U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5035

National Water-Quality Assessment Program

Source Water-Quality Assessments

Anthropogenic Organic Compounds in Ground

Water and Finished Water of Community Water

Systems near Dayton, Ohio, 2002–04

Anthropogenic Organic Compounds in Ground 

Water and Finished Water of Community Water 

Systems near Dayton, Ohio, 2002–04 

By Mary Ann Thomas 

National Water-Quality Assessment Program

Source Water-Quality Assessments

Scientific Investigations Report 2007–5035

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Thomas, M.A., 2007, Anthropogenic organic compounds in ground water and finished water of community water systems near Dayton, Ohio, 2002–04: U.S. Geological Survey Scientific Investigations Report 2007–5035, 21 p. 
Foreword

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

and timely scientific information that helps 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 quality of the Nation’s water resources is critical to 

assuring the long-term availability of water that is safe for drinking and recreation and suitable for industry, irrigation, and habitat for fish and wildlife. Population growth and increasing 

demands for multiple water uses make water availability, 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, and local information needs and decisions related to waterquality management and policy (http://water.usgs.gov/nawqa). Shaped by and coordinated with 

ongoing efforts of other Federal, State, and local agencies, the NAWQA Program is designed to 

answer: What is the condition of our Nation’s streams and ground water? How are the conditions changing over time? How do natural features and human activities affect the quality 

of streams and ground water, 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 to 2001, the NAWQA Program completed interdisciplinary assessments in 51 

of the Nation’s major river basins and aquifer systems, referred to as Study Units (http://water.

usgs.gov/ nawqa/studyu.html). Baseline conditions were established for comparison to future 

assessments, and long-term monitoring was initiated in many of the basins. During the next 

decade, 42 of the 51 Study Units will be reassessed so that 10 years of comparable monitoring 

data will be available to determine trends at many of the Nation’s streams and aquifers. The 

next 10 years of study also will fill in critical gaps in characterizing water-quality conditions, 

enhance understanding of factors that 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.

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

inform 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 water-resource issues of interest. External coordination at all levels is critical for a fully 

integrated understanding of watersheds and 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, interstate, Tribal, and local—as 

well as nongovernmental organizations, industry, academia, and other stakeholder groups. Your 

assistance and suggestions are greatly appreciated.

Robert M. Hirsch

Associate Director for Water 

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iv
v

Contents

Foreword ........................................................................................................................................................iii

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

Introduction.....................................................................................................................................................1

Description of Study Area ............................................................................................................................2

Study Methods ..............................................................................................................................................4

Well Selection .......................................................................................................................................4

Sample Collection, Analysis, and Quality Control ..........................................................................4

Interpretation of Results in a Human-Health Context.....................................................................5

Anthropogenic Organic Compounds in Ground Water During Phase 1 ...............................................6

Volatile Organic Compounds...............................................................................................................6

Pesticides ..............................................................................................................................................6

Comparison of Ground Water and Finished Water During Phase 2......................................................6

Volatile Organic Compounds...............................................................................................................9

Pesticides ..............................................................................................................................................9

Summary........................................................................................................................................................14

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

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

Glossary.........................................................................................................................................................16

Appendix 1. Comparison of anthropogenic organic compounds detected in sourceand associated finished-water samples during Phase 2 of the Source 

Water-Quality Assessment near Dayton, Ohio..............................................................18

Figures

1. Map showing location of National Water-Quality Assessment Study Units 

and Ground-Water Source Water-Quality Assessments.......................................................2

2. Map showing location of wells sampled for the Source Water-Quality 

Assessment near Dayton, Ohio, 2002–04..................................................................................3

3–5. Graphs showing:

3. Concentrations, number of detections, and benchmark quotient values 

for volatile organic compounds and pesticides for samples collected 

during Phase 1 from 15 source-water wells of community water systems 

near Dayton, Ohio ................................................................................................................7

4. Comparison of volatile organic compounds in samples collected during 

Phase 2 from five source-water wells and the associated finished water 

of community supply systems near Dayton, Ohio: concentrations and 

benchmark quotient values..............................................................................................10

5. Comparison of pesticides in samples collected during Phase 2 from 

five source-water wells and the associated finished water of community 

water systems near Dayton, Ohio: concentrations and benchmark 

quotient values...................................................................................................................13
vi

Tables

1. Selected characteristics of 15 community-water-system wells sampled 

during Phase 1 of the Source Water-Quality Assessment near Dayton, Ohio ...................4

2. Maximum concentration, detection frequency, and maximum benchmark 

quotient for regulated and unregulated compounds detected in samples 

collected during Phase 1 from 15 source-water wells of community water 

systems near Dayton, Ohio .........................................................................................................8

3. Maximum concentration, detection frequency, and maximum benchmark 

quotient for regulated and unregulated compounds detected in samples 

collected during Phase 2 from five source-water wells and the associated 

finished water of community water systems near Dayton, Ohio........................................11

Conversion Factors, Abbreviations, and Acronyms

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

kilometer (km) 0.6214 mile (mi)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

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

)

parts per billion 1.0 micrograms per liter (μg/L)

Abbreviations and Acronyms

< Less than

> Greater than

μg/L micrograms per liter

AOC Anthropogenic organic compound

BQ Benchmark Quotient

BQmax Ratio of the maximum concentration to a drinking-water benchmark

CWS Community water system

E Estimated concentration

DBP Disinfection byproduct

HBSL Health Based-Screening Level

MRL Minimum Reporting Level

OAOC Other anthropogenic organic compound

MTBE Methyl tert-butyl ether

NAWQA National Water-Quality Assessment

NWQL National Water Quality Laboratory

SWQA Source Water-Quality Assessment

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC Volatile organic compound
Abstract

Source water for 15 community-water-system (CWS) 

wells in the vicinity of Dayton, Ohio, was sampled to evaluate the occurrence of 258 anthropogenic compounds (AOCs). 

At least one AOC was detected in 12 of the 15 samples. Most 

samples contained a mixture of compounds (average of four 

compounds per sample). The compounds that were detected 

in more than 30 percent of the samples included three volatile 

organic compounds (VOCs) (trichloroethene, chloroform, and 

1,1,1-trichloroethane) and four pesticides or pesticide breakdown products (prometon, simazine, atrazine, and deethylatrazine). In general, VOCs were detected at higher concentrations 

than pesticides were; among the VOCs, the maximum detected 

concentration was 4.8 μg/L (for trichloroethene), whereas 

among the pesticides, the maximum detected concentration 

was 0.041 μg/L (for atrazine). 

During a later phase of the study, samples of source water 

from five CWS wells were compared to samples of finished 

water associated with each well. In general, VOC detections 

were higher in finished water than in source water, primarily 

due to the occurrence of trihalomethanes, which are compounds that can form during the treatment process. In contrast, 

pesticide detections were relatively similar between sourceand finished-water samples.

To assess the human-health relevance of the data, concentrations of AOCs were compared to their respective humanhealth benchmarks. For pesticides, the maximum detected concentrations were at least 2 orders of magnitude less than the 

benchmark values. However, three VOCs—trichloroethene, 

carbon tetrachloride, and tetrachloromethane—were detected 

at concentrations that approach human-health benchmarks and 

therefore may warrant inclusion in a low-concentration, trends 

monitoring program. 

