Cover photograph: Savannah River at Brighams Landing, Burke County, Georgia

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

Ground-Water Flow near the Savannah River Site, 

Georgia and South Carolina, 2002, and for 

Selected Ground-Water Management Scenarios, 

2002 and 2020

By Gregory S. Cherry

Prepared in cooperation with the U.S. Department of Energy

Scientific Investigations Report 2006–5195

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

This report is a Web-only publication: http://pubs.usgs.gov/sir/2006/5195/

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Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Cherry, G.S., 2006, Simulation and particle-tracking analysis of ground-water flow near the Savannah River Site, 

Georgia and South Carolina, 2002, and for selected water-management scenarios, 2002 and 2020: U.S. 

Geological Survey Scientific Investigations Report 2006–5195, 156 p. 
Contents

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

Introduction................................................................................................................................................ 2

Purpose and Scope ......................................................................................................................... 3

Description of Study Area .............................................................................................................. 3

Previous Investigations................................................................................................................... 6

Methods of Study............................................................................................................................. 8

Acknowledgments........................................................................................................................... 8

Hydrologic, Climatic, and Ground-Water Use Conditions, 1992–2002.............................................. 8

Precipitation...................................................................................................................................... 8

Ground-Water Use........................................................................................................................... 9

Ground-Water Levels ...................................................................................................................... 11

Streamflow........................................................................................................................................ 13

Simulation of Steady-State Ground-Water Flow, 2002 ....................................................................... 16

Updating the Model to 2002 Conditions ....................................................................................... 17

Simulated Water Budget ................................................................................................................ 20

Simulated Water-Level Changes................................................................................................... 30

Particle-Tracking and Time-of-Travel Analysis........................................................................... 31

Zone 1........................................................................................................................................ 38

Zone 2........................................................................................................................................ 40

Zone 3........................................................................................................................................ 42

Zone 4........................................................................................................................................ 42

Zone 5........................................................................................................................................ 42

Trans-River Flow ..................................................................................................................... 47

Simulation of Ground-Water Management Scenarios, 2002 and 2020 ............................................ 49

Adjustments to Boundary Conditions........................................................................................... 49

Projected Pumping .......................................................................................................................... 50

Comparison of Scenarios ............................................................................................................... 52

Limitations of Digital Simulation and Particle Tracking...................................................................... 56

Summary and Conclusions...................................................................................................................... 56

Selected References................................................................................................................................ 59

Appendix A. Scenario A—Simulation of 2002 Average Conditions .............................................. 63

Appendix B. Scenario B—Simulation of 2002 Average Conditions without Savannah 

River Site pumping ...................................................................................................................... 81

Appendix C. Scenario C—Simulation of 2020 Average Conditions............................................... 99

Appendix D. Scenario D—Simulation of 2020 Dry Conditions....................................................... 117

Appendix E. Observed and Simulated Ground-Water Levels, 1987–92 and 2002....................... 135

iii
Figures

1. Maps showing location of study area, Savannah River Site, Brighams Landing 

well-cluster site, precipitation monitoring sites, mean-annual rainfall, 1969–98, and 

physiographic provinces and districts in Georgia and South Carolina, and areal 

and local ground-water contamination at the Savannah River Site, South Carolina.... 4

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

boundary conditions for the Savannah River Site area, South Carolina, groundwater model.............................................................................................................................. 7

3. Graph showing cumulative departure from normal precipitation for Augusta, 

Georgia, and Aiken, South Carolina, July 1948 through December 2002 ....................... 9

4. Pie charts showing ground-water use in selected counties in Georgia and 

South Carolina, 1987–2000...................................................................................................... 9

5. Graphs showing water-level altitude for wells 32Y030, 32Y031, and 32Y033 at the 

Brighams Landing well-cluster site, 1995–2002.................................................................. 11

6. Potentiometric-surface maps for the Upper Three Runs aquifer, Gordon aquifer, 

Dublin aquifer system, and Midville aquifer system during 1992 and 2002, 

near the Savannah River Site, Georgia and South Carolina............................................. 12

7–10. Maps showing—

7. Mean-annual runoff in Georgia part of study area, 1941–70; and locations of 

selected U.S. Geological Survey streamflow gaging stations ................................ 14

8. Location of study area, Savannah River Site, South Carolina, model grid, and 

model boundary .............................................................................................................. 16

9. Model area, active area of source-sink layer A1, and potentiometric 

surface for the Upper Three Runs aquifer during 2002 in the Savannah 

River Site (SRS) area, South Carolina, and enlargement of SRS area................... 18

10. Estimated water-level change between the current (2002) and previously 

developed (1987–92) models for the Upper Three Runs aquifer (source-sink 

layer A1) in the Savannah River Site area, South Carolina ..................................... 21

11–16. Maps showing simulated 2002 potentiometric surface, water-level altitude, and 

location of simulated river cells for the—

11. Gordon aquifer (layer A2) in the Savannah River Site area, South Carolina........ 22

12. Millers Pond aquifer (layer A3) in the Savannah River Site area, 

South Carolina................................................................................................................. 23

13. Upper Dublin aquifer (layer A4) in the Savannah River Site area, 

South Carolina................................................................................................................. 24

14. Lower Dublin aquifer (layer A5) in the Savannah River Site area, 

South Carolina................................................................................................................. 25

15. Upper Midville aquifer (layer A6) in the Savannah River Site area, 

South Carolina................................................................................................................. 26

16. Lower Midville aquifer (layer A7) in the Savannah River Site area, 

South Carolina................................................................................................................. 27

17–18. Charts showing—

17. Simulated 1987–92 and 2002 dry water budgets........................................................ 28

18. Simulated 2002 dry conditions water budget by layer and comparison of 

budget terms with 1987–92 long-term average simulation...................................... 28

19. Graph showing mean-annual net gain in streamflow for the Savannah River 

(Augusta [02197000] to Millhaven [02197500], Georgia) and mean-annual 

streamflow for Upper Three Runs Creek (02197315) for water years 1992–2002, 

and simulated ground-water discharge for 1992 and 2002............................................... 29

20. Boxplot showing difference (residuals) between observed and simulated heads 

for the 2002 simulation ............................................................................................................ 30

iv
Figures—continued

21–26. Maps showing simulated water-level change between 1987–92 long-term average 

and 2002 dry conditions and locations of simulated pumpage in the—

21. Gordon aquifer (layer A2) in the Savannah River Site area, South Carolina........ 32

22. Millers Pond aquifer (layer A3) in the Savannah River Site area, 

South Carolina................................................................................................................. 33

23. Upper Dublin aquifer (layer A4) in the Savannah River Site area, 

South Carolina................................................................................................................. 34

24. Lower Dublin aquifer (layer A5) in the Savannah River Site area, 

South Carolina................................................................................................................. 35

25. Upper Midville aquifer (layer A6) in the Savannah River Site area, 

South Carolina................................................................................................................. 36

26. Lower Midville aquifer (layer A7) in the Savannah River Site area, 

South Carolina................................................................................................................. 37

27–31. Maps showing particle-tracking results from the simulation of 2002 dry conditions 

at selected time intervals in—

27. Zone 1 located in the northwestern part of the Savannah River Site, 

South Carolina................................................................................................................. 39

28. Zone 2 located in the central part of the Savannah River Site, 

South Carolina................................................................................................................. 41

29. Zone 3 located in the northeastern part of the Savannah River Site, 

South Carolina................................................................................................................. 43

30. Zone 4 located in the south-central part of the Savannah River Site, 

South Carolina................................................................................................................. 44

31. Zone 5 located in the eastern part of the Savannah River Site, 

South Carolina................................................................................................................. 45

32. Schematic diagram showing particle-seeding distribution for cells located 

in trans-river zones.................................................................................................................. 47

33. Map showing simulated trans-river flow for 2002 dry conditions and selected 

ground-water pathlines in map view, and selected ground-water pathlines in 

cross-sectional view along row 82 at the Savannah River Site, South Carolina.......... 48

34. Graph showing total ground-water withdrawals including irrigation (1980–2002), 

and projected pumpage including irrigation (Scenarios C and D) during 2020 for 

the eight-county study area................................................................................................... 52

A1. Chart showing simulated 2002 average conditions (Scenario A) water budget by 

layer and comparison of budget terms with 2002 dry conditions.................................... 68

A2–A7. Maps showing simulated water-level change between 2002 dry conditions and 

2002 average conditions (Scenario A), and locations of simulated pumpage in the—

A2. Gordon aquifer (layer A2) in the Savannah River Site area, 

South Carolina................................................................................................................. 69

A3. Millers Pond aquifer (layer A3) in the Savannah River Site area, 

South Carolina................................................................................................................. 70

A4. Upper Dublin aquifer (layer A4) in the Savannah River Site area, 

South Carolina................................................................................................................. 71

A5. Lower Dublin aquifer (layer A5) in the Savannah River Site area, 

South Carolina................................................................................................................. 72

A6. Upper Midville aquifer (layer A6) in the Savannah River Site area, 

South Carolina................................................................................................................. 73

A7. Lower Midville aquifer (layer A7) in the Savannah River Site area, 

South Carolina................................................................................................................. 74
vi

Figures—continued

A8–A12. Maps showing particle-tracking results from the simulation of 2002 average 

conditions (Scenario A) at selected time intervals in—

A8. Zone 1 located in the northwestern part of the Savannah River Site, 

South Carolina................................................................................................................. 75

A9. Zone 2 located in the central part of the Savannah River Site, 

South Carolina................................................................................................................. 76

A10. Zone 3 located in the northeastern part of the Savannah River Site, 

South Carolina................................................................................................................. 77

A11. Zone 4 located in the south-central part of the Savannah River Site, 

South Carolina................................................................................................................. 78

A12. Zone 5 located in the eastern part of the Savannah River Site, 

South Carolina................................................................................................................. 79

A13. Map showing simulated trans-river flow for 2002 average conditions 

(Scenario A) and selected ground-water pathlines in map view, and selected 

ground-water pathlines in cross-sectional view along row 82 (see figure 8) 

at the Savannah River Site area, South Carolina............................................................... 80

B1. Chart showing simulated 2002 average conditions without Savannah River Site 

pumping (Scenario B) water budget by layer and comparison of budget terms 

with simulated 2002 average conditions (Scenario A)...................................................... 86

B2–B7. Maps showing simulated water-level change between 2002 average conditions 

(Scenario A) and 2002 average conditions without Savannah River Site pumping 

(Scenario B), and locations of simulated pumpage in the—

B2. Gordon aquifer (layer A2) in the Savannah River Site area, South Carolina........ 87

B3. Millers Pond aquifer (layer A3) in the Savannah River Site area, 

South Carolina................................................................................................................. 88

B4. Upper Dublin aquifer (layer A4) in the Savannah River Site area, 

South Carolina................................................................................................................. 89

B5. Lower Dublin aquifer (layer A5) in the Savannah River Site area, 

South Carolina................................................................................................................. 90

B6. Upper Midville aquifer (layer A6) in the Savannah River Site area, 

South Carolina................................................................................................................. 91

B7. Lower Midville aquifer (layer A7) in the Savannah River Site area, 

South Carolina................................................................................................................. 92

B8–B12. Maps showing particle-tracking results from the simulation of 2002 average 

 conditions without Savannah River Site (SRS) pumping (Scenario B) at 

 selected time intervals in—

B8. Zone 1 located in the northwestern part of the Savannah River Site, 

South Carolina................................................................................................................. 93

B9. Zone 2 located in the central part of the Savannah River Site, 

South Carolina................................................................................................................. 94

B10. Zone 3 located in the northeastern part of the Savannah River Site, 

South Carolina................................................................................................................. 95

B11. Zone 4 located in the south-central part of the Savannah River Site, 

South Carolina................................................................................................................. 96

B12. Zone 5 located in the eastern part of the Savannah River Site, 

South Carolina................................................................................................................. 97

B13. Map showing simulated trans-river flow for 2002 average conditions without 

Savannah River Site (SRS) pumping (Scenario B) and selected ground-water 

pathlines in map view, and selected ground-water pathlines in crosssectional view along row 82 (see figure 8) at the SRS, South Carolina.......................... 98
Figures—continued

C1. Chart showing simulated 2020 average conditions (Scenario C) water budget by 

layer and comparison of budget terms with simulated 2002 average conditions 

(Scenario A).............................................................................................................................. 104

C2–C7. Maps showing simulated water-level change between 2002 average conditions 

(Scenario A) and 2020 average conditions (Scenario C), and locations of 

simulated pumpage in the —

C2. Gordon aquifer (layer A2) in the Savannah River Site area, 

South Carolina................................................................................................................. 105

C3. Millers Pond aquifer (layer A3) in the Savannah River Site area, 

South Carolina................................................................................................................. 106

C4. Upper Dublin aquifer (layer A4) in the Savannah River Site area, 

South Carolina................................................................................................................. 107

C5. Lower Dublin aquifer (layer A5) in the Savannah River Site) area, 

South Carolina................................................................................................................. 108

C6. Upper Midville aquifer (layer A6) in the Savannah River Site area, 

South Carolina................................................................................................................. 109

C7. Lower Midville aquifer (layer A7) in the Savannah River Site area, 

South Carolina................................................................................................................. 110

C8–C12. Maps showing article-tracking results from the simulation of 2020 average 

conditions (Scenario C) at selected time intervals in—

C8. Zone 1 located in the northwestern part of the Savannah River Site, 

South Carolina................................................................................................................. 111

C9. Zone 2 located in the central part of the Savannah River Site, 

South Carolina................................................................................................................. 112

C10. Zone 3 located in the northeastern part of the Savannah River Site, 

South Carolina................................................................................................................. 113

C11. Zone 4 located in the south-central part of the Savannah River Site, 

South Carolina................................................................................................................. 114

C12. Zone 5 located in the eastern part of the Savannah River Site, 

South Carolina................................................................................................................. 115

C13. Map showing simulated trans-river flow for 2020 average conditions (Scenario C) 

and selected ground-water pathlines in map view, and selected ground-water 

pathlines in cross-sectional view along row 82 (see figure 8) at the 

Savannah River Site, South Carolina.................................................................................... 116

D1. Chart showing simulated 2020 dry conditions (Scenario D) water budget by 

layer and comparison of budget terms with simulated 2002 dry conditions ................. 122

D2–D7. Maps showing simulated water-level change between 2002 dry conditions and 

2020 dry conditions (Scenario D), and locations of simulated pumpage in the—

D2. Gordon aquifer (layer A2) in the Savannah River Site area, 

South Carolina................................................................................................................. 123

D3. Millers Pond aquifer (layer A3) in the Savannah River Site area, 

South Carolina................................................................................................................. 124

D4. Upper Dublin aquifer (layer A4) in the Savannah River Site area, 

South Carolina................................................................................................................. 125

D5. Upper Midville aquifer (layer A5) in the Savannah River Site area, 

South Carolina................................................................................................................. 126

D6. Upper Midville aquifer (layer A6) in the Savannah River Site area, 

South Carolina................................................................................................................. 127

D7. Lower Midville aquifer (layer A7) in the Savannah River Site area, 

South Carolina................................................................................................................. 128

vii
Figures—continued

D8–D12. Maps showing particle-tracking results from the simulation of 2020 dry 

conditions (Scenario D) at selected time intervals in—

D8. Zone 1 located in the northwestern part of the Savannah River Site, 

South Carolina................................................................................................................. 129

D9. Zone 2 located in the central part of the Savannah River Site, 

South Carolina................................................................................................................. 130

D10. Zone 3 located in the northeastern part of the Savannah River Site, 

South Carolina................................................................................................................. 131

D11. Zone 4 located in the south-central part of the Savannah River Site, 

South Carolina................................................................................................................. 132

D12. Zone 5 located in the eastern part of the Savannah River Site, 

South Carolina................................................................................................................. 133

D13. Map showing simulated trans-river flow for 2020 dry conditions (Scenario D) 

and selected ground-water pathlines in map view, and selected groundwater pathlines in cross-sectional view along row 82 (see figure 8) at the 

Savannah River Site, South Carolina.................................................................................... 134

E1–E7. Maps showing location of wells used for the 2002 dry simulation for the —

E1. Gordon aquifer (layer A2) in the Savannah River Site area, 

South Carolina .................................................................................................................140

E2. Gordon aquifer (layer A2) (enlargement of area shown in figure E1) in the 

Savannah River Site area, South Carolina..................................................................141

E3. Millers Pond aquifer (layer A3) in the Savannah River Site area, 

South Carolina ...................................................................................................................42

E4. Upper Dublin aquifer (layer A4) in the Savannah River Site area, 

South Carolina .................................................................................................................143

E5. Lower Dublin aquifer (layer A5) in the Savannah River Site area, 

South Carolina .................................................................................................................144

E6. Upper Midville aquifer (layer A6) in the Savannah River Site area, 

South Carolina. ................................................................................................................145

E7. Lower Midville aquifer (layer A7) in the Savannah River Site area, 

South Carolina .................................................................................................................146

viii
Tables

1. Ground-water use during 1990, 1995, and 2000–2002 near the Savannah River Site, 

South Carolina.......................................................................................................................... 10

2. Mean-annual discharge to selected streams near the Savannah River Site, 

Georgia and South Carolina, water years 1992–2002 ........................................................ 15

3. Ranges of field observations and estimates for transmissivity, confining unit 

leakance, and streambed conductance by hydrogeologic unit for ground-water 

flow model near the Savannah River Site, South Carolina ................................................. 17

4. Simulated pumpage by model layer 1987–92 and 2002 ..................................................... 28

5. Comparison of calibration statistics between the 1987–92 and 2002, dry steadystate model simulations.......................................................................................................... 30

6. Time-of-travel for particles seeded in recharge areas (five zones) on Savannah 

River Site, South Carolina, and forward tracked through time to discharge areas ..... 46

7. Results of particle backtracking from trans-river areas in Georgia to recharge 

cells located in the Savannah River Site, South Carolina................................................. 49

8. Ground-water management scenarios developed for the Savannah River Site region 

and relative changes to specified heads in the source-sink layer A1, specified 

heads located along lateral boundaries in the active model layers (A2–A7), 

and simulated pumping................................................................................................................. 49

9. Ground-water use during 2002 and projected pumpage for 2020 average 

hydrologic conditions near the Savannah River Site, South Carolina and Georgia..... 50

10. Total water use for irrigation, irrigated acreage, and ground-water withdrawals 

for irrigation during 2000–2002, mean application rate during 1980–2002, and 

projected water-use for irrigation in the year 2020 for the Savannah River Site 

region, South Carolina and Georgia ..................................................................................... 51

11. Water budgets for 1987–92, 2002, and Scenarios A–D, Savannah River Site, 

South Carolina.......................................................................................................................... 54

A1. Time-of-travel for particles seeded in recharge areas (five zones) on 

Savannah River Site, South Carolina, and forward tracked through time to 

discharge areas........................................................................................................................... 67

B1. Time-of-travel for particles seeded in recharge areas (five zones) on Savannah 

River Site, South Carolina, and forward tracked through time to discharge areas ......... 85

C1. Time-of-travel for particles seeded in recharge areas (five zones) on Savannah 

River Site, South Carolina, and forward tracked through time to discharge areas. ........ 103

D1. Time-of-travel for particles seeded in recharge areas (five zones) on Savannah 

River Site, South Carolina, and forward tracked through time to discharge areas ......... 121

E1. Measured heads, simulated 1987–92 and 2002 heads, head differences, error 

criteria in wells used for previous model calibration ........................................................ 136

ix
Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2) 0.09290 square meter (m2)

square inch (in2) 6.452 square centimeter (cm2)

section (640 acres or 1 square mile) 259.0 square hectometer (hm2) 

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

gallon (gal) 3.785 cubic decimeter (dm3) 

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

Flow rate

foot per day (ft/d) 0.3048 meter per day (m/d)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second per square

mile [(ft3/s)/mi2]

 0.01093 cubic meter per second per square

kilometer [(m3/s)/km2]

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

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

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

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Radioactivity

picocurie per liter (pCi/L) 0.037 becquerel per liter (Bq/L) 

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d) 

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times foot of aquifer thickness 

[(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot squared per day (ft2/d), is used for convenience.

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.
Simulation and Particle-Tracking Analysis of 

Ground-Water Flow near the Savannah River Site, 

Georgia and South Carolina, 2002, and for 

Selected Ground-Water Management Scenarios, 

2002 and 2020

By Gregory S. Cherry

Abstract

Ground-water flow under 2002 hydrologic conditions was 

evaluated in an eight-county area in Georgia and South Carolina 

near the Savannah River Site (SRS), by updating boundary 

conditions and pumping rates in an existing U.S. Geological 

Survey (USGS) ground-water model. The original groundwater model, developed to simulate hydrologic conditions 

during 1987–92, used the quasi-three-dimensional approach by 

dividing the Floridan, Dublin, and Midville aquifer systems 

into seven aquifers. The hydrogeologic system was modeled 

using six active layers (A2–A7) that were separated by confining 

units with an overlying source-sink layer to simulate the unconfined Upper Three Runs aquifer (layer A1). Potentiometricsurface maps depicting September 2002 for major aquifers 

were used to update, evaluate, and modify boundary conditions 

used by the earlier ground-water flow model.

The model was updated using the USGS finite-difference 

code MODFLOW–2000 for mean-annual conditions during 

1987–92 and 2002. The specified heads in the source-sink layer A1 were lowered to reflect observed water-level declines during the 1998–2002 drought. These declines resulted in a decrease 

of 12.1 million gallons per day (Mgal/d) in simulated recharge 

or vertical inflow to the uppermost confined aquifer (Gordon, 

layer A2). Although ground-water pumpage in the study area 

has increased by 32 Mgal/d since 1995, most of this increase 

(17.5 Mgal/d) was from the unconfined Upper Three Runs 

aquifer (source-sink layer A1) with the remaining 14.5 Mgal/d 

assigned to the active layers within the model (A2–A7).

The simulated water budget for 2002 shows a decrease 

from the 1987–92 model from 1,040 Mgal/d to 1,035 Mgal/d. 

The decreased ground-water inflows and increased groundwater withdrawal rates reduced the simulated ground-water 

outflow to river cells in the active layers of the model by 

43 Mgal/d. The calibration statistics for all layers of the 

2002 simulation resulted in a decrease in the root mean square 

(RMS) of the residuals from 10.6 to 8.0 feet (ft). The residuals 

indicate 83.3 percent of the values for the 2002 simulation met 

the calibration error criteria established in the original model, 

whereas 88.8 percent was within the specified range for the 

1987–92 simulation. Simulated ground-water outflow to the 

Savannah River and its tributaries during water year 2002 was 

560 cubic feet per second (ft3/s), or 86 percent of the observed 

gain in mean-annual streamflow between streamflow gaging 

stations at the Millhaven, Ga., and Augusta, Ga. At Upper 

Three Runs Creek, simulated ground-water discharge during 

2002 was 110 ft3/s, or 83 percent of the observed streamflow 

at two streamflow gaging stations near the SRS. These results 

indicate that the constructed model calibrated to 1987–92 conditions and modified for 2002 dry conditions is still representative of the hydrologic system.

The USGS particle-tracking code MODPATH was used 

to generate advective water-particle pathlines and their associated time-of-travel based on MODFLOW simulations for 

1987–92, 2002, and each of four hypothetical ground-water 

management scenarios. The four hypothetical ground-water 

management scenarios represent hydrologic conditions for 

(1) reported pumping for 2002 and boundary conditions for 

an average year; (2) reported pumping for 2002 with SRS 

pumping discontinued and boundary conditions for an average 

year; (3) projected 2020 pumping and boundary conditions for 

an average year; and (4) projected 2020 pumping and boundary conditions for a dry year. The MODPATH code was used 

in forward-tracking mode to evaluate flowpaths from areas on 

the SRS and in backtracking mode to evaluate further areas of 

previously documented trans-river flow on the Georgia side of 

the Savannah River. Trans-river flow is a condition in which 

the local head gradients might allow migration of contaminants from the SRS into the underlying aquifers and beneath 

the Savannah River into Georgia.

The analysis of ground-water flowpaths using MODPATH was conducted by establishing five zones in which 

particles were seeded into model cells based on the following 

criteria: (1) occurrence of recharge from the source-sink layer 
A1 (Upper Three Runs aquifer) into layer A2 (Gordon aquifer), (2) downward flow from layer A2 (Gordon aquifer) into 

layers A3–A5 (Dublin aquifer system), (3) delineated areas of 

contamination or storage of hazardous materials on the SRS, 

and (4) defined surface-water drainage divides. Selected areas 

near streams on the SRS were not considered for the analysis 

because of localized flow regimes to nearby streams. In the 

case of trans-river flow areas, particles were placed in cells 

located on the western side of the Savannah River floodplain 

near Flowery Gap Landing in Burke County, Ga., and backtracked to recharge areas on the SRS.

