Northridge

San Fernando

Burbank

Pasadena

Alhambra

Azusa

West Covina

Data Series 356

U.S. Geological Survey

U.S. Department of the Interior

Ground-Water Quality Data in the San Fernando–San Gabriel

Study Unit, 2005—Results from the California GAMA Program

In cooperation with the California State Water Resources Control Board

A product of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program
Top photo: Looking northeast from Griffith Park. Downtown Glendale is in the middle ground, and the San Gabriel Mountains are in the background (photo taken 

July 12, 2006, by Will Bebeck. Bottom photo: By Andrea Altmann, U.S. Geological Survey.
Ground-Water Quality Data in the 

San Fernando–San Gabriel Study Unit, 

2005—Results from the California GAMA 

Program

By Michael Land and Kenneth Belitz

Prepared in cooperation with the California State Water Resources Control Board

Data Series 356

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

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

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reproduce any copyrighted materials contained within this report.

Suggested reference:

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. Available at 

http://pubs.usgs.gov/ds/356/
iii

Contents

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

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

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

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

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

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

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

Sample Collection and Analysis.........................................................................................................6

Data Reporting.......................................................................................................................................7

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

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

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

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

Ground-Water-Quality Data ..............................................................................................................10

Field Parameters........................................................................................................................10

Organic Constituents.................................................................................................................11

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

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

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

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

Microbial Indicators..................................................................................................................13

Future Work .........................................................................................................................................13

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

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

Tables. ...........................................................................................................................................................19

Appendix .......................................................................................................................................................64

Sample Collection and Analysis.......................................................................................................64

Data Reporting.....................................................................................................................................66

Laboratory Reporting Conventions .........................................................................................66

Constituents on Multiple Analytical Schedules....................................................................67

Quality Assurance...............................................................................................................................67

Blanks. .........................................................................................................................................67

Replicates....................................................................................................................................68

Matrix Spikes..............................................................................................................................68

Surrogates...................................................................................................................................68

Quality-Control Sample Results........................................................................................................69

Detections in Field and Source-Solution Blanks..................................................................69

Variability in Replicate Samples..............................................................................................70

Matrix-Spike Recoveries..........................................................................................................70

Surrogate Compound Recoveries...........................................................................................71

Appendix Tables...........................................................................................................................................72
iv

Figures

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

of the San Fernando-San Gabriel Groundwater Ambient Monitoring and 

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

Figure 2. Map showing the San Fernando-San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit showing the California 

Department of Water Resources defined ground-water basins within the 

study unit and major hydrologic features ................................................ 5

Figure 3. Maps showing the (A) eastern and (B) western study areas of the 

San Fernando-San Gabriel Groundwater Ambient Monitoring and 

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

grid cells and the location of sampled grid-cell and understanding wells ......... 7

Tables

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

San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, May to July 2005 ....................................... 20

Table 2. Water-quality indicators and classes of chemical and microbial constituents 

collected for the slow, intermediate, and fast well sampling schedules in the 

San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, May to July 2005 ....................................... 21

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

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

Laboratory schedule 2020 .................................................................. 22

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

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

Water Quality Laboratory schedule 4024 ................................................ 24

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

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

Water Quality Laboratory schedule 2003 ................................................ 25

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

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

Water Quality Laboratory schedule 2060 ................................................ 27

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

thresholds, and reporting information for the Montgomery Watson-Harza 

Laboratory .................................................................................... 29

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

information for the U.S. Geological Survey National Water Quality Laboratory 

schedule 2755 and laboratory code 2612 ................................................ 30

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

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

Laboratory schedule 1948 .................................................................. 31

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

information for the U.S. Geological Survey Trace Metal Laboratory, Boulder, 

Colorado .................................................................................... 32

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

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

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

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

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

the U.S. Geological Survey Ohio Microbiology Laboratory parameter codes 

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

Table 4. Water-quality indicators determined in the field for the San Fernando–San 

Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, 

California, May to July 2005 ............................................................... 36

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

detected in samples collected for the San Fernando–San Gabriel Groundwater 

Ambient Monitoring and Assessment (GAMA) study unit, California, May to 

July 2005 .................................................................................... 38

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

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment

(GAMA) study unit, California, May to July 2005 ....................................... 46

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

1,2,3-trichloropropane (1,2,3-TCP), and 1,4-dioxane in the ground-water 

samples collected in the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005 ...... 52

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

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, May to July 2005 ....................................... 53

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

for the San Fernando–San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit, California, May to July 2005 ........................ 54

Table 10. Trace elements detected in samples collected for the San Fernando–San Gabriel 

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

May to July 2005 ........................................................................... 55

Table 11. Inorganic arsenic and iron species detected in samples collected for the 

San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, May to July 2005 ....................................... 57

Table 12. Chromium species detected in samples collected for the San Fernando–San 

Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, 

California, May to July 2005 ............................................................... 58

Table 13. Hydrogen and oxygen isotope ratios for water, and tritium activities, in samples 

collected for the San Fernando–San Gabriel Groundwater Ambient Monitoring 

and Assessment (GAMA) study unit, California, May to July 2005 .................. 59

Table 14. Carbon isotopes in samples collected for the San Fernando–San Gabriel 

Groundwater Ambient Monitoring and Assessment (GAMA) study unit, 

California, May to July 2005 ............................................................... 60

Table 15. Results for analyses of noble gases and tritium in samples collected for the 

San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, May to July 2005 ....................................... 61

Table 16. Radioactive constituents detected in samples collected for the San Fernando–

San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study 

unit, California, May to July 2005 ......................................................... 62

Table 17. Microbial indicators detected in samples collected for the San Fernando–San 

Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, 

California, May to July 2005 ............................................................... 63
vi

Appendix tables

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

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

Quality Laboratory (NWQL) and additional contract laboratories ..................... 73

Table A2. Preferred analytical schedules for constituents appearing on multiple 

schedules for samples collected for the San Fernando–San Gabriel (SFSG) 

Groundwater Ambient Monitoring and Assessment (GAMA) study unit, 

California, May to July 2005 ............................................................... 75

Table A3. Constituents detected in field blanks collected for the San Fernando–San 

Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, 

California, May to July 2005 ............................................................... 76

Table A4. Quality-control summary for replicate analyses collected for the San Fernando–

San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study 

unit, California, May to July 2005 ......................................................... 77

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

compounds (VOCs) and gasoline oxygenates and degradates in samples 

collected for the San Fernando–San Gabriel Groundwater Ambient Monitoring 

and Assessment (GAMA) study unit, California, May to July 2005 .................. 78

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

pesticide degradates in samples collected (for NWQL schedule 2003) for the 

San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, May to July 2005 ....................................... 80

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

pesticide degradates in samples collected (for NWQL schedule 2060) for the 

San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, May to July 2005 ....................................... 82

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

interest in samples collected for the San Fernando–San Gabriel Groundwater 

Ambient Monitoring and Assessment (GAMA) study unit, California, May to 

July 2005 .................................................................................... 83

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

gasoline oxygenates and degradates, pesticides and pesticide degradates, and 

constituents of special interest in samples collected for the San Fernando–San 

Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, 

California, May to July 2005 ............................................................... 84
vii

Abbreviations and Acronyms

AB Assembly Bill (through the California State Assembly)

AL-US Action level (USEPA)

CAS Chemical Abstract Service (American Chemical Society)

CSU combined standard uncertainty E estimated or having a higher degree of uncertainty

GAMA Groundwater Ambient Monitoring and Assessment program

GPS Global Positioning System

HAL-US Lifetime Health Advisory Level (USEPA)

HPLC high-performance liquid chromatography

LRL laboratory reporting level

LSD land-surface datum

LT-MDL long-term method detection level

MCL-CA maximum contaminant level (CDPH)

MCL-US maximum contaminant level (USEPA)

MDL method detection limit

MRL minimum reporting level

MU method uncertainty

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

na not available

nc sample not collected

NL-CA California notification level (CDPH)

NWIS National Water Information System (USGS)

QC quality control

RPD relative percent difference

RSD relative standard deviation

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

SFSG San Fernando-San Gabriel study unit

SMCL-CA secondary maximum contaminant level (CDPH)

SMCL-US secondary maximum contaminant level (USEPA)

SSMDC sample-specific minimum detectable concentration

TT-US Treatment Technique (USEPA)

ULASF Upper Los Angeles Basins, San Fernando study area

ULASG Upper Los Angeles Basins, San Gabriel study area

US United States V value censored due to potential blank contamination

VPDB Vienna Peedee Belemnite

VSMOW Vienna Standard Mean Ocean Water

Organizations

CDPH California Department of Public Health

USEPA U.S. Environmental Protection Agency

LLNL Lawrence Livermore National Laboratory

MWH Montgomery Watson Harza

NAWQA National Water Quality Assessment (USGS)

NWQL National Water Quality Laboratory (USGS)

SWRCB State Water Resources Control Board (California)

USGS U.S. Geological Survey

Selected chemical names

CaCO

3 calcium carbonate

CFC chlorofluorocarbon

CO

3

–2 carbonate

DOC dissolved organic carbon

HCl hydrochloric acid
viii

HCO3

– bicarbonate

MTBE methyl tert-butyl ether

NDMA N-nitrosodimethylamine

PCE tetrachloroethene

TCP trichloropropane

TDS total dissolved solids

THM trihalomethane

VOC volatile organic compound

Units of Measure

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

km kilometer

L liter

mg milligram

mg/L milligrams per liter (parts per million)

mi mile

mL milliliter

pCi/L picocurie per liter

pmc percent modern carbon

δi

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

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

material, expressed in per mil (parts per thousand)

μg/L micrograms per liter (parts per billion)

μL microliter

μm micrometer

Notes

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

°F=(1.8×°C)+32

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

(NAVD 88).

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

25°C).

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

or micrograms per liter (μg/L). Milligrams per liter is equivalent to parts per million (ppm) and 

micrograms per liter is equivalent to parts per billion (ppb).
Abstract 

Ground-water quality in the approximately 460 square 

mile San Fernando-San Gabriel study unit (SFSG) was 

investigated between May and July 2005 as part of the Priority 

Basin Assessment Project of the Groundwater Ambient 

Monitoring and Assessment (GAMA) Program. The GAMA 

Priority Basin Assessment Project was developed in response 

to the Groundwater Quality Monitoring Act of 2001 and is 

being conducted by the U.S. Geological Survey (USGS) in 

cooperation with the California State Water Resources Control 

Board (SWRCB).

The San Fernando-San Gabriel study was designed to 

provide a spatially unbiased assessment of raw ground-water 

quality within SFSG, as well as a statistically consistent basis 

for comparing water quality throughout California. Samples 

were collected from 52 wells in Los Angeles County. Thirtyfive of the wells were selected using a spatially distributed, 

randomized grid-based method to provide statistical 

representation of the study area (grid wells), and seventeen 

wells were selected to aid in the evaluation of specific waterquality issues or changes in water chemistry along a historic 

ground-water flow path (understanding wells).

The ground-water samples were analyzed for a 

large number of synthetic organic constituents [volatile 

organic compounds (VOCs), pesticides and pesticide 

degradates], constituents of special interest [perchlorate, 

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

(1,2,3-TCP), and 1,4-dioxane], naturally occurring inorganic 

constituents (nutrients, major and minor ions, and trace 

elements), radioactive constituents, and microbial indicators. 

Naturally occurring isotopes (tritium, and carbon-14, and 

stable isotopes of hydrogen, oxygen, and carbon), and 

dissolved noble gases also were measured to help identify the 

source and age of the sampled ground water. 

Quality-control samples (blanks, replicates, samples for 

matrix spikes) were collected at approximately one-fifth (11 of 

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

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

Assessment of the quality-control results showed that the data 

had very little bias or variability and resulted in censoring of 

less than 0.7 percent (32 of 4,484 measurements) of the data 

collected for ground-water samples.

This study did not attempt to evaluate the quality of water 

delivered to consumers; after withdrawal from the ground, 

water typically is treated, disinfected, or blended with other 

waters to maintain acceptable water quality. Regulatory 

thresholds apply to treated water that is served to the 

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

context for the results, concentrations of constituents measured 

in the raw ground water were compared with health-based 

thresholds established by the U.S. Environmental Protection 

Agency (USEPA) and California Department of Public Health 

(CDPH) and thresholds established for aesthetic concerns 

(secondary maximum contaminant levels, SMCL-CA) by 

CDPH.

VOCs were detected in more than 90 percent (33 of 

35) of grid wells. For all wells sampled for SFSG, nearly 

all VOC detections were below health-based thresholds, 

and most were less than one-tenth of the threshold values. 

Samples from seven wells had at least one detection of PCE, 

TCE, tetrachloromethane, NDMA, or 1,2,3-TCP at or above 

a health-based threshold. Pesticides were detected in about 

90 percent (31 of 35) grid wells and all detections in samples 

from SFSG wells were below health-based thresholds. 

Major ions, trace elements, and nutrients in samples from 

17 SFSG wells were all below health-based thresholds, with 

the exception of one detection of nitrate that was above the 

USEPA maximum contaminant level (MCL-US). With the 

exception of 14 samples having radon-222 above the proposed 

MCL-US, radioactive constituents were below health-based 

thresholds for 16 of the SFSG wells sampled. Total dissolved 

solids in 6 of the 24 SFSG wells that were sampled had 

concentrations between the lower and upper non-enforceable 

thresholds (500 and 1,000 mg/L) set for aesthetic concerns. 

Ground-Water Quality Data in the San Fernando–San 

Gabriel Study Unit, 2005—Results from the California 

GAMA Program

By Michael Land and Kenneth Belitz
2 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Introduction 

Ground water comprises nearly one-half of the water used 

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

assess the quality of ground water in aquifers used for drinking 

water supply and to establish a program for monitoring trends 

in ground-water quality, 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.

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

three projects: Priority Basin Assessment, conducted by the 

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

Well Assessment, conducted by the SWRCB; and Special 

Studies, conducted by LLNL. 

The SWRCB initiated the GAMA Priority Basin 

Assessment Project in response to the Ground-Water Quality 

Monitoring Act of 2001 (Sections 10780-10782.3 of the 

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

public mandate to assess and monitor the quality of ground 

water used as public supply for municipalities in California. 

The project is a comprehensive assessment of statewide 

ground-water quality designed to help better understand and 

identify risks to ground-water resources, and to increase 

the availability of information about ground-water quality 

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

collaboration with the SWRCB, developed the monitoring 

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

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

are inter-agency collaboration and cooperation with local 

water agencies and well owners. Local participation in the 

project is entirely voluntary.

The GAMA Priority Basin Assessment Project is 

unique in California because the data collected during the 

study include analyses for an extensive number of chemical 

constituents at very low concentrations, analyses that are not 

available normally. A broader understanding of ground-water 

composition will be especially useful for providing an early 

indication of changes in water quality and for identifying 

the natural and human factors affecting water quality. 

Additionally, the GAMA Priority Basin Assessment Project 

will analyze a broader suite of constituents than is required by 

the California Department of Public Health (CDPH; formerly 

California Department of Health Services (CDHS)—replaced 

on July 1, 2007). An understanding of the occurrence and 

distribution of these constituents is important for the long-term 

management and protection of ground-water resources.

 The range of hydrologic, geologic, and climatic 

conditions that exist in California must be considered in 

an assessment of ground-water quality. Belitz and others 

(2003) partitioned the state into 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 public-supply wells 

are located in ground-water basins within these hydrologic 

provinces. These ground-water basins, defined by the 

California Department of Water Resources (CDWR), generally 

consist of relatively permeable, unconsolidated deposits of 

alluvial or volcanic origin (California Department of Water 

Resources, 2003). Ground-water basins were prioritized for 

sampling, based on the number of public-supply wells in 

the basin, with secondary consideration given to municipal 

ground-water use, agricultural pumping, the number of 

leaking underground fuel tanks, and pesticide applications 

within the basins (Belitz and others, 2003). In addition, some 

ground-water basins or groups of adjacent similar basins with 

relatively few public-supply wells were assigned high priority 

so that all hydrogeologic provinces would be represented in 

the subset of basins sampled. The 116 priority basins were 

grouped into 35 study units defined. Some areas not in the 

defined ground-water basins were included in several of the 

study units to achieve representation of the 20 percent of 

public-supply wells not located in the ground-water basins.

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 ground-water 

resource, (2) Trends: detection of changes in ground-water 

quality, and (3) Understanding: identification the natural and 

human factors affecting ground-water quality (Kulongoski 

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

presenting water-quality data collected in each study 

unit (Wright and others, 2005; Bennett and others, 2006; 

Kulongoski and others, 2006; Kulongoski and Belitz, 2007; 

Dawson and others, 2008). Subsequent reports will present the 

status, trends, and understanding assessments of water-quality 

in the study units.

The San Fernando-San Gabriel GAMA study unit, 

hereafter referred to as SFSG, contains three major groundwater basins, including several smaller, adjacent subbasins. 

SFSG was considered a high priority for sampling to provide 

adequate representation of the Transverse Ranges and selected 

Peninsular Ranges hydrogeologic province (Belitz and others, 

2003).
Introduction 3

Figure 1. The hydrogeologic provinces of California and the location of the San Fernando-San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit. Modified from Belitz and others (2003).

Basin and Range

Klamath

Mountains

Desert

Cascades and

Modoc Plateau

Southern 

Coast

 Ranges

Sierra

Nevada

Central

Valley

Northern

Coast

Ranges

San Diego

Drainages

Transverse Ranges and selected Peninsular Ranges

San Fernando-San Gabriel 

GAMA Study Unit

Bakersfield

San Francisco

OREGON

NEVADA

MEXICO

ARIZONA

Redding

Los Angeles

San Diego

Pacific Ocean

0 200 MILES

0 200 KILOMETERS

40

42

124 122 120 118 116 114

38

36

34

Base from U.S. Geological Survey digital elevation

data, 1999, Albers Equal Area Projection

Sacramento
4 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Purpose and Scope

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

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

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

for ground-water samples collected in SFSG. Ground-water 

samples were analyzed for organic, inorganic, and microbial 

constituents, field parameters, and chemical tracers. The 

chemical and microbial data presented in this report were 

evaluated by comparison to state and federal drinking water 

regulatory and other health-based standards that are applied to 

treated drinking water. Regulatory thresholds considered for 

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

Protection Agency (USEPA) and the California Department 

of Public Health (CDPH). The data presented in this report 

are intended to characterize the quality of untreated 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 ground-water samples will be the 

subject of subsequent publications.

Acknowledgments

The authors thank the following cooperators for their 

support: the California State Water Resources Control Board 

(SWRCB), California Department of Public Health, California 

Department of Water Resources, and Lawrence Livermore 

National Laboratory. We especially thank the well owners and 

water purveyors for their generosity in allowing the USGS to 

collect samples from their wells. Funding for this work was 

provided by State bonds authorized by Proposition 50 and 

administered by the SWRCB.

Hydrogeologic Setting 

The San Fernando-San Gabriel (SFSG) study unit 

lies within the Transverse Range and Selected Peninsular 

Ranges hydrogeologic province (fig. 1) described by Belitz 

and others (2003), and includes three ground-water basins: 

San Fernando Valley, Raymond, and San Gabriel Valley 

(California Department of Water Resources, 2003). Combined, 

these basins define the extent of SFSG, and cover an area of 

approximately 500 mi2 in Los Angeles County, California. 

(fig. 2).

In this report, the western part of the SFSG study unit

includes the San Fernando Valley ground-water basin and is 

referred to as the San Fernando study area; the eastern part of 

SFSG includes the Raymond and San Gabriel Valley groundwater basins, and collectively is referred to as the San Gabriel 

study area. The San Fernando study area (ULASF) includes 

part of the Bull Canyon, Sylmar, Tujunga, Verdugo, and Eagle 

Rock watersheds. The San Gabriel study area (ULASG) 

includes part of the Monk Hill, Pasadena, Lower Canyon, 

Upper San Gabriel River, Foothill, Live Oak, Pomona, and 

San Jose watersheds.

SFSG has approximately 3,000 ft of topographic relief. 

The major ground-water basins in SFSG are sloping gently 

with a median altitude ranging from approximately 600 to 

1,000 ft. The climate in SFSG is characterized by hot, dry 

summers and cool, moist winters, with most precipitation 

falling between the months of December and March 

(California Department of Water Resources, 2003).

The SFSG study unit is bounded to the north by the Santa 

Susana and the San Gabriel Mountains; to the east by the San 

Jose and the Chino Faults; to the south by the Santa Monica 

Mountains and the Elysian, Repetto, Merced and Puente 

Hills; and to the west by the Simi Hills. The primary waterbearing materials are composed of unconsolidated to semiconsolidated gravel, sand, and clay of Pleistocene to Recent 

age (California Department of Water Resources, 2005a,b,c). 

These sediments were deposited by alluvial fans from the 

surrounding hills and mountains. Deeper water-bearing units 

in SFSG consist of marine deposits of late Pleistocene age.

Several creeks and washes drain the SFSG study unit. 

In the western part of SFSG, water from surface channels 

drains to the Los Angeles River, where it passes through the 

Los Angeles River Narrows and into the coastal plain before 

ultimately reaching San Pedro Bay. In the eastern part of 

SFSG, water from tributary creeks and washes drains to the 

San Gabriel River or the Rio Hondo then passes through the 

Whittier Narrows before ultimately reaching San Pedro Bay.

Recharge in SFSG is from a variety of sources. Natural 

recharge mainly is from direct infiltration of precipitation 

and percolation of streamflow from the surrounding highland 

areas. Precipitation in SFSG may vary from as little as 

15 in./yr in the valley areas to as much as 31 in./yr in the 

upland areas; the average value over the three ground-water 

basins ranges from 17–21 in./yr (California Department of 

Water Resources, 2005a,b,c). Runoff—consisting of natural 

streamflow, imported water, reclaimed wastewater, industrial 

discharge, and(or) precipitation falling on impervious 

material—is often diverted to spreading basins or impounded 

at dams to enhance recharge. A lesser amount of recharge 

occurs as: (1) Subsurface flow from adjacent basins or from 

fractures in the surrounding mountains (California Department 

of Water Resources, 2005a,b,c) and (2) return flow from 

irrigation and from other distributed sources (such as leakage 

from pipes). 

Imported water for direct use and for artificial recharge 

is delivered to SFSG from several distant sources. Beginning 

in 1913, Los Angeles Water & Power began to deliver water 

from Owens Valley by means of the Los Angeles Aqueduct. In 

1941, the Metropolitan Water District of Southern California 

began to deliver water from the Colorado River by means of 

the Colorado River Aqueduct. In 1972, the Department of 

Water Resources began to deliver water from the Bay/Delta 

area by means of the West- and East-Branch State Water 

Project.
Methods 5

The combined safe yield for all basins in the SFSG 

study unit is approximately 314,000 acre-ft/yr. (California 

Department of Water Resources, 2003). Except for a 

small area of limited pumping in the San Gabriel Valley, 

ground-water extractions are controlled in all of SFSG. The 

court-ordered adjudication of the San Fernando Valley, the 

Raymond, and the San Gabriel Valley ground-water basins is 

administered by separate Watermaster appointments. 

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; (3) analyze samples using proven and 

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

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

relevant documentation. 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.

0 5 10 MILES

0 5 10 KILOMETERS

118 40’

34

20’

10’

34

00’

30’ 20’ 10’ 118 00’ 50’ 117 40’

Pasadena

Pacific Ocean Los Angeles River

Whittier

Narrows

Los Angeles Narrows

San Bernardino

County

Orange County

Los Angeles County San Jose

Fault

Chino Fault

San Gabriel River

Rio

Hondo

EXPLANATION

Well-With record in California Department

of Public Health or U.S. Geological Survey

National Water Information System (NWIS)

Database

Study areas

Fault, concealed

San Fernando

San Gabriel Mountains

Santa Monica Mountains

Santa Susana Mountains

Elysian Hills

Simi

Hills

Merced

Hills

Repetto

Hills

Puente

Hills

Water bodies

San Gabriel Stream or River

Ground-water basin boundary

 (From California Department of

 Water Resources)

Azusa

Burbank

Alhambra

Northridge

West

Covina

San Fernando

Ventura County

Raymond

Figure 2. The San Fernando-San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit showing the California 

Department of Water Resources defined ground-water basins within the study unit and major hydrologic features.
6 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Study Design

The wells selected for sampling in this study reflect 

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

spatially distributed assessment of the quality of ground-water 

resources used for public drinking water supply. Seventeen 

additional wells were selected to provide greater sampling 

density in several areas to aid in the evaluation of specific 

ground-water quality issues or to better understand changes in 

water chemistry along historic ground-water flow paths in the 

study unit.

The spatially distributed wells in each study area were 

selected using a randomized grid-based method (Scott, 1990). 

Wells listed in statewide databases maintained by the USGS 

and the CDPH were considered in this selection process. 

For the ULASG assessment, the San Gabriel study area 

was divided into 25 10 mi2

 grid cells, across the mapped 

unconsolidated deposits of the basin floor (fig. 3A). The 

objective was to select one public-supply well per grid cell. 

If a grid cell contained more than one well, each well was 

randomly assigned a rank. The highest ranking well that met 

basic sampling criteria (for example, sampling point located 

prior to water treatment, capability to pump for several hours, 

and available well-construction information) and for which 

permission to sample could be obtained was then sampled. 

If a grid cell did not contain an active or accessible well, 

an attempt was made to select from an adjacent cell. In 

this fashion, one well was selected in each cell to provide a 

spatially distributed, randomized monitoring network for each 

study area. Wells sampled as part of the spatially distributed, 

randomized grid-cell network are hereafter referred to as 

“grid wells.” Twenty-three of the 25 grid cells were sampled 

in ULASG; the other two grid cells did not contain accessible 

wells. Grid wells sampled in ULASG were numbered in the 

order of sample collection using the prefix “ULASG.”

For the ULASF assessment, the western portion of the 

San Fernando Valley had few (if any) production wells. To 

minimize the potential for unsampled cells, the sampling 

grid was refined by drawing a 1.86-mi (3-km) radius buffer 

around each well within the ULASF study area. The area 

encompassed by the circles then was divided to create 10 mi2

grid cells, 15 in all (fig. 3B). Twelve of the 15 grid cells were 

sampled; the other three grid cells did not contain suitable 

wells. Grid wells sampled in ULASF were numbered in the 

order of sample collection using the prefix “ULASF.”

Seventeen additional wells were sampled for the 

purpose of obtaining a better understanding of the source and 

movement of ground water along historic ground-water flow 

paths in each study area. Wells sampled as part of these studies 

were not included in the statistical characterization of water 

quality in SFSG because inclusion of these wells would have 

caused overrepresentation of certain cells. These additional, 

non-randomized wells were numbered in the order of sample 

collection using either the prefix “ULASFU” or “ULASGU” 

depending on the study area (“U” indicating “understanding”).

Table 1 (all tables shown in back of report) provides the 

GAMA alphanumeric identification number for each well, 

along with the date sampled, sampling schedule, well type, 

and well-construction information. Ground-water samples 

were collected from 47 public-supply wells, 3 industrial wells, 

and 2 irrigation wells between May and July 2005. A total of 

18 wells were sampled in the ULASF study area and 34 wells 

were sampled in the ULASG study area.

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. Logs for wells were 

obtained when available. Well information was recorded by 

hand in the field, verified, and then uploaded into the USGS 

National Water Information System (NWIS). In order to 

maintain confidentiality of well owners and well locations, 

well information and chemical data currently are inaccessible 

from the USGS NWIS public website.

The wells in SFSG study unit were sampled using a tiered 

analytical approach. All wells were sampled for a standard 

set of constituents, including VOCs, pesticides and pesticide 

degradates, stable isotopes of water, and tritium to provide an 

initial assessment of ground-water quality in the area. This 

standard set of constituents was termed the “fast” schedule 

(table 2). Wells on the “intermediate” schedule were sampled 

for all the constituents on the fast schedule plus perchlorate, 

NDMA, 1,2,3-TCP, 1,4-dioxane, nutrients, dissolved organic 

carbon, major and minor ions, trace elements, speciation of 

arsenic and chromium and iron, and the noble gases. Wells 

on the “slow” schedule were sampled for all the constituents 

on the intermediate schedule, plus gasoline oxygenates and 

degradates, polar pesticides and degradates, and radioactive 

and microbial constituents (table 2). 

