In cooperation with the California State Water Resources Control Board 

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

Groundwater-Quality Data for the Madera–Chowchilla

Study Unit, 2008: Results from the California GAMA Program

California Aqueduct

Chowchilla Canal

Chowchilla River

Fresno River

ar Creek

Madera

Lake

Hensley

Lake

Millerton

Lake

")

")

") Madera

Chowchilla

Merced

Fresno

Madera Canal

Fresno River

San Joaquin River

San Joaquin River

Canal

Friant-Kern

Friant

Oakhurst

U.S. Department of the Interior

U.S. Geological Survey

Data Series 455
Cover Photographs:

Top: View looking east from sampled well located northeast of Chowchilla, California (photograph taken by Jennifer Shelton, U.S. Geological Survey.)

Bottom: Well in Madera County, California (photograph taken by Mike Solt, U.S. Geological Survey.)
Groundwater-Quality Data in the 

Madera–Chowchilla Study Unit, 2008: 

Results from the California GAMA Program

By Jennifer L. Shelton, Miranda S. Fram, and Kenneth Belitz

Prepared in cooperation with the California State Water Resources Control Board

Data Series 455

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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

reproduce any copyrighted materials contained within this report.

Suggested citation:

Shelton, J.L., Fram, M.S., and Belitz, Kenneth, 2009, Groundwater-quality data for the Madera–Chowchilla study unit, 

2008: Results from the California GAMA program: U.S. Geological Survey Data Series 455, 80 p. Available at 

http://pubs.usgs.gov/ds/455.
iii

Contents

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

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

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

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

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

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

Sample Collection and Analysis.........................................................................................................8

Data Reporting.......................................................................................................................................8

Quality-Assurance................................................................................................................................8

Water-Quality Results ..................................................................................................................................8

Quality-Control Results ........................................................................................................................8

Comparison Thresholds.......................................................................................................................9

Groundwater-Quality Data ................................................................................................................10

Field Water-Quality Indicators.................................................................................................10

Constituents of Special Interest..............................................................................................11

Inorganic Constituents..............................................................................................................11

Isotopic Tracers and Noble Gases..........................................................................................12

Radioactive Constituents..........................................................................................................12

Future Work .........................................................................................................................................12

Summary .......................................................................................................................................................13

Acknowledgments.......................................................................................................................................14

References Cited..........................................................................................................................................14

Appendix .......................................................................................................................................................54

Tables ...........................................................................................................................................................19
iv

Figures

1–3. Maps showing—

 1. The hydrogeologic provinces of California and the location of the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

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

 2. The Madera–Chowchilla Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit showing locations of major cities and major 

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

 3. The Madera–Chowchilla Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit showing the distribution of study area grid 

cells and the location of sampled grid wells and flow-path wells................................7

Tables

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

for the Madera–Chowchilla Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, April and May 2008...............................................20

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

or the slow and intermediate sampling schedules in the Madera–Chowchilla 

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

April and May 2008 .....................................................................................................................21

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

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

Quality Laboratory Schedule 2020 ...........................................................................................22

3B. Low-level 1,2-dibromo-3-chloropropane (DBCP) and 1,2-dibromoethane 

(EDB), primary uses or sources, comparative thresholds, and reporting 

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

Laboratory Schedule 1306.........................................................................................................25

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

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

National Water Quality Laboratory Schedule 2033...............................................................26

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

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

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

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

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

Water Quality Laboratory Schedule 2080 ...............................................................................31

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

thresholds, and reporting information for Weck Laboratories, Inc....................................32

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

Geological Survey (USGS) National Water Quality Laboratory Schedule 2755 ...............32

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

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

Quality Laboratory Schedule 1948 ...........................................................................................33

3I. Arsenic and iron species, comparative thresholds, and reporting information 

for the U.S. Geological Survey (USGS) Trace Metal Laboratory, Boulder, 

Colorado .......................................................................................................................................34
v

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

information for laboratories ......................................................................................................34

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

for the Lawrence Livermore National Laboratory.................................................................35

4. Field water-quality indicators in samples collected for the Madera–Chowchilla 

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

April and May 2008 .....................................................................................................................36

5. Volatile organic compounds (VOCs) and low-level 1,2-dibromo-3-chloropropane 

(DBCP) and 1,2-dibromoethane (EDB) detected in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................37

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

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................38

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

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................39

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

and low-level 1,2,3-trichloropropane (1,2,3-TCP)] detected in samples collected 

in the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................40

8. Nutrients detected in samples collected for the Madera–Chowchilla 

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

April and May 2008 .....................................................................................................................42

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

or the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................44

10. Trace elements detected in samples collected for the Madera–Chowchilla 

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

April and May 2008 .....................................................................................................................46

11. Species of inorganic arsenic and iron detected in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................50

12. Results for analyses of sisotope ratios and tritium and carbon-14 activities 

in samples collected for the Madera–Chowchilla Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, April and May 2008 ...................51

13A. Uranium isotopes detected in samples collected for the Madera–Chowchilla 

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

April and May 2008 .....................................................................................................................52

13B. Gross alpha and gross beta particle activities detected in samples collected 

for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................53
vi

Appendix Tables

A1. Analytical methods used by the U.S. Geological Survey (USGS) National Water 

Quality Laboratory (NWQL) and additional contract laboratories......................................65

A2. Preferred analytical schedules for constituents appearing on multiple schedules 

for samples collected for the Madera–Chowchilla Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, April and May 2008 ...................67

A3. Constituents detected in field blanks collected for the Madera–Chowchilla 

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

April and May 2008 .....................................................................................................................68

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

constituents of special interest detected in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................69

A4B. Quality-control summary for replicate analyses of nutrients, major and minor 

ions, trace elements, and isotope tracers detected in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................70

A4C. Quality-control summary for replicate analyses of radiochemical constituents 

detected in samples collected for the Madera–Chowchilla Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, April and May 2008 ...................72

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

compounds (VOCs) in samples collected for the Madera–Chowchilla 

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

April and May 2008 .....................................................................................................................73

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

pesticide degradates in samples collected for the Madera–Chowchilla 

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

April and May 2008 .....................................................................................................................75

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

metabolites in samples collected for the Madera–Chowchilla Groundwater 

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

May 2008 ......................................................................................................................................77

A5D. Quality-control summary for matrix-spike recoveries of N-nitrosodimethylamine 

(NDMA) and low-level 1,2,3-trichloropropane (1,2,3-TCP) in samples collected 

for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.......................................................................79

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

pesticides and pesticide degradates, and polar pesticides and metabolites in 

samples collected for the Madera-Chowchilla Groundwater Ambient Monitoring 

and Assessment (GAMA) study, California, April and May 2008........................................80
vii

AL-US action level (USEPA)

CAS Chemical Abstract Service (American Chemical Society)

CSU combined standard uncertainty

D detected in groundwater samples

E estimated or having a higher degree of uncertainty

GAMA Groundwater Ambient Monitoring and Assessment program

GPS Global Positioning System

HAL-US lifetime health advisory level (USEPA)

HPLC high-performance liquid chromatography

LRL laboratory reporting level

LSD land-surface datum

LT-MDL long-term method detection level

MADCHOW Madera–Chowchilla study unit

MADCHOWFP Madera–Chowchilla study unit flow-path well prefix

MCL-US maximum contaminant level (USEPA)

MCL-CA maximum contaminant level (CDPH)

MDL method detection limit

MRL minimum reporting level

MU method uncertainty

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

na not available

nc sample not collected

np no preference

nv no values in category

NL-CA notification level (CDPH)

NWIS National Water Information System (USGS)

PCFF-GAMA portable computer field forms program designed for GAMA sampling

QC quality control

RPD relative percent difference

RSD relative standard deviation

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

SD standard deviation

SMCL-CA secondary maximum contaminant level (CDPH)

SMCL-US secondary maximum contaminant level (USEPA)

SRL study reporting level

ssLC sample-specific critical level

TDS total dissolved solids

Abbreviations and Acronyms
viii

US United States 

V constituent detected in blanks and therefore excluded from the dataset of 

groundwater-quality results 

VOC volatile organic compound

VPDB Vienna Pee Dee Belemnite

VSMOW Vienna Standard Mean Ocean Water

Organizations

CDPH California Department of Public Health

CDWR California Department of Water Resources

USEPA U.S. Environmental Protection Agency

LLNL Lawrence Livermore National Laboratory

NAWQA National Water Quality Assessment (USGS)

NWQL National Water Quality Laboratory (USGS)

SWRCB California State Water Resources Control Board 

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

WECK Weck Laboratories, Inc.

Selected chemical names

CaCO3 calcium carbonate

CO3

–2 carbonate

CO2 carbon dioxide

HCO3

– bicarbonate

MEK methyl ethyl ketone (2-butanone)

MTBE methyl tert-butyl ether

NDMA N-nitrosodimethylamine

PCE perchloroethene (tetrachloroethylene, tetrachloroethene)

TCE trichloroethene

THM trihalomethane

Units of measurement

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

Celsius and 1 atmosphere of pressure) per gram of water

ft foot (feet)

in inch

L liter

mg milligram

mg/L milligrams per liter (parts per million)

mi mile

mL milliliter

μg/L micrograms per liter (parts per billion)
ix

μL microliter

μm micrometer

pCi/L picocurie per liter

°C degrees Celsius

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

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

material, expressed as per mil

 Notes

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

 follows:

 °F=(1.8×°C)+32

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

 1988 (NAVD 88).

 Horizontal coordinate information is referenced to the North American Datum of 1983 

 (NAD 83).

 Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

 (μS/cm at 25°C).

 Concentrations of chemical constituents in water are given either in milligrams per liter 

 (mg/L) or micrograms per liter (μg/L). Milligrams per liter is equivalent to parts per 

 million 

 (ppm) and micrograms per liter is equivalent to parts per billion (ppb).
x

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Abstract 

Groundwater quality in the approximately 860-squaremile Madera–Chowchilla study unit (MADCHOW) was 

investigated in April and May 2008 as part of the Priority 

Basin Project of the Groundwater Ambient Monitoring and 

Assessment (GAMA) Program. The GAMA Priority Basin 

Project was developed in response to the Groundwater Quality 

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

Geological Survey (USGS) in cooperation with the California 

State Water Resources Control Board (SWRCB).

The study was designed to provide a spatially unbiased assessment of the quality of raw groundwater used for 

public water supplies within MADCHOW, and to facilitate 

statistically consistent comparisons of groundwater quality 

throughout California. Samples were collected from 35 wells 

in Madera, Merced, and Fresno Counties. Thirty of the wells 

were selected using a spatially distributed, randomized gridbased method to provide statistical representation of the study 

area (grid wells), and five more were selected to provide 

additional sampling density to aid in understanding processes 

affecting groundwater quality (flow-path wells). Detection 

summaries in the text and tables are given for grid wells only, 

to avoid over-representation of the water quality in areas 

adjacent to flow-path wells.

Groundwater samples were analyzed for a large number 

of synthetic organic constituents (volatile organic compounds 

[VOCs], low-level 1,2-dibromo-3-chloropropane [DBCP] and 

1,2-dibromoethane [EDB], pesticides and pesticide degradates, polar pesticides and metabolites, and pharmaceutical 

compounds), constituents of special interest (N-nitrosodimethylamine [NDMA], perchlorate, and low-level 1,2,3-trichloropropane [1,2,3-TCP]), naturally occurring inorganic constituents (nutrients, major and minor ions, and trace elements), 

and radioactive constituents (uranium isotopes, and gross 

alpha and gross beta particle activities). Naturally occurring 

isotopes and geochemical tracers (stable isotopes of hydrogen, 

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

and dissolved noble gases also were measured to help identify 

the sources and ages of the sampled groundwater. In total, 

approximately 300 constituents and field water-quality 

indicators were investigated.

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

approximately 11 percent of the wells sampled for each analysis, and the results obtained from these samples were used to 

evaluate the quality of the data for the groundwater samples. 

Field blanks rarely contained detectable concentrations of any 

constituent, suggesting that data for the groundwater samples 

were not compromised by possible contamination during 

sample collection, handling or analysis. Differences between 

replicate samples were within acceptable ranges. Matrix spike 

recoveries were within acceptable ranges for most compounds.

This study did not attempt to evaluate the quality of 

water delivered to consumers; after withdrawal from the 

ground, raw groundwater typically is treated, disinfected, or 

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

not to raw groundwater. However, to provide some context 

for the results, concentrations of constituents measured in the 

raw groundwater were compared with regulatory and nonregulatory health-based thresholds established by the U.S. 

Environmental Protection Agency (USEPA) and the California Department of Public Health (CDPH), and with aesthetic 

and technical thresholds established by CDPH. Comparisons 

between data collected for this study and drinking-water 

thresholds are for illustrative purposes only, and are not 

indicative of compliance or non-compliance with regulatory 

thresholds.

Groundwater-Quality Data in the Madera–Chowchilla 

Study Unit, 2008: Results from the California GAMA 

Program

By Jennifer L. Shelton, Miranda S. Fram, and Kenneth Belitz
2 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

The concentrations of most constituents detected in 

groundwater samples from MADCHOW wells were below 

drinking-water thresholds. Organic compounds (VOCs and 

pesticides) were detected in about 40 percent of the samples 

from grid wells, and most concentrations were less than 1/100 

of regulatory or non-regulatory health-based thresholds, 

although the concentrations of low-level DBCP in 10 percent 

and low-level EDB in 3 percent of the samples from grid wells 

were above the corresponding USEPA maximum contaminant 

levels (MCL-USs). Perchlorate was detected in 70 percent of 

the samples from grid wells, and most concentrations were 

less than one-tenth of the CDPH maximum contaminant level 

(MCL-CA). Low-level 1,2,3-TCP was detected in 33 percent of the samples from grid wells, and all concentrations 

were less than 1/1,000 of the USEPA lifetime health advisory 

level (HAL-US). Most concentrations of trace elements and 

nutrients in samples were below regulatory and non-regulatory 

health-based thresholds. Concentrations were above the MCLUS for nitrate in 7 percent of the samples from grid wells, for 

arsenic and uranium in 13 percent each of the samples from 

grid wells; and the concentration of vanadium was above the 

CDPH notification level (NL–CA) in 3 percent of the samples 

from grid wells. Detections of radioactive constituents were 

below regulatory and non-regulatory health-based thresholds 

in most samples. Combined activities of uranium isotopes 

were detected above the MCL-CA in 20 percent of the subset 

of 25 grid well samples analyzed, and gross alpha particle 

activity was detected above the MCL-US in 20 percent of 

the samples from the 30 total grid wells. Most of the samples 

from MADCHOW grid wells had concentrations of major and 

minor ions, total dissolved solids, and trace elements below 

the CDPH secondary maximum contaminant levels (SMCLCAs), which are nonenforceable thresholds set for aesthetic 

and technical concerns. Twenty percent of the samples from 

grid wells contained specific-conductance values, or concentrations of chloride, total dissolved solids, or manganese above 

the respective SMCL–CAs.

Introduction 

Groundwater comprises nearly half of the water used 

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

assess the quality of ambient groundwater in aquifers used for 

public supply and to establish a baseline groundwater quality monitoring program, the California State Water Resources 

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

Geological Survey (USGS) and Lawrence Livermore National 

Laboratory (LLNL), implemented the Groundwater Ambient 

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

swrcb.ca.gov/gama). The GAMA Program currently consists 

of three projects: GAMA Priority Basin Project, conducted by 

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

Well Project, conducted by the SWRCB; and GAMA Special 

Studies, conducted by LLNL. 

The SWRCB initiated the GAMA Priority Basin Project 

in response to legislative mandates (Supplemental Report of 

the 1999 Budget Act 1999-00 Fiscal Year, and the Groundwater Quality Monitoring Act of 2001 [Sections 10780-10782.3 

of the California Water Code, Assembly Bill 599]) to assess 

and monitor the quality of groundwater used as public supply 

for municipalities in California. The GAMA Priority Basin 

Project is a comprehensive assessment of statewide groundwater quality designed to help better understand and identify 

risks to groundwater resources, and to increase the availability 

of information about groundwater quality to the public. For 

the Priority Basin Project, the USGS, in collaboration with the 

SWRCB, developed the monitoring plan to assess groundwater basins through direct and other statistically reliable sample 

approaches (Belitz and others, 2003; State Water Resources 

Control Board, 2003). Key aspects of the project are interagency collaboration and cooperation with local water agencies and well owners. Local participation in the project is 

entirely voluntary. 

The GAMA Priority Basin Project is unique in California 

because it includes many chemical analyses that are not otherwise available in statewide water-quality monitoring datasets. 

Groundwater samples collected for the project are analyzed for 

a large number of chemical constituents using analytical methods that have much lower detection limits than those required 

by the California Department of Public Health (CDPH). 

These analyses will be especially useful for providing an early 

indication of changes in groundwater quality. In addition, the 

GAMA Priority Basin Project analyzes samples for a suite of 

constituents more extensive than that required by CDPH, and 

for a suite of chemical and isotopic tracers of hydrologic and 

geochemical processes. A broader understanding of groundwater composition will be useful for identifying the natural 

and human factors affecting water quality. Understanding the 

occurrence and distribution of chemical constituents of significance to water quality is important for the long-term management and protection of groundwater resources.
Introduction 3

 The range of hydrologic, geologic, and climatic conditions that exist in California must be considered when assessing groundwater quality. Belitz and others (2003) partitioned 

the state into ten hydrogeologic provinces, each with distinctive hydrologic, geologic, and climatic characteristics 

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

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

approximately 16,000 active and standby public-supply wells 

are located in groundwater basins within these hydrologic 

provinces. These groundwater basins, defined by the California Department of Water Resources (CDWR), generally 

consist of fairly permeable, unconsolidated deposits of alluvial 

or volcanic origin (California Department of Water Resources, 

2003). Groundwater basins were prioritized for sampling on 

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

with secondary consideration given to municipal groundwater 

use, agricultural pumping, the number of formerly leaking 

underground fuel tanks, and pesticide applications within the 

basins (Belitz and others, 2003). In addition, some groundwater basins or groups of adjacent similar basins with relatively 

few public-supply wells were assigned high priority so that all 

hydrogeologic provinces would be represented in the subset of 

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

were grouped into 35 study units. Some areas outside of the 

defined groundwater basins were included to represent the 

20 percent of public-supply wells not located in the 

groundwater basins. 

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

assessment of the current quality of the groundwater resource, 

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

(3) Understanding: identification of the natural and human 

factors affecting groundwater quality (Kulongoski and Belitz, 

2004). This report is one of a set of reports presenting waterquality data collected in each study unit (Wright and others, 

2005; Bennett and others, 2006; Kulongoski and others, 2006; 

Fram and Belitz, 2007; Kulongoski and Belitz, 2007; Burton 

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

Mathany and others, 2008; Shelton and others, 2008; Schmitt 

and others, 2008; Ray and others, 2009; Fram and others, 

2009). Subsequent reports will address the status, trends, and 

understanding aspects of the water-quality assessments.

The Madera–Chowchilla GAMA study unit, hereinafter referred to as MADCHOW, is in the southern part of the 

Central Valley Hydrogeologic Province (fig. 1) and is the 

24th study unit sampled by the GAMA Priority Basin Project. 

MADCHOW was considered a high priority for sampling on 

the basis of the number of public-supply wells, the reliance 

on groundwater for drinking-water resources, the amount of 

agricultural pumpage, the number of leaking underground fuel 

tanks, and the extent of pesticide applications (Belitz and 

others, 2003). 

Purpose and Scope

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

design and the study methods; (2) to present the results of 

quality-control tests; and (3) to present the analytical results 

for groundwater samples collected in MADCHOW. Groundwater samples were analyzed for organic and inorganic 

constituents, field parameters, isotopic tracers, and radioactive 

constituents. The chemical data presented in this report were 

evaluated by comparison to State and Federal drinking-water 

regulatory and non-regulatory health-based standards that are 

applied to treated drinking water. Thresholds considered for 

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

Protection Agency (USEPA) and CDPH. The data presented in 

this report are intended to characterize the quality of untreated, 

raw groundwater resources within the study unit, not the 

treated drinking water delivered to consumers by water purveyors. Discussion of the factors that influence the distribution 

and occurrence of the constituents detected in groundwater 

samples will be the subject of subsequent publications.

Hydrogeologic Setting 

The Madera–Chowchilla study unit (MADCHOW) is in 

the southern part of the Central Valley hydrogeologic province (fig. 1). The study unit is composed of the Madera and 

the Chowchilla groundwater subbasins of the San Joaquin 

Valley, as defined by CDWR (California Department of Water 

Resources, 2003, 2008a, and 2008b). MADCHOW covers an 

area of approximately 860 square miles (mi2), primarily in 

Madera County, with a small portion in Merced County to the 

north of the Chowchilla River and a small portion in Fresno 

County to the south of the San Joaquin River (fig. 2). The 

study unit is bounded partially on the north by the Chowchilla 

River, approximately on the west and south by the San Joaquin River, and on the east by foothills of the Sierra Nevada 

Mountains. 

Similar to most areas in the San Joaquin Valley of California, MADCHOW has a Mediterranean climate, with hot, 

dry summers, and cool, moist winters. Average annual rainfall 

is 11 inches (in.) over most of the study unit, increasing to 

15 in. per year in the foothills of the Sierra Nevada (Western 

Regional Climate Center, 2009). The primary surface-water 

features in MADCHOW are the San Joaquin, Fresno, and 

Chowchilla Rivers, and the Friant–Kern, Madera, and 

Chowchilla canals (fig. 2). 
4 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Figure 1. The hydrogeologic provinces of California and the location of the Madera–Chowchilla Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit.

0 50 100 200 MILES

0 50 100 200 KILOMETERS

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

National Elevation Dataset, 2006 

Albers Equal Area Conic Projection

124° 122° 120° 118° 116° 114°

42°

40°

38°

36°

34°

32°

Transverse

and Selected

Peninsular Ranges

Southern

California Islands

Desert

Southern

Coast

Ranges

Basin and 

Range

Sierra

Nevada

Central

Valley

Modoc

Plateau and

Cascades

Klamath

Mountains

Northern

Coast

Ranges

San Diego

Drainages

MEXICO

ARIZONA

NEVADA

OREGON

Pacific

Ocean

San Diego

Los Angeles

Bakersfield

Redding

Sacramento

San Francisco

Madera-Chowchilla 

Study Unit
Introduction 5

Figure 2. The Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing locations of major 

cities and major hydrologic features.

Delta-Mendota Canal

California Aqueduct

Chowchilla Canal

Chowchilla River

Fresno River

Madera

Lake

Hensley

Lake

Millerton

Lake

")

")

")

UV49

UV41

UV99

§ ̈¦5

UV33

UV180

UV41

MARIPOSA COUNTY

MADERA COUNTY

FRESNO COUNTY

MERCED COUNTY

Madera

Friant

Oakhurst

Chowchilla

Merced

Mendota Fresno

Canal

Madera Canal

Fresno River

Friant-Kern

San Joaquin River

San Joaquin

River

0 4 8 16 MILES

0 4 8 16 KILOMETERS

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006,

Albers Equal Area Conic Projection

EXPLANATION

MADCHOW study unit

Major roads and highways

County boundary

Streams and canals

Intermittent streams

120° 30' 120°

37°
6 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

The primary aquifer system in the San Joaquin Valley consists of Quaternary-age unconsolidated continental 

deposits. The deposits are composed of alluvial-fan and fluvial 

gravel, sand, slit, and clay sediments, interbedded with lesser 

amounts of lacustrine deposits. The sediments were derived 

from the weathering of the granitic rocks of the Sierra Nevada 

to the east. The sediments generally are coarsest in the eastern 

part of the valley along the foothills and become finer westward towards the San Joaquin River, the axial trough of the 

San Joaquin Valley (Gronberg and others, 1998). The continental deposits bearing freshwater increase in thickness from 

north to south in the San Joaquin Valley, and are up to 3,000 

feet (ft) thick in MADCHOW (Bertoldi and others, 1991). The 

Corcoran Clay the thickest of the lacustrine deposits, is present 

in the western half of MADCHOW.

Methods 

Methods used for the GAMA program were selected 

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

plan suitable for statistical analysis; (2) collect samples in a 

consistent manner statewide; (3) analyze samples using proven 

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

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

relevant documentation. The Appendix to this report contains 

detailed descriptions of the sample collection protocols and 

analytical methods, the quality-assurance methods, and the 

results of analyses of quality-control samples.

Study Design

The wells selected for sampling in this study reflect the 

combination of two well-selection strategies. Thirty “grid” 

wells were selected to provide a statistically unbiased, spatially distributed assessment of the quality of groundwater 

resources used for public drinking-water supply, and five 

additional “flow-path” wells were selected to aid in the evaluation of water-quality changes along the regional groundwater 

flow gradient and between shallow and deeper portions of the 

aquifer.

The spatially distributed wells were selected using a randomized grid-based method (Scott, 1990). MADCHOW was 

subdivided into 30 grid cells approximately 30 mi2 (78 square 

kilometers [km2]) in area (fig. 3). This grid-cell size met 

GAMA objectives for the Central Valley hydrogeologic province of a sampling density of at least one well per 38.6 mi2

(100 km2) (Bennett and others, 2006). The objective was to 

select one public-supply well per grid cell. If a grid cell contained more than one public-supply well, each well randomly 

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

sampling criteria (for example, sampling point located prior to 

treatment, capability to pump for several hours, and available 

well-construction information), and for which permission to 

sample could be obtained, then was sampled. If a grid cell 

contained no accessible public-supply wells, domestic and 

irrigation wells were considered for sampling. An attempt 

was made to select domestic and irrigation wells with depths 

and screened intervals similar to those in public-supply wells 

in the area. In this fashion, one well was selected in each cell 

to provide a spatially distributed, randomized monitoring 

network. 

Wells sampled as part of the spatially distributed, randomized grid-cell network are hereafter referred to as “grid 

wells.” The 30 grid wells sampled in MADCHOW were 

numbered in the order of sample collection with the prefix 

“MADCHOW” (fig. 3).

Five additional wells were sampled in the northern part of 

MADCHOW. These additional wells were selected to provide greater sampling density along a generalized flow path 

parallel to the regional northeast to southwest groundwater 

flow gradient (fig. 3). In addition, these flow-path wells were 

chosen to be shallower than the nearby grid wells to evaluate 

differences between shallow and deeper portions of the aquifer 

system. These five non-randomized wells were not included in 

the statistical characterization of water quality in MADCHOW 

because inclusion would have resulted in overrepresentation 

of certain grid cells. The five flow-path wells were numbered 

in the order of sample collection with the prefix “MADCHOWFP” (“FP” indicating “flow path”) (fig. 3).

Table 1 (all tables at back of report) provides the GAMA 

alphanumeric identification number for each well, along with 

the date sampled, sampling schedule, well elevation, well type, 

and well-construction information. Wells classified as “production wells” have pumps that pump the groundwater from 

the aquifer to a distribution system. The wells were sampled 

during April and May 2008. The 30 grid wells included 

19 wells classified by CDPH as public-supply wells. Publicsupply wells are not identified in table 1 because of security 

and confidentiality requirements; the number of public-supply 

wells in the grid-well network is reported to demonstrate that 

the network is representative of the parts of the aquifer in 

the study unit that are used for public supply. The remaining 

11 grid wells that were not public-supply wells were selected 

because no public-supply wells were accessible for sampling 

in some grid cells, but these eleven wells were screened 

within similar depth zones as public-supply wells within the 

study unit and included 8 irrigation and 3 domestic wells. The 

5 flow-path wells included 2 domestic wells, 1 irrigation well, 

and 2 wells classified as public-supply wells by CDPH. 

Well locations and identifications were verified using 

GPS, 1:24,000 scale USGS topographic maps, comparison 

with existing well information in USGS and CDPH databases, 

and information provided by well owners. Driller’s logs for 

wells were obtained when available. Well information was 

recorded by hand on field sheets and electronically using 

specialized software on field laptop computers. All information was verified and then uploaded into the USGS National 

Water Information System (NWIS). Well owner information is 

confidential. Well location information and all chemical data 

currently are inaccessible from NWIS’s public website.
Methods 7

Figure 3. The Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing the distribution of 

study area grid cells and the location of sampled grid wells and flow-path wells. Alphanumeric identification numbers for grid wells 

have the prefix “MADCHOW”; only the numeric portions are shown on the map. Alphanumeric identification numbers for flow-path 

wells have the prefix “MADCHOWFP”; only “FP” and the numeric portions are shown on the map.

Delta-Mendota Canal

California Aqueduc t

Chowchilla Canal

Chowchilla River

Fresno River

Madera

Lake

Hensley

Lake

Millerton

Lake

!

!

!

!

!

!

!

!

!

")

MADCHOW study unit

Major roads and highways

County boundary

Streams and canals

Intermittent streams

Grid well

Flow-path well

Madera

Fresno

Chowchilla

Merced

Mendota

MARIPOSA COUNTY

MADERA COUNTY

FRESNO COUNTY

MERCED COUNTY

Canal

Friant-Kern

Friant

Madera Canal

San Joaquin River

Oakhurst

")

")

")

0 4 8 16 MILES

0 4 8 16 KILOMETERS

Shaded relief derived from U.S. Geological Survey

National Elevation Dataset, 2006,

Albers Equal Area Conic Projection

EXPLANATION

120° 30' 120°

37°

FP-03 FP-01

01

FP-01

FP-04

07

17

15

19

06

04

21

FP-05

05

16

03

18

14

08

11

02

01

13

27

FP-02

09

25

20

29

22 23

28

26

24

30

12

10
8 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

The wells in MADCHOW were sampled using a tiered 

analytical approach. All wells were sampled for a standard 

set of constituents, including field water-quality indicators 

(alkalinity, dissolved oxygen, pH, specific conductance, and 

temperature), organic constituents (VOCs, pesticides, and lowlevel analyses of DBCP and EDB), perchlorate, and low-level 

analyses of 1,2,3-TCP, inorganic constituents (nutrients, major 

and minor ions, and trace elements), radioactive constituents 

(uranium isotopes, and gross alpha and gross beta particle 

activities), and geochemical and age-dating tracers (stable 

isotopes of hydrogen and oxygen of water, carbon isotopes, 

dissolved noble gases, and tritium). The standard set of constituents was termed the intermediate schedule (table 2). Wells 

on the slow schedule were sampled for all the constituents 

on the intermediate schedule, plus turbidity, pharmaceutical 

compounds, NDMA, and species of arsenic and iron (table 2). 

Intermediate and slow refer to the time required to sample the 

well for all the constituents on the schedule. Generally, one 

slow or two intermediate wells could be sampled in 1 day. 

Many of the other GAMA study units have had a shorter list 

of standard constituents and have termed the standard set the 

fast schedule because three or four fast wells could be sampled 

in 1 day. In MADCHOW, 25 of the wells were sampled on the 

intermediate schedule and 10 were sampled on slow schedule.

Sample Collection and Analysis

Samples were collected in accordance with the protocols 

established by the USGS National Water Quality Assessment 

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

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

dated). These sampling protocols ensure that a representative 

sample of groundwater is collected at each site and that the 

samples are collected and handled in a way that minimizes 

the potential for contamination of samples. The methods used 

for sample collection are described in the Appendix section 

“Sample Collection and Analysis”.

Tables 3A–K list the compounds analyzed in each constituent class. Groundwater samples were analyzed for 85 VOCs 

(table 3A); low-level DBCP and EDB (table 3B); 81 pesticides and pesticide degradates (table 3C); 58 polar pesticides 

and metabolites (table 3D); 14 pharmaceutical compounds 

(table 3E); 3 constituents of special interest (table 3F); 5 nutrients (table 3G); 10 major and minor ions and total dissolved 

solids (table 3H); 25 trace elements (table 3H); arsenic and 

iron species (table 3I); stable isotopes of hydrogen and oxygen 

of water, stable isotopes of carbon, and 9 radioactive constituents, including carbon-14 activity, tritium activity, gross alpha 

and gross beta particle activities (72-hour and 30-day counts), 

and uranium isotope activities (table 3J); helium stable isotope 

ratios, 5 dissolved noble gases and tritium activity (table 3K). 

The methods used for sample analysis are described in the 

Appendix section of this report “Sample Collection and 

Analysis.”

Data Reporting

The methods and conventions used for reporting the data 

are described in the Appendix of this report. Seven constituents analyzed in this study were measured by more than one 

method at the USGS National Water Quality Laboratory 

(NWQL), but only the results from the preferred method are 

reported (see Appendix section “Constituents on Multiple Analytical Schedules” and table A2). Concentrations of 1,2,3-TCP, 

and arsenic and iron, and tritium activities also were measured by more than one laboratory, and both sets of results are 

reported for these constituents. For field water-quality indicators that also were measured in the laboratory (alkalinity, pH, 

and specific conductance), the field analyses were preferred, 

although both sets of results are reported. 