The most influential factors controlling particle movement are vertical and lateral head gradients and pumping 

distribution within the active layers of the model. MODPATH 

results indicate that Upper Three Runs Creek and the alluvial 

valley of the Savannah River are the dominant sinks or areas 

of ground-water discharge with time-of-travel ranging from 

20 to greater than 2,000 years (yr). Simulated ground-water 

flowpaths for each of the four ground-water management scenarios were generally limited to areas within the SRS boundary 

because this is the area of concern for contaminant transport. 

Five particle seed zones were established in which individual particles were observed from their point of recharge 

to discharge areas located along local streams within the 

boundaries of the SRS or the Savannah River. The median 

time-of-travel listed below for each of the five zones represents a range for the five simulations (2002, Scenarios A, B, 

C, and D). In general, the elimination of pumping at the SRS 

(Scenario B) reduces the time-of-travel for particles to reach 

the discharge areas. In zone 1, median time-of-travel from 

recharge areas to discharge areas located along Upper Three 

Runs Creek and west of the SRS boundary ranges from 217 to 

264 yr. In zone 2, median time-of-travel from recharge areas 

to discharge areas located along Upper Three Runs Creek, Pen 

Branch, Fourmile Branch, and the Savannah River ranges from 

524 to 593 yr. In zone 3, median time-of-travel from recharge 

areas to discharge areas located along Upper Three Runs 

Creek ranges from 834 to 1,150 yr. In zone 4, median time-oftravel from recharge areas to discharge areas located along the 

South Carolina side of the Savannah River ranges from 395 to 

404 yr. In zone 5, median time-of-travel from recharge areas 

to discharge areas located along Lower Three Runs Creek 

and the Savannah River ranges from 1,310 to 1,350 yr. The 

longer travel times are generally associated with particles that 

penetrate deeper into the underlying aquifers before moving 

laterally toward discharge areas.

For the backtracking analysis of particles, three model 

cells located near Flowery Gap Landing (covering about 

1 square mile) on the Georgia side of the Savannah River 

were chosen based on results from forward-tracking analysis 

(zone 2), indicating these cells as common discharge areas. 

Of the 300 particles released in these three cells, as few as 

88 particles (29 percent, 2002, Scenario C) to as many as 

110 particles (37 percent, Scenario B) backtrack to recharge 

areas on the SRS (trans-river flow). Of the particles exhibiting trans-river flow, the median time-of-travel along pathlines 

range from 366 to 507 yr with north of the Pen Branch Fault. 

Backtrack time-of-travel for the shortest flowpaths ranged 

from 79 to 82 yr from trans-river flow to interstream areas 

located north of Fourmile Branch with 10 percent of these particles reaching endpoints at about 100 yr. The results indicate 

that simulations with active SRS pumping centers (1987–92, 

2002, Scenarios A, C, and D) allowed fewer particles to 

migrate to the Georgia side of the Savannah River. If these 

SRS production wells are deactivated (Scenario B), the number of particles migrating to trans-river zones increases to 

110 and the median time-of-travel decreases to about 370 yr 

with a shortest time-of-travel period of about 80 yr.

Generally, time-of-travel for particles migrating downward through the Gordon confining unit (C1) and then moving 

laterally through layer A2 (Gordon aquifer) to discharge areas 

ranges from 20 to 200 yr. For particles migrating deeper into 

layers A3 through A5 (Dublin aquifer system), time-of-travel 

generally ranges from 200 to 1,000 yr. Eliminating pumping 

on the SRS (Scenario B) reduces the depth of penetration of 

particles and shortens the pathways to discharge areas with 

median time-of-travel decreased from 15 to 70 yr in zones 1 

and 2. The second most influential factor controlling particle 

movement is the adjustment of heads in the source-sink layer A1, which affects the amount of recharge entering the system. In areas of trans-river flow, from 29 to 37 percent of the 

particles placed in three grid cells located near Flowery Gap 

Landing backtrack to recharge areas on the SRS. For these 

particles, the shortest travel time from 80 to 415 yr was for 

particles moving laterally through layer A2 (Gordon aquifer) 

and upward into the base of the source-sink layer A1 (Upper 

Three Runs aquifer) in areas south of Fourmile Branch.

Introduction

The U.S. Department of Energy (DOE), Savannah River 

Site (SRS)—located near Aiken, South Carolina (fig. 1A)—

has manufactured nuclear materials for national defense 

purposes since the early 1950s. Hazardous materials—

including tritium, other radionuclides, volatile organic compounds, and trace metals—are either disposed of or stored at 

many locations on the SRS (fig. 1B). Tritium, which is a radioactive form of hydrogen with a half-life of 12.33 years (yr), 

has been manufactured for national defense purposes since the 

1950s and must be replenished because of its relatively short 

half-life. State of Georgia officials have raised concern about 

the possible migration of tritiated water from the SRS into the 

underlying aquifers and beneath the Savannah River (transriver flow) into Georgia. During July 1991, DOE entered into 

a cooperative agreement with the U.S. Geological Survey 

(USGS) to investigate the conditions under which trans-river 

flow might develop. The Georgia Geologic Survey (GGS), 

a branch of the Georgia Environmental Protection Division 

(GaEPD), was assigned funding to drill and monitor wells for 

tritium. As part of a 1991–97 study, the USGS completed a 

   Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
steady-state ground-water flow model simulating predevelopment and 1987–92 flow conditions for the SRS and vicinity 

(Clarke and West, 1998). The model simulations included 

particle-tracking analysis of ground-water movement to 

determine time-of-travel from the present-day Savannah River 

floodplain to areas of recharge on the SRS.

The USGS, in cooperation with DOE, has been conducting additional work since July 2002 to determine the occurrence 

of trans-river flow under 2002 and future hydrologic conditions. The major objectives of this study are to (1) update the 

previously developed ground-water flow model to define and 

quantify present-day (2002) ground-water flow near SRS, and 

(2) use the updated model to describe and quantify groundwater flow near SRS under 2002 conditions and for four hypothetical ground-water management scenarios. Modifications to 

the original ground-water flow model included adjustments to 

boundary conditions and pumping. Future ground-water use 

projections to the year 2020 were based on 1980–2000 water 

use and an estimated increase of 80,000 residents for the eightcounty study area. The study included detailed particle-tracking 

analysis of ground-water flowpaths on SRS for each of the five 

simulations and assessment of potential tritium migration to the 

Georgia side of the Savannah River (trans-river flow).

Purpose and Scope

This report describes (1) changes in hydrologic and pumping conditions that have occurred since the calibration 

of the earlier (1987–92) USGS ground-water model, (2) revisions made to the model on the basis of changing hydrologic 

conditions, (3) revised calibration statistics for the model for 

2002, and (4) results of ground-water flow and particle-tracking 

analysis for 2002 and for four hypothetical ground-water management scenarios during 2002 and 2020. Synoptic groundwater-level measurements were taken in 189 wells during 

early September 2002, and potentiometric-surface maps were 

constructed (Cherry, 2003) for the Upper Three Runs and Gordon aquifers and the Dublin and Midville aquifer systems. The 

ground-water-level measurements were used as control points 

to evaluate whether the previously developed model could accurately simulate 2002 hydrologic conditions by limiting changes 

to boundary and pumping conditions. Potentiometric-surface 

maps constructed using the September 2002 data served as the 

basis for adjustments to specified heads for each of the model 

layers. Continuous and periodic ground-water-level measurements were evaluated to determine trends during 1992–2002. 

Ground-water use data from 1992 to 2002 were compiled 

for irrigation, industrial, and public supply categories using 

published reports and data files for Burke, Jefferson, Jenkins, 

Richmond, and Screven Counties, Ga., and Aiken, Allendale, 

and Barnwell Counties, S.C. (fig. 1A). During 2000, GGS 

inventoried irrigation wells within Burke, Jenkins, and Screven 

Counties and obtained information from individual farmers 

regarding crop type, irrigated acreage, well depth, and pump 

capacity. Water-use projections were made for the eight-county 

study area on the basis of expected population growth and per 

capita water use during 1980–2000 and ground-water management scenarios were developed for the year 2020 (Scenarios C 

and D). Additional ground-water management scenarios were 

developed to evaluate the effects of changing boundary conditions and pumpage on ground-water flowpaths near SRS (Scenarios A and B). Five zones were established for the placement 

of particles on the SRS based on downward head gradient and 

the location of contamination or storage of hazardous materials (fig. 1B). The particles were analyzed for movement and 

time-of-travel from recharge areas to potential discharge areas 

along local streams or the floodplain of the Savannah River. 

Additional particle analysis was performed in areas of potential 

trans-river flow, or movement from the SRS toward discharge 

areas located on the Georgia side of the Savannah River.

Description of Study Area

The 5,147 square mile (mi2) study area is in the northern 

part of the southeastern Coastal Plain physiographic province 

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. Relief is 

generally 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 can be 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 stream 

pattern. Streams that flow over the relatively softer 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). The floodplains 

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

wide expanse of swamp bordering both sides of the channel. 

The Coastal Plain is subdivided into six topographic districts 

in the study area: Coastal Terraces, Tifton Upland, Louisville Plateau, Aiken Plateau, Congaree Sand, and Fall Line 

Hills (Clark and Zisa, 1976). See Clarke and West (1997) for 

detailed descriptions of each of these features.

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

The SRS encompasses about 310 mi2, or 6 percent of the 

study area, and lies in parts of Aiken, Barnwell, and Allendale 

Counties, S.C. (fig. 1A).

Introduction 
AIKEN

BURKE

ORANGEBURG

BULLOCH

SCREVEN

LEXINGTON

SALUDA

HAMPTON

BARNWELL

JEFFERSON

EDGEFIELD

JENKINS

BAMBERG

ALLENDALE

MCCORMICK

WARREN

RICHMOND

COLUMBIA

MCDUFFIE

GLASCOCK

Augusta

Aiken

49.0

48.7

46.5

49.4

47.0

47.6

48.6

52.7

48.2

45.4

46.4

45.9

46.5

48.7

46.5

49.0

47.9

44.9

48

48

48

48

50

46

52

46

48

48

82° 81°

33°

34° Map

area

GEORGIA

SOUTH

CAROLINA

Atlantic Ocean

Savannah Coastal

Plain

Coastal

Plain

D

U

A.

Pen

Branch

Fault

Belair

Fault

D U

0 10 20 30 MILES

0 10 20 30 KILOMETERS

EXPLANATION

Brighams Landing well-cluster site

Study area

Precipitation-monitoring site

and rainfall amount

Line of equal mean-annual rainfall,

1969–98—Interval 2 inches

46

SRS

Fall Line Hills District

Aiken Plateau District

Congaree Sand District

Louisville Plateau District

Tifton Upland District

Coastal Terraces District

Coastal Plain Province

Physiographic districts from Cooke, 1936;

and LaForge and others, 1925

48.2

Base modified from U.S. Geological Survey

1:500,000-scale digital State base maps

Piedmont Province

GEORGIA

SOUTH

CAROLINA

Savannah

River

D

U

Fault—D, downthrown side;

U, upthrown side

Figure 1. (A) Location of study area, Savannah River Site (SRS), Brighams Landing well-cluster site, 

precipitation monitoring sites, mean-annual rainfall, 1969–98, and physiographic provinces and districts in 

Georgia and South Carolina (rainfall data from Southeast Regional Climate Center, accessed February 11, 

2004, at http://www.dnr.sc.gov/climate/sercc/); and (B) areal and local ground-water contamination at the 

SRS, South Carolina (modified from Arnett and Mamatey, 1996).

 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
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

33°20'

81°50' 81°40' 81°30'

33°10'

33°00'

Pen

Branch

Meyers Branch

Steel Creek

Tinker Creek

Lower

Three

Runs Creek

Newberry Creek

McBean Cr

Branch

Par

Pond

L

Lake

Hollow

Creek

Savannah River

1

2

3

5

4

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Jackson

Eagle

Point

Fourmile

New Ellenton

Upper Three Runs Creek

GEORGIA

SOUTH

CAROLINA

Localized contamination

Contaminated sites Zone and number—Used for particletracking analysis using MODPATH Areal contamination

Savannah River Site boundary

4

EXPLANATION

0 1 2 3 4

0 1 2 3 4 5 KILOMETERS

5 MILES

B.

Figure 1. (A) Location of study area, Savannah River Site (SRS), Brighams Landing well-cluster 

site, precipitation monitoring sites, mean-annual rainfall, 1969–98, and physiographic provinces 

and districts in Georgia and South Carolina (rainfall data from Southeast Regional Climate 

Center, accessed February 11, 2004, at http://www.dnr.sc.gov/climate/sercc/); and (B) areal and 

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

Arnett and Mamatey, 1996)—continued.

Introduction 
A relatively mild climate with warm, humid summers and 

mild winters characterize the study area. Wind patterns in the 

summer are dominated by winds out of the northeast off the 

Bermuda high-pressure system, and shift to a northwesterly 

direction during the winter months as fronts move through 

the area from west to east (Weber, 2003). Precipitation is 

highest in the winter months when continental storm fronts 

move through the region 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 50 inches in central Aiken County, 

S.C. (Cherry, 2003).

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 of which are 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).

Coastal Plain sedimentary strata in the study area consist 

of layers of sand, clay, and minor limestone that range in age 

from Late Cretaceous through post-Eocene. The Fall Line 

(fig. 1A) marks the approximate northern limit of the strata 

and the contact between the Coastal Plain and Piedmont physiographic provinces. 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 are generally parallel to the Fall Line. The sedimentary 

sequence unconformably overlies igneous and metamorphic 

rocks of Paleozoic, and consolidated red beds of early Mesozoic (Chowns and Williams, 1983). A generalized correlation 

of geologic units in the SRS region is shown in figure 2. See 

Falls and others (1997) for a complete description of geologic 

units in the study area.

Major structural features in the study area 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 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 normal fault that dips 

to the southeast and cuts strata of Cretaceous, Paleocene, and 

Eocene. 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).

Previous Investigations

Previous investigators in Georgia (Miller, 1986; Brooks 

and others, 1985; Clarke and others, 1985) and South Carolina 

(Logan and Euler, 1989; Bledsoe and others, 1990; Aadland 

and others, 1995) defined three principal aquifer systems near 

the SRS. The aquifer systems are, in descending order: (1) the 

Floridan aquifer system (Miller, 1986), composed largely 

of calcareous sand and limestone of Eocene; (2) the Dublin 

aquifer system (Clarke and others, 1985) composed of sand of 

Paleocene and Late Cretaceous, and (3) the Midville aquifer 

system (Clarke and others, 1985) composed of sand of Late 

Cretaceous. Although this subdivision of geologic strata was 

suitable for most regional-scale hydrologic studies, greater 

subdivision of units was required to define vertical hydraulic 

heterogeneity for detailed investigations of ground-water flow 

near the Savannah River. Falls and others (1997) divided the 

three aquifer systems into seven discrete aquifers (fig. 2):

1.The Floridan aquifer system was subdivided into the 

Upper Three Runs aquifer and the Gordon aquifer.

2.The Dublin aquifer system was subdivided into the 

Millers Pond aquifer, the upper Dublin aquifer, and the 

lower Dublin aquifer.

3.The Midville aquifer system was subdivided into the 

upper Midville aquifer and the lower Midville aquifer.

Layers of clay and silt that become more sandy in updip 

areas confine the aquifers. Where the confining units are 

sandy, they do not have lateral continuity and the aquifer 

systems coalesce. Falls and others (1997) provide a detailed 

description of the hydrogeologic framework used in the 

trans-river flow study including areal extent, thickness, and 

hydraulic properties of hydrogeologic units.

Synoptic ground-water-level measurements were taken in 

189 wells during early September 2002, and potentiometricsurface maps were constructed for the Upper Three Runs and 

Gordon aquifers and the Dublin and Midville aquifer systems 

as part of initial work for this study (Cherry, 2003). Clarke 

and West (1998) described development and calibration of 

the steady-state ground-water model for predevelopment and 

1987–92 conditions. Clarke and West (1997) provided the foundation for the earlier ground-water modeling study by reporting 

ground-water-level fluctuations and trends, water use, precipitation, and estimated ground-water contribution to streamflow. 

Cherry (2004) updated the model using MODFLOW-2000 and 

adjusted boundary conditions, pumping rates, and recharge 

values. Falls and others (1997) defined the hydrogeologic 

framework for the ground-water model by subdividing the three 

aquifer systems into seven aquifers and six confining units. 

Clarke and West (1997) presented a complete overview of 

previous geologic and hydrogeologic studies in the SRS area.

 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
HYDROGEOLOGIC REPRESENTATION

MODEL REPRESENTATION

Land surface

Confining unit

pinchout

Aquifer

pinchout

Upper Three Runs aquifer

Gordon aquifer

U

Millers Pond aquifer

Lo

pper Dublin aquifer

wer Dublin

U

aquifer

pper Midville aquifer

Lower Midville aquifer

Aquifer outcrop

A1

C1

C2

C3

C4

C5

C6

A2

A3

A4

A5

A6

A7

Savannah River

NW SE

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

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

Basal confining unit

and basement rock

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

boundary conditions for the Savannah River Site area, South Carolina, ground-water 

model (modified from Clarke and West, 1998; CU, confining unit; PE, post-Eocene).

Ground-water modeling investigations in the SRS area 

include Faye and Mayer (1990) and Aucott (1997), who conducted studies as part of the USGS Regional Aquifer-System 

Analysis Program. Several ground-water flow models were 

developed as part of hydrogeologic investigations conducted at 

the SRS. Marine and Root (1975) evaluated flow in the Tuscaloosa aquifer; Parizek and Root (1986) evaluated ground-water 

velocity at the radioactive waste management facility. Looney 

and others (1990) evaluated flow at a proposed production 

reactor site. Camp, Dresser, & McKee, Inc. (1992) evaluated 

flow at the nuclear weapons complex reconfiguration site. 

HydroGeoLogic, Inc. (1992) evaluated flow and transport at 

the TNX Area. Faye and Mayer (1990) and Delaimi (1996) 

evaluated ground-water flow transverse to the Savannah River 

using cross-sectional flow models. Flach and others (1996) 

developed a variably saturated, finite-element ground-water 

flow model of the SRS Old Burial Ground to predict tritium 

migration to Fourmile Branch. The Savannah River Technology Center (SRTC) developed the finite-element ground-water 

modeling code of Flow and Contaminant Transport (FACT) to 

predict tritium migration on a larger scale (Hamm and others, 

1997; Aleman and Hamm, 1999). The FACT code was used 

to construct ground-water models of varying scale to predict 

tritium migration to local streams (Flach and others, 1998, 

1999a, b, and 2000). The modeling effort focused on transport 

of tritium within the Upper Three Runs aquifer and the Gordon aquifer was the lowermost unit within the models.

GGS conducted an evaluation of the areal extent and 

source of tritium detected in domestic wells in Burke County, 

Ga. Summerour and others (1994) described results of the GGS 

investigation, including tritium sampling of wells and streams, 

characterization of the hydrogeologic setting and subsurface 

geology, ground-water flow directions, and a seismic survey of 

the Savannah River channel. A follow-up study (Summerour 

and others, 1998) was conducted to verify the presence of tritium in domestic wells located in Burke County, and concluded 

that the primary pathway for contamination is through tritiated 

rainfall entering the Upper Three Runs aquifer as recharge.

Introduction 
Methods of Study

This study updated an existing ground-water flow model 

of the SRS region (Clarke and West, 1998) in order to describe 

ground-water flow under 2002 conditions and to evaluate 

four hypothetical pumping scenarios for the potential to 

induce trans-river flow. Information on ground-water withdrawal during 1992–2002 on and near the SRS was compiled from the records of DOE; Washington Savannah River 

Company (WSRC); South Carolina Department of Health and 

Environmental Control (SCDHEC); Georgia Environmental 

Protection Division (GaEPD); and USGS. To provide data for 

model evaluation and possible recalibration and to determine 

if boundary conditions have changed since 1992, water-level 

data were collected from 189 wells and potentiometric-surface maps were constructed for each of the major aquifers 

(Cherry, 2003). These data served as the basis to determine if 

recalibration of the previous model was necessary. The revised 

model did not require recalibration because residuals between 

observed and simulated heads met the same error criteria 

developed during the earlier study as described in Clarke and 

West (1998, p. 29–31). After determining recalibration of the 

model would not be necessary, four ground-water management 

scenarios were developed to evaluate hypothetical increases 

in ground-water withdrawal at existing pumping centers and 

variations to boundary conditions. The USGS particle-tracking 

code MODPATH (Pollock, 1994) was used to generate advective water-particle pathlines and their associated time-of-travel 

based on MODFLOW simulations for 2002 and each of four 

ground-water management scenarios.

Acknowledgments

The author extends sincere gratitude to the many well 

owners and managers of municipal and industrial water 

systems who allowed access to their wells and provided 

additional well information. The author would like to thank 

Mike Burke of Southern Nuclear Operating Company for 

providing information on ground-water levels at Vogtle Electric Generating Plant and taking time to visit individual wells 

near the plant. Thanks also are extended to Daryl Doman, 

WSRC, for his assistance in the collection of water-level 

measurements at the well-cluster sites located on the Georgia 

side of the Savannah River. Thanks to the USGS field crew 

who conducted the synoptic survey during September 2002: 

Robert J. Allen, Donald G. Dowling, Michael D. Hamrick, 

Larry G. Harrelson, Michael F. Peck, and Sherlyn Priest. 

The author also extends thanks to members of the SRS 

and USGS technical advisory groups established to exchange 

information, review project status, and discuss technical 

approaches and findings. Members of the SRS group are 

Roger Carter, GGS; Lester Germany, DOE; Jim Hardeman, 

GaEPD; James D. Heffner, WSRC; Bob Hiergesell and Ralph 

Nichols, WSRC Savannah River National Laboratory; Bill 

Smith, GGS; Peter Stone, SCDHEC; and Gail Whitney, DOE. 

Members of the USGS group are John S. Clarke, L. Elliot 

Jones, and Eve L. Kuniansky. 

Thanks also are extended to those who made significant 

contributions to updating water-use information since the 

previous study. Julia L. Fanning (USGS) developed the wateruse database and ensured the accuracy of current estimates. 

Whitney J. Stringfield (USGS) updated the water-use data for 

the counties of Aiken, Allendale, and Barnwell. Paul Bristol 

(SCDHEC) provided the most current water-use information 

for individual permit holders. Vicki Trent (GaEPD) provided 

site-specific ground-water withdrawal estimates in the counties of Burke, Jenkins, and Screven. William F. Falls (USGS) 

developed the hydrogeologic framework and coordinated the 

field effort (water-level measurements and low-flow surveys) 

on the South Carolina side.

A special thanks is extended to Jaime A. Painter (USGS) 

for developing the project database and managing the many 

geographic information system (GIS)-based coverages. 

DáVette A. Taylor-Harris (USGS) assisted with preparation 

of GIS coverages for the final report. Thanks also are extended 

to Patricia L. Nobles (USGS editorial) and Caryl J. Wipperfurth (USGS cartography staff) for preparation of illustrations 

and review of the report. Dorothy F. Payne and Richard B. 

Winston (USGS) assisted with data sets and questions pertaining to MODFLOW-2000 and MODFLOW–graphical user 

interface (GUI).

Hydrologic, Climatic, and GroundWater Use Conditions, 1992–2002

During 1992–2002, the stream-aquifer flow interactions 

in the study area changed as the result of changes in water 

use and a prolonged drought during 1998–2002. The 

following sections describe changes to precipitation, groundwater use, ground-water levels, and streamflow during the 

10-year period.

Precipitation

Average annual precipitation for the period 1969–1998 

ranged from about 45 inches near Augusta, Ga., to greater than 

52 inches near Aiken, S.C. (Cherry, 2003). These values are 

slightly higher than the rainfall during the previous 30-year 

period (1941–70) reported in Faye and Mayer (1990). 

In this report, normal precipitation is defined as the 

average monthly rainfall during the 55-year period from 

1948–2002; cumulative departure from normal is shown 

through 2002 for Augusta, Ga., and Aiken, S.C. (fig. 3). 

