U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the Brunswick/Glynn County

Joint Water and Sewer Commission

Groundwater Flow in the Brunswick/Glynn County Area, 

Georgia, 2000–04

Scientific Investigations Report 2015–5061
Cover. East River docks, Brunswick, Glynn County, Georgia (photograph by Alan M. Cressler, USGS).
Groundwater Flow in the Brunswick/Glynn County Area, 

Georgia, 2000–04

By Gregory S. Cherry

Prepared in cooperation with the Brunswick/Glynn County 

Joint Water and Sewer Commission

Scientific Investigations Report 2015–5061

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:

Cherry, G.S., 2015, Groundwater flow in the Brunswick/Glynn County area, Georgia, 2000–04: U.S. Geological Survey 

Scientific Investigations Report 2015–5061, 88 p., http://dx.doi.org/10.3133/sir20155061.

ISSN 2328–0328 (online)
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................2

Description of Study Area ...................................................................................................................2

Previous Investigations........................................................................................................................3

Methods of Study..................................................................................................................................3

Georgia Well-Identification System...................................................................................................3

Hydrogeologic Setting...................................................................................................................................6

Surficial Aquifer System......................................................................................................................7

Brunswick Aquifer System..................................................................................................................7

Floridan Aquifer System.......................................................................................................................7

Conceptualization of Groundwater Flow ........................................................................................10

Chloride Contamination in the Brunswick Area ............................................................................10

Groundwater Use and Water Levels, 2000–04 ........................................................................................12

Groundwater Use................................................................................................................................12

Groundwater Levels ...........................................................................................................................18

Simulation of Steady-State Groundwater Flow, 2000–04 ......................................................................23

Revision of Groundwater-Flow Model.............................................................................................23

Discretization..............................................................................................................................23

Model Layers..............................................................................................................................23

Hydraulic Properties .................................................................................................................30

Boundary Conditions.................................................................................................................34

Vertical Boundaries..........................................................................................................34

Lateral Boundaries ...........................................................................................................34

Groundwater Withdrawals.......................................................................................................35

Model Calibration ......................................................................................................................35

Acceptance Criteria .........................................................................................................45

Year 2000 Calibration........................................................................................................48

Year 2004 Calibration........................................................................................................53

Simulated Potentiometric Surfaces.................................................................................................58

2000 Conditions...........................................................................................................................58

2004 Conditions...........................................................................................................................58

Simulated Water-Level Changes, 2000–04.............................................................................58

Simulated Potentiometric Profiles ..........................................................................................63

Simulated Water Budget ..........................................................................................................67

Model Sensitivity..........................................................................................................................................72

Model Limitations.........................................................................................................................................72

Summary........................................................................................................................................................75

Selected References...................................................................................................................................76

Appendix 1. Simulated and Observed Groundwater Levels, 2000 and 2004 .....................................80

Appendix 2. Location of Wells Used for 2000 and 2004 Simulations ..................................................86
iv

Figures

1. Maps showing location of 24-county coastal Georgia area, model area, major 

structural features, and 250-milligram-per-liter chloride concentration isochlor

for June 2001 and 2005 near Brunswick, Georgia...................................................................4

2. Generalized correlation chart of geologic and hydrogeologic units and

model layers ..................................................................................................................................6

3. Schematic cross sections showing conceptual models of predevelopment

(pre-1880s) and modern-day groundwater flow in the Floridan aquifer system

from the outcrop area in the northwest to the offshore area in the southeast, 

coastal Georgia.............................................................................................................................9

4. Map showing chloride concentrations in the Upper Floridan aquifer near 

the downtown Brunswick area, August 2007, and graphs showing chloride

concentration in water for selected wells in the northern and southern 

Brunswick area, 1964–2007.......................................................................................................11

5. Graphs showing estimated groundwater pumpage from the Upper and 

Lower Floridan aquifers in the model area, and Upper Floridan aquifer in 

the Glynn County area, 1980–2004...........................................................................................12

6. Graphs showing selected water-level hydrographs for the surficial aquifer, 

upper Brunswick aquifer, lower Brunswick aquifer, Upper Floridan aquifer 

upper water-bearing zone, Upper Floridan aquifer lower water-bearing zone,

Lower Floridan aquifer, and Lower Floridan aquifer Fernandina permeable zone,

in the Brunswick/Glynn County, Georgia area, 2000–04.......................................................19

7. Maps showing revised model grid, major production wells, observation wells

used during June of 2004, and outline of the 2004 chloride plume for the 

Upper Floridan aquifer in the Brunswick area.......................................................................24

8. Schematic diagram showing model layers and boundary conditions ..............................26

9. Hydrogeologic sections showing vertical discretization of hydrogeologic units

simulated by the revised model................................................................................................27

10. Maps showing hydraulic property zones for the regional model near

Brunswick/Glynn County, Georgia...........................................................................................31

11. Maps showing distribution of groundwater pumpage for 2000 for model layer 3, 

upper Brunswick aquifer; model layer 5, lower Brunswick aquifer; model layer 7,

Upper Floridan aquifer upper water-bearing zone; model layer 9, Upper Floridan

aquifer lower water-bearing zone; and model layer 11, Lower Floridan aquifer.............36

12. Maps showing distribution of groundwater pumpage for 2004 for model layer 3, 

upper Brunswick aquifer; model layer 5, lower Brunswick aquifer; model layer 7,

Upper Floridan aquifer upper water-bearing zone; model layer 9, Upper Floridan

aquifer lower water-bearing zone; and model layer 11, Lower Floridan aquifer.............41

13. Boxplots showing difference (residuals) between simulated and observed heads

for 2000 simulation in the regional model area and Brunswick/Glynn County area........48

14. Maps showing simulated 2000 potentiometric surfaces and water-level residuals

by model layer: layer 3, upper Brunswick aquifer, model area; layer 5, lower 

Brunswick aquifer, model area; layer 7, upper water-bearing zone of the Upper 

Floridan aquifer, model area; layer 9, lower water-bearing zone of the Upper 

Floridan aquifer; layer 7, upper water-bearing zone of the Upper Floridan aquifer,

Glynn County and Brunswick area enlargement; layer 9, lower water-bearing zone

of the Upper Floridan aquifer; and layer 11, Lower Floridan aquifer, model area

and Glynn County enlargement................................................................................................49
v

15. Boxplots showing difference (residuals) between simulated and observed heads

for 2004 simulation in the regional model area, and Brunswick/Glynn County area.......53

16. Maps showing simulated 2004 potentiometric surfaces and water-level residuals

by model layer: layer 3, upper Brunswick aquifer, model area; layer 5, lower 

Brunswick aquifer, model area; layer 7, upper water-bearing zone of the Upper 

Floridan aquifer, model area; layer 9, lower water-bearing zone of the Upper 

Floridan aquifer; layer 7, upper water-bearing zone of the Upper Floridan aquifer,

Glynn County and Brunswick area enlargement; layer 9, lower water-bearing zone

of the Upper Floridan aquifer; and layer 11, Lower Floridan aquifer, model area

and Glynn County enlargement................................................................................................54

17. Hydrographs showing selected water-levels and simulated heads for upper

Brunswick aquifer, Upper Floridan aquifer upper water-bearing zone, Upper 

Floridan aquifer lower water-bearing zone, Lower Floridan aquifer, and Lower 

Floridan aquifer Fernandina permeable zone, Glynn County, Georgia, 2000–2004..........59

18. Maps showing simulated water-level change from 2000 to 2004 for, model layer 3, 

upper Brunswick aquifer, model layer 5, lower Brunswick aquifer, upper waterbearing zone of Upper Floridan aquifer, lower water-bearing zone of Upper 

Floridan aquifer, and Lower Floridan aquifer.........................................................................60

19. Graphs showing simulated and observed potentiometric profiles near

chloride plume during 2000 .......................................................................................................64

20. Graphs showing simulated and observed potentiometric profiles near

chloride plume during 2004 .......................................................................................................65

21. Schematic diagram showing simulated water budget for regional model during

2000 and 2004, and water budgets in Glynn County during 2000 and 2004........................70

22. Graph showing composite-scaled sensitivity of selected model parameters.................73

2–1. Maps showing location of wells used for 2000 and 2004 simulations in 

study area; McIntosh, Glynn, and Camden Counties; and Brunswick...............................86

Tables

1. Estimated groundwater pumpage from the Upper and Lower Floridan aquifers

in the coastal area of Georgia and adjacent parts of South Carolina and Florida, 

1980 –2004 ....................................................................................................................................14

2. Water-level measurements taken during 2000 and 2004 and observed water-level 

change during the same period ...............................................................................................20

3. Water-level measurements taken during 2000 and 2004 and observed water-level 

change during the same period in the Brunswick/Glynn County area..............................22

4. Horizontal and vertical hydraulic conductivity values assigned to hydraulic

property zones for the original and revised groundwater-flow models............................28

5. Calibration statistics for simulated heads for 2000 conditions ...........................................46

6. Calibration statistics for simulated heads for 2004 conditions ...........................................47

7. Simulated and observed groundwater levels for 2000, and residuals in wells 

used to construct profiles in the Brunswick area.................................................................63

8. Simulated and observed groundwater levels for 2004, and residuals in wells 

used to construct profiles in the Brunswick area.................................................................66

9. Flow-budget components for 2000 and 2004 for entire model area...................................68

10. Flow-budget components for 2000 and 2004 in the Brunswick/Glynn County area ........69

1–1. Simulated and observed groundwater levels, 2000 and 2004 .............................................80
vi

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

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

)

Flow rate

inch per year 25.4 millimeter per year

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

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

/s)

Hydraulic conductivity

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

Transmissivity*

foot squared per day (ft2

/d) 0.0929 meter squared per day (m2/d) 

Potentiometric gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F –32)/ 1.8
vii

Supplemental Information

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

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L). 

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

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

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

Abbreviations

GaEPD Georgia Environmental Protection Division

JWSC Joint Water and Sewer Commission

LFA Lower Floridan aquifer

LWBZ lower water-bearing zone

NWIS National Water Information System 

RMSE root mean square error

SCDHEC South Carolina Department of Health and Environmental Control

UFA Upper Floridan aquifer

USGS U.S. Geological Survey

UWBZ upper water-bearing zone

WRMAC Water Resources Management Advisory Committee
viii

Acknowledgments

The author extends thanks to Keith Morgan and Billy Simmons of the Brunswick/Glynn 

County Joint Water and Sewer Commission and to James Kennedy, State Geologist, Georgia 

Environmental Protection Division (GaEPD), for support of ongoing water-resources investigations in the Brunswick/Glynn County area. During early stages of model development, members 

of the Brunswick/Glynn County Water Resources Management Advisory Committee (WRMAC) 

provided technical guidance, including development of water-management scenarios for 

evaluation by the revised model. WRMAC members were, Bobby Palmer, Chair, private citizen; 

Glenn Hoffman, Vice Chair, Hercules-Pinova Inc.; Dan McFee, City of Brunswick; Keith Morgan, 

Brunswick/Glynn County Joint Sewer and Water Commission; John Day, Jekyll Island 

Authority; Kenneth Hase, GP-Cellulose; Jim Benson, private citizen; William Francis, private 

citizen; Dick Johnston, private citizen; Hal Hart, private citizen; David Kyler, private citizen; and 

Milton Peterman, private citizen.

Special thanks are extended to Dorothy Payne of the USGS for her assistance with preliminary simulations and compilation of pumping data for 2004. Thanks are also extended to 

Alan Cressler and Welby Stayton, USGS, who collected water-level data during the June 2004 

synoptic survey, and to Jaime Painter, USGS, who provided assistance in the development of 

model input and display of model results using geographic information system techniques. 

Elliott Jones and Michael Peck, USGS, provided valuable unpublished data in the Brunswick/

Glynn County area and access to the archive of acoustic televiewer images taken from TW-26 

on Colonels Island and other test holes in the Brunswick area.
Groundwater Flow in the Brunswick/Glynn County Area, 

Georgia, 2000–04

By Gregory S. Cherry 

Abstract

An existing regional steady-state model for coastal 

Georgia, and parts of South Carolina and Florida, was revised 

to evaluate the local effects of pumping on the migration of 

high chloride (saline) water in the Upper Floridan aquifer 

located in the Brunswick/Glynn County, Georgia (Ga.) area. 

Revisions were focused on enhancing the horizontal and 

vertical resolution of the regional model grid in the vicinity of 

saline water. Modifications to the regional model consisted of 

(1) limiting grid size to a maximum of 500 feet (ft) per side 

in the vicinity of chloride contamination; (2) representing 

the upper and lower Brunswick aquifers with distinct model 

layers; (3) similarly, representing upper and lower waterbearing zones of the Upper Floridan aquifer with distinct 

model layers in Glynn and Camden Counties, Ga.; and 

(4) establishing new hydraulic-property zones in the Upper 

Floridan aquifer. The revised model simulated steady-state 

conditions that were assumed to exist during 2000 and 2004.

Calibration of the revised steady-state model using 

pumping rates from 2000 indicates a “good” match (±10 ft) 

based on 181 observations, with median residuals (simulated 

minus observed water levels) in each of the active model 

layers ranging from –8.62 to 4.67 ft, and root mean square 

error (RMSE) ranging from 10.9 to 11.4 ft. In the Brunswick/

Glynn County area, groundwater-level residuals in the upper 

water-bearing zone of the Upper Floridan aquifer (layer 7) 

indicate an “excellent” match (±5 ft) based on 41 observations 

with a median residual of –0.35 ft and RMSE of 4.32 ft. 

Calibration of the revised steady-state model using 2004 

pumping rates and adjusted specified-head input values in the 

Floridan aquifer system indicates a “good” match (±10 ft) 

based on 88 observations, with median residuals in each of 

the active model layers ranging from –6.31 to –2.05 ft, and 

RMSE ranging from –6.95 to 14.5 ft. In the Brunswick/Glynn 

County area, groundwater-level residuals in the upper waterbearing zone of the Upper Floridan aquifer (layer 7) indicate 

an “excellent” match (±5 ft) based on 32 observations with a 

median residual of –1.50 ft and RMSE of 5.34 ft. 

Simulated potentiometric surfaces for 2000 and 2004 

indicate coastward groundwater flow in the Upper and Lower 

Floridan aquifers influenced by pumping centers at Savannah, 

Jesup, and Brunswick, Ga., and indicate steep potentiometric 

gradients to the west and north of the Gulf Trough. In the 

Brunswick/Glynn County area, simulated industrial production 

wells located north of downtown Brunswick intercept local 

groundwater flow in the upper and lower water-bearing zones of 

the Upper Floridan aquifer and have created a cone of depression that locally alters the regional coastward flow direction. 

Maps of simulated water-level change during the 

2000–04 period show differences in groundwater levels in the 

Upper Floridan aquifer that range from −2.5 ft to more than 

5 ft in areas of coastal Georgia, and more than 20 ft near the 

Georgia-Florida State Line. Positive values indicate higher 

simulated water levels during 2004 than during 2000, which 

were caused by reduced pumping in the Upper Floridan 

aquifer prompted by the shutdown of a paper mill near the 

southern model boundary in 2002 and increased recharge 

following a prolonged drought during 1998–2002. 

Simulated potentiometric profiles for 2000 and 2004 

were used to evaluate the potentiometric gradients in the upper 

water-bearing zone of the Upper Floridan aquifer (layer 7) 

near the chloride plume in the downtown Brunswick area. 

Four potentiometric profiles were constructed for 2000 to 

compare the simulated and observed water levels in 13 wells 

and were oriented outward from a primary well field. The 

simulated potentiometric gradients from the four profiles for 

2000 ranged from 3.6 to 5.2 feet per mile (ft/mi) compared 

to observed values ranging from 4.1 to 5.6 ft/mi. The five 

potentiometric profiles constructed for 2004 allowed for a 

similar comparison using simulated and observed water levels 

in 18 wells. The simulated potentiometric gradients from the 

five profiles for 2000 ranged from 3.6 to 11.1 ft/mi compared 

to observed values ranging from 3.8 to 10.2 ft/mi. Simulated 

potentiometric gradients were higher for 2004 than for 2000 

because of the inclusion of a well located within the cone of 

depression near downtown Brunswick.

Composite-scaled sensitivities of the model parameters 

indicate the revised model is most sensitive to pumping rates, 

followed by the horizontal hydraulic conductivity in the Upper 

Floridan aquifer for zones along coastal Georgia. The revised 

model is least sensitive to the horizontal hydraulic conductivity of the confining units and vertical hydraulic conductivity 

of the aquifers. For parameters defined by hydraulic-property 
2 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

zones in the upper and lower water-bearing zones of the Upper 

Floridan aquifer, such as horizontal hydraulic conductivity, 

model sensitivity was not as great in the Brunswick/Glynn 

County area as other areas along coastal Georgia. The model 

exhibited more sensitivity to these parameters however, than 

to parameters representing the majority of zones defining the 

vertical hydraulic conductivity of the confining units, which 

originally were assumed to govern upward migration of 

chloride contamination into this aquifer.

Analysis of simulated water-budget components for 2000 

and 2004 indicate that specified-head boundaries in the Floridan 

aquifer system to the south and southwest of the regional 

model area control about 70 percent of inflows and nearly 

50 percent of outflows to the model region. Other water budget 

components indicate an 80-million-gallon-per-day decrease in 

pumping from the Floridan aquifer system during this period. 

Introduction

In the Brunswick/Glynn County, Georgia (Ga.) area, 

saltwater intrusion has been contaminating the Upper Floridan 

aquifer (UFA) for more than 50 years. Presently (2014), within 

an area covering several square miles of downtown Brunswick, 

the aquifer yields water that has a chloride concentration 

greater than 2,000 milligrams per liter (mg/L), well above the 

250-mg/L State and Federal secondary drinking-water standard (Georgia Environmental Protection Division, 1997; U.S. 

Environmental Protection Agency, 2000). Saltwater contamination has constrained further development of the UFA in the 

Brunswick area, prompting interest in the development of 

alternative sources of water supply, primarily from the shallower surficial and Brunswick aquifer systems. Further development of the UFA is limited to areas outside of the chloride 

plume and will be performed in a way that will minimize 

migration of groundwater with high-chloride concentrations 

and maintain hydraulic-head gradients toward active pumping 

centers in the area. The U.S. Geological Survey (USGS), in 

cooperation with the Brunswick/Glynn County Joint Water and 

Sewer Commission (JWSC) and the Georgia Environmental 

Protection Division (GaEPD), revised an existing groundwater 

model to investigate the effects of pumping on the migration 

of high-chloride water in the Brunswick/Glynn County area, 

thereby providing scientific information essential for managing 

water resources along the Georgia coast.

In this investigation, the horizontal and vertical resolutions 

of an existing regional groundwater-flow model (Payne and 

others, 2005) were increased to more accurately simulate the 

effects of pumping in the vicinity of the chloride plume near 

downtown Brunswick. The existing regional model, hereafter 

referred to as the original model, was modified by (1) reducing 

grid dimensions to a maximum of 500 feet (ft) per side in the 

vicinity of the chloride plume; (2) subdividing the Brunswick 

aquifer system into the upper and lower Brunswick aquifers; 

(3) subdividing the UFA into the upper and lower water-bearing 

zones (UWBZ and LWBZ, respectively) in Glynn and Camden 

Counties; and (4) establishing new hydraulic property zones 

in the UFA to improve model calibration in the Brunswick/

Glynn County area. The revised model is intended to establish 

a framework for the Brunswick/Glynn County area that will 

allow future investigations to evaluate the long-term effects of 

selected pumping scenarios on groundwater levels and flow 

paths near areas of chloride contamination. 

Purpose and Scope

The purpose of this report is to document the simulation 

of groundwater flow in the Brunswick/Glynn County area of 

Georgia during 2000–04. The report describes revisions to a 

previously published application of the USGS modular finitedifference computer program (MODFLOW–2000; Harbaugh 

and others, 2000) developed by Payne and others (2005) to 

simulate regional groundwater flow along the Georgia coast in 

the Brunswick and Floridan aquifer systems during 2000 – 04. 

These revisions to the original model include (1) increased 

spatial resolution near the downtown Brunswick, Ga., area, 

(2) additional hydraulic-property zones in the UFA near 

Brunswick/Glynn County area, and (3) subdivision of the 

Brunswick aquifer system and Floridan aquifer system into 

separate model layers to represent the local hydrogeology. 

The purpose of the revised model is to simulate the longterm steady-state effect of changing mean-annual pumping 

during 2000 and 2004 on groundwater levels and evaluate 

changes in hydraulic gradients near pumping centers in the 

Brunswick area. Local hydraulic gradients control the direction 

and rate of chloride migration in the Floridan aquifer system. 

Steady-state simulation was considered appropriate given the 

regional groundwater-flow characteristics of the Floridan aquifer 

system and the years 2000 and 2004 were chosen because of 

available groundwater-level (see appendix 1) and pumpage data. 

To fully document the model revision process, this report 

describes (1) revisions to the original model, (2) the boundary 

conditions used, (3) the approach used to calibrate the revised 

model, (4) water budget calculations, and (5) the sensitivity 

analysis. Additional maps and tables of groundwater levels 

and residuals (simulated minus observed groundwater levels) 

are included in support of the calibration process, along with 

a section that describes limitations of the model analysis. 

Description of Study Area

Glynn County is located in the Coastal Plain physiographic 

province on Georgia’s Atlantic Coast about 80 miles (mi) 

south of Savannah, Ga., and about 87 mi north of Jacksonville, 

Florida (Fla.; fig. 1). Glynn County encompasses about 

422 square miles (mi2) and is bordered on the north by the 

Altamaha River, which empties into the Atlantic Ocean north 

of St. Simons Island. Altitudes in Glynn County range from 0 ft 

along the coast to 40 ft in the northwestern part of the county. 

The City of Brunswick is located on a peninsula in Glynn 

County and encompasses about 50 mi2. The city is bordered by 
Introduction 3

St. Simons and Jekyll Islands to the east and by the Brunswick 

and Little Satilla Rivers to the west and south, respectively 

(fig. 1). Both rivers form tidally influenced estuaries in the 

Brunswick area.

The population of Glynn County was 79,626 in 2010 (U.S. 

Census Bureau, 2010). The primary population center of Glynn 

County is the City of Brunswick, and a secondary population 

center has developed into an urbanized area on the southern part 

of St. Simons Island. Outside the urbanized areas near the City 

of Brunswick and St. Simons Island, land use in Glynn County 

is a mixture of forest, grazed woodland, marsh, and swampland. 

Glynn County has a climate classified as warm temperate 

and fully humid, with warm summers (Kottek and others, 

2006). The average temperature for the climate-normal period 

of 1981–2010 was 68.1 degrees Fahrenheit, based on data 

compiled at St. Simons Island, Ga. (National Oceanic and 

Atmospheric Administration, 2014). Mean-annual precipitation for the same period is 45.0 inches, with the heaviest 

rainfall occurring during the months of June, August, and 

September. Glynn County is located in the central subarea of 

the 24-county coastal area designated by the GaEPD, which 

subdivided the area into northern, southern, and central 

subareas to facilitate water management practices (fig. 1). 

Previous Investigations

Because this study uses a revised version of a previously developed model (Payne and others, 2005) to evaluate 

groundwater flow in the Brunswick/Glynn County area, the 

reader is referred to the original report for a complete list of 

the literature pertaining to hydrogeologic investigations for the 

regional model area. The publications listed here pertain to the 

Brunswick/Glynn County area.

Warren (1944) discussed the occurrence of brackish 

water in a city well at Brunswick and the possibility of 

saltwater encroachment in Glynn County. Wait (1962, 1965), 

Wait and Gregg (1973), and Gregg and Zimmerman (1974) 

documented the chloride contamination problem near downtown Brunswick, which included water-level and waterchemistry data. Krause and others (1984) identified wells in 

the Glynn County area that could be used to monitor chloride 

concentration and proposed sites for installation of additional 

monitor wells in the coastal area. Randolph and Krause (1990) 

developed a subregional groundwater model of Glynn County 

and the surrounding area that was linked to a regional model 

developed earlier (Krause and Randolph, 1989). Maslia and 

Prowell (1990) inferred major northeast-southwest-trending 

faults through the downtown Brunswick area based on structural analysis of geophysical data, northeastward elongation 

of the potentiometric surface of the UFA, and breaches in 

the local confining unit that influence the area of chloride 

contamination. As part of a regional evaluation of geology and 

groundwater resources, Clarke and others (1990) described 

water-bearing units in Miocene sediments in the Glynn County 

area. Jones and Maslia (1994) presented selected groundwaterlevel and water-quality data, and aquifer properties of the UFA 

for the Brunswick area. Clarke and Krause (2000) updated 

the subregional Brunswick/Glynn County model (Randolph 

and Krause, 1990) based on a comparison to other models 

developed in the area, and used the revised model to simulate a variety of water-management scenarios in the coastal 

area of Georgia. Jones and others (2002) presented evidence 

from 2,727-foot-deep test well 33H188 (TW-26) on Colonels 

Island, indicating localized faulting and dissolution within the 

Floridan aquifer system. Cherry (2007), Cherry and Clarke 

(2008), and Cherry and others (2010 and 2011) described 

changes in the chloride plume in the Brunswick area based 

on annual chloride sampling. 

Methods of Study

This study updates and refines an existing regional 

groundwater-flow model of coastal Georgia and adjacent parts 

of South Carolina and Florida (Payne and others, 2005) to 

enable locally detailed simulation of groundwater flow in areas 

exceeding the 250-mg/L State and Federal secondary drinkingwater standard for chloride near downtown Brunswick, Ga. 

(Georgia Environmental Protection Division, 1997; U.S. 

Environmental Protection Agency, 2000).

Information about groundwater withdrawals during 

2000–04 was compiled from the records of South Carolina 

Department of Health and Environmental Control (SCDHEC), 

GaEPD, and USGS, which were developed into model input. 

The existing model grid was refined to enhance resolution 

of simulated groundwater levels in the Brunswick/Glynn 

County area. Two active model layers were added, based on 

the local hydrogeology, to represent additional water-bearing 

units within the Brunswick aquifer system and UFA. Waterlevel data for 2004 were compiled for 88 wells distributed 

throughout coastal Georgia. These data, together with data 

collected from 181 wells during 2000 (Payne and others, 

2005), were used to calculate water-level residuals representing simulated minus observed water levels. 

Georgia Well-Identification System

Wells described in this report are assigned a well identifier 

according to a system based on the index of U.S. Geological 

Survey (USGS) 7.5-minute topographic maps of Georgia. Each 

map in Georgia has been assigned a two- to three-digit number 

and letter designation (for example, 07H) beginning at the 

southwestern corner of the State. Numbers increase sequentially eastward and letters advance alphabetically northward. 

Quadrangles in the northern part of the State are designated by 

double letters: AA follows Z, and so forth. The letters “I,” “O,” 

“II,” and “OO” are not used. Wells inventoried in each quadrangle are numbered consecutively, beginning with 001. Thus, 

the fourth well inventoried in the 34H quadrangle is designated 

34H004. In the USGS National Water Information System 

(NWIS) database, this information is stored in the “Station 

Name” field; in NWIS Web, it is labeled “Site Name.”
4 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

?

?

Model boundary

Brunswick

St Marys

Jacksonville

Fernandina Beach

Jesup

Waycross

Savannah

Valdosta

GEORGIA

GEORGIA

CAROLINA

SOUTH

FLORIDA

Port Royal Sound

GEORGIA

Map area

Northern

Central

Southern

24-county coastal Georgia

 area as identified by the

 Georgia Environmental

 Protection Division 

0 25 50 75 MILES

0 25 50 75 KILOMETERS

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

digital data. Structural features modified from

Applied Coastal Research Laboratory, 2002; 

Weems and Edwards, 2001; Kellam and Gorday, 

1990; and Paull and Dillon, 1980 

CAROLINA

Figure 1. 

Waynesboro

EXPLANATION

FLORIDA

ALABAMA

SOUTH

Aiken

Ware

Dixie

Taylor

Burke

Clay

Duval

Berkeley

Clinch

Alachua

Colleton

Putnam

Jasper

Baker

Wayne

Laurens

Sumter

Orangeburg

Madison

Worth

Richland

Coffee

Columbia

Nassau

Bulloch

Long

Emanuel

Charlton Camden

Dodge

Screven

Lexington

Tift

Bryan

Wilkes

Liberty

Irwin

Suwannee

Williamsburg

Jones

Appling

St Johns

Brooks

Bibb

Glynn

Dooly

Hampton

Clarendon

Colquitt

Mitchell

Telfair

Echols

Lowndes

Berrien

Barnwell

Washington

Jasper

Lafayette

Wilcox

Hamilton

Greene

Tattnall

Hancock

Crisp

Thomas

Pierce

Jefferson

Charleston

Twiggs

Brantley

Toombs

Edgefield

Putnam

Jenkins

Dorchester

Effingham

Chatham

Wilkinson

McIntosh

Calhoun

Jefferson

Cook

Bacon

Union

Morgan

Bamberg

Walton

Monroe

Houston

Allendale

Turner

Atkinson

Gilchrist

Mccormick

Warren

Johnson

Oglethorpe

Wheeler

Richmond

Baldwin

Pulaski

Newton

Jeff Davis

Columbia

Lincoln

Evans

Lanier

Ben Hill

Candler

Bradford

McDuffie

Georgetown

Oconee

Peach

Butts

Bleckley

Macon

Gwinnett

Treutlen

Crawford

Taylor

Montgomery

Taliaferro

Glascock

Lee

Rockdale

Sumter

Henry

Beaufort

84°

32°

33°

31°

30°

83° 82° 81° 80°

Gulf Trough

Beaufort

Arch

Satilla Line

Southeast Georgia

 Embayment

COASTAL

PLAIN

Florida–Hatteras Slope

Skidaway

Island

St Simons Island

Tybee Island

Hilton Head Island

ATLANTIC

OCEAN

Altamaha River

Savannah 

River

Fall

Line

Figure 1. A, Location of 24-county coastal Georgia area, model area, major structural features, and B, 250-milligramper-liter (mg/L) chloride concentration isochlor for June 2001 and 2005 near Brunswick, Georgia (modified from Payne 

and others, 2005; Leeth and others, 2003 and 2007).