Introduction

The U.S. Geological Survey (USGS) National WaterQuality Assessment (NAWQA) Program was designed to 

document the Nation’s current water-quality conditions, identify water-quality trends, and describe factors that affect waterquality conditions and trends. Beginning in 2001, the NAWQA 

Program has been characterizing the quality of major aquifers 

used as a source of supply for larger community water systems 

(CWSs) through a new type of study called Source WaterQuality Assessments (SWQAs). As of 2006, 15 ground-water 

SWQAs have been completed in NAWQA study units around 

the Nation (fig. 1). These studies are intended to complement 

drinking-water monitoring required by Federal, state, and local 

programs, which focus primarily on posttreatment compliance 

monitoring. 

The compounds monitored for SWQAs are referred to as 

anthropogenic organic compounds (AOCs); that is, chemicals 

that are commonly derived from or related to human activity 

in industrialized societies. These include volatile organic compounds (VOCs), pesticides and pesticide breakdown products, 

and other anthropogenic organic compounds (OAOCs). VOCs 

are a subset of organic chemicals that have been produced and 

used in a variety of commercial, industrial, and household 

applications for many decades and are major components 

or additives to gasoline, paints, varnishes, glues, dyes, and 

plastics. Pesticides are used extensively throughout the United 

States to increase crop yields; enhance the esthetics of lawns, 

gardens, golf courses, and recreational areas; and protect the 

safety of the public from insect-associated diseases. OAOCs 

represent a group of compounds that are present in a wide 

range of products commonly used in homes, industry, and 

agriculture, including personal-care and domestic-use products, plant- or animal-derived biochemicals, and fumigants. 

This report focuses on an SWQA completed in the vicinity of Dayton, Ohio, which is part of the White River-Great 

and Little Miami River Basins (WHMI) study unit (fig. 1). 

The Dayton area was chosen for study because a large population relies heavily on ground water from the glacial aquifer 

system, one of the Nation’s most widespread principal aquifers 

(Warner and Arnold, 2005). 

The report has three objectives: (1) describe the occurrence of AOCs in source water of 15 CWSs in the vicinity of 

Dayton, Ohio, during 2002–2003, (2) describe and compare 

the occurrence of selected AOCs in source water and finished 

water from 5 CWSs during 2004, and (3) compare detected 

concentrations of AOCs to benchmark concentrations to evaluate the potential relevance to human health.

Anthropogenic Organic Compounds in Ground Water 

and Finished Water of Community Water Systems near 

Dayton, Ohio, 2002–04

By Mary Ann Thomas
Figure 1. Location of National Water-Quality Assessment Study Units and Ground-Water Source Water-Quality 

Assessments. 

Description of Study Area

The study area is in the vicinity of Dayton, Ohio, a 

major industrial center for southwestern Ohio and the home 

of Wright-Patterson Air Force Base. The study area includes 

a 250-mi2

 area that overlies valley-fill deposits of the glacial 

aquifer system, locally referred to as the Buried-Valley Aquifer (fig. 2). The majority of water use in Dayton and surrounding areas is from the Buried-Valley Aquifer, which has been 

designated a sole-source aquifer by the U.S. Environmental 

Protection Agency (Debrewer and others, 2000). Along the 

main valley, land use is predominantly urban, commercial, or 

residential. Agriculture (row crops and pasture) is the predominant land use in the upper reaches of the tributary valleys 

(Debrewer and others, 2000; Sheets, in press). 

The hydrogeology of the study area has been described 

by Norris and Spieker (1966), Dumouchelle (1998), Sheets 

and others (1998), Debrewer and others (2000), and Sheets 

(in press). The climate is temperate continental, and the average annual rainfall is approximately 39 in. (Debrewer and others, 2000). The topography is flat to gently rolling. Preglacial 

valleys are incised in bedrock and are filled with as much as 

300 ft of glacial deposits. The glacial deposits are predominantly coarse grained (fine sand to gravel) but are interspersed 

with layers of clay-rich till or clay (Dumouchelle, 1998). In 

areas where the till is laterally continuous, the glacial deposits are separated into two or more aquifers, the lower aquifer 

being confined or semiconfined (Norris and Spieker, 1966). 

Under natural flow conditions, the predominant source of 

ground-water recharge is precipitation, and the predominant 

discharge areas are major streams. However, heavy pumping 

in the study area induces infiltration of surface water (rivers and artificial recharge lagoons) to the aquifer (Sheets, in 

press). For the period 1997–2001, more than 300 publicly and 

privately owned wells pumped water from the glacial deposits 

at an average rate of 500,00 m3

/d (Sheets, in press). 

2 Anthropogenic Organic Compounds in Community Water Systems near Dayton, Ohio, 2002–04
Figure 2. Location of wells sampled for the Source Water-Quality Assessment near Dayton, Ohio, 2002-04. 

 

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DAYTON

MONTGOMERY COUNTY

CLARK COUNTY

GREENE COUNTY

MIAMI COUNTY

Stillwater River

Wolf Creek

Great Miami River

Little Miami River

Mad River

Great Miami River

84° 15' 00" 84° 00' 00"

39° 45' 00"

39° 52' 30"

Approximate extent of buried valleys

(from Dumouchelle, 1998)

 

0

0

6 

6 

Wells sampled during Phase 1

Wells resampled during Phase 2

KILOMETERS

MILES

EXPLANATION

Base from U.S. Geological Survey

Albers projection

Figure 2. Location of wells sampled for the Source Water-Quality Assessment near Dayton, Ohio, 2002–04. 

Description of Study Area 3
Ground-water quality of the Buried-Valley Aquifer in the 

study area was documented by Rowe and others (1999, 2004). 

In general, ground water is of the calcium-magnesium-bicarbonate type, and the pH is circumneutral (around 7). Redox 

conditions vary from oxic to anoxic. Oxic waters rarely occur 

at depths greater than 40 ft below the water table (Rowe and 

others, 1999). Anoxic waters predominate at greater depths but 

are also present at shallow depths. Ground-water ages in the 

upper 50 ft of the aquifer are generally 1 to 2 years; at greater 

depths, ground-water can be as old as 50 years (Rowe and others, 1999, 2004).

Most of the water produced by large CWSs is treated 

and blended prior to distribution to consumers. As used in this 

study, “source water” is the raw (ambient) water collected at 

the supply well prior to water treatment, “blended water” is 

a mixture of water from several ground-water sources, and 

“finished water” is the source water or blended water that is 

treated and ready to be delivered to consumers. 

Study Methods 

SWQA studies are based on nationally consistent methods for site selection, sample collection and analysis (Carter 

and others, 2007). Water-quality results are interpreted in a 

human-health context using Health-Based Screening Levels 

(Toccalino and others, 2006).

Well Selection

SWQA studies are targeted to urban areas where most of 

the water use is from a major aquifer, such as the BuriedValley Aquifer. Additional criteria for well selection are the 

following: (1) wells are least one km apart to ensure that 

contributing areas do not overlap, (2) the wells are among the 

highest producing CWSs in the study area, based on annual 

production data for a well or well field, and (3) the wells are 

not under the influence of surface water. 

For the Dayton area, most of highest-producing CWS 

wells are near rivers, and pumping induces surface-water infiltration to wells. So, the decision was made to relax the third 

well-selection criterion and select wells that were minimally 

influenced by surface-water infiltration, with the understanding that these wells would not all have high annual pumping 

rates. Identification of wells minimally influenced by surface 

water was facilitated by the use of a steady-state groundwater-flow model for the Buried-Valley Aquifer in the Dayton 

area that was developed by Dumouchelle (1998) and refined 

by Sheets (in press). Wells were deemed to be minimally influenced by surface-water infiltration if the majority of the flow 

lines to the well did not originate at a river or other surface 

water body (Rodney A. Sheets, U.S. Geological Survey, oral 

commun., 2004). However, it is possible that other wells from 

the same well fields could be under the influence of surfacewater infiltration, so a sample of blended water could show the 

effects of surface-water infiltration. The first criterion also was 

relaxed: two of the selected wells were less than 1 km apart, 

but they were on different sides of the Great Miami River, and 

it is unlikely that the contributing areas overlap. 