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

sample the well for all the analytes on the schedule. Generally, 

one slow or two intermediate or three or four fast wells could 

be sampled in one day. For the SFSG study unit, 28 of the 

ground-water wells were sampled on the fast schedule, 7 wells 

were sampled on the intermediate schedule, and 17 wells on 

the 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 ground water 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.”
Methods 7

Tables 3A–K list the compounds analyzed in each 

constituent class. Ground-water samples were analyzed for 

85 VOCs (table 3A), 8 gasoline oxygenates and degradates 

(table 3B), 122 pesticides and pesticide degradates (table 3C, 

D), 4 constituents of special interest (table 3E), 5 nutrients and 

dissolved organic carbon (table 3F), 10 major and minor ions 

and total dissolved solids, and 25 trace elements (table 3G), 

arsenic, iron, and chromium redox species (table 3H), 12 

isotopic and radioactive constituents (table 3I), 6 dissolved 

noble gases and tritium/helium age dates (table 3J), and 

4 microbial constituents (table 3K). The methods used 

for sample analysis are described in the Appendix section 

“Sample Collection and Analysis.”

Data Reporting

The methods and conventions used for reporting the 

data are described in the Appendix section “Data Reporting.” 

Ten 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 

34 10’

34 00’

118 10’ 118 00’ 50’ 117 40’

Los Angeles River

Whittier

Narrows San Bernardino County

Orange County

Los Angeles County

San Jose

Fault

Chino Fault

San Gabriel River

Rio Hondo

EXPLANATION

Fault, concealed

Elysian Hills

Merced Hills

San Gabriel Mountains

0 5 10 MILES

0 5 10 KILOMETERS

San Gabriel study area

Ground-water basin boundary (from

California Department of Water Resources)

Randomized sampling grid cell

Grid well

Understanding well .

.

10

06

Water bodies

Stream or river

Puente

Hills

.

. .

.

.

.

.

. .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

. .

.

.

.

11

10

09

08

07

06

05

04

03 02

01

23

22

21

19 20

18

17

16

15

14

13

12

11

10

09

08

07

06

05

04

03

02

01

A

Figure 3. The (A) eastern and (B) western study areas of the San Fernando-San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit showing the distribution of study area grid cells and the location of sampled grid-cell and understanding 

wells.
8 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

preferred method are reported. Arsenic, iron, chromium, and 

1,2,3-trichloropropane concentrations and tritium activities 

were measured by more than one laboratory, and both sets of 

results are reported. 

Quality-Assurance

The quality-assurance methods used for this study follow 

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 SFSG study include source-solution 

blanks, field blanks, replicates, and matrix and surrogate 

spikes. QC samples were collected to evaluate bias and 

variability of the water chemistry data that may have resulted 

0 5 10 MILES

0 5 10 KILOMETERS

118 40’

34

20’

34

10’

30’ 20’ 118 10’

Los Angeles River

Los Angeles Narrows

Los Angeles County

Ventura County

EXPLANATION

San Fernando study area

San Gabriel Mountains

Santa Susana Mountains

Ground-water basin boundary

 (from California Department of

 Water Resources)

Randomized sampling grid cell

Simi

Hills

Elysian Hills

Repetto

Hills

Grid well

Understanding well .

.

Water bodies

Stream or river

Santa Monica Mountains

.

.

.

. .

06 .

04 05

03

03

02

01

.

.

.

.

.

.

.

.

.

.

.

. 12

12

11

10

09

08

07

06

05

04

03

02

01

B

Figure 3. Continued.
Water-Quality Results 9

from sample collection, processing, storage, transportation, 

and laboratory analysis. A more detailed description of 

these methods is presented in the Appendix section “Quality 

Assurance.”

Water-Quality Results 

Results from analyses of raw (untreated) ground-water 

samples from SFSG are presented in tables 4–17. Groundwater samples collected in SFSG were analyzed for 290 

constituents, and 162 of those constituents were not detected 

in any of the samples (tables 3A–K). The results tables present 

only the constituents that were detected, and list only samples 

that had at least one constituent detected. For constituent 

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

include the number of wells at which each analyte was 

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

the number of grid wells), and the total number of constituents 

detected at each well. Results from the flow-path wells are 

presented in the tables, but these results were excluded from 

the detection frequency calculations to avoid statistically overrepresenting the areas in the vicinity of the flow paths.

Table 4 includes water-quality indicators measured in the 

field, while tables 5–17 present the results of ground-water 

analyses organized by compound classes: 

•	 Organic constituents

•	 VOCs and gasoline oxygenates and degradates 

(table 5)

•	 Pesticides and pesticide degradates (table 6)

•	 Constituents of special interest (table 7)

•	 Inorganic constituents

•	 Nutrients and dissolved organic carbon (table 8)

•	 Major and minor ions and total dissolved solids 

(table 9)

•	 Trace elements (table 10)

•	 Arsenic and iron species (table 11)

•	 Chromium species (table 12)

•	 Inorganic tracer constituents

•	 Stable isotopes of water and tritium (table 13)

•	 Carbon isotopes (table 14)

•	 Noble gases and tritium (table 15)

•	 Radioactive constituents (table 16)

•	 Microbial indicators (table 17)

Quality-Control Sample Results

Results of quality-control analyses (blanks, replicates, 

matrix spikes, and surrogates) were used to evaluate the 

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

of the blanks resulted in the censoring of less than 0.7 percent 

of the data for the ground-water samples. Replicate analyses 

indicated that variability between measurements was 

acceptably low. Matrix-spike recoveries for a number of 

organic constituents were lower than the acceptable limits, 

which indicate that these constituents might not have been 

detected in some samples if they were present at very low 

concentrations. For the analyses that used surrogates, nearly 

all surrogate recoveries were within acceptable limits. A 

more detailed description of these results is included in the 

Appendix section “Quality-Control Sample Results.”

Comparison Thresholds

Concentrations of constituents detected in ground-water 

samples were compared with CDPH (formerly California 

Department of Health Services [CDHS]–replaced on July 1, 

2007) and USEPA drinking-water health-based thresholds 

and with thresholds established for aesthetic purposes 

(U.S. Environmental Protection Agency, 2006; California 

Department of Public Health, 2007a). The chemical 

and microbial data presented in this report are meant to 

characterize the quality of the untreated ground-water 

resources within SFSG and are not intended to represent 

the treated drinking water delivered to consumers by water 

purveyors. The chemical and microbial composition of 

treated drinking water may differ from untreated ground 

water because treated drinking water may be subjected to 

disinfection, filtration, mixing with other waters, and exposure 

to the atmosphere prior to its delivery to consumers. 

The following thresholds were used for comparisons:

•	 MCL– Maximum Contaminant Level. Legally 

enforceable standards that apply to public-water 

systems and are designed to protect public health by 

limiting the levels of contaminants in drinking water. 

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 above the MCL-US 

or MCL-CA thresholds in samples collected for the 

GAMA Priority Basin Assessment Project.
10 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

•	 AL – Action Level. Legally enforceable standards that 

apply to public water systems and that 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 are the 

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

this report.

•	 TT – Treatment Technique. Legally enforceable 

standards that apply to public-water systems and 

are designed to protect public health by limiting the 

levels of microbial constituents in drinking water. 

Detections of microbial constituents above the 

treatment-technique thresholds trigger requirements 

for mandatory additional disinfection during water 

treatment. The thresholds established by the USEPA 

and CDPH are the same, and are labeled “TT-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 

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

values. The SMCL-US is used for pH because no 

SMCL-CA has been defined.

•	 NL – Notification Level. Health-based notification 

levels established by CDPH for some of the 

constituents in drinking water that lack MCLs 

(NL-CA). If a constituent is detected above its NL-CA, 

California state law requires timely notification of 

local governing bodies and recommends consumer 

notification.

•	 HAL – Lifetime Health Advisory Level. The 

maximum concentration of a constituent at which its 

presence in drinking water is not expected to cause any 

adverse carcinogenic effects for a lifetime of exposure. 

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

are calculated assuming consumption of 2 L (2.1 qt) of 

water per day over a 70-yr lifetime by a 70-kg (154-lb) 

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 10 

(RSD5-US).

For constituents with MCLs, detections in groundwater samples were compared to the MCL-US or MCL-CA. 

Constituents with SMCLs were compared with the SMCL-US. 

For chloride, sulfate, specific conductance, and total dissolved 

solids, CDPH defines “recommended” and “upper” SMCLCAs; detections of these constituents in ground-water samples 

were compared with both levels. Detected concentrations of 

constituents that lack an MCL and 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 this hierarchy of selection of 

comparison thresholds means that for constituents that have 

multiple types of established thresholds, the threshold used 

for comparison purposes may not be the one with the lowest 

concentration. The comparison thresholds used in this report 

are listed in tables 3A–K for all constituents and in tables 4–17

for constituents detected in ground-water samples from SFSG. 

Not all constituents analyzed for this study have established 

thresholds available. 

Detections of constituents at concentrations greater 

than the selected comparison threshold are marked with an 

asterisk in tables 4–17. In this study, only six constituents 

(PCE, TCE, tetrachloromethane, NDMA, 1,2,3-TCP, and 

nitrate) were detected at concentrations above health-based 

thresholds. These detections occurred in five grid wells and 

two understanding wells. One additional constituent (total 

dissolved solids) was detected at concentrations above the 

threshold set for aesthetic qualities, and occurred in three of 

the grid wells and three understanding wells.

Ground-Water-Quality Data

Field Parameters

Field measurements of turbidity, dissolved oxygen, 

water temperature, pH, specific conductance, alkalinity (and 

associated parameters), and hydrogen sulfide are presented 

in table 4. Dissolved oxygen and alkalinity are used as 

indicators of processes that control water chemistry. Specific 

conductance is the unit electrical conductivity of the water 

and is proportional to amount of total dissolved solids (TDS) 

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

the water. Six grid and two understanding wells had specific 

conductance values above the recommended lower SMCL-CA 

threshold. Dissolved oxygen was detected in all 51 samples 

collected, typically at concentrations greater than 1 mg/L.
Water-Quality Results 11

Organic Constituents

Volatile organic compounds (VOCs) are present in paints, 

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

disinfected water and are characterized by their tendency to 

evaporate. VOCs generally persist longer in ground water 

than in surface water because ground water is isolated from 

the atmosphere, hindering volatilization. Of the 88 VOCs 

analyzed, 33 were detected in ground-water samples; nearly 

all detections were below health-based thresholds, and most 

were less than one-tenth of the threshold values (table 5).

Fifteen VOCs were detected in more than 10 percent 

of samples from grid wells, and include: six solvents; three 

disinfection by-products; three refrigerants; two organic 

synthesis products; and one gasoline oxygenate. Of these 

15 VOCs, 12 were detected at concentrations below a healthbased threshold, and three were detected above: PCE in 

3 wells, TCE in 3 wells, and carbon tetrachloride in 2 wells. 

In each of these wells, similarly high concentrations had 

been previously reported for these constituents in the CDPH 

database. One or more VOCs were detected in 33 of the 35 

grid wells sampled; concentrations were below health-based 

thresholds in 31 of these wells, but above in 4 wells. Water 

from the four wells with concentrations above health-based 

thresholds is not served directly to consumers.

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 122 

pesticide or pesticide degradates analyzed, 22 were detected; 

all detections were below health-based thresholds, and nearly 

all were less than one-hundredth of the threshold values 

(table 6). Six pesticide compounds were detected in more 

than 10 percent of samples from grid wells, and include: four 

herbicides and two pesticide degradates. One or more pesticide 

compounds were detected in 31 of the 35 grid wells sampled. 

Constituents of Special Interest

Perchlorate, NDMA, 1,4-dioxane, and 1,2,3-TCP are 

constituents of special interest in California because they 

may adversely affect water quality and recently have been 

found in water supplies (California Department of Public 

Health, 2007b). Samples for these analytes were collected at 7 

intermediate wells and 17 slow wells. Perchlorate was detected 

in 10 of 24 ground-water samples however, all concentrations 

were less than the NL-CA of 6 μg/L (table 7). NDMA was 

detected in two samples; one sample (ULASGU-01) had 

a concentration (0.061 μg/L) greater than the NL-CA of 

0.01 μg/L and had not been reported previously in the CDPH 

database. 1,4-dioxane was not detected (at or above the 2 μg/L 

reporting limit) in any of the 24 samples collected.

1,2,3-TCP was detected in two samples at or above the 

NL-CA of 0.005 μg/L (table 7). One detection (ULASG-14) 

was from one of the 24 intermediate or slow samples analyzed 

using the preferred analytical method (see table 3E), and had 

not been previously reported in the CDPH database. The other 

detection (ULASF-07) was from one of 52 samples analyzed 

using an analytical method with a higher reporting limit (see 

table 3A), and had been reported previously in the CDPH 

database. Water from these wells is not served directly to 

consumers.

Inorganic Constituents

Unlike the organic constituents and the constituents 

of special interest, most of the inorganic constituents 

are naturally present in ground water, although their 

concentrations may be influenced by human activities. 

Samples for inorganic constituents were collected at 7 

intermediate and 17 slow wells.

Nutrients (nitrogen and phosphorus) and dissolved 

organic carbon present in ground water can affect biological 

activity in aquifers and in surface-water bodies that receive 

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

of ammonia, nitrite, or nitrate depending on the oxidationreduction state of the ground water. High concentrations of 

nitrate can adversely affect human health, particularly that of 

infants. 

Except for one sample, all concentrations of nitrate, 

nitrite, and ammonia measured in samples from SFSG wells 

were below health-based thresholds (table 8). In one sample, 

nitrate was detected (10.3 mg/L as N) slightly above the 

MCL-US of 10 mg/L as N. This well had a similarly high 

concentration previously reported in the CDPH database. 

Concentrations of orthophosphate and dissolved organic 

carbon were low. 

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

content, and levels of certain trace elements in ground water 

(table 9) affect the aesthetic properties of water, such as 

taste, color, and odor, and the technical properties, such as 

scaling and staining. Although there are no adverse health 

effects associated with these properties, they may reduce 

consumer satisfaction with the water or may have economic 

impacts. CDPH has established non-enforceable thresholds 

(SMCL-CA) that are based on aesthetic or technical properties 

rather than health-based concerns for the major ions chloride 

and sulfate, for TDS, and for several trace elements.

The concentrations of chloride, fluoride, and sulfate 

measured in samples collected from 24 SFSG wells were all 

below the MCL-US and SMCL-CA (table 9). Six samples 

contained TDS above the recommended lower SMCL-CA of 

500 mg/L, but below the upper SMCL-CA of 1,000 mg/L.
12 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Eighteen of the 25 trace elements analyzed in this study 

have health-based thresholds. Detections of all trace elements 

in samples from all 24 SFSG wells were below health-based 

thresholds (table 10). Three trace elements (beryllium, 

silver, and thallium) were not detected in any samples. Iron 

was detected in nine of 24 samples, at low concentrations. 

Concentrations of manganese were detected in 19 of 24 

samples with the highest value (34.8 μg/L) within half the 

SMCL of 50 μg/L. Chromium was detected in 17 of 24 

samples, with the concentration of one sample (48.9 μg/L) 

near the MCL-CA of 50 μg/L. 

Arsenic, iron, and chromium occur as different species 

depending on the oxidation-reduction state of the ground 

water. The oxidized and reduced species have different 

solubilities in ground water and may have different effects 

on human health. The relative proportions of the oxidized 

and reduced species of each element can be used to aid 

in interpretation of the oxidation-reduction state of the 

aquifer. The concentrations of total arsenic and iron, and 

the concentrations of the reduced species, arsenic-III and 

iron-II are shown in table 11. The concentrations of total 

chromium, and the concentrations of the oxidized species, 

chromium-VI is shown in table 12. Concentrations of the other 

species can be calculated by difference. The concentrations 

of arsenic, iron, and chromium reported in tables 11 and 

12 may be different than those reported in table 10 because 

different analytical methods were used (see Appendix section 

“Constituents on Multiple Analytical Schedules”). The 

concentrations reported in table 10 are considered to be more 

accurate.

Inorganic Tracer Constituents

Stable isotope ratios, tritium and carbon-14 activities, 

and noble gas concentrations can be used as tracers of natural 

processes affecting ground-water composition. Hydrogen and 

oxygen stable isotope ratios of water (table 13) can aid in the 

interpretation of ground-water recharge sources. The stable 

isotope ratios of water depend on the altitude, latitude, and 

temperature of precipitation and on the extent of evaporation 

of surface water or soil water. Noble gas concentrations 

(table 15) can be used to aid in the interpretation of groundwater recharge sources because the concentrations of the 

different noble gases depend on water temperature at the time 

of recharge.

Tritium (tables 13 and 15) and carbon-14 activities 

(table 14), and helium isotope ratios (table 15) can provide 

information about the age of the ground-water. Tritium is 

a radioactive isotope of hydrogen that is incorporated into 

the water molecule. Low levels of tritium are produced 

continuously by cosmic ray bombardment of water in the 

atmosphere, and a large amount of tritium was produced by 

atmospheric testing of nuclear weapons between 1952 and 

1963. Thus, concentrations of tritium above background 

generally indicate the presence of water recharged since the 

early 1950s. 

Helium isotope ratios (table 15) can be used in 

conjunction with tritium concentrations to estimate ages for 

young ground water. Carbon-14 (table 14) is a radioactive 

isotope of carbon that is incorporated into dissolved carbonate 

species in water. Low levels of carbon-14 are produced 

continuously by cosmic ray bombardment of nitrogen in 

the atmosphere. 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 

ground water that is several thousand years old, or has 

interacted extensively with the aquifer matrix. 

Of the inorganic tracer constituents analyzed for this 

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

measured tritium activities in samples from SFSG wells were 

less than one hundredth of the MCL-CA (tables 13 and 15).

Radioactive Constituents

Radioactivity is the release of energy or energetic 

particles during changes in the structure of the nucleus of an 

atom. Most of the radioactivity in ground water comes from 

decay of naturally occurring isotopes of uranium and thorium 

that are present in minerals in the sediments or fractured rocks 

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

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

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

during the uranium or thorium decay series. 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. For example, radium-226 emits an alpha 

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

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

The alpha and beta particles emitted during radioactive 

decay are hazardous to human health because these energetic 

particles may damage cells. Radiation damage to cell DNA 

may increase the risk of getting cancer.

Activity often is used instead of concentration for 

reporting the presence of radioactive constituents. Activity 

of radioactive constituents in ground water is measured in 

units of picocuries per liter (pCi/L), and one picocurie is 

approximately equal to two atoms decaying per minute. The 

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

beta particles emitted. 

Samples for radioactive constituents were collected at 17 

slow wells. None of these samples had an activity of radium 

or of gross alpha and beta emitters above established healthbased thresholds (table 16). In 14 of 17 samples, the activity of 

radon-222 was above the proposed MCL-US of 300 pCi/L, but 

less than the proposed alternative MCL-US of 4,000 pCi/L. 
Summary 13

Microbial Indicators

Water is disinfected during drinking-water treatment to 

prevent diseases that may be spread by water-borne microbial 

constituents derived from human or animal wastes. The 

specific viruses and bacteria responsible for diseases generally 

are not measured because routine analytical methods are not 

available. Measurements are made of more easily analyzed 

microbial constituents that serve as indicators of the presence 

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

respond to detections of microbial indicators by applying 

additional disinfection techniques to the water.

Samples for microbial indicators were collected at 

17 slow wells. No samples contained the viral indicators 

F-specific and somatic coliphage and none contained the 

bacterial indicator Escherichia coli (E. coli), however there 

was one estimated detection of the bacterial indicator total 

coliforms (table 17). The threshold for total coliforms is based 

on recurring detections, thus, the detections reported here do 

not necessarily constitute an exceedance of the MCL-US. 

Future Work

Subsequent reports will present analyses of the 

data presented in this report using a variety of statistical, 

qualitative, and quantitative approaches to assess the natural 

and human factors affecting ground-water quality. Waterquality data contained in the CDPH (formerly CADHS) 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 presented in 

this report; results of these future efforts will appear in one or 

more subsequent reports.

Summary 

Ground-water quality in the approximately 460 squaremile San Fernando-San Gabriel study unit (SFSG) was 

investigated between May and July 2005 as part of the 

Priority Basin Assessment 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 (http://www.waterboards.ca.gov/gama/). 

The Priority Basin Assessment Project was designed by the 

SWRCB and the USGS in response to the Ground-Water 

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

Water Resources Control Board, 2003). This comprehensive 

assessment of statewide ground-water quality is designed to 

identify and characterize risks to ground-water resources, and 

to increase the availability of information about ground-water 

quality to the public. SFSG was the fifth study unit sampled as 

part of the project. 

SFSG is in the central portion of the Transverse Range 

and Selected Peninsular Ranges hydrogeologic province and 

includes within it three major ground-water basins, as defined 

by the California Department of Water Resources (California 

Department of Water Resources, 2003). This report describes 

the hydrogeologic setting of the SFSG region, details the 

sampling, analytical, and quality-assurance methods used 

in the study, and presents the results of the chemical and 

microbial analyses of ground-water samples collected between 

May to July 2005. The SFSG study included assessment of 

ground-water quality from 52 wells in Los Angeles County. 

Thirty-five of the wells were selected using a spatially 

distributed, randomized grid approach to achieve statistically 

unbiased representation of ground-water used for public 

drinking-water supplies. Seventeen additional (non-grid) wells 

were selected to provide additional sampling density to aid in 

understanding processes affecting ground-water quality.

Ground-water samples were analyzed for VOCs, 

pesticides and pesticide degradates, constituents of special 

interest [perchlorate, N-nitrosodimethylamine (NDMA), 

1,2,3-trichloropropane (1,2,3-TCP), and 1,4-dioxane], 

nutrients, major and minor ions, trace elements, radioactive 

constituents, and microbial indicators. Naturally occurring 

isotopes (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 source and age of the sampled ground water. 

Quality-control samples (blanks, replicates, or samples 

for matrix spikes) were collected at about 20 percent of 

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

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

Assessment of the quality-control information resulted in 

censoring of less than 0.7 percent of the ground-water quality 

data.

This study did not attempt to evaluate the quality of 

water delivered to consumers; after withdrawal from the 

ground, water typically is treated, disinfected, and blended 

with other waters to maintain acceptable water quality. 

Regulatory thresholds apply to treated water that is served to 

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

some context for the results, concentrations of constituents 

in the raw ground water were compared with health-based 

thresholds established by the U.S. Environmental Protection 

Agency (USEPA) and California Department of Public Health 

(CDPH). 

Detections of constituents in the SFSG study unit at 

concentrations greater than the selected comparison threshold 

are marked with asterisks in tables 4–17. Four constituents 

(tetrachloroethene [PCE], trichloroethene [TCE], carbon 

tetrachloride, and nitrate) were detected at concentrations 

higher than the established maximum contaminant levels 

(MCLs). These detections occurred in 5 of the 35 grid wells 

and in 1 of the 17 understanding wells. 
14 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Two compounds had detections above CDPH notification 

levels (NL-CA): 1,2,3-trichloropropane (1,2,3-TCP) in 2 of 35 

grid wells, and N-nitrosodimethylamine (NDMA) in 1 of 17 

understanding wells.

Measurements of total dissolved solids (TDS) in 6 of 

24 samples collected were between the lower and upper 

secondary maximum contaminant level (SMCL-CAs), nonenforceable thresholds set for aesthetic concerns. Specific 

conductance, measured in the field, also was above the 

threshold set for aesthetic concerns in six grid wells and 

two understanding wells. Future work will evaluate the 

data presented in this report using a variety of statistical, 

qualitative, and quantitative approaches to assess the natural 

and human factors affecting ground-water quality.

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

May 20, 2005, at http://pubs.water.usgs.gov/twri9A3/

Wilde, F.D. and Radtke, D.B., 2003, General information and 

guidelines: U.S. Geological Survey Techniques of WaterResources Investigations, book 9, chap. A6.0, accessed May 

20, 2005, 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 May 20, 2005, 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 May 20, 2005, at http://pubs.water.usgs.

gov/twri9A5/

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

California GAMA program—Ground-water quality in the 

San Diego drainages 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.

Zaugg, S.D., Smith, S.G., Schroeder, M.P., Barber, L.B., and 

Burkhardt, M.R., 2002, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—

Determination of wastewater compounds by polystyrene 

divinylbenzene solid-phase extraction and capillary-column 

gas chromatography/mass spectrometry: U.S. Geological 

Survey Water-Resources Investigations Report 01-4186, 

37 p.
Tables 19

Tables
20 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

GAMA well 

identification no.

Sampling information Well depth 

(ft below 

LSD)

Construction information

Date Sampling 

schedule Well type

Top of highest 

perforation 

(ft below LSD)

Bottom 

perforation 

(ft below LSD)

Elevation of LSD 

(ft above 

NAVD88)

 San Fernando study area

ULASF_01 05-24-05 Fast Public-supply 600 185 486 1,693

ULASF_02 05-24-05 Fast Public-supply 488 230 435 1,143

ULASF_03 05-24-05 Fast Public-supply 377 250 355 1,293

ULASF_04 05-25-05 Fast Public-supply 800 400 780 823

ULASF_05 05-26-05 Fast Public-supply 594 195 578 724

ULASF_06 05-26-05 Fast Public-supply 490 242 418 570

ULASF_07 05-26-05 Fast Public-supply 359 109 349 653

ULASF_08 06-06-05 Slow Public-supply 400 200 380 465

ULASF_09 06-07-05 Slow Public-supply 184 50 170 1,016

ULASF_10 06-08-05 Slow Public-supply 930 268 894 662

ULASF_11 06-09-05 Fast Irrigation 480 80 480 1,783

ULASF_12 06-09-05 Intermediate Public-supply 199 84 174 448

ULASFU_01 05-25-05 Fast Public-supply 267 138 248 1,253

ULASFU_02 05-25-05 Fast Public-supply 196 110 196 1,383

ULASFU_03 06-09-05 Slow Public-supply 268 100 253 393

ULASFU_04 06-16-05 Slow Public-supply 800 400 780 823

ULASFU_05 07-19-05 Fast Industrial 610 310 600 853

ULASFU_06 07-20-05 Slow Public-supply 820 370 770 788

 San Gabriel study area

ULASG_01 06-07-05 Fast Public-supply 810 670 790 462

ULASG_02 06-08-05 Fast Public-supply 480 358 480 1,657

ULASG_03 06-08-05 Fast Public-supply 372 62 370 1,153

ULASG_04 06-14-05 Fast Public-supply 198 128 193 327

ULASG_05 06-14-05 Intermediate Public-supply 1,290 1,013 1,275 302

ULASG_06 06-14-05 Slow Public-supply 712 166 712 202

ULASG_07 06-14-05 Fast Public-supply 587 260 587 1,203

ULASG_08 06-15-05 Slow Public-supply 399 110 299 718

ULASG_09 06-15-05 Fast Public-supply 600 300 580 451

ULASG_10 06-15-05 Fast Public-supply 785 291 762 522

ULASG_11 06-16-05 Intermediate Public-supply 490 160 365 1,153

ULASG_12 06-16-05 Fast Public-supply 600 229 600 322

ULASG_13 06-16-05 Fast Public-supply 970 320 970 312

ULASG_14 06-20-05 Slow Industrial 1,000 500 1,000 553

ULASG_15 06-23-05 Slow Public-supply 400 115 340 683

ULASG_16 07-11-05 Slow Public-supply 414 157 233 800

ULASG_17 07-11-05 Fast Public-supply 186 na na 720

ULASG_18 07-12-05 Fast Public-supply 700 286 585 963

ULASG_19 07-12-05 Fast Industrial 804 260 804 305

ULASG_20 07-12-05 Fast Public-supply 500 198 484 404

ULASG_21 07-12-05 Fast Public-supply 1,152 792 1,132 503

ULASG_22 07-13-05 Fast Public-supply 785 380 765 753

ULASG_23 07-13-05 Fast Public-supply 300 na na 1,379

ULASGU_01 06-08-05 Intermediate Public-supply 699 143 437 1,228

ULASGU_02 06-13-05 Slow Irrigation 312 40 312 1,199

ULASGU_03 06-15-05 Fast Public-supply 507 280 500 609

ULASGU_04 06-21-05 Slow Public-supply 664 178 400 252

ULASGU_05 06-22-05 Slow Public-supply 1,008 360 1,008 382

ULASGU_06 07-11-05 Intermediate Public-supply 1,089 270 1,058 870

ULASGU_07 07-12-05 Slow Public-supply 800 450 780 549

ULASGU_08 07-13-05 Intermediate Public-supply 942 292 918 352

ULASGU_09 07-13-05 Slow Public-supply 600 298 581 372

ULASGU_10 07-14-05 Intermediate Public-supply 264 25 260 187

ULASGU_11 07-14-05 Slow Public-supply 580 250 580 425

Table 1. Identification, sampling, and construction information for wells sampled for the San Fernando–San Gabriel Groundwater 

Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005. 

