U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2016–1017

Prepared in cooperation with the Jekyll Island Authority

Hydrologic Conditions, Recharge, and Baseline 

Water Quality of the Surficial Aquifer System 

at Jekyll Island, Georgia, 2012–13
Cover. Sunrise over Jekyll Island, Georgia (photograph by John S. Clarke, retired, U.S. Geological Survey).
Hydrologic Conditions, Recharge, and 

Baseline Water Quality of the Surficial 

Aquifer System at Jekyll Island, Georgia, 

2012–13

By Debbie W. Gordon and Lynn J. Torak

Prepared in cooperation with the Jekyll Island Authority

Open-File Report 2016–1017

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, Director

U.S. Geological Survey, Reston, Virginia: 2016

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Gordon, D.W., and Torak, L.J., 2016, Hydrologic conditions, recharge, and baseline water quality of the surficial 

aquifer system at Jekyll Island, Georgia, 2012–13: U.S. Geological Survey Open-File Report 2016–1017, 34 p., 

http://dx.doi.org/10.3133/ofr20161017.

ISSN 2331-1258 (online)
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................4

Previous Studies ...................................................................................................................................4

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

Physiography and Drainage................................................................................................................5

Climate....................................................................................................................................................5

Hydrogeology.........................................................................................................................................8

Aquifer Formation on a Barrier Island......................................................................................8

Water-Table Zone of the Surficial Aquifer System.................................................................9

Methods of Investigation............................................................................................................................10

Volume Estimates................................................................................................................................10

Usefulness............................................................................................................................................11

Surficial Aquifer System Water Use ........................................................................................................12

Hydrologic Conditions of the Water-Table Zone of the Surficial Aquifer System .................................12

Groundwater-Flow Directions and Inferred Recharge and Discharge .....................................12

Seasonal Water-Table Fluctuations.................................................................................................16

Recharge..............................................................................................................................................18

Method One—Water Balance Method..................................................................................18

Method Two—Aquifer-Volume Change.................................................................................21

Comparison of Recharge Calculations by Both Methods...................................................22

Development Potential of the Water-Table Zone of the Surficial Aquifer System...................23

Baseline Groundwater Quality...................................................................................................................24

Summary and Conclusions.........................................................................................................................29

Selected References...................................................................................................................................30

Appendix 1. Wells Inventoried for This Study........................................................................................32

Appendix 2. Construction of Monitoring Wells......................................................................................34

Appendix 3. Groundwater-Level Measurements Made on November 8, 2012, 

April 17, 2013, and August 23, 2013..............................................................................................34
iv

Figures

1. Maps showing location of Jekyll Island, Coastal Plain, study area; and 

monitoring wells and gages, Georgia........................................................................................2

 2. Map showing land-use-based management units on Jekyll Island, Georgia....................5

3. Map showing light detection and ranging (lidar)-based altitude for central 

Jekyll Island, Georgia...................................................................................................................6

4. Graph showing average monthly period of record precipitation for 

Brunswick, Georgia, and 2013 monthly total precipitation, in inches, 

at Jekyll Island, Georgia ..............................................................................................................7

5. Maps showing sedimentation and erosion features on Jekyll Island, Georgia.................8

6. Generalized correlation chart showing the geologic and hydrogeologic units 

at Jekyll Island composing the lower coastal plain, Georgia ...............................................9

7. Graph showing ordinary least squares regression line between 

specific conductance and chloride concentration for wells completed 

in the surficial aquifer system, Jekyll Island, Georgia..........................................................11

8. Maps showing water table for, November 8, 2012; April 17, 2013; and 

August 23, 2013 on Jekyll Island, Georgia ..............................................................................13

9. Graphs showing groundwater levels, pond stage, and rainfall for 2013 

at Jekyll Island, Georgia ............................................................................................................17

10. Graphs showing monthly total precipitation, potential evapotranspiration, 

and water balance for the weather station at Brunswick, Georgia, 

October 2012–December 2013..................................................................................................18

11. Graph showing monthly potential maximum recharge for Brunswick, 

and potential maximum recharge for Jekyll Island using evapotranspiration 

data from Brunswick, in inches, October 2012–December 2013 ........................................19

12. Graphs showing monthly precipitation at Brunswick and Jekyll Island, 

Georgia, October 2012–December 2013, and period of record average 

monthly precipitation at Brunswick, Georgia ........................................................................20

13. Maps showing distribution of specific conductance during, November 2012, 

April 2013, and August 2013 in 26 wells on Jekyll Island, Georgia .....................................25

1–1. Maps showing location of, and specific conductance measured in, private 

wells inventoried for this study, Jekyll Island, Georgia, 2012..............................................33
v

Tables

1. Period of record average monthly temperature, precipitation, and 

evapotranspiration for Brunswick, Georgia.............................................................................7

2. Groundwater-quality data for the surficial aquifer system, Jekyll Island, 

Georgia, August 23, 2013 ...........................................................................................................12

3. Monthly precipitation, evapotranspiration, and water balance for 

weather station at Brunswick, Georgia, October 2012–December 2013...........................19

4. Monthly potential maximum recharge or discharge for Jekyll Island estimated

using precipitation from the Jekyll Island weather station and monthly 

evapotranspiration from the Brunswick weather station....................................................20

5. Average groundwater level difference, aquifer-volume change, and recharge

to and discharge from the water-table zone of the surficial aquifer system, 

Jekyll Island, Georgia, November 8, 2012, to August 23, 2013.............................................22

6. Specific conductance values collected from newly constructed wells, 

Jekyll Island, Georgia, November and December 2012, April and August 2013 ..............28
vi

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Volume

cubic foot (ft3) 0.02832 cubic meter (m3)

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

Recharge

inch per day (in/d) 2.54 centimeter per day (cm/d)

inch per year (in/yr) 2.54 centimeter per year (cm/yr)

Flow rate

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

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

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

Transmissivity*

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

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

°F = (1.8 ×°C)+32.

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

°C=(°F –32)/ 1.8.
vii

Datums

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

(NAVD 88).

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

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

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 in milligrams per liter (mg/L).

Abbreviations 

EPA U.S. Environmental Protection Agency

ET evapotranspiration

GIS geographic information system

JIA Jekyll Island Authority

NWIS National Water Information System 

POR period of record

PVC polyvinyl chloride

SC specific conductance

TDS total dissolved solids 

USGS U.S. Geological Survey
viii

Acknowledgments

The authors would like to thank the many residents of Jekyll Island who allowed access to their 

wells for specific conductance measurements. We also thank the Jekyll Island Authority for 

collecting weekly water-level measurements and providing that and other important data to us.
Hydrologic Conditions, Recharge, and Baseline 

Water Quality of the Surficial Aquifer System 

at Jekyll Island, Georgia, 2012–13

By Debbie W. Gordon and Lynn J. Torak

Abstract

An increase of groundwater withdrawals from the 

surficial aquifer system on Jekyll Island, Georgia, prompted 

an investigation of hydrologic conditions and water quality 

by the U.S. Geological Survey during October 2012 through 

December 2013. The study demonstrated the importance of 

rainfall as the island’s main source of recharge to maintain 

freshwater resources by replenishing the water table from the 

effects of hydrologic stresses, primarily evapotranspiration and 

pumping. Groundwater-flow directions, recharge, and water 

quality of the water-table zone on the island were investigated 

by installing 26 shallow wells and three pond staff gages to 

monitor groundwater levels and water quality in the watertable zone. Climatic data from Brunswick, Georgia, were used 

to calculate potential maximum recharge to the water-table 

zone on Jekyll Island. A weather station located on the island 

provided only precipitation data. Additional meteorological 

data from the island would enhance potential evapotranspiration estimates for recharge calculations. 

Groundwater levels and specific-conductance measurements showed the dependence of freshwater resources on 

rainfall to recharge the water-table zone of the surficial aquifer 

system and to influence groundwater flow on Jekyll Island. 

The unseasonably dry conditions during November 2012 to 

April 2013 induced saline water infiltration to the water-table 

zone from the marshland separating the Jekyll River from the 

island. A strong correlation (R2=0.97) of specific conductance 

to chloride concentration in water samples from wells installed 

in the water-table zone provided support for the determination 

of seasonal directions of groundwater flow by confirming 

salinity changes in the water-table zone. Unseasonably wet 

conditions during the late spring to August caused groundwater-flow reversals in some areas. The high dependence of 

the water-table zone in the surficial aquifer system on precipitation to replenish the aquifer with freshwater underscored the 

importance of monitoring groundwater levels, water quality, 

and water use to identify aquifer-discharge conditions that 

have the potential to promote seawater encroachment and 

degrade freshwater resources on Jekyll Island. 

Introduction

Development of groundwater resources in the shallow 

water-table zone of the surficial aquifer system for residential 

irrigation recently has increased at Jekyll Island, Georgia 

(fig. 1). The resultant water-table declines from pumping on 

this barrier island may threaten fragile coastal ecosystems by 

decreasing freshwater discharge to streams and marshlands, 

and increasing the salinity of these features by promoting 

seawater encroachment into the aquifer. Prolonged periods 

of excessively dry climatic conditions, such as drought, as 

well as sea-level rise, would compound water-table declines 

caused by increased pumping, as the freshwater supply on 

the island depends primarily on precipitation to replenish 

the aquifer. 

Minimal information is available at Jekyll Island 

concerning groundwater hydrology, including pumping rates, 

recharge, and water levels in the water-table zone of the 

surficial aquifer system. Because pumping from the watertable zone of the surficial aquifer system is likely to increase, 

establishment of baseline hydrologic and water-quality 

conditions is critical for assessing current and future impacts 

of hydrologic stress on the island’s freshwater resources and 

coastal ecosystem (AECOM, 2011). 

Jekyll Island is a Georgia State Park governed by the 

Jekyll Island Authority (JIA). The JIA established a conservation planning committee to develop a long-term plan for the 

natural resources on Jekyll Island. The mission of the conservation plan is to “preserve, maintain, manage, and restore 

Jekyll Island’s natural communities and species diversity 

while providing nature-based educational and recreational 

opportunities for the general public” (AECOM, 2011). The 

JIA is concerned that lowering the water table by increased 

pumping could adversely impact the environment through 

decreased periods of inundation in some areas, and promote 

seawater encroachment, ultimately resulting in detrimental 

salinity levels in freshwater systems and loss or degradation 

of wetlands. Objectives of the conservation plan include 

maintaining or improving salinity levels and water quality 

for salt marshes, wetland enhancement, and assessment of 
2 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

regional changes in groundwater level and water quality. 

Strategies to meet plan objectives include assessing current 

groundwater levels to determine the effects of changes on 

wetland hydrology and monitoring salinity levels in wetlands 

and ponds for saltwater intrusion (AECOM, 2011).

The U.S. Geological Survey (USGS), in cooperation 

with the JIA, initiated a study during 2012 to monitor 

groundwater levels and assess baseline water quality in the 

water-table zone of the surficial aquifer system to assist in 

meeting some of the objectives of the JIA conservation plan. 

The objectives of the study were to 

• Determine the number and distribution of shallow 

wells on Jekyll Island; 

• Identify seasonal fluctuations of groundwater levels within 

the water-table zone of the surficial aquifer system; 

• Estimate seasonal recharge to the water-table zone; and, 

• Collect baseline water-quality data for the water-table 

zone for future comparison. 

Data from this investigation add to the USGS database of 

hydrogeologic information that collectively improves regional 

characterization of surficial aquifers in coastal areas.

Base map water features and roads ©2014 Google

County lines from U.S. Geological Survey

1:100,000-scale digital data

Figure 1. 

A

T

L

A

N

T I C

O

C

E

A

N

0 5 10 15 MILES

0 5 10 15 KILOMETERS

N

Weather station and identifier—Precipitation data

WAYNE MCINTOSH

GLYNN

CAMDEN

BRANTLEY

95

25

17

17

82 Brunswick 

weather station

Jekyll

Island

Cumberland

Island

St Simons

Island

St Simons Sound

Area of map

in fig 1B

A

Brunswick

Woodbine

Brunswick R

Northwestern extent of Southeast Georgia Embayment 

Barrier Island Sequence District (Clark and Zisa, 1976)

EXPLANATION

GEORGIA

Area of

map above 

COASTAL

PLAIN

Figure 1. Location of A, Jekyll Island, Coastal Plain, study area; and B, monitoring wells and gages, Georgia.
Introduction 3

34G169

34G151

34G160

34G163

34G150

34G171

34G161

34G172

34G173

34G166

Jekyll Island 

weather station

Jekyll Island 

weather station

34G152

34G154

34G153

34G155

Staff gage 2

Staff gage 3

Staff gage 1

34G156

34G157

34G170

34G174 34G168 34G159

34G167

34G164

34G162

34G165

34G175

34G166

34G157

EXPLANATION

Monitoring well and identifier Monitoring well measured 

 weekly and identifier

Groundwater recorder 

 and identifier

Pond staff gage 

 and identifier

Base modified from ESRI Streetmap, 1:750,000. Map image is

the intellectual property of Esri and is used herein under license.