Quality-Assurance

The quality-assurance and quality-control procedures 

used for this study followed the protocols used by the USGS 

NAWQA program (Koterba and others, 1995) and described 

in the USGS National Field Manual (U.S. Geological Survey, 

variously dated). The quality-assurance plan followed by 

the NWQL, the primary laboratory used to analyze samples 

for this study, is described in Maloney (2005) and Pirkey 

and Glodt (1998). Quality-control (QC) samples collected in 

the MADCHOW study include source-solution blanks, field 

blanks, replicates, and matrix and surrogate spikes. QC samples were collected to evaluate potential contamination, bias or 

variability of the data that may have resulted from collecting, 

processing, storing, transporting, and analyzing the samples. 

Quality-control procedures and quality-control sample results 

are described in the Appendix section “Quality Assurance”.

Water-Quality Results 

Quality-Control Results

Results of quality-control analyses (blanks, replicates, 

matrix spikes, and surrogates) were used to evaluate the 

quality of the data for the groundwater samples. Of the 

approximately 300 constituents analyzed, only silica and gross 

alpha particle activity (72-hour count) were detected in at 

least one field blank collected in this study unit. On the basis 

of detections in field blanks collected for this and previous 

GAMA study units, detections reported by the laboratory for 

one organic compound (toluene) were considered suspect 

and, therefore, this constituent was removed from the set of 

groundwater quality data presented in this report (see table A3

and additional discussion in the Appendix). Results from the 

replicates confirm that the procedures used to collect and analyze the samples were consistent. Ninety-eight percent of the 

replicate pairs analyzed for constituents detected in samples 

had variability between values within acceptable limits; 
Water-Quality Results 9

additional discussion can be found in the Appendix. Median 

matrix-spike recoveries for 42 of the 224 organic constituents 

analyzed were lower than the acceptable limits (tables 3A, 3C, 

and 3D), which may indicate that these constituents might not 

have been detected in some samples if their concentrations in 

these samples had been near the LRLs. The quality-control 

results are described in the Appendix section “Quality-Control 

Results.” 

Comparison Thresholds

Concentrations of constituents detected in groundwater 

samples were compared with CDPH and USEPA regulatory 

and non-regulatory drinking-water health-based thresholds 

and thresholds established for aesthetic purposes (California 

Department of Public Health, 2008a, 2008b; U.S. Environmental Protection Agency, 2008a, 2008b). The chemical data 

presented in this report are meant to characterize the quality 

of the untreated groundwater resources within MADCHOW, 

and are not intended to represent the treated drinking water 

delivered to consumers by water purveyors. The chemical composition of treated drinking water may differ from 

untreated groundwater because treated drinking water may be 

disinfected, filtered, mixed with other waters, and exposed to 

the atmosphere before being delivered to consumers. Comparisons between concentrations of constituents in raw, untreated 

groundwater and drinking-water thresholds are for illustrative 

purposes only, and are not indicative of compliance or 

non-compliance with drinking-water regulations.

The following thresholds were used for comparisons:

• MCL—Maximum Contaminant Level. Legally 

enforceable standards that apply to public water 

systems and are designed to protect public health by 

limiting the levels of contaminants in drinking water. 

MCLs established by the USEPA are the minimum 

standards with which states are required to comply, 

and individual states may choose to set more stringent 

standards. CDPH has established MCLs for additional 

constituents not regulated by the USEPA, as well as 

lowered the threshold concentration for a number of 

constituents with MCLs established by the USEPA. In 

this report, a threshold set by the USEPA and adopted 

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

that is more stringent than the MCL-US is labeled 

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

detected at concentrations greater than an MCL-US 

or MCL-CA thresholds in samples collected for the 

GAMA Priority Basin Project, but these detections do 

not constitute violations of CDPH regulations.

• AL—Action Level. Legally enforceable standards 

that apply to public water systems and are designed to 

protect public health by limiting the levels of copper 

and lead in drinking water. Detections of copper or 

lead above the action-level thresholds trigger requirements for mandatory water treatment to reduce the 

corrosiveness of water to water pipes. The action levels 

established by the USEPA and CDPH currently are the 

same, thus the thresholds are labeled “AL-US” in this 

report.

• SMCL—Secondary Maximum Contaminant Level. 

Non-enforceable standards applied to constituents that 

affect the aesthetic qualities of drinking water, such as 

taste, odor, and color, or technical qualities of drinking 

water, such as scaling and staining. Both the USEPA 

and CDPH define SMCLs, but unlike MCLs, SMCLs 

established by CDPH are not required to be at least 

as stringent as those established by USEPA. SMCLs 

established by CDPH are used in this report (SMCLCA) for all constituents that have SMCL-CA values. 

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

has been defined.

• NL—Notification Level. Health-based notification 

levels established by CDPH for some of the constituents in drinking water that lack MCLs (NL-CA). If a 

constituent is detected above its NL-CA, California 

state law requires timely notification of local governing 

bodies and recommends consumer notification.

• HAL—Lifetime Health Advisory Level. The maximum 

concentration of a constituent at which its presence in 

drinking water is not expected to cause any adverse 

carcinogenic effects for a lifetime of exposure. HALs 

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

calculated assuming consumption of 2 liters (2.1 

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

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

person’s exposure comes from drinking water.

• RSD5—Risk-Specific Dose. The concentration of 

a constituent in drinking water corresponding to an 

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

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

RSD5s are calculated by dividing the 10-4 cancer risk 

concentration established by the USEPA by ten 

(RSD5-US).

For constituents with MCLs, detections in groundwater samples were compared to the MCL-US or MCL-CA. 
10 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Constituents with SMCLs were compared with the SMCLCA. For chloride, sulfate, specific conductance, and total 

dissolved solids, CDPH defines a “recommended” and an 

“upper” SMCL-CA; concentrations of these constituents 

in groundwater samples were compared with both levels. 

The SMCL-US values for these constituents correspond to 

the recommended SMCL-CA. Detected concentrations of 

constituents that lack an MCL or SMCL were compared to 

the NL-CA. For constituents that lack an MCL, SMCL, or 

NL-CA, detected concentrations were compared with the 

HAL-US. For constituents that lack an MCL, SMCL, NL-CA, 

or HAL-US, detected concentrations were compared with the 

RSD5-US. Note that if a constituent has more than one type of 

established threshold, using this hierarchy to select the comparison threshold will not necessarily result in selection of the 

threshold with the lowest concentration. For example, zinc has 

an SMCL-CA of 5,000 μg/L and a HAL-US of 2,000 μg/L, 

and the comparison threshold selected by this hierarchy is the 

SMCL-CA. The comparison thresholds used in this report are 

listed in tables 3A–K for all constituents and in tables 4–13 for 

constituents detected in groundwater samples from MADCHOW. Note that not all constituents analyzed for this study 

have established thresholds. Detections of constituents at 

concentrations greater than the selected comparison thresholds 

are marked with asterisks in tables 4–13. 

Groundwater-Quality Data

Results from analyses of raw (untreated) groundwater 

samples from MADCHOW are presented in tables 4–13. 

Groundwater samples collected in MADCHOW were analyzed for up to 229 organic constituents and constituents of 

special interest, of which 197 were not detected in any of the 

samples (tables 3A–D and 3F). The samples were analyzed for 

up to 64 naturally occurring inorganic constituents, isotopic 

tracers, and radioactivity (tables 3G–K). The results tables 

present only the constituents that were detected and list only 

samples in which at least one constituent was detected. The 

tables containing organic constituent classes and constituents 

of special interest that were analyzed at all of the grid wells 

include the number of wells at which each constituent was 

detected, the percentage of grid wells in which each constituent was detected, and the total number of constituents detected 

at each well (tables 5–7). Results from the flow-path wells are 

presented in the tables, but these results were excluded from 

the detection frequency calculations to avoid statistically overrepresenting the areas near the vicinity of the flow-path wells.

Table 4 includes water-quality indicators measured in the 

field and at the NWQL, and tables 5–13 present the results of 

groundwater analyses organized by constituent classes: 

• Organic constituents

• VOCs and low-level DBCP and EDB (table 5)

• Pesticides and pesticide degradates and polar pesticides and metabolites (tables 6A,6B)

• Constituents of special interest (table 7)

• Inorganic constituents

• Nutrients (table 8)

• Major and minor ions and total dissolved solids 

(table 9)

• Trace elements (table 10)

• Species of arsenic and iron (table 11)

• Isotopic tracers (table 12)

• Radioactive constituents (tables 13A,13B)

Results for pharmaceutical compounds and dissolved 

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

this report; they will be included in subsequent publications. 

Field Water-Quality Indicators

Field and laboratory measurements of turbidity, dissolved 

oxygen, water temperature, pH, specific conductance, and 

alkalinity are presented in table 4. Alkalinity and dissolved 

oxygen are used as indicators of natural processes that control 

water chemistry. The pH value indicates the acidity or basicity 

of the water. Low pH in water may contribute to corrosion 

and high pH in water may contribute to scaling. All pH values 

were within the SMCL-US range for pH, 6.5 to 8.5 standard 

units. Specific conductance is a measure of the electrical 

conductivity of the water and is proportional to the amount of 

total dissolved solids (TDS) in the water. Samples from two 

grid wells had field and laboratory specific-conductance values 

above the upper SMCL-CA, samples from three additional 

grid wells had field and laboratory specific-conductance values 

above the recommended SMCL-CA, and specific-conductance 

values for samples from the remaining 25 grid wells were 

below the recommended SMCL-CAOrganic 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. VOCs generally persist longer in groundwater than 

in surface water because groundwater is isolated from the 

atmosphere. Of the 85 VOCs and low-level DBCP and EDB 

analyzed, 12 were detected in groundwater samples; concentrations in all but 3 samples were below health-based thresholds, and most were less than about one one-hundredth of the 

threshold levels (table 5). Chloroform, a byproduct of drinking-water disinfection; 1,2-dibromo-3-chloropropane (DBCP), 

a fumigant; and perchloroethene (PCE), a solvent used for drycleaning, were detected in 10 percent or more of the grid well 

samples. Chloroform and PCE are among the most commonly 

detected VOCs in groundwater nationally (Zogorski and others, 2006). One or more VOCs were detected in samples from 

9 of the 30 grid wells. The fumigant, DBCP, was detected 

above the MCL-US in three samples from grid wells and one 

of these samples also contained the fumigant, EDB, above the 

MCL-US. 
Water-Quality Results 11

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

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

139 pesticides and pesticide degradates and polar pesticides 

and metabolites analyzed, 11 were detected in groundwater 

samples from grid wells; all concentrations were below healthbased thresholds, and all were less than 1/100 of the threshold 

values (tables 6A, 6B). The herbicides atrazine, simazine, 

and diuron, and two herbicide degradates: deethylatrazine, a 

degradate of atrazine; and 3,4-dichloroaniline, a degradate of 

diuron, were detected in 10 percent or more of the grid-well 

samples (tables 6A, 6B). Deethylatrazine, atrazine, and simazine are among the most commonly detected pesticide compounds in groundwater nationally (Gilliom and others, 2006). 

Pesticide compounds were detected in samples from 8 of the 

30 grid wells. The grid wells with detections in table 6B are a 

subset of the grid wells with detections in table 6A; therefore 

the detection frequency of 27 percent applies to both tables. 

Note the detection frequency in table 6A does not include the 

three fumigants already presented as volatile organic compounds in table 5; if these fumigants were included, the detection frequency for any pesticide(s) in the grid wells would be 

30 percent.

Constituents of Special Interest

NDMA, perchlorate, and 1,2,3-TCP are constituents of 

special interest in California because they have been detected 

recently in water supplies (California Department of Public 

Health, 2008c). Five grid wells were sampled for NDMA, 

all 30 grid wells were sampled for perchlorate and low-level 

1,2,3-TCP, and all concentrations were below health-based 

thresholds. NDMA was detected in one grid-well sample at a 

concentration of one-fourth of the NL-CA (table 7). Perchlorate was detected in 70 percent of the grid-well samples, all 

concentrations were below one-third and most were below 

one-tenth of the MCL-CA. Thirty-three percent of the grid 

well samples had detections of low-level 1,2,3-TCP, and 

all concentrations were below one one-thousandths of the 

HAL-US. 

Inorganic Constituents

Unlike the organic constituents and the constituents of 

special interest, most of the inorganic constituents naturally 

are present in groundwater, although their concentrations may 

be influenced by human activities.

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

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

depending on the oxidation-reduction state of the groundwater. High concentrations of nitrate can adversely affect human 

health, particularly the health of infants. All concentrations of 

ammonia and nitrite, and nearly all concentrations of nitrate 

measured in samples from MADCHOW grid wells were 

below health-based thresholds (table 8). Nitrate concentrations 

were above the USEPA MCL in 2 of the 30 grid well samples.

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

content, and levels of certain trace elements in groundwater 

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

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

scaling and staining. Although no adverse health effects are 

associated directly with these properties, they may reduce 

consumer satisfaction with the water or may have economic 

effects. CDPH has established non-enforceable thresholds 

(SMCL-CAs) that are based on aesthetic or technical properties rather than health-based concerns for chloride and sulfate, 

TDS, iron, manganese, silver, and zinc.

Chloride concentrations were above the upper SMCL-CA 

in 1 grid well sample, but below the recommended SMCL-CA 

in the other 29 grid well samples (table 9). TDS concentrations were above the upper SMCL-CA in 2 grid well samples, 

above the recommended SMCL-CA in 4 grid well samples, 

and below the recommended SMCL-CA in the remaining 24 

grid well samples. Sulfate concentrations were below the recommended SMCL-CA in all MADCHOW grid well samples. 

Manganese was detected at a concentration above the recommended SMCL-CA in 1 of the 30 grid well samples (table 10). 

Concentrations of iron, silver, and zinc in all MADCHOW 

grid well samples were below the recommended SMCL-CAs.

One of the major and minor ions (fluoride) and eighteen 

of the trace elements analyzed in this study have regulatory or 

non-regulatory health-based thresholds (table 3H). Detected 

concentrations of fluoride were below the MCL-CA in all 

30 MADCHOW grid well samples (table 9). Of the 18 trace 

elements with health-based thresholds, 2 were not detected 

in grid well samples; all detected concentrations of 13 of 

these trace elements were below health-based thresholds; and 

some concentrations of 3 of these trace elements (arsenic, 

vanadium, and uranium) were above health-based thresholds 

(table 10). Arsenic concentrations were above the MCL-US in 

4 of the 30 grid well samples, the concentration of vanadium 

was above the NL-CA in 1 of these samples, and uranium 

concentrations were above the MCL-US in 4 different grid 

well samples. Samples from 22 of the 30 grid wells had no 

trace elements detected at concentrations above health-based 

thresholds. 
12 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Arsenic and iron occur as different species, depending on the oxidation-reduction state of the groundwater. The 

oxidized and reduced species have different solubilities in 

groundwater and may have different effects on human health. 

The relative proportions of the oxidized and reduced species 

of each element can be used to aid in interpretation of the 

oxidation–reduction state of the aquifer. Concentrations of 

total arsenic, total iron, and the concentrations of either the 

reduced or the oxidized species of each element are reported 

in table 11. The concentration of the other species can be 

calculated by difference. The concentrations of arsenic and 

iron reported in table 11 may be different than those reported 

in table 10 because different analytical methods were used 

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

considered to be more accurate.

Isotopic Tracers and Noble Gases

Isotopic ratios of oxygen and hydrogen in water, tritium 

and carbon-14 activities, and concentrations of dissolved noble 

gases may be used as tracers of natural processes affecting 

groundwater composition and may be used to estimate the age 

of groundwater. Hydrogen and oxygen stable-isotope ratios in 

water (table 12) aid in interpretation of the sources of groundwater recharge. The stable-isotope ratios of water reflect the 

altitude, latitude, and temperature of precipitation and also 

the extent of evaporation of water from surface water bodies 

or soils prior to infiltration into the aquifer. Concentrations 

of dissolved noble gases are used to estimate the conditions 

of groundwater recharge, particularly the temperature of the 

recharge water. Noble gases dissolve in water that is in contact 

with the atmosphere, and the solubilities of the different noble 

gas species vary with temperature. Noble gas analyses were 

not completed in time to be included in this report; results will 

be presented in a subsequent publication.

Tritium and carbon-14 activities (table 12), and helium 

isotope ratios also provide information about the age (time 

since recharge) of the groundwater. Tritium is a short-lived 

radioactive isotope of hydrogen that is incorporated into 

the water molecule. Low levels of tritium are continuously 

produced by interaction of cosmic radiation with the Earth’s 

atmosphere, and a large amount of tritium was produced as a 

result atmospheric testing of nuclear weapons between 1952 

and 1963. Thus, concentrations of tritium above background 

generally indicate the presence of water recharged since the 

early 1950s. Helium isotope ratios are used in conjunction 

with tritium concentrations to estimate ages for young groundwater. Helium isotope ratio analyses were not completed in 

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

subsequent publication. Carbon-14 is a radioactive isotope of 

carbon. Low levels of carbon-14 are continuously produced 

by interaction of cosmic radiation with the Earth’s atmosphere, and incorporated into atmospheric carbon dioxide. The 

carbon dioxide dissolves in precipitation, surface water, and 

groundwater exposed to the atmosphere, thereby entering the 

hydrologic cycle. Because carbon-14 decays with a half-life of 

approximately 5,700 years, low activities of carbon-14 relative 

to modern values generally indicate presence of groundwater 

that is several thousand years old.

Of the isotopic tracer constituents analyzed for this study, 

tritium is the only one with a health-based threshold. All measured tritium activities in samples from MADCHOW wells 

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

Radioactive Constituents

Radioactivity is the release of energy or energetic 

particles during changes in the structure of the nucleus of an 

atom. Most of the radioactivity in groundwater comes from 

decay of naturally-occurring isotopes of uranium and thorium 

that are present in minerals in the sediments or fractured rocks 

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

steps, eventually forming stable isotopes of lead. In each step 

in the decay series, one radioactive element turns into a different radioactive element by emitting an alpha or a beta particle 

from its nucleus. The alpha and beta particles emitted during 

radioactive decay are hazardous to human health because these 

energetic particles may damage cells. Radiation damage to cell 

DNA may increase the risk of getting cancer.

Activity is often used instead of concentration for 

reporting the presence of radioactive constituents. Activity of 

radioactive constituents in groundwater is measured in units 

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

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

particles emitted. 

 Samples from 25 of the 30 grid wells were analyzed 

for uranium isotope activities. Five samples from grid wells 

had combined uranium isotope activities that were above the 

MCL-CA (table 13A). Four of these same samples also had 

uranium concentrations above the MCL-US (table 10). Gross 

alpha and beta particle activities were analyzed in all 30 grid 

well samples. Gross alpha particle activity (72-hour count) 

was above the MCL-US in six grid well samples and gross 

alpha particle activity (30-day count) was above the MCL-US 

in five of these same grid well samples (table 13B). 

Future Work

Subsequent reports will be focused on assessing the data 

presented in this report using a variety of statistical, qualitative, and quantitative approaches to evaluate the natural and 

human factors affecting groundwater quality. Water-quality 

data contained in the CDPH and USGS NWIS databases, and 

water-quality data available from other State and local water 

agencies will be compiled, evaluated, and used in combination with the data that are presented in this report; the results 

of these future efforts will appear in one or more subsequent 

publications.
Summary 13

Summary 

Groundwater quality in the approximately 860-squaremile Madera–Chowchilla study unit (MADCHOW) was 

investigated in April and May 2008 as part of the Priority Basin Project of Groundwater Ambient Monitoring and 

Assessment (GAMA) Program. The California State Water 

Resources Control Board (SWRCB), in collaboration with the 

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

National Laboratory, is implementing the GAMA Program. 

The Priority Basin Project was designed by the USGS and the 

SWRCB in response to the State of California’s Groundwater 

Quality Monitoring Act of 2001. The project is a comprehensive assessment of statewide groundwater quality designed to 

identify and characterize risks to groundwater resources, and 

to increase the availability of information about groundwater 

quality to the public. MADCHOW was the twenty-fourth 

study unit sampled as part of the project. 

MADCHOW is in the southern part of the Central Valley 

hydrogeologic province and is comprised of two groundwater 

subbasins of the San Joaquin Valley defined by the California Department of Water Resources. The MADCHOW study 

included an assessment of the groundwater quality in samples 

from 35 wells that are primarily in Madera County, and in 

Merced and Fresno Counties. Thirty of the wells (“grid wells”)

were selected using a randomized grid approach to achieve a 

statistically unbiased representation of groundwater used for 

public drinking-water supplies. Five more wells (“flow-path 

wells”) were selected to provide additional sampling density to 

aid in understanding processes affecting groundwater quality. 

Groundwater samples were analyzed for VOCs, low-level 

DBCP and EDB, pesticides and pesticide degradates, polar 

pesticides and metabolites, constituents of special interest 

(NDMA perchlorate, low-level 1,2,3-TCP), pharmaceutical compounds, nutrients, major and minor ions, trace elements, species of arsenic and iron, and radioactivity (uranium 

isotopes, and gross alpha and gross beta particle activities). 

Naturally occurring isotopes and geochemical tracers (stable 

isotopes of hydrogen, oxygen, and carbon, and activities of 

tritium and carbon-14) and dissolved noble gases also were 

measured to provide a data set that will be used to help interpret the sources and ages of the sampled groundwater. In total, 

approximately 300 constituents and field water-quality indicators were investigated for this study. This report describes the 

sampling, analytical, and quality-control methods used in the 

study, and presents the results of the chemical analyses made 

of the groundwater samples collected during April and May 

2008.

This study did not attempt to evaluate the quality of water 

delivered to consumers; after withdrawal from the ground, raw 

groundwater typically is treated, disinfected, and blended with 

other waters to maintain acceptable water quality. Regulatory thresholds apply to treated water that is served to the 

consumer, not to raw groundwater. However, to provide some 

context for the results, concentrations of constituents measured 

in the raw groundwater were compared with regulatory and 

non-regulatory health-based thresholds established by the U.S. 

Environmental Protection Agency (USEPA) and California 

Department of Public Health (CDPH) and thresholds established for aesthetic and technical concerns by CDPH. 

The concentrations of most constituents detected in 

groundwater samples from the 30 MADCHOW grid wells 

were below regulatory and non-regulatory drinking-water 

thresholds. One or more organic compounds (VOCs and/or 

pesticides) were detected in about 40 percent of the grid well 

samples and generally at less than 1/100 of a regulatory or 

non-regulatory health-based threshold, although the concentrations of low-level DBCP in 10 percent and low-level EDB in 

3 percent of the samples from grid wells were above the corresponding USEPA maximum contaminant levels (MCL-USs). 

Perchlorate was detected in 70 percent of the samples from 

grid wells, and most concentrations were less than 1/10 of the 

CDPH maximum contaminant level (MCL-CA). Low-level 

1,2,3-TCP was detected in 33 percent of the samples from 

grid wells, and all concentrations were less than 1/1,000 of the 

USEPA lifetime health advisory level. The concentrations of 

trace elements and nutrients were below regulatory or nonregulatory health-based thresholds with the following exceptions: nitrate was detected above the MCL-US in samples 

from 7 percent of the grid wells, arsenic and uranium each 

were detected above the MCL-US in samples from 13 percent 

each of the grid wells, and vanadium was detected above the 

CDPH notification level in samples from 3 percent of the grid 

wells. Combined activities of uranium isotopes were detected 

above the MCL-CA in 20 percent of the subset of 25 grid 

well samples analyzed, and gross alpha particle activity was 

detected above the MCL-US in 20 percent of the samples from 

the 30 total grid wells. Twenty percent of the samples from 

grid wells contained specific conductance values, or concentrations of chloride, total dissolved solids, or manganese at 

concentrations above the non-enforceable CDPH secondary 

maximum contaminant level thresholds set for aesthetic and 

technical concerns.

Subsequent reports will present evaluations of the data 

presented in this report using a variety of statistical, qualitative, and quantitative approaches to assess the natural and 

human factors affecting groundwater quality.
14 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Acknowledgments

The authors thank the well owners and water purveyors 

for their generosity in allowing the U.S. Geological Survey 

to collect samples from their wells. We also thank the following cooperators for their support: the State Water Resources 

Control Board, California Department of Public Health, California Department of Water Resources, and Lawrence Livermore National Laboratory. Two reviewers, Jan Stepek (State 

Water Resources Control Board) and Timothy Mathany (U.S. 

Geological Survey) provided comments to improve this work. 

Funding for this work was provided by State bonds authorized by Proposition 50 and administered by the State Water 

Resources Control Board.

References Cited

American Public Health Association, 1998, Standard methods 

for the examination of water and wastewater (20th ed.): 

Washington, D.C., American Public Health Association, 

American Water Works Association, and Water Environment Federation, p. 3-37–3-43.

American Society for Testing and Materials, 2002, Standard 

test method for isotopic uranium in water by radiochemistry: American Society for Testing and Materials International, D 3972–02.

Anderson, R.L., 1987, Practical statistics for analytical chemists: New York, Van Nostrand Reinhold Company, Inc., 

315 p.

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

Bryant, and Johnson, Tyler, 2003, Framework for a groundwater quality monitoring and assessment program for California: U.S. Geological Survey Water-Resources Investigations Report 03–4166, 78 p.

Bennett, G.L., V, Belitz, Kenneth, and Milby Dawson, B.J., 

2006, California GAMA Program—Ground-water quality 

data in the northern San Joaquin basin study unit, 2005: 

U.S. Geological Survey Data-Series 196, 122 p.

Bertoldi, G.L., Johnston, R.H., and Evenson, K.D., 1991, 

Ground water in the Central Valley, California—A Summary report: U.S. Geological Survey Professional Paper 

1401-A, 44 p.

Burton, C.A., and Belitz, Kenneth, 2008, Ground-water quality data in the southeast San Joaquin Valley, 2005–2006—

Results from the California GAMA Program: U.S. Geological Survey Data Series 351, 103 p.

California Department of Public Health, 2008a, California 

drinking water-related laws: Drinking water-related regulations (Title 22) (pdf document), accessed February 5, 2008, 

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

Pages/Lawbook.aspx 

California Department of Public Health, 2008b, Drinking 

water notification levels: Notification levels (pdf document), 

accessed February 5, 2008, at URL http://www.cdph.ca.gov/

certlic/drinkingwater/Pages/NotificationLevels.aspx

California Department of Public Health, 2008c, Chemicals and 

contaminants in drinking water, accessed February 5, 2008, 

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

Chemicalcontaminants.aspx

California Department of Water Resources, 2003, California’s 

groundwater: California Department of Water Resources 

Bulletin 118, 246 p., accessed February 5, 2008, at http://

www.groundwater.water.ca.gov/bulletin118

California Department of Water Resources, 2008a, California’s 

groundwater: Individual basin descriptions, Chowchilla 

Subbasin: California Department of Water Resources Bulletin 118, accessed February 5, 2008, at http://www.dpla2.

water.ca.gov/publications/groundwater/bulletin118/basins/

pdfs_desc/5-22.05.pdf

California Department of Water Resources, 2008b, California’s groundwater: Individual basin descriptions, Madera 

Subbasin: California Department of Water Resources Bulletin 118, accessed February 5, 2008, at http://www.dpla2.

water.ca.gov/publications/groundwater/bulletin118/basins/

pdfs_desc/5-22.05.pdf 

Childress, C.J.O., Foreman, W.T., Connor, B.F., and Maloney, T.J., 1999, New reporting procedures based on longterm method detection levels and some considerations for 

interpretations of water-quality data provided by the U.S. 

Geological Survey National Water Quality Laboratory: U.S. 

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

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

Abney, S.R., 1998, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of 86 volatile organic compounds in water by gas 

chromatography/mass spectrometry, including detections 

less than reporting limits: U.S. Geological Survey OpenFile Report 97-829, 78 p.

Coplen, T.B., Wildman, J.D., and Chen, J., 1991, Improvements in the gaseous hydrogen-water equilibrium technique 

for hydrogen isotope analysis: Analytical Chemistry, v. 63, 

p. 910–912.

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

oxygen isotopic abundances: Pure and Applied Chemistry, 

v. 66, p. 273–276.
References Cited 15

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

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

Jr., Revesz, K.M., Lamberty, A., Taylor, P., and DeBierve, 

P., 2002, Compilation of minimum and maximum isotope 

ratios of selected elements in naturally occurring terrestrial 

materials and reagents: U.S. Geological Survey WaterResources Investigations Report 01-4222, 98 p.

Dawson, B.J., Bennett, G.L., V, and Belitz, Kenneth, 2008, 

California GAMA Program: Ground-water quality data 

in the Southern Sacramento Valley study unit, California, 

2005: U.S. Geological Survey Data Series 285, 93 p. 

Donahue, D.J., Linick, T.W., and Jull, A.J.T., 1990, Ratio and 

background corrections for accelerator mass spectrometry 

radiocarbon measurements: Radiocarbon, v. 32, p. 135–142.

Eaton, G.F., Hudson, G.B., and Moran, J.E., 2004, Tritiumhelium-3 age-dating of groundwater in the Livermore Valley 

of California: American Chemical Society ACS Symposium 

Series, v. 868, p. 235–245.

Eichelberger, J.W., 1993, Method 504.1, 1,2-dibromoethane (EDB), 1,2-dibromo-3-chloropropane (DBCP), and 

1,2,3-trichloropropane (123TCP) in water by microextraction and gas chromatography (rev. 1.0): U.S. Environmental 

Protection Agency, 20 p.

Epstein, S., and Mayeda, T.K., 1953, Variation of O-18 content 

of water from natural sources: Geochimica et Cosmochimica Acta, v. 4, p. 213–224.

Faires, L.M., 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of metals in water by inductively coupled plasma-mass 

spectrometry: U.S. Geological Survey Open-File Report 

92-634, 28 p.

Ferrari, M.J., Fram, M.S., and Belitz, Kenneth, 2008, Groundwater quality data in the Central Sierra study unit, 2006—

Results from the California GAMA Program: U.S. Geological Survey Data Series 335, 60 p. 

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

determination of inorganic substances in water and fluvial 

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

Fishman, M.J., 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of inorganic and organic constituents in water and 

fluvial sediments: U.S. Geological Survey Open-File Report 

93-125, 217 p.

Firestone, R.B., Shirley, V.S., Baglin, C.M., Chu, S.Y.F., and 

Zipkin, J., 1996, Table of Isotopes (8th ed.): New York, John 

Wiley & Sons, 3,168 p., accessed on April 1, 2007, at http://

ie.lbl.gov/toipdf/toi20.pdf

Fram, Miranda S. and Belitz, Kenneth, 2007, Ground-water 

quality in the Southern Sierra study unit, 2006— Results 

from the California GAMA Program: U.S. Geological 

Survey Data Series 301, 78 p.

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

Ground-water quality in the Tahoe–Martis study unit, 

2007—Results from the California GAMA Program: U.S. 

Geological Survey Data Series 432, 88 p.

Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., 

Coffey, L.J., and Burkhardt, M.R., 2001, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—Determination of pesticides in water 

by graphitized carbon-based solid-phase extraction and 

high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations 

Report 01–4134, 73 p.

Furlong, E.T., Werner, S.L., Anderson, B.D., and Cahill, J.D., 

2008, Methods of analysis by the U.S. Geological Survey 

National Water Quality Laboratory—Determination of 

human-health pharmaceuticals in filtered water by chemically modified styrene-divinylbenzene resin-based soldphase extraction and high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Techniques 

and Methods, book 5, chap. A9, 56 p.

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

Geological Survey National Water Quality Laboratory—

Determination of dissolved arsenic, boron, lithium, selenium, strontium, thallium, and vanadium using inductively 

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

Open-File Report 99–093, 31 p.

Garbarino, J.R., and Damrau, D.L., 2001, Methods of analysis by the U.S. Geological Survey National Water Quality 

Laboratory—Determination of organic plus inorganic mercury in filtered and unfiltered natural water with cold vaporatomic fluorescence spectrometry: U.S. Geological Survey 

Water-Resources Investigations Report 01-4132, 16 p.

Garbarino, J.R., Kanagy, J.R., and Cree, M.E., 2006, Determination of elements in natural-water, biota, sediment, and soil 

samples using collision/reaction cell inductively coupled 

plasma-mass spectrometry: U.S. Geological Survey Techniques and Methods, book 5, chap. B1, 88 p.

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

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

Stackelberg, P.E., Thelin, G.P., and Wolock, D.M., 2006, 

The quality of our nation’s waters: Pesticides in the nation’s 

streams and ground water, 1992–2001: U.S. Geological 

Survey Circular 1291, 172 p.

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

potentiometric titration. Part II: Analyst, v. 77, p. 661–671.
16 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Grob, R.L, ed., 1995, Modern practice of gas chromatography 

(3rd ed.): New York, John Wiley & Sons, 888 p.

Gronberg, J.M., Dubrovsky, N.M., Kratzer, C.R., Domagalski, 

J.L., Brown, L.R., and Burow, K.R, 1998, Environmental 

setting and study design for assessing water quality in the 

San Joaquin–Tulare Basins, California: U.S. Geological 

Survey Water-Resources Investigations Report 97-4205, 

45 p.

