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Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios at Vogtle Electric Generation Plant, Burke County, Ga, Open-File Report 2007-1363
	ML073310491
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Site:	Vogtle
Issue date:	01/01/2007
From:	Cherry G, Clarke J; US Dept of Interior, Geological Survey (USGS)
To:	; Office of Nuclear Reactor Regulation
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	+reviewedcja 2007-1363
	Download: ML073310491 (54)
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wwII Prepared in cooperation with the U.S. Nuclear Regulatory Commission Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios at Vogtle Electric Generation Plant, Burke County, Georgia Open-File Report 2007-1363 U.S. Department of the Interior U.S. Geological Survey

Cover photograph: Vogtle Electric Generation Plant cooling towers, Burke County, Georgia Photograph by Alan M. Cressler, U.S. Geological Survey

Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios at Vogtle Electric Generation Plant, Burke County, Georgia By Gregory S. Cherry and John S. Clarke Prepared in cooperation with the U.S. Nuclear Regulatory Commission Open-File Report 2007-1363 U.S. Department of the Interior U.S. Geological Survey

U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D.Myers, Director U.S. Geological Survey, Reston, Virginia: 2007 For product and ordering information:

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Suggested citation:

Cherry, G.S., and Clarke, J.S., 2007, Simulation and particle-tracking analysis of selected ground-water pumping scenarios at Vogtle Electric Generation Plant, Burke County, Georgia: U.S. Geological Survey Open-File Report 2007-1363, 51 p.,

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

Contents Abstract ..................................................................................................................................................... 1 Introduction ................................................................................................................................................ 1 Purpose and Scope ......................................................................................................................... 1 Description of Study Area .............................................................................................................. 4 Savannah River Site and Ground-Water Contamination .................. 4 Clim ate and Runoff ................................................................................................................ 4 Hydrogeologic Setting ........................................................................................................ 5 Structural Features ................................................................................................... 6 Hydrogeologic Characteristics of the Savannah River Alluvial Valley .............. 6 Ground-W ater Flow ............................................................................................................... 6 Trans-River Flow ........................................................................................................... 13 Effect of Pen Branch Fault ....................................................................................... 13 Ground-W ater Use ................................................................................................................. 13 Sim ulation of Ground-W ater Flow .......................................................................................................... 14 Pen Branch Fault .............................................................................................................................. 16 Ground-W ater Pum ping Scenarios .......................................................................................... 17 2002 Base Case Condition ............................................................................................... 18 Scenario A............................................................................................................................... 20 Scenario B............................................................................................................................... 20 Scenario C............................................................................................................................... 35 Model Lim itations ............................................................................................................................. 43' Sum mary and Conclusions .............................................................................................. *........................ 43 References Cited ....................................................................................................................................... 44

iv Figures

1. Maps showing (A)study area, model grid, and model boundary, (B) location of Vogtle Electric Generation Plant production wells, Burke County, Georgia, and river and recharge cells in the Gordon aquifer (layer A2) and areal and local ground-water contamination at the Savannah River Site, South Carolina ............... 2

2. Schematic diagram showing hydrogeologic framework, model layers, and boundary conditions for the Vogtle Electric Generation Plant area, South Carolina, ground-water model ................................. 5

3. Map showing subsurface extent of hydrogeologic units beneath the Savannah River alluvial valley, South Carolina and Georgia .......................................................... 7

4. Diagram of conceptualized hydrogeologic framework and related ground-water flow near Vogtle Electric Generation Plant, Georgia and South Carolina ................ 8 5-8. Maps showing potentiometric surface, near Vogtle Electric Generation Plant, Georgia and South Carolina, September 2002, for the-

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

6. Gord on a quife r ......................... 7.................................................................... ............... 10

7. Dublin aq uife r system .................................................................................................. 11

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

9. Map showing particle-tracking results for the year 2002, Base Case, near Vogtle Electric Generation Plant, Georgia and South Carolina ................................ 19 10-15. Maps showing simulated water-level change for Scenario A, near Vogtle Electric Generation Plant, Georgia and South Carolina, in the-

10. Gord on a quife r .............................................................................................................. 21

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

12. Upper Dublin aquifer ............................................................................................. .. 23 13: Low er Dublin aquifer ........................................................................................... .. 24

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

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

16. Map s~howing particle-tracking results for the year 2002, Scenario A, near Vogtle Electric Generation Plant, Georgia and South Carolina ................................ 27 17- 22. Maps showing simulated water-level change for Scenario B, near Vogtle Electric Generation Plant, Georgia and South Carolina, in the-

17. Gord on a quife r .............................................................................................................. 28

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

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

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

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

22. Low er Midville aquife r ................................................................... ............................ 33

23. Map showing particle-tracking results for the year 2002, Scenario B, study area, near Vogtle Electric Generation Plant, Georgia and South Carolina ............. 34

V Figures-Continued 24-29. Maps showing simulated water-level change for Scenario C, near Vogtle Electric Generation Plant, Georgia and South Carolina, in the-

24. Go rdo n aquifer ............................................................................................................. 36

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

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

27. Low er Dublin aquifer .............................................................................................. . . 39

28. Upper M idville aquifer ...................................................................................... . .. - 40

29. Low er M idville aquifer .......................................................................................... . . 41

30. Map showing particle-tracking results for the year 2002, Scenario C, near Vogtle Electric Generation Plant, Georgia and South Carolina ............................... 42 Tables

1. Ground-water use during 2000-2002 near Vogtle Electric Generation Plant, Burke County, Georgia ................................................................................................... . . 13

2. Location and construction information for production wells at Vogtle Electric Generation Plant, Burke County, Georgia ..................................................................... 14

3. Simulated and estimated values for transmissivity, Vogtle Electric Generation Plant m odel, Georgia and South Carolina ..................................................................... 15

4. Simulated and estimated values for leakance, Vogtle Electric Generation Plant m odel, Georgia and South Carolina ..................................................................... 15

5. Simulated pumpage by model layer for 2002 Base Case, Vogtle Electric Generation Plant model, Georgia and South Carolina ....................................................... 16

6. Simulated pumpage at Vogtle Electric Generation Plant, Burke County, Georgia, for 2002 Base Case and pumping Scenarios A, B, and C........................... 18

7. Summary of simulated time of travel for 2002 Base Case and for Scenarios A, B, and C, Vogtle Electric Generation Plant model, Georgia and South Carolina ........ 18

vi Conversion Factors and Datums Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (kin)

Area square foot (fI2) 0.09290 square meter (M 2) square mile (mi 2) 2 2.590 square kilometer (kmi )

Volume gallon (gal) 3.785 liter (L) million gallons (Mgal) 3,785 cubic meter (m3 )

Flow rate gallon per minute (gal/min) 0.06309 liter per second (L/s) million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

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

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

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

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

Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios at Vogtle Electric Generation Plant, Burke County, Georgia By Gregory S. Cherry and John S. Clarke Abstract Introduction The source of ground water to production wells at Vogtle The Vogtle Electric Generation Plant (VEGP), near Electric Generation Plant (VEGP), a nuclear power plant in Waynesboro, Burke County, Georgia, is one of Southern Com-Burke County, Georgia, was simulated under existing (2002) pany's two nuclear-generating facilities in Georgia (fig. 1).

and potential future pumping conditions using an existing On August 15, 2006, Southern Nuclear Company applied to U.S. Geological Survey (USGS) MODFLOW ground-water the U.S. Nuclear Regulatory Commission (NRC) for an early flow model of a 4,455-square-mile area in the Coastal Plain site permit (ESP) for an additional two reactors at the site. As of Georgia and South Carolina. Simulation results for three part of the ESP permitting process, the NRC is charged with steady-state pumping scenarios were compared to each other development of an environmental impact statement (EIS) and to a 2002 Base Case condition. The pumping scenarios to evaluate the effects of both construction and operation of focused on pumping increases at VEGP resulting from pro- these new reactors on the site and surrounding area. The EIS jected future demands and the addition of two electrical- must describe the magnitude and nature of expected effects generating reactor units. Scenarios simulated pumping on ground water resulting from present and potential future increases at VEGP ranging from 1.09 to 3.42 million gallons ground-water withdrawal. The assessment should include the per day (Mgal/d), with one of the scenarios simulating the area of VEGP and extend for distances great enough to cover elimination of 5.3 Mgal/d of pumping at the Savannah River potentially affected aquifers, including those located within Site (SRS), a U.S. Department of Energy facility located the boundary of the U.S. Department of Energy, Savannah across the Savannah River from VEGP. The largest simulated River Site (SRS), located in South Carolina across the Savan-water-level changes at VEGP were for the scenario whereby nah River from VEGP (fig. IA, IB).

pumping at the facility was more than tripled, resulting in The addition of two new reactors (Units 3 and 4) at drawdown exceeding 4-8 feet (ft) in the aquifers screened in VEGP will require an increase in pumping from the lower the production wells. For the scenario that eliminated pumping Dublin and upper and lower Midville aquifers, which cur-at SRS, water-level rises of as much as 4-8 ft were simulated rently provide the water needed for reactor Units I and 2.

in the same aquifers at SRS. NRC would like to evaluate the effects of additional pump-Results of MODFLOW simulations were analyzed using age on ground-water flow in the surrounding area. To help the USGS particle-tracking code MODPATH to determine the evaluate these effects, and improve understanding of regional source of water and associated time of travel to VEGP produc- ground-water flow in the area, the U.S; Geological Survey tion wells. For each of the scenarios, most of the recharge to (USGS)-in cooperation with NRC-conducted a study using VEGP wells originated in an upland area near the county line an existing ground-water flow model to simulate the source of between Burke and Jefferson Counties, Georgia, with none ground water to VEGP production wells under current (2002) of the recharge originating on SRS or elsewhere in South and potential future pumping conditions.

Carolina. An exception occurs for the scenario whereby pump-ing at VEGP was more than tripled. For this scenario, some of the recharge originates in an upland area in eastern Barn-Purpose and Scope well County, South Carolina. Simulated mean time of travel This report describes the effect of current (2002) and poten-from recharge areas to VEGP wells for the Base Case and the tial future pumping on ground-water levels and flowpaths three other pumping scenarios was between about 2,700 and near VEGP for three pumping scenarios using an existing ground-3,800 years, with some variation related to changes in head water flow model (Clarke and West, 1998; Cherry, 2006) of a gradients because of pumping changes. 4,455-square-mile (mi 2 ) area near Augusta, Ga. (fig. IA).

2 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios A.

82'30' 82° 81030' 33030' 33' 32'30' Base modified from U.S. Geological Survey 0 10 20 30 MILES State base maps I I I 0 10 20 30 KILOMETERS EXPLANATION Model boundary Fault--Approximately located; D, downthrown side; U, upthrown side Figure 1. (A) Study area, model grid, and model boundary, (B) location of Vogtle Electric Generation Plant production wells, Burke County, Georgia, and river and recharge cells in the Gordon aquifer (layer A2)

(modified from Clarke and West, 1997) and areal and local ground-water contamination at the Savannah River Site, South Carolina (modified from Arnett and Mamatey, 1996; Cherry, 2006).

Introduction 3 B.