[Well sampling schedules are described in table 2. GAMA well identification no.: ULASF, San Fernando study area grid well; ULASFU, San Fernando 

study area understanding well; ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area understanding well. 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. 

Abbreviations: ft, feet; LSD, land surface datum; NAVD88, North American Vertical Datum 1988; na, not available]
Tables 21

Table 2. Water-quality indicators and classes of chemical and microbial constituents collected for the slow, 

intermediate, and fast well sampling schedules in the San Fernando–San Gabriel Groundwater Ambient Monitoring 

and Assessment (GAMA) study unit, California, May to July 2005.

[Constituents of special interest were analyzed at Montgomery Watson Harza Laboratory, Monrovia, California. Microbial 

constituents were analyzed at U.S. Geological Survey Ohio Microbiology Laboratory, Columbus, Ohio.]

Analyte classes Analyte list table Schedule

Slow Intermediate Fast

Water-quality indicators

Dissolved oxygen, temperature, specific conductance X X X

pH, alkalinity X

Turbidity X

Organic constituents

Volatile organic compounds 3A X X X

Gasoline additives and oxygenates 3B X

Pesticides 3C X X X

Pesticide degradates 3D X

Constituents of special interest

Perchlorate 3E X X

1,4-dioxane 3E X X

N-nitrosodimethylamine (NDMA) 3E X X

1,2,3-trichloropropane (1,2,3-TCP) 3E X X

Inorganic constituents

Nutrients and dissolved organic carbon 3F X X

Major and minor ions and trace elements 3G X X

Chromium abundance and species 3H X X X

Arsenic and iron abundances and species 3H X X

Stable isotopes

Stable isotopes of hydrogen and oxygen in water1 3I X X X

Stable isotopes of carbon and carbon-14 activity2,3 3I X

Radioactivity and noble gases

Tritium4 3I X X X

Tritium and noble gases5 3J X X

Radium isotopes6 3I X

Radon-222 3I X

Gross alpha and beta radioactivity6 3I X

Microbial constituents

Microbial indicators 3K X

Viral indicators 3K X

1

 Analyzed at U.S. Geological Survey Stable Isotope Laboratory, Reston, Virginia.

2

 Analyzed at the University of Waterloo, Ontario, Canada.

3

 Analyzed at University of Arizona, Accelerator Mass Spectrometry Laboratory, Tucson, Arizona.

4

 Analyzed at U.S. Geological Survey Stable Isotope and Tritium Laboratory, Menlo Park, California.

5

 Analyzed at Lawrence Livermore National Laboratory, Livermore, California.

6

 Analyzed at Eberline Analytical Services, Richmond, California.
22 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—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 National Water Quality Laboratory schedule 2020.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: Mimum 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. 

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 10E-5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; THM, trihalomethane; USGS, U.S. Geological Survey; D, detected; na, not available; μg/L, microgram per liter; —, not detected]

Constituent

(synonym or abbreviation)

Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

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

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

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

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

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

Bromodichloromethane Disinfection by-product 

(THM)

32101 75-27-4 0.028 MCL-US 1

80 D

Bromoform (tribromomethane) Disinfection by-product 

(THM)

32104 75-25-2 0.1 MCL-US 180 D

2-Butanone (MEK, methyl ethyl ketone) Solvent 81595 78-93-3 2 HAL-US 4,000 —

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

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

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

Carbon disulfide Organic synthesis 77041 75-15-0 0.038 NL-CA 160 D

Carbon tetrachloride 

(tetrachloromethane)

Solvent 32102 56-23-5 0.06 MCL-CA 0.5 D

Chlorobenzene Solvent 34301 108-90-7 0.028 MCL-CA 70 D

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

Chloroform (trichloromethane) Disinfection by-product 

(THM)

32106 67-66-3 0.024 MCL-US 1

80 D

Chloromethane Refrigerant/organic 

synthesis

34418 74-87-3 0.17 HAL-US 30 —

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

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

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

Dibromochloromethane Disinfection by-product 

(THM)

32105 124-48-1 0.10 MCL-US 802 D

1,2-Dibromo-3-chloropropane (DBCP) Fumigant 82625 96-12-8 0.51 MCL-US 0.2 —

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

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

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

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

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

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

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

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

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

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

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

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

Dichloromethane (methylene chloride) Solvent 34423 75-09-2 0.06 MCL-US 5 D

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

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

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

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

cis-1,3-Dichloropropene Fumigant 34704 10061-01-5 0.05 RSD5-US 2

4 —

trans-1,3-Dichloropropene Fumigant 34699 10061-02-6 0.09 RSD5-US 2

4 —

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

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

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

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

Geological Survey National Water Quality Laboratory schedule 2020.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: 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. 

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 10E–5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; THM, trihalomethane; USGS, U.S. Geological Survey; D, detected; na, not available; μg/L, microgram 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 National Water Quality Laboratory schedule 2020.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: Mimum 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. 

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 10E-5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory 

reporting level; THM, trihalomethane; USGS, U.S. Geological Survey; D, detected; na, not available; μg/L, microgram per liter; —, not detected]

Constituent

(synonym or abbreviation)

Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

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

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

1-Ethyl-2-methylbenzene (o-ethyl 

toluene)

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

Hexachlorobutadiene Organic synthesis 39702 87-68-3 0.14 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 0.4 na na —

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

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

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

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

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

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

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

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

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

Methyl tert-pentyl ether (tert-amyl 

methyl ether, TAME)

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

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

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

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

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

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

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

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

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

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

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

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

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

1,1,1-Trichloroethane (1,1,1-TCA) Solvent 34506 71-55-6 0.032 MCL-CA 200 D

1,1,2-Trichloroethane (1,1,2-TCA) Solvent 34511 79-00-5 0.04 MCL-CA 5 D

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

Trichlorofluoromethane (CFC-11) Refrigerant 34488 75-69-4 0.08 MCL-CA 150 D

1,2,3-Trichloropropane (1,2,3-TCP) Solvent/organic synthesis 77443 96-18-4 0.18 NL-CA 0.005 D

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

(CFC-113)

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

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

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

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

Vinyl bromide (bromoethene) Fire retardant 50002 593-60-2 0.10 na na —

Vinyl chloride (chloroethene) Organic synthesis 39175 75-01-4 0.08 MCL-CA 0.5 D

m- and p-xylene Gasoline hydrocarbon 85795 108-38-3 / 106-42-3 0.06 MCL-CA 3

1,750 D

o-xylene Gasoline hydrocarbon 77135 95-47-6 0.038 MCL-CA 3

1,750 —

1

 The MCL-US threshold for trihalomethanes is for the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.

2

 The RSD5 threshold for 1,3-dichloropropene is the sum of its isomers (cis and trans).

3

 The MCL-US threshold for xylenes is for the sum of o-xylene and m- and p-xylene.
24 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

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

U.S. Geological Survey National Water Quality Laboratory schedule 4024.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type and value: 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; MCL-US, U.S. Environmental Protection Agency maximum contaminant level; NL-CA, California Department of Public Health notification 

level. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; USGS, U.S. Geological Survey; D, detected; na, not available; μg/L, 

microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

Acetone Degradate 81552 67-64-1 1.2 na na —

tert-Amyl alcohol Oxygenate 77073 75-85-4 1.0 na na —

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

Diisopropyl ether (DIPE) Oxygenate 81577 108-20-3 0.06 na na D

Ethyl tert-butyl ether (ETBE) Oxygenate 50004 637-92-3 0.06 na na —

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

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

Methyl tert-pentyl ether (TAME) Oxygenate 50005 994-05-8 0.05 na na —
Tables 25

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

U.S. Geological Survey National Water Quality Laboratory schedule 2003.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: 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; 

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 10E–5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; USGS, U.S. Geological Survey; D, detected; na, not 

available; μg/L, microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

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

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

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

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

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

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

Carbaryl Insecticide 82680 63-25-2 0.041 RSD5-US 400 —

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

4-Chloro-2-methylphenol Herbicide degradate 61633 1570-64-5 0.0050 na na —

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

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

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

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

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

Deethylatrazine (2-Chloro-4-isopropylamino6-amino-s-triazine)Herbicide degradate 04040 6190-65-4 0.014 na na D

Desulfinylfipronil Insecticide degradate 62170 na 0.012 na na D

Desulfinylfipronil amide Insecticide degradate 62169 na 0.029 na na —

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

Diazinon, oxon Insecticide degradate 61638 962-58-3 0.006 na na —

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

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

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

Dieldrin Insecticide 39381 60-57-1 0.009 RSD5-US 0.02 —

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

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

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

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

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

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

Fenamiphos sulfone Insecticide degradate 61645 31972-44-8 0.053 na na —

Fenamiphos sulfoxide Insecticide degradate 61646 31972-43-7 0.040 na na —

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

Fipronil sulfide Insecticide degradate 62167 120067-83-6 0.013 na na D

Fipronil sulfone Insecticide degradate 62168 120068-36-2 0.024 na na D

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

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

Iprodione Fungicide 61593 36734-19-7 0.026 na na —

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

Malaoxon Insecticide degradate 61652 1634-78-2 0.039 na na —

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

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

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

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

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

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

1-Naphthol Insecticide degradate 49295 90-15-3 0.0882 na na —

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

U.S. Geological Survey National Water Quality Laboratory schedule 2003.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: 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; 

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 10E–5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; USGS, U.S. Geological Survey; D, detected; na, not 

available; μg/L, microgram per liter; —, not detected]
26 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—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 National Water Quality Laboratory schedule 2003.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: 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; 

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 10E–5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; USGS, U.S. Geological Survey; D, detected; na, not 

available; μg/L, microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

Paraoxon-methyl Insecticide degradate 61664 950-35-6 0.019 na na —

Parathion-methyl Insecticide 82667 298-00-0 0.015 HAL-US 1 —

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

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

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

Phorate oxon Insecticide degradate 61666 2600-69-3 0.027 na na —

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

Phosmet oxon Insecticide degradate 61668 3735-33-9 0.0511 na na —

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

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

Pronamide (propyzamide) Herbicide 82676 23950-58-5 0.004 RSD5-US 20 —

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

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

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

Terbufos oxon sulfone Insecticide degradate 61674 56070-15-6 0.045 na na —

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

Trifluralin Herbicide 82661 1582-09-8 0.009 HAL-US 10 —
Tables 27

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

U.S. Geological Survey National Water Quality Laboratory schedule 2060.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: 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; 

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 10E–5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; USGS, U.S. Geological Survey; D, detected; na, not 

available; μg/L, microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

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

Aldicarb1 Insecticide 49312 116-06-3 0.04 MCL-US 3 —

Aldicarb sulfone Insecticide/degradate 49313 1646-88-4 0.018 MCL-US 3 —

Aldicarb sulfoxide Degradate 49314 1646-87-3 0.022 MCL-US 4 —

Atrazine Herbicide 39632 1912-24-9 0.008 MCL-CA 1 D

Bendiocarb Insecticide 50299 22781-23-3 0.020 na na —

Benomyl Fungicide 50300 17804-35-2 0.022 na na —

Bensulfuron-methyl Herbicide 61693 83055-99-6 0.018 na na —

Bentazon Herbicide 38711 25057-89-0 0.012 MCL-CA 18 —

Bromacil Herbicide 04029 314-40-9 0.018 HAL-US 70 D

Bromoxynil Herbicide 49311 1689-84-5 0.028 na na —

Caffeine Beverages 50305 58-08-2 0.018 na na D

Carbaryl Herbicide 49310 63-25-2 0.018 RSD5-US 400 —

Carbofuran Herbicide 49309 1563-66-2 0.016 MCL-CA 18 —

Chloramben, methyl ester Herbicide 61188 7286-84-2 0.024 na na —

Chlorimuron-ethyl Herbicide 50306 90982-32-4 0.032 na na —

3-(4-chlorophenyl)-1-methyl urea Degradate 61692 5352-88-5 0.036 na na D

Clopyralid Herbicide 49305 1702-17-6 0.024 na na —

Cycloate Herbicide 04031 1134-23-2 0.014 na na —

2,4-D plus 2,4-D methyl ester (summed on a 

molar basis)2

Herbicide 66496 na 0.016 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 0.028 na na —

Deethylatrazine (2-chloro-4-isopropylamino6-amino-s-triazine)Degradate 04040 6190-65-4 0.028 na na D

Deisopropyl atrazine (2-chloro-6-ethylamino4-amino-s-triazine)Solvent 04038 1007-28-9 0.08 na na D

Dicamba Herbicide 38442 1918-00-9 0.036 HAL-US 4,000 —

Dichlorprop Herbicide 49302 120-36-5 0.028 na na —

Dinoseb Herbicide 49301 88-85-7 0.038 MCL-CA 7 —

Diphenamid Herbicide 04033 957-51-7 0.010 HAL-US 200 D

Diuron Herbicide 49300 330-54-1 0.015 HAL-US 10 D

Fenuron Herbicide 49297 101-42-8 0.019 na na —

Flumetsulam Herbicide 61694 98967-40-9 0.040 na na —

Fluometuron Herbicide 38811 2164-17-2 0.016 HAL-US 90 —

Hydroxyatrazine (2-hydroxy-4-isopropylamino6-ethylamino-s-triazine)Degradate 50355 2163-68-0 0.032 na na D

3-Hydroxycarbofuran Degradate 49308 16655-82-6 0.008 na na —

Imazaquin Herbicide 50356 81335-37-7 0.036 na na —

Imazethapyr Herbicide 50407 81335-77-5 0.038 na na D

Imidacloprid Insecticide 61695 138261-41-3 0.020 na na —

Linuron Herbicide 38478 330-55-2 0.014 na na —

MCPA (2-methyl-4-chlorophenoxyacetic acid) Herbicide 38482 94-74-6 0.030 HAL-US 30 —

MCPB (4-[2-methyl-4-chlorophenoxy] butyric 

acid)

Herbicide 38487 94-81-5 0.010 na na —

Metalaxyl Fungicide 50359 57837-19-1 0.012 na na D

Methiocarb Insecticide 38501 2032-65-7 0.010 na na —

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

U.S. Geological Survey National Water Quality Laboratory schedule 2060.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: 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; 

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 10E-5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; USGS, U.S. Geological Survey; D, detected; na, not 

available; μg/L, microgram per liter; —, not detected]
28 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

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

U.S. Geological Survey National Water Quality Laboratory schedule 2060.—Continued

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: 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; 

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 10E–5. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; USGS, U.S. Geological Survey; D, detected; na, not 

available; μg/L, microgram per liter; —, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

Methomyl Insecticide 49296 16752-77-5 0.020 HAL-US 200 —

Metsulfuron methyl1 Herbicide 61697 74223-64-6 0.025 na na —

Neburon Herbicide 49294 555-37-3 0.012 na na —

Nicosulfuron Herbicide 50364 111991-09-4 0.04 na na —

Norflurazon Herbicide 49293 27314-13-2 0.020 na na —

Oryzalin Herbicide 49292 19044-88-3 0.012 na na —

Oxamyl Insecticide 38866 23135-22-0 0.030 MCL-CA 50 —

Picloram Herbicide 49291 1918-02-01 0.032 MCL-US 500 —

Propham Herbicide 49236 122-42-9 0.030 HAL-US 100 —

Propiconazole Fungicide 50471 60207-90-1 0.010 na na —

Propoxur Insecticide 38538 114-26-1 0.008 HAL-US 3 —

Siduron Herbicide 38548 1982-49-6 0.020 na na —

Sulfometuron-methyl Herbicide 50337 74222-97-2 0.038 na na D

Tebuthiuron Herbicide 82670 34014-18-1 0.026 HAL-US 500 D

Terbacil Herbicide 04032 5902-51-2 0.016 HAL-US 90 —

Triclopyr Herbicide 49235 55335-06-3 0.026 na na —

1

Although listed as LRLs, these constituents are reported using method reporting levels (MRLs).

2

The MCL-US threshold shown is for 2,4-D (2,4-dichlorophenoxyacetic acid); no threshold currently exists for 2,4-D methyl ester.
Tables 29

Table 3E. Constituents of special interest, primary uses or sources, comparative thresholds, and reporting information for the 

Montgomery Watson Harza Laboratory.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. The laboratory entity code for the Montgomery Watson 

Harza Laboratory in the U.S. Geological Survey National Water Information System (NWIS) is CA-MWHL. Threshold type: NL-CA, California notificaiton 

level. Abbreviations: CAS, Chemical Abstract Service; MRL, minimum reporting level; USGS, U.S. Geological Survey; D, detected; μg/L, microgram per liter; 

—, not detected]

Constituent Primary use 

or source

USGS 

parameter 

code

CAS 

number

 MRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

Perchlorate Rocket fuel, fireworks, 

flares

61209 14797-73-0 0.5 NL-CA 6 D

1,2,3-Trichloropropane (TCP) Industrial solvent, 

organic synthesis

77443 96-18-4 0.005 NL-CA 0.005 D

1,4-Dioxane Industrial solvent, 

solvent stabilizer

81582 123-91-1 2 NL-CA 3 —

N-Nitrosodimethylamine 

(NDMA)

Disinfection-by-product, 

rocket fuel, plasticizer

34438 62-75-9 0.002 NL-CA 0.010 D
30 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 3F. Nutrients and dissolved organic carbon, comparative thresholds, and reporting information for the U.S. Geological Survey 

National Water Quality Laboratory schedule 2755 and laboratory code 2612.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type and value: 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; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory Level; MCL-US, U.S. Environmental Protection Agency 

maximum contaminant level. Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; USGS, U.S. Geological Survey; D, detected; 

μg/L, microgram per liter; —, not detected]

Constituent

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

Ammonia (as nitrogen) 00608 7664-41-7 0.010 HAL-US 30 —

Nitrite (as nitrogen) 00613 14797-65-0 0.008 MCL-US 1 D

Nitrate plus nitrite (as nitrogen) 00631 na 0.060 MCL-US 10 D

Total nitrogen (ammonia, nitrite, nitrate, organic 

nitrogen)

62854 17778-88-0 0.06 na na D

Phosphorus, phosphate, orthophosphate (as 

phosphorus)

00671 14265-44-2 0.006 na na D

Dissolved organic carbon (DOC) 00681 na 0.33 na na D
Tables 31

Table 3G. Major and minor ions and trace elements, comparative thresholds, and reporting information for the U.S. Geological Survey 

National Water Quality Laboratory schedule 1948.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Threshold type: 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; 

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. 

Abbreviations: CAS, Chemical Abstract Service; LRL, laboratory reporting level; USGS, U.S. Geological Survey; D, detected; mg/L, milligram per liter; 

μg/L, microgram per liter; —, not detected]

Constituent

USGS 

parameter 

code

CAS 

number

 LRL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

Major and minor ions (mg/L)

Bromide 71870 24959-67-9 0.02 na na D

Calcium 00915 7440-70-2 0.02 na na D

Chloride 00940 16887-00-6 0.2 SMCL-CA 1 250 (500) D

Fluoride 00950 16984-48-8 0.10 MCL-CA 2 D

Iodide 78165 7553-56-2 0.002 na na D

Magnesium 00925 7439-95-4 0.008 na na D

Potassium 00935 7440-09-7 0.16 na na D

Silica 00955 7631-86-9 0.04 na na D

Sodium 00930 7440-23-5 0.20 na na D

Sulfate 00945 14808-79-8 0.18 SMCL-CA 1

 250 (500) D

Residue on evaporation (total dissolved solids, TDS) 70300 na 10 SMCL-US 1 500 (1,000) D

Trace elements (μg/L)

Aluminum 01106 7429-90-5 1.6 MCL-CA 1,000 D

Antimony 01095 7440-36-0 0.2 MCL-US 6 D

Arsenic 01000 7440-38-2 0.12 MCL-US 10 D

Barium 01005 7440-39-3 0.2 MCL-CA 1,000 D

Beryllium 01010 7440-41-7 0.06 MCL-US 4 —

Boron 01020 7440-42-8 8 NL-CA 1,000 D

Cadmium 01025 7440-43-9 0.04 MCL-US 5 D

Chromium 01030 7440-47-3 0.04 MCL-CA 50 D

Cobalt 01035 7440-48-4 0.04 na na D

Copper 01040 7440-50-8 0.4 AL-US 1,300 D

Iron 01046 7439-89-6 6 SMCL-CA 300 D

Lead 01049 7439-92-1 0.08 AL-US 15 D

Lithium 01130 7439-93-2 0.6 na na D

Manganese 01056 7439-96-5 0.2 SMCL-CA 50 D

Mercury 71890 7439-97-6 0.010 MCL-US 2 D

Molybdenum 01060 7439-98-7 0.4 HAL-US 40 D

Nickel 01065 7440-02-0 0.06 MCL-CA 100 D

Selenium 01145 7782-49-2 0.08 MCL-US 50 D

Silver 01075 7440-22-4 0.20 SMCL-CA 100 —

Strontium 01080 7440-24-6 0.4 HAL-US 4,000 D

Thallium 01057 7440-28-0 0.04 MCL-US 2 —

Tungsten 01155 7440-33-7 0.06 na na D

Uranium 22703 7440-61-1 0.04 MCL-US 30 D

Vanadium 01085 7440-62-2 0.10 NL-CA 50 D

Zinc 01090 7440-66-6 0.6 HAL-US 2,000 D

1

The recommended SMCL-CA thresholds for chloride, sulfate, and TDS are listed with the upper SMCL-CA thresholds in parentheses.
32 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 3H. Arsenic, chromium, and iron species, comparative thresholds, and reporting information for the U.S. 

Geological Survey Trace Metal Laboratory, Boulder, Colorado.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. The laboratory entity code for 

the U.S. Geoogical Survey Trace Metal Laboratory in the U.S. Geological Survey National Water Information System (NWIS) is 

USGSTMCO. Threshold type: 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; 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. Abbreviations: CAS, Chemical Abstract Service; 

MDL, method detection limit; USGS, U.S. Geological Survey; D, detected; na, not available; μg/L, microgram per liter; —, not 

detected]

Constituent

(valence state) 

USGS 

parameter 

code

CAS 

number

 MDL 

(μg/L)

Threshold

Detection

Type Value 

(μg/L)

Arsenic (III) 99034 22569-72-8 1 na na —

Arsenic (total) 01000 7440-38-2 0.5 MCL-US 10 D

Chromium (VI) 01032 18540-29-9 1 na na D

Chromium (total) 01030 7440-47-3 1 MCL-CA 50 D

Iron (II) 01047 7439-89-6 2 na na D

Iron (total) 01046 7439-89-6 2 HAL-US 300 D
Tables 33

Table 3I. Isotopic and radioactive constituents, comparative thresholds, and reporting information for laboratories.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. Laboratory entity codes are listed in the footnotes. 

Stable isotope ratios are reported in the standard delta notation (δ), the ratio of a heavier isotope to more common lighter isotope of that element, relative 

to a standard reference material. Reporting level type: MRL, minimum reporting level; MU, method uncertainty; SSMDC, sample specific minimum 

detectable concentration. Threshold type: 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. 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. Abbreviations: CAS, Chemical Abstract Service; USGS, U.S. Geological Survey; D, detected; pCi/L, picocuries per liter]

Constituent 

USGS 

parameter 

code

CAS 

number

 Reporting 

level type

Reporting 

level or 

uncertainty

Threshold

Detection

Type Value 

(pCi/L)

Stable isotope ratios (per mil)

δ2

H of water1 82082 na MU 2 na na D

δ18O of water1 82085 na MU 0.20 na na D

δ13C of dissolved carbonates2 82081 na 1 sigma 0.05 na na D

Radioactive constituents (percent modern)

Carbon-143 49933 14762-75-5 1 sigma 0.0015 na na D

Radioactive constituents (pCi/L)

Gross-alpha radioactivity, 72-hour 

count4

62636 12587-46-1 SSMDC 0.42–1.9 MCL-US 15 D

Gross-alpha radioactivity, 30-day count4 62639 12587-46-1 SSMDC 0.31–2.0 MCL-US 15 D

Gross-beta radioactivity, 72-hour count4 62642 12587-47-2 SSMDC 0.52–1.0 MCL-CA 50 D

Gross-beta radioactivity, 30-day count4 62645 12587-47-2 SSMDC 0.5–1.3 MCL-CA 50 D

Radium-2264 09511 13982-63-3 SSMDC 0.009–0.019 MCL-US 5

 5 D

Radium-2284 81366 15262-20-1 SSMDC 0.08–0.19 MCL-US 5

 5 D

Radon-2226 82303 14859-67-7 SSMDC 14–35 Prop. MCL-US 7

 300 (4,000) D

Tritium8,9 07000 10028-17-8 MRL 1 MCL-CA 20,000 D

1

 U.S. Geological Survey Stable Isotope Laboratory, Reston, Virginia (USGSSIVA).

2

 University of Waterloo (contract laboratory) (CAN-UWIL).

3

 University of Arizona, Accelerator Mass Spectrometry Laboratory (contract laboratory) (AZ-UAMSL).

4

 Eberline Analytical Services (contract laboratory) (CA-EBERL).

5

 The MCL-US threshold for radium is the sum of radium-226 and radium-228.

6

 U.S. Geological Survey National Water Quality Laboratory (USGSNWQL).

7

 Two MCLs have been proposed for Radon-222. The proposed alternative MCL is in parentheses.

8

 U.S. Geological Survey Stable Isotope and Tritium Laboratory, Menlo Park, California (USGSH3CA).

9 Lawrence Livermore National Laboratory (CA-LLNL).
34 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 3J. Noble gases and tritium, comparison thresholds and reporting information for the Lawrence Livermore National 

Laboratory.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. The laboratory entity code for the Lawrence 

Livermore National Laboratory in the U.S. Geological Survey National Water Information System (NWIS) is CA-LLNL. Threshold type: 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; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental 

Protection Agency maximum contaminant level. Abbreviations: CAS, Chemical Abstract Service; MU, method uncertainty; USGS, U.S. Geological 

Survey; D, detected; na, not available; cm3STP/g, cubic centimeters of gas at standard temperature and pressure per gram of water; pCi/L, picocuries 

per liter]

Constituent 

USGS 

parameter 

code

CAS 

number

 MU 

(percent)

Reporting

units

Threshold

Detection

Type Value 

(pCi/L)

Argon 85563 7440-37-1 2 cm3

STP/g na na D

Helium-3/helium-4 61040 na/7440-59-7 0.75 atom ratio na na D

Helium-4 85561 7440-59-7 2 cm3

STP/g na na D

Krypton 85565 7439-90-9 2 cm3

STP/g na na D

Neon 61046 7440-01-09 2 cm3

STP/g na na D

Tritium 07000 10028-17-8 1 pCi/L MCL-CA 20,000 D

Xenon 85567 7440-63-3 2 cm3

STP/g na na D
Tables 35

Table 3K. Microbial constituents, comparison thresholds, and reporting information for the U.S. Geological Survey Ohio Microbiology 

Laboratory codes 90901, 90900, 99335, and 99332.

[The five-digit USGS parameter code is used to uniquely identify a specific constituent or property. The laboratory entity code for the U.S. Geological Survey 

Ohio Microbiology Laboratory in the U.S. Geological Survey National Water Information System (NWIS) is USGSOHML. Threshold type: 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; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. Environmental Protection 

Agency maximum contaminant level; TT-US, U.S. Environmental Protection Agency treatment technique—a required process intended to reduce the level of 

contamination in drinking water. Abbreviations: MDL, method detection limit; mL, milliliter; USGS, U.S. Geological Survey; D, detected; na, not available; 

—, not detected]

Constituent 

USGS 

parameter 

code

Primary 

source

 MDL 

Threshold

Detection

Type Value 

Escherichia coli1 90901 Sewage and animal 

waste indicator

1 colony/ 

100 mL

TT-US Zero —

Total coliform—including fecal 

coliform and E. coli1

90900 Sewage and animal 

waste indicator

1 colony/

100 mL

MCL-US 5 percent of samples 

positive per month

D

F-specific coliphage2 99335 Sewage and animal 

waste indicator

na TT-US 99.99 percent killed/

inactivated

—

Somatic coliphage2 99332 Sewage and animal 

waste indicator

na TT-US 99.99 percent killed/ 

inactivated

—

1

 Analyzed in the field.

2

 Analyzed by the U.S. Geological Survey Ohio Microbiology Laboratory (laboratory entity code USGSOHML).
36 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 4. Water-quality indicators determined in the field for the San Fernando–San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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 well identification no: ULASF, San Fernando study area grid well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area 

understanding well; ULASGU, San Gabriel study area understanding well. Threshold type: SMCL-CA, California Department of Public Health secondary 

maximum contaminant level; SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. The SMCL-CA for specific 

conductance has recommended and upper threshold values. The upper value is shown in parentheses. Abbreviations: GAMA, Ground water Ambient 

Monitoring and Assessment; M, detected, not quantified; NTU, nephelometric turbidity unit; RL, reporting limit or range; *, value exceeds threshold; E, 

estimated; na, not available; nc, sample not collected; mg/L, milligram per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium 

carbonate; >, greater than; <, less than; —, not detected]

GAMA well

identification

no. 

