U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007-1363

Prepared in cooperation with the U.S. Nuclear Regulatory Commission

Simulation and Particle-Tracking Analysis of

Selected Ground-Water Pumping Scenarios at

Vogtle Electric Generation Plant,

Burke County, Georgia
Cover photograph: Vogtle Electric Generation Plant cooling towers, Burke County, Georgia

Photograph by Alan M. Cressler, U.S. Geological Survey
Simulation and Particle-Tracking Analysis of 

Selected Ground-Water Pumping Scenarios at 

Vogtle Electric Generation Plant, 

Burke County, Georgia

By Gregory S. Cherry and John S. Clarke

Prepared in cooperation with the U.S. Nuclear Regulatory Commission

Open-File Report 2007–1363

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Cherry, G.S., and Clarke, J.S., 2007, Simulation and particle-tracking analysis of selected ground-water pumping scenarios 

at Vogtle Electric Generation Plant, Burke County, Georgia: U.S. Geological Survey Open-File Report 2007-1363, 51 p.,

Web-only publication at http://pubs.usgs.gov/usgspubs/of/2007/1363
Contents

Abstract...................................................................................................................................................... 1

Introduction................................................................................................................................................ 1

Purpose and Scope ......................................................................................................................... 1

Description of Study Area .............................................................................................................. 4

Savannah River Site and Ground-Water Contamination................................................. 4

Climate and Runoff ................................................................................................................ 4

Hydrogeologic Setting .......................................................................................................... 5

Structural Features....................................................................................................... 6

Hydrogeologic Characteristics of the Savannah River Alluvial Valley ................ 6

Ground-Water Flow............................................................................................................... 

Trans-River Flow ........................................................................................................... 13

Effect of Pen Branch Fault .......................................................................................... 13

Ground-Water Use................................................................................................................. 13

Simulation of Ground-Water Flow.......................................................................................................... 14

Pen Branch Fault.............................................................................................................................. 16

Ground-Water Pumping Scenarios............................................................................................... 17

2002 Base Case Condition .................................................................................................... 18

Scenario A............................................................................................................................... 20

Scenario B............................................................................................................................... 20

Scenario C............................................................................................................................... 35

Model Limitations............................................................................................................................. 43

Summary and Conclusions...................................................................................................................... 43

References Cited....................................................................................................................................... 44

iii
Figures

1. Maps showing �A) study area, model grid, and model boundary, (B) location of 

Vogtle Electric Generation Plant production wells, Burke County, Georgia, and 

river and recharge cells in the Gordon aquifer (layer A2) and areal and local 

ground-water contamination at the Savannah River Site, South Carolina.................. 2

2. Schematic diagram showing hydrogeologic framework, model layers, and 

boundary conditions for the Vogtle Electric Generation Plant area, South 

Carolina, ground-water model............................................................................................. 5

3. Map showing subsurface extent of hydrogeologic units beneath the Savannah 

River alluvial valley, South Carolina and Georgia............................................................. 7

4. Diagram of conceptualized hydrogeologic framework and related ground-water 

flow near Vogtle Electric Generation Plant, Georgia and South Carolina ................... 8

5–8. Maps showing potentiometric surface, near Vogtle Electric Generation Plant, 

Georgia and South Carolina, September 2002, for the—

5. Upper Three Runs aquifer........................................................................................... 9

6. Gordon aquifer.............................................................................................................. 10

7. Dublin aquifer system .................................................................................................. 11

8. Midville aquifer system................................................................................................ 12

9. Map showing particle-tracking results for the year 2002, Base Case, near 

Vogtle Electric Generation Plant, Georgia and South Carolina ..................................... 19

10–15. Maps showing simulated water-level change for Scenario A, near Vogtle 

Electric Generation Plant, Georgia and South Carolina, in the—

10. Gordon aquifer.............................................................................................................. 21

11. Millers Pond aquifer..................................................................................................... 22

12. Upper Dublin aquifer.................................................................................................... 23

13. Lower Dublin aquifer.................................................................................................... 24

14. Upper Midville aquifer................................................................................................. 25

15. Lower Midville aquifer................................................................................................. 26

16. Map showing particle-tracking results for the year 2002, Scenario A, near 

Vogtle Electric Generation Plant, Georgia and South Carolina ..................................... 27

17–22. Maps showing simulated water-level change for Scenario B, near Vogtle 

Electric Generation Plant, Georgia and South Carolina, in the—

17. Gordon aquifer.............................................................................................................. 28

18. Millers Pond aquifer.................................................................................................... 29

19. Upper Dublin aquifer.................................................................................................... 30

20. Lower Dublin aquifer.................................................................................................... 31

21. Upper Midville aquifer................................................................................................. 32

22. Lower Midville aquifer................................................................................................. 33

23. Map showing particle-tracking results for the year 2002, Scenario B, study 

area, near Vogtle Electric Generation Plant, Georgia and South Carolina.................. 34

iv
Figures—Continued

24–29. Maps showing simulated water-level change for Scenario C, near Vogtle 

Electric Generation Plant, Georgia and South Carolina, in the—

24. Gordon aquifer.............................................................................................................. 36

25. Millers Pond aquifer..................................................................................................... 37

26. Upper Dublin aquifer.................................................................................................... 38

27. Lower Dublin aquifer.................................................................................................... 39

28. Upper Midville aquifer................................................................................................. 40

29. Lower Midville aquifer ................................................................................................. 41

30. Map showing particle-tracking results for the year 2002, Scenario C, near 

Vogtle Electric Generation Plant, Georgia and South Carolina..................................... 42

Tables

1. Ground-water use during 2000–2002 near Vogtle Electric Generation Plant, 

Burke County, Georgia.......................................................................................................... 13

2. Location and construction information for production wells at Vogtle Electric 

Generation Plant, Burke County, Georgia.......................................................................... 14

3. Simulated and estimated values for transmissivity, Vogtle Electric Generation 

Plant model, Georgia and South Carolina.......................................................................... 15

4. Simulated and estimated values for leakance, Vogtle Electric Generation 

Plant model, Georgia and South Carolina.......................................................................... 15

5. Simulated pumpage by model layer for 2002 Base Case, Vogtle Electric 

Generation Plant model, Georgia and South Carolina............................................................ 16

6. Simulated pumpage at Vogtle Electric Generation Plant, Burke County, 

Georgia, for 2002 Base Case and pumping Scenarios A, B, and C................................ 18

7. Summary of simulated time of travel for 2002 Base Case and for Scenarios A, 

B, and C, Vogtle Electric Generation Plant model, Georgia and South Carolina ........ 18
Conversion Factors and Datums

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

million gallons (Mgal) 3,785 cubic meter (m3)

Flow rate

gallon per minute (gal/min) 0.06309 liter per second (L/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83)

Altitude, as used in this report, refers to distance above the vertical datum.

Concentrations of chemical constituents in water are given in micrograms per liter (μg/L).

vi
Abstract

The source of ground water to production wells at Vogtle 

Electric Generation Plant (VEGP), a nuclear power plant in 

Burke County, Georgia, was simulated under existing (2002) 

and potential future pumping conditions using an existing 

U.S. Geological Survey (USGS) MODFLOW ground-water 

flow model of a 4,455-square-mile area in the Coastal Plain 

of Georgia and South Carolina. Simulation results for three 

steady-state pumping scenarios were compared to each other 

and to a 2002 Base Case condition. The pumping scenarios 

focused on pumping increases at VEGP resulting from projected future demands and the addition of two electricalgenerating reactor units. Scenarios simulated pumping 

increases at VEGP ranging from 1.09 to 3.42 million gallons 

per day (Mgal/d), with one of the scenarios simulating the 

elimination of 5.3 Mgal/d of pumping at the Savannah River 

Site (SRS), a U.S. Department of Energy facility located 

across the Savannah River from VEGP. The largest simulated 

water-level changes at VEGP were for the scenario whereby 

pumping at the facility was more than tripled, resulting in 

drawdown exceeding 4–8 feet (ft) in the aquifers screened in 

the production wells. For the scenario that eliminated pumping 

at SRS, water-level rises of as much as 4–8 ft were simulated 

in the same aquifers at SRS.

Results of MODFLOW simulations were analyzed using 

the USGS particle-tracking code MODPATH to determine the 

source of water and associated time of travel to VEGP production wells. For each of the scenarios, most of the recharge to 

VEGP wells originated in an upland area near the county line 

between Burke and Jefferson Counties, Georgia, with none 

of the recharge originating on SRS or elsewhere in South 

Carolina. An exception occurs for the scenario whereby pumping at VEGP was more than tripled. For this scenario, some 

of the recharge originates in an upland area in eastern Barnwell County, South Carolina. Simulated mean time of travel 

from recharge areas to VEGP wells for the Base Case and the 

three other pumping scenarios was between about 2,700 and 

3,800 years, with some variation related to changes in head 

gradients because of pumping changes. 

Introduction

The Vogtle Electric Generation Plant (VEGP), near 

Waynesboro, Burke County, Georgia, is one of Southern Company’s two nuclear-generating facilities in Georgia (fig. 1). 

On August 15, 2006, Southern Nuclear Company applied to 

the U.S. Nuclear Regulatory Commission (NRC) for an early 

site permit (ESP) for an additional two reactors at the site. As 

part of the ESP permitting process, the NRC is charged with 

development of an environmental impact statement (EIS) 

to evaluate the effects of both construction and operation of 

these new reactors on the site and surrounding area. The EIS 

must describe the magnitude and nature of expected effects 

on ground water resulting from present and potential future 

ground-water withdrawal. The assessment should include the 

area of VEGP and extend for distances great enough to cover 

potentially affected aquifers, including those located within 

the boundary of the U.S. Department of Energy, Savannah 

River Site (SRS), located in South Carolina across the Savannah River from VEGP (fig. 1A, 1B). 

The addition of two new reactors (Units 3 and 4) at 

VEGP will require an increase in pumping from the lower 

Dublin and upper and lower Midville aquifers, which currently provide the water needed for reactor Units 1 and 2. 

NRC would like to evaluate the effects of additional pumpage on ground-water flow in the surrounding area. To help 

evaluate these effects, and improve understanding of regional 

ground-water flow in the area, the U.S. Geological Survey 

(USGS)—in cooperation with NRC—conducted a study using 

an existing ground-water flow model to simulate the source of 

ground water to VEGP production wells under current (2002) 

and potential future pumping conditions. 

Purpose and Scope

This report describes the effect of current (2002) and potential future pumping on ground-water levels and flowpaths 

near VEGP for three pumping scenarios using an existing groundwater flow model (Clarke and West, 1998; Cherry, 2006) of a 

4,455-square-mile (mi2) area near Augusta, Ga. (fig. 1A).

Simulation and Particle-Tracking Analysis of 

Selected Ground-Water Pumping Scenarios at 

Vogtle Electric Generation Plant, 

Burke County, Georgia

By Gregory S. Cherry and John S. Clarke
P-19

well

cluster

AIKEN

ALLENDALE

SCREVEN

JENKINS

BURKE

RICHMOND

SOUTH

CAROLINA

GEORGIA

GLASCOCK

WARREN

McDUFFIE

COLUMBIA

SALUDA

EDGEFIELD

Line

BARNWELL

Brier

Fall

JEFFERSON

 82°30'

33°30'

33°

 82° 81°30'

32°30'

D

U

D U

Belair

Fault

Pen

Branch

Fault

Base modified from U.S. Geological Survey 

State base maps

A.

Model boundary

D

U Fault—Approximately located; 

 D, downthrown side; U, upthrown side

EXPLANATION

0

0 10 20 30 KILOMETERS

10 20 30 MILES

Area of map in figure 1B

Aiken

Augusta

Savannah River Site

River

Savannah

Creek

Georgia South

Carolina

Atlantic Ocean

Study area

Fall Line

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

MODEL GRID

10

20 30 40 50 60 70 80

90

100

102

Figure 1. (A) Study area, model grid, and model boundary, (B) location of Vogtle Electric 

Generation Plant production wells, Burke County, Georgia, and river and recharge cells in the 

Gordon aquifer (layer A2) (modified from Clarke and West, 1997) and areal and local 

ground-water contamination at the Savannah River Site, South Carolina (modified from 

Arnett and Mamatey, 1996; Cherry, 2006).

