of special interest (perchlorate and N-nitrosodimethylamine, or 

NDMA), radioactive constituents (radon-222 and gross-alpha 

and gross-beta radioactivity), and geochemical and age-dating 

tracers (stable isotopes of carbon in dissolved inorganic 

carbon, carbon-14 abundances, stable isotopes of hydrogen 

and oxygen in water, and tritium activities). 

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

and matrix spikes) were collected at up to 11 percent of the 

wells in the Monterey–Salinas Shallow Aquifer study unit, 

and the results for these samples were used to evaluate the 

quality of the data from the groundwater samples. With 

the exception of trace elements, blanks rarely contained 

detectable concentrations of any constituent, indicating that 

contamination from sample-collection procedures was not 

a significant source of bias in the data for the groundwater 

samples. Low concentrations of some trace elements were 

detected in blanks; therefore, the data were re-censored at 

higher reporting levels. Replicate samples generally were 

within the limits of acceptable analytical reproducibility. The 

median values of matrix-spike recoveries were within the 

acceptable range (70 to 130 percent) for the volatile organic 

compounds (VOCs) and N-nitrosodimethylamine (NDMA), 

but were only approximately 64 percent for pesticides and 

pesticide degradates. 

The sample-collection protocols used in this study were 

designed to obtain representative samples of groundwater. 

The quality of groundwater can differ from the quality of 

drinking water because water chemistry can change as a result 

of contact with plumbing systems or the atmosphere; because 

of treatment, disinfection, or blending with water from other 

sources; or some combination of these. Water quality in 

domestic wells is not regulated in California, however, to 

provide context for the water-quality data presented in this 

report, results were compared to benchmarks established for 

drinking-water quality. The primary comparison benchmarks 

were maximum contaminant levels established by the 

U.S. Environmental Protection Agency and the State of 

California (MCL-US and MCL-CA, respectively). Nonregulatory benchmarks were used for constituents without 

maximum contaminant levels (MCLs), including Health 
2 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Based Screening Levels (HBSLs) developed by the USGS 

and State of California secondary maximum contaminant 

levels (SMCL-CA) and notification levels. Most constituents 

detected in samples from the Monterey–Salinas Shallow 

Aquifer study unit had concentrations less than their respective 

benchmarks.

Of the 148 organic constituents analyzed in the 100 gridwell samples, 21 were detected, and all concentrations were 

less than the benchmarks. Volatile organic compounds were 

detected in 23 of the grid wells, and pesticides and pesticide 

degradates were detected in 20 grid wells. The special-interest 

constituent NDMA was detected above the HBSL in three 

samples, one of which also had a perchlorate concentration 

greater than the MCL-CA.

Of the inorganic constituents, 6 were detected at 

concentrations above their respective MCL benchmarks 

in grid-well samples: arsenic (5 grid wells above the MCL 

of 10 micrograms per liter, μg/L), selenium (3 grid wells, 

MCL of 50 μg/L), uranium (4 grid wells, MCL of 30 μg/L), 

nitrate (16 grid wells, MCL of 10 milligrams per liter, mg/L), 

adjusted gross alpha particle activity (10 grid wells, MCL of 

15 picocuries per liter, pCi/L), and gross beta particle activity 

(1 grid well, MCL of 50 pCi/L). An additional 4 inorganic 

constituents were detected at concentrations above their 

respective HBSL benchmarks in grid-well samples: boron 

(1 grid well above the HBSL of 6,000 μg/L), manganese 

(8 grid wells, HBSL of 300 μg/L), molybdenum (6 grid wells, 

HBSL of 40 μg/L), and strontium (6 grid wells, HBSL of 

4,000 μg/L). Of the inorganic constituents, 4 were detected 

at concentrations above their non-health based SMCL 

benchmarks in grid-well samples: iron (9 grid wells above 

the SMCL of 300 μg/L), chloride (7 grid wells, SMCL of 

500 mg/L), sulfate (14 grid wells, SMCL of 500 mg/L), and 

total dissolved solids (27 grid wells, SMCL of 1,000 mg/L). 

Of the inorganic constituents analyzed in the 70 shallowwell tap sites, 10 were detected at concentrations above the 

benchmarks. Of the inorganic constituents, 3 were detected 

at concentrations above their respective MCL benchmarks 

in shallow-well tap sites: arsenic (2 shallow-well tap sites 

above the MCL of 10 μg/L), uranium (2 shallow-well tap 

sites, MCL of 30 μg/L), and nitrate (24 shallow-well tap sites, 

MCL of 10 mg/L). An additional 3 inorganic constituents were 

detected above their respective HBSL benchmarks in shallowwell tap sites: manganese (4 shallow-well tap sites above 

the HBSL of 300 μg/L), molybdenum (4 shallow-well tap 

sites, HBSL of 40 μg/L), and zinc (2 shallow-well tap sites, 

HBSL of 2,000 μg/L). Of the inorganic constituents, 4 were 

detected at concentrations above their non-health based SMCL 

benchmarks in shallow-well tap sites: iron (6 shallow-well tap 

sites above the SMCL of 300 μg/L), chloride (1 shallow-well 

tap site, SMCL of 500 mg/L), sulfate (9 shallow-well tap sites, 

SMCL of 500 mg/L), and total dissolved solids (15 shallowwell tap sites, SMCL of 1,000 mg/L).

Introduction

About one-half of the water used for the public and 

domestic drinking-water supply in California is groundwater 

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

groundwater in aquifers drinking-water supply, establish 

a baseline groundwater-quality monitoring program, and 

increase the availability of groundwater-quality data to the 

public, 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, 2015, at http://www.waterboards.

ca.gov/water_issues/programs/gama/) in 2000 in response to a 

legislative mandate (State of California, 2001a, 2001b). 

The GAMA Program currently consists of four projects: 

(1) the GAMA Priority Basin Project (PBP), led by the 

USGS (U.S. Geological Survey, 2015, California Water 

Science Center website at http://ca.water.usgs.gov/gama/); 

(2) the GAMA Domestic Well Project, led by the SWRCB; 

(3) GAMA Special Studies, led by LLNL; and (4) the 

GeoTracker GAMA publicly accessible on-line groundwaterinformation system, led by the SWRCB. The first phase of the 

GAMA-PBP (2004–12) is focused on groundwater used for 

public drinking-water supply, which is typically the deeper 

part of an aquifer system in a groundwater basin. The second 

phase of the GAMA-PBP (the subject of this report) is focused 

on the shallow-aquifer system typically used by domestic 

and small-system wells. The GAMA Domestic Well Project 

samples domestic wells in selected counties, and the GAMA 

Special Studies Project uses research methods to help explain 

the source, fate, transport, and presence of chemicals that can 

affect groundwater quality. The GeoTracker GAMA stores all 

data collected for the GAMA Program; groundwater-quality 

data and related reports collected by other State agencies, 

such as the State Water Resources Control Board-Division of 

Drinking Water (DDW; formerly the Department of Public 

Health, or CDPH), California Department of Water Resources 

(CDWR), California Department of Pesticide Regulation 

(CDPR); and data collected from environmental monitoring 

wells at contaminated or remediated sites by the SWRCB and 

regional boards.
Introduction 3

The GAMA-PBP was initiated in response to the 

Groundwater Quality Monitoring Act of 2001 to assess and 

monitor the quality of groundwater in California (State of 

California, 2001b). For the first phase of the GAMA-PBP, 

the USGS, in collaboration with the SWRCB, developed a 

monitoring plan to assess groundwater resources used for 

public drinking-water supply through statistically reliable 

sampling approaches (Belitz and others, 2003; California State 

Water Resources Control Board, 2003). Groundwater basins 

and areas outside of basins were prioritized for sampling 

primarily on the basis of the distribution of wells listed in the 

State of California’s database of public-supply wells. (The 

Drinking Water Program that regulates public-supply wells 

was transferred from the California Department of Public 

Health to the SWRCB Division of Drinking Water on July 1, 

2014.) The 35 study units sampled in the first phase (2004–

12) covered approximately 95 percent of the groundwater 

resources used for public-supply statewide. 

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

method of prioritization was required because there is no 

statewide database of private wells available to prioritize 

areas for sampling. To prioritize shallow aquifers, California 

was divided into 938 groundwater units that correspond to 

the 463 alluvial groundwater basins defined by the CDWR 

and 453 areas outside of basins (highland areas; Johnson 

and Belitz, 2014). The distribution of households relying 

on domestic wells was estimated from U.S. Census data 

(U.S. Census Bureau, 1990), and water-use and well-location 

information was compiled from well-completion reports 

(WCRs) submitted to the CDWR (Johnson and Belitz, 2015). 

The groundwater units were prioritized for sampling on the 

basis of the number and density of households relying on 

domestic wells. Groundwater units were grouped into study 

units designed to facilitate comparison of groundwater quality 

between the shallow aquifer systems assessed in the second 

phase of the GAMA-PBP and the deeper aquifer systems 

assessed in the first phase.

The Monterey–Salinas Shallow Aquifer (MS-SA) study 

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

phase of the GAMA-PBP and is in the Southern Coast Ranges 

hydrogeologic province (fig. 1).

Three types of water-quality assessments are being 

completed with the data collected in each study unit: 

(1) Status, the current quality of the groundwater resource; 

(2) Understanding, identification of the natural and human 

factors affecting groundwater quality; and (3) Trends, 

changes in groundwater quality (U.S. Geological Survey, 

2013). These three objectives were modeled after those of 

the USGS National Water Quality Assessment (NAWQA) 

Program (Hirsch and others, 1988). The sample-collection 

protocols used in this GAMA study were designed to obtain 

representative samples of groundwater. The quality of 

groundwater can differ from the quality of drinking water 

because water chemistry can change as a result of contact with 

plumbing systems or the atmosphere; because of treatment, 

disinfection, blending with water from other sources; or from 

some combination of these. 

In most groundwater basins, domestic and small-system 

wells typically are shallower than public-supply wells (for 

example, Burow and others, 2007; Burton and others, 2012). 

The shallow aquifer system assessed in this study unit is 

defined as that part of the aquifer in which domestic wells 

and small-system wells have perforated depth intervals and is 

generally shallower than the primary aquifer system used by 

public-supply wells, which was assessed in the first phase of 

the GAMA-PBP (Kulongoski and Belitz, 2011). 

This USGS data-series report is similar to other USGS 

data series reports written for the first phase of the GAMAPBP study units sampled to date but is the second in a series 

of reports (data-series report, scientific investigation report, 

and fact sheet) presenting the water-quality data collected 

for the second phase of the GAMA-PBP in the MS-SA study 

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

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

for groundwater samples collected in the MS-SA study 

unit, and (3) the results of quality-control (QC) analyses. 

Groundwater samples were analyzed for field water-quality 

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

constituents; and geochemical and isotopic tracers. To provide 

context, the water-quality data presented in this report were 

compared to regulatory and non-regulatory benchmarks 

established by the U.S. Environmental Protection Agency 

(USEPA), the State of California, and the USGS for drinking 

water that do not apply to raw (untreated) groundwater. The 

factors that influence the distribution of the constituents 

detected in groundwater samples are to be discussed in 

forthcoming publications. Published and quality-assured 

data collected for the GAMA Program are available through 

the USGS National Water Information System (NWIS) web 

interface (accessible at http://waterdata.usgs.gov/ca/nwis/) 

and the SWRCB Geotracker Database (accessible at 

https://geotracker.waterboards.ca.gov/gama/).
4 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Basin and Range

Central

Valley

Klamath

Mountains

Desert

Cascades and

Modoc Plateau

Southern Coast

Ranges

Sierra

Nevada

Northern

Coast

Ranges

Monterey-Salinas

Shallow Aquifer

study unit

(figure 2)

San Diego

Drainages

Transverse Ranges and

selected Peninsular Ranges

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

North American Datum of 1983

Provinces from Belitz and others, 2003.

sac14-0533_Figure 01

Figure 1. Hydrogeologic provinces of California and the location of the Monterey–Salinas Shallow Aquifer study unit, California 

Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project.
Methods 5

Methods

Methods used for the GAMA-PBP shallow aquifer study 

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

design a sampling plan suitable for statistical representation; 

(2) collect samples in a consistent manner; (3) to analyze 

samples by using proven and reliable laboratory methods; 

(4) to assure the quality of the groundwater data; and (5) to 

maintain data securely and with relevant documentation. 

Appendix A contains detailed descriptions of the samplecollection protocols and analytical methods, the quality 

assurance (QA) methods, and the results of analyses of QC 

samples both for the grid well and for wells sampled at a tap.

Study Design

The MS-SA study unit is in the Southern Coast Ranges 

hydrogeologic province described by Belitz and others (2003). 

The study unit covers approximately 3,020 square miles (mi2) 

in Monterey and San Luis Obispo Counties, in the central 

coast region of California (fig. 2). The MS-SA study unit 

(phase two) overlaps the area defined as the Monterey Bay 

and Salinas Valley groundwater basins (MS) study unit for 

the GAMA-PBP assessment of public-supply aquifers (phase 

one; Kulongoski and Belitz, 2011). The MS-SA study unit was 

divided into four study areas: the Santa Cruz (MS-SC) study 

area, the Pajaro Valley (MS-P) study area, the Salinas Valley 

(MS-SV) study area, and the Highlands (MS-H) study area 

(fig. 2). 

Together, the MS-SC, MS-P, and MS-SV study areas 

correspond to the MS study unit of Kulongoski and Belitz 

(2011), except that the Carmel Valley was included in the MS 

study unit, but was not included in the MS-SA study areas 

(fig. 2). The MS-SC covers about 82 mi2 and includes the 

following groundwater basins: the Felton Area, Scotts Valley, 

Santa Cruz Purisima Formation Highlands, West Santa Cruz 

Terrace, and Soquel Valley groundwater basins (California 

Department of Water Resources, 2003). The MS-P study area 

is about 138 mi2 and covers of the Pajaro Valley groundwater 

basin. The MS-SV study area is about 772 mi2 and includes 

the following groundwater subbasins of the Salinas Valley: 

180/400 Foot aquifer, East Side aquifer, Forebay aquifer, 

Upper Valley aquifer, Paso Robles area, Seaside area, and 

Corral de Tierra area. In the original GAMA-PBP MS study, 

the Salinas Valley study area included only the Forebay 

aquifer and Upper Valley aquifer subbasins; the Paso Robles 

area was defined as its own study area, and the other four 

subbasins were combined with the Pajaro Valley Basin to form 

the Monterey study area (Kulongoski and Belitz, 2007, 2011). 

For both phases of GAMA studies, the boundaries of the Paso 

Robles area were defined differently than they were by the 

CDWR (2003); only parts of the Paso Robles area mapped as 

having Quaternary alluvium as the surficial geologic unit were 

included in the GAMA studies. The hydrogeologic setting of 

the region corresponding to the MS-SC, MS-P, and MS-SV 

study areas is described in detail by Kulongoski and Belitz 

(2011), and the description is not repeated here. 

The MS-H study area covers about 2,026 mi2 surrounding 

the MS-SV study area. The MS-H study area was defined by 

the extent of the groundwater units in the highlands upgradient 

from the Salinas Valley groundwater subbasins (Johnson and 

Belitz, 2013) and approximately corresponds to the watershed 

of the Salinas River and its tributaries. The study area includes 

parts of several mountain ranges that have distinct geologic 

characteristics. On the east side of the Salinas Valley, the 

MS-H study area extends approximately to the trace of the 

San Andreas Fault in the Gabilan Range. The bedrock of 

the Gabilan Range is part of the Salinian Block and consists 

of Mesozoic granitic rocks at the north end, of the Miocene 

Pinnacles volcanic field at approximately the latitude of 

Soledad, and of variably metamorphosed Cenozoic marine 

sedimentary rocks at the southern end. On the west side of the 

Salinas Valley, the MS-H study area includes parts of the Santa 

Lucia Range, a complex mixture of Mesozoic granitic rocks 

and variably metamorphosed Cretaceous and Cenozoic marine 

sedimentary rocks (Alt and Hyndman, 2000). The southern 

part of the MS-H study area also includes the Plio-Pleistocene 

alluvium of the Paso Robles Area groundwater basin that is 

not included in the MS-SV study area.

The MS-H 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. These hardrock aquifers are recharged by infiltration of precipitation, 

snow melt, and water from lakes and streams (California 

Department of Water Resources, 2011). 

A total of 170 sites were sampled in the MS-SA study 

unit, which were selected to provide a statistically unbiased, 

spatially distributed assessment of the quality of groundwater 

resources in the shallow aquifer system. Sites were selected by 

using a grid-based method; each study area was divided into 

equal-area grid cells (Scott, 1990), and one site was randomly 

selected for sampling in each cell. 
6 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

The target grid-cell size for the three study areas in 

groundwater basins was 50 square kilometers (km2), with no 

fewer than 15 cells per study area. The MS-SC study area 

was divided into fifteen 14-km2 grid cells (fig. 3); the MS-P 

area was divided into fifteen 19-km2 grid cells (fig. 4); and the 

MS-SV study area was divided into forty 50-km2 grid cells 

(fig. 5). The MS-H study area contained relatively few wells, 

so to reduce the number of cells potentially containing no 

wells available for sampling, only a part of the study area was 

included in the gridded area. 

Figure 2. Boundaries of the Monterey–Salinas Shallow Aquifer study unit of the California Groundwater Ambient Monitoring and 

Assessment (GAMA) Priority Basin Project; the Santa Cruz, Pajaro Valley, Salinas River Valley, and Highlands study areas; major cities; 

topographic features; and hydrologic features.

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

Lake

San Antonio

Lake

Nacimiento

152

152

1

33

180

198

41

101

99

5

280

198

5

1

46

33

101

Salinas

Santa Cruz

King City

Paso Robles

Soledad

Monterey

Salinas Valley

Corral de Tierra area

Salinas Valley

Paso Robles area

Salinas Valley

Upper Valley aquifer

Salinas Valley

Forebay aquifer

Salinas Valley

East Side aquifer

Pajaro

Valley

Soquel

Valley

Santa Cruz Purisima

Formation Highlands

West Santa

Cruz Terrace

Felton area

Salinas Valley

Seaside area

Salinas Valley

180/400 Foot aquifer

Salinas RiverSalinas River

Kings River Kings River

San Joaquin RiverSan Joaquin River

San Benito River San Benito River

Fresno River resno River

Fresno SloughFresno Slough

Chowchilla RiverChowchilla River

San Juan CreekSan Juan Creek

Arroyo Seco Arroyo Seco

Los Gatos CreekLos Gatos Creek

Tule River

Cholame CreekCholame Creek

Nacimiento River

Pajaro River Pajaro River

Estrella River Estrella River

San Antonio RiverSan Antonio River

San Lorenzo CreekSan Lorenzo Creek

Huerhuero Creek

Carmel RiverCarmel River

SAN MATEO

CO

SANTA

CRUZ

CO

SANTA

CLARA

CO

STANISLAUS CO MERCED CO

SAN BENITO CO

SAN LUIS OBISPO CO

KERN CO

KINGS CO

TULARE CO

FRESNO CO

MONTEREY

CO

San Lorenzo San Lorenzo

River

MADERA

CO

Panoche CreekPanoche Creek

Santa Lucia Range

Sierra de Salinas

Range

Gabilan Range

Llagas CreekLlagas Creek

Santa Cruz Mountains

Temblor Range

La Panza Range

Monterey

Bay

Scotts Valley

EXPLANATION

County boundary

San Andreas fault zone

Salinas Paso Robles Valley study area 

Pajaro River Valley study area

Santa Cruz study area

Highlands study area 

Groundwater basins

and subbasins

0 15 30 MILES

0 15 30 KILOMETERS

Base modified from U.S. Geological Survey 

digital data, various scales

Albers Equal Area Conic Projection

North American Datum of 1983

37°

36°

30'

36°

35°

30'

122°30' 122° 121°30' 121° 120°30' 120° 119°30'

SAC15-0561_fig 02
Methods 7

The Highlands study area (fig. 6) was defined as the collective 

area of all hydrologic unit code (HUC) watersheds that were, 

in some part, within 3-km of the boundary of the Salinas 

Valley. Because the MS-H study area had so few wells, the 

target grid-cell size was 175 km2. The study area was divided 

into thirty, 175-km2 cells. Geographic features can force a grid 

cell to be divided into multiple pieces to obtain the designated 

coverage area for each cell. For instance, a single grid cell 

may have parts on both sides of the Salinas Valley.

Figure 3. Distribution of grid cells, location of grid wells, and topographic features in the Santa Cruz study area of the Monterey–

Salinas Shallow Aquifer study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project.

MS-SC15

SC14

SC13

SC12

SC11

SC10

SC09

SC08

SC07

SC06

SC05

SC04

SC03

SC02

SC01

122° 121°50’

37°

5’

36°

55’

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

EXPLANATION

SC08

Santa Cruz study area Santa Cruz grid well and identifier

 "MS-" identifier has been omitted

Santa Cruz grid cell

Santa Cruz Mountains 

Pacific Ocean

Monterey 

Bay

Base modified from U.S. Geological Survey 

digital data, various scales

Albers Equal Area Conic Projection

North American Datum of 1983

sac14-0533_fig3
8 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Figure 4. Distribution of grid cells, the location of grid wells, and topographic features in the Pajaro Valley study area of the Monterey–

Salinas Shallow Aquifer study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project.

P15

P14

P13

P12

P11

P10

P09

P08

P07

P06

P05

P04

P03

P02

P01

37°

36°

55’

36°

50’

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

121°55’ 121°45’ 121°35’

EXPLANATION

Pajaro Valley study area

Pajaro grid cell

Pajaro Valley grid well and identifier

 "MS-" identifier has been omitted

P08

Santa Cruz 

Mountains 

Monterey

Bay 

Base modified from U.S. Geological Survey 

digital data, various scales

Albers Equal Area Conic Projection

North American Datum of 1983

sac14-0533_fig4
Methods 9

Figure 5. Distribution of grid cells, location of sampled grid wells, and topographic features in the Salinas Valley and Paso Robles 

study areas of the Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) 

Priority Basin Project: A, northern part; B, southern part.

0 10 20 MILES

0 10 20 KILOMETERS

122° 121°30’ 121° 120°30’

36°

30’

36°

EXPLANATION

Salinas Paso Robles Valley

 study area 

Salinas Paso Robles

 Valley grid cell

Salinas Paso Robles Valley

 grid well and identifier

 "MS-" identifier has been omitted

SV15

5

5 15

15

Pacific Ocean

Monterey

Bay 

A

SV38

SV37

SV36

SV35

SV34

SV33

SV32

SV31

SV30

SV29

SV27

SV26

SV25

SV24

SV23

SV22

SV21

SV20

SV19

SV18

SV17

SV16

SV15

SV12

SV11

SV10

SV09

SV08

SV07

SV06

SV05

SV04

SV03

Base modified from U.S. Geological Survey 

digital data, various scales

Albers Equal Area Conic Projection

North American Datum of 1983

Gabilan Mountains

Santa Lucia Range

Sierra de Salinas Range

sac14-0533_fig5a

Monterey
10 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Figure 5.—Continued

121° 120°30’ 120°

36°

35°

30’

EXPLANATION

0 10 20 MILES

0 10 20 KILOMETERS

Salinas Paso Robles Valley

 study area 

Salinas Paso Robles

 Valley grid cell

Salinas Paso Robles Valley

 grid well and identifier

 "MS-" identifier has been omitted

SV40

5

5

15

15

Pacific Ocean

B

SV40

SV28 SV39

SV14

SV13

SV02

SV01 Temblor Mountains

La Panza Range

Santa Lucia Range

Base modified from U.S. Geological Survey 

digital data, various scales

Albers Equal Area Conic Projection

North American Datum of 1983

sac14-0533_fig5b
Methods 11

Figure 6. Distribution of the study-area cells, the location of sampled grid wells, and topographic features in the Highlands study area 

of the Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority 

Basin Project.

0 5 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

121°30' 121° 120°30' 120°

36°

30'

36°

35°

30'

Base modified from U.S. Geological Survey 

digital data, various scales

Albers Equal Area Conic Projection

North American Datum of 1983 5 15

15

Highlands study area Highlands grid well and identifier

 "MS-" identifier has been omitted

H08

Grid cell boundary

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

H30

H29

H28

H27

H26

H24 H25

H23

H22

H21

H20

H19

H18

H17

H16 H15

H14

H13

H12

H11

H10

H09

H08

H07

H06

H05

H04

H03

H02

H01

Pinnacles

National

Park

Temblor Mountains

La Panza Range

Santa Lucia Range

Sierra de Salinas Range

Gabilan Mountains

sac14-0533_fig6

Monterey
12 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

One well was selected for sampling in each of the 

one-hundred grid cells in the MS-SA study unit. Wells were 

primarily identified from CDWR well-completion reports 

(WCRs). The WCRs for domestic wells that contained 

location and well-construction information and were shallower 

than the median depth of the primary aquifer system used 

by public-supply wells in the study area were compiled for 

each grid cell. To ensure that wells were randomly selected, 

a random latitude-longitude point was defined in each cell, 

and wells closest to the random point were given highest 

priority. Wells were visited in descending order of priority 

until permission to sample a suitable well was obtained. For 

study-area cells that had exhausted available WCRs or had 

none on file, potential wells were identified by door-to-door 

canvassing. Wells in these cells were sampled when a well 

owner volunteered to participate in the MS-SA study. Basic 

sampling criteria (for example, a sampling point that is prior 

to water treatment or the capacity to pump for an extended 

period) were considered prior to sampling.

The 100 grid wells sampled in the MS-SA study unit 

were named by using the prefixes “S-MS-P” for wells in 

the Pajaro Valley study area, “S-MS-SC” for wells in the 

Santa Cruz study area, “S-MS-SV” for wells in the Salinas 

Valley, and “S-MS-H” for wells in the Highlands study area. 

A sequence number defined by the number of the grid cell in 

which the samples were collected in each study area was then 

added, creating a unique alphanumeric GAMA identification 

number. 

The GAMA identification number for grid wells, the 

date sampled, well type, well elevation, available wellconstruction information, and the depth to the water level are 

shown in table 1. Groundwater samples were collected from 

October 2012 to May 2013. Well types in table 1 are identified 

as production or spring. Any site with a pump that brought 

groundwater to the land surface was considered a production 

well, whereas any site where the groundwater level intersected 

the land surface was considered a spring. Grid wells included 

99 production wells and 1 spring, but for simplicity, all 

sampled sites are referred to as wells for the remainder of this 

report. 

Well locations were verified by using a global positioning 

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

comparison with existing well information in databases of 

the USGS and the State ; and information provided by well 

owners, WCRs, or other sources of construction information. 

Well locations and information were recorded by hand on 

field sheets. All information was verified and then uploaded 

into the USGS NWIS. Well owner and well-use information is 

confidential.

To increase the spatial density of data for inorganic 

constituents (nutrients, trace elements, and major ions), 

70 additional sites (“shallow-well tap sites”) were sampled in 

the MS-P and MS-SV study areas. Each grid cell in the MS-P 

study area was divided into two 9.5-km2 subcells (fig. 7), 

and each grid cell in the MS-SV study area was divided 

into three 17-km2 subcells (figs. 8A, B). The 95 subcells that 

did not contain a grid well were searched for appropriated 

sampling sites. Potential sites were identified from CDWR 

WCRs and door-to-door canvassing. The site requirements 

were less stringent than those used for selection of the grid 

wells. Examination of WCRs during selection of the grid 

wells indicated that most wells in the MS-SV and MS-P 

study areas that were coded as domestic wells on WCRs 

were shallower than the public-supply wells sampled in the 

same areas by Kulongoski and Belitz (2007, 2011); therefore, 

sites lacking WCRs or well-construction information were 

considered eligible for sampling if the site was supplied by 

a domestic well. In some MS-SV and MS-P areas, irrigation 

wells and small system public-supply wells were as shallow as 

domestic wells and were considered eligible for sampling as 

shallow-well tap sites. In most cases, the sampling point was 

a hose bib on the outside of a dwelling and was commonly 

downstream of a pressure tank. Sites with wells not capable 

of running for long periods of time were considered eligible 

for sampling as wells were not required to be purged prior 

to sampling. The first eligible site for which permission to 

sample could be obtained was selected for sampling, and sites 

were sampled in 70 of the 95 available subcells. These 70 sites 

are referred to as “shallow-well tap sites” to distinguish 

them from the 100 grid wells. The shallow-well tap sites 

were assigned GAMA identification numbers on basis of the 

GAMA identification of the grid well in the cell, the prefix “T” 

appended to the end of the grid-well GAMA identification, and 

a sequence number (1 or 2) for the number of the subcell.
Methods 13

Figure 7. Distribution of the grid cells and subcells, the location of shallow-well tap sites, and topographic features in the Pajaro 

Valley study area of the Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient Monitoring Assessment (GAMA) 

Priority Basin Project.

P15

P14

P13

P12

P11

P10

P09

P08

P07

P06

P05

P04

 P03

P02

P01

P15-T1

P14-T1

P13-T1

P12-T1

P11-T1

P10-T1

P09-T1

P08-T1

Pajaro Valley study area

Pajaro Valley subcell

Pajaro Valley grid cell

Pajaro Valley grid well

 and identifier

Pajaro Valley shallow-well tap 

 sites and identifier

 "MS-" identifier has been omitted

P08

P08-T1

P07-T1

P06-T1

P05-T1

P04-T1

P03-T1

P02-T1

P01-T1

Base modified from U.S. Geological Survey 

digital data, various scales

Albers Equal Area Conic Projection

North American Datum of 1983

37°

36°

55'

36°

50'

EXPLANATION

121°55' 121°35'

Pacific Ocean

Monterey Bay

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

121°45'

Santa Cruz 

Mountains 

sac14-0533_fig07
14 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Figure 8. Distribution of the grid cells and subcells, the location of shallow-well tap sites, and topographic features in the Salinas 

Valley and Paso Robles study area of the Monterey–Salinas Shallow Aquifer study unit, California Groundwater Ambient Monitoring 

Assessment (GAMA) Priority Basin Project: A, northern part, and B, southern part.

SV34-T2

SV34-T1

SV21-T1 SV20-T2

SV08-T1

SV08-T2

SV06-T2

SV06-T1

SV05-T1

SV05-T2

SV04-T2

SV04-T1

SV19-T2

SV09-T2

SV09-T1

SV19-T1

SV18-T1

SV35-T1

SV35-T2

SV36-T2

SV36-T1

SV22-T2

SV33-T1

SV37-T1

SV32-T1

SV23-T1

SV24-T2

SV25-T1

SV11-T2

SV11-T1

SV24-T1

SV30-T1

SV17-T1

SV16-T1

SV29-T1

SV26-T1

SV27-T1

SV16-T2

SV17-T2

SV22-T1

SV26-T2

SV26

SV12

SV16 SV29

SV29-T2

SV27

SV15

SV21-T2

SV20-T1

SV25-T2

sac14-0533_fig08a

A

5

5

15

0 10 15 20 MILES

0 10 20 KILOMETERS

122° 121°30' 121°

36°

30'

36°

EXPLANATION

Salinas Paso Robles 

Valley study area 

Salinas Paso Robles

 Valley grid cell

Salinas Paso Robles

 Valley subcell

Salinas Paso Robles Valley shallow-

 well tap site and identifier

 "MS-" identifier has been omitted

SV27-T1

Base modified from U.S. Geological Survey 

digital data, various scales

Albers Equal Area Conic Projection

North American Datum of 1983

Salinas Paso Robles Valley

 grid well and identifier

P08

Pacific Ocean

Monterey Bay

SV35

SV34

SV06

SV05

SV23 SV38

SV31 SV17

SV10

SV11

SV24 SV30

SV22

SV03

SV18

SV04

SV09

SV37

SV33

SV21

SV07

SV20 SV08 SV19

SV36

SV32

SV25

Monterey
Methods 15

121° 120°30’

36°

35°

30’

EXPLANATION

Base modified from U.S. Geological Survey and 

other Federal and State digital data, various scales

Albers Equal Area Conic Projection

North American Datum of 1983

0 10 20 MILES

0 10 20 KILOMETERS

5

5

15

15

Salinas Paso Robles

 Valley study area 

Salinas Paso Robles

 Valley grid cell

Salinas Paso Robles

 Valley subcell

Salinas Paso Robles Valley shallow-

 well tap site and identifier

 "MS-" identifier has been omitted

SV01-T1

Salinas Paso Robles Valley

 grid well and identifier

P08

Pacific Ocean

SV13-T1

SV13-T2

SV03-T2

SV02-T2

SV02-T1

SV01-T2

SV01-T1

SV40-T1

SV03-T1

sac14-0533_fig08b

B

SV01

SV40

SV39

SV28

SV02

SV14

SV13

Figure 8.—Continued
16 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Sample Collection and Analysis

Samples from the 100 grid wells were collected in 

accordance with the USGS National Field Manual (NFM; 

U.S. Geological Survey, variously dated) and modified USGS 

NAWQA Program sampling protocols (Koterba and others, 

1995). These sampling protocols were followed so that 

representative samples of groundwater were collected at each 

well and to ensure that the samples were collected and handled 

in a manner that minimized the potential for contamination. 

Samples from the 70 domestic well-tap sites were collected by 

using a modified version of these methods (see appendix A).

All 100 grid wells in the MS-SA study unit were sampled 

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

compounds analyzed in each constituent class. Groundwater 

samples were analyzed for volatile organic compounds 

(VOCs, table 3A), pesticides and pesticide degradates 

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

trace elements (table 3D), nutrients (table 3E), major ions 

(table 3F), age-dating and geochemical tracers and radioactive 

constituents (table 3G), and dissolved noble gases (table 3H). 

The shallow-well tap sites were sampled for a subset of the 

constituents measured in the samples from the grid wells: trace 

elements, nutrients, and major ions.

The methods used for sample collection and analysis are 

described in the “Sample Collection and Analysis” section in 

appendix A.

Data Reporting

The methods and conventions used for reporting the data 

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

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

conductance—were measured in the field and at the USGS 

NWQL. Results from both measurements are reported. 

Bicarbonate and carbonate concentrations were calculated 

from the pH and alkalinity results.

Comparison Benchmarks

The sample-collection protocols used in this study were 

designed to obtain representative samples of groundwater. 

The quality of groundwater can differ from the quality of 

drinking water because water chemistry can change as a result 

of contact with plumbing systems or the atmosphere; because 

of treatment, disinfection, or blending with water from 

other sources; or some combination of these. Water quality 

in domestic wells is not regulated in California; however, 

to provide context for the water-quality data presented in 

this report, results were compared to regulatory and nonregulatory benchmarks established for drinking-water quality. 

A constituent can have values for more than one type of 

benchmark, and the different benchmarks must be prioritized 

in order to develop a consistent set of comparisons. For the 

second phase of the GAMA-PBP, benchmarks were selected in 

the following order of priority:

Maximum Contaminant Level—MCL. The MCLs 

are legally enforceable standards that apply to publicwater systems and are designed to protect public health 

by limiting the levels of contaminants in drinking water 

(U.S. Environmental Protection Agency, 2012); California 

State Water Resources Control Board, Division of Drinking 

Water, 2015). The MCLs established by the USEPA are the 

minimum standards to which states are required to comply, 

and individual states may choose to set more stringent 

standards. California 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 State of 

California is labeled “MCL-US,” and one set by the State of 

California that is more stringent than the MCL-US is labeled 

“MCL-CA”. Well owners are notified when constituents are 

detected at concentrations greater than an MCL-US or an 

MCL-CA benchmark in samples collected for the GAMAPBP, but these detections do not constitute violations of 

regulations even if the well was a public drinking-water 

source. As of 2016, Hawaii is the only state that has 

established an MCL (MCL-HI) for 1,2,3-Trichloropropane 

(table 3A). For lead and copper, the health-based legally 

enforceable standards that apply to public-water systems are 

called “action levels.” Detections of copper or lead in public 

water supplies greater than the action-level benchmarks trigger 

requirements for mandatory water treatment to reduce the 

corrosiveness of water to pipes. The action levels established 

by the USEPA and State of California are the same; thus, 

these benchmarks are labeled “AL-US” in this report. A total 

of 104 constituents analyzed for in this study have MCL-US, 

MCL-CA, or AL-US benchmarks.
Methods 17

Health-Based Screening Level—HBSL. The HBSLs 

are non-regulatory and non-enforceable water-quality 

benchmarks developed by the USGS in collaboration with 

the USEPA, New Jersey Department of Environmental 

Protection, and Oregon Health & Science University. The 

HBSLs are established by using the same methodologies 

implemented by the USEPA when establishing drinking-water 

guidelines and are based on the most recent human-health 

toxicity information available (Toccalino and others, 2012). 

The HBSLs are not established for constituents that have 

MCL-US benchmarks. The HBSLs have been established 

for many constituents that also have USEPA non-regulatory 

health-based benchmarks and for a large number of organic 

constituents for which the USEPA has not yet established 

benchmarks. For carcinogenic constituents, the HBSL range 

represents the constituent concentration in drinking water 

that represents an increased estimated lifetime cancer risk of 

1 chance in 1 million to 1 chance in 100 thousand (Toccalino 

and others, 2012). For non-carcinogens, the HBSLs follow 

the USEPA assumptions about lifetime ingestion and are 

calculated by assuming consumption of 2 liters (2.1 quarts) 

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

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

comes from drinking water. For noncarcinogens, the HBSL 

concentration is the maximum concentration in drinking water 

that a lifetime of exposure is not expected to cause any adverse 

effects (Toccalino and others, 2012). Of the constituents 

analyzed for in this study, 63 have HBSL benchmarks.

Other non-regulatory health-based benchmarks. A 

total of 45 constituents analyzed for in this study have a nonregulatory health-based benchmark established by the USEPA 

or the State of California, but do not also have an HBSL. 

These benchmarks are, in order of priority, the USEPA lifetime 

health advisory level (HAL-US), the USEPA risk-specific 

dose (RSD5-US), and the State of California notification 

level (NL-CA). The HAL-US is 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, and it is calculated by assuming 

consumption of 2 liters (2.1 quarts) of water per day during a 

70-year lifetime by a 70-kilogram (154-pound) adult and that 

20 percent of a person’s exposure comes from drinking water 

(U.S. Environmental Protection Agency, 2012). Because the 

methods used to calculate HAL-US and HBSL benchmarks 

are the same, for constituents having both an HAL-US and an 

HBSL, the two generally have the same value. The RSD5-US 

is the concentration of a constituent in drinking water that 

corresponds to an additional estimated lifetime cancer risk 

of 1 in 100,000. The RSD5 is an acronym for risk-specific 

dose at the 10–5 risk level (10–5 is 1 per 100,000). The RSD5s 

are calculated by dividing the 10–4 cancer risk concentration 

established by the USEPA (U.S. Environmental Protection 

Agency, 2012) by 10. The NL-CA is a health-based standard 

established by the State for some of the constituents in 

drinking water that lack MCLs (Division of Drinking Water, 

2014). If a constituent is detected in drinking water in a 

public-water system at concentrations greater than its NL-CA, 

California State law requires timely notification of local 

governing bodies and recommends consumer notification. 

Secondary Maximum Contaminant Level—SMCL. 

The SMCLs are 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 the State define SMCLs, but unlike 

MCLs, SMCLs established by the State are not required to 

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

chloride, sulfate, specific conductance, and TDS, the State 

of California defines a “recommended” and an “upper” 

SMCL-CA (U.S. Environmental Protection Agency, 2013); 

detections of these constituents in groundwater samples were 

compared with the upper level. The SMCL-US levels for these 

constituents correspond to their recommended SMCL-CAs. 

The SMCL-US is used for pH because a SMCL-CA has not 

been defined.

Using this hierarchy to select the comparison benchmark 

for a constituent with more than one type of established 

benchmark does not necessarily result in selection of the 

benchmark with the lowest concentration. For example, the 

HBSL for boron is 6,000 μg/L, and the NL-CA is 1,000 μg/L, 

but the comparison benchmark selected by this hierarchy is 

the HBSL. The comparison benchmarks for all constituents 

measured for this study are listed in tables 3A–H, and those 

for constituents detected in groundwater samples from the 

MS-SA study unit are listed in tables 4–13 and are illustrated 

in figure 9. Established benchmarks were not available for all 

constituents analyzed for this study.
18 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Figure 9. Hierarchies used by the California Groundwater 

Ambient Monitoring Assessment (GAMA) Priority Basin Project to 

select benchmarks for comparison with groundwater-quality data.

Quality-Assurance Methods

The quality-assurance and quality-control (QA/QC) 

procedures used for this study followed the protocols used 

by the NAWQA Program (Koterba and others, 1995) and are 

described in the NFM (U.S. Geological Survey, variously 

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

laboratory used to analyze samples for this study, is described 

in Stevenson (2012). The QC samples collected in the 

MS-SA study unit were blanks, replicates, and matrix and 

surrogate spikes, which were collected to evaluate potential 

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

that could have resulted from sample collection, processing, 

storage, transportation, and laboratory analysis. The QA/QC 

procedures and results are described in the “Quality-Control 

Methods and Results” section in appendix A.

Water-Quality Results

Quality-Control Results

Three types of QC samples (blanks, replicates, and 

matrix spikes) were collected at up to 11 percent of the wells 

in the MS-SA study unit, and results of QC analyses were 

used to evaluate the quality of the data from the groundwater 

samples. With the exception of some trace elements, few 

constituents were detected in the blanks, and the detected 

concentrations were generally below the reporting labels used 

by the laboratory. On the basis of detections in field blanks 

collected for this and for previous GAMA-PBP study units, 

the “study reporting levels” (SRLs) for three volatile organic 

compounds and eight trace elements were raised (see table A-2

and the “Detections in Field Blanks and Application of SRLs” 

section in appendix A). Detections of these constituents 

where concentrations were less than the respective SRL were 

reported as non-detections for VOCs and were coded by a 

less than or equal to symbol for trace elements in this report. 

Additionally, three VOCs and one trace element (cobalt) 

were detected in some samples; however an assessment of 

QC results for this and other GAMA-PBP studies indicated 

that these detections are likely attributable to extrinsic 

contamination and are not representative of groundwater. 

Detections of the three VOCs and all results for cobalt were 

not presented in this report. 

Results from the replicates confirm that the procedures 

used to collect and analyze the samples were consistent. The 

variability for nearly all of the replicate pairs for constituents 

detected in samples was within the acceptable limits (see 

tables A-3A–C). The constituent iron showed high variability 

in two replicate samples. The criteria for acceptable replication 

are described in the “Quality-Control Methods and Results” 

section in appendix A.

Regulatory

 health based

Non-regulatory

 aesthetic based

Non-regulatory

 health based

Type of benchmark

Hierarchies used by GAMA-PBP

to select benchmarks for

comparison with water-quality data

HBSL

MCL-CA

MCL-US

AL-US

NL-CA

HAL-US

RSD5-US

SMCL-CA

Second phase

(2012 and ongoing) 

MCL-CA

MCL-US

AL-US

HAL-US

RSD5-US

SMCL-CA

First phase

(2004–12) 

NL-CA

EXPLANATION

AL-US U.S. Environmental Protection 

 Agency (USEPA) action level

HAL-US USEPA lifetime health 

 advisory level

HBSL USGS health-based 

 screening level

MCL-CA California Division of Drinking Water

 maximum contaminant level

MCL-US USEPA maximum contaminant 

 level 

NL-CA California notification level 

RSD5-US USEPA risk-specific dose at a 

 risk factor of 10–5

SMCL-CA California secondary maximum 

 contaminant level

Abbreviations

Increasing order of priority

sac14-0533fig09
Water-Quality Results 19

The median values of matrix-spike recoveries were 

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

organic compounds and N-nitrosodimethylamine (NDMA). 

Midian values of matrix-spike recoveries were below 

70 percent for pesticides and pesticide degradates (table 3B; 

see table A-4A–B). The constituents that had low recoveries 

might not have been detected in some samples if they were 

present in the samples at concentrations near the laboratory 

reporting levels (LRLs). High recoveries of constituents 

can indicate that reported concentrations could be greater 

than what was truly present in the sample. The QC results 

are described in the “Quality-Control Methods and Results” 

section in appendix A.

Groundwater-Quality Data

Results from analyses of untreated groundwater samples 

from the MS-SA study unit are presented in tables 4–13

for grid wells and for wells sampled at taps. Groundwater 

samples collected in the MS-SA study unit were analyzed for 

over 200 constituents and water-quality indicators; of these, 

106 constituents were not detected in any of the samples. 

Detections of constituents at concentrations greater than the 

selected comparative benchmarks listed in tables 3A–H are 

marked with an asterisk (*) in tables 4–13.

For organic and special-interest constituents, the results 

tables include only those constituents that were detected and 

those wells that had detections. For the organic constituents, 

the following summary statistics are presented for all of the 

grid wells: the number of wells for which each analyte was 

detected, the frequency at which it was detected (in relation 

to the number of grid wells in the study unit), and the total 

number of constituents detected for each well. For the 

inorganic, isotopic, and radioactive constituents, the tables 

include all of the constituents and wells that were analyzed. 