Characteristics of the 15 selected wells are listed in 

table 1. The wells were 60–158 ft deep, and the open intervals 

were 12–50 ft long. For 14 of the 15 wells, annual average 

production rates during 2002 were estimated to range from 

120 to 2,080 Mgal, with an average value of 980 Mgal. One of 

the wells was not in use during 2002, although other wells in 

the same well field were. 

Table 1. Selected characteristics of 15 community-watersystem wells sampled during Phase 1 of the Source WaterQuality Assessment near Dayton, Ohio. 

Well depth, 

in feet 

Length of 

open interval, 

in feet 

Annual pumping, 

in millions 

of gallons 

60 12 223

77 30 111

80 25 120

83 20 80

84 30 138

94 20 0

94 24 568

123 25 217

125 17 62

136 38 260

146 50 389

148 15 35

152 50 200

157 50 275

158 30 88

Sample Collection, Analysis, and Quality Control 

The study was done in two phases. For Phase 1, sourcewater samples were collected from the 15 CWS wells mentioned previously. The samples were collected at the wellhead 

before any treatment. Established USGS protocols were 

followed for sample collection and preservation (Koterba and 

others, 1995). Samples were analyzed for 88 VOCs, 120 pesticides, and 50 OAOCs (Carter and others, 2007). 

For Phase 2, a subset of the wells was resampled. Five 

wells were selected for resampling on the basis of relatively 

high frequency or concentration of AOC detections during Phase 1. The finished water associated with each of the 

4 Anthropogenic Organic Compounds in Community Water Systems near Dayton, Ohio, 2002–04
five source-water wells also was analyzed. Finished-water 

samples were collected after treatment and blending but before 

distribution. Finished-water samples were stabilized during 

collection by the addition of a dechlorination agent (ascorbic 

acid) and, for certain contaminant groups, pH buffers. Samples 

were analyzed for VOCs, pesticides, and OAOCs, in addition 

to 19 acetamide herbicides and breakdown products (Carter 

and others, 2007). 

During both phases of study, quality-control samples 

(equipment blanks, field blanks, source-solution blanks, 

replicates, and field spikes) were collected and analyzed in 

accordance with established protocols (Koterba and others, 

1995; Carter and others, 2007). 

Samples were analyzed at the USGS National Water 

Quality Laboratory in Denver, Colo., by USGS-approved 

analytical methods (Zaugg and others, 1995; Lindley and 

others, 1996; Connor and others, 1998; Furlong and others, 

2001; Sandstrom and others, 2001; Zaugg and others, 2002; 

and Madsen and others, 2003). Analyses for the additional 

acetamide herbicides and breakdown products collected for 

Phase 2 were done at the Organic Geochemistry Research 

Group Laboratory in Lawrence, Kansas (Lee and Strahan, 

2003). 

On a national scale, all data (including source-water, 

finished-water, and quality-control samples) from each SWQA 

study were collectively reviewed each year. The goals were to 

evaluate variability and potential bias from systematic contamination. No systematic contamination was found for VOCs 

(D.A. Bender, U.S. Geological Survey, written commun., 

2006) or pesticides (J.A. Hopple, U.S. Geological Survey, 

written commun., 2006). On the other hand, analysis of OAOC 

field and laboratory blank data indicated possible systematic 

contamination for several compounds. Of the 7 compounds 

detected during the study in the Dayton area, six were identified as possible contaminants because of their frequent 

occurrence in field blanks (J.A. Kingsbury, U.S. Geological 

Survey, written commun., 2006) or laboratory blanks resulting from laboratory procedures used prior to 2005 (Zaugg and 

Leiker, 2006). For the current study, the single OAOC that was 

not identified as a possible contaminant was detected in one 

sample at a concentration too small to be quantified. For these 

reasons, OAOC detections are not included in this report. 

Interpretation of Results in a Human-Health 

Context

Historically, the USGS has assessed water-quality by 

comparing measured concentrations to USEPA Maximum 

Contaminant Levels (MCLs) for regulated compounds 

(U.S. Environmental Protection Agency, 2002) and drinkingwater guidelines for unregulated compounds. However, 

MCLs and drinking-water guidelines have not been established for more than 85 percent of the compounds monitored 

by SWQAs. Health-Based Screening Levels (HBSLs) were 

developed to provide a more complete understanding of the 

significance of water-quality data (Toccalino and others, 

2006). HBSLs are benchmark concentrations of contaminants 

in water that may be of potential concern for human health, if 

exceeded. HBSLs supplement existing MCLs and drinkingwater guidelines. For regulated compounds, the HBSL is the 

same as the Maximum Contaminant Level (MCL). 

Benchmark Quotient (BQ) values are used as a means of 

comparing measured concentrations of contaminants to their 

respective human-health benchmarks (Toccalino and others, 

2006). The BQ value is the ratio of a measured concentration of a compound to its MCL or HBSL. For a particular 

compound, the BQmax is the maximum BQ value for all 

samples in a dataset. BQmax values greater than 0.1 identify 

compounds that may warrant inclusion in a low-concentration, 

trends-monitoring program. BQmax values greater than or 

equal to 1.0 identify concentrations that may be of potential 

human-health concern (Toccalino and others, 2006). 

Consumer confidence reports and source-water quality assessments.—

Since 1999, the U.S. Environmental Protection Agency (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/ccrfact.html). CCRs are the centerpiece 

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

Drinking Water Act. Each CCR lists fundamental information about 

drinking water: 

•	 The source of the drinking water. 

•	 A brief summary of the susceptibility to contamination of the 

local drinking-water source.

•	 The concentrations (or range of concentrations) of any contaminants found in local drinking water, as well as their USEPA Maximum Contaminant Levels (MCLs) for comparison. MCLs are 

legally enforceable drinking-water standards and are the highest 

allowed concentrations of contaminants in drinking water.

•	 Phone numbers for additional sources of information.

Information in each CCR is specific to a particular water utility. Water 

utilities analyze finished-water samples primarily for regulated contaminants (that is, those with MCLs) using USEPA analytical methods for the 

purpose of compliance monitoring. In contrast, USGS Source WaterQuality Assessments (SWQAs) are not done for compliance monitoring 

and encompass data from multiple water utilities spatially distributed 

across the Nation. As part of SWQAs, both source- and finished-water 

samples are analyzed by USGS analytical methods, where source water 

is the raw (ambient) water collected at a supply well prior to water 

treatment, and finished water is the treated water sampled prior to 

its entering the distribution system. USGS analytical methods used in 

SWQAs typically have lower analytical reporting levels than those used 

in compliance monitoring; contaminant detection frequencies reported 

in SWQA reports may therefore be higher than detection frequencies for 

the same contaminants reported in CCRs. In SWQAs, concentrations of 

regulated and unregulated contaminants in source and finished water 

are compared to MCLs and Health-Based Screening Levels (HBSLs), 

respectively. HBSLs are estimates of benchmark concentrations of 

contaminants in water that may be of potential human-health concern 

and are consistent with USEPA Office of Water methodologies for setting 

non-enforceable drinking-water guideline values. HBSLs are not legally 

enforceable regulatory standards, and water utilities are not required to 

compare contaminant monitoring results to HBSLs. 

