Clackamas River

Elm Fork Trinity River

Cache la Poudre River Truckee River

White River

Chattahoochee 

River

Neuse River

Potomac

 River

Running Gutter Brook

Clackamas River

Elm Fork Trinity River

Cache la Poudre River Truckee River

White River

Chattahoochee 

River

Neuse River

Potomac

 River

Running Gutter Brook

0 200 400 MILES

0 200 400 KILOMETERS

Base from U.S. Geological Survey digital 

data, 1996, 1:2,000,000

Albers Equal-Area Conic projection

Standard parallels 29°30′ N and 45°5′ N, 

central meridian 96° W

North American Datum of 1983

Only source-water samples collected

Source- and finished-water samples collected

EXPLANATION

Figure 1. The nine community water systems monitored are spatially distributed 

across the Nation. The community water systems withdrawing from the nine 

streams vary in size, serving from about 3,000 people to about 2 million people. Water 

treatment at most of the systems is conventional, which typically includes the steps of 

coagulation, flocculation, sedimentation, filtration, and disinfection.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008–3094

December 2008 Printed on recycled paper

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

Man-Made Organic Compounds in Source Water of Nine 

Community Water Systems that Withdraw from Streams, 2002–05

I

nitial findings from a national study by the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) characterize the occurrence of about 250 anthropogenic organic compounds in source water (defined 

as water collected at a surface-water intake prior to water treatment) at nine community water systems in nine States in the 

Nation (fig. 1). The organic compounds analyzed in this study are primarily man-made and include pesticides, solvents, 

gasoline hydrocarbons, personal-care and domestic-use products, disinfection by-products, and manufacturing additives. The 

study also describes and compares the occurrence of selected compounds detected in source water with their occurrence in 

finished water, which is defined as water that has passed through treatment processes but prior to distribution. This fact sheet 

summarizes major findings and implications of the study and serves as a companion product to two USGS reports that present 

more detailed and technical information for the nine systems studied during 2002–05 (Carter and others, 2007; Kingsbury and 

others, 2008).

Occurrence of Organic Compounds 

in Source Water and Their 

Relevance to Human-Health 

Benchmarks

About one-half (134) of the organic 

compounds analyzed in this study were 

detected in at least one sample collected 

during 2002–04 at the nine source-water 

intakes. In total, 119 compounds for 

which samples were analyzed were not 

detected at all in source water. Concentrations of detected compounds generally 

were less than 1 μg/L and less than available human-health benchmarks.

Recent advances in laboratory 

analytical methods have given scientists the ability to detect a wide variety 

of contaminants in the environment at 

low concentrations—typically as low as 

0.02 microgram per liter (μg/L), which 

generally is 100 to 1,000 times lower than 

most drinking-water standards. Detections reported in this study, therefore, 

do not necessarily indicate a concern to 

human health but rather provide a characterization of the low-level environmental 

occurrence of a wide variety of chemicals 

not commonly monitored in sources of 

drinking water.

Concentrations of detected 

compounds generally were less than 

1 μg/L, and annual mean concentrations 

of all compounds were less than humanhealth benchmarks. As such, adverse 

effects to human health are not expected 

(subject to limitations of available 

human-health benchmarks). Comparison 

of measured concentrations to humanhealth benchmarks (see inset), provides 

an initial perspective on the potential 

importance of “man-made” organic 

compounds present in source water. Only 

three compounds (atrazine, acetochlor, 

and dieldrin) were detected in source 

water at concentrations greater than a 

human-health benchmark when singlesample concentrations were considered.
Figure 2. The total number of compounds and their total concentration in 

samples generally increased with the amount of agricultural and urban land use 

in a watershed, and the presence of wastewater discharge upstream from the 

community water system, which explains, in part, why relatively large numbers of 

compounds were detected at the Elm Fork Trinity, White, Neuse, Chattahoochee, 

and Potomac Rivers.

0 10 20 30 40 50 60 70 80 90 100

0

10

20

30

MEDIAN NUMBER OF COMPOUNDS DETECTED

2.5 to 4

Median total concentration, 

 in micrograms per liter

1 to 1.5

0.2 to 0.5

Less than 0.05

PERCENTAGE OF AGRICULTURAL AND URBAN LAND USE IN WATERSHED

Elm Fork Trinity River White River

Neuse River

Potomac River

Chattahoochee River

Running Gutter Brook

Clackamas River

Truckee River

Cache la Poudre River

Compounds Commonly Detected in 

Source Water

The compounds most commonly 

detected, in more than one-half of the 

source-water samples, include the disinfection by-product chloroform; the herbicides simazine, atrazine, metolachlor, 

and DEA, a degradate of atrazine; and 

the fragrance HHCB. The number of 

compounds detected and their total 

concentrations were largest at sourcewater withdrawal sites with considerable agricultural and urban land in their 

watersheds.