Water-quality indicators measured in the field and at the 

NWQL are included in table 4A for grid wells and table 4B for 

shallow-well tap sites. The results of groundwater analyses, 

organized by constituent class, are presented in tables 5–13:

• Organic constituents.

• Volatile organic compounds (table 5).

• Pesticides and pesticide degradates (table 6).

• Constituents of special interest (table 7).

• Inorganic constituents.

• Trace elements (table 8A for grid wells and table 8B

for shallow-well tap sites).

• Nutrients (table 9A for grid wells and table 9B for 

shallow-well tap sites).

• Major and minor ions, silica, and total dissolved 

solids (table 10A for grid wells and table 10B for 

shallow-well tap sites).

• Radioactive constituents (table 11).

• Isotopic tracers (table 12).

• Noble gases (table 13).

Water-Quality Indicators

Field measurements of dissolved oxygen, water 

temperature, and field and laboratory measurements of pH, 

specific conductance (SC), and alkalinity are presented in 

table 4A for grid wells and table 4B for shallow-well tap sites, 

along with values calculated for bicarbonate and carbonate 

from pH and alkalinity measurements. 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. The SC is a 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 

at 5 percent of the MS-SA study unit grid wells; five well 

samples had field pH values less than 6.5 (table 4A). Low pH 

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

in water can contribute to scaling. Laboratory pH values can 

differ from field pH values because the pH of groundwater can 

change when it is removed from its ambient environment and 

exposed to the atmosphere. Field pH values were outside of 

the SMCL-US range for about 3 percent of the MS-SA study 

unit shallow-well tap sites; two samples had field pH values 

less than 6.5, but none of the samples had field pH values 

greater than 8.5 (table 4B). Field SC values were greater than 

the upper SMCL-CA of 1,600 microsiemens per centimeter at 

25 degrees Celsius (μS/cm at 25 °C) for 24 of the 100 gridwell samples (table 4A). Field SC values were greater than 

the upper SMCL-CA of 1,600 (μS/cm at 25 °C) for 15 of the 

70 shallow-well tap sites (table 4B).

Organic Constituents

Volatile organic compounds (VOCs) are present in paints, 

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

disinfected water, and are characterized by their tendency 

to evaporate because groundwater is isolated from the 

atmosphere, VOCs generally persist longer in groundwater 

than in surface water. Of the 85 VOCs analyzed for the 

MS-SA study unit, 14 were detected in groundwater samples, 

and all of the concentrations detected were less than healthbased benchmarks (table 5). One or more VOC was detected 

in 23 of the 100 grid-well samples (a 23-percent detection 

frequency). One VOC was detected at a frequency above 

10 percent. The trihalomethane chloroform (trichloromethane) 

was the most frequently detected VOC in the study unit 

(about 13 percent detection frequency). Chloroform is among 

the most commonly detected of the VOCs in groundwater 

nationally (Zogorski and others, 2006). The second most 

commonly detected VOC was the solvent perchloroethylene 

(PCE), which was detected at a frequency of 8 percent in the 

grid wells. 
20 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Pesticides include herbicides, insecticides, and fungicides 

that 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 

MS-SA study unit, 7 were detected in groundwater samples, 

but all concentrations were less than health-based benchmark 

concentrations (table 6). One or more pesticide or pesticide 

degradate was detected in 20 of the 99 MS-SA study-unit 

grid-well samples (a 20-percent detection frequency). The 

herbicide simazine was detected in more than 10 percent of 

the samples. Simazine is among the Nation’s most commonly 

detected pesticide compounds in groundwater (Gilliom 

and others, 2006). The herbicide degradate deethylatrazine 

(2-chloro-4-isopropylamino-6-amino-s-triazine) was detected 

in more than 9 percent of the samples. Deethylatriazine is 

a degradate of atrazine, which is also a commonly detected 

pesticide in groundwater.

Constituents of Special Interest

Perchlorate and NDMA were classified as constituents 

of special interest at the inception of the GAMA-PBP in 2003 

because they had recently been detected in some drinkingwater supplies in California, and the State was considering 

whether or not to pursue future regulation of these constituents 

(Belitz and others, 2003). An MCL-CA for perchlorate was 

established in 2007 (Division of Drinking Water, 2013). 

Perchlorate was detected in 60 of 100 grid-well samples 

(60 percent detection frequency); one well (S-MS-SV29) had 

a concentration greater than the MCL-CA of 6 micrograms 

per liter (μg/L; table 7). Of 100 grid-well samples, NDMA 

was detected in 7 (a 7 percent detection frequency); of these, 

3 detections were concentrations greater than the HBSL 

of 0.007 μg/L, and, in one of these wells, the perchlorate 

concentration was greater than the MCL-CA as well.

Inorganic Constituents

Unlike the organic constituents, most inorganic 

constituents are present naturally in groundwater, although 

their concentrations can be influenced by human activities. 

Of the 33 trace elements and major and minor ions 

analyzed and detected in the MS-SA study unit (tables 8, 10), 

21 have regulatory or non-regulatory health-based benchmarks 

(table 3D, 3F). Of these 21 constituents, 7 constituents 

were detected at concentrations greater than their respective 

benchmarks; all detections of the remaining 14 constituents 

were at concentrations less than their respective benchmarks. 

Arsenic was detected at concentrations greater than the 

MCL-US of 10 μg/L in five grid wells; boron was detected at 

a concentration greater than the HBSL of 6,000 μg/L in one 

grid well; manganese was detected at concentrations greater 

the HBSL of 300 μg/L in eight grid wells; molybdenum was 

detected at concentrations greater than the HBSL of 40 μg/L in 

six grid wells; selenium was detected at concentrations greater 

than the MCL-US of 50 μg/L in three grid wells; strontium 

was detected at concentrations greater than the HBSL of 

4,000 μg/L in six grid wells; and uranium was detected at 

concentrations greater than the MCL-US of 30 μg/L in four 

grid wells (table 8A). 

Of the trace elements and major and minor ions 

analyzed in the shallow-well tap sites, arsenic was detected 

at a concentration greater than the MCL-US of 10 μg/L 

in two shallow-well tap sites; manganese was detected at 

concentrations greater the HBSL of 300 μg/L in four shallowwell tap sites; molybdenum was detected at concentrations 

greater than the HBSL of 40 μg/L in four shallow-well tap 

sites; uranium was detected at concentrations greater than 

the MCL-US of 30 μg/L in two shallow-well tap sites; and 

zinc was detected at concentrations greater than the HBSL of 

2,000 μg/L in two shallow-well tap sites (table 8). 

Nutrients (nitrogen and phosphorus) present in 

groundwater can affect biological activity in aquifers and 

in surface-water bodies that receive groundwater discharge. 

Inorganic nitrogen can be present in the form of ammonia, 

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

the groundwater. High concentrations of nitrate can adversely 

affect human health, particularly the health of infants. 

Groundwater samples from 16 grid wells had nitrate (nitrate 

plus nitrate as N) concentrations greater than the MCL-US 

of 10 mg/L (table 9A). All other nutrient concentrations in 

MS-SA grid wells were less than health-based benchmarks. 

Groundwater samples from the 24 shallow-well tap sites had 

nitrate (nitrate plus nitrate as N) concentrations greater than 

the MCL-US of 10 mg/L (table 9B).

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 no adverse health effects are directly associated with 

these properties, they can reduce consumer satisfaction with 

the water or have economic effects. The SWRCB-DDW has 

established non-enforceable benchmarks (SMCL-CAs) that 

are based on aesthetic properties rather than on human-health 

concerns for iron, manganese, silver, zinc, chloride, sulfate, 

and TDS. Manganese, silver, and zinc also have HBSLs, 

which are used as comparison benchmarks in this study 

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

have concentrations affected by the oxidation-reduction state 

of the groundwater. Precipitation of minerals containing iron 

or manganese can cause orange, brown, or black staining of 

surfaces. 

Iron concentrations greater than the SMCL-CA of 

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

Chloride and sulfate concentrations were greater than the 

upper recommended SMCL-CA of 500 mg/L in 7 and 

14 grid-well samples, respectively (table 10A). The TDS 

concentrations were greater than the upper recommended 

SMCL-CA of 1,000 mg/L in 27 grid-well samples (table 10A). 
Water-Quality Results 21

Iron concentrations were greater than the SMCL-CA 

of 300 μg/L in six shallow-well tap-site samples (table 8B). 

Chloride and sulfate concentrations were greater than the 

upper recommended SMCL-CA of 500 mg/L in one and nine 

shallow-well tap-site samples, respectively (table 10B). The 

TDS concentrations were greater than the upper recommended 

SMCL-CA of 1,000 mg/L in 15 shallow-well tap-site samples 

(table 10B).

Radioactivity is the release of energy or energetic 

particles during changes in the structure of the nucleus of an 

atom. Most radioactivity in groundwater comes from decay 

of natural isotopes of uranium and thorium that are present 

in minerals in the sediments or fractured rocks of the aquifer. 

Uranium and thorium decay in a series of steps to eventually 

form 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, beta, or other particle from its nucleus. Alpha and beta 

particles emitted during radioactive decay can be hazardous 

to human health because these energetic particles can damage 

cells. Radiation damage to cell DNA can increase the risk of 

getting cancer. Activity often is used instead of concentration 

for reporting the presence of radioactive constituents. Activity 

of radioactive constituents in groundwater is measured in units 

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

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

decaying is determined by measuring the particles or energy 

emitted. 

Radon-222, gross alpha particle, and gross beta particle 

activities were measured in samples in the MS-SA study unit. 

Radon-222 activity was not detected in any of the grid-well 

samples at levels greater than the proposed MCL-US of 

4,000 pCi/L (table 11). The proposed MCL-US applies if a 

state or a local water agency has an approved multimedia 

mitigation program that addresses radon levels of indoor 

air quality (U.S. Environmental Protection Agency, 1999). 

The MCL-US of 15 pCi/L for gross alpha particle activity 

applies to the adjusted gross alpha, not to the measured 

gross alpha. Adjusted gross alpha is equal to the measured 

gross alpha minus the alpha activity attributable to uranium. 

Uranium activities were estimated from the measured uranium 

concentrations by using a conversion factor of 0.7 (Federal 

Register, 2000). Adjusted gross-alpha particle activity 

(72-hour count) was greater than the MCL-US of 15 pCi/L 

in 10 samples, 3 of which also had gross alpha radioactivity 

(30-day count) greater than the benchmark (table 11). Three 

additional grid-well samples that had no results for gross alpha 

and gross beta radioactivities had uranium concentrations 

greater than the MCL-US (table 8A). Gross beta radioactivity 

(72-hour count) was greater than the MCL-CA of 50 pCi/L in 

one grid-well sample (table 11).

Isotopic Tracers

Isotopic tracers can be used to help interpret hydrologic 

processes affecting groundwater quality (Clark and Fritz, 

1997). Tritium activities (table 12) and helium isotopes 

provide information about the age (time since recharge) of 

groundwater. Tritium is a short-lived radioactive isotope of 

hydrogen that is incorporated into the water molecule. Low 

levels of tritium are produced continuously by interaction 

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

amount of tritium was produced as a result of atmospheric 

testing of nuclear weapons between 1952 and 1963. Thus, 

concentrations of tritium greater than background generally 

indicate the presence of water recharged after the early 

1950s. Helium isotopes are used in conjunction with tritium 

concentrations to estimate ages for young groundwater. Of the 

isotope-tracer constituents analyzed for this study, tritium is 

the only one with a health-based benchmark. The measured 

tritium activities in samples from the MS-SA study unit were 

less than 1/1,000 of the MCL-CA benchmark (table 12). 

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

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

produced continuously by interaction of cosmic radiation with 

the Earth’s atmosphere and 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 5,730 years, low 

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

indicate a presence of groundwater that is several thousand 

years old or more.

The stable isotopic ratios of hydrogen and oxygen 

in water (table 12) aid in the interpretation of the sources 

of groundwater recharge (see the “Notation” section in 

appendix A for a description of how stable isotopic ratios are 

derived and reported). These stable isotopic ratios reflect the 

altitude, latitude, and temperature of precipitation and the 

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

soils prior to infiltration into the aquifer.

Gases dissolve in water that is in contact with the 

atmosphere, and the solubilities of the different gas 

species vary with temperature. Noble-gas concentrations 

in groundwater are a function of the partial pressure of the 

gases and the temperature and salinity of water at the time 

of recharge. Concentrations of dissolved noble gases can 

be used to estimate the conditions of groundwater recharge, 

particularly the temperature of the water when it was last in 

contact with the atmosphere. Results of 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 GAMAPBP project staff.
22 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Future Work

Further GAMA reports for the MS-SA study unit will 

focus 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 MS-SA study unit. If available, 

additional water-quality data are to be compiled, evaluated, 

and used with the data presented in this report.

Summary

Groundwater quality in the approximately 3,020-squaremile Monterey–Salinas Shallow Aquifer (MS-SA) study unit 

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

October 2012 to May 2013 as part of the California State 

Water Resources Control Board (SWRCB) Groundwater 

Ambient Monitoring and Assessment (GAMA) Program’s 

priority Basin Project (PBP). The GAMA Program was 

created to provide a comprehensive baseline of groundwater 

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

of the Groundwater Quality Monitoring Act of 2001 (Sections 

10780–10782.3 of the California Water Code, Assembly Bill 

599) to assess and monitor the quality of groundwater. The 

GAMA-PBP is being carried out by the USGS in cooperation 

with the SWRCB and Lawrence Livermore National 

Laboratory.

The GAMA MS-SA study was designed to provide 

a spatially unbiased assessment of untreated-groundwater 

quality in the shallow aquifer system and to facilitate 

statistically consistent comparisons of untreated groundwater 

quality throughout California. The shallow aquifer system is 

defined as that part of the aquifer in which domestic wells are 

drilled, and it is generally shallower than the depth intervals 

of the wells listed in the California State Water Resources 

Control Board-Division of Drinking Water (SWRCB-DDW) 

database for the MS-SA study unit. The quality of groundwater 

in shallow or deeper water-bearing zones can differ from that 

in the primary aquifer system; shallow groundwater can be 

more vulnerable to surficial contamination.

This assessment characterized the quality of groundwater 

in the MS-SA study unit, not the quality of drinking water 

used by consumers served by public drinking-water suppliers; 

after withdrawal from the aquifer, groundwater can be treated 

prior to use as drinking water. Domestic and small watersupply systems that usually tap shallow aquifers rarely treat 

the drinking water, however. Regulatory benchmarks apply 

to treated water that is served to the consumer of the public 

water sources, not to untreated groundwater. To provide 

some context for the results, however, concentrations of 

constituents measured in the untreated groundwater were 

compared with regulatory and non-regulatory health-based 

benchmarks established by the U.S. Environmental Protection 

Agency (USEPA), SWRCB-DDW, and USGS and with nonregulatory benchmarks established for aesthetic concerns by 

SWRCB-DDW.

The MS-SA study unit is in the Southern Coast Ranges 

hydrogeologic province and includes groundwater basins 

defined by the California Department of Water Resources 

and surrounding highlands areas outside of the groundwater 

basins. The MS-SA study included assessment of the 

groundwater quality from 100 grid wells in Monterey and 

San Luis Obispo Counties. The wells were selected by 

using a randomized grid approach to achieve a statistically 

unbiased representation of groundwater used mostly for 

domestic drinking-water sources (grid wells). Additionally, 

samples were collected from 70 wells sampled at taps in the 

MS-SV and MS-P study areas in order to provide a greater 

spatial density of data to define the distribution of inorganic 

constituents. 

Field water-quality indicators were measured, and 

samples for analysis of inorganic constituents were collected 

at all 170 sites. In addition to these constituents, the samples 

from grid wells were analyzed for organic constituents, 

constituents of special interest, radioactive constituents, 

and geochemical and age-dating tracers. In total, over 

200 constituents were measured for this study.

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

and matrix spikes) were collected at up to 11 percent of 

the wells in the MS-SA study unit, and the results for these 

samples were used to evaluate the quality of the data for the 

groundwater samples. With the exception of trace elements, 

blanks rarely contained detectable concentrations of any 

constituent, indicating that contamination from samplecollection procedures was not a significant source of bias in 

the data for the groundwater samples. Low concentrations 

of some trace elements were detected in blanks; therefore, 

the data were re-censored with higher reporting levels. 

Replicate samples generally were within the limits of 

acceptable analytical reproducibility. The median values of 

matrix-spike recoveries were within the acceptable range 

(70 to 130 percent) for the volatile organic compounds 

(VOCs) and N-nitrosodimethylamine (NDMA), but were 

only approximately 64 percent for pesticides and pesticide 

degradates.

Of the 148 organic constituents analyzed in the 100 gridwell samples, 21 were detected, and all concentrations were 

less than the benchmarks. The VOCs were detected in 23 of 

the grid wells, and pesticides and pesticide degradates were 

detected in 20 grid wells. The special-interest constituent 

NDMA was detected above the health-based screening level 

(HBSL) in three samples, one of which also had a perchlorate 

concentration greater than the MCL-CA.
References Cited 23

Of the inorganic constituents, 6 were detected at 

concentrations above their respective maximum contaminant 

level (MCL) benchmarks in grid-well samples: arsenic was 

detected in 5 grid wells (MCL is 10 μg/L), selenium in 3 grid 

wells (50 μg/L), uranium in 4 grid wells (30 μg/L), nitrate in 

16 grid wells (10 mg/L), adjusted gross alpha particle activity 

in 10 grid wells (15 pCi/L), and gross beta particle activity in 

1 grid well (50 pCi/L). An additional 4 inorganic constituents 

were detected at concentrations above their respective HBSL 

benchmarks in grid-well samples: boron in one grid well 

(6,000 μg/L), manganese in eight grid wells (300 μg/L), 

molybdenum in 6 grid wells (40 μg/L), and strontium in 6 grid 

wells (4,000 μg/L). Of the inorganic constituents, 4 were 

detected at concentrations above their non-health-based 

secondary maximum contaminant level (SMCL) benchmarks 

in grid-well samples: iron in 9 grid wells (300 μg/L), 

chloride in 7 grid wells (500 mg/L), sulfate in 14 grid wells 

(500 mg/L), and TDS in 27 grid wells (1,000 mg/L). 

Of the inorganic constituents analyzed in the 70 shallowwell tap sites, 10 were detected at concentrations above the 

benchmarks. Of the inorganic constituents, 3 were detected 

at concentrations above their respective MCL benchmarks 

in shallow-well tap sites: arsenic at 2 shallow-well tap 

sites (MCL is 10 μg/L), uranium at 2 shallow-well tap sites 

(30 μg/L), and nitrate at 24 shallow-well tap site (10 mg/L). 

An additional 3 inorganic constituents were detected above 

their respective HBSL benchmarks in shallow-well tap 

sites: manganese at 4 shallow-well tap sites (300 μg/L), 

molybdenum at 4 shallow-well tap sites (40 μg/L), and zinc 

at 2 shallow-well tap sites (2,000 μg/L). Of the inorganic 

constituents, 4 were detected at concentrations above their 

non-health based SMCL benchmarks in shallow-well tap 

sites: iron in 6 shallow-well tap sites (300 μg/L), chloride in 

1 shallow-well tap site (500 mg/L), sulfate in 9 shallow-well 

tap sites (500 mg/L), and TDS in 15 shallow-well tap sites 

(1,000 mg/L).

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of Northern and Central California: Missoula, Montana, 

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Belitz, Kenneth, Dubrovsky, N.M., Burow, Karen, 

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a ground-water quality monitoring and assessment program 

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Investigations Report 2003–4166, 78 p., 

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Burow, K.R., Dubrovsky, N.M., and Shelton, J.L., 2007, 

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Burton, C.A., Shelton, J.L., and Belitz, Kenneth, 2012, Status 

and understanding of groundwater quality in the two 

southern San Joaquin Valley study units, 2005–2006—

California GAMA Priority Basin Project: U.S. Geological 

Survey Scientific Investigations Report 2011–5218, 106 p., 

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California Department of Water Resources, 2003, California’s 

groundwater update 2003: California Department of Water 

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

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

update2003.cfm.

California Department of Water Resources, 2011, 

Water Facts 1—Ground water in fractured hard rock, 

accessed January 18, 2013, at http://www.water.ca.gov/

waterconditions/drought/docs/water_facts_1.pdf.

California State Water Resources Control Board, 2003, 

Report to the Governor and Legislature—A comprehensive 

groundwater quality monitoring program for California: 

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

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

docs/final_ab_599_rpt_to_legis_7_31_03.pdf.

California State Water Resources Control Board, 2009, 

Geotracker GAMA: State Water Resources Control 

Board database, accessed June 11, 2013, at 

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

California State Water Resources Control Board, 2015, 

California drinking water-related laws: Drinking waterrelated regulations (Title 22) (pdf document), accessed 

August 3, 2015, at http://www.waterboards.ca.gov/

drinking_water/certlic/drinkingwater/Lawbook.shtml.

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

hydrogeology: Boca Raton, Florida, CRC Press LLC, 352 p.

Division of Drinking Water, 2010, Drinking water notification 

levels and response levels—An overview: California 

Department of Public Health Drinking Water Program, 

14 p., accessed 2016, at http://www.swrcb.ca.gov/drinking_

water/certlic/drinkingwater/documents/notificationlevels/

notificationlevels.pdf.

Department of Drinking Water, 2013, California regulations 

related to drinking water, Title 22: Code of regulations, 

339 p., accessed 2016, at http://www.waterboards.ca.gov/

drinking_water/certlic/drinkingwater/Perchlorate.shtml.

Faure, Gunter, and Mensing, T.M., 2004, Isotopes—Principles 

and applications (3d ed.): Hoboken, N.J., John Wiley & 

Sons, Inc., 928 p.
24 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Federal Register, 2000, National primary drinking water 

regulations; radionuclides; final rule, accessed on 

April 20, 2015, at https://www.federalregister.gov/

articles/2000/12/07/00-30421/national-primary-drinkingwater-regulations-radionuclides-final-rule.

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

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

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

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

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

U.S. Geological Survey Circular 1291, 173 p., 

https://pubs.er.usgs.gov/publication/cir1291.

Hirsch, R.M., Alley, W.M., and Wilber, W.G., 1988, 

Concepts for a national water-quality assessment program, 

U.S. Geological Survey Circular 1021, 42 p., 

https://pubs.er.usgs.gov/publication/cir1021.

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

groundwater units: U.S. Geological Survey Data Series 796, 

34 p., http://dx.doi.org/10.3133/ds796.

Johnson, T.D., and Belitz, Kenneth, 2015, Identifying the 

location and population served by domestic wells in 

California: Journal of Hydrology: Regional Studies, v. 3, 

p. 31–86, doi:10.1016/j.ejrh.2014.09.002, http://www.

sciencedirect.com/science/article/pii/S2214581814000305.

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

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

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

Survey Circular 1344, 52 p., 

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

1995, Ground-water data-collection protocols and 

procedures for the National Water-Quality Assessment 

Program—Collection and documentation of waterquality samples and related data: U.S. Geological Survey 

Open-File Report 95–399, 114 p., 

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Kulongoski, J.T., and Belitz, Kenneth, 2007, Ground-water 

quality data in the Monterey Bay and Salinas Valley basins, 

California, 2005—Results from the California GAMA 

program: U.S. Geological Survey Data Series 258, 84 p., 

https://pubs.er.usgs.gov/publication/ds258.

Kulongoski, J.T., and Belitz, Kenneth, 2011, Status and 

understanding of groundwater quality in the Monterey 

Bay and Salinas Valley basins, 2005: California 

GAMA priority basin project: U.S. Geological Survey 

Scientific Investigations Report 2011–5058, 60 p., 

https://pubs.er.usgs.gov/publication/sir20115058.

Scott, J.C., 1990, Computerized stratified random siteselection approaches for design of a ground-water-quality 

sampling network: U.S. Geological Survey WaterResources Investigations Report 90–4101, 109 p., 

https://pubs.er.usgs.gov/publication/wri904101.

Soddy, Frederick, 1913, Radioactivity: Annual Reports 

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

http://dx.doi.org/10.1039/AR9131000262.

State of California, 2001a, Assembly Bill No. 599, chap. 522, 

4 p., accessed October 27, 2011, at http://www.swrcb.

ca.gov/gama/docs/ab_599_bill_20011005_chaptered.pdf.

State of California, 2001b, Groundwater Monitoring Act of 

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

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

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

11000&file=10780-10782.3.

Stevenson, D.L., 2012, Quality management system, 

U.S. Geological Survey National Water Quality 

Laboratory: unpublished U.S. Geological Survey 

Report, version 2.0, January 3, 2012, 74 p., 

http://nwql.usgs.gov/elec/QMS_v2.pdf.

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

and Zogorski, J.S., 2012, Health-based screening levels 

for evaluating water-quality data: U.S. Geological 

Survey, National Water-Quality Assessment Program, 

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

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

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

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

U.S. Environmental Protection Agency, 1999, National 

primary drinking water regulations; Radon-222: Federal 

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

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

of the Drinking Water Standards and Health Advisories, 

EPA 822-S-12-001, https://www.epa.gov/sites/production/

files/2015-09/documents/dwstandards2012.pdf.

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drinking water regulations: Guidance for nuisance 

chemicals, accessed April 20, 2015, at http://water.epa.gov/

drink/contaminants/secondarystandards.cfm.

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

field manual for the collection of water-quality data: 

U.S. Geological Survey Techniques of Water-Resources 

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

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

U.S. Geological Survey, 2013a, What is the GAMA?: 

California Water Science Center website, accessed June 6, 

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

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

Ambient Monitoring and Assessment (GAMA) Program 

Priority Basin Project—Shallow aquifer assessment: 

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

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

ca.water.usgs.gov/gama/includes/GAMA_publications.html.
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Zogorski, J.S., Carter, J.M., Ivahnenko, Tamara, 

Lapham, W.W., Moran, M.J., Rowe, B.L., Squillace, P.J., 

and Toccalino, P.L., 2006, Volatile organic compounds 

in the Nation’s ground water and drinking-water supply 

wells: U.S. Geological Survey Circular 1292, 101 p., 

https://pubs.er.usgs.gov/publication/cir1292.
26 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Tables

Table 1. Identification, sampling, construction, and water-level information for grid wells sampled for the Monterey–Salinas Shallow 

Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to 

May 2013.

[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 (NAVD 88). GAMA well identification numbers: S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well; 

S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well. Abbreviations: ft, feet; mm/dd/yyyy, month/day/year; na, not available]

Sampling information Construction information Depth 

to 

water level 

(ft below LSD)

GAMA well 

identification 

number

Date 

sampled 

(mm/dd/yyyy)

Well 

type

Altitude 

of LSD 

(ft above NAVD 88)

Well 

depth 

(ft below LSD)

Depth to top 

perforation 

(ft below LSD)

Depth to bottom 

perforation 

(ft below LSD)

MS-SA study unit grid wells (100 wells sampled)

Santa Cruz study area wells (15 wells sampled)

S-MS-SC01 01/10/2013 Production 59 300 na na 185

S-MS-SC02 01/10/2013 Production 372 520 380 520 na

S-MS-SC03 12/10/2012 Production 560 122 60 122 38.3

S-MS-SC04 01/08/2013 Production 929 100 32 100 na

S-MS-SC05 01/14/2013 Production 423 510 390 510 108.5

S-MS-SC06 02/12/2013 Production 632 325 85 325 na

S-MS-SC07 03/06/2013 Production 49 116 60 116 na

S-MS-SC08 03/04/2013 Production 117 150 106 150 41.1

S-MS-SC09 03/18/2013 Production 632 440 na na na

S-MS-SC10 02/04/2013 Production 739 136 116 136 109.1

S-MS-SC11 12/10/2012 Production 412 170 70 170 29

S-MS-SC12 01/09/2013 Production 811 244 100 244 82.5

S-MS-SC13 03/06/2013 Production 1,596 900 500 800 na

S-MS-SC14 01/08/2013 Production 410 240 100 240 na

S-MS-SC15 02/14/2013 Production 373 270 220 270 16.9

Pajaro Valley study area (15 wells sampled)

S-MS-P01 02/11/2013 Production 179 378 na na na

S-MS-P02 02/05/2013 Production 141 200 80 190 136.8

S-MS-P03 01/07/2013 Production 154 290 180 290 93

S-MS-P04 02/05/2013 Production 465 600 480 590 407.2

S-MS-P05 02/11/2013 Spring 262 0 na na na

S-MS-P06 04/25/2013 Production 53 200 160 190 na

S-MS-P07 03/05/2013 Production 83 190 140 160 na

S-MS-P08 03/05/2013 Production 90 180 128 176 na

S-MS-P09 02/13/2013 Production 33 180 140 180 na

S-MS-P10 03/04/2013 Production 157 260 220 260 na

S-MS-P11 02/06/2013 Production 123 300 260 300 113.5

S-MS-P12 02/12/2013 Production 96 460 340 440 84.9

S-MS-P13 02/06/2013 Production 95 440 310 430 79.9

S-MS-P14 02/07/2013 Production 198 520 420 520 na

S-MS-P15 02/07/2013 Production 528 480 na na 80.8
Tables 27

Sampling information Construction information Depth 

to 

water level 

(ft below LSD)

GAMA well 

identification 

number

Date 

sampled 

(mm/dd/yyyy)

Well 

type

Altitude 

of LSD 

(ft above NAVD 88)

Well 

depth 

(ft below LSD)

Depth to top 

perforation 

(ft below LSD)

Depth to bottom 

perforation 

(ft below LSD)

MS-SA study unit grid wells (100 wells sampled)—Continued

Salinas Valley study area (40 wells sampled) 

S-MS-SV01 11/08/2012 Production 864 280 140 280 na

S-MS-SV02 03/20/2013 Production 673 290 170 290 59.7

S-MS-SV03 10/31/2012 Production 571 460 210 450 na

S-MS-SV04 10/29/2012 Production 352 340 140 340 na

S-MS-SV05 10/30/2012 Production 388 500 160 480 219.7

S-MS-SV06 11/08/2012 Production 121 275 20 275 na

S-MS-SV07 11/08/2012 Production 10 392 352 392 na

S-MS-SV08 11/05/2012 Production 34 290 258 288 43.4

S-MS-SV09 10/29/2012 Production 370 700 449 700 255.4

S-MS-SV10 03/19/2013 Production 243 190 150 190 81.4

S-MS-SV11 11/06/2012 Production 385 410 370 410 na

S-MS-SV12 11/07/2012 Production 546 258 178 258 147.9

S-MS-SV13 03/13/2013 Production 598 340 120 330 na

S-MS-SV14 03/13/2013 Production 593 395 na na 46.6

S-MS-SV15 11/27/2012 Production 530 180 100 180 na

S-MS-SV16 02/26/2013 Production 287 165 120 160 na

S-MS-SV17 11/26/2012 Production 197 160 100 160 38.9

S-MS-SV18 12/13/2012 Production 149 85 na na 37.1

S-MS-SV19 10/30/2012 Production 38 370 355 365 51.5

S-MS-SV20 11/05/2012 Production 42 500 na na 53.4

S-MS-SV21 11/05/2012 Production 62 240 200 240 na

S-MS-SV22 03/14/2013 Production 120 540 420 540 na

S-MS-SV23 01/29/2013 Production 179 300 na na na

S-MS-SV24 11/06/2012 Production 293 670 550 650 na

S-MS-SV25 03/20/2013 Production 333 275 115 220 na

S-MS-SV26 03/14/2013 Production 425 100 60 100 na

S-MS-SV27 02/26/2013 Production 471 130 80 130 na

S-MS-SV28 03/26/2013 Production 870 127 na na na

S-MS-SV29 11/08/2012 Production 345 84 70 80 na

S-MS-SV30 03/19/2013 Production 257 200 na na na

Table 1. Identification, sampling, construction, and water-level information for grid wells sampled for the Monterey–Salinas Shallow 

Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to 

May 2013.—Continued

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

American Vertical Datum of 1988 (NAVD 88). GAMA well identification numbers: S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well; 

S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well. Abbreviations: ft, feet; mm/dd/yyyy, month/day/year; na, not available]
28 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Sampling information Construction information Depth 

to 

water level 

(ft below LSD)

GAMA well 

identification 

number

Date 

sampled 

(mm/dd/yyyy)

Well 

type

Altitude 

of LSD 

(ft above NAVD 88)

Well 

depth 

(ft below LSD)

Depth to top 

perforation 

(ft below LSD)

Depth to bottom 

perforation 

(ft below LSD)

MS-SA study unit grid wells (100 wells sampled)—Continued

Salinas Valley study area (40 wells sampled)—Continued

S-MS-SV31 03/12/2013 Production 224 125 na na na

S-MS-SV32 04/25/2013 Production 198 285 na na na

S-MS-SV33 11/05/2012 Production 138 260 220 260 143

S-MS-SV34 11/07/2012 Production 594 630 168 609 na

S-MS-SV35 03/07/2013 Production 421 472 432 472 na

S-MS-SV36 11/06/2012 Production 245 700 480 680 na

S-MS-SV37 11/01/2012 Production 452 330 160 320 na

S-MS-SV38 04/08/2013 Production 269 200 112 166 na

S-MS-SV39 04/24/2013 Production 1,091 322 152 312 na

S-MS-SV40 03/21/2013 Production 1,213 292 na na na

Highlands study area (30 wells sampled) 

S-MS-H01 12/12/2012 Production 1,153 480 180 480 na

S-MS-H02 01/17/2013 Production 1,342 360 160 360 na

S-MS-H03 01/16/2013 Production 784 na na na 21.9

S-MS-H04 11/27/2012 Production 1,146 235 115 235 77.7

S-MS-H05 01/16/2013 Production 1,236 na na na 276.5

S-MS-H06 12/11/2012 Production 764 400 200 380 na

S-MS-H07 04/11/2013 Production 604 24 na na na

S-MS-H08 02/28/2013 Production 678 100 na na na

S-MS-H09 11/29/2012 Production 819 140 80 140 76.7

S-MS-H10 11/28/2012 Production 842 118 na na 70.6

S-MS-H11 11/28/2012 Production 771 410 na na na

S-MS-H12 12/12/2012 Production 1,074 137 na na na

S-MS-H13 04/10/2013 Production 1,987 480 na na na

S-MS-H14 01/15/2013 Production 1,636 740 600 740 na

S-MS-H15 12/11/2012 Production 1,077 470 410 470 423.5

S-MS-H16 01/17/2013 Production 881 320 260 320 183.6

S-MS-H17 04/09/2013 Production 763 400 200 400 na

S-MS-H18 01/30/2013 Production 509 400 na na na

S-MS-H19 03/25/2013 Production 529 150 na na na

S-MS-H20 04/11/2013 Production 1610 125 50 125 na

Table 1. Identification, sampling, construction, and water-level information for grid wells sampled for the Monterey–Salinas Shallow 

Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to 

May 2013.—Continued

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

American Vertical Datum of 1988 (NAVD 88). GAMA well identification numbers: S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well; 

S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well. Abbreviations: ft, feet; mm/dd/yyyy, month/day/year; na, not available]
Tables 29

Sampling information Construction information Depth 

to 

water level 

(ft below LSD)

GAMA well 

identification 

number

Date 

sampled 

(mm/dd/yyyy)

Well 

type

Altitude 

of LSD 

(ft above NAVD 88)

Well 

depth 

(ft below LSD)

Depth to top 

perforation 

(ft below LSD)

Depth to bottom 

perforation 

(ft below LSD)

MS-SA study unit grid wells (100 wells sampled)—Continued

Highlands study area (30 wells sampled)—Continued

S-MS-H21 04/23/2013 Production 758 400 380 400 na

S-MS-H22 04/23/2013 Production 2,057 154 na na na

S-MS-H23 01/15/2013 Production 1,468 695 520 695 na

S-MS-H24 01/31/2013 Production 1,112 500 300 500 na

S-MS-H25 05/23/2013 Production 2,084 na na na na

S-MS-H26 01/29/2013 Production 1,368 505 105 405 na

S-MS-H27 04/09/2013 Production 1,619 500 na na na

S-MS-H28 04/22/2013 Production 1,253 60 na na na

S-MS-H29 01/30/2013 Production 961 88 34 50 na

S-MS-H30 02/25/2013 Production 1,990 425 380 na na

Table 1. Identification, sampling, construction, and water-level information for grid wells sampled for the Monterey–Salinas Shallow 

Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to 

May 2013.—Continued

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

American Vertical Datum of 1988 (NAVD 88). GAMA well identification numbers: S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well; 

S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well. Abbreviations: ft, feet; mm/dd/yyyy, month/day/year; na, not available]
30 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Table 2. Classes of chemical constituents and field water-quality indicators measured in groundwater samples from the Monterey–

Salinas Shallow Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin 

Project, October 2012 to May 2013.

[—, no data]

Constituent classes Constituent-list table Results table

Field water-quality indicators 

Dissolved oxygen, temperature, pH, and specific conductance — 4A, 4B

Field alkalinity, bicarbonate, and carbonate — 4A

Organic constituents

Volatile organic compounds (VOCs) 3A 5

Pesticides and pesticide degradates 3B 6

Constituent of special interest

Perchlorate 3C 7

N-Nitrosodimethylamine (NDMA) 3C 7

Inorganic constituents

Trace elements 3D 8A, 8B

Nutrients 3E 9A, 9B

Major and minor ions, silica, and total dissolved solids (TDS) 3F 10A, 10B

Laboratory alkalinity, bicarbonate, and carbonate 3F 4A, 4B

Radioactive constituents

Radon-222 3G 11

Gross alpha and gross beta radioactivity (72-hour and 30-day counts) 3G 11

Isotopic tracers

Stable isotopes of hydrogen and oxygen in water 3G 12

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

Tritium 3G 12

Noble gases 3H 13
Tables 31

Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparison benchmarks, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) Schedule 2020.

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

as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; HBSL, USGS Health-Based 

Screening Level; MCL-CA, California maximum contaminant level; MCL-HI, Hawaii Department of Health maximum contaminant level; MCL-US, USEPA 

maximum contaminant level; NL-CA, California notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. 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. Abbreviations: CAS, Chemical Abstracts Service; CASRN®, Chemical Abstracts Service Registry Number®; LRL, laboratory reporting level; 

SRL, study reporting level; THM, trihalomethane; D, detected in groundwater samples; na, not available; μg/L, micrograms per liter; —, not detected]

Constituent 

(synonym or 

abbreviation)

Primary use 

or 

source

USGS 

parameter 

code

CASRN®1 LRL 

(μg/L)

Benchmark 

type2

Benchmark 

level 

(μg/L)2

Detection

Acetone Solvent 81552 67-64-1 3.4 HBSL (na) 6,000 (na) —3

Acrylonitrile Organic synthesis 34215 107-13-1 0.48 HBSL (RSD5-US) 0.6 (0.6) —

tert-Amyl methyl ether 

(TAME)

Gasoline oxygenate 50005 994-05-8 0.06 na na D

Benzene Gasoline hydrocarbon 34030 71-43-2 0.026 MCL-CA 1 —

Bromobenzene Solvent 81555 108-86-1 0.022 HBSL (HAL-US) 60 (60) —

Bromochloromethane Fire retardant 77297 74-97-5 0.06 HBSL (HAL-US) 90 (90) —

Bromodichloromethane Disinfection byproduct (THM) 32101 75-27-4 0.034 MCL-US 480 D

Bromoform 

(Tribromomethane)

Disinfection byproduct (THM) 32104 75-25-2 0.1 MCL-US 480 D

Bromomethane 

(Methyl bromide)

Fumigant 34413 74-83-9 0.2 HBSL (HAL-US) 100 (10) —

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

sec-Butylbenzene Gasoline hydrocarbon 77350 135-98-8 0.034 NL-CA 260 —

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

Carbon disulfide Organic synthesis 77041 75-15-0 0.1 HBSL (NL-CA) 700 (160) D

Carbon tetrachloride 

(Tetrachloromethane)

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

Chlorobenzene Solvent 34301 108-90-7 0.026 MCL-CA 70 —

Chloroethane Solvent 34311 75-00-3 0.06 na na —

Chloroform 

(Trichloromethane)

Disinfection byproduct (THM) 32106 67-66-3 0.03 MCL-US 480 D

Chloromethane Solvent 34418 74-87-3 0.1 na na —

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

2-Chlorotoluene Solvent 77275 95-49-8 0.028 HBSL (NL-CA) 100 (140) —

4-Chlorotoluene Solvent 77277 106-43-4 0.042 HBSL (NL-CA) 100 (140) —

Dibromochloromethane Disinfection byproduct (THM) 32105 124-48-1 0.12 MCL-US 480 D

1,2-Dibromo-3-chloropropane (DBCP)Fumigant 82625 96-12-8 0.4 MCL-US 0.2 —

1,2-Dibromoethane 

(EDB)

Fumigant 77651 106-93-4 0.028 MCL-US 0.05 —

Dibromomethane Solvent 30217 74-95-3 0.05 na na —

1,2-Dichlorobenzene Solvent 34536 95-50-1 0.028 MCL-US 600 —

1,3-Dichlorobenzene Solvent 34566 541-73-1 0.024 HBSL (HAL-US) 600 (600) —

1,4-Dichlorobenzene Fumigant 34571 106-46-7 0.026 MCL-CA 5 —

trans-1,4-Dichloro2-butene

Organic synthesis 73547 110-57-6 2 na na —
32 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Constituent 

(synonym or 

abbreviation)

Primary use 

or 

source

USGS 

parameter 

code

CASRN®1 LRL 

(μg/L)

Benchmark 

type2

Benchmark 

level 

(μg/L)2

Detection

Dichlorodifluoromethane 

(CFC-12)

Refrigerant 34668 75-71-8 0.1 HBSL (NL-CA) 1,000 (1,000) D

1,1-Dichloroethane 

(1,1-DCA)

Solvent 34496 75-34-3 0.044 MCL-CA 5 —

1,2-Dichloroethane 

(1,2-DCA)

Solvent 32103 107-06-2 0.08 MCL-CA 0.5 —

1,1-Dichloroethene 

(1,1-DCE)

Organic synthesis 34501 75-35-4 0.022 MCL-CA 6 —

cis-1,2-Dichloroethene 

(cis-1,2-DCE)

Solvent 77093 156-59-2 0.022 MCL-CA 6 —

trans-1,2-Dichloroethene 

(trans-1,2-DCE)

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

1,2-Dichloropropane Fumigant 34541 78-87-5 0.026 MCL-US 5 D

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

2,2-Dichloropropane Fumigant 77170 594-20-7 0.06 na na —

1,1-Dichloropropene Organic synthesis 77168 563-58-6 0.04 na na —

cis-1,3-Dichloropropene Fumigant 34704 10061-01-5 0.1 MCL-CA 0.5 —

trans-1,3-Dichloropropene

Fumigant 34699 10061-02-6 0.14 MCL-CA 0.5 —

Diethyl ether Solvent 81576 60-29-7 0.1 HBSL 1,000 —

Diisopropyl ether 

(DIPE)

Gasoline oxygenate 81577 108-20-3 0.06 na na —

Ethylbenzene Gasoline hydrocarbon 34371 100-41-4 0.036 MCL-CA 300 —

Ethyl tert-butyl ether 

(ETBE)

Gasoline oxygenate 50004 637-92-3 0.032 na na —

Ethyl methacrylate Organic synthesis 73570 97-63-2 0.2 na na —

o-Ethyl toluene (1-Ethyl2-methyl benzene)

Gasoline hydrocarbon 77220 611-14-3 0.032 na na —

Hexachlorobutadiene Organic synthesis 39702 87-68-3 0.08 HBSL (RSD5-US) 90 (9) —

Hexachloroethane Solvent 34396 67-72-1 0.1 HBSL (HAL-US) 0.7 (1) —

2-Hexanone (n-Butyl 

methyl ketone)

Solvent 77103 591-78-6 0.4 HBSL (na) 40 (na) —

Iodomethane 

(Methyl iodide)

Organic synthesis 77424 74-88-4 0.26 na na —

Isopropylbenzene Gasoline hydrocarbon 77223 98-82-8 0.042 HBSL (NL-CA) 700 (770) —

4-Isopropyl-1-methyl 

benzene

Gasoline hydrocarbon 77356 99-87-6 0.06 na na —

Methyl acrylate Organic synthesis 49991 96-33-3 0.8 na na —

Methyl acrylonitrile Organic synthesis 81593 126-98-7 0.26 HBSL (na) 0.7 —

Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparison benchmarks, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) Schedule 2020.—Continued

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

as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; HBSL, USGS Health-Based 

Screening Level; MCL-CA, California maximum contaminant level; MCL-HI, Hawaii Department of Health maximum contaminant level; MCL-US, USEPA 

maximum contaminant level; NL-CA, California notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. 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. Abbreviations: CAS, Chemical Abstracts Service; CASRN®, Chemical Abstracts Service Registry Number®; LRL, laboratory reporting level; 

SRL, study reporting level; THM, trihalomethane; D, detected in groundwater samples; na, not available; μg/L, micrograms per liter; —, not detected]
Tables 33

Constituent 

(synonym or 

abbreviation)

Primary use 

or 

source

USGS 

parameter 

code

CASRN®1 LRL 

(μg/L)

Benchmark 

type2

Benchmark 

level 

(μg/L)2

Detection

Methyl tert-butyl ether 

(MTBE)

Gasoline oxygenate 78032 1634-04-4 0.1 MCL-CA 13 D

Methyl iso-butyl ketone 

(MIBK)

Solvent 78133 108-10-1 0.32 NL-CA 120 —

Methylene chloride 

(Dichloromethane)

Solvent 34423 75-09-2 0.04 MCL-US 5 —

Methyl ethyl ketone 

(2-butanone, MEK)

Solvent 81595 78-93-3 1.6 HBSL (HAL-US) 4,000 (4,000) —3

Methyl methacrylate Organic synthesis 81597 80-62-6 0.22 HBSL (na) 10,000 (na) —

Naphthalene Gasoline hydrocarbon 34696 91-20-3 0.18 HBSL (NL-CA) 100 (17) —

Perchloroethene (PCE, 

Tetrachloroethene)

Solvent 34475 127-18-4 0.026 MCL-US 5 D 

n-Propylbenzene Solvent 77224 103-65-1 0.036 NL-CA 260 —

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

1,1,1,2-TetrachloroethaneSolvent 77562 630-20-6 0.04 HBSL (HAL-US) 70 (70) —

1,1,2,2-TetrachloroethaneSolvent 34516 79-34-5 0.14 MCL-CA 1 —

Tetrahydrofuran Solvent 81607 109-99-9 1.4 na na —3

1,2,3,4-TetramethylbenzeneGasoline hydrocarbon 49999 488-23-3 0.1 na na —

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

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

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

1,2,4-Trichlorobenzene Solvent 34551 120-82-1 0.08 MCL-CA 5 —

1,1,1-Trichloroethane 

(1,1,1-TCA)

Solvent 34506 71-55-6 0.03 MCL-US 200 —

1,1,2-Trichloroethane 

(1,1,2-TCA)

Solvent 34511 79-00-5 0.046 MCL-US 5 —

Trichloroethene (TCE) Solvent 39180 79-01-6 0.022 MCL-US 5 —

Trichlorofluoromethane 

(CFC-11)

Refrigerant 34488 75-69-4 0.06 MCL-CA 150 D

1,2,3-Trichloropropane 

(1,2,3-TCP)

Solvent/organic synthesis 77443 96-18-4 0.12 MCL-HI5 (NL-CA) 0.6 (0.005) —

Trichlorotrifluoroethane 

(CFC-113)

Refrigerant 77652 76-13-1 0.022 MCL-CA 1,200 D

1,2,3-Trimethylbenzene Gasoline hydrocarbon 77221 526-73-8 0.06 na na —

1,2,4-Trimethylbenzene Gasoline hydrocarbon 77222 95-63-6 0.032 NL-CA 330 —

1,3,5-Trimethylbenzene Organic synthesis 77226 108-67-8 0.032 NL-CA 330 —

Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparison benchmarks, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) Schedule 2020.—Continued

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

as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; HBSL, USGS Health-Based 

Screening Level; MCL-CA, California maximum contaminant level; MCL-HI, Hawaii Department of Health maximum contaminant level; MCL-US, USEPA 

maximum contaminant level; NL-CA, California notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. 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. Abbreviations: CAS, Chemical Abstracts Service; CASRN®, Chemical Abstracts Service Registry Number®; LRL, laboratory reporting level; 

SRL, study reporting level; THM, trihalomethane; D, detected in groundwater samples; na, not available; μg/L, micrograms per liter; —, not detected]
34 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Constituent 

(synonym or 

abbreviation)

Primary use 

or 

source

USGS 

parameter 

code

CASRN®1 LRL 

(μg/L)

Benchmark 

type2

Benchmark 

level 

(μg/L)2

Detection

Vinyl bromide 

(Bromoethene)

Fire retardant 50002 593-60-2 0.12 na na —

Vinyl chloride 

(Chloroethene)

Organic synthesis 39175 75-01-4 0.06 MCL-CA 0.5 —

m- plus p-Xylene Gasoline hydrocarbon 85795 108-38-3 / 

106-42-3

0.08 MCL-CA 61,750 —

o-Xylene Gasoline hydrocarbon 77135 95-47-6 0.032 MCL-CA 6

1,750 —

1

This report contains CASRNs®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs 

through CAS Client ServicesSM.

