U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5200

National Water-Quality Assessment Program 

Source Water-Quality Assessments

Anthropogenic Organic Compounds in Source Water of 

Selected Community Water Systems that Use Groundwater, 

2002–05
Cover. Photographs of a pump house and public supply wells that are typical for wells sampled for this study.

Photographs by Nicholas Smith.
Anthropogenic Organic Compounds in 

Source Water of Selected Community 

Water Systems that Use Groundwater, 

2002–05

By Jessica A. Hopple, Gregory C. Delzer, and James A. Kingsbury

National Water-Quality Assessment Program 

Source Water-Quality Assessments

Scientific Investigations Report 2009–5200

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

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

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Suggested citation:

Hopple, J.A., Delzer, G.C., and Kingsbury, J.A., 2009, Anthropogenic organic compounds in source water of 

selected community water systems that use groundwater, 2002–05: U.S. Geological Survey Scientific 

Investigations Report 2009–5200, 74 p.
iii

Foreword

The U.S. Geological Survey (USGS) is committed to providing the Nation with credible scientific 

information that helps to enhance and protect the overall quality of life and that facilitates effective 

management of water, biological, energy, and mineral resources (http://www.usgs.gov/). Information on the Nation’s water resources is critical to ensuring long-term availability of water that is safe 

for drinking and recreation and is suitable for industry, irrigation, and fish and wildlife. Population 

growth and increasing demands for water make the availability of that water, now measured in 

terms of quantity and quality, even more essential to the long-term sustainability of our communities 

and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to 

support national, regional, State, and local information needs and decisions related to water-quality 

management and policy (http://water.usgs.gov/nawqa). The NAWQA Program is designed to answer: 

What is the condition of our Nation’s streams and groundwater? How are conditions changing over 

time? How do natural features and human activities affect the quality of streams and groundwater, and where are those effects most pronounced? By combining information on water chemistry, 

physical characteristics, stream habitat, and aquatic life, the NAWQA Program aims to provide 

science-based insights for current and emerging water issues and priorities. From 1991-2001, the 

NAWQA Program completed interdisciplinary assessments and established a baseline understanding 

of water-quality conditions in 51 of the Nation’s river basins and aquifers, referred to as Study Units 

(http://water.usgs.gov/nawqa/studyu.html). 

Multiple national and regional assessments are ongoing in the second decade (2001–2012) of 

the NAWQA Program as 42 of the 51 Study Units are reassessed. These assessments extend the 

findings in the Study Units by determining status and trends at sites that have been consistently 

monitored for more than a decade, and filling critical gaps in characterizing the quality of surface 

water and groundwater. For example, increased emphasis has been placed on assessing the quality 

of source water and finished water associated with many of the Nation’s largest community water 

systems. During the second decade, NAWQA is addressing five national priority topics that build 

an understanding of how natural features and human activities affect water quality, and establish 

links between sources of contaminants, the transport of those contaminants through the hydrologic 

system, and the potential effects of contaminants on humans and aquatic ecosystems. Included are 

topics on the fate of agricultural chemicals, effects of urbanization on stream ecosystems, bioaccumulation of mercury in stream ecosystems, effects of nutrient enrichment on aquatic ecosystems, 

and transport of contaminants to public-supply wells. These topical studies are conducted in those 

Study Units most affected by these issues; they comprise a set of multi-Study-Unit designs for 

systematic national assessment. In addition, national syntheses of information on pesticides, volatile 

organic compounds (VOCs), nutrients, selected trace elements, and aquatic ecology are continuing.

The USGS aims to disseminate credible, timely, and relevant science information to address practical 

and effective water-resource management and strategies that protect and restore water quality. We 

hope this NAWQA publication will provide you with insights and information to meet your needs, 

and will foster increased citizen awareness and involvement in the protection and restoration of our 

Nation’s waters. 

The USGS recognizes that a national assessment by a single program cannot address all waterresource issues of interest. External coordination at all levels is critical for cost-effective management, regulation, and conservation of our Nation’s water resources. The NAWQA Program, therefore, 

depends on advice and information from other agencies—Federal, State, regional, interstate, Tribal, 

and local—as well as nongovernmental organizations, industry, academia, and other stakeholder 

groups. Your assistance and suggestions are greatly appreciated.

Matthew C. Larsen 

Associate Director for Water
iv

Contents

Foreword .........................................................................................................................................................ii

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

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

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

Acknowledgments................................................................................................................................3

Study Design and Methods..........................................................................................................................3

Characteristics of Selected Community Water System Wells......................................................5

Compounds Monitored ........................................................................................................................5

Sample Collection and Protocols.......................................................................................................9

Analytical Methods...............................................................................................................................9

Quality Assurance ..............................................................................................................................10

Human-Health Benchmarks Used in a Screening-Level Assessment ......................................10

Anthropogenic Organic Compounds in Source Water Used by Community 

Water Systems, 2002–05 ...............................................................................................................12

Commonly Detected Compounds.....................................................................................................14

Herbicide Degradates at Selected Sites ........................................................................................17

Comparison to Human-Health Benchmarks...................................................................................19

Mixtures of Compounds.....................................................................................................................19

Factors that May Affect Source-Water Quality.............................................................................21

Comparisons of Selected Organic Compounds in Source Water and Finished 

Water Sampled in 2004 and 2005 .................................................................................................24

Commonly Detected Compounds.....................................................................................................24

Comparison to Human-Health Benchmarks...................................................................................26

Comparison of Source- and Finished-Water Quality ....................................................................26

Nonblended Finished Water ....................................................................................................26

Blended Finished Water ...........................................................................................................29

Mixtures................................................................................................................................................30

Summary........................................................................................................................................................30

References....................................................................................................................................................33

Appendix 1. Summary statistics and human-health benchmarks for anthropogenic 

organic compounds analyzed in source-water samples collected during 

October 2002–July 2005 ............................................................................................................38

Appendix 2. Selected characteristics of community water system wells sampled 

for Source Water-Quality Assessments, 2002–05 .................................................................54

Appendix 3. Summary statistics and human-health benchmarks for anthropogenic 

organic compounds analyzed in source- and finished-water samples 

collected during June 2004–September 2005 .......................................................................60
v

Figures

1. Map showing locations of source water, finished water, and principal 

aquifers throughout the United States included as part of the Source 

Water-Quality Assessment (SWQA) component of the National WaterQuality Assessment (NAWQA) Program during 2002–05.......................................................4

2–14. Graphs showing:

2. The distribution of well depths included in Source Water-Quality 

Assessments, 2002–05, varied by lithology and principal aquifer...............................7

3. Source-water samples collected from wells east of the Mississippi 

River had more anthropogenic organic compounds detected and 

greater total concentrations of compounds than did source-water 

samples collected from wells west of the Mississippi River during 

October 2002–July 2005 ....................................................................................................13

4. Twelve of 258 anthropogenic organic compounds analyzed at all sites 

were detected using no common assessment level in 10 percent or 

more of source-water samples collected from 221 community water 

system wells during October 2002–July 2005 ...............................................................15

5. Similar compounds were detected but detection frequencies were 

greater for compounds detected commonly in source-water samples 

collected for Source Water-Quality Assessments during October 2002–

July 2005 than in groundwater sampled for other National Water-Quality 

Assessment studies for herbicides and herbicide degradates and 

the disinfection by-product chloroform, the gasoline oxygenate 

methyl tert-butyl ether, and solvents..............................................................................17

6. Summed concentrations of degradates generally were greater than 

concentrations of parent compounds for chloroacetanilide degradates 

and generally were similar to or greater than concentrations of parent 

compounds for triazine degradates in source-water samples collected 

October 2002–July 2005 ....................................................................................................18

7. Concentrations of commonly detected compounds were generally 

less than 1 microgram per liter and generally much less than 

one-tenth of human-health benchmarks for samples collected 

October 2002–July 2005 ....................................................................................................20

8. The number of anthropogenic organic compounds detected as 

mixtures in source-water samples collected during October 2002–

July 2005 generally was greater in source water from shallow wells 

than from deep wells.........................................................................................................21

9. The 12 most commonly detected compounds had greater detection 

frequencies and greater numbers of compounds detected in sourcewater samples from shallower wells than from deeper wells during 

October 2002–July 2005 ....................................................................................................22

10. Large differences in occurrence of the 12 most commonly detected 

compounds were not attributable to aquifer lithology although fewer 

compounds generally were detected in source-water samples from 

wells completed in sandstone and carbonate rocks than from wells 

completed in other lithology groups. Most samples collected during 

October 2002–July 2005 contained fewer than three compounds for 

each of the four lithology groups ....................................................................................23
vi

Tables

1. Characteristics of principal aquifers or aquifer systems and median well 

depth for sites included in Source Water-Quality Assessments, 2002–05..........................6

2. Primary-use groups for compounds analyzed for Source Water-Quality 

Assessment studies .....................................................................................................................8

3. Summary of compounds detected in 5 percent or more of field blanks 

collected for Source Water-Quality Assessments, 2002–05 ...............................................11

4. Detection frequencies of compounds detected in 10 percent or more of 

source-water samples by principal aquifer using no assessment level, 

October 2002–July 2005 .............................................................................................................16

5. Detection frequency of compounds detected in 10 percent or more of 

source- and (or) finished-water samples collected during 

June 2004–September 2005 ......................................................................................................25

Conversion Factors and Datums

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

million gallons (Mgal) 3,785 cubic meter (m3)

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

11. Concentrations of commonly detected anthropogenic organic 

compounds were less than human-health benchmarks in finishedwater samples collected during June 2004–September 2005....................................27

12. Concentrations of anthropogenic organic compounds (excluding 

disinfection by-products) in source and associated nonblended 

finished water generally were similar when detected in both source 

and finished water for samples collected during 

June 2004–September 2005 .............................................................................................28

13. Concentrations of anthropogenic organic compounds (excluding 

disinfection by-products) in source and associated blended finished 

water generally were similar when detected in both source and 

finished water for samples collected during June 2004–September 2005 ..............29

14. Both source- and finished-water samples collected during the 

June 2004–September 2005 sampling typically contained mixtures of 

two or more compounds...................................................................................................31
vii

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

(NAVD 88).

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

Abbreviations and Symbols

< less than

μg/L micrograms per liter

1,1,1-TCA 1,1,1-trichloroethane

BQ benchmark quotient

BTEX benzene, toluene, ethylbenzene, and xylenes

CCR Consumer Confidence Report

cis-1,2-DCE cis-1,2-dichloroethene

CWS community water system

DBP disinfection by-product

DEET N,N,-diethyl-meta-toluamide

E estimated

GC/MS gas chromatography/mass spectrometry

HBSL Health-Based Screening Level

HPLC/MS high-performance liquid chromatography/mass spectrometry

LRL laboratory reporting level

MCL Maximum Contaminant Level

MTBE methyl tert-butyl ether

NAWQA National Water-Quality Assessment

NWQL National Water Quality Laboratory

OGRL Organic Geochemistry Research Group Laboratory

PAH polynuclear aromatic hydrocarbon

PCE tetrachloroethene; perchloroethene

PVC polyvinyl chloride

QC quality control

SPE solid-phase extraction

SWQA Source Water-Quality Assessment

TCE trichloroethene

THM trihalomethane

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC volatile organic compound
viii

Definitions

Term Definition

Benchmark quotient (BQ) Ratio of the concentration of a contaminant to its Maximum Contaminant Level (MCL) value for a regulated compound or to its HealthBased Screening Level (HBSL) value for an unregulated compound. 

Annual mean BQs greater than 1 identify concentrations of potential 

human-health concern. BQs greater than 0.1 identify compounds that 

may warrant inclusion in a low-concentration, trends-monitoring 

program.

Blended water As used in this report, finished water that has been blended with one or 

more different groundwater sources. Community water systems that 

blend with surface water were not analyzed.

Community water system 

(CWS)

A public water system with 15 or more connections and serving 25 

or more year-round residents and thus subject to USEPA and State 

regulations enforcing the Safe Drinking Water Act. A CWS serves a 

residential population, such as a municipality, mobile home park, or 

nursing home.

Concentration of potential 

human-health concern

As used in this report: (1) for a regulated compound with a U.S. Environmental Protection Agency (USEPA) drinking-water standard, 

a concentration greater than the MCL; and (2) for an unregulated 

compound, a concentration greater than the HBSL.

Drinking-water guideline As used in this report, a threshold concentration that has no regulatory 

status but is issued in an advisory capacity by the USEPA or State 

agencies.

Drinking-water standard As used in this report, a threshold concentration that is legally enforceable (such as MCLs) by the USEPA or State agencies.

Finished water Water is “finished” when it has passed through all the processes in a 

water-treatment plant and is ready to be delivered to consumers.

Health-Based Screening 

Level (HBSL)

Benchmark concentrations of contaminants in water that may be of 

potential concern for human health, if exceeded. HBSLs are nonenforceable benchmarks that were developed by the U.S. Geological 

Survey (USGS) in collaboration with the USEPA and others using 

(1) USEPA Office of Water methodologies for establishing drinkingwater guidelines, and (2) the most recent USEPA peer-reviewed, 

publicly available human-health toxicity information.

Human-health benchmarks As used in this report, human-health benchmarks include USEPA MCL 

values and HBSL values.

Maximum Contaminant 

Level (MCL)

USEPA drinking-water standard that is legally enforceable, and that 

sets the maximum permissible level of a contaminant in water that is 

delivered to any user of a public water system.

Quench Stop a chemical reaction; as used in this report, the addition of ascorbic 

acid to scavenge free chlorine in samples.

Regulated compound As used in this report, a compound for which a Federal drinking-water 

standard has been established by the USEPA.

Source water Source water is the raw (ambient) water collected at the supply well or 

surface-water intake prior to water treatment used to produce finished 

water.

Unregulated compound As used in this report, a compound for which no Federal drinking-water 

standard has been established. Note that a compound that is unregulated by the USEPA in drinking water under the Safe Drinking Water 

Act may be regulated in other contexts and under other statutes.
Anthropogenic Organic Compounds in Source Water 

of Selected Community Water Systems that Use 

Groundwater, 2002–05

By Jessica A. Hopple, Gregory C. Delzer, and James A. Kingsbury

Abstract

Source water, defined as groundwater collected from a 

community water system well prior to water treatment, was 

sampled from 221 wells during October 2002 to July 2005 

and analyzed for 258 anthropogenic organic compounds. Most 

of these compounds are unregulated in drinking water and 

include pesticides and pesticide degradates, gasoline hydrocarbons, personal-care and domestic-use products, and solvents. 

The laboratory analytical methods used in the study have 

detection levels that commonly are 100 to 1,000 times lower 

than State and Federal standards and guidelines for protecting 

water quality. Detections of anthropogenic organic compounds 

do not necessarily indicate a concern to human health but 

rather help to identify emerging issues and track changes in 

occurrence and concentrations over time.

Less than one-half (120) of the 258 compounds were 

detected in at least one source-water sample. Chloroform, in 

36 percent of samples, was the most commonly detected of 

the 12 compounds that were in about 10 percent or more of 

source-water samples. The herbicides atrazine, metolachlor, 

prometon, and simazine also were among the commonly 

detected compounds. The commonly detected degradates of 

atrazine—deethylatrazine and deisopropylatrazine—as well as 

degradates of acetochlor and alachlor, generally were detected 

at concentrations similar to or greater than concentrations 

of the parent herbicide. The compounds perchloroethene, 

trichloroethene, 1,1,1-trichloroethane, methyl tert-butyl ether, 

and cis-1,2-dichloroethene also were detected commonly. The 

most commonly detected compounds in source-water samples 

generally were among those detected commonly across the 

country and reported in previous studies by the U.S. Geological Survey’s National Water-Quality Assessment Program.

Relatively few compounds were detected at concentrations greater than human-health benchmarks, and 84 percent of 

the concentrations were two or more orders of magnitude less 

than benchmarks. Five compounds (perchloroethene, trichloroethene, 1,2-dibromoethane, acrylonitrile, and dieldrin) were 

detected at concentrations greater than their human-health 

benchmark. The human-health benchmarks used for comparison were U.S. Environmental Protection Agency Maximum 

Contaminant Levels (MCLs) for regulated compounds 

and Health-Based Screening Levels developed by the U.S. 

Geological Survey in collaboration with the U.S. Environmental Protection Agency and other agencies for unregulated 

compounds. About one-half of all detected compounds do not 

have human-health benchmarks or adequate toxicity information to evaluate results in a human-health context.

Ninety-four source-water and finished-water (water that 

has passed through all the treatment processes but prior to 

distribution) sites were sampled at selected community water 

systems during June 2004 to September 2005. Most of the 

samples were analyzed for compounds that were detected 

commonly or at relatively high concentrations during the 

initial source-water sampling. The majority of the finishedwater samples represented water blended with water from 

one or more other wells. Thirty-four samples were from water 

systems that did not blend water from sampled wells with 

water from other wells prior to distribution.

The comparison of source- and finished-water samples 

represents an initial assessment of whether compounds present 

in source water also are present in finished water and is not 

intended as an evaluation of water-treatment efficacy. The 

treatment used at the majority of the community water systems 

sampled is disinfection, which, in general, is not designed to 

remove the compounds monitored in this study.

Concentrations of all compounds detected in finished 

water were less than their human-health benchmarks. Two 

detections of perchloroethene and one detection of trichloroethene in finished water had concentrations within an order 

of magnitude of the MCL. Concentrations of disinfection 

by-products were expected to increase in finished water relative to source water because of disinfection. The MCL for 

concentrations of disinfection by-products analyzed in this 

study is for total trihalomethanes, and concentrations were 

within an order of magnitude of the MCL in finished water 

from nine sites, but only three detections of chloroform and 

one detection of bromoform were within an order of magnitude of the MCL. Concentrations of all other compounds 

were more than an order of magnitude less than human-health 

benchmarks.
2 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

About one-half (57 percent) of the detections from the 

34 community water systems where finished water was not 

blended with other source water were in both source and 

finished water, and concentrations were similar, with the 

exception of disinfection by-products. Most of the detections 

were gasoline-related compounds, herbicides and herbicide 

degradates, and solvents. Results for blended finished-water 

samples generally were similar to nonblended finished-water 

samples, and blending did not always reduce concentrations 

to less than the laboratory reporting level. Differences in the 

occurrence of compounds in source and finished water could 

be the result of water treatment, volatilization, blending, or 

analytical variability at concentrations near or less than the 

laboratory reporting level. Large changes in concentration 

from source to finished water of solvents in a few samples 

likely are attributable to additional water treatment steps used 

by the CWS to treat water known to contain elevated concentrations of organic compounds.

Mixtures of two or more compounds were detected in 

about 70 percent of source-water samples and in 82 percent 

of finished-water samples. Mixtures occur more commonly 

in finished water than source water because of the formation 

of disinfection by-products in finished water. The potential human-health significance of the frequent presence of 

mixtures of organic compounds in finished water remains 

largely unknown.

Introduction

Groundwater is an important supply of drinking water in 

the United States, and the study of aquifers is a large component of the U.S. Geological Survey’s (USGS) National WaterQuality Assessment (NAWQA) Program. NAWQA studies 

have added to the understanding of the chemical quality of 

water in locally and regionally important aquifers. Many 

pesticides, volatile organic compounds (VOCs), and other 

compounds are monitored as part of these aquifer studies, 

which are designed to provide an overall representation of the 

water-quality condition of the Nation’s aquifers.

The occurrence of anthropogenic organic compounds 

in groundwater has been documented for many years (for 

example, Westrick and others, 1984; U.S. Environmental 

Protection Agency, 2002) and recently reported by Gilliom and 

others (2006) and Zogorski and others (2006). Drinking water 

is monitored routinely for regulated compounds. However, 

relatively few studies have specifically focused on the quality 

of source water used by community water systems (CWSs) as 

well as the associated finished water, particularly for organic 

compounds that are not regulated under the Safe Drinking 

Water Act (U.S. Environmental Protection Agency, 2008). 

Collectively, findings from these studies highlight the need for 

continued monitoring and evaluation of organic compounds 

found in sources of drinking water, referred to as source 

waters, using nationally consistent analytical methods and 

assessment techniques. In the current study, source water is 

defined as groundwater withdrawn from a CWS well prior to 

water treatment, and finished water is defined as water that has 

passed through all treatment processes, prior to distribution.

From 1992 to 2001, the NAWQA Program assessed the 

quality of ambient surface-water and groundwater resources 

in 51 major river basins and aquifer systems across the Nation 

(http://water.usgs.gov/nawqa/studies/study_units.html). 

Beginning in 2002, NAWQA initiated “Source Water-Quality 

Assessments” (SWQAs) at selected CWSs across the United 

States. The long-term goal is to complete about 30 surfacewater and 30 groundwater SWQAs by 2012 (Delzer and 

Hamilton, 2007; Kingsbury and others, 2008). The primary 

emphasis of SWQAs is to characterize the occurrence of 

a large number of anthropogenic organic compounds that 

are predominantly unregulated by the U.S. Environmental 

Protection Agency (USEPA) in sources of drinking water. 

In addition, SWQAs are intended to provide a preliminary, 

broad-based assessment of selected compounds found in 

source water and the associated finished water. These studies 

contribute to specific science goals and priorities of the USGS, 

which in part, include assessment of environmental risk to 

public health and the quality of water used for drinking water, 

as important aspects of accounting for the freshwater resources 

of the Nation (U.S. Geological Survey, 2007).

The laboratory analytical methods used in SWQA studies 

have relatively low detection levels—commonly 100 to 

1,000 times lower than State and Federal standards and guidelines for protecting water quality. Detections, therefore, do 

not necessarily indicate a concern to human health, but rather 

help to identify emerging issues and track changes in occurrence and concentrations over time. SWQAs complement 

existing drinking-water monitoring required by Federal, State, 

and local programs, which focus primarily on post-treatment 

compliance monitoring of contaminants regulated by USEPA 

in drinking water to meet requirements of the Safe Drinking 

Water Act. Most of the compounds analyzed in SWQA studies 

are not included in other source-water and finished-water 

monitoring programs, such as the Unregulated Contaminant 

Monitoring Program (U.S. Environmental Protection Agency, 

2007a) and the U.S. Department of Agriculture’s Pesticide 

Data Program (U.S. Department of Agriculture, 2008).

Since 1999, the USEPA has required water suppliers to 

provide annual drinking-water quality reports called Consumer 

Confidence Reports (CCRs) to their customers (http://www.

epa.gov/safewater/ccr/). CCRs are the centerpiece of the 

right-to-know provisions of the 1996 Amendments to the Safe 

Drinking Water Act. Each CCR provides consumers with 

fundamental information about their drinking water, including 

(1) the source of the drinking water, (2) a brief summary of 

the susceptibility to contamination of the local drinking-water 

source, (3) the concentrations (or range of concentrations) of 

any contaminants found in local drinking water, as well as 

their USEPA Maximum Contaminant Levels (MCLs), which 

are legally enforceable drinking-water standards and are the 

highest allowed concentrations of contaminants in drinking 
Study Design and Methods 3

water, and (4) telephone numbers for additional sources of 

information.

Information in CCRs is specific to a particular water 

utility. Water utilities analyze finished-water samples primarily 

for regulated compounds using USEPA analytical methods for 

compliance monitoring. Analytical methods used in SWQAs 

include many more compounds and typically have lower 

analytical reporting levels than those used in USEPA analytical methods; therefore, compound detection frequencies in 

SWQA reports may be higher than those reported in CCRs.

Purpose and Scope

The primary purpose of this report is to characterize 

anthropogenic organic compounds in source water of selected 

CWSs that use groundwater. The focus of this report is on the 

first 15 groundwater SWQAs. The aquifers monitored (hereafter termed principal aquifers) as part of these efforts were 

studied because they account for the majority of the estimated 

withdrawals of groundwater for drinking-water supply in the 

United States (Lapham and others, 2005; Maupin and Barber, 

2005). This report also compares findings to previous resource 

assessments. The occurrence of 258 anthropogenic organic 

compounds (Appendix 1) in source water from 221 wells 

sampled from 12 principal aquifers across the United States 

by the NAWQA Program during October 2002 to July 2005 

is described. Source-water samples were analyzed for 

compounds that included pesticides and pesticide degradates, 

gasoline hydrocarbons, personal-care and domestic-use products, and solvents. An additional 3 herbicides and 16 herbicide 

degradates were analyzed in samples from 73 of the 221 wells 

located in areas where these compounds likely are used. The 

report describes (1) the occurrence of compounds in source 

water and highlights those that occur most commonly; (2) the 

comparison of concentrations of detected compounds to 

available human-health benchmarks; and (3) the characterization of the number of compounds co-occurring in source 

water as mixtures. Although this study was not designed to 

examine specific sources and (or) factors causing and affecting the occurrence and concentrations of compounds in 

source water, additional perspective is added by highlighting 

general patterns and associations as appropriate, including 

those related to geographic location, well depth, and general 

lithology.

A secondary purpose of this report is to provide comparisons of selected compounds in source water with their 

occurrence in finished water. Samples of source water, and 

associated samples of finished water, were collected during 

June 2004 to September 2005 from 94 of the 221 wells. 

Sampling during this period generally focused on analytical suites that included compounds found to occur most 

commonly or at relatively high concentrations in source water 

during the initial sampling (2002–05). The sampling design 

and resulting comparisons were not intended to characterize water-treatment efficacy, but to provide a preliminary 

indication of the potential importance of compounds found in 

source water and the quality of finished water prior to distribution. In general, the types of treatment used by the CWSs that 

were sampled were not specifically designed to remove most 

of the organic compounds monitored. Distinctions were made 

in the analyses for wells that did not blend water (34 of the 94) 

and wells that did blend water (60 of the 94) when comparing source- and finished-water concentrations. Analytical 

results for source-water and finished-water samples, as well 

as quality-assurance samples, are summarized in Carter and 

others (2007).