A
Introduction 5

Figure 1. A, Location of 24-county coastal Georgia area, model area, major structural features, and B, 250-milligramper-liter (mg/L) chloride concentration isochlor for June 2001 and 2005 near Brunswick, Georgia (modified from Payne 

and others, 2005; Leeth and others, 2003 and 2007).—Continued

Figure 1. —Continued

UV25

17

341

17

82

4TH AVE

4TH STREET

NEWCASTLE STREET

303

32

99 

25 

520 

17

341

25 

95

St Simons Soun

B

d

runswi c k River

Turtle River

East River

Oglethorpe Bay

GLYNN

COUNTY

CAMDEN

COUNTY

81°40' 81°35' 81°30' 81°25' 81°20'

31°15'

31°10'

31°05'

0 2 3 4 1 5 MILES

0 2 3 41 5 KILOMETERS

Base modified from the National Atlas 

of the United States, 2008

Roads, 1:100,000 scale

Coastline-Hydrology, 1:1,000,000 scale

Brunswick

St. Simons

Island

Jekyll

Island

Colonels

Island

Andrews

Island

Little

Satilla

River

Colonels Island

TW-26

0 0.5 1 MILE

0 0.5 1 KILOMETER

EXPLANATION

Line of equal 250-mg/L

 chloride concentration

USGS well and identifer

June 2001

June 2005

TW-26

N

CAMDEN

COUNTY

Area of

map above

GLYNN

COUNTY

B
6 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Hydrogeologic Setting

Coastal Plain sediments consist of consolidated to 

unconsolidated layers of sand and clay, to semiconsolidated 

to dense layers of limestone and dolomite, which range in 

age from Late Cretaceous to Holocene (fig. 2). In general, 

these hydrogeologic units have been divided into aquifers and 

confining units based upon water-yielding characteristics, with 

relatively high permeability layers forming aquifers and lowpermeability layers forming confining units. These sedimentary units unconformably overlie igneous, metamorphic, and 

sedimentary rocks of Paleozoic to Mesozoic age and reach a 

maximum thickness of 5,500 ft in Camden County (Wait and 

Davis, 1986). The thickness of sedimentary units varies and 

is influenced by major structural features in the area, such as 

the Southeast Georgia Embayment, Beaufort Arch, and Gulf 

Trough (fig. 1).

The Southeast Georgia Embayment (Miller, 1986) is 

a shallow east-to-northeast plunging syncline that accumulated Coastal Plain sediments to a maximum thickness in 

the Camden County area (fig. 1). It is postulated that subsidence occurred at a moderate rate from the Late Cretaceous 

to late Cenozoic, which allowed sediments to accumulate 

(Miller, 1986).

Upper 

permeable 

zone5

 

Lower Middle Upper

PostMiocene

Miocene

Eocene

Oligocene

Paleocene

Upper

Cretaceous

Undifferentiated

Suwannee Limestone

Ocala Limestone

Avon Park Formation

Oldsmar Formation

Cedar Keys Formation

Undifferentiated

Water-table zone Upper Floridan aquifer

Floridan aquifer system

Floridan aquifer system

Lower Floridan aquifer

Fernandina 

permeable 

zone

Confining unit Not

modeled

Lower Floridan

confining unit

Lazaretto Creek Formation Upper Floridan confining unit

Lower Coastal Plain3

Geologic unit4 Hydrogeologic unit

Barnwell Group

Undifferentiated

Santee Limestone

Upper Coastal Plain1

Congaree

Formation

Geologic unit

Snapp Formation

Ellenton Formation

(undifferentiated)

Upper 

Three 

Runs

aquifer

Confining unit

Gordon

aquifer

Hydrogeologic 

unit

Steel Creek 

Formation

Black Creek Group

(undifferentiated)

Confining unit 2

Upper Dublin 

aquifer

1

Modified from Falls and others, 1997.

2

In local areas includes Millers Pond aquifer. 

3

Modified from Randolph and others, 1991; Clarke and Krause, 2000.

Confining

unit

Upper waterbearing zone

Upper 

Floridan semiconfining unit

Lower waterbearing zone

Lower Middle Upper

Series

Stage

Model

layer

Savannah Brunswick

1

GHB

(not

modeled)

2

3

4

6

10

11

5

7

8

9

Figure 2.

4

Modified from Randolph and others, 1991; Weems and Edwards, 2001.

5

Modified from Clarke and others, 1990; Krause and Randolph, 1989.

Upper

Brunswick

 aquifer

Lower

Brunswick

 aquifer

Upper waterbearing zone

Lower waterbearing zone

Tigerleap Member of

Parachucla Formation

Parachucla Formation

Marks Head Formation

Coosawhatchie Formation

Ebenezer Formation

Surficial aquifer system Brunswick aquifer system

Confining

unit

Confining unit

Figure 2. Generalized correlation chart of geologic and hydrogeologic units and model layers (modified from Payne 

and others, 2005; GHB, general-head boundary).
Hydrogeologic Setting 7

The Beaufort Arch (Siple, 1960) elevated coastal plain 

sediments in the area northeast of Savannah, including Hilton 

Head Island, South Carolina (S.C.). The formation of the arch 

thinned Coastal Plain sediments and brought them close to 

land surface, where they dip and thicken southward toward the 

Southeast Georgia Embayment. 

The Gulf Trough (Herrick and Vorhis, 1963) is a zone of 

low-permeability, fine-grained clastic sediments and clay-rich 

carbonates that act as a barrier and impede groundwater flow 

toward the coast. This feature is identified on potentiometric 

surfaces of the UFA as increased hydraulic gradients near 

the Gulf Trough that decrease south of the feature (Peck and 

McFadden, 2004).

Another feature, less prominent than the Gulf Trough, is 

the Satilla Line, which is a postulated hydrologic boundary 

identified by GaEPD that could influence groundwater flow 

in the UFA (fig. 1). The feature’s existence is based on a 

change in the configuration of the potentiometric surface of 

the UFA, and by linear changes depicted on aeromagnetic, 

aeroradioactivity, gravity, and isopach maps; however, its 

geologic origin and nature are unknown. 

The following descriptions of the surficial, Brunswick, 

and Floridan aquifer systems are based on their characteristics 

in the lower Coastal Plain physiographic province (fig. 2).

Surficial Aquifer System

The surficial aquifer system consists of interlayered 

lenses of sand, clay, and thin limestone beds of Miocene to 

Holocene age (Clarke, 2003). The surficial aquifer system 

contains a water-table zone and as many as two confined 

zones in the southern part of the study area where sediments 

are thickest (Southeast Georgia Embayment). In Glynn 

County, the surficial aquifer system contains a water-table 

zone and a single confined zone (Clarke and others, 1990). 

The reported transmissivity of the water-table zone ranges 

from 14 to 6,700 feet squared per day (ft2/d), whereas the 

reported transmissivity of the confined zone ranges from 

150 to 6,000 ft2/d (Clarke, 2003). In the original model, one 

confined zone is recognized and grouped into the upper model 

layer with the confining units of the surficial and Brunswick 

aquifer systems (Payne and others, 2005, fig. 2).

The surficial aquifer system is separated from the 

underlying Brunswick aquifer system by a confining unit 

consisting of silty clay and dense, phosphatic limestone of 

lower to middle Miocene age (fig. 2). Wait and Gregg (1973) 

reported the vertical hydraulic conductivity of this unit at 

Brunswick ranges from 5.3×10–5 to 1.3×10–4 feet per day 

(ft/d), as determined from laboratory analysis of core samples. 

Brunswick Aquifer System

The Brunswick aquifer system consists of two waterbearing zones―the upper Brunswick aquifer and the 

lower Brunswick aquifer (fig. 2; Clarke, 2003). The upper 

Brunswick aquifer consists of poorly sorted, fine to coarse, 

slightly phosphatic and dolomitic quartz sand and dense 

phosphatic limestone (Clarke and others, 1990; Leeth, 1999). 

The lower Brunswick aquifer consists of poorly sorted, fine to 

coarse, phosphatic, dolomitic sand (Clarke and others, 1990). 

In general, the upper Brunswick aquifer is thinner, and as a 

result, has lower transmissivity than the lower Brunswick 

aquifer. Reported transmissivity of the upper Brunswick 

aquifer ranges from 20 to 3,500 ft2/d, whereas the reported 

transmissivity of the lower Brunswick aquifer ranges from 

2,000 to 4,700 ft2/d (Clarke, 2003). The highest transmissivity 

values for both aquifers were reported near the Southeast 

Georgia Embayment where the units reach a maximum thickness in the Glynn County area (Clarke, 2003). The lower 

Brunswick confining unit (fig. 2) consists of weakly lithified 

shales and mudstones (Weems and Edwards, 2001). Outside 

the Southeast Georgia Embayment, the Brunswick aquifer 

system thins, or is discontinuous, and has a greater percentage 

of fine-grained sediments (Clarke, 2003). The original model 

of Payne and others (2005) considered the upper and the 

lower Brunswick aquifers as one model layer with combined 

thickness and one assigned hydraulic conductivity value. The 

current study subdivided this unit into two layers throughout 

the revised model to account for variability in layer thickness 

and hydraulic properties.

The Brunswick aquifer system is separated from the 

underlying Floridan aquifer system by a confining unit 

consisting of layers of silty clay and dense phosphatic dolomite of Oligocene age (fig. 2; Clarke, 2003). The reported 

vertical hydraulic conductivity of this confining unit ranges 

from 2.3×10–4 to about 3 ft/d (Clarke and others, 2004), with 

one value estimated to be 1.1×10–2 ft/d in the Brunswick area. 

Floridan Aquifer System

The Floridan aquifer system consists of the UFA and 

Lower Floridan aquifer (LFA), which are composed of mostly 

Paleocene to Oligocene carbonate rocks that locally include 

Upper Cretaceous rocks (fig. 2; Miller, 1986; Krause and 

Randolph, 1989). The Floridan aquifer system extends from 

coastal areas in southeastern South Carolina, westward across 

the coastal plain of Georgia and Alabama, and southward, 

covering Florida. The thickness of the Floridan aquifer system 

in the model area varies from less than 100 ft in aquifer 

outcrop areas of South Carolina to about 2,600 ft near the 

City of Brunswick (Krause and Randolph, 1989).
8 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

The UFA is highly productive and consists of Eocene 

to Oligocene age limestone and dolomite (fig. 2; Clarke and 

others, 1990). The aquifer crops out at or near land surface 

in the northwestern part of the study area and near Valdosta 

in Lowndes County, Ga., where the aquifer is unconfined or 

semiconfined (fig. 1). To the southeast, the aquifer becomes 

progressively more deeply buried and confined. In this report, 

clastic sediments of the Upper Three Runs aquifer (Falls and 

others, 1997) in the upper Coastal Plain that are hydraulically 

connected to carbonate deposits of the lower Coastal Plain 

are included as part of the UFA (fig. 3). The transition from 

carbonate to clastic deposits generally occurs north of the 

Gulf Trough. 

The reported transmissivity of the UFA and equivalent 

clastic units ranges from 530 ft2/d in Beaufort County, S.C., to 

600,000 ft2/d in Coffee County, Ga. (Clarke and others, 2004). 

Large variability in the range of transmissivity where the UFA 

is largely composed of carbonate may indicate the influence 

of fractures or solution openings and related anisotropic 

distribution of hydraulic properties (Warner and Aulenbach, 

1999; Clarke and others, 2004). Maslia (1987) attributed 

greater anisotropy between local- and regional-scale tests 

at the City of Brunswick to preferential flow along vertical 

solution channels associated with high-angle reverse faults 

and fractures. 

In the original model (Payne and others, 2005), the UFA 

was simulated as a single layer. For this study, the aquifer 

was subdivided into the UWBZ and LWBZ as identified by 

Wait and Gregg (1973) in the Brunswick/Glynn County area 

(fig. 2). Wait and Gregg (1973) concluded the UWBZ is more 

productive, as indicated by pumping data from a well that 

tapped both zones; the upper zone contributed 70 percent of 

the flow and lower zone contributed the remainder. However, 

large cavities have been reported in the LWBZ and one 

cavity present at a depth of 945 to 947 ft below land surface 

increased the flow from 600 gallons per minute (gal/min) to 

4,200 gal/min (Wait, 1965). In the Brunswick area, the UWBZ 

is about 165 ft thick separated from the LWBZ by a semiconfining unit of about 160 ft of soft dolostone (fig. 2; Jones and 

Maslia, 1994). Locally the LWBZ has a thickness of 100 ft 

and extends to a depth of 970 ft. The UFA is underlain by a 

confining unit of dense recrystallized limestone and dolomite 

of middle to late Eocene age that hydraulically separates the 

UFA from the LFA by varying degrees (fig. 2). The UWBZ 

of the UFA is in the uppermost part of the Ocala Limestone 

and the Suwanee Limestone, which has been made extremely 

permeable by the development of secondary porosity caused 

by the migration of groundwater along bedding planes, joints, 

and fractures (L. Elliott Jones, U.S. Geological Survey, written 

commun., 2014).

Locally in the Brunswick area, the confining unit is 

breached by fractures or solution openings that enhance 

the exchange of water between the UFA and LFA (fig. 3; 

Krause and Randolph, 1989; Maslia and Prowell, 1990). 

These features probably have allowed saline water from 

the Fernandina permeable zone (described later) to migrate 

upward, primarily into the UWBZ of the UFA, where pressures are lower because of large-scale pumping by local 

industry. According to Maslia and Prowell (1990), four 

major northeast-southwest trending faults are indicated by 

geophysical data that show anomalous or irregular surfaces 

in the A–D marker beds near downtown Brunswick, which 

can be explained by a system of local folding and faulting. 

The marker beds, first recognized by Wait and Gregg (1973), 

represent natural gamma spikes interpreted as depositional 

unconformities that were created by a Miocene transgression. The marker beds form regular surfaces outside the 

Brunswick/Glynn County area. The LFA is composed mainly 

of dolomitic limestone of early and middle Eocene age; at 

the City of Brunswick, however, it includes highly permeable limestone of Paleocene and Late Cretaceous age (fig. 2; 

Krause and Randolph, 1989). In the northwestern part of the 

model area, the clastic Gordon aquifer (Brooks and others, 

1985; Falls and others, 1997) is an updip unit that is hydraulically connected to the LFA (fig. 3). Reported transmissivity 

of the LFA ranges from 170 ft2/d in Barnwell County, S.C., to 

43,000 ft2/d in Camden County, Ga. (Clarke and others, 2004). 

In southeastern Georgia and northeastern Florida, 

the LFA includes a saline water-bearing unit known as 

the Fernandina permeable zone, which is deeply buried, 

cavernous, and highly permeable (fig. 3; Krause and 

Randolph, 1989). The lateral extent of this unit is uncertain 

because a deep drilling program conducted for the Coastal 

Sound Science Initiative identified the unit near downtown 

Brunswick, but not farther north on St. Simons Island and in 

McIntosh County (Falls and others, 2005). The Fernandina 

permeable zone is present at a depth of about 2,100 ft in 

USGS 2,727-ft-deep test well (TW–26) on Colonels Island 

and is important in the Brunswick area because it is probably the local source of saline water (Jones and others, 2002). 

Maslia and Prowell (1990) postulated a system of vertical 

fractures and faults serve as a pathway for saline water migration from the Fernandina permeable zone into shallower units 

(fig. 3). Additional evidence of the presence of this unit was 

also obtained in deep test well (TW–26) on Colonels Island 

in Glynn County, about 3 mi west-southwest of downtown 

Brunswick. Acoustic televiewer images inside the borehole 

indicated the presence of large dissolution cavities at a depth 

of 2,475 ft near what appeared to be a high-angle fault and (or) 

fracture zones (Jones and others, 2002). 
Hydrogeologic Setting 9

 ?

NW

SE

Gulf

Trough

Discharge

Atlantic Ocean

Surficial aquifer

Brunswick

Recharge area

Recharge area

Water level about 65 feet above land surface

Flowing well

Upper Brunswick

 aquifer

Lower

 Brunswick

 aquifer

NW

SE

Brunswick

Water level about 10 feet below land surface

Pumping well

Fracture

in rock

Well depth

1,000 feet

NOT TO SCALE

VERTICAL SCALE GREATLY EXAGGERATED

A. Predevelopment

B. Modern day

Upper Floridan aquifer

Lower Floridan aquifer

Upper confining unit

Middle semiconfining unit

Lower semiconfining unit

Fernandina

permeable zone

Aquifer system base

Land surface

Sea level

Figure 3.

Upper Three

Runs aquifer

Gordon aquifer

Freshwater

EXPLANATION

Very saline water

Slightly to moderately

 saline water

Confining unit

Potentiometric surface of 

 Upper Floridan aquifer

General direction of 

 groundwater flow

NW

SE

Atlantic

Ocean

GEORGIA

FLORIDA

Trace of sections

SOUTH

CAROLINA

Figure 3. Schematic cross sections showing conceptual models of A, predevelopment 

(pre-1880s) and B, modern-day groundwater flow in the Floridan aquifer system from the 

outcrop area in the northwest (NW) to the offshore area in the southeast (SE), coastal 

Georgia (modified from Krause and Randolph, 1989).
10 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Conceptualization of Groundwater Flow

Most of groundwater recharge to the system occurs in 

outcrop areas of the Floridan aquifer system northwest of the 

Gulf Trough (fig. 3). Precipitation infiltrates land surface as 

direct recharge to the surficial aquifer and continues to flow 

downward into the deeper units. Some shallow flow paths 

capture infiltrating precipitation and contribute base flow 

locally to streams. 

Prior to development, groundwater flow laterally 

descended toward the coast and then moved upward from 

deeper to shallower units near the ocean. Currently (2014), 

groundwater flow paths are influenced by pumping from the 

UFA, which has induced increased upward groundwater flow 

into the aquifer from the underlying Fernandina permeable 

zone through vertical fractures and faults (fig. 3). Maslia and 

Prowell (1990) postulated the location of four major northeastsouthwest-trending faults near the downtown Brunswick area, 

as well as fractures located at the intersection of these faults 

that have promoted the development of conduits, thereby 

allowing upward migration of saline groundwater into the 

UFA in response to pumping. This pumping in the UFA 

increased the natural upward hydraulic gradient from the 

Fernandina permeable zone toward the UFA and enhanced 

local groundwater flow from the overlying Brunswick 

aquifer system downward into the UFA to supply water to 

production wells.

Areas of groundwater recharge and discharge are influenced by outcrop locations of the hydrogeologic units and 

their subsurface extent beneath stream alluvium. Generally, 

recharge areas correspond to relatively high-altitude interstream divides, and discharge areas correspond to low-lying 

stream valleys (Clarke and West, 1998). Local recharge areas 

for the regional groundwater-flow system are south of the 

Fall Line and west of the Gulf Trough, with mean-annual 

recharge rates in the Savannah River Basin estimated at 

14.5 inches per year (in/yr) (Faye and Mayer, 1990). East of 

the Gulf Trough, annual recharge to the regional groundwaterflow system ranges from near 0 to 2.4 in/yr, as inferred from 

estimates of stream base flow during a drought period (Priest, 

2004). Base-flow estimates determined by Priest (2004) at 

14 streamgaging stations ranged from 4.4 to 10.0 in/yr and 

were used as annual recharge rates for the original groundwater-flow model (Payne and others, 2005). 

Groundwater-flow directions and water quality in the 

regional aquifer system respond to changes in recharge and 

pumping. When pumping exceeds recharge, saline water 

migrates upward through a network of faults and fractures 

located near downtown Brunswick. When recharge exceeds 

pumping, freshwater moving through the aquifer system does not 

completely flush the saline water from the aquifer, and residual 

solute can remain for an extended period of time. This condition 

can contribute to the long-term degradation of the aquifer once 

saline water has migrated into the system from below. 

Chloride Contamination in the Brunswick Area

In the Brunswick area, saline water has been contaminating the UFA since the late 1950s and has constrained 

development of the aquifer. During 2009, the chloride contamination covered a 2-mi2

 area of downtown Brunswick and 

chloride concentrations within this area exceeded 2,000 mg/L 

(fig. 4; Cherry and others, 2011), well above the 250-mg/L 

State and Federal secondary drinking-water standard (Georgia 

Environmental Protection Division, 1997; U.S. Environmental 

Protection Agency, 2000). 

Since the late 1950s, the USGS has collected water 

samples from the UFA in the Brunswick area and documented 

increasing chloride concentrations in response to increased 

groundwater withdrawals (fig. 4). Pumping resulted in lowered 

water levels and an upward hydraulic gradient between the 

saline portions of the Fernandina permeable zone and the 

normally fresh UFA. Saline water probably is entering the 

UFA through localized, vertically oriented conduits of relatively high permeability and moving laterally in response to 

pumpage within the UWBZ. Acoustic televiewer images from 

test well 33H188 (TW-26) provide evidence of features that 

appear to be high-angle fault and/or fracture zones at a depth 

near 2,475 ft (Jones and others, 2002). The chloride concentration of sea water is about 20,000 mg/L, and the water taken 

from the bottom of the Fernandina permeable zone at test 

well 33H188 was about 30,000 mg/L in 1982 (Krause and 

Randolph, 1989). The chloride plume has stabilized in recent 

years, most likely because local horizontal hydraulic gradients 

have been maintained and groundwater withdrawals by local 

industry and by regional groundwater users over the coastal 

region have decreased (Cherry, 2007; Cherry and Clarke, 

2008; Cherry and others, 2010 and 2011). 
Hydrogeologic Setting 11

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

30

894

269

433

137

981

353

326

360

551

2,180

16.6

27.5

18.4

1,620

2,180

1,800

1,870

15.2 80.9

1,450

49.1

21.3

23.2

2,540

22.5

0

500

1,000

1,500

2,000

2,500

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

34H514

Chloride concentration, 

in milligrams per liter

Well 34H393

Interval tapped, 615–723 ft bls

Upper water-bearing zone

Northern Brunswick area Southern Brunswick area

Well 34H403

Interval tapped, 788–982 ft bls

Lower water-bearing zone

500

1,000

1,500

2,000

2,500

3,000

3,500

1965 1970 1975 1980 1985 1990 1995 2000 2005

Well 33H127

Open interval 823–925 ft bls

Lower water-bearing zone

Well 33H133

Open interval 520–790 ft bls

Upper water-bearing zone

34H505

33H325

33H133

34H403

34H393

33H127

!

Chloride concentration, in

 milligrams per liter (mg/L)

EXPLANATION

Sampling point and chloride 

 concentration, in mg/L

Monitoring well and identifier

0 to 250

251 to 750

751 to 1,250

1,251 to 1,750

1,751 to 2,250

2,251 to 2,570

Real-time specific conductance 

 monitoring site and identifier

326

Base from U.S. Geological Survey digital files,1:24,000, Brunswick West, 1993; Brunswick East, 1979

0 0.25 0.75

0 0.25 0.50 0.75

0.50 1 MILE

1 KILOMETER

Figure 4. 

N

34H403

34H514

Map

area

Glynn

County

Figure 4. Chloride concentrations in the Upper Floridan aquifer near the downtown Brunswick area, 

August 2007, and chloride concentration in water for selected wells in the northern and southern 

Brunswick area, 1964–2007.
12 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Groundwater Use and Water Levels, 

2000–04

 The location and magnitude of groundwater withdrawals at pumping centers may affect groundwater levels 

substantially in the Brunswick/Glynn County area. Changes 

in pumping rates and the addition of new pumping centers 

may alter the configuration of potentiometric surfaces, reverse 

groundwater-flow directions, and increase seasonal and longterm water-level fluctuations in the aquifers. During 2000–04, 

groundwater levels in the UFA in the Brunswick/Glynn 

County area were affected by the shutdown of the Durango 

Paper Company mill near St. Marys, Ga. (fig. 1). In addition, 

a prolonged drought adversely affected groundwater levels 

during 1998–2002. The following sections describe changes 

to groundwater use and groundwater levels during the 5-year 

period of model simulation.

Groundwater Use

The UFA and LFA supply the study area with sufficient 

quantities of groundwater, with average withdrawals during 

2000 totaling 682 and 133 million gallons per day (Mgal/d), 

respectively (Payne and others, 2005). Groundwater withdrawals from the UFA and LFA in 2004 were less than during 

2000, with average withdrawals totaling 612 and 116 Mgal/d, 

respectively. Pumping from the UFA and LFA during 1980–

2004 is summarized in table 1 and shown in figure 5A, both 

of which indicate groundwater use increasing steadily and 

peaking during 2000. Considerably less groundwater was 

withdrawn from the Brunswick aquifer system during 2004 

(1.75 Mgal/d) than from the UFA and LFA, although withdrawals from the Brunswick aquifer system have increased 

since 2000 as a result of GaEPD restrictions on further development of the UFA.

County aggregate and site-specific data were used to estimate average annual pumpage for 2000 and 2004 using procedures described by Taylor and others (2003). Groundwater-use 

data for 2000 were based on county aggregate pumping estimates for Florida (Marella, 2004), Georgia (Fanning; 2003),

and South Carolina (W.L. Stringfield , U.S. Geological 

Survey, written commun., 2002). Site-specific data along 

with pumping rates were compiled for Georgia (J.L. Fanning, 

U.S. Geological Survey, written commun., 2002), South 

Carolina (P. Bristol, South Carolina Department of Health and 

Environmental Control, written commun., 2003), and Florida 

(Sepúlveda, 2002). Pumping estimates for 2004 reflect a 

combination of site-specific data for 2004 (J.L. Fanning, 

U.S. Geological Survey, written commun., 2006; P. Bristol, 

South Carolina Department of Health and Environmental 

Control, written commun., 2006; R.L. Marella, U.S. 

Geological Survey, written commun., 2006) and county 

aggregate data for 2000 (Marella, 2004; Fanning, 2003; 

W.L. Stringfield, U.S. Geological Survey, written commun., 

2002). Because county aggregate data were not available 

for 2004, county aggregate estimates for 2000 were used as 

a basis for estimating usage for 2004. Use of these data for 

both time periods is considered reasonable for Glynn County 

because agricultural pumpage in the county is minimal, and 

rural population (domestic supply) showed little change during 

this period. In other parts of the coastal area, use of aggregate 

data for 2000 could have resulted in an overestimation of 

water use during 2004 because generally wetter conditions 

existed during 2004 compared to 2000. 

0

100

200

300

400

500

600

700

800

900

Figure 5. 

EXPLANATION

0

20

40

60

80

100

120

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

Upper Floridan aquifer

A

B

Pumpage, in million gallons per day

Lower Floridan aquifer

Figure 5. Estimated groundwater pumpage from the 

A, Upper and Lower Floridan aquifers in the model area, 

and B, Upper Floridan aquifer in the Glynn County area, 

1980–2004. Table 1 provides county totals and data sources.
Groundwater Use and Water Levels, 2000–04 13

Along the Georgia coast, the estimated pumping 

distributions during 2000 and 2004 were comparable at 

major pumping centers located near Savannah, Jesup, and 

Brunswick, Ga. Concerns about overdevelopment of the 

UFA prompted the GaEPD to implement an interim water 

management plan for coastal Georgia (Georgia Environmental 

Protection Division, 2005), which restricted withdrawal from 

the UFA in parts of the coastal area, resulting in decreased 

withdrawals overall (fig. 5). 

In general, permitted groundwater withdrawals have 

decreased across the State since 2001 by about 12 percent 

because of conservation efforts made by industrial and 

municipal users (Leeth and others, 2007). The largest change 

in water use in coastal Georgia during 2000–04 was attributed to the shutdown of the Durango Paper Company mill 

in October 2002, which deactivated production wells at the 

facility. The paper mill near St. Marys was about 30 mi south 

of the City of Brunswick, and pumped 35.5 Mgal/d from the 

UFA while in operation (Peck and others, 2004).

Groundwater is an important resource in counties 

located along coastal Georgia and parts of coastal areas in 

Florida and South Carolina because of population growth 

and industrial development. The largest withdrawals from 

the UFA in 2004 occurred in Chatham (63 Mgal/d), Wayne 

(63 Mgal/d), and Glynn (54 Mgal/d) Counties, Ga. During 

2000–04, the largest change in pumpage occurred in 

Camden County, which decreased from 51 Mgal/d in 2000 

to 6.3 Mgal/d in 2004, with most of the decrease attributed 

to the shutdown of the Durango Paper Company mill in 

October 2002 (Peck and others, 2004). Average daily pumpage 

from the UFA and its updip equivalents during 2004 exceeded 

10 Mgal/d in Duval and Nassau Counties, Fla.; in Beaufort 

County, S.C.; and in Burke, Chatham, Coffee, Dooly, Glynn, 

Jefferson, Liberty, Pulaski, Screven, Washington, Wayne, 

and Wilcox Counties, Ga. (table 1). Average daily pumpage 

in the LFA and its updip equivalents during 2004 exceeded 

1 Mgal/d in Duval and Nassau Counties, Fla.; and in Burke, 

Coffee, Crisp, Dooly, Jefferson, Laurens, Pulaski, Screven, 

Washington, and Wilcox Counties, Ga. (table 1). The largest 

withdrawal from the LFA during 2004 occurred in Duval 

County, Fla., where pumpage exceeded 82 Mgal/d (table 1).

During 1980–2000, total daily pumpage from the 

UFA increased by 17 percent, from 583 Mgal/d during 

1980, to a peak of 682 Mgal/d during 2000 (Payne and others, 

2005). During 2004, estimated total daily pumpage from 

the UFA decreased to about 612 Mgal/d. The reduction 

could be lower than 612 Mgal/d because the 2000 aggregate water-use rate used for the 2004 estimate does not 

account for possible reduced agricultural usage that could 

have resulted from the generally wetter 2004 conditions 

compared with 2000. 