Copyright ©2014 Esri and its licensors. All rights reserved

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

Figure 1.—Continued

A

T

L

A

N

T I C

O

C

E

A

N

Jekyll River

Monitoring well and identifier—

 Sampled for water-quality analyses

Staff gage 3

81°25'30"

31°05'30"

31°05'00"

31°04'30"

31°04'00"

31°03'30"

81°25'00" 81°24'30" 81°24'00"

JEKYLL ISL A N D

34G158

34G168

34G170

Weather station

 and identifier—

 Precipitation data

B

Figure 1. Location of A, Jekyll Island, Coastal Plain, study area; and B, monitoring wells and gages, Georgia.—Continued
4 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Purpose and Scope

This report documents hydrologic conditions and water 

quality in the water-table zone of the surficial aquifer system 

on Jekyll Island from October 2012 through December 2013. 

The study area encompasses the populated central portion of 

Jekyll Island (fig. 1B) where shallow residential wells have 

been installed primarily for lawn irrigation. The number and 

distribution of wells completed in the water-table zone of the 

surficial aquifer system have been described using results 

from an inventory of 89 wells made during November 2012. 

Seasonal groundwater-level measurements made in 26 wells 

(fig. 1B) installed in the water-table zone during this study 

between November 2012 and August 2013 were supported 

by weekly groundwater-level and pond-stage measurements 

(recorded by JIA) to describe groundwater-level fluctuations 

on the island. Selected field water-quality properties of specific 

conductance and water temperature were measured at these 

26 wells to assess water quality. 

Seasonal recharge to Jekyll Island’s water-table zone 

was estimated from meteorological conditions measured 

on the island and at a nearby weather station in Brunswick, 

Ga. (fig. 1A). Groundwater recharge was estimated using 

water-balance calculations derived from precipitation, 

evapotranspiration (combined evaporation from wet surfaces 

and water-vapor release, or transpiration, from plants), 

and water-use estimates. The potential maximum recharge 

attainable on the island was estimated from a water balance 

derived from precipitation and potential evapotranspiration. 

Net recharge to (or discharge from) the water-table zone was 

calculated as the change in aquifer volume resulting from 

groundwater levels measured on November 8, 2012, and 

April 17 and August 23, 2013. All data collected during this 

investigation were entered into the USGS National Water 

Information System (NWIS; http://waterdata.usgs.gov/nwis) 

database from a geographic information system (GIS) database developed for this study.

Previous Studies

Several hydrologic studies pertinent to the evaluation of 

hydrologic conditions on Jekyll Island have been performed. 

A recent publication by Henry (2014) describes the geology 

of the Georgia Coast with an emphasis on sedimentation and 

erosional processes that led to the creation of Georgia’s barrier 

island system, which includes Jekyll Island. Dilsaver (2004) 

discusses the formation of barrier island systems during the 

past 2 million years that resulted in the present barrier island 

system along the Georgia Coast. Clarke and others (1990) 

describe the geology and groundwater resources of the coastal 

area of Georgia and present well yields and surficial-aquifer 

properties in Glynn County. Watson (1982) presents well 

yields from shallow sands in Glynn County, and Leeth (1999) 

reports well yields and surficial-aquifer properties in Camden 

County. Chowns and others (2008) describe the stratigraphy 

and geology of coastal Georgia. Cherry and others (2010, 

2011) describe groundwater conditions in the Brunswick–

Glynn County area of Georgia during 2009 and 2010.

Description of Study Area

Jekyll Island is located in Glynn County, just off the 

southeastern coast of Georgia, between St. Simons Island 

and Cumberland Island (fig. 1A). The island is bordered on 

the west by the Brunswick and Jekyll Rivers and on the east 

by the Atlantic Ocean (fig. 2). The island encompasses about 

9 square miles (mi2; about 5,800 acres) and has more than 

1,750 ac of salt- and brackish-water tidal marsh, located 

primarily on the western part of the island and along streams 

(AECOM, 2011). The interior of the island contains mostly 

upland forest. Several ponds are located on the island, and 

dunes provide topographic relief between the coastline and 

the interior.

Land use on Jekyll Island is primarily forest and marsh 

(Cherry and others, 2011), and has been divided into six 

categories based on similarities in location, management 

requirements, and ecological function (AECOM, 2011). The 

categories and respective total acreages are as follows (fig. 2): 

• beach and interdunal swale, including beach, 

primary dune, and an early successional back 

dune/swale system (475 acres); 

• dry hammock, including naturally vegetated forested 

systems in the southern third of the island (368 acres); 

• coastal marsh, including salt marshes, coastal creeks, 

and small forested islands (1,906 acres); 

• upland forest, including pine and oak forests in the 

northern third of the island along with pockets of 

forested freshwater wetlands (1,069 acres); 

• golf course, including forested systems within the 

golf courses, and the adjacent forested, freshwater 

wetlands (930 acres, four golf courses); and 

• urban/park, including residential, commercial, 

historical district, and park land along the altered 

natural systems (1,099 acres).
Introduction 5

Physiography and Drainage

Jekyll Island is located in the Barrier Island Sequence 

District of the Coastal Plain physiographic province (Clark 

and Zisa, 1976; fig. 1A). Land surface altitude ranges from 

sea level [0 feet (ft)] along the coast and the Jekyll River to 

about 45 ft along the dunes and in the northern interior part 

of the island (fig. 3). 

Jekyll Island is bordered on the northwest by the Brunswick River, on the southwest by Jekyll Sound, on the east 

by the Atlantic Ocean, and on the west by the Jekyll River, 

which connects the Brunswick River to Jekyll Sound (figs. 

2 and 3). Surface water generally drains from the interior of 

the island westward toward the wetlands and Jekyll River, 

eastward toward the Atlantic Ocean, and omni-directionally, 

converging in the southern part of the island at a large pond.

Climate

Although formal climatological records for Jekyll 

Island do not exist, climate records for nearby weather 

stations located along and near Georgia’s 100-mile (mi) 

coastline provide insight into temperature and precipitation conditions on the Island (coastline data for Georgia 

obtained from U.S. Census Bureau, 2012). As one island 

in a sequence of barrier islands along the Georgia coast, 

JekyllIsland exhibits similarities in meteorological and 

climatologic conditions with the other islands and inland 

regions located within a relatively short distance of the 

coastline. The climate on Jekyll Island is moderate with 

temperatures averaging around 90 degrees Fahrenheit (°F) 

in the summer and in the middle 50s during winter months. 

Precipitation typically is in excess of 50 inches per year 

with drier months during winter and about 20 inches of rain 

during summer months (hurricane season; The University 

of Georgia, Georgia State Climate Office, Driftmier 

Engineering Center, 1998)

No suitable long-term climate data are available for 

Jekyll Island, so climate data from a weather station in 

Brunswick, Glynn County, Georgia, located at the College 

of Coastal Georgia (Brunswick weather station, fig. 1) are 

presented and used along with precipitation data collected 

during this study on Jekyll Island to estimate the water 

balance. The period of record for the Brunswick weather 

station is 1999 to 2014, the average monthly high temperature ranges from 64 (January) to 91 °F (July and August), 

the average monthly minimum temperature ranges from 

43 (January) to 73 °F (July and August), and the average 

annual precipitation is 50.7 inches (table 1; Georgia Automated Environmental Monitoring Network, 2016). Monthly 

total precipitation compiled for the weather station on 

Jekyll Island for 2013 shows that the island received above 

average precipitation during several months including April, 

May, August, September, and November (fig. 4; table 1). 

Brunswick River

ATLANTIC OCEAN

Jekyll

Sound

Jekyll Island

Golf Course

Management unit

EXPLANATION

Beach and interdunal swale 

 (475.2 acres)

Figure 2. 

N

Dry hammock (368.4 acres)

Coastal marsh (1,905.7 acres)

Upland forest (1,068.9 acres)

Golf course (929.6 acres)

Urban/park (1,099.4 acres)

0 2,000 4,000 FEET

0 500 1,000 METERS

520

RIVERVIEW DRIVE

BEACHVIEW DRIVE

Jekyll River

Figure 2. Land-use-based management units on Jekyll Island, 

Georgia (modified from AECOM, 2011).
6 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

k

S RIVERVIEW DR

RIVERVIEW DRIVE

N BEACHVIEW DRIVE 

BEN FORTSON PKY

CLAM CREEK RD

S BEACHVIEW DR

ST50 ST50

520

520

81°26' 81°25' 81°24'

31°06'

31°05'

31°04'

31°03'

Base modified from ESRI Streetmap, 1:750,000. Map image is

the intellectual property of Esri and is used herein under license.

Copyright ©2014 Esri and its licensors. All rights reserved

A

T

L

A

N

T I C

O

C

E

A

N

Jekyll RIver

Brunswick

River

Jekyll

Sound

–2.32 to 0.28

>0.28 to 3.64

>3.64 to 6.06

>6.06 to 8.48

>8.48 to 10.72

>10.72 to 12.77

>12.77 to 14.64

>14.64 to 16.87

>16.87 to 20.97

>20.97 to 45.20

0 0.5 1 MILE

0 0.5 1 KILOMETER

Figure 3. 

Land-surface altitude—

 In feet. Datum is NAVD 88

EXPLANATION

Figure 3. Light detection and ranging (lidar)-based altitude for central Jekyll Island, Georgia. 
Introduction 7

Figure 4. 

0

Jan. Feb. Mar. Apr. May

Month

June July Aug. Sept. Oct. Nov. Dec.

2

4

6

8

Monthly average precipitation, in inches

10

12

2013 monthly total

Table 1. Period of record (1999 to 2012) average monthly temperature, precipitation, and evapotranspiration (ET) for Brunswick, Georgia.

[Data from Georgia Automated Environmental Monitoring Network, 2016; °F, degrees Fahrenheit]

January February March April May June July August September October November December

Average monthly temperature (°F)

High 64 66 72 78 84 89 91 91 87 80 71 65

Low 43 45 51 57 65 71 73 73 70 61 51 45

Mean 53 56 61 68 75 80 82 82 78 71 61 55

Average monthly total precipitation (inches)

3.0 3.3 3.8 2.9 3.4 5.6 6.3 6.8 7.2 3.7 2.0 2.7

Average monthly mean ET (inches)

1.09 1.76 2.95 4.27 5.15 5.15 5.19 4.60 3.68 2.57 1.56 0.65

Figure 4. Average monthly period of record 

precipitation for Brunswick, Georgia, and 2013 

monthly total precipitation, in inches, at Jekyll 

Island, Georgia (Georgia Automated Environmental 

Monitoring Network, 2016).
8 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

during the geologically recent Pleistocene epoch, which began 

almost 2 million years ago (Henry, 2014). Periodic stabilization in sea level has created seven identifiable lines of barrier 

islands on the Coastal Plain. Two barrier island formations 

deposited during the past 2 million years resulted in the 

present barrier island system along the Georgia coast, with 

the creation of a barrier island chain known as the Pleistocene 

Silver Bluff Formation (Dilsaver, 2004) (“Pleistocene Barrier 

Island Facies,” shown in fig. 5). 

During the Holocene (10,000 years ago to present), 

sea-level rise caused by melting glaciers led to the development of Holocene barrier formations that “migrated shoreward 

and become welded onto the Silver Bluff [Formation] 

islands” (Dilsaver, 2004) (“Holocene Barrier Island Facies,” 

shown on fig. 5). “Jekyll Island is a composite barrier island 

consisting of a core of beach and dune deposits formed during 

the previous, and slightly higher, worldwide sea level of the 

Pleistocene Silver Bluff [compared with current sea level], 

approximately 40,000 to 50,000 years ago” (Henry, 2014). 

The constant deposition of eroded material along a 

fluctuating coastline caused layering of sediments and created 

distinct strata that reflect the varying source material eroded 

Hydrogeology

The hydrogeology of Jekyll Island is governed by various 

episodes of sedimentation and erosion unique to the formation of barrier islands located along Georgia’s coast. These 

erosional and depositional episodes resulted in the formation 

of a surficial aquifer system on Jekyll Island that contains a 

water-table zone of interest to this study.