A screening-level assessment of the potential significance 

of detected compounds in source and finished waters to human 

health was made, when possible, by comparing measured 

concentrations to human-health benchmarks. Measured 

concentrations of compounds that are regulated in drinking 

water were compared to USEPA MCLs, and concentrations 

of unregulated compounds were compared to Health-Based 

Screening Levels (HBSLs) developed by the USGS in collaboration with USEPA and others (Toccalino and others, 2003). 

The screening-level assessment provides an initial perspective on the potential importance of anthropogenic organic 

compounds detected and is not a substitute for comprehensive 

risk assessment, which includes many more factors, such as 

additional avenues of exposure.

Acknowledgments

The authors thank personnel at each of the CWSs for 

their assistance in the collection of samples. The authors also 

acknowledge Robert Gilliom, John Zogorski, William Wilber, 

Jeffrey Stoner, and Pixie Hamilton of the USGS and Philip 

Berger of the USEPA for their constructive review comments.

Study Design and Methods

CWS wells selected for SWQA monitoring met several 

criteria. Specifically, wells are located in NAWQA study 

areas where SWQA data can be compared to groundwater 

resource-assessment data collected as part of the NAWQA 

Program during 1992–2001, and wells are screened in one of 

62 principal aquifers (fig. 1). Selected wells generally have 

relatively high pumping rates (in comparison to other wells 

in the sampling area) and are at least 1,000 meters (0.62 mile) 

apart to minimize overlapping contributing areas. In general, 

wells sampled in this study are considered relatively susceptible to anthropogenic contamination because of the large 

pumping rates (generally greater than 500 gallons per minute) 

and large contributing areas. The results of this study are, 

therefore, not necessarily representative of many CWS wells, 

particularly those with relatively small pumping rates, less 

than 500 gallons per minute.
Figure 1. Source water and finished water were assessed in 12 principal aquifers throughout the United 

States as part of the Source Water-Quality Assessment (SWQA) component of the National Water-Quality 

Assessment (NAWQA) Program during 2002–05.

1

River

Mississippi

G

G

G

G

EXPLANATION

Coastal Lowlands aquifer system

Edwards-Trinity aquifer system

Denver Basin aquifer system

California Coastal Basin aquifers

Central Valley aquifer system

Surficial aquifer system (overlying the Floridan)

Floridan aquifer system

Biscayne aquifer

Glacial deposits aquifer system

Cambrian-Ordovician aquifer system

Mississippi Embayment-Texas Coastal Uplands 

 aquifer system 

Northern Atlantic Coastal Plain aquifer system

High Plains aquifer

Rio Grande aquifer system

New England crystalline-rock aquifers

Valley and Ridge aquifers—Carbonate-rock aquifers 

 are patterned

Hawaiian volcanic-rock aquifers—locally overlain by 

Basin-fill aquifers sedimentary deposits

Carbonate-rock aquifers

Basin and Range

Basin-fill aquifers

Basaltic-rock aquifers

Columbia Plateau

Early Mesozoic aquifers

Carbonate-rock aquifers

Crystalline-rock aquifers

Piedmont and Blue Ridge

Basin-fill aquifers

Basaltic-rock aquifers

Snake River Plain

Principal aquifer (from U.S. Geological 

 Survey, 2003)

Approximate location of groundwater SWQA study area

Wells completed in the glacial deposits aquifer system 

4 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater
Study Design and Methods 5

The types of water treatment or prior monitoring results, 

including those for compliance monitoring, were not considered in the selection process. In addition, several criteria were 

used to eliminate wells, including (1) proximity to coastal 

or bay areas, which could be affected by saltwater intrusion; 

(2) wells with strong connections to streams (under the influence of surface water); and (3) wells used for injection or 

withdrawal for artificial recharge.

Typically, about 15 wells were sampled in each of the 

SWQA studies. In the Florida and Minnesota/Wisconsin 

SWQAs, 30 wells were sampled (table 1). Fifteen wells 

in both unconfined and semiconfined parts of the Floridan 

aquifer system were sampled for the Florida SWQA. For the 

Minnesota/Wisconsin SWQA, 15 of the sampled wells were 

completed in the Cambrian-Ordovician aquifer system, and 15 

of the sampled wells were completed in the glacial deposits 

aquifer system.

The Kruskal-Wallis rank-sum test (Helsel and Hirsch, 

1992) was used to identify differences between groups of sites 

for analyses presented in this report. A p-value less than 0.05 

was used to indicate statistical significance.

Characteristics of Selected Community Water 

System Wells

The principal aquifers sampled in this study range in 

areal extent from about 6,800 to more than 950,000 square 

miles (table 1); however, wells sampled for SWQAs typically were clustered around one or two urban or suburban 

areas. For the purpose of this study, the 221 sampled wells 

were grouped into four general lithology groups: (1) unconsolidated glacial deposits (44 wells); (2) unconsolidated and 

semiconsolidated sediments, which include sand, gravel, and 

to a lesser extent boulders and silt (77 wells); (3) sandstone 

and carbonate rocks (72 wells); and (4) igneous and metamorphic (crystalline) rocks (28 wells) (fig. 2A; table 1; Appendix 2). Wells completed in the unconsolidated glacial deposits 

were separated from wells completed in unconsolidated and 

semiconsolidated sediments because of significantly different 

well depths (median depths of 124 and 523 feet (ft) below land 

surface, respectively) (Kruskal-Wallis rank-sum test p-value 

less than 0.0001).

Depth to water, and consequently well depth, varies 

considerably among and within study areas (table 1; fig. 2B; 

Appendix 2). Median well depths within each principal aquifer 

range from 124 to 1,394 ft. The shallowest median well depth 

is for wells completed in the glacial deposits aquifer system, 

and the deepest median well depth is for wells completed in 

the Coastal Lowlands aquifer system (table 1; fig. 2B; Appendix 2). Many of the deepest wells are located in the western 

part of the Nation, and the shallowest wells are located east 

of the Mississippi River. Although wells in the unconsolidated and semiconsolidated group have the second shallowest median depth, the range in well depth is large (120 to 

2,070 ft). Well depth and lithology for each well are presented 

in Appendix 2.

CWSs that participated in SWQAs include single-well 

systems and systems with multiple wells. In many cases where 

systems have multiple wells, the CWSs blend water before or 

after water treatment. The water-treatment process predominantly used by the CWSs was disinfection with chlorine. 

Additional water-treatment steps, including granular activated 

carbon and air-stripping towers, were used by CWSs when 

source water was known to be contaminated with organic 

compounds.

Compounds Monitored

Compounds included for monitoring were selected on the 

basis of known or potential human-health concerns, analytical capabilities, and whether the compounds typically are not 

monitored in source and (or) finished water. Some compounds 

without known human-health concerns, such as caffeine, were 

included as potential indicators or surrogates for contaminants that were not monitored. Most of the 258 compounds 

monitored at all sites are not regulated in drinking water and 

typically are not monitored by CWSs; however, 38 compounds 

do have an established USEPA MCL for drinking water and 

are monitored in finished water by CWSs. Several inorganic 

compounds, such as arsenic and nitrate, were considered 

for monitoring but were not included because they typically 

are monitored by CWSs and, thus, would not have provided 

new information. Additionally, only compounds that could 

be analyzed using USGS approved analytical methods were 

considered for monitoring.

For the purposes of this report, the compounds were 

grouped into 13 categories on the basis of their primary 

use or source (table 2; Appendix 1). The number of 

compounds in each of the 13 categories (hereafter termed 

“use groups”) ranges from 3 to 82. About one-half of the 

compounds analyzed are pesticides, which include three use 

groups—herbicides and herbicide degradates, insecticides 

and insecticide degradates, and fungicides. About 90 VOCs 

are categorized in six use groups, including disinfection 

by-products; fumigant-related compounds; gasoline hydrocarbons, oxygenates, and oxygenate degradates; organic 

synthesis compounds; refrigerants and propellants; and 

solvents. Pesticides and VOCs have been included routinely 

in data collection by the NAWQA Program since its inception (1991); however, most of the compounds in the remaining four groups have not been analyzed previously by the 

NAWQA Program. These four use groups are personal-care 

and domestic-use products, such as triclosan (an anti-bacterial 

agent in many hand soaps), detergent metabolites, and 

fragrance compounds; manufacturing additives, such as plasticizers and fire retardants; pavement- and combustion-derived 

compounds, which are predominantly polynuclear aromatic 

hydrocarbons; and plant- and animal-derived biochemicals, 

such as cholesterol.
Table 1. Characteristics of principal aquifers or aquifer systems and median well depth for sites included in Source Water-Quality Assessments, 2002–05.

[SWQA, Source Water-Quality Assessment; Mgal/d, million gallons per day]

Principal aquifer or system in which 

SWQA was conducted

State(s) in which 

SWQA was located General lithologies Number of wells sampled Median well depth (feet) Approximate areal extent of aquifer (square miles) Withdrawals for public supply in 20001 (Mgal/d)

Basin and Range basin-fill aquifers2 Nevada Unconsolidated and semiconsolidated 

sediments

15 470 163,386 1,081

Cambrian-Ordovician aquifer system3 Minnesota, Wisconsin Sandstone and carbonate rocks 15 408 177,355 590Central Valley aquifer system California Unconsolidated and semiconsolidated 

sediments

15 248 20,305 839

Coastal Lowlands aquifer system Texas Unconsolidated and semiconsolidated 

sediments

15 1,394 197,211 724

Columbia Plateau basin-fill and 

basaltic-rock aquifers

Washington Igneous and metamorphic rocks 

Unconsolidated and semiconsolidated 

sediments

13

2

750 4188; 1,171 43,521 223

Denver Basin aquifer system Colorado Sandstone and carbonate rocks 12 561 6,788 17Edwards-Trinity aquifer system Texas Sandstone and carbonate rocks 15 848 75,012 411Floridan aquifer system5 Florida Sandstone and carbonate rocks 30 563 112,684 1,555Glacial deposits aquifer system3,6,7 Connecticut, 

Minnesota, Ohio, Wisconsin

Unconsolidated glacial deposits 44 124 953,148 1,950

High Plains aquifer Nebraska Unconsolidated and semiconsolidated 

sediments

15 292 176,534 389

Piedmont and Blue Ridge crystallinerock aquifers8 Maryland, Virginia Igneous and metamorphic rocks 15 300 86,489 92Rio Grande aquifer system New Mexico Unconsolidated and semiconsolidated 

sediments

15 1,287 29,249 240

1Maupin and Barber (2005).2Rosen and others (2006).3Tornes and others (2007).4Depths for two wells; median not calculated.5Metz and others (2006).6Trombley and others (2007).7Thomas (2007).8Banks and Reyes (2009).

6 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater
Figure 2. The distribution of well depths included in Source Water-Quality Assessments, 2002–05, varied by A, lithology; and 

B, principal aquifer. [Color-coding of principal aquifer corresponds to color-coding of the lithology group.] WELL DEPTH, IN FEET

Unconsolidated

glacial deposits

Unconsolidated and

semiconsolidated

sediments

Sandstone and

carbonate rocks

Igneous and

metamorphic rocks

0

450

900

1,350

1,800

2,250

LITHOLOGY, IN ORDER OF INCREASING MEDIAN WELL DEPTH

(44) (77) (72) (28)

A

EXPLANATION

Number of values 

75th percentile

Median

25th percentile

Outlier data value more 

 than 1.5 times the interquartile 

 range outside the quartile

Data value less than or equal 

 to 1.5 times the interquartile

 range outside the quartile

Interquartile

range

(28)

B

(44) (15) (15) (15) (15) (15) (12) (30) (15) (15) (15) (15)

1 2 3 4 5 6 7 8 9 10 11 12

PRINCIPAL AQUIFER, IN ORDER OF INCREASING MEDIAN WELL DEPTH

WELL DEPTH, IN FEET

0

450

900

1,350

1,800

2,250

1

2

3

4

5

6

7

8

*9

10

11

12

Glacial deposits aquifer system

Central Valley aquifer system

High Plains aquifer

Piedmont and Blue Ridge 

 crystalline-rock aquifers

Cambrian-Ordovician aquifer 

 system

Basin and Range basin-fill 

 aquifers

Denver Basin aquifer system

Floridan aquifer system

Columbia Plateau basin-fill 

 and basaltic-rock aquifers

Edwards-Trinity aquifer system

Rio Grande aquifer system

Coastal Lowlands aquifer 

 system

*Two of the wells were com-

 pleted in unconsolidated and 

 semiconsolidated sediments. 

Study Design and Methods 7
Table 2. Primary-use groups for compounds analyzed for Source Water-Quality Assessment studies (from Carter and others, 2007).

[BTEX: benzene, toluene, ethylbenzene, and xylenes]

Primary use or source group Description

Number of 

compounds analyzed 

in each group

Disinfection by-products Trihalomethanes, (poly)haloacetic acids, and other compounds that are produced 

from the transformation of organic compounds during the disinfection of water and 

wastewater through chlorination, ozonation, or other chemical methods.

4

Fumigant-related compounds Chemicals that may be present in commercial fumigant products, which produce a 

gas, vapor, fumes, or smoke intended to destroy, repel, or control unwanted organisms, such as insects, bacteria, or rodents. These include fumigant active ingredients as well as their degradates and their manufacturing by-products.

9

Fungicides Pesticides used to kill unwanted fungi. 7

Gasoline hydrocarbons, 

oxygenates, and oxygenate 

degradates

Gasoline hydrocarbons are straight, branched, and (or) cyclic organic compounds 

that are highly volatile, contain only carbon and hydrogen atoms, and are common 

ingredients in gasoline and other petroleum products. Of these compounds, 

BTEX compounds are among those present in the highest proportions in gasoline. 

Oxygenates, such as methyl tert-butyl ether (MTBE), are compounds that contain 

only carbon, hydrogen, and oxygen atoms and commonly are added to gasoline to 

improve the efficiency of combustion. Oxygenate degradates are formed during the 

production, storage, release, and (or) use of gasoline oxygenates or following their 

release into the environment.

27

Herbicides and herbicide 

degradates1

Pesticides designed to kill unwanted plants (herbicides) and compounds produced 

from the transformation of the parent herbicide following application (degradates).

82

Insecticides and insecticide 

degradates

Pesticides designed to kill unwanted insects (insecticides) and compounds produced 

from the transformation of the parent insecticide following application (degradates).

51

Manufacturing additives Compounds used in commercial formulations of chemical products in order to 

improve the effectiveness of the product, including plasticizers (to increase the 

flexibility of plastics), fire retardants, corrosion inhibitors, and pesticide adjuvants.

7

Organic synthesis compounds Chemicals used as precursors in the manufacture of other organic compounds. Chloroethylene (vinyl chloride), for example, is an organic synthesis compound used to 

produce polyvinyl chloride (PVC) plastics.

18

Pavement- and combustionderived compoundsOrganic substances, such as polynuclear aromatic hydrocarbons (PAHs), that are 

derived from either (1) the materials used to construct and seal parking lots and 

other paved surfaces or (2) the combustion of other non-halogenated organic 

compounds, most commonly gasoline, oil, coal, and other fossil fuels.

5

Personal-care and domesticuse productsCompounds that are present in commercial products sold for personal or residential 

use, such as fragrances, pharmaceuticals, insect repellants, dyes, detergents, disinfectants, shampoos, and chemicals used in fire extinguishers.

26

Plant- or animal-derived 

biochemicals

Naturally occurring compounds that are produced by plants or animals, either through 

direct biosynthesis or through the metabolic alteration of compounds ingested or 

taken up from other sources. These compounds are predominantly unsaturated 

solid alcohols of the steroid group naturally occurring in fatty tissues of plants and 

animals and present in animal fecal material.

5

Refrigerants and propellants Volatile compounds that are used for commercial or domestic refrigeration, as 

blowing agents in the manufacture of packaging and other highly porous materials, or for dispensing other substances from spray cans and other aerosol delivery 

devices.

3

Solvents Compounds used to dissolve other substances. Two of the more common solvents are 

trichloroethene (TCE) and perchloroethene (tetrachloroethene, PCE).

33

Total number of compounds 277

1

Herbicides and herbicide degradates include 3 herbicides and 16 herbicide degradates monitored in additional samples collected at 73 selected sites. A total 

of 258 compounds were monitored at all sites.

8 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater
Study Design and Methods 9

Sample Collection and Protocols

Source-water samples were collected at the wellhead 

before any treatment and processed using standard USGS 

sampling protocols (Koterba and others, 1995). The 221 wells 

were sampled one time during October 2002 to July 2005 and 

were analyzed for 258 compounds (Appendix 1). Samples 

from a subset of 73 wells also were analyzed for an additional 

3 herbicides and 16 herbicide degradates in study areas where 

these herbicides likely are used.

During a second sampling phase from June 2004 to 

September 2005, source and finished water were sampled at 

94 sites (Carter and others, 2007). Most of these source- and 

finished-water sample pairs (79) were from sites at which 

source water was sampled a second time. These 79 wells were 

selected for resampling source water and collecting a finishedwater sample because several compounds were detected or 

compounds were detected at high concentrations in the first 

source-water sample. The source- and finished-water samples 

from these sites generally were analyzed by using the analytical methods that included the compounds detected in the first 

sample. Because relatively few compounds were detected in 

source-water samples collected during 2003 from the Denver 

Basin aquifer system, these sites were not sampled during 

the second phase, and thus, no finished-water samples were 

collected for these sites. Since 2005, the SWQA studies are 

now conducted in one sampling phase where both source 

water and finished water associated with 15 wells are sampled 

at the same time. All studies included in this report followed 

the two-phase sampling approach with the exception of the 

Rio Grande aquifer system.

Finished-water samples were collected following all of 

the treatment steps and prior to the water entering the distribution system. Finished-water samples typically contain free 

chlorine, which can degrade organic compounds that may be 

present in the samples. Therefore, a dechlorination reagent 

(ascorbic acid or sodium thiosulfate) and, for certain samples, 

pH buffers were added to finished-water samples during 

sample collection to “quench” free chlorine and stabilize the 

samples prior to analysis (Winslow and others, 2001). As 

a result, finished-water samples are considered to be representative of the quality of water prior to distribution but not 

necessarily representative of the quality of water at the tap. 

The additional contact time of the water with disinfectants 

in the distribution system may allow some compounds to be 

transformed or degraded, whereas other compounds, such as 

disinfection by-products, may continue to form in the distribution system.

Analytical Methods

Samples were analyzed using USGS approved analytical methods at the USGS National Water Quality Laboratory 

(NWQL) in Denver, Colorado, including gas chromatography/

mass spectrometry (GC/MS) and high-performance liquid 

chromatography/mass spectrometry (HPLC/MS). Samples 

for VOC analyses were chilled upon collection, and samples 

for one of the two VOC analytical methods was preserved 

with 1:1 hydrochloric acid. Samples for both VOC analytical 

methods were analyzed by purge and trap GC/MS (Connor 

and others, 1998; Rose and Sandstrom, 2003). Samples for 

analyses of pesticides and other semivolatile compounds were 

filtered in the field through a 0.7-micron baked glass-fiber 

filter and chilled. These samples were extracted at the NWQL 

on solid-phase extraction (SPE) cartridges to concentrate the 

analytes from the filtered samples. SPE cartridges then were 

eluted with a solvent, and the extracts were analyzed by either 

GC/MS or HPLC/MS methods (Zaugg and others, 1995, 2002; 

Lindley and others, 1996; Furlong and others, 2001; Sandstrom and others, 2001; Madsen and others, 2003). At a subset 

of sites, an additional sample was collected for the analysis 

of 3 herbicides and 16 herbicide degradates. These samples 

were analyzed using HPLC/MS by the Organic Geochemistry 

Research Group Laboratory (OGRL), in Lawrence, Kansas 

(Lee and Strahan, 2003).

The analytical methods used at the NWQL and OGRL 

allow for the identification and quantification of compounds 

at low concentrations, in some cases as low as a few parts per 

trillion. Each analytical method has different ranges in sensitivity for its suite of analytes. Thus, the laboratory reporting 

levels (LRLs) for the compounds analyzed for SWQAs span 

four orders of magnitude, from 0.003 to 6.0 micrograms per 

liter (μg/L) (Appendix 1) with a median of 0.06 μg/L. Some 

reported concentrations are qualified as estimated (indicated 

with an “E”), which means the identification of the compound 

is reliable, but the concentration has greater uncertainty than 

unqualified concentrations reported for the same compound. 

These concentrations are estimated for one of several reasons: 

(1) they are less than the lowest calibration standard; (2) the 

sample matrix interfered with measurement of the compound; 

(3) surrogates added to the sample indicated poor performance 

during the analysis; or (4) the compound consistently has poor 

recoveries, and therefore, concentrations are always reported 

as estimated.

The sensitivity of the analytical methods differs among 

compounds and can affect the detection frequencies of the 

compounds analyzed. Compounds with low LRLs likely will 

be detected more commonly than those with high reporting 

levels, given equal concentration distributions in the environment. In order to compare detection frequencies between 

compounds, a common assessment level is needed to account 

for the different LRLs. In this report, a common assessment level of 0.1 μg/L is used. This concentration is near the 

median LRL of 0.06 μg/L for all of the compounds analyzed. 

Analytical results for compounds detected in source water 

are presented both with and without an assessment level. 

Unless otherwise specified, no assessment level was used. 

When concentrations of individual compounds in source- and 

finished-water samples are compared, no assessment level 

is used and all concentrations are evaluated, including those 

qualified as estimated.
10 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

Quality Assurance 

Similar types and numbers of quality-control (QC) 

samples were collected in each of the study areas. These QC 

samples, including field blanks, replicates, and matrix spikes, 

were evaluated together because sampling equipment and 

cleaning procedures, as well as sample collection and processing, were the same for all sites. Field blanks were processed 

in the field in the same manner as environmental samples 

and consisted of nitrogen-purged organic-free blank water. 

Field-blank results are used to characterize the positive bias 

or contamination that may affect sample analytical results. 

Source-solution blanks, which also consisted of nitrogenpurged organic-free blank water, were analyzed for a subset 

of field blanks and analytical methods to assure the integrity 

of the water used for blanks. Replicate samples are used to 

characterize the amount of variability associated with sample 

collection, processing, and analysis. Matrix spikes provide 

information about recoveries of organic compounds.

The majority of the field-blank data did not indicate 

potential contamination that could bias the environmental data. 

Overall, 254 of the 277 compounds monitored either were not 

detected or were detected in less than 5 percent of field blanks. 

However, field blanks collected during this study indicated 

that some compounds potentially were affected by contamination that could bias the environmental data (table 3). Data for 

these compounds were removed from the dataset or results 

were censored to account for this potential bias as follows. 

Phenol and N,N-diethyl-meta-toluamide (DEET) were 

detected in 82 and 39 percent of field blanks, respectively, 

and were removed from the dataset because of pervasive 

contamination in field blanks. Although the field-blank data 

did not identify systematic error that affected sample results 

for these compounds, the quality of data for both compounds 

was unknown.

Three compounds—benzophenone, isophorone, and 

para-nonylphenol—were removed from the dataset because 

of systematic contamination from the “quenching” reagents 

added to finished-water samples (table 3). Most field blanks 

collected during the second phase of sampling included the 

ascorbic acid and buffer that were added to finished-water 

samples to quench the free chlorine. These three compounds 

were detected at low concentrations in most of the blanks, 

indicating that the “quenching” reagents are a source of 

contamination for the three compounds. Follow-up analyses 

by the NWQL confirmed the presence of these compounds in 

the buffer added to samples (Mark Sandstrom, U.S. Geological Survey, oral commun., 2005).

Nineteen additional compounds were detected in more 

than 5 percent of field blanks (table 3). The occurrence of 

these compounds in field blanks was evaluated to determine 

if potential bias was associated with specific SWQAs. If a 

compound was detected in 50 percent or more of field blanks 

from a SWQA, all of the data for that constituent from that 

SWQA were removed from the dataset. If a compound was 

detected in 5 percent or more of field blanks collected at the 

remaining sites, the environmental data for that compound 

were censored at the maximum field-blank concentration to 

account for the potential bias indicated by field blanks. If a 

compound was detected in less than 5 percent of the field 

blanks remaining after removal of the field blanks from 

SWQAs with greater than 50-percent occurrence, no additional censoring was done.

Twenty-one compounds were detected in less than 

5 percent of field blanks and usually at concentrations less 

than the LRL (Appendix 1). Data for these compounds are 

included in this report because the potential for contamination 

in the environmental samples was considered to be low and 

did not affect the overall interpretation of the study.

Prior to implementation of the addition of ascorbic acid 

(quenching agent) to finished-water samples during the second 

phase of sampling, the NWQL evaluated the effect of this 

quenching agent and buffer on compound recoveries. Results 

indicated that recoveries were not affected by the addition 

of these reagents (Mark Sandstrom, U.S. Geological Survey, 

written commun., 2006). Additionally, during the second 

sampling phase, matrix spikes were collected to further characterize analytical method performance with the addition of 

ascorbic acid to finished-water samples. Results to date (2008) 

indicate that median spike recoveries generally were within 

acceptable limits for most compounds that are not always 

reported as estimated concentrations (Valder and others, 

2008). Results of paired spiked finished-water samples, one 

with quenching reagents and the other without, indicate that 

several compounds degrade in the presence of free chlorine 

(Valder and others, 2008). These results highlight the fact that 

additional contact time of finished water in the distribution 

system would affect the concentrations of several compounds 

analyzed in this study. Environmental and selected qualityassurance data for this study are available in Carter and others 

(2007).

Human-Health Benchmarks Used in a 

Screening-Level Assessment

Concentrations of regulated compounds—those with 

USEPA MCLs—were compared to MCLs, and concentrations of unregulated compounds—those without USEPA 

MCLs—were compared to Health-Based Screening Levels 

(HBSLs), when available (Toccalino, Norman, and others 

2006). Comparisons to human-health benchmarks are used in 

this report to identify concentrations of potential human-health 

concern and to provide an initial perspective on the potential 

importance of the anthropogenic organic compounds detected. 