Study Methods 5
Anthropogenic Organic Compounds in 

Ground Water During Phase 1

For Phase 1 of the SWQA study near Dayton, samples 

were collected from 15 CWS wells between November 2002 

and January 2003. The complete dataset is available in Shindel 

and others (2003). Summaries of the detected AOCs are presented in figure 3 and table 2. 

At least one AOC was detected in 12 of the 15 samples. 

Most samples had a mixture of AOCs; an average of four 

compounds per sample were detected. The maximum number 

of AOC detections in a single sample was 13.

The minimum reporting levels for detected compounds 

varied from 0.2 to 0.005 μg/L. For a true comparison of analytical results among different AOCs, each compound should 

have the same reporting level, because compounds with low 

reporting levels may be detected more frequently than those 

with higher reporting levels. However, for the purposes of this 

report, comparisons are made among AOCs regardless of the 

varied reporting levels.

Volatile Organic Compounds

Eleven VOCs were detected in source-water samples 

(fig. 3A, table 2). The VOCs detected most frequently—in 

more than 30 percent of the samples—were trichloroethene 

(TCE), 1,1,1-trichloroethane, and chloroform. TCE is a 

solvent primarily used in dry cleaning but also used for paint 

and ink formulation, and rubber processing (Zogorski and 

others, 2006). 1,1,1-trichloroethane is a solvent used for dying, 

textile processing, cosmetics, and aerosols (Zogorski and others, 2006). Chloroform is one of four disinfection byproducts 

(DBPs) produced during the chlorination of drinking water 

and wastewater. Chloroform can enter the ground water if 

chlorinated water is used for irrigation or leaks from distribution lines, pools, or septic systems (Thiros, 2000). Chloroform 

can also be formed by dehalogenation of tetrachloromethane 

or from natural sources (Ivahnenko and Barbash, 2004). 

The maximum VOC concentration detected was 4.8 μg/L 

(for trichloroethene). Human-health benchmarks were available for nine of the VOCs detected. For seven of these compounds, concentrations were low relative to the human-health 

benchmarks; BQmax values were 1–5 orders of magnitude 

below 0.1 (table 1, fig 3A). However, two VOCS had BQmax 

values greater than 0.1 and therefore might warrant inclusion 

in a low-concentration, trends-monitoring program (Toccalino 

and others, 2006). Trichloroethene had a BQmax value of 

0.96, and carbon tetrachloride had a BQmax value of 0.14. 

Pesticides 

Ten pesticide compounds were detected in the sourcewater samples collected during Phase 1 of the study (fig. 3B, 

table 2). All of the pesticide compounds detected were herbicides. Four herbicides were detected in more than 30 percent 

of samples: prometon, simazine, atrazine, and deethylatrazine. 

Prometon is an herbicide that is primarily used in nonagricultural settings—roadsides, and residential or commercial 

areas. Simazine has both agricultural and nonagricultural uses 

(U.S. Geological Survey, 1999). Atrazine is an herbicide that 

is widely used on corn and soybeans, and deethylatrazine is a 

breakdown product of atrazine. Of the 32 pesticide detections, 

more than half (53 percent) were derived from atrazine and its 

breakdown products (deethylatrazine, deisopropylatrazine, or 

2-hydroxyatrazine). The high detection frequency for atrazine 

and its breakdown products might be related to widespread 

use and persistence in ground water (Kruger and others, 1995; 

Barbash and others, 1999). 

The maximum pesticide concentration detected was 

0.041 μg/L (for atrazine). In general, pesticides were detected 

at lower concentrations than VOCs; the maximum pesticide 

concentration was 2 orders of magnitude less than the maximum VOC concentration (fig. 3A and 3B). Human-health 

benchmarks were available for eight of the pesticides detected, 

and BQmax values were 1–6 orders of magnitude below 0.1 

(table 2). A human-health benchmark was not available for 

deethylatrazine, which was detected in almost half of the 

samples. 

6 Anthropogenic Organic Compounds in Community Water Systems near Dayton, Ohio, 2002–04
Trichloroethene

Chloroform

Bromodichloromethane

Carbon tetrachloride

1,1,1-Trichloroethane

cis-1,2-Dichloroethene

1,1-Dichloroethane1

Tetrachloroethene

Toluene

0.00001 10

CONCENTRATION, IN MICROGRAMS PER LITER

0.0001 0.001 0.01 0.1 1

Methyl tert-butyl ether 

Figure 3. Concentrations, number of detections, and benchmark quotient values for samples collected 

during Phase 1 from 15 source-water wells of community water systems near Dayton, Ohio. 

EXPLANATION

Greater than or equal to 0.1

 The compound may warrant inclusion in a low-concentration, trends-monitoring program 

 Greater than or equal to 1.0

 The concentration may be of potential human-health concern 

BENCHMARK QUOTIENT VALUE

0.001 0.01 0.1 1

A

 Imazaquin

 Simazine

 2-Hydroxyatrazine

 Prometon

 Deethylatrazine1

 Atrazine

Deisopropylatraizine1

 Metolachlor 

 Tebuthiuron2

 Bromacil

10 0.00001 0.0001

Carbon disulfide

(MTBE)

1,2

NUMBER OF DETECTIONS

2

CONCENTRATION, IN MICROGRAMS PER LITER BENCHMARK QUOTIENT VALUE

0.00001 10 0.0000001 1

NUMBER OF DETECTIONS

 3

0.0001 0.001 0.01 0.1 1 0.00001 0.0001 0.001 0.01 0.1

B

6

6

5

3

3

2

1

1

1

1

2

7

6

5

5

2

1

1

1

1

2Presence of compound verified, but concentration not quantified. 

Benchmark quotient value 

 Ratio of the detected concentration of a compound to its Maximum Contaminant Level or Health-Based Screening Level

A, Volatile organic compounds. B, Pesticides. 

1Benchmark quotient value could not be determined because compound does not have a Maximum Contaminant Level or

 Health-Based Screening Level.

Figure 3. Concentrations, number of detections, and benchmark quotient values for samples collected during Phase 1 

from 15 source-water wells of community water systems near Dayton, Ohio. A, Volatile organic compounds. B, Pesticides.

Comparison of Ground Water and Finished Water During Phase 2 7
Table 2. Maximum concentration, detection frequency, and maximum benchmark quotient for regulated and unregulated compounds 

detected in samples collected during Phase 1 from 15 source-water wells of community water systems near Dayton, Ohio. 

[USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; MCL, Maximum Contaminant Level; HBSL, Health-Based Screening Level; 

BQmax, maximum Benchmark Quotient = ratio of maximum compound concentration to MCL or HBSL value; E, estimated value; <, less than; M, presence of 

compound verified, but concentration not quantified; --, not available. A regulated compound is one for which Federal and (or) state drinking-water standards 

have been established; an unregulated compound is one for which no Federal and (or) state drinking-water standards exist.] 