2

For constituents with HBSLs, the benchmark types and values of other non-regulatory health-based benchmarks are listed in parentheses for comparison.

3

Study reporting levels (SRLs) determined on the basis of the quality-control data collected between May 2004 and September 2010 for the first 21 study 

units of the California Groundwater Ambient Monitoring and Assessment Priority Basin Project (Fram and others, 2012) resulted in censoring all groundwater 

detections when applied to 3 VOCs for the Monterey–Salinas Shallow Aquifer study unit. All detections of acetone, 2-butanone, and tetrahydrofuran were 

censored from this dataset and coded in the NWIS database as “reviewed and rejected.” See appendix table A–2 for more information about VOC SRLs.

4

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

5

 Currently (2016), Hawaii is the only jurisdiction that has an enforcable maximum contaminant level for 1,2,3-TCP (Hooker, E.P., Fulcher, K.G., and 

Gibb, H.J., 2012, Report to the Hawaii Department of Health, Safe Drinking Water Branch, regarding the human health risks of 1,2,3-trichloropropane in tap 

water: Tetra Tech Services, 101 p., accessed June 12, 2013, at http://eha-web.doh.hawaii.gov/eha-cma/documents/fd65a6d2-73d1-4d5c-88c6-97a47ba36650).

6

The MCL-CA benchmarks for m- plus p-xylene and o-xylene is the sum of all three xylene compounds.

Table 3A. Volatile organic compounds (VOCs), primary uses or sources, comparison benchmarks, and reporting information for the 

U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) Schedule 2020.—Continued

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

as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; HBSL, USGS Health-Based 

Screening Level; MCL-CA, California maximum contaminant level; MCL-HI, Hawaii Department of Health maximum contaminant level; MCL-US, USEPA 

maximum contaminant level; NL-CA, California notification level; RSD5-US, USEPA risk-specific dose at a risk factor of 10–5. 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. Abbreviations: CAS, Chemical Abstracts Service; CASRN®, Chemical Abstracts Service Registry Number®; LRL, laboratory reporting level; 

SRL, study reporting level; THM, trihalomethane; D, detected in groundwater samples; na, not available; μg/L, micrograms per liter; —, not detected]
Tables 35

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

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

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

as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; HBSL, USGS Health-Based 

Screening Level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; 

RSD5-US, USEPA risk specific dose at a risk factor of 10–5. 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. Abbreviations: CASRN®, Chemical Abstracts Service 

Registry Number®; D, detected in groundwater samples; LRL, laboratory reporting level; na, not available; μg/L, micrograms per liter; —, not detected]

Constituent 

(synonym or abbreviation)

Primary use 

or 

source

USGS 

parameter 

code

CASRN® LRL 

(μg/L)

Benchmark 

type1

Benchmark 

level 

(μg/L)1

Detection

Acetochlor Herbicide 49260 34256-82-1 0.01 HBSL 10 —

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

Atrazine Herbicide 39632 1912-24-9 0.008 MCL-CA 1 D

Azinphos-methyl Insecticide 82686 86-50-0 0.12 HBSL (na) 10 (na) —

Azinphos-methyl oxon Insecticide degradate 61635 961-22-8 0.042 na na —2

Benfluralin Herbicide 82673 1861-40-1 0.014 HBSL 4 —2

Carbaryl Insecticide 82680 63-25-2 0.06 HBSL3 (RSD5-US) 400 (400) —

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

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

Chlorpyrifos Insecticide 38933 2921-88-2 0.0036 HBSL (HAL-US) 2 (2) D 

Chlorpyrifos oxon Insecticide degradate 61636 5598-15-2 0.08 HBSL 0.8 — 

Cyfluthrin Insecticide 61585 68359-37-5 0.016 HBSL 200 —2

Cypermethrin Insecticide 61586 52315-07-8 0.02 HBSL 40 —2

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

Deethylatrazine (2-Chloro-4-isopropylamino-6-amino-s-triazine)Herbicide degradate 04040 6190-65-4 0.006 na na D2

Desulfinylfipronil Insecticide degradate 62170 na 0.012 na na —

Desulfinylfipronil amide Insecticide degradate 62169 na 0.029 na na —

Diazinon Insecticide 39572 333-41-5 0.006 HBSL (NL-CA) 1 (1.2) —

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

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

Dicrotophos Insecticide 38454 141-66-2 0.08 HBSL 0.05 —2

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

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

Dimethoate Insecticide 82662 60-51-5 0.006 HBSL (na) 2 (na) D2

Ethion Insecticide 82346 563-12-2 0.01 HBSL (na) 4 (na) —2

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

2-Ethyl-6-methylaniline Herbicide degradate 61620 24549-06-2 0.01 na na —

Fenamiphos Insecticide 61591 22224-92-6 0.03 HBSL (HAL-US) 0.7 (0.7) — 

Fenamiphos sulfone Insecticide degradate 61645 31972-44-8 0.054 na na — 

Fenamiphos sulfoxide Insecticide degradate 61646 31972-43-7 0.08 na na —2

Fipronil Insecticide 62166 120068-37-3 0.018 HBSL 0.1 —

Fipronil sulfide Insecticide degradate 62167 120067-83-6 0.012 na na —

Fipronil sulfone Insecticide degradate 62168 120068-36-2 0.024 na na —2

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

Hexazinone Herbicide 04025 51235-04-2 0.012 HBSL (HAL-US) 400 (400) D2
36 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Constituent 

(synonym or abbreviation)

Primary use 

or 

source

USGS 

parameter 

code

CASRN® LRL 

(μg/L)

Benchmark 

type1

Benchmark 

level 

(μg/L)1

Detection

Iprodione Fungicide 61593 36734-19-7 0.014 HBSL 80 —2

Isofenphos Insecticide 61594 25311-71-1 0.008 HBSL 6 —

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

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

Metalaxyl Fungicide 61596 57837-19-1 0.014 HBSL 500 —

Methidathion Insecticide 61598 950-37-8 0.012 HBSL 1 — 

Metolachlor Herbicide 39415 51218-45-2 0.02 HBSL (HAL-US) 700 (700) —

Metribuzin Herbicide 82630 21087-64-9 0.012 HBSL (HAL-US) 90 (70) — 

Myclobutanil Fungicide 61599 88671-89-0 0.01 HBSL 200 — 

1-Naphthol Insecticide degradate 49295 90-15-3 0.036 na na —2

Paraoxon-methyl Insecticide degradate 61664 950-35-6 0.014 na na —2

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

Pendimethalin Herbicide 82683 40487-42-1 0.012 HBSL 20 D2

cis-Permethrin Insecticide 82687 54774-45-7 0.01 HBSL 400 —2

Phorate Insecticide 82664 298-02-2 0.02 HBSL 4 —2

Phorate oxon Insecticide degradate 61666 2600-69-3 0.027 na na — 

Phosmet Insecticide 61601 732-11-6 0.08 HBSL 4 — 

Phosmet oxon Insecticide degradate 61668 3735-33-9 0.0511 na na —2

Prometon Herbicide 04037 1610-18-0 0.012 HBSL (HAL-US) 400 (400) —

Prometryn Herbicide 04036 7287-19-6 0.01 HBSL 300 —

Pronamide (Propyzamide) Herbicide 82676 23950-58-5 0.0036 HBSL (RSD5-US) 10 (10) — 

Simazine Herbicide 04035 122-34-9 0.006 MCL-US 4 D 

Tebuthiuron Herbicide 82670 34014-18-1 0.028 HBSL (HAL-US) 1,000 (500) —

Terbufos Insecticide 82675 13071-79-9 0.018 HBSL (HAL-US) 0.4 (0.4) —2

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 0.045 na na —2

Terbuthylazine Herbicide 04022 5915-41-3 0.008 HBSL 2 —

Tribufos Defoliant 61610 78-48-8 0.018 HBSL 7 —2

Trifluralin Herbicide 82661 1582-09-8 0.018 HBSL (HAL-US) 20 (10) —2

1

For constituents with HBSLs, the benchmark types and values of other non-regulatory health-based benchmarks are listed in parentheses for comparison.

2

The median matrix-spike recovery was less than 70 percent. Low recoveries could indicate that the compound might not have been detected in some samples 

if it was present at very low concentrations.

3

An HBSL range of 40 to 4,000 μg/L is defined; 400 μg/L is selected as the comparison benchmark in this report.

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

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

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

as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; HBSL, USGS Health-Based 

Screening Level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; 

RSD5-US, USEPA risk specific dose at a risk factor of 10–5. 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. Other abbreviations: CASRN®, Chemical Abstracts 

Service Registry Number®; D, detected in groundwater samples; LRL, laboratory reporting level; na, not available; μg/L, micrograms per liter; —, not detected]
Tables 37

Table 3C. Constituents of special interest, primary uses or sources, comparison benchmarks, and reporting information for analyses 

performed by Weck Laboratories, Inc. (Weck), City of Industry, California.

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

of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency (USEPA) maximum 

contaminant level; NL-CA, California notification level. 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. Abbreviations: CASRN®, Chemical Abstracts Service Registry 

Number®; D, detected in groundwater samples; MRL, minimum reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter] 

Constituent 

(synonym or abbreviation)

Primary use 

or 

source

USGS 

parameter 

code

CASRN® MRL 

(μg/L)

Benchmark 

type

Benchmark 

level 

(μg/L)

Detection

Perchlorate Rocket fuel, fireworks, 

flares, natural

63790 14797-73-0 0.10 MCL-CA 6 D

N-Nitrosodimethylamine (NDMA) Disinfection byproduct 34438 62-75-9 0.002 NL-CA 0.01 D

Table 3D. Trace elements, comparison benchmarks, and reporting information for the U.S. Geological Survey (USGS) National Water 

Quality Laboratory (NWQL) Schedule 1948.

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

of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HAL-US, U.S. Environmental Protection Agency 

(USEPA) lifetime health advisory level; HBSL, USGS health-based screening level; MCL CA, California maximum contaminant level; MCL-US, USEPA 

maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. 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. Abbreviations: CASRN®, Chemical Abstracts Service Registry Number®; D, detected in groundwater samples; LT-MDL, long-term method 

detection level; na, not available; μg/L, micrograms per liter]

Constituent USGS 

parameter code CASRN® LT-MDL (μg/L)

Benchmark 

type1

Benchmark level 

(μg/L)1 Detection

Aluminum 01106 7429-90-5 2.2 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.027 MCL-US 6 D

Arsenic 01000 7440-38-2 0.03 MCL-US 10 D

Barium 01005 7440-39-3 0.07 MCL-CA 1,000 D

Beryllium 01010 7440-41-7 0.006 MCL-US 4 D

Boron 01020 7440-42-8 3 HBSL (NL-CA) 6,000 (1,000) D

Cadmium 01025 7440-43-9 0.016 MCL-US 5 D

Chromium 01030 7440-47-3 0.07 MCL-CA 50 D

Cobalt 01035 7440-48-4 0.021 na na na2

Copper 01040 7440-50-8 0.08 AL-US 1,300 D

Iron 01046 7439-89-6 3.2 SMCL-CA 300 D

Lead 01049 7439-92-1 0.025 AL-US 15 D

Lithium 01130 7439-93-2 0.22 na na D

Manganese 01056 7439-96-5 0.13 HBSL (SMCL-CA) 300 (50) D

Molybdenum 01060 7439-98-7 0.014 HBSL (HAL-US) 40 (40) D

Nickel 01065 7440-02-0 0.09 MCL-CA 100 D

Selenium 01145 7782-49-2 0.03 MCL-US 50 D

Silver 01075 7440-22-4 0.005 HBSL (SMCL-CA) 100 (100) D

Strontium 01080 7440-24-6 0.2 HBSL (HAL-US) 4,000 (4,000) D

Thallium 01057 7440-28-0 0.01 MCL-US 2 D

Uranium 22703 7440-61-1 0.003 MCL-US 30 D

Vanadium 01085 7440-62-2 0.08 NL-CA 50 D

Zinc 01090 7440-66-6 1.4 HBSL (SMCL-CA) 2,000 (5,000) D

1

For constituents with HBSLs, the benchmark types and values of other non-regulatory health-based benchmarks are listed in parentheses for comparison.

2

On the basis of quality-control data collected October 2009 through March 2013, all results for cobalt were coded as reviewed and rejected in the USGS 

National Water Information System (NWIS) database and are not presented in this report (Davis, T.A., Olsen, L.D., Fram, M.S., and Belitz, Kenneth, 2014, 

Updated study reporting levels (SRLs) for trace-element data collected for the California Groundwater Ambient Monitoring and Assessment Priority Basin 

Project, October 2009–March 2013: U.S. Geological Survey Scientific Investigations Report 2014–5105, 52 p., http://dx.doi.org/10.3133/sir20145105).
38 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Table 3E. Nutrients, comparison benchmarks, and reporting information for the U.S. Geological Survey (USGS) National Water Quality 

Laboratory (NWQL) Schedule 2755.

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

of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) lifetime health advisory level; MCL-CA, California maximum 

contaminant level; MCL-US, USEPA maximum contaminant level. 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. Abbreviations: CASRN®, Chemical Abstracts 

Service Registry Number®; D, detected in groundwater samples; LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams 

per liter; na, not available]

Constituent

USGS 

parameter 

code

CASRN®

 LT-MDL 

or MDL 

(mg/L)

Benchmark 

type 

Benchmark 

level 

(mg/L)

Detection

Ammonia (as nitrogen) 00608 7664-41-7 0.010 HAL-US 124.7 D

Nitrite (as nitrogen) 00613 14797-65-0 0.0010 MCL-US 1 D

Nitrite plus nitrate (as nitrogen)2 00631 na 0.04 MCL-US 10 D

Total nitrogen (ammonia + nitrite + nitrate + organic nitrogen) 62854 17778-88-0 0.05 na na D

Orthophosphate (as phosphorus) 00671 14265-44-2 0.004 na na D

1

The HAL-US is 30 mg/L “as ammonia.” To facilitate comparison to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L “as 

nitrogen.”

2

Nitrite plus nitrate (as nitrogen) is referred to as nitrate in the text for clarity.

Table 3F. Major and minor ions, silica, total dissolved solids (TDS), and alkalinity, comparison benchmarks, and reporting information 

for the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) Schedule 1948.

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

as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency (USEPA) 

maximum contaminant level; SMCL-CA, California secondary maximum contaminant level. 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. Abbreviations: CaCO3, 

calcium carbonate; CASRN®, Chemical Abstracts Service Registry Number®; D, detected in groundwater samples; LT-MDL, long-term method detection level; 

MDL, method detection limit; mg/L, milligrams per liter; na, not available; SiO2, silicon dioxide]

Constituent 

(synonym or abbreviation)

USGS 

parameter 

code

CASRN®

LT-MDL 

or MDL 

(mg/L)

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 1250 (500) D

Fluoride 00950 16984-48-8 0.04 MCL-CA 2 D

Magnesium 00925 7439-95-4 0.011 na na D

Potassium 00935 7440-09-7 0.03 na na D

Sodium 00930 7440-23-5 0.06 na na D

Sulfate 00945 14808-79-8 0.09 SMCL-CA 1250 (500) D

Silica (as SiO2) 00955 7631-86-9 0.018 na na D

Total dissolved solids (TDS) 70300 na 10 SMCL-CA 1500 (1,000) D

Laboratory alkalinity (as CaCO3) 2 29801 na 4.6 na na D

1

The SMCL-CA for chloride, sulfate, and TDS have recommended and upper benchmark values. The upper benchmark value is shown in parentheses.

2

Laboratory alkalinity results are presented in table 4.
Tables 39

Table 3G. Isotopic tracers, radioactive constituents, comparison benchmarks, and reporting information for laboratory analyses.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Stable isotope ratios are reported in the standard delta 

notation (δ), the ratio of a heavier isotope to the more common lighter isotope of that element, relative to a standard reference material. Laboratory entity 

codes in the USGS National Water Information System (NWIS) for laboratories other than the USGS National Water Quality Laboratory (NWQL) are given 

in parentheses after the laboratory names in table footnotes. Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark 

types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. 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. Elements: C, carbon; H, hydrogen; O, oxygen. Reporting units: pCi/L, picocuries per liter. Abbreviations: CASRN®, 

Chemical Abstracts Service Registry Number®; CSU, 1-sigma combined standard uncertainty; D, detected in groundwater samples; na, not available; pmc, 

percent modern carbon; ssLC, sample-specific critical level; USGS, U.S. Geological Survey]

Constituent

USGS 

parameter 

code

CASRN® Reporting 

level

Reporting 

uncertainty

Reporting 

units

Benchmark 

type

Benchmark 

level Detection

Isotopic tracers

d2H in water1 82082 na na 2 per mil na na D

d18O in water1 82085 na na 0.20 per mil na na D

d13C in dissolved inorganic carbon2 82081 na na 0.05 per mil na na D

Radioactive constituents

Carbon-142 49933 14762-75-5 na 0.0015 pmc na na D

Tritium3 07000 10028-17-8 ssLC CSU pCi/L MCL-CA 20,000 D

Radon-2224 82303 14859-67-7 ssLC CSU pCi/L MCL-US 

(Proposed) 

4,000 D

Gross alpha radioactivity, 

72-hour and 30-day counts5

62636, 

62639

12587-46-1 ssLC CSU pCi/L MCL-US 615 D

Gross beta radioactivity, 

72-hour and 30-day counts5

62642, 

62645

12587-47-2 ssLC CSU pCi/L MCL-CA 50 D

1

USGS Stable Isotope Laboratory, Reston, Virginia.

2

Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry Facility, Woods Hole, Massachusetts.

3

USGS Stable Isotope and Tritium Laboratory, Menlo Park, California. 

4

USGS National Water Quality Laboratory.

5

Eberline Analytical Services, Richmond, California.

6

The MCL-US benchmark for gross alpha activity applies to adjusted gross alpha, which is equal to measured gross alpha activity minus uranium activity.

Table 3H. Noble gases, comparative thresholds, and reporting information for dissolved gases analyzed by the Lawrence Livermore 

National Laboratory (LLNL).

[Results for noble gas analyses by the LLNL are stored in a database maintained by Groundwater Ambient Monitoring and Assessment Priority Basin 

Project project staff. Benchmark types and benchmark levels as of May 23, 2013. Abbreviations: CASRN®, Chemical Abstracts Service Registry Number®; 

cm3STP/g, cubic centimeters of gas at standard temperature and pressure per gram of water; D, detected in groundwater samples; MU, method uncertainty; 

na, not available]

Constituent CASRNs®1 MU 

(percent)

Reporting 

units

Benchmark 

type

Benchmark 

level Detection

Noble gases 

Argon 7440-37-1 2 cm3STP/g na na D

Helium-3 / Helium-4 ratio na / 7440-59-7 0.75 atom ratio na na D

Helium-4 7440-59-7 2 cm3STP/g na na D

Krypton 7439-90-9 2 cm3STP/g na na D

Neon 7440-01-09 2 cm3STP/g na na D

Xenon 7440-63-3 2 cm3STP/g na na D

1

This report contains CASRNs®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs 

through CAS Client ServicesSM.
Table 4A. Water-quality indicators in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification numbers: S-MS-H, Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study aSalinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: SMCL-CA, CaliforniSMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. Abbreviations: CaCO3, calcium carbonate; mg/L, milligrams per liter; na, not availreporting level or range; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; *, concentration greater than the benchmark level; **, concentration greater than than; >, greater than; °C, degrees Celsius; —, not detected] GAMA well identification number Dissolved oxygen, field (mg/L) (00300) Water temperature, field (°C) (00010) pH, field (standard units) (00400) pH, laboratory (standard units) (00403) Specific conductance, field (μS/cm at 25 °C) (00095) Specific conductance, laboratory (μS/cm at 25 °C) (90095) Alkalinity, field (mg/L as CaCO3) (29802) Alkalinity, laboratory (mg/L as CaCO3) (29801) Bicarbonate, field (mg/L) (63786) Bicarbon

laborato

(mg/L

Benchmark type na na SMCL-US SMCL-US SMCL-CA SMCL-CA na na na na Benchmark level na na <6.5 or >8.5 <6.5 or >8.5 1900 (1,600) 1900 (1,600) na na na na RL 0.2 0.0–38.5 0–14 0–14 5 5 1 4.6 1 1 MS-SA study unit grid wells (100 wells sampled) Santa Cruz study area wells (15 wells sampled) S-MS-SC01 <0.2 20.0 7.2 7.2 1,240 1,250 160 186 194 226 S-MS-SC02 0.7 18.0 7.3 7.6 430 530 nc 163 nc 198 S-MS-SC03 0.5 15.0 6.7 6.8 1,170 1,120 nc 137 nc 167 S-MS-SC04 <0.2 16.5 7.0 7.2 961 1,000 nc 213 nc 259 S-MS-SC05 0.2 21.5 7.1 7.5 994 1,110 nc 365 nc 445 S-MS-SC06 1.7 19.5 7.5 7.8 368 377 nc 153 nc 186 S-MS-SC07 <0.2 20.0 7.7 7.9 496 383 nc 157 nc 191 S-MS-SC08 <0.2 18.5 7.4 7.5 **1,760 **1,810 330 339 401 412 S-MS-SC09 0.4 18.0 7.2 7.6 878 862 nc 330 nc 402 S-MS-SC10 5.2 15.0 6.9 7.2 580 607 nc 250 nc 305 S-MS-SC11 1.3 17.5 7.0 7.2 252 259 nc 98.4 nc 120 S-MS-SC12 0.3 17.0 6.9 6.9 470 509 nc 226 nc 275 S-MS-SC13 0.4 17.0 7.3 7.6 511 541 nc 225 nc 274 S-MS-SC14 <0.2 14.0 7.7 7.9 398 406 nc 202 nc 245 S-MS-SC15 <0.2 15.0 7.4 7.7 660 678 nc 283 nc 344 
GAMA 

well 

identification 

number

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

Water 

temperature, 

field 

(°C) 

(00010)

pH, field 

(standard 

units) 

(00400)

pH, 

laboratory 

(standard 

units) 

(00403)

Specific 

conductance, 

field 

(μS/cm at 

25 °C) 

(00095)

Specific 

conductance, 

laboratory 

(μS/cm at 

25 °C) 

(90095)

Alkalinity, 

field 

(mg/L 

as 

CaCO3) 

(29802)

Alkalinity, 

laboratory 

(mg/L 

as 

CaCO3) 

(29801)

Bicarbonate, 

field 

(mg/L) 

(63786)

Bicarbon

laborato

(mg/L

MS-SA study unit grid wells (100 wells sampled)—ContinuedPajaro Valley grid wells (15 wells sampled) S-MS-P01 4.5 19.0 7.6 7.8 416 439 159 168 193 204 S-MS-P02 7.0 17.0 7.2 7.2 210 212 nc 85.7 nc 104 S-MS-P03 <0.2 18.5 8.1 8.1 586 597 nc 240 nc 289 S-MS-P04 6.9 16.5 7.2 7.4 375 382 nc 106 nc 129 S-MS-P05 3.7 11.0 *6.0 *6.3 278 284 nc 54.4 nc 66 S-MS-P06 0.5 17.0 7.3 7.6 746 752 nc 222 nc 270 S-MS-P07 6.8 18.0 7.1 7.5 **1,790 **1,800 nc 114 nc 139 S-MS-P08 8.0 18.5 6.9 7.3 295 293 nc 72.7 nc 89 S-MS-P09 <0.2 18.0 7.1 7.4 **5,290 **5,270 nc 182 nc 222 S-MS-P10 7.8 18.5 7.4 7.5 446 416 nc 87.7 nc 107 S-MS-P11 2.2 17.0 7.7 7.9 538 537 206 221 250 268 S-MS-P12 0.9 20.0 7.6 7.7 691 702 nc 238 nc 289 S-MS-P13 0.6 18.0 7.4 7.6 1,210 1,190 nc 314 nc 382 S-MS-P14 1.8 21.0 7.5 7.7 746 747 nc 295 nc 359 S-MS-P15 6.0 17.5 7.4 7.9 424 430 nc 116 nc 141 Salinas Valley grid wells (40 wells sampled)S-MS-SV01 5.2 19.5 7.2 7.6 786 778 nc 238 nc 290 S-MS-SV02 0.3 20.5 7.3 7.6 1,230 1,210 nc 270 nc 329 S-MS-SV03 4.1 18.5 6.8 7.2 1,120 1,130 nc 225 nc 274 S-MS-SV04 0.7 17.5 *6.2 6.6 698 731 nc 103 nc 126 S-MS-SV05 6.2 20.0 *6.4 6.7 1,460 1,480 48.7 53.2 59.4 65 

Table 4A. Water-quality indicators in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. —Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification numbers: S-MS-H, Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study aSalinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: SMCL-CA, Californicontaminant level; SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. Abbreviations: CaCO3, calcium carbonate; mg/L, milligrams penot collected; RL, reporting level or range; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; *, concentration greater than the benchmark level; **, concentbenchmark; <, less than; >, greater than; °C, degrees Celsius; —, not detected]
GAMA well identification number Dissolved oxygen, field (mg/L) (00300) Water temperature, field (°C) (00010) pH, field (standard units) (00400) pH, laboratory (standard units) (00403) Specific conductance, field (μS/cm at 25 °C) (00095) Specific conductance, laboratory (μS/cm at 25 °C) (90095) Alkalinity, field (mg/L as CaCO3) (29802) Alkalinity, laboratory (mg/L as CaCO3) (29801) Bicarbonate, field (mg/L) (63786) Bicarbon

laborato

(mg/L

MS-SA study unit grid wells (100 wells sampled)—Continued Salinas Valley grid wells (40 wells sampled)—Continued S-MS-SV06 6.6 18.5 7.1 7.5 828 838 nc 179 nc 218 S-MS-SV07 2.2 19.0 7.6 7.8 **2,690 **2,140 nc 170 nc 206 S-MS-SV08 1.8 20.5 7.4 7.8 844 824 nc 196 nc 238 S-MS-SV09 6.2 19.0 6.5 6.8 1,220 1,260 nc 104 nc 127 S-MS-SV10 6.1 18.0 7.0 7.4 1,310 1,290 nc 210 nc 256 S-MS-SV11 6.0 15.0 7.6 7.8 382 437 nc 138 nc 168 S-MS-SV12 5.9 20.0 7.4 7.8 704 697 148 155 180 189 S-MS-SV13 0.4 23.0 7.7 7.9 **1,940 **1,930 nc 452 nc 549 S-MS-SV14 1.5 23.5 7.1 7.4 1,510 1,500 228 245 277 298 S-MS-SV15 1.0 17.5 7.5 7.6 669 682 nc 193 nc 235 S-MS-SV16 3.0 17.5 7.7 7.7 647 654 nc 178 nc 216 S-MS-SV17 6.8 19.0 7.5 7.7 506 531 nc 136 nc 165 S-MS-SV18 1.2 17.0 7.2 7.5 981 997 nc 249 nc 303 S-MS-SV19 1.4 20.0 7.4 7.7 737 765 nc 208 nc 253 S-MS-SV20 0.8 19.5 7.1 7.4 1,570 **1,620 nc 378 nc 460 S-MS-SV21 — 17.0 *6.4 6.8 **2,840 **3,050 nc 90.4 nc 110 S-MS-SV22 2.3 16.5 7.2 7.7 1,240 1,150 nc 243 nc 296 S-MS-SV23 1.1 16.5 7.3 7.6 893 917 nc 198 nc 241 S-MS-SV24 1.1 22.5 7.5 7.8 629 691 nc 186 nc 226 S-MS-SV25 0.6 17.5 7.4 7.7 743 734 nc 194 nc 236 

Table 4A. Water-quality indicators in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. —Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification numbers: S-MS-H, Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study aSalinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: SMCL-CA, Californicontaminant level; SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. Abbreviations: CaCO3, calcium carbonate; mg/L, milligrams penot collected; RL, reporting level or range; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; *, concentration greater than the benchmark level; **, concentbenchmark; <, less than; >, greater than; °C, degrees Celsius; —, not detected]
GAMA 

well 

identification 

number

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

Water 

temperature, 

field 

(°C) 

(00010)

pH, field 

(standard 

units) 

(00400)

pH, 

laboratory 

(standard 

units) 

(00403)

Specific 

conductance, 

field 

(μS/cm at 

25 °C) 

(00095)

Specific 

conductance, 

laboratory 

(μS/cm at 

25 °C) 

(90095)

Alkalinity, 

field 

(mg/L 

as 

CaCO3) 

(29802)

Alkalinity, 

laboratory 

(mg/L 

as 

CaCO3) 

(29801)

Bicarbonate, 

field 

(mg/L) 

(63786)

Bicarbon

laborato

(mg/L

MS-SA study unit grid wells (100 wells sampled)—ContinuedSalinas Valley grid wells (40 wells sampled)—ContinuedS-MS-SV26 0.3 19.5 7.0 7.4 **2,910 *2,890 nc 261 nc 318 S-MS-SV27 2.5 17.0 7.5 7.7 433 438 nc 149 nc 181 S-MS-SV28 2.8 20.5 7.7 7.8 671 688 229 232 278 282 S-MS-SV29 4.4 19.5 7.2 7.5 **3,970 **3,990 nc 197 nc 240 S-MS-SV30 3.2 16.5 7.2 7.5 **3,940 **4,000 303 340 369 414 S-MS-SV31 4.6 17.0 7.5 7.7 876 883 nc 184 nc 224 S-MS-SV32 4.4 20.0 7.1 7.4 1,530 1,540 nc 251 nc 306 S-MS-SV33 — 19.0 6.6 7.1 438 470 nc 69.1 nc 84 S-MS-SV34 2.4 20.5 7.4 7.6 376 406 88.6 95.7 108 116 S-MS-SV35 0.3 22.5 7.3 7.8 796 930 nc 189 nc 230 S-MS-SV36 9.5 18.0 6.6 7.2 1,270 1,260 nc 124 nc 151 S-MS-SV37 6.6 17.0 6.9 7.3 687 711 nc 230 nc 280 S-MS-SV38 3.7 19.0 7.1 7.4 **2,230 **2,260 nc 206 nc 251 S-MS-SV39 <0.2 21.5 7.2 7.5 **2,260 **2,200 nc 200 nc 243 S-MS-SV40 4.2 19.0 7.0 7.3 1,450 1,450 nc 199 nc 242 Highlands grid wells (30 wells sampled) S-MS-H01 0.2 13.5 7.9 8.0 821 819 243 258 293 312 S-MS-H02 0.2 20.5 6.9 7.2 **2,560 **2,510 nc 214 nc 261 S-MS-H03 <0.2 17.5 7.2 7.4 1,050 1,050 nc 343 nc 418 S-MS-H04 4.3 20.5 7.0 7.1 1,060 1,070 3na 438 179 534 S-MS-H05 <0.2 24.0 7.5 7.7 **2,240 **2,200 406 413 492 502 

Table 4A. Water-quality indicators in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. —Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification numbers: S-MS-H, Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study aSalinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: SMCL-CA, Californicontaminant level; SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. Abbreviations: CaCO3, calcium carbonate; mg/L, milligrams penot collected; RL, reporting level or range; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; *, concentration greater than the benchmark level; **, concentbenchmark; <, less than; >, greater than; °C, degrees Celsius; —, not detected]
GAMA well identification number Dissolved oxygen, field (mg/L) (00300) Water temperature, field (°C) (00010) pH, field (standard units) (00400) pH, laboratory (standard units) (00403) Specific conductance, field (μS/cm at 25 °C) (00095) Specific conductance, laboratory (μS/cm at 25 °C) (90095) Alkalinity, field (mg/L as CaCO3) (29802) Alkalinity, laboratory (mg/L as CaCO3) (29801) Bicarbonate, field (mg/L) (63786) Bicarbon

laborato

(mg/L

MS-SA study unit grid wells (100 wells sampled)—Continued Highlands grid wells (30 wells sampled)—Continued S-MS-H06 2.1 19.5 7.0 7.3 607 626 nc 211 nc 257 S-MS-H07 7.5 16.0 6.7 7.2 1,040 1,060 nc 294 nc 358 S-MS-H08 6.2 18.5 7.1 7.3 **2,850 **2,870 nc 458 nc 558 S-MS-H09 0.2 19.5 *6.4 6.8 **3,880 **3,950 nc 473 nc 577 S-MS-H10 <0.2 19.0 6.9 7.1 **2,610 **2,640 nc 234 nc 285 S-MS-H11 1.0 24.0 7.8 8.0 1,040 1,040 nc 326 nc 395 S-MS-H12 4.2 18.5 7.2 7.4 1140 1,010 nc 242 nc 295 S-MS-H13 4.9 21.0 6.9 7.4 **2,230 **2,320 nc 259 nc 316 S-MS-H14 <0.2 31.5 6.9 7.2 **8,210 **9,730 nc 1730 nc 2108 S-MS-H15 0.2 24.0 8.2 8.3 572 569 nc 209 nc 251 S-MS-H16 3.1 22.0 7.7 8.0 555 559 nc 174 nc 211 S-MS-H17 6.1 24.0 7.5 7.7 594 593 nc 179 nc 218 S-MS-H18 4.4 24.0 7.4 7.6 **2,100 **2,120 nc 138 nc 168 S-MS-H19 6.3 17.5 6.9 7.3 683 695 nc 233 nc 284 S-MS-H20 5.8 19.0 7.0 7.3 **2,170 **2,200 242 258 295 314 S-MS-H21 <0.2 26.5 7.2 7.4 **1,810 **1,830 nc 174 nc 212 S-MS-H22 1.0 21.0 7.0 7.3 985 984 nc 309 nc 376 S-MS-H23 7.1 20.5 7.5 7.7 601 619 nc 214 nc 260 S-MS-H24 1.9 23.0 7.0 7.3 **2,540 **2,770 nc 146 nc 178 S-MS-H25 8.3 22.0 7.5 7.9 *946 963 nc 312 nc 379 

Table 4A. Water-quality indicators in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. —Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification numbers: S-MS-H, Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study aSalinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: SMCL-CA, Californicontaminant level; SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. Abbreviations: CaCO3, calcium carbonate; mg/L, milligrams penot collected; RL, reporting level or range; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; *, concentration greater than the benchmark level; **, concentbenchmark; <, less than; >, greater than; °C, degrees Celsius; —, not detected]
GAMA 

well 

identification 

number

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

Water 

temperature, 

field 

(°C) 

(00010)

pH, field 

(standard 

units) 

(00400)

pH, 

laboratory 

(standard 

units) 

(00403)

Specific 

conductance, 

field 

(μS/cm at 

25 °C) 

(00095)

Specific 

conductance, 

laboratory 

(μS/cm at 

25 °C) 

(90095)

Alkalinity, 

field 

(mg/L 

as 

CaCO3) 

(29802)

Alkalinity, 

laboratory 

(mg/L 

as 

CaCO3) 

(29801)

Bicarbonate, 

field 

(mg/L) 

(63786)

Bicarbon

laborato

(mg/L

MS-SA study unit grid wells (100 wells sampled)—ContinuedHighlands grid wells (30 wells sampled)—ContinuedS-MS-H26 5.9 22.0 7.6 7.8 992 1,010 122 129 148 157 S-MS-H27 3.1 21.0 7.1 7.6 831 842 nc 271 nc 330 S-MS-H28 0.6 17.0 7.0 7.3 **2,180 **2,220 nc 474 nc 577 S-MS-H29 4.8 19.0 7.3 7.5 **3,710 **3,720 nc 269 nc 327 S-MS-H30 5.9 20.0 7.2 7.5 1,040 1,030 nc 224 nc 273 

1The SMCL-CA for specific conductance has recommended and upper benchmark values. The upper value is shown in parentheses.2Bicarbonate and carbonate concentrations were calculated from the laboratory alkalinity and pH values by using the advanced speciation method (http://or.water.usgs.gov/alk

pK2 = 10.33, and pKW = 14.

3Possible sample swap; value rejected.