Turbidity

(NTU)

(63676)

Dissolved 

oxygen 

(mg/L)

(00300)

 Water 

temperature 

(degrees 

Celsius)

(00010)

pH, field

(standard

units)

(00400)

Specific 

conductance, field

(μS/cm @ 25 

degrees C)

(00095)

Alkalinity,

field 

(mg/L as 

CaCO3

)

(29802)

Bicarbonate

(mg/L)

(63786)

Carbonate

(mg/L)

(63788)

Sulfide

(unfiltered,

sniff test)

(71875)

Threshold type na na na SMCL-US SMCL-CA na na na na

Threshold level na na na <6.5, >8.5 900 (1,600) na na na na

Grid wells

ULASF-01 nc 7.0 22.0 nc 405 nc nc nc —

ULASF-02 nc 5.8 21.5 nc 455 nc nc nc —

ULASF-03 nc 7.4 19.5 nc 555 nc nc nc M

ULASF-04 nc 1.5 18.0 nc 447 nc nc nc —

ULASF-05 nc 0.5 23.5 nc * 1,240 nc nc nc M

ULASF-06 nc 0.6 23.5 nc * 1,300 nc nc nc —

ULASF-07 nc 4.4 21.5 nc 685 nc nc nc —

ULASF-08 0.1 4.2 23.5 7.4 758 187 226 <1 —

ULASF-09 0.1 5.8 20.0 6.6 * 1,080 167 204 <1 —

ULASF-10 <0.1 4.2 22.5 7.7 740 174 211 <1 —

ULASF-11 nc 1.5 24.5 nc * 1,110 nc nc nc nc

ULASF-12 nc 6.9 23.0 nc 822 1 213 259 <1 nc

ULASG-01 nc 3.4 21.0 nc * 1,140 nc nc nc nc

ULASG-02 nc 12 18.5 nc 430 nc nc nc nc

ULASG-03 nc 8.6 20.0 nc 429 nc nc nc nc

ULASG-04 nc 7.8 19.5 nc 474 nc nc nc —

ULASG-05 nc 8.7 20.5 nc 427 1 182 221 1 —

ULASG-06 0.1 1.5 19.0 7.4 852 183 222 1 —

ULASG-07 nc 9.0 16.0 nc 498 nc nc nc —

ULASG-08 0.2 7.6 22.0 7.5 636 155 188 1 nc

ULASG-09 nc E8 19.5 nc 292 nc nc nc —

ULASG-10 nc 8.2 19.5 nc 581 nc nc nc —

ULASG-11 nc 11 18.0 nc 543 1 172 209 <1 —

ULASG-12 nc nc 18.0 nc 480 nc nc nc —

ULASG-13 nc 1.8 24.0 nc 310 nc nc nc —

ULASG-14 4.4 4.6 21.5 7.6 495 182 221 1 —

ULASG-15 0.2 5.2 16.5 7.4 313 151 183 <1 —

ULASG-16 0.2 6.5 21.5 7.0 564 132 160 <1 —

ULASG-17 nc 2.6 21.5 nc * 1,100 nc nc nc —

ULASG-18 nc 8.3 20.0 nc 492 nc nc nc —

ULASG-19 nc 4.9 22.5 nc 382 nc nc nc —

ULASG-20 nc 2.5 22.5 nc 488 nc nc nc —

ULASG-21 nc 7.9 21.0 nc 674 nc nc nc —

ULASG-22 nc 6.2 21.0 nc 450 nc nc nc —

ULASG-23 nc 9.3 19.0 nc 485 nc nc nc —

Table 4. Water-quality indicators determined in the field for the San Fernando–San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit, California, May to July 2005.

[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 well identification no: ULASF, San Fernando study area grid well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area 

understanding well; ULASGU, San Gabriel study area understanding well. Threshold type: SMCL-CA, California Department of Public Health secondary 

maximum contaminant level; SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. The SMCL-CA for specific 

conductance has recommended and upper threshold values. The upper value is shown in parentheses. Abbreviations: GAMA, Ground water Ambient 

Monitoring and Assessment; M, detected, not quantified; NTU, nephelometric turbidity unit; RL, reporting limit or range; *, value exceeds threshold; E, 

estimated; na, not available; nc, sample not collected; mg/L, milligram per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium 

carbonate; >, greater than; <, less than; —, not detected]
Tables 37

Table 4. Water-quality indicators determined in the field for the San Fernando–San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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 well identification no: ULASF, San Fernando study area grid well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area 

understanding well; ULASGU, San Gabriel study area understanding well. Threshold type: SMCL-CA, California Department of Public Health secondary 

maximum contaminant level; SMCL-US, U.S. Environmental Protection Agency secondary maximum contaminant level. The SMCL-CA for specific 

conductance has recommended and upper threshold values. The upper value is shown in parentheses. Abbreviations: GAMA, Ground water Ambient 

Monitoring and Assessment; M, detected, not quantified; NTU, nephelometric turbidity unit; RL, reporting limit or range; *, value exceeds threshold; E, 

estimated; na, not available; nc, sample not collected; mg/L, milligram per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium 

carbonate; >, greater than; <, less than; —, not detected]

GAMA well

identification

no. 

Turbidity

(NTU)

(63676)

Dissolved 

oxygen 

(mg/L)

(00300)

 Water 

temperature 

(degrees 

Celsius)

(00010)

pH, field

(standard

units)

(00400)

Specific 

conductance, field

(μS/cm @ 25 

degrees C)

(00095)

Alkalinity,

field 

(mg/L as 

CaCO3

)

(29802)

Bicarbonate

(mg/L)

(63786)

Carbonate

(mg/L)

(63788)

Sulfide

(unfiltered,

sniff test)

(71875)

Threshold type na na na SMCL-US SMCL-CA na na na na

Threshold level na na na <6.5, >8.5 900 (1,600) na na na na

Understanding wells

ULASFU-01 nc 6.8 20.0 nc 792 nc nc nc —

ULASFU-02 nc 5.6 20.5 nc 823 nc nc nc M

ULASFU-03 0.1 4.7 21.0 6.9 * 957 222 270 <1 —

ULASFU-04 0.1 7.6 17.0 7.3 637 230 279 <1 nc

ULASFU-05 nc 3.4 17.5 nc 559 nc nc nc nc

ULASFU-06 0.2 8.1 18.5 7.2 605 188 228 1 nc

ULASGU-01 nc 11 20.5 nc 475 1 135 164 <1 —

ULASGU-02 0.1 3.3 18.5 6.6 * 906 230 281 <1 nc

ULASGU-03 nc 5.5 18.5 nc 532 nc nc nc —

ULASGU-04 0.1 7.4 21.5 7.5 484 176 213 <1 —

ULASGU-05 0.2 6.5 21.0 7.5 394 163 198 <1 —

ULASGU-06 nc 6.2 22.0 nc 559 1 131 159 <1 —

ULASGU-07 <0.1 2.6 24.0 8.2 351 109 129 2 —

ULASGU-08 nc 6.1 20.5 nc 360 1 164 199 <1 M

ULASGU-09 0.1 4.8 16.5 7.5 445 203 245 1 —

ULASGU-10 nc 7.2 22.0 nc 820 1 159 194 <1 —

ULASGU-11 0.1 8.3 17.0 7.5 329 142 172 1 —

 1 Alkalinity determined by fixed endpoint (pH 4.5) titration at the U.S. Geological Survey, National Water Quality Laboratory, Denver, Colorado.
38 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 5. Volatile organic compounds (VOCs) and gasoline oxygenates and degradates detected in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[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. 

Samples from all 52 wells were analyzed, but only samples with detections are listed. GAMA well identification no: ULASF, San Fernando study area grid 

well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; 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 Health notification level. Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; VOC, volatile organic 

compounds; E, estimated; na, not available; *, indicates value above threshold value; μg/L, microgram per liter; —, not detected]

GAMA well

identification

no. 

Solvent

Tetrachloroethene

(μg/L)

(34475)

Trichloroethene 

(μg/L)

(39180)

 1,1- 

Dichloroethane 

(μg/L)

(34496)

cis-1,2-

Dichloroethene

(μg/L)

(77093)

Tetrachloromethane

(μg/L)

(32102)

1,1,1-

Trichloroethane

(μg/L)

(34506)

1,2-

Dichlorobenzene

(μg/L)

(34536)

trans-1,2-

Dichloroethene

(μg/L)

(34546)

1,1,1,2-

Trichloroethane

(μg/L)

(77562)

Threshold type MCL-US MCL-US MCL-CA MCL-CA MCL-CA MCL-US MCL-US MCL-CA HAL-US

Threshold level 5 5 5 6 0.5 200 600 10 70

LRL 0.03 0.038 0.035 0.024 0.06 0.032 0.048 0.032 0.03

Grid wells (n = 35 wells)

ULASF-01 E0.09 — — — — — — — —

ULASF-02 E0.01 0.38 E0.01 — — — — — —

ULASF-03 — — — — — — — — —

ULASF-04 0.47 0.84 — E0.03 — — — — —

ULASF-05 E0.04 0.11 — — — — — — —

ULASF-06 0.20 0.23 — E0.02 — E0.01 — — —

ULASF-07 * 220 * 40.3 E0.03 1.30 0.31 E0.02 — E0.01 E0.06

ULASF-08 * 37.4 * 77.6 — 0.31 0.41 — — E0.01 —

ULASF-09 1.89 0.11 E0.06 E0.02 E0.03 — — — —

ULASF-10 1.18 3.65 E0.04 0.15 E0.06 — — — —

ULASF-11 — — — — — — — — —

ULASF-12 * 12.9 * 24.5 E0.06 0.17 * 0.85 E0.03 — E0.01 E0.03

ULASG-01 0.18 — — — — — — — —

ULASG-02 E0.02 — — — — E0.02 — — —

ULASG-03 E0.03 — — — — — — — —

ULASG-04 0.73 — — — — E0.01 — — —

ULASG-05 — — — — 0.30 — — — —

ULASG-06 2.82 0.38 E0.04 0.21 — — — — —

ULASG-07 0.47 2.93 E0.09 E0.02 * 2.77 — — — —

ULASG-08 0.23 1.44 0.18 0.39 E0.04 — — — —

ULASG-10 3.70 E0.04 — — E0.03 — E0.02 — —

ULASG-11 0.12 E0.08 E0.03 — — — — — —

ULASG-12 E0.05 0.17 E0.04 E0.01 — — — — —

ULASG-13 E0.03 E0.02 — — — — — — —

ULASG-14 — — — — — — — — —

ULASG-16 0.13 — — — — — — — —

ULASG-17 1.79 E0.06 E0.03 — E0.04 E0.02 — — —

ULASG-18 E0.02 — E0.06 — — — E0.04 — —

ULASG-19 E0.14 1.37 — E0.04 — — — — —

ULASG-20 E0.10 0.27 E0.02 E0.01 — — — — —

ULASG-21 E0.16 — — — — — E0.04 — —

ULASG-22 E0.02 — — — E0.03 — — — —

ULASG-23 E0.03 — — — — — — — —

Number of detections 29 19 13 13 11 6 3 3 2

Detection frequency

(percent)

83 54 37 37 31 17 9 9 6
Tables 39

GAMA well

identification

no. 

Solvent Gasoline

1,1,2-

Trichloroethane 

(μg/L)

(34511)

 1,2- 

Dichloroethane 

(μg/L)

(32103)

Dichloromethane

(μg/L)

(34423)

1,2-

Dichloropropane

(μg/L)

(34541)

1,3-

Dichlorobenzene

(μg/L)

(34566)

Chlorobenzene

(μg/L)

(34301)

Benzene

(μg/L)

(34030)

Toluene

(μg/L)

(34010)

mXylene- plus

p-xylene

(μg/L)

(85795)

Threshold type MCL-US MCL-CA MCL-US MCL-US HAL-US MCL-CA MCL-CA MCL-CA MCL-CA

Threshold level 5 5 5 5 600 70 1 150 1,750

LRL 0.04 0.13 0.06 0.029 0.03 0.028 0.021 0.02 0.06

Grid wells (n = 35 wells)

ULASF-01 — — — — — — — — —

ULASF-02 — — — — — — — — —

ULASF-03 — — — — — — — — —

ULASF-04 — — — — — — — — —

ULASF-05 — — — — — — — — —

ULASF-06 — — — — — — — — —

ULASF-07 0.15 E0.1 — E0.06 — — E0.01 0.26 —

ULASF-08 — — — — — — — — —

ULASF-09 — — — — — — — — —

ULASF-10 — — — — — — — — —

ULASF-11 — — — — — — — 0.35 —

ULASF-12 E0.07 E0.1 — — — — E0.01 — —

ULASG-01 — — — — — — — — —

ULASG-02 — — — — — — — — —

ULASG-03 — — — — — — — 0.03 —

ULASG-04 — — — — — — — — —

ULASG-05 — — — — — — — — —

ULASG-06 — — — — — — — — —

ULASG-07 — — — — — — — — —

ULASG-08 — — E0.04 — — — — — —

ULASG-10 — — — — — — — — —

ULASG-11 — — — — — — — — —

ULASG-12 — — — — — — — — —

ULASG-13 — — — — — — — — —

ULASG-14 — — — — — — — — —

ULASG-16 — — — — — — — — —

ULASG-17 — — — — — — — — —

ULASG-18 — — — — E0.02 — — — —

ULASG-19 — — — — — — — — —

ULASG-20 — — — — — — — — —

ULASG-21 — — — — — — — — —

ULASG-22 — — — — — — — — —

ULASG-23 — — E0.04 — — — — — —

Number of detections 2 2 2 1 1 — 2 2 —

Detection frequency

(percent)

6 6 6 3 3 — 6 6 —

Table 5. Volatile organic compounds (VOCs) and gasoline oxygenates and degradates detected in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 52 wells were analyzed, but only samples with detections are listed. GAMA well identification no: ULASF, San Fernando study area grid 

well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; 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 Health notification level. Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; VOC, volatile organic 

compounds; E, estimated; na, not available; *, indicates value above threshold value; μg/L, microgram per liter; —, not detected]
40 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

GAMA well

identification

no. 

Gasoline oxygenate Fumigant Disinfection by-product Solvent, 

organic

Methyl

tert-butyl

ether

(μg/L) 

(78032)

Diisopropyl

ether

(μg/L) 

(81577)

1,4-

Dichlorobenzene

(μg/L)

(34571)

Trichloromethane

(μg/L)

(32106)

Bromodichloromethane

(μg/L)

(32101)

Dichlorodifluoromethane

(μg/L)

(32105)

Tribromomethane

(μg/L)

(32104)

1,2,3-

Trichloropropane

(μg/L)

(77443)

Threshold type MCL-CA na MCL-CA MCL-US MCL-US MCL-US MCL-US NL-CA

Threshold level 13 na 5 1

80 180 180 180 0.005

LRL 0.04 0.04 0.034 0.024 0.028 0.1 0.1 0.18

Grid wells (n = 35 wells)

ULASF-01 — — — E0.03 — — — —

ULASF-02 — — — 0.11 — — — —

ULASF-03 — — — 0.54 E0.03 — — —

ULASF-04 E0.04 — — E0.04 — — — —

ULASF-05 — — — — — — — —

ULASF-06 — — — E0.05 — — — —

ULASF-07 — E0.03 — 2.40 E0.06 — — * 0.40

ULASF-08 — — — 0.33 — — — —

ULASF-09 0.2 — — 0.44 0.14 — — —

ULASF-10 — — — 0.17 — — — —

ULASF-11 — — — — — — — —

ULASF-12 E0.1 — — 0.74 E0.08 — — —

ULASG-01 — — — 0.29 E0.08 — — —

ULASG-02 E0.1 — — 0.97 0.17 — — —

ULASG-03 — — — 0.34 E0.09 — — —

ULASG-04 0.1 — — E0.02 — — — —

ULASG-05 — — — — — — — —

ULASG-06 0.8 — — E0.08 — — — —

ULASG-07 — — — 0.95 E0.05 — — —

ULASG-08 — — — 0.82 0.27 E0.1 — —

ULASG-10 — — — E0.05 — — — —

ULASG-11 — — — 1.16 0.19 — — —

ULASG-12 0.2 — — 0.79 0.11 0.2 0.40 —

ULASG-13 — — — — — — — —

ULASG-14 — — — E0.03 — — — —

ULASG-16 — — — E0.09 E0.05 — — —

ULASG-17 E0.1 — — 3.23 0.12 — — —

ULASG-18 — — E0.03 0.90 0.13 — — —

ULASG-19 — — — E0.06 E0.03 E0.1 0.31 —

ULASG-20 0.2 — — E0.07 — — — —

ULASG-21 — — — E0.07 E0.03 — — —

ULASG-22 0.2 — — E0.02 — — — —

ULASG-23 — — — 7.46 0.58 E0.1 — —

Number of detections 10 1 1 29 17 4 2 1

Detection frequency

(percent)

29 3 3 83 49 11 6 3

Table 5. Volatile organic compounds (VOCs) and gasoline oxygenates and degradates detected in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 52 wells were analyzed, but only samples with detections are listed. GAMA well identification no: ULASF, San Fernando study area grid 

well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; 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 Health notification level. Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; VOC, volatile organic 

compounds; E, estimated; na, not available; *, indicates value above threshold value; μg/L, microgram per liter; —, not detected]
Tables 41

Table 5. Volatile organic compounds (VOCs) and gasoline oxygenates and degradates detected in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 52 wells were analyzed, but only samples with detections are listed. GAMA well identification no: ULASF, San Fernando study area grid 

well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; 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 Health notification level. Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; VOC, volatile organic 

compounds; E, estimated; na, not available; *, indicates value above threshold value; μg/L, microgram per liter; —, not detected]

GAMA well

identification

no. 

Refrigerant Organic synthesis

VOC 

detections 

per well

Dichlorodifluorom

ethane

(μg/L)

(34668)

1,1,2-

Trichloro1,2,2-

trifluoroethane

(μg/L)

(77652)

Trichlorofluoromethane

(μg/L)

(34488)

1,1-

Dichloroethene

(μg/L)

(34501)

Carbon

disulfide

(μg/L) 

(77041)

1,2,4-

Trimethylbenzene

(μg/L) 

(77222)

Vinyl

chloride

(μg/L) 

(39175)

Threshold type NL-CA MCL-CA MCL-CA MCL-CA NL-CA NL-CA MCL-CA

Threshold level 1,000 1,200 150 6 160 330 0.5

LRL 0.18 0.038 0.08 0.024 0.038 0.056 0.08

Grid wells (n = 35 wells)

ULASF-01 — — — — — — — 2

ULASF-02 — — — E0.02 — — — 5

ULASF-03 — — — — — — — 2

ULASF-04 E0.06 — 0.52 0.11 — — — 8

ULASF-05 — — — — — — — 2

ULASF-06 — — — — — — — 5

ULASF-07 — E0.15 — 0.63 — — — 19

ULASF-08 — — — 0.21 — — — 7

ULASF-09 E0.13 — — — — — — 9

ULASF-10 E0.32 — — E0.02 — — — 8

ULASF-11 — — — — — — — 1

ULASF-12 — E0.02 0.41 1.10 — — — 17

ULASG-01 — — — — — — — 3

ULASG-02 — — — — — — — 5

ULASG-03 — — — 0.12 — — — 4

ULASG-04 — 1.42 0.34 — — — — 6

ULASG-05 — — — — — — — 1

ULASG-06 — — — E0.06 — — — 7

ULASG-07 — E0.14 — E0.09 — — — 9

ULASG-08 — — — E0.04 — — — 10

ULASG-10 — — — — — — — 5

ULASG-11 E0.17 — — — — — — 6

ULASG-12 E0.06 — — — — — — 10

ULASG-13 — — — — — — — 2

ULASG-14 — — — — — — — 1

ULASG-16 — — — — — — — 3

ULASG-17 — 1.26 E0.09 E0.07 E0.03 — — 12

ULASG-18 — — — — E0.06 — — 8

ULASG-19 E0.18 — — — E0.03 — — 9

ULASG-20 E0.10 — — — — — — 7

ULASG-21 — — — — E0.03 — — 5

ULASG-22 — — — — E0.03 — — 5

ULASG-23 — — — — E0.03 — — 6

Number of detections 7 5 4 11 6 — — 209

Detection frequency

(percent)

20 14 11 31 17 — — 2

94
42 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

GAMA well

identification

no. 

Solvent

Tetrachloroethene

(μg/L)

(34475)

Trichloroethene 

(μg/L)

(39180)

1,1-

Dichloroethene

(μg/L)

(34496)

cis-1,2-

Dichloroethene

(μg/L)

(77093)

Tetrachloromethane

(μg/L)

(32102)

1,1,1-

Trichloroethane

(μg/L)

(34506)

1,2-

Dichlorobenzene

(μg/L)

(34536)

trans-1,2-

Dichloroethene

(μg/L)

(34546)

1,1,1,2-

Trichloroethane

(μg/L)

(77562)

Threshold type MCL-US MCL-US MCL-CA MCL-CA MCL-CA MCL-US MCL-US MCL-CA HAL-US

Threshold level 5 5 5 6 0.5 200 600 10 70

LRL 0.03 0.038 0.035 0.024 0.06 0.032 0.048 0.032 0.03

Understanding wells (n = 17 wells)

ULASFU-01 2.58 0.14 0.13 0.22 — — E0.03 — —

ULASFU-02 0.33 E0.04 E0.08 — — — — — —

ULASFU-03 *12.1 *11.9 E0.03 0.38 0.21 E0.02 — — —

ULASFU-04 0.84 3.29 E0.03 E0.05 E0.02 E0.07 — — —

ULASFU-05 E0.07 E0.03 E0.07 .10 — — — — —

ULASFU-06 E0.08 0.45 — E0.03 E0.07 E0.06 — — —

ULASGU-01 E0.06 — — — E0.03 — — — —

ULASGU-02 — — — — — — — — —

ULASGU-03 — — — — — — — — —

ULASGU-04 0.95 0.14 — 0.13 — — — — —

ULASGU-05 E0.05 E0.05 — — — — — — —

ULASGU-06 E0.06 — — — 0.23 — — — —

ULASGU-07 — — — — E0.01 — — — —

ULASGU-08 E0.04 0.19 — — — — — — —

ULASGU-10 — — — — — — — — —

ULASGU-11 0.43 0.12 — E0.04 — — — — —

Table 5. Volatile organic compounds (VOCs) and gasoline oxygenates and degradates detected in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 52 wells were analyzed, but only samples with detections are listed. GAMA well identification no: ULASF, San Fernando study area grid 

well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; 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 Health notification level. Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; VOC, volatile organic 

compounds; E, estimated; na, not available; *, indicates value above threshold value; μg/L, microgram per liter; —, not detected]
Tables 43

Table 5. Volatile organic compounds (VOCs) and gasoline oxygenates and degradates detected in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 52 wells were analyzed, but only samples with detections are listed. GAMA well identification no: ULASF, San Fernando study area grid 

well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; 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 Health notification level. Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; VOC, volatile organic 

compounds; E, estimated; na, not available; *, indicates value above threshold value; μg/L, microgram per liter; —, not detected]

GAMA well

identification

no. 

Solvent Gasoline

1,1,2-

Trichloroethane 

(μg/L)

(34511)

 1,2- 

Dichloroethane 

(μg/L)

(32103)

Dichloromethane

(μg/L)

(34423)

1,2-

Dichloropropane

(μg/L)

(34541)

1,3-

Dichlorobenzene

(μg/L)

(34566)

Chlorobenzene

(μg/L)

(34301)

Benzene

(μg/L)

(34030)

Toluene

(μg/L)

(34010)

mXylene- plus

p-xylene

(μg/L)

(85795)

Threshold type MCL-US MCL-CA MCL-US MCL-US HAL-US MCL-CA MCL-CA MCL-CA MCL-CA

Threshold level 5 5 5 5 600 70 1 150 1,750

LRL 0.04 0.13 0.06 0.029 0.03 0.028 0.021 0.02 0.06

Understanding wells (n = 17 wells)

ULASFU-01 — — E0.10 — E0.05 — — — —

ULASFU-02 — — E0.03 — — — — — —

ULASFU-03 — E0.1 — — — — — — —

ULASFU-04 — — — — — — — — —

ULASFU-05 — — — E0.06 — E0.04 E0.02 — —

ULASFU-06 — 0.2 — — — — — — E0.02

ULASGU-01 — — — — — — — — —

ULASGU-02 — — — — — — — — —

ULASGU-03 — — — — — — — — —

ULASGU-04 — — — — — — — — —

ULASGU-05 — — — — — — — — —

ULASGU-06 — — — — — — — — —

ULASGU-07 — — — — — — — — —

ULASGU-08 — — — — — — — — —

ULASGU-10 — — — — — — — — —

ULASGU-11 — — — — — — — — —
44 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 5. Volatile organic compounds (VOCs) and gasoline oxygenates and degradates detected in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 52 wells were analyzed, but only samples with detections are listed. GAMA well identification no: ULASF, San Fernando study area grid 

well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; 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 Health notification level. Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; VOC, volatile organic 

compounds; E, estimated; na, not available; *, indicates value above threshold value; μg/L, microgram per liter; —, not detected]

GAMA well

identification

no. 

Gasoline oxygenate Fumigant Disinfection by-product Solvent, 

organic

Methyl

tert-butyl

ether

(μg/L) 

(78032)

Diisopropyl

ether

(μg/L) 

(81577)

1,4-

Dichlorobenzene

(μg/L)

(34571)

Trichloromethane

(μg/L)

(32106)

Bromodichloromethane

(μg/L)

(32101)

Dibromochloromethane

(μg/L)

(32105)

Tribromomethane

(μg/L)

(32104)

1,2,3-

Trichloropropane

(μg/L)

(77443)

Threshold type MCL-CA na MCL-CA MCL-US MCL-US MCL-US MCL-US NL-CA

Threshold level 13 na 5 1

80 180 180 180 0.005

LRL 0.04 0.04 0.034 0.024 0.028 0.1 0.1 0.18

Understanding wells (n = 17 wells)

ULASFU-01 0.3 — E0.02 1.62 0.22 E0.1 — —

ULASFU-02 0.3 — — 1.65 0.84 0.3 — —

ULASFU-03 E0.1 — — 0.71 0.15 — — —

ULASFU-04 — — — E0.08 — — — —

ULASFU-05 E0.1 — 0.26 E0.03 E0.02 — — —

ULASFU-06 — — — E0.06 — — — —

ULASGU-01 0.1 — — .19 E0.07 — — —

ULASGU-02 — — — E0.02 — — — —

ULASGU-03 — — — E0.02 — — — —

ULASGU-04 — — — E0.02 — — — —

ULASGU-05 — — — — — — — —

ULASGU-06 1.2 — — 0.15 E0.04 — — —

ULASGU-07 — — — — — — — —

ULASGU-08 — — — E0.01 — — — —

ULASGU-10 — — — — — — — —

ULASGU-11 — — — — — — — —
Tables 45

Table 5. Volatile organic compounds (VOCs) and gasoline oxygenates and degradates detected in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 52 wells were analyzed, but only samples with detections are listed. GAMA well identification no: ULASF, San Fernando study area grid 

well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; HAL-US, U.S. Environmental Protection Agency Lifetime Health Advisory; 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 Health notification level. Abbreviations: GAMA, Ground water Ambient Monitoring and Assessment; VOC, volatile organic 

compounds; E, estimated; na, not available; *, indicates value above threshold value; μg/L, microgram per liter; —, not detected]

GAMA well

identification

no. 