Regulated (r) 

or unregulated (u) 

compound 

Chemical 

Abstracts 

Service 

registry 

number 

Number of 

detections 

for source 

water 

Detection 

frequency 

(percent) 

Minimum 

reporting 

level 

(μg/L) 

Maximum 

concentration 

for source water 

(μg/L) 

USEPA MCL1 or 

HBSL 

concentration 

(μg/L) 

BQmax 

for 

source 

water 

Volatile organic compounds

Trichloroethene ( r) 79-01-6 6 40 0.04 4.82 5 0.96

Chloroform ( r) 67-66-3 6 40 .02 1.40 2

80 .0175

1,1,1-Trichloroethane 

(r) 71-55-6 5 33 .03 .21 200 .001

cis-1,2-Dichloroethene (r) 156-59-2 3 20 .04 .14 100 .0014

Tetrachloroethene (r) 127-18-4 3 20 .03 .13 5 .026

Toluene (r) 108-88-3 2 13 .05 E .04 1000 E .00004

1,1-Dichloroethane (u) 75-34-3 2 13 .04 E .04 -- --

Carbon tetrachloride (r) 56-23-5 1 7 .06 .68 5 .136

Carbon disulfide (u) 75-15-0 1 7 .07 .21 3

700 .0003

Bromodichloromethane 

(r) 75-27-4 1 7 .05 E .02 2

80 E .0002

Methyl tert-butyl ether 

(MTBE) (u) 1634-04-4 1 7 .2 M -- --

Total number of VOC 

detections 31

Pesticides

Deethylatrazine (u) 6190-65-4 7 47 .006 E .029 -- --

Prometon (u) 1610-18-0 6 40 .01 .04 3

100 .0004

Atrazine (r) 1912-24-9 5 33 .007 .041 3 .0137

Simazine (r) 122-34-9 5 33 .005 .009 4 .0023

Deisopropylatrazine (u) 1007-28-9 3 20 .04 E .01 -- --

2-Hydroxyatrazine (u) 2163-68-0 2 13 .008 E .035 3

70 E .0005

Metolachlor (u) 51218-45-2 1 7 .013 .031 3

70 .0004

Imazaquin (u) 81335-37-7 1 7 .02 E .01 3

2,000 E .00001

Bromacil (u) 314-40-9 1 7 .03 E .01 3

70 E .0001

Tebuthiuron (u) 34014-18-1 1 7 .02 M 3

1,000 --

Total number of pesticide 

detections 32

Total number of detections 

for all compounds 73

1

U.S. Environmental Protection Agency (2003, 2004). 

2

MCL is for total trihalomethanes. 

3

Denotes HBSL (Toccalino and others, 2003). 

8 Anthropogenic Organic Compounds in Community Water Systems near Dayton, Ohio, 2002–04
Comparison of Ground Water and 

Finished Water During Phase 2

For Phase 2 of the study, 5 of the 15 CWS wells were 

resampled during June and July 2004. Two samples were collected at each site: (1) a sample of the source water, similar to 

that collected during Phase 1, and (2) a sample of the finished water associated with the source-water well. All of the 

finished-water samples had been blended with ground water 

from three to seven other CWS wells from the same well field. 

In addition, all samples of finished water were treated by 

chlorination, filtration, chemical oxidation, fluoridation, and 

one or more of the following: pH adjustment, ion exchange, or 

air stripping. The complete dataset is available in Shindel and 

others (2005). 

It is not feasible to characterize the overall frequency of 

occurrence of compounds using data from Phase 2 because 

(1) the results are biased to the AOCs detected most frequently, and (2) not all samples were analyzed for the same 

compounds. Therefore, the focus of this section of the report is 

on comparing AOC detections in source water to the associated finished water. 

Volatile Organic Compounds

A total of 14 VOCs were detected in samples collected 

during Phase 2 (fig. 4, table 3). In source-water samples, 8 different compounds were detected, and the total number of VOC 

detections was 21. The eight compounds detected in source 

water during Phase 2 were also detected during Phase 1. 

VOCs were detected more frequently in finished water 

than in source water (fig 4, table 3). For finished-water 

samples, 13 different compounds were detected, and the total 

number of detections was 37. In all, six different compounds 

were detected in finished water but not source water. Disinfection byproducts (DBPs) accounted for more than half (20 of 

the 37) of the VOC detections in finished water but less than 

15 percent (3 of 21) in source water. Chloroform, bromodichloromethane, dibromochloromethane, and bromoform are 

DBPs that were detected in all five finished-water samples 

(table 3). Although chloroform can be from natural sources, 

the detection of associated DBPs suggests that the source of 

chloroform is related to the input of chlorinated water or other 

anthropogenic sources of chloroform (Ivahnenko and Barbash, 

2004). In addition to DBPs, the other compounds that were 

detected in finished water but not source water were m-and 

p-xlyene, ethylbenzene, and trans-1,2-dichloroethene. 

The presence of AOCs in finished water but not source 

water might be related to the fact that source water is from a 

single well, whereas finished water is a blend of water from 

three to seven other wells that may have different production rates, depths, and (or) zones of contribution than the 

single source-water well that was sampled. Another possible 

explanation is that compounds were introduced as the water 

traveled between the points where source-water and finishedwater samples were collected. Regardless of what accounts for 

the differences, the results indicate that monitoring VOCs in 

source water does not necessarily characterize the occurrence 

of VOCs in finished water (Metz and others, in press). Of the 

VOCs detected during Phase 2 sampling, half were detected in 

either the source water or finished water, but not both. 

Of the 14 VOCs detected in either source or finished 

water, 13 had human-health benchmarks. For most (10 of 13), 

detected concentrations were 2–5 orders of magnitude less 

than human-health benchmarks. However, three VOCs had 

BQmax values greater than 0.1 and therefore may warrant 

inclusion in a low-concentration, trends-monitoring program 

(Toccalino and others, 2006). Trichloroethene and carbon tetrachloride had BQmax values greater than 0.1 for source water 

but not finished water. These are the same VOCs identified as 

being of potential concern for source water sampled during 

Phase 1. In addition, tetrachloroethene had a BQmax value 

greater than 0.1 for finished water but not source water. 

Pesticides 

A total of 22 individual pesticides were detected. Most 

of the pesticides (18 of 22) were detected in both source and 

finished water at similar concentrations (table 3 and fig. 5). 

But overall, finished water had more pesticide detections (55) 

than source water did (45). 

In all, 9 of the 10 pesticides detected during Phase 1 

were also detected during Phase 2. However, during Phase 2, 

samples were analyzed for 19 additional pesticides or pesticide breakdown products that were not analyzed for during 

Phase 1. For example, metolachlor ESA and metolachlor OA 

were detected in every sample of source and finished water 

during Phase 2 but were not sampled for during Phase 1. 

Concentrations of detected pesticides in source water 

and finished water were similar and ranged from 0.008 to 

0.77 μg/L in the source water and from E0.004 to 0.8 μg/L 

in finished water (fig. 5). Human-health benchmarks were 

available for 11 of the 22 pesticides, and BQmax values for 

those compounds were 1–5 orders of magnitude less than 0.1 

(fig. 5). 

Comparison of Ground Water and Finished Water During Phase 2 9
Figure 4. Comparison of volatile organic compounds in samples collected during Phase 2 from five source-water wells 

and the associated finished water of community supply systems near Dayton, Ohio. A, Concentrations. B, Benchmark 

quotient values. 

Figure 4. Comparison of volatile organic compounds in samples collected during Phase 2 from five sourcewater wells and the associated finished water of community supply systems near Dayton, Ohio. 