Hahn, G.J., and Meeker, W.Q., 1991, Statistical intervals: a 

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

392 p. 

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

characteristics of natural water: U.S. Geological Survey 

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

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

D.S., and Maupin, M.A., 2004, Estimated use of water in 

the United States in 2000: U.S. Geological Survey Circular 

1268, 46 p.

Jull, A.J.T., Burr, G.S., McHargue, L.R., Lange, T.E., Lifton, 

N.A., Beck, J.W., Donahue, D.J., and Lal, D., 2004, New 

frontiers in dating of geological, paleoclimatic, and anthropological applications using accelerator mass spectrometric 

measurements of 14C and 10Be in diverse samples: Global 

and Planetary Change, v. 41, p. 309–323.

Kolpin, D.W., Furlong, E.T., Meyer, M.T., Thurman, E.M., 

Zaugg, S.D., Barber, L.B., and Buxton, H.T., 2002, Pharmaceuticals, hormones and other organic wastewater contaminants in U.S. streams, 1999–2000: Environmental Science 

& Technology, v. 36, no. 6, p. 1202–1211. 

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 water-quality samples and 

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

95-399, 113 p.

Krieger, H.L., and Whittaker, E.L., 1980, Prescribed procedures for measurement of radioactivity in drinking water: 

U.S. Environmental Protection Agency EPA-600-4-80-032, 

142 p. Available from the National Technical Information 

Service (http://www.ntis.gov) as PB80-224744.

Kulongoski, J.T., and Belitz, Kenneth, 2004, Groundwater 

ambient monitoring and assessment program: U.S. Geological Survey Fact Sheet 2004–3088, 2 p.

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

Ground-water quality data in the North San Francisco 

Bay Hydrogeologic provinces, California, 2004: Results 

from the California Groundwater Ambient Monitoring and 

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

Data Series 167, 100 p.

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.

Land, Michael and Belitz, Kenneth, 2008, Ground-water 

quality data in the San Fernando–San Gabriel study unit, 

2005—Results from the California GAMA Program: U.S. 

Geological Survey Data Series 356, 84 p.

Landon, Matthew K., and Belitz, Kenneth, 2008, Groundwater quality data in the Central Eastside San Joaquin Basin 

2006—Results from the California GAMA Program: U.S. 

Geological Survey Data Series 325, 88 p. 

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

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

Survey Techniques of Water-Resources Investigations, book 

9, chap. A2, accessed February, 2008, at http://pubs.water.

usgs.gov/twri9A2/

Lewis, M.E., 2006, Dissolved Oxygen (ver. 2.1): U.S. Geological Survey Techniques of Water-Resources Investigations, 

book 9, chap. A6.2, accessed February 5, 2008, at http://

pubs.water.usgs.gov/twri9A6.2/

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

Determination of low concentrations of acetochlor in water 

by automated solid-phase extraction and gas chromatography with mass selective detection: Journal of AOAC 

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

Madsen, J.E., Sandstrom, M.W., and Zaugg, S.D., 2003, Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory—A method supplement for the 

determination of fipronil and degradates in water by gas 

chromatography/mass spectrometry: U.S. Geological Survey Open-File Report 02–462, 11 p.

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

Geological Survey National Water Quality Laboratory: U.S. 

Geological Survey Open-File Report 2005-1263, accessed 

February 5, 2008, at http://pubs.usgs.gov/of/2005/1263/pdf/

OFR2005-1263.pdf

Mathany, T.M., Land, Michael, and Belitz, Kenneth, 2008, 

Ground-water quality data in the Coastal Los Angeles Basin 

Study Unit, 2006: Results from the California GAMA Program: U.S. Geological Survey Data Series 387, 98 p. 

McCleskey, R.B., Nordstrom, D.K., and Ball, J.W., 2003, 

Metal interferences and their removal prior to the determination of As(T) and As(III) in acid mine waters by hydride 

generation atomic absorption spectrometry: U.S. Geological 

Survey Water-Resources Investigations Report 03–4117.
References Cited 17

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

Interpreting and reporting radiological water-quality data: 

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

chap. B6, 33 p.

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

Survey National Water Quality Laboratory—Determination 

of chromium in water by graphite furnace atomic absorption spectrophotometry: U.S. Geological Survey Open-File 

Report 93-449, 16 p.

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

from streams and ground water sampled during water years 

1992–2001: U.S. Geological Survey Scientific Investigations Report 2005-5106, 27 p.

Moran, J.E., Hudson, G.B., Eaton, G.F., and Leif, R., 2002, A 

contamination vulnerability assessment for the Livermore–

Amador and Niles Cone Groundwater Basins: Lawrence 

Livermore National Laboratory internal report UCRLAR-148831, 25 p.

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

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

in drinking water by purge and trap gas chromatography/

mass spectrometry (February 2002): California Department of Health Services, Division of Drinking Water 

and Environmental Management, Sanitation and Radiation Laboratories Branch, accessed February 5, 2008, at 

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

Drinkingwaterlabs/TCPbyPT-GCMS.pdf

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

by the U.S. Geological Survey National Water Quality 

Laboratory—Evaluation of alkaline persulfate digestion 

as an alternative to Kjeldahl digestion for determination of 

total and dissolved nitrogen and phosphorous in water: U.S. 

Geological Survey Water-Resources Investigations Report 

03–4174, 33 p.

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

U.S. Geological Survey National Water Quality Laboratory: 

U.S. Geological Survey Fact Sheet 026-98, 4 p., http://pubs.

er.usgs.gov/usgspubs/fs/fs02698 

Plomley, J.B., Koester, C.J., and March, R.E., 1994, Determination of NDMA in complex environmental matrices by 

quadrupole ion storage tandem mass spectrometry enhanced 

by unidirectional ion ejection: Analytical Chemistry, v. 66, 

no. 24, p. 4,437–4,443.

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

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

Techniques of Water-Resources Investigations, book 9, 

chap. A6.3, accessed February 5, 2008, at http://pubs.water.

usgs.gov/twri9A6.3/

Ray, M.C., Kulongoski, J.T., and Belitz, Kenneth, 2009, 

Ground-water quality data in the San Francisco Bay study 

unit, 2007: Results from the California GAMA program: 

U.S. Geological Survey Data Series 396, 93 p.

Rounds, S.A., 2006, Alkalinity and acid neutralizing capacity (ver. 3): U.S. Geological Survey Techniques of WaterResources Investigations, book 9, chap. A6.6, accessed 

February 5, 2008, at http://pubs.water.usgs.gov/twri9A6.6/

Sandstrom, M.W., Stroppel, M.E., Foreman, W.T., and Schroeder, M.P., 2001, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of moderate-use pesticides and selected degradates in 

water by C-18 solid-phase extraction and gas chromatography/mass spectrometry: U.S. Geological Survey WaterResources Investigations Report 01-4098, 70 p.

Schmitt, S., Fram, M.S., Milby Dawson, B.J., Belitz, Kenneth, 

2008, Ground-water quality data in the middle Sacramento 

Valley study unit, 2006—Results from the California 

GAMA program: U.S. Geological Survey Data Series 385, 

100 p.

Scott, J.C., 1990, Computerized stratified random site selection approaches for design of a groundwater quality sampling network: U.S. Geological Survey Water-Resources 

Investigations Report 90-4101, 109 p.

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

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

volatile organic compounds in active public supply wells as 

groundwater tracers in the Los Angeles physiographic basin, 

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

Investigations Report 01-4188, 29 p.

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, 100 p. http://www.waterboards.ca.gov/

gama/docs/final_ab_599_rpt_to_legis_7_31_03.pdf

Stookey, L.L., 1970, FerroZine—A new spectrophotometric 

reagent for iron: Analytical Chemistry, v. 42, p. 779–781.

Stumm, W., and Morgan, J.J., 1996, Aquatic Chemistry: 

Chemical equilibria and rates in natural waters, 3rd ed: New 

York, John Wiley & Sons, 1,022 p.

Thatcher, L.L., Janzer, V.J., and Edwards, K.W., 1977, Methods for the determination of radioactive substances in water: 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 5, chap. A5, 95 p.

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

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

95-352, 120 p.
18 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

To, T.B., Nordstrom, D.K., Cunningham, K.M., Ball, J.W., 

and McCleskey, R.B., 1998, New method for the direct 

determination of dissolved Fe(III) concentration in acid 

mine waters: Environmental Science and Technology, v. 33, 

p. 807–813. 

U.S. Environmental Protection Agency, 1989, Semivolatile 

organic compounds by isotope dilution GSMS (July 1989): 

Washington D.C., U.S. Environmental Protection Agency, 

68 p.

U.S. Environmental Protection Agency, 2002, Guidelines for 

establishing procedures for the analysis of pollutants: U.S. 

Code of Federal Regulations, Title 40, 136 p.

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

Determination of perchlorate in drinking water by liquid 

chromatography electrospray ionization mass spectrometry 

(Revision 1.0, January 2005): Office of Ground Water 

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

34 p. accessed February 5, 2008, at http://www.epa.gov/

safewater/methods/pdfs/methods/met331_0.pdf

U.S. Environmental Protection Agency, 2008a, Drinking water contaminants: U.S. Environmental Protection 

Agency, accessed February 5, 2008, at http://www.epa.gov/

safewater/contaminants/index.html

U.S. Environmental Protection Agency, 2008b, Drinking water 

health advisories: 2006 Drinking water standards and health 

advisory tables (pdf document): U.S. Environmental Protection Agency, accessed February 5, 2008, at URL http://www.

epa.gov/waterscience/criteria/drinking/

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 February 5, 2008, at http://water.

usgs.gov/owq/FieldManual/ 

U.S. Geological Survey, 2008, June 2008 Quarterly Method 

Report: U.S. Geological Survey Branch of Quality Systems, 

Organic Blind Sample Project, Lab Schedule 2033, accessed 

March 19, 2009, at http://bqs.usgs.gov/OBSP/Reports/

June2008Quarterly.html

Weiss, R.F., 1968, Piggyback sampler for dissolved gas studies on sealed water samples: Deep Sea Research, v. 15, 

p. 721–735.

Western Regional Climate Center, 2009, Western Regional 

Climate Center, Summary climate data for central California, average monthly precipitation data for Madera, California, and for Friant Government Camp, California: Western 

Regional Climate Center, accessed May 22, 2009, at http://

water.usgs.gov/owq/FieldManual

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

Survey Techniques of Water-Resources Investigations, book 

9, chap. A6.1, accessed February, 2008, at http://pubs.water.

usgs.gov/twri9A6.1/

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

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

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

February 5, 2008, at http://pubs.water.usgs.gov/twri9A3/

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

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

February 5, 2008, at http://pubs.water.usgs.gov/twri9A6.4/

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

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

of Water-Resources Investigations, book 9, chap. A6.0, 

accessed February 5, 2008, at http://pubs.water.usgs.gov/

twri9A6.0/

Wilde, F.D., Radtke, D.B., Gibs, J., and Iwatsubo, R.T., 1999, 

Collection of water samples: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A4, 

accessed February 5, 2008, at http://pubs.water.usgs.gov/

twri9A4/

Wilde, F.D., Radtke, D.B., Gibs, J., and Iwatsubo, R.T., 2004, 

Processing of water samples: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A5, 

accessed February 5, 2008, at http://pubs.water.usgs.gov/

twri9A5/

Wright, M.T., Belitz, Kenneth, and Burton, C.A., 2005, California GAMA program—Groundwater quality in the San 

Diego drainages hydrologic province, California, 2004: U.S. 

Geological Survey Data Series 129, 91 p.

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

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

Survey National Water Quality Laboratory—Determination 

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

capillary-column gas chromatography/mass spectrometry: 

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

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

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

P.L., 2006, Volatile organic compounds in the Nation’s 

ground water and drinking-water supply wells: U.S. 

Geological Survey Circular 1292, 101 p.
Tables 19

Tables
20 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

GAMA 

identification 

number

Date 

(m/dd/yyyy)

Sampling 

schedule

Elevation 

of LSD 

(ft above 

NAVD88)

Well 

type

Well depth 

(ft below 

LSD)

Top 

perforation 

(ft below 

LSD)

Bottom 

perforation

 (ft below 

LSD)

Grid wells

MADCHOW-01 4/14/2008 Intermediate 248 Production 592 210 588

MADCHOW-02 4/15/2008 Intermediate 252 Production 600 240 600

MADCHOW-03 4/15/2008 Intermediate 274 Production 540 240 520

MADCHOW-04 4/16/2008 Intermediate 339 Production 480 180 470

MADCHOW-05 4/16/2008 Intermediate 356 Production 3401 na na

MADCHOW-06 4/17/2008 Intermediate 325 Production na na na

MADCHOW-07 4/21/2008 Slow 346 Production >3002 na na

MADCHOW-08 4/22/2008 Slow 286 Production 820 420 810

MADCHOW-09 4/22/2008 Intermediate 220 Production 234 na na

MADCHOW-10 4/24/2008 Slow 236 Production 8301 506 830

MADCHOW-11 4/24/2008 Intermediate 284 Production 780 385 770

MADCHOW-12 4/28/2008 Intermediate 143 Production 300 240 300

MADCHOW-13 4/29/2008 Intermediate 223 Production 670 500 660

MADCHOW-14 4/30/2008 Intermediate 238 Production 360 na na

MADCHOW-15 4/30/2008 Intermediate 363 Production 450 390 450

MADCHOW-16 5/1/2008 Intermediate 291 Production 740 330 740

MADCHOW-17 5/1/2008 Intermediate 487 Production 1401 na na

MADCHOW-18 5/6/2008 Intermediate 268 Production 330 210 280

MADCHOW-19 5/6/2008 Intermediate 295 Production 200 140 na

MADCHOW-20 5/7/2008 Intermediate 177 Production na na na

MADCHOW-21 5/7/2008 Intermediate 428 Production 320 240 320

MADCHOW-22 5/8/2008 Slow 144 Production na na na

MADCHOW-23 5/12/2008 Slow 123 Production 655 400 655

MADCHOW-24 5/13/2008 Intermediate 168 Production 294 244 na

MADCHOW-25 5/13/2008 Intermediate 180 Production na na na

MADCHOW-26 5/14/2008 Intermediate 154 Production 510 210 510

MADCHOW-27 5/14/2008 Intermediate 202 Production 480 240 480

MADCHOW-28 5/19/2008 Intermediate 172 Production 240 204 212

MADCHOW-29 5/20/2008 Intermediate 177 Production 340 160 324

MADCHOW-30 5/21/2008 Intermediate 155 Production 388 358 388

Flow-path wells 

MADCHOWFP-01 4/23/2008 Slow 145 Production 254 212 na

MADCHOWFP-02 5/5/2008 Slow 249 Production 377 242 na

MADCHOWFP-03 5/15/2008 Slow 122 Production 198 163 na

MADCHOWFP-04 5/21/2008 Slow 296 Production 200 184 196

MADCHOWFP-05 5/22/2008 Slow 340 Production 340 240 340

1

Well depth estimated from reported hole depth, pump service records, or personal communication from well driller.

2

Well depth measured to be deeper than the length of the 300-foot calibrated electric sounder.

Table 1. Identification, sampling, and construction information for wells sampled for the Madera–Chowchilla Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, April and May 2008. 

[GAMA well identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path 

well. Sampling schedule: Sampling schedules are shown in table 2. Land-surface datum (LSD) is a datum plane that is approximately at land surface at each 

well. The elevation of the LSD is described in feet above the North American Vertical Datum 1988. Other abbreviations: ft, foot; LSD, land surface datum; 

NAVD88, North American Vertical Datum 1988; na, not available; >, greater than]
Tables 21

Constituent classes Slow schedule 

(10 wells)

Intermediate schedule 

(25 wells)

Analyte list 

table

Results 

table

Field water-quality indicators

Alkalinity, dissolved oxygen, pH, specific conductance, and 

temperature

X X — 4

Turbidity X — — 4

Organic constituents

Volatile organic compounds (VOCs) X X 3A 5

Low-level 1,2-dibromo-3-chloropropane (DBCP) and 1,2-dibromoethane (EDB)X X 3B 5

Pesticides and pesticide degredates X X 3C 6A

Polar pesticides and metabolites X X 3D 6B

Pharmaceutical compounds X — 3E —(1)

Constituents of special interest

N-Nitrosodimethylamine (NDMA) X — 3F 7

Perchlorate X X 3F 7

Low-level 1,2,3-trichloropropane (1,2,3-TCP) X X 3F 7

Inorganic constituents

Nutrients X X 3G 8

Major and minor ions and trace elements X X 3H 9, 10

Arsenic and iron species X — 3I 11

Isotopic tracers

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

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

Radioactivity and noble gases

Tritium activity X X 3J 12

Tritium activity and noble gases X X 3K —(1)

Gross alpha and gross beta particle activities X X 3J 13

Uranium isotope activities X X 3J 13

1

Data will be presented in subsequent publications.

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

schedules in the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.

[X, constituent class collected; —, constituent class not collected or no table]
22 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

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

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

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

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

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

laboratory reporting level; THM, trihalomethane; D, detected in ground-water samples (table 5); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number1

 LRL 

(μg/L)

Threshold 

type2

Threshold 

level 

(μg/L)

Detection

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

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

tert-Amyl methyl ether 

(TAME)

Gasoline oxygenate 50005 994-05-8 0.06 na na —

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

Bromobenzene Solvent 81555 108-86-1 0.02 na na —

Bromochloromethane Fire retardant 77297 74-97-5 0.06 HAL-US 90 —

Bromodichloromethane Disinfection by-product (THM) 32101 75-27-4 0.04 MCL-US 380 D

Bromoform 

(Tribromomethane)

Disinfection by-product (THM) 32104 75-25-2 0.08 MCL-US 380 D

Bromomethane (Methyl 

bromide)

Fumigant 34413 74-83-9 0.4 HAL-US 10 —

n-Butylbenzene Gasoline hydrocarbon 77342 104-51-8 0.14 NL-CA 260 —

sec-Butylbenzene Gasoline hydrocarbon 77350 135-98-8 0.04 NL-CA 260 —

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

Carbon disulfide Organic synthesis 77041 75-15-0 0.06 NL-CA 160 —

Carbon tetrachloride 

(Tetrachloromethane)

Solvent 32102 56-23-5 0.08 MCL-CA 0.5 —

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

Chloroethane Solvent 34311 75-00-3 0.1 na na —

Chloroform 

(Trichloromethane)

Disinfection by-product (THM) 32106 67-66-3 0.02 MCL-US 380 D

Chloromethane Solvent 34418 74-87-3 0.1 HAL-US 30 —

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

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

4-Chlorotoluene Solvent 77277 106-43-4 0.04 NL-CA 140 —

Dibromochloromethane Disinfection by-product (THM) 32105 124-48-1 0.12 MCL-US 380 D

1,2-Dibromo-3-chloropropane (DBCP)Fumigant 82625 96-12-8 0.5 MCL-US 0.2 D

1,2-Dibromoethane (EDB) Fumigant 77651 106-93-4 0.04 MCL-US 0.05 D

Dibromomethane Solvent 30217 74-95-3 0.04 na na —

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

1,3-Dichlorobenzene Solvent 34566 541-73-1 0.04 HAL-US 600 —

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

trans-1,4-Dichloro-2-butene Organic synthesis 73547 110-57-6 0.6 na na —

Dichlorodifluoromethane 

(CFC-12)

Refrigerant 34668 75-71-8 0.14 NL-CA 1,000 —

1,1-Dichloroethane 

(1,1-DCA)

Solvent 34496 75-34-3 0.04 MCL-CA 5 D

1,2-Dichloroethane 

(1,2-DCA)

Solvent 32103 107-06-2 0.06 MCL-CA 0.5 —

1,1-Dichloroethene 

(1,1-DCE)

Organic synthesis 34501 75-35-4 0.02 MCL-CA 6 —

cis-1,2-Dichloroethene 

(cis-1,2-DCE)

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

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

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

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

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

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

laboratory reporting level; THM, trihalomethane; D, detected in ground-water samples (table 5); na, not available; μg/L, micrograms per liter; —, not detected]
Tables 23

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

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

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

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

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

laboratory reporting level; THM, trihalomethane; D, detected in ground-water samples (table 5); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number1

 LRL 

(μg/L)

Threshold 

type2

Threshold 

level 

(μg/L)

Detection

trans-1,2-Dichloroethene 

(trans-1,2-DCE)

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

1,2-Dichloropropane Fumigant 34541 78-87-5 0.02 MCL-US 5 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 RSD5-US 4

4 —

trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.1 RSD5-US 4

4 —

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

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

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

Ethyl tert-butyl ether 

(ETBE)

Gasoline oxygenate 50004 637-92-3 0.04 na na —

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

o-Ethyl toluene (1-Ethyl-2-

methyl benzene)

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

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

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

2-Hexanone (n-Butyl 

methyl ketone)

Solvent 77103 591-78-6 0.6 na na —

Iodomethane (Methyl 

iodide)

Organic synthesis 77424 74-88-4 0.4 na na —

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

4-Isopropyl-1-methyl 

benzene

Gasoline hydrocarbon 77356 99-87-6 0.08 na na —

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

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

Methyl tert-butyl ether 

(MTBE)

Gasoline oxygenate 78032 1634-04-4 0.1 MCL-CA 13 —

Methyl iso-butyl ketone 

(MIBK)

Solvent 78133 108-10-1 0.4 NL-CA 120 —

Methylene chloride 

(Dichloromethane)

Solvent 34423 75-09-2 0.04 MCL-US 5 —

Methyl ethyl ketone 

(2-butanone, MEK)

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

Methyl methacrylate Organic synthesis 81597 80-62-6 0.2 na na —

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

Perchloroethene 

(Tetrachloroethene, PCE)

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

n-Propylbenzene Solvent 77224 103-65-1 0.04 NL-CA 260 —

Styrene Gasoline hydrocarbon 77128 100-42-5 0.04 MCL-US 100 —(5)

1,1,1,2-Tetrachloroethane Solvent 77562 630-20-6 0.04 HAL-US 70 —

1,1,2,2-Tetrachloroethane Solvent 34516 79-34-5 0.1 MCL-CA 1 —

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

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

1,2,3,5-Tetramethylbenzene Gasoline hydrocarbon 50000 527-53-7 0.12 na na —
24 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

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

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

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

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

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

laboratory reporting level; THM, trihalomethane; D, detected in ground-water samples (table 5); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number1

 LRL 

(μg/L)

Threshold 

type2

Threshold 

level 

(μg/L)

Detection

Toluene Gasoline hydrocarbon 34010 108-88-3 0.018 MCL-CA 150 —(6)

1,2,3-Trichlorobenzene Organic synthesis 77613 87-61-6 0.08 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 0.02 MCL-CA 200 —

1,1,2-Trichloroethane 

(1,1,2-TCA)

Solvent 34511 79-00-5 0.06 MCL-CA 5 —

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

Trichlorofluoromethane 

(CFC-11)

Refrigerant 34488 75-69-4 0.08 MCL-CA 150 —

1,2,3-Trichloropropane 

(1,2,3-TCP)

Solvent/organic synthesis 77443 96-18-4 0.12 HAL-US 40 —

Trichlorotrifluoroethane 

(CFC-113)

Refrigerant 77652 76-13-1 0.04 MCL-CA 1,200 —

1,2,3-Trimethylbenzene Gasoline hydrocarbon 77221 526-73-8 0.08 na na —

1,2,4-Trimethylbenzene Gasoline hydrocarbon 77222 95-63-6 0.04 NL-CA 330 D

1,3,5-Trimethylbenzene Organic synthesis 77226 108-67-8 0.04 NL-CA 330 —

Vinyl bromide 

(Bromoethene)

Fire retardant 50002 593-60-2 0.12 na na —

Vinyl chloride 

(Chloroethene)

Organic synthesis 39175 75-01-4 0.08 MCL-CA 0.5 —

m- and p-Xylene Gasoline hydrocarbon 85795 108-38-3/ 

106-42-3

0.08 MCL-CA 71,750 —

o-Xylene Gasoline hydrocarbon 77135 95-47-6 0.04 MCL-CA 7

1,750 — 1This report contains CAS Registry Numbers®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the 

CAS Registry Numbers® through CAS Client ServicesSM. 2

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 3

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

4

The RSD5 threshold for 1,3-dichloropropene is the sum of its isomers (cis and trans). 5

The median matrix-spike recovery was less than 70 percent. Low recoveries may indicate that the compound might not have been detected in some samples 

if it was present at very low concentrations. 6

All detections of toluene were V-coded based on frequency of detections in field blanks and source solution blanks from the previous 23 GAMA study units 

and were excluded from the dataset of ground-water quality results. 7

The MCL-CA thresholds for m- and p-Xylene and o-Xylene is for the sum of all three xylene compounds.
Tables 25

Constituent Primary use 

or source

USGS 

parameter 

code

CAS number LRL 

(μg/L)

Threshold 

type1

Threshold level 

(μg/L) Detection

1,2-Dibromo-3-chloropropane (DBCP)Fumigant 82625 96-12-8 0.030 MCL-US 0.2 D 

1,2-Dibromoethane 

(EDB)

Fumigant 77651 106-93-4 0.02 MCL-US 0.05 D 

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

Table 3B. Low-level 1,2-dibromo-3-chloropropane (DBCP) and 1,2-dibromoethane (EDB), primary uses or sources, comparative 

thresholds, and reporting information for the U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 1306.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: MCL-US, U.S. Environmental Protection Agency maximum contaminant level. Other abbreviations: CAS, Chemical Abstract Service; LRL, 

laboratory reporting level; D, detected in ground-water samples (table 5); μg/L, micrograms per liter]
26 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

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

U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2033.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples 

(table 6A); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent

Primary 

use or 

source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold 

type1

Threshold 

level 

(μg/L)

Detection

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

Alachlor Herbicide 46342 15972-60-8 0.006 MCL-US 2 —

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

Azinphos-methyl Insecticide 82686 86-50-0 0.12 na na —(2)

Azinphos-methyl oxon Insecticide degradate 61635 961-22-8 0.042 na na —(2)

Benfluralin Herbicide 82673 1861-40-1 0.01 na na —(2)

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

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

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 0.005 na na —(2)

Chlorpyrifos Insecticide 38933 2921-88-2 0.005 HAL-US 2 —(2)

Chlorpyrifos-oxon Insecticide degradate 61636 5598-15-2 0.0562 na na —(2)

Cyanazine Herbicide 04041 21725-46-2 0.02 HAL-US 1 —

Cyfluthrin Insecticide 61585 68359-37-5 0.016 na na —(2)

λ-Cyhalothrin Insecticide 61595 91465-08-6 0.004 na na —(2)

Cypermethrin Insecticide 61586 52315-07-8 0.014 na na —(2)

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

Deethylatrazine (2-Chloro4-isopropylamino-6-

amino-s-triazine)

Herbicide degradate 04040 6190-65-4 0.014 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 0.005 HAL-US 1 —

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

3,5-Dichloroaniline Herbicide degradate 61627 626-43-7 0.008 na na —

Dichlorvos Insecticide 38775 62-73-7 0.013 na na —(2)

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

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

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

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

Disulfoton Insecticide 82677 298-04-4 0.04 HAL-US 0.7 —(2)

Disulfoton sulfone Insecticide degradate 61640 2497-06-5 0.014 na na —

α-Endosulfan Insecticide 34362 959-98-8 0.006 na na —

Endosulfan sulfate Insecticide degradate 61590 1031-07-8 0.022 na na —

Ethion Insecticide 82346 563-12-2 0.006 na na —(2)

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

Ethoprop Herbicide 82672 13194-48-4 0.012 na na —

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

U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2033.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples 

(table 6A); na, not available; μg/L, micrograms per liter; —, not detected]
Tables 27

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

U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2033.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples 

(table 6A); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent

Primary 

use or 

source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold 

type1

Threshold 

level 

(μg/L)

Detection

S-Ethyl-dipropylthiocarbamate (EPTC)

Herbicide 82668 759-94-4 0.002 na na —

2-Ethyl-6-methylaniline Herbicide degradate 61620 24549-06-2 0.01 na na —

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

Fenamiphos sulfone Insecticide degradate 61645 31972-44-8 0.053 na na —

Fenamiphos sulfoxide Insecticide degradate 61646 31972-43-7 0.2 na na —(2)

Fipronil Insecticide 62166 120068-37-3 0.02 na na —

Fipronil sulfide Insecticide degradate 62167 120067-83-6 0.013 na na —

Fipronil sulfone Insecticide degradate 62168 120068-36-2 0.024 na na —(2)

Fonofos Insecticide 04095 944-22-9 0.01 HAL-US 10 —

Hexazinone Herbicide 04025 51235-04-2 0.008 HAL-US 400 D2

Iprodione Fungicide 61593 36734-19-7 0.01 na na —(2)

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

Malaoxon Insecticide degradate 61652 1634-78-2 0.02 na na —(2)

Malathion Insecticide 39532 121-75-5 0.016 HAL-US 100 —

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

Methidathion Insecticide 61598 950-37-8 0.004 na na —

Metolachlor Herbicide 39415 51218-45-2 0.01 HAL-US 700 —

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

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

Myclobutanil Fungicide 61599 88671-89-0 0.01 na na —

1-Naphthol Insecticide degradate 49295 90-15-3 0.04 na na —(2)

Oxyfluorfen Herbicide 61600 42874-03-3 0.006 na na —(2)

Paraoxon-methyl Insecticide degradate 61664 950-35-6 0.01 na na —(2)

Parathion-methyl Insecticide 82667 298-00-0 0.008 HAL-US 1 —(2)

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

cis-Permethrin Insecticide 82687 54774-45-7 0.01 na na —(2)

Phorate Insecticide 82664 298-02-2 0.04 na na —(2)

Phorate oxon Insecticide degradate 61666 2600-69-3 0.027 na na —

Phosmet Insecticide 61601 732-11-6 0.0079 na na —(2)

Phosmet oxon Insecticide degradate 61668 3735-33-9 0.0511 na na —(2)

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

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

Pronamide Herbicide 82676 23950-58-5 0.004 RSD5-US 20 —

Propanil Herbicide 82679 709-98-8 0.006 na na —

Propargite Insecticide 82685 2312-35-8 0.04 na na —(2)

cis-Propiconazole Fungicide 79846 60207-90-1 0.006 na na —
28 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

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

U.S. Geological Survey (USGS) National Water Quality Laboratory Schedule 2033.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in ground-water samples 

(table 6A); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent

Primary 

use or 

source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold 

type1

Threshold 

level 

(μg/L)

Detection

trans-Propiconazole Fungicide 79847 60207-90-1 0.02 na na —

Simazine Herbicide 04035 122-34-9 0.006 MCL-US 4 D

Tebuthiuron Herbicide 82670 34014-18-1 0.016 HAL-US 500 D2

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

Terbufos Insecticide 82675 13071-79-9 0.018 HAL-US 0.4 —

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 0.045 na na —(2)

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

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

Tribufos Defoliant 61610 78-48-8 0.035 na na —(2)

Trifluralin Herbicide 82661 1582-09-8 0.009 HAL-US 10 —(2)

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

The median matrix-spike recovery was less than 70 percent. Low recoveries may indicate that the compound might not have been detected in some samples 

if it was present at very low concentrations. 
Tables 29

Table 3D. Polar pesticides and metabolites, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey (USGS) National Water Quality Laboratory Schedule 2060.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk 

specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; IRL, interim reporting level; D, 

detected in ground-water samples (table 6B); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent

Primary 

use or 

source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold 

type1

Threshold 

level 

(μg/L)

Detection

Acifluorfen Herbicide 49315 50594-66-6 0.04 na na —(2)

Aldicarb Insecticide 49312 116-06-3 0.12 MCL-US 3 —

Aldicarb sulfone Degradate 49313 1646-88-4 0.080 MCL-US 3 —

Aldicarb sulfoxide Degradate 49314 1646-87-3 0.060 MCL-US 4 —

Atrazine Herbicide 39632 1912-24-9 0.040 MCL-CA 1 D3

Bendiocarb Insecticide 50299 22781-23-3 0.040 na na —

Benomyl Fungicide 50300 17804-35-2 0.040 na na —

Bensulfuron-methyl Herbicide 61693 83055-99-6 0.060 na na —

Bentazon Herbicide 38711 25057-89-0 0.040 MCL-CA 18 —(2)

Bromacil Herbicide 04029 314-40-9 0.02 HAL-US 70 D 

Bromoxynil Herbicide 49311 1689-84-5 0.120 na na —(2)

Caffeine Beverages 50305 58-08-2 0.060 na na —

Carbaryl Herbicide 49310 63-25-2 0.040 RSD5-US 400 —

Carbofuran Herbicide 49309 1563-66-2 0.020 MCL-CA 18 —

Chloramben, methyl ester Herbicide 61188 7286-84-2 0.100 na na —

Chlorimuron-ethyl Herbicide 50306 90982-32-4 0.080 na na —

3-(4-Chlorophenyl)-1-methyl 

urea 

Degradate 61692 5352-88-5 0.120 na na —

Clopyralid Herbicide 49305 1702-17-6 0.060 na na —

Cycloate Herbicide 04031 1134-23-2 0.02 na na —(2)

2,4-D plus 2,4-D methyl ester Herbicides 66496 na 0.024 MCL-US 70 —

2,4-DB (4-(2,4-Dichlorophenoxy)butyric acid)Herbicide 38746 94-82-6 0.020 na na —

DCPA (Dacthal) monoacid Degradate 49304 887-54-7 0.020 na na —

Deethylatrazine (2-Chloro-4-

isopropylamino-6-amino-striazine)

Degradate 04040 6190-65-4 0.06 na na D3

Deisopropyl atrazine (2-Chloro6-ethylamino-4-amino-striazine)Degradate 04038 1007-28-9 0.08 na na D 

Dicamba Herbicide 38442 1918-00-9 0.040 HAL-US 4000 —(2)

Dichlorprop Herbicide 49302 120-36-5 0.020 na na —

Dinoseb (Dinitrobutyl phenol) Herbicide 49301 88-85-7 0.040 MCL-CA 7 D2

Diphenamid Herbicide 04033 957-51-7 0.04 HAL-US 200 —

Diuron Herbicide 49300 330-54-1 0.040 HAL-US 10 D 

Fenuron Herbicide 49297 101-42-8 0.040 na na —

Flumetsulam Herbicide 61694 98967-40-9 0.060 na na —

Fluometuron Herbicide 38811 2164-17-2 0.040 HAL-US 90 —

Table 3D. Polar pesticides and metabolites, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

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

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk 

specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; IRL, interim reporting level; D, 

detected in ground-water samples (table 6B); na, not available; μg/L, micrograms per liter; —, not detected]
30 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table 3D. Polar pesticides and metabolites, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey (USGS) National Water Quality Laboratory Schedule 2060.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk 

specific dose at a risk factor of 10–5. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; IRL, interim reporting level; D, 

detected in ground-water samples (table 6B); na, not available; μg/L, micrograms per liter; —, not detected]

Constituent

Primary 

use or 

source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold 

type1

Threshold 

level 

(μg/L)

Detection

Hydroxyatrazine (2-Hydroxy4-isopropylamino-6-ethylamino-s-triazine)Degradate 50355 2163-68-0 0.040 na na —

3-Hydroxycarbofuran Degradate 49308 16655-82-6 0.040 na na —

Imazaquin Herbicide 50356 81335-37-7 0.040 na na —(5)

Imazethapyr Herbicide 50407 81335-77-5 0.040 na na D5

Imidacloprid Insecticide 61695 138261-41-3 0.060 na na —

Linuron Herbicide 38478 330-55-2 0.020 na na —

MCPA (2-Methyl-4-chlorophenoxyacetic acid) Herbicide 38482 94-74-6 0.060 HAL-US 30 —

MCPB (4-(2-Methyl-4-chlorophenoxy)butyric acid)Herbicide 38487 94-81-5 0.060 na na —(2)

Metalaxyl Fungicide 50359 57837-19-1 0.020 na na —

Methiocarb Insecticide 38501 2032-65-7 0.040 na na —

Methomyl Insecticide 49296 16752-77-5 0.120 HAL-US 200 —

Metsulfuron methyl4 Herbicide 61697 74223-64-6 0.144 na na —

Neburon Herbicide 49294 555-37-3 0.020 na na —

Nicosulfuron Herbicide 50364 111991-09-4 0.10 na na —(5)

Norflurazon Herbicide 49293 27314-13-2 0.020 na na D

Oryzalin Herbicide 49292 19044-88-3 0.040 na na —

Oxamyl Insecticide 38866 23135-22-0 0.120 MCL-CA 50 —

Picloram Herbicide 49291 1918-02-01 0.120 MCL-US 500 —

Propham Herbicide 49236 122-42-9 0.040 HAL-US 100 —

Propiconazole Fungicide 50471 60207-90-1 0.040 na na —

Propoxur Insecticide 38538 114-26-1 0.040 na na —

Siduron Herbicide 38548 1982-49-6 0.020 na na —

Sulfometuron-methyl Herbicide 50337 74222-97-2 0.060 na na —

Tebuthiuron Herbicide 82670 34014-18-1 0.040 HAL-US 500 D3

Terbacil Herbicide 04032 5902-51-2 0.04 HAL-US 90 —

Triclopyr Herbicide 49235 55335-06-3 0.080 na na — 1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

The median matrix-spike recovery was less than 70 percent. Low recoveries may indicate that the compound might not have been detected in some samples 

if it was present at very low concentrations. 3

Compounds analyzed in Schedule 2033 and 2060, but values are reported for the preferred Schedule 2033.