Refrigerant Organic synthesis

VOC 

detections 

per well

Dichlorodifluorom

ethane

(μg/L)

(34668)

1,1,2-

Trichloro1,2,2-

trifluoroethane

(μg/L)

(77652)

Trichlorofluoromethane

(μg/L)

(34488)

1,1-

Dichloroethene

(μg/L)

(34501)

Carbon

disulfide

(μg/L) 

(77041)

1,2,4-

Trimethylbenzene

(μg/L) 

(77222)

Vinyl

chloride

(μg/L) 

(39175)

Threshold type NL-CA MCL-CA MCL-CA MCL-CA NL-CA NL-CA MCL-CA

Threshold level 1,000 1,200 150 6 160 330 0.5

LRL 0.18 0.038 0.08 0.024 0.038 0.056 0.08

Understanding wells (n = 17 wells)

ULASFU-01 E0.40 — — — — — — 13

ULASFU-02 — E0.03 — — — — — 9

ULASFU-03 E0.29 E0.02 0.22 0.25 — — — 14

ULASFU-04 E0.08 0 .24 24 0.25 — — — 11

ULASFU-05 — — — — — — 0.1 12

ULASFU-06 — — — E0.03 — 0.14 — 10

ULASGU-01 — — — — — — — 5

ULASGU-02 — — — — — — — 1

ULASGU-03 — — — — — — — 1

ULASGU-04 — — — — — — — 4

ULASGU-05 — — — — — — — 2

ULASGU-06 E0.09 — — — E0.02 — — 7

ULASGU-07 — — — — — — — 1

ULASGU-08 E0.03 — — — E0.04 — — 5

ULASGU-10 — — — — E0.04 — — 1

ULASGU-11 — — — E0.03 — — — 4

1

 The MCL-US threshold for trihalomethanes is the sum of chloroform, bromoform, bromodichloromethane, and dibromochloromethane.

2

 Frequency of detection of at least one VOC in the grid wells.
46 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

GAMA well

identification

no. 

Degradate

2-Chloro4-isopropylamino6-amino-striazine

(μg/L)

(04040)

3,4-

Dichloroaniline

(μg/L)

(61625)

2-Chloro-6-

ethylamino4-amino-striazine

(μg/L)

(04038)

3-(4-Chlorophenyl)-1-

methyl urea

(μg/L)

(61692)

Fipronil

sulfide

(μg/L)

(62167)

2-Hydroxy4-isopropylamino-6-

ethylaminos-triazine

(μg/L)

(50355)

Desulfinyl

fipronil

(μg/L)

(62170)

Fipronil

sulfone 

(μg/L)

(62168)

Threshold type

Threshold level

LRL 0.006 0.0045 0.08 0.036 0.013 0.032 0.012 0.024

Grid wells (n = 35 wells)

ULASF-01 — — nc nc — nc — —

ULASF-02 — — nc nc — nc — —

ULASF-04 E0.009 — nc nc — nc — —

ULASF-05 E0.003 — nc nc — nc — —

ULASF-06 E0.004 — nc nc — nc — —

ULASF-07 E0.044 — nc nc — nc — —

ULASF-08 E0.004 — — — — — — —

ULASF-09 E0.014 — E0.02 — — — — —

ULASF-10 E0.007 — E0.01 — — — — —

ULASF-12 E0.005 — — — — — — —

ULASG-01 E0.018 — nc nc — nc — —

ULASG-02 E0.009 — nc nc — nc — —

ULASG-03 E0.006 — nc nc — nc — —

ULASG-04 E0.045 — nc nc — nc — —

ULASG-06 E0.021 E0.006 E0.01 E0.01 E0.007 — — —

ULASG-07 E0.005 — nc nc — nc — —

ULASG-08 E0.021 — — — — — — —

ULASG-09 — — nc nc — nc — —

ULASG-10 E0.022 E0.007 nc nc — nc — —

ULASG-11 E0.014 E0.002 E0.02 — — — — —

ULASG-12 E0.042 — nc nc — nc — —

ULASG-14 E0.004 — — — — — — —

ULASG-15 — E0.003 — — — — — —

ULASG-16 E0.025 E0.007 E0.01 — — — — —

ULASG-17 E0.037 — nc nc — nc — —

ULASG-18 E0.006 — nc nc — nc — —

ULASG-19 E0.005 — nc nc — nc — —

ULASG-20 E0.010 E0.009 nc nc — nc — —

ULASG-21 E0.008 — nc nc — nc — —

ULASG-22 E0.019 E0.002 nc nc — nc — —

ULASG-23 E0.005 — nc nc — nc — —

Number of detections 27 7 nc nc 1 nc nc nc

Detection frequency

(percent)

77 20 nc nc 3 nc nc nc

Table 6. Pesticides and pesticide degradates detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[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. 

Samples from all 51 wells were analyzed on schedule 2003, and 24 wells on schedule 2060, but only samples with detections are listed. GAMA well 

identification no: ULASF, San Fernando study area grid well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding 

well; ULASGU, San Gabriel study area understanding well. Threshold type: 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; HAL-US, U.S. Environmental Protection 

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

Health maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific does at a risk factor of 10E—5. Abbreviations: GAMA, 

Groundwater Ambient Monitoring and Assessment; LRL, laboratory reporting level; E, estimated value; nc, not collected or not computed; μg/L, microgram per 

liter; —, not detected]
Tables 47

Table 6. Pesticides and pesticide degradates detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 51 wells were analyzed on schedule 2003, and 24 wells on schedule 2060, but only samples with detections are listed. GAMA well 

identification no: ULASF, San Fernando study area grid well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding 

well; ULASGU, San Gabriel study area understanding well. Threshold type: 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; HAL-US, U.S. Environmental Protection 

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

Health maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific does at a risk factor of 10E—5. Abbreviations: GAMA, 

Groundwater Ambient Monitoring and Assessment; LRL, laboratory reporting level; E, estimated value; nc, not collected or not computed; μg/L, microgram per 

liter; —, not detected]

GAMA well

identification

no. 

Herbicide

Simazine

(μg/L)

(04035)

Atrazine

(μg/L)

(39632)

Prometon 

(μg/L)

(04037)

Tebuthiuron

(μg/L)

(82670)

Diuron

(μg/L)

(49300)

Hexazinone

(μg/L)

(04025)

Bromacil

(μg/L)

(04029)

Metolachlor

(μg/L)

(39415)

Diphenamid

(μg/L)

(04033)

Threshold type MCL-US MCL-CA HAL-US HAL-US RSD5-US HAL-US HAL-US HAL-US HAL-US

Threshold level 4 1 100 500 20 400 700 700 200

LRL 0.005 0.007 0.01 0.016 0.015 0.0129 0.018 0.006 0.01

Grid wells (n = 35 wells)

ULASF-01 0.015 — — — nc — nc — nc

ULASF-02 0.013 — — — nc — nc — nc

ULASF-04 0.045 0.008 E0.01 0.02 nc — nc — nc

ULASF-05 — — — — nc — nc — nc

ULASF-06 — — — — nc — nc — nc

ULASF-07 0.026 0.023 — — nc — nc — nc

ULASF-08 0.012 E0.006 E0.01 — — — — — —

ULASF-09 0.044 0.026 — E0.02 — — E0.01 — —

ULASF-10 0.005 0.009 — — — — — — —

ULASF-12 0.005 E0.006 — — — — 0.04 — —

ULASG-01 0.072 0.020 — 0.03 nc — nc — nc

ULASG-02 0.030 0.007 — — nc — nc — nc

ULASG-03 0.005 — — — nc — nc — nc

ULASG-04 0.067 0.081 — — nc — nc — nc

ULASG-06 0.067 0.030 0.01 E0.01 0.05 E0.007 — E0.002 —

ULASG-07 0.015 E0.007 — — nc — nc — nc

ULASG-08 0.010 0.029 — — 0.02 — — — E0.01

ULASG-09 0.011 — — — nc — nc — nc

ULASG-10 0.022 0.116 — — nc — nc — nc

ULASG-11 0.023 0.018 — — — — — — —

ULASG-12 0.125 0.084 — — nc — nc — nc

ULASG-14 0.017 — — — — — — — —

ULASG-15 0.008 — — — — — — — —

ULASG-16 0.023 0.028 E0.01 — 0.07 — — — —

ULASG-17 0.012 0.047 — 0.14 nc 0.058 nc — nc

ULASG-18 0.009 E0.007 — — nc — nc — nc

ULASG-19 — E0.005 — — nc — nc — nc

ULASG-20 0.140 0.150 E0.01 — nc E0.007 nc E0.002 nc

ULASG-21 — — — — nc — nc — nc

ULASG-22 0.030 0.021 — — nc — nc — nc

ULASG-23 0.010 E0.004 E0.01 — nc — nc — nc

Number of detections 27 22 6 5 nc 3 nc 2 nc

Detection frequency

(percent)

77 63 17 14 nc 9 nc 6 nc
48 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 6. Pesticides and pesticide degradates detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 51 wells were analyzed on schedule 2003, and 24 wells on schedule 2060, but only samples with detections are listed. GAMA well 

identification no: ULASF, San Fernando study area grid well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding 

well; ULASGU, San Gabriel study area understanding well. Threshold type: 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; HAL-US, U.S. Environmental Protection 

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

Health maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific does at a risk factor of 10E—5. Abbreviations: GAMA, 

Groundwater Ambient Monitoring and Assessment; LRL, laboratory reporting level; E, estimated value; nc, not collected or not computed; μg/L, microgram per 

liter; —, not detected]

GAMA well

identification

no. 

Herbicide Fungicide Insecticide

Pesticide 

detections 

per well

Imazethapyr

(μg/L)

(50407)

Sulfometuron

(μg/L)

(50337)

Metalaxyl 

(μg/L)

(61596)

Myclo

butanil

(μg/L)

(61599)

Fipronil

(μg/L)

(62166)

Threshold type

Threshold level

LRL 0.038 0.038 0.0051 0.008 0.016

Grid wells (n = 35 wells)

ULASF-01 nc nc — — — 1

ULASF-02 nc nc — — — 1

ULASF-04 nc nc — — — 5

ULASF-05 nc nc — — — 1

ULASF-06 nc nc — — — 1

ULASF-07 nc nc — — — 3

ULASF-08 — — — — — 4

ULASF-09 — — — — — 4

ULASF-10 — — — — — 3

ULASF-12 — — — — — 3

ULASG-01 nc nc — — — 4

ULASG-02 nc nc — — — 3

ULASG-03 nc nc — — — 2

ULASG-04 nc nc — — — 3

ULASG-06 E0.02 — 0.015 — E0.008 15

ULASG-07 nc nc — — — 3

ULASG-08 — — — — — 5

ULASG-09 nc nc — — — 1

ULASG-10 nc nc — — — 4

ULASG-11 — — — — — 5

ULASG-12 nc nc — — — 3

ULASG-14 — — — — — 2

ULASG-15 — — — — — 2

ULASG-16 — — — — — 7

ULASG-17 nc nc — — — 5

ULASG-18 nc nc — — — 3

ULASG-19 nc nc — — — 2

ULASG-20 nc nc 0.144 0.009 — 9

ULASG-21 nc nc — — — 1

ULASG-22 nc nc — — — 4

ULASG-23 nc nc — — — 4

Number of detections nc nc 2 1 1 113

Detection frequency

(percent)

nc nc 6 3 3 1

89
Tables 49

Table 6. Pesticides and pesticide degradates detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 51 wells were analyzed on schedule 2003, and 24 wells on schedule 2060, but only samples with detections are listed. GAMA well 

identification no: ULASF, San Fernando study area grid well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding 

well; ULASGU, San Gabriel study area understanding well. Threshold type: 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; HAL-US, U.S. Environmental Protection 

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

Health maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific does at a risk factor of 10E—5. Abbreviations: GAMA, 

Groundwater Ambient Monitoring and Assessment; LRL, laboratory reporting level; E, estimated value; nc, not collected or not computed; μg/L, microgram per 

liter; —, not detected]

GAMA well

identification

no. 

Degradate

2-Chloro4-isopropylamino6-amino-striazine

(μg/L)

(04040)

3,4-

Dichloroaniline

(μg/L)

(61625)

2-Chloro-6-

ethylamino4-amino-striazine

(μg/L)

(04038)

3-(4-Chlorophenyl)-1-

methyl urea

(μg/L)

(61692)

Fipronil

sulfide

(μg/L)

(62167)

2-Hydroxy4-isopropylamino-6-

ethylaminos-triazine

(μg/L)

(50355)

Desulfinyl

fipronil

(μg/L)

(62170)

Fipronil

sulfone 

(μg/L)

(62168)

Threshold type

Threshold level

LRL 0.006 0.0045 0.08 0.036 0.013 0.032 0.012 0.016

Understanding wells (n = 16 wells)

ULASFU-01 E0.011 — nc nc — nc — —

ULASFU-02 E0.009 — nc nc — nc — —

ULASFU-03 E0.012 — — — — — — —

ULASFU-04 E0.014 E0.013 E0.02 — — — — —

ULASFU-05 E0.005 — nc nc — nc — —

ULASFU-06 E0.015 E0.005 E0.03 — — — — —

ULASGU-01 E0.010 — E0.02 — — — — —

ULASGU-02 E0.005 — E0.02 — — — — —

ULASGU-03 nc nc nc nc nc nc nc nc

ULASGU-04 E0.005 — — — — — — —

ULASGU-06 E0.004 — — — — — — —

ULASGU-07 — — — — — — — —

ULASGU-09 E0.004 — — — — — — —

ULASGU-10 E0.006 E0.003 — E0.01 E0.006 0.035 E0.005 E0.006

ULASGU-11 E0.007 — — — — — — —
50 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 6. Pesticides and pesticide degradates detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 51 wells were analyzed on schedule 2003, and 24 wells on schedule 2060, but only samples with detections are listed. GAMA well 

identification no: ULASF, San Fernando study area grid well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding 

well; ULASGU, San Gabriel study area understanding well. Threshold type: 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; HAL-US, U.S. Environmental Protection 

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

Health maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific does at a risk factor of 10E—5. Abbreviations: GAMA, 

Groundwater Ambient Monitoring and Assessment; LRL, laboratory reporting level; E, estimated; nc, not collected or not computed; μg/L, microgram per liter; 

—, not detected]

GAMA well

identification

no. 

Herbicide

Simazine

(μg/L)

(04035)

Atrazine

(μg/L)

(39632)

Prometon 

(μg/L)

(04037)

Tebuthiuron

(μg/L)

(82670)

Diuron

(μg/L)

(49300)

Hexazinone

(μg/L)

(04025)

Bromacil

(μg/L)

(04029)

Metolachlor

(μg/L)

(39415)

Diphenamid

(μg/L)

(04033)

Threshold type MCL-US MCL-CA HAL-US HAL-US RSD5-US HAL-US HAL-US HAL-US HAL-US

Threshold level 4 1 100 500 20 400 70 700 200

LRL 0.05 0.007 0.01 0.016 0.015 0.0129 0.0018 0.006 0.01

Understanding wells (n = 16 wells)

ULASFU-01 0.013 0.015 — — nc — nc — nc

ULASFU-02 0.012 0.009 — 0.03 nc — nc — nc

ULASFU-03 0.012 0.014 E0.01 E0.04 — — — — —

ULASFU-04 0.067 0.015 — E0.01 0.05 — — E0.004 —

ULASFU-05 0.015 E0.005 — 0.04 nc — nc — nc

ULASFU-06 0.042 0.021 — — 0.05 — — — —

ULASGU-01 0.007 0.011 — — — — — — 0.01

ULASGU-02 0.031 — — — — — — — —

ULASGU-03 nc nc nc nc nc nc nc nc nc

ULASGU-04 0.008 E0.007 — 0.02 — — — E0.005 —

ULASGU-06 0.009 E0.004 E0.01 — — — — — 0.02

ULASGU-07 — E0.004 — — — — — — —

ULASGU-09 0.007 E0.006 — — — — — — —

ULASGU-10 0.051 0.008 0.01 — 0.10 — — — —

ULASGU-11 0.014 E0.007 0.04 — — — — — —
Tables 51

Table 6. Pesticides and pesticide degradates detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[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. 

Samples from all 51 wells were analyzed on schedule 2003, and 24 wells on schedule 2060, but only samples with detections are listed. GAMA well 

identification no: ULASF, San Fernando study area grid well; ULASG, San Gabriel study area grid well; ULASFU, San Fernando study area understanding 

well; ULASGU, San Gabriel study area understanding well. Threshold type: 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; HAL-US, U.S. Environmental Protection 

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

Health maximum contaminant level; RSD5-US, U.S. Environmental Protection Agency risk specific does at a risk factor of 10E—5. Abbreviations: GAMA, 

Groundwater Ambient Monitoring and Assessment; LRL, laboratory reporting level; E, estimated value; nc, not collected or not computed; μg/L, microgram per 

liter; —, not detected]

GAMA well

identification

no. 

Herbicide Fungicide Insecticide

Pesticide 

detections 

per well

Imazethapyr

(μg/L)

(50407)

Sulfometuron

(μg/L)

(50337)

Metalaxyl 

(μg/L)

(61596)

Myclo

butanil

(μg/L)

(61599)

Fipronil

(μg/L)

(62166)

Threshold type

Threshold level

LRL 0.038 0.038 0.00051 0.008 0.016

Understanding wells (n = 16 wells)

ULASFU-01 nc nc — — — 3

ULASFU-02 nc nc — — — 4

ULASFU-03 — — — — — 5

ULASFU-04 — — — — — 8

ULASFU-05 nc nc — — — 4

ULASFU-06 — — — — — 6

ULASGU-01 — — — — — 5

ULASGU-02 — — — — — 3

ULASGU-03 nc nc nc nc nc —

ULASGU-04 — — E0.004 — — 6

ULASGU-06 — — — — — 5

ULASGU-07 — — — — — 1

ULASGU-09 — — — — — 3

ULASGU-10 — 0.064 — — E0.008 13

ULASGU-11 — — — — — 4

1

Frequency of detection of at least one pesticide or pesticide degradate in the grid wells.
52 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

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

1,2,3-trichloropropane (1,2,3-TCP), and 1,4-dioxane in the ground-water samples collected in the 

San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, 

California, May to July 2005.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey (USGS) parameter 

code used to uniquely identify a specific constituent or property. The laboratory entity code for the Montgomery 

Watson Harza Laboratory in the USGS National Water Information System (NWIS) is CA-MWHL. Samples 

from 24 intermediate and slow wells were analyzed; only wells with at least one detection are listed. GAMA well 

identification no.: ULASF, San Fernando study area grid well; ULASFU, San Fernando study area understanding 

well; ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area understanding well. Threshold 

type: NL-CA, California Department of Public Health notification level. Abbreviations: GAMA, Ground water 

Ambient Monitoring and Assessment; MRL, method reporting limit; μg/L, microgram per liter; *, indicates value 

equal to or above threshold level; —, not detected]

GAMA well 

identification no. 

Perchlorate

(μg/L)

(61209)

N-nitrosodimethylamine

(NMDA)

(μg/L)

(34438)

 1,2,3-

trichloropropane

(μg/L)

(77443)

1,4-dioxane

(μg/L)

(81582)

Threshold type NL-CA NL-CA NL-CA NL-CA

Threshold level 6 0.01 0.005 3

MRL 0.5 0.002 0.005 2

ULASF-12 2.3 — — —

ULASFU-03 2.7 — — —

ULASFU-04 2.0 — — —

ULASFU-06 3.1 — — —

ULASG-06 — 0.0044 — —

ULASG-08 3.8 — — —

ULASG-11 2.5 — — —

ULASG-14 — — * 0.005 —

ULASG-16 0.77 — — —

ULASGU-01 4.1 * 0.061 — —

ULASGU-02 1.7 — — —

ULASGU-07 0.76 — — —
Tables 53

Table 8. Nutrients and dissolved organic carbon in samples collected for the San Fernando–San Gabriel Groundwater 

Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a 

specific constituent or property. Samples from 24 intermediate and slow wells were analyzed; only wells with at least one detection are listed. GAMA 

well identification no.: ULASF, San Fernando study area grid well; ULASFU, San Fernando study area understanding well; ULASG, San Gabriel 

study area grid well; ULASGU, San Gabriel study area understanding well. Threshold type: 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; 

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. Abbreviations: GAMA, Ground water Ambient 

Monitoring and Assessment; LRL, laboratory reporting level; E, estimated value; V, analyte detected in sample and an associated blank, thus data 

are not included in ground-water quality assessment; mg/L, milligram per liter; na, not available; *, indicates value above threshold level; —, not 

detected]

GAMA well 

identification no. 

Ammonia, 

as nitrogen

(mg/L)

(00608)

Nitrite plus

nitrate, as

nitrogen

(mg/L)

(00631)

 Nitrite,

as nitrogen

(mg/L)

(00613)

Total nitrogen

(nitrate + nitrite 

+ ammonia + 

organic-nitrogen) 

as nitrogen

(mg/L)

(62854)

Phosphorus,

as orthophosphate

(mg/L)

(00671)

Dissolved

organic carbon

(DOC)

(mg/L)

(00681)

Threshold type HAL-US MCL-US MCL-US na na na

Threshold level 25 10 1 na na na

LRL 0.010 0.060 0.008 0.06 0.006 0.33

ULASF-08 — 3.02 E0.006 3.06 0.015 V0.3

ULASF-09 — 9.74 — 1

 9.61 0.024 V1.0

ULASF-10 — 1.90 — 1

 1.83 0.022 V0.2

ULASF-12 — 8.98 — 1

 8.37 0.046 nc

ULASFU-03 — 8.70 — 8.73 0.075 V0.5

ULASFU-04 — 2.97 — 3.06 0.051 V0.5

ULASFU-06 — 3.05 — 3.30 0.037 V0.4

ULASG-05 — 0.66 — 1

 0.65 0.040 nc

ULASG-06 — 1.91 — 2.03 0.008 V0.7

ULASG-08 — *10.3 — 10.5 0.018 V0.4

ULASG-11 — 5.00 — 1

 4.91 0.020 nc

ULASG-14 — 1.09 — 1

 1.08 E0.005 V0.2

ULASG-15 — 0.79 — 0.85 E0.003 V0.6

ULASG-16 — 3.59 — 3.69 0.036 V0.4

ULASGU-01 — 8.51 — 8.67 0.008 nc

ULASGU-02 — 6.06 — 1

 5.84 0.019 V0.8

ULASGU-04 — 1.47 — 1

 1.41 0.031 V0.3

ULASGU-05 — 3.64 — 1

 3.63 0.046 V0.3

ULASGU-06 — 5.80 — 1

 5.66 0.022 nc

ULASGU-07 — 2.56 — 2.67 0.012 V0.3

ULASGU-08 — 1.17 — 1.20 0.048 nc

ULASGU-09 — 0.54 — 0.56 0.006 V0.4

ULASGU-10 — 2.05 — 1

 2.00 0.017 nc

ULASGU-11 — 0.97 — 0.98 0.006 V0.5

1

Total nitrogen in these samples is less than the sum of the filtered nitrogen analytes, but falls within the U.S. Geological Survey National Water 

Quality Laboratory acceptance criteria of a 10-percent relative percent difference.
54 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 9. Major and minor ions and total dissolved solids detected in samples collected for the San Fernando–San Gabriel Groundwater 

Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[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 24 intermediate and slow wells were analyzed. GAMA well identification no.: ULASF, San Fernando study area grid 

well; ULASFU, San Fernando study area understanding well; ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; MCL-CA, California Department of Public Healtlh maximum contaminant level; 

SMCL-CA, California Department of Public Health secondary maximum contaminant level. The SMCL-CA for chloride, sulfate, and total dissolved solids 

have recommended and upper threshold values. The upper value is shown in parentheses. Abbreviations: GAMA, Ground water Ambient Monitoring and 

Assessment; LRL, laboratory reporting level; E, estimated value; mg/L, milligram per liter; *, indicates value above threshold level; —, not detected]

GAMA well 

identification 

no. 

Calcium

(mg/L)

(00915)

Magnesium

(mg/L)

(00925)

 Potassium

(mg/L)

(00935)

Sodium

(mg/L)

(00930)

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 

(residue on 

evaporation) 

(mg/L)

(70300)

Threshold type na na na na na SMCL-CA MCL-CA na na SMCL-CA SMCL-CA

Threshold level na na na na na 250 (500) 2 na na 250 (500) 500 (1,000)

LRL 0.02 0.008 0.16 0.2 0.02 0.2 0.1 0.002 0.04 0.18 10

ULASF_08 76.8 19.4 4.26 52.0 0.22 44.2 0.5 0.034 24.7 122 490

ULASF_09 113 41.9 3.44 44.2 0.23 111 0.2 0.005 45.6 166 * 702

ULASF_10 63.3 14.3 3.88 68.8 0.31 58.5 0.4 0.055 24.3 101 454

ULASF_12 94.2 34.4 2.42 39.5 0.28 66.1 0.3 E0.002 39.7 103 * 549

ULASFU_03 96.0 36.6 2.90 54.0 0.35 75.1 0.3 0.003 40.8 121 * 608

ULASFU_04 81.7 21.3 3.77 27.4 0.13 16.1 0.5 E0.001 28.7 73.3 394

ULASFU_06 81.0 18.6 4.16 24.3 0.10 16.7 0.3 E0.002 24.7 91.7 383

ULASG_05 52.7 12.4 3.00 19.1 0.02 12.1 0.5 — 28.0 25.7 272

ULASG_06 96.5 19.2 5.39 50.4 0.20 82.6 0.3 0.014 22.7 116 * 543

ULASG_08 65.2 20.2 2.25 35.6 0.11 40.4 0.7 E0.001 26.1 65.0 400

ULASG_11 67.5 22.0 2.32 18.6 0.08 25.9 0.6 E0.001 29.6 60.7 354

ULASG_14 58.1 13.7 4.39 28.0 0.10 29.0 0.3 — 18.3 30.1 287

ULASG_15 38.6 11.2 3.07 21.7 0.02 6.39 0.3 E0.001 14.3 17.0 199

ULASG_16 48.7 17.7 2.78 43.3 0.20 58.4 0.6 E0.001 26.2 54.1 353

ULASGU_01 52.7 6.86 1.86 35.7 0.06 16.7 0.2 — 22.5 52.4 318

ULASGU_02 98.2 35.2 3.04 41.2 0.17 62.2 0.8 0.008 33.8 108 * 599

ULASGU_04 56.5 13.0 3.49 34.3 0.06 23.3 0.4 E0.002 27.6 41.0 302

ULASGU_05 47.4 13.2 1.43 24.0 0.03 9.73 0.8 — 27.1 17.1 242

ULASGU_06 56.5 14.6 1.78 32.8 0.08 32.6 1.1 — 24.2 66.8 339

ULASGU_07 20.4 1.24 0.64 52.5 0.05 13.1 1.1 0.007 15.3 33.1 222

ULASGU_08 40.4 10.5 1.03 24.0 0.14 6.87 0.9 — 25.2 13.5 224

ULASGU_09 64.9 13.3 3.61 10.6 0.16 10.4 0.3 E0.001 17.0 23.4 268

ULASGU_10 60.8 15.3 5.66 91.2 — 90.3 0.4 0.014 19.5 121 * 511

ULASGU_11 46.1 8.80 3.08 9.91 0.04 7.57 0.3 E0.001 16.2 18.3 200
Tables 55

GAMA well 

identification 

no. 

Aluminum

(μg/L)

(01106)

Antimony

(μgL)

(01095)

 Arsenic

(μg/L)

(01000)

Barium

(μg/L)

(01005)

Boron

(μg/L)

(01020)

Cadmium

(μg/L)

(01025)

Chromium

(μg/L)

(01030)

Cobalt

(μg/L)

(01035)

Copper

(μg/L)

(01040)

Iron

(μg/L)

(01046)

Lead

(μg/L)

(01049)

Threshold type MCL-CA MCL-US MCL-US MCL-CA NL-CA MCL-US MCL-CA na AL-US SMCL-CA AL-US

Threshold level 1,000 6 10 1,000 1,000 5 50 na 1,300 300 15

LRL 1.6 0.2 0.12 0.2 8 0.04 0.04 0.04 0.4 6 0.08

ULASF_08 E1.5 — 0.6 66 241 0.05 4.8 0.199 50.4 E5 0.34

ULASF_09 — — 0.5 121 123 E0.02 E0.5 0.374 4.0 E4 0.43

ULASF_10 E1.1 — 0.6 69 295 E0.03 2.4 0.098 1.2 — 0.09

ULASF_12 E1.3 — 0.6 72 87 — 48.9 00.153 32.1 — 1.07

ULASFU_03 E1.1 — 0.6 86 221 E0.04 3.3 0.197 3.2 — 0.49

ULASFU_04 E1.1 — 0.3 111 190 — E0.5 0.142 0.8 — 0.16

ULASFU_06 1.8 — 0.4 105 106 — 1.6 0.156 2.0 — 0.25

ULASG_05 E1.2 E0.15 2.7 109 38 E0.02 6.0 E0.339 2.0 — 0.11

ULASG_06 2.3 E0.18 1.5 117 163 0.04 1.8 1.78 3.2 — 0.67

ULASG_08 E1.4 E0.14 0.7 41 128 — 5.1 0.127 3.6 — 0.55

ULASG_11 E0.9 E0.18 0.8 36 87 — — 0.109 4.4 E5 2.80

ULASG_14 E1.0 0.38 3.1 114 78 — — 0.102 1.3 6 0.57

ULASG_15 E1.5 0.46 2.5 84 78 — — 0.081 1.5 — 0.10

ULASG_16 E0.8 — 0.6 74 183 E0.03 — 0.09 4.3 23 1.23

ULASGU_01 E0.9 — 1.4 46 52 — 2.4 0.086 1.5 — 0.41

ULASGU_02 — — 0.4 121 66 — — 0.194 3.1 — 0.42

ULASGU_04 E0.8 E0.16 2.6 127 57 — 5.5 00.196 0.9 — 1.16

ULASGU_05 E1.4 — 0.6 19 269 — 8.8 0.085 2.2 — 0.56

ULASGU_06 1.8 0.25 0.8 31 98 0.04 5.7 0.097 1.5 7 0.58

ULASGU_07 5.1 E0.18 3.4 11 153 E0.03 4.6 0.039 0.5 — 0.15

ULASGU_08 — — 0.8 22 206 — 8.6 0.043 1.8 E3 0.34

ULASGU_09 E1.1 0.22 2.0 154 64 — 1.0 0.102 1.0 E5 0.37

ULASGU_10 — E0.18 1.9 53 252 0.04 — 2.88 3.4 7 0.11

ULASGU_11 E1.5 0.28 2.2 98 63 — — .093 1.4 — 0.39

Table 10. Trace elements detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit, California, May to July 2005.