As of June 2008, 38 of the compounds monitored in this study 

have an established USEPA MCL (U.S. Environmental Protection Agency, 2006) and 112 have an HBSL (Toccalino and 

others, 2008). HBSLs have not been developed for the remaining 127 unregulated compounds because of a lack of toxicity 

information. Therefore, the potential human-health significance of these compounds cannot be evaluated at this time 
Table 3. Summary of compounds detected in 5 percent or more of field blanks collected for Source Water-Quality Assessments, 

2002–05.

[N, number of field blanks; USGS, U.S. Geological Survey; SWQAs, Source Water-Quality Assessments; μg/L, micrograms per liter; NA, not applicable]

Compound (N)

USGS 

parameter 

code

Number of SWQAs 

for which compound 

was removed from all 

samples in the dataset

Number of detections 

censored at the 

maximum field-blank 

concentration

Maximum 

field-blank 

concentration 

(μg/L)

Compounds removed from dataset

Benzophenone (38) 62067 15 All data removed 0.15

Isophorone1 34409 15 All data removed .006

N,N-diethyl-meta-toluamide (DEET) (39) 62082 15 All data removed 1.1

para-Nonylphenol (total) (38) 62085 15 All data removed 2.6

Phenol (27) 34466 15 All data removed 1.9

Compounds removed from SWQA

1,2,4-Trimethylbenzene (41) 77222 2 0 0.036

Alachlor ethane sulfonic acid (6) 50009 1 0 .03

Benzene (41) 34030 2 0 .013

Chlorobenzene (41) 34301 1 0 .028

Chloroform (41) 32106 3 0 .198

Ethylbenzene (41) 34371 2 0 .022

m- and p-Xylene (41) 85795 3 0 .08

Menthol (38) 62080 1 0 .043

Methylene chloride (41) 34423 2 0 .094

o-Xylene (41) 77135 2 0 .021

Tri(2-butoxyethyl)phosphate (38) 62093 1 0 2.8

Triphenyl phosphate (38) 62092 1 0 .088

Compounds removed from SWQA or censored at the maximum field-blank concentration

Acetone (41) 81552 3 4 11.7

Acetophenone (38) 62064 2 1 .3

Caffeine (25) 50305 3 2 .004

Carbon disulfide (41) 77041 2 10 .109

Toluene (41) 34010 6 6 .05

Compounds censored at the maximum field-blank concentration

Bisphenol A (34) 62069 NA 19 0.94

p-Cresol (38) 62084 NA 2 .013

1

Detected in less than 5 percent of samples; however, the data were removed because of systematic contamination from reagents added to finished-water 

samples.

Study Design and Methods 11
12 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

(Toccalino, Rowe, and Norman, 2006). These human-health 

benchmarks typically are concentrations in drinking water that 

are not anticipated to cause adverse effects from a lifetime of 

exposure (Toccalino, 2007; U.S. Environmental Protection 

Agency, 2008).

MCLs are legally enforceable USEPA drinking-water 

standards that set the maximum permissible level of a 

contaminant in water that is delivered by public water systems 

(U.S. Environmental Protection Agency, 2008). MCLs are 

applicable only to finished-water samples in the regulatory 

framework; however, an assessment of source-water concentrations in relation to benchmarks provides an indication to 

water-resource managers and CWSs of potential concerns in 

the absence of the effects of factors, such as water treatment 

and distribution.

HBSLs are benchmark concentrations of compounds in 

water that, if exceeded, may be of concern to human health. 

HBSLs are non-enforceable benchmarks that were developed 

by the USGS in collaboration with the USEPA and others 

using: (1) USEPA Office of Water methodologies for establishing drinking-water guidelines, and (2) the most recent, 

USEPA peer-reviewed, publicly available human-health 

toxicity information (Toccalino and others, 2003; Toccalino 

and others, 2006). As a result, HBSL values are equivalent to 

existing USEPA drinking-water guideline values, such as Lifetime Health Advisory and Cancer Risk Concentration values 

(when they exist), except for unregulated contaminants for 

which more recent toxicity information has become available 

(Toccalino, 2007).

Concentrations of compounds in single samples of both 

source water and finished water were compared to humanhealth benchmarks as a screening-level assessment. This 

comparison identifies compounds with concentrations that 

approached or were greater than benchmarks to aid in assessing their potential relevance to human health. For these 

comparisons, benchmark quotient (BQ) values—the ratio of a 

concentration of a compound to its benchmark—were calculated. A BQ value greater than 1 represents a concentration 

greater than a benchmark. A BQ value greater than 0.1 can 

be used to identify compounds that may warrant additional 

monitoring (Toccalino, Rowe, and Norman, 2006). A threshold BQ of 0.1 is consistent with various State and Federal 

practices (for example, see U.S. Environmental Protection 

Agency, 1998). Monitoring for these contaminants would 

enable analysis of trends in their occurrence and may provide 

an early indication if concentrations approach human-health 

benchmarks.

Anthropogenic Organic Compounds 

in Source Water Used by Community 

Water Systems, 2002–05

Source-water samples were collected from 221 wells 

during October 2002 to September 2005. All samples were 

analyzed for 258 anthropogenic organic compounds, and 

samples from a subset of 73 wells were collected and analyzed 

for an additional 3 herbicides and 16 degradates in areas where 

these herbicides likely are used. Because these compounds 

were not monitored at all of the wells, the following characterization focuses on compounds that were monitored at all sites, 

and the 3 herbicides and 16 herbicide degradates are described 

separately.

More than one-half (138) of the 258 compounds monitored at all sites were not detected in any source-water samples 

(5 compounds were removed from the dataset because of dataquality concerns). Of the 120 compounds that were detected, 

52 were detected only once (Appendix 1). Concentrations of 

compounds typically were less than 1 μg/L, and only 6 percent 

of the concentrations of detected compounds were greater than 

1 μg/L. A variety of compounds were detected as indicated 

by the fact that at least two compounds from each of the 

13 use groups in which the compounds were categorized were 

detected (Appendix 1). The laboratory analytical methods 

used in this study have detection levels that are commonly 

100 to 1,000 times lower than State and Federal standards and 

guidelines for protecting water quality. Detections of these 

compounds do not necessarily indicate a concern to human 

health but rather help to identify emerging issues and track 

changes in occurrence and concentrations over time.

Detections of compounds in source water varied regionally, as shown by comparisons between wells located west of 

the Mississippi River (total of 117 wells) and those east of or 

near the Mississippi River (total of 104 wells; fig. 3); wells in 

Minnesota were included with wells east of the Mississippi 

River. Specifically, more compounds generally were detected 

per sample from wells in principal aquifers east of the Mississippi River than west of the Mississippi River (Kruskal-Wallis 

rank-sum test p-value = 0.0001; fig. 3A). Seventy-nine percent 

of samples from wells east of the Mississippi River had at 

least one compound detected and as many as 35 compounds 

(median = 3) detected in one sample. In contrast, 65 percent 

of samples from wells west of the Mississippi River had at 

least one compound detected and as many as 18 compounds 

(median = 1) detected in one sample. More herbicides and 

herbicide degradates were detected in samples from wells east 
Figure 3. Source-water samples collected from wells east of the Mississippi River had A, more anthropogenic organic compounds 

detected; and B, greater total concentrations of compounds than did source-water samples collected from wells west of the Mississippi 

River during October 2002–July 2005.

East West

LOCATION RELATIVE TO THE MISSISSIPPI RIVER

TOTAL CONCENTRATION OF COMPOUNDS IN A SAMPLE, IN MICROGRAMS PER LITER

0.001

0.01

0.1

1

10

100

1,000

10,000

25

20

15

10

5

0

35

30

40

NUMBER OF COMPOUNDS DETECTED PER SAMPLE

B 104 117

104 117

EXPLANATION

Number of values 

75th percentile

Median

25th percentile

Outlier data value more 

than 1.5 times the interquartile 

range outside the quartile

Data value less than or equal 

to 1.5 times the interquartile

 range outside the quartile

117

Interquartile

range

A

Anthropogenic Organic Compounds in Source Water Used by Community Water Systems, 2002–05 13
14 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

of the Mississippi River than in samples from wells west of 

the Mississippi River. Some of the factors that may account 

for a larger number of detected compounds in the east include 

generally higher groundwater recharge rates, shallower well 

depths, shallower depths to groundwater, greater population 

densities, and a greater intensity of herbicide use in agricultural areas than in the west (Gilliom and others, 2006). The 

total concentrations of compounds detected in samples from 

wells east of the Mississippi River were greater (median of 

0.172 μg/L) than those in the west (median of 0.036 μg/L; 

fig. 3B).

Compounds were characterized in this report as 

commonly occurring when they were detected in about 

10 percent or more of samples using no assessment level. By 

this definition, 12 compounds were detected commonly (fig. 4; 

Appendix 1). The commonly detected compounds represented 

four of the use groups, including disinfection by-products; 

gasoline hydrocarbons, oxygenates, and oxygenate degradates; 

herbicides and herbicide degradates; and solvents.

Commonly Detected Compounds

Most of the 258 compounds monitored at each site were 

detected infrequently; only 12 compounds were detected in 

about 10 percent or more of samples using no assessment 

level (fig. 4; Appendix 1). Chloroform, deethylatrazine (a 

degradate of atrazine), atrazine, and perchloroethene (PCE) 

were detected in about 20 percent or more of samples. Fewer 

compounds were detected when a common assessment level 

of 0.1 μg/L was used; only two compounds—chloroform and 

PCE—were detected in 10 percent or more of source-water 

samples (fig. 4). Detection frequencies of most of the other 

compounds were less than 5 percent when using a common 

assessment level. The smaller detection frequencies that were 

based on a common assessment level compared to using no 

assessment level illustrate the low concentrations at which 

many of these compounds were detected.

Samples from 5 of the 12 principal aquifers accounted for 

the majority of the detections of these compounds; the average 

detection frequencies for these 5 principal aquifers were 

greater than 20 percent and as large as 45 percent (table 4). 

Sampled wells in 4 of these 5 principal aquifers—the glacial 

deposits aquifer system, Central Valley aquifer system, High 

Plains aquifer, and Piedmont and Blue Ridge crystallinerock aquifers—had the shallowest median well depths of 

the 12 aquifers (fig. 2B). Sampled wells in the fifth principal 

aquifer, the Edwards-Trinity aquifer system, were deeper and 

ranked 10 of 12 in median well depth.

Chloroform was the most commonly detected compound 

in this study and was detected in 36 percent of samples. Chloroform was detected in 8 of the 12 principal aquifers; chloroform was removed from the datasets for three of the SWQAs 

because of data-quality concerns (table 3) and was not 

detected in any wells in the Rio Grande aquifer system, which 

was the principal aquifer with wells with the second deepest 

median well depth (table 4; fig. 2B). In general, chloroform 

was detected more commonly in principal aquifers with the 

shallowest median well depths and less commonly in principal aquifers with the deepest median well depths. In samples 

from several of the principal aquifers, one or more additional 

disinfection by-products (DBPs)—bromodichloromethane, 

dibromochloromethane, and (or) bromoform—were detected 

when chloroform was detected. This co-occurrence indicates 

that recharge of chlorinated water to the aquifers is a possible 

source of chloroform and is consistent with previous findings 

from the NAWQA Program (Ivahnenko and Barbash, 2004; 

Ivahnenko and Zogorski, 2006). Potential sources of chloroform and other DBPs include chlorinated water used to irrigate 

lawns, golf courses, parks, gardens, and other areas; septic 

systems; regulated discharge of chlorinated waters to recharge 

facilities; and leakage of chlorinated water from swimming 

pools, spas, and distribution systems used for drinking water 

or wastewater sewers (Ivahnenko and Barbash, 2004).

One-half of the most commonly detected compounds 

were herbicides or herbicide degradates (table 4; fig. 4). The 

common detection of these compounds may be related to their 

widespread use, the large number of compounds analyzed in 

this use group compared to the other 12 use groups, and lower 

LRLs compared to other compounds (Appendix 1). Atrazine, 

simazine, prometon, and metolachlor have both agricultural 

and nonagricultural uses. Atrazine and metolachlor are two of 

the most heavily used agricultural herbicides with much of the 

use for corn production, but they also are used in urban areas 

(Gilliom and others, 2006). Simazine and prometon are used 

in nonagricultural areas for weed control and along rights-ofway, but simazine also is used for agriculture (Gilliom and 

other, 2006). Deethylatrazine, a degradate of atrazine, was 

detected more commonly than atrazine. Deisopropylatrazine, 

a degradate of both atrazine and simazine, was detected less 

commonly than either parent compound. Gilliom and others 

(2006) found that natural features, such as hydrogeology and 

soil characteristics, and agricultural management practices, 

such as irrigation and draining, are stronger factors than the 

influence of land use and pesticide use on the geographic 

distribution of pesticides in groundwater.

The remaining five commonly occurring compounds 

are in two use groups: gasoline hydrocarbons, oxygenates, 

and oxygenate degradates; and solvents (table 4; fig. 4). The 

gasoline oxygenate methyl tert-butyl ether (MTBE) was 

used voluntarily by refineries for the Nation’s Reformulated 

Gasoline Program, and MTBE production peaked in the 

1990s (Zogorski and others, 2006). In a national assessment 

of source waters used by CWSs, MTBE was one of the most 

commonly detected VOCs (Carter and others, 2006). Detections of MTBE in groundwater, after only being used since the 

1990s, indicate how quickly mobile and persistent compounds 

can affect groundwater quality (Zogorski and others, 2006). 

Also, the occurrence of relatively recently introduced 

compounds in source water is a potential indicator of aquifer 

susceptibility because the presence of MTBE indicates that a 

component of recent recharge is contributing to a well.
Figure 4. Twelve of 258 anthropogenic organic compounds analyzed at all sites were detected using no 

common assessment level in 10 percent or more of source-water samples collected from 221 community 

water system wells during October 2002–July 2005. Only two compounds were detected in 10 percent or 

more of samples when a common assessment level was used. [DBP, disinfection by-product; gasoline 

oxygenate is in the gasoline hydrocarbons, oxygenates, and oxygenate degradates use group.]

DETECTION FREQUENCY, IN PERCENT

Assessment level of 0.1 microgram per liter

All detections

EXPLANATION

0 10 20 30 40 50

cis-1,2-Dichloroethene

1,1,1-Trichloroethane

Trichloroethene

Perchloroethene

Metolachlor

Prometon

Deisopropylatrazine

Simazine

Atrazine

Deethylatrazine

Methyl tert-butyl ether

Chloroform DBP

Gasoline oxygenate

Herbicides 

and 

herbicide 

degradates 

Solvents

Anthropogenic Organic Compounds in Source Water Used by Community Water Systems, 2002–05 15

Four solvents—PCE, trichloroethene (TCE), cis-1,2-

dichloroethene (cis-1,2-DCE), and 1,1,1-trichloroethane 

(1,1,1-TCA)—were detected commonly, and generally at 

higher concentrations than herbicides and herbicide degradates (Appendix 1). PCE was detected in all principal aquifers 

with the exception of wells in the Coastal Lowlands aquifer 

system (table 4), which had some of the deepest wells sampled 

in this study. The common occurrence of these solvents in 

groundwater is related to widespread use, relatively high 

solubility, and the fact that they are not readily degraded in 

groundwater, except under reducing conditions (Pankow and 

Cherry, 1996; Beek, 2001). Generally, two or more of these 

solvents were detected in the same sample. The co-occurrence 

of TCE and cis-1,2-DCE with PCE in some cases could be the 

result of degradation of PCE to these compounds. However, 

both TCE and cis-1,2-DCE have the potential to be primary 

contaminants because of their use in industrial and commercial settings. Determining whether the occurrence of these 

compounds is related to degradation or use is beyond the 

scope of this report.

The compounds detected in 10 percent or more of 

samples in this study generally correspond to those detected 

most commonly in groundwater across the country as part 

of the NAWQA Program, although detection frequencies generally were higher in this study than in previous 

NAWQA studies (fig. 5). Deethylatrazine, atrazine, simazine, prometon, and metolachlor were the most commonly 

detected pesticides in groundwater sampled by the NAWQA 

Program during 1992–2001 (fig. 5A; Gilliom and others, 

2006). Similarly, chloroform, which was the most commonly 

detected compound in this study, also was the most commonly 

detected VOC in aquifers sampled by the NAWQA Program 
Table 4. Detection frequencies of compounds detected in 10 percent or more of source-water samples by principal aquifer using no assessment level, October 2002–July 2005.

[Principal aquifers are listed in order of shallowest to deepest median well depth. Numbers in bold type indicate detection in more than 50 percent of samples. DBP, disinfection by-product; MTBE, methyl tertbutyl ether; --, data removed from dataset because of data-quality concerns; NA, not applicable]

Principal aquifer

Average 

detection 

frequency of the 

12 commonly 

detected 

compounds 

(percent)

DBP

Gasoline 

oxygenate Herbicides and herbicide degradates Solvents

Chloroform MTBE Deethyl- atrazine Atrazine Simazine Deiso- propyl- atrazine Prome- ton Metol- achlor Per- chloro- ethene Tri- chloro- ethene cis- 1,2-Di- chloro- ethene 1,1,1- Tri- chloro- ethane

Glacial deposits aquifer 

system

27 43 32 36 30 30 16 25 14 27 30 14 36

Central Valley aquifer 

system

33 87 7 67 60 60 53 0 13 40 7 0 7

High Plains aquifer 21 20 0 60 60 13 13 0 13 27 27 13 0Piedmont and Blue Ridge 

crystalline-rock aquifers

145 -- 67 100 80 33 54 27 73 20 13 7 20

Cambrian-Ordovician 

aquifer system

13 20 0 20 20 0 0 7 7 7 33 40 7

Basin and Range basin-fill 

aquifers

9 33 7 20 20 7 7 0 0 13 0 7 0

Denver Basin aquifer 

system

1

4 -- 8 8 8 0 0 8 0 8 0 0 0

Floridan aquifer system 13 43 3 33 23 13 7 17 0 13 3 3 0Columbia Plateau basinfill and basaltic-rock 

aquifers

8 27 0 7 13 7 0 7 7 7 7 13 0

Edwards-Trinity aquifer 

system

22 60 0 53 47 13 7 13 7 53 13 0 0

Rio Grande aquifer system 3 0 0 0 0 0 0 0 0 7 13 13 0Coastal Lowlands aquifer 

system

1 13 0 0 0 0 0 0 0 0 0 0 0

Number of principal 

aquifers in which the compound was detected

NA 9 6 10 10 8 7 7 7 11 9 8 4

1Average calculated using 11 compounds.

16 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater
Figure 5. Similar compounds were detected but detection frequencies were greater for compounds detected commonly in 

source-water samples collected for Source Water-Quality Assessments during October 2002–July 2005 than in groundwater 

sampled for other National Water-Quality Assessment studies for A, herbicides and herbicide degradates; and B, the 

disinfection by-product chloroform, the gasoline oxygenate methyl tert-butyl ether, and solvents.

A

Source Water-Quality Assessment 

 sites (2002−2005)

National groundwater pesticide data 

 (1992−2001) (Gilliom and others, 2006)

All detections

Detections equal to or greater than 

 0.1 microgram per liter

All detections

Detections equal to or greater than 

 0.1 microgram per liter

EXPLANATION

National groundwater volatile organic 

 compound data (1985−2001)

 (Zogorski and others, 2006)

All detections

Detections equal to or greater than 

 0.2 microgram per liter

Atrazine

Deethylatrazine

Metolachlor

Simazine

Prometon

0 10 20 30 40

DETECTION FREQUENCY, IN PERCENT

B

cis-1,2-Dichloroethene

1,1,1-Trichloroethane

Trichloroethene

Perchloroethene

Methyl tert-butyl ether

Chloroform

Solvents

Gasoline oxygenate

Disinfection by-product

Herbicides and herbicide degradates

Anthropogenic Organic Compounds in Source Water Used by Community Water Systems, 2002–05 17

during 1985–2001 (Zogorski and others, 2006; fig. 5B) and 

in a national study of source water from CWSs that included 

groundwater and surface-water supplies (Grady, 2003). 

The compounds MTBE, PCE, TCE, and 1,1,1-TCA also 

were among the most commonly detected VOCs in aquifers 

sampled by the NAWQA Program (Zogorski and others, 2006; 

fig. 5B). Of the 12 commonly detected compounds in this 

study, cis-1,2-DCE is the only compound that was not among 

the most commonly detected VOCs in the national NAWQA 

VOC study during 1985–2001.

The higher detection frequencies for most of the 

commonly detected compounds in this study as compared to 

the detection frequencies in previous national studies (Gilliom 

and others, 2006; Zogorski and others, 2006; fig. 5) may 

be related to the type of wells sampled. Many of the wells 

sampled for the NAWQA Program were relatively low-capacity wells, such as domestic wells. The CWS wells sampled in 

this study are relatively high capacity and likely have larger 

contributing areas than do most domestic wells. Zogorski 

and others (2006) also observed larger detection frequencies 

in samples from public-supply wells than in samples from 

domestic wells.

Herbicide Degradates at Selected Sites

Additional samples were collected from 73 wells in 

the Cambrian-Ordovician aquifer system, glacial deposits 

aquifer system, High Plains aquifer, Piedmont and Blue Ridge 

crystalline-rock aquifers, and Rio Grande aquifer system and 

analyzed for 3 herbicides and 16 degradates. These degradates 

were analyzed because parent herbicides had potential use in 

these study areas and because of the similar or greater persis-
Figure 6. Summed concentrations of degradates generally were greater than concentrations 

of parent compounds for chloroacetanilide degradates and generally were similar to or greater 

than concentrations of parent compounds for triazine degradates in source-water samples 

collected October 2002–July 2005. [Sum of acetochlor degradates: acetochlor ethane sulfonic 

acid and acetochlor oxanilic acid; alachlor degradates: alachlor ethane sulfonic acid, alachlor 

ethane sulfonic acid 2nd amide, and alachlor oxanilic acid; metolachlor degradates: metolachlor 

ethane sulfonic acid and metolachlor oxanilic acid; atrazine degradates: deethylatrazine, 

deisopropylatrazine, 2-hydroxyatrazine, and deethyldeisopropylatrazine.]

0.001 0.01 0.1 1 10

0.001

0.01

0.1

1

10

SUMMED DEGRADATE CONCENTRATION, IN MICROGRAMS PER LITER

PARENT CONCENTRATION, IN MICROGRAMS PER LITER

1:1

Nondetections set to 0.001

Atrazine (4)

Acetochlor (2)

Alachlor (3)

Metolachlor (2)

Triazine

Chloroacetanilides

Number of degradate

compounds detected

(2)

18 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

others, 2004). These results highlight the fact that information 

on the occurrence and concentrations of degradates may be as 

important as information for the parent compound for some 

pesticides particularly if the degradate toxicity or mode of 

action is similar to that of the parent compound.

Acetochlor, alachlor, and metolachlor degradates do not 

have drinking-water standards but are listed on the USEPA 

drinking-water Contaminant Candidate List and are included 

in the Unregulated Contaminant Monitoring Program (U.S. 

Environmental Protection Agency, 2007a). The USEPA 

uses occurrence data along with information on health risks, 

analytical methods, and treatment technologies to determine 

tence of some degradates relative to the parent compound 

(Thurman and others, 1992; Kalkhoff and others, 1998).

Of the chloroacetanilide herbicides detected, alachlor 

and metolachlor degradates generally were detected more 

commonly, and summed degradate concentrations generally 

were greater than the parent herbicide concentration (fig. 6; 

Appendix 1). Acetochlor and its degradates were detected in 

a sample from one well. The summed degradate concentrations of the triazine herbicide atrazine generally were similar 

to or greater than atrazine concentrations (fig. 6). A similar 

relation was observed between concentrations of these same 

parent herbicides and their degradates in groundwater samples 

collected in the Upper Illinois River Basin (Groschen and 
Anthropogenic Organic Compounds in Source Water Used by Community Water Systems, 2002–05 19

whether any of the listed pesticide degradates are candidates 

for future drinking-water standards.

Comparison to Human-Health Benchmarks

About one-half of the compounds detected in source 

water have a human-health benchmark to which concentrations in samples can be compared. Concentrations of 

compounds in source water were compared to human-health 

benchmarks, as part of a screening level assessment; however, 

MCLs are not directly applicable to source-water samples. 

Five compounds (1,2-dibromoethane, dieldrin, acrylonitrile, 

PCE, and TCE) were detected in source water at concentrations greater than their applicable human-health benchmark 

(BQ values greater than 1; Appendix 1). BQ values for all 

other detected compounds were one or more orders of magnitude less than 1, and 84 percent of the concentrations had BQ 

values that were two or more orders of magnitude less than 1.

Seven of the 12 commonly detected compounds have 

MCLs and two have HBSLs to which concentrations in 

samples were compared. Of these commonly detected 

compounds, only PCE and TCE were detected in samples at 

concentrations greater than the human-health benchmark (one 

sample for PCE and two samples for TCE; fig. 7). Although 

PCE and TCE were detected in more than 10 percent of the 

samples, few of the measured concentrations were within an 

order of magnitude of the MCL (BQ values greater than 0.1; 

fig. 7).

Concentrations of those compounds commonly detected 

that have human-health benchmarks generally are not high 

enough to be of human-health concern as individual contaminants. All chloroform concentrations and all summed trihalomethane (THM) concentrations were less than the 80 μg/L 

MCL for the sum of chloroform, bromodichloromethane, 

dibromochloromethane, and bromoform. All herbicide concentrations were less than their applicable human-health benchmark; only one atrazine concentration was within an order of 

magnitude of the MCL (fig. 7). The commonly detected herbicide degradates deethylatrazine and deisopropylatrazine do not 

have human-health benchmarks. The summed concentrations 

of atrazine and its chlorinated degradates were less than the 

MCL of 3 μg/L in all samples.