81°50' 81*40' 81o30'

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psiie, nirt SArea-chlorinated nuclides, metals, sulfate -K'ndPrea "zz/ -

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Base modified from U.S. Geological Survey 0 1 2 3 4 5 MILES 1:24,000-scale digital data I III . j 0 1 2 3 4 5KILOMETERS EXPLANATION Contaminated sites Simulated river cell SAreal contamination V Simulated recharge cell 0 Localized contamination 0 Plant Vogtle production well 31Z 003 and identification number 0 Fault-Approximately located; u D, downthrown side; U, upthrown side Figure 1. . (A) Study area, model grid, and model boundary, (B) location of Vogtle Electric Generation Plant production wells, Burke County, Georgia, and river and recharge cells in the Gordon aquifer (layer A2) (modified from Clarke and West, 1997) and areal and local ground-water contamination at the Savannah River Site, South Carolina (modified from Arnett and Mamatey, 1996; Cherry, 2006).-Continued

4 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Simulated water levels were compared to a Base Case repre- Runs aquifer. The potential for movement of contaminated senting 2002 pumping rates throughout the model area. water into aquifers beneath the Upper Three Runs aquifer at A particle-tracking analysis was conducted for each scenario SRSis dependent on the hydraulic conductivity of interven-to determine the source of water for VEGP production wells. ing confining units and the magnitude of downward hydraulic For each scenario, the pumping distribution, simulated water- gradient (see Ground-Water Flow section).

level changes, 'and ground-water flowpaths are described The only documented occurrence of ground-water relative to the Base Case. Limitations of the model analysis contaminants into aquifers beneath the Upper Three Runs also are provided. that the authors are aware of occurred in the vicinity of the A/M Area on SRS (see location, fig. IB). In this area, Chris-tensen and Gordon (1983) reported volatile organic com-Description of Study Area pounds were detected at depths as great as 480 ft, affecting water-bearing zones in the "Congaree Formation" (Gordon The study area is in the northern part of the southeastern aquifer) and "Tuscaloosa Formation" (lower Dublin aquifer).

Coastal Plain physiographic province (Clark and Zisa, 1976)

Contamination in the Congaree Formation was attributed to of Georgia and South Carolina (fig. IA). The Fall Line marks the discontinuity of the "green clay" that forms the confining the boundary between Coastal Plain sediments and crystalline unit beneath the Upper Three Runs aquifer. Contamination of rocks of the Piedmont physiographic province and forms the the Tuscaloosa Formation was attributed to a poor grout seal approximate northern limit of the study area. Topographic in well 53A, which enabled downward migration of contami-relief generally is greatest near the Fall Line, becoming pro-nated ground water into deeper zones. During the first half of gressively less toward the south and east. Altitudes range from 2007, Washington Savannah River Company (2007) reported as high as 650 feet (ft) near the Fall Line to less than 100 ft in concentrations of trichloroethylene in the A/M Area of as high the southern part of the study area and in the valleys of major as 18,000 micrograms per liter (ýtg/L) in the composite "Lost streams, such as the Savannah River or Brier Creek. A steep Lake aquifer zone" (Gordon aquifer) and as high as 3,200 iAg/L bluff is present along the western bank of the Savannah River in the "Crouch Branch aquifer" (upper and lower Dublin in southern Richmond County and most of Burke County, Ga.

aquifers). Contaminants in both aquifers Occur in southwest-Relief along the Savannah River bluff is as much as 160 ft trending plumes with concentrations exceeding 5 Vg/L across a from the top of the bluff to the valley floor.

distance of nearly 21,000 ft in the Lost Lake aquifer zone, and The Coastal Plain province is well to moderately dis-nearly 15,000 ft in the Crouch Branch.aquifer. Contaminants sected by streams and has a well-developed dendritic drainage in the source areas are being removed using recovery wells pattern. Streams that flow over the relatively soft Coastal Plain and above-ground air strippers (Washington Savannah River sediments develop wider floodplains and greater meander Company, 2007).

frequency than streams that flow over hard crystalline rocks of the Piedmont (Clark and Zisa, 1976). Most of the floodplain near the principal rivers, such as the Savannah River, has a Climate and Runoff wide expanse of swamp bordering both sides of the channel.

A relatively mild' climate with warm, humid summers Forestry and agriculture are the predominant land uses and mild winters characterizes the study area. Precipitation in the study area; major crops are pine timber, cotton, and is highest during the winter months when continental storm soybeans. Kaolin is mined in parts of the study area. The fronts move through the region and during July and August largest cities in the study area are Augusta, Ga., with a when afternoon thunderstorms caused by daytime heating are population of 194,950 during 2000; and Aiken, S.C., with a common. Average annual precipitation in the study area for population of 25,460 during 2000 (U.S. Bureau of the Census, the period 1969-98, ranged from about 46 inches in Burke accessed February 3, 2003, at http://www.census.gov/).

County, Ga., to greater than 52 inches in central Aiken County, S.C. (Southeast Regional Climate Center, accessed Febru-Savannah River Site and ary 11, 2004, at http://www.dnrsc.gov/climate/sercc/).

Ground-Water Contamination The Savannah River is the major surface-water feature in the study area and is the boundary between Georgia and South The SRS encompasses a 310-mi2 area across the Savannah Carolina. The river drains an area of about 10,580 mi 2 River from VEGP in parts of Aiken, Barnwell, and Allendale (1,140 mi 2 in the study area) and empties into the Atlantic Counties, S.C. (fig. I A, I B). The facility has manufactured Ocean near Savannah, Ga. During 1941-70, the average nuclear materials for national defense since the early 1950s. A annual runoff in Georgia ranged from less than 0.9 cubic feet variety of hazardous materials--incltding radionuclides, vola- per second per square mile [(ft3/s)/mi 2 ] of drainage area in tile organic compounds, and heavy metals-are either disposed southern Screven, Jenkins, Burke, and Jefferson Counties, and of or stored at several locations at SRS. Contamination of in northern Richmond and Jefferson Counties, to greater than ground water has been detected at several locations on the site 1.1 (ft3/s)/mi2 in eastern Richmond and Burke Counties (Faye (fig. I B) with contamination mostly limited to the Upper Three and Mayer, 1990).

Introduction 5 North- South-west HYDROGEOLOGIC REPRESENTATION east EXPLANATION Hydrogeologic representation Stream alluvium

Aquifer Confining unit ICU)

Basal confining unit and basement rock PE Post-Eocene Model representation

[ Source-sink specified head Active model cells Cells receiving recharge River cells Aquifer pinchout-Represented as zone oflow transmissivity Lateral specified head boundary No-flow boundary Confining unit-Represented as vertical conductance term 1 Confining unit pinchout-Represented as zone of high vertical conductance Riverbed conductance At, C1 Modellayer Figure 2. Schematic diagram showing hydrogeologic framework, model layers, and boundary conditions for the Vogtle Electric Generation Plant area, South Carolina (ground-water model modified from Clarke and West, 1998; Cherry, 2006).

Hydrogeologic Setting for most regional-scale hydrogeologic studies, greater subdivi-sion of units was required to define vertical hydraulic heteroge-Coastal Plain sedimentary strata in the study area consist neity for detailed investigations of ground-water flow near the of layers of sand, clay, and limestone, which range in age from Savannah River. Accordingly, the three aquifer systems were Upper Cretaceous through post-Eocene (fig. 2). The Fall Line divided into seven aquifers (fig. 2):

(fig. I A) marks the approximate inner margin of Coastal Plain sediments. The strata dip and progressively thicken fr'om the " the Floridan aquifer system was subdivided into the Upper Three Runs aquifer and the Gordon Fall Line to the southeast, with an estimated thickness of aquifer (Aadland and others, 1995);

2,700 ft in the southern part of the study area (Wait and Davis, 1986). The strata crop out in discontinuous belts that generally

the Dublin aquifer system was subdivided into the are parallel to the Fall Line. The sedimentary sequence uncon- Millers Pond aquifer, the upper Dublin aquifer and formably overlies Paleozoic igneous and metamorphic rocks, and the lower Dublin aquifer (Falls and others, 1997); and consolidated Mesozoic red beds (Chowns and Williams, 1983)

Coastal Plain sediments comprise three principal aquifer " the Midville aquifer system was subdivided into systems near VEGP. In descending order, these aquifer systems the upper Midville aquifer and the lower Midville are (1) the Floridan aquifer system, originally defined by Miller aquifer (Falls and others, 1997).

(1986) and later redefined by Aadland and others (1995)- The aquifers are separated and confined by layers of clay comprised largely of Eocene calcareous sand and limestone; and silt, which become progressively sandy and discontinuous (2) the Dublin aquifer system (Clarke and others, 1985)-com- in updip areas. The aquifer systems coalesce where the confin-prised of Paleocene and Late Cretaceous sand; and (3) the Mid- ing units become sandy. See Falls and others (1997) for a ville aquifer systerm (Clarke and others, 1985)--comprised of complete description of geologic and hydrogeologic units in Late Cretaceous sand. Although this subdivision was suitable the study area.

6 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Structural Features movement of groundwater (and pollutants) between aquifers."

Because of the uncertainty of these features, they were not Major structural features in the study area (fig. IA) include included in the ground-water model developed by Clarke and the Belair Fault (Prowell and O'Connor, 1978) and the Pen West (1998). If additional data become available to confirm Branch Fault (Price and others, 1991). The Belair Fault is a the presence of these features, it may be desirable to incorpo-northeast-trending, high-angle reverse fault that dips to the rate them into future ground-water models of the area.

southeast and has a maximum vertical displacement of 100 ft at the base of Coastal Plain strata (Prowell and O'Connor, 1978).

The Pen Branch Fault is a northeast-trending, high-angle reverse Ground-Water Flow fault that dips to the southeast. On SRS, the fault consists of a 1.8-mile (mi)-wide zone of subparallel faults and some fault The ground-water flow system near VEGP is gener-splays (Snipes and others, 1993). The fault is downthrown ally considered to be in a state of equilibrium (steady state),

on the northwestern side, and maximum displacement ranges whereby rates of aquifer recharge and discharge are about from 100 ft at the base of Coastal Plain strata to 30 ft at the top equal, and there is an insignificant loss of water from aquifer of the Eocene Dry Branch Formation (Price and others, 1991). storage (Clarke and West, 1998). Recharge enters the ground-water system in upland areas and moves downgradient toward Seismic data from Burke County, Ga., suggest the Pen Branch Fault zone is about 0.86-mi wide and includes "short points of discharge (fig. 4). Much of the recharge water is fractures" or "stress-release faults" (Summerour and others, discharged from the shallow flow system into tributaries of the 1998). These features appear to cut confining units overlying Savannah River. A smaller percentage of recharge infiltrates the Millers Pond aquifer, upper and lower Dublin aquifers, through clayey confining units and enters the deeper interme-diate and regional ground-water flow systems (fig. 4).

and upper and lower Midville aquifers; however, it is unclear whether they cut into the confining unit overlying the Gordon Topography plays an important role in defining the posi-aquifer (Summerour and others, 1998). The Pen Branch Fault tion of areas of potential downward and upward flow. Clarke zone includes the area of VEGP (fig. IA, 1B). The effects of and West (1997) present maps showing head differences and the Pen Branch Fault on sediment deposition and hydraulic the potential for flow between adjacent units in the study area.