Withdrawals from the LFA during 1980–2004 showed 

a similar pattern to those from the UFA. Estimated withdrawals from the LFA increased by 14 percent from a low 

of 117 Mgal/d during 1980 to a peak of 133 Mgal/d during 

2000 (Payne and others, 2005), followed by a decrease to 

116 Mgal/d during 2004 (table 1). 

During 2000–04, total pumpage from the Brunswick 

aquifer system increased from 0.24 Mgal/d during 2000 

to 3.25 Mgal/d during 2004 (Payne and others, 2005; 

Vicki Trent, Georgia Environmental Protection Division, 

written commun., November 15, 2010). The pumpage increase 

for the Brunswick aquifer can be attributed to greater use for 

golf-course irrigation in the Glynn County area and recently 

constructed public-supply wells in the Golden Isles area of 

Glynn County (Cherry and others, 2011). 
14 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Table 1. Estimated groundwater pumpage from the Upper and Lower Floridan aquifers in the coastal area of Georgia and adjacent 

parts of South Carolina and Florida, 1980 –2004.—Continued

[UFA, Upper Floridan aquifer; LFA, Lower Floridan aquifer]

County

Pumpage, in million gallons per day 

1980 1985 1990 

UFA LFA UFA LFA UFA LFA 

Florida 

Baker 1.72 0.26 2.88 0.43 3.68 0.55 

Columbia 3.05 0.00 4.79 0.00 5.07 0.00 

Duval 53.96 92.52 47.44 99.13 41.91 100.46 

Hamilton 0.10 0.00 0.30 0.00 0.44 0.00 

Nassau 44.09 2.51 46.76 2.16 49.72 2.00 

Georgia 

Appling 5.71 0.00 2.60 0.00 2.10 0.00 

Atkinson 1.89 0.00 1.50 0.00 0.58 0.00 

Bacon 2.63 0.00 2.28 0.00 2.11 0.00 

Ben Hill 3.71 0.21 4.92 0.39 3.34 0.38 

Berrien 2.43 0.41 3.26 0.53 2.80 0.45 

Bleckley 5.59 0.87 4.28 0.63 3.29 0.41 

Brantley 1.46 0.00 1.63 0.00 1.83 0.00 

Bryan 0.67 0.00 0.87 0.00 1.03 0.00 

Bulloch 3.75 0.23 2.71 0.20 5.87 0.16 

Burke 10.30 1.60 6.34 0.92 5.82 0.83 

Camden 37.12 0.00 42.98 0.00 45.74 0.00 

Candler 1.83 0.26 2.57 0.34 1.64 0.17 

Charlton 6.50 0.00 1.22 0.00 1.38 0.00 

Chatham 79.75 3.58 78.98 3.20 85.54 4.13 

Clinch 0.85 0.00 0.72 0.00 0.65 0.00 

Coffee 12.59 1.49 7.98 0.78 5.60 0.25 

Crisp 3.16 0.32 3.45 0.28 5.31 0.78 

Dodge 7.02 1.01 3.95 0.52 2.40 0.22 

Dooly 6.30 0.96 9.45 1.46 3.18 0.41 

Echols 0.17 0.00 0.18 0.00 0.25 0.00 

Effingham 2.26 0.02 2.06 0.01 4.98 0.03 

Emanuel 7.34 0.85 5.30 0.68 4.18 0.36 

Evans 0.38 0.05 0.31 0.04 0.38 0.05 

Glascock 0.73 0.04 0.72 0.02 0.99 0.02 

Glynn 95.40 0.00 77.84 0.00 82.02 0.00 

Irwin 1.96 0.25 1.86 0.21 2.15 0.26 

Jeff Davis 5.11 0.81 5.80 0.89 4.77 0.66 

Jefferson 4.97 0.69 9.90 1.44 8.85 1.03 

Jenkins 2.74 0.41 2.65 0.37 2.45 0.33 

Johnson 1.37 0.17 1.81 0.26 0.92 0.12 
Groundwater Use and Water Levels, 2000–04 15

Table 1. Estimated groundwater pumpage from the Upper and Lower Floridan aquifers in the coastal area of Georgia and adjacent 

parts of South Carolina and Florida, 1980–2004.—Continued

[UFA, Upper Floridan aquifer; LFA, Lower Floridan aquifer]

Pumpage, in million gallons per day

1995 1997 2000 2004 County

UFA LFA UFA LFA UFA LFA UFA LFA

Florida

2.11 0.32 2.11 0.32 2.11 0.32 3.24 0.44 Baker

6.92 0.00 6.57 0.00 6.04 0.00 6.04 0.00 Columbia

43.91 95.01 44.83 99.48 44.40 95.98 50.86 82.80 Duval

0.44 0.00 0.46 0.00 0.49 0.00 0.49 0.00 Hamilton

46.66 2.09 50.19 2.18 49.38 2.21 37.56 2.16 Nassau

Georgia

2.38 0.00 2.47 0.00 4.17 0.00 4.08 0.00 Appling

1.58 0.00 1.58 0.00 2.91 0.00 3.07 0.00 Atkinson

2.47 0.00 2.21 0.00 4.04 0.00 4.63 0.00 Bacon

10.97 1.30 10.98 1.30 7.57 0.59 6.49 0.59 Ben Hill

4.65 0.67 4.66 0.67 5.33 0.77 5.33 0.75 Berrien

2.35 0.40 2.35 0.40 6.66 1.00 6.02 0.95 Bleckley

1.90 0.00 1.94 0.00 1.30 0.00 0.94 0.00 Brantley

1.06 0.00 1.70 0.00 1.60 0.00 2.63 0.00 Bryan

7.83 0.31 5.05 0.32 5.70 0.32 5.64 0.32 Bulloch

8.16 1.26 8.22 1.27 22.34 3.24 18.61 3.24 Burke

47.15 0.00 45.83 0.00 50.55 0.00 6.31 0.00 Camden

1.67 0.19 1.70 0.19 2.79 0.37 2.59 0.37 Candler

1.45 0.00 0.95 0.00 1.25 0.00 1.29 0.00 Charlton

75.84 3.76 70.66 3.78 68.15 3.23 63.24 0.09 Chatham

1.03 0.00 1.04 0.00 1.44 0.00 1.47 0.00 Clinch

7.59 0.47 7.52 0.53 15.23 1.73 14.37 1.73 Coffee

10.28 1.58 10.24 1.59 8.56 1.30 9.46 1.30 Crisp

4.28 0.46 4.28 0.46 3.96 0.41 5.22 0.41 Dodge

9.25 1.29 9.25 1.29 18.68 2.93 18.68 2.93 Dooly

1.04 0.00 1.77 0.00 2.88 0.00 2.88 0.00 Echols

5.98 0.04 4.42 0.03 4.62 0.03 6.85 0.03 Effingham

4.51 0.52 4.53 0.52 4.22 0.48 3.54 0.48 Emanuel

0.49 0.06 0.46 0.06 0.70 0.09 2.76 0.09 Evans

1.34 0.02 1.35 0.02 1.36 0.02 0.31 0.02 Glascock

63.68 0.00 61.61 0.00 61.14 0.00 53.60 0.00 Glynn

5.75 0.87 5.75 0.87 6.25 0.96 6.25 0.96 Irwin

3.09 0.40 3.09 0.40 3.84 0.47 3.84 0.47 Jeff Davis

7.76 0.76 7.62 0.97 12.06 1.68 12.06 1.68 Jefferson

3.19 0.47 3.13 0.46 4.03 0.61 3.92 0.61 Jenkins

1.83 0.27 1.83 0.27 2.12 0.32 2.12 0.32 Johnson
16 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Table 1. Estimated groundwater pumpage from the Upper and Lower Floridan aquifers in the coastal area of Georgia and adjacent 

parts of South Carolina and Florida, 1980–2004.—Continued

[UFA, Upper Floridan aquifer; LFA, Lower Floridan aquifer]

County

Pumpage, in million gallons per day 

1980 1985 1990 

UFA LFA UFA LFA UFA LFA 

Georgia—Continued 

Lanier 3.07 0.00 2.92 0.00 1.69 0.00 

Laurens 4.32 0.74 4.15 0.62 4.23 0.60 

Liberty 13.62 0.00 14.58 0.00 17.97 0.00 

Long 0.29 0.01 0.24 0.01 0.23 0.01 

McIntosh 0.70 0.00 1.03 0.00 0.76 0.00 

Montgomery 0.89 0.11 1.51 0.20 0.94 0.10 

Pierce 2.64 0.00 2.03 0.00 1.80 0.00 

Pulaski 6.94 1.11 8.27 1.31 6.87 1.09 

Screven 7.90 1.18 7.19 1.03 7.87 0.40 

Tattnall 1.56 0.06 1.89 0.09 1.77 0.08 

Telfair 3.28 0.48 4.62 0.55 3.30 0.32 

Tift 1.89 0.33 2.19 0.38 2.61 0.46 

Toombs 2.87 0.24 3.91 0.31 3.61 0.20 

Treutlan 0.49 0.06 0.54 0.05 0.79 0.06 

Turner 1.02 0.17 1.00 0.17 0.93 0.16 

Ware 6.25 0.00 7.25 0.00 6.20 0.00 

Washington 10.01 1.52 12.24 1.89 13.02 1.96 

Wayne 74.54 0.00 69.80 0.00 69.27 0.00 

Wheeler 1.60 0.21 0.83 0.10 0.61 0.06 

Wilcox 4.06 0.68 9.84 1.69 5.40 0.90 

South Carolina 

Allendale 7.84 0.00 7.84 0.00 8.31 0.00 

Bamberg 1.99 0.00 1.99 0.00 2.09 0.00 

Barnwell 1.15 0.00 1.15 0.00 3.32 0.00 

Beaufort 0.85 0.00 20.80 0.05 17.48 0.01 

Colleton 0.00 0.35 0.00 0.55 0.00 0.56 

Hampton 3.21 0.00 3.21 0.00 3.95 0.00 

Jasper 1.25 0.01 1.16 0.00 1.97 0.00 

Totals 582.81 116.78 584.49 123.89 579.96 121.03 
Groundwater Use and Water Levels, 2000–04 17

Table 1. Estimated groundwater pumpage from the Upper and Lower Floridan aquifers in the coastal area of Georgia and adjacent 

parts of South Carolina and Florida, 1980–2004.—Continued

[UFA, Upper Floridan aquifer; LFA, Lower Floridan aquifer]

Pumpage, in million gallons per day

1995 1997 2000 2004 County

UFA LFA UFA LFA UFA LFA UFA LFA

Georgia—Continued

2.02 0.00 2.02 0.00 1.97 0.00 1.72 0.00 Lanier

5.78 0.97 5.81 0.95 7.94 1.31 7.96 1.31 Laurens

15.91 0.00 16.10 0.00 15.69 0.00 15.56 0.00 Liberty

0.27 0.02 0.27 0.02 0.69 0.07 1.20 0.07 Long

1.07 0.00 1.09 0.00 0.85 0.00 0.94 0.00 McIntosh

2.40 0.33 2.40 0.33 1.61 0.19 1.61 0.19 Montgomery

3.24 0.00 3.42 0.00 6.22 0.00 6.18 0.00 Pierce

8.59 1.31 8.53 1.35 11.46 1.81 11.46 1.81 Pulaski

6.36 0.66 6.93 0.69 16.24 2.32 15.25 2.32 Screven

3.53 0.28 3.59 0.28 3.66 0.15 2.74 0.15 Tattnall

6.33 0.83 6.33 0.82 4.00 0.42 4.36 0.42 Telfair

3.95 0.69 3.80 0.66 3.57 0.62 3.57 0.62 Tift

3.65 0.27 4.17 0.27 6.30 0.69 6.64 0.69 Toombs

1.31 0.12 1.31 0.12 1.10 0.11 1.13 0.11 Treutlan

2.91 0.50 2.92 0.50 2.57 0.44 2.57 0.44 Turner

5.51 0.00 5.97 0.00 8.45 0.00 5.82 0.00 Ware

14.39 2.16 14.88 2.04 16.01 2.07 16.01 2.07 Washington

64.89 0.00 63.59 0.00 63.47 0.00 63.12 0.00 Wayne

2.22 0.34 2.22 0.34 1.07 0.14 1.07 0.19 Wheeler

8.43 1.43 8.43 1.43 14.74 2.53 14.74 2.53 Wilcox

South Carolina

9.44 0.00 9.85 0.00 9.59 0.00 9.25 0.00 Allendale

2.52 0.00 4.04 0.00 6.32 0.00 6.32 0.00 Bamberg

2.91 0.00 4.90 0.00 7.50 0.00 7.39 0.00 Barnwell

19.56 0.01 33.58 0.09 21.44 0.26 18.21 0.03 Beaufort

0.00 0.58 0.00 0.47 0.00 0.51 0.15 0.24 Colleton

4.32 0.00 5.99 0.00 8.63 0.00 7.97 0.00 Hampton

1.31 0.00 2.13 0.01 3.34 0.01 2.80 0.01 Jasper

603.42 123.02 616.62 127.75 682.31 132.71 612.13 115.94 Totals
18 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Groundwater Levels

Groundwater levels vary seasonally and are affected by 

precipitation, evapotranspiration, and pumping. Groundwater 

levels generally are highest in the winter through early spring 

when evapotranspiration is lowest and irrigation withdrawals 

are minimal; groundwater levels are lowest during summer 

and fall when evapotranspiration and pumping rates are 

highest. A map and water-level hydrographs for selected 

wells in the Brunswick aquifer system, UFA, and LFA during 

2000–04 for Glynn County are shown in figure 6.

During 2003–04, above-normal rainfall following the 

drought of 1998–2002 and the reduction in groundwater 

withdrawals from major aquifers resulted in increased water 

levels. Some wells recorded historic lows during the fall of 

2002, but recovered to near normal levels, or in some cases 

above-normal levels in 2004 (Leeth and others, 2007). The 

most pronounced water-level rise was in the St. Marys, 

Camden County area, in response to closure of the Durango 

Paper Company mill in October 2002, which resulted in 

a water-level rise of more than 200 ft at the center of the 

cone of depression and water-level increases ranging from 

4 to 10 ft in outlying areas of Camden County (Peck and 

others, 2004). During 2003–04, above-normal rainfall ended 

the cycle of drought in Georgia that lasted from 1998 to 

2002. The rainfall amounts for 2003 at 10 stations located in 

hydrogeologic unit areas of outcrop (aquifer-recharge zones) 

ranged from 8 to 34 percent above normal (The Southeast 

Regional Climate Center, 2009). As a result of the increase 

in rainfall and recharge to the regional aquifer system, water 

levels for June 2004 in the Brunswick aquifer system, UFA, 

and LFA (fig. 6) generally were higher than during 2000. 

The exceptions occurred in two wells in the Savannah area 

(39Q026 and 39Q028) having open intervals in the Brunswick 

aquifer system and one well in Effingham County, (35T003) 

completed in the UFA, which indicated water-level declines 

from in 2000 to 2004. These wells could be influenced by 

localized pumping.

Data from eight observation wells open to the Brunswick 

aquifer system indicate a general water-level rise during 

2000–04 throughout the study area (table 2). Overall, the 

differences in water-level measurements from 2000 to 2004 

range from –1.04 ft (well 39Q028; Chatham County) to 

19.29 ft (well 33D071; Camden County), with an average 

increase of 3.97 ft. In the Brunswick/Glynn County area, water 

levels in two observation wells rose 3.04 ft (well 34H437) 

and 4.56 ft (well 33G028) over the 5-year period (table 3). 

Graphs for wells 33J062 and 34H492, completed in the lower 

Brunswick and surficial aquifers, respectively, show waterlevel rises during 2000–04, with most of the rise occurring 

during 2002 (fig. 6). The largest rise occurred in well 33J062, 

located in the western part of Glynn County, away from any 

pumping centers.

In the UWBZ, water-level measurements taken in 

35 wells during 2000–04 indicate water-level declines and 

rises ranging from –29.29 to 11.84 ft, respectively, with an 

average water-level rise of 4.03 ft (table 2). In the Brunswick/

Glynn County area, water levels in 19 wells completed in the 

UWBZ rose from 1.05 to 7.93 ft, with an average water-level 

rise of 4.94 ft (table 3). Water levels in well 33H133 show a 

water-level rise during 2000–04, with about 6 ft of the rise 

occurring during 2002 (fig. 6). Water-level data for the LWBZ 

are sparse but indicate a water-level rise of 7.25 ft in one well 

in downtown Brunswick (33H127; table 3; fig. 6), which is 

consistent with water-level changes in the overlying UWBZ 

of the UFA.

In the LFA, 2000 and 2004 water-level data from eight 

observation wells indicate rises ranging from 1.73 to 27.09 ft, 

with an average increase of 7.14 ft (table 2). The 27.09-ft 

water-level rise observed in well 33D073 was due, in part 

to the shutdown of the Durango Paper Company mill during 

2002 (Peck and others, 2004). In the Brunswick/Glynn County 

area, 2000 and 2004 water-level data from five observation 

wells indicate water-level rises ranging from 2.69 to 7.68 ft, 

with an average increase of 5.06 ft (table 3). Water levels 

in LFA well 34H436 rose during 2000–04, with most of the 

increase occurring during 2002 (fig. 6). In well 33H188, 

completed in the Fernandina permeable zone of the LFA, 

water levels declined from 2000 through early 2002, followed 

by a sharp rise thereafter (fig. 6). 
Groundwater Use and Water Levels, 2000–04 19

33J062

34H436

34H437

33H127

33H133

33H188

34H492

95

341

17

82

4

5

6

7

8

9

10

11

12

Well 34H492—Surficial aquifer

4

5

6

7

8

9

10

11

12

Well 34H437—Upper Brunswick aquifer

16

17

18

19

20

21

22

23

24

25

26 Well 33J062—Lower Brunswick aquifer Water level, in feet above NAVD 88

Water level, in feet above 

or below (–) NAVD 88

–5

0

5

10

15

20

Well 33H127—Upper Floridan aquifer LWBZ

5

10

15

20

25 Well 34H436—Lower Floridan aquifer 

5

10

15

20

25 Well 33H188—Lower Floridan aquifer FPZ

Figure 6. 

–6

–4

–2

0

2

4

6

8

10

12

14

16 Well 33H133—Upper Floridan aquifer UWBZ

WAYNE

BRANTLEY

GLYNN

CAMDEN

MCINTOSH

ATLANTIC

OCEAN

St Simons

Island

N

0 5 10 MILES

0 5 10 KILOMETERS

2000 2001 2002 2003 2004 2000 2001 2002 2003 2004

2000 2001 2002 2003 2004

2000 2001 2002 2003 2004

2000 2001 2002 2003 2004

2000 2001 2002 2003 2004

EXPLANATION

Well

Water level, in feet above or below (–) NAVD 88

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

Brunswick

2000 2001 2002 2003 2004

Blank where

data missing

Jekyll

Island

Figure 6. Selected water-level hydrographs for the surficial aquifer, upper Brunswick aquifer, lower Brunswick aquifer, 

Upper Floridan aquifer upper water-bearing zone (UWBZ), Upper Floridan aquifer lower water-bearing zone (LWBZ), 

Lower Floridan aquifer, and Lower Floridan aquifer Fernandina permeable zone (FPZ), in the Brunswick/Glynn County, 

Georgia area, 2000–04.
20 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Table 2. Water-level measurements taken during 2000 and 2004 and observed water-level change 

during the same period.—Continued

[NAVD 88, North American Vertical Datum of 1988; see fig. 2–1 for well locations]

Well

identifier County

Water level,

in feet above or below NAVD 88

Water-level change

from 2000 to 2004,

2000 2004 in feet

Upper Brunswick aquifer (UBA)

32L016 Wayne 15.79 17.60 1.81

33D071 Camden –2.07 17.22 19.29

33G028 Glynn 16.75 21.31 4.56

34H437 Glynn 5.88 8.92 3.04

39Q026 Chatham –2.31 –3.29 –0.98

39Q028 Chatham –2.21 –3.25 –1.04

35S008 Effingham 12.09 13.42 1.33

36N012 Bryan –26.18 –22.43 3.75

UBA mean 3.97

Upper water-bearing zone of Upper Floridan aquifer (UWBZUFA)

21T001 Laurens 220.19 223.66 3.47

26R001 Toombs 103.85 106.63 2.78

27E004 Charlton 40.54 43.76 3.22

32L015 Wayne 8.22 13.48 5.26

32R002 Bulloch 18.01 22.35 4.34

33E007 Camden 15.26 27.10 11.84

33E027 Camden 23.51 34.11 10.60

33G008 Glynn 18.72 23.16 4.44

33H120 Glynn –2.99 3.08 6.07

33H130 Glynn –4.59 2.18 6.77

33H133 Glynn –0.89 3.77 4.66

33H177 Glynn 21.16 28.24 7.08

33H207 Glynn 4.16 8.09 3.93

33M004 Long 0.40 6.36 5.96

34G002 Glynn 17.62 22.37 4.75

34G009 Glynn 35.50 38.73 3.23

34G016 Glynn 23.69 28.28 4.59

34G020 Glynn 26.18 30.10 3.92

34H112 Glynn 6.62 12.85 6.23

34H117 Glynn 4.54 10.47 5.93

34H125 Glynn 4.45 12.38 7.93

34H344 Glynn 3.25 6.22 2.97

34H355 Glynn 3.88 8.46 4.58

34H371 Glynn 10.83 15.54 4.71

34H373 Glynn –1.07 3.98 5.05

34H393 Glynn 8.53 14.56 6.03

34H469 Glynn 5.56 6.61 1.05

35T003 Effingham 31.40 2.11 –29.29

36Q008 Chatham –90.48 –82.07 8.41

36Q020 Chatham –42.17 –38.20 3.97
Groundwater Use and Water Levels, 2000–04 21

Table 2. Water-level measurements taken during 2000 and 2004 and observed water-level change 

during the same period.—Continued

[NAVD 88, North American Vertical Datum of 1988; see fig. 2–1 for well locations]

Well

identifier County

Water level,

in feet above or below NAVD 88

Water-level change

from 2000 to 2004,

2000 2004 in feet

Upper water-bearing zone of Upper Floridan aquifer (UWBZUFA)—Continued

37P114 Chatham –46.02 –43.63 2.39

37Q016 Chatham –82.22 –76.98 5.24

37Q185 Chatham –99.22 –95.22 4.00

38Q002 Chatham –30.36 –28.11 2.25

39Q003 Chatham –27.90 –25.21 2.69

UWBZUFA mean 4.03

Lower water-bearing zone of Upper Floridan aquifer (LWBZUFA)

33H127 Glynn 0.60 7.85 7.25

33H154 Glynn –27.58 –17.85 9.73

34H334 Glynn 7.51 12.42 4.91

34H403 Glynn 10.12 16.27 6.15

LWBZUFA mean 7.01

Lower Floridan aquifer (LFA)

33D073 Camden 3.58 30.67 27.09

33H188 Glynn 12.46 20.14 7.68

33H206 Glynn 8.40 14.01 5.61

33J044 Glynn 13.89 19.13 5.24

34H391 Glynn 9.18 11.87 2.69

34H436 Glynn 11.70 15.80 4.10

35P109 Bryan –21.83 –18.87 2.96

39Q024 Chatham –31.67 –29.94 1.73

LFA mean 7.14
22 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Table 3. Water-level measurements taken during 2000 and 2004 and 

observed water-level change during the same period in the Brunswick/

Glynn County area.

[NAVD 88, North American Vertical Datum of 1988; see fig. 2–1 for well locations]

Well

identifier

Water level, in feet

above or below NAVD 88

Water-level change 

from 2000 to 2004,

2000 2004 in feet

Upper Brunswick aquifer (UBA)

33G028 16.75 21.31 4.56

34H437 5.88 8.92 3.04

Mean 3.80

Upper water-bearing zone of Upper Floridan aquifer (UWBZUFA)

33G008 18.72 23.16 4.44

33H120 –2.99 3.08 6.07

33H130 –4.59 2.18 6.77

33H133 –0.89 3.77 4.66

33H177 21.16 28.24 7.08

33H207 4.16 8.09 3.93

34G002 17.62 22.37 4.75

34G009 35.50 38.73 3.23

34G016 23.70 28.28 4.58

34G020 26.18 30.10 3.92

34H112 6.62 12.85 6.23

34H117 4.54 10.47 5.93

34H125 4.45 12.38 7.93

34H344 3.25 6.22 2.97

34H355 3.88 8.46 4.58

34H371 10.80 15.54 4.74

34H373 –1.07 3.98 5.05

34H393 8.53 14.56 6.03

34H469 5.56 6.61 1.05

Mean 4.94

Lower water-bearing zone of Upper Floridan aquifer (LWBZUFA)

33H127 0.60 7.85 7.25

33H154 –27.58 –17.85 9.73

34H334 7.51 12.42 4.91

34H403 10.12 16.27 6.15

Mean 7.01

Lower Floridan aquifer (LFA)

33H188 12.46 20.14 7.68

33H206 8.40 14.01 5.61

33J044 13.89 19.13 5.24

34H391 9.18 11.87 2.69

34H436 11.70 15.80 4.10

Mean 5.06
Simulation of Steady-State Groundwater Flow, 2000–04 23

Simulation of Steady-State 

Groundwater Flow, 2000–04

The digital groundwater-flow model originally 

developed to simulate regional confined groundwater flow 

in the coastal area of Georgia, Florida, South Carolina, 

and adjacent offshore areas (Payne and others, 2005) was 

revised to evaluate hydraulic gradients in the Brunswick/

Glynn County area. The original model was developed 

using MODFLOW–2000 (Harbaugh and others, 2000), and 

simulated steady-state flow for predevelopment, 1980, and 

2000 conditions. Details of the original model development 

are provided in Payne and others (2005) and are briefly 

described in the following sections. Steady-state simulations 

were also considered reasonable for the revised model 

because of the focus on changes in mean-annual pumping 

for 2000 and 2004. According to Payne and others (2005), 

the original model was tested for transient response and the 

results indicated that relatively extreme changes in stress 

were required to affect a transient response. Locally in the 

Brunswick/Glynn County area, groundwater flow in the 

Upper Floridan aquifer is considered to be in equilibrium 

where recharge to the aquifer is balanced by natural discharge 

and pumping (Krause and Randolph, 1989). In addition, 

calculations comparing the estimated rate at which water 

derived from storage for the period from 1945 to 1986 

with a mean pumping value of 70.8 Mgal/d from the Upper 

Floridan aquifer over the 42-year period indicated that 

less than 0.1 percent of the 1986 pumpage was derived 

from storage (L.E. Jones, U.S. Geological Survey, written 

commun., November 2014). Therefore, the assumption of 

nearly steady-state conditions for the Upper Floridan aquifer 

in Glynn County because of the negligible contributions of 

water from aquifer storage is reasonable.

Revision of Groundwater-Flow Model

To develop the revised model, the original model was 

modified in terms of grid size (discretization), model layers, 

hydraulic properties, boundary conditions, use of pumping 

rates for 2004, and recalibration to observed water levels. The 

original model focused on the Floridan aquifer system at a 

regional scale with reduced grid spacing in the Savannah and 

Brunswick areas for further evaluation, whereas the addition of layers/zones in the revised model based on the local 

hydrogeology improve the simulation of the steep hydraulic 

gradients that have formed in the Brunswick area as a result 

of pumping. These modifications allowed a more accurate 

computed solution of head in the Brunswick/Glynn County 

area along with head gradients and leakage rates that were 

not possible with the original model. 

Discretization

The original model encompasses 42,155 mi2 and consists 

of 119 rows and 108 columns, with cell sizes ranging from 

4,000×5,000 ft (0.7 mi2) to 16,500×16,500 ft (9.8 mi2). 

Because of the focus on the Brunswick/Glynn County area in 

the current study, a refined grid spacing was chosen to enable 

more accurate simulation of the steep head gradients near 

cones of depression. Graphical grid-generation tools from the 

graphical user interface Argus ONE enabled visual adjustment 

of grid position and density. The revised grid configuration has 

the same orientation as the original model, but the number of 

rows and columns has been increased to 424 and 452, respectively (fig. 7). The variable cell sizes range from 500×500 ft 

(0.009 mi2) near downtown Brunswick, to 5,000×5,000 ft 

(0.90 mi2) near the edges of the model area. The irregular grid 

configuration results in elongated cells along the outer margins 

of the model having aspect ratios as large as 10:1 between row 

and column spacings. This large aspect ratio is approaching 

the recommended limit, above which numerical errors could 

occur (de Marsily, 1986, p. 351). 

Model Layers

Layers used in the original model to vertically discretize 

groundwater flow were modified in the revised model to simulate the local hydrogeology in the Brunswick/Glynn County 

area. The original model contained layers for the surficial 

aquifer system (layer 1), Brunswick aquifer system (layer 3), 

UFA (layer 5), and LFA (layer 7), and for intervening 

confining units between these aquifers (layers 2, 4, and 6). 

The revised model contains four additional layers to detail the 

vertical representation of the Brunswick aquifer system and 

Upper Floridan aquifer. As shown in figure 8 and table 4, the 

Brunswick aquifer system has been subdivided into the upper 

Brunswick aquifer (layer 3) and lower Brunswick aquifer 

(layer 5) with an intervening confining unit (layer 4), and the 

UFA has been subdivided into the UWBZ (layer 7) and the 

LWBZ (layer 9) with an intervening confining unit (layer 8).

Published data were used to assign altitudes to the top 

of each unit represented in the original model. Published 

literature (Brooks and others, 1985; Charm and others, 

1969; Clarke and others, 1990; Hathaway and others, 

1981; Kellam and Gorday, 1990; Miller, 1986; Scholle, 

1979; Steele and McDowell, 1998) provided information 

to construct contour maps showing the altitude of the top 

of each layer and this information was modified using well 

information collected as part of the Coastal Sound Science 

Initiative (Falls and others, 2001; Foyle and others, 2001). In 

the Brunswick/Glynn County area, the UWBZ and LWBZ 

(model layers 7 and 9) were extended to include all of Glynn 

County and neighboring Camden County. Beyond these 
24 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

GLYNN

Figure 7. 