Table 4A. Water-quality indicators in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. —Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. GAMA well identification numbers: S-MS-H, Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study aSalinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: SMCL-CA, Californicontaminant level; SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. Abbreviations: CaCO3, calcium carbonate; mg/L, milligrams penot collected; RL, reporting level or range; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; *, concentration greater than the benchmark level; **, concentbenchmark; <, less than; >, greater than; °C, degrees Celsius; —, not detected]
46 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Table 4B. Water-quality indicators in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) 

study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were 

analyzed. Information about the constituents is given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer 

Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–Salinas Shallow Aquifer Valley and Plains study area tap sample. Benchmark type, benchmark 

level, and LT-MDL as of May 23, 2013. Benchmark types: SMCL-CA, California secondary maximum contaminant level; SMCL-US, U.S. Environmental 

Protection Agency secondary maximum contaminant level. Abbreviations: CaCO3, calcium carbonate; mg/L, milligrams per liter; na, not available; 

RL, reporting level or range; USGS, U.S. Geological Survey; *, measured value less than the benchmark level; **, concentration greater than the upper 

benchmark level; °C, degrees Celsius; μS/cm, microsiemens per centimeter; <, less than; >, greater than]

GAMA tap 

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, 

laboratory2

(mg/L)

Carbonate, 

laboratory2

(mg/L)

Benchmark type na na SMCL-US SMCL-US SMCL-CA SMCL-CA na na na

Benchmark na na <6.5 or >8.5 <6.5 or >8.5 1900 (1,600) 1900 (1,600) na na na

RL 0.2 0.0–38.5 0–14 0–14 5 5 1 1 1

MS-SA shallow-well tap-site samples (70 taps sampled) 

Pajaro Valley study area shallow-well tap-site samples (15 taps sampled) 

S-MS-P01-T1 8.6 15.0 7.1 7.4 474 484 119 145 0.08

S-MS-P02-T1 6.5 17.0 7.4 7.8 314 320 131 159 0.18

S-MS-P03-T1 8.3 18.0 7.7 8 167 167 77.2 94 0.22

S-MS-P04-T1 4.8 16.0 7.8 8.1 405 415 200 242 0.70

S-MS-P05-T1 na 17.0 6.7 7 508 528 85.7 104 0.02

S-MS-P06-T1 3.9 15.0 6.9 7.3 636 644 177 216 0.08

S-MS-P07-T1 na 18.0 *6.1 6.6 646 653 20.6 25 0.00

S-MS-P08-T1 na 16.0 7.8 8.1 810 817 94.3 114 0.33

S-MS-P09-T1 na 20.0 6.8 7.2 746 751 76.8 94 0.03

S-MS-P10-T1 1.3 18.5 7.2 7.7 768 769 314 382 0.28

S-MS-P11-T1 na 22.5 6.9 7.3 1,290 1,300 406 495 0.18

S-MS-P12-T1 na 18.5 7.2 7.6 1,260 1,280 379 461 0.34

S-MS-P13-T1 na 16.5 6.6 7.2 355 360 79 96 0.02

S-MS-P14-T1 na 17.0 6.9 7.4 755 762 127 155 0.06

S-MS-P15-T1 na 19.0 6.5 6.9 551 557 103 126 0.02

Salinas Valley study area shallow-well tap-site samples (40 taps sampled) 

S-MS-SV01-T1 6.7 14.0 *5.8 6.9 328 333 109 133 0.00

S-MS-SV01-T2 7.2 17.0 7.2 7.6 **1,910 **1,940 280 341 0.25

S-MS-SV02-T1 9.3 14.5 7.4 7.5 724 731 190 231 0.27

S-MS-SV02-T2 7.5 21.0 7.1 7.6 987 976 249 303 0.18

S-MS-SV03-T1 7.4 20.5 7.7 8 360 362 138 167 0.39

S-MS-SV03-T2 1.6 19.0 7 7.4 **2,010 **2,030 205 250 0.11

S-MS-SV04-T1 10.7 14.0 7.8 8.2 844 845 252 305 0.89

S-MS-SV04-T2 3.5 20.0 6.7 7.1 1,540 1,530 247 301 0.07

S-MS-SV05-T1 0.6 17.5 7 7.6 1,340 1,360 314 382 0.18

S-MS-SV05-T2 6.7 15.0 6.6 7.8 1,050 1,060 239 291 0.05
Tables 47

GAMA tap 

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, 

laboratory2

(mg/L)

Carbonate, 

laboratory2

(mg/L)

MS-SA shallow-well tap-site samples (70 taps sampled)—Continued

Salinas Valley study area shallow-well tap-site samples (40 taps sampled)—Continued

S-MS-SV06-T1 2.7 18.5 7.3 7.6 646 657 118 144 0.13

S-MS-SV06-T2 7 21.0 7 7.6 827 843 116 141 0.07

S-MS-SV08-T1 0.8 16.0 7.2 7.4 **4,920 **4,990 183 223 0.16

S-MS-SV08-T2 0.8 15.5 7.5 7.7 976 1,000 285 346 0.50

S-MS-SV09-T1 1.4 15.0 7.1 7.4 907 924 230 280 0.16

S-MS-SV09-T2 2.7 13.0 7.3 7.6 813 824 232 282 0.26

S-MS-SV11-T1 4.4 13.0 7.2 7.5 **1,610 **1,620 329 401 0.29

S-MS-SV11-T2 6.1 17.0 7.2 7.5 **1,850 **1,900 221 269 0.20

S-MS-SV13-T1 0.3 19.0 8 7.9 **1,770 **1,810 265 320 1.47

S-MS-SV13-T2 0.4 20.5 7.5 7.9 949 945 248 301 0.44

S-MS-SV16-T1 4.1 17.0 7.3 7.6 1,330 E1340 212 258 0.24

S-MS-SV16-T2 5.4 20.5 7 7.6 1,380 1,450 249 303 0.14

S-MS-SV17-T1 5.5 16.5 7.1 7.4 **2,020 **2,050 197 240 0.14

S-MS-SV17-T2 4.4 17.0 7.3 7.6 1,560 1,580 176 214 0.20

S-MS-SV18-T1 3.6 16.0 7.6 7.8 **1,770 **1780 374 454 0.83

S-MS-SV19-T1 3.6 19.0 7 7.5 912 923 306 373 0.17

S-MS-SV19-T2 0.1 19.5 7.2 7.7 881 880 224 273 0.20

S-MS-SV20-T1 0.9 15.5 7.2 7.5 1,460 1,480 169 206 0.15

S-MS-SV20-T2 1.5 20.0 7.5 7.9 611 620 158 192 0.28

S-MS-SV21-T1 5.6 14.0 7.4 7.7 586 587 186 226 0.26

S-MS-SV21-T2 6.2 18.5 6.8 7.4 1,400 1,410 156 190 0.06

S-MS-SV22-T1 6.7 16.5 7.2 7.4 **2,490 **2,460 345 420 0.31

S-MS-SV22-T2 5.9 20.0 6.9 7.2 837 824 182 222 0.08

S-MS-SV23-T1 10.8 13.5 7.8 7.8 **2,350 **2,360 286 347 1.01

S-MS-SV24-T1 10.2 17.0 7.7 7.8 570 578 155 188 0.43

Table 4B. Water-quality indicators in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) 

study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were 

analyzed. Information about the constituents is given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer 

Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–Salinas Shallow Aquifer Valley and Plains study area tap sample. Benchmark type, benchmark 

level, and LT-MDL as of May 23, 2013. Benchmark types: SMCL-CA, California secondary maximum contaminant level; SMCL-US, U.S. Environmental 

Protection Agency secondary maximum contaminant level. Abbreviations: CaCO3, calcium carbonate; mg/L, milligrams per liter; na, not available; 

RL, reporting level or range; USGS, U.S. Geological Survey; *, measured value less than the benchmark level; **, concentration greater than the upper 

benchmark level; °C, degrees Celsius; μS/cm, microsiemens per centimeter; <, less than; >, greater than]
48 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

GAMA tap 

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, 

laboratory2

(mg/L)

Carbonate, 

laboratory2

(mg/L)

MS-SA shallow-well tap-site samples (70 taps sampled)—Continued

Salinas Valley study area shallow-well tap-site samples (40 taps sampled)—Continued

S-MS-SV24-T2 8.1 16.0 7.5 7.9 389 394 124 151 0.22

S-MS-SV25-T1 3.2 17.0 7.2 7.6 **2,430 **2,420 322 392 0.29

S-MS-SV25-T2 2.1 16.5 7.3 7.7 **1,640 **1,630 277 337 0.31

S-MS-SV26-T1 2.5 19.0 7.5 7.8 427 426 139 169 0.25

S-MS-SV26-T2 6.2 17.0 7 7.5 **2,880 **2,940 272 331 0.15

S-MS-SV27-T1 1.2 24.0 7.1 7.3 **2,430 **2,430 296 360 0.21

S-MS-SV29-T1 6.9 18.0 7.1 7.5 **2,820 **2,850 232 283 0.16

S-MS-SV29-T2 6.3 21.0 7.5 7.9 608 605 157 191 0.28

S-MS-SV30-T1 6.8 17.0 7.8 8 1,060 1,070 212 257 0.75

S-MS-SV32-T1 8 20.0 7.2 7.5 1,160 1,180 224 273 0.20

S-MS-SV33-T1 4.8 23.0 7.1 7.5 584 585 177 216 0.12

S-MS-SV33-T2 4.9 17.0 6.7 7 1,050 1,040 216 263 0.06

S-MS-SV34-T1 8 14.5 6.8 7.1 293 292 55.8 68 0.02

S-MS-SV34-T2 8.7 16.0 6.7 7.1 383 385 62.5 76 0.02

S-MS-SV35-T1 6 13.0 6.7 7.5 945 937 255 311 0.07

S-MS-SV35-T2 7.8 17.0 7.3 7.6 964 952 161 196 0.18

S-MS-SV36-T1 9.5 14.5 7.1 7.5 1,120 1,130 178 217 0.13

S-MS-SV36-T2 8 15.0 7.2 7.5 1,520 1,530 130 158 0.12

S-MS-SV37-T1 8.6 21.0 7.1 7.5 700 711 195 237 0.14

S-MS-SV40-T1 E11.1 E14.6 6.5 7.8 553 558 196 239 0.03

1

The SMCL-CA for specific conductance has recommended and upper benchmark values. The upper value is shown in parentheses.

2

Bicarbonate and carbonate concentrations were calculated from the laboratory alkalinity and pH values by using the advanced speciation method 

(http://or.water.usgs.gov/alk/methods.html) with pK1 = 6.35, pK2 = 10.33, and pKW = 14.

Table 4B. Water-quality indicators in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) 

study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were 

analyzed. Information about the constituents is given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer 

Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–Salinas Shallow Aquifer Valley and Plains study area tap sample. Benchmark type, benchmark 

level, and LT-MDL as of May 23, 2013. Benchmark types: SMCL-CA, California secondary maximum contaminant level; SMCL-US, U.S. Environmental 

Protection Agency secondary maximum contaminant level. Abbreviations: CaCO3, calcium carbonate; mg/L, milligrams per liter; na, not available; 

RL, reporting level or range; USGS, U.S. Geological Survey; *, measured value less than the benchmark level; **, concentration greater than the upper 

benchmark level; °C, degrees Celsius; μS/cm, microsiemens per centimeter; <, less than; >, greater than]
Table 5. Volatile organic compounds (VOCs) detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid wells were analyzed, bdetections are listed. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 100 grid wells. All constituents are lwell identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area welSalinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benchmark levels, and repo2013. Benchmark types: HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maxNL-CA, California notification level. 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-US or no MCL-US exists. Abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; <LT-MDL, value reported by laboratory level and is therefore not counted as a detection; na, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; —, not detected]

Primary use 

or source

Trihalomethanes Solvent Refrigerant

Natural, 

organic 

synthesis

Gasoline oxygenate

Gasol

hydroc

bon 

GAMA 

well 

identification 

number

Chloroform 

(tri-chloromethane) 

(μg/L) 

(32106)

Bromoform 

(tri-bromomethane) 

(μg/L) 

(32104)

Bromodichloromethane 

(μg/L) 

(32101)

Dibromochloromethane 

(μg/L) 

(32105)

Per-chloroethylene 

(PCE) 

(μg/L) 

(34475)

Carbon 

tetrachloride 

(Tetrachloromethane) 

(μg/L) 

(32102)

Trichlorofluoromethane 

(CFC-11) 

(μg/L) 

(34488)

Trichlorotrifluoroethane 

(CFC-113) 

(μg/L) 

(77652)

Dichlorodifluoromethane 

(CFC-12) 

(μg/L) 

(34668)

Carbon 

disulfide 

(μg/L) 

(77041)

Methyl 

tert-butyl 

ether 

(MTBE) 

(μg/L) 

(78032)

Methyl tertpentyl ether, 

tert-Amyl 

methyl ether 

(TAME) 

(μg/L) 

(50005)

Tolue

(μg/

(3401

Benchmark 

type

MCL-US MCL-US MCL-US MCL-US MCL-US MCL-CA MCL-CA MCL-CA NL-CA NL-CA MCL-CA na MCL-

Benchmark 

level

180 180 180 180 5 0.5 150 1,200 1,000 160 13 na 150 

LRL or SRL 0.03 0.1 0.034 0.12 0.026 0.06 0.06 0.022 0.1 20.1 0.1 0.06 20.6MS-SA study unit grid wells (100 wells sampled)Detection 

frequency (percent)

13 2 1 1 8 1 2 2 2 2 3 1 1 

Total 

detections (number)

— — — — — — — — — — — — — 

Santa Cruz study area wells (15 wells sampled)S-MS-SC02 0.04 — — — — — — — — — — — — S-MS-SC08 — — — — 0.022 — — — — — — — — S-MS-SC12 — — — — — — — 0.162 — — — — — S-MS-SC13 — — — — 0.035 — — — — — — — — 
Primary use or source Trihalomethanes Solvent Refrigerant Natural, organic synthesis Gasoline oxygenate Gasol

hydroc

bon 

GAMA well identification number Chloroform (tri-chloro- methane) (μg/L) (32106) Bromo- form (tri-bro- mometh- ane) (μg/L) (32104) Bromodi- chloro- methane (μg/L) (32101) Di- bromo- chloro- methane (μg/L) (32105) Per-chloro- ethylene (PCE) (μg/L) (34475) Carbon tetra- chloride (Tetra- chloro- methane) (μg/L) (32102) Tri- chloro- fluoro- methane (CFC-11) (μg/L) (34488) Tri- chloro- trifluoro- ethane (CFC-113) (μg/L) (77652) Dichloro- difluoro- methane (CFC-12) (μg/L) (34668) Carbon disulfide (μg/L) (77041) Methyl tert-butyl ether (MTBE) (μg/L) (78032) Methyl tert- pentyl ether, tert-Amyl methyl ether (TAME) (μg/L) (50005) Tolue

(μg/

(3401

MS-SA study unit grid wells (100 wells sampled)—Continued Pajaro Valley study area wells (15 wells sampled) S-MS-P04 0.11 0.11 — — 0.055 — — — — — 1.27 — — S-MS-P08 0.03 — — — 0.013 — — — — — — — — S-MS-P10 E0.04 — — — — — — — — — — — — S-MS-P12 <LT-MDL — — — — — — — — — — — — S-MS-P15 0.61 — — — — — — — — — — — — Salinas Valley study area wells (40 wells sampled) S-MS-SV03 — — — — <LT-MDL — — — — — — — — S-MS-SV04 <LT-MDL — — — 0.02 — — — — — — — — S-MS-SV08 0.87 E1 0.258 0.25 — — — — — — — — — S-MS-SV09 — — — — 0.077 — — — — — — — — S-MS-SV15 0.02 — — — — — — — — — — — — S-MS-SV20 — — — — — — 0.05 0.032 E0.16 — — — — S-MS-SV26 — — — — — — — — — E3.6 — — — S-MS-SV29 — — — — — — <LT-MDL — — — — — — S-MS-SV32 — — — — — 0.03 — — — — — — — S-MS-SV33 0.02 — — — — — — — — — — — — 

Table 5. Volatile organic compounds (VOCs) detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid wells were analyzed, bdetections are listed. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 100 grid wells. All constituents are lwell identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area welSalinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benchmark levels, and repo2013. Benchmark types: HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maxNL-CA, California notification level. 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-US or no MCL-US exists. Abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; <LT-MDL, value reported by laboratory level and is therefore not counted as a detection; na, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; —, not detected]
Primary use 

or source

Trihalomethanes Solvent Refrigerant

Natural, 

organic 

synthesis

Gasoline oxygenate

Gasol

hydroc

bon 

GAMA 

well 

identification 

number

Chloroform 

(tri-chloromethane) 

(μg/L) 

(32106)

Bromoform 

(tri-bromomethane) 

(μg/L) 

(32104)

Bromodichloromethane 

(μg/L) 

(32101)

Dibromochloromethane 

(μg/L) 

(32105)

Per-chloroethylene 

(PCE) 

(μg/L) 

(34475)

Carbon 

tetrachloride 

(Tetrachloromethane) 

(μg/L) 

(32102)

Trichlorofluoromethane 

(CFC-11) 

(μg/L) 

(34488)

Trichlorotrifluoroethane 

(CFC-113) 

(μg/L) 

(77652)

Dichlorodifluoromethane 

(CFC-12) 

(μg/L) 

(34668)

Carbon 

disulfide 

(μg/L) 

(77041)

Methyl 

tert-butyl 

ether 

(MTBE) 

(μg/L) 

(78032)

Methyl tertpentyl ether, 

tert-Amyl 

methyl ether 

(TAME) 

(μg/L) 

(50005)

Tolue

(μg/

(3401

MS-SA study unit grid wells (100 wells sampled)—ContinuedSalinas Valley study area wells (40 wells sampled) S-MS-SV34 0.61 — — — — — — — — — — — — S-MS-SV35 1.4 — — — 0.121 — — — — E0.6 — 0.03 10.8 S-MS-SV38 — — — — 0.03 — — — — — — — — Highlands study area wells (30 wells sampled) S-MS-H09 0.04 — — — — — — — — — — — — S-MS-H144 0.05 — — — — — — — — — — — — S-MS-H20 0.03 — — — — — — — — — — — — S-MS-H25 — — — — — — — — — — 0.47 — — 

1The MCL-US threshold for trihalomethanes is for the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.2Study 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 carbon disulfide, m- plus p-xylene, and toluene at concentrations less than the respective SRL were reclassififor carbon disulfide is greater than the SRL (0.03 μg/L), and is listed as the reporting level in this table. The SRLs could not be determined for three other VOCs (acetone, 2-butainstead all detections for these VOCs were coded in the USGS database as “reviewed and rejected” and are not presented in this report. See appendix table A–2 for more informa

3Reported value is less than the long-term method detection level.4Sample was not preserved with acid to a pH of less than 2 at time of collection.

Table 5. Volatile organic compounds (VOCs) detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid wells were analyzed, bdetections are listed. Detected constituents are grouped by primary use or source and listed in order of decreasing detection frequency in the 100 grid wells. All constituents are lwell identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area welSalinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benchmark levels, and repo2013. Benchmark types: HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maxNL-CA, California notification level. 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-US or no MCL-US exists. Abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory reporting level; <LT-MDL, value reported by laboratory level and is therefore not counted as a detection; na, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; —, not detected]
Table 6. Pesticides and pesticide degradates detected in grid-well samples collected for the Monterey-Salinas Shallow Aquifer (MS-SA) study unit, Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. [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 99 wells with detections are listed. Detected constituents are grouped by primary use or source and then listed in order of decreasing detection frequency in the 99 grid wells. All constituGAMA well identification number: S-MS-H, Monterey-Salinas Shallow Aquifer Highlands study area well; S-MS-SV, Monterey-Salinas Shallow Aquifer Salinas Valley study benchmark levels, and reporting levels as of May 23, 2013. Benchmark type: HBSL, USGS health-based screening level; MCL-CA; California Department of Public Health mMCL-US, U.S. Environmental Protection Agency (EPA) maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory re—, not detected; <LT-MDL, value reported by laboratory was less than the long-term method detection level and is therefore not counted as a detection; μg/L, micrograms per li

GAMA well identification number Herbicide Herbicide degradate Insecticide 

Simazine (μg/L) (04035) Atrazine (μg/L) (39632) Hexazinone (μg/L) (04025) Pendimethalin (μg/L) (82683) Deethylatrazine (μg/L) (04040) Dimethoate (μg/L) (82662) Chlorpyrifos (μg/L) (38933) Benchmark type MCL-US MCL-CA HBSL HBSL na HBSL HBSL 

Benchmark level 4 1 400 20 na 2 2 LRL 0.006 0.008 0.012 0.012 0.01 0.006 0.0036 MS-SA study unit grid wells (99 wells sampled) 2 Detection frequency (percent) 15 5 1 1 9 1 1 Total number of detections — — — — — — — Salinas Valley study area wells (40 wells sampled) S-MS-SV02 0.006 E0.005 — — E0.006 — — S-MS-SV10 0.016 E0.004 — — E0.006 — — S-MS-SV12 0.007 — — — <LT-MDL 1 — — S-MS-SV16 E0.005 — — — — — — S-MS-SV20 — <LT-MDL 1 — — E0.006 — — S-MS-SV23 E0.004 — — — — — — S-MS-SV25 0.006 — — — — — — S-MS-SV27 E0.005 — — — — — — S-MS-SV29 0.006 — — — — — — S-MS-SV30 E0.004 — — — E0.006 — — S-MS-SV31 E0.005 — — — — — — S-MS-SV32 E0.005 — — — <LT-MDL 1 — — S-MS-SV35 — E0.005 — E0.011 — E0.0036 E0.0028 S-MS-SV36 — <LT-MDL 1 — — E0.005 — — S-MS-SV37 E0.004 — — — — — — 
GAMA well identification number Herbicide Herbicide degradate Insecticide 

Simazine (μg/L) (04035) Atrazine (μg/L) (39632) Hexazinone (μg/L) (04025) Pendimethalin (μg/L) (82683) Deethylatrazine (μg/L) (04040) Dimethoate (μg/L) (82662) Chlorpyrifos (μg/L) (38933) MS-SA study unit grid wells (99 wells sampled) 2—Continued Salinas Valley study area wells (40 wells sampled)—Continued S-MS-SV38 0.019 — — — — — — 

S-MS-SV40 — — — — E0.006 — — Highlands study area wells (30 wells sampled) S-MS-H12 0.017 0.033 E0.006 — 0.066 — — S-MS-H16 E0.004 E0.004 — — E0.005 — — S-MS-H18 — — — — E0.005 — — 

1 The USGS National Water Quality Laboratory (NWQL) reports detections with concentrations less than long-term method detection levels (LT-MDL). Detections with conc

have greater than a 1 percent probability of being false positive detections and therefore do not meet the criteria for detections established for the GAMA Priority Basin Project (Constituents detected only at concentrations less than LT-MDLs, and groundwater samples for which the only constituents detected had concentrations less than LT-MDLs are ndetections at concentrations less than LT-MDLs occurred in groundwater samples that also had detections of other constituents at concentrations greater than LT-MDLs. The foutable 6, indicating the result is considered a non-detection by the GAMA Priority Basin Project. 2 The NWQL reported detections of 17 constituents in the sample from well S-MS-P06 in the Pajaro study area. After careful review, the GAMA Priority Basin Project decideWell S-MS-P06 is therefore considered to have not been analyzed for pesticides and degradates. Samples from well S-MS-P06 had no detections of volatile organic compounds, 2.91 mg/L as nitrogen, and had a tritium activity of 0.73 pCi/L (0.23 tritium units). These characteristics indicate that the groundwater is unlikely to be strongly affected by modand therefore detection of 17 pesticides and degradates would be highly improbable. In addition, 16 of the 17 constituents were not detected in any other samples from the MS-Sconstituents had no detections in any of the other 2,813 samples collected by the GAMA Priority Basin Project between May 2004 and May 2016. Of the 17 constituents, 11 werdegradates. In the other 2,813 GAMA Priority Basin Project samples, the maximum number of insecticides or insecticide degradates detected in a single sample was 5. Based on detections reported in S-MS-P06 were considered highly unlikely to reflect the actual occurrence of pesticides in the groundwater, and the pesticide data for S-MS-P06 were rejeTable 6. Pesticides and pesticide degradates detected in grid-well samples collected for the Monterey-Salinas Shallow Aquifer (MS-SA) study unit, Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—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 99 wells with detections are listed. Detected constituents are grouped by primary use or source and then listed in order of decreasing detection frequency in the 99 grid wells. All constituGAMA well identification number: S-MS-H, Monterey-Salinas Shallow Aquifer Highlands study area well; S-MS-SV, Monterey-Salinas Shallow Aquifer Salinas Valley study benchmark levels, and reporting levels as of May 23, 2013. Benchmark type: HBSL, USGS health-based screening level; MCL-CA; California Department of Public Health mMCL-US, U.S. Environmental Protection Agency (EPA) maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. Other abbreviations: E, estimated or having a higher degree of uncertainty; LRL, laboratory re—, not detected; <LT-MDL, value reported by laboratory was less than the long-term method detection level and is therefore not counted as a detection; μg/L, micrograms per li
54 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

GAMA well 

identification 

number

Perchlorate 

(μg/L) 

(63790)

N-Nitrosodimethylamine 

(μg/L) 

(34438)

Benchmark type MCL-CA NL-CA

Benchmark level 6 0.01

MRL 0.10 0.002

MS-SA study unit grid wells (100 wells sampled) 

Santa Cruz study area wells (15 wells sampled)

S-MS-SC09 — 0.0027

S-MS-SC10 0.12 —

Pajaro Valley study area wells (15 wells sampled)

S-MS-P01 0.20 —

S-MS-P02 0.23 —

S-MS-P04 0.44 —

S-MS-P05 0.35 —

S-MS-P06 0.77 —

S-MS-P07 4.75 —

S-MS-P08 0.71 —

S-MS-P09 0.47 —

S-MS-P10 0.75 —

S-MS-P12 0.23 —

S-MS-P14 0.18 —

S-MS-P15 0.73 —

Salinas Valley study area wells (40 wells sampled)

S-MS-SV01 0.92 —

S-MS-SV02 0.14 —

S-MS-SV03 0.99 —

S-MS-SV04 0.36 —

S-MS-SV05 1.98 —

S-MS-SV07 0.26 —

S-MS-SV08 0.15 —

S-MS-SV09 1.61 —

S-MS-SV10 2.69 —

S-MS-SV12 1.44 0.0036

GAMA well 

identification 

number

Perchlorate 

(μg/L) 

(63790)

N-Nitrosodimethylamine 

(μg/L) 

(34438)

MS-SA study unit grid wells (100 wells sampled)—Continued

Salinas Valley study area wells (40 wells sampled)—Continued

S-MS-SV14 0.19 —

S-MS-SV15 1.24 —

S-MS-SV17 0.72 —

S-MS-SV18 0.69 —

S-MS-SV20 1.44 —

S-MS-SV21 2.01 —

S-MS-SV22 0.42 —

S-MS-SV23 0.41 —

S-MS-SV24 — 0.0039

S-MS-SV25 0.12 —

S-MS-SV28 0.25 —

S-MS-SV29 *7.09 *0.0211

S-MS-SV30 2.49 0.0056

S-MS-SV32 3.34 —

S-MS-SV33 0.91 —

S-MS-SV34 0.52 —

S-MS-SV36 1.77 *0.0258

S-MS-SV37 0.33 —

S-MS-SV38 1.51 *0.0227

S-MS-SV40 0.63 —

Highlands study area wells (30 wells sampled) 

S-MS-H04 0.50 —

S-MS-H08 0.21 —

S-MS-H12 1.03 —

S-MS-H15 0.34 —

S-MS-H16 1.27 —

Table 7. Constituents of special interest detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) 

study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 

100 wells were analyzed, but only samples with detections are listed. Information about the constituents is given in table 3C. GAMA well identification 

numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area 

well. Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; 

MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California notification level. 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. 

Abbreviations: MRL, minimum reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark]
Tables 55

GAMA well 

identification 

number

Perchlorate 

(μg/L) 

(63790)

N-Nitrosodimethylamine 

(μg/L) 

(34438)

MS-SA study unit grid wells (100 wells sampled)—Continued

Highlands study area wells (30 wells sampled)—Continued

S-MS-H17 3.02 —

S-MS-H18 3.04 —

S-MS-H19 0.41 —

S-MS-H20 4.72 —

S-MS-H21 0.42 —

S-MS-H22 0.30 —

S-MS-H23 3.17 —

S-MS-H24 0.32 —

S-MS-H25 1.99 —

S-MS-H26 2.76 —

S-MS-H27 1.39 —

S-MS-H29 2.09 —

S-MS-H30 2.46 —

Table 7. Constituents of special interest detected in grid-well 

samples collected for the Monterey–Salinas Shallow Aquifer 

(MS-SA) study unit, California Groundwater Ambient Monitoring 

and Assessment (GAMA) Priority Basin Project, October 2012 to 

May 2013.—Continued

[The five-digit USGS parameter code below the constituent name is used to 

uniquely identify a specific constituent or property. Samples from all 100 wells 

were analyzed, but only samples with detections are listed. Information 

about the constituents is given in table 3C. GAMA well identification 

numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area 

well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area 

well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area 

well. Benchmark types, benchmark levels, and reporting levels as of May 23, 

2013. Benchmark types: MCL-CA, California maximum contaminant level; 

MCL-US, U.S. Environmental Protection Agency maximum contaminant 

level; NL-CA, California notification level. 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. Abbreviations: MRL, minimum reporting level; 

USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration 

greater than the benchmark]
Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 

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) 

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US HBSL MCL-US MCL-CA AL-US Benchmark level 1,000 6 10 1,000 4 6,000 5 50 1,300 LT-MDL or SRL 2.2 0.027 0.04 0.10 0.006 3 0.016 0.07 12.1 MS-SA study unit grid wells (100 wells sampled) Santa Cruz study area wells (15 wells sampled) S-MS-SC01 — 0.03 0.09 54.1 0.044 569 — — — S-MS-SC02 2.3 0.046 0.14 23.1 0.008 291 0.026 — ≤0.9 S-MS-SC03 — — 0.57 42 0.014 76 — — ≤1.3 S-MS-SC04 2.5 — 0.09 12.1 — 112 0.016 — 3.0 S-MS-SC05 — — 0.26 37.4 0.02 498 — — — S-MS-SC06 3.2 — 0.58 39.5 — 54 — — ≤0.96 S-MS-SC07 3.3 — — 13.4 — 60 — 0.12 — S-MS-SC08 11.0 — — 11.7 2.15 68 — — — S-MS-SC09 3.8 0.059 0.35 6.41 0.006 197 — — ≤2.0 S-MS-SC10 — 0.042 2.8 2.3 — 15 — 7.5 2.6 S-MS-SC11 2.3 0.03 *12.9 4.57 — 18 — 0.21 ≤1.8 S-MS-SC12 3.2 — 0.35 81.6 — 42 — 0.44 2.8 S-MS-SC13 2.9 0.044 0.34 47.8 0.007 129 — — ≤1.5 S-MS-SC14 3.8 — 2.5 11.5 — 20 — — — S-MS-SC15 2.6 — 0.25 27.2 0.012 251 — 0.09 — 
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) 

MS-SA study unit grid wells (100 wells sampled)—ContinuedPajaro Valley study area wells (15 wells sampled)S-MS-P01 2.7 — 0.24 7.12 — 62 — 20.4 3.2 S-MS-P02 2.7 — 0.35 9.77 — 17 — 34.3 3.6 S-MS-P03 2.7 — 2.0 1.44 — 32 — — — S-MS-P04 5.0 — 0.14 7.98 — 18 — 19.9 — S-MS-P05 4.5 — 0.14 243 — 14 0.051 0.44 — S-MS-P06 — — 0.4 55.8 — 66 — 4.1 3.7 S-MS-P07 4.4 — 1.1 160 0.819 55 — 1.2 — S-MS-P08 2.4 — 0.54 26.8 — 29 — 24.4 ≤1.2 S-MS-P09 6.6 — 0.61 304 3.01 308 0.238 15.9 5.6 S-MS-P10 2.6 — 0.57 39.3 — 47 — 10.9 ≤1.0 S-MS-P11 21.4 — 1.5 57.3 — 150 — 11.4 — S-MS-P12 — 0.03 1.3 51.2 — 164 — 12.1 ≤0.88 S-MS-P13 — 0.05 0.6 142 0.015 410 0.02 — — S-MS-P14 — — 0.4 85.3 0.01 294 0.02 9.4 ≤1.3 S-MS-P15 3.2 0.106 4.6 20.2 — 33 — 9.1 — Salinas Valley study area wells (40 wells sampled)S-MS-SV01 2.3 0.061 4.2 294 — 32 0.024 1.1 ≤0.83 S-MS-SV02 2.3 0.052 1.4 120 0.012 378 0.052 0.84 — S-MS-SV03 — 0.032 *21.3 38.3 0.009 70 — — ≤1.6 S-MS-SV04 2.7 0.061 *33.7 53.3 0.023 66 0.054 0.1 ≤1.5 S-MS-SV05 3.2 0.082 5.9 169 0.015 90 1.55 0.56 7.4 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
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) 

MS-SA study unit grid wells (100 wells sampled)—Continued Salinas Valley study area wells (40 wells sampled)—Continued S-MS-SV06 — — 0.78 201 — 85 — — — S-MS-SV07 6.6 — 3.7 54.1 — 85 0.072 6.5 — S-MS-SV08 — 0.056 1.4 49.6 — 106 0.05 4.7 ≤1.1 S-MS-SV09 — 0.031 0.15 33.7 0.014 37 — — 11.2 S-MS-SV10 — — 0.51 51.8 — 79 0.068 11.5 4.9 S-MS-SV11 — 0.052 0.71 44.8 — 22 0.097 0.99 — S-MS-SV12 2.6 0.093 *22.7 144 — 98 0.547 1.9 — S-MS-SV13 — 0.03 0.28 135 0.009 83 — — — S-MS-SV14 — 0.054 0.92 13.9 0.014 314 0.084 — ≤1.1 S-MS-SV15 — 0.113 1.3 53.7 — 100 0.154 0.7 ≤0.99 S-MS-SV16 — 0.155 2.5 25.3 — 165 0.254 0.62 ≤1.2 S-MS-SV17 — 0.053 0.83 47.7 — 101 0.074 2.1 ≤1.4 S-MS-SV18 — 0.034 0.72 63.6 — 151 0.084 1.8 6.4 S-MS-SV19 — 0.072 1.2 70.9 — 90 0.08 1.9 — S-MS-SV20 — 0.049 1.1 79.7 — 187 0.018 2.9 — S-MS-SV21 4.4 — 0.33 308 — 31 — 17 3.8 S-MS-SV22 — 0.062 1.2 59.1 — 162 0.088 3.0 2.6 S-MS-SV23 — 0.058 1.1 91.3 — 88 0.142 2.5 — S-MS-SV24 2.3 0.051 1.5 32.3 0.012 279 0.071 4.6 ≤1 S-MS-SV25 2.3 0.129 2.2 38.5 — 152 0.13 1.1 ≤1.1 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
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) 

MS-SA study unit grid wells (100 wells sampled)—ContinuedSalinas Valley study area wells (40 wells sampled)—ContinuedS-MS-SV26 4.4 0.084 0.12 20.4 0.538 21,890 — — — S-MS-SV27 — 0.116 1.3 36.8 — 98 0.087 0.47 ≤0.96 S-MS-SV28 — 0.052 1.6 53.2 0.016 371 0.038 — — S-MS-SV29 4.4 0.113 1.0 72 0.04 21,360 0.7 8.9 4.7 S-MS-SV30 6.6 0.118 1.7 25.8 1.15 21,440 0.434 9.9 — S-MS-SV31 — 0.127 2.3 16.5 0.006 206 0.109 0.52 — S-MS-SV32 — — 0.68 47.2 — 124 — 4.8 2.2 S-MS-SV33 3.4 — 0.38 41.8 — 37 — 15.1 — S-MS-SV34 — 0.031 0.67 27.2 — 25 — 4.2 ≤1.2 S-MS-SV35 23.2 0.084 6.7 144 0.01 311 0.058 0.57 — S-MS-SV36 — 0.072 1.6 42.8 — 31 0.018 0.68 3.3 S-MS-SV37 — 0.033 1.0 61.9 0.009 246 0.022 0.3 — S-MS-SV38 — 0.119 0.78 206 0.017 400 0.02 2.2 4.3 S-MS-SV39 11.0 0.317 5.3 19.2 0.192 21,180 0.082 — — S-MS-SV40 — 0.07 0.8 62.2 0.008 193 0.019 1.0 — Highlands study area wells (30 wells sampled) S-MS-H01 — — — 10.4 — 152 — — — S-MS-H02 4.4 — 0.12 18.4 0.123 41 — — — S-MS-H03 — 0.092 0.81 122 — 69 0.08 — 1.4 S-MS-H04 3.4 0.069 6.2 40.2 — 32 0.103 2.1 ≤1.4 S-MS-H05 4.4 — 0.09 14.1 0.072 682 — — — 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
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) 

MS-SA study unit grid wells (100 wells sampled)—Continued Highlands study area wells (30 wells sampled)—Continued S-MS-H06 3.3 — 1.0 124 0.008 47 1.14 — 2.3 S-MS-H07 — — 0.1 49.7 0.008 27 0.031 0.12 4.5 S-MS-H08 4.4 0.117 1.5 12.8 0.869 617 0.207 0.22 — S-MS-H09 4.4 — 0.49 11.8 0.028 146 0.183 — 7.0 S-MS-H10 4.4 — 0.16 14.5 0.022 344 0.597 — — S-MS-H11 — 0.129 7.8 24.1 0.024 21,220 0.239 — — S-MS-H12 — 0.045 1.3 80.7 — 85 0.041 0.33 2.4 S-MS-H13 6.6 — 0.15 52.1 0.162 81 — — — S-MS-H14 21.8 — 0.9 493 0.425 *12,700 — — — S-MS-H15 6.6 0.162 4.2 117 — 129 0.094 — — S-MS-H16 — 0.063 6.8 141 — 161 0.163 3.7 ≤1.0 S-MS-H17 2.6 0.047 2.0 176 — 74 0.031 2.3 ≤2.0 S-MS-H18 — 0.088 0.99 8.79 0.051 21,370 0.637 1.0 3.3 S-MS-H19 — 0.029 0.9 70.2 0.014 297 0.025 0.21 2.2 S-MS-H20 3.2 0.029 0.43 455 0.019 114 — 0.13 2.3 S-MS-H21 6.6 — 6.1 28.2 0.031 608 0.894 — — S-MS-H22 3.2 — 40.12 425.7 0.008 88 0.031 —4 — S-MS-H23 — 0.069 *10.7 164 0.006 174 0.022 5.0 — S-MS-H24 4.4 — 1.6 53.8 1.4 723 0.05 0.56 ≤1.6 S-MS-H25 2.2 0.097 7.3 254 0.017 443 0.07 1.1 3.4 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
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) 

MS-SA study unit grid wells (100 wells sampled)—ContinuedHighlands study area wells (30 wells sampled)—ContinuedS-MS-H26 2.6 — 1.9 38.9 0.019 499 0.057 3.6 ≤1.6 S-MS-H27 — 0.11 3.7 46.7 — 106 0.068 0.18 — S-MS-H28 6.6 0.198 2.4 13.9 0.225 532 0.187 — — S-MS-H29 6.6 0.109 7.2 15.9 2.71 21,190 0.134 3.1 — S-MS-H30 — 1.3 3.7 77.5 0.009 41 0.019 — 4.0 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
GAMA well identification number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) 

Benchmark type na HBSL HBSL MCL-CA MCL-US HBSL HBSL MCL-US na MCL-UBenchmark level na 300 40 100 50 100 4,000 2 na 30 LT-MDL or SRL 0.22 10.66 10.023 10.21 0.03 0.005 0.2 0.01 10.023 0.004 MS-SA study unit grid wells (100 wells sampled)—Continued Santa Cruz study area wells (15 wells sampled)—Continued S-MS-SC01 98.2 *398 0.165 0.7 0.05 — 647 0.08 0.030 0.007 S-MS-SC02 51.6 9.32 8.82 0.9 0.03 — 352 — 0.130 0.048 S-MS-SC03 82.1 *1,280 1.38 4.9 0.05 — 796 — — 0.004 S-MS-SC04 64.5 *427 5.24 0.7 — — 275 — 0.042 — S-MS-SC05 72.6 3149 4.37 0.7 — — 457 — 4.40 0.03 S-MS-SC06 38 2.89 2.19 0.3 — — 345 — 0.127 0.025 S-MS-SC07 29.2 44.1 2.25 ≤0.2 — — 323 — 0.286 — S-MS-SC08 94.2 3268 10.9 0.5 — — 1,420 — — 0.024 S-MS-SC09 135 12.4 1.57 0.8 — — 502 — 0.084 8.26 S-MS-SC10 14.8 ≤0.52 0.305 1.1 0.36 — 308 — 0.080 0.637 S-MS-SC11 37.4 27.5 1.31 0.4 0.04 — 120 — ≤0.010 0.09 S-MS-SC12 38.8 *346 1.15 2.0 0.09 — 400 — — 0.027 S-MS-SC13 65 372.1 1.47 0.3 — — 304 — ≤0.023 0.024 S-MS-SC14 14.5 *533 0.464 0.3 — — 137 — ≤0.018 — S-MS-SC15 16.8 3190 0.626 0.2 — — 172 — 0.245 0.035 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
GAMA well 

identification 

number

Lithium 

(μg/L) 

(01130) 

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

MS-SA study unit grid wells (100 wells sampled)—ContinuedPajaro Valley study area wells (15 wells sampled)—ContinuedS-MS-P01 6.36 — 1.56 ≤0.2 0.62 — 191 — — 0.313 S-MS-P02 5.33 — 0.327 0.3 0.35 — 74 — — 0.014 S-MS-P03 6.49 33.4 1.16 0.3 — — 144 — ≤0.020 0.411 S-MS-P04 3.45 1.56 0.062 0.9 0.13 — 174 — — 0.1 S-MS-P05 1.47 ≤0.54 0.075 4.6 0.06 — 200 — — 0.006 S-MS-P06 17.9 — 0.468 0.5 1.3 — 438 — — 0.7 S-MS-P07 12.3 — 1.81 0.7 0.60 — 1,100 — — 0.899 S-MS-P08 2.83 18 0.174 0.9 0.59 — 117 — — 0.022 S-MS-P09 10.4 388.5 2.82 2.5 0.64 0.027 3,510 — — 1.81 S-MS-P10 4.81 ≤0.48 0.677 0.3 0.85 — 164 — 0.025 0.027 S-MS-P11 12.2 5.41 2.03 0.3 2.6 — 360 — 0.036 0.904 S-MS-P12 14.3 5.35 4.14 0.4 9.6 — 675 — 0.098 2.89 S-MS-P13 13.9 *356 4.41 0.6 0.10 — 928 — ≤0.014 0.865 S-MS-P14 10.1 48.9 6.8 0.4 0.20 — 555 — 0.078 2.55 S-MS-P15 11.6 ≤0.56 1.93 0.4 1.2 — 195 — 0.921 0.253 Salinas Valley study area wells (40 wells sampled)S-MS-SV01 13.9 — 3.19 0.5 1.7 — 496 — — 3.03 S-MS-SV02 32 0.72 11.9 3.4 0.64 — 1,250 — ≤0.020 9.45 S-MS-SV03 65.5 ≤0.34 2.35 0.5 1.4 0.007 378 — 0.074 2.12 S-MS-SV04 31.3 3263 2.68 0.7 0.77 — 208 — ≤0.010 0.024 S-MS-SV05 18.9 ≤0.24 3.46 3.4 4.8 0.005 362 — 0.025 0.021 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
GAMA well identification number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) 

MS-SA study unit grid wells (100 wells sampled)—Continued Salinas Valley study area wells (40 wells sampled)—Continued S-MS-SV06 8.02 37.4 4.5 0.4 0.07 — 419 — 0.034 0.008 S-MS-SV07 26.1 1.24 4.94 0.5 0.87 0.025 894 — 0.038 2.59 S-MS-SV08 17.7 0.97 5.18 0.4 1.4 — 579 — 0.025 7.13 S-MS-SV09 78.2 3.54 1.47 1.0 2.7 0.005 365 — ≤0.023 5.43 S-MS-SV10 24.5 ≤0.16 6.12 0.8 4.8 0.006 720 — 0.044 7.79 S-MS-SV11 6.79 1.06 7.53 0.3 0.74 — 240 — 0.146 2.28 S-MS-SV12 10.6 — 6.62 0.5 3.6 — 172 — ≤0.019 3.3 S-MS-SV13 45.3 21.8 0.392 ≤0.1 0.13 — 477 — 0.051 0.172 S-MS-SV14 111 2.87 32.3 0.8 4.6 — 1,290 — ≤0.013 13.7 S-MS-SV15 11.2 — 8.75 0.4 6.1 — 426 — — 3.96 S-MS-SV16 15.4 ≤0.27 11 0.6 2.3 — 356 — — 3.18 S-MS-SV17 8.97 — 5.7 ≤0.2 1.6 — 304 — 0.058 3.15 S-MS-SV18 12.7 ≤0.6 8.12 0.8 6.8 — 535 — — 8.77 S-MS-SV19 19.1 5.17 6.2 0.5 0.43 — 474 — ≤0.014 7.19 S-MS-SV20 41.4 ≤0.36 2.52 0.6 6.3 — 1,210 — 0.024 22 S-MS-SV21 8.3 1.14 0.543 6.7 4.0 0.01 1,530 — — 0.329 S-MS-SV22 17.2 — 6.4 0.9 6.5 — 761 — ≤0.014 10.5 S-MS-SV23 9.28 ≤0.32 3.57 1.0 4.4 — 527 — ≤0.022 10 S-MS-SV24 34.4 ≤0.43 25.5 0.2 0.78 — 457 — ≤0.015 8.15 S-MS-SV25 13.8 — 8.16 0.5 1.9 — 459 — — 4.16 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
GAMA well 

identification 

number

Lithium 

(μg/L) 

(01130) 

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

MS-SA study unit grid wells (100 wells sampled)—ContinuedSalinas Valley study area wells (40 wells sampled)—ContinuedS-MS-SV26 116 3103 0.245 0.7 0.12 — 1,990 0.22 0.043 0.313 S-MS-SV27 10 3.89 5.07 0.3 0.53 — 285 — ≤0.012 1.17 S-MS-SV28 112 8.68 16.8 ≤0.2 *72.8 — 1,060 — 0.035 6.95 S-MS-SV29 255 1.41 5.47 1.5 14.6 0.024 *4,130 — — 4.42 S-MS-SV30 36.4 — 3.03 5.3 *51.9 — 1,940 — — *33 S-MS-SV31 27.5 11.7 11 0.7 4.6 — 423 — ≤0.018 1.56 S-MS-SV32 34.9 2.13 1.96 0.6 5.0 — 860 — — 9.47 S-MS-SV33 8.45 ≤0.22 0.555 1.3 1.1 — 124 — — 0.035 S-MS-SV34 12.4 29.1 0.992 0.3 0.51 — 108 — 0.506 0.314 S-MS-SV35 8.58 356 16.6 0.8 0.04 — 412 — 0.153 0.137 S-MS-SV36 37.8 0.8 3.18 0.6 0.65 — 488 — ≤0.011 7.53 S-MS-SV37 27.6 — 6.65 0.4 0.68 — 265 — 0.037 6.4 S-MS-SV38 40 5.59 5.14 2.2 2.9 0.012 1,410 — — 9.33 S-MS-SV39 196 3149 39.6 1.3 0.42 — *4,490 0.03 0.050 19.5 S-MS-SV40 23.5 — 1.42 0.7 10.7 — 1,120 — 0.025 5.75 Highlands study area wells (30 wells sampled) S-MS-H01 29.8 1.32 0.794 ≤0.2 — — 460 — 0.218 0.009 S-MS-H02 323 *2,700 0.441 1.3 0.06 — 1,490 — — 1.27 S-MS-H03 10.9 3114 4.44 1.6 8.4 — 1,050 — — 2.48 S-MS-H04 8.7 1.07 17.9 3.3 1.6 — 546 0.03 ≤0.019 2.03 S-MS-H05 170 3.84 0.336 0.5 — — *4,680 — 0.182 0.34 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
GAMA well identification number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) 

MS-SA study unit grid wells (100 wells sampled)—Continued Highlands study area wells (30 wells sampled)—Continued S-MS-H06 7.22 2.81 11.8 3.6 0.14 — 462 — ≤0.013 0.102 S-MS-H07 15.5 8.02 3.79 0.9 0.64 — 766 — ≤0.022 4.85 S-MS-H08 138 11.5 *47.9 7.3 8.6 — 1,400 — — 14.2 S-MS-H09 174 390.3 9.2 3.2 0.15 — *4,700 — 0.046 0.857 S-MS-H10 79.9 *498 *304 1.0 0.13 — 1,090 — 0.040 0.059 S-MS-H11 57.4 15.1 *126 — 0.03 — 372 — 0.178 9.25 S-MS-H12 45.3 1.14 4.04 1.0 6.6 — 913 — — 9.26 S-MS-H13 127 37.2 6.66 0.3 — — *5,080 — 0.086 6.84 S-MS-H14 767 43.6 3.14 0.5 0.98 — 2,180 — 0.384 — S-MS-H15 14.2 9.87 2.84 2.2 0.43 — 584 — 0.038 2.71 S-MS-H16 72.9 6.54 28.8 0.2 4.2 — 871 — 0.135 11.9 S-MS-H17 44.8 — 11.3 ≤0.2 1.2 — 556 — ≤0.017 4.78 S-MS-H18 142 1.63 *240 0.6 19.4 — 821 — ≤0.011 4.9 S-MS-H19 27.4 1.22 7.25 0.4 0.79 — 278 — 0.057 5.85 S-MS-H20 27.4 0.85 0.703 0.5 1.6 0.191 1,560 — 0.065 1.5 S-MS-H21 95.7 382.9 *334 0.5 22.1 — 984 — — *41.9 S-MS-H22 60.4 3,4133 18.4 40.4 40.59 — 41,100 — ≤0.023 40.81 S-MS-H23 61.3 — 6.99 0.4 7.9 — 692 — 0.038 9.54 S-MS-H24 62.2 — 2 1.7 1.4 — *5,000 — ≤0.022 15.6 S-MS-H25 115 — 23.7 0.3 5.5 0.007 1,100 — ≤0.020 *34.9 

Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
GAMA well 

identification 

number

Lithium 

(μg/L) 

(01130) 

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

MS-SA study unit grid wells (100 wells sampled)—ContinuedHighlands study area wells (30 wells sampled)—ContinuedS-MS-H26 55.8 — 15.5 0.3 10.9 — 1,340 — 0.312 6.69 S-MS-H27 101 4.23 22.6 0.6 *84.8 — 887 — 0.052 16.2 S-MS-H28 271 — *41.7 2.8 2.9 — 1,270 0.05 — *53.5 S-MS-H29 348 0.94 38.7 1.5 19.3 — 1,660 — 0.033 9.43 S-MS-H30 27.2 4.27 4.05 0.6 0.65 — 1,500 0.05 0.096 0.879 

1The SRLs are based on quality-control results from October 2009 through March 2013 (Davis, T.A., Olsen, L.D., Fram, M.S., and Belitz, Kenneth, 2014, Updated study repo

element data collected for the GAMA Priority Basin Project, October 2009–March 2013: U.S. Geological Survey Scientific Investigations Report 2014–5105, 52 p., http://dx.doAll results for cobalt were censored from this dataset and coded in the USGS National Water Information System (NWIS) database as “reviewed and rejected.” All detections of molybdenum, nickel, tungsten, and zinc at concentrations less than the respective SRLs are reported as less than or equal to (≤) the value reported by the laboratory.

