GEORGIA

EXPLANATION

Watershed boundary

City of Atlanta water intake

Land cover

Water

Urban

Forest/shrub

Pasture/agriculture

HALL

Atlanta

UNION

GWINNETT

WH ITE

COBB

CHEROKEE

RABUN

BANKS

DEKALB DOUGLAS

FULTON

LUMPKIN

FORSYTH

TOWNS

DAWSON

HABERSHAM

 Lake

Sidney

Lanier

Chattahoochee

Base from U.S. Geological Survey 1:100,000-scale digital data

0 5 10 MILES

0 5 10 KILOMETERS

River

84°00'

83°30'

84°30'

34°00'

34°30'

Figure 1.  The upper Chattahoochee River

provides drinking-water supply and wastewater

dilution and removal for approximately 3 million

people in the Atlanta metropolitan area. The

land area upstream from Lake Sidney Lanier

is mostly forested with urbanized lands rapidly

increasing downstream from the reservoir.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3062

June 2011

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

Organic Compounds Assessed in Chattahoochee River Water 

Used for Public Supply near Atlanta, Georgia, 2004–05

Organic compounds studied in a U.S. Geological Survey (USGS) assessment of water samples collected from the Chattahoochee 

River and from the City of Atlanta public supply system generally are manmade and include pesticides, solvents, gasoline 

hydrocarbons, personal-care and domestic-use products, refrigerants, and propellants. A total of 50 of the 266 compounds were 

detected at least once in source-water samples collected at the drinking-water intake for the City of Atlanta, one of several 

municipalities that rely on the Chattahoochee River for its water supply. The diversity of compounds detected reflects the 

range of contaminant sources upstream from Atlanta, including urban and agricultural runoff, treated wastewater outfalls, and 

groundwater discharge. Five compounds were detected year round in source water, including three herbicides commonly used 

on agricultural and urban lands, a disinfection by-product, and a gasoline hydrocarbon. About 70 percent of the 33 commonly 

detected compounds in source water (detected in at least 20 percent of all samples) also were detected in finished water (after 

treatment but prior to distribution). Concentrations for all of the detected compounds were less than human-health benchmarks, 

which are available for about one-half of the detected compounds.

Introduction

An investigation by the U.S. Geological 

Survey (USGS) National Water-Quality 

Assessment (NAWQA) Program characterized 

the occurrence of 266 organic compounds 

in source water and finished water from the 

Chattahoochee River, which is the main watersupply source for the Atlanta metropolitan 

area (fig. 1). Source water is stream water 

collected at a surface-water intake prior to 

water treatment, and finished water is water 

that has passed through treatment processes 

prior to distribution. Samples were collected 

approximately monthly during 2004–05 

and included 15 paired source-water and 

finished-water samples. Samples were 

collected during winter-spring high flow 

and summer-fall low flow, but storm events 

were not targeted during this Source WaterQuality Assessment (SWQA) study. Samples 

were analyzed for pesticides and degradates, 

gasoline hydrocarbons, solvents, disinfection 

by-products, personal care and domesticuse products, and other organic compounds. 

Community water systems are required 

to monitor regulated organic compounds 

under the Safe Drinking Water Act of 1996 

(U.S. Environmental Protection Agency, 

1998); however, most compounds included 

in this study are not regulated by Federal 

drinking-water standards (U.S. Environmental 

Protection Agency, 2007a). The Chattahoochee 

River study is part of an ongoing NAWQA 

investigation of community water systems 

across the United States. Additional details 

about the national study are given in Carter 

and others (2007).
2

Compound

Percent detection

Source 

water 

Finished 

water 

Disinfection by-products

Bromodichloromethane0 100

Bromoform 0 31

Chloroform 92 100

Dibromochloromethane0 100

Fungicide

Benomyl 23 0

Gasoline hydrocarbons

Benzene 25 0

m- and p-Xylene 8 62

Methyl tert-butyl 

ether

25 0

Toluene 100 100

Herbicide and hebicide degradates

2,4-D 62 100

3,4-Dichloroaniline 92 0

Atrazine 100 100

Deethylatrazine 46 69

Deisopropylatrazine 46 77

Diuron 46 46

Hydroxy atrazine 23 0

MCPA 46 62

Metolachlor 46 23

Pendimethalin 31 23

Prometon 69 31

Simazine 100 100

Table 1.  A total of 33 compounds were commonly detected (in at least 20 percent of

the samples) in source water and 27 compounds in finished water. 

