Figure 1. About 11,500 square miles of the Potomac River Basin are upstream 

from major community water systems that serve the Washington, D.C., metropolitan 

area, including Washington Aqueduct. The area includes a large amount of forest 

(60 percent of the area), agriculture (about 35 percent), and urban areas, all of which 

can potentially affect source-water quality. About 500 million gallons per day are taken 

directly from the Potomac River near Washington, D.C., to serve water needs of about 

5 million people. http:/www.potomacriver.org/cms/.

0 10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

WASHINGTON, D.C.

Waynesboro

Harrisonburg

Frederick

Cumberland

Gettysburg

Muddy Cr

PENNSYLVANYA

MARYLAND

MARYLAND

WEST VIRGINIA

VIRGINIA

VIRGINIA

Accotick Cr

Conococheague Cr

S Fk S Br Potomac River

South Branch

Capapon River

Opequon Creek

Shenandoah River

Goose Creek

Occoquan River

North Branch

North Fork

South Fork

Mononcacy River

Anacostia R

78°W

77°W

38°N

39°N

40°N

79°W

38°N

Potomac

Potomac

River

River

Urban

EXPLANATION

Agriculture

Forest

Water

Land use modified from Vogelmann and others (1997)

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2007–3085

November 2008

Prepared as part of the National Water-Quality Assessment Program, Source Water-Quality Assessment

Organic Compounds in Potomac River Water Used for Public 

Supply near Washington, D.C., 2003–05

Printed on recycled paper

Organic compounds studied in this U.S. Geological Survey (USGS) assessment generally are man-made, including, in part, pesticides, solvents, gasoline hydrocarbons, personal-care and domestic-use products, and refrigerants and propellants. 

A total of 85 of 277 compounds were detected at least once among the 25 samples collected approximately monthly during 2003–05 

at the intake of the Washington Aqueduct, one of several community water systems on the Potomac River upstream from Washington, D.C. The diversity of compounds detected indicate a variety of different sources and uses (including wastewater discharge, 

industrial, agricultural, domestic, and others) and different pathways (including treated wastewater outfalls located upstream, overland runoff, and ground-water discharge) to drinking-water supplies. Seven compounds were detected year-round in source-water 

intake samples, including selected herbicide compounds commonly used in the Potomac River Basin and in other agricultural 

areas across the United States. Two-thirds of the 26 compounds detected most commonly in source water (in at least 20 percent of 

the samples) also were detected most commonly in finished water (after treatment but prior to distribution). Concentrations for all 

detected compounds in source and finished water generally were less than 0.1 microgram per liter and always less than humanhealth benchmarks, which are available for about one-half of the detected compounds. On the basis of this screening-level assessment, adverse effects to human health are expected to be negligible (subject to limitations of available human-health benchmarks).

Introduction

An investigation by the National WaterQuality Assessment (NAWQA) Program 

of the USGS characterizes the occurrence 

of 277 organic compounds in source water 

(defined as stream water collected at a 

surface-water intake prior to water treatment) and finished water (defined as water 

that has passed through treatment processes 

but prior to distribution) at the Washington 

Aqueduct, one of several community water 

systems that uses the Potomac River as its 

sole source of water supply upstream from 

Washington, D.C. (fig. 1). Samples were 

collected approximately monthly from 

the Potomac River during 2003–05 and 

included 25 source- and 13 finished-water 

samples. The samples were analyzed for 

pesticides and selected pesticide degradates, solvents, gasoline hydrocarbons, 

disinfection by-products, personal care 

and domestic-use products, and other 

compounds. Community water systems 

are required to monitor finished water for 

compounds regulated under the Safe Drinking Water Act. Most of the compounds 

included in this study are not regulated 

under U.S. Environmental Protection 

Agency (USEPA) Federal drinking-water 

standards (U.S. Environmental Protection 

Agency, 2007a). The Potomac River study 

is part of an ongoing national NAWQA 

investigation of community water systems 

across the United States. More detailed 

information and references on the sampling 
What "Detections" May 

Mean to Human Health

The analytical methods used 

in this study have low detection levels—typically 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 the 

environmental presence of a wide 

variety of chemicals not commonly 

monitored in water resources and 

to track changes in their occurrence and concentrations over 

time. These findings complement 

ongoing 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. Many of the compounds 

analyzed by USGS are not included 

in other source- and finished-water 

monitoring programs such as the 

Unregulated Contaminant Monitoring Regulation (U.S. Environmental 

Protection Agency, 2007a) and the 

U.S. Department of Agriculture’s 

Pesticide Data Program (U.S. 