2Concentration of boron greater the NL-CA of 1,000 μg/L.3Concentration of manganese greater than the SMCL-CA of 50 μg/L.4Results for the environmental and replicate samples collected at S-MS-H22 were outside the limits of acceptible precision for 13 inorganic constituents, including the trace el

mium, iron, manganese, nickel, selenium, strontium, uranium, vanadium, and zinc. See appendix table A–3B for more information.Table 8A. Trace elements detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwand Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3D. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: AL-US, U.S. Environmental Protection Agency (USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, Calevel; MCL-US, USEPA maximum contaminant level; NL-CA, California notification level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminas 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. Abbreviations: LT-MDL, lona, not available; SRL, study reporting level; USGS, U.S. Geological Survey; μg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, 
Table 8B. Trace elements detected in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, CaliforMonitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informais given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–SValley and Plains study area tap sample. Benchmark type, benchmark level, LT-MDL, and Study Reporting Level as of May 23, 2013. Benchmark types: AL-US, U.S. Environ(USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: LT-MDL, long-term method detection limit; na, not available; SRL, study reporting level; USGS, Uμg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, less than or equal to] GAMA tap 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) 

Benchmark type MCL-CA MCL-US MCL-US MCL-CA MCL-US HBSL MCL-US MCL-CA AL-US Benchmark level 1,000 6 10 1,000 4 6,000 5 50 1,300 LT-MDL or SRL 2.2 0.027 0.04 0.10 0.006 3 0.016 0.07 12.1 MS-SA study unit shallow-well tap-site samples (70 taps sampled) Pajaro Valley study area shallow-well tap-site samples (15 taps sampled) S-MS-P01-T1 2.4 — 0.25 12.2 — 22 — 9.4 2.4 S-MS-P02-T1 3.5 — 0.15 1.19 — 16 — 30.4 ≤0.95 S-MS-P03-T1 3.8 — 0.16 1.16 — 10 — 36 10.3 S-MS-P04-T1 3.9 — 6.4 3.63 — 16 — — — S-MS-P05-T1 3.8 0.071 0.12 103 — 17 0.524 0.09 3.1 S-MS-P06-T1 — 0.058 0.36 54.8 — 65 0.016 0.66 13.9 S-MS-P07-T1 13.3 0.032 0.19 66.9 — 91 0.103 — 11.5 S-MS-P08-T1 — — *12.6 59.4 0.006 59 0.017 — — S-MS-P09-T1 3.3 — 0.3 71.2 — 28 0.016 8.7 7.1 S-MS-P10-T1 — 0.038 0.65 69.4 0.008 140 — 6.1 3.5 S-MS-P11-T1 2.6 0.218 3.8 386 0.007 136 0.025 — — S-MS-P12-T1 — 0.076 0.59 79.8 0.008 216 0.033 2.5 3.8 S-MS-P13-T1 3.1 — 0.33 29.4 — 25 — 11 2.4 S-MS-P14-T1 2.5 — 0.23 107 — 29 0.078 0.23 3.8 S-MS-P15-T1 3.2 — 0.28 58.0 — 22 — 10.1 15.7 
GAMA tap 

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) 

MS-SA study unit shallow-well tap-site samples (70 taps sampled)—ContinuedSalinas Valley study area shallow-well tap sites (55 taps sampled) S-MS-SV01-T1 2.3 0.098 0.56 43.3 — 38 0.053 — 2.6 S-MS-SV01-T2 — 0.282 4.1 36.2 — 141 2.14 0.64 5.6 S-MS-SV02-T1 — 0.155 1.5 52.6 — 67 0.182 0.29 ≤1.7 S-MS-SV02-T2 — 0.057 2.8 481 0.009 181 0.034 2 3.4 S-MS-SV03-T1 2.5 0.144 2.1 188 — 47 0.023 10.9 7.1 S-MS-SV03-T2 2.3 — 5.4 17.8 — 64 0.141 — — S-MS-SV04-T1 2.8 0.046 1.8 49.4 0.006 56 0.082 1.6 6.0 S-MS-SV04-T2 3.0 0.168 6.1 54.9 0.03 109 2.72 0.07 — S-MS-SV05-T1 — 0.053 1.8 97.0 — 183 1.05 — ≤1.7 S-MS-SV05-T2 3.2 0.045 2.3 73.2 0.009 93 0.095 0.17 23.6 S-MS-SV06-T1 — 0.049 1.7 40.0 — 110 0.112 2.5 2.4 S-MS-SV06-T2 — 0.076 2.2 54.2 — 96 0.085 0.45 6.5 S-MS-SV08-T1 11.0 — 0.74 161 — 232 — — — S-MS-SV08-T2 — 0.059 0.96 77.5 0.007 167 0.934 — 39.7 S-MS-SV09-T1 — — 0.38 36.8 — 83 0.073 1.2 4.7 S-MS-SV09-T2 — 0.037 0.62 61.1 0.009 104 0.091 0.29 ≤1.5 S-MS-SV11-T1 — 0.042 2.6 14.1 0.009 172 0.054 — 3.8 S-MS-SV11-T2 — 0.069 0.43 180 0.01 141 0.878 0.38 ≤1.5 S-MS-SV13-T1 — 0.034 1.3 14.8 0.082 22,000 0.053 — — S-MS-SV13-T2 2.4 0.117 4.4 62.4 0.015 460 0.06 1.1 ≤0.99 

Table 8B. Trace elements detected in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, CaliforMonitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informais given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–SValley and Plains study area tap sample. Benchmark type, benchmark level, LT-MDL, and Study Reporting Level as of May 23, 2013. Benchmark types: AL-US, U.S. Environ(USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: LT-MDL, long-term method detection limit; na, not available; SRL, study reporting level; USGS, Uμg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, less than or equal to] 
GAMA tap 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) 

MS-SA study unit shallow-well tap-site samples (70 taps sampled)—Continued Salinas Valley study area shallow-well tap sites (55 taps sampled)—Continued S-MS-SV16-T1 — 0.154 2.8 33.6 0.007 178 0.366 1.2 ≤0.86 S-MS-SV16-T2 — 0.09 6.3 214 — 152 2.49 1.4 26.4 S-MS-SV17-T1 — 0.063 0.57 71.8 — 58 1.15 2.2 2.7 S-MS-SV17-T2 — 0.091 2.5 68.7 0.008 171 0.117 4.2 2.2 S-MS-SV18-T1 — 0.105 3.3 70.1 0.021 220 0.652 — ≤1.1 S-MS-SV19-T1 — 0.055 1.1 70.2 — 122 0.211 1.2 6.4 S-MS-SV19-T2 — 0.048 1.3 47.6 — 156 0.092 0.5 24.5 S-MS-SV20-T1 — 0.052 1.3 295 — 51 0.017 4.1 5.1 S-MS-SV20-T2 2.7 0.029 1.0 68.2 — 34 0.028 0.93 — S-MS-SV21-T1 — 0.054 3.0 70.0 — 131 0.033 4.7 5.5 S-MS-SV21-T2 — 0.041 0.51 236 — 21 0.02 3.9 5.0 S-MS-SV22-T1 — 0.044 0.86 35.0 0.013 424 0.049 8.9 — S-MS-SV22-T2 19.8 0.168 1.2 23.1 0.007 22 0.097 0.2 ≤2.0 S-MS-SV23-T1 11.0 — 1.2 36.2 3.21 394 — 4.8 9.3 S-MS-SV24-T1 — 0.167 2.9 27.8 — 96 0.085 1.2 ≤1.3 S-MS-SV24-T2 — 0.061 0.77 44.2 — 16 0.095 0.76 2.8 S-MS-SV25-T1 — 0.105 1.5 49.1 0.03 887 0.137 23.3 3.2 S-MS-SV25-T2 — 0.099 1.5 58.3 0.016 490 0.11 13.9 2.6 S-MS-SV26-T1 — 0.147 1.9 31.4 — 134 0.03 0.19 — S-MS-SV26-T2 4.4 0.928 3.7 51.4 0.057 705 0.925 — ≤1.6 

Table 8B. Trace elements detected in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, CaliforMonitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informais given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–SValley and Plains study area tap sample. Benchmark type, benchmark level, LT-MDL, and Study Reporting Level as of May 23, 2013. Benchmark types: AL-US, U.S. Environ(USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: LT-MDL, long-term method detection limit; na, not available; SRL, study reporting level; USGS, Uμg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, less than or equal to] 
GAMA tap 

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) 

MS-SA study unit shallow-well tap-site samples (70 taps sampled)—ContinuedSalinas Valley study area shallow-well tap sites (55 taps sampled)—ContinuedS-MS-SV27-T1 2.3 0.033 3.0 19.8 0.019 497 0.047 — — S-MS-SV29-T1 6.6 0.125 1.6 17.1 0.589 741 0.299 2.8 — S-MS-SV29-T2 — 0.092 1.9 42.7 — 180 0.056 0.32 22.0 S-MS-SV30-T1 — 0.118 2.4 33.0 0.011 280 0.045 2.1 36.7 S-MS-SV32-T1 2.9 — 0.41 136 — 38 0.027 0.73 ≤1.0 S-MS-SV33-T1 — 0.078 5.2 31.9 0.01 101 0.023 5.1 ≤1.5 S-MS-SV33-T2 2.5 0.17 0.32 206 0.01 54 0.017 1.2 6.3 S-MS-SV34-T1 2.5 — 0.13 39.4 — 24 0.046 2.2 93.7 S-MS-SV34-T2 — — 0.21 53.6 — 21 — 9.2 27.2 S-MS-SV35-T1 — 0.107 0.39 286 — 43 — 0.11 14.4 S-MS-SV35-T2 — 0.094 0.37 148 — 26 0.028 1.3 5.9 S-MS-SV36-T1 — 0.109 *18.8 42.1 0.008 107 0.036 0.27 3.5 S-MS-SV36-T2 — 0.054 0.71 92.7 — 34 0.03 0.13 17.9 S-MS-SV37-T1 — — 0.59 43.6 — 75 0.034 0.16 3.4 S-MS-SV40-T1 — 0.048 0.92 36.0 — 78 1.99 0.88 ≤1.2 

Table 8B. Trace elements detected in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, CaliforMonitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informais given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–SValley and Plains study area tap sample. Benchmark type, benchmark level, LT-MDL, and Study Reporting Level as of May 23, 2013. Benchmark types: AL-US, U.S. Environ(USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: LT-MDL, long-term method detection limit; na, not available; SRL, study reporting level; USGS, Uμg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, less than or equal to] 
GAMA tap identification number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) 

Benchmark type na HBSL HBSL MCL-CA MCL-US HBSL HBSL MCL-US na MCL-US Benchmark level na 300 40 100 50 100 4,000 2 na 30 LT-MDL or SRL 0.22 10.66 0.023 10.21 0.03 0.005 0.2 0.01 0.023 0.004 MS-SA study unit shallow-well tap-site samples (70 taps sampled)—Continued Pajaro Valley study area shallow-well tap-site samples (15 taps sampled)—Continued S-MS-P01-T1 4.42 ≤0.25 0.2 0.22 0.11 0.005 217 — — 0.047 S-MS-P02-T1 11.9 2.31 0.1 ≤0.16 0.38 — 128 0.01 — 0.175 S-MS-P03-T1 2.94 ≤0.31 0.1 — 0.16 0.005 54.6 0.02 ≤0.013 0.009 S-MS-P04-T1 13.3 12.5 0.6 ≤0.15 — — 197 0.02 0.029 0.007 S-MS-P05-T1 7.52 3270 0.3 4.6 0.56 — 455 — — 0.008 S-MS-P06-T1 11.4 0.7 1.5 4.3 1.2 — 348 0.02 — 0.43 S-MS-P07-T1 4.89 *1,210 0.9 3.1 — — 307 0.02 — 0.058 S-MS-P08-T1 28.5 388.2 2.1 ≤0.19 0.05 — 510 — 0.116 0.022 S-MS-P09-T1 2.27 1.61 0.3 1.8 1.1 — 353 — — 0.028 S-MS-P10-T1 16.8 2.34 2.3 0.92 2.2 — 494 0.01 — 1.87 S-MS-P11-T1 9.79 *4,210 8.6 1.7 0.23 — 801 — ≤0.02 3.41 S-MS-P12-T1 22.3 1.19 8.1 1.7 6.1 — 968 — 0.031 13.3 S-MS-P13-T1 4.07 1.18 0.3 2.2 0.81 — 125 — — 0.009 S-MS-P14-T1 3.16 12.2 0.3 2.4 0.32 — 421 — — 0.033 S-MS-P15-T1 3.67 2.08 0.2 3.1 0.68 — 308 — — 0.044 

Table 8B. Trace elements detected in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, CaliforMonitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informais given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–SValley and Plains study area tap sample. Benchmark type, benchmark level, LT-MDL, and Study Reporting Level as of May 23, 2013. Benchmark types: AL-US, U.S. Environ(USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: LT-MDL, long-term method detection limit; na, not available; SRL, study reporting level; USGS, Uμg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, less than or equal to] 
GAMA tap 

identification 

number

Lithium 

(μg/L) 

(01130) 

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

MS-SA study unit shallow-well tap-site samples (70 taps sampled)—ContinuedSalinas Valley study area shallow-well tap sites (55 taps sampled)—ContinuedS-MS-SV01-T1 10.1 4.16 1.2 0.82 0.19 — 199 — — 0.442 S-MS-SV01-T2 15.3 ≤0.22 *56.6 3.1 25.9 — 1,400 — 0.147 24.7 S-MS-SV02-T1 9.11 0.84 6.6 0.82 7.1 — 508 — 0.041 2.85 S-MS-SV02-T2 34.9 ≤0.43 4.0 0.62 3.0 — 688 — ≤0.01 4.78 S-MS-SV03-T1 6.19 ≤0.16 2.5 0.24 1.0 — 261 — 0.028 0.93 S-MS-SV03-T2 43.2 3185 *62.3 0.86 0.11 — 859 — 0.119 2.47 S-MS-SV04-T1 19.2 ≤0.39 6.0 0.27 1.8 — 604 — 0.052 8.37 S-MS-SV04-T2 34.7 47.9 *69.1 11.3 5.0 0.006 558 — — 6.85 S-MS-SV05-T1 21.0 3267 9.2 2.2 5.0 — 872 — 0.054 17.5 S-MS-SV05-T2 38.8 1.6 10.8 0.96 1.9 0.008 422 — ≤0.019 2.91 S-MS-SV06-T1 14.1 ≤0.47 5.6 0.28 0.6 0.006 346 — ≤0.015 1.19 S-MS-SV06-T2 23.7 32.8 2.4 3.0 2.5 — 366 — ≤0.014 0.384 S-MS-SV08-T1 50.4 29.5 5.9 3.3 0.22 — 2,540 — — 12.8 S-MS-SV08-T2 15.2 43.1 13.6 1.4 0.15 0.018 562 — ≤0.012 8.94 S-MS-SV09-T1 15.4 0.92 4.4 0.62 2.8 — 489 — ≤0.017 8.76 S-MS-SV09-T2 15.4 7.58 4.1 0.3 2.6 — 592 — 0.042 6.62 S-MS-SV11-T1 32.9 38.5 23.4 1.1 0.08 — 1,280 — — 12.7 S-MS-SV11-T2 17.0 8.62 2.7 4.2 4.5 0.013 1,040 — 0.03 9.28 S-MS-SV13-T1 53.4 375.4 26.5 0.27 0.13 — 890 0.04 0.735 8.04 S-MS-SV13-T2 75.4 ≤0.35 20.0 0.28 3.6 0.006 1,130 — 0.058 16.2 

Table 8B. Trace elements detected in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, CaliforMonitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informais given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–SValley and Plains study area tap sample. Benchmark type, benchmark level, LT-MDL, and Study Reporting Level as of May 23, 2013. Benchmark types: AL-US, U.S. Environ(USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: LT-MDL, long-term method detection limit; na, not available; SRL, study reporting level; USGS, Uμg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, less than or equal to] 
GAMA tap identification number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver (μg/L) (01075) Strontium (μg/L) (01080) Thallium (μg/L) (01057) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) 

MS-SA study unit shallow-well tap-site samples (70 taps sampled)—Continued Salinas Valley study area shallow-well tap sites (55 taps sampled)—Continued S-MS-SV16-T1 23.8 0.87 10.6 1.1 7.7 — 785 — — 7.43 S-MS-SV16-T2 46.5 1.07 *40.4 1.5 10.7 0.008 347 — — 8.24 S-MS-SV17-T1 17.0 ≤0.43 3.8 1.1 7.1 0.01 1,000 — 0.024 15.5 S-MS-SV17-T2 23.2 ≤0.2 4.7 0.74 20.2 — 945 — — 5.15 S-MS-SV18-T1 15.9 *1,120 34.2 1.6 41.6 — 1,070 — 0.05 *50.1 S-MS-SV19-T1 9.03 355.7 15.2 2.3 3.8 — 548 — — 8.85 S-MS-SV19-T2 18.1 9.0 3.8 0.58 1.8 — 424 — 0.05 6.63 S-MS-SV20-T1 37.1 0.68 1.5 1.6 0.76 0.007 1,030 — 0.025 3.9 S-MS-SV20-T2 20.5 1.39 0.4 — 0.22 0.017 357 — ≤0.012 1.28 S-MS-SV21-T1 34.2 ≤0.33 8.1 0.92 0.65 — 267 — 0.025 2.18 S-MS-SV21-T2 12.8 — 1.6 0.75 0.78 — 784 — — 5.08 S-MS-SV22-T1 30.3 0.95 3.9 1.3 6.3 — 1,180 — ≤0.012 28.1 S-MS-SV22-T2 0.72 385 0.6 1.3 0.31 — 90.3 0.01 0.106 0.029 S-MS-SV23-T1 37.2 1.32 7.1 1.5 4.6 — 1,390 — — 24.2 S-MS-SV24-T1 10.3 ≤0.48 7.1 0.47 1.5 — 358 — ≤0.013 2.01 S-MS-SV24-T2 5.64 ≤0.55 3.1 0.26 0.81 0.008 221 — 0.055 1.8 S-MS-SV25-T1 47.8 ≤0.16 5.4 1.8 6.6 — 1,260 — — 12.1 S-MS-SV25-T2 29.7 — 5.1 1.7 5.9 — 928 — — 7.67 S-MS-SV26-T1 10.2 1.4 6.5 0.4 0.63 — 275 — — 1.33 S-MS-SV26-T2 59.1 *1,820 35.1 28.0 14.3 — 2,190 — — *42.8 

Table 8B. Trace elements detected in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, CaliforMonitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informais given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–SValley and Plains study area tap sample. Benchmark type, benchmark level, LT-MDL, and Study Reporting Level as of May 23, 2013. Benchmark types: AL-US, U.S. Environ(USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: LT-MDL, long-term method detection limit; na, not available; SRL, study reporting level; USGS, Uμg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, less than or equal to] 
GAMA tap 

identification 

number

Lithium 

(μg/L) 

(01130) 

Manganese 

(μg/L) 

(01056) 

Molybdenum 

(μg/L) 

(01060) 

Nickel 

(μg/L) 

(01065) 

Selenium 

(μg/L) 

(01145) 

Silver 

(μg/L) 

(01075) 

Strontium 

(μg/L) 

(01080)

Thallium 

(μg/L) 

(01057) 

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

MS-SA study unit shallow-well tap-site samples (70 taps sampled)—ContinuedSalinas Valley study area shallow-well tap sites (55 taps sampled)—ContinuedS-MS-SV27-T1 265 3202 15.6 0.97 0.12 0.006 3,100 — 0.118 0.635 S-MS-SV29-T1 153 0.99 13.9 6.5 11.2 — 1,980 — — 14.9 S-MS-SV29-T2 14.8 3.02 8.0 0.44 1.2 — 376 — 0.043 1.11 S-MS-SV30-T1 17.9 ≤0.35 5.2 1.2 3.8 — 663 — ≤0.017 5.58 S-MS-SV32-T1 31.4 ≤0.66 5.2 0.41 1.5 0.006 592 — ≤0.011 10.6 S-MS-SV33-T1 29.1 ≤0.53 6.3 0.26 0.92 0.006 232 — 0.034 2.67 S-MS-SV33-T2 13.1 0.78 1.2 1.7 0.27 — 544 — — 8.99 S-MS-SV34-T1 2.36 11.6 0.1 1.6 0.41 0.006 109 — — 0.015 S-MS-SV34-T2 2.25 2.46 0.1 1.9 0.53 — 182 — — 0.009 S-MS-SV35-T1 19.3 3166 5.6 1.8 0.31 — 538 — — 3.04 S-MS-SV35-T2 10.5 3.98 1.5 0.46 0.46 — 573 — — 11.9 S-MS-SV36-T1 59.7 6.8 11.8 1.2 0.93 0.01 284 — 0.184 3.93 S-MS-SV36-T2 41.6 12.7 2.3 0.92 0.68 0.013 685 — — 2.67 S-MS-SV37-T1 25.8 0.91 6.1 0.29 1.3 0.015 264 — — 2.63 S-MS-SV40-T1 17.9 ≤0.21 3.0 0.68 1.7 — 421 — 0.06 4.36 

1The SRLs were based on examination of quality-control results from October 2009 through March 2013 (Davis, T.A., Olsen, L.D., Fram, M.S., and Belitz, Kenneth, 2014, U

(SRLs) for trace-element data collected for the California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2009–March 2013: U.S. GInvestigations Report 2014–5105, 52 p., http://dx.doi.org/10.3133/sir20145105). All results for cobalt were censored from this dataset and coded in the USGS National Water Indatabase as “reviewed and rejected.” All detections of copper, iron, lead, manganese, molybdenum, nickel, tungsten, and zinc at concentrations less than their respective SRLs ato (≤) the value reported by the laboratory.

2Concentration of boron greater than the NL-CA of 1,000 μg/L.3Concentration of manganese greater than the SMCL-CA of 50 μg/L.

Table 8B. Trace elements detected in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, CaliforMonitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informais given in table 3D. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–SValley and Plains study area tap sample. Benchmark type, benchmark level, LT-MDL, and Study Reporting Level as of May 23, 2013. Benchmark types: AL-US, U.S. Environ(USEPA) action level; HBSL, USGS health-based screening level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level; NL-CA, SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: LT-MDL, long-term method detection limit; na, not available; SRL, study reporting level; USGS, Uμg/L, micrograms per liter; *, concentration greater than the benchmark level; —, not detected; ≤, less than or equal to] 
76 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Table 9A. Nutrients detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California 

Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid 

wells were analyzed, but only samples with detections are listed. Information about the constituents is given in table 3E. GAMA well identification 

numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. 

Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) 

lifetime health advisory level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level. 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. Abbreviations: LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, not available; 

USGS, U.S. Geological Survey; *, concentration greater than the benchmark level; —, not detected]

GAMA 

well 

identification 

number

Ammonia 

(as nitrogen) 

(mg/L) 

(00608)

Nitrite 

(as nitrogen) 

(mg/L) 

(00613)

Nitrite plus nitrate 

(as nitrogen)1

(mg/L) 

(00631)

Total nitrogen 

(ammonia + nitrate + 

nitrite + organic nitrogen) 

(mg/L) 

(62854)

Orthophosphate 

(as phosphorus) 

(mg/L) 

(00671)

Benchmark type HAL-US MCL-US MCL-US na na

Benchmark level 224.7 1 10 na na

LT-MDL or MDL 0.010 0.0010 0.04 0.05 0.004

MS-SA study unit grid wells (100 wells sampled) 

Santa Cruz study area wells (15 wells sampled)

S-MS-SC01 0.97 — — 1.06 0.061

S-MS-SC02 0.15 0.007 0.13 0.30 0.032

S-MS-SC03 0.51 0.002 — 0.54 0.042

S-MS-SC04 1.1 0.012 0.15 1.31 0.084

S-MS-SC05 0.78 0.002 — 0.88 0.152

S-MS-SC06 0.12 0.021 0.15 0.28 0.074

S-MS-SC07 0.46 — — 0.46 0.054

S-MS-SC08 0.39 0.001 — 0.44 0.039

S-MS-SC09 0.07 0.033 0.43 0.54 0.04

S-MS-SC10 — — 2.68 2.77 0.269

S-MS-SC11 0.03 — 0.33 0.35 0.329

S-MS-SC12 0.56 0.001 0.23 0.79 0.097

S-MS-SC13 0.12 0.006 0.68 0.84 0.155

S-MS-SC14 0.02 — — — 0.05

S-MS-SC15 0.41 — — 0.43 0.092

Pajaro Valley study area wells (15 wells sampled) 

S-MS-P01 — — 1.68 1.71 0.121

S-MS-P02 — — 0.46 0.43 0.139

S-MS-P03 0.04 0.002 — 0.06 0.018

S-MS-P04 — — 5.79 6.14 0.064

S-MS-P05 — — 5.38 5.92 0.033

S-MS-P06 — — 2.91 2.86 0.035

S-MS-P07 — — *64.3 57.7 0.08

S-MS-P08 — — 1.19 1.23 0.173

S-MS-P09 0.15 — 2.14 2.2 0.097

S-MS-P10 — — *11.1 10.5 0.165
Tables 77

GAMA 

well 

identification 

number

Ammonia 

(as nitrogen) 

(mg/L) 

(00608)

Nitrite 

(as nitrogen) 

(mg/L) 

(00613)

Nitrite plus nitrate 

(as nitrogen)1

(mg/L) 

(00631)

Total nitrogen 

(ammonia + nitrate + 

nitrite + organic nitrogen) 

(mg/L) 

(62854)

Orthophosphate 

(as phosphorus) 

(mg/L) 

(00671)

MS-SA study unit grid wells (100 wells sampled)—Continued

Pajaro Valley study area wells (15 wells sampled)—Continued

S-MS-P11 0.01 — 0.08 0.11 0.095

S-MS-P12 — — 0.93 0.98 0.019

S-MS-P13 0.02 — — 0.06 0.025

S-MS-P14 — — 0.20 0.19 0.036

S-MS-P15 — — 1.11 1.15 0.083

Salinas Valley study area wells (40 wells sampled) 

S-MS-SV01 — — 7.35 7.46 0.015

S-MS-SV02 — — 1.30 1.41 0.027

S-MS-SV03 — 0.001 3.53 3.54 0.182

S-MS-SV04 — — 2.36 2.39 0.776

S-MS-SV05 — — 1.46 1.52 0.534

S-MS-SV06 0.25 0.026 0.19 0.41 0.137

S-MS-SV07 — — 0.63 0.64 0.021

S-MS-SV08 — — 0.44 0.39 0.016

S-MS-SV09 — — *18.1 34.0 0.015

S-MS-SV10 0.01 — *35.9 39.5 0.048

S-MS-SV11 — — 0.21 0.19 0.018

S-MS-SV12 — — 4.72 4.83 0.02

S-MS-SV13 0.29 — — 0.30 0.03

S-MS-SV14 — — 0.61 0.62 0.018

S-MS-SV15 — — 1.14 1.18 0.067

S-MS-SV16 — — 1.56 1.62 0.037

S-MS-SV17 — — 2.50 3.13 0.023

S-MS-SV18 — — *12.1 11.9 0.061

S-MS-SV19 — 0.001 0.15 0.14 0.021

S-MS-SV20 — — *10.2 20.5 0.019

Table 9A. Nutrients detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California 

Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid 

wells were analyzed, but only samples with detections are listed. Information about the constituents is given in table 3E. GAMA well identification 

numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. 

Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) 

lifetime health advisory level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level. 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. Abbreviations: LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, not available; 

USGS, U.S. Geological Survey; *, concentration greater than the benchmark level; —, not detected]
78 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

GAMA 

well 

identification 

number

Ammonia 

(as nitrogen) 

(mg/L) 

(00608)

Nitrite 

(as nitrogen) 

(mg/L) 

(00613)

Nitrite plus nitrate 

(as nitrogen)1

(mg/L) 

(00631)

Total nitrogen 

(ammonia + nitrate + 

nitrite + organic nitrogen) 

(mg/L) 

(62854)

Orthophosphate 

(as phosphorus) 

(mg/L) 

(00671)

MS-SA study unit grid wells (100 wells sampled)—Continued

Salinas Valley study area wells (40 wells sampled)—Continued

S-MS-SV21 — 0.001 *13.5 27.5 0.071

S-MS-SV22 — — *12.5 12.7 0.024

S-MS-SV23 — — 8.60 8.25 0.041

S-MS-SV24 — 0.003 0.21 0.15 0.014

S-MS-SV25 — — *10.3 10.5 0.034

S-MS-SV26 0.69 — — 0.75 0.047

S-MS-SV27 — 0.001 0.27 0.29 0.063

S-MS-SV28 0.13 — 0.35 0.5 0.015

S-MS-SV29 — — *30.3 27.9 0.03

S-MS-SV30 0.01 — *70.9 71.2 0.042

S-MS-SV31 — — 4.83 4.94 0.052

S-MS-SV32 — — *15.6 14.7 0.039

S-MS-SV33 — — 1.11 1.12 0.171

S-MS-SV34 — 0.002 0.29 0.26 0.085

S-MS-SV35 0.06 — — 0.06 0.073

S-MS-SV36 — — *50.2 50.2 0.067

S-MS-SV37 — — 3.53 3.63 0.051

S-MS-SV38 — — *16.6 16.8 0.014

S-MS-SV39 0.08 — — 0.05 0.017

S-MS-SV40 — — 4.88 4.86 0.016

Highlands study area wells (30 wells sampled)

S-MS-H01 0.35 0.001 — 0.40 0.021

S-MS-H02 0.10 0.002 — 0.14 0.017

S-MS-H03 0.05 0.002 0.65 0.75 0.091

S-MS-H04 — — 1.23 1.26 0.023

S-MS-H05 1.7 0.003 — 1.97 0.011

Table 9A. Nutrients detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California 

Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid 

wells were analyzed, but only samples with detections are listed. Information about the constituents is given in table 3E. GAMA well identification 

numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. 

Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) 

lifetime health advisory level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level. 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. Abbreviations: LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, not available; 

USGS, U.S. Geological Survey; *, concentration greater than the benchmark level; —, not detected]
Tables 79

GAMA 

well 

identification 

number

Ammonia 

(as nitrogen) 

(mg/L) 

(00608)

Nitrite 

(as nitrogen) 

(mg/L) 

(00613)

Nitrite plus nitrate 

(as nitrogen)1

(mg/L) 

(00631)

Total nitrogen 

(ammonia + nitrate + 

nitrite + organic nitrogen) 

(mg/L) 

(62854)

Orthophosphate 

(as phosphorus) 

(mg/L) 

(00671)

MS-SA study unit grid wells (100 wells sampled)—Continued

Highlands study area wells (30 wells sampled)—Continued

S-MS-H06 0.02 0.035 0.25 0.28 0.128

S-MS-H07 — — 0.07 0.15 0.006

S-MS-H08 0.23 — 2.52 2.92 0.057

S-MS-H09 9.2 0.001 0.05 9.46 0.009

S-MS-H10 0.15 — — 0.21 0.089

S-MS-H11 0.12 — — 0.10 0.018

S-MS-H12 — — 5.32 5.42 0.022

S-MS-H13 0.07 — — — 0.019

S-MS-H14 25.2 0.001 — 23.5 0.148

S-MS-H15 — 0.001 0.75 0.76 0.025

S-MS-H16 0.01 0.001 3.93 4.09 0.027

S-MS-H17 — — 9.99 10.1 0.014

S-MS-H18 — — 8.64 8.78 0.025

S-MS-H19 — — 2.33 2.35 0.034

S-MS-H20 — — *23.5 21.2 0.022

S-MS-H21 0.49 0.018 0.47 0.97 0.014

S-MS-H22 0.71 0.02 2.14 2.91 0.029

S-MS-H23 — — 8.02 8.01 0.031

S-MS-H24 — — 1.81 1.85 0.017

S-MS-H25 — — 7.67 8.15 0.021

S-MS-H26 — — *15.4 14.9 0.009

S-MS-H27 — — 6.52 6.87 0.029

S-MS-H28 — — — 0.21 0.073

S-MS-H29 — — 6.81 6.89 0.131

S-MS-H30 — 0.006 0.14 0.12 0.009

1

Nitrite plus nitrate (as nitrogen) is referred to as nitrate in the text for clarity.

2

The HAL-US is 30 mg/L “as ammonia.” To facilitate comparison to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L “as 

nitrogen.”

Table 9A. Nutrients detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California 

Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid 

wells were analyzed, but only samples with detections are listed. Information about the constituents is given in table 3E. GAMA well identification 

numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area 

well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. 

Benchmark types, benchmark levels, and reporting levels as of May 23, 2013. Benchmark types: HAL-US, U.S. Environmental Protection Agency (USEPA) 

lifetime health advisory level; MCL-CA, California maximum contaminant level; MCL-US, USEPA maximum contaminant level. 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. Abbreviations: LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, not available; 

USGS, U.S. Geological Survey; *, concentration greater than the benchmark level; —, not detected]
80 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

GAMA 

tap 

identification 

number

Nitrite plus nitrate 

(as nitrogen)1

(mg/L) 

(00631)

Benchmark type MCL-US

Benchmark 10

LT-MDL 0.04

MS-SA shallow-well tap-site samples (70 taps sampled) 

Pajaro Valley study area shallow-well tap-site samples 

(15 taps sampled) 

S-MS-P01-T1 *12.6

S-MS-P02-T1 0.48

S-MS-P03-T1 0.33

S-MS-P04-T1 —

S-MS-P05-T1 *19.5

S-MS-P06-T1 7.71

S-MS-P07-T1 5.44

S-MS-P08-T1 0.13

S-MS-P09-T1 *20.6

S-MS-P10-T1 2.58

S-MS-P11-T1 —

S-MS-P12-T1 *17.1

S-MS-P13-T1 4.34

S-MS-P14-T1 *11.2

S-MS-P15-T1 7.03

Salinas Valley study area shallow-well tap-site samples 

(40 wells sampled) 

S-MS-SV01-T1 0.97

S-MS-SV01-T2 7.01

S-MS-SV02-T1 1.03

S-MS-SV02-T2 8.12

S-MS-SV03-T1 3.90

S-MS-SV03-T2 —

S-MS-SV04-T1 2.06

S-MS-SV04-T2 0.23

S-MS-SV05-T1 8.54

S-MS-SV05-T2 0.51

GAMA 

tap 

identification 

number

Nitrite plus nitrate 

(as nitrogen)1

(mg/L) 

(00631)

MS-SA shallow-well tap-site samples (70 taps sampled)—Continued

Salinas Valley study area shallow-well tap-site samples 

(40 wells sampled)—Continued

S-MS-SV06-T1 2.30

S-MS-SV06-T2 5.93

S-MS-SV08-T1 —

S-MS-SV08-T2 3.85

S-MS-SV09-T1 2.38

S-MS-SV09-T2 1.80

S-MS-SV11-T1 0.18

S-MS-SV11-T2 *51.5

S-MS-SV13-T1 —

S-MS-SV13-T2 2.90

S-MS-SV16-T1 *21.8

S-MS-SV16-T2 *31.4

S-MS-SV17-T1 *54.6

S-MS-SV17-T2 *17.5

S-MS-SV18-T1 *17.7

S-MS-SV19-T1 6.85

S-MS-SV19-T2 2.24

S-MS-SV20-T1 1.68

S-MS-SV20-T2 0.44

S-MS-SV21-T1 0.67

S-MS-SV21-T2 *27.0

S-MS-SV22-T1 *65.6

S-MS-SV22-T2 7.42

S-MS-SV23-T1 *56.4

S-MS-SV24-T1 5.33

Table 9B. Nutrients detected in shallow-well tap-site samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, 

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps 

were analyzed. Information about the constituents is given in tables 3E–F. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow 

Aquifer Pajaro Valley study area shallow-well tap-site sample; S-MS-SV01-T1, Monterey–Salinas Shallow Aquifer Valley and Plains study area shallowwell tap sample. Benchmark type, benchmark level, and LT-MDL as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; 

MCL-US, U.S. Environmental Protection Agency (USEPA) maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US 

when the MCL-US and MCL-CA are identical. Abbreviations: LT-MDL, long-term method detection limit; mg/L, milligrams per liter; USGS, U.S. Geological 

Survey; *, concentration greater than the recommended benchmark level; —, not detected]
Tables 81

GAMA 

tap 

identification 

number

Nitrite plus nitrate 

(as nitrogen)1

(mg/L) 

(00631)

MS-SA shallow-well tap-site samples (70 taps sampled)—Continued

Salinas Valley study area shallow-well tap-site samples 

(40 wells sampled)—Continued

S-MS-SV24-T2 1.91

S-MS-SV25-T1 *45.1

S-MS-SV25-T2 *38.2

S-MS-SV26-T1 0.44

S-MS-SV26-T2 *23.5

S-MS-SV27-T1 —

S-MS-SV29-T1 *40.4

S-MS-SV29-T2 1.55

S-MS-SV30-T1 *15.3

S-MS-SV32-T1 *11

S-MS-SV33-T1 1.13

S-MS-SV33-T2 *28.4

S-MS-SV34-T1 3.81

S-MS-SV34-T2 *10.9

S-MS-SV35-T1 0.08

S-MS-SV35-T2 *42.6

S-MS-SV36-T1 *21.1

S-MS-SV36-T2 5.23

S-MS-SV37-T1 5.79

S-MS-SV40-T1 9.26

1

Nitrite plus nitrate (as nitrogen) is referred to as nitrate in the text for 

clarity.

2

The HAL-US (USEPA lifetime health advisory level) is 30 mg/L “as 

ammonia.” To facilitate comparison to the analytical results, we have 

converted and reported this HAL-US as 24.7 mg/L “as nitrogen.”

Table 9B. Nutrients detected in shallow-well tap-site samples 

collected for the Monterey–Salinas Shallow Aquifer (MS-SA) 

study unit, California Groundwater Ambient Monitoring and 

Assessment (GAMA) Priority Basin Project, October 2012 to 

May 2013.—Continued

[The five-digit USGS parameter code below the constituent name is used to 

uniquely identify a specific constituent or property. Samples from all 70 taps 

were analyzed. Information about the constituents is given in tables 3E–F. 

GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas 

Shallow Aquifer Pajaro Valley study area shallow-well tap-site sample; 

S-MS-SV01-T1, Monterey–Salinas Shallow Aquifer Valley and Plains 

study area shallow-well tap sample. Benchmark type, benchmark level, 

and LT-MDL as of May 23, 2013. Benchmark types: MCL-CA, California 

maximum contaminant level; MCL-US, U.S. Environmental Protection 

Agency (USEPA) maximum contaminant level. Maximum contaminant 

level benchmarks are listed as MCL-US when the MCL-US and MCL-CA 

are identical. Abbreviations: LT-MDL, long-term method detection limit; 

mg/L, milligrams per liter; USGS, U.S. Geological Survey; *, concentration 

greater than the recommended benchmark level; —, not detected
Table 10A. Major and minor ions, silica, and total dissolved solids (TDS) detected in grid-well samples collected for the Monterey–Salinas Shallow ACalifornia Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3F. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency (USEPA) maximum contamCalifornia secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCLthan the MCL-US or no MCL-US exists. The SMCL-CA benchmarks for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark leveAbbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchmark level; —, not detected] GAMA well identification number Bromide (mg/L) (71870) Calcium (mg/L) (00915) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

Benchmark type na na SMCL-CA MCL-CA na na na SMCL-CA Benchmark level na na 250 (500) 2 na na na 250 (500) LT-MDL or MDL 0.010 0.022 0.06 0.04 0.011 0.03 0.06 0.09 MS-SA study unit grid wells (100 wells sampled) Santa Cruz study area wells (15 wells sampled) S-MS-SC01 0.72 86.6 218 0.92 12.9 6.46 149 113 S-MS-SC02 0.10 34.1 35.0 0.9 15.8 5.78 61.9 77.7 S-MS-SC03 0.18 137 54.2 0.55 42.4 5.13 50.4 368 S-MS-SC04 — 81.2 53.9 0.24 57.2 13.1 48.8 248 S-MS-SC05 — 58.4 68.1 0.76 24.8 4.39 157 138 S-MS-SC06 0.03 40.6 9.01 0.14 16.4 7.47 11.3 37.2 S-MS-SC07 0.08 39.2 11.1 0.22 15.4 4.89 15.4 32.0 S-MS-SC08 0.54 176 203 0.16 100 7.08 63.8 399 S-MS-SC09 0.10 84.7 31.6 0.1 18.4 5.08 81.1 107 S-MS-SC10 0.10 94.5 30.8 0.09 13.4 1.73 16.5 23.8 S-MS-SC11 E0.034 17.4 11.9 0.18 17.0 2.84 9.27 16.1 S-MS-SC12 0.10 52.4 16.3 0.16 20.5 12.5 23.2 32.0 S-MS-SC13 0.08 42.7 12.2 0.16 18.0 11.4 41.9 46.4 S-MS-SC14 0.07 49.1 8.38 0.15 19.8 2.33 11.0 12.8 S-MS-SC15 0.14 34 41.6 0.09 27.1 2.01 77.7 31.5 
GAMA 

well 

identification 

number

Bromide 

(mg/L) 

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

MS-SA study unit grid wells (100 wells sampled)—ContinuedPajaro Valley study area wells (15 wells sampled)S-MS-P01 0.07 31.6 19.7 0.21 25.9 2.22 19.2 33.7 S-MS-P02 0.04 10.2 10.7 0.14 12.4 1.0 15.2 7.78 S-MS-P03 0.11 41.6 37.8 0.14 38.4 4.66 28.7 30.1 S-MS-P04 0.06 28.5 29.0 0.05 22.3 1.07 13.0 23.2 S-MS-P05 0.10 15.8 27.1 — 11.2 0.34 20.8 22.6 S-MS-P06 0.15 75.9 44.1 0.16 34.5 2.83 25.0 111 S-MS-P07 — 127 251 0.07 95.4 5.57 84.8 209 S-MS-P08 0.13 12.2 41.9 0.18 11.4 1.17 27.8 6.02 S-MS-P09 4.96 500 **1,650 0.11 323 5.6 105 234 S-MS-P10 0.18 24.9 36.2 0.16 14.9 1.21 30.0 16.4 S-MS-P11 0.08 49.1 28.1 0.22 23.8 2.21 33.0 36.2 S-MS-P12 0.11 62.8 37.7 0.21 32.6 2.98 39.7 92.2 S-MS-P13 0.39 103 119 0.2 64.8 2.11 61.6 197 S-MS-P14 0.14 49.3 45.3 0.12 37.9 2.33 55.6 51.9 S-MS-P15 0.17 32.3 58.1 0.18 7.13 1.25 41.2 7.95 Salinas Valley study area wells (40 wells sampled)S-MS-SV01 0.23 95.6 78.1 0.22 32.2 1.15 22.2 32.0 S-MS-SV02 0.36 94.1 160 10.23 49.1 2.7 88.3 131 S-MS-SV03 0.51 70.3 206 0.12 23.1 2.64 126 21.5 S-MS-SV04 0.39 29.9 147 0.33 16.4 2.63 92.4 21.9 S-MS-SV05 1.07 36 408 0.19 34.8 4.67 195 31.0 

Table 10A. Major and minor ions, silica, and total dissolved solids (TDS) detected in grid-well samples collected for the Monterey–Salinas Shallow ACalifornia Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3F. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency (USEPA) maximum contamCalifornia secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCLthan the MCL-US or no MCL-US exists. The SMCL-CA benchmarks for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark leveAbbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchmark level; —, not detected]
GAMA well identification number Bromide (mg/L) (71870) Calcium (mg/L) (00915) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

MS-SA study unit grid wells (100 wells sampled)—Continued Salinas Valley study area wells (40 wells sampled)—Continued S-MS-SV06 0.40 57.7 122 0.12 17.9 4.05 93.3 61.5 S-MS-SV07 E1.63 133 **524 0.28 53.1 3.5 198 88.9 S-MS-SV08 0.21 101 47.3 0.15 24.7 3.88 48.9 175 S-MS-SV09 0.64 75.1 254 0.19 23.7 1.74 131 51.0 S-MS-SV10 0.50 114 139 0.35 46.1 2.36 81.4 132 S-MS-SV11 0.03 56.0 8.49 0.21 13.0 2.56 18.6 74.3 S-MS-SV12 E0.195 64.6 68.7 0.13 15.4 2.37 62.0 83.0 S-MS-SV13 1.09 19.2 289 0.32 11.2 2.65 360 118 S-MS-SV14 0.26 150 39.7 0.29 68.4 4.63 101 **574 S-MS-SV15 E0.233 72.1 53.0 0.24 27.6 1.51 32.0 76.9 S-MS-SV16 0.11 51.5 31.6 0.25 25.8 1.6 47.6 116 S-MS-SV17 0.10 56.3 33.1 0.24 13.8 3.19 32.1 69.8 S-MS-SV18 0.21 114 47.4 0.27 34.3 3.99 57.2 179 S-MS-SV19 NC 94.2 34.4 0.16 24.5 3.91 40.2 149 S-MS-SV20 E0.582 160 215 0.17 53.2 5.37 110 114 S-MS-SV21 22.00 203 **922 0.05 140 4.69 151 28.1 S-MS-SV22 0.23 126 64.1 0.15 47.1 3.54 60.4 239 S-MS-SV23 0.23 126 50.9 0.15 29.3 3.64 31.1 185 S-MS-SV24 0.12 53.9 36.2 0.26 29.2 2.55 55.6 126 S-MS-SV25 0.13 71.5 31.3 10.22 29.7 1.84 41.4 126 

Table 10A. Major and minor ions, silica, and total dissolved solids (TDS) detected in grid-well samples collected for the Monterey–Salinas Shallow ACalifornia Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3F. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency (USEPA) maximum contamCalifornia secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCLthan the MCL-US or no MCL-US exists. The SMCL-CA benchmarks for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark leveAbbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchmark level; —, not detected]
GAMA 

well 

identification 

number

Bromide 

(mg/L) 

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

MS-SA study unit grid wells (100 wells sampled)—ContinuedSalinas Valley study area wells (40 wells sampled)—ContinuedS-MS-SV26 1.50 211 458 0.27 86.9 6.97 307 **932 S-MS-SV27 0.06 42.1 14.2 0.22 18.1 1.28 23.6 61.1 S-MS-SV28 0.18 38.2 40.5 10.17 20.4 2.43 73.4 67.6 S-MS-SV29 2.65 308 **972 0.08 123 10.0 335 350 S-MS-SV30 1.62 376 315 E0.08 175 6.78 347 **1,430 S-MS-SV31 0.31 48.6 59.7 0.29 35.5 2.18 85.3 176 S-MS-SV32 0.67 127 155 0.41 54.8 4.36 130 301 S-MS-SV33 22.89 15.8 95.5 0.18 12.5 1.58 58.0 7.11 S-MS-SV34 0.22 18.4 66.3 0.22 10.4 2.34 53.1 7.31 S-MS-SV35 0.46 40.6 154 0.36 14.3 2.3 107 8.92 S-MS-SV36 1.30 97.1 159 0.49 42.9 2.56 90.8 70.6 S-MS-SV37 0.24 64.1 63.7 0.85 23.1 3.17 51.6 26.7 S-MS-SV38 1.22 154 **506 0.52 64.1 6.49 201 112 S-MS-SV39 1.15 137 331 0.21 33.3 7.0 329 **528 S-MS-SV40 0.59 221 200 10.08 25.1 3.41 57.1 256 Highlands study area wells (30 wells sampled) S-MS-H01 0.09 23.9 16.5 0.19 14.9 3.97 135 152 S-MS-H02 0.53 300 134 1.01 111 9.6 135 **1,110 S-MS-H03 0.17 149 47.2 0.3 36.1 0.61 39.3 185 S-MS-H04 0.12 126 33.3 0.26 64.1 1.6 21.6 122 S-MS-H05 0.26 43.8 71.3 0.83 58.2 5.47 199 **658 

Table 10A. Major and minor ions, silica, and total dissolved solids (TDS) detected in grid-well samples collected for the Monterey–Salinas Shallow ACalifornia Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3F. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency (USEPA) maximum contamCalifornia secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCLthan the MCL-US or no MCL-US exists. The SMCL-CA benchmarks for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark leveAbbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchmark level; —, not detected]
GAMA well identification number Bromide (mg/L) (71870) Calcium (mg/L) (00915) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

MS-SA study unit grid wells (100 wells sampled)—Continued Highlands study area wells (30 wells sampled)—Continued S-MS-H06 0.22 62.9 60.9 0.35 16.7 2.28 46.8 23.8 S-MS-H07 0.34 122 91.0 0.30 30.4 5.74 57.6 156 S-MS-H08 0.82 299 93.4 1.2 157 9.03 219 **1,210 S-MS-H09 0.83 617 299 0.24 241 17.3 98.9 **1,750 S-MS-H10 E0.924 343 240 0.77 138 3.84 114 **1,040 S-MS-H11 0.19 18.2 40.0 0.38 10.8 2.19 207 165 S-MS-H12 0.26 96.2 86.6 0.23 28.4 3.7 70.9 122 S-MS-H13 0.39 220 99.1 0.44 184 8.44 108 **1,080 S-MS-H14 14.80 52.7 **2,520 0.29 17.6 34.3 2,160 1.0 S-MS-H15 NC 15.2 29.8 0.46 7.7 1.3 101 40.2 S-MS-H16 0.21 35.8 55.4 0.41 27.1 2.04 36.7 18.8 S-MS-H17 0.17 49.6 48.7 0.40 22.2 2.52 38.2 14.0 S-MS-H18 1.53 116 381 0.5 43.6 9.68 262 323 S-MS-H19 0.23 58.4 61.7 10.77 21.4 3.37 46.6 26.6 S-MS-H20 1.46 232 **525 0.54 53.3 3.92 122 85.3 S-MS-H21 0.86 150 183 0.38 36.6 8.87 200 **541 S-MS-H22 0.38 118 35.8 0.25 42.1 35.12 358.1 179 S-MS-H23 — 52.3 32.3 0.53 31.2 1.91 28.4 33.7 S-MS-H24 1.17 361 496 0.05 63.5 13.1 394 **737 S-MS-H25 0.37 50.6 107 1.26 31.3 1.12 110 17.8 

Table 10A. Major and minor ions, silica, and total dissolved solids (TDS) detected in grid-well samples collected for the Monterey–Salinas Shallow ACalifornia Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3F. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency (USEPA) maximum contamCalifornia secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCLthan the MCL-US or no MCL-US exists. The SMCL-CA benchmarks for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark leveAbbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchmark level; —, not detected]
GAMA 

well 

identification 

number

Bromide 

(mg/L) 

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

MS-SA study unit grid wells (100 wells sampled)—ContinuedHighlands study area wells (30 wells sampled)—ContinuedS-MS-H26 0.44 63 125 0.55 9.22 2.58 122 120 S-MS-H27 0.09 76.5 23.1 0.49 46.8 3.11 39.4 131 S-MS-H28 0.34 258 33.4 0.34 100 6.14 159 **868 S-MS-H29 1.78 241 351 — 101 24.6 478 **1,320 S-MS-H30 0.45 106 149 0.57 34.0 3.77 53.0 103 

1Fluoride results were not reported by the USGS National Water Quality Laboratory (NWQL) for five MS-SA groundwater samples: S-MS-SV02, S-MS-SV25, S-MS-28, S-M2Results for the environmental and replicate samples collected at S-MS-SV21 and S-MS-SV33 were outside the limits of acceptable precision for bromide; possible dilution e

more information. 

3Results for the environmental and replicate samples collected at S-MS-H22 were outside the limits of acceptible precision for 13 inorganic constituents, including the major a

sodium. See appendix table A–3B for more information.Table 10A. Major and minor ions, silica, and total dissolved solids (TDS) detected in grid-well samples collected for the Monterey–Salinas Shallow ACalifornia Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 wells were analyzed. Inforis given in table 3F. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types, benclevels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency (USEPA) maximum contamCalifornia secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCLthan the MCL-US or no MCL-US exists. The SMCL-CA benchmarks for chloride, sulfate, and TDS have recommended and upper benchmark levels. The upper benchmark leveAbbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detection level; MDL, method detection limit; mg/L, milligrams per liter; na, SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchmark level; —, not detected]
Table 10B. Major and minor ions, silica, and total dissolved solids (TDS) detected in shallow-well tap-site samples collected for the Monterey–Salinstudy unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informagiven in tables 3E–F. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–and Plains study area tap sample. Benchmark type, benchmark level, and LT-MDL as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MProtection Agency (USEPA) maximum contaminant level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. The SMCL-CA benchmark for chloride, sulfate, and TDS havbenchmark levels. The upper benchmark level is shown in parentheses. Abbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detecdetection limit; mg/L, milligrams per liter; na, not available; nc, not collected; SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchm

GAMA tap identification number Bromide (mg/L) (71870) Calcium (mg/L) (00915) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

Benchmark type na na SMCL-CA MCL-CA na na na SMCL-CA Benchmark level na na 250 (500) 2 na na na 250 (500) LT-MDL or MDL 0.010 0.022 0.06 0.04 0.011 0.03 0.06 0.09 MS-SA study unit wells shallow-well tap-site samples (70 taps sampled) Pajaro Valley study area shallow-well tap-site samples (15 taps sampled) S-MS-P01-T1 0.19 25.0 34.3 0.08 24.2 1.37 32.7 30.2 S-MS-P02-T1 0.08 27.0 20.8 0.09 17.6 1.66 13.7 3.85 S-MS-P03-T1 E0.032 10.2 7.2 0.12 11.0 0.87 8.68 1.14 S-MS-P04-T1 0.04 34.8 11.1 0.14 27.4 2.43 13.7 13.8 S-MS-P05-T1 0.48 37.7 42.5 0.06 16.2 2.31 40.8 47.7 S-MS-P06-T1 1.58 63.5 26.8 0.21 29.9 1.33 28.7 97.3 S-MS-P07-T1 0.06 57.9 19.5 0.2 29.0 2.47 28.1 258 S-MS-P08-T1 0.59 53.7 177 0.1 17.0 3.25 79.9 26.9 S-MS-P09-T1 1.72 36.4 113 0.15 29.5 1.88 60.9 41.3 S-MS-P10-T1 0.17 80.4 34.6 0.15 35.1 2.6 42.6 60.2 S-MS-P11-T1 0.35 113 173 0.27 66.5 2.68 57.9 42.9 S-MS-P12-T1 2.25 186 59.1 0.31 41.3 1.91 47 191 S-MS-P13-T1 0.26 15.7 45.2 0.2 12.8 0.94 37.4 12.4 S-MS-P14-T1 0.52 52.2 117 0.15 22.4 1.75 62.5 33.8 S-MS-P15-T1 0.80 30.7 71.6 0.14 20.6 1.33 49.3 34.3 
GAMA 

tap 

identification 

number

Bromide 

(mg/L) 

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

MS-SA study unit wells shallow-well tap-site samples (70 taps sampled)—ContinuedSalinas Valley study area shallow-well tap-site samples (40 taps sampled)S-MS-SV01-T1 0.10 29.6 30.1 0.27 7.07 1.03 26.2 11.3 S-MS-SV01-T2 0.72 258 200 0.15 67.6 1.57 94.4 **541 S-MS-SV02-T1 0.10 79.8 42.1 0.28 29.7 0.96 34.6 141 S-MS-SV02-T2 0.43 100 142 0.22 36.0 1.84 49.4 37.2 S-MS-SV03-T1 0.07 34.1 15.3 0.12 16.0 1.28 16.7 14.4 S-MS-SV03-T2 0.61 296 166 E0.09 105 4.94 41.5 **790 S-MS-SV04-T1 0.21 100 69.9 NC 23.9 3.14 49.3 107 S-MS-SV04-T2 0.77 144 250 NC 34.5 5.46 137 202 S-MS-SV05-T1 0.40 155 108 0.21 51.1 4.38 79.7 249 S-MS-SV05-T2 0.55 74.5 182 0.23 25.9 4.02 106 36.9 S-MS-SV06-T1 0.31 55.2 90.7 0.27 19.6 2.98 43.4 61.2 S-MS-SV06-T2 0.51 54.6 137 0.14 17.4 4.11 88 69.6 S-MS-SV08-T1 4.75 464 **1,460 0.06 135 11.1 333 204 S-MS-SV08-T2 0.28 98.1 60.2 0.22 34.2 4.32 77.8 162 S-MS-SV09-T1 0.26 118 64.5 0.34 27.2 4.09 49.3 165 S-MS-SV09-T2 0.18 97.1 37.4 NC 24.8 4.21 45 163 S-MS-SV11-T1 0.28 166 49.3 0.66 71.3 2.95 119 **532 S-MS-SV11-T2 0.70 204 273 0.17 55.2 5.74 96.9 165 S-MS-SV13-T1 0.90 46.9 242 0.29 22.8 2.79 301 304 S-MS-SV13-T2 0.23 46.1 87.2 0.4 47.1 2.63 85.4 135 

Table 10B. Major and minor ions, silica, and total dissolved solids (TDS) detected in shallow-well tap-site samples collected for the Monterey–Salinstudy unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informagiven in tables 3E–F. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–and Plains study area tap sample. Benchmark type, benchmark level, and LT-MDL as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MProtection Agency (USEPA) maximum contaminant level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. The SMCL-CA benchmark for chloride, sulfate, and TDS havbenchmark levels. The upper benchmark level is shown in parentheses. Abbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detecdetection limit; mg/L, milligrams per liter; na, not available; nc, not collected; SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchm
GAMA tap identification number Bromide (mg/L) (71870) Calcium (mg/L) (00915) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Sulfate (mg/L) (00945) 

MS-SA study unit wells shallow-well tap-site samples (70 taps sampled)—Continued Salinas Valley study area shallow-well tap-site samples (40 taps sampled)—Continued S-MS-SV16-T1 2.94 131 85.1 0.25 53.5 2.8 88.3 328 S-MS-SV16-T2 0.60 163 199 0.51 36.2 3.87 86.4 107 S-MS-SV17-T1 0.66 242 238 0.11 68.3 5.81 86.6 358 S-MS-SV17-T2 0.70 152 243 0.14 58.6 3.36 79.2 228 S-MS-SV18-T1 0.45 155 75.1 NC 86.7 3.93 141 **517 S-MS-SV19-T1 0.26 96.8 35.2 0.49 39.6 2.52 47 130 S-MS-SV19-T2 0.21 74.0 48.5 0.37 32.4 3.21 74.7 180 S-MS-SV20-T1 1.10 161 338 0.12 42.9 3.71 61.1 37.1 S-MS-SV20-T2 0.33 48.7 96.5 NC 15.5 2.37 57.1 12.0 S-MS-SV21-T1 E0.112 35.4 63.3 0.29 10.8 2.11 68.3 19.1 S-MS-SV21-T2 0.94 155 265 0.23 36.8 2.59 60.3 38.3 S-MS-SV22-T1 0.94 215 194 0.18 98.5 4.74 204 491 S-MS-SV22-T2 0.44 71.9 125 0.46 30.6 3.07 60.2 132 S-MS-SV23-T1 0.80 209 192 0.13 105 4.87 162 **592 S-MS-SV24-T1 0.09 54.2 25.2 0.29 23.6 1.49 30.8 89.7 S-MS-SV24-T2 0.03 49.8 7.75 0.21 12.7 2.25 15.1 63.9 S-MS-SV25-T1 0.78 175 184 0.17 99.0 3.84 236 **662 S-MS-SV25-T2 0.38 133 86.2 0.19 71.6 2.74 129 389 S-MS-SV26-T1 0.08 42.8 21.9 NC 17.1 1.52 23.4 51.3 S-MS-SV26-T2 0.84 345 226 0.2 130 4.54 206 **1,160 

Table 10B. Major and minor ions, silica, and total dissolved solids (TDS) detected in shallow-well tap-site samples collected for the Monterey–Salinstudy unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informagiven in tables 3E–F. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–and Plains study area tap sample. Benchmark type, benchmark level, and LT-MDL as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MProtection Agency (USEPA) maximum contaminant level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. The SMCL-CA benchmark for chloride, sulfate, and TDS havbenchmark levels. The upper benchmark level is shown in parentheses. Abbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detecdetection limit; mg/L, milligrams per liter; na, not available; nc, not collected; SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchm
GAMA 

tap 

identification 

number

Bromide 

(mg/L) 

(71870) 

Calcium 

(mg/L) 

(00915) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935) 

Sodium 

(mg/L) 

(00930) 

Sulfate 

(mg/L) 

(00945) 

MS-SA study unit wells shallow-well tap-site samples (70 taps sampled)—ContinuedSalinas Valley study area shallow-well tap-site samples (40 taps sampled)—ContinuedS-MS-SV27-T1 0.69 234 137 — 122 21.6 163 **986 S-MS-SV29-T1 1.03 264 306 0.18 113 7.46 211 **892 S-MS-SV29-T2 0.15 51.0 46.1 0.29 21.4 1.65 45.2 87.2 S-MS-SV30-T1 0.25 95.6 60.1 0.24 45.7 2.17 68.6 224 S-MS-SV32-T1 0.67 95.3 208 0.42 39.3 4.68 86.5 19.2 S-MS-SV33-T1 E0.133 30.6 64.1 0.82 14.0 2.47 73.7 19.1 S-MS-SV33-T2 1.71 113 100 NC 23.4 1.39 68.7 81.2 S-MS-SV34-T1 0.13 11.7 44.2 0.13 8.52 1.44 30.3 3.68 S-MS-SV34-T2 0.14 18.1 44.1 0.14 11.4 1.2 36.4 13.7 S-MS-SV35-T1 3.12 131 68.8 NC 24.7 1.43 41.4 165 S-MS-SV35-T2 1.98 109 69.3 NC 22.6 1.87 48.6 70.3 S-MS-SV36-T1 0.53 72.2 190 1.55 36.4 2.07 99.2 22.1 S-MS-SV36-T2 0.94 109 390 0.28 44.1 1.84 112 6.9 S-MS-SV37-T1 0.31 38.8 85.1 0.83 22.7 2.76 77.2 12.8 S-MS-SV40-T1 0.08 75.9 18.1 NC 13.5 2.21 27.7 37.7 

1Nitrite plus nitrate (as nitrogen) is referred to as nitrate in the text for clarity.

Table 10B. Major and minor ions, silica, and total dissolved solids (TDS) detected in shallow-well tap-site samples collected for the Monterey–Salinstudy unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 70 taps were analyzed. Informagiven in tables 3E–F. GAMA well identification numbers: S-MS-P01-T1, Monterey–Salinas Shallow Aquifer Pajaro Valley study area tap sample; S-MS-SV01-T1, Monterey–and Plains study area tap sample. Benchmark type, benchmark level, and LT-MDL as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MProtection Agency (USEPA) maximum contaminant level; SMCL-CA, California secondary maximum contaminant level. Maximum contaminant level benchmarks are listed as and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. The SMCL-CA benchmark for chloride, sulfate, and TDS havbenchmark levels. The upper benchmark level is shown in parentheses. Abbreviations: E, estimated or having a higher degree of uncertainty; LT-MDL, long-term method detecdetection limit; mg/L, milligrams per liter; na, not available; nc, not collected; SiO2, silicon dioxide; USGS, U.S. Geological Survey; **, concentration greater than upper benchm
Table 11. Radioactive constituents detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013. [The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid wells were analyzed. Iconstituents is given in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). GAMA well identification numbers: S-Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer SaS-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark levels as of May 23, 2013. Benchmark types: MCL-CA, Califorlevel; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: CSU, 1-sigma combined standard uncertainty; nc, not collected; pCi/L, picocuriUSGS, U.S. Geological Survey; *, concentration greater than the recommended benchmark level; —, not detected; ±, plus or minus] GAMA well identification number Radon-222 (pCi/L) (82303) Gross alpha radioactivity, 72-hour count (pCi/L) (62636) Gross alpha radioactivity, 30-day count (pCi/L) (62639) Gross beta radioactivity, 72-hour count (pCi/L) (62642) 

Benchmark type Proposed MCL-US MCL-US1 MCL-US1 MCL-CA Benchmark 4,000 15 15 50 RL Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC Result ± CSU ssLC RMS-SA grid wells (100 wells sampled) Santa Cruz study area wells (15 wells sampled) S-MS-SC01 600 ± 36 11.876 10.3 ± 2.1 1.2 3.1 ± 1.3 1.6 7.56 ± 0.61 0.53 S-MS-SC02 1,646 ± 91 11.944 6.0 ± 1.1 0.6 — 1.1 7.57 ± 0.65 0.63 S-MS-SC03 1,920 ± 110 14.128 *42.2 ± 5.2 1.4 13 ± 2 0.8 18.1 ± 1.2 0.57 S-MS-SC04 226 ± 17 11.799 — 0.8 — 1 211± 1 0.96 S-MS-SC05 413 ± 27 13.474 1.9 ± 1.2 1.6 — 1.6 4.82 ± 0.66 0.82 S-MS-SC06 214 ± 17 12.269 — 0.58 — 0.95 6.9 ± 0.6 0.61 S-MS-SC07 253 ± 19 13.063 1.19 ± 0.48 0.45 — 0.61 4.0 ± 0.5 0.64 S-MS-SC08 368 ± 24 11.698 — 2.3 — 2.1 8.34 ± 0.88 0.98 S-MS-SC09 350 ± 24 12.751 9.8 ± 1.8 1.1 5.0 ± 1.4 1.5 3.82 ± 0.68 0.92 S-MS-SC10 295 ± 21 13.413 0.92 ± 0.66 0.74 0.87 ± 0.66 0.76 1.4 ± 0.6 0.94 S-MS-SC11 308 ± 22 13.972 — 0.67 — 0.62 2.65 ± 0.57 0.79 S-MS-SC12 524 ± 33 13.737 0.41 ± 0.38 0.37 — 1 11.6 ± 0.91 0.81 S-MS-SC13 304 ± 21 13.210 2.51 ± 0.75 0.61 — 0.78 11.5 ± 0.91 0.78 S-MS-SC14 274 ± 19 11.711 1 ± 0.47 0.53 — 0.7 1.86 ± 0.36 0.5 S-MS-SC15 nc3 nc — 1.2 — 1.1 2.33 ± 0.66 1 
GAMA 

well 

identification 

number

Radon-222 

(pCi/L)

(82303)

Gross alpha radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha radioactivity, 

30-day count 

(pCi/L)

(62639)

Gross beta radioactivity, 

72-hour count 

(pCi/L) 

(62642)

MS-SA grid wells (100 wells sampled)—ContinuedPajaro Valley study area wells (15 wells sampled)S-MS-P01 211 ± 17 13.690 1.1 ± 0.51 0.55 — 0.91 2.35 ± 0.36 0.5 S-MS-P02 178 ± 14 11.558 0.46 ± 0.26 0.34 — 0.57 0.94 ± 0.27 0.41 S-MS-P03 352 ± 23 11.804 — 0.7 — 0.64 4.13 ± 0.55 0.74 S-MS-P04 285 ± 20 11.527 — 0.47 — 0.72 0.93 ± 0.38 0.58 S-MS-P05 1,567 ± 88 13.826 1.00 ± 0.39 0.45 — 0.91 0.80 ± 0.32 0.48 S-MS-P06 265 ± 21 17.214 nc4 nc nc4 nc nc4 nc S-MS-P07 388 ± 25 11.003 5 ± 2 2.3 3.3 ± 1.8 2 6.16 ± 0.73 0.93 S-MS-P08 272 ± 19 11.118 1.02 ± 0.61 0.55 — 0.76 1.9 ± 0.56 0.82 S-MS-P09 217 ± 16 10.685 — 5.3 — 6.3 2.3 ± 1.5 2.3 S-MS-P10 272 ± 19 11.499 0.6 ± 0.4 0.44 — 0.7 1.1 ± 0.41 0.64 S-MS-P11 309 ± 21 10.775 1.05 ± 0.61 0.67 0.77 ± 0.56 0.7 1.44 ± 0.51 0.81 S-MS-P12 509 ± 32 12.463 1.27 ± 0.86 1 2.6 ± 0.8 0.65 3.1 ± 0.58 0.86 S-MS-P13 346 ± 23 10.921 3.1 ± 1.1 1.2 — 1.5 2.78 ± 0.48 0.66 S-MS-P14 nc3 nc 4.4 ± 1.1 1 4.3 ± 1.2 1.1 21.82 ± 0.66 1 S-MS-P15 5427 ± 34 27.600 2.25 ± 0.98 1 — 1.1 20.71 ± 0.55 0.89 S-MS-SV01 889 ± 51 11.628 4.5 ± 1.1 1.2 1.92 ± 0.92 0.95 1.18 ± 0.55 0.86 S-MS-SV02 324 ± 21 10.418 10.9 ± 2.5 2.2 9.3 ± 2.4 2.2 3.18 ± 0.77 1.1 S-MS-SV03 490 ± 31 12.774 6.2 ± 1.7 1.4 2.3 ± 1.2 1.6 1.6 ± 0.5 0.74 S-MS-SV04 625 ± 39 14.831 20.48 ± 0.65 0.8 — 0.81 22.58 ± 0.46 0.64 S-MS-SV05 286 ± 21 13.260 4.9 ± 1.8 2 — 1.3 24.5 ± 0.6 0.76 

Table 11. Radioactive constituents detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid wells were analyzed. Iconstituents is given in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). GAMA well identification numbers: S-Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer SaS-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark levels as of May 23, 2013. Benchmark types: MCL-CA, Califorlevel; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: CSU, 1-sigma combined standard uncertainty; nc, not collected; pCi/L, picocuriUSGS, U.S. Geological Survey; *, concentration greater than the recommended benchmark level; —, not detected; ±, plus or minus]
GAMA well identification number Radon-222 (pCi/L) (82303) Gross alpha radioactivity, 72-hour count (pCi/L) (62636) Gross alpha radioactivity, 30-day count (pCi/L) (62639) Gross beta radioactivity, 72-hour count (pCi/L) (62642) 

MS-SA grid wells (100 wells sampled)—Continued Salinas Valley study area wells (40 wells sampled) S-MS-SV06 284 ± 20 11.788 3.6 ± 1.1 1.2 — 0.81 3.57 ± 0.63 0.89 S-MS-SV07 233 ± 17 11.596 5.2 ± 2.1 2.3 — 2.5 4.11 ± 0.93 1.3 S-MS-SV08 347 ± 24 13.768 10.4 ± 1.8 1.1 6.8 ± 1.6 1.2 4.34 ± 0.47 0.55 S-MS-SV09 1,830 ± 100 15.068 2.7 ± 1.5 2 — 1.6 22.09 ± 0.44 0.62 S-MS-SV10 564 ± 34 11.349 7.6 ± 2.5 2.6 — 2.3 3.6 ± 0.68 0.96 S-MS-SV11 841 ± 49 12.443 4.24 ± 0.91 0.68 2.67 ± 0.75 0.62 2.5 ± 0.49 0.7 S-MS-SV12 1,011 ± 58 13.112 4.1 ± 1.1 0.91 2.8 ± 0.8 0.7 1.42 ± 0.56 0.84 S-MS-SV13 3,930 ± 210 11.459 10.4 ± 3.1 3.5 11.2 ± 2.8 2.4 23.7 ± 0.73 1 S-MS-SV14 453 ± 28 11.497 13.8 ± 2.8 2.1 8.3 ± 2.1 1.9 25.69 ± 0.63 0.76 S-MS-SV15 631 ± 39 13.778 4.04 ± 0.99 0.76 2.09 ± 0.83 0.84 1.38 ± 0.51 0.8 S-MS-SV16 687 ± 41 12.760 3 ± 1 1.1 2.4 ± 0.88 0.89 1.9 ± 0.61 0.96 S-MS-SV17 665 ± 41 14.993 5 ± 1 0.77 2.41 ± 0.79 0.73 3.02 ± 0.49 0.67 S-MS-SV18 774 ± 45 11.453 7.6 ± 1.6 1.3 2.81 ± 0.95 0.65 3.36 ± 0.63 0.83 S-MS-SV19 nc3 nc 12.2 ± 1.9 0.86 9.0 ± 1.6 0.84 3.48 ± 0.73 1 S-MS-SV20 289 ± 21 14.060 *22.4 ± 3.9 2.5 13.3 ± 2.7 1.9 6.74 ± 0.84 1.1 S-MS-SV21 276 ± 20 14.145 — 4.3 — 4 4.4 ± 1.1 1.6 S-MS-SV22 378 ± 24 10.601 29.9 ± 2.3 2.3 8.2 ± 1.9 1.3 23.12 ± 0.52 0.72 S-MS-SV23 379 ± 25 13.514 9 ± 1.8 1 6.9 ± 1.5 1.3 4.01 ± 0.47 0.56 S-MS-SV24 705 ± 42 13.522 8.9 ± 1.6 1.2 6.4 ± 1.3 0.81 3.09 ± 0.58 0.8 S-MS-SV25 534 ± 32 10.626 3 ± 1 1 — 1.2 1.65 ± 0.38 0.54 

Table 11. Radioactive constituents detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid wells were analyzed. Iconstituents is given in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). GAMA well identification numbers: S-Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer SaS-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark levels as of May 23, 2013. Benchmark types: MCL-CA, Califorlevel; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: CSU, 1-sigma combined standard uncertainty; nc, not collected; pCi/L, picocuriUSGS, U.S. Geological Survey; *, concentration greater than the recommended benchmark level; —, not detected; ±, plus or minus]
GAMA 

well 

identification 

number

Radon-222 

(pCi/L)

(82303)

Gross alpha radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha radioactivity, 

30-day count 

(pCi/L)

(62639)

Gross beta radioactivity, 

72-hour count 

(pCi/L) 

(62642)

MS-SA grid wells (100 wells sampled)—ContinuedSalinas Valley study area wells (40 wells sampled)—ContinuedS-MS-SV26 588 ± 35 10.795 —2 4.8 — 3.3 28.2 ± 1.1 1.5 S-MS-SV27 629 ± 38 12.975 1.76 ± 0.63 0.72 1.7 ± 0.67 0.63 2.63 ± 0.52 0.76 S-MS-SV28 655 ± 40 13.382 9.8 ± 1.7 0.75 9.6 ± 1.8 1.1 2.79 ± 0.67 1 S-MS-SV29 467 ± 29 11.697 — 5.3 — 5.2 8.6 ± 1.4 1.9 S-MS-SV30 465 ± 29 11.252 *38 ± 7.6 3.9 *31.5 ± 6.8 4.7 7.5 ± 1.5 2.3 S-MS-SV31 491 ± 31 13.186 2.3 ± 1.3 1.7 — 1.4 22.23 ± 0.39 0.56 S-MS-SV32 700 ± 44 17.476 nc4 nc nc4 nc nc4 nc S-MS-SV33 489 ± 31 14.022 — 0.75 — 0.58 2.3 ± 0.5 0.71 S-MS-SV34 2,300 ± 130 12.298 1.31 ± 0.52 0.53 — 0.8 2.8 ± 0.37 0.48 S-MS-SV35 1,341 ± 75 11.122 8.0 ± 1.5 1.2 — 1.1 4.74 ± 0.65 0.87 S-MS-SV36 nc3 nc 11.1 ± 2.4 2 2.8 ± 1.6 1.7 6.26 ± 0.83 0.98 S-MS-SV37 1,447 ± 80 10.617 6.6 ± 1.3 0.84 4 ± 1 0.73 3.43 ± 0.58 0.8 S-MS-SV38 292 ± 21 12.672 *16 ± 4 3.6 8.4 ± 2.8 2.9 7.8 ± 1.1 1.5 S-MS-SV39 756 ± 44 11.885 nc4 nc nc4 nc nc4 nc S-MS-SV40 348 ± 23 11.237 14.8 ± 2.7 1.6 6.2 ± 1.8 1.6 24.2 ± 0.6 0.8 Highlands study area wells (30 wells sampled) S-MS-H01 324 ± 22 13.316 0.81 ± 0.85 1.1 2.61 ± 0.84 0.58 2.71 ± 0.72 1 S-MS-H02 2,220 ± 120 11.281 *212 ± 24 3.9 *35.2 ± 5.7 3.3 *63.8 ± 3.9 1.4 S-MS-H03 1,424 ± 79 10.484 1.96 ± 0.97 1.2 1.93 ± 0.87 0.98 1.0 ± 0.6 0.89 S-MS-H04 496 ± 31 13.361 3 ± 1 1 — 1.5 1.09 ± 0.39 0.6 S-MS-H05 895 ± 52 12.938 *17.9 ± 3.9 3.3 13.8 ± 3.1 2.2 14.5 ± 1.2 1 

Table 11. Radioactive constituents detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid wells were analyzed. Iconstituents is given in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). GAMA well identification numbers: S-Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer SaS-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark levels as of May 23, 2013. Benchmark types: MCL-CA, Califorlevel; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: CSU, 1-sigma combined standard uncertainty; nc, not collected; pCi/L, picocuriUSGS, U.S. Geological Survey; *, concentration greater than the recommended benchmark level; —, not detected; ±, plus or minus]
GAMA well identification number Radon-222 (pCi/L) (82303) Gross alpha radioactivity, 72-hour count (pCi/L) (62636) Gross alpha radioactivity, 30-day count (pCi/L) (62639) Gross beta radioactivity, 72-hour count (pCi/L) (62642) 

MS-SA grid wells (100 wells sampled)—Continued Highlands study area wells (30 wells sampled)—Continued S-MS-H06 274 ± 20 14.025 2.04 ± 0.88 0.91 1.22 ± 0.66 0.69 3.6 ± 0.63 0.86 S-MS-H07 530 ± 32 11.005 26.0 ± 1.6 1.6 4.2 ± 1.6 1.6 26.34 ± 0.58 0.59 S-MS-H08 1,779 ± 98 10.763 2*23.9 ± 5.6 4.8 5.2 ± 3.4 4.5 29.5 ± 1.4 1.8 S-MS-H09 158 ± 13 11.305 19 ± 5 4.7 — 6 18.8 ± 1.7 1.8 S-MS-H10 507 ± 32 12.801 4.7 ±1.8 1.9 — 2.4 4.97 ± 0.75 0.98 S-MS-H11 892 ± 52 12.613 7.6 ± 1.7 1.5 9.3 ± 1.8 1 2.36 ± 0.47 0.68 S-MS-H12 732 ± 43 12.527 7.9 ± 1.9 1.8 6.4 ± 1.9 1.8 4.01 ± 0.59 0.76 S-MS-H13 2,660 ± 140 10.679 *73.6 ± 9.7 2.5 *22.5 ± 4.5 3.2 28 ± 2 1.4 S-MS-H14 452 ± 28 11.410 na6 na na6 na 31.4 ± 3.8 4.7 S-MS-H15 593 ± 36 13.743 2.79 ±0.85 0.78 1.99 ± 0.73 0.71 1.56 ± 0.47 0.71 S-MS-H16 582 ± 35 11.392 *18.2 ± 2.3 0.67 10.4 ± 1.5 0.54 2.09 ± 0.51 0.74 S-MS-H17 502 ± 31 11.282 8.6 ± 1.5 0.84 3.4 ± 1.1 1.1 2.85 ± 0.57 0.85 S-MS-H18 2,100 ± 120 11.753 7.4 ± 2.3 2.3 5.6 ± 2.5 2.6 10.9 ± 0.92 0.87 S-MS-H19 1,390 ± 79 15.288 5.6 ± 1.3 1.1 3 ± 1 1 3.88 ± 0.45 0.55 S-MS-H20 247 ± 18 10.896 29.5 ± 3.2 3.3 — 4 25.1 ± 1.2 1.7 S-MS-H21 1,599 ± 90 13.605 nc4 nc nc4 nc nc4 nc S-MS-H22 723 ± 43 13.218 nc4 nc nc4 nc nc4 nc S-MS-H23 435 ± 28 11.489 11.7 ± 1.7 0.57 6.8 ± 1.3 0.88 1.98 ± 0.51 0.75 S-MS-H24 410 ± 26 10.358 *33 ± 5.9 3.4 12.7 ± 3.9 3.9 8.3 ± 1.2 1.6 S-MS-H25 591 ± 35 11.311 nc4 nc nc4 nc nc4 nc 

Table 11. Radioactive constituents detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid wells were analyzed. Iconstituents is given in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). GAMA well identification numbers: S-Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer SaS-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark levels as of May 23, 2013. Benchmark types: MCL-CA, Califorlevel; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: CSU, 1-sigma combined standard uncertainty; nc, not collected; pCi/L, picocuriUSGS, U.S. Geological Survey; *, concentration greater than the recommended benchmark level; —, not detected; ±, plus or minus]
GAMA 

well 

identification 

number

Radon-222 

(pCi/L)

(82303)

Gross alpha radioactivity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha radioactivity, 

30-day count 

(pCi/L)

(62639)

Gross beta radioactivity, 

72-hour count 

(pCi/L) 

(62642)

MS-SA grid wells (100 wells sampled)—ContinuedHighlands study area wells (30 wells sampled)—ContinuedS-MS-H26 463 ± 30 13.357 14.9 ± 2.3 0.87 8.2 ± 1.5 0.99 4.02 ± 0.73 0.99 S-MS-H27 233 ± 17 11.120 14.1 ± 2.2 1.1 10.8 ± 1.9 1.2 4.46 ± 0.79 0.96 S-MS-H28 1,860 ± 100 12.871 nc4 nc nc4 nc nc4 nc S-MS-H29 791 ± 46 11.566 13.2 ± 4.2 4.4 7.9 ± 3.7 4.4 26.4 ± 2.1 1.9 S-MS-H30 218 ± 17 13.829 3.2 ± 1.3 1.5 — 1.4 2.59 ± 0.71 1 

1The MCL-US applies to adjusted gross alpha radioactivity, which is equal to gross alpha radioactivity minus uranium activity. Results were not adjusted for uranium activity.2Counted 4 to 6 days after sample collection.3Radon samples were not collected for four MS-SA grid wells: S-MS-SC15, S-MS-P14, S-MS-SV19, and S-MS-SV36. Sampling factors that affected those grid-well samples 

running a well, no sample tank before pressure tank, and sample vial broke during shipment to the laboratory.