4

Value is an IRL rather than an LRL.

5

The median laboratory matrix-spike recovery was greater than 130 percent. High recoveries may indicate that reported values could be higher than what is in 

the sample.
Tables 31

Constituent

Primary 

use or 

source

USGS 

parameter 

code

CAS number MDL1

(μg/L)

Threshold 

type

Threshold 

level 

(μg/L)

Acetaminophen Analgesic 62000 103-90-2 0.60 na na

Albuterol Anti-inflammatory; bronchodilator 62020 18559-94-9 0.03 na na

Caffeine Stimulant 50305 58-08-2 0.40 na na

Carbamazapine Anticonvulsant; analgesic; mood 

stabilizer

62793 298-46-4 0.02 na na

Codeine Opioid narcotic 62003 76-57-3 0.02 na na

Cotinine Nicotine metabolite 62005 486-56-6 0.03 na na

Dehydronifedipine Antianginal metabolite 62004 67035-22-7 0.03 na na

Diltiazem Antianginal; antihypertensive 62008 42399-41-7 0.02 na na

Diphenhydramine Antihistamine 62796 58-73-1 0.03 na na

1,7-Dimethylxanthine Caffeine metabolite 62030 611-59-6 0.10 na na

Sulfamethoxazole Antibacterial, antiprotozoal 62021 723-46-6 0.05 na na

Thiabendazole Anthelmintic 62801 148-79-8 0.02 na na

Trimethoprim Antibacterial 62023 738-70-5 0.01 na na

Warfarin Anticoagulant 62024 81-81-2 0.03 na na

Table 3E. Pharmaceutical compounds, primary uses or sources, comparative thresholds, and reporting information for the U.S. 

Geological Survey (USGS) National Water Quality Laboratory Schedule 2080.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. Other 

abbreviations: CAS, Chemical Abstract Service; MDL, method detection limit; na, not available; SRL, study reporting level; μg/L, micrograms per liter]

 1The California Groundwater Ambient Monitoring and Assessment (GAMA) program uses more conservative reporting limits for the pharmaceutical compounds than those used by the USGS National Water Quality Laboratory (NWQL). The data for samples from this study unit were reported by the NWQL with 

interim laboratory reporting limits, and results below the interim method detection limits were included in the dataset. The GAMA program examined laboratory 

quality-control data and decided that the rate of false-positive detections was too high using this set of reporting limits. The reporting limits used by GAMA have 

significantly higher concentrations than those originally reported with the data, and GAMA does not report results below the selected method detection limits. 

For albuterol, carbamazepine, codeine, cotinine, dehydronifedipine, diltiazem, 1,7-dimethylxanthine, sulfamethoxazole, thiabendazole, trimethoprim, and warfarin, the MDLs correspond to the long-term method detection limits determined by the USGS Branch of Quality Systems in October 2007 (BQS LT-MDL). For 

acetaminophen, caffeine, and diphenhydramine, the MDLs correspond to the effective method detection limits determined from assessment of quality-control 

data associated with GAMA samples collected from May 2004 through September 2007 (GAMA SRL). The GAMA SRLs are higher than the BQS LT-MDLs 

for those compounds. Detections reported by the USGS National Water Quality Laboratory with concentrations lower than the BQS LT-MDL or GAMA SRL are 

reported as nondetects by the GAMA program. 
32 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Constituent

Primary 

use or 

source

USGS 

parameter 

code

CAS number MRL 

(μg/L)

Threshold 

type1

Threshold 

level 

(μg/L)

Detection

N-Nitrosodimethylamine 

(NDMA)

Rocket fuel, plasticizer, disinfection by-product34438 62-75-9 0.0020 NL-CA 0.010 D

Perchlorate Rocket fuel, fireworks, flares, 

natural, fertilizer

61209 14797-73-0 0.10 MCL-CA 6 D

1,2,3-Trichloropropane 

(1,2,3-TCP)

Fumigant, solvent 77443 96-18-4 0.0050 HAL-US 40 D

Table 3F. Constituents of special interest, primary uses or sources, comparative thresholds, and reporting information for Weck 

Laboratories, Inc. 

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

of April 14, 2008. Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public 

Health maximum contaminant level; NL-CA, California Department of Public Health notification level. Other abbreviations: CAS, Chemical Abstract Service; 

MRL, minimum reporting level; D, detected in ground-water samples (table 7); μg/L, micrograms per liter]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

Table 3G. Nutrients, comparative thresholds, and reporting information for the U.S. Geological Survey (USGS) National Water Quality 

Laboratory Schedule 2755.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. Other abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; D, detected in groundwater samples (table 8); na, 

not available; mg/L, milligrams per liter] 

Constituent

USGS 

parameter 

code

CAS number LRL 

(mg/L)

Threshold 

type1

Threshold 

level 

(mg/L)

Detection

Ammonia (as nitrogen) 00608 7664-41-7 0.02 HAL-US 224.7 D

Nitrite (as nitrogen) 00613 14797-65-0 0.002 MCL-US 1 D

Nitrite plus nitrate (as nitrogen) 00631 na 0.04 MCL-US 10 D

Nitrogen, total (ammonia, nitrite, nitrate, 

organic nitrogen)

62854 17778-88-0 0.06 na na D

Orthophosphate, as phosphorus 00671 14265-44-2 0.006 na na D

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

 The HAL-US is 30 mg/L "as ammonia." To facilitate comparson to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L "as 

nitrogen." 
Tables 33

Constituent

USGS 

parameter 

code

CAS number LRL Threshold 

type1

Threshold 

level Detection

Major and minor ions (mg/L)

Bromide 71870 24959-67-9 20.02 na na D

Calcium 00915 7440-70-2 0.04 na na D

Chloride 00940 16887-00-6 0.12 SMCL-CA 3250 (500) D

Fluoride 00950 16984-48-8 0.12 MCL-CA 2 D

Iodide 71865 7553-56-2 0.002 na na D

Magnesium 00925 7439-95-4 0.02 na na D

Potassium 00935 7440-09-7 0.02 na na D

Silica 00955 7631-86-9 0.018 na na D

Sodium 00930 7440-23-5 0.12 na na D

Sulfate 00945 14808-79-8 0.18 SMCL-CA 350 (500) D

Total dissolved solids (TDS; residue on 

evaporation, ROE)

70300 na 10 SMCL-CA 3500 (1,000) D

Trace elements (μg/L)

Aluminum 01106 7429-90-5 1.6 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.14 MCL-US 6 D

Arsenic 01000 7440-38-2 0.06 MCL-US 10 D

Barium 01005 7440-39-3 0.4 MCL-CA 1,000 D

Beryllium 01010 7440-41-7 0.008 MCL-US 4 D

Boron 01020 7440-42-8 6 NL-CA 1,000 D

Cadmium 01025 7440-43-9 0.04 MCL-US 5 D

Chromium 01030 7440-47-3 0.12 MCL-CA 50 D

Cobalt 01035 7440-48-4 0.02 na na D

Copper 01040 7440-50-8 1.0 AL-US 1,300 D

Iron 01046 7439-89-6 8 SMCL-CA 300 D

Lead 01049 7439-92-1 0.08 AL-US 15 D

Lithium 01130 7439-93-2 1.0 na na D

Manganese 01056 7439-96-5 0.2 SMCL-CA 50 D

Mercury 71890 7439-97-6 0.01 MCL-US 2 —

Molybdenum 01060 7439-98-7 0.2 HAL-US 40 D

Nickel 01065 7440-02-0 0.2 MCL-CA 100 D

Selenium 01145 7782-49-2 0.04 MCL-US 50 D

Silver 01075 7440-22-4 0.1 SMCL-CA 100 D

Strontium 01080 7440-24-6 0.8 HAL-US 4,000 D

Thallium 01057 7440-28-0 0.04 MCL-US 2 —(4)

Tungsten 01155 7440-33-7 0.06 na na D

Uranium 22703 7440-61-1 0.02 MCL-US 30 D

Vanadium 01085 7440-62-2 0.04 NL-CA 50 D

Zinc 01090 7440-66-6 1.8 SMCL-CA5 5,000 D 1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

Value is an IRL rather than an LRL.

3

The recommended SMCL-CA thresholds for chloride, sulfate, and TDS are listed with the upper SMCL-CA thresholds in parentheses.

4

The laboratory raised the LRL to 0.12 mg/L in the MADCHOWFP-03 sample collected on 5/15/08 at 1040 and thallium was not detected.

5

The secondary maximum contaminant level for zinc is listed as SMCL-CA since SMCLs established by California Department of Public Health are used in 

this report for all constituents that have SMCL-CAs.

Table 3H. Major and minor ions and trace elements, comparative thresholds, and reporting information for the U.S. Geological Survey 

(USGS) National Water Quality Laboratory Schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; 

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

NL-CA, California Department of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. 

Other abbreviations: CAS, Chemical Abstract Service; IRL, interim reporting level; LRL, laboratory reporting level; D, detected in groundwater samples 

(tables 9 and 10); na, not available; mg/L, milligrams per liter; μg/L, micrograms per liter; —, not detected]
34 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table 3I. Arsenic and iron species, comparative thresholds, and reporting information for the U.S. Geological Survey (USGS) Trace 

Metal Laboratory, Boulder, Colorado.

[The five-digit USGS parameter code is used to uniquely identify a specific constituents or property. Thresholds and threshold levels as of April 14, 2008. 

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

maximum contaminant level; na, not available; mg/L, micrograms per liter. Other abbreviations: CAS, Chemical Abstract Service; MDL, method detection 

limit; D, detected in ground-water samples (table 11)]

Constituent 

(valence state)

USGS 

parameter 

code

CAS number MDL 

(μg/L)

Threshold 

type1

Threshold 

level 

(μg/L)

Detection

Arsenic (III) 99034 22569-72-8 1 na na D 

Arsenic (total) 99033 7440-38-2 0.5 MCL-US 10 D 

Iron (II) 01047 7439-89-6 2 na na D 

Iron (total) 01046 7439-89-6 2 SMCL-CA 300 D 

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.

Constituent

USGS 

parameter 

code

CAS number

Reporting 

level 

type

Reporting 

level or 

uncertainty

Threshold 

type1

Threshold 

level Detection

Stable isotope ratios (per mil)

δ2H of water2 82082 na MU 2 na na D

δ18O of water2 82085 na MU 0.20 na na D

δ13C of dissolved carbonates3 82081 na 1 sigma 0.05 na na D

Radioactive constituent (percent modern)

Carbon-144 49933 14762-75-5 1 sigma 0.0015 na na D

Radioactive constituents (pCi/L)

Tritium5 07000 10028-17-8 MRL 0.3 MCL-CA 20,000 D

Gross alpha particle activity, 72-hour 

and 30-day counts6

62636, 62639 12587-46-1 ssLC CSU MCL-US 15 D

Gross beta particle activity, 72-hour and 

30-day counts6

62642, 62645 12587-47-2 ssLC CSU MCL-CA 50 D

Uranium-2346 22610 13966-29-5 ssLC CSU MCL-CA7 20 D

Uranium-2356 22620 15117-96-1 ssLC CSU MCL-CA7 20 D

Uranium-2386 22603 7440-61-1 ssLC CSU MCL-CA7 20 D

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

USGS Stable Isotope Laboratory, Reston, Virginia.

4

University of Arizona, Accelerator Mass Spectrometry Laboratory (contract laboratory).

5

USGS Stable Isotope and Tritium Laboratory, Menlo Park, California.

6

Eberline Analytical Services (contract laboratory).

7

The MCL-CA threshold for uranium is the sum of uranium-234, uranium-235, and uranium-238.

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

[The five-digit U.S. Geological Survey (USGS) parameter code is used to uniquely identify a specific constituent or property. Stable isotope ratios are reported 

in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard reference material. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. 

Environmental Protection Agency maximum contaminant level. Other abbreviations: H, hydrogen; O, oxygen; C, carbon; CAS, Chemical Abstract Service; 

CSU, 1-sigma combined standard uncertainty; CV, critical value; MRL, minimum reporting level; MU, method uncertainty; na, not available; pCi/L, picocuries 

per liter; ssLC, sample-specific critical level; D, detected in ground-water samples (tables 12 and 13)]
Tables 35

Constituent

USGS 

parameter 

code

CAS number MU 

(percent)

Reporting 

units

Threshold 

type1

Threshold 

level 

(pCi/L)

Helium-3/Helium-4 61040 na / 7440-59-7 0.75 atom ratio na na

Argon 85563 7440-37-1 2 cm3 STP/g na na

Helium-4 85561 7440-59-7 2 cm3 STP/g na na

Krypton 85565 7439-90-9 2 cm3 STP/g na na

Neon 61046 7440-01-09 2 cm3 STP/g na na

Xenon 85567 7440-63-3 2 cm3 STP/g na na

Tritium 07000 10028-17-8 1 pCi/L MCL-CA 20,000

Table 3K. Noble gases and tritium, comparison thresholds, and reporting information for the Lawrence Livermore National Laboratory.

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

as of April 14, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level. Other abbreviations: CAS, Chemical 

Abstract Service; MU, method uncertainty; na, not available; cm3 STP/g, cubic centimeters of gas at standard temperature and pressure per gram of water; pCi/L, 

picocuries per liter]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists.
36 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

GAMA identification 

number

Turbidity, 

field 

(NTU) 

(63676)

Dissolved 

oxygen, 

field 

(mg/L) 

(00300) 

Water 

temperature, 

field 

(oC) 

(00010)

pH, 

lab 

(standard 

units) 

00403)

pH, 

field 

(standard 

units) 

(00400)

Specific 

conductance, 

lab 

(μS/cm 

at 25 oC)

 (90095)

Specific 

conductance, 

field 

(μS/cm 

at 25 oC) 

(00095)

Alkalinity, 

lab 

(mg/L as 

CaCO3) 

(29801)

Alkalinity, 

field 

(mg/L as 

CaCO3) 

(29802)

Threshold type SMCL-CA na na SMCL-US SMCL-US SMCL-CA SMCL-CA na na

Threshold level 5 na na <6.5 or >8.5 <6.5 or >8.5 1900 (1,600) 1900 (1,600) na na

[RL] [0.1] [0.2] [0.0 - 38.5] [0-14] [0-14] [5] [5] [1] [1]

Grid wells

MADCHOW-01 nc 5.1 20.5 7.1 6.8 489 485 185 nc

MADCHOW-02 nc 6.5 22.0 7.5 7.3 203 202 65 nc

MADCHOW-03 nc 3.3 20.5 7.4 7.2 218 218 76 nc

MADCHOW-04 nc 1.4 19.5 7.7 7.3 166 165 77 nc

MADCHOW-05 nc nc 24.5 7.3 7.0 267 272 97 nc

MADCHOW-06 nc 5.7 22.5 7.9 7.8 397 413 132 nc

MADCHOW-07 0.9 4.5 22.0 7.6 7.3 324 325 105 100

MADCHOW-08 1.0 1.7 23.0 7.7 7.5 317 317 94 92

MADCHOW-09 1.6 7.7 19.5 7.3 7.1 759 760 253 nc

MADCHOW-10 0.8 4.5 22.0 7.8 7.7 211 213 71 67

MADCHOW-11 1.0 7.5 24.0 7.7 7.5 324 330 94 nc

MADCHOW-12 nc 0.3 24.0 8.2 8.0 **1,800 **1,850 82 nc

MADCHOW-13 nc 4.5 22.5 7.9 7.7 206 207 73 nc

MADCHOW-14 nc 6.1 21.0 7.8 7.7 194 194 67 nc

MADCHOW-15 0.1 1.4 23.5 7.5 7.1 168 165 69 nc

MADCHOW-16 nc 4.2 24.5 7.6 7.4 233 237 76 nc

MADCHOW-17 nc 5.7 21.5 7.5 7.2 389 395 152 nc

MADCHOW-18 nc 7.2 20.5 7.2 6.8 452 467 148 nc

MADCHOW-19 nc 4.0 21.5 7.5 7.0 244 245 87 nc

MADCHOW-20 nc 7.1 20.0 7.4 7.1 * 948 *983 338 nc

MADCHOW-21 nc 6.7 23.5 7.3 7.0 253 268 94 nc

MADCHOW-22 0.6 1.2 22.0 8.1 8.0 278 282 93 88

MADCHOW-23 0.4 0.7 22.0 8.4 8.4 275 272 106 102

MADCHOW-24 nc 5.7 21.0 7.2 8.0 302 317 84 nc

MADCHOW-25 nc 5.7 21.0 7.2 7.0 **1,650 **1,650 536 nc

MADCHOW-26 nc 6.0 20.5 7.3 7.0 *1,300 *1,310 264 nc

MADCHOW-27 nc 1.6 20.5 7.8 7.6 422 425 157 nc

MADCHOW-28 nc 7.5 21.0 7.3 6.9 *1,270 *1,290 394 nc

MADCHOW-29 nc 7.2 21.5 7.5 7.2 745 744 279 nc

MADCHOW-30 nc 3.0 22.5 8.4 8.4 272 275 67 nc

Flow-path wells

MADCHOWFP-01 2.9 8.2 21.0 7.6 7.4 812 820 263 256

MADCHOWFP-02 0.1 6.0 21.5 7.9 7.5 221 225 71 68

MADCHOWFP-03 0.4 7.8 19.0 7.1 6.8 **5,740 **5,870 182 178

MADCHOWFP-04 0.2 3.3 20.0 7.4 7.4 255 255 83 81

MADCHOWFP-05 0.5 1.3 23.0 7.8 7.6 399 402 136 134

Table 4. Field water-quality indicators in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, April and May 2008.

[The five digit number below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. 

GAMA Identification number: MADCHOW, Madera-Chowchilla study unit grid well; MADCHOWFP, Madera-Chowchilla unit flow-path well; Thresholds 

and threshold levels as of April 14, 2008. Threshold type: SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level; SMCLCA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: oC, degrees celsius; mg/L, milligrams per liter; nc, 

sample not collected; na, not available; NTU, nephelometric turbidity unit; RL, reporting limit or range; μS/cm, microsiemens per centimeter; CaCO3, calcium 

carbonate; <, less than; >, greater than; *, value above threshold level or outside threshold range; **, value above upper threshold level]

1

The SMCL-CA for specific conductance has recommended and upper threshold levels. The upper level is shown in parentheses.
Tables 37

Table 5. Volatile organic compounds (VOCs) and low-level 1,2-dibromo-3-chloropropane (DBCP) and 1,2-dibromoethane (EDB) detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all thirty-five wells were analyzed, but only samples with detections are listed. Analytes are grouped by primary use or source and listed in order of decreasing detection frequency in the thirty grid wells. All analytes are listed in tables 3A and 3B. GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA; California Department of Public Health maximum contaminant level; NL-CA, California Department of Public Health notification level. Other abbreviations: E, estimated value; LRL, laboratory reporting level; V, constituent detected in blanks and therefore excluded from the dataset of ground-water quality results; μg/L, micrograms per liter; —, not detected; *, value above threshold level]

GAMA 

identification 

 number

Disinfection by-products (THMs) Fumigants Solvents Gasoline hydrocarbons

VOC 

detections 

per well

Chloroform 

(μg/L) 

(32106)

Bromodichloro

methane 

(μg/L) 

(32101)

Dibromochloromethane 

(μg/L) 

(32105)

Bromoform 

(μg/L) 

(32104)

1,2-Dibromo3-chloro 

propane 

(DBCP) 

(μg/L) 

(82625)

1,2-

Dichloropropane 

(μg/L) 

(34541)

1,2-Dibromoethane 

(EDB) (μg/L) 

(77651)

Perchloroethene 

(PCE) 

(μg/L) 

(34475)

Trichloroethene 

(TCE) 

(μg/L) 

(39180)

1,1-

Dichloroethane 

(μg/L) 

(34496)

cis-1,2-

Dichloroethene 

(μg/L) 

(77093)

1,2,4-

Trimethylbenzene 

(μg/L) 

(77222)

Toluene 

(μg/L) 

(34010)

Threshold type1 MCL-US MCL-US MCL-US MCL-US MCL-US MCL-CA MCL-US MCL-US MCL-US MCL-US MCL-US NL-CA MCL-CAThreshold level 280 280 280 280 0.2 5 0.02 5 5 5 6 330 150[LRL] [0.02] [0.04] [0.12] [0.08] [0.030] [0.02] [0.04] [0.04] [0.02] [0.04] [0.02] [0.04] [0.018]

Grid wells

MADCHOW-01 E0.08 E0.06 0.2 0.91 *0.35 E0.06 *E0.05 0.21 — E0.05 — — — 9MADCHOW-03 E0.02 — — — — — — 2.27 0.3 — 0.31 — — 4MADCHOW-04 E0.06 — — — — — — — — — — — — 1MADCHOW-05 E0.03 — — — — — — — — — — — — 1MADCHOW-09 E0.04 — — — — — — E0.06 E0.03 — — — — 3MADCHOW-18 — — — — *0.51 E0.06 — — — — — — — 2MADCHOW-19 — — — — *0.82 — — — — — — — — 1MADCHOW-23 — — — — — — — — — — — — V0.02 0MADCHOW-25 — — — — — — — — — — — E0.08 — 1MADCHOW-27 — — — — — — — — — — — E0.09 — 1Number of 

detections

5 1 1 1 3 2 1 3 2 1 1 2 0

Detection 

frequency (percent)

16.7 3.3 3.3 3.3 10 6.7 3.3 10 6.7 3.3 3.3 6.7 0 330

Flow-path wells

MADCHOWFP-01 E0.04 — — — — — — — — — — — — 1

1Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.2The MCL-US threshold for trihalomethanes is the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.3Frequency of detection of at least one VOC in the grid wells. Detections with V remark codes are not included.
38 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table 6A. Pesticides and pesticide degradates detected in samples collected for the Madera–Chowchilla Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, April and May 2008.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all thirty-five wells were analyzed, but only samples with detections are listed. Analytes are listed in order of decreasing detection 

frequency in the thirty grid wells. All analytes are listed in table 3C. GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; 

MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA; California 

Department of Public Health maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level; μg/L, micrograms per 

liter; —, not detected]

GAMA 

identification 

number

Deethylatrazine 

(μg/L) 

(04040)

Simazine 

(μg/L) 

(04035)

3,4-Dichloroaniline 

(μg/L) 

(61625)

Atrazine 

(μg/L) 

(39632)

Hexazinone 

(μg/L) 

(04025)

Tebuthiuron 

(μg/L) 

(82670) Pesticide 

detections 

Threshold type per well 1 na MCL-US MCL-CA MCL-CA HAL-US HAL-US

Threshold level na 4 1 1 400 500

[LRL] [0.014] [0.006] [0.006] [0.007] [0.008] [0.016]

Grid wells

MADCHOW-01 E0.015 E0.006 E0.005 0.009 — — 4

MADCHOW-03 E0.007 — — — — — 1

MADCHOW-04 — 0.018 E0.004 — — — 2

MADCHOW-06 — 0.011 — — — E0.01 2

MADCHOW-09 E0.007 E0.006 E0.009 — — — 3

MADCHOW-18 E0.056 E0.007 E0.005 0.039 — — 4

MADCHOW-26 E0.018 — E0.004 E0.005 0.009 — 4

MADCHOW-29 E0.006 0.018 — — — — 2

Number of detections 6 6 5 3 1 1

Detection frequency 

(percent)

20 20 17 10 3 3 227

Flow-path wells

MADCHOWFP-01 E0.038 — — 0.008 0.011 — 3

MADCHOWFP-03 — — E0.004 — 0.010 — 2

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

Frequency of detection of at least one pesticide or pesticide degradate in the grid wells. The grid wells with detections in table 6B are a subset of the grid 

wells with detections in table 6A, therefore the detection frequency of 27 percent applies to both tables. Note the detection frequency in table 6A does not 

include the three fumigants already presented as volatile organic compounds in table 5; if these fumigants were included, the detection frequency for any 

pesticide(s) in the grid wells would be 30 percent. 
Tables 39

GAMA identification 

number

Diuron 

(μg/L) 

(49300)

Bromacil 

(μg/L) 

(04029)

Deisopropyl 

atrazine 

(μg/L) 

(04038)

Dinoseb 

(μg/L) 

(49301)

Norflurazon 

(μg/L) 

(49293)

Imazethapyr 

(μg/L) 

(50407) Pesticide 

detections 

Threshold type per well 1 RSD5-US HAL-US na MCL-US na na

Threshold level 20 70 na 7 na na

[LRL] [0.04] [0.02] [0.08] [0.04] [0.02] [0.04]

Grid wells

MADCHOW-01 E0.04 — — — — — 3

MADCHOW-09 0.15 0.03 — — — — 3

MADCHOW-18 0.08 E0.01 E0.03 E0.04 — — 6

MADCHOW-29 — — — — E0.01 — 2

Number of detections3 2 1 1 1 0

Detection frequency 

(percent)

10 7 3 3 3 0 (2)

Flow-path wells

MADCHOWFP-03 E0.01 — — — — E0.01 2

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

The grid wells with detections in table 6B are a subset of the grid wells with detections in table 6A, therefore the detection frequency of 27 percent reported 

in table 6A applies to both tables. Note the detection frequency reported in table 6A does not include the three fumigants already presented as volatile organic 

compounds in table 5; if these fumigants were included, the detection frequency for any pesticide(s) in the grid wells would be 30 percent. 