EXPLANATION

Production well

June 2004 observation well

Outline of chloride plume, 2004—Modified

 from Leeth and others, 2007

Model grid

Model-boundary nodes

Specified head

No-flow

Area of dense model grid—Grid spacing 

 progressively increases by a factor of

 1.5 from a minimum of 500 feet to a

 maximum of 5,000 feet

Map area

on facing

page

SOUTH

GEORGIA CAROLINA

Model area

FLORIDA

N

0 15 30 45 60 MILES

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

Figure 7. Revised model grid, major production wells, observation wells used during June of 2004, 

and outline of the 2004 chloride plume for the Upper Floridan aquifer in the Brunswick area.
Simulation of Steady-State Groundwater Flow, 2000–04 25

0 3,000 6,000 FEET

0 500 1,000 1,500 METERS

0 5 10 MILES0 5 10 KILOMETERS

GLYNN

Brunswick

Map area

shown

at right

Figure 7. —Continued

N N

Base from U.S. Geological Survey 1:100,000-scale digital data Base from U.S. Geological Survey digital files,1:24,000, Brunswick West, 1993; Brunswick East, 1979

Figure 7. Revised model grid, major production wells, observation wells used during June of 2004, and outline of the 2004 chloride plume for the Upper Floridan aquifer in the Brunswick area.—Continued
26 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Figure 8. 

EXPLANATION

General-head boundary—Represents water table or equivalent freshwater head 

 that provides flow to underlying confined aquifers. Flow is restricted by a 

 conductance term, which is equivalent to hydraulic conductivity 

No-flow boundary

No-flow or fixed-head boundary

Offshore area—Equivalent freshwater head of overlying saltwater column 

Onshore area—Water-table head

Aquifer

Confining unit

Onshore Offshore

Layer 3

Layer 2

Confined zone of surficial aquifer system Layer 1

Upper Brunswick aquifer

Upper Floridan aquifer—Lower water-bearing zone

Lower Floridan aquifer

Layer 4

Layer 5

Layer 6

Upper Floridan aquifer—Upper water-bearing zone Layer 7

Lower Brunswick aquifer

Layer 8

Layer 9

Layer 10

Layer 11

Figure 8. Schematic diagram showing model layers and boundary conditions.

areas, the UFA was considered to be one unit that includes 

model layers 7 through 9. In addition, where the UWBZ and 

LWBZ are absent, a minimal thickness of 1 ft was assigned 

to fulfill the requirements of MODFLOW–2000 (Harbaugh 

and others, 2000) for a continuous model layer to exist across 

the entire model area, and that layer of minimal thickness was 

assigned the hydraulic conductivity of the overlying layer. A 

schematic diagram (fig. 8) and hydrogeologic sections (fig. 9) 

along the approximate strike and dip of geologic formations 

illustrate how model layer thicknesses vary over the model 

domain. The Brunswick aquifer system (layers 3–5) varies 

in thickness, ranging from 300 to 400 ft along the Brunswick 

peninsula and thins to the north toward the Savannah area. The 

combined thickness of the UWBZ and LWBZ of the UFA and 

intervening confining unit (layers 7–9) reaches about 400 ft 

near the Brunswick peninsula. In the Glynn/Camden County 

area, the thickness of the UWBZ (layer 7) of the UFA is highly 

variable ranging from 26 to 266 ft with an average thickness 

of 139 ft. The semiconfining unit (layer 8) ranges in thickness from 34 to 265 ft with an average thickness of 85 ft. The 

thickness of the LWBZ (layer 9) of the UFA is less variable 

ranging from 86 to 193 ft with an average thickness of 163 ft. 

The UFA thins toward the Gulf Trough and thickens to 800 ft 

beneath the Atlantic Ocean. The hydrogeologic section along 

the Georgia coast (B–B′ ) illustrates how hydrogeologic units 

generally thicken toward the Southeast Georgia Embayment 

where the LFA reaches thicknesses greater than 2,000 ft 

(fig. 9). 
Simulation of Steady-State Groundwater Flow, 2000–04 27

500

700

100

0

–100

–500

–900

–1,300

–1,700

–2,100

–2,500

–2,900

–3,300

–3,700

SOUTHWEST NORTHEAST

B

NORTHWEST SOUTHEAST

A A'

B'

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210

VERTICAL SCALE GREATLY EXAGGERATED

DATUM IS NORTH AMERICAN VERTICAL DATUM OF 1988

VERTICAL SCALE GREATLY EXAGGERATED

DATUM IS NORTH AMERICAN VERTICAL DATUM OF 1988

Brunswick

peninsula Savannah

MILES

600

800

200

0

–200

–600

–1000

–1,400

–1,800

–2,200

–2,600

–3,000

–3,400

–3,800

ATLANTIC OCEAN

Brunswick

peninsula

Low hydraulic-conductivity zone in model

 corresponding to Gulf Trough

FEET

FEET

SOUTH

GEORGIA CAROLINA

FLORIDA

A'

A

B

B'

Model 

area

EXPLANATION

Layer and unit

1 Surficial aquifer system

2, 4, and 6 Brunswick aquifer system confining unit, lower Brunswick

 aquifer confining unit, and Upper Floridan confining unit

3 Upper Brunswick aquifer

5 Lower Brunswick aquifer

7 and 9 Upper and lower water-bearing zones of the Upper Floridan aquifer

8 Lower water-bearing zone of the Upper Floridan aquifer confining unit

10 Lower Floridan confining unit

11 Lower Floridan aquifer

A'A Line of section

Figure 9. Figure 9. Hydrogeologic sections showing vertical discretization of hydrogeologic units simulated by the revised model.
28 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Table 4. Horizontal and vertical hydraulic conductivity values assigned to hydraulic property zones for the original (Payne and others, 

2005) and revised groundwater-flow models.—Continued

[—, not applicable; UWBZ, upper water-bearing zone; LWBZ, lower water-bearing zone; Kh, horizontal hydraulic conductivity; Kv, vertical hydraulic 

conductivity; ft/day, foot per day]

Unit Layer

Payne and others (2005)

Unit Layer

Revised model

Hydraulic

property

zone

Hydraulic conductivity,

Kh and Kv,

in feet per day

Hydraulic

property

zone (fig. 9)

Hydraulic conductivity,

Kh and Kv,

in feet per day

Surficial aquifer 1 — 70 Surficial aquifer 1 — 105

Confining unit 2 C1 0.00017 Confining unit 2 C1 0.00257

C2 0.20000 C2 0.20000

C3 0.00001 C3 0.00001

C4 0.00010 C4 0.00010

C5 0.00010 C5 0.00010

Brunswick 3 B1 50 Upper Brunswick 3 B1 10

 aquifer system C1 0.00017 aquifer C1 0.00257

C2 0.20000 C2 0.20000

C3 0.00001 C3 0.00001

C4 0.00010 C4 0.00010

— — Confining unit 4 B1 0.02

— — C1 0.00257

— — C2 0.20000

— — C3 0.00001

— — C4 0.00010

— — Lower Brunswick 5 B1 20

— — aquifer C1 0.00257

— — C2 0.20000

— — C3 0.00001

— — C4 0.00010

Confining unit 4 C1 0.00017 Confining unit 6 C1 0.00257

C2 0.20000 C2 0.20000

C3 0.00001 C3 0.00001

C4 0.00010 C4 0.00010

C5 0.00010 C5 0.00010

Upper Floridan 5 F1 34 UWBZ of Upper 7 F1 40

 aquifer F2 2 Floridan aquifer F2 20

F3 100 F3 150

F4 70 F4 65

F5 394 F5 225

F6 2,819 F6 3,415

F7 150 F7 750

F8 2,727 F8 3,000

F9 100 F9 150

F10 56 F10 84

F11 94 F11 126

F12 25 F12 25

— — F13 300

— — F14 240

— — F15 200

— — F16a 76

— — F17b 398
Simulation of Steady-State Groundwater Flow, 2000–04 29

Table 4. Horizontal and vertical hydraulic conductivity values assigned to hydraulic property zones for the original (Payne and others, 

2005) and revised groundwater-flow models.—Continued

[—, not applicable; UWBZ, upper water-bearing zone; LWBZ, lower water-bearing zone; Kh, horizontal hydraulic conductivity; Kv, vertical hydraulic 

conductivity; ft/day, foot per day]

Unit Layer

Payne and others (2005)

Unit Layer

Revised model

Hydraulic

property

zone

Hydraulic conductivity,

Kh and Kv,

in feet per day

Hydraulic

property

zone (fig. 9)

Hydraulic conductivity,

Kh and Kv,

in feet per day

Confining unit — — Confining unit 8 F1 40

— — F2 20

— — F3 150

— — F4 65

— — F5 225

— — F6 3,415

— — F7 0.2

— — F8 0.2

— — F9 150

— — F10 84

— — F11 126

— — F12 25

— — F13 0.2

— — F14 0.2

— — F15 0.2

— — F16a 76

— — F17b 398

LWBZ of Upper — — LWBZ of Upper 9 F1 40

 Floridan aquifer — — Floridan aquifer F2 20

— — F3 150

— — F4 65

— — F5 225

— — F6 3,415

— — F7 750

— — F8 3,000

— — F9 150

— — F10 84

— — F11 126

— — F12 25

— — F13 270

— — F14 200

— — F15 125

— — F16a 76

— — F17b 398

Confining unit 6 — 0.02000 Confining unit 10 LFC1 0.02000

— — LFC2a 0.20000

— — LFC3b 10.00000

Lower Floridan 7 — 10 Lower Floridan 11 LF1 10

 aquifer — — aquifer LF2a 100

— — LF3b 15.8

a

Clarke and others (2010); LFC2 Kh=0.2 ft/day, Kv=0.02 ft/day

b Clarke and others (2011); LFC3 Kv=0.2 ft/day, LF3 Kh=15.8 ft/day, Kv=1.6 ft/day
30 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Hydraulic Properties

In the Brunswick/Glynn County area, the original model 

contained designated homogeneous and isotropic hydraulic 

property zones for all aquifers and confining units except the 

UFA, which consisted of two zones within Glynn County. 

For the revised model, additional zones were designated on 

the basis of available aquifer-test and geologic data (fig. 10; 

table 4). These data include the vertical (Kv ) and horizontal 

(Kh ) hydraulic conductivity for all model layers, which were 

used as initial estimates in the revised model prior to any 

model adjustments (Clarke and others, 2004). Additional zones 

were created (F13, F14, and F15) within the UFA (layers 7–9) 

near the Brunswick area to further adjust hydraulic properties within zone F7 of the original model. In addition, zones 

F16 and F17 were added based on aquifer tests in the Floridan 

aquifer system at Hunter Army Airfield and Fort Stewart 

(Clarke and others, 2010, 2011). During model calibration, 

adjustments were made to hydraulic property zones to provide 

a better match between observed and simulated water levels in 

the area. 

The surficial aquifer (layer 1) was represented by a 

single zone and assigned a Kh

 value of 70 ft/d throughout the 

model domain in the original model. This value was increased 

to 105 ft/d in the revised model to provide a better match 

to observed values. The confining unit beneath the surficial 

aquifer (layer 2), was areally represented in both models 

by five zones that were assigned Kh values ranging from 

0.00001 to 0.2 ft/d (table 4). 

The Brunswick aquifer system was represented 

differently by the two models. In the original model, the 

Brunswick aquifer system was simulated by a single layer 

(3) that was areally subdivided into five zones with Kh values 

ranging from 0.00001 to 50 ft/d. Zone B1 in the original 

model corresponded to the approximate extent of the most 

permeable part of the aquifer system and was assigned a 

uniform value of 50 ft/d. In the revised model, three layers 

(3, 4, and 5) vertically subdivide the Brunswick aquifer 

system, and zone B1 represents a less permeable part of the 

aquifer (layer 4) juxtaposed between two more permeable 

parts (layers 3 and 5), with each layer assigned a uniform 

value for Kh and Kv (table 4). Within each model, the respective assigned values for C1, C2, C3, and C4 did not change 

between layers (table 4).

 The UFA in the original model was represented as a 

single layer (5) areally subdivided into 12 hydraulic property zones, with Kh

 ranging from 2 ft/d in zone F2 (in the 

Gulf Trough region), to 2,819 ft/d in zone F6 (southwest of 

Glynn County) (fig. 10; table 4). By comparison, a single 

hydraulic property zone (F7) having a Kh of 150 ft/d was 

used in the original model to represent the UFA in the 

majority of Glynn County. To enable more detailed simulation of groundwater flow in the Brunswick/Glynn County 

area than was available using the original model, the UFA 

in the revised model has been vertically subdivided into 

the UWBZ (layer 7) and LWBZ (layer 9), separated by a 

confining unit (layer 8; fig. 8). Each of these new layers 

contained the same 12 zones used in the original model, plus 

an additional 3 zones in the Brunswick area to represent 

variations in Kh (fig. 10; table 4). The adjusted Kh of 750 ft/d 

for the revised model in hydraulic property zone (F7) multiplied by the average thickness of the UWBZ of 139 ft yields 

a simulated transmissivity of 104,000 ft2/d. Results from a 

subregional December 1962 aquifer test using 16 observation wells open to the UWBZ located at distances ranging 

from 15,400 to 71,400 ft from a pumping well tapping both 

the UWBZ and LWBZ near Brunswick indicated an average 

transmissivity value of 88,200 ft2/d for Glynn County (Jones 

and Maslia, 1994). Previously reported transmissivity values 

for the UFA in the Brunswick/Glynn County area were about 

150,000 to 200,000 ft2/d, but likely included both the UWBZ 

and LWBZ (Wait and Gregg, 1973). A localized aquifer test 

in the Brunswick area performed during July 1985 using 

16 observation wells open to the UWBZ and pumping from 

the UWBZ yielded much lower transmissivity values (Jones 

and Maslia, 1994). The time-drawdown plots were matched 

manually to the Hantush-Jacob type curve with an excellent fit in six observation wells located at distances ranging 

from 700 to 6,300 ft with an average transmissivity value 

for the UWBZ of 61,000 ft2/d. During December 1986, a 

localized aquifer test performed in the southern portion of 

the Brunswick peninsula using two observation wells open 

to the UWBZ and pumping from a public-supply well open 

to the UWBZ produced computed transmissivity values of 

23,400 and 32,500 ft2/d, respectively (Jones and Maslia, 

1994). Jones and Maslia (1994) reported on another aquifer 

test performed in April 1990 in which a public-supply well 

open to the UWBZ located just north of the chloride plume 

was pumped for 24-hours with a computed transmissivity 

value from a nearby UWBZ observation well of 57,000 ft2/d. 

Borehole flowmeter tests (Wait and Gregg, 1973) indicated 

that the UWBZ contained a higher Kh than the LWBZ, based 

on UWBZ contribution of 70 percent of the water from wells 

tapping both zones.

Zones in the UWBZ were designated as follows:

• Zone F13 (Kh= 300 ft/d) represents an area of intensive 

groundwater pumping near the northwestern part of the 

chloride plume and also contains steep hydraulic gradients 

toward the pumping centers at the Georgia-Pacific 

Cellulose plant. 

• Zone F14 (Kh= 240 ft/d) represents a transitional area 

between the pumping centers to the north of downtown 

Brunswick and an area of low hydraulic conductivity at 

the southern end of the chloride plume to the south. 

• Zone F15 (Kh= 200 ft/d) contains steep hydraulic gradients 

in the potentiometric surface of the UFA that are not 

attributed to groundwater pumping, thus indicating a 

decrease in Kh. 
Simulation of Steady-State Groundwater Flow, 2000–04 31

C1

C3

C4

B1

C2

C1

C3

C5

C4

Surficial aquifer system

(layer 1)

Figure 10.

C2

N

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

Brunswick aquifer system

(layers 3, 4, and 5)

Confining unit

(layer 2)

GA

FL

SC

GA

Hydraulic-property zone

EXPLANATION

C1

SOUTH

GEORGIA CAROLINA

FLORIDA

Model

area

Figure 10. Hydraulic property zones for the regional model (Payne and others, 2005) near Brunswick/Glynn County, Georgia.
32 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Fort 

Stewart

Hunter

Army

Airfield

F10

F1

F2

F6

F11

F8

F7

F5

F3

F9

F12

F17

F4

F13, F14, F15

(See enlargement

of Glynn CountyBrunswick area)

F16

C1

C3

C5

C4

C2

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

N

Upper Floridan aquifer

(layers 7, 8, and 8)

Upper Floridan confining unit

(layer 6)

GA

FL

SC

GA

GLYNN COUNTY

Hydraulic-property zone

EXPLANATION

C1

Figure 10.—Continued

SOUTH

GEORGIA CAROLINA

FLORIDA

Model

area

0 5 10 MILES

0 5 10 KILOMETERS

F7

F13

F14

F15

Figure 10. Hydraulic property zones for the regional model (Payne and others, 2005) near Brunswick/Glynn County, 

Georgia.—Continued
Simulation of Steady-State Groundwater Flow, 2000–04 33

LFC1

LFC2

LFC3

LF1

LF2

LF3

N

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

Lower Floridan aquifer

(layer 11)

Lower Floridan confining unit

(layer 10)

GA

FL

SC

GA

Hydraulic-property zone

EXPLANATION

C1

Figure 10.—Continued

SOUTH

GEORGIA CAROLINA

FLORIDA

Model

area

Figure 10. Hydraulic property zones for the regional model (Payne and others, 2005) near Brunswick/Glynn County, 

Georgia.—Continued
34 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

For the LWBZ, the following additional aquifer property 

zones provided detail to the computed potentiometric surface 

in the Brunswick/Glynn County area that was not available 

from simulations using the original model:

• Zone F13 (Kh= 270 ft/d) represents a region of high 

groundwater flow to wells with correspondingly little 

groundwater-level decline. 

• Zone F14 (Kh= 200 ft/d) represents a transition zone 

between pumping centers to the north of downtown 

Brunswick and low-permeability, less productive aquifer 

material to the south. 

• Zone F15(Kh=125 ft/d) represents an area of lowpermeability material south of the pumping centers.

A Kv value of 0.2 ft/d was assigned to hydraulic property 

zones F7, F8, F13, F14, and F15 in the Camden/Glynn County 

area for the confining unit (layer 8) to allow leakage between 

the UWBZ and LWBZ of the UFA. This assigned Kv value 

was the same Kv value used for the confining unit to simulate 

interaquifer leakage from the UFA to the LFA in zone F17 

located near Fort Stewart (Clarke and others, 2011). Outside of this subregional area consisting of five zones model 

layers 7, 8 and 9 representing the UFA have the same horizontal hydraulic conductivity. In general, hydraulic conductivity 

values were greater than those used in the original model 

for most of the zones in the UWBZ of the UFA (table 4), 

and a suitable fit between observed and simulated heads was 

achieved for calibration. One exception was for zones F4 and 

F5, where hydraulic conductivity values were decreased to 

better represent the cone of depression near Chatham County, 

Ga., with simulated groundwater levels. 

Zones F16 and F17 (fig. 10) were based on the revised 

model’s ability to simulate interaquifer leakage from the UFA 

to the LFA through the confining unit caused by pumping in 

newly constructed LFA wells near Hunter Army Airfield and 

Fort Stewart, Ga. (Clarke and others, 2010 and 2011). Based 

on 72-hour aquifer tests, two distinct zones of hydraulic 

conductivity were created in modified models of these areas to 

simulate hydraulic property variations in the lower confining 

unit of the LFA (fig. 10; table 4). 

Boundary Conditions

Boundaries used in the revised model generally conformed 

to those used in the original model and are based on locations of 

natural-flow boundaries where available (figs. 7 and 8). Artificial 

boundaries were used where natural-flow boundaries were 

unavailable. Payne and others (2005) contains a complete discussion of boundary conditions used in the original model. The main 

adjustments to boundaries in the revised model involve updated 

changes to reflect hydrologic conditions during 2004, including 

adjustment of groundwater levels along specified-head boundaries. 

Vertical Boundaries

The lowermost boundary represents the no-flow condition present at the contact between the LFA (layer 11) and 

underlying low-permeability sediments of Paleocene age and 

older. The altitude of this no-flow boundary varies greatly over 

the model area and depends on the orientation of this contact 

with regard to geologic structure (strike and dip). In general, 

this no-flow boundary reaches its greatest depth near the 

Southeast Georgia Embayment.

The uppermost boundary of the revised model represents 

a general-head condition; controlling heads represent the estimated water table for onshore areas (Peck and Payne, 2003), 

and a conductance term helps regulate the amount of recharge 

to, or discharge from, onshore and offshore areas. In the 

onshore area, this boundary condition was applied to the uppermost active aquifer cell in the model, which could be layer 1, 

2, or 5, depending on which unit crops out at land surface. The 

conductance term and the simulated and controlling hydraulic 

heads along the boundary contributed to model computations 

of reasonable recharge rates that were compared with those 

derived from base-flow calculations (Priest, 2004) and others 

associated with similar hydrologic settings (Williamson and 

others, 1990). The general-head boundary represents a sourcesink boundary in the unconfined portion of the surficial aquifer 

that facilitates water exchange into (recharge) and out of 

(discharge) the confined, regional groundwater system. 

In the offshore area, a general-head boundary was placed 

above the top active cells of model layer 1. The controlling 

head in this area of the model represents the freshwater 

equivalent of the saltwater head; hydraulic conductance is 

assumed to be constant; and thickness between the controlling 

head and active cells of layer 1 generally is limited to several 

feet. Sensitivity analyses performed on the parameters that 

define the general-head boundary indicated that their values 

do not substantially affect simulated results, and that flow 

from the confined system in the offshore area is assumed to 

be controlled predominantly by the hydraulic properties of the 

confining units, model layers 2 through 6. 

Lateral Boundaries

Lateral boundary conditions for the revised model 

were selected to coincide as closely with assumed no-flow 

boundaries or groundwater divides as defined by Payne and 

others (2005) in the original model. With the exception of the 

Floridan aquifer system (layers 7–11), lateral boundaries for 

all other layers are designated as no-flow boundaries.

Simulated flow in the Floridan aquifer system is bounded 

laterally by a combination of no-flow and specified-head 

boundaries. The northwestern boundary of the model is defined 

as a no-flow boundary because it is located at the approximate 

updip extent of the Floridan aquifer system or its equivalent, as 

defined by Miller (1986). The onshore part of the northeastern 

flow boundary was designated as a no-flow boundary because, 

according to Ransom and White (1999), estimated flow lines 

drawn on the potentiometric-surface map indicate parallel flow 

to this boundary. This boundary also extends offshore and is 

connected to the eastern no-flow boundary. 

To the southwest and south of the model area, the 

Floridan aquifer system extends beyond the model boundaries; 
Simulation of Steady-State Groundwater Flow, 2000–04 35

therefore, a specified-head boundary was used to allow flow 

into the model. The original model assigned values to the 

specified-head boundary based on potentiometric surfaces of 

the UFA that correspond to specific years of the simulation to 

incorporate temporal changes in head that affect flow patterns 

and directions. Potentiometric-surface maps for May 1980 

(Johnston and others, 1981), May 1998 (Peck and others, 

1999), and September 2000 (Peck and McFadden, 2004) were 

used to assign heads along the specified-head boundary. 

Heads along the southwestern boundary in the revised 

model were adjusted on the basis of observed water-level 

changes presented by Peck and others (2004). Water levels 

near the southwestern boundary were affected by the shutdown of the Durango Paper Company mill near St. Marys, 

Camden County, during 2002, which caused 5- to 10-ft waterlevel rises in the UFA by May 2003 (Peck and others, 2004). 

Specified-head values were adjusted accordingly in the UWBZ 

(layer 7) and LWBZ (layer 9) and the intervening confining 

unit (layer 8) to account for the increased water levels. 

Similarly, heads also were changed in the LFA (layer 11) 

and overlying confining unit (layer 10). 

Groundwater Withdrawals

Groundwater withdrawals were compiled for input to 

the revised model in preparation for steady-state simulation 

of 2000 and 2004 conditions. Pumpage for 2004 was estimated using site-specific data for 2004 and county-aggregate 

estimates for 2000. Year 2000 estimates were used for 2004 

because estimated values were not available for that year. 

Pumpage was assigned to nodes of the model cells using 

procedures described in Taylor and others (2003).

Pumpage assigned to single layers in the original model 

was redistributed to multiple layers representing the Brunswick 

and Floridan aquifer systems in the revised model based on the 

thickness of the aquifers, or water-bearing zones, because the 

actual contribution to pumpage from each water-bearing zone 

could not be determined. The redistribution of pumpage from 

single layers in the original model to one or more layers in the 

revised model involved the following reassignments:

• Brunswick aquifer system—layer 3 (original model) 

reassigned to layers 3 and 5 (revised model) to 

represent pumpage in the upper and lower Brunswick 

aquifers, respectively;

• UFA—layer 5 (original model) reassigned to layers 

7 and 9 (revised model) to represent pumpage in the 

UWBZ and LWBZ, respectively;

• LFA—layer 7 (original model) represented as pumpage 

in layer 11 (revised model).

For the 2000 simulation, pumpage was aggregated to 

nodal locations in the model grid in model layers 3 and 5 

(Brunswick aquifer system, fig. 11). Nodes representing 

pumpage in the multiple layers of the revised model corresponded with the nodal locations of pumpage in the single 

layer of the original model. Pumpage at actual well locations 

was not represented as such in the original model nor the 

revised model. 

For the 2004 simulation, pumpage was identified at 

specific well locations in the Brunswick aquifer system in the 

Glynn County area (fig. 12). This pumpage was represented in 

the revised model as simulated withdrawal at the closest nodes 

in the model grid. 

The 2000 and the 2004 steady-state simulations both 

show pumping centers in the UFA (layers 7 and 9) near 

Savannah, Jesup, and Brunswick, Ga. (figs. 11C–D and 

12C–D). Production wells open to the UFA were assumed 

to penetrate the entire aquifer and pumping was distributed 

based on the thickness of the UWBZ and LWBZ of the UFA 

(layers 7 and 9). During the 2004 simulation, pumping was 

eliminated at the Durango Paper Company mill near St. 

Marys for a reduction of 36 Mgal/d in model layers 7 and 9 

(fig. 12C–D). In the Brunswick/Glynn County area, the number 

of active industrial production wells decreased in the northern 

part of the city. Water-supply wells near Brunswick generally are open to the UWBZ and LWBZ, but do not tap 

water-bearing units beneath the UFA (L. Elliott Jones, U.S. 

Geological Survey, written commun., 2014). Current-meter 

data and well depth information at the Pinova and GP Cellulose 

well fields indicate that the estimated contribution from the 

UWBZ to total water pumped from the UFA ranged between 

30 to 45 percent (Jones and Maslia, 1994; L. Elliott Jones, U.S. 

Geological Survey, written commun., 2014). Pumping in the 

LFA (layer 11) is concentrated mostly north of Jacksonville, 

Fla., in both simulations, with pumpage from some active wells 

located in Chatham County, Ga., during the 2000 simulation. 

Model Calibration

The revised model was calibrated by adjusting hydraulic 

properties and boundary conditions so that simulated groundwater levels reasonably matched observed water levels 

during 2004. Although initial simulations utilized hydraulic 

properties derived from calibration of the original model, an 

improved match of simulated to observed groundwater levels 

was obtained for the UWBZ and upper and lower Brunswick 

aquifers with the revised model by rezoning and adjusting 

hydraulic conductivity values in the Brunswick/Glynn County 

area. The revised model was further evaluated using pumping 

estimates for 2000 in conjunction with observed water levels 

during 2000 to obtain the best possible match of simulated 

to observed water levels in the Brunswick/Glynn County 

area. Additionally, the calibrated revised model allowed grid 

refinement near the area of chloride contamination in the City 

of Brunswick to accurately simulate hydraulic gradients and 

groundwater-flow directions near industrial pumping centers. 

The simulated hydraulic gradients, or potentiometric gradients, near downtown Brunswick are important because they 

control the direction and rate of chloride movement within 

the plume area. Changes in potentiometric gradients over 

extended periods could alter the shape and the extent of the 

chloride plume. 
36 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Figure 11. 