properties of hydrogeologic units is unknown; however, there In interstream areas throughout most of the study area, the may be some local effects on the hydrologic system (see Effect potential for flow between the Gordon aquifer and overlying of Pen Branch Fault section). Upper Three Runs aquifer is downward, indicating possible recharge by ground-water leakage from the Upper Three Runs aquifer to the Gordon aquifer (Clarke and West, 1997). Con-Hydrogeologic Characteristics of the versely, in stream valleys and throughout much of the southern Savannah River Alluvial Valley part of the study area, the potential for ground-water flow is The hydrogeologic characteristics of the Savannah River upward, indicating possible discharge from the Gordon aquifer alluvial valley (fig. 3) greatly influence the configuration of to the Upper Three Runs aquifer.

potentiometric surfaces, ground-water flow directions, and The Savannah River serves as the major hydrologic drain stream-aquifer relations. To determine the effect of palen-river in the VEGP area, with its floodplain considered to represent channel incision on hydrogeologic units, a map was constructed the same or nearly the same hydrologic condition as the river that shows the subsurface extent of hydrogeologic units (Clarke and West, 1997). Each of the seven aquifers was beneath the mantle of alluvial'deposits in the Savannah River incised by the paleo-Saannah River channel and covered floodplain (fig. 3). The map indicates that each of the seven with an infill of permeable alluvium (fig. 3), allowing direct aquifers was incised by the paleo-Savannah River channel and hydraulic interconnection between the aquifers and the river covered with an infill of permeable alluvium, allowing direct (Clarke and West, 1997). This hydraulic connection allows hydraulic connection of the aquifers and river along parts of water in confined aquifers to discharge into the river-by way the river's reach. The lateral extent of the paleo-river channel of the alluvium-and may induce ground water to flow updip.

incision corresponds to the width of the Savannah River alluvial Hydraulic connection between confined aquifers and the valley and includes the modern-day alluvial bottom and ter- Savannah River can be inferred from potentiometric-surface races as mapped by Prowell (1994). The width of the alluvial maps (figs. 5-8) that show ground-water discharge areas along valley ranges from a minimum of about 0.5 mi near the Fall the Savannah River valley as lows or depressions in the poten-Line to about 7 mi near the Richmond-Burke County line. tiometric surface (Clarke and West, 1997). Ground water flows Summerour and others (1998) reported the possible pres- toward the depressions from all directions; however, down-ence of several "channel features" along a seismic profile col- stream from the depressions, the influence of the river on the lected by Waddell and others (1995) in eastern Burke County, aquifers becomes progressively diminished, and ground water outside of the present Savannah River valley. These features resumes the regional gradient toward the southeast. In these are believed to cover an area about 3,000 ft wide, extending to downstream areas, a ground-water divide or "saddle" (Siple, about 500 ft deep; however, their presence was not confirmed 1960, 1967) in the potentiometric surface is perpendicular to by drilling. Summerour and others (1998) suggested that "the the river and separates upstream from downstream ground-channels, if real, could provide a potential pathway for the water flow.

Introduction 7 82' 81o30, 33o30' 33' Base modified from U.S. Geological Survey State base maps EXPLANATION Hydrogeologic units EmUpper Three Runs aquifer Upper Dublin confining unit l Upper Midville aquifer Gordon confining unit Upper Dublin aquifer Lower Midville confining unit EEGordon aquifer Lower Dublin confining unit Lower Midville aquifer Millers Pond confining unit 7 Lower Dublin aquifer Pre-Cretaceous basement rock Millers Pond aquifer Upper Midville confining unit Pen Branch Fault-Approximately located; D, downthrown side; U, upthrown side u

Figure 3. Subsurface extent of hydrogeologic units beneath the Savannah River alluvial valley, South Carolina and Georgia (modified from Clarke and West, 1997).

8 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios South Carolina

,iN !* .:ii .:.*

Regional Water table LOCAL FLOW

.. . .. .. SYSTEM 4>.....

1/4.

. . I . .. . . . .

INTERMEDIATE FLOW

. .. . . . . . SYSTEM REGIONAL FLOW SYSTEM

-) . .. . . . . . . . . . .. . . . . . .. . . . . . .. . .

L NOT TO SCALE EXPLANATION Aquifer M Alluvium Unsaturated zone Confining unit Saturated zone

[ Pre-Cretaceous basement rock

-*Direction of ground-water flow-Queried where unknown Figure 4. Conceptualized hydrogeologic framework and related ground-water flow near Vogtle Electric Generation Plant, Georgia and South Carolina (modified from Atkins and others, 1996).

Introduction 9 81050' 81°40' 81°30, 33020.

33010' 33o00' Base modified from U.S. Geological Survey 0 1 2 3 4 5 MILES 1:24,000-scale digital data IOI 0 I I I2 I4 I LI 0 1 2 3 4 5 KILOMETERS EXPLANATION V*!'*:

Active area of source-sink layer Al

- 140 - Potentiometric contour- Shows altitude at which

.water level would have stood in tightly cased wells in the Upper Three Runs aquifer during September 2002.

Contour interval 40 feet. Datum is NAVD 88 Direction of ground-water flow 0

U Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side Observation well Figure 5. Potentiometric surface for the Upper Three Runs aquifer, near Vogtle Electric Generation Plant, Georgia and South Car'olina, September 2002 (modified from Cherry, 2003).

10 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios 81050' 81040' 81o30' 240 33*2011 Par Pond 33o10' c4b

31Z077 31Z074 31Z015 * * /"/

31Z0730" 33o'0 ":*' 31Z076/

0S Base modified from U.S. Geological Survey 0 1 2 3 4 5 MILES 1:24,000-scale digital data [ I In I I II I I I EXPLANATION 0 1 2 3 4 5 KILOMETERS Active area of source-sink layer Al

- 140 - Potentiometric contour-Shows altitude at which Map area water level would have stood in tightly cased wells in the Gordon aquifer during September 2002.

Contour interval 20 feet. Datum is NAVD 88 AledlDirection of ground-wtrfo

,', ,,.... 0 Pen Branch Fault-Approximately located; U, D, downthrown side; U, upthrown side crven Production well-Screened in the Gordon aquifer 31Z076 Observation well-Near Pen Branch Fault in which 0 simulated water level was 4-26 feet higher than observed. Number is well identification Figure 6. Potentiometric surface for the Gordon aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

Introduction 11 81050' 81*40' 81 30' 33°20'

-10J j,

Base modified from U.S. Geological Survey 0 1 2 3 4 5 MILES 1:24,000-scale digital data IlIII I I ll.I

,EXPLANATION 0 1 2 3 4 5KILOMETERS Aiken 7; Active area of source-sink layer Al

\ ,, Ma area - 140 - Potentiometric contour--Shows altitude at which

" 0,* ; - water level would have stood in tightly cased wells

*i in the Dublin aquifer system during September 2002.

Contour interval 20 feet. Datum is NAVD 88 Bure F-. Direction of ground-water flow i**s* U Pen Branch Fault--Approximately located;

[* D,downthrown side; U,upthrown side

Production well--Screened in the upper and lower Dublin aquifer and Millers Pond aquifer Figure 1. Potentiometric surface for the Dublin aquifer system, near Vogtle Electric Generation PI'ant, Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

12 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios 81W50' 81'40' 81'30'

, :ý 33*20" :

33°00'0

Base modified from U.S. Geological Survey' 0 1 2 3 4 5 MILES 1:24,000-scale digital date I IiI

*EXPLANATION 0 1 2 3 4 5 KILOMETERS Active area of source-sink layer Al

, Map are - 140 -- Potentiometric contour--Shows altitude at which

,* *;:*"water level would have stood in tightly cased wells

-\Alenda Contour interval 20 feet. Datum is NAVD 88 Burke * - - Direction ot ground-water flow JekUs1 Pen Branch Fault--Approximately located;

\,,..crve U 0, downthrown side; U,upthrown side

Production @ well--Screened in the upper and lower Midville aquifer Figure 8. Potentiometric surface for the Midville aquifer system, near Vogtle Electric Generation Plant, Georgia and South Carolina, September 2002 (modified from Cherry, 2003).

Introduction 13 Because flow directions derived from potentiometric- Effect of Pen Branch Fault surface maps do not account for the vertical component of The Pen Branch Fault may have a local effect on ground-flow, Clarke and West (1998) applied the USGS particle-water flow. In the central part of the SRS, water levels in the tracking code MODPATH (Pollock, 1994) to characterize Gordon aquifer near the P-19 well cluster site are anomalously three-dimensional ground-water flow near the Savannah River.

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

This technique is applied in this report to simulate ground-The high water level in this area may be the result of the offset water flowpaths from the production wells at VEGP to their of the Pen Branch Fault, whereby sediments of the Gordon recharge areas.

aquifer are juxtaposed against sediments of the Upper Three Runs aquifer (Aadland and others, 1991). Because the units Trans-River Flow are in hydraulic connection near the fault, water levels and Trans-riverflow is a term that describes a condition water chemistry of the Gordon aquifer are similar to those of whereby ground water originating on one side of a river the Upper Three Runs aquifer (Clarke and West, 1997).

migrates to the other side of the river through confined aquifers that underlie the river. Although some ground water could discharge into the river floodplain or alluvium on the Ground-Water Use opposite side of the river from its point of origin, this flow Ground-water use in the study area during 2000-2002 likely would return to the river. Return flow would occur (W.J. Stringfield, U.S. Geological Survey, written commun.,

because a slight hydraulic gradient exists toward the river 2002; Fanning, 2003) was about 117 million gallons per day along the floodplain. Flow lines on potentiometric-surface (Mgal/d) (table 1), most of which was for irrigation (54 per-maps of the confined Gordon aquifer and Dublin and Midville cent) and public supply (26 percent). In Georgia, most of the aquifer systems (figs. 6-8) suggest possible occurrences of ground water used for irrigation is withdrawn from the Upper trans-river flow for a short distance into Georgia prior to Three Runs aquifer in Jenkins County and southern Screven discharge into the Savannah River (Clarke and West, 1997). County, and from the Upper Three Runs and Gordon aquifers Flow lines on the map for the Upper Three Runs aquifer, in Jefferson, Burke, and northern Screven Counties. In South however, do not indicate trans-river flow (fig. 5). Carolina, most irrigation wells in Barnwell and Allendale Counties pump water from the Upper Three Runs and Gordon aquifers. Ground-water use for public supply and industrial and mining purposes is mainly from the Dublin and Midville aquifer systems in both States.

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

[Modified from Cherry, 2006]

Georgia Burke 3.87 21.23 0.15 0.90 0.03 0.78 26.96 Jefferson 1.84 6.92 3.82 0.64 0.03 0.00 13.25 Jenkins 0.54 3.94 0.01 0.33 0.02 0.00 4.84 Richmond 14.88 5.22 2.87 0.22 0.02 0.00 23.21 Screven 1.15 15.62 1.82 0.74 0.03 0.00 19.36 South Carolina Ak-en 4.82 .,07.98 .K6-06~ -.0.80 00o 0.00 12.66, t -, Allendale - 1.20 5.62 <2.50. ;:;, 0.27 :r ":* 0.;000.:

0.00 9.59 2.73 ~3i73 , : 0.41 0.00 7.50ý Total-Georgia 22.28 52.93 8.67 2.83 0.13 0.78 87.62 Total-South Carolina 8.75 10.33 8.97 1.70 0.00 0.00 29.75 Total-eight counties 31.03 63.26 17.64 4.53 0.13 0.78 117.37

'See figure ]A for location Data sources: County totals for Georgia are from Fanning (1997, 2003) and Pierce and others (1982); total water-use data for South Carolina front Lonon and others (1983), and W.J. Stringfield (U.S. Geological Survey, written commun., 2002); site-specific data for irrigation wells located in Georgia from J.L. Fanning (U.S. Geological Survey, written commun., 2003) and V. P. Trent (Georgia Geologic Survey, written commun., 2003); and site-specific data for permitted wells located in South Carolina from Paul Bristol and Peter Stone (South Carolina Department of Health and Environmental Control, written commun., 2003).