Finished water

Source water

(raw)

EXPLANATION

Greater than or equal to 0.1

 The compound may warrant inclusion in a low-concentration, trends-monitoring program 

Greater than or equal to 1.0

 Compounds

 detected in both

source and finished

 Compound

detected only

in source water

Compounds

 detected only 

in finished water

Trichloroethene 

1,1,1-Trichloroethane

trans-1,2-Dichloroethene 

Ethylbenzene 

m- and p-Xylene 

Bromodichloromethane 

Bromoform 

Dibromochloromethane

Chloroform 

1,1-Dichloroethane 

Tetrachloroethene

Carbon tetrachloride 

Toluene 

cis-1,2-Dichloroethene 

0.00001 10

BENCHMARK QUOTIENT VALUE

CONCENTRATION, IN MICROGRAMS PER LITER

0.0001 0.001 0.01 0.1 1

0.00001 0.0001 0.001 0.01 0.1 1 10

Trichloroethene

1,1,1-Trichloroethane 

trans-1,2-Dichloroethene 

Ethylbenzene

m- and p-Xylene

Bromodichloromethane 

Bromoform 

Dibromochloromethane 

Chloroform 

1,1-Dichloroethane1

Tetrachloroethene

Carbon tetrachloride 

Toluene 

cis-1,2-Dichloroethene 

 water 

 Compounds

 detected in both

source and finished

 Compound

 detected only

in source water 

Compounds

detected only 

in finished water 

 water 

A

B

A, Concentrations. B, Benchmark quotient values. 

(treated and blended)

Benchmark quotient value

 The concentration may be of potential human-health concern 

 Ratio of the detected concentration of a compound to its Maximum Contaminant Level or 

1Benchmark quotient value cound not be determined because compound does not have a Maximum Contaminant Level or

 Health-Based Screening Level 

 Health-Based Screening Level

10 Anthropogenic Organic Compounds in Community Water Systems near Dayton, Ohio, 2002–04
Table 3. Maximum concentration, detection frequency, and maximum benchmark quotient for regulated and unregulated compounds detected in samples 

collected during Phase 2 from five source-water wells and the associated finished water of community water systems near Dayton, Ohio.[USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; MCL, Maximum Contamination Level; HBSL, Health-Based Screening Level; BQmax, maximum Benchmark Quotient = ratio of maximum detected compound concentration to MCL or HBSL value; concentration; E, estimated value; <, less than; M, presence of compound verified, but concentration not quantified; --, not available. A regulated compound is one for which Federal and (or) State drinking-water standards have been established; an unregulated is one for which Federal and (or) State drinking water standards have not been established; ESA, ethane sulfonic acid; OA, oxanilic acid] 

Number of detections

Maximum

concentration

(μg/L) BQmax

Regulated (r) 

or unregulated (u) 

compound

Chemical 

Abstracts 

Service 

registry 

number

Number of 

samples 

collected

Source 

water

Finished 

water

Minimum 

reporting 

limit 

(μg/L)

Source 

water

Finished 

water

USEPA 

MCL1 or 

HBSL 

(μg/L)

Source 

water

Finished 

water

Volatile organic compounds

Trichloroethene (r) 79-01-6 10 4 3 0.04 3.29 0.21 5 0.658 0.042

1,1,1-Trichloroethane (r) 71-55-6 10 4 2 .03 .2 .09 200 .001 .0004

Chloroform (r) 67-66-3 10 3 5 .02 1.33 1.09 280 .0167 .0136

Tetrachloroethene (r) 127-18-4 10 3 3 .06 .15 .56 5 .030 .112

Toluene (r) 108-88-3 10 3 2 .05 E.01 E.01 1000 E.00001 E.00001

cis-1,2-Dichloroethene (r) 156-59-2 10 2 2 .02 .08 1.20 100 .0008 .0120

Carbon tetrachloride (r) 56-23-5 10 1 1 .06 .52 E.02 5 .104 E.004

1,1-Dichloroethane (u) 75-34-3 10 1 0 .04 .04 -- -- -- --Dibromochloromethane (r) 124-48-1 10 0 5 .1 -- 4 280 -- .05

Bromoform (r) 75-25-2 10 0 5 .10 -- 1.98 280 -- .025Bromodichloromethane (r) 75-27-4 10 0 5 .03 -- 2.12 280 -- .026

m- and p-Xylene (r) 108-38-3

106-42-3

10 0 2 .06 -- E.08 410,000 -- E.00001

trans-1,2-Dichloroethene (r) 150-60-5 10 0 1 .03 -- E.02 100 -- E.0002

Ethylbenzene (r) 100-41-4 10 0 1 .03 -- E.02 700 -- E.00003

Total number of VOC 

detections 21 37

Pesticides

Metolachlor ESA (u) 17118-09-5 10 5 5 .02 .5 .48 -- -- --

Metolachlor OA (u) 152019-73-3 10 5 5 .02 .28 .33 -- -- --Prometon (u) 1610-18-0 9 4 4 .5 .02 .03 3100 .0002 .0003

Acetochlor ESA (u) 187022-11-3 10 3 4 .02 .77 .8 -- -- --

Atrazine (r) 1912-24-9 10 3 3 .009 .025 .032 3 .0083 .0107

Deisopropylatrazine (u) 1007-28-9 10 3 3 .01 .01 .01 -- -- --

Comparison of Ground Water and Finished Water During Phase 2 11
Table 3. Maximum concentration, detection frequency, and maximum benchmark quotient for regulated and unregulated compounds detected in samples 

collected during Phase 2 from five source-water wells and the associated finished water of community water systems near Dayton, Ohio.—Continued[USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; MCL, Maximum Contamination Level; HBSL, Health-Based Screening Level; BQmax, maximum Benchmark Quotient = ratio of maximum detected compound concentration to MCL or HBSL value; concentration; E, estimated value; <, less than; M, presence of compound verified, but concentration not quantified; --, not available. A regulated compound is one for which Federal and (or) State drinking-water standards have been established; an unregulated is one for which Federal and (or) State drinking water standards have not been established; ESA, ethane sulfonic acid; OA, oxanilic acid] 

Number of detections

Maximum

concentration

(μg/L) BQmax

Regulated (r) 

or unregulated (u) 

compound

Chemical 

Abstracts 

Service 

registry 

number

Number of 

samples 

collected

Source 

water

Finished 

water

Minimum 

reporting 

limit 

(μg/L)

Source 

water

Finished 

water

USEPA 

MCL1 or 

HBSL 

(μg/L)

Source 

water

Finished 

water

Pesticides—Continued

Deethylatrazine (u) 6190-65-4 10 3 3 0.006 0.015 0.018 -- -- --

Alachlor ESA (u) 142363-53-9 10 3 4 .02 .13 .12 -- -- --

Acetochlor OA (u) 184992-44-4 10 2 4 .02 .41 .53 -- -- --

2-Hydroxyatrazine (u) 2163-68-0 10 2 4 .008 .022 .023 370 0.0003 0.0003

Alachlor OA (u) 171262-17-2 10 2 2 .02 .04 .06 -- -- --

Simazine (r) 122-34-9 8 2 3 .005 .008 .012 4 .002 .003

Acetochlor/metolachlor 

2nd amide ESA (u)

- 10 1 2 .02 .10 .12 -- -- --

Metolachlor (u) 51218-45-2 9 1 2 .013 .020 .021 370 .0003 .00030

Imazaquin (u) 81335-37-7 10 1 2 .02 E.02 .02 32,000 E.00001 .00001Sulfometuron-methyl (u) 74222-97-2 10 1 1 .009 .035 E.007 -- -- --

Flumetsulam (u) 98967-40-9 10 1 1 .01 E.02 .01 37,000 <0.00001 <.00001

Chlorimuron-ethyl (u) 90982-32-4 10 1 1 .010 E.016 .019 3600 E.00003 .00003

Bromacil (u) 314-40-9 10 1 0 .03 E.01 -- 370 E.00014 --

Dimethenamid ESA (u) 205939-58-8 10 1 0 .02 .02 -- -- -- --

Metribuzin (u) 21087-64-9 8 0 1 .006 -- E.004 390 -- E.00004

Imazethapyr (u) 81335-77-5 10 0 1 .02 --

M 32000 -- --

Total number of pesticide 

detections 45 54

Total number of detections 

for all compounds 68 92

1U.S. Environmental Protection Agency (2003, 2004).2MCL is for total trihalomethanes.3Denotes HBSL (Toccalino and others, 2003).4MCL is for the sum of concentrations of mixed isomers of xylene. 