The gasoline oxygenate MTBE does not have a humanhealth benchmark; however, the USEPA Office of Water 

placed MTBE on the Contaminant Candidate List for further 

evaluation to determine whether a drinking-water standard 

should be established (U.S. Environmental Protection Agency, 

2007b). MTBE is included in the Unregulated Contaminant 

Monitoring Program (U.S. Environmental Protection Agency, 

2007a), which requires large public water systems and a selection of small and medium public water systems to monitor 

for selected compounds in their water supplies. The greatest 

measured concentration of MTBE (1.88 μg/L) was considerably less than the lower control level of 20 μg/L recommended 

by USEPA in 1997 to prevent taste and odor effects (U.S. 

Environmental Protection Agency, 1997).

Concentrations of compounds that were not detected 

commonly also were less than applicable human-health benchmarks in most samples (Appendix 1). Three compounds—

1,2-dibromoethane, dieldrin, and acrylonitrile—were each 

detected once at concentrations greater than their humanhealth benchmark (BQ values greater than 1). The MCL for 

1,2-dibromoethane is 0.05 μg/L, and the reported concentration was 0.072 μg/L. Dieldrin and acrylonitrile both have 

HBSLs with relatively low concentrations of 0.002 μg/L and 

0.06 μg/L, respectively, and had reported concentrations of 

0.024 μg/L and 0.504 μg/L, respectively (Appendix 1). Five 

compounds—benzene, alachlor, vinyl chloride, 1,1-dichloroethene, and carbon tetrachloride—were each detected once at 

concentrations within an order of magnitude of their humanhealth benchmark (BQ values greater than 0.1).

Mixtures of Compounds

Mixtures can occur in groundwater because of the persistence of compounds, presence of parent compounds and their 

degradates, co-occurrence of compounds in the source material 

such as gasoline, and widespread use and overlapping sources 

of compounds (Squillace and others, 2002). The potential 

human-health effects of mixtures of organic compounds are 

largely unknown and have not been extensively studied. The 

effect of one compound on another’s toxicity may be additive, 

antagonistic (one compound may lessen the effect of another), 

or synergistic; much of the growing concern about exposure to 

mixtures of compounds is related to the potential for synergistic effects (Carpenter and others, 2002). Synergism is when 

the effect of exposure to a mixture is greater than, or different 

from, the additive effect of the compounds. Drinking-water 

standards (MCLs) and other human-health benchmarks generally are based on toxicity data for individual compounds, and 

the effects of specific mixtures of compounds at low levels are 

not well understood. With a few exceptions for pesticides with 

common modes of action, human-health benchmarks generally 

are not available for specific mixtures. Continued research is 

needed on potential toxicity of such compound mixtures, and 

evaluation of the potential effects of mixtures is an increasingly important component of the risk assessment methods 

used by the USEPA, the Agency for Toxic Substances and 

Disease Registry (2004), and other agencies.

Although concentrations at which most compounds 

were detected were relatively low (less than 1 μg/L) and 

concentrations greater than the human-health benchmark 

were uncommon, 55 percent of the source-water samples 

contained mixtures of two or more compounds (fig. 8). The 

most common mixtures included those compounds detected 

most commonly, such as chloroform, MTBE, herbicides and 

herbicide degradates, and solvents.

Mixtures occurred more commonly, and with greater 

numbers of compounds, in samples from shallow wells than in 
Figure 7. Concentrations of commonly detected compounds were A, generally less than 1 microgram per liter; and 

B, generally much less than one-tenth of human-health benchmarks for samples collected October 2002–July 2005.

BQ = 0.1 BQ = 1

0.001 0.01 0.1 1 10 100 1,000

CONCENTRATION, IN MICROGRAMS PER LITER

Methyl tert-butyl ether

Chloroform

Metolachlor

Prometon

Deisopropylatrazine

Simazine

Atrazine

Deethylatrazine

cis-1,2-Dichloroethene

1,1,1-Trichloroethane

Trichloroethene

Perchloroethene

A

0.0001 0.001 0.01 0.1 1 10 100

BENCHMARK QUOTIENT (BQ) VALUE

0.000001 0.00001

B

Chloroform

Metolachlor

Prometon

Simazine

Atrazine

cis-1,2-Dichloroethene

1,1,1-Trichloroethane

Trichloroethene

Perchloroethene

Disinfection by-product

Gasoline oxygenate

Herbicides and herbicide degradates

Solvents

Disinfection

by-product

Herbicides

Solvents

EXPLANATION

Bold type indicates an unregulated compound and underlined type indicates the 

unregulated compound does not have a Health-Based Screening Level

Note: Disinfection by-products are compared to the Maximum Contaminant Level of 

80 micrograms per liter for the sum of four trihalomethanes.

Maximum Contaminant Level (MCL)

Health-Based Screening Level (HBSL)

Human-health benchmark

20 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater
NUMBER OF COMPOUNDS DETECTED IN SAMPLE

0

20

40

60

80

100

38 to 213 feet (53 wells)

215 to 401 feet (55 wells)

403 to 748 feet (53 wells)

750 to 2,070 feet (55 wells)

0 4 8 12 16 20 24 28 32 36

PERCENTAGE OF SAMPLES WITH EQUAL OR GREATER NUMBER OF DETECTED COMPOUNDS 

WELL DEPTH QUARTILE

Figure 8. The number of anthropogenic organic compounds detected as mixtures in source-water samples collected 

during October 2002–July 2005 generally was greater in source water from shallow wells than from deep wells.

Anthropogenic Organic Compounds in Source Water Used by Community Water Systems, 2002–05 21

samples from deep wells (fig. 8). Wells were divided into four 

groups using well depth quartiles. Two or more compounds 

were detected in 74 and 73 percent of the samples from the 

two shallowest groups of wells (38–213 ft and 215–401 ft, 

respectively; fig. 8). Two or more compounds were detected in 

47 and 27 percent of the samples from wells in the two deepest 

groups (403–748 ft and 750–2,070 ft, respectively). For the 

well groups with depths less than about 750 ft, a similar 

percentage of wells (4–9 percent) had 11 or more compounds 

detected in a sample (fig. 8). The maximum number of 

compounds in a sample from the deepest wells (750 ft and 

greater) was nine (fig. 8).

The common co-occurrence of organic compounds in 

source waters as mixtures indicates a need to better understand which specific combinations of compounds occur most 

commonly and which mixtures may be a potential concern 

for human health. Identification of specific combinations 

of compounds would provide perspective on patterns of 

co-occurrence that may be important as more is learned about 

sources and potential health effects of mixtures. These are 

important research topics for the future, but are beyond the 

scope of this report.

Factors that May Affect Source-Water Quality

Many different factors may affect the occurrence of the 

anthropogenic organic compounds monitored in this study. 

Some of the most important factors likely related to sourcewater quality include the use of a compound in the contributing area of the well, pumping capacity of the well, recharge, 

average groundwater residence time, and aquifer geochemistry. A detailed evaluation of these factors was beyond the 

scope of this study. A general characterization of the occurrence of commonly detected compounds with respect to 

factors such as well depth and aquifer lithology helps to put 

the results into context and explain some of the differences in 

the occurrence of compounds among sites.

The occurrence of the 12 most commonly detected 

compounds was associated with well depth (Kruskal-Wallis 

rank-sum test p-value < 0.0001; fig. 9). One or more of 

the 12 most commonly detected compounds were found 

in 77 percent of samples from the shallowest well group 

(38–213 ft), and the occurrence decreased to 29 percent of 

samples from the deepest well group (750–2,070 ft; fig. 9A). 

Similarly, the number of compounds in a sample generally 

decreased as well depth increased (fig. 9B). No compounds 
NUMBER OF THE MOST COMMONLY DETECTED COMPOUNDS 

DETECTED PER SAMPLE

B 53 55 53 55

Interquartile

range

0

25

50

75

100

PERCENTAGE OF SAMPLES IN WHICH ONE OR MORE OF THE MOST 

COMMONLY DETECTED COMPOUNDS WERE DETECTED 

38–213 215–401 403–748 750–2,070

WELL DEPTH QUARTILE, IN FEET

A 53 55 53 55

EXPLANATION

Number of values 

75th percentile

Median

25th percentile

Outlier data value more 

 than 1.5 times the interquartile 

 range outside the quartile

Data value less than or equal 

 to 1.5 times the interquartile

 range outside the quartile

55

38–213 215–401 403–748 750–2,070

WELL DEPTH QUARTILE, IN FEET

0

2

4

6

8

10

12

14

Figure 9. The 12 most commonly detected compounds had A, greater detection frequencies; and B, greater numbers of compounds 

detected in source-water samples from shallower wells than from deeper wells during October 2002–July 2005.

22 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater
Unconsolidated 

glacial

deposits

Unconsolidated 

and 

semiconsolidated

sediments

Sandstone

 and 

carbonate

rocks

Igneous

and 

metamorphic

rocks

LITHOLOGY, IN ORDER OF INCREASING MEDIAN WELL DEPTH

44 77 72 28

NUMBER OF THE MOST COMMONLY DETECTED COMPOUNDS DETECTED PER SAMPLE

0

2

4

6

8

10

12

14 EXPLANATION

Number of values 

75th percentile

Median

25th percentile

Outlier data value more 

 than 1.5 times the interquartile 

 range outside the quartile

Data value less than or equal 

 to 1.5 times the interquartile

 range outside the quartile

28

Interquartile

range

Figure 10. Large differences in occurrence of the 12 most commonly detected compounds were not attributable to aquifer lithology 

although fewer compounds generally were detected in source-water samples from wells completed in sandstone and carbonate rocks 

than from wells completed in other lithology groups. Most samples collected during October 2002–July 2005 contained fewer than three 

compounds for each of the four lithology groups.

Anthropogenic Organic Compounds in Source Water Used by Community Water Systems, 2002–05 23

were detected in samples from one-half of the wells in 

the deepest well group. The more common occurrence of 

compounds in samples from shallow wells than deep wells 

likely is a result of shorter average groundwater residence 

times in shallow wells.

Large differences in the occurrence of the 12 most 

commonly detected compounds generally were not attributable 

to aquifer lithology. Wells were divided into four lithology 

groups. Most samples from all four lithology groups contained 

fewer than three of the most commonly detected compounds 

(fig. 10). The number of compounds detected was significantly 

different between the sandstone and carbonate rocks group 

and the other three lithology groups (Kruskal-Wallis rank-sum 

test p-value = 0.02), and one-half of the samples from the 

sandstone and carbonate rocks group did not have a detection 

of any commonly detected compound. Wells in this lithology 

group, however, include some of the deepest wells that were 

sampled; one-half of the sampled wells are deeper than 548 ft 
24 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

and the deepest well is 1,800 ft (fig. 2A). Samples from wells 

completed in unconsolidated glacial deposits generally had 

the largest number of detections (fig. 10), but these wells were 

among the shallowest sampled (median well depth of 124 ft).

Comparisons of Selected Organic 

Compounds in Source Water and 

Finished Water Sampled in 2004 

and 2005

In addition to characterizing the occurrence of these 

compounds in source water, a secondary purpose of this report 

is to provide comparisons of selected compounds in source 

water with their occurrence in finished water (water that has 

passed through treatment processes but prior to distribution). 

During June 2004–September 2005, samples of source water 

and finished water were collected from 94 wells. Sampling 

of most (79) of these wells during this timeframe generally 

focused on analytical suites that included compounds found 

to occur most commonly or at relatively high concentrations 

during the initial source-water sampling from October 2002 

to July 2005. The remaining 15 sites were those in the Rio 

Grande aquifer system, where source-water samples were only 

collected one time, and all samples (both source and finished) 

were analyzed for all 258 compounds plus the additional 

3 herbicides and 16 herbicide degradates. The source-water 

results for wells in the Rio Grande aquifer system were 

included in the source-water characterization presented previously for 2002–05 and are included in this section along with 

the associated finished-water results. In general, the number 

of compounds analyzed in most source- and finished-water 

samples was less than the 258 compounds that were analyzed 

in all source-water samples during 2002–05. As a result of 

the more targeted sampling, the detection frequencies of 

compounds in source water would be expected to be greater 

than during the previous sampling. Finished-water samples 

were analyzed for the same compounds that were analyzed for 

in the associated source-water samples.

Finished-water samples were collected following all 

water-treatment processes and before the water entered the 

distribution system at each CWS. Finished-water samples 

from 34 CWS wells were not blended with water from other 

wells prior to distribution; however, 60 finished-water samples 

represented water blended with water from one or more wells 

at the CWS. In either case, only one well was sampled for 

source-water characterization. Differences in occurrence and 

concentrations of compounds between source and finished 

water might be expected for blended finished-water samples 

because of dilution or addition of compounds from wells not 

monitored. Other possible factors, in addition to blending, 

that could cause differences in occurrence between sourceand finished-water samples include inadequate time allowed 

between collecting source- and finished-water samples, the 

inadvertent addition of compounds in finished water from 

pipes and other plumbing, treatment-plant maintenance, volatilization, or potential analytical variability associated with 

low concentrations at or near LRLs.

The comparison of source- and finished-water samples in 

this report is not intended as an evaluation of water-treatment 

efficacy at CWSs, which would require precise timing of 

sampling at different stages of water treatment; rather, the 

results represent an initial assessment of whether compounds 

present in source water also are present in finished water. The 

CWSs sampled generally are typical of many systems across 

the Nation where chlorine disinfection is the primary watertreatment process used. It is important to note that, in general, 

disinfection is not designed to remove the organic compounds 

detected in this study. However, when source water is known 

to contain regulated compounds at concentrations near or 

greater than an MCL, CWSs may blend with cleaner water 

sources or use additional water treatment, such as granular 

activated carbon or air-stripping towers, to remove organic 

compounds.

The formation of disinfection by-products as a result 

of the disinfection of drinking water is well documented 

(Rook, 1974). Disinfection by-products include, for example, 

the THMs chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Other common disinfection 

by-products include chlorate, chloral hydrate, haloacetic 

acids, and haloacetonitriles; however, these other disinfection by-products were not monitored in this study. Disinfection by-products form when organic matter in source water 

reacts with the added disinfectant used to protect the drinking 

supply against water-borne pathogens such as Escherichia coli

and Norovirus. Consequently, concentrations of THMs are 

expected to be greater in finished water than in source water.

Finished-water samples were “quenched” with ascorbic 

acid at the time of sample collection to scavenge the free 

chlorine that might react with any compounds present in the 

sample. Therefore, finished-water data are not necessarily 

representative of drinking-water quality at the tap (or point of 

delivery) because additional contact time with free chlorine 

in the distribution system may change concentrations of some 

of the constituents detected in the finished water at the sample 

collection point.

Commonly Detected Compounds

When all compounds from the 2004–05 sampling of 

source water and finished water are considered, 99 compounds 

were detected. Of these 99 compounds, 84 compounds were 

detected in source water and 75 compounds were detected 

in finished water; however, 33 and 24 of those compounds, 

respectively, were detected only once. Thirty-one compounds 

were detected commonly (defined as detected in 10 percent 

or more of samples) in either source- or finished-water 

samples (table 5). The majority of these compounds were 

in the herbicide and herbicide degradates and solvents use 
Table 5. Detection frequency of compounds detected in 10 percent or more of source- and (or) finished-water samples collected 

during June 2004–September 2005.

[Bold type indicates compounds that were detected commonly in samples collected during October 2002–July 2005. ND, not detected]

Compound (number of source-water samples/number of 

finished-water samples)

Detection frequency (percent)

Source water Finished water

Disinfection by-products

Bromodichloromethane (71/71) 13 79

Bromoform (71/71) 7.0 62

Chloroform (56/56) 57 88

Dibromochloromethane (71/71) 7.0 72

Fumigant-related compound

1,4-Dichlorobenzene (71/71) 11 11

Gasoline hydrocarbons, oxygenates, and oxygenate degradates

m- and p-Xylene (64/64) ND 14

Methyl tert-butyl ether (71/71) 16 16

Herbicides and herbicide degradates

2-Hydroxyatrazine (61/59) 28 29

Acetochlor ethane sulfonic acid (32/32) 19 19

Acetochlor oxanilic acid (32/32) 9.4 19

Acetochlor/metolachlor ethane sulfonic acid 2nd amide (32/32) 3.1 13

Alachlor ethane sulfonic acid (17/17) 77 77

Alachlor ethane sulfonic acid 2nd amide (32/32) 13 13

Alachlor oxanilic acid (32/32) 25 28

Atrazine (66/66) 59 55

Bentazon (61/59) 13 6.8

Deethylatrazine (66/66) 56 53

Deisopropylatrazine (61/59) 31 20

Metolachlor (64/65) 13 11

Metolachlor ethane sulfonic acid (32/32) 47 41

Metolachlor oxanilic acid (32/32) 38 34

Metsulfuron methyl (61/59) ND 12

Prometon (61/62) 25 19

Simazine (48/48) 46 46

Manufacturing additive

Triphenyl phosphate (53/55) 1.9 20

Solvents

1,1,1-Trichloroethane (71/71) 20 14

1,1-Dichloroethane (71/71) 13 8.5

1,1-Dichloroethene (71/71) 11 8.5

cis-1,2-Dichloroethene (71/71) 20 18

Perchloroethene (71/71) 39 37

Trichloroethene (71/71) 27 23

Comparisons of Selected Organic Compounds in Source Water and Finished Water Sampled in 2004 and 2005 25
26 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

groups. Detection frequencies of all compounds detected in 

source or finished water are summarized in Appendix 3. The 

characterization of results in this section of the report focuses 

on the 31 commonly detected compounds because relatively 

little information can be inferred from compounds that were 

detected in only a few samples.

In general, the 12 compounds that were detected 

commonly in source water during the October 2002–July 2005 

sampling also were detected commonly in source water during 

the June 2004–September 2005 sampling and at greater detection frequencies (table 5; Appendix 1). Nineteen additional 

compounds were detected in more than 10 percent of either 

source- or finished-water samples (table 5). This, however, is 

to be expected based on the well selection strategy followed 

for the 2004–05 source- and finished-water sampling for 

this study, which focused on wells that had samples with 

compounds detected commonly or at large concentrations 

during the initial (2002–05) source-water sampling. Two 

compounds, m- and p-xylene and metsulfuron methyl, were 

detected only in finished water. However, detection of m- and 

p-xylene and metsulfuron methyl was primarily in blended 

finished-water samples (6 of 9 samples and 6 of 7 samples, 

respectively). The occurrence of these compounds primarily 

in blended finished-water samples may be the result of their 

presence in water from wells that were not sampled as part of 

this study.

With the exception of the disinfection by-products, 

detection frequencies of most (17) of the commonly detected 

compounds were similar (difference of 5 percent or less) 

between source water and finished water (table 5), even 

though 60 of the 94 finished-water samples were from CWSs 

that blend water. For the eight compounds with detection 

frequencies in finished water that differed by 6 percent or 

more from detection frequencies in source water, about twothirds of the sites were CWSs with blended finished water. 

The detection frequencies for bentazon differed by 6 percent 

between source and finished water; however, all of these 

finished-water samples were nonblended. The four THMs 

were detected in source water, but detection frequencies were 

much greater in finished water. Chloroform was the most 

commonly detected disinfection by-product in finished water 

(88 percent), followed by bromodichloromethane (79 percent), 

dibromochloromethane (72 percent), and bromoform 

(62 percent; table 5).

Comparison to Human-Health Benchmarks

Concentrations of all compounds commonly detected 

in finished water were less than their human-health benchmarks. More than one-half of the commonly detected 

compounds have a human-health benchmark to which 

concentrations were compared; 13 compounds have an 

MCL and 5 compounds have an HBSL (fig. 11). Eight of the 

commonly detected compounds (1,4-dichlorobenzene, m- and 

p-xylene, 2-hydroxyatrazine, bentazon, metolachlor, metsulfuron methyl, prometon, and 1,1,1-TCA) had finished-water 

concentrations that were two to six orders of magnitude 

less than the human-heath benchmarks. Concentrations of 

compounds detected in fewer than 10 percent of finished-water 

samples were more than an order of magnitude less than their 

applicable benchmarks (BQ values of 0.1 or less; Appendix 1).

Concentrations of disinfection by-products were expected 

to increase in finished water relative to source water because 

of disinfection. The MCL for total THMs is 80 μg/L, and 

summed concentrations were less than this benchmark in 

finished water from all wells sampled (fig. 11; Appendix 1). 

The concentrations of total THMs were within an order of 

magnitude (BQ values greater than 0.1) of the MCL in finished 

water from nine sites, but only three detections of chloroform and one detection of bromoform were within an order 

of magnitude of the MCL (fig. 11; Appendix 3). The solvents 

PCE (two detections) and TCE (one detection) were the only 

other compounds detected in finished water at concentrations 

within an order of magnitude of the MCL.

Comparison of Source- and Finished-Water 

Quality

Finished water from 60 of the source-water sites included 

in this study consisted of a blend of water from the sampled 

source-water well and from one or more additional wells 

located in the well field. The blending of water from additional wells complicates the comparison of occurrence of 

compounds between source water and the associated finished 

water. Source and blended finished water are compared using 

no assessment level to generally characterize how occurrence 

in samples from CWSs that blend water may differ from 

systems that do not blend water. The comparisons of occurrence between source and finished water are not intended to 

be an evaluation of water-treatment efficacy at CWSs. Rather, 

the results characterize the extent to which compounds present 

in source water also are present in finished water. Disinfection 

by-products are not included in the following sections comparing source- and finished-water quality; however, they are 

included in the discussion of mixtures.

Nonblended Finished Water

Sixty-six compounds were detected in source- and (or) 

finished-water samples from the 34 sites where finished 

water was not blended with other source water. Of these 

66 compounds, 51 were detected in at least one source-water 

sample and 49 were detected in at least one finished-water 

sample. Some compounds were detected only one time; 

15 compounds were detected one time in source water only 

and 12 compounds were detected one time in finished water 

only. Relatively little information can be inferred from 

compounds that were detected only once in either source or 

finished water.

More than one-half (57 percent) of the detections 

were in both source and finished water, and the concentrations were similar (fig. 12). The difference in concentrations 
Note: Disinfection by-products are compared to the Maximum Contaminant Level (MCL) 

of 80 micrograms per liter for the sum of four trihalomethanes, and xylene isomers are 

compared to the MCL of 10,000 micrograms per liter for total xylenes.

Herbicides and 

herbicide degradates

Solvents

Disinfection by-products

Fumigant-related compound

Gasoline compound

Trichloroethene

Perchloroethene

cis-1,2-Dichloroethene

1,1-Dichloroethene

1,1,1-Trichloroethane

Simazine

Prometon

Metsulfuron methyl

Metolachlor

Bentazon

Atrazine

 2-Hydroxyatrazine

m- and p-Xylene

1,4-Dichlorobenzene

Dibromochloromethane

Chloroform

Bromoform

Bromodichloromethane

0.0001 0.001 0.1 10 100

BENCHMARK QUOTIENT (BQ) VALUE

EXPLANATION

0.000001 0.00001 0.01 1

Bold type indicates an unregulated compound

BQ = 0.1 BQ = 1

Figure 11. Concentrations of commonly detected anthropogenic organic compounds were less 

than human-health benchmarks in finished-water samples collected during June 2004–September 

2005.

Comparisons of Selected Organic Compounds in Source Water and Finished Water Sampled in 2004 and 2005 27

generally was less than 50 percent with a median difference of 

13 percent. Most of the detections in both source and finished 

water were for gasoline-related compounds (gasoline hydrocarbons, oxygenates, and oxygenate degradates), herbicides 

and herbicide degradates, and solvents (fig. 12).

In some cases where compounds were present in both 

source and finished water, concentrations were much lower 

(percentage difference greater than 100) in finished water 

than in source water (fig. 12). For example, three solvents—

1,1,1-TCA, PCE, and TCE, which were detected in source 

water at concentrations greater than 3 μg/L—had concentrations less than 1 μg/L in finished water (fig. 12). This decrease 

in concentration between source and finished water likely is 

attributable to additional water-treatment steps, such as granular activated carbon and (or) air-stripping towers, used by a 

CWS to treat water known to contain elevated concentrations 

of organic compounds. Other detections of these compounds 

in source water at concentrations less than 1 μg/L typically 

had a similar concentration in finished water.

Twenty-seven percent of the detections of compounds 

in source water did not have a corresponding detection in 

finished water (fig. 12). The majority of compounds were 

detected at concentrations less than 1 μg/L, and many were 

detected at concentrations near or less than the LRL and were 

estimated concentrations. Several possibilities, such as transformation or removal during water treatment, particularly if 

additional treatment steps are used to treat the water because 

of known contamination, volatilization, accidental introduction at the wellhead from plumbing or fixtures, or analytical 

variability at concentrations near or less than the LRL, may 

account for the detection of a compound in source water only. 

Disinfection of source water may reduce concentrations of 
0.001 0.01 0.1 1 10 100 1,000 10,000

SOURCE-WATER CONCENTRATION, IN MICROGRAMS PER LITER

FINISHED-WATER CONCENTRATION, IN MICROGRAMS PER LITER

0.001

0.01

0.1

1

10

100

1,000

10,000

Fumigant-related compounds

Fungicides and fungicide degradates

Gasoline hydrocarbons, oxygenates, 

 and oxygenate degradates

Herbicides and herbicide degradates

Insecticides and insecticide degradates

Manufacturing additives

Organic synthesis compounds

Pavement- and combustion-derived 

 compounds

Personal-care and domestic-use products

Refrigerants and propellants

Solvents

EXPLANATION

Acetone

Tetrahydrofuran Methyl ethyl ketone

Nondetections set to 0.001

Perchloroethene

1,1,1-Trichloroethane

Trichloroethene

Methyl isobutyl ketone

m- and p-Xylene

o-Xylene

Primary use or source group

1:1

Figure 12. Concentrations of anthropogenic organic compounds (excluding disinfection by-products) in source and associated 

nonblended finished water generally were similar when detected in both source and finished water for samples collected during 

June 2004–September 2005.