14 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios At VEGP, three wells are each screened in the lower Dublin and upper and lower Midville aquifers, and are used to Simulation of Ground-Water Flow supply water to operating reactor Units I and 2 (wells 31Z002, The model used in this study is described in detail in 31Z003, and 31Z080; fig. IB; table 2). Screened intervals Clarke and West (1998) and Cherry (2006); only a brief of wells at VEGP were obtained from drillers records and description is included herein. Clarke and West (1998) entered into the USGS National Water Information System simulated predevelopment and 1987-92 conditions using (http://waterdata.usgs.gov/ga/nwis/inventory).To determine the MODFLOW finite-difference simulator (McDonald and the aquifer supplying water to each screened interval, altitudes Harbaugh, 1988). Cherry (2006) updated the model to simu-of screened intervals were compared to maps showing the late 2002 hydrologic conditions using the MODFLOW-2000 altitude of the tops of hydrogeologic units using a Geographic simulator (Harbaugh and others, 2000). Both studies simulated Information System (Harrelson and others, 1997).

steady-state conditions for each time period. Steady-state During 2002, the wells at VEGP supplied an average simulations were deemed appropriate because of the minimal 724 gal/min (1.04 Mgal/d). The addition of two additional observed changes in hydraulic head or ground-water discharge reactor units is projected to result in an increase in ground- to streams from predevelopment (pre- 1953) t6-1987-92 water pumping of 1.09 Mgal/d (Mark Notich, U.S. Nuclear (Clarke and West, 1997). These minor fluctuations are an indi-Regulatory Commission, written commun., April 10, 2007).

cation that the ground-water system generally was in a state of If ground-water pumping during the startup of these reactors equilibrium and any contributions from aquifer storage were is similar to that during the startup of the original two reactors minor. These assumptions are believed to remain valid for the during 1988, then the initial increase in pumping could be as study area for this investigation.

high as 3.42 Mgal/d. The model encompasses an area of about 4,455 mi2 At SRS, estimated pumpage was 5.30 Mgal/d during (fig. 1) and includes seven aquifers and seven confining units.

2002 (Cherry, 2006). A variety of multiaquifer wells com- These units crop out near the Fall Line and generally dip and pleted in the Gordon aquifer and Dublin and Midville aquifer thicken to the southeast. Aquifer units are, in descending systems provide water supply at SRS. order (fig. 2):

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

[USGS, U.S. Geological Survey; 0, degree; ', minute; ", second; Aquifer: LD, lower Dublin; UM, upper Midville; LM, lower Midville]

Land-surface Screened interval Pouto KUSGS well Well Latitde Lonitde lttue Year (feet below Aqie capaodcityo

'identification' number Lnnstructeiu dland (ftd surdace) Aqif allone Top Bottornm minute) 3l1tZ002 TW-1 33'08'28 81'45'42" 219 1972 505 535 LD 1,200 555 585 LD 695 705 UM 730 750 UM 815 850 LM 31 Z080 IMU-2A 33'08'39" 81046'00" 235 1983 480 510,* LD >2, 112 630< L650 690 ~79',/ 1M 2

31Z003 MU-1 33008'47" 81045'37" 197 1977 437 462 LD 3,334 468 483 LD 498 512 LD 536 546 LD 550 572 LD 676 696 UM 720 732 LM 788 820 LM Igpp f*orro JRt mnrIn-r~ntinn 2

Now called MU-5

Simulation of Ground-Water Flow 15

- the unconfined Upper Three Runs aquifer modeled cal conductance to simulate leakance between layers. Esti-as a source-sink layer (specified head layer A 1); mated and calibrated transmissivity values are listed in table 3 aid leakance values are listed in table 4 (Clarke and West,

- the confined Gordon aquifer (layer A2); 1998). For the MODPATH particle-tracking analysis, a uniform

- the Dublin aquifer system consisting of the Millers porosity of 30 percent was assigned to aquifer layers and 50 per-Pond aquifer (layer A3), upper Dublin aquifer cent was assigned to confining units (Clarke and West, 1998).

(layer A4), and lower Dublin aquifer (layer A5); and The finite-difference grid for the model is aligned nearly parallel to the Savannah River and to the regional dip of the

- the Midville aquifer system consisting of the upper hydrogeologic units, and consists of 130 rows and 102 col-Midville aquifer (layer A6) and lower Midville umns (13,260 grid cells) with a variable grid spacing ranging aquifer (layer A7). in size from 0.33 mi by 0.33 mi to 2 mi by 2.5 mi (fig. IA).

The thickness, extent, and other hydraulic properties of The model grid area encompasses about 4,455 mi5, of which these units, as well as the model development process are about 3,250 mi is actively simulated. Grid density is higher described in detail in Clarke and West (1998). A schematic dia- near the Savannah River (including the Savannah River Site gram showing model layers and boundary conditions is shown and VEGP) to enable simulation of steeper head gradients in figure 2. As in the original model of Clarke and West (1998), (fig. 1A). Each aquifer unit is represented with one layer of confining units are not actively simulated, but instead use verti- grid cells in the vertical dimension.

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

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

" ~Transmnissivity, insquare foot per day' Aquifr. , Estimated basedon field data'_ _ __ Simulated_...........

Aquir~ r;'- numiber2-#ofvle .Siutd

',o vaue 'MinimumiP7Maximium ~Mean, Minimnum, Maximum Mean'.~

Gordon aquifer A2 18 180 12,200 4,500 100 24,700 10,350 Millers Pond aquifer A3 10 195 2,000 1,000 10 3,900 1,310 Upper Dublin aquifer A4 17 555 25,200 5,830 10 20,000 7,220 Lower Dublin aquifer A5 21 40 8.900 3,940 10 25,500 10,030 Upper Midville aquifer A6 15 1,300 5,430 2,760 10 12,390 6,270 Lower Midville aquifer A7 37 800 25,500 8,900 515 34,395 19,020

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

'Mean value weighted according to cell area.

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

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

e-ckance, infeet per day per footof confining unit thickness' Hydrogeologic

. * .. * } '

5 ?

Layer

'** ** 4**"

- - - } *' i* ....-

Esimate'd * "**

eaIkance2' 4,*/;'.<( .*i*44, .44" Simulated___________

~#of values "Minimunm Maximum ,Mean Minimum >Maximum Mea'iia Gordon confining unit Cl 6 4.7 x 10-1 1.2 x 10-1 2.1 x 10-1 9.0 x 10-8 1.3 x 10-1 1.7 x 10' Millers Pond confining unit C2 - 3.9 x 10-1 8.7 x 10- 1.9 x 10-2 Upper Dublin confining unit C3 9 1.8x 10-6 1.6x 10-3 3.6x 10' 1.2 x 10-1 7.3 x 10-1 1.2 x 10-l Lower Dublin confining unit C4 1 2.4 x 10-5 2.4 x 10-5 2.4 x 10-1 3.0 x 10-7 6.5 x 10-3 6.6 x 10-3 Upper Midville confining unit C5 11 6.7 x 10-7 3.4 x 101 7.6 x 10-5 2.1 x 10-7 1.0 x 10-' 9.7 x 10-V Lower Midville confining unit C6 1 1.0 x 1075 1.0 x 10-1 1.0 x 10-5 7.7 x 10-1 3.6 x 10-' 9.0 x 10-3 Includes low permeability layers within aquifer layers.

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

'Mean value weighted according to cell area.

16 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Lateral model boundaries are a combination of no-flow Table 5. Simulated pumpage by model layer for 2002 Base Case, and specified head for layers A2-A7. For all layers, the south- Vogtle Electric Generation Plant model, Georgia and South Carolina.

eastern boundary is simulated as a specified-head condition. [Modified from Cherry, 2006]

For layers A2-A3, the southwestern boundary is simulated as no-flow, corresponding to the position of a ground-water Auir Model Year 20 upgi divide. Parts of the eastern boundary for layers A2 and A3 are layer mi iion gallons perday, simulated as specified head and no-flow. For layers A4-A7, Gordon A2 10.7 most of the western boundary is simulated as no-flow, corre- Millers Pond A3 7.3 sponding to the position of a ground-water divide. The eastern boundary for layers A4-A7 is simulated mostly as a specified- Upper Dublin A4 5.4 head condition. Specified heads for each layer in the model Lower Dublin A5 14.6 are based on potentiometric surface maps for September 2002 Upper Midville A6 9.8 (figs. 5-8) and generally are lower than in the original Clarke Lower Midville A7 19.4 and West (1998) model to reflect effects of the 1998-2002 All layers 67.2 drought (Cherry, 2006).

The bottom boundary of the model is no-flow, whereas the top boundary represented by layer A l is set as a source-sink specified-head condition with controlling specified heads based on water levels from the 2002 potentiometric-surface map of the Upper Three Runs aquifer (Cherry, 2003). Flow in

The calibrated model used for this study showed a the deeper active layers (A2-A7) of the model is simulated reasonable fit to simulated water levels. Water-level residuals through a combination of active cells, specified head cells, represent the difference between simulated and observed water recharge cells, and river cells. levels, with positive values indicating that simulated values Most recharge to the simulated ground-water system were greater than observed values. For the 1987-92 simula-was provided by leakage from layer A 1, with a comparatively tion, the model was calibrated using the average observed smaller amount derived from recharge cells in layers A2-A7. water levels at 313 model cells, with a mean of residuals of Total simulated recharge is about 930 Mgal/d of which 0.8 ft and a root mean square (RMS) of the residuals of 10.6 ft 777 Mgal/d were derived by leakage from layer A 1, and (Clarke and West, 1998). For the 2002 simulation, model 153 Mgal/d were derived from recharge assigned to outcrop calibration was evaluated based on observations at 172 wells areas of hydrogeologic units (Cherry, 2006). during September 2002, with a mean of residuals of 2.8 ft and Average annual pumpage for 2002 was assigned to a RMS of the residuals of 8.0 ft (Cherry, 2006).

model cells based on site-specific and county-aggregate data (table 1). Site-specific data are available for public supply, thermoelectric, industrial, and mining use and are assigned to Pen Branch Fault known well locations. County' aggregate agricultural pumping data were equally divided and assigned to known agricultural The Pen Branch Fault may locally affect ground-water well locations Domestic and commercial and livestock use flow in the study area (see Effect of Pen Branch Fault section).