[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 24 intermediate and slow wells were analyzed. GAMA well identification no.: ULASF, San Fernando study area grid well; 

ULASFU, San Fernando study area understanding well; ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area understanding well. 

Threshold type: 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; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. 

Environmental Protection Agency maximum contaminant level; AL-US, U.S. Environmental Protection Agency action level; NL-CA, California Department 

of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Abbreviations: GAMA. 

Groundwater Ambient Monitoring and Assessment; LRL, laboratory reporting level; E, estimated value; μg/L, microgram per liter; *, indicates value above 

threshold level; —, not detected]
56 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 10. Trace elements detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit, California, May to July 2005.—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 24 intermediate and slow wells were analyzed. GAMA well identification no.: ULASF, San Fernando study area grid well; 

ULASFU, San Fernando study area understanding well; ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area understanding well. 

Threshold type: 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; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. 

Environmental Protection Agency maximum contaminant level; AL-US, U.S. Environmental Protection Agency action level; NL-CA, California Department 

of Public Health notification level; SMCL-CA, California Department of Public Health secondary maximum contaminant level. Abbreviations: GAMA. 

Groundwater Ambient Monitoring and Assessment; LRL, laboratory reporting level; E, estimated value; μg/L, microgram per liter; *, indicates value above 

threshold level; —, not detected]

GAMA well 

identification 

no. 

Lithium

(μg/L)

(01130)

Manganese

(μgL)

(01056)

Mercury

(μg/L)

(71890)

Molybdenum

(μg/L)

(01060)

Nickel

(μg/L)

(01065)

Selenium

(μg/L)

(01145)

Strontium

(μg/L)

(01080)

Tungsten

(μg/L)

(01155)

Uranium

(μg/L)

(22703)

Vanadium

(μg/L)

(01085)

Zinc

(μg/L)

(01090)

Threshold type na SMCL-CA MCL-US HAL-US MCL-CA MCL-US HAL-US na MCL-US NL-CA SMCL-CA

Threshold level na 50 2 40 100 50 4,000 na 30 50 5,000

LRL 0.6 0.2 0.01 0.4 0.06 0.08 0.4 0.06 0.04 0.1 0.6

ULASF_08 3.6 9.7 — 10.2 4.11 2.4 653 — 6.12 5.3 4.1

ULASF_09 3.4 E0.1 E0.007 4.2 5.74 0.8 925 — 9.25 4.2 3.7

ULASF_10 3.5 1.1 0.019 13.9 1.71 0.7 559 — 3.12 7.5 E0.4

ULASF_12 2.4 E0.1 — 2.8 2.45 0.7 550 — 3.23 6.6 6.8

ULASFU_03 2.8 E0.1 — 2.4 3.68 1.4 590 — 4.53 6.6 1.9

ULASFU_04 1.8 — — 7.2 2.99 0.7 594 — 5.15 3.7 1.0

ULASFU_06 0.8 E0.2 E0.010 3.4 2.71 2.4 526 — 4.28 3.7 2.7

ULASG_05 1.4 E0.1 — 5.8 3.26 0.5 281 — 2.63 5.0 2.2

ULASG_06 1.3 0.3 — 1.3 4.54 E0.3 646 — 3.47 2.3 8.8

ULASG_08 3.7 0.8 0.383 7.2 2.62 0.5 474 — 13.0 6.7 3.3

ULASG_11 0.6 E0.1 0.020 5.3 2.31 0.4 465 — 12.4 3.3 11.2

ULASG_14 E0.3 1.6 — 1.5 9.92 0.5 559 — 2.16 2.0 8.7

ULASG_15 2.4 — — 2.2 1.81 E0.3 336 — 1.48 1.6 2.6

ULASG_16 0.6 2.7 — 3.6 2.05 1.4 265 — 1.98 4.3 7.2

ULASGU_01 1.7 E0.1 — 1.9 1.53 0.5 395 — 1.8 7.1 9.7

ULASGU_02 4.8 E0.2 0.012 2.2 3.62 E0.2 563 — 2.12 2.8 22.8

ULASGU_04 1.7 — — 4.6 2.29 0.5 333 — 1.75 5.5 1.2

ULASGU_05 E0.6 E0.1 — 5.0 2.36 E0.4 273 — 2.50 5.6 3.5

ULASGU_06 E0.5 2.0 — 15.1 1.92 E0.4 393 — 15.2 10.9 5.3

ULASGU_07 0.6 — E0.005 11.0 0.72 — 179 2.9 2.60 24.5 0.7

ULASGU_08 0.7 0.7 — 3.3 1.75 E0.4 248 — 1.64 5.1 5.2

ULASGU_09 E0.5 E0.1 — 1.6 2.46 — 606 — 3.04 1.8 0.9

ULASGU_10 3.0 34.8 — 4.3 5.71 1.7 420 — 1.36 2.3 2.8

ULASGU_11 E0.4 — — 1.7 1.38 E0.3 420 — 1.68 2.4 1.7
Tables 57

Table 11. Inorganic arsenic and iron species detected in 

samples collected for the San Fernando–San Gabriel Groundwater 

Ambient Monitoring and Assessment (GAMA) study unit, 

California, May to July 2005.

[The five-digit number in parentheses below the constituent name is the U.S. 

Geological Survey (USGS) parameter code is used to uniquely identify a 

specific constituent or property. The laboratory entity code for the USGS 

Trace Metals Laboratory in the USGS National Water Information System 

(NWIS) is USGSTMCO. Samples from 24 intermediate and slow wells 

were analyzed; only wells with at least one detection are listed. GAMA well 

identification no.: ULASF, San Fernando study area grid well; ULASFU, 

San Fernando study area understanding well; ULASG, San Gabriel study area 

grid well; ULASGU, San Gabriel study area understanding well. Threshold 

type: 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; MCL-CA, California 

Department of Public Health maximum contaminant level; MCL-US, U.S. 

Environmental Protection Agency maximum contaminant level; SMCL-CA, 

California Department of Public Health secondary maximum contaminant 

level. Abbreviations: GAMA, Ground water Ambient Monitoring and 

Assessment; MDL, method detection limit; na, not available; μg/L, microgram 

per liter; —, not detected]

GAMA well 

identification no. 

Arsenic

(μg/L)

(99033)

Arsenic III

(μgL)

(99034)

 Iron

(μg/L)

(01046)

Iron III

(μg/L)

(01047)

Threshold type MCL-US na SMCL-CA na

Threshold level 10 na 300 na

MDL 0.5222

ULASF_08——4—

ULASF_09————

ULASF_10————

ULASF_12————

ULASFU_03————

ULASFU_04————

ULASFU_06————

ULASG_05 2.2———

ULASG_06 1.5———

ULASG_08 0.9—3—

ULASG_11 0.6—3—

ULASG_14 2.9—4—

ULASG_15 2.1———

ULASG_16 0.6— 23 14

ULASGU_01 1.0—2—

ULASGU_02————

ULASGU_04 1.5———

ULASGU_05————

ULASGU_06 0.9—5—

ULASGU_07 2.6———

ULASGU_08 0.5

———

ULASGU_09 1.7———

ULASGU_10 1.7—43

ULASGU_11 1.9———
58 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 12. Chromium species detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit, California, May to July 2005.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a specific 

constituent or property. The laboratory entity code for the USGS Trace Metals Laboratory in the USGS National Water Information System (NWIS) is 

USGSTMCO. Samples from 52 wells were analyzed for chromium. GAMA well identification no.: ULASF, San Fernando study area grid well; ULASFU, San 

Fernando study area understanding well; ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area understanding well. Threshold type:

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

Agency maximum contaminant level. Abbreviations: GAMA, Ground water Ambient Monitoring and Assessment; MDL, method detection limit; μg/L, 

micrograms per liter; *, indicates value above threshold level; V, analyte detected in sample and an associated blank, thus data are not included in ground-water 

quality assessment; —, not detected]

GAMA well 

identification no. 

Chromium

(μg/L)

(01030)

Chromium (VI)

(μgL)

(01032)

Threshold type MCL-CA na

Threshold level 50 na

MDL 1 1

Grid wells (n = 35 wells)

ULASF_01 11.5 11.7

ULASF_02 12.7 13.4

ULASF_03 13.0 13.1

ULASF_04 9.3 9.8

ULASF_05 15.8 13.3

ULASF_06 17.9 16.5

ULASF_07 14.7 16.9

ULASF_08 18.4 13.2

ULASF_09 11.8 11.0

ULASF_10 V2.6 V2.2

ULASF_11 17.7 11.9

ULASF_12 * 62.2 58.9

ULASG_01 22.1 20.0

ULASG_02 17.6 18.3

ULASG_03 22.3 17.5

ULASG_04 1.3 1.9

ULASG_05 6.0 5.4

ULASG_06 V1.9 V1.3

ULASG_07 2.9 2.1

ULASG_08 V7.2 V5.2

ULASG_09 1.0 —

ULASG_10 5.0 3.8

ULASG_12 1.7 1.5

ULASG_13 3.2 2.9

ULASG_15 1.9 2.1

ULASG_16 2.4 2.1

ULASG_17 2.5 1.8

ULASG_18 2.8 2.4

ULASG_19 17.3 27.2

ULASG_20 — 1.9

ULASG_21 5.7 5.5

ULASG_22 8.5 8.2

ULASG_23 5.6 6.0

Number of detections 29 29

Detection frequency

(percent)

91 91

GAMA well 

identification no. 

Chromium

(μg/L)

(01030)

Chromium (VI)

(μgL)

(01032)

Threshold type MCL-CA na

Threshold level 50 na

MDL 1 1

Understanding wells (n = 17 wells)

ULASFU_01 12.8 11.4

ULASFU_02 14.1 13.4

ULASFU_03 V3.5 V3.9

ULASFU_04 V1.1 V—

ULASFU_05 1.7 1.8

ULASFU_06 3.2 4.1

ULASGU_01 23.5 18.4

ULASGU_04 V6.5 V5.2

ULASGU_05 11.1 10.9

ULASGU_06 4.8 5.3

ULASGU_07 7.7 6.8

ULASGU_08 11.9 11.5

ULASGU_09 2.3 2.0

ULASGU_10 4.9 5.4

ULASGU_11 2.3 1.9
Tables 59

Table 13. Hydrogen and oxygen isotope ratios for water, and tritium activities, in samples collected for the San Fernando–San Gabriel 

Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a specific 

constituent or property. Samples from all 52 wells were analyzed for stable isotopes of water; samples from 51 wells were analyzed for tritium. 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 well identification No.: ULASF, San Fernando study area grid well; ULASFU, San Fernando study area understanding well; 

ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area understanding well. Threshold type: 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; 

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

level. Laboratory: Isotopes analyzed at USGS Stable Isotope Laboratory, Reston, Virginia (USGSSIVA); Tritium analyzed at USGS Stable Isotope and Tritium 

Laboratory, Menlo Park, California (USGSH3CA). Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; pCi/L, picocuries per liter; 

na, not available; nc, sample not collected; —, not detected]

GAMA well 

identification no. 

δ2

H

(per mil)

(82082

δ18O

(per mil)

(82085)

Tritium

(pCi/L)

(07000)

Threshold type na na MCL-CA

Threshold level na na 20,000

Grid wells (n = 35 wells)

ULASF_01 –44.2 –6.80 4.8

ULASF_02 –54.8 –8.25 5.1

ULASF_03 –52.9 –8.00 3.5

ULASF_04 –51.7 –8.02 16.3

ULASF_05 –41.5 –6.71 —

ULASF_06 –49.2 –7.14 3.5

ULASF_07 –54.7 –7.90 14.1

ULASF_08 –52.4 –7.67 3.2

ULASF_09 –54.5 –7.61 20.5

ULASF_10 –51.6 –7.66 3.8

ULASF_11 –53.4 –8.30 —

ULASF_12 –46.3 –6.71 7.0

ULASG_01 –45.4 –6.45 8.0

ULASG_02 –56.2 –8.63 9.9

ULASG_03 –59.9 –8.96 10.9

ULASG_04 –48.0 –6.41 18.6

ULASG_05 –51.5 –7.81 —

ULASG_06 –59.1 –8.36 19.5

ULASG_07 –49.6 –7.57 17.0

ULASG_08 –47.6 –7.20 6.1

ULASG_09 –61.2 –9.27 12.8

ULASG_10 –43.6 –6.52 5.1

ULASG_11 –48.9 –7.57 15.0

ULASG_12 –50.6 –6.94 13.8

ULASG_13 –47.0 –7.28 —

ULASG_14 –59.4 –8.42 13.4

ULASG_15 –60.5 –9.22 14.7

ULASG_16 –61.4 –8.57 12.2

ULASG_17 –50.8 –7.68 9.0

ULASG_18 –47.7 –7.46 10.9

ULASG_19 –47.0 –7.34 4.5

ULASG_20 –59.2 –8.27 13.4

ULASG_21 –45.4 –7.00 5.1

ULASG_22 –45.9 –7.29 7.0

ULASG_23 –60.8 –9.27 14.7

Number of detections 31

Detection frequency

(percent)

89

GAMA well 

identification No. 

δ2

H

(per mil)

(82082

δ18O

(per mil)

(82085)

Tritium

(pCi/L)

(07000)

Threshold type na na MCL-CA

Threshold level na na 20,000

Understanding wells (n = 17 wells)

ULASFU_01 –50.1 –7.70 13.1

ULASFU_02 –50.4 –7.81 18.6

ULASFU_03 –47.4 –7.01 16.0

ULASFU_04 –54.6 –8.05 10.9

ULASFU_05 –54.8 –7.57 15.4

ULASFU_06 –54.3 –8.01 6.7

ULASGU_01 –60.2 –9.13 7.7

ULASGU_02 –47.7 –7.26 14.1

ULASGU_03 –59.2 –8.62 nc

ULASGU_04 –51.8 –8.06 2.9

ULASGU_05 –44.1 –7.09 —

ULASGU_06 –47.3 –7.33 9.0

ULASGU_07 –47.1 –7.11 1.0

ULASGU_08 –46.0 –7.38 —

ULASGU_09 –58.0 –8.53 13.4

ULASGU_10 –55.6 –7.78 22.7

ULASGU_11 –61.3 –9.00 17.0
60 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 14. Carbon isotopes in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit, California, May to July 2005.

[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 17 slow wells were analyzed for the 

isotopes of carbon. 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. Laboratory: carbon 

stable isotopes analyzed at University of Waterloo (contract laboratory) 

(CAN-UWIL); Carbon-14 analyzed at University of Arizona, Accelerator 

Mass Spectrometry Laboratory (contract laboratory) (AZ-UAMSL). GAMA 

well identification no.: ULASF, San Fernando study area grid well; 

ULASFU, San Fernando study area understanding well; ULASG, San Gabriel 

study area grid well; ULASGU, San Gabriel study area understanding well. 

Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; 

na, not available]

GAMA well 

identification no. 

δ13C

(per mil)

(82081)

Carbon-14

(percent modern)

(49933)

Threshold type na na

Threshold level na na

ULASF_08 –13.8 78.4

ULASF_09 –16.0 99.5

ULASF_10 –14.9 79.1

ULASFU_03 –16.7 104

ULASFU_04 –14.3 104

ULASFU_06 –12.4 102

ULASG_06 –13.2 91.9

ULASG_08 –14.9 93.0

ULASG_14 –12.7 97.1

ULASG_15 –11.4 96.4

ULASG_16 –15.2 103

ULASGU_02 –15.3 105

ULASGU_04 –11.8 83.2

ULASGU_05 –13.2 85.8

ULASGU_07 –14.6 72.4

ULASGU_09 –13.2 98.9

ULASGU_11 –11.5 99.9
Tables 61

Table 15. Results for analyses of noble gases and tritium in samples collected for the San Fernando–San Gabriel Groundwater 

Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey (USGS) parameter code used to uniquely identify a specific 

constituent or property. The laboratory entity code for the Lawrence Livermore National Laboratory in the USGS National Water Information System (NWIS) 

is CA-LLNL. Samples collected from 24 intermediate and slow wells were analyzed. GAMA well identification no.: ULASF, San Fernando study area grid 

well; ULASFU, San Fernando study area understanding well; ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area understanding well. 

Threshold type: 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; MCL-CA, California Department of Public Health maximum contaminant level; MCL-US, U.S. 

Environmental Protection Agency maximum contaminant level. Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; cm3 STP g-1, cubic 

centimeters at standard temperature and pressure per gram of water; na, not available; nc, sample not collected; pCi/L, picocuries per liter]

GAMA well 

identification no. 

Collection

date

Tritium

(pCi/L)

(07000)

Tritium

measurement

uncertainty

(±)

(pCi/L)

(07001)

Dissolved

gas analysis

date

Helium-3/

helium-4

(atom 

ratio)

(61040)

Helium-4

(85561)

Neon

(61046)

Argon

(85563)

Krypton

(85565)

Xenon

(85567)

(cm3

 STP g–1)

× 10–6 ×10–7 ×10–7 × 10–4 ×10–7 ×10–8

Threshold type MCL-CA na na na na na na na na na

Threshold level 20,000 na na na na na na na na na

ULASF_08 06-06-05 3.8 0.2 08-10-05 0.73 3.00 4.28 4.83 0.96 1.19

ULASF_09 06-07-05 20.9 0.8 08-10-05 1.29 0.66 2.51 3.66 0.79 1.02

ULASF_10 06-08-05 4.7 0.3 08-10-05 0.31 7.32 4.59 4.93 0.99 1.24

ULASF_12 06-09-05 7.0 0.5 08-10-05 1.07 1.31 4.03 4.98 0.97 1.16

ULASFU_03 06-09-05 16.2 0.7 08-10-05 1.28 0.76 2.37 3.55 0.77 1.01

ULASFU_04 06-16-05 11.0 0.5 08-11-05 1.43 1.73 6.56 6.31 1.17 1.37

ULASFU_06 07-20-05 8.1 0.4 08-18-05 1.49 1.07 4.20 4.97 0.99 1.21

ULASG_05 06-14-05 1.0 0.2 08-11-05 1.25 1.69 3.91 4.55 0.92 1.18

ULASG_06 06-14-05 21.4 0.8 08-11-05 1.64 0.71 2.83 3.83 0.81 1.04

ULASG_07 06-14-05 15.8 0.7 08-11-05 1.41 2.56 9.35 8.03 1.34 1.53

ULASG_08 06-15-05 nc nc 08-11-05 1.52 0.67 2.67 3.75 0.83 1.04

ULASG_14 06-20-05 16.1 0.7 08-12-05 1.37 1.57 6.55 6.65 1.21 1.43

ULASG_15 06-23-05 13.5 0.6 08-12-05 1.36 0.83 3.39 4.24 0.92 1.19

ULASG_16 07-11-05 nc nc 08-17-05 1.39 1.04 4.36 5.01 0.93 1.12

ULASGU_01 06-08-05 7.7 0.4 08-10-05 1.29 1.32 4.84 5.60 1.07 1.34

ULASGU_02 06-13-05 16.6 0.7 08-11-05 1.11 0.85 2.37 3.61 0.80 1.07

ULASGU_04 06-21-05 4.3 0.3 08-12-05 1.17 1.93 3.55 4.31 0.91 1.13

ULASGU_05 06-22-05 1.1 0.1 08-12-05 1.06 1.08 3.29 4.27 0.90 1.12

ULASGU_06 07-11-05 9.7 0.5 08-17-05 0.53 2.43 3.07 3.94 0.83 1.10

ULASGU_07 07-12-05 0.9 0.2 08-17-05 0.29 5.22 2.74 3.90 0.85 1.13

ULASGU_08 07-13-05 1.5 0.2 08-17-05 1.13 1.10 3.54 4.52 0.95 1.22

ULASGU_09 07-13-05 12.8 0.6 08-17-05 1.42 1.17 4.69 5.00 1.01 1.25

ULASGU_10 07-14-05 23.0 0.9 08-17-05 1.38 1.50 5.88 6.60 1.26 1.37

ULASGU_11 07-14-05 14.6 0.7 08-17-05 1.40 1.72 6.61 6.05 1.14 1.38
62 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table 16. Radioactive constituents detected in samples collected for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[The five-digit number in parentheses below the constituent name is the U.S. Geological Survey (USGS) parameter code used to uniquely identify 

a specific constituent or property. Samples from 17 slow wells were analyzed. GAMA well identification no.: ULASF, San Fernando study area 

grid well; ULASFU, San Fernando study area understanding well; ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area 

understanding well. Threshold type: 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; MCL-CA, California Department of Public Health maximum 

contaminant level; MCL-US, U.S. Environmental Protection Agency maximum contaminant level. The MCL-US threshold for radium is the sum 

of radium-226 and radium-228. Two MCLs have been proposed for radon-222. The proposed alternative MCL is in parenthesis. Laboratory: 

All constituents except radon-222 were analyzed at Eberline Analytical Services (contract laboratory) (CA-EBERL); Radon-222 was analyzed at 

the USGS National Water Quality Laboratory (USGSNWQL). Abbreviations: GAMA, Groundwater Ambient Monitoring and Assessment; E, 

estimated value; V, analyte detected in sample and an associated blank, thus data are not included in ground-water quality assessment; nc, sample not 

collected; pCi/L, picocuries per liter; *, indicates value above threshold level; <, less than]

GAMA well 

identification no. 

Gross-alpha

radioactivity

(pCi/L)

Gross-beta

radioactivity

(pCi/L) Radium-226

(pCi/L)

(09511)

Radium-228

(pCi/L)

(81366)

Radon-222

(pCi/L)

(82303) 72-hour 

count

(62636)

30-day 

count

(62639)

72-hour 

count

(62642)

30-day 

count

(62645)

Threshold type MCL-US MCL-US MCL-CA MCL-CA MCL-US MCL-US Proposed 

MCL-US

Threshold level 15 15 50 50 5 5 300, (4,000)

ULASF_08 E4.40 <2.40 6.00 5.90 0.089 E0.41 * 360

ULASF_09 11.80 11.50 5.53 11.50 0.146 0.58 * 660

ULASF_10 E2.08 <2.00 4.19 4.81 E0.052 <0.44 * 330

ULASFU_03 3.75 E0.88 E2.84 4.43 E0.056 <0.44 * 500

ULASFU_04 4.92 E3.18 4.46 5.59 0.075 <0.50 * 440

ULASFU_06 3.46 E2.48 5.38 4.45 0.144 <0.55 * 410

ULASG_06 E2.77 <2.30 6.67 6.60 E0.076 <0.51 nc

ULASG_08 12.00 12.70 4.58 9.10 0.091 <0.62 * 840

ULASG_14 E0.91 E1.43 4.83 4.95 E0.064 <0.46 * 380

ULASG_15 2.64 E0.98 3.88 3.19 V0.023 E0.28 20

ULASG_16 E2.02 E1.24 E3.14 E3.49 0.086 <0.42 * 930

ULASGU_02 E2.50 E1.04 E3.97 4.21 0.094 V0.23 * 460

ULASGU_04 E2.69 E1.98 3.91 3.58 E0.053 E0.29 260

ULASGU_05 E2.36 E2.82 E1.58 E2.21 E0.046 E0.38 * 360

ULASGU_07 E2.70 E1.48 <2.40 E1.43 V0.016 <0.42 * 490

ULASGU_09 E1.82 E1.77 E2.60 4.13 0.068 <0.42 * 350

ULASGU_11 <1.90 E0.58 E4.20 4.42 0.077 <0.53 * 360
Tables 63

Table 17. Microbial indicators detected in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, May to July 2005.

[The five-digit number in parentheses below the constituent name is the U.S. Geological 

Survey (USGS) parameter code used to uniquely identify a specific constituent or property. 

Samples from 17 slow wells were analyzed. GAMA well identification no.: ULASF, San 

Fernando study area grid well; ULASFU, San Fernando study area understanding well; 

ULASG, San Gabriel study area grid well; ULASGU, San Gabriel study area understanding 

well. Threshold type: 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; MCL-CA, California Department of Public 

Health maximum contaminant level; MCL-US, U.S. Environmental Protection Agency 

maximum contaminant level; TT-US, U.S. Environmental Protection Agency treatment 

technique. Laboratory: F-specific and somatic coliphage were analyzed by the USGS 

Ohio Microbiology Laboratory (laboratory entity code USGSOHML); E. coli and total 

coliform colonies were analyzed in the field. Abbreviations: GAMA, Groundwater Ambient 

Monitoring and Assessment; E, estimated value; mL, milliliter; nc, not collected; —, not 

detected]

GAMA well 

identification no.

F-specific

coliphage

(99335)

Somatic

coliphage

(99332)

E.-coli

colonies/

100 mL

(90901)

Total 

coliforms

colonies/

100 mL

(90900)

Threshold type TT-US TT-US TT-US MCL-US

Threshold level 99.9 percent 

killed/

inactive

99.9 percent 

killed/

inactive

No fecal 

coliforms are 

allowed

5 percent of 

samples per 

month

ULASFU_06—— nc nc

ULASG_08 nc nc——

ULASGU_11 —– —–— E5
64 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Appendix 

This appendix includes discussions of the methods 

used to collect and analyze ground-water samples and report 

the data for SFSG. These methods were selected to obtain 

representative samples of the ground water from each well and 

to minimize the potential for contamination of the samples or 

bias in the data. Procedures used to collect and assess qualitycontrol data, and the results of the quality-control assessments 

also are discussed.

Sample Collection and Analysis

Ground-water samples were collected using standard and 

modified protocols in the USGS National Field Manual (U.S. 

Geological Survey, variously dated) and by Koterba and others 

(1995), and protocols described by Weiss (1968); Shelton 

and others (2001); Ball and McClesky (2003a,b); and Wright 

and others (2005). Prior to sampling, each well was pumped 

continuously o purge at least three casing-volumes of water 

from the well (Wilde and others, 1999). Wells were sampled 

using Teflon tubing with brass and stainless-steel fittings 

attached to a sampling point on the well discharge pipe as 

close to the well as possible. The sampling point always was 

located upstream of any well-head treatment system or water 

storage tank. If a chlorinating system was attached to the well, 

the chlorinator was shut off at least 24 hours prior to purging 

and sampling the well to remove all chlorine from the system. 

For the fast and intermediate schedules (see table 1), samples 

were collected at the well head using a foot-long length 

of Teflon tubing. For the slow schedule, the samples were 

collected inside an enclosed chamber located inside a mobile 

laboratory and connected to the well head by a 10–50 ft length 

of the Teflon tubing (Lane and others, 2003). All fittings 

and lengths of tubing were cleaned between samples (Wilde, 

2004).

Field measurements were made in accordance with 

protocols in the USGS National Field Manual (Radtke and 

others, 1998a,b; Rounds and Wilde, 2001; Radtke and others, 

2003; Anderson, 2004; Radtke and others, 2004). At wells 

on the fast or intermediate schedule, SC and temperature 

were measured directly by dipping a conductivity probe 

and thermometer into a sample cup. DO was measured by a 

modified Winkler titration procedure. Sulfide (presence or 

absence of a “rotten egg” smell in the water) was determined 

by a serendipitous sniff test (J. Barbash, USGS, written 

commun., 2002). At wells on the slow schedule, ground water 

was diverted through a flow-through chamber fitted with a 

multi-probe sonde that simultaneously measures turbidity, DO, 

temperature, pH, and SC. All probes were calibrated daily. 