28 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

some compounds through degradation or transformation. For 

example, degradation of organophosphate pesticides as a result 

of chlorination has been documented (Aizawa and others, 

1994). Although finished-water samples were quenched to 

inhibit the effect of free chlorine on the compounds monitored 

by SWQAs, some reactions may occur quickly within the 

water-treatment system, before the finished-water sample was 

collected. For those compounds monitored by SWQAs, Valder 

and others (2008) documented the degradation of several 

compounds as a result of chlorination of source water. In addition, some compounds, particularly solvents and other VOCs, 

may be volatilized at the CWS during the treatment process, 

especially if water treatment includes aeration.

Occurrence in source water and not in finished water 

may not necessarily reflect a change as a result of water 

treatment but may result from maintenance at the wellhead. 

For example, acetone, methyl ethyl ketone, and tetrahydrofuran were detected in source water at concentrations 

greater than 50 μg/L but not in the associated finished-water 

sample (fig. 12; Appendix 3). These three compounds were 

not detected in source water from the same well in the initial 

sample collected during October 2002–July 2005. In samples 

from another well, tetrahydrofuran and methyl ethyl ketone 

were detected in the intial source water sample at concentrations greater than 300 μg/L, but only tetrahydrofurn was 

detected in the second sample at a concentration of 1.1 μg/L. 

The presence of these compounds at high concentrations in 

only one source-water sample may be the result of maintenance at the sampling point at the well; however, this possible 

source was not confirmed.

Less than one-quarter (16 percent) of the detections in 

finished water (excluding disinfection by-products) did not 

have a corresponding detection in source water (fig. 12). 

Concentrations generally were low (near the LRL); however, 

concentrations of methyl isobutyl ketone, m- and p-xylene, 

and o-xylene were greater than 1 μg/L in one sample. Determining the possible sources of the compounds that were 

detected only in finished water was beyond the scope of this 
Fumigant-related compounds

Fungicides and fungicide degradates

Gasoline hydrocarbons, oxygenates, 

 and oxygenate degradates

Herbicides and herbicide degradates

Insecticides and insecticide degradates

Manufacturing additives

Organic synthesis compounds

Pavement- and combustion-derived 

 compounds

Personal-care and domestic-use products

Refrigerants and propellants

Solvents

Plant- or animal-derived biochemicals

EXPLANATION

Trichloroethene

SOURCE-WATER CONCENTRATION, IN MICROGRAMS PER LITER

FINISHED-WATER CONCENTRATION, IN MICROGRAMS PER LITER

0.001

0.01

0.1

1

10

100

1,000

10,000

0.001 0.01 0.1 1 10 100 1,000 10,000

Nondetections set to 0.001 Primary use or source group

1:1

1,1-Dichloroethene 1,1-Dichloroethane and

1,1,1-Trichloroethane

Trichloroethene

Figure 13. Concentrations of anthropogenic organic compounds (excluding disinfection by-products) in source and associated 

blended finished water generally were similar when detected in both source and finished water for samples collected during 

June 2004–September 2005.

Comparisons of Selected Organic Compounds in Source Water and Finished Water Sampled in 2004 and 2005 29

study. However, possible sources of these compounds include 

sealants used at pipe connections or minor components of 

chemicals used for water treatment. Several herbicides or 

herbicide degradates also were detected only in finished water, 

and most were detected at concentrations less than 0.1 μg/L. 

Given the low concentrations of these detections and the 

unlikely event that herbicides would be introduced to the 

finished water, analytical variability of concentrations near the 

LRL is a possible explanation for these unmatched detections.

Blended Finished Water

Water from 60 of the 94 source-water wells was blended 

with water from other wells before distribution. Although 

the comparison between source and blended finished water 

is complicated by the addition of water that has not been 

monitored, the occurrence of compounds for CWSs that 

blended water (fig. 13) generally was similar to the occurrence 

of compounds for CWSs that did not blend water (fig. 12) 

in that one-half of all detections of compounds were in both 

source and finished water. Compounds from the herbicides 

and herbicide degradates and the solvents use groups were 

detected most commonly when a compound was detected in 

both source and finished water (fig. 13).

The variability in concentrations between source water 

and the associated finished water (scatter around the 1:1 line) 

generally was greater for blended than for nonblended 

finished water (figs. 12, 13). For the CWSs that blended water, 

deviation from the 1:1 line for detections in both source and 

finished water (fig. 13) may largely be due to blending or to 

some extent the result of water treatment, particularly where 

additional treatment steps are used to reduce concentrations of 

known contaminants. Determining the cause for these changes 

was beyond the scope of this study.

One-half of the detections of compounds were either 

in source or finished water only. Blending could account for 

many of these unmatched detections especially at low concentrations (less than 0.1 μg/L), but other factors, such as maintenance and chemical use at the CWS, also could account for 
30 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

unmatched detections. Some solvents (1,1,1-TCA, 1,1-dichloroethane, 1,1-dichloroethene, and TCE) detected at concentrations greater than 5 μg/L in source water from one well were 

not detected in the finished-water sample (fig. 13). The CWS 

where this sample was collected treats the drinking water with 

granular activated carbon to reduce concentrations of contaminants known to be present in the source water (Jim Stark, 

U.S. Geological Survey, written commun., 2008). These large 

decreases in concentration likely are predominantly the result 

of the additional water-treatment processes used at this CWS; 

however, in some cases blending may contribute to reducing 

concentrations.

The frequent occurrence of several compounds in both 

source water and the associated blended finished water further 

demonstrates the importance of source-water characterization 

and wellhead protection. About one-half of the detections of 

compounds in source water had corresponding detections in 

the associated finished water and generally were similar to 

results for nonblended water. Finished water from more than 

one-half of the CWSs in the study was blended; however, 

blending did not always reduce concentrations to less than the 

LRL. These findings indicate that the protection of sourcewater quality may be the most effective mechanism to ensure 

high-quality drinking water. That is, preventing or minimizing 

the possibility of occurrence of contaminants may be preferable to treating the water after source-water contamination has 

occurred.

Mixtures

One objective of the comparison between source and 

finished water was to evaluate potential differences in 

the frequency of occurrence and complexity of mixtures 

of organic compounds. The characterization of mixtures 

presented in this section includes disinfection by-products in 

both nonblended and blended finished water. About 70 and 

82 percent of source- and finished-water samples, respectively, 

contained mixtures of two or more compounds (fig. 14). About 

one-half of the source-water samples contained mixtures of 

five or more compounds (median = 12), and about one-half of 

the finished-water samples contained mixtures of six or more 

compounds (median = 13). Mixtures occur more commonly 

in finished water than in source water partly because of the 

formation of disinfection by-products in finished water, which 

increases the number of compounds detected in finished 

water relative to source water (fig. 14). The percentages 

of mixtures of organic compounds were greater in sourcewater samples collected during the second phase of sampling 

(June 2004–September 2005) than during the initial phase of 

sampling (October 2002–July 2005), because sampling during 

the second phase focused on wells where compounds were 

detected most commonly or at relatively higher concentrations during the initial phase. However, the characterization of 

mixtures in source and finished water represents a minimum 

number of compounds in a sample because most samples were 

not analyzed for all of the analytical suites used in the initial 

sampling. In particular, not all samples were analyzed for the 

suite of compounds that included the disinfection by-products.

As described previously in relation to mixture occurrence 

in source water, the potential human-health significance of 

the common occurrence of mixtures of organic compounds 

remains largely unknown. The common occurrence of 

mixtures in both source- and finished-water samples points to 

a need for identifying the specific combinations of compounds 

that occur most commonly and identifying the compounds that 

may be a potential concern for human health. Identification 

of specific combinations of compounds would provide initial 

perspective on co-occurrence that may be important as more is 

learned about sources and potential health effects of mixtures. 

Again, these are important research topics, but are beyond the 

scope of this report.

Summary

During October 2002 to July 2005, source-water samples 

were collected from 221 wells completed in 12 principal 

aquifers in the United States as part of the Source WaterQuality Assessment (SWQA) component of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) 

Program. Each community water system (CWS) well was 

sampled once for analysis of 258 anthropogenic organic 

compounds to characterize the quality of the source water. 

Most of these compounds are unregulated in drinking water 

and include pesticides and pesticide degradates, gasoline 

hydrocarbons, personal-care and domestic-use products, and 

solvents. Source- and finished-water (after treatment and 

before distribution) samples were collected during June 2004 

to September 2005 from selected sites to characterize the 

extent to which compounds detected in the source water were 

present in the finished water.

The CWSs that participated in SWQAs ranged in size 

from single-well systems to systems with multiple wells. In 

many cases where CWSs have multiple wells, the CWSs blend 

water before or after water treatment. The water-treatment 

process predominantly used by the CWSs was disinfection 

with chlorine. Additional water-treatment steps were used by 

CWSs when source water was known to be contaminated with 

organic compounds. These additional water-treatment steps 

included granular activated carbon and air-stripping towers.

Of the 258 compounds analyzed in samples from all 

221 wells, 120 compounds were detected in at least one 

source-water sample. However, 52 compounds were detected 

only once, and many were detected infrequently and at 

concentrations less than 0.1 microgram per liter (μg/L). The 

laboratory analytical methods used in this study have detection 

levels that are commonly 100 to 1,000 times lower than State 

and Federal standards and guidelines for protecting water 

quality. Detections of these compounds do not necessarily 

indicate a concern to human health but rather help to identify 
0 4 8 12 16 20 24 28

0

20

40

60

80

100

NUMBER OF COMPOUNDS DETECTED IN SAMPLE

Finished water

Source water

PERCENTAGE OF SAMPLES WITH EQUAL OR GREATER NUMBER OF DETECTED COMPOUNDS

Figure 14. Both source- and finished-water samples collected during the June 2004–September 2005 sampling 

typically contained mixtures of two or more compounds.

Summary 31

emerging issues and track changes in occurrence and concentrations over time.

The occurrence of compounds in source water varied 

regionally. More compounds and greater total concentrations generally were detected in samples from wells east of 

the Mississippi River than in samples from wells west of the 

Mississippi River. Factors that may account for these differences in occurrence include generally higher groundwater 

recharge rates, shallower well depths, shallower depths to 

groundwater, greater population densities, and more intense 

use of agricultural herbicides east of the Mississippi River 

than west of the Mississippi River.

Twelve compounds were detected in about 10 percent or 

more of source-water. Chloroform was the most commonly 

detected compound in this study and was detected in 

36 percent of samples. One-half of the commonly detected 

compounds in this study were herbicides and herbicide 

degradates (deethylatrazine, atrazine, simazine, prometon, 

metolachlor, and deisopropylatrazine) likely because of their 

widespread use, the large number of compounds analyzed 

in this group, and the low levels at which these compounds 

were analyzed. The compounds perchloroethene (PCE), 

trichloroethene (TCE), 1,1,1-trichloroethane, methyl tertbutyl ether, and cis-1,2-dichloroethene also were detected 

commonly. The most commonly detected compounds in 

source-water samples generally were among those detected 

commonly across the country and reported in previous studies 

by the NAWQA Program.

Samples were collected from a subset of 73 wells and 

analyzed for an additional 3 herbicides and 16 degradates 

in locations where the parent herbicides had potential use. 

Degradates of both alachlor and metolachlor were detected 

more commonly and at similar or greater concentrations than 

concentrations of the parent herbicide. These results highlight 

the fact that information about the occurrence and concentrations of degradates may be as important as information about 

the parent compound for some pesticides, particularly if the 

degradate toxicity or mode of action is similar to that of the 

parent compound.

Detections of compounds at concentrations greater than 

a human-health benchmark were infrequent, and only five 

compounds were detected in source water at a concentration 

greater than the human-health benchmark. Concentration of 

compounds in source water were compared to human-health 
32 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

benchmarks as part of a screening level assessment; however, 

Maximum Contaminant Levels (MCLs) are not directly 

applicable to source-water samples. Measured concentrations of compounds that are regulated in drinking water were 

compared to U.S. Environmental Protection Agency (USEPA) 

MCLs, and concentrations of unregulated compounds were 

compared to Health-Based Screening Levels developed by 

the U.S. Geological Survey in collaboration with USEPA and 

others. Concentrations of TCE were greater than the MCL in 

two samples, and 1,2-dibromoethane and PCE were detected 

in one sample each at a concentration greater than the MCL. 

Acrylonitrile and dieldrin were detected at concentrations 

greater than their respective Health-Based Screening Levels 

in one sample each. All other compounds were detected at 

concentrations less than available human-health benchmarks, 

and 84 percent of the concentrations were two or more orders 

of magnitude less than the benchmark. About one-half of all 

detected compounds do not have human-health benchmarks or 

adequate toxicity information to evaluate results in a humanhealth context. 

About 55 percent of source-water samples contained 

mixtures of two or more compounds. The most common 

mixtures included those compounds detected most commonly, 

such as chloroform, MTBE, herbicides and herbicide degradates, and solvents. Mixtures of compounds occurred more 

commonly and with greater numbers of compounds in water 

from shallow wells than in water from deep wells. Two or 

more compounds were detected in 74 and 73 percent of the 

samples from the two shallowest groups of wells (38–213 feet 

and 215–401 feet, respectively).

The comparison of source- and finished-water quality 

in this report represents an initial assessment of whether 

compounds present in source water also are present in finished 

water. Source-water samples from 94 wells and associated finished-water samples were collected from June 2004 

to September 2005. Most of these samples were analyzed 

for fewer compounds than during the initial source-water 

sampling. Samples were analyzed for those compounds 

detected commonly or at relatively high concentrations during 

the initial source-water sampling. Finished-water samples 

were collected following all of the treatment steps and before 

distribution. The assessment of compounds detected in sourceand finished-water samples is not intended as an evaluation of 

water-treatment efficacy at CWS. In general, the types of treatment used by the CWSs that were sampled were not specifically designed to remove most of the organic compounds 

monitored in this study. Finished-water data are not necessarily representative of drinking-water quality at the tap (or point 

of delivery). Additional contact time with disinfectants in the 

distribution system may change concentrations of some of 

the compounds detected in the finished water at the samplecollection point.

Thirty-one compounds were detected commonly (defined 

as detected in 10 percent or more of samples) in either sourceor finished-water samples during June 2004–September 2005 

and included the 12 compounds detected commonly during the 

initial sampling from October 2002 to July 2005. The majority 

of the compounds were in the herbicide and herbicide degradates and solvents use groups. With the exception of the disinfection by-products, which are expected to form in finished 

water, the detection frequencies of most (17) of the commonly 

detected compounds were similar (difference of 5 percent or 

less) between source and finished water. For those compounds 

with detection frequencies that differed by 6 percent or more 

between source and finished water, about two-thirds of the 

sites were CWSs with blended finished water.

Concentrations of all compounds commonly detected in 

finished water were less than their human-health benchmarks, 

which are available for about one-half of the compounds 

detected in finished-water samples. Eight of the commonly 

detected compounds (1,4-dichlorobenzene, m- and p-xylene, 

2-hydroxyatrazine, bentazon, metolachlor, metsulfuron 

methyl, prometon, and 1,1,1-trichloroethane) had finishedwater concentrations that were two to six orders of magnitude 

less than the human-health benchmarks. The summed concentrations of the trihalomethanes for all of the finished-water 

samples were less than the MCL of 80 μg/L. The concentrations of total trihalomethanes were within an order of magnitude of the MCL in finished water from nine sites, but only 

three detections of chloroform and one detection of bromoform were within an order of magnitude of the MCL. Two 

detections of PCE and one detection of TCE in finished water 

had concentrations within an order of magnitude of the MCL, 

and concentrations of all other compounds were more than an 

order of magnitude less than the benchmark.

Differences in the occurrence of compounds in source 

or finished water could result from water treatment, blending, 

volatilization, or analytical variability at concentrations near or 

less than the laboratory reporting level. At the 34 sites where 

finished water was not blended, about one-half (57 percent) 

of the detections were in both source and finished water, and 

concentrations were similar. Large changes in concentrations from source to finished water in a few samples likely 

are attributable to additional water treatment steps used by 

the CWS to treat water known to contain elevated concentrations of organic compounds. Finished water from 60 of the 

source-water wells sampled in the study was a blend of water 

from two or more wells. Although the comparison between 

source and blended finished water is complicated by the 

addition of water that has not been monitored, the occurrence 

of compounds for CWSs that blended water generally was 

similar to the occurrence of compounds for CWSs that did not 

blend water in that one-half of all detections of compounds 

were in both source and finished water.

Compounds occur more commonly as mixtures in 

finished water than in source water because of the formation of 

disinfection by-products in finished water. Mixtures of two or 

more compounds were detected in about 70 percent of sourcewater samples and in 82 percent of finished-water samples. 

Although concentrations of compounds detected typically 

were considerably less than human-health benchmarks, the 

frequent occurrence of mixtures in finished waters indicates a 
References 33

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Appendixes
38 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002– July 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, bench- mark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Envi- ronmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset] Compound CASRN1 Number of detections for ground- water Number of samples Detection frequency (percent) Laboratory reporting level (μg/L) Maximum con- centration for groundwater (μg/L) Human-health benchmark (μg/L) Type of human-health benchmark Number of con- centrations with BQ >0.1; (1) number of concentrations with BQ >1 All data Censored at 0.1 μg/L Disinfection by-products Chloroform 67–66–3 65 180 36.1 12.8 0.024 5.48 280 MCL -- Bromodichloromethane 75–27–4 17 221 7.7 2.7 .028 .788 280 MCL -- Bromoform 75–25–2 10 221 4.5 3.6 .1 1.9 280 MCL -- Dibromochloromethane 124–48–1 8 221 3.6 3.6 .1 1.01 280 MCL -- Fumigant-related compounds 1,2-Dichloropropane 78–87–5 3 221 1.4 ND 0.029 E0.092 5 MCL -- 1,2-Dibromoethane 106–93–4 1 221 .5 ND .036 E.072 .05 MCL 1(1) 1,2-Dibromo-3-chloro- propane 96–12–8 0 221 ND ND .51 ND .2 MCL -- 1,3-Dichloropropane (CCL) 142–28–9 0 221 ND ND .06 ND -- -- -- 1,4-Dichlorobenzene3 106–46–7 0 221 ND ND .034 ND 75 MCL -- 2,2-Dichloropropane (CCL) 594–20–7 0 221 ND ND .05 ND -- -- -- Bromomethane (CCL) 74–83–9 0 221 ND ND .33 ND 100 HBSL -- cis-1,3-Dichloropropene (CCL) 10061–01–5 0 221 ND ND .05 ND 4,5.3 HBSL -- trans-1,3-Dichloropro- pene (CCL) 10061–02–6 0 221 ND ND .09 ND 4,5.3 HBSL -- Fungicides and fungicide degradates Metalaxyl 57837–19–1 2 221 0.9 ND 0.007 0.035 600 HBSL -- Myclobutanil 88671–89–0 1 221 .5 ND .033 .011 200 HBSL -- Propiconazole 60207–90–1 1 215 .5 ND .01 E.005 70 HBSL -- Benomyl 17804–35–2 0 215 ND ND .022 ND 40 HBSL --

Chlorothalonil 1897–45–6 0 215 ND ND .035 ND 5 HBSL --
Appendixes 39

Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002–July 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset]

Compound CASRN1

Number of 

detections 

for 

groundwater

Number 

of 

samples

Detection frequency 

(percent) Laboratory 

reporting level 

(μg/L)

Maximum concentration for 

groundwater 

(μg/L)

Human-health 

benchmark 

(μg/L)

Type of 

human-health 

benchmark

Number of concentrations with 

BQ >0.1; 

(1) number of 

concentrations 

with BQ >1

All data Censored at 0.1 μg/L

Fungicides and fungicide degradates—Continued

Iprodione 36734–19–7 0 221 ND ND 0.026 ND 40.8 HBSL --Pentachlorophenol 87–86–5 0 211 ND ND 2 ND 1 MCL --

Gasoline hydrocarbons, oxygenates, and oxygenate degradates

Methyl tert-butyl ether 

(MTBE) (CCL)

1634–04–4 28 221 12.7 6.8 0.1 1.88 -- -- --

1,2,4-Trimethylbenzene 

(CCL)

95–63–6 4 176 2.3 .6 .056 2.37 -- -- --

Benzene 71–43–2 4 192 2.1 1.0 .021 .631 5 MCL 1tert-Amyl methyl ether 

(TAME)

994–05–8 3 221 1.4 .9 .04 .281 -- -- --

m- and p-Xylene 106–42–3; 

108–38–3

2 161 1.2 .6 .06 3.28 610,000 MCL --

1,2,3,4-Tetramethylbenzene 488–23–3 2 221 .9 .5 .14 .921 -- -- --1-Ethyl-2-methylbenzene (o-Ethyl 

toluene)

611–14–3 2 221 .9 .9 .06 .666 -- -- --

Isopropylbenzene3 98–82–8 2 221 .9 ND .038 E.073 700 HBSL --Ethylbenzene 100–41–4 1 176 .6 .6 .03 .517 700 MCL --o-Xylene 95–47–6 1 176 .6 .6 .038 2.84 610,000 MCL --1,2,3,5-Tetramethylbenzene 527–53–7 1 221 .5 .5 .18 1.48 -- -- --1,2,3-Trimethylbenzene 526–73–8 1 221 .5 .5 .09 1.51 -- -- --1,3,5-Trimethylbenzene 108–67–8 1 221 .5 .5 .044 .942 -- -- --1-Methylnaphthalene3 90–12–0 1 217 .5 .5 .5 E.12 -- -- --
40 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002– July 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, bench- mark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Envi- ronmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset] Compound CASRN1 Number of detections for ground- water Number of samples Detection frequency (percent) Laboratory reporting level (μg/L) Maximum con- centration for groundwater (μg/L) Human-health benchmark (μg/L) Type of human-health benchmark Number of con- centrations with BQ >0.1; (1) number of concentrations with BQ >1 All data Censored at 0.1 μg/L Gasoline hydrocarbons, oxygenates, and oxygenate degradates—Continued 2,6-Dimethylnaphtha- lene 581–42–0 1 217 0.5 ND 0.5 E0.003 -- -- -- 2-Methylnaphthalene3 91–57–6 1 217 .5 .5 .5 E.23 30 HBSL -- Diisopropyl ether (DIPE) 108–20–3 1 221 .5 .5 .1 .159 -- -- -- Naphthalene (CCL) 91–20–3 1 221 .5 .5 .52 .956 100 HBSL --

n-Butylbenzene 104–51–8 1 221 .5 ND .14 E.069 -- -- --p-Isopropyltoluene 

(CCL)

99–87–6 1 221 .5 ND .08 E.063 -- -- --

sec-Butylbenzene 135–98–8 1 221 .5 ND .06 E.065 -- -- --tert-Amyl alcohol 

(2-Methyl-2-butanol)

75–85–4 0 119 ND ND 1 ND -- -- --

Ethyl tert-butyl ether 

(ETBE)

637–92–3 0 221 ND ND .03 ND -- -- --

Styrene3 100–42–5 0 221 ND ND .042 ND 100 MCL --tert-Butyl alcohol 75–65–0 0 119 ND ND 1 ND -- -- --tert-Butylbenzene 98–06–6 0 221 ND ND .08 ND -- -- --Toluene 108–88–3 0 117 ND ND .02 ND 1,000 MCL --

Herbicides and herbicide degradates

Alachlor ethane 

sulfonic acid

-- 20 58 34.5 22.4 0.02 0.64 -- -- --

Deethylatrazine (DEA) 

(CCL)

6190–65–4 76 221 34.4 4.1 .014 .38 -- -- --

Atrazine 1912–24–9 66 221 29.9 3.2 .007 .335 3 MCL 1Metolachlor ethane 

sulfonic acid

-- 21 73 28.8 21.9 .02 2.72 -- -- --
Appendixes 41

Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002–July 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset]

Compound CASRN1

Number of 

detections 

for 

groundwater

Number 

of 

samples

Detection frequency 

(percent) Laboratory 

reporting level 

(μg/L)

Maximum concentration for 

groundwater 

(μg/L)

Human-health 

benchmark 

(μg/L)

Type of 

human-health 

benchmark

Number of concentrations with 

BQ >0.1; 

(1) number of 

concentrations 

with BQ >1

All data Censored at 0.1 μg/L

Herbicides and herbicide degradates—Continued

Simazine 122–34–9 37 221 16.7 0.5 0.005 0.114 4 MCL --Metolachlor oxanilic 

acid

-- 11 73 15.1 9.6 .02 2.96 -- -- --

Deisopropylatrazine 

(DIA)

1007–28–9 28 215 13.0 .5 .08 .12 -- -- --

Prometon (CCL) 1610–18–0 25 221 11.3 ND .01 .036 400 HBSL --Metolachlor (CCL)3 51218–45–2 24 221 10.9 .9 .006 3.58 700 HBSL --2-Hydroxyatrazine 2163–68–0 20 215 9.3 ND .032 E.035 70 HBSL --Alachlor ethane 

sulfonic acid 2nd amide

-- 4 43 9.3 ND .02 .05 -- -- --

Alachlor oxanilic acid -- 4 73 5.5 2.7 .02 1.23 -- -- --Bentazon 25057–89–0 8 215 3.7 .5 .024 E.49 200 HBSL --Diuron (CCL) 330–54–1 7 215 3.3 .5 .016 E.166 42 HBSL --Bromacil 314–40–9 7 216 3.2 .5 .018 .338 70 HBSL --3,4-Dichloroaniline 95–76–1 3 221 1.4 ND .0045 .009 -- -- --Acetochlor ethane 

sulfonic acid

-- 1 73 1.4 ND .02 .07 -- -- --

Acetochlor oxanilic 

acid

-- 1 73 1.4 1.4 .02 .12 -- -- --

Alachlor 15972–60–8 3 221 1.4 .5 .005 .249 2 MCL 1Metsulfuron methyl3 74223–64–6 3 214 1.4 ND .067 E.035 2,000 HBSL --Dinoseb 88–85–7 2 215 .9 ND .038 E.005 7 MCL --Hexazinone 51235–04–2 1 113 .9 ND .026 E.008 400 HBSL --Imazaquin 81335–37–7 2 215 .9 ND .036 E.01 2,000 HBSL --
42 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002– July 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, bench- mark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Envi- ronmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset] Compound CASRN1 Number of detections for ground- water Number of samples Detection frequency (percent) Laboratory reporting level (μg/L) Maximum con- centration for groundwater (μg/L) Human-health benchmark (μg/L) Type of human-health benchmark Number of con- centrations with BQ >0.1; (1) number of concentrations with BQ >1 All data Censored at 0.1 μg/L Herbicides and herbicide degradates—Continued Imazethapyr3 81335–77–5 2 215 0.9 ND 0.038 E0.007 2,000 HBSL -- Norflurazon 27314–13–2 2 215 .9 ND .02 E.026 10 HBSL -- Picloram 1918–02–1 2 215 .9 ND .032 .085 500 MCL -- Sulfometuron-methyl 74222–97–2 2 215 .9 ND .09 E.004 2,000 HBSL -- Tebuthiuron 34014–18–1 2 218 .9 ND .026 E.03 1,000 HBSL -- 2,4–D 94–75–7 1 215 .5 ND .038 E.009 70 MCL -- Acetochlor (CCL) 34256–82–1 1 221 .5 ND .006 .037 4