Aquifer Formation on a Barrier Island

The following descriptions of the formation of Georgia’s 

barrier islands from Henry (2014) and Dilsaver (2004) provide 

insight into sedimentation and erosion patterns that led to the 

formation of Jekyll Island and the water-table zone of the 

surficial aquifer system. The barrier islands (and water-table 

zone) are composed of dune and beach ridge sands formed 

by the interaction of wind, waves, currents, sand supply, and 

a slowly rising or stable sea level (Henry, 2014). The lower

Coastal Plain, containing the Barrier Island Sequence District 

(fig. 1A), described previously, extends 65 mi inland from the 

coast and is distinguished by the ocean’s highest incursion 

Approximately 50,000 years

before present

Figure 5.

Approximately 5,000 years

before present

Present (2014)

Pleistocene

barrier island

facies

Pleistocene

barrier island

facies

Pleistocene

Silver Bluff

shoreline

facies

50,000 years

before

present

Holocene

barrier island

facies

Holocene

back-barrier

facies Holocene

5,000 years

before

present

Holocene

Deposition

Erosion

Jekyll Creek

Dominant littoral drift

Recurved spits

Dunes/beach ridges

Figure 5. Sedimentation and erosion features on Jekyll Island, Georgia (Henry, 2014).
Introduction 9

away from the mainland and carried to the ocean by rivers 

(Dilsaver, 2004). Barrier islands, such as Jekyll Island, border 

the modern (Holocene) Georgia coast but are separated 

from the mainland by relatively deep tidal inlets, or sounds, 

creating a hydrogeology different than that of the mainland. 

Extensive sand shoal systems were deposited seaward of the 

inlets and central portions of the islands adding complexity 

to this hydrogeology (Henry, 2014). As described by Henry 

(2014), the Georgia Coast is a tide-dominated, low-wave 

energy coast due to its ebb-tide deltas, inlets, and relatively 

short, wide barrier islands. The ebb-tide-delta; the alongshore, 

downcurrent-drift-of-sediment (“dominant littoral drift,” 

[fig. 5]); and the adjacent dynamic beach and dune system 

make up the coastal sand-sharing system where sand from the 

southern portion of one island welds onto and nourishes the 

northern (upcurrent) portion of an adjacent barrier island to 

the south. Disturbances to the system, such as inlet dredging, 

jetties, or shoreline armoring, disrupt the flow of sand to the 

downcurrent shorelines (fig. 5; Henry, 2014).

Water-Table Zone of the Surficial Aquifer System

The aforementioned erosional and depositional processes 

leading to the formation of Jekyll Island also created the 

water-table zone of the surficial aquifer system (fig. 6). Sands 

and muds of the Pleistocene Silver Bluff Formation (Chowns 

and others, 2008), Holocene dune sands, and undifferentiated 

Post-Miocene sediments deposited during formation of the 

barrier island, described in the previous section, constitute the 

shallow water-table zone of interest for this recharge study.

Although well yields from the surficial aquifer system 

on Jekyll Island have not been quantified through aquifer 

tests, yields of wells installed in surficial-aquifer material 

along the Georgia coast near Jekyll Island may give an 

indication of expected well yields on the island. Typical 

wells drilled to approximately 40 ft in sands in Glynn County 

yielded 1–5 gallons per minute (gal/min) (Watson, 1982). 

Clarke and others (1990) and Leeth (1999) reported well 

yields of 2–140 gal/min, with transmissivity ranging from 

14 to 6,700 feet squared per day (ft2/d), for a water-table zone 

underlain by confined zones within the surficial aquifer system 

in Glynn and Camden Counties, Georgia.

Figure 6. Generalized correlation chart showing the geologic 

and hydrogeologic units at Jekyll Island composing the lower 

coastal plain, Georgia. Lower Middle Upper

Post-Miocene

Miocene

Eocene

Oligocene

Paleocene

Upper

Cretaceous

Suwannee Limestone

Ocala Limestone

Avon Park Formation

Oldsmar Formation

Cedar Keys Formation

Water-table zone Upper Floridan aquifer

Floridan aquifer system

Lower Floridan aquifer

Fernandina 

permeable 

zone

Lower Floridan

confining unit

Lazaretto Creek Formation

Lower Coastal Plain1

Geologic unit

Undifferentiated

Undifferentiated

2 Hydrogeologic unit

Confining

unit

Confining unit

Upper waterbearing zone

Upper

Floridan semiconfining unit 

Lower waterbearing zone

Lower Middle Upper

Series

Savannah Brunswick

Upper

Brunswick

 aquifer

Lower

Brunswick

 aquifer

Upper waterbearing zone

Lower waterbearing zone

Holocene3

dune sands

Silver Bluff 3

Formation

Tiger Leap Member of

Parachucla Formation

Parachucla Formation

Marks Head Formation

Coosawhatchie Formation

of the Hawthorn Group

Ebenezer Formation

Surficial aquifer system Brunswick aquifer system

Figure 6. 

Holocene

Pleistocene

Pliocene

Confining

unit

Confining

unit

Upper Floridan confining unit

1

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

2

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

3

Modified from Chowns and others, 2008.
10 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Methods of Investigation

Several methods of investigation were used during this 

study to estimate the volume of water available and to determine the usefulness of the available water. Data were collected 

and compiled from new and existing sources to estimate water 

availability. Specific conductance data were collected to give 

an indication of the usefulness of the water.

Volume Estimates

An inventory of 89 existing residential wells assumed to 

be open to the water-table zone of the surficial aquifer system 

was performed during July 31–August 2, 2012 (appendix 1, 

table 1–1). Construction information for these wells was not 

available, and access was not adequate to obtain water-level 

measurements; therefore, the residential wells could not be 

used as monitoring wells for this study. Twenty-six shallow 

monitoring wells were installed to more accurately define the 

water-table surface of the surficial aquifer system (fig. 1B). The 

wells range from 7.4 to 29.0 ft in depth and were constructed 

using schedule 40, 2-inch-diameter polyvinyl chloride (PVC) 

pipe with screens 5 ft in length and a 0.01-inch slot size 

(appendix 2, table 2–1). The monitoring wells were used to 

collect water-level data and to measure specific conductance. 

Lithologic samples were collected during well construction 

and used to characterize the soil type and geology.

Water levels were measured and recorded using a 

combination of continuous recorders, weekly measurements, 

and periodic measurements during dry and wet seasons. Two 

USGS-constructed wells were equipped with continuous 

recorders—well 34G172 in an upland recharge area in the 

center of the island and well 34G168 in a lowland discharge 

area in the northwestern part of the island. Weekly water-level 

measurements were made in six wells and at three pond staff 

gages (fig. 1B).

To determine seasonal variations in groundwater levels, 

in addition to the weakly and continuous water-level measurements, three water-table maps were constructed using data 

collected during three different times of the year. The maps 

were used to determine areas of recharge, discharge, and 

the direction of groundwater flow, and they serve as a basis 

for recharge computations. Determinations of recharge and 

discharge areas, as well as groundwater flow direction, were 

made on the basis of two criteria: (1) recharge typically occurs 

at higher altitudes and discharge typically occurs at lower 

altitudes, and (2) groundwater flows perpendicular to watertable contours and toward discharge areas.

Recharge calculations for Jekyll Island required meteorological data not available from the Jekyll Island weather 

station (fig. 1B), which supplied only rainfall data from 

October 2012 through December 2013. Other rainfall data 

and evapotranspiration values were obtained from a weather 

station at Brunswick, Georgia, identified in figure 1A as the 

Brunswick weather station (The University of Georgia College 

of Agricultural & Environmental Sciences, 2015).

Two methods were used to estimate recharge to the 

water-table zone of the surficial aquifer system. The first 

method (method one) is a simple water-balance equation using 

precipitation and evapotranspiration data. Recharge estimates 

based on this first method represent the potential maximum 

recharge estimates since the only factors considered in the 

equation are precipitation and evapotranspiration. The second 

method (method two) is based on the differences in watertable altitudes during a wet and dry period; this method allows 

estimation of aquifer-volume change and computation of net 

usable recharge (or discharge), because all influences to the 

hydrologic system are reflected in the water levels. Therefore, recharge estimated using method one is the potential 

maximum recharge, and recharge estimated using method two 

is the net usable recharge.

For method one, the potential maximum recharge to 

the water-table zone of the surficial aquifer system on Jekyll 

Island was calculated using the following water-balance 

equation (Healy, 2010),

R = P − ET, (1)

where 

R = unit recharge to the surficial aquifer system 

(recharge volume per unit area) [length];

P = precipitation [length]; and,

ET = evapotranspiration [length].

Method two, net useable recharge or discharge, uses the 

altitude of the water table. The altitude of the water table (or 

groundwater level) responds to precipitation (mostly rainfall) 

and evapotranspiration, and other hydrologic stresses, such as 

pumping, surface runoff to ponds, groundwater discharge to 

streams, and soil-moisture changes, as mentioned previously. 

Barometric-pressure changes, tides, and seawater rise also 

affect the water table. Groundwater-level measurements 

made during a given time period document changes to the 

water table and aquifer volume that indicate either net usable 

recharge (positive aquifer-volume change during a wet time 

period) or discharge (negative aquifer-volume change during 

a dry time period) with regard to the water-table zone of the 

surficial aquifer system. Differences in water-table altitudes 

during the wet and dry periods allow estimation of aquifervolume change and computation of net usable recharge (or 

discharge) in a manner similar to that of the “water-table 

fluctuation” method of Healy (2010). Usable recharge is the 

water available for potential development.

Aquifer-volume change and subsequent net usable 

recharge or discharge were calculated on Jekyll Island 

from groundwater levels measured on November 8, 2012, 

and April 17 and August 23, 2013 (appendix 3, table 3–1). 

The area of Jekyll Island, which is about 9 mi2 or 

250,905,600 square feet (ft2), was used in aquifer-volume 

and recharge (or discharge) calculations. When multiplied 
Methods of Investigation 11

by aquifer porosity, aquifer-volume change during a wet 

time period (positive aquifer-volume change) represents net 

usable recharge, Rnet, to the water-table aquifer and is given 

by (Buddemeier and Schloss, 2000),

Rnet=n×[V(t

2

)−V(t

1

)] [Length3]; (2)

 where,

V(t

2

) is aquifer volume at the end of the wet time 

period, t

2

 (high groundwater levels) 

[Length3];

V(t

1

) is aquifer volume at the beginning of the wet 

time period, t

1

 (low groundwater levels) 

[Length3]; and,

n is porosity [0] (dimensionless).

Discharge from the water-table zone of the surficial aquifer 

system also is given by equation 2 with the following changes: 

V(t

2

) represents aquifer volume at the end of a dry time 

period (low groundwater levels); and V(t

1

) represents aquifer 

volume at the beginning of a dry time period (high groundwater levels), such that the difference, V(t

2

)−V(t

1

), yields a 

negative aquifer-volume change.

A porosity of 0.21 (21 percent by volume) was used to 

compute Rnet according to equation 2. This value is characteristic of the porosity of sand containing some intermittent silt 

and clay (Fetter, 2001), which is similar to the barrier island 

sediments composing the water-table zone of the surficial 

aquifer system on Jekyll Island. 

Calculation of Rnet by equation 2 can be simplified 

by factoring the area of Jekyll Island, about 9 mi2 or 

250,905,600 ft2, from the aquifer volumes, V(t

2

) and V(t

1

), 

and expressing Rnet as a function of the average change in 

groundwater levels during two time periods, t

2

 and t

1

, as, 

Rnet=n×A×[havg (t

2

)−havg (t

1

)] [Length3]; (3)

where

A is the area of Jekyll Island; and

havg (t

2

) and havg (t

1

) are average groundwater levels 

calculated from water levels measured 

at the beginning (t

1

) and end (t

2

) of the 

time period.

Usefulness

Specific conductance analyzed from water samples 

taken at the six baseline wells was plotted against chloride 

concentration to determine the correlation between the two 

constituents (fig. 7). In general, specific conductance (SC) is 

a measure of water’s ability to conduct an electric current. 

Water that contains a high concentration of dissolved solids, 

especially salts, typically contains high values of SC. Specific 

conductance has been shown to be a reasonable surrogate for 

chloride concentration (Cherry and others, 2010, 2011).

A linear regression of the chloride-concentration and 

specific-conductance data from the six baseline wells on Jekyll 

Island resulted in a coefficient of determination (R2 value) of 

0.75, indicating that a relatively good linear relation existed 

for specific conductance to estimate chloride concentration. 