Table 6B. Polar pesticides and metabolites detected in samples collected for the Madera–Chowchilla Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, April and May 2008.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all thirty-five wells except MADCHOW-17 were analyzed. Only samples with detections are listed. Analytes are listed in order of 

decreasing detection frequency in the twenty-nine grid wells. All analytes are listed in table 3D. GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera-Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold 

type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-US, U.S. Environmental Protection Agency maximum contaminant 

level; RSD5-US, U.S. Environmental Protection Agency risk specific dose at a risk factor of 10–5. Other abbreviations: E, estimated value; LRL, laboratory 

reporting level; μg/L, micrograms per liter; na, not available; —, not detected]
40 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table 7. Constituents of special interest (N-nitrosodimethylamine [NDMA], perchlorate, and low-level 1,2,3-trichloropropane [1,2,3-

TCP]) detected in samples collected in the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, April and May 2008.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Information about the analytes given in table 3F. Samples from all thirty-five wells were analyzed for 1,2,3-TCP, samples from 34 wells were 

analyzed for perchlorate, and samples from ten slow wells were analyzed for NDMA. GAMA identification number: MADCHOW, Madera–Chowchilla study 

unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: HAL-US, 

U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; NL-CA, 

California Department of Public Health notification level. Other abbreviations: MRL, minimum reporting level; μg/L, micrograms per liter; nc, sample not 

collected; —, not detected]

GAMA identification number

N-Nitrosodimethylamine 

(NDMA) (μg/L) 

(34438)

Perchlorate 

(μg/L) 

(61209)

1,2,3-Trichloropropane 

(μg/L) 

(77443)

Threshold type1 NL-CA MCL-CA HAL-US

Threshold level 0.01 6 40

[MRL] [0.0020] [0.10] [0.0050]

Grid wells

MADCHOW-01 nc 0.22 0.0161

MADCHOW-02 nc 0.19 —

MADCHOW-03 nc — —

MADCHOW-04 nc — —

MADCHOW-05 nc 0.63 —

MADCHOW-06 nc 0.23 0.0237

MADCHOW-07 0.0025 0.84 —

MADCHOW-08 — — —

MADCHOW-09 nc 1.80 0.0055

MADCHOW-10 — — 0.0069

MADCHOW-11 nc 0.15 —

MADCHOW-12 nc — —

MADCHOW-13 nc 0.12 —

MADCHOW-14 nc 0.20 —

MADCHOW-15 nc — 0.0052

MADCHOW-16 nc 0.22 0.0050

MADCHOW-17 nc 0.53 —

MADCHOW-18 nc 0.82 0.0288

MADCHOW-19 nc 0.17 —

MADCHOW-20 nc 0.16 0.0052

Table 7. Constituents of special interest (N-nitrosodimethylamine [NDMA], perchlorate, and low-level 1,2,3-trichloropropane [1,2,3-

TCP]) detected in samples collected in the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, April and May 2008.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Information about the analytes given in table 3F. Samples from all thirty-five wells were analyzed for 1,2,3-TCP, samples from 34 wells were 

analyzed for perchlorate, and samples from ten slow wells were analyzed for NDMA. GAMA identification number: MADCHOW, Madera–Chowchilla study 

unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: HAL-US, 

U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; NL-CA, 

California Department of Public Health notification level. Other abbreviations: MRL, minimum reporting level; μg/L, micrograms per liter; nc, sample not 

collected; —, not detected]
Tables 41

Table 7. Constituents of special interest (N-nitrosodimethylamine [NDMA], perchlorate, and low-level 1,2,3-trichloropropane [1,2,3-

TCP]) detected in samples collected in the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, 

California, April and May 2008.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Information about the analytes given in table 3F. Samples from all thirty-five wells were analyzed for 1,2,3-TCP, samples from 34 wells were 

analyzed for perchlorate, and samples from ten slow wells were analyzed for NDMA. GAMA identification number: MADCHOW, Madera–Chowchilla study 

unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: HAL-US, 

U.S. Environmental Protection Agency lifetime health advisory level; MCL-CA, California Department of Public Health maximum contaminant level; NL-CA, 

California Department of Public Health notification level. Other abbreviations: MRL, minimum reporting level; μg/L, micrograms per liter; nc, sample not 

collected; —, not detected]

GAMA identification number

N-Nitrosodimethylamine 

(NDMA) (μg/L) 

(34438)

Perchlorate 

(μg/L) 

(61209)

1,2,3-Trichloropropane 

(μg/L) 

(77443)

Threshold type1 NL-CA MCL-CA HAL-US

Threshold level 0.01 6 40

[MRL] [0.0020] [0.10] [0.0050]

MADCHOW-21 nc 0.88 —

MADCHOW-22 — — 0.0052

MADCHOW-23 — — —

MADCHOW-24 nc 0.30 —

MADCHOW-25 nc 0.16 —

MADCHOW-26 nc 0.13 —

MADCHOW-27 nc — 0.0198

MADCHOW-28 nc 0.91 —

MADCHOW-29 nc 0.29 —

MADCHOW-30 nc 0.27 —

Number of wells with detections 1 21 10

Detection frequency (percent)2 not calculated 70 33

Flow-path wells

MADCHOWFP-01 — 0.66 —

MADCHOWFP-02 — nc 0.0051

MADCHOWFP-03 — 0.11 —

MADCHOWFP-04 — — —

MADCHOWFP-05 — — — 1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

Frequency of detection for constituents of special interest analyzed in the 30 grid wells sampled. 
42 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table 8. Nutrients detected in s amples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.—Continued

[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all thirty-five wells were analyzed. Information about the analytes given in table 3G. GAMA identification number: MADCHOW, 

Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level; mg/L, milligrams per liter; na, not available; —, not detected; 

*, value above threshold level]

GAMA 

identification 

number

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite plus 

nitrate, 

as nitrogen 

(mg/L) 

(00631)

 Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Total nitrogen 

(ammonia + nitrite 

+ nitrate + organicnitrogen), 

as nitrogen 

(mg/L) 

(62854)

Orthophosphate, 

as phosphorous 

(mg/L) 

(00671)

Threshold type1 HAL-US MCL-US MCL-US na na

Threshold level 224.7 10 1 na na

[LRL] [0.02] [0.04] [0.002] [0.06] [0.006]

Grid wells

MADCHOW-01 — 3.88 — 4.03 0.048

MADCHOW-02 — 2.16 — 2.23 0.057

MADCHOW-03 — 0.78 — 0.81 0.058

MADCHOW-04 — 0.42 — 0.45 0.094

MADCHOW-05 — 2.88 — 2.96 0.033

MADCHOW-06 — 4.18 — 4.23 0.018

MADCHOW-07 — 4.07 — 4.20 0.024

MADCHOW-08 — 0.54 — 0.56 0.044

MADCHOW-09 — *10.3 — 10.9 0.028

MADCHOW-10 — 0.50 — 0.52 0.038

MADCHOW-11 — 1.00 — 1.04 0.041

MADCHOW-12 0.027 — — — 0.017

MADCHOW-13 — 0.85 — 0.86 0.048

MADCHOW-14 — 1.24 — 1.21 0.032

MADCHOW-15 — 0.87 — 0.88 0.104

MADCHOW-16 — 1.03 — 1.05 0.040

MADCHOW-17 E0.012 5.49 — 5.60 0.148

MADCHOW-18 E0.014 5.96 — 6.03 0.082

MADCHOW-19 — 1.75 — 1.89 0.047

MADCHOW-20 — 6.00 — 6.29 0.044

MADCHOW-21 — 5.43 — 5.67 0.153

MADCHOW-22 — 1.56 0.01 1.56 0.029

MADCHOW-23 — 0.34 0.01 0.34 0.035

MADCHOW-24 — 2.78 — 2.84 0.024

MADCHOW-25 — *38.6 — 38.7 0.056

MADCHOW-26 — 3.00 — 2.93 0.051

MADCHOW-27 — 1.16 — 1.25 0.064

Table 8. Nutrients detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.

[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all thirty-five wells were analyzed. Information about the analytes given in table 3G. GAMA identification number: MADCHOW, 

Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level; mg/L, milligrams per liter; na, not available; —, not detected; 

*, value above threshold level]
Tables 43

Table 8. Nutrients detected in s amples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.—Continued

[The five digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from all thirty-five wells were analyzed. Information about the analytes given in table 3G. GAMA identification number: MADCHOW, 

Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. 

Threshold type: HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; MCL-US, U.S. Environmental Protection Agency maximum 

contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level; mg/L, milligrams per liter; na, not available; —, not detected; 

*, value above threshold level]

GAMA 

identification 

number

Ammonia, 

as nitrogen 

(mg/L) 

(00608)

Nitrite plus 

nitrate, 

as nitrogen 

(mg/L) 

(00631)

 Nitrite, 

as nitrogen 

(mg/L) 

(00613)

Total nitrogen 

(ammonia + nitrite 

+ nitrate + organicnitrogen), 

as nitrogen 

(mg/L) 

(62854)

Orthophosphate, 

as phosphorous 

(mg/L) 

(00671)

Threshold type1 HAL-US MCL-US MCL-US na na

Threshold level 224.7 10 1 na na

[LRL] [0.02] [0.04] [0.002] [0.06] [0.006]

MADCHOW-28 — 8.57 — 9.17 0.053

MADCHOW-29 — 6.44 — 6.55 0.041

MADCHOW-30 — 3.10 — 3.17 0.017

Flow-path wells

MADCHOWFP-01 — 9.95 — 10.5 0.026

MADCHOWFP-02 E0.011 1.33 — 1.46 0.044

MADCHOWFP-03 — 9.97 — 10.6 0.037

MADCHOWFP-04 — 0.22 E0.001 0.23 0.108

MADCHOWFP-05 0.034 — — E0.03 0.025

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

 The HAL-US is 30 mg/L "as ammonia." To facilitate comparson to the analytical results, we have converted and reported this HAL-US as 24.7 mg/L "as 

nitrogen."
44 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program Table 9. Major and minor ions and total dissolved solids detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued [The five digit number in parenthesis below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all thirty-five wells were analyzed. Information about analytes given in table 3H. GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: LRL, laboratory reporting level; mg/L, milligrams per liter; E, estimated value; na, not available; —, not detected; *, value above threshold level; **, value above upper threshold level] GAMA identification number Calcium (mg/L) (00915) Magnesium (mg/L) (00925) Potassium (mg/L) (00935) Sodium (mg/L) (00930) Bicarbonate1 (mg/L) Carbonate1 (mg/L) Bromide (mg/L) (71870) Chloride (mg/L) (00940) Fluoride (mg/L) (00950) Iodide (mg/L) (71865) Silica (mg/L) (00955) Sulfate (mg/L) (00945) Total dissolved solids (TDS) (mg/L) (70300) Threshold type2 na na na na na na na SMCL-CA MCL-CA na na SMCL-CA SMCL-CA Threshold level na na na na na na na 3250 (500) 2 na na 3250 (500) 3500 (1,000) [LRL] [0.04] [0.02] [0.02] [0.2] [1] [1] [0.02] [0.12] [0.12] [0.002] [0.018] [0.18] [10] Grid wells MADCHOW-01 48.7 15.5 6.39 27.5 225

— 0.05 25.2 E0.09 E0.002 68.9 14.4 340

MADCHOW-02 15.4 4.53 3.04 19.3 79

— 0.04 16.3 0.17 0.004 72.8 3.13 182

MADCHOW-03 16.6 4.63 2.78 20.8 92

— 0.04 17.4 E0.12 E0.001 60.7 4.05 172

MADCHOW-04 13.6 5.46 2.86 11.7 93

— E0.02 3.99 E0.11 0.009 43.6 2.73 129

MADCHOW-05 19.9 6.60 1.86 24.2 118

— 0.07 15.0 0.24 E0.002 73.8 7.43 222

MADCHOW-06 32.8 3.29 4.36 42.9 160 1 0.10 21.7 0.13 0.022 29.5 22.5 261MADCHOW-07 27.8 8.51 2.19 23.6 128

— 0.08 13.3 0.34 0.007 69.9 24.3 264

MADCHOW-08 24.1 6.31 4.52 22.7 114

— 0.08 33.9 0.16 0.025 71.2 7.78 243

MADCHOW-09 78.4 23.5 2.71 34.3 308

— 0.13 58.1 0.15 0.004 54.6 18.3 475

MADCHOW-10 13.6 3.32 6.35 18.9 86

— 0.05 19.5 0.15 0.007 73.2 2.97 193

MADCHOW-11 25.1 6.12 4.12 25.2 114

— 0.09 33.8 0.14 0.023 69.4 11.0 257

MADCHOW-12 64.5 16.1 2.00 258 98 1 1.87 **506

— 0.880 16.3 E0.88 **1,070

MADCHOW-13 7.38 2.61 1.58 33.0 88

— 0.05 16.6 0.13 0.009 59.1 3.31 180

MADCHOW-14 13.1 5.02 1.72 16.4 81

— 0.05 15.5 0.12

— 62.8 2.70 176

MADCHOW-15 8.41 3.58 3.21 19.7 84

— 0.03 9.06 0.21 E0.001 48.2 1.91 144

MADCHOW-16 16.6 4.97 2.87 23.5 92

— 0.06 21.3 0.20 0.007 80.7 3.54 209

MADCHOW-17 41.8 12.6 2.45 18.3 185

— 0.07 13.6 E0.12 0.002 43.6 11.6 273

MADCHOW-18 39.0 13.0 6.28 32.1 180

— 0.09 22.6 0.15 0.002 73.2 26.9 337

MADCHOW-19 17.6 8.12 4.40 17.8 106

— 0.06 15.0 0.15 E0.002 74.7 8.44 202

MADCHOW-20 102 27.0 5.39 63.5 411

— 0.13 61.4 E0.10 0.005 63.9 62.0 *632

MADCHOW-21 18.7 7.09 1.87 21.7 114

— 0.07 10.1 0.20 E0.001 86.3 2.87 246

MADCHOW-22 24.2 3.11 1.80 28.0 112 1 0.06 25.2 0.16 0.013 56.6 4.39 220MADCHOW-23 7.17 1.47 1.53 55.4 126 1.4 0.07 22.9 0.29 0.028 39.7 4.70 198MADCHOW-24 23.0 4.50 2.15 26.9 102

— 0.07 29.1 0.12 E0.002 33.4 4.93 199

Table 9. Major and minor ions and total dissolved solids detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.[The five digit number in parenthesis below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all thirty-five wells were analyzed. Information about analytes given in table 3H. GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: LRL, laboratory reporting level; mg/L, milligrams per liter; E, estimated value; na, not available; —, not detected; *, value above threshold level; **, value above upper threshold level]
Tables 45

Table 9. Major and minor ions and total dissolved solids detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued[The five digit number in parenthesis below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all thirty-five wells were analyzed. Information about analytes given in table 3H. GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: LRL, laboratory reporting level; mg/L, milligrams per liter; E, estimated value; na, not available; —, not detected; *, value above threshold level; **, value above upper threshold level]

GAMA 

identification 

number

Calcium 

(mg/L) 

(00915) 

Magnesium 

(mg/L) 

(00925) 

Potassium 

(mg/L) 

(00935) 

Sodium 

(mg/L) 

(00930) 

Bicarbonate1

(mg/L)

Carbonate1

(mg/L)

Bromide 

(mg/L) 

(71870) 

Chloride 

(mg/L) 

(00940) 

Fluoride 

(mg/L) 

(00950) 

Iodide 

(mg/L) 

(71865)

Silica 

(mg/L) 

(00955) 

Sulfate 

(mg/L) 

(00945) 

Total 

dissolved 

solids 

(TDS) 

(mg/L) 

(70300)

Threshold type2 na na na na na na na SMCL-CA MCL-CA na na SMCL-CA SMCL-CAThreshold level na na na na na na na 3250 (500) 2 na na 3250 (500) 3500 (1,000)[LRL] [0.04] [0.02] [0.02] [0.2] [1] [1] [0.02] [0.12] [0.12] [0.002] [0.018] [0.18] [10]MADCHOW-25 181 57.4 7.01 85.8 653 — 0.23 120 E0.10 0.038 64.2 35.9 **1,040MADCHOW-26 135 35.0 6.86 81.6 321 — 0.19 222 0.13 0.018 67.0 60.4 *854MADCHOW-27 35.4 8.67 2.20 43.5 190 1 0.06 19.4 0.16 0.018 68.6 28.5 280MADCHOW-28 145 35.7 6.77 60.9 480 — 0.21 152 E0.09 0.007 63.6 26.7 *773MADCHOW-29 76.3 19.7 3.87 53.6 339 — 0.08 30.6 E0.08 0.004 58.0 45.8 *504MADCHOW-30 15.6 1.00 1.33 38.9 80 1 0.09 29.9 0.15 E0.002 16.3 5.70 162

Flow-path wells

MADCHOWFP-01 90.9 15.9 5.14 45.1 320 1 0.15 72.7 E0.07 0.005 64.8 19.7 * 528MADCHOWFP-02 18.8 4.74 2.36 17.9 86 — 0.06 20.0 E0.09 E0.001 62.4 3.54 195MADCHOWFP-03 658 112 10.6 298 222 — 2.12 **1,850 — 0.021 59.5 25.0 **4,340MADCHOWFP-04 19.7 4.71 4.06 20.4 101 — 0.06 23.9 0.14 0.021 63.2 3.49 202MADCHOWFP-05 40.0 8.39 3.20 32.0 165 — 0.07 15.0 0.25 0.038 71.0 43.5 309

1Bicarbonate and carbonate concentrations were calculated from the laboratory alkalinity and pH values (table 4) using the advanced speciation method (http://or.water.usgs.gov/alk/methods.html) with 

pK1 = 6.35, pK2 = 10.33, and pKW = 14.

2Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US exists.3The SMCL-CA for chloride, sulfate, and total dissolved solids have recommended and upper threshold levels. The upper level is shown in parentheses. 
46 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program Table 10. Trace elements detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued [The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all thirty-five wells were analyzed. Mercury and thallium were analyzed, but not detected. Table 3H contains additional information about the analytes. Values less than the study reporting level (SRL) are reported with a less than or equal to sign (≤). GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; μg/L, micro- grams per liter; —, not detected; *, value above threshold level; ≤, less than or equal to] GAMA identification number Aluminum (μg/L) (01106) Antimony (μg/L) (01095) Arsenic (μg/L) (01000) Barium (μg/L) (01005) Beryllium (μg/L) (01010) Boron (μg/L) (01020) Cadmium (μg/L) (01025) Chromium (μg/L) (01030) Cobalt (μg/L) (01035) Copper (μg/L) (01040) Iron (μg/L) (01046) Lead (μg/L) (01049) [LRL] or [SRL]1 [1.6]1 [0.14] [0.06] [0.36]1 [0.008] [6] [0.04] [0.421 [0.02] [1.7]1 [6]1 [0.651 Threshold type2 MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US Threshold level 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 15 Grid wells MADCHOW-01

—

— 0.75 182

— 38

— 1.3 0.06 2.0 ≤5 ≤0.64

MADCHOW-02

—

— 1.7 54

— 23

— 2.8

—

— 12 ≤0.12

MADCHOW-03

—

— 1.2 51

— 26

— 0.98

—

—

— ≤0.07

MADCHOW-04

—

— 2.2 12

— 21

— 0.65

—

—

— ≤0.24

MADCHOW-05

—

— 2.6 81

— 21 0.06 1.6 0.02 ≤0.8

— ≤0.41

MADCHOW-06 ≤1.0

— 2.2 37

— 30

— 0.69 0.04 ≤1.0

— ≤0.26

MADCHOW-07

—

— *10.8 66

— 19

— 1.2 E0.01

—

— ≤0.15

MADCHOW-08 ≤1.0 E0.09 *12.6 98

— 24

— 0.98

— ≤0.8

— ≤0.33

MADCHOW-09

—

— 0.79 329

— 17 E0.03 3.0 0.06 ≤1.4 18 ≤0.65

MADCHOW-10 2.4 E0.08 2.2 118

— 33

— 2.0

—

—

— ≤0.06

MADCHOW-11 ≤0.9

— 7.9 99 E0.005 32

— 1.4

— ≤1.3

— ≤0.09

MADCHOW-12 ≤1.1

— *20.3 868 E0.01 51 E0.03

— 0.03

— 86

—

MADCHOW-13 ≤0.8

— 3.8 31

— 22

— 2.9

—

—

— ≤0.21

MADCHOW-14

—

— 2.3 52

— 26

— 4.4

—

—

— ≤0.14

MADCHOW-15

—

— 2.1 43

— 19

— ≤0.40

— ≤0.5

— ≤0.20

MADCHOW-16 ≤1.0

— 2.6 118

— 31

— 2.2

—

—

—

—

MADCHOW-17

—

— 1.6 96

— 14

— 0.67 0.02

—

— ≤0.07

MADCHOW-18

—

— 0.92 172

— 29

— 1.1 E0.02 ≤0.8

— ≤0.33

MADCHOW-19 1.8

— 3.8 97

— 17

— 1.4

—

—

—

—

MADCHOW-20

—

— 2.6 159

— 32

— 3.5 0.03 ≤0.8 ≤5 0.84

MADCHOW-21 1.7

— 2.0 118 E0.01 11

— 1.1 E0.01

—

—

—

MADCHOW-22 ≤0.9 E0.08 7.4 507

— 18

—

— E0.01

—

—

—

MADCHOW-23 1.7 E0.09 *16.2 164

— 32

—

—

—

—

— ≤0.12

Table 10. Trace elements detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all thirty-five wells were analyzed. Mercury and thallium were analyzed, but not detected. Table 3H contains additional information about the analytes. Values less than the study reporting level (SRL) are reported with a less than or equal to sign (≤). GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; SMCLCA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; μg/L, micrograms per liter; —, not detected; *, value above threshold level; ≤, less than or equal to]
Tables 47

Table 10. Trace elements detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all thirty-five wells were analyzed. Mercury and thallium were analyzed, but not detected. Table 3H contains additional information about the analytes. Values less than the study reporting level (SRL) are reported with a less than or equal to sign (≤). GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; μg/L, micrograms per liter; —, not detected; *, value above threshold level; ≤, less than or equal to]

GAMA 

identification 

number

Aluminum 

(μg/L) (01106)

Antimony 

(μg/L) (01095)

Arsenic (μg/L) 

(01000)

Barium (μg/L) 

(01005)

Beryllium 

(μg/L) (01010)

Boron (μg/L) 

(01020)

Cadmium 

(μg/L) (01025)

Chromium 

(μg/L) (01030)

Cobalt (μg/L) 

(01035)

Copper (μg/L) 

(01040)

Iron (μg/L) 

(01046)

Lead (μg/L) 

(01049)

[LRL] or [SRL]1 [1.6]1 [0.14] [0.06] [0.36]1 [0.008] [6] [0.04] [0.421 [0.02] [1.7]1 [6]1 [0.651Threshold type2 MCL-CA MCL-US MCL-US MCL-CA MCL-US NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-USThreshold level 1,000 6 10 1,000 4 1,000 5 50 na 1,300 300 15MADCHOW-24 ≤1.2 — 1.9 59 — 14 E0.02 8.6 E0.01 — ≤5 1.10MADCHOW-25 1.9 — 1.6 557 — 43 E0.02 1.4 0.16 2.0 — ≤0.45MADCHOW-26 1.7 — 2.7 252 — 40 E0.02 3.0 0.07 ≤1.4 — 1.10MADCHOW-27 2.1 E0.09 6.3 236 — 47 — 0.53 E0.02 — ≤5 2.38MADCHOW-28 1.9 — 2.0 471 — 20 — 3.7 0.06 ≤0.9 — ≤0.10MADCHOW-29 1.7 — 1.8 154 — 32 — 2.2 0.03 ≤0.5 — 0.90MADCHOW-30 3.1 — 2.4 27 — 16 — 14.8 — — ≤4 ≤0.07

Flow-path wells

MADCHOWFP-01 — — 3.8 350 — 20 E0.03 2.8 0.05 ≤0.9 — ≤0.04MADCHOWFP-02 — — 1.9 117 E0.004 15 — 2.3 — — — 2.69MADCHOWFP-03 E2.7 — 3.1 *2,170 — 32 E0.09 1.1 0.32 — E12 ≤0.42MADCHOWFP-04 1.8 — 1.2 177 — 20 — ≤0.15 E0.01 — 22 ≤0.15MADCHOWFP-05 ≤1.6 — 2.7 51 — 32 — — 0.02 — 75 —
48 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program Table 10. Trace elements detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued [The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all thirty-five wells were analyzed. Mercury and thallium were analyzed, but not detected. Table 3H contains additional information about the analytes. Values less than the study reporting level (SRL) are reported with a less than or equal to sign (≤). GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow- path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; μg/L, micrograms per liter; —, not detected; *, value above threshold level; ≤, less than or equal to] GAMA identification number Lithium (μg/L) (01130) Manganese (μg/L) (01056) Molybdenum (μg/L) (01060) Nickel (μg/L) (01065) Selenium (μg/L) (01145) Silver, dissolved (μg/L) (01075) Strontium (μg/L) (01080) Tungsten (μg/L) (01155) Uranium (μg/L) (22703) Vanadium (μg/L) (01085) Zinc (μg/L) (01090) [LRL] or [SRL]1 [1] [0.2]1 [0.2] [0.36]1 [0.04] [0.1] [0.8] [0.11]1 [0.02] [0.1]1 [4.8]1 Threshold type2 na SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US na MCL-US NL-CA SMCL-CA3 Threshold level na 50 40 100 50 100 4,000 na 30 50 5,000 Grid wells MADCHOW-01 2.6 0.6 1.4 0.80 0.06

— 370

— 8.64 14.8 ≤4.5

MADCHOW-02 1.1 0.6 2.5 ≤0.28 0.12

— 114

— 0.28 25.1 9.8

MADCHOW-03 1.1

— 2.2 ≤0.11 0.09

— 135

— 0.18 19.1 4.9

MADCHOW-04 2.0 ≤0.2 1.5

— E0.02

— 108 ≤0.08 1.61 7.0 ≤0.94

MADCHOW-05 1.9 1.9 3.7 ≤0.27 0.77

— 160 ≤0.06 0.28 19.6 301

MADCHOW-06 5.4

— 2.9 ≤0.19 0.28

— 87.0 0.15 12.8 22.7 21.2

MADCHOW-07 10.6

— 4.0 ≤0.22 1.6

— 238 ≤0.03 0.25 19.6 16.6

MADCHOW-08 3.3 6.5 2.9 ≤0.17 0.93

— 237 ≤0.11 2.63 2.6 ≤3.3

MADCHOW-09 1.7 4.7 0.4 0.37 0.30

— 715 ≤0.06 6.28 13.0 96.5

MADCHOW-10 4.9 3.4 1.7

— 0.12

— 147 0.64 0.17 9.3

—

MADCHOW-11 5.2 29.5 3.0 ≤0.17 0.54

— 238 ≤0.10 0.55 4.7 ≤1.2

MADCHOW-12 7.1 *420 1.9 ≤0.23 0.09

— 632 0.38 E0.01 0.33 ≤1.4

MADCHOW-13 1.6 ≤0.2 2.7

— 0.13

— 67.2 0.13 0.14 44.9 10.8

MADCHOW-14 5.7 0.3 1.9

— 0.16

— 104 0.22 0.23 24.7 8.1

MADCHOW-15 E0.90

— 6.5

— 0.08

— 112 ≤0.11 0.18 8.4 27.2

MADCHOW-16 1.6 1.5 3.9

— 0.13

— 145 ≤0.07 0.18 21.8 ≤2.3

MADCHOW-17 11.6

— 0.8 ≤0.14 0.34

— 268

— 1.32 37.1 6.9

MADCHOW-18 3.3 ≤0.2 2.1 ≤0.28 0.07

— 351

— 1.42 16.2 ≤3.0

MADCHOW-19

—

— 2.7 ≤0.12 0.34

— 166 ≤0.05 0.45 13.1 28.3

MADCHOW-20 20.0

— 1.2 0.45 0.38

— 861 0.17 *52.7 14.3 ≤1.1

MADCHOW-21 E0.80 0.4 0.8 ≤0.17 0.31

— 163 ≤0.04 0.40 29.2 16.0

MADCHOW-22 2.8 24.9 1.8 ≤0.10 0.34

— 176 0.19 0.77 27.1 ≤4.7

MADCHOW-23 2.2 10.0 3.1

— 0.09

— 68.5 1.2 0.59 *108 ≤3.2
Tables 49

Table 10. Trace elements detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from all thirty-five wells were analyzed. Mercury and thallium were analyzed, but not detected. Table 3H contains additional information about the analytes. Values less than the study reporting level (SRL) are reported with a less than or equal to sign (≤). GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flowpath well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA; California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification level; AL-US, U.S. Environmental Protection Agency action level; HAL-US, U.S. Environmental Protection Agency lifetime health advisory level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Other abbreviations: E, estimated value; LRL, laboratory reporting level, na, not available; μg/L, micrograms per liter; —, not detected; *, value above threshold level; ≤, less than or equal to]

GAMA identification 

number

Lithium 

(μg/L) 

(01130)

Manganese 

(μg/L) 

(01056)

Molybdenum

 (μg/L) 

(01060)

Nickel 

(μg/L) 

(01065)

Selenium 

(μg/L) 

(01145)

Silver, 

dissolved 

(μg/L) 

(01075)

Strontium 

(μg/L) 

(01080)

Tungsten 

(μg/L) 

(01155)

Uranium 

(μg/L) 

(22703)

Vanadium 

(μg/L) 

(01085)

Zinc 

(μg/L) 

(01090)

[LRL] or [SRL]1 [1] [0.2]1 [0.2] [0.36]1 [0.04] [0.1] [0.8] [0.11]1 [0.02] [0.1]1 [4.8]1Threshold type2 na SMCL-CA HAL-US MCL-CA MCL-US SMCL-CA HAL-US na MCL-US NL-CA SMCL-CA3Threshold level na 50 40 100 50 100 4,000 na 30 50 5,000MADCHOW-24 1.6 0.8 3.0 ≤0.19 0.24 — 189 ≤0.09 1.53 23.9 15.4MADCHOW-25 18.2 ≤0.1 0.8 1.9 0.10 — 1,650 ≤0.09 *87.0 20.1 ≤2.8MADCHOW-26 24.7 — 1.8 1.2 0.24 — 1,030 0.18 *47.3 13.7 ≤2.0MADCHOW-27 8.7 ≤0.1 2.1 ≤0.29 0.58 — 302 1.4 12.2 20.3 ≤2.1MADCHOW-28 15.8 ≤0.1 0.8 0.65 0.34 — 1,260 ≤0.09 29.8 13.0 64.9MADCHOW-29 12.1 0.3 2.1 0.40 0.30 — 556 0.18 *56.1 12.0 ≤1.5MADCHOW-30 E0.60 ≤0.1 2.8 ≤0.10 0.41 — 122 0.14 0.46 34.6 —

Flow-path wells

MADCHOWFP-01 8.9 3.7 0.9 0.46 0.41 — 803 0.17 15.7 16.9 22.9MADCHOWFP-02 1.9 — 0.8 — 0.14 — 188 ≤0.11 0.19 13.6 —MADCHOWFP-03 25.6 — E0.5 4.2 0.36 E0.3 * 6,160 — 24.4 9.80 150MADCHOWFP-04 2.7 16.1 1.7 ≤0.20 0.07 — 166 0.16 0.26 4.40 19.6MADCHOWFP-05 18.0 32.0 5.8 ≤0.25 E0.02 — 313 ≤0.09 — ≤0.05 38.0

1Result is ≤ reported value, based on QC data (including but not limited to field blanks, source-solution blanks, trip blanks, NWQL set blanks, NWQL blank water certificates, and BQS Blank 

Program data).

2Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower than the MCL-US or no MCL-US 

exists.

3The secondary maximum contaminant level for zinc is listed as SMCL-CA since SMCLs established by CDPH are used in this report for all constituents that have SMCL-CAs.
50 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

GAMA 

identification 

number

Arsenic 

(μg/L) 

Arsenic (III) 

(μg/L) 

Iron 

(μg/L) 

Iron (II) 

(μg/L) 

Threshold type1 MCL-US na SMCL-CA na

Threshold level 10 na 300 na

[MDL] [0.5] [1] [2] [2]

Grid wells

MADCHOW-07 2.3 — — —

MADCHOW-08 3.1 — — —

MADCHOW-22 1.8 — — —

MADCHOW-23 3.4 — — —

Flow-path wells

MADCHOWFP-01 0.8 — — —

MADCHOWFP-03 0.5 — 4 4

MADCHOWFP-04 — — 16 6

MADCHOWFP-05 1.0 2.2 63 4

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 

Table 11. Species of inorganic arsenic and iron detected in samples collected for the Madera–Chowchilla Groundwater Ambient 

Monitoring and Assessment (GAMA) study, California, April and May 2008.

[Data in this table analyzed at U.S. Geological Survey Trace Metal Laboratory in Boulder, Colorado using research methods and are not stored in the USGS 

NWIS database. Information about analytes given in table 3I. Samples from the ten slow wells were analyzed. GAMA identification number: MADCHOW, 

Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. 