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey

1:100,000-scale digital data

A

0.000001 to 0.000250

0.000251 to 0.000500

>0.000500

Model grid

Nodal pumping rate—In million gallons per

 day, during 2000, layer 3. Specific wells 

 were not identified for this pumping period

EXPLANATION

N

SOUTH

GEORGIA CAROLINA

Approximate extent

of Brunswick FLOR

aquifer system IDA

Model

area

Figure 11. Distribution of groundwater pumpage for 2000 for A, model layer 3, upper Brunswick 

aquifer; B, model layer 5, lower Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper 

water-bearing zone; D, model layer 9, Upper Floridan aquifer lower water-bearing zone; and 

E, model layer 11, Lower Floridan aquifer.
Simulation of Steady-State Groundwater Flow, 2000–04 37

0.000001 to 0.000250

0.000251 to 0.000500

>0.000500

Model grid

Nodal pumping rate—In million gallons per

 day, during 2000, layer 5. Specific wells 

 were not identified for this pumping period

EXPLANATION

Figure 11.—Continued

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey

1:100,000-scale digital data

B

N

SOUTH

GEORGIA CAROLINA

Approximate extent

of Brunswick FLOR

aquifer system IDA

Model

area

Figure 11. Distribution of groundwater pumpage for 2000 for A, model layer 3, upper Brunswick 

aquifer; B, model layer 5, lower Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper 

water-bearing zone; D, model layer 9, Upper Floridan aquifer lower water-bearing zone; and 

E, model layer 11, Lower Floridan aquifer.—Continued
38 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

GLYNN

Brunswick

Map area

shown

at right

Jesup

Savannah

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

N

Map area

shown

below, left

SOUTH

GEORGIA CAROLINA

Model

area

Base from U.S. Geological Survey digital files,1:24,000, Brunswick West, 1993; Brunswick East, 1979

Model grid

EXPLANATION

0 5 10 MILES

0 5 10 KILOMETERS

Pumping rate per well—In million

 gallons per day, during 2000, layer 7

<0.1

0.1 to 0.5

>0.5 to 1.0

>1.0 to 2.0

>2.0

Figure 11.—Continued

0 0.5 1 MILE

0 0.5 1 KILOMETER

N N

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

C

Figure 11. Distribution of groundwater pumpage for 2000 for A, model layer 3, upper Brunswick aquifer; B, model layer 5, lower 

Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper water-bearing zone; D, model layer 9, Upper Floridan aquifer lower 

water-bearing zone; and E, model layer 11, Lower Floridan aquifer.—Continued
Simulation of Steady-State Groundwater Flow, 2000–04 39

GLYNN

Brunswick

Map area

shown

at right

Jesup

Savannah

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

N

D SOUTH

GEORGIA CAROLINA

Model

area

Base from U.S. Geological Survey digital files,1:24,000, Brunswick West, 1993; Brunswick East, 1979

Model grid

EXPLANATION

0 5 10 MILES

0 5 10 KILOMETERS

Pumping rate per well—In million

 gallons per day, during 2000, layer 9

<0.1

0.1 to 0.5

>0.5 to 1.0

>1.0 to 2.0

>2.0

Figure 11.—Continued

0 0.5 1 MILE

0 0.5 1 KILOMETER

N N

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

Map area

shown

below, left

Figure 11. Distribution of groundwater pumpage for 2000 for A, model layer 3, upper Brunswick aquifer; B, model layer 5, lower 

Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper water-bearing zone; D, model layer 9, Upper Floridan aquifer lower 

water-bearing zone; and E, model layer 11, Lower Floridan aquifer.—Continued
40 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

N

Jacksonville

SOUTH

GEORGIA CAROLINA

Model

area

Model grid

EXPLANATION

Pumping rate per well—In million

 gallons per day, during 2000, layer 11

<0.1

0.1 to 0.5

>0.5

Figure 11.—Continued

E

Figure 11. Distribution of groundwater pumpage for 2000 for A, model layer 3, upper Brunswick aquifer; B, model layer 

5, lower Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper water-bearing zone; D, model layer 9, Upper 

Floridan aquifer lower water-bearing zone; and E, model layer 11, Lower Floridan aquifer.—Continued
Simulation of Steady-State Groundwater Flow, 2000–04 41

Figure 12. Distribution of groundwater pumpage for 2004 for A, model layer 3, upper Brunswick 

aquifer; B, model layer 5, lower Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper 

water-bearing zone; D, model layer 9, Upper Floridan aquifer lower water-bearing zone; and E, model 

layer 11, Lower Floridan aquifer.

<0.01

0.01 to <0.1

0.1 to 0.5 

Model grid

Pumping rate per well—In million 

 gallons per day, during 2004, layer 3 

EXPLANATION

Figure 12. 

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey

1:100,000-scale digital data

A

N

SOUTH

GEORGIA CAROLINA

Approximate extent

of Brunswick FLOR

aquifer system IDA

Model

area
42 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey

1:100,000-scale digital data

<0.01

0.01 to <0.1

0.1 to 0.5 

Model grid

Pumping rate per well—In million 

 gallons per day, during 2004, layer 5 

EXPLANATION

Figure 12.

B

N

SOUTH

GEORGIA CAROLINA

Approximate extent

of Brunswick FLOR

aquifer system IDA

Model

area

Figure 12. Distribution of groundwater pumpage for 2004 for A, model layer 3, upper Brunswick aquifer; 

B, model layer 5, lower Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper water-bearing 

zone; D, model layer 9, Upper Floridan aquifer lower water-bearing zone; and E, model layer 11, Lower 

Floridan aquifer.—Continued
Simulation of Steady-State Groundwater Flow, 2000–04 43

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

N

St Marys

GLYNN

Brunswick

Map area

shown

at right

C SOUTH

GEORGIA CAROLINA

FLORIDA

Model

area

Base from U.S. Geological Survey digital files,1:24,000, Brunswick West, 1993; Brunswick East, 1979

Model grid

EXPLANATION

0 5 10 MILES

0 5 10 KILOMETERS

Pumping rate per well—In million

 gallons per day, during 2004, layer 7

<0.1

0.1 to 0.5

>0.5 to 1.0

>1.0 to 2.0

>2.0

Figure 12.—Continued

0 0.5 1 MILE

0 0.5 1 KILOMETER

N N

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

Map area

shown

below, left

Figure 12. Distribution of groundwater pumpage for 2004 for A, model layer 3, upper Brunswick aquifer; B, model layer 5, lower 

Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper water-bearing zone; D, model layer 9, Upper Floridan aquifer lower 

water-bearing zone; and E, model layer 11, Lower Floridan aquifer.—Continued
44 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

St Marys

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

N

GLYNN

Brunswick

Map area

shown

at right

D SOUTH

GEORGIA CAROLINA

Model

area

Base from U.S. Geological Survey digital files,1:24,000, Brunswick West, 1993; Brunswick East, 1979

Model grid

EXPLANATION

0 5 10 MILES

0 5 10 KILOMETERS

Pumping rate per well—In million

 gallons per day, during 2000, layer 9

<0.1

0.1 to 0.5

>0.5 to 1.0

>1.0 to 2.0

>2.0

Figure 12..—Continued

0 0.5 1 MILE

0 0.5 1 KILOMETER

N N

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

Map area

shown

below, left

Figure 12. Distribution of groundwater pumpage for 2004 for A, model layer 3, upper Brunswick aquifer; B, model layer 5, lower 

Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper water-bearing zone; D, model layer 9, Upper Floridan aquifer lower 

water-bearing zone; and E, model layer 11, Lower Floridan aquifer.—Continued
Simulation of Steady-State Groundwater Flow, 2000–04 45

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

N

SOUTH

GEORGIA CAROLINA

Model

area

Model grid

EXPLANATION

Pumping rate per well—In million

 gallons per day, during 2000, layer 11

<0.1

0.1 to 0.5

>0.5 to 1.0

>1.0 to 2.0

>2.0

Figure 12.—Continued

E

Parameter-estimation techniques were used to adjust 

hydraulic properties in an efficient manner that (1) eliminated 

the need for time-intensive, trial-and-error, manual techniques 

of achieving calibration and (2) resulted in a distribution of 

hydraulic conductivity that nearly satisfied the calibration 

criterion of matching simulated to observed groundwater 

levels. Minor adjustments were made to the parameter estimation results to obtain a calibrated model of steady-state 2004 

conditions. The calibrated model then simulated steady-state 

2000 pumping and boundary conditions. 

Acceptance Criteria

Model performance for 2000 and 2004 conditions was 

evaluated on the basis of differences (residuals) between simulated and observed water levels as well as their corresponding 

mean, median, and root-mean-square-error (RMSE) statistics 

(tables 5 and 6). The mean residual is a good indicator of bias 

in the differences between observed and simulated heads. The 

median residual eliminates the bias in the data and is more 

robust than the mean in the presence of outlier values. RMSE, 

derived from residuals as the square root of the average deviation of the residuals from zero, yields a measure of overall 

fit of simulated to observed groundwater levels. The calibration criteria used near the Brunswick/Glynn County area in 

the revised model were more stringent than those used in the 

original model because of the relatively low topographic relief 

in the area and the availability of 5-ft contour intervals on 

local topographic maps. For altitudes determined from topographic maps near the downtown Brunswick area, one-half 

the contour interval (2.5 ft) is considered to be the accuracy of 

well data, including groundwater-level measurements, formation altitudes, and so forth. Generally, the vertical accuracy 

of land-surface altitude is about 1 ft if the well location has 

been surveyed or global-positioning instrumentation has been 

utilized. The observation accuracy, therefore, is the assumed 

accuracy of water-level observations at a well and was determined to be 4.6 ft for 2000 water-level conditions used in the 

original model. The original model considered the accuracy of 

land-surface altitude and seasonal variability in water levels to 

have the largest influence on observation accuracy. Additional 

errors inherent to observations (Kuniansky and others, 2003) 

imply that a calibration criterion of twice the standard deviation of observational accuracy, or 9.2 ft for the 2000 waterlevel conditions, is reasonable. Therefore, the calibration 

criterion was rounded to 10 ft for the original model. For the 

revised model, the calibration target for the 2000 and 2004 

simulations was 10 ft for areas outside Glynn County and 

5 ft near downtown Brunswick. The primary objective of the 

calibration was to achieve the best possible match of simulated 

groundwater levels to observed values in the UWBZ of the 

UFA near the Brunswick/Glynn County area Few observations were available for calibration of the Brunswick aquifer 

system, LWBZ of the UFA, and the LFA. 

Figure 12. Distribution of groundwater pumpage for 2004. for A, model layer 3, upper Brunswick aquifer; B, model 

layer 5, lower Brunswick aquifer; C, model layer 7, Upper Floridan aquifer upper water-bearing zone; D, model layer 9, 

Upper Floridan aquifer lower water-bearing zone; and E, model layer 11, Lower Floridan aquifer.—Continued
46 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Table 5. Calibration statistics for simulated heads for 2000 conditions.

[UWBZ, upper water-bearing zone; LWBZ, lower water-bearing zone; residual equals simulated minus observed head; —, not calculated because less 

than 10 values]

Calibration statistic

Upper

Brunswick

aquifer

(layer 3)

Lower

Brunswick

aquifer

(layer 5)

UWBZ of

Upper Floridan

aquifer

(layer 7)

LWBZ of

Upper Floridan

aquifer

(layer 9)

Lower

Floridan

aquifer

(layer 11)

Regional model area

Number of observations 7 3 155 5 11

Range of observations (feet) 30.2 38.3 319 34.2 142

Maximum negative residual (feet) – 8.82 –3.18 –19.5 –10.0 – 6.10

Maximum positive residual (feet) 12.8 15.5 52.0 13.1 32.4

Mean residual (feet) –1.39 5.66 0.92 –4.57 3.72

Median residual (feet) –2.00 4.67 –0.76 –8.62 0.47

Root-mean square error residual 

(feet)

— — 10.9 — 11.4

Residuals within 10-foot 

error criteria (percent)

86 67 77 40 82

Residuals within 5-foot 

error criteria (percent)

43 67 53 0 64

Glynn County

Number of observations 2 1 41 5 7

Range of observations (feet) 8.48 — 40.1 34.2 18.3

Maximum negative residual (feet) – 6.01 — –19.5 –10.0 – 6.10

Maximum positive residual (feet) 2.69 — 4.29 13.1 9.38

Mean residual (feet) –1.66 — –1.30 –4.57 – 0.42

Median residual (feet) — — –0.35 –8.62 –1.93

Root-mean square error residual 

(feet)

— — 4.32 — —

Residuals within 10-foot 

error criteria (percent)

100 100 95 40 100

Residuals within 5-foot 

error criteria (percent)

50 100 88 0 71
Simulation of Steady-State Groundwater Flow, 2000–04 47

Table 6. Calibration statistics for simulated heads for 2004 conditions.

[UWBZ, upper water-bearing zone; LWBZ, lower water-bearing zone; residual equals simulated minus observed head; —, not calculated because less 

than 10 values]

Calibration statistic

Upper

Brunswick

aquifer

(layer 3)

Lower

Brunswick

aquifer

(layer 5)

UWBZ of

Upper Floridan

aquifer

(layer 7)

LWBZ of

Upper Floridan

aquifer

(layer 9)

Lower

Floridan

aquifer

(layer 11)

Regional model area

Number of observations 14 4 52 5 13

Range of observations (feet) 144 44.5 319 34.2 91.7

Maximum negative residual (feet) –28.6 –12.5 –18.9 – 6.15 –37.6

Maximum positive residual (feet) 9.30 10.6 18.3 20.8 24.2

Mean residual (feet) –5.60 –3.62 –2.64 1.20 –3.61

Median residual (feet) –3.57 – 6.31 –2.05 –3.30 –3.73

Root-mean square error residual 

(feet)

11.6 — 6.95 — 14.5

Residuals within 10-foot

error criteria (percent)

79 50 83 80 54

Residuals within 5-foot

error criteria (percent)

43 0 60 60 38

Glynn County

Number of observations 6 2 32 5 7

Range of observations (feet) 33.8 13.6 42.9 34.2 12.1

Maximum negative residual (feet) –13.7 –12.5 –18.9 – 6.15 –10.9

Maximum positive residual (feet) 9.30 – 6.26 3.98 20.8 1.98

Mean residual (feet) –0.77 –9.38 –2.56 1.20 –4.50

Median residual (feet) –0.66 — –1.50 –3.30 –3.73

Root-mean square error residual 

(feet)

— — 5.34 — —

Residuals within 10-foot

error criteria (percent)

83 50 91 80 86

Residuals within 5-foot

error criteria (percent)

67 0 75 60 71
48 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Year 2000 Calibration

Groundwater levels measured in 181 wells during 2000 

(fig. 13A; table 5) were used to determine the acceptance of 

simulated groundwater levels as a criterion for calibrating the 

revised model. Of these 181 measurements, 7 were derived 

from the upper Brunswick aquifer (layer 3), 3 were from the 

lower Brunswick aquifer (layer 5), 155 were from the UWBZ 

of the UFA (layer 7), 5 were from the LWBZ of the UFA 

(layer 9), and 11 were from the LFA (layer 11).

Over the regional model area, residuals, or simulated minus observed water-level altitudes, calculated for 

155 wells tapping the UWBZ of the UFA (layer 7) ranged 

from –19.5 to 52.0 ft, with a mean of 0.92 ft, a median of 

–0.76 ft, and an RMSE of 10.9 ft (fig. 13A; table 5). In the 

Brunswick/Glynn County area, the mean residual based on 

41 measured groundwater levels was –1.30 ft, with a median 

value of –0.35 ft, and an RMSE of 4.32 ft (fig. 13B). 

Residuals in the LWBZ of the UFA (layer 9) were derived 

from 5 observations and ranged from −10.0 to 13.1 ft with 

a mean residual of −4.57 ft and median residual of –8.62 ft, 

indicating poor model performance in the Brunswick/Glynn 

County area (fig. 13B; table 5). Mean residuals for the LFA 

(layer 11) were larger, with 3.72 ft for the regional model area 

and −0.42 ft in the Brunswick/Glynn County area, which was 

considered acceptable. This disparity was also evident in the 

median value of 0.47 ft for the regional model area versus 

−1.93 ft in the Brunswick/Glynn County area (fig.13A–B).

The maps shown in figure 14A–B indicate observation 

data were sparse for model layers 3 and 5, with the maximum 

residuals either located near the edge of model boundaries or 

near the cone of depression in Chatham County. The spatial 

distribution of the observation data and the influence of 

pumping in the Chatham County area did not allow adjustments to hydraulic conductivity that would provide a better 

fit. In the Brunswick/Glynn County area, groundwater-flow 

directions in model layers 3 and 5 were generally from west 

to east with a maximum residual of 2.69 ft and a minimum of 

−6.01 ft (fig. 14A–B; table 5). 

Maps showing simulated 2000 potentiometric surfaces 

and water-level residuals by model layer: A, layer 3, upper 

Brunswick aquifer, model area; B, layer 5, lower Brunswick 

aquifer, model area; C, layer 7, upper water-bearing zone 

of the Upper Floridan aquifer, model area; D, layer 9, lower 

water-bearing zone of the Upper Floridan aquifer; E, layer 7, 

upper water-bearing zone of the Upper Floridan aquifer, Glynn 

County and Brunswick area enlargement; and F, layer 11, 

Lower Floridan aquifer, model area. The distribution of 

residuals for model layer 7 shows generally positive values 

north of Glynn County and west of the Gulf Trough with a 

cluster of negative values at wells along the coastal plain of 

Georgia (fig. 14C), indicative of the model’s inability to dissipate higher-than-observed simulated hydraulic head across 

the Gulf Trough. The increased hydraulic conductivity of the 

hydraulic property zone representing the Gulf Trough would 

lower simulated hydraulic head to the north and west of the 

Gulf Trough and, likewise, increase simulated hydraulic head 

downgradient of the Gulf Trough to the south and east along 

the Coastal Plain. The effect of increasing the simulated watertransmitting ability of the Gulf Trough on groundwater-level 

residuals would simultaneously drive the positive residuals 

upgradient of the Gulf Trough and the negative residuals 

downgradient of the Gulf Trough closer to zero, thereby 

improving calibration. In the Brunswick/Glynn County area, 

the distribution of residuals in model layer 7 indicates a good 

match outside the cone of depression, with generally negative 

residual values on the Brunswick peninsula (fig. 14E; table 5). 

The mean residual for the 2000 simulation in model layer 7 of 

−1.30 ft is generally well within the established error criterion 

of 5 ft, but the lower simulated heads could be caused by an 

overestimation of pumping in the Brunswick area, insufficient 

simulated interaquifer leakage from the LFA into the UFA, 

and (or) adjustments made to the specified-head boundary for 

the Floridan aquifer system (layers 7–11). The distribution 

–20

–10

0

10

20

30 181 7 3 155 5 11

Residuals, in feet

A

–30

56 2 1 41 5 7

–20

–10

0

10

20

30

All 3 5 7 9 11

Layer

B

Figure 13.

–30

56

EXPLANATION 

Number of values

Individual observation

90th percentile

10th percentile

75th percentile

50th percentile

(median)

25th percentile

Figure 13. Boxplots showing difference (residuals) 

between simulated and observed heads for 2000

simulation in A, the regional model area and 

B, Brunswick/Glynn County area.
Simulation of Steady-State Groundwater Flow, 2000–04 49

Savannah

Savannah

A. Upper Brunswick aquifer

 (layer 3)

Model boundary

GA

FL

SC

GA

B. Lower Brunswick aquifer

 (layer 5)

Figure 14.

20

10

0

–10

40

60

80 100

120

20

40

60

80

100

120

20

20

10

0

–10

–20

–30

–40

–20

–30

–40

N

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

EXPLANATION

Simulated potentiometric contour—

 Shows simulated 2000 potentiometric

 surface, in feet. Hachures indicate

 depression. Contour intervals 10 and

 20 feet. Datum is NAVD 88

Water-level residual, in feet—

 Represents simulated minus

 observed water levels

0 to –5

0 to 5

5 to 10

10 to 20

–5 to –10

60

SOUTH

GEORGIA CAROLINA

Model area

Approximate extent

of Brunswick

aquifer system

FLORIDA

Figure 14. Simulated 2000 potentiometric surfaces and water-level residuals by model layer: A, layer 3, upper Brunswick 

aquifer, model area; B, layer 5, lower Brunswick aquifer, model area; C, layer 7, upper water-bearing zone of the Upper 

Floridan aquifer, model area; D, layer 9, lower water-bearing zone of the Upper Floridan aquifer; E, layer 7, upper waterbearing zone of the Upper Floridan aquifer, Glynn County and Brunswick area enlargement; F, layer 9, lower water-bearing 

zone of the Upper Floridan aquifer; and G, layer 11, Lower Floridan aquifer, model area and Glynn County enlargement.
50 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Savannah

Jesup

Savannah

Jesup

l l l l l l l l l l l l

l l l l l l l l l l l l

l l l l l l l l l

l l l l l l l l l l l l

l l l l l l l l l l l l l l

l

l l l l l l l

20

0

0

–20

–40

–60

–20

20

60

80

200

40

240

260

260

240

260

280 300

320

100

120

140

160

180

200

220

340

0

20

0

–20

–40

–60

–80

40

60

80

100

120

140

160

180

200

220

240

260

280

260

240

–20

260

300

N

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

EXPLANATION

Simulated potentiometric contour—

 Shows simulated 2000 potentiometric

 surface, in feet. Hachures indicate

 depression. Contour interval 20 feet.

 Datum is NAVD 88

Water-level residual, in feet—

 Represents simulated minus

 observed water levels

60

Model boundary

GA

FL

SC

GA

–10 to –19.6

–5 to –10

0 to –5

0 to 5

5 to 10

10 to 20

20 to 30

> 30

Figure 14.—Continued

SOUTH

CAROLINA GEORGIA

Model area

FLORIDA

C. Upper water-bearing zone of

 Upper Floridan aquifer

 (layer 7)

D. Lower water-bearing zone of

 Upper Floridan aquifer

 (layer 9)

See figure 15E

for enlargements

Figure 14. Simulated 2000 potentiometric surfaces and water-level residuals by model layer: A, layer 3, upper Brunswick 

aquifer, model area; B, layer 5, lower Brunswick aquifer, model area; C, layer 7, upper water-bearing zone of the Upper Floridan 

aquifer, model area; D, layer 9, lower water-bearing zone of the Upper Floridan aquifer; E, layer 7, upper water-bearing zone of 

the Upper Floridan aquifer, Glynn County and Brunswick area enlargement; F, layer 9, lower water-bearing zone of the Upper 

Floridan aquifer; and G, layer 11, Lower Floridan aquifer, model area and Glynn County enlargement.—Continued
Simulation of Steady-State Groundwater Flow, 2000–04 51

5

0

15

 Jekyll

Island

GLYNN COUNTY

Brunswick

10

10

–5

l l l l l l l l l l

l

l l l l l l l l l

l l l l l l l l l l

l

l l l l l l

E. Upper water-bearing zone of Upper Floridan aquifer

 (layer 7)

10

15

20

25

Map area shown at right

0 5 10 MILES

0 5 10 KILOMETERS

N

N

0 1 2 MILES

0 1 2 KILOMETERS

–10 to –19.6

–5 to –10

0 to –5

0 to 5

Base from U.S. Geological Survey digital files,1:24,000

Brunswick West, 1993; Brunswick East, 1979

EXPLANATION

Simulated potentiometric contour—

 Shows simulated 2000 potentiometric

 surface, in feet. Hachures indicate

 depression. Contour interval 5 feet.

 Datum is NAVD 88

Water-level residual, in feet—Represents

 simulated minus observed water levels

10

Base from U.S. Geological Survey 

1:100,000-scale digital data

Figure 14.—Continued

Figure 14. Simulated 2000 potentiometric surfaces and water-level residuals by model layer: A, layer 3, upper Brunswick 

aquifer, model area; B, layer 5, lower Brunswick aquifer, model area; C, layer 7, upper water-bearing zone of the Upper Floridan 

aquifer, model area; D, layer 9, lower water-bearing zone of the Upper Floridan aquifer; E, layer 7, upper water-bearing zone of 

the Upper Floridan aquifer, Glynn County and Brunswick area enlargement; F, layer 9, lower water-bearing zone of the Upper 

Floridan aquifer; and G, layer 11, Lower Floridan aquifer, model area and Glynn County enlargement.—Continued
52 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Savannah

0

–40

–60

–80

80

100

120

140

160

180

200

220

240

260

260

240

–5 to –10

0 to –5

0 to 5

5 to 10

10 to 20

Area of

map below

20

40

60

–20

0

F. Lower Floridan aquifer

 (layer 11)

5

10

15

20

25

10 l l l l l l l l l l l l l l l l l l l l l l l l l l

l l l l l l l

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

0 5 10 MILES

0 5 10 KILOMETERS

N

N

GLYNN COUNTY

EXPLANATION

Simulated potentiometric contour—

 Shows simulated 2000 potentiometric

 surface, in feet. Hachures indicate

 depression. Contour intervals 20 feet

 (top map) and 5 feet (bottom map).

 Datum is NAVD 88

Water-level residual, in feet—

 Represents simulated minus

 observed water levels

60

Model boundary

GA

FL

SC

GA

Figure 14.—Continued

SOUTH

CAROLINA GEORGIA

Model area

FLORIDA

Figure 14. Simulated 2000 potentiometric surfaces and water-level residuals by model layer: A, layer 3, 

upper Brunswick aquifer, model area; B, layer 5, lower Brunswick aquifer, model area; C, layer 7, upper 

water-bearing zone of the Upper Floridan aquifer, model area; D, layer 9, lower water-bearing zone of the 

Upper Floridan aquifer; E, layer 7, upper water-bearing zone of the Upper Floridan aquifer, Glynn County 

and Brunswick area enlargement; F, layer 9, lower water-bearing zone of the Upper Floridan aquifer; and 

G, layer 11, Lower Floridan aquifer, model area and Glynn County enlargement.—Continued
Simulation of Steady-State Groundwater Flow, 2000–04 53

of residuals for model layer 11 indicates generally positively 

skewed residuals in the northern part of the model and negatively skewed residuals to the south of Chatham County. In the 

Brunswick/Glynn County area, the distribution of residuals in 

model layer 11 shows mostly negative values near the area of 

influence for pumping in model layers 7 and 9 near downtown 

Brunswick with 5 of the 7 wells (71 percent) falling within the 

established 5-ft calibration criterion (fig. 14F ). 

Year 2004 Calibration

Groundwater levels measured in 88 wells during 2004 

(fig. 15; table 6) were used to determine the acceptance of 

simulated groundwater levels as a criterion for calibrating the 

revised model. Of these 88 measurements, 14 were derived 

from the upper Brunswick aquifer (layer 3), 4 were from the 

lower Brunswick aquifer (layer 5), 52 were from the UWBZ of 

the UFA (layer 7), 5 were from the LWBZ of the UFA (layer 9), 

and 13 were from the LFA (layer 11). For the regional model 

area, residuals for model layer 7 ranged from −18.9 to 18.3 ft, 

with a mean of −2.64 ft, median of −2.05 ft, and an RMSE 

of 6.95 ft. In the Brunswick/Glynn County area, residuals 

from 32 observation wells in model layer 7 ranged from 

−18.9 to 3.98 ft, with a mean of −2.56 ft, median of −1.50 ft and 

an RMSE of 5.34 ft (fig. 15; table 6). For the regional model 

area for model layer 3, residuals from 14 observation wells open 

to the Brunswick aquifer system ranged from −28.6 to 9.30 ft, 

with a mean of −5.60 ft, median of −3.57 ft, and an RMSE 

of 11.6 ft. For model layer 5, residuals from four observation 

wells ranged from −12.5 to 10.6 ft, with a mean of −3.62 ft. 

For model layer 9, residuals from five wells located near downtown Brunswick ranged from −6.15 to 20.8 ft, with a mean 

of 1.20 ft and a median of −3.30 ft. Over the entire regional 

model area for model layer 11, residuals from the 13 observation wells ranged from −37.6 to 24.2 ft, with a mean of −3.61 ft, 

median of −3.73 ft, and an RMSE of 14.5 ft. The percentage of 

residuals within the 10-ft calibration target of observed values 

over the regional model area was 79 percent for model layer 3, 

50 percent for model layer 5, 83 percent for model layer 7, 

80 percent for model layer 9, and 54 percent for model layer 11. 

When the more stringent 5-ft calibration target was applied to 

residuals in the Brunswick/Glynn County area, the percentage 

within the target was 75 percent for model layer 7, 60 percent 

for model layer 9, and 71 percent for model layer 11. 

For the year 2004 calibration, the map showing distribution of water-level residuals for the upper Brunswick aquifer 

(layer 3) indicates mostly negative values near the northern 

extent of the aquifer and in the Brunswick/Glynn County 

area except for several positive values located in northern 

Glynn County (fig. 16A). Water-level residuals for the lower 

Brunswick aquifer (layer 5) are negative, except for one 

positive value located in Bryan County (fig. 16B). Residuals 

for the UWBZ of the UFA (layer 7) are negative south of the 

Brunswick/Glynn County area and positive near the Gulf 

Trough and on the outer edge of the cone of depression in the 

Savannah area (fig. 16C). In the Brunswick/Glynn County 

area, the distribution of water-level residuals in the UWBZ 

88 14 4 52 5 13

53 7 2 32 5 7

Figure 15.

A

–20

–10

0

10

20

30

Residuals, in feet –30

B

–20

–10

0

10

20

30

–30

All 3 5 7 9 11

Layer

53

EXPLANATION 

Number of values

Individual observation

90th percentile

10th percentile

75th percentile

50th percentile

(median)

25th percentile

Figure 15. Boxplots showing difference (residuals) 

between simulated and observed heads for 2004 

simulation in the A, regional model area, and 

B, Brunswick/Glynn County area.

of the UFA (layer 7) indicates a “good” match, with a mean 

residual of −2.56 ft and 75 percent of the values within the 

established error criterion of 5 ft (fig. 16E; table 6). However, 

the map showing the distribution of water-level residuals indicates an “excellent” match in the downtown Brunswick area 

but large negative values for wells located on Jekyll Island 

between the 15- and 20-ft simulated potentiometric contours. 

The map showing the distribution of water-level residuals for 

the LWBZ of the UFA (layer 9) includes 1 positive value and 

4 negative values located south of and near the cone of depression, with a mean residual of 1.20 ft (fig. 16F; table 6). The 

map showing distribution of water-level residuals for the LFA 

(layer 11) indicates values are negatively skewed, except for 

several positive values in the Brunswick/Glynn County area 

and three others located within the cone of depression to the 

north (fig. 16G; table 6). 
54 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

0

–20

–40

20

20

40

60

80 100

120

0

–20 –40

20

40

60

80

100

120

20

N

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

EXPLANATION

Simulated potentiometric contour—

 Shows simulated 2004 potentiometric

 surface, in feet. Hachures indicate

 depression. Contour interval 20 feet.

 Datum is NAVD 88

Water-level residual, in feet—

 Represents simulated minus

 observed water levels

0 to –5

0 to 5

5 to 10

10 to 20

–5 to –10

–10 to –20

–20 to –30

60

A. Upper Brunswick aquifer

 (layer 3)

Model boundary

GA

FL

SC

GA

B. Lower Brunswick aquifer

 (layer 5)

SOUTH

GEORGIA CAROLINA

Model area

Approximate extent

of Brunswick

aquifer system

FLORIDA

Figure 16.