12 Anthropogenic Organic Compounds in Community Water Systems near Dayton, Ohio, 2002–04
Figure 5. Comparison of pesticides in samples collected during Phase 2 from five source-water wells and the associated 

finished water of community water systems near Dayton, Ohio. A, Concentrations. B, Benchmark quotient values. 

 Metolachlor ESA

 Metolachlor OA 

 Imazaquin 

 Sulfometuron-methyl

Simazine

 2-Hydroxyatrazine

 Acetochlor OA 

 Prometon

 Alachlor ESA 

 Acetochlor ESA

 Deethylatrazine

 Atrazine

 Deisopropylatraizine

0.00001 10

CONCENTRATION, IN MICROGRAMS PER LITER

0.0001 0.001 0.01 0.1 1

 Alachlor OA 

Figure 5. Comparison of pesticides in samples collected during Phase 2 from five source-water wells and 

A, Concentrations. B, Benchmark quotient values. 

Source water 

Finished water 

EXPLANATION

Greater than or equal to 0.1

 The compound may warrant inclusion in a low-concentration, trends-monitoring program 

Greater than or equal to 1.0

 The concentration may be a potential human-health concern 

 Compounds

 detected in both

source and finished

 Compounds detected

 only in source water 

BENCHMARK QUOTIENT VALUE

0.000001 0.00001 0.0001 0.001 0.01 0.1 1

 water 

B

 Compounds detected

 only in finished water 

A

 Flumetsulam 

 Metribuzin 

 Imazethapyr

2

 Metolachlor 

 Dimethenamid ESA 

 Chlorimuron-ethyl

 Bromacil

 Compounds detected

 only in source water 

 Compounds detected

 only in finished water

 Compounds

 detected in both

source and finished

 water 

 Metolachlor ESA1

 Metolachlor OA1

 Imazaquin 

 Sulfometuron-methyl1

 Acetochlor/metolachlor 2d amide ESA1

 Simazine 

 2-Hydroxyatrazine 

 Acetochlor OA1

 Prometon 

 Alachlor ESA1

 Acetochlor ESA1

 Deethylatrazine1

 Atrazine 

 Deisopropylatraizine1

 Alachlor OA1

 Flumetsulam 

 Metribuzin 

 Imazethapyr2

 Metolachlor 

 Dimethenamid ESA1

 Chlorimuron-ethyl 

 Bromacil 

the associated finished water of community water systems near Dayton, Ohio. 

 Acetochlor/metolachlor 2d amide ESA

Benchmark quotient value

 Ratio of the detected concentration of a compound to its Maximum Contaminant Level or 

1Benchmark quotient value could not be determined because compound does not have a Maximum Contaminant Level or Health-Based Screening Level. 2Presence of compound verified, but concentration not quantified.

(raw) 

(blended and treated)

Health-Based Screening Level 

Comparison of Ground Water and Finished Water During Phase 2 13
Summary

The U.S. Geological Survey National Water-Quality 

Assessment Program is assessing the quality of major aquifers used as a source of supply for community water systems 

(CWSs) in urban areas. These studies, called Source WaterQuality Assessments (SWQAs), are being done at several 

locations around the Nation, and this report focuses on a 

SWQA completed in valley-fill deposits of the glacial aquifer 

system near Dayton, Ohio. 

The study was done in two phases. Phase 1 was completed during November–January 2002–03. The goal was to 

characterize the occurrence of 258 anthropogenic organic 

compounds (AOCs) in the source water from 15 CWS wells. 

In those samples, 11 volatile organic compounds (VOCs) and 

10 pesticides were detected. At least one AOC was detected 

in 12 of the 15 samples. Most samples contained a mixture 

of compounds (average of four compounds per sample). The 

maximum number of AOC detections in a single sample was 

13. 

The VOCs detected in more than 30 percent of the 

samples were trichloroethene (a common dry-cleaning solvent), chloroform (a possible disinfection byproduct), and 

1,1,1-trichloroethane (a solvent). The pesticides that were 

detected in more than 30 percent of the samples were prometon (an herbicide primarily used in nonagricultural settings), 

simazine (an herbicide with agricultural and nonagricultural 

uses), atrazine (an herbicide commonly used on corn and soybeans), and deethylatrazine (a breakdown product of atrazine). 

Of the 32 pesticide detections, more than half were atrazine or 

one of its breakdown products (deethylatrazine, deisopropylatrazine, or 2-hydroxyatrazine). 

The goal of the second phase of the study was to compare AOC detections in source (raw) water with the associated 

finished (blended and treated) water. Five of the 15 CWS wells 

along with their associated finished water were resampled during June and July 2004. 

In general, pesticides were detected in both source and 

finished water at similar concentrations. In contrast, VOCs 

were detected more frequently in finished-water than sourcewater samples. Increased detection of VOCs in finished water 

might be due to the creation of disinfection byproducts (DBPs) 

during chlorination. Other possible explanations are that compounds could have been introduced (1) during blending with 

water from other wells or (2) at some point in the water system, between locations where samples of source and finished 

water were collected. 

Human-health benchmarks were available for 13 of the 

detected VOCs. Three VOCs (trichloroethene, carbon tetrachloride, and tetrachloroethene) were detected at concentrations approaching human-health benchmarks, and therefore 

may warrant inclusion in a low-concentration, trends-monitoring program. Of the 11 pesticides with human-health benchmarks, all were detected at concentrations at least 2 orders of 

magnitude less than their human-health benchmark values. 

Acknowledgments

The author is grateful to the public and private organizations that furnished information used in this study and for 

permitting the collection of samples for water-quality analyses. The author acknowledges the valuable assistance of USGS 

employees Tom Schumann and John Tertuliani (for sample 

collection and data compilation) and Jessica Hopple and Greg 

Delzer (for guidance on the structure, content, and wording of 

selected sections of the report). 

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Glossary

A

Anthropogenic As used in this report, derived from or 

related to human activities. 

B

Benchmark Quotient (BQ) Ratio of the concentration of 

a contaminant to its Maximum Contaminant Level (MCL) 

value for a regulated compound or to its Health Based-Screening Level (HBSL) value for an unregulated compound. BQs 

greater than 1.0 identify concentrations of potential humanhealth 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 ground-water sources. 

Finished water blended with surface water was not sampled as 

part of this study.

BQmax Ratio of the maximum concentration of a contaminant to its MCL or HBSL value. 

C

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 regulations enforcing the 

Safe Drinking Water Act. A CWS serves a residential population, such as a municipality, mobile home park, or nursing 

home. This report discusses community water systems that use 

ground water.

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 Maximum Contaminant 

Level; and (2) for an unregulated compound, a concentration 

greater than the Health-Based Screening Level.

D

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.

16 Anthropogenic Organic Compounds in Community Water Systems near Dayton, Ohio, 2002–04
E

F

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.

G

H

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 USGS 

in collaboration with the USEPA and others using USEPA 

methodologies for establishing drinking-water guidelines and 

the most current, USEPA peer-reviewed, publicly available 

human-health toxicity information. 