Detected compounds represent a 

variety of sources and uses (including 

industrial, agricultural, domestic, and 

others); therefore, different pathways 

(including overland runoff and groundwater and wastewater discharges) to 

the sources of drinking-water supplies 

are possible. In general, the number 

of compounds detected and their total 

concentration were largest at sourcewater withdrawal sites for the five 

community water systems with considerable agricultural and urban land in their 

watersheds: the Elm Fork Trinity River 

in Texas, the White River in Indiana, 

the Neuse River in North Carolina, the 

Chattahoochee River in Georgia, and the 

Potomac River in Maryland (fig. 2).

Chloroform—As the most frequently 

detected compound, chloroform was 

detected in nearly 70 percent of all 

samples and in samples from eight of 

the nine stream sites. Chloroform is a 

common disinfection by-product formed 

during the treatment of wastewater and 

municipal drinking water and also has 

many industrial uses, including the 

production of refrigerants for home air 

conditioners and large commercial freezers. The compound was detected yearround at five of the nine sites. The Elm 

Fork Trinity, Neuse, Potomac, and White 

Rivers have major upstream wastewater 

discharges in their watersheds, which also 

may contribute to the common occurrence of HHCB, a musk fragrance used 

in personal-care products. The fifth site, 

Running Gutter Brook, does not receive 

any major wastewater discharge. Chloroform can have multiple sources including 

lawn irrigation using treated drinking 

water, leaking drinking-water distribution lines, and leaking sewerage or septic 

systems, and it also forms naturally in 

some soils by microbial processes. An 

understanding of local hydrology and 

all possible sources of contaminants is 

needed to fully characterize source-water 

quality.

Herbicides—Simazine, atrazine, 

degradates (breakdown product) of 

atrazine (DEA and deisopropylatrazine), 

metolachlor, prometon, and 2,4–D were 

detected in about 50 percent or more 

of samples at six of the nine sampled 

Summary of Major Findings 

•	About one-half (134) of the 

organic compounds analyzed in 

this study were detected in at least 

one source-water sample collected 

at the nine source-water intakes. 

In total, 119 compounds for which 

samples were analyzed were not 

detected at all.

•	Concentrations generally were 

less than 1 microgram per liter, 

and annual mean concentrations 

of all compounds were less than 

available human-health benchmarks in source- and finishedwater samples. On the basis of 

this screening-level assessment 

of compounds, adverse effects to 

human health are not expected.

•	 The most commonly detected 

compounds in source water were 

the disinfection by-product chloroform; the herbicides simazine, 

atrazine, metolachlor, and deethylatrazine (DEA), a degradate of 

atrazine; and the musk fragrance 

hexahydrohexamethylcyclopentabenzopyran (HHCB).

•	 The number of compounds 

detected and their total concentration were largest at source-water 

withdrawal sites for community 

water systems with considerable 

agricultural and urban land in 

their watersheds.

•	 Most of the compounds detected 

commonly in source-water 

samples (about two-thirds) 

also were detected commonly 

in finished-water samples at 

relatively similar concentrations 

but almost always at concentrations less than available humanhealth benchmarks.

•	 Organic compounds typically did 

not occur alone. More than 75 

percent of source- and finishedwater samples contained five or 

more organic compounds, and 

about one-half of the samples 

contained 14 or more compounds, 

typically including degradates.
sites. Some of these compounds—

including simazine, atrazine, DEA, and 

metolachlor—were detected year-round 

in samples from Elm Fork Trinity, 

Potomac, and White Rivers, which 

drain watersheds with large amounts of 

agricultural or mixed (including some 

urban) land use. Continuous occurrence 

may be attributed, in part, to inputs from 

ground-water discharge. Few herbicides 

were detected in samples collected from 

the Cache la Poudre, Clackamas, and 

Truckee Rivers and from Running Gutter 

Brook, which drain relatively undeveloped watersheds. The occurrence of 

herbicides and their degradates generally 

reflects patterns in land use and chemical use. The most commonly occurring 

herbicides in source water for community water systems correspond to those 

detected most frequently in ambient 

stream water across the Nation (Gilliom 

and others, 2006).

Comparisons Between Source 

Water and Finished Water

About two-thirds of the compounds 

detected commonly in source water also 

were detected in finished water and at 

relatively similar concentrations and 

were almost always at concentrations 

lower than available human-health 

benchmarks.