The sample from well 34G158 contained a low chloride 

concentration of 43 milligrams per liter (mg/L) and a fairly 

high SC value of 1,147 microsiemens per centimeter at 

25 degrees Celsius (μS/cm at 25 °C), relative to the other 

five samples. This sample also had an alkalinity of 375 mg/L, 

much higher than that of any other sample (table 2). The 

high SC in well 34G158 is probably due to carbonate and 

(or) bicarbonate being the dominant anion in the sample, 

as indicated by the high alkalinity. In addition, when this 

well was drilled and developed, the water pumped from the 

well remained cloudy, unlike the water from the other wells. 

Removing well 34G158 data from the graph yielded a linear 

correlation with R2 = 0.97, which indicates the linear relation 

is very good and may be used with confidence to estimate 

chloride concentration in samples not affected by carbonate 

or bicarbonate (fig. 2). Using information from the best-fit 

regression, the following relation was obtained:

Chloride concentration (in mg/L)=

Specific conductance (in μS/cm)×0.291−50.988 μS/cm

where

 0.291 represents the slope of the regression line, and

−50.988 μS/cm represents the y-intercept.

This relation is similar to the one established by Cherry and 

others (2011) for samples collected from the Upper Floridan 

aquifer near Brunswick, Georgia. 

y=0.2694x–70.468 

R2=0.7535

y=0.291x–50.988 

R2=0.9683

0

100

200

300

400

500

600

0 500 1,000 1,500 2,000 2,500

Chloride concentration, in milligrams per liter

Specific conductance, in microsiemens per centimeter

at 25 degrees Celsius

Figure 7.

34G158

34G157

34G161

34G154

34G164

34G163

Figure 7. Ordinary least squares regression line between 

specific conductance and chloride concentration for wells 

completed in the surficial aquifer system, Jekyll Island, 

Georgia. The solid line represents all six data points, 

whereas the dashed line excludes the anomalous data 

point from well 34G158.
12 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Surficial Aquifer System Water Use 

Most of the inventoried residential wells are less than 

40 ft deep, consistent with wells in Glynn and Camden Counties, Georgia, from which well-yield information had been 

mentioned in a previous section. The well inventory for this 

study confirmed that well water from private wells on Jekyll 

Island is used mostly for lawn irrigation. Municipal water is 

provided by the JIA from wells pumping from the Brunswick 

and Upper Floridan aquifer systems (fig. 6). The total number 

of wells inventoried (89) constituted about one quarter of the 

350 total residential wells installed on Jekyll Island (John 

Day, JIA, oral commun., July 31, 2012), and is assumed 

herein to be a representative sample of the total population of 

residential wells (350) on the island. These 350 wells supply 

water to about half of the 700 residences on Jekyll Island 

(James Kennedy, Georgia Environmental Protection Division, 

written commun., January 26, 2008).

According to the U.S. Environmental Protection Agency 

(EPA), the average U.S. household uses 320 gallons per day 

(gal/d), about 96 gal/d of which is used for outdoor purposes 

(U.S. Environmental Protection Agency, 2014). Assuming the 

350 residential wells on Jekyll Island use water for outdoor 

purposes (lawn irrigation) at a rate of about 96 gal/d, then an 

estimated 33,600 gal/d (350 residences multiplied by 96 gal/d) 

of water is pumped from the water-table zone of the surficial 

aquifer system by residential wells on Jekyll Island.

Hydrologic Conditions of the Water-Table 

Zone of the Surficial Aquifer System

Hydrologic conditions affecting the quantity and distribution of freshwater resources in the water-table zone of the 

surficial aquifer system on Jekyll Island were investigated to 

assess water availability and use and to inform management 

decisions regarding development potential of the island’s 

water resources. Groundwater-flow directions inferred 

from water-level measurements and supported by specificcapacity data helped identify areas of potential recharge to 

and discharge from the water-table zone. Meteorological 

data collected during this study and similar data compiled 

from the Brunswick weather station contributed to recharge 

estimates calculated for the island. Evaluating the hydrologic 

conditions of the water-table zone promoted understanding 

of the hydrologic stresses affecting recharge and provided the 

essential elements for investigating hydrologic conditions that 

contribute to the water resources on Jekyll Island.

Groundwater-Flow Directions and Inferred 

Recharge and Discharge

Directions of groundwater flow in the water-table 

zone of the surficial aquifer system were determined from 

water-table maps constructed using groundwater levels that 

were measured in the 26 wells installed during this study 

(fig. 1B and appendices 2 and 3). Groundwater-level measurements made on November 8, 2012, April 17, 2013, and 

August 23, 2013, provided the basis for seasonal water-table 

maps to delineate groundwater-flow directions and infer 

potential recharge and discharge areas (fig. 8A–C). Three 

pond staff gages installed during this study (fig. 1B) identified 

the surface expression of the water table on Jekyll Island and 

support the delineation of recharge and discharge areas in the 

water-table zone. Two criteria were used to identify groundwater-flow directions and infer recharge and discharge areas 

from the water-table maps: (1) groundwater flows perpendicular to water-table contours, from high to low water-level 

altitudes; and (2) recharge generally occurs where water-table 

contours indicate divergent groundwater flow at relatively 

high water-level altitudes; discharge generally occurs where 

water-table contours indicate convergent groundwater flow at 

relatively low water-level altitudes. 

Table 2. Groundwater-quality data for the surficial aquifer system, Jekyll Island, Georgia, August 23, 2013.

[TDS, total dissolved solids; mg/L, milligrams per liter; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; CaCO3 , 

calcium carbonate]

USGS

well

identifier

TDS

concentration

(mg/L)

pH

Specific

conductance

(μS/cm at 25 °C)

Chloride

concentration

(mg/L)

Alkalinity

(mg/L)

Hardness

(mg/L as CaCO3)

34G154 1,875 5.74 984 260 35 Too turbid

34G157 2,993 5.66 2,008 555 10 Too turbid

34G158 1,025 6.23 1,147 43 375 340

34G161 840 5.61 1,073 199 25 340

34G163 214 4.63 130 17 <10 120

34G164 547 6.01 330 31 55 160
Hydrologic Conditions of the Water-Table Zone of the Surficial Aquifer System 13

Base modified from ESRI Streetmap, 1:750,000. Map image is

the intellectual property of Esri and is used herein under license.

Copyright ©2014 Esri and its licensors. All rights reserved

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

Figure 8A. 

A

T

L

A

N

T I C

O

C

E

A

N

Jekyll River

EXPLANATION

Water-table contour—

 Shows altitude of water

 table, November 8, 2012.

 Contour interval 1 foot.

 Datum is NAVD 88

General direction of

 groundwater flow

Monitoring well and

 water level—In feet

 above NAVD 88

2

2.15

81°25'30"

31°05'30"

31°05'00"

31°04'30"

31°04'00"

31°03'30"

81°25'00" 81°24'30" 81°24'00"

3.36

3.52

4.84

0.97

1.96

3.81

3.57

6.11

4.65

6.26

6.06

5.52

A. November 8, 2012

1.85

3.20

2.95

3.70

4.72

4.68

3.13

7.42

4.23

3.10

6.76 6.58

6.61

2.15

8.52 5.86

9.33

4

4

3

3

1

2

2

5

4

4

5

2

3

6

6

7

8

9

7

Figure 8. Water table for, A, November 8, 2012; B, April 17, 2013; and C, August 23, 2013 on Jekyll Island, Georgia.
14 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Base modified from ESRI Streetmap, 1:750,000. Map image is

the intellectual property of Esri and is used herein under license.

Copyright ©2014 Esri and its licensors. All rights reserved

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

A

T

L

A

N

T I C

O

C

E

A

N

Jekyll River

B. April 17, 2013

EXPLANATION

Water-table contour—

 Shows altitude of water

 table, April 17, 2013.

 Contour interval 1 foot.

 Datum is NAVD 88

General direction of

 groundwater flow

Monitoring well and

 water level—In feet

 above NAVD 88

2

2.15

Figure 8B.—Continued

81°25'30"

31°05'30"

31°05'00"

31°04'30"

31°04'00"

31°03'30"

81°25'00" 81°24'30" 81°24'00"

3.97

3.38

4.45

6.06

6.14

5.27

3.59

2.40

5.43

5.00

4.51

7.47

7.93

5.55 5.36

4.19

2.98

7.19

2.15

2.15

3.07

4.21

4.06

2.79

0.27

1.73

4.47

3.18

7

4

1

4

6

3

3

2

6

6

1

3

2

4

5

5

4

3

7

Figure 8. Water table for, A, November 8, 2012; B, April 17, 2013; and C, August 23, 2013 on Jekyll Island, Georgia.—

Continued
Hydrologic Conditions of the Water-Table Zone of the Surficial Aquifer System 15

Base modified from ESRI Streetmap, 1:750,000. Map image is

the intellectual property of Esri and is used herein under license.

Copyright ©2014 Esri and its licensors. All rights reserved

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

A

T

L

A

N

T I C

O

C

E

A

N

Jekyll River

C. August 23, 2013

EXPLANATION

Water-table contour—

 Shows altitude of water

 table, August 23, 2013.

 Contour interval 1 foot.

 Datum is NAVD 88

General direction of

 groundwater flow

Monitoring well and

 water level—In feet

 above NAVD 88

2

2.62

Figure 8C.—Continued

81°25'30"

31°05'30"

31°05'00"

31°04'30"

31°04'00"

31°03'30"

81°25'00" 81°24'30" 81°24'00"

2.62

5.36

8.11

3.78

4.43

6.57

5.46

5.25

4.62

5.44

5.68

6.56

6.53

4.16

3.05

3.53

2.55

0.76

4.57

3.55

4.10

4.93

4.79

6.69

8.82

6.32

6.27

1

8

3

4

7

4

4

7

2

3

4

6

2

6

4

5

3

5

8

Figure 8. Water table for, A, November 8, 2012; B, April 17, 2013; and C, August 23, 2013 on Jekyll Island, Georgia.—

Continued
16 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Maps depicting the water table of the water-table zone 

of the surficial aquifer system indicate complex groundwaterflow directions that infer recharge and discharge areas on 

Jekyll Island. Closed 6-, 7-, and 8-ft water-table contours 

encircle relatively high water levels near the southwestern 

part of the island, indicating recharge during the three 

measurement periods (November 8, 2012, April 17, 2013, and 

August 23, 2013) (figs. 8A–C). During the April 17, 2013, 

measurement period, the 6-ft water-table contour encircled 

a small pond near the center of the island, indicating that the 

pond functioned as a recharge area to the water-table zone 

(fig. 8B). The pond possibly accumulated direct precipitation 

and surface runoff of precipitation, which elevated the pond 

stage and water table (see “Staff gage 1,” fig. 9), creating a 

recharge area for the water-table zone of the surficial aquifer 

system. The pond stage at staff gage 1 rose about 0.3 ft 

following rainfall recorded on Jekyll Island during early 

May 2013 (fig. 9). This elevated pond stage could have further 

contributed to recharge of the water-table zone that could not 

be depicted by water levels measured in April 2013.

Another recharge area located east of the area described 

above is inferred from the closed 6- to 9-ft water-table 

contours that resulted from the November 8, 2012, groundwater-level measurements (fig. 8A). The water table declined 

slightly more than a foot by the April 17, 2013, measurement 

period (fig. 8B), and then increased nearly a foot by the 

August 23, 2013, measurement period (fig. 8C), perhaps the 

result of relatively low rainfall in the spring, lawn irrigation, 

and relatively high rainfall during August, 2013 (fig. 9). The 

seasonal effects of rainfall and lawn irrigation on groundwater 

levels are described in the next section of this report. 

Several areas of groundwater discharge from the watertable zone of the surficial aquifer system on Jekyll Island 

were inferred from the seasonal water-table maps prepared 

from groundwater levels and pond stages measured during 

November 8, 2012, April 17, 2013, and August 23, 2013 

(figs. 8A–C). The recharge area established in the southwestern part of the island, described above, provided the 

hydraulic potential for discharge westward into the Jekyll 

River (figs. 8A, C). In the south-central part of the island, the 

3-, 4-, and 5-ft water-table contours indicated groundwater 

discharge and converging flow toward a large pond. Watertable contours for the three measurement periods indicated that 

the recharge areas previously discussed supply groundwater 

to this pond. Further, the pond seems to stabilize groundwater 

levels surrounding it, maintaining a stage almost exclusively 

between 2 and 3 ft (see “Staff gage 3,” fig. 9) during the 

measurement periods. 