During 1992–98, precipitation at Augusta and Aiken mostly 

was above normal as indicated by the upward slope on the 

cumulative-departure graph (fig. 3). A prolonged drought 

during 1998–2002 resulted in below-normal precipitation, 

as indicated by a steep downward slope on the cumula-

 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
tive-departure graph (fig. 3). The cumulative departure from 

normal decreased from +42 inches at Aiken and +32 inches 

at Augusta during mid-1998 to about 0 inches by the end of 

2002. The recent drought of 1998–2002 is overshadowed by 

the severity of the drought in the early to mid-1950s, during 

which the cumulative departure from normal was –90.1 inches 

at Aiken and –48.7 inches at Augusta. A study using treering analysis that examined the past 325 years indicates that 

a drought of 2 or more years on average can be expected in 

Georgia about once in 25 years (Stooksbury, 2003).

C

U

M

ULATIVE DEPA

R

T

U

RE FR

O

M

N

O

R

M

AL PRECIPITATIO

N, IN IN

C

HES

–100

–50

0

50

100

Normal

Augusta, Georgia

JULY

1948

JULY

1958

JULY

1968

JULY

1978

JULY

1988

JULY

1998

DEC

2002

–100

–50

0

50

100

Normal

Aiken, South Carolina

Figure 3. Cumulative departure from normal 

precipitation for Augusta, Georgia, and Aiken, South 

Carolina, July 1948 through December 2002 (location of 

precipitation sites shown in figure 1; data from Southeast Regional Climate Center, accessed February 11, 

2004, at http://www.dnr.sc.gov/climate/sercc/).

Ground-Water Use

Ground-water use in the eight-county study area showed 

a substantial increase during the past 10 years (fig. 4). Clarke 

and West (1997) reported that during 1987–92, total groundwater use was about 80 million gallons per day (Mgal/d). By 

1995, the total ground-water use was about 85.4 Mgal/d (Fanning, 1997), and by 2000–2002 (Fanning, 2003; W.J. Stringfield, U.S. Geological Survey, written commun., 2002) total 

ground-water use had risen to about 117 Mgal/d (table 1).

The largest increase in ground-water use between 1995 

and 2000 was in Burke, Jefferson, and Screven Counties, Ga., 

and Allendale and Barnwell Counties, S.C. (fig. 4, table 1). 

In these counties, ground-water use for irrigation increased 

from 16.7 Mgal/d during 1995 to 53.1 Mgal/d during 2000 and 

irrigated acreage increased from 61,690 acres during 1995 to 

97,690 acres during 2000 (Fanning, 2003). 

Spatial distribution of irrigation pumping within the 

hydrogeologic units simulated by the model was based on sitespecific data (well depth, open interval, and pump capacity) 

and interpolating aquifer altitudes at each well location. 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.

55.2 Mgal/d 51.8 Mgal/d

87.6 Mgal/d

24.9 Mgal/d 33.6 Mgal/d 29.0 Mgal/d

GROUND-WATER WITHDRAWALS

In million gallons per day (Mgal/d)

1987–92 1995 2000

Counties in Georgia

Counties in South Carolina

Burke Jefferson Jenkins

Richmond Screven

Aiken Allendale Barnwell

Figure 4. Ground-water use in selected counties in 

Georgia and South Carolina, 1987–2000 (see table 1 

for county totals and data sources).

Hydrologic, Climatic, and Ground-Water Use Conditions, 1992–2002 9
Table 1. Ground-water use during 1990, 1995, and 2000–2002 near the Savannah River Site, South Carolina.

[Ga., Georgia; S.C., South Carolina; do., ditto]

Year State County

Pumpage, in million gallons per day

Public 

supply Irrigation Industrial mining

Domestic and 

commercial Livestock

Thermoelectric 

power

Total

1990 Ga. Burke 1.20 2.57 0.00 0.91 0.04 2.27 6.99

do. Jefferson 1.86 2.60 4.78 0.64 0.04 0 9.92

do. Jenkins 0.58 1.86 0.11 0.32 0.02 do. 2.89

do. Richmond 13.18 0.96 2.55 0.87 0.02 do. 17.58

do. Screven 1.07 3.96 2.30 0.74 0.04 do. 8.11

S.C. Aiken 3.26 1.44 9.84 2.11 0.35 do. 17.00

do. Allendale 0.66 4.78 2.40 0.43 0.04 do. 8.31

do. Barnwell 2.54 0.02 0.16 0.52 0.48 do. 3.72

Total—Ga. 17.89 11.95 9.74 3.48 0.16 2.27 45.49

Total—S.C. 6.46 6.24 12.40 3.06 0.87 0 29.03

Total—eight county 24.35 18.19 22.14 6.54 1.03 2.27 74.52

1995 Ga. Burke 1.17 7.08 0 0.88 0.04 0.78 9.95

do. Jefferson 1.89 2.28 3.18 0.70 0.03 0 8.08

do. Jenkins 0.52 2.92 0.01 0.35 0.02 do. 3.82

do. Richmond 13.87 5.12 3.58 0.79 0.02 do. 23.38

do. Screven 0.87 3.24 1.69 0.72 0.04 do. 6.56

S.C. Aiken 9.75 0.01 9.40 1.31 0.35 do. 20.82

do. Allendale 0.85 4.10 4.03 0.42 0.04 do. 9.44

do. Barnwell 2.21 0 0 0.62 0.48 do. 3.31

Total—Ga. 18.32 20.64 8.46 3.44 0.15 0.78 51.79

Total—S.C. 12.81 4.11 13.43 2.35 0.87 0 33.57

Total—eight county 31.13 24.75 21.89 5.79 1.02 0.78 85.36

2000–2002 Ga. Burke 3.87 21.23 0.15 0.90 0.03 0.78 26.96

do. Jefferson 1.84 6.92 3.82 0.64 0.03 0 13.25

do. Jenkins 0.54 3.94 0.01 0.33 0.02 do. 4.84

do. Richmond 14.88 5.22 2.87 0.22 0.02 do. 23.21

do. Screven 1.15 15.62 1.82 0.74 0.03 do. 19.36

S.C. Aiken 4.82 0.98 6.06 0.80 0 do. 12.66

do. Allendale 1.20 5.62 2.50 0.27 do. do. 9.59

do. Barnwell 2.73 3.73 0.41 0.63 do. do. 7.50

Total—Ga. 22.28 52.93 8.67 2.83 0.13 0.78 87.62

Total—S.C. 8.75 10.33 8.97 1.70 0 0 29.75

Total—eight county 31.03 63.26 17.64 4.53 0.13 0.78 117.37

Data sources: County totals for Georgia are from Fanning (1997, 2003) and Pierce and others (1982). Lonon and others (1983) and W.J. Stringfield 

(U.S. Geological Survey, written commun., 2002) provided total water-use data for South Carolina. J.L. Fanning (U.S. Geological Survey, written commun., 

2003) and V. P. Trent (Georgia Geologic Survey, written commun., 2003) provided site-specific data for irrigation wells located in Georgia. Paul Bristol and 

Peter Stone (South Carolina Department of Health and Environmental Control, written commun., 2003) provided site-specific data for permitted wells 

located in South Carolina.

10 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
Ground-water use for public supply increased from 

24.4 Mgal/d during 1990 to 31.0 Mgal/d during 2000–2002 

(table 1). Burke and Richmond Counties in Georgia and 

Aiken County in South Carolina accounted for the most of the 

6.6 Mgal/d increase during the 10-year period. The Richmond 

County Water System alone accounted for about 1.4 Mgal/d of 

the increase; 13.2 Mgal/d was withdrawn during 2000–2002 

(Fanning, 2003), primarily from the Midville aquifer system. 

Ground-water use for industrial and mining purposes 

showed a moderate decrease from 22.1 Mgal/d during 1990 to 

17.6 Mgal/d during 2002. Most of the decrease can be attributed to reduced withdrawal at the SRS from 9.0 Mgal/d during 

1990 to 5.4 Mgal/d during 2002 (R.A. Hiergesell, Westinghouse Savannah River Company, written commun., 2002). The 

other ground-water use categories of domestic/commercial, livestock, and thermoelectric power remained relatively constant 

during 1990–2002 (J.L. Fanning, U.S. Geological Survey, 

written commun., 2002).

Ground-Water Levels

During 1992–2002, water levels in each of the major 

aquifers generally declined because of below-normal precipitation and increased ground-water use. Declines, based on 

periodic water-level measurements, in the Upper Three Runs 

aquifer ranged from 2 to 5 ft in northeastern Burke County and 

were greater than 20 ft in southern Burke and Screven Counties 

(Cherry, 2003). Water-level trends in the Gordon aquifer and 

Dublin and Midville aquifer systems are shown on the hydrographs for wells at Brighams Landing in the Savannah River 

valley in Burke County (fig. 5). Water-level declines at Brighams 

Landing were most pronounced in the Gordon aquifer with progressively less declines in the deeper Dublin and Midville aquifer systems, respectively (figs. 1A). In well 32Y033, completed 

in the Gordon aquifer, the water level declined about 16 ft, from 

a daily mean water-level altitude of 120.4 ft during September 

1995 to 104.4 ft during September 2002 (fig. 5). Steep seasonal 

decline in ground-water levels from 1998 to 2002 coincides with 

the growing season and heavy ground-water use for irrigation in 

eastern Burke County and northeastern Screven County during the period of drought. In well 32Y031, completed in the 

Dublin aquifer system, the water level declined about 7 ft during the same period (fig. 5). The water level in well 32Y030 

completed in the Midville aquifer system declined about 5 ft 

from September 1995 to September 2002 (fig. 5).

The potentiometric-surface map for the Upper Three 

Runs aquifer was constructed using water-level data from 

78 wells (fig. 6A). The map reflects the water-level decline 

that occurred during 1992–2002, especially in topographically 

higher areas in Burke County, Ga., and Barnwell and Allendale Counties, S.C. Decreased water-level altitudes are illustrated by the northern shift of the 140- and 180-ft contours in 

Allendale and Barnwell Counties, S.C. Despite these declines, 

the general contours are similar to the previous map for 1987–

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

aquifer is the source-sink layer for the ground-water model, 

it surface during 1992–2002. The areas of greatest water-level 

decline in the Upper Three Runs aquifer occurred in northern 

Jenkins and Screven Counties because of increased groundwater pumpage for irrigation. In these counties, the estimated 

water-level decline ranged from 10 ft to as high as 50 ft. Estimated water use from the Upper Three Runs aquifer increased 

by about 6 Mgal/d during 1992–2002 in Burke, Jenkins, and 

Screven Counties, resulting in water-level declines.

WATER-LEVEL ALTIT

U

DE, IN FEET

ABO

VE N

AV

D 88

100

110

115

105

120

130

125

Well 32Y033 (Gordon aquifer)

1995 1996

Blank

where

data

missing

1997 1998 1999 2000 2001 2002

150

155

160

165

Well 32Y031 (Dublin aquifer system)

170

175

180

185

Well 32Y030 (Midville aquifer system)

Figure 5. Water-level altitude for wells 32Y030, 32Y031, 

and 32Y033 at the Brighams Landing well-cluster site, 

1995–2002 (see figure 1 for cluster location).

Hydrologic, Climatic, and Ground-Water Use Conditions, 1992–2002 11
220

180

200

260

160

280 100

200

220

180

240

200

220

160

140

120

180

200

220

240

160

180

220

240

260

140

280

180

160

160

180

220

240

120

160

180 140

200 200

140

160

120

200

140

220

120

140

160

200

240

260

100

80

140

180

180 180

200

120

120

100

180

180

200

160

260

200

100

160

140

200

220

180

140

100

220

300

260

140

100

180

220

140

140

180

100

220

260

Brier Creek

McBean

Creek

Upper Three Runs Creek

Creek

Hollow

Savannah

River

Pen Br

Lower Three Runs Creek

EXPLANATION

Well data point

A. Upper Three Runs aquifer

C. Dublin aquifer system

B. Gordon aquifer

D. Midville aquifer system

Estimated potentiometric contour—Shows altitude at which

water level would have stood in tightly cased wells during 2002.

Contour interval 20 or 40 feet. Datum is NAVD 88

Estimated potentiometric contour—Shows altitude at which water

level would have stood in tightly cased wells during 1992. Contour

interval 20 or 40 feet. Datum is NAVD 88 (Clarke and West, 1997)

220

220

0 5 10 MILES

0 5 10 KILOMETERS

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

82°00' 81°45' 81°30'

33°15'

33°30'

33°00'

SC

GA Map area

AIKEN

RICHMOND JEFFERSON

BURKE JENKINS

SCREVEN

ALLENDALE

BARNWELL

SRS

Figure 6. Potentiometric-surface maps for the (A) Upper Three Runs aquifer, (B) Gordon aquifer, (C) Dublin aquifer 

system, and (D) Midville aquifer system during 1992 and 2002, near the Savannah River Site, Georgia and South Carolina 

(from Cherry, 2003).

12 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
The potentiometric-surface map for the Gordon aquifer 

was constructed using water-level data from 49 wells (fig. 6B). 

The map shows the effect of drought and ground-water withdrawal on the potentiometric surface. Water-level declines are 

indicated by a northwestern shift of the 120- and 140-ft contours 

in Georgia, and by a northern shift of the 120-, 140-, 160-, and 

180-ft contours in South Carolina. Perhaps the most pronounced 

effect on the configuration of the potentiometric surface is near 

a ground-water divide beneath the Savannah River. Here, some 

ground water flows updip toward the area where the ancient 

Savannah River breached the confining unit overlying the 

Gordon aquifer, and another segment flows southward toward 

the coast. The overall decline in aquifer water-level altitude for 

the Gordon aquifer is best illustrated by the 120-ft contour that 

crossed the Savannah River during 1992, but is replaced during 2002 by the 100-ft contour. Thus, the ground-water divide 

beneath the river has moved northeast since 1992.

The potentiometric-surface map for the Dublin aquifer 

system was constructed using water-level data from 32 wells 

(fig. 6C). Water-level declines are indicated on the map by the 

westward shift of the 160-ft contour in Georgia, and by the 

northern shift of the 160-, 180-, 200-, and 220-ft contours in 

South Carolina. The southeastern shift of the 140-ft contour 

beneath the Savannah River reflects water-level decline and 

shows an apparent movement of the position of the groundwater divide in the southern part of the study area.

The potentiometric-surface map for the Midville aquifer 

system was constructed using water-level data from 30 wells 

(fig. 6D). Water-level decline is indicated by the westward 

shift of the 180-, 200-, and 220-ft contours in Georgia, and 

by the northern shift of the 180-, 200-, and 220-ft contours 

in South Carolina. Further evidence of water-level decline is 

indicated by eastward shift of the 160-ft contour beneath the 

Savannah River. In addition, it appears that the 180-ft contour, 

which formerly intersected the river near Brighams Landing, 

did not intersect the river within the study area during 2002.

Streamflow

The Savannah River is the major surface-water drain in 

the study area and is the State line between Georgia and South 

Carolina (fig. 7). The river drains an area of about 10,580 mi2

(1,140 mi2 of which are in the study area) and empties into 

the Atlantic Ocean near Savannah, Ga. Streamflow has been 

regulated since 1954 with the impoundment of Thurmond 

Lake storage reservoir located 22 mi upstream from Augusta. 

Major tributaries of the Savannah River are, in downstream 

order; Horse Creek, Hollow Creek, Upper Three Runs Creek, 

Fourmile Branch, Pen Branch, Steel Creek, and Lower Three 

Runs Creek in South Carolina; and Butler Creek, Spirit Creek, 

McBean Creek, and Brier Creek in Georgia (fig. 7). Analysis of ground-water discharge to local streams in the study 

area using many techniques including hydrograph separation concluded that the ground-water contribution to nearby 

streams during an average period is nearly 60 percent of the 

total streamflow and 80 percent during dry periods (Priest and 

Clarke, 2003). During 1941–70, the mean-annual runoff in 

Georgia (fig. 7) ranged from less than 0.9 (ft3/s)/mi2 of drainage area in southern Screven, Jenkins, Burke, and Jefferson 

Counties, and in northern Richmond and Jefferson Counties 

to more than 1.1 (ft3/s)/mi2 in eastern Richmond and Burke 

Counties (Faye and Mayer, 1990).

Estimates of mean-annual ground-water discharge in the 

Savannah River Basin (encompassing about 35 percent of the 

actively simulated model area) range from 10.8 to 19.8 inches 

per year (in/yr) with an average of 14.5 in/yr (Clarke and West, 

1998). These estimates are based on the gain in ground-water 

discharge (as streamflow) between the Augusta streamflow 

gage (02197000), located near the Fall Line, and Millhaven 

streamflow gage (02197500), located near the southern boundary of the model (fig. 7). Analyses of the streamflow gains 

since the previous study (see table 2) indicates several water 

years (WY) (October 1 of previous year through September 30 

of designated year) with streamflow gains well above the 

14.5 in/yr average reported by Clarke and West (1997). These 

streamflow gains are a combination of ground-water discharge 

and a strong overland component of stormwater runoff. The 

annual net gain in streamflow between the two stations during 1992–2002 ranged from 7.7 to 28.5 in/yr, with an average of 15.9 in/yr. The period of record can be characterized 

by 4 years of above average streamflow (WY 1993, 1995, 

1996, and 1998) and 7 years of below average streamflow 

(WY 1992, 1994, 1997, and 1999–2002) with a 4-year period 

of drought from 1999 through 2002.

In the northern half of the SRS, Upper Three Runs Creek 

has breached the confining unit of the Gordon aquifer and 

functions as an important ground-water discharge area for the 

Gordon aquifer and the Dublin aquifer system, as indicated 

by the shape of the potentiometric-surface maps for the two 

aquifers (figs. 6B, 6C). The net gain in streamflow along 

Upper Three Runs Creek is evident when comparing the 

mean-annual streamflow between streamflow gages 02197300 

and 02197315, with a contributing drainage area of 116 mi2 

(fig. 7 and table 2). Clarke and West (1997) reported meanannual ground-water discharge computed using hydrograph 

separation between the two streamflow gages was 23.5 in/yr 

during 1987–92. During 1992–2002, mean-annual streamflow 

gain along this reach ranges from 7.6 in/yr during a dry year 

(WY 2002) to 23.6 in/yr during a wet year (WY 1993) and 

averages 15.1 in/yr (table 2).

Hydrologic, Climatic, and Ground-Water Use Conditions, 1992–2002 1
Augusta

Millhaven

AIKEN

BARNWELL

ALLENDALE

SCREVEN JENKINS

BURKE JEFFERSON

RICHMOND

GEORGIA

Base modified from U.S. Geological Survey

1:500,000-scale digital State base maps

SO

UTH CAROLINA

Savannah River

Site

021973565

02197315

02197320

02197310

02197344

02197348

02197400

02197300

02197000

02197500 02198000

Upper

Lower Three Runs Creek

Br Pen

Steel

Three Runs

Br

Cr

Fourmile

Brier Creek

Spirit Creek

Butler Creek

McBean Creek

Savannah

River

Hollow

Creek

Horse Creek

Creeek

0.9

1.0

1.1

1.0

0.9

0

0 10 20 30 KILOMETERS

10 20 30 MILES

EDGEFIELD

SALUDA

COLUMBIA

GLASCOCK

McDUFFIE

WARREN

82°30'

33°30'

33°00'

82°00' 81°30'

32°30'

GEORGIA

Augusta

Study

area

SOUTH

CAROLINA

Savannah

EXPLANATION

02198000

1.0 Line of equal mean-annual runoff, 1941–70—

Interval 0.1 cubic foot per square mile of drainage area

Streamflow gaging station and identification number—

See table 2

Figure 7. Mean-annual runoff in Georgia part of study area, 1941–70 (modified from Faye and Mayer, 1990); 

and locations of selected U.S. Geological Survey streamflow gaging stations.

14  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
Table 2. Mean-annual discharge to selected streams near the Savannah River Site, Georgia and South Carolina, water years 1992 –2002.

[Water year, October 1 of previous year through September 30 of designated year; mi2, square miles; ft3/s, cubic feet per second; in/yr, inches per year; NA, not available; SRS, S.C., South Carolina; Ga., Georgia]

Station 

number Station name

Drainage 

area 

(mi2)

Intermediate 

drainage 

area (mi2)

Water year

Mean-annual stream discharge (ft3/s)

1992 1993 1994 1995 1996 1997 1998 1999 2000 

Upper Three Runs Creek Basin, S.C.

2197300 Upper Three Runs Creek near New Ellenton 87 NA 108 118 110 126 117 98 113 100 82 2197310 Upper Three Runs Creek above Road C, SRS 176 89 232 274 235 294 236 206 NA NA 169 2197315 Upper Three Runs Creek at Road A, SRS 203 27 256 320 239 284 245 214 301 206 174 

Net gain in stream discharge between 

stations 2197300 and 2197315

NA 116 148 202 129 158 128 116 188 106 92 

Net gain in stream discharge in in/yr 17.4 23.6 15.1 18.5 15.0 13.6 22.0 12.4 10.8 

Savannah River Basin

2197000 Savannah River at Augusta, Ga. 7,508 NA 7,660 15,400 8,370 11,110 11,800 9,010 14,150 5,830 4,750 2197320 Savannah River near Jackson, S.C. 8,110 602 8,380 16,680 9,410 12,120 12,991 10,160 15,250 6,960 5,300 2197500 Savannah River at Burtons Ferry near 

Millhaven, Ga.

8,650 540 8,740 17,800 9,650 12,750 13,440 9,950 16,550 6,710 5,465 

Net gain in stream discharge between 

stations 2197000 and 2197500

NA 1,142 1,080 2,400 1,280 1,640 1,640 940 2,400 880 715 

Net gain in stream discharge in in/yr 12.9 28.5 15.2 19.5 19.5 11.2 28.5 10.5 8.5 

Savannah River Site, S.C.

2197344 Fourmile Branch at Road A12.2 22 NA 40 58 28 37 28 23 45 21 18 2197348 Pen Branch at Road A-13 21 NA 235 48 51 56 45 28 34 15 13 21973565 Steel Creek at Road A NA NA 117 118 82 86 62 52 53 24 19 2197400 Lower Three Runs Creek near Snelling, S.C. 59 NA 85 102 80 60 60 41 118 49 40 

Brier Creek Basin, Ga.

2198000 Brier Creek at Millhaven, Ga. 646 NA 596 904 521 821 595 437 1,090 378 297 
Simulation of Steady-State 

Ground-Water Flow, 2002

The USGS conducted a ground-water modeling investigation of ground-water flow and stream-aquifer relations during 1991–97 (Clarke and West, 1998). During that study, the 

ground-water flow system was simulated with a series of six 

steady-state pumping periods; 1953–60, 1961–70, 1971–75, 

1976–80, 1981–86, and 1987–92. Results were summarized 

for the predevelopment (pre-1953) and modern-day (1987–92) 

simulations, with hydrographs of selected wells presented for 

interim periods. Steady-state ground-water flow was simulated 

using the USGS three-dimensional finite-difference model, 

MODFLOW (McDonald and Harbaugh, 1988). 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 was generally in a 

state of equilibrium and any contributions from aquifer storage 

were minor. The flow system was modeled using a quasi-threedimensional approach with seven layers—six active layers and 

an overlying source-sink layer—that are separated to varying 

degrees by six confining units (fig. 2). 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. 8). The model grid area encompasses about 

4,455 mi2, of which about 3,250 mi2 is actively simulated.

SOUTH

CAROLINA

GEORGIA

82°30'

33°30'

33°00'

82°00' 81°30'

32°30'

0

0 10 20 30 KILOMETERS

10 20 30 MILES

ROW

COLUMN

MODEL

BOUNDARY

Aiken

Augusta

Base modified from U.S. Geological Survey

1:500,000-scale digital State base maps

SRS

GEORGIA

SOUTH

CAROLINA

Study area

Savannah

River

BURKE

RICHMOND McDUFFIE WARREN

GLASCOCK

COLUMBIA

JEFFERSON

AIKEN

ALLENDALE

SCREVEN JENKINS

BARNWELL

SALUDA

EDGEFIELD

1

10

20 30 40 50 60 70 80 90

100 102

10

20

30

40

50

60

70

80

90

100

110

120

130

1

Figure 8. Location of study area, 

Savannah River Site, South Carolina, 

model grid, and model boundary 

(modified from Clarke and West, 1998).