1 HBSL --

Clopyralid 1702–17–6 1 215 .5 ND .067 E.013 -- -- --Deethyldeisopropylatrazine (DDA) 3397–62–4 1 213 .5 ND .04 E.069 -- -- --Fluometuron 2164–17–2 1 215 .5 ND .016 E.004 4 HBSL --Metribuzin (CCL) 21087–64–9 1 221 .5 ND .028 .01 90 HBSL --Siduron 1982–49–6 1 215 .5 ND .02 E.012 1,000 HBSL --Terbacil (CCL) 5902–51–2 1 215 .5 ND .026 E.06 90 HBSL --2,4–D methyl ester 1928–38–7 0 215 ND ND .19 ND -- -- --2,4–DB 94–82–6 0 215 ND ND .02 ND 200 HBSL --2,6-Diethylaniline 579–66–8 0 221 ND ND .006 ND -- -- --2-Chloro-2,6-diethylacetanilide 6967–29–9 0 221 ND ND .0065 ND -- -- --2-Ethyl-6-methylaniline 24549–06–2 0 221 ND ND .01 ND -- -- --3(4-Chlorophenyl)-1-

methyl urea

5352–88–5 0 215 ND ND .036 ND -- -- --

4-Chloro-2-methylphenol 1570–64–5 0 221 ND ND .005 ND -- -- --
Appendixes 43

Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002–July 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset]

Compound CASRN1

Number of 

detections 

for 

groundwater

Number 

of 

samples

Detection frequency 

(percent) Laboratory 

reporting level 

(μg/L)

Maximum concentration for 

groundwater 

(μg/L)

Human-health 

benchmark 

(μg/L)

Type of 

human-health 

benchmark

Number of concentrations with 

BQ >0.1; 

(1) number of 

concentrations 

with BQ >1

All data Censored at 0.1 μg/L

Herbicides and herbicide degradates—Continued

Acetochlor sulfynilacetic acid -- 0 73 ND ND 0.02 ND -- -- --

Acetochlor/metolachlor 

ethane sulfonic acid 2nd amide 

-- 0 43 ND ND .02 ND -- -- --

Acifluorfen 50594–66–6 0 215 ND ND .028 ND 90 HBSL --Alachlor sulfynilacetic 

acid

140939–16–8 0 73 ND ND .02 ND -- -- --

Benfluralin 1861–40–1 0 221 ND ND .01 ND 4 HBSL --Bensulfuron-methyl 83055–99–6 0 215 ND ND .018 ND 1,000 HBSL --Bromoxynil 1689–84–5 0 215 ND ND .044 ND 10 HBSL --Chloramben, methyl 

ester

7286–84–2 0 215 ND ND .024 ND -- -- --

Chlorimuron-ethyl 90982–32–4 0 215 ND ND .032 ND 600 HBSL --Cycloate 1134–23–2 0 215 ND ND .014 ND 40 HBSL --Dacthal 1861–32–1 0 221 ND ND .003 ND 70 HBSL --Dacthal monoacid 

(CCL)

887–54–7 0 215 ND ND .028 ND -- -- --

Dicamba 1918–00–9 0 213 ND ND .036 ND 3,000 HBSL --Dichlorprop 120–36–5 0 215 ND ND .028 ND 300 HBSL --Dimethenamid 87674–68–8 0 43 ND ND .02 ND -- -- --Dimethenamid ethane 

sulfonic acid

-- 0 73 ND ND .02 ND -- -- --

Dimethenamid oxanilic 

acid

-- 0 73 ND ND .02 ND -- -- --

Diphenamid 957–51–7 0 215 ND ND .01 ND 200 HBSL --
44 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002– July 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, bench- mark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Envi- ronmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset] Compound CASRN1 Number of detections for ground- water Number of samples Detection frequency (percent) Laboratory reporting level (μg/L) Maximum con- centration for groundwater (μg/L) Human-health benchmark (μg/L) Type of human-health benchmark Number of con- centrations with BQ >0.1; (1) number of concentrations with BQ >1 All data Censored at 0.1 μg/L Herbicides and herbicide degradates—Continued Fenuron 101–42–8 0 215 ND ND 0.1 ND -- -- -- Flufenacet 142459–58–3 0 43 ND ND .02 ND -- -- -- Flufenacet ethane sulfonic acid -- 0 73 ND ND .02 ND -- -- -- Flufenacet oxanilic acid -- 0 73 ND ND .02 ND -- -- -- Flumetsulam 98967–40–9 0 215 ND ND .04 ND 7,000 HBSL -- Linuron (CCL) 330–55–2 0 215 ND ND .014 ND 5 HBSL -- MCPA 94–74–6 0 207 ND ND .07 ND 30 HBSL -- MCPB 94–81–5 0 215 ND ND .1 ND 100 HBSL -- Neburon 555–37–3 0 215 ND ND .012 ND -- -- -- Nicosulfuron 111991–09–4 0 215 ND ND .04 ND 9,000 HBSL -- Oryzalin 19044–88–3 0 215 ND ND .023 ND 4

4 HBSL --

Pendimethalin 40487–42–1 0 221 ND ND .022 ND 70 HBSL --Prometryn 7287–19–6 0 221 ND ND .0059 ND 300 HBSL --Propachlor 1918–16–7 0 17 ND ND .02 ND 4

1 HBSL --

Propachlor ethane 

sulfonic acid

-- 0 73 ND ND .05 ND -- -- --

Propachlor oxanilic acid -- 0 73 ND ND .02 ND -- -- --Propham 122–42–9 0 215 ND ND .03 ND 100 HBSL --Propyzamide 23950–58–5 0 221 ND ND .004 ND 4

1 HBSL --

Terbuthylazine 5915–41–3 0 221 ND ND .0083 ND 2 HBSL --Triclopyr 55335–06–3 0 215 ND ND .026 ND 400 HBSL --Trifluralin 1582–09–8 0 221 ND ND .009 ND 20 HBSL --
Appendixes 45

Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002–July 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset]

Compound CASRN1

Number of 

detections 

for 

groundwater

Number 

of 

samples

Detection frequency 

(percent) Laboratory 

reporting level 

(μg/L)

Maximum concentration for 

groundwater 

(μg/L)

Human-health 

benchmark 

(μg/L)

Type of 

human-health 

benchmark

Number of concentrations with 

BQ >0.1; 

(1) number of 

concentrations 

with BQ >1

All data Censored at 0.1 μg/L

Insecticides and insecticide degradates

Carbofuran 1563–66–2 3 215 1.4 ND 0.016 0.005 40 MCL --Imidacloprid 138261–41–3 3 215 1.4 ND .02 .023 400 HBSL --1-Naphthol 90–15–3 1 221 .5 ND .0882 E.006 -- -- --Aldicarb sulfone 1646–88–4 1 215 .5 ND .018 E.007 77 HBSL --Carbaryl 63–25–2 1 215 .5 ND .018 E.012 440 HBSL --Chlorpyrofos, oxygen 

analog

5598–15–2 1 221 .5 ND .0562 E.017 -- -- --

Dieldrin 60–57–1 1 221 .5 ND .009 .024 4.002 HBSL 1(1)Fipronil 120068–37–3 1 221 .5 ND .016 E.008 -- -- --Fipronil sulfide 120067–83–6 1 221 .5 ND .013 .007 -- -- --Fipronil sulfone 120068–36–2 1 221 .5 ND .024 .02 -- -- --Fonofos, oxygen analog 944–21–8 1 206 .5 ND .0029 .002 -- -- --3-Hydroxycarbofuran 16655–82–6 0 215 ND ND .008 ND -- -- --3-Ketocarbofuran 16709–30–1 0 213 ND ND 1.5 ND -- -- --Aldicarb 116–06–3 0 215 ND ND .15 ND 79 HBSL --Aldicarb sulfoxide 1646–87–3 0 215 ND ND .1 ND 77 HBSL --Azinphos-methyl 86–50–0 0 221 ND ND .05 ND 10 HBSL --Azinphos-methyl-oxon 961–22–8 0 221 ND ND .042 ND -- -- --Bendiocarb 22781–23–3 0 215 ND ND .08 ND 9 HBSL --Chlorpyrifos 2921–88–2 0 221 ND ND .005 ND 2 HBSL --cis-Permethrin 54774–45–7 0 221 ND ND .006 ND 4,84 HBSL --Cyfluthrin 68359–37–5 0 221 ND ND .053 ND 200 HBSL --Cypermethrin 52315–07–8 0 221 ND ND .046 ND 40 HBSL --Desulfinylfipronil -- 0 221 ND ND .012 ND -- -- --
46 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002– July 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, bench- mark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Envi- ronmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset] Compound CASRN1 Number of detections for ground- water Number of samples Detection frequency (percent) Laboratory reporting level (μg/L) Maximum con- centration for groundwater (μg/L) Human-health benchmark (μg/L) Type of human-health benchmark Number of con- centrations with BQ >0.1; (1) number of concentrations with BQ >1 All data Censored at 0.1 μg/L Insecticides and insecticide degradates—Continued Desulfinylfipronil amide -- 0 221 ND ND 0.029 ND -- -- -- Diazinon (CCL) 333–41–5 0 221 ND ND .005 ND 1 HBSL -- Diazinon, oxygen analog 962–58–3 0 221 ND ND .006 ND -- -- -- Dichlorvos 62–73–7 0 221 ND ND .013 ND .4 HBSL -- Dicrotophos 141–66–2 0 221 ND ND .0843 ND .05 HBSL -- Dimethoate 60–51–5 0 221 ND ND .0061 ND 2 HBSL -- Ethion 563–12–2 0 221 ND ND .016 ND 4 HBSL -- Ethion monoxon 17356–42–2 0 221 ND ND .021 ND -- -- -- Fenamiphos 22224–92–6 0 221 ND ND .029 ND .7 HBSL -- Fenamiphos sulfone 31972–44–8 0 221 ND ND .053 ND -- -- -- Fenamiphos sulfoxide 31972–43–7 0 200 ND ND .04 ND -- -- -- Fonofos (CCL) 944–22–9 0 221 ND ND .0053 ND 10 HBSL -- Isofenphos 25311–71–1 0 221 ND ND .011 ND 6 HBSL -- Malaoxon 1634–78–2 0 221 ND ND .039 ND -- -- -- Malathion 121–75–5 0 221 ND ND .027 ND 50 HBSL -- Methidathion 950–37–8 0 221 ND ND .0087 ND 1 HBSL -- Methiocarb 2032–65–7 0 215 ND ND .034 ND 40 HBSL -- Methomyl 16752–77–5 0 215 ND ND .07 ND 200 HBSL -- Oxamyl 23135–22–0 0 215 ND ND .05 ND 200 MCL -- Paraoxon-methyl 950–35–6 0 221 ND ND .019 ND -- -- -- Parathion-methyl 298–00–0 0 221 ND ND .015 ND 1 HBSL -- Phorate 298–02–2 0 221 ND ND .055 ND 4 HBSL --

Phorate oxon 2600–69–3 0 221 ND ND .027 ND -- -- --
Appendixes 47

Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002–July 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset]

Compound CASRN1

Number of 

detections 

for 

groundwater

Number 

of 

samples

Detection frequency 

(percent) Laboratory 

reporting level 

(μg/L)

Maximum concentration for 

groundwater 

(μg/L)

Human-health 

benchmark 

(μg/L)

Type of 

human-health 

benchmark

Number of concentrations with 

BQ >0.1; 

(1) number of 

concentrations 

with BQ >1

All data Censored at 0.1 μg/L

Insecticides and insecticide degradates—Continued

Phosmet 732–11–6 0 211 ND ND 0.0079 ND 8 HBSL --Phosmet oxon 3735–33–9 0 201 ND ND .0511 ND -- -- --Propoxur 114–26–1 0 215 ND ND .008 ND 49 HBSL --Terbufos (CCL) 13071–79–9 0 221 ND ND .017 ND .4 HBSL --Terbufos-oxygenanalog sulfone 56070–15–6 0 221 ND ND .045 ND -- -- --

Manufacturing additives

Triphenyl phosphate 115–86–6 6 202 3.0 ND 0.5 E0.095 -- -- --Tributyl phosphate 126–73–8 5 217 2.3 0.5 .5 E.12 -- -- --Bisphenol A 80–05–7 2 212 .9 .9 1 6.4 400 HBSL --Tri(2-chloroethyl)

phosphate3

115–96–8 2 217 .9 ND .5 E.049 -- -- --

Tris(dichlorisopropyl)phosphate 13674–87–8 2 217 .9 ND .5 E.022 -- -- --Tri(2-butoxyethyl)phosphate 78–51–3 1 203 .5 .5 .5 E.14 -- -- --5-Methyl-1H-benzotriazole 136–85–6 0 215 ND ND 2 ND -- -- --

Organic synthesis compounds

Carbon disulfide 75–15–0 3 175 1.7 1.7 0.038 12.7 700 HBSL --Vinyl chloride 75–01–4 2 221 .9 .9 .08 .7 2 MCL 1Acrylonitrile 107–13–1 1 221 .5 .5 .8 E.504 4.06 HBSL 1(1)Anthraquinone 84–65–1 1 217 .5 .5 .5 E.11 -- -- --Carbazole 86–74–8 1 217 .5 ND .5 E.081 -- -- --
48 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002– July 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, bench- mark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Envi- ronmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset] Compound CASRN1 Number of detections for ground- water Number of samples Detection frequency (percent) Laboratory reporting level (μg/L) Maximum con- centration for groundwater (μg/L) Human-health benchmark (μg/L) Type of human-health benchmark Number of con- centrations with BQ >0.1; (1) number of concentrations with BQ >1 All data Censored at 0.1 μg/L Organic synthesis compounds—Continued 1,1-Dichloropropene (CCL) 563–58–6 0 221 ND ND 0.026 ND -- -- -- 1,2,3-Trichlorobenzene 87–61–6 0 221 ND ND .18 ND -- -- -- 1,2,3-Trichloropropane 96–18–4 0 221 ND ND .18 ND 40 HBSL -- 3-Chloro-1-propene 107–05–1 0 221 ND ND .5 ND -- -- -- Chloromethane 74–87–3 0 221 ND ND .17 ND 30 HBSL -- Ethyl methacrylate (Ethyl 2-methyl-2- propanoate) 97–63–2 0 221 ND ND .18 ND -- -- -- Hexachlorobutadiene (CCL) 87–68–3 0 221 ND ND .14 ND 4.9 HBSL -- Iodomethane 74–88–4 0 221 ND ND .5 ND -- -- -- Methyl acrylate (Methyl-2-propeno- ate) 96–33–3 0 221 ND ND 1 ND -- -- -- Methyl acrylonitrile (2-Methyl-2-propene­ nitrile) 126–98–7 0 221 ND ND .4 ND .7 HBSL -- Methyl methacrylate (Methyl 2-methyl-2- propenoate) 80–62–6 0 221 ND ND .2 ND 10,000 HBSL -- trans-1,4-Dichloro-2- butene 110–57–6 0 221 ND ND .7 ND -- -- -- Vinyl bromide 593–60–2 0 221 ND ND .1 ND -- -- --
Appendixes 49

Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002–July 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset]

Compound CASRN1

Number of 

detections 

for 

groundwater

Number 

of 

samples

Detection frequency 

(percent) Laboratory 

reporting level 

(μg/L)

Maximum concentration for 

groundwater 

(μg/L)

Human-health 

benchmark 

(μg/L)

Type of 

human-health 

benchmark

Number of concentrations with 

BQ >0.1; 

(1) number of 

concentrations 

with BQ >1

All data Censored at 0.1 μg/L

Pavement- and combustion-derived compounds

Fluoranthene 206–44–0 5 217 2.3 ND 0.5 E0.044 300 HBSL --Pyrene 129–00–0 5 216 2.3 ND .5 E.046 200 HBSL --Phenanthrene3 85–01–8 3 217 1.4 ND .5 E.016 -- -- --Anthracene 120–12–7 1 217 .5 ND .5 E.024 2,000 HBSL --Benzo[a]pyrene 50–32–8 0 217 ND ND .5 ND .2 MCL --

Personal-care and domestic-use products

Caffeine 58–08–2 10 168 6.0 ND 0.018 0.0171 -- -- --Hexahydrohexamethylcyclopentabenzopyran (HHCB)3 1222–05–5 7 217 3.2 ND .5 E.036 -- -- --Menthol 89–78–1 6 203 3.0 1 .5 E.2 -- -- --Octylphenol diethoxylate (total)3 -- 4 217 1.8 .9 1 E.12 -- -- --4-tert-Octylphenol 140–66–9 3 217 1.4 ND 1 E.087 -- -- --Methyl salicylate3 119–36–8 3 217 1.4 .5 .5 E.11 4,000 HBSL --Octylphenol monoethoxylate (total) -- 3 217 1.4 1.4 1 E.59 -- -- --4-Cumylphenol 599–64–4 1 217 .5 .5 1 E.18 -- -- --Acetyl hexamethyl 

tetrahydronaphthalene (AHTN)3

21145–77–7 1 217 .5 ND .5 E.005 -- -- --

Indole 120–72–9 1 217 .5 ND .5 E.08 -- -- --Triclosan 3380–34–5 1 217 .5 ND 1 E.065 -- -- --3-tert-Butyl-4-hydroxy 

anisole (BHA)

25013–16–5 0 217 ND ND 5 ND -- -- --

4-n-Octylphenol 1806–26–4 0 217 ND ND 1 ND -- -- --
50 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002– July 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, bench- mark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Envi- ronmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset] Compound CASRN1 Number of detections for ground- water Number of samples Detection frequency (percent) Laboratory reporting level (μg/L) Maximum con- centration for groundwater (μg/L) Human-health benchmark (μg/L) Type of human-health benchmark Number of con- centrations with BQ >0.1; (1) number of concentrations with BQ >1 All data Censored at 0.1 μg/L Personal-care and domestic-use products—Continued Nonylphenol diethoxyl- ate (total) 26027–38–2 0 217 ND ND 5 ND -- -- -- Acetophenone 98–86–2 0 187 ND ND .5 ND 700 HBSL -- Benzophenone 119–61–9 --

R -- -- .5 ND -- -- --

Bromochloromethane 74–97–5 0 221 ND ND .12 ND 90 HBSL --Camphor3 76–22–2 0 217 ND ND .5 ND -- -- --Cotinine 486–56–6 0 118 ND ND 1 ND -- -- --d-Limonene 5989–27–5 0 217 ND ND .5 ND -- -- --Isoborneol 124–76–5 0 217 ND ND .5 ND -- -- --Isoquinoline 119–65–3 0 217 ND ND .5 ND -- -- --N,N-diethyl-meta-toluamide (DEET) 134–62–3 --

R -- -- .5 ND -- -- --

para-Nonylphenol 

(total)

84852–15–3 --

R -- -- 5 ND -- -- --

Phenol 108–95–2 --

R -- -- .5 ND 2,000 HBSL --

Triethyl citrate (Ethyl 

citrate)

77–93–0 0 217 ND ND .5 ND -- -- --

Plant- or animal-derived biochemicals

3-beta-Coprostanol 360–68–9 2 217 0.9 0.9 2 E0.34 -- -- --Cholesterol3 57–88–5 2 217 .9 .9 2 E.53 -- -- --3-Methyl-1(H)-indole 

(Skatole)

83–34–1 1 217 .5 ND 1 E.027 -- -- --

beta-Sitosterol 83–46–5 1 217 .5 .5 2 E.39 -- -- --beta-Stigmastanol 19466–47–8 1 217 .5 .5 2 E.36 -- -- --
Appendixes 51

Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002–July 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset]

Compound CASRN1

Number of 

detections 

for 

groundwater

Number 

of 

samples

Detection frequency 

(percent) Laboratory 

reporting level 

(μg/L)

Maximum concentration for 

groundwater 

(μg/L)

Human-health 

benchmark 

(μg/L)

Type of 

human-health 

benchmark

Number of concentrations with 

BQ >0.1; 

(1) number of 

concentrations 

with BQ >1

All data Censored at 0.1 μg/L

Refrigerants and propellants

Trichlorofluoromethane 

(CFC-11)3

75–69–4 5 221 2.3 0.5 0.08 0.275 2,000 HBSL --

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

trifluoroethane (CFC-113)

76–13–1 4 221 1.8 .9 .038 1.06 200,000 HBSL --

Dichlorodifluoromethane (CFC-12) 75–71–8 3 221 1.4 .5 .18 E.145 1,000 HBSL --

Solvents

Perchloroethene (PCE)3 127–18–4 43 221 19.5 10 0.03 5.47 5 MCL 4(1)Trichloroethene (TCE) 79–01–6 31 221 14.0 6.3 .038 69.5 5 MCL 3(2)1,1,1-Trichloroethane 71–55–6 21 221 9.5 3.2 .032 16.7 200 MCL --cis-1,2-Dichloroethene 156–59–2 21 221 9.5 4.1 .024 1.5 70 MCL --1,1-Dichloroethane 

(CCL)

75–34–3 13 221 5.9 2.7 .035 4.88 -- -- --

1,1-Dichloroethene 75–35–4 11 221 5.0 1.8 .024 6.53 7 MCL 11,2-Dichloroethane 107–06–2 4 221 1.8 1.4 .13 .2 5 MCL --p-Cresol 106–44–5 4 217 1.8 .9 1 E.19 -- -- --trans-1,2-Dichloroethene 156–60–5 4 221 1.8 .5 .032 E.11 100 MCL --Carbon tetrachloride 

(Tetrachloromethane)

56–23–5 3 221 1.4 .5 .06 .677 5 MCL 1

1,1,2-Trichloroethane 79–00–5 1 220 .5 ND .04 E.08 5 MCL --Methyl isobutyl ketone 

(4-Methyl-2-pentanone; MIBK)

108–10–1 1 221 .5 .5 .37 E.766 -- -- --

Dibromomethane 74–95–3 1 221 .5 ND .05 E.065 -- -- --
52 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 1. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source-water samples collected during October 2002– July 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest detection frequency. CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, bench- mark quotient; >, greater than; MCL, Maximum Contaminant Level; --, none; ND, not detected; E, estimated value; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Envi- ronmental Protection Agency, 2005); HBSL, Health-Based Screening Level; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset] Compound CASRN1 Number of detections for ground- water Number of samples Detection frequency (percent) Laboratory reporting level (μg/L) Maximum con- centration for groundwater (μg/L) Human-health benchmark (μg/L) Type of human-health benchmark Number of con- centrations with BQ >0.1; (1) number of concentrations with BQ >1 All data Censored at 0.1 μg/L Solvents—Continued Methyl ethyl ketone (MEK)3 78–93–3 1 221 0.5 0.5 2 330.2 4,000 HBSL --

n-Propylbenzene 103–65–1 1 221 .5 .5 .042 .108 -- -- --Tetrahydrofuran3 109–99–9 1 221 .5 .5 1.2 1,020 -- -- --1,1,1,2-Tetrachloroethane 630–20–6 0 221 ND ND .03 ND 70 HBSL --1,1,2,2-Tetrachloroethane (CCL) 79–34–5 0 221 ND ND .08 ND .3 HBSL --Diethyl ether 

(1,1’-Oxybisethane)

60–29–7 0 221 ND ND .08 ND 1,000 HBSL --

1,2,4-Trichlorobenzene 120–82–1 0 221 ND ND .12 ND 70 MCL --1,2-Dichlorobenzene 95–50–1 0 221 ND ND .048 ND 600 MCL --1,3-Dichlorobenzene 541–73–1 0 221 ND ND .03 ND 600 HBSL --2-Chlorotoluene 95–49–8 0 221 ND ND .04 ND 100 HBSL --2-Hexanone 591–78–6 0 221 ND ND .4 ND -- -- --4-Chlorotoluene 106–43–4 0 221 ND ND .05 ND 100 HBSL --Acetone 67–64–1 0 161 ND ND 6 ND 6,000 HBSL --Bromobenzene (CCL) 108–86–1 0 221 ND ND .028 ND -- -- --Chlorobenzene 108–90–7 0 206 ND ND .028 ND 100 MCL --Chloroethane 75–00–3 0 221 ND ND .12 ND -- -- --Hexachloroethane 67–72–1 0 221 ND ND .14 ND .7 HBSL --Isophorone3 78–59–1 --

R -- -- .5 ND 100 HBSL --

Methyl acetate 79–20–9 0 119 ND ND .43 ND -- -- --Methylene chloride 

(Dichloromethane)

75–09–2 0 192 ND ND .06 ND 5 MCL --
Appendixes 53

1This report contains CASRNs, which is a Registered Trademark of the American Chemical Society. The Chemical Abstracts Service (CAS) recommends the verification of the CASRNs through CAS Client 

ServicesSM.