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

maximum contaminant level. Other abbreviations: MDL, method detection limit; na, not available; μg/L, micrograms per liter; —, not detected]
Tables 51

GAMA 

identification 

number

δ2H 

(per mil) 

(82082)

δ18O 

(per mil) 

(82085)

Tritium 

(pCi/L) 

(07000)

δ13C 

(per mil) 

(82081)

Carbon-14 

(percent modern) 

(49933)

Threshold type1 na na MCL-CA na na

Threshold level na na 20,000 na na

Grid wells

MADCHOW-01 –76.1 –10.53 19.8 –15.78 119

MADCHOW-02 –68.0 –9.43 0.6 -19.08 78

MADCHOW-03 –73.6 –10.16 3.1 –17.93 80

MADCHOW-04 –87.4 –12.01 12.9 –15.75 104

MADCHOW-05 –59.4 –7.88 1.1 –15.44 76

MADCHOW-06 –55.7 –7.30 5.4 –18.47 102

MADCHOW-07 –56.1 –7.22 1.3 –15.18 52

MADCHOW-08 –63.4 –8.89 1.0 –16.02 50

MADCHOW-09 9.7 –10.78 16.7 –11.33 113

MADCHOW-10 –66.8 –9.34 <0.3 –14.01 63

MADCHOW-11 –63.7 –8.84 <0.3 –13.89 44

MADCHOW-12 –72.5 –9.87 0.8 –15.35 7

MADCHOW-13 –69.9 –9.74 1.2 –14.17 61

MADCHOW-14 –68.3 –9.59 1.0 –13.46 82

MADCHOW-15 –81.8 –11.19 0.5 –24.17 38

MADCHOW-16 –68.3 –9.63 0.4 –15.65 58

MADCHOW-17 4.5 –7.09 9.9 –16.27 110

MADCHOW-18 –74.9 –10.39 22.6 –13.87 113

MADCHOW-19 –66.6 –8.94 2.7 –13.81 70

MADCHOW-20 –70.9 –9.54 1.3 –15.94 107

MADCHOW-21 –56.5 –7.15 <0.3 –16.74 68

MADCHOW-22 –67.7 –9.32 0.5 –15.57 16

MADCHOW-23 –78.6 –10.54 <0.3 –19.60 5

MADCHOW-24 –67.7 –9.16 4.7 –14.97 54

MADCHOW-25 –62.3 –8.38 3.5 –10.78 112

MADCHOW-26 –65.7 –9.17 0.8 –16.75 100

MADCHOW-27 –88.1 –12.05 27.2 –16.72 98

MADCHOW-28 –75.6 –10.39 21.6 –12.46 112

MADCHOW-29 –70.5 –9.66 8.7 .24 107

MADCHOW-30 –60.5 –8.06 1.1 –19.05 22

Flow-path wells

MADCHOWFP-01 –73.0 –9.69 15.9 –13.80 99

MADCHOWFP-02 –68.6 –9.47 0.8 –16.54 86

MADCHOWFP-03 –72.2 –9.47 8.7 –16.79 104

MADCHOWFP-04 –75.2 –10.55 7.5 –16.58 96

MADCHOWFP-05 –58.4 –7.79 0.5 –14.17 11

Table 12. Results for analyses of stable isotope ratios and tritium and carbon-14 activities in samples collected for the Madera–

Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Information about analytes given in table 3J. Samples from all thirty-five wells were analyzed. Stable isotope ratios are reported in the standard 

delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to a standard reference material. GAMA identification 

number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold 

levels as of April 14, 2008. Threshold type: MCL-CA, California Department of Public Health maximum contaminant level. Other abbreviations: na, not 

available; pCi/L, picocuries per liter; <, less than]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 
52 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

GAMA 

identification 

number

Uranium-234 

(pCi/L) 

(22610)

Uranium-235 

(pCi/L) 

(22620)

Uranium-238 

(pCi/L) 

(22603)

Threshold type1 MCL-CA MCL-CA MCL-CA

Threshold level 220 220 220

Reporting level 

method result ± CSU ssLC result ± CSU ssLC result ± CSU ssLC

Grid wells

MADCHOW-01 4.00 ± 0.21 0.024 0.140 ± 0.029 0.015 2.90 ± 0.16 0.015

MADCHOW-02 nc nc nc nc nc nc

MADCHOW-03 nc nc nc nc nc nc

MADCHOW-04 nc nc nc nc nc nc

MADCHOW-05 nc nc nc nc nc nc

MADCHOW-06 nc nc nc nc nc nc

MADCHOW-07 0.200 ± 0.030 0.013 — 0.012 0.100 ± 0.021 0.0095

MADCHOW-08 1.100 ± 0.086 0.014 0.027 ± 0.011 0.012 0.920 ± 0.079 0.010

MADCHOW-09 3.30 ± 0.18 0.020 0.110 ± 0.024 0.011 2.20 ± 0.13 0.013

MADCHOW-10 0.120 ± 0.022 0.017 — 0.012 0.067 ± 0.015 0.0071

MADCHOW-11 0.280 ± 0.045 0.022 0.020 ± 0.013 0.015 0.180 ± 0.033 0.013

MADCHOW-12 0.039 ± 0.017 0.013 — 0.016 0.022 ± 0.012 0.013

MADCHOW-13 0.058 ± 0.020 0.011 — 0.014 0.063 ± 0.020 0.011

MADCHOW-14 0.140 ± 0.028 0.013 — 0.015 0.086 ± 0.022 0.013

MADCHOW-15 0.120 ± 0.030 0.020 — 0.017 0.140 ± 0.031 0.014

MADCHOW-16 0.180 ± 0.034 0.013 — 0.015 0.066 ± 0.022 0.013

MADCHOW-17 0.490 ± 0.058 0.018 0.020 ± 0.013 0.015 0.510 ± 0.059 0.013

MADCHOW-18 0.680 ± 0.055 0.017 0.050 ± 0.014 0.012 0.440 ± 0.042 0.012

MADCHOW-19 0.370 ± 0.036 0.0069 0.018 ± 0.011 0.0084 0.140 ± 0.022 0.012

MADCHOW-20 *24.0 ± 1.1 0.050 *1.50 ± 0.10 0.013 *15.00 ± 0.66 0.047

MADCHOW-21 0.320 ± 0.035 0.0068 0.011 ± 0.007 0.0083 0.260 ± 0.028 0.0068

MADCHOW-22 0.340 ± 0.035 0.0068 — 0.0082 0.270 ± 0.031 0.0068

MADCHOW-23 0.320 ± 0.036 0.0087 — 0.011 0.260 ± 0.036 0.0087

MADCHOW-24 0.820 ± 0.064 0.0092 0.0140 ± 0.0095 0.011 0.400 ± 0.043 0.0092

MADCHOW-25 *39.0 ± 1.7 0.056 *1.30 ± 0.10 0.013 *26.0 ± 1.1 0.051

MADCHOW-26 *23.0 ± 1.7 0.17 *0.86 ± 0.22 0.10 *14.0 ± 1.1 0.17

MADCHOW-27 5.90 ± 0.28 0.018 0.220 ± 0.028 0.0078 3.70 ± 0.19 0.017

MADCHOW-28 *17.0 ± 1.2 0.11 *0.65 ± 0.14 0.079 *9.00 ± 0.74 0.11

MADCHOW-29 *27.0 ± 1.9 0.13 *0.98 ± 0.20 0.088 *19.0 ± 1.4 0.13

MADCHOW-30 0.270 ± 0.032 0.021 — 0.012 0.160 ± 0.023 0.010

Flow-path wells

MADCHOWFP-01 9.20 ± 0.44 0.030 0.290 ± 0.044 0.012 5.00 ± 0.26 0.027

MADCHOWFP-02 0.140 ± 0.028 0.015 — 0.013 0.076 ± 0.018 0.010

MADCHOWFP-03 10.00 ± 0.46 0.021 0.290 ± 0.034 0.011 6.20 ± 0.29 0.018

MADCHOWFP-04 0.220 ± 0.027 0.011 — 0.011 0.082 ± 0.017 0.0093

MADCHOWFP-05 nc nc nc nc nc nc

Table 13A. Uranium isotopes detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, April and May 2008.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent or property. Samples from twenty-nine wells were analyzed. Table 3J contains additional information about the analytes. Measured values less than the 

sample-specific critical level (ssLC) are reported as nondetects (—). GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; 

MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-CA, California 

Department of Public Health maximum contaminant level. Other abbreviations: CSU, 1-sigma combined standard uncertainty; pCi/L, picocuries per liter; nc, 

sample not collected; *, value above threshold level]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

The MCL-US threshold for uranium is the sum of uranium-234, uranium-235, and uranium-238.
Tables 53

Table 13B. Gross alpha and gross beta particle activities detected in samples collected for the Madera–Chowchilla Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from the ten slow wells were analyzed. Table 3J contains additional information about the analytes. The reference nuclide for measurement of gross alpha is thorium-230 and the reference nuclide for measurement of gross beta is cesium-137. Measured values less than the sample-specific 

critical level (ssLC) are reported as nondetects (—). Values less than activities measured in field blanks (table A3A) are reported with a less than or equal to 

sign (≤). GAMA identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path 

well. Thresholds and threshold levels as of April 14, 2008. Threshold type: MCL-US, U.S. Environmental Protection Agency maximum contaminant level; 

MCL-CA, California Department of Public Health maximum contaminant level. Other abbreviations: CSU, 1-sigma combined standard uncertainty; pCi/L, 

picocuries per liter; *, value above threshold level; ≤, less than or equal to]

GAMA 

identification 

number

Gross alpha 

particle 

activity, 

72-hour count 

(pCi/L) 

(62636)

Gross alpha 

particle 

activity, 

30-day count 

(pCi/L) 

(62639)

Gross beta 

particle 

activity, 

72-hour count 

(pCi/L) 

(62642)

Gross beta 

particle 

activity, 

30-day count 

(pCi/L) 

(62645)

Threshold type1 MCL-US MCL-US MCL-CA MCL-CA

Threshold value 15 15 50 50

Reporting level method result ± CSU ssLC result ± CSU ssLC result ± CSU ssLC result ± CSU ssLC

Grid wells

MADCHOW-01 7.3 ± 1.2 0.63 5.9 ± 1.2 0.38 6.30 ± 0.61 0.70 7.90 ± 0.82 0.82

MADCHOW-02 1.50 ± 0.52 0.48 0.77 ± 0.48 0.57 3.00 ± 0.52 0.7 2.60 ± 0.50 0.68

MADCHOW-03 — 1.0 0.62 ± 0.43 0.51 4.20 ± 0.55 0.68 2.90 ± 0.47 0.61

MADCHOW-04 1.80 ± 0.58 0.51 0.59 ± 0.36 0.43 3.50 ± 0.73 1.0 2.50 ± 0.44 0.61

MADCHOW-05 — 0.78 — 0.64 2.30 ± 0.47 0.68 3.00 ± 0.77 1.2

MADCHOW-06 *18.0 ± 2.3 0.98 *18.0 ± 2.6 0.79 5.30 ± 0.53 0.57 7.10 ± 0.89 1.2

MADCHOW-07 1.00 ± 0.562 0.60 — 0.60 2.00 ± 0.712 1.1 ≤1.70 ± 0.50 0.74

MADCHOW-08 2.10 ± 0.73 0.90 2.30 ± 0.83 0.83 4.20 ± 0.60 0.83 5.20 ± 0.66 0.82

MADCHOW-09 7.3 ± 1.4 0.98 1.80 ± 0.54 0.56 2.70 ± 0.572 0.79 4.90 ± 0.46 0.49

MADCHOW-10 1.40 ± 0.38 0.35 0.68 ± 0.49 0.64 5.00 ± 0.57 0.72 6.00 ± 0.77 1.0

MADCHOW-11 0.84 ± 0.43 0.54 1.40 ± 0.62 0.67 4.20 ± 0.44 0.51 4.30 ± 0.69 1.0

MADCHOW-12 4.1 ± 1.7 2.1 — 2.3 2.30 ± 0.56 0.83 3.00 ± 0.52 0.72

MADCHOW-13 ≤0.65 ± 0.31 0.37 — 0.89 1.40 ± 0.34 0.51 ≤1.00 ± 0.55 0.87

MADCHOW-14 ≤0.55 ± 0.33 0.43 — 0.57 1.60 ± 0.34 0.49 ≤1.50 ± 0.41 0.60

MADCHOW-15 ≤0.65 ± 0.34 0.43 — 0.57 3.30 ± 0.51 0.72 3.40 ± 0.50 0.63

MADCHOW-16 1.60 ± 0.44 0.43 — 0.40 2.90 ± 0.47 0.70 2.30 ± 0.56 0.85

MADCHOW-17 —(3) 0.48 1.20 ± 0.52 0.60 1.90 ± 0.443 0.62 2.50 ± 0.40 0.54

MADCHOW-18 4.00 ± 0.77 0.40 1.40 ± 0.68 0.68 6.50 ± 0.56 0.53 6.80 ± 0.75 0.86

MADCHOW-19 2.60 ± 0.66 0.40 1.40 ± 0.62 0.68 4.80 ± 0.55 0.61 4.10 ± 0.55 0.70

MADCHOW-20 *52.0 ± 6.2 1.6 *30.0 ± 4.1 1.5 7.60 ± 0.86 1.1 18.0 ± 1.3 0.92

MADCHOW-21 — 1.0 1.70 ± 0.67 0.74 — 0.71 2.20 ± 0.66 1.0

MADCHOW-22 2.30 ± 0.55 0.49 1.50 ± 0.62 0.70 1.70 ± 0.35 0.50 2.80 ± 0.48 0.66

MADCHOW-23 1.30 ± 0.81 0.93 2.00 ± 0.68 0.60 1.10 ± 0.65 0.98 1.90 ± 0.49 0.70

MADCHOW-24 2.50 ± 0.70 0.62 1.50 ± 0.57 0.56 2.50 ± 0.50 0.69 2.60 ± 0.51 0.70

MADCHOW-25 *72.0 ± 8.8 2.1 *41.0 ± 5.7 2.0 11.0 ± 1.2 1.4 31.0 ± 2.0 1.1

MADCHOW-26 *29.0 ± 4.1 1.6 *28.0 ± 3.9 1.8 8.1 ± 1.1 1.5 18.0 ± 1.3 0.89

MADCHOW-27 10.0 ± 1.8 1.0 7.4 ± 1.4 0.61 3.80 ± 0.59 0.80 5.40 ± 0.67 0.79

MADCHOW-28 *31.0 ± 4.3 1.6 14.0 ± 2.7 2.2 9.20 ± 0.75 0.70 14.0 ± 1.1 1.0

MADCHOW-29 *39.0 ± 4.6 0.99 *20.0 ± 2.6 0.78 5.20 ± 0.58 0.77 18.0 ± 1.1 0.49

MADCHOW-30 — 0.69 — 0.60 1.40 ± 0.42 0.62 ≤1.30 ± 0.43 0.63

Flow-path wells

MADCHOWFP-01 *24.0 ± 3.1 0.95 12.0 ± 1.9 0.89 6.80 ± 0.75 0.84 9.30 ± 0.91 0.99

MADCHOWFP-02 — 0.55 0.73 ± 0.40 0.43 2.90 ± 0.72 1.0 2.20 ± 0.66 1.0

MADCHOWFP-03 *31.0 ± 8.2 7.8 *16.0 ± 5.8 6.1 17.0 ± 3.9 6.0 17.0 ± 2.3 2.9

MADCHOWFP-04 — 1.0 — 0.89 4.90 ± 0.66 0.88 3.70 ± 0.63 0.87

MADCHOWFP-05 2.40 ± 0.60 0.48 — 0.55 3.70 ± 0.63 0.88 3.40 ± 0.42 0.51

Table 13B. Gross alpha and gross beta particle activities detected in samples collected for the Madera–Chowchilla Groundwater 

Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey parameter code used to uniquely identify a specific constituent 

or property. Samples from the ten slow wells were analyzed. Table 3J contains additional information about the analytes. The reference nuclide for measurement 

of gross alpha is thorium-230 and the reference nuclide for measurement of gross beta is cesium-137. Measured values less than the sample-specific critical level 

(ssLC) are reported as nondetects (—). Values less than activities measured in field blanks (table A3A) are reported with a less than or equal to sign (≤). GAMA 

identification number: MADCHOW, Madera–Chowchilla study unit grid well; MADCHOWFP, Madera–Chowchilla study unit flow-path well. Thresholds and 

threshold levels as of April 14, 2008. Threshold type: MCL-US, U.S. Environmental Protection Agency maximum contaminant level; MCL-CA, California 

Department of Public Health maximum contaminant level. Other abbreviations: CSU, 1-sigma combined standard uncertainty; pCi/L, picocuries per liter; *, 

value above threshold level; ≤, less than or equal to]

1

Maximum contaminant level thresholds are listed as MCL-US when the MCL-US and MCL-CA are identical, and as MCL-CA when the MCL-CA is lower 

than the MCL-US or no MCL-US exists. 2

72-hour holding time exceeded by 1 day.

3

72-hour holding time exceeded by 2 days.
54 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Appendix 

This appendix includes discussions of the methods used 

to collect and analyze groundwater samples, the conventions 

used in reporting the resulting water-quality data, the methods 

used for quality assurance, and the results of quality-control 

assessments. 

Sample Collection and Analysis

Groundwater samples were collected using standard and 

modified USGS protocols from the USGS NAWQA program 

(Koterba and others, 1995) and the USGS National Field 

Manual (U.S. Geological Survey, variously dated), and protocols described by Weiss (1968), Shelton and others (2001), 

and Wright and others (2005). 

Prior to sampling, each well was pumped continuously 

in order to purge at least three casing-volumes of water from 

the well (Wilde and others, 1999). All wells sampled were production wells so the existing pump on the well was used for 

sampling. Groundwater samples were collected through Teflon 

tubing attached to a sampling point on the well discharge pipe 

with brass and stainless-steel fittings. The sampling point was 

located as close as possible to the well-head and upstream 

of any water-storage tanks. The sampling point was always 

located upstream of any well-head treatment system (if any). 

If a chlorinating system was attached to the well, the chlorinator was shut off prior to purging and sampling the well in 

order to clear all chlorine out of the system and the absence of 

free chlorine was verified using Hach field kits. Samples were 

collected inside an enclosed chamber located inside a mobile 

laboratory and connected to the sampling point by a 10- to 

50- foot length of Teflon tubing (Lane and others, 2003). All 

fittings and lengths of tubing were cleaned after each sample 

was collected (Wilde, 2004).

For the field water-quality indicator measurements, 

groundwater was pumped through a flow-through chamber fitted with a multi-probe meter that simultaneously measures the 

field water-quality indicators—dissolved oxygen, pH, specific 

conductance, and temperature. Field measurements were made 

in accordance with protocols in the USGS National Field 

Manual (Radtke and others, 2005; Wilde and Radtke, 2005; 

Lewis, 2006; Wilde, 2006; Wilde and others, 2006). All sensors on the multi-probe meter were calibrated daily. Measured 

dissolved oxygen, pH, specific conductance, and temperature 

values were recorded at 5-minute intervals for at least 30 

minutes, and after these values remained stable for 20 minutes, 

samples to be analyzed in laboratories were collected. At wells 

sampled on the slow schedule, turbidity also was measured. 

Turbidity was measured in the mobile laboratory with a calibrated turbidity meter (Wilde and Gibbs, 1998). Field measurements and instrument calibrations were recorded by hand 

on field record sheets and electronically in PCFF-GAMA, a 

software package designed by the USGS with support from 

the GAMA program. Analytical service requests also were 

managed by PCFF-GAMA. Information from PCFF-GAMA 

was uploaded directly into NWIS after samples were collected 

each week. 

For analyses requiring filtered water, groundwater was 

diverted through a 0.45-μm pore size vented capsule filter, a 

disk filter, or a baked glass-fiber filter depending on the protocol for the analysis (Wilde and others, 1999; Wilde and others, 

2004). Prior to sample collection, polyethylene sample bottles 

were pre-rinsed three times using deionized water, and then 

once with sample water before sample collection. Samples 

requiring acidification were acidified to a pH of 2 or less with 

the appropriate acids using ampoules of certified, traceable 

concentrated acids obtained from the USGS National Water 

Quality Laboratory (NWQL).

Samples collected to be analyzed for VOCs, low-level 

DBCP and EDB, pesticides, pharmaceuticals, nutrients, major 

ions, and trace elements were stored on ice, and shipped 

overnight in coolers with ice to the NWQL within three days 

of sample collection (samples were shipped daily whenever 

possible). Samples to be analyzed for gross alpha and gross 

beta particle activities were shipped overnight within two days 

of sample collection (samples were shipped daily whenever 

possible). Samples to be analyzed for NDMA, perchlorate, 

and low-level 1,2,3-TCP were stored on ice and shipped in 

coolers with ice overnight at the end of each week. Samples 

to be analyzed for stable isotopes of hydrogen and oxygen of 

water, uranium and carbon isotopes, tritium, and noble gases 

were shipped in batches after the last sample was collected in 

the study unit.

Detailed sampling protocols for individual analyses and 

groups of constituents are described by Koterba and others (2005) and the USGS National Field Manual (Wilde and 

others, 1999; Wilde and others, 2004) and in the references 

for analytical methods listed in table A1. The brief descriptions given here are organized in the order that samples were 

collected at each well. VOCs, low-level DBCP and EDB, and 

low-level 1,2,3-TCP samples were collected in 40-mL sample 

vials that were purged with three vial volumes of sample water 

before bottom filling to eliminate entrainment of ambient air. 

Six normal (6 N) hydrochloric acid was added as a preservative to the VOC samples, but not to the low-level DBCP and 

EDB samples, or the low-level 1,2,3-TCP samples. Samples 

to be analyzed for perchlorate were collected in a plastic 

bottle and then filtered in two or three 20-mL aliquots through 

a syringe-tip filter into a sterilized 125-mL bottle. Tritium 

samples were collected by bottom filling two 1-L polyethylene 

bottles with unfiltered groundwater, after first overfilling the 

each bottle with three volumes of water. Samples for analysis 

of stable isotopes of hydrogen and oxygen of water were collected in 60-mL clear glass bottles filled with unfiltered water, 

sealed with conical caps, and secured with electrical tape to 

prevent leakage and evaporation.
Appendix 55

Samples to be analyzed for pesticides and pesticide degradation products, polar pesticides and metabolites, pharmaceutical compounds, and NDMA were collected in 1-L baked 

amber bottles. Pesticides, polar pesticides, and pharmaceutical 

samples were filtered through a baked, 0.3-μm nominal poresize glass fiber during collection, whereas the NDMA samples 

were filtered at Weck Laboratories, Inc. prior to analysis. 

Ground water samples to be analyzed for inorganic and 

radioactive constituents were filtered through a 0.45-μm poresize Whatman capsule filter. Two 250-mL polyethylene bottles 

were filled for each sample to be analyzed for major and 

minor ions, trace elements, and total dissolved solids; one with 

filtered groundwater and the other with unfiltered groundwater 

(Wilde and others, 2004). The 250-mL filtered sample was 

then preserved with 7.5 N nitric acid. Samples to be used for 

field and laboratory alkalinity titrations were filtered into 

500-mL polyethylene bottles. Samples to be analyzed for species of arsenic and iron were filtered into 250-mL polyethylene 

bottles that were covered with tape to prevent light exposure, 

and preserved with 6 N hydrochloric acid. Samples to be analyzed for nutrients were filtered into 125-mL brown polyethylene bottles. Samples to be analyzed for uranium isotopes, and 

gross alpha and gross beta particle activities were filtered into 

1-L polyethylene bottles and acidified with nitric acid. Carbon 

isotope samples were filtered and bottom filled into two 

500-mL glass bottles that were first overfilled with three bottle 

volumes of groundwater. These samples had no headspace and 

were sealed with a conical cap to prevent interaction between 

the sample and ambient air. 

Samples to be analyzed for noble gases were collected 

from the sampling point on the well discharge pipe. Noble 

gases were collected in 3/8-in copper tubes using reinforced 

nylon tubing connected to the hose bib at the wellhead. 

Ground water was flushed through the tubing to dislodge 

bubbles before flow was restricted with a back pressure valve. 

Clamps on either side of the copper tube were then tightened, 

trapping a sample of groundwater for analyses of noble gases 

(Weiss, 1968). 

Alkalinity of filtered samples was measured in the mobile 

laboratory (“field” alkalinity) using Gran’s titration method 

(Rounds, 2006; Gran, 1952; Stumm and Morgan, 1996). Titration data were entered directly into PCFF-GAMA, and the 

concentrations of bicarbonate (HCO3

-

) and carbonate (CO3

2-) 

were calculated automatically from the titration data using the 

advanced speciation method. Concentrations of HCO3

-

 and 

CO3

2- also were calculated from the laboratory alkalinity and 

pH measurements. Calculations were made in a spreadsheet 

using the advanced speciation method (http://or.water.usgs.

gov/alk/methods.html) with pK1 = 6.35, pK2 = 10.33, and 

pKW = 14.

Nine laboratories performed chemical analyses for this 

study (table A1), although most of the analyses were performed at the NWQL or by labs contracted by the NWQL. The 

NWQL maintains a rigorous quality-assurance program (Pirkey and Glodt, 1998; Maloney, 2005). Laboratory quality-control 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. Methoddetection limits are tested continuously and laboratory reporting levels updated accordingly. NWQL maintains National 

Environmental Laboratory Accreditation Program (NELAP) 

and other certifications (http://nwql.usgs.gov/lab_cert.shtml). 

In addition, the Branch of Quality Systems within the USGS 

Office of Water Quality maintains independent oversight of 

quality assurance at the NWQL and laboratories contracted by 

the NWQL. In addition, the Branch of Quality Systems runs 

the National Field Quality Assurance program that includes 

annual testing of all USGS field personnel for proficiency 

in making field water-quality measurements (http://qadata.

cr.usgs.gov/nfqa/). Results for analyses made at the NWQL or 

by laboratories contracted by the NWQL are uploaded from 

the laboratory directly into NWIS from the laboratory. Results 

of analyses made at other laboratories are compiled in a project Access (Microsoft, Redmond, WA) database and uploaded 

from there into NWIS. 

Data Reporting

The following section details the laboratory reporting 

conventions and the constituents that are determined by 

multiple methods or by multiple laboratories.

Reporting Limits

The USGS NWQL uses the laboratory reporting level 

(LRL) as a threshold for reporting analytical results. The LRL 

is set to reduce the chance of reporting a false negative (not 

detecting a compound when it is actually present in a sample) 

to less than 1 percent (Childress and others, 1999). The LRL 

usually is set at two times the long-term method detection 

level (LT-MDL). The LT-MDL is derived from the standard deviation for at least 24 method detection limit (MDL) 

determinations made over an extended period of time. The 

MDL is the minimum concentration of a substance that can 

be measured and reported with 99 percent confidence that the 

concentration is greater than zero (at the MDL there is less 

than 1 percent chance of a false positive) (Childress and others, 1999; U.S. Environmental Protection Agency, 2002). The 

USGS NWQL updates LRL values regularly and the values 

listed in this report were in effect when groundwater samples 

from the MADCHOW study unit (April and May 2008) were 

analyzed.

Concentrations between the LRL and the LT-MDL are 

reported as “estimated” concentrations (designated with an 

“E” before the values in the tables and text). In rare cases, concentrations above the LRL may be reported as E-coded values. 

These cases may occur if the concentration was outside the 

range of the calibration standards, if the sample was diluted 

before analysis, or if the result did not meet all laboratory 

quality-control criteria (Childress and others, 1999). 
56 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Some constituents in this study are reported using minimum reporting levels (MRLs) or method uncertainties. The 

MRL is the smallest measurable concentration of a constituent 

that may be reliably reported using a given analytical method 

(Timme, 1995). The method uncertainty generally indicates 

the precision of a particular analytical measurement; it gives a 

range of values wherein the true value will be found. 

Results for most constituents are presented using the 

LRL or MRL values provided by the analyzing laboratories. A 

couple of constituents are reported using the IRL provided by 

the laboratory. The IRL is an interim reporting level. Results 

for some constituents are presented using study reporting 

levels (SRLs) derived from assessing data from quality-control 

samples associated with groundwater samples collected as 

part of the GAMA project. The SRLs for trace elements were 

determined by statistical assessment of results from the field 

blanks collected in the first 20 GAMA study units (May 2004 

through January 2008) (L.D. Olsen and M.S. Fram, U.S. 

Geological Survey, written commun., 2008). The assessment 

used order statistics and binomial probabilities to construct 

an upper confidence limit (Hahn and Meeker, 1991) for the 

maximum concentration of constituents potentially introduced 

while groundwater samples were collected, handled, transported, and analyzed. The resulting SRLs for trace elements 

were set at concentrations representing a confidence limit of 

90 percent for the 90th percentile of the 86 field blanks used in 

the assessment. The SRLs for major and minor ions, nutrients, species of arsenic and iron, and radioactive constituents 

were determined by assessment of results from field blanks 

collected in MADCHOW. The maximum concentration of a 

constituent potentially introduced while groundwater samples 

were collected, handled, transported, and analyzed was defined 

as the maximum concentration of the constituent measured in 

blanks collected in MADCHOW. 

For most constituents, this maximum concentration was 

below the LRL or MRL for the constituent. Data for such constituents are reported as “<” (less than) the LRL or MRL. For 

some constituents, this maximum concentration was greater 

than the LRL or MRL, and therefore was defined as the SRL. 

Detections of those constituents reported by the laboratory 

with concentrations greater than the LRL or MDL but less than 

the SRL are given in tables 10 and 13B with a less-than-orequal-to (≤) sign preceding the reported value.

The methods used to analyze radiochemical constituents 

(uranium isotopes and gross alpha and gross beta particle 

activities) measure activities by using counting techniques 

(table A1). The reporting limits for radiochemical constituents 

are based on sample-specific critical levels (ssLC) (McCurdy 

and others, 2008). The critical level is analogous to the 

LT-MDL used for reporting analytical results for organic 

and 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 in 

the sample with less than a 5-percent probability of a false 

positive detection. The critical level depends on instrument 

background, counting times for the sample and background, 

and the characteristics of the instrument being used and the 

nuclide being measured. Sample-specific critical levels are 

used because the critical level also depends on sample size and 

sample yield during analytical processing. An ssLC is calculated for each sample, and the measured activity in the sample 

is compared to the ssLC associated with that sample. Measured 

activities less than the ssLC are reported as nondetects. 

The analytical uncertainties associated with measuring 

activities are sensitive to sample-specific parameters also, 

including sample size, sample yield during analytical processing, and time elapsed between sample collection and various 

steps in the analytical procedure, as well as parameters associated with the instrumentation. Therefore, measured activities 

of radioactive constituents are reported with sample-specific 

uncertainties. Activities of uranium isotopes, and gross alpha 

and gross beta particle activities are reported with samplespecific 1-sigma combined standard uncertainties (CSU). 

Notation

Stable isotopic compositions of oxygen, hydrogen, and 

carbon are reported as relative isotope ratios in units of per mil 

using the standard delta notation (Coplen and others, 2002):

 i eE

R

R

i

= − 



 



 sampl

reference

 per mil

where 

is the at

1 1i , 000

omic mass of the heavier isotope of

element 

is the elemen

,

E t (O for oxygen-18, C for carbon, 

or H for hydrogen), 

Rsample is the ratio of the abundance of the heavier 

isotope of the element ( O, C, or H) to 

that of the lighter is

18 13 2

otope of the element, 

( O, C, or H) in the sample, a 16 12 1 nd

is the ratio of the abundance of the heavier 

i

Rreference

sotope of the element to the lighter isotope

of the element in the reference material.

The reference material for oxygen and hydrogen is Vienna 

Standard Mean Ocean Water (VSMOW), which is assigned 

δ18O and δ2H values of 0 per mil (note than δ2H is sometimes 

referred to as δD because the common name of the heavier 

isotope of hydrogen, hydrogen-2, is deuterium). The reference material for carbon is Vienna Peedee Belemnite (VPDB), 

which is assigned a δ13C value of 0 per mil. Positive values 

indicate enrichment of the heavier isotope and negative values 

indicate depletion of the heavier isotope, compared to the 

ratios observed in the standard reference mater.
Appendix 57

Constituents on Multiple Analytical Schedules

Fourteen constituents targeted in this study were measured by more than one analytical schedule or more than 

one laboratory (table A2). The preferred methods for these 

constituents were selected on the basis of the procedure 

recommended by the NWQL (http://wwwnwql.cr.usgs.gov/

USGS/Preferred_method_selection_procedure.html). Methods 

with full approval are preferred over those with provisional 

approval and approved methods are favored over research 

methods. The method having greater accuracy and precision 

and lower LRLs for the overlapping constituents is usually 

preferred. However, the method having higher LRLs may be 

selected as the preferred method to provide consistency with 

the historical data analyzed by the same method. 

For the two constituents on NWQL Schedules 2020 

(VOCs; table 3A) and 1306 (low-level DBCP and EDB; 

table 3B), the preferred method was Schedule 1306 because 

it has lower LRLs. For the constituents on NWQL Schedules 

2033 (pesticides and pesticide degradates; table 3C) and 2060 

(polar pesticides and metabolites; table 3D), the preferred 

method was Schedule 2033 for three constituents to provide 

consistency with historical data, and Schedule 2060 for two 

constituents due to better method performance for these 

constituents (table A2). Only the results from the preferred 

method are reported. 

The constituent 1,2,3-TCP is measured at the USGS 

NWQL laboratory (Schedule 2020; table 3A) and is measured 

using a lower method reporting level at Weck Laboratories, 

Inc. (table 3F) and both results are reported. Tritium also is 

measured at two laboratories: Lawrence Livermore National 

Laboratory (LLNL) (table 3K) and U.S. Geological Survey 

Stable Isotope and Tritium Laboratory (SITL) (table 3J), but 

only the data from SITL was available for reporting at the time 

of this publication. 

For arsenic and iron concentrations, the approved 

method, Schedule 1948, used by the NWQL (table 3H) are 

preferred over the research methods used by the USGS Trace 

Metal Laboratory (table 3I). The concentrations measured by 

the Trace Metal Laboratory are used only to calculate ratios of 

redox species for each element, As(V)

As(III)

 for arsenic, and 

Fe(III)

Fe(II)

 for iron; for example,

Fe(III)

Fe(II)

Fe(T) - Fe(II)

Fe(II)

where 

Fe(T) is the total i

=

ron concentration (measured),

Fe(II) is the concentration of ferrous iron (measured), and

Fe(III) is the concentration of ferric iron (calculated).

The field water-quality indicators—pH, specific conductance, and alkalinity—were measured in the field and at the 

NWQL. The field measurements are the preferred method 

for all three constituents; however, both are reported because 

laboratory alkalinity measurements were made on a greater 

number of samples. Field values are generally preferred 

because field conditions are considered more representative of 

groundwater conditions (Hem, 1985).

Quality Assurance

The purpose of quality-assurance is to identify which data 

best represent environmental conditions and which may have 

been affected by contamination or bias during sample collection, processing, storage, transportation, and (or) laboratory 

analysis. Four types of quality-control (QC) tests were used in 

this study: blanks were collected to assess contamination during sample collection, handling or analysis; replicate samples 

were collected to assess reproducibility; matrix-spike tests 

were done to assess accuracy of laboratory analytical methods; 

and surrogate compounds were added to samples analyzed 

for organic constituents to assess bias of laboratory analytical 

methods. 