[DEET, N,N-diethyl-meta-toluamide; HHCB, hexahydrohexamethylcyclopentabenzopyran; MCPA, 

2-methyl-4-chlorophenoxyacetic acid]

Compound

Percent detection

Source 

water 

Finished 

water 

Insecticides

Diazinon 23 0

Carbaryl 31 31

Fipronil 77 0

Fipronil sulfide 31 0

Fipronil sulfone 23 0

Desulfinylfipronil 54 23

Manufacturing additives

Tris(2-butoxyethyl) 

phosphate

23 8

Tris(dichloroisopropyl)phosphate

46 31

Organic Synthesis Compound

Anthraquinone 23 0

Personal-care and domestic-use products

Caffeine 85 85

DEET 85 77

HHCB 85 69

4-Nonylphenol 

diethoxylate

23 38

para-Nonylphenol 15 27

Phenol 77 8

Plant- or animal-derived biochemicals

Cholesterol 38 8

Solvents

Acetone 0 31

Methyl ethyl ketone 0 23

Methylene chloride 0 46

p-Cresol 23 0

Occurrence of Organic Compounds 

in Source Water

About one-fifth of the 266 compounds 

characterized were detected in at 

least one source-water sample; a few 

compounds were detected in nearly 

all samples. The detected compounds 

represent many different sources and 

uses and include pesticides, solvents, 

gasoline hydrocarbons, and personalcare products. Five compounds were 

detected year-round, including herbicide compounds commonly used in 

the Chattahoochee River Basin.

Recent advances in laboratory 

analytical methods have given scientists 

the tools to detect a wide variety of 

contaminants at low concentrations in the 

environment—often 100 to 1,000 times 

lower than drinking-water standards (see 

inset, “What ‘Detections’ Might Mean 

to Human Health”). Of the 266 organic 

compounds characterized in this study, 

50 were detected in at least one sourcewater sample from the Chattahoochee 

River. Thirty-three of these compounds 

were commonly detected, that is, found in 

at least 20 percent of the samples (table 1). 

The majority of the compounds detected 

were pesticide and pesticide degradates, 

but gasoline hydrocarbons, manufacturing 

additives, and personal-care and domesticuse products also were found. These 

compounds are among the most commonly 

detected contaminants in surface and 

groundwater across the Nation (Gilliom and 

others, 2006; Zogorski and others, 2006).

Five compounds (chloroform, 

atrazine, simazine, 3,4-dichloroaniline, 

and toluene) were present in source water 

throughout the year (detected in more 

than 90 percent of samples). Chloroform 

is a by-product of water treatment and 

may result from upstream wastewater 

discharges. Atrazine, simazine, and 

3,4-dichloroaniline are herbicides that are 

commonly used on lawns, golf courses, 

and ornamental plantings in the Atlanta 

metropolitan area and in agricultural 

areas upstream from Atlanta. Toluene is 

a gasoline hydrocarbon that has many 

sources, including transportation and 

industrial uses.

What “Detections” Might Mean to Human Health 

The analytical methods used in this study have low detection levels—often 

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

water quality. Detections, therefore, do not necessarily indicate a concern to human 

health. Rather, they help to identify the environmental presence of a wide variety of 

chemicals not commonly monitored in water resources, and they help 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 the 

U.S. Environmental Protection Agency in drinking water. Many of the compounds 

analyzed by the USGS are not included in other source-water and finished-water 

monitoring programs, such as the Unregulated Contaminant Monitoring Program 

(U.S. Environmental Protection Agency, 2007b) and the U.S. Department of Agriculture 

Pesticide Data Program (U.S. Department of Agriculture, 2008).
3

Comparisons Between Source 

Water and Finished Water

About 70 percent of the 33 compounds

commonly detected in source water 

were detected in finished water and 

generally at similar concentrations.

Comparisons between source water 

and finished water are not intended to 

characterize treatment efficacy, but to 

provide a preliminary indication of the 

potential importance of compounds 

detected in source water to the quality 

of finished water before distribution 

(see inset, “Finished-Water Sampling, 

Water Treatment, and Significance of 

Comparisons to Source Water”). Eighteen 

of the most commonly detected organic 

compounds in source water also were 

commonly detected in finished water and 

often at similar low-level concentrations. 