Figure 16. Simulated 2004 potentiometric surfaces and water-level residuals by model layer: A, layer 3, upper Brunswick 

aquifer, model area; B, layer 5, lower Brunswick aquifer, model area; C, layer 7, upper water-bearing zone of the Upper 

Floridan aquifer, model area; D, layer 9, lower water-bearing zone of the Upper Floridan aquifer; E, layer 7, upper waterbearing zone of the Upper Floridan aquifer, Glynn County and Brunswick area enlargement; F, layer 9, lower water-bearing 

zone of the Upper Floridan aquifer; and G, layer 11, Lower Floridan aquifer, model area and Glynn County enlargement.
Simulation of Steady-State Groundwater Flow, 2000–04 55

See figure 16E

for enlargements

Savannah

Jesup

Savannah

Jesup

l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l

l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l

0

260

240

260

240

260

220

200

280

300

180

160

140

120

100

80

60

40

20

0

180

–20

–40

–20 –60

–80

260

240

260

240

260

220

200

180

160

140

120

100

80

60

40

20

0

280 320 300

220

–20

–40

0

–20 –60

–80

340

N

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

EXPLANATION

Simulated potentiometric contour—

 Shows simulated 2004 potentiometric

 surface, in feet. Hachures indicate

 depression. Contour interval 20 feet.

 Datum is NAVD 88

Water-level residual, in feet—

 Represents simulated minus

 observed water levels

60

Model boundary

GA

FL

SC

GA

–10 to –20

–5 to –10

0 to –5

0 to 5

5 to 10

10 to 20

C. Upper water-bearing zone of

 Upper Floridan aquifer

 (layer 7)

D. Lower water-bearing zone of

 Upper Floridan aquifer

 (layer 9)

Figure 16.—Continued

SOUTH

CAROLINA GEORGIA

Model area

FLORIDA

Figure 16. Simulated 2004 potentiometric surfaces and water-level residuals by model layer: A, layer 3, upper Brunswick 

aquifer, model area; B, layer 5, lower Brunswick aquifer, model area; C, layer 7, upper water-bearing zone of the Upper Floridan 

aquifer, model area; D, layer 9, lower water-bearing zone of the Upper Floridan aquifer; E, layer 7, upper water-bearing zone of 

the Upper Floridan aquifer, Glynn County and Brunswick area enlargement; F, layer 9, lower water-bearing zone of the Upper 

Floridan aquifer; and G, layer 11, Lower Floridan aquifer, model area and Glynn County enlargement.—Continued
56 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Area of map below

E. Upper water-bearing zone of Upper Floridan aquifer

 (layer 7)

F. Lower water-bearing zone of Upper Floridan aquifer

 (layer 9)

10

5

5

15

20

0

–5

10

15

5

0

20

25

20

25

15

15

Brunswick

0 5 10 MILES

0 5 10 KILOMETERS

N

GLYNN COUNTY

Base from U.S. Geological Survey digital files,1:24,000, Brunswick West, 1993; Brunswick East, 1979

0 0.5 1 MILE

0 0.5 1 KILOMETER

N

Base from U.S. Geological Survey 

1:100,000-scale digital data

EXPLANATION

Simulated potentiometric contour—

 Shows simulated 2004 potentiometric

 surface, in feet. Hachures indicate

 depression. Contour interval 5 feet.

 Datum is NAVD 88

Water-level residual, in feet—

 Represents simulated minus

 observed water levels

10

–10 to –20

–5 to –10

0 to –5

0 to 5

5 to 10

10 to 20

Figure 16.—Continued

Brunswick

 Jekyll

Island

Figure 16. Simulated 2004 potentiometric surfaces 

and water-level residuals by model layer: A, layer 

3, upper Brunswick aquifer, model area; B, layer 5, 

lower Brunswick aquifer, model area; C, layer 7, upper 

water-bearing zone of the Upper Floridan aquifer, 

model area; D, layer 9, lower water-bearing zone of the 

Upper Floridan aquifer; E, layer 7, upper water-bearing 

zone of the Upper Floridan aquifer, Glynn County and 

Brunswick area enlargement; F, layer 9, lower waterbearing zone of the Upper Floridan aquifer; and G, layer 

11, Lower Floridan aquifer, model area and Glynn County 

enlargement.—Continued
Simulation of Steady-State Groundwater Flow, 2000–04 57

Savannah

240

260

240

220

200

180

160

140

120

260

280 300

100

80

60

40

20

180

0

–20

–40

–20 –60

–80

0

260

10

15

20

25

15

G. Lower Floridan aquifer

 (layer 11)

l l l l l l l l

l l

l l l l l l l l l l l l

l l l l l l l l l

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

0 5 10 MILES

0 5 10 KILOMETERS

N

N

GLYNN COUNTY

Brunswick

EXPLANATION

Simulated potentiometric contour—

 Shows simulated 2004 potentiometric

 surface, in feet. Hachures indicate

 depression. Contour intervals 20 feet

 (top map) and 5 feet (bottom map).

 Datum is NAVD 88

Water-level residual, in feet—

 Represents simulated minus

 observed water levels

60

Model boundary

GA

FL

SC

GA

–10 to –20

–20 to –30

–5 to –10

0 to –5

0 to 5

5 to 10

10 to 20

20 to 30

Area of

map below

Figure 16.—Continued

SOUTH

CAROLINA GEORGIA

Model area

FLORIDA

Figure 16. Simulated 2004 potentiometric surfaces and water-level residuals by model layer: A, layer 3, upper 

Brunswick aquifer, model area; B, layer 5, lower Brunswick aquifer, model area; C, layer 7, upper water-bearing 

zone of the Upper Floridan aquifer, model area; D, layer 9, lower water-bearing zone of the Upper Floridan 

aquifer; E, layer 7, upper water-bearing zone of the Upper Floridan aquifer, Glynn County and Brunswick area 

enlargement; F, layer 9, lower water-bearing zone of the Upper Floridan aquifer; and G, layer 11, Lower Floridan 

aquifer, model area and Glynn County enlargement.—Continued
58 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Simulated Potentiometric Surfaces

The steady-state simulated potentiometric surfaces 

for 2000 and 2004 indicate groundwater flow from upland 

regions to the north and west toward the coast, where flow 

converges at pumping centers near Chatham County, Ga., and 

Brunswick/Glynn County, Ga. The simulated potentiometric 

surface maps also show impeded groundwater flow, evidenced 

by steep potentiometric gradients in upland areas north and 

west of the Gulf Trough and flatter gradients near the coast 

where the Floridan aquifer system is more productive. 

2000 Conditions

Simulated potentiometric surfaces of the Brunswick 

aquifer system (layers 3 and 5) for 2000 indicate steep potentiometric gradients, with simulated water-level altitudes ranging 

from about 120 ft in the northwestern extent of the aquifer 

system to below −40 ft near the city of Savannah (fig. 14A–B). 

The simulated potentiometric contours for the Brunswick 

aquifer system indicate groundwater-flow patterns similar to 

those of the Floridan aquifer system (fig. 14F ) and influenced 

by pumping in the underlying aquifer in the Chatham County 

area. Simulated potentiometric surface maps of the UFA 

(layers 7 and 9) for 2000 show steep potentiometric gradients in the upland areas north and west of the Gulf Trough, 

with groundwater flow toward the coast (fig. 14C–D). South 

and east of the Gulf Trough, potentiometric gradients flatten 

and groundwater-flow directions are influenced by a cone of 

depression centered in the Savannah area, which alters the 

regional coastward flow pattern. The broad area of influence 

for this cone of depression is indicated by the 0-ft contour, 

which extends to an area of pumping to the southwest near 

Jesup, Ga., and north into Jasper and Beaufort Counties, S.C. 

The simulated water-level altitudes near the center of pumping 

in Savannah are below −60 ft in layer 7 and below −80 ft in 

layer 9, respectively. In the Brunswick/Glynn County area, 

potentiometric contours indicate groundwater flow from west 

to east, with a cone of depression near downtown Brunswick 

locally altering the coastward flow pattern (fig. 14E). The 

cone of depression, centered in an active industrial well field, 

intercepts groundwater flow from the west and south with 

simulated head altitudes below −5 ft. The simulated potentiometric contour map for 2000 in the LFA (layer 11) indicates 

groundwater-flow patterns similar to those in the UFA, with 

a cone of depression influenced by pumping in the overlying 

layers in the Chatham County area (fig. 14F). 

2004 Conditions

Simulated potentiometric surfaces of the Brunswick 

aquifer system (layers 3 and 5) for 2004 (fig. 16A–B) indicate 

groundwater flow from upland areas to the west toward the 

cone of depression in the Savannah area created by pumping 

in the underlying UFA. Another groundwater-flow direction 

parallels the coast from the Brunswick/Glynn County area 

northward toward the Savannah area. Simulated potentiometric surface maps of the UFA (layers 7 and 9) for 2004 

show steep potentiometric gradients in the upland areas north 

and west of the Gulf Trough, with coastward groundwater 

flow (fig. 16C–D). Groundwater-flow directions are influenced 

by a cone of depression centered in the Savannah area that 

alters the coastward flow pattern. The broad area of influence for this cone of depression is evident by the 0-ft contour, 

which extends to an area of pumping to the southwest near 

Jesup, Ga., and north into Jasper and Beaufort Counties, S.C. 

Simulated potentiometric contours in the Savannah area show 

water-level altitudes below −60 ft in layer 7 and below −80 ft 

in layer 9, respectively. In the Brunswick/Glynn County area, 

potentiometric contours indicate groundwater flow from west 

to east, with a cone of depression near downtown Brunswick 

locally altering the coastward flow pattern (fig. 16E–F ). 

The cone of depression near the active industrial well field 

intercepts groundwater flow from the west and south, with 

simulated head altitudes below −5 ft. The simulated potentiometric contour map for 2004 in the LFA (layer 11) indicates 

groundwater-flow patterns similar to those in the UFA with 

a cone of depression influenced by pumping in the overlying 

layers in the Chatham County area (fig. 16G). 

Simulated Water-Level Changes, 2000–04

Steady-state simulations for 2000 and 2004 were 

compared for the regional model area by computing waterlevel changes, which indicated water-level rises because of a 

decrease in pumpage from 2000 to 2004. Changes in simulated groundwater levels for the Brunswick aquifer system 

(layers 3 and 5) were influenced by changes in pumping rates 

from 2000 to 2004. Simulated water levels (and changes) 

indicate water-level rises in Glynn County, corresponding to 

a decrease in pumpage during this period, with the exception 

of the Brunswick aquifer system (layers 3 and 5), which had 

an increase in pumping rates from 2000 to 2004 and resulted 

in a concurrent decrease in water levels. Simulated water 

levels and changes for 2000 and 2004 agree with water-level 

increases documented in continuous recording wells 33H133, 

33H127, 34H436, and 33H188 (fig. 17). Simulated water 

levels and changes in well 34H437 for 2000 and 2004 indicated a decrease of 3.30 ft, while continuous water-level data 

indicated an increase of 3.04 ft. 

Simulated water-levels declined from 2000 to 2004 

in the Brunswick aquifer system (layers 3 and 5) in the 

Brunswick/Glynn County area in response to increased 

pumpage. During this period, water levels declined more 

than 10 ft near activated Golden Isles public-supply wells 

in northern Glynn County. Water-levels declined more than 

5 ft near new golf-course irrigation wells on Jekyll Island 

in Glynn County (fig. 18A–B). These wells contributed to a 

6-fold increase in combined pumpage from the Brunswick 

aquifer system (layers 3 and 5) during this period, from 

0.24 Mgal/d in 2000 to 1.75 Mgal/d in 2004. 
Simulation of Steady-State Groundwater Flow, 2000–04 59

Figure 17. Hydrographs showing selected water-levels and simulated heads for A, upper Brunswick aquifer; 

B, Upper Floridan aquifer upper water-bearing zone (UWBZ); C, Upper Floridan aquifer lower water-bearing 

zone (LWBZ); D, Lower Floridan aquifer; and E, Lower Floridan aquifer Fernandina permeable zone (FPZ), 

Glynn County, Georgia, 2000–2004.

95

341

17

82

Blank where

data missing

4

5

6

7

8

9

10

11

12

A. Well 34H437—Upper Brunswick aquifer

 (layer 3)

–6

–4

–2

0

2

4

6

8

10

12

14

16

B. Well 33H133—Upper Floridan aquifer 

 (UWBZ, layer 7)

Water level, in feet above NAVD 88

–5

0

5

10

15

20

C. Well 33H127—Upper Floridan aquifer

 (LWBZ, layer 9)

5

10

15

20

25

D. Well 34H436—Lower Floridan aquifer

 (layer 11) 

Figure 17.

5

10

15

20

25

E. Well 33H188—Lower Floridan aquifer

 (FPZ, layer 11)

WAYNE

BRANTLEY

GLYNN

CAMDEN

MCINTOSH

ATLANTIC

OCEAN

St Simons

Island

Jekyll

Island

N

0 5 10 MILES

0 5 10 KILOMETERS

2000 2001 2002 2003 2004

2000 2001 2002 2003 2004 2000 2001 2002 2003 2004 2000 2001 2002 2003 2004

2000 2001 2002 2003 2004

EXPLANATION

Well

Water level

Observed

Simulated

Water level, in feet above

or below (–) NAVD 88

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

Brunswick

33H127

33H133

34H436

34H437

33H188

Blank where

data missing
60 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Figure 18. 

Simulated water-level change—

 Computed by subtracting simulated 

 potentiometric surface for 2000 from

 simulated potentiometric surface

 for 2004. Interval, in feet, is variable

–2.5

–5

–2.5

0

–2.5

–10

–2.5

–5

–2.5

0

–2.5

–5

–10

2.5

2.5

–5

N

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

EXPLANATION

2.5

A. Upper Brunswick aquifer

 (layer 3)

Model boundary

GA

FL

SC

GA

B. Lower Brunswick aquifer

 (layer 5)

SOUTH

GEORGIA CAROLINA

Model area

Approximate extent

of Brunswick

aquifer system

FLORIDA

Figure 18. Simulated water-level change from 2000 to 2004 for A, model layer 3, upper Brunswick aquifer, 

B, model layer 5, lower Brunswick aquifer, C, upper water-bearing zone of Upper Floridan aquifer, D, lower 

water-bearing zone of Upper Floridan aquifer, and E, Lower Floridan aquifer.
Simulation of Steady-State Groundwater Flow, 2000–04 61

Savannah

Waynesboro

Savannah

Waynesboro

–2.5

–2.5

–5

0

0

0

0

2.5 5

10

0

–2.5

–5

–2.5

–2.5

0

2.5 –5

2.5

5

5

7.5

10

20

7.5

7.5

10

0

–2.5

–5

0

0

–2.5

–2.5

–2.5

0

2.5 5 0

10

–2.5

–5

0

–2.5

0

2.5

2.5

5

5

7.5

10

7.5

20

7.5

10

0

–2.5

–5

–5

–2.5

–5

N

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

Figure 18.—Continued 

Simulated water-level change—

 Computed by subtracting simulated 

 potentiometric surface for 2000 from

 simulated potentiometric surface

 for 2004. Interval, in feet, is variable

Model boundary

GA

FL

SC

GA

C. Upper water-bearing zone of

 Upper Floridan aquifer

 (layer 7)

D. Lower water-bearing zone of

 Upper Floridan aquifer

 (layer 9)

EXPLANATION

2.5

SOUTH

CAROLINA GEORGIA

Model area

FLORIDA

Figure 18. Simulated water-level change from 2000 to 2004 for A, model layer 3, upper Brunswick aquifer, 

B, model layer 5, lower Brunswick aquifer, C, upper water-bearing zone of Upper Floridan aquifer, D, lower 

water-bearing zone of Upper Floridan aquifer, and E, Lower Floridan aquifer.—Continued
62 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Simulated water-level changes from 2000 to 2004 in 

the UFA (layers 7 and 9) were influenced by decreases in 

pumpage caused by the shutdown of the Durango Paper 

Company mill near St. Marys and local decreases in pumping 

rates near the cities of Savannah in Chatham County, Ga., 

and Waynesboro in Burke County, Ga. (fig. 18C–D). Closure 

of the Durango Paper Company mill corresponded with a 

35.5 Mgal/d decrease in pumping rates in the UFA that, when 

simulated, caused more than 20 ft of groundwater-level rise 

near the pumping center and smaller water-level rises in the 

southern coastal area of Georgia ranging from 2.5 to more 

than 7.5 ft. 

In Glynn County, simulated water-level increases in the 

UFA (layers 7 and 9) were caused by decreases in pumping 

rates represented in the steady-state models from 2000 to 

2004. Simulated groundwater-level increases generally ranged 

between 2.5 and 5 ft, with the greatest simulated increase 

occurring near downtown Brunswick. Decreases in pumping 

rates in the UFA from 61 Mgal/d during 2000 to 53.8 Mgal/d 

during 2004, represented in the models, contributed to the 

rises in simulated water levels. Decreases in simulated 

pumping rates that correspond with pumpage decline near the 

10

0

0

–10 –2.5

–5 –5

–2.5

2.5

2.5

5

5

5

2.5

5

–2.5

0

0 0

0

2.5

5

10

0

–2.5

–2.5

–5

–5

–2.5

–5 –2.5

0

5 –2.5

N

0 30 45 60 MILES 15

0 30 45 60 KILOMETERS 15

Base from U.S. Geological Survey

1:100,000-scale digital data

Figure 18.—Continued 

Simulated water-level change—

 Computed by subtracting simulated 

 potentiometric surface for 2000 from

 simulated potentiometric surface

 for 2004. Interval, in feet, is variable

Model boundary

GA

FL

SC

GA

E. Lower Floridan aquifer

 (layer 11)

EXPLANATION

2.5

SOUTH

CAROLINA GEORGIA

Model area

FLORIDA

city of Savannah caused localized simulated rises in water 

levels of up to 2.5 ft. 

A similar decrease in pumping rates occurred in the UFA 

near Waynesboro in Burke County as in Savannah, discussed 

above; however, a corresponding simulated water-level rise of 

more than 10 ft resulted from this simulated pumpage reduction (fig. 18C–D). Inspection of hydraulic properties associated with both locations indicated that the lower hydraulic 

conductivity near Waynesboro, relative to Savannah, would 

elicit a larger groundwater-level response to pumpage there 

than in Savannah.

Simulated pumpage reductions corresponding to the shutdown of the Durango Paper Company mill had a similar effect 

on simulated water levels in the LFA (layer 11; fig. 18E) as 

on the UFA (fig. 18C–D). Simulated water-level rises of more 

than 10 ft occurred near the center of pumping, with the 2.5-ft 

contour extending through the central part of Glynn County. 

The simulated water-level rises in the LFA near the cities of 

Savannah and Waynesboro indicate that simulated groundwater levels responded to simulated pumpage reductions in the 

UFA (layers 7 and 9), indicating a strong hydraulic connection 

between the UFA and LFA.

Figure 18. Simulated water-level change from 2000 to 2004 for A, model layer 3, upper Brunswick aquifer, 

B, model layer 5, lower Brunswick aquifer, C, upper water-bearing zone of Upper Floridan aquifer, D, lower 

water-bearing zone of Upper Floridan aquifer, and E, Lower Floridan aquifer.—Continued
Simulation of Steady-State Groundwater Flow, 2000–04 63

Simulated Potentiometric Profiles

Simulated potentiometric profiles were constructed 

for 2000 and 2004 to evaluate hydraulic gradients in the 

UWBZ of the UFA (layer 7) near the chloride plume and 

the cone of depression caused by production wells in the 

area (figs. 19 and 20). The profiles for 2000 and 2004 were 

selected based on available water-level data and principle 

groundwater-flow directions within the chloride plume. The 

principle direction of groundwater flow in the downtown 

Brunswick area is from south to north, with flow paths toward 

the northwest near the major well field. Potentiometric gradients determine groundwater-flow direction and rate in addition to influencing the shape and extent of the chloride plume. 

Potential changes in pumping could alter potentiometric 

gradients, the direction of groundwater flow, and the shape 

of the chloride plume. Simulated potentiometric gradients 

for 2000 were based on four potentiometric profiles (A−D; 

fig. 19) constructed using water-level data from 13 observation 

wells having a collective mean residual of –0.19 ft. Simulated 

potentiometric gradients from these four profiles ranged 

from 3.6 to 5.2 feet per mile (ft/mi). Simulated potentiometric gradients for 2004 were based on five potentiometric 

profiles (A−E; fig. 20) constructed using water-level data from 

18 observation wells having a collective mean residual of 

–0.18 ft. Simulated potentiometric gradients from these five 

profiles ranged from 4.3 to 11.1 ft/mi.

Simulated potentiometric gradients for 2000 approximated observed gradients in the four potentiometric profiles 

(A−D) constructed in close proximity to the chloride plume. In 

potentiometric profile A, simulated water levels were about 1 ft 

higher than observed water levels, with the simulated potentiometric gradient of 4.3 ft/mi, similar to the observed gradient of 

4.5 ft/mi (fig. 19; table 7). In potentiometric profile B, the simulated potentiometric gradient of 5.2 ft/mi nearly matched the 

observed gradient of 5.6 ft/mi. Well 33H130, used to construct 

potentiometric profile B, represents the observation well 

located closest to the cone of depression caused by pumping, 

with a simulated water level of –4.10 ft and an observed water 

level of –4.59 ft. In potentiometric profile C, simulated water 

levels were slightly higher than observed water levels, but 

potentiometric gradients were similar with a simulated value 

of 4.4 ft/mi and observed value of 5.3 ft/mi. Potentiometric 

profile C covers an area where groundwater flow shifts to a 

northwesterly direction toward a major well field, as indicated by the potentiometric contours shown in figure 14. 

Potentiometric profile D consists of nine wells oriented parallel 

to a primary groundwater-flow direction from south to north 

toward industrial production wells. The water levels in potentiometric profile D illustrate the difficulty in matching observed 

and simulated values because of the apparent water-level 

fluctuations evident in wells 34H373 and 34H355. However, 

the plotted simulated and observed water levels indicate a 

reasonable match with a simulated potentiometric gradient of 

3.6 ft/mi compared to an observed gradient of 4.1 ft/mi.

Table 7. Simulated and observed groundwater levels for 2000, and residuals in wells used to construct 

profiles in the Brunswick area.

[NAVD 88, North American Vertical Datum of 1988; —, not available; residual equals simulated minus observed water level; 

hydraulic gradients calculated using simulated heads at the endpoints of profiles; see figure 19 for location of profiles]

Well

identifier Profile(s)

2000 water level, in feet above

or below (–) NAVD 88 Residual,

in feet

Simulated

potentiometric

gradient, in

feet per mile Simulated Observed

33H120 A –1.69 –2.99 1.30 —

34H392 A 4.23 3.33 0.90 4.3 (A)

33H130 B – 4.10 – 4.59 0.49 —

34H424 B, D 1.13 1.04 0.09 5.2 (B)

33H133 C –1.51 – 0.89 – 0.62 —

34H355 C, D 2.46 3.88 –1.42 4.4 (C)

34H373 D 1.93 –1.07 3.00 —

34H125 D 4.10 4.45 – 0.35 —

34H117 D 4.87 4.54 0.33 —

34H112 D 5.86 6.62 – 0.76 —

34H393 D 7.27 8.53 –1.26 —

34H371 D 7.97 10.80 –2.83 —

34H097 D 10.40 11.80 –1.40 3.6 (D)
64 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

A

Figure 19. Simulated and observed petentiometric profiles near chloride plume during 2000.

–6

–4

–2

0

2

4

6

8

33H120

34H392

Distance 7,350 feet

–6

–4

–2

0

2

4

6

8

33H130

34H424

Distance 5,280 feet

–6

–4

–2

0

2

4

6

8

33H133

34H355

Distance 4,740 feet

–5

0

5

10

15

34H424

34H117

Distance 13,800 feet

34H373

34H355

34H125

34H112

34H393

34H097

34H371

B

C

D

Water level, in feet above or below (–) NAVD 88

VERTICAL SCALE GREATLY EXAGGERATED

0 3,000 6,000 FEET

0 500 1,000 1,500 METERS

A

B

C D

A' A'

B'

B' C'

C'

D'

D'

A'

N

Base from U.S. Geological Survey 

digital files,1:24,000

Brunswick West, 1993

Brunswick East, 1979

A Water-level profile

Observation well and identifier

EXPLANATION

2000 water level

Observed

Simulated 

[Map] [Graphs]

Outline of chloride plume, 2004—

 Modified from Leeth and

 others, 2006

33H120

33H130

34H424

34H373

34H125

34H117

34H112

34H393 34H371

34H097

33H355

33H133

34H392

33H130

Figure 19. Simulated and observed potentiometric profiles near chloride plume during 2000.
Simulation of Steady-State Groundwater Flow, 2000–04 65

A

33H211

33H211

33H211

33H211

33H120

Distance 4,140 feet

–6

–4

–2

0

2

4

6

8

Figure 20. Simulated and observed petentiometric profiles near chloride plume during 2004.

Distance 6,330 feet

33H207

–6

–4

–2

0

2

4

6

8

–6

–4

–2

0

2

4

6

8

33H130

33H469

Distance 7,070 feet

Distance 7,330 feet

33H133 34H374

–6

–4

–2

0

2

4

6

8

Water level, in feet above or below (–) NAVD 88

Distance 14,700 feet

VERTICAL SCALE GREATLY EXAGGERATED 34H374 34H401 34H400 34H355 34H128 34H434

34H125

34H117

34H112

34H393

34H371

34H095

0

5

10

15

20

C

0 3,000 6,000 FEET

0 500 1,000 1,500 METERS

B

B’

E

D

A

A'

C'

D'

E'

N

Base from U.S. Geological Survey 

digital files,1:24,000

Brunswick West, 1993

Brunswick East, 1979

A Water-level profile

Observation well 

 and identifier

EXPLANATION

2004 water level

Observed

Simulated 

[Map] [Graphs]

Outline of chloride plume,

 2004—Modified from

 Leeth and others, 2006

A'

B B'

C C'

D D'

E E'

33H207

33H211

33H120

33H130

33H133

33H469

34H374 34H401

34H355

34H400

34H128

34H434

34H125

34H117

34H393

34H371

34H095

34H112

33H211

A'

Figure 20. Simulated and observed potentiometric profiles near chloride plume during 2004.
66 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Simulated potentiometric gradients for 2004 approximated observed gradients in the five potentiometric profiles 

(A−E ) constructed in close proximity to the chloride plume. 

The potentiometric profiles for 2000 and 2004 differed slightly 

because the availability of observation water-level data 

differed between years (figs. 19 and 20; tables 7 and 8). In 

addition, water-level data available for well 33H211 allowed 

the 2004 potentiometric profiles to be constructed in close 

proximity to a major industrial well field. Consequently, 

simulated potentiometric gradients for 2004 were higher than 

the gradients for 2000. In potentiometric profile A, simulated water levels were lower than observed water levels in 

well 33H211 and higher than observed water levels in well 

33H120, and have a simulated potentiometric gradient of 

11.0 ft/mi, higher than the observed gradient of 9.2 ft/mi 

(fig. 20; table 8). In potentiometric profile B, simulated water 

levels nearly matched observed values and have a simulated 

potentiometric gradient of 11.1 ft/mi and an observed gradient 

of 10.2 ft/mi. In potentiometric profile C, simulated water 

levels were higher than observed water levels in well 33H130 

and lower than observed values in wells 33H211 and 33H469 

and have a simulated potentiometric gradient of 7.9 ft/mi 

compared to an observed gradient of 8.0 ft/mi. In potentiometric profile D, residuals in wells 33H211 and 33H133 of 

–0.43 and 0.77 ft, respectively, indicate a reasonable match 

over this part of the potentiometric profile, with a residual 

of –1.20 ft at the endpoint in well 34H374. The water levels 

have a simulated potentiometric gradient of 7.6 ft/mi, slightly 

lower than the observed gradient of 8.2 ft/mi. Potentiometric 

profile E consisted of 12 wells oriented parallel to a primary 

groundwater-flow direction from south to north toward industrial production wells. The observed water levels in potentiometric profile E show fluctuations of nearly 5 ft over the 

northern part of the profile without any apparent influence by 

localized pumping. Potentiometric profile E shows observed 

water levels are higher than simulated values in wells 34H374, 

34H400, 34H125, 34H112, 34H393, 34H371, and 34H095, 

but a comparison of graphed water levels over the entire 

profile indicates a reasonable match between simulated and 

observed values. The plotted simulated and observed water 

levels show a similar trend, with a simulated potentiometric 

gradient of 3.6 ft/mi and an observed gradient of 3.8 ft/mi. 

Table 8. Simulated and observed groundwater levels for 2004, and residuals in wells used to construct 

profiles in the Brunswick area.

[NAVD 88, North American Vertical Datum of 1988; —, not available; residual equals simulated minus observed water level; 

hydraulic gradients calculated using simulated heads at the endpoints of profiles; see figure 20 for location of profiles]

Well

identifier Profile(s)

2004 water level,

in feet above NAVD 88 Residual,

in feet

Simulated

potentiometric

gradient, in

feet per mile Simulated Observed

33H211 A, B, C, D – 4.59 – 4.16 – 0.43 —

33H120 A 4.05 3.08 0.97 11.0 (A)

33H207 B 7.76 8.09 – 0.33 11.1 (B)

33H130 C 2.69 2.18 0.51 —

33H469 C 6.05 6.61 – 0.56 7.9 (C)

33H133 D 4.54 3.77 0.77 —

34H374 D, E 6.00 7.20 –1.20 7.4 (D)

34H401 E 6.51 2.53 3.98 —

34H400 E 7.12 4.34 2.78 —

34H355 E 7.90 8.46 – 0.56 —

34H128 E 8.26 8.13 0.13 —

34H434 E 8.86 6.13 2.73 —

34H125 E 9.20 12.40 –3.20 —

34H117 E 10.30 10.50 – 0.20 —

34H112 E 11.04 12.90 –1.86 —

34H393 E 12.32 14.60 –2.28 —

34H371 E 12.89 15.50 –2.61 —

34H095 E 15.99 17.90 –1.91 4.3 (E)
Simulation of Steady-State Groundwater Flow, 2000–04 67

Simulated Water Budget

The simulated 2000 and 2004 water budgets consist of 

the following major components of inflow and outflow to the 

groundwater-flow system: (1) inflow from the general-head 

boundaries, (2) inflow across lateral specified-head boundaries, (3) outflow to the general-head boundary, (4) discharge 

to wells, and (5) outflow across lateral specified-head boundaries. The 2000 and 2004 flows were characterized using 

the MODFLOW postprocessor ZONEBUDGET (Harbaugh, 

1990). Flow calculations were summarized by model layer 

and by zone within each layer. Some zones were established to 

account for inflow and outflow across specified- and generalhead boundaries, flow between the layers, and flow along the 

coastline in a manner described by Payne and others (2005).