Samples of source and finished 

water were collected during 2004–05 

at eight of the nine community water 

system sites. Finished-water samples 

were collected after source-water samples 

NAWQA Approach to Source Water-Quality Assessments and 

Comparisons to Other Monitoring

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

to characterize the quality of water in selected rivers used as a source of supply 

to selected community water systems in the United States (Delzer and Hamilton, 

2007). The long-term goal of this effort is to complete assessments by 2013 at 

about 30 systems that withdraw water from streams by using standard protocols 

and nationally consistent methods. NAWQA findings are intended to complement 

ongoing drinking-water monitoring required by Federal, State, and local programs, 

which focus primarily on post-treatment compliance monitoring of contaminants 

regulated by the U.S. Environmental Protection Agency in drinking water (http://

www.epa.gov/safewater/ccr/index.html). Many of the compounds analyzed by 

USGS are unregulated and not required to be monitored under the Federal Safe 

Drinking Water Act. In addition, many of these compounds are not included in 

other source-water and finished-water monitoring programs such as the Unregulated Contaminant Monitoring Regulation (U.S. Environmental Protection Agency, 

2007) and the U.S. Department of Agriculture’s Pesticide Data Program (U.S. 

Department of Agriculture, 2008).

for the disinfection by-products. Annual 

mean concentrations of the sum of the 

four disinfection by-products analyzed in 

finished-water samples were less than the 

Maximum Contaminant Level of 80 μg/L 

for total trihalomethanes.

About two-thirds of the compounds 

that were characterized as commonly 

occurring in source-water samples (that 

is, compounds detected in 10 percent 

or more of samples) also were detected 

in finished-water samples at relatively 

similar detection frequencies and concentrations. Differences in concentrations for 

these compounds between source water 

and the associated finished-water sample 

generally were less than 25 percent. For 

example, when atrazine was present in 

source water, it was usually detected in 

finished water at a similar concentration 

(fig. 3). Some exceptions included the 

insecticides fipronil and diazinon, which 

were more commonly found in source 

water but not in finished water, in part 

because of degradation or transformation associated with chlorine disinfection (Valder and others, 2008; fig. 3). In 

addition, disinfection by-products were 

detected more frequently in finished 

water than in source water, which is an 

expected consequence of the water treatment process.

Seasonal variations in source water 

typcially were reflected in finishedwater quality—Multiple samples were 

collected to characterize variability in 

source- and finished-water samples at 

each of the community water systems. 

Analyses of these samples showed 

variations in the detection frequency and 

concentration of selected compounds in 

source water at most sites, in large part 

because of different hydrologic pathways 

to the streams, streamflow, sources of the 

compounds, and chemical use. Several 

compounds were detected year-round 

in both source- and finished-water 

samples. Wastewater discharge may be 

a relatively constant source for some of 

these compounds, such as chloroform or 

HHCB. Herbicides and herbicide degradates had the most pronounced seasonal 

change in concentration throughout the 

year, but the magnitude and timing of 

these changes varied among the sites. For 

example, atrazine concentrations at the 

White River varied by tenfold or more 

during the year, whereas concentrations 

at the Neuse River varied less (fig. 4). 

The highest concentrations generally 

and time was allowed to account for 

the retention time in the treatment plant 

(which ranged from 1 hour to 5 days). In 

general, the routine treatment steps used 

by the eight community water systems, 

which are typical of many systems 

across the Nation, are not designed to 

specifically remove most of the organic 

compounds monitored in this study (see 

inset). The resulting comparisons are 

therefore not intended to characterize 

treatment efficacy, but rather to provide 

a preliminary indication of the potential significance of the presence of the 

organic compounds most commonly 

detected in source water to the quality of 

finished water prior to distribution.

Results of the analyses of samples 

of finished water were similar to those 

for source water in that annual mean 

concentrations of organic compounds 

were less than human-health benchmarks. 

On the basis of this screening-level 

assessment, adverse effects to human 

health from consumption of the water are 

not expected. Annual mean concentrations of all compounds in finished water 

were lower than available human-health 

benchmarks. Maximum concentrations of only two compounds (atrazine 

and benzo[a]pyrene) were detected in 

finished water at concentrations greater 

than a human-health benchmark when 

single-sample concentrations were 

considered. Maximum concentrations of 

most other compounds were from two 

to five orders of magnitude less than 

their human-health benchmarks, except 
Figure 3. Although water treatment steps used by the eight water systems differ somewhat, large differences in the 

amount of change in concentration between source water and finished water generally were not observed for most 

compounds, such as atrazine, that had similar detection frequencies in source and finished water. Some compounds, for 

example fipronil, were present in source water but were not detected in finished water, likely because of degradation or 

transformation as a result of disinfection with chlorine.