Vogtle Electric

Generation Plant

Figure 1.  (A) Study area, model grid, and model boundary, (B) location of Vogtle Electric Generation Plant

production wells, Burke County, Georgia, and river and recharge cells in the Gordon aquifer (layer A2)

(modified from Clarke and West, 1997) and areal and local ground-water contamination at the Savannah River

Site, South Carolina (modified from Arnett and Mamatey, 1996; Cherry, 2006).

 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
L

Lake

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Eagle

Point

GEORGIA

SOUTH

CAROLINA

D

U Fault—Approximately located; 

 D, downthrown side; U, upthrown side

Simulated recharge cell

Plant Vogtle production well

 and identification number

Simulated river cell

Localized contamination

Contaminated sites

Areal contamination

EXPLANATION

0 1 2 3 4

0 1 2 3 4 5 KILOMETERS

5 MILES

D

U

B.

Figure 1. (A) Study area, model grid, and model boundary, (B) location of Vogtle Electric 

Generation Plant production wells, Burke County, Georgia, and river and recharge cells in the 

Gordon aquifer (layer A2) (modified from Clarke and West, 1998b) and areal and local 

ground-water contamination at the Savannah River Site, South Carolina (modified from 

Arnett and Mamatey, 1996; Cherry, 2006).—Continued

31Z080

31Z002

31Z003

31Z003

Savannah River Site

Pen

Branch

Fault

R Area—

radionuclides,

cadmium

 A/M Area—

chlorinated

volatile organics

radionuclides,

metals ,

nitrate

D Area—chlorinated

volatile organics, radionuclides, metals, sulfate

TNX Area—

chlorinated volatile

organics,

radionuclides,

pesticides, nitrate

Sanitary landfill—

chlorinated volatile

organics, radionuclides, metals

C, K, L and P Areas—

chlorinated volatile organics, 

tritium, other radionuclides, 

metals

Separations and WasteManagement Area 

chlorinated volatile organics,

tritium, other radionuclides,

 metals, sulfate, nitrate

• P-19

well

cluster

Pen Branch

Meyers

Branch

Steel Creek

Tinker Creek

Lower

Three

Runs

Creek

Newberry Creek

McBean

Creek

Branch

Par

Pond

Hollow

Creek

Savannah River

Fourmile

Upper Three Runs Creek

81°50' 81°40' 81°30'

33°10'

33°00'

Vogtle Electric

Generation Plant

Figure 1. (A) Study area, model grid, and model boundary, (B) location of Vogtle Electric 

Generation Plant production wells, Burke County, Georgia, and river and recharge cells in the 

Gordon aquifer (layer A2) (modified from Clarke and West, 1997) and areal and local groundwater contamination at the Savannah River Site, South Carolina (modified from Arnett and 

Mamatey, 1996; Cherry, 2006).—Continued

Introduction 
Simulated water levels were compared to a Base Case representing 2002 pumping rates throughout the model area. 

A particle-tracking analysis was conducted for each scenario 

to determine the source of water for VEGP production wells. 

For each scenario, the pumping distribution, simulated waterlevel changes, and ground-water flowpaths are described 

relative to the Base Case. Limitations of the model analysis 

also are provided.

Description of Study Area

The study area is in the northern part of the southeastern 

Coastal Plain physiographic province (Clark and Zisa, 1976) 

of Georgia and South Carolina (fig. 1A). The Fall Line marks 

the boundary between Coastal Plain sediments and crystalline 

rocks of the Piedmont physiographic province and forms the 

approximate northern limit of the study area. Topographic 

relief generally is greatest near the Fall Line, becoming progressively less toward the south and east. Altitudes range from 

as high as 650 feet (ft) near the Fall Line to less than 100 ft in 

the southern part of the study area and in the valleys of major 

streams, such as the Savannah River or Brier Creek. A steep 

bluff is present along the western bank of the Savannah River 

in southern Richmond County and most of Burke County, Ga. 

Relief along the Savannah River bluff is as much as 160 ft 

from the top of the bluff to the valley floor.

The Coastal Plain province is well to moderately dissected by streams and has a well-developed dendritic drainage 

pattern. Streams that flow over the relatively soft Coastal Plain 

sediments develop wider floodplains and greater mean­der 

frequency than streams that flow over hard crystalline rocks of 

the Piedmont (Clark and Zisa, 1976). Most of the floodplain 

near the principal rivers, such as the Savannah River, has a 

wide expanse of swamp bordering both sides of the channel.

Forestry and agriculture are the predominant land uses 

in the study area; major crops are pine timber, cotton, and 

soybeans. Kaolin is mined in parts of the study area. The 

largest cities in the study area are Augusta, Ga., with a 

population of 194,950 during 2000; and Aiken, S.C., with a 

population of 25,460 during 2000 (U.S. Bureau of the Census, 

accessed February 3, 2003, at http://www.census.gov/). 

Savannah River Site and 

Ground-Water Contamination

The SRS encompasses a 310-mi2 area across the Savannah 

River from VEGP in parts of Aiken, Barn­well, and Allen­dale 

Counties, S.C. (fig. 1A, 1B). The facility has manufactured 

nuclear materials for national defense since the early 1950s. A 

variety of hazardous materials—including radionuclides, volatile organic compounds, and heavy metals—are either disposed 

of or stored at several locations at SRS. Contamination of 

ground water has been detected at several locations on the site 

(fig. 1B) with contamination mostly limited to the Upper Three 

Runs aquifer. The potential for movement of contaminated 

water into aquifers beneath the Upper Three Runs aquifer at 

SRS is dependent on the hydraulic con­ductivity of intervening confining units and the magnitude of downward hydraulic 

gradient (see Ground-Water Flow section). 

The only documented occurrence of ground-water 

contaminants into aquifers beneath the Upper Three Runs 

that the authors are aware of occurred in the vicinity of the 

A/M Area on SRS (see location, fig. 1B). In this area, Christensen and Gordon (1983) reported volatile organic compounds were detected at depths as great as 480 ft, affecting 

water-bearing zones in the “Congaree Formation” (Gordon 

aquifer) and “Tuscaloosa Formation” (lower Dublin aquifer). 

Contamination in the Congaree Formation was attributed to 

the discontinuity of the “green clay” that forms the confining 

unit beneath the Upper Three Runs aquifer. Contamination of 

the Tuscaloosa Formation was attributed to a poor grout seal 

in well 53A, which enabled downward migration of contaminated ground water into deeper zones. During the first half of 

2007, Washington Savannah River Company (2007) reported 

concentrations of trichloroethylene in the A/M Area of as high 

as 18,000 micrograms per liter (μg/L) in the composite “Lost 

Lake aquifer zone” (Gordon aquifer) and as high as 3,200 μg/L 

in the “Crouch Branch aquifer” (upper and lower Dublin 

aquifers). Contaminants in both aquifers occur in southwesttrending plumes with concentrations exceeding 5 μg/L across a 

distance of nearly 21,000 ft in the Lost Lake aquifer zone, and 

nearly 15,000 ft in the Crouch Branch aquifer. Contaminants 

in the source areas are being removed using recovery wells 

and above-ground air strippers (Washington Savannah River 

Company, 2007).

Climate and Runoff

A relatively mild climate with warm, humid summers 

and mild winters characterizes the study area. Precipitation 

is highest during the winter months when continental storm 

fronts move through the region and during July and August 

when afternoon thunderstorms caused by daytime heating are 

common. Average annual precipitation in the study area for 

the period 1969–98, ranged from about 46 inches in Burke 

County, Ga., to greater than 52 inches in central Aiken County, 

S.C. (Southeast Regional Climate Center, accessed February 11, 2004, at http://www.dnr.sc.gov/climate/sercc/).

The Savannah River is the major surface-water feature in 

the study area and is the boundary between Georgia and South 

Carolina. The river drains an area of about 10,580 mi2

(1,140 mi2 in the study area) and empties into the Atlantic 

Ocean near Savannah, Ga. During 1941–70, the aver­age 

annual runoff in Georgia ranged from less than 0.9 cubic feet 

per second per square mile [(ft3/s)/mi2] of drainage area in 

southern Screven, Jenkins, Burke, and Jefferson Counties, and 

in northern Richmond and Jefferson Counties, to greater than 

1.1 (ft3/s)/mi2 in eastern Richmond and Burke Counties (Faye 

and Mayer, 1990).

 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
Hydrogeologic Setting

Coastal Plain sedimentary strata in the study area consist 

of layers of sand, clay, and limestone, which range in age from 

Upper Cretaceous through post-Eocene (fig. 2). The Fall Line 

(fig. 1A) marks the approximate inner margin of Coastal Plain 

sediments. The strata dip and progressively thicken from the 

Fall Line to the southeast, with an estimated thickness of 

2,700 ft in the southern part of the study area (Wait and Davis, 

1986). The strata crop out in discontinuous belts that generally 

are parallel to the Fall Line. The sedimentary sequence unconformably overlies Paleozoic igneous and metamorphic rocks, and 

consolidated Mesozoic red beds (Chowns and Williams, 1983) 

Coastal Plain sediments comprise three principal aquifer 

systems near VEGP. In descending order, these aquifer systems 

are (1) the Floridan aquifer system, originally defined by Miller 

(1986) and later redefined by Aadland and others (1995)—

comprised largely of Eocene calcareous sand and limestone; 

(2) the Dublin aquifer system (Clarke and others, 1985)—comprised of Paleocene and Late Cretaceous sand; and (3) the Midville aquifer system (Clarke and others, 1985)—comprised of 

Late Cretaceous sand. Although this subdivision was suitable 

for most regional-scale hydrogeologic studies, greater subdivision of units was required to define vertical hydraulic heterogeneity for detailed investigations of ground-water flow near the 

Savannah River. Accordingly, the three aquifer systems were 

divided into seven aquifers (fig. 2):

the Floridan aquifer system was subdivided into 

the Upper Three Runs aquifer and the Gordon 

aquifer (Aadland and others, 1995);

the Dublin aquifer system was subdivided into the 

Millers Pond aquifer, the upper Dublin aquifer and 

the lower Dublin aquifer (Falls and others, 1997); and

the Midville aquifer system was subdivided into 

the upper Midville aquifer and the lower Midville 

aquifer (Falls and others, 1997).

The aquifers are separated and confined by layers of clay 

and silt, which become progressively sandy and discontinuous 

in updip areas. The aquifer systems coalesce where the confining units become sandy. See Falls and others (1997) for a 

complete description of geologic and hydrogeologic units in 

the study area.

•

•

•

HYDROGEOLOGIC REPRESENTATION

MODEL REPRESENTATION

Land surface

Confining unit

pinchout

Aquifer

pinchout

Upper Three Runs aquifer

Gordon aquifer

Millers Pond aquifer

Upper Dublin aquifer

Lower Dublin aquifer

Upper Midville aquifer

Lower Midville aquifer

Aquifer outcrop

Fall

line

A1

C1

C2

C3

C4

C5

C6

(Upper Three Runs aquifer)

(Gordon aquifer)

(Millers Pond aquifer)

(Upper Dublin aquifer)

(Lower Dublin aquifer)

(Lower Midville aquifer)

(Upper Midville aquifer)

A2

A3

A4

A5

A6

A7

Savannah River

NorthwestSoutheast

Midville

aquifer

system

Dublin

Upper

Midville CU

Millers Pond CU

aquifer

system

Floridan

aquifer

system

PE Eocene Paleocene Upper Cretaceous

Cretaceous Tertiary

Series

System

Hydrologic

unit

Figure 2. Schematic diagram showing hydrogeologic framework, model layers, and boundary 

conditions for the Vogtle Electric Generation Plant area, South Carolina, ground-water model 

(modified from Clarke and West, 1998; Cherry, 2006).