The entire simulated groundwater inflow to the model 

area for 2000 totaled 1,730 Mgal/d, of which 28.3 percent 

(489 Mgal/d) constituted inflow from the general-head 

boundaries and 71.7 percent (1,241 Mgal/d) represented 

inflow from lateral specified-head boundaries in model 

layers 7, 8, 9, and 11 (table 9; fig. 21A). Simulated groundwater outflow totaled 1,730 Mgal/d, of which 3.9 percent 

(67.1 Mgal/d) represented groundwater outflow to the 

general-head boundaries, and another 49.2 percent 

(852 Mgal/d) constituted outflow at lateral specified-head 

boundaries. Simulated discharge to wells totaled 811 Mgal/d, 

or 46.9 percent of outflow, and was divided among the 

Brunswick aquifer system (layers 3 and 5; 0.24 Mgal/d), the 

UWBZ and LWBZ of the UFA (layers 7 and 9; 679 Mgal/d), 

and the LFA (layer 11; 131 Mgal/d). Net inflow to the model 

area along lateral specified-head boundaries totaled about 

370 Mgal/d for the UFA (layers 7–9) and 18.6 Mgal/d for the 

LFA (table 9; fig. 21A).

Simulated inflow to the model for 2004 totaled 

1,540 Mgal/d, and was divided between general-head boundaries (470 Mgal/d, or 30.5 percent), and lateral specifiedhead boundaries in layers 7, 8, 9, and 11 (1,070 Mgal/d, or 

69.5 percent) (table 9; fig. 21B). Outflow from the model 

totaled 1,540 Mgal/d, of which 4.8 percent (74.2 Mgal/d) 

represented groundwater outflow to the general-head 

boundaries, and another 47.6 percent (733 Mgal/d) was 

attributed to outflow at lateral specified-head boundaries. 

The remaining 47.6 percent (733 Mgal/d) represented simulated discharge to wells from the Brunswick aquifer system 

(layers 3 and 5; 1.75 Mgal/d), the UWBZ and LWBZ of the 

UFA (layers 7 and 9; 619 Mgal/d), and the LFA (layer 11; 

112 Mgal/d). Net inflow along lateral specified-head boundaries totaled about 315 Mgal/d into the UFA (layers 7–9), and 

22.1 Mgal/d into the LFA (table 9; fig. 21B). 

A comparison of the major components for 2000 and 

2004 indicates higher inflow values through the general-head 

boundary in layer 1 for the 2000 simulation. The 78-Mgal/d 

greater pumping rate during 2000, relative to 2004 induced 

an additional 19.3 Mgal/d of inflow through the general-head 

boundaries in layers 1, 2, and 7, and an additional 171 Mgal/d 

of inflow to the model through the specified-head boundary 

in layers 7, 8, 9, and 11 when compared to the 2004 budget. 

The comparison between the simulated water budgets for 2000 

and 2004 indicates increased inflows in the UFA along the 

southern specified-head boundary. According to Payne and 

others (2005), these inflows are reasonable because the UFA 

extends far beyond this specified-head boundary throughout 

Florida (Miller, 1986) and potentially could contribute groundwater into the modeled area. The resulting inflows along 

this boundary decreased from 1,241 Mgal/d during 2000 to 

1,070 Mgal/d for the 2004 simulation, which subdivided the 

UFA (layer 5) into the UWBZ and LWBZ (layers 7 and 9) and 

the intervening confining unit (layer 8). 

An analysis similar to that described for general headboundaries in the Brunswick/Glynn County area indicated 

that specified-head boundaries adjacent to Glynn County are 

located sufficiently far from the pumping centers to yield 

a significant contribution to the water budget (fig. 21C–D; 

table 10). In the Brunswick/Glynn County area, simulated 

pumping totaled 60.9 Mgal/d during 2000 and 55.2 Mgal/d 

during 2004. Outflows to the general-head boundary in 

model layer 1 of 4.0 and 5.8 Mgal/d (for 2000 and 2004 

simulated conditions, respectively) exceeded inflows of 

0.35 and 0.21 Mgal/d, respectively, along the same boundary.
68 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Table 9. Flow-budget components for 2000 and 2004 for entire model area.

[Results from MODFLOW model; all values in million gallons per day; —, not applicable]

Model

unit

From

generalhead

boundary,

onshore

From

generalhead

boundary,

offshore

From

specifiedhead

boundary

Total

To

generalhead

boundary,

onshore

To

generalhead

boundary,

offshore

To

specifiedhead

boundary

Discharge

to wells Total

2000 inflow 2000 outflow

1 264.00 1.29 — 265.29 33.08 0.54 — — 33.62

2 77.39 — — 77.39 8.07 — — — 8.07

3 — — — — — — — 0.11 0.11

4 — — — — — — — — —

5 — — — — — — — 0.13 0.13

6 — — — — — — — — —

7 138.20 — 461.53 599.73 21.32 — 323.10 320.31 664.73

8 — — 252.20 252.20 — — 175.34 — 175.34

9 — — 500.00 500.00 — — 344.99 359.11 704.10

10 — — 0.01 0.01 — — — — —

11 — — 27.13 27.13 — — 8.50 131.49 139.99

Total, all units 479.59 1.29 1,240.87 1,721.75 62.47 0.54 851.93 811.15 1,726.09

Percentage of 

total flow

27.9 0.1 72.1 100.0 3.6 0.03 49.4 47.0 100.0

2004 inflow 2004 outflow

1 237.45 1.68 — 239.13 40.17 0.75 — — 40.92

2 83.68 — — 83.68 7.31 — — — 7.31

3 — — — — — — — 0.79 0.79

4 — — — — — — — — —

5 — — — — — — — 0.96 0.96

6 — — — — — — — — —

7 139.29 — 511.91 651.20 20.62 — 424.32 290.17 735.11

8 — — 58.36 58.36 — — 32.28 — 32.28

9 — — 469.93 469.93 — — 268.56 329.11 597.67

10 — — 0.01 0.01 — — — — —

11 — — 30.02 30.02 — — 7.91 111.92 119.83

Total, all units 460.42 1.68 1,070.23 1,532.33 68.10 0.75 733.07 732.95 1,534.87

Percentage of 

total flow

30.1 0.1 69.8 100.0 4.4 0.04 47.8 47.8 100.0
Simulation of Steady-State Groundwater Flow, 2000–04 69

Table 10. Flow-budget components for 2000 and 2004 in the Brunswick/Glynn County area.

[Results from MODFLOW model; all values in million gallons per day; —, not applicable]

Model

unit

From

general-head

boundary,

onshore

Across 

county

boundaries

Total

To

general-head

boundary,

onshore

Across 

county

boundaries

Discharge

to wells Total

2000 inflow 2000 outflow

1 0.35 4.89 5.24 3.96 1.59 — 5.55

2 — — — — — — —

3 — 0.14 0.14 — 0.07 0.05 0.12

4 — — — — — — —

5 — 0.35 0.35 — 0.18 0.06 0.24

6 — — — — — — —

7 — 42.51 42.51 — 15.34 24.32 39.66

8 — 0.26 0.26 — 2.25 — 2.25

9 — 50.10 50.10 — 16.57 36.46 53.03

10 — — — — — — —

11 — 4.21 4.21 — 1.96 0.00 1.96

Total, all units 0.35 102.46 102.81 3.96 37.96 60.89 102.81

Percentage of 

total flow

0.3 99.7 100.0 3.9 36.9 59.2 100.0

2004 inflow 2004 outflow

1 0.21 8.12 8.33 5.80 2.62 — 8.42

2 — — — — — — —

3 — 0.31 0.31 — 0.05 0.64 0.69

4 — — — — — — —

5 — 0.78 0.78 — 0.12 0.81 0.93

6 — — — — — — —

7 — 38.31 38.31 — 14.56 19.64 34.20

8 — 0.02 0.02 — 0.47 — 0.47

9 — 45.19 45.19 — 15.64 34.14 49.78

10 — — — — — — —

11 — 3.84 3.84 — 2.29 0.00 2.29

Total, all units 0.21 96.57 96.78 5.80 35.75 55.23 96.78

Percentage of 

total flow

0.2 99.8 100.0 6.0 36.9 57.1 100.0
70 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

1.68

0.753

30.0

7.91

6.24

4.23

EXPLANATION

General-head boundary 

Interunit leakage

Lateral fixed-head

 boundary 

Pumpage

329

Groundwater flow, in million gallons 

 per day, and budget component

0.753

1.68

6.24

4.23

238

40.2

270

71.5

293

15.6

0.794 (layer 3)

292

16.2

292

16.1

0.959 (layer 5)

292

17.0

292

17.0

290

(layer 7)

350

159

346

129

329

(layer 9)

171

81.5

171

81.4

512

424 58.4

32.3 470

269 0.008

0.002 30.0

7.91

B. 112 (layer 11) 2004

A. 2000

Figure 21. 

84.7

7.32

139

20.6

NOT TO SCALE

NOT TO SCALE

 Lower Floridan aquifer (layer 11)

Surficial aquifer system (layer 1)

Brunswick aquifer system confining unit (layer 2)

Upper Brunswick aquifer (layer 3)

Lower Brunswick confining unit (layer 4)

Lower Brunswick aquifer (layer 5)

Upper Floridan confining unit (layer 6)

Upper water-bearing zone Upper Floridan aquifer (layer 7)

Lower water-bearing zone Upper Floridan confining unit

(layer 8)

Lower water-bearing zone Upper Floridan aquifer (layer 9)

Lower Floridan confining unit (layer 10)

Onshore Offshore

264

33.1 0.54

1.29

7.32

3.25

294

61.8

317

11.7

0.112 (layer 3)

317

11.6

317

11.6

317

11.7

317

11.7

331

90.5

0.129 (layer 5)

320

(layer 7)

364

46.8

359 (layer 9)

193

80.5

193

80.4

131 (layer 11)

462

323 252

175 500

345 0.008

0.003 27.1

8.5

77.4

8.07

138

21.3

SOUTH

GEORGIA CAROLINA

FLORIDA

Model

area

Figure 21. Schematic diagram showing simulated water budget for regional model during A, 2000 and B, 2004, and 

water budgets in Glynn County during C, 2000 and D, 2004.
Simulation of Steady-State Groundwater Flow, 2000–04 71

5.80

0.208

0.058

0.148 8.12

2.62

0.058

0.148

0.637 (layer 3)

0

0

0.022

0.312 0.483

0.046

0

0

0.022

0.483

0.776

0.125

0.623

0.002

0.811 (layer 5)

0

0 0.002

0.623

19.6

(layer 7)

38.3

14.6 8.84

5.35

0.024

0.471 8.60

5.56

45.2

15.6 4.36

5.90

0.001

0.001

5.90

4.35 3.84

2.29

34.1

(layer 9)

0 (layer 11)

0.348

3.96

4.89

1.59 0.034

0.337

0.034

0.337

0.045 (layer 3)

0

0

0.024

0.139 0.301

0.068

0.024

0 0.301

0

0.063 (layer 5)

0.353

0.184 0.022

0.193

0

0 0.022

0.193

24.3

(layer 7)

5.32

42.5 2.64

15.3 0.261

2.25 4.37

3.68

6.96

4.71

50.1

16.6

36.5

(layer 9)

0.001

0.001 4.71

6.96

4.21

1.96

0 (layer 11)

D. 2004

C. 2000

Figure 21.—Continued

NOT TO SCALE

NOT TO SCALE

1.68

0.753

30.0

7.91

6.24

4.23

EXPLANATION

General-head boundary 

Interunit leakage

Lateral flow through

 county boundary

Pumpage

329

Groundwater flow, in million gallons 

 per day, and budget component

 Lower Floridan aquifer (layer 11)

Surficial aquifer system (layer 1)

Brunswick aquifer system confining unit (layer 2)

Upper Brunswick aquifer (layer 3)

Lower Brunswick confining unit (layer 4)

Lower Brunswick aquifer (layer 5)

Upper Floridan confining unit (layer 6)

Upper water-bearing zone Upper Floridan aquifer (layer 7)

Lower water-bearing zone Upper Floridan confining unit

(layer 8)

Lower water-bearing zone Upper Floridan aquifer (layer 9)

Lower Floridan confining unit (layer 10)

GLYNN

COUNTY

Figure 21. Schematic diagram showing simulated water budget for regional model during A, 2000 and B, 2004, and 

water budgets in Glynn County during C, 2000 and D, 2004.—Continued
72 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Model Sensitivity

The sensitivity of the calibrated revised steady-state 

model was evaluated to determine the relative importance 

of introduced hydraulic conductivity parameters in the 

Brunswick/Glynn County area. The original model used 

the perturbation method to examine model sensitivity to 

pumping and to the specified-head boundary condition 

along the southern boundary (Payne and others, 2005). The 

composite-scaled sensitivity analysis for the original model 

indicated high sensitivity to pumping rates. Therefore, 2000 

pumping rates were increased by 10 percent and the resulting 

changes in simulated heads and flow rates were documented. 

The specified-head boundary along the southern edge of the 

original model was increased by 10 ft and the resulting rise 

in simulated water levels mapped. Published maps indicate 

increases in simulated water levels in the Brunswick/Glynn 

County area of about 8 ft. The results of the 10-percent 

increase in 2000 pumping rates indicate simulated water-level 

decreases ranging between 2 and 6 ft in the Brunswick/Glynn 

County area. These perturbations were not repeated for the 

revised model because of similarities in model construction, 

and the reader is referred to Payne and others (2005) for full 

details of this analysis.

The current study focused on the composite-scaled 

sensitivity analysis of the revised model in the Brunswick/

Glynn County area. Composite-scaled sensitivities for comparable parameters are calculated using the sensitivity equation 

described in MODFLOW–2000 (Hill and others, 2000), and 

as described in Hill (1998), composite-scaled sensitivity is a 

dimensionless measure of the change in calculated head with 

respect to the value of a parameter. The resulting sensitivities 

are independent of the actual values of the observations. A 

large composite-scaled sensitivity indicates a relatively high 

sensitivity of the model to changes in a given parameter, 

whereas a small composite-scaled sensitivity indicates low 

model sensitivity to such changes. Composite-scaled sensitivities were used to evaluate the relative sensitivities of the model 

to pumping rate, vertical and horizontal hydraulic conductivity, 

and the conductance of the general-head boundary.

Composite-scaled sensitivities for parameters in both the 

2000 and 2004 simulations indicate that the model is approximately 5.2 and 4.5 times more sensitive to pumping rate (wells) 

for both years than to the parameter with the next highest 

composite-scaled sensitivity (fig. 22). Although the model 

is more sensitive to the horizontal hydraulic conductivity of 

the UFA (layers 7, 8, and 9) than to several vertical hydraulic 

conductivities (CU5Kv, CU1Kv, CU3Kv, and CU2Kv), 

composite-scale sensitivities (which range from 0.17 to 2.2) 

are about an order of magnitude or two less than the parameter 

with the highest composite-scaled sensitivity, wells. The other 

parameters representing vertical hydraulic conductivities in 

the aquifers (layers 3, 5, 7, 9, and 11) and horizontal hydraulic 

conductivities of the confining units (layers 2, 4, 6, 8, and 10) 

yielded negligible composite-scale sensitivities and are not 

included in figure 22. The horizontal hydraulic conductivity 

parameters having the highest composite-scaled sensitivity 

represented zones south of the Gulf Trough (UF4Kh, UF6Kh, 

UF5Kh, UF8Kh, UF12Kh, and UF7Kh). 

Parameters created for the revised model to subdivide 

the UWBZ and LWBZ of the UFA in the Brunswick/Glynn 

County area yielded composite-scaled sensitivities near or 

below one (UF16Kh, UF15Kh, UF18Kh, UF14Kh, UF17Kh, 

and UF13Kh, fig. 22). The calculated composite-scaled 

sensitivities varied between the 2000 and 2004 simulations, 

with the 2000 simulation having greater values (ghb, UF11Kh, 

SURFKh, CU1Kv, UF2Kh, and UF1Kh). 

Model Limitations

The original model was constructed to simulate groundwater flow in the Floridan aquifer system, which encompasses parts of Georgia, South Carolina, Alabama, and all 

of Florida. The spatial representation of hydrogeologic units 

and discretization of these subsurface units into model layers 

generalize and simplify the subsurface and areal details of 

aquifer geometry, which imposes limitations on model accuracy. For example, the location of specified-head boundaries 

in the Floridan aquifer system permits groundwater to enter 

the model area near the Florida-Georgia State Line but does 

not allow groundwater levels to change along this boundary 

in response to pumping in the Brunswick/Glynn County area, 

located a few miles north of the state line. 

The results obtained from steady-state simulations 

using the revised model developed for the Brunswick/Glynn 

County area are subject to uncertainty and errors inherent to 

the numerical approximation of the groundwater flow equation by finite-difference methods (Remson and others, 1971), 

and to the same limitations of model application inherent with 

discretization and sparse subsurface data as those documented 

in the original model (Payne and others, 2005). 

All groundwater models represent a simplification of a 

complex natural physical system and undoubtedly limit its 

representation with incomplete information derived from 

sparse point data to define continuous subsurface phenomena 

at discrete locations. The use of a coarse finite-difference grid 

in the upland regions of the study area limits model representation of the geometry of the physical extent of aquifers and 

confining units. Because these upland regions are located far 

from the areas of interest containing pumpage, the effect of 

this limitation on the computed solution of hydraulic head is 

minimal. The constraint that finite-difference grids adhere to 

an orthogonal system of discretization limits the ability of the 

computed solution of hydraulic head to represent curvature or 

hydraulic gradients in potentiometric surfaces. 
Model Limitations 73

Composite-scaled sensitivity

Parameter

2000

2004

Figure 22. Composite-scaled sensitivity of selected model parameters.

Wells

UF4KhUF6Kh

ghb

UF5KhUF8Kh

UF12Kh

UF7Kh

LFKh

CU5Kv

SURFKh

UF10Kh

CU1Kv

UF2Kh

LF4Kh

CU3Kv

UF16Kh

UF1Kh

BWK2Kh

UF19KhUF15Kh

UF18KhUF14Kh

UF17Kh

UF13Kh

UF3Kh

LF2Kh

UF11Kh

UF9Kh

BWKKh

UF20Kh

CU2Kv

0

10

20

30

40

50

Parameter Parameter value,

 in feet per day Description 2000 2004

Wells Variable* Pumping rates for calibration years 40.14580 41.81030

UF4Kh 65 Layers 7, 8, 9 horizontal conductivity, zone F4 7.73801 9.26664

UF6Kh 3,415 Layers 7, 8, 9 horizontal conductivity, zone F6 7.41630 7.47791

ghb Variable General head conductance 8.94834 6.48703

UF5Kh 225 Layers 7, 8, 9 horizontal conductivity, zone F5 6.95877 6.02565

UF8Kh 3,000 Layers 7, 9 horizontal conductivity, zone F8 4.70962 4.93006

UF12Kh 25 Layers 7, 8, 9 horizontal conductivity, zone F12 3.46161 5.53846

UF7Kh 750 Layers 7, 9 horizontal conductivity, zone F7 3.59709 3.75728

UF11Kh 126 Layers 7, 8, 9 horizontal conductivity, zone F11 4.14568 0.59530

LFKh 10 Layer 11 horizontal conductivity, zone LF1 2.58205 2.73266

CU5Kv 0.0001 Layers 2, 4, 6 vertical conductivity, zone C5 1.66574 2.15184

SURFKh 105 Layer 1 horizontal conductivity 2.76374 2.08909

UF10Kh 84 Layers 7, 8, 9 horizontal conductivity, zone F10 2.30015 1.91941

CU1Kv 0.00257 Layers 2, 3, 4, 5, 6 vertical conductivity, zone C1 2.70998 1.43039

UF2Kh 20 Layers 7, 8, 9 horizontal conductivity, zone F2 2.90912 1.29613

UF1Kh 40 Layers 7, 8, 9 horizontal conductivity, zone F1 2.51353 1.07800

UF19Kh 76 Layers 7, 8, 9 horizontal conductivity, zone F16 1.21027 0.95156

LF4Kh 10 Layer 11 horizontal conductivity, part of LF1 0.84559 1.52898

CU3Kv 0.00001 Layers 2, 3, 4, 5, 6 vertical conductivity, zone C3 0.90203 1.12795

UF16Kh 270 Layer 9 horizontal conductivity, zone F13 0.44931 0.89108

BWK2Kh 20 Layer 5 horizontal conductivity, zone B1 0.32023 0.99669

UF15Kh 200 Layer 7 horizontal conductivity, zone F15 0.62053 0.74247

UF18Kh 125 Layer 9 horizontal conductivity, zone F15 0.49485 0.59128

UF14Kh 240 Layer 7 horizontal conductivity, zone F14 0.53939 0.65909

UF17Kh 200 Layer 9 horizontal conductivity, zone F14 0.43380 0.63197

UF13Kh 300 Layer 7 horizontal conductivity, zone F13 0.47157 0.85707

UF3Kh 150 Layers 7, 8, 9 horizontal conductivity, zone F3 0.67167 0.76259

LF2Kh 100.6 Layer 11 horizontal conductivity, zone LF2 0.73069 0.77664

UF9Kh 150 Layers 7, 8, 9 horizontal conductivity, zone F9 0.29767 0.44361

BWKKh 10 Layer 3 horizontal conductivity, zone B1 0.15316 0.40920

UF20Kh 398 Layers 7, 8, 9 horizontal conductivity, zone F17 0.28703 0.23041

CU2Kv 0.20 Layers 2, 3, 4, 5, 6 vertical conductivity, zone C2 0.24392 0.16557

*Cubic feet per day

Composite-scaled sensitivity

Figure 22. Composite-scaled sensitivity of selected model parameters.
74 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

The original model discretized the study area into large 

grid cells on the fringes of the areas of interest, and used 

small grid cells to focus on providing a detailed simulation 

of hydraulic head in the areas of interest, namely, in and near 

the cities of Savannah and Brunswick. Grid cells as small as 

4,000 by 5,000 ft were used in areas where detailed simulated groundwater levels were required to be computed with 

the original model, such discretization provided a computed 

solution of hydraulic head in the center of the grid cell. This 

computed value applied to the entire grid cell area, about 

0.8 to 1 mi2, which was inadequate for representing local 

pumping effects such as drawdown cones and changes in 

hydraulic gradient. Trial-and-error testing of alternate grid 

spacing indicated that square grid cells measuring 500 ft per 

side would provide adequate representation of pumping effects 

on the potentiometric surfaces in and near pumping centers 

in the UFA at Savannah and in the Brunswick/Glynn County 

area. This fine grid spacing was expanded near the City of 

Savannah, however, to improve computational efficiency of 

the model, which sacrificed accuracy in the computed solution 

in Chatham County. 

Additional data have become available for the Brunswick 

aquifer system since the original model was constructed 

that allowed the upper and lower Brunswick aquifers to be 

included in the revised model. Most of the new aquifer-test 

data are from the vicinity of Glynn County, however, and the 

lateral extent of the system as well as the aquifer properties 

remain uncertain outside this area. The units are assumed to 

be continuous but could be isolated in areas because of locally 

reduced permeabilities and aquifer thinning.

The UFA was represented by layer 5 in the original model 

and was subdivided in the revised model into the UWBZ, 

intervening confining unit, and the LWBZ, represented as 

layers 7 through 9, respectively. The extent of this subdivision was limited to Glynn and Camden Counties, however. 

Outside these counties, the intervening confining unit was 

assigned the same hydraulic conductivity as the model layers 

above and below because the extent of distinct water-bearing 

zones in the UFA remained uncertain. Water-level data were 

available from only five wells for the LWBZ of the UFA 

(layer 9), which provided few points to calibrate simulated 

water levels against and proved difficult to match in both 2000 

and 2004. The pumping distribution was assigned for model 

layers 7 and 9 in the Brunswick/Glynn County area based on 

aquifer thickness, but the flowmeter data needed to determine 

the relative contributions from each of the units were either 

uncertain or conflicting.

The revised groundwater-flow model was calibrated to 

hydrologic conditions during September 2000 and June 2004 

using steady-state simulations that did not account for 

temporal variations. Transient simulations would consider 

small-scale changes and seasonal responses to recharge 

and pumping but were beyond the scope of this study. 

Groundwater hydrographs (fig. 6) indicate time-varying water 

levels, which give rise to time-varying hydraulic gradients 

and configurations of the potentiometric surface. Pumping 

rates are not sufficiently constant over time, nor are boundary 

conditions, to warrant the use of a steady-state model. Storage 

effects in the aquifer and confining units delay the drawdown 

response to pumping, and such aquifer and confining unit 

responses may not be fully realized before the pumping stress 

changes, which creates another condition to which the aquifer 

and confining unit would respond through time. The steadystate models of 2000 and 2004 conditions do not represent 

such time-varying elements of the groundwater-flow system, 

which severely limits the model’s usefulness in comparing 

computed steady-state solutions of hydraulic head to water 

levels measured in a non-steady-state aquifer condition. 

Boundary conditions play an important role in the calibration of the revised model, but impose a severe limitation 

on the model’s ability to represent the actual aquifer response 

to pumping. The flow budgets for the 2000 and 2004 steadystate simulations indicate the specified-head boundaries in 

model layers 7 through 11 account for nearly 70 percent of the 

inflows (1,240 Mgal/d, year 2000; 1,070 Mgal/d, year 2004) 

and about 50 percent of the outflows (852 Mgal/d, year 2000; 

733 Mgal/d, year 2004). Almost all of the water pumped is 

derived from either induced inflow or reduced outflow across 

specified-head boundaries. The general-head boundary in 

model layers 1, 2, and 5 supplies about 30 percent of the 

inflows (480 Mgal/d, 2000; 460 Mgal/d, 2004) as simulated 

recharge, with the amount controlled by a conductance term, 

but the specified-head boundary can become an unlimited 

supply of simulated recharge to the groundwater system and 

can be increased by increasing pumping. The observed head 

data for 2004 were limited but were used to assign specifiedhead values along the extent of this boundary. This boundary 

condition will supply limitless quantities of water in response 

to pumping and cannot be constrained, such as assigning 

recharge to specific areas of the model. The inherent assumption is that the specified-head boundary is sufficiently far from 

the area of primary interest such that cones of depression do 

not intersect the specified-head boundary during the simulation. The same assumption applies to general-head boundaries.

Pumping uncertainty results from errors in data-collection 

procedures, errors in reporting, overestimating or underestimating county-wide water use, and uncertainties in the assignment of pumping to model layers. Large discrepancies can 

exist between site-specific and non-site-specific data, which 

would assign higher pumping rates to non-site-specific wells 

and possibly alter input hydraulic-property data to a given area 

of the model.
Summary 75

Summary

Modifications to the original regional MODFLOW 

groundwater-flow model of coastal Georgia and adjacent 

parts of Florida and South Carolina allowed a revised model 

to be utilized in the evaluation of hydraulic gradients in the 

Upper Floridan aquifer near downtown Brunswick for 2000 

and 2004. Reducing the finite-difference grid spacing in the 

downtown Brunswick area from the original 4,000×5,000 feet 

(ft) to 500×500 ft permitted the simulation of hydraulic gradients that closely matched observed hydraulic gradients near 

a cone of depression resulting from large-scale pumping near 

active production wells. Modifications to model layering for 

the revised model consisted of (1) subdividing the Brunswick 

aquifer system into two aquifer layers (layers 3 and 5) 

separated by an intervening confining unit (layer 4) and 

(2) subdividing the Upper Floridan aquifer into upper and 

lower water-bearing zones with distinct layers (layers 7 and 9) 

separated by a confining unit (layer 8). Additional hydraulic 

property zones were established for the Brunswick aquifer 

system (layers 3–5) and Floridan aquifer system (layers 7–9) 

based on additional aquifer-test data and hydrogeologic 

structure. Additional adjustments to hydraulic-property zones 

improved the match between simulated and observed water 

levels for 2000 and 2004. 

Calibration of the revised model using 2000 pumping 

rates from the original model indicated a “good” match 

(±10 ft), with mean residuals (simulated minus observed 

water level) in each of the active model layers ranging 

from – 4.57 to 5.66 ft, median residuals ranging from 

–8.62 to 4.67 ft, and root mean square error (RMSE) ranging 

from 10.9 to 11.4 ft. In the Brunswick/Glynn County area, calibration in the upper water-bearing zone of the Upper Floridan 

aquifer (layer 7) for 2000 improved with a mean residual of 

–1.30 ft, median residual of –0.35 ft, and a RMSE of 4.32 ft. 

Calibrations of the revised model using of 2004 

pumping and boundary conditions indicate a “good’ match 

(±10 ft), with mean residuals in each active model layer 

ranging from –5.60 to 1.20 ft, median residuals ranging from 

– 6.31 to –2.05 ft, and a RMSE ranging from 6.95 to 14.5 ft. 

The match between simulated and observed water levels in 

the upper water-bearing zone of the Upper Floridan aquifer 

(layer 7) for 2004 improved from the original model results, 

with a mean residual of –2.56 ft, median residual of –1.50 ft, 

and a RMSE of 5.34 ft. 

Comparison of simulated water levels from 2000 to 2004 

indicate water-level rises, with the exception of the Brunswick 

aquifer system (layers 3 and 5), where pumpage increases 

resulted in groundwater-level declines. Simulated water-level 

changes in the Upper Floridan aquifer ranged from –2.5 to 5 ft 

in coastal Georgia and exceeded 20 ft near the Georgia-Florida 

State Line because of pumpage reductions following closure of a 

nearby paper mill during 2002. In the Brunswick/Glynn County 

area, the simulated water levels for 2000 and 2004 matched 

the rising water levels in four continuous recording wells. An 

increase in simulated pumping during 2004 in the Brunswick 

aquifer system (layers 3 and 5) resulted in a 3.30-ft decline in 

simulated water levels from 2000 to 2004 near well 34H437, 

although observed water levels indicated a rise of 3.04 ft. 

