Ground-Water Flow
Study in the Vicinity of the Savannah River Site, South Carolina and Georgia
Many regions of the United States are planning for increased
water-supply demands as a result of population and industrial growth.
Ground water often is the most practical source of new water supply
because of its general good quality and availability near the source
of need. However, ground water is vulnerable to contamination and,
once contaminated, presents near insoluble remediation problems.
Thus, many communities are justifiably concerned about maintaining the
good quality of their ground-water reservoirs. One area of such
concern is along the South Carolina-Georgia state line in the vicinity
of the U.S. Department of Energy, Savannah River Site
(SRS).
INTRODUCTION
The U.S. Department of Energy (DOE), Savannah River Site (SRS)
(fig. 1) has manufactured nuclear materials for the National defense
since the early 1950's. A variety of hazardous materials, including
radionuclides, volatile organic compounds, and trace metals, are
either disposed of or stored at several locations at the SRS.
Figure 1. Location of study area and test sites.
Ground water originating in the vicinity of the SRS is
thought to flow westward and discharge to the Savannah River. However,
ground-water flowpaths in the vicinity of the Savannah River are
poorly understood and need to be defined to determine the potential
for contaminated ground water to migrate from the SRS, beneath the
Savannah River, into Georgia. Contamination of ground water has been
detected at several locations within the site (fig. 2).
Figure 2. Areal and local ground-water contamination sites
at the Savannah River Site. Modified from Westinghouse Savannah
River Company, 1994.
A and M areas--chlorinated volatile organics, radionuclides, metals,
nitrate
C, K, L, and P areas--tritium, other radionuclides, metals, chlorinated
volatile organics
D area--metals, radionuclides, sulfate, chlorinated volatile organics
R area--radionuclides, cadmium
Sanitary landfill--chlorinated volatile organics, radionuclides, metals
Separations and waste-management areas--tritium, other radionuclides,
metals, nitrate, chlorinated volatile organics, sulfate
TNX area--chlorinated volatile organics, radionuclides, pesticides, nitrate
Two issues raised concerning the possible migration of contaminated
ground water offsite from the SRS are:
- Is ground water flowing from the SRS through aquifers in South
Carolina and beneath the Savannah River into Georgia (herein called
trans-river flow)?
- Under what pumping scenarios could such ground-water movement occur?
Description of Study Area
The study area covers 4,592 square miles (mi² )
in the northern part of the Coastal Plain of Georgia and South
Carolina (fig. 1). The SRS covers about 300 mi² , or 7
percent of the study area (fig. 2). The northern limit of the study
area and boundary between the Coastal Plain and Piedmont is marked by
the Fall Line. Coastal Plain sedimentary rocks consist of alternating
layers of sand, clay, and lesser amounts of limestone that
progressively thicken from the Fall Line to the southeast, reaching an
estimated thickness of 2,700 ft in the southern part of the study
area. These rocks comprise highly permeable water-bearing units
through which ground water readily flows (aquifers), and low
permeability confining units that restrict the flow of ground
water.
Silvaculture and agriculture are the predominant land uses in the
study area where pine timber, cotton, and soybeans are major crops.
Kaolin is mined in parts of the study area. The largest cities in the
study area are Augusta, Ga.--population 44, 639; and Aiken,
S.C.--population 19,872 in 1990 (U.S. Department of Census, 1991).
Trans-River Flow
Trans-river flow is a term that describes a condition whereby ground
water originating on one side of a river migrates beneath the river
floodplain to discharge points located on the other side of the river.
Natural factors controlling the potential for trans-river flow include
(1) water-bearing properties of aquifers and confining units; (2)
thickness and areal extent of confining units; and (3) hydraulic
gradient.
The Savannah River acts as a hydrologic "sink" into which ground water
from surrounding and underlying aquifers discharge (fig. 3). This
sink is thought to have formed as the river eroded through the
uppermost confining units and was subsequently filled with permeable
alluvium. It is possible, however, that some ground water can flow
beneath the river to the opposite side of the river from its point of
origin in response to natural or human-induced hydraulic
gradients.
Figure 3. Possible ground-water flow conditions beneath Savannah River.
SRS GROUND-WATER STUDY
Because of the highly complex nature of ground-water flow in the SRS
region, the DOE in 1991 requested that the U.S. Geological Survey
(USGS) conduct a study to define ground-water flow and stream-aquifer
relations in the Savannah River basin in the vicinity of SRS. Other
participants in the 6-year study include the Georgia Department of
Natural Resources, Clemson University, and the University of
Georgia. A committee consisting of representatives from SRS and
Georgia and South Carolina State agencies provides technical oversite.
The major objective of the study is to quantitatively describe
ground-water flow in the vicinity of the SRS and the Savannah River,
including evaluation of stream-aquifer relations, to determine whether
trans-river flow is occurring. Effects of selected hypothetical
pumping scenarios on the potential for trans-river flow also are being
evaluated. The study is being implemented in two phases.