A1, C1

Hydrogeologic representation

Model representation

Model layer

Aquifer

Stream alluvium

EXPLANATION

Source-sink

 specified head

Active model cells

River cells

Aquifer pinchout—

 Represented as zone 

 of low transmissivity

Cells receiving recharge

Confining unit—

 Represented as vertical 

 conductance term

Confining unit pinchout—

 Represented as zone of 

 high vertical conductance

Riverbed conductance

Lateral specified 

 head boundary

No-flow boundary

Confining unit (CU)

Post-Eocene

Basal confining unit

 and basement rock

 PE

Figure 2. Schematic diagram showing hydrogeologic framework, model layers, and boundary conditions for the Vogtle 

Electric Generation Plant area, South Carolina (ground-water model modified from Clarke and West, 1998; Cherry, 2006).

Introduction 
Structural Features

Major structural features in the study area (fig. 1A) in­clude 

the Belair Fault (Prowell and O’Connor, 1978) and the Pen 

Branch Fault (Price and others, 1991). The Belair Fault is a 

northeast-trending, high-angle reverse fault that dips to the 

southeast and has a maximum vertical displacement of 100 ft at 

the base of Coastal Plain strata (Prowell and O’Connor, 1978). 

The Pen Branch Fault is a northeast-trending, high-angle reverse 

fault that dips to the southeast. On SRS, the fault consists of a 

1.8-mile (mi)-wide zone of subparallel faults and some fault 

splays (Snipes and others, 1993). The fault is down­thrown 

on the northwestern side, and maximum displacement ranges 

from 100 ft at the base of Coastal Plain strata to 30 ft at the top 

of the Eocene Dry Branch Formation (Price and others, 1991). 

Seismic data from Burke County, Ga., suggest the Pen 

Branch Fault zone is about 0.86-mi wide and includes “short 

fractures” or “stress-release faults” (Summerour and others, 

1998). These features appear to cut confining units overlying 

the Millers Pond aquifer, upper and lower Dublin aquifers, 

and upper and lower Midville aquifers; however, it is unclear 

whether they cut into the confining unit overlying the Gordon 

aquifer (Summerour and others, 1998). The Pen Branch Fault 

zone includes the area of VEGP (fig. 1A, 1B). The effects of 

the Pen Branch Fault on sediment deposition and hydraulic 

properties of hydrogeologic units is unknown; however, there 

may be some local effects on the hydrologic system (see Effect 

of Pen Branch Fault section). 

Hydrogeologic Characteristics of the 

Savannah River Alluvial Valley

The hydrogeologic characteristics of the Savannah River 

alluvial valley (fig. 3) greatly influence the configuration of 

potentiometric surfaces, ground-water flow directions, and 

stream-aquifer relations. To determine the effect of paleo-river 

channel incision on hydrogeologic units, a map was constructed 

that shows the subsurface extent of hydrogeologic units 

beneath the mantle of alluvial deposits in the Savannah River 

floodplain (fig. 3). The map indicates that each of the seven 

aquifers was incised by the paleo-Savannah River channel and 

covered with an infill of permeable alluvium, allowing direct 

hydraulic connection of the aquifers and river along parts of 

the river’s reach. The lateral extent of the paleo-river channel 

incision corresponds to the width of the Savannah River alluvial 

valley and includes the modern-day alluvial bottom and terraces as mapped by Prowell (1994). The width of the alluvial 

valley ranges from a minimum of about 0.5 mi near the Fall 

Line to about 7 mi near the Richmond–Burke County line.

Summerour and others (1998) reported the possible presence of several “channel features” along a seismic profile collected by Waddell and others (1995) in eastern Burke County, 

outside of the present Savannah River valley. These features 

are believed to cover an area about 3,000 ft wide, extending to 

about 500 ft deep; however, their presence was not confirmed 

by drilling. Summerour and others (1998) suggested that “the 

channels, if real, could provide a potential pathway for the 

movement of groundwater (and pollutants) between aquifers.” 

Because of the uncertainty of these features, they were not 

included in the ground-water model developed by Clarke and 

West (1998). If additional data become available to confirm 

the presence of these features, it may be desirable to incorporate them into future ground-water models of the area.

Ground-Water Flow

The ground-water flow system near VEGP is generally considered to be in a state of equilibrium (steady state), 

whereby rates of aquifer recharge and discharge are about 

equal, and there is an insignificant loss of water from aquifer 

storage (Clarke and West, 1998). Recharge enters the groundwater system in upland areas and moves downgradient toward 

points of discharge (fig. 4). Much of the recharge water is 

discharged from the shallow flow system into tributaries of the 

Savannah River. A smaller percentage of recharge infiltrates 

through clayey confining units and enters the deeper intermediate and regional ground-water flow systems (fig. 4).

Topography plays an important role in defining the position of areas of potential downward and upward flow. Clarke 

and West (1997) present maps showing head differences and 

the potential for flow between adjacent units in the study area. 

In interstream areas throughout most of the study area, the 

potential for flow between the Gordon aquifer and overlying 

Upper Three Runs aquifer is downward, indicating possible 

recharge by ground-water leakage from the Upper Three Runs 

aquifer to the Gordon aquifer (Clarke and West, 1997). Conversely, in stream valleys and throughout much of the southern 

part of the study area, the potential for ground-water flow is 

upward, indicating possible discharge from the Gordon aquifer 

to the Upper Three Runs aquifer. 

The Savannah River serves as the major hydrologic drain 

in the VEGP area, with its floodplain considered to represent 

the same or nearly the same hydrologic condition as the river 

(Clarke and West, 1997). Each of the seven aquifers was 

incised by the paleo-Savannah River channel and covered 

with an infill of permeable alluvium (fig. 3), allowing direct 

hydraulic interconnection between the aquifers and the river 

(Clarke and West, 1997). This hydraulic connection allows 

water in confined aquifers to discharge into the river—by way 

of the alluvium—and may induce ground water to flow updip.

Hydraulic connection between confined aquifers and the 

Savannah River can be inferred from potentiometric-surface 

maps (figs. 5–8) that show ground-water discharge areas along 

the Savannah River valley as lows or depressions in the potentiometric surface (Clarke and West, 1997). Ground water flows 

toward the depressions from all directions; however, downstream from the depressions, the influence of the river on the 

aquifers becomes progressively diminished, and ground water 

resumes the regional gradient toward the southeast. In these 

downstream areas, a ground-water divide or “saddle” (Siple, 

1960, 1967) in the potentiometric surface is perpendicular to 

the river and separates upstream from downstream groundwater flow. 

 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
Upper

Brier

Creek

Creek

Newberry

Savannah

River

Three

Creek

Runs

Pen Branch

Fourmile

Branch

33°30'

33°

82° 81°30'

Base modified from U.S. Geological Survey 

State base maps

0

0 10 KILOMETERS

10 MILES

5

5

Aiken

Barnwell

Allendale

Screven Jenkins

Richmond

Burke Jefferson

Hampton

Area of

enlargement FALL LINE

Savannah River Site

GEORGIA

CAROLINA

SOUTH

EXPLANATION

Hydrogeologic units

Upper Three Runs aquifer

Gordon confining unit

Gordon aquifer

Millers Pond confining unit

Millers Pond aquifer

Upper Dublin confining unit

Upper Dublin aquifer

Lower Dublin confining unit

Lower Dublin aquifer

Upper Midville confining unit

Upper Midville aquifer

Lower Midville confining unit

Lower Midville aquifer

Pre-Cretaceous basement rock

Figure 3. Subsurface extent of hydrogeologic units beneath the Savannah River alluvial valley, 

South Carolina and Georgia (modified from Clarke and West, 1998a).

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

P-19

well

cluster

D

U

Vogtle Electric

Generation Plant

Figure 3 Subsurface extent of hydrogeologic units beneath the Savannah River alluvial valley, 

South Carolina and Georgia (modified from Clarke and West, 1997).

Introduction 
Savannah

River

Georgia

South Carolina

EXPLANATION

REGIONAL

FLOW

SYSTEM

LOCAL FLOW

SYSTEM

INTERMEDIATE

FLOW

SYSTEM

Tributary

stream Regional

ground-water divide

Unsaturated zone

 Saturated zone

Direction of ground-water flow—Queried where unknown

Alluvium

Water table

Confining unit

Pre-Cretaceous

 basement rock

Aquifer

NOT TO SCALE

Figure 4. Conceptualized hydrogeologic framework and related ground-water flow 

near Vogtle Electric Generation Plant, Georgia and South Carolina (modified from 

Atkins and others, 1996).

? ? ?

Figure 4. Conceptualized hydrogeologic framework and related groundwater flow near Vogtle Electric Generation Plant, Georgia and South Carolina 

(modified from Atkins and others, 1996).

 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
Savannah River Site

33°20'

81°50' 81°40' 81°30'

33°10'

33°00'

D

U

Meyers

Branch

Steel Creek

Tinker Creek

Lower Three

Runs Creek

Newberry Creek

McBean Creek

Branch

Par

Pond

 L

Lake

Hollow

Creek

Savannah River

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Jackson

Fourmile

Upper Three Runs Creek

GEORGIA

SOUTH

CAROLINA

Brier Creek

Pen

Branch

100

100

140

140

180

180

180

180

140

220

220

260

260

180

Figure 5. Potentiometric surface near Vogtle Electric Generation Plant for the Upper Three 

Runs aquifer, Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

0 1 2 3 4

0 1 2 3 4 5 KILOMETERS

5 MILES

140

EXPLANATION

Potentiometric contour—Shows altitude at which 

 water level would have stood in tightly cased wells

 in the Upper Three Runs aquifer during September 2002.

 Contour interval 40 feet. Datum is NAVD 88

Active area of source-sink layer A1

Observation well

Direction of ground-water flow

D

U

Pen Branch Fault—Approximately located; 

 D, downthrown side; U, upthrown side

Model area

Map area

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

GA

SC

Jefferson

P-19

well

cluster

Vogtle Electric

Generation Plant

Figure . Potentiometric surface for the Upper Three Runs aquifer, near Vogtle Electric

Generation Plant, Georgia and South Carolina, September 2002 modified from Cherry, 2003).

Introduction 
Savannah River Site

33°20'

81°50' 81°40' 81°30'

33°10'

33°00'

Figure 6. Potentiometric surface near Vogtle Electric Generation Plant for the Gordon aquifer, 

Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

EXPLANATION

Potentiometric contour—Shows altitude at which 

 water level would have stood in tightly cased wells

 in the Gordon aquifer during September 2002.

 Contour interval 20 feet. Datum is NAVD 88

Active area of source-sink layer A1

140

0 1 2 3 4

0 1 2 3 4 5 KILOMETERS

5 MILES

Production well—Screened in the Gordon aquifer

Observation well—Near Pen Branch Fault in which

 simulated water level was 4–26 feet higher than 

 observed. Number is well identification

Direction of ground-water flow

Model area

Map area

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

GA

SC

Jefferson

D

U

120

140

160

200

240

100

140

180

120

100

160

200

220

240

220

31Z077

31Z076

31Z074

31Z073

31Z015

31Z076

Branch

Meyers Branch Steel Creek

Tinker Creek

Creek

Newberry

Branch

Par

Pond

 L

Lake

Hollow

Creek

Savannah River

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Jackson

Fourmile

Upper Three Runs Creek

GEORGIA

SOUTH

CAROLINA

Brier

Creek

Lower Three Runs Creek

D

U

Pen Branch Fault—Approximately located; 

 D, downthrown side; U, upthrown side

Pen

McBean Creek

Vogtle Electric

Generation Plant

P-19

well

cluster

Figure 6.  Potentiometric surface for the Gordon aquifer, near Vogtle Electric Generation Plant,

Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

10 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
33°20'

81°50' 81°40' 81°30'

33°10'

33°00'

0 1 2 3 4

0 1 2 3 4 5 KILOMETERS

5 MILES

Figure 7. Potentiometric surface near Vogtle Electric Generation Plant for the Dublin aquifer 

system, Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

140

EXPLANATION

Potentiometric contour—Shows altitude at which 

 water level would have stood in tightly cased wells

 in the Dublin aquifer system during September 2002.