1 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
Calibration of the original SRS model (1987–92) was 

accomplished by adjusting hydrologic properties until a “best 

fit” was obtained between simulated and observed water levels 

along with a comparison between simulated ground-water 

discharge data and measured data obtained from streams and 

rivers. Model adjustments also were controlled by consideration 

of “realistic” values for a given hydrologic property based on 

available field data and accepted limits reported in the literature. Recharge values were assigned to aquifer outcrop areas 

(layers A2–A7) for individual cells as direct recharge or in cells 

supplied by inflows from the source-sink layer A1, and were 

held below the maximum acceptable limit of 20 in/yr (Clarke 

and West, 1998; fig. 2). The model-calculated downward vertical flux from the source-sink layer A1 represents recharge that 

has infiltrated downward through the Upper Three Runs aquifer. 

Hydrologic properties that were adjusted during model calibration were confining unit leakance, streambed conductance, 

and transmissivity, with most adjustment made to confining 

unit leakance and streambed conductance (Clarke and West, 

1998). These parameters and their corresponding ranges within 

the study area are summarized in table 3. Boundary conditions adjusted during calibration consisted of head values in 

the source-sink layer A1; head values along lateral boundaries in deep layers A2 through A7; river stage; and recharge. 

Simulations using steady-state conditions were deemed suitable 

because long-term water levels and ground-water discharge 

from aquifers to rivers and streams showed little change during 

predevelopment (pre-1953) and modern-day periods (1987–92, 

Clarke and West, 1998, p. 31). In addition, Clarke and West 

(1998) conducted a series of transient response tests to determine if the model is sensitive to the effects of storage and the 

results indicate that contribution from storage to be negligible. 

Sensitivity analysis of the major input parameters indicate that 

ground-water levels and the area of trans-river flow mostly were 

influenced by changes in specified head in the source-sink layer A1, whereas ground-water discharge to streams mostly was 

influenced by changes in river stage (Clarke and West, 1998).

Updating the Model to 2002 Conditions

The existing regional ground-water model (Clarke and 

West, 1998) was reformatted to a newer version of MODFLOW (MODFLOW-2000; Harbaugh and others, 2000), 

which incorporates altitudes of the top and bottom of each 

hydrogeologic unit. The model was updated to 2002 hydrologic conditions by modifying boundary conditions and 

pumping stresses on the ground-water system. A steady-state 

simulation of 2002 hydrologic conditions was deemed approTable 3. Ranges of field observations and estimates for transmissivity, confining unit leakance, and streambed conductance by 

hydrogeologic unit for ground-water flow model near the Savannah River Site, South Carolina (modified from Clarke and West, 1998).

[ft2/d, foot squared per day; min, minimum; max, maximum; ft/d, foot per day; NA, not applicable]

Hydrogeologic 

unit

Layer 

number

Number 

of field 

observations

Transmissivity 

(ft2/d)

Reported 

hydraulic 

conductivity 

(ft/d)

Estimated 

leakance1

Number of 

riverbed 

conductance 

values

Streambed 

conductivity 

(ft2/d)

Min. Max. Mean Min. Max. Mean Min. Max. Mean

Upper Three 

Runs aquifer

A1 8 500 9,500 3,260 8 NA NA NA

Gordon confining unit C1 6 4.7E-6 1.2E-2 2.1E-3 244 0.1 1,600 140

Gordon aquifer A2 18 180 12,200 4,460 2–18 NA NA NA 443 240 1.6E+6 81,000

Millers Pond 

confining unit

C2 0 NA NA NA 42 1,400 31,000 13,000

Millers Pond aquifer A3 10 195 2,000 1,020 7 NA NA NA 58 28,000 1.6E+6 121,000

Upper Dublin 

confining unit

C3 9 1.8E-6 1.6E-3 3.6E-4 62 2.3 6,100 1,200

Upper Dublin aquifer A4 17 555 25,200 5,830 0.7 NA NA NA 207 8.6 648,000 44,000

Lower Dublin 

confining unit

C4 1 2.4E-5 2.4E-5 2.4E-5 113 1.0 6,100 720

Lower Dublin aquifer A5 21 40 8,900 3,940 0.4–56 NA NA NA 176 550 1.6E+6 95,000

Upper Midville 

confining unit

C5 11 6.7E-7 3.9E-4 7.6E-5 88 140 207,000 25,000

Upper Midville aquifer A6 15 1,300 5,430 2,760 30 NA NA NA 57 1,400 2.5E+6 294,000

Lower Midville 

confining unit

C6 1 1.0E-5 1.0E-5 1.0E-5 61 0.6 6,100 790

Lower Midville aquifer A7 37 800 25,500 8,900 65–140 NA NA NA 108 95 406,000 85,000

1

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

Simulation of Steady-State Ground-Water Flow, 2002 17
priate because of the conclusion from transient response tests 

conducted for the original model that changes in pumpage 

are short term and that the model results are insensitive to 

changes in storage (Clarke and West, 1998). The finitedifference grid and hydraulic properties were not changed for 

the 2002 simulation.

Boundary conditions for the 2002 simulation were 

modified based on observed changes in climatic conditions 

and ground-water levels. Adjustments to heads in the sourcesink layer A1 and specified heads along lateral boundaries 

were made to match closely published potentiometric-surface 

maps for September 2002 (Cherry, 2003; figs. 6A and 9). 

82°30'

33°30'

33°00'

82°00' 81°30'

32°30'

0

0 10 20 30 KILOMETERS

10 20 30 MILES Base modified from U.S. Geological Survey

1:500,000-scale digital State base maps

60

100

100

140

140

180

180

220

220

260

260

220

300

260

EXPLANATION

Potentiometric contour—Shows altitude at which

water level would have stood in tightly cased wells

in the Upper Three Runs aquifer during 2002.

Contour interval 40 feet. Datum is NAVD 88

Active area of source-sink layer A1

Observation well and water-level elevation

140

GEORGIA

SOUTH

CAROLINA

MODEL AREA

SRS

Area of map in figure 9B

A.

Savannah

River

126

233

212

168

179 152

55

48

95

91

96

91

98 102

100

104

135

87

88

86

96

95

104

110

111

116

126

147

153

157

201

183 222

261

199

268

313

283

322

330

379

240

228

149

67

63

158

92

118

206 233

166

179

174

248

211

127

120

103

260 233 233

189

GEORGIA

SOUTH

CAROLINA

Study area

Figure 9. (A) Model area, active area of 

source-sink layer A1, and potentiometric 

surface for the Upper Three Runs aquifer 

during 2002 in the Savannah River Site 

(SRS) area, South Carolina (Cherry, 2003), 

and (B) enlargement of SRS area.

1 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
33°20'

81°50' 81°40' 81°30'

33°10'

33°00'

Pen Branch

Meyers Branch

Steel Creek

Tinker Creek

Lower Three Runs Creek

Newberry Creek

McBean Cr

Branch

Par

Pond

L

Lake

Hollow

Creek

Savannah River

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Jackson

Eagle

Point

Fourmile

New Ellenton

Upper Three Runs Creek

GEORGIA

SOUTH CAROLINA

100

10

1

0

40

140

180

180

180

180

140

220

220

260

260

180

212

270

222

177

229

202

232

252

191

188 204

234 281

267 264

269

268

201

204 230

158

92

118

179

194

192 151

155 189

121

149

200

112

112

122

155 212

228

266

255

255 314

217

111

175

186 198

152

208

257

210

164

146 226

190

185

177

173

177

207

160

122

100

211

126

162

0 1 2 3 4

0 1 2 3 4 5 KILOMETERS

5 MILES

B.

EXPLANATION

Potentiometric contour—Shows altitude at which

water level would have stood in tightly cased wells

in the Upper Three Runs aquifer during 2002.

Contour interval 40 feet. Datum is NAVD 88

Active area of source-sink layer A1

Observation well and water-level elevation

140

Savannah River Site

Simulation of Steady-State Ground-Water Flow, 2002 19

Figure 9. (A) Model area, active area of source-sink layer A1, and potentiometric surface for 

the Upper Three Runs aquifer during 2002 in the Savannah River Site (SRS) area, South Carolina 

(Cherry, 2003) and (B) enlargement of SRS area—continued.
The observed water levels during 2002 were generally lower 

because of the prolonged drought; a comparison of water-level 

measurements is shown in figure 10. In the Upper Three Runs 

aquifer, 964 water-level measurements were made during 

1987–92 compared with 147 made during September of 2002. 

A direct comparison was made for 82 wells with water-level 

measurements in both sampling periods (fig. 10). Water-level 

measurements taken during 1987–92 were compared to the 

constructed potentiometric surface for 2002 to assign waterlevel changes in areas lacking sufficient data in 2002. This 

was done by performing an interpolation using the splinetension method with grid cell dimensions of 98 ft per side. 

Thus, sufficient coverage was provided to generate contours of 

the difference between 1987–92 and 2002 water levels using 

a combination of measured and interpolated data (fig. 10). 

The extreme water-level declines ranging from –18.9 to 

–25.2 in the northern parts of Screven and Jenkins Counties 

are indicative of the combined effects of drought and groundwater pumpage for irrigation in the Upper Three Runs aquifer. 

On the SRS, the water-level declines are less and range from 

–5.8 to –20.0 (fig. 10). The resulting contoured water-level 

changes indicate areas with water-level declines greater than 

– 40 ft in northern Jenkins County and eastern Jefferson 

County near the model boundary. The interpolated potentiometric-surface map for the Upper Three Runs aquifer during 

2002 was the basis for assigning head values to each of the 

13,260 grid centroids in the source-sink layer A1 and comparing the values used for the calibrated 1987–92 steady-state 

simulation (Clarke and West, 1998).

Specified heads in model layers A2–A7 were lowered 

to reflect water-level declines attributed to the drought period 

(figs. 11–16). In the Gordon aquifer (layer A2), the specified heads along the southern boundary of the model were 

lowered 10 ft and those cells located along the northeastern 

model boundary were lowered by 5 ft (fig. 11). In the Dublin 

aquifer system (layers A3–A5), specified heads along the 

southern boundary of the model were lowered 8 ft and those 

along the northeastern model boundary were lowered by 5 ft 

(figs. 12–14). In model layers A3–A5, additional specifiedhead cells are located along the southeastern model boundary 

near Barnwell and Allendale Counties. These specified head 

cells were lowered by 10 ft from the values assigned to the 

previous model.

In the Midville aquifer system (layers A6–A7), specified-head values along the southern model boundary were 

lowered 6 ft and along the northeastern model boundary by 

5 ft (figs. 15 –16). These model layers (layers A6 –A7) had 

additional specified-head cells located along the northern and 

northwestern model boundaries, which were lowered 6 and 

10 ft, respectively.

Ground-water withdrawal rates increased by 42.8 Mgal/d 

from 1990 to the drought period during 2000–2002 (table 1). 

A part of this pumpage, however, is assigned to the sourcesink layer A1 of the model and is not accounted for in the 

active layers of the model (layers A2–A7). The large waterlevel declines in the Upper Three Runs aquifer documented by 

2002 water-level measurements indicate some of this decrease 

is because of increased ground-water use for irrigation. The 

previously developed model of Clarke and West (1998) 

assigned 52.7 Mgal/d to active layers of the model (layers A2–

A7), which accounts for 22 Mgal/d not actively simulated in 

the source-sink layer A1. A similar approach was used for 

2002 to assign 67.2 Mgal/d to active layers (layers A2–A7) 

with about 50 Mgal/d of pumping accounted for in the sourcesink layer A1 (table 4). The total pumping for a given well 

was distributed evenly among the aquifers penetrated with a 

standard open interval of 100 ft if the well depth was known.

The model simulated ground-water discharge to streams 

from the active layers of the model (layers A2–A7) using river 

cells that are located in the updip areas of the aquifers along 

the Savannah River and its major tributaries where the streams 

have incised into the aquifers and confining units (figs. 11–16). 

For the purpose of the steady-state simulations, return flow to 

the source-sink layer A1 is considered as ground-water discharge to streams and occurs along areas such as Brier Creek 

(table 2 and fig. 6A). Assigned river-stage altitudes and hydraulic properties for each river cell remained unchanged from the 

earlier model for the 2002 steady-state simulation (table 3).

The altitude of stream stage (river cells) for the 

1987–92 model was estimated from digitized altitude 

contours (U.S. Geological Survey, 1989) using GIS, and 

from limited well data in the Savannah River floodplain. 

These values are considered an estimation of long-term 

average stage conditions. The river-stage altitude values assigned in the 1987–92 model also were used in the 

2002 simulation. This is considered reasonable for the Savannah River because streamflow is regulated by minimum flow 

requirements and steady upstream releases for power production at Thurmond Lake north of Augusta, Ga.

Simulated Water Budget

The simulated water budget for 2002 (dry conditions) is 

1,035 Mgal/d compared with 1,040 Mgal/d for the 1987–92 

simulation (fig. 17). The lowering of the heads in the sourcesink layer A1 to match the potentiometric-surface map of the 

Upper Three Runs aquifer resulted in decreased flow through 

the stream-aquifer system. Overall, recharge from the sourcesink layer A1 was reduced from 789 Mgal/d to 777 Mgal/d, 

which represents a minor change of only 1.5 percent (fig. 18). 

The recharge assigned to the outcrop areas of the hydrogeologic units (see fig. 2) remained constant for the 2002 simulation at 153 Mgal/d, which represents 16.5 percent of the total 

929.5 Mgal/d simulated recharge to the ground-water system 

(figs. 17–18).

20 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
SOUTH

CAROLINA

GEORGIA

82°30'

33°30'

33°00'

82°00' 81°30'

32°30'

0

0 10 20 30 KILOMETERS

10 20 30 MILES

Model boundary

MODEL

BOUNDARY

Aiken

Augusta

Base modified from U.S. Geological Survey

1:500,000-scale digital State base maps

–5

–5

–5

–5 –

–5 10

0

–20

–30

5

–40

–50

10

–20

0

–20

–5

0

0

–5

0

–5

–5

–10

–20

–40

–5

0

–10

–30

0

0

–30

–10

–10

–10

–10

0

0

0

0

–10

–20

0

0

0

–20

–10

BURKE

RICHMOND

GLASCOCK

COLUMBIA

JEFFERSON

AIKEN

ALLENDALE

SCREVEN JENKINS

BARNWELL

EDGEFIELD

SALUDA

McDUFFIE WARREN

EXPLANATION

Estimated water-level

change, in feet

–30

–20

–10

–5

0

5

10

10 Line of equal estimated water-level

change-—Interval, in feet, is variable

Savannah River

Site

Difference between 1992 and 2002 observation

Observation well and water-level change

Difference between 1992 observation and

interpolated value from 2002 potentiometric

surface (Cherry, 2003)

Savannah

River

GEORGIA

SOUTH

CAROLINA

Study area

–10.0

Figure 10. Estimated water-level change between the current (2002) and previously developed (1987–92) models 

for the Upper Three Runs aquifer (source-sink layer A1) in the Savannah River Site area, South Carolina.

Simulation of Steady-State Ground-Water Flow, 2002 21
80

100

100

120

120

140

160

180

200

220

240

260

280

300

320

120

100

140

160

180

200

220

240

260

280

320

SOUTH CAROLINA

GEORGIA

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

0 5 10 15 MILES

0 5 10 15 KILOMETERS

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

N

Change of specified head values

1992–2002, –10 feet

Change of specified head

values 1992–2002, –5 feet

EXPLANATION

Simulated river cell

Simulated potentiometric contour—

Shows simulated potentiometric surface

for the Gordon aquifer (layer A2) during 2002.

Contour interval 20 feet. Datum is NAVD 88

Actively simulated area

Specified head

140

Savannah

River

122

122

73

115

146

212

206

223

253

190

185

184

165

171

131

162

148

105

107

97

96

101

147

171

178

185

202 208

159

164

175

171

131 167

112

126

253

250 181

121

117

140 144

81

100

185

180

176

156

201

SOUTH

CAROLINA

GEORGIA

SRS

Map area

N

Brighams Landing

well-cluster site

Observation well and water-level altitude—

See figures E1 and E2 for well numbers

Figure 11. Simulated 2002 potentiometric surface, water-level altitude, and location of simulated river cells for the 

Gordon aquifer (layer A2) in the Savannah River Site (SRS) area, South Carolina.

22 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
80

100

120

120

140

160

160

180

180

200

200

220

220

24

0

260

280

320

300

120

100

140

160

180

200

220

240

260

280

320

300

SOUTH CAROLINA

GEORGIA

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

D

U

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

122

147

204

168

134

156

140

Change of specified head values

1992–2002, –8 feet

Change of specified

head values

1992–2002, –10 feet

EXPLANATION

Simulated river cell

Simulated potentiometric contour—Shows simulated

potentiometric surface for the Millers Pond aquifer

(layer A3) during 2002. Contour interval 20 feet.

Datum is NAVD 88

Actively simulated area

Specified head

140

Observation well and water-level altitude—

See figure E3 for well numbers

Savannah River

122

U

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

SOUTH

CAROLINA

GEORGIA

SRS

Map area

N

Figure 12. Simulated 2002 potentiometric surface, water-level altitude, and location of simulated river cells for the 

Millers Pond aquifer (layer A3) in the Savannah River Site (SRS) area, South Carolina.

Simulation of Steady-State Ground-Water Flow, 2002 23
SOUTH CAROLINA

GEORGIA

140

140

16

1

0

80

200

220

24

0

26

28

0

0

320

300

160

180

200

220

240

260

280

300

140

120

320

100

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

SOUTH

CAROLINA

GEORGIA

SRS

Map area

N

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

235

201 213

260

209

199

186

184

163

144

158

169

165 165

175

169

158

148

148

160

184

136

175

172

175 175

177

Change of specified head values

1992–2002, –8 feet

Change of specified head

values 1992–2002, –10 feet

Change of specified head

values 1992–2002, –5 feet

EXPLANATION

Simulated river cell

Simulated potentiometric contour—

Shows simulated potentiometric surface

for the upper Dublin aquifer (layer A4)

during 2002. Contour interval 20 feet.

Datum is NAVD 88

Actively simulated area

Specified head

140

Savannah River

Observation well and water-level altitude—

See figure E4 for well numbers

Figure 13. Simulated 2002 potentiometric surface, water-level altitude, and location of simulated river cells for the 

upper Dublin aquifer (layer A4) in the Savannah River Site (SRS) area, South Carolina.

24  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
SOUTH

CAROLINA

GEORGIA

140

140

160

180

200

220

240

260 280

320

300

140

120

160

180

200

220

240

260

280

320

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

SOUTH

CAROLINA

GEORGIA

SRS

Map area

N

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

369

137

149

155

148 159

199

210

167

158

162

165 169

175

167

174

166

199

175

177

161

171

169

188

216

249

233

266

Change of specified head values

1992–2002, –8 feet

Change of specified head

values 1992–2002, –10 feet

Change of specified head

values 1992–2002, –5 feet

EXPLANATION

Simulated river cell

Simulated potentiometric contour—

Shows simulated potentiometric surface

for the lower Dublin aquifer (A5)

during 2002. Contour interval 20 feet.

Datum is NAVD 88

Actively simulated area

Specified head

140

Savannah River

Observation well and water-level altitude—

See figure E5 for well numbers

148

Brighams Landing

well-cluster site

Figure 14. Simulated 2002 potentiometric surface, water-level altitude, and location of simulated river cells for the 

lower Dublin aquifer (layer A5) in the Savannah River Site (SRS) area, South Carolina.

Simulation of Steady-State Ground-Water Flow, 2002 25
280

160

180

200

220

240

260

180

320

300

140

120

200

220

240

260

280

300

320

260

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

SOUTH

CAROLINA

GEORGIA

SRS

Map area

N

SOUTH

CAROLINA

GEORGIA

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

182

182

181 188

182

175

164

169

169

172 176

166

162

149

192

216

233 266

204

209

179

177

173

176

Change of specified head values

1992–2002, –6 feet

Change of specified head values

1992–2002, –6 feet

Change of specified head

values 1992–2002, –10 feet

Change of specified head

values 1992–2002, –5 feet

EXPLANATION

Simulated river cell

Simulated potentiometric contour—

Shows simulated potentiometric surface

for the upper Midville aquifer (layer A6)

during 2002. Contour interval 20 feet.

Datum is NAVD 88

Actively simulated area

Specified head

140

Observation well and water-level altitude—

See figure E6 for well numbers

Savannah River

Figure 15. Simulated 2002 potentiometric surface, water-level altitude, and location of simulated river cells for the 

upper Midville aquifer (layer A6) in the Savannah River Site (SRS) area, South Carolina.

26  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
160

180

180

140

120

200

220

240

260

280

320

300

200

220

240

260

280

300

320

260

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

SOUTH

CAROLINA

GEORGIA

SRS

Map area

N

SOUTH

CAROLINA

GEORGIA

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

366

58

78 56

151

130

113

162

150

154

164

170

169

174

175

166

185

171 184

190

212

212

173 179

177

183

181 187

187

205

209

118

118

Change of specified head values

1992–2002, –6 feet

Change of specified head values

1992–2002, –6 feet

Change of specified head

values 1992–2002, –10 feet

Change of specified head

values 1992–2002, –5 feet

EXPLANATION

Simulated river cell

Simulated potentiometric contour—

Shows simulated potentiometric surface

for the lower Midville aquifer (layer A7)

during 2002. Contour interval 20 feet.

Datum is NAVD 88

Actively simulated area

Specified head

140

Savannah River

Observation well and water-level altitude—

See figure E7 for well numbers

Brighams Landing

well-cluster site

Figure 16. Simulated 2002 potentiometric surface, water-level altitude, and location of simulated river cells for the 

lower Midville aquifer (layer A7) in the Savannah River Site (SRS) area, South Carolina.

Simulation of Steady-State Ground-Water Flow, 2002 27
EXPLANATION

Inflow or outflow across

lateral boundary

Recharge

Discharge to rivers

Ground-water pumpage

Flux, in million gallons

per day (Mgal/day)

105.1

106

929.5 933.4 67.2

35.8

2002 dry

Total simulated regional flux

through ground-water system

equals 1,040 Mgal/day

Total simulated regional flux

through ground-water system

equals 1,035 Mgal/day

99.2

941.4 957.0 52.6

32.4

1987–92 (Clarke and West, 1998)

Figure 17. Simulated 1987–92 (Clarke and 

West, 1998) and 2002 dry water budgets.

Applied recharge

EXPLANATION

Inflow or outflow across

lateral boundaries

Discharge to rivers

Discharge to pumping

Confining unit

Vertical flow upward or

downward across

confining unit

Value, in millions of

gallons per day

Difference from

1987–92 value,

in millions of

gallons per day

52.8 (0)

2.8 (–2.3)

515 (+14.4) 777 (–11.9)

201 (–23)

10.7 (+0.8)

313 (–4.8) 414 (–12.6)

0 (0)

2.0 (–0.9)

293 (–4.6) 380 (–18.8)

11.5 (0)

2.8 (–1.0)

286 (–3.9) 335 (–18.8)

45.4 (0)

6.2 (+1.2)

217 (–1.9) 219 (–13.4)

26.6 (0)

26.2 (+2.8)

190 (–3.1)

178

178 (–8.4)

16.5 (0)

65.1 (+1.6)

4.7 (+1.9)

7.8 (–0.4)

7.3 (+5.2)

1.6 (+0.9)

43.5 (–3.0)

5.4 (+1.6)

3.4 (+1.2)

79.2 (–7.4)

14.6 (+5.1)

4.3 (–0.1)

49.0 (–3.3)

9.8 (+3.2)

9.0 (–2.5)

38.1 (–4.0)

19.4 (–1.4)

12.8 (+2.2)

C1 (Gordon CU)

C2 (MIllers Pond CU)

C3 (Upper Dublin CU)

C4 (Lower Dublin CU)

C5 (Upper Midville CU)

C6 (Lower Midville CU)

Layer A2

(Gordon aquifer)

Layer A3

(Millers Pond aquifer)

Layer A4

(Upper Dublin aquifer)

Layer A5

(Lower Dublin aquifer)

Layer A6

(Upper Midville aquifer)

Layer A7

(Lower Midville aquifer)

(–8.4)

Layer A1

(source sink,

Upper Three Runs aquifer)

CU

Figure 18. Simulated 2002 dry conditions water budget 

by layer and comparison of budget terms with 1987–92 

long-term average simulation (Clarke and West, 1998).

Table 4. Simulated pumpage by model layer 1987–92 and 2002.