0.001 0.01 0.1 1 10

Fipronil 1:1

Concentration in source water

Concentration in source water greater than in finished water

greater than in finished water

Concentration in finished water

greater than in source water

0.001

0.01

0.1

1

10

CONCENTRATION IN FINISHED WATER, 

IN MICROGRAMS PER LITER

CONCENTRATION IN SOURCE WATER, IN MICROGRAMS PER LITER

Atrazine

EXPLANATION

Chattahoochee River

Neuse River

Running Gutter Brook

Potomac River

Elm Fork Trinity River

White River

Clackamas River

Note: Nondetections set to 0.001 microgram per liter

1:1

0.001 0.01 0.1 1 10

occurred in the spring after chemicals 

were applied in row-crop areas. For many 

compounds, such as atrazine, changes in 

concentration over time in source water 

were reflected in the associated finished 

water (fig. 4). Differences in atrazine 

concentrations in source and finished 

water at the Neuse River between February and June may be related to the use of 

powdered activated carbon for taste- and 

odor-compounds.

Mixtures and Pesticide 

Degradates

Individual compounds typically 

did not occur alone. More than 75 

percent of source- and finished-water 

samples contained mixtures of five 

or more compounds. About one-half 

of the samples contained 14 or more 

compounds (fig. 5), typically including 

degradates.

The most commonly occurring 

compounds in mixtures, not surprisingly, 

were the individual compounds that were 

detected most frequently. These include 

the herbicides atrazine (and its degradate DEA), metolachlor, simazine, and 

prometon, as well as one or more disinfection by-products, such as chloroform, 

particularly in finished water. In finishedwater samples, disinfection by-products 

increased the number of compounds in a 

sample relative to the associated sourcewater sample.

Mixtures of compounds commonly 

included pesticide degradates. For 

example, atrazine was found with one or 

more of its degradates, such as DEA, in 

nearly 95 percent of samples in which 

it was detected. At three of the sites—

Human-Health Benchmarks Used in This Study

A screening-level assessment of the potential effects of detected compounds 

on human health was based on a comparison of annual mean concentrations 

in source- and finished-water samples to available human-health benchmarks. 

Specifically, concentrations of the regulated compounds were compared to U.S. 

Environmental Protection Agency Maximum Contaminant Levels (MCLs), and 

concentrations of unregulated compounds for which the USEPA has published 

toxicity information were compared to USGS Health-Based Screening Levels 

(HBSLs; Toccalino and others, 2007). About one-half of detected compounds 

do not have human-health benchmarks or adequate toxicity information for 

evaluating results in a human-health context. This screening-level assessment 

provides an initial perspective on the potential significance of man-made organic 

compounds in source water; it is not a substitute for a comprehensive risk assessment, which includes consideration of many more factors, such as additional 

avenues of exposure.

Potomac, Elm Fork Trinity, and White 

Rivers—DEA was detected in every 

sample with its parent compound, but 

typically at concentrations less than those 

of atrazine.

Degradates of the herbicides 

metolachlor, alachlor, and acetochlor 

were analyzed in samples from the Elm 

Fork Trinity, Neuse, Potomac, and White 

Rivers—watersheds in which these 

herbicides were most likely to be used. 

Like atrazine, these degradates gener-
Figure 4. Seasonal changes in atrazine concentrations in source water were reflected in the associated finished 

water. At most community water systems, finished-water concentrations generally were similar to or less than those in 

source water. Lower concentrations in finished water compared to source water at the Neuse River may be the result 

of seasonal use of powdered activated carbon for taste- and odor-compounds.

Figure 5. Samples of both source and finished water typically contained mixtures 

of compounds. One-half of finished-water samples contained 15 or more compounds. 

Disinfection by-products in finished water and degradates in both source and 

finished water contributed to common mixtures.

Neuse River White River

0.001

0.01

0.1

1

10

CONCENTRATION, IN MICROGRAMS PER LITERCONCENTRATION, IN MICROGRAMS PER LITER

6/1/2004 10/16/2004 3/2/2005 7/17/2005 6/1/2004 10/16/2004 3/2/2005 7/17/2005

0.001

0.01

0.1

1

10

Source water

Finished water

Source water

Finished water

15 compounds

14 compounds

0 10 20 30 40 50

NUMBER OF COMPOUNDS IN A SAMPLE

0

20

40

60

80

100

Source water

Finished water

PERCENTAGE OF SAMPLES WITH EQUAL OR GREATER 

NUMBER OF COMPOUNDS

ally were detected with their parent 

compounds. In contrast to atrazine, 

however, the summed concentrations of 

degradates for metolachlor and alachlor 

typically were greater than those of their 

parent herbicides, which is most likely 

due to the chemical properties of these 

herbicides. Specifically, atrazine is more 

mobile and chemically stable, allowing it 

to persist in the hydrologic system longer 

than metolachlor and alachlor. Little is 

known about the potential effects of most 

herbicide degradates on human health.