4Gross alpha and beta were not collected for some wells due to laboratory contract ending.5Radon sample was analyzed after radon half-life of 3.92 days.6The raw reported values for gross alpha radioactivity for S-MS-H14 had CSUs up to 11 pCi/L and ssLCs up to 17 pCi/L. Because of the high uncertainty of the results and be

greater than the MCL-US for gross alpha radioactivity, the results were considered unreliable. Gross alpha radioacitivity (72-hour count and the 30-day count) were coded as “reUSGS National Water Information Systems (NWIS) database and are not presented in this report.Table 11. Radioactive constituents detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Samples from all 100 grid wells were analyzed. Iconstituents is given in table 3G. Measured values less than the sample-specific critical level (ssLC) are reported as non-detections (—). GAMA well identification numbers: S-Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer SaS-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark levels as of May 23, 2013. Benchmark types: MCL-CA, Califorlevel; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Maximum contaminant level benchmarks are listed as MCL-US when the MCL-US and MMCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists. Abbreviations: CSU, 1-sigma combined standard uncertainty; nc, not collected; pCi/L, picocuriUSGS, U.S. Geological Survey; *, concentration greater than the recommended benchmark level; —, not detected; ±, plus or minus]
98 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Table 12. Isotopic tracers detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, 

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about the 

constituents is given in table 3G. Samples from all 100 grid wells were analyzed. Stable isotope ratios of hydrogen, oxygen, and carbon are reported in the 

standard delta notation (δ), the ratio of a heavier isotope to a 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 numbers: S-MS-H, Monterey–

Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas 

Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark 

levels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. 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. Abbreviations: C, Carbon; CSU, 1-sigma combined standard uncertainty; H, hydrogen; na, not 

available; O, oxygen; pCi/L, picocuries per liter; RL, reporting level; USGS, U.S. Geological Survey; —, not detected; ±, plus or minus]

GAMA 

well 

identification 

number

δ13C in dissolved 

inorganic carbon 

(per mil) 

(82081)

C-14 

in water 

(percent modern) 

(49933)

δ2H 

in water 

(per mil) 

(82082)

δ18O 

in water 

(per mil) 

(82085)

Tritium 

(pCi/L) 

(07000)

Benchmark type na na na na MCL-CA

Benchmark na na na na 20,000

[RL] na na na na Result ± CSU ssLC

MS-SA study unit grid wells (100 wells sampled)

Santa Cruz study area wells (15 wells sampled)

S-MS-SC01 –16.19 40.39 –35.7 –5.66 1.49 ± 0.34 0.31

S-MS-SC02 –14.56 33.33 –31.9 –5.38 — 0.47

S-MS-SC03 –18.67 76.27 –32.9 –5.70 3.95 ± 0.39 0.32

S-MS-SC04 –17.82 62.52 –36.3 –5.88 2.26 ± 0.40 0.36

S-MS-SC05 –14.76 27.31 –36.7 –6.06 1.57 ± 0.38 0.36

S-MS-SC06 –13.60 46.84 –36.8 –5.92 0.74 ± 0.26 0.25

S-MS-SC07 –14.45 45.24 –34.5 –5.80 — 0.50

S-MS-SC08 –15.68 64.54 –31.7 –5.17 3.72 ± 0.51 0.46

S-MS-SC09 –16.22 61.04 –36.3 –5.97 — 0.24

S-MS-SC10 –17.79 86.09 –36.0 –5.90 3.66 ± 0.39 0.33

S-MS-SC11 –17.88 104.90 –34.5 –5.72 4.40 ± 0.40 0.32

S-MS-SC12 –19.23 92.60 –35.0 –6.02 4.01 ± 0.56 0.51

S-MS-SC13 –16.31 75.43 –36.4 –6.20 0.42 ± 0.42 0.41

S-MS-SC14 –16.42 75.04 –37.8 –6.17 — 0.46

S-MS-SC15 na1 na1 –37.4 –6.19 1.45 ± 0.26 0.24

Pajaro Valley study area wells (15 wells sampled)

S-MS-P01 –14.42 76.09 –37.2 –6.14 0.54 ± 0.25 0.24

S-MS-P02 –19.54 69.69 –37.6 –6.03 — 0.24

S-MS-P03 –18.97 67.04 –34.2 –5.64 — 0.46

S-MS-P04 –17.60 101.30 –36.3 –5.84 3.52 ± 0.39 0.33

S-MS-P05 –20.52 102.00 –36.1 –5.87 6.04 ± 0.37 0.25

S-MS-P06 –16.81 78.81 –37.4 –5.87 0.73 ± 0.45 0.44

S-MS-P07 –18.24 97.02 –35.5 –5.49 6.11 ± 0.53 0.44

S-MS-P08 –18.12 91.35 –40.6 –6.13 0.79 ± 0.52 0.51

S-MS-P09 –16.32 80.61 –38.8 –5.88 0.48 ± 0.25 0.24

S-MS-P10 –18.92 89.61 –38.9 –6.02 4.45 ± 0.49 0.42
Tables 99

GAMA 

well 

identification 

number

δ13C in dissolved 

inorganic carbon 

(per mil) 

(82081)

C-14 

in water 

(percent modern) 

(49933)

δ2H 

in water 

(per mil) 

(82082)

δ18O 

in water 

(per mil) 

(82085)

Tritium 

(pCi/L) 

(07000)

MS-SA study unit grid wells (100 wells sampled)—Continued

Pajaro Valley study area wells (15 wells sampled)—Continued

S-MS-P11 –15.05 71.45 –38.1 –6.17 — 0.24

S-MS-P12 –15.69 43.88 –39.4 –6.05 — 0.24

S-MS-P13 –13.95 84.35 –37.4 –5.36 4.18 ± 0.32 0.24

S-MS-P14 –15.74 74.95 –41.9 –6.23 — 0.24

S-MS-P15 –12.49 54.22 –42.0 –6.42 — 0.24

Salinas Valley study area wells (40 wells sampled)

S-MS-SV01 –13.37 41.95 –38.7 –5.66 2.52 ± 0.28 0.24

S-MS-SV02 –12.91 79.74 –40.6 –5.97 3.12 ± 0.29 0.24

S-MS-SV03 –17.30 65.36 –45.2 –6.65 1.22 ± 0.27 0.26

S-MS-SV04 –18.74 93.53 –44.7 –6.67 0.84 ± 0.29 0.28

S-MS-SV05 –16.44 75.15 –42.8 –6.21 4.41 ± 0.31 0.24

S-MS-SV06 –13.22 52.72 –40.8 –5.98 3.86 ± 0.42 0.35

S-MS-SV07 –13.61 43.76 –43.5 –6.46 — 0.35

S-MS-SV08 –12.95 54.62 –45.2 –6.82 2.94 ± 0.27 0.23

S-MS-SV09 –17.27 102.70 –44.4 –6.58 4.76 ± 0.33 0.25

S-MS-SV10 –14.56 98.47 –46.0 –6.77 2.29 ± 0.29 0.25

S-MS-SV11 –9.88 79.76 –44.6 –6.79 0.64 ± 0.44 0.43

S-MS-SV12 –12.36 65.58 –39.7 –5.60 1.85 ± 0.28 0.26

S-MS-SV13 –10.90 0.81 –56.9 –7.88 — 0.43

S-MS-SV14 –11.65 40.89 –50.1 –7.15 — 0.26

S-MS-SV15 –14.10 90.19 –32.5 –4.43 4.61 ± 0.49 0.41

S-MS-SV16 –13.28 97.88 –30.9 –4.21 4.50 ± 0.48 0.42

S-MS-SV17 –10.34 78.92 –46.4 –7.17 1.20 ± 0.38 0.36

S-MS-SV18 –15.16 100.40 –35.0 –5.04 4.52 ± 0.52 0.46

S-MS-SV19 –11.73 72.98 –41.0 –6.30 0.59 ± 0.25 0.25

S-MS-SV20 –16.25 88.14 –40.7 –5.72 1.55 ± 0.29 0.27

Table 12. Isotopic tracers detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, 

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about the 

constituents is given in table 3G. Samples from all 100 grid wells were analyzed. Stable isotope ratios of hydrogen, oxygen, and carbon are reported in the 

standard delta notation (δ), the ratio of a heavier isotope to a 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 numbers: S-MS-H, Monterey–

Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas 

Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark 

levels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. 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. Abbreviations: C, Carbon; CSU, 1-sigma combined standard uncertainty; H, hydrogen; na, not 

available; O, oxygen; pCi/L, picocuries per liter; RL, reporting level; USGS, U.S. Geological Survey; —, not detected; ±, plus or minus]
100 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

GAMA 

well 

identification 

number

δ13C in dissolved 

inorganic carbon 

(per mil) 

(82081)

C-14 

in water 

(percent modern) 

(49933)

δ2H 

in water 

(per mil) 

(82082)

δ18O 

in water 

(per mil) 

(82085)

Tritium 

(pCi/L) 

(07000)

MS-SA study unit grid wells (100 wells sampled)—Continued

Salinas Valley study area wells (40 wells sampled)—Continued

S-MS-SV21 –17.82 80.59 –39.5 –5.98 — 0.35

S-MS-SV22 –14.01 98.68 –37.3 –5.74 6.05 ± 0.35 0.23

S-MS-SV23 –13.10 97.83 –39.3 –5.85 3.74 ± 0.39 0.32

S-MS-SV24 –11.85 32.54 –37.9 –5.80 — 0.35

S-MS-SV25 –13.50 99.66 –30.9 –4.35 4.31 ± 0.35 0.27

S-MS-SV26 –13.79 89.13 –39.0 –5.56 2.58 ± 0.27 0.22

S-MS-SV27 –12.81 96.29 –32.9 –4.66 4.26 ± 0.56 0.50

S-MS-SV28 –12.85 17.18 –52.5 –7.25 — 0.22

S-MS-SV29 –15.79 77.75 –40.6 –5.07 1.44 ± 0.39 0.37

S-MS-SV30 –14.73 109.20 –36.2 –5.05 5.24 ± 0.34 0.24

S-MS-SV31 –13.25 100.40 –32.0 –4.45 5.71 ± 0.60 0.51

S-MS-SV32 –14.21 88.88 –43.7 –6.49 — 0.43

S-MS-SV33 –18.15 84.55 –40.4 –6.12 — 0.35

S-MS-SV34 –16.43 59.71 –40.7 –6.39 — 0.31

S-MS-SV35 –9.79 44.06 –43.2 –6.52 0.70 ± 0.43 0.42

S-MS-SV36 –14.97 102.20 –42.1 –6.05 3.70 ± 0.29 0.23

S-MS-SV37 –14.91 104.30 –46.7 –6.88 5.32 ± 0.33 0.24

S-MS-SV38 –20.28 68.79 –46.9 –6.18 3.70 ± 0.34 0.27

S-MS-SV39 –11.95 38.32 –53.7 –7.18 0.96 ± 0.44 0.43

S-MS-SV40 –15.50 81.43 –49.2 –6.78 1.97 ± 0.29 0.26

Highlands study area wells (30 wells sampled)

S-MS-H01 –9.93 0.67 –50.6 –7.34 — 0.45

S-MS-H02 –12.02 37.37 –44.2 –6.49 1.53 ± 0.40 0.38

S-MS-H03 –15.03 79.27 –35.7 –5.46 3.38 ± 0.40 0.35

S-MS-H04 –11.49 23.20 –38.9 –5.67 — 0.37

S-MS-H05 –13.83 5.16 –53.2 –7.84 — 0.36

Table 12. Isotopic tracers detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, 

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about the 

constituents is given in table 3G. Samples from all 100 grid wells were analyzed. Stable isotope ratios of hydrogen, oxygen, and carbon are reported in the 

standard delta notation (δ), the ratio of a heavier isotope to a 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 numbers: S-MS-H, Monterey–

Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas 

Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark 

levels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. 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. Abbreviations: C, Carbon; CSU, 1-sigma combined standard uncertainty; H, hydrogen; na, not 

available; O, oxygen; pCi/L, picocuries per liter; RL, reporting level; USGS, U.S. Geological Survey; —, not detected; ±, plus or minus]
Tables 101

GAMA 

well 

identification 

number

δ13C in dissolved 

inorganic carbon 

(per mil) 

(82081)

C-14 

in water 

(percent modern) 

(49933)

δ2H 

in water 

(per mil) 

(82082)

δ18O 

in water 

(per mil) 

(82085)

Tritium 

(pCi/L) 

(07000)

MS-SA study unit grid wells (100 wells sampled)—Continued

Highlands study area wells (30 wells sampled)—Continued

S-MS-H06 –11.16 16.30 –38.9 –5.82 — 0.34

S-MS-H07 –14.95 104.30 –50.1 –7.40 3.17 ± 0.47 0.42

S-MS-H08 –7.02 21.04 –53.4 –7.41 1.06 ± 0.42 0.41

S-MS-H09 –9.93 13.54 –46.3 –6.55 — 0.43

S-MS-H10 –13.27 80.74 –44.1 –6.12 1.72 ± 0.38 0.35

S-MS-H11 –9.52 0.53 –58.1 –8.02 — 0.47

S-MS-H12 –15.34 95.43 –44.7 –6.47 2.68 ± 0.49 0.46

S-MS-H13 –13.45 58.63 –49.5 –7.04 — 0.25

S-MS-H14 4.40 0.09 –51.8 –6.57 — 0.34

S-MS-H15 –13.48 7.52 –53.9 –7.39 — 0.36

S-MS-H16 –13.08 51.79 –45.7 –6.10 — 0.37

S-MS-H17 –11.73 38.05 –47.3 –6.30 — 0.25

S-MS-H18 –10.23 26.98 –43.9 –5.64 — 0.34

S-MS-H19 –15.06 104.20 –46.1 –6.78 4.92 ± 0.34 0.24

S-MS-H20 –13.20 106.80 –50.3 –6.57 4.66 ± 0.35 0.26

S-MS-H21 –15.14 97.00 –47.1 –5.91 — 0.42

S-MS-H22 –11.90 47.65 –50.3 –7.16 0.94 ± 0.44 0.43

S-MS-H23 –13.01 71.99 –45.3 –6.01 1.02 ± 0.37 0.36

S-MS-H24 –13.80 51.38 –51.5 –7.10 — 0.33

S-MS-H25 –14.84 92.78 –52.2 –6.48 1.62 ± 0.31 0.29

S-MS-H26 –10.38 10.29 –56.4 –7.45 — 0.33

S-MS-H27 –12.91 71.84 –51.3 –7.07 1.81 0.23

S-MS-H28 –11.34 16.20 –47.6 –6.90 4.70 ± 0.31 0.22

S-MS-H29 –11.50 68.67 –47.6 –6.36 — 0.33

S-MS-H30 –11.44 48.86 –53.0 –7.48 — 0.33

1

Bottle broke before sample could be analyzed.

Table 12. Isotopic tracers detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, 

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued

[The five-digit USGS parameter code below the constituent name is used to uniquely identify a specific constituent or property. Information about the 

constituents is given in table 3G. Samples from all 100 grid wells were analyzed. Stable isotope ratios of hydrogen, oxygen, and carbon are reported in the 

standard delta notation (δ), the ratio of a heavier isotope to a 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 numbers: S-MS-H, Monterey–

Salinas Shallow Aquifer Highlands study area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas 

Shallow Aquifer Santa Cruz study area well; S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Benchmark types and benchmark 

levels as of May 23, 2013. Benchmark types: MCL-CA, California maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. 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. Abbreviations: C, Carbon; CSU, 1-sigma combined standard uncertainty; H, hydrogen; na, not 

available; O, oxygen; pCi/L, picocuries per liter; RL, reporting level; USGS, U.S. Geological Survey; —, not detected; ±, plus or minus]
102 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Table 13. Dissolved noble gases detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study 

unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

[Information about the constituents is given in table 3H. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study 

area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; 

S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Abbreviations: cm3STP/g H2O, cubic centimeters at standard temperature and 

pressure per gram of water; nv, no value]

GAMA 

identification 

number

Helium-4 

(cm3STP/g H2O) 

(85561)

Neon 

(cm3STP/g H2O) 

(61046)

Argon 

(cm3STP/g H2O) 

(85563)

Krypton 

(cm3STP/g H2O) 

(85565)

Xenon 

(cm3STP/g H2O) 

(85567)

Helium-3/Helium-4 

(atom ratio) 

(61040)

× 10–7 × 10–7 × 10–4 × 10–8 × 10–8 × 10–6

MS-SA study unit grid wells (100 wells sampled) 

Santa Cruz study area wells (15 wells sampled)

S-MS-SC01 7.14 2.95 4.83 8.88 1.43 1.05

S-MS-SC02 2.06 2.69 4.18 9.19 1.38 0.57

S-MS-SC03 0.51 2.22 3.84 8.41 1.31 1.38

S-MS-SC04 0.87 3.43 4.31 9.02 1.28 1.40

S-MS-SC05 4.52 3.03 4.59 9.72 1.39 0.27

S-MS-SC06 0.54 2.33 3.80 8.47 1.24 1.39

S-MS-SC07 0.70 2.36 3.83 8.42 1.20 1.12

S-MS-SC08 0.78 3.41 4.69 9.28 1.24 1.50

S-MS-SC09 0.56 2.45 4.15 9.58 1.51 1.30

S-MS-SC10 0.46 1.93 3.53 8.17 1.20 1.34

S-MS-SC11 1.36 5.14 5.49 10.23 1.34 1.52

S-MS-SC12 1.06 4.33 5.21 10.13 1.51 1.41

S-MS-SC13 1.22 5.14 5.46 10.65 1.53 1.37

S-MS-SC14 0.88 3.61 4.86 10.07 1.38 1.38

S-MS-SC15 nv nv nv nv nv nv

Pajaro Valley study area wells (15 wells sampled)

S-MS-P01 1.34 5.24 5.50 10.91 1.47 1.38

S-MS-P02 0.80 3.26 4.09 8.97 1.18 1.39

S-MS-P03 0.56 2.39 4.08 9.17 1.34 1.36

S-MS-P04 0.49 2.10 3.47 7.89 1.10 1.35

S-MS-P05 11.85 38.23 12.50 31.84 2.96 1.19

S-MS-P06 3.81 2.83 4.34 9.57 1.35 0.41

S-MS-P07 0.60 2.45 3.85 8.59 1.18 1.64

S-MS-P08 0.47 1.95 3.31 7.47 1.07 1.36

S-MS-P09 0.57 2.22 3.53 7.97 1.15 1.32

S-MS-P10 0.54 2.26 3.64 8.17 1.13 1.44

S-MS-P11 0.83 3.44 4.98 10.26 1.64 1.30

S-MS-P12 0.74 3.01 4.34 9.48 1.33 1.33

S-MS-P13 0.57 2.39 3.78 8.31 1.19 2.28

S-MS-P14 0.64 2.42 3.87 8.85 1.29 1.20

S-MS-P15 0.77 3.00 3.95 8.42 1.22 1.30
Tables 103

GAMA 

identification 

number

Helium-4 

(cm3STP/g H2O) 

(85561)

Neon 

(cm3STP/g H2O) 

(61046)

Argon 

(cm3STP/g H2O) 

(85563)

Krypton 

(cm3STP/g H2O) 

(85565)

Xenon 

(cm3STP/g H2O) 

(85567)

Helium-3/Helium-4 

(atom ratio) 

(61040)

× 10–7 × 10–7 × 10–4 × 10–8 × 10–8 × 10–6

MS-SA study unit grid wells (100 wells sampled)—Continued

Salinas Valley study area wells (40 wells sampled)

S-MS-SV01 1.47 4.50 5.03 9.84 1.31 0.99

S-MS-SV02 0.80 2.30 3.65 8.35 1.12 1.08

S-MS-SV03 0.46 1.87 3.50 8.26 1.12 1.31

S-MS-SV04 0.69 2.81 4.19 8.29 1.15 1.31

S-MS-SV05 0.46 1.89 3.20 7.26 0.99 1.31

S-MS-SV06 4.89 19.95 10.56 19.39 2.13 1.39

S-MS-SV07 2.98 3.26 4.51 9.38 1.39 0.34

S-MS-SV08 1.32 3.18 4.28 9.65 1.29 0.95

S-MS-SV09 0.75 2.91 3.93 8.49 1.23 1.43

S-MS-SV10 0.68 2.82 4.01 8.96 1.25 1.45

S-MS-SV11 1.22 5.33 5.33 10.33 1.35 1.53

S-MS-SV12 0.59 2.27 3.49 7.72 1.05 1.36

S-MS-SV13 28.74 2.49 3.86 8.46 1.27 0.27

S-MS-SV14 1.26 3.53 4.26 8.82 1.13 0.99

S-MS-SV15 0.49 2.09 3.49 7.92 1.10 1.41

S-MS-SV17 0.87 3.53 4.62 9.45 1.43 1.53

S-MS-SV18 0.61 2.56 3.78 8.35 1.14 1.47

S-MS-SV20 0.66 2.41 3.80 8.66 1.30 1.38

S-MS-SV21 0.57 2.24 3.61 8.02 1.13 1.32

S-MS-SV22 0.67 2.47 3.86 8.83 1.16 2.04

S-MS-SV23 0.68 2.69 4.07 8.78 1.23 1.56

S-MS-SV24 1.48 2.30 3.76 8.79 1.14 0.86

S-MS-SV25 0.54 2.25 3.51 7.85 1.14 1.46

S-MS-SV26 38.84 1.92 3.29 7.49 1.06 0.50

S-MS-SV27 0.47 1.98 3.41 7.83 1.10 1.47

S-MS-SV28 1.43 2.32 3.56 8.09 1.08 0.59

S-MS-SV29 4.30 2.12 3.30 7.46 0.97 0.52

S-MS-SV30 0.66 2.62 3.72 8.19 1.15 1.48

Table 13. Dissolved noble gases detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study 

unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

—Continued

[Information about the constituents is given in table 3H. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study 

area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; 

S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Abbreviations: cm3STP/g H2O, cubic centimeters at standard temperature and 

pressure per gram of water; nv, no value]
104 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

GAMA 

identification 

number

Helium-4 

(cm3STP/g H2O) 

(85561)

Neon 

(cm3STP/g H2O) 

(61046)

Argon 

(cm3STP/g H2O) 

(85563)

Krypton 

(cm3STP/g H2O) 

(85565)

Xenon 

(cm3STP/g H2O) 

(85567)

Helium-3/Helium-4 

(atom ratio) 

(61040)

× 10–7 × 10–7 × 10–4 × 10–8 × 10–8 × 10–6

MS-SA study unit grid wells (100 wells sampled)—Continued

Salinas Valley study area wells (40 wells sampled)—Continued

S-MS-SV31 0.73 2.63 3.86 8.55 1.12 1.31

S-MS-SV32 0.92 2.60 3.92 8.62 1.19 1.11

S-MS-SV33 0.52 2.07 3.40 7.75 1.08 1.31

S-MS-SV34 1.10 2.38 3.58 7.83 1.06 0.74

S-MS-SV35 nv nv nv nv nv nv

S-MS-SV36 nv nv nv nv nv nv

S-MS-SV37 1.28 4.62 4.95 9.18 1.24 1.33

S-MS-SV38 3.41 2.22 3.45 7.39 1.10 0.30

S-MS-SV39 1.67 2.32 3.59 7.63 1.11 0.81

S-MS-SV40 1.04 3.36 4.43 9.14 1.19 1.40

Highland study area wells (30 wells sampled)

S-MS-H01 8.13 2.72 4.30 9.82 1.42 1.40

S-MS-H02 4.29 2.98 4.18 8.75 1.19 0.26

S-MS-H03 1.23 2.38 3.63 7.90 1.05 0.65

S-MS-H04 5.70 2.25 3.29 7.24 1.04 1.35

S-MS-H05 1.03 3.08 4.48 9.79 1.23 0.09

S-MS-H07 0.57 2.18 3.74 8.51 1.24 1.22

S-MS-H08 0.50 1.86 3.17 6.73 0.95 1.23

S-MS-H09 0.75 2.56 3.58 7.81 1.24 1.17

S-MS-H10 8.51 2.78 4.09 8.82 1.32 0.25

S-MS-H11 0.66 2.17 3.52 7.90 1.07 1.17

S-MS-H12 0.87 3.39 4.38 9.10 1.18 1.42

S-MS-H13 1.56 3.29 4.43 9.18 1.21 0.53

S-MS-H15 0.95 2.71 3.76 8.25 1.12 0.91

S-MS-H16 0.58 2.27 3.35 7.07 0.98 1.37

S-MS-H17 0.58 2.21 3.15 6.71 0.86 1.24

S-MS-H18 8.17 2.21 3.23 6.76 0.91 0.46

S-MS-H19 0.48 2.02 3.38 7.61 1.13 1.38

S-MS-H20 0.54 2.03 3.16 6.86 0.94 1.37

S-MS-H21 5.01 1.66 2.75 6.11 0.82 0.47

S-MS-H22 1.36 2.31 3.55 7.77 1.06 0.55

Table 13. Dissolved noble gases detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study 

unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

—Continued

[Information about the constituents is given in table 3H. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study 

area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; 

S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Abbreviations: cm3STP/g H2O, cubic centimeters at standard temperature and 

pressure per gram of water; nv, no value]
Tables 105

GAMA 

identification 

number

Helium-4 

(cm3STP/g H2O) 

(85561)

Neon 

(cm3STP/g H2O) 

(61046)

Argon 

(cm3STP/g H2O) 

(85563)

Krypton 

(cm3STP/g H2O) 

(85565)

Xenon 

(cm3STP/g H2O) 

(85567)

Helium-3/Helium-4 

(atom ratio) 

(61040)

× 10–7 × 10–7 × 10–4 × 10–8 × 10–8 × 10–6

MS-SA study unit grid wells (100 wells sampled)—Continued

Highland study area wells (30 wells sampled)—Continued

S-MS-H23 0.62 2.55 3.56 7.53 1.03 1.37

S-MS-H24 1.31 2.38 3.69 8.21 1.16 0.95

S-MS-H25 0.43 1.85 3.02 6.74 0.96 1.39

S-MS-H26 0.76 2.08 3.29 7.45 0.97 0.96

S-MS-H27 0.95 3.92 5.47 11.29 1.57 1.33

S-MS-H28 0.56 2.35 3.82 8.65 1.16 1.32

S-MS-H29 0.64 2.18 3.28 7.16 1.00 1.21

S-MS-H30 0.78 2.72 3.68 7.81 1.04 1.14

Table 13. Dissolved noble gases detected in grid-well samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study 

unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

—Continued

[Information about the constituents is given in table 3H. GAMA well identification numbers: S-MS-H, Monterey–Salinas Shallow Aquifer Highlands study 

area well; S-MS-P, Monterey–Salinas Shallow Aquifer Pajaro Valley study area well; S-MS-SC, Monterey–Salinas Shallow Aquifer Santa Cruz study area well; 

S-MS-SV, Monterey–Salinas Shallow Aquifer Salinas Valley study area well. Abbreviations: cm3STP/g H2O, cubic centimeters at standard temperature and 

pressure per gram of water; nv, no value]
106 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013
This appendix includes discussions of the methods used 

to collect and analyze groundwater samples and to report the 

resulting water-quality data for wells and shallow-well tap 

sites. These methods were selected to obtain representative 

samples of the groundwater from each well and to minimize 

the potential for contamination of the samples or bias in the 

data. Procedures used to collect and assess quality control 

(QC) data and the results of the QC assessments also are 

discussed. 

In the Monterey–Salinas Shallow Aquifer (MS-SA) 

study unit, both for grid wells and wells sampled at the tap, 

groundwater samples were collected, and quality assurance 

(QA) procedures were implemented, by using standard and 

modified U.S. Geological Survey (USGS) protocols from the 

National Water Quality and Assessment (NAWQA) Program 

(Koterba and others, 1995), the National Field Manual (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 National Water Quality 

Laboratory (NWQL), the primary laboratory used to analyze 

samples for this study, is described in Stevenson (2012).

Sample Collection and Analysis

Three protocols were used to collect samples for this 

study because three types of sites were sampled; ninety-nine 

pumping wells were sampled as grid wells, 1 spring was 

sampled as a grid well, and 70 sites with pumping wells or 

holding tanks were sampled as shallow-well tap sites. Sites 

classified as pumping wells are vertically drilled into the 

ground and have pumps that bring the groundwater from the 

aquifer. The spring site was classified as a spring because 

groundwater could discharge naturally where the aquifer 

intersected the land surface and flow into the distribution 

system without the use of a pump. In most cases, grid wells 

were pumped continuously to purge at least three casing 

volumes of water from the well prior to sampling (Wilde and 

others, 1999). In some cases, continuous pumping was limited, 

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 the grid well before sampling. The limitation 

on pumping did not allow sufficient time to complete the 

sampling of a few wells, and some constituent groups were not 

collected from these wells. If a well could not be pumped long 

enough to remove three casing volumes during the purge prior 

to sampling it was noted in the field notes for future reference. 

Purging was not required for the spring site because the water 

was already flowing continuously. Wells at the shallow-well 

tap sites were not purged prior to sample collection and, in 

some cases, were pumped intermittently.

Sites were sampled by using Teflon® tubing with brass 

and stainless-steel fittings attached to a sampling point 

(usually a hose-bib fitting). For grid wells and the one spring, 

the sampling point was as close to the well head as possible 

on the well-discharge pipe. The sampling point was upstream 

from water-storage tanks and from well-head treatment 

systems, if present. 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. For the shallow-well tap sites, 

the sampling point was on the outside of the house and often 

was downstream of a storage tank. All samples were collected 

outdoors by connecting a 1–3-foot (ft) length of Teflon® tubing 

to the sampling point (Lane and others, 2003). All fittings 

and lengths of tubing were cleaned between samples (Wilde, 

2004). 

Both for grid wells and shallow-well tap sites, 

measurements of field water-quality parameters were taken 

by routing water through a flow-through chamber that was 

attached to the sampling point and fitted with a multi-probe 

meter that simultaneously measured the field water-quality 

indicators dissolved oxygen, temperature, pH, and specific 

conductance (SC). Field measurements were made in 

accordance with protocols in the NFM (Radtke and others, 

2005; Wilde and Radtke, 2005; Lewis, 2006; Wilde, 2006; Ritz 

and Collins, 2008; Ritz and Collins, 2008). All sensors on the 

multi-probe meter were calibrated daily. Measured dissolved 

oxygen, temperature, pH, and SC values were recorded at 

3 to 5-minute intervals, and when these values remained 

stable, samples for laboratory analyses were collected. Field 

measurements and instrument calibrations were recorded 

by hand on field record sheets and electronically in the 

Personal Computer Field Form (PCFF) program. Analytical 

service requests for the NWQL were managed by the PCFF 

program, whereas analytical service requests for non-NWQL 

analysis were entered into laboratory-specific spreadsheets. 

Information from the PCFF was uploaded directly into the 

USGS National Water Information System (NWIS) at the end 

of every week of sample collection. 

Appendix A
108 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

The protocols for preparing, filling, and shipping sample 

bottles were the same at grid wells and shallow-well tap 

sites. Polyethylene sample bottles were pre-rinsed three times 

with deionized water and then once with native water before 

sample collection. Samples requiring acidification were 

acidified to a pH between 2 and 1 by using the appropriate 

acids from ampoules of certified, traceable concentrated 

acids obtained from the NWQL. Temperature-sensitive 

samples were stored on ice prior to and during daily shipping 

to the various laboratories. The non-temperature-sensitive 

samples for tritium, stable isotopes of hydrogen and oxygen 

in water, and dissolved noble gases were shipped monthly. 

Temperature-sensitive or time-sensitive samples for volatile 

organic compounds (VOCs), pesticides and pesticide 

degradates, N-nitrosodimethylamine (NDMA), perchlorate, 

trace elements, nutrients, major and minor ions, silica, total 

dissolved solids (TDS), laboratory alkalinity, radon-222, and 

gross alpha and gross beta radioactivity were shipped daily 

whenever possible. The temperature-sensitive samples for 

analysis of stable isotopes of carbon in dissolved inorganic 

carbon and analysis of carbon-14 abundance were stored 

on ice, archived in a laboratory refrigerator, and shipped 

after results of the laboratory alkalinity measurements were 

received. 

Detailed sampling protocols for individual analyses 

and groups of analytes are described in Koterba and others 

(1995), the NFM (Wilde and others, 1999, 2004; Wilde 2008, 

2009), and in the references for analytical methods listed in 

table A–1; only brief descriptions are given here. Samples 

for analyses of VOCs were collected in 40-milliliter (mL) 

glass baked-amber sample vials that were purged with three 

vial volumes of unfiltered groundwater before bottom-filling 

to minimize atmospheric contamination. One to one (1:1) 

hydrochloric acid to water (HCl:H2O) solution was added as 

a preservative to the VOC samples. Each groundwater sample 

to be analyzed for perchlorate was collected in a 125-mL 

polystyrene bottle and then filtered in two or three 20-mL 

aliquots of water through a 0.20-micrometer (μm) pore-size 

Corning® syringe-tip disk filter into a sterilized 125-mL 

bottle. Samples for the analyses of tritium were collected in 

one 1-liter (L) polyethylene bottle and one 1-L glass bottle, 

both of which were purged with three volumes of unfiltered 

groundwater before bottom filling to avoid atmospheric 

contamination. Samples for analysis of stable isotopes of 

hydrogen and oxygen in water were collected in 60-mL 

clear-glass bottles filled with unfiltered groundwater, sealed 

with conical caps, and secured with electrical tape to prevent 

leakage and evaporation.

Groundwater samples for analysis of pesticides and 

pesticide degradates were collected in 1-L baked-amber glass 

bottles. These samples were filtered through a 0.7-μm nominal 

pore-size glass-fiber filter during collection. 

Groundwater samples for trace elements, major and 

minor ions, silica, laboratory alkalinity and TDS analyses 

required filling one 250-mL polyethylene bottle with unfiltered 

groundwater and one 500-mL and one 250-mL polyethylene 

bottle with filtered groundwater (Wilde and others, 2004). 

Filtration was done by using a 0.45-μm pore-size PALL®

unvented capsule filter that was pre-rinsed with 2 L of 

deionized water and then rinsed with 1 L of groundwater 

prior to sampling. Each 250-mL filtered sample then was 

preserved with 7.5-Normal (N) nitric acid. Nutrient samples 

were collected by filtering groundwater into 125-mL brownpolyethylene bottles. Samples analyzed for gross alpha and 

gross beta radioactivity were filtered into 1-L polyethylene 

bottles and acidified with 7.5-N nitric acid. Stable isotopes 

of carbon in dissolved inorganic carbon and carbon-14 

abundance samples were collected in 500-mL glass bottles that 

were purged with three volumes of filtered groundwater before 

bottom-filling. These samples had no headspace and were 

sealed with conical caps to avoid atmospheric contamination. 

For the collection of water samples for samples of 

radon‐222, a stainless-steel and Teflon® valve assembly was 

attached to the hose bib at the well head (Wilde and others, 

2004). The valve was partially closed to create back pressure, 

and a 10-mL groundwater sample was taken through a Teflon®

septum on the valve assembly by using a stainless-steel needle 

attached to a glass syringe. The sample was then injected 

into a 25-mL vial partially filled with a scintillation mixture 

(mineral oil and 1,2,4-trimethylbenzene) and shaken. The vial 

then was placed in an insulated cardboard tube to protect the 

sample during shipping. 

Dissolved noble gases were collected in three-eighthsinch-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 were then tightened, trapping a 

sample of groundwater for analyses of dissolved noble gases 

(Kulongoski and Hilton, 2011). 

Field alkalinity was measured in a mobile laboratory 

at the well site. Samples for field alkalinity titrations were 

collected by filtering groundwater into a 250-mL polyethylene 

bottle. Alkalinity was measured on filtered samples by using 

the Gran titration method (Gran, 1952). Titration data were 

entered directly into the PCFF and the concentrations of 

bicarbonate (HCO3

–

) and carbonate (CO3

2–) were automatically 

calculated from the titration data by using the advanced 

speciation method (http://or.water.usgs.gov/alk/methods.html), 

where pK1 = 6.35, pK2 = 10.33, and pKW = 14. Concentrations 

of HCO3

–

 and CO3

2– also were calculated from the laboratory 

alkalinity and laboratory pH measurements. 
Appendix A 109

Seven laboratories performed chemical analyses for 

this study (table A–1), although most of the analyses were 

performed at the NWQL or by laboratories contracted by the 

NWQL. The NWQL maintains a rigorous QA program (Pirkey 

and Glodt, 1998; Maloney, 2005). Laboratory QC samples, 

including method blanks, continuing calibration-verification 

standards, standard-reference samples, reagent spikes, external 

certified-reference materials, and external blind proficiency 

samples are analyzed regularly. Method detection limits 

are tested continuously, and laboratory reporting levels are 

updated accordingly. The NWQL maintains the National 

Environmental Laboratory Accreditation Program (NELAP) 

and other certifications (http://www.nelac-institute.org/

content/NELAP/accred-bodies.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), which includes annual testing of all USGS 

field personnel for proficiency in making field water-quality 

measurements (https://bqs.usgs.gov/nfqa/). Results for 

analyses from the NWQL or from laboratories contracted by 

the NWQL were uploaded directly into NWIS. Results for 

analyses from other laboratories are compiled in a project 

database and, from there, uploaded to NWIS.

Data Reporting

The following section gives details for the laboratory 

reporting conventions and the constituents that are determined 

by multiple methods or by multiple laboratories.

Reporting Levels

The USGS NWQL uses two thresholds for reporting 

results: the long-term method detection level (LT-MDL) and 

the laboratory reporting level (LRL). The LT-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. The LT-MDL is statistically derived from 

concentrations in blank samples measured over an entire year 

(Childress and others, 1999; U.S. Environmental Protection 

Agency, 1999; Connor, 2012). The LRL is usually set at twice 

the LT-MDL for each constituent. The probability of reporting 

a false negative for a sample that contains a concentration of a 

constituent greater than or equal to the LRL is predicted to be 

less than or equal to 1 percent (Childress and others, 1999). 

Since October 2010, value-qualifier codes are included 

with results in the USGS NWIS database for reported values 

less than the LRL. The value-qualifier code “n” indicates 

results between the LT-MDL and LRL, and “b” indicates 

results less than the lowest calibration standard. For organic 

constituents with mass spectrometric methods classified as 

“information rich,” results less than the LT-MDL are often 

reported by the NWQL; these results are denoted with the 

value-qualifier “t” in the USGS NWIS database and are 

reported as “<MDL” in tables 5 and 6. Detections with 

concentrations less than the LT-MDL have greater than 

1 percent probability of being false positive detections and 

therefore do not meet the criteria for detections established 

for the GAMA Priority Basin Project (Fram and others, 

2012). Values greater than the LRLs are sometimes reported 

as having a higher degree of uncertainty, which is coded by 

the letter “E” preceding the values in the tables and text. The 

E-coded values can result from detections outside the range 

of calibration standards, from detections that did not meet all 

laboratory QC criteria, and from samples that were diluted 

prior to analysis (Childress and others, 1999).

Non-detections are reported in the USGS NWIS 

database as less than the reporting level for each constituent. 

The reporting level for organics is the LRL. For inorganic 

constituents, the reporting level is often the LT-MDL. 

Exceptions are bromide, nitrite, and nitrite plus nitrate, which 

are reported by using the method detection limit (MDL). 

Like the LT-MDL, 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; however, the MDL is calculated from a small number 

of replicate analyses of a low-concentration spike sample 

(Childress and others, 1999; U.S. Environmental Protection 

Agency, 1999). Total dissolved solids, perchlorate, and NDMA 

are reported by using minimum reporting levels (MRLs). The 

MRL is the smallest measurable concentration of a constituent 

that can be reliably reported by using a given analytical 

method (Timme, 1995). 

The USGS NWQL updates reporting levels regularly, and 

the values listed in this report were in effect during the period 

that groundwater samples from the MS-SA study unit were 

analyzed (October 2012 to May 2013). 

Isotopes of hydrogen, oxygen, and carbon 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 will be found. 

Results for most constituents are presented by using the 

LRL, LT-MDL, MDL, MRL, or MU values provided by the 

analyzing laboratories. Results for some organic and inorganic 

constituents are presented by using study reporting levels 

(SRLs) derived from assessment of data from QC samples 

associated with groundwater samples collected as part of the 

Groundwater Ambient Monitoring and Assessment-Priority 

Basin Project (GAMA-PBP; see “Assessment of Blank 

Results and SRLs” in this appendix).
110 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

The reporting limits for radiochemical constituents 

(carbon-14, tritium, radon-222, and gross-alpha and grossbeta radioactivity) were based on sample-specific critical 

levels (ssLC; McCurdy and others, 2008). The critical level 

is analogous to the LT-MDL used for reporting results for 

organic and non-radioactive inorganic constituents. In this 

report, the critical level is defined as the minimum measured 

activity that indicates a positive detection of the radionuclide 

where there is less than a 5 percent probability of a falsepositive detection. Sample-specific critical levels are used 

for radiochemical measurements because the critical level is 

sensitive to sample size and sample yield and is dependent 

on instrument background, counting times for the sample and 

background, and the characteristics of the instrument used 

and the nuclide being measured. The measured activity in the 

sample is compared to the ssLC calculated for that sample. 

Measured activities less than the ssLC are reported as nondetections with a dash (—) in the data tables. 

The analytical uncertainties associated with measured 

activities are also sensitive to sample size and yield, counting 

times, and instrument characteristics. Therefore, measured 

activities of radioactive constituents are reported with samplespecific combined standard uncertainties. The combined 

standard uncertainty is reported at the 68 percent confidence 

level (1-sigma).

Notation

Stable isotopic compositions of oxygen, carbon, and 

hydrogen are reported as relative isotope ratios in units of per 

mil by using the standard delta notation (Coplen, 2011):

iE Rsample

Rreference = 



 



 −1 (1)

where

i is the atomic mass of the heavier isotope of 

the element,

E is the element (H for hydrogen, O for oxygen, 

C for carbon),

Rsample is the ratio of the abundance of the heavier 

isotope of the element (2H, 18O, 13C) to the 

lighter isotope of the element (1H, 16O, 12C) 

in the sample, and

Rreference is the ratio of the abundance of the heavier 

isotope of the element to the lighter isotope 

of the element in the reference material.

The reference material for oxygen and hydrogen is 

Vienna Standard Mean Ocean Water (VSMOW), which has 

assigned δ18O and δ2H values of 0 per mil (Coplen and others, 

2002; Coplen, 2011). The reference material for carbon is 

Vienna Pee Dee Belemnite (VPDB), which has an assigned 

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 standardreference material.

Constituents Measured in the Field and the 

Laboratory

Field water-quality indicators—pH, SC, and alkalinity—

were measured in the field and at the NWQL. The field 

measurements are generally the preferred method for all 

three constituents, because field conditions are considered 

more representative of groundwater conditions (Hem, 1985). 

Laboratory values for all three constituents were significantly 

greater than field values (Wilcoxon signed-rank test, p<0.001 

for all three tests). The increase in the pH of the groundwater 

samples between field and laboratory measurements (table 4) 

can be explained by equilibration of the samples with the 

atmosphere after collection and by analytical issues that can 

introduce bias to the laboratory values (Fram and others, 

2009).

The reason for the difference between field and 

laboratory SC values is unknown. The differences between 

the field and laboratory values were small; the percent relative 

standard deviation (percent RSD) was less than 1 percent 

for 53 percent of the samples and less than 10 percent (the 

criteria for acceptable replicate pairs) for 98 percent of the 

samples. One sample with a field SC value less than the upper 

benchmark had a laboratory SC value greater than the upper 

benchmark (S-MS-SV20). 

The increase in alkalinity values between field and 

laboratory measurements (tables 4A, 4B) could be explained 

by differences among the methods used to measure alkalinity 

in the field and in the laboratory (Bennett and Fram, 2014). 

The importance of the systematic difference between the field 

and laboratory alkalinity values was evaluated by comparing 

cation-anion balances for major-on analyses for samples 

calculated with the field and laboratory alkalinity values 

(Bennett and Fram, 2014) and the differences are too small to 

disrupt the cation-anion balances.
Appendix A 111

Quality-Control Methods and Results

The purpose of QC is to identify which data best 

represent environmental conditions and which could 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; and (4) surrogate compounds were 

added to samples analyzed for organic constituents to assess 

potential bias of laboratory analytical methods. Two types of 

QC measurements were collected at shallow-well tap sites: 

blanks and replicates. Matrix-spike and surrogate analysis 

were not collected at wells sampled at the tap because samples 

for analysis of VOCs and pesticides were not collected at 

these sites. The QC measurements for the grid wells and the 

wells sampled at the tap were pooled together for assessment 

because the same equipment was used for sample collection, 

handling, and transport.

Assessment of Blank Results and Study 

Reporting Levels

The primary purposes of collecting blanks are to evaluate 

the potential contamination of samples by constituents of 

interest during sample handling or analysis and to identify and 

mitigate the sources of contamination. Results from blanks 

collected for the MS-SA study unit and for previous GAMA 

study units were used to establish SRLs for some constituents 

detected in blanks. Concentrations of SRLs can be higher than 

the reporting levels used by the laboratory. Detections reported 

by the laboratory with concentrations less than SRLs could 

have significant contamination bias. These data were flagged 

with appropriate remark codes (described in subsequent 

sections) and were rejected from subsequent use, including 

calculations of detection frequency.

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., 

2013). Nitrogen-purged, organic-free blank water was used for 

blanks of organic constituents, and inorganic-free blank water 

was used for blanks of other constituents. 

One source-solution blank was collected during MS-SA, 

because a new lot of blank water was released by NWQL, to 

assess potential contamination of samples during transport 

and analysis and potential contamination of the certified 

blank water obtained from the NWQL. A “lot” is a unique 

batch of blank water with defined production and expiration 

dates. The source-solution blank was collected in the field 

mobile laboratory by pouring blank water directly into sample 

containers that were preserved, shipped, and analyzed in the 

same manner as the groundwater samples. Source-solution 

blanks were analyzed for VOCs, NDMA, perchlorate, 

trace elements, major and minor ions, silica, and TDS. One 

additional source-solution blank was collected at a sampling 

site for perchlorate analysis.

Field blanks were collected to assess potential 

contamination of samples during collection, processing, 

transport, and analysis. To collect field blanks at the sampling 

sites, blank water was either pumped or poured through the 

sampling equipment (fittings and tubing) used to collect 

groundwater samples, then processed and transported by 

using the same protocols used for the groundwater samples. 

Four liters of blank water were pumped or poured through the 

sampling equipment before each field blank was collected. 

Field blanks were analyzed for VOCs, pesticides and pesticide 

degradates, NDMA, perchlorate, trace elements, nutrients, 

major and minor ions, silica, and TDS. 

Field or source-solution blanks were not collected for 

gross alpha and gross beta radioactivity or radon because the 

laboratory determines an ssLC value for each sample. The 

ssLC is the minimum measured value that indicates a non-zero 

amount of the radionuclide in the sample; in other words, it is 

an amount of the radionuclide that is statistically 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 dissolve into any solution used 

to collect a blank, making it impractical to collect a blank 

for these analytes. Isotopic ratios of carbon, hydrogen, and 

oxygen are an intrinsic property of any of these elements; 

therefore, the concept of a blank does not apply to these ratios.

Determining Study Reporting Levels

The SRLs were determined for VOCs by Fram and others 

(2012) on the basis of statistical assessments of results from 

field blanks, source-solution blanks, laboratory instrument 

blanks, and groundwater samples collected for the first 

32 GAMA-PBP study units (May 2004–September 2010). The 

SRLs were established for those VOCs that had evidence of 

potential contamination due to field or laboratory processes: 

1,2,4-trimethylbenzene (0.56 micrograms per liter, μg/L), 

carbon disulfide (0.03 μg/L), chloroform (0.02 μg/L, which 

only applies to monitoring wells that were not sampled in this 

study), ethylbenzene (0.06 μg/L), toluene (0.69 μg/L), m- plus 

p-xylenes (0.33 μg/L), and o-xylene (0.12 μg/L). Three VOCs 

(acetone, 2-butanone, and tetrahydrofuran) had no upper limit 

on the concentrations that could be attributed to extrinsic 

contamination; detections of these constituents have been 

attributed to methanol used to clean field equipment or cement 

used to join polyvinyl chloride (PVC) piping (Fram and 

others, 2012). Detections of VOCs having concentrations less 

than the SRLs are reported as non-detections in table 5.
112 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

The SRLs were determined for trace elements on the 

basis of statistical assessments of results from field blanks, 

source-solution blanks, and laboratory blanks collected for the 

first 20 GAMA-PBP study units (May 2004–January 2008), 

as described by Olsen and others (2010), and for additional 

GAMA-PBP study units (March 2006 through March 2013) as 

described by Davis and others (2014). These assessments used 

order statistics and binomial probabilities to construct an upper 

confidence limit (Hahn and Meeker, 1991) for the maximum 

concentration of each constituent possibly introduced while 

groundwater samples were collected, handled, transported, and 

analyzed. The 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). Detections of trace elements 

having concentrations less than the SRLs are marked with a 

less than or equal to (≤) symbol preceding the reported value 

on table 8 to indicate that the true value could be less than or 

equal to the reported value (including the possibility of being 

a non-detection). One additional trace element (cobalt) had 

no upper limit on the concentrations that could be attributed 

to extrinsic contamination; cobalt can be introduced by 

capsule filters used for processing water samples (Davis and 

others, 2014). All groundwater results for cobalt were coded 

as “reviewed and rejected” in the NWIS database and are not 

presented in this report.

Detections in Field Blanks and Application of Study 

Reporting Levels

Constituents were not detected in field blanks for the 

following constituent groups or constituents: pesticides and 

pesticide degradates (13 field blanks), perchlorate (14 field 

blanks), and TDS (19 field blanks).