2The U.S. Environmental Protection Agency’s MCL of 80 μg/L is for the sum of the concentrations of four trihalomethanes.3Compound was detected in only one field blank.4HBSL values shown for carcinogens represent the low end (10–6) of the HBSL range (10–6 to 10–4 cancer risk level) (Toccalino, Norman, and others, 2006).5The sum of concentrations from cis-1,3- and trans-1,3-dichloropropene may be compared to the HBSL range (0.3–30 μg/L) for the mixed isomer of 1,3-dichloropropene, CASRN 542–75–6.6The concentrations from m- and p-xylene and o-xylene may be compared to the MCL (10,000 μg/L) for mixed xylenes, CASRN 1330–20–7. 7U.S. Environmental Protection Agency Office of Water recommends that the concentration of any combination of two or more of the three aldicarb compounds should not be greater than 7 μg/L because of 

similar mode of action.

8Concentrations of cis-permethrin may be compared to the HBSL range (4–400 μg/L) for permethrin, CASRN 52645–53–1.
54 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

Appendix 2. Selected characteristics of community water system wells sampled for Source Water-Quality Assessments, 

2002–05.—Continued

[NA, not available; -- not applicable]

Primary lithology Site name Well depth 

(feet) Blended

Basin and Range basin-fill aquifers

Unconsolidated and semiconsolidated sediments NVBR-0001 510 --

Unconsolidated and semiconsolidated sediments NVBR-0002 590 --

Unconsolidated and semiconsolidated sediments NVBR-0003 560 --

Unconsolidated and semiconsolidated sediments NVBR-0004 195 --

Unconsolidated and semiconsolidated sediments NVBR-0005 820 --

Unconsolidated and semiconsolidated sediments NVBR-0006 470 --

Unconsolidated and semiconsolidated sediments NVBR-0007 470 Yes1

Unconsolidated and semiconsolidated sediments NVBR-0008 1,250 --

Unconsolidated and semiconsolidated sediments NVBR-0009 400 Yes1

Unconsolidated and semiconsolidated sediments NVBR-0010 455 --

Unconsolidated and semiconsolidated sediments NVBR-0011 200 --

Unconsolidated and semiconsolidated sediments NVBR-0012 620 --

Unconsolidated and semiconsolidated sediments NVBR-0013 600 --

Unconsolidated and semiconsolidated sediments NVBR-0014 400 --

Unconsolidated and semiconsolidated sediments NVBR-0015 330 --

Cambrian-Ordovician aquifer system

Sandstone and carbonate rock UMIS-0001 403 Yes1

Sandstone and carbonate rock UMIS-0002 493 Yes1

Sandstone and carbonate rock UMIS-0003 500 --

Sandstone and carbonate rock UMIS-0004 399 Yes1

Sandstone and carbonate rock UMIS-0005 407 --

Sandstone and carbonate rock UMIS-0006 408 --

Sandstone and carbonate rock UMIS-0007 500 --

Sandstone and carbonate rock UMIS-0008 401 --

Sandstone and carbonate rock UMIS-0009 495 Yes1

Sandstone and carbonate rock UMIS-0010 548 Yes1

Sandstone and carbonate rock UMIS-0011 387 Yes1

Sandstone and carbonate rock UMIS-0012 507 No1

Sandstone and carbonate rock UMIS-0013 513 --

Sandstone and carbonate rock UMIS-0014 345 Yes1

Sandstone and carbonate rock UMIS-0015 317 --

Central Valley aquifer system

Unconsolidated and semiconsolidated sediments SANJ-0001 215 Yes1

Unconsolidated and semiconsolidated sediments SANJ-0002 208 --

Unconsolidated and semiconsolidated sediments SANJ-0003 250 Yes1

Unconsolidated and semiconsolidated sediments SANJ-0004 220 --

Unconsolidated and semiconsolidated sediments SANJ-0005 216 Yes1

Unconsolidated and semiconsolidated sediments SANJ-0006 262 Yes1

Unconsolidated and semiconsolidated sediments SANJ-0007 220 Yes1

Unconsolidated and semiconsolidated sediments SANJ-0008 218 --
Appendixes 55

Appendix 2. Selected characteristics of community water system wells sampled for Source Water-Quality Assessments, 

2002–05.—Continued

[NA, not available; -- not applicable]

Primary lithology Site name Well depth 

(feet) Blended

Central Valley aquifer system—Continued

Unconsolidated and semiconsolidated sediments SANJ-0009 302 Yes1

Unconsolidated and semiconsolidated sediments SANJ-0010 245 --

Unconsolidated and semiconsolidated sediments SANJ-0011 391 Yes1

Unconsolidated and semiconsolidated sediments SANJ-0012 220 Yes1

Unconsolidated and semiconsolidated sediments SANJ-0013 307 Yes1

Unconsolidated and semiconsolidated sediments SANJ-0014 385 --

Unconsolidated and semiconsolidated sediments SANJ-0015 415 Yes1

Coastal Lowlands aquifer system

Unconsolidated and semiconsolidated sediments TRIN-0001 1,012 --

Unconsolidated and semiconsolidated sediments TRIN-0002 1,394 --

Unconsolidated and semiconsolidated sediments TRIN-0003 1,370 --

Unconsolidated and semiconsolidated sediments TRIN-0004 1,665 --

Unconsolidated and semiconsolidated sediments TRIN-0005 1,135 --

Unconsolidated and semiconsolidated sediments TRIN-0006 1,712 Yes1

Unconsolidated and semiconsolidated sediments TRIN-0007 1,374 Yes1

Unconsolidated and semiconsolidated sediments TRIN-0008 1,200 --

Unconsolidated and semiconsolidated sediments TRIN-0009 1,379 --

Unconsolidated and semiconsolidated sediments TRIN-0010 1,480 --

Unconsolidated and semiconsolidated sediments TRIN-0011 1,438 --

Unconsolidated and semiconsolidated sediments TRIN-0012 1,444 --

Unconsolidated and semiconsolidated sediments TRIN-0013 1,480 --

Unconsolidated and semiconsolidated sediments TRIN-0014 1,050 Yes1

Unconsolidated and semiconsolidated sediments TRIN-0015 1,630 Yes1

Columbia Plateau basin-fill and basaltic-rock aquifers

Igneous and metamorphic rocks CCYK-0001 954 --

Igneous and metamorphic rocks CCYK-0002 919 --

Unconsolidated and semiconsolidated sediments CCYK-0003 188 No1

Unconsolidated and semiconsolidated sediments CCYK-0004 1,171 --

Igneous and metamorphic rocks CCYK-0005 1,624 --

Igneous and metamorphic rocks CCYK-0006 1,011 --

Igneous and metamorphic rocks CCYK-0007 718 No1

Igneous and metamorphic rocks CCYK-0008 900 --

Igneous and metamorphic rocks CCYK-0009 1,320 --

Igneous and metamorphic rocks CCYK-0010 368 --

Igneous and metamorphic rocks CCYK-0011 617 --

Igneous and metamorphic rocks CCYK-0012 750 No1

Igneous and metamorphic rocks CCYK-0013 380 No1

Igneous and metamorphic rocks CCYK-0014 618 --

Igneous and metamorphic rocks CCYK-0015 525 --
56 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

Appendix 2. Selected characteristics of community water system wells sampled for Source Water-Quality Assessments, 

2002–05.—Continued

[NA, not available; -- not applicable]

Primary lithology Site name Well depth 

(feet) Blended

Denver Basin aquifer system

Sandstone and carbonate rock SPLT-0001 536 --

Sandstone and carbonate rock SPLT-0002 1,115 --

Sandstone and carbonate rock SPLT-0003 390 --

Sandstone and carbonate rock SPLT-0004 850 --

Sandstone and carbonate rock SPLT-0005 575 --

Sandstone and carbonate rock SPLT-0006 740 --

Sandstone and carbonate rock SPLT-0007 NA --

Sandstone and carbonate rock SPLT-0008 NA --

Sandstone and carbonate rock SPLT-0009 433 --

Sandstone and carbonate rock SPLT-0010 561 --

Sandstone and carbonate rock SPLT-0011 245 --

Sandstone and carbonate rock SPLT-0012 NA --

Edwards-Trinity aquifer system

Sandstone and carbonate rock SCTX-0001 525 --

Sandstone and carbonate rock SCTX-0002 1,800 --

Sandstone and carbonate rock SCTX-0003 1,040 --

Sandstone and carbonate rock SCTX-0004 1,114 --

Sandstone and carbonate rock SCTX-0005 1,150 Yes1

Sandstone and carbonate rock SCTX-0006 748 No1

Sandstone and carbonate rock SCTX-0007 760 --

Sandstone and carbonate rock SCTX-0008 808 Yes1

Sandstone and carbonate rock SCTX-0009 1,050 Yes1

Sandstone and carbonate rock SCTX-0010 877 --

Sandstone and carbonate rock SCTX-0011 848 Yes1

Sandstone and carbonate rock SCTX-0012 870 --

Sandstone and carbonate rock SCTX-0013 811 Yes1

Sandstone and carbonate rock SCTX-0014 710 Yes1

Sandstone and carbonate rock SCTX-0015 365 No1

Floridan aquifer system

Sandstone and carbonate rock GAFL-0001 405 --

Sandstone and carbonate rock GAFL-0002 305 Yes1

Sandstone and carbonate rock GAFL-0003 105 --

Sandstone and carbonate rock GAFL-0004 174 Yes1

Sandstone and carbonate rock GAFL-0005 700 --

Sandstone and carbonate rock GAFL-0006 350 --

Sandstone and carbonate rock GAFL-0007 590 --

Sandstone and carbonate rock GAFL-0008 601 --

Sandstone and carbonate rock GAFL-0009 610 Yes1

Sandstone and carbonate rock GAFL-0010 550 --

Sandstone and carbonate rock GAFL-0011 700 --
Appendixes 57

Appendix 2. Selected characteristics of community water system wells sampled for Source Water-Quality Assessments, 

2002–05.—Continued

[NA, not available; -- not applicable]

Primary lithology Site name Well depth 

(feet) Blended

Floridan aquifer system—Continued

Sandstone and carbonate rock GAFL-0012 311 --

Sandstone and carbonate rock GAFL-0013 575 No1

Sandstone and carbonate rock GAFL-0014 90 Yes1

Sandstone and carbonate rock GAFL-0015 840 No1

Sandstone and carbonate rock GAFL-0016 750 Yes1

Sandstone and carbonate rock GAFL-0017 300 --

Sandstone and carbonate rock GAFL-0018 705 --

Sandstone and carbonate rock GAFL-0019 121 --

Sandstone and carbonate rock GAFL-0020 702 --

Sandstone and carbonate rock GAFL-0021 150 --

Sandstone and carbonate rock GAFL-0022 710 --

Sandstone and carbonate rock GAFL-0023 710 --

Sandstone and carbonate rock GAFL-0024 430 No1

Sandstone and carbonate rock GAFL-0025 350 No1

Sandstone and carbonate rock GAFL-0026 625 No1

Sandstone and carbonate rock GAFL-0027 484 --

Sandstone and carbonate rock GAFL-0028 400 No1

Sandstone and carbonate rock GAFL-0029 600 --

Sandstone and carbonate rock GAFL-0030 602 --

Glacial deposits aquifer system

Unconsolidated glacial deposits WHMI-0001 123 Yes1

Unconsolidated glacial deposits WHMI-0002 151 --

Unconsolidated glacial deposits WHMI-0003 125 --

Unconsolidated glacial deposits WHMI-0004 77 --

Unconsolidated glacial deposits WHMI-0005 80 --

Unconsolidated glacial deposits WHMI-0006 83 --

Unconsolidated glacial deposits WHMI-0007 152 --

Unconsolidated glacial deposits WHMI-0008 60 Yes1

Unconsolidated glacial deposits WHMI-0009 157 --

Unconsolidated glacial deposits WHMI-0010 137 --

Unconsolidated glacial deposits WHMI-0011 61 Yes1

Unconsolidated glacial deposits WHMI-0012 146 Yes1

Unconsolidated glacial deposits WHMI-0013 94 --

Unconsolidated glacial deposits WHMI-0014 84 Yes1

Unconsolidated glacial deposits CONN-0001 83 --

Unconsolidated glacial deposits CONN-0002 70 --

Unconsolidated glacial deposits CONN-0003 76 Yes1

Unconsolidated glacial deposits CONN-0004 64 Yes1

Unconsolidated glacial deposits CONN-0005 40 No1

Unconsolidated glacial deposits CONN-0006 38 --
58 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater

Appendix 2. Selected characteristics of community water system wells sampled for Source Water-Quality Assessments, 

2002–05.—Continued

[NA, not available; -- not applicable]

Primary lithology Site name Well depth 

(feet) Blended

Glacial deposits aquifer system—Continued

Unconsolidated glacial deposits CONN-0007 54 No1

Unconsolidated glacial deposits CONN-0008 102 No1

Unconsolidated glacial deposits CONN-0009 126 No1

Unconsolidated glacial deposits CONN-0010 90 No1

Unconsolidated glacial deposits CONN-0011 40 Yes1

Unconsolidated glacial deposits CONN-0012 70 No1

Unconsolidated glacial deposits CONN-0013 130 --

Unconsolidated glacial deposits CONN-0014 93 No1

Unconsolidated glacial deposits CONN-0015 58 --

Unconsolidated glacial deposits UMIS-0016 292 --

Unconsolidated glacial deposits UMIS-0017 152 Yes1

Unconsolidated glacial deposits UMIS-0018 215 --

Unconsolidated glacial deposits UMIS-0019 194 --

Unconsolidated glacial deposits UMIS-0020 100 --

Unconsolidated glacial deposits UMIS-0021 205 --

Unconsolidated glacial deposits UMIS-0022 199 Yes1

Unconsolidated glacial deposits UMIS-0023 213 --

Unconsolidated glacial deposits UMIS-0024 270 Yes1

Unconsolidated glacial deposits UMIS-0025 197 Yes1

Unconsolidated glacial deposits UMIS-0026 157 --

Unconsolidated glacial deposits UMIS-0027 310 --

Unconsolidated glacial deposits UMIS-0028 250 --

Unconsolidated glacial deposits UMIS-0029 217 --

Unconsolidated glacial deposits UMIS-0030 344 No1

High Plains aquifer

Unconsolidated and semiconsolidated sediments HPGW-0001 190 Yes1

Unconsolidated and semiconsolidated sediments HPGW-0002 381 --

Unconsolidated and semiconsolidated sediments HPGW-0003 195 --

Unconsolidated and semiconsolidated sediments HPGW-0004 253 --

Unconsolidated and semiconsolidated sediments HPGW-0005 292 --

Unconsolidated and semiconsolidated sediments HPGW-0006 356 --

Unconsolidated and semiconsolidated sediments HPGW-0007 340 --

Unconsolidated and semiconsolidated sediments HPGW-0008 369 --

Unconsolidated and semiconsolidated sediments HPGW-0009 218 --

Unconsolidated and semiconsolidated sediments HPGW-0010 380 --

Unconsolidated and semiconsolidated sediments HPGW-0011 228 --

Unconsolidated and semiconsolidated sediments HPGW-0012 394 --

Unconsolidated and semiconsolidated sediments HPGW-0013 120 Yes1

Unconsolidated and semiconsolidated sediments HPGW-0014 425 --

Unconsolidated and semiconsolidated sediments HPGW-0015 136 --
Appendixes 59

Appendix 2. Selected characteristics of community water system wells sampled for Source Water-Quality Assessments, 

2002–05.—Continued

[NA, not available; -- not applicable]

Primary lithology Site name Well depth 

(feet) Blended

Piedmont and Blue Ridge crystalline-rock aquifers

Igneous and metamorphic rocks PODL-0001 400 --

Igneous and metamorphic rocks PODL-0002 705 --

Igneous and metamorphic rocks PODL-0003 386 --

Igneous and metamorphic rocks PODL-0004 NA No1

Igneous and metamorphic rocks PODL-0005 280 No1

Igneous and metamorphic rocks PODL-0006 200 --

Igneous and metamorphic rocks PODL-0007 95 Yes1

Igneous and metamorphic rocks PODL-0008 182 No1

Igneous and metamorphic rocks PODL-0009 300 Yes1

Igneous and metamorphic rocks PODL-0010 NA Yes1

Igneous and metamorphic rocks PODL-0011 642 Yes1

Igneous and metamorphic rocks PODL-0012 500 No1

Igneous and metamorphic rocks PODL-0013 623 No1

Igneous and metamorphic rocks PODL-0014 241 --

Igneous and metamorphic rocks PODL-0015 300 No1

Rio Grande aquifer system

Unconsolidated and semiconsolidated sediments RIOG-0001 1,400 No1

Unconsolidated and semiconsolidated sediments RIOG-0002 1,166 Yes1

Unconsolidated and semiconsolidated sediments RIOG-0003 996 Yes1

Unconsolidated and semiconsolidated sediments RIOG-0004 1,191 Yes1

Unconsolidated and semiconsolidated sediments RIOG-0005 1,670 Yes1

Unconsolidated and semiconsolidated sediments RIOG-0006 1,287 Yes1

Unconsolidated and semiconsolidated sediments RIOG-0007 814 Yes1

Unconsolidated and semiconsolidated sediments RIOG-0008 984 Yes1

Unconsolidated and semiconsolidated sediments RIOG-0009 1,194 Yes1

Unconsolidated and semiconsolidated sediments RIOG-0010 1,730 No1

Unconsolidated and semiconsolidated sediments RIOG-0011 2,070 No1

Unconsolidated and semiconsolidated sediments RIOG-0012 1,957 No1

Unconsolidated and semiconsolidated sediments RIOG-0013 1,020 No1

Unconsolidated and semiconsolidated sediments RIOG-0014 2,010 No1

Unconsolidated and semiconsolidated sediments RIOG-0015 1,487 No1

1

Site re-sampled during the second phase for source water and finished water.
60 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protec- tion Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level] Compound CASRN1 Number of samples Detection frequency (percent) Maximum concentration (μg/L) Human-health benchmark (μg/L) Number of concentrations with BQ > 0.1; (1) number of concentrations with BQ >1 Source water/ Finished water Source water Finished water Source water Finished water Source water Finished water Disinfection by-products Chloroform 67–66–3 56/56 57 88 3.25 36.3 280 -- 3 Bromodichloromethane 75–27–4 71/71 13 79 .204 7.48 280 -- -- Dibromochloromethane 124–48–1 71/71 7.0 72 .433 7.95 280 -- -- Bromoform 75–25–2 71/71 7.0 62 .396 8.37 280 -- 1 Trihalomethanes -- 71/71 57 88 3.28 45.3 80 -- 9 Fumigant-related compounds 1,4-Dichlorobenzene 106–46–7 71/71 11 11 E0.048 E0.056 75 -- -- 1,2-Dichloropropane 78–87–5 71/71 1.4 ND E.025 ND 5 -- -- 1,2-Dibromo-3-chloro- propane 96–12–8 71/71 ND ND ND ND .2 -- -- 1,2-Dibromoethane 106–93–4 71/71 ND ND ND ND .05 -- -- 1,3-Dichloropropane (CCL) 142–28–9 71/71 ND ND ND ND -- -- -- 2,2-Dichloropropane (CCL) 594–20–7 71/71 ND ND ND ND -- -- -- Bromomethane (CCL) 74–83–9 71/71 ND ND ND ND 100 -- -- cis-1,3-Dichloropropene (CCL) 10061–01–5 71/71 ND ND ND ND 3,4.3 -- -- trans-1,3-Dichloropro- pene (CCL) 10061–02–6 71/71 ND ND ND ND 3,4.3 -- -- Fungicides and fungicide degradates Benomyl 17804–35–2 61/59 3.3 3.4 E0.026 E0.026 40 -- -- Metalaxyl 57837–19–1 48/48 2.1 2.1 .01 .071 600 -- -- Chlorothalonil 1897–45–6 61/59 ND ND ND ND 5 -- --

Iprodione 36734–19–7 48/48 ND ND ND ND 3.8 -- --Myclobutanil 88671–89–0 48/48 ND ND ND ND 200 -- --
Appendixes 61

Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level]

Compound CASRN1

Number of 

samples 

Detection frequency 

(percent)

Maximum concentration 

(μg/L) Human-health benchmark 

(μg/L)

Number of concentrations with 

BQ > 0.1; (1) number of 

concentrations with BQ >1

Source water/ 

Finished water

Source 

water

Finished 

water

Source 

water

Finished 

water

Source 

water

Finished 

water

Fungicides and fungicide degradates—Continued

Pentachlorophenol 87–86–5 42/44 ND ND ND ND 1 -- --Propiconazole 60207–90–1 61/59 ND ND ND ND 70 -- --

Gasoline hydrocarbons, oxygenates, and oxygenate degradates

Methyl tert-butyl ether 

(MTBE) (CCL)

1634–04–4 71/71 16 16 7.84 6.03 -- -- --

Benzene 71–43–2 66/66 4.5 1.5 .13 .12 5 -- --tert-Amyl methyl ether 

(TAME)

994–05–8 71/71 4.2 4.2 .935 .66 -- -- --

Diisopropyl ether 

(DIPE)

108–20–3 71/71 2.8 2.8 .165 .148 -- -- --

Ethyl tert-butyl ether 

(ETBE)

637–92–3 71/71 1.4 1.4 .241 .15 -- -- --

m- and p-Xylene 106–42–3; 

108–38–3

64/64 ND 14 ND 2.26 510,000 -- --

Ethylbenzene 100–41–4 64/64 ND 9.4 ND .593 700 -- --o-Xylene 95–47–6 66/66 ND 9.1 ND 1.03 510,000 -- --1-Methylnaphthalene 90–12–0 55/57 ND 1.8 ND E.014 -- -- --2-Methylnaphthalene 91–57–6 55/57 ND 1.8 ND E.025 30 -- --1,2,3,4-Tetramethylbenzene 488–23–3 71/71 ND ND ND ND -- -- --1,2,3,5-Tetramethylbenzene 527–53–7 71/71 ND ND ND ND -- -- --1,2,3-Trimethylbenzene 526–73–8 71/71 ND ND ND ND -- -- --1,2,4-Trimethylbenzene 

(CCL)

95–63–6 64/64 ND ND ND ND -- -- --

1,3,5-Trimethylbenzene 108–67–8 71/71 ND ND ND ND -- -- --
62 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protec- tion Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level] Compound CASRN1 Number of samples Detection frequency (percent) Maximum concentration (μg/L) Human-health benchmark (μg/L) Number of concentrations with BQ > 0.1; (1) number of concentrations with BQ >1 Source water/ Finished water Source water Finished water Source water Finished water Source water Finished water Gasoline hydrocarbons, oxygenates, and oxygenate degradates—Continued 1-Ethyl-2-methylben- zene (o-Ethyl toluene) 611–14–3 71/71 ND ND ND ND -- -- -- 2,6-Dimethylnaphtha- lene 581–42–0 55/57 ND ND ND ND -- -- -- tert-Amyl alcohol (2-Methyl-2-butanol) 75–85–4 15/15 ND ND ND ND -- -- -- Isopropylbenzene 98–82–8 71/71 ND ND ND ND 700 -- -- Naphthalene (CCL) 91–20–3 71/71 ND ND ND ND 100 -- --

n-Butylbenzene 104–51–8 71/71 ND ND ND ND -- -- --p-Isopropyltoluene 

(CCL)

99–87–6 71/71 ND ND ND ND -- -- --

sec-Butylbenzene 135–98–8 71/71 ND ND ND ND -- -- --Styrene 100–42–5 71/71 ND ND ND ND 100 -- --tert-Butyl alcohol 75–65–0 15/15 ND ND ND ND -- -- --tert-Butylbenzene 98–06–6 71/71 ND ND ND ND -- -- --Toluene 108–88–3 34/34 ND ND ND ND 1,000 -- --

Herbicides and herbicide degradates

Alachlor ethane sulfonic 

acid

-- 17/17 77 77 0.68 0.53 -- -- --

Atrazine 1912–24–9 66/66 59 55 .23 .203 3 -- --Deethylatrazine (DEA) 

(CCL)

6190–65–4 66/66 56 53 .288 .151 -- -- --

Metolachlor ethane 

sulfonic acid

-- 32/32 47 41 3.95 2.89 -- -- --

Simazine 122–34–9 48/48 46 46 .047 .044 4 -- --
Appendixes 63

Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level]

Compound CASRN1

Number of 

samples 

Detection frequency 

(percent)

Maximum concentration 

(μg/L) Human-health benchmark 

(μg/L)

Number of concentrations with 

BQ > 0.1; (1) number of 

concentrations with BQ >1

Source water/ 

Finished water

Source 

water

Finished 

water

Source 

water

Finished 

water

Source 

water

Finished 

water

Herbicides and herbicide degradates—Continued

Metolachlor oxanilic 

acid

-- 32/32 38 34 3.77 2.99 -- -- --

Deisopropylatrazine 

(DIA)

1007–28–9 61/59 31 20 .138 .058 -- -- --

2-Hydroxyatrazine 2163–68–0 61/59 28 29 E.029 E.023 70 -- --Alachlor oxanilic acid -- 32/32 25 28 .84 .75 -- -- --Prometon (CCL) 1610–18–0 61/62 25 19 .024 .03 400 -- --Acetochlor ethane 

sulfonic acid

-- 32/32 19 19 .77 .8 -- -- --

Bentazon 25057–89–0 61/59 13 6.8 E.748 E.37 200 -- --Alachlor ethane sulfonic 

acid 2nd amide

-- 32/32 13 13 .1 .21 -- -- --

Metolachlor (CCL) 51218–45–2 64/65 13 11 .04 .021 700 -- --Acetochlor oxanilic acid -- 32/32 9.4 19 .41 .53 -- -- --Bromacil 314–40–9 79/78 7.6 ND .258 ND 70 -- --Diuron (CCL) 330–54–1 61/59 6.6 1.7 .113 .099 32 -- --Flufenacet 142459–