 Contour interval 20 feet. Datum is NAVD 88

Active area of source-sink layer A1

Production well—Screened in the upper and lower

 Dublin aquifer and Millers Pond aquifer

Direction of ground-water flow

D

U

Pen Branch Fault—Approximately located; 

 D, downthrown side; U, upthrown side

Model area

Map area

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

GA

SC

Jefferson

D

U

220

160

120

180

140

200

Meyers Branch

Steel Creek

Tinker Creek

Newberry Creek

Branch

Par

Pond

 L

Lake

Hollow

Creek

Savannah River

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Jackson

Fourmile

New

Ellenton

Upper Three Runs Creek

GEORGIA

SOUTH

CAROLINA

Brier Creek

Lower Three

Runs Creek

Savannah River Site

Pen

Branch

McBean Creek

P-19

well

cluster

Vogtle Electric

Generation Plant

Figure 7. Potentiometric surface for the Dublin aquifer system, near Vogtle Electric Generation 

Plant, Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

Introduction 11
33°20'

81°50' 81°40' 81°30'

33°10'

33°00'

0 1 2 3 4

0 1 2 3 4 5 KILOMETERS

5 MILES

Figure 8. Potentiometric surface near Vogtle Electric Generation Plant for the Midville aquifer 

system, Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

140

EXPLANATION

Potentiometric contour—Shows altitude at which 

 water level would have stood in tightly cased wells

 in the Midville aquifer system during September 2002.

 Contour interval 20 feet. Datum is NAVD 88

Active area of source-sink layer A1

Production well—Screened in the upper and lower

 Midville aquifer

Direction of ground-water flow

Model area

Map area

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

GA

SC

Jefferson

180

220

180

160

200

Pen

Branch

Steel Creek

Tinker Creek

Newberry Creek

Branch

Par

Pond

 L

Lake

Savannah River

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Jackson

Fourmile

New

Ellenton

Upper Three Runs Creek

GEORGIA

SOUTH

CAROLINA

Brier Creek

Hollow Creek

Lower Three

Runs Creek

Meyers Branch

Savannah River Site

McBean Creek

D

U

Pen Branch Fault—Approximately located; 

 D, downthrown side; U, upthrown side

D

U

P-19

well

cluster

Vogtle Electric

Generation Plant

Figure 8.  Potentiometric surface for the Midville aquifer system, near Vogtle Electric Generation

Plant, Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

12 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
Because flow directions derived from potentiometricsurface maps do not account for the vertical component of 

flow, Clarke and West (1998) applied the USGS particletracking code MODPATH (Pollock, 1994) to characterize 

three-dimensional ground-water flow near the Savannah River. 

This technique is applied in this report to simulate groundwater flowpaths from the production wells at VEGP to their 

recharge areas.

Trans-River Flow

Trans-river flow is a term that describes a condition 

whereby ground water originating on one side of a river 

migrates to the other side of the river through confined 

aquifers that underlie the river. Although some ground water 

could discharge into the river floodplain or alluvium on the 

opposite side of the river from its point of origin, this flow 

likely would return to the river. Return flow would occur 

because a slight hydraulic gradient exists toward the river 

along the floodplain. Flow lines on potentiometric-surface 

maps of the confined Gordon aquifer and Dublin and Midville 

aquifer systems (figs. 6–8) suggest possible occurrences of 

trans-river flow for a short distance into Georgia prior to 

discharge into the Savannah River (Clarke and West, 1997). 

Flow lines on the map for the Upper Three Runs aquifer, 

however, do not indicate trans-river flow (fig. 5).

Effect of Pen Branch Fault

The Pen Branch Fault may have a local effect on groundwater flow. In the central part of the SRS, water levels in the 

Gordon aquifer near the P-19 well cluster site are anomalously 

high, producing a mound in the potentiometric surface (fig. 6). 

The high water level in this area may be the result of the offset 

of the Pen Branch Fault, whereby sediments of the Gordon 

aquifer are juxtaposed against sediments of the Upper Three 

Runs aquifer (Aadland and others, 1991). Because the units 

are in hydraulic connection near the fault, water levels and 

water chemistry of the Gordon aquifer are similar to those of 

the Upper Three Runs aquifer (Clarke and West, 1997).

Ground-Water Use

Ground-water use in the study area during 2000–2002 

(W.J. Stringfield, U.S. Geological Survey, written commun., 

2002; Fanning, 2003) was about 117 million gallons per day 

(Mgal/d) (table 1), most of which was for irrigation (54 percent) and public supply (26 percent). In Georgia, most of the 

ground water used for irrigation is withdrawn from the Upper 

Three Runs aquifer in Jenkins County and southern Screven 

County, and from the Upper Three Runs and Gordon aquifers 

in Jefferson, Burke, and northern Screven Counties. In South 

Carolina, most irrigation wells in Barnwell and Allendale 

Counties pump water from the Upper Three Runs and Gordon 

aquifers. Ground-water use for public supply and industrial 

and mining purposes is mainly from the Dublin and Midville 

aquifer systems in both States.

Table 1. Ground-water use during 2000–2002 near Vogtle Electric Generation Plant, Burke County, Georgia.

[Modified from Cherry, 2006]

State County1

Pumpage, in million gallons per day

Public 

supply Irrigation Industrial and mining

Domestic and 

commercial Livestock Thermoelectric Total

Georgia Burke 3.87 21.23 0.15 0.90 0.03 0.78 26.96

Jefferson 1.84 6.92 3.82 0.64 0.03 0.00 13.25

Jenkins 0.54 3.94 0.01 0.33 0.02 0.00 4.84

Richmond 14.88 5.22 2.87 0.22 0.02 0.00 23.21

Screven 1.15 15.62 1.82 0.74 0.03 0.00 19.36

South Carolina Aiken 4.82 0.98 6.06 0.80 0.00 0.00 12.66

Allendale 1.20 5.62 2.50 0.27 0.00 0.00 9.59

Barnwell 2.73 3.73 0.41 0.63 0.00 0.00 7.50

Total—Georgia 22.28 52.93 8.67 2.83 0.13 0.78 87.62

Total—South Carolina 8.75 10.33 8.97 1.70 0.00 0.00 29.75

Total—eight counties 31.03 63.26 17.64 4.53 0.13 0.78 117.37

1

See figure 1A for location

Data sources: County totals for Georgia are from Fanning (1997, 2003) and Pierce and others (1982); total water-use data for South Carolina from Lonon 

and others (1983), and W.J. Stringfield (U.S. Geological Survey, written commun., 2002); site-specific data for irrigation wells located in Georgia from 

J.L. Fanning (U.S. Geological Survey, written commun., 2003) and V. P. Trent (Georgia Geologic Survey, written commun., 2003); and site-specific data 

for permitted wells located in South Carolina from Paul Bristol and Peter Stone (South Carolina Department of Health and Environmental Control, written 

commun., 2003).

Introduction 13
At VEGP, three wells are each screened in the lower 

Dublin and upper and lower Midville aquifers, and are used to 

supply water to operating reactor Units 1 and 2 (wells 31Z002, 

31Z003, and 31Z080; fig. 1B; table 2). Screened intervals 

of wells at VEGP were obtained from drillers records and 

entered into the USGS National Water Information System 

(http://waterdata.usgs.gov/ga/nwis/inventory). To determine 

the aquifer supplying water to each screened interval, altitudes 

of screened intervals were compared to maps showing the 

altitude of the tops of hydrogeologic units using a Geographic 

Information System (Harrelson and others, 1997).

During 2002, the wells at VEGP supplied an average 

724 gal/min (1.04 Mgal/d). The addition of two additional 

reactor units is projected to result in an increase in groundwater pumping of 1.09 Mgal/d (Mark Notich, U.S. Nuclear 

Regulatory Commission, written commun., April 10, 2007). 

If ground-water pumping during the startup of these reactors 

is similar to that during the startup of the original two reactors 

during 1988, then the initial increase in pumping could be as 

high as 3.42 Mgal/d.

At SRS, estimated pumpage was 5.30 Mgal/d during 

2002 (Cherry, 2006). A variety of multiaquifer wells completed in the Gordon aquifer and Dublin and Midville aquifer 

systems provide water supply at SRS.

Simulation of Ground-Water Flow

The model used in this study is described in detail in 

Clarke and West (1998) and Cherry (2006); only a brief 

description is included herein. Clarke and West (1998) 

simulated predevelopment and 1987–92 conditions using 

the MODFLOW finite-difference simulator (McDonald and 

Harbaugh, 1988). Cherry (2006) updated the model to simulate 2002 hydrologic conditions using the MODFLOW-2000 

simulator (Harbaugh and others, 2000). Both studies simulated 

steady-state conditions for each time period. Steady-state 

simulations were deemed appropriate because of the minimal 

observed changes in hydraulic head or ground-water discharge 

to streams from predevelopment (pre-1953) to 1987–92 

(Clarke and West, 1997). These minor fluctuations are an indication that the ground-water system generally was in a state of 

equilibrium and any contributions from aquifer storage were 

minor. These assumptions are believed to remain valid for the 

study area for this investigation.

The model encompasses an area of about 4,455 mi2

(fig. 1) and includes seven aquifers and seven confining units. 

These units crop out near the Fall Line and generally dip and 

thicken to the southeast. Aquifer units are, in descending 

order (fig. 2):

Table 2. Location and construction information for production wells at Vogtle Electric Generation Plant, Burke County, Georgia.

[USGS, U.S. Geological Survey; °, degree; ', minute; ", second; Aquifer: LD, lower Dublin; UM, upper Midville; LM, lower Midville]

USGS well 

identification1

Well 

number Latitude Longitude

Land-surface 

altitude 

(feet)

Year 

constructed

Screened interval 

(feet below 

land surface) Aquifer

Production 

capacity 

(gallons per 

Top Bottom minute)

31Z002 TW-1 33°08'28" 81°45'42" 219 1972 505 535 LD 1,200

555 585 LD

695 705 UM

730 750 UM

815 850 LM

31Z080 MU-2A 33°08'39" 81°46'00" 235 1983 480 510 LD 2,112

550 570 LD

630 650 LD

690 790 UM

31Z003 2

MU-1 33°08'47" 81°45'37" 197 1977 437 462 LD 3,334

468 483 LD

498 512 LD

536 546 LD

550 572 LD

676 696 UM

720 732 LM

788 820 LM

 1See figure 1B for location

2

Now called MU-5

14  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
the unconfined Upper Three Runs aquifer modeled 

as a source-sink layer (specified head layer A1); 

the confined Gordon aquifer (layer A2);

the Dublin aquifer system consisting of the Millers 

Pond aquifer (layer A3), upper Dublin aquifer 

(layer A4), and lower Dublin aquifer (layer A5); and

the Midville aquifer system consisting of the upper 

Midville aquifer (layer A6) and lower Midville 

aquifer (layer A7).

The thickness, extent, and other hydraulic properties of 

these units, as well as the model development process are 

described in detail in Clarke and West (1998). A schematic diagram showing model layers and boundary conditions is shown 

in figure 2. As in the original model of Clarke and West (1998), 

confining units are not actively simulated, but instead use verti-

•

•

•

•

cal conductance to simulate leakance between layers. Estimated and calibrated transmissivity values are listed in table 3 

and leakance values are listed in table 4 (Clarke and West, 

1998). For the MODPATH particle-tracking analysis, a uniform 

porosity of 30 percent was assigned to aquifer layers and 50 percent was assigned to confining units (Clarke and West, 1998).