Measured values were recorded at 5-minute intervals, for at 

least 30 minutes, and when these values remained stable for 20 

minutes, samples for laboratory analyses were then collected. 

Field measurements and instrument calibrations were recorded 

by hand on field record sheets.

For analyses requiring filtered water, ground water was 

diverted through a 0.45-μm pore size vented capsule filter, 

a disk filter, or a baked glass-fiber filter depending on the 

protocol for the analysis (Wilde and others, 1999; 2004). 

Prior to sample collection, polyethylene sample bottles were 

pre-rinsed two times using deionized water, and then rinsed 

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).

Temperature-sensitive samples were stored on ice prior 

to and during daily shipping to the various laboratories. The 

non-temperature sensitive samples for tritium, noble gases, 

chromium species, and stable isotopes were shipped monthly, 

while samples for volatile organic compounds, pesticides, 

compounds of special interest, dissolved organic carbon, 

radium isotopes, gross alpha and beta radioactivity, and 

radon-222 samples were shipped daily. 

Detailed sampling protocols for individual analyses and 

groups of analytes are described in Koterba and others (1995) 

and the USGS National Field Manual (Wilde and others, 

1999; 2004) and in the references for analytical methods listed 

in table A1; only brief descriptions are given here. Volatile 

organic compounds (VOCs) and gasoline oxygenates and 

degradates, and 1,2,3-trichloropropane (1,2,3-TCP) samples 

were collected in 40-mL sample baked amber glass vials 

that were purged with three vial volumes of sample water 

before bottom filling to eliminate atmospheric contamination. 

Six normal (6 N) hydrochloric acid (HCl) was added as a 

preservative to the VOC samples, but not to the gasoline 

oxygenate and degradate samples, or the 1,2,3-TCP samples. 

Perchlorate samples were collected in a 125-mL polyethylene 

bottle. Tritium samples were collected by bottom filling 

two 1-L polyethylene bottles with unfiltered ground water, 

after first overfilling the bottle with three volumes of water. 

Samples for analysis of the stable isotopes of water were 

collected in 60-mL clear glass bottles filled with unfiltered 

water, sealed with a conical cap, and secured with electrical 

tape to prevent leakage and evaporation.

Pesticides and pesticide degradation products, 

1,4-Dioxane, and N-nitrosodimethylamine (NDMA) samples 

were collected in 1-L baked amber glass bottles. Pesticide 

samples were filtered through a glass-fiber membrane during 

collection, whereas the NDMA samples were filtered at the 

Montgomery Watson Harza (MWH) Laboratory prior to 

analysis. 
Appendix 65

Ground-water samples for major and minor ions, trace 

elements, alkalinity, and total dissolved solids analyses 

required filling one 250-mL polyethylene bottle with raw 

groundwater, and one 500-mL and one 250-mL polyethylene 

bottle with filtered ground water (Wilde and others, 2004). 

Filtration was achieved using a Whatman capsule filter with 

a 0.45 μm pore size. Each 250-mL filtered sample then was 

preserved with 7.5-N nitric acid. Mercury samples were 

collected by filtering ground water into 250-mL glass bottles 

and preserving each with 6-N hydrochloric acid. Samples 

for arsenic and iron species were filtered into 250-mL 

polyethylene bottles that were covered with opaque tape to 

prevent light exposure, and preserved with 6-N hydrochloric 

acid. Nutrient samples were filtered into 125-mL brown 

polyethylene bottles. Radium isotopes and gross alpha and 

beta radiation samples were filtered into 1-L polyethylene 

bottles and acidified with nitric acid. Carbon isotope samples 

were filtered and bottom filled into two 500-mL glass bottles 

that were first overfilled with three bottle volumes of ground 

water. These samples had no headspace, and were sealed with 

a conical cap to avoid atmospheric contamination. Samples for 

alkalinity titrations were collected by filtering ground water 

into 500-mL polyethylene bottles.

DOC, chromium, radon-222, dissolved gases, and 

microbial constituents were collected from the hose bib at 

the well head, regardless of the sampling schedule (fast, 

intermediate or slow). DOC was collected after rinsing the 

sampling equipment with universal blank water (Wilde 

and others, 2004). Using a 50-mL syringe and 0.45-μm 

polyethersulfone disk filter, each ground-water sample then 

was filtered into a 125-mL baked glass bottle and preserved 

with 4.5-N sulfuric acid. 

Samples for chromium species were collected from 

the hose bib at the well head using a 10-mL syringe with an 

attached 0.45-μm disk filter. After the syringe was rinsed 

thoroughly and filled with ground water, 4 mL was forced 

through the disk filter; the next 2 mL of the ground water was 

filtered slowly into a small centrifuge vial for analysis of total 

chromium. Hexavalent chromium, Cr (VI), was then collected 

by attaching a small cation exchange column to the syringe 

filter, and after conditioning the column with 2 mL of sample 

water, 2 mL was collected in a second centrifuge vial. Both 

vials were preserved with 10 μL of 7.5-N nitric acid (Ball and 

McClesky, 2003a,b).

For the collection of radon-222, a stainless steel and 

Teflon valve assembly was attached to the sampling port at 

the well head (Wilde and others, 2004). The valve was closed 

partially to create back pressure, and a 10-mL sample was 

taken through a Teflon septum on the value assembly using a 

glass syringe affixed with a stainless steel needle. The sample 

then was injected into a 25-mL vial filled partially with 

scintillation mixture (mineral oil) and shaken. The vial then 

was placed in a cardboard tube to shield it from light during 

shipping. 

Noble gases were collected in 3/8-in. copper tubes 

using reinforced nylon tubing connected to the hose bib at 

the wellhead. Ground water was flushed through the tubing 

to dislodge bubbles before flow was restricted with a back 

pressure valve. Then, clamps on either side of the copper tube 

were tightened, trapping a sample of ground water for analyses 

of noble gases (Weiss, 1968). 

Samples for analysis of microbial constituents also were 

collected at the well head (Bushon, 2003; Myers, 2004). Prior 

to the collection of samples, the sampling port was sterilized 

using isopropyl alcohol and ground water was run through 

the sampling port for at least 3 minutes to remove any traces 

of the sterilizing agent. Two sterilized 250-mL bottles then 

were filled with ground water for coliform analyses (total 

and Escherichia coliform determinations), and one sterilized 

3-L carboy was filled for coliphage analyses (F-specific and 

somatic coliphage determinations).

Nine laboratories performed chemical and microbial 

analyses for the SFSG study (table A1), although most of 

the analyses were performed at the NWQL or at laboratories 

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. Method detection 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/Public/Performance/publiclabcertcoverpage.html). 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. The Branch of Quality Systems also 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://nfqa.

cr.usgs.gov/). Results for analyses made at the NWQL or by 

laboratories contracted by the NWQL are uploaded directly 

into NWIS by the NWQL. Laboratory quality-control data 

also are stored in NWIS.
66 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Turbidity, alkalinity, total coliforms and Escherichia

coliform (E. coli) were measured in the mobile laboratory 

at the well site. Turbidity was measured in the field with a 

calibrated turbidity meter. Total coliforms and E. coli plates 

were prepared using sterilized equipment and reagents 

(Myers, 2004). Plates were counted under an ultraviolet light, 

following a 22–24-hour incubation time. Alkalinity and the 

concentrations of bicarbonate (HCO3

-

) and carbonate (CO3

2-) 

were measured on filtered samples by Gran’s titration method 

(Gran, 1950; 1952). Concentrations of HCO3

-

 and CO3

2-

also were calculated from the laboratory alkalinity and pH 

measurements. Calculations were made using the advanced 

speciation method (http://or.water.usgs.gov/alk/methods.html) 

with pK1 = 6.35, pK2 = 10.33, and pKW = 14. 

Data Reporting

Laboratory Reporting Conventions

The USGS NWQL uses the laboratory reporting level 

(LRL) as a threshold for reporting analytical results. The 

LRL is set to minimize the reporting of false negatives (not 

detecting a compound when actually is it 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 of at least 24 MDL determinations made over an 

extended period of time. The method detection limit (MDL) 

is the minimum concentration of a substance that can be 

measured and reported with 99 percent confidence that the 

concentration is greater than zero (at MDL there is less than 

1 percent chance of a false positive) (U.S. Environmental 

Protection Agency, 2002a). The USGS NWQL monitors and 

updates LT-MDLs and LRLs regularly, and the values in this 

report were in effect during the period of analyses for samples 

from the SFSG study unit.

Detections between the LRL and the LT-MDL are 

reported as estimated concentrations (designated with 

an “E” before the values in the tables and text). For 

information-rich methods, detections below the LRL have 

high certainty of detection, but the precise concentration is 

uncertain. Information-rich methods are those that utilize gas 

chromatography or high-performance liquid chromatography 

(HPLC) with mass spectrometry detection (VOCs, gasoline 

oxygenates and degradates, pesticides). For these methods, 

compounds are identified by presence of characteristic 

fragmentation patterns in their mass spectra in addition 

to being quantified by measurement of peak areas at their 

chromatographic retention times. E-coded values also 

may result from detections outside the range of calibration 

standards, from detections that did not meet all laboratory 

quality-control criteria, and from samples that were diluted 

prior to analysis (Childress and others, 1999). 

Some concentrations in this study are reported using 

minimum reporting levels (MRLs) or method uncertainties. 

The MRL is the smallest measurable concentration of a 

constituent that may be reported reliably 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. 

Detections that may have resulted from sample 

contamination are reported with a “V” before the values in the 

tables. The potential for sample contamination was assessed 

using results from field, source-solution, and laboratory 

blanks.

The reporting levels for some radiochemical constituents 

(gross-alpha radioactivity, gross-beta radioactivity, 

radium-226, and radium-228) are based on a sample-specific 

minimum detectable concentration (SSMDC), a samplespecific critical value, and the combined standard uncertainty 

(CSU) (Bennett and others, 2006). A result above the critical 

value represents a greater-than-95-percent certainty that the 

result is greater than zero (significantly different from the 

instrument’s background response to a blank sample), and a 

result above the SSMDC represents a greater-than-95-percent 

certainty that the result is greater than the critical value. 

Using these reporting level elements, three unique cases 

were possible when screening the raw analytical data. If the 

analytical result was less than the critical value (case 1), the 

analyte was considered not detected, and the concentration 

was reported on table 16 as less than the SSMDC. If the 

analytical result was greater than the critical value, the ratio 

of the CSU to the analytical result was calculated as a percent 

(percent relative CSU). For those samples with percent relative 

CSU greater than 20 percent (case 2), concentrations were 

reported as estimated values (designated by an “E” preceding 

the value). For those samples with percent relative CSU less 

than 20 percent (case 3), concentrations were reported on 

table 16 with no qualifiers.

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):

δ

i

E

R

R

E

sample

eference

i

= − 















1 1 × ,000

Where

is the heavier isotope ( O C or H)

is the ratio of the ab

18 12 , , , 2

Rsample undance of the heavier 

isotope to thelighterisotope

O 16 1 , 2

C or H in thesample,

is the ratio of the abun

, 1 ( )

Rreference dance of the heavier 

isotope to the lighter isotope 

O16 , C, or H in the reference 

material.

12 1 ( )
Appendix 67

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. 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 material.

Constituents on Multiple Analytical Schedules

Fifteen constituents targeted in the SFSG study were 

determined by more than one analytical schedule or more 

than one laboratory (table A2). Results from certain analytical 

schedules are preferred over others because the methodology 

is more accurate or precise and generally yields greater 

sensitivity for a given compound. 

The preferred method for constituents analyzed at 

USGS laboratories was selected based on 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 with greater accuracy and 

precision and lower LRLs for the overlapping constituents is 

preferred. A method may be selected as the preferred method 

to provide consistency with historical data analyzed by the 

same method. If a VOC, gasoline oxygenate or degradate, 

pesticide, or pesticide degradate appears on multiple analytical 

schedules, then only the measurement determined by the 

preferred method is reported. For arsenic, chromium, and iron 

concentrations, the standard method used by the NWQL is 

preferred over the research method used by the USGS Trace 

Metal Laboratory, although both are reported. For 1,2,3-TCP, 

the method used by the MWH Laboratory is preferred over 

the method used by the NWQL, although both are reported. 

Tritium results from both the USGS Stable Isotope and 

Tritium Laboratory and LLNL are reported.

Quality Assurance

The purpose of quality-assurance is to identify which 

data best represent environmental conditions and which 

may have been affected by contamination or bias during 

sample collection, processing, storage, transportation, or 

laboratory analysis. Four types of quality-control (QC) tests 

were used in this study: blank samples were collected to 

assess contamination; replicate samples were collected to 

assess reproducibility; matrix spike tests were done to assess 

accuracy of laboratory analytical methods; and surrogate 

compounds were added to samples analyzed for organic 

constituents to assess bias of laboratory analytical methods. 

In this report, detections of analytes in ground-water samples 

that may have resulted from contamination were censored. 

Censored data were included in the data tables and flagged 

with a “V” remark, but was not included in assessments of 

ground-water quality. The evaluation of QC data presented in 

this report was based on results for QC samples collected for 

SFSG. A holistic evaluation using results from QC samples 

collected from many study units will be presented in a 

subsequent report.

The quality-assurance 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 blank samples 

(blanks) are to evaluate the magnitude of potential 

contamination of samples with analytes of interest, and to 

identify and mitigate sources of contamination. Blanks were 

collected using water (nitrogen-purged “universal” blank 

water) certified by the NWQL to contain less than the LRL 

or MRL of the analytes investigated in the study. At about 10 

percent of the SFSG wells sampled, two types of blanks were 

collected: source-solution and field blanks. Source-solution 

blanks were collected to verify that the blank water used for 

the field blanks was free of the analytes of interest. Field 

blanks were collected to assess potential contamination of 

samples during collection, processing, transport, and analysis. 

Blanks were analyzed for VOCs, gasoline oxygenates and 

degradates, pesticides, pesticide degradates, perchlorate, 

NDMA, 1,4-dioxane, 1,2,3-TCP, nutrients, dissolved 

organic carbon, major and minor ions, trace elements, iron, 

arsenic, and chromium species, and radioactive constituents 

(table A3). Blank samples were not collected for the following 

constituents: stable isotopes, tritium, carbon isotopes, or noble 

gases.

Source-solution blanks were collected at selected 

sampling sites by pouring blank water directly into sample 

containers that were preserved, stored, shipped, and analyzed 

in the same manner as the ground-water samples. For field 

blanks, blank water either was pumped or poured through 

the sampling equipment (fittings and tubing) used to collect 

ground water, then processed and transported using the same 

protocols for the ground-water samples. 
68 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

All detections of the constituents of interest in field 

blanks required investigation of the magnitude and potential 

source of the contamination. If a constituent was detected in 

a source-solution blank at a concentration similar to that in 

field blanks from the same lot of blank water, then the source 

blank water was interpreted as the origin of the contamination 

in the field blanks, and detections of that constituent in field 

blanks collected using the same lot of source blank water 

could not be used to evaluated potential contamination during 

collection, processing, transport, or analysis of the samples. 

If a field blank detection could not be attributed to the source 

blank water, then the ground-water samples collected prior to, 

and following the contaminated field blank were evaluated. 

If the constituent was not detected in the ground-water 

sample collected prior to the contaminated field blank, then 

contamination of that field blank due to carry-over was ruled 

out. If non-detections were reported in field blanks or groundwater samples collected after ground-water samples containing 

high concentrations of the constituent, then carry-over 

contamination was considered unlikely in the whole dataset. 

If carry-over contamination in the dataset could not be ruled 

out, then all detections in ground-water samples and field 

blanks collected after a ground-water sample containing a high 

concentration of the constituent were examined for potential 

censoring. 

The censoring level was defined as the highest 

concentration of the constituent detected in a field blank 

plus one-half the LRL for that constituent. Detections of the 

constituent in ground-water samples at concentrations less 

than this censoring level were censored. Censored values are 

indicated by a ‘V’ preceding the value in the data tables, and 

these values are excluded from the assessment of groundwater quality.

Replicates

Sequential replicate samples were collected to assess 

variability that may result from the processing and analyses of 

inorganic and organic constituents. Relative standard deviation 

(RSD) of the measured values was used in determining 

the variability between replicate pairs for each compound 

(table A4). The RSD is defined as the standard deviation 

divided by the mean concentration for each replicate pair of 

samples, multiplied by 100 percent. If one value in a sample 

pair was reported as a non-detection and the other value was 

reported as an estimate below the LRL or MRL, the RSD was 

set to zero because the values were analytically identical. If 

one value in a sample pair was reported as a non-detection and 

the other value was greater than the LRL or MRL, then the 

non-detection value was set equal to one-quarter of the LRL 

and the RSD was calculated (Hamlin and others, 2002). If one 

value in a sample pair was reported as an estimate below the 

LRL or MRL, and the other value was greater than the LRL 

or MRL, no adjustment was made for the RSD calculation. 

Values of RSD less than 20 percent are considered acceptable 

in this study. An RSD value of 20 percent corresponds to 

a relative percent difference (RPD) value of 29 percent. 

High RSD values for a compound may be the result of 

analytical uncertainty at low concentrations, particularly for 

concentrations within an order of magnitude of LT-MDL or 

MDL. Sequential replicate samples were collected at up to 

18 percent of the wells sampled.

Matrix Spikes

Addition of a known concentration of a constituent 

(‘spike’) to a replicate environmental sample enables the 

laboratory to determine the effect of the matrix, in this case 

ground water, on the analytical technique used to measure the 

constituent. The 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 

performing the analysis. Low matrix-spike recovery may 

indicate that the compound might not be detected in some 

samples if it were present at very low concentrations. Low 

and high matrix-spike recoveries may be a potential concern 

if the concentration of a compound in a ground-water 

sample is close to the MCL: a low recovery could result in a 

measured concentration falsely below the MCL, whereas, a 

high recovery could result in a measured concentration falsely 

above the MCL.

Acceptable ranges for matrix-spike recoveries are based 

on the acceptable ranges established for laboratory “set” spike 

recoveries. Laboratory set spikes are aliquots of laboratory 

blank water to which the same spike solution used for the 

matrix spikes has been added. One set spike is analyzed with 

each set of samples. Acceptable ranges for set spike recoveries 

are 70–130 percent for constituents listed in tables 3A and 3B

(Connor and others, 1998; Zaugg and others, 2002; Rose and 

Sandstrom, 2003), and 60–120 percent for constituents listed 

in table 3C and 3D (Sandstrom and others, 2001). Based on 

these ranges, 70–130 percent was defined as the acceptable 

range for matrix-spike recoveries for organic compounds in 

the SFSG study. 

Matrix spikes were performed for VOCs, gasoline 

oxygenate and degradate compounds, pesticide and 

pesticide degradates compounds, and NDMA, 1,4-dioxane, 

and 1,2,3-TCP because the analytical methods for these 

constituents are chromatographic methods that may be 

susceptible to matrix interferences. Replicate samples for 

matrix-spike additions were collected at 8 percent of the wells 

sampled in SFSG, although not all analyte classes were tested 

at every well (tables A5A–D).
Appendix 69

Surrogates

Surrogate compounds (surrogates) are added to 

environmental samples in the laboratory prior to analysis 

in order to evaluate the recovery of similar constituents. 

Surrogate compounds were added to all of the ground-water 

and quality-control samples that were analyzed for VOCs, 

gasoline oxygenate and degradates, pesticide compounds, 

NDMA, 1,4-dioxane, and 1,2,3-TCP (table A6). Most of the 

surrogate compounds are deuterated analogs of compounds 

being analyzed. For example, the surrogate toluene-d8 

used 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 70–130 percent recovery of surrogates 

generally is considered acceptable, values outside this range 

indicate possible problems with the processing and analysis of 

samples (table A6) (Connor and others, 1998; Sandstrom and 

others, 2001).

Quality-Control Sample Results

Detections in Field and Source-Solution Blanks

Field and source-solution blanks were collected at 

approximately 10 percent of the sites sampled in SFSG. 

Table A3 presents a summary of constituents detected in the 

field blanks. Seven organic compounds were detected. 

Caffeine was detected in one of the five field blanks at 

a concentration of 0.007 μg/L. Caffeine was not detected 

in ground-water samples collected the day of and the day 

following the field blank detection; hence, no ground-water 

sample detections were censored as a result.

Six VOCs were detected in three of the five field blank 

samples, while no VOCs were detected in the other two blank 

samples. The six VOCs (maximum blank concentration in 

parentheses) include: ethylbenzene (0.06 μg/L), m-xylene 

plus p-xylene (E0.33 μg/L), o-xylene (E0.12 μg/L), 

tetrachloroethene (E0.15 μg/L), toluene (0.08 μg/L), and 

trichloroethene (0.09 μg/L). Ground-water samples collected 

the day prior to, the day of, and the day following each of the 

field blanks with detections of ethylbenzene, m-xylene plus 

p-xylene, or o-xylene were free from these constituents; hence 

no ground-water sample detections were censored as a result 

of these blank detections. 

Toluene was detected in three of the five field blanks. 

Toluene blank detections were examined, relative to the wellsampling schedule, to evaluate the potential for contamination 

from the sampling equipment used. Two field blank detections 

occurred at sites collected on the slow well schedule. However, 

toluene was not detected in any ground-water sample collected 

on the slow well schedule; therefore, these ground-water 

samples were not censored. The third field blank (collected on 

the fast well schedule) had a toluene concentration equal to 

the associated source-solution blank (E0.01 μg/L). However, 

toluene was not detected in ground-water samples collected 

on the day of (nor at the site prior to or following) the third 

blank detection. Additionally, toluene was not detected in two 

other field blank samples collected on the fast well schedule. 

Therefore, no ground-water sample detections of toluene 

(collected on the fast well schedule) were censored. Toluene 

concentrations observed in the environmental samples had a 

maximum concentration of 0.03 μg/L, which is less than one 

thousandth the MCL-CA of 150 μg/L.

Tetrachloroethene (PCE) and trichloroethene (TCE) were 

each detected in one field blank that was collected on the slow 

well schedule during the first week of sampling (June 6–9). 

These two constituents also were detected in every groundwater sample collected on the slow schedule during the same 

week. Given the relatively high concentration of PCE and 

TCE (37.4 and 77.6 μg/L, respectively) in water sampled 

from the first ground-water well (ULASF-08), and nondetection in the associated source-solution blank, the effect of 

“carryover” was evaluated as a plausible source of bias in the 

VOC concentrations during the week of June 6. Carry-over 

between samples is very rare because the procedures used to 

clean the equipment between samples 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 ground-water sample or field blank collected with the 

same equipment. For each VOC detected in the ULASF-08 

sample, the concentration of that particular VOC in subsequent 

samples did not show a consistent decreasing pattern; rather, 

the concentration always increased at some point during the 

week. Also, there was not a general agreement in the change 

of VOCs, relative to one another. Finally, a non-detection of 

both PCE and TCE in ground water sampled from the first 

slow well during the following week (ULASG-05) effectively 

limits this evaluation to the week of June 6. 
70 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Field blanks were collected at 3 of the 24 (intermediate 

and slow) sites sampled for the analysis of major ions, trace 

elements, and nutrients. Bromide was detected in one field 

blank at a concentration of E0.01 mg/L, and silica was 

detected in all three field blanks at a maximum concentration 

of 0.28 mg/L. All of the environmental samples analyzed 

had concentrations of bromide and silica 10 times and 50 

times greater (respectively) than the blank detections; thus 

no ground-water detections were censored on the basis of 

detections in the field blanks. Nickel was detected in one field 

blank at a concentration of 0.04 μg/L. All of the environmental 

samples analyzed during this week had nickel concentrations 

50 times greater than the blank; thus, no ground-water 

detections of nickel were censored. Total nitrogen (TN) 

was detected in two of three field blanks at a maximum 

concentration of 0.20 mg/L. The corresponding environmental 

samples had concentrations of TN 20 times greater than the 

blank detections. Additionally, neither blank sample had 

a detection of ammonia, nitrite, or nitrate. As a result, no 

ground-water detections of TN were censored. 

Field blanks were collected at 3 of the 52 sites sampled 

for chromium speciation analysis at the USGS Trace Metal 

Laboratory (TML); 3 of the 17 sites also were sampled for 

arsenic and iron speciation analyses. One field blank contained 

10 μg/L total chromium and 9.9 μg/L chromium VI; these 

species were not detected in the field blank collected at 

the same time for analysis by the NWQL. As a result, six 

detections of chromium species in ground-water samples 

analyzed by the TML at concentrations less than 11 μg/L were 

censored (table 12). None of the field blanks contained arsenic 

or iron.

Field blanks were collected at 2 of the 17 sites sampled 

for the analysis of dissolved organic carbon (DOC). DOC 

was detected in both field blanks at concentrations of 0.9 and 

4.3 mg/L, and greater than nearly all of the environmental 

detections. As a result, all 17 ground-water detections for 

DOC were censored (with a ‘V’ code). Low concentrations 

of DOC were detected in field blanks collected in previous 

GAMA study units (Bennett and others, 2006; Kulongoski and 

Belitz, 2007).

Field blanks for the analysis of radioactive constituents 

(Radium-226 and -228, gross alpha and gross beta 

radioactivity) were collected at 2 of the 17 slow sites. 

Radium-226 was detected at an activity of E0.028 pCi/L in 

one blank, and 2 of 17 detections in the ground-water samples 

were censored (with a ‘V’ code) as a result. Radium-288 

was detected at an activity of E0.24 pCi/L in the same blank, 

and one of six detections were censored as a result. No other 

radioactive constituents were detected in the field blanks.

No compounds were detected in field blanks for 

pesticides or pesticide degradates (five field blanks), 

arsenic and iron speciation analyses at the USGS Trace 

Metal Laboratory (three field blanks), and four constituents 

of special interest (perchlorate, NDMA, 1,2,3-TCP, and 

1,4-dioxane; three field blanks each).

Variability in Replicate Samples

Table A4 summarize the results of replicate analyses for 

constituents detected in ground-water samples collected in 

the SFSG study. A total of 286 replicate analyses were made 

for constituents detected in at least one ground-water sample. 

Replicate analyses that were non-detections are not reported in 

table A4. Concentrations or activities in the environmental and 

replicate samples are reported for all replicate analyses with 

RSD values greater than 20 percent. Most replicate analyses 

collected during SFGS had RSD values less than 5 percent. 

Twelve constituents had RSD values greater than the 

acceptable limit of 20 percent, and include: perchlorate, 

aluminum, arsenic, copper, lead, manganese, thallium, zinc, 

gross alpha radioactivity, tritium analyzed by the USGS 

Tritium Laboratory; and total iron and total chromium 

analyzed by the USGS Trace Metal Laboratory. Except for 

aluminum, replicate analyses with RSD values greater than 

20 percent had an absolute uncertainty less than twice the LRL 

for their respective constituents. At these low concentrations, 

small deviations in measured values result in a large RSD 

value. The cause for the large absolute uncertainty (14.9 μg/L) 

between one set of replicate analyses for aluminum is 

unknown.

The tritium replicate analyses were within laboratory 

analytical uncertainty of one another. Since the variability 

in measurements of most replicate analyses occurred at low 

concentrations, and all well below regulatory thresholds, 

variability was not of QC concern. Therefore, no SFSG data 

were censored as a result of variability in replicate analyses.

Matrix-Spike Recoveries

Tables A5A–D present a summary of matrix-spike 

recoveries for the SFSG study unit. Four environmental 

samples were spiked with VOCs to calculate matrix-spike 

recoveries (table A5A). Sixty-five of the 88 VOCs had spike 

recoveries within the acceptable range of 70 and 130 percent. 

Fourteen of 33 VOCs detected in ground-water samples had 

spike recoveries within the acceptable range. Twenty-two 

VOCs had at least one matrix-spike recovery greater than 

130 percent, and 14 of these compounds were detected in 

ground-water samples. Of these 14 compounds, PCE and 

tetrachloromethane had 4 and 1 detections (respectively) 

above a health-based threshold. To evaluate the potential affect 

of a high matrix-spike recovery for these compounds, 

Concentrations in the ground-water samples were 

compared to the MCLs (or other health-based thresholds) and 

multiplied by their respective maximum spike recoveries. In 

this scenario, all previous detections above the MCL remained 

above their respective spike-adjusted MCLs. Styrene had 

1 of 4 matrix-spike recoveries below 70 percent and was 

not detected in any ground-water samples. [NOTE—low 

recoveries may indicate that the compound might not have 

been detected in some samples if it was present at very low 

concentrations]. 
Appendix 71

Four ground-water samples were spiked with pesticide 

compounds in order to calculate matrix spike recoveries 

(for NWQL schedule 2003; table 3C). Thirty-three of the 

60 pesticide compounds had spike recoveries within the 

acceptable range of 70 and 130 percent (table A5B). Eleven 

of the 14 pesticide compounds detected in ground-water 

samples had spike recoveries within the acceptable range. 