Department of Agriculture, 2008).

Table 1. A total of 35 of 277 organic compounds were detected commonly (in at least 

20 percent of the samples) in source water and (or) finished water. Twenty-six compounds 

were detected commonly in source water, and about two-thirds of these compounds (17) 

also were detected commonly in finished water. The diversity of compounds indicate a 

variety of different uses—including industrial, agricultural, and domestic—and different 

pathways—including treated wastewater outfalls located upstream, overland runoff, and 

ground-water discharge—of the compounds entering drinking-water supplies.

[Black text indicates compounds detected in both source and finished water; orange text indicates compounds 

detected in only source water; blue text indicates compounds detected in only finished water; italics indicates 

pesticide degradates; ESA, ethane sulfonic acid; OA, oxanilic acid]

Herbicides and herbicide degradates

Atrazine

Deethylatrazine (DEA)

Metolachlor

Metolachlor ESA

Simazine

2-Hydroxy atrazine

Deisopropyl atrazine

Metolachlor OA

Alachlor ESA

2,4–D

Prometon

Diuron

3,4-Dichloroaniline

Acetochlor/metolachlor 2nd amide ESA

Insecticides and insecticide degradates

Desulfinyl fipronil

Fipronil

Diazinon

Carbaryl

Plant- or animal-derived biochemicals

Cholesterol

3-beta-Coprostanol

Personal care and domestic-use products

HHCB (Hexahydrohexamethylcyclopentabenzopyran)

Manufacturing additives

FYROL CEF (Tri(2-chloroethyl) phosphate)

FYROL PCF (Tris(dichloroisopropyl) 

phosphate)

Gasoline hydrocarbons and oxygenates

MTBE (methyl tert-butyl ether)

Benzene

Pavement- and combustion-derived compounds

Phenanthrene

Fluoranthene

Pyrene

Solvents

Carbon tetrachloride

Methylene chloride

Organic synthesis compounds

Anthraquinone

Carbazole

Disinfection by-products

Chloroform

Bromodichloromethane

Dibromochloromethane

design, methodology, specific compounds 

monitored, and the national study are 

described by Carter and others (2007). 

Additional USGS information on water 

quality in the Potomac River Basin is 

available in a companion NAWQA study 

(Ator and others, 1998).

Occurrence of Organic 

Compounds in Source Water drinking-water standards (see inset). 

Eighty-five of the 277 compounds were 

detected in at least one source-water 

sample. A total of 192 compounds were not 

detected in any samples (Carter and others, 

2007; Kingsbury and others, 2008).

Twenty-six compounds were detected 

in at least 20 percent of the source-water 

samples (table 1). Overall, the compounds 

detected most commonly in water from the 

Potomac River are among those most commonly detected in ambient stream water in 

the Potomac River Basin (Ator and others, 

1998) and across the Nation (Gilliom and 

others, 2006).

Seven compounds were detected yearround (in more than 95 percent of the 

source-water samples). The continuous 

occurrence may be attributed to groundwater discharge and (or) treated wastewater discharge from municipalities 

located upstream (Ator and others, 1998; 

Kingsbury and others, 2008). Three of the 

compounds include the herbicides atrazine, 

metolachlor, and simazine, which commonly are used on row crops and for weed 

control in urban and residential areas in the 

Potomac River Basin and across the Nation 

(Ator and others, 1998; Gilliom and others, 

2006). Herbicide degradates (or “breakdown products”), including deethylatrazine 

(DEA), metolachlor ethane sulfonic acid 

(ESA), and metolachlor oxanilic acid (OA), 

also were present year-round. The seventh 

compound detected year-round is the disinfection by-product chloroform, which may 

be related to treated wastewater outfalls 

(Kingsbury and others, 2008).

About one-third of the 277 compounds 

were detected in at least one sourcewater sample. These compounds 

represent many different sources and 

uses and include pesticides, gasoline 

hydrocarbons, personal care products, 

and solvents. Seven compounds were 

detected year-round, including selected 

herbicide compounds commonly used in 

the Potomac River Basin.