Aquifer Model 

layer

Pumpage, 

in million gallons per day

1

1987–92 2002

Gordon A2 9.9 10.7

Millers Pond A3 2.1 7.3

Upper Dublin A4 3.8 5.4

Lower Dublin A5 9.5 14.6

Upper Midville A6 6.6 9.8

Lower Midville A7 20.8 19.4

All layers 52.7 67.2

1

Clarke and West (1998)

28  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
Simulated ground-water pumpage for 2002 was 

14.6 Mgal/d more than that during 1987–92. This represents 

40 percent of the 36.5 Mgal/d increase in ground-water pumpage in the study area (fig. 17), with the remaining 21.9 Mgal/d 

either outside the simulated area or included in the sourcesink layer A1, which was not actively simulated by the model 

(see figs. 2, 4, and 9). The lower simulated recharge from the 

source-sink layer A1 and increase in ground-water withdrawal 

reduced the simulated ground-water discharge to streams by 

23.6 Mgal/d (fig. 17). Lowering of the specified-head boundaries in the lower layers of the model (A2–A7) induced an 

additional 6.8 Mgal/d of inflow into the ground-water system, 

which also increased the outflow along lateral boundaries by 

3.4 Mgal/d.

A more detailed analysis of the simulated water budget 

for 2002 shows the flow through each of the model layers and how each of the flow components changed relative 

to the 1987–92 simulation (fig. 18). Lowering the heads in 

the source-sink layer A1 reduced the inflow to layer A2 by 

11.9 Mgal/d, but increased the outflow to the source-sink 

layer A1 by 14.4 Mgal/d, which was considered as discharge 

to streams for the overall budget. In model layers A2–A5, 

reduced downward leakage through the confining units and 

lowering of the specified heads along the lateral boundaries reduced the overall net water into each of these layers by 

12.6 to 18.8 Mgal/d. The overall decrease in ground-water 

inflows to these layers and a 0.8- to 5.2-Mgal/d increase in 

pumping rates reduced ground-water discharge to river cells 

by 0.4 to 23 Mgal/d (fig. 18). Vertical leakage through confining unit C5 to the Midville aquifer system (layers A6 and A7) 

was 13.4 Mgal/d less than for the previous model. This 

contributed to decreased flow in the Midville aquifer system 

(layers A6 and A7). In model layer A6, lower specified heads 

and a 3.2-Mgal/d increase in pumping resulted in increased 

lateral inflow and decreased lateral out flow, and in decreased 

discharge to river cells. In layer A7, lateral inflow increased 

and discharge to rivers decreased, despite a 1.4-Mgal/d 

decrease in pumpage (fig. 18). These changes are likely the 

result of lowered head in the source-sink layer A1, which 

resulted in decreased leakage to the aquifer.

During 2002, simulated ground-water discharge to the 

Savannah River and its tributary streams was 60 cubic feet 

per second (ft3/s) (38.8 Mgal/d) lower than that simulated for 

1987–92 (fig. 19). Similarly, simulated ground-water discharge to Upper Three Runs Creek was 12 ft3/s (7.8 Mgal/d) 

lower than simulated for 1987–92. These decreases reflect 

the severity of the 1998–2002 drought, as was simulated by 

lowering specified-head cells in the model. Simulated groundwater outflows to the Savannah River and its tributaries during 

2002 was 560 ft3/s, or 86 percent of the observed gain in 

mean-annual streamflow between the Millhaven and Augusta 

streamflow gaging stations for WY 2002 (October 1, 2001, 

through September 30, 2002, table 2, fig. 19). The observed 

gain between these two streamflow gaging stations is considered a good indicator of ground-water contributions within the 

Savannah River Basin (Clarke and West, 1997, p. 93). 

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

WATER YEAR

S

T

REA

MFLO

W, IN

C

UBIC FEET PER

SEC

O

N

D (ft3/s)

124 ft3/s

112 ft3/s

Upper Three Runs Creek

1

10

100

1,000

10,000

560 ft3/s

620 ft3/s Simulated ground-water discharge

Savannah River

Figure 19. Mean-annual net gain in streamflow for the Savannah River (Augusta [02197000] to Millhaven 

[02197500], Georgia) and mean-annual streamflow for Upper Three Runs Creek (02197315) for water years 

1992–2002, and simulated ground-water discharge for 1992 and 2002. See figure 7 for locations.

Simulation of Steady-State Ground-Water Flow, 2002 29
At Upper Three Runs Creek, simulated ground-water discharge during 2002 was 110 ft3/s, or 83 percent of the 

observed streamflow at gaging station 02197315 during 

WY 2002 (table 2, fig. 19). The simulated ground-water 

discharge approximates findings from a recent study, which 

concluded that ground-water contribution to nearby streams 

during a dry period is nearly 80 percent of the total streamflow 

in upland coastal areas (Priest and Clarke, 2003).

Simulated Water-Level Changes

Model results indicate that the previously calibrated 

model (Clarke and West, 1998) is still representative of 

the hydrologic system. The earlier model was calibrated to 

1987–92 conditions using the average observed water levels 

at 313 model cells, whereas the current model evaluation used 

observed water levels during September of 2002 at 172 well 

locations (table 5, Appendix E). The residuals represent the 

difference between simulated and observed water levels, with 

positive values indicating that simulated values were greater 

than observed values. The error criteria is determined by evaluating uncertainties associated with each observed measurement such as land-surface altitude, water-level measurement, 

seasonal water-level fluctuations, and difference in hydraulic 

head across a given grid cell (Clarke and West, 1998, p. 31; 

Appendix E). The mean of residuals for all layers was 0.8 ft 

during 1987–92 compared with 2.8 ft during 2002 (table 5 and 

fig. 20). The root mean square (RSM) of the residuals for all 

layers decreased from 10.6 ft during 1987–92 to 8.0 ft during 

2002. The RSM of the residuals showed an improvement from 

the 1987–92 model in layers A4 (from 7.4 to 4.5 ft), A5 (from 

9.5 to 5.5 ft), A6 (from 8.5 to 3.1 ft), and A7 (from 13.2 to 

8.9 ft). The RSM increased in layers A2 (from 11.5 to 12.1 ft) 

and A3 (from 9 to 12 ft). Overall, the percentage of residuals 

within the established error criteria was 83.3 percent for the 

2002 simulation and 88.2 percent for the 1987–92 simulation. 

Simulated water levels were compared for the steady-state 

simulations 1987–92 and 2002 after designating simulated 

water levels for the 1987–92 model as initial heads for the 

2002 simulation. The computed water-level changes are shown 

for each active layer of the model (figs. 21–26). Most of the 

simulated water-level change is attributed to the lowering 

of specified heads in the source-sink layer and along lateral 

boundaries of the model. The simulated water-level changes 

were generally largest near southern Burke County and northern Jenkins and Screven Counties because of observed waterlevel declines in the Upper Three Runs aquifer.

Table 5. Comparison of calibration statistics between the 1987–92 and 2002, dry steady-state model simulations.

Aquifer 

(model layer)

Number of 

observations

Mean of 

residuals (foot)

Root mean square 

of residuals (foot)

1

1987–92 2002 11987–92 2002 11987–92 2002

Gordon (A2) 136 54 –0.1 2.5 11.5 12.1

Millers Pond (A3) 10 7 5.4 9.6 9.0 12.0

Upper Dublin (A4) 54 27 1.2 1.5 7.4 4.5

Lower Dublin (A5) 40 29 1.0 0.9 9.5 5.5

Upper Midville (A6) 28 24 –2.8 0.6 8.5 3.1

Lower Midville (A7) 45 31 4.1 6.5 13.2 8.9

All layers (A2–A7) 313 172 0.8 2.8 10.6 8.0

1

Clarke and West (1998)

EXPLANATION

90th

75th

50th (Median)

25th

10th

RESIDUALS, IN FEET

NUMBER OF OBSERVATIONS

172 54 7 27 29 24 31 25

20

15

10

5

0

–5

–10

–15

–20

ALL A2 A3 A4 A5 A6 A7

LAYERS

Percentile

Figure 20. Difference (residuals) between observed 

and simulated heads for the 2002 simulation.

3
In layer A2, the largest simulated water-level declines 

from 35 ft to more than 40 ft occur near lateral no-flow 

boundaries of the model in northern Jenkins County and 

central Jefferson County (fig. 21). In simulated water levels 

in southern Burke County and northern Screven County, 

water-level declines ranging from 20 to 30 ft as a result of 

decreased heads in the source-sink layer A1 and pumping 

from 12 nearby irrigation wells that withdrew a combined 

1.1 Mgal/d from layer A2. On the SRS, Upper Three Runs 

Creek is simulated using river cells in layer A2, which remain 

constant and would represent areas of no head change. From 

areas near Upper Three Runs Creek, simulated water-level 

declines increase to the south in Barnwell County and are 

generally greater than –5 ft throughout the southern half of 

the SRS.

In layer A3, the largest simulated water-level changes 

occur near model boundaries in central Jefferson County 

(–20 ft) and northern Jenkins County (–40 ft). The large 

decreases in simulated water levels in these areas are the 

result of reduced inflows from the source-sink layer A1 into 

the underlying layers (figs. 18 and 22). In addition to changes 

in the source-sink layer A1, specified heads in layer A3 

located along the southern and eastern model boundaries 

were lowered 8–10 ft (fig. 12). In central Burke County, 

14 production wells used for irrigation withdrew a combined 

2.6 Mgal/d from layer A3, and simulated water-level changes 

range between –15 and –25 ft. In northern Screven County, 

13 production wells used for irrigation withdrew a combined 

2.1 Mgal/d, and simulated water levels for 2002 declined by 

more than 20 ft. On the SRS, simulated water-level decline 

of greater than 5 ft was similar to those in overlying layer A2 

(figs. 21–22). 

In layers A4 and A5, only slight changes in water levels 

were simulated across most of the model area because of relatively minor increases in pumpage from the previous model of 

1.2 Mgal/d (layer A4) and 0.9 Mgal/d (layer A5), respectively 

(figs. 23–24). The largest declines of 30 ft occurred along the 

northwestern model boundary as a result of nearby pumping, decreased head in the overlying source-sink layer A1, 

and effects of the no-flow boundary conditions applied in 

that area. On the SRS and surrounding areas, the simulated 

water-level change was generally between –5 and –10 ft. In 

southern Burke and northern Screven Counties, the simulated 

water-level decline was between 10 and 15 ft.

In layers A6 and A7, the simulated water-level decline 

was less than 10 ft across most of the model area (figs. 25–26). 

The largest declines of greater than 30 ft occurred along the 

northwestern model boundary, and are likely the result of a 

combination of reduced head in the source-sink layer A1, 

upward interaquifer leakage in response to pumping in overlying layers, and effects of the no-flow boundary condition, 

which limited the amount of water available to flow laterally into the aquifer. On the SRS, the simulated water-level 

changes generally range between –2.5 and –5 ft.

Particle-Tracking and 

Time-of-Travel Analysis

The USGS particle-tracking code MODPATH (Pollock, 

1994) was used to generate advective water-particle pathlines 

and their associated time of travel based on MODFLOW 

simulations for 1987–92, 2002, and each of four ground-water 

management scenarios. MODPATH computes three-dimensional flow directions and time-of-travel using imaginary 

particles in either a forward-tracking mode that follows direction of ground-water flow toward ground-water discharge 

areas or a backtracking mode from discharge areas toward 

recharge areas. For the current study, MODPATH was used to 

assess ground-water flow in both a forward- and backtracking 

mode. This section describes results of forward tracking; the 

section “Trans-River Flow” describes results of backtracking. 

For all simulations, the active model layers (layers A2–A7) 

were assigned a uniform effective porosity of 30 percent and 

the confining units (layers C1 through C6) assigned a value of 

50 percent to match values from the previous model (Clarke 

and West, 1998, p. 86). 

The MODPATH code was used in forward-tracking mode 

to evaluate flowpaths from areas on the SRS. The analysis was conducted by establishing zones in which particles 

were seeded into model cells based on the following criteria: 

(1) occurrence of recharge from the source-sink layer A1 

(Upper Three Runs aquifer) into layer A2 (Gordon aquifer), 

(2) downward flow from layer A2 (Gordon aquifer) into 

layers A3 through A5 (Dublin aquifer system), (3) delineated 

areas of contamination or storage of hazardous materials 

on the SRS, and (4) defined surface-water drainage divides. 

Selected areas near streams on the SRS were not considered 

for the analysis because of localized flow regimes characterized by short time-of-travel and discharge to either Upper 

Three Runs Creek or other streams on the SRS. 

Five particle seed zones were established where individual particles were observed from their point of recharge 

to discharge areas located near local streams or along the 

floodplain of the Savannah River (fig. 1B). Within each zone, 

four particles were placed in each model cell at the base of the 

source-sink layer A1 (Upper Three Runs aquifer) or top of the 

Gordon confining unit (C1). Downward movement of particles 

within the source-sink layer A1 (Upper Three Runs aquifer) 

cannot be calculated by MODPATH. According to modeling 

results presented by Flach and others (2000), however, downward travel times within the Upper Three Runs aquifer can be 

expected to be several decades near C Area. Also, the Gordon 

confining unit (C1) is generally from 20 to 30 ft thick between 

D Area and K Area and time-of-travel from the base of the 

Upper Three Runs aquifer (source-sink layer A1) into the 

Gordon aquifer (layer A2) is about 10 yr. For each simulation, 

movement of particles at selected time intervals are shown 

using only one particle per cell to avoid clutter and to enable 

distinguishing individual pathlines. 

Simulation of Steady-State Ground-Water Flow, 2002 1
SOUTH CAROLINA

GEORGIA

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps –5 –10

–15

–20

–20

–5

0

–10

–15

–20

–30

–40

–5

–25

–35

–5

–15

–30

–25

–20

–5

–5

–10

–10

GA

SC

SRS

Map area

N

AIKEN

BURKE

SCREVEN

BARNWELL

JEFFERSON

JENKINS

ALLENDALE

RICHMOND

EXPLANATION

Simulated river cell

Production well screened in the Gordon aquifer

Specified head

–30

–20

–10

–5

0

10 Line of equal simulated water-level

change—- Interval is 5 feet

Simulated water-level change, in feet—

Computed by subtracting simulated potentiometric

surface for 1987–92 (Clarke and West, 1998)

from simulated potentiometric surface for

2002 dry conditions

Savannah River

Figure 21. Simulated water-level change between 1987–92 long-term average and 2002 dry conditions and locations 

of simulated pumpage in the Gordon aquifer (layer A2) in the Savannah River Site (SRS) area, South Carolina.

32 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
D

U

U

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

SOUTH CAROLINA

GEORGIA

–5 –10

–10

–15

–20

–20

–5

0

–15

–20

–30

–40

–5

–5

–5

–15

–20

–10 –15

–20

–15

–10

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

EXPLANATION

Simulated river cell

Production well screened in the Millers Pond aquifer

Specified head

–30

–20

–10

–5

0

10 Line of equal simulated water-level

change—- Interval, in feet, is variable

Simulated water-level change, in feet—

Computed by subtracting simulated potentiometric

surface for 1987–92 (Clarke and West, 1998)

from simulated potentiometric surface for

2002 dry conditions

Savannah River

SRS

N GA

SC

Map area AIKEN

BURKE

SCREVEN

BARNWELL

JEFFERSON

JENKINS

ALLENDALE

RICHMOND

Figure 22. Simulated water-level change between 1987–92 long-term average and 2002 dry conditions and locations 

of simulated pumpage in the Millers Pond aquifer (layer A3) in the Savannah River Site (SRS) area, South Carolina.

Simulation of Steady-State Ground-Water Flow, 2002  33
SOUTH CAROLINA

GEORGIA

–5

–10

–10

–15

–5

–10

–1

–2

5

–

0

25

–30

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

SRS

N GA

SC

Map area AIKEN

BURKE

SCREVEN

BARNWELL

JEFFERSON

JENKINS

ALLENDALE

RICHMOND

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

EXPLANATION

Simulated river cell

Production well screened in the upper Dublin aquifer

Specified head

–30

–20

–10

–5

10 Line of equal simulated water-level

change—- Interval is 5 feet

Simulated water-level change, in feet—

Computed by subtracting simulated potentiometric

surface for 1987–92 (Clarke and West, 1998)

from simulated potentiometric surface for

2002 dry conditions

Savannah River

Figure 23. Simulated water-level change between 1987–92 long-term average and 2002 dry conditions and locations 

of simulated pumpage in the upper Dublin aquifer (layer A4) in the Savannah River Site (SRS) area, South Carolina.

34  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
SOUTH

CAROLINA

GEORGIA

–5

–10

–15

–15

–20

–30

–25

–5

–10

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

SRS

N GA

SC

Map area AIKEN

BURKE

SCREVEN

BARNWELL

JEFFERSON

JENKINS

ALLENDALE

RICHMOND

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

EXPLANATION

Simulated river cell

Production well screened in the lower Dublin aquifer

Specified head

–30

–20

–10

–5

10 Line of equal simulated water-level

change—- Interval is 5 feet

Simulated water-level change, in feet—

Computed by subtracting simulated potentiometric

surface for 1987–92 (Clarke and West, 1998)

from simulated potentiometric surface for

2002 dry conditions

Savannah River

Figure 24. Simulated water-level change between 1987–92 long-term average and 2002 dry conditions and locations 

of simulated pumpage in the lower Dublin aquifer (layer A5) in the Savannah River Site (SRS) area, South Carolina.

Simulation of Steady-State Ground-Water Flow, 2002  35
–2.5

–5

–7.5

–10

0

–5

–10

–7.5

–7.5

–1

–

5

2

–2

0

5

–30

–2.5

–5

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

SRS

N GA

SC

Map area AIKEN

BURKE

SCREVEN

BARNWELL

JEFFERSON

JENKINS

ALLENDALE

RICHMOND

SOUTH

CAROLINA

GEORGIA

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

EXPLANATION

Simulated river cell

Production well screened in the upper Midville aquifer

Specified head

–30

–20

–10

–5

10 Line of equal simulated water-level

change—- Interval, in feet, is variable

Simulated water-level change, in feet—

Computed by subtracting simulated potentiometric

surface for 1987–92 (Clarke and West, 1998)

from simulated potentiometric surface for

2002 dry conditions

Savannah River

Figure 25. Simulated water-level change between 1987–92 long-term average and 2002 dry conditions and locations 

of simulated pumpage in the upper Midville aquifer (layer A6) in the Savannah River Site (SRS) area, South Carolina.

36  
0

–2.5

–5

–2.5

–7.5

–10

–15

–20

–25

–30

–5

–7.5

–10

10

1

1

20

30

40

50

60

70

80

90

100

110

120

130

10 20 30 40 50 60 70 80 90 100 102

SRS

N GA

SC

Map area AIKEN

BURKE

SCREVEN

BARNWELL

JEFFERSON

JENKINS

ALLENDALE

RICHMOND

SOUTH

CAROLINA

GEORGIA

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Base modified from

U.S. Geological Survey

1:500,000-scale digital

State base maps

EXPLANATION

Simulated river cell

Production well screened in the lower Midville aquifer

Specified head

–30

–20

–10

–5

10 Line of equal simulated water-level

change—- Interval, in feet, is variable

Simulated water-level change, in feet—

Computed by subtracting simulated potentiometric

surface for 1987–92 (Clarke and West, 1998)

from simulated potentiometric surface for

2002 dry conditions

Savannah River

Figure 26. Simulated water-level change between 1987–92 long-term average and 2002 dry conditions and locations 

of simulated pumpage in the lower Midville aquifer (layer A7) in the Savannah River Site (SRS) area, South Carolina.

Simulation of Steady-State Ground-Water Flow, 2002 
In zones 1 and 2, time intervals of 100 and 200 years (yr) were 

selected for display purposes because of the shorter time-oftravel. In zones 3 through 5, time intervals of 200 and 500 yr 

were used based on longer time-of-travel. For all five zones, 

flowpaths are presented for the entire time-of-travel to the 

final discharge location. The discharge areas on the SRS are 

represented in the model as: (1) river cells in layer A2 (Gordon aquifer) along Upper Three Runs Creek and the Savannah 

River, (2) return flow to the source-sink layer A1 simulating 

local streamflow, and (3) zones of well production in the Dublin and Midville aquifer systems. It should be noted that the 

Savannah River and its alluvial valley encompass a large area 

that is nearly 7 mi wide near Hollow Creek and about 4 mi 

wide farther south near the mouth of Upper Three Runs Creek 

(fig. 1B). The alluvial deposits are generally from 30 to 50 ft 

thick, and thin to the southeast along the course of the river 

(Leeth and Nagle, 1996). 

MODPATH results indicate that for the 2002 simulation, 

Upper Three Runs Creek and the alluvial valley of the Savannah River are the dominant sinks or areas of ground-water 

discharge with time-of-travel ranging from 20 yr to greater 

than 2,000 yr (figs. 27–31). Generally, time-of-travel for 

particles that migrate downward through the Gordon confining 

unit (C1) and then move laterally through layer A2 (Gordon 

aquifer) to discharge areas ranges from 20 to 200 yr. For 

particles migrating deeper into layers A3 through A5 (Dublin 

aquifer system), time-of-travel generally ranges from 200 to 

1,000 yr. Although pathlines are substantially longer and timeof-travel is slowed by additional confining units (C2–C4), 

eventual particle movement is laterally toward ground-water 

discharge areas where particles can migrate upward. Groundwater movement and discharge outside the SRS boundary 

is limited to recharge areas from: (1) zone 1 moving toward 

Eagle Point at greater than 100-yr time-of-travel (fig. 27), 

(2) zone 2 moving near trans-river flow areas at greater than 

200-yr time-of-travel (fig. 28), (3) zone 3 moving toward an 

area north of Flowery Gap Landing at greater than 1,000-yr 

time-of-travel (fig. 29), (4) zone 4 moving toward irrigation 

wells located in Allendale County at greater than 200-yr timeof-travel (fig 30); and (5) zone 5 moving toward Lower Three 

Runs Creek and the Savannah River at greater than 200-yr 

time-of-travel (fig. 31).

Zone 1

In zone 1, located in the northwestern part of the SRS, 

the mean time-of-travel for particles to reach discharge areas 

using the model depicting 2002 conditions was 294 yr (fig. 27; 

table 6). The primary discharge areas for zone 1 occur along 

the middle sections of Upper Three Runs Creek to the south 

and the alluvial valley of the Savannah River to the southwest 

(fig. 27). The A/M Area of the SRS occupies the western part 

of zone 1 and has production wells screened in the Dublin 

and Midville aquifer systems. The A/M Area is the site of a 

large chlorinated solvent plume and concern has been raised 

about possible contamination migrating toward public-supply 

wells in the town of Jackson, S.C., located west of the SRS 

boundary (Westinghouse Savannah River Company, 2004). 

Ground-water models constructed to evaluate plume migration have focused on the interaction of the Upper Three Runs 

(subdivided into three units) and Gordon aquifers (Hiergesell 

and others, 1994). The ground-water models indicate that 

eventual discharge areas from the primary plume would occur 

along Upper Three Runs Creek and Eagle Point (Westinghouse Savannah River Company, 2004). For this study, particletracking analysis indicates downward movement in the 

upper half of zone 1 into the Dublin aquifer system, with some 

migration as deep as the upper Midville aquifer before moving 

laterally toward Upper Three Runs Creek. In zone 1, layer A3 

(Millers Pond aquifer) is either thin or absent, so downward 

movement from the Gordon aquifer (layer A2) is through the 

confining units overlying layers A4–A6 (Dublin and Midville 

aquifer systems).

Once the particles enter the deeper aquifers, lateral movement is initiated toward the south prior to upward migration 

toward discharge areas within layer A2 (Gordon aquifer). The 

shortest time-of-travel from zone 1 ranges from 22 to 94 yr 

(table 6) and occurs when particles do not penetrate beneath 

layer A2 and move laterally for short distances in layer A2 

before discharging to areas along Upper Three Runs Creek.