The finite-difference grid for the model is aligned nearly 

parallel to the Savannah River and to the regional dip of the 

hydrogeologic units, and consists of 130 rows and 102 columns (13,260 grid cells) with a variable grid spacing ranging 

in size from 0.33 mi by 0.33 mi to 2 mi by 2.5 mi (fig. 1A). 

The model grid area encompasses about 4,455 mi2, of which 

about 3,250 miis actively simulated. Grid density is higher 

near the Savannah River (including the Savannah River Site 

and VEGP) to enable simulation of steeper head gradients 

(fig. 1A). Each aquifer unit is represented with one layer of 

grid cells in the vertical dimension. 

Table 3. Simulated and estimated values for transmissivity, Vogtle Electric Generation Plant model, Georgia and South Carolina.

[#, number; from Clarke and West (1998)]

Aquifer Layer 

number

Transmissivity, in square foot per day

Estimated based on field data1 Simulated

# of values Minimum Maximum Mean Minimum Maximum Mean2

Gordon aquifer A2 18 180 12,200 4,500 100 24,700 10,350

Millers Pond aquifer A3 10 195 2,000 1,000 10 3,900 1,310

Upper Dublin aquifer A4 17 555 25,200 5,830 10 20,000 7,220

Lower Dublin aquifer A5 21 40 8,900 3,940 10 25,500 10,030

Upper Midville aquifer A6 15 1,300 5,430 2,760 10 12,390 6,270

Lower Midville aquifer A7 37 800 25,500 8,900 515 34,395 19,020

1

Determined from aquifer tests and estimated from specific-capacity data and from borehole-resistivity logs.

2

Mean value weighted according to cell area.

Table 4. Simulated and estimated values for leakance, Vogtle Electric Generation Plant model, Georgia and South Carolina.

[#, number; —, not measured; from Clarke and West (1998)]

Hydrogeologic 

unit

Layer 

number

Leakance, in feet per day per foot of confining unit thickness1

Estimated leakance2 Simulated

# of values Minimum Maximum Mean Minimum Maximum Mean3

Gordon confining unit C1 6 4.7 × 10–6 1.2 × 10–2 2.1 × 10–3 9.0 × 10–8 1.3 × 10–3 1.7 × 10–4

Millers Pond confining unit C2 — — — — 3.9 × 10–6 8.7 × 10–1 1.9 × 10–2

Upper Dublin confining unit C3 9 1.8 × 10–6 1.6 × 10–3 3.6 × 10–4 1.2 × 10–6 7.3 × 10–3 1.2 × 10–3

Lower Dublin confining unit C4 1 2.4 × 10–5 2.4 × 10–5 2.4 × 10–5 3.0 × 10–7 6.5 × 10–3 6.6 × 10–3

Upper Midville confining unit C5 11 6.7 × 10–7 3.4 × 10–4 7.6 × 10–5 2.1 × 10–7 1.0 × 10–1 9.7 × 10–4

Lower Midville confining unit C6 1 1.0 × 10–5 1.0 × 10–5 1.0 × 10–5 7.7 × 10–5 3.6 × 10–1 9.0 × 10–3

1

Includes low permeability layers within aquifer layers.

2

Estimated by dividing the vertical hydraulic conductivity unit by the thickness of the confining unit.

3

Mean value weighted according to cell area.

Simulation of Ground-Water Flow 15
Lateral model boundaries are a combination of no-flow 

and specified head for layers A2–A7. For all layers, the southeastern boundary is simulated as a specified-head condition. 

For layers A2–A3, the southwestern boundary is simulated 

as no-flow, corresponding to the position of a ground-water 

divide. Parts of the eastern boundary for layers A2 and A3 are 

simulated as specified head and no-flow. For layers A4–A7, 

most of the western boundary is simulated as no-flow, corresponding to the position of a ground-water divide. The eastern 

boundary for layers A4–A7 is simulated mostly as a specifiedhead condition. Specified heads for each layer in the model 

are based on potentiometric surface maps for September 2002 

(figs. 5–8) and generally are lower than in the original Clarke 

and West (1998) model to reflect effects of the 1998–2002 

drought (Cherry, 2006).

The bottom boundary of the model is no-flow, whereas 

the top boundary represented by layer A1 is set as a sourcesink specified-head condition with controlling specified heads 

based on water levels from the 2002 potentiometric-surface 

map of the Upper Three Runs aquifer (Cherry, 2003). Flow in 

the deeper active layers (A2–A7) of the model is simulated 

through a combination of active cells, specified head cells, 

recharge cells, and river cells. 

Most recharge to the simulated ground-water system 

was provided by leakage from layer A1, with a comparatively 

smaller amount derived from recharge cells in layers A2–A7. 

Total simulated recharge is about 930 Mgal/d of which 

777 Mgal/d were derived by leakage from layer A1, and 

153 Mgal/d were derived from recharge assigned to outcrop 

areas of hydrogeologic units (Cherry, 2006).

Average annual pumpage for 2002 was assigned to 

model cells based on site-specific and county-aggregate data 

(table 1). Site-specific data are available for public supply, 

thermoelectric, industrial, and mining use and are assigned to 

known well locations. County aggregate agricultural pumping 

data were equally divided and assigned to known agricultural 

well locations Domestic and commercial and livestock use 

were not simulated by the model because these uses accounted 

for less than 4 percent of total study area pumpage during 

2002 (table 1) with most of the withdrawal derived from shallow wells completed in the Upper Three Runs aquifer.

Where multi-aquifer wells are completed in several 

aquifer layers (such as at VEGP and SRS), pumpage was 

evenly proportioned to the various screened intervals in 

each well. Of the total study area ground-water use during 2000–2002 of 117 Mgal/d, 67.2 Mgal/d were simulated 

from active layers (table 5) A2 (Gordon aquifer), A3 (Millers 

Pond aquifer), A4 (upper Dublin aquifer), A5 (lower Dublin 

aquifer), A6 (upper Midville aquifer), and A7 (lower Midville 

aquifer). The remaining 49.8 Mgal/d were from the Upper 

Three Runs aquifer (layer A1), which is not actively simulated. The influence of pumpage from the Upper Three Runs 

aquifer on the overall flow system during 2002 is simulated by 

changing the head in that layer based on water-level measurements during September 2002 (fig. 5).

The calibrated model used for this study showed a 

reasonable fit to simulated water levels. Water-level residuals 

represent the difference between simulated and observed water 

levels, with positive values indicating that simulated values 

were greater than observed values. For the 1987–92 simulation, the model was calibrated using the average observed 

water levels at 313 model cells, with a mean of residuals of 

0.8 ft and a root mean square (RMS) of the residuals of 10.6 ft 

(Clarke and West, 1998). For the 2002 simulation, model 

calibration was evaluated based on observations at 172 wells 

during September 2002, with a mean of residuals of 2.8 ft and 

a RMS of the residuals of 8.0 ft (Cherry, 2006).

Pen Branch Fault

The Pen Branch Fault may locally affect ground-water 

flow in the study area (see Effect of Pen Branch Fault section). 

Although hydraulic characteristics of the fault are unknown, 

the possible effects of the fault are incorporated into the model 

as follows: (1) by variations in depth, thickness, and hydraulic 

properties of model layers near the fault; and (2) by incorporation of river cells where incision of the Gordon aquifer 

(layer A2) is believed to occur along the southern side of the 

fault in the Savannah River alluvial valley (fig. 1A). 

Hydraulic properties of the upper and lower Dublin 

aquifers (model layers A4 and A5) were adjusted along the 

southern side of the fault during model calibration (Clarke 

and West, 1998). A zone of high transmissivity—greater than 

15,000 feet squared per day (ft2/d) and extending as much 

as 6 mi south of the fault—was required in the two layers to 

achieve calibration of the model. Although there are no field 

data to confirm this zone of higher transmissivity, it is possible 

that such a zone exists based on calibration results. Construction of test wells and aquifer testing in this area would be 

required to confirm the presence of a high transmissivity zone.

Table 5. Simulated pumpage by model layer for 2002 Base Case, 

Vogtle Electric Generation Plant model, Georgia and South Carolina. 

[Modified from Cherry, 2006]

Aquifer Model 

layer

Year 2002 pumpage, in 

million gallons per day

Gordon A2 10.7

Millers Pond A3 7.3

Upper Dublin A4 5.4

Lower Dublin A5 14.6

Upper Midville A6 9.8

Lower Midville A7 19.4

All layers 67.2

16  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
Maps showing the altitude of the top of hydrogeologic 

units (Falls and others, 1997) indicate that uplift along the 

southern side of the Pen Branch Fault resulted in shallower 

depths of units compared to equivalent units north of the fault. 

Near the Pen Branch Fault and the P-19 well cluster site on 

SRS, simulated head values for the Gordon aquifer (layer A2) 

during 1987–92 are considerably lower than observed values, 

with a residual of –81.1 ft (Clarke and West, 1998). Clarke 

and West (1997) reported that the anomalously high observed 

head in the Gordon aquifer in this area may be the result 

of (1) a high degree of aquifer interconnection between the 

Upper Three Runs and Gordon aquifers due to the Pen Branch 

Fault (Aadland and others, 1991), or (2) the possibility that 

the water-level measurement in the Gordon aquifer at the 

P-19 well cluster site may not be representative of the head in 

layer A2 because of problems with well construction or measurement error. Because the reason for the high water level in 

the Gordon aquifer was not definitively established, the earlier 

study (Clarke and West, 1998) did not adjust model parameters to attempt to match water levels in the Gordon aquifer at 

the P-19 well cluster. Simulation of higher head in the Gordon 

aquifer in this area would require increasing the leakance of 

the Gordon confining unit (layer C1) to enable greater connection between the Upper Three Runs and Gordon aquifers.

In the Savannah River valley, uplift along the southern 

side of the Pen Branch Fault and erosion by the paleoSavannah River appears to have resulted in exposure of 

the Gordon aquifer (layer A2) in a local area (fig. 3). This 

local exposure is simulated in the model as river cells in the 

Gordon aquifer that enables a higher degree of connection 

between the Gordon aquifer and the Savannah River (fig. 1B). 

Despite this adjustment, simulated water levels in the Gordon 

aquifer (layer A2) near this feature during 2002 generally 

are high in the model, ranging from 4 to 26 ft higher than 

observed levels (wells 31Z015, 31Z073, 31Z074, 31Z076, 

and 31Z077; fig. 6). 

Another area where uplift on the southern side of the fault 

is represented by the model occurs between Pen Branch and 

Four Mile Branch on SRS (fig. 1B). In this upland area adjacent to the Savannah River Valley, units overlying the Gordon 

aquifer appear to have been eroded away and the aquifer is 

near land surface. Here, the Gordon aquifer is simulated using 

recharge cells, which enable direct infiltration of precipitation 

into the aquifer.

Several hypothesized channel features (Summerour and 

others, 1998) along a seismic profile near the Pen Branch Fault 

in eastern Burke County, Ga., were not incorporated into the 

ground-water model because their existence was not confirmed by test drilling. According to Summerour and others 

(1998), these features potentially could affect a zone 3,000 ft 

wide and 500 ft deep, and provide a potential pathway for 

movement of ground water between aquifers. If such a feature 

were simulated, high vertical hydraulic conductivity would 

be assigned to confining units overlying layers A2–A7, and 

would facilitate movement of water between the zones. This 

modification could result in reducing the simulated head in 

the Gordon aquifer by allowing water to discharge from the 

unit and would reduce the aforementioned difference between 

observed and simulated head. Because the presence, depth, 

and areal extent of these features, are unknown, they were not 

simulated by the current model.

Ground-Water Pumping Scenarios

The updated and calibrated model (Cherry, 2006) was 

used to simulate the effect of current and potential future 

pumping on ground-water levels and flowpaths near VEGP for 

a Base Case and three pumping scenarios (table 6). The Base 

Case represents 2002 pumping rates throughout the model 

area (Cherry, 2006). The three scenarios were designed to 

simulate steady-state water levels resulting from (1) pumping 

increases at VEGP with pumping elsewhere in the study area 

held at 2002 rates (Scenarios A and C), and (2) the effects of 

increased pumping at VEGP combined with a shutdown of 

pumping at the SRS (Scenario B). 