Recent advances in laboratory analytical methods have given scientists the tools 

to detect a wide variety of contaminants in 

the environment at low concentrations—

typically 100 to 1,000 times lower than 
Finished-Water Sampling, Water Treatment, and Significance of 

Comparisons to Source Water

The Washington Aqueduct uses conventional water treatment: coagulation/flocculation using aluminum sulfate sedimentation, filtration through anthracite and sand, 

and disinfection with chlorine and chloramine. Powdered activated carbon is used 

occasionally to treat for taste and odor issues. Finished-water samples were collected 

at the Washington Aqueduct approximately 48 hours after source-water samples to 

account for treatment plant retention time of the water (L. Nolan, U.S. Army Corps 

of Engineers, oral commun., 2003). Some differences between source- and finishedwater quality might be attributable to changes in source-water quality that are not 

represented by the finished-water samples because of sample timing and variations in 

retention time, and potential analytic variability associated with low concentrations 

at or near laboratory reporting levels (Kingsbury and others, 2008). It also is possible 

that some compounds detected in source water were removed or transformed during 

the treatment process into compounds that were not monitored as part of this study.

The study sampling design and resulting comparisons are not intended to characterize treatment efficacy, but to provide a preliminary indication of the potential 

importance of compounds found in source water to the quality of finished water prior 

to distribution. In general, conventional treatment is not specifically designed to 

remove most of the organic compounds monitored in this study.

Comparisons Between Source and 

Finished Water

About two-thirds of the compounds 

detected most commonly in source 

water also were detected most commonly in finished water, and generally 

at similar concentrations, typically less 

than 0.1 microgram per liter.

A more detailed analysis of the most 

commonly occurring herbicides highlights interesting relations between parent 

and degradate compounds in source and 

finished water. The percentage of detections 

and concentrations of parent and degradate compounds were relatively similar in 

source and finished water (fig. 2). Herbicide 

degradation mostly is driven by microbial 

activity in the soil zone before reaching 

the water table (Gilliom and others, 2006). 

Although concentrations of parent compounds generally are highest during spring 

applications, both the parent and degradate 

compounds were detected year-round. This 

is, in part, due to continuous contributions from ground-water discharge to the 

Potomac River and its tributaries (Ator and 

others, 1998).

Summed concentrations of degradate 

compounds typically were similar to or 

greater than the parent herbicide concentrations, such as for atrazine, although 

summed concentrations of degradates can 

be less than parent concentrations due to 

differences in chemical properties and 

usage. Specifically, atrazine is chemically 

more stable, allowing it to persist longer 

in the hydrologic system than metolachlor, 

which tends to break down more quickly 

in the soil zone (Gilliom and others, 2006). 

As a result, the degradate metolachlor ESA 

was detected at concentrations 10 times 

greater than its parent concentrations in 

most samples. Alachlor presents a different story. Use of the herbicide alachlor 

has decreased substantially in recent years 

(Gilliom and others, 2006). As a result, 

the parent compound was not detected, but 

its degradate alachlor ESA was detected 

in about 65 percent of the source-water 

samples. In fact, alachlor ESA was one of 

the most commonly detected compounds, 

probably because it is still present in discharging ground water.

Transformation can result in the conversion of a parent compound to a compound 

that is commonly less toxic, but some degradates have toxicities that are similar to, or 

greater than, that of their parent pesticide 

(Gilliom and others, 2006). Herbicide degradate compounds are not regulated under 

the Safe Drinking Water Act; however, 

all large public water systems (including 

Washington Aqueduct) and 800 medium 

and small water systems nationwide are 

required under USEPA’s Unregulated 

Contaminant Monitoring Rule 2 to monitor 

for three parent acetanilides (acetochlor, 

alachlor, and metolachlor) and six degradates (acetochlor ESA, acetochlor OA, 

alachlor ESA, alachlor OA, metolachlor 

ESA, and metolachlor OA) during a 

12-month period between January 2008 

and December 2010 (U.S. Environmental 

Protection Agency, 2007b, c).

Comparisons between source and finished water are not intended to characterize 

treatment efficacy, but to provide a preliminary indication of the potential importance 

of compounds found in source water to the 

quality of finished water prior to distribution (see inset).

Seventeen of the 26 most commonly 

detected compounds in source water also 

were detected commonly in finished water 

for paired samples, and typically at lower 

or similar low-level concentrations (fig. 2). 

Two compounds in particular, metolachlor 

ESA and chloroform, were detected in 

100 percent of both source- and finishedwater samples, although concentrations of 

chloroform in source-water samples were 

low, with most at less than 0.1 microgram 

per liter.