General ground-water flow directions are either south 

toward Upper Three Runs Creek or southwest from the 

A/M Area toward the SRS boundary (fig. 27). At the 100-yr 

time-of-travel interval, some particles have migrated laterally 

for distances ranging from 1 to 3 mi, with downward movement as deep as layer A5 (lower Dublin aquifer). At 200 years, 

several particles are captured in A/M Area production wells 

screened in the lower Dublin and upper Midville aquifers 

(layers A5 and A6). These wells intercept ground water that 

has been recharged outside the areas of contamination to the 

northeast and is moving laterally to the southwest with downward movement into the lower layers. The 200-yr time interval 

approximates the median time-of-travel of 231 yr (table 6) and 

particle endpoints delineate the ground-water discharge zones 

in the alluvial valley of the Savannah River and along sections 

of Upper Three Runs Creek (fig. 27). Particles not intercepted 

by the A/M Area production wells continue movement toward 

the southwest and migrate downward into layer A7 (lower 

Midville aquifer). At the SRS boundary, vertical movement is 

initiated upward through layers A6 (upper Midville aquifer) 

into layer A2 (Gordon aquifer) and particles are discharged 

along the alluvial valley east of Eagle Point (fig. 27). Several 

particles have travel times exceeding 1,000 yr as a result of 

low head gradients in the Gordon aquifer (layer A2) along the 

alluvial valley of the Savannah River. These stagnation areas 

result in slow movement in the area at times ranging from 

600 to 700 yr.

38  
Base modified from U.S. Geological Survey

1:24,000-scale digital data

BARNWELL

AIKEN

C. Final

1,113 years

B. 200 years

A. 100 years

Upper Three

Runs Creek

Separations and

Waste Management

Area R Area

A/M

Area

Fourmile Branch

Tinker Creek

Tims Branch

Hollow

Creek

Eagle

Point

N

EXPLANATION

Ground-water contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

Zone 1

Savannah River Site (SRS)

boundary

Point source of contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

Pathline and endpoint—

Particle placed at base

of source-sink layer A1

in individual cells

SC

GA

SRS

N

Model area

Map area

Jackson

New Ellenton

3 MILES

0 1 2 3 KILOMETERS

0 1 2

Figure 27. Particle-tracking results from the simulation of 2002 dry 

conditions at selected time intervals in zone 1 located in the northwestern part of the Savannah River Site, South Carolina.

Simulation of Steady-State Ground-Water Flow, 2002  39
Zone 2

In zone 2, located between the Separations and Waste 

Management Area and K Area, primary discharge areas for 

the 2002 simulation occur to the west along Upper Three 

Runs Creek or to the south along Pen Branch (fig. 28). Zone 2 

includes three areas where ground-water contamination has 

been documented: (1) Separations and Waste Management 

Area, (2) K Area, and (3) C Area (fig. 28). The primary concern in these areas is that tritiated water from earlier operations, formerly stored in seepage basins between 1959 and 

1970, could enter into the ground-water system and migrate 

to discharge areas (Flach and others, 2000). A tritium release 

of about 1,600 curies occurred during 1977 near the K Area 

(Flach and others, 1999a). The model developed by Flach 

and others (1999a) to predict solute transport determined 

that tritium concentrations greater than the Federal drinking 

water standard of 20,000 picocuries per liter (pCi/L) would 

begin to appear north of Pen Branch during 1998 and would 

peak during 2020 at values near 240,000 pCi/L. Zone 2 was 

delineated based on the downward gradient from layer A2 

(Gordon aquifer) into layers A3–A5 (Dublin aquifer system). 

Surrounding areas near zone 2, upward gradients are common 

from layer A2 (Gordon aquifer) into the source-sink layer A1 

(Upper Three Runs aquifer), and flow is toward the stream 

reaches of Fourmile Branch and Pen Branch. Baseflow studies 

conducted along these stream segments from 1997 to 1998 

indicate gaining streams as a result of ground-water discharge 

from the Upper Three Runs aquifer (Flach and others, 1999b).

Particle-tracking results for the 2002 simulation in zone 2 

indicate that ground-water discharge occurs along Upper 

Three Runs Creek, Fourmile Branch, and Pen Branch with a 

mean time-of-travel of 917 yr (table 6). The mean time-oftravel represents movement from the base of the source-sink 

layer A1 through layer A2 (Gordon aquifer) into layers A3–

A5 (Dublin aquifer system) before moving laterally toward 

discharge areas located along Upper Three Runs Creek and the 

Savannah River (fig. 28 and table 6).

In the northern part of zone 2, east of the Separations 

and Waste Management Area, pathlines generally are toward 

Upper Three Runs Creek and particles penetrate into layer A4 

(upper Dublin aquifer). At 100 years, the shortest particle 

flowpaths migrate downward through the Gordon confining 

unit and move laterally through layer A2 (Gordon aquifer) to 

discharge areas near the Separations and Waste Management 

Area along Upper Three Runs Creek (fig. 28). At 200 years, 

some particles that are influenced by a strong downward 

gradient penetrate as deep as layer A5 (lower Dublin aquifer) 

while particles moving laterally through layer A2 (Gordon 

aquifer) have moved across the Separations and Waste Management Area toward Upper Three Runs Creek. Ground-water 

flowpaths are dominated by pathlines toward Upper Three 

Runs Creek with some particles moving directly underneath 

the creek for great distances before discharge to river cells 

(fig. 28).

In C Area, ground-water flowpaths move westward 

through layer A2 (Gordon aquifer) and pass beneath 

Fourmile Branch to discharge areas along Upper Three Runs 

Creek. The mean time-of-travel for these particles is 365 yr, 

with values ranging between 290 and 470 yr. In the areas 

located between C Area and R Area, depth of penetration is 

into layers A4–A5 (upper and lower Dublin aquifers) with 

travel times for downward migration ranging from 100 to 

300 yr prior to moving laterally to discharge areas along Upper 

Three Runs Creek. South of C Area, pathlines diverge along 

the general ground-water divide between Upper Three Runs 

Creek and Pen Branch. Here flowpaths are northward toward 

Upper Three Runs Creek, southward toward Pen Branch, or 

westward toward trans-river zones along the Georgia side of 

the Savannah River (fig. 28).

Particles terminating on the Georgia side of the Savannah 

River (trans-river flow) originate in the area between D Area 

and K Area in the southern part of zone 2. Trans-river particles 

moving toward the Savannah River either take a direct westerly flowpath south of D Area or move northwestward toward 

Upper Three Runs Creek before redirecting toward the south 

(fig. 28). The shortest time-of-travel to trans-river zones is 

about 200 yr through layer A2 (Gordon aquifer) from recharge 

areas, about 2 mi west of K Area (fig. 28). Time-of-travel to 

trans-river zones varies depending on the discharge cell, and 

ranges from 400 to 2,000 yr for the southernmost cell and 

from 1,000 to 7,300 yr for the adjacent cell. The longer travel 

times generally involve flowpaths that have greater depth of 

penetration into the Dublin aquifer system before moving 

laterally toward the Savannah River. In addition, the stagnation of flow near the Savannah River is because of low head 

gradients in layer A2 (Gordon aquifer), which results in longer 

travel times.

4
Jackson

Base modified from U.S. Geological Survey

1:24,000-scale digital data

0 1 2 3 4

0 1 2 3 4

5 MILES

5 KILOMETERS

C. Final

9,425 years

B. 200 years

A. 100 years

BARNWELL

AIKEN

GEORGIA

BURKE

CAR

SOUTH

OLINA

Separations

and Waste

Management

Area

R Area

L Area

K

Area

C

Area

D

Area

TNX Area

A/M

Area

P Area

Fourmile

Pen Branch

Meyers Branch Steel Creek

Upper Three Runs Creek

Newberry Creek

Branch

Par

Pond

L

Lake

Flowery Gap Landing

Plant Vogtle

SC

GA

SRS

N

N

Model area

Map area

EXPLANATION

Ground-water contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

Zone 2

Savannah River Site (SRS)

boundary

Point source of contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

Pathline and endpoint—

Particle placed at base

of source-sink layer A1

in individual cells

Simulation of Steady-State Ground-Water Flow, 2002  41

Figure 28. Particle-tracking results from the simulation of 2002 dry 

conditions at selected time intervals in zone 2 located in the central 

part of the Savannah River Site, South Carolina.
Zone 3

In zone 3, located within the Tinker Creek drainage basin, 

ground-water flowpaths in the 2002 simulation are dominated 

by large vertical head gradients and westward flow toward 

discharge areas along Upper Three Runs Creek (figs. 1B

and 29). Zone 3 is located to the northeast away from any 

contamination sources, but the criteria for downward groundwater flow from layer A2 (Gordon aquifer) to the lower layers 

(A3 through A5, Dublin aquifer system) was met, so further 

analysis was performed. The mean time-of-travel in zone 3 is 

1,100 yr with a maximum value of 9,724 yr (table 6). Particle 

positions and pathlines at the 500-yr time-of-travel interval 

indicate nearly 25 percent of the particles have discharged 

along Upper Three Runs Creek while several have moved 

south toward K Area (fig. 29). Generally, the shorter flowpaths 

involve lateral migration in layers A2 and A4 (Gordon and 

upper Dublin aquifers) followed by vertical movement toward 

Upper Three Runs Creek. In zone 3, layer A3 (Millers Pond 

aquifer) is either thin or absent and increases in thickness 

south of the Pen Branch Fault. The longer flowpaths (beyond 

K, P, and L Areas) penetrate as deep as layer A5 (lower Dublin 

aquifer) before initiating lateral movement. By 1,000 years, 

some particles have migrated farther west along Upper Three 

Runs Creek and south through layer A5 (lower Dublin aquifer) 

to areas near Pen Branch (fig. 29). Time-of-travel for upward 

migration from layer A5 (lower Dublin aquifer) to discharge 

points within the source-sink layer A1 east of the Savannah 

River ranges from 300 to 600 yr.

Zone 4

In zone 4, located south of P Area, simulated flowpaths 

are generally south toward discharge areas on the eastern side 

of the Savannah River (fig. 30). Simulated time-of-travel in 

zone 4 is slowed by movement through the Gordon confining unit (C1), which has a thickness of about 25 ft in zone 4. 

Travel times through this unit range from 100 to 500 yr. 

Maximum depth of penetration is downward into layer A3 

(Millers Pond aquifer) with most particles moving laterally 

through layer A2 (Gordon aquifer). The primary ground-water 

discharge areas for zone 4 are located in the Savannah River 

valley between Pen Branch and Steel Creek, and between 

Steel Creek and Furse Mill Creek. In these areas, movement is 

upward from layer A2 (Gordon aquifer) into the source-sink 

layer A1 (Upper Three Runs aquifer). Mean time-of-travel for 

the 2002 simulation in zone 4 was 505 yr and ranges from a 

minimum of 125 yr to a maximum of 1,589 yr (table 6). By 

200 years (fig. 30), several particles have moved beyond the 

SRS boundary into Allendale County, S.C., while particles 

originating in the southern part of the zone remain in the 

Gordon confining unit (C1). By 500 years, most particles have 

migrated to areas near the two discharge zones with some particles showing minimal lateral or downward movement. These 

particles eventually move toward discharge areas located 

west of Steel Creek, while some migrate farther south toward 

Allendale County (fig. 30).

Zone 5

In zone 5, located in areas adjacent to Par Pond, simulated 

ground-water flowpaths are similar to those of zone 4 with 

southward movement and downward penetration into layers A3 

through A5 (Dublin aquifer system, fig. 31). The primary 

ground-water discharge areas for zone 5 are in the Savannah 

River valley between Pen Branch and Steel Creek, and between 

Steel Creek and Furse Mill Creek. Here, particle movement is 

upward from layer A2 (Gordon aquifer) into the source-sink 

layer A1 (Upper Three Runs aquifer). Mean time-of-travel for 

the 2002 simulation in zone 5 was 1,553 yr and ranged from 

a minimum of 34 yr to a maximum of 16,045 yr (table 6). By 

200 years, about 2 percent of the particles have discharged into 

the source-sink layer A1 along Lower Three Runs Creek with 

the remaining active particles moving near P Area or in proximity to the southern SRS boundary (fig. 31). Maximum depth of 

particle penetration within the initial 200 yr interval is near the 

bottom of layer A2 (Gordon aquifer). By 500 yr, lateral movement of particles continues in a southwesterly direction with 

several particles reaching the two principle discharge areas. A 

third area of simulated discharge occurs within an active production well withdrawing water from layers A3 and A5 (Millers 

Pond and lower Dublin aquifers). The irrigation well, located in 

Allendale County, S.C., intercepts particles moving southward 

with travel times ranging from 660 to 14,800 yr.

42 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
Jackson

Base modified from U.S. Geological Survey

1:24,000-scale digital data

6 MILES

6 KILOMETERS

C. Final

9,724 years

B. 1,000 years

A. 500 years

BARNWELL

AIKEN

BURKE

GEORGIA

0

0 2 4

2 4

Separations

and Waste

Management

Area

R Area

L Area

C TNX Area Area

A/M Area

P Area

Fourmile

Pen Branch

Meyers Branch Steel Cr

Upper Three Runs Creek

Newberry Cree

M

k

cBean Cr

Branch

Par

Pond

L

Lake

Flowery

Gap

Landing

Plant Vogtle

SOUTH

CAROLINA

K

Area D

Area

Hollow

Creek

Lower Three Runs Creek

SC

GA

SRS

N

N

Model area

Map area

EXPLANATION

Ground-water contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

Zone 3

Savannah River Site (SRS)

boundary

Pathline and endpoint—

Particle placed at base

of source-sink layer A1

in individual cells

Point source of contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

Figure 29. Particle-tracking results from the simulation of 2002 dry 

conditions at selected time intervals in zone 3 located in the northeastern part of the Savannah River Site, South Carolina.

Simulation of Steady-State Ground-Water Flow, 2002  43
Base modified from U.S. Geological Survey

1:24,000-scale digital data

5 MILES

C. Final

1,589 years

B. 500 years

A. 200 years

BARNWELL

ALLENDALE

AIKEN

BURKE

GEORGIA

C

SOUTH

AROLINA

0 1 2 3 4

0 1 2 3 4 5 KILOMETERS

L Area

P Area

Fourmile Branch

Furse Mill Creek

Little Sweetwater Creek

Steel Cr

Lower Three Runs Creek

L

Lake

K

Area

D

Area

Meyers

Branch

Furse Cr

Pen Branch

SC

GA

SRS

N

N

Model area

Map area

EXPLANATION

Ground-water contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

Zone 4

Savannah River Site (SRS)

boundary

Pathline and endpoint—

Particle placed at base

of source-sink layer A1

in individual cells

Point source of contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

Figure 30. Particle-tracking results from the simulation of 2002 dry 

conditions at selected time intervals in zone 4 located in the southcentral part of the Savannah River Site, South Carolina.

44  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
Jackson

0 2 4 6 MILES

0 2 4 6 KILOMETERS

BARNWELL

AIKEN

CAR

SOUTH

OLINA

GEORGIA

BURKE

ALLENDALE

Base modified from U.S. Geological Survey

1:24,000-scale digital data

C. Final

16,045 years

B. 500 years

A. 200 years Separations

and Waste

Management

Area

R

Area

L Area

C

Area

A/M Area

P

Area

Fourmile

Pen Branch

Meyers Br

Steel Cr

Upper Three Runs Creek

Lower Three Runs Creek

Newberry Cree

M

k

cBean Cr

Branch

Par

Pond

L

Lake

Flowery Gap

Landing

Plant Vogtle

K

Area

D

Area

Hollow Creek

TNX Area

Furse Mill Cr

Little Sweetwater Cr

Furse Cr

EXPLANATION

Ground-water contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

Zone 5

Savannah River Site (SRS)

boundary

Pathline and endpoint—

Particle placed at base

of source-sink layer A1

in individual cells

Point source of contamination

(modified from Westinghouse

Savannah River Company, 1996).

See figure 1B for description

SC

GA

SRS

N

N

Model area

Map area

Simulation of Steady-State Ground-Water Flow, 2002  45

Figure 31. Particle-tracking results from the simulation of 2002 dry 

conditions at selected time intervals in zone 5 located in the eastern 

part of the Savannah River Site, South Carolina.
Table 6. Time-of-travel for particles seeded in recharge areas (five zones) on Savannah River Site, South Carolina, and 

forward tracked through time to discharge areas.

[All time-of-travel values shown are in years]

Zone 

number

Number of 

particles 

applied

Statistic

1

1987–92 2002

Scenario

A B C D

Boundary conditions

Wet Dry Average Average Average Dry

Time-of-time, in years

Zone 1 984 Mean 301 294 294 249 293 293

90th percentile 545 561 552 440 550 560

75th percentile 404 412 407 335 408 417

Median 264 231 228 217 228 234

25th percentile 166 164 163 150 163 149

10th percentile 92 94 91 64 91 94

Maximum 2,121 1,113 2,481 1,294 1,393 1,284

Minimum 19 22 21 20 21 22

Zone 2 1,148 Mean 823 917 848 866 861 928

90th percentile 1,289 1,554 1,364 1,524 1,384 1,587

75th percentile 828 874 813 819 827 875

Median 543 591 561 524 564 593

25th percentile 367 408 388 323 388 407

10th percentile 212 218 222 144 220 213

Maximum 6,715 9,425 6,703 27,276 6,699 11,426

Minimum 28 30 29 29 29 30

Zone 3 1,161 Mean 1,051 1,100 1,095 947 1,085 1,120

90th percentile 1,553 1,740 1,804 1,764 1,773 1,856

75th percentile 1,275 1,419 1,375 1,339 1,373 1,429

Median 1,020 1,146 1,105 834 1,084 1,142

25th percentile 442 523 470 411 469 518

10th percentile 178 207 183 181 183 207

Maximum 58,102 9,724 11,778 5,916 14,658 9,916

Minimum 61 80 63 63 63 79

Zone 4 882 Mean 522 505 508 494 495 502

90th percentile 961 969 949 926 940 967

75th percentile 624 595 600 592 595 594

Median 402 404 398 395 397 402

25th percentile 324 335 329 327 327 335

10th percentile 225 238 233 232 229 236

Maximum 2,870 1,589 5,741 3,015 1,560 1,647

Minimum 123 125 124 143 122 123

Zone 5 668 Mean 1,570 1,553 1,532 1,491 1,532 1,552

90th percentile 2,296 2,218 2,391 2,303 2,453 2,207

75th percentile 1,575 1,609 1,628 1,596 1,612 1,626

Median 1,340 1,337 1,349 1,307 1,348 1,354

25th percentile 1,132 966 1,052 998 1,138 1,108

10th percentile 672 444 510 460 463 434

Maximum 13,217 16,045 12,874 11,443 12,071 19,304

Minimum 38 34 36 36 36 34

1

Clarke and West (1998)

46  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
Trans-River Flow

The USGS particle-tracking code MODPATH (version 3; 

Pollock, 1994) also was used in backtracking mode by calculating particle movement from documented areas of trans-river 

flow (Clarke and West, 1998, p. 89). Particles were placed 

in trans-river flow areas, located on the western side of the 

Savannah River floodplain in Burke County, Ga., and backtracked to recharge areas on the SRS. The original particletracking analysis for 1987–92 (Clarke and West, 1998) applied 

five particles to each model cell, centrally positioning each 

particle from bottom to top at 25-percent increments of aquifer 

thickness. To improve definition of flowpaths and corresponding recharge areas for the 2002 model, a greater number of 

particles were applied to each model cell, at 10-percent thickness increments for particles closest to the cell walls, and at 

20-percent thickness increments for particles located in the 

cell interior for a total of 100 particles per cell (fig. 32). 

The most recent release of MODPATH (version 3) 

includes MODPATH-PLOT, which allows particle-tracking 

profiles to be viewed along a designated row or column of 

the model. The MODPATH program uses output from each 

steady-state simulation (1987–92, 2002, and Scenarios A–D; 

Appendixes A–D) to calculate particle positions and time-oftravel along horizontal cell faces and at the top and bottom of 

each hydrogeologic unit. The results are presented for a profile 

along row 82 of the model (fig. 8), which includes documented 

areas of trans-river flow on the Georgia side of the Savannah 

River and recharge areas on the SRS located between D Area 

and K Area (fig. 33). Figure 33 shows flowpaths in map view 

and along the profile with 100-yr increments of time shown as 

dots on the flowlines.

For the backtracking of particles, three model cells 

located near Flowery Gap Landing (covering about 1 mi2) on 

the Georgia side of the Savannah River were chosen based on 

results from the 1987–92 simulation (Clarke and West, 1998, 

p. 89) and on results from zone 2 (forward-tracking mode) that 

indicate that the area west of the Savannah River is a common 

point of ground-water discharge. Of the 300 particles applied 

in the three cells for the 2002 dry simulation, 88 particles 

(29 percent) backtrack to recharge areas on the SRS compared 

with 93 particles (31 percent) for the 1987–92 simulation 

(table 7). The remaining particles backtracked to recharge 

areas on the Georgia side of the Savannah River.

Simulated flowpaths for 2002 indicate that time-of-travel 

from trans-river areas in Georgia to recharge areas near central 

SRS (D Area and K Area) range from about 82 to 1,519 yr 

(table 7, fig. 33). Mean time-of-travel for trans-river particles 

for 2002 is 518 yr compared with 534 yr for the 1987–92 

simulation (table 7). The shortest travel time (from 82 to 

415 yr) was for particles moving laterally through layer A2 

(Gordon aquifer) and upward into the base of the source-sink 

layer A1 (Upper Three Runs aquifer) near D Area and K Area 

(fig. 33). The point of recharge for these particles is the same 

interstream area south of Fourmile Branch, documented in 

Clarke and West (1998). Based on time-of-travel for the 2002 

simulation, particles with greater depth of penetration into 

layers A3 through A5 (Dublin aquifer system) had longer 

flowpaths and travel times ranging from 340 to 1,519 yr. 

These particles move downward from trans-river flow areas 

into the lower layers A3 though A5 (Dublin aquifer system) 

before migrating laterally toward D Area and K Area where 

the final movement is upward toward recharge areas at the 

base of the source-sink layer A1 (Upper Three Runs aquifer). 

In the 1987–92 simulation, several particles move laterally 

through the Dublin aquifer system to recharge areas north of 

Pen Branch. The time-of-travel for these particles ranges from 

about 1,600 to 2,356 yr.

Seeded

particles Single

model cell

20 percent

THICKNESS INTERVAL

10

percent

10

percent

Figure 32. Schematic diagram showing particle-seeding 

distribution for cells located in trans-river zones.

Simulation of Steady-State Ground-Water Flow, 2002  47
11987–92 2002

Simulation

Boundary conditions Long-term average Dry

Particles released 300 300

Recharge on SRS 93 88

Mean 534 518

90th percentile 978 985

75th percentile 753 785

Median 486 481

25th percentile 140 147

10th percentile 102 104

Maximum 2,356 1,519

Minimum 80 82

Time-of-travel, in years

1

Clarke and West, 1998

250

150

50

NAVD 88

50

150

250

350

Feet

Georgia South

Carolina

VERTICAL EXAGGERATION

IS X50

0 1 2 MILES

0 1 2 KILOMETERS

A A'

Savannah River

Meyers

Branch

D Area

K Area L Area

P Area

C Area

TNX Area

AIKEN COUNTY

Pen Branch

Savannah River

Site

Upper Three Runs Creek

River Savannah

S

G

C

A

Fourmile Branch

SAVANNAH RIVER SITE

Base modified from U.S. Geological Survey

1:24,000-scale digital data

Separations and Waste

Management Area

Steel Creek

Steel Creek L

Lake

BURKE

COUNTY

BARNWELL

COUNTY

Flowery Gap Landing

S

G

C

A

SRS

N

Model area

Map area

A1

A2

A4

A5

A3

A

A'

A1

EXPLANATION

A A'

Ground-water

contamination

Map Cross section

Particle path and

total years of travel

Line of section 100-year time-oftravel interval

Active model layer

Hydrogeologic

contact

Savannah River

alluvial valley

Aquifer Recharge cell

Selected

discharge cell

Confining unit

110

A.

B.

0 1 2 3 MILES

0 1 2 3 KILOMETERS

110

110

180

180

530

530

1,400

630

630

850

850

N

C1

C2

C3

C4

C5

R Area

Figure 33. (A) Simulated trans-river flow for 2002 dry conditions and selected ground-water pathlines in 

map view, and (B) selected ground-water pathlines in cross-sectional view along row 82 (see figure 8) at 

the Savannah River Site (SRS), South Carolina.