were not simulated by the model because these uses accounted Although hydraulic characteristics of the fault are unknown, for less than 4 percent of total study area pumpage during the possible effects of the fault are incorporated into the model 2002 (table 1) with most of the withdrawal derived from shal- as follows: (1) by variations in depth, thickness, and hydraulic low wells completed in the Upper Three Runs aquifer. properties of model layers near the fault; and (2) by incor-Where multi-aquifer wells are completed in several poration of river cells where incision of the Gordon aquifer aquifer layers (such as at VEGP and SRS), pumpage was (layer A2) is believed to occur along the southern side of the evenly proportioned to the various screened intervals in fault in the Savannah River alluvial valley (fig. IA).

each well. Of the total study area ground-water use dur- Hydraulic properties of the upper and lower Dublin

.ling 2000-2002 of 117 Mgal/d, 67.2 Mgal/d were simulated aquifers (model layers A4 and A5) were adjusted along the from active layers (table 5) A2 (Gordon aquifer), A3 (Millers southern side of the fault during model calibration (Clarke Pond aquifer), A4 (upper Dublin aquifer), A5 (lower Dublin and West, 1998). A zone of high transmissivity-greater than aquifer), A6 (upper Midville aquifer), and A7 (lower Midville 15,000 feet squared per day (ft2/d) and extending'as much aquifer). The remaining 49.8 Mgal/d were from the Upper as 6 mi south of the fault-was required in the two layers to Three Runs aquifer (layer AI), which is not actively simu- achieve calibration of the model. Although there are no field lated. The influence of pumpage from the Upper Three Runs data to confirm this zone of-higher transmissivity, it is possible aquifer on the overall flow system during 2002 is simulated by that such a zone exists based on calibration results. Construc-changing the head in that layer based on water-level measure- tion of test wells and aquifer testing in this area would be ments during September 2002 (fig. 5). required to confirm the presence of a high transmissivity zone.

Simulation of Ground-Water Flow 17 Maps showing the altitude of the top of hydrogeologic would facilitate movement of water between the zones. This units (Falls and others, 1997) indicate that uplift along the modification could result in reducing the simulated head in southern side of the Pen Branch Fault resulted in shallower the Gordon aquifer by allowing water to discharge from the depths of units compared to equivalent units north of the fault. unit and would reduce the aforementioned difference between Near the Pen Branch Fault and the P-19 well cluster site on observed and simulated head. Because the presence, depth, SRS, simulated head values for the Gordon aquifer (layer A2) and areal extent of these features, are unknown, they were not during 1987-92 are considerably lower than observed values, simulated by the current model.

with a residual of -81.1 ft (Clarke and West, 1998). Clarke and West (1997) reported that the anomalously high observed Ground-Water Pumping Scenarios head in the Gordon aquifer in this area may be the result of (1) a high degree of aquifer interconnection between the The updated and calibrated model (Cherry, 2006) was Upper Three Runs and Gordon aquifers due to the Pen Branch used to simulate the effect of current and potential future Fault (Aadland and others, 1991), or (2) the possibility that pumping on ground-water levels and flowpaths near VEGP for the water-level measurement in the Gordon aquifer at the a Base Case and three pumping-scenarios (table 6). The Base P-I19 well cluster site may not be representative of the head in Case represents 2002 pumping rates throughout the model layer A2 because of problems with well construction or mea- area (Cherry, 2006). The three scenarios were designed to surement error. Because the reason for the high water level in simulate steady-state water levels resulting from (1) pumping the Gordon aquifer was not definitively established, the earlier increases at VEGP with pumping elsewhere in the study area study (Clarke and West- 1998) did not adjust model param- held at 2002 rates (Scenarios A and C), and (2) the effects of eters to attempt to match water levels in the Gordon aquifer at increased pumping at VEGP combined with a shutdown of the P-19 well cluster. Simulation of higher head in the Gordon pumping at the SRS (Scenario B).

aquifer in this area would require increasing the leakance of Steady-state conditions in response to pumping changes the Gordon confining unit (layer C1) to enable greater connec- are believed to be reached rapidly in the study area. Clarke and tion between the Upper Three Runs and Gordon aquifers. West (1998) indicated that for each of six stress periods during In the Savannah River valley, uplift along the southern 1953-92, "heads showed an almost instantaneous stabiliza-

side of the Pen Branch Fault and erosion by the paleo- tion, suggesting that the prevalence of steady-state conditions Savannah River appears to have resulted in exposure of were achieved immediately following a change in pumpage."

the Gordon aquifer (layer A2) in a local area (fig. 3). This For each scenario, the pumping distribution, simulated water-local exposure is simulated in the model as river cells in the level changes, and ground-water flowpaths are described rela-Gordon aquifer that enables a higher degree of connection tive to the year 2002 Base Case.

between the Gordon aquifer and the Savannah River (fig. IB). A particle-tracking analysis was conducted for the Base Despite this adjustment, simulated water levels in the Gordon Case and for each scenario to determine the source of water aquifer (layer A2) near this feature during 2002 generally withdrawn from the VEGP production wells. The USGS are high in the model, ranging from 4 to 26 ft higher than particle-tracking code MODPATH (Pollock, 1994) was used observed levels (wells 31Z015, 31Z073, 31 Z074, 31Z076, to generate advective water-particle pathlines and their and 31Z077; fig. 6). associated time of travel based on the MODFLOW simula-Another area where uplift on the southern side of the fault tions. MODPATH was used to compute three-dimensional is represented by the model occurs between Pen Branch and flow directions and time of travel using imaginary particles Four Mile Branch on SRS (fig. IB). In this upland area adja- in a backtracking mode from the production wells at VEGP cent to the Savannah River.Valley, units overlying the Gordon toward recharge areas in a map perspective. Generally, the aquifer appear to have been eroded away and the aquifer is greater the number of particles applied vertically and horizon-near land surface. Here, the Gordon aquifer is simulated using tally in a model cell, the more accurate the definition of flow-recharge cells, which enable direct infiltration of precipitation paths for a given model layer. For this study, particles were into the aquifer. placed at the center of each of the three grid cells containing a Several hypothesized channel features (Summerour and VEGP production well at increments representing 10 percent others, 1998) along a seismic profile near the Pen Branch Fault of the aquifer thickness (10 total particles per aquifer layer in in eastern Burke County, Ga., were ndt incorporated into the each of the three grid cells). Particles were placed in the lower ground-water model because their existence was not con- Dublin (layer A5), and upper (layer A6) and lower Midville firmed by test drilling. According to Summerour and others (layer A7) aquifers, which provide water to the VEGP pro-(1998), these features potentially could affect a zone 3,000 ft duction wells. To avoid clutter and simplify display of particle wide and 500 ft deep, and provide a potential pathway for flowpaths on maps, the number of particles displayed on the movement of ground water between aquifers. If such a feature figure was reduced from 10 to 5. Simulated time of travel for were simulated, high vertical hydraulic conductivity would all particles (10 per model cell) is summarized for the Base be assigned to confining units overlying layers A2-A7, and Case and for Scenarios A-C in table 7.

18 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Table 6. Simulated pumpage at Vogtle Electric Generation Plant, Burke County, Georgia, for 2002 Base Case and pumping Scenarios A, B, and C.

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

,Pumping rate~

Scenario Remarks Base Case 2002 724 1.04 Current conditions for existing reactor units A 1,482 2.13 Additional pumping capacity of new reactor units at average projected withdrawal rates B 1,482 2.13 Additional pumping capacity of new reactor units at average projected withdrawal rates and elimination of 5.3 Mgal/d purnpage at Savannah River Site C 3,099 4.46 Scenario represents a higher rate of withdrawal for the proposed new reactor units during their startup period (3.42 Mgal/d), and continuation of year 2002 pumping rates (1.04 Mgal/d) in the existing reactor units. The higher withdrawal in the new reactors is similar to that reported during 1988 for the startup of the existing reactors. Southern Nuclear Company has noted that the high pumping rates during startup of Units I and 2 were related to achieving water-quality criteria and not to ground-water demand by the facilities. Water treatment methods are now used to achieve the water-quality criteria and have greatly reduced ground-water pumping rates (Mark Nodich, U.S. Nuclear Regulatory Commission, written commun., September 10, 2007).

Table 7. Summary of simulated time of travel for 2002 Base Case 2002 Base Case Condition and for Scenarios A, B, and C,Vogtle Electric Generation Plant model, Georgia and South Carolina. The year 2002 simulation represents the Base Case for comparison to each of the pumping scenarios. The simulated

[Ten particles were assigned to each aquifer layer in 3 model cells for a total hydrologic condition during 2002 represents effects of the of 30 particles per layer]

1998-2002 drought in which irrigation pumpage was above average and recharge and boundary-condition head were low bSim ulted tmmof travel iin~years :

due to decreased precipitation. Results of model simulations Allayer Statistic B~ase Case fScenario : for 2002 are presented in Cherry (2006); results of particle-tracking analyses at VEGP are presented herein.

The simulated 2002 potentiometric-surface maps for the Lower Dublin Mean 2,700 2,700 2,700 3,800-(A5) Median 2,700 2,600 2,700 3,000 Dublin and Midville aquifer systems (figs. 7 and 8, respec-tively) indicate VEGP is within the Savannah River regional Maximum 3,600 3,700 3,900 12,600 ground-water discharge zone in which the principal direction Minimum 2,100 2,100 2,100 1,800 of ground-water flow is toward the Savannah River. None of the various scenarios resulted in large changes in the con-

( :;,.,,,:-;-Median 6: ,2800

2. ,:::::2,700 *2,700, 2,50*1* figuration of the simulated potentiometric surface and related ground-water flow directions.

The source of water to the VEGP production wells, as indicated by MODPATH analysis for year 2002, is recharge Lower Midville Mean 3,100 3,100 3,200 2,800 occurring in an upland area near the county line between (A7) Median 2,900 2,800 2,800 2,500 Burke and Jefferson Counties, Ga. (fig. 9), with none of the Maximum 3,800 4,200 4,600 4,000 water originating on SRS or elsewhere in South Carolina.

Simulated mean time of travel from recharge areas to the Minimum 2,700 2,400 2,400 2,400 VEGP production wells are about 2,700 years (yr) in the lower Dublin aquifer and about 3,100 yr in the upper and lower Midville aquifers (table 7). The fastest simulated time of travel, about 2,100 yr, was for a particle in the lower Dublin aquifer, and the longest was about 3,800 yr for a particle in the lower Midville aquifer.