The remaining 9 of the 26 most commonly detected compounds in source 

water were not detected as commonly in 

finished water. These include the insecticides fipronil, diazinon, and carbaryl, and 

their decreased detection in finished water 

may be due to degradation or transformation associated with disinfection treatment 

(Valder and others, 2008). Cholesterol 

and 3-beta-coprostanol also were detected 

commonly in source water but not as 

commonly in finished water (fig. 2). Processes affecting the occurrence of these 

plant or animal-derived biochemicals are 

not well understood.

A total of nine compounds were detected 

commonly in finished water but not commonly in source water. These include two 

disinfection by-products (bromodichloromethane and dibromochloromethane; 

table 2), as well as carbon tetrachloride and 

methylene chloride (fig. 2). The presence 

of disinfection by-products in finished 

water is well documented, understood, and 

regulated, and is an expected outcome of 

drinking-water disinfection. The source of 

low-level detections of carbon tetrachloride 

in finished-water samples may be due to its 

presence as a contaminant in the chlorine 

used for disinfection (Christman, 1980), 

or possibly as a disinfection by-product 

(Krasner and others, 2006). The source of 

low-level detections of methylene chloride 

is not known.

Detections and concentrations of 

commonly used herbicides and their 

degradates are relatively similar in 

source and finished water. Occurrence and concentrations of degradate 

compounds compared to their respective parent compounds differ compound 

by compound, depending on chemical properties, use, and hydrologic 

pathways.

A Closer Look at Agricultural 

Herbicides and Degradates 
Figure 2. Seventeen of the 26 compounds detected commonly in source water also were 

detected commonly in finished water for paired samples, and typically at similar low-level 

concentrations. Some compounds detected commonly in source water were removed or 

transformed during treatment and therefore were not detected in finished water (horizontal 

x-axis). Other compounds were detected only in finished water (vertical y-axis). (Note: The 

occurrence of disinfection by-products, such as chloroform, is not shown in this figure.)

0.001

0.01

0.1

1

10

0.001 0.01 0.1 1

SOURCE-WATER CONCENTRATION, IN MICROGRAMS PER LITER

FINISHED-WATER CONCENTRATION, IN MICROGRAMS PER LITER

Metolachlor ethane sulfonic acid (ESA) and

 metolachlor oxanilic acid (OA)

Metolachlor

Deethylatrazine (DEA), deisopropyl-atrazine (DIA), and

 2-hydroxyatrazine

Atrazine

Other commonly detected compounds

3-beta-coprostanol,

Benzene cholesterol

Fipronil, carbaryl, diazinon,

3,4-dichloroaniline

Carbon tetrachloride

Methylene chloride, 

phenanthrene,

pyrene

Human-Health 

Benchmarks Used 

in This Assessment

A screening-level assessment 

of the potential significance of 

detected compounds to human 

health was based on a comparison of measured concentrations 

to available human-health benchmarks. Specifically, concentrations of regulated compounds 

were compared to USEPA 

Maximum Contaminant Levels 

(MCLs), and concentrations of 

unregulated compounds that have 

USEPA published toxicity information were compared to USGS 

Health-Based Screening Levels, 

which were developed in collaboration with USEPA, New Jersey 

Department of Environmental 

Protection, and Oregon Health 

& Science University (HBSLs; 

Toccalino and others, 2007). 

About one-half of the detected 

compounds do not have humanhealth benchmarks or adequate 

toxicity information for evaluating results in a human-health 

context. Human-health benchmarks are developed for individual compounds and not mixtures. 

The screening-level assessment 

provides an initial perspective 

on the potential importance of 

“man-made” organic compounds 

in source water; it is not a substitute for a comprehensive risk 

assessment, which includes many 

more factors, such as additional 

avenues of exposure.

Potential Effects on Human Health

Although the type of conventional water 

treatment used by this community water 

system (which is typical of many systems across the Nation) is not specifically 

designed to remove most of the organic 

compounds, concentrations generally 

were less than 0.1 microgram per liter. 

For perspective, reporting limits for public 

drinking-water commonly are set through 

Federal regulations at 0.5 microgram per 

liter, and water utilities generally are not 

required to measure below this limit.