48  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
Simulation of Ground-Water 

Management Scenarios, 2002 and 2020

Four hypothetical ground-water management scenarios 

were developed to assess the effect of changing pumping and 

boundary conditions on ground-water flow and the potential 

migration of contaminants from the SRS. The four scenarios 

represent hydrologic conditions for (A) reported pumping for 

2002 and boundary conditions for an average year, (B) reported 

pumping for 2002 with SRS pumping discontinued and boundary conditions for an average year, (C) projected 2020 pumping 

and boundary conditions for an average year, and (D) projected 

2020 pumping and boundary conditions for a dry year (table 8). 

Results of the four scenarios are summarized briefly below, 

but are described in detail including maps, tables, and schematic diagrams in Appendixes A–D. Projected 2020 pumping 

assumes average hydrologic condition; this is less than 2002 

pumping, which was during an extreme drought.

Adjustments to Boundary Conditions

The previous model simulation (1987–92) represents 

hydrologic conditions during a relatively average period, 

whereas the current model (2002) simulates extreme drought 

conditions (table 8). In both simulations, the heads assigned 

in the source-sink layer A1 and along lateral boundaries were 

based on potentiometric-surface maps (Clarke and West, 1997; 

Cherry, 2003) for their respective time periods. In three of four 

ground-water management scenarios (Scenarios A, B, and C), 

the specified heads in the source-sink layer A1 and along lateral

boundaries (layers A2–A7) of the model were averaged between 

long-term average (1987–92) and extremely dry (2002) hydrologic conditions. In the remaining pumping scenario (Scenario D), 

specified heads in the source-sink layer A1 and along lateral 

boundaries (layers A2–A7) of the model were adjusted to 

represent dry hydrologic conditions similar to the 2002 simulation. The focus of the discussion is on the forward tracking of 

particles from zones 1 and 2, and backtracking of particles from 

the trans-river area on the Georgia side of the Savannah River as 

a result of potential migration of tritiated water from the SRS. 

Zones 3–5 represent areas of minimal contamination and the 

median time-of-travel ranges from 395 to 1,354 yr (table 6).

Table 7. Results of particle backtracking from trans-river areas in Georgia to recharge cells 

located in the Savannah River Site, South Carolina.

1

1987–92 2002

Scenario

A B C D

Boundary conditions

Wet Dry Average Average Average Dry

Particles released 300 300 300 300 300 300

Trans-river particles 93 88 89 110 88 92

Time-of-travel, in years

Mean 534 518 516 460 541 535

90th percentile 978 985 934 904 940 1,011

75th percentile 753 785 736 722 757 757

Median 486 481 462 366 454 507

25th percentile 140 147 145 120 148 151

10th percentile 102 104 103 110 103 103

Maximum 2,356 1,519 2,299 2,572 2,305 1,845

Minimum 80 82 81 79 81 79

1

Clarke and West (1998)

Table 8. Ground-water management scenarios developed for the Savannah River Site region and relative changes to specified heads 

in the source-sink layer A1, specified heads located along lateral boundaries in the active model layers (A2–A7), and simulated pumping.

[Mgal/d, million gallons per day]

Simulated condition 11987–92 2002

Scenario

2002 2020

A B C D

Source-sink layer A1, specified heads Long-term average Dry Average Average Average Dry

Lateral specified head boundaries, layers A2–A7 Long-term average Dry Average Average Average Dry

Pumpage (active layers A2–A7), in mgal/d 52.7 67.2 67.2 61.9 55.3 56.9

1

Clarke and West (1998)

Simulation of Ground-Water Management Scenarios, 2002 and 2020  49
Projected Pumping

Pumping projections in the SRS region through 2020 

(Scenarios C and D) were developed (1) for public supply 

and industry based on water-management plans and population-growth projections, and (2) for irrigation based on an 

“average” quantity of water applied (gallons per acre per 

day, gal/acre/day) to the total irrigated acreage of 106,000 

(93 percent of 2000 estimate).

Population in the eight-county study area is expected to 

increase by 80,000 residents by the year 2020 (table 9) with 

most of the growth centered around the Augusta, Ga., and 

North Augusta, S.C., areas and the counties of Richmond, 

Ga., and Aiken, S.C. (Rutherford & Associates, 2000a, b, 

and c; U.S. Census Bureau, accessed February 3, 2003, at 

http://www.census.gov/; J.M. Dole, Lower Savannah Council 

of Governments, written commun., 2003). Most rural 

communities have experienced an overall decline in population during the past 70 years, which has stabilized during the 

past 20 years, and modest increases are predicted by the year 

2020. The analysis of water-use trends and population growth 

during 1980–2000 is available from many sources (Fanning, 

1997, 2003; Fanning and others, 1992; Harrelson and others, 

2002; Lonon and others, 1983; Newcome, 1995, 2000; Pierce 

and Barber, 1982; Pierce and others, 1982, 1984; Rutherford & 

Associates, 2000a, b, and c; Stringfield, 1989; Trent and 

others, 1990; Turlington and others, 1987; U.S. Census 

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

U.S. Geological Survey, accessed February 11, 2003, at 

http://water.usgs.gov/watuse/), which were used to estimate a 

ground-water use of 102 Mgal/d in the year 2020 (table 9).

Table 9. Ground-water use during 2002 and projected pumpage for 2020 average hydrologic conditions near the Savannah River Site, 

South Carolina and Georgia.

[Ga., Georgia; S.C., South Carolina; do., ditto]

Year State County Population1

Pumpage, in million gallons per day

Public 

supply2

Irrigation3 Industrial 

mining

Domestic and 

commercial

Livestock Thermo­electric 

power

Total

2002 Ga. Burke 22,794 1.42 21.23 0.09 0.90 0.03 1.17 24.84

do. Jefferson 17,138 1.76 6.92 4.01 0.64 0.03 0 13.36

do. Jenkins 8,647 0.54 3.94 0.01 0.33 0.02 do. 4.84

do. Richmond 197,842 12.59 2.63 2.47 0.02 0.02 do. 17.74

do. Screven 15,201 1.06 15.62 1.82 0.79 0.03 do. 19.32

S.C. Aiken 145,276 13.54 1.19 4.50 0 0 do. 19.23

do. Allendale 10,949 0.84 10.16 1.97 do. do. do. 12.97

do. Barnwell 23,407 2.32 0.32 0 do. do. do. 2.64

Total—Ga. 261,622 17.37 50.34 8.40 2.68 0.13 1.17 80.10

Total—S.C. 179,632 16.70 11.67 6.47 0 0 0 34.84

Total—eight county 441,254 34.07 62.01 14.87 2.68 0.13 1.17 114.94

2020 Ga. Burke 430,647 1.47 11.46 0.00 0.90 0.03 1.17 15.03

do. Jefferson 517,190 1.87 5.38 3.59 0.64 0.03 0 11.51

do. Jenkins 410,388 0.67 4.62 0.01 0.33 0.02 do. 5.65

do. Richmond 6216,400 15.32 0.63 2.87 0.22 0.02 do. 19.06

do. Screven 421,916 1.39 9.94 2.00 0.79 0.03 do. 14.16

S.C. Aiken 7188,525 14.42 0.39 5.08 0.80 0.18 do. 20.87

do. Allendale 711,090 1.02 3.07 4.67 0.36 0.04 do. 9.16

do. Barnwell 727,230 2.90 2.32 0.72 0.73 0 do. 6.67

Total—Ga. 296,541 20.73 32.03 8.47 2.88 0.13 1.17 65.41

Total—S.C. 226,845 18.34 5.78 10.47 1.89 0.22 0 36.70

Total—eight county 523,386 39.07 37.81 18.94 4.77 0.35 1.17 102.11

1

U.S. Census Bureau, accessed February 3, 2003, at http:www.census.gov/ 2

J.L. Fanning, U.S. Geological Survey, written commun., 2003. 

3

Kerry Harrison, University of Georgia, Cooperative Extension Service, written commun., 2003. 

4

Rutherford & Associates, 2000a, b, c. 

5

Central Savannah River Area Regional Development Center, 2003. 

6

Mike Little & Associates, 1996.

7

J.M. Dole, Lower Savannah Council of Government, written commun., 2003.

50 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
The total projected increase in water demand for public 

supply (12 Mgal/d from 2002 to 2020) will perhaps be met by 

additional surface-water withdrawals from the Savannah River 

and increased ground-water withdrawals of 5 Mgal/d. These 

projections are based on the per capita water use of 150 gallons per day applied to the entire eight-county study area. In 

general, population centers located in the northern part of the 

study area such as Augusta, Ga., and North Augusta, S.C., 

rely on surface-water filtration plants along the Savannah 

River near the Fall Line. Farther south in Richmond County, 

Ga., and Aiken County, S.C., downdip sediments thicken 

and well yields provide sufficient amounts of ground water 

for public supply. Future pumping estimates represent a shift 

in the distribution of pumpage from irrigation wells in rural 

areas to public-supply wells in areas of projected population 

growth. In these areas, projected increases for public-supply 

wells range from 5 to 25 percent from current rates (Fanning, 

2003; Mike Little & Associates, 1996; Rutherford & Associates, 2000a, b, and c; J.M. Dole, Lower Savannah Council 

of Governments, written commun., 2003; P.A. Stone, South 

Carolina Department of Health and Environmental Control, 

written commun., 2003; table 9). One area of anticipated 

growth is near Augusta, Ga., particularly in the southern part 

of Richmond County, Ga., where ground-water withdrawals 

from the Midville aquifer system are expected to increase by 

2.7 Mgal/d. Low to moderate growth rates can be expected 

in Burke, Jenkins, and Screven Counties, Ga., as a result of 

highway expansion on the Savannah River Parkway between 

Augusta and Savannah (Rutherford & Associates, 2000a, b, 

and c; G.M. Brewer, Georgia Department of Transportation, 

written commun., 2003; table 9). According to population 

growth estimates for South Carolina (J.M. Dole, Lower Savannah Council of Governments, written commun., 2003), the 

area of the highest anticipated growth rate is Aiken County. 

Additional water demands in this area will be met through a 

combination of increased surface-water withdrawals from the 

Savannah River and well production near the City of Aiken 

(P.A. Stone, South Carolina Department of Health and Environmental Control, written commun., 2003).

Because irrigation withdrawal can be substantially higher 

during periods of drought, two projections were completed to 

the year 2020—one for average climatic conditions (Scenario C) and one for average dry climatic conditions (Scenario D). 

Estimated values for 2020 were derived by multiplying projected acres of irrigated land in each county by an average application rate derived during the period 1980–2002 (table 10). 

Table 10. Total water use for irrigation, irrigated acreage, and ground-water withdrawals for irrigation during 2000–2002, mean 

application rate during 1980–2002, and projected water-use for irrigation in the year 2020 for the Savannah River Site region, 

South Carolina and Georgia.

 [Mgal/d, million gallons per day; gal/acre/day, gallons per acre per day; Ga., Georgia; S.C., South Carolina]

County/state

2000–2002 1980–2002 2020—Projected

Total water use 

for irrigation 

(Mgal/d)

Irrigated 

acreage

Ground-water withdrawals for irrigation

Mean application rate 

(gal/acre/day)

Total water use 

for irrigation 

(Mgal/d)

Ground-water 

withdrawals for 

irrigation (Mgal/d)

Irrigated 

acreage Mgal/d (Percent)

Burke, Ga. 28.36 27,530 21.23 74.9 526 15.30 11.46 25,713

Jefferson, Ga. 17.29 24,190 6.92 40 477 13.44 5.38 22,593

Jenkins, Ga. 5.78 12,200 3.94 68.2 443 6.78 4.62 11,395

Richmond, Ga. 6.63 1,450 5.22 78.7 1,265 0.81 0.63 1,354

Screven, Ga. 21.53 24,660 15.62 72.5 534 13.70 9.94 23,032

Aiken, S.C. 3.94 2,150 0.98 24.9 868 1.56 0.39 2,008

Allendale, S.C. 14.06 10,620 5.62 40 1,090 7.69 3.07 9,919

Barnwell, S.C. 12.45 10,690 3.73 30 615 7.74 2.32 9,984

Total—Ga. 79.59 90,030 52.93 66.5 560 50.03 32.03 84,088

Total —S.C. 30.45 23,460 10.33 33.9 900 16.99 5.78 21,912

Total—eight county 110.04 113,490 63.26 57.5 617 67.02 37.81 106,000

Data sources: County totals for irrigation and irrigated acreage for Georgia are from Fanning (2003) and Pierce and others (1982). Lonon and others 

(1983) and W.J. Stringfield (U.S. Geological Survey, written commun., 2002) provided total water use for irrigation and irrigated acreage for South Carolina. 

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

for irrigation wells located in Georgia. Paul Bristol (South Carolina Department of Health and Environmental Control, written commun., 2003) provided sitespecific data for irrigation wells located in South Carolina.

Simulation of Ground-Water Management Scenarios, 2002 and 2020  51
The mean application rate used for counties in Georgia was 

560 gal/acre/day (7.5 in/yr) and was considerably lower than 

the rate of 900 gal/acre/day (12.1 in/yr) for counties in South 

Carolina. These values were adjusted prior to multiplying 

by the estimated irrigated acreage to obtain the total water 

use for irrigation in 2020. The two adjusted application rates 

were 595 gal/acre/day (8.0 in/yr) for counties in Georgia and 

775 gal/acre/day (10.4 in/yr) for counties in South Carolina. 

The estimates for total water use for irrigation for each county 

were adjusted using existing ratios of surface to ground-water 

irrigation pumpage during 2000–2002 to determine the pumping rate for 2020 (table 10). Projected annual ground-water use 

for irrigation for average conditions (Scenario C) during 2020 

is 38 Mgal/d and for typical dry conditions (Scenario D) is 

43 Mgal/d (fig. 34). Both of these values represent a decrease 

from the estimated irrigation use of 63 Mgal/d during the 

drought of 2002. As Stooksbury (2003) noted, the severity of 

the 2002 drought was considered extreme, so an “average” 

application rate for dry conditions was considered to represent a 60:40 mix of normal and dry conditions. According 

to this formula, the application rate for a wet year (436 gal/

acre/day—1995) was multiplied by 0.6 and then added to 

the resulting multiplication of the application for a dry year 

(960 gal/acre/day—2000) by 0.4. Thus, the resulting application rate used for typical dry conditions (Scenario D) was 

662 gal/acre/day. The projected ground-water use for 2020 in 

the water-use categories of commercial, industrial, and thermoelectric power was held at either the 2000 or 2002 groundwater withdrawal rates.

0

20

40

60

80

100

120

140

Irrigation

Scenario C

(average)

Scenario D

(dry)

1980 1985 1990 1995 2000 2002 2020 PU

MPA

GE, IN

MILLIO

N

G

ALLO

N

S PER

D

AY

Total ground-water use

Figure 34. Total ground-water withdrawals including 

irrigation (1980–2002), and projected pumpage including irrigation (Scenarios C and D) during 2020 for the 

eight-county study area (see table 1 for county totals 

from 1990 to 2000 and data sources; table 10 for county 

totals from 2002 and projections to 2020).

52 Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site

Comparison of Scenarios

The most influential factors controlling particle movement are vertical and lateral head gradients and pumping distribution within the active layers of the model. The specified 

heads in the source-sink layer A1 control the vertical movement of water entering the ground-water system as recharge 

and influence the lateral head gradient from contaminant 

source areas to discharge areas along creeks and rivers. In 

three of four ground-water management scenarios (Scenarios A, B, and C), the specified heads in the source-sink 

layer A1 and along lateral boundaries (layers A2–A7) of the 

model were averaged between long-term average (1987–92) 

and dry (2002) hydrologic conditions. In the remaining pumping scenario (Scenario D), specified heads in the source-sink 

layer A1 and along lateral boundaries (layers A2–A7) of the 

model were adjusted to represent dry hydrologic conditions 

similar to 2002. Results and discussion of each of the scenarios is presented in Appendixes A–D. A comparison of budget 

terms of the steady-state simulations for each model layers is 

included in table 11.

In zone 1, median time-of-travel from recharge areas to 

discharge areas along Upper Three Runs Creek and west of 

the SRS boundary ranges from 217 to 264 yr for all simulations (table 6). Pumpage in the A/M Area of SRS has the 

most influence on particle movement and depth of penetration 

for this area of the model. Ground-water withdrawals from 

this area were 3.3 Mgal/d during 2002 (R.A. Hiergesell, Westinghouse Savannah River Company, written commun., 2002). 

This pumping rate was used for Scenarios A, C, and D. For 

the period from 1987 to 1992, the pumping rate was slightly 

less at 2.6 Mgal/d (Clarke and West, 1998). Most of this 

production is from the Dublin and Midville aquifer systems 

(model layers A4–A7). Scenario B was developed for measuring the effects of pumping in the event of the closure of the 

SRS and pumping rates declining to zero. In general, eliminating pumping in the A/M Area reduces the depth of penetration of particles and shortens the pathways to discharge 

areas. The median time-of-travel for Scenario B in zone 1 is 

217 yr compared with 228 yr for Scenario A (table 6). The 

second most influential factor controlling particle movement 

is the adjustment of heads in the source-sink layer A1, which 

affects the amount of recharge entering the system and flow 

though each of the confining units. In the SRS, the variability 

in recharge entering the ground-water system through the 

source-sink layer A1 is 1.4 Mgal/d between wet (1987–92) 

and dry (2002 and Scenario D) hydrologic conditions. The 

reduction in flow through each of the confining units lowers 

the simulated heads in each of the active layers of the model 

(layers A2–A7), which reduces the horizontal gradient toward 

discharge areas. 
In general, median time-of-travel for both simulations of dry 

conditions (2002 and Scenario D) were longer at 231 and 

234 yr, respectively. Overall, the mean time-of-travel is similar 

for simulations with active SRS pumping (2002, Scenarios A, 

C, and D; table 6) with a reduction of about 50 yr when pumping is eliminated (Scenario B). All particles originating in zone 

1 eventually migrate to discharge areas along the floodplain 

of the Savannah River west of the SRS boundary or to the 

south along Upper Three Runs Creek. Although downward 

movement of particles generally extends into the Dublin and 

Midville aquifer systems, migration is upward to discharge 

areas in the Gordon aquifer (layer A2).

In zone 2, median time-of-travel from recharge areas to 

discharge areas along Upper Three Runs Creek, Pen Branch, 

Fourmile Branch, and the Savannah River ranges from 524 

to 593 yr (table 6). In general, particles migrate downward 

with depth of penetration into the Dublin aquifer system 

before migrating laterally toward discharge areas. General 

particle movement is initially lateral for short distances, and 

then movement is upward toward discharge areas within the 

Gordon aquifer (layer A2), or as return flow to the sourcesink layer A1. The model is most sensitive to pumpage with 

1.3 Mgal/d withdrawn during 2002 (R.A. Hiergesell, Westinghouse Savannah River Company, written commun., 2002) 

where the pumping rate was held constant for Scenarios A, C, 

and D with most of the production from the Midville aquifer 

system (layers A6–A7). Scenario B was developed to simulate 

the effects of pumping in the event of the SRS closure with 

pumping eliminated. For the period from 1987 to 1992, the 

pumping rate was 3.7 Mgal/d higher in zone 2 than during 

2002 (Clarke and West, 1998). The median time-of-travel for 

Scenario B (SRS shutdown) of 524 yr is less than the value for 

Scenario A (561 yr), which indicates the depth of penetration 

for particles is reduced and lateral movement toward discharge 

areas is predominant. The variability in recharge entering 

the ground-water system though the source-sink layer A1 

in zone 2 is about 1.0 Mgal/d between long-term average 

(1987–92) and dry (2002 and Scenario D) hydrologic conditions. The reduction in flow though each of the confining units 

lowers the simulated heads in each of the active layers of the 

model (layers A2–A7), which reduces the horizontal gradient 

toward discharge areas. An example of this is the median timeof-travel of 543 yr for the 1987–92 simulation, which is less 

than each of the median values for the other simulations (2002, 

Scenarios A, C, and D; table 6) owing steeper lateral head 

gradients in the active layers of the model. The earliest arrival 

times to trans-river areas located on the Georgia side of the 

Savannah River is 120 yr for particles originating in recharge 

areas located about 1 mi southeast of D Area. Particle movement is dominated by lateral migration through the Gordon 

aquifer (layer A2) toward the Savannah River. From the State 

line, these particles migrate farther to the west and eventually 

discharge to the adjacent cell (row 81, column 47; fig. 33) 

located near Flowery Gap Landing, which is a river cell 

simulating the contact between the Gordon aquifer (layer A2) 

and the alluvial floodplain of the Savannah River. The timeof-travel for this short distance ranges from 240 to 260 yr, 

which gives an indication of the relatively flat head gradients 

near the discharge area. In extreme cases, the time-of-travel 

in this same zone can range from 2,000 to 3,000 yr. This cell 

(row 81, column 47; fig. 33) represents the farthest westward 

potential movement of particles and is not influenced by any 

local pumping. The closest pumping center on the Georgia 

side of the Savannah River is located 3 mi south at the Vogtle 

Electric Generating Plant in Burke County. Of the 1,148 particles released in zone 2 (table 6) using the forward-tracking 

mode, 6 percent (69 particles) migrate toward trans-river zones 

located on the Georgia side of the Savannah River.

Areas of trans-river flow were evaluated further using 

MODPATH in backtracking mode as a comparison to forward-tracking mode from zone 2 in the SRS. Although other 

areas of trans-river flow exist according to model simulations 

(Clarke and West, 1998), the focus of this evaluation is on 

potential migration of contaminants from the SRS to the 

Georgia side of the Savannah River.

For the backtracking of particles, three model cells 

located near Flowery Gap Landing (covering about 1 mi2) on 

the Georgia side of the Savannah River were chosen based 

on results from the previous model (Clarke and West, 1998, 

p. 89). Also, particle tracking results from zone 2 (forwardtracking mode) indicate that the area west of the Savannah 

River on the Georgia side (trans-river zone) is a common 

point of ground-water discharge. The results indicate that 

simulations with active SRS pumping centers (1987–92, 2002, 

Scenarios A, C, and D) moved fewer particles to the Georgia 

side of the Savannah River and ranged from 88 to 93 particles 

(table 7). If these SRS production wells are deactivated (Scenario B), the number of particles migrating to trans-river zones 

increases to 110 and the median time-of-travel decreases to 

about 370 yr (table 7).

