Atlanta

City of

The U.S. Geological Survey and City of Atlanta 

Water-Quality and Water-Quantity Monitoring Network

Population growth and urbani­zation affect 

the landscape, and the quality and quantity of water in nearby rivers and streams, 

as well as downstream receiving waters 

(Ellis, 1999). Typical impacts include: 

(1) disruption of the hydrologic cycle 

through increases in the extent of impervious surfaces (e.g., roads, roofs, sidewalks) that increase the velo­city and volume of surface-water runoff; (2) increased 

chemical loads to local and downstream 

receiving waters from industrial sources, 

non­point-source runoff, leaking sewer 

systems, and sewer overflows; (3) direct 

or indirect soil contamination from industrial sources, power-generating facilities, 

and landfills; and (4) reduction in the 

quantity and quality of aquatic habitats 

(Driver and Troutman, 1989; Ellis, 1999; 

Rose and Peters, 2001).

Atlanta, Georgia, is one of the fastestgrowing urban areas in the United States. 

Between the early 1970s and 2000, 

the population of Metropolitan Atlanta 

increased by about 125 percent; at the 

same time, urbanization increas­ed up to 

210 percent (Peters and Kandell, 1999; 

Atlanta Regional Commission, 2004; 

Elizabeth Kramer, University of Georgia, oral commun., 2004). As a result, 

the City of Atlanta’s (COA) storm, 

sanitary, and combined sewers have been 

unable to meet current demands. About 

15 percent of the current COA sew­er 

system is combined (stormwater and sanitary waste in the same pipe). During dry 

periods, all sewer flows are discharged 

to waste­water treatment plants; whereas 

under wet conditions, some of these 

flows are sent to combined treatment 

facilities (see map). When this occurs, 

the combined flow is screened to remove 

solids, and disinfected, prior to being 

discharged to local streams. On average, 

there are more than 300 combined sewer 

overflows (CSOs) per year from Atlanta’s 

six existing CSO facilities (Clean Water 

Atlanta, 2004).

Fact Sheet 2005 – 3126

April 2006

During 1998, the COA entered into a consent decree to reduce the incid­ence of CSOs, 

and other discharges, to permitted limits 

(U.S. District Court, 1998). Compliance with 

the consent decree is scheduled during 2007 

for CSOs and 2014 for sanitary sewer overflows (SSOs), and is based on an improved 

infrastructure that includes the construction 

of two large tunnels (about 360-milliongallon combined capacity) for the storage 

and conveyance of combined stormwater and 

sanitary waste to two new treatment facilities. Further, the COA plans to reduce the 

relative size of the existing combined system 

from 15 to 10 percent of the total. Lastly, the 

COA is required to monitor all SSOs, as well 

as the impact of stormwater, on downstream 

water quality (Clean Water Atlanta, 2004).

85

20

20

285

75

85

75

400

Nickajack Cr Sandy

Creek

Proctor Cr

Utoy

S Utoy Cr

N Fk Camp Cr

South

South

Sugar Cr

Intrenchment Cr

Doolittle Cr

Lullwater Cr

North Fork

Peavine Cr

Peachtree Cr

Nancy

Woodall Cr

Creek

Shoal Cr

Conley Cr

River

River

Camp Cr

Wolf Cr

Cr

South Fork

Cr

Base from U.S. Geological Survey 

1:100,000-scale digital data

N

0 1 2

0 1 2 3 KILOMETERS

3 MILES

NAN-2 NAN-3

NAN-1

PRO-2

PRO-3

PRO-1

PEA-1

PEA-2

PEA-3

PEA-5

PEA-4

UTO-1 UTO-3

SOU-2

SOU-3

INT-1

SAN-1

SOU-1

UTO-2

WOO-1

LUL-1

Atlanta Regional Commission 

planning area

Map area

Gwinnett

Cherokee

Cobb

Clayton Rockdale Henry Fayette

Douglas

Fulton DeKalb

EXPLANATION

Sampling site and identification

Continuous water quality and quantity,

 periodic water quality

Continuous water quantity, 

 periodic water quality

Periodic water quality

Combined sewer overflow facility

Watershed

City of Atlanta boundary

Nancy Creek

Peachtree Creek

Proctor Creek

Sandy Creek

Intrenchment Creek

South River

Utoy Creek

SOU-3

SAN-1

WOO-1

U.S. Department of the Interior

U.S. Geological Survey Printed on recycled paper
During 2001, the COA asked the U.S. 