Simulation of Ground-Water Flow 19 Base modified from U.S. Geological Survey 0 5 10MILES 1:24,000-scale digital data i I I I I 0 ' 5 10 KILOMETERS EXPLANATION S Vogtle Electric Generation Plant Model boundary D Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side U

Simulated ground-water flowpath-Particles placed at the center of each of the three grid cells containing a Plant Vogtle production well at increments representing 10 percent of the aquifer thickness (10 total particles per aquifer layer per cell). Five particle flowpaths for each layer are shown on map to avoid clutter Lower Dublin aquifer

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

20 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Scenario A Scenario B Scenario A simulates a 1.09-Mgal/d increase in average Scenario B simulates a 1.09-Mgal/d increase in pumping pumping rates at VEGP for the operation of existing reactors at VEGP, as was simulated in Scenario A, and total elimina-(Units I and 2) and an increase for the proposed new reactors tion of 5.3 Mgal/d pumping at the SRS facility (table 6). For (Units 3 and 4). The pumping increase was distributed evenly this scenario, the 1.09 Mgal/d increase was distributed evenly among the three production wells at VEGP. Simulated water- among three production wells at VEGP completed in the

.level changes are shown in figures 10-15; particle-tracking lower Dublin and upper and lower Midville aquifers, and the results are shown in figure 16 and listed in table 7. 5.3 Mgal/d decrease was subtracted evenly among 12 produc-For Scenario A, water-level changes were minimal, tion wells at the SRS completed in one or more of the follow-with maximum declines of greater than 0.25 ft in the Gordon ing aquifers: Gordon, Millers Pond, upper and lower Dublin, aquifer (fig. 10), greater than 0.5 ft in the Millers Pond aquifer and upper and lower Midville. Simulated water-level changes (fig. 11), greater than 1 ft in the upper and lower Dublin aqui- are shown in figures 17- 22; particle-tracking results are fers (figs. 12 and 13, respectively), and greater than 2 ft in the shown in figure 23 and listed in table 7.

upper and lower Midville aquifers (figs. 14 and 15, respec- For Scenario B, the largest water-level changes were tively). Drawdown response in the shallow aquifers (Gordon, on SRS, with maximum increases of greater than 4 ft in the Millers Pond, and upper Dublin) is due to leakage through Gordon aquifer, greater than 1 ft in the Millers Pond aquifer, confining units in response to decreased head in the pumped greater than 4 ft in the upper Dublin aquifer (fig. 19), greater zones (lower Dublin and upper and lower Midville aquifers). than 8 ft in the lower Dublin aquifer (fig. 20), and greater In the upper and lower Dublin and upper and lower Midville than 4 ft in the upper and lower Midville aquifers (figs. 21 aquifers, the zone of pumping influence (defined as greater and 22, respectively). At VEGP, the magnitude and extent of than 0.5 ft of change) extends from about 3 to 4.5 mi onto SRS water-level decline resulting from increased pumping was less in South Carolina (figs. 12-15). pronounced than that observed in Scenario A for an equiva-For Scenario A, the source of water to VEGP production lent increase in pumping. The water-level rise resulting from wells, as indicated by MODPATH analysis, is recharge in an elimination of SRS pumping reduced the effect of pumping upland area near the county line between Burke and Jefferson at VEGP on ground-water levels. Maximum declines near Counties, Ga. (fig. 16). Simulation results indicate that none of .VEGP were greater than 2 ft in the upper and lower Midville the recharge originated on SRS or elsewhere in South Caro- aquifers (figs. 21 and 22, respectively), greater than 1 ft in the lina, despite the small amount of drawdown extending into lower Dublin aquifer (fig. 20), and greater than 0.5 ft in the that area in the lower and upper Dublin and lower and upper upper Dublin aquifer (fig. 19). There was no observed change Midville aquifers (figs. 12-15). Because vertical-head gradi- at VEGP in the overlying Gordon and Millers Pond aquifers ents are steep beneath the Savannah River alluvial valley, large (figs. 17 and 18, respectively).

changes in head are required to induce flow from the other Despite the large water-level rise at SRS, the source of side of the river. Mean simulated time of travel from recharge water to VEGP production wells, as indicated by MODPATH areas to the VEGP wells for Scenario A are about 2,700 yr in analysis (fig. 23), remained nearly identical to Scenario A the lower Dublin aquifer and about 3,100 yr in the upper and (fig. 16). Simulation results indicate that ground-water lower Midville aquifers (table 7). The fastest simulated time recharge is provided in an upland area near the county line of travel, about 2,100 yr, was for a particle in the lower Dublin between Burke and Jefferson Counties, Ga. (fig. 23), with a aquifer and the slowest was about 4,700 yr for a particle in the mean simulated time of travel of about 2,700 yr in the lower upper Midville aquifer. Dublin aquifer; about 3,300 yr in the tipper Midville aquifer; and about 3,200 yr in the lower Midville aquifer (table 7). The fastest simulated time of travel was for a particle in the lower Dublin aquifer (about 2,100 yr), and slowest was for a particle in the upper Midville aquifer (about 5,200 yr). As was the case for Scenario A, none of the recharge originated on SRS or elsewhere in South Carolina.

Simulation of Ground-Water Flow 21 Base modified from U.S. Geological Survey 0 5 10 MILES i I I I 1:24,000-scale digital data 0 5 10 KILOMETERS EXPLANATION Up Vogtle Electric Generation Plant 0 Fault-Approximately located; D,downthrown side; U,upthrown side U

- -0,25 - Line of equal simulated water-level change-Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario A(see table 6 for description of scenario)

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

22 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data I I EXPLANATION 0 5 10 KILOMETERS Vogtle Electric Generation Plant 0 Pen Branch Fault-Approximately located; 0, downthrown side; U, upthrown side U

- -0.5 - Line of equal simulated water-level change-Interval, in feet, is 0.25.

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario A (see table 6 for description of scenario)

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

Simulation of Ground-Water Flow 23 Base modified from U.S. Geological Survey 0 5 .10MILES I I I 1:24,000-scale digital data 0 5 10 KILOMETERS EXPLANATION t Vogtle Electric Generation Plant D Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side U

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

Computed by subtracting the simulated-potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario A *

(see table 6 for description of scenario)

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

24 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data I I I 0 5 10 KILOMETERS EXPLANATION tP Vogtle Electric Generation Plant Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side U

-- -1 - Line of equal simulated water-level change-Interval, in feet, is 0.5.

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario A (see table 6 for description of scenario) 0 Production well-Completed in the lower Dublin aquifer in which pumping was adjusted for scenario Figure 13. Simulated water-level change for Scenario A in the lower Dublin aquifer, near.Vogtle Electric Generation Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow 25 Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data i I I I I 0 5 10 KILOMETERS EXPLANATION Up Vogtle Electric Generation Plant 0

- - Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side Line of equal simulated water-level change-Interval, in feet, is variable.

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from thesimulated potentiometric surface for Scenario A (see table 6 for description of scenario) 0 Production well-Completed inthe upper Midville aquifer inwhich pumping was adjusted for scenario Figure 14. Simulated water-level change for Scenario A in the upper Midville aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

26 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey 0 5 10MILES 1:24,000-scale digital data i I I I I 0 5 10 KILOMETERS EXPLANATION I Vogtle Electric Generation Plant Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side U

- Line of equal simulated water-level change-Interval, in feet, is variable, Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario A (see table 6 for description of scenario) 0 Production well-Completed in the lower Midville aquifer in which pumping was adjusted for scenario Figure 15. Simulated water-level change for Scenario A in the lower Midville aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow 27 Base modified from U.S, Geological Survey 0 5 10MILES 1:24,000-scale digital data I I I 0 5 10 KILOMETERS EXPLANATION

£? Vogtle Electric Generation Plant Model boundary 0 Pen Branch Fault-Approximately located; 0, downthrown side; U, upthrown side U

Simulated ground-waterflowpath--Particles placed at the center of each of the three grid cells containing a Plant Vogtle production well at increments representing 10 percent of the aquifer thickness (10 total particles per aquifer layer per cell). Five particle flowpaths for each layer are shown on map to avoid clutter Lower Dublin aquifer Upper Midville aquifer Lower Midville aquifer Figure 16. Particle-tracking results for the year 2002, Scenario A, near Vogtle Electric Generation Plant, Georgia and South Carolina.

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

Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data I II I 0 5 10 KILOMETERS EXPLANATION U Vogtle Electric Generation Plant 0 Pen Branch Fault-Approximately located; D, downthrown side; U, upthrown side U

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario B (see table 6 for description of scenario) 0 Production well-Completed in the Gordon aquifer in which pumping was adjusted for scenario Figure 17. Simulated water-level change for Scenario B inthe Gordon aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow 29 Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data i I I I I 0 5 10 KILOMETERS EXPLANATION

[P Vogtle Electric Generation Plant Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario B (see table 6 for description of scenario) 0 Production well-Completed in the Millers Pond aquifer in which pumping was adjusted for scenario Figure 18. Simulated water-level change for Scenario B in the Millers Pond aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

30 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data i I I I I 0 5 10 KILOMETERS EXPLANATION T Vogtle Electric Generation Plant o_ Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side U

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario B (see table 6 for description of scenario) 0 Production well-Completed in the upper Dublin aquifer in which pumping was adjusted for scenario Figure 19. Simulated water-level change for Scenario B in the upper Dublin aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow 31 Base modified from U.S. Geological Survey 0 5 10 MILES I I I 1:24,000-scale digital data 0 5 10KILOMETERS EXPLANATION E Vogtle Electric Generation Plant 0 Pen Branch Fault-Approximately located; D, downthrown side; U, upthrown side U

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario B (see table 6 for description of scenario) o Production well-Completed in the lower Dublin aquifer in which pumping was adjusted for scenario Figure 20. Simulated water-level change for Scenario B in the lower Dublin aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

32 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey u 5 10 MILES 1:24,000-scale digital data i I I I I 0 5 10 KILOMETERS EXPLANATION U Vogtle Electric Generation Plant 0 Pen Branch Fault-Approximately located; D, downthrown side; U, upthrown side U

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario B (see table 6 for description of scenariol, 0 Production well-Completed in the upper Midville aquifer in which pumping was adjusted for scenario Figure 21. Simulated water-level change for Scenario B in the upper Midville aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow 33 a 5 10MILES Base modified from U.S. Geological Survey 1:24,000-scale digital data I I 0 5 10 KILOMETERS EXPLANATION Ep Vogtle Electric Generation Plant O Pen Branch Fault-Approximately located; D, downthrown side; U,upthrown side U

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario B (see table 6 for description of scenario) 0 Production well-Completed in the lower Midville aquifer in which pumping was adjusted for scenario Figure 22. Simulated water-level change for Scenario B in the lower Midville aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

34 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey .0 5 10 MILES 1:24,000-scale digital data I I I I I 0 5 10 KILOMETERS EXPLANATION E Vogtle Electric Generation Plant Model boundary 0 Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side U

Simulated ground-water flowpath-Particles placed at the center of each of the three grid cells containing a Plant Vogtle production well at increments representing 10 percent of the aquifer thickness (10 total particles per aquifer layer per cell). Five particle flowpaths for each layer are shown on map to avoid clutter

. .... Lower Dublin aquifer Upper Midville aquifer-Lower Midville aquifer Figure 23. Particle-tracking results for the year 2002, Scenario B, study area, near Vogtle Electric Generation Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow 35 Scenario C lower Midville aquifers (figs. 28 and 29, respectively).