Steady-state conditions in response to pumping changes 

are believed to be reached rapidly in the study area. Clarke and 

West (1998) indicated that for each of six stress periods during 

1953–92, “heads showed an almost instantaneous stabilization, suggesting that the prevalence of steady-state conditions 

were achieved immediately following a change in pumpage.” 

For each scenario, the pumping distribution, simulated waterlevel changes, and ground-water flowpaths are described relative to the year 2002 Base Case.

A particle-tracking analysis was conducted for the Base 

Case and for each scenario to determine the source of water 

withdrawn from the VEGP production wells. The USGS 

particle-tracking code MODPATH (Pollock, 1994) was used 

to generate advective water-particle pathlines and their 

associated time of travel based on the MODFLOW simulations. MODPATH was used to compute three-dimensional 

flow directions and time of travel using imaginary particles 

in a backtracking mode from the production wells at VEGP 

toward recharge areas in a map perspective. Generally, the 

greater the number of particles applied vertically and horizontally in a model cell, the more accurate the definition of flowpaths for a given model layer. For this study, particles were 

placed at the center of each of the three grid cells containing a 

VEGP production well at increments representing 10 percent 

of the aquifer thickness (10 total particles per aquifer layer in 

each of the three grid cells). Particles were placed in the lower 

Dublin (layer A5), and upper (layer A6) and lower Midville 

(layer A7) aquifers, which provide water to the VEGP production wells. To avoid clutter and simplify display of particle 

flowpaths on maps, the number of particles displayed on the 

figure was reduced from 10 to 5. Simulated time of travel for 

all particles (10 per model cell) is summarized for the Base 

Case and for Scenarios A–C in table 7.

Simulation of Ground-Water Flow 17
2002 Base Case Condition

The year 2002 simulation represents the Base Case for 

comparison to each of the pumping scenarios. The simulated 

hydrologic condition during 2002 represents effects of the 

1998–2002 drought in which irrigation pumpage was above 

average and recharge and boundary-condition head were low 

due to decreased precipitation. Results of model simulations 

for 2002 are presented in Cherry (2006); results of particletracking analyses at VEGP are presented herein. 

The simulated 2002 potentiometric-surface maps for the 

Dublin and Midville aquifer systems (figs. 7 and 8, respectively) indicate VEGP is within the Savannah River regional 

ground-water discharge zone in which the principal direction 

of ground-water flow is toward the Savannah River. None of 

the various scenarios resulted in large changes in the configuration of the simulated potentiometric surface and related 

ground-water flow directions.

The source of water to the VEGP production wells, as 

indicated by MODPATH analysis for year 2002, is recharge 

occurring in an upland area near the county line between 

Burke and Jefferson Counties, Ga. (fig. 9), with none of the 

water originating on SRS or elsewhere in South Carolina. 

Simulated mean time of travel from recharge areas to the 

VEGP production wells are about 2,700 years (yr) in the 

lower Dublin aquifer and about 3,100 yr in the upper and 

lower Midville aquifers (table 7). The fastest simulated time 

of travel, about 2,100 yr, was for a particle in the lower Dublin 

aquifer, and the longest was about 3,800 yr for a particle in 

the lower Midville aquifer.

Table 7. Summary of simulated time of travel for 2002 Base Case 

and for Scenarios A, B, and C, Vogtle Electric Generation Plant 

model, Georgia and South Carolina.

[Ten particles were assigned to each aquifer layer in 3 model cells for a total 

of 30 particles per layer]

Aquifer 

(model layer) Statistic

Simulated time of travel in years

Base Case Scenario

2002 A B C 

Lower Dublin

(A5)

Mean 2,700 2,700 2,700 3,800

Median 2,700 2,600 2,700 3,000

Maximum 3,600 3,700 3,900 12,600

Minimum 2,100 2,100 2,100 1,800

Upper Midville

(A6)

Mean 3,100 3,100 3,300 2,800

Median 2,800 2,700 2,700 2,500

Maximum 3,700 4,700 5,200 4,000

Minimum 2,700 2,300 2,300 1,800

Lower Midville

(A7)

Mean 3,100 3,100 3,200 2,800

Median 2,900 2,800 2,800 2,500

Maximum 3,800 4,200 4,600 4,000

Minimum 2,700 2,400 2,400 2,400

Table 6. Simulated pumpage at Vogtle Electric Generation Plant, Burke County, Georgia, for 2002 Base Case and pumping 

Scenarios A, B, and C. 

[gal/min, gallons per minute; Mgal/d, million gallons per day]

Scenario Pumping rate Remarks

gal/min Mgal/d

Base Case 2002 724 1.04 Current conditions for existing reactor units

A 1,482 2.13 Additional pumping capacity of new reactor units at average projected withdrawal rates

B 1,482 2.13 Additional pumping capacity of new reactor units at average projected withdrawal rates and 

elimination of 5.3 Mgal/d pumpage at Savannah River Site

C 3,099 4.46 Scenario represents a higher rate of withdrawal for the proposed new reactor units 

during their startup period (3.42 Mgal/d), and continuation of year 2002 pumping rates 

(1.04 Mgal/d) in the existing reactor units. The higher withdrawal in the new reactors 

is similar to that reported during 1988 for the startup of the existing reactors. Southern 

Nuclear Company has noted that the high pumping rates during startup of Units 1 and 2 

were related to achieving water-quality criteria and not to ground-water demand by the 

facilities. Water treatment methods are now used to achieve the water-quality criteria and 

have greatly reduced ground-water pumping rates (Mark Nodich, U.S. Nuclear Regulatory 

Commission, written commun., September 10, 2007).

18  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
Georgia

South

 Carolina

Study

area

Lower Dublin aquifer

Upper Midville aquifer

Lower Midville aquifer

D

U

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Simulated ground-water flowpath—Particles placed at the center of 

 each of the three grid cells containing a Plant Vogtle production well

 at increments representing 10 percent of the aquifer thickness 

 (10 total particles per aquifer layer per cell). Five particle flowpaths

 for each layer are shown on map to avoid clutter

Vogtle Electric Generation Plant

Figure 9. Particle-tracking results for the year 2002, Base Case, near Vogtle Electric Generation Plant, Georgia and South Carolina.

EXPLANATION

Base modified from U.S. Geological Survey

1:24,000-scale digital data

0 5 10 MILES

0 5 10 KILOMETERS

GEORGIA

AIKEN RICHMOND

JEFFERSON

ALLENDALE

BURKE

SCREVEN

JENKINS

River Savannah

Creek

Upper Three Runs Creek

Brier

BARNWELL

Savannah River Site

N

Model boundary

SOUTH

CAROLINA

Figure 9. Particle-tracking results for the year 2002, Base Case, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

Simulation of Ground-Water Flow 19
Scenario A

Scenario A simulates a 1.09-Mgal/d increase in average 

pumping rates at VEGP for the operation of existing reactors 

(Units 1 and 2) and an increase for the proposed new reactors 

(Units 3 and 4). The pumping increase was distributed evenly 

among the three production wells at VEGP. Simulated waterlevel changes are shown in figures 10–15; particle-tracking 

results are shown in figure 16 and listed in table 7.

For Scenario A, water-level changes were minimal, 

with maximum declines of greater than 0.25 ft in the Gordon 

aquifer (fig. 10), greater than 0.5 ft in the Millers Pond aquifer 

(fig. 11), greater than 1 ft in the upper and lower Dublin aquifers (figs. 12 and 13, respectively), and greater than 2 ft in the 

upper and lower Midville aquifers (figs. 14 and 15, respectively). Drawdown response in the shallow aquifers (Gordon, 

Millers Pond, and upper Dublin) is due to leakage through 

confining units in response to decreased head in the pumped 

zones (lower Dublin and upper and lower Midville aquifers). 

In the upper and lower Dublin and upper and lower Midville 

aquifers, the zone of pumping influence (defined as greater 

than 0.5 ft of change) extends from about 3 to 4.5 mi onto SRS 

in South Carolina (figs. 12–15).

For Scenario A, the source of water to VEGP production 

wells, as indicated by MODPATH analysis, is recharge in an 

upland area near the county line between Burke and Jefferson 

Counties, Ga. (fig. 16). Simulation results indicate that none of 

the recharge originated on SRS or elsewhere in South Carolina, despite the small amount of drawdown extending into 

that area in the lower and upper Dublin and lower and upper 

Midville aquifers (figs. 12–15). Because vertical-head gradients are steep beneath the Savannah River alluvial valley, large 

changes in head are required to induce flow from the other 

side of the river. Mean simulated time of travel from recharge 

areas to the VEGP wells for Scenario A are about 2,700 yr in 

the lower Dublin aquifer and about 3,100 yr in the upper and 

lower Midville aquifers (table 7). The fastest simulated time 

of travel, about 2,100 yr, was for a particle in the lower Dublin 

aquifer and the slowest was about 4,700 yr for a particle in the 

upper Midville aquifer.

Scenario B

Scenario B simulates a 1.09-Mgal/d increase in pumping 

at VEGP, as was simulated in Scenario A, and total elimination of 5.3 Mgal/d pumping at the SRS facility (table 6). For 

this scenario, the 1.09 Mgal/d increase was distributed evenly 

among three production wells at VEGP completed in the 

lower Dublin and upper and lower Midville aquifers, and the 

5.3 Mgal/d decrease was subtracted evenly among 12 production wells at the SRS completed in one or more of the following aquifers: Gordon, Millers Pond, upper and lower Dublin, 

and upper and lower Midville. Simulated water-level changes 

are shown in figures 17– 22; particle-tracking results are 

shown in figure 23 and listed in table 7.

For Scenario B, the largest water-level changes were 

on SRS, with maximum increases of greater than 4 ft in the 

Gordon aquifer, greater than 1 ft in the Millers Pond aquifer, 

greater than 4 ft in the upper Dublin aquifer (fig. 19), greater 

than 8 ft in the lower Dublin aquifer (fig. 20), and greater 

than 4 ft in the upper and lower Midville aquifers (figs. 21 

and 22, respectively). At VEGP, the magnitude and extent of 

water-level decline resulting from increased pumping was less 

pronounced than that observed in Scenario A for an equivalent increase in pumping. The water-level rise resulting from 

elimination of SRS pumping reduced the effect of pumping 

at VEGP on ground-water levels. Maximum declines near 

VEGP were greater than 2 ft in the upper and lower Midville 

aquifers (figs. 21 and 22, respectively), greater than 1 ft in the 

lower Dublin aquifer (fig. 20), and greater than 0.5 ft in the 

upper Dublin aquifer (fig. 19). There was no observed change 

at VEGP in the overlying Gordon and Millers Pond aquifers 

(figs. 17 and 18, respectively).

Despite the large water-level rise at SRS, the source of 

water to VEGP production wells, as indicated by MODPATH 

analysis (fig. 23), remained nearly identical to Scenario A 

(fig. 16). Simulation results indicate that ground-water 

recharge is provided in an upland area near the county line 

between Burke and Jefferson Counties, Ga. (fig. 23), with a 

mean simulated time of travel of about 2,700 yr in the lower 

Dublin aquifer; about 3,300 yr in the upper Midville aquifer; 

and about 3,200 yr in the lower Midville aquifer (table 7). The 

fastest simulated time of travel was for a particle in the lower 

Dublin aquifer (about 2,100 yr), and slowest was for a particle 

in the upper Midville aquifer (about 5,200 yr). As was the case 

for Scenario A, none of the recharge originated on SRS or 

elsewhere in South Carolina.