Concentrations of 10 compounds that 

were detected commonly in source and (or) 

finished water were greater than or equal to 

0.1 microgram per liter (table 2). In general, 

compounds with concentrations greater than 

0.1 microgram per liter, such as atrazine, 

metolachlor degradates, and the gasoline 

oxygenate methyl tert-butyl ether (MTBE), 

reflect their relatively widespread use in 

the Potomac River Basin and their physical properties that allow them to persist in 

the environment (Gilliom and others, 2006; 

Zogorski and others, 2006). Concentrations did not exceed USEPA drinking-water 

standards (MCLs) for regulated compounds 

(table 2) in any sample. Concentrations also 

were less than USGS Health-Based Screening Levels (HBSLs) established for selected 

unregulated compounds (see inset).

The USGS screening-level assessment 

also identified compounds at concentrations less than, but within a factor of 10, 

of human-health benchmarks. Only four 

regulated compounds were detected at 

concentrations less than, but within a factor 

of 10 of the USEPA MCL, including atrazine and total trihalomethanes (including 

chloroform, bromodichloromethane, and 

dibromochloromethane) (table 2). The regulated compound carbon tetrachloride was 

commonly detected in finished water but 

concentrations were not within a factor of 

10 of the USEPA MCL (table 2). Although 

these compounds are regularly monitored 

in finished water by community water 

systems, those occuring in 20 percent or 

more of source-water samples and with 

concentrations within a factor of 10 of 

their MCL may warrant their consideration in low-concentration trends monitoring to better understand their transport 

and fate within the watershed. Humanhealth benchmarks are not available for 

the remaining five compounds that were 

detected most commonly at concentrations greater than 0.1 microgram per liter 

(table 2).

An important consideration in assessing potential effects for human health 

is the common occurrence of mixtures 

of organic compounds in source- and 

finished-water samples. For example, 

the median number of compounds in 

Concentrations for all detected compounds in source and finished water 

generally were less than 0.1 microgram 

per liter and always less than humanhealth benchmarks, which are available for about one-half of the detected 

compounds. On the basis of this 

screening-level assessment, adverse 

effects to human health are expected to 

be negligible (subject to limitations of 

available human-health benchmarks, 

see inset).
Source Water-Quality Assessments by the NAWQA Program 

Conducted Across the Nation

Beginning in 2002, NAWQA initiated “Source Water-Quality Assessments” 

(SWQAs) at selected community water systems across the United States (Delzer 

and Hamilton, 2007). The long-term goal is to complete as many as 30 SWQAs at 

systems that withdraw water from streams by 2012 using standard protocols and 

nationally consistent methods (U.S. Geological Survey, 1997–2006).

This fact sheet highlights findings from the Potomac River study, which is one of 

the first nine community water systems sampled. The fact sheet serves as a companion product to a USGS Data Series Report and a USGS Scientific Investigations 

Report that present findings for the nine systems across the United States (Carter and 

others, 2007; Kingsbury and others, 2008). http://water.usgs.gov/nawqa/swqa

Table 2. Only 10 compounds that were commonly detected in source and (or) finished water had concentrations greater than 

0.1 microgram per liter. None of these concentrations exceeded a human-health benchmark; however, benchmarks are only available for 

5 of the 10 compounds included in this table.

[μg/L, microgram per liter; MCL, Maximum Contaminant Level; HBSL, Health-Based Screening Level; ESA, ethane sulfonic acid; OA, oxanilic acid; MTBE, 

methyl tert-butyl ether; --, no data; E, estimated; ND, not detected]

Name of compound Number of samples Percent occurrence1 Reporting level2

(μg/L)

MCL or 

HBSL3

(μg/L)

Maximum concentration 

(μg/L)

Source water Finished water Source water Finished water Source water Finished water

Herbicides and herbicide degradates4

Atrazine 25 13 28 23 0.007 3 1.750 0.258

Metolachlor ESA 20 10 90 90 .05 -- .770 1.860

Metolachlor OA 20 10 20 20 .05 -- .160 .220

Gasoline hydrocarbons and oxygenates

MTBE 25 13 48 54 0.17 -- 0.850 0.363

Solvents

Carbon tetrachloride 25 13 0 31 0.06 5 ND 0.158

Disinfection by-products

Chloroform 25 13 4 100 0.24

80 total 

THMs5

0.130 40.55

Bromodichloromethane 25 13 0 100 .048 ND 12.00

Dibromochloromethane 25 13 0 100 .18 ND 1.88

Plant- or animal-derived biochemicals

Cholesterol 25 13 24 8 2 -- E1.20 E0.47

3-beta-Coprostanol 25 13 20 8 2 -- E1.0 E.25

1

 Percent occurrence of samples with concentrations equal to or greater than 0.1 μg/L; estimated concentrations are used for compounds that have reporting level greater than 

0.1 μg/L.