In this report, the detection of an organic constituent 

(toluene) in a groundwater sample that may have resulted from 

contamination during sample collection, handling, or analysis was flagged with a “V” remark code in the results table 

(table 5), and was not considered a detection for calculations 

of detection frequencies in water-quality assessments. Detections of inorganic constituents in groundwater samples that 

may have resulted from contamination during sample collection, handling, or analysis were flagged with a “≤” symbol to 

indicate that the amount of potential contamination may have 

been sufficient to give a false positive relative to the stated 

reporting level. Because of the possible contamination, the 

actual concentration in the groundwater sample may be less 

than or equal to “≤” the measured concentration. The evaluation of QC data presented in this report was based on results 

for QC samples collected for MADCHOW and on results for 

QC samples collected for the 20 GAMA study units sampled 

from May 2004 through January 2008. 

The quality-assurance protocols used for this study 

followed the protocols used by the USGS NAWQA program (Koterba and others, 1995) and described in the USGS 

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

dated). The quality-assurance plan followed by the NWQL, 

the primary laboratory used to analyze samples for this study, 

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

Blanks

The primary purposes of collecting blanks are to evaluate the magnitude of potential contamination of samples 

with constituents of interest during sample collection, handling, or analysis, and to identify and mitigate sources of this 

contamination. 
58 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Blank Collection and Analysis

Blanks were collected using blank water certified by the 

NWQL to contain less than the LRL or MRL of the constituents investigated in the study (http://wwwnwql.cr.usgs.gov/

USGS/OBW/obw.html). Nitrogen-purged, organic-free blank 

water was used for field blanks of organic constituents, and 

inorganic-free blank water was used for field blanks of other 

constituents. Two types of blanks were collected: source-solution and field blanks. Source-solution blanks were collected 

to assess potential contamination of samples during transport 

and analysis, and potential contamination of the certified blank 

water obtained from the USGS NWQL. Field blanks were 

collected to assess potential contamination of samples during 

collection, processing, transport, and analysis. 

For MADCHOW, blanks were collected at approximately 11 percent of the 35 wells sampled. Field blanks were 

analyzed for VOCs; low-level DBCP and EDB; pesticides 

and pesticide degradates; polar pesticides and metabolites; 

pharmaceuticals; NDMA; perchlorate; low-level 1,2,3-TCP; 

nutrients; major and minor ions; trace elements; arsenic and 

iron speciation; and gross alpha and gross beta particle activities (table A3). Blank water certified to be free of tritium and 

noble gasses was not available, thus field blanks were not 

collected and analyzed for these constituents. The concept 

of blank samples does not apply to analyses of stable isotope 

ratios because the constituents (oxygen and hydrogen in water, 

and carbon in dissolved inorganic carbon) are in all samples.

Source-solution blanks were collected at the sampling 

site by pouring blank water directly into sample containers 

that were preserved, stored, shipped, and analyzed in the same 

manner as the groundwater samples. For field blanks, blank 

water was either pumped or poured through the sampling 

equipment (fittings and tubing) used to collect groundwater, 

then processed, transported, and analyzed using the same 

protocols used for the groundwater samples. Eight to 12 L 

of blank water were pumped or poured through the sampling 

equipment before each field blank was collected.

Assessment of Blanks

Contamination in blanks may originate from several 

different types of sources that require different strategies to 

assess the potential for contamination of groundwater samples 

during sample collection, handling, or analysis. Four primary 

modes of contamination are assessed in the event of detections 

in field-blanks or unusual results in groundwater samples: (1) 

impurities in the water used to collect the blanks, (2) contamination during sample collection and handling from a known 

source or condition present at the field site, (3) carry-over of 

material from one sample to the next sample collected with 

the same sampling equipment, and (4) systematic and random contamination from field and laboratory equipment and 

processes. The fourth source of contamination (systematic and 

random) was addressed using a larger set of field blank results 

from multiple studies, in addition to the results from field 

blanks collected during the MADCHOW study. The development of this approach and its methods are described by L.D. 

Olsen and M.S. Fram (U.S. Geological Survey, written commun., 2008).

The first potential mode of contamination evaluated 

was the presence of impurities in the blank water. Because 

the blanks were collected using blank water certified by the 

NWQL to contain less than the LRL or MRL of the constituents investigated in the study, the blank water itself is very 

rarely the source of constituents detected in field blanks. 

However, the certification process is sometimes completed 

after the blank water has been shipped and used, thus, the certificates of analysis must always be checked for any detectable 

concentrations.

The second potential mode evaluated was contamination from identifiable, known sources at a specific field site. 

Contamination from specific sources may produce distinctive 

patterns of detections (particularly of VOC constituents) in 

field blanks and groundwater samples. Substances that may be 

encountered at the field site, such as lubricants (for example, 

WD-40), cements used on PVC-piping, exhaust fumes from 

pump engines, and the methanol used to clean sample lines, 

contain recognizable associations of VOC constituents. For 

example, cements used on PVC-piping are composed of 

primarily of tetrahydrofuran, acetone, methyl ethyl ketone 

(MEK), and cyclohexanone (not analyzed in this study). 

However, detecting these recognizable associations of VOC 

constituents in groundwater samples does not necessarily 

indicate contamination during sample collection because these 

VOC constituents also may occur together in groundwater.

If a recognizable association of VOC constituents was 

detected in a field blank or in a groundwater sample, the field 

notes and photographs from the site at which the sample was 

collected were examined for conditions that may have caused 

the field blank or the groundwater sample to be contaminated. 

If the constituents were present in the field blank and the 

groundwater sample from the same site at similar concentrations and the field notes or photographs indicated that the 

probable contaminant source was present, the detections of 

those constituents in the groundwater sample were V-coded, 

and all other groundwater samples collected at sites where 

the same condition may have occurred were considered for 

V-coding. If the constituents were detected in a groundwater 

sample and not in the associated field blank, or in a groundwater sample from a site where no blanks were collected, and the 

field notes or photographs indicated conditions that may have 

resulted in contamination of the groundwater sample during 

sample collection, the data were considered for V-coding. If 

no conditions that may have resulted in contamination of the 

groundwater sample during sample collection were identified 

in the field notes or photographs, V-codes were not applied on 

this basis. 
Appendix 59

The third potential mode of contamination evaluated was 

“carry-over” from the previous groundwater sample or field 

blank collected with the same equipment. Carry-over between 

samples is very rare because the procedures used to clean the 

equipment after each use have been developed and extensively tested to assure that carry-over does not occur. Potential 

carry-over was evaluated using time-series analysis to look for 

patterns suggestive of carry-over of constituents from a sample 

with high concentrations to the next groundwater sample or 

field blank collected with the same equipment. If nondetects 

were reported for a constituent in field blanks or groundwater 

samples collected after groundwater samples containing high 

concentrations of the constituent, then carry-over was ruled 

out as a mode of contamination for that constituent. 

The fourth potential mode of contamination evaluated was random or systematic contamination from field or 

laboratory equipment or processes. All detections in field 

blanks which could not be accounted for by impurities in the 

source-solution water, specific known conditions at field sites, 

or carry-over between samples were evaluated for random 

contamination. Random contamination in field and laboratory 

processes has an equal chance of affecting each groundwater 

sample thus, strategies for flagging detections of constituents 

subject to random contamination in field and laboratory processes must be applied to all groundwater samples.

Different notation was used for flagging results for 

organic and inorganic constituents that may have been affected 

by contamination during sample collection, handling, or analysis. Inorganic constituents are naturally present in groundwater, and the concerns about inorganic constituents usually are 

related to concentration, rather than detection (presence or 

absence). In contrast, concerns about organic constituents usually are related to both detection and concentration. Therefore, 

different schemas are used for assessing and flagging data for 

organic and inorganic constituents.

Results for organic constituents that may have been 

affected by contamination during sample collection, handling, or analysis were flagged with V-codes. The purpose 

of V-coding was to flag detections that have a greater than 

acceptable probability of being false-positive detections. A 

false-positive detection of a constituent is an apparent detection that is caused by contamination during the sample collection, handling, or analysis of a groundwater sample that would 

otherwise not have a detection of that constituent. Results 

labeled with V-codes were not considered to be detections of 

the constituent for this study and were not included in calculations of detection frequencies for organic constituents.

The V-coding level was defined as the highest concentration of the constituent detected in a field blank plus the 

LT-MDL (equal to one-half the LRL) for that constituent. 

The following example illustrates why the V-coding level 

is defined in this way. In this example, the LT-MDL for the 

constituent is 0.10 μg/L, the true concentration in the groundwater sample is 0.05 μg/L, and the highest concentration 

measured in a field blank is 0.20 μg/L. It is assumed that the 

highest concentration measured in a field blank represents the 

maximum amount of contamination that groundwater samples 

may receive during collection, handling, transport, or analysis. 

If the groundwater sample is not affected by contamination 

during collection, handling, transport, or analysis, the measured concentration will be reported as a nondetect (0.05 μg/L 

is less than the LT-MDL of 0.10 μg/L). If the maximum 

amount of contamination (0.20 μg/L) occurs, then the measured concentration will be 0.25 μg/L, which is reported as a 

detection of the constituent. Therefore, by setting the V-coding 

level at 0.30 μg/L (the LT-MDL of 0.10 μg/L plus the potential 

maximum amount of contamination of 0.20 μg/L), detections 

that might be false-positive detections are removed from of the 

dataset. 

Results for inorganic constituents that may have been 

affected by contamination during sample collection, handling, 

transport, or analysis were flagged with a less than or equal to 

symbol (≤). The ≤ symbol means that the true concentration of 

the constituent in the groundwater sample is less than or equal 

to the measured concentration (including the possibility that it 

may be less than the LT-MDL and therefore a nondetect). For 

trace elements, the concentration cutoff, hereinafter referred to 

as the study reporting level (SRL), for assigning the ≤ symbol 

was determined from a statistical assessment of results for 86 

field blanks collected between May 2004 and January 2008 

(L.D. Olsen and M.S. Fram, U.S. Geological Survey, written 

commun., 2008). For all other inorganic constituents, the SRL 

for assigning the ≤ symbol was determined from assessing 

the field blanks collected at MADCHOW sites only. The SRL 

was defined as equaling the highest concentration measured 

in the 4 field blanks collected at MADCHOW sites (field 

blanks were collected at approximately 11 percent of the wells 

sampled).

Replicates

Sequential replicate samples were collected to assess the 

precision of the water-quality data. Estimates of data precision 

are needed to assess whether differences between concentrations in samples are due to differences in groundwater quality 

or to variability that may result from collecting, processing, 

and analyzing the samples.

Two methods for measuring variability were needed to 

adequately assess precision over the broad range of measured 

concentrations of most constituents. The variability between 

measured concentrations in the pairs of sequential replicate 

samples was represented by the standard deviation (SD) for 

low concentrations and by relative standard deviation (RSD) 

for high concentrations (Anderson, 1987; Mueller and Titus, 

2005). The RSD is defined as the SD divided by the mean 

concentration for each replicate pair of samples, expressed as 

a percentage. The boundary between concentrations for which 

variability is assessed with SD and concentrations for which 

variability is assessed with RSD was defined as 5 times the 

LRL for each constituent. 
60 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

For this study, acceptable precision for replicate sample 

pairs is defined as follows:

• For concentrations less than 5 times the LRL (<5 LRL), 

an SD of less than 1⁄2 LRL is acceptable

• For concentrations greater than (or equal to) 5 times 

the LRL (≥5 LRL), an RSD of less than 10 percent is 

acceptable. For comparison, an RSD of 10 percent is 

equivalent to a relative percent difference (RPD) of 

14 percent. 

• For activities of radiochemical constituents (excluding 

tritium and carbon isotopes because CSU data are not 

available), the presence of overlap between the results 

(value ± 1-sigma CSU) is acceptable

If results from replicate sample pairs indicate that precision is unacceptable for a constituent, and no specific reason 

can be identified, this greater variability must be considered 

when the data are used for the purposes of comparison. If 

measured concentrations are slightly above a water-quality 

threshold, then actual concentrations could be slightly below 

that threshold. Similarly, if measured concentrations are 

slightly below a water-quality threshold, then actual concentrations could be slightly above. Also, if a constituent has 

high variability in replicate sample pairs, a larger difference 

between concentrations measured in two samples is required 

to conclude that the two samples have significantly different 

concentrations. 

For organic and inorganic constituents (except for 

radiochemical constituents, but including tritium and carbon isotopes), if both values for a replicate sample pair were 

reported as detections, then the SD was calculated if the mean 

concentration was <5 LRL for the constituent, or the RSD 

was calculated if the mean concentration was ≥5 LRL for the 

constituent. If both values were reported as nondetects, the 

variability was set to zero by definition. Cases other than two 

detections or two nondetects were treated as follows:

• For organic constituents, if one or both values were 

assigned a V-code, neither SD nor RSD was calculated. 

A V-code indicates that the constituent was detected in 

blanks and was excluded from the dataset of groundwater quality results. The data might not represent the 

concentration of the constituent in the groundwater 

sample.

• For organic and inorganic constituents, if one value 

was reported as a nondetect, and the other value was 

reported as a detection below the LRL, a value of zero 

was substituted for the nondetect and the SD calculated. Substituting zero for the nondetect yields the 

maximum estimate of variability for the replicate pair.

For inorganic constituents, if one value for a sample 

pair was reported as a nondetect and the other value 

was reported as a ≤-coded value less than the SRL, 

or if both values were reported as ≤-coded values less 

than the SRL, neither SD nor RSD was calculated, 

because the values may be analytically identical. The 

≤-code indicates that the value is a maximum potential concentration, and that concentration may be low 

enough to be reported as a nondetect. 

• For organic and inorganic constituents (including 

tritium and carbon isotopes), if one value was reported 

as a nondetect and the other value was reported as a 

detection greater than the LRL, the variability for the 

pair was considered unacceptable.

Matrix Spikes

Adding a known concentration of a constituent (‘spike’) 

to a replicate environmental sample enables the analyzing 

laboratory to determine the effect of the matrix, in this case 

groundwater, on the analytical technique used to measure the 

constituent. The known compounds added in matrix spikes 

are the same as those being analyzed in the method. This 

enables an analysis of matrix interferences on a compound-bycompound basis. Matrix spikes were added at the laboratory 

doing the analysis. Low matrix-spike recovery may indicate 

that the compound might not be detected in some samples if it 

was present at very low concentrations. Low and high matrixspike recoveries may be a concern if the concentration of a 

compound in a groundwater sample is close to the MCL: a 

low recovery could falsely result in a measured concentration 

below the MCL, whereas a high recovery could falsely result 

in a measured concentration above the MCL.

The GAMA program defined the data quality objective 

for acceptable matrix-spike recoveries as 70 to 130 percent. 

Constituents with matrix-spike recoveries outside of this 

range were flagged as having unacceptable recoveries in 

tables 3A,C,D (none of the constituents listed in table 3F had 

unacceptable matrix-spike recoveries). For many constituents, 

an acceptable range of 70 to 130 percent for matrix spike 

recovery was more restrictive than the acceptable control limits for laboratory “set” spike recoveries. Laboratory set spikes 

are aliquots of laboratory blank water to which the same spike 

solution used for the matrix spikes has been added. One set 

spike is analyzed with each set of samples. Acceptable control 

limits for set spikes are defined relative to the long-term variability in recovery. For example, for many NWQL schedules 

acceptable set spike recovery is within plus or minus three 

F-pseudosigma of the median recovery for at least 30 set 

spikes (Conner and others, 1998; Rose and Sandstrom, 2003). 

For NWQL schedule 2080 (pharmaceuticals), acceptable set 

spike recovery is within plus or minus two standard deviations 

of the long-term mean recovery (Furlong and others, 2008). 

Results for pharmaceuticals are not presented in this report; 

they will be included in subsequent publications.
Appendix 61

Matrix-spike recovery tests were done for VOCs, pesticides, polar pesticides, pharmaceuticals, NDMA, and lowlevel 1,2,3-TCP because the analytical methods for these constituents are chromatographic methods that may be susceptible 

to matrix interferences. Replicate samples for matrix-spike 

recovery tests were collected at 11 to 14 percent of the wells 

sampled for the various analytical schedules.

Surrogates

Surrogate compounds are added to environmental 

samples in the laboratory before analysis in order to evaluate 

the recovery of similar constituents. Surrogate compounds 

were added in the laboratory to all groundwater and qualitycontrol samples that were analyzed for VOCs, pesticides and 

pesticide degradates, polar pesticides and metabolites, and 

pharmaceuticals by the NWQL (table A6); note pharmaceutical data will be presented in a subsequent report. Most of the 

surrogate compounds are deuterated analogs of compounds 

being analyzed. For example, the surrogate toluene-d8 used 

for the VOC analytical method has the same chemical structure as toluene, except that the eight hydrogen-1 atoms on 

the molecule have been replaced by deuterium (hydrogen-2). 

Toluene-d8 and toluene behave very similarly in the analytical procedure, but the small mass difference between the two 

results in slightly different chromatographic retention times 

thus the use of a toluene-d8 surrogate does not interfere with 

the analysis of toluene (Grob, 1995). Only 0.015 percent of 

hydrogen atoms are deuterium (Firestone and others, 1996), 

thus deuterated compounds like toluene-d8 do not occur naturally and are not found in environmental samples. Surrogates 

are used to identify general problems that may arise during 

sample analysis that could affect the analysis results for all 

compounds in that sample. Potential problems include matrix 

interferences (such as high levels of dissolved organic carbon) 

that produce a positive bias, or incomplete laboratory recovery (possibly due to improper maintenance and calibration 

of analytical equipment) that produces a negative bias. A 70 

to 130 percent recovery of surrogates is generally considered 

acceptable; values outside this range indicate possible problems with the processing and analysis of samples (Connor and 

others, 1998; Sandstrom and others, 2001).

Quality-Control Results

Detections in Field and Source-Solution Blanks

Table A3 presents a summary of detections in field 

blanks. Four field blanks and source-solution blanks were collected during sampling in MADCHOW for analysis of VOCs, 

and there were no detections. Concentrations of toluene 

between E0.01 μg/L and E0.08 μg/L were detected in approximately 40 percent of the field and source-solution blanks 

in other study units (Wright and others, 2005; Bennett and 

others, 2006; Kulongoski and others, 2006; Fram and Belitz, 

2007; Kulongoski and Belitz, 2007; Dawson and others, 

2008; Ferrari and others, 2008; and Landon and Belitz, 2008). 

Because the certificates of analysis stated that no toluene was 

detected in the lots of nitrogen-purged, organic-free blank 

water used when the MADCHOW samples were collected, 

the source blank water was not considered to be the source of 

the contamination. The source of the toluene is not known. 

Because toluene is detected frequently in both source-solution 

and field blanks, all toluene detections in groundwater samples 

collected in GAMA study units are subject to V-coding at a 

level based on the concentrations detected in the blanks. The 

concentration of toluene detected in one MADCHOW groundwater sample was E0.02 μg/L; this detection was V-coded 

and excluded from the dataset of groundwater quality results 

(tables 5, A3). 

Four field blanks were analyzed for low-level DBCP and 

EDB and there were no detections. 

Five field blanks were analyzed for pesticides and pesticide degradates, three field blanks were analyzed for polar 

pesticides and metabolites, and there were no detections.

Two field blanks were analyzed for NDMA and four 

field blanks were analyzed for low-level 1,2,3-TCP, and there 

were no detections. Three field blanks and source-solution 

blanks were collected for analysis of perchlorate, perchlorate 

was detected in a source-solution blank at a concentration of 

0.27 mg/L, but not detected in any of the field blanks including the field blank collected at the same time as the sourcesolution blank. The source of this detection is unknown. No 

groundwater samples were V-coded based on this detection. 

Four field blanks were analyzed for nutrients, and there 

were no detections.
62 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Four field blanks were analyzed for major and minor 

ions, and silica was detected in two field blanks at concentrations of 0.020 and 0.034 mg/L (table A3). The field blank 

with a silica concentration of 0.020 mg/L was accompanied 

by a source-solution blank with no detection and the sourcesolution for the other field blank was not analyzed. The lowest 

concentration of silica detected in groundwater samples 

was 16.3 mg/L (table 9) which is greater than 0.043 mg/L 

(0.034 mg/L, the highest concentration in the field blank, plus 

0.009 mg/L, one-half the LRL), thus no groundwater data 

were flagged.

The GAMA study reporting levels (SRLs), instead of the 

results from the four field blanks collected at MADCHOW 

sites, were used to determine which trace element data should 

be flagged; SRLs are based on the results for 86 field blanks 

collected between May 2004 and January 2008 (L.D. Olsen 

and M.S. Fram, U.S. Geological Survey, written commun., 

2008). Aluminum, barium, chromium, copper, iron, lead, manganese, nickel, tungsten, vanadium, and zinc have SRLs which 

are tabled instead of LRLs in table 10. Measured values that 

are less than the SRL are flagged with a ≤ symbol in table 10. 

No trace elements were detected in field blanks collected at 

MADCHOW sites, but at least one groundwater sample for 

each of the trace elements listed above with SRLs, except for 

barium, was flagged with a ≤ symbol in table 10 because the 

measured values in groundwater samples were less than the 

respective SRLs (table A3). 

Two field blanks were collected for the analysis of arsenic and iron by the USGS Trace Metals laboratory in Boulder, 

Colorado, and there were no detections.

Four field blanks were analyzed for gross alpha and 

gross beta particle activities. Gross alpha particle activity 

(72-hour count) was detected in two field blanks, activities 

were 0.23 ± 0.17 and 0.24 ± 0.17 pCi/L (table A3). Three 

groundwater samples contained activities of 0.65 ± 0.31 , 0.55 

± 0.33, and 0.65 ± 0.34 pCi/L (table 13B). The lower confidence limit of the activities measured in these three groundwater samples are less than 0.41 pCi/L, the upper confidence 

limit of the maximum activity measured in a blank; thus the 

activities in the groundwater samples were flagged with a ≤ 

symbol (table 13B). Gross beta particle activity (30-day count) 

was detected in one field blank at an activity of 0.78 ± 0.45 

pCi/L (table A3). Four groundwater samples contained gross 

beta particle activities (30-day count) less than 1.23 pCi/L, the 

upper confidence limit measured in a blank, and thus, were 

flagged with a ≤ symbol (table 13B). 

Variability in Replicate Samples

Tables A4A–C summarize the results of replicate analyses 

for constituents detected in groundwater samples collected 

in the MADCHOW study. Replicate analyses were made on 

about 14 percent of the samples collected. Of the 1,402 replicate pairs of constituents analyzed (counted by constituent), 

417 were analyzed for constituents detected in at least one 

groundwater sample. Of these 417 pairs, 10 had results outside 

the limits for acceptable precision. Results for replicate analyses for constituents that were not detected are not reported in 

tables A4A–C. 

Five replicate pairs of samples were analyzed for organic 

constituents and nearly all pairs were comprised of two values 

reported as nondetects (table A4A). V-coded data for toluene was not calculated because the data are not considered 

representative of the groundwater. All of the pairs had two 

concentrations with an RSD value of less than 10 percent 

(for concentrations five times greater than the LRL), or two 

concentrations with an SD value of less than one-half of the 

LRL (for concentrations less than five times the LRL), or 

two nondetects (table A4A). These results indicated data for 

groundwater samples from the MADCHOW study unit had 

variability within acceptable ranges. 

Replicate pairs of samples were analyzed for constituents 

of special interest at Weck Laboratories, Inc.. Five replicate 

pairs of samples were analyzed for constituents of special 

interest collected at all 35 MADCHOW sites (perchlorate 

and low-level 1,2,3-TCP) and two replicate pairs of samples 

were analyzed for NDMA collected at only the 10 slow sites 

(table A4A). Both replicate pairs analyzed for NDMA were 

comprised of two values reported as nondetects and two of the 

five replicate pairs each analyzed for perchlorate and low-level 

1,2,3-TCP were comprised of detections with concentrations 

less than five times the corresponding MRLs and SDs were 

less than one-half of the MRL (tables 3F and A4A). These 

results indicated data for groundwater samples from the MADCHOW study unit had variability within acceptable ranges.

Five replicate pairs of samples were analyzed for nutrients, major and minor ions, trace elements, and isotope tracers 

and two replicate pairs of samples were analyzed for trace 

element species. Over 97 percent of the pairs yielded two 

concentrations with a SD value less than one-half of the LRL, 

MDL, or MRL (for concentrations less than five times the 

LRL, MDL, or MRL), an RSD value of less than 10 percent 

(for concentrations five times greater than or equal to the LRL, 

MDL, or MRL), or two nondetects (table A4B). These results 

indicated data for groundwater samples from the MADCHOW 

study unit had variability within acceptable ranges.

One replicate pair each for lithium and manganese had an 

RSD value greater than 10 percent. There is no drinking-water 

threshold for lithium to compare measured concentrations in 

groundwater samples to but the elevated RSD will be taken 

into account in assessments of groundwater quality. However, 

the concentrations detected in the replicate pair for manganese 

were 3.7 and 2.5 μg/L, which were less than one-tenth of the 

SMCL-CA for manganese (table 3H). The less than acceptable precision at this low concentration will not affect the 

assessments of groundwater quality being made by the GAMA 

Priority Basin Project. 
Appendix 63

Two replicate pairs of samples were analyzed for species 

of arsenic and iron by the USGS Trace Metals Laboratory in 

Boulder, Colorado. Both replicate pairs analyzed for species 

of arsenic yielded detections with concentrations less than five 

times the corresponding MDL and SDs were less than one-half 

of the MDL (tables 3I and A4B). These results indicated data 

for groundwater samples from the MADCHOW study unit had 

variability within acceptable ranges.

Results in four out of the five replicate pairs of samples 

analyzed for tritium and carbon isotopes (δ13C of dissolved 

carbonates and carbon-14) indicated data for groundwater 

samples from the MADCHOW study unit had variability 

within acceptable ranges for these constituents (table A4B). 

The SD was not calculated for 1 replicate pair for tritium analyses because the environmental value was reported as a detect 

just above the MRL and the replicate value was reported as 

a nondetect and less than the MRL (0.4, <0.3). The RSD was 

greater than 10 percent in 1 of the replicate pair analyses of 

each of the carbon isotopes.

Five replicate pairs of samples were analyzed for 

gross alpha and gross beta particle activities, and two replicate pairs of samples were analyzed for uranium isotopes 

(table A4C). Acceptable precision for radiochemical constituents is defined as the presence of overlap between the results 

(value + 1-sigma CSU) for the two analyses, where the range 

between the lower confidence limit of the activity measured 

in the groundwater sample and the upper confidence limit of 

the activity measured in the groundwater sample overlaps 

the range between the lower confidence limit of the activity measured in the replicate groundwater sample and the 

upper confidence limit of the activity measured in the replicate groundwater sample. Eighty-six percent of the replicate 

pairs were comprised of overlapping values and, therefore, 

were considered acceptable. One replicate pair each for gross 

alpha particle activity (72-hour count), gross alpha particle 

activity (30-day count), gross beta particle activity (30-day 

count), uranium-234, and uranium-235 were comprised of 

non-overlapping values. However, the activities were less 

than one-third of the corresponding MCL-US and MCL-CA 

thresholds (table 3J). The less-than-acceptable precision for 

these constituents at these low activities will not affect the 

assessments of groundwater quality being made by the GAMA 

Priority Basin Project.

Matrix-Spike Recoveries

Tables A5A–A5D presents a summary of matrix-spike 

recoveries for the MADCHOW study. Addition of a spike 

or known concentration of a constituent to an environmental 

sample enables the analyzing laboratory to determine the 

effect of the matrix, in this case groundwater, on the analytical 

technique used to measure the constituent. Acceptable results 

for matrix-spike recovery tests were defined as median recoveries between 70 and 130 percent.

Five environmental samples were spiked with VOCs to 

calculate matrix-spike recoveries (table A5A). The median 

recoveries for all 83 VOC compounds for which there is a 

spike available for the preferred method of analyses were 

within 70 to 130 percent. There is no NWQL Schedule 1306 

spike available for the two fumigants (DBCP and EDB) 

analyzed in NWQL Schedules 2020 and 1306. Only results 

from Schedule 1306, the preferred method, are reported for 

these constituents. Two VOC spike compounds had at least 

one matrix-spike recovery greater than 130 percent; however, 

none were detected in groundwater samples. Six VOC spike 

compounds had at least one matrix-spike recovery less than 

70 percent, but these compounds were not detected in groundwater samples. Low recoveries may indicate that the compound might not have been detected in some samples if it was 

present at very low concentrations.

Five groundwater samples were spiked with pesticide and 

pesticide degradate compounds in order to calculate matrixspike recoveries (table A5B). The median recoveries for 48 

of the 81 compounds were within 70 to 130 percent. Almost 

two-thirds of the compounds (52 out of 81) had at least 1 

matrix-spike recovery less than 70 percent, and 35 compounds 

had median recoveries less than 70 percent. For 23 compounds 

all 5 matrix-spike recovery tests yielded recoveries less 

than 70 percent. Three of these compounds, deethylatrazine, 

hexazinone, and tebuthiuron, were detected in groundwater 

samples (table 6A). [NOTE – low recoveries may indicate that 

the compound might not have been detected in some samples 

if it was present at very low concentrations]. A similar pattern 

of unusually low matrix-spike recoveries that started in March 

2008 was noted in an assessment of Schedule 2033 method 

performance by Organic Blind Sample Program of the Branch 

of Quality Systems (U.S. Geological Survey, 2008). The 

Organic Blind Sample Project (OBSP) of the Branch of Quality Systems (BQS) assesses the operational performance of 

organic analytical methods used for determining water-quality 

parameters for the USGS National Water Quality Laboratory 

(NWQL) by means of blind submissions of Quality Assurance 

(QA) samples. 
64 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Four groundwater samples were spiked with polar pesticide and metabolite compounds in order to calculate matrixspike recoveries (table A5C). The median recoveries for 46 of 

the 55 compounds were within 70 to 130 percent. Out of 55 

total compounds, 11 compounds had at least 1 matrix-spike 

recovery less than 70 percent and 7 compounds had median 

recoveries less than 70 percent. One of these compounds, 

dinoseb, was detected in groundwater samples (table 6B). 

(NOTE – low recoveries may indicate that the compound 

might not have been detected in some samples if it was present at very low concentrations.) For one compound all four 

matrix-spike recovery tests yielded recoveries less than 70 percent. Seven compounds had at least one matrix-spike recovery 

greater than 130 percent and three compounds had median 

recoveries greater than 130 percent. One of these compounds, 

imazethapyr, was detected in groundwater samples (table 6B). 

The one detection of imazethapyr in a groundwater sample 

was reported by the laboratory with an E-code to indicate 

greater uncertainty in the magnitude of the reported concentration (table 6B).

Results for pharmaceutical compounds are not presented 

in this report; they will be included in subsequent publications.

One groundwater sample was spiked with NDMA and 

five groundwater samples were spiked with 1,2,3-TCP in order 

to calculate matrix-spike recovery (table A5D). Results for 

matrix-spike recovery tests were within 70 and 130 percent. 

Tests yielded spike recoveries for 1,2,3-TCP ranging from 86 

to 112 percent, with a median recovery of 105 percent.