Human-Health Benchmarks As used in this report, these 

include USEPA MCL values and HBSL values developed 

collaboratively by the U.S. Geological Survey, USEPA, New 

Jersey Department of Environmental Protection, and Oregon 

Health & Science University.

I

J

K

L

M

Maximum Contaminant Level (MCL) A USEPA drinkingwater 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 at which no 

known or anticipated adverse effect on the health of persons 

occurs and which allows an adequate margin of safety.

N

O

P

Q

R

Regulated Compound As used in this report, a compound 

for which a Federal and (or) state drinking-water standard has 

been established.

S

Source Water Source water is the raw (ambient) water collected at the supply well or surface-water intake prior to the 

treatment process used to produce finished water.

T

U

Unregulated Compound As used in this report, a compound 

for which no Federal and (or) state drinking-water standard 

has been established. Note that a compound that is unregulated 

under the Safe Drinking Water Act may be regulated in other 

contexts and under other statutes. 

V

W

X

Y

Z

Glossary 17
18 Anthropogenic Organic Compounds in Community Water Systems near Dayton, Ohio, 2002–04

Well 

identifier

Detected anthropogenic 

organic compound 

(regulated (r) 

or unregulated (u))

Source 

water 

(μg/L)

Finished 

water 

(μg/L)

Volatile organic compounds

1 Trichloroethene (r) ND 0.17

2 Trichloroethene (r) E 0.03 ND

3 Trichloroethene (r) E .06 E .03

4 Trichloroethene (r) 3.29 .21

5 Trichloroethene (r) .28 ND

1 1,1,1-Trichloroethane (r) E .08 E .09

3 1,1,1-Trichloroethane (r) E .05 E .02

4 1,1,1-Trichloroethane (r) .20 ND

5 1,1,1-Trichloroethane (r) E .05 ND

1 Chloroform (r) E .02 .63

2 Chloroform (r) ND 1.09

3 Chloroform (r) ND .18

4 Chloroform (r) 1.33 .56

5 Chloroform (r) E .07 .65

1 Tetrachloroethene (r) ND .56

3 Tetrachloroethene (r) .15 E .06

4 Tetrachloroethene (r) E .06 E .03

5 Tetrachloroethene (r) .11 ND

1 Toluene (r) E .01 ND

2 Toluene (r) E .01 E .01

4 Toluene (r) E .01 E .01

1 cis-1,2-Dichloroethene (r) E .02 .19

2 cis-1,2-Dichloroethene (r) E .08 1.20

4 Carbon tetrachloride (r) .52 E .02

3 1,1-Dichloroethane (u) E .04 ND

1 Dibromochloromethane (r) ND 4.0

2 Dibromochloromethane (r) ND 1.00

3 Dibromochloromethane (r) ND .7

4 Dibromochloromethane (r) ND 2.4

5 Dibromochloromethane (r) ND 2.0

1 Bromoform (r) ND 1.98

2 Bromoform (r) ND .18

3 Bromoform (r) ND .35

4 Bromoform (r) ND 1.53

5 Bromoform (r) ND .73

1 Bromodichloromethane (r) ND 2.12

2 Bromodichloromethane (r) ND 1.49

3 Bromodichloromethane (r) ND .51

4 Bromodichloromethane (r) ND 1.36

5 Bromodichloromethane (r) ND 1.53

4 m- and p-Xylene (r) ND E .05

5 m- and p-Xylene (r) ND E .08

1 trans-1,2-Dichloroethene (r) ND E .02

5 Ethlybenzene (r) ND E .02

Well 

identifier

Detected anthropogenic 

organic compound 

(regulated (r) 

or unregulated (u))

Source 

water 

(μg/L)

Finished 

water 

(μg/L)

Pesticides

1 Metolachlor ESA (u) 0.1 0.13

2 Metolachlor ESA (u) .5 .48

3 Metolachlor ESA (u) .08 .12

4 Metolachlor ESA (u) .03 .03

5 Metolachlor ESA (u) .13 .19

1 Metolachlor OA (u) .03 .04

2 Metolachlor OA (u) .28 .33

3 Metolachlor OA (u) .03 .04

4 Metolachlor OA (u) .02 .02

5 Metolachlor OA (u) .04 .1

1 Prometon (u) M .01

2 Prometon (u) .01 .02

4 Prometon (u) .01 .02

5 Prometon (u) .02 .03

1 Acetochlor ESA (u) .02 .03

2 Acetochlor ESA (u) .77 .8

3 Acetochlor ESA (u) .02 .03

5 Acetochlor ESA (u) ND .08

1 Atrazine (r) E .001 .016

2 Atrazine (r) .025 .032

5 Atrazine (r) .009 .027

1 Deisopropylatrazine (u) M M

2 Deisopropylatrazine (u) E .02 E .01

5 Deisopropylatrazine (u) E .01 E .01

1 Deethylatrazine (u) E .002 .006

2 Deethylatrazine (u) E .015 .018

5 Deethylatrazine (u) E .010 .018

2 Alachlor ESA (u) .13 .12

3 Alachlor ESA (u) .04 .02

4 Alachlor ESA (u) ND .02

5 Alachlor ESA (u) .04 .05

2 Acetochlor OA (u) .41 .53

3 Acetochlor OA (u) .02 .02

5 Acetochlor OA (u) ND .05

1 2-Hydroxyatrazine (u) ND .023

2 2-Hydroxyatrazine (u) E .022 .022

3 2-Hydroxyatrazine (u) ND .006

5 2-Hydroxyatrazine (u) E .005 .016

2 Alachlor OA (u) .04 .06

3 Alachlor OA (u) .02 ND

4 Alachlor OA (u) ND .02

1 Simazine (r) ND .002

2 Simazine (r) .008 .009

5 Simazine (r) .006 .012

Appendix 1. Comparison of anthropogenic organic compounds detected in source- and associated finished-water samples during 

Phase 2 of the Source Water-Quality Assessment near Dayton, Ohio.

[E; estimated value; ND; no detection; μg/L, micrograms per liter; ESA, ethane sulfonic acid; OA, oxanilic acid]
Well 

identifier

Detected anthropogenic 

organic compound 

(regulated (r) 

or unregulated (u))

Source 

water 

(μg/L)

Finished 

water 

(μg/L)

Pesticides—Continued

2 Acetochlor/Metolachlor 2nd

amide ESA (u) 

0.1 0.12

5 Acetochlor/Metolachlor 2nd

amide ESA (u) 

ND .03

1 Metolachlor (u) ND E .005

2 Metolachlor (u) .020 .021

2 Imazaquin (u) E .020 .020

5 Imazaquin (u) ND .008

5 Sulfometuron-methyl (u) .035 .007

2 Flumetsulam (u) E .02 .01

2 Chlorimuron-ethyl (u) E .016 .019

4 Bromacil (u) E .01 ND

2 Dimethenamid ESA (u) .02 ND

2 Metribuzin (u) ND E .004

1 Imazethapyr (u) ND M

Appendix 1. Comparison of anthropogenic organic compounds detected in source- and associated finished-water samples during 

Phase 2 of the Source Water-Quality Assessment near Dayton, Ohio.—Continued

[E; estimated value; ND; no detection; μg/L, micrograms per liter; ESA, ethane sulfonic acid; OA, oxanilic acid]

Appendix 1 19

M.A. Thomas—Anthropogenic Organic Compounds in Ground Water and Finished Water of Community Water Systems near Dayton, Ohio, 2002–04

Scientific Investigations Report 2007–5035