58–3

32/32 6.2 3.1 .02 .04 -- -- --

Flumetsulam 98967–40–9 60/59 3.3 5.1 E.122 E.098 7,000 -- --Acetochlor/metolachlor 

ethane sulfonic acid 2nd amide

-- 32/32 3.1 13 .1 .12 -- -- --

Dimethenamid ethane 

sulfonic acid

-- 32/32 3.1 ND .02 ND -- -- --

3,4-Dichloroaniline 95–76–1 48/48 2.1 4.2 E.002 .01 -- -- --Hexazinone 51235–04–2 48/48 2.1 ND .017 ND 400 -- --
64 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protec- tion Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level] Compound CASRN1 Number of samples Detection frequency (percent) Maximum concentration (μg/L) Human-health benchmark (μg/L) Number of concentrations with BQ > 0.1; (1) number of concentrations with BQ >1 Source water/ Finished water Source water Finished water Source water Finished water Source water Finished water Herbicides and herbicide degradates—Continued Imazaquin 81335–37–7 61/59 1.6 3.4 E0.016 E0.017 2,000 -- -- 3(4-Chlorophenyl)-1- methyl urea 5352–88–5 61/59 1.6 1.7 E.004 E.004 -- -- -- Chlorimuron-ethyl 90982–32–4 61/59 1.6 1.7 E.016 E.019 600 -- -- Oryzalin 19044–88–3 61/59 1.6 1.7 E.01 E.075 3

4 -- --

Sulfometuron-methyl 74222–97–2 61/59 1.6 1.7 .036 E.007 2,000 -- --Triclopyr 55335–06–3 61/59 1.6 1.7 .032 .026 400 -- --Deethyldeisopropylatrazine (DDA) 3397–62–4 61/59 1.6 ND E.052 ND -- -- --Nicosulfuron 111991–09–4 61/59 1.6 ND E.006 ND 9,000 -- --Terbacil (CCL) 5902–51–2 61/59 1.6 ND E.023 ND 90 -- --Tebuthiuron 34014–18–1 66/66 1.5 3 .034 .03 1,000 -- --Metsulfuron methyl 74223–64–6 61/59 ND 12 ND E.105 2,000 -- --4-Chloro-2-methylphenol 1570–64–5 48/48 ND 4.2 ND E.006 -- -- --Metribuzin (CCL) 21087–64–9 48/48 ND 2.1 ND E.004 90 -- --Imazethapyr 81335–77–5 61/59 ND 1.7 ND E.004 2,000 -- --Picloram 1918–02–1 61/59 ND 1.7 ND .151 500 -- --2,4–D 94–75–7 61/59 ND ND ND ND 70 -- --2,4–D methyl ester 1928–38–7 61/59 ND ND ND ND -- -- --2,4–DB 94–82–6 61/59 ND ND ND ND 200 -- --2,6-Diethylaniline 579–66–8 48/48 ND ND ND ND -- -- --2-Chloro-2,6-diethylacetanilide 6967–29–9 48/48 ND ND ND ND -- -- --2-Ethyl-6-methylaniline 24549–06–2 48/48 ND ND ND ND -- -- --
Appendixes 65

Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level]

Compound CASRN1

Number of 

samples 

Detection frequency 

(percent)

Maximum concentration 

(μg/L) Human-health benchmark 

(μg/L)

Number of concentrations with 

BQ > 0.1; (1) number of 

concentrations with BQ >1

Source water/ 

Finished water

Source 

water

Finished 

water

Source 

water

Finished 

water

Source 

water

Finished 

water

Herbicides and herbicide degradates—Continued

Acetochlor (CCL) 34256–82–1 51/51 ND ND ND ND 31 -- --Acetochlor sulfynilacetic acid -- 32/32 ND ND ND ND -- -- --Acifluorfen 50594–66–6 61/59 ND ND ND ND 90 -- --Alachlor 15972–60–8 51/51 ND ND ND ND 2 -- --Alachlor sulfynilacetic 

acid

140939–

16–8

32/32 ND ND ND ND -- -- --

Benfluralin 1861–40–1 48/48 ND ND ND ND 4 -- --Bensulfuron-methyl 83055–99–6 61/59 ND ND ND ND 1,000 -- --Bromoxynil 1689–84–5 61/59 ND ND ND ND 10 -- --Chloramben, methyl 

ester

7286–84–2 61/59 ND ND ND ND -- -- --

Clopyralid 1702–17–6 61/59 ND ND ND ND -- -- --Cycloate 1134–23–2 61/59 ND ND ND ND 40 -- --Dacthal 1861–32–1 48/48 ND ND ND ND 70 -- --Dacthal monoacid 

(CCL)

887–54–7 61/59 ND ND ND ND -- -- --

Dicamba 1918–00–9 61/59 ND ND ND ND 3,000 -- --Dichlorprop 120–36–5 61/59 ND ND ND ND 300 -- --Dimethenamid 87674–68–8 32/32 ND ND ND ND -- -- --Dimethenamid oxanilic 

acid

-- 32/32 ND ND ND ND -- -- --

Dinoseb 88–85–7 61/59 ND ND ND ND 7 -- --Diphenamid 957–51–7 61/59 ND ND ND ND 200 -- --Fenuron 101–42–8 61/59 ND ND ND ND -- -- --
66 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protec- tion Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level] Compound CASRN1 Number of samples Detection frequency (percent) Maximum concentration (μg/L) Human-health benchmark (μg/L) Number of concentrations with BQ > 0.1; (1) number of concentrations with BQ >1 Source water/ Finished water Source water Finished water Source water Finished water Source water Finished water Herbicides and herbicide degradates—Continued Flufenacet ethane sulfonic acid -- 32/32 ND ND ND ND -- -- -- Flufenacet oxanilic acid -- 32/32 ND ND ND ND -- -- -- Fluometuron 2164–17–2 61/59 ND ND ND ND 4 -- -- Linuron (CCL) 330–55–2 61/59 ND ND ND ND 5 -- -- MCPA 94–74–6 58/57 ND ND ND ND 30 -- -- MCPB 94–81–5 61/59 ND ND ND ND 100 -- -- Neburon 555–37–3 61/59 ND ND ND ND -- -- -- Norflurazon 27314–13–2 61/59 ND ND ND ND 10 -- -- Pendimethalin 40487–42–1 48/48 ND ND ND ND 70 -- -- Prometryn 7287–19–6 48/48 ND ND ND ND 300 -- -- Propachlor 1918–16–7 20/20 ND ND ND ND 3

1 -- --

Propachlor ethane 

sulfonic acid

-- 32/32 ND ND ND ND -- -- --

Propachlor oxanilic acid -- 32/32 ND ND ND ND -- -- --Propham 122–42–9 61/59 ND ND ND ND 100 -- --Propyzamide 23950–58–5 48/48 ND ND ND ND 3

1 -- --

Siduron 1982–49–6 61/59 ND ND ND ND 1,000 -- --Terbuthylazine 5915–41–3 48/48 ND ND ND ND 2 -- --Trifluralin 1582–09–8 48/48 ND ND ND ND 20 -- --

Insecticides and insecticide degradates

Imidacloprid 138261–

41–3

61/59 6.6 5.1 0.017 0.016 400 -- --

Fipronil 120068–

37–3

48/48 4.2 ND E.006 ND -- -- --
Appendixes 67

Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level]

Compound CASRN1

Number of 

samples 

Detection frequency 

(percent)

Maximum concentration 

(μg/L) Human-health benchmark 

(μg/L)

Number of concentrations with 

BQ > 0.1; (1) number of 

concentrations with BQ >1

Source water/ 

Finished water

Source 

water

Finished 

water

Source 

water

Finished 

water

Source 

water

Finished 

water

Insecticides and insecticide degradates—Continued

Fipronil sulfide 120067–

83–6

48/48 2.1 2.1 E0.007 E0.008 -- -- --

Diazinon (CCL) 333–41–5 61/62 1.6 1.6 .01 .005 21 -- --1-Naphthol 90–15–3 48/48 ND ND ND ND -- -- --3-Hydroxycarbofuran 16655–82–6 61/59 ND ND ND ND -- -- --3-Ketocarbofuran 16709–30–1 59/57 ND ND ND ND -- -- --Aldicarb 116–06–3 61/59 ND ND ND ND 69 -- --Aldicarb sulfone 1646–88–4 61/59 ND ND ND ND 67 -- --Aldicarb sulfoxide 1646–87–3 61/59 ND ND ND ND 67 -- --Azinphos-methyl 86–50–0 48/48 ND ND ND ND 210 -- --Azinphos-methyl-oxon 961–22–8 48/48 ND ND ND ND -- -- --Bendiocarb 22781–23–3 61/59 ND ND ND ND 9 -- --Carbaryl 63–25–2 61/59 ND ND ND ND 340 -- --Carbofuran 1563–66–2 61/59 ND ND ND ND 40 -- --Chlorpyrifos 2921–88–2 61/62 ND ND ND ND 2 -- --Chlorpyrofos, oxygen 

analog

5598–15–2 48/48 ND ND ND ND -- -- --

cis-Permethrin 54774–45–7 48/48 ND ND ND ND 3,74 -- --Cyfluthrin 68359–37–5 48/48 ND ND ND ND 200 -- --Cypermethrin 52315–07–8 48/48 ND ND ND ND 40 -- --Desulfinylfipronil -- 48/48 ND ND ND ND -- -- --Desulfinylfipronil amide -- 48/48 ND ND ND ND -- -- --Diazinon, oxygen 

analog

962–58–3 38/38 ND ND ND ND -- -- --

Dichlorvos 62–73–7 49/49 ND ND ND ND .4 -- --
68 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protec- tion Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level] Compound CASRN1 Number of samples Detection frequency (percent) Maximum concentration (μg/L) Human-health benchmark (μg/L) Number of concentrations with BQ > 0.1; (1) number of concentrations with BQ >1 Source water/ Finished water Source water Finished water Source water Finished water Source water Finished water Insecticides and insecticide degradates—Continued Dicrotophos 141–66–2 48/48 ND ND ND ND 0.05 -- -- Dieldrin 60–57–1 48/48 ND ND ND ND 3.002 -- -- Dimethoate 60–51–5 48/48 ND ND ND ND 2 -- -- Ethion 563–12–2 48/48 ND ND ND ND 4 -- -- Ethion monoxon 17356–42–2 48/48 ND ND ND ND -- -- -- Fenamiphos 22224–92–6 48/48 ND ND ND ND .7 -- -- Fenamiphos sulfone 31972–44–8 48/48 ND ND ND ND -- -- -- Fenamiphos sulfoxide 31972–43–7 48/48 ND ND ND ND -- -- -- Fipronil sulfone 120068– 36–2 48/48 ND ND ND ND -- -- -- Fonofos (CCL) 944–22–9 48/48 ND ND ND ND 10 -- -- Fonofos, oxygen analog 944–21–8 23/23 ND ND ND ND -- -- -- Isofenphos 25311–71–1 48/48 ND ND ND ND 6 -- -- Malaoxon 1634–78–2 48/48 ND ND ND ND -- -- -- Malathion 121–75–5 48/48 ND ND ND ND 50 -- -- Methidathion 950–37–8 48/48 ND ND ND ND 1 -- -- Methiocarb 2032–65–7 61/59 ND ND ND ND 40 -- -- Methomyl 16752–77–5 61/59 ND ND ND ND 200 -- -- Oxamyl 23135–22–0 61/59 ND ND ND ND 200 -- -- Paraoxon-methyl 950–35–6 48/48 ND ND ND ND -- -- -- Parathion-methyl 298–00–0 48/48 ND ND ND ND 1 -- -- Phorate 298–02–2 48/48 ND ND ND ND 4 -- -- Phorate oxon 2600–69–3 48/48 ND ND ND ND -- -- --

Phosmet 732–11–6 34/34 ND ND ND ND 2

8 -- --

Phosmet oxon 3735–33–9 32/33 ND ND ND ND -- -- --
Appendixes 69

Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level]

Compound CASRN1

Number of 

samples 

Detection frequency 

(percent)

Maximum concentration 

(μg/L) Human-health benchmark 

(μg/L)

Number of concentrations with 

BQ > 0.1; (1) number of 

concentrations with BQ >1

Source water/ 

Finished water

Source 

water

Finished 

water

Source 

water

Finished 

water

Source 

water

Finished 

water

Insecticides and insecticide degradates—Continued

Propoxur 114–26–1 61/59 ND ND ND ND 39 -- --Terbufos (CCL) 13071–79–9 48/48 ND ND ND ND .4 -- --Terbufos-oxygen-analog 

sulfone

56070–15–6 48/48 ND ND ND ND -- -- --

Manufacturing additives

Tributyl phosphate 126–73–8 55/57 9.1 1.8 E0.16 E0.009 -- -- --Tri(2-chloroethyl)

phosphate

115–96–8 55/57 5.5 1.8 E.13 E.099 -- -- --

Tris(dichlorisopropyl)

phosphate

13674–87–8 55/57 5.5 ND E.081 ND -- -- --

Tri(2-butoxyethyl)

phosphate

78–51–3 41/43 2.4 4.7 E.18 E.33 -- -- --

Bisphenol A 80–05–7 43/47 2.3 ND 2.5 ND 400 -- --Triphenyl phosphate 115–86–6 53/55 1.9 20 E.083 E.26 -- -- --5-Methyl-1H-benzotriazole 136–85–6 53/55 ND ND ND ND -- -- --

Organic synthesis compounds

Carbon disulfide 75–15–0 63/64 1.6 ND 0.116 ND 700 -- --Vinyl chloride 75–01–4 71/71 1.4 ND .4 ND 2 1 --Chloromethane 74–87–3 71/71 ND 2.8 ND E.116 30 -- --Carbazole 86–74–8 55/57 ND 1.8 ND E.005 -- -- --1,1-Dichloropropene 

(CCL)

563–58–6 71/71 ND ND ND ND -- -- --

1,2,3-Trichlorobenzene 87–61–6 71/71 ND ND ND ND -- -- --1,2,3-Trichloropropane 96–18–4 71/71 ND ND ND ND 40 -- --3-Chloro-1-propene 107–05–1 71/71 ND ND ND ND -- -- --
70 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protec- tion Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level] Compound CASRN1 Number of samples Detection frequency (percent) Maximum concentration (μg/L) Human-health benchmark (μg/L) Number of concentrations with BQ > 0.1; (1) number of concentrations with BQ >1 Source water/ Finished water Source water Finished water Source water Finished water Source water Finished water Organic synthesis compounds—Continued Acrylonitrile 107–13–1 71/71 ND ND ND ND 30.06 -- -- Anthraquinone 84–65–1 55/57 ND ND ND ND -- -- -- Ethyl methacrylate (Ethyl 2-methyl-2- propanoate) 97–63–2 71/71 ND ND ND ND -- -- -- Hexachlorobutadiene (CCL) 87–68–3 71/71 ND ND ND ND 3.9 -- -- Iodomethane 74–88–4 71/71 ND ND ND ND -- -- -- Methyl acrylate (Methyl-2-propeno- ate) 96–33–3 71/71 ND ND ND ND -- -- -- Methyl acrylonitrile (2-Methyl-2-propene­ nitrile) 126–98–7 71/71 ND ND ND ND .7 -- -- Methyl methacrylate (Methyl 2-methyl-2- propenoate) 80–62–6 71/71 ND ND ND ND 10,000 -- -- trans-1,4-Dichloro-2- butene 110–57–6 71/71 ND ND ND ND -- -- -- Vinyl bromide 593–60–2 71/71 ND ND ND ND -- -- -- Pavement- and combustion-derived compounds Phenanthrene 85–01–8 55/57 3.6 5.3 E0.017 E0.02 -- -- -- Anthracene 120–12–7 55/57 ND ND ND ND 2,000 -- -- Benzo[a]pyrene 50–32–8 55/57 ND ND ND ND .2 -- -- Fluoranthene 206–44–0 55/57 ND ND ND ND 300 -- --

Pyrene 129–00–0 55/57 ND ND ND ND 200 -- --
Appendixes 71

Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level]

Compound CASRN1

Number of 

samples 

Detection frequency 

(percent)

Maximum concentration 

(μg/L) Human-health benchmark 

(μg/L)

Number of concentrations with 

BQ > 0.1; (1) number of 

concentrations with BQ >1

Source water/ 

Finished water

Source 

water

Finished 

water

Source 

water

Finished 

water

Source 

water

Finished 

water

Personal-care and domestic-use products

Hexahydrohexamethylcyclopentabenzopyran (HHCB) 1222–05–5 55/57 5.5 3.5 E0.081 E0.088 -- -- --Caffeine 58–08–2 40/38 5.0 ND E.006 ND -- -- --Acetyl hexamethyl 

tetrahydronaphthalene (AHTN)

21145–77–7 55/57 3.6 ND E.079 ND -- -- --

Nonylphenol diethoxylate (total) 26027–38–2 55/57 3.6 ND E3.2 ND -- -- --Octylphenol diethoxylate (total) -- 55/57 3.6 ND E.089 ND -- -- --Octylphenol monoethoxylate (total) -- 55/57 3.6 ND E.32 ND -- -- --Methyl salicylate 119–36–8 55/57 1.8 3.5 E.014 E.06 4,000 -- --Camphor 76–22–2 55/57 1.8 1.8 E.004 E.013 -- -- --4-tert-Octylphenol 140–66–9 55/57 1.8 ND E.079 ND -- -- --Menthol 89–78–1 41/43 ND 2.3 ND E.033 -- --3-tert-Butyl-4-hydroxy 

anisole (BHA)

25013–16–5 55/57 ND ND ND ND -- -- --

4-Cumylphenol 599–64–4 55/57 ND ND ND ND -- -- --4-n-Octylphenol 1806–26–4 55/57 ND ND ND ND -- -- --Acetophenone 98–86–2 49/51 ND ND ND ND 700 -- --Benzophenone 119–61–9 R -- -- -- -- -- -- --Bromochloromethane 74–97–5 71/71 ND ND ND ND 90 -- --Cotinine 486–56–6 54/55 ND ND ND ND -- -- --d-Limonene 5989–27–5 55/57 ND ND ND ND -- -- --
72 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protec- tion Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level] Compound CASRN1 Number of samples Detection frequency (percent) Maximum concentration (μg/L) Human-health benchmark (μg/L) Number of concentrations with BQ > 0.1; (1) number of concentrations with BQ >1 Source water/ Finished water Source water Finished water Source water Finished water Source water Finished water Personal-care and domestic-use products—Continued Indole 120–72–9 55/57 ND ND ND ND -- -- -- Isoborneol 124–76–5 55/57 ND ND ND ND -- -- -- Isoquinoline 119–65–3 55/57 ND ND ND ND -- -- -- N,N-diethyl-meta-tolu­ amide (DEET) 134–62–3

R -- -- -- -- -- -- --

para-Nonylphenol 

(total)

84852–15–3

R -- -- -- -- -- -- --

Phenol 108–95–2

R -- -- -- -- 2,000 -- --

Triclosan 3380–34–5 55/57 ND ND ND ND -- -- --Triethyl citrate (Ethyl 

citrate)

77–93–0 55/57 ND ND ND ND -- -- --

Plant- or animal-derived biochemicals

beta-Stigmastanol 19466–47–8 55/57 1.8 ND E0.52 ND -- -- --3-beta-Coprostanol 360–68–9 55/57 ND ND ND ND -- -- --3-Methyl-1(H)-indole 

(Skatole)

83–34–1 55/57 ND ND ND ND -- -- --

beta-Sitosterol 83–46–5 55/57 ND ND ND ND -- -- --Cholesterol 57–88–5 55/57 ND ND ND ND -- -- --

Refrigerants and propellants

Trichlorofluoromethane 

(CFC-11)

75–69–4 71/71 2.8 2.8 E0.134 0.152 2,000 -- --

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

trifluoroethane (CFC113)

76–13–1 71/71 2.8 ND .394 ND 200,000 -- --

Dichlorodifluoromethane (CFC-12) 75–71–8 71/71 1.4 2.8 E.05 E.083 1,000 -- --
Appendixes 73

Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued[Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protection Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level]

Compound CASRN1

Number of 

samples 

Detection frequency 

(percent)

Maximum concentration 

(μg/L) Human-health benchmark 

(μg/L)

Number of concentrations with 

BQ > 0.1; (1) number of 

concentrations with BQ >1

Source water/ 

Finished water

Source 

water

Finished 

water

Source 

water

Finished 

water

Source 

water

Finished 

water

Solvents

Perchloroethene (PCE) 127–18–4 71/71 39 37 8.02 0.561 5 4(1) 2Trichloroethene (TCE) 79–01–6 71/71 27 23 64 .63 5 3(1) 1cis-1,2-Dichloroethene 156–59–2 71/71 20 18 2.4 2.19 70 -- --1,1,1-Trichloroethane 71–55–6 71/71 20 14 5.07 1.12 200 -- --1,1-Dichloroethane 

(CCL)

75–34–3 71/71 13 8.5 5.11 .347 -- -- --

1,1-Dichloroethene 75–35–4 71/71 11 8.5 7.02 .129 7 1(1) --trans-1,2-Dichloroethene 156–60–5 71/71 4.2 5.6 .18 .15 100 -- --Carbon tetrachloride 

(Tetrachloromethane)

56–23–5 71/71 2.8 8.5 .52 .5 5 1 --

Tetrahydrofuran 109–99–9 71/71 2.8 ND 278.9 ND -- -- --Acetone 67–64–1 56/56 1.8 ND 68.4 ND 6,000 -- --1,2-Dichloroethane 107–06–2 71/71 1.4 ND E.084 ND 5 -- --Methyl ethyl ketone 

(MEK)

78–93–3 71/71 1.4 ND 1,142 ND 4,000 1 --

Chlorobenzene 108–90–7 61/61 ND 1.6 ND E.014 100 -- --Methyl isobutyl ketone 

(4-Methyl-2-pentanone)

108–10–1 71/71 ND 1.4 ND 3.3 -- -- --

1,1,1,2-Tetrachloroethane 630–20–6 71/71 ND ND ND ND 70 -- --1,1,2,2-Tetrachloroethane (CCL) 79–34–5 71/71 ND ND ND ND .3 -- --1,1,2-Trichloroethane 79–00–5 71/71 ND ND ND ND 5 -- --Diethyl ether 

(1,1’-Oxybisethane)

60–29–7 71/71 ND ND ND ND 1,000 -- --
74 Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater Appendix 3. Summary statistics and human-health benchmarks for anthropogenic organic compounds analyzed in source- and finished-water samples collected during June 2004–September 2005 (use groups obtained from Carter and others, 2007).—Continued [Compounds within each primary-use category are listed in order from highest to lowest source-water detection frequency. Human-health benchmarks in bold type are Maximum Contaminant Levels (MCLs); CASRN, Chemical Abstracts Service Registry Number®; μg/L, micrograms per liter; BQ, benchmark quotient; >, greater than; --, none; E, estimated value; ND, not detected; CCL, U.S. Environmental Protec- tion Agency’s Contaminant Candidate List 2 (U.S. Environmental Protection Agency, 2005); MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(2-methyl-4-chlorophenoxy) butyric acid; R, compound removed from the dataset; HBSL, Health-Based Screening Level] Compound CASRN1 Number of samples Detection frequency (percent) Maximum concentration (μg/L) Human-health benchmark (μg/L) Number of concentrations with BQ > 0.1; (1) number of concentrations with BQ >1 Source water/ Finished water Source water Finished water Source water Finished water Source water Finished water Solvents—Continued 1,2,4-Trichlorobenzene 120–82–1 71/71 ND ND ND ND 70 -- -- 1,2-Dichlorobenzene 95–50–1 71/71 ND ND ND ND 600 -- -- 1,3-Dichlorobenzene 541–73–1 71/71 ND ND ND ND 600 -- -- 2-Chlorotoluene 95–49–8 71/71 ND ND ND ND 100 -- -- 2-Hexanone 591–78–6 71/71 ND ND ND ND -- -- -- 4-Chlorotoluene 106–43–4 71/71 ND ND ND ND 100 -- -- Bromobenzene (CCL) 108–86–1 71/71 ND ND ND ND -- -- -- Chloroethane 75–00–3 71/71 ND ND ND ND -- -- -- Dibromomethane 74–95–3 71/71 ND ND ND ND -- -- -- Hexachloroethane 67–72–1 71/71 ND ND ND ND .7 -- -- Isophorone 78–59–1

R -- -- -- -- 100 -- --

Methyl acetate 79–20–9 15/15 ND ND ND ND -- -- --Methylene chloride 

(Dichloromethane)

75–09–2 56/56 ND ND ND ND 5 -- --

n-Propylbenzene 103–65–1 71/71 ND ND ND ND -- -- --p-Cresol 106–44–5 55/57 ND ND ND ND -- -- --

1This report contains CASRNs, which is a Registered Trademark of the American Chemical Society. The Chemical Abstracts Service (CAS) recommends the verification of the CASRNs through CAS Client 

ServicesSM.

2The U.S. Environmental Protection Agency’s MCL of 80 μg/L is for the sum of the concentrations of four trihalomethanes.3HBSL values shown for carcinogens represent the low end (10–6) of the HBSL range (10–6 to 10–4 cancer risk level) (Toccalino, Norman, and others, 2006).4The sum of concentrations from cis-1,3- and trans-1,3-dichloropropene may be compared to the HBSL range (0.3–30 μg/L) for the mixed isomer of 1,3-dichloropropene, CASRN 542–75–6.5The concentrations from 

m- and 

p-xylene and o-xylene may be compared to the MCL (10,000 μg/L) for mixed xylenes, CASRN 1330–20–7. 

6U.S. Environmental Protection Agency Office of Water recommends that the concentration of any combination of two or more of the three aldicarb compounds should not be greater than 7 μg/L because of 

similar mode of action.

7Concentrations of cis-permethrin may be compared to the HBSL range (4–400 μg/L) for permethrin, Chemical Abstract Service Registry Number 52645–53–1.

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Hopple and others—Anthropogenic Organic Compounds in Source Water of Selected Community Water Systems that Use Groundwater, 2002–05—SIR 2009–5200

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