These compounds included pesticides 

and degradates (2,4-D, deethylatrazine, 

deisopropylatrazine, diuron, MCPA, 

metolachlor, pendimethalin, prometon, 

simazine, carbaryl, desulfinylfipronil), 

personal care and domestic-use products 

(4-nonylphenol diethoxylate, caffeine, 

DEET, HHCB), and three additional 

compounds (chloroform, toluene, 

tris(dichloroisopropyl)phosphate; 

table 1). The herbicides 2,4-D, atrazine, 

and simazine were detected in 100 percent 

of the finished water samples, although at 

low concentrations. These pesticides are 

widely used in the Chattahoochee River 

watershed and across the Nation and have 

been frequently detected in surface water 

in the Atlanta metropolitan area (Frick and 

Dalton, 2005; Hughes and Moon, 2009).

Three disinfection by-products were

detected in 100 percent of finished samples

(bromodichloromethane, dibromochloromethane, chloroform), and one was 

frequently detected (bromoform). With 

the exception of chloroform, none of these 

compounds were detected in source-water 

samples. These by-products form when 

organic carbon in source water reacts with 

disinfectants, such as chlorine and (or) 

bromine. The presence of these compounds 

in finished water is well documented, 

understood, and expected as an outcome of 

drinking-water disinfection (Rook, 1974; 

Krasner and others, 2006). The presence 

of chloroform in source water could result 

from upstream wastewater discharges. 

Several compounds, including acetone, 

methyl ethyl ketone, m- and p-xylene, and 

para-nonylphenol, were detected in low 

concentrations in finished water but were 

not detected in source water. The presence 

of these compounds in finished water is not 

fully understood. 

A Closer Look at Herbicides and 

Herbicide Degradates

The herbicides atrazine and 

simazine were detected in all of 

the source- and finished-water 

samples at concentrations below 

drinking-water standards. The 

similar concentrations measured 

in both source and finished water 

suggest that current treatment 

processes are ineffective at 

removing these compounds at the 

low concentrations measured.

The herbicides atrazine and simazine 

were detected in 100 percent of the sourceand finished-water samples collected, with 

maximum concentration about 10 times 

lower than U.S. Environmental Protection 

Agency (USEPA) maximum contaminant 

levels (MCL) for drinking water (table 2).

The concentrations of most of the herbicides detected were similar for both source 

Finished-Water Sampling, Water Treatment, and Significance of 

Comparisons to Source Water 

The City of Atlanta uses conventional water-treatment processes at the 

Chattahoochee Water Treatment Plant, including pre-screening; disinfection with 

sodium hypochlorite and chlorine; flocculation using alum; disinfection with sodium 

hypochlorite and chlorine; sedimentation; filtration through anthracite coal, sand, and 

coarse gravel using dual media filters; post-chemical addition (fluoride, phosphate, 

lime, and more chlorine); clear well storage; and distribution. Finished-water samples 

were collected approximately 5 hours after source-water samples were collected to 

account for treatment-plant retention time of the water (Frick and Dalton, 2005). 

Some differences between source- and finished-water quality may be attributable to 

sample timing and variations in retention time, as well as potential analytic variability 

associated with low concentrations at or near laboratory reporting levels (Kingsbury 

and others, 2008). It is also possible that some compounds detected in source water 

were 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 detected in source water to the quality of 

finished water before distribution. In general, conventional treatment is not specifically 

designed to remove most of the organic compounds monitored in this study.

and finished water, indicating that the 

treatment system may not be effectively 

removing these compounds. Both atrazine 

and simazine were detected year round, 

although concentrations greatly increased 

during the winter months likely because 

of pre-emergent applications prior to the 

spring growing season. A similar seasonal 

increase in these herbicides was observed 

in several smaller watersheds in the Atlanta 

metropolitan area, although concentrations 

in these smaller streams were higher, at 

times exceeding the USEPA MCL (Hughes 

and Moon, 2009).

The data collected for this study do 

not indicate an immediate health threat 

based on existing drinking-water standards. 

However, from 4 to 12 pesticides and 

pesticide degradates were detected in each 

finished-water sample, and the health effects 

of pesticide mixtures is not well understood. 

In addition, the atrazine degradates 

deisopropylatrazine and deethylatrazine 

were detected in about 70 percent of the 

finished-water samples. The transformation 

of parent pesticides to degradates generally 

results in less toxic compounds, but some 

degradates may have toxicities that are 

similar to, or greater than, those of the 

parent pesticide (Gilliom and others, 

2006). None of the degradate compounds 

measured are currently regulated under the 

Safe Drinking Water Act.
4

0.001 

0.01 

0.1 

1 

10 

100 

0.001 0.01 0.1 1 10 100 

Finished-water concentration, in micrograms per liter

Source-water concentration, in micrograms per liter

1:1 ratio

Disinfection by-products

Fungicide

EXPLANATION

Gasoline hydrocarbons 

Herbicides

Insecticides

Personal-care and domestic-

 use products

Pesticides

Solvents

Figure 2.  Many of the most commonly detected compounds had similar concentrations

in source and finished water (plot along the 1:1 line). All of the disinfection by-products had

higher concentrations in finished water than source water (plot above the 1:1 line); those that

plot along the y-axis were not detected in source water. Similarly, many of the insecticides

and some of the personal care and domestic-use products plot along the x-axis, indicating

that they were not detected in finished water. With the exception of disinfection by-products,

nearly all compounds have concentrations less than 1 microgram per liter.