2

 Reporting level shown is higher value of either source or finished water.

3

 MCL values are shown in bold.

4

 Herbicide degradates are shown in italics.

5

 MCL of 80 is for total THMs (trihalomethanes), including chloroform, bromoform, bromodichloromethane, and dibromochloromethane.

source-water samples at the Potomac River 

was 17. This is comparible to findings from 

eight additional community water systems 

sampled by the USGS (Kingsbury and 

others, 2008). The potential human-health 

effects of mixtures of co-occuring organic 

compounds are largely unknown and have 

not been extensively studied. The effect of 

one compound on another’s toxicity may be 

additive, antagonistic, or synergistic. 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 because 

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 (Gilliom and 

others, 2006).

Potomac River Findings in a 

National Context and Possible 

Implications

Overall, the compounds detected most 

commonly in water from the Potomac River 

(tables 1 and 2) are among those most commonly detected in ambient stream water and 

ground water across the Nation (Gilliom 

and others, 2006; Zogorski and others, 

2006). In addition, the occurrence and 

concentrations of compounds in source and 

finished water sampled from the Potomac 

River were similar to those detected at other 

community water systems sampled as part 

of an ongoing national NAWQA investigation of rivers, many of which have upstream 

wastewater facilities and that drain considerable agricultural and urban land 

(Kingsbury and others, 2008). Findings in 

a national context, however, are considered 

preliminary because some compounds 

included in this study have only recently 

been monitored systematically in source 

and finished water, including, for example, 

plant- or animal-derived biochemicals (such 

as cholesterol and 3-beta-coprostanol) and 

those used for personal care, such as acetyl 

hexamethyl tetrahydronaphthalene (AHTN) 

and hexahydrohexamethylcyclopentabenzopyran (HHCB). Continued research 

is needed to better understand sources, 

transport mechanisms, trends, fate in the 

environment, and possible linkages of these 

compounds to human health.
For more information, contact:

Mike Brayton, U.S. Geological Survey, (443) 498–5598, mbrayton@usgs.gov

Judy Denver, U.S. Geological Survey, (302) 734–2506, jmdenver@usgs.gov

Greg Delzer, National Coordinator, (605) 394–3230, gcdelzer@usgs.gov

USGS will continue to collaborate with, 

and complement the work of other Federal, 

State, and local organizations, and continue 

to communicate findings and possible 

implications and future needs, including, 

for example:

♦ Increased emphasis on watershed management and source-water protection 

strategies to help minimize the sources 

and transport of compounds to source 

water and ultimately to finished water.

♦ Continued research to enhance toxicity 

information for commonly occurring 

unregulated compounds and mixtures 

that are commonly detected in source 

and finished water.

♦ Current and future monitoring and 

assessment to identify compounds not 

typically monitored in source water but 

commonly present in finished water, 

which may ultimately identify or lead to 

the development of treatment technologies for their removal.

References Cited

Ator, S.W., Blomquist, J.D., Brakebill, J.W., 

Denis, J.M., Ferrari, M.J., Miller, C.V., and 

Zappia, H., 1998, Water quality in the Potomac River Basin, Maryland, Pennsylvania, 

Virginia, West Virginia, and the District of 

Columbia, 1992–96: U.S. Geological Survey 

Circular 1166, 38 p., available at http://pubs.

usgs.gov/circ/circ1166/.

Carter, J.M., Delzer, G.C., Kingsbury, J.A., and 

Hopple, J.A., 2007, Concentration data for 

anthropogenic organic compounds in ground 

water, surface water, and finished water of 

selected community water systems in the 

United States, 2002–05: U.S. Geological Survey Data Series 268, 30 p., available at http://

pubs.usgs.gov/ds/2007/268/.

Christman, R.F., 1980, Chemistry of the use 

of chlorine in water and food processing in

Jolley, R.L., Brungs, W.A., and Cumming, 

R.B., eds., Water chlorination, environmental 

impact and health effects: Ann Arbor, Mich., 

Ann Arbor Science Publishers, Inc., v. 3, 

1,171 p.