Groundwater levels measured during three periods in 

2012 and 2013, defined previously, and pond stages recorded 

during these periods indicate that the eastern coast of Jekyll 

Island represents the principal discharge area for the watertable zone of the surficial aquifer system (figs. 8A–C). The 

recharge area inferred from the 6- to 9-ft closed contours 

creates a relatively steep hydraulic gradient toward the coast 

in the east-central part of the island. This positive hydraulic 

gradient is maintained, although diminished, at the northern 

and southern extents of this recharge area along the eastern 

coast of the island.

Groundwater levels measured in the north-central part 

of Jekyll Island indicate that the water-table zone of the 

surficial aquifer system in this region fluctuates seasonally 

between recharge and discharge (figs. 8A–C). The 2- and 3-ft 

water-table contours in the north-central part of Jekyll Island 

during November 8, 2012, indicate converging groundwater 

flow and discharge westward toward the marshland adjacent 

to the Jekyll River. Diverging groundwater flow indicating 

groundwater recharge is inferred from the November 8, 2013, 

measurements in the area enclosed by the northernmost 4-ft 

water-table contour (fig. 8A). Groundwater levels measured 

during April 17, 2013, however, delineated a discharge 

area of the water-table zone in the opposite direction to that 

identified by the November 8, 2012, water levels. That is, for 

April 17, 2013, the 2- and 3-ft water-table contours indicate 

flow eastward toward a wetland located in the east-central part 

of the island (fig. 8B). During the August 23, 2013, measurement period, the 4-ft water-table contours infer discharge areas 

at the location of this east-central-island marsh, with groundwater flow westward toward the marshland located adjacent 

to the Jekyll River where the November 8, 2012, groundwater 

levels also indicated discharge (fig. 8A).

Seasonal Water-Table Fluctuations

During 2013, weekly water-level measurements were 

made in 6 of the 26 wells installed for this study in the watertable zone of the surficial aquifer system, and continuous 

water levels were recorded in 2 of these wells to identify 

seasonal fluctuations in the water table (fig. 9; see fig. 1 for 

locations). Weekly and continuously measured water levels 

ranged from 0.5 to 12.21 ft below land surface during 2013, 

fluctuating in response to rainfall, or lack thereof, recorded 

at the Jekyll Island weather station (see fig. 1 for location). 

All weekly and continuously measured wells began 2013 

with seasonal-low water levels, a result of low rainfall during 

November and December 2012 (fig. 9). Rainfall on Jekyll 

Island during late February, late March, and early May 2013 

triggered sharp water-level increases. Most of the weekly and 

continuously measured wells exhibited a water-level increase 

by the end of 2013, indicating annual net recharge to the 

water-table zone of the surficial aquifer system.

The seasonal water-level decline in the water-table zone of 

the surficial aquifer system during May–August 2013 (fig. 9)

possibly resulted from residential lawn irrigation and subsequent evapotranspiration of the water applied as well as natural 

vegetative uptake. Weekly and continuous water levels indicate 

a steady decline interrupted briefly by early June rainfall.

Weekly and continuously recorded water levels in the 

water-table zone of the surficial aquifer system on Jekyll 

Island exhibited a relatively rapid rise followed by an almostas-rapid decline in response to rainfall amounts (fig. 9). This 

near-term water-level response to hydrologic stress indicates 
Hydrologic Conditions of the Water-Table Zone of the Surficial Aquifer System 17 Depth to water level, in feet below land surface Daily depth to water level, in feet below land surface

Figure 9.

0

1

2

3

4

5

Precipitation, in inches 

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4 Staff gage 3

5.2

5.0

5.4

5.6

5.8

6.0

6.2

6.4

6.6

6.8

7.0 Staff gage 2

6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

Staff gage 1

J F M A M J J

2013

Pond stage, in feet above NAVD 88

A S O N D

7

6

5

4

3

Well 34G153

11

10

9

8

7

6

5

Well 34G159

Well 34G168 Well 34G172 Jekyll Island

7

6

5

4

3 Well 34G165

Water level measured weekly

Continuous water level Precipitation

Pond stage

13

11

12

10

9

7

8

Well 34G170

0

1

2

3

4

5

Well 34G174

7

6

5

4

3

Well 34G175

J F M A M J J A S O N D

2013

J F M A M J J A S O N D

2013

J F M A M J J A S O N D

2013

J F M A M J J A S O N D

2013

J F M A M J J A S O N D

2013

0 

1 

2 

3 

4 

1 

2 

3 

4 

5 

6 

Figure 9. Groundwater levels, pond stage, and rainfall for 2013 at Jekyll Island, Georgia. 
18 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

a strong dependence of the water-table zone on recharge from 

precipitation to maintain the water table on Jekyll Island. 

Further, water-level declines resulting from low precipitation 

confirm the inability of the water-table zone of the surficial 

aquifer system to maintain the height of the water table in the 

absence of rainfall. 

Recharge

Recharge to the water-table zone of the surficial aquifer 

system on Jekyll Island occurs when the amount of precipitation exceeds the cumulative effect of negative hydrologic 

stresses acting on the island, such as evapotranspiration, 

pumping, runoff to streams, storage uptake of infiltrated 

precipitation by the unsaturated zone (soil-moisture changes), 

and tidal, sea-level rise, and barometric effects. Two methods 

were used to estimate recharge to the water-table zone of the 

surficial aquifer system. Method one calculated the potential 

maximum recharge as a positive water balance between 

precipitation and evapotranspiration. Method two estimated 

net, or usable, recharge as volumetric differences between 

seasonal high and low groundwater levels.

Method One—Water Balance Method

Recharge computed with the water-balance equation 1 

represents the maximum amount of unit precipitation (precipitation volume per unit area) that would infiltrate land surface and 

elevate the water table. Ideally, in the absence of negative hydrologic stresses other than evapotranspiration, precipitation that 

infiltrates land surface would represent the maximum amount of 

recharge available to the water-table zone of the surficial aquifer 

system. Other hydrologic stresses in addition to evapotranspiration, such as pumping from ponds or wells completed in the 

water-table zone of the surficial aquifer system, would decrease 

recharge from that indicated in equation 1. Because the natural 

land surface and water-table zone of the surficial aquifer system 

of Jekyll Island is composed of permeable sand, surface-water 

flow, direct runoff, change in storage, and drainage through the 

unsaturated zone, as discussed in Healy (2010), also decreases 

recharge from the maximum amount given by equation 1. All 

references to recharge and discharge estimates derived from 

equation 1 are estimates of the potential maximum recharge or 

precipitation excess, respectively. 

Precipitation and evapotranspiration values at 

Brunswick, Georgia, were used in estimating recharge on 

Jekyll Island according to equation 1 (tables 1, 3; fig. 10). 

For the period October 2012–December 2013, equation 1 

was used to compute monthly recharge (R). Monthly water 

balances were obtained from the Brunswick weather station 

by combining monthly precipitation (P) data with monthly 

potential evapotranspiration (ET) values (fig. 10, table 3). 

The Priestly Taylor equation was used to compute monthly 

potential ET from weather-station data (Matthew Evans, 

Electronics Engineer, The University of Georgia, Griffin, Ga., 

Monthly total precipitation, in inches Monthly total evapotranspiration, in inches

O N

2012 2013

D J F M A M J J A S O N D

Figure 10.

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

–4

–3

–2

–1

0

2

1

3

Potential maximum recharge or discharge (–) , in inches

Figure 10. Monthly total A, precipitation, B, potential 

evapotranspiration, and C, water balance (potential 

maximum recharge) for the weather station at 

Brunswick, Georgia, October 2012–December 2013 

(data from The University of Georgia College of 

Agricultural & Environmental Sciences, 2015).
Hydrologic Conditions of the Water-Table Zone of the Surficial Aquifer System 19

written commun., April 4, 2013; Priestley and Taylor, 1972). 

The CRA.Clima.Evapotranspiration Web site details the 

Priestly Taylor potential evapotranspiration formulation 

(CRA-CIN, 2009).

Recharge for the period October 2012–December 2013 

was calculated for Jekyll Island according to equation 1 using 

monthly potential evapotranspiration for the weather station at 

Brunswick (fig. 10) and monthly precipitation recorded at the 

Jekyll Island weather station (table 4). 

Monthly recharge computed for Brunswick (table 3) 

was compared with monthly recharge estimated for the island 

(table 4) to identify the effects of precipitation recorded at 

Jekyll Island on spatial and temporal variations in recharge for 

the period October 2012–December 2013. Because monthly 

potential evapotranspiration computed for Brunswick also was 

used to compute monthly recharge on Jekyll Island, differences in corresponding monthly recharge estimates (fig. 11) 

are solely the result of differences between monthly precipitation recorded on the island and monthly precipitation recorded 

at Brunswick (fig. 12). Similarities in monthly recharge 

estimates for Jekyll Island and the monthly recharge computed 

for Brunswick occurred during November 2012–April 2013, 

and during June, and October–December 2013, when the 

average of monthly precipitation at the Brunswick weather 

station compared well with monthly precipitation on the 

island (figs. 11 and 12). Disparities between monthly recharge 

estimated for the island and that estimated for Brunswick 

for the remaining months of the study period, October 2012, 

May, and July-September 2013, are due to precipitation 

on Jekyll Island differing considerably from the monthly 

precipitation recorded at the Brunswick weather station.

Table 3. Monthly precipitation, evapotranspiration, and water 

balance (potential maximum recharge) for weather station at 

Brunswick, Georgia, October 2012–December 2013.

[Data from The University of Georgia College of Agricultural & Environmental Sciences (2015). Brunswick, Georgia, 31.167 °N., 81.5 °W., altitude 

of 13 feet (4 meters)]

Month and

year 

Precipitation 

(inches)

Evapotranspiration 

(inches)

Water

 balance 

(inches)

October 2012 1.43 3.14 –1.71

November 2012 0.39 1.66 –1.28

December 2012 2.49 0.81 1.68

January 2013 0.65 1.58 –0.93

February 2013 4.00 1.89 2.11

March 2013 2.77 3.75 –0.99

April 2013 3.83 4.77 –0.94

May 2013 2.47 6.07 –3.60

June 2013 6.04 5.82 0.22

July 2013 5.76 5.87 –0.11

August 2013 6.14 5.50 0.64

September 2013 6.38 4.20 2.19

October 2013 0.85 3.14 –2.28

November 2013 3.63 1.48 2.15

December 2013 2.64 0.85 1.79

2013 totals 45.16 44.92 0.25

2013 averages 3.80 3.70 0.021 Maximum potential recharge, in inches 

Brunswick, Georgia

Jekyll Island 

EXPLANATION

Oct. Nov.

2012 2013

Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Figure 11.

–4 

–3 

–2 

–1 

0 

1 

2 

3 

4 

5 

6 

Figure 11. Monthly potential maximum recharge for Brunswick, and potential maximum recharge for Jekyll 

Island using evapotranspiration data from Brunswick, in inches, October 2012–December 2013 (data from 

The University of Georgia College of Agricultural & Environmental Sciences, 2015).
20 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Table 4. Monthly potential maximum recharge or discharge for Jekyll Island estimated using precipitation from the Jekyll 

Island weather station and monthly evapotranspiration from the Brunswick weather station.

[Data source for evapotranspiration (ET) is The University of Georgia College of Agricultural & Environmental Sciences (2015); Jekyll Island 

area=9 square miles=250,905,600 square feet]

Month and

year 

Jekyll Island 

monthly

precipitation

(inches)

2012–13 ET from 

Brunswick

weather station

(inches)

Maximum 

recharge or

discharge (–)

(inches)

Potential maximum recharge or discharge (–)

Feet Cubic feet Million

gallons

October 2012 5.80 3.14 2.66 0.22 55,617,408 416

November 2012 0.36 1.66 –1.30 –0.11 –27,181,440 –203

December 2012 1.92 0.81 1.11 0.09 23,208,768 174

January 2013 0.61 1.58 –0.97 –0.08 –20,281,536 –152

February 2013 3.66 1.89 1.77 0.15 37,008,576 277

March 2013 2.22 3.75 –1.53 –0.13 –31,990,464 –239

April 2013 3.40 4.77 –1.37 –0.11 –28,645,056 –214

May 2013 6.61 6.07 0.54 0.04 11290752 84

June 2013 6.20 5.82 0.38 0.03 7945344 59

July 2013 3.92 5.87 –1.95 –0.16 –40772160 –305

August 2013 10.51 5.50 5.01 0.42 104,753,088 784

September 2013 9.48 4.20 5.28 0.44 110,398,464 826

October 2013 0.55 3.14 –2.59 –0.22 –54,153,792 –405

November 2013 3.57 1.48 2.09 0.17 43,699,392 327

December 2013 2.19 0.85 1.34 0.11 28,017,792 210

Totals 52.92 44.92 8.00 0.87 218,915,136 1,638

Monthly averages 4.41 3.70 0.67 0.06 14,594,342 109

Figure 12. 