Simulated potentiometric profiles for 2000 and 2004 

were used to evaluate the potentiometric gradients in the upper 

water-bearing zone of the Upper Floridan aquifer (layer 7) 

near the chloride plume and the cone of depression caused by 

production wells in the area. In the Brunswick area, groundwater-flow directions were consistent for both years, with flow 

paths oriented from south to north and southeast to northwest 

close to the cone of depression. For 2000, four potentiometric 

profiles were constructed and simulated and observed water 

levels were compared in 13 wells, yielding a mean residual of 

–0.19 ft. The simulated potentiometric gradients of the four 

profiles, which ranged from 3.6 to 5.2 feet per mile (ft/mi), 

were comparable to the observed values, which ranged from 

4.1 to 5.6 ft/mi. For 2004, five potentiometric profiles were 

constructed and simulated and observed water levels were 

compared in 18 wells, yielding a mean residual of –0.18 ft. 

The simulated potentiometric gradients of the five profiles, 

which ranged from 3.6 to 11.1 ft/mi, were comparable to 

the observed values, which ranged from 3.8 to 10.2 ft/mi. 

Simulated potentiometric gradients were higher for 2004 than 

2000, because four of the 2004 profiles included a well located 

within the cone of depression near downtown Brunswick.

Composite-scaled sensitivities of key hydrologic parameters indicate that the revised model is most sensitive to 

changes in pumping rates, and at least an order of magnitude 

more so than to changes in the horizontal hydraulic conductivity of zones in the Upper Floridan aquifer and the conductance of the general-head boundary. The revised groundwaterflow model is least sensitive to changes in the horizontal 

hydraulic conductivity of the confining units and the vertical 

hydraulic conductivity of the aquifers.

The revised model is subject to the limitations documented in the original model associated with the relatively 

sparse data available to assign parameters to the groundwaterflow system and inaccuracies with numerically representing 

complex aquifer geometry and curved potentiometric surfaces 

with an orthogonal-grid-based approximation using finitedifferent techniques embodied in MODFLOW–2000. The 

values assigned to specified-head boundaries in the Floridan 

aquifer system (layers 7–11) have the greatest effect on water 

inflows to pumping centers in the Brunswick/Glynn County 

area and are based on sparse data for 2000 and 2004. The 

flow budgets for 2000 and 2004 indicate the specified-head 

boundaries in the Floridan aquifer system (layers 7–11) 

provide nearly 70 percent of the model inflows and about 

50 percent of the model outflows. A major limitation of the 

revised model’s ability to assess the effects of pumpage on the 

aquifer system and chloride migration hinges on the model’s 

dependence on flow from specified-head boundaries to supply 

most of the water to the pumping centers. These boundary 

conditions regulate changes to hydraulic gradients in response 

to pumpage changes by supplying limitless quantities of water 

to satisfy pumping demand. 
76 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Selected References

Applied Coastal Research Laboratory, Georgia Southern 

University, 2002, Gulf Trough and Satilla Line data 

analysis: Georgia Geologic Survey Project Report 48, 15 p.

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

Hydrogeology of the Gordon aquifer system of eastcentral Georgia: Georgia Geologic Survey Information 

Circular 75, 41 p. (Also available at http://ga.water.usgs.

gov/publications/ggs/ic-75/.)

Charm, W.B., Nesteroff, W.D., and Valdes, Sylvia, 1969, 

Detailed stratigraphic description of the JOIDES cores 

on the continental margin off Florida: U.S. Geological 

Survey Professional Paper 581–D, 13 p. (Also available 

at http://pubs.er.usgs.gov/publication/pp581D.)

Cherry, G.S., 2007, U.S. Geological Survey Georgia Water 

Science Center and City of Brunswick–Glynn County 

Cooperative Water Program—Summary of activities, 

July 2005 through June 2006: U.S. Geological Survey 

Open-File Report 2006–1368, 64 p. (Also available at 

http://pubs.usgs.gov/of/2006/1368/.)

Cherry, G.S., and Clarke, J.S., 2008, Groundwater conditions and studies in the Brunswick-Glynn County 

area, Georgia, 2007: U.S. Geological Survey OpenFile Report 2008–1297, 42 p. (Also available at 

http://pubs.usgs.gov/of/2008/1297/.)

Cherry, G.S., Peck M.F., Painter, J.A., and Stayton, W.L., 

2010, Groundwater conditions and studies in the 

Brunswick-Glynn County area, Georgia, 2008: U.S. 

Geological Survey Open-File Report 2009–1275, 54 p. 

(Also available at http://pubs.usgs.gov/of/2009/1275/.)

Cherry, G.S., Peck, M.F., Painter, J.A., and Stayton, W.L., 

2011, Groundwater conditions and studies in the BrunswickGlynn County area, Georgia, 2009: U.S. Geological Scientific 

Investigations Report 2011–5087, 58 p. (Also available at 

http://pubs.usgs.gov/sir/2011/5087/.)

Clarke, J.S., 2003, The surficial and Brunswick aquifer 

systems—Alternative groundwater resources for coastal 

Georgia, in Hatcher, K.J., ed., Proceedings of the 2003 

Georgia Water Resources Conference, April 23–24, 2003: 

Athens, Ga., University of Georgia, Institute of Ecology, 

CD–ROM. (Also available at http://ga.water.usgs.gov/

publications/other/gwrc2003/pdf/Clarke-GWRC2003.pdf.)

Clarke, J.S., Cherry, G.S., and Gonthier, G.J., 2011, 

Hydrogeology and water quality of the Floridan aquifer 

system and effects of Lower Floridan aquifer pumping 

on the Upper Floridan aquifer at Fort Stewart, Georgia: 

U.S. Geological Survey Scientific Investigations Report 

2011–5065, 59 p. (Also available at http://pubs.usgs.gov/

sir/2011/5065/.)

Clarke, J.S., Hacke, C.M., and Peck, M.F., 1990, Geology 

and groundwater resources of the coastal area of Georgia: 

Georgia Geologic Survey Bulletin 113, 106 p. (Also available at http://ga.water.usgs.gov/publications/ggs/bull-113/.)

Clarke, J.S., and Krause, R.E., 2000, Design, revision, and 

application of ground-water flow models for simulation of 

selected water-management scenarios in the coastal area of 

Georgia and adjacent parts of South Carolina and Florida: 

U.S. Geological Survey Water-Resources Investigations 

Report 00–4084, 93 p. (Also available at http://pubs.usgs.

gov/wri/wri00-4084.)

Clarke, J.S., Leeth, D.C., Taylor-Harris, DáVette, Painter, J.A., 

and Labowski, J.L., 2004, Summary of hydraulic properties 

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Table 1–1. Simulated and observed groundwater levels, 2000 and 2004.—Continued

[Simulated and observed groundwater levels are above or below (–) NAVD 88; observed values for 2000 are during September; observed values for 2004 are 

during June; see fig. 2–1 for well locations; —, no data]

Well

identifier

Model

layer

Simulated and observed groundwater levels and difference, in feet Water-level change,

in feet, 

2000 calibration 2004 calibration from 2000 to 2004

Simulated Observed Difference Simulated Observed Difference Observed Simulated

30E002 3 25.88 27.87 –1.99 — — — — —

31U009 3 — — — 112.46 122.13 –9.67 — —

32L016 3 16.15 15.79 0.36 14.13 17.60 –3.47 1.81 –2.02

33D071 3 10.69 –2.07 12.76 14.08 17.22 –3.14 19.29 3.39

33J065 3 — — — 9.54 11.91 –2.37 — —

33G028 3 10.74 16.75 –6.01 7.59 21.31 –13.72 4.56 –3.15

34H144 3 — — — 4.64 3.60 1.04 — —

34H437 3 8.56 5.88 2.68 5.26 8.92 –3.66 3.04 –3.30

34J077 3 — — — –3.16 –12.46 9.30 — —

34J081 3 — — — 2.28 –2.50 4.78 — —

34S008 3 — — — 17.15 45.76 –28.61 — —

35Q050 3 — — — –18.98 2.73 –21.71 — —

35T005 3 — — — 20.16 13.14 7.02 — —

39Q026 3 –11.02 –2.31 –8.71 –10.34 –3.29 –7.05 –0.98 0.68

39Q028 3 –11.03 –2.21 –8.82 –10.34 –3.25 –7.09 –1.04 0.69

33J062 5 — — — 9.57 22.09 –12.52 — —

34J078 5 6.38 3.71 2.67 — — — — —

34J080 5 — — — 2.28 8.55 –6.27 — —

35S008 5 8.90 12.10 –3.20 7.06 13.41 –6.35 1.31 –1.84

36N012 5 –10.67 –26.18 15.51 –11.78 –22.43 10.65 3.75 –1.11

21T001 7 226.54 220.19 6.35 223.03 223.66 –0.63 3.47 –3.51

25Q001 7 107.49 96.75 10.74 — — — — —

26M003 7 41.29 35.84 5.45 — — — — —

26Q002 7 76.88 49.95 26.93 — — — — —

26R001 7 127.24 103.85 23.39 124.97 106.63 18.34 2.78 –2.27

27E004 7 38.91 40.54 –1.63 39.14 43.76 –4.62 3.22 0.23

27G003 7 — — — 37.50 44.53 –7.03 — —

27G006 7 37.40 40.48 –3.08 — — — — —

27M001 7 37.74 33.07 4.67 — — — — —

27Q002 7 76.68 44.97 31.71 — — — — —

27R003 7 121.43 90.67 30.76 — — — — —

27R004 7 97.39 92.42 4.97 — — — — —

27S002 7 138.45 99.21 39.24 — — — — —

28D001 7 36.68 37.79 –1.11 — — — — —

28K001 7 35.11 44.39 –9.28 — — — — —

28R001 7 92.25 59.40 32.85 — — — — —

Appendix 1
Appendix 1 81

Table 1–1. Simulated and observed groundwater levels, 2000 and 2004.—Continued

[Simulated and observed groundwater levels are above or below (–) NAVD 88; observed values for 2000 are during September; observed values for 2004 are 

during June; see fig. 2–1 for well locations; —, no data]

Well

identifier

Model

layer

Simulated and observed groundwater levels and difference, in feet Water-level change,

in feet, 

2000 calibration 2004 calibration from 2000 to 2004

Simulated Observed Difference Simulated Observed Difference Observed Simulated

28S003 7 122.08 106.51 15.57 — — — — —

28S004 7 115.66 88.15 27.51 — — — — —

28T001 7 155.33 103.29 52.04 — — — — —

29L005 7 21.37 27.08 –5.71 — — — — —

29M002 7 24.19 36.04 –11.85 — — — — —

29N003 7 20.62 32.16 –11.54 — — — — —

29Q001 7 38.04 29.59 8.45 — — — — —

29R001 7 65.42 33.05 32.37 — — — — —

29R003 7 59.92 34.98 24.94 — — — — —

29T009 7 136.53 113.32 23.21 — — — — —

29V001 7 164.70 160.00 4.70 — — — — —

29W002 7 179.53 167.92 11.61 — — — — —

30E007 7 32.99 32.30 0.69 — — — — —

30F004 7 29.53 34.70 –5.17 — — — — —

30H003 7 32.14 27.58 4.56 — — — — —

30H005 7 31.99 37.35 –5.36 — — — — —

30L003 7 2.06 13.95 –11.89 — — — — —

30L011 7 21.82 20.91 0.91 — — — — —

30L012 7 9.59 19.53 –9.94 — — — — —

30M003 7 0.97 11.03 –10.06 — — — — —

30M007 7 9.53 19.26 –9.73 — — — — —

30N002 7 11.73 21.25 –9.52 — — — — —

30P003 7 18.70 5.12 13.58 — — — — —

30R005 7 31.20 23.74 7.46 — — — — —

30U005 7 119.67 114.98 4.69 — — — — —

30V002 7 136.70 138.79 –2.09 — — — — —

30X003 7 164.80 161.82 2.98 — — — — —

31E001 7 26.40 30.10 –3.70 — — — — —

31F022 7 26.86 32.77 –5.91 — — — — —

31H005 7 29.38 32.70 –3.32 — — — — —

31R001 7 27.97 23.64 4.33 — — — — —

31S008 7 33.46 41.96 –8.50 — — — — —

31T010 7 78.58 54.95 23.63 — — — — —

31U008 7 — — — 110.07 117.01 –6.94 — —

31V008 7 107.34 122.83 –15.49 — — — — —

31V014 7 109.39 118.09 –8.70 — — — — —

32E031 7 23.35 29.56 –6.21 — — — — —

32E038 7 21.98 25.46 –3.48 — — — — —

32F008 7 24.34 32.28 –7.94 — — — — —

32G007 7 24.46 27.09 –2.63 — — — — —
82 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Table 1–1. Simulated and observed groundwater levels, 2000 and 2004.—Continued

[Simulated and observed groundwater levels are above or below (–) NAVD 88; observed values for 2000 are during September; observed values for 2004 are 

during June; see fig. 2–1 for well locations; —, no data]

Well

identifier

Model

layer

Simulated and observed groundwater levels and difference, in feet Water-level change,

in feet, 

2000 calibration 2004 calibration from 2000 to 2004

Simulated Observed Difference Simulated Observed Difference Observed Simulated

32G015 7 23.20 29.95 –6.75 — — — — —

32H001 7 22.10 21.56 0.54 — — — — —

32J003 7 20.06 23.34 –3.28 — — — — —

32L004 7 7.84 10.55 –2.71 — — — — —

32L015 7 4.29 8.22 –3.93 2.10 13.48 –11.38 5.26 –2.19

32N010 7 –1.57 10.14 –11.71 — — — — —

32N012 7 –0.97 4.49 –5.46 — — — — —

32R002 7 23.27 18.01 5.26 22.60 22.35 0.25 4.34 –0.67

32U005 7 81.36 96.50 –15.14 — — — — —

33D004 7 –11.10 1.91 –13.01 — — — — —

33D069 7 –8.55 2.99 –11.54 — — — — —

33E007 7 11.46 15.26 –3.80 21.17 27.10 –5.93 11.84 9.71

33E009 7 17.94 30.97 –13.03 — — — — —

33E027 7 15.98 23.51 –7.53 22.54 34.11 –11.57 10.60 6.56

33F003 7 17.78 26.15 –8.37 — — — — —

33G002 7 — — — 20.93 23.48 –2.55 — —

33G003 7 17.75 22.86 –5.11 — — — — —

33G008 7 17.53 18.72 –1.19 20.74 23.16 –2.42 4.44 3.21

33G024 7 — — — 22.68 29.87 –7.19 — —

33H120 7 –1.69 –2.99 1.30 4.05 3.08 0.97 6.07 5.74

33H130 7 –4.10 –4.59 0.49 2.69 2.18 0.51 6.77 6.79

33H133 7 –1.51 –0.89 –0.62 4.54 3.77 0.77 4.66 6.05

33H141 7 9.18 7.24 1.94 — — — — —

33H164 7 17.37 15.08 2.29 — — — — —

33H174 7 8.99 9.33 –0.34 — — — — —

33H177 7 19.72 21.16 –1.44 22.39 28.20 –5.81 7.04 2.67

33H180 7 3.14 –1.15 4.29 — — — — —

33H190 7 8.05 8.03 0.02 — — — — —

33H193 7 — — — 19.14 22.38 –3.24 — —

33H207 7 2.64 4.16 –1.52 7.76 8.09 –0.33 3.93 5.12

33H211 7 — — — –4.59 –4.16 –0.43 — —

33H213 7 — — — –1.62 –1.72 0.10 — —

33J027 7 14.20 14.31 –0.11 — — — — —

33L027 7 6.13 6.98 –0.85 — — — — —

33M004 7 –0.70 0.40 –1.10 –3.17 6.36 –9.53 5.96 –2.47

33N089 7 –2.12 –5.48 3.36 — — — — —

33U009 7 62.42 67.18 –4.76 — — — — —

33U019 7 58.16 73.10 –14.94 — — — — —

33U021 7 62.31 71.15 –8.84 — — — — —

33U023 7 57.92 75.30 –17.38 — — — — —
Appendix 1 83

Table 1–1. Simulated and observed groundwater levels, 2000 and 2004.—Continued

[Simulated and observed groundwater levels are above or below (–) NAVD 88; observed values for 2000 are during September; observed values for 2004 are 

during June; see fig. 2–1 for well locations; —, no data]

Well

identifier

Model

layer

Simulated and observed groundwater levels and difference, in feet Water-level change,

in feet, 

2000 calibration 2004 calibration from 2000 to 2004

Simulated Observed Difference Simulated Observed Difference Observed Simulated

33V020 7 70.67 76.70 –6.03 — — — — —

33V021 7 85.97 98.50 –12.53 — — — — —

34G002 7 12.64 17.60 –4.96 16.44 22.40 –5.96 4.80 3.80

34G003 7 — — — 20.14 25.90 –5.76 — —

34G009 7 16.03 35.50 –19.47 19.81 38.70 –18.89 3.20 3.78

34G016 7 14.25 23.70 –9.45 17.92 28.30 –10.38 4.60 3.67

34G017 7 — — — 17.28 26.10 –8.82 — —

34G020 7 15.46 26.20 –10.74 19.10 30.10 –11.00 3.90 3.64

34H062 7 3.25 0.26 2.99 — — — — —

34H085 7 5.15 4.23 0.92 — — — — —

34H095 7 — — — 15.99 17.85 –1.86 — —

34H097 7 10.40 11.80 –1.40 — — — — —

34H112 7 5.86 6.62 –0.76 11.04 12.90 –1.86 6.28 5.18

34H117 7 4.87 4.54 0.33 10.30 10.50 –0.20 5.96 5.43

34H125 7 4.10 4.45 –0.35 9.20 12.40 –3.20 7.95 5.10

34H128 7 — — — 8.26 8.13 0.13 — —

34H328 7 8.94 8.78 0.16 — — — — —

34H344 7 1.97 3.25 –1.28 6.24 6.22 0.02 2.97 4.27

34H355 7 2.46 3.88 –1.42 7.90 8.46 –0.56 4.58 5.44

34H357 7 7.85 8.74 –0.89 — — — — —

34H371 7 7.97 10.80 –2.83 12.89 15.50 –2.61 4.70 4.92

34H373 7 1.93 –1.07 –2.65 7.02 3.98 3.04 5.05 10.74

34H374 7 — — — 6.00 7.20 –1.20 — —

34H392 7 4.23 3.33 0.90 — — — — —

34H393 7 7.27 8.53 –1.26 12.32 14.60 –2.28 6.07 5.05

34H400 7 — — — 7.12 4.34 2.78 — —

34H401 7 — — — 6.51 2.53 3.98 — —

34H403 7 7.65 10.10 –2.45 — — — — —

34H408 7 5.40 2.25 3.15 — — — — —

34H410 7 6.67 7.85 –1.18 — — — — —

34H424 7 1.13 1.04 0.09 — — — — —

34H434 7 — — — 8.86 6.13 2.73 — —

34H469 7 0.38 5.56 –5.18 6.05 6.61 –0.56 1.05 5.67

34J029 7 9.42 8.09 1.33 — — — — —

34J051 7 9.64 9.65 –0.01 — — — — —

34K073 7 7.17 1.97 5.20 — — — — —

34K095 7 7.04 1.78 5.26 — — — — —

34L048 7 2.70 8.06 –5.36 — — — — —

34L060 7 –0.54 –3.00 2.46 — — — — —

34L061 7 2.47 4.17 –1.70 — — — — —
84 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Table 1–1. Simulated and observed groundwater levels, 2000 and 2004.—Continued

[Simulated and observed groundwater levels are above or below (–) NAVD 88; observed values for 2000 are during September; observed values for 2004 are 

during June; see fig. 2–1 for well locations; —, no data]

Well

identifier

Model

layer

Simulated and observed groundwater levels and difference, in feet Water-level change,

in feet, 

2000 calibration 2004 calibration from 2000 to 2004

Simulated Observed Difference Simulated Observed Difference Observed Simulated

34M070 7 –1.59 –6.32 4.73 — — — — —

34M075 7 –3.73 –9.49 5.76 — — — — —

34M076 7 –2.27 –4.20 1.93 — — — — —

34N089 7 –10.56 –14.30 3.74 –13.28 –9.60 –3.68 4.70 –2.72

34R039 7 0.02 –5.48 5.50 — — — — —

34V004 7 71.45 74.60 –3.15 — — — — —

35H044 7 10.27 9.94 0.33 — — — — —

35K069 7 3.21 –0.79 4.00 — — — — —

35L068 7 –0.72 –2.83 2.11 — — — — —

35M013 7 –4.21 –11.90 7.69 –5.06 –6.40 1.34 5.50 –0.85

35R018 7 –22.38 –18.10 –4.28 — — — — —

35T003 7 16.22 31.40 –15.18 15.27 2.11 13.16 –29.29 –0.95

36M018 7 –8.99 –16.90 7.91 — — — — —

36Q008 7 –86.74 –90.50 3.76 –86.81 –82.10 –4.71 8.40 –0.07

36Q019 7 –47.60 –38.10 –9.50 — — — — —

36Q020 7 –47.27 –42.20 –5.07 –48.65 –38.20 –10.45 4.00 –1.38

36Q300 7 –56.26 –54.30 –1.96 — — — — —

37P005 7 –50.36 –52.50 2.14 — — — — —

37P006 7 –56.91 –54.40 –2.51 — — — — —

37P114 7 –43.59 –46.00 2.41 –44.61 –43.60 –1.01 2.40 –1.02

37Q016 7 –83.53 –82.20 –1.33 –85.21 –77.00 –8.21 5.20 –1.68

37Q033 7 –75.34 –75.80 0.46 — — — — —

37Q043 7 –56.68 –57.00 0.32 — — — — —

37Q185 7 –108.99 –99.20 –9.79 –110.21 –95.20 –15.01 4.00 –1.22

38Q002 7 –23.12 –30.40 7.28 –22.32 –28.10 5.78 2.30 0.80

39Q003 7 –17.52 –27.90 10.38 –17.15 –25.20 8.05 2.70 0.37

BFT–1810 7 –4.20 –0.75 –3.45 — — — — —

BFT–1813 7 –4.88 –3.50 –1.38 — — — — —

BFT–429 7 –4.30 –5.90 1.60 — — — — —

D–3840 7 –12.46 –13.20 0.74 — — — — —

HAM–83 7 25.82 4.40 21.42 — — — — —

N–62 7 –7.92 –17.90 9.98 — — — — —

33H127 9 –2.17 0.60 –2.77 4.55 7.85 –3.30 7.25 6.72

33H154 9 –4.78 –27.58 22.80 2.99 –17.90 20.89 9.68 7.77

34H334 9 2.40 7.51 –5.11 6.27 12.40 –6.13 4.89 3.87

34H402 9 — — — 6.53 8.20 –1.67 — —

34H403 9 7.65 10.12 –2.47 12.57 16.30 –3.73 6.18 4.92

32Y033 11 142.71 110.00 32.71 — — — — —

33D073 11 4.67 3.58 1.09 18.26 30.70 –12.44 27.12 13.59

33H188 11 13.67 12.50 1.17 17.24 20.10 –2.86 7.60 3.57
Appendix 1 85

Table 1–1. Simulated and observed groundwater levels, 2000 and 2004.—Continued

[Simulated and observed groundwater levels are above or below (–) NAVD 88; observed values for 2000 are during September; observed values for 2004 are 

during June; see fig. 2–1 for well locations; —, no data]

Well

identifier

Model

layer

Simulated and observed groundwater levels and difference, in feet Water-level change,

in feet, 

2000 calibration 2004 calibration from 2000 to 2004

Simulated Observed Difference Simulated Observed Difference Observed Simulated

33H206 11 6.47 8.40 –1.93 11.01 14.00 –2.99 5.60 4.54

33J044 11 11.81 13.90 –2.09 14.57 19.10 –4.53 5.20 2.76

34G036 11 13.99 20.10 –6.11 — — — — —

34H391 11 9.65 9.18 0.47 13.86 11.90 1.96 2.72 4.21

34H399 11 11.14 1.76 9.38 — — — — —

34H436 11 7.85 11.70 –3.85 12.07 15.80 –3.73 4.10 4.22

34H495 11 — — — 13.06 24.00 –10.94 — —

34H500 11 — — — 13.05 21.40 –8.35 — —

35L085 11 — — — –2.76 –10.10 7.34 — —

35P109 11 –25.94 –21.80 –4.14 –28.98 –18.90 –10.08 2.90 –3.04

37Q186 11 — — — –98.59 –61.00 –37.59 — —

38Q201 11 — — — –22.36 –46.60 24.24 — —

39Q024 11 –17.28 –31.70 14.42 –16.83 –29.90 13.07 1.80 0.45
86 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

Dooly

Crisp

Pulaski

Wilcox

Houston Bleckley

Dodge

Twiggs

Wilkinson

Laurens

Telfair

Wheeler

Johnson

Washington

Jefferson

Glascock

Burke

Jenkins

Emanuel

Treutlen Candler

Screven

Bulloch

Effingham

Evans Bryan

Tattnall

Toombs Montgomery

Liberty

Long

Jeff Davis Appling

Coffee

Ben Hill

Irwin

Turner

Tift

Berrien Atkinson

Clinch

Lanier

Echols

Ware

Bacon

Pierce

Brantley

Wayne

Charlton Camden

Glynn

Nassau

Duval

Baker

Columbia

McIntosh

Chatham

Jasper

Hampton

Allendale

Barnwell

Bamberg

Collenton

Beaufort

N-62

HAM83

33V020

33U023

36Q020

36Q019

34V004

34R039

29L005

32R002 36Q008

36M018

35R018

33U009

33V021

32N010

33U021

33U019

33N089

32W006

32U005

32N012

31V014

28R001

32L004

31S008

31R001

31H005

31V008

31T010

30X003

30V002

30U005

30R005

30P003

30N002

30L003

30H005

29W002

30M007

30L011

29T009

29V001

29R003

29Q001

29N003

29M002

28T001

28S004

28W002

28S003

36Q300

28K001

28D001

27M001

26M003

27G006

26Q002 25Q001

21T001

27S002

27R004

27R003

37P114

35T003

27E004

26R001

D-3840

34N089

BFT429

37P006

BFT1810

BFT1813

31U008

35T005

35Q050

37P005

37Q185

37Q033

37Q016

37Q043

32L015

30M003

30L012

29R001

27Q002

30H003

31U009

32L016

37Q186

32Y033

39Q024

35P109

38Q002

38Q201

39Q003

39Q026

39Q028

34S008

36N012

27G003

33M004

35S008

30E002

30E007

Figure 1–1.

A

SOUTH

CAROLINA GEORGIA

FLORIDA

Map

area

N

Well and identifier

EXPLANATION

0 15 30 45 60 MILES

0 30 45 60 KILOMETERS 15

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

30E002

Model boundary

Figure 2–1. Location of wells used for 2000 and 2004 simulations in A, study area; B, McIntosh, Glynn, 

and Camden Counties (enlarged); and C, Brunswick (enlarged).

Appendix 2
Appendix 2 87

Base from U.S. Geological Survey

1:100,000-scale digital data

Map

area

Map area of part C

33D073

34G036

33D071

34K095

34K073

34L060

34M076

34M075

34M070

34L061

34L048

35L068

35H044

34J051

34J029

34G020

34G016

34H328

34G009

33L027

33J027

33H190

33G002

33F003

33F003

33H177

33H174

33H164

34H410

32H001

34H408

33E027

33E009

33E007

32G015

32G007

32F008

32E038

32E031

31F022

31E001

30F004

32J003

34H357

33D069

35K069

33G003

34H141

33H188

34H144

34J078

33G028

33D004

Well and identifier

EXPLANATION

34J077 33J044

35L085

34G017

33G008

33G024

34G003

33H193

35M013

33J062

33J065

34J081

34J080

MCINTOSH

GLYNN

CAMDEN

0 5 10 MILES

0 5 10 KILOMETERS

Figure 1–1.—Continued

B

SOUTH

CAROLINA GEORGIA

Model boundary

FLORIDA

N

Figure 2–1. Location of wells used for 2000 and 2004 simulations in A, study area; B, McIntosh, Glynn, 

and Camden Counties (enlarged); and C, Brunswick (enlarged).—Continued
88 Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

33H206

34H436

34H399

Brunswick

34H424

34H125

34H097

34H112

34H085

34H062

34G002

33H120

33H180

33H133

34H403

34H393

34H392

34H355

34H371

33H207

34H391

34H495 34H500

33H154

33H127

34H402

34H334

TURTLE

East River

Oglethorpe Bay

RIVER

34H095

34H095

34H128

34H117

34H434

34H400

34H344 34H373

34H401

34H374

33H130 34H469

33H211

33H213

34H437

Well and identifier

EXPLANATION

0 0.2 0.4 0.6 0.8 1 MILE

0 0.2 0.4 0.6 0.8 1 KILOMETER

C

Figure 1–1—Continued

GLYNN COUNTY

Andrews Island

N

Base from U.S. Geological Survey 

1:100,000-scale digital data

Figure 2–1. Location of wells used for 2000 and 2004 simulations in A, study area; B, McIntosh, Glynn, 

and Camden Counties (enlarged); and C, Brunswick (enlarged).—Continued
Manuscript approved April 22, 2015

Prepared by the USGS Science Publishing Network

Raleigh Publishing Service Center

Edited by Michael Deacon

Illustrations and layout by Caryl J. Wipperfurth

For more information concerning this report, contact:

Director, South Atlantic Water Science Center

North Carolina–South Carolina–Georgia

720 Gracern Road, Suite 129

Columbia, SC 29210

Phone: (803) 750-6100

http://ga.water.usgs.gov/
ISSN 2328–0328 (online)

http://dx.doi.org/10.3133/sir20155061

Cherry—Groundwater Flow in the Brunswick/Glynn County Area, Georgia, 2000–04

—Scientific Investigations Report 2015–5061