Geological Survey (USGS), in conjunction with CH2M Hill, to de­sign a waterquality and water-quantity monitoring 

network that would fulfill the requirements 

of the consent decree, provide an evaluation of the planned infrastructural improvements, and monitor the ongoing state of 

the COA’s water quality (see Sampling 

Design). The monitoring pro­gram provides 

real-time measure­ments of water quantity 

and precipitation, as well as water quality 

(e.g., pH, turbidity), com­bined with manual 

and automated sampling, and subsequent 

chemical and biological analyses. Constituents include major ions (e.g., sodium, 

sulfate), metals (e.g., zinc, lead), nutrients 

(e.g., nitrogen, phosphor­us), bacteria (e.g.,

fecal coliform), and wastewater tracers. 

The current COA monitoring pro­gram is 

one of the largest in the United States.

PROGRAM OBJECTIVES AND 

SAMPLING DESIGN 

The design criteria for the COA monitoring program include: (1) consolidating 

all water-quality moni­toring (stormwater and sanitary sewer) into a single 

consistent pro­gram; (2) determining 

current water-quality conditions for 

evaluating the impact of infrastructural 

improve­ments; (3) locating sources of 

water-quality impairments throughout 

the city; (4) documenting water-quality 

changes in response to infrastructural 

improvements; (5) providing an assessment of long-term water-quality trends; 

and (6) over time, as monitoring data 

accrue, altering the net­work to improve 

effectiveness and limit costs. 

The COA monitoring network consists of 

21 long-term sites. Eleven of these are “fully 

instrumented” to provide real-time data on 

water temperature, pH, specific conductance, dissolved oxygen, tur­bidity (intended

as a surrogate for suspended sediment 

concentration), water level (gage height,

intended as a surrogate for discharge), and 

precipitation. Data are transmitted hourly 

and are available on a public Web site

(http://ga.water.usgs.gov). Two sites only

measure water level and rainfall as an aid to 

stormwater monitoring. The eight remaining sites are used to as­sess water quality.

SAMPLING AND ANALYSES

All the fully instrumented sites (11) are 

equipped to collect stormflow samples 

Measurement Explanation

Stage The water level in a stream; indicates the flow conditions 

(baseflow, flooding).

Discharge The volume of water flowing past a point; can be used to 

determine loads—the amount of sediment or a particular 

chemical transported by the stream.

Water temperature Measured to show the daily and seasonal changes in stream 

temperature; can be elevated in urban streams by runoff from 

sun-heated pavement and roofs, and sewage discharges.

pH A measure of the acidity of stream water; typical streams have 

nearly neutral pH (7.0) but can become elevated (basic) or 

lowered (acidic) due to the presence of contaminants.

Specific conductance A measure of the water’s ability to conduct electricity; the 

conductivity of stream water increases as the quantity of 

dissolved ions increases.

Turbidity A measure of the ability of light to penetrate the water column 

in the stream; this is affected by the presence of some dissolved 

chemicals, but high turbidity usually results from increased 

suspended sediment in streams.

Dissolved oxygen Measured to show the daily and seasonal changes in the level 

of oxygen in a stream— low oxygen levels can have severe ecological impacts and may be indicative of sewage or wastewater.