Oct. Nov.

2012 2013

Precipitation, in inches

Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

0 

2 

4 

6 

8 

10 

12 

Brunswick, Georgia

 2012–13

 Period of record

Jekyll Island, 2012–13

EXPLANATION

Figure 12. Monthly precipitation at Brunswick and Jekyll Island, Georgia, October 2012–December 2013, and 

period of record average monthly precipitation at Brunswick, Georgia (data from The University of Georgia College 

of Agricultural & Environmental Sciences, 2015; Georgia Automated Environmental Monitoring Network, 2016).
Hydrologic Conditions of the Water-Table Zone of the Surficial Aquifer System 21

Seasonal variations in evapotranspiration caused by 

changes in vegetation growth, and differences in precipitation 

recorded on Jekyll Island from that recorded at the Brunswick 

weather station, affected the seasonality of recharge. Lowvegetation growth during November 2012 resulted in low 

evapotranspiration (table 3), which would have promoted 

recharge under normal (period-of-record [POR] average) 

precipitation conditions (fig. 12); however, low precipitation 

during November 2012 resulted in discharge from the 

water-table zone instead of recharge (fig. 11; tables 3 and 4). 

Conversely, above-POR-average precipitation at the two 

stations (tables 3 and 4) during November 2013 allowed 

recharge to occur in the water-table zone. Unseasonably high 

precipitation on Jekyll Island during October 2012, compared 

with POR-average precipitation at the Brunswick weather 

stations (fig. 12), established recharge conditions in the watertable zone on Jekyll Island for that month, although discharge 

conditions were produced because of below-POR-average 

precipitation at the Brunswick weather station (fig. 11). 

During the following October (2013), below-POR-average 

precipitation at the two weather stations (fig. 12) established 

discharge conditions in the water-table zone on the island and 

at Brunswick (fig. 11). 

Seasonal-high-average evapotranspiration estimates at the 

Brunswick weather station during May and June 2013 (table 3) 

offset relatively high monthly precipitation on Jekyll Island 

(table 4; fig. 12) to produce less than 1 inch of recharge to the 

water-table zone on the island for the 2 months combined, 

while the Brunswick weather station posted an average 

discharge of about 3.6 inches during May and an average 

recharge of about 0.22 inch during June (fig. 11). Relatively 

low precipitation on Jekyll Island during July 2013 reversed 

slight recharge conditions on the island during the previous 

2 months, resulting in almost 2 inches of discharge from the 

water-table zone. By comparison, average precipitation at the 

Brunswick weather station during July 2013 resulted in just 

0.1 inch of discharge.

The most notable differences in monthly recharge on 

Jekyll Island, compared with the monthly recharge calculated 

at the Brunswick weather station, occurred during August and 

September 2013, and demonstrate the effect of precipitation on 

recharge to the water-table zone of the surficial aquifer system 

on the island (figs. 11 and 12; tables 3 and 4). About 20 inches 

of rain fell on Jekyll Island during these 2 months, resulting 

in more than 10 inches of recharge to the water-table zone. 

By comparison, about 13.2 inches of rain was recorded at the 

Brunswick weather station during August and September 2013 

combined, resulting in about 2.8 inches of recharge during the 

2-month period.

Monthly values of unit recharge, R (equation 1), to the 

water-table zone of the surficial aquifer system on Jekyll 

Island translate to recharge volumes by multiplying the 

unit recharge by the approximate island area of about 9 mi2

(table 4). Like unit recharge values computed and discussed 

previously, the magnitude of recharge volumes are affected 

by variations in precipitation and evapotranspiration. For 

example, the 5.8 inches of precipitation recorded on Jekyll 

Island during October 2012 resulted in a recharge volume 

of about 416 million gallons (Mgal). During October 2013, 

however, the 0.55 inch of precipitation that fell on the island 

resulted in a discharge volume from the water-table zone of 

about 405 Mgal. Similar comparisons of monthly precipitation 

establishing discharge conditions during November 2012 

and recharge conditions during November 2013 indicate the 

importance of precipitation on recharge to, or discharge from, 

the water-table zone. During November 2012, 0.36 inch of 

precipitation produced a discharge of 203 Mgal; whereas, 

3.57 inches of precipitation during November 2013 resulted 

in a recharge volume of 327 Mgal. 

Hydrologic stresses, such as pumping from the watertable zone, uptake of infiltrating precipitation as soil moisture, 

surface runoff, tides, and barometric pressure variations, 

discussed previously, can decrease recharge (or discharge) 

volumes accordingly. Conversely, additional recharge may 

occur from lawn irrigation by homeowners who do not have 

private wells and so they use municipal water provided the JIA 

from the Upper Floridan and Brunswick aquifer systems. The 

combined effects of all hydrologic influences acting on the 

water-table zone are manifested in changes in altitude of the 

water table, which can be used to estimate changes in aquifer 

volume and net usable recharge to the water-table zone of the 

surficial aquifer system on Jekyll Island, as described in the 

following section. 

Method Two—Aquifer-Volume Change

The recharge volumes in the water-table zone of the 

surficial aquifer system on Jekyll Island derived from method 

one, recharge, R, of equation 1, should exceed method two, 

net recharge, Rnet, computed by equation 2 because of the 

manner in which hydrologic stresses are considered in the 

computation of each recharge term. The method one recharge, 

R, is the maximum potential recharge because it takes into 

consideration evapotranspiration as the only hydrologic 

stress acting to decrease the precipitation amount available 

to recharge the water-table zone. By comparison, the method 

two recharge, Rnet uses the effects of all hydrologic stresses 

acting on the water-table zone, such as pumping from ponds 

or wells completed in the water-table zone of the surficial 

aquifer system, in addition to evapotranspiration to estimate 

net, or usable, recharge from aquifer-volume changes that 

are defined by changes in altitude of the water table. Because 

aquifer-volume change, V(t

2

)−V(t

1

), in equation 2, is based on 

groundwater levels that have been affected by all hydrologic 

stresses, the resulting value of Rnet, would be less than the 

method one potential maximum recharge volume derived from 

R in equation 1, which uses evapotranspiration as the only 

hydrologic stress acting on the water-table zone.
22 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Equation 3 was used to calculate Rnet. Positive groundwater-level differences, havg (t

2

)−havg (t

1

), yield positive aquifervolume change and recharge, Rnet, to the water-table zone; 

negative groundwater-level differences indicate discharge 

from the water-table zone. 

Estimates of net recharge, Rnet, according to equation 3, 

were calculated from groundwater levels measured in wells 

completed in the water-table zone of the surficial aquifer 

system on Jekyll Island on November 8, 2012, and April 17 

and August 23, 2013 (table 3–1). Results from two time 

periods developed from these measurements indicate that 

discharge of about 102 Mgal occurred from the water-table 

zone during the first time period, November 8, 2012, to 

April 17, 2013, when discharge most likely was expected, 

and recharge of about 272 Mgal occurred during the second 

time period, April 17 to August 23, 2013, when recharge 

most likely was expected (table 5), according to climate 

information provided by the Georgia State Climate Office 

(see “Climate” section). Typically in the Southeast, the 

combination of low evapotranspiration, and high precipitation 

during late fall through spring, produces recharge conditions. For Georgia’s barrier island system, however, winter 

typically is the drier season, and other hydrologic stresses 

in addition to evapotranspiration have combined to produce 

a discharge condition in the water-table zone during the 

November 8, 2012, to April 17, 2013 time period, as indicated 

by the negative aquifer-volume change during the time period. 

Low precipitation on Jekyll Island during November 2012 

through January 2013, paired with precipitation comparable 

to the POR average precipitation for the Brunswick weather 

station during February 2013 (fig. 12) confirm winter as a dry 

season and produced the discharge condition in the watertable zone during this time. Conversely, high precipitation 

during May and August 2013, coupled with precipitation that 

compared well with the POR average precipitation for the 

Brunswick weather station during June 2013, overcame high 

evapotranspiration during late-spring to mid-summer (fig. 12; 

table 1) to produce recharge conditions in the water-table zone 

during the April 17 to August 23, 2013 time period (table 5).

Comparison of Recharge Calculations by 

Both Methods

Comparison of recharge and discharge estimates for 

the water-table zone of the surficial aquifer system on 

Jekyll Island, calculated using method one, recharge (R, in 

equation 1) and method two, aquifer-volume change (Rnet, in 

equation 3), was difficult because the first method takes into 

account only monthly, total precipitation and monthly potential evapotranspiration; whereas the second method takes into 

account all hydrologic influences but utilizes data collected 

at three points in time—November 8, 2012, April 17, 2013, 

and August 23, 2013. Monthly average estimates of recharge 

or discharge volumes were calculated for both methods 

(tables 4 and 5). Monthly average estimates for recharge 

Table 5. Average groundwater level difference, aquifer-volume change, and recharge to and discharge 

from the water-table zone of the surficial aquifer system, Jekyll Island, Georgia, November 8, 2012, to 

August 23, 2013.

[Positive values indicate net usable recharge, Rnet; —, not applicable] 

Time period

Average groundwater-level

difference

(in feet)

Aquifervolume

change1

(cubic feet)

Recharge or

discharge (–) 

volume2

(

cubic feet)

Recharge or

discharge (–)

volume

 (million gallons)

November 8, 2012, to 

April 17, 2013

–0.26 –65,235,456 –13,699,446 –102

April 17 to August 23, 2013 0.69 173,124,864 36,356,221 272

November 8, 2012, to 

August 23, 2013

0.43 107,889,408 22,656,776 170

Monthly average — — — 17

1

Average groundwater difference multiplied by area of Jekyll Island, 9 square miles=250,905,600 square feet, 

to obtain aquifer volume change, in cubic feet.

2

Aquifer-volume change multiplied by porosity (0.21) to obtain recharge or discharge volume, in cubic feet.
Hydrologic Conditions of the Water-Table Zone of the Surficial Aquifer System 23

volumes calculated using the method one, R, was 109 Mgal. 

Monthly average estimates of recharge or discharge volumes 

calculated using method two, Rnet, was 17 Mgal.

The apparent over-estimation of R by equation 1 

demonstrates the inability of the simple water-balance method 

to account for hydrologic influences acting on the water-table 

zone other than evapotranspiration. These other hydrologic 

influences, including the existing removal of water from 

the surficial aquifer system via irrigation pumping, would 

decrease the potential maximum recharge R to an actual, or 

net usable recharge amount, which is more closely represented 

by Rnet than R, as the former is derived from groundwater 

levels that have adjusted to all hydrologic influences acting 

on the water-table zone during the time that water levels 

were measured. 

Development Potential of the Water-Table Zone 

of the Surficial Aquifer System

The development potential of the water-table zone in the 

surficial aquifer system on Jekyll Island can be inferred from 

the volume of water contained in the aquifer at an altitude 

above sea level. Groundwater levels below sea level would 

promote seawater encroachment to the water-table zone and 

degrade the freshwater resource on the island. The threat of 

seawater encroachment to the water-table zone of the surficial 

aquifer system likely will increase in the future as sea level 

rises (Intergovernmental Panel on Climate Change, 2013). 

Net recharge to the water-table zone of the surficial aquifer 

system can maintain the water table above sea level, prevent 

degradation of the freshwater supply, and allow development 

of the water resource. Dry climatic conditions compounded 

by increased pumping could decrease net recharge to the 

water-table zone and possibly establish discharge conditions in the water-table zone, negating any development 

potential previously established by net recharge conditions. 

Monitoring water use and maintaining groundwater-level 

altitudes above sea level could safeguard against discharge 

conditions in the water-table zone that could lead to aquifer 

degradation from decreased net recharge and the formation 

of discharge conditions.

A conservative estimate of development potential 

for the water-table zone in the surficial aquifer system on 

Jekyll Island would not only maintain groundwater-level 

altitudes above sea level, but would utilize only the positive 

groundwater-level changes during periods of net recharge. For 

example, the 0.69-ft average increase in the water table during 

the time period from April 17 to August 23, 2013, indicates net 

recharge to the water-table zone and a development potential 

of 272 Mgal (table 5). In other words, 272 Mgal could have 

been withdrawn from the water-table zone during this period 

at the expense of utilizing only the 0.69-ft average increase 

in groundwater levels on the island. Theoretically, at the end 

of the time period on August 23, 2013, the configuration of 

the water table would be identical to the configuration on 

April 17, 2013 (fig. 8B), because only the net recharge to the 

water-table zone gained during the time period was developed 

for use. 