Table A–2 presents a summary of detections in the field 

blanks and the SRLs applied for the MS-SA study unit. For 

VOCs and nutrients, 14 field blanks were collected; 12 field 

blanks were collected for NDMA; 19 field blanks for trace 

elements; and 21 field blanks for nitrate plus nitrite. Fewer 

field blanks were collected for VOCs and NDMA than for 

trace elements and nitrate, because samples for VOCs and 

NDMA were only collected at grid wells, whereas samples for 

trace elements and nitrate were collected at grid wells and at 

shallow-well tap sites. Two additional field blanks were not 

collected in accordance to GAMA protocols, and the results 

were reviewed and rejected. No constituents were detected in 

the source-solution blanks collected during the MS-SA study 

unit.

For the MS-SA study unit, VOCs were not detected in 

the field blanks (table A–2). Of the six VOCs with applicable 

SRLs defined by Fram and others (2012), three were detected 

in groundwater samples from the MS-SA study unit: carbon 

disulfide, toluene, and m- plus p-xylene. The current LRL for 

carbon disulfide (0.1 μg/L) is greater than the SRL, and the 

two groundwater detections were at concentrations greater 

than the SRL (tables 5, A–2). Two of the three detections of 

toluene (MS-SC-15 at 0.04 μg/L and MS-SV-30 at 0.02 μg/L) 

and the one detection of m- plus p-xylene (MS-SC-15 at 

0.16 μg/L) were at concentrations less than their respective 

SRLs and were re-classified as non-detections. Additionally, 

all detections for acetone (two samples), 2-butanone (two 

samples), and tetrahydrofuran (three samples) were rejected 

because of their likely origination from extrinsic sources, 

such as methanol used to clean equipment or cement used on 

PVC piping that is sometimes connected to domestic wells, 

rather than from the groundwater (Fram and others, 2012). 

Although these VOCs had no upper limit for an SRL, none 

of the uncensored results in the MS-SA study for acetone or 

2-butanone were greater than the benchmarks of 6,000 and 

4,000 μg/L, respectively. 

The special-interest constituent NDMA was detected 

in 1 out of 12 field blanks; the detected concentration 

(0.00254 μg/L) was below the range of concentrations 

observed in groundwater samples (tables A–2, 7). The low 

detection frequency and concentration of NDMA in the field 

blanks indicated that contamination bias did not likely affect 

groundwater results. 

Seven of the eight trace elements with SRLs defined by 

Davis and others (2014) were detected in at least one MS-SA 

field blank, and most of the detections were at concentrations 

less than the updated SRLs (table A–2). Exceptions included 

one detection of molybdenum at 0.044 μg/L, one detection of 

tungsten at 0.03 μg/L, and one detection of zinc at 8.6 μg/L 

(table A–2). Three other trace elements were detected in 

MS-SA field blanks: antimony (0.139 μg/L), boron (32 μg/L), 

and thallium (0.02 μg/L). The SRLs were not defined for 

these constituents. It was determined from the low-detection 

frequency and concentration in field blanks of both antimony 

and thallium that contamination of samples for these 

constituents was unlikely to significantly affect groundwater 

results. For the field blank with a boron detection, the NWQL 

reported in the certificate of analysis for the blank water used 

to collect the field blank (NWQL Lot number 81202) that the 

water contained elevated concentrations of boron (James A. 

Lewis, NWQL, written commun., August 2013). 

Nitrite and nitrite plus nitrate (as nitrogen) were each 

detected in one field blank at their respective detection 

levels: 0.001 mg/L for nitrite and 0.04 mg/L for nitrite plus 

nitrate (table A–2). It was not necessary to define SRLs for 

any nutrients, because of the low-detection frequency and 

concentration of the constituents in field blanks.
Appendix A 113

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 reflect differences in groundwater 

quality or the variability that can result from collecting, 

processing, and analyzing the samples. Chemical constituents 

(tables A–3A–B) and radiochemical constituents (table A–3C) 

were assessed by using the different (but similar) approaches 

explained in following sections.

Assessment of Replicate Samples

Three methods for measuring variability were needed to 

adequately assess precision over the broad range of measured 

concentrations of most constituents. The variability between 

measured concentrations in the pairs of sequential replicate 

samples was represented by the standard deviation (SD) for 

low concentrations and by relative standard deviation (RSD) 

for high concentrations (Anderson, 1987; Mueller and Titus, 

2005). The RSD is defined as the SD divided by the mean 

concentration for each replicate pair of samples expressed as 

a percentage. The boundary between concentrations for which 

variability is assessed with SD and concentrations for which 

variability was assessed with RSD was defined as five times 

the reporting level (RL) for each constituent. The RL can be 

the MDL or MRL for a constituent, as listed in tables 3A–F.

Replicate pairs of analyses of all constituents, except for 

radiochemical constituents, were evaluated as described in the 

following paragraphs. 

If both values were reported as non-detections, the 

variability was considered acceptable. Values reported with 

the less than or equal to (≤) symbol were considered nondetections for this purpose. The less than or equal to (≤) code 

indicated that the reported value was less than the SRL, and 

the concentration had an unacceptable likelihood of being 

fully or partly attributed to contamination bias. If both values 

were reported as detections, the SD was calculated if the 

mean concentration was less than 5 RL for the constituent, 

and the RSD was calculated if the mean concentration was 

greater than or equal to 5 RL for the constituent. Acceptable 

precision was defined as having a SD less than or equal to the 

LT-MDL or having a RSD less than or equal to 10 percent. For 

comparison, a RSD of 10 percent is equivalent to a relative 

percent difference of 14 percent.

For organic and special-interest constituents, if one 

value was reported as a non-detection and the other value was 

reported as a detection greater than the LT-MDL (or MRL for 

special-interest constituents), the variability for the pair was 

considered unacceptable. For inorganics, if one value was a 

non-detection and the other value was greater than the LRL, 

the variability of the pair was considered unacceptable. If one 

value was coded as less than or equal to the reported value 

and the other value was a detection greater than the SRL, then 

the SD for the two reported values was calculated; acceptable 

precision was defined as having a SD less than or equal to 

one-half the SRL. 

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 (2)

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 normalized absolute difference 

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 indicated that 

precision was unacceptable for a constituent and no specific 

reason could be identified, then this greater variability had 

to be considered when interpreting the data. If measured 

concentrations were slightly greater than a water-quality 

benchmark, then actual concentrations could be slightly less 

than that benchmark. Similarly, if measured concentrations 

were slightly less than a water-quality benchmark, then actual 

concentrations could be slightly greater than a benchmark. 

Also, if a constituent concentration showed high variability 

in replicate sample pairs, then a greater difference between 

concentrations measured in two samples was required to 

conclude that the two samples had significantly different 

concentrations.

Variability in Replicate Samples

Tables A–3A–C summarizes the results of replicate 

analyses for constituents detected in groundwater samples 

collected in the MS-SA study unit. Replicate analyses 

were made at 8 to 29 grid wells depending on constituent, 

representing approximately 30 percent of all the samples 

collected at grid-well sites. Replicate analyses were planned to 

be collected at seven of the wells sampled at the taps, but only 

two replicate analyses were able to be collected, representing 

approximately 3 percent of all wells sampled at taps. 
114 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Of the 5,575 replicate pairs of constituents collected, 

1,027 pairs had a detection in one or both samples of the pair. 

Of these 1,027 pairs, 51 pairs had results outside of the limits 

for acceptable precision, including results for the organic 

and special-interest constituents bromodichloromethane, 

bromoform, chloroform, perchloroethylene, deethylatrazine, 

simazine, and NDMA and all the inorganic constituents, 

except aluminum, beryllium, lead, silver, thallium, vanadium, 

ammonia (as nitrogen), nitrate plus nitrate, calcium, chloride, 

sulfate, silica, and the stable isotopes of water and carbon-14. 

Results for replicate analyses for constituents that were 

not detected in groundwater samples are not reported in 

tables A–3A–C. All replicate pairs for perchlorate, isotopic 

tracers, and radioactive constituents were within acceptable 

precision. 

For the each of the 85 VOCs, 29 replicate pairs of 

samples were analyzed. Of the 2,465 replicate pairs analyzed, 

the results of 1 replicate pair for perchloroethylene was 

composed of a non-detection and a detected concentration 

between the LT-MDL and LRL (table A–3A). One replicate 

pair each of bromodichloromethane, bromoform, and 

chloroform had an RSD greater than 10 percent. For the 

63 pesticides compounds, 29 replicate pairs of samples were 

analyzed. Of the 1,827 replicate pairs, results from 1 pair of 

deethylatrazine and 1 pair of simazine were composed of a 

detected concentration between the LT-MDL and LRL and a 

non-detection (table A–3A). Of the 9 replicate pairs analyzed 

for NDMA, 1 pair was composed of a detected concentration 

between the LT-MDL and LRL and a non-detection 

(table A–3A). 

Of the 1,170 replicate sample pairs analyzed for trace 

elements and major and minor ions, results for 43 pairs had 

unacceptable precision. Of these 43 pairs of results, 13 pairs 

involved 1 replicate pair of samples collected at grid-well site 

S-MS-H22 (table A–3B), indicating that the poor precision 

for these 13 pairs could be the result of an inadvertent sample 

switch at the laboratory or in the field. The sample is annotated 

in tables 8 and 10. 

Thirty-one replicate pairs of samples were analyzed 

for nitrate, and twenty-nine replicate pairs of samples were 

analyzed for the other nutrient constituents. Replicate pairs of 

nitrate were within acceptable precision. Replicate pairs for 

nitrite, total nitrogen and orthophosphate each had one or two 

pairs outside of acceptable precision (table A–3B). 

Eight to nine replicate pairs were analyzed for 

isotopic tracers. All pairs were within acceptable precision 

(table A–3B).

Nine replicate pairs of samples were analyzed for gross 

alpha and gross beta radioactivities, and ten replicate pairs of 

samples were analyzed for radon-222. All pairs were within 

acceptable precision (table A–3C).

Detected concentrations in environmental samples were 

not modified on the basis of the replicate analyses.

Matrix Spikes

The addition of a known concentration of a constituent 

(spike) to a replicate sample from the environment 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 compound-bycompound basis. For this study, matrix spikes were added by 

the laboratory performing the analysis rather than in the field. 

Low matrix-spike recovery can indicate that the compound 

might not be detected in some samples if it was present at very 

low concentrations. Low and high matrix-spike recoveries can 

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 health-based benchmark.

Assessment of Matrix Spikes

Matrix spikes were assessed for VOCs, NDMA, and 

pesticides and pesticide degradates, because the analytical 

methods for these constituents could be susceptible to matrix 

interferences. The GAMA-PBP defined the data-quality 

objective range for acceptable median matrix-spike recoveries 

as 70 to 130 percent, with recovery, R, for each constituent 

defined as follows:

R percent

C C

C percent S U

EXP

( ) = − ×100 (3)

where

CS is the concentration measured in the spiked 

sample,

CU is the concentration measured in the unspiked 

sample, and

CEXP is the expected concentration added through 

spiking.

Only constituents that had median matrix-spike 

recoveries outside of this range were flagged as having 

unacceptable recoveries. For some constituents, the range of 

70 to 130 percent for median matrix-spike recovery was more 

restrictive than the control limits used by the laboratory for 

recoveries in set spikes composed of laboratory blank water.
Appendix A 115

Matrix-Spike Recoveries

Tables A–4A–B present a summary of matrix-spike 

recoveries for the MS-SA study unit. Replicate samples for 

spike additions of organic constituents were collected at 12 of 

the 100 grid wells for VOCs and pesticides and pesticide 

degradates (12 percent of all the wells sampled). Samples 

for spike additions of NDMA were collected at 12 of the 

100 grid wells, but 2 sample sets were not analyzed within the 

laboratory hold time and were excluded, leaving 10 spiked 

samples (10 percent of all the wells sampled). Groundwater 

from the 70 wells sampled at the taps was not analyzed for 

these constituents.

Groundwater samples were spiked with 85 VOCs to 

calculate matrix-spike recoveries. Median matrix-spike 

recoveries were between 70 and 130 percent for all VOCs 

(table A–4A). The special-interest constituent NDMA was 

analyzed at Weck Laboratories Inc., and matrix-spike results 

were within the acceptable range and are presented in 

table A–4A.

Groundwater samples were spiked with 63 pesticides 

and pesticide degradates to calculate matrix-spike recoveries. 

Median matrix-spike recoveries were less than 70 percent for 

23 compounds, of which, 10 were detected in groundwater 

samples (table A–4B). Low matrix-spike recoveries could 

indicate the compound was not detected in some samples, if it 

was present at very low concentrations. 

Detected concentrations in environmental samples 

were not modified on the basis of the matrix-spike recovery 

analysis.

Surrogate Compound Recoveries

Table A–5 presents a summary of the surrogate recoveries 

for the MS-SA study unit. The table lists the surrogates, 

the analytical schedule for which each surrogate was used, 

the number of analyses for field blanks and environmental 

samples, the number of surrogate recoveries less than 

70 percent, and the number of surrogate recoveries greater 

than 130 percent for the blank and environmental samples. 

Field blanks and environmental samples were considered 

separately to assess whether or not the matrices present in 

environmental samples affected surrogate recoveries.

Most surrogate recoveries for the field blanks and 

environmental samples were within the acceptable range of 

70 percent to 130 percent. For VOC analyses, about 30 percent 

of field blanks and about 47 percent of environmental samples 

had surrogate recoveries for 1, 2-dichloroethane-d4 greater 

than 130 percent. All other VOC surrogates were within the 

acceptable range. For pesticides and pesticide degradates, the 

diazinon-d10 surrogate recoveries were less than 70 percent 

in 62 percent of the field blanks and 58 percent of the 

environmental samples. The α-HCH-d6 surrogate recoveries 

were less than 70 percent in one field blank sample and greater 

than 130 percent in one field blank sample. The recoveries for 

all environmental samples were within the acceptable range.

Detected concentrations in environmental samples were 

not modified on the basis of the surrogate-recovery analysis.

Other Quality-Control Results

Two other laboratory QC issues arose during the analysis 

of samples collected for the MS-SA study unit: holding times 

were exceeded for the analyses of NDMA, radon, and gross 

alpha and gross beta radioactivity samples, and laboratory QC 

tests indicated bias in the results of some of the trace elements. 

Holding time refers to the time in calendar days from 

sample collection to the analysis of the sample. Analyses 

for some samples in the MS-SA study unit were completed 

after the recommended maximum holding time because 

of a scheduling error at the laboratory or shipping error. 

A delay in the analysis at the laboratory can result in 

different measured concentrations than what was in the 

sample. Two spiked samples for NDMA were analyzed 

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

recommended holding time, and the results were omitted 

from the total count of spiked samples (table A–4A). No 

environmental samples for NDMA were analyzed past the 

holding time.

The gross alpha and beta radioactivity reported results 

are the amounts measured in the samples. Radioactive decay 

between the time of sample collection and measurement 

can change the gross alpha and gross beta radioactivity of a 

sample (Arndt, 2010). At least one sample for the analysis of 

gross alpha and gross beta radioactivity (72-hour counts) was 

analyzed 4 to 6 days after sample collection for every 15 gridwell samples. These samples are noted in the results table. 

The results for gross alpha radioactivity were reviewed, 

and results for one grid-well sample (S-MS-H14) were 

rejected. The combined standard uncertainties for the raw 

gross alpha radioactivity 72-hour and 30-day counts results 

were 10 and 11 picocuries per liter (pCi/L), respectively, 

and the sample specific critical levels were 16 and 17 pCi/L, 

respectively. Because of the high uncertainty of the results, 

and because the detection levels were greater than the 

MCL-US for gross alpha radioactivity, the results were 

considered inconclusive for the purpose of this report. The 

results were not coded by the laboratory as analyzed after 

the holding time, and the reason for the high uncertainty is 

unknown. 

Results for one grid-well sample (S-MS-P15) for radon 

was analyzed after the radon half-life of 3.92 days. The 

combined standard uncertainty for the raw radon radioactivity 

result was 34 pCi/L, and the sample specific critical level 

was 27.6 pCi/L. The result was well below the MCL-US and 

is noted as analyzed after the radon half-life in the results 

table 11.
116 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Potential bias indicated from laboratory QC tests is an 

issue that must be investigated to determine whether or not 

the environmental sample data are affected. The BQS operates 

independent, quality-assurance projects called the Inorganic 

Blind Sample Project (IBSP) and Blind Blank Program (BBP) 

to monitor and evaluate the quality of results for analyses of 

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

TDS by the NWQL. The IBSP submits standard-reference 

samples consisting of natural-matrix water samples spiked 

with known concentrations of the inorganic constituents 

(Farrar and Long, 1997). The IBSP samples are disguised as 

regular environmental samples for submission to the NWQL; 

the BBP samples are disguised as regular field blanks. The 

BQS uses results from the IBSP and BBP samples to evaluate 

potential bias in the results reported by the NWQL. 

The BQS summaries from October 2012 to May 2013 

were examined. The BQS reported that eight inorganic 

constituents showed evidence of bias during this period: there 

was a positive bias for chromium (approximately 4 percent), 

barium (approximately 7 percent), cadmium (approximately 

6 percent), lead (approximately 5 percent), molybdenum 

(approximately 6 percent), thallium (approximately 3 percent), 

and zinc (approximately 4 percent), and there was a negative 

bias for ammonia (approximately 1 percent). Examination of 

the results for the IBSP samples for these eight constituents 

indicated that the analytical biases reported by the BQS were 

not high or low enough relative to the constituent benchmarks 

to warrant adding or subtracting the biases from sample results 

for the data collected for the MS-SA study unit.

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120 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

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Table A–1. Analytical methods used for the determination of organic and inorganic constituents by the U.S. Geological Survey (USGS) National Wat(NWQL) and contract laboratories.[Laboratory entity codes in the USGS National Water Information System (NWIS) for laboratories other than the USGS National Water Quality Laboratory (NWQL) are given inames. Abbreviations: USEPA, U.S. Environmental Protection Agency]

Analyte Analytical method Laboratory and analytical schedule 

Water-quality indicators

Field parameters Calibrated field meters and test kits USGS field measurement U.S. Geological 

Organic constituents

Volatile organic compounds Purge and trap capillary gas chromatography/

mass spectrometry

NWQL, Schedule 2020 Connor and other

Pesticides and pesticide 

degradates

Solid-phase extraction and gas 

chromatography/mass spectrometry

NWQL, Schedule 2003 Zaugg and others

1996; SandstroMadsen and ot

Constituents of special interest

Perchlorate Liquid chromatography with mass 

spectrometry/mass spectrometry (USEPA Method 331.0)

Weck Laboratories, Inc., City of Industry, 

California (CA-WECK), standard operating procedure ORG099.R01

U.S. Environmen

N-Nitrosodimethylamine 

(NDMA)

Isotopic dilution with gas chromatography 

and chemical-ionization mass spectrometry (USEPA Method 1625 modified)

Weck Laboratories, Inc., City of Industry, 

California (CA-WECK), standard operating procedure ORG065.R10

U.S. Environmen

Plomley and o

Inorganic constituents

Major and minor ions and 

trace elements 

Atomic absorption spectrometry, colorimetry, 

ion-exchange chromatography, inductivelycoupled plasma atomic emission spectrometry, and mass spectrometry

NWQL, Schedule 1948 Fishman and Frie

Fishman, 19931999; America1998; Garbarin

Nutrients Alkaline persulfate digestion, Kjedahl 

digestion

NWQL, Schedule 2755 Fishman, 1993; P

2011

Isotopic tracers

Stable isotopes of hydrogen 

and oxygen in water

Gaseous hydrogen and carbon dioxide—

water equilibration and stable-isotope mass spectrometry

USGS Stable Isotope Laboratory, Reston, Virginia 

(USGSSIVA), NWQL Schedule 1142

Epstein and May

others, 1991; C

Stable isotopes of carbon in 

dissolved inorganic carbon and carbon-14 abundance

Accelerator mass spectrometry Woods Hole Oceanographic Institution, National 

Ocean Sciences Accelerator Mass Spectrometry Facility [NOSAMS], Woods Hole, Massachusetts (MA-WHAMS), NWQL Schedule 2255

Vogel and others

others, 1990; MGagnon and Joothers, 1994; S

Tritium Electrolytic enrichment-liquid scintillation USGS Stable Isotope and Tritium Laboratory 

[SITL], Menlo Park, California (USGSH3CA), NWQL Schedule 1565

Thatcher and oth
Analyte Analytical method Laboratory and analytical schedule 

Radioactive constituents Radon-222 Liquid scintillation counting NWQL, Schedule 1369 American Society 

1998 Gross alpha and gross beta radioactivity (72-hour and 30-day count) Alpha and beta activity counting (USEPA Method 900.0) Eberline Analytical Services, Richmond, California (CA-EBERL), NWQL Schedule 1792 Krieger and Whit

Noble gases Noble gases Helium-3 in-growth and mass spectrometry Lawrence Livermore National Laboratory [LLNL], Livermore, California (CA LLNL) Moran and others

Eaton and othe

Table A–1. Analytical methods used for the determination of organic and inorganic constituents by the U.S. Geological Survey (USGS) National Wat(NWQL) and contract laboratories.—Continued [Laboratory entity codes in the USGS National Water Information System (NWIS) for laboratories other than the USGS National Water Quality Laboratory (NWQL) are given inames. Abbreviations: USEPA, U.S. Environmental Protection Agency]
Appendix A 123

Table A–2. Constituents detected in field blanks and study reporting levels (SRLs) used for the Monterey–Salinas Shallow Aquifer 

(MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to 

May 2013.

[mg/L, milligrams per liter; na, not applicable; nv, no value in category; RL, reporting level; USGS, U.S. Geological Survey; VOC, volatile organic compound; 

μg/L, micrograms per liter; —, not detected; ≤, less than or equal to]

Constituent

Number of 

field blank 

detections / 

total number 

of field blank 

samples

RL

Concentration(s) 

detected 

in 

field 

blank 

sample(s)

SRL 

Source 

of 

SRL

Number of 

groundwater 

results≤-coded 

/ total number 

of groundwater 

detections

Number of 

groundwater 

results 

coded as 

“reviewed and 

rejected”

Volatile organic compounds (VOCs) (μg/L)

Acetone 0/14 3.4 — nv1 Fram and others, 2012 na 2

Carbon disulfide 0/14 0.1 — 0.03 Fram and others, 2012 0/2 na

Methyl ethyl ketone 

(2-butanone)

0/14 1.6 — nv1 na na 2

Tetrahydrofuran 0/14 1.4 — nv1 na na 4

Toluene 0/14 0.02 — 0.69 Fram and others, 2012 2/3 na

m- plus p-Xylene 0/14 0.08 — 0.33 Fram and others, 2012 1/1 na

Constituents of special interest (μg/L)

N-Nitrosodimethylamine (NDMA)

1/12 0.002 0.0025 nv na 0/8 na

Trace elements (μg/L)

Antimony 1/19 0.135 0.139 nv na 0/113 na

Boron 1/19 3 132 nv na 0/170 na

Cobalt 18/19 0.023 0.034 to 0.243 nv1 Davis and others, 2014 na all

Copper 4/19 0.08 0.8 to 1.8 2.1 Davis and others, 2014 63/112 na

Iron 0/19 4 — 6 Davis and others, 2014 10/48 na

Lead 5/19 0.025 0.03 to 0.21 0.82 Davis and others, 2014 132/154 na

Manganese 6/19 0.15 0.15 to 0.41 0.66 Davis and others, 2014 31/149 na

Molybdenum 2/19 0.014 0.044, 0.022 0.023 Davis and others, 2014 0/170 na

Nickel 1/19 0.09 0.11 0.21 Davis and others, 2014 7/167 na

Thallium 1/19 0.01 0.02 nv na 0/14 na

Tungsten 1/19 0.01 0.03 0.023 Davis and others, 2014 79/110 na

Zinc 7/19 1.4 1.7 to 8.6 6.2 Davis and others, 2014 57/155 na

Nutrients (mg/L)

Nitrite (as nitrogen) 1/14 0.001 0.001 nv na na na

Nitrite plus nitrate 

(as nitrogen) 

1/21 0.04 0.04 nv na na na

1

All detections of the three VOCs acetone, 2-butanone, and tetrahydrofuran and all results for cobalt were coded as “reviewed and rejected” in the 

USGS National Water Information System database and are not presented in tables 5 and 8. 

2

The blank water used to collect the field blank with a boron detection was reported by the U.S. Geological Survey National Water Quality Laboratory to have 

elevated concentrations of boron.
124 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Table A–3A. Quality-control summary for replicate pair analyses of organic constituents and special-interest constituents in samples 

collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment 

(GAMA) Priority Basin Project, October 2012 to May 2013.

[Constituents for which all replicate pairs were non-detections are not listed. Replicate pairs with one value reported as a non-detection and the other value 

reported at a concentration greater than the LT-MDL are included with the number of replicate pairs with standard deviations (SDs) greater than the LT-MDL. 

Abbreviations: LRL, laboratory reporting level; LT-MDL, long-term method detection level; nv, no value; RL, reporting level; RSD, relative standard deviation; 

USGS, U.S. Geological Survey; μg/L, micrograms per liter; —, not detected; >, greater than]

Constituent

Number 

of nondetections 

/ number of 

replicate pairs

Number of SDs > 

LT-MDL / number of 

replicate pairs with 

concentration less 

than 5 times the RL 

Concentrations of 

replicates with 

SDs greater than 

1⁄2 LRL 

(environmental, 

replicate) 

Number of RSDs 

greater than 10 

percent/ number 

of replicates with 

concentration greater 

than 5 times the LRL

Concentrations of 

replicates with 

RSDs greater than 

10 percent 

(environmental, replicate) 

Volatile organic compounds (VOCs) (μg/L) 

Bromodichloromethane 28/29 nv nv, — 1/1 0.258, 0.205 —

Bromoform 

(Tribromomethane)

27/29 0/1 nv, — 1/1 10.998, 0.708 —

Chloroform 

(Trichloromethane)

24/29 0/3 nv, — 2/2 0.874, 0.695 0.612, 0.776

Dibromochloromethane 28/29 0/1 nv, — nv nv —

Dichlorodifluoromethane28/29 0/1 nv, — nv nv —

1,1,2-Trichloro1,2,2-trifluoroethane27/29 0/1 nv, — 0/1 nv —

Methyl tert-butyl ether 

(MTBE)

28/29 nv nv, — 0/1 nv —

Perchloroethene (PCE) 24/29 1/5 —, 0.033 nv nv —

Trichlorofluoromethane 27/29 0/2 nv, — nv nv —

Pesticides and pesticide degradates (μg/L) 

Atrazine 26/29 0/3 nv, — nv nv —

Deethylatrazine 23/29 1/5 0.003, — 0/1 nv —

Hexazinone 28/29 0/1 nv, — nv nv —

Simazine 24/29 1/5 0.004, — nv nv —

Constituents of special interest (μg/L) 

Perchlorate 3/9 0/3 nv, — 0/3 nv —

N-Nitrosodimethylamine (NDMA)

8/9 1/1 0.003, — nv nv —

1

Reported values were E-coded by the USGS National Water Quality Laboratory (NWQL) for having greater uncertainty.
Table A–3B. Quality-control summary for replicate pair analyses of inorganic constituents in samples collected for the Monterey–Salinas Shallow ACalifornia Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.[Constituents for which all replicate pairs were non-detections are not listed. Abbreviations: C, carbon; H, hydrogen; LRL, laboratory reporting level; LT-MDL, long-term methmg/L, milligrams per liter; nv, no value; O, oxygen; RL, reporting level; RSD, relative standard deviation in percent; SD, standard deviation; μg/L, micrograms per liter; —, not 

Constituent

Number of 

non-detect 

or ≤-coded 

replicates/

number of 

replicates 

Number of SDs 

greater than LT-MDL / 

number of replicates 

with concentration 

less than 5 times 

the RL

Concentrations 

of replicates 

with SDs 

greater than 

1⁄2 LRL 

(environmental, replicate) 

Number of RSDs 

greater than 

10 percent/ number 

of replicates with 

concentration greater 

than 5 times the RL

(envir

Trace elements (μg/L)

Aluminum 17/31 0/14 nv — nv nv Antimony 9/31 1/22 0.113, — — nv nv Arsenic 0/31 0/2 nv — 1/29 10.119, 0.323 Barium 0/31 nv nv — 1/31 125.7, 20.9 Beryllium 15/31 0/15 nv — 0/1 nv Boron 0/31 nv nv — 2/31 25.4, 29.5 Cadmium 8/31 0/15 nv — 2/8 0.700, 0.590 Chromium 5/31 1/5 1—, 0.277 — 1/21 4.68, 3.88 Copper 23/31 1/7 11.19, 7.43 — 0/1 nv Iron 12/31 2/17 33.6, ≤5.68 134.6, 21.5 1/2 60.9, 40.5 Lead 27/31 0/4 nv — nv nv Lithium 0/31 nv nv — 1/31 12.36, 14.67 Manganese 13/31 2/10 1.41, 0.90 1.6, 0.86 2/8 29.1, 35.2 Molybdenum 0/31 0/1 nv — 2/30 0.543, 0.637 Nickel 3/31 1/23 10.361, 0.689 — 0/5 nv Selenium 1/31 0/4 nv — 3/26 6.28, 5.41 Silver 22/31 0/8 nv — 0/1 nv Strontium 0/31 nv nv — 1/31 11,100, 868 Thallium 30/31 0/1 nv — nv nv Tungsten 13/31 0/15 nv — 1/3 0.506, 0.594 Uranium 0/31 nv nv — 3/31 7.13, 8.54 Vanadium 0/31 1/2 1—, 0.265 — 0/29 nv Zinc 13/31 1/11 25.8, 20.9 — 1/7 197.4, 73.7 
Constituent Number of non-detect or ≤-coded replicates/ number of replicates Number of SDs greater than LT-MDL / number of replicates with concentration less than 5 times the RL Concentrations of replicates with SDs greater than 1⁄2 LRL (environmental, replicate) Number of RSDs greater than 10 percent/ number of replicates with concentration greater than 5 times the RL 

(envir

Nutrients (mg/L) Ammonia (as nitrogen) 24/29 0/1 nv — 0/4 nv 

Nitrite plus nitrate (as nitrogen)2 1/31 nv nv — 0/30 nv Nitrite (as nitrogen) 22/29 1/5 0.0029, — — 0/2 nv Total nitrogen (ammonia + nitrite + nitrate + organic nitrogen) 0/29 0/3 nv — 2/26 1.12, 1.96 Orthophosphate (as phosphorus) 0/29 0/8 nv — 1/21 0.064, 0.050 

Major and minor ions, silica, and total dissolved solids (TDS) (mg/L) Calcium 0/31 nv nv — 0/31 nv 

Chloride 0/31 nv nv — 0/31 nv Fluoride 0/31 0/15 nv — 0/16 nv Magnesium 0/31 nv nv — 1/31 24.7, 29.0 Potassium 0/31 nv nv — 2/31 3.88, 4.50 Sodium 0/31 nv nv — 2/31 48.9, 68.3 Bromide 2/31 nv nv — 2/31 2.9, 0.29 Sulfate 0/31 nv nv — 0/31 nv Silica (as SiO2) 0/31 nv nv — 0/31 nv TDS 0/31 nv nv — 1/31 368, 313 

Isotope tracers

δ2H of water (per mil) 0/9 nv nv — 0/9 nv δ18O of water (per mil) 0/9 nv nv — 0/9 nv δ13C of dissolved inorganic carbon (per mil) 0/8 nv nv — 0/8 nv C-14 of water (percent modern) 0/8 nv nv — 0/8 nv 

1One replicate pair had precision outside the acceptable limits for 13 inorganic constituents, possibly indicating a sample collection or analysis error. Results for the environm

tables 8 and 10.

2Nitrite plus nitrate (as nitrogen) is referred to as nitrate in the text for clarity.3Two replicate pairs of bromide were outside the limits of acceptable precision. Reported concentrations may have been affected by dilution calculation errors; however, the U

Laboratory (NWQL) verified results for both replicate pairs. Results for the environmental samples were annotated in table 10.Table A–3B. Quality-control summary for replicate pair analyses of inorganic constituents in samples collected for the Monterey–Salinas Shallow ACalifornia Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued[Constituents for which all replicate pairs were non-detections are not listed. Abbreviations: C, carbon; H, hydrogen; LRL, laboratory reporting level; LT-MDL, long-term methmg/L, milligrams per liter; nv, no value; O, oxygen; RL, reporting level; RSD, relative standard deviation in percent; SD, standard deviation; μg/L, micrograms per liter; —, not 
Appendix A 127

Table A–3C. Quality-control summary for replicate pair analyses of radioactive constituents in samples collected for the Monterey–

Salinas Shallow Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin 

Project, October 2012 to May 2013.

[For activities of radioactive constituents, a replicate pair analyses is defined as acceptable if the p-value for the normalized absolute difference is less than the 

significance level, α = 0.05. Abbreviations: nv, no values; >, greater than]

Constituent

Number of 

non-detections / 

number of 

replicate pairs 

Number of 

detections paired 

with 

non-detections

Number of replicate 

pairs with p > 0.05 /

number of 

replicate pairs 

Activities for replicate 

pairs with p > 0.05 

(environmental sample, 

replicate sample)

Gross alpha radioactivity, 72-hour count 1/9 0 0/9 nv

Gross alpha radioactivity, 30-day count 3/9 1 0/9 nv

Gross beta radioactivity, 72-hour count 0/9 0 0/9 nv

Gross beta radioactivity, 30-day count 1/9 0 0/9 nv

Radon-222 0/10 0 0/10 nv

Table A–4A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and the special interest 

constituent N-nitrosodimethylamine (NDMA) in samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, 

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.

[Acceptable recovery range is between 70 and 130 percent]

Constituent 

(synonym or abbreviation)

Number of matrix-spike 

samples collected

Minimum recovery 

(percent)

Maximum recovery 

(percent)

Median recovery 

(percent)

Acetone 12 100 125 117

Acrylonitrile 12 100 120 109

tert-Amyl methyl ether (TAME)1 12 94 104 101

Benzene 12 94 107 102

Bromobenzene 12 89 98 95

Bromochloromethane 12 93 107 98

Bromodichloromethane1 12 85 108 88

Bromoform (Tribromomethane)1 12 82 104 86

Bromomethane (Methyl bromide) 12 64 118 99

n-Butylbenzene 12 76 101 91

sec-Butylbenzene 12 86 107 97

tert-Butylbenzene 12 95 109 100

Carbon disulfide1 12 75 102 87

Carbon tetrachloride (Tetrachloromethane)1 12 85 108 92

Chlorobenzene 12 86 102 97

Chloroethane 12 81 125 100

Chloroform (Trichloromethane) 1 12 84 104 97

Chloromethane 12 95 139 108

3-Chloropropene 12 90 110 103

2-Chlorotoluene 12 94 108 104

4-Chlorotoluene 12 90 110 103

Dibromochloromethane1 12 81 105 88

1,2-Dibromo-3-chloropropane (DBCP) 12 80 104 91

1,2-Dibromoethane (EDB) 12 76 105 96

Dibromomethane1 12 90 113 94

1,2-Dichlorobenzene 12 88 114 106
128 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Constituent 

(synonym or abbreviation)

Number of matrix-spike 

samples collected

Minimum recovery 

(percent)

Maximum recovery 

(percent)

Median recovery 

(percent)

1,3-Dichlorobenzene 12 89 101 96

1,4-Dichlorobenzene 12 90 113 101

trans-1,4-Dichloro-2-butene 12 87 122 99

Dichlorodifluoromethane (CFC-12)1 12 80 128 109

1,1-Dichloroethane (1,1-DCA) 12 92 118 100

1,2-Dichloroethane (1,2-DCA) 12 94 121 99

1,1-Dichloroethene (1,1-DCE) 12 92 112 97

cis-1,2-Dichloroethene (cis-1,2-DCE) 12 93 101 98

trans-1,2-Dichloroethene (trans-1,2-DCE) 12 92 106 97

1,2-Dichloropropane1 12 77 104 94

1,3-Dichloropropane 12 85 111 99

2,2-Dichloropropane 12 78 95 84

1,1-Dichloropropene 12 84 98 94

cis-1,3-Dichloropropene 12 88 97 91

trans-1,3-Dichloropropene 12 75 90 85

Diethyl ether 12 98 113 108

Diisopropyl ether (DIPE) 12 93 113 105

Ethylbenzene 12 88 102 95

Ethyl tert-butyl ether (ETBE) 12 96 111 104

Ethyl methacrylate 12 85 100 96

o-Ethyl toluene (1-Ethyl-2-methyl benzene) 12 94 108 99

Hexachlorobutadiene 12 70 103 89

Hexachloroethane 12 76 103 89

2-Hexanone (n-Butyl methyl ketone) 12 81 111 104

Iodomethane (Methyl iodide) 12 99 119 107

Isopropylbenzene 12 88 104 94

4-Isopropyl-1-methyl benzene 12 83 103 92

Methyl acrylate 12 95 116 107

Methyl acrylonitrile 12 97 118 107

Methyl tert-butyl ether (MTBE)1 12 97 114 107

Methyl iso-butyl ketone (MIBK) 12 89 114 102

Methylene chloride (Dichloromethane) 12 95 119 99

Methyl ethyl ketone (2-butanone, MEK) 12 82 119 105

Methyl methacrylate 12 82 103 95

Naphthalene 12 83 103 92

N-Nitrosodimethylamine (NDMA)1, 2 3

10 83 139 102

Perchloroethene (PCE, Tetrachloroethene)1 12 82 157 92

n-Propylbenzene 12 87 105 97

Styrene 12 35 102 94

1,1,1,2-Tetrachloroethane 12 86 103 92

1,1,2,2-Tetrachloroethane 12 85 112 95

Table A–4A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and the special interest 

constituent N-nitrosodimethylamine (NDMA) in samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, 

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued

[Acceptable recovery range is between 70 and 130 percent]
Appendix A 129

Constituent 

(synonym or abbreviation)

Number of matrix-spike 

samples collected

Minimum recovery 

(percent)

Maximum recovery 

(percent)

Median recovery 

(percent)

Tetrahydrofuran 12 40 125 107

1,2,3,4-Tetramethylbenzene 12 84 108 95

1,2,3,5-Tetramethylbenzene 12 88 114 99

Toluene1 12 96 125 103

1,2,3-Trichlorobenzene 12 85 109 99

1,2,4-Trichlorobenzene 12 77 97 93

1,1,1-Trichloroethane (1,1,1-TCA) 12 86 114 98

1,1,2-Trichloroethane (1,1,2-TCA) 12 88 111 96

Trichloroethene (TCE) 12 90 100 94

Trichlorofluoromethane (CFC-11)1 12 90 117 107

1,2,3-Trichloropropane (1,2,3-TCP) 12 91 111 97

Trichlorotrifluoroethane (CFC-113)1 12 88 108 95

1,2,3-Trimethylbenzene 12 94 116 103

1,2,4-Trimethylbenzene 12 92 116 105

1,3,5-Trimethylbenzene 12 90 107 98

Vinyl bromide (Bromoethene) 12 82 118 101

Vinyl chloride (Chloroethene) 12 87 124 100

m- plus p-Xylene 12 94 109 99

o-Xylene 12 87 105 97

1

Constituent detected in groundwater sample(s).

2

Spike results from Weck Laboratories, Inc.

3

Twelve spike samples were collected; however two samples were not analyzed within the holding time for NDMA and were not included in the assessment of 

matrix spike results.

4

Tetrahydrofuran was detected in the matrix spike sample and the associated groundwater sample at concentrations five to six times the expected spike 

fortification concentration, resulting in an unusually low spike recovery.

Table A–4A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and the special interest 

constituent N-nitrosodimethylamine (NDMA) in samples collected for the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, 

California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin Project, October 2012 to May 2013.—Continued

[Acceptable recovery range is between 70 and 130 percent]
130 Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013

Table A–4B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority 

Basin Project, October 2012 to May 2013.

[Acceptable recovery range is between 70 and 130 percent]

Constituent 

(synonym or abbreviation)

Number of matrix-spike 

samples collected

Minimum recovery 

(percent)

Maximum recovery 

(percent)

Median recovery 

(percent)

Acetochlor 12 64 135 79

Alachlor 12 71 132 85

Atrazine1 12 74 108 86

Azinphos-methyl 12 63 103 82

Azinphos-methyl oxon 12 30 112 63

Benfluralin1 12 42 100 57

Carbaryl 12 76 141 92

2-Chloro-2,6-diethylacetanilide 12 74 127 84

4-Chloro-2-methylphenol 12 57 90 74

Chlorpyrifos1 12 59 101 72

Chlorpyrifos oxon 12 16 81 77

Cyfluthrin 12 45 89 54

Cypermethrin1 12 49 88 55

DCPA (Dacthal)1 12 76 110 91

Deethylatrazine (2-Chloro-4-isopropylamino6-amino-s-triazine, CIAT)112 41 122 57

Desulfinylfipronil1 12 74 120 96

Desulfinylfipronil amide 12 77 189 106

Diazinon1 12 78 110 87

3,4-Dichloroaniline1 12 69 105 82

Dichlorvos 12 12 39 16

Dicrotophos 12 9 78 22

Dieldrin1 12 62 91 79

2,6-Diethylaniline 12 77 98 91

Dimethoate1 12 32 74 55

Ethion1 12 57 102 69

Ethion monoxon 12 63 115 76

2-Ethyl-6-methylaniline 12 82 94 89

Fenamiphos 12 61 178 78

Fenamiphos sulfone 12 52 115 77

Fenamiphos sulfoxide 12 7 77 26

Fipronil1 12 76 161 88

Fipronil sulfide1 12 51 119 73

Fipronil sulfone1 12 47 112 68

Fonofos 12 65 94 79

Hexazinone1 12 37 97 49

Iprodione 12 43 91 63

Isofenphos1 12 69 140 82

Malaoxon 12 63 131 73

Malathion 12 64 120 79

Metalaxyl 12 76 142 90
Appendix A 131

Constituent 

(synonym or abbreviation)

Number of matrix-spike 

samples collected

Minimum recovery 

(percent)

Maximum recovery 

(percent)

Median recovery 

(percent)

Methidathion 12 65 114 78

Metolachlor1 12 61 123 72

Metribuzin 12 69 114 83

Myclobutanil 12 58 126 74

1-Naphthol 12 10 58 30

Paraoxon-methyl 12 36 111 53

Parathion-methyl 12 72 159 80

Pendimethalin1 12 55 134 69

cis-Permethrin1 12 45 84 53

Phorate 12 43 81 56

Phorate oxon 12 51 137 74

Phosmet 12 6 78 75

Phosmet oxon 12 45 50 49

Prometon 12 27 123 83

Prometryn1 12 67 121 80

Pronamide 12 49 123 81

Simazine1 12 68 107 81

Tebuthiuron 12 101 211 116

Terbufos 12 51 82 67

Terbufos oxon sulfone 12 51 129 61

Terbuthylazine 12 79 110 89

Tribufos1 12 38 84 50

Trifluralin1 12 43 105 59

1

Constituent detected in groundwater sample(s).

Table A–4B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority 

Basin Project, October 2012 to May 2013.—Continued

[Acceptable recovery range is between 70 and 130 percent]
Table A–5. Quality-control summary for surrogate compound recoveries of volatile organic compounds (VOCs) and pesticides and pesticide degradfor the Monterey–Salinas Shallow Aquifer (MS-SA) study unit, California Groundwater Ambient Monitoring and Assessment (GAMA) Priority Basin PrMay 2013. [NWQL, U.S. Geological Survey National Water Quality Laboratory; VOC, volitile organic compound; <, less than; >, greater than] Surrogate compound NWQL analytical schedule Constituent class analyzed Number of blanks analyzed Median recovery in blanks (percent) Number of surrogate recoveries <70 percent in blanks Number of surrogate recoveries >130 percent in blanks Number of groundwater samples analyzed Median recovery in groundwater samples (percent) Number of surr

recoveries <70 percent 

groundwate

samples 

1-Bromo-4-fluorobenzene 2020 VOC 13 89 0 0 100 88 0 1,2-Dichloroethane-d4 2020 VOC 13 126 0 4 100 127 0 Toluene-d8 2020 VOC 13 98 0 0 100 96 0 Diazinon-d10 2003 Pesticide 13 66 8 0 102 68 59 α-HCH-d6 2003 Pesticide 13 89 1 1 102 89 0 
Prepared by the Sacramento Publishing Service Center.

For more information concerning this report, contact:

Director

U.S. Geological Survey

California Water Science Center

6000 J Street, Placer Hall

Sacramento, CA 95819

dc_ca@usgs.gov

or visit our Web site at:

http://ca.water.usgs.gov
Goldrath and others—Groundwater-Quality Data in the Monterey–Salinas Shallow Aquifer Study Unit, 2013: Results from the California GAMA 

Program—Data Series 987, ver. 1.1

ISSN 2327-638X (online)

http://dx.doi.org/10.3133/DS987