20 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
–0.25

Figure 10. Simulated water-level change for Scenario A in the Gordon aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

D

U

Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Computed by subtracting

 the simulated potentiometric surface for 2002 Base Case from the 

 simulated potentiometric surface for Scenario A (see table 6 for 

 description of scenario)

–0.25

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

Upper Three

Runs Creek

GEORGIA

CAROLINA

SOUTH

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 10. Simulated water-level change for Scenario A in the Gordon aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

Simulation of Ground-Water Flow  21
–0.5

–0.25

Figure 11. Simulated water-level change for Scenario A in the Millers Pond aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is 0.25. 

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario A 

 (see table 6 for description of scenario)

–0.5

GEORGIA

CAROLINA

SOUTH

Upper Three

Runs Creek

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 11. Simulated water-level change for Scenario A in the Millers Pond aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

22  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
–1

–0.5

Figure 12. Simulated water-level change for Scenario A in the upper Dublin aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is 0.5.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario A 

 (see table 6 for description of scenario)

GEORGIA

CAROLINA

SOUTH

–0.5

Upper Three

Runs Creek

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 12. Simulated water-level change for Scenario A in the upper Dublin aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow  23
–1

–0.5

Figure 13. Simulated water-level change for Scenario A in the lower Dublin aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina. 

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Line of equal simulated water-level change—Interval, in feet, is 0.5.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario A 

 (see table 6 for description of scenario)

–1

GEORGIA

CAROLINA

SOUTH

Production well—Completed in the lower Dublin aquifer in which pumping 

 was adjusted for scenario

Upper Three

Runs Creek

Savannah River Site

Vogtle Electric Generation Plant

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 13. Simulated water-level change for Scenario A in the lower Dublin aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

24  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
–1

–0.5

–2

Figure 14. Simulated water-level change for Scenario A in the upper Midville aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5 10 MILES

0 5 10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

–1

GEORGIA

CAROLINA

SOUTH

Upper Three

Runs Creek

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario A 

 (see table 6 for description of scenario)

Production well—Completed in the upper Midville aquifer in which pumping 

 was adjusted for scenario

Savannah River Site

Vogtle Electric Generation Plant

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 14. Simulated water-level change for Scenario A in the upper Midville aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow  25
–1

–0.5

–2

Figure 15. Simulated water-level change for Scenario A in the lower Midville aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

Upper Three

Runs Creek

D

U

–1

Production well—Completed in the lower Midville aquifer in which pumping 

 was adjusted for scenario

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario A 

 (see table 6 for description of scenario)

GEORGIA

CAROLINA

SOUTH

Savannah River Site

Vogtle Electric Generation Plant

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 15. Simulated water-level change for Scenario A in the lower Midville aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

26  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
0 5 10 MILES

0 5 10 KILOMETERS

AIKEN RICHMOND

JEFFERSON

ALLENDALE

BURKE

SCREVEN

JENKINS

River Savannah

Creek

Upper Three Runs Creek

Brier

BARNWELL

Savannah River Site

N

Figure 16. Particle-tracking results for the year 2002, Scenario A, near Vogtle Electric Generation Plant, Georgia and 

South Carolina.

Lower Dublin aquifer

Upper Midville aquifer

Lower Midville aquifer

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Simulated ground-water flowpath—Particles placed at the center of 

 each of the three grid cells containing a Plant Vogtle production well

 at increments representing 10 percent of the aquifer thickness 

 (10 total particles per aquifer layer per cell). Five particle flowpaths

 for each layer are shown on map to avoid clutter

Vogtle Electric Generation Plant

EXPLANATION

Model boundary

D

U

GEORGIA

SOUTH

CAROLINA

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Georgia

South

 Carolina

Study

area

Figure 16. Particle-tracking results for the year 2002, Scenario A, near Vogtle Electric Generation Plant, Georgia and 

South Carolina.

Simulation of Ground-Water Flow  27
2

2

4

0.5

1

1

Figure 17. Simulated water-level change for Scenario B in the Gordon aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario B 

 (see table 6 for description of scenario)

0.5

Upper Three

Runs Creek

GEORGIA

CAROLINA

SOUTH

Production well—Completed in the Gordon aquifer in which pumping was 

 adjusted for scenario

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 17. Simulated water-level change for Scenario B in the Gordon aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

28  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
0.5

1

Figure 18. Simulated water-level change for Scenario B in the Millers Pond aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is 0.5.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario B 

 (see table 6 for description of scenario)

0.5

GEORGIA

CAROLINA

SOUTH

Production well—Completed in the Millers Pond aquifer in which pumping

 was adjusted for scenario

Savannah River Site

Upper Three

Runs Creek

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 18. Simulated water-level change for Scenario B in the Millers Pond aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow  29
–0.5

2

2

4

0.5

1

0

Figure 19. Simulated water-level change for Scenario B in the upper Dublin aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario B 

 (see table 6 for description of scenario)

0.5

Upper Three

Runs Creek

GEORGIA

CAROLINA

SOUTH

Production well—Completed in the upper Dublin aquifer in which pumping 

 was adjusted for scenario

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 19. Simulated water-level change for Scenario B in the upper Dublin aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

30 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
–0.5

2

2

4

8

–1

0.5

1

0

Figure 20. Simulated water-level change for Scenario B in the lower Dublin aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

GEORGIA

CAROLINA

SOUTH

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario B 

 (see table 6 for description of scenario)

–1

Production well—Completed in the lower Dublin aquifer in which pumping was 

 adjusted for scenario

Savannah River Site

Upper Three

Runs Creek

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 20. Simulated water-level change for Scenario B in the lower Dublin aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow  31
0.5

–0.5

2

1

0

4

–1

–2

Figure 21. Simulated water-level change for Scenario B in the upper Midville aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5 10 MILES

0 5 10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

–1

Upper Three

Runs Creek

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario B 

 (see table 6 for description of scenario)

Production well—Completed in the upper Midville aquifer in which pumping 

 was adjusted for scenario

GEORGIA

CAROLINA

SOUTH

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 21. Simulated water-level change for Scenario B in the upper Midville aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

32  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
–0.5

2

4

–1

–2

0.5

1

0

Figure 22. Simulated water-level change for Scenario B in the lower Midville aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario B 

 (see table 6 for description of scenario)

0.5

Upper Three

Runs Creek

GEORGIA

CAROLINA

SOUTH

Production well—Completed in the lower Midville aquifer in which pumping 

 was adjusted for scenario 

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 22. Simulated water-level change for Scenario B in the lower Midville aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

Simulation of Ground-Water Flow  33
Base modified from U.S. Geological Survey

1:24,000-scale digital data

0 5 10 MILES

0 5 10 KILOMETERS

AIKEN RICHMOND

JEFFERSON

ALLENDALE

BURKE

SCREVEN

JENKINS

River Savannah

Creek

Upper Three Runs Creek

Brier

BARNWELL

Savannah River Site

N

Figure 23. Particle-tracking results for the year 2002, Scenario B, study area, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

Lower Dublin aquifer

Upper Midville aquifer

Lower Midville aquifer

D

U

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Simulated ground-water flowpath—Particles placed at the center of 

 each of the three grid cells containing a Plant Vogtle production well

 at increments representing 10 percent of the aquifer thickness 

 (10 total particles per aquifer layer per cell). Five particle flowpaths

 for each layer are shown on map to avoid clutter

Vogtle Electric Generation Plant

EXPLANATION

Model boundary

GEORGIA

SOUTH

CAROLINA

Georgia

South

 Carolina

Study

area

Figure 23. Particle-tracking results for the year 2002, Scenario B, study area, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

34  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
Scenario C

Scenario C simulates a 3.42-Mgal/d increase in pumping 

at VEGP that represents a 2.33-Mgal/d higher rate of withdrawal than was simulated for Scenario A for the proposed 

new reactor units (table 6). The higher withdrawal for wells 

providing water to the new reactors is similar to that reported 

for the startup of the two existing reactors (Units 1 and 2) during 1988 (Mark Notich, U.S. Nuclear Regulatory Commission, 

written commun., April 10, 2007). Southern Nuclear Company has noted that the high pumping rates during startup of 

Units 1 and 2 were related to achieving water-quality criteria 

and not to ground-water demand by the facilities. Water 

treatment methods are now used to achieve the water-quality 

criteria and have greatly reduced ground-water pumping 

rates (Mark Nodich, U.S. Nuclear Regulatory Commission, 

written commun., September 10, 2007).

Although pumping rates simulated by Scenario C are 

viewed as implausible for long-term operation of proposed 

Units 3 and 4, and the pumping rates are not proposed by 

Southern Nuclear Company, the scenario is designed to 

simulate pumping rates necessary to draw ground water 

from South Carolina to the VEGP production wells. The 

3.42-Mgal/d increase was distributed evenly among three 

production wells at VEGP. Simulated water-level changes are 

shown in figures 24–29; particle-tracking results are shown 

on figure 30 and listed in table 7. 

The maximum simulated drawdown for Scenario C was 

greater than 1 ft in the Gordon aquifer (fig. 24), greater than 

2 ft in the Millers Pond aquifer (fig. 25), greater than 4 ft in 

the upper Dublin aquifer (fig. 26), greater than 4 ft in the lower 

Dublin aquifer (fig. 27), and greater than 8 ft in the upper and 

lower Midville aquifers (figs. 28 and 29, respectively). 

The extent of drawdown is largest for Scenario C 

when compared to Scenarios A and B, with the 0.5-ft 

drawdown contour in the upper and lower Midville aquifers 

extending about 29 mi to the southwestern model boundary 

in Jenkins and Screven Counties, Ga., and about 14 mi 

eastward into SRS (figs. 28 and 29, respectively). In the 

overlying Gordon, Millers Pond, and upper Dublin aquifers 

(figs. 24–26, respectively), drawdown response is due to 

leakage through confining units in response to decreased head 

in the production zones (lower Dublin and upper and lower 

Midville aquifers, figs. 27–29, respectively). 

For Scenario C, the source of water to VEGP production wells, as indicated by MODPATH analysis (fig. 30), is 

recharge at a somewhat different location than that simulated 

for Scenario A (fig. 16). As was the case for Scenario A, 

simulation results indicate that much of the ground-water 

recharge for Scenario C occurs in an upland area near the 

county line between Burke and Jefferson Counties, Ga.; 

however, there is an additional source of water in an upland 

area in eastern Barnwell County, S.C. As was the case for 

Scenarios A and B, none of the recharge originated on SRS. 

When compared to Scenarios A and B, simulated mean time 

of travel for Scenario C (table 7) was slower in the lower Dublin aquifer (about 3,800 yr), and faster in the upper and lower 

Midville aquifers (about 2,800 yr). For Scenario C, the fastest 

simulated time of travel of about 1,800 yr was for particles 

in the lower Dublin and upper Midville aquifers and slowest (about 12,600 yr) was for a particle in the lower Dublin 

aquifer. The slower time of travel in the lower Dublin aquifer 

may be the result of the greater length and extent of flowlines 

shown on figure 30. 

Simulation of Ground-Water Flow  35
–1

–0.5

–0.5

Figure 24. Simulated water-level change for Scenario C in the Gordon aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is 0.5.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario C 

 (see table 6 for description of scenario)

–0.5

GEORGIA

CAROLINA

SOUTH

Upper Three

Runs Creek

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 24. Simulated water-level change for Scenario C in the Gordon aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

36  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
–1

–0.5

–0.5

–2

0 5

0 5

10 MILES

10 KILOMETERS

Figure 25. Simulated water-level change for Scenario C in the Millers Pond aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

N

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

Upper Three

Runs Creek

GEORGIA

CAROLINA

SOUTH

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario C 

 (see table 6 for description of scenario)

Upper Three

Runs Creek

–1

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 25. Simulated water-level change for Scenario C in the Millers Pond aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow  37
–1

–0.5

–2

–4

0 5

0 5

10 MILES

10 KILOMETERS

Figure 26. Simulated water-level change for Scenario C in the upper Dublin aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

GEORGIA

CAROLINA

SOUTH

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario C 

 (see table 6 for description of scenario)

Upper Three

Runs Creek

–1

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 26. Simulated water-level change for Scenario C in the upper Dublin aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

38  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
–1

–0.5

–2

–4

Figure 27. Simulated water-level change for Scenario C in the lower Dublin aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario C 

 (see table 6 for description of scenario)

0.5

Production well—Completed in the lower Dublin aquifer in which pumping 

 was adjusted for scenario

GEORGIA

CAROLINA

SOUTH

Upper Three

Runs Creek

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 27. Simulated water-level change for Scenario C in the lower Dublin aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow  39
–1

–0.5

–2

–4

–8

Figure 28. Simulated water-level change for Scenario C in the upper Midville aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario C 

 (see table 6 for description of scenario)

0.5

Production well—Completed in the upper Midville aquifer in which pumping 

 was adjusted for scenario

GEORGIA

CAROLINA

SOUTH

Upper Three

Runs Creek

Savannah River Site

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 28. Simulated water-level change for Scenario C in the upper Midville aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

40 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
–1

–0.5

–2

–4

–8

Figure 29. Simulated water-level change for Scenario C in the lower Midville aquifer, near Vogtle Electric Generation Plant, 

Georgia and South Carolina.