A negative development potential for the water-table 

zone in the surficial aquifer system occurs when discharge 

conditions exist on Jekyll Island. For example, the discharge 

of 102 Mgal from the water-table zone inferred from 

groundwater levels measured on November 8, 2012, and 

April 17, 2013, resulted in an average water-table decline of 

0.26 ft on the island (table 5). Additional negative hydrologic 

stresses in excess of 102 Mgal, such as from increased 

pumping, would further lower the water table from the level 

already exhibited during the period. 

Antecedent recharge or discharge conditions could 

be used to determine the development potential in the 

water-table zone of the surficial aquifer system on Jekyll 

Island. Increases in the water table during recharge conditions could be reserved for development of water resources 

during a future discharge condition. The converse situation 

of developing water resources, and incurring subsequent 

lowering of the water table, during periods of net discharge in 

anticipation of future recharge conditions could have negative 

and deleterious consequences on the water-table aquifer if 

prolonged discharge conditions could not be offset by watertable increases during a future, net-recharge condition. In this 

example, the freshwater of the water-table zone would be 

threatened by excessive water-level declines that could extend 

below sea level, promoting seawater encroachment. Consider 

the following hypothetical example based on groundwater 

levels measured during the period of November 8, 2012, to 

August 23, 2013. The net-average increase in the water table 

on Jekyll Island of 0.43 ft indicated by groundwater-level 

measurements for this time period (table 5) implies that if 

recharge was predicted to occur with the magnitude indicated 

by groundwater-level measurements during the wet period 

of April 17 to August 23, 2013, then the expected gain in 

water resources given by this recharge condition could have 

been utilized during the preceding dry (discharge) period of 

November 8, 2012, to April 17, 2013. The net-recharge condition that occurred during the wet period of April 17 to August 

23, 2013 was uncertain, however, and increased development 

of water resources during the preceding discharge period by 

this amount (0.43 ft, or 170 million gallons per day [Mgal/d], 

table 5) may not have been offset by the future recharge 

condition. The period of record average precipitation and 

evapotranspiration at Brunswick, Georgia, suggests that in a 

typical year the water level would increase by about 12 inches 

(table 1).
24 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Baseline Groundwater Quality

To assess the usability of the water resource and to 

corroborate estimations of flow direction inferred from 

water-table elevations, samples were collected to establish 

baseline groundwater-quality conditions. The samples were 

collected on August 23, 2013, from six wells installed during 

this study as part of the 26-well monitoring network (fig. 1B). 

Water-quality analyses yielded values for alkalinity, hardness, 

pH, specific conductance, total dissolved solids (TDS), and 

chloride concentration (table 2) that can be used as a basis 

for comparison during future investigations. In addition, field 

measurements of specific conductance and temperature were 

taken in water samples collected from 89 existing residential 

wells assumed to be completed in the water-table zone of the 

surficial aquifer system. A map showing well locations and 

specific-conductance values for selected residential wells 

(fig. 1–1) and a table showing SC and temperature data for the 

89 residential wells (table 1–1) is provided in appendix 1.

Specific conductance was measured in water samples 

from the 26-well network during November 2012, April 2013, 

and August 2013 to identify spatial and temporal variations 

that could indicate similar variations in chloride concentration 

related to groundwater-flow directions in the water-table 

zone of the surficial aquifer system on Jekyll Island (fig. 13, 

table 6). Variations in specific conductance at well 34G157, 

located adjacent to the marshland on the west side of 

the island, indicated relatively low specific conductance 

(605 μS/cm) during the November 2012 sampling period 

(fig. 13A), when groundwater flowed westward from an 

apparent recharge area in the central part of the island toward 

the marshland (fig. 8A). In contrast, during April 2013, 

groundwater flowed from the marshland eastward past the 

same well and toward a swampy area in the central part of the 

island (fig. 8B). Commensurate with this change in groundwater-flow direction, which seemingly transported relatively 

high saline water into the water-table zone, is a relatively high 

specific conductance of 2,268 μS/cm measured in a water 

sample at well 34G157 during April 2013 (fig. 13B, table 6). 

As the groundwater-flow direction again shifted westward in 

this area during August 2013, specific conductance in water 

sampled at well 35G157 decreased to 1,618 μS/cm, indicating 

a replenishment of the water-table zone with freshwater from 

the central part of the island between April and August 2013 

(compare figs. 8B and 8C for groundwater-flow directions, and 

figs. 13B and 13C for specific conductance values). 

Similar relations between specific conductance (and 

chloride concentration) and groundwater-flow directions 

inferred at well 34G157 also can be inferred at well 34G161 

(figs. 8 and 13, table 6). Specific conductance from water 

samples taken at this well indicate fairly constant waterquality conditions, with SC values increasing slightly from 

549 μS/cm during November 2012 to 657 μS/cm during 

April 2013. Groundwater-flow directions during these 

sampling periods indicate that freshwater recharging the 

water-table zone near a pond in the central part of the island 

was flowing southward past well 34G161. In comparison, 

the recharge area to the north of the well that was established 

during November 2012 and April 2013 seems less defined 

during August 2013, which might have allowed saline water 

from the marshland to the northwest of the well to infiltrate the 

water-table zone, as indicated by a specific conductance value 

of 1,507 μS/cm measured in a water sample taken at this well 

during August 2013. 
Baseline Groundwater Quality 25

Figure 13. Distribution of specific conductance during, A, November 2012, B, April 2013, and C, August 2013 in 

26 wells on Jekyll Island, Georgia.

81°25'30"

31°05'30"

31°05'00"

31°04'30"

31°04'00"

31°03'30"

81°25'00" 81°24'30" 81°24'00"

605

197

240

440

1,302

138

425

420

197

201

283 257

549

357

235

273

119

248

427

730

1,580

674

604

623 309

211

Base modified from ESRI Streetmap, 1:750,000. Map image is

the intellectual property of Esri and is used herein under license.

Copyright ©2014 Esri and its licensors. All rights reserved

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

A

T

L

A

N

T I C

O

C

E

A

N

Jekyll River

Figure 13A.

EXPLANATION

Monitoring well and specific

 conductance value—In

 microsiemens per centimeter

 at 25 degrees Celsius

427

A. November 2012
26 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Base modified from ESRI Streetmap, 1:750,000. Map image is

the intellectual property of Esri and is used herein under license.

Copyright ©2014 Esri and its licensors. All rights reserved

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

A

T

L

A

N

T I C

O

C

E

A

N

Jekyll River

B. April 2013

EXPLANATION

Monitoring well and specific

 conductance value—In

 microsiemens per centimeter

 at 25 degrees Celsius

467

Figure 13B.—Continued

81°25'30"

31°05'30"

31°05'00"

31°04'30"

31°04'00"

31°03'30"

81°25'00" 81°24'30" 81°24'00"

2,268

459

249

694

1,444

135

327

456

140

224

338 288

657

572

219

785

134

295

467

1,126

774

866

726

840 347

Figure 13. Distribution of specific conductance during, A, November 2012, B, April 2013, and C, August 2013 in 

26 wells on Jekyll Island, Georgia.
Baseline Groundwater Quality 27

Base modified from ESRI Streetmap, 1:750,000. Map image is

the intellectual property of Esri and is used herein under license.

Copyright ©2014 Esri and its licensors. All rights reserved

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

A

T

L

A

N

T I C

O

C

E

A

N

Jekyll River

C. August 2013

EXPLANATION

Monitoring well and specific

 conductance value—In

 microsiemens per centimeter

 at 25 degrees Celsius

466

Figure 13C.—Continued

81°25'30"

31°05'30"

31°05'00"

31°04'30"

31°04'00"

31°03'30"

81°25'00" 81°24'30" 81°24'00"

1,618

461

238

365

1,179

137

339

329

229

326 432

1,507

511

231

80

269

466

1,215

752

973

677

1,028 346

233

Figure 13. Distribution of specific conductance during, A, November 2012, B, April 2013, and C, August 2013 in 

26 wells on Jekyll Island, Georgia.
28 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Table 6. Specific conductance values collected from newly constructed wells, Jekyll Island, Georgia, 

November and December 2012, April and August 2013.

[μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; values shown in red are samples with chloride concentrations 

that exceed Federal and State secondary drinking-water standards. The standard for chloride concentration is 250 milligrams per 

liter (Georgia Environmental Protection Division, 1997; U.S. Environmental Protection Agency, 2000), which corresponds to a 

specific conductance value of 1,000 μS/cm at 25 °C; —, no data]

USGS

well

identifier

Well depth below 

land surface

(feet)

Specific conductance (μS/cm at 25 °C)

November 2012 December 2012 April 2013 August 2013

34G150 18.1 197 178 140 —

34G151 11.2 240 228 249 238

34G152 13.0 357 403 572 511

34G153 10.0 273 311 785 —

34G154 19.6 730 910 1,126 1,215

34G155 15.5 235 239 219 231

34G156 9.4 119 124 134 80

34G157 19.4 605 614 2,268 1,618

34G158 12.8 1,302 1,327 1,444 1,179

34G159 12.5 604 774 726 677

34G160 11.6 440 560 694 365

34G161 12.2 549 580 657 1,507

34G162 10.9 420 721 456 329

34G163 10.8 138 177 135 137

34G164 24.3 425 420 327 339

34G165 19.6 201 217 224 229

34G166 11.8 427 467 467 466

34G167 15.3 248 336 295 269

34G168 18.8 309 295 347 346

34G169 19.4 211 201 170 233

34G170 27.9 197 481 459 461

34G171 14.0 257 288 288 432

34G172 29.0 1,580 758 774 752

34G173 7.4 674 1,020 866 973

34G174 7.4 623 737 840 1,028

34G175 7.8 283 339 338 326
Summary and Conclusions 29

Summary and Conclusions

Jekyll Island is part of Georgia’s barrier island system 

formed with a hydrogeologic framework that established 

freshwater resources in a water-table zone of the surficial 

aquifer system which, like the entire island, is composed 

of marine beach sands and reworked mainland sediments. 

Infiltration of rainfall is a major provider of freshwater 

recharge to the island and is more than adequate to support 

a water-table zone in the surficial aquifer system that holds 

back seawater encroachment, at current hydrologic conditions, 

by maintaining groundwater levels above sea level in the 

island sediments. 

Precipitation varies both seasonally and geographically 

more than evapotranspiration on and adjacent to Jekyll Island. 

While evapotranspiration continues at seasonal rates and is 

minimally affected by dry or wet climatic conditions, precipitation affects recharge to the water-table zone of the surficial 

aquifer system, causing seasonal reversals of recharge-todischarge conditions, or vice versa, with unseasonably low or 

high rainfall. Most of the weekly and continuously measured 

wells exhibited a water-level increase of about 5 inches by the 

end of 2013, thus indicating that the surficial aquifer system 

was being recharged during the study period. The period of 

record average precipitation and evapotranspiration at Brunswick, Georgia, suggests that in a typical year the water level 

would increase by about 12 inches.

Development potential of freshwater resources in the 

water-table zone of the surficial aquifer system on Jekyll 

Island hinges on the ability to maintain groundwater-level 

altitudes above sea level. Careful balancing of the natural 

and man-made hydrologic stresses acting on the water-table 

zone will determine whether groundwater-level altitudes will 

support a freshwater resource in a water table situated above 

sea level, or whether the combination of negative hydrologic 

stresses, such as evapotranspiration and groundwater pumping, 

will lower the water table below sea level, promoting seawater 

encroachment and degradation of the freshwater resource on 

the island. Because the configuration of the water table is a 

manifestation of all hydrologic influences acting on the watertable zone at a given time, monitoring groundwater levels, 

water use, and water quality could help identify potential 

seawater-encroachment conditions. Managing freshwater 

recharge to the water-table zone from infiltration of precipitation, and mitigating discharge conditions in the water-table 

zone by limiting pumping, is essential to maintain the water 

table above sea level and to preserve the development potential and freshwater resources on the island.