Potential Effects on Human Health

Concentrations of all detected compounds were less than human-health 

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 benchmarks, see 

inset “Human-Health Benchmarks 

Used in This Assessment”).

Twenty-two organic compounds 

frequently detected in source and finished 

water were measured at concentrations 

above 0.1 microgram per liter (μg/L; 

table 2). Generally compounds from most 

of the major groups that were analyzed 

were detected, including disinfection 

by-products, pesticides, industrial 

compounds, and personal-care products. 

The prevalence of the compounds reflects 

their widespread use within the highly 

developed and populated Chattahoochee 

River Basin and the physical properties that 

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 humanhealth benchmarks. Specifically, 

concentrations of regulated compounds 

were compared to USEPA maximum 

contaminant levels, 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 (Toccalino and 

others, 2008). About one-half of the 

detected compounds do not have 

human-health benchmarks or adequate 

toxicity information for evaluating 

results in a human-health context. 

Human-health benchmarks have been 

developed for individual compounds 

but not mixtures. The screeninglevel assessment provides an initial 

perspective on the potential importance 

of manmade 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.

allow them to persist in the environment 

(Gilliom and others, 2006; Zogorski and 

others, 2006). 

Concentrations of none of the 

regulated compounds exceeded USEPA 

drinking-water standards (MCLs), 

and all concentrations were less than 

USGS Health-Based Screening Levels 

(HBSLs) that were developed for 

unregulated compounds (table 2; see 

inset “Human-Health Benchmarks Used 

in this Assessment”). Human-health 

benchmarks are not available for nine of 

the commonly occurring compounds that 

exceeded a concentration of 0.1 μg/L. 

The concentrations of four compounds 

were 10 times lower than their USEPA 

MCL or USGS HBSL human-health 

benchmarks—the disinfection by-products 

bromodichloromethane and chloroform 

and the herbicides atrazine and simazine 

(table 2). These compounds may warrant 

consideration for monitoring of lowconcentration trends, especially because 

of the high concentrations of simazine 

that exceeded the USEPA MCL and were 

detected in Atlanta-area streams in a 

previous study (Hughes and Moon, 2009). 

An important consideration in 

assessing the potential effects on human 

health is the common occurrence of 

mixtures of organic compounds in sourceand finished-water samples. For example, 

the median number of compounds in 

source- and finished-water samples was 

19 and 17, respectively. This number is 

comparable to findings from eight other 

community water systems sampled by 

the USGS (Kingsbury and others, 2008). 

The potential human-health effects 

of mixtures of co-occurring organic 

compounds are largely unknown and 

have not been studied extensively. The 

effect of one compound on another’s 

toxicity might be additive, antagonistic, 

or synergistic (Hayes and others, 2006). 

With a few exceptions for pesticides with 

common modes of action, human-health 

benchmarks generally are not available 

for specific mixtures. Because MCLs and 

other human-health benchmarks are based 

on toxicity data for individual compounds, 

continued research is needed on the 

effects of specific mixtures of compounds 

at low concentration levels (Gilliom and 

others, 2006).
5

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

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

only 13 of the 23 compounds shown in this table.

[Reporting level shown is higher value of either source or finished water; μg/L, microgram per liter; DEET, N,N-diethyl-meta-toluamide; HHCB, hexahydrohexamethylcyclopentabenzopyran; MCPA, 2-methyl-4-chlorophenoxyacetic acid; E, estimated concentration; M, presence verified but not quantified; 

MCL, maximum contaminant level; HBSL, Health-Based Screening Level; ND, not detected; —, no human-health benchmark available]

Compound

Number of 

samples analyzed

Percent detection 

> 0.1 μg/L Reporting 

level, 

μg/L

MCL or 

HBSL

Maximum concentration 

(μg/L)