Four compounds had at least one spike recovery greater 

than 130 percent, and two of these compounds (hexazinone, 

tebuthiuron) were detected in ground-water samples. Twentyfour compounds had at least one spike recovery below 

70 percent and four of these compounds (deethylatrazine, 

3,4-dichloroaniline, fipronil sulfone, hexazinone) were 

detected in ground-water samples. [NOTE—low recoveries 

may indicate that the compound might not have been detected 

in some samples if it was present at very low concentrations].

One ground-water sample was spiked with polar pesticide 

or pesticide degradate compounds to calculate matrix-spike 

recoveries (for NWQL schedule 2060; table 3D). Forty-seven 

of the 57 compounds had recoveries within the acceptable 

range of 70–130 percent (table A5C). Eight of nine polar 

pesticide or pesticide degradate compounds detected in 

ground-water samples had spike recoveries within the 

acceptable range. Four compounds had a recovery greater than 

130 percent, and none of these were detected in ground-water 

samples. Six compounds had a recovery less than 70 percent, 

and only one (deisopropyl atrazine) was detected in groundwater samples. [NOTE—low recoveries may indicate that the 

compound might not have been detected in some samples if it 

was present at very low concentrations].

Two ground-water samples were spiked with perchlorate, 

1,2,3-TCP, 1,4-dioxane, and NDMA. All spike recoveries 

for these compounds were within the acceptable range of 

70–130 percent (table A5D). No ground-water sample data 

were adjusted on the basis of matrix-spike recovery data. 

Surrogate Compound Recoveries

Surrogate recovery data are provided in table A6, 

including the identity of each surrogate; the analytical 

schedule on which it was applied; the number of analyses 

for blanks and ground-water samples; the number of 

surrogate recoveries below 70 percent, and the number of 

surrogate recoveries above 130 percent for the blank and 

environmental samples. Blank and environmental samples 

were considered separately to assess whether the matrices 

present in environmental samples affect surrogate recoveries. 

No systematic differences between surrogate recoveries in 

blank and environmental samples were observed. Greater 

than 90 percent of the blank and environmental samples had 

surrogate recoveries between the acceptable limit of 70 and 

130 percent. Surrogate recoveries were in the acceptable 

range of 70–130 percent recovery for 95 percent of VOC and 

gasoline oxygenate and degradate analyses, 92 percent of 

pesticide analyses, and 83 percent of analyses for 1,2,3-TCP, 

1,4-dioxane, and NDMA. No ground-water sample detections 

were censored as a result of surrogate recovery data.
72 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Appendix Tables
Appendix Tables 73

Analyte Analytical method Laboratory and 

analytical schedule Citation(s)

Water-quality indicators

Field parameters Calibrated field meters and kits USGS field measurement U.S. Geological Survey, 2005

Organic constituents

VOCs Purge and trap capillary gas 

chromatography/mass 

spectrometry

NWQL, schedule 2020 Connor and others, 1998

Gasoline oxygenates Heated purge and trap/gas 

chromatography/mass 

spectrometry 

NWQL, schedule 4024 Rose and Sandstrom, 2003

Pesticides Solid-phase extraction and 

gas chromatography/mass 

spectrometry

NWQL, schedules 2003 

and 2060

Zaugg and others, 1995; Lindley and 

others, 1996; Furlong and others, 

2001; Sandstrom and others, 2001; 

Madsen and others, 2003

Constituents of special interest

Perchlorate Ion chromatography and mass 

spectrometry 

Montgomery Watson Harza 

Laboratory

Hautman and others, 1999

N-Nitrosodimethylamine Gas chromatography and mass 

spectrometry 

Montgomery Watson Harza 

Laboratory

U.S. Environmental Protection 

Agency, 1996; 1999

1,2,3-Trichloropropane Gas chromatography/electron 

capture detector

Montgomery Watson Harza 

Laboratory

U.S. Environmental Protection 

Agency, 1995

1,4-Dioxane Gas chromatography and mass 

spectrometry 

Montgomery Watson Harza 

Laboratory

U.S. Environmental Protection 

Agency, 1996

Inorganic constituents

Nutrients Alkaline persulfate digestion, 

Kjedahl digestion

NWQL, schedule 2755 Fishman, 1993; Patton and 

Kryskalla, 2003

Dissolved organic carbon UV-promoted persulfate oxidation 

and infrared spectrometry

NWQL, schedule 2613 Brenton and Arnett, 1993

Major and minor ions, trace 

elements and nutrients

Atomic absorption spectrometry, 

colorimetry, ion-exchange 

chromatography, inductivelycoupled 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

Chromium, arsenic and iron 

species

Various techniques of 

ultraviolet visible (UV-VIS) 

spectrophotometry and atomic 

absorbance spectroscopy

USGS Trace Metal Laboratory, 

Boulder, Colorado

Stookey, 1970; To and others, 1998; 

Ball and McCleskey, 2003a,b; 

McCleskey and others, 2003

Table A1. Analytical methods used for the determination of organic, inorganic, and microbial constituents by the U.S. Geological 

Survey (USGS) National Water Quality Laboratory (NWQL) and additional contract laboratories.

[Analytical method: MI agar, supplemental nutrient agar in which coliforms (total and Escherichia) produce distinctly different fluorescence under ultraviolet 

lighting. Abbreviations: NWQL, National Water-Quality Laboratory; USGS, U.S. Geological Survey; USEPA, U.S. Environmental Protection Agency; UV, 

ultraviolte; VOCs, volatile organic compounds]
74 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Analyte Analytical method Laboratory and 

analytical schedule Citation(s)

Stable isotopes

Stable isotopes of water Gaseous hydrogen and carbon 

dioxide-water equilibration and 

stable-isotope mass spectrometry

USGS Stable Isotope Laboratory, 

Reston, Virginia

Epstein and Mayeda, 1953; Coplen 

and others, 1991; Coplen, 1994

Carbon isotopes Accelerator mass spectrometry University of Waterloo, 

Environmental Isotope 

Lab; University of Arizona 

Accelerator Mass Spectrometry 

Lab

Donahue and others, 1990; Jull and 

others, 2004

Radioactivity and gases

Tritium Electrolytic enrichment-liquid 

scintillation

USGS Stable Isotope and Tritium 

Laboratory, Menlo Park, 

California

Thatcher and others, 1977

Tritium and noble gases Helium-3 in-growth and mass 

spectrometry

Lawrence Livermore National 

Laboratory

Moran and others, 2002; Eaton and 

others, 2004

Radon-222 Liquid scintillation counting NWQL, schedule 1369 American Society for Testing and 

Materials, 1998

Radium 226/228 Alpha activity counting Eberline Analytical Services, 

NWQL method 1262

U.S. Environmental Protection 

Agency, 1980 (USEPA methods 

903 and 904)

Gross alpha and beta 

radioactivity

Alpha and beta activity counting Eberline Analytical Services, 

NWQL method 1792

U.S. Environmental Protection 

Agency, 1980 (USEPA method 

900.0)

Microbial constituents

F-specific and somatic 

coliphage

Single-agar layer (SAL) and 

two-step enrichment methods

USGS Ohio Water Microbiology 

Laboratory

U.S. Environmental Protection 

Agency, 2001

Total and escherichia

coliform

Membrane filter technique 

with "MI agar"

USGS field measurement U.S. Environmental Protection 

Agency, 2002b

Table A1. Analytical methods used for the determination of organic, inorganic, and microbial constituents by the U.S. Geological 

Survey (USGS) National Water Quality Laboratory (NWQL) and additional contract laboratories.—Continued

[Analytical method: MI agar, supplemental nutrient agar in which coliforms (total and Escherichia) produce distinctly different fluorescence under ultraviolet 

lighting. Abbreviations: NWQL, National Water-Quality Laboratory; USGS, U.S. Geological Survey; USEPA, U.S. Environmental Protection Agency; UV, 

ultraviolte; VOCs, volatile organic compounds]
Appendix Tables 75

Table A2. Preferred analytical schedules for constituents appearing on multiple schedules for samples 

collected for the San Fernando–San Gabriel (SFSG) Groundwater Ambient Monitoring and Assessment 

(GAMA) study unit, California, May to July 2005.

[Preferred analytical schedule, the method of analysis with the greatest accuracy and precision out of the ones used for a 

particular compound. LLNL, Lawrence Livermore National Laboratory; MWH, Montgomery Watson Harza Laboratory; 

SITL, U.S. Geological Survey Stable Isotope and Tritium Laboratory; TML, U.S. Geological Survey Trace Metal Laboratory. 

Abbreviations: VOC, volatile organic compound]

Constituent Primary constituent

classification

Analytical

schedules

Preferred

analytical

schedule

Results from preferred method reported

Acetone VOC, gasoline degradate 2020, 4024 2020

Atrazine Pesticide 2003, 2060 2003

Carbaryl Pesticide 2003, 2060 2003

Deethyl atrazine (2-Chloro-4-

isopropylamino-6-amino-s-triazine)

Pesticide degradate 2003, 2060 2003

Diisopropyl ether (DIPE) VOC, gasoline oxygenate 2020, 4024 2020

Ethyl tert-butyl ether (ETBE) VOC, gasoline oxygenate 2020, 4024 2020

Metalaxyl Pesticide 2003, 2060 2003

Methyl tert-butyl ether (MTBE) VOC, gasoline oxygenate 2020, 4024 2020

Methyl tert-pentyl ether VOC, gasoline oxygenate 2020, 4024 2020

Tebuthiuron Pesticide 2003, 2060 2003

1,2,3-Trichloropropane (1,2,3-TCP) VOC 2020, MHW MWH

Results from both methods reported

Arsenic, total Trace element 1948, TML 1948

Chromium, total Trace element 1948, TML 1948

Iron, total Trace element 1948, TML 1948

Tritium Radioactive LLNL, SITL both
76 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table A3. Constituents detected in field blanks collected for the San Fernando–San Gabriel Groundwater Ambient Monitoring and 

Assessment (GAMA) study unit, California, May to July 2005.

[Censored data are reported but not used in summary statistics. Abbreviations: E, estimated value; mg/L, milligram per liter; pCi/L, picocuries per liter; <, less 

than; μg/L, microgram per liter; —, not detected]

Constituent

Number of field 

blank detections/

analyses

Maximum 

concentration 

detected in field 

blanks

Minimum 

concentration 

detected in groundwater samples

Number of 

ground-water 

samples 

censored

Organic constituents (μg/L)

Caffeine 1/5 E0.007 0.012 0

Ethylbenzene1 2/5 0.06 — 0

m-Xylene plus p-Xylene1 2/5 0.33 E0.02 0

o-Xylene1 2/5 0.12 — 0

Tetrachloroethene 1/5 0.15 E0.01 0

Toluene1 3/5 0.08 0.03 0

Trichloroethene 1/5 0.09 E0.02 0

Inorganic constituents (mg/L)

Dissolved organic carbon 2/2 4.3 0.20 17

Bromide 1/3 E0.01 0.10 0

Chromium, total2 1/3 0.010 <0.001 6

Chromium, VI2 1/3 0.009 <0.001 6

Nickel 1/3 3 E0.04 0.72 3 0

Silica 3/3 0.28 14.3 0

Total nitrogen (as N) 2/3 0.20 0.56 0

Radioactive constituents (pCi/L)

Radium-226 1/2 0.028 0.016 2

Radium-228 1/2 0.24 0.23 1

1

 Constituent detected in source-solution and associated field blank.

2

 Chromium analyses made by U.S. Geological Survey Trace Metal Laboratory.

3

 Concentration in microgram per liter (μg/L).
Appendix Tables 77

Table A4. Quality-control summary for replicate analyses collected for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[Abbreviations: RSD, relative standard deviation in percent; na, not applicable (no pairs with RSDs greater than 20 percent); <, less than; — , not detected]

Constituent

Number of RSDs 

greater than 

20 percent/number of 

replicate pairs

Maximum RSD 

(percent)

Median of RSDs 

greater than zero 

(percent)

Concentrations 

for pairs with 

RSD greater 

than 20 percent 

(environmental/

replicate)

Organic constituents

Volatile organic compounds 0/5 15 <1 na

Gasoline oxygenates and degradates 0/2 — — na

Pesticides and degradates 0/5 14 <1 na

Polar pesticides and degradates 0/3 11 <1 na

Constituents of special interest

Perchlorate 1/3 20 12 (2.0/1.5)

1,2,3-Trichloropropane, 1,4-Dioxane, and 

N-Nitrosodimethylamine

0/3 — — na

Nutrients, major and minor ions

All nutrients, major and minor ions 0/3 9 <1 na

Trace elements

Aluminum 1/3 123 63 (1.1/16)

Arsenic 1/3 20 11 (0.3/0.4)

Copper 1/3 47 8 (0.5/1.0)

Lead 1/3 26 13 (0.16/0.11)

Manganese 1/3 47 47 (E0.1/E0.2)

Thallium 1/3 106 106 (<0.04/0.07)

Zinc 1/3 35 9 (1.0/E0.6)

All additional trace elements 0/3 18 1 na

U.S. Geological Survey Trace Metals Laboratory

Iron, total 1/3 35 35 (3/5)

Iron (II) 0/3 — — na

Arsenic, total 0/3 17 8 na

Arsenic (III) 0/3 — — na

Chromium, total 1/5 26 13 (1.01/1.6)

Chromium (VI) 0/5 16 9 na

Istopes, radioactivity, and noble gases

Gross-alpha radioactivity, 30-day count 1/1 79 — (E3.2/E0.9)

Carbon-13/carbon-12 ratio; carbon-14 0/2 14 1 na

Noble gases 0/1 1 1 na

Deuterium/protium ratio; oxygen-18/oxygen-16 

ratio

0/5 2 <1 na

Tritium1 1/5 35 9 (1.0/0.6)

Microbial indicators

F-specific and somatic coliphage, E. Coli, and 

total coliforms 0/2 — — na

1

Analyses performed at U.S. Geological Survey, Meno Park, California.
78 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and gasoline oxygenates and 

degradates in samples collected for the San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study 

unit, California, May to July 2005.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spiked samples

Recovery (percent)

Minimum Maximum Median

Acetone1 4 100 122 117

tert-Amyl alcohol 2 98 98 98

Acrylonitrile 4 97 133 115

Benzene2 4 109 132 119

Bromobenzene 4 100 115 110

Bromochloromethane 4 103 132 114

Bromodichloromethane2 4 106 132 119

Bromoform (tribromomethane)2 4 104 113 108

2-Butanone (MEK, methyl ethyl ketone) 4 102 116 111

tert-butyl alcohol (TBA) 2 92 92 92

n-Butylbenzene 4 88 110 99

sec-Butylbenzene 4 98 130 114

tert-Butylbenzene 4 103 136 119

Carbon disulfide2 4 89 117 108

Carbon tetrachloride (tetrachloromethane)2 4 102 139 124

Chlorobenzene2 4 98 110 107

Chloroethane 4 106 133 119

Chloroform (trichloromethane)2 4 106 311 125

Chloromethane 4 106 131 119

3-chloro-1-propene 4 101 127 119

2-chlorotoluene 4 100 121 112

4-chlorotoluene 4 95 118 107

Dibromochloromethane2 4 101 125 115

1,2-Dibromo-3-chloropropane (DBCP) 4 98 117 114

1,2-Dibromoethane (EDB) 4 100 117 110

Dibromomethane 4 102 126 117

1,2-Dichlorobenzene2 4 94 132 116

1,3-Dichlorobenzene2 4 94 126 116

1,4-Dichlorobenzene2 4 96 123 114

trans-1,4-Dichloro-2-butene 4 105 147 129

Dichlorodifluoromethane (CFC-12)2 4 76 98 87

1,1-Dichloroethane2 4 100 133 118

1,2-Dichloroethane2 4 107 131 119

1,1-Dichloroethene (DCE)2 4 98 122 112

cis-1,2-Dichloroethene2 4 103 128 117

trans-1,2-Dichloroethene2 4 102 130 118

Dichloromethane (methylene chloride)2 4 103 131 113

1,2-Dichloropropane2 4 98 117 107

1,3-Dichloropropane 4 107 125 116

2,2-Dichloropropane 4 92 117 112

1,1-Dichloropropene 4 102 125 116

cis-1,3-Dichloropropene 4 93 105 97

trans-1,3-Dichloropropene 4 98 124 115

Diethyl ether 4 100 113 113

Diisopropyl ether (DIPE)1,2 4 98 111 105

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and gasoline oxygenates and 

degradates in samples collected for the San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study 

unit, California, May to July 2005.

[Acceptable recovery range is between 70 and 130 percent]
Appendix Tables 79

Table A5A. Quality-control summary for matrix-spike recoveries of volatile organic compounds (VOCs) and gasoline oxygenates and 

degradates in samples collected for the San Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study 

unit, California, May to July 2005.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spiked samples

Recovery (percent)

Minimum Maximum Median

Ethylbenzene 4 102 123 113

Ethyl tert-butyl ether (ETBE)1 4 94 104 102

Ethyl methacrylate 4 94 105 100

1-Ethyl-2-methylbenzene (o-ethyl toluene) 4 93 121 108

Hexachlorobutadiene 4 99 115 103

Hexachloroethane 4 101 123 112

2-Hexanone (n-butyl methyl ketone) 4 104 118 111

Isopropylbenzene (cumene) 4 104 128 113

4-Isopropyl-1-methylbenzene 4 94 127 111

Methyl acetate 2 103 106 104

Methyl acrylate 4 100 120 111

Methyl acrylonitrile 4 99 128 113

Methyl bromide (bromomethane) 4 98 151 143

Methyl tert-butyl ether (MTBE)1,2 4 92 110 102

Methyl iodide (iodomethane) 4 77 120 108

Methyl isobutyl ketone (MIBK) 4 94 105 103

Methyl methacrylate 4 93 93 93

Methyl tert-pentyl ether (tert-amyl methyl ether, TAME)1 4 96 105 101

Naphthalene 4 94 126 104

n-propylbenzene 4 96 121 109

Styrene 4 9 130 99

1,1,1,2-Tetrachloroethane2 4 102 127 113

1,1,2,2-Tetrachloroethane 4 103 127 118

Tetrachloroethene (PCE)2 4 108 225 155

Tetrahydrofuran 4 102 123 112

1,2,3,4-tetramethylbenzene 4 111 126 118

1,2,3,5-tetramethylbenzene 4 115 128 124

Toluene2 4 102 119 113

1,2,3-trichlorobenzene 4 102 110 108

1,2,4-Trichlorobenzene 4 88 106 97

1,1,1-Trichloroethane (1,1,1-TCA)2 4 104 132 122

1,1,2-Trichloroethane (1,1,2-TCA)2 4 100 129 116

Trichloroethene (TCE)2 4 92 118 111

Trichlorofluoromethane (CFC-11)2 4 –200 132 115

1,2,3-Trichloropropane (1,2,3-TCP)2 4 98 121 112

1,1,2-Trichloro-1,2,2-trifluoroethane (CFC-113)2 4 102 277 120

1,2,3-Trimethylbenzene 4 97 124 111

1,2,4-Trimethylbenzene2 4 95 130 116

1,3,5-Trimethylbenzene 4 91 128 111

Vinyl bromide (bromoethene) 4 106 138 125

Vinyl chloride (chloroethene)2 4 115 144 135

m- and p-Xylene2 4 100 120 109

o-Xylene 4 98 118 106

 1 Constituents on schedules 2020 and 4024; only values from schedule 2020 are reported because it is the preferred analytical schedule. 

2 Constituents detected in ground-water samples.
80 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradages in samples collected (for 

u.U.S. Geological Survey National Water Quality Laboratory schedule 2003) for the San Fernando-San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spiked samples

Recovery (percent)

Minimum Maximum Median

Acetochlor 4 86 108 98

Alachlor 4 93 108 103

Atrazine1,2 4 91 108 107

Azinphos-methyl 4 58 101 79

Azinphos-methyl-oxon 4 41 73 59

Benfluralin 4 62 73 72

Carbaryl2 4 102 136 114

2-Chloro-2,6-diethylacetanilide 4 95 116 107

4-Chloro-2-methylphenol 4 56 75 59

Chlorpyrifos 4 98 113 101

Chlorpyrofos, oxygen analog 4 18 56 34

Cyfluthrin 4 46 69 54

Cypermethrin 4 47 65 53

Dacthal (DCPA) 4 102 114 103

Deethylatrazine (2-chloro-4-isopropylamino-6-

amino-s-triazine)1,2

4 41 48 46

Desulfinylfipronil1 4 89 99 93

Desulfinylfipronil amide 4 62 77 71

Diazinon 4 91 108 96

Diazinon, oxon 4 83 99 92

3,4-Dichloroaniline1 4 59 85 79

Dichlorvos 4 27 56 48

Dicrotophos 4 27 37 34

Dieldrin 4 84 116 97

2,6-Diethylaniline 4 90 96 92

Dimethoate 4 26 35 29

Ethion 4 75 90 85

Ethion monoxon 4 72 93 91

2-Ethyl-6-methylaniline 4 80 94 88

Fenamiphos 4 73 93 86

Fenamiphos sulfone 4 58 80 70

Fenamiphos sulfoxide 4 36 47 44

Fipronil1 4 73 91 90

Fipronil sulfide1 4 84 96 89

Fipronil sulfone1 4 53 81 67

Fonofos 4 90 100 93

Hexazinone1 4 68 141 80

Isofenphos 4 102 113 107

Malaoxon 4 80 106 96

Malathion 4 104 137 110

Metalaxyl1,2 4 91 104 100

Methidathion 4 92 111 100

Metolachlor1 4 109 122 114

Metribuzin 4 78 88 86

Myclobutanil1 4 79 95 89

1-Naphthol 4 18 54 20

Paraoxon-methyl 4 62 74 63

Parathion-methyl 4 73 86 83

Pendimethalin 4 74 105 92

cis-Permethrin 4 58 71 62

Phorate 4 49 91 82

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected (for 

U.S. Geological Survey National Water Quality Laboratory schedule 2003) for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[Acceptable recovery range is between 70 and 130 percent]
Appendix Tables 81

Table A5B. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected (for 

U.S. Geological Survey National Water Quality Laboratory schedule 2003) for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.—Continued

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spiked samples

Recovery (percent)

Minimum Maximum Median

Phorate oxon 4 64 102 96

Prometon1 4 93 108 97

Prometryn 4 97 112 106

Pronamide (Propyzamide) 4 91 100 100

Simazine1 4 88 104 97

Tebuthiuron1,2 4 99 233 170

Terbufos 4 73 108 88

Terbufos oxon sulfone 4 93 112 109

Terbuthylazine 4 102 110 105

Trifluralin 4 70 80 77

1

 Constituents detected in ground-water samples.

2

 Constituents on schedules 2003 and 2060; only values from schedule 2003 are reported because it is the preferred analytical schedule.
82 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Constituent Number of 

spiked samples

Recovery 

(percent)

Acifluorfen 1 122

Aldicarb 1 15

Aldicarb sulfone 1 66

Aldicarb sulfoxide 1 12

Atrazine1 1 87

Bendiocarb 1 95

Benomyl 1 80

Bensulfuron-methyl 1 91

Bentazon 1 102

Bromacil1 1 95

Bromoxynil 1 84

Caffeine1 1 106

Carbaryl 1 110

Carbofuran 1 105

Chloramben, methyl ester 1 91

Chlorimuron-ethyl 1 61

Clopyralid 1 69

Cycloate 1 99

2,4-D plus 2,4-D methyl ester 

(summed on a molar basis)

1 106

2,4-DB [4-(2,4-dichlorophenoxy)

butyric acid]

1 77

DCPA (dacthal) monoacid 1 117

Deethylatrazine (2-chloro-4-

isopropylamino-6-amino-striazine)1

1 68

Deisopropyl atrazine (2-chloro-6-

ethylamino-4-amino-s-triazine)1

1 62

Dicamba 1 99

Dichlorprop 1 95

Dinoseb 1 110

Diphenamid1 1 106

Diuron1 1 128

Fenuron 1 106

Constituent Number of 

spiked samples

Recovery 

(percent)

Flumetsulam 1 142

Fluometuron 1 113

Hydroxyatrazine (2-hydroxy-4-

isopropylamino-6-ethylaminos-triazine)1

1 122

3-Hydroxycarbofuran 1 95

Imazaquin 1 142

Imazethapyr1 1 117

Imidacloprid 1 131

Linuron 1 102

MCPA (2-methyl-4-

chlorophenoxyacetic acid) 

1 80

MCPB [4-(2-methyl-4-

chlorophenoxy) butyric acid]

1 77

Metalaxyl1 1 106

Methiocarb 1 104

Methomyl 1 6

Metsulfuron methyl 1 11

3-(4-Chlorophenyl)-1-methyl 

urea1

1 106

Neburon 1 102

Nicosulfuron 1 99

Norflurazon 1 110

Oryzalin 1 95

Oxamyl 1 102

Picloram 1 99

Propham 1 84

Propiconazole 1 95

Propoxur 1 91

Siduron 1 113

Sulfometuron-methyl1 1 85

Tebuthiuron1 1 114

Terbacil 1 119

Triclopyr 1 99

Table A5C. Quality-control summary for matrix-spike recoveries of pesticides and pesticide degradates in samples collected (for 

U.S. Geological Survey National Water Quality Laboratory schedule 2060) for the San Fernando–San Gabriel Groundwater Ambient 

Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[Acceptable recovery range is between 70 and 130 percent]

1

 Constituents detected in ground-water samples.
Appendix Tables 83

Table A5D. Quality-control summary for matrix-spike recoveries of constituents of special interest in samples collected for the San 

Fernando–San Gabriel Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[Acceptable recovery range is between 70 and 130 percent]

Constituent Number of 

spiked samples

Recovery (percent)

Minimum Maximum Median

Perchlorate1 2 83 102 93

1,2,3-Trichloropropane (TCP)1 2 98 101 100

1,4-Dioxane 2 93 99 96

N-Nitrosdimethylamine (NDMA)1 2 81 98 90

1

 Constituents detected in ground-water samples.
84 Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program

Table A6. Quality-control summary for surrogate recoveries of volatile organic compounds, gasoline oxygenates and degradates, 

pesticides and pesticide degradates, and constituents of special interest in samples collected for the San Fernando–San Gabriel 

Groundwater Ambient Monitoring and Assessment (GAMA) study unit, California, May to July 2005.

[Abbreviations: MWH, Montgomery Watson Harza Laboratory; VOC, volatile organic compound]

Surrogate Analytical 

schedule

Constituent or 

constituent 

class 

analyzed

Blank samples Non-blank samples

Number 

of 

analyses

Median 

recovery 

(percent)

Number of surrogate 

recoveries Number 

of 

analyses

Median 

recovery 

(percent)

Number of surrogate 

recoveries

Below 70 

percent

Above 130 

percent

Below 70 

percent

Above 130 

percent

1,2-Dichloroethane-d42020, 4024 VOCs, gasoline 

oxygenates

9 121 0 0 57 104 0 6

1-Bromo-4-fluorobenzene2020, 4024 VOCs, gasoline 

oxygenates

9 83 2 0 57 93 4 0

Isobutyl alcohol-d6 4024 Gasoline 

oxygenates

2 92 0 0 19 92 0 0

Toluene-d8 2020, 4024 VOCs, gasoline 

oxygenates

9 99 0 0 57 100 0 0

alpha-HCH-d6 2003 Pesticides and 

degradates

5 98 0 0 56 96 0 0

Diazinon-d10 2003 Pesticides and 

degradates

5 92 0 0 55 95 0 0

2,4,5-T (2,4,5-

trichlorophenoxyacetic acid)

2060 Polar pesticides 

and 

degradates

2 90 0 0 28 103 1 0

Barban 2060 Polar pesticides 

and 

degradates

2 85 0 0 28 95 0 2

Caffeine-13C 2060 Polar pesticides 

and 

degradates

2 144 0 1 28 127 0 12

2-Fluorobiphenyl MWH 1,4-Dioxane 4 92 0 0 27 87 1 0

NDMA-d6 MWH NDMA 4 72 2 0 27 83 6 0

Nitrobenzene-d5 MWH 1,4-Dioxane 4 94 0 0 27 91 0 0

Terphenyl-d14 MWH 1,4-Dioxane 4 76 1 0 27 62 16 0

Toluene-d8 MWH 1,2,3-TCP 4 100 0 0 27 98 0 0
Land and Belitz–Ground-Water Quality Data in the San Fernando–San Gabriel Study Unit, 2005—Results from the California GAMA Program–Data Series 356

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