The response of the water table to precipitation 

demonstrated by groundwater levels in wells completed in 

the water-table zone on Jekyll island indicates that the barrier 

island sediments of the surficial aquifer system can drain and 

transmit water equally well in multiple directions. Although 

this is a desirable characteristic for an aquifer to possess, the 

water-table zone of the surficial aquifer system is vulnerable 

to depletion from overpumping of wells installed in this 

hydrogeologic unit or from prolonged or extreme dry climatic 

conditions under current pumping rates or potential increases 

in mean sea level. The water table cannot be maintained at 

a given height unless it receives recharge from precipitation 

at a rate that equals or exceeds the combined stresses of 

evapotranspiration, pumping, overland runoff, groundwater 

flow to ponds, soil-moisture uptake, tides, barometric pressure 

changes, and sea-level rise. Failure to maintain the water 

table at a height above sea level will induce seawater to 

encroach into the water-table zone of the surficial aquifer 

system and increase the salinity of water in the water-table 

zone decreasing its utility as a resource. The threat of seawater 

encroachment to the water-table zone of the surficial aquifer 

system likely will increase in the future as sea level rises. 

The current distribution of 26 wells installed during this 

study in the water-table zone of the surficial aquifer system on 

Jekyll Island, coupled with three pond staff gages, constitutes 

a data-collection network from which groundwater-level 

and water-quality conditions can be monitored for future 

evaluation of freshwater resources. Although the Brunswick 

weather station provided useful evapotranspiration values for 

calculating potential maximum recharge, a weather station on 

Jekyll Island that measures meteorological conditions needed 

to compute evapotranspiration on the island would enhance 

the certainty of recharge calculations and contribute toward 

understanding the hydrology of Jekyll Island and of Georgia’s 

barrier island system in general. Water applied as irrigation 

was considered consumptive for this study. Further study is 

needed to determine if this water is fully consumptive or to 

some degree contributes to recharge.
30 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Selected References

AECOM, 2011, Jekyll Island Conservation Plan: AECOM, 

Orlando, Florida, 80 p., accessed December 3, 2014, at 

http://issuu.com/jekyllisland/docs/9-25conservation_plan_

combined/1?e=6212058/7823870.

Arbogast, A.F., 2014, Maritime vs. continental effect, in

Discovering physical geography (3d ed): John Wiley & 

Sons, accessed March 26, 2015, at http://www.wiley.com/

college/arbogast/047143860X/geo_interactions/ch05/

maritime_continental_effect/index.htm. [Online animation/

module to accompany text.] 

Buddemeier, R.W. and Schloss, J.A., 2000, Groundwater 

Storage and Flow, Web site accessed September 29, 2015, 

http://www.kgs.ku.edu/HighPlains/atlas/apgengw.htm.

Cherry, G.S., Peck, M.F., Painter, J.A., and Stayton, W.L., 

2010, Groundwater conditions and studies in the BrunswickGlynn County area, Georgia, 2008: U.S. Geological Survey 

Open-File Report 2009–1275, 54 p., accessed January 18, 2011,

at http://pubs.usgs.gov/of/2009/1275/.

Cherry, G.S., Peck, M.F., Painter, J.A., and Stayton, W.L., 

2011, Groundwater conditions in the Brunswick–Glynn 

County area, Georgia, 2009: U.S. Geological Survey 

Scientific Investigations Report 2011–5087, 58 p.

Chowns, T.M., Schultz, B.S., Griffin, J.R., and Crook, M.R., Jr.,

2008, Relocation of Brunswick River and other estuaries 

on the Georgia, USA coast as a consequence of Holocene 

transgression: Southeastern Geology, v. 45, no. 3, 

p. 143–159.

Clark, W.Z., and Zisa, A.C., 1976, Physiographic map 

of Georgia: Georgia Geological Survey, 1 sheet, scale 

1:2,000,000.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, held 

April 23–24, 2003, at the University of Georgia. Institute 

of Ecology: The University of Georgia, Athens, Georgia. 

Clarke, J.S., Hacke, C.M., and Peck, M.F., 1990, Geology 

and ground-water resources of the coastal area of Georgia: 

Georgia Geologic Survey Information Circular 113, 106 p.

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.

CRA–CIN, 2009, Priestley-Taylor equation: CRA.Clima.

Evapotranspiration Web site accessed April 2, 2015,

at http://agsys.cra-cin.it/tools/evapotranspiration/

help/Priestley-Taylor.html.

Dilsaver, L.M., 2004, Cumberland Island National Seashore: 

a history of conservation conflict: Charlottesville, Va., 

University of Virginia Press, 323 p.

Fetter, C.W., 2001, Applied hydrogeology (4th ed.): Upper 

Saddle River, N.J., Prentice-Hall, 598 p.

Georgia Automated Environmental Monitoring Network, 2016,

College of Coastal Georgia—Brunswick, Glynn County,

Georgia: Georgia Automated Environmental Monitoring

Network Web site accessed February 22, 2016, at

http://www.georgiaweather.net/index.php?content=

gp&site=BRUNSW.

Georgia Environmental Protection Division, 1997, Secondary 

Maximum Contaminant Levels for drinking water—

Environmental Rule 391–3–5–19, revised October 1997: 

Official Code of Georgia Annotated Statutes, Statute 12–5–170

(Georgia Safe Drinking Water Act) [variously paged].

Healy, R.W., 2010, Estimating groundwater recharge: United 

Kingdom, Cambridge University Press, 245 p.

Henry, V.J., 2014, Geology of the Georgia Coast in

New Georgia Encyclopedia: Georgia Humanities Council 

and the University of Georgia Press, accessed March 19, 2015,

at http://www.georgiaencyclopedia.org/articles/sciencemedicine/geology-georgia-coast.

Intergovernmental Panel on Climate Change, 2013, Summary 

for policymakers, in Climate Change 2013—The physical 

science basis, Contribution of Working Group I to the 

fifth assessment report of the Intergovernmental Panel on 

Climate Change [T.F. Stocker, D. Qin, G.-K. Plattner, M. 

Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex 

and P.M. Midgley, eds.]: Cambridge, U.K., and New York,

Cambridge University Press, p. 1–30, accessed January 12, 2016,

at http://dx.doi.org/10.1017/CBO9781107415324.004.

 Jekyll Island Authority, 2011a, Jekyll Island Conservation 

Plan Part 1: AECOM, Orlando, FL, 39 p.

Jekyll Island Authority, 2011b, Jekyll Island Conservation 

Plan Part 2: AECOM, Orlando, FL, 79 p.

Leeth, D.C., 1999, Hydrogeology of the surficial aquifer in the 

vicinity of a former landfill, Naval Submarine Base Kings 

Bay, Camden County, Georgia: U.S. Geological Survey 

Water-Resources Investigations Report 98–4246, 28 p. 

Media Insights.com [2014], Jekyll Island Weather, accessed 

April 4, 2014, and March 18, 2015 at http://www.jekyll

island.org/Weather.html.

Priestley, C.H.B., and Taylor, R.J., 1972: On the assessment 

of surface heat flux and evaporation using large-scale

parameters: Monthly Weather Review, v. 100, p. 81–92, 

http://dx.doi.org/10.1175/1520-0493(1972)100<0081:

OTAOSH>2.3.CO;2.
Selected References 31

Randolph, R.B., Pernik, Maribeth, and Garza, Regina, 1991, 

Water-supply potential of the Floridan aquifer system in the 

coastal area of Georgia—A digital model approach: Georgia 

Geologic Survey Bulletin 116, 30 p.

The University of Georgia College of Agricultural & Environmental Sciences, 2015, Georgia Climate Information: 

GaClimate.org Web site accessed March 19, 2015, at 

http://www.gaclimate.com. 

The University of Georgia, Georgia State Climate Office, 

Driftmier Engineering Center, 1998, Climatology of 

the Georgia coastal plain: Accessed March 18, 2015, at 

http://coastgis.marsci.uga.edu/summit/_notes/coastal.pdf.

University of Illinois, 2010, Effects of cloud cover: WW2010 

Web site accessed April 2, 2015, at http://ww2010.atmos.

uiuc.edu/(Gh)/guides/mtr/fcst/tmps/cld.rxml.

U.S. Census Bureau, 2012: U.S. Census Bureau data: 

U.S. Census Bureau Web site accessed March 18, 2015, 

at https://www.census.gov/ compendia/statab/2012/

tables/12s0364.pdf. 

U.S. Environmental Protection Agency, 2000 (revised), 

Maximum Contaminant Levels (Part 143, National 

Secondary Drinking-Water Regulations): U.S. Code of 

Federal Regulations, Title 40, parts 100–149.

U.S. Environmental Protection Agency [2014?], Outdoor 

water use in the United States: Water Sense Web page, 

accessed April 1, 2014, at http://www.epa.gov/watersense/

pubs/outdoor.html. 

U.S. Geological Survey, [2014], Geolex-Significant 

Publications: National Geologic Map Database accessed 

September 19, 2014, at http://ngmdb.usgs.gov/Geolex/

UnitRefs/MarksHeadRefs_2647.html.

Watson, T.W., 1982, Aquifer potential of the shallow sediments of the coastal area of Georgia, in Proceedings of 

the second symposium on the Geology of the southeastern 

coastal plain: Georgia Geologic Survey Information 

Circular 53, p. 191.

Weems, R.E., and Edwards, L.E., 2001, Geology of Oligocene,

Miocene, and younger deposits in the coastal area of 

Georgia: Georgia Geologic Survey Bulletin 131, 124 p.
32 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Appendix 1. Wells Inventoried for This Study

Table 1–1 showing the location of existing wells inventoried and specific conductance and temperature data collected, 

Jekyll Island, Georgia, is available online at http://dx.doi.org/10.3133/ofr20161017.
Appendix 1 33

Base modified from ESRI Streetmap, 1:750,000. Map image is

the intellectual property of Esri and is used herein under license.

Copyright ©2014 Esri and its licensors. All rights reserved

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

A

T

L

A

N

T I C

O

C

E

A

N

Jekyll River

Figure 1–1. 

EXPLANATION

Monitoring well and identifier—

 Number in parentheses is 

 specific conductance, in 

 microsiemens per centimeter

 at 25 degrees Celsius

81°25'30"

31°05'30"

31°05'00"

31°04'30"

31°04'00"

31°03'30"

81°25'00" 81°24'30" 81°24'00"

34G061 (625)

34G062 (516)

34G064 (226)

34G066 (369) 

34G071 (742)

34G074 (444)

34G076 (498)

34G078 (462)

34G083 (175)

34G084 (293)

34G089 (804)

34G090 (548)

34G092 (465)

34G098 (276)

34G099 (402)

34G101 (437)

34G104 (864)

34G105 (485)

34G106 (390)

34G109 (602) 34G108 (305)

34G110 (401)

34G113 (443)

34G114 (137)

34G116 (296)

34G117 (564)

34G118 (645)

34G122 (208)

34G127 (260)

34G131 (430)

34G139 (257)

34G141 (218)

34G141 (218)

34G149 (569)

34G069 (286)

Figure 1–1. Location of, and specific conductance measured in, private wells inventoried for this study, Jekyll 

Island, Georgia, 2012.
34 Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13

Appendix 2. Construction of Monitoring Wells

Twenty-six shallow monitoring wells were installed to more accurately characterize the water-table zone of the surficial 

aquifer system than previously defined with the distribution of existing wells (fig. 1B). These wells include three cluster sites where 

two adjacent wells were installed at different depths to provide information about local vertical hydraulic gradients and waterquality variations within the surficial aquifer system. The wells range in depth from 7.4 to 29.1 ft below land surface and were 

constructed using schedule 40, 2-inch-diameter PVC pipe with screens lengths of 5 ft and a slot size of 0.01 inch (table 2–1). The 

monitoring wells were used to collect water-level data and to measure specific conductance. Lithologic samples were collected 

during well construction and used to characterize the soil type and geology.

Two USGS-constructed wells were equipped with continuous recorders—well 34G172, located in an upland recharge area in 

the center of the island and well 34G168, located in a lowland discharge area in the northwestern part of the island.

Table 2–1 showing well construction information for monitoring wells installed for this study, Jekyll Island, Georgia, is 

available online at http://dx.doi.org/10.3133/ofr20161017.

Appendix 3. Groundwater-Level Measurements Made on November 8, 2012, 

April 17, 2013, and August 23, 2013

Table 3–1 showing groundwater levels measured on Jekyll Island, Georgia, November 8, 2012, April 17 and August 23, 2013,

is available online at http://dx.doi.org/10.3133/ofr20161017.
Manuscript approved on February 11, 2016

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 about this publication contact:

Director, South Atlantic Water Science Center

U.S. Geological Survey

720 Gracern Road

Columbia, SC 29210

http://www.usgs.gov/water/southatlantic/
Gordon and Torak—Hydrologic Conditions, Recharge, and Baseline Water Quality of the Surficial Aquifer System at Jekyll Island, Ga., 2012–13—Open-File Report 2016–1017

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20161017