Continuous measurements recorded and available in real time (hourly) 

on the Web at http://ga.water.usgs.gov

Analysis Sample medium1 Examples

Major ions Filtered water Ions such as sodium, potassium, iron, 

and chloride.

Nutrients Filtered water and

suspended sediment

Compounds containing nitrogen, phosphorus, 

and carbon.

Trace metals Filtered water and

suspended sediment

Metals that occur in small quantities 

such as lead, copper, and zinc.

Bacteria Filtered water Microorganisms that are indicators of 

contaminated water such as fecal coliform 

and Escherichia coli.

Wastewater

tracers2

Filtered water A variety of chemicals that provide an indication of wastewater contamination such as 

food additives, fragrances, antioxidants, flame 

retardants, plasticizers, industrial solvents, 

disinfectants, fecal sterols, polycyclic aromatic 

hydrocarbons, and high-use domestic pesticides.

1

Dissolved constituents are transported in the water; suspended constituents 

typically are associated with the sediment that is transported in the water.

2

Analysis completed during 2005.

Laboratory analyses for the City of Atlanta monitoring program

using programmable autosamplers. These

samples are im­portant because much 

of the sus­pended sediment, sedimentassociated and dissolved chemical transport occurs during storms (Horowitz, 

1995; Peters and Kandell, 1999; Rose and 

Peters, 2001). Further, local rainfall tends 

to be convective; that is, it occurs in the 

late afternoon and evenings when manual 

sampling is logistically difficult. Lastly, 

even though the USGS office is physically 

close to most sampling sites, heavy traffic, 

combined with the rapid response of COA 

streams to rainfall, makes it likely that relying solely on manual sampling could lead 

to the loss of information about the initial 

“flush” from numerous nonpoint sources. 

Collecting samples from the first “flush” 

is important because it may contain substantial amounts of suspended sediment, 

as well as chemical and biological constituents (e.g., Larsen and others, 1999). 

This real-time data-collection ef­fort is 

complemented with a two-part manual 

sampling program. Part one is a pair of 
intensive synoptic (temporal snapshots) surveys; one conducted during high flow and 

one conducted during baseflow. The synoptic surveys encompass 43 sites beyond

those in the long-term net­work. They were 

selected to: (1) increase the resolution of 

the net­work; (2) identify additional sources 

of water-quality impairment that may 

require monitoring; (3) provide a broader 

context for evaluating and interpreting 

long-term water-quality monitoring data; 

and (4) provide additional benchmark data

to evalu­ate the impact of infrastructural 

im­provements. The paired high-flow/

baseflow approach also is indicative of the 

relative impact of point (baseflow) and nonpoint sources (high flow) on water quality.

Part two of the manual sampling program is the collection of nonconvective 

storm and scheduled samples. Standard 

USGS procedures ensure the collection 

of representative sam­ples (e.g., Edwards 

and Glysson, 1999). Each site is sampled 

12 times per year and is intended to cover 

at least 80 percent of the an­nual range of 

water discharges at each long-term site.

The manual sampling program provides 

chemical and biological data that cannot 

be obtained with real-time measuring 

equipment (e.g., trace elements, nutrients, 

bacteria). It also is used to calibrate/

validate the real-time data probes and the 

samples collected by the auto­samplers. 

This is necessary because the sondes and 

autosamplers are at fixed positions in each 

stream cross section; thus, they collect point 

mea­surements/samples that may not be representative. To evaluate this, and to develop 

appropriate correction factors if needed, a 

series of con­current (simultaneous) measurements/samples must be collected over a 

range of flows. Both samples are measured/analyzed for the same constituents 

and compared. When necessary, appropriate 

correction factors are developed so that 

data from the sondes and autosamplers 

are representative (e.g., Horowitz, 1995). 

Past studies indicate that it may take from 

20- to 30-paired measure­ments/samples to 

evaluate the need for, and to develop, correction fact­ors; often, these factors are site 

specific, and differ within the same stream 

(Horowitz, 1995; Christen­sen, 2001).