Surrogate Compound Recoveries

Surrogate compounds were added to environmental 

samples in the laboratory and analyzed to evaluate the recovery of similar constituents. Table A6 lists each surrogate, the 

analytical schedule on which it was applied, the number of 

analyses for blank and of groundwater samples (environmental 

samples, replicates, and matrix-spike samples), the number 

of surrogate recoveries below 70 percent, and the number of 

surrogate recoveries above 130 percent for the blanks and the 

groundwater samples. Blank and groundwater samples were 

considered separately to assess whether the matrices present in 

groundwater samples affect surrogate recoveries. The presence 

of sample matrices may decrease the recovery of caffeine-13C 

(table A6). However, because the median matrix-spike recoveries of 84 percent of the polar pesticides and metabolites were 

within acceptable ranges, this change in surrogate recovery 

did not have a noticeable effect on the data. More than 

95 percent of the surrogate recoveries for VOCs and 90 percent of the surrogate recoveries for pesticide compounds were 

in the acceptable ranges.
Appendix 65

Table A1. Analytical methods used by the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) and additional 

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 in parentheses after the laboratory names]

Constituent classes Analytical Method Laboratory and 

analytical schedule Citation(s)

Field water-quality indicators

Field parameters Calibrated field meters and test kits USGS field measurement U.S. Geological Survey, variously 

dated

Organic constituents

Volatile organic compounds 

(VOCs)

Purge and trap capillary gas chromatography/mass spectrometryNWQL, Schedule 2020 Connor and others, 1998

Low-level 1,2-dibromo-3-chloropropane (DBCP) and 1,2-dibromoethane (EDB)Micro-extraction and gas chromatography/electron-capture 

detection

NWQL, Schedule 1306 Eichelberger, 1993 (USEPA 

method 504.1)

Pesticides and degradates Solid-phase extraction and gas 

chromatography/mass spectrometry

NWQL, Schedule 2033 Zaugg and others, 1995; Lindley 

and others, 1996; Madsen and 

others, 2003; Sandstrom and 

others, 2001

Polar pesticides and metabolites Solid-phase extraction and highperformance liquid chromatography (HPLC)/mass spectrometry with selective-ion monitoringNWQL, Schedule 2060 Furlong and others, 2001

Pharmaceuticals Solid-phase extraction and HPLC/

mass spectrometry

NWQL, Schedule 2080 Kolpin and others, 2002; Furlong 

and others, 2008

Constituents of special interest

N-Nitrosodimethylamine (NDMA) Isotopic dilution chromatography/

chemical ionization mass spectrometry

Weck Laboratories, Inc., standard 

operating procedure 

ORG065.R10

U.S. Environmental Protection 

Agency, 1989; Plomley and others, 1994

Perchlorate Chromatography/mass spectrometry Weck Laboratories, Inc., standard 

operating procedure 

ORG099.R01

U.S. Environmental Protection 

Agency, 2005

Low level 1,2,3-trichloropropane 

(1,2,3-TCP)

Isotopic dilution purge and trap/gas 

chromatography/mass spectrometry 

Weck Laboratories, Inc., standard 

operating procedure ORG083

Okamoto and others, 2002

Inorganic constituents

Nutrients Alkaline persulfate digestion, 

Kjedahl digestion

NWQL, Schedule 2755 Fishman, 1993; Patton and Kryskalla, 2003

Major and minor ions and trace 

elements

Atomic absorption spectrometry, 

colorimetry, ion-exchange chromatography, inductively-coupled 

plasma atomic emission spectrometry and mass spectrometry

NWQL, Schedule 1948 Fishman and Friedman, 1989; 

Fishman, 1993; Faires, 1993; 

McLain, 1993; Garbarino, 1999; 

Garbarino and Damrau, 2001; 

American Public Health Association, 1998; Garbarino and 

others, 2006

Arsenic and iron speciation Various techniques of ultraviolet 

visible (UV-VIS) spectrophotometry and atomic absorbance 

spectroscopy

USGS Trace Metal Laboratory, 

Boulder, Colorado (USGSTMCO)

Stookey, 1970; To and others, 

1998; McCleskey and others, 

2003

Table A1. Analytical methods used by the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) and additional 

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 in parentheses after the laboratory names]
66 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table A1. Analytical methods used by the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) and additional 

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 in parentheses after the laboratory names]

Constituent classes Analytical Method Laboratory and 

analytical schedule Citation(s)

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 Mayeda, 1953; Coplen 

and others, 1991; Coplen, 1994

Stable isotopes of carbon and 

carbon-14 activity

Accelerator mass spectrometry University of Waterloo, Environmental Isotope Lab (CANUWIL), NWQL Schedule 2015; 

University of Arizona Accelerator Mass Spectrometry Lab 

(AZ-UAMSL), NWQL Schedule 

2015

Donahue and others, 1990; Jull and 

others, 2004

Radioactivity and gases

Tritium activity Electrolytic enrichment-liquid 

scintillation

USGS Stable Isotope and Tritium 

Laboratory, Menlo Park, California (USGSH3CA)

Thatcher and others, 1977

Tritium activity and noble gases Helium-3 in-growth and mass 

spectrometry

Lawrence Livermore National 

Laboratory (CA-LLNL)

Moran and others, 2002; Eaton and 

others, 2004

Uranium isotope activities Chemical separations and alphaparticle spectrometry Eberline Analytical Services 

(CA-EBERL), NWQL Schedule 

1130 

American Society for Testing and 

Materials, 2002

Gross alpha and gross beta particle 

activities

Alpha and beta activity counting Eberline Analytical Services, 

NWQL Schedule 1792

Krieger and Whittaker, 1980 

(USEPA method 900.0)
Appendix 67

Constituent Primary constituent classification Analytical schedules Preferred analytical schedule

Results from preferred method reported

Atrazine Pesticide 2033, 2060 2033

Carbofuran Herbicide 2033, 2060 2060

Deethylatrazine (2-Chloro-4-isopropylamino-6-amino-s-triazine)Pesticide degradate 2033, 2060 2033

DBCP (1,2-Dibromo-3-chloropropane)VOC, fumigant 1306, 2020 1306

EDB (1,2-Dibromoethane) VOC, fumigant 1306, 2020 1306

Metalaxyl Fungicide 2033, 2060 2060

Tebuthiuron Pesticide 2033, 2060 2033

Results from both methods reported

Alkalinity Field water-quality indicator field, 1948 field

Arsenic, total Trace element 1948, TML 1948

Iron, total Trace element 1948, TML 1948

pH Field water-quality indicator field, 1948 field

Specific conductance Field water-quality indicator field, 1948 field

1,2,3-Trichloropropane 

(1,2,3-TCP)

VOC Weck, 2020 np

Tritium Inorganic tracer LLNL, SITL np

Table A2. Preferred analytical schedules for constituents appearing on multiple schedules for samples collected for the Madera–

Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.

[Preferred analytical schedules are generally the methods of analysis with the greatest accuracy and precision out of the ones used for the compound in question 

except in cases where consistency with historic data analyzed using the same method is preferred. LLNL, Lawrence Livermore National Laboratory; Weck, 

Weck Laboratories, Inc.; SITL, U.S. Geological Survey Stable Isotope and Tritium Laboratory; TML, U.S. Geological Survey Trace Metal Laboratory, Boulder, 

Colorado; VOC, volatile organic compound; np, no preference]
68 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Constituent

Number of 

field blank detections/ 

number of field blanks

Concentration 

detected in 

field blanks

Number of

ground-water samples

V-coded or ≤-coded

Organic constituents (mg/L)

Toluene 0/4 — 11

Constituents of special interest (mg/L)

Perchlorate 20/3 — 0

Major and minor ions (mg/L)

Silica 2/4 0.020, 0.034 0

Trace elements (μg/L)

Aluminum3 0/4 — 9

Chromium3 0/4 — 2

Copper3 0/4 — 12

Iron3 0/4 — 5

Lead3 0/4 — 23

Manganese3 0/4 — 7

Nickel3 0/4 — 18

Tungsten3 0/4 — 15

Vanadium3 0/4 — 1

Zinc3 0/4 — 14

Radioactivity (pCi/L)

Gross alpha particle activity, 

72-hour count

4

2/4 0.23 ± 0.17, 0.24 ± 0.17 3

Gross beta particle activity, 

72-hour count

4

0/4 — 0

Gross beta particle activity, 

30-day count

1/4 0.78 ± 0.45 4

1

Toluene V-coded based on frequency of detections in field blanks and source solution blanks from the previous 23 GAMA study units.

2

Perchlorate was detected in a source solution blank at a concentration of 0.27 mg/L, but not in the associated field blank.

3

Constituents have a study reporting level (SRL) defined based on examination of GAMA quality-control samples collected from May 2004 through January 

2008 (L.D. Olsen and M.S. Fram, U.S. Geological Survey, written commun., 2008). 4

72-hour holding time exceeded by 1 day for one 'SLOW' field blank sample reported as a nondetect.

Table A3. Constituents detected in field blanks collected for the Madera–Chowchilla Groundwater Ambient Monitoring and 

Assessment (GAMA) study, California, April and May 2008.

[V-coded data for ground-water samples are excluded from the dataset of ground-water quality results because the constituents were detected in blanks at similar 

concentrations or were determined to be a result of contamination during sample collection. Abbreviations: SRL, study reporting level; μg/L, micrograms per 

liter; mg/L, milligrams per liter; — not detected; pCi/L, picocuries per liter; ≤, less than or equal to]
Appendix 69

Constituent

Number replicates with 

nondetects/total number 

of replicates

Number of SDs greater than 

1⁄2 the LRL /number of replicates 

with concentrations less than 

5 times the LRL

Number of RSDs greater than 

10 percent/number of replicates 

with concentrations greater than 

5 times the LRL

Volatile organic compounds

Bromodichloromethane 4/5 0/1 nv

Bromoform (Tribromomethane) 4/5 nv 0/1

Chloroform (Trichloromethane) 3/5 0/2 nv

Dibromochloromethane 4/5 0/1 nv

1,1-Dichloroethane (1,1-DCA) 4/5 0/1 nv

cis-1,2-Dichloroethene (cis-1,2-

DCE)

5/5 nv nv

1,2-Dichloropropane 3/5 0/2 nv

Perchloroethene (Tetrachloroethene, PCE)4/5 nv 0/1

Trichloroethene (TCE) 5/5 nv nv

1,2,4-Trimethylbenzene 5/5 nv nv

Low-level 1,2-dibromo-3-chloropropane (DBCP) and 1,2-dibromoethane (EDB)

1,2-Dibromo-3-chloropropane 

(DBCP)

3/5 0/2 nv

1,2-Dibromoethane (EDB) 4/5 0/1 nv

Pesticides and pesticide degradates

Atrazine 2/5 0/2 0/1

Azinphos-methyl oxon 1 5/5 nv nv

Deethylatrazine (2-Chloro-4-

isopropylamino-6-amino-striazine)

2/5 0/3 nv

3,4-Dichloroaniline 3/5 0/2 nv

Hexazinone 4/5 0/1 nv

Phosmet oxon 2 4/4 nv nv

Simazine 3/5 0/2 nv

Tebuthiuron 5/5 nv nv

Polar pesticides and metabolites

Bromacil 4/5 0/1 nv

Deisopropyl atrazine (2-Chloro-6-

ethylamino-4-amino-s-triazine)

4/5 0/1 nv

Dinoseb (Dinitrobutyl phenol) 4/5 0/1 nv

Diuron 2/5 0/3 nv

Imazethapyr 5/5 nv nv

Norflurazon 5/5 nv nv

Constituents of special interest

N-Nitrosodimethylamine (NDMA) 2/2 nv nv

Perchlorate 2/5 0/3 nv

Low-level 1,2,3-trichloropropane 

(1,2,3-TCP)

2/5 0/3 nv

1

Laboratory reporting level raised from 0.042 to 0.6 for ground-water sample from MADCHOW-18 and associated replicate.

2

Laboratory unable to determine selected constituents in replicate sample associated with ground-water sample collected from MADCHOW-15 due to matrix 

interference. 

Table A4A. Quality-control summary for replicate analyses of organic constituents and constituents of special interest detected in 

samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and 

May 2008.

[SD, standard deviation; RSD, percent relative standard deviation; LRL, laboratory reporting limit; nv, no values in category]
70 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table A4B. Quality-control summary for replicate analyses of nutrients, major and minor ions, trace elements, and isotope tracers 

detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

April and May 2008.—Continued

[Stable isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to 

a standard reference material. Other abbreviations: SD, standard deviation; RSD, percent relative standard deviation; LRL, laboratory reporting limit; mg/L, 

micrograms per liter; mg/L, milligrams per liter; pCi/L, picocuries per liter, nv, no values in category; ≤, less than or equal to]

Constituent

Number of 

nondetect or ≤-coded 

replicates/total 

number of 

replicates

Number of SDs 

greater than 

1⁄2 the LRL, MDL, 

or MRL/number 

of replicates with

 concentrations 

or activities less 

than 5 times 

the LRL, MDL, 

or MRL

Concentrations 

or activities of 

replicates with 

SDs greater than 

1⁄2 LRL, MDL, or MRL 

(environmental, 

replicate)

Number of RSDs 

greater than 

10 percent/number 

of replicates with 

concentrations 

or activities 

greater than 

5 times the 

LRL, MDL, or MRL

Concentrations 

or activities of 

replicates with RSDs 

greater than 

10 percent 

(environmental, 

replicate) 

Nutrients, concentrations in mg/L

Ammonia, as nitrogen 4/5 0/1 nv nv nv

Nitrite, as nitrogen 4/5 nv nv 0/1 nv

Nitrate plus nitrite, as 

nitrogen

0/5 nv nv 0/5 nv

Nitrogen, total, as 

nitrogen

0/5 nv nv 0/5 nv

Orthophosphate, as 

phosphorus

0/5 0/1 nv 0/4 nv

Major and minor ions, concentrations in mg/L

Bromide 0/5 0/4 nv 0/1 nv

Calcium 0/5 nv nv 0/5 nv

Chloride 0/5 nv nv 0/5 nv

Fluoride 0/5 0/5 nv nv nv

Iodide 0/5 0/4 nv 0/1 nv

Magnesium 0/5 nv nv 0/5 nv

Potassium 0/5 nv nv 0/5 nv

Silica 0/5 nv nv 0/5 nv

Sodium 0/5 nv nv 0/5 nv

Sulfate 0/5 nv nv 0/5 nv

Total dissolved solids 

(TDS; residue on 

evaporation, ROE)

0/5 nv nv 0/5 nv

Trace elements, concentrations in μg/L

Aluminum 4/5 0/1 nv nv nv

Antimony 4/5 0/1 nv nv nv

Arsenic 0/5 nv nv 0/5 nv

Barium 0/5 nv nv 0/5 nv

Beryllium 0/5 nv nv nv nv

Boron 0/5 0/2 nv 0/3 nv

Cadmium 4/5 0/1 nv nv nv

Chromium 0/5 0/2 nv 0/3 nv

Cobalt 1/5 0/4 nv nv nv

Copper 1/5 0/4 nv nv nv

Iron 4/5 0/1 nv nv nv

Lead 0/5 0/4 nv 0/1 nv

Lithium 0/5 0/4 nv 1/1 (8.9, 10)

Manganese 1/5 0/2 nv 1/2 (3.7, 2.5)

Molybdenum 0/5 0/1 nv 0/4 nv

Table A4B. Quality-control summary for replicate analyses of nutrients, major and minor ions, trace elements, and isotope tracers 

detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

April and May 2008.

[Stable isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to 

a standard reference material. SD, standard deviation; RSD, percent relative standard deviation; LRL, laboratory reporting limit; mg/L, micrograms per liter; 

mg/L, milligrams per liter; pCi/L, picocuries per liter, nv, no values in category; ≤, less than or equal to]
Appendix 71

Table A4B. Quality-control summary for replicate analyses of nutrients, major and minor ions, trace elements, and isotope tracers 

detected in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, 

April and May 2008.—Continued

[Stable isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative to 

a standard reference material. Other abbreviations: SD, standard deviation; RSD, percent relative standard deviation; LRL, laboratory reporting limit; mg/L, 

micrograms per liter; mg/L, milligrams per liter; pCi/L, picocuries per liter, nv, no values in category; ≤, less than or equal to]

Constituent

Number of 

nondetect or ≤-coded 

replicates/total 

number of 

replicates

Number of SDs 

greater than 

1⁄2 the LRL, MDL, 

or MRL/number 

of replicates with

 concentrations 

or activities less 

than 5 times 

the LRL, MDL, 

or MRL

Concentrations 

or activities of 

replicates with 

SDs greater than 

1⁄2 LRL, MDL, or MRL 

(environmental, 

replicate)

Number of RSDs 

greater than 

10 percent/number 

of replicates with 

concentrations 

or activities 

greater than 

5 times the 

LRL, MDL, or MRL

Concentrations 

or activities of 

replicates with RSDs 

greater than 

10 percent 

(environmental, 

replicate) 

Nickel 2/5 0/3 nv nv nv

Selenium 0/5 0/4 nv 0/1 nv

Silver 5/5 nv nv nv nv

Strontium 0/5 nv nv 0/5 nv

Tungsten 2/5 0/2 nv 0/1 nv

Uranium 0/5 nv nv 0/5 nv

Vanadium 0/5 nv nv 0/5 nv

Zinc 0/5 0/3 nv 0/2 nv

Arsenic and iron species, concentrations in μg/L

Arsenic, total 0/2 0/2 nv nv nv

Arsenic (III) 2/2 nv nv nv nv

Iron, total 2/2 nv nv nv nv

Iron (II) 2/2 nv nv nv nv

Isotopic tracers, in units as noted

δ2H (per mil) 0/5 nv nv 0/5 nv

δ18O (per mil) 0/5 nv nv 0/5 nv

Tritium (pCi/L) 1/5 1nv 1nv 0/3 nv

δ13C of dissolved carbonates (per mil)0/5 nv nv 1/5 (–13.87, –16.63)

Carbon-14 (percent 

modern)

0/5 nv nv 1/5 (5, 4)

1

The SD was not calculated because the variability for 1 replicate pair was considered outside the limits for acceptable precision since the environmental value 

was reported as a detect just above the MRL and the replicate value was reported as a nondetect and less than the MRL (0.4, <0.3).
72 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Constituent

Number of non-overlapping 

values/total number 

of replicates

Activites for replicates 

with non-overlapping values 

(environmental, replicate) 

(pCi/L)

Gross alpha particle activity, 72 hour count 1/5 (1.3 ± 0.81, —)

Gross alpha particle activity, 30 day count 1/5 (2.0 ± 0.68, 0.62 ± 0.46)

Gross beta particle activity, 72 hour count 0/5 nv

Gross beta particle activity, 30 day count 1/5 (6.8 ± 0.75, 3.9 ± 0.92)

Uranium-234 1/4 (0.12 ± 0.030, 0.059 ± 0.024)

Uranium-235 1/4 (0.29 ± 0.044, 0.20 ± 0.034)

Uranium-238 0/4 nv

Table A4C. Quality-control summary for replicate analyses of radiochemical constituents detected in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.

[Non-overlapping, results are reported as “+” for the upper confidence interval and “–” for the lower confidence interval of the activity measured in the groundwater sample, which provides a range of activity possible for overlap. pCi/L, picocuries per liter; —, not detected (sample result is less than critical value); nv, 

no values in category]
Appendix 73

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued

[Acceptable recovery range is between 70 and 130 percent; na, not available]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetone 5 75 122 103

Acrylonitrile 5 104 127 115

tert-Amyl methyl ether (TAME) 5 91 110 100

Benzene 5 105 111 107

Bromobenzene 5 102 113 104

Bromochloromethane 5 109 118 111

Bromodichloromethane1 5 103 118 106

Bromoform (Tribromomethane)1 5 87 120 105

Bromomethane (Methyl bromide) 5 62 117 99

n-Butylbenzene 5 89 100 91

sec-Butylbenzene 5 96 108 100

tert-Butylbenzene 5 99 114 102

Carbon disulfide 5 71 93 87

Carbon tetrachloride (Tetrachloromethane) 5 104 111 109

Chlorobenzene 5 102 109 107

Chloroethane 5 91 117 114

Chloroform (Trichloromethane)1 5 109 120 110

Chloromethane 5 81 105 103

3-Chloropropene 5 67 125 118

2-Chlorotoluene 5 103 110 106

4-Chlorotoluene 5 99 103 102

Dibromochloromethane1 5 98 114 105

1,2-Dibromo-3-chloropropane (DBCP)1,2 na na na na

1,2-Dibromoethane (EDB)1,2 na na na na

Dibromomethane 5 104 117 106

1,2-Dichlorobenzene 5 107 118 112

1,3-Dichlorobenzene 5 103 117 106

1,4-Dichlorobenzene 5 102 112 104

trans-1,4-Dichloro-2-butene 5 96 109 104

Dichlorodifluoromethane (CFC-12) 5 62 82 77

1,1-Dichloroethane (1,1-DCA)1 5 109 114 111

1,2-Dichloroethane (1,2-DCA) 5 103 109 105

1,1-Dichloroethene (1,1-DCE) 5 93 104 100

cis-1,2-Dichloroethene (cis-1,2-DCE)1 5 104 113 108

trans-1,2-Dichloroethene (trans-1,2-DCE) 5 109 120 114

1,2-Dichloropropane 5 105 114 108

1,3-Dichloropropane 5 108 119 110

2,2-Dichloropropane 5 78 103 88

1,1-Dichloropropene 5 94 104 99

cis-1,3-Dichloropropene 5 86 105 95

trans-1,3-Dichloropropene 5 88 109 96

Diethyl ether 5 106 122 119

Diisopropyl ether (DIPE) 5 95 118 110

Ethylbenzene 5 95 108 100

Ethyl tert-butyl ether (ETBE) 5 92 111 102

Ethyl methacrylate 5 92 105 103

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

benzene)

5 92 103 96

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.

[Acceptable recovery range is between 70 and 130 percent; na, not available]
74 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued

[Acceptable recovery range is between 70 and 130 percent; na, not available]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Hexachlorobutadiene 5 79 88 82

Hexachloroethane 5 93 110 100

2-Hexanone (n-Butyl methyl ketone) 5 94 118 108

Iodomethane (Methyl iodide) 5 76 139 124

Isopropylbenzene 5 88 108 94

4-Isopropyl-1-methyl benzene 5 88 102 95

Methyl acrylate 5 108 118 109

Methyl acrylonitrile 5 110 126 118

Methyl tert-butyl ether (MTBE) 5 88 110 102

Methyl iso-butyl ketone (MIBK) 5 97 112 108

Methylene chloride (Dichloromethane) 5 98 115 108

Methyl ethyl ketone (2-butanone, MEK) 5 97 110 105

Methyl methacrylate 5 88 108 103

Naphthalene 5 89 137 112

Perchloroethene (PCE, Tetrachloroethene)1 5 104 116 107

n-Propylbenzene 5 91 100 95

Styrene 5 6 106 7

1,1,1,2-Tetrachloroethane 5 108 130 111

1,1,2,2-Tetrachloroethane 5 106 127 111

Tetrahydrofuran 5 101 120 109

1,2,3,4-Tetramethylbenzene 5 85 130 89

1,2,3,5-Tetramethylbenzene 5 53 131 97

Toluene1 5 104 106 104

1,2,3-Trichlorobenzene 5 104 124 107

1,2,4-Trichlorobenzene 5 92 113 96

1,1,1-Trichloroethane (1,1,1-TCA) 5 102 110 108

1,1,2-Trichloroethane (1,1,2-TCA) 5 103 127 106

Trichloroethene (TCE)1 5 101 105 103

Trichlorofluoromethane (CFC-11) 5 95 108 99

1,2,3-Trichloropropane (1,2,3-TCP) 5 98 116 106

Trichlorotrifluoroethane (CFC-113) 5 85 99 88

1,2,3-Trimethylbenzene 5 98 116 102

1,2,4-Trimethylbenzene1 5 92 110 104

1,3,5-Trimethylbenzene 5 49 104 97

Vinyl bromide (Bromoethene) 5 84 109 103

Vinyl chloride (Chloroethene) 5 99 113 103

m- and p-Xylene 5 96 107 104

o-Xylene 5 89 106 99

1

Constituents detected in ground-water samples.

2

Constituents on Schedules 2020 and 1306; only values from the preferred method (Schedule 1306) are reported; there is no spike solution available for 

Schedule 1306.
Appendix 75

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued

[Acceptable recovery range is between 70 and 130 percent; na, not available]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acetochlor 5 83 91 86

Alachlor 5 83 91 89

Atrazine1,2 5 81 94 87

Azinphos-methyl 5 54 96 68

Azinphos-methyl oxon 5 22 64 38

Benfluralin 5 54 60 57

Carbaryl 5 90 107 98

Carbofuran3 na na na na

2-Chloro-2,6-diethylacetanilide 5 79 94 88

4-Chloro-2-methylphenol 5 42 78 60

Chlorpyrifos 5 42 82 67

Chlorpyrifos-oxon 5 14 69 19

Cyanazine 5 48 94 82

Cyfluthrin 5 37 52 46

λ-Cyhalothrin 5 29 36 34

Cypermethrin 5 38 55 45

DCPA (Dacthal) 5 90 95 92

Deethylatrazine (2-Chloro-4-isopropylamino-6-amino-s-triazine)1,2

4

4 450 61 56

Desulfinylfipronil 5 89 101 90

Desulfinylfipronil amide 5 29 103 81

Diazinon 5 70 85 82

3,4-Dichloroaniline1 5 64 73 70

3,5-Dichloroaniline 5 75 81 80

Dichlorvos 5 4 58 16

Dicrotophos 5 18 84 37

Dieldrin 5 74 102 83

2,6-Diethylaniline 5 73 84 80

Dimethoate 5 12 49 37

Disulfoton 5 42 69 63

Disulfoton sulfone 5 63 88 74

α-Endosulfan 5 64 84 73

Endosulfan sulfate 5 66 77 74

Ethion 5 50 64 57

Ethion monoxon 5 62 73 66

Ethoprop 5 78 100 88

S-Ethyl-dipropylthiocarbamate (EPTC) 5 82 86 84

2-Ethyl-6-methylaniline 5 70 84 80

Fenamiphos 5 70 87 72

Fenamiphos sulfone 5 49 81 76

Fenamiphos sulfoxide 5 4 38 24

Fipronil 5 64 88 74

Fipronil sulfide 5 66 96 78

Fipronil sulfone 5 55 76 62

Fonofos 5 72 80 77

Hexazinone1 5 22 58 45

Iprodione 5 45 58 45

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.

[Acceptable recovery range is between 70 and 130 percent; na, not available]
76 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued

[Acceptable recovery range is between 70 and 130 percent; na, not available]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Isofenphos 5 65 90 81

Malaoxon 5 52 74 67

Malathion 5 70 86 82

Metalaxyl3 na na na na

Methidathion 5 71 85 77

Metolachlor 5 79 93 92

Metribuzin 5 50 80 75

Molinate 5 82 88 85

Myclobutanil 5 67 90 77

1-Naphthol 5 12 50 16

Oxyfluorfen 5 52 79 56

Paraoxon-methyl 5 35 55 46

Parathion-methyl 5 61 94 68

Pendimethalin 5 75 86 77

cis-Permethrin 5 39 55 41

Phorate 5 41 70 62

Phorate oxon 5 78 96 94

Phosmet 5 6 23 13

Phosmet oxon 5 6 52 21

Prometon 5 72 85 74

Prometryn 5 80 92 86

Pronamide 5 71 84 79

Propanil 5 80 100 87

Propargite 5 42 58 55

cis-Propiconazole 5 74 101 82

trans-Propiconazole 5 69 89 78

Simazine1 5 58 90 82

Tebuthiuron1,2 5 37 40 37

Tefluthrin 5 57 73 71

Terbufos 5 57 73 71

Terbufos oxon sulfone 5 60 74 61

Terbuthylazine 5 87 94 91

Thiobencarb 5 78 99 94

Tribufos 5 33 49 47

Trifluralin 5 64 70 66 1

Constituents detected in ground-water samples.

2

Constituents on Schedule 2033 and 2060; only values from Schedule 2033 are reported because it is the preferred analytical schedule.

3

Constituents on Schedules 2033 and 2060; only values from Schedule 2060 are reported because it is the preferred analytical schedule.

4

The spike concentration was too small relative to the environmental concentration so the negative spike recovery for one result is not valid and not reported.
Appendix 77

Table A5C. Quality-control summary for matrix-spike recoveries of polar pesticides and metabolites in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued

[Acceptable recovery range is between 70 and 130 percent; na, not available]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Acifluorfen 4 50 71 64

Aldicarb 4 57 84 74

Aldicarb sulfone 4 68 104 96

Aldicarb sulfoxide 4 97 112 102

Atrazine1,2 na na na na

Bendiocarb 4 84 91 87

Benomyl 4 72 139 96

Bensulfuron-methyl 4 98 132 119

Bentazon 4 42 100 58

Bromacil1 4 86 94 87

Bromoxynil 4 44 96 54

Caffeine 4 70 112 94

Carbaryl 4 87 91 89

Carbofuran3 4 97 106 103

Chloramben, methyl ester 4 71 100 77

Chlorimuron-ethyl 4 94 142 129

3-(4-Chlorophenyl)-1-methyl urea 4 70 104 84

Clopyralid 4 73 88 74

Cycloate 4 62 90 68

2,4-D plus 2,4-D methyl ester 4 78 83 80

2,4-DB (4-(2,4-Dichlorophenoxy)butyric acid) 4 71 75 73

DCPA (Dacthal) monoacid 4 71 86 75

Deethylatrazine (2-Chloro-4-isopropylamino6-amino-s-triazine)1,2na na na na

Deisopropyl atrazine (2-Chloro-6-ethylamino4-amino-s-triazine)14 87 92 88

Dicamba 4 62 80 68

Dichlorprop 4 88 99 93

Dinoseb (Dinitrobutyl phenol)1 4 38 85 63

Diphenamid 4 99 108 104

Diuron1 4 97 108 101

Fenuron 4 102 114 109

Flumetsulam 4 92 123 110

Fluometuron 4 98 101 99

Hydroxyatrazine (2-Hydroxy-4-isopropylamino6-ethylamino-s-triazine)4 85 97 97

3-Hydroxycarbofuran 4 90 120 105

Imazaquin 4 111 253 171

Imazethapyr1 4 111 195 151

Imidacloprid 4 94 110 104

Linuron 4 89 99 92

MCPA (2-Methyl-4-chlorophenoxyacetic acid) 4 84 98 88

MCPB (4-(2-Methyl-4-chlorophenoxy)butyric 

acid)

4 64 67 66

Metalaxyl3 4 93 102 95

Methiocarb 4 86 101 90

Methomyl 4 94 106 101

Metsulfuron methyl 4 71 134 107

Table A5C. Quality-control summary for matrix-spike recoveries of polar pesticides and metabolites in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.

[Acceptable recovery range is between 70 and 130 percent; na, not available]
78 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Table A5C. Quality-control summary for matrix-spike recoveries of polar pesticides and metabolites in samples collected for the 

Madera–Chowchilla Groundwater Ambient Monitoring and Assessment (GAMA) study, California, April and May 2008.—Continued

[Acceptable recovery range is between 70 and 130 percent; na, not available]

Constituent Number of 

spike samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

Neburon 4 83 94 89

Nicosulfuron 4 190 379 262

Norflurazon1 4 92 116 104

Oryzalin 4 69 83 76

Oxamyl 4 92 100 96

Picloram 4 70 93 74

Propham 4 67 90 78

Propiconazole 4 77 94 85

Propoxur 4 95 107 103

Siduron 4 94 125 112

Sulfometuron-methyl 4 108 130 121

Tebuthiuron1,2 na na na na

Terbacil 4 82 94 91

Triclopyr 4 74 90 82 1

Constituents detected in ground-water samples.

2

Constituents on Schedule 2033 and 2060; only values from Schedule 2033 are reported because it is the preferred analytical schedule.

3

Constituents on Schedules 2033 and 2060; only values from Schedule 2060 are reported because it is the preferred analytical schedule.
Appendix 79

Table A5D. Quality-control summary for matrix-spike recoveries of N-nitrosodimethylamine (NDMA) and low-level 

1,2,3-trichloropropane (1,2,3-TCP) in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment

(GAMA) study, California, April and May 2008.

[Acceptable recovery range is between 70 and 130 percent]

Constituent

Number 

of spike 

samples

Minimum 

recovery 

(percent)

Maximum 

recovery 

(percent)

Median 

recovery 

(percent)

N-Nitrosdimethylamine (NDMA)1 1 80 80 80

Low-level 1,2,3-trichloropropane (1,2,3-TCP)1 5 86 112 105

1

Constituents detected in ground-water samples. 
80 Groundwater-Quality Data in the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program

Surrogate Analytical 

schedule

Constitutent 

or constituent 

class analyzed

Number of 

analyses

Median 

recovery 

(percent)

Number of 

surrogate 

recoveries 

below 

70 percent

Number of 

surrogate 

recoveries 

above 

130 percent

Blanks

1-Bromo-4-fluorobenzene 2020 VOC 4 82 0 0

1,2-Dichloroethane-d4 2020 VOC 4 115 0 1

Toluene-d8 2020 VOC 4 93 0 0

Diazinon-d10 2033 Pesticide 4 92 1 0

α-HCH-d6 2033 Pesticide 4 88 0 0

Barban 2060 Polar pesticide 3 87 0 0

Caffeine-13C 2060 Polar pesticide 3 93 0 0

2,4,5-T 2060 Polar pesticide 3 80 0 0

Ground-water, replicate, and matrix-spike test samples

1-Bromo-4-fluorobenzene 2020 VOC 35 80 1 0

1,2-Dichloroethane-d4 2020 VOC 35 120 0 4

Toluene-d8 2020 VOC 35 94 0 0

Diazinon-d10 2033 Pesticide 35 84 7 0

α-HCH-d6 2033 Pesticide 35 90 0 0

Barban 2060 Polar pesticide 34 84 1 0

Caffeine-13C 2060 Polar pesticide 34 83 7 0

2,4,5-T 2060 Polar pesticide 34 84 0 0

Table A6. Quality-control summary for surrogate recoveries of volatile organic compounds, pesticides and pesticide degradates, and 

polar pesticides and metabolites in samples collected for the Madera–Chowchilla Groundwater Ambient Monitoring and Assessment 

(GAMA) study, California, April and May 2008.

[VOC, volatile organic compound] 
Manuscript approved for publication, June 25, 2009

Prepared by the USGS Publishing Network,

Publishing Service Center, Sacramento, California

For more information concerning the research in this report, contact the

California Water Science Center Director,

U.S. Geological Survey, 6000 J Street

Sacramento, California 95819

http://ca.water.usgs.gov
Bea

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Shelton and others—Groundwater-Quality Data for the Madera–Chowchilla Study Unit, 2008: Results from the California GAMA Program—Data Series 455