The extent of drawdown is largest for Scenario C Scenario C simulates a 3.42-Mgal/d increase in pumping when compared to Scenarios A and B, with the 0.5-ft at VEGP that represents a 2.33-Mgal/d higher rate of with- drawdown contour in the upper and lower Midville aquifers drawal than was simulated for Scenario A for the proposed extending about 29 mi to the southwestern model boundary new reactor units (table 6). The higher withdrawal for wells in Jenkins and Screven Counties, Ga., and about 14 mi providing water to the new reactors is similar to that reported eastward into SRS (figs.'28 and 29, respectively). In the for the startup of the two existing reactors (Units I and 2) dur- overlying Gordon, Millers Pond, and upper Dublin aquifers ing 1988 (Mark Notich, U.S Nuclear Regulatory Commission, (figs.. 24-26, respectively), drawdown response is due to written commun., April 10, 2007). Southern Nuclear Com- leakage through confining units in response to decreased head pany has noted that the high pumping rates during startup of in the production zones (lower Dublin and upper and lower Units I and 2 were related to achieving water-quality criteria Midville aquifers, figs. 27-29, respectively).

and not to ground-water demand by the facilities. Water For Scenario C, the source of water to VEGP produc-treatment methods are now used to achieve the water-quality tion wells, as indicated by MODPATH analysis (fig. 30), is criteria and have greatly reduced ground-water pumping recharge at a somewhat different location than that simulated rates (Mark Nodich, U.S. Nuclear Regulatory Commission, for Scenario A (fig. 16). As was the case for Scenario A, written commun., September 10, 2007). simulation results indicate that much of the ground-water Although pumping rates simulated by Scenario C are recharge for Scenario C occurs in an upland area near the viewed as implausible for long-term operation.of proposed county line between Burke and Jefferson Counties, Ga.;

Units 3 and 4, and the pumping rates are not proposed by however, there is an additional source of water in an upland Southern Nuclear Company, the scenario is designed to area in eastern Barnwell County, S.C. As was the case for

simulate pumping rates necessary to draw ground water Scenarios A and B, none of the recharge originated on SRS.

from South Carolina to the VEGP production wells. The When compared to Scenarios A and B, simulated mean time 3.42-Mgal/d increase was distributed evenly among three of travel for Scenario C (table 7) was slower in the lower Dub-production wells at VEGP. Simulated water-level changes are lin aquifer (about 3,800 yr), and faster in the upper and lower shown in figures 24-29; particle-tracking results are shown Midville aquifers (about 2,800 yr). For Scenario C, the fastest on figure 30 and listed in table 7. simulated time of travel of about 1,800 yr was for particles The maximum simulated drawdown for Scenario C was in the lower Dublin and upper Midville aquifers and slow-greater than 1 ft in the Gordon aquifer (fig. 24), greater than est (about 12,600 yr) was for a particle in the lower Dublin 2 ft in the Millers Pond aquifer (fig. 25), greater than 4 ft in aquifer. The slower time of travel in the lower Dublin aquifer the upper Dublin aquifer (fig. 26), greater than 4 ft in the lower may be the result of the greater length and extent of flowlines Dublin aquifer (fig. 27), and greater than 8 ft in the upper and shown on figure 30.

36 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data i I I I 0 5 10 KILOMETERS EXPLANATION tP Vogtle Electric Generation Plant 0 Pen Branch Fault-Approximately located; D, downthrown side; U, upthrown side u

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario C (see table 6 for description of scenario)

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

Simulation of Ground-Water Flow 37 0 5 10MILES Base modified from U.S. Geological Survey 1:24,000-scale digital data I 0 5 10 KILOMETERS EXPLANATION 1:5: Vogtle Electric Generation Plant D Pen Branch Fault-Approximately located; D, downthrown side; U, upthrown side u

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

Computed by subtracting the simulated potehtiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario C (see table 6 for description of scenario)

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

38 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey 0 5 10MILES 1:24,000-scale digital data i I 0 5 10 KILOMETERS EXPLANATION EP Vogtle Electric Generation Plant D Pen Branch Fault-Approximately located; D, downthrown side; U, upthrown side U

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario C (see table 6 for description of scenario)

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

Simulation of Ground-Water Flow 39 Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data i I I I I 0 5 10 KILOMETERS EXPLANATION J:P Vogtle Electric Generation Plant

.2. Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side U

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario C (see table 6 for description of scenario) 0 Production well-Completed in the lower Dublin aquifer in which pumping was adjusted for scenario Figure 27. Simulated water-level change for Scenario C in the lower Dublin aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

40 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey 0 5 10MILES 1:24,000-scale digital data i I I I 0 5 10 KILOMETERS EXPLANATION t:? Vogtle Electric Generation Plant D Pen Branch Fault-Approximately located; 0, downthrown side; U, upthrown side U

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

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario C (see table 6 for description of scenario)

Production well-Completed in the upper Midville aquifer in which pumping was adjusted for scenario Figure 28. Simulated water-level change for Scenario C in the upper Midville aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

Simulation of Ground-Water Flow 41 Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data 0 5 10KILOMETERS EXPLANATION Up Vogtle Electric Generation Plant a) Pen Branch Fault-Approximately located; D, downthrown side; U, upthrown side u

-1 Line of equal simulated water-level change-Interval, in feet, is variable.

Computed by subtracting the simulated potentiometric surface for 2002 Base Case from the simulated potentiometric surface for Scenario C (see table 6 for description of scenario) 0 Production well-Completed in the lower Midville aquifer in which pumping was adjusted for scenario Figure 29. Simulated water-level change for Scenario C in the lower Midville aquifer, near Vogtle Electric Generation Plant, Georgia and South Carolina.

42 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios Base modified from U.S. Geological Survey 0 5 10 MILES 1:24,000-scale digital data i I I I ]

0 5 10 KILOMETERS EXPLANATION U Vogtle Electric Generation Plant Model boundary Pen Branch Fault-Approximately located; D,downthrown side; U,upthrown side U

Simulated ground-water flowpath-Particles placed at the center of each of the three grid cells containing a Plant Vogtle production well at increments representing 10 percent of the aquifer thickness (10 total particles per aquifer layer per cell). Five particle flowpaths for each layer are shown on map to avoid clutter Lower Dublin aquifer Upper Midville aquifer Lower Midville aquifer Figure 30. Particle-tracking results for the year 2002, Scenario C, near Vogtle Electric Generation Plant, Georgia and South Carolina.

Summary and Conclusions 43 Model Limitations Particle tracking using MODPATH is controlled largely by lateral and vertical head gradients, along with the hydraulic The steady-state simulations presented herein are properties of the aquifers and confining units. In the VEGP believed to depict reasonably changes in ground-water levels area, data on the vertical hydraulic conductivity of aquifers, that resulted from pumping increases of 1.09 to 3.42 Mgal/d streambeds, and confining units are sparse. An additional at VEGP and from a pumping decrease of 5.3 Mgal/d at SRS, limitation of particle tracking using MODPATHis the inability which together represent less than I percent of the total simu- to determine whether a particle of water exits the flow system lated ground-water flow of 1,035 Mgal/d for 2002 (Cherry, in a model cell containing a weak sink. A weak sink can be 2006). Because these pumping changes are of low magnitude described as a discharge well that does not remove all the and occur near the center of the simulated area, lateral bound- water entering a cell, so that some water continues to move aries generally have little influence on simulation results. through the system. Finally, the no-flow boundary condi-An exception occurs for Scenario C in which drawdown in tion along the southwestern boundary of the model limits the the upper and lower Midville aquifers extends to the model's available area for a simulated flowpath. This limitation may southwestern "no-flow" boundary. Simulated drawdown that have resulted in faster simulated time of travel in the lower reaches a no-flow boundary results in higher Values than Dublin aquifer for Scenario C than might have occurred if the would occur if the boundary was not intercepted. Steady-state no-flow boundary was located farther away from the pumping simulations are believed to be representative of local hydro- at VEGP.

logic conditions because response to changes in pumpage is short term and previous testing indicates the model is insensitive to changes in storage (Clarke and West, 1998).

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

Summary and Conclusions used for this investigation is based on a drought period (2002) An updated and calibrated MODFLOW ground-water in which boundary head was lowered to reflect decreased flow model (Cherry, 2006) was used to simulate the effect of recharge to the ground-water system. It is likely that boundary current and potential future pumping on ground-water levels conditions reflecting average or wet periods would result in and flowpaths near Vogtle Electric Generation Plant (VEGP),

somewhat different patterns of water-level change than were Ga., for a Base Case representing year 2002 conditions and simulated for this study. Despite these possible variations, it is three pumping scenarios:

likely that ground-water flowpaths and recharge areas would Scenario A simulates a 1.09-million gallons per day be largely the same. (Mgal/d) increase in pumping at VEGP assuming average The ground-water flow model used in this study is subject withdrawal rates with the operation of existing reactors to the limitations described in Cherry (2006). These limita- (Units I and 2) and the proposed new reactors (Units 3 and 4).

tions include error and uncertainty in field measurements of Scenario B simulates a 1.09-Mgal/d increase in pumping water level and in estimates of pumping, limitations of the at VEGP, as was simulated in Scenario A, combined with a conceptual models, approximations made in representing the shutdown of the SRS facility (reduction of 5.3 Mgal/d).

physical properties of the flow system and errors inherent in Scenario C simulates a 3.42-Mgal/d increase in pump-estimating the spatial distribution of these properties, approxi- ing at VEGP that represents a higher rate of withdrawal for mations made in the formulation and application of model the proposed new reactor units during their startup period boundary and initial conditions, errors associated with numeri- (3.42 Mgal/d), and continuation of year 2002 pumping rates cal approximation and solution of the mathematical model of (1.04 Mgal/d) in the existing-reactor units.

the flow system, and assumptions made in using the models to Maximum water-level change resulting from increased predict the future behavior Of the flow system. pumping at VEGP (without changes at Savannah River Site In some local areas near the Pen Branch Fault, simulated (SRS) or elsewhere in the study area) were simulated in the water leyels poorly, matched observed water levels in the pumped layers at VEGP-the lower Dublin and upper and Gordon aquifer (layer A2). Near the P- 19 well cluster site on lower Midville aquifers. Simulated maximum declines in these SRS, and in the Savannah River alluvial valley near VEGP, units were from I to greater than 2 feet (ft) for Scenario A and simulated head was consistently lower than the observed head. from 4 to greater than 8 ft for Scenario C. Although none of The reasons for this mismatch are unknown; however, a local- the VEGP wells are completed in the upper Dublin aquifer, ized hydraulic connection between layers A l (Upper Three simulated water-level changes were similar to those observed Runs) and A2 (Gordon) near the Pen Branch Fault on SRS has in the pumped lower Dublin aquifer, suggesting a large degree been suggested by previous investigators (Aadland and others, of interconnection between the two aquifers. A muted water-1991). Because the reason for the high water level in the level decline from 0.25 to greater than 2 ft was simulated in Gordon aquifer was not substantiated by field investigations, the shallow Gordon and Millers Pond aquifers for Scenarios it was decided by previous investigators (Clarke and West, A and C as the result of leakage through confining units in 1998) not to account for this effect in the calibration of the response to decreased head in the production zones (lower ground-water flow model. Dublin and Lipper and lower Midville aquifers).