Most of the sampling and analytical 

procedures are standard. The exceptions 

relate to suspended-sediment sampling 

and analyses for the entire program, 

the low-flow syn­optic survey, and the 

measurement of wastewater tracers in 

both the manual and automatic sampling phases of the program. The COA 

monitoring program determines sediment-associated con­stituents directly on 

dewatered mat­erial. This method tends 

to provide more representative chemical 

data than the standard approach 

(Horo­witz and others, 2001). 

During the low-flow synoptic survey, 

suspended sediment was not collected 

for chemical analyses; in­stead, representative bed-sediment samples were used as 

a surrogate. However, to better represent 

sus­pended sediment, only the less than 

63-micrometer fractions were analyzed 

(e.g., Horo­witz and others, 1999; 

Meybeck and others, 2004).

The COA monitoring program makes 

extensive use of data that fall into a 

class of compounds titled sewage tracers, or organic waste­water contaminants. 

This class represents various chemical 

types (fun­gi­cides, pharmaceuticals, fire 

re­tardants, household chemicals, etc.) that 

have been found in streams near to, as well 

as downstream from, wastewater sources

(Kolpin and others, 2004). These analyses 

are intended to identify wastewater, especially leaking sewer or septic systems.

SCHEDULING

The monitoring program began during 

early 2002. The high- and low-flow synoptic surveys were completed by the end 

of June and August 2003, re­spectively. 

Manual sampling at the long-term monitoring sites began in July–August 2003; 

the first instru­mentally collected stormwater sam­ples also were collected during 

the same period. Currently (2006), both 

types of sample collections are ongoing. 

Based on the synoptic surveys, a fully 

instrumented site was added on Woodall 

Creek in January 2005. 

Calibration and validation of the realtime data sondes and autosamplers began 

with the manual sampling program. Based 

on 12 samples per site, per year, and the 

need for 20 –30 paired samples/measurements over a range of flow conditions, 

calibration/validat­ion, and the development of correct­ion factors, if required, 

could take from 2 to 4 years. Once 

completed, manual sampling will 

decline to a level commensurate with 

Samples are collected during all weather conditions for the City of Atlanta monitoring program. USGS personnel are shown collecting water 

samples at Nancy Creek during floods caused by Hurricane Ivan (2004). Collecting samples during high stream flows is important because as much 

as 90 percent of the material carried by a stream may be transported during floods and high flows. This is readily apparent in most Atlanta area 

streams and rivers because of the increased turbidity (muddiness) of the streams during higher flows. Photographs by Andrew C. Hickey, USGS.
ensuring contin­ued data validity. The 

monitoring program is scheduled to 

continue at least through 2007, when the 

infra­structural improvements are scheduled for completion.

REFERENCES CITED

Atlanta Regional Commission, 2004, 

accessed July 22, 2004, at 

http://www.atlantaregional.com

Christensen, V.G., 2001, Characterization of 

surface-water quality based on real-time 

monitoring and regression analysis, Quivira 

National Wildlife Refuge, south-central 

Kansas, December 1998 through June 2001: 

U.S. Geological Survey Water-Resources 

Investigations Report 01- 4248, 28 p.

Clean Water Atlanta, 2004, accessed August 17, 

2004, at http://www.cleanwateratlanta.org

Driver, N.E., and Troutman, B.M., 1989, 

Regression models for estimat­ing urban 

storm-runoff quality and quantity in the 

United States: Journal of Hydrology 109, 

p. 221–236.

Edwards, T.K, and Glysson, G.D., 1999, Field 

methods for measurement of fluvial sediment: U. S. Geological Survey Techniques 

of Water-Resources Investigations, book 3, 

chap. C2: 118 p.

Ellis, J.B. (ed.), 1999, Impacts of urban 

growth on surface water and groundwater qua­lity: International Association 

of Hydrological Sciences (IAHS) 

Publication No. 259, 437 p.