Source

water

Finished

water

Source

water

Finished 

water

Source

water

Finished 

water

Disinfection by-products

Bromodichloromethane 12 13 0 100 0.028 ND 9.34

Chloroform 12 13 0 100 0.1 80a E 0.04 36.7

Dibromochloromethane 12 13 0 100 0.1 ND 1.7

Fungicide

Benomyl 13 13 7 0 0.022 40 E 0.141 ND

Gasoline hydrocarbon

Methyl tert-butyl ether 12 13 25 0 0.1 — E 0.1 ND

Herbicides

2,4-D 13 13 54 69 0.038 70 E 0.48 0.41

Atrazine 13 13 23 23 0.007 3 0.304 0.345

Diuron 13 13 8 8 0.016 2 0.15 0.12

MCPA 13 13 31 31 0.07 30 E 0.44 E 0.39

Simazine 13 13 38 62 0.005 4 0.698 0.73

Insecticide

Carbaryl 13 13 8 0 0.018 40 0.25 0.04

Manufacturing additives

Tris(2-butoxyethyl) 

phosphate

13 13 23 8 0.5 — E 0.4 E 0.1

Tris(dichloroisopropyl) 

phosphate

8 10 13 13 0.5 — E 0.1 E 0.1

Organic synthesis compound

Anthraquinone 12 13 17 0 0.5 — E 0.1 ND

Personal-care and domestic-use products

Caffeine 13 13 8 0 0.018 — 0.117 0.061

DEET 13 8 85 38 0.5 — E 0.2 E 0.1

HHCB 13 13 54 15 0.5 — E 0.1 E 0.1

4-Nonylphenol 

diethoxylate

13 13 23 38 5 — 2 3

Phenol 13 13 77 8 0.5 2,000 2.1 E 0.1

Plant- or animal-derived biochemicals

Cholesterol 8 13 0 8 2 — M E 1

Solvents

Acetone 12 13 0 31 6 6,000 ND E 2

Methyl ethyl ketone 12 13 0 23 2 4,000 ND 4.1

aMCL of 80 μg/L is for total trihalomethanes (chloroform, bromodichloromethane, dibromochloromethane, and bromoform). Water utility comparison 

to the MCL is based on a moving average of quarterly samples collected at specific points in the distribution system (4 per treatment plant).
Chattahoochee River Findings 

in a National Context and 

Possible Implications

Many of the compounds detected most 

commonly in water from the Chattahoochee 

River (tables 1 and 2) are among the most 

commonly detected in ambient stream water 

and groundwater across the Nation (Gilliom 

and others, 2006; Zogorski and others, 2006).

In addition, the occurrence and concentrations 

of compounds in source- and finished-water 

samples collected from the Chattahoochee 

River are similar to those detected at other 

community water systems, which were 

sampled for a USGS study of anthropogenic 

compounds (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 those used 

for personal care, including caffeine, DEET, 

and 4-nonylphenol diethoxylate. Continued 

research is needed to better understand 

sources, transport mechanisms, trends, 

fate in the environment, and possible links 

among these compounds and human health.

The USGS will continue to collaborate with and complement the work of other 

Federal, State, and local organizations, 

and communicate findings and possible 

implications and future needs such as:

• 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 better understand 

and communicate the relevance of 

organic compounds detected in untreated 

source water and treated finished water, 

the toxicity of these compounds and 

mixtures of these compounds, and the 

possible implications for human health 

and the environment. 

• Current and future monitoring to identify 

compounds not typically evaluated in 

source water, but commonly present in 

finished water.

6

Source Water-Quality Assessments Conducted across the Nation as 

part of the NAWQA Program 

Beginning in 2002, the NAWQA Program initiated a Source Water-Quality Assessment 

(SWQA) Program to characterize the quality of water used as a source of supply at selected 

community water systems across the United States (Delzer and Hamilton, 2007). The longterm goal of the SWQA Program is to complete as many as 30 assessments by 2012 at systems

that withdraw water from streams using standard protocols and nationally consistent methods

(U.S. Geological Survey, variously dated). This fact sheet highlights findings from the 

Chattahoochee River study, which is one of the first nine community water systems sampled 

as part of the SWQA Program. The fact sheet serves as a companion product to USGS Data 

Series 268 and USGS Scientific Investigations Report 2008–5208, which present findings for

the nine systems across the United States (Carter and others, 2007; Kingsbury and others, 2008).

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water.usgs.gov/twri9A/.

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. (http://pubs.usgs.

gov/circ/circ1292/)

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.

Contacts for additional information:

Brian Hughes, U.S. Geological Survey

770-903-9162, wbhughes@usgs.gov

Greg Delzer, U.S. Geological Survey, SWQA Coordinator

605-394-3230, gcdelzer@usgs.gov

By W. Brian Hughes and Cristal L. Younker