Phase I
Phase I of the study, completed in
1994, defined the geologic, hydrologic, and water-quality conditions
in the SRS area through field investigations, test drilling, data
analysis, and ground-water flow modeling (Clarke 1992). Elements of
phase I included
- drilling 18 test wells at five cluster
sites on the Georgia side
of the Savannah River to define geology, hydrologic, and water-quality
conditions;
- analyzing geologic data from 5 test and 110 existing well sites
to determine the depth, thickness, and areal extent of seven aquifers
and six confining units beneath the SRS and the Savannah River;
- analyzing geologic data from 18 shallow borings drilled in the
flood plain to determine how deeply the ancient Savannah River has cut
into underlying aquifers;
- conducting aquifer tests in 14 test and 14 existing wells to
determine water-bearing properties of aquifers;
- sampling water from 14 test and 2 existing wells to determine
chemical quality of ground water;
- installing continuous water-level monitors in 16 test and 2
existing wells to monitor ground-water levels;
- constructing maps showing ground-water levels and flow
directions in major aquifers for prepumping (pre-1953) and modern-day
(1992) conditions;
- developing a geographic information system (GIS) data base for
more than 4,000 wells and linking the GIS to a ground-water flow
model; and
- developing a ground-water flow model to simulate prepumping
conditions in seven aquifers.
Water Quality
Analysis of water sampled from 14 test wells and 2 existing municipal
wells indicate that the water is within the U.S. Environmental
Protection Agency (USEPA) primary drinking-water standards (1993)
having no detectable concentrations of contaminants in the deeply
buried aquifers. Concentrations of tritium below the USEPA maximum
contaminant level of 20,000 parts per liter (U.S. Environmental
Protection Agency, 1993) were detected in one 100-foot deep well in
northern Burke County, Ga. (Clarke and others, 1994). The source and
extent of tritium concentrations in shallow ground water in Georgia
were reported by Summerour and others (1994).
Phase II
During phase II, a more focused site-specific data collection program
near the Savannah River will be implemented using geologic and
water-quality data from phase I. Based on data and flow-model
simulations conducted during phase I, the area having the greatest
potential for trans-river flow is near the Burke-Screven County, Ga.,
line south of the SRS. To provide better definition of ground-water
flow conditions in this area, several wells are planned at a cluster
site during phase II. Calibration of the ground-water flow model from
prepumping to modern-day (1992) conditions is to be completed. Model
simulation of hypothetical pumping scenarios that might induce
trans-river flow are planned. Upon completion of phase II, a
long-term network is planned to monitor ground-water levels and
water-quality data near the Savannah River.
For information on SRS project findings, reports and abstracts
prepared by project staff are listed on this page.
REFERENCES
Clarke, J.S., 1992, Evaluation of ground-water flow and
quality in the vicinity of the Savannah River Site, Georgia and South
Carolina in Abstracts with Programs, Southeastern Section: Boulder,
Co., The Geological Society of America, v. 24, no. 4,
p. 47.
Clarke, J.S., Falls, W.F., Edwards, L.E., Fredricksen, N.O.,
Bybell, L.M., Gibson, T.G., and Litwin, R.J., 1994, Geologic,
hydrolo-gic, and water-quality data for a multi-aquifer system in
Coastal Plain sediments near Millers Pond, Burke County, Georgia:
Georgia Geologic Survey Information Circular 96, 34 p.
Summerour, J.H., Shapiro, E.A., Lineback, J.A., Huddlestun,
P.F., and Hughes, A.C., 1994, An investigation of tritium in the
Gordon and other aquifers in Burke County, Georgia---Final Report,
Georgia Geologic Survey Information Circular 95, 93 p.
U.S. Bureau of the Census, 1991, Census data---Georgia and
South Carolina in Census of Population and Housing, 1990 [machine
readable data files]: Washington, D.C., U.S. Department of the
Census, Public Law (P.L.) 94-171
U.S. Environmental Protection Agency, 1993, Maximum
contaminant levels (subpart B of part 141, National primary
drinking-water regulations): U.S. Code of Federal Regulations, Title
40, parts 100 to 149, revised July 1, 1993,
p. 600.
Westinghouse Savannah River Company, 1994, Savannah River
Site environmental report for 1993: Westinghouse Savannah River
Company, Aiken, S.C., WSRC-TR-94-075, prepared for
U.S. Department of Energy, contract no. DE-AC09-89SR18035, variously
paged.
For more information, please contact
- District Chief
- U.S. Geological Survey
- 3039 Amwiler Road Suite 130
- Atlanta, Georgia 30362
- (404) 903-9100
Additional earth science information can be found by accessing the
USGS Home Page on the World Wide Web at
http://www.usgs.gov or the USGS, Georgia Water Resources
Home Page at http://ga.water.usgs.gov, or by
calling 1-800-426-9000.
Ground-water flow study in the vicinity of the Savannah River Site,
South Carolina and Georgia by John S. Clarke
U.S. Department of Interior
U.S. Geological Survey
Fact Sheet FS-178-95
August 1995
The URL for this page is
<http://ga.water.usgs.gov/publications/fs178_95/fs178_95.html>.