Horowitz, A.J., 1995, The use of suspended 

sediment and associated trace elements in 

water quality studies: Wallingford, United 

Kingdom, IAHS Special Publication No. 4, 

IAHS Press, 58 p.

Horowitz, A.J., Elrick, K.A., and Smith, J.J., 

2001, Estimating suspend­ed sediment and 

trace element fluxes in large river basins: 

methodological consider­at­ions as applied 

to the NASQAN program: Hydro­logical 

Processes 15, p. 1,107–1,132.

Horowitz, A.J., Meybeck, Michel, Idlafkih, 

Zayed, and Biger, Erwan, 1999, Variations 

in trace element geochemistry in the Seine 

River Basin based on floodplain deposits 

and bed sediments: Hydrological Processes 

13, p. 1,329 –1,340.

Kolpin, D.W., Skopec, M.P., Meyer, M.T., 

Furlong, E.T., and Zaugg, S.D., 2004, Urban 

contribution of pharmaceuticals and other 

organic wastewater contami­n­ants to streams 

during differ­ing flow conditions: The Science 

of the Total Environ­ment 328, p. 119 –130.

Larsen, Torben, Broch, Kristen, and 

Andersen, M.R., 1999, First flush effects 

in urban catchment area in Aalborg, Water 

Science and Technology 37, p. 251–257.

Meybeck, Michel, Horowitz, A.J., and 

Grosbois, C.A., 2004, The geochemistry 

of Seine River Basin particulate matter: 

distribution of an integrated metal pollution 

index: The Science of the Total Environment 328, p. 219 – 236.

Peters, N.E., and Kandell, S.J., 1999, Evaluation of stream water quality in Atlanta, 

Georgia and the surrounding region, in

Ellis, J.B. (ed.), Impacts of urban growth 

on surface water and groundwater quality: 

IAHS Publication No. 259, p. 279 –290.

Rose, Seth, and Peters, N.E., 2001, Effects of 

urbanization on streamflow in the Atlanta 

area (Georgia, USA): a com­parative hydrological approach: Hydro­log­ical Processes 

15, p. 1,441–1,457.

U.S. District Court, North­ern District of 

Georgia, Atlanta Division, 1998, Civil 

Action File No. 1:95-CV-2550-TWT. 

State-of-the-art equipment, such as this acoustic Doppler profiler, 

is used to measure streamflows. These instruments use sophisticated electronics to determine the speed of the water and to 

measure the cross section of the stream channel. Photograph 

by Andrew C. Hickey, USGS.

Eleven of the 21 sites for the City of Atlanta monitoring program, 

such as this one at Woodall Creek, are equipped with streamflow 

and water-quality instruments that collect and transmit data via 

a satellite linkup. These data are updated several times a day and 

displayed on the USGS Web site at http://ga.water.usgs.gov. 

Photograph by Andrew C. Hickey, USGS.

By Arthur J. Horowitz and W. Brian Hughes

Design and layout by Caryl J. Wipperfurth

For more information contact:

Urban Hydrology Chief

3039 Amwiler Road Suite 130

Atlanta, Georgia 30360

770-903-9162

Or visit the following Web sites:

http://ga2.er.usgs.gov/urban/atlanta

http://ga.water.usgs.gov

http://www.usgs.gov

http://www.cleanwateratlanta.org

http://www.atlantaga.gov

U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

The City of Atlanta monitoring program 

is overseen by a Technical Advisory 

Committee (TAC) that meets quarterly to 

review project plans and progress. The 

TAC includes representatives from the 

following organizations:

Upper Chattahoochee Riverkeeper—

Chair, Sally Bethea

U.S. Environmental Protection Agency

Georgia Environmental Protection Division

Cobb County–Marietta Water Authority

Gwinnett County Department of 

Public Utilities

Georgia Institute of Technology

The University of Georgia

Georgia State University