EXPLANATION

0 5

0 5

10 MILES

10 KILOMETERS

N

Brier

ALLENDALE

AIKEN

SCREVEN

JENKINS

BURKE

RICHMOND

BARNWELL

Base modified from U.S. Geological Survey

1:24,000-scale digital data

D

U

River

Savannah

Creek

D

U

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Vogtle Electric Generation Plant

Line of equal simulated water-level change—Interval, in feet, is variable.

 Computed by subtracting the simulated potentiometric surface for 

 2002 Base Case from the simulated potentiometric surface for Scenario C 

 (see table 6 for description of scenario)

–1

Production well—Completed in the lower Midville aquifer in which pumping 

 was adjusted for scenario 

GEORGIA

CAROLINA

SOUTH

Upper Three

Runs Creek

Savannah River Site

Aiken

Jenkins

Burke

Screven

Allendale

Barnwell

Richmond

SC

GA

Map area

Figure 29. Simulated water-level change for Scenario C in the lower Midville aquifer, near Vogtle Electric Generation 

Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow  41
Base modified from U.S. Geological Survey

1:24,000-scale digital data

0 5 10 MILES

0 5 10 KILOMETERS

AIKEN RICHMOND

JEFFERSON

ALLENDALE

BURKE

SCREVEN

JENKINS

River Savannah

Creek

Upper Three Runs Creek

Brier

BARNWELL

Savannah River Site

N

Figure 30. Particle-tracking results for the year 2002, Scenario C, near Vogtle Electric Generation Plant, Georgia and 

South Carolina.

Lower Dublin aquifer

Upper Midville aquifer

Lower Midville aquifer

Pen Branch Fault—Approximately located; D, downthrown side; U, upthrown side

Simulated ground-water flowpath—Particles placed at the center of 

 each of the three grid cells containing a Plant Vogtle production well

 at increments representing 10 percent of the aquifer thickness 

 (10 total particles per aquifer layer per cell). Five particle flowpaths

 for each layer are shown on map to avoid clutter

Vogtle Electric Generation Plant

EXPLANATION

Model boundary

D

U

D

U

GEORGIA

SOUTH

CAROLINA

Georgia

South

 Carolina

Study

area

Figure 30. Particle-tracking results for the year 2002, Scenario C, near Vogtle Electric Generation Plant, Georgia and 

South Carolina.

42  Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios
Model Limitations

The steady-state simulations presented herein are 

believed to depict reasonably changes in ground-water levels 

that resulted from pumping increases of 1.09 to 3.42 Mgal/d 

at VEGP and from a pumping decrease of 5.3 Mgal/d at SRS, 

which together represent less than 1 percent of the total simulated ground-water flow of 1,035 Mgal/d for 2002 (Cherry, 

2006). Because these pumping changes are of low magnitude 

and occur near the center of the simulated area, lateral boundaries generally have little influence on simulation results. 

An exception occurs for Scenario C in which drawdown in 

the upper and lower Midville aquifers extends to the model’s 

southwestern “no-flow” boundary. Simulated drawdown that 

reaches a no-flow boundary results in higher values than 

would occur if the boundary was not intercepted. Steady-state 

simulations are believed to be representative of local hydrologic conditions because response to changes in pumpage 

is short term and previous testing indicates the model is 

insensitive to changes in storage (Clarke and West, 1998).

The revised ground-water flow model (Cherry, 2006) 

used for this investigation is based on a drought period (2002) 

in which boundary head was lowered to reflect decreased 

recharge to the ground-water system. It is likely that boundary 

conditions reflecting average or wet periods would result in 

somewhat different patterns of water-level change than were 

simulated for this study. Despite these possible variations, it is 

likely that ground-water flowpaths and recharge areas would 

be largely the same.

The ground-water flow model used in this study is subject 

to the limitations described in Cherry (2006). These limitations include error and uncertainty in field measurements of 

water level and in estimates of pumping, limitations of the 

conceptual models, approximations made in representing the 

physical properties of the flow system and errors inherent in 

estimating the spatial distribution of these properties, approximations made in the formulation and application of model 

boundary and initial conditions, errors associated with numerical approximation and solution of the mathematical model of 

the flow system, and assumptions made in using the models to 

predict the future behavior of the flow system. 

In some local areas near the Pen Branch Fault, simulated 

water levels poorly matched observed water levels in the 

Gordon aquifer (layer A2). Near the P-19 well cluster site on 

SRS, and in the Savannah River alluvial valley near VEGP, 

simulated head was consistently lower than the observed head. 

The reasons for this mismatch are unknown; however, a localized hydraulic connection between layers A1 (Upper Three 

Runs) and A2 (Gordon) near the Pen Branch Fault on SRS has 

been suggested by previous investigators (Aadland and others, 

1991). Because the reason for the high water level in the 

Gordon aquifer was not substantiated by field investigations, 

it was decided by previous investigators (Clarke and West, 

1998) not to account for this effect in the calibration of the 

ground-water flow model.

Particle tracking using MODPATH is controlled largely 

by lateral and vertical head gradients, along with the hydraulic 

properties of the aquifers and confining units. In the VEGP 

area, data on the vertical hydraulic conductivity of aquifers, 

streambeds, and confining units are sparse. An additional 

limitation of particle tracking using MODPATH is the inability 

to determine whether a particle of water exits the flow system 

in a model cell containing a weak sink. A weak sink can be 

described as a discharge well that does not remove all the 

water entering a cell, so that some water continues to move 

through the system. Finally, the no-flow boundary condition along the southwestern boundary of the model limits the 

available area for a simulated flowpath. This limitation may 

have resulted in faster simulated time of travel in the lower 

Dublin aquifer for Scenario C than might have occurred if the 

no-flow boundary was located farther away from the pumping 

at VEGP.

Summary and Conclusions

An updated and calibrated MODFLOW ground-water 

flow model (Cherry, 2006) was used to simulate the effect of 

current and potential future pumping on ground-water levels 

and flowpaths near Vogtle Electric Generation Plant (VEGP), 

Ga., for a Base Case representing year 2002 conditions and 

three pumping scenarios:

Scenario A simulates a 1.09-million gallons per day 

(Mgal/d) increase in pumping at VEGP assuming average 

withdrawal rates with the operation of existing reactors 

(Units 1 and 2) and the proposed new reactors (Units 3 and 4). 

Scenario B simulates a 1.09-Mgal/d increase in pumping 

at VEGP, as was simulated in Scenario A, combined with a 

shutdown of the SRS facility (reduction of 5.3 Mgal/d). 

Scenario C simulates a 3.42-Mgal/d increase in pumping at VEGP that represents a higher rate of withdrawal for 

the proposed new reactor units during their startup period 

(3.42 Mgal/d), and continuation of year 2002 pumping rates 

(1.04 Mgal/d) in the existing reactor units.

Maximum water-level change resulting from increased 

pumping at VEGP (without changes at Savannah River Site 

(SRS) or elsewhere in the study area) were simulated in the 

pumped layers at VEGP—the lower Dublin and upper and 

lower Midville aquifers. Simulated maximum declines in these 

units were from 1 to greater than 2 feet (ft) for Scenario A and 

from 4 to greater than 8 ft for Scenario C. Although none of 

the VEGP wells are completed in the upper Dublin aquifer, 

simulated water-level changes were similar to those observed 

in the pumped lower Dublin aquifer, suggesting a large degree 

of interconnection between the two aquifers. A muted waterlevel decline from 0.25 to greater than 2 ft was simulated in 

the shallow Gordon and Millers Pond aquifers for Scenarios 

A and C as the result of leakage through confining units in 

response to decreased head in the production zones (lower 

Dublin and upper and lower Midville aquifers). 

Summary and Conclusions  43
The largest simulated water-level changes at VEGP were 

for Scenario C, which represents a tripling of current pumpage at the facility. Although such pumping rates are viewed as 

implausible for long-term operation of proposed Units 3 and 4, 

and are not proposed by Southern Nuclear Company, the scenario is designed to simulate pumping rates necessary to draw 

ground water from South Carolina to the VEGP production 

wells. For this scenario, drawdown was greater than 8 ft in the 

upper and lower Midville aquifers, and greater than 4 ft in the 

upper and lower Dublin aquifers. Drawdown exceeding 0.5 ft 

in these aquifers extended about 29 miles (mi) to the southwestern model boundary in Jenkins and Screven Counties, 

Ga., and about 14 mi eastward onto SRS in South Carolina.

For Scenario B, elimination of pumping at SRS resulted 

in large water-level changes near SRS, with rises of greater 

than 8 ft in the lower Dublin aquifer and greater than 4 ft in 

the upper Dublin and upper and lower Midville aquifers. At 

VEGP, the magnitude and extent of water-level decline resulting from increased pumping was less than in Scenario A with 

maximum declines of greater than 2 ft in the upper and lower 

Midville aquifers, greater than 1 ft in the lower Dublin aquifer, 

and greater than 0.5 ft in the upper Dublin aquifer. The waterlevel rise resulting from elimination of SRS pumping reduced 

the effect of pumping at VEGP on ground-water levels. 

Results of MODFLOW simulations were analyzed using 

the USGS particle-tracking code MODPATH (Pollock, 1994) 

to determine the source of water and associated time of travel 

to VEGP production wells. For each of the scenarios, most of 

the recharge to VEGP wells originated in an upland area near 

the county line between Burke and Jefferson Counties, Ga., 

with none of the recharge originating on SRS or elsewhere in 

South Carolina. An exception occurs for Scenario C, in which 

some of the recharge originates in an upland area in eastern 

Barnwell County, S.C. Simulated mean time of travel from 

recharge areas to the VEGP wells for the Base Case and the 

three scenarios was between about 2,700 and 3,800 years, 

with some variation related to changes in head gradients due 

to pumping changes. 

References Cited

Aadland, R.K., Gellici, J.A., and Thayer, Paul, 1995, 

Hydrogeologic framework of west-central South Carolina: 

South Carolina Department of Natural Resources, Water 

Resources Division Report 5, 200 p.

Aadland, R.K., Harris, M.K., Lewis, C.M., Gaughan, T.F., and 

Westbrook, T.M., 1991, Hydrostratigraphy of the general 

separations area, Savannah River Site (SRS), South Carolina: 

Aiken, S.C., U.S. Department of Energy Report WSRCRP-91-13, Westinghouse Savannah River Company, 114 p.

Arnett, M.W., and Mamatey, A.R., eds.,1996, Savannah River 

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Waddell, M.G., Keith, J.F., and Domoarcki, W.J., 1995, High 
Manuscript approved for publication, October 23, 2007

Prepared by USGS Georgia Water Science Center

Edited and page layout by Patricia L. Nobles

Graphics by Bonnie J. Turcott

For more information concerning the research in this report, contact 

USGS Georgia Water Science Center, Atlanta, 

telephone: 770-903-9100