Delzer, G.C., and Hamilton, P.A., 2007, National 

Water-Quality Assessment Program—Source 

Water-Quality Assessments: U.S. Geological 

Survey Fact Sheet 2007–3069, 2 p., available 

at http://pubs.usgs.gov/fs/2007/3069/.

Gilliom, R.J., Barbash, J.E., Crawford, C.G., 

Hamilton, P.A., Martin, J.D., Nakagaki, 

Naomi, Nowell, L.H., Scott, J.C., Stackelberg, P.E., Thelin, G.P., and Wolock, D.M., 

2006, The quality of our Nation’s waters—

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water, 1992–2001: U.S. Geological Survey 

Circular 1291, 172 p., available at http://pubs.

usgs.gov/circ/2005/1291/.

Kingsbury, J.A., Delzer, G.C., and Hopple, J.A., 

2008, Anthropogenic organic compounds in 

source water of nine community water systems that withdraw from streams, 2002–05: 

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http://pubs.usgs.gov/sir/2008/5208/.

Krasner, S.W., Weinberg, H.S., Richardson, 

S.D., Pastor, S.J., Chinn, R., Sclimenti, M.J., 

Onstad, G.D., and Thurston, A.D. Jr., 2006, 

Occurrence of a new generation of disinfection byproducts: Environmental Science and 

Technology, v. 40, no. 23, p. 7,175–7,185.

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

Zogorski, J.S., 2007, Health-Based Screening 

Levels—A tool for evaluating what waterquality data may mean to human health: U.S. 

Geological Survey, National Water-Quality 

Assessment Program, accessed June 5, 2008, 

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

U.S. Department of Agriculture, 2008, Agricultural Research Service (ARS), Pesticide 

properties database, accessed March 6, 2008, 

at http://www.ams.usda.gov/science/pdp/.

U.S. Environmental Protection Agency, 2007a, 

Setting standards for safe drinking water: 

U.S. Environmental Protection Agency, 

Office of Ground Water and Drinking Water, 

accessed June 1, 2007, at http://www.epa.gov/

safewater/standard/setting.html

U.S. Environmental Protection Agency, 2007b, 

Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water Systems Revisions; Final Rule: Federal Register, January 4, 

2007, v. 72, no. 2, p. 367. 

Any use of trade, product, or firm names is for 

descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Publishing support provided by the

USGS Helena Publishing Service Center

USGS promotes public access to water-quality information

This fact sheet, additional data and investigations reports, and other information are 

available on the World Wide Web at http://water.usgs.gov/nawqa/swqa. Included at 

this Web site are downloadable data on organic compound occurrence, information 

on sampling designs and methodology, background on data analyses, and frequently 

asked questions.

U.S. Environmental Protection Agency, 2007c, 

Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water Systems Revisions; Correction. Federal Register, January 

26, 2007, v. 72, no. 17, p. 3,916.

U.S. Geological Survey, 1997–2006, National 

field manual for the collection of water-quality data: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 9, 

chaps. A1–A9, available at http://water.usgs.

gov/owq/FieldManual/ (chapters were originally published during 1997–1999; updates 

and revisions are ongoing and are summarized 

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

mastererrata.html).

Valder, J.F., Delzer, G.C., Price, C.V., and 

Sandstrom, M.W., 2008, Study design and 

percent recoveries of anthropogenic organic 

compounds with and without the addition 

of ascorbic acid to preserve water samples 

containing free chlorine, 2004–06: U.S. Geological Survey Open-File Report 2008–1226, 

85 p., available at http://pubs.usgs.gov/

ofr/2008/1226/.

Volgelmann, J.E., Sohl, T.L., Campbell, P.V., 

and Shaw, D.M., 1997, Regional land cover 

characterization using Landsat and other spatial data input [abs.] in Developing the tools 

to meet the Nation’s monitoring needs—The 

evolution of EMAP: Third Environmental 

Monitoring and Assesment Program (EMAP) 

Research Symposium, April 8–11, 1997, 

Albany, New York, p. 10.

Zogorski, J.S., Carter, J.M., Ivahnenko, Tamara, 

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

Squillace, P.J., and Toccalino, P.L., 2006, 

The quality of our Nation’s waters—Volatile 

organic compounds in the Nation’s ground 

water and drinking-water supply wells: 

U.S. Geological Survey Circular 1292, 

101 p., available at http://pubs.usgs.gov/circ/

circ1292/.

By Michael J. Brayton, Judith M. Denver, 

Gregory C. Delzer, and Pixie A. Hamilton