Simulation of Ground-Water Management Scenarios, 2002 and 2020 
Table 11. Water budgets for 1987–92, 2002, and Scenarios A–D, Savannah River Site, South Carolina.—Continued

[A with number, aquifer; C with number, confining unit]

Aquifer Model 

layer

Simulated flows 

inflow or outflow

1

1987–92 2002

Scenario 

A B C D 

Boundary condition

Wet Dry Average Average Average Dry

Million gallons per day

Upper Three Runs 2A1 Inflows:

Across source-sink layer3 788.6 776.7 783.1 781.0 778.9 773.2

Layer A2 to A1 through C1 500.8 515.2 502.8 503.2 506.4 518.3

Total—Layer A1 inflows 1,289.5 1,291.8 1,285.9 1,284.2 1,285.3 1,291.5

2

A1 Outflows:

Across source-sink layer4 500.8 515.2 502.8 503.2 506.4 518.3

Layer A1 to A2 through C1 788.6 776.7 783.1 781.0 778.9 773.2

Total—Layer A1 outflows 1,289.5 1,291.8 1,285.9 1,284.2 1,285.3 1,291.5

Gordon A2 Inflows:

Across lateral boundaries 5.1 2.8 3.6 3.6 3.6 2.8

Recharge (aquifer outcrop areas) 52.8 52.8 52.8 52.8 52.8 52.8

Layer A1 to A2 through C1 788.6 776.7 783.1 781.0 778.9 773.2

Layer A3 to A2 through C2 317.4 312.6 312.9 315.1 315.5 314.8

Total—Layer A2 inflows 1,164.0 1,144.9 1,152.5 1,152.5 1,150.8 1,143.8

A2 Outflows:

Across lateral boundaries 2.8 4.7 3.4 3.4 3.4 4.7

Active wells 9.9 10.7 10.7 10.7 8.0 8.8

Streams (ground-water discharge) 224.0 200.6 212.0 213.9 212.9 201.3

Layer A2 to A1 through C1 500.8 515.2 502.8 503.2 506.4 518.3

Layer A2 to A3 through C2 426.4 413.8 423.6 421.5 420.2 410.8

Total—Layer A2 outflows 1,164.0 1,144.9 1,152.5 1,152.6 1,150.8 1,143.8

Millers Pond A3 Inflows:

Across lateral boundaries 2.9 2.0 2.5 2.5 2.5 2.0

Layer A2 to A3 through C2 426.4 413.8 423.6 421.5 420.2 410.8

Layer A4 to A3 through C3 297.8 293.2 293.8 296.1 296.2 295.4

Total—Layer A3 inflows 727.0 709.1 720.0 720.0 718.8 708.3

A3 Outflows:

Across lateral boundaries 0.7 1.6 1.1 1.1 1.1 1.6

Active wells 2.1 7.3 7.3 7.3 4.4 5.0

Streams (ground-water discharge) 8.2 7.8 8.0 8.1 8.1 7.9

Layer A3 to A2 through C2 317.4 312.6 312.9 315.1 315.5 314.8

Layer A3 to A4 through C3 398.6 379.8 390.6 388.4 389.7 379.0

Total—Layer A3 outflows 727.1 709.1 720.0 720.0 718.8 708.3

Upper Dublin A4 Inflows:

Across lateral boundaries 3.8 2.8 3.5 3.5 2.8 2.2

Recharge (aquifer outcrop areas) 11.5 11.5 11.5 11.5 11.5 11.5

Layer A3 to A4 through C3 398.6 379.8 390.6 388.4 389.7 379.0

Layer A5 to A4 through C4 290.2 286.3 287.1 289.5 288.6 287.7

Total—Layer A4 inflows 704.1 680.5 692.7 693.0 692.6 680.4

A4 Outflows:

Across lateral boundaries 2.2 3.4 2.6 2.6 2.8 3.7

Active wells 3.8 5.4 5.4 5.2 3.9 4.1

Streams (ground-water discharge) 46.5 43.5 44.7 45.0 45.0 43.8

Layer A4 to A3 through C3 297.8 293.2 293.8 296.1 296.2 295.4

Layer A4 to A5 through C4 353.8 335.0 346.3 344.1 344.8 333.4

Total—Layer A4 outflows 704.1 680.5 692.8 693.0 692.7 680.4

54  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
Table 11. Water budgets for 1987–92, 2002, and Scenarios A–D, Savannah River Site, South Carolina.—Continued

[A with number, aquifer; C with number, confining unit]

Aquifer Model 

layer

Simulated flows 

inflow or outflow

1

1987–92 2002

Scenario 

A B C D 

Boundary condition

Wet Dry Average Average Average Dry

Million gallons per day

Lower Dublin A5 Inflows:

Across lateral boundaries 5.0 6.2 6.2 6.1 4.9 4.9

Recharge (aquifer outcrop areas) 45.4 45.4 45.4 45.4 45.4 45.4

Layer A4 to A5 through C4 353.8 335 346.3 344.1 344.8 333.4

Layer A6 to A5 through C5 219.1 217.2 217.5 219.4 218.4 217.9

Total—Layer A5 inflows 623.4 603.8 615.3 615.1 613.5 601.6

A5 Outflows:

Across lateral boundaries 4.4 4.3 4.2 4.3 4.5 4.7

Active wells 9.5 14.6 14.6 12.6 12.3 11.7

Streams (ground-water discharge) 86.6 79.2 82.5 82.6 82.6 79.2

Layer A5 to A4 through C4 290.2 286.3 287.1 289.5 288.6 287.7

Layer A5 to A6 through C5 232.8 219.4 226.9 226.1 225.7 218.4

Total—Layer A5 outflows 623.5 603.9 615.4 615.2 613.6 601.7

Upper Midville A6 Inflows:

Across lateral boundaries 23.4 26.2 24.4 24.4 24.4 26.2

Streams (ground-water recharge) 0.3 0.3 0.2 0.2 0.2 0.3

Recharge (aquifer outcrop areas) 26.6 26.6 26.6 26.6 26.6 26.6

Layer A5 to A6 through C5 232.8 219.4 226.9 226.1 225.7 218.4

Layer A7 to A6 through C6 193.4 190.3 191.6 192.4 192 190.7

Total—Layer A6 inflows 476.6 462.8 469.8 469.8 468.9 462.2

A6 Outflows:

Across lateral boundaries 11.5 9.0 9.8 9.9 9.8 9.1

Active wells 6.6 9.8 9.8 8.2 7.6 8.1

Streams (ground-water discharge) 53.3 49.0 51.4 51.4 51.5 49.2

Layer A6 to A5 through C5 219.1 217.2 217.5 219.4 218.4 217.9

Layer A6 to A7 through C6 186.3 177.9 181.6 181.2 181.8 178.3

Total—Layer A6 outflows 476.8 463 470.1 470.1 469.2 462.4

Lower Midville A7 Inflows:

Across lateral boundaries 63.5 65.1 63.6 63.5 63.6 65.1

Streams (gound-water recharge) 0.2 0.7 0.2 0.2 0.3 0.8

Recharge (aquifer outcrop areas) 16.5 16.5 16.5 16.5 16.5 16.5

Layer A6 to A7 through C6 186.3 177.9 181.6 181.2 181.8 178.3

Total—Layer A7 inflows 266.4 260.1 261.9 261.3 262.2 260.7

A7 Outflows:

Across lateral boundaries 10.6 12.8 11.4 11.5 11.4 12.9

Active wells 20.8 19.4 19.4 17.9 19.2 19.3

Streams (ground-water discharge) 42.1 38.1 39.9 39.9 40.1 38.3

Layer A7 to A6 through C6 193.4 190.3 191.6 192.4 192 190.7

Total—Layer A7 outflows 266.8 260.5 262.3 261.7 262.6 261.1

1

Clarke and West (1998).

2

Inactive, source-sink layer.

3

Simulated recharge derived from vertical leakage from specified head cells in source/sink layer into underlying units.

4

Simulated discharge derived from vertical leakage from underlying units into specified head cells in source/sink layer.

Simulation of Ground-Water Management Scenarios, 2002 and 2020  55
Limitations of Digital Simulation 

and Particle Tracking

The digital ground-water flow model developed for the 

study area is subject to uncertainties inherent in ground-water 

models, such as small number of control sites for hydraulic 

properties and placement of vertical and lateral boundaries. 

The objective was to develop a model that can respond to 

applied hydrologic changes and simulate movement of ground 

water through a seven-layer aquifer system near the Savannah 

River Site on a regional scale. The model achieves the original 

objectives, but is limited by simplification of the hydrogeologic framework, and obtaining sufficient measurements to 

define properly a complex system can be difficult. Some of the 

model boundaries are not coincident with natural boundaries 

and are placed at sufficient distance to limit their effect on the 

area of interest. Also, distribution of the pumpage for each 

active production well was based on well depth, and divided 

equally between the aquifers penetrated. Analysis of individual wells using a flowmeter generally indicates that most of 

the production is from discrete zones. The relative importance 

of hydraulic properties and boundary conditions on the calibrated model results are presented in the section “Sensitivity 

Analysis” (Clarke and West, 1998). Steady-state simulations 

were deemed satisfactory because of minor observed seasonal 

fluctuations in each of the aquifers, which are generally less 

than 4 ft (Clarke and West, 1997).

The model was designed with a finer grid resolution near 

the SRS to allow a more accurate representation of localized 

ground-water flowpaths and to simulate steep aquifer gradients near outcrop areas. Lateral discretization of the model 

into a variably spaced grid required an averaging of hydraulic 

properties such as specified heads in the source-sink layer A1 

for each model cell and along lateral boundaries in the active 

layers of the model (layers A2–A7). In outlying areas near the 

model boundaries, increased cell dimensions forced greater 

generalization of field conditions.

Representation of flow in the uppermost layer A1, the 

Upper Three Runs aquifer, was simulated as a source-sink 

inactive layer. Assigned heads in this layer were often averaged between long-term average (1987–92) and dry conditions 

(2002), and, in certain cases, the model could not simulate the 

lateral observed variation despite grid refinement. In addition, the Upper Three Runs aquifer may consist of at least 

two aquifers (Flach and others, 1998, 1999a, b, and c), which 

would require discretization into several active model layers. 

The focus of this study, however, was on a regional scale and 

ground-water flow within the confined aquifers, which are the 

active layers of the model (layers A2–A7). The Upper Three 

Runs aquifer (layer A1) was simulated using specified heads 

to allow water to enter the ground-water system as recharge or 

exit as localized flow to streams.

The three-dimensional distribution of head is, in turn, a 

major control on the configuration of flowpaths in the groundwater system (Franke and others, 1998). The lateral and 

vertical head gradients, along with the hydraulic properties of 

the aquifers and confining units, influence the direction and 

flow rate through a ground-water system. Additional controls 

affecting the movement of ground water are pumping centers 

and assigned effective porosity in the aquifers and confining 

units. In the SRS area, data on the vertical hydraulic conductivity of aquifers, streambeds, and confining units are sparse.

An additional limitation of particle tracking using MODPATH is its inability to determine whether a particle of water 

exits the system in a 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. Further grid refinement near selected 

wells is one possible solution, but is considered impractical 

given the number of production wells in the study area.

MODPATH results presented herein do not allow for 

weak sinks, and, thus, are indicative of the worst-case scenario for trans-river flow––that which allows water to travel 

from one side of the river to another without being intercepted 

by wells that are weak sinks. Also, MODPATH simulates 

advective transport and does not account for any adsorption or 

diffusion in the ground-water flowpaths, which also provides a 

worst-case scenario.

Summary and Conclusions

This report documents the use of an existing U.S. Geological Survey (USGS) digital ground-water flow model to 

evaluate potential flowpaths from the Savannah River Site 

(SRS). The U.S. Department of Energy (DOE), SRS facility has manufactured nuclear materials for national defense 

purposes since the early 1950s. A variety of hazardous materials including tritium, other radionuclides, volatile organic 

compounds, and trace metals are either disposed of or stored 

at many locations on the SRS. State of Georgia officials have 

raised concern about the possible migration of tritiated water 

from the SRS into the underlying aquifers and beneath the 

Savannah River (trans-river flow) into Georgia. The model 

was used to document (1) changes in hydrologic and pumping 

conditions that have occurred since the calibration of the earlier (1987–92) USGS ground-water model, (2) ground-water 

flowpaths and particle tracking during previous (1987–92) 

and 2002 hydrologic conditions, and (3) comparison of results 

from previous simulations (1987–92, 2002) and from four 

hypothetical pumping scenarios during 2002 and 2020.

In the earlier 1987–92 simulation, total ground-water use 

was about 80 million gallons per day (Mgal/d) in the eightcounty area. By 1995, the total ground-water use was about 

85.4 Mgal/d and increased to 117 Mgal/d by 2000. The major 

increase in documented ground-water use between 1995 and 

2000 is for Burke, Jefferson, and Screven Counties, Ga.; and 

Allendale and Barnwell Counties, S.C. In these counties, 

ground-water use for irrigation increased from 16.7 Mgal/d 

during 1995 to 53.1 Mgal/d during 2000, and irrigated acreage 

56  Simulated and Particle-Tracking Analysis of Ground-Water Flow near Savannah River Site
increased by 36,000 acres during the same period. Groundwater use for public supply increased from 24.4 Mgal/d during 

1990 to 31.0 Mgal/d during 2000, with Burke and Richmond 

Counties, Ga., and Aiken County, S.C., accounting for most of 

the increase during the 10-year period. Ground-water use for 

industrial and mining purposes decreased from 22.1 Mgal/d 

during 1990 to 17.6 Mgal/d during 2000, primarily because of 

the decrease in ground-water use at the SRS from 9.0 Mgal/d 

during 1990 to 5.3 Mgal/d during 2002.

During 1992–2002, water levels in each of the major 

aquifers generally declined because of below-normal precipitation and increased ground-water use. Declines, based on 

periodic water-level measurements, in the Upper Three Runs 

aquifer ranged from 2 to 5 feet (ft) in northeastern Burke 

County, Ga., and were greater than 20 ft in southern Burke 

and Screven Counties, Ga. Water-level declines at Brighams 

Landing, Ga., were most pronounced in the Gordon aquifer (16 ft) as a result of ground-water use for irrigation with 

smaller declines in the deeper Dublin and Midville aquifer 

systems (7 and 5 ft, respectively).

During the previous study, the flow system was modeled 

using a quasi-three-dimensional approach with seven layers—

six active layers and an overlying source-sink layer—that 

are separated to varying degrees by six confining units. The 

model grid area encompasses about 4,455 square miles (mi2), 

of which about 3,250 mi2 is actively simulated. Boundary 

conditions adjusted during the 1987–92 calibration process 

consisted of specified-head values in the source-sink layer A1 

and specified-head values along lateral boundaries in active 

layers A2–A7.

To provide data for model calibration and to determine 

if boundary conditions have changed since 1992, water-level 

data were collected from 189 wells and potentiometric-surface 

maps were constructed for each of the major aquifers. The 

potentiometric-surface maps served as the basis for adjustments to boundary conditions and were used to determine that 

recalibration of the previous model was unnecessary; however, 

the previous model was updated to a newer version of the 

USGS finite-difference code (MODFLOW–2000). Adjustments to heads in the source-sink layer (layer A1, Upper Three 

Runs aquifer) of the model and specified heads along lateral 

boundaries in the active layers A2–A7 were made to match 

closely the constructed potentiometric-surface maps. The root 

mean square (RSM) of the residuals for all layers decreased 

from 10.6 ft during 1987–92 to 8.0 ft during 2002, which is an 

indication that the model is representative of 2002 dry conditions. Simulated ground-water outflows to the Savannah River 

and its tributaries during 2002 was 560 cubic feet per second, 

or 87 percent of the observed gain in mean-annual streamflow 

between the Millhaven and Augusta streamflow gaging stations for water year 2002.

The simulated water budget for 2002 conditions was 

1,035 Mgal/d compared with 1,040 Mgal/d during the 1987–

92 simulation. Lowering the heads in the source-sink layer A1 

to match the potentiometric-surface map of the Upper Three 

Runs aquifer for 2002 reduced the simulated recharge to 

the Gordon aquifer (A2) from 789 Mgal/d (1987–92) to 

777 Mgal/d (2002). Recharge applied to the outcrop areas of 

the hydrogeologic units remained constant for the 2002 simulation at 153 Mgal/d, which represents 16.4 percent of the 

total 930-Mgal/d simulated recharge to the ground-water system. Simulated ground-water withdrawal for 2002 increased 

by 14.5 Mgal/d from the 1987–92 model. The remaining 

22-Mgal/d increase in ground-water use either was outside the 

simulated area (Screven and Jefferson Counties, Ga.) or was 

included in the source-sink layer A1, which was not actively 

simulated for the Upper Three Runs aquifer. The combination 

of reduced inflow to the source-sink layer A1 and simulated 

increase in pumpage reduced the simulated ground-water 

discharge to streams by about 24 Mgal/d.

The USGS particle-tracking code MODPATH was used 

in backtracking mode to seed areas of document trans-river 

flow, near Flowery Gap Landing along the Savannah River, in 

a 1-mi2 marshy area located in Burke County, Ga. To improve 

definition of flowpaths and corresponding recharge areas for 

each simulation, a greater number of particles were applied to 

each model cell for the updated model compared to the 

1987–92 model. Also, the MODPATH code was used in 

forward-tracking mode to evaluate flowpaths from areas of 

contamination on the SRS. Five particle seed zones were 

established in which individual particles were observed 

from their point of recharge to discharge areas located along 

stream segments. For each zone, four particles were placed in 

individual cells at the base of the source-sink layer A1 (Upper 

Three Runs aquifer)/top of the Gordon confining unit (C1) 

before initiating forward movement. The model is not capable 

of calculating vertical travel times through the source-sink 

layer A1 (Upper Three Runs aquifer); however, modeling 

results using a finite-element code encompassing C Area and 

K Area on the SRS indicate travel times downward within the 

Upper Three Runs aquifer of several decades. In backtracking 

mode, travel times are computed to the base of the sourcesink layer A1 (Upper Three Runs aquifer), which does not 

include travel times within the uppermost aquifer. The Gordon 

confining unit (C1) is generally from 20 to 30 ft thick between 

D Area and K Area and time-of-travel from the base of the 

Upper Three Runs aquifer (source-sink layer A1) into the 

Gordon aquifer (layer A2) is about 10 years (yr).

The results from the MODPATH forward-tracking analysis indicate that Upper Three Runs Creek and the alluvial valley of the Savannah River are the dominant sinks or areas of 

ground-water discharge with time-of-travel ranging from 20 yr 

to greater than 2,000 yr. Generally, time-of-travel for particles 

migrating downward through the Gordon confining unit (C1) 

and then moving laterally through layer A2 (Gordon aquifer) 

to discharge areas ranges from 20 to 200 yr. For particles 

migrating deeper into layers A3 through A5 (Dublin aquifer 

system), time-of-travel generally ranges from 200 to 1,000 yr. 

Four hypothetical ground-water management scenarios 

were developed to assess the effect of changing pumping and 

boundary conditions on ground-water flow and the potential 

migration of tritiated water from the SRS. These scenarios 

Summary and Conclusions 
represent hydrologic conditions for: (A) 2002 observed pumping and boundary conditions for an average year; (B) 2002 

observed pumping and boundary conditions for an average 

year with SRS pumping discontinued; (C) projected 2020 

pumping and boundary conditions for an average year; and 

(D) projected 2020 pumping and boundary conditions for a 

dry year. In the 1987–92 and 2002 simulations, the assigned 

heads in the source-sink layer A1 were based on the constructed potentiometric-surface maps of the Upper Three 

Runs aquifer. In three of the four ground-water management 

scenarios (Scenarios A, B, and C), the specified heads in the 

source-sink layer A1 and along lateral boundaries (layers A2–

A7) of the model were averaged between long-term average (1987–92) and dry (2002) hydrologic conditions. In the 

remaining ground-water management scenario (Scenario D), 

specified heads in the source-sink layer A1 and along lateral 

boundaries (A2 through A7) of the model were adjusted to 

represent dry hydrologic conditions similar to 2002. 

Pumping projections in the SRS vicinity through 2020 

(Scenarios C and D) were developed (1) for public supply 

and industry, based on water-management plans and population-growth projections; and (2) for irrigation based on an 

“average” quantity of water applied (gallons per acre per day) 

to the total irrigated acreage of 106,000. Population in the 

eight-county study area is expected to increase by 80,000 residents by the year 2020 with most of the growth centered 

around the Augusta, Ga., North Augusta, S.C., areas and the 

counties of Richmond, Ga., and Aiken, S.C. The analysis of 

water-use trends and population growth during the period of 

1980–2000 were used to estimate ground-water use in the year 

2020. The total projected increase in water demand for public 

supply (12 Mgal/d from 2002 to 2020) may be met through 

a combination of additional surface-water withdrawals from 

the Savannah River and increased ground-water withdrawals 

of 5 Mgal/d from the major aquifers. Pumping projections 

represent a redistribution of pumpage from irrigation wells in 

rural areas to production wells for public supply in areas of 

anticipated population growth. 

The overall demand for ground water is projected to 

decrease from 115 Mgal/d during 2002 to 102 Mgal/d during 2020 given the severity of the drought during 2002 and 

reduced water requirements for irrigation during “average” 

hydrologic conditions. Because withdrawal rates for irrigation can be substantially higher during periods of drought, two 

projections were completed to the year 2020—one for average 

climatic conditions (Scenario C) and one for dry climatic 

conditions (Scenario D). Estimated values for 2020 were 

derived by multiplying the projected 106,000 acres of irrigated 

land by county application rates for average (1980–2000) and 

typical dry conditions. These estimates were adjusted using 

existing ratios of surface water (39 percent) to ground water 

(61 percent) irrigation pumpage to determine the percentage of irrigation usage from ground-water sources. Projected 

annual ground-water use for irrigation for average conditions 

during 2020 is 38 Mgal/d and for dry conditions is 43 Mgal/d. 

Both of these values represent a decrease from the estimated 

irrigation use of 63 Mgal/d during the drought of 2002. The 

severity of the 2002 drought was considered extreme, so the 

application rate for dry conditions was adjusted to represent 

a 60:40 ratio of average and dry conditions. This resulted in a 

lower calculated application rate of 662 gal/acre/day (Scenario D) compared with that of 960 gal/acre/day estimated during 

the drought year of 2000 and used in the 2002 simulation.

Simulated ground-water flowpaths for each of the four 

ground-water management scenarios were generally limited 

to areas within the SRS boundary because this is the area of 

concern for transport of tritium. Water that originated at the 

base of the Upper Three Runs aquifer (source-sink layer A1) 

generally discharged into the Gordon aquifer (layer A2) within 

the SRS boundaries. Common ground-water discharge areas 

include Upper Three Runs Creek (layer A2) and the alluvial valley of the Savannah River (source-sink layer A1 and 

layer A2). All calculated time-of-travel for particles does not 

include downward movement within the source-sink layer A1 

(Upper Three Runs aquifer), which according to model simulations conducted by the SRS could take several decades. Five 

particle seed zones were established where individual particles 

were observed from their point of recharge to discharge areas 

located along local streams within the boundaries of the SRS 

or the Savannah River. 

Appropriate ranges for median time-of-travel of particles from each of five zones are represented for all simulations, including 1987–92, 2002, and the four ground-water 

management scenarios (Scenarios A–D). In zone 1, median 

time-of-travel from recharge areas to discharge areas located 

along Upper Three Runs Creek and west of the SRS boundary 

ranges from 217 to 264 yr. In zone 2, median time-of-travel 

from recharge areas to discharge areas located along Upper 

Three Runs Creek, Pen Branch, Fourmile Branch, and the 

Savannah River ranges from 524 to 593 yr. In zone 3, median 

time-of-travel from recharge areas to discharge areas located 

along Upper Three Runs Creek ranges from 834 to 1,150 yr. 

In zone 4, median time-of-travel from recharge areas to 

discharge areas located along the South Carolina side of the 

Savannah River ranges from 395 to 404 yr. In zone 5, median 

time-of-travel from recharge areas to discharge areas located 

along Lower Three Runs Creek and the Savannah River ranges 

from 1,310 to 1,350 yr. 

Ground-water movement and discharge for each of the 

four ground-water management scenarios outside the SRS 

boundary is limited to recharge areas from: (1) zone 1 moving 

toward Eagle Point located in Aiken County, S.C., at greater 

than 100-yr time-of-travel; (2) zone 2 moving near trans-river 

flow areas located in Georgia at greater than 200-yr time-oftravel; (3) zone 4 moving toward irrigation wells located in 

Allendale County, S.C., at greater than 200-yr time-of-travel; 

and (4) zone 5 moving toward Lower Three Runs Creek and 

the Savannah River located in Allendale County, S.C., at 

greater than 200-yr time-of-travel. Time-of-travel for each of 

the scenarios varies only slightly with the exception of Scenario B, which allows particles placed near deactivated wells 

on the SRS to migrate laterally to discharge areas with shorter 

58  
travel times. When active, the SRS production wells screened 

in the Dublin and Midville aquifer systems (layers A3–A7) 

create a steep vertical gradient that permits particles to 

penetrate deeper into the lower layers of the model, thereby 

increasing the overall time-of-travel. 

For the backtracking analysis of particles, three model 

cells located near Flowery Gap Landing (covering about 1 mi2) 

on the Georgia side of the Savannah River were chosen based 

on results from forward-tracking analysis (zone 2), indicating 

these cells as common discharge areas. Of the 300 particles 

released in these three cells, as few as 88 particles (29 percent, 

2002, Scenario C) to as many as 110 particles (37 percent, 

Scenario B) backtracked to recharge areas on the SRS (transriver flow). Of the particles exhibiting trans-river flow, the 

median time-of-travel along pathlines ranged from 366 to 

507 yr with primary recharge areas located between D Area 

and K Area. Backtrack time-of-travel for the shortest flowpaths ranged from 79 to 82 yr from trans-river flow to interstream areas located between D Area and K Area with 10 percent of these particles reaching endpoints at about 100 yr. The 

results indicate that simulations with active SRS pumping 

centers (1987–92, 2002, Scenarios A, C, and D) allowed fewer 

particles to migrate to the Georgia side of the Savannah River. 

If these SRS production wells are deactivated (Scenario B), the 

number of particles migrating to trans-river zones increases to 

110 and the median time-of-travel decreases to about 370 yr 

with a shortest time-of-travel period of about 80 yr.

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Manuscript approved for publication, August 1, 2006

Prepared by USGS Georgia Water Science Center

Edited by Patricia L. Nobles

Graphics by Caryl J. Wipperfurth

For more information concerning the research in this report, contact

USGS Georgia Water Science Center, Atlanta,

telephone: 770-903-9100