44 Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios The largest simulated water-level changes at VEGP were Arnett, M.W., and Mamatey, A.R., eds.,1996, Savannah River for Scenario C, which represents a tripling of current pump- Site environmental report for 1995: Prepared for U.S.

age at the facility. Although such pumping rates are viewed as Department of Energy by Westinghouse Savannah River implausible for long-term operation of proposed Units 3 and 4, Company, Aiken, S.C., WSRC-TR-96-0075, 271 p.

and are not proposed by Southern Nuclear Company, the sce-nario is designed to simulate pumping rates necessary to draw Cherry, G.S., 2003, Precipitation, ground-water use, and ground water from South Carolina to the VEGP production ground-water levels in the vicinity of the Savannah River wells. For this scenario, drawdown was greater than 8 ft in the Site, Georgia and South Carolina, 1992-2002, in Hatcher, K.J., ed., Proceedings of the 2003 Georgia Water Resources upper and lower Midville aquifers, and greater than 4 ft in the upper and lower Dublin aquifers. Drawdown exceeding 0.5 ft Conference, April 23-24, 2003: Athens, Ga., The Univer-in these aquifers extended about 29 miles (mi) to the south- sity of Georgia, Institute of Ecology, CD-ROM, online at western model boundary in Jenkins and Screven Counties, http://ga.water,usgs.gov/pubs/other/gwrc2003/pdf Ga., and about 14 mi eastward onto SRS in South Carolina.

For Scenario B, elimination of pumping at SRS resulted Cherry, G.S., 2006, Simulation and particle-tracking analysis of ground-water flow near the Savannah River Site, Georgia in large water-level changes near SRS, with rises of greater and South Carolina, 2002, and for selected water-manage-than 8 ft in the lower Dublin aquifer and greater than 4 ft in the upper Dublin and upper and lower Midville aquifers. At ment scenarios, 2002 and 2020: U.S. Geological Survey Scientific Investigations Report 2006-5195, 156 p., Web-VEGP, the magnitude and extent of water-level decline result-ing from increased pumping was less than in Scenario A with only publication at http://pubs.usgs.gov/sir/2006/51951.

maximum declines of greater than 2 ft in the upper and lower Chowns, T.M., and Williams, C.T., 1983, Pre-Cretaceous Midville aquifers, greater than 1 ft in the lower Dublin aquifer, rocks beneath the Georgia Coastal Plain-Regional and greater than 0.5 ft in the upper Dublin aquifer. The water- implications, in Gohn, G.S., ed., Studies related to the level rise resulting from elimination of SRS pumping reduced Charleston, South Carolina earthquake of 1886-Tectonics the effect of pumping at VEGP on ground-water levels. and seismicity: U.S. Geological Survey Professional Results of MODFLOW simulations were analyzed using Paper 1313-L, p. LI-L42, online at http://pubs.er.usgs.

the USGS particle-tracking code MODPATH (Pollock, 1994) gov/usgspubs/pp/ppl313 to determine the source of water and associated time of travel to VEGP production wells. For each of the scenarios, most of Christensen, E.J., and Gordon, D.E., 1983, Technical the recharge to VEGP wells originated in an upland area near summary of groundwater quality protection program at the county line between Burke and Jefferson Counties, Ga., Savannah River Plant-Volume 1, site geohydrology and with none of the recharge originating on SRS or elsewhere in solid and hazardous wastes: E.I. du Pond de Nemours and South Carolina. An exception occurs for Scenario C, in which Company, Savannah River Laboratory, Aiken, S.C., pre-some of the recharge originates in an upland area in eastern pared for the U.S. Department of Energy under contract Barnwell County, S.C. Simulated mean time of travel from DE-AC09-76SR00001, variously paged.

recharge areas to the VEGP wells for theBase Case and the three scenarios was between about 2,700 and 3,800 years, Clark, W.Z., and Zisa,A.C., 1976, Physiographic map of Georgia: Georgia Geologic Survey, I sheet, with some variation related to changes in head gradients due to pumping changes. scale 1:2,000,000.

Clarke, J.S., Brooks, Rebekah, and Faye, R.E., 1985, Hydro-.

geology of the Dublin and Midville aquifer systems of east References Cited central Georgia: Georgia Geologic Survey Information Circular 74, 62 p.

Aadland, R.K., Gellici, J.A., and Thayer, Paul, 1995, Hydrogeologic framework of west-central South Carolina: Clarke, J.S., and West, C.T., 1997, Ground-water levels, prede-South Carolina Department of Natural Resources, Water Velopment ground-water flow, and stream-aquifer relations Resources Division Report 5, 200 p. in the vicinity of the Savannah River Site, Georgia and South Carolina: U.S. Geological Survey Water-Resources Aadland, R.K., Harris, M.K., Lewis, C.M., Gaughan, T.F., and Investigations Report 97-4197, 120 p., 1 plate, online at Westbrook, T.M., 1991, Hydrostratigraphy of the general http://pubs.usgs.gov/wri/wri97-4197/.

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

Aiken, S.C., U.S. Department of Energy Report WSRC- Clarke, J.S., and West, C.T., 1998, Simulation of ground-water RP-91-13, Westinghouse Savannah River Company, 114 p. flow and stream-aquifer relations in the vicinity of the Savannah River Site, Georgia and South Carolina, prede-Atkins, J.B., Journey, C.A., and Clarke, J.S., 1996, Estimation velopment through 1992: U.S. Geological Survey Water-of ground-water discharge to streams in the central Savannah Resources Investigations Report 98-4062, 134 p., online at River basin of Georgia and South Carolina: U.S. Geological http://pubs.usgs.gov/wri/wri98-4062/.

Survey Water Resources Investigations Report 96-4179, 46 p.

References Cited. 45 Falls, W.F., Baum, J.S., Harrelson, L.G., Brown, L.H., and Pollock, D.W., 1994, Users Guide for MODPATH/MOD-Jerden, J.L., Jr., 1997, Geology and hydrogeology of PATH-PLOT, Version 3-A particle tracking post-process-Cretaceous and Tertiary strata, and confinement in the ing package for MODFLOW, the U.S. Geological Survey vicinity of the U.S. Department of Energy Savannah River finite-difference ground-water flow model: U.S. Geological Site, South Carolina and Georgia: U.S. Geological Survey Survey Open-File Report 94-464, 248 p., online at Water-Resources Investigations Report 97-4245, 125 p., http://pubs.er usgs.gov/usgspubs/ofr/ofr94464 onliný at http.//pubs.er usgs.gov/usgspubs/wri/wri974245 Price, Van, Fallaw, W.C., and McKinney, J.B., 1991, Geologic Fanning, J.L., 1997, Water use in Georgia by county for 1995: setting of the new production reactor within the Savannah Georgia Geologic Survey Information Circular 101, 95 p. River Site (U): Westinghouse Savannah River Company, report no. WSRC-RP-91-96, ESH-EMS-90171, 80 p.

Fanning, J.L., 2003, Water use in Georgia by county for 2000 and water-use trends for 1980-2000: Georgia Geologic Prowell, D.C., 1994, Preliminary geologic map of the Survey Information Circular 106, 176 p., online at http:// Barnwell 30 min x 60 min quadrangle, South Carolina and ga.waterusgs.gov/pubs/other/ggs-icl06/. Georgia: U.S. Geological Survey Open-File Report 94-673, 38 p., 1 plate, scale 1:100,000, online at http://pubs.erusgs.

Faye, R.E., and Mayer, G.C., 1990, Ground-water flow and gov/usgspubs/ofr/ofr94673 stream-aquifer relations in the northern Coastal Plain of Georgia and adjacent parts of Alabama and South Carolina: Prowell, D.C., and O'Connor, B.J., 1978, Belair fault zone-U.S. Geological Water-Resources Investigations Report 88- Evidence of Tertiary fault displacement in eastern Georgia:

4143, 83 p., online at http://pubs.erusgs.gov/usgspubs/wri/ Geology, v. 6, p. 681-684.

wri884143 Siple, G.E., 1960, Piezometric levels in the Cretaceous sand Harbaugh, AW., Banta, E.R., Hill, M.C., and McDonald, M.G., aquifer of the Savannah River Basin: Georgia Mineral 2000, MODFLOW-2000, The U.S. Geological Survey Newsletter, v. 8, no. 4, winter 1960, p. 163-166.

modular ground-water model-User guide to modularization Siple, G;E., 1967, Geology and ground water of the Savannah concepts and the ground-water flow process: U.S. Geologi-River Plant and vicinity, South Carolina: U.S. Geological cal Survey Open-File Report 00-92, 121 p., online at http.//

Survey Water-Supply Paper 1841, 113 p., online at water usgs.gov/nrp/gwsoftware/modflow2000/ofrOO-92.pdf http://pubs.er usgs.gov/usgspubs/wsp/wsp1841 Harrelson, L.E., Falls, W.F., and Clarke, J.S., 1997, Selected Snipes, D.S., Fallaw, W.C., Price, Van, Jr., and Cumbest, R.J.,

well data in the vicinity of the Savannah River Site, South 1993, The Pen Branch Fault-Documentation of Late Carolina and Georgia: U.S. Geological Survey Open-File Report 97-657A, 215 p., 10 plates, online at http://pubs. Cretaceous-Tertiary faulting in the Coastal Plain of South er usgs.gov/usgspubs/ofr/ofr96657A Carolina: Southeastern Geology, v. 33, no. 4, October 1993,

p. 195-218.

Lonon, G.E., Burnette, C.B., and Morris, H.J., 1983, Water use in South Carolina, 1980: South Carolina Water Resources Summerour, J.H., Shapiro, E.A., and Huddlestun, RE, 1998, Commission Report 138, 20 p. An investigation of Tritium in the Gordon and other aquifers in Burke County, Georgia, Phase II-Final report: Georgia McDonald, M.G., and Harbaugh, A.W., 1988, A modular Geologic Survey Information Circular 102, 72 p.

finite-difference ground-water flow model: U.S. Geologi-cal Survey Techniques of Water-Resources Investigations Waddell, M.G., Keith,J.F., and Domoarcki, W.J., 1995, High report, book 6, chap. Al, variously paged, online at http:// resolution seismic characterization GGS-1, Burke County, pubs. erusgs.gov/usgspubs/twri/twriO6A1 Ga.: University of South Carolina Project Report to Georgia Geologic Survey, ESRI Technical Report 95-F129-1, 20 p.

Miller, J.A., 1986, Hydrogeologic framework of the Floridan aquifer system in Florida and in parts of Georgia, Alabama, Wait, R.L., and Davis, M.E., 1986, Configuration and hydrol and South Carolina: U.S. Geological Survey Professional ogy of the pre-Cretaceous rocks underlying the southeast Paper 1403-B, 91 p., online at http.//pubs.erusgs.gov/ ern Coastal Plain aquifer system: U.S. Geological Survey usgspubs/pp/ppJ403B Water-Resources Investigations Report 86-4010, 1 sheet, scale 1:2,000,000, online at http://pubs.erusgs.gov/

Pierce, R.R., Barber, N.L., and Stiles, H.R., 1982, Water use usgspubs/wri/wri864010 in Georgia by county forl980: Georgia Geologic Survey Information Circular 59, 180 p. Washington Savannah River Company, 2007, Semi-annual 2007 M-Area and metallurgical laboratory hazardous waste management facilities groundwater monitoring and corrective action report (U), volume 1: Aiken, S.C.,

U.S. Department of Energy Report WSRC-RP-2007-4039, prepared for the U.S. Department of Energy under contract no. DE-AC09-96-SR18500, variously paged.

Manuscript approved for publication, October 23, 2007 Prepared by USGS Georgia Water Science Center Edited and page layout by Patricia L.Nobles Graphics by Bonnie J. Turcott For more information concerning the research in this report, contact USGS Georgia Water Science Center, Atlanta, telephone: 770-903-9100

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