Possible Implications and Utility of 

These Findings

Many of the compounds detected 

most commonly in source- and finishedwater samples were among those most 

commonly detected in ambient stream 

water across the Nation (Gilliom and 

others, 2006). In addition, the occurrence of many compounds in source and 

finished water was similar at community water systems on rivers that have 

upstream wastewater facilities and that 

drain large areas of agricultural and urban 

land. Any application of these findings 

to a national perspective, however, must 

be considered preliminary because they 

reflect conditions at only a few community water systems, and some compounds 

included in this study have only recently 

been monitored systematically in source 

and finished water (including, for 

example, compounds used in personalcare products, such as HHCB). Continued 

research is needed to better understand 

the sources, transport mechanisms, fate 

in the environment, and possible effects 

of these compounds to human health. In 

addition to other agencies and universities, research examining these issues 

is being conducted by the USGS Toxic 

Substances Hydrology Program (see 

http://toxics.usgs.gov/) and the NAWQA 

Program. Resource management and 

research efforts might include the following:

•	Emphasizing watershed management 

and source-water protection strategies 

to help manage the sources and transport of compounds to source water and 

ultimately to finished water.

•	Continuing development of toxicity 

information for commonly occur-
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 Helena and 

Lafayette Publishing Service Centers.

ring unregulated compounds, their 

degradates, and common mixtures 

of compounds in source water and 

finished water. The common occurrence of mixtures of compounds means 

that the total combined toxicity in 

source water may be greater than that 

of any single compound that is present. 

Continued research is needed because 

human-health benchmarks are based on 

toxicity data for individual compounds, 

and the additive or synergistic effects 

of mixtures of compounds at low levels 

are not well understood. 

•	Monitoring and assessing organic 

compounds that are not commonly 

monitored in water supplies but are 

present in finished water, which may 

ultimately lead to the development or 

implementation of treatment technologies for their removal.

References

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., http://pubs.usgs.

gov/ds/2007/268/.

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., 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—Pesticides in 

the Nation’s streams and ground water, 

1992–2001: U.S. Geological Survey 

Circular 1291, 172 p., 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: U.S. Geological 

Survey Scientific Investigations Report 

2008–5208, 66 p., http://pubs.usgs.gov/

sir/2008/5208/.

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

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

Screening Levels—A tool for evaluating 

what water-quality 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 Data Program: accessed March 

6, 2008, at http://www.ams.usda.gov/

science/pdp/.

U.S. Environmental Protection Agency, 

2007, Unregulated Contaminant 

Monitoring Program: U.S. Environmental Protection Agency, accessed June 10, 

2008, at http://www.epa.gov/safewater/

ucmr/index.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 OpenFile Report 2008–1226, 85 p., http://

pubs.usgs.gov/of/2008/1226/.

USGS promotes public access 

to information

This fact sheet is free of charge, 

and also is available on the Web 

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

swqa/. Also included at the NAWQA 

Web site are downloadable data on 

organic compounds, information on 

sampling designs and methodology 

(Carter and others, 2007; Kingsbury and others, 2008; Valder and 

others, 2008), and frequently asked 

questions (FAQs).

Finished-Water Sampling, Water Treatment, and Significance of 

Comparisons to Source Water

Water treatment processes differ among the systems sampled. Specifically, 

treatment at five of the systems is considered conventional, including the steps of 

coagulation, flocculation, sedimentation, filtration, and disinfection. One water 

system uses slow sand filtration and disinfection, a second system adds ozone as 

a preliminary treatment step to conventional treatment, and a third system uses 

direct filtration treatment that follows many of the steps used in conventional treatment.

Washington Aqueduct on the Potomac River 

in Washington, D.C.

By James A. Kingsbury, Gregory C. 

Delzer, and Pixie A. Hamilton

For additional information:

James Kingsbury, Senior Scientist 

jakingsb@usgs.gov, 

(615) 837-4762

Gregory Delzer, 

SWQA National Coordinator 

gcdelzer@usgs.gov, 

(605) 394-3230